Copyright © 2007, European Society of Cardiology
Regulation of endothelial barrier function during flow-induced conversion to an arterial phenotype
aInstitute of Physiology, Medical Faculty Dresden of the TU-Dresden, 01307 Dresden, Germany
bDepartement of Nanobiophotonics, Max-Planck-Institut für biophysikalische Chemie, 37077 Göttingen, Germany
cCentre for Clinical Pharmacology and Therapeutics, University College London, London, WC1E 6BT, UK
dDepartment of Medical Microbiology, University of Manitoba, Winnipeg, Canada MB R3E 0W3
eSpecial Pathogens Program, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, Canada MB R3E 3R2
* Corresponding author. Institut für Physiologie, der Medizinischen Fakultät Carl-Gustav-Carus, Tu-Dresden, Fiedlerstrasse 42, 01307 Dresden, Germany. Tel.: +49 351 4586 007; fax: +49 351 4586 301. Hans.Schnittler{at}tu-dresden.de
Objective Flow-induced conversion of endothelial cells into an elongated arterial phenotype requires a coordinated regulation of cell junctions. Here we investigated the effect of acute and chronic flow on junction regulation.
Methods and results Using an extended experimental setup that allows analyses of endothelial barrier function under flow conditions, we found a flow-induced upregulation of the transendothelial electrical resistance within minutes. This was accompanied by an increase in actin filaments along the junctions and vascular endothelial (VE)-cadherin clustering, which was identified at nanoscale resolution by stimulated emission depletion microscopy. In addition, a transient tyrosine phosphorylation of VE-cadherin and catenins occurred within minutes following the onset of flow. VE-cadherin and actin distribution were maintained under chronic flow over 24 h and associated with the upregulation of VE-cadherin and 
-catenin expression, thus compensating for the cell elongation-mediated increase in cell border length. Importantly, all observed effects were rac1 dependent as verified by the inhibitory effect of dominant negative N17rac1.
Conclusion These results show that flow-induced conversion of endothelial cells into an arterial phenotype occurs while intercellular junctions remain intact. The data place rac1 in a central multimodal regulatory position that might be important in the development of vascular diseases, such as arteriosclerosis.
KEYWORDS HUVEC, human umbilical vein endothelial cells; PSF, point spread function; STED, Stimulated emission depletion; TER, transendothelial electrical resistance.