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H. L. Deissler, G. E. Lang; VEGF165 and Ranibizumab Strongly Influence Expression and Localization of the Tight Junction Protein Claudin-1 - It Is Not All About Occludin?!. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2642.
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Potential therapeutic effects of VEGF-inhibitors like the humanised VEGF-specific antibody ranibizumab are currently tested in the treatment of macular edema. VEGF165-elevated permeability of retinal endothelial cells is, at least in part, due to intracellular redistribution of tight junction protein(s). Tight junctions are protein complexes which are involved in the control of the paracellular signaling pathway of these cells.
We studied the effect of VEGF165 and ranibizumab on the protein composition of tight junctions in immortalized bovine retinal endothelial cells (iBREC) by immunofluorescence staining and Western-blot analyses.
Tight junction proteins ZO-1, occludin, claudin-1, claudin-3 and claudin-5 were expressed in the plasma membrane of confluent iBREC, but were located in the cytoplasm in non-confluent cells. Claudins 2 and 4 which are specific for epithelial cells, could not be detected in this cell type. Double-immunofluorescence staining indicated co-localization of claudin-1 and claudin-5, whereas ZO-1 and occludin were not co-localized with claudin-5. VEGF121 (10 and 100 ng/ml) or low concentrations of VEGF165 (10 ng/ml) did not markedly influence localization of tight junction proteins. In contrast, plasma membrane staining of tight junction proteins occludin and claudin-1 disappeared after treatment of iBREC with 100 ng/ml VEGF165 for 3 days which was observed together with an intensified intracellular staining of occludin. Claudin-3, claudin-5 were not and ZO-1 only weakly affected. Addition of 100 µg/ml ranibizumab restored plasma membrane localization of occludin and claudin-1 within 24 h. Only for claudin-1, variation of total protein expression corresponded with observed effects of VEGF165 and ranibizumab. Changes in the phosphorylation pattern of occludin were observed after treatment of iBREC with VEGF165 for 1 h, but not after 3 days.
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