Prefrontal cortex expression of chromatin modifier genes in male WSP and WSR mice changes across ethanol dependence, withdrawal, and abstinence

Abstract

Alcohol-use disorder (AUD) is a relapsing disorder associated with excessive ethanol consumption. Recent studies support the involvement of epigenetic mechanisms in the development of AUD. Studies carried out so far have focused on a few specific epigenetic modifications. The goal of this project was to investigate gene expression changes of epigenetic regulators that mediate a broad array of chromatin modifications after chronic alcohol exposure, chronic alcohol exposure followed by 8 h withdrawal, and chronic alcohol exposure followed by 21 days of abstinence in Withdrawal-Resistant (WSR) and Withdrawal Seizure-Prone (WSP) selected mouse lines. We found that chronic vapor exposure to highly intoxicating levels of ethanol alters the expression of several chromatin remodeling genes measured by quantitative PCR array analyses. The identified effects were independent of selected lines, which, however, displayed baseline differences in epigenetic gene expression. We reported dysregulation in the expression of genes involved in histone acetylation, deacetylation, lysine and arginine methylation and ubiquitination, and in DNA methylation during chronic ethanol exposure and withdrawal, but not after 21 days of abstinence. Ethanol-induced changes are consistent with decreased histone acetylation and with decreased deposition of the permissive ubiquitination mark H2BK120ub, associated with reduced transcription. On the other hand, ethanol-induced changes in the expression of genes involved in histone lysine methylation are consistent with increased transcription. The net result of these modifications on gene expression is likely to depend on the combination of the specific histone tail modifications present at a given time on a given promoter. Since alcohol does not modulate gene expression unidirectionally, it is not surprising that alcohol does not unidirectionally alter chromatin structure toward a closed or open state, as suggested by the results of this study.

Stable Histone Methylation Changes at Proteoglycan Network Genes Following Ethanol Exposure

“…Total RNA was isolated using RNA STAT-60 (Tel Test Inc., Friendswood, TX, United States) with genomic DNA removal using the DNA-Free RNA Kit (Zymo Research) as described previously (Hashimoto et al, 2017) and RNA integrity was determined using a 1% agarose gel stained with SYBR Gold (Thermo Fisher Scientific, Waltham, MA, United States) and quantitated by UV spectroscopy.…”

Affective Behavior in Withdrawal Seizure–Prone and Withdrawal Seizure–Resistant Mice during Long‐Term Alcohol Abstinence

“…Interestingly, these selected lines have been tested for differences on various other EtOH‐related phenotypes, with mixed results. For example, although WSP and WSR mice show differences in the Drinking‐in‐the‐Dark paradigm (Crabbe et al., ) and exhibit differentially altered prefrontal cortical gene expression during forced abstinence (Hashimoto et al., , ; Wilhelm et al., ), they do not significantly differ in free‐choice EtOH drinking, operant EtOH self‐administration, or expression of the alcohol deprivation effect (ADE; Ford et al., ; Crabbe et al., ; Rosenwasser et al., ). Currently, however, nothing is known regarding possible persistent withdrawal‐associated affective disruptions in these selected lines.…”

Epigenetic mediators and consequences of excessive alcohol consumption

“…In this special issue on epigenetics, Cervera-Juanes, Wilhelm, Park, Grant, & Ferguson (this issue) show that within the nucleus accumbens core, which is involved in neurocircuitry for intoxication and withdrawal, chronic low level drinking results in DNA hypomethylation, and high levels of drinking result in hypermethylation. In the prefrontal cortex, which is involved in neurocircuitry for craving, Hashimoto, Gavin, Wiren, Crabbe, and Guizzetti (this issue) show altered gene expression for proteins needed for histone and DNA epigenetic modification creation and maintenance, and they show that ethanol withdrawal has a larger effect on gene expression than ethanol exposure or abstinence. Interestingly, Hashimoto et al show that covalent modifications may act in opposition, with altered transcript expression of epigenetic modifiers that lead to open and closed chromatin conformations.…”

“…The studies outlined here show how alcohol exposure can affect the epigenome, from AUDs, to prenatal alcohol exposure, to cross-generational effects. More work is needed to understand the interaction of all the methods of epigenetic modifications, including less commonly explored factors such as histone phosphorylation, arginine methylation (see Hashimoto et al, this issue), ubiquitination, sumoylation, citrullination, ADP-ribosolyation, as well as the dynamics of DNA methylation removal through 5-hydroxymethyl cysteine. Additionally, the interactions of long non-coding RNAs in normal neuronal development in disease are just beginning to be discovered and will provide an extra layer of complexity to gene expression regulation (Fatica & Bozzoni, 2014; Wapinski & Chang, 2011).…”