Targeted disruption of iNOS prevents LPS-induced S-nitrosation of IRβ/IRS-1 and Akt and insulin resistance in muscle of mice

We have previously demonstrated that the insulin resistance associated with inducible nitric oxide synthase (iNOS) induction in two different models of obesity, diet-induced obesity and the ob/ob mice, is mediated by S-nitrosation of proteins involved in insulin signal transduction: insulin receptor beta-subunit (IR beta), insulin receptor substrate 1(IRS-1), and Akt. S-nitrosation of IR beta and Akt impairs their kinase activities, and S-nitrosation of IRS-1 reduces its tissue expression. In this study, we observed that LPS-induced insulin resistance in the muscle of wildtype mice, as demonstrated by reduced insulin-induced tyrosine phosphorylation of IR beta and IRS-1, reduced IRS-1 expression and reduced insulin-induced serine phosphorylation of Akt. This resistance occurred in parallel with enhanced iNOS expression, which was accompanied by S-nitrosation of IR beta/IRS-1 and Akt. In the muscle of iNOS(-/-) mice, we did not observe enhanced iNOS expression or any S-nitrosation of IR beta/IRS-1 and Akt after LPS treatment. Moreover, insulin resistance was not present. The preservation of insulin-induced tyrosine phosphorylation of IR beta and IRS-1, of IRS-1 protein expression, and of insulin-induced serine phosphorylation of Akt observed in LPS-treated iNOS(-/-) mice strongly suggests that the insulin resistance induced by LPS is iNOS mediated, probably through S-nitrosation of proteins of early steps of insulin signaling.