Abstract 021: ARHGEF26 is a Novel Genetic Risk Factor for Vascular Inflammation and Coronary Artery Disease

Abstract

Vascular inflammation drives the initiation and progression of coronary artery disease (CAD). However, the underlying genetic factors are not well understood. We performed a genome-wide association study in UK Biobank testing 9 million DNA variants for association with CAD (4,831 cases, 115,455 controls), followed by a meta-analysis with previous results. We identified ARHGEF26 (Rho guanine nucleotide exchange factor 26) as a novel locus significantly associated with CAD (combined OR=1.08, 95% CI 1.06-1.11, P=1.02 х 10 –9 ). We hypothesized that ARHGEF26 regulates vascular inflammation by affecting the function of vascular cells. Focusing on the haplotype tagged by the lead variant rs12493885 (ARHGEF26 p.Val29Leu), we performed eQTL and allele-specific expression analyses. There is no significant ARHGEF26 transcription alteration or allelic imbalance associated with the risk allele in human coronary artery samples. Promoter luciferase assay showed no significant difference between the reference and alternative haplotypes. In contrast, expression of exogenous Leu29 mutant after depletion of endogenous ARHGEF26 led to rescued phenotypes consistently exceeding those observed with overexpression of wild-type ARHGEF26, including increased leukocyte transendothelial migration, leukocyte adhesion on endothelial cells, and smooth muscle cell proliferation. These data suggest that the CAD-risk allele (Leu29) may lead to a gain of protein function in vascular cells. To identify the molecular mechanism, we compared the nucleotide-exchange activity between the wild-type and mutant proteins and found no significant difference. Evaluation of ARHGEF26 protein stability by cycloheximide chase showed the Leu29 mutant displayed longer half-life than wild-type ARHGEF26, suggesting the gain-of-function phenotypes of Leu29 in cells may be secondary to its resistance to degradation. Quantitative proteomics revealed differential protein interaction between the wild-type and Leu29 ARHGEF26 in endothelial cells, highlighting critical inflammatory pathways impacted by the CAD-risk allele. In summary, our work identified a novel genetic risk factor for CAD, and enabled discovery of novel CAD-causing pathways in vascular inflammation.