Stefan Gauer

ABCB1 Genotype of the Donor but Not of the Recipient Is a Major Risk Factor for Cyclosporine-Related Nephrotoxicity after Renal Transplantation

Cyclosporine (CsA) nephrotoxicity is a severe complication in organ transplantation because it leads to impaired renal function and chronic allograft nephropathy, which is a major predictor of graft loss. Animal models and in vivo studies indicate that the transmembrane efflux pump P-glycoprotein contributes substantially to CsA nephrotoxicity. It was hypothesized that the TT genotype at the ABCB1 3435C-->T polymorphism, which is associated with decreased expression of P-glycoprotein in renal tissue, is a risk factor for developing CsA nephrotoxicity. In a case-control study, 18 of 97 patients developed CsA nephrotoxicity and showed complete recovery of renal function in all cases when switched to a calcineurin inhibitor-free regimen. Both recipients and donors were genotyped for ABCB1 polymorphisms at the positions 3435C-->T and 2677G-->T/A. For controlling for population stratification, two additional polymorphisms, CYP2D6*4 and CYP3A5*3, with intermediate allelic frequencies were studied. The P-glycoprotein low expressor genotype 3435TT only of renal organ donors but not of the recipients was overrepresented in patients with CsA nephrotoxicity as compared with patients without toxicity (chi2 = 10.5; P = 0.005). CsA dosage, trough levels, and the concentration per dose ratio were not different between the patient groups. In a multivariate model that included several other nongenetic covariates, only the donors ABCB1 3435TT genotype was strongly associated with CsA nephrotoxicity (odds ratio, 13.4; 95% confidence interval, 1.2 to 148; P = 0.034). A dominant role of the donors ABCB1 genotype was identified for development of CsA nephrotoxicity. This suggests that P-glycoprotein is an important factor in CsA nephrotoxicity.

Prediction of Acute Renal Allograft Rejection by Urinary Monokine Induced by IFN-γ (MIG)

Early diagnosis of acute allograft rejection (AR) is still decisive for long-term renal allograft survival. The aim of this study was to define the role of the chemokine monokine induced by IFN-γ (MIG) (CXCL9) and IFN-γ–inducible protein 10 (IP-10) (CXCL10) as early markers of AR in renal transplantation (NTX). In a prospective study, 69 de novo renal transplant recipients were monitored and urine samples were collected after NTX for a median of 29 d. In pH-adjusted urine, MIG and IP-10 were determined by modified ELISA. AR was clinically diagnosed in 15 of 69 recipients and confirmed by biopsy in 14 of 15 AR patients (Banff classification). Corresponding to CXCR3-positive infiltrates in renal tissue, urinary MIG was elevated in 14 of 15 AR patients with a median of 2809 pg/ml (quartile 25% and 75% = 870 and 13,000; n = 15), being significantly ( P P P

Osteopontin is expressed by adult human osteoarthritic chondrocytes: protein and mRNA analysis of normal and osteoarthritic cartilage

Osteopontin, a sulfated phosphoprotein with cell binding and matrix binding properties, is expressed in a variety of tissues. In the embryonic growth plate, osteopontin expression was found in bone-forming cells and in hypertrophic chondrocytes. In this study, the expression of osteopontin was analyzed in normal and osteoarthritic human knee cartilage. Immunohistochemistry, using a monoclonal anti-osteopontin antibody was negative on normal cartilage. These results were confirmed in Western blot experiments, using partially purified extracts of normal knee cartilage. No osteopontin gene expression was observed in chondrocytes of adult healthy cartilage, however, in the subchondral bone plate, expression of osteopontin mRNA was detected in the osteoblasts. In cartilage from patients with osteoarthritis, osteopontin could be detected by immunohistochemistry, Western blot analysis, in situ hybridization, and Northern blot analysis. A qualitative analysis indicated that osteopontin protein deposition and mRNA expression increase with the severity of the osteoarthritic lesions and the disintegration of the cartilaginous matrix. Osteopontin expression in the cartilage was limited to the chondrocytes of the upper deep zone, showing cellular and territorial deposition. The strongest osteopontin detection was found in deep zone chondrocytes and in clusters of proliferating chondrocytes from samples with severe osteoarthritic lesions. These data show the expression of osteopontin in adult human osteoarthritic chondrocytes, suggesting that chondrocyte differentiation and the expression of differentiation markers in osteoarthritic cartilage resembles that of epiphyseal growth plate chondrocytes.

Characterization of CXCL16 and ADAM10 in the normal and transplanted kidney

The chemokine CXCL16 plays an important role in the recruitment of leukocytes to sites of inflammation influencing the course of experimental glomerulonephritis. Here we show that human kidneys highly express CXCL16 in the distal tubule, connecting tubule and principal cells of the collecting duct with weak expression in the thick ascending limb of Henle. Beside the membrane localization, a soluble form of CXCL16 can be proteolytically released which acts as a chemotactic factor. In human renal tissue the expression pattern of the disintegrin-like metalloproteinase ADAM10 is similar to that of CXCL16, suggesting ADAM10 can potentially cleave CXCL16 in vivo. When we tested this in primary tubular cells we found that blockade of ADAM10 activity inhibited the IFN-gamma induced release of soluble CXCL16. Acute tubular damage in renal allografts was associated with elevated urinary CXCL16 and this correlated with focally increased apical CXCL16 expression in the distal tubules and collecting ducts. Renal allograft biopsies, with a histopathological diagnosis of acute interstitial rejection, showed increased basolateral ADAM10 expression together with high numbers of infiltrating T cells. Our results suggest that CXCL16 and ADAM10 are involved in the recruitment of T cells to the kidney and play an important role in inflammatory kidney diseases.

Cyclosporin A and tacrolimus induce renal Erk1/2 pathway via ROS-induced and metalloproteinase-dependent EGF-receptor signaling

We previously demonstrated that the widely used immunosuppressive drugs cyclosporin A (CsA) and tacrolimus (FK506), independent of immunophilin binding, can activate profibrogenic transforming growth factor β (TGFβ)/Smad signaling cascades in rat renal mesangial cells (MC). Here we report that both peptidyl-prolyl cis/trans isomerase (PPIase) inhibitors activate the extracellular-signaling regulated kinase (ERK) a member of the mitogen activated protein kinase (MAPK) and induce a rapid and transient increase in ERK phosphorylation. The MEK inhibitor U0126, the reactive oxygen species (ROS) scavenger N-acetyl-cysteine (NAC), a cell-permeant superoxide dismutase (SOD) and stigmatellin, an inhibitor of mitochondrial cytochrome bc1 complex strongly attenuated the increase in ERK1/2 phosphorylation triggered by PPIase inhibitors. Moreover, neutralizing antibodies against heparin binding-epidermal growth factor (HB-EGF), and inhibition of the EGF receptor by either small interfering (si)RNA or AG1478, demonstrate that ERK activation by both PPIase inhibitors is mediated via HB-EGF-induced EGF receptor (EGFR) tyrosine kinase activation. The strong inhibitory effects achieved by GM6001 and TAPI-2 furthermore implicate the involvement of a desintegrin and metalloproteinase 17 (ADAM17). Concomitantly, the PPIase inhibitor-induced ADAM17 secretase activity was significantly reduced by SOD and stigmatellin thus suggesting that mitochondrial ROS play a primary role in PPIase inhibitor-induced and ADAM17-mediated HB-EGF shedding. Functionally, both immunosuppressants caused a strong increase in MC proliferation which was similarly impeded when cells were treated in the presence of NAC, TAPI-2 or AG1478, respectively. Our data suggest that CsA and FK506, via ROS-dependent and ADAM17-catalyzed HB-EGF shedding induce the mitogenic ERK1/2 signaling cascade in renal MC.

Synergistic induction of osteopontin by aldosterone and inflammatory cytokines in mesangial cells

Hypertensive nephrosclerosis is characterized by activation of the renin–angiotensin–aldosterone system in combination with an inflammatory response characterized by an infiltration of T‐cells and mononuclear cells, which release proinflammatory cytokines like IL‐1β/TNFα. In various models of experimental hypertensive disease the chemokine osteopontin (OPN) enhances further leukocyte infiltration. Therefore, we investigated the induction of OPN expression in renal mesangial cells (MCs) by aldosterone and the inflammatory cytokines IL‐1β/TNFα. Incubation with aldosterone resulted in a time‐ and concentration‐dependent increase in OPN mRNA and protein. OPN mRNA expression followed a biphasic time course with an early increase between 4 and 8 h and the second phase starting at 14 h. The early phase was independent of protein synthesis, indicating a direct effect of aldosterone. Aldosterone‐mediated induction of OPN was prevented by spironolactone, indicative of a receptor‐mediated aldosterone effect. The mineralocorticoid receptor (MR) was identified in MCs by RT‐PCR and immunoprecipitation, and shown to interact with a putative aldosterone‐response element of the OPN promoter. The proinflammatory cytokines IL‐1β and TNFα only marginally affected OPN expression in MCs. However, coincubation of aldosterone and the cytokines synergistically increased OPN mRNA and protein levels. Since the synergistic effect on OPN mRNA was inhibited by diphenyleneiodonium, we assume an involvement of reactive oxygen species (ROS). We conclude that the chemokine OPN is a target gene of aldosterone in renal MCs, which is activated via the MR, and that proinflammatory cytokines enhance aldosterone‐dependent OPN expression. In vivo, this may result in further leukocyte infiltration aggravating hypertensive nephrosclerosis. J. Cell. Biochem. 103: 615–623, 2008.

Multidrug resistance-related protein 2 genotype of the donor affects kidney graft function.

Objectives We tested the effect of kidney-specific multidrug resistance-related protein (MRP2, ABCC2) deficiency on renal organic solute disposition as well as on renal protein and gene expression. Furthermore, we investigated whether a particular kidney donor ABCC2 genotype is associated with delayed graft function in patients. Methods A new MRP2-deficient rat strain was established. Renal cross-transplantations were performed between congenic MRP2-deficient and wild-type rats. Renal disposition of MRP2 substrates was investigated in native and transplanted rats. Proteomic analyses and transcriptional profiling were performed in rat kidney graft cortices. Ninety-eight human kidney donor–recipient pairs were genotyped for five ABCC2 polymorphisms. The relationship between delayed graft function and ABCC2 genetic variants in donors and recipients was analyzed by backward stepwise logistic regression. Results In rats, the absence of renal MRP2 reduced renal bilirubin glucuronide excretion at pathologic plasma concentrations, modified renal p-aminohippurate excretion and did not affect renal morphine-6-glucuronide excretion. Renal MRP2 deficiency led to renal cortical protein or mRNA upregulation of glutathione transferase isoenzymes, glutaredoxin 2, and heme oxygenase-1. In patients, a particular donor ABCC2 genotype was associated with an increased incidence of delayed graft function. Conclusion Kidney graft-specific MRP2 deficiency has mild effects on the renal excretion of some organic solutes under experimental conditions and induces a protein and gene expression pattern indicative of activated antioxidant defense mechanisms. This suggests that MRP2 is a determinant of the redox status in tubular epithelial cells and thus of the susceptibility to renal damage under conditions of treatment with multiple drugs and increased oxygen radical formation.

ADAM10 is expressed in human podocytes and found in urinary vesicles of patients with glomerular kidney diseases

BackgroundThe importance of the Notch signaling in the development of glomerular diseases has been recently described. Therefore we analyzed in podocytes the expression and activity of ADAM10, one important component of the Notch signaling complex.MethodsBy Western blot, immunofluorescence and immunohistochemistry analysis we characterized the expression of ADAM10 in human podocytes, human urine and human renal tissue.ResultsWe present evidence, that differentiated human podocytes possessed increased amounts of mature ADAM10 and released elevated levels of L1 adhesion molecule, one well known substrate of ADAM10. By using specific siRNA and metalloproteinase inhibitors we demonstrate that ADAM10 is involved in the cleavage of L1 in human podocytes. Injury of podocytes enhanced the ADAM10 mediated cleavage of L1. In addition, we detected ADAM10 in urinary podocytes from patients with kidney diseases and in tissue sections of normal human kidney. Finally, we found elevated levels of ADAM10 in urinary vesicles of patients with glomerular kidney diseases.ConclusionsThe activity of ADAM10 in human podocytes may play an important role in the development of glomerular kidney diseases.

Immunohistochemical and mRNA Localization of the Angiotensin II Receptor Subtype 2 (AT2) in Follicular Granulosa Cells of the Rat Ovary

A local renin-angiotensin system (RAS), including specific angiotensin II receptor subtypes, is present in the rat ovary. Immunohistochemistry using a polyclonal antibody and mRNA in situ hybridization were performed on perfusion-fixed, paraffin-embedded ovaries obtained from untreated sexually mature, normally cycling rats. Immunofluorescent staining revealed an exclusive and distinct labeling of follicular granulosa cells showing a plaque-like expression pattern at the cell borders, being detectable in different stages of atretic degeneration. On adjacent sections the expression of the respective mRNA could be shown in granulosa cells of the same follicle. The AT2 receptor may be implicated in the ovarian atretic process by influencing follicular cell-cell communication.

Short-term preconditioning enhances the therapeutic potential of adipose-derived stromal/stem cell-conditioned medium in cisplatin-induced acute kidney injury.

The development of new strategies to preserve renal function after acute kidney injury (AKI) is necessary due to limited clinical intervention options. The organ-protective effects of mesenchymal stromal/stem cells (MSCs) and their conditioned medium (CM) have been investigated demonstrating that both separately promoted tubular recovery and ameliorated the outcome of AKI. Nevertheless, strategies to optimise the regenerative potential of both are highly needed. Here we investigated the effects of CM from adipose-derived MSCs (ASCs) preincubated in a hypoxic environment (Hyp). Protective factors were investigated by PCR analysis and a protein array in vitro. The expression of 64 of the 308 proteins assayed was found to be more than two-fold increased after Hyp. CM of Hyp-pretreated ASCs (pCM) was used to enhance regeneration in a mouse model of cisplatin-induced AKI (cisAKI). Renal function was assessed by measurements of markers for AKI and serum cytokine levels. The pCM significantly ameliorated serum creatinine and neutrophil gelatinase-associated lipocalin values, and also the levels of inflammatory cytokines IL-1β and IL-6 in the serum of mice with AKI. Our work clearly showed that a Hyp preconditioning significantly increases the release of protective factors in ASCs and enhances the therapeutic effects of CM in cisAKI in mice.