Sublytic membrane-attack-complex activation and VEGF secretion in retinal pigment epithelial cells

Abstract

Uncontrolled activation of the alternative complement pathway and secretion of vascular endothelial growth factor (VEGF) are thought to be associated with age-related macular degeneration (AMD). Previously, we have shown that in RPE monolayers, oxidative stress induced by H 2O 2 exposure reduced complement inhibition on the cell surface. The resulting increased level of sublytic complement activation resulted in VEGF release, which disrupted the barrier facility of these cells as determined by transepithelial resistance (TER) measurements. Here, we have asked whether other environmental factors known to be associated with AMD, such as A2E, iron, and smoking, similarly sensitize the RPE to complement attack. Exposure of RPE monolayers with stable TER to A2E, ferric ammonium citrate (FAC), and smoke-extract at pathological concentrations resulted in significant increase in oxidative stress as determined by reactive oxygen species and superoxide measurements. However, an additional challenge with normal human serum only resulted in a decrease in TER in H 2O 2-exposed cells as reported previously, whereas A2E-, FAC-, and smoke-extract-treated cells were unaffected. Effects on TER were directly correlated with the release of VEGF. Taken together, identifying which AMD-associated stimuli result in sublytic MAC induction of VEGF secretion might offer novel opportunities to selectively inhibit pathological VEGF release. © 2012 Springer Science+Business Media, LLC.