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Myosin-II inhibition and soft 2D matrix maximize multinucleation and cellular projections typical of

Jae-Won Shin1, Joe Swift, Kyle R Spinler

  • 1Pharmacology Graduate Group, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.

Proceedings of the National Academy of Sciences of the United States of America
|June 29, 2011
PubMed

Insights

Inhibiting myosin-II in megakaryocytes (MKs) paradoxically boosts polyploidy and platelet production. This discovery offers new insights into megakaryopoiesis and platelet generation, especially on soft matrices.

Area of Science:

  • Cell Biology
  • Hematopoiesis
  • Biophysics

Background:

  • Myosin-II typically promotes cell division, membrane rigidity, and matrix adhesion.
  • Megakaryocytes (MKs) with distended membranes are characteristic of low myosin activity on soft matrices.
  • Paradoxically, myosin mutations impair MKs and platelets, suggesting a complex role.

Purpose of the Study:

  • To investigate the effect of sustained myosin-II inhibition on megakaryocyte polyploidy and platelet generation.
  • To explore the influence of matrix properties on myosin-II's role in MK-poiesis.
  • To elucidate the molecular mechanisms underlying myosin-II's regulation of MKs and platelet formation.

Main Methods:

  • Reversible inhibition of myosin-II over multiple cell cycles.
  • Analysis of polyploid megakaryocyte and other cell type increases.
  • Assessment of proplatelet-like projection formation under shear stress.
  • Proteomic analysis of MKs using label-free mass spectrometry and ProPF analysis.
  • In vitro and in vivo platelet generation assays in xenografted mice.

Main Results:

  • Sustained myosin-II inhibition increased polyploid MKs by 3- to 10-fold.
  • Brief inhibition induced distensible, proplatelet-like projections that fragmented under shear.
  • Soft, 2D collagenous matrices maximized these effects, mimicking perivascular niches.
  • Myosin inhibition led to upregulation of cytoskeletal and adhesion machinery.
  • Myosin-inhibited MKs produced more platelets in vitro and in vivo, with enhanced platelet function upon stimulation.

Conclusions:

  • Myosin-II acts as a central, matrix-regulated node in megakaryopoiesis and platelet generation.
  • Reversible myosin-II inhibition is a novel strategy to enhance polyploidy and platelet production.
  • Matrix softness and dimensionality critically modulate myosin-II's function in MKs.
  • Phospho-regulation of myosin-II heavy chain enables lineage-specific signaling for increased polyploidy.

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