Jens Gerth

Autoantibodies against thrombospondin type 1 domain–containing 7A induce membranous nephropathy

Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults, and one-third of patients develop end-stage renal disease (ESRD). Circulating autoantibodies against the podocyte surface antigens phospholipase A2 receptor 1 (PLA2R1) and the recently identified thrombospondin type 1 domain-containing 7A (THSD7A) are assumed to cause the disease in the majority of patients. The pathogenicity of these antibodies, however, has not been directly proven. Here, we have reported the analysis and characterization of a male patient with THSD7A-associated MN who progressed to ESRD and subsequently underwent renal transplantation. MN rapidly recurred after transplantation. Enhanced staining for THSD7A was observed in the kidney allograft, and detectable anti-THSD7A antibodies were present in the serum before and after transplantation, suggesting that these antibodies induced a recurrence of MN in the renal transplant. In contrast to PLA2R1, THSD7A was expressed on both human and murine podocytes, enabling the evaluation of whether anti-THSD7A antibodies cause MN in mice. We demonstrated that human anti-THSD7A antibodies specifically bind to murine THSD7A on podocyte foot processes, induce proteinuria, and initiate a histopathological pattern that is typical of MN. Furthermore, anti-THSD7A antibodies induced marked cytoskeletal rearrangement in primary murine glomerular epithelial cells as well as in human embryonic kidney 293 cells. Our findings support a causative role of anti-THSD7A antibodies in the development of MN.

Polyomavirus DNA and RNA detection in renal allograft biopsies: results from a European multicenter study.

Polyomavirus mediated nephropathy is an increasingly recognized complication in renal transplant recipients. In all, 362 renal biopsies collected from 15 European transplant centers were analyzed for presence of Polyomavirus nucleic acid (BK virus [BKV] and JC virus [JCV]). We evaluated 302 biopsies of patients with renal allograft dysfunction, including three with known BKV allograft nephropathy (BKVAN), and 60 native kidney biopsies. BKV DNA was detected in 8 of the 302 (2.6 %) biopsies obtained for transplant dysfunction, but in none of the controls. BKV RNA, indicating active viral replication, was found in all BKV DNA positive biopsies available for mRNA expression studies. Retrospective immunohistochemical staining was positive for SV40 large T antigen in all seven evaluated biopsies. BKV DNA and RNA were detected in biopsy tissues from patients with inconspicuous light microscopy for BKVAN. Further studies will evaluate the potential of intrarenal viral BKV RNA as an early predictor for BKVAN.

Pregnancy-associated thrombotic thrombocytopenic purpura.

Thrombocytopenia during pregnancy is a common diagnostic and management problem. Several differential diagnosis must be considered including manifestations of thrombotic thrombocytopenic purpura (TTP). We report here on a case of a 21-year-old pregnant woman who presented initially severe thrombocytopenia (8 Gpt/l) in the 20(th)+1 week of gestation. The patient had an antibody against ADAMTS13, and enzyme activity was <5%. Immediate plasmapheresis treatment was initiated, followed by plasma infusions, and again plasmapheresis. A male neonate was delivered by caesarean section in the 32(nd )week of gestation. The child had an uncomplicated postnatal development. After delivery, the mothers platelet count and ADAMTS13 activity increased to normal values. This case shows interesting aspects of TTP in pregnancy and a close cooperation between obstetricians, nephrologists and pediatricians is necessary for a successful outcome of the pregnancy.

Collagen type VIII expression in human diabetic nephropathy

Background  Collagen type VIII is a non‐fibrillar short‐chain collagen that may modulate migration, proliferation and adherence of various cells. Only very sparse information exists on collagen type VIII expression in human diabetic nephropathy.

Vitamin B6 Metabolism in Chronic Kidney Disease – Relation to Transsulfuration, Advanced Glycation and Cardiovascular Disease

Background: Vitamin deficiency is common in chronic kidney disease (CKD). Data on B6 supply and possible relationships to cardiovascular events (CVE) in CKD are rare. Pyridoxamine exerts inhibitory effects on the formation of advanced glycation endproducts (AGE) implicated in the pathogenesis of CKD and atherosclerosis. Methods: In 48 CKD patients at stage 2–4, 72 hemodialysis patients (HD), 38 renal transplant recipients (RTR) and 141 healthy controls (mean age 58 ± 13, 61 ± 12, 50 ± 12 and 54 ± 16 years, respectively), plasma and red blood cell (RBC) concentrations of pyridoxal-5′-phosphate (PLP), pyridoxal (PL), 4-pyridoxic acid (PA), pyridoxamine-5′-phosphate (PMP) and of the AGE pentosidine were measured by high-performance liquid chromatography, NΕ-(carboxymethyl)lysine and imidazolone by an ELISA, and total homocysteine and cystathionine by gas chromatography-mass spectrometry. Results: Despite routine low-dose vitamin supplementation in HD, plasma PLP was decreased in HD (79 ± 69 nmol/l) compared with CKD stage 2–4 patients (497 ± 944 nmol/l), RTR (416 ± 604 nmol/l) and controls (159 ± 230 nmol/l; p < 0.001). Plasma PA was significantly increased in HD (11,667 ± 17,871 nmol/l) in comparison with CKD stage 2–4 (435 ± 441 nmol/l), RTR (583 ± 668 nmol/l) and controls (46 ± 49 nmol/l; p < 0.001). B6 forms were significantly affected by renal function (R = 0.792, p < 0.001 for CKD stage 2–4). There was no relation of vitamers with a history of CVE. Relationships between B6 forms and AGE (RBC-PMP with pentosidine in CKD stage 2–4: R = –0.351, p < 0.05) were found. Conclusion: HD patients showed a deficiency in PLP in plasma but not in RBC. Prospective trials are needed to elucidate the potential role of elevated PA on cardiovascular and renal outcome in CKD. Vitamin B6 supplementation might be successful in preventing AGE-related pathologies.

A single-center experience with BK virus nephropathy.

BACKGROUND BK virus nephropathy has an increasing role in renal transplant dysfunction, since new, highly potent immunosuppressive drugs have been introduced into therapy following renal transplantation. Diagnosis of acute impairment of renal transplant function is complicated by difficulty in differentiating BK virus nephropathy from acute rejection. PATIENTS AND METHODS We retrospectively described the findings and therapeutic approaches of 6 consecutive patients with BK virus nephropathy in our transplantation center (75 - 80 transplantations/ year). BK virus nephropathy was classified according to Drachenberg et al. [2004]. RESULTS We observed an incidence rate of < 1% for BK nephropathy in our center. Four patients had a pattern B whereas 2 patients revealed a pattern C of BK virus nephropathy. Focal C4d-positive staining of peritubular capillaries were found in 2 of the 6 cases. For earlier detection of BK nephropathy, a diagnostic algorithm for each patient after renal transplantation was established. Urine was continuously monitored by cytology for decoy cells and PCR for BK virus DNA. If PCR was also positive for the BK virus in plasma, biopsy of the renal allograft was performed. Thereby diagnosis could be confirmed sooner. For treatment of BK nephropathy in our center, we reduced immunosuppressive agents and initiated a virustatic treatment with cidofovir in the first 3 cases. However, results were not satisfactory and two allografts were lost. We then reconsidered our therapeutic approach and switched the immunosuppressive treatment to leflunomide with consistent low dose steroids. We use therapeutic drug monitoring for leflunomide and aim at a target level of 40 - 100 microg/ml. We lost no allograft with BK nephropathy since using this therapeutic approach. CONCLUSION In our center, leflunomide therapy, but not cidofovir, was effective in patients with BK virus nephropathy of the renal allograft.

Transdifferentiation of Endothelial and Renal Tubular Epithelial Cells into Myofibroblast-Like Cells under in vitro Conditions: A Morphological Analysis

Renal fibrosis is a hallmark of progressive kidney disease and is characterized by an accumulation of extracellular-matrix-synthesizing cells in the glomerulus and tubulointerstitium. This population of myofibroblast-like cells (MFLC) is heterogeneous. It has been experimentally shown, for example, that tubular epithelial cells could change their phenotype into MFLC under certain circumstances, a process called epithelial-mesenchymal transdifferentiation. However, MFLC may also originate from other sources. Therefore, we examined whether endothelial cells (EDC) are able to transdifferentiate into MFLC in vitro. We compared potential differences between syngeneic tubular epithelial cells (EPC) and EDC during transdifferentiation into MFLC using bovine and porcine EDC isolated from pulmonary arteries, and glomerular capillaries. Renal tubular EPC were prepared from bovine renal cortical tissue by collagenase digestion and isolation from homogeneous cell monolayers. Bovine renal tubular EPC stained positive for cytokeratin. Furthermore, tubular EPC selectively incoporated labeled bovine serum albumin, a typical property of differentiated renal tubular cells. EDC were characterized by the absence of epithelial markers (e.g. cytokeratin), but stained positive for vWF. The transdifferentiation of EDC into MFLC occurs sequentially in two steps: First, by a rapid reversible transformation in postconfluent or clonal cultures without the need of cytokine stimulation and second, by a prolonged secondary step in the presence of the transformation-accelerating cytokines and the absence of adherently growing EDC. Thus, EDC that are able to sprout can also irreversibly transdifferentiate into MFLC. On the other hand, prolonged incubation of EPC in the presence of cytokines such as transforming growth factor-β1 and tumor necrosis factor-α leads only to a very small number of MFLC without the ability to further proliferate. Our in vitro data suggest that EDC can more easily transdifferentiate into MFLC than syngeneic renal tubular EPC.

Proteinuria after conversion to sirolimus in kidney transplant recipients: impact of pre-existing proteinuria, graft function, and angiotensin-converting enzyme inhibitors/angiotensin-receptor antagonists

Marx C, Busch M, Ott U, Gerth J, Wolf G. Proteinuria after conversion to sirolimus in kidney transplant recipients: impact of pre‐existing proteinuria, graft function, and angiotensin‐converting enzyme inhibitors/angiotensin‐receptor antagonists.
Clin Transplant 2009 DOI:10.1111/j.1399‐0012.2009.01142.x.
© 2009 John Wiley & Sons A/S.

Interleukin 4 Co-Stimulates the PDGF-BB- and bFGF-Mediated Proliferation of Mesangial Cells and Myofibroblasts

Background: Although many mediators involved in the pathogenesis of fibrosis are known, its precise mechanism is still unknown. In vitro experiments may contribute to the recognition of cellular changes which also take place during fibrosis. Methods: Renal tubular epithelial cells (EPC), mesangial cells (MC) and glomerular endothelial cells (GEDC) as well as endothelial cells (EDC) and myofibroblasts (MF) from cattle were isolated to measure the proliferation and protein synthesis in the presence of individual and combined cytokines/growth factors in cell cultures. Results: Cytokines stimulating or permitting the proliferation of myofibroblast-like cells (MFLC) (MC and MF), caused damage of endothelial cells (EDC, GEDC), whereas EPC were stable. The proliferation of MFLC was strongly stimulated by PDGF-BB and bFGF and elevated more than twofold in the presence of interleukin 4 (IL-4), but IL-4 alone had no effect. Furthermore, the proliferation of transdifferentiated endothelial cells (TEC), obtained by incubation of EDC with TNFα and bFGF, was stimulated with both PDGF-BB/IL-4 and bFGF/IL-4 in the same way and proved to be stable with respect to TNFα. Conclusion: Interleukin 4 co-stimulates the PDGF-BB- and bFGF-mediated proliferation of MC, MF, and TEC. TNFα does not inhibit the proliferation of extracellular matrix-synthesizing cells, but has an inhibitory or even toxic effect on EDC and GEDC. It may be concluded that cytokines released in inflamed renal tissue influence tubulointerstitial cells in different ways, resulting in progressive tissue damage and fibrosis in which the EDC would be the most sensitive cells. Thus, we speculate that microvascular injury in these areas leads to ischemia and malnutrition of tubular EPC and may be responsible for ongoing tubular damage and resulting renal interstitial fibrosis.

Are tissue samples from two different anatomical areas of the kidney necessary for adequate diagnosis

BACKGROUND An accurate histological diagnosis is of fundamental importance for the therapy and prognosis of many kidney diseases. However, it remains unclear whether a single biopsy is representative of changes in the whole kidney. METHODS To compare the quantity and quality of renal biopsy material taken from two separate areas from one kidney, we prospectively biopsied the renal cortex at the central third and at one of the kidney poles of 103 consecutive 61 native and 42 transplanted kidneys. With two biopsy cores from each kidney we sampled 14.5 ± 8.5 glomeruli/procedure. RESULTS The length of the biopsy core, the number of glomeruli/core and the markers of chronic renal damage (degree of interstitial fibrosis, proportion of global or segmental scared glomeruli) were not influenced by biopsy location (pole compared with central third locations). Moreover, there was no significant difference in the number of arteries in biopsies obtained from the two different biopsy areas. The percentage between renal cortex and medulla was not influenced by the biopsy area in all kidneys, but transplanted kidney biopsies contained more medulla than specimens from native kidneys. In patients with native kidneys and lower estimated creatinine clearances, there was a nonsignificant trend towards higher variations in the degree of interstitial fibrosis between the two cores, but a coincidence cannot be excluded. There was no significant difference in global sclerotic glomeruli in regard to the biopsy location. CONCLUSION We conclude that a renal biopsy composed of two cores from different areas of the kidney provides enough material for histological diagnosis. However, despite the variety of different renal diseases, sampling errors are minimal and obtaining two biopsies from different areas of the kidney does not lead to clinically useful information which would alter the management of patients.