Human skeletal muscle cell differentiation is associated with changes in myogenic markers and enhanced insulin-mediated MAPK and PKB phosphorylation.

Abstract

We hypothesized that myogenic differentiation of HSMC would yield a more insulin responsive phenotype. We assessed expression of several proteins involved in insulin action or myogenesis during differentiation of primary human skeletal muscle cultures (HSMC). Differentiation increased creatine kinase activity and expression of desmin and myocyte enhancer factor (MEF)2C. No change in expression was observed for big mitogen-activated protein kinase (BMK1/ERK5), MEF2A, insulin receptor (IR), hexokinase II, and IR substrates 1 and 2, while expression of glycogen synthase, extracellular signal-regulated kinase 1 and 2 (ERK1/2 MAP kinase) and the insulin responsive aminopeptidase increased after differentiation. In contrast to protein kinase B (PKB)a, expression of (PKB)b increased, with differentiation. Both basal and insulin-stimulated PI 3-kinase activity increased with differentiation. Insulin-mediated phosphorylation of PKB and ERK1/2 MAP kinase increased after differentiation. Components of the insulin-signalling machinery are expressed in myoblast and myotube HSMC; however, insulin responsiveness to PKB and ERK MAP kinase phosphorylation increases with differentiation.