Protective role for nitric oxide during the endoplasmic reticulum stress response in pancreatic β-cells

Higher requirements for disulfide bond formation in professional secretory cells may affect intracellular redox homeostasis, particularly during an endoplasmic reticulum ( ER) stress response. To assess this hypothesis, we investigated the effects of the ER stress response on the major redox couple ( GSH/ GSSG), endogenous ROS production, expression of genes involved in ER oxidative protein folding, general antioxidant defense, and thiol metabolism by use of the well-validated MIN6 beta-cell as a model and mouse islets. The data revealed that glucose concentration- dependent decreases in the GSH/ GSSG ratio were further decreased significantly by ER-derived oxidative stress induced by inhibiting ER- associated degradation with the specific proteasome inhibitor lactacystin ( 10 mu M) in mouse islets. Notably, minimal cell death was observed during 12- h treatments. This was likely attributed to the upregulation of genes encoding the rate limiting enzyme for glutathione synthesis (gamma-glutamylcysteine ligase), as well as genes involved in antioxidant defense ( glutathione peroxidase, peroxiredoxin1) and ER protein folding ( Grp78/ BiP, PDI, Ero1). Gene expression and reporter assays with a NO synthase inhibitor ( N-omega-nitro- L-arginine methyl ester, 1 - 10 mM) indicated that endogenous NO production was essential for the upregulation of several ER stress- responsive genes. Specifically, gel shift analyses demonstrate NO- independent binding of the transcription factor NF- E2- related factor to the antioxidant response element Gclc- ARE4 in MIN6 cells. However, endogenous NO production was necessary for activation of Gclc- ARE4- driven reporter gene expression. Together, these data reveal a distinct protective role for NO during the ER stress response, which helps to dissipate ROS and promote beta- cell survival.