title: Targeting platelet GPIbβ reduces platelet adhesion, GPIb signaling and thrombin generation and prevents arterial thrombosis.
abstract: OBJECTIVE
  The glycoprotein (GP) Ib-V-IX complex regulates the adhesion, activation, and procoagulant activity of platelets. We previously reported that RAM.1, a rat monoclonal antibody directed against the extracellular domain of mouse GPIbβ, diminished adhesion of platelets and chinese hamster ovary cells transfected with the human GPIb-IX complex to von Willebrand factor under flow conditions. Here, we further evaluated the functional importance of GPIbβ by studying the impact of RAM.1 on GPIb-mediated platelet responses and in vitro and in vivo thrombus formation.
  
  
  RESULTS
  We show that RAM.1 dramatically reduced GPIb-mediated filopodia extension of chinese hamster ovary GPIb-IX cells after adhesion to von Willebrand factor. RAM.1 also reduced filopodia extension and GPIb-mediated Ca(2+) signaling after adhesion of mouse platelets to von Willebrand factor. RAM.1 inhibited thrombin generation in platelet-rich plasma without impairing phosphatidylserine exposure. In addition, RAM.1 reduced thrombus formation after perfusion of mouse whole blood over collagen in a shear-dependent manner. This effect was confirmed in vivo, because injection of F(ab)'2 fragments of RAM.1 diminished thrombus formation induced by laser beam injury of mesenteric arterioles and forceps injury of the abdominal aorta. In contrast, RAM.1 F(ab)'2 did not prolong the tail-bleeding time or increase the volume of blood lost.
  
  
  CONCLUSIONS
  These findings are the first evidence that targeting a subunit other than GPIbα can lead to an antithrombotic effect via the GPIb-V-IX complex. This could represent an alternative way to reduce thrombus formation with a minor impact on hemostasis.
authors.affiliation: Inserm UMR-S949, Université Université de Strasbourg, Etablissement Français du Sang-Alsace (EFS-Alsace), Strasbourg, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Maurer
authors.forename: Chaojun
authors.initials: C
authors.lastname: Tang
authors.forename: Mathieu
authors.initials: M
authors.lastname: Schaff
authors.forename: Catherine
authors.initials: C
authors.lastname: Bourdon
authors.forename: Nicolas
authors.initials: N
authors.lastname: Receveur
authors.forename: Catherine
authors.initials: C
authors.lastname: Ravanat
authors.forename: Anita
authors.initials: A
authors.lastname: Eckly
authors.forename: Béatrice
authors.initials: B
authors.lastname: Hechler
authors.forename: Christian
authors.initials: C
authors.lastname: Gachet
authors.forename: Francois
authors.initials: F
authors.lastname: Lanza
authors.forename: Pierre H
authors.initials: PH
authors.lastname: Mangin
mesh_terms: D000818:Animals; D001157:Arterial Occlusive Diseases / Q000503:physiopathology / Q000517:prevention & control*; D001760:Bleeding Time; D002448:Cell Adhesion / Q000502:physiology; D006224:Cricetinae; D004195:Disease Models, Animal; D006801:Humans; D051379:Mice; D010973:Platelet Adhesiveness / Q000235:genetics / Q000502:physiology*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics / Q000378:metabolism*; D011897:Random Allocation; D051381:Rats; D012680:Sensitivity and Specificity; D015398:Signal Transduction; D050611:Sodium-Phosphate Cotransporter Proteins, Type III / Q000235:genetics / Q000378:metabolism*; D013927:Thrombosis / Q000503:physiopathology / Q000517:prevention & control*; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D019038:Platelet Glycoprotein GPIb-IX Complex; C493566:Slc20a2 protein, rat; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D014841:von Willebrand Factor
keywords: hemostasis; platelets; thrombosis; von Willebrand factor