Complement System Dysregulation and Inflammation in the Retinal Pigment Epithelium of a Mouse Model for Stargardt Macular Degeneration

Roxana A Radu,Jane Hu,Quan Yuan,Darcy L Welch,Jacob Makshanoff,Marcia Lloyd,Stephen Mcmullen,Gabriel H Travis,Dean Bok

doi:10.1074/jbc.m110.191866

Abstract

Accumulation of vitamin A-derived lipofuscin fluorophores in the retinal pigment epithelium (RPE) is a pathologic feature of recessive Stargardt macular dystrophy, a blinding disease caused by dysfunction or loss of the ABCA4 transporter in rods and cones. Age-related macular degeneration, a prevalent blinding disease of the elderly, is strongly associated with mutations in the genes for complement regulatory proteins (CRP), causing chronic inflammation of the RPE. Here we explore the possible relationship between lipofuscin accumulation and complement activation in vivo. Using the abca4(-/-) mouse model for recessive Stargardt, we investigated the role of lipofuscin fluorophores (A2E-lipofuscin) on oxidative stress and complement activation. We observed higher expression of oxidative-stress genes and elevated products of lipid peroxidation in eyes from abca4(-/-) versus wild-type mice. We also observed higher levels of complement-activation products in abca4(-/-) RPE cells. Unexpectedly, expression of multiple CRPs, which protect cells from attack by the complement system, were lower in abca4(-/-) versus wild-type RPE. To test whether acute exposure of healthy RPE cells to A2E-lipofuscin affects oxidative stress and expression of CRPs, we fed cultured fetal-derived human RPE cells with rod outer segments from wild-type or abca4(-/-) retinas. In contrast to RPE cells in abca4(-/-) mice, human RPE cells exposed to abca4(-/-) rod outer segments adaptively increased expression of both oxidative-stress and CRP genes. These results suggest that A2E accumulation causes oxidative stress, complement activation, and down-regulation of protective CRP in the Stargardt mouse model. Thus, Stargardt disease and age-related macular degeneration may both be caused by chronic inflammation of the RPE.

Highlights

Age-related macular degeneration (AMD)5 is the leading cause of severe vision loss in the elderly
Using the abca4؊/؊ mouse model for recessive Stargardt, we investigated the role of lipofuscin fluorophores (A2E-lipofuscin) on oxidative stress and complement activation
Using the albino abca4Ϫ/Ϫ mouse as a model, we show that accumulation of lipofuscin fluorophores is associated with increased oxidative stress and complement activation in vivo

Summary

Introduction

Age-related macular degeneration (AMD) is the leading cause of severe vision loss in the elderly. In AMD, complement system dysregulation due to CRP dysfunction results in chronic inflammation of the retinal pigment epithelium (RPE) [13] This cell monolayer is critical for sustained viability of the adjacent photoreceptors. A pathological hallmark of AMD is the formation of extracellular deposits called drusen within Bruch’s membrane, beneath the RPE [14] Another etiologic feature of AMD is oxidative damage [15]. Using the albino abca4Ϫ/Ϫ mouse as a model, we show that accumulation of lipofuscin fluorophores is associated with increased oxidative stress and complement activation in vivo. These observations suggest that chronic inflammation of the RPE due to local activation of complement represents a common etiologic feature of AMD and Stargardt disease

Methods

Results

Conclusion