FAK mediates BMP9-induced osteogenic differentiation via Wnt and MAPK signaling pathway in synovial mesenchymal stem cells

Objective: Focal adhesion kinase (FAK) has critical functions in proliferation and differentiation of many cell types, however, the role of FAK on BMP9-induced osteogenic differentiation in SMSCs has not been characted. The purpose of current study is to explore the mechanism of FAK on the BMP9-induced osteogenesis of SMSCs in vitro and in vivo. Methods: The optimal dose of BMP9 was determined by incubation in different BMP9 concentrations, then cells were transfected with siRNA-induced FAK knockdown in BMP9-induced osteogenesis. Cell proliferation, migration, the osteogenic capacity, and the underlying mechanism were further detected in vitro. Imaging and pathological examination were conducted to observe the bone formation in vivo. Results: Our findings suggested that BMP9 could obviously promote FAK phosphorylation in osteogenic conditions. In contrast, FAK knockdown significantly decreased the cell proliferation, migration, the osteogenic capacity of SMSCs. To be specific, FAK knockdown could markedly inhibit the Writ and MAPK signal pathway of SMSCs induced by BMP9. Besides, FAK knockdown could also effectively inhibit BMP-9-induced bone formation in vivo. Conclusion: FAK plays a pivotal role in promoting BMP9-induced osteogenesis of SMSCs, which is probably via activating Wnt and MAPK pathway.