title: Expression of gremlin, a bone morphogenetic protein antagonist,is associated with vascular calcification in uraemia.
abstract: BACKGROUND
  Vascular calcification has been widely recognized as a significant contributor to cardiovascular risk in patients with chronic kidney disease. Recent evidence suggests that BMP-7 decreases the vascular calcification observed in uraemic rats, while BMP-2 could also be participating in this process. Gremlin, a bone morphogenetic protein antagonist, has been detected in rat aortic vascular smooth muscle cells (VSMCs), and since the role of the VSMCs into vascular calcification in uraemia is considered critical in this process, we hypothesized that gremlin could be participating in its pathogenesis. With this aim, we studied its expression in aorta from uraemic rats with calcitriol-induced vascular calcification and in 16-vessel biopsies of uraemic patients undergoing kidney transplantation.
  
  
  METHODS
  Gremlin was detected by in situ hybridization (ISH) and immunohistochemistry (IMH). BMP-7, BMP-2 and BMP-2 receptor (BMPR2) were detected by IMH. Vascular calcification was assessed by the von Kossa staining method. Sham-operated and 5/6 nephrectomized rats (NFX) (1.2%P) were treated with vehicle or calcitriol (80 ng/kg, intraperitoneally every other day). Rats were killed after 4 weeks of treatment, and abdominal aorta was dissected for assessment of gremlin expression and vascular calcification. Epigastric arteries were obtained from dialysis patients during kidney transplantation procedure. Arteries from kidney donors were also studied.
  
  
  RESULTS
  NFX rats developed a mild vascular calcification, whereas NFX-calcitriol rats developed a severe vascular and tissue calcification. A marked overexpression of gremlin was observed in the vascular media of aorta from NFX-calcitriol rats as compared with NFX and sham-calcitriol groups (4.8 +/- 1.3 versus 0.59 +/- 0.17 versus 0.19 +/- 0.07 percentage/mm(2), P < 0.01), and correlated with the BMP-2 and BMPR2 expression. Sham rats showed minimal or null gremlin expression. BMP-7 was not found in sham or calcified arteries. In human studies, we observed strong expression of gremlin mRNA and protein in the media layer of vessels from uraemic patients as compared with those from normal humans (staining score 3.72 +/- 0.95 versus 0.91 +/- 0.08 percentage/mm(2), P < 0.05).
  
  
  CONCLUSIONS
  We observed a marked gremlin overexpression in the media layer of vessels in uraemic rats and patients in association with vascular calcification and BMP-2 expression. We postulate that gremlin may play a role in the vascular calcification process in uraemia, and its interaction with BMP-7 or BMP-2 remains to be elucidated.
authors.affiliation: Department of Nephrology, School of Medicine, Universidad Católica de Chile, Lira 85, Santiago, Chile. ajara@med.puc.cl
authors.forename: Aquiles
authors.initials: A
authors.lastname: Jara
authors.forename: Cecilia
authors.initials: C
authors.lastname: Chacón
authors.forename: María Eugenia
authors.initials: ME
authors.lastname: Burgos
authors.forename: Alejandra
authors.initials: A
authors.lastname: Droguett
authors.forename: Andrés
authors.initials: A
authors.lastname: Valdivieso
authors.forename: Mireya
authors.initials: M
authors.lastname: Ortiz
authors.forename: Pablo
authors.initials: P
authors.lastname: Troncoso
authors.forename: Sergio
authors.initials: S
authors.lastname: Mezzano
mesh_terms: D000818:Animals; D001018:Aortic Diseases / Q000473:pathology / Q000503:physiopathology*; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors*; D002114:Calcinosis / Q000503:physiopathology*; D004195:Disease Models, Animal; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis*; D016030:Kidney Transplantation; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D014511:Uremia / Q000150:complications* / Q000601:surgery
chemical_list: D019485:Bone Morphogenetic Proteins; C486399:GREM1 protein, human; D036341:Intercellular Signaling Peptides and Proteins