title: BMP-7 blocks mesenchymal conversion of mesothelial cells and prevents peritoneal damage induced by dialysis fluid exposure.
abstract: BACKGROUND
  During peritoneal dialysis (PD), mesothelial cells (MC) undergo an epithelial-to-mesenchymal transition (EMT), and this process is associated with peritoneal membrane (PM) damage. Bone morphogenic protein-7 (BMP-7) antagonizes transforming growth factor (TGF)-beta1, modulates EMT and protects against fibrosis. Herein, we analysed the modulating role of BMP-7 on EMT of MC in vitro and its protective effects in a rat PD model.
  
  
  METHODS
  Epitheliod or non-epitheliod MC were analysed for the expression of BMP-7, TGF-beta1, activated Smads, epithelial cadherin (E-cadherin), collagen I, alpha smooth muscle cell actin (alpha-SMA) and vascular endothelial growth factor (VEGF) using standard procedures. Rats were daily instilled with PD fluid with or without BMP-7 during 5 weeks. Histological analyses were carried out in parietal peritoneum. Fibrosis was quantified with van Gieson or Masson's trichrome staining. Vasculature, activated macrophages and invading MC were quantified by immunofluorescence analysis. Quantification of infiltrating leukocytes and MC density in liver imprints was performed by May-Grünwald-Giemsa staining. Hyaluronic acid levels were determined by ELISA.
  
  
  RESULTS
  MC constitutively expressed BMP-7, and its expression was downregulated during EMT. Treatment with recombinant BMP-7 resulted in blockade of TGF-beta1-induced EMT of MC. We provide evidence of a Smad-dependent mechanism for the blockade of EMT. Exposure of rat peritoneum to PD fluid resulted in inflammatory and regenerative responses, invasion of the compact zone by MC, fibrosis and angiogenesis. Administration of BMP-7 decreased the number of invading MC and reduced fibrosis and angiogenesis. In contrast, BMP-7 had no effect on inflammatory and regenerative responses, suggesting that these are EMT-independent, and probably upstream, processes.
  
  
  CONCLUSIONS
  Data point to a balance between BMP-7 and TGF-beta1 in the control of EMT and indicate that blockade of EMT may be a therapeutic approach to ameliorate peritoneal membrane damage during PD.
authors.affiliation: Unidad de Biología Molecular, Hospital Universitario de la Princesa, Madrid, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Loureiro
authors.forename: Margot
authors.initials: M
authors.lastname: Schilte
authors.forename: Abelardo
authors.initials: A
authors.lastname: Aguilera
authors.forename: Patricia
authors.initials: P
authors.lastname: Albar-Vizcaíno
authors.forename: Marta
authors.initials: M
authors.lastname: Ramírez-Huesca
authors.forename: M Luisa
authors.initials: ML
authors.lastname: Pérez-Lozano
authors.forename: Guadalupe
authors.initials: G
authors.lastname: González-Mateo
authors.forename: Luiz S
authors.initials: LS
authors.lastname: Aroeira
authors.forename: Rafael
authors.initials: R
authors.lastname: Selgas
authors.forename: Lorea
authors.initials: L
authors.lastname: Mendoza
authors.forename: Alberto
authors.initials: A
authors.lastname: Ortiz
authors.forename: Marta
authors.initials: M
authors.lastname: Ruíz-Ortega
authors.forename: Jacob
authors.initials: J
authors.lastname: van den Born
authors.forename: Robert H J
authors.initials: RH
authors.lastname: Beelen
authors.forename: Manuel
authors.initials: M
authors.lastname: López-Cabrera
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D055419:Bone Morphogenetic Protein 7 / Q000502:physiology*; D015820:Cadherins / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D004848:Epithelium / Q000378:metabolism*; D005355:Fibrosis; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008648:Mesoderm / Q000378:metabolism*; D010530:Peritoneal Dialysis; D010537:Peritoneum / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D051785:Smad Proteins / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000037:antagonists & inhibitors
chemical_list: D000199:Actins; D055419:Bone Morphogenetic Protein 7; D015820:Cadherins; D051785:Smad Proteins; D053773:Transforming Growth Factor beta1