CXCL12 Derived From Endothelial Cells Promotes Atherosclerosis to Drive Coronary Artery Disease
Authors: Yvonne Döring, Emiel P.C. van der Vorst, Johan Duchene, Yvonne Jansen, Selin Gencer, Kiril Bidzhekov, Dorothee Atzler, Donato Santovito, Daniel J. Rader, Danish Saleheen, Christian Weber
Journal: Circulation (2019)

genome-wide association studies ◼ inflammation G enome-wide association studies have established a link between the genomic locus 10q11, which hosts the CXCL12 gene, and the risk for coronary artery disease (CAD). 1 CAD risk alleles downstream of CXCL12 have been associated with plasma levels of the chemokine CXCL12 2 ; however, the nature and directionality of this association remain elusive.Recently, a Mendelian randomization study identifying genetic determinants of biomarkers in the populations of ORIGIN (Outcome Reduction With Initial Glargine Intervention) and CARDIoGRAM (Coronary Artery Disease Genome Wide Replication and Met-Analysis) revealed CXCL12 as a causal mediator of CAD, supported by epidemiological analysis showing a 15% higher risk for cardiovascular events per SD of increased CXCL12 plasma levels in ORIGIN. 3To detail the association between CXCL12 and CAD, we conducted a meta-analysis of genomewide association studies performed in the EPIC-Norfolk (European Prospective Investigation into Cancer) and PROMIS (Pakistan Risk of Myocardial Infarction Study) cohorts (n=12,657; filters: INFO≥0.5,MAF≥0.01,HWE≥1×10 -6 , only SNPs appearing in both cohorts).The study was approved by an institutional review committee, and subjects gave informed consent.Applying conditional analysis, we newly identified rs2802492, an intergenic SNP near CXCL12, to be independently associated with CXCL12 plasma levels (β=0.016;P=3.24×10 -8 ) as determined by ELISA (α-isoform, R&D Systems Quantikine kit) 2 and with increased risk for CAD (odds ratio, 1.047; P=1.27×10 -6 ), corroborating CXCL12 as a driver of CAD.No linkage disequilibrium (r 2 >0.8) was found between rs2802492 and the CAD-associated SNPs rs1746048 1 and intergenic rs1482478. 3Notably, when specifically tested for association with CXCL12 expression using the eQTL calculator in the GTEx dataset, analysis for rs2802492 but not rs1482478 yielded a nominal P<0.05 in the tibial artery, with a consistent direction of effect.However, these data await validation in biological models, namely murine atherosclerosis, to elucidate mechanisms by which CXCL12 mediates CAD.This is particularly relevant, because we found CXCR4, the receptor of CXCL12, to confer cell-specific atheroprotective effects preserving endothelial function and contractile smooth muscle cell (SMC) phenotype in mice, while reduced CXCR4 expression was associated with CAD risk in humans, 4 indicating complex effects of this ligand-receptor axis in atherosclerosis and CAD.To unravel mechanisms underlying the association of plasma CXCL12 and CAD, we used set of models interrogating the impact of cell-specific CXCL12-deficiency on atherosclerosis in apolipoprotein E-deficient (Apoe -/-) mice subjected to a Western diet (21% fat, 0.15-0.2%cholesterol) for 12 weeks (Figure), as described. 4Notably, atherosclerotic lesion area, composition, and inflammation, as assessed by collagen and macrophage content, in the aorta of mice with CXCL12-deficiency in all somatic cells (Ubi-12-KO) did not differ from controls (Ubi-12-WT), although CXCL12 plasma levels were almost undetectable, suggesting opposing roles of CXCL12 or targeted receptors from different cell types.Hence, we generated chimeric mice with CXCL12 deficiency in bone marrow-derived hematopoietic (Hem-12-KO) versus nonhematopoietic resident cells (Res-12-KO) by reciprocal bone marrow trans-