sigma-1 receptors protect RGC-5 cells from apoptosis by regulating intracellular calcium, Bax levels, and caspase-3 activation.
OBJECTIVE
sigma-1 Receptor ligands prevent neuronal death associated with glutamate excitotoxicity both in vitro and in vivo. However, the molecular mechanism of the neuroprotective effect remains to be elucidated. The present study was undertaken to determine whether sigma-1 receptor agonists provide neuroprotection by decreasing glutamate-induced calcium mobilization and preventing apoptotic gene expression.


METHODS
Cell death was measured by using a calcein-AM/propidium iodide cell-survival assay. Western blot analysis determined the expression levels of Bax in normal RGC-5 cells. Caspase-3 activation after glutamate treatment was determined with a carboxyfluorescein caspase-3 detection kit. Glutamate-induced intracellular calcium mobilization was measured by using ratiometric calcium imaging.


RESULTS
sigma-1 Receptor-overexpressing RGC-5 (RGC-5-S1R) cells had lower glutamate-induced intracellular calcium mobilization than did normal RGC-5 cells, and the sigma-1 receptor ligand (+)-SKF10047 reduced the glutamate calcium response in normal and RGC-5-S1R cells. (+)-SKF10047 protected RGC-5 cells from glutamate-induced cell death, and the RGC-5-S1R cells showed a significant resistance to glutamate-induced apoptosis compared with the control RGC-5 cells. BD1047, a sigma-1 receptor antagonist, blocked the protective effect of (+)-SKF10047. Western blot analysis showed that (+)-SKF10047 inhibited the increase in Bax after glutamate treatments. Glutamate-mediated cell death involved activation of caspase-3, and sigma-1 receptor activation prevented an increase in caspase-3 expression.


CONCLUSIONS
The results suggest that sigma-1 receptors regulate intracellular calcium levels and prevent activation of proapoptotic genes, thus promoting retinal ganglion cell survival. The sigma-1 ligands appear to be neuroprotective and are a potential target for neuroprotective therapeutics.
Tchedre
Kissaou T
KT
University of North Texas Health Science Center, Department of Biomedical Sciences, Fort Worth, Texas 76107, USA.
Yorio
Thomas
T
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology; D019610:Cytoprotection; D004789:Enzyme Activation; D005029:Ethylenediamines / Q000494:pharmacology; D005260:Female; D005452:Fluoresceins / Q000378:metabolism; D018698:Glutamic Acid / Q000633:toxicity; D008297:Male; D008856:Microscopy, Fluorescence; D010620:Phenazocine / Q000031:analogs & derivatives / Q000494:pharmacology; D011419:Propidium / Q000378:metabolism; D051381:Rats; D011921:Rats, Inbred WKY; D017480:Receptors, sigma / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D014162:Transfection; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein / Q000378:metabolism*; D000097605:Sigma-1 Receptor
D002118:Calcium; D053148:Caspase 3; D005029:Ethylenediamines; D005452:Fluoresceins; D018698:Glutamic Acid; D010620:Phenazocine; D011419:Propidium; D017480:Receptors, sigma; D051028:bcl-2-Associated X Protein; D000097605:Sigma-1 Receptor; C494828:Bax protein, rat; C085925:calcein AM; C097963:N-(2-(3,4-Dichlorphenyl)ethyl)-N,N',N'-trimethyl-1,2-ethandiamin; C012134:SK&F 10047