MATRIX-BOUND THROMBOSPONDIN PROMOTES ANGIOGENESIS IN-VITRO

Thrombospondin (TSP) is a multidomain adhesive protein postulated to p lay an important role in the biological activity of the extracellular matrix. To test this hypothesis, TSP-containing fibrin and collagen ma trices were evaluated for their capacity to support angiogenesis and c ell growth from explants of rat aorta. This serum-free model allowed u s to study the angiogenic effect of TSP without the interference of at tachment and growth factors present in serum. TSP promoted dose-depend ent growth of microvessels and fibroblast-like cells. The number of mi crovessels in TSP-containing collagen and fibrin gels increased by 136 and 94%, respectively. The TSP effect was due in part to cell prolife ration since a 97% increase in [H-3]thymidine incorporation by the aor tic culture was observed. The effect was TSP-specific because TSP prep arations adsorbed with anti-TSP antibody showed no activity. TSP did n ot promote angiogenesis directly since no TSP-dependent growth of isol ated endothelial cells could be demonstrated. Rather TSP directly stim ulated the growth of aortic culture-derived myofibroblasts which in tu rn promoted microvessel formation when cocultured with the aortic expl ants. Angiogenesis was also stimulated by myofibroblast-conditioned me dium. Partial characterization of the conditioned medium suggests that the angiogenic activity is due to heparin-binding protein(s) with mol ecular weight >30 kD. These results indicate that matrix-bound TSP can indirectly promote microvessel formation through growth-promoting eff ects on myofibroblasts and that TSP may be an important stimulator of angiogenesis and wound healing in vivo.