CD44 in glomerulonephritis: expression in human renal biopsies, the Thy 1.1 model, and by cultured mesangial cells

Role of CD44 expressed in renal tubules during maladaptive repair in renal fibrogenesis in an allopurinol-induced rat model of chronic kidney disease

The kidney is a major target organ for the adverse effects of pharmaceuticals; renal tubular epithelial cells (TECs) are particularly vulnerable to drug-induced toxicity. TECs have regenerative capacity; however, maladaptive repair of TECs after injury leads to renal fibrosis, resulting in chronic kidney disease (CKD). We previously reported the specific expression of CD44 in failed-repair TECs of rat CKD model induced by ischemia reperfusion injury. Here, we investigated the pathophysiological role of CD44 in renal fibrogenesis in allopurinol-treated rat CKD model. Dilated or atrophic TECs expressing CD44 in fibrotic areas were collected by laser microdissection and subjected to microarray analysis. Gene ontology showed that extracellular matrix (ECM)-related genes were upregulated and differentiation-related genes were downregulated in dilated/atrophic TECs. Ingenuity Pathway Analysis identified CD44 as an upstream regulator of fibrosis-related genes, including Fn1, which encodes fibronectin. Immunohistochemistry demonstrated that dilated/atrophic TECs expressing CD44 showed decreases in differentiation markers of TECs and clear expression of mesenchymal markers during basement membrane attachment. In situ hybridization revealed an increase in Fn1 mRNA in the cytoplasm of dilated/atrophic TECs, whereas fibronectin was localized in the stroma around these TECs, supporting the production/secretion of ECM by dilated/atrophic TECs. Overall, these data indicated that dilated/atrophic TECs underwent a partial epithelial-mesenchymal transition (pEMT) and that CD44 promoted renal fibrogenesis via induction of ECM production in failed-repair TECs exhibiting pEMT. CD44 was detected in the urine and serum of APL-treated rats, which may reflect the expression of CD44 in the kidney.

Transcriptome analysis of renal ischemia/reperfusion (I/R) injury in BAFF and BAFF-R deficient mice

Acute kidney injury (AKI) accompanies with high morbidity and mortality. Incomplete renal recovery can lead to chronic and finally end-stage kidney disease, which results in the requirement of lifelong dialysis or kidney transplantation. Consequently, finding predictive biomarker and therefore developing preventive therapeutic approaches is an urgent need. For this purpose, a better understanding of the mechanism underlying AKI is necessary. The cytokine BAFF (B cell activating factor) is related to AKI by supporting B cells, which in turn play an important role in inflammatory processes and the production of antibodies. In our study, we investigated the role of BAFF and its receptor BAFF-R in the early phase of AKI. Therefore, we performed the well-established ischemia/reperfusion (I/R) model in BAFF (B6.129S2-Tnfsf13btm1Msc/J) and BAFF-R (B6(Cg)-Tnfrsf13ctm1Mass/J) deficient mice. Transcriptome of ischemic and contralateral control kidneys was analyzed and compared to wildtype littermates. We detected the upregulation of Lcn2, Lyz2, Cd44, Fn1 and Il1rn in ischemic kidneys as well as the downregulation of Kl. Furthermore, we revealed different expression patterns in BAFF and BAFF-R knockout mice. Compared to wildtype littermates, up- and downregulation of each investigated gene were higher in BAFF-R knockout and lower in BAFF knockout. Our findings indicate a positive impact of BAFF knockout in early phase of AKI, while BAFF-R knockout seems to worsen I/R injury. In addition, our study shows for the first time a remarkable renal upregulation of Lyz2 in a murine I/R model. Therefore, we consider Lyz2 as conceivable predictive or early biomarker in case of I/R and AKI.

The Endothelial Glycocalyx as a Target of Ischemia and Reperfusion Injury in Kidney Transplantation-Where Have We Gone So Far?

The damage of the endothelial glycocalyx as a consequence of ischemia and/or reperfusion injury (IRI) following kidney transplantation has come at the spotlight of research due to potential associations with delayed graft function, acute rejection as well as long-term allograft dysfunction. The disintegration of the endothelial glycocalyx induced by IRI is the crucial event which exposes the denuded endothelial cells to further inflammatory and oxidative damage. The aim of our review is to present the currently available data regarding complex links between shedding of the glycocalyx components, like syndecan-1, hyaluronan, heparan sulphate, and CD44 with the activation of intricate immune system responses, including toll-like receptors, cytokines and pro-inflammatory transcription factors. Evidence on modes of protection of the endothelial glycocalyx and subsequently maintenance of endothelial permeability as well as novel nephroprotective molecules such as sphingosine-1 phosphate (S1P), are also depicted. Although advances in technology are making the visualization and the analysis of the endothelial glycocalyx possible, currently available evidence is mostly experimental. Ongoing progress in understanding the complex impact of IRI on the endothelial glycocalyx, opens up a new era of research in the field of organ transplantation and clinical studies are of utmost importance for the future.

Inhibition of lysyl oxidase ameliorates renal injury by inhibiting CD44-mediated pericyte detachment and loss of peritubular capillaries

Renal fibrosis is a common pathological manifestation of almost all forms of kidney disease irrespective of the etiological cause. Microvascular rarefaction represents itself as an important phenomenon associated with renal fibrosis and shows strong correlation with decline in renal functions. Lysyl oxidase (LOX) catalyzes crosslinking of extracellular matrix (ECM) proteins including collagens, plays an important role in stabilization of degradation resistant matrix. Since, there seems to be a causal link between deposition of excessive ECM and microvascular rarefaction, we investigated the effects of reduction in renal fibrosis on microvascular rarefaction in acute as well as end stage kidney. We used a well-established unilateral ureteral obstruction (UUO)-induced renal fibrosis model to produce renal fibrosis in animals. We treated animals with a LOX inhibitor, β-aminopropionitrile (BAPN, 100 mg/kg, i.p.) and investigated effects on renal fibrosis and microvascular rarefaction. We observed that LOX inhibition was associated with reduction in collagen deposition in UUO-induced renal fibrosis animal model. Further, ECM normalization by LOX inhibition decreased the loss of peritubular capillaries (PTCs) in fibrotic kidney in acute study while the LOX inhibition failed to inhibit PTCs loss in end stage kidney. The results of present study suggested that inhibition of LOX reduces collagen deposition and renal fibrosis. Further, the reduction in fibrosis fails to protect from PTCs loss in chronic study suggesting the absence of strong link between reduction in fibrosis and improvement in PTCs in an end stage kidney.

Kidney-in-a-lymph node: A novel organogenesis assay to model human renal development and test nephron progenitor cell fates

Stem cell-derived organoids are emerging as sophisticated models for studying development and disease and as potential sources for developing organ substitutes. Unfortunately, although organoids containing renal structures have been generated from mouse and human pluripotent stem cells, there are still critical unanswered questions that are difficult to attain via in vitro systems, including whether these nonvascularized organoids have a stable and physiologically relevant phenotype or whether a suitable transplantation site for long-term in vivo studies can be identified. Even orthotopic engraftment of organoid cultures in the adult does not provide an environment conducive to vascularization and functional differentiation. Previously, we showed that the lymph node offers an alternative transplantation site where mouse metanephroi can differentiate into mature renal structures with excretory, homeostatic, and endocrine functions. Here, we show that the lymph node lends itself well as a niche to also grow human primary kidney rudiments and can additionally be viewed as a platform to interrogate emerging renal organoid cultures. Our study has a wide-ranging impact for tissue engineering approaches to rebuild functional tissues in vivo including-but not limited to-the kidney.

C3a and suPAR drive versican V1 expression in tubular cells of focal segmental glomerulosclerosis

Chronic tubulointerstitial injury impacts the prognosis of focal segmental glomerulosclerosis (FSGS). We found that the level of versican V1 was increased in tubular cells of FSGS patients. Tubular cell-derived versican V1 induced proliferation and collagen synthesis by activating the CD44/Smad3 pathway in fibroblasts. Both urine C3a and suPAR were increased and bound to the tubular cells in FSGS patients. C3a promoted the transcription of versican by activating the AKT/β-catenin pathway. C3aR knockout decreased the expression of versican in Adriamycin-treated (ADR-treated) mice. On the other hand, suPAR bound to integrin β6 and activated Rac1, which bound to SRp40 at the 5' end of exon 7 in versican pre-mRNA. This binding inhibited the 3'-end splicing of intron 6 and the base-pair interactions between intron 6 and intron 8, leading to the formation of versican V1. Cotreatment with ADR and suPAR specifically increased the level of versican V1 in tubulointerstitial tissues and caused more obvious interstitial fibrosis in mice than treatment with only ADR. Altogether, our results show that C3a and suPAR drive versican V1 expression in tubular cells by promoting transcription and splicing, respectively, and the increases in tubular cell-derived versican V1 induce interstitial fibrosis by activating fibroblasts in FSGS.

Retinoic acid improves nephrotoxic serum-induced glomerulonephritis through activation of podocyte retinoic acid receptor α

Proliferation of glomerular epithelial cells, including podocytes, is a key histologic feature of crescentic glomerulonephritis. We previously found that retinoic acid (RA) inhibits proliferation and induces differentiation of podocytes by activating RA receptor-α (RARα) in a murine model of HIV-associated nephropathy. Here, we examined whether RA would similarly protect podocytes against nephrotoxic serum-induced crescentic glomerulonephritis and whether this effect was mediated by podocyte RARα. RA treatment markedly improved renal function and reduced the number of crescentic lesions in nephritic wild-type mice, while this protection was largely lost in mice with podocyte-specific ablation of Rara (Pod-Rara knockout). At a cellular level, RA significantly restored the expression of podocyte differentiation markers in nephritic wild-type mice, but not in nephritic Pod-Rara knockout mice. Furthermore, RA suppressed the expression of cell injury, proliferation, and parietal epithelial cell markers in nephritic wild-type mice, all of which were significantly dampened in nephritic Pod-Rara knockout mice. Interestingly, RA treatment led to the coexpression of podocyte and parietal epithelial cell markers in a small subset of glomerular cells in nephritic mice, suggesting that RA may induce transdifferentiation of parietal epithelial cells toward a podocyte phenotype. In vitro, RA directly inhibited the proliferation of parietal epithelial cells and enhanced the expression of podocyte markers. In vivo lineage tracing of labeled parietal epithelial cells confirmed that RA increased the number of parietal epithelial cells expressing podocyte markers in nephritic glomeruli. Thus, RA attenuates crescentic glomerulonephritis primarily through RARα-mediated protection of podocytes and in part through the inhibition of parietal epithelial cell proliferation and induction of their transdifferentiation into podocytes.

Early life stress induces immune priming in kidneys of adult male rats

Early life stress (ELS) in humans is associated with elevated proinflammatory markers. We hypothesized that ELS induces activation of the immune response in a rat model of ELS, maternal separation (MatSep), in adulthood. MatSep involves separating pups from the dam from postnatal day 2 to postnatal day 14 for 3 h/day. Control rats are nonseparated littermates. We determined circulating and renal immune cell numbers, renal immune cell activation markers, renal cytokine levels, and the renal inflammatory gene expression response to low-dose lipopolysaccharide (LPS) in male MatSep and control rats. We observed that MatSep did not change the percentage of gated events for circulating CD3⁺, CD4⁺, CD8⁺, and CD4⁺/Foxp3⁺ cells or absolute numbers of mononuclear and T cells in the circulation and kidneys; however, MatSep led to an increase in activation of renal neutrophils as well as CD44⁺ cells. Renal toll-like receptor 4 (TLR4) and interleukin 1 beta (IL-1β) was significantly increased in MatSep rats, specifically in the outer and inner medulla and distal nephron, respectively. Evaluation of renal inflammatory genes showed that in response to a low-dose LPS challenge (2 mg/kg iv) a total of 20 genes were significantly altered in kidneys from MatSep rats (17 genes were upregulated and 3 were downregulated), as opposed to no significant differences in gene expression in control vs. control + LPS groups. Taken together, these findings indicate that MatSep induces priming of the immune response in the kidney.

Renal Fibrosis mRNA Classifier: Validation in Experimental Lithium-Induced Interstitial Fibrosis in the Rat Kidney

Accurate diagnosis of fibrosis is of paramount clinical importance. A human fibrosis classifier based on metzincins and related genes (MARGS) was described previously. In this investigation, expression changes of MARGS genes were explored and evaluated to examine whether the MARGS-based algorithm has any diagnostic value in a rat model of lithium nephropathy. Male Wistar rats (n = 12) were divided into 2 groups (n = 6). One group was given a diet containing lithium (40 mmol/kg food for 7 days, followed by 60mmol/kg food for the rest of the experimental period), while a control group (n = 6) was fed a normal diet. After six months, animals were sacrificed and the renal cortex and medulla of both kidneys removed for analysis. Gene expression changes were analysed using 24 GeneChip^® Affymetrix Rat Exon 1.0 ST arrays. Statistically relevant genes (p-value<0.05, fold change>1.5, t-test) were further examined. Matrix metalloproteinase-2 (MMP2), CD44, and nephroblastoma overexpressed gene (NOV) were overexpressed in the medulla and cortex of lithium-fed rats compared to the control group. TGFβ2 was overrepresented in the cortex of lithium-fed animals 1.5-fold, and 1.3-fold in the medulla of the same animals. In Gene Set Enrichment Analysis (GSEA), both the medulla and cortex of lithium-fed animals showed an enrichment of the MARGS, TGFβ network, and extracellular matrix (ECM) gene sets, while the cortex expression signature was enriched in additional fibrosis-related-genes and the medulla was also enriched in immune response pathways. Importantly, the MARGS-based fibrosis classifier was able to classify all samples correctly. Immunohistochemistry and qPCR confirmed the up-regulation of NOV, CD44, and TGFβ2. The MARGS classifier represents a cross-organ and cross-species classifier of fibrotic conditions and may help to design a test to diagnose and to monitor fibrosis. The results also provide evidence for a common pathway in the pathogenesis of fibrosis.

Opposite role of CD44-standard and CD44-variant-3 in tubular injury and development of renal fibrosis during chronic obstructive nephropathy

Chronic kidney diseases (CKDs) are characterized by tubular atrophy and interstitial fibrosis. We previously showed that in obstructive nephropathy de novo CD44 renal expression contributes to renal fibrosis but attenuates tubular damage/apoptosis. As CD44-standard (CD44s) has been linked to TGF-β1-mediated actions and CD44-variant-3 (CD44v3) favors HGF-c-Met binding, we compared the functional properties of these CD44 isoforms in the progression of obstructive nephropathy, using specific CD44-variant knockout/knockin mice. The presence of CD44v3 diminished tubular damage during obstructive nephropathy, decreased apoptosis, and increased proliferation of tubular epithelial cells, and prevented renal fibrosis development. In contrast, expression of CD44s led to increased tubular damage and tubular epithelial cell apoptosis, and more renal fibrosis. A relative increase in renal β-catenin expression, HGF production, and HGF/c-Met signaling, together with a relative inhibition of TGF-β1 downstream signaling and TGF-β type I receptor expression, was found in CD44v3 mice compared with CD44s littermates. In line with this, Wnt3a/HGF treatment of tubular cells resulted in higher β-catenin/p-AKT levels in CD44v3(+) tubular epithelial cells, whereas TGF-β1 induced a mild collagen I upregulation in CD44v3(+) mouse embryonic fibroblasts as compared with CD44s(+) cells. Thus, CD44s and CD44v3 exert opposite roles in the progression of obstructive nephropathy, with CD44v3-v10 being the protective isoform that delays evolution of the renal pathology.

CD44v3-v10 reduces the profibrotic effects of TGF-β1 and attenuates tubular injury in the early stage of chronic obstructive nephropathy

CD44 family members are cell surface glycoproteins, which are expressed on tubular epithelial cells (TEC) solely upon kidney injury and are involved in renal fibrosis development. Renal interstitial fibrosis is the final manifestation of chronic kidney diseases and is regulated by a complex network of cytokines, including the profibrotic factor transforming growth factor-β1 (TGF-β1) and the two antifibrotic cytokines bone morphogenic protein-7 (BMP-7) and hepatocyte growth factor (HGF). The present study investigates the potential role of CD44 standard (CD44s) and CD44v3-v10 (CD44v3) isoforms as modulators of the balance between TGF-β1 and HGF/BMP-7. CD44s is the shortest and most common isoform. CD44v3-v10 (CD44v3) has heparan sulfate moieties, which enable the binding to HGF/BMP-7, and hence, might exert renoprotective effects. Using transgenic mice overexpressing either CD44s or CD44v3 specifically on proximal TEC, we found that in vitro the overexpression of CD44v3 on primary TEC renders cells less susceptible to TGF-β1 profibrotic actions and more sensitive to BMP-7 and HGF compared with TEC overexpressing CD44s. One day after unilateral ureteric obstruction, obstructed kidneys from CD44v3 transgenic mice showed less tubular damage and myofibroblasts accumulation, which was associated with decreased TGF-β1 signaling and increased BMP-7 synthesis and signaling compared with kidneys from wild-type and CD44s transgenic mice. These data suggest that CD44v3 plays a renoprotective role in early stage of chronic obstructive nephropathy.

The Role of Hyaluronan and CD44 in the Pathogenesis of Lupus Nephritis

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease that affects multiorgan systems. Lupus nephritis is one of the most severe manifestations of SLE whereby immune-mediated inflammation can lead to permanent damage within the glomerular, tubulo-interstitial, and vascular compartments of the kidney, resulting in acute or chronic renal failure. The mechanisms that regulate host inflammatory responses and tissue injury are incompletely understood. Accumulating evidence suggests that hyaluronan and its interaction with its cell surface receptor CD44 plays an important role in mediating pathogenic mechanisms in SLE. This paper discusses the putative mechanisms through which hyaluronan and CD44 contribute to the pathogenesis of SLE, with particular emphasis on lupus nephritis.

High-throughput profiling of tissue and tissue model microarrays: Combined transmitted light and 3-color fluorescence digital pathology

For many years pathologists have used Hematoxylin and Eosin (H&E), single marker immunohistochemistry (IHC) and in situ hybridization with manual analysis by microscopy or at best simple digital imaging. There is a growing trend to update pathology to a digital workflow to improve objectivity and productivity, as has been done in radiology. There is also a need for tissue-based multivariate biomarker assays to improve the accuracy of diagnostic, prognostic, and predictive testing. Multivariate tests are not compatible with the traditional single marker, manual analysis pathology methods but instead require a digital platform with brightfield and fluorescence imaging, quantitative image analysis, and informatics. Here we describe the use of the Hamamatsu NanoZoomer Digital Pathology slide scanner with HCImage software for combined brightfield and multiplexed fluorescence biomarker analysis and highlight its applications in biomarker research and pathology testing. This combined approach will be an important aid to pathologists in making critical diagnoses.

Intragraft tubular vimentin and CD44 expression correlate with long-term renal allograft function and interstitial fibrosis and tubular atrophy

BACKGROUND

Development of interstitial fibrosis and tubular atrophy (IF/TA) is the main histologic feature involved in renal allograft deterioration. The aim of this study was to validate whether de novo tubular expression of CD44 (transmembrane glycoprotein) and vimentin (mesenchymal cell marker), both involved in renal fibrosis, can operate as surrogate markers for late IF/TA and renal function. Furthermore, we wanted to establish the interrater reproducibility for the scoring system, which can be a problem in histologic assessments.

METHODS

Six-month protocol renal allograft biopsies (n=30 for matching 12 months estimated glomerular filtration rate (eGFR) from which 20 matched the 12-month protocol biopsy) were immunostained for CD44 and vimentin, semiquantitatively scored by three observers of two centers, and correlated with IF/TA and eGFR at 12 months.

RESULTS

The interobserver agreement was excellent for CD44 (Kendall's W-coefficient: 0.69; P<0.001) and vimentin (Kendall's W-coefficient: 0.79; P<0.001). CD44 and vimentin expression at 6 months were significantly correlated with IF/TA (rho=0.481 for CD44 and rho=0.619 for vimentin) and eGFR (rho=-0.569 for CD44 and rho=-0.376 for vimentin) at 12 months.

CONCLUSIONS

Summarizing, de novo tubular expression of CD44 and vimentin can function as surrogate marker for IF/TA and eGFR at 12 months. Further area under receiver operator characteristic curve analysis has to establish the predictive value for both biomarkers.

Altered P-selectin and CD44 expression in the renal tissues and peripheral blood of children with IgA nephropathy

OBJECTIVE

To understand the role of P-selectin (CD62P) and CD44 in mediating immune inflammation in the nephrotic process of children with IgA nephropathy (IgAN), cooperative expression of CD62P and CD44 in peripheral blood and renal tissues of IgAN children was investigated and its association with changes of histopathologic, serologic, and urinary properties was tested.

MATERIAL AND METHODS

Forty-six IgAN children were divided into three groups according to pathologic grades and clinical features. Fifteen blood samples from normal children and four normal renal biopsy specimens were used as controls. Plasma level of CD62P was detected by double antibody sandwich immunoradiometric assay; ELISA was used to determine serum level of CD44. Expression of CD62P and CD44 in renal tissues was determined by immunohistochemistry.

RESULTS

Cooperative expression of CD62P and CD44 was detected in renal tissues and peripheral blood of IgAN children. Altered expression of CD62P and CD44 in peripheral blood significantly correlated not only with hematuria, proteinuria, serum cholesterol, and albumin, and with urine NAG and beta(2)-MG, but also with degree of tubulointerstitial injury in IgAN children.

CONCLUSION

The evidence supported CD62P and CD44 as initial and promoting factors mediating immune inflammation in the nephrotic process in IgAN children. The cooperative expression profiles of CD62P and CD44 in renal tissues and peripheral blood combined with serologic and urinary predictors may be important in diagnosis of progression in children with IgAN.

Renal expression of CD44 correlates with acute renal allograft rejection

As CD44 is involved in the activation, proliferation, adhesion, and extravasation of lymphocytes, we hypothesized that CD44 could be involved in the pathogenesis of acute renal allograft rejection. Renal biopsies and plasma were collected from patients suffering an episode of acute renal allograft rejection. CD44 and its ligands, hyaluronic acid (HA) and osteopontin, were analyzed retrospectively by immunohistochemistry and, computer-aided, morphometric analysis. Soluble CD44 (sCD44) and osteopontin in the plasma were determined by enzyme-linked immunosorbent assay. During acute rejection episodes, CD44 and its ligands, HA and osteopontin, were upregulated in the renal allograft. Also, increased sCD44 plasma levels were observed, which correlated with both tubular expression of CD44 and the extent of infiltrate. No differences could be detected between the different pathologic grades of rejection. Upregulation of tubular CD44 and increased levels of circulating sCD44 may reflect a common pathogenic mechanism during acute renal rejection and could be useful markers in the diagnosis of acute renal rejection.

CD44 Disruption Prevents Degeneration of the Capillary Network in Obstructive NephropathyviaReduction of TGF-β1–Induced Apoptosis

CD44 is a glycoprotein that is involved in inflammation and cell-cell/cell-matrix interactions, is upregulated in the kidney upon injury, and leads to fibrosis through enhancement of TGF-beta1 signaling. Absence of CD44 prevents development of renal fibrosis in unilateral ureteral obstruction (UUO). A hallmark of development of renal fibrosis is the degeneration of the capillary network. This study shows that CD44 is upregulated on capillary endothelial cells during UUO. For elucidation of the role of CD44 on peritubular endothelial cells in UUO, capillary network degeneration was compared in CD44+/+ and CD44-/- mice. As expected, degeneration of the capillary network was observed in CD44+/+ mice during UUO, associated with increased endothelial apoptosis. However, in the absence of CD44, degeneration of the network is prevented as a result of a decrease in the rate of apoptosis in endothelial cells. The divergence in endothelial apoptosis is not correlated to differential vascular endothelial growth factor or thrombospondin-1 expression. For further investigation of capillary regression, CD44+/+ and CD44-/- peritubular capillary endothelial cell lines were established. With the use of these cells, it is shown that interaction between CD44 and its ligand hyaluronic acid enhances the proapoptotic effect of TGF-beta1 but not thrombospondin-1 on endothelial cells, contributing to the degeneration of the capillary network. Blocking interaction between hyaluronic acid and CD44 therefore may be a potential therapeutic opportunity to preserve the capillary network and prevent the development of fibrosis in chronic renal disease.

Pre-transplant plasma and cellular levels of CD44 correlate with acute renal allograft rejection

BACKGROUND

Since CD44 is involved in activation, proliferation, rolling and extravasation of lymphocytes, we hypothesized that it could be involved in the pathophysiology of acute renal allograft rejection.

METHODS

Plasma and peripheral blood mononuclear cells (PBMCs) were collected from patients 24 h prior to transplantation and analysed retrospectively. Soluble CD44, interleukin-2 receptor (IL-2R), intracellular adhesion molecule-1 (ICAM-1) and C-reactive protein (CRP) in plasma were determined by enzyme-linked immunosorbent assay (ELISA). Cellular CD44 expression on peripheral lymphocytes was determined by flow cytometric analysis.

RESULTS

Patients who later developed renal allograft rejection had statistically significantly increased soluble CD44 levels, but not soluble ICAM-1, IL-2R or CRP in plasma prior to transplantation. In addition, cellular CD44 on T-lymphocytes was decreased 24 h prior to transplantation in patients that would reject their allograft, compared with patients without rejection. Additionally, plasma CD44 and cellular CD44 revealed an inversely proportional correlation. Lipopolysaccharide (LPS)-induced immune activation did not influence plasma or cellular CD44 levels in healthy volunteers, suggesting that more specific factors influence the shedding of CD44 on T lymphocytes, leading to increased risk of renal allograft rejection.

CONCLUSION

Although the exact mechanism remains to be elucidated and further research is required, soluble CD44 levels and cellular surface CD44 on T lymphocytes prior to transplantation might be useful as predictive markers for the occurrence of acute renal rejection.

Protection against renal ischemia reperfusion injury by CD44 disruption

Inflammation contributes to renal ischemia reperfusion (I/R) injury, potentially causing renal dysfunction. The inflammatory infiltrate mainly consists of neutrophils, which are deleterious for the renal tissue. Because CD44 is expressed by neutrophils and is rapidly upregulated by capillary endothelial cells after I/R injury, it was hypothesized that CD44 might play an important role in the development of I/R injury. This study showed that rapid CD44 upregulation on renal capillary endothelial cells mediates neutrophil recruitment to the postischemic tissue. Hence, CD44 deficiency led to decreased influx of neutrophils regardless of comparable levels in chemotactic factors expressed in the kidney. The reduced influx of neutrophils was associated with preserved renal function and morphology. Adoptive transfer experiments of labeled neutrophils revealed that endothelial CD44 rather than neutrophil CD44 mediates neutrophil migration. Activation of neutrophils increased cell-surface expression of hyaluronic acid (HA). Altogether, a novel mechanism in the recruitment of neutrophils that involves interaction of endothelial CD44 and neutrophil HA was found. Either blocking endothelial CD44 or removal of neutrophil HA decreased rolling and adhesion of neutrophils. Administration of anti-CD44 to mice reduced the influx of neutrophils into the postischemic tissue, associated with renal function preservation. Therefore, anti-CD44-based therapies may contribute to prevent or reduce renal I/R injury.

Heparan sulfate proteoglycans in glomerular inflammation

Heparan sulfate proteoglycans (HSPGs) are glycoproteins consisting of a core protein to which linear heparan sulfate side chains are covalently attached. These heparan sulfate side chains can be modified at different positions by several enzymes, which include N-deacetylases, N- and O-sulfotransferases, and an epimerase. These heparan sulfate modifications give rise to an enormous structural diversity, which corresponds to the variety of biologic functions mediated by heparan sulfate, including its role in inflammation. The HSPGs in the glomerular basement membrane (GBM), perlecan, agrin, and collagen XVIII, play an important role in the charge-selective permeability of the glomerular filter. In addition to these HSPGs, various cell types express HSPGs at their cell surface, which include syndecans, glypicans, CD44, and betaglycan. During inflammation, HSPGs, especially heparan sulfate, in the extracellular matrix (ECM) and at the surface of endothelial cells bind chemokines, which establishes a local concentration gradient recruiting leukocytes. Endothelial and leukocyte cell surface HSPGs also play a role in their direct adhesive interactions via other cell surface adhesion molecules, such as selectins and beta2 integrin. Activated leukocytes and endothelial cells exert heparanase activity, resulting in degradation of heparan sulfate moieties in the ECM, which facilitates leukocyte passage into tissues and the release of heparan sulfate-bound factors. In various renal inflammatory diseases the expression of agrin and GBM-associated heparan sulfate is decreased, while the expression of CD44 is increased. Heparan sulfate or heparin preparations affect inflammatory cell behavior and have promising therapeutic, anti-inflammatory properties by preventing leukocyte adhesion/influx and tissue damage.

Tubular CD44 expression in renal allograft biopsies

CD44 is a type I transmembrane glycoprotein serving as a cell adhesion receptor, whose main ligand is hyaluronic acid, but also may interact with collagen, laminin, fibronectin, and osteopontin. This marker is involved in cell migration, homing, activation, metastasis, and inflammation. Tubular CD44 expression has been shown to correlate with scarring in renal diseases, but there is little data on allograft biopsies. This deficiency is important since experimental studies have shown that blockade of the CD44-hyaluronic acid interaction may prolong allograft survival. In an attempt to clarify the role of tubular CD44 expression in renal allografts, CD44 expression was determined immunohistochemically in 37 allograft and 10 implantation biopsies, as the percentage of tubules expressing this marker. For implantation biopsies the mean tubular CD44 expression was 6% +/- 14%; for allograft biopsies, 13% +/- 20% (P =.17, Mann-Whitney U). By the Spearman correlation test, CD44 expression did not correlate with Banff scores, but was moderately correlated with serum creatinine values at the time of biopsy (P =.017, r =.4). These findings suggest an important role of tubular CD44 expression in renal allografts. It appears to be induced by more than one pathway, resulting in a pattern of expression that correlated with renal function. However larger series are required before recommending the routine use of this marker.

Surface antigens of human mesangial cells: impact of growth surface or IL-1alpha

The interactions of mesangial cells (MC) with their environment are important events in glomerular physiology and pathology, yet a detailed characterization of the MC-surface antigens mediating these interactions is still lacking. In this study, a comparative phenotype analysis of primary human MC in culture using 191 monoclonal antibodies directed against 108 antigens was performed by flow-cytometry. The MC were grown on three different surfaces (human matrix, fibronectin, polystyrene) and cultured in the presence or absence of IL-1alpha. Seventy-one antibodies recognizing 35 different antigens (integrins: CD29, 49b, 49c, 49e, 51, 61; immunoglobulin gene family: CD54, 58, 90, 106, 146, 147, 166; growth factor receptors: CD105, 140b; apoptosis related: CD95; hemostatis related: CD141, 142; miscellaneous: CD44, 109, 138, 151, 157, 165, and 11 nonclustered antigens) reacted with mesangial cells. CD58, 109, 146, 147, 151, 157, 165, and 166 are reported for the first time to be present on human mesangial cells. In comparison to growth on polystyrene, CD44, 54, 95, 105, 109, 140b, 146, 147, 157, 165 and 166, were up-regulated on fibronectin, and CD44, 54, 90, 95, 105, 106, 109, 138, 140b, 141, 142, 146, 147, 151, 157, 165 and 166 were up-regulated on human matrix. The stimulation by IL-1alpha up-regulated CD44, 49e, 51, 54, 61, 106 on MC on polystyrene; CD49e, 51, 61, 106, 146, 165 on MC on fibronectin, and CD49e, 51, 54 on MC grown on human matrix. This analysis of surface antigen expression provides new information to enable a better understanding of the role of mesangial cells in glomerular pathophysiology.

CD44 expression in IgA nephropathy

Immunoglobulin A (IgA) nephropathy is a frequent, chronic renal disease characterized by a broad spectrum of clinical presentations and pathologic findings. CD44, a family of type I transmembrane glycoproteins involved in cell-cell and cell-matrix interactions, may orchestrate partially the cascade of inflammation, accumulation of myofibroblasts, and fibrosis leading to end-stage renal disease. To clarify the possible role of CD44 in the progression of IgA nephropathy, the expression of CD44 in glomeruli and the tubulointerstitial compartment was analyzed in 25 renal biopsy specimens of patients with IgA nephropathy and was correlated to histopathologic, serologic, and urinary parameters. The expression of CD44 correlated significantly with the degree of glomerular and interstitial damage, even better than the accumulation of alpha-smooth muscle actin-positive myofibroblasts, which is recognized as a reliable marker for the progression of IgA nephropathy. A positive correlation also was found between proteinuria and the expression of CD44 in the tubulointerstitial compartment. The glomerular and tubulointerstitial expression of CD44 correlated with the degree of renal damage in IgA nephropathy and could be a reliable marker of the progression of IgA nephropathy. CD44 may have a pivotal role in the cascade of renal inflammation and fibrosis.

Tubular lesions and tubular cell adhesion molecules for the prognosis of lupus nephritis

BACKGROUND

To assess the prognostic value of tubular lesions and cell adhesion molecules' expression, a retrospective study with immunohistochemistry was performed on 152 patients presenting lupus nephritis from January 1985 to December 1999.

METHODS

The following clinical parameters were recorded: age, sex, race, time of systemic lupus erythematosus (SLE) diagnosis, time of the biopsy, proteinuria, creatininemia, and renal function at the end of follow-up. All biopsies were re-evaluated according to a tubular grading, an inflammatory grading, the percentage of sclerosed glomeruli, the percentage of crescents, and the current WHO classification. Immunohistochemistry was performed with anti-CD40, anti-CD44, and anti-intercellular adhesion molecule-1 (anti-ICAM-1) antibodies.

RESULTS

Patients were 136 women (89.5%) and 16 men with a mean age of 31.2 years +/- 12.8 at the time of biopsy. The mean follow-up period was 94.3 months +/- 64.1. Eighty-eight biopsies (58%) showed various degrees of tubular atrophy. Males (P = 0.001) and tubular grading (P = 0.0001) were linked with renal survival in univariate and multivariate analysis. CD40 (P = 0.01) and ICAM-1 (P = 0.001) tubular expressions were linked with renal survival. ICAM-1 tubular expression provided additional information for the prognosis of the patients with biopsies showing tubular atrophy (P = 0.005) or not (P = 0.05).

CONCLUSIONS

Our study shows that tubular lesions are good indicator of lupus nephritis outcome. Furthermore, tubular expression of cell adhesion molecules like ICAM-1 and CD40 also serves to predict the outcome.

Preferential binding of polyethylene glycol-coated liposomes containing a novel cationic lipid, TRX-20, to human subendthelial cells via chondroitin sulfate

PURPOSE

To design novel cationic liposomes, polyethylene glycol (PEG)-coated cationic liposomes containing a newly synthesized cationic lipid, 3,5-dipentadecyloxybenzamidine hydrochloride (TRX-20) were formulated and their cellular binding and uptake investigated in vitro in the following cells: human subendothelial cells (aortic smooth muscle cells and mesangial cells) and human endothelial cells.

METHODS

Three different PEG-coated cationic liposomes were prepared by the extrusion method, and their mean particle size and zeta potential were determined. Rhodamine-labeled PEG-coated cationic liposomes were incubated with smooth muscle cells, mesangial cells, and endothelial cells at 37 degrees C for 24 h. The amounts of cellular binding and uptake of liposomes were estimated by measuring the cell-associated fluorescence intensity of rhodamine. To investigate the binding property of the liposomes, the changes of the binding to the cells pretreated by various kinds of glycosaminoglycan lyases were examined. Fluorescence microscopy-is used to seek localization of liposomes in the cells.

RESULTS

The cellular binding and uptake of PEG-coated cationic liposomes to smooth muscle cells was depended strongly on the chemical species of cationic lipids in these liposomes. Smooth muscle cells bound higher amount of PEG-coated TRX-20 liposomes than other cationic liposomes containing N-(1-(2.3-dioleoyloxy) propyl)-N, N, N-trimethylammonium salts or N-(alpha-(trimethylammonio)acetyl)-D-glutamate chloride. Despite of the higher affinity of PEG-coated TRX-20 liposomes for subendothelial cells, their binding to endothelial cells was very small. The binding to subendothelial cells was inhibited when cells were pretreated by certain kinds of chondroitinase, but not by heparitinase. These results suggest that PEG-coated TRX-20 liposomes have strong and selective binding property to subendothelial cells by interacting with certain kinds of chondroitin sulfate proteoglycans (not with heparan sulfate proteoglycans) on the cell surface and in the extracellular matrix of the cells. This binding feature was different from that reported for other cationic liposomes.

CONCLUSIONS

PEG-coated TRX-20 liposomes can strongly and selectively bind to subendothelial cells via certain kinds of chondroitin sulfate proteoglycans and would have an advantage to use as a specific drug delivery system.

Up-regulation of the tumour-associated marker CD44V6 in experimental kidney disease

CD44 is an adhesion molecule involved in a wide range of cell-cell and cell-matrix interactions. The standard form of CD44 (CD44S) is a 85-90-kD glycoprotein, but alternative splicing of RNA encoding 10 variable exons (V1-V10) can give rise to many different CD44 variant protein isoforms of higher molecular weight. CD44 isoforms containing the V6 exon play a crucial role in tumour metastasis and lymphocyte activation. However, the role of CD44V6 in the kidney is unknown. The aim of this study was to examined renal CD44V6 expression in health, disease and in vitro. Immunohistochemistry staining with the V6-specific 1.1ASML antibody identified constitutive CD44V6 expression by occasional cortical tubular epithelial cells and medullary tubules in normal rat kidney. In immune-induced kidney disease (rat anti-glomerular basement membrane glomerulonephritis), there was a marked increase in CD44V6 expression by cortical tubules, particularly in areas of tubulointerstitial damage, which was associated with focal macrophage infiltration. There was also a marked increase in CD44V6 expression by damaged tubules in a model of non-immune kidney disease (unilateral ureteric obstruction). Reverse transcription-polymerase chain reaction revealed a complex pattern of CD44V6-containing mRNA isoforms in normal rat kidney. This pattern of CD44V6 splicing was essentially unaltered in disease. The NRK52E normal rat kidney tubular epithelial cell line expresses both CD44S and CD44V6. Stimulation of NRK52E cells with IL-1 or transforming growth factor-beta 1 induced a two-to-five-fold increase in the expression of both CD44S and CD44V6. Furthermore, triggering of NRK52E cells by antibodies to CD44S or CD44V6, but not isotype control antibodies, induced secretion of monocyte chemoattractant protein-1. In conclusion, this study has identified expression of the tumour-associated marker CD44V6 in tubular epithelial cells in normal and diseased rat kidney, and suggests that signalling through the CD44V6 molecule may participate in the pathogenesis of experimental kidney disease.

Alpha8 integrin in glomerular mesangial cells and in experimental glomerulonephritis

BACKGROUND

Mesangial cell (MC) proliferation and extracellular matrix accumulation are typical responses of renal glomeruli to injury. Extracellular matrix components are known to affect MC behavior, which is mediated primarily via integrin receptors of the beta1 family. In addition to alpha1, alpha3, alpha5, and alpha6 chains of beta1 integrins, recent studies have shown the alpha8 chain to be expressed in glomeruli and renal vasculature. alpha8beta1 can serve as a receptor for fibronectin, which is abundant in the mesangium. We investigated the glomerular expression pattern of the alpha8 chain in renal tissues of mouse, rat, and humans as well as in cultured MCs. In addition, the regulation of alpha8 expression in MCs was studied in culture and in nephritic rats.

METHODS

The expression of alpha8 protein in kidney tissue and cultured MCs was investigated by immunohistochemistry, immunocytochemistry, and Western blotting. The effects of TGF-beta1 on alpha8 mRNA levels in MCs were studied by Northern blot analysis. In addition, time course studies of glomerular abundance and localization of alpha8 were performed in rats with mesangioproliferative anti-Thy1.1 nephritis.

RESULTS

In tissue sections of normal human, rat, and mouse kidney, we found strong immunohistochemical staining for alpha8 in the mesangium and in the media of renal arterioles. Double staining for alpha8 and Thy1.1, a surface antigen of rat MCs, showed alpha8 to be specifically expressed in MCs but not in glomerular endothelial and epithelial cells. In anti-Thy1.1 nephritis of rats, the glomerular abundance of alpha8 protein was reduced in the early mesangiolytic phase but was increased greatly with subsequent MC proliferation, peaking at day 6 of disease. At later stages of this reversible form of nephritis, the number of MCs and the extent mesangial alpha8 staining declined to control levels. Cell culture experiments revealed that freshly plated MCs organize alpha8 into focal contacts within one hour after attachment to fibronectin and vitronectin substrata, showing colocalization with focal contact proteins vinculin and talin. Stimulation of MCs with transforming growth factor-beta1 led to increases of alpha8 mRNA and protein levels.

CONCLUSIONS

These results show that in human, rat, and mouse glomeruli, alpha8 integrin is strongly and exclusively expressed in MCs. Gene expression of alpha8 is regulated in cultured MCs, and alpha8 protein abundance is regulated in vivo and in MC culture. It is currently unclear what functional properties this integrin receptor protein has with regard to MC anchorage to extracellular matrix and modulation of the MC phenotype in normal and diseased glomeruli. However, in view of its abundance in the mesangium, alpha8beta1 integrin could be an important MC receptor of matrix ligands and may play a role in the embryology, physiology, and pathophysiology of the glomerular capillary tuft.

Mechanisms of Hyaluronan-Induced Up-Regulation of ICAM-1 and VCAM-1 Expression by Murine Kidney Tubular Epithelial Cells: Hyaluronan Triggers Cell Adhesion Molecule Expression Through a Mechanism Involving Activation of Nuclear Factor-κB and Activating Protein-1

The matrix constituent hyaluronan (HA) markedly accumulates in inflammatory lesions. To gain insight into the biologic significance of this phenomenon we tested the hypothesis that HA could regulate cell adhesion molecule expression in epithelial cells. Using a clonal line of mouse cortical tubular (MCT) cells we found that fragmented intermediate m.w., but not high m.w., HA markedly increased ICAM-1 and VCAM-1 steady state mRNA and cell surface expression. Up-regulation of ICAM-1 and VCAM-1 mRNA by HA was preceded by a marked increase in NF-κB and activating protein-1 DNA binding activity in MCT cells. Transcript levels for the NF-κB inhibitor IκBα and for the activating protein-1 constituents c-jun and c-fos also increased in response to HA stimulation of tubular cells. Inhibition of NF-κB with the serine protease inhibitor N-tosyl-l-phenylalanine chloromethyl ketone blocked the HA-mediated expression of ICAM-1 and VCAM-1 in MCT cells. In conclusion, HA displays proinflammatory effects by directly stimulating the expression of the cell adhesion molecules ICAM-1 and VCAM-1 in mouse kidney epithelial cells. HA could thereby play an important role in leukocyte adhesion in inflammatory renal diseases.

Adhesion molecules in the glomerular mesangium

Experimental evidence indicates that extensive "cross-talk" exists between glomerular cells, extracellular matrix molecules and soluble mediator substances affecting the proliferative and secretory phenotype of glomerular mesangial cells. Both matrix and cytokines regulate mesangial cell behavior in vitro and in vivo after binding to specific cell surface receptors. It appears as if the concerted action of insoluble and soluble ligands on mesangial cells involves a reciprocal regulation of matrix molecules and cytokines as well as expression and affinity of their respective receptors. Elucidation of the potential biologic and clinical relevance of cell-matrix interactions in the glomerular mesangium represents a challenging goal in current kidney research. This brief review summarizes recent investigations concerning regulation of expression and function of adhesion molecules and matrix receptors in the mesangium. In addition to results from cell culture studies, descriptive findings on expression and regulation of adhesion molecules and their potential role for altered mesangial cell behavior in glomerular disease is considered.