M2 Macrophage Exosomes Promote Bone Regeneration Via Mitophagy

Senescent bone marrow mesenchymal stem cells (O-BMSCs) exhibit reduced osteogenic potential due to senescence-associated secretory phenotype (SASP). While M2 macrophage-derived exosomes (M2-Exos) show regenerative capacity, their mechanism in aging remains unclear[1-3]. [1] BI J, et al. Age-related bone diseases: Role of inflammaging [J]. J Autoimmun, 2024, 143: 103169. [2] BORLONGAN M C, et al. Stem Cells for Aging-Related Disorders [J]. Stem Cell Rev Rep, 2021, 17(6): 2054-2058. [3] KUSHIOKA J, et al. Bone regeneration in inflammation with aging and cell-based immunomodulatory therapy [J]. Inflamm Regen, 2023, 43(1): 29. O-BMSCs were isolated from 18-month-old male SD rats. RT-qPCR and Western blotting assessed osteogenic/SASP/autophagy markers. Mitochondrial ROS and autophagic flux were evaluated by confocal microscopy and flow cytometry. For in vivo studies, MBG-loaded M2-Exos were implanted in critical-sized calvarial defects of aged SD rats, with bone regeneration assessed by micro-CT. In vitro, M2-Exos activated PINK1/Parkin-mediated mitophagy in O-BMSCs, reducing ROS levels and suppressing SASP, thereby enhancing osteogenic differentiation. This effect was reversed by the autophagy inhibitor cyclosporine A (CSA). In vivo, MBG-loaded M2-Exos synergistically ameliorated age-associated bone microstructure deterioration, BMD reduction, and SASP accumulation. M2-Exos attenuate SASP and enhance bone regeneration through mitophagy activation, suggesting a novel therapeutic approach for age-related bone disorders.