title: Traction force dynamics predict gap formation in activated endothelium.
abstract: In many pathological conditions the endothelium becomes activated and dysfunctional, resulting in hyperpermeability and plasma leakage. No specific therapies are available yet to control endothelial barrier function, which is regulated by inter-endothelial junctions and the generation of acto-myosin-based contractile forces in the context of cell-cell and cell-matrix interactions. However, the spatiotemporal distribution and stimulus-induced reorganization of these integral forces remain largely unknown. Traction force microscopy of human endothelial monolayers was used to visualize contractile forces in resting cells and during thrombin-induced hyperpermeability. Simultaneously, information about endothelial monolayer integrity, adherens junctions and cytoskeletal proteins (F-actin) were captured. This revealed a heterogeneous distribution of traction forces, with nuclear areas showing lower and cell-cell junctions higher traction forces than the whole-monolayer average. Moreover, junctional forces were asymmetrically distributed among neighboring cells. Force vector orientation analysis showed a good correlation with the alignment of F-actin and revealed contractile forces in newly formed filopodia and lamellipodia-like protrusions within the monolayer. Finally, unstable areas, showing high force fluctuations within the monolayer were prone to form inter-endothelial gaps upon stimulation with thrombin. To conclude, contractile traction forces are heterogeneously distributed within endothelial monolayers and force instability, rather than force magnitude, predicts the stimulus-induced formation of intercellular gaps.
authors: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
authors: Erik T
authors: ET
authors: Valent
authors: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
authors: Geerten P
authors: GP
authors: van Nieuw Amerongen
authors: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
authors: Victor W M
authors: VWM
authors: van Hinsbergh
authors: Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands. Electronic address: p.hordijk@vumc.nl.
authors: Peter L
authors: PL
authors: Hordijk
mesh_terms: D000199:Actins / Q000378:metabolism; D001696:Biomechanical Phenomena / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D013917:Thrombin / Q000494:pharmacology
chemical_list: D000199:Actins; D013917:Thrombin
keywords: Barrier integrity; Endothelium; F-actin; Traction force microscopy; VE-cadherin