MSCs-Derived Exosomes Attenuate Acute Brain Injury and Inhibit Microglial Inflammation by Reversing CysLT2R-ERK1/2 Mediated Microglia M1 Polarization

Inflammatory responses play a major role in the pathophysiology of cerebral ischemia. Mesenchymal stem cell-derived exosomes (MSC-exos) have important anti-inflammatory effects on the treatment of organ injury. This study aimed to determine the anti-inflammatory effect and furtherly investigate the potential mechanism of MSC-exos on acute cerebral ischemia. MSC-exos were isolated by ultracentrifugation, characterized by transmission electron microscopy and FACS. Rats subjected to middle cerebral artery occlusion/reperfusion (MCAO/R) surgery were administered MSC-exos through the tail vein. In vitro, microglia exposed to oxygen- and glucose-deprivation (OGD) and leukotrienes were used to study the protective mechanism of exosomes against ischemia/reperfusion-induced inflammation. The intake of exosomes into microglia was visualized through immunofluorescence staining. The results showed that MSC-exos treatment significantly improved motor, learning and memory abilities of MCAO/R rats 7 days later. The production of pro-inflammatory factors decreased, while the anti-inflammatory cytokines and neurotrophic factors increased both in the cortex and hippocampus of ischemic hemisphere as well as in the culture supernatant of microglia treated with OGD and NMLTC4. MSC-exos treatment also significantly inhibited M1 microglia polarization and increased M2 microglia cells. Furthermore, western blot analysis demonstrated that CysLT2R expression and ERK1/2 phosphorylation were downregulated both in vivo and in vitro. Thus, MSC-exos attenuated brain injury and inhibited microglial inflammation by reversing CysLT2R-ERK1/2 mediated microglia M1 polarization.