FBXO32 and sarcopenia: Two muscle-specific E3 ligases, muscle ring finger-1 (MuRF-1) and muscle atrophy F-box protein (MAFbx) –or atrogin-1– (Schiaffino et al., 2013) have been identified and their expression is commonly used as a marker of UPS activity in secondary sarcopenia models (Milan et al., 2015).