Long noncoding RNA taurine-upregulated gene 1 (TUG1) is considered to be involved in postischemic cerebral inflammation, whereas polysialic acid (polySia, PSA), the product of St8sia2, constitutes polysialylated neural adhesion cell molecule (PSA-NCAM) in both mice and humans and that cerebral PSA-NCAM level is elevated in neuronal progenitor cells in response to transient focal ischemia. Herein, we aim to identify novel miRNAs that bridge the functions of St8sia2 and TUG1 in ischemia-associated injuries. In both in vivo (C57BL/6J mouse ischemia/reperfusion, I/R model) and in vitro (mouse neuroblastoma N2A cell oxygen glucose deprivation/reoxygenation, OGD model) settings, we observed upregulated TUG1 and St8sia2 after the induction of ischemic injury, accompanied by reduced miR-3072-3p expression. We performed siRNA-induced TUG1 knockdown combined with the induction of ischemic injury; the results showed that inhibiting TUG1 expression led to the reduced infarct area and improved neurological deficit. Through bioinformatics analysis, miR-3072-3p was found to target both St8sia2 and TUG1, which was subsequently verified by the luciferase reporter system and RNA binding protein immunoprecipitation assay. Also, the addition of miR-3072-3p mimic/inhibitor resulted in reduced/elevated St8sia2 expression at the protein level. Further studies revealed that in both in vivo and in vitro settings, TUG1 bound competitively to miR-3072-3p to regulate St8sia2 expression and promote apoptosis. In summary, targeting the TUG1/miR-3072-3p/St8sia2 regulatory cascade, a novel cascade we identified in cerebral ischemia injury, may render feasible therapeutic possibilities for overcoming cerebral ischemic insults.
BackgroundEpigenetic histone methylation plays a crucial role in cerebral ischemic injury, particularly in the context of ischemic stroke. However, the complete understanding of regulators involved in histone methylation, such as Enhancer of Zeste Homolog 2 (EZH2), along with their functional effects and underlying mechanisms, remains incomplete.MethodsHere, we employed a rat model of MCAO (Middle cerebral artery occlusion) and an OGD (Oxygen‐Glucose Deprivation) model of primary cortical neurons to study the role of EZH2 and H3K27me3 in cerebral ischemia‐reperfusion injury. The infarct volume was measured through TTC staining, while cell apoptosis was detected using TUNEL staining. The mRNA expression levels were quantified through quantitative real‐time polymerase chain reaction (qPCR), whereas protein expressions were evaluated via western blotting and immunofluorescence experiments.ResultsThe expression levels of EZH2 and H3K27me3 were upregulated in OGD; these expression levels were further enhanced by GSK‐J4 but reduced by EPZ‐6438 and AKT inhibitor (LY294002) under OGD conditions. Similar trends were observed for mTOR, AKT, and PI3K while contrasting results were noted for UTX and JMJD3. The phosphorylation levels of mTOR, AKT, and PI3K were activated by OGD, further stimulated by GSK‐J4, but inhibited by EPZ‐6438 and AKT inhibitor. Inhibition of EZH2 or AKT effectively counteracted OGD‐/MCAO‐induced cell apoptosis. Additionally, inhibition of EZH2 or AKT mitigated MCAO‐induced infarct size and neurological deficit in vivo.ConclusionsCollectively, our results demonstrate that EZH2 inhibition exerts a protective effect against ischemic brain injury by modulating the H3K27me3/PI3K/AKT/mTOR signaling pathway. The results provide novel insights into potential therapeutic mechanisms for stroke treatment.
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