Selected ABCB1, ABCB4 and ABCC2 Polymorphisms Do Not Enhance the Risk of Drug-Induced Hepatotoxicity in a Spanish Cohort

Background and Aims

Flawed ABC transporter functions may contribute to increased risk of drug-induced liver injury (DILI). We aimed to analyse the influence of genetic variations in ABC transporters on the risk of DILI development and clinical presentations in a large Spanish DILI cohort.

Methods

A total of ten polymorphisms in ABCB1 (1236T>C, 2677G>T,A, 3435T>C), ABCB4 (1954A>G) and ABCC2 (−1774G>del, −1549A>G, −24C>T, 1249G>A, 3972C>T and 4544G>A) were genotyped using Taqman 5′ allelic discrimination assays or sequencing in 141 Spanish DILI patients and 161 controls. The influence of specific genotypes, alleles and haplotypes on the risk of DILI development and clinical presentations was analysed.

Results

None of the individual polymorphisms or haplotypes was found to be associated with DILI development. Carriers homozygous for the ABCC2 −1774del allele were however only found in DILI patients. Hence, this genotype could potentially be associated with increased risk, though its low frequency in our Spanish cohort prevented a final conclusion. Furthermore, carriers homozygous for the ABCC2 −1774G/−1549A/−24T/1249G/3972T/4544G haplotype were found to have a higher propensity for total bilirubin elevations when developing DILI.

Conclusions

Our findings do not support a role for the analysed polymorphisms in the ABCB1, ABCB4 and ABCC2 transporter genes in DILI development in Spanish patients. The ABCC2 −1774deldel genotype was however restricted to DILI cases and could potentially contribute to enhanced DILI susceptibility.     

Polymorphisms in ABC Transporter Genes and Concentrations of Mercury in Newborns – Evidence from Two Mediterranean Birth Cohorts

Background

The genetic background may influence methylmercury (MeHg) metabolism and neurotoxicity. ATP binding cassette (ABC) transporters actively transport various xenobiotics across biological membranes.

Objective

To investigate the role of ABC polymorphisms as modifiers of prenatal exposure to MeHg.

Methods

The study population consisted of participants (n = 1651) in two birth cohorts, one in Italy and Greece (PHIME) and the other in Spain (INMA). Women were recruited during pregnancy in Italy and Spain, and during the perinatal period in Greece. Total mercury concentrations were measured in cord blood samples by atomic absorption spectrometry. Maternal fish intake during pregnancy was determined from questionnaires. Polymorphisms (n = 5) in the ABC genes ABCA1, ABCB1, ABCC1 and ABCC2 were analysed in both cohorts.

Results

ABCB1 rs2032582, ABCC1 rs11075290, and ABCC2 rs2273697 modified the associations between maternal fish intake and cord blood mercury concentrations. The overall interaction coefficient between rs2032582 and log2-transformed fish intake was negative for carriers of GT (β = −0.29, 95%CI −0.47, −0.12) and TT (β = −0.49, 95%CI −0.71, −0.26) versus GG, meaning that for a doubling in fish intake of the mothers, children with the rs2032582 GG genotype accumulated 35% more mercury than children with TT. For rs11075290, the interaction coefficient was negative for carriers of TC (β = −0.12, 95%CI −0.33, 0.09), and TT (β = −0.28, 95%CI −0.51, −0.06) versus CC. For rs2273697, the interaction coefficient was positive when combining GA+AA (β = 0.16, 95%CI 0.01, 0.32) versus GG.

Conclusion

The ABC transporters appear to play a role in accumulation of MeHg during early development.     

Molecular evolutionary analysis of ABCB5: the ancestral gene is a full transporter with potentially deleterious single nucleotide polymorphisms

Background

ABCB5 is a member of the ABC protein superfamily, which includes the transporters ABCB1, ABCC1 and ABCG2 responsible for causing drug resistance in cancer patients and also several other transporters that have been linked to human disease. The ABCB5 full transporter (ABCB5.ts) is expressed in human testis and its functional significance is presently unknown. Another variant of this transporter, ABCB5 beta posses a “half-transporter-like” structure and is expressed in melanoma stem cells, normal melanocytes, and other types of pigment cells. ABCB5 beta has important clinical implications, as it may be involved with multidrug resistance in melanoma stem cells, allowing these stem cells to survive chemotherapeutic regimes.

Methodology/Principal Findings

We constructed and examined in detail topological structures of the human ABCB5 protein and determined in-silico the cSNPs (coding single nucleotide polymorphisms) that may affect its function. Evolutionary analysis of ABCB5 indicated that ABCB5, ABCB1, ABCB4, and ABCB11 share a common ancestor, which began duplicating early in the evolutionary history of chordates. This suggests that ABCB5 has evolved as a full transporter throughout its evolutionary history.

Conclusions/Significance

From our in-silco analysis of cSNPs we found that a large number of non-synonymous cSNPs map to important functional regions of the protein suggesting that these SNPs if present in human populations may play a role in diseases associated with ABCB5. From phylogenetic analyses, we have shown that ABCB5 evolved as a full transporter throughout its evolutionary history with an absence of any major shifts in selection between the various lineages suggesting that the function of ABCB5 has been maintained during mammalian evolution. This finding would suggest that ABCB5 beta may have evolved to play a specific role in human pigment cells and/or melanoma cells where it is predominantly expressed.     

Drug Transporter Genetic Variants Are Not Associated with TDF-Related Renal Dysfunction in Patients with HIV-1 Infection: A Pharmacogenetic Study

Objective

To investigate whether single nucleotide polymorphisms (SNP) of drug transporter proteins for TDF is a risk factor for TDF-related renal function decrement.

Methods

This study investigated the association between 3 SNPs (ABCC2–24, 1249, and ABCB1 2677), which are shown to be associated with TDF-induced tubulopathy, and clinically important renal outcomes (>10ml/min/1.73m² decrement in eGFR relative to baseline, >25% decrement in eGFR, and eGFR <60ml/min/1.73m²) in 703 HIV-1-infected Japanese patients who initiated TDF-containing antiretroviral therapy (ART). Genotyping was performed by allelic discrimination using TaqMan 5’-nuclease assays.

Results

95% of the study patients were males and 66% were treatment-naïve, with median CD4 count of 249/μl, median baseline eGFR of 96ml/min/1.73m² (IQR 84.6–109.2), and median exposure to TDF of 3.66 years (IQR 1.93–5.59). The frequencies of genotypes at -24, 1249 of ABCC2, and 2677 of ABCB1 were neither different between patients with decrement in eGFR of >10ml/min/1.73m² and those without such decrement (ABCC2: -24, p = 0.53, 1249, p = 0.68; ABCB1: 2677, p = 0.74), nor between those without and with the other two renal outcomes (>25% decrement: ABCC2: -24, p = 0.83, 1249, p = 0.97, ABCB1: 2677, p = 0.40; eGFR <60ml/min/1.73m²: ABCC2: -24, p = 0.51, 1249, p = 0.81, ABCB1: 2677, p = 0.94). Logistic regression analysis showed that the risk genotype of the three SNPs were not associated with any of the three renal outcomes, respectively. Logistic regression model that applied either dominant, recessive, or additive model yielded the same results.

Conclusions

SNPs of the drug transporters for TDF are not associated with clinically important renal outcomes in patients who initiated TDF-containing ART.     

Binding site of ABC transporter homology models confirmed by ABCB1 crystal structure

The human ATP-binding cassette (ABC) transporters ABCB1, ABCC4 and ABCC5 are involved in resistance to chemotherapeutic agents. Here we present molecular models of ABCB1, ABCC4 and ABCC5 by homology based on a wide open inward-facing conformation of Escherichia coli MsbA, which were constructed in order to elucidate differences in the electrostatic and molecular features of their drug recognition conformations. As a quality assurance of the methodology, the ABCB1 model was compared to an ABCB1 X-ray crystal structure, and with published cross-linking and site directed mutagenesis data of ABCB1. Amino acids Ile306 (TMH5), Ile340 (TMH6), Phe343 (TMH6), Phe728 (TMH7), and Val982 (TMH12), form a putative substrate recognition site in the ABCB1 model, which is confirmed by both the ABCB1 X-ray crystal structure and the site-directed mutagenesis studies. The ABCB1, ABCC4 and ABCC5 models display distinct differences in the electrostatic properties of their drug recognition sites.     

Involvement of ABCB1 and ABCC1 transporters in sea urchin Echinometra lucunter fertilization

Fertilization is an ordered sequence of cellular interactions that promotes gamete fusion to form a new individual. Since the pioneering work of Oskar Hertwig conducted on sea urchins, echinoderms have contributed to the understanding of cellular and molecular aspects of the fertilization processes. Studies on sea urchin spermatozoa reported the involvement of a plasma membrane protein that belongs to the ABC proteins superfamily in the acrosome reaction. ABC transporters are expressed in membranes of eukaryotic and prokaryotic cells, and are associated with the transport of several compounds or ions across biomembranes. We aimed to investigate ABCB1 and ABCC1 transporter activity in sea urchin spermatozoa and their involvement in fertilization. Our results indicate that Echinometra lucunter spermatozoa exhibit a low intracellular calcein accumulation (18.5% stained cells); however, the ABC blockers reversin205, verapamil, and MK571 increased dye accumulation (93.0–96.6% stained cells). We also demonstrated that pharmacologically blocking ABCB1 and ABCC1 decreased spermatozoa fertilizing capacity (70% inhibition), and this phenotype was independent of extracellular calcium. These data suggest that functional spermatozoa ABCB1 and ABCC1 transporters are crucial for a successful fertilization. Additional studies must be performed to investigate the involvement of membrane lipid homeostasis in the fertilization process. Mol. Reprod. Dev. 79: 861–869, 2012. © 2012 Wiley Periodicals, Inc.     

Phloroglucinol inhibits the bioactivities of endothelial progenitor cells and suppresses tumor angiogenesis in LLC-tumor-bearing mice

Background

There is increasing evidence that phloroglucinol, a compound from Ecklonia cava, induces the apoptosis of cancer cells, eventually suppressing tumor angiogenesis.

Methodology/Principal Findings

This is the first report on phloroglucinol''s ability to potentially inhibit the functional bioactivities of endothelial progenitor cells (EPCs) and thereby attenuate tumor growth and angiogenesis in the Lewis lung carcinoma (LLC)-tumor-bearing mouse model. Although Phloroglucinol did not affect their cell toxicity, it specifically inhibited vascular endothelial growth factor (VEGF) dependent migration and capillary-like tube formation of EPCs. Our matrigel plug assay clearly indicated that orally injected phloroglucinol effectively disrupts VEGF-induced neovessel formation. Moreover, we demonstrated that when phloroglucinol is orally administered, it significantly inhibits tumor growth and angiogenesis as well as CD45⁻/CD34⁺ progenitor mobilization into peripheral blood in vivo in the LLC-tumor-bearing mouse model.

Conclusions/Significance

These results suggest a novel role for phloroglucinol: Phloroglucinol might be a modulator of circulating EPC bioactivities, eventually suppressing tumorigenesis. Therefore, phloroglucinol might be a candidate compound for biosafe drugs that target tumor angiogenesis.     

Effect of ABCB1 and ABCC3 polymorphisms on osteosarcoma survival after chemotherapy: a pharmacogenetic study

Background

Standard treatment for osteosarcoma patients consists of a combination of cisplatin, adriamycin, and methotrexate before surgical resection of the primary tumour, followed by postoperative chemotherapy including vincristine and cyclophosphamide. Unfortunately, many patients still relapse or suffer adverse events. We examined whether common germline polymorphisms in chemotherapeutic transporter and metabolic pathway genes of the drugs used in standard osteosarcoma treatment may predict treatment response.

Methodology/Principal Findings

In this study we screened 102 osteosarcoma patients for 346 Single Nucleotide Polymorphisms (SNPs) and 2 Copy Number Variants (CNVs) in 24 genes involved in the metabolism or transport of cisplatin, adriamycin, methotrexate, vincristine, and cyclophosphamide. We studied the association of the genotypes with tumour response and overall survival. We found that four SNPs in two ATP-binding cassette genes were significantly associated with overall survival: rs4148416 in ABCC3 (per-allele HR = 8.14, 95%CI = 2.73-20.2, p-value = 5.1×10⁻⁵), and three SNPs in ABCB1, rs4148737 (per-allele HR = 3.66, 95%CI = 1.85–6.11, p-value = 6.9×10⁻⁵), rs1128503 and rs10276036 (r² = 1, per-allele HR = 0.24, 95%CI = 0.11–0.47 p-value = 7.9×10⁻⁵). Associations with these SNPs remained statistically significant after correction for multiple testing (all corrected p-values [permutation test] ≤0.03).

Conclusions

Our findings suggest that these polymorphisms may affect osteosarcoma treatment efficacy. If these associations are independently validated, these variants could be used as genetic predictors of clinical outcome in the treatment of osteosarcoma, helping in the design of individualized therapy.     

Impaired thymic selection and abnormal antigen-specific T cell responses in Foxn1(Δ/Δ) mutant mice

Background

Foxn1^Δ/Δ mutant mice have a specific defect in thymic development, characterized by a block in TEC differentiation at an intermediate progenitor stage, and blocks in thymocyte development at both the DN1 and DP cell stages, resulting in the production of abnormally functioning T cells that develop from an atypical progenitor population. In the current study, we tested the effects of these defects on thymic selection.

Methodology/Principal Findings

We used Foxn1^Δ/Δ; DO11 Tg and Foxn1^Δ/Δ; OT1 Tg mice as positive selection and Foxn1^Δ/Δ; MHCII I-E mice as negative selection models. We also used an in vivo system of antigen-specific reactivity to test the function of peripheral T cells. Our data show that the capacity for positive and negative selection of both CD4 and CD8 SP thymocytes was reduced in Foxn1^Δ/Δ mutants compared to Foxn1^+/Δ control mice. These defects were associated with reduction of both MHC Class I and Class II expression, although the resulting peripheral T cells have a broad TCR Vβ repertoire. In this deficient thymic environment, immature CD4 and CD8 SP thymocytes emigrate from the thymus into the periphery. These T cells had an incompletely activated profile under stimulation of the TCR signal in vitro, and were either hypersensitive or hyporesponsive to antigen-specific stimulation in vivo. These cell-autonomous defects were compounded by the hypocellular peripheral environment caused by low thymic output.

Conclusions/Significance

These data show that a primary defect in the thymic microenvironment can cause both direct defects in selection which can in turn cause indirect effects on the periphery, exacerbating functional defects in T cells.     

The bile acid receptor GPBAR-1 (TGR5) modulates integrity of intestinal barrier and immune response to experimental colitis

Background

GP-BAR1, a member G protein coupled receptor superfamily, is a cell surface bile acid-activated receptor highly expressed in the ileum and colon. In monocytes, ligation of GP-BAR1 by secondary bile acids results in a cAMP-dependent attenuation of cytokine generation.

Aims

To investigate the role GP-BAR1 in regulating intestinal homeostasis and inflammation-driven immune dysfunction in rodent models of colitis.

Methods

Colitis was induced in wild type and GP-BAR1^−/− mice by DSS and TNBS administration. Potential GP-BAR1 agonists were identified by in silico screening and computational docking studies.

Results

GP-BAR1^−/− mice develop an abnormal morphology of colonic mucous cells and an altered molecular architecture of epithelial tight junctions with increased expression and abnormal subcellular distribution of zonulin 1 resulting in increased intestinal permeability and susceptibility to develop severe colitis in response to DSS at early stage of life. By in silico screening and docking studies we identified ciprofloxacin as a GP-BAR1 ligand. In monocytes, ciprofloxacin increases cAMP concentrations and attenuates TNFα release induced by TLR4 ligation in a GP-BAR1 dependent manner. Treating mice rendered colitic by TNBS with ciprofloxacin and oleanolic acid, a well characterized GP-BAR1 ligand, abrogates signs and symptoms of colitis. Colonic expression of GP-BAR1 mRNA increases in rodent models of colitis and tissues from Crohn''s disease patients. Flow cytometry analysis demonstrates that ≈90% of CD14+ cells isolated from the lamina propria of TNBS-treated mice stained positively for GP-BAR1.

Conclusions

GP-BAR1 regulates intestinal barrier structure. Its expression increases in rodent models of colitis and Crohn''s disease. Ciprofloxacin is a GP-BAR1 ligand.     

Spry1 is expressed in hemangioblasts and negatively regulates primitive hematopoiesis and endothelial cell function

Background

Development of the hematopoietic and endothelial lineages derives from a common mesodermal precursor, the Flk1⁺ hemangioblast. However, the signaling pathways that regulate the development of hematopoietic and endothelial cells from this common progenitor cell remains incompletely understood. Using mouse models with a conditional Spry1 transgene, and a Spry1 knockout mouse, we investigated the role of Spry1 in the development of the endothelial and hematopoietic lineages during development.

Methodology/Principal Findings

Quantitative RT-PCR analysis demonstrates that Spry1, Spry2, and Spry4 are expressed in Flk1⁺ hemangioblasts in vivo, and decline significantly in c-Kit⁺ and CD41⁺ hematopoietic progenitors, while expression is maintained in developing endothelial cells. Tie2-Cre-mediated over-expression of Spry1 results in embryonic lethality. At E9.5 Spry1;Tie2-Cre embryos show near normal endothelial cell development and vessel patterning but have reduced hematopoiesis. FACS analysis shows a reduction of primitive hematopoietic progenitors and erythroblastic cells in Spry1;Tie2-Cre embryos compared to controls. Colony forming assays confirm the hematopoietic defects in Spry1;Tie2-Cre transgenic embryos. Immunostaining shows a significant reduction of CD41 or CD71 and dpERK co-stained cells in Spry1;Tie2-Cre embryos compared to controls, whereas the number of VEC⁺ and dpERK co-stained cells is comparable. Compared to controls, Spry1;Tie2-Cre embryos also show a decrease in proliferation and an increase in apoptosis. Furthermore, loss of Spry1 results in an increase of CD41⁺ and CD71⁺ cells at E9.5 compared with controls.

Conclusions/Significance

These data indicate that primitive hematopoietic cells derive from Tie2-expressing hemangioblasts and that Spry1 over expression inhibits primitive hematopoietic progenitor and erythroblastic cell development and expansion while having no obvious effect on endothelial cell development.     

Regulation of function by dimerization through the amino-terminal membrane-spanning domain of human ABCC1/MRP1

Overexpression of some ATP-binding cassette (ABC) membrane transporters such as ABCB1/P-glycoprotein/MDR1 and ABCC1/MRP1 causes multidrug resistance in cancer chemotherapy. It has been thought that half-ABC transporters with one nucleotide-binding domain and one membrane-spanning domain (MSD) likely work as dimers, whereas full-length transporters with two nucleotide-binding domains and two or three MSDs function as monomers. In this study, we examined the oligomeric status of the human full-length ABC transporter ABCC1/MRP1 using several biochemical approaches. We found 1) that it is a homodimer, 2) that the dimerization domain is located in the amino-terminal MSD0L0 (where L0 is loop 0) region, and 3) that MSD0L0 has a dominant-negative function when coexpressed with wild-type ABCC1/MRP1. These findings suggest that ABCC1/MRP1 may exist and function as a dimer and that MSD0L0 likely plays some structural and regulatory functions. It is also tempting to propose that the MSD0L0-mediated dimerization may be targeted for therapeutic development to sensitize ABCC1/MRP1-mediated drug resistance in cancer chemotherapy.     

The N-terminal extension domain of the C. elegans half-molecule ABC transporter, HMT-1, is required for protein-protein interactions and function

Background

Members of the HMT-1 (heavy metal tolerance factor 1) subfamily of the ATP-binding cassette (ABC) transporter superfamily detoxify heavy metals and have unique topology: they are half-molecule ABC transporters that, in addition to a single transmembrane domain (TMD1) and a single nucleotide-binding domain (NBD1), possess a hydrophobic NH2-terminal extension (NTE). These structural features distinguish HMTs from other ABC transporters in different species including Drosophila and humans. Functional ABC transporters, however, are comprised of at least four-domains (two TMDs and two NDBs) formed from either a single polypeptide or by the association of two or four separate subunits. Whether HMTs act as oligomers and what role the NTE domain plays in their function have not been determined.

Methodology/Principal Findings

In this study, we examined the oligomeric status of Caenorhabditis elegans HMT-1 and the functional significance of its NTE using gel-filtration chromatography in combination with the mating-based split-ubiquitin yeast two-hybrid system (mbSUS) and functional in vivo assays. We found that HMT-1 exists in a protein complex in C. elegans. Studies in S. cerevisiae showed that HMT-1 at a minimum homodimerizes and that oligomerization is essential for HMT-1 to confer cadmium tolerance. We also established that the NTE domain plays an important structural and functional role: it is essential for HMT-1 oligomerization and Cd-detoxification function. However, the NTE itself was not sufficient for oligomerization suggesting that multiple structural features of HMT-1 must associate to form a functional transporter.

Conclusions

The prominence of heavy metals as environmental toxins and the remarkable conservation of HMT-1 structural architecture and function in different species reinforce the value of continued studies of HMT-1 in model systems for identifying functional domains in HMT1 of humans.     

Insight into the interaction of metal ions with TroA from Streptococcus suis

Background

The scavenging ability of sufficient divalent metal ions is pivotal for pathogenic bacteria to survive in the host. ATP-binding cassette (ABC)-type metal transporters provide a considerable amount of different transition metals for bacterial growth. TroA is a substrate binding protein for uptake of multiple metal ions. However, the function and structure of the TroA homologue from the epidemic Streptococcus suis isolates (SsTroA) have not been characterized.

Methodology/Principal Findings

Here we determined the crystal structure of SsTroA from a highly pathogenic streptococcal toxic shock syndrome (STSS)-causing Streptococcus suis in complex with zinc. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that apo-SsTroA binds Zn²⁺ and Mn²⁺. Both metals bind to SsTroA with nanomolar affinity and stabilize the protein against thermal unfolding. Zn²⁺ and Mn²⁺ induce distinct conformational changes in SsTroA compared with the apo form as confirmed by both circular dichroism (CD) and nuclear magnetic resonance (NMR) spectra. NMR data also revealed that Zn²⁺/Mn²⁺ bind to SsTroA in either the same site or an adjacent region. Finally, we found that the folding of the metal-bound protein is more compact than the corresponding apoprotein.

Conclusions/Significance

Our findings reveal a mechanism for uptake of metal ions in S. suis and this mechanism provides a reasonable explanation as to how SsTroA operates in metal transport.     

Molecular Strategy to Reduce In Vivo Collagen Barrier Promotes Entry of NCX1 Positive Inducible Pluripotent Stem Cells (iPSCNCX1+) into Ischemic (or Injured) Myocardium

Objective

The purpose of this study was to assess the effect of collagen composition on engraftment of progenitor cells within infarcted myocardium.

Background

We previously reported that intramyocardial penetration of stem/progenitor cells in epicardial patches was enhanced when collagen was reduced in hearts overexpressing adenylyl cyclase-6 (AC6). In this study we hypothesized an alternative strategy wherein overexpression of microRNA-29b (miR-29b), inhibiting mRNAs that encode cardiac fibroblast proteins involved in fibrosis, would similarly facilitate progenitor cell migration into infarcted rat myocardium.

Methods

In vitro: A tri-cell patch (Tri-P) consisting of cardiac sodium-calcium exchanger-1 (NCX1) positive iPSC (iPSC^NCX1+), endothelial cells (EC), and mouse embryonic fibroblasts (MEF) was created, co-cultured, and seeded on isolated peritoneum. The expression of fibrosis-related genes was analyzed in cardiac fibroblasts (CFb) by qPCR and Western blot. In vivo: Nude rat hearts were administered mimic miRNA-29b (miR-29b), miRNA-29b inhibitor (Anti-29b), or negative mimic (Ctrl) before creation of an ischemically induced regional myocardial infarction (MI). The Tri-P was placed over the infarcted region 7 days later. Angiomyogenesis was analyzed by micro-CT imaging and immunofluorescent staining. Echocardiography was performed weekly.

Results

The number of green fluorescent protein positive (GFP⁺) cells, capillary density, and heart function were significantly increased in hearts overexpressing miR-29b as compared with Ctrl and Anti-29b groups. Conversely, down-regulation of miR-29b with anti-29b in vitro and in vivo induced interstitial fibrosis and cardiac remodeling.

Conclusion

Overexpression of miR-29b significantly reduced scar formation after MI and facilitated iPSC^NCX1+ penetration from the cell patch into the infarcted area, resulting in restoration of heart function after MI.     

Fractalkine expression induces endothelial progenitor cell lysis by natural killer cells

Background

Circulating 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 Findings

We 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.

Conclusions

Our 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.