Vascular CXCR4 Limits Atherosclerosis by Maintaining Arterial Integrity

Abstract

Background The CXCL12/CXCR4 chemokine ligand/receptor axis controls (progenitor) cell homeostasis and trafficking. So far, an atheroprotective role of CXCL12/CXCR4 has only been implied through pharmacological intervention, particularly as the somatic deletion of the CXCR4 gene in mice is embryonically lethal. Moreover, cell-specific effects of CXCR4 in the arterial wall and underlying mechanisms remain elusive, prompting us to investigate the relevance of CXCR4 in vascular cell types for atheroprotection. Methods We examined the role of vascular CXCR4 in atherosclerosis and plaque composition by inducing an endothelial cell (EC, BmxCreERT2-driven)-specific or smooth muscle cell (SMC, SmmhcCreERT2- or TaglnCre-driven)-specific-deficiency of CXCR4 in an apolipoprotein E-deficient mouse model. To identify underlying mechanisms for effects of CXCR4, we studied endothelial permeability, intravital leukocyte adhesion, involvement of the Akt/WNT/β-catenin signaling pathway and relevant phosphatases in VE-cadherin expression and function, vascular tone in aortic rings, cholesterol efflux from macrophages, and expression of SMC phenotypic markers. Finally, we analyzed associations of common genetic variants at the CXCR4 locus with the risk for coronary heart disease, along with CXCR4 transcript expression in human atherosclerotic plaques. Results The cell-specific deletion of CXCR4 in arterial ECs (n=12-15) or SMCs (n=13-24) markedly increased atherosclerotic lesion formation in hyperlipidemic mice. Endothelial barrier function was promoted by CXCL12/CXCR4, which triggered Akt/WNT/β-catenin-signaling to drive VE-cadherin expression and stabilized junctional VE-cadherin complexes through associated phosphatases. Conversely, endothelial CXCR4-deficiency caused arterial leakage and inflammatory leukocyte recruitment during atherogenesis. In arterial SMCs, CXCR4 sustained normal vascular reactivity and contractile responses, whereas CXCR4-deficiency favored a synthetic phenotype, the occurrence of macrophage-like SMCs in the lesions, and impaired cholesterol efflux. Regression analyses in humans (n=259,796) identified the C-allele at rs2322864 within the CXCR4 locus to be associated with increased risk for coronary heart disease. In line, C/C risk genotype carriers showed reduced CXCR4 expression in carotid artery plaques (n=188), which was furthermore associated with symptomatic disease. Conclusions Our data clearly establish that vascular CXCR4 limits atherosclerosis by maintaining arterial integrity, preserving endothelial barrier function, and a normal contractile SMC phenotype. Enhancing these beneficial functions of arterial CXCR4 by selective modulators might open novel therapeutic options in atherosclerosis.

CXCR4-binding PET tracers link monocyte recruitment and endothelial injury in murine atherosclerosis

“…We did not directly demonstrate how endothelial CXCR4 is associated with monocyte recruitment in atherosclerosis. However, based on the literature that reendothelialization of arteries, endothelial proliferation (39), and reduced atherosclerosis (21) is linked to CXCR4 expression and function, we argue that CXCR4 itself has a protective role. Additional recent RNA sequencing data analysis of locally regenerating ECs to recover from endothelial injury in vivo shows enhancement of CXCR4 expression (45).…”

“…5B). Since CXCR4 blocking or endothelial specific CXCR4 deficiency was earlier reported to enhance Evans Blue leakage from aortic arches (21), this colocalization likely reflects a compensatory attempt of the endothelium to combat elevated permeability.…”

“…Considering that CXCR4 locus in human has been reported to be as a key determinant in coronary heart disease (21) these new findings underscore the possibility that CXCR4-targeted PET tracers or perhaps the 64 Cu-DOTA-vMIP-II tracer may report critical information about plaque status in a clinical setting.…”

“…Additional recent RNA sequencing data analysis of locally regenerating ECs to recover from endothelial injury in vivo shows enhancement of CXCR4 expression (45). Endothelial CXCR4 is also reported to be athero-protective through attenuating vascular permeability by enhancing VE-cadherin expression and stabilizing VE-cadherin complexes (21). However, despite its likely protective functional role, the induction of its expression is known to be a consequence of endothelial injury (39) and thus its expression correlates with active plaque.…”

“…Moreover, vascular permeability is known to be increased at atherosclerotic lesions (29,30). Endothelial CXCR4 attenuates vascular permeability through enhancement of VEcadherin expression and stabilization of junctional VE-cadherin complexes (21). Therefore, we wondered whether endothelial CXCR4 expression is upregulated to compensate for enhanced vascular permeability at atherosclerotic lesions.…”