Adolescent Alcohol Exposure Epigenetically Suppresses Amygdala Arc Enhancer RNA Expression to Confer Adult Anxiety Susceptibility
Adolescent intermittent ethanol (AIE) exposure is an emerging risk factor for adult psychopathology, such as anxiety disorders. Enhancer RNAs (eRNAs) are short noncoding RNAs transcribed from enhancer regions that regulate synaptic plasticity–associated gene expression, including Arc, but their role in AIE-induced susceptibility to anxiety in adulthood is unknown.
Rats were exposed to AIE (ethanol exposure 2 days on/off) or intermittent normal saline during postnatal days 28 to 41 and allowed to grow to adulthood for analysis of behavior and biochemical measures. Some AIE rats and rats with intermittent normal saline exposure were exposed to an acute challenge with ethanol in adulthood. Cohorts of alcohol-naïve adult rats were cannulated in the central nucleus of amygdala and infused with either Kdm6b small interfering RNA or an antisense locked nucleic acid oligonucleotide specific to Arc eRNA before behavioral and biochemical analysis.
AIE adult rats displayed heightened anxiety and decreased Arc eRNA expression, which is regulated epigenetically through decreased Kdm6b expression. This triggered condensed chromatin at the synaptic activity response element site and promoter of the Arc gene, facilitating increased negative elongation factor binding to the Arc promoter and decreasing Arc expression in the amygdala. Knockdown of Kdm6b or Arc eRNA expression in the central nucleus of amygdala provoked anxiety in alcohol-naïve adult rats and recapitulated the molecular and epigenetic phenotypes of AIE.
These data suggest that eRNA regulation via epigenetic reprogramming in the amygdala, particularly at the Arc synaptic activity response element site, contributes to adult anxiety after adolescent alcohol exposure.
In essence the study shows that alcohol use during adolescence can modify gene expression in the brain, leading to susceptibility to anxiety and alcohol abuse in adulthood.
The researchers in the study investigated the impact of alcohol on the microRNA within the amygdala of rats. They administered alcohol to the adolescent rats and measured the changing levels of a specific microRNA known as miR-137. The levels of miR-137 were found to increase in rats who consumed alcohol.
This increment in the microRNA led to a lower expression of the proteins fundamental to the development of healthy neuron growth and branching. Further to this, in adulthood, these rats demonstrated a marked increase in anxious behaviors in comparison to control rats, as well as an increased preference for alcohol.
Researchers then inhibited miR-137 in the amygdala and found that the anxious behaviors and alcohol preference reduced, showing that the detrimental impact of adolescent alcohol consumption was reversible through amending its impact on the microRNA.
The study has implications for potential new therapies for both anxiety disorder, alcohol abuse problems, and potentially other mental health disorders.