Intramyocellular lipid accumulation attenuates insulin signal transduction in human myocytes

Abstract

Cellular mechanisms that contribute to metabolic abnormalities in lipid metabolism and the development of insulin resistance in obese muscle are unclear. The purpose of this study was to determine if there are changes in lipid uptake or oxidation that may cause accumulation of intracellular lipid which are known to be related to insulin resistance. Myocytes were isolated and cultured from lean and obese subjects and Akt activation (phosphorylation) was measured in response to insulin. Fatty acid (FA) uptake was measured using a QBT fluorescent assay kit employed with a BODIPY-dodecanoic analog. The rate of fatty acid oxidation (FAO) and the incorporation of FA into intracellular lipids were assayed using radiolabeled [14C] oleate. Obese myocytes exhibited a 75% reduction in insulin signal transduction compared to lean as measured by p-AKT. FA uptake significantly increased 3-fold in obese compared to lean which corresponded with a 33% reduction in FAO and a 30% increase in glycerolipid storage in obese muscle cells. When incubated with 100uM FA the lean myocytes showed a 41% decrease in p-AKT compared with the control indicating the addition of FA increased insulin resistance. Our findings suggest that insulin resistance in skeletal muscle of obese individuals may result from lipid accumulation, secondary to increased uptake and depressed oxidation of FA.