Overexpression of glycogen synthase kinase 3β sensitizes neuronal cells to ethanol toxicity

Abstract

The developing central nervous system (CNS) is particularly susceptible to ethanol toxicity. The loss of neurons underlies many of the behavioral deficits observed in fetal alcohol spectrum disorders (FASD). The mechanisms of ethanol‐induced neuronal loss, however, remain incompletely elucidated. We demonstrated that glycogen synthase kinase 3β (GSK3β), a multifunctional serine/threonine kinase, was involved in ethanol neurotoxicity. The activity of GSK3β is negatively regulated by its phosphorylation at serine 9 (Ser9). Ethanol induced dephosphorylation of GSK3β at Ser9 and the activation of Bax as well as caspase‐3 in the developing mouse brain. These ethanol‐induced alterations were ameliorated by the pretreatment of a GSK3β inhibitor, lithium. To determine the role of GSK3β in ethanol neurotoxicity, we overexpressed wild‐type (WT), S9A mutant or dominant‐negative (DN) mutant GSK3β in a neuronal cell line (SK‐N‐MC). Ethanol only modestly reduced the viability of parental SK‐N‐MC cells but drastically induced caspase‐3 activation and apoptosis in cells overexpressing WT or S9A GSK3β, indicating that the high levels of GSK3β or the active form of GSK3β increased cellular sensitivity to ethanol. Contrarily, overexpression of DN GSK3β conferred resistance to ethanol toxicity. Lithium and other specific GSK3β inhibitors abolished the hypersensitivity to ethanol caused by WT or S9A overexpression. Bax, a proapoptotic protein, is a substrate of GSK3β. Cells overexpressing WT or S9A GSK3β were much more sensitive to ethanol‐induced Bax activation than parental SK‐N‐MC cells. Our results indicate that GSK3β may be a mediator of ethanol neurotoxicity, and its expression status in a cell may determine ethanol vulnerability.