The role of E3 ubiquitin-ligases MuRF-1 and MAFbx in loss of skeletal muscle mass

• MuRF-1 and MAFbx regulate pathological and physiological skeletal muscle atrophy.
• MuRF-1 and MAFbx are regulated by the FOXO, MAPK and NF-kB signaling pathways.
• Clinical evidence for MuRF-1 and MAFbx role in common human pathologies is lacking.
• Lifestyle factors (nutrition, exercise, smoking, etc.) affect MuRF-1 and MAFbx regulation.
• Inhibitors of MuRF-1 and MAFbx expression prevent muscle loss in experimental models.

The ubiquitin–proteasome system (UPS) is the main regulatory mechanism of protein degradation in skeletal muscle. The ubiquitin-ligase enzymes (E3s) have a central role in determining the selectivity and specificity of the UPS. Since their identification in 2001, the muscle specific E3s, muscle RING finger-1 (MuRF-1) and muscle atrophy F-box (MAFbx), have been shown to be implicated in the regulation of skeletal muscle atrophy in various pathological and physiological conditions. This review aims to explore the involvement of MuRF-1 and MAFbx in catabolism of skeletal muscle during various pathologies, such as cancer cachexia, sarcopenia of aging, chronic kidney disease (CKD), diabetes, and chronic obstructive pulmonary disease (COPD). In addition, the effects of various lifestyle and modifiable factors (e.g. nutrition, exercise, cigarette smoking, and alcohol) on MuRF-1 and MAFbx regulation will be discussed. Finally, evidence of potential strategies to protect against skeletal muscle wasting through inhibition of MuRF-1 and MAFbx expression will be explored.