title: Thrombocytopathy leading to impaired in vivo haemostasis and thrombosis in platelet type von Willebrand disease.
abstract: Platelet defects due to hyper-responsive GPIbα causing enhanced VWF interaction, counter-intuitively result in bleeding rather than thrombosis. The historical explanation of platelet/VWF clearance fails to explain mechanisms of impaired haemostasis particularly in light of reported poor platelet binding to fibrinogen. This study aimed to evaluate the defects of platelets with hyper-responsive GPIbα and their contribution to impaired in vivo thrombosis. Using the PT-VWD mouse model, platelets from the hTgG233Vwere compared to control hTgWTmice. Platelets' pro-coagulant capacity was evaluated using flowcytometry assessment of P-selectin and annexin V. Whole blood platelet aggregation in response to ADP, collagen and thrombin was tested. Clot kinetics using laser injury thrombosis model and the effect of GPIbα inhibition in vivo using 6B4; a monoclonal antibody, were evaluated. Thrombin-induced platelet P-selectin and PS exposure were significantly reduced in hTgG233Vcompared to hTgWTand not significantly different when compared to unstimulated platelets. The hTgG233Vplatelets aggregated normally in response to collagen, and had a delayed response to ADP and thrombin, when compared to hTgWTplatelets. Laser injury showed significant impairment of in vivo thrombus formation in hTgG233Vcompared to hTgWTmice. There was a significant lag in in vitro clot formation in turbidity assay but no impairment in thrombin generation was observed using thromboelastography. The in vivo inhibition of GPIbα facilitated new - unstable - clot formation but did not improve the lag. We conclude platelets with hyper-responsive GPIbα have complex intrinsic defects beyond the previously described mechanisms. Abnormal signalling through GPIbα and potential therapy using inhibitors require further investigations.
authors.forename: Harmanpreet
authors.initials: H
authors.lastname: Kaur
authors.forename: Kathryn
authors.initials: K
authors.lastname: Corscadden
authors.forename: Jerry
authors.initials: J
authors.lastname: Ware
authors.affiliation: Dr. Maha Othman, MD MSc PhD, Associate Professor, Department of Biomedical and Molecular Sciences, School of Medicine, Queen's University, Boterell Hall room 513, Kingston, Ontario K7L 3N6, Canada, Tel.: +1 613 533 6108, Fax: +1 613 533 2022, E-mail: othman@queensu.ca.
authors.forename: Maha
authors.initials: M
authors.lastname: Othman
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001780:Blood Coagulation Tests; D001791:Blood Platelet Disorders / Q000097:blood / Q000150:complications* / Q000175:diagnosis / Q000235:genetics; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D003094:Collagen / Q000494:pharmacology; D004195:Disease Models, Animal; D020022:Genetic Predisposition to Disease; D006487:Hemostasis; D006801:Humans; D007700:Kinetics; D008822:Mice, Transgenic; D009154:Mutation; D010641:Phenotype; D015539:Platelet Activation / Q000187:drug effects; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism; D013927:Thrombosis / Q000097:blood / Q000175:diagnosis / Q000209:etiology*; D014842:von Willebrand Diseases / Q000097:blood / Q000150:complications* / Q000175:diagnosis / Q000235:genetics
chemical_list: D019038:Platelet Glycoprotein GPIb-IX Complex; C094990:adhesion receptor; D000244:Adenosine Diphosphate; D003094:Collagen; D013917:Thrombin
keywords: GPIbα inhibition; hyperresponsive GPIbα; platelet activation; platelet bleeding disorders; thrombin