PARTIAL CHARACTERIZATION OF THE HUMAN RETINAL ENDOTHELIAL-CELL TIGHT AND ADHERENS JUNCTION COMPLEXES

PURPOSE. In diabetic retinopathy and macular edema, the blood-retinal barrier fails to function properly, and there is transvascular leakage of proteins and solutes. The tight junction protein occludin and the adherens junction protein cadherin-5 have been shown to be critical to maintaining the endothelial barrier and regulating paracellular trans port of large vessel endothelia. However, the expression and distribut ion of these junc tion proteins in the retinal endothelium is not well characterized. METHODS. Human and bovine retinal endothelial cells we re isolated as described previously. Western blot analysis and now cyt ometry techniques were used to assay for the presence of occludin, zon ula occludens-1 (ZO-1), cadherin-5, and beta-catenin. The subcellular localization of the proteins was visualized by immunohistochemistry pe rformed on cultured human retinal endothelial cells and cryosections o f bovine retina. RESULTS. Western blot analysis and flow cytometry tec hniques found occludin, ZO-1, cadherin-5, and beta-catenin in cultured human retinal endothelial cells. Immunofluorescence staining of cultu red retinal endothelial cells and cryosections of bovine retina showed junctional localization of occludin, ZO-1, cadherin-5, and beta-caten in. CONCLUSIONS. This report demonstrates the expression of occludin a nd cadherin-5 in retinal endothelial cells and their localization to s ites of cell-cell contact. Expression of their respective regulatory p roteins, ZO-1 and beta-catenin, at sites of cell-cell contact suggests that occludin and cadherin-5 play a role in maintaining the retinal e ndothelial barrier.