title: von Willebrand factor arginine 1205 substitution results in accelerated macrophage-dependent clearance in vivo.
abstract: BACKGROUND
  Enhanced von Willebrand factor (VWF) clearance is important in the etiology of type 1 and type 2 von Willebrand disease (VWD). More than 20 different VWF point mutations have already been reported in patients with enhanced clearance. These include the VWD-Vicenza variant, which is characterized by an Arg1205His substitution in the VWF D3 domain. Critically, however, the molecular mechanisms through which single amino acid substitutions in VWF result in enhanced clearance of this complex multimeric glycoprotein have not been defined.
  
  
  OBJECTIVE
  In this study, we have investigated the biological basis underlying the enhanced clearance of the VWF-R1205H variant.
  
  
  METHODS
  Using VWF(-/-) mice, in vivo clearance rates were determined for a series of full-length and truncated recombinant VWF variants. In addition, the role of macrophages in modulating enhanced VWD-Vicenza clearance was investigated using clodronate liposome administration.
  
  
  RESULTS
  Our findings demonstrate that substitutions of R1205 with histidine, cysteine or serine all result in markedly reduced survival of full-length recombinant VWF. Importantly, D'A3 fragments containing these same R1205 substitutions also demonstrated significantly enhanced clearance. In contrast to the reduced in vivo survival observed with R1205H, clearance of R1204H was not enhanced. Recent studies have demonstrated that hepatic and splenic macrophages play key roles in regulating VWF clearance. Importantly, macrophage-depletion also served to markedly attenuate the enhanced clearance phenotypes associated with VWF-R1205H, VWF-R1205S and VWF-R1205C.
  
  
  CONCLUSIONS
  Collectively, these novel findings demonstrate a specific and critical role for the R1205 residue in modulating macrophage-mediated clearance of VWF in vivo.
authors.affiliation: Haemostasis Research Group, Institute of Molecular Medicine, Trinity Centre for Health Sciences, St James's Hospital, Trinity College Dublin, Dublin, Ireland.
authors.forename: O
authors.initials: O
authors.lastname: Rawley
authors.forename: J M
authors.initials: JM
authors.lastname: O'Sullivan
authors.forename: A
authors.initials: A
authors.lastname: Chion
authors.forename: S
authors.initials: S
authors.lastname: Keyes
authors.forename: M
authors.initials: M
authors.lastname: Lavin
authors.forename: N
authors.initials: N
authors.lastname: van Rooijen
authors.forename: T M
authors.initials: TM
authors.lastname: Brophy
authors.forename: P
authors.initials: P
authors.lastname: Fallon
authors.forename: R J S
authors.initials: RJ
authors.lastname: Preston
authors.forename: J S
authors.initials: JS
authors.lastname: O'Donnell
mesh_terms: D000818:Animals; D001120:Arginine / Q000737:chemistry*; D008264:Macrophages / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D014841:von Willebrand Factor / Q000737:chemistry / Q000502:physiology*
chemical_list: D014841:von Willebrand Factor; D001120:Arginine
keywords: glycosylation; metabolic clearance rate; von Willebrand disease, Type 1; von Willebrand disease, Type 2; von Willebrand factor