Endogenous sulfur dioxide deficiency impairs bone regeneration through abolishing S-sulfenylating p38 at cysteine 211

Bone defects result in substantial medical expenses and a diminished quality of life for patients. Macrophage polarization is crucial in the bone regeneration process mediated by bone marrow-derived mesenchymal stem cells (BMSCs). macrophage-derived sulfur dioxide (SO₂), the fourth endogenous gas signaling molecule, following hydrogen sulfide (H₂S), has been shown to regulate macrophage chemotaxis and inflammatory responses. Nevertheless, the specific regulatory effects and mechanisms of macrophage-derived SO₂ on bone regeneration are not yet fully understood. This study reveals for the first time that the absence of macrophage-derived SO₂ promotes M1 macrophage polarization, whereas the administration of exogenous SO₂ donors inhibits M1 polarization. The deficiency of macrophage-derived SO₂ results in impaired osteogenic differentiation of BMSCs, whereas the administration of SO₂ donors enhances this differentiation process. Further investigations have elucidated that p38α MAPK (p38) is crucial in mediating SO₂'s effects on M1 macrophage polarization and BMSCs osteogenic differentiation. Mechanistically, SO₂ induces S-sulfenylation of p38 in macrophages, an effect that can be reversed by the thiol reductant dithiothreitol. Additionally, the C211S mutation in p38 abrogates the SO₂-induced S-sulfenylation of p38, thereby preventing the inhibition of p38 activation and subsequently disrupting the regulation of M1 macrophage polarization and BMSCs osteogenic differentiation. In a model of mouse calvarial bone defects, we consistently observed that inhibiting SO₂ production using the SO₂-generating enzyme inhibitor HDX impaired bone regeneration capacity in mice, whereas the administration of an SO₂ donor enhanced this capacity. In summary, macrophage-derived SO₂ S-sulfenylates p38 at cysteine 211, thereby suppressing p38 activation, which inhibits M1 polarization and subsequently maintains the osteogenic differentiation of BMSCs. This study is the first to elucidate the role and mechanism of SO₂ in sustaining osteogenesis, offering a novel strategy for addressing bone defect-related disorders.