Extracellular vesicles-transmitted miR-21a-5p altered microglia polarization after hypoxia-ischemic injury in neonatal mice via STAT3 pathways

Abstract Background We previously reported that mesenchymal stromal cells (MSCs)-derived extracellular vesicles (EVs) exhibit protective effects in hypoxia-ischemia (HI) brain damage. The neuroprotective action was connected with its anti-inflammatory effect. However, the mechanisms involved with this effect have not been determined. Methods A modified version of the Rice-Vannucci method was performed on postnatal day 7 mouse pups to induce neonatal HI brain injury. The model of oxygen-glucose deprivation (OGD) was established in BV-2 cells to mimic HI injury in vitro. Mice or BV-2 cells received EVs and EVs-miR-21ainhibitor at indicative time post-injury. In vivo, brain water content and TTC staining were used to evaluate the effects of EVs on HI brain injury. Immunofluorescence staining was used to observe the effect of EVs on the polarization of microglia. The effect of EVs on p-STAT3 was assessed by Western blot. In vitro, the effect of EVs on cell survival was evaluated by CCK8. Expression of miR-21a-5p and inflammatory factors was measured using qRT-PCR. Dual-Luciferase Reporter Assay was performed to illustrate the link between miR-21a-5p and STAT3. The role of miR-21a-5p in EVs on HI injury and ODG injury was further investigated by using EVs-miR-21ainhibitor.Results By using OGD mimicking HI injury in vitro, we found that MSCs-EVs treatment elevated cell viability following OGD exposure in BV-2 cells. MSCs-EVs treatment impeded microglia-mediated neuroinflammation, shifted microglia toward M2 polarization, and suppressed the phosphorylation of selective signal transducer and activator of transcription 3 (STAT3) in microglia after HI exposure in vitro and in vivo. In light of miR-21a-5p being the most highly expressed miRNA in MSCs-EVs interacting with the STAT3 pathway, further work focused on this pathway. Notably, MSCs-EVs treatment increased HI-reduced miR-21a-5p levels in BV-2 cells. Diminishing miR-21a-5p in MSCs-EVs partially attenuated its effect on microglia polarization and STAT3 phosphorylation following HI exposure in vitro and in vivo. Conclusions Our study suggested that MSCs-EVs attenuated HI brain damage in neonatal mice via shuttling miR-21a-5p, which induced microglia M2 polarization by targeting STAT3.