ELUCIDATION ON THE MECHANISM OF CAMKKα AS A PRO-GROWTH KINASE IN MOUSE SKELETAL MUSCLE

Abstract

Type 2 diabetes affects ~25 million people in the U.S., and is the primary cause of non-traumatic lower limb amputation and the leading cause of blindness in adults. Major risk factors for the development of type 2 diabetes are obesity and inactivity. As such, physical activity and exercise are the most commonly prescribed therapies to prevent and ameliorate type 2 diabetes. Specifically, resistance exercise has been found to be beneficial on two levels. 1) Glucose uptake is increased in exercising skeletal muscle, which is crucial as skeletal muscle accounts for ~85% of insulin-stimulated glucose uptake and the insulin effect is blunted in type 2 diabetes. 2) Post resistance exercise, muscle protein synthesis is highly active, which stimulates glucose uptake to provide ATP and carbons for anabolism. For individuals that are unable to exercise, it is critical to elucidate the mechanisms by which resistance exercise stimulates these processes, to discover potential therapeutic targets. Ca2+/Calmodulin-dependent protein kinase kinase [Alpha] (CaMKK[Alpha]) is one such potential therapeutic target. CaMKK[Alpha] is activated by increases in intracellular Ca2+, and has been shown to simultaneously stimulate glucose uptake and protein synthesis in skeletal muscle. The work herein demonstrates that CaMKK[Alpha] 1) is not completely dependent on glucose transporter 4 (GLUT4) to stimulate muscle glucose uptake, suggesting that CaMKK[Alpha] stimulated glucose uptake would not compete with insulin or contraction stimulated glucose uptake; 2) is necessary and sufficient for maximal pentose phosphate pathway (a metabolic pathway that utilizes glucose to produce ribose-5-phosphate, which is necessary for nucleotide synthesis) flux, during muscle growth, and 3) putatively phosphorylates 8 newly identified protein substrates, discovered using an analog sensitive kinase and the ATP analog, Methylbutyl-ATP-gamma-thiophosphate. Altogether, the data suggests CaMKK[Alpha] stimulates glucose uptake via an unidentified glucose transporter. The increased glucose partly provides carbons for the pentose phosphate pathway, and eventual nucleotide synthesis for RNA and DNA synthesis. CaMKK[Alpha] mimics several effects of resistance exercise training on skeletal muscle and is a promising target for pharmaceutical therapies.