Vitamin D3 metabolites induce osteogenic differentiation in human dental pulp and human dental follicle cells

Vitamin D3 metabolites regulate the bone metabolism and 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) is known to play an important role in teeth mineralization. However, little is known about the potential of vitamin D as an osteogenic inducer in human dental pulp (hDPCs) and dental follicle cells (hDFCs) in vitro. Therefore, we investigated the effects of vitamin D3 metabolites 1α,25(OH)2D3 and 25-hydroxyvitamin D3 (25OHD3) on proliferation and osteogenic differentiation of hDPCs and hDFCs in vitro. We also examined whether vitamin D3 metabolic enzymes were regulated in hDFCs and hDPCs. Cell proliferation was decreased by both metabolites in hDPCs and hDFCs. Vitamin D3 metabolites increased ALP activity and induced mineralization when osteogenic supplements (OS; l-ascorbic acid-2-phosphate + β-glycerophosphate) were added, though the expression of osteocalcin (OC) and osteopontin (OPN) were regulated without the addition of OS. CYP24 and CYP27B1 expressions were upregulated by vitamin D3 metabolites and 25OHD3 was converted into 1α,25(OH)2D3 in the culture medium. These results confirm that 1α,25(OH)2D3 (10 and 100 nM) and 25OHD3 (500 nM) can be used as osteogenic inducers synergistically with osteogenic supplements for differentiation of hDPCs and hDFCs. Furthermore, our findings strengthen our knowledge about the role of hDPCs and hDFCs as vitamin D3 target cells.