SIRT1 and sarcopenia: To determine whether the correction of 1,25(OH)2D deficiency-induced sarcopenia by Sirt1 overexpression in MSCs is related to inhibition of skeletal muscle cell senescence caused by 1,25(OH)2D deficiency, we collected tibialis anterior muscle from 2-month-old wild-type, 1α(OH)ase−/− and Sirt1Tg1α(OH)ase−/− mice and performed p16 and p21 immunofluorescence staining on cryosections to compare changes in skeletal muscle cell senescence between genotypes.