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.

L-Cysteine attenuates osteopontin-mediated neuroinflammation following hypoxia-ischemia insult in neonatal mice by inducing S-sulfhydration of Stat3.

We previously show that L-Cysteine administration significantly suppresses hypoxia-ischemia (HI)-induced neuroinflammation in neonatal mice through releasing H2S. In this study we conducted proteomics analysis to explore the potential biomarkers or molecular therapeutic targets associated with anti-inflammatory effect of L-Cysteine in neonatal mice following HI insult. HI brain injury was induced in postnatal day 7 (P7) neonatal mice. The pups were administered L-Cysteine (5 mg/kg) at 24, 48, and 72 h post-HI. By conducting TMT-based proteomics analysis, we confirmed that osteopontin (OPN) was the most upregulated protein in ipsilateral cortex 72 h following HI insult. Moreover, OPN was expressed in CD11b+/CD45low cells and infiltrating CD11b+/CD45high cells after HI exposure. Intracerebroventricular injection of OPN antibody blocked OPN expression, significantly attenuated brain damage, reduced pro-inflammatory cytokine levels and suppressed cerebral recruitment of CD11b+/CD45high immune cells following HI insult. L-Cysteine administration reduced OPN expression in CD11b+/CD45high immune cells, concomitant with improving the behavior in Y-maze test and suppressing cerebral recruitment of CD11b+/CD45high immune cells post-HI insult. Moreover, L-Cysteine administration suppressed the Stat3 activation by inducing S-sulfhydration of Stat3. Intracerebroventricular injection of Stat3 siRNA not only decreased OPN expression, but also reversed HI brain damage. Our data demonstrate that L-Cysteine administration effectively attenuates the OPN-mediated neuroinflammation by inducing S-sulfhydration of Stat3, which contributes to its anti-inflammatory effect following HI insult in neonatal mice. Blocking OPN expression may serve as a new target for therapeutic intervention for perinatal HI brain injury.