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

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 (0-100 ng/ml, 18 h), 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.