Abstract 21021: Functional Regulatory Mechanism of Smooth Muscle Cell-Restricted LMOD1 Coronary Artery Disease Locus

Abstract

Coronary artery disease (CAD) remains the leading cause of mortality and morbidity worldwide and has an estimated heritability of 40%. Meta-analyses of genome-wide association studies have now identified 73 genome-wide significant loci and the most recent multi-ethnic meta-analysis identified a number of arterial wall-specific loci. One of these loci include the smooth muscle cell-restricted factor, LMOD1 (Leiomodin 1), a member of the actin filament nucleator family that is highly enriched in smooth muscle tissues including main arteries and visceral organs of the gastrointestinal system. We hypothesized that LMOD1 may serve as a potent marker of the phenotypic modulation of smooth muscle cells during atherosclerosis. We recently identified a non-coding regulatory variant, rs34091558, which is in linkage disequilibrium with the lead CAD GWAS variant, rs2820315 (P=7.7E-10; OR=1.05). However, the causal mechanism for how these variants alter LMOD1 expression/function and CAD risk remains unclear. Expression quantitative trait loci (eQTL) mapping in GTEx and STARNET databases confirmed that rs34091558 is among the top eQTLs for LMOD1 in vascular tissues. Allelic expression imbalance analyses in heterozygous HCASMC donors further demonstrated cis-acting effects on LMOD1 gene expression. Position weight matrix (PWM) motif analyses identified the protective allele at rs34091558 to form a consensus forkhead box O3 (FOXO3) binding motif, which is predicted to be disrupted by the risk allele. FOXO3 chromatin immunoprecipitation and reporter assays demonstrated reduced FOXO3 binding and transcriptional activity by the risk allele in HCASMC. Platelet-derived growth factor BB (PDGF-BB) stimulation also significantly reduced LMOD1 expression coincident with FOXO3 knockdown. Finally, both gain and loss-of-function for FOXO3 and LMOD1 in HCASMC delineated a regulatory circuit by which LMOD1 decreased HCASMC proliferation and migration and increased cell contraction. Taken together, these results provide compelling functional evidence that: 1) common genetic variation is associated with dysregulation of LMOD1 expression, and 2) changes in vessel wall processes through LMOD1 dysregulation may partially explain the heritable risk for CAD.