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Wang J.,Georgia Regents University | Wang J.,James and Jean Culver Vision Discovery Institute | Shanmugam A.,Georgia Regents University | Shanmugam A.,James and Jean Culver Vision Discovery Institute | And 7 more authors.
Free Radical Biology and Medicine | Year: 2015

Abstract Oxidative stress figures prominently in retinal diseases, including diabetic retinopathy, and glaucoma. Ligands for σ1R, a unique transmembrane protein localized to the endoplasmic reticulum, mitochondria, and nuclear and plasma membranes, have profound retinal neuroprotective properties in vitro and in vivo. Studies to determine the mechanism of σ1R-mediated retinal neuroprotection have focused mainly on neurons. Little is known about the effects of σ1R on Müller cell function, yet these radial glial cells are essential for homeostatic support of the retina. Here we investigated whether σ1R mediates the oxidative stress response of Müller cells using wild-type (WT) and σ1R-knockout (σ1RKO) mice. We observed increased endogenous reactive oxygen species (ROS) levels in σ1RKO Müller cells compared to WT, which was accompanied by decreased expression of Sod1, catalase, Nqo1, Hmox1, Gstm6, and Gpx1. The protein levels of SOD1, CAT, NQO1, and GPX1 were also significantly decreased. The genes encoding these antioxidants contain an antioxidant response element (ARE), which under stress is activated by NRF2, a transcription factor that typically resides in the cytoplasm bound by KEAP1. In the σ1RKO Müller cells Nrf2 expression was decreased significantly at the gene (and protein) level, whereas Keap1 gene (and protein) levels were markedly increased. NRF2-ARE binding affinity was decreased markedly in σ1RKO Müller cells. We investigated system xc-, the cystine-glutamate exchanger important for synthesis of glutathione (GSH), and observed decreased function in σ1RKO Müller cells compared to WT as well as decreased GSH and GSH/GSSG ratios. This was accompanied by decreased gene and protein levels of xCT, the unique component of system xc-. We conclude that Müller glial cells lacking σ1R manifest elevated ROS, perturbation of antioxidant balance, suppression of NRF2 signaling, and impaired function of system xc-. The data suggest that the oxidative stress-mediating function of retinal Müller glial cells may be compromised in the absence of σ1R. The neuroprotective role of σ1R may be linked directly to the oxidative stress-mediating properties of supportive glial cells. © 2015 Elsevier Inc.

Zhao J.,James and Jean Culver Vision Discovery Institute | Zhao J.,Georgia Regents University | Mysona B.A.,James and Jean Culver Vision Discovery Institute | Mysona B.A.,Georgia Regents University | And 11 more authors.
Investigative Ophthalmology and Visual Science | Year: 2016

PURPOSE. To evaluate, in vivo, the effects of the sigma-1 receptor (σR1) agonist, (+)- pentazocine, on N-methyl-D-aspartate (NMDA)-mediated retinal excitotoxicity. METHODS. Intravitreal NMDA injections were performed in C57BL/6J mice (wild type [WT]) and σR1-/- (σR1 knockout [KO]) mice. Fellow eyes were injected with phosphate-buffered saline (PBS). An experimental cohort of WT and σR1 KO mice was administered (+)- pentazocine by intraperitoneal injection, and untreated animals served as controls. Retinas derived from mice were flat-mounted and labeled for retinal ganglion cells (RGCs). The number of RGCs was compared between NMDA and PBS-injected eyes for all groups. Apoptosis was assessed using TUNEL assay. Levels of extracellular-signal–regulated kinases (ERK1/2) were analyzed by Western blot. RESULTS. N-methyl-D-aspartate induced a significant increase in TUNEL-positive nuclei and a dose-dependent loss of RGCs. Mice deficient in σR1 showed greater RGC loss (≈80%) than WT animals (≈50%). (+)-Pentazocine treatment promoted neuronal survival, and this effect was prevented by deletion of σR1. (+)-Pentazocine treatment resulted in enhanced activation of ERK at the 6-hour time point following NMDA injection. The (+)-pentazocine–induced ERK activation was diminished in σR1 KO mice. CONCLUSIONS. Targeting σR1 activation prevented RGC death while enhancing activation of the mitogen-activated protein kinase (MAPK), ERK1/2. Sigma-1 receptor is a promising therapeutic target for retinal neurodegenerative diseases. © 2016, Association for Research in Vision and Ophthalmology Inc. All rights reserved.

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