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The abnormal proplatelet formation in MYH 9‐related macrothrombocytopenia results from an increased actomyosin contractility and is rescued by myosin IIA inhibition
Author(s) -
Chen Y.,
Boukour S.,
Milloud R.,
Favier R.,
Saposnik B.,
Schlegel N.,
Nurden A.,
Raslova H.,
Vainchenker W.,
Balland M.,
Nurden P.,
Debili N.
Publication year - 2013
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.12436
Subject(s) - contractility , myosin , chemistry , biophysics , microbiology and biotechnology , medicine , biochemistry , biology
Summary Background Mutations in the MYH 9 gene cause autosomal dominant MYH 9‐related diseases ( MYH 9‐ RD ) that associate macrothrombocytopenia with various other clinical conditions. The mechanisms giving rise to giant platelets remain poorly understood. Objectives/Patients To study the proplatelet formation ( PPF ) derived from megakaryocytes ( MKs ) generated in vitro from 11 patients with MYH 9‐ RD with different mutations, compared with controls. Methods Proplatelet formation from cultured patients' MK s was evaluated with or without blebbistatin or the ROCK inhibitor Y27632. Myosin IIA and actin distribution were studied in spreading MK s on different surfaces by immunoconfocal analysis. Kinetic studies of contractility were performed on spreading MK s and the impact of blebbistatin on the maturation of the patients' MK s was evaluated by electron microscopy. Results and Conclusions We show that in vitro MK s of 11 patients formed significantly fewer proplatelets than controls. MK s from MYH 9‐ RD displayed an abnormal spreading on polylysine, fibronectin and collagen, with a disorganized actin network and a marked increase in stress fiber formation. Traction force microscopy studies demonstrated an elevated level of contractile forces in adherent mutated MK s. The myosin II inhibitor blebbistatin and the ROCK inhibitor Y27632 both rescued the proplatelet formation defect and normalized the ultrastructural characteristics of MYH 9‐ RD MK s. Altogether, our results show that in MYH 9‐ RD , mutations modify the overall MYH 9 function and provoke a proplatelet defect through an excess of actomyosin contractility in spreading MK s. These results may promote new therapeutic strategies aimed at reducing this actomyosin contractility.