The Impact of Obesity, Muscle Contraction, and Insulin on Skeletal Muscle Lipids, A Metabolomic Approach

Abstract

Using hindlimb perfusions and metabolic analysis by mass spectrometry, we examined changes in several specific intramuscular (whole gastrocnemius) lipid pools in lean and obese Zucker rats following acute stimulation by contraction, insulin, or contraction+ insulin. Both contraction and surprisingly, insulin, lowered intramuscular triglyceride (TAG) (∼25%) and diacylglycerol (DAG) (30-70%) content in lean and obese rats. Contraction+ insulin had an additive effect on lowering TAG and DAG in muscle of obese rats, but had no effect on levels in lean counterparts. Contraction did not significantly alter total long chain acyl-CoA (LCACoA) levels in either group; however, insulin alone and contraction+ insulin increased LCACoA (∼20%) in muscle of obese. Profiling of mitochondrial-derived acylcarnitine esters suggested increased fatty acid supply and β-oxidative flux in mitochondria of obese compared to lean animals under basal conditions. In both lean and obese muscles, contraction caused phosphorylation (inactivation) of acetyl CoA carboxylase (pACC) and a corresponding decrease in malonyl-CoA; conditions that favor high rates of fat oxidation. Accordingly, in lean animals, these contraction-mediated events were accompanied by elevations in most fatty acylcarnitine species, consistent with increased catabolism of lipid substrate. In contrast, the initially high levels of acylcarnitines in obese muscles were either decreased or unchanged with contraction, possibly due to enhanced TCA activity that enabled a complete oxidation of the heavy fatty acid load. Finally, acylcarnitine profiling of the contraction+ insulin condition revealed a complex dynamic that was distinct between the lean and obese states. These results provide a novel lipidomic view of skeletal muscle from lean and obese rats challenged by contrasting physiological stimuli.