Sigma-1 Receptor Regulates Mitochondrial Function in Glucose- and Oxygen-Deprived Retinal Ganglion Cells

PURPOSE. Understanding the role of mitochondria in retinal ganglion cells (RGCs) is relevant to human disease as studies have shown mitochondrial abnormalities in primary open-angle glaucoma patients. This study seeks to determine the effects of the sigma-1 receptor (sigma-1r) and its agonists on mitochondrial function in oxygen-and glucose-deprived (OGD) purified neonatal RGCs. METHODS. Retinal ganglion cells were isolated from rat pups and subjected to OGD in varying conditions in the presence or absence of sigma-1r agonist and antagonist and following addition of an AAV2-sigma-1r vector that was used to increase sigma-1r expression. Western blots and immunofluorescence microscopy validated findings. Mitochondrial function was determined by measuring mitochondrial membrane potential (Delta psi(m)) using the dye, fluorescence tetraethylbenzimidazolylcarbocyanineiodide (JC-1), and determination of cytochrome c oxidase activity using a cytochrome c oxidase assay kit. Caspase 3 and 7 activities were also measured using a luminescent assay kit. RESULTS. Oxygen and glucose deprivation in RGCs resulted in decreased mitochondrial membrane potential and cytochrome c oxidase activity when compared with normoxic RGCs. sigma-1r agonists or overexpression of the sigma-1r restored the mitochondrial membrane potential comparable to normoxic conditions, while sigma-1r antagonists abolished these effects. Oxygen and glucose depreavtation induced decreases in cytochrome c activity were partially restored by overexpression or activation of sigma-1r. Caspase activity was increased in response to OGD and was decreased by the addition of sigma-1r agonist, pentazocine, and following sigma-1r overexpression. CONCLUSIONS. These data suggest that activation and/or overexpression of sigma-1r restores RGCs mitochondrial function following OGD and that mitochondrial function is vital to the function of RGCs.