LIM kinase/cofilin dysregulation promotes macrothrombocytopenia in severe von Willebrand disease-type 2B
Alexandre Kauskot, … , Cécile V. Denis, Dominique Baruch
Alexandre Kauskot, … , Cécile V. Denis, Dominique Baruch
Published October 6, 2016
Citation Information: JCI Insight. 2016;1(16):e88643. https://doi.org/10.1172/jci.insight.88643.
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Research Article Hematology

LIM kinase/cofilin dysregulation promotes macrothrombocytopenia in severe von Willebrand disease-type 2B

Abstract

von Willebrand disease type 2B (VWD-type 2B) is characterized by gain-of-function mutations of von Willebrand factor (vWF) that enhance its binding to platelet glycoprotein Ibα and alter the protein’s multimeric structure. Patients with VWD-type 2B display variable extents of bleeding associated with macrothrombocytopenia and sometimes with thrombopathy. Here, we addressed the molecular mechanism underlying the severe macrothrombocytopenia both in a knockin murine model for VWD-type 2B by introducing the p.V1316M mutation in the murine Vwf gene and in a patient bearing this mutation. We provide evidence of a profound defect in megakaryocyte (MK) function since: (a) the extent of proplatelet formation was drastically decreased in 2B MKs, with thick proplatelet extensions and large swellings; and (b) 2B MKs presented actin disorganization that was controlled by upregulation of the RhoA/LIM kinase (LIMK)/cofilin pathway. In vitro and in vivo inhibition of the LIMK/cofilin signaling pathway rescued actin turnover and restored normal proplatelet formation, platelet count, and platelet size. These data indicate, to our knowledge for the first time, that the severe macrothrombocytopenia in VWD-type 2B p.V1316M is due to an MK dysfunction that originates from a constitutive activation of the RhoA/LIMK/cofilin pathway and actin disorganization. This suggests a potentially new function of vWF during platelet formation that involves regulation of actin dynamics.

Authors

Alexandre Kauskot, Sonia Poirault-Chassac, Frédéric Adam, Vincent Muczynski, Gabriel Aymé, Caterina Casari, Jean-Claude Bordet, Christelle Soukaseum, Chantal Rothschild, Valérie Proulle, Audrey Pietrzyk-Nivau, Eliane Berrou, Olivier D. Christophe, Jean-Philippe Rosa, Peter J. Lenting, Marijke Bryckaert, Cécile V. Denis, Dominique Baruch

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Figure 10

Scheme of the regulation of actin turnover by LIM kinase (LIMK)/cofilin in WT and type 2B mutant vWF/p.V1316M (2B) megakaryocytes (MKs).

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Scheme of the regulation of actin turnover by LIM kinase (LIMK)/cofilin ...
LIMKs influence the architecture of the actin cytoskeleton by regulating the activity of the cofilin family proteins. In WT mice, the equilibrium between nonphosphorylated and phosphorylated cofilin stimulates severance and depolymerization of actin, and promotes actin filament turnover, leading to proper platelet production. By contrast, in 2B MKs, the inactivation of cofilin by phosphorylation at Ser3 is upregulated. This leads to cofilin losing its ability to bind actin and then suppresses actin turnover (2). RhoA/ROCK regulates the LIMK/cofilin pathway in WT MKs and is upregulated in 2B MKs. ROCK, RhoA kinase.