Focal adhesion kinase regulates insulin resistance in skeletal muscle

Abstract

On the basis of our previous studies, we investigated the possible role of focal adhesion kinase (FAK) in the development of insulin resistance in skeletal muscle, a major organ responsible for insulin-stimulated glucose uptake. Insulin-resistant C2C12 skeletal muscle cells were transfected with FAK wild-type or FAK mutant plasmids, knocked down using small interfering RNA (siRNA), and their effects on the levels and activities of insulin-signalling molecules and on glucose uptake were determined. A significant decrease in tyrosine phosphorylation of FAK in insulin-resistant C2C12 cells was observed. A similar decrease was observed in skeletal muscle obtained from insulin-resistant Sprague-Dawley rats fed a high-fat diet. Increased levels of FAK in insulin-resistant C2C12 skeletal muscle cells increased insulin sensitivity and glucose uptake. These effects were reversed by an increase in the level of kinase activity mutant FAK or suppression of endogenous FAK by siRNA. FAK was also found to interact downstream with insulin receptor substrate-1, phosphatidylinositol 3-kinase and protein kinase C and glycogen synthase kinase 3beta, leading to translocation of glucose transporter 4 and resulting in the regulation of glucose uptake. The present study provides strong evidence that the modulation of FAK level regulates the insulin sensitivity of skeletal muscle cells. The results demonstrate a direct role of FAK in insulin-resistant skeletal muscle cells for the first time.