FBXO32 and serum lipopolysaccharide activity: To further investigate the LPS-induced atrophy of myotubes, we measured two muscle-enriched ubiquitin ligases, atrogin-1/MAFbx and MuRF1, which are key enzymes in the ubiquitin–proteasome degradation pathway, a known contributor to endotoxemia or sepsis associated muscle atrophy18–21.