Ethanol induced acetylation of histone at G9a exon1 and G9a-mediated histone H3 dimethylation leads to neurodegeneration in neonatal mice

Abstract

The transient exposure of immature rodents to ethanol during postnatal day 7 (P7), comparable to a time point within the third trimester of human pregnancy, induces neurodegeneration. However, the molecular mechanisms underlying the deleterious effects of ethanol on the developing brain are poorly understood. In our previous study, we showed that a high dose administration of ethanol at P7 enhances G9a and leads to caspase-3-mediated degradation of dimethylated H3 on lysine 9 (H3K9me2). In this study, we investigated the potential role of epigenetic changes at G9a exon1, G9a-mediated H3 dimethylation on neurodegeneration and G9a-associated proteins in the P7 brain following exposure to a low dose of ethanol. We found that a low dose of ethanol induces mild neurodegeneration in P7 mice, enhances specific acetylation of H3 on lysine 14 (H3K14ace) at G9a exon1, G9a protein levels, augments the dimethylation of H3K9 and H3 lysine 27 (H3K27me2). However, neither dimethylated H3K9 nor K27 underwent degradation. Pharmacological inhibition of G9a activity prior to ethanol treatment prevented H3 dimethylation and neurodegeneration. Further, our immunoprecipitation data suggest that G9a directly associates with DNA methyltransferase (DNMT3A) and methyl-CpG-binding protein 2 (MeCP2). In addition, DNMT3A and MeCP2 protein levels were enhanced by a low dose of ethanol that was shown to induce mild neurodegeneration. Collectively, these epigenetic alterations lead to association of G9a, DNMT3A and MeCP2 to form a larger repressive complex and have a significant role in low dose ethanol-induced neurodegeneration in the developing brain.

Ethanol deregulates Mecp2/MeCP2 in differentiating neural stem cells via interplay between 5-methylcytosine and 5-hydroxymethylcytosine at the Mecp2 regulatory elements

“…Therefore, our observations on ethanol withdrawal downregulating Mecp2/MeCP2 expression is in agreement with several other reports where prenatal ethanol exposure as well as preconception ethanol exposure (and subsequent withdrawal) led to decreased level of MeCP2 in a brain region-specific manner Kim et al, 2013Kim et al, , 2014Perkins et al, 2013). Comparing our data with previous reports that were earlier mentioned in the introduction (Bekdash et al, 2013;Chen et al, 2013;Gangisetty et al, 2014;Guo et al, 2012;Kim et al, 2013Kim et al, , 2014Perkins et al, 2013;Subbanna et al, 2014;Tunc-Ozcan et al, 2013), it is possible that the effect of ethanol on Mecp2/MeCP2 expression is influenced by multiple factors. This could include the type of ethanol treatment (binge exposure, continuous exposure and withdrawal), amount or concentration of ethanol, type of rodent model used in the study (mouse or rats), developmental stage (different embryonic time points or adult), brain regions and cell types within a certain brain region (specific neuronal subtype).…”

“…The discrepancies in these studies regarding the effect of ethanol on MeCP2 expression could be attributed to multiple factors such as the model of study (in vivo animal models or in vitro cultured cells), stage of embryonic development, specific brain region or cell type within a brain region, concentration and duration of ethanol treatment (Bekdash et al, 2013;Chen et al, 2013;Gangisetty et al, 2014;Guo et al, 2012;Kim et al, 2013Kim et al, , 2014Perkins et al, 2013;Subbanna et al, 2014;Tunc-Ozcan et al, 2013). Further supporting the role of MeCP2 in alcoholism, a recent study demonstrated the regulatory effect of MeCP2 on sensitivity to ethanol and drinking ethanol (Repunte-Canonigo et al, 2014).…”

Epigenetic Modifications, Alcoholic Brain and Potential Drug Targets

“…Furthermore, in a study, histone acetylation was found to play a crucial role in regulating the transcriptional activity and contribute to the drug-induced alterations in gene expression and behavior. Similarly, a study found that ethanol treatment upregulates the HAT activity in adolescent prefrontal cortex and increases histone (H3 or H4) acetylation of the promoter region of genes cFos, Cdk5, and FosB [53] . Gene expression studies provide further evidence on the role of histone acetylation in alcoholism.…”

“…In a recent study, intermittent alcohol treatment altered methylation in the promoter region of cFos, Cdk5, FosB, and BDNF genes [53] . These genes were previously found to be associated with behavioral abnormalities characterizing drug addiction [54,55] .…”

“…Alcohol-induced alterations in histone acetylation are studied in the expression of several genes, including CBP, NPY [65] , FosB [53] , NR2B [69] , pronociceptin, and prodynorphin [70] . Both the amygdaloid pCREB and CBP levels are notably raised by acute ethanol exposure and decreased in rats undergoing withdrawal after chronic ethanol exposure.…”