One-carbon metabolism supports S-adenosylmethionine and m6A methylation to control the osteogenesis of bone marrow stem cells and bone formation.

ABSTRACT

The skeleton is a metabolically active organ undergoing continuous remodeling initiated by bone marrow stem cells (BMSCs). Recent research has demonstrated that BMSCs adapt the metabolic pathways to drive the osteogenic differentiation and bone formation, but the mechanism involved remains largely elusive. Here, using a comprehensive targeted metabolome and transcriptome profiling, we revealed that one-carbon metabolism was promoted following osteogenic induction of BMSCs. Methotrexate (MTX), an inhibitor of one-carbon metabolism that blocks S-adenosylmethionine (SAM) generation, led to decreased N6-methyladenosine (m6A) methylation level and inhibited osteogenic capacity. Increasing intracellular SAM generation through betaine addition rescued the suppressed m6A content and osteogenesis in MTX-treated cells. Using S-adenosylhomocysteine (SAH) to inhibit the m6A level, the osteogenic activity of BMSCs was consequently impeded. We also demonstrated that the pro-osteogenic effect of m6A methylation mediated by one-carbon metabolism could be attributed to HIF-1α and glycolysis pathway. This was supported by the findings that dimethyloxalyl glycine rescued the osteogenic potential in MTX-treated and SAH-treated cells by upregulating HIF-1α and key glycolytic enzymes expression. Importantly, betaine supplementation attenuated MTX-induced m6A methylation decrease and bone loss via promoting the abundance of SAM in rat. Collectively, these results revealed that one-carbon metabolite SAM was a potential promoter in BMSC osteogenesis via the augmentation of m6A methylation, and the cross talk between metabolic reprogramming, epigenetic modification, and transcriptional regulation of BMSCs might provide strategies for bone regeneration.

The bone is a self-renewing tissue that continues to reshape throughout life. Bone marrow mesenchymal stem cells (BMSCs) are essential for bone homeostasis as they are capable of osteogenic differentiation. Recent evidence suggests that BMSCs drive the osteogenic differentiation through metabolic reprogramming, but the mechanism remains unclear. In this paper, we explored the metabolic alteration following osteogenic induction of BMSCs and found that one-carbon metabolism was obviously promoted in this process. The underlining mechanisms of the osteogenic potential driven by one-carbon metabolism seem to be its contribution on N6-methyladenosine (m6A) methylation and consequent glycolysis level by providing methyl donor. We demonstrated that one-carbon metabolism-mediated m6A methylation was a potential promoter in BMSC osteogenesis, and metabolic-epigenetic coupling might provide novel therapeutic targets for bone regeneration.