Abstract
Dynamics of the actin cytoskeleton and VE‐cadherin, both implicated in the control of endothelial permeability, are poorly understood. Using live cell imaging of confluent human umbilical vein endothelial cells (EC) expressing either GFP‐actin or GFP‐VE‐ cadherin, we tested the hypothesis that inflammatory agents disrupt the cortical actin cytoskeleton and VE‐cadherin localization at intercellular junctions. Time‐lapse images were recorded during baseline and after addition of agents that either increase permeability (10 μM histamine, 1 U/ml thrombin) or decrease permeability [0.5–2 μM sphingosine‐1‐phosphate (S1P); 2 μM S1P1 receptor agonist SEW2871]. Transendothelial electrical resistance (TER) served as an index of barrier function. The results revealed an unexpected finding: Actin‐rich local lamellipodia frequently protrude and retract between EC. Histamine and thrombin both significantly decreased local lamellipodia protrusion frequency. Conversely, S1P and SEW2871 rapidly increased protrusion frequency concomitant with an increase in TER. Changes in VE‐cadherin were slower, although normally continuous VE‐cadherin was clearly disrupted by thrombin or histamine. In summary, our results suggest a novel concept that local lamellipodia may help regulate the paracellular passage of fluids and solutes across the endothelium. Supported by NIH R01HL098215 and R21AA020049.
Published Version
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