Page 166 - Haematologica-5

Haematologica 2018 Volume 103(5):898-907
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Institute of Cardiovascular Sciences, IBR Building, College of Medical and Dental
Ferrata Storti Foundation
Hemostasis
Immobilized fibrinogen activates human platelets through glycoprotein VI
Pierre H Mangin,1 Marie-Blanche Onselaer,2 Nicolas Receveur,1 Nicolas Le Lay,3 Alexander T Hardy,2 Clare Wilson,4 Ximena Sanchez,5 Stéphane Loyau,3 Arnaud Dupuis,1 Amir K Babar,6 Jeanette LC Miller,6 Helen Philippou,4 Craig E Hughes,2,8 Andrew B Herr,6 Robert AS Ariëns,4 Diego Mezzano,5 Martine Jandrot-Perrus,3,7 Christian Gachet1 and Steve P. Watson2,9
1Université de Strasbourg, INSERM, EFS Grand-Est, BPPS UMR-S 1255, FMTS, France;
Sciences, University of Birmingham, UK; 3Université de Paris Diderot, INSERM UMR_S1148, Hôpital Bichat, Paris, France ; 4Thrombosis and Tissue Repair Group, Institute of Cardiovascular and Metabolic Medicine, University of Leeds, UK; 5Laboratorio de Hemostasia, Pontificia Universidad Catolica de Chile, Santiago, Chile; 6Division of Immunobiology, Center for Systems Immunology & Division of Infectious Diseases, Cincinnati, OH, USA; 7Acticor Biotech, Hôpital Bichat, INSERM, UMR-S 1148, Paris, France; 8Institute for Cardiovascular and Metabolic Research, Harborne Building, University of Reading, UK and 9Centre of Membrane Proteins and Receptors (COMPARE), Universities of Birmingham and Nottingham, Midlands, UK
ABSTRACT
Glycoprotein VI, a major platelet activation receptor for collagen and fibrin, is considered a particularly promising, safe antithrom- botic target. In this study, we show that human glycoprotein VI signals upon platelet adhesion to fibrinogen. Full spreading of human platelets on fibrinogen was abolished in platelets from glycoprotein VI- deficient patients suggesting that fibrinogen activates platelets through glycoprotein VI. While mouse platelets failed to spread on fibrinogen, human-glycoprotein VI-transgenic mouse platelets showed full spreading and increased Ca2+ signaling through the tyrosine kinase Syk. Direct bind- ing of fibrinogen to human glycoprotein VI was shown by surface plas- mon resonance and by increased adhesion to fibrinogen of human glyco- protein VI-transfected RBL-2H3 cells relative to mock-transfected cells. Blockade of human glycoprotein VI with the Fab of the monoclonal anti- body 9O12 impaired platelet aggregation on preformed platelet aggre- gates in flowing blood independent of collagen and fibrin exposure. These results demonstrate that human glycoprotein VI binds to immobi- lized fibrinogen and show that this contributes to platelet spreading and platelet aggregation under flow.
Introduction
The immunoglobulin receptor glycoprotein (GP) VI is expressed on megakary- ocytes and platelets. GPVI associates with the Fc receptor (FcR) γ-chain in the membrane, and with the Src family kinases (SFK) Lyn and Fyn through its cytosolic tail.1 Ligand binding clusters GPVI at the platelet surface promoting phosphoryla- tion of the immunoreceptor tyrosine-based motif (ITAM) of the FcR γ-chain by SFK.2–4 This results in the recruitment of Syk and formation of a LAT-based signalo- some that activates PLCγ2 leading to an increase in Ca2+, activation of integrin and secretion of granules.5
GPVI is widely known as a platelet activation receptor for fibrillar collagen.5 However, in recent years, GPVI has been shown to bind to additional ligands, including subendothelial and plasma adhesive proteins such as laminins and fib- rin,6–8 the hormone adiponectin and the transmembrane protein emmprin.9,10 Several of these interactions are relatively weak and of unclear significance. For example, GPVI supports adhesion and efficient activation of platelets to collagen
Correspondence:
pierre.mangin@efs.sante.fr or s.p.watson@bham.ac.uk
Received: October 20, 2017. Accepted: February 13, 2018. Pre-published: February 22, 2018.
doi:10.3324/haematol.2017.182972
Check the online version for the most updated information on this article, online supplements, and information on authorship & disclosures: www.haematologica.org/content/103/5/898
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