BMP-7 blocks mesenchymal conversion of mesothelial cells and prevents peritoneal damage induced by dialysis fluid exposure.
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.
Loureiro
Jesús
J
Unidad de Biología Molecular, Hospital Universitario de la Princesa, Madrid, Spain.
Schilte
Margot
M
Aguilera
Abelardo
A
Albar-Vizcaíno
Patricia
P
Ramírez-Huesca
Marta
M
Pérez-Lozano
M Luisa
ML
González-Mateo
Guadalupe
G
Aroeira
Luiz S
LS
Selgas
Rafael
R
Mendoza
Lorea
L
Ortiz
Alberto
A
Ruíz-Ortega
Marta
M
van den Born
Jacob
J
Beelen
Robert H J
RH
López-Cabrera
Manuel
M
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
D000199:Actins; D055419:Bone Morphogenetic Protein 7; D015820:Cadherins; D051785:Smad Proteins; D053773:Transforming Growth Factor beta1