Fluid Shear Stress Stimulates Phosphorylation of Akt in Human Endothelial Cells

Abstract

Abstract-Fluid shear stress alters the morphology and function of the endothelium by activating several kinases.Furthermore, shear stress potently inhibits 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 shear stress exposure. The stimulation of Akt phosphorylation by shear stress thereby seemed to be mediated by the phosphoinositide 3-OH kinase (PI3K), as evidenced by the significant inhibition of shear stress-induced Akt phosphorylation by the PI3K inhibitors wortmannin (20 nmol/L) and Ly294002 (10 mol/L). In addition, pharmacological inhibition of PI3K reduced the antiapoptotic effect of shear stress against growth factor depletion-induced apoptosis. Most important, overexpression of a dominant-negative Akt mutant significantly inhibited the apoptosissuppressive effect of shear stress against serum depletion-induced apoptosis, thus indicating the direct involvement of shear stress-induced Akt phosphorylation for inhibition of endothelial cell apoptosis. These results define a novel shear stress-stimulated signal transduction pathway, namely, activation of the serine/threonine kinase Akt, which may contribute to the profound changes in endothelial morphology and function by shear stress. (Circ Res. 1998;83:334-341.)

Stress and mTORture signaling

“…These cells endure fluid shear stress, which contributes to the inhibition of cell death. Shear stress led to a timedependent increase in PKB phosphorylation and increased survival of endothelial cells in response to serum depletion under shear stress conditions (Dimmeler et al, 1998). Fluid flow also activated S6K1 in a rapamycindependent manner.…”

VEGF receptor 2 and the adherens junction as a mechanical transducer in vascular endothelial cells

“…6A). After the exposure of endothelial cells to physiological levels of LSS, Akt1 becomes phosphorylated (27,28). Akt1 phosphorylation also was associated with the activation of the VEGFR2 by either VEGF-A or shear stress (27,28).…”

Inhibition of Vascular Endothelial Growth Factor (VEGF) Signaling in Cancer Causes Loss of Endothelial Fenestrations, Regression of Tumor Vessels, and Appearance of Basement Membrane Ghosts

“…28 Cessation of flow would eliminate the shear stress that plays a role in endothelial cell survival. 47 Methods that detect changes in blood flow may prove useful in assessing early evidence of VEGF/VEGFR inhibition, but the effects would be restricted to responsive vessels, and overall tumor blood flow may not reflect the magnitude of changes in individual vessels. 32 …”