Engineered Extracellular Vesicles Derived from Juvenile Mice Enhance Mitochondrial Function in the Aging Bone Microenvironment and Achieve Rejuvenation.

Aging-related bone degeneration and impaired healing capacity remain significant challenges in regenerative medicine, necessitating innovative, efficient, and targeted strategies to restore bone health. Here, we engineered extracellular vesicles (EVs) derived from the serum of pretreated juvenile mice, with the goals of reversing aging, enhancing osteogenic potential, and increasing bioavailability to rejuvenate the aging bone environment. First, we established bone healing models representing different phases of healing to identify the EV type with the highest potential for improving the bone microenvironment in older individuals. Second, we employed DSS6 for bone targeting to enhance the biological effects of the selected EVs in vivo. The engineered EVs effectively targeted bone repair sites and promoted fracture healing more effectively than unmodified EVs in older mice. RNA sequencing revealed that the translocase of outer mitochondrial membrane 7 (Tomm7) is crucial for the underlying mechanism. Silencing Tomm7 significantly diminished the positive regulatory effects of the EVs. Specifically, the engineered EVs may enhance mitochondrial function in aging cells by activating the Tomm7-mediated Pink1/Parkin mitophagy pathway, promoting stemness recovery in aging bone marrow stromal cells (BMSCs) and reversing the adverse conditions of the aging bone microenvironment. Overall, the developed engineered EVs derived from serum from juvenile mice offer an alternative approach for treating aging bones. The identified underlying biological mechanisms provide a valuable reference for precision treatment of aging bones in the future.