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 the reduction in satellite cell numbers in skeletal muscle caused by 1,25(OH)2D deficiency, we collected tibialis anterior muscle from 2-month-old male wild-type, 1α(OH)ase−/− and Sirt1Tg1α(OH)ase−/− mice, and performed Pax7 immunofluorescence staining on cryosections to compare changes in skeletal muscle satellite cell numbers between genotypes.