Periodontal ligament‐associated protein‐1 knockout mice regulate the differentiation of osteoclasts and osteoblasts through TGF‐β1/Smad signaling pathway

Abstract It has been known that periodontal ligament‐associated protein‐1 (PLAP‐1/Asporin) not only inhibits cartilage formation in osteoarthritis, but it also influences the healing of skull defect. However, the effect and mechanism of PLAP‐1/Asporin on the mutual regulation of osteoclasts and osteoblasts in periodontitis are not clear. In this study, we utilized a PLAP‐1/Asporin gene knockout (KO) mouse model to research this unknown issue. We cultured mouse bone marrow mesenchymal stem cells with Porphyromonas gingivalis lipopolysaccharide ( P.g . LPS) for osteogenic induction in vitro. The molecular mechanism of PLAP‐1/Asporin in the regulation of osteoblasts was detected by immunoprecipitation, immunofluorescence, and inhibitors of signaling pathways. The results showed that the KO of PLAP‐1/Asporin promoted osteogenic differentiation through transforming growth factor beta 1 (TGF‐β1)/Smad3 in inflammatory environments. We further found the KO of PLAP‐1/Asporin inhibited osteoclast differentiation and promoted osteogenic differentiation through the TGF‐β1/Smad signaling pathway in an inflammatory coculture system. The experimental periodontitis model was established by silk ligation and the alveolar bone formation in PLAP‐1/Asporin KO mice was promoted through TGF‐β1/Smad3 signaling pathway. The subcutaneous osteogenesis model in nude mice also confirmed that the KO of PLAP‐1/Asporin promoted bone formation by the histochemical staining. In conclusion, PLAP‐1/Asporin regulated the differentiation of osteoclasts and osteoblasts through TGF‐β1/Smad signaling pathway. The results of this study lay a theoretical foundation for the further study of the pathological mechanism underlying alveolar bone resorption, and the prevention and treatment of periodontitis.