Tumour necrosis factor‐α‐mediated disruption of cerebrovascular endothelial barrier integrity in vitro involves the production of proinflammatory interleukin‐6

The co‐involvement of tumour necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) during blood‐brain barrier (BBB) injury has been reported in various models of neuroinflammation, although the precise functional interplay between these archetypal proinflammatory cytokines remains largely undefined within this context. In the current paper, we tested the hypothesis that TNF‐α‐mediated BBB disruption is measurably attributable in‐part to induction of microvascular endothelial IL‐6 production. In initial experiments, we observed that treatment of human brain microvascular endothelial cells (HBMvECs) with TNF‐α (0–100 ng/mL, 0–24 h) robustly elicited both time‐ and dose‐dependent induction of IL‐6 expression and release, as well as expression of the IL‐6 family receptor, GP130. Further experiments demonstrated that the TNF‐α‐dependent generation of reactive oxygen species, down‐regulation of adherens/tight junction proteins, and concomitant elevation of HBMvEC permeability, were all significantly attenuated by blockade of IL‐6 signalling using either an anti‐IL‐6 neutralizing antibody or an IL‐6 siRNA. Based on these observations, we conclude that TNF‐α treatment of HBMvECs in vitro activates IL‐6 production and signalling, events that were shown to synergize with TNF‐α actions to elicit HBMvEC permeabilization. These novel findings offer a constructive insight into the specific contribution of downstream cytokine induction to the injurious actions of TNF‐α at the BBB microvascular endothelium interface. The co‐involvement of tumour necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) during blood–brain barrier (BBB) injury has been widely reported. Using human brain microvascular endothelial cells (HBMvEC), we show that TNF‐α‐mediated BBB disruption is measurably attributable in‐part to induction of endothelial IL‐6 production and signalling. We demonstrate that the TNF‐α‐dependent generation of reactive oxygen species (ROS), down‐regulation of interendothelial junctions, and concomitant elevation of HBMvEC permeability, could be significantly attenuated by using either an IL‐6 neutralizing antibody or an IL‐6‐specific siRNA. These findings provide insight into the complex nature of proinflammatory cytokine injury at the BBB microvascular endothelium interface. The co‐involvement of tumour necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) during blood–brain barrier (BBB) injury has been widely reported. Using human brain microvascular endothelial cells (HBMvEC),