Effect of Cells Derived from Periodontal Ligament Tissue on Bone Formation

Background/Aim: Recent reports indicate that sclerostin is secreted by periodontal ligament tissue-derived (PDL) cells during orthodontic force loading and that the secreted sclerostin contributes to bone metabolism. However, the detailed mechanism is poorly understood. The aim of this study was to determine how PDL cells affect bone formation. Materials and Methods: Rat periodontal ligament tissue was immunohistochemically stained for sclerostin. Cultured primary PDL cells, osteoblasts, and skin fibroblasts (Sfbs) isolated from rat periodontal ligament tissue, calvaria, and skin, respectively, were examined. Osteoblasts were cultured with control conditioned medium (Cont-CDM) and PDL cell culture conditioned medium (PDL-CDM) for up to 21 days. Cultured osteoblasts were then stained with alkaline phosphatase and von Kossa stain. Osteoblasts cultured in each conditioned medium were analyzed by real-time quantitative PCR for bone Gla protein (Bgp), Axin2, and Ki67 expression. PDL cells used to obtain conditioned medium were analyzed for Sost, Ectodin and Wnt1 expression and compared with expression in Sfbs. Results: Expression of sclerostin was observed in periodontal ligament tissue by immunohistochemical staining. The formation of mineralization nodules was inhibited in PDL-CDM compared with ContCDM in osteoblast culture. In PDL-CDM, the expression levels of Bgp and Axin2 in osteoblasts were decreased compared with Cont-CDM. In PDL cells, expression levels of Sost and Ectodin were much higher than in Sfbs; however, expression of Wnt1 was lower in PDL cells compared with Sfbs. Conclusion: PDL cells secrete various proteins, including sclerostin and suppress osteogenesis in osteoblasts through the canonical Wnt pathway.