Ethanol-Induced Effects of the Microtranscriptome on Natural Gene Expression

Abstract

Reliable, minimally invasive biomarkers that predict the extent of alcoholism-induced CNS damage are currently lacking. This limits the selection of rational interventions and hampers the ability to gauge therapeutic effects. Developing biomarkers that indicate early CNS damage may prove useful in deterring the emergence of alcohol use disorders (AUDs). Extracellular microRNAs (miRNAs) can be informative molecular indicators of neuronal gene expression alterations. They repress large fractions of protein-coding genes and are highly-involved in intercellular signaling between both proximal and distal neurons. This work has focused on (1) examining whether extracellular miRNAs in the serum of individuals diagnosed with AUDs can be used as biomarkers of alcohol-induced brain damage, (2) determining in vivo the ethanol-inducedeffects imparted by miRNAs and their targets in the brain, (3) evaluating their role ininterventions that can reverse behavioral impairment and (4) testing the ability of extracellular miRNAs to transfer ethanol-induced pathologies to ethanol-naive cells. There are five major findings from this work. First, two independent quantification technologies demonstrated comparable differences in miRNA expression levels betweenAUDs and controls and revealed significant correlations between candidate miRNA biomarkers and medical, neuroimaging and drinking parameters. Second, in rats manymiRNAs significantly altered by ethanol in the hippocampus following maternal or postnatal exposure were also changed in the serum. Moreover, postnatal consumption activated cell-cycle pathways in the hippocampus while maternal exposure affected unfolded protein response pathways in adolescent offspring. Third, the lack of social motivation seen following fetal exposure was reversed as a result of social enrichment. Analysis of the integrated data in the amygdala and ventral striatum revealed several functional gene networks whose activation patterns following fetal ethanol exposure were reversed by social enrichment. Fourth, transfer of purified exosomes from ethanol-exposed to ethanol-naive cells conferred many gene expression changes consistent with ethanol exposure. Lastly, examination of all the data revealed consistent changes in miRNAs that independently converged on cell death, cell proliferation and cell cycle regulatory processes, regardless of the species, paradigm and source. The findings in this work illustrate the utility of miRNAs as peripheral biomarkers of AUDs and suggest novel epigenetic mechanisms affected by alcohol.