Bis-Retinoid A2E Induces an Increase of Basic Fibroblast Growth Factor via Inhibition of Extracellular Signal-Regulated Kinases 1/2 Pathway in Retinal Pigment Epithelium Cells and Facilitates Phagocytosis.

Delphine Balmer,Linda Bapst-Wicht,Natacha Nanchen,Raphael Roduit,Christian G Bochet,Aswin Pyakurel,Martine Emery

doi:10.3389/fnagi.2017.00043

Abstract

Age-related macular degeneration (ARMD) is the leading cause of vision loss in developed countries. Hallmarks of the disease are well known; indeed, this pathology is characterized by lipofuscin accumulation, is principally composed of lipid-containing residues of lysosomal digestion. The N-retinyl-N-retinylidene ethanolamine (A2E) retinoid which is thought to be a cytotoxic component for RPE is the best-characterized component of lipofuscin so far. Even if no direct correlation between A2E spatial distribution and lipofuscin fluorescence has been established in aged human RPE, modified forms or metabolites of A2E could be involved in ARMD pathology. Mitogen-activated protein kinase (MAPK) pathways have been involved in many pathologies, but not in ARMD. Therefore, we wanted to analyze the effects of A2E on MAPKs in polarized ARPE19 and isolated mouse RPE cells. We showed that long-term exposure of polarized ARPE19 cells to low A2E dose induces a strong decrease of the extracellular signal-regulated kinases' (ERK1/2) activity. In addition, we showed that A2E, via ERK1/2 decrease, induces a significant decrease of the retinal pigment epithelium-specific protein 65 kDa (RPE65) expression in ARPE19 cells and isolated mouse RPE. In the meantime, we showed that the decrease of ERK1/2 activity mediates an increase of basic fibroblast growth factor (bFGF) mRNA expression and secretion that induces an increase in phagocytosis via a paracrine effect. We suggest that the accumulation of deposits coming from outer segments (OS) could be explained by both an increase of bFGF-induced phagocytosis and by the decrease of clearance by A2E. The bFGF angiogenic protein may therefore be an attractive target to treat ARMD.

Highlights

Age-related macular degeneration (ARMD) is the most significant cause of blindness in individuals over 50 years of age
No significant difference was observed for p38, and JNKp46/54 activities, whereas ERK1/2 activity is increased 2-fold when ARPE19 cells are cultured on transwell filters (Figure 1B)
Accepted by the scientific community working on retinal pigment epithelium (RPE), the polarization of ARPE19 cells when cultured on filters is essential to preserve the function and gene expression of these cells

Summary

Introduction

ARMD is the most significant cause of blindness in individuals over 50 years of age This pathology is defined by the presence of drusens, hyper- and hypo-pigmentation of retinal pigment epithelium (RPE) cells, RPE and photoreceptor apoptosis and choroidal neovascularization (CNV). The dry form is characterized by the formation of drusen (extracellular debris and deposits) between the RPE cells and Bruch’s membrane. This accumulation is toxic for RPE cells, which serve metabolic and supportive functions that are vital for retinal photoreceptors (Fine et al, 2000). A2E inhibits retinoid isomerohydrolase activity by direct interaction with the retinal pigment epithelium-specific protein 65 kDa (RPE65), a key protein in the visual cycle (Moiseyev et al, 2010)

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Conclusion