COMPARISON OF TIGHT JUNCTION PERMEABILITY FOR ALBUMIN IN IRIS PIGMENT-EPITHELIUM AND RETINAL-PIGMENT EPITHELIUM IN-VITRO

Background: The degenerative retinal diseases are one of the major cau ses of visual loss in the western world. Although heterologous RPE tra nsplants rescue the photoreceptors in the dystrophic rat model, reject ion remains a major limiting factor. Given the common embryonic origin , iris pigment epithelial (IPE) cells might be able to take over the f unctions of retinal pigment epithelial (RPE) cells, serving as an auto logous graft for transplantation and thereby preventing rejection. One of the main functions of RPE cells is the generation of tight junctio ns which form the outer blood-retinal barrier. In this study we compar ed the tight junction permeabilities of IPE and RPE cells isolated fro m Long Evans rats by measuring their albumin clearances. Methods: IPE and RPE cells were cultured on semipermeable filter supports with and without the addition of 0.02% ethylenediaminetetraacetic acid (EDTA). At selected intervals, the albumin clearances of the IPE and RPE cells were measured spectrophotometrically and compared. The morphology of the cells was compared using electron microscopy and fluorescent label ing. Results: IPE and RPE cells both restricted the passage of albumin in vitro. After the modulation of tight junctions with 0.02% EDTA, th e clearance increased in both types of cells in a similar fashion. The morphology of tight junctions was visualized with electron microscopy . Conclusion: These results indicate that the functional barrier for m acromolecules is similar in IPE and RPE cells in vitro. This raises th e possibility that IPE cells would form tight junctions in the subreti nal space, thereby substituting for the blood-retinal barrier normally formed by RPE cells.