Cross-species molecular dissection across alcohol behavioral domains

Abstract

This review summarizes the proceedings of a symposium presented at the "Alcoholism and Stress: A Framework for Future Treatment Strategies" conference held in Volterra, Italy on May 9-12, 2017. Psychiatric diseases, including alcohol-use disorders (AUDs), are influenced through complex interactions of genes, neurobiological pathways, and environmental influences. A better understanding of the common neurobiological mechanisms underlying an AUD necessitates an integrative approach, involving a systematic assessment of diverse species and phenotype measures. As part of the World Congress on Stress and Alcoholism, this symposium provided a detailed account of current strategies to identify mechanisms underlying the development and progression of AUDs. Dr. Sean Farris discussed the integration and organization of transcriptome and postmortem human brain data to identify brain regional- and cell type-specific differences related to excessive alcohol consumption that are conserved across species. Dr. Brien Riley presented the results of a genome-wide association study of DSM-IV alcohol dependence; although replication of genetic associations with alcohol phenotypes in humans remains challenging, model organism studies show that COL6A3, KLF12, and RYR3 affect behavioral responses to ethanol, and provide substantial evidence for their role in human alcohol-related traits. Dr. Rob Williams expanded upon the systematic characterization of extensive genetic-genomic resources for quantifying and clarifying phenotypes across species that are relevant to precision medicine in human disease. The symposium concluded with Dr. Robert Hitzemann's description of transcriptome studies in a mouse model selectively bred for high alcohol ("binge-like") consumption and a non-human primate model of long-term alcohol consumption. Together, the different components of this session provided an overview of systems-based approaches that are pioneering the experimental prioritization and validation of novel genes and gene networks linked with a range of behavioral phenotypes associated with stress and AUDs.

Keywords: Alcohol-use disorder; Co-expression networks; Genome-wide association study; RNA-Seq; Recombinant inbred mice; Species conservation; Systems biology; Transcriptome.

Figure 1.

COL6A3 results. A) LocusZoom plot of human COL6A3 GWAS signal. B) RNAi-induced gene knockdown of C16E9.1 reduced sensitivity to ethanol in C. elegans. C) Col6a3 mouse whole brain expression is significantly correlated with total handling induced convulsion (HIC) score (sum of baseline subtracted HIC at 4, 6 and 7 hrs after 4 g/kg intraperitoneal ethanol). D) Col6a3 mouse whole brain expression is negatively correlated with ethanol 2-bottle choice voluntary consumption.

Figure 2.

KLF12 results. A) LocusZoom plot of human KLF12 GWAS signal. B) Knockout of klf3, the C. elegans ortholog of KLF12, blocks the development of acute functional tolerance (AFT). C) Mouse basal Klf12 expression in prefrontal cortex (PFC) is significantly correlated with locomotor activity 0–5 minutes after 2.25 g/kg intraperitoneal ethanol. D) Mouse basal Klf12 expression in nucleus accumbens (Nac) is suggestively correlated with the development of acute functional tolerance (AFT).

Figure 3.

RYR3 results. A) LocusZoom plot of human RYR3 GWAS signal. B) Knockout of unc-1168, the single C. elegans ryanodine receptor gene, reduces initial sensitivity. C) Rapid tolerance was significantly reduced in RyR^d03686 homozygous flies and in RyR^{d03686/k04913} transheterozygous flies compared to w¹¹¹⁸ controls and RyR heterozygous animals (^#, Bonferroni multiple comparison, p<0.05). D) Dantrolene treatment (0, 0.9, 2.9 mg/kg IP) dose-dependently reduced the motivation to self-administer ethanol. Breakpoint was defined as the maximum number of presses completed on an exponential progressive ratio schedule for ethanol reinforcement. Data represent mean ± SEM, * p < 0.05, n = 12.

Figure 4.

Two massive CIE gene expression data sets are accessible at www.genenetwork.org. Left: Published Phase 1 CIE and control data includes RNA-seq assays of mRNA levels in the mesocorticolimbic region. Right: Phase 2 (unpublished but accessible data by Mulligan and colleagues) includes CIE and control data generated using exon arrays (Affymetrix MTA/Clariom D arrays) for midbrain and (soon) for several other brain regions.