Pre-mRNA Missplicing of Mcl-1 is Involved in Ethanol Induced Neurotoxicity

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Pre-mRNA missplicing of Mcl-1 is involved in ethanol induced neurotoxicity Heavy and chronic ethanol exposure can cause significant structural and functional damage to the adult brain. The developing nervous system is even more vulnerable to ethanol exposure. Prenatal exposure of ethanol during pregnancy can lead to fetal alcohol spectrum disorders (FASD), characterized by malformation of the nervous system and mental retardation. The most devastating consequence of ethanol exposure is the neurotoxicity associated with the depletion of neurons. It is crucial to elucidate mechanisms of neuroapoptosis in order to develop effective therapeutic approaches to overcome ethanol-induced neuropathologies. Regulation of splice variants in the brain can modulate protein functions, which may ultimately affect behaviors associated with alcohol dependence and ethanol-mediated neurotoxicity. Limited number of studies has shown that pre-mRNA splicing patterns of genes are potentially altered and involved in behavior changes associated with alcoholism. Since alcohol consumption is associated with neurotoxicity, it is possible that altered splicing of survival and pro-survival factors during the development of alcoholism may contribute to the neurotoxicity. Our preliminary data suggest that ethanol exposure can lead to pre-mRNA missplicing of Mcl-1, a pro-survival member of the Bcl-2 family, by downregulating the expression levels of serine/arginine rich splicing factor 1 (SRSF1). The pre-mRNA of Mcl-1 can be alternatively spliced to remove exon 2, which produces shortened form of Mcl-1, named Mcl-1S. While the longer gene product Mcl-1L enhances cell survival, the alternatively spliced shorter gene product Mcl-1S promotes apoptosis. Our preliminary data has indicated that ethanol exposure to neurons leads to a decrease in the ratio of Mcl-1L/Mcl-1S by favoring pro- apoptotic Mcl-1S splicing over anti-apoptotic Mcl-1L isoform suggesting that Mcl-1S may play a crucial role in neurotoxicity associated with alcohol consumption. Therefore, we hypothesize that ethanol-induced altered expression of serine/arginine rich splicing factors leads to missplicing of Mcl-1, which contributes to ethanol- mediated neurotoxicity. We propose to examine our hypothesis by (i) investigating the impact of ethanol exposure on expression levels of serine/arginine rich alternative splicing factors (SR family proteins) in neurons, (ii) determining the effect of ethanol exposure on alternative pre-mRNA splicing of Mcl-1 and other candidate antiapoptotic and proapoptotic genes, and (iii) examining the role of SRSF1 and alcohol-induced isoforms of Mcl-1 in neurotoxicity and neuronal functions by utilizing genetic, biochemical, and neurophysiological approach.