A novel, quantitative model for study of endothelial cell migration and sprout formation within three-dimensional collagen matrices

Interactions between migratory endothelial cells (ECs) and surrounding extr acellular matrix (ECM) are of central importance to vascular growth. Here, we present a new model of EC migration and morphogenesis within three-dimen sional ECM termed "radial invasion of matrix by aggregated cells" (RIMAC). In the RIMAC model, single aggregates of defined numbers of bovine aortic E Cs were embedded within small, lenticular gels of type I collagen supported by annuli of nylon mesh. Culture of the gels in nutrient media resulted in quantifiable, reproducible, radial migration of ECs into the collagen. The angiogenic proteins basic fibroblast growth factor (bFGF) and vascular end othelial growth factor (VEGF) each stimulated migration of ECs in a concent ration-dependent manner. In combination, bFGF and VEGF stimulated migration synergistically. In contrast, transforming growth factor-beta 1 inhibited migration of ECs. Low concentrations (0.1-0.5 ng/ml) of VEGF induced ECs to form multicellular sprouts, some of which possessed lumen-like spaces. Mit omycin C, an inhibitor of cell proliferation, did not affect the migration of ECs into collagen induced by 0.5 ng/ml VEGF but moderately inhibited mig ration induced by 5 ng/ml VEGF. Increasing the density (concentration) of t he collagen gel inhibited the migration of single ECs and increased the bra nching and anastomosis of multicellular sprouts. We conclude that the RIMAC model is a highly efficacious assay for the screening of potentially angio genic and angiostatic compounds and, moreover, is advantageous for mechanis tic studies of vascular morphogenesis. (C) 1999 Academic Press.