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

Departamento de Clínica Médica, Universidade Estadual de Campinas, UNICAMP, Campinas, Sao Paulo, Brazil

Submitted 6 September 2005 ; accepted in final form 11 April 2006

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 -subunit (IR), insulin receptor substrate 1(IRS-1), and Akt. S-nitrosation of IR 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 wild-type mice, as demonstrated by reduced insulin-induced tyrosine phosphorylation of IR 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/IRS-1 and Akt. In the muscle of iNOS^–/– mice, we did not observe enhanced iNOS expression or any S-nitrosation of IR/IRS-1 and Akt after LPS treatment. Moreover, insulin resistance was not present. The preservation of insulin-induced tyrosine phosphorylation of IR 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.

inducible nitric oxide synthase; lipopolysaccharide; insulin receptor -subunit; insulin receptor substrate-1

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