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      Podocyte Phenotypes as Defined by Expression and Distribution of GLEPP1 in the Developing Glomerulus and in Nephrotic Glomeruli from MCD, CNF, and FSGS

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          Abstract

          Glomerular epithelial protein 1 (GLEPP1) is a podocyte receptor membrane protein tyrosine phosphatase located on the apical cell membrane of visceral glomerular epithelial cell (VGEC) foot processes. Double label immunofluorescence, immunoelectron microscopy, and peroxidase immunohistochemistry were used to map the GLEPP1 distribution in the developing glomerulus and in minimal-change nephropathy (MCN), congenital nephrotic syndrome of the Finnish type, and focal-segmental glomerulosclerosis (FSGS). In MCN GLEPP1 was shifted away from the glomerular basement membrane on the apical cell membrane of effaced foot processes. These data are compatible with the previously suggested concept that MCN can be considered a form of dedifferentiation of the podocyte phenotype. Similarly, changes seen in congenital nephrotic syndrome of the Finnish type can be considered a consequence of failure to complete normal podocyte development. In FSGS glomeruli GLEPP1 was frequently absent from VGECs, even when no sclerosis was detectable in that glomerulus. Therefore, in FSGS, VGECs may lose GLEPP1, and this loss appears to occur in the absence of scarring and may, therefore, precede the scarring process. We speculate that a changed VGEC phenotype that does not express GLEPP1 might have properties similar to the early undifferentiated VGEC developmental phenotype. GLEPP1 distribution pattern and absence from glomeruli of individuals with nephrotic syndrome may, therefore, represent a useful phenotypic marker.

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          Most cited references 3

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          Circulating factor associated with increased glomerular permeability to albumin in recurrent focal segmental glomerulosclerosis.

          Heavy proteinuria and progressive renal injury recur after transplantation in up to 40 percent of patients with renal failure caused by idiopathic focal segmental glomerulosclerosis. A circulating factor may be responsible for this recurrence. To determine whether patients with focal segmental glomerulosclerosis have a circulating factor capable of causing glomerular injury, we tested serum samples from 100 patients with the disorder in an in vitro assay of glomerular permeability to albumin. Of the 56 patients who had undergone renal transplantation, 33 had recurrences. Sixty-four patients, many of whom had undergone transplantation, were being treated with dialysis. Thirty-one patients with other renal diseases and nine normal subjects were also studied. The 33 patients with recurrent focal segmental glomerulosclerosis after transplantation had a higher mean (+/-SE) value for permeability to albumin (0.47+/-0.06) than the normal subjects (0.06+/-0.07) or the patients who did not have recurrences (0.14+/-0.06). After plasmapheresis in six patients with recurrences, the permeability was reduced (from 0.79+/-0.06 to 0.10+/-0.05, P = 0.008), and proteinuria was significantly decreased. Patients with corticosteroid-sensitive nephrotic syndrome or with membranous nephropathy after transplantation had low levels of serum activity. The circulating factor bound to protein A and hydrophobic-interaction columns and had an apparent molecular mass of about 50 kd. A circulating factor found in some patients with focal segmental glomerulosclerosis is associated with recurrent disease after renal transplantation and may be responsible for initiating the renal injury.
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            The tight junction protein ZO-1 is concentrated along slit diaphragms of the glomerular epithelium

            The foot processes of glomerular epithelial cells of the mammalian kidney are firmly attached to one another by shallow intercellular junctions or slit diaphragms of unknown composition. We have investigated the molecular nature of these junctions using an antibody that recognizes ZO-1, a protein that is specific for the tight junction or zonula occludens. By immunoblotting the affinity purified anti-ZO-1 IgG recognizes a single 225-kD band in kidney cortex and in slit diaphragm-enriched fractions as in other tissues. When ZO-1 was localized by immunofluorescence in kidney tissue of adult rats, the protein was detected in epithelia of all segments of the nephron, but the glomerular epithelium was much more intensely stained than any other epithelium. Among tubule epithelia the signal for ZO-1 correlated with the known fibril content and physiologic tightness of the junctions, i.e., it was highest in distal and collecting tubules and lowest in the proximal tubule. By immunoelectron microscopy ZO-1 was found to be concentrated on the cytoplasmic surface of the tight junctional membrane. Within the glomerulus ZO-1 was localized predominantly in the epithelial foot processes where it was concentrated precisely at the points of insertion of the slit diaphragms into the lateral cell membrane. Its distribution appeared to be continuous along the continuous slit membrane junction. When ZO-1 was localized in differentiating glomeruli in the newborn rat kidney, it was present early in development when the apical junctional complexes between presumptive podocytes are composed of typical tight and adhering junctions. It remained associated with these junctions during the time they migrate down the lateral cell surface, disappear and are replaced by slit diaphragms. The distribution of ZO-1 and the close developmental relationship between the two junctions suggest that the slit diaphragm is a variant of the tight junction that shares with it at least one structural protein and the functional property of defining distinctive plasmalemmal domains. The glomerular epithelium is unique among renal epithelia in that ZO-1 is present, but the intercellular spaces are wide open and no fibrils are seen by freeze fracture. The presence of ZO-1 along slit membranes indicates that expression of ZO-1 alone does not lead to tight junction assembly.
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              Molecular cloning of cDNAs encoding human GLEPP1, a membrane protein tyrosine phosphatase: characterization of the GLEPP1 protein distribution in human kidney and assignment of the GLEPP1 gene to human chromosome 12p12-p13.

              Human glomerular epithelial protein 1 (GLEPP1), a receptor-like membrane protein tyrosine phosphatase (PTPase), was cloned and sequenced from a human renal cortical cDNA library. The human nucleotide and derived amino acid sequences were, respectively, 90 and 97% identical to those of rabbit. Human GLEPP1 is predicted to contain 1188 amino acids. The predicted mature protein is 1159 amino acids long and contains a large extracellular domain, a single transmembrane domain, and a single intracellular PTPase domain. Monoclonal and polyclonal antibodies raised against a human GLEPP1 fusion protein recognized a protein with distribution restricted to the glomerulus in human kidney and with an apparent molecular weight of approximately 200 kDa. The GLEPP1 gene was assigned to human chromosome 12p12-p13 by fluorescence in situ hybridization.
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                Author and article information

                Journal
                EXN
                Nephron Exp Nephrol
                10.1159/issn.1660-2129
                Cardiorenal Medicine
                S. Karger AG
                1660-2129
                1998
                June 1998
                22 May 1998
                : 6
                : 3
                : 234-244
                Affiliations
                Departments of a Internal Medicine, b Pediatrics and c Pathology, University of Michigan, Ann Arbor, Mich., USA
                Article
                20528 Exp Nephrol 1998;6:234–244
                10.1159/000020528
                © 1998 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 6, Tables: 1, References: 21, Pages: 11
                Product
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/20528
                Categories
                Original Paper

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