Sigma receptor 1 modulates endoplasmic reticulum stress in retinal neurons.
OBJECTIVE
To investigate the mechanism of σ receptor 1 (σR1) neuroprotection in retinal neurons.


METHODS
Oxidative stress, which is implicated in diabetic retinopathy, was induced in mouse primary ganglion cells (GCs) and RGC-5 cells, and the effect of the σR1 ligand (+)-pentazocine on pro- and anti-apoptotic and endoplasmic reticulum (ER) stress gene expression was examined. Binding of σR1 to BiP, an ER chaperone protein, and σR1 phosphorylation status were examined by immunoprecipitation. Retinas were harvested from Ins2Akita/+ diabetic mice treated with (+)-pentazocine, and the expression of ER stress genes and of the retinal transcriptome was evaluated.


RESULTS
Oxidative stress induced the death of primary GCs and RGC-5 cells. The effect was decreased by the application of (+)-pentazocine. Stress increased σR1 binding to BiP and enhanced σR1 phosphorylation in RGC-5 cells. BiP binding was prevented, and σR1 phosphorylation decreased in the presence of (+)-pentazocine. The ER stress proteins PERK, ATF4, ATF6, IRE1α, and CHOP were upregulated in RGC-5 cells during oxidative stress, but decreased in the presence of (+)-pentazocine. A similar phenomenon was observed in retinas of Ins2Akita/+ diabetic mice. Retinal transcriptome analysis of Ins2Akita/+ mice compared with wild-type revealed differential expression of the genes critically involved in oxidative stress, differentiation, and cell death. The expression profile of those genes was reversed when the Ins2Akita/+ mice were treated with (+)-pentazocine.


CONCLUSIONS
In retinal neurons, the molecular chaperone σR1 binds BiP under stressful conditions; (+)-pentazocine may exert its effects by dissociating σR1 from BiP. As stress in retinal cells increases, phosphorylation of σR1 is increased, which is attenuated when agonists bind to the receptor.
Ha
Yonju
Y
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912-2000, USA.
Dun
Ying
Y
Thangaraju
Muthusamy
M
Duplantier
Jennifer
J
Dong
Zheng
Z
Liu
Kebin
K
Ganapathy
Vadivel
V
Smith
Sylvia B
SB
D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism; D051702:Activating Transcription Factor 6 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002460:Cell Line; D003930:Diabetic Retinopathy / Q000188:drug therapy / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004722:Endoribonucleases / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006360:Heat-Shock Proteins / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D051379:Mice; D008810:Mice, Inbred C57BL; D046228:Microarray Analysis; D008856:Microscopy, Fluorescence; D018384:Oxidative Stress; D010423:Pentazocine / Q000494:pharmacology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017480:Receptors, sigma / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism; D000097605:Sigma-1 Receptor
D051701:Activating Transcription Factor 4; D051702:Activating Transcription Factor 6; D000091342:Endoplasmic Reticulum Chaperone BiP; D004722:Endoribonucleases; D006360:Heat-Shock Proteins; D010423:Pentazocine; D017346:Protein Serine-Threonine Kinases; D017480:Receptors, sigma; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; D000097605:Sigma-1 Receptor; C081452:Atf4 protein, mouse; C497112:Atf6 protein, mouse; C497250:Ddit3 protein, mouse; C510185:Ern1 protein, mouse
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