Page 134 - Haematologica Vol. 107 - September 2022

ARTICLE - Hemostasis
The impact of aberrant von Willebrand factor-GPIba interaction on megakaryopoiesis and platelets in humanized type 2B von Willebrand disease model mouse
Sachiko Kanaji,1,2 Yosuke Morodomi,1 Hartmut Weiler,2 Alessandro Zarpellon,1,3 Robert R. Montgomery,2,4,5 Zaverio M. Ruggeri1,3 and Taisuke Kanaji1,2
1Department of Molecular Medicine, MERU-Roon Research Center on Vascular Biology, The Scripps Research Institute, La Jolla, CA; 2Blood Research Institute, Blood Center of Wisconsin, Versiti, Milwaukee, WI; 3MERU-VasImmune, Inc., San Diego, CA; 4Children's Research Institute, Children's Hospital of Wisconsin, Milwaukee, WI and 5Department of Pediatrics, Medical College of Wisconsin, Milwaukee, WI, USA
Abstract
Type 2B von Willebrand disease (VWD) is caused by gain-of-function mutations in von Willebrand factor (VWF). Increased VWF affinity for GPIba results in loss of high molecular weight multimers and enhanced platelet clearance, both contributing to the bleeding phenotype. Severity of the symptoms vary among type 2B VWD patients, with some developing thrombocytopenia only under stress conditions. Efforts have been made to study underlying pathophysiology for platelet abnormalities, but animal studies have been limited because of species specificity in the VWF-GPIba interaction. Here, we generated a severe form of type 2B VWD (p.V1316M) knockin mice in the context of human VWF exon 28 (encoding A1 and A2 domains) and crossed them with human GPIba transgenic strain. Heterozygous mutant mice recapitulated the phenotype of type 2B VWD in autosomal dominant manner and presented severe macrothrombocy- topenia. Of note, platelets remaining in the circulation had extracytoplasmic GPIba shed-off from the cell surface. Reciprocal bone marrow transplantation determined mutant VWF produced from endothelial cells as the major cause of the platelet phenotype in type 2B VWD mice. Moreover, altered megakaryocyte maturation in the bone marrow and enhanced extramedullary megakaryopoiesis in the spleen were observed. Interestingly, injection of anti-VWF A1 blocking antibody (NMC-4) not only ameliorated platelet count and GPIba expression, but also reversed MK ploidy shift. In conclusion, we present a type 2B VWD mouse model with humanized VWF-GPIba interaction which demonstrated direct influence of aberrant VWF-GPIba binding on megakaryocytes.
Correspondence: S. Kanaji skana@scripps.edu
Received: Accepted: Prepublished:
December 22, 2021. February 2, 2022. February 10, 2022.
https://doi.org/10.3324/haematol.2021.280561
©2022 Ferrata Storti Foundation Published under a CC BY-NC license
Introduction
Von Willebrand disease (VWD) is a common inherited bleeding disorder caused by defects in the function or synthesis of von Willebrand factor (VWF).1 VWD is classi- fied into three primary categories: type 1, type 2, and type 3. Among them, type 2B VWD represents variants with in- creased affinity for platelet GPIba, which is paradoxically associated with bleeding symptoms, not thrombosis.2,3 It has been known that enhanced binding of gain-of-func- tion mutant VWF to platelets and accelerated clearance, in combination with higher susceptibility to ADAMTS13, re- sult in loss of the largest VWF multimers and thrombo- cytopenia.2-4 Of note, clinical manifestations and results of laboratory tests are heterogeneous among type 2B VWD
patients, depending on the mutations involved.5 In addi- tion, one unsolved issue in the pathophysiology of type 2B VWD is the regulatory mechanism of aberrant VWF A1- GPIba on megakaryocytes (MK) and thrombopoiesis. In addition to accelerated platelet clearance, impaired megakaryopoiesis have also been implicated as the cause of thrombocytopenia.6,7
To date, limited research of VWD using mouse models have been reported due to species-incompatibility of VWF A1-GPIba interaction. Previous efforts have been made to overcome species-specificity in VWF A1-GPIba interaction.8 However, later study found that single amino acid substitutions may not be sufficient to fully convert the species-specific binding property,9 suggesting that re- placement of the entire VWF A1 is desired to mimic human
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