Epigenetic Effects in HPA Axis Genes Associated with Cortical Thickness, ERP Components and SUD Outcome

β-Endorphin influences sedative and ataxic effects of alcohol

Beta-endorphin (β-E) is an opioid peptide linked to the behavioral effects of ethanol. For example, β-E provides negative feedback to inhibit the hypothalamic-pituitary-adrenal (HPA) stress axis, and neuroadaptation of this system to ethanol may facilitate sex differences in disordered drinking. Locomotor sensitivity to ethanol may also influence the risk for addiction; however, the role of β-E in psychomotor effects of ethanol is not fully understood. We examined the role of β-E and sex on locomotor effects of ethanol using adult male and female wild-type C57BL/6J and β-E deficient B6.129S2-Pomctm1Low/J mice in a parallel rod floor apparatus following 0.75 or 2.0 g/kg ethanol. Beginning 15 min after intraperitoneal injection, we recorded foot slips, distance traveled, slips per meter, first instance of immobility, and total time spent off-balance (lying on the floor) over 15 min, and collected blood for analysis of ethanol concentration 60 min after injection. Overall, β-E deficient mice were more sedated and ataxic following ethanol; at the lower dose they slipped more frequently and had a higher rate of slips per meter traveled. At the higher dose, β-E deficient mice were predominantly sedated, slipping less frequently, and traveling less, as well as spending more time off-balance and becoming immobile sooner. Genotype interacted with sex in that male β-E deficient mice slipped more frequently than their female counterparts, suggesting that β-E may elicit sex-dependent effects of ethanol-induced ataxia. Blood ethanol concentration did not differ between any group, suggesting that behavioral differences result from altered sensitivity to ethanol. Our data support the contention that β-E modulates the locomotor effects of ethanol and may influence ataxia in a sex-dependent manner. These findings help elucidate the role of β-E in diverging behavioral responses to ethanol and may aid the development of targeted treatments for alcohol use disorders.

Inter- and transgenerational heritability of preconception chronic stress or alcohol exposure: Translational outcomes in brain and behavior

Chronic stress and alcohol (ethanol) use are highly interrelated and can change an individual's behavior through molecular adaptations that do not change the DNA sequence, but instead change gene expression. A recent wealth of research has found that these nongenomic changes can be transmitted across generations, which could partially account for the "missing heritability" observed in genome-wide association studies of alcohol use disorder and other stress-related neuropsychiatric disorders. In this review, we summarize the molecular and behavioral outcomes of nongenomic inheritance of chronic stress and ethanol exposure and the germline mechanisms that could give rise to this heritability. In doing so, we outline the need for further research to: (1) Investigate individual germline mechanisms of paternal, maternal, and biparental nongenomic chronic stress- and ethanol-related inheritance; (2) Synthesize and dissect cross-generational chronic stress and ethanol exposure; (3) Determine cross-generational molecular outcomes of preconception ethanol exposure that contribute to alcohol-related disease risk, using cancer as an example. A detailed understanding of the cross-generational nongenomic effects of stress and/or ethanol will yield novel insight into the impact of ancestral perturbations on disease risk across generations and uncover actionable targets to improve human health.

Adaptor protein complex 2 in the orbitofrontal cortex predicts alcohol use disorder

Alcohol use disorder (AUD) is a life-threatening disease characterized by compulsive drinking, cognitive deficits, and social impairment that continue despite negative consequences. The inability of individuals with AUD to regulate drinking may involve functional deficits in cortical areas that normally balance actions that have aspects of both reward and risk. Among these, the orbitofrontal cortex (OFC) is critically involved in goal-directed behavior and is thought to maintain a representation of reward value that guides decision making. In the present study, we analyzed post-mortem OFC brain samples collected from age- and sex-matched control subjects and those with AUD using proteomics, bioinformatics, machine learning, and reverse genetics approaches. Of the 4,500+ total unique proteins identified in the proteomics screen, there were 47 proteins that differed significantly by sex that were enriched in processes regulating extracellular matrix and axonal structure. Gene ontology enrichment analysis revealed that proteins differentially expressed in AUD cases were involved in synaptic and mitochondrial function, as well as transmembrane transporter activity. Alcohol-sensitive OFC proteins also mapped to abnormal social behaviors and social interactions. Machine learning analysis of the post-mortem OFC proteome revealed dysregulation of presynaptic (e.g., AP2A1) and mitochondrial proteins that predicted the occurrence and severity of AUD. Using a reverse genetics approach to validate a target protein, we found that prefrontal Ap2a1 expression significantly correlated with voluntary alcohol drinking in male and female genetically diverse mouse strains. Moreover, recombinant inbred strains that inherited the C57BL/6J allele at the Ap2a1 interval consumed higher amounts of alcohol than those that inherited the DBA/2J allele. Together, these findings highlight the impact of excessive alcohol consumption on the human OFC proteome and identify important cross-species cortical mechanisms and proteins that control drinking in individuals with AUD.

A whole exome sequencing study to identify rare variants in multiplex families with alcohol use disorder

Background

Alcohol use disorder (AUD) runs in families and is accompanied by genetic variation. Some families exhibit an extreme susceptibility in which multiple cases are found and often with an early onset of the disorder. Large scale genome-wide association studies have identified several genes with impressive statistical probabilities. Most of these genes are common variants. Our goal was to perform exome sequencing in families characterized by multiple cases (multiplex families) to determine if rare variants might be segregating with disease status.

Methods

A case-control approach was used to leverage the power of a large control sample of unrelated individuals (N = 8,983) with exome sequencing [Institute for Genomic Medicine (IGM)], for comparison with probands with AUD (N = 53) from families selected for AUD multiplex status. The probands were sequenced at IGM using similar protocols to those used for the archival controls. Specifically, the presence of a same-sex pair of adult siblings with AUD was the minimal criteria for inclusion. Using a gene-based collapsing analysis strategy, a search for qualifying variants within the sequence data was undertaken to identify ultra-rare non-synonymous variants.

Results

We searched 18,666 protein coding genes to identify an excess of rare deleterious genetic variation using whole exome sequence data in the 53 AUD individuals from a total of 282 family members. To complete a case/control analysis of unrelated individuals, probands were compared to unrelated controls. Case enrichment for 16 genes with significance at 10-4 and one at 10-5 are plausible candidates for follow-up studies. Six genes were ultra rare [minor allele frequency (MAF) of 0.0005]: CDSN, CHRNA9, IFT43, TLR6, SELENBP1, and GMPPB. Eight genes with MAF of 0.001: ZNF514, OXGR1, DIEXF, TMX4, MTBP, PON2, CRHBP, and ANKRD46 were identified along with three protein-truncating variants associated with loss-of-function: AGTRAP, ANKRD46, and PPA1. Using an ancestry filtered control group (N = 2,814), nine genes were found; three were also significant in the comparison to the larger control group including CHRNA9 previously implicated in alcohol and nicotine dependence.

Conclusion

This study implicates ultra-rare loss-of-function genes in AUD cases. Among the genes identified include those previously reported for nicotine and alcohol dependence (CHRNA9 and CRHBP).