A Central Role for H2O2 in Insulin Signal Transduction in Cardiac Myocytes

Abstract

Molecular mechanisms of insulin action have been extensively characterized in the classic insulin target tissues: fat, liver, and skeletal muscle. But in cardiac myocytes (CM), understanding of insulin‐modulated signaling pathways has lagged far behind. Early studies of insulin action implicated a physiological role for H2O2, but the relationships between insulin and H2O2 in CM signal transduction are almost entirely unexplored. In these studies, we identified a role for H2O2 in insulin signaling pathways in adult mouse CM. Insulin promoted the rapid (maximal at 5 min) robust (10‐ to 18‐fold) and reversible phosphorylation of insulin receptorβTyr1146/1150; IRS‐1 Tyr895; and Akt Ser473/308; these responses all had an EC50 of 1 nM insulin (n=3‐7). Insulin‐dependent phosphorylation of IRS‐1 Ser636/639, mTOR Ser2448, p70S6 Thr389/421, and S6 Ser235/Ser236 showed a slower time course (maximal at 30 min), again with an EC50 of 1 nM insulin and with robust phosphorylation responses (6‐ to 40‐fold increases from baseline; n=3‐7). All of these phosphorylation responses were blocked by the NADPH oxidase inhibitors apocynin and VAS2870, implicating NADPH oxidase‐derived reactive oxygen species in modulating insulin‐dependent phosphorylation responses. Importantly, the cell‐permeant derivatized enzyme PEG‐catalase (which degrades H2O2) attenuated all these insulin‐dependent phosphorylation responses. Our findings implicate NADPH oxidase‐generated H2O2 as a critical determinant of insulin‐dependent signaling responses in CM, and may have important implications for the abnormalities in cardiac function seen in disease states associated with oxidative stress. Research support: NIH and AHA.