Regulation of endothelial barrier function during flow-induced conversion to an arterial phenotype

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-cadberin and alpha-catenin expression, thus compensating for the cell elongation-mediated increase in cell border length. Importantly, all observed effects were racl 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 racl in a central multimodal regulatory position that might be important in the development of vascular diseases, such as arteriosclerosis. (c) 2007 European Society of Cardiology. Published by Elsevier B.V All rights reserved.