טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShai Ayelet
SubjectThe Regulation of Expression of Angiogenic Genes by Shear
Stress in Vascular Endothelial Cells
DepartmentDepartment of Medicine
Supervisors Professor Israel Vlodavsky
Ms. Nitzan Resnick


Abstract

Changes in shear forces experienced by the endothelium promote formation of new vessels. They induce signal transduction events, leading to changes in gene expression.

The VEGF and the Angiopoietin growth factors are central to vascular development.  VEGFR-2 is the major receptor for VEGF. Binding of VEGFR-2 to the adherens junction proteins VE-cadherin and b-catenin is essential for transmission of survival signals via the kinase Akt.

We hypothesized that shear stress (SS) changes induce blood vessel formation by regulating the expression and activation of the VEGF and Angiopoietin receptors.

The expression of VEGFR-2 increased rapidly after the onset of flow, while that of VEGFR-1 and Tie1 decreases. Tie2 increased after 2 hours. Short intervals of SS didn't result in phosphorylation of VEGFR-2. A rapid and sustained nuclear translocation of VEGFR-2 was observed, with its rapid but transient attachment to the adherens junctions and to the actin cytoskeleton. Simultaneously, VE-cadherin and b-catenin accumulated at cell-cell contacts and attached to the endothelial cytoskeleton. SS induced formation of a complex containing VEGFR-2, VE-cadherin and b-catenin. In cells lacking VE-cadherin, neither the phosphorylation of Akt and P38, nor VEGFR-2 nuclear translocation were induced. Also, induction of a reporter gene regulated by a promoter containing an SSRE failed to occur, suggesting that the complex adherens junction-VEGFR2 functions as a SS transducer.

Using the novel siRNA technique VEGFR-2 was partially inhibited. SS mediated Akt phosphorylation was attenuated.

We suggest that VEGFR-2 is activated by mechanical forces, and can function as a mechanical transducer.