Contextual role for angiopoietins and TGFbeta1 in blood vessel stabilization.

We used a 3D in-vitro model of angiogenesis to investigate the effects of different growth factors on vessel formation and stabilization in vitro. Vascular endothelial growth factor (VEGF) was the only factor that induced the formation, elongation and sprouting of capillary-like structures (CLS) by bovine retinal capillary endothelial cells (BREC), an effect that was dose-dependent and saturable. Basic fibroblast growth factor 2 (FGF2) enhanced capillary formation in the presence of VEGF, leading to a more complex network of CLS and a higher rate of BrdU incorporation than VEGF alone, indicating that whereas VEGF acts as a morphogen, FGF2 is primarily a mitogen. Addition of transforming growth factor beta1 (TGFbeta1) to the 3D assay along with VEGF and FGF2, reduced tube formation in a dose-dependent manner. When added at the time of cell plating TGFbeta1 completely suppressed formation of VEGF/FGF2-stimulated CLS. Angiopoietin 1 (Ang1) prevented regression of the TGFbeta1-induced CLS, an effect that was blocked by angiopoietin 2 (Ang2), but required the continuous presence of VEGF.