Epigenetic Mechanism and Treatment of Fetal Alcohol Exposure-Induced Memory Impairment and Metabolic Dysregulation

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Fetal alcohol spectrum disorder (FASD), the result of fetal alcohol exposure (FAE), affects 2-11% of children worldwide with no treatments in sight. In my thesis work, I aimed to identify underlying biological mechanisms of the FAE-induced hippocampus-based cognitive deficits that would lead to identify potential treatment targets to reverse the deficits. The cause of the specific cognitive vulnerability due to FAE is not yet known, however previous studies in my lab indicated hypothyroxinemic profile of the ethanol-consuming pregnant rat as a possible mechanism. Low levels of thyroxine (T4) in the fetal brain disturb neurodevelopment. Administering T4 to the ethanol-consuming dams reverses their hypothyroxinemia and alleviates the hippocampus-based cognitive deficits of their adult FAE offspring. Here we utilized the constructive effects of T4 supplementation to the ethanol-consuming dams as a start point. First, we conducted a dose response study and found the optimum dose of T4 administered to ethanol-consuming dams that reversed the FAE-altered hippocampal phenotypes in adult offspring. Next, we aimed to identify whether FAE impairs hippocampus-dependent learning and memory processes in the second-generation (F2) progeny, and whether low dose T4 administration to the ethanol-consuming dams can prevent it. In utero ethanol exposed first generation females (F1) and their F2 (SB F2) progeny exhibited fear memory deficits and T4 administration to the ethanol-consuming mothers of F1 females reversed these deficits via altering allele-specific and total expression of thyroid hormone-regulated type 3 deiodinase (Dio3) in the hippocampus. We then described that F1 offspring displayed insulin resistance in the glucose tolerance test (GTT), which was reflected in SB F2 progeny as glucose metabolism dysfunction and reversed by T4 administration to the ethanol-consuming grandmother. It is well known that insulin pathway genes are involved in the hippocampus-based learning and memory processes, especially imprinted insulin-like growth factor 2 (Igf2) gene. Therefore, we investigated the involvement of insulin pathway genes in the FAE-caused hippocampal deficits. We developed an ex vivo model, where ethanol administration occurs in vivo via the pregnant mother and the subsequent primary hippocampal culture makes it possible to screen for drug targets that reverse the FAE-induced molecular changes. Our data revealed persistent and parallel influence of FAE on the gene expression profiles of selected insulin pathway genes in the in vivo fetal hippocampus and the ex vivo primary hippocampal culture. This ex vivo model suggested that T4 and the insulin sensitizer metformin are potential treatments for FASD, post-exposure to alcohol. Subsequent in vivo study, where FAE neonates were treated with T4 or metformin, confirmed the potential of T4 or metformin as treatments for FASD-induced cognitive deficits. The mechanism of action is via normalizing hippocampal transcript levels of DNA methyltransferase 1 (Dnmt1), and those of Dio3 and Igf2. In summary, disturbances in methylation maintenance and total and/or allelic expression of imprinted genes are potential mediators of FAE-induced hippocampus-based cognitive deficits. The findings that T4 and metformin can reverse the detrimental effects of FAE on these biological and cognitive processes is of significance since these are FDA-approved, widely used medications, which could be assessed as treatments for FASD in clinical studies.

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  • 03/12/2018
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