ATF4 and Atrophy: Going forward, it will be interesting to determine whether the ATF4–C/EBPβ heterodimer participates in other forms of skeletal muscle atrophy that were not investigated here, including age-related muscle atrophy and fasting-induced muscle atrophy (which require ATF4 (2, 4, 5)) and cancer-induced muscle atrophy (which requires C/EBPβ (49, 50)).