Mechanism of ischemic brain injury repair by endothelial progenitor cell-derived exosomes

Ischemic stroke is a refractory disease that seriously endangers human health and life. The main treatment aim of stroke is to alleviate brain injury. The present study aimed to investigate the effects and mechanisms of endothelial progenitor cell (EPC)-derived exosomes in repairing ischemic brain injury. Sprague-Dawley rat models of cerebral ischemia-reperfusion (IR) injury were established by middle cerebral artery occlusion. The IR model rats were then treated with PBS, EPC or exosomes; untreated and Sham rats were used as control. EPCs were obtained from tibias and femurs, and exosomes were isolated from the EPCs and characterized. To measure brain injury, 2,3,5-triphenyltetrazolium chloride staining was used to measure the infarct area, neurological deficit was scored, hematoxylin and eosin staining was used to examine pathological changes and TUNEL staining was used to quantify apoptosis. Immunofluorescence staining and reverse transcription-quantitative PCR were used to determine CD31 and VEGF protein and mRNA expressions, respectively, and western blot analysis was used out to measure the protein expression levels of Wnt3a, GSK-3 beta and phosphorylated (p)-GSK-3 beta. Compared with rats in the Control and Sham groups, in IR model rats the nerve fibers were slightly necrotic and swollen and the number of nerve cells was reduced. Following EPC treatment, the brain tissue exhibited mild liquefaction and degeneration in the small focus area with mild edema in the stroma. The numbers of nerve cells decreased, and the distribution of nerve cells was not very uniform; proliferation of glial cells was observed. Following treatment with exosomes, the distribution of nerve cells was more uniform with less degeneration and necrosis; the proliferation of glial cells was remarkable. Compared with the Control group, the infarct size, neurological defect score, percentage of apoptotic cells, expression of CD31, VEGF, Wnt3a, and p-GSK-3 beta were significantly higher in the IR model (P < 0.05). After EPC and exosome treatments, the infarct size, neurological defect score, percentage of apoptotic cells, expression of Wnt3a, and p-GSK-3 beta were significantly reduced (P < 0.05), whereas the mRNA and protein expression levels of CD31 and VEGF were significantly increased (P < 0.05). Results from the present study demonstrated that EPC-derived exosomes may alleviate ischemic injury by inhibiting apoptosis and promoting angiogenesis. These findings suggested that exosomes may have a protective role for nerve cells and may be a potentially effective option for treating stroke. However, human clinical studies are needed to validate these findings from animals.