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      Protective effect of epigallocatechin-3-gallate (EGCG) via Nrf2 pathway against oxalate-induced epithelial mesenchymal transition (EMT) of renal tubular cells

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          Abstract

          This study evaluated effect of oxalate on epithelial mesenchymal transition (EMT) and potential anti-fibrotic property of epigallocatechin-3-gallate (EGCG). MDCK renal tubular cells were incubated with 0.5 mM sodium oxalate for 24-h with/without 1-h pretreatment with 25 μM EGCG. Microscopic examination, immunoblotting and immunofluorescence staining revealed that oxalate-treated cells gained mesenchymal phenotypes by fibroblast-like morphological change and increasing expression of vimentin and fibronectin, while levels of epithelial markers (E-cadherin, occludin, cytokeratin and ZO-1) were decreased. EGCG pretreatment could prevent all these changes and molecular mechanisms underlying the prevention by EGCG were most likely due to reduced production of intracellular ROS through activation of Nrf2 signaling and increased catalase anti-oxidant enzyme. Knockdown of Nrf2 by small interfering RNA (siRNA) abrogated all the effects of EGCG, confirming that the EGCG protection against oxalate-induced EMT was mediated via Nrf2. Taken together, our data indicate that oxalate turned on EMT of renal tubular cells that could be prevented by EGCG via Nrf2 pathway. These findings also shed light onto development of novel therapeutics or preventive strategies of renal fibrosis in the future.

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          Most cited references33

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          Evidence that fibroblasts derive from epithelium during tissue fibrosis.

          Interstitial fibroblasts are principal effector cells of organ fibrosis in kidneys, lungs, and liver. While some view fibroblasts in adult tissues as nothing more than primitive mesenchymal cells surviving embryologic development, they differ from mesenchymal cells in their unique expression of fibroblast-specific protein-1 (FSP1). This difference raises questions about their origin. Using bone marrow chimeras and transgenic reporter mice, we show here that interstitial kidney fibroblasts derive from two sources. A small number of FSP1(+), CD34(-) fibroblasts migrate to normal interstitial spaces from bone marrow. More surprisingly, however, FSP1(+) fibroblasts also arise in large numbers by local epithelial-mesenchymal transition (EMT) during renal fibrogenesis. Both populations of fibroblasts express collagen type I and expand by cell division during tissue fibrosis. Our findings suggest that a substantial number of organ fibroblasts appear through a novel reversal in the direction of epithelial cell fate. As a general mechanism, this change in fate highlights the potential plasticity of differentiated cells in adult tissues under pathologic conditions.
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            Identification and characterization of a fibroblast marker: FSP1

            We performed subtractive and differential hybridization for transcript comparison between murine fibroblasts and isogenic epithelium, and observed only a few novel intracellular genes which were relatively specific for fibroblasts. One such gene encodes a filament-associated, calcium-binding protein, fibroblast-specific protein 1 (FSP1). The promoter/enhancer region driving this gene is active in fibroblasts but not in epithelium, mesangial cells or embryonic endoderm. During development, FSP1 is first detected by in situ hybridization after day 8.5 as a postgastrulation event, and is associated with cells of mesenchymal origin or of fibroblastic phenotype. Polyclonal antiserum raised to recombinant FSP1 protein stained the cytoplasm of fibroblasts, but not epithelium. Only occasional cells stain with specific anti-FSP1 antibodies in normal parenchymal tissue. However, in kidneys fibrosing from persistent inflammation, many fibroblasts could be identified in interstitial sites of collagen deposition and also in tubular epithelium adjacent to the inflammatory process. This pattern of anti-FSP1 staining during tissue fibrosis suggests, as a hypothesis, that fibroblasts in some cases arise, as needed, from the local conversion of epithelium. Consistent with this notion that FSP1 may be involved in the transition from epithelium to fibroblasts are experiments in which the in vitro overexpression of FSP1 cDNA in tubular epithelium is accompanied by conversion to a mesenchymal phenotype, as characterized by a more stellate and elongated fibroblast- like appearance, a reduction in cytokeratin, and new expression of vimentin. Similarly, tubular epithelium submerged in type I collagen gels exhibited the conversion to a fibroblast phenotype which includes de novo expression of FSP1 and vimentin. Use of the FSP1 marker, therefore, should further facilitate both the in vivo studies of fibrogenesis and the mapping of cell fate among fibroblasts.
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              Epithelial to mesenchymal transition in renal fibrogenesis: pathologic significance, molecular mechanism, and therapeutic intervention.

              Youhua Liu (2004)
              Mature tubular epithelial cells in adult kidney can undergo epithelial-to-mesenchymal transition (EMT), a phenotypic conversion that is fundamentally linked to the pathogenesis of renal interstitial fibrosis. Emerging evidence indicates that a large proportion of interstitial fibroblasts are actually originated from tubular epithelial cells via EMT in diseased kidney. Moreover, selective blockade of EMT in a mouse genetic model dramatically reduces fibrotic lesions after obstructive injury, underscoring a definite importance of EMT in renal fibrogenesis. Tubular EMT is proposed as an orchestrated, highly regulated process that consists of four key steps: (1) loss of epithelial cell adhesion; (2) de novo alpha-smooth muscle actin expression and actin reorganization; (3) disruption of tubular basement membrane; and (4) enhanced cell migration and invasion. Of the many factors that regulate EMT in different ways, transforming growth factor-beta1 is the most potent inducer that is capable of initiating and completing the entire EMT course, whereas hepatocyte growth factor and bone morphogenetic protein-7 act as EMT inhibitors both in vitro and in vivo. Multiple intracellular signaling pathways have been implicated in mediating EMT, in which Smad/integrin-linked kinase may play a central role. This article attempts to provide a comprehensive review of recent advances on understanding the pathologic significance, molecular mechanism, and therapeutic intervention of EMT in the setting of chronic renal fibrosis.
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                Author and article information

                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group
                2045-2322
                25 July 2016
                2016
                : 6
                : 30233
                Affiliations
                [1 ]Medical Proteomics Unit, Office for Research and Development, Faculty of Medicine Siriraj Hospital, and Center for Research in Complex Systems Science, Mahidol University , Bangkok 10700, Thailand
                Author notes
                Article
                srep30233
                10.1038/srep30233
                4958994
                27452398
                5300f785-ff0d-4cbd-a36d-8b2cf9b2754c
                Copyright © 2016, Macmillan Publishers Limited

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 24 February 2016
                : 01 July 2016
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