Abstract 610: Functional Relationship of The CARS2 Locus to Coronary Artery Disease

In a recent meta-analysis of GWAS for cardiovascular disease (CAD) with imputation from 1000 Genomes (Nat Genet 2015), we identified 202 significant CAD associated variants (FDR q< 0.05) in 129 loci. Seven independent association signals were identified in a gene cluster at chromosome 13q34 including rs61969072. This SNP is located in an intergenic region proximal to the ING1 , CARKD and CARS2 genes. Expression data (eQTL) obtained from the GTEx Project demonstrate a strong association of rs61969072 with CARS2 mRNA abundance in artery with decreased CARS2 expression in carriers of the risk G allele, hinting that CARS2 may be a causal CAD gene. CARS2 encodes a putative mitochondrial cysteinyl t-RNA synthetase. Bioinformatics data (BioGPS) indicate high gene expression of CARS2 in monocytes, a precursor of macrophages. Having then demonstrated that CARS2 mRNA expression is decreased in M1 macrophages compared to M0 and M2 macrophages, we examined the role of CARS2 in the anti-inflammatory pathway in macrophages using THP-1 cells, a macrophage model system. Gene expression profiling of 84 key players of the inflammatory response was performed on siRNA mediated knockdown of CARS2 samples. Comparisons between knockdown and control samples (n=4) identified 12 upregulated and 4 down regulated genes with ≥ 1.25 or ≤0.75 fold difference in expression (p<0.05). Gene Set Enrichment Analysis (GSEA), using inflammatory response PCR array data, identified the interleukin-10 signaling pathway as an enriched category (FDR q<0.05). IL-10 has an atheroprotective effect against plaque rupture and thrombus formation by influencing the local inflammatory process in the lesion. IL-10 activates the STAT3 cascade, where phosphorylated STAT3 homodimers translocate to the nucleus to activate specific target effector genes which repress the proinflammatory genes at the transcriptional level. IL-10 induced STAT3 phosphorylation was measured by Western blotting in THP-1 cells. In response to IL-10, CARS2 knockdown samples showed dampened STAT3 phosphorylation compared to control suggesting that CARS2 serves an anti-inflammatory function within the IL-10 signaling pathway.