Coronary artery disease (CAD) is the leading cause of death worldwide. Genome-wide association studies (GWAS) have identified more than 200 loci associated with CAD. Here, we investigated the functional effects of a locus tagged by rs61969072 (T/G), with the common allele (T) associated with protection from CAD.
Expression quantitative trait loci (eQTL) analysis demonstrated a strong association between rs61969072 and CARS2 gene expression, which increased with the T allele, in various human tissues. CARS2 encodes the mitochondrial cysteinyl-tRNA synthetase, an enzyme that attaches cysteine to its cognate tRNA. We hypothesized that CARS2 is a candidate causal gene and that CARS2 confers a protective effect against CAD.
We characterized CARS2 expression in macrophages and demonstrated decreased expression in pro-inflammatory M1 macrophages. Gene expression profiling following CARS2 siRNA knockdown revealed increased levels of several pro-inflammatory cytokines. Functional enrichment analysis identified the anti-inflammatory IL-10 signaling pathway, and western blotting showed that CARS2 attenuated IL-10 pathway activation through STAT3 phosphorylation. We also demonstrated that macrophage CARS2 knockdown in a macrophage/smooth muscle cell (SMC) co-culture model elicited gene expression changes indicative of a less contractile, pro-inflammatory, SMC phenotype.
We then performed an in-depth analysis of differentially expressed genes following CARS2 knockdown. Several inflammatory pathways and functions were affected, particularly Protein Kinase R (PKR), implicated in Interferon Induction and Antiviral Response. Downstream of PKR is the NF-κB signaling pathway; CARS2 knockdown led to increased NF-κB protein expression but not activation, as measured by a luciferase reporter assay.
Finally, we investigated potential mitochondrial mechanisms that could lead to inflammation. Reduced CARS2 levels were found to decrease mitochondrial membrane potential. However, there was a decrease in reactive oxygen species (ROS) levels and no changes in mitochondrial DNA release, metabolism, or mitochondrial bioenergetics. While ROS are often considered harmful due to their role in oxidative damage and inflammation, studies have shown that under certain contexts, ROS can have protective effects. Further studies are required to understand the mechanisms underlying the anti-inflammatory effects of CARS2.
Overall, my findings highlight a novel anti-inflammatory role of CARS2 in human macrophages, consistent with the CAD protective effect of a common GWAS-identified variant.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/45735 |
| Date | 14 December 2023 |
| Creators | Dang, Anh-Thu |
| Contributors | McPherson, Phyllis |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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