BMSC-Derived Exosomal miR-21a-5p Ameliorates Blood–Brain Barrier Injury and Hemorrhagic Transformation

Hemorrhagic transformation (HT) and disruption of the blood-brain barrier (BBB) injury are critical pathological features of ischemic stroke, profoundly influencing the natural course of the disease and treatment outcome. This study aims to elucidate how bone marrow stromal cell-derived exosome (BMSC-exo) influence BBB injury and HT and the related molecular mechanisms, focusing on the core function of exosome miR-21a-5p. The HT model induced by middle cerebral artery occlusion (MCAO-HT) was treated with tail vein injection of BMSCs-exo, and HT, BBB injury and brain damage were assessed by mNSS score, triphenyltetrazolium chloride (TTC) staining, evan's blue (EB)/hemoglobin leakage assay, and HE staining. High abundance miRNAs in BMSC-exo were identified by Small RNA sequence. BMSC-exo miR-21a-5p was modulated using inhibitor and mimic, following by exploring the function of miR-21a-5p in an MCAO-HT animal model and an BBB model. BMSCs-exo effectively enhanced neurological recovery, minimized infarct size, mitigated BBB leakage, and upregulated the expression of Claudin-5/Occludin/ZO-1 in the MCAO-HT model. Five hundred and seventy-one miRNAs were identified in BMSCs-exo, and the targets of the TOP 10 miRNAs in abundance were enriched in TLR, NF-κB, and MMPs pathways. In in vitro experiments, BMSCs-exo rescued oxygen glucose deprivation/reperfusion-induced BBB injury by delivering miR-21a-5p, characterized by an increase in trans epithellal electric resistance and tight junction protein levels and a decrease in permeability, which was dependent on the inhibition of TLR2/NF-κB pathway and the levels and enzymatic activities of MMP2/9. In in vivo experiments, miR-21a-5p knockdown impaired the neuroprotective effects of BMSCs-exo, whereas miR-21a-5p overexpressing lentivirus alone significantly ameliorated brain injury and inhibited the TLR2/NF-κB pathway and the levels and enzymatic activities of MMP2/9 in the MCAO-HT model. BMSCs-exo mitigates BBB disruption and HT by delivering miR-21a-5p to inhibit the TLR2/NF-κB pathway, downregulate the levels and enzymatic activities of MMP-2/9 and protect tight junction proteins.