Differential potassium channel gene regulation in BXD mice reveals novel targets for pharmacogenetic therapies to reduce heavy alcohol drinking

Abstract

Alcohol (ethanol) dependence is a chronic relapsing brain disorder partially influenced by genetics and characterized by an inability to regulate harmful levels of drinking. Emerging evidence has linked genes that encode KV7, KIR, and KCa2 K+ channels with variation in alcohol-related behaviors in rodents and humans. This led us to experimentally test relations between K+ channel genes and escalation of drinking in a chronic intermittent ethanol (CIE) exposure model of dependence in BXD recombinant inbred strains of mice. Transcript levels for K+ channel genes in the prefrontal cortex (PFC) and nucleus accumbens (NAc) covary with voluntary ethanol drinking in a non-dependent cohort. Transcripts that encode KV7 channels covary negatively with drinking in non-dependent BXD strains. Using a pharmacological approach to validate the genetic findings, C57BL/6J mice were allowed intermittent access to ethanol to establish baseline consumption before they were treated with retigabine, an FDA-approved KV7 channel positive modulator. Systemic administration significantly reduced drinking, and consistent with previous evidence, retigabine was more effective at reducing voluntary consumption in high-drinking than low-drinking subjects. We evaluated the specific K+ channel genes that were most sensitive to CIE exposure and identified a gene subset in the NAc and PFC dysregulated in the alcohol-dependent BXD cohort. CIE-induced modulation of nine genes in the NAc and six genes in the PFC covaried well with the changes in drinking induced by ethanol dependence. Here we identified novel candidate genes in the NAc and PFC that are regulated by ethanol dependence and correlate with voluntary drinking in non-dependent and dependent BXD mice. The findings that Kcnq expression correlate with drinking and that retigabine reduces consumption suggest that KV7 channels could be pharmacogenetic targets to treat individuals with alcohol addiction.

Promising Pharmacogenetic Targets for Treating Alcohol Use Disorder: Evidence from Preclinical Models

“…And finally, an SNP in the KCNMA1 gene, which encodes the α1 subunit of K Ca 1.1 was significantly associated with the develop ment of alcohol dependence [89,90] and subjective response to alcohol [107]. These associations are sup ported by experimental evidence showing a negative correlation between Kcnma1 and alcohol consump tion [76] and a role for this gene in the development of tolerance [108][109][110]. Given that many of these K + channel genes are altered in postmortem brain tissue from alco holics (Table 2) [78,103,111], further preclinical research into the potential involvement of K V 2.1/2, K V 4.1 and K Ca 1.1 in regulating alcohol consumption is warranted, but will require better pharmacological tools.…”

“…Additionally, transcript levels of the gene encoding the K V 2.1 chan nel protein, KCNB1, was increased in hippo campus from alcoholic postmortem brain [103], and expression of both KCNB1 and KCNB2 in the superior frontal gyrus were strongly associated with lifetime drinking in alcoholics [78]. In a preclinical model, expression of Kcnb1 in the nucleus accumbens correlated nega tively with alcohol intake in BXD mice [76], indicat ing a potential role of the KCNB family in regulating alcohol consumption across species. Another voltage gated K + channel identified through GWAS explora tion was KCND2 that encodes for the K V 4.2 channel that regulate rapidly inactivating Atype K + current (I A ).…”

“…Images were acquired with permission from [79] and subsequently modified. Promising pharmacogenetic targets for treating alcohol use disorder: evidence from preclinical models Review ferential expression of Kcnq5 across strains negatively correlated with drinking, further implicating this family of K + channels in regulating alcohol drink ing [76]. Using whole genome sequencing, a recent study reported that Kcnq5 was differentially expressed between low and high alcohol drinking rat lines [85], and multiple reports identify transcript changes in the KCNQ family of genes in alcoholic brain and pre clinical models (Table 2).…”

“…However, in support of the evidence linking KCNQ and alcoholism, SNPs associated with human alcohol consumption have also been reported in KCNQ1 and KCNQ5 [89,90]. To test the viability of the Kcnq family of genes as a pharmacogenetics target, several preclinical studies have demonstrated that sys temic administration of the K V 7 channel opener, reti gabine, significantly reduces alcohol consumption in both rats and mice [74,76,91], and is most efficacious in those that display a heavy drinking phenotype [74,76]. What is particularly encouraging about these stud ies is that retigabine is already US FDA approved to treat epileptic disorders and is welltolerated in the clinical population, and while there is some evidence that alcohol alters pharmacokinetics of retigabine in moderate drinkers, it did not alter the pharmaco dynamics measures or the adverse effects of retiga bine [92].…”

“…All K + channels are responsible, in some respect, for stabilizing the membrane potential, stimulating repo larization and regulating neuronal excitability (see Figure 1) [67,68]. While better known for their role in epileptic disorders [68,69], a number of clinical and preclinical studies have identified a potential role for genetic variants in K + channel genes as mediators of alcohol consumption and dependence [70][71][72][73][74][75][76][77][78].…”