FBXO32 and muscular atrophy: The UPS begins with the ubiquitination of target proteins, after which E3 ligases recognize the degraded protein and ligate ubiquitin to the substrate for degradation.97 Two pivotal E3 ligases, i.e., muscle RING-finger protein-1 (MuRF1) and muscle atrophy F-box (MAFbx/Atrogin-1), were shown to regulate skeletal muscle atrophy by triggering the degradation of different muscle proteins.