REGULATION OF IN-VITRO GLIA-INDUCED MICROVESSEL MORPHOGENESIS BY UROKINASE

Plasminogen activators (PAs) regulate a variety of processes involved in tissue morphogenesis and differentiation. We used a coculture syste m in which microvascular endothelial cells are induced by glial cells to form capillary-like structures in order to examine the role of urok inase-type PA (uPA) during microvessel morphogenesis within the centra l nervous system (CNS). Endothelia-derived uPA activity decreased seve nfold within glial-endothelial cocultures when capillary-like structur es were formed. Incubation of cocultures with concentrations of phorbo l 12-myristate 13-acetate (0.1 and 1.0 nM) that induced endothelial uP A activity (45-210%) inhibited endothelial differentiation (25-70%). F urthermore, incubation of cocultures with proteolytically active low m olecular weight uPA (5-500 IU/ml) inhibited endothelial differentiatio n (37-75%), whereas the amino terminal cell-binding fragment of uPA ha d minimal effect. Inhibition of plasminogen activation in cocultures w ith the serine protease/plasmin inhibitors aprotinin and soybean tryps in inhibitor increased glia-induced capillary-like structure formation (96-98%). These findings establish a paracrine/autocrine function for urokinase and its inhibitors in regulating endothelial responses to p erivascular glia and provide insight into mechanisms of microvascular reactions to CNS pathology.