Shear Stress Activates eNOS at the Endothelial Apical Surface Through β1 Containing Integrins and Caveolae

There is now a large body of evidence demonstrating that fluid mechanical forces generated by blood flowing through the vasculature play a direct role in regulating endothelial cell structure and function. Integrin receptors that localize to the basal surface of the endothelium participate in both outside-in and inside-out signaling events that influence endothelial gene expression and morphology in response to flow. Our analyses of apical plasma membranes derived from cultured bovine aortic endothelial cells revealed that integrins are also expressed on this cell surface. Here, we tested whether these integrins participate in mechanotransduction events that are known to occur on the endothelial cell luminal/apical membrane. We found that apically expressed β1 integrins are rapidly activated in response to acute shear stress. Blockade of β1 integrin activation attenuated a shear-induced signaling cascade involving Src-family kinase, PI3-kinase, Akt and eNOS on this cell surface. In addition, β1 integrin activation and associated signaling events were dependent on the structural integrity of caveolae but not the actin cytoskeleton. Taken together, these data indicate that endothelial responses to shear stress are mediated by spatially distinct pools of integrins.