Abstract 1915: Simvastatin Regulates Insulin Signaling in Endothelial Cells via Activation of AMP-Activated Protein Kinase
Statins exert pleiotropic effects upon the cardiovascular system, but the role of statins in modulation of insulin signaling remains incompletely defined. In these studies, we explore the effects of simvastatin on insulin pathways in bovine aortic endothelial cells (BAEC), and propose a novel mechanism linking these pathways that involves AMP-activated protein kinase (AMPK). Treatment of BAEC with 100 nM insulin promotes the rapid phosphorylation of Akt (3.8±0.2-fold increase; n=4; p<0.01), glycogen synthase kinase-3β (GSK3β, 2.7±0.5-fold increase; n=4; p<0.01), as well as that of critical substrates in the mammalian target of rapamycin (mTOR) axis including mTOR (2.8±0.2-fold increase; n=4; p<0.02) and p70S6K (3.2±0.5-fold increase; n=4; p<0.02). However, in cells pretreated with simvastatin (10 μM for 24 hr), these insulin-dependent phosphorylations are significantly attenuated (62±10%, 48±12%, 53±9%, and 58±13% reduction in the phosphorylation of Akt, GSK3β, mTOR, and p70S6K, respectively; p<0.02; n=4). Given our findings on the modulation of these key metabolic enzymes by simvastatin, we explored the effects of insulin and simvastatin on AMPK. We found that insulin promotes a rapid (within minutes) and robust increase in phosphorylation of both AMPK and its substrate acetyl CoA carboxylase (2.5±0.4-fold increase; n=4; p<0.01). Importantly, transfection of BAEC with siRNA targeting AMPK results in enhanced insulin-dependent phosphorylation of Akt (57±9% enhancement compared to cells transfected with control siRNA; n=4; p<0.015), as well as significant increases in phosphorylation of GSK3β, mTOR, and p70S6K (55±12% enhancement; n=4; p<0.02), indicating a key regulatory role for AMPK in insulin-dependent metabolic signaling. Importantly, in cells transfected with AMPK siRNA, simvastatin treatment no longer attenuates insulin signaling to these substrates, suggesting that AMPK is required for the regulation of insulin pathways by statins. Taken together, these results establish that simvastatin modulates critical insulin responses in endothelial cells, and provide new insights into the roles of AMPK in linking insulin- and statin-regulated metabolic signaling pathways in the vascular wall.