Cytokine-mediated dysregulation of zonula occludens-1 properties in human brain microvascular endothelium

Abstract

Zonula occludens-1 (ZO-1) is essential to the proper assembly of interendothelial junction complexes that control blood–brain barrier (BBB) integrity. The goal of the current paper was to improve our understanding of how proinflammatory cytokines modulate ZO-1 properties within the human BBB microvascular endothelium. In this respect, we investigated the effects of TNF-α and IL-6 on ZO-1 using human brain microvascular endothelial cells (HBMvECs). Following treatment of HBMvECs with either cytokine (0–100ng/ml, 18h), we observed significantly decreased ZO-1 expression and ZO-1:occludin co-association, in parallel with increased ZO-1 phosphorylation (pTyr and pThr). All effects were dose-dependent. Either cytokine also caused extensive cell-cell border delocalization of ZO-1 in parallel with elevated HBMvEC permeability. Furthermore, pre-treatment of HBMvECs with antioxidants (superoxide dismutase, catalase, apocynin, N-acetylcysteine), or employing targeted inhibition of NADPH oxidase activation (NSC23766, gp91/p47 siRNA), were all found to comparably attenuate the cytokine-dependent decrease in ZO-1 protein expression. In summary, we present an in vitro model of how different proinflammatory cytokines can dysregulate ZO-1 properties in HBMvECs. A causal role for NADPH oxidase activation and oxidant signalling is also confirmed. Our findings add mechanistic depth to current in vivo models of BBB injury manifesting ZO-1 dysregulation.