title: Abnormal VWF modifies megakaryocytopoiesis: studies of platelets and megakaryocyte cultures from patients with von Willebrand disease type 2B.
abstract: von Willebrand factor (VWF) is an essential mediator of platelet adhesion to the vessel wall, but little is known about its role in megakaryocytopoiesis. VWF and its platelet receptor, glycoprotein Ibalpha (GPIbalpha), are both expressed during megakaryocyte (MK) maturation. This study was designed to evaluate whether the enhanced VWF-GPIbalpha interactions typical of patients with von Willebrand disease type 2B (VWD2B) modify platelet production. Platelets from 9 patients with VWD2B with 7 different gain-of-function mutations were examined by electron microscopy (EM) and immunofluorescence labeling. For the patients with VWD2B, EM characteristically showed variable numbers of structurally abnormal giant platelets, sometimes in agglutinates. Cultures of MKs from controls performed with or without purified VWF confirmed a positive influence of VWF on platelet production with specific inhibition by an antibody blocking VWF binding to GPIbalpha. VWD2B MK cultures examined by EM showed a disorganized demarcation membrane system and abnormal granule distribution. They produced platelets with structural abnormalities typical of VWD2B. Confocal examination of MK revealed limited extension of pseudopods with few large proplatelets. These results confirm that megakaryocytopoiesis is modified by the enhanced VWF-GPIbalpha interactions. These data obtained for controls and patients with VWD2B suggest a novel regulatory role of VWF-GPIbalpha interactions in platelet production.
authors.affiliation: Centre de Référence des Pathologies Plaquettaires, Plateforme Technologique et d'Innovation Biomédicale, Hôpital Xavier Arnozan, Pessac, France.
authors.forename: Paquita
authors.initials: P
authors.lastname: Nurden
authors.forename: Giuliana
authors.initials: G
authors.lastname: Gobbi
authors.forename: Alan
authors.initials: A
authors.lastname: Nurden
authors.forename: Jocelyne
authors.initials: J
authors.lastname: Enouf
authors.forename: Ibtissam
authors.initials: I
authors.lastname: Youlyouz-Marfak
authors.forename: Cecilia
authors.initials: C
authors.lastname: Carubbi
authors.forename: Silvia
authors.initials: S
authors.lastname: La Marca
authors.forename: Margherita
authors.initials: M
authors.lastname: Punzo
authors.forename: Luciano
authors.initials: L
authors.lastname: Baronciani
authors.forename: Luigi
authors.initials: L
authors.lastname: De Marco
authors.forename: Marco
authors.initials: M
authors.lastname: Vitale
authors.forename: Augusto B
authors.initials: AB
authors.lastname: Federici
mesh_terms: D019943:Amino Acid Substitution; D001792:Blood Platelets / Q000473:pathology* / Q000648:ultrastructure; D002462:Cell Membrane / Q000648:ultrastructure; D048429:Cell Size; D002478:Cells, Cultured / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D006801:Humans; D008533:Megakaryocytes / Q000187:drug effects / Q000473:pathology*; D008562:Membrane Glycoproteins / Q000502:physiology*; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D020125:Mutation, Missense; D019038:Platelet Glycoprotein GPIb-IX Complex; D017354:Point Mutation; D025941:Protein Interaction Mapping; D034061:Thrombopoiesis / Q000187:drug effects / Q000502:physiology*; D013926:Thrombopoietin / Q000494:pharmacology; D056728:von Willebrand Disease, Type 2 / Q000097:blood* / Q000235:genetics; D014841:von Willebrand Factor / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*
chemical_list: D008562:Membrane Glycoproteins; D019038:Platelet Glycoprotein GPIb-IX Complex; C094990:adhesion receptor; D014841:von Willebrand Factor; D013926:Thrombopoietin