Atherogenic Lipids Induce Adhesion of Human Coronary Artery Smooth Muscle Cells to Macrophages by Up-regulating Chemokine CX3CL1 on Smooth Muscle Cells in a TNFα-NFκB-dependent Manner

Abstract

Recent genetic evidence has implicated the adhesive chemokine CX3CL1 and its leukocyte receptor CX3CR1 in atherosclerosis. We previously proposed a mechanism involving foam cell anchorage to vascular smooth muscle cells because: 1) CX3CL1 and CX3CR1 are expressed by both cell types in mouse and human atherosclerotic lesions; 2) foam cells are reduced in lesions in cx3cr1 ؊/؊ apoE ؊/؊ mice; and 3) proatherogenic lipids (oxidized low density lipoprotein [oxLDL] and oxidized linoleic acid derivatives) induce adhesion of primary human macrophages to primary human coronary artery smooth muscle cells (CASMCs) in vitro in a macrophage CX3CR1-dependent manner. Here we analyze this concept further by testing whether atherogenic lipids regulate expression and function of CX3CL1 and CX3CR1 on CASMCs. We found that both oxLDL and oxidized linoleic acid derivatives indirectly up-regulated CASMC CX3CL1 at both the protein and mRNA levels through an autocrine feedback loop involving tumor necrosis factor ␣ production and NF-B signaling. Oxidized lipids also up-regulated CASMC CX3CR1 but through a different mechanism. Oxidized lipid stimulation also increased adhesion of macrophages to CASMCs when CASMCs were stimulated prior to assay, and a synergistic pro-adhesive effect was observed when both cell types were prestimulated. Selective inhibition with a CX3CL1-specific blocking antibody indicated that adhesion was strongly CASMC CX3CL1-dependent. These findings support the hypothesis that CX3CR1 and CX3CL1 mediate heterotypic anchorage of foam cells to CASMCs in the context of atherosclerosis and suggest that this chemokine/chemokine receptor pair may be considered as a pro-inflammatory target for therapeutic intervention in atherosclerotic cardiovascular disease.Atherosclerosis involves a complex interplay of inflammatory cells, vascular elements, and lipoproteins coordinated by adhesion molecules, cytokines, and chemokines (1, 2). Oxidation of low density lipoprotein (LDL) 3 and its accumulation in the subendothelial space are key initiating events that promote accumulation of leukocytes and other cell types that organize over time to form plaque (3). Leukocyte recruitment mechanisms are unclear; however, recent genetic data from mouse and man have implicated members of the chemokine family, a large group of leukocyte chemoattractants active at G proteincoupled receptors (4). Of these, the evidence for CX3CL1 (also known as fractalkine) and its receptor CX3CR1 is particularly strong (5-10). CX3CL1 is an atypical multimodular chemokine that exists both in membrane-tethered and shed forms. The immobilized form consists of a chemokine domain anchored to the plasma membrane through an extended mucin-like stalk, a transmembrane helix, and an intracellular domain (11). Transmembrane CX3CL1 is an adhesion molecule that mediates integrin-independent cell capture by binding to CX3CR1 on target cells (12). Following protease-mediated release of the chemokine domain (13, 14), CX3CL1 may also promote classical chemotactic responses of ...

Chemokine Receptor CX3CR1 Mediates Skin Wound Healing by Promoting Macrophage and Fibroblast Accumulation and Function

“…Fifth, labeled BM-derived cells from WT donor mice accumulated in large numbers in wound sites of both recipient WT and CX3CR1 KO mice on day 6 after injury, a time point when macrophages are the major leukocyte subset found in the wound, whereas accumulation was markedly reduced when the donor mouse was CX3CR1 KO. A similar role for CX3CR1 in mediating macrophage accumulation in diseased tissue has been reported in a mouse model of atherosclerosis, and CX3CR1 has been implicated directly in human atherosclerotic cardiovascular disease (26,45,46). However, heretofore the chemokine signals regulating macrophage accumulation in healing wounds had not been clearly delineated.…”

Differential expression of the fractalkine chemokine receptor (CX3CR1) in human monocytes during differentiation

“…CX 3 CL1 is prominently expressed by multiple non-hematopoietic cell types, including muscle, neurons, renal cells, epithelial and endothelial cells, under inflammatory and pathological conditions. 15,23,[44][45][46][47][48][49][50] Under those conditions, CX 3 CL1 may facilitate the adhesion and transmigration of Mos. 51 Additionally, it has been recently proposed that a direct and evolutionary conserved role for CX 3 CR1-CX 3 CL1 interactions is involved in Mo survival.…”

“…Accordingly, the importance of the CX 3 CR1-CX 3 CL1 axis in pathogenesis has been highlighted in several studies. It is involved in atherosclerosis, 26,[41][42]45,46 vascular and renal inflammation 37,48,53 and cancer, 50 it stimulates actin reorganization in microglia 49,54 and it promotes leukocyte-renal endothelial cell interactions during hemolytic uremic syndrome, thereby contributing to the renal microvascular dysfunction and thrombotic microangiopathy. 55,56 To improve our understanding of the biological role of the interaction between fractalkine and CX 3 CR1 in monocytic populations, we analyzed CX 3 CR1 surface protein expression as well as mRNA expression in freshly Mo, MAC and DC populations.…”

T Cell CX3CR1 Mediates Excess Atherosclerotic Inflammation in Renal Impairment

“…First, CX3CR1 is highly expressed on monocytes and mediates their adhesion to endothelial cells 28,29 and smooth muscle cells. 21 The absence of systemic CX3CR1 impedes monocyte accumulation in the plaque in an aorta transplantation model. 30 Its role in aortic accumulation of other leukocytes has not been reported.…”