Histone methyltransferase enzyme enhancer of zeste homolog 2 counteracts ischemic brain injury via H3K27me3‐mediated regulation of PI3K/AKT/mTOR signaling pathway

Abstract Background Epigenetic 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. Methods Here, 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. Results The 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. Conclusions Collectively, 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.