Fractalkine has anti-apoptotic and proliferative effects on human vascular smooth muscle cells via epidermal growth factor receptor signalling

Abstract

AimsFractalkine (CX3CL1) is a membrane-bound chemokine that signals through the G protein-coupled receptor CX3CR1 that is implicated in the development of atherosclerosis. We have previously reported that CX3CR1 is expressed by primary human coronary artery smooth muscle cells (CASMC), where it mediates chemotaxis towards CX3CL1. We sought to determine the effect of CX3CL1 on CASMC survival and proliferation and elucidate the signalling mechanisms involved.Methods and resultsCX3CL1 significantly reduces staurosporine-induced apoptosis of CASMC, as quantified by caspase 3 immunostaining and Annexin-V flow cytometry. Furthermore, CX3CL1 is a potent mitogen for primary CASMC and induces phosphorylation of extracellular signal-regulated kinase (ERK) and Akt, measured by western blotting. Inhibition of either ERK or phosphoinositide 3-kinase (PI3K) signalling abrogates proliferation, while only PI3K signalling is involved in the anti-apoptotic effects of CX3CL1. We describe a novel and specific small molecule antagonist of CX3CR1 (AZ12201182) which abrogates the mitogenic and anti-apoptotic effects of CX3CL1 on CASMC. Pharmacological inhibition of the epidermal growth factor receptor (EGFR) blocks CASMC survival and DNA synthesis, indicating a previously undocumented role for EGFR signalling in response to CX3CL1 involving release of a soluble EGFR ligand. Specifically, CX3CL1 induces shedding of epiregulin and increases epiregulin mRNA expression 20-fold within 2 h. Finally, antibody neutralization of epiregulin abrogates the mitogenic effect of CX3CL1.ConclusionWe have demonstrated two novel and important functions of CX3CL1 on primary human SMCs: anti-apoptosis and proliferation, both mediated via epiregulin-induced EGFR signalling. Our data have important implications in vascular pathologies including atherosclerosis, restenosis, and transplant accelerated arteriosclerosis, where the balance of SMC proliferation and apoptosis critically determines both plaque stability and vessel stenosis.

Do not let death do us part: ‘find-me’ signals in communication between dying cells and the phagocytes

“…83 In addition to increasing phagocytosis, FKN has also been associated with anti-inflammatory actions such as providing neuroprotection during glutamate toxicity, 84,85 modulating TNF-α secretion by microglia, 86 and promoting proliferative effects, 87,88 which may all have important roles in different settings of cell clearance. However, clarification is needed as to which processed form is responsible for these FKN effects.…”

T Cell CX3CR1 Mediates Excess Atherosclerotic Inflammation in Renal Impairment

“…30 Its role in aortic accumulation of other leukocytes has not been reported. Second, CX3CR1 inhibits apoptosis of smooth muscle cells 31 2/2 macrophages undergo excess cell death in hepatic fibrosis 36 and renal candidiasis 37 and fibrosis. 38 CX3CR1 is upregulated on T cells in inflammation, CX3CR1 protects T H2 and T H1 cells from apoptosis, and cytokine production is higher in CX3CR1 + than CX3CR1 -T H1 cells.…”

Fractalkine: A Survivor's Guide

“…Fractalkine is the unique ligand for the chemokine receptor CX3CR1, which is expressed on monocytes, natural killer cells, T cells, and smooth muscle cells, 12,13 where it mediates functions including migration, adhesion, and proliferation. [12][13][14] Gathering evidence suggests that the promotion of cell survival may be a key function of fractalkine operating under both homeostatic and inflammatory conditions, thus contributing to the progression of multiple diseases. This brief review will discuss our current knowledge of fractalkine as a survival factor in several disease models and the relevance of this to vascular disease.…”