Human Periodontal Ligament Cells Express Osteoblast-like Characters by Induction

Objectives: To observe the reactions of human periodontal ligament cells (hPDLCs) while they are induced in vitro by mechanical force and 1¦Á,25(OH)2 vitaminD3 respectively. Methods: Four to eight passages of hPDLCs were loaded with intermittent stretching force for 0, 2, 4, 6, 12, 24 hours. Expressions of alkaline phosphotase (ALP), osteocalcin (OCN) and osteoprotegerin (OPG) mRNA were examined by in situ hybridisation, and secreted ALP, OCN and OPG proteins in culture media were measured by biochemistry assay, radioimmunoassay and ELISA respectively. Also hPDLCs were cultured with 10-8 M 1¦Á,25(OH)2 vitaminD3 for 0, 2, 4, 6 days. The expressions of mRNA for OPG and RANKL were examined by RT-PCR. The secreted OPG protein in the culture media was detected by ELISA. Results: 1. Before force loading, hPDLCs expressed ALP and OPG, but not OCN. 2. After force loading, hPDLCs exhibited a stronger signal for ALP mRNA and a moderately intense positive signal for OCN mRNA, while OPG mRNA was decreased especially at the early phase after force loading (P<0.05). 3. In culture media, the level of OCN protein was increased in the late of the 24 hours loading period (P <0.05), while there were two peaks of ALP expression which appeared at the 2nd to 4th hour and the 24th hour (P <0.01) during force loading period. OPG protein was decreased after force loading (P <0.05). 4. Without any induction, OPG and RANKL were expressed by hPDLCs. OPG expression was down-regulated by 10-8M 1¦Á,25(OH)2 vitaminD3 in a time dependent manner, while RANKL mRNA was up-regulated. The ratio of OPG/RANKL was decreased. Conclusions: HPDLCs express osteoblast-like characters by induction of force and 1¦Á,25(OH)2vitamin D3 in vitro. Supported by Natural Scientific Foundation of China (30070821) and the "985" Foundation of Peking University Health Science Centre.