Ethanol Induces Epigenetic Modulation of Prodynorphin and Pronociceptin Gene Expression in the Rat Amygdala Complex

Abstract

Several studies demonstrated the role of the endogenous opioid system in the development of susceptibility to alcohol dependence. Recently, we reported that binge intragastric administration of ethanol induces selective alterations of pronociceptin and prodynorphin gene expression in the rat amygdala complex depending on the days of exposures and on the development of tolerance and dependence. The aim of the present study was to investigate the potential epigenetic mechanisms leading to these alcohol-induced changes in gene expression. Specific histone modifications and DNA methylation at opioid peptide precursor promoters were analyzed by chromatin immunoprecipitation and real-time methylation-specific PCR, respectively. We found a linkage between gene expression alterations and epigenetic modulation at pronociceptin and prodynorphin promoters following alcohol treatment. In animals treated for 1 day, we observed a reversed correlation, with a decrease of histone 3 lysine 27 trimethylation (repressive mark) and an increase of histone 3 lysine 9 acetylation (activating mark), associated with both gene expression up-regulation. In rats treated with alcohol for up to 5 days, we found an increase in histone 3 lysine 9 acetylation in the pronociceptin promoter providing further evidence of the already proposed possible role for histone deacetylases for addiction treatment. No significant alterations in DNA methylation and histone 3 lysine 4 trimethylation following different alcohol exposures were present, suggesting the selectivity of epigenetic effects induced by alcohol. These data demonstrate that ethanol induces selective epigenetic changes, thus better defining the role of opioid peptides in the ethanol-induced effects in the amygdala complex.

DNA Methylation, Substance Use and Addiction: a Systematic Review of Recent Animal and Human Research from a Developmental Perspective

“…Tissue-and gene-specific DNAm alterations were identified by one study in folate-regulating genes [27]. Finally, no associations were found in opioid-related genes Pdny and Pnoc in the rat amygdala [28], as well as imprinting-control genes H19 and Rasgfl in mouse sperm [14].…”

“…Furthermore, hypermethylation of the serotonin receptor 3A (HTR3A) was identified in relation to alcohol exposure across both humans [42] and rodents [23]. Finally, a null association between alcohol exposure and methylation in the opioid signaling genes PDNY and PNOC was reported in human blood [42] and brain tissue in rats [28]. Despite these consistent findings, it is noteworthy that genes investigated by candidate studies did not typically converge with those identified by studies using hypothesis-free, epigenome-wide analyses.…”

Stable Histone Methylation Changes at Proteoglycan Network Genes Following Ethanol Exposure

“…Studies of patients with alcohol dependence have identified ethanol-induced changes to histone modifications in the brain (Zhou et al, 2011; Ponomarev et al, 2012). In the rat amygdala, acute ethanol increases global and prodynorphin and pronociceptin promoter histone acetylation levels (Pandey et al, 2008; D’Addario et al, 2013), and reduces prodynophin and pronociceptin H3K27me3 binding (D’Addario et al, 2013). Moreover, in the hippocampus, ethanol-induced histone H3 acetylation and H3K4me3 have been found to regulate expression of brain derived neurotrophic factor (BDNF) exons (Stragier et al, 2015).…”

Antagonism of κ opioid receptor in the nucleus accumbens prevents the depressive-like behaviors following prolonged morphine abstinence

“…There is increasing evidence showing that activation of κ opioid receptor produces depressive-like disorders in human and rodents [12][13][14][15][16][17][18][19], whereas blockade of κ opioid receptor produces antidepressive-like effects [20][21][22][23]. Chronic exposure to cocaine, morphine, heroin and alcohol have been shown to be associated with increased dynorphins expression in different brain regions, such as striatum, NAc and amygdala, and potentiated endogenous signaling through κ opioid receptor [24][25][26][27][28][29][30].…”