TRAF6 coordinates the activation of autophagy and ubiquitin-proteasome systems in atrophying skeletal muscle.

Skeletal muscle wasting is a major reason for morbidity and mortality in many chronic disease states, disuse conditions and aging. The ubiquitin-proteasome and autophagy-lysosomal systems are the two major proteolytic pathways involved in regulation of both physiological and pathological muscle wasting. Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is an important adaptor protein involved in receptor-mediated activation of various signaling pathways in response to cytokines and bacterial products. TRAF6 also possesses E3 ubiquitin ligase activity causing lysine-63-linked polyubiquitination of target proteins. We have uncovered a novel role of TRAF6 in regulation of skeletal muscle mass. Muscle-wasting stimuli upregulate the expression, as well as the auto-ubiquitination, of TRAF6 leading to downstream activation of major catabolic pathways in skeletal muscle. Muscle-specific depletion of TRAF6 preserves skeletal muscle mass in a mouse model of cancer cachexia or denervation. Inhibition of TRAF6 also blocks the expression of the components of the ubiquitin-proteasome system (UPS) and autophagosome formation in atrophying skeletal muscle. While more investigations are required to understand its mechanisms of action in skeletal muscle, our results indicate that blocking TRAF6 activity can be used as a therapeutic approach to preserve skeletal muscle mass and function in different disease states and conditions.