In COPD, increased proteolysis is mainly mediated by an overactivation of the ubiquitin (26S)–proteasome system, activated via the muscle-specific E3-ubiquitin ligases Atrogin-1/MAFbx and TRIM63/MuRF-1, also named atrogenes, which are increased in COPD quadriceps [118,165]. The gene discussed is TRIM63; the disease is chronic obstructive pulmonary disease.