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 8

Active RhoA is upregulated in type 2B mutant vWF/p.V1316M (2B) megakaryocytes (MKs) and controls the phosphorylation of LIM kinase (LIMK) and cofilin.

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Active RhoA is upregulated in type 2B mutant vWF/p.V1316M (2B) megakaryo...
(A) Pull-down assays of RhoA-GTP were performed in WT and 2B mature MKs. Western blot and quantification of RhoA and Rhoa-GTP. Statistical significance was determined by Student’s t test. ***P < 0.001, n = 3. (B) Western blot of LIMK and cofilin phosphorylation in WT and 2B MKs in the presence or the absence of the RhoA kinase (ROCK) inhibitor, Y-27632. Mature MKs were incubated for 3 hours with Y-27632 (10 μM) or DMSO (0.2%) and then lysed in SDS denaturing buffer. n = 3. These samples were run in the same gel but the lanes were noncontiguous, as indicated by the separate boxes. (C) Mature MKs after thrombopoietin-induced differentiation in culture were incubated over a fibrinogen matrix for 5 hours in the presence or absence of the ROCK inhibitor (10 μM) or DMSO (0.2%) used as control. Representative images of MKs forming proplatelets. Scale bars: 50 μm. Quantification of the percentage of proplatelet-forming MKs (top graph) and the number of proplatelets/MK (bottom graph) in 3 separate experiments. Statistical significance was determined by 1-way ANOVA followed by Dunnett’s test (50–75 MKs were analyzed/experiment). *P < 0.05, ***P < 0.001.