Age-related GSS promoter methylation in BMSCs drives osteoporosis and the reversal by targeted GSH delivery

Age-related osteoporosis arises from bone tissue with inadequate metabolic support for osteogenesis. We identified that DNA methylation-mediated suppression of glutathione synthetase (GSS) represents an upstream lesion limiting endogenous glutathione (GSH) synthesis and supply in aged bone, thereby constraining osteoblast differentiation. In turn, impaired GSH synthesis exacerbates oxidative stress levels and diminishes osteogenic capacity, and this metabolic bottleneck is independent of substrate availability: cysteine supplementation neither restored GSH synthesis flux in aged bone nor rescued its osteogenic deficits. To overcome this limitation, we developed an exosome-based GSH delivery platform using electroporation to efficiently load GSH. These exosomes are derived from CXCR4-enriched bone marrow mesenchymal stem cells (BMSCs), leveraging CXCR4-mediated homing to the bone marrow niche to enhance bone retention, stabilize GSH during loading and circulation, and elevate local GSH pools at osteogenic sites. In aged bone, this targeted system sustainably delivers GSH, alleviates oxidative stress, improves mitochondrial function, delays cellular senescence, and promotes osteogenesis. In summary, while DNA methylation acts upstream to constrain GSH synthesis in aging bone, therapeutically correcting the resultant metabolic deficit via bone-homing exosome–mediated GSH delivery restores osteogenic function and improves bone metabolism in aged individuals. • Age‑related GSS hypermethylation in BMSCs lowers GSH synthesis and limits osteogenic differentiation. • GSH deficiency heightens oxidative stress and mitochondrial dysfunction, accelerating cellular senescence. • CXCR4‑enriched BMSC exosomes loaded with GSH enhance marrow homing, cargo stability, and delivery. • Targeted exosomal GSH delivery restores local GSH, rescues osteogenesis, and improves bone microarchitecture.