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      Imaging Podocyte Dynamics

      a, b , c

      Cardiorenal Medicine

      S. Karger AG

      Imaging, Podocyte, Cytoskeleton, Actin, Glomerulus

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          Abstract

          Cytoskeletal dynamics play important roles during normal podocyte development, in maintenance of the healthy glomerular filter, and in glomerular pathology. During the past few years, essential progress has been made in understanding the molecular mechanisms that govern podocyte cytoskeletal dynamics, nevertheless this knowledge remains incomplete. Examination of the podocyte cytoskeleton presents unique challenges to the experimentalist who is faced with attempting to model a morphologically complex cell that is situated in a complex microenvironment. This review will summarize recent progress in understanding cytoskeletal dynamics in the podocyte and will review modern imaging techniques relevant to studying this area of podocyte biology.

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          Most cited references 37

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          Rearrangements of the cytoskeleton and cell contacts induce process formation during differentiation of conditionally immortalized mouse podocyte cell lines.

          Mature podocytes are among the most complex differentiated cells and possess a highly branched array of foot processes that are essential to glomerular filtration in the kidney. Such differentiated podocytes are unable to replicate and culturing of primary podocytes results in rapid growth arrest. Therefore, conditionally immortalized mouse podocyte clones (MPC) were established, which are highly proliferative when cultured under permissive conditions. Nonpermissive conditions render the majority of MPC cells growth arrested within 6 days and induce many characteristics of differentiated podocytes. Both proliferating and differentiating MPC cells express the WT-1 protein and an ordered array of actin fibers and microtubules extends into the forming cellular processes during differentiation, reminiscent of podocyte processes in vivo. These cytoskeletal rearrangements and process formation are accompanied by the onset of synaptopodin synthesis, an actin-associated protein marking specifically differentiated podocytes. In addition, focal contacts are rearranged into an ordered pattern in differentiating MPC cells. Most importantly, electrophysiological studies demonstrate that differentiated MPC cells respond to the vasoactive peptide bradykinin by changes in intracellular calcium concentration. These results suggest a regulatory role of podocytes in glomerular filtration. Taken together, these studies establish that conditionally immortalized MPC cells retain a differentiation potential similar to podocytes in vivo. Therefore, the determinative steps of podocyte differentiation and process formation are studied for the first time using an inducible in vitro model.
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            TRPC6 is a glomerular slit diaphragm-associated channel required for normal renal function.

            Progressive kidney failure is a genetically and clinically heterogeneous group of disorders. Podocyte foot processes and the interposed glomerular slit diaphragm are essential components of the permeability barrier in the kidney. Mutations in genes encoding structural proteins of the podocyte lead to the development of proteinuria, resulting in progressive kidney failure and focal segmental glomerulosclerosis. Here, we show that the canonical transient receptor potential 6 (TRPC6) ion channel is expressed in podocytes and is a component of the glomerular slit diaphragm. We identified five families with autosomal dominant focal segmental glomerulosclerosis in which disease segregated with mutations in the gene TRPC6 on chromosome 11q. Two of the TRPC6 mutants had increased current amplitudes. These data show that TRPC6 channel activity at the slit diaphragm is essential for proper regulation of podocyte structure and function.
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              Antagonism between Ena/VASP proteins and actin filament capping regulates fibroblast motility.

              Cell motility requires lamellipodial protrusion, a process driven by actin polymerization. Ena/VASP proteins accumulate in protruding lamellipodia and promote the rapid actin-driven motility of the pathogen Listeria. In contrast, Ena/VASP negatively regulate cell translocation. To resolve this paradox, we analyzed the function of Ena/VASP during lamellipodial protrusion. Ena/VASP-deficient lamellipodia protruded slower but more persistently, consistent with their increased cell translocation rates. Actin networks in Ena/VASP-deficient lamellipodia contained shorter, more highly branched filaments compared to controls. Lamellipodia with excess Ena/VASP contained longer, less branched filaments. In vitro, Ena/VASP promoted actin filament elongation by interacting with barbed ends, shielding them from capping protein. We conclude that Ena/VASP regulates cell motility by controlling the geometry of actin filament networks within lamellipodia.
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                Author and article information

                Journal
                NEE
                Nephron Exp Nephrol
                10.1159/issn.1660-2129
                Cardiorenal Medicine
                S. Karger AG
                978-3-8055-8074-8
                978-3-318-01315-3
                1660-2129
                2006
                March 2006
                13 March 2006
                : 103
                : 2
                : e69-e74
                Affiliations
                aDivision of Nephrology and Immunology, University Hospital, RWTH, Aachen, and bInstitute for Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany; cDivision of Nephrology, University of Michigan Medical School, Ann Arbor, Mich., USA
                Article
                90619 Nephron Exp Nephrol 2006;103:e69–e74
                10.1159/000090619
                16543767
                © 2006 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: 3, References: 55, Pages: 1
                Product
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/90619
                Categories
                Microscopic Imaging

                Cardiovascular Medicine, Nephrology

                Imaging, Glomerulus, Actin, Cytoskeleton, Podocyte

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