Science Topics – 103

Unveiling the initial events during endothelial barrier disruption: Specific roles of di-phosphorylation of myosin light chain and actin bundle formation at the cell periphery
Mayumi Hirano (Katsuya Hirano)

The endothelial barrier dysfunction plays a critical role in the early phase of the development of various vascular diseases. Thrombin, one of the most potent stimulants causing barrier disruption, has been reported to induce the phosphorylation of myosin light chain (MCL) and actin stress fibers, thereby causing barrier disruption. The present study proposes the specific roles of MLC di-phosphorylation (ppMLC) and actin bundle formation at the cell periphery as initial events during thrombin-induced endothelial barrier disruption, based on the observations obtained with the measurement of trans-endothelial electrical resistance, Phos-tag SDS-PAGE analysis of MLC phosphorylation, fluorescence staining and phosphorylation-deficient mutants of MLC. Our findings are new in two aspect. First, the study demonstrates that ppMLC plays a temporally and spatially distinct role from pMLC during endothelial barrier disruption (Fig. a). Second, the study demonstrate that actin fibers forms the periphery bundles before forming stress fibers. We also demonstrates that this peripheral actin bundles are temporally and spatially associated with ppMLC. Furthermore, we elucidate that the degree of maturity of the cell-cell adhesion determines which pattern of actin filaments, peripheral bundles or stress fibers, is induced as an initial event. Our study therefore proposes that thrombin induces ppMLC and actin bundle formation at the cell periphery in the initial phase of the barrier disruption. This initial events loosens the inter-endothelial junction, thereby causing an increase in endothelial permeability as well as rearrangement of actin fibers to the stress fibers, which contributes to the sustained increase in permeability (Fig. b). The present study unveils the initial events during endothelial barrier disruption, which have been overlooked in the previous studies.

Mayumi Hirano, Katsuya Hirano*. Myosin di-phosphorylation and peripheral actin bundle formation as initial events during endothelial barrier disruption. Sci Rep 6: 20989, 2016 doi: 10.1038/srep20989
*Corresponding authors

  1. Department of Molecular Cardiology, Graduate School of Medical Sciences, Kyushu University
  2. Department of Cardiovascular Physiology, Faculty of Medicine, Kagawa University