Young bone marrow mesenchymal stem cell-derived exosomes promote perfusion recovery and tissue repair via the miR-455-5p/Bach1 axis after hindlimb ischemia

Lower-limb ischemia caused by peripheral arterial disease (PAD) results in sustained perfusion impairment and tissue injury, and effective regenerative therapies remain limited. Bone marrow mesenchymal stem cell-derived exosomes (BMSC-exos) are a promising cell-free therapeutic strategy for ischemic repair, but whether donor age affects their efficacy and underlying mechanisms remains unclear. Exosomes isolated from young and older rat BMSCs were characterized by transmission electron microscopy, particle-size analysis, and exosomal marker expression. Their effects were evaluated in a unilateral rat hindlimb ischemia (HLI) model with delayed intramuscular administration and in oxygen-glucose deprivation/reoxygenation (OGD/R)-injured human umbilical vein endothelial cells (HUVECs). Blood perfusion, histopathology, endothelial proliferation, migration, tube formation, and angiogenesis-related proteins were assessed. miRNA sequencing, bioinformatic analysis, dual-luciferase assays, Bach1 overexpression, and miR-455-5p inhibition were used to investigate the underlying mechanism. Both young and older BMSC-exos improved post-ischemic perfusion recovery, whereas young BMSC-exos showed superior overall reparative effects. Older BMSC-exos also increased VEGF and CD105 expression in ischemic muscle versus the Model group (adjusted P = 0.0312 and 0.0319), although young BMSC-exos induced greater increases than older BMSC-exos (adjusted P = 0.0373 and 0.0319, respectively). In OGD/R-injured HUVECs, older BMSC-exos improved colony formation, migration, and tube formation versus OGD/R alone (adjusted P = 0.0465, 0.0264, and 0.0363), while young BMSC-exos exerted stronger effects than older BMSC-exos (adjusted P = 0.0051, 0.0033, and 0.0326). Young BMSC-exos also suppressed Bach1 protein more effectively than older BMSC-exos (adjusted P = 0.0249). Bach1 overexpression attenuated the pro-angiogenic effects of young BMSC-exos. miRNA sequencing revealed distinct age-related exosomal miRNA profiles and identified miR-455-5p as a key candidate regulator. miR-455-5p directly bound the Bach1 3′UTR and reduced Bach1 expression. Inhibition of miR-455-5p in young BMSC-exos significantly weakened their beneficial effects both in vitro and in vivo. Young BMSC-exos exhibit superior pro-angiogenic and tissue-reparative activity in HLI compared with older BMSC-exos. These effects are mediated, at least in part, by exosomal miR-455-5p targeting Bach1, supporting young BMSC-exos as a promising cell-free nanotherapeutic strategy for ischemic limb repair.