Abstract 284: The Fibroblast Growth Factor System Regulates Vascular Integrity and Permeability
Background: Despite its versatile action on a wide variety of biological processes, the precise role of the fibroblast growth factor (FGF) family in the vascular system is under-characterized. We have recently shown, using a conditional transgenic mouse line, that the FGF system is indispensable for neovascularization in adult mice.
Methods: Two complementary approaches to disrupt FGF signaling were employed:
conditional transgenic mice expressing the dominant-negative form of FGF-R1 (FGF-R1DN) in the endothelium under the tetracycline-regulated Tie2 promoter and
adenovirus-mediated systemic expression of soluble FGFR-IgFc chimera proteins (sFGFR).
In addition, an endothelial cell (EC) culture system was used for molecular-based analyses.
Results: Micro-CT, fluorescent microsphere and Evans blue assays demonstrated increased vascular permeability in FGF-R1DN mice and sFGF-R1IIIc mice, strongly suggesting that lack of FGF signaling impairs basal vascular integrity. Further studies using in vivo CD31/VE-cadherin staining of the endothelium and scanning electron microscopy (SEM) revealed that disruption of FGF signaling in the arterial wall specifically affects EC junctions. In vitro studies demonstrated that inhibition of FGF signaling resulted in disappearance of VE-cadherin and other junction proteins from cell-cell contacts without changing total expression levels of these proteins or cell density/viability. As a result, EC permeability was increased in FGF-R1DN EC, which was due to intercellular gaps seen by SEM. Co-immunoprecipitation experiments revealed disruption of FGF signaling led to decreased p120-catenin association with VE-cadherin, accompanied by increased VE-cadherin phosphorylation. In FGF-R1DN EC, the Csk-binding VE-cadherin mutant (Y685E) restored VE-cadherin junction localization. This suggests that FGF signaling is required for Csk recruitment to VE-cadherin, thus negatively controlling local Src activities which can lead to VE-cadherin phosphorylation and internalization.
Conclusion: The FGF system regulates VE-cadherin stability at adherens junctions by increasing p120 and Csk binding to VE-cadherin, which in turn plays an important role in the maintenance of vascular integrity.