Transforming growth factor-beta mediates astrocyte-specific regulation of brain endothelial anticoagulant factors

Background and Purpose-Astrocytes are potent regulators of brain capillary endothelial cell function. Recently, astrocytes were shown to regulate brai n capillary endothelial expression of the fibrinolytic enzyme tissue plasmi nogen activator (tPA) and the anticoagulant thrombomodulin (TM). To study t he mechanism of this process, we examined the hypothesis that astrocyte reg ulation of endothelial tPA and TM is mediated by transforming growth factor -beta (TGF-beta). Methods-Brain capillary endothelial cells were grown in blood-brain barrier models. We examined astrocyte-endothelial cocultures, endothelial monocult ures, and astrocyte-conditioned media (ACM) for the expression of TGF-beta. We also incubated endothelial cells with ACM to determine the role of TGF- beta. Following 24 hours of incubation, we assayed for tPA and TM mRNA, as well as tPA and TM activity. Results-Astrocyte-endothelial cocultures and ACM exhibited significantly hi gher levels of active TGF-beta than brain endothelial monocultures and endo thelial cells grown in nonconditioned media, respectively. Brain endothelia l cells incubated with ACM exhibited reduced tPA and TM mRNA and activity, Treatment with. exogenous TGF-beta produced dose-dependent reductions in tP A and TM. The effects of ACM on both tPA and TM were blocked by TGF-beta ne utralizing antibody. Conclusions-These data indicate that TGF-beta mediates astrocyte regulation of brain capillary endothelial expression of tPA and TM.