The present invention discloses for the first time that the insulin receptor (IR) is a target of Herstatin, which modulates IR and IR-mediated intracellular signaling. In preferred aspects, Herstatin binds at nM concentrations to cell-surface IR, up-regulates basal IR expression by several-fold, induces the accumulation of pro-IR, and stimulates insulin activation of the ERK pathway. Moreover, these changes in insulin signaling are accompanied by alterations in IGF-IR expression, IRS-2 levels, and the serine phosphorylation state of both IRS-1 and IRS-2. Preferred aspects provide novel therapeutic methods and pharmaceutical compositions for treatment of conditions associated with altered IR expression or IR-mediated signaling, including but not limited to insulin resistance syndrome, pre-diabetic conditions, metabolic syndrome, type 1 and type 2 diabetes, cardiac disease, diabetes-associated vascular disease, atherosclerosis, hypertension, diabetes-associated lipid metabolism disorders (dyslipidemia), obesity, critical illness, neurodegenerative disorders, and combinations thereof, and cancer.