VEGF spatially directs angiogenesis during metanephric development in vitro.

Vascular endothelial growth factor (VEGF) is required for endothelial cell differentiation, vasculogenesis, and normal glomerular vascularization. To examine whether VEGF plays a role as a chemoattractant for the developing kidney vasculature, avascular metanephric kidneys from rat embryos (E14) were cocultured with endothelial cells. To determine whether VEGF directly provides chemoattractive guidance for migration, we examined migration of endothelial cells toward VEGF-coated beads. Mouse glomerular endothelial cells expressing beta-galactosidase (MGEC) were isolated from Flk-1(+/-) heterozygous mice and passaged 4-12 times. Upon 24 h culture on collagen I gels MGEC formed a lattice or capillary-like network. Embryonic metanephroi were cocultured with MGEC on collagen I gels for 1-6 days in defined media, stained for beta-galactosidase, and examined by light microscopy. Metanephric organs induced a rearrangement of the endothelial cell lattice and attracted MGEC. MGEC invaded the metanephric organs forming capillary-like structures within and surrounding the forming nephrons. This process was accelerated and amplified by low oxygen (3% O(2)) and was prevented by anti-VEGF neutralizing antibodies. MGECs migrated toward VEGF-coated beads, whereas PBS-coated beads did not alter MGEC networks. We conclude that VEGF produced by the differentiating nephrons acts as a chemoattractant providing spatial direction to developing capillaries toward forming nephrons during metanephric development in vitro.