To investigate the therapeutic mechanism of action of transplanted stem cells and develop exosome-based nanotherapeutics for ischemic stroke, we assessed the effect of exosomes (Exos) produced by human umbilical cord mesenchymal stem cells (hUMSCs) on microglia-mediated neuroinflammation after ischemic stroke. Our results found that injected hUMSC-Exos were able to access the site of ischemic damage and could be internalized by cells both in vivo and in vitro. In vitro, treatment with hUMSC-Exos attenuated microglia-mediated inflammation after oxygen-glucose deprivation (OGD). In vivo results demonstrated that treatment with hUMSC-Exos significantly reduced infarct volume, attenuated behavioral deficits, and ameliorated microglia activation, as measured three days post-transient brain ischemia. Furthermore, miR-146a-5p knockdown (miR-146a-5p k/d Exos) partially reversed the neuroprotective effect of hUMSC-Exos. Our mechanistic study demonstrated that miR-146a-5p in hUMSC-Exos reduces microglial-mediated neuroinflammatory response through IRAK1/TRAF6 pathway. We conclude that miR-146a-5p derived from hUMSC-Exos can attenuate microglia-mediated neuroinflammation and consequent neural deficits following ischemic stroke. These results elucidate a potential therapeutic mechanism of action of mesenchymal stem cells and provide evidence that hUMSC-Exos represent a potential cell-free therapeutic option for ischemic stroke.
Keywords: exosomes; ischemic stroke; mesenchymal stem/stromal cell; microRNA; neuroinflammation.