Gla-Rich Protein Acts as a Calcification Inhibitor in the Human Cardiovascular System

Carla S. B. Viegas, Marta S. Rafael, Jose L. Enriquez, Alexandra Teixeira, Rui Vitorino, Ines M. Luis, Ruben M. Costa, Sofia Santos, Sofia Cavaco, José Neves, Maria dos Anjos López de Macedo, Brecht A. G. Willems, Cees Vermeer, Dina C. Simes

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Abstract

Objective-Vascular and valvular calcifications are pathological processes regulated by resident cells, and depending on a complex interplay between calcification promoters and inhibitors, resembling skeletal metabolism. Here, we study the role of the vitamin K-dependent Gla-rich protein (GRP) in vascular and valvular calcification processes.

Approach and Results-Immunohistochemistry and quantitative polymerase chain reaction showed that GRP expression and accumulation are upregulated with calcification simultaneously with osteocalcin and matrix Gla protein (MGP). Using conformation-specific antibodies, both gamma-carboxylated GRP and undercarboxylated GRP species were found accumulated at the sites of mineral deposits, whereas undercarboxylated GRP was predominant in calcified aortic valve disease valvular interstitial cells. Mineral-bound GRP, MGP, and fetuin-A were identified by mass spectrometry. Using an ex vivo model of vascular calcification, gamma-carboxylated GRP but not undercarboxylated GRP was shown to inhibit calcification and osteochondrogenic differentiation through alpha-smooth muscle actin upregulation and osteopontin downregulation. Immunoprecipitation assays showed that GRP is part of an MGP-fetuin-A complex at the sites of valvular calcification. Moreover, extracellular vesicles released from normal vascular smooth muscle cells are loaded with GRP, MGP, and fetuin-A, whereas under calcifying conditions, released extracellular vesicles show increased calcium loading and GRP and MGP depletion.

Conclusions-GRP is an inhibitor of vascular and valvular calcification involved in calcium homeostasis. Its function might be associated with prevention of calcium-induced signaling pathways and direct mineral binding to inhibit crystal formation/maturation. Our data show that GRP is a new player in mineralization competence of extracellular vesicles possibly associated with the fetuin-A-MGP calcification inhibitory system. GRP activity was found to be dependent on its gamma-carboxylation status, with potential clinical relevance.

Original languageEnglish
Pages (from-to)399-408
Number of pages10
JournalArteriosclerosis, thrombosis, and vascular biology
Volume35
Issue number2
DOIs
Publication statusPublished - Feb 2015

Keywords

  • aortic valve, calcification of
  • gene expression
  • multivesicular bodies
  • vascular calcification
  • MUSCLE-CELL CALCIFICATION
  • VASCULAR CALCIFICATION
  • AORTIC-STENOSIS
  • MATRIX VESICLES
  • VITAMIN-K
  • ATHEROSCLEROTIC PLAQUES
  • GAMMA-CARBOXYLATION
  • FETUIN-A
  • DISEASE
  • CARTILAGE

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