Proceedings of The Physiological Society
University of York (2002) J Physiol 539P, S023
Effect of hypoxia on the expression of tight junction proteins in endothelial and epithelial cells
S. Fischer*, A. Reinel, M. Wiesnet, D. Renz* and W. Schaper
Max-Planck Institute for Physiological and Clinical Research, *Department of Anesthesiology and Intensive Care and Department of Experimental Cardiology, 61231 Bad Nauheim, Germany
Hypoxia is known to increase the permeability across endothelial as well as epithelial cell monolayers, which in vivo can lead to the development of vasogenic oedema. The paracellular permeability across these cell monolayers is regulated by specialized intercellular structures like the tight junctions (TJ). Tight junctions in epithelial cells are much stronger than those in endothelial cells, which was confirmed by measurements of the transcellular resistance values across cell monolayers consisting of murine submandibular gland carcinoma cells (CSG) and brain-derived microvascular endothelial cells (BMEC). Hypoxia-induced hyper-permeability of BMEC and CSG was prevented in the presence of a neutralizing antibody to vascular endothelial growth factor (VEGF) and by the nitric oxide synthase inhibitor N G-monomethyl-L-arginine, suggesting that hypoxia-induced permeability in CSG is mediated by a mechanism similar to that in BMEC. This mechanism involves an autocrine effect of VEGF, which is essentially dependent on reducing conditions stabilizing the second messenger NO as the mediator of changes in barrier function of BMEC. Accordingly, VEGF itself increased the permeability of the CSG monolayer only in the presence of the antioxidant α-lipoic acid. Hypoxia reduced the protein expression of the tight junction proteins, zonula occludens-1 (ZO-1), zonula occludens-2 (ZO-2), and occludin after 24 h of hypoxia in BMEC to 32 ± 8, 48 ± 4 and 30 ± 12 % (n = 4; mean ± S.E.M.). The protein level of ZO-1, ZO-2, and occludin after 24 h of hypoxia in CSG was not significantly different from those determined in BMEC. The protein expression of the TJ proteins is regulated differentially in both types of cells because the mRNA expression of ZO-1 and ZO-2 was not changed after 24 h of hypoxia, whereas occludin mRNA expression was decreased to the same extent as the protein level. Results suggest that the paracellular permeability during hypoxia across the CSG monolayer is regulated by a mechanism similar to that across the BMEC monolayer, which involves changes in the expression of TJ proteins.
Where applicable, experiments conform with Society ethical requirements