RETINAL-PIGMENT EPITHELIAL-CELLS FROM DYSTROPHIC RATS FORM NORMAL TIGHT JUNCTIONS IN-VITRO

Purpose. In the genetically defective Royal College of Surgeons (RCS) rat model for retinal degeneration, a breakdown occurs in the retinal pigment epithelial (RPE) cell tight junctions just as the photorecepto rs begin to degenerate. These experiments sought to determine the impa ct of the RPE genetic defect on this alteration in the RPE cell tight junctions. Methods. Retinal pigment epithelial cell cultures prepared from RCS and control rats were treated with hormonally defined medium (HDM), base medium conditioned by RCS or control retinas, or unconditi oned base medium. The tight junctions formed by these cultures were as sayed functionally by measuring transepithelial electrical resistance and permeability. Junction structure was evaluated by immunolocalizati on of the tight junction protein zonula occludens 1 and of the junctio n-associated actin microfilaments. Results. Retinal pigment epithelial cultures from dystrophic rats formed structurally and functionally no rmal tight junctions when maintained in hormonally defined medium. The junctions remained stable when the medium bathing the apical surface was switched to base medium preconditioned by normal retinas. In contr ast, cultures treated with medium preconditioned by degenerating dystr ophic retinas or with unconditioned medium exhibited a breakdown in th eir tight junctions. Conclusions. Retinal pigment epithelial cells iso lated from dystrophic RCS rats can form tight junctions normally in vi tro. Normal, but not dystrophic, retinas release factors that support RPE tight junctions. Therefore, the junctional abnormality seen in dys trophic rat RPE cells in vivo is probably caused by the loss of trophi c factors normally provided by the healthy neural retina rather than b y a direct effect of the genetic defect on the tight junctions.