Calpain inhibition and insulin action in cultured human muscle cells.
Variation in the calpain 10 gene has been reported to increase susceptibility to type 2 diabetes. Part of this susceptibility appears to be mediated by a decrease in whole body insulin sensitivity. As skeletal muscle is the primary tissue site of the peripheral insulin resistance in type 2 diabetes, the aim of this study was to use a human skeletal muscle cell culture system to explore the effects of calpain inhibition on insulin action. Calpain 10 mRNA and protein expression was examined in cultured myoblasts, myotubes, and whole skeletal muscle from non-diabetic subjects using RT-PCR and Western blotting. Changes in insulin-stimulated glucose uptake and glycogen synthesis in response to the calpain inhibitors ALLN and ALLM were measured. Calpain 10 expression was confirmed in cultured human myoblasts, myotubes, and native skeletal muscle. Insulin-stimulated glucose uptake was significantly decreased following preincubation with ALLN [404+/-40 vs 505+/-55 (mean+/-SEM)pmol/mg/min; with vs without ALLN: p = 0.04] and ALLM [455+/-38 vs 550+/-50 pmol/mg/min; with vs without ALLM: p = 0.025] in day 7 fused myotubes, but not in myoblasts. Neither ALLN nor ALLM affected insulin-stimulated glycogen synthesis in myoblasts or myotubes. These studies confirm calpain 10 expression in cultured human muscle cells and support a role for calpains in insulin-stimulated glucose uptake in human skeletal muscle cells that may be relevant to the pathogenesis of the peripheral insulin resistance in type 2 diabetes.