title: Cytoskeletal perturbation leads to platelet dysfunction and thrombocytopenia in variant forms of Glanzmann thrombasthenia.
abstract: Several patients have been reported to have variant dominant forms of Glanzmann thrombasthenia, associated with macrothrombocytopenia and caused by gain-of-function mutations of ITGB3 or ITGA2B leading to reduced surface expression and constitutive activation of integrin αIIbβ3. The mechanisms leading to a bleeding phenotype of these patients have never been addressed. The aim of this study was to unravel the mechanism by which ITGB3 mutations causing activation of αIIbβ3 lead to platelet dysfunction and macrothrombocytopenia. Using platelets from two patients carrying the β3 del647-686 mutation and Chinese hamster ovary cells expressing different αIIbβ3-activating mutations, we showed that reduced surface expression of αIIbβ3 is due to receptor internalization. Moreover, we demonstrated that permanent triggering of αIIbβ3-mediated outside-in signaling causes an impairment of cytoskeletal reorganization arresting actin turnover at the stage of polymerization. The induction of actin polymerization by jasplakinolide, a natural toxin that promotes actin nucleation and prevents depolymerization of stress fibers, in control platelets produced an impairment of platelet function similar to that of patients with variant forms of dominant Glanzmann thrombasthenia. del647-686β3-transduced murine megakaryocytes generated proplatelets with a reduced number of large tips and asymmetric barbell-proplatelets, suggesting that impaired cytoskeletal rearrangement is the cause of macrothrombocytopenia. These data show that impaired cytoskeletal remodeling caused by a constitutively activated αIIbβ3 is the main effector of platelet dysfunction and macrothrombocytopenia, and thus of bleeding, in variant forms of dominant Glanzmann thrombasthenia.
authors.affiliation: Department of Medicine, Section of Internal and Cardiovascular Medicine, University of Perugia, Italy.
authors.forename: Loredana
authors.initials: L
authors.lastname: Bury
authors.affiliation: Department of Medicine, Section of Internal and Cardiovascular Medicine, University of Perugia, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Falcinelli
authors.affiliation: Department of Medicine, Section of Neurology, University of Perugia, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Chiasserini
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School and Program in Cellular and Molecular Medicine, Children's Hospital, Boston, MA, USA.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
authors.affiliation: Hematology Division, Department of Medicine, Brigham and Women's Hospital, Vascular Biology Program, Boston Children's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Italiano
authors.affiliation: Department of Medicine, Section of Internal and Cardiovascular Medicine, University of Perugia, Italy paolo.gresele@unipg.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Gresele
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism* / Q000473:pathology; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D039421:Integrin alpha2 / Q000235:genetics / Q000378:metabolism; D039661:Integrin beta3 / Q000235:genetics / Q000378:metabolism; D008297:Male; D009154:Mutation; D013915:Thrombasthenia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D013921:Thrombocytopenia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
chemical_list: C056564:ITGA2B protein, human; C061248:ITGB3 protein, human; D039421:Integrin alpha2; D039661:Integrin beta3