Fractalkine expression on human renal tubular epithelial cells: potential role in mononuclear cell adhesion

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.

Regulation and function of CX3CR1 and its ligand CX3CL1 in kidney disease

Attraction, retention, and differentiation of leukocytes to and within the kidney are governed by chemokines. The chemokine CX3CL1 (fractalkine) and its receptor CX3CR1 are exemplary in this regard as they are highly expressed and further upregulated in a range of kidney diseases. CX3CL1 is chiefly produced by renal endothelium and tubular epithelium, where it promotes leukocyte attraction. Recent data suggest that in addition to established soluble mediators, cellular interactions may enhance CX3CL1 expression. The receptor CX3CR1 is essential in myeloid phagocyte homing to the kidney at homeostasis, after acute cell depletion and in inflammation. CX3CR1 and its ligand are highly regulated in human kidney diseases such as IgA nephritis, systemic lupus erythematosus, and inflammatory conditions such as transplant rejection. A mechanistic role of CX3CR1 has been established in experimental models of nephrotoxic nephritis and renal candidiasis. It is debated in fibrosis. Recent publications demonstrate a role for CX3CR1⁺ myeloid cells in radio-contrast-agent and sepsis-induced kidney damage. Systemically, circulating CX3CR1⁺ monocytes reversibly increase in individuals with renal impairment and correlate with their cardiovascular risk. In this review, we discuss role and regulatory mechanisms of the CX3CL1-CX3CR1 axis in both localized and systemic effects of renal inflammation.

CX3CR1 at V249M and T280M Gene Polymorphism and Its Potential Risk for End-Stage Renal Diseases in Egyptian Patients

CX3CL1-CX3CR1 pathway may be one of the future treatment targets to delay the progression of end-stage renal diseases. This study aimed to evaluate the CX3CR gene polymorphism in Egyptian patients with ESRD and its relation to fractalkine blood level. The study included 100 patients with ESRD on dialysis, 61 males and 39 females with mean age 51.02 ± 7.8 years. The V2491 genotype revealed a significant increase in the frequency of GG genotype in healthy control (83%) compared to patients [69%] with a significant increase in GA in patients [30%] compared to control subjects [15%], P = 0.03. T280M study showed a statistically significant prevalence of TT genotype in healthy control subjects [86%-OR 95% CI 1.7] compared to patients [70%] with a significant increase in the prevalence of TA in patients [29%] compared to control subjects [13%], P = 0.01. There was a significant increase in fractalkine levels in genotypes GA + AA [503.04±224.1] pg/ml compared to genotype GG [423.6 210.3], P = 0.03. Moreover, there was a significant increase in the blood level of fractalkine in genotype TA + AA [498.8 219.6] compared to genotype TT [426.8±212.8], P = 0.05. In conclusion, our study showed that both V2491-GA genotype and T280M-TA are associated with potential risk for end-stage renal disease in Egyptian patients.

The miR-561-5p/CX3CL1 Signaling Axis Regulates Pulmonary Metastasis in Hepatocellular Carcinoma Involving CX3CR1+ Natural Killer Cells Infiltration

Natural killer (NK) cell can inhibit tumor initiation and regulates metastatic dissemination, acting as key mediators of the innate immune response. Intrinsic factors modulating NK cells infiltration and its anticancer activity remain poorly characterized. We investigated the roles of dysregulation of micro(mi)RNAs and NK cells in progression of hepatocellular carcinoma (HCC).

Methods: Small RNA sequencing were used to detect the miRNA profiles of tumor tissues from HCC patients with (n=14) or without (n=13) pulmonary metastasis and HCC cell lines with different pulmonary metastatic potentials. Chemokine expression profiling and bioinformatics were used to detect the downstream target of candidate target. In gain- and loss-of-function assays were used to investigate the role of miRNA in HCC progression. Different subsets of NK cells were isolated and used for chemotaxis and functional assays in vivo and in vitro. In situ hybridization and immunohistochemical analyses were performed to detect the expression of miRNA in tumor tissues from 242 HCC patients undergoing curative resection from 2010.

Results: Three miRNAs (miR-137, miR-149-5p, and miR-561-5p) were identified to be associated with pulmonary metastasis in patients with HCC. miR-561-5p was most highly overexpressed in metastatic HCC tissues and high-metastatic-potential HCC cell lines. In gain- and loss-of-function assays in a murine model, miR-561-5p promoted tumor growth and spread to the lungs. Yet, miR-561-5p did not appear to affect cellular proliferation and migration in vitro. Bioinformatics and chemokine expression profiling identified chemokine (C-X₃-C motif) ligand 1 (CX₃CL1) as a potential target of miR-561-5p. Furthermore, miR-561-5p promoted tumorigenesis and metastasis via CX₃CL1-dependent regulation of CX₃CR1⁺ NK cell infiltration and function. CX₃CR1⁺ NK cells demonstrated stronger in vivo anti-metastatic activity relative to CX₃CR1^- NK cells. CX₃CL1 stimulated chemotactic migration and cytotoxicity in CX₃CR1⁺ NK cells via STAT3 signaling. Blockade of CX₃CL1, CX₃CR1, or of pSTAT3 signaling pathways attenuated the antitumor responses. Clinical samples exhibited a negative correlation between miR-561-5p expression and levels of CX₃CL1 and CX₃CR1⁺ NK cells. High miR-561-5p abundance, low CX₃CL1 levels, and low numbers of CX₃CR1⁺ NK cells were associated with adverse prognosis.

Conclusion: We delineated a miR-561-5p/CX3CL1/NK cell axis that drives HCC metastasis and demonstrated that CX₃CR1⁺ NK cells serve as potent antitumor therapeutic effectors.

Aptamer micelles targeting fractalkine-expressing cancer cells in vitro and in vivo

In this work we hypothesized that the chemokine fractalkine can serve as a cancer molecular target. We engineered aptamer micelles functionalized with an outer poly(ethylene glycol) (PEG) corona, and investigated the extent and efficacy of using them as a targeting tool against fractalkine-expressing colon adenocarcinoma cells. In vitro cell binding results showed that aptamer micelles bound and internalized to fractalkine-expressing cancer cells with the majority of the micelles found free in the cytoplasm. Minimal surface binding was observed by healthy cells. Even though partial PEGylation did not prevent serum adsorption, micelles were highly resistant to endonuclease and exonuclease degradation. In vivo biodistribution studies and confocal studies demonstrated that even though both aptamer and control micelles showed tumor accumulation, only the aptamer micelles internalized into fractalkine-expressing cancer cells, thus demonstrating the potential of the approach and showing that fractalkine may serve as a specific target for nanoparticle delivery to cancer cells.

CX3CL1/CX3CR1 Axis, as the Therapeutic Potential in Renal Diseases: Friend or Foe?

The fractalkine receptor chemokine (C-X3-C motif) receptor 1 (CX3CR1) and its highly selective ligand CX3CL1 mediate chemotaxis and adhesion of immune cells, which are involved in the pathogenesis and progression of numerous inflammatory disorders and malignancies. The CX3CL1/CX3CR1 axis has recently drawn attention as a potential therapeutic target because it is involved in the ontogeny, homeostatic migration, or colonization of renal phagocytes. We performed a Medline/PubMed search to detect recently published studies that explored the relationship between the CX3CL1/CX3CR1 axis and renal diseases and disorders, including diabetic nephropathy, renal allograft rejection, infectious renal diseases, IgA nephropathy, fibrotic kidney disease, lupus nephritis and glomerulonephritis, acute kidney injury and renal carcinoma. Most studies demonstrated its role in promoting renal pathopoiesis; however, several recent studies showed that the CX3CL1/CX3CR1 axis could also reduce renal pathopoiesis. Thus, the CX3CL1/CX3CR1 axis is now considered to be a double-edged sword that could provide novel perspectives into the pathogenesis and treatment of renal diseases and disorders.

Association of chemokine receptor CX3CR1 V249I and T280M polymorphisms with chronic kidney disease

The chemokine fractalkine (CX3CL1) and its receptor CX3CR1 are involved in the activation of leukocytes. Two common single-nucleotide polymorphisms of the CX3CR1 gene, V249I and T280M, have been associated with reduced fractalkine signaling, leading to decreased adhesive function and leukocyte chemotaxis. We hypothesized that variation in the CX3CR1 gene could be associated with chronic kidney disease (CKD), a disease of inflammatory activation. We studied the association between CX3CR1 V249I and T280M polymorphisms, and fractalkine and highly sensitive C-reactive protein (hs-CRP) levels in 123 patients with CKD and 100 healthy controls (HCs). Genotype analysis was done by polymerase chain reaction-restriction fragment length polymorphism, and fractalkine and hs-CRP levels were analyzed by enzyme-linked immunosorbent assay. MM genotype of T280M was absent in CKD patients, while in controls it was seen in 1% of the individuals. The allele frequencies in both the groups were similar (P = 0.059). Compared to HC, M280M + T280M genotype was more frequent in CKD (P = 0.041). The frequency of II genotype of V249I was 0.8% in CKD, whereas in HC, it was 2%. I249I + V249I genotype was more frequent in CKD as compared to HC (P = 0.034). No difference in allelic frequency of V249I was noted between the two groups (P = 0.061, odds ratios = 1.74, 95% confidence intervals = 0.96–3.12). Plasma fractalkine and serum hs-CRP levels were higher in CKD subjects (P = 0.004 and P < 0.0001). No association of either genotype was found with fractalkine and hs-CRP levels. Polymorphisms at I249 and M280 genotype in CX3CR1 gene are associated with CKD; however, there was no association of fractalkine or inflammatory marker with these genotypes.

Associations of fractalkine receptor (CX3CR1) and CCR5 gene variants with hypertension, diabetes and atherosclerosis in chronic renal failure patients undergoing hemodialysis

PURPOSE

We aimed to investigate the associations of fractalkine receptor (CX3CR1) V249I, T280M and CCR5-59029 A/G gene polymorphisms in chronic renal failure (CRF) subjects undergoing hemodialysis and to evaluate possible associations of these polymorphisms with hypertension (HT), diabetes mellitus (DM) and atherosclerosis (AS).

METHODS

A total of 225 CRF subjects undergoing hemodialysis and 201 healthy controls were enrolled in the study. CRF subjects were divided into three major subgroups according to comorbidities including HT (n = 127), DM (n = 65) and AS (n = 33). Genotyping was done using polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

The II genotype and I allele frequencies of CX3CR1 V249I polymorphism were found significantly more frequent in CRF subjects, CRF subjects with DM and CRF subjects with AS compared with controls (p < 0.05 for all comparisons). G allele frequency of CCR5 polymorphism was found significantly more prevalent in CRF subjects with DM than that of controls. Further, GG genotype and G allele frequencies of CCR5 polymorphism were significantly more prevalent in CRF subjects with AS compared with controls (p < 0.05). We also explored these polymorphisms among CRF subjects with and without following comorbidities: HT, DM, AS. We found significant association between CRF subjects with HT and without HT in terms of genotype and allele frequencies of V249I polymorphism (p < 0.05). CX3CR1 T280M polymorphism was not found significantly different in none of the comparisons.

CONCLUSION

These data demonstrate possible associations between CX3CR1 V249I and CCR5-59029 A/G polymorphisms and/or HT, DM and AS in CRF subjects.

New molecular insights in diabetic nephropathy

Diabetes mellitus represents one of the major causes of functional kidney impairment. The review highlights the most significant steps made over the last decades in understanding the molecular basis of diabetic nephropathy (DN), which may provide reliable biomarkers for early diagnosis and prognosis, along with new molecular targets for personalized medicine. There is an increased interest in developing new therapeutic strategies to slow DN progression for improving patients' quality of life and reducing all-cause morbidity and disease-associated mortality. It is highly important to have a science-based medical attitude when facing diabetic patients with associated comorbidities and risk of rapid evolution toward end-stage renal disease. The data discussed herein were mainly from MEDLINE and PubMed articles published in English from 1990 to 2015 and from up-to-date. The search term was "diabetic nephropathy and oxidative stress".

Upregulation of KSRP by miR-27b provides IFN-γ-induced post-transcriptional regulation of CX3CL1 in liver epithelial cells

Aberrant cellular responses to pro-inflammatory cytokines, such as IFN-γ, are pathogenic features in many chronic inflammatory diseases. A variety of feedback regulatory pathways have evolved to prevent an inappropriate cellular reaction to these pro-inflammatory cytokines. CX3CL1 is a unique chemokine and plays an important role in chronic liver diseases. We report here that IFN-γ stimulation induces a transient CX3CL1 production in liver epithelial cells (i.e., hepatocytes and biliary epithelial cells). This transient CX3CL1 production is accompanied with a destabilization of CX3CL1 mRNA associated with the induction of the KH-type splicing regulatory protein (KSRP). IFN-γ treatment of liver epithelial cells decreases expression level of miR-27b, a miRNA that targets the 3′ untranslated region of KSRP mRNA resulting in translational suppression. Induction of KSRP following IFN-γ stimulation depends on the downregulation of miR-27b. Functional manipulation of KSRP or miR-27b caused reciprocal alterations in CX3CL1 mRNA stability in liver epithelial cells. Moreover, transfection of miR-27b precursor influences CX3CL1-associated chemotaxis effects of biliary epithelial cells to Jurkat T cells. These findings suggest that miR-27b-mediated post-transcriptional suppression controls the expression of KSRP in liver epithelial cells, and upregulation of KSRP destabilizes CX3CL1 mRNA, providing fine-tuning of cellular inflammatory reactions in response to IFN-γ stimulation.

Fractalkine-CX3CR1-dependent recruitment and retention of human CD1c+ myeloid dendritic cells by in vitro-activated proximal tubular epithelial cells

Chemokines play pivotal roles in tissue recruitment and retention of leukocytes, with CX3CR1 recently identified as a chemokine receptor that selectively targets mouse kidney dendritic cells (DCs). We have previously demonstrated increased tubulointerstitial recruitment of human transforming growth factor-β (TGF-β)-producing DCs in renal fibrosis and chronic kidney disease (CKD). However, little is known about the mechanism of human DC recruitment and retention within the renal interstitium. We identified CD1c+ DCs as the predominant source of profibrotic TGF-β and highest expressors of the fractalkine receptor CX3CR1 within the renal DC compartment. Immunohistochemical analysis of diseased human kidney biopsies showed colocalization of CD1c+ DCs with fractalkine-positive proximal tubular epithelial cells (PTECs). Human primary PTEC activation with interferon-γ and tumor necrosis factor-α induced both secreted and surface fractalkine expression. In line with this, we found fractalkine-dependent chemotaxis of CD1c+ DCs to supernatant from activated PTECs. Finally, in comparison with unactivated PTECs, we showed significantly increased adhesion of CD1c+ DCs to activated PTECs via a fractalkine-dependent mechanism. Thus, TGF-β-producing CD1c+ DCs are recruited and retained in the renal tubulointerstitium by PTEC-derived fractalkine. These cells are then positioned to play a role in the development of fibrosis and progression of chronic kidney disease.

Non-coding RNAs in epithelial immunity to Cryptosporidium infection

Cryptosporidium spp. is a protozoan parasite that infects the gastrointestinal epithelium and causes diarrhoeal disease worldwide. It is one of the most common pathogens responsible for moderate to severe diarrhoea in children younger than 2 years. Because of the 'minimally invasive' nature of Cryptosporidium infection, mucosal epithelial cells are critical to the host's anti-Cryptosporidium immunity. Gastrointestinal epithelial cells not only provide the first and most rapid defence against Cryptosporidium infection, they also mobilize immune effector cells to the infection site to activate adaptive immunity. Recent advances in genomic research have revealed the existence of a large number of non-protein-coding RNA transcripts, so called non-coding RNAs (ncRNAs), in mammalian cells. Some ncRNAs may be key regulators for diverse biological functions, including innate immune responses. Specifically, ncRNAs may modulate epithelial immune responses at every step of the innate immune network following Cryptosporidium infection, including production of antimicrobial molecules, expression of cytokines/chemokines, release of epithelial cell-derived exosomes, and feedback regulation of immune homoeostasis. This review briefly summarizes the current science on ncRNA regulation of innate immunity to Cryptosporidium, with a focus on microRNA-associated epithelial immune responses.

Substantial proliferation of human renal tubular epithelial cell-reactive CD4+CD28null memory T cells, which is resistant to tacrolimus and everolimus

BACKGROUND

In spite of maintenance treatment with immunosuppressive drugs, tubulitis still occurs and can lead to structural kidney graft damage. We hypothesize that human renal tubular epithelial cells (TECs) trigger selective proliferation of recipient T-cell subsets with variable sensitivity to immunosuppressive drugs.

METHODS

Recipient peripheral blood mononuclear cells were cocultured with donor-derived TECs for 7 days. The proliferation of the total CD4 T-cell pool was assessed. Next, we analyzed which CD4 T-cell subset proliferated and how this response was affected by tacrolimus, everolimus, prednisolone, and mycophenolic acid (MPA) in clinically relevant concentrations.

RESULTS

CD4 T-cell proliferation upon TEC encounter was mainly executed by memory T cells. Interestingly, 38%±7% of the proliferating CD4 T-cell pool showed a CD28 phenotype. These proliferating CD4CD28 memory T cells produced high levels of interferon-γ, tumor necrosis factor-α, and the cytolitic protease granzyme B. TEC-reactive CD4 T-cell proliferation was significantly suppressed by tacrolimus, everolimus, prednisolone, and MPA (P<0.05). Surprisingly and in contrast to prednisolone and MPA, neither tacrolimus nor everolimus could inhibit the CD4CD28 T-cell proliferative response.

CONCLUSION

Our data show substantial proliferation of TEC-reactive CD4CD28 memory T cells, which are resistant to tacrolimus and everolimus. This phenomenon might play an important mechanistic role during cellular rejection under full immunosuppression.

Role of chemokines in proteinuric kidney disorders

Experimental and human studies have shown that proteinuria contributes to the progression of renal disease. Overexposure to filtered proteins promotes the expression and release of chemokines by tubular epithelial cells, thus leading to inflammatory cell recruitment and renal impairment. This review focuses on recent progress in cellular and molecular understanding of the role of chemokines in the pathogenesis of proteinuria-induced renal injury, as well as their clinical implications and therapeutic potential.

Histone deacetylases and NF-kB signaling coordinate expression of CX3CL1 in epithelial cells in response to microbial challenge by suppressing miR-424 and miR-503

The NF-kB pathway is key to epithelial immune defense and has been implicated in secretion of antimicrobial peptides, release of cytokines/chemokines to mobilize immune effector cells, and activation of adaptive immunity. The expression of many inflammatory genes following infection involves the remodeling of the chromatin structure. We reported here that histone deacetylases (HDACs) and NF-kB signaling coordinate expression of CX3CL1 in epithelial cells following Cryptosporidium parvum infection. Upregulation of CX3CL1 was detected in cultured human biliary epithelial cells following infection. Expression of miR-424 and miR-503 was downregulated, and was involved in the induction of CX3CL1 in infected cells. C. parvum infection suppressed transcription of the mir-424-503 gene in a NF-kB- and HDAC-dependent manner. Increased promoter recruitment of NF-kB p50 and HDACs, and decreased promoter H3 acetylation associated with the mir-424-503 gene were observed in infected cells. Upregulation of CX3CL1 in biliary epithelial cells and increased infiltration of CX3CR1⁺ cells were detected during C. parvum infection in vivo. Induction of CX3CL1 and downregulation of miR-424 and miR-503 were also detected in epithelial cells in response to LPS stimulation. The above results indicate that HDACs and NF-kB signaling coordinate epithelial expression of CX3CL1 to promote mucosal antimicrobial defense through suppression of the mir-424-503 gene.

NF-κB-mediated inverse regulation of fractalkine and CX3CR1 during CLP-induced sepsis

Fractalkine is a unique member of the CX3C chemokine family by unfolding its potential through the chemokine (C-X3-C motif) receptor 1 (CX3CR1) with dual function acting both as an adhesion molecule and a soluble chemokine. The regulation of this chemokine is still not clear. Therefore, we were interested in the regulation of fractalkine and of CX3CR1 in experimental sepsis. In addition, we investigated the role of NF-κB for the regulation of fractalkine and of CX3CR1. Using a mouse model of cecal ligation and puncture (CLP)-induced sepsis, we found elevated fractalkine mRNA levels in the heart, lung, kidney, and liver, as well as increased plasma levels 24 and 48h after CLP, respectively. In parallel, CLP resulted in a significant downregulation of CX3CR1 mRNA receptor expression in all investigated murine tissues. Septic mice that were pretreated with the selective NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) were found to have a decreased liberation of proinflammtory cytokines such as TNF-α, IL-1β, IL-6, or IFN-γ. Further PDTC pretreatment attenuated CLP-induced downregulation of CX3CR1 mRNA as well as CLP-induced upregulation of fractalkine mRNA expression in the heart, lung, kidney, liver, and the increase in fractalkine plasma levels of septic mice. In addition, CLP-induced downregulation of renal CX3CR1 protein expression was inhibited by PDTC-pretreatment. Taken together, our data indicate a CLP-induced inverse regulation of the expression between the relating ligand and the receptor with an upregulation of fractalkine and downregulation of CX3CR1, which seems to be mediated by the transcripting factor NF-κB likely via reduced liberation of proinflammtory cytokines in the whole murine organism.

Fractalkine and other chemokines in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by the autoimmune injury of small intrahepatic bile duct. On this basis, it has been suggested that the targeted biliary epithelial cells (BEC) play an active role in the perpetuation of autoimmunity by attracting immune cells via chemokine secretion. To address this issue, we challenged BEC using multiple toll-like receptor (TLR) ligands as well as autologous liver infiltrating mononuclear cells (LMNC) with subsequent measurement of BEC phenotype and chemokine production and LMNC chemotaxis by quantifying specific chemokines, specially CX3CL1 (fractalkine). We submit the hypothesis that BEC are in fact the innocent victims of the autoimmune injury and that the adaptive immune response is critical in PBC.

Impact of chemokine receptor CX3CR1 in human renal allograft rejection

Chemokine receptors play pivotal roles for leukocyte recruitment in acute and chronic inflammatory processes. This study was performed to analyze the expression, distribution and cellular localization of CX3CR1 in human renal transplant biopsies and to assess its role as potential diagnostic and prognostic marker. CX3CR1 was prospectively analyzed in 174 renal graft biopsies from patients with normal morphology (n=76), antibody-mediated acute rejection (n=6), acute tubulointerstitial rejection (n=27), acute vascular rejection (n=31), and with acute tubulus necrosis (n=34). Double immunofluorescence was additionally performed for CX3CR1 and CD4, CD8, CD20, CD68, and CD209/DC-SIGN. The number of CX3CR1 positive interstitial cells was significantly higher in the biopsies with acute tubulointerstitial and acute vascular rejection as compared to normal renal allograft biopsies. CX3CR1 positive cells were mainly CD68 positive monocytes/macrophages and CD209/DC-SIGN positive dendritic cells. The percentage of the CX3CR1 positive staining area was a predictor for steroid responsiveness and for worse clinical outcome 3 and 12 months after transplantation. CX3CR1 positive macrophages and/or dendritic cells are significantly elevated in acute renal allograft rejection. As CX3CR1 was associated with outcome parameters, it has to be further evaluated as a prognostic marker in human renal transplantation.

Role of CX3C-chemokine CX3C-L/fractalkine expression in a model of slowly progressive renal failure

BACKGROUND

The chemokine/chemokine receptor pair CX(3)C-L/CX(3)C-R is suspected to play a role in renal fibrogenesis. The aim of this study was to investigate their function in an animal model of slowly progressive chronic renal failure.

METHODS

Functional data were analysed in folic acid nephropathy (FAN) at different time points (up to day 142 after induction). Immunostaining for CX(3)C-L, CD3, S100A4, collagen type I, fibronectin, alpha-smooth muscle actin, Tamm-horsfall protein, aquaporin 1 and 2 as well as quantitative real-time PCR (qRT-PCR) for CX(3)C-L, CX(3)C-R and fibroblast-specific protein 1 (FSP-1) were performed. Additionally, regulatory mechanisms and functional activity of CX(3)C-L in murine proximal and distal tubular epithelial cells as well as in fibroblasts were investigated.

RESULTS

CX(3)C-L/GAPDH ratio was upregulated in FAN 3.4-fold at day 7 further increasing up to 7.1-fold at day 106. The expression of mRNA CX(3)C-L correlated well with CX(3)C-R (R(2) = 0.96), the number of infiltrating CD3+ cells (R(2) = 0.60) and the degree of tubulointerstitial fibrosis (R(2) = 0.56) and moderately with FSP-1 (R(2) = 0.33). Interleukin-1beta, tumour necrosis factor-alpha, transforming growth factor-beta as well as the reactive oxygen species (ROS) H(2)O(2) were identified by qRT-PCR as inductors of CX(3)C-L/fractalkine (FKN) in tubular epithelial cells. Functionally, CX(3)C-L/FKN chemoattracts peripheral blood mononuclear cells, activates several aspects of fibrogenesis and induces the mitogen-activated protein kinases in renal fibroblasts.

CONCLUSIONS

In FAN, there is a good correlation between the expression of CX(3)C-L with markers of interstitial inflammation and fibrosis which may result from upregulation by pro-inflammatory and pro-fibrotic cytokines as well as by ROS in tubular epithelial cells. The FKN system may promote renal inflammation and renal fibrogenesis.

Therapeutic RNA silencing of Cys-X3-Cys chemokine ligand 1 gene prevents mice from adenovirus vector-induced acute liver injury

Gene therapy using adenovirus vectors may induce acute liver injury. Tissue injury induced by an adenovirus is likely associated with elevated expression of the Cys-X3-Cys chemokine ligand 1 (CX(3)CL1)/fractalkine (FKN) protein at the site of inflammation. However, the extent to which the actions of FKN contribute to liver injury remains unclear. We induced acute liver injury in mice by a hydrodynamics-based injection of adenovirus vector, which was confirmed to depend on the presence of natural killer (NK) cells and NK-dependent interferon-gamma (IFN-gamma). When the transferred adenovirus vector was inserted with the FKN gene, the severity of liver injury increased with much more Cys-X3-Cys chemokine receptor 1 (CX(3)CR1)-positive NK cell recruitment into the liver because of exogenous overproduction of FKN protein. Moreover, when production of endogenous FKN protein was silenced by inserting FKN-small interfering RNA into the adenovirus vector or was neutralized by an FKN-specific antibody, the adenovirus-induced acute severe liver injury was notably prevented with much lower hepatic NK cell infiltration and a significant reduction in the serum levels of IFN-gamma.

CONCLUSION

Our findings suggest a strategy to prevent or alleviate adenovirus vector-induced acute liver injury by blocking FKN-CX(3)CR1 interaction in adenovirus vector-based gene therapy.

Tubular kidney injury molecule-1 (KIM-1) in human renal disease

KIM-1, a transmembrane tubular protein with unknown function, is undetectable in normal kidneys, but is markedly induced in experimental renal injury. The KIM-1 ectodomain is cleaved, detectable in urine, and reflects renal damage. KIM-1 expression in human renal biopsies and its correlation with urinary KIM-1 (uKIM-1) is unknown. In biopsies from various renal diseases (n = 102) and controls (n = 7), the fraction of KIM-1 positive tubules and different renal damage parameters were scored. Double labelling was performed for KIM-1 with macrophages (MØ), alpha-smooth muscle actin (alpha-SMA), proximal (aquaporin-1) and distal (E-cadherin) tubular markers and a dedifferentiation marker (vimentin). uKIM-1 at the time of biopsy (n = 53) was measured by ELISA. Renal KIM-1 was significantly increased in all diseases versus controls (p < 0.05), except minimal change. KIM-1 was primarily expressed at the luminal side of dedifferentiated proximal tubules, in areas with fibrosis (alpha-SMA) and inflammation (MØ). Independent of the disease, renal KIM-1 correlated positively with renal damage, negatively with renal function, but not with proteinuria. uKIM-1 was increased in renal patients versus controls (p < 0.001), including minimal change, and correlated positively with tissue KIM-1 and MØ, negatively with renal function, but not with proteinuria. In conclusion, KIM-1 is upregulated in renal disease and is associated with renal fibrosis and inflammation. uKIM-1 is also associated with inflammation and renal function, and reflects tissue KIM-1, indicating that it can be used as a non-invasive biomarker in renal disease.

Elevated levels of fractalkine expression and accumulation of CD16+ monocytes in glomeruli of active lupus nephritis

BACKGROUND

Fractalkine (Fkn) is a chemokine that affects cells expressing its receptor, CX3CR1, including CD16-positive (CD16+) monocytes/macrophages (CD16+ Mos). The relationship of levels of glomerular Fkn expression and infiltration by CD16+ Mos with the severity and diversity of glomerular lesions in human lupus nephritis is not known.

STUDY DESIGN

Retrospective cross-sectional analysis of variables observed in biopsy specimens.

SETTINGS & PARTICIPANTS

88 patients with systemic lupus erythematosus.

PREDICTOR

Histological class and severity of lupus nephritis according to the International Society of Nephrology/Renal Pathology Society and clinicopathologic factors.

OUTCOMES

Outcome variables are assays related to the degree of glomerular Fkn expression and CD16+ Mo infiltration.

MEASUREMENTS

Immunohistological grading of Fkn staining, number of CD16+ Mos, and messenger RNA levels of Fkn and CD16 in glomeruli.

RESULTS

Patients with proliferative lupus nephritis (class III and IV glomeruli) showed significantly greater glomerular Fkn expression and CD16+ Mo counts than those with other classes. Infiltrating CD16+ Mos within glomeruli expressed CX3CR1. Moreover, glomerular Fkn expression significantly correlated with the histopathologic activity index and CD16+ Mo counts, and CD16+ Mo counts significantly correlated with serum levels of blood urea nitrogen, complement (CH50), and anti-DNA antibody; estimated glomerular filtration rate; and urinary protein excretion. Glucocorticoid therapy had a tendency to decrease both glomerular Fkn expression and CD16+ Mo counts.

LIMITATIONS

Only frozen biopsy specimens (from 49 patients) were analyzed for the evaluation of glomerular Fkn expression.

CONCLUSION

Disease activity and proliferative glomerular lupus nephritis lesions are associated with the glomerular Fkn expression and CD16+ Mo accumulation.

Expression of fractalkine, CX3CR1, and vascular endothelial growth factor in human chronic renal allograft rejection

AIM

Fractalkine/CX3CR1 system may contribute to the pathogenesis of renal allograft chronic rejection (CR). Vascular endothelial growth factor (VEGF) is an endothelial mitogen, which shows increased expression in inflammation and vasculopathy. This study sought describe the expression and distribution of Fractalkine/CX3CR1 and VEGF, and their relationship to human renal allograft CR.

METHODS

Renal tissue from 10 patients with CR was examined for Fractalkine/CX3CR1 and VEGF protein by immunohistochemistry for comparison with patients displaying hyperacute rejection (n = 10), acute rejection (n = 10), and normal kidneys (n = 10). All patients were selected based upon histologically proven diagnoses between 1992 and 2003.

RESULTS

Immunohistochemistry revealed that Fractalkine/CX3CR1 were mostly expressed in the tubulointerstitium and tubular epithelial cell basolateral membrane. Some vessels showed positive staining for Fractalkine/CX3CR1 as well as occasionally glomerular parietal wall cells. Among the CR group, VEGF was mostly expressed in tubular epithelium and the tubulointerstitium. A proportion of glomeruli and vessels had positive staining for VEGF, which was up-regulated most strikingly in the interstitial compartment in CR. There was markedly increased expression of Fractalkine/CX3CR1 and VEGF protein in the interstitium of the CR compared with other groups (P < .05). VEGF colocalized with the expression of Fractalkine/CX3CR1.

CONCLUSION

Fractalkine/CX3CR1 and VEGF may play an important role in the development of interstitial fibrosis via mononuclear cell-induced cytokine production and myofibroblast stimulation in CR. Further studies are necessary to identify the role in the pathogenesis of CR.

Comparison of cyclosporine versus mycophenolate mofetil on expression of Fractalkine and CX3CR1 in chronic allograft nephropathy

INTRODUCTION

We sought to investigate whether there was a difference between cyclosporine (CsA) and mycophenolate mofetil (MMF) to affect the expression of Fractalkine/CX3CR1 in chronic allograft nephropathy (CAN).

METHODS

The Sprague-Dawley Wistar rat accelerated kidney sclerosis model was performed as modified from the procedure of Kamada. Recipients were divided into three oral treatment groups (each group n = 8): group A was CsA 10 mg/kg . d for 10 days followed by vehicle; group B was CsA 10 mg/kg . d for 10 days followed by CsA 6 mg/kg.d; group C was CsA 10 mg/kg . d for 10 days followed by MMF 20 mg/kg . d. Pathological changes graded according to Banff 97 Standards were observed at 4, 8, and 12 weeks posttransplantation. The immunohistochemistry and quantitative real-time fluorescence polymerase chain reaction (PCR) were used to assess the distribution and expression of Fractalkine/CX3CR1 in the grafted kidney.

RESULTS

Fractalkine/CX3CR1 were mostly expressed in the tubulointerstitium and tubular epithelial cell basolateral membrane. A proportion of the vessel showed positive staining for Fractalkine/CX3CR1, occasionally in glomerular parietal wall cells. The expression of Fractalkine/CX3CR1 in grafted kidneys at all the time points was significantly less in the MMF than in the CsA group or the control group (P < .05). Real-time fluorescence quantitative PCR revealed similar outcomes as immunohistochemistry. The expression of Fractalkine coincided with CX3CR1.

CONCLUSION

Fractalkine/CX3CR1 may play an important role in the development of interstitial fibrosis in CAN. Different immunosuppressants have various effects on expression of the Fractalkine/CX3CR1.

Expression and targeting of CX3CL1 (fractalkine) in renal tubular epithelial cells

The chemokine CX3CL1 plays a key role in glomerulonephritis and can act as both chemoattractant and adhesion molecule. CX3CL1 also is upregulated in tubulointerstitial injury, but little is known about the subcellular distribution and function of CX3CL1 in renal tubular epithelial cells (RTEC). Unexpectedly, it was found that CX3CL1 is expressed predominantly on the apical surface of tubular epithelium in human renal transplant biopsy specimens with acute rejection or acute tubular necrosis. For studying the targeting of CX3CL1 in polarized RTEC, MDCK cells that expressed untagged or green fluorescent protein-tagged CX3CL1 were generated. The chemokine was present on the apical membrane and in subapical vesicles. Apical targeting of CX3CL1 was not due to signals that were conferred by its intracellular domain, to associations with lipid rafts, or to O-glycosylation but, rather, depended on N-linked glycosylation of the protein. With the use of fluorescence recovery after photobleaching, it was found that CX3CL1 is immobile in the apical membrane. However, CX3CL1 partitioned with the triton-soluble rather than -insoluble cellular fraction, indicating that it is not associated directly with the actin cytoskeleton or with lipid rafts. Accordingly, disruption of rafts through cholesterol depletion did not render CX3CL1 mobile. For exploration of potential functions of apical CX3CL1, binding of CX3CR1-expressing leukocytes to polarized RTEC was examined. Leukocyte adhesion to the luminal surface was enhanced significantly when CX3CL1 was present. These data demonstrate that CX3CL1 is expressed preferentially on the apical membrane of RTEC and suggest a novel function for the chemokine in recruitment and retention of leukocytes in tubulointerstitial inflammation.

Involvement of the fractalkine pathway in the pathogenesis of childhood hemolytic uremic syndrome

Thrombotic microangiopathy and acute renal failure are cardinal features of postdiarrheal hemolytic uremic syndrome (HUS). These conditions are related to endothelial and epithelial cell damage induced by Shiga toxin (Stx) through the interaction with its globotriaosyl ceramide receptor. However, inflammatory processes contribute to the pathogenesis of HUS by sensitizing cells to Stx fractalkine (FKN), a CX(3)C transmembrane chemokine expressed on epithelial and endothelial cells upon activation, is involved in the selective migration and adhesion of specific leukocyte subsets to tissues. Here, we demonstrated a selective depletion of circulating mononuclear leukocytes expressing the receptor for FKN (CX(3)CR1) in patients with HUS. We found a unique phenotype in children with HUS distinct from that seen in healthy, uremic, or infected controls, in which monocytes lost CX(3)CR1, down-modulated CD62L, and increased CD16. In addition, the CD56(dim) natural killer (NK) subpopulation was decreased, leading to an altered peripheral CD56(dim)/CD56(bright) ratio from 10.0 to 4.5. It is noteworthy that a negative correlation existed between the percentage of circulating CX(3)CR1(+) leukocytes and the severity of renal failure. Finally, CX(3)CR1(+) leukocytes were observed in renal biopsies from patients with HUS. We suggest that the interaction of CX(3)CR1(+) cells with FKN present on activated endothelial cells may contribute to renal injury in HUS.

Leukocyte recruitment and vascular injury in diabetic nephropathy

Different types of activated leukocytes play a crucial role in the pathogenesis of most kidney diseases from acute to chronic stages; however, diabetic nephropathy was not considered an inflammatory disease in the past. This view is changing now because there is a growing body of evidence implicating inflammatory cells at every stage of diabetic nephropathy. Renal tissue macrophages, T cells, and neutrophils produce various reactive oxygen species, proinflammatory cytokines, metalloproteinases, and growth factors, which modulate the local response and increase inflammation within the diabetic kidney. Although the precise mechanisms that direct leukocyte homing into renal tissues are not fully identified, it has been reported that intercellular adhesion molecule-1 and the chemokines CCL2 and CX3CL1 probably are involved in leukocyte migration in diabetic nephropathy. This review focuses on the molecular mechanisms of leukocyte recruitment into the diabetic kidney and the involvement of immigrated immune cells in the damage to renal tissues.

Urinary biomarkers in lupus nephritis

There has long been a need for biomarkers of disease activity in lupus nephritis (LN). Such markers ideally would be capable of detecting early sub-clinical disease and could be used to gauge response to therapy thus obviating the need for serial renal biopsies. Since urine can be readily obtained it lends itself as an obvious biological sample. Much of the focus has been on the measurement of urinary chemokines and cytokines in patients with LN. Elevations in urinary IL-6 and IL-10 had initially been reported to be associated with disease activity in LN but these markers have proven to be less reliable in larger studies. We and others have recently reported that MCP-1, a key chemokine involved in monocyte chemotaxis can be consistently found at high levels in the urine of patients with active LN. Moreover urinary MCP-1 levels decline with treatment of nephritis. In contrast urinary IL-8, a chemokine involved primarily in neutrophil chemotaxis is not a good predictor of disease activity in LN. Further longitudinal studies with larger numbers of patients are needed to determine the utility of urinary biomarkers such as MCP-1 which may act as surrogates of ongoing inflammation in LN.

Mechanisms of Disease: cell death in acute renal failure and emerging evidence for a protective role of erythropoietin

Acute renal failure--characterized by a sudden loss of the ability of the kidneys to excrete nitrogenous waste, and to maintain electrolyte homeostasis and fluid balance--is a frequently encountered clinical problem, particularly in the intensive care unit. Unfortunately, advances in supportive interventions have done little to reduce the high mortality associated with this condition. Might erythropoietin (EPO) have utility as a therapeutic agent in acute renal failure? This hormone mediates anti-apoptotic effects in the bone marrow, facilitating maturation and differentiation of erythroid progenitors. New evidence indicates that EPO also exerts anti-apoptotic effects in the brain, heart and vasculature, which can limit the degree of organ damage. Here, we review the emerging biological role of EPO in the kidney and the pathophysiology of ischemia-reperfusion injury in an attempt to understand the therapeutic potential of EPO in acute renal failure.

Agonist of peroxisome proliferator-activated receptor-gamma, rosiglitazone, reduces renal injury and dysfunction in a murine sepsis model

BACKGROUND

Agonists of the peroxisome proliferator-activated receptor-gamma may help to regulate inflammation by modulating the production of inflammatory mediators and adhesion molecules. The purpose of this study was to determine the protective effects of rosiglitazone on renal injury in a sepsis model and to explore the mechanism.

METHODS

In lipopolysaccharide (LPS)-induced mouse sepsis, we examined the effect of rosiglitazone on LPS-induced overproduction of inflammatory mediators, on the expression of adhesion molecules in renal tubular epithelial cells and on renal function. The mechanism of the protective effect was investigated in vitro using human renal tubular epithelial cells.

RESULTS

Rosiglitazone significantly decreased serum tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta levels during sepsis. The levels of blood urea nitrogen and creatinine were significantly lower in mice pre-treated with rosiglitazone than that in LPS-treated mice. Rosiglitazone reduced the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in tubular epithelial cells and interstitium of LPS-treated mice. Pre-treatment with rosiglitazone reduced the infiltration of macrophages/monocytes in renal tissue. In cultured tubular epithelial cells, rosiglitazone significantly decreased the expression of ICAM-1 and VCAM-1 induced by TNF-alpha or IL-1beta, inhibited the degradation of inhibitor kappaBalpha (IkappaBalpha) and blocked the activation of the p65 subunit of nuclear factor (NF)-kappaB.

CONCLUSIONS

These results indicate that pre-treatment with rosiglitazone attenuated the production of TNF-alpha and IL-1beta and reduced adhesion molecule expression in renal tubular epithelial cells of LPS-treated mice. Rosiglitazone has an anti-inflammatory effect in renal tubular epithelial cells through the inhibition of NF-kappaB activation.

Fractalkine and CX3CR1 are involved in the recruitment of intraepithelial lymphocytes of intrahepatic bile ducts

Fractalkine is a chemokine with both chemoattractant and cell-adhesive functions, and in the intestine it is involved with its receptor CX3CR1 in the chemoattraction and recruitment of intraepithelial lymphocytes. We examined the pathophysiological roles of fractalkine and CX3CR1 in normal and diseased bile ducts. Expression of fractalkine and CX3CR1 were examined in liver tissues from patients with primary biliary cirrhosis (17 cases) and controls (9 cases of primary sclerosing cholangitis, 10 cases of extrahepatic biliary obstruction, 20 cases of chronic viral hepatitis C, and 18 cases of histologically normal livers). Expression of fractalkine in biliary epithelial cells (BECs) in response to cytokine treatments was examined using a human cholangiocarcinoma cell line (HuCC-T1) and human intrahepatic BEC line. The chemotaxis of CX3CR1-expressing monocytes (THP-1) toward fractalkine was assayed using chemotaxis chambers. Fractalkine messenger RNA/protein were expressed on BECs of normal and diseased bile ducts, and their expression was upregulated in injured bile ducts of primary biliary cirrhosis. CX3CR1 was expressed on infiltrating mononuclear cells in portal tracts and on CD3(+), CD4(+), and CD8(+) intraepithelial lymphocytes of injured bile ducts in primary biliary cirrhosis. Fractalkine messenger RNA expression was upregulated in two cultured BECs on treatment with lipopolysaccharide and Th1-cytokines (interleukin 1beta, interferon gamma, and tumor necrosis factor alpha). THP-1 cells showed chemotaxis toward fractalkine secreted by cultured cells. In conclusion, Th1-cytokine predominance and lipopolysaccharide in the microenvironment of injured bile ducts resulting from primary biliary cirrhosis induce the upregulation of fractalkine expression in BECs, followed by the chemoattraction of CX3CR1-expressing mononuclear cells, including CD4(+) and CD8(+) T cells, and their adhesion to BECs and the accumulation of biliary intraepithelial lymphocytes.

Quantitative gene expression analysis of fractalkine using laser microdissection in biopsies from kidney allografts with acute rejection

Percutaneous biopsy of the kidney remains the gold standard to establish a diagnosis in renal diseases. Only semiquantitative assessments of gene expression on biopsies have been possible so far. We studied gene expression of the chemokine fractalkine (FKN) in 12 biopsies from laser microdissected kidney allografts that showed histologic signs of acute rejection and 10 controls. As quantified by real-time PCR, the relative tubular FKN expression increased from 1.0 [0.81 to 2.95] (median [range]) in controls to 12.44 [0.90 to 191.0] in acute rejection (P < .01); glomerular FKN expression from 1.3 [0.07 to 27.44] to 12.22 [1.32 to 50.23] (P < .05); and vascular expression, from 0.72 [0.37 to 5.11] to 7.07 [1.19 to 73.49] (P < .01). Furthermore, there was a trend toward higher glomerular FKN expression among patients with more severe rejection. Our results suggest a role of FKN in acute renal allograft rejection.

Protein overload induces fractalkine upregulation in proximal tubular cells through nuclear factor kappaB- and p38 mitogen-activated protein kinase-dependent pathways

Investigated was the effect of high albumin concentrations on proximal tubular cell expression of fractalkine. Human proximal tubular cells (HK-2) were incubated with human serum albumin (HSA), which induced a dose-dependent increase in fractalkine mRNA associated with increased levels of both membrane-bound and soluble forms of the protein. To evaluate the role of nuclear factor kappaB (NF-kappaB) activation in HSA-induced fractalkine mRNA, HK-2 cells were infected with a recombinant adenovirus encoding the natural inhibitor of NF-kappaB, IkBalpha; a 43% reduction of fractalkine mRNA levels resulted. Similarly, when cells were infected with the recombinant adenovirus expressing dominant negative mutant of the IkB kinase 2, a 55% inhibition of fractalkine mRNA was achieved. p38 mitogen-activated protein kinase was activated by HSA and was involved in NF-kappaB-dependent transcription of fractalkine. In kidneys of mice with bovine serum albumin overload proteinuria, fractalkine mRNA levels were 2.3-fold greater than those of controls. Fractalkine expression was also induced in tubular epithelial cells in this model. Anti-CXCR1 antibody treatment limited interstitial accumulation of mononuclear cells. Protein overload is a promoter of fractalkine gene induction mediated by NF-kappaB and p38 activation in proximal tubular cells. Fractalkine might contribute to direct mononuclear cells into peritubular interstitium and enhance their adhesion property, which in turn would favor inflammation and disease progression.

Fractalkine/CX3CL1 production by human airway smooth muscle cells: induction by IFN-gamma and TNF-alpha and regulation by TGF-beta and corticosteroids

Chemokine synthesis by airway smooth muscle cells (ASMC) may be an important process underlying inflammatory cell recruitment in airway inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD). Fractalkine (FKN) is a recently described CX(3)C chemokine that has dual functions, serving as both a cell adhesion molecule and a chemoattractant for monocytes and T cells, expressing its unique receptor, CX(3)CR1. We investigated FKN expression by human ASMC in response to the proinflammatory cytokines IL-1beta, TNF-alpha, and IFN-gamma, the T helper 2-type cytokines IL-4, IL-10, and IL-13, and the fibrogenic cytokine transforming growth factor (TGF)-beta. Neither of these cytokines alone had any significant effect on ASMC FKN production. Combined stimulation with IFN-gamma and TNF-alpha induced FKN mRNA and protein expression in a time- and concentration-dependent manner. TGF-beta had a significant inhibitory effect on cytokine-induced FKN mRNA and protein expression. Dexamethasone (10(-8)-10(-6) M) significantly upregulated cytokine-induced FKN mRNA and protein expression. Finally, we used selective inhibitors of the mitogen-activated protein kinases c-Jun NH(2)-terminal kinase (JNK) (SP-610025), p38 (SB-203580), and extracellular signal-regulated kinase (PD-98095) to investigate their role in FKN production. SP-610025 (25 microM) and SB-203580 (20 microM), but not PD-98095, significantly attenuated cytokine-induced FKN protein synthesis. IFN-gamma- and TNF-alpha-induced JNK phosphorylation remained unaltered in the presence of TGF-beta but was inhibited by dexamethasone, indicating that JNK is not involved in TGF-beta- or dexamethasone-mediated regulation of FKN production. In summary, FKN production by human ASMC in vitro is regulated by inflammatory and anti-inflammatory factors.

Ischemic acute renal failure: An inflammatory disease?

Inflammation plays a major role in the pathophysiology of acute renal failure resulting from ischemia. In this review, we discuss the contribution of endothelial and epithelial cells and leukocytes to this inflammatory response. The roles of cytokines/chemokines in the injury and recovery phase are reviewed. The ability of the mouse kidney to be protected by prior exposure to ischemia or urinary tract obstruction is discussed as a potential model to emulate as we search for pharmacologic agents that will serve to protect the kidney against injury. Understanding the inflammatory response prevalent in ischemic kidney injury will facilitate identification of molecular targets for therapeutic intervention.

Immunohistochemical assessment of fractalkine, inflammatory cells, and human herpesvirus 7 in human salivary glands

Human fractalkine (CX3CL1), a delta-chemokine, is implicated in the mediation of multiple cell functions. In addition to serving as a chemotactic factor for mononuclear cell subtypes, membrane-bound fractalkine may promote viral infection by interacting with virions that encode putative fractalkine-binding proteins. Fractalkine expression in normal epithelial tissues studied to date is either constitutive or is upregulated with inflammation. In salivary glands, the expression of fractalkine is unknown. Moreover, salivary glands are a major site for the persistent and productive infection by human herpesvirus (HHV)-7, which encodes two putative fractalkine-binding gene products, U12 and U51. Surprisingly, the cellular distribution of HHV-7 in major salivary glands has not been explored. We therefore determined by immunohistochemistry the cellular localization of fractalkine in three different salivary glands: parotid, submandibular, and labial glands. Fractalkine expression was highly variable, ranging from high to undetectable levels. We further examined the association of fractalkine with inflammatory cell infiltration or HHV-7 infection of salivary epithelial cells. Inflammatory cells were always adjacent to epithelial cells expressing fractalkine, consistent with a function of fractalkine in inflammatory cell recruitment and/or retention in salivary glands. In contrast, HHV-7-infected epithelial cells did not always express fractalkine, suggesting that fractalkine may not be an absolute requirement for viral entry.

Fractalkine in vascular biology: from basic research to clinical disease

Fractalkine (now also called CX3CL1) is a unique chemokine that functions not only as a chemoattractant but also as an adhesion molecule and is expressed on endothelial cells activated by proinflammatory cytokines, such as interferon-gamma and tumor necrosis factor-alpha. The fractalkine receptor, CX3CR1, is expressed on cytotoxic effector lymphocytes, including natural killer (NK) cells and cytotoxic T lymphocytes, which contain high levels of intracellular perforin and granzyme B, and on macrophages. Soluble fractalkine causes migration of NK cells, cytotoxic T lymphocytes, and macrophages, whereas the membrane-bound form captures and enhances the subsequent migration of these cells in response to secondary stimulation with other chemokines. Furthermore, stimulation through membrane-bound fractalkine activates NK cells, leading to increased cytotoxicity and interferon-gamma production. Recently, accumulating evidence has shown that fractalkine is involved in the pathogenesis of various clinical disease states or processes, such as atherosclerosis, glomerulonephritis, cardiac allograft rejection, and rheumatoid arthritis. In addition, polymorphisms in CX3CR1, which reduce its binding activity to fractalkine, have been reported to increase the risk of HIV disease and to reduce the risk of coronary artery disease. This review will examine new concepts underlying fractalkine-mediated leukocyte migration and tissue damage, focusing primarily on the pathophysiological roles of fractalkine in various clinical conditions, especially in atherosclerosis and vascular injury.

Expression of CX3CL1/fractalkine by mesangial cells in vitro and in acute anti-Thy1 glomerulonephritis in rats

BACKGROUND

Mesangial cells (MCs) can promote glomerular macrophage accumulation in glomerulonephritis through production of a variety of chemokines. This study investigated the potential of MCs to synthesize CX3CL1/fractalkine, a CX3C chemokine, both in vitro and in acute anti-Thy1 glomerulonephritis in rats.

METHODS

Anti-Thy1 glomerulonephritis was induced in Wistar rats by a single injection of mouse anti-rat Thy1.1 antibody intravenously. Glomerular mRNAs for CX3CL1/fractalkine, CCL2/monocyte chemoattractant protein (MCP)-1, and their cognate receptors, CX3CR1 and CCR2, were determined by northern blot analysis or reverse-transcription polymerase chain reaction. CX3CL1/fractalkine mRNA and protein expression in vivo was localized by in situ hybridization and immunohistochemistry. Monocytes/macrophages and activated MCs were detected by immunohistochemistry. Regulation of CX3CL1/fractalkine expression in cultured MCs was determined by northern and western blot analysis.

RESULTS

After induction of anti-Thy1 disease, glomerular CX3CL1/fractalkine mRNA was significantly up-regulated, peaking at 2 h and sustaining into day 5 of the nephritis. A corresponding increase in urinary CX3CL1/fractalkine protein was evident after day 1 of the nephritis, but became more prominent during the MC proliferative phase (days 3-5). Meanwhile, induction of glomerular CCL2/MCP-1 mRNA and urinary CCL2/MCP-1 protein occurred within 24 h, and was barely detectable after day 3 of the nephritis. Urinary CCL2/MCP-1, but not CX3CL1/fractalkine, correlated with glomerular macrophage accumulation (r = 0.936, P<0.01) and glomerular CCR2 mRNA expression (r = 0.965, P<0.01). In contrast, only urinary CX3CL1/fractalkine coincided temporally to glomerular mRNA for CX3CR1 (r = 0.809, P < 0.01). Combined in situ hybridization and immunohistochemistry revealed that activated MCs were a major source for CX3CL1/fractalkine mRNA and protein during days 3-5 of the nephritis. Incubation of cultured MCs with tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, platelet-derived growth factor (PDGF)-AB or basic fibroblast growth factor (bFGF) significantly up-regulated CX3CL1/fractalkine mRNA and protein expression. This cytokine- and growth factor-stimulated CX3CL1/fractalkine expression could be abolished by the nuclear factor-kappaB inhibitors, curcumin and MG132.

CONCLUSIONS

Our data demonstrate that activated MCs are a source for the augmented glomerular CX3CL1/fractalkine expression during the proliferative phase of acute anti-Thy1 glomerulonephritis. Up-regulation of MC CX3CL1/fractalkine by TNF-alpha, IL-1beta, PDGF-AB and bFGF is mediated, at least in part, via the nuclear factor-kappaB signalling pathway. The differential expression of CCL2/MCP-1 and CX3CL1/fractalkine may sequentially recruit distinct subsets of monocytes to the glomerulus during acute anti-Thy1 glomerulonephritis.

Enhanced disease and pulmonary eosinophilia associated with formalin-inactivated respiratory syncytial virus vaccination are linked to G glycoprotein CX3C-CX3CR1 interaction and expression of substance P

Vaccination with formalin-inactivated respiratory syncytial virus (FI-RSV) vaccine or RSV G glycoprotein results in enhanced pulmonary disease after live RSV infection. Enhanced pulmonary disease is characterized by pulmonary eosinophilia and is associated with a substantial inflammatory response. We show that the absence of the G glycoprotein or G glycoprotein CX3C motif during FI-RSV vaccination or RSV challenge of FI-RSV-vaccinated mice, or treatment with anti-substance P or anti-CX3CR1 antibodies, reduces or eliminates enhanced pulmonary disease, modifies T-cell receptor Vbeta usage, and alters CC and CXC chemokine expression. These data suggest that the G glycoprotein, and in particular the G glycoprotein CX3C motif, is key in the enhanced inflammatory response to FI-RSV vaccination, possibly through the induction of substance P.

Fractalkine is not a major chemoattractant for the migration of neutrophils across microvascular endothelium

Inflammatory responses during sepsis are determined by leucocyte recruitment into inflamed tissues. Both chemokines and adhesion molecules are believed to be involved in this process. As fractalkine exists as transmembrane protein with cell adhesion properties and as soluble chemotactic factor, the present study was conducted to study the role of fractalkine, produced by microvascular and macrovascular endothelial cells, in neutrophil recruitment. Lung microvascular endothelial cells (LMVECs) stimulated with lipopolysaccharide, tumour necrosis factor-alpha or interleukin-1 (IL-1) produced much more fractalkine compared with the macrovascular human umbilical vein endothelial cells (HUVECs). No differences were found between microvascular endothelial cells of different organs. Chemotactic activity in supernatants was significantly stronger in stimulated LMVEC when compared with HUVEC. Although recombinant fractalkine induced migration of neutrophils, IL-8 and monocyte chemoattractant protein-1 were found to be more strictly required. In vivo fractalkine was strongly upregulated in septic lung and kidney. Our data suggest that fractalkine production per se does not explain the preference for inflammation in the lung of septic patients.

Chemokines and chemokine receptors in renal pathology

PURPOSE OF REVIEW

Chemokines are members of the largest group of chemotactic cytokines, and were the first shown to be able to engage specific subpopulations of inflammatory cells. Accordingly, our expanding knowledge in chemokine biology has enlarged our understanding of inflammatory cell interactions, lymphopoesis, specificity of cell recruitment, and a variety of human diseases. This review covers recent developments on chemokines in renal diseases.

RECENT FINDINGS

Intrinsic renal cells are capable of chemokine expression in vitro and in vivo, and the involved induction pathways are becoming increasingly defined. Differential chemokine expression during the time course of disease, followed by an infiltration of cells expressing the corresponding receptors has been described in animal models. Therapeutic efficacy of chemokine blockade has been demonstrated in a variety of disease models, including progressive interstitial fibrosis. Chemokine receptors are differentially expressed and localized to specific parenchymal compartments in human renal diseases, as revealed by studies of renal biopsies, and some functional roles of specific chemokine/receptor interactions can be deduced through the correlation of patterns of expression, genetic variations and disease courses.

SUMMARY

Chemokines play an important role in renal inflammation. Although the treatment of patients with renal diseases using chemokine receptor blocking agents has not yet reached clinical practice, a recent body of data indicates that human renal disease might be amenable to such approaches.