Glutathione depletion results in S-nitrosylation of protein disulfide isomerase in neuroblastoma cells

Aims: Protein disulfide isomerase (PDI) is an essential enzyme involved in oxidative protein folding. PDI is S-nitrosylated in the brains of Alzheimer's disease patients, and S-nitrosylated PDI is considered one of main causes of Alzheimer's disease. However, the mechanisms underlying PDI S-nitrosylation have not yet been elucidated. Because glutathione (GSH) depletion is a pathological feature of Alzheimer's disease, we investigated the effect of GSH depletion on the S-nitrosylation level of PDI.Main methods: SH-SY5Y cells, which is a human derived neuroblastoma cells, were used in this study. Glutamate and buthionine sulfoximine (BSO) were used as GSH depletors. S-nitrosylated PDI was detected by biotin-switch assay.Key findings: GSH depletion by glutamate, a cystine/glutamate antiporter xCT inhibitor, increased S-nitrosylated PDI at C343 in SH-SY5Y cells, and induced IRE1 alpha phosphorylation. BSO, a gamma-glutamylcysteine synthetase in-hibitor, also increased S-nitrosylated PDI and phosphorylated IRE1 alpha upon GSH depletion. Because S-nitrosylated PDI at C343 is stable in neuro cells, S-nitrosylated PDI by GSH depletion progresses to neurodegeneration by the induction of endoplasmic reticulum stress via phosphorylated IRE1 alpha signaling from the early to late stage. Furthermore, treatment with neohesperidin, but not N-acetylcysteine (NAC), improved PDI S-nitrosylation level in GSH-depleted SH-SY5Y cells because nitrosylated compound of NAC induces PDI S-nitrosylation. Significance: The results of our study provide a new insight into the mechanisms of neurodegeneration, and may be useful for the development of drugs for Alzheimer's diseases.

Automated summary

Protein disulfide isomerase (PDI) is involved in oxidative protein folding and S-nitrosylated PDI is considered a main cause of Alzheimer's disease. The mechanisms of PDI S-nitrosylation are not yet understood. GSH depletion is a pathological feature of Alzheimer's disease, so this study investigated the effect of GSH depletion on PDI S-nitrosylation.