The Role of Presenilin-1 in the Excitotoxicity of Ethanol Withdrawal

Presenilin-1 (PS1) is a core component of g-secretase that is involved in neurodegeneration. We have previously shown that PS1 interacts with a mitogen-activated protein kinase [(MAPK) jun-NH2-terminal-kinase], and another MAPK (p38) is activated by ethanol withdrawal (EW), abrupt termination from chronic ethanol exposure. EW is excitotoxic in nature, induces glutamate upregulation, and provokes neuronal damage. Here, we explored a potential mechanistic pathway involving glutamate, p38 (p38 alpha isozyme), and PS1 that may mediate EW-induced excitotoxic stress. We used the prefrontal cortex of male rats withdrawn from a chronic ethanol diet. Additionally, we used ethanol-withdrawn HT22 cells (mouse hippocampal) treated with the inhibitor of glutamate receptors [dizocilpine (MK-801)], p38 alpha (SB203580; 4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl] pyridine), or g-secretase [N-[N- (3,5-difluorophenacetyl)- l-alanyl]-S-phenylglycine t-butyl ester (DAPT)] during EW. Separately, ethanol-free HT22 cells were exposed to glutamate with or without SB203580 or DAPT. Protein levels, mRNA levels, and cell viability were assessed using immunoblotting, qualitative polymerase chain reaction, and calcein assay, respectively. The prefrontal cortex of ethanol-withdrawn rats or HT22 cells showed an increase in PS1 and p38 alpha, which was attenuated by MK-801 and SB203580, but mimicked by glutamate treatment to ethanol-free HT22 cells. DAPT attenuated the toxic effect of EW or glutamate on HT22 cells. These results suggest that PS1 expression is triggered by glutamate through p38 alpha, contributing to the excitotoxic stimulus of EW.