Estrogen, via ESR2 receptor, prevents oxidative stress-induced Müller cell death and stimulates FGF2 production independently of NRF2, attenuating retinal degeneration

Abstract

In this study, we aimed to investigate the effects of the deficient antioxidative gene, nuclear factor-erythroid 2-related factor 2 (Nrf2), on 17β-estradiol (E₂)-mediated oxidative stress response, with a specific focus on growth factor production and cell death in Müller cells and retinal tissue. Administration of hydrogen peroxide (H₂O₂) reduced the viability of Müller cells derived from Nrf2 wild-type (WT) and knockout (KO) mice. However, this effect was more significant in the KO cells than in the WT cells. Pretreatment with E₂ inhibited H₂O₂-induced cell death in both Nrf2 WT and KO Müller cell genotypes. Small interfering RNA-mediated gene silencing of estrogen receptor 2 (Esr2) attenuated the cell survival-promoting activity of E₂ in Nrf2 KO Müller cells, while other identified estrogen receptors, Esr1 or G protein-coupled estrogen receptor 1 (Gper1), had no effect. Western blotting revealed higher ESR2 expression levels in Nrf2 KO cells than in WT Müller cells. Conditioned media from E₂-and H₂O₂-treated Nrf2 WT or KO Müller cells enhanced the dissociated retinal cell viability compared with H₂O₂-treated cells. Both quantitative reverse-transcription polymerase chain reaction assay (qRT-PCR) and enzyme-linked immunosorbent assay exhibited a significant increase in fibroblast growth factor 2 (FGF2) expression levels in E₂-and H₂O₂-treated Nrf2 WT and KO Müller cells compared to those in E₂-treated cells. In vivo, administration of N-methyl-N-nitrosourea (MNU) reduced the thickness and cell density of the outer nuclear layer (ONL) in Nrf2 KO mice and enhanced the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells in the ONL. However, E₂ administration attenuated these defects in MNU-treated mice. Concomitant administration of MNU and E₂ enhanced FGF2 protein levels in retinal lysates of Nrf2 KO mice. In conclusion, E₂ demonstrated a significant role in preventing oxidative stress-induced retinal cell death by stimulating FGF2 production in Müller cells, independent of the Nrf2 gene. Based on these findings, we anticipate that exogenous administration of estrogens or ESR2-selective agonists could aid in treating patients with oxidative stress-related retinal degenerative diseases such as age-related macular degeneration and retinitis pigmentosa.