ATG7-driven mitophagy in BMSC@CS hydrogel reprograms metabolism to boost bone regeneration

Bone regeneration remains a formidable challenging due to impaired energy metabolism and the limited osteogenic potential of transplanted stem cells. Mitochondrial homeostasis orchestrates osteogenesis, with mitophagy maintaining the metabolic rhythm essential for bone formation. However, the role of autophagy related gene 7(ATG7), a pivotal regulator of mitochondrial function, in bone regeneration remains elusive. In this study, we developed a ATG7-overexpressing bone marrow mesenchymal stem cells (ATG7-BMSCs) encapsulated within a thermoresponsive chitosan (CS) hydrogel, creating a biocompatible, living platform capable of adapting to physiological conditions. The hydrogel exhibited excellent injectability, physiological gelation at 37 °C, and prolonged biocompatibility, providing a favorable microenvironment for stem cell survival and proliferation. The system was evaluated through in vitro assays for mitochondrial function and osteogenic differentiation, as well as in vivo using rat cranial and femoral defect models. Mechanistically, ATG7 activation enhanced mitophagy, preserved mitochondrial integrity, reduced reactive oxygen species (ROS) accumulation, and reactivated oxidative phosphorylation via the PI3K-AKT signaling pathway, thereby reprogramming osteogenic metabolism and promoting differentiation. Conversely, ATG7 deficiency led to mitochondrial dysfunction, glycolytic dependence, and impaired bone formation. In vivo, the ATG7-BMSC@CS hydrogel markedly accelerated new bone formation and mineral density recovery while maintaining excellent injectability, biocompatibility, and systemic safety. Collectively, this study identifies ATG7-driven mitophagy as a critical regulator of osteogenic metabolism and bone formation, and establishes a smart, living hydrogel platform that seamlessly integrates metabolic reprogramming with stem cell delivery. This strategy provides a conceptual blueprint for next-generation, metabolism-oriented bone repair at the intersection of cell biology, biomaterials, and precision medicine.