Functional Interrogation of the COL4A1/COL4A2 and SMAD3 Coronary Artery Disease Loci

• Main Author: Turner, Adam
• Other Authors: McPherson, Ruth
• Language: en
• Published: Université d'Ottawa / University of Ottawa 2016
• Subjects: Genetics; Atherosclerosis
• Online Access: http://hdl.handle.net/10393/35248; http://dx.doi.org/10.20381/ruor-206

Coronary artery disease (CAD) is the leading cause of death worldwide caused by a complex array of environmental and genetic factors. In recent years, the CARDIoGRAM Consortium has identified dozens of novel CAD-associated loci, including COL4A1/COL4A2 and SMAD3. The goals of this project were two-fold. First, to identify functional CAD-associated SNPs (single nucleotide polymorphisms) at these loci and investigate how these common polymorphisms alter CAD risk. Second, to determine if the COL4A1/COL4A2 and SMAD3 loci display both biological interaction and statistical interaction in the context of atherosclerosis. COL4A1 and COL4A2 are critical components of vascular basement membranes and have many additional roles in the vessel wall. SMAD3 is a transcription factor that is a key mediator in the canonical TGFβ signaling pathway. In the first section of this thesis, I show that COL4A1/COL4A2 and SMAD3 display biological interaction in that the TGFβ-mediated upregulation of COL4A1 and COL4A2 is dependent on SMAD3. Furthermore, we were able to identify a COL4A2-SMAD3 SNP pair that displayed a highly significant statistical interaction for CAD association, highlighting that perturbations of the SMAD3/type IV collagen signaling axis contribute to the pathogenesis of atherosclerosis. The second section details the characterization of a novel functional CAD-associated SNP at the SMAD3 locus. The rs17293632 SNP, highly linked to the rs56062135 index SNP reported by CARDIoGRAM, disrupts a conserved AP-1 binding site in intron 1 of the SMAD3 gene. rs17293632 lies within a strong enhancer in many cell types, including arterial smooth muscle cells. The minor, protective allele (T) at rs17293632 disrupts binding of AP-1 proteins, lowers the activity of this enhancer and lowers SMAD3 mRNA levels in humans in both whole blood and carotid plaque tissue. Altogether, AP-1 regulation of SMAD3 enhancer activity suggests a novel regulatory mechanism relevant to the pathogenesis of CAD. The third section summarizes efforts to characterize the mechanisms whereby the independent rs4773144 and rs9515203 SNPs at the COL4A1/COL4A2 locus associate highly with CAD. We were unable to identify causal SNPs at the COL4A1/COL4A2 locus, highlighting the challenges of post-GWAS characterization of some CAD-associated loci. The experiments with SNPs at COL4A1/COL4A2 demonstrate the challenges in defining mechanisms whereby noncoding DNA variants can lead to common disease.