NR4A1 Promotes Cerebral Ischemia Reperfusion Injury by Repressing Mfn2-Mediated Mitophagy and Inactivating the MAPK–ERK–CREB Signaling Pathway

Abstract

Mitochondrial dysfunction has been acknowledged as the key pathogenic mechanism in cerebral ischemia-reperfusion (IR) injury. Mitophagy is the protective system used to sustain mitochondrial homeostasis. However, the upstream regulator of mitophagy in response to brain IR injury is not completely understood. Nuclear receptor subfamily 4 group A member 1 (NR4A1) has been found to be associated with mitochondrial protection in a number of diseases. The aim of our study is to explore the functional role of NR4A1 in cerebral IR injury, with a particular focus on its influence on mitophagy. Wild-type mice and NR4A1-knockout mice were used to generate cerebral IR injury in vivo. Mitochondrial function and mitophagy were detected via immunofluorescence assays and western blotting. Cellular apoptosis was determined via MTT assays, caspase-3 activity and western blotting. Our data revealed that NR4A1 was significantly increased in the reperfused brain tissues. Genetic ablation of NR4A1 reduced the cerebral infarction area and repressed neuronal apoptosis. The functional study demonstrated that NR4A1 modulated cerebral IR injury by inducing mitochondrial damage. Higher NR4A1 promoted mitochondrial potential reduction, evoked cellular oxidative stress, interrupted ATP generation, and initiated caspase-9-dependent apoptosis. Mechanistically, NR4A1 induced mitochondrial damage by disrupting Mfn2-mediated mitophagy. Knockdown of NR4A1 elevated Mfn2 expression and therefore reversed mitophagic activity, sending a prosurvival signal for mitochondria in the setting of cerebral IR injury. Further, we demonstrated that NR4A1 modulated Mfn2 expression via the MAPK-ERK-CREB signaling pathway. Blockade of the ERK pathway could abrogate the permissive effect of NR4A1 deletion on mitophagic activation, contributing to neuronal mitochondrial apoptosis. Overall, our results demonstrate that the pathogenesis of cerebral IR injury is closely associated with a drop in protective mitophagy due to increased NR4A1 through the MAPK-ERK-CREB signaling pathway.

Role of Mitofusins and Mitophagy in Life or Death Decisions

“…Furthermore, in Nr4a1-deficient cells, blockage of the MAPK-ERK-CREB signaling pathway decreased the levels of Mfn2 and no longer allowed apoptotic inhibition. In sum, this study points to an important role of Mfn2 and of the MAPK-ERK-CREB pathway in the brain, by controlling mitophagy and apoptosis upon IR injury (Zhang and Yu, 2018). The importance of MFN2 in the interplay between mitophagy and apoptosis was confirmed in the context of coronary heart disease, however instead involving the AMPK-CREB pathway (Li P. et al, 2020).…”

“…The role ERK-MFN2 in mitophagy was also described in cerebral ischemia-reperfusion (IR) injury (Zhang and Yu, 2018). Here, decreased mitophagy and increased apoptosis are associated with brain damage.…”

Role of Mitophagy in Cardiovascular Disease

“…Excessive mitophagy reduced mitochondrial quality which, in turn, caused energy shortage and mitochondrial dysfunction [145]. Furthermore, blockade of the MAPK-ERK-CREB signaling pathway upregulated NR4A1 and repressed Mfn2-mediated mitophagy, thus expanding the area of cerebral infarction and increasing neuronal apoptosis [181]. In cardiomyocytes, damaged mitochondria are sequestered in rab5-positive early endosomes via the ESCRT mechanism, which depends on Parkin, and the loss of rab5 function increases the susceptibility of embryonic fibroblasts and cardiomyocytes to cell death [182].…”

Mammalian STE20‑like kinase 1 regulates pancreatic cancer cell survival and migration through Mfn2‑mediated mitophagy

“…autophagy is a process that maintains the homeostasis of the microenvironment inside cells via non-selective degradation and phagocytosis of abnormal organelles, proteins and lipids in the cytoplasm (18,19). Mitofusin 2 (Mfn2)-mediated mitophagy is a process by which cells selectively remove damaged or dysfunctional mitochondria via autophagy to maintain the balance between mitochondrial quantity and quality (20)(21)(22). numerous studies have confirmed that Mfn2-mediated mitophagy plays a crucial role in tumor origin, homeostasis, invasiveness and drug resistance (23,24).…”