Key result
Gain-of-function GP1BA variants in platelet-type von Willebrand disease cause constitutive binding of VWF to GPIbα, triggering a Lyn-PECAM1 inhibitory pathway that leads to platelet dysfunction.
Why the study?
While platelet dysfunction may contribute to the bleeding phenotype in platelet-type von Willebrand disease, information on its characteristics and causes was lacking.
Identifies Lyn-PECAM1 pathway in Pt-VWD platelet dysfunction; leaves open targeted therapies and broader GPIbα research.
Platelet-type von Willebrand disease (PT-VWD) is an inherited platelet disorder. It is characterized by macrothrombocytopenia and mucocutaneous bleeding, of variable severity, due to gain-of-function variants of GP1BA conferring to glycoprotein Ibα (GPIbα) enhanced affinity for von Willebrand factor (VWF). The bleeding tendency is conventionally attributed to thrombocytopenia and large VWF-multimer depletion. However, while some indications suggest that platelet dysfunction may contribute to the bleeding phenotype, no information on its characteristics and causes are available. The aim of the present study was to characterize platelet dysfunction in PT-VWD and shed light on its mechanism. Platelets from a PT-VWD patient carrying the p.M239V variant, and from PT-VWD mice carrying the p.G233V variant, showed a remarkable platelet function defect, with impaired aggregation, defective granule secretion and reduced adhesion under static and flow conditions. VWFbinding to GPIbα is known to trigger intracellular signaling involving Src-family kinases (SFK). We found that constitutive phosphorylation of the platelet SFK Lyn induces a negative-feedback loop downregulating platelet activation through phosphorylation of PECAM1 on Tyr686 and that this is triggered by the constitutive binding of VWF to GPIbα. These data show, for the first time, that the abnormal triggering of inhibitory signals mediated by Lyn and PECAM1 may lead to platelet dysfunction. In conclusion, our study unravels the mechanism of platelet dysfunction in PT-VWD caused by deranged inhibitory signaling. This is triggered by the constitutive binding of VWF to GPIbα which may significantly contribute to the bleeding phenotype of these patients.
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Bury et al. (2021) studied Platelet-type von Willebrand disease (n=1). Gain-of-function GP1BA variants vs. Wild-type GP1BA was evaluated on Platelet aggregation, granule secretion, and Lyn/PECAM1 phosphorylation. Gain-of-function GP1BA variants in platelet-type von Willebrand disease cause constitutive binding of VWF to GPIbα, triggering a Lyn-PECAM1 inhibitory pathway that leads to platelet dysfunction.
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