Matrix-bound thrombospondin promotes angiogenesis in vitro.
Thrombospondin (TSP) is a multidomain adhesive protein postulated to play an important role in the biological activity of the extracellular matrix. To test this hypothesis, TSP-containing fibrin and collagen matrices were evaluated for their capacity to support angiogenesis and cell growth from explants of rat aorta. This serum-free model allowed us to study the angiogenic effect of TSP without the interference of attachment and growth factors present in serum. TSP promoted dose-dependent growth of microvessels and fibroblast-like cells. The number of microvessels in TSP-containing collagen and fibrin gels increased by 136 and 94%, respectively. The TSP effect was due in part to cell proliferation since a 97% increase in [3H]thymidine incorporation by the aortic culture was observed. The effect was TSP-specific because TSP preparations adsorbed with anti-TSP antibody showed no activity. TSP did not promote angiogenesis directly since no TSP-dependent growth of isolated endothelial cells could be demonstrated. Rather TSP directly stimulated the growth of aortic culture-derived myofibroblasts which in turn promoted microvessel formation when cocultured with the aortic explants. Angiogenesis was also stimulated by myofibroblast-conditioned medium. Partial characterization of the conditioned medium suggests that the angiogenic activity is due to heparin-binding protein(s) with molecular weight > 30 kD. These results indicate that matrix-bound TSP can indirectly promote microvessel formation through growth-promoting effects on myofibroblasts and that TSP may be an important stimulator of angiogenesis and wound healing in vivo.
Nicosia
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Department of Pathology and Laboratory Medicine, Medical College of Pennsylvania, Philadelphia 19129.
Tuszynski
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GP
D000818:Animals; D001011:Aorta / Q000166:cytology*; D002417:Cattle; D002455:Cell Division; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology*; D005337:Fibrin / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000502:physiology*; D008833:Microcirculation / Q000166:cytology; D009389:Neovascularization, Pathologic; D051381:Rats; D019699:Thrombospondins
D008562:Membrane Glycoproteins; D019699:Thrombospondins; D005337:Fibrin; D003094:Collagen