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.