Loss of the tight junction proteins occludin and zonula occludens-1 from cerebral vascular endothelium during neutrophil-induced blood–brain barrier breakdown in vivo
Section snippets
Experimental animals
Male Lewis rats aged either three weeks (30–40 g, juvenile) or 12 weeks (>300 g, adult) were obtained from Harlan-OLAC (Bicester, Oxfordshire, U.K.). All animals were housed under standard conditions, with pelleted food and water available ad libitum.
Stereotaxic surgery
Stereotaxic surgery was performed as described previously.[36]Briefly, anaesthetized rats were held in a stereotaxic frame and the skull and brain exposed. One hundred units of human recombinant interleukin-1β (IL-1β; juveniles: n=12; adults: n=6) or
Interleukin-1β induces neutrophil-dependent blood–brain barrier breakdown in juvenile, but not adult, rats
One hundred units of human recombinant IL-1β induced neutrophil adhesion to blood vessels and BBB breakdown when injected into the striatum of juvenile, but not adult, rats. The tracer HRP is normally excluded from the brain by the BBB, but injected juvenile animals showed extensive HRP accumulation throughout the tissue of the injected hemisphere (Fig. 1D). This breakdown of the BBB in the juvenile animal is wholly neutrophil dependent,[5]allowing us to dissect out the response of the
Discussion
We have examined, for the first time in vivo, the molecular events which occur within the cerebral vascular endothelium during neutrophil-dependent BBB breakdown. We describe data which show that the cerebral vascular endothelium is an active participant in the recruitment of neutrophils to the brain parenchyma. A generalized reponse of the endothelial cells to injection of IL-1β was the up-regulation of ICAM-1, seen in most of the vasculature within the injected hemisphere. A more specific
Conclusion
Our knowledge of the events that occur in vivo during BBB breakdown is still very limited. The data presented in this paper have demonstrated, for the first time in vivo, alterations in both signalling and junctional components during cell-mediated BBB breakdown. Interestingly, only a particular subset of vessels within the brain will permit leucocyte migration, although it is not known why only these vessels become the targets for leucocyte adhesion and migration. We have begun to generate a
Acknowledgements
We would like to thank Dr M. Itoh for the anti-ZO-1 antibody and Dr K. Miller for the anti-VE-cadherin antibody. We also thank Sara Fearn and Mandy Townsend for technical assistance. This work was supported by the Medical Research Council.
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