title: Insights into the association of Gla-rich protein and osteoarthritis, novel splice variants and γ-carboxylation status.
abstract: METHODS
  Gla-rich protein (GRP) is a vitamin K dependent protein, characterized by a high density of γ-carboxylated Glu residues, shown to accumulate in mouse and sturgeon cartilage and at sites of skin and vascular calcification in humans. Therefore, we investigated the involvement of GRP in pathological calcification in osteoarthritis (OA).
  
  
  RESULTS
  Comparative analysis of GRP patterning at transcriptional and translational levels was performed between controls and OA patients. Using a RT-PCR strategy we unveiled two novel splice variants in human-GRP-F5 and F6-potentially characterized by the loss of full γ-carboxylation and secretion functional motifs. GRP-F1 is shown to be the predominant splice variant expressed in mouse and human adult tissues, particularly in OA cartilage, while an overexpressing human cell model points it as the major γ-carboxylated isoform. Using validated conformational antibodies detecting carboxylated or undercarboxylated GRP (c/uc GRP), we have demonstrated cGRP accumulation in controls, whereas ucGRP was the predominant form in OA-affected tissues, colocalizing at sites of ectopic calcification.
  
  
  CONCLUSIONS
  Overall, our results indicate the predominance of GRP-F1, and a clear association of ucGRP with OA cartilage and synovial membrane. Levels of vitamin K should be further assessed in these patients to determine its potential therapeutic use as a supplement in OA treatment.
authors.affiliation: Centre of Marine Sciences (CCMAR), University of Algarve, Faro, Portugal.
authors.forename: Marta S
authors.initials: MS
authors.lastname: Rafael
authors.forename: Sofia
authors.initials: S
authors.lastname: Cavaco
authors.forename: Carla S B
authors.initials: CS
authors.lastname: Viegas
authors.forename: Sofia
authors.initials: S
authors.lastname: Santos
authors.forename: Acácio
authors.initials: A
authors.lastname: Ramos
authors.forename: Brecht A G
authors.initials: BA
authors.lastname: Willems
authors.forename: Marjolein
authors.initials: M
authors.lastname: Herfs
authors.forename: Elke
authors.initials: E
authors.lastname: Theuwissen
authors.forename: Cees
authors.initials: C
authors.lastname: Vermeer
authors.forename: Dina C
authors.initials: DC
authors.lastname: Simes
mesh_terms: D000368:Aged; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002114:Calcinosis / Q000209:etiology*; D002356:Cartilage / Q000196:embryology / Q000378:metabolism*; D016326:Extracellular Matrix Proteins; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D013045:Species Specificity
chemical_list: D016326:Extracellular Matrix Proteins; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D011994:Recombinant Proteins; C528959:Ucma protein, human; C528958:Ucma protein, mouse; D018698:Glutamic Acid
keywords: Alternative splicing; Gla-rich protein; Osteoarthritis; Vitamin K; γ-Carboxylation