title: Impaired megakaryocytopoiesis in type 2B von Willebrand disease with severe thrombocytopenia.
abstract: In type 2B von Willebrand disease, there is spontaneous binding of mutated von Willebrand factor (VWF) multimers to platelets. Here we report a family in which severe thrombocytopenia may also be linked to abnormal megakaryocytopoiesis. A heterozygous mutation in the VWF A1 domain gave a R1308P substitution in an interactive site for glycoprotein Ibalpha (GPIbalpha). Electron microscopy showed clusters of platelets in close contact. Binding of antibodies to the GPIbalpha N-terminal domain was decreased, whereas GPIX and GPV were normally detected. In Western blotting (WB), GPIbalpha, alphaIIb, and beta3 were normally present. Proteins involved in Ca(2+) homeostasis were analyzed by quantitating platelet mRNA or by WB. Plasma membrane Ca(2+) ATPase (PMCA)-4b and type III inositol trisphosphate receptor (InsP(3)-R3) were selectively increased. The presence of degradation products of polyadenosine diphosphate (ADP)-ribose polymerase protein (PARP) suggested ongoing caspase-3 activity. These were findings typical of immature normal megakaryocytes cultured from peripheral blood CD34(+) cells with TPO. Significantly, megakaryocytes from the patients in culture produced self-associated and interwoven proplatelets. Immunolocalization showed VWF not only associated with platelets, but already on the megakaryocyte surface and within internal channels. In this family, type 2B VWD is clearly associated with abnormal platelet production.
authors.affiliation: Centre de Référence des Pathologies Plaquettaires and Institut Fédératif de Recherche No. 4, Laboratoire d'Hématologie, Hôpital Cardiologique, 33604 Pessac, France. paquita.nurden@cnrshl.u-bordeaux2.fr
authors.forename: Paquita
authors.initials: P
authors.lastname: Nurden
authors.forename: Najet
authors.initials: N
authors.lastname: Debili
authors.forename: William
authors.initials: W
authors.lastname: Vainchenker
authors.forename: Regis
authors.initials: R
authors.lastname: Bobe
authors.forename: Raymonde
authors.initials: R
authors.lastname: Bredoux
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Corvazier
authors.forename: Robert
authors.initials: R
authors.lastname: Combrie
authors.forename: Edith
authors.initials: E
authors.lastname: Fressinaud
authors.forename: Dominique
authors.initials: D
authors.lastname: Meyer
authors.forename: Alan T
authors.initials: AT
authors.lastname: Nurden
authors.forename: Jocelyne
authors.initials: J
authors.lastname: Enouf
mesh_terms: D001792:Blood Platelets / Q000648:ultrastructure; D020013:Calcium Signaling; D020169:Caspases / Q000097:blood; D005260:Female; D006410:Hematopoiesis; D006801:Humans; D008297:Male; D008533:Megakaryocytes / Q000378:metabolism / Q000473:pathology*; D008854:Microscopy, Electron; D008875:Middle Aged; D009154:Mutation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D013921:Thrombocytopenia / Q000097:blood* / Q000209:etiology / Q000473:pathology; D034061:Thrombopoiesis / Q000235:genetics; D014842:von Willebrand Diseases / Q000097:blood* / Q000145:classification / Q000235:genetics / Q000473:pathology; D014841:von Willebrand Factor / Q000235:genetics
chemical_list: D010980:Platelet Membrane Glycoproteins; D014841:von Willebrand Factor; D020169:Caspases