A role for histone acetylation mechanisms in adolescent alcohol exposure-induced deficits in hippocampal brain-derived neurotrophic factor expression and neurogenesis markers in adulthood

Abstract

Binge drinking during adolescence is a risk factor for neuropsychiatric disorders that can develop later in life. Histone acetylation is an important epigenetic mechanism that contributes to neurodevelopment. We investigated the effects of adolescent intermittent ethanol (AIE) exposure, as opposed to normal saline (AIS) exposure, on histone acetylation-mediated regulation of brainderived neurotrophic factor (BDNF) expression and developmental stages of neurogenesis (proliferating and immature neurons) in the hippocampus in adulthood. AIE exposure increased whole hippocampal histone deacetylase (HDAC) activity and decreased binding protein of cyclic adenosine monophosphate response element binding protein (CBP) and histone H3-K9 acetylation levels in the CA1, CA2, and CA3 regions of the hippocampus. BDNF protein and exon IV mRNA levels in the CA1 and CA3 regions of the hippocampus of AIE exposed adult rats were decreased as compared to AIS exposed adult rats. AIE induced anxiety-like behaviors and deficits in histone H3 acetylation at BDNF exon IV promoter in the hippocampus during adulthood, which were reversed by treatment with the HDAC inhibitor, trichostatin A (TSA). Similarly, neurogenesis was inhibited by AIE in adulthood as demonstrated by the decrease in Ki-67 and doublecortin (DCX)-positive cells in the dentate gyrus, which was normalized by TSA treatment. These results indicate that AIE exposure increases HDACs and decreases CBP levels that may be associated with a decrease in histone H3 acetylation in the hippocampus. These epigenetic changes potentially decrease BDNF expression and inhibit neurogenesis in the hippocampus that may be involved in AIE-induced behavioral abnormalities, including anxiety, in adulthood.

Adolescent alcohol exposure alters lysine demethylase 1 (LSD1) expression and histone methylation in the amygdala during adulthood

“…While acute ethanol exposure increased percent of open arm entries and percent time spent in the open arms in AIS adult rats (AIS+ EtOH) compared to normal saline-exposed (AIS+ Saline) rats ( p <0.01-0.001), AIE+ EtOH animals returned to baseline levels of anxiety-like behavior after acute ethanol challenge (Figure 6A). As reported earlier (Pandey et al, 2015; Sakharkar et al, 2016), here we also observed that AIE induced anxiety-like behaviors in adulthood. Closed arm entries were not significantly altered between groups, indicating no significant differences in general activity.…”

“…On PND 28-41, adolescent rats received 8 intraperitoneal (i.p.) injections of ethanol (2 g/kg, 20% w/v) or an equivalent dose of normal saline using a 2 days on-2 days off dosing schedule, similar to previous studies in other labs (Alaux-Cantin et al, 2013; Pascual et al, 2009) and our lab (Pandey et al, 2015; Sakharkar et al, 2016). Notably, the dose of ethanol used in this study was not sufficient to induce sedation, but instead produced anxiolytic–like behaviors in adolescent rats (Sakharkar et al, 2014).…”

“…Recent work in our lab has demonstrated that adolescent intermittent ethanol (AIE) exposure leads to increased histone deacetylase isoform 2 (HDAC2) expression, decreased histone H3 lysine 9 (H3K9) acetylation, and decreased expression of crucial synaptic plasticity genes such as brain-derived neurotrophic factor ( Bdnf ) and activity-regulated cytoskeletal protein ( Arc ), leading to decreased dendritic spine density in the central nucleus of the amygdala (CeA) and medial nucleus of the amygdala (MeA) in adulthood (Pandey et al, 2015). Notably, AIE-exposed rats display anxiety-like behaviors and increased alcohol consumption in adulthood compared to adolescent intermittent saline (AIS)-exposed control animals (Pandey et al, 2015; Sakharkar et al, 2016). …”

“…We also examined mRNA expression of LSD1-interacting proteins ( Jade2 , AR , and TLX ) and H3K9 demethylases ( Kdm4a , Kdm4c , Kdm4d , and Phf8 ) in the amygdala of AIE adults. It has been shown that Bdnf exon IV expression is regulated by epigenetic mechanisms in the brain (Moonat et al, 2013; Pandey et al, 2015; Roth et al, 2009; Sakharkar et al, 2016), and its expression is decreased in the amygdala after AIE in adulthood (Pandey et al, 2015). To gain insight into the pathogenesis of AIE-induced anxiety-like behaviors (Pandey et al, 2015), we exposed AIS and AIE animals to an acute ethanol challenge in adulthood prior to testing for anxiety-like behavior.…”

Adolescent binge ethanol exposure alters specific forebrain cholinergic cell populations and leads to selective functional deficits in the prefrontal cortex

“…AIE has been associated with dysfunction in key learning and memory structures in adult rodents. Although AIE leads to decreased neurogenesis within the hippocampus (Geil et al, 2014; Vetreno and Crews, 2015; Sakharkar et al, 2016), AIE’s detrimental effects on spatial memory are inconclusive (Risher et al, 2013; Swartzwelder et al, 2015; Beaudet et al, 2016). Following AIE, there is also a significant loss in the number of cholinergic neurons within the medial septum/diagonal band (MS/DB), which projects to the hippocampus, and the Nucleus basalis of Meynert (NbM) that projects to the cortex (Ehlers et al, 2011; Vetreno et al, 2014; Boutros et al, 2015).…”