Abstract
BackgroundCirculating CD34+ cells, a population that includes endothelial progenitors, participate in the maintenance of endothelial integrity. Better understanding of the mechanisms that regulate their survival is crucial to improve their regenerative activity in cardiovascular and renal diseases. Chemokine-receptor cross talk is critical in regulating cell homeostasis. We hypothesized that cell surface expression of the chemokine fractalkine (FKN) could target progenitor cell injury by Natural Killer (NK) cells, thereby limiting their availability for vascular repair.Methodology/Principal FindingsWe show that CD34+-derived Endothelial Colony Forming Cells (ECFC) can express FKN in response to TNF-α and IFN-γ inflammatory cytokines and that FKN expression by ECFC stimulates NK cell adhesion, NK cell-mediated ECFC lysis and microparticles release in vitro. The specific involvement of membrane FKN in these processes was demonstrated using FKN-transfected ECFC and anti-FKN blocking antibody. FKN expression was also evidenced on circulating CD34+ progenitor cells and was detected at higher frequency in kidney transplant recipients, when compared to healthy controls. The proportion of CD34+ cells expressing FKN was identified as an independent variable inversely correlated to CD34+ progenitor cell count. We further showed that treatment of CD34+ circulating cells isolated from adult blood donors with transplant serum or TNF-α/IFN-γ can induce FKN expression.ConclusionsOur data highlights a novel mechanism by which FKN expression on CD34+ progenitor cells may target their NK cell mediated killing and participate to their immune depletion in transplant recipients. Considering the numerous diseased contexts shown to promote FKN expression, our data identify FKN as a hallmark of altered progenitor cell homeostasis with potential implications in better evaluation of vascular repair in patients.
Highlights
Endothelium dysfunction plays a central role in the pathogenesis of vascular disorders
Our data highlights a novel mechanism by which FKN expression on CD34+ progenitor cells may target their Natural Killer (NK) cell mediated killing and participate to their immune depletion in transplant recipients
FKN expression on endothelial colony forming cells (ECFC) was confirmed by immunofluorescence microscopy (Fig. 1C), using co-staining with CD31 antibody used to attest the endothelial differentiation of CD34+-derived progenitors
Summary
Endothelium dysfunction plays a central role in the pathogenesis of vascular disorders. Evidence has accumulated to show how endothelial integrity results from a critical balance between damage and repair processes. Repair of injured endothelium does not solely depend on vessel wall endothelial cells and on circulating progenitors originating from the bone marrow or other niches[1]. EPC have the specific ability to differentiate into endothelial cells and integrate into damaged endothelial layer and play major role in new vessel formation [3,4,5]. Altered EPC numbers and function have been described in patients with renal failure [7,8,9] This defect could contribute to accelerated arteriosclerosis and high cardiovascular morbidity observed in chronic kidney disease. We hypothesized that cell surface expression of the chemokine fractalkine (FKN) could target progenitor cell injury by Natural Killer (NK) cells, thereby limiting their availability for vascular repair
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