The delivery of miR-21a-5p by extracellular vesicles induces microglial polarization via the STAT3 pathway following hypoxia-ischemia in neonatal mice

Extracellular vesicles(EVs)from mesenchymal stromal cells(MSCs)have previously been shown to protect against brain injury caused by hypoxia-ischemia(HI).The neuroprotective effects have been found to relate to the anti-inflammatory effects of EVs.However,the underlying mechanisms have not previously been determined.In this study,we induced oxygen-glucose deprivation in BV-2 cells(a microglia cell line),which mimics HI in vitro,and found that treatment with MSCs-EVs increased the cell viability.The treatment was also found to reduce the expression of pro-inflammatory cytokines,induce the polarization of microglia towards the M2 phenotype,and suppress the phosphorylation of selective signal transducer and activator of transcription 3(STAT3)in the microglia.These results were also obtained in vivo using neonatal mice with induced HI.We investigated the potential role of miR-21a-5p in mediating these effects,as it is the most highly expressed miRNA in MSCs-EVs and interacts with the STAT3 pathway.We found that treatment with MSCs-EVs increased the levels of miR-21a-5p in BV-2 cells,which had been lowered following oxygen-glucose deprivation.When the level of miR-21a-5p in the MSCs-EVs was reduced,the effects on microglial polarization and STAT3 phosphorylation were reduced,for both the in vitro and in vivo HI models.These results indicate that MSCs-EVs attenuate HI brain injury in neonatal mice by shuttling miR-21a-5p,which induces microglial M2 polarization by targeting STAT3.

Neuroprotective mechanism of L-cysteine after subarachnoid hemorrhage

Hydrogen sulfide,which can be generated in the central nervous system from the sulfhydryl-containing amino acid,L-cysteine,by cystathionine-β-synthase,may exert protective effects in experimental subarachnoid hemorrhage;however,the mechanism underlying this effect is unknown.This study explored the mechanism using a subarachnoid hemorrhage rat model induced by an endovascular perforation technique.Rats were treated with an intraperitoneal injection of 100 mM L-cysteine(30μL)30 minutes after subarachnoid hemorrhage.At 48 hours after subarachnoid hemorrhage,hematoxylin-eosin staining was used to detect changes in prefrontal cortex cells.L-cysteine significantly reduced cell edema.Neurological function was assessed using a modified Garcia score.Brain water content was measured by the wet-dry method.L-cysteine significantly reduced neurological deficits and cerebral edema after subarachnoid hemorrhage.Immunofluorescence was used to detect the number of activated microglia.Reverse transcription-polymerase chain reaction(RT-PCR)was used to detect the levels of interleukin 1β and CD86 mRNA in the prefrontal cortex.L-cysteine inhibited microglial activation in the prefrontal cortex and reduced the mRNA levels of interleukin 1βand CD86.RT-PCR and western blot analysis of the complement system showed that L-cysteine reduced expression of the complement factors,C1q,C3αand its receptor C3aR1,and the deposition of C1q in the prefrontal cortex.Dihydroethidium staining was applied to detect changes in reactive oxygen species,and immunohistochemistry was used to detect the number of NRF2-and HO-1-positive cells.L-cysteine reduced the level of reactive oxygen species in the prefrontal cortex and the number of NRF2-and HO-1-positive cells.Western blot assays and immunohistochemistry were used to detect the protein levels of CHOP and GRP78 in the prefrontal cortex and the number of CHOP-and GRP78-positive cells.L-cysteine reduced CHOP and GRP78 levels and the number of CHOP-and GRP78-positive cells.The cystathionine-β-synthase inhibitor,aminooxyacetic acid,significantly reversed the above neuroprotective effects of L-cysteine.Taken together,L-cysteine can play a neuroprotective role by regulating neuroinflammation,complement deposition,oxidative stress and endoplasmic reticulum stress.The study was approved by the Animals Ethics Committee of Shandong University,China on February 22,2016(approval No.LL-201602022).