Oligonucleotide, oligonucleotide conjugate and composition and use thereof

Abstract

The present disclosure provides a single-stranded oligonucleotide, wherein the single-stranded oligonucleotide has a length of 16-30 nucleotides and can inhibit the expression of PCSK9 mRNA by the mechanism of RNA interference (RNAi); wherein each nucleotide in the single- stranded oligonucleotide independently of one another is a modified or unmodified nucleotide; and wherein in the single-stranded oligonucleotide, at least one nucleotide is a nucleotide X, and at least one nucleotide is a fluoro modified nucleotide; and in a 5' to 3' direction, the 13th nucleotide is a substituted alkoxy modified nucleotide; the 14th nucleotide is a nucleotide X; and each of the 15th nucleotide and all the subsequent nucleotides independently of one another is a modified nucleotide; and each nucleotide X is independently a deoxyribonucleotide or an unmodified nucleotide. The present disclosure also provides a double-stranded oligonucleotide, an oligonucleotide conjugate and a pharmaceutical composition comprising the single-stranded oligonucleotide as an antisense strand.

Description

OLIGONUCLEOTIDE, OLIGONUCLEOTIDE CONJUGATE AND COMPOSITIONAND USE THEREOFTECHNICAL FIELDThe present disclosure relates to a single-stranded oligonucleotide, a double-stranded oligonucleotide, an oligonucleotide conjugate, a pharmaceutically acceptable salt, a pharmaceutical composition, and uses and preparation methods thereof.BACKGROUND OF THE INVENTIONDyslipidemia (also referred to as hyperlipidemia) refers to a systemic disease involving a higher plasma lipid content than normal value, which is caused by abnormal metabolism and transportation of fat, and severely threatens the health of patients worldwide. The currently available medicaments for treating dyslipidemia mainly include statins, cholesterol absorption inhibitors, resins, probucol, fibrates and niacins and derivatives thereof. The proprotein convertase subtilisin / kexin type 9 (PCSK9) gene plays an important role in lipid metabolism, especially in cholesterol metabolism. The plasma cholesterol levels can be effectively lowered by inhibiting the expression of PCSK9 gene. Therefore, silencing the expression of PCSK9 gene at gene level will undoubtedly represent the most ideal treatment means. Small interfering RNA (siRNA) can inhibit or block the expression of any target gene of interest in a sequence-specific manner based on the mechanism of RNA interference (RNAi), thereby achieving the purpose of treating diseases.In the study of drug development of oligonucleotides, including single-stranded oligonucleotides and double-stranded oligonucleotides, efforts to improve the modification of oligonucleotides have never stopped. In single-stranded oligonucleotides (such as ASO and ssRNAi) and antisense strands of double-stranded oligonucleotides (such as siRNA), the type, position, and number of modifications may have a significant impact on key properties of oligonucleotides, including pharmacodynamic activity, stability, and long-term effectiveness. Although the prior art has disclosed a large number of modification schemes of oligonucleotides, how to improve the modification of oligonucleotides, especially singlestranded oligonucleotides and antisense strands of double-stranded oligonucleotides, to obtain oligonucleotides with higher activity, higher stability and / or long-term effectiveness is still the direction of research and development in this field.SUMMARY OF THE INVENTIONThe present invention provides a single-stranded oligonucleotide. The single- stranded oligonucleotide, the double-stranded oligonucleotide and the oligonucleotide conjugate comprising the single-stranded oligonucleotide of the present disclosure as an antisense strand all exhibit good pharmaceutical activity and stability when targeting PCSK9 mRNA.In one aspect, the present disclosure provides a single-stranded oligonucleotide, wherein the single-stranded oligonucleotide has a length of 16-30 nucleotides and can inhibit the expression of PCSK9 mRNA by the mechanism of RNA interference (RNAi); wherein each nucleotide in the single-stranded oligonucleotide independently of one another is a modified or unmodified nucleotide; wherein in the single-stranded oligonucleotide, at least one nucleotide is a nucleotide X, and at least one nucleotide is a fluoro modified nucleotide; and in a 5’ to 3’ direction, the 13th nucleotide in the single-stranded oligonucleotide is a substituted alkoxy modified nucleotide; the 14th nucleotide in the single-stranded oligonucleotide is a nucleotide X; and each of the 15th nucleotide and all the subsequent nucleotides in the singlestranded oligonucleotide independently of one another is a modified nucleotide; and each nucleotide X is independently a deoxynucleotide or an unmodified nucleotide.In another aspect, the present disclosure provides a double-stranded oligonucleotide comprising a sense strand and an antisense strand, wherein each nucleotide in the sense strand is a modified or unmodified nucleotide, and the sense strand and the antisense strand are at least partially reverse complementary to form a double-stranded region, and wherein the antisense strand is the single-stranded oligonucleotide of the present disclosure.In yet another aspect, the present disclosure further provides an oligonucleotide conjugate comprising an oligonucleotide group and a delivery group conjugated to the oligonucleotide group, wherein the oligonucleotide group is a group formed by removing one or more atoms or of atomic groups from any one of the single-stranded oligonucleotide and the double-stranded oligonucleotide provided in the present disclosure.In yet another aspect, the present disclosure further provides a pharmaceutically acceptable salt of the single-stranded oligonucleotide, the double-stranded oligonucleotide or the oligonucleotide conjugate of the present disclosure.In yet another aspect, the present disclosure further provides a pharmaceutical composition comprising one or more of the single-stranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, and the pharmaceutically acceptable salt of the present disclosure, and a pharmaceutically acceptable excipient.In yet another aspect, the present disclosure further provides use of one or more of the single-stranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt, and the pharmaceutical composition of the present disclosure in the manufacture of a medicament for treating and / or preventing a disease or symptom associated with the level of PCSK9 mRNA.In yet another aspect, the present disclosure further provides a method for treating and / or preventing a disease or symptom associated with the level of PCSK9 mRNA, comprising administering to a subject in need thereof an effective amount of one or more of the singlestranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt, and the pharmaceutical composition of the present disclosure.In yet another aspect, the present disclosure further provides a method for regulating PCSK9 mRNA in a cell, comprising contacting the cell with an effective amount of one or more of the single-stranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt, and the pharmaceutical composition of the present disclosure.In yet another aspect, the present disclosure further provides one or more of the single-stranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt, and the pharmaceutical composition of the present disclosure for use as a medicament.In yet another aspect, the present disclosure also provides a cell expressing PCSK9 mRNA, comprising one or more of the single-stranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt, and the pharmaceutical composition of the present disclosure.Furthermore, the present disclosure also provides a kit comprising one or more of the singlestranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt, and the pharmaceutical composition of the present disclosure.INCORPORATION BY REFERENCEAll publications, including patents, patent applications or non-patent documents, as mentioned in this description are incorporated herein by reference to the extent as if each individual publication was specifically and separately incorporated herein by reference.BENEFICIAL EFFECTSOne or more of the double-stranded oligonucleotide, the oligonucleotide conjugate and the pharmaceutical composition comprising the single-stranded oligonucleotide of the present disclosure as an antisense strand exhibits good activity for regulating PCSK9 mRNA, e.g., having good stability and inhibitory activity against PCSK9 mRNA in cells and / or in a subject, and therefore has good application prospects.The double-stranded oligonucleotide (e.g., siRNA), the oligonucleotide conjugate and / or the pharmaceutical composition of the present disclosure comprising the single-stranded oligonucleotide of the present disclosure as an antisense strand exhibit excellent inhibitory effect against PCSK9 mRNA and / or PCSK9 protein. For example, the conjugates of the present disclosure can maintain inhibitory activity against plasma PCSK9 protein in vivo over a prolonged period, and exhibit excellent inhibition rate against plasma PCSK9 protein in the mice administered with various conjugates of the present disclosure over the entire experimental period, suggesting the long-term effectiveness of the conjugates of the present disclosure. The conjugates provided by the present disclosure show an inhibition rate of 75% or higher, and even up to 89% or higher on day 8; an inhibition rate of 79% or higher, and even up to 89% or higher on day 15; an inhibition rate of 76% or higher, and even up to 82% or higher on day 29; and an inhibition rate of 62% or higher, and even up to 81% or higher on day 43. In another aspect, the conjugates provided by the present disclosure can maintain inhibitory activity against plasma PCSK9 protein in vivo over a prolonged period. During the entire experimental period, the conjugates provided by the present disclosure show an inhibition rate of 84% or higher against plasma PCSK9 protein in mice: after 29 days, Conjugate 5 shows significantly higher inhibition rate against plasma PCSK9 protein in mice than the reference conjugate, and especially on day 43, it still maintains an inhibition rate of 87% or higher against plasma PCSK9 protein in mice, which is more than 2-fold higher than the average value of the reference conjugate.This indicates that the conjugates of the present disclosure have good activity for regulating PCSK9 mRNA and / or PCSK9 protein, and exhibit significantly higher pharmaceutical activity in the preparation of a medicament for treating and / or preventing diseases or symptoms associated with the expression of PCSK9 mRNA, and thus have excellent development prospects.DETAILED DESCRIPTION OF THE INVENTIONThe specific embodiments of the present disclosure are described in detail in the following parts.It should be understood that the specific embodiments described herein are only for the purpose of illustration and explanation of the present disclosure and are not intended to limit the present disclosure.In the present disclosure, PCSK9 mRNA refers to PCSK9 mRNA expressed in mammalian cells. In the present disclosure, PCSK9 mRNA refers to the mRNA having a sequence as shown in Genbank Accession No.NM_174936.3. Further, unless otherwise indicated, the term “PCSK9 gene” used in the present disclosure refers to the gene transcribed into the above-mentioned PCSK9 mRNA.DefinitionsIn the context of the present disclosure, the expressions “complementary” and “reverse complementary” can be interchangeably used, and have a well-known meaning in the art; namely, in a double-stranded nucleic acid structure, each base in one strand forms a hydrogen bond between base pair with a base in the other strand in a complementary manner to realize base pairing and form a Watson-Crick base pair. A “base pair” refers to two bases that form base pairing. In DNA, a purine base adenine (A) is always paired with a pyrimidine base thymine (T) (or uracil (U) in RNA); and a purine base guanine (G) is always paired with a pyrimidine base cytosine (C). Each base pair comprises a purine and a pyrimidine. When an adenine in one strand is always paired with a thymine (or uracil) in another strand, and a guanine is always paired with a cytosine, these two strands are considered as being complementary each other; and the sequence of a strand can be deduced from the sequence of its complementary strand. When the bases are modified, as long as the above purine-pyrimidine pairing relationship (including but not limited to the number and strength of hydrogen bonds between the bases) is not affected, these modified bases are also considered to be able to form complementary pairing. Correspondingly, a “mismatch” or “base mismatch” in the art means that between two singlestranded nucleic acids, the bases at corresponding positions are not presented in a manner of complementary pairing; when an abasic nucleotide is present at a corresponding position, it is also considered as forming a mismatch with the base on the other strand.In the context of the present disclosure, “at least partially reverse complementary”, “basically reverse complementary”, “substantially reverse complementary”, and “completely reverse complementary” can be used to refer to the base pairing between the nucleotide sequences of two single nucleic acid strands, namely, between a single- stranded oligonucleotide and PCSK9 mRNA, or between a single-stranded oligonucleotide and a nucleotide sequence m, or between the sense strand and the antisense strand of a double-stranded oligonucleotide (e.g., siRNA), orbetween the antisense strand of a double-stranded oligonucleotide and PCSK9 mRNA. Unless otherwise specified, “at least partially reverse complementary” means that there are no more than 50% base mismatches between two nucleotide sequences capable of forming a doublestranded region over the hypothetically or actually formed double-stranded region; “basically reverse complementary” means that there are no more than 3 base mismatches between two nucleotide sequences capable of forming a double-stranded region over the hypothetically or actually formed double-stranded region; “substantially reverse complementary” means that there is no more than 1 base mismatch between two nucleotide sequences capable of forming a double-stranded region over the hypothetically or actually formed double-stranded region; and “completely reverse complementary” means that there is no base mismatch between two nucleotide sequences capable of forming a double-stranded region over the hypothetically or actually formed double-stranded region. When two nucleotide sequences are “at least partially reverse complementary”, “basically reverse complementary”, “substantially reverse complementary”, or “completely reverse complementary”, they can anneal to form a doublestranded hybrid consisting of Watson-Crick base pairs.Unless otherwise specified, when a shorter segment of nucleotide sequence and another longer segment of nucleotide sequence are referred to as being “completely reverse complementary”, it means that the two segments of nucleotide sequences are completely reverse complementary over the entire nucleotide length of the shorter nucleotide sequence. For example, “the singlestranded oligonucleotide of the present disclosure being completely reverse complementary to PCSK9 mRNA” means that they are completely reverse complementary over the entire length of the single-stranded oligonucleotide of the present disclosure; in other words, the singlestranded oligonucleotide can form a double-stranded hybrid with PCSK9 mRNA by forming a Watson-Crick base pair between each nucleotide in the single-stranded oligonucleotide and a corresponding nucleotide in PCSK9 mRNA.In the context of the present disclosure, “double-stranded region” is a double-stranded structure formed between the shortest nucleotide sequences (including all bases that form base pairs) in each single strand of the hypothetically or actually formed double-stranded nucleic acid structure. Thus, the double-stranded region consists of all base pairs and all base mismatches located among the base pairs in the double-stranded nucleic acid structure. In some embodiments, the double-stranded nucleic acid structure comprises a double-stranded region and one or more overhanging terminals consisting of all the nucleotides that are located outside the double-stranded region and do not form base-pairing in one or two single strands of the double-stranded nucleic acid structure. In some embodiments, the double-stranded nucleic acidstructure includes only the double-stranded region.The two nucleotide sequences capable of forming a double-stranded region may have identical or different lengths. In some embodiments, the double-stranded nucleic acid structure includes only the double-stranded region. In this case, the two nucleotide sequences forming a doublestranded nucleic acid structure have an equal length; “at least partially reverse complementary” means that there are no more than 50% base mismatches between the two nucleotide sequences; “basically reverse complementary” means that there are no more than 3 base mismatches between the two nucleotide sequences; “substantially reverse complementary” means that there is no more than 1 base mismatch between the two nucleotide sequences; and “completely reverse complementary” means that there is no base mismatch between the two nucleotide sequences. In some embodiments, the two nucleotide sequences forming a double-stranded region have an equal length; the double-stranded nucleic acid structure comprises a doublestranded region and one overhanging terminal of each the nucleotide sequences, and the overhanging terminals of the two nucleotide sequences have an equal length. In some embodiments, the two nucleotide sequences forming a double-stranded region have different lengths; and the double-stranded nucleic acid structure comprises a double-stranded region and one or more overhanging terminals of the longer nucleotide sequence. For example, in some embodiments, the sense strand and the antisense strand of the double-stranded oligonucleotide have different lengths. For instance, when the double-stranded oligonucleotide is an siRNA, the sense strand with a shorter length typically represents the shorter nucleotide sequence, and the antisense strand with a longer length represents the longer nucleotide sequence; and the doublestranded nucleic acid structure comprises a double-stranded region and one overhanging terminal of the antisense strand.In the context of the present disclosure, the expression that “the nucleotide sequence A is basically reverse complementary, substantially reverse complementary or completely reverse complementary to the nucleotide sequence B over a length of X nucleotides” means that the nucleotide sequence A comprises a segment of a contiguous nucleotide sequence A’ having a length of X, , and the nucleotide sequence A’ is basically reverse complementary, substantially reverse complementary or completely reverse complementary to a segment of a contiguous nucleotide sequence B’ also having a length of X in the nucleotide sequence B.Unless otherwise specified, in the context of the present disclosure, when the oligonucleotides and / or oligonucleotide conjugates in the uses or methods of the present disclosure (which include, but are not limited to, the oligonucleotides and / or oligonucleotide conjugates represented by any of the structural formulae in the uses or methods of the present disclosure)are separately mentioned, they may also refer to the pharmaceutically acceptable salts of the oligonucleotides and / or oligonucleotide conjugates depending on the context.In the context of the present disclosure, particularly in the description of the method for preparing the single-stranded oligonucleotide, the double-stranded oligonucleotide, the pharmaceutical composition, or the oligonucleotide conjugate of the present disclosure, unless otherwise specified, the “nucleoside monomer” refers to, according to the kind and sequence of the nucleotides in the single-stranded oligonucleotide, the double-stranded oligonucleotide or the oligonucleotide conjugate to be prepared, “unmodified or modified RNA phosphoramidites used in solid phase phosphoramidite synthesis” (sometimes, RNA phosphoramidites are referred to as Nucleoside phosphoramidites elsewhere). Solid phase phosphoramidite synthesis is a well- known method used in RNA synthesis to those skilled in the art. Nucleoside monomers used in the present disclosure can all be commercially available.Various protecting groups (such as hydroxyl or amino protecting groups) can be used in the present disclosure. In the context of the present disclosure, protecting groups render chemical functional groups inert to specific reaction conditions, and can be added to and removed from such functional groups in a molecule without substantially damaging the remainder of the molecule. Representative hydroxyl protecting groups are disclosed in Beaucage, et al., Tetrahedron 1992, 48, 2223-2311, and also in Peter G.M. Wuts, GREEN’s Protective Groups in Organic Synthesis, Chapter 2, 5th edition, John Wiley & Sons Inc., New Jersey, 2014, each of which is hereby incorporated by reference in its entirety. In some embodiments, the protecting group is stable under basic conditions but can be removed under acidic conditions. In some embodiments, non-exclusive examples of hydroxyl protecting groups used herein include dimethoxytrityl (DMT), monomethoxytrityl, 9-phenylxanthen-9-yl (Pixyl), and 9-(p- methoxyphenyl)xanthen-9-yl (Mox). In some embodiments, non-exclusive examples of hydroxyl protecting groups used herein comprise Tr (trityl), MMTr (4-methoxytrityl), DMTr (4,4’-dimethoxytrityl), and TMTr (4,4’,4”-trimethoxytrityl).The term “subject”, as used herein, refers to any animal, e.g., mammal or marsupial. The subject of the present disclosure includes, but is not limited to, human, non-human primate (e.g., rhesus or other kinds of macaque), mouse, pig, horse, donkey, cow, rabbit, sheep, rat, and any kind of poultry.As used herein, the term “treatment” refers to a method for obtaining advantageous or desired result, including but not limited to, therapeutic benefit. “Therapeutic benefit” means eradication or amelioration of potential disorder to be treated. Also, therapeutic benefit is achieved byeradicating or ameliorating one or more of physiological symptoms associated with a potential disorder such that an amelioration is observed in a subject, although the subject may still be afflicted with the potential disorder.As used herein, the term “prevention” refers to a method for obtaining advantageous or desired result, including but not limited to, prophylactic benefit. For obtaining “prophylactic benefit”, the single-stranded oligonucleotide, the double-stranded oligonucleotide, the pharmaceutical composition, or the oligonucleotide conjugate of the present disclosure could be administered to a subject at risk of developing a disease associated with PCSK9 mRNA, or to a subject reporting one or more physiological symptoms of the disease associated with PCSK9 mRNA, even though the diagnosis of the disease may not have been made. In some embodiments, “prevention” involves interfering in the level of PCSK9 mRNA or PCSK9 protein by administering the single-stranded oligonucleotide, the double-stranded oligonucleotide, the pharmaceutical composition, or the oligonucleotide conjugate to a subject at risk of developing a particular disease before the risk of the particular disease develops into a clear disease progress, thereby reducing or eliminating the risk of the disease.Single-stranded oligonucleotide of the present disclosureThe present disclosure provides a single-stranded oligonucleotide, wherein the single-stranded oligonucleotide has a length of 16-30 nucleotides, and the composition of the single-stranded oligonucleotide enables it to inhibit the expression of PCSK9 mRNA by the mechanism of RNA interference (RNAi); wherein each nucleotide in the single-stranded oligonucleotide independently of one another is a modified or unmodified nucleotide; and wherein in the single-stranded oligonucleotide, at least one nucleotide is a nucleotide X, and at least one nucleotide is a fluoro modified nucleotide; and in a 5’ to 3’ direction, the 13th nucleotide in the single-stranded oligonucleotide is a substituted alkoxy modified nucleotide; the 14th nucleotide in the single-stranded oligonucleotide is a nucleotide X; and each of the 15th nucleotide and all the subsequent nucleotides in the single-stranded oligonucleotide independently of one another is a modified nucleotide; and each nucleotide X is independently a deoxynucleotide or an unmodified nucleotide.In the present disclosure, by regulating the expression level of PCSK9 mRNA and / or changing the PCSK9 protein level, the disease associated with the expression level of PCSK9 mRNA and / or the PCSK9 protein level can be treated or prevented.The inventors have surprisingly found that the single-stranded oligonucleotide of the present disclosure, and the double-stranded oligonucleotide and the oligonucleotide conjugatecomprising the single-stranded oligonucleotide of the present disclosure as an antisense strand exhibit good stability and inhibitory activity against PCSK9 mRNA in cells and / or in a subject, and therefore have good application prospects.To exert an RNAi effect, the single-stranded oligonucleotide of the present disclosure has a length of 16-30 nucleotides. In some embodiments, the single-stranded oligonucleotide of the present disclosure has a length of 17-28, 19-27, or 20-25 nucleotides. In some embodiments, the single-stranded oligonucleotide of the present disclosure has a length of 19, 21 or 23 nucleotides. In this case, the single-stranded oligonucleotide, and the double-stranded oligonucleotide and the oligonucleotide conjugate comprising the single-stranded oligonucleotide of the present disclosure as an antisense strand have a better synthesis cost, and exhibit a better balance between stability and RNAi activity.In the single-stranded oligonucleotide of the present disclosure, at least one nucleotide is a nucleotide X, and at least one nucleotide is a fluoro modified nucleotide; and in a 5’ to 3’ direction, the 14th nucleotide in the single-stranded oligonucleotide is a nucleotide X; the 13th nucleotide in the single-stranded oligonucleotide is a substituted alkoxy modified nucleotide; and each of the 15th nucleotide and all the subsequent nucleotides in the single-stranded oligonucleotide independently of one another is a modified nucleotide. Particularly, the inventors have found that by including the above-mentioned fluoro modified nucleotide, substituted alkoxy modified nucleotide and nucleotide X, the single- stranded oligonucleotide of the present disclosure can effectively maintain higher inhibitory activity against PCSK9 mRNA of the single-stranded oligonucleotide, the double-stranded oligonucleotide and the oligonucleotide conjugate, while retaining their stability. In some embodiments, the number of the nucleotide X in the single-stranded oligonucleotide is 1-3, such as 1, 2 or 3. In some embodiments, in a 5’ to 3’ direction, the 12th and 14th nucleotides in the single-stranded oligonucleotide independently of one another are the nucleotide X. In some embodiments, in a 5’ to 3’ direction, only the 14th nucleotide in the single-stranded oligonucleotide is the nucleotide X.Each nucleotide X is independently selected from a deoxynucleotide or an unmodified nucleotide. In the context of the present disclosure, an “unmodified nucleotide” refers to a ribonucleotide (RNA) in which base and ribose are not modified; that is, the nucleotide base is a natural ribobase (one of A, U, C, G, and T), and the hydroxyl group at the 2’-position of the ribose of the nucleotide is an unprotected hydroxyl group (2’ -OH). Correspondingly, a “modified nucleotide” refers to a nucleotide with base modification, or a nucleotide in which the 2’ -hydroxyl of the ribose of the nucleotide is replaced by another atom or group, or refers to anucleotide analogue. In some embodiments, in a 5’ to 3’ direction, the 14th nucleotide or the 12th and 14th nucleotides in the single-stranded oligonucleotide are deoxynucleotides, and other nucleotide X is an unmodified nucleotide. In some embodiments, in a 5’ to 3’ direction, the 14th nucleotide in the single-stranded oligonucleotide is a deoxynucleotide, and each of other nucleotides independently of one another is a modified nucleotide.In some embodiments, the number of the modified nucleotides accounts for 50% or higher, 70% or higher, or 85% or higher of all the nucleotides in the single-stranded oligonucleotide of the present disclosure. In some embodiments, the number of the unmodified nucleotides in the single-stranded oligonucleotide of the present disclosure is no more than 5 or no more than 4. In some embodiments, the number of the unmodified nucleotides in the single-stranded oligonucleotide of the present disclosure is no more than 3, no more than 2, or no more than 1. In some embodiments, the number of the unmodified nucleotides in the single-stranded oligonucleotide is 2 or 1. In some embodiments, each of all nucleotides in the single-stranded oligonucleotide independently of one another is a modified nucleotide.As described above, the single-stranded oligonucleotide of the present disclosure further comprises fluoro modified nucleotides, in addition to nucleotide X and substituted alkoxy modified nucleotides. In some embodiments, the number of fluoro modified nucleotides is 2-7. In some embodiments, in a 5’ to 3’ direction, the fluoro modified nucleotides refer to 2 to 5 nucleotides of the 2nd, 5th, 6th, 7th, 12th, 16th, 18th, and 19th nucleotides in the single-stranded oligonucleotide. In some embodiments, in a 5’ to 3’ direction, the fluoro modified nucleotides refer to 1 or 2 nucleotides of the 2nd and 12th nucleotides, 1 or 2 nucleotides of the 5th to 7th nucleotides, and 0-2 nucleotides of the 16th to 19th nucleotides in the single-stranded oligonucleotide. In some embodiments, in a 5’ to 3’ direction, the fluoro modified nucleotides refer to the 2nd and 6th nucleotides in the single-stranded oligonucleotide. In some embodiments, in a 5’ to 3’ direction, the fluoro modified nucleotides refer to the 2nd, 6th and 16th nucleotides in the single-stranded oligonucleotide. In some embodiments, in a 5’ to 3’ direction, the fluoro modified nucleotides refer to the 2nd, 5th, 7th, 12th, and 16th nucleotides in the single-stranded oligonucleotide. In some embodiments, in a 5’ to 3’ direction, the fluoro modified nucleotides refer to the 2nd, 7th, 12th, 16th, and 19th nucleotides in the singlestranded oligonucleotide. In some embodiments, in a 5’ to 3’ direction, the fluoro modified nucleotides refer to the 2nd, 6th, 12th, 16th, and 19th nucleotides in the single-stranded oligonucleotide.In some embodiments, in the single-stranded oligonucleotide, in a 5’ to 3’ direction, except for the 13th and 14th nucleotides and the fluoro modified nucleotides in the single-strandedoligonucleotide, each modified nucleotide is independently one selected from an alkoxy modified nucleotide, a substituted alkoxy modified nucleotide, an alkyl modified nucleotide, a substituted alkyl modified nucleotide, an amine modified nucleotide, a thermally destabilizing nucleotide, and a BNA. In some embodiments, in the single-stranded oligonucleotide, in a 5’ to 3’ direction, except for the 13th and 14th nucleotides and the fluoro modified nucleotides in the single-stranded oligonucleotide, each modified nucleotide is independently one selected from an alkoxy modified nucleotide, a substituted alkoxy modified nucleotide, and a thermally destabilizing nucleotide.In some embodiments, the number of the substituted alkoxy modified nucleotides in the singlestranded oligonucleotide is no more than 3. In some embodiments, the number of the substituted alkoxy modified nucleotides in the single-stranded oligonucleotide is no more than 2. In some embodiments, the number of the substituted alkoxy modified nucleotides in the single- stranded oligonucleotide is 1.In some embodiments, the single-stranded oligonucleotide comprises no thermally destabilizing nucleotide. In some embodiments, the number of the thermally destabilizing nucleotides is no more than 2. In some embodiments, the number of the thermally destabilizing nucleotides is 1 or 2. In some embodiments, except for the substituted alkoxy modified nucleotide, nucleotide X, fluoro modified nucleotide, and thermally destabilizing nucleotide, each of the modified nucleotides is independently an alkoxy modified nucleotide.In the context of the present disclosure, a “thermally destabilizing nucleotide” refers to a nucleotide containing thermally destabilizing modification(s). The thermally destabilizing refers to a modification that reduces the thermal dissociation temperature of an oligonucleotide duplex having such modification(s) by at least 0.5°C as compared with an oligonucleotide duplex having an unmodified nucleotide at the corresponding position. Exemplary thermally destabilizing modifications can be found in paragraphs

[0236] -

[0251] of the description of PCT publication WO2018 / 098328 Al.In some embodiments, the thermolabile modified nucleotide is one of an acyclic nucleotide or an isonucleotide.An acyclic nucleotide is a nucleotide in which a sugar ring in the nucleotide is opened. In some embodiments, the acyclic nucleotide can be an unlocked nucleic acid (UNA) and a glycerol nucleic acid (GNA), wherein the UNA is as shown by Formula (15), and the GNAis as shown by Formula (16):Formula (15) Formula (16)In the Formula (15) and the Formula (16), R is selected from H, OH or alkoxy (O-alkyl); and “Base” represents a nucleic acid base, such as A, U, G, C, or T.An isonucleotide is a compound which is formed by altering the position of the base on the ribose ring in a nucleotide. In some embodiments, the isonucleotide can be a compound which is formed by transferring a base from 1’ -position to 2’ -position or 3 ’-position on the ribose ring, as shown by Formula (17) or (18).In the above compounds of Formula (17) and Formula (18), “Base” represents a nucleic acid base, such as A, U, G, C, or T; and R is H, OH, F, or a non-fluoro group described above.Formula (17) Formula (18)In some embodiments, the thermolabile modified nucleotide is one selected from the group consisting of GNA as shown by Formula (27 A), 2’-0Me abasic nucleotide as shown by Formula (27B), 3’-0Me modified nucleotide as shown by Formula (27C), 5’-Me modified nucleotide as shown by Formula (27D), SNA as shown by Formula (27E), hGNA as shown by Formula (27F), hhGNA as shown by Formula (27G), mGNA as shown by Formula (27H), TNA as shown by Formula (271), and h’GNA as shown by Formula (27J), UNA as shown by Formula (27K), or Hyp-spacer as shown by Formula (27L):Formula (271); Formula (27 J); Formula (27K);In the above compounds of Formula (27A)-(27L), “Base” represents a nucleic acid base, such as, A, U, G, C, or T; and R27 is selected from H, OH, F, alkoxy, alkyl, or alkoxy substituted alkyl. * indicates that the carbon atom is chiral, and the compound can be in R configuration, or in S configuration, or can be a racemic mixture of R and S configurations. In some embodiments, each thermolabile modified nucleotide is independently GNA as shown by Formula (27 A).In the context of the present disclosure, a BNA is a nucleotide that is constrained or is not accessible. BNA can contain a 5-membered, 6-membered or 7-membered ring bridged structure with a “fixed” C3’-endo sugar puckering. The bridge is typically incorporated at the 2’ and ’position of the ribose to afford a 2’, 4’ -BNA nucleotide. In some embodiments, the BNA can be LNA, ENA and cET BNA, wherein LNA is as shown by Formula (12), ENA is as shown by Formula (13) and cET BNA is as shown by Formula (14).Formula (12) Formula (13) Formula (14)In some embodiments, for ease of synthesis, each alkoxy modified nucleotide independently of one another is a 2’-methoxy modified nucleotide (2’-OMe) as shown by Formula (8). In some embodiments, the 2’-amino modified nucleotide (2’-NH2) is as shown by Formula (9). In some embodiments, the 2’-deoxy nucleotide (DNA) is as shown by Formula (10).Formula (7) Formula (8) Formula (9) Formula (10)In the above compounds of Formulae (7)-(10) and ( 12)-(14), “Base” represents a nucleic acid base, such as A, U, G, C, or T.In the context of the present disclosure, a “fluoro modified nucleotide”, a “2’ -fluoro modified nucleotide”, a “nucleotide in which 2’-hydroxyl of the ribose group is substituted with fluoro”, and a “nucleotide with 2’-fluororibosyl” have the same meaning, referring to the compound as shown by Formula (7) formed by substituting the 2’ -hydroxyl of the nucleotide with fluoro. A “methoxy modified nucleotide”, a “2’-methoxy modified nucleotide”, a “nucleotide in which 2’- hydroxyl of the ribose group is substituted with methoxy”, and a “nucleotide with 2’- methoxyribosyl“ have the same meaning, referring to the compound as shown by Formula (8) formed by substituting the 2’ -hydroxyl of the ribose group of the nucleotide with methoxy.In some embodiments, the single-stranded oligonucleotide of the present disclosure has a length of 19-23 nucleotides, and in a 5’ to 3’ direction, the 13th nucleotide is a substituted alkoxy modified nucleotide, the 14th nucleotide is a nucleotide X, one of the 5th to 7th nucleotides is a fluoro modified nucleotide, the 2nd and the 16th nucleotides are fluoro modified nucleotides, the 3rd nucleotide is an alkoxy modified nucleotide or a substituted alkoxy modified nucleotide, the 5th nucleotide is an alkoxy modified nucleotide or a substituted alkoxy modified nucleotidewhen it is not a fluoro modified nucleotide, and each remaining nucleotide in the single-stranded oligonucleotide independently of one another is an alkoxy modified nucleotide.In some embodiments, the single-stranded oligonucleotide of the present disclosure has a length of 21 nucleotides, and in a 5’ to 3’ direction, the 13th nucleotide is a substituted alkoxy modified nucleotide, the 14th nucleotide is a nucleotide X, the 2nd, 6th and 16th nucleotides are fluoro modified nucleotides, the 3rd and 5th nucleotides are alkoxy modified nucleotides or substituted alkoxy modified nucleotides, and each remaining nucleotide in the single-stranded oligonucleotide independently of one another is an alkoxy modified nucleotide.In some embodiments, each nucleotide X in the single-stranded oligonucleotide of the present disclosure refers to a deoxynucleotide. In some embodiments, each alkoxy modified nucleotide in the single-stranded oligonucleotide of the present disclosure refers to a methoxy modified nucleotide. In some embodiments, each substituted alkoxy modified nucleotide in the singlestranded oligonucleotide of the present disclosure refers to a 2’-O-methoxyethyl modified nucleotide. In some embodiments, each BNA in the single-stranded oligonucleotide of the present disclosure refers to LNA or cET BNA. In some embodiments, each thermally destabilizing nucleotide in the single-stranded oligonucleotide of the present disclosure refers to GNA.In some embodiments, at least 2 of the linking groups linking adjacent nucleotides in the singlestranded oligonucleotide are each independently phosphate ester groups with modification group(s). In some embodiments, 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the single-stranded oligonucleotide of the present disclosure are each independently phosphate ester groups with modification group(s). In some embodiments, 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 3’ terminal of the single-stranded oligonucleotide of the present disclosure are each independently phosphate ester groups with modification group(s). In some embodiments, 2 of the linking groups linking adjacent nucleotides of the 1st to 3rd nucleotides at 5’ terminal of the single-stranded oligonucleotide of the present disclosure, or 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the single-stranded oligonucleotide of the present disclosure are each independently phosphate ester groups with modification group(s). In some embodiments, 2 of the linking groups linking adjacent nucleotides of the 1st to 3rd nucleotides at 3’ terminal of the single-stranded oligonucleotide of the present disclosure, or 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 3’ terminal of the single-stranded oligonucleotide of the present disclosure are each independently phosphate ester groups with modification group(s). In some embodiments,in the single-stranded oligonucleotide of the present disclosure, if the single-stranded oligonucleotide comprises unmodified nucleotides, then one or both of the two linking groups linking each of the unmodified nucleotides and adjacent nucleotides thereof are each independently phosphate ester groups with modification group(s). The modified phosphate ester groups can render the single-stranded oligonucleotide of the present disclosure to better resist the action of exonucleases, and enhance the stability of the oligonucleotide in a subject.In some embodiments, 2-6 of the linking groups linking adjacent nucleotides in the singlestranded oligonucleotide are each independently phosphate ester groups with modification group(s). In some embodiments, 3 or 4 of the linking groups linking adjacent nucleotides in the single-stranded oligonucleotide are each independently phosphate ester groups with modification group(s). In some embodiments, the linking groups linking adjacent nucleotides of the 1st to 3rd nucleotides at 5’ terminal and the linking groups linking adjacent nucleotides of the 1st to 3rd nucleotides at 3’ terminal of the single- stranded oligonucleotide are each independently phosphate ester groups with modification group(s). In some embodiments, if the single-stranded oligonucleotide comprises unmodified nucleotides, then one or both of the two linking groups linking each of the unmodified nucleotides and adjacent nucleotides thereof are each independently phosphate ester groups with modification group(s). In some embodiments, each of the phosphate ester groups with modification group(s) is independently a phosphorothioate group having the structure as shown by Formula (28):Formula (28)In some embodiments, the 5’-terminal nucleotide of the single-stranded oligonucleotide is a 5’- hydroxy nucleotide, a 5 ’-phosphate nucleotide or a 5 ’-phosphate analogue modified nucleotide, wherein the 5 ’-hydroxy nucleotide has the structure as shown by Formula (29); the 5 ’-phosphate nucleotide has the structure as shown by Formula (30); and the 5 ’-phosphate analogue modified nucleotide is one selected from the nucleotides as shown by Formulae (31)-(34):Formula (31) Formula (32) Formula (33) Formula (34); wherein R is one selected from H, OH, OCH3, and F; Base represents a nucleic acid base selected from A, U, C, G, or T.In some embodiments, the 5’-phosphate nucleotide is a nucleotide with 5’-phosphate modification as shown by Formula (30); the 5’-phosphate analogue modified nucleotide is a nucleotide with 5’-(E)-vinylphosphonat (E-VP) modification as shown by Formula (31) or a phosphorothioate modified nucleotide as shown by Formula (33). In some embodiments, the 5’- terminal nucleotide of the single-stranded oligonucleotide is a 5’-hydroxy nucleotide, or a nucleotide with 5’-(E)-vinylphosphonate (E-VP) modification. In some embodiments, the 5’- terminal nucleotide is a 5’-(E)-vinylphosphonate (E-VP) modified nucleotide, which can further increase one or more of the stability, pharmacodynamic activity and long-term effectiveness of the single-stranded oligonucleotide, and the double-stranded oligonucleotide and the oligonucleotide conjugate comprising the single-stranded oligonucleotide of the present disclosure in a subject.In some embodiments, the single-stranded oligonucleotide of the present disclosure has a length of 21 nucleotides, and in a 5’ to 3’ direction, the 13th nucleotide is a 2’-O-methoxyethyl modified nucleotide, the 14th nucleotide is a deoxynucleotide, the 2nd, 6th and 16th nucleotides are fluoro modified nucleotides, and each remaining nucleotide in the single-stranded oligonucleotide independently of one another is a methoxy modified nucleotide; the linking groups linking any two adjacent nucleotides of the 1st to the 3rd nucleotides at 5’ terminal and the linking groups linking any two adjacent nucleotides of the 1st to the 3rd nucleotides at 3’ terminal are phosphorothioate groups; and the 5’ terminal nucleotide is a 5 ’-hydroxy nucleotide as shown by Formula (29) or a 5 ’-vinyl phosphate modified nucleotide as shown by Formula (31).As described above, the composition of the single-stranded oligonucleotide of the presentdisclosure enables the single-stranded oligonucleotide to inhibit the expression of PCSK9 mRNAby the mechanism of RNA interference (RNAi). In some embodiments, the singlestranded oligonucleotide of the present disclosure has sufficient complementarity with PCSK9 mRNA to mediate an RNAi effect. In some embodiments, the single-stranded oligonucleotide of the present disclosure is sufficiently complementary to PCSK9 mRNA. In the context of the present disclosure, “sufficiently complementary” means that complementarity between the single-stranded oligonucleotide of the present disclosure and PCSK9 mRNA is sufficient to enable the single-stranded oligonucleotide to reduce or eliminate the production of the protein encoded by PCSK9 mRNA through an RNAi effect. In some embodiments, “sufficiently complementary” means that the single-stranded oligonucleotide of the present disclosure is basically reverse complementary, substantially reverse complementary or completely reverse complementary to PCSK9 mRNA over a length of at least 16 nucleotides, such as over a length of 16-25 nucleotides, or over a length of 18-23 nucleotides, or over a length of 19-21 nucleotides. In some embodiments, the single-stranded oligonucleotide of the present disclosure is completely reverse complementary to PCSK9 mRNA.In some embodiments, two segments of nucleotide sequences that are “sufficiently complementary” can comprise internal regions that are completely reverse complementary (e.g., being completely reverse complementary over a length of at least 6, 8 or 10 nucleotides). In some embodiments, the single-stranded oligonucleotide of the present disclosure is completely reverse complementary to PCSK9 mRNA at least over the seed region, wherein the “seed region” refers to the region of the nucleotides at positions 2 to 8 of the single-stranded oligonucleotide of the present disclosure. In this case, the single-stranded oligonucleotide of the present disclosure can better mediate an RNAi effect and inhibit the level of PCSK9 mRNA. In some embodiments, the single-stranded oligonucleotide is substantially reverse complementary or completely reverse complementary to PCSK9 mRNA over a length of at least 16 nucleotides. In some embodiments, in the 5’ to 3’ direction, the 2nd to 19th nucleotides in the single-stranded oligonucleotide are completely reverse complementary to PCSK9 mRNA. In some embodiments, in the 5’ to 3’ direction, except for the nucleotide at position 1 at 5’ terminal, the nucleotide sequence of the single-stranded oligonucleotide is completely reverse complementary to PCSK9 mRNA. In some embodiments, all the nucleotides of the singlestranded oligonucleotide are completely reverse complementary to PCSK9 mRNA.In some embodiments, the single-stranded oligonucleotide is basically reverse complementary, substantially reverse complementary or completely reverse complementary to a segment of a contiguous nucleotide sequence m in PCSK9 mRNA, wherein the length of the nucleotidesequence m is not greater than the length of the single- stranded oligonucleotide, and the nucleotide sequence m and the single-stranded oligonucleotide have an equal length, or have a length difference of no more than 8 nucleotides or 1-5 nucleotides.In some embodiments, the nucleotide sequence m has a length of at least 16 nucleotides, or 16- 25 nucleotides, or 18-23 nucleotides, or 19-21 nucleotides; or the nucleotide sequence m has a length of 19, 21 or 23 nucleotides.In some embodiments, the single-stranded oligonucleotide and the nucleotide sequence m have an equal length, and at least the nucleotide sequence of the single-stranded oligonucleotide, except for the terminal nucleotides, is completely reverse complementary to the nucleotide sequence m; in this case, the double-stranded oligonucleotide or oligonucleotide conjugate comprising the single-stranded oligonucleotide of the present disclosure as an antisense strand could further improve the inhibitory effect against PCSK9 mRNA. In some embodiments, in a 5’ to 3’ direction, the nucleotide sequence of the single- stranded oligonucleotide, except for the nucleotide at position 1, is substantially reverse complementary to the nucleotide sequence m. In some embodiments, in a 5’ to 3’ direction, the nucleotide sequence of the single-stranded oligonucleotide, except for the nucleotide at position 1, is completely reverse complementary to the nucleotide sequence m. In some embodiments, all the nucleotides of the single-stranded oligonucleotide are completely reverse complementary to the nucleotide sequence m.In some embodiments, the single-stranded oligonucleotide of the present disclosure can be the following first, second, third, or fourth single-stranded oligonucleotide. Each single-stranded oligonucleotide will be described below, respectively.First single-stranded oligonucleotideIn some embodiments, the present disclosure provides a first single-stranded oligonucleotide, wherein the single-stranded oligonucleotide comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 2 with no more than 3 base differences:5’ - Z2AGUUACAAAAGCAAAACA -3’ (SEQ ID NO: 2), wherein Z2 is A or U; the nucleotide sequence II comprises a nucleotide Z’2 at the position corresponding to Z2, wherein Z’2 is the first nucleotide at 5’ terminal of the single-stranded oligonucleotide. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 2 with no more than 3 base differences.In the context of the present disclosure, “position correspondence” refers to the same position in a nucleotide sequence when counting from the same terminal of the nucleotide sequence. Forexample, the first nucleotide at 5’ terminal of the nucleotide sequence II is a nucleotide at the position corresponding to the first nucleotide of SEQ ID NO: 2.In some embodiments, each U in the nucleotide sequence of the single-stranded oligonucleotide, double-stranded oligonucleotide or oligonucleotide conjugate of the present disclosure can be optionally replaced by T. These base differences will neither significantly reduce the inhibitory activity against PCSK9 mRNA of the single-stranded oligonucleotides, double-stranded oligonucleotides and oligonucleotide conjugates, nor increase the off-target effect of the siRNA. These single-stranded oligonucleotides, double-stranded oligonucleotides and oligonucleotide conjugates comprising the base differences are also within the protection scope of the present disclosure.In some embodiments, there is no more than one base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 2 with 1 base difference. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2 can include a difference at the position of Z’2 and / or a base difference at any other nucleotide position in the nucleotide sequence II. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2 can include a base difference at the position of Z’2 and / or a base difference at a nucleotide position adjacent to Z’2. In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 2 with no base difference.In some embodiments, the difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2 includes a difference at the position of Z’2, wherein Z’2 is selected from G or C. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2 is a difference at the position of Z’2, wherein Z’2 is selected from C or G.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotide sequence IV, wherein the nucleotide sequence IV is linked to 3’ terminal of the nucleotide sequence II, and has a length of 1, 2, 3 or 4 nucleotides, and each nucleotide in the nucleotide sequence IV is independently one non-fluoro modified nucleotide; the nucleotide sequence IV is substantially reverse complementary or completely reverse complementary to PCSK9 mRNA, and each of the non-fluoro modified nucleotides is independently one selected from a 2’-methoxy modified nucleotide, a 2’-CI-3 alkyl modified nucleotide, a 2’-amino modified nucleotide, a 2’-substituted amino modified nucleotide, and a thermally destabilizing nucleotide. In some embodiments, the nucleotide sequence IV has a length of 2 nucleotides.In some embodiments, the nucleotide sequence IV has a length of 1 nucleotide, and the base is G; or the nucleotide sequence IV has a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition is GG; or the nucleotide sequence IV has a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition is GGU; or the nucleotide sequence IV has a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition is GGUC.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotide sequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1 to 3 nucleotides, and is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II; after the single-stranded oligonucleotide and a sense strand form a double-stranded oligonucleotide, the nucleotide sequence V constitutes a 3’ overhanging terminal of the antisense strand of the double-stranded oligonucleotide.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides; and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA.In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II; and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GG or UU.In some embodiments, the single-stranded oligonucleotide comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 2, and the nucleotide sequence V has a base composition of GG.Second single-stranded oligonucleotideIn some embodiments, the present disclosure provides a second single-stranded oligonucleotide, wherein the single-stranded oligonucleotide comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 4 with no more than 3 base differences:5’ - Z4UAUCUUCAAGUUACAAAA -3’ (SEQ ID NO: 4), wherein Z4 is A or U; the nucleotide sequence II comprises a nucleotide Z’4 at the position corresponding to Z4, wherein Z’4 is the first nucleotide at 5’ terminal of the single-stranded oligonucleotide. In one embodiment, the nucleotide sequence II thus comprises or consists ofthe nucleotide sequence as shown in SEQ ID NO: 4 with no more than 3 base differences. In some embodiments, there is no more than one base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 4 with 1 base difference. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4 can include a difference at the position of Z’4 and / or a base difference at any other nucleotide position in the nucleotide sequence II. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4 can include a base difference at the position of Z’4 and / or a base difference at a nucleotide position adjacent to Z’4. In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 4 with no base difference.In some embodiments, the difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4 includes a difference at the position of Z’4, wherein Z’4 is selected from G or C. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4 is a difference at the position of Z’4, wherein Z’4 is selected from C or G.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotide sequence IV, wherein the nucleotide sequence IV is linked to 3’ terminal of the nucleotide sequence II, and has a length of 1, 2, 3 or 4 nucleotides, and each nucleotide in the nucleotide sequence IV is independently one non-fluoro modified nucleotides; the nucleotide sequence IV is substantially reverse complementary or completely reverse complementary to PCSK9 mRNA, and each of the non-fluoro modified nucleotides is independently one selected from a 2’- methoxy modified nucleotide, a 2’-CI-3 alkyl modified nucleotide, a 2’-amino modified nucleotide, a 2’-substituted amino modified nucleotide, and a thermally destabilizing nucleotide. In some embodiments, the nucleotide sequence IV has a length of 2 nucleotides.In some embodiments, the nucleotide sequence IV has a length of 1 nucleotide, and the base is G; or the nucleotide sequence IV has a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition is GC; or the nucleotide sequence IV has a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition is GCA; or the nucleotide sequence IV has a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition is GCAA.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotidesequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1 to 3 nucleotides, and is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II; after the single-stranded oligonucleotide and a sense strand form a double-stranded oligonucleotide, the nucleotide sequence V constitutes a 3’ overhanging terminal of the antisense strand of the double-stranded oligonucleotide.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides; and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA. In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II; and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GC or UU.In some embodiments, the single-stranded oligonucleotide comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 4, and the nucleotide sequence V has a base composition of GC.Third single-stranded oligonucleotideIn some embodiments, the present disclosure provides a third single-stranded oligonucleotide, wherein the single-stranded oligonucleotide comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 6 with no more than 3 base differences:5’ - Z6ACAGGUCUAGAAAAGUUG -3’ (SEQ ID NO: 6), wherein Ze is A or U; the nucleotide sequence II comprises a nucleotide Z’e at the position corresponding to Ze, wherein Z’e is the first nucleotide at 5’ terminal of the single-stranded oligonucleotide. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 6 with no more than 3 base differences. In some embodiments, there is no more than one base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 6 with 1 base difference. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6 can include a difference at the position of Z’e and / or a base difference at any other nucleotide position in the nucleotide sequence II. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6 can include a base differenceat the position of Z’e and / or a base difference at a nucleotide position adjacent to Z’ &. In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 6 with no base difference.In some embodiments, the difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6 includes a difference at the position of Z’e, wherein Z’e is selected from G or C. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2 is a difference at the position of Z’e, wherein Z’e is selected from C or G.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotide sequence IV, wherein the nucleotide sequence IV is linked to 3’ terminal of the nucleotide sequence II, and has a length of 1, 2, 3 or 4 nucleotides, and each nucleotide in the nucleotide sequence IV is independently one non-fluoro modified nucleotides; the nucleotide sequence IV is substantially reverse complementary or completely reverse complementary to PCSK9 mRNA, and each of the non-fluoro modified nucleotides is independently one selected from a 2’- methoxy modified nucleotide, a 2’-CI-3 alkyl modified nucleotide, a 2’-amino modified nucleotide, a 2’-substituted amino modified nucleotide, and a thermally destabilizing nucleotide. In some embodiments, the nucleotide sequence IV has a length of 2 nucleotides.In some embodiments, the nucleotide sequence IV has a length of 1 nucleotide, and the base is G; or the nucleotide sequence IV has a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition is GC; or the nucleotide sequence IV has a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition is GCU; or the nucleotide sequence IV has a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition is GCUG.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotide sequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1 to 3 nucleotides, and is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II; after the single-stranded oligonucleotide and a sense strand form a double-stranded oligonucleotide, the nucleotide sequence V constitutes a 3’ overhanging terminal of the antisense strand of the double-stranded oligonucleotide.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides; and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA.In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II; and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GC or UU.In some embodiments, the single-stranded oligonucleotide comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 6, and the nucleotide sequence V has a base composition of GC.Fourth single-stranded oligonucleotideIn some embodiments, the present disclosure provides a fourth single-stranded oligonucleotide, wherein the single-stranded oligonucleotide comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 8 with no more than 3 base differences:5’ - Z8CAGGUCUAGAAAAGUUGG -3’ (SEQ ID NO: 8), wherein Z8is A or U; the nucleotide sequence II comprises a nucleotide Z’8at the position corresponding to Z8, wherein Z’8is the first nucleotide at 5’ terminal of the single-stranded oligonucleotide. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 8 with no more than 3 base differences. In some embodiments, there is no more than one base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 8 with 1 base difference. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8 can include a difference at the position of Z’8and / or a base difference at any other nucleotide position in the nucleotide sequence II. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8 can include a base difference at the position of Z’8and / or a base difference at a nucleotide position adjacent to Z’8. In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8. In one embodiment, the nucleotide sequence II thus comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 8 with no base difference.In some embodiments, the difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8 includes a difference at the position of Z’8, wherein Z’8is selected from G or C. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8 is a difference at the positionof Z’s, wherein Z’s is selected from C or G.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotide sequence IV, wherein the nucleotide sequence IV is linked to 3’ terminal of the nucleotide sequence II, and has a length of 1, 2, 3 or 4 nucleotides, and each nucleotide in the nucleotide sequence IV is independently one non-fluoro modified nucleotides; the nucleotide sequence IV is substantially reverse complementary or completely reverse complementary to PCSK9 mRNA, and each of the non-fluoro modified nucleotides is independently one selected from a 2’- methoxy modified nucleotide, a 2’-CI-3 alkyl modified nucleotide, a 2’-amino modified nucleotide, a 2’-substituted amino modified nucleotide, and a thermally destabilizing nucleotide. In some embodiments, the nucleotide sequence IV has a length of 2 nucleotides.In some embodiments, the nucleotide sequence IV has a length of 1 nucleotide, and the base is C; or the nucleotide sequence IV has a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition is CU; or the nucleotide sequence IV has a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition is CUG; or the nucleotide sequence IV has a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition is CUGU.In some embodiments, the single-stranded oligonucleotide further comprises a nucleotide sequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1 to 3 nucleotides, and is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II; after the single-stranded oligonucleotide and a sense strand form a double-stranded oligonucleotide, the nucleotide sequence V constitutes a 3’ overhanging terminal of the antisense strand of the double-stranded oligonucleotide.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides; and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA. In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II; and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from CU or UU.In some embodiments, the single-stranded oligonucleotide comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 8, and the nucleotide sequence V has a base composition of CU.In some embodiments, the single-stranded oligonucleotide is the antisense strand of any one of siRNA 1 to siRNA 4 as show in Table 1; alternatively, the single-stranded oligonucleotide is the antisense strand of any one ofConjugates 1 to 5 as show in Table 2.In some embodiments, the single-stranded oligonucleotide of the present disclosure can independently exert pharmacodynamic activity. In some embodiments, the single-stranded oligonucleotide of the present disclosure is an antisense oligonucleotide (ASO). In some embodiments, the single-stranded oligonucleotide of the present disclosure is a single-stranded RNAi (ssRNAi) compound. In some embodiments, the single-stranded oligonucleotide of the present disclosure exerts pharmacodynamic activity as a single strand (e.g., an antisense strand) of a double-stranded oligonucleotide.The double-stranded oligonucleotide of the present disclosureIn another aspect, the present disclosure also provides a double-stranded oligonucleotide comprising a sense strand and an antisense strand, wherein each nucleotide in the sense strand is a modified or unmodified nucleotide, and the sense strand and the antisense strand are at least partially reverse complementary to form a double-stranded region, and wherein the antisense strand is the above single-stranded oligonucleotide of the present disclosure.In the double-stranded oligonucleotide of the present disclosure, the sense strand and the antisense strand each have a length of 19-26 nucleotides. In some embodiments, the length of the antisense strand is not shorter than the length of the sense strand. In some embodiments, the sense strand has a length of 19-23 nucleotides. As such, the length ratio of the sense strand to the antisense strand in the double-stranded oligonucleotide of the present disclosure can be 19 / 19, 19 / 20, 19 / 21, 19 / 22, 20 / 20, 20 / 21, 20 / 22, 20 / 23, 21 / 21, 21 / 22, 21 / 23, 21 / 24, 22 / 22, 22 / 23, 22 / 24, 22 / 25, 23 / 23, 23 / 24, 23 / 25, or 23 / 26. In some embodiments, the sense strand has a length of 15- 26 or 17-24 nucleotides. In some embodiments, the sense strand has a length of 19-21 nucleotides. In some embodiments, for ease of synthesis, the sense strand has a length of 19-21 nucleotides, and the antisense strand has a length of 19-23 nucleotides. In some embodiments, the sense strand and the antisense strand have a length difference of 0-5 nucleotides. In some embodiments, the length of the sense strand is not greater than the length of the antisense strand. In some embodiments, the sense strand and the antisense strand have an equal length of 19, 20 or 21 nucleotides. In some embodiments, the sense strand has a length of 19-21 nucleotides, the antisense strand has a length of 20-24 nucleotides, and the length of the antisense strand is greater than the length of the sense strand by 1-3 nucleotides. In some embodiments, the length of the antisense strand is greater than the length of the sense strand by 2 nucleotides. In some embodiments, the sense strand has a length of 19 nucleotides, and the antisense strand has a length of 21 nucleotides; or the sense strand has a length of 21 nucleotides, and the antisensestrand has a length of 21 nucleotides; or the sense strand has a length of 21 nucleotides, and the antisense strand has a length of 23 nucleotides. In some embodiments, the sense strand has a length of 19 nucleotides, and the antisense strand has a length of 21 nucleotides. In some embodiments, the sense strand has a length of 21 nucleotides, and the antisense strand has a length of 23 nucleotides.In some embodiments, in the sense strand of the double-stranded oligonucleotide of the present disclosure, in the direction from 3’ terminal to 5’ terminal, 2 to 3 nucleotides of the 11th to 13th nucleotides of the sense strand are fluoro modified nucleotides, and the first nucleotide and / or the last nucleotide of the sense strand is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide (abbreviated as invab or ia, having the structure as shown by Formula (35)). In some embodiments, in the direction from 3’ terminal to 5’ terminal, the first nucleotide of the sense strand is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide. In some embodiments, in addition to the above-mentioned fluoro modified nucleotides and inverted abasic deoxyribonucleotide, the nucleotides at the remaining positions in the sense strand independently of one another are non-fluoro modified nucleotides, and each of the non- fluoro modified nucleotides is independently one selected from an alkoxy modified nucleotide, an alkyl modified nucleotide, an amine modified nucleotide, and a thermally destabilizing nucleotide.Formula (35)In some embodiments, the oxygen atom directly linked to the ribose ring, as shown in Formula (35) can be linked to the 3’ phosphate group of the penultimate nucleotide at 3’ terminal of the sense strand. In some embodiments, the oxygen atom directly linked to the ribose ring as shown in Formula (35) can be linked to the 3’ phosphate group of the 3’ terminal nucleotide of the sense strand, and the oxygen atom linked to the ribose ring via a methylene group as shown in Formula (35) can be linked to a hydrogen atom, a hydroxyl protecting group, or a delivery group as described below.In some embodiments, the oxygen atom linked to the ribose ring via a methylene group as shown in Formula (35) can be linked to the 5’ phosphate group of the penultimate nucleotide at 5’ terminal of the sense strand. In some embodiments, the oxygen atom linked to the ribose ring via a methylene group as shown in Formula (35) is linked to the 5’ phosphate group of the penultimate nucleotide at 5’ terminal of the sense strand, and the oxygen atom directly linked to the ribose ring as shown in Formula (35) can be linked to a hydrogen atom, a hydroxyl protecting group, or a delivery group as described below.In some embodiments, in the direction from 3’ terminal to 5’ terminal, the 11th and 13th nucleotides or the 11th to 13th nucleotides in the sense strand are fluoro modified nucleotides, the first and / or last nucleotide in the sense strand is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions of the sense strand are all alkoxy modified nucleotides.In some embodiments, the sense strand comprises 19-21 nucleotides, and the antisense strand comprises 21-23 nucleotides; in the direction from 3’ terminal to 5’ terminal, the 11th and 13th nucleotides or the 11th to 13th nucleotides of the sense strand are fluoro modified nucleotides, the first and / or last nucleotide of the sense strand is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions independently of one another are alkoxy modified nucleotides. In this case, through the position coordination of the modified nucleotides in the sense strand and the antisense strand, the doublestranded oligonucleotide of the present disclosure exhibits better stability and / or RISC complexforming activity, thereby demonstrating stable and efficient inhibitory activity against PCSK9 mRNA. In some embodiments, each of the alkoxy modified nucleotides independently of one another is a methoxy modified nucleotide.In some embodiments, in the sense strand, at least one of the linking groups linking two adjacent nucleotides is a phosphate ester group with modification group(s), and the phosphate ester group with modification group(s) is present in at least one position of the positions between two adjacent nucleotides of the 1st to the 5th nucleotides at 5’ terminal of the sense strand and the positions between two adjacent nucleotides of the 1st to the 5th nucleotides at 3’ terminal of the sense strand. In this case, the double-stranded oligonucleotide of the present disclosure achieves a good balance between the ability to resist exonucleases and PCSK9 mRNA, thereby showing enhanced stability while maintaining highly efficient inhibitory activity against PCSK9 mRNA. In some embodiments, 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the sense strand, and / or 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 3’ terminal of the sense strand are each independentlyphosphate ester groups with modification group(s). In some embodiments, all 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the sense strand are each independently phosphate ester groups with modification group(s). In some embodiments, all 4 groups of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 3’ terminal of the sense strand are each independently phosphate ester groups with modification group(s). In some embodiments, the linking groups linking two adjacent nucleotides of the 1st to 3rd, 1st to 4th or 1st to 5th nucleotides at 5’ terminal and / or 3’ terminal of the sense strand are phosphate ester groups with modification group(s). In some embodiments, the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the sense strand are phosphate ester groups with modification group(s). The definition and selection range of the phosphate ester group with modification group(s) are the same as the above phosphate ester group with modification group(s) of the antisense strand of the present disclosure. In some embodiments, each phosphate ester group with modification group(s) is independently a phosphorothioate group having the structure as shown by Formula (28).In some embodiments, the sense strand is the sense strand of any one of siRNA 1 to siRNA 4 as shown in Table 1; in some embodiments, the sense strand is the sense strand of any one of Conjugates 1 to 5 as shown in Table 2.In some embodiments, the sense strand comprises 19-21 nucleotides and the antisense strand comprises 21-23 nucleotides; in the direction from 3’ terminal to 5’ terminal in the sense strand, the 11th and 13th nucleotides, or the 11th to 13th nucleotides are fluoro modified nucleotides, the first nucleotide and / or the last nucleotide of the sense strand are an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions independently of one another are alkoxy modified nucleotides; 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the sense strand and / or 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 3’ terminal of the sense strand are each independently phosphate ester groups with modification group(s).In some embodiments, the sense strand comprises 19-21 nucleotides and the antisense strand comprises 21-23 nucleotides; in the direction from 3’ terminal to 5’ terminal in the sense strand, the 11th to 13th nucleotides are fluoro modified nucleotides, the first nucleotide is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions independently of one another are alkoxy modified nucleotides; 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of thesense strand and / or 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 3’ terminal of the sense strand are each independently phosphate ester groups with modification group(s); in a 5’ to 3’ direction in the antisense strand, the 13th nucleotide is a substituted alkoxy modified nucleotide, the 14th nucleotide is a nucleotide X, the 2nd, 6th and 16th nucleotides are fluoro modified nucleotides, and each remaining nucleotide in the antisense strand independently of one another is an alkoxy modified nucleotide; the linking groups linking any two adjacent nucleotides of the 1st to the 3rd nucleotides at 5’ terminal and the linking groups linking any two adjacent nucleotides of the 1st to the 3rd nucleotides at 3’ terminal of the antisense strand independently of one another are phosphate ester groups with modification group(s); and the 5’ terminal nucleotide of the antisense strand is a 5 ’-hydroxy nucleotides as shown by Formula (29) or 5’-vinyl phosphate modified nucleotides as shown by Formula (31). In some embodiments, the linking groups linking every two adjacent nucleotides of the 1st to 2nd, 1st to 3rd, 1st to 4th, or 1st to 5th nucleotides at 5’ terminal and / or 3’ terminal of the sense strand are phosphate ester groups with modification group(s), and the linking groups linking the remaining adjacent nucleotides of the sense strand are phosphate ester groups. In some embodiments, the linking groups linking every two adjacent nucleotides of the 1st to 3rd, 1st to 4th or 1st to 5th nucleotides at 5’ terminal of the sense strand are phosphate ester groups with modification group(s), and the linking groups linking the remaining adjacent nucleotides of the sense strand are phosphate ester groups. In some embodiments, the linking groups linking two adjacent nucleotides of the 1st to 2rd, 1st to 3rd, 1st to 4th, or 1st to 5th nucleotides at 3’ terminal of the sense strand are phosphate ester groups with modification group(s), and the linking groups linking the remaining adjacent nucleotides of the sense strand are phosphate ester groups. In some embodiments, the phosphate ester group with modification group(s) is a phosphorothioate group having the structure as shown by Formula (28), and the alkoxy modified nucleotide is a 2’ -methoxy modified nucleotide.In some embodiments, the sense strand comprises 19 nucleotides and the antisense strand comprises 21 nucleotides; in the direction from 3’ terminal to 5’ terminal in the sense strand, the 11th and 13th nucleotides are fluoro modified nucleotides, the first nucleotide is an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions independently of one another are methoxy modified nucleotides; the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the sense strand are phosphorothioate groups.In some embodiments, in the double-stranded oligonucleotide of the present disclosure, the sense strand comprises 19 nucleotides and the antisense strand comprises 21 nucleotides; in the direction from 3’ terminal to 5’ terminal in the sense strand, the 11th to 13th nucleotides arefluoro modified nucleotides, the first nucleotide is an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions independently of one another are methoxy modified nucleotides; 1 to 4 of the linking groups linking adjacent nucleotides of the 1st to 5th nucleotides at 5’ terminal of the sense strand is each independently a phosphorothioate group; in a 5’ to 3’ direction in the antisense strand, the 13th nucleotide is a 2’-O-methoxyethyl modified nucleotide, the 14th nucleotide is a deoxynucleotide, the 2nd, 6th and 16th nucleotides are fluoro modified nucleotides, and each remaining nucleotide in the antisense strand independently of one another is a methoxy modified nucleotide; in the antisense strand, the linking groups linking two adjacent nucleotides of the 1st to the 3rd nucleotides at 5’ terminal and the linking groups linking two adjacent nucleotides of the 1st to the 3rd nucleotides at 3’ terminal of the antisense strand are phosphorothioate groups; and the 5’ terminal nucleotide in the antisense strand is a 5’-hydroxy nucleotide as shown by Formula (29) or a 5’-vinyl phosphate modified nucleotide as shown by Formula (31).By adopting above modification schemes, the single- stranded oligonucleotide, the doublestranded oligonucleotide, the conjugate and / or the pharmaceutical composition of the present disclosure could achieve a good balance between PCSK9 mRNA regulatory activity and in vivo stability. In the context of the present disclosure, a “modification scheme” refers to a combination of nucleotide ribose modifications, phosphate modifications, 5’ terminal modifications, and / or base modifications which are unrelated or weakly related to specific sequences and are in different numbers, positions, and types. In some embodiments, by adopting the above modification schemes, the double-stranded oligonucleotide of the present disclosure could maintain excellent stability without significantly reducing the original pharmaceutical activity of the double-stranded oligonucleotide, to achieve a good balance between PCSK9 mRNA regulatory activity and in vivo stability. In some embodiments, the double-stranded oligonucleotide of the present disclosure is siRNA, and by adopting the above modification schemes, the double-stranded oligonucleotide of the present disclosure could maintain excellent stability without significantly reducing the original RNAi activity of the siRNA, to achieve a good balance between inhibitory activity against PCSK9 mRNA and in vivo stability.In some embodiments, the double-stranded oligonucleotide of the present disclosure consists of a double-stranded region that is substantially reverse complementary or completely reverse complementary, and one or two overhanging terminals of the sense strand and / or one or two overhanging terminals of the antisense strand. In some embodiments, the double-stranded oligonucleotide of the present disclosure consists of a double-stranded region that is substantially reverse complementary or completely reverse complementary and one overhangingterminal of the antisense strand.In some embodiments, the double-stranded region formed by the sense strand and the antisense strand comprises at least 16 base pairs. In some embodiments, the double-stranded region formed by the sense strand and the antisense strand comprises 16-23 base pairs. In some embodiments, the double-stranded region formed by the sense strand and the antisense strand comprises 18, 19, 20, or 21 base pairs.In the context of the present disclosure, a “double-stranded region” is a double-stranded structure formed between the shortest nucleotide sequences (including all bases that form base pairs) in each single strand of a double-stranded nucleic acid structure. Thus, the doublestranded region consists of all base pairs and all base mismatches located among the base pairs in the double-stranded nucleic acid structure. In some embodiments, the number of the base mismatches is no more than 20%, 15%, 10%, or 5% of the total number of the base pairs that form the double-stranded region. In some embodiments, the number of the base mismatches in the double-stranded region is no more than 3, no more than 2, or no more than 1. In some embodiments, the double-stranded nucleic acid structure comprises a double-stranded region and one or more overhanging terminals consisting of the nucleotides that do not form base pairing in one or two single strands. In some embodiments, the double-stranded nucleic acid structure includes only the double-stranded region.In some embodiments, the sense and antisense strands form a double-stranded region spanning at least 16 nucleotide positions; that is, the double-stranded region formed by the sense strand and the antisense strand comprises at least 16 base pairs. In the context of the present disclosure, each base pair that forms a double-stranded region is independently complementary or mismatched. In some embodiments, the sense strand and the antisense strand form a doublestranded region spanning 16-23 nucleotide positions; that is, the double-stranded region formed by the sense strand and the antisense strand comprises 16-23 base pairs. In some embodiments, the sense strand and the antisense strand form a double-stranded region spanning 18, 19, 20, or 21 nucleotide positions; that is, the double-stranded region formed by the sense strand and the antisense strand comprises 18, 19, 20, or 21 base pairs. In some embodiments, the sense strand and the antisense strand are substantially reverse complementary or completely reverse complementary within the double-stranded region. In some embodiments, the sense strand and the antisense strand of the double-stranded oligonucleotide of the present disclosure are substantially reverse complementary or completely reverse complementary over the entire nucleotide length.In some embodiments, the sense strand and the antisense strand are basically reversecomplementary, substantially reverse complementary, or completely reverse complementary. In some embodiments, the sense strand and the antisense strand are substantially reverse complementary or completely reverse complementary within the double-stranded region. In some embodiments, in a 5’ to 3’ direction, at least the nucleotide sequence of the sense strand, except for the first and the last nucleotides, is substantially reverse complementary or completely reverse complementary to the antisense strand. In some embodiments, in a 5’ to 3’ direction, the nucleotide sequence of the sense strand, except for the last nucleotide, is completely reverse complementary to the antisense strand; or all the nucleotides of the sense strand are completely reverse complementary to the antisense strand.In some embodiments, in the double-stranded oligonucleotide of the present disclosure, the unmodified equivalent sequence of the sense strand comprises a nucleotide sequence having an equal length to the nucleotide sequence m with no more than 3 base differences, no more than 1 base difference, or no base difference, wherein the nucleotide sequence m is defined and selected as described above.In the context, an “unmodified equivalent sequence” refers to an oligonucleotide sequence that does not comprise any ribose ring modification, base modification, and phosphate backbone modification as compared with the original sequence which serves as the alignment reference. For example, the unmodified equivalent sequence of VPAmsCfsdTGmsUmia is ACUGUN, wherein N is A, C, G, or U.In the context, when a nucleotide sequence has a “base difference” from another nucleotide sequence, it means that the bases of the nucleotides at the same position therebetween are changed. For example, if a nucleotide base in the second sequence is A and the nucleotide base at the same position in the first sequence is U, C, G or T, then these two nucleotide sequences are considered as having a base difference at this position. When a base is modified, if the modification does not affect the purine-pyrimidine pairing relationship when the above doublestranded nucleic acid structure is formed, the modified base and the original base are considered as having no base difference therebetween. In some embodiments, it is considered that there is no base difference between U and T. In some embodiments, it is considered that there is no base difference between C and 5-methylcytosine (5mC). In some embodiments, if a nucleotide at a position is replaced with an abasic nucleotide or a nucleotide analogue thereof, it is also considered that there is a base difference at the position. When two nucleotide sequences are aligned to determine the number of base differences, they are aligned in a manner that minimizes the number of base differences among all alignment manners and the base differences are determined according to this alignment manner. In this case, “same position” means thecorresponding positions between the two nucleotide sequences in this alignment manner. For example, if when positions 1-5 of a nucleotide sequence A are aligned with positions 2-6 of a nucleotide sequence B in the same direction, the number of base differences is minimum as compared with other alignment manners, then “same position” means that position 1 of the nucleotide sequence A is aligned to position 2 of the nucleotide sequence B, position 2 of the nucleotide sequence A is aligned to position 3 of the nucleotide sequence B, and so on. In some embodiments, the number of base differences between two nucleotide sequences of different lengths refers to the number of base differences calculated within the nucleotide sequence segments spanning from the first nucleotide with no base difference to the last nucleotide with no base difference when the sequences are aligned in the above manner that minimizes the number of base differences. In some embodiments, the number of base differences between two nucleotide sequences of identical length means that the total number of base differences between the first nucleotide to the last nucleotide of any nucleotide sequence and the first nucleotide to the last nucleotide of another nucleotide sequence in the same direction. In some embodiments, no base difference between two nucleotide sequences of different lengths means that there is no base difference between the first nucleotide to the last nucleotide of the shorter nucleotide sequence and the nucleotide at each corresponding position of another nucleotide sequence in the same direction. In some embodiments, no base difference between two nucleotide sequences of identical length means that there is no base difference between the first nucleotide to the last nucleotide of one nucleotide sequence and the first nucleotide to the last nucleotide of another nucleotide sequence in the same direction. The double-stranded oligonucleotides of the present disclosure can be a variety of doublestranded oligonucleotides capable of regulating PCSK9 mRNA expression. In some embodiments, they can be double-stranded oligonucleotides that inhibit or down-regulate PCSK9 mRNA expression (such as siRNA); in some embodiments, they can be double-stranded oligonucleotides that activate or up-regulate PCSK9 mRNA expression (such as saRNA). In some embodiments, the double-stranded oligonucleotide is siRNA.In some embodiments, the double-stranded oligonucleotide of the present disclosure can be the following first, second, third, or fourth double-stranded oligonucleotide. Each double-stranded oligonucleotide will be described below, respectively.First double-stranded oligonucleotideIn some embodiments, the present disclosure provides a first double-stranded oligonucleotide, which comprises a sense strand and an antisense strand, wherein the sense strand comprises anucleotide sequence I, and the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 1 with no more than 3 base differences; and the antisense strand comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 2 with no more than 3 base differences: 5’ - UGUUUUGCUUUUGUAACUZi -3’ (SEQ ID NO: 1);5’ - Z2AGUUACAAAAGCAAAACA -3’ (SEQ ID NO: 2), wherein Zi is U, A or ia, wherein ia is an inverted abasic deoxyribonucleotide, and Z2 is A or U; the nucleotide sequence I comprises a nucleotide Z’i at the position corresponding to Zi; the nucleotide sequence II comprises a nucleotide Z’2 at the position corresponding to Z2, wherein Z’2 is the first nucleotide at 5’ terminal of the antisense strand. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 1 with no more than 3 base differences and the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 2 with no more than 3 base differences. In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II.In some embodiments, there is no more than 1 base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 1, and / or there is no more than 1 base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 1 with 1 base difference and / or the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 2 with 1 base difference.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 1 can include a difference at the position of Z’ 1 and / or a base difference at any other nucleotide position in the nucleotide sequence I.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 1 can include a base difference at the position of Z’ 1 and / or a base difference at a nucleotide position adjacent to Z’i.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: l is a base difference at the position of Z’ 1, wherein Z’ 1 is preferably an inverted abasic deoxyribonucleotide.In some embodiments, there is no base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 1. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 1 with nobase difference.In some embodiments, the difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2 includes a base difference at the position of Z’2, wherein Z’2 is selected from C or G. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2 is a difference at the position of Z’2, wherein Z’2 is selected from C or G.In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 2. Thus, in one embodiment, the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 2 with no base difference.In some embodiments, in a 5’ to 3’ direction, the 2nd to 19th nucleotides in the nucleotide sequence II are completely reverse complementary to PCSK9 mRNA. In some embodiments, the nucleotide sequence II is completely reverse complementary to the nucleotide sequence I; or there is a base mismatch between the second nucleotide in the nucleotide sequence II in a 5’ to 3’ direction and the second nucleotide in the nucleotide sequence I in the direction from 3’ terminal to 5’ terminal. By incorporating this base mismatch, higher inhibitory activity against PCSK9 mRNA can be achieved while maintaining low off-target effect.In some embodiments, the sense strand further comprises a nucleotide sequence III, and the antisense strand further comprises a nucleotide sequence IV, wherein the nucleotide sequence III has a length of 1, 2, 3 or 4 nucleotides, the nucleotide sequence IV and the nucleotide sequence III have an equal length and are substantially reverse complementary or completely reverse complementary to each other, and the nucleotide sequence III is linked to 5’ terminal of the nucleotide sequence I.In some embodiments, in a 5’ to 3’ direction, the nucleotide sequence III and the nucleotide sequence IV both have a length of 1 nucleotide, the base of the nucleotide sequence III is C, and the base of the nucleotide sequence IV is G; in this case, the length ratio of the sense strand to the antisense strand is 20 / 20. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is CC, and the base composition of the nucleotide sequence IV is GG; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21.Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is ACC, and the base composition of the nucleotide sequence IV is GGU; in this case, the length ratio of the sense strand to the antisense strand is 22 / 22. Alternatively, the nucleotide sequenceIII and the nucleotide sequence IV both have a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is GACC, and the base composition of the nucleotide sequence IV is GGUC; in this case, the length ratio of the sense strand to the antisense strand is 23 / 23. In some embodiments, the nucleotide sequence III and the nucleotide sequence IV have a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is CC, and the base composition of the nucleotide sequence IV is GG; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21.In some embodiments, the antisense strand further comprises a nucleotide sequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1-3 nucleotides and is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II, and after formation of the double-stranded oligonucleotide, constitutes a 3’ overhanging terminal of the antisense strand.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides, and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA.In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GG or UU.In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 2, the nucleotide sequence I consists of SEQ ID NO: 1, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GG.Second double-stranded oligonucleotideIn some embodiments, the present disclosure provides a second double-stranded oligonucleotide, which comprises a sense strand and an antisense strand, wherein the sense strand comprises a nucleotide sequence I, and the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 3 with no more than 3 base differences; and the antisense strand comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 4 with no more than 3 base differences:5’ - UUUUGUAACUUGAAGAUAZ3-3’ (SEQ ID NO: 3); 5’ - Z4UAUCUUCAAGUUACAAAA -3’ (SEQ ID NO: 4), wherein Z3 is U, A or ia and Z4 is A or U; the nucleotide sequence I comprises a nucleotide Z’3 at the position corresponding to Z3; the nucleotide sequence II comprises a nucleotide Z’4 at the position corresponding to Z4, wherein Z’4 is the first nucleotide at 5’ terminal of the antisense strand. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 3 with no more than 3 base differences and the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 4 with no more than 3 base differences.In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II.In some embodiments, there is no more than 1 base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 3, and / or there is no more than 1 base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 3 with 1 base difference and / or the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 4 with 1 base difference. Therein, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 3 can include a difference at the position of Z’3 and / or a base difference at any other nucleotide position in the nucleotide sequence I.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 3 can include a base difference at the position of Z’3 and / or a base difference at a nucleotide position adjacent to Z’3.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 3 is a base difference at the position of Z’3, wherein Z’3 is preferably an inverted abasic deoxyribonucleotide.In some embodiments, there is no base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 3. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 3 with no base difference.In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4 includes a base difference at the position of Z’4, wherein Z’4 is selected from C or G. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4 is a base differenceat the position of Z’4, wherein Z’4 is selected from C or G.In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 4. Thus, in one embodiment, the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 4 with no base difference.In some embodiments, in a 5’ to 3’ direction, the 2nd to 19th nucleotides in the nucleotide sequence II are completely reverse complementary to PCSK9 mRNA. In some embodiments, the nucleotide sequence II is completely reverse complementary to the nucleotide sequence I. Alternatively, there is a base mismatch between the second nucleotide in the nucleotide sequence II in a 5’ to 3’ direction and the second nucleotide in the nucleotide sequence I in the direction from 3’ terminal to 5’ terminal. By incorporating this base mismatch, higher inhibitory activity against PCSK9 mRNA can be achieved while maintaining low off-target effect.In some embodiments, the sense strand further comprises a nucleotide sequence III, and the antisense strand further comprises a nucleotide sequence IV, wherein the nucleotide sequence III has a length of 1, 2, 3 or 4 nucleotides, the nucleotide sequence IV and the nucleotide sequence III have an equal length and are substantially reverse complementary or completely reverse complementary to each other, and the nucleotide sequence III is linked to 5’ terminal of the nucleotide sequence I.In some embodiments, in a 5’ to 3’ direction, the nucleotide sequence III and the nucleotide sequence IV both have a length of 1 nucleotide, the base of the nucleotide sequence III is C, and the base of the nucleotide sequence IV is G; in this case, the length ratio of the sense strand to the antisense strand is 20 / 20. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is GC, and the base composition of the nucleotide sequence IV is GC; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21.Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is UGC, and the base composition of the nucleotide sequence IV is GCA; in this case, the length ratio of the sense strand to the antisense strand is 22 / 22. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is UUGC, and the base composition of the nucleotide sequence IV is GCAA; in this case, the length ratio of the sense strand to the antisense strand is 23 / 23. In some embodiments, the nucleotide sequence III and the nucleotide sequence IV have a length of 2 nucleotides, and in a 5’ to 3’ direction, the basecomposition of the nucleotide sequence III is GC, and the base composition of the nucleotide sequence IV is GC; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21.In some embodiments, the antisense strand further comprises a nucleotide sequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1-3 nucleotides, is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II, and after formation of the double-stranded oligonucleotide, constitutes a 3’ overhanging terminal of the antisense strand.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides, and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA.In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GC or UU.In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 4, the nucleotide sequence I consists of SEQ ID NO: 3, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the nucleotide sequence V has a base composition of GC.Third double-stranded oligonucleotideIn some embodiments, the present disclosure provides a third double-stranded oligonucleotide, which comprises a sense strand and an antisense strand, wherein the sense strand comprises a nucleotide sequence I, and the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 6 with no more than 3 base differences; and the antisense strand comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 6 with no more than 3 base differences: 5’- CAACUUUUCUAGACCUGUZs -3’ (SEQ ID NO: 5);5’ - Z6ACAGGUCUAGAAAAGUUG -3’ (SEQ ID NO: 6), wherein Z5 is U, A or ia, and Ze is A or U; the nucleotide sequence I comprises a nucleotide Z’5 at the position corresponding to Z5; the nucleotide sequence II comprises a nucleotide Z’ & at the position corresponding to Ze, wherein Z’e is the first nucleotide at 5’ terminal of the antisense strand. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 5 with no more than 3 base differences and thenucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 6 with no more than 3 base differences.In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II.In some embodiments, there is no more than 1 base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 5, and / or there is no more than 1 base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 5 with 1 base difference and / or the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 6 with 1 base difference. Therein, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 5 can include a difference at the position of Z’s, and / or a base difference at any other nucleotide position in the nucleotide sequence I.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 5 can include a base difference at the position of Z’s and / or a base difference at a nucleotide position adjacent to ZIn some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 5 is a base difference at the position of Z wherein Z’s is preferably an inverted abasic deoxyribonucleotide.In some embodiments, there is no base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 5. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 5 with no base difference.In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6 includes a base difference at the position of Z’e, wherein Z’e is selected from C or G. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6 is a base difference at the position of Z’e, wherein Z’e is selected from C or G.In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 6. Thus, in one embodiment, the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 6 with no base difference.In some embodiments, in a 5’ to 3’ direction, the 2nd to 19th nucleotides in the nucleotide sequence II are completely reverse complementary to PCSK9 mRNA. In some embodiments,the nucleotide sequence II is completely reverse complementary to the nucleotide sequence I. Alternatively, there is a base mismatch between the second nucleotide in the nucleotide sequence II in a 5’ to 3’ direction and the second nucleotide in the nucleotide sequence I in the direction from 3’ terminal to 5’ terminal. By incorporating this base mismatch, higher inhibitory activity against PCSK9 mRNA can be achieved while maintaining low off-target effect.In some embodiments, the sense strand further comprises a nucleotide sequence III, and the antisense strand further comprises a nucleotide sequence IV, wherein the nucleotide sequence III has a length of 1, 2, 3 or 4 nucleotides, the nucleotide sequence IV and the nucleotide sequence III have an equal length and are substantially reverse complementary or completely reverse complementary to each other, and the nucleotide sequence III is linked to 5’ terminal of the nucleotide sequence I.In some embodiments, in a 5’ to 3’ direction, the nucleotide sequence III and the nucleotide sequence IV both have a length of 1 nucleotide, the base of the nucleotide sequence III is C, and the base of the nucleotide sequence IV is G; in this case, the length ratio of the sense strand to the antisense strand is 20 / 20. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is GC, and the base composition of the nucleotide sequence IV is GC; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is AGC, and the base composition of the nucleotide sequence IV is GCU; in this case, the length ratio of the sense strand to the antisense strand is 22 / 22. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is CAGC, and the base composition of the nucleotide sequence IV is GCUG; in this case, the length ratio of the sense strand to the antisense strand is 23 / 23. In some embodiments, the nucleotide sequence III and the nucleotide sequence IV have a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is GC, and the base composition of the nucleotide sequence IV is GC; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21.In some embodiments, the antisense strand further comprises a nucleotide sequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1-3 nucleotides, is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II, and after formation of the double-strandedoligonucleotide, constitutes a 3’ overhanging terminal of the antisense strand.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides, and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA.In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GC or UU.In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 6, the nucleotide sequence I consists of SEQ ID NO: 5, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the nucleotide sequence V has a base composition of GC.Fourth double-stranded oligonucleotideIn some embodiments, the present disclosure provides a fourth double-stranded oligonucleotide, which comprises a sense strand and an antisense strand, wherein the sense strand comprises a nucleotide sequence I, and the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 7 with no more than 3 base differences; and the antisense strand comprises a nucleotide sequence II, and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 8 with no more than 3 base differences: 5’- CCAACUUUUCUAGACCUGZ7 -3’ (SEQ ID NO: 7);5’ - ZsCAGGUCUAGAAAAGUUGG -3’ (SEQ ID NO: 8), wherein Z7 is U, A or ia, and Zs is A or U; the nucleotide sequence I comprises a nucleotide Z’7 at the position corresponding to Z7; the nucleotide sequence II comprises a nucleotide Z’s at the position corresponding to Zs, wherein Z’s is the first nucleotide at 5’ terminal of the antisense strand. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 7 with no more than 3 base differences and the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 8 with no more than 3 base differences.In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II.In some embodiments, there is no more than 1 base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 7, and / or there is no more than 1 base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ IDNO: 8. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 7 with 1 base difference and / or the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 8 with 1 base difference. Therein, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 7 can include a difference at the position of Z’7, and / or a base difference at any other nucleotide position in the nucleotide sequence I.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 7 can include a base difference at the position of Z’7, and / or a base difference at a nucleotide position adjacent to Z’7.In some embodiments, the base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 7 is a base difference at the position of Z’7, wherein Z’7 is preferably an inverted abasic deoxyribonucleotide.In some embodiments, there is no base difference between the nucleotide sequence I and the nucleotide sequence shown in SEQ ID NO: 7. Thus, in one embodiment, the nucleotide sequence I comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 7 with no base difference.In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8 includes a base difference at the position of Z’s, wherein Z’s is selected from C or G. In some embodiments, the base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8 is a difference at the position of Z’s, wherein Z’s is selected from C or G.In some embodiments, there is no base difference between the nucleotide sequence II and the nucleotide sequence shown in SEQ ID NO: 8. Thus, in one embodiment, the nucleotide sequence II comprises or consists of the nucleotide sequence as shown in SEQ ID NO: 8 with no base difference.In some embodiments, in a 5’ to 3’ direction, the 2nd to 19th nucleotides in the nucleotide sequence II are completely reverse complementary to PCSK9 mRNA. In some embodiments, the nucleotide sequence II is completely reverse complementary to the nucleotide sequence I. Alternatively, there is a base mismatch between the second nucleotide in the nucleotide sequence II in a 5’ to 3’ direction and the second nucleotide in the nucleotide sequence I in the direction from 3’ terminal to 5’ terminal. By incorporating this base mismatch, higher inhibitory activity against PCSK9 mRNA can be achieved while maintaining low off-target effect.In some embodiments, the sense strand further comprises a nucleotide sequence III, and the antisense strand further comprises a nucleotide sequence IV, wherein the nucleotide sequence IIIhas a length of 1, 2, 3 or 4 nucleotides, the nucleotide sequence IV and the nucleotide sequence III have an equal length and are substantially reverse complementary or completely reverse complementary to each other, and the nucleotide sequence III is linked to 5’ terminal of the nucleotide sequence I.In some embodiments, in a 5’ to 3’ direction, the nucleotide sequence III and the nucleotide sequence IV both have a length of 1 nucleotide, the base of the nucleotide sequence III is G, and the base of the nucleotide sequence IV is C; in this case, the length ratio of the sense strand to the antisense strand is 20 / 20. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is AG, and the base composition of the nucleotide sequence IV is CU; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 3 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is CAG, and the base composition of the nucleotide sequence IV is CUG; in this case, the length ratio of the sense strand to the antisense strand is 22 / 22. Alternatively, the nucleotide sequence III and the nucleotide sequence IV both have a length of 4 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is ACAG, and the base composition of the nucleotide sequence IV is CUGU; in this case, the length ratio of the sense strand to the antisense strand is 23 / 23. In some embodiments, the nucleotide sequence III and the nucleotide sequence IV have a length of 2 nucleotides, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence III is AG, and the base composition of the nucleotide sequence IV is CU; in this case, the length ratio of the sense strand to the antisense strand is 21 / 21.In some embodiments, the antisense strand further comprises a nucleotide sequence V, wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide, and the nucleotide sequence V has a length of 1-3 nucleotides, is linked to 3’ terminal of the nucleotide sequence IV or the nucleotide sequence II, and after formation of the double-stranded oligonucleotide, constitutes a 3’ overhanging terminal of the antisense strand.In some embodiments, the nucleotide sequence V has a length of 2 nucleotides, and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymine deoxyribonucleotides, 2 contiguous uracil nucleotides, or is completely reverse complementary to PCSK9 mRNA. In some embodiments, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the base composition of the nucleotide sequence V is selected from GC or UU.In some embodiments, the sense strand comprises only the nucleotide sequence I, and the antisense strand comprises only the nucleotide sequence II and the nucleotide sequence V, wherein the nucleotide sequence II consists of SEQ ID NO: 8, the nucleotide sequence I consists of SEQ ID NO: 7, the nucleotide sequence V is linked to 3’ terminal of the nucleotide sequence II, and in a 5’ to 3’ direction, the nucleotide sequence V has a base composition of CU.In some embodiments, the double-stranded oligonucleotide is one of siRNA 1 to siRNA 4 as shown in Table 1 below:Table 1 The siRNA sequences of the present disclosureTherein, C, G, U, A and T represent the base composition of the nucleotides; o represents that the nucleotide represented by a capital letter adjacent to the left side of the letter o is an alkoxy modified nucleotide; f represents that the nucleotide represented by a capital letter adjacent to the left side of the letter f is a fluoro modified nucleotide; e represents that the nucleotide represented by a capital letter adjacent to the left side of the letter e is a substituted alkoxy modified nucleotide; d represents that the nucleotide represented by a capital letter adjacent to the right side of the letter d is a deoxynucleotide; s represents that the two nucleotides represented by capital letters adjacent to both sides of the letter s are linked by a phosphorothioate linkage; Pl represents that the nucleotide represented by a capital letter adjacent to the right side of Pl is a 5’-phosphate nucleotide, a 5’-hydroxy nucleotide, a 5’- phosphorothioate modified nucleotide (Ps), or a 5 ’-vinyl phosphate (VP) modified nucleotides; ia represents an inverted abasic deoxyribonucleotide; and in the above sequences, each U can be independently interchanged with T, and / or each C can be independently replaced by 5mC, and such replacement does not significantly reduce PCSK9 mRNA expression regulatory activity and / or off-target effect inhibitory activity of the double-stranded oligonucleotides. In someembodiments, each alkoxy modified nucleotide is a 2’ -methoxy modified nucleotide. In some embodiments, each substituted alkoxy modified nucleotide is a 2’-O-methoxyethyl (represented by moe) modified nucleotide.The single-stranded oligonucleotide and / or double-stranded oligonucleotide provided in the present disclosure can be obtained by conventional methods in the art for preparing oligonucleotides, such as solid phase synthesis method and liquid phase synthesis method. For solid phase synthesis, commercial customization services are already available. A modified nucleotide group can be introduced into the single-stranded oligonucleotide and / or doublestranded oligonucleotide of the present disclosure by using a nucleoside monomer having the corresponding modification, wherein the methods for preparing the nucleoside monomer having the corresponding modification and the methods for introducing the modified nucleotide group into the single-stranded oligonucleotide and / or double- stranded oligonucleotide are also well- known to those skilled in the art. All modified nucleoside monomers could be either commercially available or prepared by known methods.The single-stranded oligonucleotide and the double-stranded oligonucleotides of the present disclosure can be used alone, or form a pharmaceutical composition with a pharmaceutically acceptable carrier, or form an oligonucleotide conjugate by binding to a delivery group, or be used in other forms. An effective amount of the single- stranded oligonucleotide, doublestranded oligonucleotide, pharmaceutical composition or oligonucleotide conjugate is contacted with a cell to regulate PCSK9 mRNA, or an effective amount of the single- stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate or pharmaceutical composition of the present disclosure is administered to a subject to regulate PCSK9 mRNA, thereby achieving the purpose of treating a pathological condition or disease related to the level of PCSK9 mRNA.The oligonucleotide conjugatesIn another aspect, the present disclosure provides an oligonucleotide conjugate comprising a oligonucleotide group and a delivery group conjugated to the oligonucleotide group, wherein the oligonucleotide group is independently a group formed by removing one or more atoms or atomic groups from the single-stranded oligonucleotide or the double-stranded oligonucleotide provided in the present disclosure. The oligonucleotide group formed by such removal has at least the same or essentially the same RNAi function as the single-stranded oligonucleotide or the double-stranded oligonucleotide per se. In some embodiments, the oligonucleotide group is a group formed by removing one atom or atomic group, such as a hydrogen atom, a hydroxygroup or a phosphate ester group from the single-stranded oligonucleotide or the doublestranded oligonucleotide provided in the present disclosure.In the context of the present disclosure, unless otherwise specified, “conjugation” means that two or more chemical moieties each having specific function are linked to each other via a covalent linkage. Correspondingly, a “conjugate” refers to a compound formed by covalent linkage of individual chemical moieties. Furthermore, an “oligonucleotide conjugate” represents a compound formed by covalently linking one or more chemical moieties each with specific functions to an oligonucleotide. According to the context, an oligonucleotide conjugate should be understood as a general term of multiple oligonucleotide conjugates or as an oligonucleotide conjugate as shown by a chemical formula. In the context of the present disclosure, a “conjugation molecule” should be understood as a specific compound capable of being conjugated to an oligonucleotide via reactions, thereby finally forming the specific compound of the oligonucleotide conjugate of the present disclosure.The delivery group is a group for delivering a single-stranded oligonucleotide group or a double-stranded oligonucleotide group to a cell that expresses PCSK9 mRNA. In some embodiments, the delivery group comprises a linking group and pharmaceutically acceptable targeting group(s), and the single-stranded oligonucleotide group or the double-stranded oligonucleotide group, the linking group and the targeting group(s) are sequentially linked covalently or non-covalently, and each of the targeting groups is independently selected from any ligand group capable of binding to a cell surface receptor. In some embodiments, the targeting group(s) targets liver. In some embodiments, at least one or each of said targeting groups is independently selected from ligands that can bind to asialoglycoprotein receptors on the surface of mammalian hepatocytes.In some embodiments, the number of the targeting groups is 1-6. In one embodiment, the number of the targeting groups is 2-4.The oligonucleotide group could be non-covalently or covalently conjugated to the delivery group; for example, the oligonucleotide group is covalently conjugated to the delivery group. In some embodiments, the oligonucleotide group is a double-stranded oligonucleotide group, and the conjugation site between the double-stranded oligonucleotide group and the delivery group can be at 3’ terminal or 5’ terminal of the sense strand, or at 3’ terminal or 5’ terminal of the antisense strand of the double-stranded oligonucleotide, or within the internal sequence of the double-stranded oligonucleotide. In some specific embodiments, the conjugation site between the double-stranded oligonucleotide group and the delivery group is at 3 ’-terminal of the sense strand of the double-stranded oligonucleotide.In some embodiments, the delivery group can be linked to any position of the nucleotide, such as the phosphate group, the 2’-, 3’- or 5’-hydroxyl group of the ribose or the base. When the delivery group is linked to the 3’- or 5’-terminal of the single-stranded oligonucleotide or the sense strand of the double-stranded oligonucleotide, the delivery group is typically linked to the oxygen atom formed by removing a hydrogen atom from the 3’ - or 5 ’-hydroxyl group of the nucleotide; when the delivery group is linked to an internal sequence of the single- stranded oligonucleotide or the double-stranded oligonucleotide, the delivery group is typically linked to a phosphate group, a ribose ring or a base. In some embodiments, the delivery group can be linked to the 3 ’-hydroxyl group of a nucleotide in the internal sequence of the single- stranded oligonucleotide or the double-stranded oligonucleotide when the nucleotides are linked via a 2’- 5 ’-phosphodiester bond. For various linking modes, reference can be made to the following nonpatent document: Muthiah Manoharan et.al. siRNA conjugates carrying sequentially assembled trivalent N-acetylgalactosamine linked through nucleosides elicit robust gene silencing in vivo in hepatocytes. ACS Chemical biology, 2015, 10 (5): 1181-7, which is incorporated herein by reference in its entirety.In some embodiments, the oligonucleotide and the delivery group can be linked by an acid- labile or reducible chemical bond which can be degraded under the acidic environment of cell endosomes, such that the double-stranded oligonucleotide group is converted to the oligonucleotide in free state. For non-degradable conjugation modes, the delivery group can be linked to the single-stranded oligonucleotide group or the sense strand of the double-stranded oligonucleotide group, thereby minimizing the effect of conjugation on the activity of the double-stranded oligonucleotide group.The targeting group can be linked to the oligonucleotide group via an appropriate linking group, and the appropriate linking group can be selected by those skilled in the art according to the specific type of the targeting group. For example, when the targeting group is a group that targets a hepatocyte surface receptor, the types of these linking groups and targeting groups and the linking modes with the oligonucleotide can be found in the disclosures of W02015006740A2, which is incorporated herein by reference in its entirety.In some embodiments, at least one or each of the targeting groups is selected from any ligand capable of binding to a cell surface receptor of a cell expressing PCSK9 mRNA. In some embodiments, each of said targeting groups is independently a ligand that has affinity to asialoglycoprotein receptors on the surface of mammalian hepatocytes. In some embodiments, each of said targeting groups is independently an asialoglycoprotein or a sugar. In some embodiments, each of said targeting groups is independently selected from the groups formedby removing one atom or group from the following sugars: D-mannopyranose, L- mannopyranose, D-arabinose, D-xylofuranose, L-xylofuranose, D-glucose, L-glucose, D- galactose, L-galactose, a-D-mannofuranose, P-D-mannofuranose, a-D-mannopyranose, P-D- mannopyranose, a-D-glucopyranose, P-D-glucopyranose, a-D-glucofuranose, P-D- glucofuranose, a-D-fructofuranose, a-D-fructopyranose, a-D-galactopyranose, P-D- galactopyranose, a-D-galactofuranose, P-D-galactofuranose, glucosamine, sialic acid, galactosamine, N-acetylgalactosamine, N-trifluoroacetylgalactosamine, N- propionylgalactosamine, N-n-butyrylgalactosamine, N-isobutyrylgalactosamine, 2-amino-3-O- [(R)-l -carboxy ethyl]-2-deoxy-P-D-glucopyranose, 2-deoxy-2-methylamino-L-glucopyranose, 4,6-dideoxy-4-formamido-2,3-di-O-methyl-D-mannopyranose, 2-deoxy-2-sulfoamino-D- glucopyranose, N-glycolyl-a-neuraminic acid, 5-thio-P-D-glucopyranose, methyl 2,3,4-tris-O- acetyl-l-thio-6-O-trityl-a-D-glucopyranoside, 4-thio-P-D-galactopyranose, ethyl 3,4,6,7-tetra- O-acetyl-2-deoxy-l,5-dithio-a-D-glucoheptopyranoside, 2,5-anhydro-D-allononitrile, ribose, D- ribose, D-4-thioribose, L-ribose, and L-4-thioribose.In some embodiments, at least one or each of said targeting groups is a galactose group or an N- acetylgalactosamine group. In some embodiments, each of said targeting groups is an N- acetylgalactosamine group. In some embodiments, the oligonucleotide group can regulate the expression level of PCSK9 mRNAin hepatic parenchymal cells.The delivery groups in the oligonucleotide conjugates of the present disclosure can be various delivery groups known to the skilled persons in the field of oligonucleotide drugs.In some embodiments, the linking group in the oligonucleotide conjugate of the present disclosure has a structure as shown in Formula (301):Formula (301) wherein k is an integer of 1-5, -JW ' represents the site where the group is covalently linked; all LAare linked to the same atom in Lc; alternatively, each LAis independently linked to different atoms in Lc.In some embodiments, Lchas a structure as shown in -NH-C(H)n30i(CH2O-)k, wherein k is an integer of 1-3 and n301=3-k; LBhas a length of 5-20 atoms. In some embodiments, each LAisindependently a straight-chain alkylene group of 5-20 carbon atoms in length, in which one or more methylene groups are optionally substituted by any one or more groups selected from the following groups consist of: C(O), NH, O, S, 1,2,3-triazolylene, succinimidylene.In some embodiments, LAhas a structure containing amide bonds as shown in Formula (302) and LBhas a structure as shown in Formula (303):Formula (303) wherein nso2, q302, and P302 independently of one another are an integer of 2-6, and optionally, n302, q302, and P302 independently of one another are 2 or 3; mos is an integer of 4-16, and optionally, mos is an integer of 8-12, — represents the site where the group is covalently linked.In some embodiments, the linking group has a structure as shown in Formula (304) or Formula (305):Formula (304)Formula (305)In the linking group, each LAis respectively linked to a targeting group by an ether bond, and is linked by forming an ether bond with the Lcpart via the oxygen atom of the hydroxyl group in the Lcpart; LBis linked by forming an amide bond with the nitrogen atom of the amino group in the Lcpart via the carbonyl group in Formula (303), and is linked by forming a phosphate ester bond or phosphorothioate bond with the double-stranded oligonucleotide group via an oxygen atom in Formula (303). In some embodiments, the oligonucleotide conjugates provided in the present disclosure have a structure as shown in Formula (305A):Formula (305 A) wherein Nu represents the oligonucleotide group formed by the single-stranded oligonucleotide or the double-stranded oligonucleotides provided in the present disclosure.In some embodiments, the linking group in the oligonucleotide conjugates of the present disclosure has the structure as shown in Formula (306):wherein nsoe is an integer of 0-3, and each psoe is independently an integer of 1-6, — - represents the site where the group is covalently linked; the linking group is linked by forming an ether bond with the targeting group via the oxygen atom marked by *; the linking group is linked by forming a phosphate ester bond or a phosphorothioate bond with the double-stranded oligonucleotide via at least one of the oxygen atom marked by #, and the remaining oxygen atom marked by # is linked to a hydrogen atom to form a hydroxyl group, or is linked to a C1-C3 alkyl group to form a C1-C3 alkoxy group;In some embodiments, the oligonucleotide conjugate of the present disclosure has the structure as shown in Formula (307):Formula (307)wherein Nu represents the oligonucleotide group formed by the single-stranded oligonucleotide or the double-stranded oligonucleotides provided in the present disclosure.In some embodiments, the oligonucleotide conjugate of the present disclosure has the structure as shown in Formula (308):Formula (308), wherein mos is an integer selected from 2-4;Each maos is independently an integer selected from 2-5;Each R308 is independently a hydrogen atom, methyl or ethyl, or two R308 linked to the same carbon atom form a carbonyl group with the carbon atom;One of the groups independently of one another represented by AO is an oligonucleotide group, which is a group formed by removing an atom or an atomic group from the single-stranded oligonucleotide or the double-stranded oligonucleotides of the present disclosure; each remaining Ao group is independently a targeting group, and each targeting group is identical or different, and has the same definition and selection range as those described above. each Li is independently a divalent linking group of 1-70 or 3-25 atoms in length;— - represents the site where the group is covalently linked.In some embodiments, each Li is independently a straight-chain alkylene group of 1-70 or 1-20 carbon atoms in length, wherein one or more carbon atoms are optionally replaced with any one or more groups selected from the group consisting of: C(O), NH, O, S, CH=N, S(O)2, OP(O)2, OP(O)(S), C2-C10 alkeylene, C2-C10 alkynylene, Ce-Cio arylene, C3-C18 heterocyclylene, and C5- C10 heteroarylene; and the straight-chain alkylene group optionally has any one or more substituents selected from the group consisting of: C1-C10 alkyl, Ce-Cio aryl, C5-C10 heteroaryl, C1-C10 haloalkyl, -OC1-C10 alkyl, -OC1-C10 alkylphenyl, -C1-C10 alkyl-OH, -OC1-C10 haloalkyl, -SC1-C10 alkyl, -SC1-C10 alkylphenyl, -C1-C10 alkyl-SH, -SC1-C10 haloalkyl, halo substituent, -OH, -SH, -NH2, -C1-C10 alkyl-NH2, -N(Ci-Cio alkyl)(Ci-Cio alkyl), -NH(Ci-Cio alkyl), N(Ci- C10 alkyl)(Ci-Cio alkylphenyl), -NH(Ci-Cio alkylphenyl), cyano, nitro, -CO2H, -C(O)O(Ci-Cio alkyl), -CON(Ci-Cio alkyl)(Ci-Cio alkyl), -CONH(Ci-Cio alkyl), -CONH2, -NHC(O)(Ci- C10 alkyl), -NHC(O)(phenyl), -N(Ci-Cio alkyl)C(0)(Ci-Cio alkyl), -N(Ci-C10 alkyl)C(O)(phenyl), -C(0)Ci-Cio alkyl, -C(0)Ci-Cio alkylphenyl, -C(0)Ci-Cio haloalkyl, -OC(0)Ci-Cio alkyl, -S02(Ci-Cio alkyl), -SO2(phenyl), -S02(Ci-Cio haloalkyl), -SO2NH2, -S02NH(CI-CIO alkyl), -SO2NH(phenyl), -NHS02(CI-CIO alkyl), -NHSO2(phenyl), and -NHS02(CI-CIO haloalkyl).As used herein, “alkyl” refers to a straight-chain and branched alkyl group having an indicated number of carbon atoms, usually 1 to 20 carbon atoms, for example, 1 to 10 carbon atoms, such as 1 to 8 or 1 to 6 carbon atoms. For example, Ci-Ce alkyl encompasses both straight-chain and branched alkyl of 1 to 6 carbon atoms. When mentioning an alkyl residue having a specific number of carbon atoms, all branched and straight-chain forms having that number of carbon atoms are intended to be encompassed; thus, for example, “butyl” is meant to include n-butyl, sec-butyl, isobutyl, and t-butyl; “propyl” includes n-propyl and isopropyl. Alkylene is a subset of alkyl, referring to a residue which is the same as alkyl, but has two attachment positions. As used herein, “saturated alkyl” refers to an alkyl group in which all carbon atoms are linked by single bonds and contain no carbon-carbon double bonds and / or carbon-carbon triple bonds.As used herein, “alkenyl” refers to an unsaturated branched or straight-chain hydrocarbon group having at least one carbon-carbon double bond which is obtained by respectively removing one hydrogen molecule from two adjacent carbon atoms of the parent alkyl. The group can be in either cis or trans configuration of the double bond. Typical alkenyl groups include, but not limited to, ethenyl; propenyl, such as, prop-l-en-l-yl, prop-l-en-2-yl, prop-2-en-l-yl (allyl), prop-2-en-2-yl; butenyl, such as, but-l-en-l-yl, but-l-en-2-yl, 2-methyl-prop-l-en-l-yl, but-2- en-l-yl, but-2-en-l-yl, but-2-en-2-yl, buta-l,3-dien-l-yl, buta-l,3-dien-2-yl; and the like. In certain embodiments, an alkenyl group has 2 to 20 carbon atoms, and in other embodiments, 2 to 10, 2 to 8, or 2 to 6 carbon atoms. Alkenylene is a subset of alkenyl, referring to a residue which is the same as alkenyl, but has two attachment positions.As used herein, “alkynyl” refers to an unsaturated branched or straight-chain hydrocarbon group having at least one carbon-carbon triple bond which is obtained by respectively removing two hydrogen molecules from two adjacent carbon atoms of the parent alkyl. Typical alkynyl groups include, but not limited to, ethynyl; propynyl, such as, prop-l-yn-l-yl, prop-2-yn-l-yl; butynyl, such as, but-l-yn-l-yl, but-l-yn-3-yl, but-3-yn-l-yl; and the like. In certain embodiments, an alkynyl group has 2 to 20 carbon atoms, and in other embodiments, 2 to 10, 2 to 8, or 2 to 6 carbon atoms. Alkynylene is a subset of alkynyl, referring to a residue which is the same as alkynyl, but has two attachment positions.As used herein, “alkoxy” refers to an alkyl group having an indicated number of carbon atoms attached through an oxygen bridge, such as, methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, pentyloxy, 2-pentyloxy, isopentyloxy, neopentyloxy, hexyloxy, 2- hexyloxy, 3-hexyloxy, 3 -methylpentyloxy, and the like. An alkoxy groups usually have 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms attached through an oxygen bridge.As used herein, “aryl” refers to a group derived from an aromatic monocyclic or multicyclic hydrocarbon ring system by removing a hydrogen atom from a ring carbon atom. The aromatic monocyclic or multicyclic hydrocarbon ring system contains only hydrogen and carbon, including six to eighteen carbon atoms, wherein at least one ring in the ring system is fully unsaturated, z.e., it contains a cyclic, delocalized (4n+2) ^-electron system in accordance with the Hiickel theory. Aryl groups include, but not limited to, phenyl, fluorenyl, naphthyl, and the like. Arylene is a subset of aryl, referring to a residue which is the same as aryl, but has two attachment positions.“Heteroaryl” refers to a group derived from a 3- to 18-membered aromatic ring radical, comprising two to seventeen carbon atoms and one to six heteroatoms selected from nitrogen, oxygen and sulfur. As used herein, a heteroaryl group can be a monocyclic, bicyclic, tricyclic, or tetracyclic ring system, wherein at least one ring in the ring system is fully unsaturated, z.e., it contains a cyclic, delocalized (4n+2) ^-electron system in accordance with the Hiickel theory. Heteroaryl includes fused or bridged ring systems. In some embodiments, the heteroatom in the heteroaryl group is an oxidized heteroatom. In some embodiments, the heteroaryl group comprises one or more nitrogen atoms. In some embodiments, one or more of the nitrogen atoms in the heteroaryl group are quaternized nitrogen atom(s). The heteroaryl is linked to the rest of the molecule through any ring atom. Examples of heteroaryl groups include, but not limited to, 1,2,3-triazolylene, azepinyl, acridinyl, benzimidazolyl, benzindolyl, 1,3-benzodioxazolyl, benzofuranyl, benzoxazolyl, benzo[d]thiazolyl, benzothiadiazolyl, benzo[Z>][l,4]dioxepinyl, benzo[b][l,4]oxazinyl, 1,4-benzodioxanyl, benzonaphthofuranyl, benzoxazolyl, benzodi oxolyl, benzodioxinyl, benzopyranyl, benzopyranonyl, benzofuranyl, benzofuranonyl, benzothienyl, benzothieno[3,2-d]pyrimidinyl, benzotriazolyl, benzo[4,6]imidazo[l,2-a]pyridinyl, carbazolyl, cinnolinyl, cyclopenta[d]pyrimidinyl, 6,7-dihydro-5H-cyclopenta[4,5]thieno[2,3-d]pyrimidinyl, 5,6-dihydrobenzo[h]quinazolinyl, 5,6-dihydrobenzo[h]cinnolinyl, 6,7-dihydro-5H-benzo[6,7]cyclohepta[l,2-c]pyridazinyl, dibenzofuranyl, dibenzothienyl, furanyl, furanonyl, furo[3,2-c]pyridinyl, 5,6,7,8,9,10-hexahydrocycloocta[d]pyrimidinyl, 5,6,7,8,9,10-hexahydrocycloocta[d]pyridazinyl,5,6,7,8,9,10-hexahydrocycloocta[d]pyridinyl, isothiazolyl, imidazolyl, indazolyl, indolyl, isoindolyl, indolinyl, isoindolinyl, isoquinolyl, indolizinyl, isoxazolyl,5.8-methano-5,6,7,8-tetrahydroquinazolinyl, naphthyridinyl, 1,6-naphthyri dinonyl, oxadiazolyl, 2-oxoazepinyl, oxazolyl, oxiranyl, 5,6,6a,7,8,9,10,10a-octahydrobenzo[h]quinazolinyl,1 -phenyl- UT-pyrrolyl, phenazinyl, phenothiazinyl, phenoxazinyl, phthalazinyl, pteridinyl, purinyl, pyrrolyl, pyrazolyl, pyrazolo[3,4-d]pyrimidinyl, pyridinyl, pyrido[3,2-d]pyrimidinyl, pyrido[3,4-d]pyrimidinyl, pyrazinyl, pyrimidinyl, pyridazinyl, pyrrolyl, quinazolinyl, quinoxalinyl, quinolinyl, tetrahydroquinolinyl, 5,6,7,8-tetrahydroquinazolinyl,5.6.7.8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidinyl,6.7.8.9-tetrahydro-5H-cyclohepta[4,5]thieno[2,3-d]pyrimidinyl, 5,6,7,8-tetrahydropyrido[4,5-c]pyridazinyl, thiazolyl, thiadiazolyl, triazolyl, tetrazolyl, triazinyl, thieno[2,3-d]pyrimidinyl, thieno[3,2-d]pyrimidinyl, thieno[2,3-c]pridinyl, and thienyl.In the context of the present disclosure, a “substituted” group, such as substituted alkyl group, substituted alkoxy group, substituted amino group, substituted aliphatic group, substituted heteroaliphatic group, substituted acyl group, substituted aryl group, or substituted heteroaryl group, unless otherwise specified, refers to a group formed by replacing hydrogen atom(s) in the group with one or more substituents. For example, “substituted alkoxy group” refers to an alkoxy group formed by replacing one or more hydrogen atoms in the alkoxy group with substituent(s). Those skilled in the art could understand that the compounds that can be used in the present disclosure could comprise various substituents, as long as the introduction of the substituents does not affect the functions of the present disclosure and can realize the purpose of the present disclosure. In some embodiments, the substituent is selected from the group consisting of the following groups: C1-C10 alkyl, Ce-Cio aryl, C5-C10 heteroaryl, Ci- C10 haloalkyl, -OC1-C10 alkyl, -OC1-C10 alkylphenyl, -C1-C10 alkyl-OH, -OC1-C10 haloalkyl, -SC1-C10 alkyl, -SC1-C10 alkylphenyl, -C1-C10 alkyl-SH, -SC1-C10 haloalkyl, halo substituent, -OH, -SH, -NH2, -C1-C10 alkyl-NH2, -N(Ci-Cio alkyl)(Ci-Cio alkyl), -NH(Ci-Cio alkyl), -N(Ci- C10 alkyl)( C1-C10 alkylphenyl), -NH(Ci-Cio alkylphenyl), -CN, -NO2, -CO2H, -C(O)OCi- C10 alkyl, -CON(Ci-Cio alkyl)(Ci-Cio alkyl), -CONH(Ci-Cio alkyl), -CONH2, -NHC(O)(Ci- C10 alkyl), -NHC(O)(phenyl), -N(Ci-Cio alkyl)C(0)(Ci-Cio alkyl), -N(Ci-C10 alkyl)C(O)(phenyl), -C(0)Ci-Cio alkyl, -C(0)Ci-Cio alkylphenyl, -C(0)Ci-Cio haloalkyl, -OC(0)Ci-Cio alkyl, -S02(Ci-Cio alkyl), -SO2(phenyl), -S02(Ci-Cio haloalkyl), -SO2NH2, -S02NH(CI-CIO alkyl), -SO2NH(phenyl), -NHS02(CI-CIO alkyl), -NHSO2(phenyl), and -NHS02(CI-CIO haloalkyl). In some embodiments, the substituent is one of -C1-C3 alkyl, -Ce-Cs aryl, -O-C1-C3 alkyl, -O-(Ci-C3 alkyl)phenyl, halogen, -OH, -NH2, -CN, or -NO2.Those skilled in the art would understand, with respect to any group containing one or more substituents, that such groups are not intended to introduce any substitution or substitution pattern that is sterically impractical, synthetically non-feasible and / or inherently unstable. Those skilled in the art would understand that, although Li is defined as a linking group formed by substitution or replacement starting from a linear alkylene for convenience, but it may not be a linear group or be named differently, such as an amine or alkenyl produced by the above replacement and / or substitution. Unless otherwise specified, in the chemical structure of the present disclosure, the "length" of any group means that the number of atoms in the longest atomic chain of the group without counting hydrogen atoms; in the calculation of the length of a group, when there are multiple linking modes between two atoms (e.g. if two atoms belong to the same cyclic group, then there are at least 2 atomic chains contain the two atoms), the length is calculated according to the shortest atomic chain between the two atoms. For example, for 1,4-cyclohexanediyl, 1,4-piperidinediyl, 1,4-phenylene, 1,4-piperazinediyl, the length is calculated as 4 atoms, while for 1,2-cyclopentanediyl, the length is calculated as only 2 atoms. The function of Li covalently linked to Ao, which represents the double-stranded oligonucleotide group, is to covalently link the oligonucleotide group to the targeting group, so that the oligonucleotide conjugate containing the oligonucleotide group enters the cell expressing PCSK9 mRNA through the targeting action of the targeting group, and does not affect the oligonucleotide group’s ability to regulate the level of PCSK9 mRNA after entering the cell expressing PCSK9 mRNA. Thus, in some embodiments, Li that is covalently linked to Ao, which represents the oligonucleotide group, is 3-20 atoms, or 4-15 atoms, or 5-12 atoms in length. In some embodiments, Li that is covalently linked to Ao, which represents the oligonucleotide group, is selected from a linking combination of one or more of Al, A2, A4, A5, A10, A16, A18, and A19 and a phosphate ester group or modified phosphate ester group:(Al) (A2) (A4) (A5)wherein j 1 is an integer of 2-10;— - represents the site where the group is covalently linked.In some embodiments, R2 is selected from a linking combination of at least 2 of Al, A2, A4, A10 and Al 6 and a phosphate ester group or modified phosphate ester group; in some embodiments, R2 is selected from a linking combination of at least 2 of Al, A2, and A10 and a phosphate ester group or modified phosphate ester group.In some embodiments, Li that is covalently linked to Ao, which represents the oligonucleotide group, has a structure as shown in Formula (Bl), (B2), (B3), or (B4):wherein represents the site where the group is covalently linked. LBI and LB2 are identical or different and are independently selected from one of the following groups or any linking combinations: -(CH2)qi-, -CH(OH)-, -CH(CH2OH)-, -NH-, -O-, -S-, 1,4- cyclohexanediyl, 1,4-piperidinediyl, 1,4-phenylene, 1,4-piperazinediyl, and pyrrolidinediyl, wherein ql is an integer of 1-6, LBI and LB2 independently of one another are 1-20 atoms inlength. In some embodiments, LBI and LB2 independently of one another have a length of 1-10 atoms. In some embodiments, LBI and LB2 independently of one another have a length of 1-6 atoms.LBS is selected from one of a phosphate ester group, a phosphorothioate group and a phosphorodithioate group, and is covalently linked to the remaining oxygen atom after removing a hydrogen atom from the 5’ hydroxyl group of the ribose of the 5’ terminal nucleotide or the 3’ hydroxyl group of the ribose of the 3’ terminal nucleotide in the sense strand or antisense strand of the double-stranded oligonucleotide group. In some embodiments, LB3 is a phosphate ester group and is covalently linked to the remaining oxygen atom after removing a hydrogen atom from the 5’ hydroxyl group of the ribose of the 5’ terminal nucleotide or the 3’ hydroxyl group of the ribose of the 3’ terminal nucleotide in the sense strand of the doublestranded oligonucleotide group.In some embodiments, in the case where the oligonucleotide conjugate of the present disclosure is prepared by a solid phase synthesis process, Li covalently linked to Ao, which represents a double-stranded oligonucleotide group, needs to simultaneously comprise a linking site linked to the N atom on the nitrogenous backbone, a linking site linked to the oligonucleotide group, and a functional group that can be linked to the solid phase support. In some embodiments, in Li covalently linked to Ao, which represents the oligonucleotide group, the site linked to the N atom on the nitrogenous backbone forms an amide bond with the N atom, and is covalently linked to the oligonucleotide group by a phosphate ester bond, and the functional group capable of linking to the solid phase support is a hydroxyl group or an amino group. In some embodiments, R2 is B5, B6, B5’ or B6’ :wherein — - represents the site where the group is covalently linked. q2 is an integer of 1-10; in some embodiments, q2 is an integer of 1-5.The function of Li covalently linked to Ao, which represents the targeting group, is to place the targeting group in a suitable spatial position, so as to better bind to the receptor to specifically target and enter relevant cells or tissues. Thus, Li covalently linked to AO, which represents the targeting group, can be used in the present disclosure, as long as it has an appropriate length and its chemical properties do not have a significant effect on delivery. In some embodiments, each Li covalently linked to Ao, which represents the targeting group, is independently a divalent linking group of 3-25 atoms in length. In some embodiments, each Li covalently linked to Ao, which represents the targeting group, is independently has a length of 4-15 atoms. In some embodiments, each Li covalently linked to Ao, which represents the targeting group, has a length of 5-10 atoms. In some embodiments, each Li covalently linked to Ao, which represents the targeting group, has an identical length.In some embodiments, each Li covalently linked to Ao, which represents the targeting group, is the identical or different, and independently selected from a group consisting of the groups shown in Formulae (L3)-(L18) and any linking combination thereof:wherein each j 1 is an integer of 2-10; each R’ is independently a hydrogen atom or C1-C3 alkyl group; represents the site where the group is covalently linked.For ease synthesis and / or stable chemical property, in some embodiments, each Li covalently linked to Ao, which represents the targeting group, is independently a linking combination of at least 2 linking units, wherein each linking unit independently has the structure as shown in any of Formulae (L3)-(L7). In some embodiments, each linking unit independently has the structure as shown in any of Formulae (L3), (L4) and (L7). For ease synthesis, in some embodiments, each Li covalently linked to Ao, which represents the targeting group, comprises a carbonyl group linked to the nitrogen atom as shown in Formula (308).In some embodiments, each Li covalently linked to Ao, which represents the targeting group, independently has the structure as shown in Formula (L20) or (L21):wherein j2 is an integer of 4 to 9 and j3 is 1 or 2. In some embodiments, j2 is 5, 6, or 7 and j3 is 1. In some embodiments, each Li covalently linked to Ao, which represents the targeting group, is identical.In the conjugates of the present disclosure, the number of targeting groups and the spacing between targeting groups are the number and spacing that can provide an appropriate spatial configuration for multiple targeting groups. For this purpose, n308 and each m308 areindependently integers selected from the integer of 2-4. In some embodiments, n308 is 3 or 4, so that the number of targeting groups in the conjugate of the present disclosure is 3 or 4, such that the targeting group could better bind to hepatocyte surface receptors. In some embodiments, n308 is 3, and each m308 is independently 3 or 4.Those skilled in the art would understand that when each R308 is independently a hydrogen atom, methyl or ethyl, it will not affect the delivery effect of the oligonucleotide conjugate and could realize the purpose of the present disclosure. In some embodiments, for ease synthesis, each R308 independently of one another is a hydrogen atom.In the conjugates of the present disclosure, each targeting group is identical or different, and independently selected from ligand groups capable of binding to cell surface receptors. In some embodiments, at least one or each targeting group is a group capable of targeting the liver. In some embodiments, at least one or each of targeting groups is a ligand that has affinity to asialoglycoprotein receptor (ASGPR) on the surface of mammalian hepatic parenchymal cells. In some embodiments, each targeting group is a galactose group or N-acetylgalactosamine (GalNAc) group formed by removing one atom or group from galactose or N- acetylgalactosamine.In some embodiments, the oligonucleotide conjugate of the present disclosure has the structure as shown in Formula (403), (404), (405), (406), (407), (408), (409), (410), (411), (412), (413), (414), (415), (416), (417), (418), (419), (420), (421), or (422):Formula (403)Formula (406)Formula (409)Formula (412)Formula (415)Formula (418)Formula (421)Formula (422) wherein Nu represents an oligonucleotide group, such as a single-stranded oligonucleotide group or a double-stranded oligonucleotide group formed by the single- stranded oligonucleotide or double-stranded oligonucleotide provided in the present disclosure. In some embodiments, the oligonucleotide group is a double-stranded oligonucleotide group, and the P atom shown in the above structural formula is covalently linked to the 3 ’-terminal nucleotide of the sense strand of the double-stranded oligonucleotide group. In some embodiments, the 3 ’-terminal nucleotide of the sense strand of the double-stranded oligonucleotide group is an inverted abasic deoxynucleotide, and the P atom shown in the above structural formula is covalently linked to the double-stranded oligonucleotide group by substituting the hydrogen atom in the hydroxyl group (which is linked to the ribose ring via a methylene group) in the 3 ’-terminal inverted abasic deoxynucleotide of the sense strand of the double-stranded oligonucleotide group represented by Nu. In some embodiments, the P atom shown in Formulae (403) to (422) is covalently linked to the remaining oxygen atom after removing one hydrogen atom from the ribose 3 ’-hydroxyl group of the 3 ’-terminal nucleotide in the sense strand of the double-stranded oligonucleotide group represented by Nu. In some embodiments, the P atom shown in Formulae (403) to (422) is covalently linked to the oxygen atom (which is linked to the ribose ring via a methylene group) in the inverted abasic deoxynucleotide ia represented by formula (35) at the 3 ’-terminal of the sense strand of the siRNA represented by Nu, thereby being covalently linked to the sense strand of the siRNA.In some embodiments, the oligonucleotide group comprised in the oligonucleotide conjugate ofthe present disclosure can be a siRNA group formed by removing an atom or atomic group of a siRNA, in which case the oligonucleotide conjugate of the present disclosure is also referred to siRNA conjugate. In some embodiments, the oligonucleotide group comprised in the oligonucleotide conjugate of the present disclosure can be, for example, a siRNA group formed by the siRNA listed in Table 1. The siRNA conjugates comprising these siRNA groups exhibit excellent stability and high inhibitory activity against PCSK9 mRNA. In some embodiments, the oligonucleotide conjugate of the present disclosure is one of Conjugate 1 to Conjugate 5 listed in Table 2.Preparation of the oligonucleotide conjugates of the present disclosureThose skilled in the art can prepare the oligonucleotide conjugates of the present disclosure by various suitable methods. For example, in the solid phase synthesis method, when the nucleoside monomers are linked one by one according to the sequences and modification schemes of the sense strand and antisense strand of the double-stranded oligonucleotides of the present disclosure, the oligonucleotide conjugate of the present disclosure can be synthesized by introducing the delivery group through the methods already described in detail in the prior art. For example, W02015006740A2 describes in detail the preparation methods of various oligonucleotide conjugates. In the case that the double-stranded oligonucleotide is a siRNA, the oligonucleotide conjugate of the present disclosure can also be obtained by the methods well- known to those skilled in the art. For example, W02014025805A1 describes the preparation method of the structure as shown in Formula (305A); Rajeev el al.. ChemBioChem 2015, 16, 903-908 describes the preparation method of the structure as shown in Formula (307); the Chinese patent application CN110959011 A also describes in detail the preparation method of the oligonucleotide conjugate having the structure as shown in Formula (308), all of which are hereby incorporated by reference in their entirety.Pharmaceutically acceptable saltOn the other hand, the present disclosure also provides the pharmaceutically acceptable salts of the single-stranded oligonucleotides, double-stranded oligonucleotides or oligonucleotide conjugates of the present disclosure. Pharmaceutically acceptable salts are known to those skilled in the art. By forming the salt, the pharmaceutically acceptable salts of the singlestranded oligonucleotides, double-stranded oligonucleotides or oligonucleotide conjugates of the present disclosure can exhibit better solubility, bioavailability, or stability than the singlestranded oligonucleotides, double-stranded oligonucleotides or oligonucleotide conjugatesthemselves.In some embodiments, in the single-stranded oligonucleotides, the double-stranded oligonucleotide or oligonucleotide conjugate of the present disclosure, adjacent nucleotides are linked via a phosphodiester bond or phosphorothioate diester bond. The non-bridging oxygen or sulfur atom in the phosphodiester bond or phosphorothioate diester bond is negatively charged, and can be present in the form of hydroxyl or sulfhydryl. Moreover, the hydrogen ion in the hydroxyl or sulfhydryl can be partially or completely substituted with a cation. The cation can be any cation, such as a metal cation, an ammonium cation NH4+or an organic ammonium cation. Furthermore, there may also be groups capable of forming salts (such as phosphate group) in the delivery group. For the purpose of improving solubility and / or improving bioavailability, in some embodiments, the pharmaceutically acceptable salts are water-soluble salts of some or all of the single-stranded oligonucleotides, double-stranded oligonucleotides or oligonucleotide conjugates. In some embodiments, the water-soluble salts can be amine salts, alkali metal salts or alkaline earth metal salts. In some embodiments, the amine salts are selected from one or more of ammonium salts, methylamine salts, tertiary amine salts, and quaternary ammonium salts, the alkali metal salts are selected from potassium salts or sodium salts, and the alkaline earth metal salts are selected from calcium salts or magnesium salts. In some embodiments, the tertiary amine salts are triethylamine salts, triisopropylamine salts or N,N- diisopropylethylamine salts. In some embodiments, the pharmaceutically acceptable salts of the single-stranded oligonucleotides, double-stranded oligonucleotides or oligonucleotide conjugates are sodium salts or partial sodium salts of the single-stranded oligonucleotides, double-stranded oligonucleotides or oligonucleotide conjugates. In some embodiments, the pharmaceutically acceptable salts of the double-stranded oligonucleotides or oligonucleotide conjugates are a mixture of methylamine salts and ammonium salts of the double-stranded oligonucleotides or oligonucleotide conjugates. In some embodiments, the pharmaceutically acceptable salts are salts or partial salts of the single-stranded oligonucleotides, double-stranded oligonucleotides, or oligonucleotide conjugates, and the salts are one or more of methylamine salts, triethylamine salts, or sodium salts.Pharmaceutical compositionOn the other hand, the present disclosure also provides a pharmaceutical composition, comprising one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate and their pharmaceutically acceptable salt provided in the present disclosure, and a pharmaceutically acceptable excipient.Pharmaceutically acceptable excipient is one or more of various conventional ingredients in the art, such as one or more of a solvent, a protectant, an osmotic pressure regulator, and other pharmaceutically acceptable carriers.For example, when the pharmaceutical composition is an injection solution, the pharmaceutically acceptable excipient is a solvent, such as one or more of deionized water, water for injection, physiological saline, ethanol, ethanol aqueous solution, and pH buffer. The pH buffer can be a tris(hydroxymethyl) aminomethane hydrochloride buffer with a pH of 7.5- 8.5, and / or a phosphate buffer with a pH of 5.5-8.5, preferably a phosphate buffer with a pH of 5.5-8.5.The dosage of the solvent is adjusted according to the required solution concentration, and the concentration of the oligonucleotide conjugate in the injection solution can be 0.01 mg / mL-20 mg / mL, 0.1 mg / mL-10 mg / mL / or 0.5 mg / mL-5 mg / mL, as calculated based on the oligonucleotide group.The protectant can be at least one of inositol, sorbitol, sucrose, trehalose, mannose, maltose, lactose, and glucose. The content of the protectant can be from 0.01 wt % to 30 wt % on the basis of the total weight of the pharmaceutical composition.The osmotic pressure regulator can be sodium chloride and / or potassium chloride. The content of the osmotic pressure regulator allows the osmotic pressure of the pharmaceutical composition to be 200-700 milliosmol / kg (mOsm / kg). Depending on the desired osmotic pressure, those skilled in the art can readily determine the content of the osmotic pressure regulator. In some embodiments, the dosage of the formulation prepared by the pharmaceutical composition during administration can be adjusted according to different administration manners.In some embodiments, the pharmaceutical composition can be a liquid formulation, for example, an injection solution; or a lyophilized powder for injection, which is mixed with a liquid excipient to form a liquid formulation upon administration. The liquid formulation can be administered by, but not limited to, subcutaneous route, intramuscular route or intravenous injection, and also can be administered to, but not limited to, lung by spray, or other organ tissues (such as liver) through lung by spray, or the pharmaceutical composition can be delivered by oral route or other manners. In some embodiments, the pharmaceutical composition is administered by subcutaneous injection.Other pharmaceutically acceptable carrier can be a conventional carrier used in the field of double-stranded oligonucleotide administration, for example, but not limited to, one or more of magnetic nanoparticles (such as FesO4 and Fe2O3-based nanoparticle), carbon nanotubes, mesoporous silicon, calcium phosphate nanoparticles, polyethylenimine (PEI), polyamidoamine(PAMAM) dendrimer, poly(L-lysine) (PLL), chitosan, l,2-dioleoyl-3 -trimethylammonium - propane (DOTAP), poly(D&L-lactic / glycolic acid) copolymer (PLGA), poly(2-aminoethyl ethylene phosphate) (PPEEA), poly(2-dimethylaminoethyl methacrylate) (PDMAEMA), and derivatives thereof.In some embodiments, in the pharmaceutical composition, there are no special requirements for the contents of the oligonucleotide and the pharmaceutically acceptable carrier. In some embodiments, the ratio of the oligonucleotide or the oligonucleotide in the oligonucleotide conjugate to the pharmaceutically acceptable carrier is 1 : (1-500) by weight; in some embodiments, the ratio is 1 : (1-50) by weight.In some embodiments, the pharmaceutical composition can be in the form of a liposome formulation. In some embodiments, the pharmaceutically acceptable carrier used in the liposome formulation comprises an amine-containing transfection compound (hereinafter also referred to as an organic amine), a helper lipid and / or a PEGylated lipid. Therein, the organic amine, the helper lipid and the PEGylated lipid can be respectively selected from one or more of the amine- containing transfection compounds or the pharmaceutically acceptable salts or derivatives thereof, the helper lipids, and the PEGylated lipids as described in the Chinese patent application CN103380113A, which is incorporated herein by reference in its entirety.In some embodiments, the organic amine can be a compound as shown in Formula (201) as described in the Chinese patent application CN103380113A or a pharmaceutically acceptable salt thereof:Formula (201) wherein:Xioi and X102 independently of one another are selected from O, S, N-A and C-A, wherein A ishydrogen or a C1-C20 hydrocarbon chain;Y101 and Z101 independently of one another are selected from C=O, C=S, S=O, CH-OH and SO2; R101, R102, R103, R104, Rios, R106 and R107 independently of one another are selected from hydrogen; a cyclic or an acyclic, substituted or unsubstituted, branched or straight-chain aliphatic group; a cyclic or an acyclic, substituted or unsubstituted, branched or straight-chain heteroaliphatic group; a substituted or unsubstituted, branched or straight-chain acyl group; a substituted or unsubstituted, branched or straight-chain aryl group, or a substituted or unsubstituted, branched or straight-chain heteroaryl group; x is an integer of 1 - 10; n is an integer of 1 - 3, m is an integer of 0 - 20, p is 0 or 1; and wherein if m=p=0, then R102 is hydrogen, and if at least one of n or m is 2, then R103 and nitrogen atom in Formula (201) form a structure as shown in Formula (202) or (203):Formula (202) Formula (203) wherein g, e and f independently of one another are an integer of 1 - 6; “HCC” represents a hydrocarbon chain; and each *N represents a nitrogen atom in Formula (201).In some embodiments, R103 is a polyamine. In other embodiments, R103 is a ketal. In some embodiments, each of R101 and Ruu in the Formula (201) is independently any of substituted or unsubstituted, branched or straight-chain alkyl or alkenyl groups which have 3 - 20 carbon atoms (such as 8 - 18 carbon atoms) and 0 - 4 double bonds (such as 0 - 2 double bonds).In some embodiments, if each of n and m is independently 1 or 3, then R103 represents any of the following Formulae (204)-(213):Formula (209)wherein in Formula (204) - Formula (213), g, e, and f independently of one another are an integer of 1-6; each “HCC” represents a hydrocarbon chain; and each * represents a potential attachment position of R103 to the nitrogen atom in Formula (201), wherein each H at any * position can be replaced to realize the attachment to the nitrogen atom in Formula (201). Those skilled in the art can obtain the compound as shown in Formula (201) by any reasonablemethod. In some embodiments, the compound as shown in Formula (201) can be prepared according to the description in the Chinese patent application CN103380113A.In some embodiments, the organic amine is an organic amine as shown in Formula (214) and / or an organic amine as shown in Formula (215):Formula (215)The helper lipid is cholesterol, cholesterol analogue and / or cholesterol derivative.The PEGylated lipid is l,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine-N- [methoxy(polyethylene glycol)]-2000.In some embodiments, the molar ratio among the organic amine, the helper lipid, and the PEGylated lipid in the pharmaceutical composition is (19.7-80): (19.7-80): (0.3-50); for example, the molar ratio can be (50-70): (20-40): (3-20).In some embodiments, the pharmaceutical composition particles formed by the oligonucleotide or oligonucleotide conjugate of the present disclosure and the above amine-containing transfection agents have an average diameter from about 30 nm to about 200 nm, typically from about 40 nm to about 135 nm; and more typically, the average diameter of the liposome particles is from about 50 nm to about 120 nm, from about 50 nm to about 100 nm, from about 60 nm to about 90 nm, or from about 70 nm to about 90 nm, for example, the average diameter of theliposome particles is about 30, 40, 50, 60, 70, 75, 80, 85, 90, 100, 110, 120, 130, 140, 150, or 160 nm.In some embodiments, in the pharmaceutical composition formed by the oligonucleotide or oligonucleotide conjugate of the present disclosure and the above amine-containing transfection agents, the weight ratio (weight / weight ratio) of the oligonucleotide or oligonucleotide conjugate to total lipids (e.g., the organic amines, the helper lipids and / or the PEGylated lipids), ranges from about 1 : 1 to about 1 :50, from about 1 : 1 to about 1 :30, from about 1 :3 to about 1 :20, from about 1 :4 to about 1 : 18, from about 1 :5 to about 1 : 17, from about 1 :5 to about 1 : 15, from about 1 :5 to about 1 : 12, from about 1 :6 to about 1 : 12, or from about 1 :6 to about 1 : 10. For example, the weight ratio of the oligonucleotide or oligonucleotide conjugate of the present disclosure to total lipids is about 1 :5, 1 :6, 1 :7, 1 :8, 1 :9, 1 : 10, 1 : 11, 1 : 12, 1 : 13, 1 : 14, 1 : 15, 1 :16, 1 : 17, or 1 : 18.In some embodiments, the pharmaceutical composition can be marketed with each component being separate, and be in the form of a liquid formulation when used. In some embodiments, the pharmaceutical composition formed by the oligonucleotide or oligonucleotide conjugate of the present disclosure and the above pharmaceutically acceptable carrier can be prepared by various known methods, except replacing the existing siRNA with the oligonucleotide or oligonucleotide conjugate of the present disclosure. In some embodiments, the pharmaceutical composition can be prepared according to the following process.The organic amines, helper lipids and PEGylated lipids are suspended in alcohol at a molar ratio as described above and mixed homogeneously to yield a lipid solution; the alcohol is used in an amount such that the resultant lipid solution is present at a total mass concentration of 2 to 25 mg / mL, e.g., 8 to 18 mg / mL. The alcohol is a pharmaceutically acceptable alcohol, such as an alcohol that is liquid at about room temperature, for example, one or more of ethanol, propylene glycol, benzyl alcohol, glycerol, PEG 200, PEG 300, and PEG 400, such as ethanol.The oligonucleotide or oligonucleotide conjugate of the present disclosure is dissolved in a buffered salt solution to produce an aqueous solution of the oligonucleotide or oligonucleotide conjugate. The buffered salt solution has a concentration of 0.05 to 0.5 M, such as 0.1 to 0.2 M. The pH of the buffered salt solution is adjusted to 4.0 to 5.5, such as 5.0 to 5.2. The buffered salt solution is used in an amount such that the oligonucleotide or the oligonucleotide in the oligonucleotide conjugate is present at a concentration of less than 0.6 mg / ml, such as 0.2 to 0.4 mg / mL. The buffered salt can be one or more selected from the group consisting of soluble acetate and soluble citrate, such as sodium acetate and / or potassium acetate.The lipid solution and the aqueous solution of the oligonucleotide or the oligonucleotideconjugate are mixed. The product obtained after mixing is incubated at a temperature of 40 to 60°C for at least 2 minutes (e.g., 5 to 30 minutes) to produce an incubated liposome formulation. The volume ratio of the lipid solution to the aqueous solution of the oligonucleotide or oligonucleotide conjugate is 1 : (2-5).The incubated liposome formulation is concentrated or diluted, purified to remove impurities, and then sterilized to obtain the pharmaceutical composition of the present disclosure, which has the following physicochemical parameters: a pH of 6.5 to 8, an encapsulation efficiency of more than 80%, a particle size of 40 to 200 nm, a poly dispersity index of less than 0.30, and an osmotic pressure of 250 to 400 mOsm / kg; for example, the physicochemical parameters can be as follows: a pH of 7.2 to 7.6, an encapsulation efficiency of more than 90%, a particle size of 60 to 100 nm, a poly dispersity index of less than 0.20, and an osmotic pressure of 300 to 400 mOsm / kg.Therein, the concentration or dilution step can be performed before, after or simultaneously with the step of removing impurity. The method for removing impurities can be any of various existing methods, for example, ultrafiltration using a 100 kDa hollow fiber column, a PBS at pH 7.4 as an ultrafiltration exchange solution and a tangential flow system. The method for sterilization can be any of various existing methods, such as filtration sterilization with a 0.22 pm filter.Use of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition of the present disclosureThe present disclosure further provides use of one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition of the present disclosure in the manufacture of a medicament for treating and / or preventing a disease or symptom associated with the level of PCSK9 mRNA. In some embodiments, the disease or symptom associated with the level of PCSK9 mRNA is dyslipidemia; alternatively, the dyslipidemia is hypercholesterolemia, hypertriglyceridemia, or atherosclerosis.The present disclosure further provides a method for treating and / or preventing a disease or symptom associated with the level of PCSK9 mRNA, comprising administering to a subject in need thereof an effective amount of one or more of the single- stranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt and the pharmaceutical composition.In another aspect, the present disclosure also provides one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt, and pharmaceutical composition for use as a medicament.In addition, the present disclosure further provides a method for regulating the expression level of PCSK9 mRNAin a cell, comprising contacting the cell with an effective amount of one or more of the single-stranded oligonucleotide, the double-stranded oligonucleotide, the oligonucleotide conjugate, the pharmaceutically acceptable salt, and the pharmaceutical composition of the present disclosure.As used herein, the term “administration / administer” refers to delivering one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt, and pharmaceutical composition into a subject’s body by a method or a route that at least partly locates one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt, and pharmaceutical composition of the present disclosure at a desired site to produce a desired effect. The administration routes suitable for the methods of the present disclosure include topical administration and systemic administration. In general, topical administration results in the delivery of a greater amount of one or more of single-stranded oligonucleotides, doublestranded oligonucleotides, oligonucleotide conjugates, pharmaceutically acceptable salts, and pharmaceutical compositions of the present disclosure to a particular site as compared with the whole body of the subject; while systemic administration results in the delivery of one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt, and pharmaceutical composition of the present disclosure to substantially the whole body of the subject.The administration to a subject can be achieved by any suitable routes known in the art, including but not limited to, oral or parenteral route, such as intravenous administration, intramuscular administration, subcutaneous administration, transdermal administration, intratracheal administration (aerosol), pulmonary administration, nasal administration, rectal administration, and topical administration (including buccal administration and sublingual administration). The administration frequency can be once or more times daily, weekly, biweekly, triweekly, monthly, or yearly.The dose of one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition of the present disclosure can be a conventional dose in the art, which can be determined according to various parameters, especially age, weight and gender of a subject.Toxicity and efficacy can be measured in cell cultures or experimental animals by standard pharmaceutical procedures, for example, by determining LD50 (the lethal dose that causes 50% population death) and ED50 (the dose that can cause 50% of the maximum response intensity in a quantitative response, and that causes 50% of the experimental subjects to have a positive response in a qualitative response). The dose range for human use can be derived based on the data obtained from cell culture assays and animal studies.When administering the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and / or pharmaceutical composition of the present disclosure, for example, to male or female C57BL / 6J or C3H / HeNCrlVr mice with an age of 6-12 weeks old and a body weight of 18-25 g, for siRNA conjugate formed by siRNA and pharmaceutically acceptable conjugate molecule, the amount of the siRNA can be 0.001-100 mg / kg body weight, in some embodiments 0.01-50 mg / kg body weight, in further embodiments 0.05-20 mg / kg body weight, in still further embodiments 0.1-15 mg / kg body weight, and in still yet further embodiments 0.1-10 mg / kg body weight, as calculated based on the amount of the siRNA or the amount of the siRNA in pharmaceutical composition and / or siRNA conjugate. When administering the siRNA, pharmaceutical composition, and / or siRNA conjugate of the present disclosure, the above amounts can be preferred.In the case where the expressions of PCSK9 mRNA in cells are inhibited by using the method of the present disclosure, the amount of the oligonucleotide in one or more of the provided oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition can be readily determined by those skilled in the art according to the desired effects. For example, in some embodiments, when the oligonucleotide is a siRNA, and the oligonucleotide conjugate is a siRNA conjugate, the amount of the siRNA in the siRNA conjugate provided is an amount sufficient to reduce the level of PCSK9 mRNA and result in an extracellular concentration of 1 pM to 1 pM, or 0.01 nM to 100 nM, or 0.05 nM to 50 nM, or 0.05 nM to about 5 nM on the surface of the target cells. The amount required to achieve this local concentration will vary with various factors, including the delivery method, the delivery site, the number of cell layers between the delivery site and the target cells or tissues, the delivery route (topical or systemic), etc. The concentration at the delivery site can be significantly higher than that on the surface of the target cells or tissues.KitsThe present disclosure provides a kit comprising one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceuticallyacceptable salt and pharmaceutical composition of the present disclosure.In some embodiments, the kit of the present disclosure can provide one or more of the singlestranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition of the present disclosure in one container. In some embodiments, the kit of the present disclosure can comprise a container comprising pharmaceutically acceptable excipients. In some embodiments, the kit of the present disclosure can further comprise additional ingredients, such as stabilizers or preservatives. In some embodiments, the kit of the present disclosure can comprise at least one additional therapeutic agent in other container than the container providing one or more of the singlestranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition of the present disclosure. In some embodiments, the kit can comprise an instruction for mixing one or more of the singlestranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition of the present disclosure with pharmaceutically acceptable carriers and / or excipients or other ingredients (if any).In the kit of the present disclosure, one or more of the single-stranded oligonucleotide, doublestranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition, and / or the pharmaceutically acceptable excipients can be provided in any form, e.g., in a liquid form, a dry form, or a lyophilized form. In some embodiments, one or more of the single-stranded oligonucleotide, double-stranded oligonucleotide, oligonucleotide conjugate, pharmaceutically acceptable salt and pharmaceutical composition, and optional pharmaceutically acceptable excipients are substantially pure and / or sterile. In some embodiments, sterile water can be provided in the kit of the present disclosure.Hereinafter, the present disclosure will be further illustrated with reference to the Examples, but is not limited thereto.Without wishing to be limited, the invention is further described in detail in the following embodiments and the Examples regarding the exemplary embodiments where the doublestranded oligonucleotide in the pharmaceutically compositions, oligonucleotides and / or oligonucleotide conjugates of the present disclosure is a small interfering RNA (siRNA). In this case, the double-stranded oligonucleotides, pharmaceutically compositions, and oligonucleotide conjugates of the present disclosure are siRNA, pharmaceutically compositions comprising siRNA and siRNA conjugates, respectively. In the context of the present disclosure, for ease ofdescription, the siRNA, the pharmaceutically composition comprising the siRNA and the siRNA conjugate in these embodiments are also referred to as the siRNA of the present disclosure, the pharmaceutically composition of the present disclosure and the siRNA conjugate of the present disclosure. It does not mean that the double-stranded oligonucleotide of the present disclosure can only be siRNA, instead, the double-stranded oligonucleotide can be other variants disclosed in the present disclosure or known to those skilled in the art, such as small activating RNA (saRNA). It can be envisaged that, based on the detailed illustration of the siRNA, the pharmaceutically composition comprising the siRNA, and the siRNA conjugate, other doublestranded oligonucleotides would function similarly when being used alone or forming the pharmaceutically compositions and / or oligonucleotide conjugates of the present disclosure.ExamplesUnless otherwise specified, the reagents and cultures used in the following Examples are all commercially available products, and the operations used (such as nucleic acid electrophoresis and real-time PCR) are carried out according to the methods described in Molecular Cloning (Cold Spring Harbor Laboratory (1989)).Preparation Examples 1-5: Synthesis of the siRNA Conjugates provided by the present disclosureAccording to the preparation method described in Preparation Example 13 of CN110959011 A, Conjugates 1-5 in Table 2 below are prepared, while the only difference is that the sense strands and antisense strands of the siRNA contained in the siRNA conjugates are as shown in Table 2 respectively; for the nucleic acid sequence having the sense strand and antisense strand sequences of the siRNAs in Conjugates 1-5 in Table 2 below, nucleoside phosphoramidite monomers were linked one by one to synthesize the sense strand and antisense strand of the siRNA conjugate. After the synthesis was completed, for Conjugates 1-4, the synthesized product were purified by centrifugal ultrafiltration and desalination using 3K (MWCO) ultrafiltration tubes. For Conjugate 5, the synthesized product was first purified by a self-packed column with strong anion exchange packing, and then purified by desalination using a HiPrep 26 / 13 Desalting prepacked column.Conjugates 1-4 are respectively mixtures of methylamine salts and ammonium salts of the compounds having the structure shown in formula (403), and Conjugate 5 is the sodium salt of the compound having the structure shown in Formula (403), wherein the P atom shown in formula (403) is covalently linked to the oxygen atom (which is linked to the ribose ring via amethylene group) in the inverted abasic deoxynucleotide ia represented by formula (35) at the 3 ’-terminal of the sense strand of the siRNA represented by Nu, thereby being covalently linked to the sense strand of the siRNA. Moreover, the siRNA contained in the siRNA conjugate has the siRNA sequences corresponding to Conjugates 1-5 in Table 2.Formula (403)Each siRNA conjugate was diluted to a concentration of 0.2 mg / mL (calculated based on siRNA) using ultrapure water (Milli-Q ultrapure water instrument, resistivity 18.2 MQ*cm at 25°C), and then molecular weight detection was performed using a liquid chromatography-mass spectrometer (LC-MS, purchased from Waters, model: LCT Premier). Among them, for Conjugate 1 : the theoretical value of the sense strand is 7319.277 and the measured value is 7318.02; the theoretical value of the antisense strand is 7133.985 and the measured value is 7132.61. For Conjugate 2: the theoretical value of the sense strand is 7412.429 and the measured value is 7411.04; the theoretical value of the antisense strand is 6999.820 and the measured value is 6998.54. For Conjugate 3: the theoretical value of the sense strand is 7323.368 and the measured value is 7322.04; the theoretical value of the antisense strand is 7119.899 and the measured value is 7118.48. For Conjugate 4: the theoretical value of the sense strand is 7322.384 and the measured value is 7321.06; the theoretical value of the antisense strand is 7096.857 and the measured value is 7095.59. For Conjugate 5: the theoretical value of the sense strand is 7322.38 and the measured value is 7321; the theoretical value of the antisense strand is 7175.85 and the measured value is 7172. The fact that the measured values are consistent with the theoretical values indicate that the synthesized Conjugates 1-5 contain the designed target double-stranded nucleic acid sequences.Table 2 the siRNA sequences in the siRNA conjugatesTherein, C, G, U, A and T represent the base composition of the nucleotides; m represents that the nucleotide represented by a capital letter adjacent to the left side of the letter m is a 2’- methoxy modified nucleotide; f represents that the nucleotide represented by a capital letter adjacent to the left side of the letter f is a 2’ -fluoro modified nucleotide; s represents that the two nucleotides represented by capital letters adjacent to both sides of the letter s are linked by a phosphorothioate linkage; d represents that the nucleotide represented by a capital letter adjacent to the right side of the letter d is a deoxynucleotide; ia represents an inverted abasicdeoxyribonucleotide; VP represents that the nucleotide represented by a capital letter adjacent to the right side of this letter combination is a 5’-VP modified nucleotide; the letter combination moe represents that the nucleotide represented by a capital letter adjacent to the left side of this letter combination is a 2’-O-methoxyethyl modified nucleotide.Comparative Preparation Example 1 : Synthesis of Reference Conjugate 1Reference Conjugates 1 and 2 in Table 2 are prepared by solid-phase synthesis following the same method as that in Preparation Example 1. For Reference Conjugate 1, the theoretical value of the sense strand is 7426.265 and the measured value is 7425.05; the theoretical value of the antisense strand is 7084.880 and the measured value is 7083.90. For Reference Conjugate 2: the theoretical value of the sense strand is 7426.27 and the measured value is 7425.2; the theoretical value of the antisense strand is 7084.88 and the measured value is 7084. Reference Conjugate 1 is a mixture of methylamine salts and ammonium salts of the compound having the structure shown in Formula (403), and Reference Conjugate 2 is the sodium salt of the compound having the structure shown in Formula (403), wherein the conjugate groups of Reference Conjugate 1 and Reference Conjugate 2 are linked to the 3’-position of the ribose of the 3’-terminal nucleotide of the sense strand of the siRNA represented by Nu. Moreover, the siRNA contained in this siRNA conjugate has the siRNA sequences corresponding to Reference Conjugate 1 and Reference Conjugate 2 in Table 2. Reference Conjugate 1 and Reference Conjugate 2 have the same sequence and modifications but differ in salt forms. Reference Conjugate l is a siRNA conjugate of which the sequence is shifted by one nucleotide relative to that of Conjugate 1, and Reference Conjugate 1 and Conjugate 1 have different modification schemes.Experimental Example 1 : In vivo inhibitory activity of the Conjugates of the present disclosure This experimental Example investigates the in vivo activity of Conjugates 1-4 of the present disclosure in mice.The prepared Conjugates 1-4 and Reference Conjugate 1 were dissolved in PBS to prepare injection solutions with a concentration of 0.6 mg / mL.Thirty PCSK9 humanized mice (strain: C5I^ I6 moc-Pcsk9em2(hpcSK9) / Smoc, grade: SPF, gender: female, purchased from Shanghai Model Organisms Center, Inc.) were randomly divided into groups indicated as Test Groups 1-5 and a Blank Control Group (5 mice per group). Mice in Test Groups 1-5 were administered injection solutions of Conjugates 1-4 and Reference Conjugate 1 at a dose of 3 mg / kg body weight subcutaneous injection in the abdominal region; mice in the Blank Control Group were administered with PBS solution with an administration volume of 5mL / kg body weight.Taking the administration day as Day 1, blood samples were collected from all animals via orbital sinus bleeding once before administration, and then once on Day 8, Day 15, Day 29, and Day 43 after administration. Animals were fasted for 4-6 hours before blood collection. All blood collection procedures used EDTAK2 anticoagulant blood collection tubes. The blood samples were centrifuged 1800 g for 15 minutes at 2-8°C to separate plasma. The plasma PCSK9 protein levels were measured using a human PCSK9 ELISA detection kit (R&D, MANL30) according to the operation steps in the instruction.Taking the value before administration as the baseline, the inhibition rate against plasma PCSK9 protein in the test groups was calculated as follows:Inhibition rate of the drug against plasma PCSK9 protein = (1 - value after administration / value before administration) x 100%Table 4 The inhibition rate against plasma PCSK9 protein in miceNote: SD represents Standard Deviation.As can be seen from the results in Table 4, the conjugates provided in the present disclosure can maintain the inhibitory activity against plasma PCSK9 protein in vivo over an extended period. Compared with Reference Conjugate 1, the inhibition rate on Day 8 is over 75%, and can even reach over 89%; on Day 15, the inhibition rate is over 79%, and can even reach over 89%. In particular, Conjugate 1 has a higher inhibition rate than Reference Conjugate 1, which has substantially the same sequence but a different modification scheme. On Day 29, the inhibition rate is over 76%, and can even reach over 82%; on Day 43, the inhibition rate is over 62%, and can even reach over 81%.Experimental Example 2: In vivo inhibitory activity of the Conjugates of the present disclosure This experimental example investigates the in vivo activity of Conjugate 5 of the present disclosure in mice.The inhibitory activities against plasma PCSK9 protein of Conjugate 5 and Reference Conjugate 2 in PCSK9 humanized mice were determined according to the method in Experimental Example 1, except that the conjugates used were Conjugate 5 and Reference Conjugate 2. The results are listed in Table 5.Table 5 The inhibition rate against plasma PCSK9 protein of the conjugates in miceAs can be seen from the results in Table 5, all conjugates provided in the present disclosure can maintain the inhibitory activity against plasma PCSK9 protein in vivo over an extended period. Throughout the test period, the inhibition rate against plasma PCSK9 protein of Conjugate 5 in mice is over 84%. After Day 29, the inhibition rate against plasma PCSK9 protein of Conjugate 5 in mice is significantly higher than that of the reference conjugate; especially on Day 43, the inhibition rate against plasma PCSK9 protein of Conjugate 5 in mice still remain over 87%, which is more than 2-fold higher than the average value of Reference Conjugate 2.Some embodiments of the present disclosure are described in detail above, but the present disclosure is not limited to the specific details of the above embodiments. Various simple variations to the technical solutions of the present disclosure can be made within the scope of the technical concept of the present disclosure, and these simple variations are also within the scope of the present disclosure.In addition, it should be noted that the specific technical features described in some of the above embodiments can be combined in any appropriate manner provided that no contradiction is caused. In order to avoid unnecessary repetition, the present disclosure does not separately describe various possible combination manners.Furthermore, various different embodiments of the present disclosure can also be combined arbitrarily, as long as they do not deviate from the concept of the present disclosure, and such combinations shall also be deemed as content disclosed by the present disclosure.

Claims

CLAIMS1. A single-stranded oligonucleotide, wherein the single-stranded oligonucleotide has a length of 16-30 nucleotides and can inhibit the expression of PCSK9 mRNAby the mechanism of RNA interference (RNAi); wherein each nucleotide in the single-stranded oligonucleotide independently of one another is a modified or an unmodified nucleotide; and wherein in the single-stranded oligonucleotide, at least one nucleotide is a nucleotide X, at least one nucleotide is a fluoro modified nucleotide; and in a 5’ to 3’ direction, the 13th nucleotide in the single- stranded oligonucleotide is a substituted alkoxy modified nucleotide; the 14th nucleotide in the single-stranded oligonucleotide is a nucleotide X; and each of the 15th nucleotide and all the subsequent nucleotides in the singlestranded oligonucleotide independently of one another is a modified nucleotide; and each nucleotide X is independently a deoxynucleotide or an unmodified nucleotide.

2. The single-stranded oligonucleotide according to claim 1, wherein the single-stranded oligonucleotide has a length of 17-28, 19-27, or 20-25 nucleotides; or the single-stranded oligonucleotide has a length of 19, 21 or 23 nucleotides.

3. The single-stranded oligonucleotide according to claim 1 or 2, wherein the number of the nucleotide X is 1-3, such as 1-2, such as 1.

4. The single-stranded oligonucleotide according to any one of claims 1-3, wherein in a 5’ to 3’ direction, the 12th and 14th nucleotides in the single-stranded oligonucleotide independently of one another are the nucleotide X; or only the 14th nucleotide is a nucleotide X.

5. The single-stranded oligonucleotide according to any one of claims 1-4, wherein the number of the unmodified nucleotides is no more than 5, no more than 4, no more than 3, no more than 2 or no more than 1; or each of all nucleotides in the single-stranded oligonucleotide independently of one another is a modified nucleotide.

6. The single-stranded oligonucleotide according to any one of claims 1-5, wherein the number of the fluoro modified nucleotides is 2-7 such as 2-5, such as 3.

7. The single-stranded oligonucleotide according to any one of claims 1-6, wherein in a 5’ to 3’ direction, the fluoro modified nucleotides are one or more nucleotides, such as 2-7 nucleotides, such as 2-5 nucleotides, such as 3 nucleotides, selected from the group consisting of the 2nd, 5th, 6th, 7th, 12th, 16th, 18th and 19th nucleotides in the single-stranded oligonucleotide.

8. The single-stranded oligonucleotide according to any one of claims 1-7, wherein in a 5’to 3’ direction, the fluoro modified nucleotides are one or two nucleotides selected from the group consisting of the 2nd and 12th nucleotides, one or two nucleotides selected from the group consisting of the 5th to 7th nucleotides, and 0-2 nucleotides selected from the group consisting of the 16th to 19th nucleotides, in the single-stranded oligonucleotide; and / or in a 5’ to 3’ direction, the fluoro modified nucleotides are one or more nucleotides, or all nucleotides, selected from the group consisting of the 2nd and 6th nucleotides; or the group consisting of the 2nd, 6th, and 16th nucleotides; or the group consisting of the 2nd, 5th, 7th, 12th, and 16th nucleotides; or the group consisting of the 2nd, 7th, 12th, 16th, and 19th nucleotides; or the group consisting of the 2nd, 6th, 12th, 16th, and 19th nucleotides in the single-stranded oligonucleotide.

9. The single-stranded oligonucleotide according to any one of claims 1-8, wherein except for the 13th and 14th nucleotides (in a 5’ to 3’ direction) and the fluoro modified nucleotides, each modified nucleotide in the single-stranded oligonucleotide is independently selected from the group consisting of an alkoxy modified nucleotide, a substituted alkoxy modified nucleotide, an alkyl modified nucleotide, a substituted alkyl modified nucleotide, an amine modified nucleotide, a thermally destabilizing nucleotide, and a BNA, such as the group consisting of an alkoxy modified nucleotide, a substituted alkoxy modified nucleotide and a thermally destabilizing nucleotide.

10. The single-stranded oligonucleotide according to claim 9, wherein the number of substituted alkoxy modified nucleotides is no more than 3; and / or the number of thermally destabilizing nucleotides is no more than 2.

11. The single-stranded oligonucleotide according to any one of claims 1-10, wherein the single-stranded oligonucleotide has a length of 19-23 nucleotides, and / or in a 5’ to 3’ direction in the single-stranded oligonucleotide, the 13th nucleotide is said substituted alkoxy modified nucleotide, the 14th nucleotide is said nucleotide X, one of the 5th to 7th nucleotides is a fluoro modified nucleotide, the 2nd nucleotide and the 16th nucleotide are fluoro modified nucleotides, the 3rd nucleotide is an alkoxy modified nucleotide or a substituted alkoxy modified nucleotide, the 5th nucleotide is an alkoxy modified nucleotide or a substituted alkoxy modified nucleotide when it is not a fluoro modified nucleotide, and each remaining nucleotide in the single-stranded oligonucleotide independently of one another is an alkoxy modified nucleotide.

12. The single-stranded oligonucleotide according to any one of claims 1-11, wherein the single-stranded oligonucleotide has a length of 21 nucleotides, and / orin a 5’ to 3’ direction, the 13th nucleotide is said substituted alkoxy modified nucleotide, the 14th nucleotide is said nucleotide X, the 2nd, 6th and 16th nucleotides are fluoro modified nucleotides, the 3rd or 5th nucleotides are alkoxy modified nucleotides or substituted alkoxy modified nucleotides, and each remaining nucleotide in the single-stranded oligonucleotide independently of one another is an alkoxy modified nucleotide.

13. The single-stranded oligonucleotide according to any one of claims 1-12, wherein each nucleotide X is a deoxynucleotide; and / or each alkoxy modified nucleotide is a methoxy modified nucleotide; and / or each substituted alkoxy modified nucleotide is a 2’-O-methoxyethyl modified nucleotide; and / or each thermally destabilizing nucleotide is GNA.

14. The single-stranded oligonucleotide according to any one of claims 1-13, wherein at least 2 of the linking groups linking adjacent nucleotides in the single-stranded oligonucleotide are each independently phosphate ester groups with modification group(s).

15. The single-stranded oligonucleotide according to any one of claims 1-14, wherein1 to 4 of the linking groups linking adjacent nucleotides between the 1st and 5th nucleotides at the 5’ terminal of the single-stranded oligonucleotide, and / or 1 to 4 of the linking groups linking adjacent nucleotides between the 1st and 5th nucleotides at the 3’ terminal of the single-stranded oligonucleotide are each independently phosphate ester groups with modification group(s); and / or if the single-stranded oligonucleotide comprises unmodified nucleotides, then one or both of the two linking groups linking each of the unmodified nucleotides and adjacent nucleotides thereof are each independently phosphate ester groups with modification group(s); and / or2 to 6, or 4 of the linking groups linking adjacent nucleotides in the single-stranded oligonucleotide are each independently phosphate ester groups with modification group(s).

16. The single-stranded oligonucleotide according to any one of claims 1-15, wherein one or more, such as all, of the linking groups linking adjacent nucleotides between the 1st and 3rd nucleotides at the 5’ terminal of the single-stranded oligonucleotide, and / or one or more, such as all, of the linking groups linking adjacent nucleotides between the 1st and 3rd nucleotides at the 3’ terminal of the single-stranded oligonucleotide are each independently phosphate ester groups with modification group(s); and / or if the single-stranded oligonucleotide comprises unmodified nucleotides, then one or both of the two linking groups linking each of the unmodified nucleotides and adjacent nucleotides thereof are each independently phosphate ester groups with modification group(s).

17. The single-stranded oligonucleotide according to any one of claims 14-16, wherein each of the phosphate ester groups with modification group(s) is independently a phosphorothioate group having the structure as shown by Formula (28):Formula (28).

18. The single-stranded oligonucleotide according to any one of claims 1-17, wherein the 5’-terminal nucleotide of the single-stranded oligonucleotide is a 5’-hydroxy nucleotide, a 5’- phosphate nucleotide or a 5 ’-phosphate analogue modified nucleotide; wherein the 5 ’-hydroxy nucleotide has the structure as shown by Formula (29); the 5 ’-phosphate nucleotide has the structure as shown by Formula (30); and the 5’-phosphate analogue modified nucleotide is one selected from the nucleotides as shown by Formulae (31)-(34):F ormul a (31 ) F ormul a (32) Formula (33) Formula (34); wherein R is one selected from H, OH, OCH3, and F; and the Base is a nucleic acid base selected from A, U, C, G, and T.

19. The single-stranded oligonucleotide according to any one of claims 1-18, wherein the single-stranded oligonucleotide has a length of 21 nucleotides, and / or in a 5’ to 3’ direction in the single-stranded oligonucleotide, the 13th nucleotide is a 2’-O- methoxyethyl modified nucleotide, the 14th nucleotide is a deoxynucleotide, the 2nd, 6th and16th nucleotides are fluoro modified nucleotides, and each remaining nucleotide in the singlestranded oligonucleotide independently of one another is a methoxy modified nucleotide; and / or the linking groups linking any two adjacent nucleotides between the 1st and the 3rd nucleotides at the 5’ terminal of the single- stranded oligonucleotide and the linking groups linking any two adjacent nucleotides between the 1st and the 3rd nucleotides at the 3’ terminal of the singlestranded oligonucleotide are phosphorothioate groups; and / or the 5’ terminal nucleotide is a 5’-hydroxy nucleotide as shown by Formula (29) or a 5’-vinyl phosphate modified nucleotide as shown by Formula (31).

20. The single-stranded oligonucleotide according to any one of claims 1-19, wherein the single-stranded oligonucleotide is reverse complementary to a nucleotide sequence m, which is a contiguous nucleotide sequence segment in the PCSK9 mRNA with no more than 3, such as no more than 2, such as 1, base mismatch(es); or the single- stranded oligonucleotide is completely reverse complementary to said contiguous nucleotide sequence m in PCSK9 mRNA without any base mismatch; wherein optionally, the length of the nucleotide sequence m is not greater than the length of the single-stranded oligonucleotide, and the nucleotide sequence m and the single-stranded oligonucleotide have an equal length, or have a length difference of 1-5 nucleotides or no more than 8 nucleotides; and / or the nucleotide sequence m has a length of at least 16 nucleotides, 16-25 nucleotides, 18-23 nucleotides, or 19-21 nucleotides; and / or the single-stranded oligonucleotide and the nucleotide sequence m have an equal length, and the single-stranded oligonucleotide, except for the terminal nucleotides at position 1, 1-3 or 1-5 at the 5’ terminal (in a 5’ to 3’ direction) and / or the 3’ terminal (in a 3’ to 5’ direction), is completely reverse complementary to the nucleotide sequence m; and / or the single-stranded oligonucleotide, except for the nucleotide at position 1 (in a 5’ to 3’ direction), is reverse complementary to the nucleotide sequence m with 1 base mismatch, or the single-stranded oligonucleotide, except for the nucleotide at position 1 (in a 5’ to 3’ direction), is completely reverse complementary to the nucleotide sequence m, or the single-stranded oligonucleotide is completely reverse complementary to the nucleotide sequence m.

21. The single-stranded oligonucleotide according to any one of claims 1 to 20, wherein the single-stranded oligonucleotide comprises a nucleotide sequence II, and wherein the nucleotide sequence II is one of the sequences as shown in the following i) to iv):i) the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 2 with no more than 3 base differences:5’ - Z2AGUUACAAAAGCAAAACA -3’ (SEQ ID NO: 2), wherein Z2 is A or U; the nucleotide sequence II comprises a nucleotide Z’2 at the position corresponding to Z2; and Z’2 is the first nucleotide at the 5’ terminal of the single-stranded oligonucleotide sequence; ii) the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 4 with no more than 3 base differences:5’ - Z4UAUCUUCAAGUUACAAAA -3’ (SEQ ID NO: 4), wherein Z4 is A or U; the nucleotide sequence II comprises a nucleotide Z’4 at the position corresponding to Z4; and Z’4 is the first nucleotide at the 5’ terminal of the single-stranded oligonucleotide sequence; iii) the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 6 with no more than 3 base differences:5’ - Z6ACAGGUCUAGAAAAGUUG -3’ (SEQ ID NO: 6), wherein Ze is A or U; the nucleotide sequence II comprises a nucleotide Z’ & at the position corresponding to Ze; and Z’e is the first nucleotide at the 5’ terminal of the single-stranded oligonucleotide sequence; iv) the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 8 with no more than 3 base differences:5’ - ZsCAGGUCUAGAAAAGUUGG -3’ (SEQ ID NO: 8), wherein Zs is A or U; the nucleotide sequence II comprises a nucleotide Z’s at the position corresponding to Zs; and Z’s is the first nucleotide at the 5’ terminal of the single-stranded oligonucleotide sequence.

22. The single-stranded oligonucleotide according to claim 21, wherein the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 2 have no more than 1 base difference; or the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 4 have no more than 1 base difference; or the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 6 have no more than 1 base difference; or the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 8 have no more than 1 base difference; or the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 2 have nobase difference; or the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 4 have no base difference; or the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 6 have no base difference; or the nucleotide sequence II and the nucleotide sequence as shown in SEQ ID NO: 8 have no base difference.

23. The single-stranded oligonucleotide according to claim 21 or 22, wherein the singlestranded oligonucleotide further comprises a nucleotide sequence IV; wherein the nucleotide sequence IV is linked to the 3’ terminal of the nucleotide sequence II and has a length of 1, 2, 3 or 4 nucleotides, such as 2 nucleotides; each nucleotide in the nucleotide sequence IV is independently a non-fluoro modified nucleotide; the nucleotide sequence IV is reverse complementary to the PCSK9 mRNA with 1 base mismatch or is completely reverse complementary to the PCSK9 mRNA; each of the non-fluoro modified nucleotides is independently selected from the group consisting of a 2’ -methoxy modified nucleotide, a 2’-Ci- 3 alkyl modified nucleotide, a 2’-amino modified nucleotide, a 2’-substituted-amino modified nucleotide, and a thermally destabilizing nucleotide; and / or the nucleotide sequence IV has a length of 2 nucleotides.

24. The single-stranded oligonucleotide according to any one of claims 21-23, wherein the single-stranded oligonucleotide further comprises a nucleotide sequence V; wherein each nucleotide in the nucleotide sequence V is independently a non-fluoro modified nucleotide; the nucleotide sequence V has a length of 1, 2 or 3 nucleotides, such as 2 nucleotides, and is linked to the 3’ terminal of the nucleotide sequence II or the nucleotide sequence IV; wherein upon formation of a double-stranded oligonucleotide between the singlestranded oligonucleotide and a sense strand, the single- stranded oligonucleotide is the antisense strand and the nucleotide sequence V constitutes a 3’ overhanging terminal of the antisense strand of the double-stranded oligonucleotide; and / or the nucleotide sequence V has a length of 2 nucleotides; and in a 5’ to 3’ direction, the nucleotide sequence V comprises 2 contiguous thymidine deoxynucleotides or 2 contiguous uridine nucleotides, or is completely reverse complementary to the PCSK9 mRNA; or the single-stranded oligonucleotide comprises or consists of a nucleotide sequence as defined by the antisense strand of any one of siRNAl to siRNA4 as shown in Table 1; or the single-stranded oligonucleotide comprises or consists of a nucleotide sequence as definedby the antisense strand of any one of Conjugates 1 to 5 as shown in Table 2.

25. A double-stranded oligonucleotide, comprising a sense strand and an antisense strand, wherein each nucleotide in the sense strand is a modified or an unmodified nucleotide, and the sense strand and the antisense strand are at least partly reverse complementary to form a double-stranded region, and wherein the antisense strand is the single-stranded oligonucleotide according to any one of claims 1 to 24.

26. The double-stranded oligonucleotide according to claim 25, wherein the sense strand has a length of 15-26, 17-24 or 19-23 nucleotides; or the sense strand has a length of 19-21 nucleotides.

27. The double-stranded oligonucleotide according to claim 26, wherein the sense strand and the antisense strand have a length difference of 0-5 nucleotides; or the length of the sense strand is not greater than the length of the antisense strand; or the sense strand and the antisense strand have an equal length of 19, 20 or 21 nucleotides; or the sense strand has a length of 19-21 nucleotides, the antisense strand has a length of 20-24 nucleotides, the length of the antisense strand is greater than the length of the sense strand by 1-3 nucleotides; or the length of the antisense strand is greater than the length of the sense strand by 2 nucleotides; or the sense strand has a length of 19 nucleotides, and the antisense strand has a length of 21 nucleotides; or the sense strand has a length of 21 nucleotides and the antisense strand has a length of 21 nucleotides; or the sense strand has a length of 21 nucleotides, and the antisense strand has a length of 23 nucleotides.

28. The double-stranded oligonucleotide according to any one of claims 25-27, wherein in a 5’ to 3’ direction, 2 to 3 nucleotides of the 11th to 13th nucleotides in the sense strand are fluoro modified nucleotides, the first nucleotide and / or the last nucleotide is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions in the sense strand independently of one another are non-fluoro modified nucleotides, and each of the non-fluoro modified nucleotides is independently selected from the group consisting of an alkoxy modified nucleotide, an alkyl modified nucleotide, an amine modified nucleotide, and a thermally destabilizing nucleotide.

29. The double-stranded oligonucleotide according to claim 28, wherein in a 5’ to 3’ direction, the 11th and the 13th nucleotides or the 11th to 13th nucleotides in the sense strand are fluoro modified nucleotides, the first nucleotide and / or the last nucleotide is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions of the sense strand independently of one another are alkoxy modifiednucleotides.

30. The double-stranded oligonucleotide according to claim 28 or 29, wherein each of the alkoxy modified nucleotides independently of one another is a methoxy modified nucleotide.

31. The double-stranded oligonucleotide according to any one of claims 25 to 30, wherein in the sense strand, at least one of the linking groups linking two adjacent nucleotides is a phosphate ester group with modification group(s), and the phosphate ester group with modification group(s) is present at at least one position between two adjacent nucleotides within the 1st to the 5th nucleotides at the 5’ terminal of the sense strand and between two adjacent nucleotides within the 1st to the 5th nucleotides at the 3’ terminal of the sense strand.

32. The double-stranded oligonucleotide according to claim 31, wherein 1 to 4, such as all 4, of the linking groups linking any two adjacent nucleotides between the 1st nucleotide and the 5th nucleotide at the 5’ terminal of the sense strand are each independently phosphate ester groups with modification group(s); and / or 1 to 4, such as all 4, of the linking groups linking any two adjacent nucleotides between the 1st nucleotide and the 5th nucleotide at the 3’ terminal of the sense strand are each independently phosphate ester groups with modification group(s); and / or wherein each of the phosphate ester groups with modification group(s) is independently a phosphorothioate group having the structure as shown by Formula (28); and / or wherein the sense strand comprises or consists of a nucleotide sequence as defined by the sense strand of any one of siRNAl-siRNA4 as shown in Table 1; or wherein the sense strand comprises or consists of a nucleotide sequence as defined by the sense strand of any one of Conjugates 1-5 as shown in Table 2.

33. The double-stranded oligonucleotide according to any one of claims 25-32, wherein the sense strand comprises 19-21 nucleotides and the antisense strand comprises 21-23 nucleotides;and / or in a 3’ to 5’ direction in the sense strand, the 11th and 13th nucleotides, or the 11th to 13th nucleotides are fluoro modified nucleotides, the first and / or the last nucleotide is a methoxy modified nucleotide or an inverted abasic deoxyribonucleotides, and the nucleotides at the remaining positions independently of one another are alkoxy modified nucleotides; and / or 1 to 4, such as all 4, of the linking groups linking adjacent nucleotides between the 1st and the 5th nucleotides at the 5’ terminal of the sense strand and / or 1 to 4, such as all 4, of the linking groups linking adjacent nucleotides between the 1st and the 5th nucleotides at the 3’ terminal of the sense strand are each independently phosphate ester groups with modification group(s).

34. The double-stranded oligonucleotide according to any one of claims 25-33, whereinthe sense strand comprises 19-21 nucleotides and the antisense strand comprises 21-23 nucleotides; and / or in a 3’ to 5’ direction in the sense strand, the 11th to 13th nucleotides are fluoro modified nucleotides, the first nucleotide is an alkoxy modified nucleotide or an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions independently of one another are alkoxy modified nucleotides; and / or1 to 4, such as all 4, of the linking groups linking adjacent nucleotides between the 1st and the 5th nucleotides at the 5’ terminal of the sense strand and / or 1 to 4, such as all 4, of the linking groups linking adjacent nucleotides between the 1st and the 5th nucleotides at the 3’ terminal of the sense strand are each independently phosphate ester groups with modification group(s); and / or in a 5’ to 3’ direction in the antisense strand, the 13th nucleotide is said substituted alkoxy modified nucleotide; the 14th nucleotide is said nucleotide X; the 2nd, 6th and 16th nucleotides are fluoro modified nucleotides, and each remaining nucleotide in the antisense strand independently of one another is an alkoxy modified nucleotide; and / or one or more, such as all, of the linking groups linking any two adjacent nucleotides between the 1st and the 3rd nucleotides at the 5’ terminal and / or one or more, such as all, of the linking groups linking any two adjacent nucleotides between the 1st and the 3rd nucleotides at the 3’ terminal of the antisense strand independently of one another are phosphate ester groups with modification group(s); and / or the 5’ terminal nucleotide of the antisense strand is a 5’-hydroxy nucleotide as shown by Formula (29) or a 5’-vinyl phosphate modified nucleotide as shown by Formula (31).

35. The double-stranded oligonucleotide according to any one of claims 25-34, wherein the sense strand comprises 19 nucleotides and the antisense strand comprises 21 nucleotides; and / or in a 3’ to 5’ direction in the sense strand, the 11th to 13th nucleotides are fluoro modified nucleotides, the first nucleotide is an inverted abasic deoxyribonucleotide, and the nucleotides at the remaining positions independently of one another are methoxy modified nucleotides; one or more, such as all, of the linking groups linking adjacent nucleotides between the 1st and the 5th nucleotides at the 5’ terminal of the sense strand are phosphorothioate groups; and / or in a 5’ to 3’ direction in the antisense strand, the 13th nucleotide is a 2’-O-methoxyethyl modified nucleotide, the 14th nucleotide is a deoxynucleotide, the 2nd, 6th and 16th nucleotides are fluoro modified nucleotides, and each remaining nucleotide in the antisense strand independently of one another is a methoxy modified nucleotide; one or more, such asall, of the linking groups linking any two adjacent nucleotides between the 1st and the 3rd nucleotides at the 5’ terminal and the linking groups linking any two adjacent nucleotides between the 1st and the 3rd nucleotides at the 3’ terminal of the antisense strand independently of one another are phosphorothioate groups; and / or the 5’ terminal nucleotide of the antisense strand is a 5’-hydroxy nucleotide as shown by Formula (29) or a 5’-vinyl phosphate modified nucleotide as shown by Formula (31).

36. The double-stranded oligonucleotide according to any one of claims 25-35, wherein the sense strand is reverse complementary to the antisense strand with no more than 3, such as no more than 2, such as 1, base mismatch(es); or the sense strand is completely reverse complementary to the antisense strand without any base mismatch; or in a 5’ to 3’ direction, at least the nucleotide sequence of the sense strand, except for the first nucleotide and the last nucleotide, is reverse complementary with 1 base mismatch to the antisense strand or is completely reverse complementary to the antisense strand; or in a 5’ to 3’ direction, the nucleotide sequence of the sense strand, except for the last nucleotide, is completely reverse complementary to the antisense strand; or the sense strand is completely reverse complementary to the antisense strand; or the sense strand comprises a nucleotide sequence having an equal length to the nucleotide sequence m with no more than 3 base differences, no more than 1 base difference, or no base difference; wherein the nucleotide sequence m is said contiguous nucleotide sequence segment in the PCSK9 mRNA; and / or the nucleotide sequence m has a length of at least 16 nucleotides, 16-25 nucleotides, 18-23 nucleotides, or 19-21 nucleotides.

37. The double-stranded oligonucleotide according to any one of claims 25-36, wherein the double-stranded oligonucleotide is an siRNA.

38. The double-stranded oligonucleotide according to any one of claims 25-37, wherein the sense strand comprises a nucleotide sequence I; the antisense strand comprises the nucleotide sequence II; and the double-stranded oligonucleotide is one group of the sequences as shown in the following i) to vi): i) the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 1 with no more than 3 base differences; and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 2 with no more than 3 base differences: 5’- UGUUUUGCUUUUGUAACUZi -3’ (SEQ ID NO: 1);5’- Z2AGUUACAAAAGCAAAACA -3’ (SEQ ID NO: 2), wherein Zi is U, A or ia; Z2 is A or U; ia represents an inverted abasic deoxyribonucleotide; the nucleotide sequence I comprises a nucleotide Z’i at the position corresponding to Zi; thenucleotide sequence II comprises a nucleotide Z’2 at the position corresponding to Z2; and Z’2 is the first nucleotide at the 5’ terminal of the antisense strand; ii) the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 3 with no more than 3 base differences; and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 4 with no more than 3 base differences:5’- UUUUGUAACUUGAAGAUAZ3 -3’ (SEQ ID NO: 3);5’- Z4UAUCUUCAAGUUACAAAA -3’ (SEQ ID NO: 4), wherein Z3 is U, A or ia; Z4 is A or U; the nucleotide sequence I comprises a nucleotide Z’3 at the position corresponding to Z3; the nucleotide sequence II comprises a nucleotide Z’4 at the position corresponding to Z4; and Z’4 is the first nucleotide at the 5’ terminal of the antisense strand; iii) the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 5 with no more than 3 base differences; and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 6 with no more than 3 base differences:5’- CAACUUUUCUAGACCUGUZs -3’ (SEQ ID NO: 5);5’- Z6ACAGGUCUAGAAAAGUUG -3’ (SEQ ID NO: 6), wherein Z5 is U, A or ia; Ze is A or U; the nucleotide sequence I comprises a nucleotide Z’5 at the position corresponding to Z5; the nucleotide sequence II comprises a nucleotide Z’e at the position corresponding to Ze; and Z’e is the first nucleotide at the 5’ terminal of the antisense strand; iv) the nucleotide sequence I has an equal length to the nucleotide sequence as shown in SEQ ID NO: 7 with no more than 3 base differences; and the nucleotide sequence II has an equal length to the nucleotide sequence as shown in SEQ ID NO: 8 with no more than 3 base differences:5’- CCAACUUUUCUAGACCUGZ7 -3’ (SEQ ID NO: 7);5’- ZsCAGGUCUAGAAAAGUUGG -3’ (SEQ ID NO: 8), wherein Z7 is U, A or ia; Zs is A or U; the nucleotide sequence I comprises a nucleotide Z’7 at the position corresponding to Z7; the nucleotide sequence II comprises a nucleotide Z’s at the position corresponding to Zs; and Z’s is the first nucleotide at the 5’ terminal of the antisense strand.

39. The double-stranded oligonucleotide according to claim 38, wherein the nucleotide sequence I has no more than 1 base difference from the nucleotide sequence as shown in SEQID NO: 1, 3, 5 or 7; and the nucleotide sequence II has no more than 1 base difference from the nucleotide sequence as shown in SEQ ID NO: 2, 4, 6 or 8.

40. The double-stranded oligonucleotide according to claim 38 or 39, wherein the doublestranded oligonucleotide is the double-stranded oligonucleotide of any one of siRNAl to siRNA4 as shown in Table 1.

41. An oligonucleotide conjugate, comprising an oligonucleotide group and a delivery group conjugated to the oligonucleotide group, wherein the oligonucleotide group is independently a group formed by removing one or more atoms or atomic groups from the single-stranded oligonucleotide according to any one of claims 1-24 or the double-stranded oligonucleotide according to any one of claims 25-40.

42. The oligonucleotide conjugate according to claim 41, wherein the delivery group comprises a linking group and at least one pharmaceutically acceptable targeting group, and the oligonucleotide group, the linking group and said at least one targeting group are sequentially linked covalently or non-covalently, wherein said at least one targeting group is independently selected from a ligand capable of binding to the asialoglycoprotein receptor on the surface of mammalian hepatocytes; and / or the oligonucleotide group in the oligonucleotide conjugate is a siRNA group formed from the siRNAs listed in Table 1; and / or the oligonucleotide conjugate has the structure as shown in Formula (403),Formula (403), in Formula (403), Nu is an oligonucleotide group; such as the oligonucleotide group formed by removing one or more atoms or atomic groups from the double-stranded oligonucleotide group according to any one of claims 25-40, wherein the P atom is covalently linked to the 3’terminal nucleotide in the sense strand of the double-stranded oligonucleotide group; or, the 3’ terminal nucleotide in the sense strand of the double-stranded oligonucleotide group is an inverted abasic deoxyribonucleotide, and the P atom is covalently linked to the double-stranded oligonucleotide group by substituting a hydrogen atom in the hydroxyl in the inverted abasic deoxyribonucleotide at 3’ terminal of the sense strand of the double-stranded oligonucleotide group, wherein the hydroxyl is linked to the ribose ring via a methylene group; and / or the oligonucleotide conjugate is one of the Conjugates 1-5 as listed in Table 2.

43. A pharmaceutically acceptable salt of the single-stranded oligonucleotide according to any one of claims 1-24, the double-stranded oligonucleotide according to any one of claims 25- 40, or the oligonucleotide conjugate according to claim 41 or 42; wherein optionally, the pharmaceutically acceptable salt is a partial or completely water- soluble salt of the single-stranded oligonucleotide, the double-stranded oligonucleotide or the oligonucleotide conjugate; wherein the water-soluble salt is optionally an amine salt, an alkali metal salt or an alkaline earth metal salt; wherein the amine salt is optionally one or more selected from an ammonium salt, a methylamine salt, a tertiary amine salt, and a quaternary ammonium salt; and / or the alkali metal salt is optionally one or more selected from a potassium salt and a sodium salt; and / or the alkaline earth metal salt is optionally one or more selected from a calcium salt and a magnesium salt; wherein the tertiary amine salt is optionally one or more selected from a triethylamine salt, a triisopropylamine salt and an N,N-diisopropylethylamine salt; or wherein optionally, the pharmaceutically acceptable salt is a salt or partial salt of the singlestranded oligonucleotide, the double-stranded oligonucleotide or the oligonucleotide conjugate, wherein the salt is optionally one or more selected from a methylamine salt, a triethylamine salt and a sodium salt.

44. A pharmaceutical composition, comprising one or more of the single-stranded oligonucleotide according to any one of claims 1-24, the double-stranded oligonucleotide according to any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, and the pharmaceutically acceptable salt according to claim 43, and a pharmaceutically acceptable excipient; wherein optionally, the pharmaceutically acceptable excipient is one or more selected from a solvent, a protectant, an osmotic pressure regulator, and other pharmaceutically acceptable carriers;wherein the solvent is optionally one or more selected from deionized water, water for injection, a pH buffer, a physiological saline, ethanol and an ethanol aqueous solution.

45. Use of one or more of the single-stranded oligonucleotide of any one of claims 1-24, the double-stranded oligonucleotide of any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, the pharmaceutically acceptable salt according to claim 43, and the pharmaceutical composition of claim 44 in the manufacture of a medicament for treating and / or preventing a disease or a symptom associated with the expression level of PCSK9 mRNA.

46. The use according to claim 45, wherein the disease or the symptom associated with the expression level of PCSK9 mRNA is dyslipidemia; such as dyslipidemia selected from the group consisting of hypercholesterolemia, hypertriglyceridemia and atherosclerosis.

47. A method for treating and / or preventing a disease or a symptom associated with the expression level of PCSK9 mRNA, comprising administering to a subject in need thereof an effective amount of one or more of the single-stranded oligonucleotide of any one of claims 1- 24, the double-stranded oligonucleotide of any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, the pharmaceutically acceptable salt of claim 43, and the pharmaceutical composition of claim 44.

48. The method according to claim 47, wherein the disease or the symptom associated with the expression level of PCSK9 mRNA is dyslipidemia, such as dyslipidemia selected from the group consisting of hypercholesterolemia, hypertriglyceridemia and atherosclerosis.

49. A method for regulating the expression level of PCSK9 mRNA in a cell, comprising contacting the cell with an effective amount of one or more of the single- stranded oligonucleotide of any one of claims 1-24, the double-stranded oligonucleotide of any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, the pharmaceutically acceptable salt of claim 43, and the pharmaceutical composition of claim 44.

50. One or more of the single-stranded oligonucleotide according to any one of claims 1- 24, the double-stranded oligonucleotide according to any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, the pharmaceutically acceptable salt according to claim 43, and the pharmaceutical composition according to claim 44, for use as a medicament.

51. One or more of the single-stranded oligonucleotide according to any one of claims 1- 24, the double-stranded oligonucleotide according to any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, the pharmaceutically acceptable salt according to claim 43, and the pharmaceutical composition according to claim 44, for use inthe treatment and / or prevention of a disease or a symptom associated with the expression level of PCSK9 mRNA, such as dyslipidemia, such as dyslipidemia selected from the group consisting of hypercholesterolemia, hypertriglyceridemia and atherosclerosis.

52. A cell expressing PCSK9 mRNA, comprising one or more of the single-stranded oligonucleotide according to any one of claims 1-24, the double-stranded oligonucleotide according to any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, the pharmaceutically acceptable salt according to claim 43, and the pharmaceutical composition according to claim 44.

53. A kit comprising one or more of the single-stranded oligonucleotide according to any one of claims 1-24, the double-stranded oligonucleotide according to any one of claims 25-40, the oligonucleotide conjugate according to claim 41 or 42, the pharmaceutically acceptable salt according to claim 43, and the pharmaceutical composition according to claim 44; and an optional instructions for use.

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