Helen M. Kamens - US grants

DESCRIPTION (provided by applicant): One way to study the biological underpinnings of complex traits is to make use of simple behaviors that can predict complex traits. The use of these simple behaviors, or endophenotypes, are proving useful in understanding drug abuse and addiction. One such behavior is locomotor stimulation in response to a drug. Current evidence suggests that there is a common gene or quantitative trait locus (QTL) on chromosome 9 that influences sensitivity to cocaine, ethanol, and methamphetamine. This QTL will be confirmed with a congenic mouse strain that has a C57BL/6J region of chromosome 9 introgressed on a DBA/2J background. The role of nicotinic acetylcholine (nACh) receptors in drug induced stimulation will then be examined by using pharmacologic and molecular techniques. Specifically, the role of nACh receptors containing an a3 subunit will be examined because this represents one potential candidate gene that resides in the chromosome 9 QTL region. In addition to receptor antagonist studies, quantitative reverse transcriptasepolymerase chain reaction will be employed to examine mRNA expression and autoradiography will be used to examine receptor density differences. These data will provide evidence for the involvement of nACh receptors in drug-induced stimulation and in drug use and abuse.

DESCRIPTION (provided by applicant): Alcohol and nicotine are commonly co-abused substances. Genetic studies have provided evidence that genes influence the responses to both of these drugs independently, but more recently there have been data to suggest that common gene(s) are likely to influence responses to both drugs. There is an abundant amount of animal research providing evidence that neuronal nicotinic acetylcholine receptors, in particular 1422- containing receptors are involved in the behavioral responses to nicotine. Important for this proposal, these receptors have also been implicated in sensitivity to some effects of alcohol. Nicotinic acetylcholine receptors containing the 14 and 22 subunits have been shown to play a key role in regulating dopamine release in brain regions known to be important for underlying responses to abused drugs. This proposal focuses on the role of natural variation in these receptor subunits in alcohol and nicotine behaviors. Two samples will be used to determine if single nucleotide polymorphisms (SNPs) in the genes encoding these subunits influence sensitivity to alcohol and nicotine phenotypes. DNA and phenotypic data that have already been collected from the Colorado Center for Antisocial Drug Dependence (CADD) and the National Youth Survey (NYS) studies will be available for analysis. The candidate will examine the influence of these genes using resequencing and family-based association tests. Furthermore, the SNPs found to be associated with alcohol or nicotine behaviors will be functionally characterized using luciferase-based gene expression assays. Through this project the candidate will achieve her short-term goal of learning human statistical genetics, molecular genetics and bioinformatics tools. To learn these methods the candidate will attend coursework, symposia, workshops and conferences, in addition to having regular meeting with her mentors. All mentors of this project are faculty fellows at the Institute for Behavioral Genetics. This environment is ideal for such training because of the Institute's long history in studying questions related to the genetics of substance abuse in humans and using animal and molecular approaches. This new training will complement the candidate's prior training in mouse behavioral genetics and will be important for the candidate's long-term goal of becoming an independent researcher. With this additional training in human statistical and molecular genetics the candidate hopes to ultimately evaluate translational questions between model organism and human populations. PUBLIC HEALTH RELEVANCE: Alcohol and nicotine are by far the most commonly co-abused substances and there is evidence that common gene(s) may underlie the response to both drugs. The proposed project will increase our knowledge of the genetic influence the responses to these drugs and may be informative for the development of treatment strategies.

Project Summary/Abstract Progress in our ability to evaluate the interaction between genetic effects and environmental factors in understanding risk for nicotine dependence has been significantly impeded by inadequate single study sample sizes and meta analyses that are necessarily limited to the estimation of effect sizes for research questions that have been previously addressed within single studies. Fortunately, recent methodological innovations now permit the combination of data sets that differ in terms of study design, populations, and measures. This integrative data analysis (IDA) allows us to pool the raw data from multiple studies, allowing us to test new hypotheses and results in more powerful, more comprehensive, and more rigorous studies than we achieve through analysis of single studies or by using traditional meta analytic techniques. The present research will combine both an innovative approach (IDA) and innovative statistical methods (moderated nonlinear factor analysis; MNLFA and time-varying effects models; TVEM), to evaluate the association between genetic variants in the CHRNA5/CHRNA3/CHRNB4 and CHRNA6/CHRNB3 regions and nicotine dependence symptoms across levels of smoking exposure. Taking advantage of existing resources, we will pool extant data from the Social Emotional Contexts of Adolescent Smoking Project (SECASP), The National Longitudinal Study of Adolescent Health (AddHealth), the National Youth Survey Family Study (NYSFS) and the Study of Addiction: Genetics and Environment (SAGE) to evaluate changes in the association between SNPs in the acetylcholine receptor gene clusters and an empirically harmonized nicotine dependence score across levels of smoking exposure and to estimate the additional contribution of timing of smoking exposure in explaining the association between individual genetic variants and nicotine dependence symptoms. The innovative methods of data integration with MNLFA will allow us to begin to explore exposure varying effects in an extremely cost-effective manner in that we will leverage previous investment in tracking, contacting, assessing, and collecting DNA from 4 large studies assessing adolescents and adults. The empirically based nicotine dependence symptom score derived from the cross-study MNLFA model will provide a much more sensitive measure of the nicotine dependence phenotype than traditional methods of scoring within study, and one that is uniquely harmonized to account for between study differences.