FBXO32 and Skeletal muscle atrophy: More recently, it has been shown that IGF-1 can also block the transcriptional upregulation of the key mediators of skeletal muscle atrophy, the ubiquitin-ligases MuRF1 (muscle RING finger-1 protein) and MAFbx (muscle atrophy F-box protein, also called Atrogin-1) [23].