title: Extracellular pyrophosphate is reduced in aortic interstitial valve cells acquiring a calcifying profile: implications for aortic valve calcification.
abstract: OBJECTIVE
  Pyrophosphate (PPi) is a potent inhibitor of ectopic mineralization but its role during aortic valve calcification is not known.
  
  
  METHODS
  Anti-calcific effect of PPi was investigated by using an in vitro model of serum-driven calcification of collagen sponges and decellularized porcine aortic valve leaflets. Bovine interstitial valve cells (VIC), seeded either within the collagen matrices or in transwell chambers, were used to test cellular ability to inhibit serum-induced calcification. PPi metabolism was investigated in clonal VIC harboring different calcifying potential.
  
  
  RESULTS
  In a cell-free system, high serum levels induced a dose-dependent calcification of type I collagen matrices which was prevented by PPi and ATP supplementation. Blockade of serum-driven calcification by PPi and ATP was also observed when using decellularized porcine aortic valve leaflets. A similar anti-calcific effect was also seen for bovine VIC, either statically seeded into the collagen matrices or co-cultured by using a transwell system. However, when we performed co-culture experiments by using clonal VIC harboring different calcifying potential, we observed that the subset of cells acquiring a pro-calcific profile lost the ability to protect the collagen from serum-driven calcification. Pro-calcific differentiation of the clonal VIC was accompanied by increase in ALP along with significant reduction in NPP activity and ATP/PPi extracellular accumulation. These changes were not observed in the clonal subtype with lower propensity towards calcification.
  
  
  CONCLUSIONS
  We showed that PPi and ATP are potent inhibitors of serum-driven calcification of collagen matrix and that their extracellular accumulation is reduced in calcifying VIC.
authors.affiliation: Department of Medicine, University of Padova, Italy; Medicina Interna Iˆ, Ca' Foncello Hospital, Treviso, Italy. Electronic address: marcello.rattazzi@unipd.it.
authors.forename: Marcello
authors.initials: M
authors.lastname: Rattazzi
authors.affiliation: Department of Medicine, University of Padova, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Bertacco
authors.affiliation: Department of Cardiac, Thoracic and Vascular Sciences, University of Padova, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Iop
authors.affiliation: Department of Medicine, University of Padova, Italy.
authors.forename: Susanna
authors.initials: S
authors.lastname: D'Andrea
authors.affiliation: Department of Medicine, University of Padova, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Puato
authors.affiliation: Department of Medicine, University of Padova, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Buso
authors.affiliation: Department of Chemical Sciences, University of Padova, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Causin
authors.affiliation: Department of Cardiac, Thoracic and Vascular Sciences, University of Padova, Italy.
authors.forename: Gino
authors.initials: G
authors.lastname: Gerosa
authors.affiliation: Department of Medicine, University of Padova, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Faggin
authors.affiliation: Department of Medicine, University of Padova, Italy; Medicina Interna Iˆ, Ca' Foncello Hospital, Treviso, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Pauletto
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000378:metabolism* / Q000473:pathology*; D001021:Aortic Valve / Q000378:metabolism / Q000473:pathology*; D001024:Aortic Valve Stenosis / Q000378:metabolism*; D002114:Calcinosis / Q000378:metabolism*; D002118:Calcium / Q000737:chemistry; D002417:Cattle; D002454:Cell Differentiation; D002474:Cell-Free System; D003001:Cloning, Molecular; D003094:Collagen / Q000737:chemistry; D011756:Diphosphates / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D009711:Nucleotides / Q000737:chemistry; D013552:Swine; D014961:X-Ray Diffraction
chemical_list: D011756:Diphosphates; D009711:Nucleotides; C107241:diphosphoric acid; D000255:Adenosine Triphosphate; D003094:Collagen; D000469:Alkaline Phosphatase; D002118:Calcium
keywords: ATP; Aortic stenosis; Aortic valve calcification; Interstitial valve cells; Pyrophosphate