Molecular mechanisms of acute ethanol behaviors in C. elegans
Jill Bettinger and Andrew Davies
The development of alcohol use disorder (AUD) is strongly influenced by both genetics and environment. Here we seek to test several hypotheses that relate to both genetic and environmental influences on the level of response (LR) to alcohol. LR is an acute measure that is a strong endophenotype for predisposition to develop AUD. Individuals with a low LR have a higher likelihood to develop AUD in the future. LR represents a combination of a variety of factors including the initial sensitivity to alcohol as well as the rate at which tolerance builds during an exposure to alcohol (called acute functional tolerance (AFT)). Using a model genetic organism, the nematode C. elegans, we can assess the impact of genetics and environment on both initial sensitivity and the development of AFT. Here, we focus on two major biological questions: Aim 1 directly tests several potential roles for the dietary omega-3 fatty acid eicosapentaenoic acid (EPA) in these responses to alcohol. Previously we have shown that EPA is critical for allowing the development of AFT in C. elegans, that altering EPA levels in the diet alters behavioral responses to alcohol in mice, and that variation in human genes that are important for determining EPA levels are associated with AUD and alcohol consumption. Here we seek to understand the mechanisms by which EPA alters LR, in particular the development of AFT. We propose that EPA is important in altering aspects of membrane biophysics that regulate the sensitivity of membrane-bound protein targets of alcohol. Further, we will identify specific lipid species containing EPA that play a role in determining LR. Finally, we will test whether candidate genes, which we have shown to be differentially regulated in animals with or without EPA, are important for modulating LR. In Aim 2, we will test how a group of genes known to be important for axon pathfinding or cell positioning affects LR, and if this is due to a developmental effect or if they have a role at the time of alcohol exposure. Previously we asked if a group of genes that are associated with externalizing behaviors (e.g. impulsive and risky behaviors) in humans played a role in responses to alcohol in C. elegans. Loss of function mutations in many of the C. elegans orthologs of these human genes altered acute behavioral responses to alcohol. Further, a significant number of these genes had previously been shown to play developmental roles in axon guidance or cell positioning of neurons. We hypothesize that because AFT is an acute response happening during the exposure to alcohol, that the genes that play a role in AFT will also have an active role at the time of alcohol exposure. We will confirm such a role and identify other genes that act in the same functional pathways to mediate these alcohol responses. Pursuit of both major questions has the potential to identify fundamental aspects of biology for the mechanism of action of alcohol and for the development of acute functional tolerance to the drug. Each of the genes identified in this research represents a potential candidate gene for predisposition to develop AUD, as genetic variation in the orthologous human genes can alter an individual’s LR.