Spermidine Promotes Bone Marrow Mesenchymal Stem Cell Ossification Under Inflammation

To explore the impact and underlying mechanism of key metabolites in osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) under inflammation conditions. BMSCs were isolated from the femurs and tibias of 2-3-week-old Sprague-Dawley (SD) rats and cultured in accordance with the guidelines of the Institutional Animal Ethics Committee. Targeted metabolomic analyses were performed during BMSC osteogenic differentiation, both with and without inflammatory stimulation induced by lipopolysaccharide (LPS). The osteogenic potential of BMSCs under LPS stimulation, spermidine(SPD) addintion, and the presence of inhibitor of N6-methyladenosine (m6A) methylation S-adenosylhomocysteine (SAH) was assessed using qRT-PCR, western blot (WB), ALP activity assays, and alizarin red staining. Cell immunofluorescence was utilized to measure the level of m6A methylation. Autophagy was measured by qRT-PCR and WB. An inflammatory mandibular defects rat model was established via local LPS injection, with SPD interavation administered. Micro-Computed Tomography (Micro-CT), histology, and immunofluorescence staining were employed to evaluate bone restoration capacity following SPD addition. SPD was dramatically decreased in BMSCs under inflammatory conditions. Exogenous SPD supplementation enhanced BMSC osteogenesis, increased m6A methylation, and activated autophagy, conversely, SAH reduced m6A methylation, autophagy level and negated SPD's osteogenic effects. Consistently, SPD supplementation enhanced m6A methylation and facilitated bone regeneration in a rat model of inflammatory mandibular defects. This study demonstrates that SPD promotes the osteogenic potential of BMSCs through an m6A methylation–autophagy axis under inflammatory conditions, providing a novel therapeutic approach for inflammatory bone diseases.