BMP9-Smad1/5/9 Signalling Mediates Osteogenic Differentiation and Alveolar Bone Remodelling in hPDLFs

OBJECTIVES: This study aimed to investigate the role of BMP9-Smad1/5/9 in the osteogenic differentiation and alveolar bone remodelling of Human periodontal ligament fibroblasts (hPDLFs) under the action of cyclic tensile stress (CTS). METHODS: An orthodontic tooth movement (OTM) model was established in Sprague-Dawley (SD) rats, the expression status of OCN and BMP9 was measured using immunohistochemistry. hPDLFs were subjected to CTS treatment (10% elongation, 0.5 Hz) to simulate the mechanical microenvironment during orthodontic treatment. The activity of ALP was detected by colorimetric assay and azo coupling staining, respectively. Mineralized nodules were visualized by Alizarin red staining. The expression levels of osteogenesis-related genes including RUNX2, ALP, and OCN were evaluated. To determine the role of BMP9-Smad1/5/9 in CTS-induced osteogenic differentiation, BMP9-Smad1/5/9 signalling was diminished by small RNA against BMP9 and the inhibitor of Smad signalling, the potential of osteogenic differentiation was assessed. RESULTS: BMP9 expression was upregulated in the tension-side periodontal ligament tissues of SD rats, as well as in hPDLFs stimulated by CTS. hPDLFs exhibited increased osteogenic differentiation potential under CTS induction, as evidenced by increased ALP activity, upregulated expression of osteogenesis-related genes, increased mineralized nodule formation and ALP staining. Mechanistically, CTS elevated the phosphorylation levels of Smad1/5/9. Silencing BMP9 attenuated CTS-induced osteogenic differentiation and reduced Smad1/5/9 phosphorylation. Moreover, inhibition of BMP9-Smad1/5/9 signalling pathway suppressed the osteogenic potential of hPDLFs. CONCLUSIONS: CTS increased the osteogenic potential of hPDLFs. Silencing of BMP9 and inhibition of the BMP9-Smad1/5/9 signalling inhibited the osteogenic differentiation of hPDLFs induced by CTS. CLINICAL RELEVANCE: These findings provide mechanistic insights into periodontal tissue remodelling and may contribute to the development of strategies to accelerate orthodontic tooth movement in clinical practice.