Cross-species epigenetic regulation of nucleus accumbens KCNN3 transcript variants by excessive ethanol drinking and dependence

Abstract

The underlying genetic and epigenetic mechanisms driving functional adaptations in neuronal excitability and excessive alcohol intake are poorly understood. Given that small-conductance Ca 2+ -activated K + (KCa2 or SK) channels encoded by the KCNN family of genes have emerged from preclinical studies as a crucial target that contributes to heavy drinking and alcohol-induced functional neuroadaptations, we performed a cross-species analysis of KCNN3 methylation, gene expression, and polymorphisms of alcohol-drinking monkeys and alcohol dependent mice. Because of the alternative promoters in KCNN3, we analyzed expression of the different transcript variants that when translated influence surface trafficking and function of KCa2 channels. In heavy drinking rhesus macaques and alcohol dependent C57BL/6J mice, bisulfite sequencing analysis of the nucleus accumbens revealed a differentially methylated region in exon 1A of KCNN3 that overlaps with a predicted promoter sequence. The hypermethylation of KCNN3 in monkey and mouse accumbens paralleled an increase in expression of alternative transcript variants that encode apamin-insensitive and dominant-negative KCa2 channel isoforms. A polymorphic repeat in macaque KCNN3 encoded by exon 1 did not correlate with alcohol drinking. At the protein level, KCa2.3 channel expression in the accumbens was significantly reduced in very heavy drinking monkeys. Together, our cross-species findings on epigenetic dysregulation of KCNN3 by heavy alcohol drinking and dependence represent a complex mechanism that utilizes alternative promoters to impact firing of accumbens neurons. Thus, these results provide support for hypermethylation of KCNN3 by excessive alcohol drinking as a possible key molecular mechanism underlying harmful alcohol intake and alcohol use disorder.

Kcnn3 as a target for treating aberrant behaviors in stressed, ethanol-dependent mice

“…In addition, chronic ethanol exposure in rodents reduced KCa2 channel function and/or expression in the accumbens core, orbitofrontal cortex, medial prefrontal cortex, ventral hippocampus, and ventral tegmental area (36,47,(56)(57)(58), and KCNN2 expression was reduced in postmortem BLA and frontal cortex of individuals with AUD (59). In a recent study, heavy ethanol drinking and ethanol dependence hypermethylated exon 1A of KCNN3 and increased expression of apamin-insensitive and dominantnegative isoforms of KCa2.3 channels in the nucleus accumbens of mice and monkeys (60). Using the same bioinformatic analysis as was used for the BLA, accumbens expression of Kcnn2 or Kcnn3 was not enriched with correlations for anxiety-related phenotypes in BXD RI strains (data not show).…”