FLUID SHEAR-STRESS STIMULATES PHOSPHORYLATION OF AKT IN HUMAN ENDOTHELIAL-CELLS - INVOLVEMENT IN SUPPRESSION OF APOPTOSIS

Fluid shear stress alters the morphology and function of the endotheli um by activating several kinases. Furthermore, shear stress potently i nhibits apoptosis of endothelial cells. Since activation of Akt kinase has been shown to prevent cell death, we investigated the effects of shear stress on Akt phosphorylation. To test the hypothesis that shear stress interacts with the Akt kinase pathway, human umbilical venous endothelial cells were exposed to laminar shear stress (15 dyne/cm(2)) . Western blotting with specific antibodies against the phosphorylated Akt demonstrated a time-dependent stimulation of Akt phosphorylation by shear stress with a maximal increase up to 6-fold after 1 hour of s hear stress exposure. The stimulation of Akt phosphorylation by shear stress thereby seemed to be mediated by the phosphoinositide 3-OH kina se (PI3K), as evidenced by the significant inhibition of shear stress- induced Akt phosphorylation by the PI3K inhibitors wortmannin (20 nmol /L) and Ly294002 (10 mu mol/L). In addition, pharmacological inhibitio n of PI3K reduced the antiapoptotic effect of shear stress against gro wth factor depletion-induced apoptosis. Most important, overexpression of a dominant-negative Akt mutant significantly inhibited the apoptos is-suppressive effect of shear stress against serum depletion-induced apoptosis, thus indicating the direct involvement of shear stress-indu ced Akt phosphorylation for inhibition of endothelial cell apoptosis. These results define a novel shear stress-stimulated signal transducti on pathway, namely, activation of the serine/threonine kinase Akt, whi ch may contribute to the profound changes in endothelial morphology an d function by shear stress.