The Neuroprotective Mechanism Of M2 Microglial Derived Exosome In A Mouse Model Of Cerebral Ischemia

Background: Microglia plays a critical role in modulating cell death and neurobehavioral recovery after brain injury either by direct cell-cell interaction or indirect secretion of trophic factors.It is well documented that exosomes can deliver bioactive molecules to recipient cells to modulate cell function.Here,we aim to determine whether M2 microglia exert neuroprotective effects after ischemic stroke through exosome mediated cell-cell interaction.Methods: M2 microglia-derived exosomes were intravenously injected into the mouse brain immediately after middle cerebral artery occlusion.Infarct volume,neurological score,and neuronal apoptosis were examined after 3 days of ischemic stroke.Exosome RNA,target protein in neurons and brain tissue were collected for the mechanistic study.Results: Our results showed that M2 microglia-derived exosome was uptake by neurons in vitro and in vivo.M2 microglia-derived exosome treatment attenuated neuronal apoptosis after oxygen-glucose deprivation(p<0.05).In vivo results showed that M2 microglia-derived exosome treatment significantly reduced infarct volume and attenuated behavioral deficits after 3 days of transient brain ischemia(p<0.05).While injecting with miR-124 knocked down M2 microglia-derived exosome partially reversed the neuroprotective effect.Since USP14 was the direct down-stream target of miR-124,injection of miR-124 k/d M2-exosome plus IU1(USP 14inhibitor)achieved similar neuroprotective effect as M2-exosome.Further exosomal microarray results show that miR-124 was highly expressed and demonstrated as one of the functional targets.In addition,miR-186,miR-142,miR-483,miR-126,miR-146 could be suggested as the main miRNAs in the future experiments.Conclusions: We demonstrated that M2 microglia-derived exosomes attenuated ischemic brain injury and promoted neuronal survival via exosomal miR-124 and its down-stream target USP14.M2 microglia derived exosome represents a promising avenue for treating ischemic stroke.