Localization of VE-cadherin in plasmalemmal cholesterol rich microdomains and the effects of cholesterol depletion on VE-cadherin mediated cell-cell adhesion

VE-cadherin is the predominant adhesion molecule in vascular endothelial cells being responsible for maintenance of the endothelial barrier function by forming adhesive contacts (adherens junctions) to neighbouring cells. We found by use of single molecule fluorescence microscopy that VE-cadherin is localised in preformed clusters when not inside adherens junctions. These clusters depend on the integrity of the actin cytoskeleton and are localised in cholesterol rich microdomains of mature endothelial cells as found by membrane fractionation. The ability to form and maintain VE-cadherin based junctions was probed using the laser tweezer technique, and we found that cholesterol depletion has dramatical effects on VE-cadherin mediated adhesion. While a 30\% reduction of the cholesterol-level results in an increase of adhesion, excessive cholesterol depletion by about 60\% leads to an almost complete loss of VE-cadherin function. Nevertheless, the cadherin concentration in the membrane and the single molecule kinetic parameters of the cadherin are not changed. Our results suggest that the actin cytoskeleton, junction-associated proteins and protein-lipid assemblies in cholesterol-rich microdomains mutually stabilise each other to form functional adhesion contacts.