MEF2D upregulation protects neurons from oxygen–glucose deprivation/re-oxygenation-induced injury by enhancing Nrf2 activation
Introduction
Cerebral ischemia/reperfusion injury is a frequent clinical pathological problem caused by cerebral artery blockage; it results in insufficient oxygen and glucose supply to the brain (Yang and Betz, 1994). The ischemic conditions cause irreversible brain damage that is further exacerbated after blood reperfusion (Yang and Betz, 1994). Cerebral ischemia/reperfusion injury has become the leading cause of mortality and disability, an issue that causes severe societal burdens worldwide (Ovbiagele et al., 2013). However, effective therapy for clinical management of cerebral ischemia/reperfusion injury is still limited. To date, the precise molecular mechanisms that underlie this pathological condition remain largely unknown. Cerebral ischemia/reperfusion injury is accompanied by excessive reactive oxygen species (ROS) generation that contributes to induce neuronal apoptosis and brain damage (Lei et al., 2011, Wiklund et al., 2018). Therefore, it appears reasonable that ameliorating the oxidative stress triggered by cerebral ischemia/reperfusion injury may be a potential therapeutic approach for this disease.
Myocyte enhancer factor 2D (MEF2D) is a member of the MEF2 transcription factor protein family that plays a crucial role in regulating the development and function of the nervous system (Shalizi and Bonni, 2005). Notably, MEF2D has emerged as a pro-survival factor for neurons under neurotoxic conditions. MEF2D suppression promotes the apoptosis of embryonic hippocampal neurons (Salma and McDermott, 2012). MEF2D inactivation contributes to the induction of neuronal apoptosis after intracerebral hemorrhage in a rat model (Ke et al., 2015). MEF2D upregulation protects neurons from the 1-methyl-4-phenylpyridinium-ion- and 6-hydroxydopamine-induced neurotoxicity, findings that imply a key role for MEF2D in Parkinson's disease (Kim et al., 2011, Hu et al., 2015, Guo et al., 2017). Moreover, MEF2D contributes to reduce ROS generation induced by glutamate in hippocampal neurons (Chen et al., 2017). Therefore, MEF2D is a promising target for providing neuroprotection.
Nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a member of basic leucine transcription factor family, is a major regulator of the cellular antioxidant system (Hayes and Dinkova-Kostova, 2014). Nrf2 activation can induce multiple stress-associated cytoprotective genes that ameliorate oxidative damage in response to various adverse stimuli (Yamamoto et al., 2018). Oxidative stress induces Nrf2 protein stabilization and accumulation; it is then translocated into the nucleus, where it initiates gene transcription by binding to antioxidant response elements (AREs) (Suzuki and Yamamoto, 2015). Emerging evidence demonstrates that Nrf2 activation confers neuroprotective effects during cerebral ischemia/reperfusion injury, and thereby may serve as a promising therapeutic target (Zhang et al., 2017, Liu et al., 2019).
Although MEF2D is suggested to be a pro-survival factor for neurons, whether MEF2D contributes to protect neurons from cerebral ischemia/reperfusion injury remains unclear. The current study was designed to investigate the role of MEF2D in regulating oxygen–glucose deprivation/re-oxygenation (OGD/R)-induced neuronal injury. Our results demonstrated that MEF2D expression was significantly induced in neurons in response to OGD/R injury. MEF2D upregulation significantly rescued the decreased viability of OGD/R-injured neurons and suppressed OGD/R-induced apoptosis and ROS production. Moreover, MEF2D overexpression contributed to the activation of Nrf2/ARE antioxidant signaling. Nrf2 inhibition partially blocked the MEF2D-mediated neuroprotective effect in OGD/R-exposed neurons. Overall, these results reveal that MEF2D overexpression attenuates OGD/R-induced injury by enhancing Nrf2-mediated antioxidant signaling.
Section snippets
MEF2D expression was induced by OGD/R injury in HT22 neurons
To investigate whether MEF2D is involved in regulating OGD/R-induced neuronal injury, we examined its expression pattern in HT22 neurons following OGD/R exposure. MEF2D expression was significantly induced in OGD-exposed neurons after 12-h reperfusion, peaked at 24-h reperfusion, and then decreased at 36-h reperfusion (Fig. 1A). MEF2D protein also exhibited a similar expression pattern in OGD/R-exposed neurons, as detected by western blot (Fig. 1B). These results indicate that MEF2D may
Discussion
Our study for the first time provides compelling evidence that MEF2D contributes to the protection of neurons against OGD/R-induced injury in vitro. We found that MEF2D upregulation significantly suppressed OGD/R-induced apoptosis and ROS production in HT22 neurons. Moreover, we uncovered that MEF2D protected neurons from OGD/R-induced injury by enhancing Nrf2/ARE signaling (Fig. 6). This study demonstrates a novel mechanism by which MEF2D exerts its neuroprotective function.
MEF2D is implicated
Cell culture and treatment
The mouse HT22 neuronal cell line was provided by BeNa Culture Collection (Kunshan, China) and cultured in high-glucose Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% fetal bovine serum (Gibco; Thermo Fisher Scientific, Waltham, MA, USA). HT22 neurons were grown at 37 °C in a humidified incubator with 5% CO2. For induction of the in vitro OGD/R model, HT22 neurons were incubated in glucose-free DMEM and grown in an anaerobic chamber (5% O2, 10% CO2, and 85% N2) for 8 h. HT22
CRediT authorship contribution statement
Nan Wang: Conceptualization, Investigation, Writing - original draft. Weiwei Yang: Methodology. Lan Li: Methodology. Ming Tian: Conceptualization, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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