Increased Plasma Soluble Fractalkine in Patients with Chronic Heart Failure and Its Clinical Significance

Defining the effects of traffic-related air pollution on the human plasma proteome using an aptamer proteomic array: A dose-dependent increase in atherosclerosis-related proteins

BACKGROUND

Traffic-related air pollution (TRAP) is a critical risk factor and major contributor to respiratory and cardiovascular disease (CVD). The effects of TRAP beyond the lungs can be related to changes in circulatory proteins. However, such TRAP-mediated changes have not been defined in an unbiased manner using a controlled human model.

OBJECTIVE

To detail global protein changes (the proteome) in plasma following exposure to inhaled diesel exhaust (DE), a paradigm of TRAP, using controlled human exposures.

METHODS

In one protocol, ex-smokers and never-smokers were exposed to filtered air (FA) and DE (300 μg PM_2.5/m³), on order-randomized days, for 2 h. In a second protocol, independent never-smoking participants were exposed to lower concentrations of DE (20, 50 or 150 μg PM_2.5/m³) and FA, for 4 h, on order-randomized days. Each exposure was separated by 4 weeks of washout. Plasma samples obtained 24 h post-exposure from ex-smokers (n = 6) were first probed using Slow off-rate modified aptamer proteomic array. Plasma from never-smokers (n = 11) was used for independent assessment of proteins selected from the proteomics study by immunoblotting.

RESULTS

Proteomics analyses revealed that DE significantly altered 342 proteins in plasma of ex-smokers (n = 6). The top 20 proteins therein were primarily associated with inflammation and CVD. Plasma from never-smokers (n = 11) was used for independent assessment of 6 proteins, amongst the top 10 proteins increased by DE in the proteomics study, for immunoblotting. The abundance of all six proteins (fractalkine, apolipoproteins (APOB and APOM), IL18R1, MIP-3 and MMP-12) was significantly increased by DE in plasma of these never-smokers. DE-mediated increase was shown to be concentration-dependent for fractalkine, APOB and MMP-12, all biomarkers of atherosclerosis, which correlated with plasma levels of IL-6, a subclinical marker of CVD, in independent participants.

CONCLUSION

This investigation details changes in the human plasma proteome due to TRAP. We identify specific atherosclerosis-related proteins that increase concentration-dependently across a range of TRAP levels applicable worldwide.

Fractalkine (CX3CL1) and Its Receptor CX3CR1: A Promising Therapeutic Target in Chronic Kidney Disease?

Innate immune cells are key contributors to kidney inflammation and fibrosis. Infiltration of the renal parenchyma by innate immune cells is governed by multiple signalling pathways. Since the discovery of the chemokine fractalkine (CX3CL1) and its receptor, CX3CR1 over twenty years ago, a wealth of evidence has emerged linking CX3CL1-CX3CR1 signalling to renal pathologies in both acute and chronic kidney diseases (CKD). However, despite the extent of data indicating a pathogenic role for this pathway in kidney disease and its complications, no human trials of targeted therapeutic agents have been reported. Although acute autoimmune kidney disease is often successfully treated with immunomodulatory medications, there is a notable lack of treatment options for patients with progressive fibrotic CKD. In this article we revisit the CX3CL1-CX3CR1 axis and its functional roles. Furthermore we review the accumulating evidence that CX3CL1-CX3CR1 interactions mediate important events in the intra-renal pathophysiology of CKD progression, particularly via recruitment of innate immune cells into the kidney. We also consider the role that systemic activation of the CX3CL1-CX3CR1 axis in renal disease contributes to CKD-associated cardiovascular disease. Based on this evidence, we highlight the potential for therapies targeting CX3CL1 or CX3CR1 to benefit people living with CKD.

Association of fractalkine with functional severity of heart failure and impact on clopidogrel efficacy in patients with ischemic heart disease

INTRODUCTION

Patients with heart failure (HF) display elevated levels of soluble fractalkine, a chemokine involved in inflammation processes, atherosclerosis and platelet activation. Further, fractalkine has been associated with reduced pharmacodynamic (PD) responsiveness to clopidogrel. The aim of this study was to investigate the association of fractalkine with the severity of HF and its impact on platelet activation and clopidogrel response in patients with coronary artery disease (CAD) with and without HF.

MATERIALS AND METHODS

This prospective PD study included 116 stable CAD patients on DAPT with aspirin and clopidogrel. Subjects were classified in two groups: patients with HF and reduced (<40%) left ventricular ejection fraction (HFrEF group, n = 56) and patients without HF (no HF group, n = 60). Clinical severity of HF was graded according to NYHA classification. Platelet function assays included vasodilator-stimulated phosphoprotein assay, multiple electrode aggregometry and light transmittance aggregometry. Fractalkine and P-selectin concentrations were determined by ELISA.

RESULTS

Fractalkine levels progressively increased with the severity of the disease in the HFrEF group (NYHA I: 471.2 ± 52.4 pg/ml, NYHA II: 500.5 ± 38.4 pg/ml, NYHA III: 638.9 ± 54.3 pg/ml, p for linear trend 0.023). Numerically higher concentrations of fractalkine were observed in the HFrEF group compared to the no HF group with borderline significance (p = 0.052). No significant differences in clopidogrel-induced platelet inhibition according to fractalkine values were observed in any of the groups.

CONCLUSIONS

Fractalkine levels were increased in patients with HFrEF and positively associated with the functional severity of the disease. No evident impact of fractalkine on clopidogrel PD efficacy was found.

A novel role of FKN/CX3CR1 in promoting osteogenic transformation of VSMCs and atherosclerotic calcification

Fractalkine (FKN) and its specific receptor CX3CR1 play a critical role in the pathogenesis of atherosclerosis including recruitment of vascular cells and the development of inflammation. However, its contribution to regulating the development of atherosclerotic calcification has not been well documented. Osteogenic transformation of vascular smooth muscle cells (VSMCs) is critical in the development of calcification in atherosclerotic lesions. In this study, for the first time, we evaluated the effect of FKN/CX3CR1 on the progression of VSMCs calcification and defined molecular signaling that is operative in the FKN/CX3CR1-induced osteogenic transformation of VSMCs. We found that high-fat diet induced atherosclerotic calcification in vivo was markedly inhibited in the Apolipoprotein E (ApoE) and CX3CR1 deficient (ApoE^-/-/CX3CR1^-/-) mice compared with their control littermates. FKN and CX3CR1 were both expressed in VSMCs and up-regulated by oxidized low-density lipoprotein (ox-LDL). FKN/CX3CR1 promoted the expression of osteogenic markers, including osteopontin (OPN), bone morphogenetic protein (BMP)-2 and alkaline phosphatase (ALP) and decreased VSMCs markers, including smooth muscle (SM) α-actin and SM22-α in a dose-dependent manner. The essential role of FKN/CX3CR1 in VSMCs calcification was further confirmed by lentivirus-mediated knockdown or overexpression of CX3CR1 blocked or accelerated osteogenic transformation of VSMCs. This response was associated with reciprocal up- and down-regulation of osteogenic factor, runt-related transcription factor 2 (RUNX2), transcription factors in osteoclast differentiation, receptor activator of nuclear factor-κB (RANK), RANK ligand (RNAKL) and osteoprotegerin (OPG), respectively. Inhibition of FKN/CX3CR1-activated Jak2/Stat3 signaling by the Jak/Stat inhibitor AG490 blocked osteogenic transformation of VSMCs and RUNX2 induction concurrently. Taken together, our data uncovered novel roles of FKN/CX3CR1 in promoting VSMC osteogenic transformation and atherosclerotic calcification by activating RUNX2 through Jak2/Stat3 signaling pathway and suppressing OPG. Our findings suggest that targeting FKN/CX3CR1 may provide new strategies for the prevention and treatment of atherosclerotic calcification.