Sigma 1 receptor regulates the oxidative stress response in primary retinal Müller glial cells via NRF2 signaling and system xc(-), the Na(+)-independent glutamate-cystine exchanger.
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.
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912-2000, USA; James and Jean Culver Vision Discovery Institute, Augusta, GA 30912-2000, USA.
Jing
J
Wang
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912-2000, USA; James and Jean Culver Vision Discovery Institute, Augusta, GA 30912-2000, USA.
Arul
A
Shanmugam
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912-2000, USA; James and Jean Culver Vision Discovery Institute, Augusta, GA 30912-2000, USA.
Shanu
S
Markand
Harold L. Dorris Neurological Research Institute, The Scripps Research Institute, La Jolla, CA 92037, USA.
Eric
E
Zorrilla
James and Jean Culver Vision Discovery Institute, Augusta, GA 30912-2000, USA; Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2000, USA.
Vadivel
V
Ganapathy
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912-2000, USA; James and Jean Culver Vision Discovery Institute, Augusta, GA 30912-2000, USA; Department of Ophthalmology, Medical College of Georgia, Georgia Regents University, Augusta, GA 30912-2000, USA. Electronic address: sbsmith@gru.edu.
Sylvia B
SB
Smith
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D027182:Amino Acid Transport System y+ / Q000378:metabolism*; D000818:Animals; D061745:Antioxidant Response Elements; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism; D063928:Ependymoglial Cells / Q000378:metabolism*; D005260:Female; D005978:Glutathione / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D018384:Oxidative Stress; D061251:Primary Cell Culture; D017382:Reactive Oxygen Species / Q000378:metabolism; D017480:Receptors, sigma / Q000502:physiology*; D015398:Signal Transduction; D015533:Transcriptional Activation; D000097605:Sigma-1 Receptor
D048868:Adaptor Proteins, Signal Transducing; D027182:Amino Acid Transport System y+; D003598:Cytoskeletal Proteins; D005978:Glutathione; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; D017382:Reactive Oxygen Species; D017480:Receptors, sigma; D000097605:Sigma-1 Receptor; C117301:Keap1 protein, mouse; C495636:Nfe2l2 protein, mouse; C492255:Slc7a11 protein, mouse
Free radicals; Mouse; Nrf2; Retina; Retinal Müller glial cells; Sigma 1 receptor; System x(c)(−); xCT