Endothelial cell-astrocyte interactions and TGFβ are required for induction of blood-neural barrier properties

We sought to establish a blood-neural barrier (BNB) model of astrocyte contact with endothelial cells (EC) to test the hypothesis that transforming growth factor beta (TGFbeta) promotes an EC barrier-phenotype. Astrocyte-EC contact induced BNB properties in EC. Transendothelial resistance was augmented by direct contact between astrocytes-EC, but not by astrocyte-conditioned medium or astrocyte-EC coculture conditioned medium. Coculture of EC and astrocytes led to significant increase in endothelial occludin levels and junctional localization. EC gamma-glutamyl-transferase (GGT) activity was increased by direct contact with astrocytes, by conditioned medium from cocultures or by TGFbeta1. Coculture inhibited EC proliferation with no effect on astrocyte proliferation. A neutralizing antibody to TGFbeta decreased GGT activity in cocultures and increased cell number. Whereas total TGFbeta was not significantly altered by coculture, activated TGFbeta increased in astrocyte-EC cocultures. In summary, astrocyte-EC contact induces BNB characteristics in EC and locally activated TGFbeta is responsible for part of the induction. (C) 2004 Elsevier B.V. All rights reserved.