Laminar Shear Stress Upregulates Integrin Expression

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Abstract
—Laminar shear stress exerts important effects on endothelial cell (EC) function and inhibits apoptosis of ECs induced by various stimuli. The mechanism by which hemodynamic forces, such as shear stress, are transduced into cellular signaling is still not known. Located at the cell surface, integrins, which are required for cell adhesion and cell survival, are potential mechanotransducers. Therefore, we investigated the effect of shear stress on integrin expression in ECs. Shear stress time-dependently increased the mRNA expression of the fibronectin receptor subunits α5 and β1 with a maximum at 6 hours (283±41% and 215±27% of control, respectively). In addition, the protein levels of the fibronectin receptor subunits α5 and β1 were enhanced with a maximum at 12 hours of shear stress exposure (343±53% and 212±38% of control, respectively). The shear stress–induced upregulation of integrins is independent of nitric oxide. Furthermore, we confirmed the enhanced functional activity of α5β1 integrin expression by FACS analysis. As a functional consequence, human umbilical vein ECs, which were preexposed to shear stress, revealed a significantly increased attachment (178±10% of static controls) and a more pronounced extracellular signal–regulated kinase 1 and 2 activation in response to cell attachment. Finally, we demonstrated that shear stress requires RGD-sensitive integrins to mediate its antiapoptotic effect. Taken together, these results define a novel mechanism by which shear stress may exert its atheroprotective effects via upregulation of integrins to support EC adhesion and survival.