Endothelium-fibrinolysis system interaction.
The role of urokinase-type plasminogen activator (u-PA) in capillary growth was investigated using cultured bovine endothelial cells (BCE) on type I collagen gels and analyzed by morphometry for quantitative assessment of angiogenesis in vitro. BCE migrated into the gel matrix and formed capillary-like networks. The morphometrical analyses by measuring the length of tube formation enabled us to evaluate the effects of fibrinolytic proteases and several reagents. The addition of plasminogen up to 25 micrograms/ml to the gels significantly increased the extent of tube formation of BCE in a dose-dependent manner. Basic fibroblast growth factor (10 ng/ml) increased tube formation only in the presence of plasminogen. These enhancing effects on angiogenesis appeared to be related to the activation of fibrinolysis by u-PA derived from BCE, because they were suppressed by the addition of anti-u-PA IgG and anti-plasmin reagents such as aprotinin and alpha 2 anti-plasmin. Transforming growth factor beta also enhanced tube formation of BCE, but tumor necrosis factor alpha and interleukin-1 suppressed the tube formation. The quantitative assay of angiogenesis may be useful for clarifying the mechanism of neovascularization under pathological conditions.