RESUMO
Proteolysis of fibrin matrices by endothelial cells plays essential roles in the migratory and morphogenic differentiation processes underlying angiogenesis. Using an in vitro fibrinolysis model consisting of human umbilical vein endothelial cells (HUVECs) embedded in a three dimensional fibrin matrix, we show that VEGF, an angiogenic cytokine that plays a crucial role in the onset of angiogenesis, is a potent activator of HUVEC-mediated fibrinolysis. This VEGF-dependent fibrin degradation was completely abrogated by inhibitors of either the plasminogen activator/plasmin or matrix metalloproteinases (MMP) proteolytic systems, suggesting the involvement of both classes of proteases in fibrin degradation. Accordingly, VEGF-induced fibrinolysis correlated with an increase in the expression of tPA and of some MMPs, such as MT2-MMP and was completely blocked by a neutralizing antibody against tPA. Overall, these results indicate that efficient proteolysis of three dimensional fibrin matrices during VEGF-mediated angiogenesis involves a complex interplay between the MMP and plasmin-mediated proteolytic systems.
Assuntos
Indutores da Angiogênese/farmacologia , Endotélio Vascular/efeitos dos fármacos , Fibrinólise/efeitos dos fármacos , Fator A de Crescimento do Endotélio Vascular/farmacologia , Células Cultivadas , Células Endoteliais/efeitos dos fármacos , Endotélio Vascular/metabolismo , Fibrina/metabolismo , Humanos , Metaloproteinases da Matriz/biossíntese , Neovascularização Fisiológica/efeitos dos fármacos , Ativador de Plasminogênio Tecidual/biossíntese , Regulação para Cima , Receptor 2 de Fatores de Crescimento do Endotélio Vascular/biossínteseRESUMO
The vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptors play essential and complementary roles in angiogenesis and combined inhibition of these receptors has been shown to result in potent antitumor activity in vivo. In this study, we report that ellagic acid (EA), a natural polyphenol found in fruits and nuts, inhibits VEGF-induced phosphorylation of VEGFR-2 in endothelial cell (EC) as well as PDGF-induced phosphorylation of PDGFR in smooth muscle cells, leading to the inhibition of downstream signaling triggered by these receptors. EA also specifically inhibited VEGF-induced migration of ECs as well as their differentiation into capillary-like tubular structures and abolished PDGF-dependent smooth muscle cell migration. Interestingly, EA presents a greater selectivity for normal cells than for tumor cells since the migration of the U87 and HT1080 cell lines were much less affected by this molecule. The identification of EA as a naturally occurring dual inhibitor of VEGF and PDGF receptors suggests that this molecule possesses important antiangiogenic properties that may be helpful for the prevention and treatment of cancer.