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This study aimed to explore whether long noncoding RNA (lncRNA) maternally expressed gene 3 (MEG3) affects the polarization of microglia in cerebral ischemia-reperfusion (I/R) injury through regulating Kruppel-like factor 4 (KLF4). A middle cerebral artery occlusion/reperfusion-induced (MCAO/R-induced) mouse model was established as an in vivo model. Oxygen and glucose confinement/reoxygenation-induced (OGD/R-induced) microglia (BV2 cells) were used as an in vitro model. RNA pull-down and RNA immunoprecipitation were used to detect the binding between MEG3 and KLF4. The MEG3 expression was signally elevated in the MCAO/R-induced mice or OGD/R-induced BV2 cells. The inhibition of MEG3 reversed the effects of OGD/R injury on the polarization and inflammation of BV2 cells. Moreover, MEG3 bound to KLF4 and inhibited its protein expression. Furthermore, the overexpression of MEG3 promoted M1 polarization and inflammation but inhibited M2 polarization by inhibiting KLF4 in BV2 cells. The transfection of small interfering RNAs against MEG3 inhibited M1 polarization and inflammation and promoted M2 polarization in vitro and in vivo. Inhibition of MEG3 can alleviate cerebral I/R injury via regulating the polarization of microglia through KLF4.NEW & NOTEWORTHY To study the role of long noncoding RNA (lncRNA) maternally expressed gene 3 (MEG3) in cerebral ischemia-reperfusion (I/R) injury, we clarified the mechanism by which lncRNA MEG3 regulates the secretion of inflammatory cytokines in microglia through in vitro and in vivo experiments. We discovered that inhibition of MEG3 could alleviate cerebral I/R injury via inhibiting M1 polarization and promoting M2 polarization through Kruppel-like factor 4 (KLF4), indicating an effective theoretical basis for potential therapeutic targets of cerebral I/R injury.

Severe cerebral ischemia/reperfusion injury has been shown to induce high-level autophagy and neuronal death. Therefore, it is extremely important to search for a target that inhibits autophagy activation. Long non-coding RNA MEG3 participates in autophagy. However, it remains unclear whether it can be targeted to regulate cerebral ischemia/reperfusion injury. Our results revealed that in oxygen and glucose deprivation/reoxygenation-treated HT22 cells, MEG3 expression was obviously upregulated, and autophagy was increased, while knockdown of MEG3 expression greatly reduced autophagy. Furthermore, MEG3 bound miR-181c-5p and inhibited its expression, while miR-181c-5p bound to autophagy-related gene ATG7 and inhibited its expression. Further experiments revealed that mir-181c-5p overexpression reversed the effect of MEG3 on autophagy and ATG7 expression in HT22 cells subjected to oxygen and glucose deprivation/reoxygenation. In vivo experiments revealed that MEG3 knockdown suppressed autophagy, infarct volume and behavioral deficits in cerebral ischemia/reperfusion mice. These findings suggest that MEG3 knockdown inhibited autophagy and alleviated cerebral ischemia/reperfusion injury through the miR-181c-5p/ATG7 signaling pathway. Therefore, MEG3 can be considered as an intervention target for the treatment of cerebral ischemia/reperfusion injury. This study was approved by the Animal Ethics Committee of the First Affiliated Hospital of Zhengzhou University, China (approval No. XF20190538) on January 4, 2019.