FETAL ALCOHOL EXPOSURE IN RATS LEADS TO LONG-TERM CHANGES IN DNA METHYLATION PATTERNS OF TASTE-RELATED GENES IN POSTNATAL TONGUE

Background Considerable evidence indicates that there are potential long-term consequences of maternal alcohol consumption. Such exposures can lead to postnatal changes in the formation and function of brain circuits involved in learning, memory, and reward processing, and increase subsequent risks of alcohol abuse in later life. Although much interest has focused on the central areas affected by such exposures, less attention has been paid to the effects such exposures produce in the peripheral gustatory system. Here, we studied the potential molecular adaptations produced by fetal alcohol exposure in the postnatal chemosensory system by studying DNA methylation changes in Circumvallate Papillae (CV) taste cells in postnatal rats. Methods Pregnant Long Evans rats were divided into two weight-matched groups. Within each group the dams were randomly assigned to one of two dietary treatments (ET: ethanol, FCL: free choice liquid). Dams in the ET group were given ad libitum access to a liquid ethanol containing diet, with increasing amounts of ethanol between gestational (G) days 6–10, and full strength dose during G11-20. In the full strength diet, ethanol provided 35% of an animal's daily calories. Moreover, the timing of these administrations also exposed the fetus to ethanol during the developmental period (G11–20) of olfactory and orosensory systems. After delivery, rats born to dams in the ET group or the FCL group were chosen at random and sacrificed during mid-adolescence at P42. DNA samples were isolated from the CV of tongues, followed by genome-wide differential methylation analysis using the Rat Methyl-Seq DMR Capture kit (Agilent) and Illumina NexteraXT sequencing protocol. Results Differentially methylated cytosine residues were observed within and at the promoter regions of a large amount of olfactory receptor, taste receptor, oral-irritation, and gustatory signal transduction genes. Detailed examination of the methylation patterns of oro-sensory genes revealed interesting features of alternation. We also tested the ability of Partial Least Squares Discriminant Analysis (PLS-DA) to identify specific cytosine residues that could separate the two groups of ET and FCL prenatal-exposed rats. This indicated that cytosine resides with the most distinguishing power appeared to be located in close proximity to each other, corroborating the Runs test results. Thus, prenatal ET exposure could lead to the formation of cis-acting methylation blocks that strongly regulate or coordinate the expression of chemosensory-related genes, and fundamentally alter taste perception and taste preferences. Furthermore, pathway analysis revealed enrichment of genes involved in signal transduction pathways and epigenetic modification pathways, including genes such as Grm3, S1pr1, Prkacb, Hdac7 and Kcnmb4. Discussion Our results are the first evidences indicating that in addition to central nerves system effects, fetal alcohol exposure induced alcohol preference in later life could also be produced by altered patterns of DNA methylation in the peripheral gustatory system, via dysregulated expression of oro-sensory-related genes.