LUMEN FORMATION AND OTHER ANGIOGENIC ACTIVITIES OF CULTURED CAPILLARYENDOTHELIAL-CELLS ARE INHIBITED BY THROMBOSPONDIN-1

The large secreted glycoprotein thrombospondin-1 is a potent inhibitor of neovascularization in vivo In order to better understand its mecha nism of action, we have. determined the full range of deficits thrombo spondin can impose on cultured capillary endothelial cells. Exogenousl y added thrombospondin-1 blocked the ability of these cells to organiz e into cords. It blocked the migration of endothelial cells and vascul ar smooth muscle cells, but not that of fibroblasts, neutrophils, or k eratinocytes, demonstrating specificity. Conversely, when the endogeno us thrombospondin-1 produced by the endothelial cells was inactivated using antibodies that can neutralize its inhibition of neovascularizat ion in vivo, migration toward basic fibroblast growth factor and cord formation were stimulated, and sparsely plated cells developed cylindr ical cavities. These cavities formed by vesicle fusion, extended the d epth of the cell, and appeared to be incipient lumens, staining positi vely for the luminal marker angiotensin converting enzyme. Antiangioge nic levels of thrombospondin-1 had no measurable effect on the overall level of activity of soluble gelatinases or on urokinase plasminogen activator produced by activated endothelial cells. Coupled with previo usly published data, these results demonstrate thrombospondin-1. is a multifaceted inhibitor able to block the entire program of dedifferent iation and redifferentiation essential to the formation of new vessels . They also support the contention that the endogenously produced prot ein contributes to the quiescence of the normal vasculature. (C) 1997 Academic Press.