Decorin inhibits endothelial migration and tube-like structure formation: Role of thrombospondin-1

Interactions between endothelial cell receptors and the extracellular matri x (ECM) play a critical, yet poorly understood role in angiogenesis. Based on the anti-adhesive role of decorin, we hypothesized that decorin binding to ECM molecules such as thrombospondin-1 (TSP-1) plays a regulatory role i n endothelial tube-like structure (TLS) formation. To test this hypothesis, endothelial cells were plated on TSP-1, decorin, or mixed substrates of TS P-1 plus decorin. TLS formation was induced by applying type I collagen on the confluent endothelial monolayer. Cartilage decorin inhibited the format ion of TLSs in a concentration-dependent manner. On substrates of high deco rin concentrations (2.5 and 5.0 mug/cm(2)) the reduction in TLSs was due ei ther to a reduction in the number of adhering cells or to decreased cell mi gration. At low decorin concentrations (0.05 and 0.25 mug/cm(2)) the reduct ion in TLSs was independent of the number of attached cells, Time-lapse vid eo microscopy revealed that decorin substrates facilitated homotypic aggreg ation and isolated cord formation at the expense of endothelial migration a nd TLS formation. Consistent with the reduced migration, endothelial cells formed fewer vinculin-positive focal adhesions and actin-stress fibers on d ecorin substrates. Endothelial migration and TLS formation were also signif icantly inhibited by skin decorin and the protein core of cartilage decorin . The inhibition of TLS formation by the protein core of cartilage decorin was potentiated by TSP-1. These findings suggest that decorin alone or in c ombination with TSP-1 interferes with the activation of endothelial cell re ceptors by ECM molecules, thus blocking intracellular signals that induce c ytoskeletal reorganization, migration, and TLS formation, (C) 2001 Academic Press.