Youthful Stem Cell Microenvironments: Rejuvenating Aged Bone Repair Through Mitochondrial Homeostasis Remodeling

Abstract Extracellular matrix (ECM) derived from mesenchymal stem cells regulates antioxidant properties and bone metabolism by providing a favorable extracellular microenvironment. However, its functional role and molecular mechanism in mitochondrial function regulation and aged bone regeneration remain insufficiently elucidated. This proteomic analysis has revealed a greater abundance of proteins supporting mitochondrial function in the young ECM (Y‐ECM) secreted by young bone marrow‐derived mesenchymal stem cells (BMMSCs) compared to the aged ECM (A‐ECM). Further studies demonstrate that Y‐ECM significantly rejuvenates mitochondrial energy metabolism in adult BMMSCs (A‐BMMSCs) through the promotion of mitochondrial respiratory functions and amelioration of oxidative stress. A‐BMMSCs cultured on Y‐ECM exhibited enhanced multi‐lineage differentiation potentials in vitro and ectopic bone formation in vivo. Mechanistically, silencing of silent information regulator type 3 (SIRT3) gene abolished the protective impact of Y‐ECM on A‐BMMSCs. Notably, a novel composite biomaterial combining hyaluronic acid methacrylate hydrogel microspheres with Y‐ECM is developed, which yielded substantial improvements in the healing of bone defects in an aged rat model. Collectively, these findings underscore the pivotal role of Y‐ECM in maintaining mitochondrial redox homeostasis and present a promising therapeutic strategy for the repair of aged bone defects.