A novel AhR ligand, 2AI, protects the retina from environmental stress.

Mark A Gutierrez,Shaun Mooney,Thelma Y Garcia,Arvind Ramanathan,Sonnet S Davis,Andrew Rosko,Samiha Mateen,Deepak A Lamba,Troy D Hubbard,Gary H Perdew,Kylie P Mitchell,Steven M Nguyen,Joana Neves

doi:10.1038/srep29025

Abstract

Various retinal degenerative diseases including dry and neovascular age-related macular degeneration (AMD), retinitis pigmentosa, and diabetic retinopathy are associated with the degeneration of the retinal pigmented epithelial (RPE) layer of the retina. This consequently results in the death of rod and cone photoreceptors that they support, structurally and functionally leading to legal or complete blindness. Therefore, developing therapeutic strategies to preserve cellular homeostasis in the RPE would be a favorable asset in the clinic. The aryl hydrocarbon receptor (AhR) is a conserved, environmental ligand-dependent, per ARNT-sim (PAS) domain containing bHLH transcription factor that mediates adaptive response to stress via its downstream transcriptional targets. Using in silico, in vitro and in vivo assays, we identified 2,2′-aminophenyl indole (2AI) as a potent synthetic ligand of AhR that protects RPE cells in vitro from lipid peroxidation cytotoxicity mediated by 4-hydroxynonenal (4HNE) as well as the retina in vivo from light-damage. Additionally, metabolic characterization of this molecule by LC-MS suggests that 2AI alters the lipid metabolism of RPE cells, enhancing the intracellular levels of palmitoleic acid. Finally, we show that, as a downstream effector of 2AI-mediated AhR activation, palmitoleic acid protects RPE cells from 4HNE-mediated stress, and light mediated retinal degeneration in mice.

Highlights

Retinal pigmented epithelium (RPE) cells are important for maintaining intercellular homeostasis in the retina
Knock-out of aryl hydrocarbon receptor (AhR) in mice leads to progressive retinal degeneration[9] and in human retinas, there is a progressive decline in AhR signaling without a measurable change in AhR abundance[9]
Following exposure to light conditions which lead to photoreceptor apoptosis in the Balb/C mice (Fig. S1A), there is a change in the localization of AhR in the photoreceptor cells (Fig. 1D–D’) with a concomitant increase in the photoreceptor segments while the retinal pigmented epithelial (RPE) layer still expressed high-levels of AhR which was localized in the nuclei while the inner retina expression is unchanged (Fig. 1D–D”)

Summary

Introduction

Retinal pigmented epithelium (RPE) cells are important for maintaining intercellular homeostasis in the retina. One of the more significantly noted features of the RPE is the capacity to phagocytose and metabolize outer segments that are shed by the light-sensitive rod and cone photoreceptors[3,4] Dysregulation of this function has a potential to play a role in the degeneration of the retina[5]. Developing strategies to maintain the function and cellular homeostasis of the RPE is a significant point of investigation with regards to preventing retinal degeneration in humans. In this context, the Aryl hydrocarbon receptor (AhR) has been implicated to play a role in maintaining retinal homeostasis[8,9]. We identified the omega-7 monounsaturated fatty acid commonly known as palmitoleic acid, as a downstream effector of 2AI, which we show to be protective against 4HNE treatment in human RPE cells and light-mediated toxicity in the murine retina

Methods

Results

Conclusion