Gremlin: A novel mediator of epithelial mesenchymal transition and fibrosis in chronic allograft nephropathy
ABSTRACT Chronic allograft nephropathy (CAN) is the most frequent cause of chronic dysfunction and late loss of renal allografts. Epithelial mesenchymal transition (EMT) has been identified as responsible for the presence of activated interstitial fibroblasts (myofibroblasts) and transforming growth factor beta (TGF-beta)/Smad is the key signaling mediator. It has been proposed that the bone morphogenetic protein 7 (BMP-7) antagonist, Gremlin, could participate in EMT, as a downstream mediator of TGF-beta.
We evaluated 33 renal allograft biopsies, 16 of which showed CAN, versus 17 controls. By in situ hybridization we studied the expression of TGF-beta and Gremlin mRNA. Gremlin, BMP-7, E-cadherin, and alpha-smooth muscle actin (alpha-SMA) proteins were evaluated by immunohistochemistry and Smad3 activation by Southwestern. In cultured human tubuloepithelial cells (HK2 cell line), Gremlin induction by TGF-beta was studied by confocal microscopy.
Among renal biopsies of transplanted patients with CAN, we detected up-regulation of TGF-beta in colocalization with Gremlin (RNA and protein), mainly in areas of tubulointerstitial fibrosis. In the same tubules, we observed decreased expression of E-cadherin and induction of vimentin and alpha-SMA. BMP-7 was significantly decreased in the CAN biopsies. In addition, HK2 stimulated with TGF-beta (1 ng/mL) induced Gremlin production at 72 hours.
We postulated that Gremlin is a downstream mediator of TGF-beta, suggesting a role for Gremlin in EMT observed in CAN.
- SourceAvailable from: Raquel Rodrigues-Diez[Show abstract] [Hide abstract]
ABSTRACT: Gremlin is a developmental gene upregulated in human chronic kidney disease and in renal cells in response to transforming growth factor- β (TGF- β ). Epithelial mesenchymal transition (EMT) is one process involved in renal fibrosis. In tubular epithelial cells we have recently described that Gremlin induces EMT and acts as a downstream TGF- β mediator. Our aim was to investigate whether Gremlin participates in EMT by the regulation of the Smad pathway. Stimulation of human tubular epithelial cells (HK2) with Gremlin caused an early activation of the Smad signaling pathway (Smad 2/3 phosphorylation, nuclear translocation, and Smad-dependent gene transcription). The blockade of TGF- β , by a neutralizing antibody against active TGF- β , did not modify Gremlin-induced early Smad activation. These data show that Gremlin directly, by a TGF- β independent process, activates the Smad pathway. In tubular epithelial cells long-term incubation with Gremlin increased TGF- β production and caused a sustained Smad activation and a phenotype conversion into myofibroblasts-like cells. Smad 7 overexpression, which blocks Smad 2/3 activation, diminished EMT changes observed in Gremlin-transfected tubuloepithelial cells. TGF- β neutralization also diminished Gremlin-induced EMT changes. In conclusion, we propose that Gremlin could participate in renal fibrosis by inducing EMT in tubular epithelial cells through activation of Smad pathway and induction of TGF- β .BioMed Research International 05/2014; 2014. DOI:10.1155/2014/802841 · 2.71 Impact Factor
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ABSTRACT: Long-term peritoneal dialysis (PD) can lead to fibrotic changes in the peritoneum, characterized by loss of mesothelial cells (MCs) and thickening of the submesothelial area with an accumulation of collagen and myofibroblasts. The origin of myofibroblasts is a central question in peritoneal fibrosis that remains unanswered at present. Numerous clinical and experimental studies have suggested that MCs, through epithelial-mesenchymal transition (EMT), contribute to the pool of peritoneal myofibroblasts. However, recent work has placed significant doubts on the paradigm of EMT in organ fibrogenesis (in the kidney particularly), highlighting the need to reconsider the role of EMT in the generation of myofibroblasts in peritoneal fibrosis. In particular, selective cell isolation and lineage-tracing experiments have suggested the existence of progenitor cells in the peritoneum, which are able to switch to fibroblast-like cells when stimulated by the local environment. These findings highlight the plastic nature of MCs and its contribution to peritoneal fibrogenesis. In this review, we summarize the key findings and caveats of EMT in organ fibrogenesis, with a focus on PD-related peritoneal fibrosis, and discuss the potential of peritoneal MCs as a source of myofibroblasts. Copyright © 2015 International Society for Peritoneal Dialysis.Peritoneal dialysis international: journal of the International Society for Peritoneal Dialysis 02/2015; 35(1):14-25. DOI:10.3747/pdi.2014.00188 · 2.20 Impact Factor
Conference Paper: On the rectangular grid representation of general CNN networks[Show abstract] [Hide abstract]
ABSTRACT: Although the cellular neural net (CNN) paradigm in its original form provides a suitable framework for investigating problems defined on arbitrary regular grids, the neural chips available or under design and the available simulators are all restricted to a rectangular structure. It is not at all self-evident, however, that the rectangular structure is the most suitable to represent every practical problems. In this paper we demonstrate that several CNNs of various regular grids can be mapped onto the typical eight-neighbour rectangular one, by applying weight matrices of periodic space-variance. By adopting this option, the applicability of cellular neural chips and simulators can be extended to investigate problems of essentially arbitrary grid structuresCellular Neural Networks and Their Applications, 2000. (CNNA 2000). Proceedings of the 2000 6th IEEE International Workshop on; 02/2000