The Expression of OPG and RANKL in Human Periodontal Ligament Cells with the Effects of 1alpha,25(OH)₂ vitamin D3 and Mechanical Force Loading

The receptor activator of nuclear factor kappa B ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG), are important bone metabolism cytokines, directly controling osteoclastogenesis. It is believed that periodontal ligament cells play a vital role in maintaining the homeostasis of periodontal tissues and release cytokines to affect alveolar bone metabolism. Objectives: To observe the expression of OPG and RANKL in cultured human periodontal ligament cells (hPDLCs) derived from permanent teeth with and without the influence of 1alpha,25(OH)2 vitamin D3 (1¦Á,25(OH)2vitD3) and mechanical force loading. Methods: HPDLCs cultured in vitro by explant method were induced by 10-8M 1¦Á,25(OH)2vitD3 for 6 days and also loaded with intermittent mechanical force for 24 hours. The expression of OPG and RANKL mRNA in hPDLCs were indicated by RT-PCR after hPDLCs were incubated with 10-8M 1¦Á,25(OH)2vitD3 for 0, 2, 4, 6 days. And the effects of mechanical force loading on OPG expression in hPDLCs at mRNA level were shown by in situ hybridization at 0, 2nd, 4th, 6th, 12th, 24th. At the same time points, the OPG proteins which were secreted into the conditional media by hPDLCs were detected by ELISA. Results: Both OPG and RANKL were expressed in hPDLCs. OPG mRNA and protein expression were down-regulated by induction of 10-8M 1¦Á,25(OH)2vitD3 in a time dependent manner, while RANKL mRNA was up-regulated by the same treatment, and thus the ratio of OPG/RANKL was decreased. With the loading of mechanical force, the OPG expression at mRNA and protein levels were down-regulated, especially at the first 6 hours after the force loading (p<0.05). Conclusion: OPG and RANKL were expressed in hPDLCs at mRNA and protein levels, which was regulated by 1¦Á,25(OH)2vitD3 and mechanical force. Supported by Natural Scientific Foundation of China (30070821) and the "985" Grant of Peking University Medical Science Center.