PEDF Inhibits VEGF-E Induced Permeability of RPE Cells

Abstract

Purpose:: The healthy retinal pigment epithelium (RPE) forms part of the blood-retinal barrier. However, after eye surgery, injury, or in disease, RPE permeability can increase, leading to subretinal fluid accumulation and reduced visual acuity. This project investigated the mutual roles of pigment-epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) in the maintenance of RPE permeability.

Methods:: Trans-epithelial resistance measurements were utilized to characterize the barrier function of monolayer cultured ARPE-19 and primary porcine RPE cells grown in transwell plates. Cells were treated with 0.05 to 500 ng/mL VEGF-E or PlGF in the absence or presence of 0.005 to 5 ng/mL PEDF. VEGF-E, PlGF, and PEDF were administered either apically or basolaterally. In addition, confluent monolayers were pretreated with 0.5 ng/mL DAPT, a γ-secretase inhibitor, to determine if PEDF responses involved the actions of γ-secretase.

Results:: Apically-administered VEGF-E increases RPE permeability in a dose-dependent manner with an EC₅₀ of 0.2 ng/mL. PlGF or basolaterally administered VEGF-E did not increase permeability in either the ARPE-19 or the primary porcine RPE cells. Apically-administered PEDF inhibited the 5 ng/mL VEGF-E-induced permeability increase in a dose dependent manner, with an IC₅₀ of 0.03 ng/mL. However, the inhibitory response was reversed by pretreatment with DAPT. Basolaterally-applied PEDF did not inhibit VEGF-E signaling.

Conclusions:: These data provide evidence that apically-oriented VEGFR2 receptors mediate the RPE permeability increase. However, PEDF can prevent the increase in permeability that is induced by VEGF-E through the action of γ-secretase. γ-secretase, which has not been shown before to have a role in PEDF response in RPE cells, also takes part in ß-amyloid production, one of the components of drusen. Therefore, an imbalance in the production and apical secretion of VEGF and PEDF by RPE cells may contribute to the accumulation of subretinal fluid. Moreover, the same mechanism, which maintains the blood-retinal barrier, may also promote the appearance of drusen and the development of age-related macular degeneration.

Keywords: retinal pigment epithelium • edema • inflammation