Sigma-1 Receptor Stimulation Provides Protection Against Oxidative Damage Through Suppression of ER Stress Responses in the Human Lens

Abstract

Purpose: : Sigma-1 receptor binding affinity has been reported to be increased under oxidative stress. Sigma receptors are mainly located on the Endoplasmic Reticulum (ER) membrane and are reported to have regulatory actions on calcium signalling. In the present study we used cells and tissue from the human lens to elucidate the relationship between sigma-1 receptor, ER stress and oxidative stress induced damage.

Methods: : The current study employed whole human lens cultures isolated from donor eyes in conjunction with the human lens cell line FHL124. Cell viability was determined using the MTS assay. Western blot methods were used to assess expression of Sigma-1 receptor and ER stress proteins (Bip, IRE1, ATF6 and pEIF2α). Apoptosis was detected using: western blotting techniques to determine changes in protein expression of pro-Caspase-3 and 12; the TUNEL assay; through detection of LDH release into the bathing medium.

Results: : Exposure of the human lens cell line FHL 124 to increasing doses of H₂0₂ led to reduced cell viability. Moreover, reduction in pro-forms of caspase 12 and 3 were observed in response to H₂O₂. In response to 30 µM H2O2, level of Bip, ATF6, IRE1 and pEIF2α were significantly increased within 4 hours of exposure. Moreover, sigma-1 receptor expression was markedly increased in response to H₂O₂ induced oxidative stress. Application of 10 and 30 µM (+)-pentazocine, a sigma 1 receptor agonist, significantly inhibited the H₂O₂ induce cell death. In addition, the oxidative stress induced reduction of pro-caspase 3 and 12 was suppressed by (+)-pentazocine. Moreover, the induction of ER stress proteins Bip and EIF2a following oxidative insult were also suppressed by (+)-pentazocine. When applied to cultured human lenses, (+)-pentazocine again demonstrated protection against H₂O₂ induced opacity, LDH release and apoptotic cell death.

Conclusions: : Stimulation of the sigma-1 receptor provides significant protection against oxidative damage. This protection is likely to result from a suppression, but not ablation of the ER stress response. Stimulation of Sigma-1 receptor is therefore a putative therapeutic approach to delay the onset of cataract.

Keywords: cataract • oxidation/oxidative or free radical damage • receptors