Human CD16+ monocytes promote a pro-atherosclerotic endothelial cell phenotype via CX3CR1–CX3CL1 interaction

Abstract

Aims Monocytes are central for atherosclerotic vascular inflammation. The human non-classical, patrolling subtype, which expresses high levels of CD16 and fractalkine receptor CX3CR1, strongly associates with cardiovascular events. This is most marked in renal failure, a condition with excess atherosclerosis morbidity. The underlying mechanism is not understood. This study investigated how human CD16+ monocytes modulate endothelial cell function. Methods and Results In patients with kidney failure, CD16+ monocyte counts were elevated and dynamically decreased within a year after transplantation, chiefly due to a drop in CD14+CD16+ cells. The CX3CR1 ligand CX3CL1 was similarly elevated in the circulation of humans and mice with renal impairment. CX3CL1 upregulation was also observed close to macrophage rich human coronary artery plaques. To investigate a mechanistic basis of this association, CD16+CX3CR1HIGH monocytes were co-incubated with primary human endothelium in vitro. Compared to classical CD14+ monocytes or transwell cocultures, CD16+ monocytes enhanced endothelial STAT1 and NFκB p65 phosphorylation, upregulated expression of CX3CL1 and IL-1β, numerous CCL and CXCL chemokines and molecules promoting leukocyte patrolling and adhesion such as ICAM1 and VCAM1. Genes required for vasodilatation including eNOS decreased while endothelial collagen production increased. Uremic patients’ monocytes enhanced endothelial CX3CL1 even more markedly. Their receptor CX3CR1 was required for enhanced aortic endothelial stiffness in murine atherosclerosis with renal impairment. CX3CR1 dose-dependently modulated monocyte-contact-dependent gene expression in human endothelium. Conclusions By demonstrating endothelial proatherosclerotic gene regulation in direct contact with CD16+ monocytes, in part via cellular CX3CR1-CX3CL1 interaction, our data delineate a mechanism how this celltype can increase cardiovascular risk. Translational Perspective Human CD16+ monocytes strongly associate with cardiovascular disease. Our data show that they induce primary human arterial and venous endothelial chemokine and adhesion molecule expression and increase mediators of vascular stiffness in direct interaction of the endothelium with CX3CR1. CD16+ monocytes reversibly increase in human kidney failure. Our results propose CD16+ monocytes as mediators of cardiovascular events including the reversible vascular phenotype of patients with kidney failure. Interference with their direct contact to the endothelium may represent a causal therapeutic approach in this high-risk patient group.

Regulation and function of CX3CR1 and its ligand CX3CL1 in kidney disease

“…This cell type expresses CX3CR1 on its surface. The amount of surface CX3CR1 per individual monocyte was decreased in CKD in some (Liakopoulos et al 2018), but not other studies (Roy-Chowdhury et al 2020). In a gene expression analysis of human monocytes, both, the nonclassical monocyte marker CD16 and CX3CR1, were expressed at significantly higher levels on monocytes in patients with chronic kidney disease and cardiovascular events compared to all other groups (Schepers et al 2015).…”

“…Interestingly, the increase in this cell type is reversible with kidney transplantation (Ulrich et al 2008;Vereyken et al 2013;Sekerkova et al 2014;Roy-Chowdhury et al 2020). This suggests that the phenotype is related to uremia, rather than the presence of a damaged kidney.…”

Inflammatory Chemokines in Atherosclerosis

“…During atherosclerosis, monocytes expressing CX3CR1 bind and adhere to the endothelium, which expresses mCX3CL1 [ 138 ]. Certainly, CD16 + CX3CR1 HIGH monocytes enhanced endothelial STAT1 and NFκB p65 phosphorylation resulting in an upregulated expression of CX3CL1 and IL-1β, and ICAM1 and VCAM1, compared to classical CD14 + monocytes [ 139 ]. This describes the mechanism by which CX3CR1 and its ligands can increase cardiovascular risk.…”

A Sex-Stratified Analysis of Monocyte Phenotypes Associated with HIV Infection in Uganda

“…We found that PLWH had an increased expression and density of CX3CR1 on total monocytes as well as across the three monocyte subsets. The CX3CR1 chemokine receptor is involved in adhesion and migration of monocytes into the tissues, and has an important role in atherogenesis and plaque development [27,28]. Whether CX3CR1 expression is enhanced in PWLH on chronic ART has been under debate.…”