¹Department of Human Anatomy and Histology and ⁴Department of Biomedical Sciences and Human Oncology University of Bari Medical School, Bari, Italy; ²Institute of Pharmacological Sciences, University of Siena Medical School, Siena, Italy; ³Department of Pharmacology, University of Firenze Medical School, Firenze, Italy; ⁵Department of Biomedical Sciences and Biotechnology, University of Brescia Medical School, Brescia, Italy.
 

Fibroblast growth factor-2 (FGF2) and vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) exert their angiogenic activity by interacting with endothelial cells in a distinct manner. In this study we investigated the morphological features of endothelial cells of the chick embryo chorioallantoic membrane (CAM) microvasculature after stimulation by FGF2 or VEGF. 

In order to provide a continuous delivery of the growth factor, we utilized a recently developed gelatin sponge/CAM assay in which a limited number of FGF2- or VEGF-transfected cells were adsorbed onto gelatin sponges and applied on the top of the embryonic membrane at day 8 of development. Their angiogenic activity was compared to that exerted by a single bolus of the corresponding human recombinant growth factor. 

All the angiogenic stimuli induced a comparable vasoproliferative response, as demonstrated by the appearance of similar numbers of immature blood vessels inside the sponge at day 12. No angiogenic response was observed in CAMs implanted with the corresponding parental cell lines or vehicle. Transmission electron microscopy demonstrated that only VEGF-overexpressing cells were able to modify the phenotype of the endothelium of the preexisting blood vessels at the boundary between the implant and the surrounding CAM mesenchyme. The endothelial lining of 30% of these vessels showed segmental attenuations, was frequently interrupted, and became fenestrated, mimicking what observed in tumor vasculature. In contrast, the vessels consisted of continuous endothelium sealed by tight junctions in all the other experimental conditions. 

These results indicate that FGF2 and VEGF interact with endothelial cells of the CAM in a distinct manner. Both growth factors induce a potent angiogenic response, but only VEGF delivered in a continuous manner by VEGF-transfectants is able to modify the phenotype of the otherwise quiescent endothelium of CAM blood microvessels. The gelatin sponge/CAM assay may represent a new model to study the mechanisms leading to endothelial fenestration in tumor growth.

J. Vasc. Res. 2001, 38:389-97