Enhanced osteogenic differentiation of human periodontal ligament cells by mature osteoclasts

Objective: Several in vitro studies have shown that reverse signaling from osteoclasts regulates osteoblast differentiation and mineralization. However, none of these studies have reported the effects of this signaling pathway on periodontal ligament (PDL) cells. Therefore, in this study, we aimed to investigate the interaction between receptor activators of nuclear factor kappa B (RANK) released from mature human osteoclasts and the membranous RANK ligand (RANKL) in human PDL cells. Methods: Multinucleated mature human osteoclasts were differentiated from peripheral blood mononuclear cells upon incubation with recombinant macrophage colony-stimulating factor and RANKL. Mature osteoclasts and human PDL cells were characterized. A mature osteoclast-conditioned medium (OC-CM) was used to induce osteogenic differentiation of PDL cells. Mechanistic analysis of RANK-RANKL reverse signaling were conducted to determine the regulation of osteogenic induction using conditioned medium from mature osteoclasts treated with GW4869 (GW-OC-CM) or PDL cells pretreated with recombinant human osteoprotegerin (OPG). Results: OC-CM significantly upregulated the mRNA expression of osteogenic genes and enhanced the osteogenic differentiation and biomineralization of PDL cells (p < 0.05). GW-OC-CM significantly reduced the expression of osteogenic genes, osteogenic differentiation, and biomineralization in PDL cells (p < 0.05). Similarly, the pretreatment of PDL cells with OPG before OC-CM treatment significantly reduced the osteogenic induction of PDL cells (p < 0.05). Conclusion: Mature osteoclasts can induce osteogenesis in human PDL cells via RANK-RANKL reverse signaling.