title: von Willebrand factor mutation promotes thrombocytopathy by inhibiting integrin αIIbβ3.
abstract: von Willebrand disease type 2B (vWD-type 2B) is characterized by gain-of-function mutations in von Willebrand factor (vWF) that enhance its binding to the glycoprotein Ib-IX-V complex on platelets. Patients with vWD-type 2B have a bleeding tendency that is linked to loss of vWF multimers and/or thrombocytopenia. In this study, we uncovered evidence that platelet dysfunction is a third possible mechanism for bleeding tendency. We found that platelet aggregation, secretion, and spreading were diminished due to inhibition of integrin αIIbβ3 in platelets from mice expressing a vWD-type 2B-associated vWF (vWF/p.V1316M), platelets from a patient with the same mutation, and control platelets pretreated with recombinant vWF/p.V1316M. Impaired platelet function coincided with reduced thrombus growth. Further, αIIbβ3 activation and activation of the small GTPase Rap1 were impaired by vWF/p.V1316M following exposure to platelet agonists (thrombin, ADP, or convulxin). Conversely, thrombin- or ADP-induced Ca2+ store release, which is required for αIIbβ3 activation, was normal, indicating that vWF/p.V1316M acts downstream of Ca2+ release and upstream of Rap1. We found normal Syk phosphorylation and PLCγ2 activation following collagen receptor signaling, further implying that vWF/p.V1316M acts directly on or downstream of Ca2+ release. These data indicate that the vWD-type 2B mutation p.V1316M is associated with severe thrombocytopathy, which likely contributes to the bleeding tendency in vWD-type 2B.
authors.forename: Caterina
authors.initials: C
authors.lastname: Casari
authors.forename: Eliane
authors.initials: E
authors.lastname: Berrou
authors.forename: Marilyne
authors.initials: M
authors.lastname: Lebret
authors.forename: Frédéric
authors.initials: F
authors.lastname: Adam
authors.forename: Alexandre
authors.initials: A
authors.lastname: Kauskot
authors.forename: Régis
authors.initials: R
authors.lastname: Bobe
authors.forename: Céline
authors.initials: C
authors.lastname: Desconclois
authors.forename: Edith
authors.initials: E
authors.lastname: Fressinaud
authors.forename: Olivier D
authors.initials: OD
authors.lastname: Christophe
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lenting
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Rosa
authors.forename: Cécile V
authors.initials: CV
authors.lastname: Denis
authors.forename: Marijke
authors.initials: M
authors.lastname: Bryckaert
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D006474:Hemorrhagic Disorders / Q000209:etiology* / Q000503:physiopathology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D020125:Mutation, Missense; D051966:Phospholipase C gamma / Q000502:physiology; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000235:genetics*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors* / Q000502:physiology; D017354:Point Mutation; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D038981:Receptors, Collagen / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D000072377:Syk Kinase; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism; D056728:von Willebrand Disease, Type 2 / Q000097:blood / Q000235:genetics*; D014841:von Willebrand Factor / Q000235:genetics* / Q000502:physiology
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D038981:Receptors, Collagen; D011993:Recombinant Fusion Proteins; D014841:von Willebrand Factor; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D051966:Phospholipase C gamma; D020827:rap1 GTP-Binding Proteins