Spermidine promotes osteogenic differentiation of BMSCs via the m6A methylation-autophagy axis under inflammatory stress.

Disordered osteogenic potential in bone marrow mesenchymal stem cells (BMSCs) is a hallmark of inflammatory jaw diseases. Recent studies suggest that inflammatory stimulating disrupts energy metabolism during BMSC osteogenesis. However, the impact of key metabolites on BMSC ossification remains unclear. In this study, a comprehensive targeted metabolomics analysis was performed during BMSC osteogenic differentiation, with and without inflammatory stimulation induced by lipopolysaccharide (LPS). We identified a significant downregulation of spermidine (SPD), along with methylated purines and pyrimidines, in the inflammatory environment. Exogenous SPD supplementation enhanced BMSC osteogenesis and increased N6-methyladenosine (m6A) methylation. Mechanistically, SPD elevated S-adenosylmethionine (SAM) levels and upregulated the methyltransferases METTL3 and METTL14. Similarly, betaine, a promoter of SAM synthesis, increased m6A methylation and improved BMSC osteogenic potential. In contrast, the METTL3/METTL14 inhibitor S-adenosylhomocysteine (SAH) reduced m6A methylation and negated SPD's osteogenic effects. This suggests that SPD enhances BMSC osteogenesis through m6A methylation regulation. Furthermore, SPD activated autophagy in BMSCs, while SAH inhibited SPD-induced autophagy. Notably, treatment with rapamycin (Rap), an autophagy inducer, restored both autophagy and osteogenic differentiation impaired by SAH. In vivo, SPD supplementation enhanced m6A methylation and facilitated bone regeneration in a rat model of inflammatory mandibular defects. In conclusion, 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 jaw diseases.