Association of neuropeptide y polymorphism with the occurrence of type 1 and type 2 alcoholism

Meta-Analysis on the Association of Neuropeptide Y rs16139 Variant With the Risk of Alcoholism

Introduction: The neuropeptide-Y (NPY) is involved in the development of alcoholism through NPY receptors. A T>C mutation causes substitution of leucine to proline at codon 7 (L7P; rs16139) in the signal peptide of neuropeptide Y is known to cause a 42% increase in plasma NPY levels. Studies that analyzed the association between NPY rs16139 and alcoholism risk did not demonstrate conclusive evidence for this relationship. The present study aims to evaluate the association between NPY gene rs16139 variant and alcohol dependence. Method: An electronic search of databases including PubMed and Google Scholar was performed to retrieve studies investigating the association between NPY rs16139 and alcoholism. The pooled odds ratio (OR) with 95% confidence interval (CI) was calculated in allelic and dominant genetic models. Sensitivity analyses and publication bias were assessed in our meta-analysis. The meta-analysis was conducted using the MetaGenyo web tool. Result: Significant heterogeneity was observed across studies (p < 0.001). Our results have shown that there is no significant association between NPY rs16139 variant and the risk of alcoholism in allelic (OR = 0.98, 95% CI 0.70-1.38, p = 0.921) and dominant models (OR = 0.98, 95% CI 0.69-1.40, p = 0.919). Begg's funnel plot and Egger's test have not shown publication bias (p = 0.332). Conclusion: To the best of our knowledge, this is the first meta-analysis that evaluates the relationship between the NPY rs16139 polymorphism and the risk of alcoholism. Our large-scale meta-analysis suggests that NPY rs16139 polymorphism is not associated with alcoholism. However, further studies are needed to increase our understanding of the relationship between NPY variants in alcoholism.

Flying Together: Drosophila as a Tool to Understand the Genetics of Human Alcoholism

Alcohol use disorder (AUD) exacts an immense toll on individuals, families, and society. Genetic factors determine up to 60% of an individual's risk of developing problematic alcohol habits. Effective AUD prevention and treatment requires knowledge of the genes that predispose people to alcoholism, play a role in alcohol responses, and/or contribute to the development of addiction. As a highly tractable and translatable genetic and behavioral model organism, Drosophila melanogaster has proven valuable to uncover important genes and mechanistic pathways that have obvious orthologs in humans and that help explain the complexities of addiction. Vinegar flies exhibit remarkably strong face and mechanistic validity as a model for AUDs, permitting many advancements in the quest to understand human genetic involvement in this disease. These advancements occur via approaches that essentially fall into one of two categories: (1) discovering candidate genes via human genome-wide association studies (GWAS), transcriptomics on post-mortem tissue from AUD patients, or relevant physiological connections, then using reverse genetics in flies to validate candidate genes' roles and investigate their molecular function in the context of alcohol. (2) Utilizing flies to discover candidate genes through unbiased screens, GWAS, quantitative trait locus analyses, transcriptomics, or single-gene studies, then validating their translational role in human genetic surveys. In this review, we highlight the utility of Drosophila as a model for alcoholism by surveying recent advances in our understanding of human AUDs that resulted from these various approaches. We summarize the genes that are conserved in alcohol-related function between humans and flies. We also provide insight into some advantages and limitations of these approaches. Overall, this review demonstrates how Drosophila have and can be used to answer important genetic questions about alcohol addiction.

Drosophila and Caenorhabditis elegans as Discovery Platforms for Genes Involved in Human Alcohol Use Disorder

BACKGROUND

Despite the profound clinical significance and strong heritability of alcohol use disorder (AUD), we do not yet have a comprehensive understanding of the naturally occurring genetic variance within the human genome that drives its development. This lack of understanding is likely to be due in part to the large phenotypic and genetic heterogeneities that underlie human AUD. As a complement to genetic studies in humans, many laboratories are using the invertebrate model organisms (iMOs) Drosophila melanogaster (fruit fly) and Caenorhabditis elegans (nematode worm) to identify genetic mechanisms that influence the effects of alcohol (ethanol) on behavior. While these extremely powerful models have identified many genes that influence the behavioral responses to alcohol, in most cases it has remained unclear whether results from behavioral-genetic studies in iMOs are directly applicable to understanding the genetic basis of human AUD.

METHODS

In this review, we critically evaluate the utility of the fly and worm models for identifying genes that influence AUD in humans.

RESULTS

Based on results published through early 2015, studies in flies and worms have identified 91 and 50 genes, respectively, that influence 1 or more aspects of behavioral responses to alcohol. Collectively, these fly and worm genes correspond to 293 orthologous genes in humans. Intriguingly, 51 of these 293 human genes have been implicated in AUD by at least 1 study in human populations.

CONCLUSIONS

Our analyses strongly suggest that the Drosophila and C. elegans models have considerable utility for identifying orthologs of genes that influence human AUD.

NPY signaling inhibits extended amygdala CRF neurons to suppress binge alcohol drinking

Binge alcohol drinking is a tremendous public health problem because it leads to the development of numerous pathologies, including alcohol abuse and anxiety. It is thought to do so by hijacking brain systems that regulate stress and reward, including neuropeptide Y (NPY) and corticotropin-releasing factor (CRF). The central actions of NPY and CRF have opposing functions in the regulation of emotional and reward-seeking behaviors; thus, dysfunctional interactions between these peptidergic systems could be involved in the development of these pathologies. We used converging physiological, pharmacological and chemogenetic approaches to identify a precise neural mechanism in the bed nucleus of the stria terminalis (BNST), a limbic brain region involved in pathological reward and anxiety behaviors, underlying the interactions between NPY and CRF in the regulation of binge alcohol drinking in both mice and monkeys. We found that NPY Y1 receptor (Y1R) activation in the BNST suppressed binge alcohol drinking by enhancing inhibitory synaptic transmission specifically in CRF neurons via a previously unknown Gi-mediated, PKA-dependent postsynaptic mechanism. Furthermore, chronic alcohol drinking led to persistent alterations in Y1R function in the BNST of both mice and monkeys, highlighting the enduring, conserved nature of this effect across mammalian species. Together, these data provide both a cellular locus and signaling framework for the development of new therapeutics for treatment of neuropsychiatric diseases, including alcohol use disorders.

Neuropeptide Y signaling in the central nucleus of amygdala regulates alcohol-drinking and anxiety-like behaviors of alcohol-preferring rats

BACKGROUND

The neuropeptide Y (NPY) system of the central nucleus of amygdala (CeA) has been shown to be involved in anxiety and alcoholism. In this study, we investigated the molecular mechanisms by which NPY in the CeA regulates anxiety and alcohol drinking behaviors using alcohol-preferring (P) rats as an animal model.

METHODS

Alcohol-preferring rats were bilaterally cannulated targeting the CeA and infused with artificial cerebrospinal fluid (aCSF) or NPY. Alcohol drinking and anxiety-like behaviors were assessed by the 2-bottle free-choice paradigm and light/dark box (LDB) exploration test, respectively. The levels of NPY and related signaling proteins were determined by the gold immunolabeling procedure. The mRNA levels of NPY were measured by in situ RT-PCR. Double-immunofluorescence labeling was performed to observe the colocalization of NPY and Ca(2+)/calmodulin-dependent protein kinase IV (CaMK IV).

RESULTS

We found that NPY infusion into the CeA produced anxiolytic effects, as measured by the LDB exploration test, and also decreased alcohol intake in P rats. NPY infusion into the CeA significantly increased levels of CaMK IV and phosphorylated cAMP responsive element-binding (pCREB) protein and increased mRNA and protein levels of NPY, but produced no changes in protein levels of CREB or the catalytic alpha-subunit of protein kinase A (PKA-Calpha) in the CeA. We also observed that alcohol intake produced anxiolytic effects in P rats in the LDB test and also increased NPY expression and protein levels of pCREB and PKA-Calpha without modulating protein levels of CREB or CaMK IV, in both the CeA and medial nucleus of amygdala. In addition, we found that CaMK IV-positive cells were co-localized with NPY in amygdaloid structures of P rats.

CONCLUSIONS

These results suggest that NPY infusion may increase the expression of endogenous NPY in the CeA, which is most likely attributable to an increase in CaMK IV-dependent CREB phosphorylation and this molecular mechanism may be involved in regulating anxiety and alcohol drinking behaviors of P rats.

Neuropeptide Y receptor genes are associated with alcohol dependence, alcohol withdrawal phenotypes, and cocaine dependence

BACKGROUND

Several lines of evidence in both human and animal studies suggest that variation in neuropeptide Y (NPY) or its receptor genes (NPY1R, NPY2R and NPY5R) is associated with alcohol dependence as well as alcohol withdrawal symptoms. Additional studies suggest that cocaine may affect NPY expression.

METHODS

A total of 39 single nucleotide polymorphisms (SNPs) were genotyped across NPY and its 3 receptor genes in a sample of 1,923 subjects from 219 multiplex alcoholic families of European American descent recruited as part of the Collaborative Studies on the Genetics of Alcoholism (COGA) study. Family-based association analysis was performed to test the primary hypothesis that variation in these genes is associated with alcohol dependence. Secondary analyses evaluated whether there was an association of these SNPs with symptoms of alcohol withdrawal, cocaine dependence, or comorbid alcohol and cocaine dependence.

RESULTS

Although variations in NPY itself were not associated with these phenotypes, variations in 2 NPY-receptor genes were. SNPs in NPY2R provided significant evidence of association with alcohol dependence, alcohol withdrawal symptoms, comorbid alcohol and cocaine dependence, and cocaine dependence (all p < 0.03). Haplotype analyses strengthened the evidence for these phenotypes (global 0.0004 < p < 0.005). SNPs in NPY5R demonstrated significant association with alcohol withdrawal characterized by seizures (p < 0.05).

CONCLUSION

These results indicate that sequence variations in NPY receptor genes are associated with alcohol dependence, particularly a severe subtype of alcohol dependence characterized by withdrawal symptoms, comorbid alcohol and cocaine dependence, and cocaine dependence.

The next challenge for psychiatric genetics: characterizing the risk associated with identified genes

BACKGROUND

As advances in genetics further our ability to identify genes influencing psychiatric disorders, the next challenge facing psychiatric genetics is to characterize the risk associated with specific genetic variants in order to better understand how these susceptibility genes are involved in the pathways leading to illness.

METHODS

To further this goal, findings from behavior genetic analyses about how genetic influences act can be used to guide hypothesis testing about the effects associated with specific genes.

RESULTS

Using the phenotype of alcohol dependence as an example, this paper provides an overview of how the integration of behavioral and statistical genetics can advance our knowledge about the genetics of psychiatric disorders. Areas currently being investigated in behavior genetics include careful delineation of phenotypes, to examine the heritability of various aspects of normal and abnormal behavior; developmental changes in the nature and magnitude of genetic and environmental effects; the extent to which different behaviors are influenced by common genes; and different forms of gene-environment correlation and interaction.

CONCLUSIONS

Understanding how specific genes are involved in these processes has the potential to significantly enhance our understanding of the development of psychiatric disorders.

Alcoholism: genes and mechanisms

Alcoholism is a chronic relapsing/remitting disease that is frequently unrecognized and untreated, in part because of the partial efficacy of treatment. Only approximately one-third of patients remain abstinent and one-third have fully relapsed 1 year after withdrawal from alcohol, with treated patients doing substantially better than untreated [1]. The partial effectiveness of strategies for prevention and treatment, and variation in clinical course and side effects, represent a challenge and an opportunity to better understand the neurobiology of addiction. The strong heritability of alcoholism suggests the existence of inherited functional variants of genes that alter the metabolism of alcohol and variants of other genes that alter the neurobiologies of reward, executive cognitive function, anxiety/dysphoria, and neuronal plasticity. Each of these neurobiologies has been identified as a critical domain in the addictions. Functional alleles that alter alcoholism-related intermediate phenotypes include common alcohol dehydrogenase 1B and aldehyde dehydrogenase 2 variants that cause the aversive flushing reaction; catechol-O-methyltransferase (COMT) Val158Met leading to differences in three aspects of neurobiology: executive cognitive function, stress/anxiety response, and opioid function; opioid receptor μ1 (OPRM1) Asn40Asp, which may serve as a gatekeeper molecule in the action of naltrexone, a drug used in alcoholism treatment; and HTTLPR, which alters serotonin transporter function and appears to affect stress response and anxiety/dysphoria, which are factors relevant to initial vulnerability, the process of addiction, and relapse.

Genes associated with addiction: alcoholism, opiate, and cocaine addiction

Drug addiction is a complex disorder that has a large spectrum of causes. Vulnerability to addiction has been shown in twin studies to have a robust genetic component. This genetic basis for addiction has general and specific components for each drug abused. Although many genes have been implicated in drug addiction, only a handful have either been replicated to have an association or to have an identified functional mechanism related to specific effects of abused drugs. A few selected genetic variants that currently look promising for the study of alcohol, opiate, and cocaine addiction are discussed in this article.