Effects of Ethanol on Insulin Signaling in the Brain

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DESCRIPTION (provided by applicant): Chronic gestational exposure to ethanol is teratogenic and causes major structural abnormalities in the central nervous system (CNS) including microcephaly and cerebellar hypoplasia. Insulin mediates CNS growth, development, and function, and ethanol has profound inhibitory effects on insulin signaling in neuronal cells. Using in vitro exposure models, we detected ethanol inhibition of insulin signaling, beginning at the level of its receptor and extending downstream through pathways that regulate neuronal survival. Importantly, ethanol inhibition of insulin-stimulated tyrosyl phosphorylation of the insulin receptor substrate-1 (IRS1) and downstream activation of PI3 kinase have been linked neuronal cell death mediated by impaired survival mechanisms, increased apoptosis, and mitochondrial (Mt) dysfunction. Recent preliminary experiments showed that cerebellar hypoplasia caused by chronic gestational exposure to ethanol is associated with similar types but probably greater degrees of impaired insulin signaling, and that neuronal loss is mediated by both apoptosis and Mt dysfunction. In addition, we obtained evidence that ethanol impairs signaling through both IRS1-dependent and IRS1-independent pathways in the developing brain. Since gestational exposure to ethanol does not inhibit insulin receptor protein expression, we hypothesize that the impaired insulin signaling is mediated by abnormalities in receptor function related to binding affinity, phosphorylation, or tyrosine kinase activation. Further studies are required to understand the mechanisms by which ethanol exerts its adverse effects on insulin-stimulated viability and Mt function during development, and determine the degree to which similar abnormalities occur with different levels of ethanol exposure. In this application, we propose to: 1) examine the degrees to which low, moderate, or high levels of chronic gestational ethanol exposure impair insulin stimulated neuronal viability and Mt function; 2) determine the mechanisms by which ethanol causes Mt dysfunction or apoptosis; 3) characterize the insulin signaling pathways that are inhibited by chronic gestational exposure to ethanol; and 4) validate the roles of specific impairments as mediators of neuronal Mt dysfunction. The studies will utilize insulin-stimulated post-mitotic primary cerebellar granule neuron cultures generated from ethanol-exposed and control rat pups since the cerebellum is a major target of ethanol neurotoxicity and cerebellar granule neurons are both responsive to insulin and functionally impaired by ethanol. These investigations could lead to new approaches for rescuing neuronal cells from the adverse effects of chronic gestational exposure to ethanol.