Pigment epithelium-derived factor protects retinal pigment epithelium from oxidant-mediated barrier dysfunction

Retinal pigment epithelium (RPE) cells form a monolayer at the blood–retina barrier between the retina and choriocapillaries. The barrier function may be damaged by multiple stresses to the cell, including the repeated exposure to oxidants that are generated by photoreceptor cell turnover. The purpose of our study was to document the protective effect of pigment epithelium-derived factor (PEDF), a tropic factor produced by the RPE, on H2O2-induced RPE barrier dysfunction. When assayed by a FITC-labeled dextran transepithelial flux, the increased permeability of the RPE barrier (induced by H2O2) was prevented by PEDF pretreatment. To further explore the mechanism leading to this permeability change, we investigated the distribution of cytoskeleton and junctional proteins. The redistribution of the two junctional proteins occludin, and N-cadherin and actin reorganization in RPE, induced by H2O2, can be prevented by PEDF pretreatment. PEDF can also prevent H2O2-induced stress kinase p38/27-kDa heat shock protein signaling which is known to mediate actin rearrangement. These findings indicated that PEDF can stabilize actin, maintain normal membrane occludin and N-cadherin structure, and preserve the barrier function of RPE cells against oxidative stress.