The molecular regulation of skeletal muscle mass

1. The maintenance of skeletal muscle mass is determined by a fine balance between protein synthesis and protein degradation. Skeletal mass is increased when there is a net gain in protein synthesis which can occur following progressive exercise training. In contrast, skeletal muscle mass is lost when degradation occurs more rapidly than synthesis and is observed in numerous conditions including neuromuscular disease, chronic disease, ageing, as well as following limb immobilization, or prolonged bed rest due to injury or trauma. 2. Understanding the molecular pathways that regulate skeletal muscle protein synthesis and protein degradation is vital for identifying potential therapeutic targets that can attenuate muscle atrophy during disease and disuse. 3. The regulation of skeletal mass is complex and involves the precise co-ordination of several intracellular signalling pathways. This review will focus on the role and regulation of pathways involving Akt, atrogin-1 and MuRF1 (atrogenes), PGC-1α and STARS, with exercise and disease.