Osteogenic induction and 1,25-dihydroxyvitamin D3 oppositely regulate the proliferation and expression of RANKL and the vitamin D receptor of human periodontal ligament cells

Objective

Human periodontal ligament cells (hPDLCs) may play an important role in osteoclastogenesis in alveolar bone by expressing the receptor activator of NF-KappaB ligand (RANKL) and osteoprotegerin (OPG). The present study aimed to investigate the differences between the effects of osteogenic induction and 1,25-dihydroxyvitamin D₃ (VD₃) on hPDLC proliferation and the expression of RANKL, osteoprotegerin, and the vitamin D receptor (VDR) in hPDLCs.

Methods

Primary cultures of 11 hPDLC populations from 11 donors were obtained. Three samples of each hPDLC population from passage 3 were, respectively, treated with osteogenic induction medium, 10⁻⁸ M VD₃, or vehicle as a control. Cell proliferation at days 0, 1, 3, 5, and 7 was estimated with the MTT method. At day 6, the mRNA levels of RANKL, OPG and VDR were determined with real-time RT-PCR.

Results

Osteogenic induction significantly promoted hPDLC proliferation, while VD₃ inhibited proliferation. Osteogenic induction significantly down-regulated the mRNA level of RANKL by 1.61-fold (P = 0.033) and decreased the level of VDR by 2.13-fold (P = 0.003), while there was no change in the level of OPG and OPG/RANKL ratio with osteogenic induction. On the contrary, VD₃ significantly up-regulated the level of RANKL by 9.58-fold (P = 0.001) and increased the level of VDR by 3.15-fold (P = 0.004), while down-regulating the OPG/RANKL ratio by 7.14-fold (P = 0.004).

Conclusion

Osteogenic induction and VD₃ exert opposite effects in regulating hPDLC proliferation and mRNA expression of RANKL and VDR. This may induce hPDLCs to play different roles in alveolar bone metabolism.