Identification and validation of genes affecting aortic lesions in mice

Abstract

Atherosclerosis represents the most significant risk factor for coronary artery disease (CAD), the leading cause of death in developed countries. To better understand the pathogenesis of atherosclerosis, we applied a likeli-hood-based model selection method to infer gene-disease causality relationships for the aortic lesion trait in a segregating mouse population demonstrating a spectrum of susceptibility to developing atherosclerotic lesions. We identified 292 genes that tested causal for aortic lesions from liver and adipose tissues of these mice, and we experimentally validated one of these candidate causal genes, complement component 3a receptor 1 (C3ar1), using a knockout mouse model. We also found that genes identified by this method overlapped with genes progressively regulated in the aortic arches of 2 mouse models of atherosclerosis during atherosclerotic lesion development. By comparing our gene set with findings from public human genome-wide association studies (GWAS) of CAD and related traits, we found that 5 genes identified by our study overlapped with published studies in humans in which they were identified as risk factors for multiple atherosclerosis-related pathologies, including myocardial infarction, serum uric acid levels, mean platelet volume, aortic root size, and heart failure. Candidate causal genes were also found to be enriched with CAD risk polymorphisms identified by the Wellcome Trust Case Control Consortium (WTCCC). Our findings therefore validate the ability of causality testing procedures to provide insights into the mechanisms underlying atherosclerosis development.

Figure 1. Linkage map of lesion candidate causal genes in adipose (A) and liver (B) tissue and aortic lesion trait in the BxH Apoe^–/– F2 cross.

Chromosomes are plotted on the x axis. The candidate causal genes are arranged on the y axis based on their similarities in the eQTL mapping patterns using agglomerative hierarchical clustering, whereas the cQTL for aortic lesion trait in females was plotted separately at the bottom and was not part of the hierarchical clustering. The color bar to the right shows the spectrum of lod scores.

Figure 2. Characterization of aortic lesion size in C3ar1 Apoe double KO mice.

Data are presented as mean ± SD. C3ar1^+/+Apoe^–/–, C3ar1^+/–Apoe^–/–, and C3ar1^–/–Apoe^–/– mice are labeled WT, Het, and Homo, respectively. The sample sizes for male WT, male Het, male Homo, female WT, female Het, and female Homo are 10, 13, 9, 13, 12, and 12, respectively. P values for significant differences (2-sided Student’s t test) are indicated.