Proteome analysis reveals phosphorylation of ATP synthase β-subunit in human skeletal muscle and proteins with potential roles in type 2 diabetes

Insulin resistance in skeletal muscle is a hallmark feature of type 2 diabetes. An increasing number of enzymes and metabolic pathways have been implicated in the development of insulin resistance. However, the primary cellular cause of insulin resistance remains uncertain. Proteome analysis can quantitate a large number of proteins and their post-translational modifications simultaneously and is a powerful tool to study polygenic diseases like type 2 diabetes. Using this approach on human skeletal muscle biopsies, we have identified eight potential protein markers for type 2 diabetes in the fasting state. The observed changes in protein expression indicate increased cellular stress, e.g. up-regulation of two heat shock proteins, and perturbations in ATP (re)synthesis and mitochondrial metabolism, e.g. down-regulation of ATP synthase 6-subunit and creatine kinase B, in skeletal muscle of patients with type 2 diabetes. Phosphorylation appears to play a key, potentially coordinating role for most of the proteins identified in this study. In particular, we demonstrated that the catalytic beta-subunit of ATP synthase is phosphorylated in vivo and that the levels of a down-regulated ATP synthase beta-subunit phosphoisoform in diabetic muscle correlated inversely with fasting plasma glucose levels. These data suggest a role for phosphorylation of ATP synthase beta-subunit in the regulation of ATP synthesis and that alterations in the regulation of ATP synthesis and cellular stress proteins may contribute to the pathogenesis of type 2 diabetes.