Active vitamin D and vitamin D analogs stimulate fibroblast growth factor 23 production in osteocyte-like cells via the vitamin D receptor

Osteocytes play an important role in the regulation of serum phosphorus by producing Fibroblast Growth Factor 23 (FGF23). FGF23 production is stimulated by 1α,25-dihydroxyvitamin D in osteocytes. However, it is unclear whether vitamin D induces FGF23 production in osteocytes directly. Therefore, we investigated vitamin D-induced FGF23 production in osteocyte-like cells derived from MC3T3-E1 osteocyte progenitor cells. We also investigated differences in the induction of FGF23 by 1α,25-dihydroxyvitamin D and various vitamin D analogs. MC3T3-E1 cells were differentiated into osteocyte-like cells (MCT3-E1-OLCs) by treatment with various agents including β-glycerophosphate and ascorbic acid. MCT3-E1-OLCs were stimulated with 1α,25-dihydroxyvitamin D₃ and subsequent FGF23 gene expression was 2631 ± 605 times higher compared with untreated cells. The expression of FGF23 in MCT3-E1-OLCs transfected with a knockdown sequence against vitamin D receptor (VDR) was significantly decreased compared with that in cells transfected with the control vector. Therefore, the induction of FGF23 in osteocytes by vitamin D may be primarily mediated via VDR. The potential of 25(OH)vitamin D₃, paricalcitol, and maxacalcitol to induce FGF23 production was almost the same as that of 1α,25-dihydroxyvitamin D₃. However, falecalcitriol and eldecalcitol demonstrated a reduced potential to induce FGF23 compared with 1α,25-dihydroxyvitamin D₃. Our results demonstrate that FGF23 induction is different among the analogs of 1α,25-dihydroxyvitamin D₃. Therefore, an appropriate vitamin D analog should be chosen for each patient with mineral and bone disorder, considering its effect on FGF23 production.