GLP-1RAs and Muscle Atrophy In previous experiments, exendin-4 (Ex-4) inhibited the expression of myostatin (MSTN), atrophy-factor F-box only protein 32 (atrogin-1) and muscle ring finger protein 1 (MuRF-1) in dexamethasone-treated C2C12 myotubes.376–378 In a dexamethasone-induced muscle atrophy model, Ex-4 ameliorated muscle atrophy by inhibiting muscle atrophy factor and enhancing myogenic factors (MyoG and MyoD), thereby increasing muscle mass and function. This evidence concerns the gene MSTN and Atrophy.