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Programmed suppression of oxidative phosphorylation and mitochondrial function by gestational alcohol exposure correlate with global increases in H3K9me2 that do not suppress transcription

ABSTRACT: Purpose: A critical question emerging in the field of developmental toxicology is whether alterations in chromatin structure induced by toxicant exposure control patterns of gene expression or instead are structural changes that arise due to a nuclear stress response. Previously, we used a mouse model to conduct a three-way comparison between control offspring, alcohol-exposed but phenotypically normal animals, and alcohol-exposed offspring exhibiting craniofacial and central nervous system structural defects.In the cerebral cortex of animals exhibiting alcohol-induced dysgenesis, we identified a dramatic increase in the enrichment of dimethylated histone H3, lysine 9 (H3K9me2) within the regulatory regions of key developmental factors driving histogenesis in the brain. Whether this change in chromatin structure is causally involved in the development of structural defects remains unknown. Methods: We isolated total RNA from the GD17 cortex using the RNeasy Plus Mini Kit (catalog # 74134, Qiagen) according to the manufacturer's instructions. Before RNASeq library preparation, we randomized samples and generated sequencing libraries using the TruSeq RNA Sample Preparation kit (catalog # RS-122-2001, Illumina). We sequenced pooled samples using an Illumina HiSeq 2500 at Whitehead Genomic Services (Cambridge, MA). The sequencing data were demultiplexed, aligned using STAR with default parameters (Dobin et al., 2013), and referenced against the Mus musculus genome (UCSC version mm10). Results: To identify transcriptional differences distinguishing affected fetuses from unaffected offspring, we returned to our previously published, early gestational binge model of maternal alcohol exposure (Veazey et al., 2015). Here, dams were intraperitoneally administered injections of either vehicle or alcohol on gestational-day seven. On gestational-day 17 (GD17), stage-matched control and alcohol- exposed fetuses were dissected and scored for both ocular and craniofacial congenital defects. After determining the sex of each fetus using PCR analysis targeting the Y-chromosome, we found that the majority of affected samples (13/17; 76%) were female. We then isolated RNA from the GD17 fetal cortex of three (n=3) control, EtOH-exposed unaffected, and EtOH-exposed affected offspring and conducted deep-sequencing analysis of the cortex transcriptome. Our sequencing analyses identified a small number (88) of differentially expressed transcripts between the control and unaffected samples. In contrast, comparisons between control and affected, as well as unaffected and affected, identified 876 (412 downregulated, 522 upregulated) and 2281 (1432 downregulated, 1041 upregulated) differentially expressed genes, respectively Conclusions: Alterations in the genetic pathways regulating oxidative phosphorylation and mitochondrial dysfunction distinguish alcohol-exposed affected vs. unaffected offspring.

ORGANISM(S): Mus musculus

PROVIDER: GSE163300 | GEO | 2021/03/31

REPOSITORIES: GEO

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Project description:Adolescent binge alcohol exposure has been previously shown to have long-lasting effects on the expression of hypothalamic genes that regulate the stress response, even in the absence of subsequent adult alcohol exposure. Those data suggested that alcohol can induce permanent gene expression changes, potentially through epigenetic modifications. Importantly, epigenetic modifications can be transmitted to future generations therefore, in these studies we investigated the effects of adolescent binge alcohol exposure on hypothalamic gene expression patterns in the F1 generation offspring. It has been well documented that maternal alcohol exposure during fetal development can have devastating neurological consequences. However, less is known about the consequences of maternal and/or paternal alcohol exposure outside of the gestational time frame. Here, we exposed adolescent male and female rats to a repeated binge EtOH exposure paradigm and then mated them in adulthood. Hypothalamic samples were taken from the offspring of these animals at postnatal day (PND) 7 and subjected to a genome-wide microarray analysis followed by qRT-PCR for selected genes. Importantly, the parents were not intoxicated at the time of mating and were not exposed to EtOH at any time during gestation therefore, the offspring were never directly exposed to EtOH. Our results showed that the offspring of alcohol-exposed parents had significant differences in the expression of hypothalamic genes that mediate neurogenesis and synaptic plasticity during neurodevelopment, genes important for directing chromatin remodeling, posttranslational modifications or transcription regulation, as well as genes involved in regulation of obesity and reproductive function. These data demonstrate that repeated binge alcohol exposure during pubertal development can potentially have detrimental effects on future offspring even in the absence of direct fetal alcohol exposure. Male and female Wistar rats were purchased from Charles River Laboratories (Wilmington, MA) at weaning (postnatal day (PND) 23) and allowed to acclimate for 7 days after arrival. Animals were handled for 5 min./once/day beginning at PND 30. Pubertal EtOH exposure began on PND 37, which is defined as peri-puberty. Animals were undisturbed following the first exposure of our binge EtOH exposure paradigm until PND 68 (late puberty/early adult) at which time they received a second exposure to the same treatment paradigm. During the duration of the experiment, males and females were separately housed in pairs on a 12:12 light/dark cycle with lights on at 0700 h with food and water available ad libitum. Binge Exposure Paradigm and Treatment Design. Rats were handled 5min./once/day for 7 d prior to treatment to control for nonspecific stress responses. At 37 d, animals were given 3 g/kg EtOH (20% v/v in tap water; N = 3/sex), or tap water alone (N = 3/sex), once/day via oral gavage at 10:00 AM to avoid disrupting normal feeding patterns. This process was repeated according to the following schedule for a total duration of 8 consecutive days: 3 d EtOH, 2 d tap water, 3 d EtOH. Control animals were given tap water alone once/day for 8 consecutive days. Our previous studies showed that this repeated binge-pattern EtOH paradigm does not affect body weight/growth curves and consistently results in blood alcohol concentrations (BAC) of 150-180 mg/dl in males and 210-240 mg/dl in females. We and others have previously used this paradigm as a model for the pattern of binge alcohol consumption observed in adolescents and BAC achieved are similar to those observed in humans following a binge drinking episode . After peri-pubertal treatments, animals were left undisturbed in their home cage until PND 68 when each group was again exposed to their respective treatment (i.e. control or binge EtOH. We waited 24 hours after the last dose of EtOH to ensure that blood alcohol concentrations in the parents were undetectable at the time of mating (data not shown). Animals were grouped into mating pairs: binge male + binge female (N = 3 pairs); water male + water female (N = 3 pairs). All of the females gave birth to 12-16 pups approximately 28 d after being housed with a male, indicating that conception took place approximately 6 d after pairing; therefore, the pups were never directly exposed to alcohol at any time. At PND 7 pups were deeply anesthetized on ice and sacrificed. Brains were rapidly removed, the hypothalamus microdissected on ice, and then stored in -80ºC until further processing for a genome-wide analysis on hypothalamic total RNA samples using a chip-based microarray (Southern California Genotyping Consortium, SCGC, Illumina Rat Ref-12). The PND 7 time point was chosen because the extent of rat neurodevelopment at PND 7 is roughly equivalent to that of a human infant at birth

Project description:Background Maternal consumption of alcohol during pregnancy is associated with a range of physical, cognitive and behavioural outcomes in the offspring which are collectively called fetal alcohol spectrum disorders. We and others have proposed that epigenetic modifications, such as DNA methylation and post-translational histone modifications, mediate the effects of prenatal alcohol exposure on gene expression and, ultimately, phenotype. Here we use an inbred C57BL/6J mouse model of early gestational ethanol exposure equivalent, developmentally, to the first 3-4 weeks of pregnancy in humans to examine the long-term effects on gene expression and epigenetic state in the hippocampus. Results Gene expression analysis in the hippocampus revealed sex- and age-specific up-regulation of solute carrier family 17 member 6 (Slc17a6), which encodes vesicular glutamate transporter 2 (VGLUT2). Transcriptional up-regulation correlated with decreased DNA methylation and enrichment of histone H3 lysine 4 trimethylation, an active chromatin mark, at the Slc17a6 promoter. In contrast to Slc17a6 mRNA levels, hippocampal VGLUT2 protein levels were significantly decreased in adult ethanol-exposed offspring, suggesting an additional level of post-transcriptional control. MicroRNA expression profiling in the hippocampus identified four ethanol-sensitive microRNAs, of which miR-467b-5p was predicted to target Slc17a6. In vitro reporter assays showed that miR-467b-5p specifically interacted with the 3’ UTR of Slc17a6, suggesting that it contributes to the reduction of hippocampal VGLUT2 in vivo. A significant correlation between microRNA expression in the hippocampus and serum of ethanol-exposed offspring was also observed. Conclusions Prenatal ethanol exposure has complex transcriptional and post-transcriptional effects on Slc17a6 (VGLUT2) expression in the mouse hippocampus. These effects are observed following a relatively moderate exposure that is restricted to early pregnancy, modelling human consumption of alcohol before pregnancy is confirmed, and are only apparent in male offspring in adulthood. We propose that altered epigenetic and microRNA-mediated regulation of glutamate neurotransmission in the hippocampus contributes to the cognitive and behavioural phenotypes observed in fetal alcohol spectrum disorders. Our findings also support the idea that circulating microRNAs could be used as biomarkers of early gestational ethanol exposure and/or hippocampal dysfunction.

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Programmed suppression of oxidative phosphorylation and mitochondrial function by gestational alcohol exposure correlate with global increases in H3K9me2 that do not suppress transcription

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