Coronary artery disease (CAD) remains the number one cause of morbidity and mortality in the world. CAD or atherosclerosis of the coronary arteries, results from the interaction of environmental and genetic risks factors and it is postulated that 50% of the susceptibility to CAD is genetic. With knowledge of specific genetic predispositions, people at risk could be screened earlier before the disease onset. I used information from genome wide association studies (GWASs) approach to characterize some of the genetic polymorphisms that increase the risk of CAD in large case-control studies. From the first top hit of the GWASs of CAD, I found that the CAD risk polymorphisms at the 9p21.3 risk locus are associated with increased human aortic smooth muscle cells (HAoSMCs) proliferation and down regulation of the expression of genes in the vicinity of the 9p21.3 risk locus, CDKN2A (p16) and CDKN2B (p15). Extensive bioinformatics scanning of the 58 kb long 9p21.3 risk locus identified two polymorphisms that disrupt the binding of TEA-domain (TEAD) transcription factors that play a role in controlling cell cycle. Over-expression of TEAD3 or TEAD4 in HAoSMCs homozygous for the non-risk allele led to increased expression of p16, while cells homozygous for the risk allele failed to respond. TEAD factors interact with SMAD3 to mediate TGFβ induction of p16 expression. HAoSMCs homozygous for the risk allele failed to induce p16 in response to TGFβ treatment. The disrupted binding of TEAD factors to its sites at the 9p21.3 risk locus is responsible for the impaired TEAD/ TGFβ induction of p16 at the 9p21.3 risk locus.
From another hit of GWASs, I characterized a gain-of-function polymorphism (rs12960) in a mitochondrial protease called spastic paraplegia 7 (SPG7). This variant escaped a novel phosphorylation regulated processing which rendered SPG7 constitutively active. HAoSMCs carrying the risk alleles showed increased protease activity and mitochondrial reactive oxygen species production (mROS). Increased mROS production led to increased cellular proliferation and mitochondrial fusion. Cellular proliferation and mROS production are potential risk factors for CAD.
GWASs discovered variants at PCSK9 that are linked to the risk of CAD. The mechanism on how PCSK9 has a major effect on the incidence of CAD-associated events relative to his effect on LDL-C is not clear. To address this, I measured plasma PCSK9 levels in two large angiographic case-control studies using ELISA. I found that plasma PCSK9 was significantly higher in patients with acute myocardial infarction (AMI) compared to those with CAD only or CAD with a previous (non-acute) MI. The association between plasma PCSK9 levels and AMI was independent of LDL-C. My work suggests that plasma PCSK9 levels could affect AMI by mechanisms independent of LDL-C.
My PhD work points to the importance of backing up the GWASs and genetics data with functional studies to understand the mechanism of how these variants and genes increases the risk of CAD.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/32382 |
| Date | January 2015 |
| Creators | Almontashiri, Naif Ahmad |
| Contributors | Stewart, Alexandre |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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