Skeletal muscle atrophy is induced by Fbxw7β via atrogene upregulation.

Muscle atrophy decreases skeletal muscle mass and is induced by inherited cachectic symptoms, genetic disorders, and sarcopenia. However, the molecular pathways associated with the onset of muscle atrophy are still unclear. In this study, we evaluated Fbxw7, a gene associated with the development of muscle atrophy in vitro and in vivo. Among the three Fbxw7 isoforms, ectopically overexpressed Fbxw7 induced the expression of myogenin and major atrogene markers (atrogin-1 and MuRF-1) and reduced myoblast differentiation. In addition, endogenous expression of Fbxw7 was also upregulated by dexamethasone, which mimics muscle atrophy in vitro, accompanied by induction of myogenin and atrogene expression in primary myoblasts. Functional analysis of Fbxw7 using short hairpin RNA (shRNA) and a dominant-negative mutant (Fbox) suggested that Fbxw7 regulated muscle atrophy in vitro and in vivo. In particular, Fbox did not reduce the sizes of muscle fibers and did not induce myogenin and atrogene expression in vivo. Therefore, our findings demonstrated, for the first time, that Fbxw7 induced muscle atrophic phenotypes via atrogenes in adult muscle precursor cells and myofibers; this mechanism could be a potential therapeutic target for skeletal muscle atrophy.