S-Glutathiolation of p21ras by Peroxynitrite Mediates Endothelial Insulin Resistance Caused by Oxidized Low-Density Lipoprotein

OBJECTIVE: To understand the mechanism by which oxidants are linked to insulin resistance, bovine aortic endothelial cells were exposed to oxidized low-density lipoproteins (oxLDL) or peroxynitrite. METHODS AND RESULTS: OxLDL transiently increased phosphorylation of Erk and Akt within 5 minutes, but 60 minutes later, resulted in decreased insulin-induced Akt phosphorylation. OxLDL promoted a 2- to 5-fold increase in oxidant generation as measured by dihydrorhodamine or dihydroethidium oxidation that was ascribed to peroxynitrite. Exogenous peroxynitrite (25 to 100 micromol/L) or oxidized glutathione mimicked the effects of oxLDL. OxLDL increased the S-glutathiolation of p21ras, and adenoviral transfection with either a mutant p21ras (C118S) lacking the predominant site of S-glutathiolation or a dominant-negative mutant restored insulin-induced Akt phosphorylation. The requirement for oxidant-mediated S-glutathiolation and activation of p21ras in mediating insulin resistance was further implicated by showing that insulin signaling was restored by Mek inhibitors or by overexpression of glutaredoxin-1. Furthermore, oxLDL increased Erk-dependent phosphorylation of insulin receptor substrate-1 serine-616 that was prevented by inhibiting oxidant generation, Erk activation, or by the p21ras C118S mutant. CONCLUSIONS: This study provides direct evidence for a novel molecular mechanism by which oxidants can induce insulin resistance via S-glutathiolation of p21ras and Erk-dependent inhibition of insulin signaling.