Periodontal ligament-associated protein-1 promotes osteoclastogenesis in mice by modulating TGF-β1/Smad1 pathway

BackgroundPeriodontal ligament-associated protein-1 (PLAP-1), an important target molecule of osteoarthritis research, may affect alveolar bone resorption. The aim of our study was to comprehensively and systematically detect the effect of PLAP-1 on alveolar bone resorption and the underlying mechanism in PLAP-1 knockout mouse models.MethodsWe used a PLAP-1 knockout (C57BL/6N-Plap-1-/-) mouse model to investigate the effect of PLAP-1 on osteoclast differentiation and the underlying mechanism by adding Porphyromonas gingivalis lipopolysaccharide to stimulate bone marrow-derived macrophages. The effect of PLAP-1 on alveolar bone resorption and the underlying mechanism were studied using a ligature periodontitis model, with microcomputed tomography imaging, immunochemistry, and immunofluorescence.ResultsThe in vitro analysis results demonstrated that PLAP-1 knockout significantly inhibited osteoclast differentiation under both normal and inflammatory conditions. Bioinformatic analysis, immunofluorescence, and co-immunoprecipitation showed colocalization and interaction between PLAP-1 and transforming growth factor beta 1 (TGF-beta 1). The phosphorylation of Smad1 was reduced in the PLAP-1 knockout cells compared with that in the cells from wild-type mice. The in vivo analysis results demonstrated that PLAP-1 knockout decreased bone resorption and the levels of osteoclast differentiation markers in experimental periodontitis compared with those in wild-type mice. Immunofluorescence staining confirmed colocalization of PLAP-1 and TGF-beta 1 in the experimental periodontitis model. The phosphorylation level of Smad1 was significantly reduced in PLAP-1 knockout mice compared with that in wild-type mice.ConclusionsThis study revealed that the knockout of PLAP-1 inhibits osteoclast differentiation and decreases alveolar bone resorption through the TGF-beta 1/Smad1 signaling pathway, which could serve as an innovative target for the prevention and treatment of periodontitis.