Abstract
Purpose :
The clinical success of neutralizing vascular endothelial growth factor (VEGF) has unequivocally identified VEGF as a driver of edema that underlies a variety of blinding conditions. VEGF is not the only input that is received and integrated by the endothelium to control barrier function. For instance, permeability of blood vessels is also under the control of the large and ubiquitously expressed transforming growth factor beta (TGFb) family. In this project we tested the hypothesis that members of the TGFb family influence VEGF-mediated control of the endothelial cell barrier.
Methods :
To determine if there was a functional relationship between TGFb family members and VEGF, we compared the effect of BMP-9, TGFb1 and activin A on VEGF-driven permeability of primary human retinal endothelial cells. Cell permeability was assessed by measuring changes in electrical resistance using electrical cell-substrate impedance sensing. Western blotting was used to assess expression of VEGFR2, effectors downstream of VEGFR2, protein tyrosine phosphatases and VEGFR2 phosphorylation. The contribution of pathway components was evaluated using pharmacological and siRNA-based approaches.
Results :
While BMP-9 and TGFb1 had no effect on VEGF-induced permeability, activin A limited the extent to which VEGF was able to relax the barrier. This activin A effect was associated with reduced activation of VEGFR2 and its downstream effectors (PLCg, Src, eNOS, Erk and Akt), and increased expression of vascular endothelial tyrosine phosphatase (VE-PTP). Reducing the expression or activity of VE-PTP overcame the effect of activin A. These observations indicate that activin A suppresses responsiveness of cells to VEGF, and that the underlying mechanism involves VE-PTP-mediated dephosphorylation of VEGFR2.
Conclusions :
Members of the TGFb family, such as activin A, limit VEGF-dependent relaxation of the endothelial cell barrier. The underlying mechanism involves upregulation of VE-PTP, which dephosphorylates VEGFR2. Thus targeting VE-PTP may enhance (instead of reduce) permeability of blood vessels when the level of activin A is high.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.