In vivo angiogenic activity of urokinase: role of endogenous fibroblast growth factor-2

In vitro experimental evidences suggest that the proteolytic degradation of the extracellular matrix (ECM) by activation of the urokinase-type plasmin ogen activator (uPA)/plasmin system may affect growth factor activity and b ioavailability, However, no direct in vivo observations were available to s upport this hypothesis. Here we demonstrate that endothelial GM 7373 cells overexpressing human uPA (uPA-R5 cells) cause the release of I-125-labeled fibroblast growth factor-2 (FGF2) from endothelial ECM in a plasmin-depende nt manner. Accordingly, uPA-R5 cells are angiogenic in vivo when applied on the top of the chorioallantoic membrane (CAM) of the chick embryo. In cont rast, mock-transfected Neo2 cells are unable to release ECM-bound I-125-FGF 2 and are poorly angiogenic. Neovascularization elicited by uPA-R5 cells is significantly reduced by neutralizing anti-FGF2 antibodies to values simil ar to those observed in Neo2 cell-treated CAMs, Accordingly, purified human uPA stimulates neovascularization of the CAM in the absence of an inflamma tory response. The angiogenic activity of uPA is significantly inhibited by neutralizing anti-FGF2 antibodies or by pretreatment with phenylmethylsulf onyl fluoride. The non-catalytic, receptor-binding aminoterminal fragment o f uPA is instead non angiogenic. Taken together, the data indicate that uPA is able to induce angiogenesis in vivo via a plasmin-dependent degradation of ECM that causes the mobilization of stored endogenous FGF2.