MYF5 and vitamin D deficiency: Accelerated protein breakdown and decelerated protein synthesis induced by vitamin D deficiency were found to be associated with increased expression of atrophy-related genes (Atrogin-1 and MuRF1) and proteasomal subunit genes (Psc2 and Psc8) and decreased expression of myogenic genes (MyoD, MyoG, and Myf5), respectively.