Activating Transcription Factor 4-mediated Mitochondrial Unfolded Protein Response Alleviates Hippocampal Neuronal Damage in an In Vitro Model of Epileptiform Discharges

The mitochondrial unfolded protein response (mtUPR) has been shown to restore protein homeostasis and cell function under stress, and recent studies have confirmed that the activating transcription factor 4 (ATF4) regulates mtUPR. However, the role of ATF4-mediated mtUPR in a hippocampal neuronal culture model of seizures remains unclear. Our results showed that the expression of mtUPR-related proteins (HSP60 and CLpP) increased in primary hippocampal neurons with seizures induced by a magnesium-free solution, suggesting mtUPR activation. Furthermore, ATF4 overexpression by lentiviral vector transfection enhanced the expression of HSP60 and CLpP, whereas ATF4 low expression by lentiviral vector transfection weakened the expression of HSP60 and CLpP. In addition, ATF4 overexpression increased neuronal viability and reduced seizure-induced apoptosis. ATF4 overexpression reduced reactive oxygen species (ROS) production and improved mitochondrial membrane potential damage during seizures. Moreover, ATF4 overexpression reduced the BCL2-associated X protein (Bax) expression and increased the expression of B-cell lymphoma 2 (BCL2). In contrast, ATF4 expression showed the opposite trend. In conclusion, our results showed that ATF4-mediated mtUPR may delay the cascade activation of apoptotic pathways by reducing ROS-mediated oxidative stress, thereby attenuating seizure-induced stress injury.