Nd. Tran et al., Astrocyte regulation of endothelial tissue plasminogen activator in a blood-brain barrier model, J CEREBR B, 18(12), 1998, pp. 1316-1324
Expression of tissue plasminogen activator (tPA) substantially determines e
ndothelial-dependent fibrinolysis. We used a blood-brain barrier (BBB) mode
l to analyze regulation of brain capillary endothelial tPA and its inhibito
r, plasminogen activator inhibitor-1 (PAI-1). This model consists of cocult
ure of murine astrocytes with bovine brain capillary endothelial cells grow
n as capillary-like structures (CS); after 1 week. astrocytes become extens
ively associated with CS, and the BBB-associated enzyme gamma-glutamyl tran
speptidase is present. We measured tPA and PAI-I mRNA and tPA activity in t
his model. Reverse transcription-polymerase chain reaction (RT-PCR) studies
showed similar tPA and PAI-I mRNA levels after 1 day mono-culture (endothe
lial cells only) versus astrocyte-endothelial coculture preparations. After
7 days (i.e., when elements of the BBB are present), astrocyte-endothelial
cocultures (compared with endothelial mono-cultures) showed a 50.7% +/- 27
.1% (mean +/- SD) reduction in tPA mRNA (P < 0.03) and a 183.3% +/- 86.98 i
ncrease in PAI-I mRNA expression (P < 0.02). Moreover, 7-day cocultures dem
onstrated reduced tPA activity compared with mono-cultures (14.6 +/- 2.9 IU
/mL versus 30.2 +/- 7.7 IU/mL, P < 0.01); 1-day cocultures and mono-culture
s had similar tPA activity. These findings demonstrate that astrocytes regu
late brain capillary endothelial expression of tPA when elements of the BBB
phenotype are present in this model. These data suggest an important role
for astrocytes in the regulation of brain capillary endothelial fibrinolysi
s.