NR4A2 Exacerbates Cerebral Ischemic Brain Injury via Modulating microRNA-652/Mul1 Pathway

BACKGROUND: Nuclear receptor subfamily group A member 2 (NR4A2), a transcription factor, was suggested to be involved in the pathogenesis of ischemic stroke. Nevertheless, the specific role of NR4A2 in ischemic brain injury has yet to be elucidated. Our aim was to probe the mechanisms behind the repression of microRNA (miRNA) expression resulting from NR4A2 regulation in ischemic brain injury. METHODS: A rat model with transient global cerebral ischemia (tGCI) was established, followed by HE staining and immunohistochemistry for verification. Subsequently, NR4A2 expression in rat brain tissues was detected by RT-qPCR, Western blot and immunohistochemistry. Then, PC12 cells were treated with NR4A2 alteration and subjected to oxygen-glucose deprivation (OGD) for cerebral ischemia simulation. Cell viability, apoptosis and cycle distribution were detected by CCK-8 and flow cytometry, respectively. miR-652 expression in rat brain tissues and cells was then detected by RT-qPCR, and then the targeting mRNAs of miR-652 were predicted through bioinformatic websites. Finally, the effect of miR-652 and mitochondrial E3 ubiquitin ligase 1 (Mul1) on the PC12 cell activity after OGD treatment was verified by rescue experiments. RESULTS: NR4A2 and Mul1 were expressed highly in brain tissues of rats with tGCI, while miR-652 was expressed poorly. NR4A2 inhibited the expression of miR-652 by transcription, thus blocking the inhibition of miR-652 on Mul1 to repress PC12 cell activity and promote apoptosis and G0/G1 cell cycle arrest. CONCLUSION: The transcription factor NR4A2 mediates the expression of Mul1 through transcriptional repression of miR-652, thus promoting ischemic brain injury.