Lack of Insulin Receptor Substrate-2 Causes Progressive Neointima Formation in Response to Vessel Injury

Background— Insulin resistance is associated with atherosclerosis, but its mechanism is unknown. It has been reported that insulin receptor substrate (IRS)-1 deficient ( IRS-1 −/− ) mice showed insulin resistance without type 2 diabetes, whereas the IRS-2 deficient ( IRS-2 −/− ) mice showed insulin resistance with type 2 diabetes. Methods and Results— We investigated neointima formation in the IRS-1 −/− and IRS-2 −/− mice at 8 and 20 weeks. The IRS-2 −/− mice showed much greater neointima formation than the IRS-1 −/− and wild-type mice at 8 weeks. At 20 weeks, the IRS-2 −/− mice had greater neointima formation than the IRS-1 −/− mice, which showed more enhanced neointima formation than the wild-type mice. The IRS-1 −/− and IRS-2 −/− mice had dyslipidemia, hypertension, and insulin resistance. The IRS-2 −/− mice had more metabolic abnormalities than the IRS-1 −/− mice at 8 and 20 weeks. IRS-2 expression was detected, but IRS-1 expression was not detected in the vessels. Conclusions— The neointima formation in the IRS-1 −/− and IRS-2 −/− mice appears to be related to abnormalities induced by the altered metabolic milieu in insulin-resistant states. Moreover, because neointima formation was much greater in the IRS-2 −/− mice than in the IRS-1 −/− mice at 8 and 20 weeks, it is suggested that a lack of IRS-2 renders the vasculature more susceptible to injury in the abnormal metabolic milieu, and IRS-2 may have a protective effect on neointima formation. We conclude that IRS-2 is protective and retards the development of neointima formation in insulin-resistant states.