Epigenetic regulation of GABAergic neurotransmission and neurosteroid biosynthesis in alcohol use disorder.

BACKGROUND Alcohol use disorder (AUD) is a chronic relapsing brain disorder. GABAA receptor (GABAAR) subunits are a target for the pharmacological effects of alcohol. Neurosteroids play an important role in the fine-tuning of GABAAR function in the brain. Recently, we have shown that AUD is associated with changes in DNA methylation mechanisms. However, the role of DNA methylation in the regulation of neurosteroid biosynthesis and GABAergic neurotransmission in AUD subjects remain under-investigated. METHODS In a cohort of postmortem brains from 20 male controls and AUD subjects, we investigated the expression of GABAAR subunits and neurosteroid biosynthetic enzymes and their regulation by DNA methylation mechanisms. Neurosteroid levels were quantified by gas chromatography-mass spectrometry. RESULTS The α2 subunit expression was reduced due to increased DNA methylation at the gene promoter region in the cerebellum of AUD subjects, a brain area particularly sensitive to the effects of alcohol. Alcohol-induced alteration in GABAAR subunits was also observed in the prefrontal cortex. Neurosteroid biosynthesis was also affected with reduced cerebellar expression of the 18kDa translocator protein and 3α-hydroxysteroid dehydrogenase (3α-HSD) mRNAs. Notably, increased DNA methylation levels were observed at the promoter region of 3α-HSD. These changes were associated with markedly reduced levels of allopregnanolone and pregnanolone in the cerebellum. CONCLUSION Given the key role of neurosteroids in modulating the strength of GABAAR-mediated inhibition, our data suggest that alcohol-induced impairments in GABAergic neurotransmission might be profoundly impacted by reduced neurosteroid biosynthesis most likely via DNA hypermethylation.