AKT2 deficiency causes sarcopenia and metabolic disorder of skeletal muscle

Skeletal muscle is responsible for the majority of glucose disposal in the body. Insulin resistance in the skeletal muscle accounts for 85-90% of the impairment of total body glucose disposal in patients with tye 2 diabetes (T2D). However, the mechanism remains controversial. AKT2 is a protein kinase performing important functions in the regulation of glucose metabolism. We observed that mice deficient for AKT2 (AKT2 KO) exhibited decreased body weight and lean mass and showed impaired glucose tolerance, compared to their age- and gender-matched wild type mice (WT). Therefore, to test whether AKT2 deficiency causes deficits in skeletal muscle development and metabolism, we analyzed the expression of molecules related to skeletal muscle development, glucose uptake and metabolism in young (3 months) and old (8 months) mice. We found that AMPK phosphorylation and MEF2A expression were downregulated in young AKT2 KO mice, and this downregulation was inverted by AMPK activation. We also observed reduced mtDNA abundance and reduced expression of genes involved in mitochondrial biogenesis in the skeletal muscle of adult AKT2 KO mice, which was prevented by AMPK activation. However, GLUT4 expression was regulated by AKT2 in an AMPK-independent manner in skeletal muscle. During high-fat-diet (HFD)-induced obesity, AKT2 KO mice exhibited increased insulin resistance compared to WT mice. Our study establishes a new and important function of AKT2 in regulating glucose uptake and AMPK-dependent development and mitochondrial biogenesis in skeletal muscle.