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.