Selenomethionine (Se-Met) Induces the Cystine/Glutamate Exchanger SLC7A11 in Cultured Human Retinal Pigment Epithelial (RPE) Cells: Implications for Antioxidant Therapy in Aging Retina.

Sudha Ananth,Manuela Bartoli,Vadivel Ganapathy,Muthusamy Thangaraju,Seiji Miyauchi,Pamela M Martin,Ravirajsinh N Jadeja

doi:10.3390/antiox10010009

Abstract

Oxidative damage has been identified as a major causative factor in degenerative diseases of the retina; retinal pigment epithelial (RPE) cells are at high risk. Hence, identifying novel strategies for increasing the antioxidant capacity of RPE cells, the purpose of this study, is important. Specifically, we evaluated the influence of selenium in the form of selenomethionine (Se-Met) in cultured RPE cells on system xc- expression and functional activity and on cellular levels of glutathione, a major cellular antioxidant. ARPE-19 and mouse RPE cells were cultured with and without selenomethionine (Se-Met), the principal form of selenium in the diet. Promoter activity assay, uptake assay, RT-PCR, northern and western blots, and immunofluorescence were used to analyze the expression of xc-, Nrf2, and its target genes. Se-Met activated Nrf2 and induced the expression and function of xc- in RPE. Other target genes of Nrf2 were also induced. System xc- consists of two subunits, and Se-Met induced the subunit responsible for transport activity (SLC7A11). Selenocysteine also induced xc- but with less potency. The effect of Se-met on xc- was associated with an increase in maximal velocity and an increase in substrate affinity. Se-Met increased the cellular levels of glutathione in the control, an oxidatively stressed RPE. The Se-Met effect was selective; under identical conditions, taurine transport was not affected and Na+-coupled glutamate transport was inhibited. This study demonstrates that Se-Met enhances the antioxidant capacity of RPE by inducing the transporter xc- with a consequent increase in glutathione.

Highlights

Previous studies have demonstrated the natural antioxidant properties of selenium-containing compounds, a property thought to be related primarily to their incorporation into selenoproteins like the glutathione peroxidases (GPXs) and thioredoxin reductases (TXNRDs) [15,16]; our present findings provide a novel additional mechanism to explain the antioxidant feature of these compounds
We evaluated the expression of a number of other well-known Nrf2 target genes and/or selenoproteins including glutamate-cysteine ligase catalytic subunit (GCLC), glutamate-cysteine ligase regulatory subunit (GCLM), heme oxygenase 1 (HO-1), glutathione S-transferase A1 (GSTA1), glutathione S-transferase A2 (GSTA2), glutathione peroxidase 1 (GPX1), thioredoxin reductase (TXNRD), and NAD(P)H oxidase/quinone 1 (NQO1) (Figure 1D)
The current study demonstrates that selenomethionine, the major form of dietary selenium in humans, protects retinal pigment epithelial (RPE) cells from pro-oxidant injury via a multimodal Nrf2related mechanism

Summary

Introduction

Oxidative damage has been identified as a major causative factor in degenerative diseases of the retina; retinal pigment epithelial (RPE) cells are at high risk. We evaluated the influence of selenium in the form of selenomethionine (Se-Met) in cultured RPE cells on system xc- expression and functional activity and on cellular levels of glutathione, a major cellular antioxidant. Se-Met activated Nrf and induced the expression and function of xcin RPE. This study demonstrates that Se-Met enhances the antioxidant capacity of RPE by inducing the transporter xcwith a consequent increase in glutathione. The repertoire of clinical and experimental studies implicating oxidative stress as a principal causative factor and retinal pigment epithelium (RPE) as a primary site of pathology in the disease is quite large and steadily expanding [1,2,3,4].

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Conclusion