Abstract 164: Identification of Genetic Regulators of the Atherosclerosis-Associated Metabolite Trimethylamine-N-Oxide in the Diversity Outbred Mice Population

Abstract

Dietary choline and its derivatives have been associated with various aspects of lipid metabolism. Recently, the choline metabolite trimethylamine-N-oxide (TMAO) has been associated with atherosclerosis in both mice and humans. Traditional studies of atherosclerosis in mice use genetic or dietary manipulation to induce atherosclerosis in inbred mouse strains. However, traditional quantitative trait locus (QTL) mapping studies using inbred strains often identify large genomic regions, containing many genes, due to limited recombination and/or sample size which hamper candidate gene identification and translation of these results into possible risk factors and therapeutic targets. As an alternative approach, here we use the multi-parental Diversity Outbred (DO) mouse panel for genetic mapping in order to aid in the identification of causal genes and variants associated with TMAO and its precursor choline. We fed DO mice either a high-fat, cholesterol-containing (HFCA) diet or a low-fat, high-protein diet for 18 weeks and measured circulating metabolites at baseline and after diet. Among our highly significant loci, we detected a 4.6 Mb QTL interval on Chromosome 12 (LOD = 10.0, p<0.05) associated with plasma concentrations of the metabolite trimethylamine-N-oxide at baseline, containing 116 genes; the same QTL was also identified after dietary treatment (LOD= 6.7, p<0.1). By using a database of mouse gene expression and measuring gene expression in the eight progenitor strains by RNA-Sequencing, we identified three potential candidate genes, including the positional candidate gene Numb, which encodes a clathrin adapter with a role in endocytosis that was recently shown to modulate intestinal cholesterol absorption. We show that TMAO and Numb exhibit inverse strain variation across the DO founder strains and that the novel Chromosome 12 TMAO locus co-localizes with a highly significant cis-expression QTL for Numb, indicating a potential functional relationship.