title: Gremlin is a downstream profibrotic mediator of transforming growth factor-beta in cultured renal cells.
abstract: OBJECTIVE
  Chronic kidney disease is characterized by accumulation of extracellular matrix in the tubulointerstitial area. Fibroblasts are the main matrix-producing cells. One source of activated fibroblasts is the epithelial mesenchymal transition (EMT). In cultured tubular epithelial cells, transforming growth factor-β (TGF-β1) induced Gremlin production associated with EMT phenotypic changes, and therefore Gremlin has been proposed as a downstream TGF-β1 mediator. Gremlin is a developmental gene upregulated in chronic kidney diseases associated with matrix accumulation, but its direct role in the modulation of renal fibrosis and its relation with TGF-β has not been investigated.
  
  
  METHODS
  Murine renal fibroblasts and human tubular epithelial cells were studied. Renal fibrosis was determined by evaluation of key profibrotic factors, extracellular matrix proteins (ECM) and EMT markers by Western blot/confocal microscopy or real-time PCR. Endogenous Gremlin was targeted with small interfering RNA.
  
  
  RESULTS
  In murine fibroblasts, stimulation with recombinant Gremlin upregulated profibrotic genes, such as TGF-β1, and augmented the production of ECM proteins, including type I collagen. The blockade of endogenous Gremlin with small interfering RNA inhibited TGF-β1-induced ECM upregulation. In tubular epithelial cells Gremlin also increased profibrotic genes and caused EMT changes: phenotypic modulation to myofibroblast-like morphology, loss of epithelial markers and in-duction of mesenchymal markers. Moreover, Gremlin gene silencing inhibited TGF-β1-induced EMT changes.
  
  
  CONCLUSIONS
  Gremlin directly activates profibrotic events in cul-tured renal fibroblasts and tubular epithelial cells. Moreover, endogenous Gremlin blockade inhibited TGF-β-mediated matrix production and EMT, suggesting that Gremlin could be a novel therapeutic target for renal fibrosis.
authors.affiliation: Cellular Biology in Renal Diseases Laboratory, Fundación Jiménez Díaz, Universidad Autónoma, Madrid, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Rodrigues-Diez
authors.forename: Carolina
authors.initials: C
authors.lastname: Lavoz
authors.forename: Gisselle
authors.initials: G
authors.lastname: Carvajal
authors.forename: Sandra
authors.initials: S
authors.lastname: Rayego-Mateos
authors.forename: Raul R
authors.initials: RR
authors.lastname: Rodrigues Diez
authors.forename: Alberto
authors.initials: A
authors.lastname: Ortiz
authors.forename: Jesús
authors.initials: J
authors.lastname: Egido
authors.forename: Sergio
authors.initials: S
authors.lastname: Mezzano
authors.forename: Marta
authors.initials: M
authors.lastname: Ruiz-Ortega
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D016207:Cytokines; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D058750:Epithelial-Mesenchymal Transition / Q000235:genetics / Q000502:physiology; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D005355:Fibrosis; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D034741:RNA, Small Interfering / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*
chemical_list: D016207:Cytokines; D036341:Intercellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; D016212:Transforming Growth Factor beta; C113178:Grem1 protein, mouse; C486399:GREM1 protein, human