SIRT5 promotes the osteo-inductive potential of BMP9 by stabilizing the HIF-1α protein in mouse embryonic fibroblasts.

Bone morphogenetic protein 9 (BMP9) exhibits remarkable osteogenic potential. However, the intricate mechanisms driving this function of BMP9 remain elusive. This study endeavors to investigate the potential role of sirtuin 5 (SIRT5) in enhancing BMP9's osteogenic capacity and decipher the underlying molecular pathways. To achieve this aim, we employed real-time PCR, western blotting, histochemical staining, and a cranial defect repair model to assess the impact of SIRT5 on BMP9-mediated osteogenesis. We utilized real-time PCR, western blotting, immunofluorescent staining, and immunoprecipitation assay to explore the associated mechanisms. Our results revealed that SIRT5 significantly up-regulated BMP9-induced osteogenic markers, while SIRT5 knockdown reduced their expression. Concurrently, hypoxia-inducible factor 1 subunit alpha (HIF-1α) level was increased by SIRT5, but reduced by SIRT5 knockdown. Notably, HIF-1α potentiated the SIRT5's ability to strengthen BMP9's osteogenic potential, whereas HIF-1α silencing reduced this effect, which was confirmed by bone defect repair assay. The acetylation and malonylation levels of HIF-1α were reduced by SIRT5, which may enhance its stability to promote BMP9's osteogenic effect. Conversely, SIRT5 knockdown reversed these effects and promoted the degradation of HIF-1α. Collectively, our results demonstrated that the BMP9's osteogenic potential could be promoted by SIRT5, potentially through stabilizing HIF-1α by reducing its acetylation and malonylation modification. This discovery may offer a novel strategy to accelerate bone tissue engineering by enhancing osteogenic differentiation, and it also sheds light on the possible mechanisms underlying BMP9-mediated osteogenic differentiation.