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      Chemical chaperon 4-phenylbutyrate protects against the endoplasmic reticulum stress-mediated renal fibrosis in vivo and in vitro

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          Renal tubulointerstitial fibrosis is the common and final pathologic change of kidney in end-stage renal disease. Interesting, endoplasmic reticulum (ER) stress is known to contribute to the pathophysiological mechanisms during the development of renal fibrosis. Here, we investigated the effects of chemical chaperon sodium 4-phenylbutyrate (4-PBA) on renal fibrosis in vivo and in vitro. In a rat unilateral ureteral obstruction (UUO) model, 4-PBA mimicked endogenous ER chaperon in the kidneys and significantly reduced glucose regulated protein 78 (GRP78), CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP), activating transcription factor 4 (ATF4), and phosphorylated JNK protein expressions as well as restored spliced X-box-binding protein 1 (XBP1) expressions in the kidneys of UUO rats. 4-PBA also attenuated the increases of α-smooth muscle actin (α-SMA), connective tissue growth factor (CTGF) protein expressions, tubulointerstitial fibrosis, and apoptosis in the kidneys of UUO rats. Moreover, transforming growth factor (TGF)-β markedly increased ER stress-associated molecules, profibrotic factors, and apoptotic markers in the renal tubular cells (NRK-52E), all of which could be significantly counteracted by 4-PBA treatment. 4-PBA also diminished TGF-β-increased CTGF promoter activity and CTGF mRNA expression in NRK-52E cells. Taken together, our results indicated that 4-PBA acts as an ER chaperone to ameliorate ER stress-induced renal tubular cell apoptosis and renal fibrosis.

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          Most cited references 37

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          ER stress induces cleavage of membrane-bound ATF6 by the same proteases that process SREBPs.

          ATF6 is a membrane-bound transcription factor that activates genes in the endoplasmic reticulum (ER) stress response. When unfolded proteins accumulate in the ER, ATF6 is cleaved to release its cytoplasmic domain, which enters the nucleus. Here, we show that ATF6 is processed by Site-1 protease (S1P) and Site-2 protease (S2P), the enzymes that process SREBPs in response to cholesterol deprivation. ATF6 processing was blocked completely in cells lacking S2P and partially in cells lacking S1P. ATF6 processing required the RxxL and asparagine/proline motifs, known requirements for S1P and S2P processing, respectively. Cells lacking S2P failed to induce GRP78, an ATF6 target, in response to ER stress. ATF6 processing did not require SCAP, which is essential for SREBP processing. We conclude that S1P and S2P are required for the ER stress response as well as for lipid synthesis.
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            Renal fibrosis: new insights into the pathogenesis and therapeutics.

             Youhua Liu (2005)
            Renal fibrosis is the inevitable consequence of an excessive accumulation of extracellular matrix that occurs in virtually every type of chronic kidney disease. The pathogenesis of renal fibrosis is a progressive process that ultimately leads to end-stage renal failure, a devastating disorder that requires dialysis or kidney transplantation. In a simplistic view, renal fibrosis represents a failed wound-healing process of the kidney tissue after chronic, sustained injury. Several cellular pathways, including mesangial and fibroblast activation as well as tubular epithelial-mesenchymal transition, have been identified as the major avenues for the generation of the matrix-producing cells in diseased conditions. Among the many fibrogenic factors that regulate renal fibrotic process, transforming growth factor-beta (TGF-beta) is one that plays a central role. Although defective matrix degradation may contribute to tissue scarring, the exact action and mechanisms of the matrix-degrading enzymes in the injured kidney have become increasingly complicated. Recent discoveries on endogenous antifibrotic factors have evolved novel strategies aimed at antagonizing the fibrogenic action of TGF-beta/Smad signaling. Many therapeutic interventions appear effective in animal models; however, translation of these promising results into humans in the clinical setting remains a daunting task. This mini-review attempts to highlight the recent progress in our understanding of the cellular and molecular pathways leading to renal fibrosis, and discusses the challenges and opportunities in developing therapeutic strategies.
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              Identification of a member of the MAPKKK family as a potential mediator of TGF-beta signal transduction.

              The mitogen-activated protein kinase (MAPK) pathway is a conserved eukaryotic signaling module that converts receptor signals into various outputs. MAPK is activated through phosphorylation by MAPK kinase (MAPKK), which is first activated by MAPKK kinase (MAPKKK). A genetic selection based on a MAPK pathway in yeast was used to identify a mouse protein kinase (TAK1) distinct from other members of the MAPKKK family. TAK1 was shown to participate in regulation of transcription by transforming growth factor-beta (TGF-beta). Furthermore, kinase activity of TAK1 was stimulated in response to TGF-beta and bone morphogenetic protein. These results suggest that TAK1 functions as a mediator in the signaling pathway of TGF-beta superfamily members.

                Author and article information

                Impact Journals LLC
                19 April 2016
                3 March 2016
                : 7
                : 16
                : 22116-22127
                1 Graduate Institute of Toxicology, College of Medicine, National Taiwan University, Taipei, Taiwan
                2 Department of Pediatrics, National Taiwan University Hospital, Taipei, Taiwan
                3 Department of Medical Research, China Medical University Hospital, China Medical University, Taichung, Taiwan
                4 Department of Internal Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
                5 Department of Geriatrics and Gerontology, National Taiwan University Hospital, Taipei, Taiwan
                6 Superintendent's Office, National Taiwan University Hospital, Chu-Tung Branch, Taipei, Taiwan
                7 Department of Dentistry, Taipei Chang Gang Memorial Hospital, Chang Gang University, Taipei, Taiwan
                8 Department of Integrated Diagnostics & Therapeutics, National Taiwan University Hospital, Taipei, Taiwan
                Author notes
                Correspondence to: Chih-Kang Chiang, ckchiang@
                Copyright: © 2016 Liu et al.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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