Marissa A. Ehringer - US grants

DESCRIPTION (provided by applicant): Twin, adoption, and family studies have provided evidence that genes play an important role in alcohol and tobacco abuse. Moreover, epidemiological and biometrical genetics studies have shown that there is high comorbidity between alcohol and tobacco use, which may be due to overlapping genetic factors. Converging evidence from pharmacological research and the study of mouse models of alcohol- and tobacco-related phenotypes also supports the hypothesis that the same neurological pathways are activated by both substances. Recent evidence has implicated the neuronal nicotinic receptors (nAChRs) as critical targets of these drugs. Several nicotinic receptors are known to be involved in mediating the release of dopamine in response to alcohol and nicotine. These receptors (the alpha4-6 and beta2-3 subunits) may play an important role in regulating the dopaminergic reward pathway, which has been strongly implicated in contributing to the pleasurable feelings associated with substance use. This project seeks to examine the genes for the alpha4-6, beta2-3 nAChR subunits for their possible role in contributing to the development of alcohol and tobacco problem use. The candidate will examine these genes in a sample of sibling pairs for which DMA and phenotypic data have already been collected as a part of the National Longitudinal Study of Adolescent Health (Add Health). The candidate will utilize computational bioinformatics methods to identify potential functional single nucleotide polymorphisms (SNPs) within these genes in order to optimally select the SNPs and determine the genotypes of these in the subjects. Several statistical methods will be used to test for association and/or linkage with individual SNPs or haplotypes and alcohol or tobacco problem use. The skills to perform bioinformatics and statistical genetics will be developed through coursework, symposia, workshops, conferences, and consultations with mentors. Training will take place at the Institute for Behavioral Genetics, a unique environment where the candidate will have regular interactions with experts in behavior genetics and substance use disorders. This project will allow the candidate to achieve her short-term goals of learning computational bioinformatics methods, as well as advanced statistical genetics methods to analyze the data, while accumulating evidence that these genes may contribute to alcohol and tobacco problem use. It will also promote her long-term career goals of establishing an independent research career in behavior genetics of alcohol and tobacco use and provide a foundation for future studies.

DESCRIPTION (provided by applicant): Human genetic studies have identified the cluster of nicotinic receptor genes (CHRNA5/A3/B4) on chromosome 15 as strong candidates for association with drug abuse-related behaviors, including smoking, alcohol phenotypes, and cocaine dependence. These genes have also been associated with lung cancer, but it is remains unclear what aspects of this association may be mediated through smoking behavior. In addition, we have found evidence that the intergenic region between the CHRNA3 and CHRNB4 genes is associated with more general measures of disinhibitory behavior, including conduct disorder, which is a known risk factor for early initiation of drugs and later problems. There is evidence from molecular, pharmacological, and animal studies that transcriptional regulation of these genes is likely to be co-regulated and complex, and that the 13 and 24 subunits might be good targets for development of smoking cessation drugs. We have initiated studies to assess the putative functional differences of alleles for SNPs that have been implicated in our human genetic studies. Our results provide evidence that at least two SNPs in this region may lead to differences in gene expression, using luciferase-gene assays in immortalized cell culture lines and in primary mouse neuronal embryonic cell cultures. The goals of this application are to extend these findings in several ways. First, we will use these assays to evaluate how the DNA sequence surrounding these SNPs may affect their ability to differentially drive gene expression ("promoter bashing"). Second, we will examine the effects of these SNPs in different cell types, including a variety of immortalized neuronal cells, lung cancer cells, and primary mouse neuronal embryonic cells (gene x cell type interaction). Third, we will challenge the cells with nicotine to assess whether this drug modifies gene expression patterns (gene x environment interaction). Fourth, we will determine whether allele-specific changes in gene expression using the luciferase assays lead to corresponding differences in protein subunit and receptor expression. Finally, we will assess function of nicotinic receptors whose subunit constituents were generated using our in vitro system containing different alleles for individual SNPs and haplotypes of SNPs. We expect the methods developed and applied to these genes to be easily applied to future studies of other nicotinic receptor genes that may also be associated with drug abuse-related behaviors. PUBLIC HEALTH RELEVANCE: Results from this project will facilitate a better understanding of how naturally occurring variations in the CHRNA3 and CHRNB4 genes might contribute to the underlying molecular mechanisms responsible for individual differences in behaviors relevant to drug use and abuse. Such knowledge should lead to the development of improved prevention and treatment of individuals who suffer from these disorders.

DESCRIPTION (provided by applicant): Alcohol and nicotine dependence commonly co-occur and a variety of research suggests some of this co-morbidity may be due to overlapping genetic factors. Converging evidence from electrophysiology studies and rodent models of alcohol- and tobacco-related phenotypes supports the hypothesis that neuronal nicotinic receptors (nAChRs) may be a common site of action for these drugs. The nAChRs are ligand-gated ion channels containing a central cation pore that act as the primary targets for nicotine and the endogenous agonist acytelcholine. Alcohol appears to play a role in modulating the pharmacological properties of nicotine binding at nAChRs, usually by enhancing receptor function. Furthermore, several nicotinic receptor subtypes are known to be present on dopaminergic neurons and involved in mediating the release of dopamine in response to alcohol and nicotine. Through this mesolimbic dopaminergic pathway, these receptors (including the 13-7 and 22-4 subunits) may contribute to the rewarding properties associated with substance use. Recent work has provided evidence that several of the human nAChR subunit genes are associated with alcohol and nicotine behaviors in humans, including age of initiation, early subjective response, and dependence. This proposal will extend these human studies in three ways. First, the human genes for the 13-6 and 22-4 nAChR subunits will be resequenced using DNA samples from 100 individuals to identify novel variations. Second, multiple variations in these genes will be characterized in a sample of 4,146 individuals, for which DNA and alcohol and nicotine behavioral data have already been collected, to test for associations between specific DNA variations and these behaviors. Third, laboratory-based methods will be conducted to determine whether specific variations lead differences in gene expression using cell culture assays. PUBLIC HEALTH RELEVANCE: Results from each of these aims will facilitate a better understanding of how naturally occurring variations in these genes might contribute to the underlying molecular mechanisms responsible for differences in alcohol and nicotine behaviors. Such knowledge should lead to the development of improved prevention and treatment of individuals who suffer from these disorders.

PROJECT SUMMARY Over the past 5-10 years, the opioid epidemic has become a national crisis in the United States. Currently, few good treatment options exist, and little is known about the underlying mechanisms contributing to risk for addiction and to drug effects on the brain. This project addresses both of these issues using a rat genetic model to identify genetic contributions to phenotypes associated with the development of opioid use disorders. We will identify oxycodone-related phenotypic, genotypic, and RNA expression differences within the HXB/BXH RI strains and 15 additional inbred rat strains for which genetic data are available, drawn from the Hybrid Rat Diversity Panel (HRDP). Our preliminary phenotypic data suggest that the founder strains SHR/OlaIpcv and BN-Lx/Cub, along with the ACI strain, differ on many of the phenotypic traits assessed including the self-administration of oxycodone. In Aim 1, 48 inbred rat strains will be assessed for multiple oxycodone-related behavioral phenotypes, including measures of analgesia. Quantitative trait loci (QTL) associated with these behaviors will be identified using existing genetic data. In Aim 2, we will perform RNA sequencing using tissue from the nucleus accumbens and amygdala in naïve animals and in rats following oxycodone self-administration. This will identify genes that differ by strain, which will be informative about baseline risk by genotype, and also identify genes that differ in response to oxycodone (shared and unshared across strains). Because genes do not operate independently, but work in networks and pathways, Aim 3 will employ a systems genetics approach to identify genetic networks involved in baseline differences across strains and in the response to oxycodone self-administration. Across all aims, we will compare the QTL regions, RNA expression differences, and gene network pathways to those found by others in the field using complementary rodent models and/or human studies (including our collaborator Dr. Olivier George) in order to narrow focus on priority genes and pathways.