Repeated vapor ethanol exposure induces transient histone modifications in the brain that are modified by genotype and brain region

Abstract

Background: Emerging research implicates ethanol (EtOH)-induced epigenetic modifications in regulating gene expression and EtOH consumption. However, consensus on specific epigenetic modifications induced by EtOH has not yet emerged, making it challenging to identify mechanisms and develop targeted treatments. We hypothesized that chronic intermittent EtOH (CIE) induces persistent changes in histone modifications across the cerebral cortex (CCx), nucleus accumbens (NAc), and prefrontal cortex (PFC), and that these histone modifications are altered in a knock-in mouse strain with altered sensitivity to EtOH.Methods: C57BL/6J (B6) mice and α1SHLA knockin mice on a B6 background were exposed to 16 h of vapor EtOH or room air followed by 8 h of room air for 4 consecutive days and sacrificed at multiple time points up to 72 h following exposure. Histone modifications were assessed using Western blot and dot blot. RT-qPCR was used to study expression of chromatin modifying enzymes in NAc and PFC.Results: In NAc, CIE significantly increased acetylation of histone subunit H3 at lysine 9 (H3K9ac) but not lysine 14 (H3K14ac) or lysine 27 (H3K27ac). In PFC, CIE significantly increased H3K9ac but not H3K14 or H3K27ac. There were no significant changes at 8 or 72 h after EtOH exposure in either NAc or PFC. CIE was also associated with increased expression of Kat2b, Kat5, and Tet1 in NAc but not PFC. In CCx, CIE had a significant effect on levels of H3K18ac; there was also a significant effect of the α1SHLA mutation on levels of H3K27me3, H3K14ac, and H3K18ac as well as a trend for H3S10pK14ac.Conclusions: The EtOH-induced histone modifications observed were transient and varied significantly between brain regions. A genetic mutation that altered sensitivity to EtOH was associated with altered induction of histone modifications during CIE. These results have implications for studying EtOH-induced histone modifications and EtOH sensitivity.

Disconnect between alcohol-induced alterations in chromatin structure and gene transcription in a mouse embryonic stem cell model of exposure

“…For example, work from a number of laboratories have demonstrated both acute and long-term EtOH exposures influence patterns of DNA methylation (Ungerer et al, 2013). Further, our group and others have reported persistent alterations in post-translational histone modifications both in vitro and in vivo (Bekdash, Zhang & Sarkar, 2013; Finegersh et al, 2015; Govorko, Bekdash, Zhang & Sarkar, 2012; Moonat, Sakharkar, Zhang, Tang & Pandey, 2013; Pal-Bhadra et al, 2007; Pan et al, 2014; Subbanna & Basavarajappa, 2014; Veazey, Carnahan, Muller, Miranda & Golding, 2013; Veazey, Parnell, Miranda & Golding, 2015; Zhang, Ho, Vega, Burne & Chong, 2015). Collectively, these published studies suggest alcohol has the capacity to induce alterations in chromatin structure and that in select instances, these changes are heritable through cell division, persist well beyond the initial encounter, and have the potential to contribute to the genesis of FASD birth defects.…”

“…For example, work examining the consequences of EtOH exposure in adult hepatocytes reported significant increases in H3K9me2 during the exposure phase while similar studies in cortical neuronal cultures observed an increase in H3K9ac and a loss of H3K9me2 (Pal-Bhadra et al, 2007; Qiang, Denny, Lieu, Carreon & Li, 2011). Similarly, in a chronic intermittent in vivo model of exposure, EtOH increased H3K9ac within the nucleus accumbens and prefrontal cortex regions of the mouse brain (Finegersh et al, 2015). In contrast, we observe loss of H3K9ac during the exposure period and H3K9 hypermethylation during both the period of exposure, as well as the recovery phase.…”

DNA modifications in models of alcohol use disorders

“…In a mouse model of chronic intermittent alcohol exposure, TET1 mRNA expression was increased in the nucleus accumbens, but not in cortex, after 4 days of ethanol vapor (Finegersh et al, 2015b). DNA modifications were not measured in this study, but the change in TET1 implies possible downstream changes in 5mC and 5hmC.…”

Epigenetic mediators and consequences of excessive alcohol consumption

“…Yet, these data corroborate evidence of potential maladaptive hypomethylation, specifically of Grin2b , in the dorsal striatum, contributing to increased alcohol consumption (Wang et al, 2010; Wong, Tauck, Fong, & Kendig, 1998). Additionally, epigenetic markers have been shown to vary between brain regions (Finegersh et al, 2015) and can be further complicated by comorbid conditions, including stress (Meyer, Long, Fanselow, & Spigelman, 2013; Moonat & Pandey, 2012; reviewed in Palmisano & Pandey, this issue). …”