Contrasting effects of IRS-1 versus IRS-2 gene disruption on carbohydrate and lipid metabolism in vivo

Abstract

To examine the impact of homozygous genetic disruption of insulin receptor substrate (IRS)-1 (IRS-1 -/-) or IRS-2 (IRS-2 -/-) on basal and insulin-stimulated carbohydrate and lipid metabolism in vivo, we infused 18-h fasted mice (wild-type (WT), IRS-1 -/-, and IRS-2 -/-) with [3- 3H]glucose and [ 2H 5]glycerol and assessed rates of glucose and glycerol turnover under basal (0-90 min) and hyperinsulinemic-euglycemic clamp (90-210 min; 5 mM glucose, and 5 milliunits of insulin·kg -1·min -1) conditions. Both IRS-1 -/- and IRS-2 -/- mice were insulin-resistant as reflected by markedly impaired insulin-stimulated whole-body glucose utilization compared with WT mice. Insulin resistance in the IRS-1 -/- mice could be ascribed mainly to decreased insulin-stimulated peripheral glucose metabolism. In contrast, IRS-2 -/- mice displayed multiple defects in insulin-mediated carbohydrate metabolism as reflected by (i) decreased peripheral glucose utilization, (ii) decreased suppression of endogenous glucose production, and (iii) decreased hepatic glycogen synthesis. Additionally, IRS-2 -/- mice also showed marked insulin resistance in adipose tissue as reflected by reduced suppression of plasma free fatty acid concentrations and glycerol turnover during the hyperinsulinemic-euglycemic clamp. These data suggest important tissue-specific roles for IRS-1 and IRS-2 in mediating the effect of insulin on carbohydrate and lipid metabolism in vivo in mice. IRS-1 appears to have its major role in muscle, whereas IRS-2 appears to impact on liver, muscle, and adipose tissue.