Critical role of the JNK-p53-GADD45α apoptotic cascade in mediating oxidative cytotoxicity in hippocampal neurons

BACKGROUND AND PURPOSE Glutamate-induced oxidative stress plays a critical role in the induction of neuronal cell death in a number of disease states. We sought to determine the role of the c-Jun NH2-terminal kinase (JNK)-p53-growth arrest and DNA damage-inducible gene (GADD) 45 alpha apoptotic cascade in mediating glutamate-induced oxidative cytotoxicity in hippocampal neuronal cells. EXPERIMENTAL APPROACH HT22 cells, a mouse hippocampal neuronal cell line, were treated with glutamate to induce oxidative stress in vitro. Kainic acid-induced oxidative damage to the hippocampus in rats was used as an in vivo model. The signalling molecules along the JNK-p53-GADD45 alpha cascade were probed with various means to determine their contributions to oxidative neurotoxicity. KEY RESULTS Treatment of HT22 cells with glutamate increased the mRNA and protein levels of GADD45 alpha, and these increases were suppressed by p53 knock-down. Knock-down of either p53 or GADD45 alpha also prevented glutamate-induced cell death. Glutamate-induced p53 activation was preceded by accumulation of reactive oxygen species, and co-treatment with N-acetyl-cysteine prevented glutamate-induced p53 activation and GADD45 alpha expression. Knock-down of MKK4 or JNK, or the presence of SP600125 (a JNK inhibitor), each inhibited glutamate-induced p53 activation and GADD45 alpha expression. In addition, we also confirmed the involvement of GADD45 alpha in mediating kainic acid-induced hippocampal oxidative neurotoxicity in vivo. CONCLUSIONS AND IMPLICATIONS Activation of the JNK-p53-GADD45 alpha cascade played a critical role in mediating oxidative cytotoxicity in hippocampal neurons. Pharmacological inhibition of this signalling cascade may provide an effective strategy for neuroprotection.