Application of COL21A1 and APEX1 in IgAN

Abstract

The invention belongs to the field of biology, and discloses an application of COL21A1 and APEX1 in IgAN. The inventor finds that COL21A1 and APEX1 are related to diagnosis and progression of the IgA nephropathy through research, the IgA nephropathy can be well diagnosed or the progression of the IgA nephropathy can be well determined by detecting COL21A1 and / or APEX1, a basis is expected to be provided for early diagnosis of IgAN, and a new way is provided for treatment intervention and disease management of the IgA nephropathy.

Description

Technical Field

[0001] The invention belongs to the biological field, and particularly relates to the application of COL21A1 and APEX1 in IgAN. Background Art

[0002] IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Approximately 30%-45% of patients progress to renal failure (KF) within 20-25 years after diagnosis, and there has long been a lack of effective treatment. Literature reports that the incidence of IgAN in adults is at least 2.5 / 100,000 per year, and its prevalence has obvious geographical distribution differences worldwide, with the highest incidence in East Asia and the lowest incidence in Central Africa. The occurrence of IgAN may be related to upper respiratory tract infections, with the peak incidence in the 20s and 30s, and male patients are more common. The susceptibility to IgAN and the risk of disease progression are affected by the combined effects of genetic and environmental factors.

[0003] There is currently no disease-specific treatment for IgAN; clinically, the goal is to control the patient's blood pressure and maintain the patient's renal function, and the treatment is carried out accordingly according to the severity of the disease; patients with mild abnormal urine, normal blood pressure and normal glomerular filtration rate usually perform well and only need regular monitoring; for patients in other situations, treatment options are limited, generally through non-specific treatments such as RAS blockers to reduce blood pressure and proteinuria, and other general treatments such as lipid-lowering, sodium intake control, smoking cessation, avoidance of non-steroidal anti-inflammatory drugs and other nephrotoxins; for patients with a large number of crescent formations, immunosuppressants combined with steroids can be used for treatment. However, IgAN currently still faces a series of problems in treatment, such as individual differences, lack of specific drugs, high recurrence rate and a series of complications. Early intervention and follow-up treatment may help prevent or delay the development of renal failure and reduce the number of patients requiring renal replacement therapy.

[0004] IgA nephropathy (IgAN) refers to a primary glomerular disease characterized by the deposition of IgA or IgA in the mesangial region of the glomerulus, and is the most common cause of glomerular hematuria. The pathogenesis of IgAN is very complex, involving abnormalities of the immune system, genetic factors, inflammatory responses, and changes in the local environment of the kidney, which is still unclear. The core feature of IgAN is that the immune system abnormally produces and accumulates polymeric IgA1 (mainly IgA1 subtype) immune complexes. These IgA immune complexes are deposited in the glomeruli, triggering local inflammatory responses. Abnormal IgA1 molecules usually have a high degree of glycosylation heterogeneity due to incomplete O-sugar chains. After IgA deposition, it can activate the complement system and cells in the glomerulus, including mesangial cells and endothelial cells, to produce inflammatory mediators such as cytokines and chemokines, further recruiting immune cells to the kidneys. These cells produce inflammatory mediators, inducing further immune cell infiltration and activation, exacerbating kidney damage. Long-term inflammatory response leads to renal interstitial fibrosis, which is stimulated by the production of profibrotic factors (such as transforming growth factor-β, TGF-β) to stimulate interstitial cells (such as fibroblasts and tubular epithelial cells to transdifferentiate into myofibroblasts) to produce large amounts of collagen and other extracellular matrix proteins. Renal interstitial fibrosis is a key mechanism leading to the gradual loss of renal function. In addition, genetic factors, environment and epigenetics also play an important role in the pathogenesis of IgAN. Genetic studies have found that IgAN patients have specific genetic susceptibility areas, which involve multiple aspects such as immune regulation and complement activation. This shows that IgAN is a multi-gene genetic disease and genetic factors play an important role in the development of the disease. Summary of the invention

[0005] The object of the present invention is to overcome at least one disadvantage of the prior art and provide application of COL21A1 and APEX1 in IgAN.

[0006] The technical solution adopted by the present invention is: The first aspect of the present invention provides: Use of a protein quantitative reagent in preparing a reagent for diagnosing IgA nephropathy or determining the progression of IgA nephropathy, wherein the protein is COL21A1 and / or APEX1.

[0007] In some application examples, the sample detected by the protein quantification reagent is kidney tissue.

[0008] The second aspect of the present invention provides: A system for diagnosing or determining the prognosis of IgA nephropathy, comprising: A protein quantification device, used to determine the expression level of COL21A1 and / or APEX1 protein in the tissue sample to be tested; An analysis device for determining the risk of IgA nephropathy based on the expression of COL21A1 and / or APEX1 protein in the human body; The result output device outputs the analysis result of the analysis device.

[0009] In some examples of the system, the protein quantification device is a liquid chromatography-mass spectrometry or protein immunohistochemistry analysis device.

[0010] In some examples of the systems, a significantly increased expression level of COL21A1 indicates a high risk of IgA nephropathy.

[0011] In some examples of the systems, a significant increase in the expression of APEX1 indicates worsening of IgA nephropathy.

[0012] In some embodiments of the present invention, the sample is kidney tissue.

[0013] In some examples of the system, the significantly increased expression level refers to an expression level that is at least 1.5 times higher than the normal level.

[0014] The beneficial effects of the present invention are: The inventors have found that COL21A1 and APEX1 are related to the diagnosis and progression of IgA nephropathy. By detecting COL21A1 and / or APEX1, IgA nephropathy can be well diagnosed or the progression of IgA nephropathy can be determined, which is expected to provide a basis for the early diagnosis of IgAN and provide a new approach for therapeutic intervention and disease management of IgA nephropathy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the result of differentially expressed proteins analysis in different areas of the kidney.

[0016] Figure 2 It is an analysis of the functions of different areas of the kidney.

[0017] Figure 3 It is the WGCNA of different regions of the kidney.

[0018] Figure 4 It is a potential key protein analysis result for diagnosing IgAN.

[0019] Figure 5 Is the proteomic data of IgAN deterioration.

[0020] Figure 6 is the expression level of COL21A1 and the ROC curve.

[0021] Figure 7 is the expression level of APEX1 and the ROC curve.

[0022] Figure 8It is the immune characteristics of renal tubules in IgAN group and NC group. DETAILED DESCRIPTION

[0023] List of abbreviations IgAN:IgA nephropathy; CKD: chronic kidney disease; ESRD: end-stage renal disease; LCM: laser capture microdissection; DIA: Data Independent Acquisition; SAT-MS: Sequential windowed acquisition of all theoretical mass spectra; DDA: Data Dependence Acquisition; DEPs: differentially expressed proteins; GO: Gene Ontology KEGG: Kyoto Encyclopedia of Genes and Genomes; Gene set enrichment analysis; ssGSEA: Single sample gene set enrichment analysis; WGCNA: weighted gene co-expression network analysis; AUC: Area under the curve; STEM: Short Time-series Expression Miner.

[0024] The technical solution of the present invention is further explained below in conjunction with experimental data.

[0025] patient This study included 18 patients who were newly diagnosed with IgA nephropathy based on renal biopsy pathology at the First Affiliated Hospital of Jinan University, Guangzhou, China. According to the grading system proposed by Lee et al, 5 patients were classified as grade II, 8 as grade III, and 5 as grade IV. None of these patients had clinical or serological indications of autoimmune disease, Henoch-Schönlein purpura, liver disease, or malignancy. In addition, 11 individuals with normal renal biopsy results were selected as controls. This study was approved by the Ethics Committee of the First Affiliated Hospital of Jinan University, Guangzhou, China.

[0026] Specimen preparation and LCM Each formalin-fixed, paraffin-embedded renal tissue sample was sliced ​​using a pathological microtome to obtain tissue sections with a thickness of 10 μm. Subsequently, these sections were transferred to framed membrane slides specially prepared for laser capture microdissection (PET frame slides, No. 11505190, Leica Microsystems, Germany). Subsequent processes included dewaxing, drying, and laser capture microdissection on the prepared tissue sections. Data acquisition We extracted proteins from tissue sections, followed by enzymatic digestion and desalting. Subsequently, MaxQuant software (version 1.5.3.30) was used to process and identify data-dependent acquisition (DDA) data. For the analysis of data-independent acquisition (DIA) data, we used Spectronaut (version 12) and indexed retention time (iRT) peptides to calibrate retention times.

[0027] Identification of differential protein expression Initially, we established protein expression profiles for each sample in IgA nephropathy (IgAN) and control groups. Following this, we utilized the Limma package in R to identify proteins that showed significantly altered expression levels between the IgAN group and the control group. These differentially expressed proteins (DEPs) were defined with a statistically significant threshold of P < 0.05 and a fold change greater than 1.5-fold. Enrichment analysis of differentially expressed proteins (DEPs) was performed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) and was supported by the clusterProfiler package in R. Gene set enrichment analysis (GSEA) was also performed using the same package and the results were considered statistically significant at P < 0.05. Coexpression analysis (WGCNA) was performed to identify networks of co-expressed differentially expressed proteins. Genes were grouped into different modules using the WGCNA package in R.

[0028] In summary, the process involves the identification and weighting of connections between gene pairs, which is determined by their relative expression levels in multiple samples. Subsequently, we transformed the adjacency matrix into a topological overlap matrix (TOM) to assess the connectivity between genes in the network. We then used hierarchical clustering to detect gene clusters (modules) with high interconnectivity, based on their connectivity and covariance coefficients. The minimum size of the gene dendrogram was set to 25. We chose an appropriate soft threshold power to define significant positive correlations between genes within each module.

[0029] In addition, we collected proteomic information associated with the selected modules to facilitate subsequent in-depth analysis. LASSO regression In our study, we constructed a binomial LASSO model including differential expression proteins (DEPs) using the glmnet package in R. We determined the optimal lambda value by 10-fold cross validation to ensure that it minimized the partial likelihood bias. In our study, proteins associated with this optimal lambda were identified as key biomarkers. Short time series expression secondary analysis To identify molecular features associated with the progression of IgA nephropathy, we used STEM (Short Time-series Expression Miner) analysis to classify protein expression profiles from healthy controls and IgAN stages II, III, and IV. Before analysis, the expression data were normalized and the STEM clustering method was applied. Before analysis, the expression data were normalized and the stem clustering method was applied. We established a minimum absolute expression change value of 0.5 as a filter for molecule selection and limited the correlation threshold between any two models to 0.9. Gene profiles with a p-value < 0.05 determined based on the number of clustered genes were considered to be significantly enriched gene clusters. Functional enrichment analysis of profile 25 by metscape To analyze the proteins within profile 25 in tubules and stroma, we performed pathway enrichment analysis using metscape (available at https: / / metascape.org). For this analysis, we configured specific parameters, including a minimum overlap of 3 and a p-value cutoff of 0.05.

[0030] Statistical data analysis All statistical analyses in this study were performed using R software (version 4.3.1). We defined proteins as differentially expressed if they met the criteria of p value less than 0.05 and FC greater than 1.5 or less than 0.67. The relationship between clinical parameters and proteins was analyzed using Spearman correlation. To assess statistical significance, we selected a range of tests depending on the specific data characteristics: unpaired two-tailed t-test, Mann-Whitney U test, adjusted t-test, permutation test, likelihood ratio test, or Wilcoxon rank sum test. The choice of test method was determined by the distribution and nature of the data being analyzed.

[0031] result Patient characteristics The clinical characteristics of lgAN patients (n=11) are shown in Table 1 , and normal control renal tissue (NC) (n=10) was included.

[0032] Table 1 Clinical characteristics of patients

[0033] Protein profiling of glomeruli, tubules, and interstitium in 131 patients with IgAN and normal controls. The proteomic analysis approach in our study is shown in Figure 1a. It illustrates the proteomic analysis of different renal tissue regions, integrating data-independent acquisition (DIA) for protein quantification. The initial mass spectrometry data acquisition was performed in data-dependent acquisition (DDA) mode. Our library contained 81,369 peptides and 8,310 proteins. A total of 86 samples provided mass spectrometry (MS) data in DIA mode, and 50,894 peptides and 2,982 proteins were quantified using MSstats software. In this study, MSstats software was used to correct for intra-system errors and normalize each sample. The significance of differentially expressed proteins (DEPs) was evaluated according to pre-determined control groups and linear mixed-effects models. We applied two filtering criteria: Fold change greater than 1.5 and p value less than 0.05 to identify significant DEPs. Based on these criteria, we determined that 114 proteins were significantly upregulated and 74 proteins were significantly downregulated in the glomeruli of IgAN patients compared with controls (IgAN-g / CG-G), as shown in Figure 1b. In the tubular zone (IgAN-T / CG-T), 266 proteins were significantly upregulated and 122 proteins were significantly downregulated, as shown in Figure 1c. There were 232 differentially expressed proteins in the interstitial zone (IgAN-I / CG-I), of which 112 were upregulated and 117 were downregulated, as shown in Figure 1d. This in-depth analysis revealed changes in the expression of specific proteins in IgAN and helped to understand the molecular basis of the disease.

[0034] Figure 1Analysis of differentially expressed proteins in different regions of the kidney. Schematic diagram of proteomic analysis. Volcano plots from different renal compartments, a glomerulus, c tubules, and d interstitium. Functional analysis patterns in different regions of the kidney To elucidate the role of DEPs in IgA nephropathy (IgAN) and normal controls (NC), we performed gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. These analyses focused on DEPs in three different renal regions: glomerulus, tubules, and interstitium. GO enrichment results revealed specific pathway enrichments in each region. The glomerulus was mainly enriched in energy and metabolic pathways (Fig. 2a), while the tubules were significantly enriched in immune and inflammatory pathways ( Figure 2 b). Renal interstitium is mainly enriched in adhesion and extracellular matrix interaction pathways ( Figure 2 c). Meanwhile, KEGG enrichment analysis provided insights into the involvement of unique pathways. The tubules were uniquely involved in the phagosome, complement, and coagulation cascade pathways, while the glomerulus was uniquely involved in the fatty acid biosynthesis pathway. Notably, the ecm receptor interaction pathway was a focus of the renal interstitium (Fig. 2d). In addition, we performed gene set enrichment analysis (GSEA) on these pathways of interest. The analysis showed that the complement and coagulation cascade pathways were significantly activated in the tubules (Fig. 2e), the fatty acid elongation pathway was activated in the glomerulus (Fig. 2f), and the ecm receptor interaction pathway was significantly activated in the renal interstitium (Fig. 2g). These findings provide a deeper understanding of the molecular mechanisms and pathway involvement of IgAN in different regions of the kidney.

[0035] Figure 2 Functional analysis of different regions of the kidney. GO enrichment analysis of DEPs in different renal compartments (a glomerulus, b tubule, c interstitium). d Comparison of KEGG pathways of DEPs in glomerulus, tubule, and interstitium. e GSEA enrichment map of complement and coagulation cascade pathways. f GSEA enrichment map of glomerular fatty acid degradation pathway. g GSEA enrichment map of interstitial ECM receptor interaction pathway. Immune cell infiltration pattern characterized by tubules IgA nephropathy (IgAN) is considered an immune-mediated disease, and our results emphasize that immune dysregulation mainly occurs in the renal tubules. This alteration of the intrarenal immune microenvironment plays an important role in the progression of IgAN. To describe the differences in immune cell infiltration between IgAN and normal control (NC) groups, we used two computational methods: single sample gene set enrichment analysis (ssGSEA) and CIBERSORT, and the results are shown in Figure 8 , Figure 8(A) Venn diagram of WGCNA and DEP, (B) stacking plot of tubular immune cell content. (C) Box plot of immune signatures between IgAN and NC groups determined using CIBERSORT analysis. (D) Box plot of immune signatures between IgAN and NC groups determined using ssGSEA analysis. Our analysis using CIBERSORT showed that several cell types had higher immune signature scores in the renal tubules of the IgAN group, including T cell CD8, resting NK cells, M0 macrophages, activated dendritic cells, resting mast cells, eosinophils, and neutrophils ( Figure 8 At the same time, ssGSEA results showed that the central memory and effector memory CD8 T cells in the IgAN group were significantly activated ( Figure 8 Based on these findings, we hypothesized that CD8 T cells play a crucial role in mediating the immune dysregulation observed in the tubules during IgAN. This insight into the immune landscape of IgAN enhances our understanding of the disease pathophysiology and may guide future therapeutic strategies targeting specific immune components in the tubules, particularly CD8 T cells. Identification of co-expressed gene modules in different kidney regions In our study, Weighted Gene Co-expression Network Analysis (WGCNA) was used to identify protein modules in which multiple proteins were co-expressed in different kidney regions. We selected specific soft threshold capacities (β) to ensure the formation of biologically meaningful scale-free networks in different kidney regions: β of 10 for glomeruli (Fig. 3a), β of 6 for tubules (Fig. 3d), and β of 6 for interstitial regions (Fig. 3g). These selections were based on achieving scale-independent properties of >0.9. Subsequent hierarchical clustering analysis and application of a dynamic branch-cutting method on the gene dendrite graph classified the proteins into different modules. In glomeruli, proteins were classified into nine modules, of which blue, brown, and turquoise modules were significantly associated with IgAN ( Figure 3 c), and were therefore selected for further analysis. In the renal tubules, proteins were organized into 6 modules. Among them, the gray and yellow modules were identified as significantly associated with IgAN (Figure 3f), and therefore they were selected for more in-depth analysis. Similarly, in the interstitial region, proteins were divided into 7 modules, and the gray and turquoise modules were significantly associated with IgAN (Figure 3i) and were selected for further exploration. Overall, a total of 711 genes were found to be significantly associated with IgAN in these analyses. This comprehensive approach using WGCNA provides a detailed understanding of protein interactions and networks in different kidney regions affected by IgAN, providing valuable insights into the molecular basis of this disease.

[0036] Figure 3 WGCNA of different regions of the kidney. Correlation of soft threshold power with scale-free topological model. A glomerulus, d tubule, g interstitium. Gene dendrogram obtained by averaging linkage hierarchical clustering proteins. Different colors represent different modules. B glomerulus, e tubule, h interstitium. Module-trait relationship. G glomerulus, f tubule, I interstitium. Identification of key proteins associated with IgAN In our study, we employed Venn diagrams to analyze the intersection of differentially expressed proteins with key module proteins. This approach allowed us to identify 63 overlapping protein regions, as shown in ( Figure 8 ). To pinpoint the characteristic proteins, we applied Lasso regression and divided all samples in the dataset into a training set (70%) and a validation set (30%). The lasso model was constructed using the 63 overlapping proteins in the training set, and a lambda (λ) value of 18 was selected to determine the proteins that best predicted IgAN, as shown in Figure 4a. From this model, we obtained the signatures of 18 proteins with non-zero coefficients (Figure 4b). The area under the curve (AUC) of this protein signature reached an impressive 97.57% and 97.19% in the training and validation sets, respectively, indicating a strong predictive ability (Figure 4c). We found several key proteins whose expression was altered in IgAN. COL21A1 and COL18A1 were upregulated in IgAN patients, while LAMB2, HSP90AA1, and ACTN4 were downregulated (Figures 4d-h). Therefore, we selected these significantly altered proteins as potential diagnostic markers for IgAN. COL21A1, COL18A1, LAMB2, HSP90AA1, and ACTN4 proteins are expected to improve the accuracy of IgAN diagnosis, potentially leading to earlier detection and more effective management of the disease.

[0037] Figure 4Potential key proteins for diagnosing IgAN. Protein feature selection of the optimal parameter (lambda) in the ALasso model. b LASSO coefficient profiles of 18 differentially expressed proteins selected by the optimal parameter λ. c Receiver operating characteristic (ROC) curves of gene signatures in the training and validation sets. d, e, f, g, h Differences in the expression of key proteins between IgAN patients and the control group, *0.01 < p < 0.05, **0.001 < p < 0.01, ***p < 0.001. To elucidate the proteomic changes associated with disease deterioration in patients with IgA nephropathy and the changes in protein expression associated with IgAN deterioration, we employed Short Time-series Expression Miner (STEM) analysis. This method was applied to healthy controls (NC) as well as stages II, III, and IV of IgAN to obtain different profiles characterizing protein expression behavior. We found four different protein profiles in the renal tubules, which showed different expression behaviors in the normal control (NC), IgAN II, IgAN III, and IgAN IV groups. These expression profiles were identified as numbers 8, 11, 23, and 25 (Figure 5a, permutation test, P < 0.05). We also found four significant protein profiles in the interstitium, which had different expression behaviors in the NC, IgAN II, IgAN III, and IgAN IV groups, including profiles 15, 21, 24, and 25 (Figure 5b, permutation test, P < 0.05). Subsequently, by using a Venn diagram, we compared the overlapping elements of profile 25 in the tubular and interstitial regions (Figure 5c), and we were able to screen 41 overlapping proteins, which increased with the increase in Lee's pathological grade, indicating a positive correlation between them. To investigate the relationship between protein expression levels and clinical characteristics, we performed a correlation analysis. The focus of this analysis was the protein expression characteristics of IgAN patients and the key clinical feature of proteinuria. We found a total of 2 proteins (APEX1, C4A) defined as being positively correlated with proteinuria ( Figure 5 d). On the metscape platform, the proteins in profile 25 were significantly enriched in extracellular matrix organization, actin filament-based movement, and coronavirus COVID - 19 ( Figure 5 e).

[0038] Figure 5Proteomic data of IgAN exacerbation. Proteomic profiles of STEM analysis. Protein expression profiles of NC, IgAN II, IgAN III, and IgAN IV were obtained by STEM analysis. The profile ID is shown in the upper left corner of the profile, a tubule. interstitial. c Venn diagram of tubule and interstitial profile 25. d Correlation analysis of upregulated proteins with corresponding proteinuria clinical features to identify proteins in acute exacerbation. Functional analysis of tubule and interstitial profile 25 in the emetscape platform (P < 0.05).

[0039] Nephron refers to the functional unit of the kidney. It is the basic unit of kidney structure and function, and together with the collecting duct, it completes the urinary function. The human body has a strong reserve of nephrons, which allows for unilateral kidney transplantation. However, if the number of functional nephrons decreases to less than 30%, renal failure will occur; if it drops to less than 10%, it will be life-threatening. Nephrons are composed of glomeruli and renal tubules.

[0040] By comparing the glomeruli and tubules of IgAN and normal groups, we found that COL21A1 was highly expressed in both glomeruli and tubules, but the high expression in tubules was not statistically significant. The ROC curve showed that it had a high diagnostic value in both (AUC>0.7) ( Figure 6 , Figure, a, the expression level of COL21A1 in glomerulus, b, the ROC curve of COL21A1 in glomerulus, c, the expression level of COL21A1 in renal tubules, d, the ROC curve of COL21A1 in renal tubules).

[0041] By comparing the glomeruli and renal tubules of IgAN and normal groups, we found that APEX1 was highly expressed in both glomeruli and renal tubules. The ROC curve showed that it had a high diagnostic value in both (AUC>0.7), and the diagnostic value was higher in the renal tubules ( Figure 7 , Figure, a, the expression level of APEX1 in glomerulus, b, the ROC curve of APEX1 in glomerulus, c, the expression level of APEX1 in renal tubules, d, the ROC curve of APEX1 in renal tubules).

[0042] in conclusion In conclusion, our study has identified major mechanisms leading to substructural changes in IgA nephropathy (IgAN) that differ between individuals. COL21A1 and APEX1 may be useful for monitoring disease progression and assessing the effectiveness of therapeutic interventions.

[0043] The above is a further detailed description of the present invention, which should not be regarded as a limitation on the specific implementation of the present invention. For ordinary technicians in the technical field to which the present invention belongs, simple deduction or replacement without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. Use of a protein quantitative reagent in the preparation of a reagent for diagnosing IgA nephropathy or determining the progression of IgA nephropathy, wherein the protein is COL21A1 and / or APEX1.

2. The use according to claim 1, characterized in that: The sample detected by the protein quantitative reagent is kidney tissue.

3. A system for diagnosing or determining the prognosis of IgA nephropathy, comprising: A protein quantification device, used to determine the expression level of COL21A1 and / or APEX1 protein in the tissue sample to be tested; An analysis device for determining the risk of IgA nephropathy based on the expression of COL21A1 and / or APEX1 protein in the human body; The result output device outputs the analysis result of the analysis device.

4. The system according to claim 3, characterized in that The protein quantitative device is a liquid chromatography-mass spectrometry and protein immunohistochemistry analysis device.

5. The system according to claim 3, characterized in that A significantly increased expression of COL21A1 indicates a high risk of IgA nephropathy.

6. The system according to claim 3, characterized in that The significant increase in the APEX1 expression level indicates that the IgA nephropathy is getting worse.

7. The system according to claim 3, characterized in that The sample is kidney tissue.

8. The system according to claim 5 or 6, characterized in that: The significantly increased expression level refers to an expression level that is at least 1.5 times higher than the normal level.

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