FTO-engineered extracellular vesicles from bone marrow mesenchymal stem cells ameliorate Staphylococcus aureus-induced osteomyelitis via m6A-dependent suppression of autophagy and pyroptosis

Bone marrow mesenchymal stem cells (BM-MSCs) ameliorate various orthopedic diseases through the secretion of extracellular vesicles (EVs). This study investigates the effects of FTO-overexpressing BM-MSCs-derived EVs (FTO-EVs) on osteocyte autophagy and pyroptosis in Staphylococcus aureus-associated osteomyelitis (OM). The expression levels of N6-methyladenosine regulators were investigated in bone tissues and serum EVs obtained from patients with OM. Osteoblast MC3T3-E1 and osteocyte MLO-Y4 cells were induced with Staphylococcal Protein A (SpA) to simulate in vitro OM models, and murine OM models were established by bone drilling followed by local injection of Staphylococcus aureus suspension, both of which were treated with EVs. Fat mass and obesity-associated protein (FTO) was downregulated in the bone tissues or serum EVs from OM patients compare to healthy control. Compared with negative control EVs, FTO-EVs significantly increased FTO expression, elevated cell viability, and inhibited cell death, ATG2A/ATG14-mediated autophagy and NLRP3-mediated pyroptosis in SpA-induced MC3T3-E1 and MLO-Y4 cells. Treatment with FTO-EVs significantly ameliorated bone damage in OM model mice, upregulated the expression of pro-survival proteins in bone tissue, while downregulating key markers of autophagy and pyroptosis. Mechanistically, FTO-EVs N6-methyladenosine dependently downregulated the expression of ATG2A, ATG14 and NLRP3 to modulate autophagy and pyroptosis in SpA-induced MC3T3-E1 and MLO-Y4 cells. In summary, this study confirms the role of BM-MSCs-derived FTO-EVs in inhibiting the progression of Staphylococcus aureus-related OM both in vivo and in vitro, providing promising therapeutic strategies for clinical treatment.