Lipopolysaccharide from Prevotella nigrescens stimulates osteoclastogenesis in cocultures of bone marrow mononuclear cells and primary osteoblasts

Background and Objective: Lipopolysaccharide is thought to be a major virulence factor of pathogens associated with periodontal diseases and is believed to stimulate bone resorption in vivo. Although Prevotella nigrescens has been implicated in periodontitis, its role in osteoclastogenesis has not been reported. In this study, we investigated the effects of lipopolysaccharide from P. nigrescens on the formation of osteoclasts and the production of cytokines related to osteoclast differentiation. Material and Methods: Mouse bone marrow mononuclear cells were cultured in the presence of macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa B ligand (RANKL), with or without lipopolysaccharide. Bone marrow mononuclear cells were also cocultured with calvarial osteoblastic cells in the presence or absence of lipopolysaccharide. Osteoclast formation was determined by tartrate-resistant acid phosphatase cytochemistry. The production of osteoprotegerin (OPG), M-CSF, tumor necrosis factor alpha (TNF-alpha), transforming growth factor-beta (TGF-beta) and prostaglandin E-2 (PGE(2)) was determined by enzyme-linked immunosorbent assay (ELISA). Results: P. nigrescens lipopolysaccharide inhibited osteoclast differentiation from bone marrow mononuclear cells cultured in the presence of M-CSF and RANKL. However, in the coculture system, P. nigrescens lipopolysaccharide stimulated osteoclastogenesis. Notably, P. nigrescens lipopolysaccharide decreased OPG production but increased TGF-beta secretion. In addition, treatment with P. nigrescens lipopolysaccharide increased PGE(2) production during the late stage of the culture period. There was no difference in M-CSF and TNF-alpha production. Conclusion: These results demonstrate that P. nigrescens lipopolysaccharide stimulates osteoclastogenesis in the coculture system by decreasing the production of OPG and increasing the production of TGF-beta and PGE(2). Through the mechanisms involving these factors, P. nigrescens lipopolysaccharide may cause alveolar bone resorption in periodontal diseases.