Selenite cataracts: Activation of endoplasmic reticulum stress and loss of Nrf2/Keap1-dependent stress protection

• Published in: Biochimica et biophysica acta 2014-09, Vol.1842 (9), p.1794-1805
• Main Authors: Palsamy, Periyasamy, Bidasee, Keshore R., Shinohara, Toshimichi
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Blotting, Western; Cataract; Cataract - chemically induced; Cataract - metabolism; Cataract - pathology; Cell Proliferation; Cells, Cultured; DNA Methylation - drug effects; Endoplasmic Reticulum Stress - drug effects; Endoplasmic Reticulum-Associated Degradation - drug effects; Epithelial Cells - drug effects; Epithelial Cells - metabolism; Epithelial Cells - pathology; ER stress; Human lens epithelial cells; Humans; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Keap1 promoter demethylation; Kelch-Like ECH-Associated Protein 1; Lens, Crystalline - drug effects; Lens, Crystalline - metabolism; Lens, Crystalline - pathology; NF-E2-Related Factor 2 - genetics; NF-E2-Related Factor 2 - metabolism; Oxidative Stress; Promoter Regions, Genetic - genetics; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species - metabolism; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; Sodium selenite; Sodium Selenite - pharmacology; Trace Elements - pharmacology; Unfolded Protein Response
• ISSN: 0925-4439; 0006-3002; 1879-260X
• DOI: 10.1016/j.bbadis.2014.06.028

Cataract-induced by sodium selenite in suckling rats is one of the suitable animal models to study the basic mechanism of human cataract formation. The aim of this present investigation is to study the endoplasmic reticulum (ER) stress-mediated activation of unfolded protein response (UPR), overproduction of reactive oxygen species (ROS), and suppression of Nrf2/Keap1-dependent antioxidant protection through endoplasmic reticulum-associated degradation (ERAD) pathway and Keap1 promoter DNA demethylation in human lens epithelial cells (HLECs) treated with sodium selenite. Lenses enucleated from sodium selenite injected rats generated overproduction of ROS in lens epithelial cells and newly formed lens fiber cells resulting in massive lens epithelial cells death after 1–5days. All these lenses developed nuclear cataracts after 4–5days. Sodium selenite treated HLECs induced ER stress and activated the UPR leading to release of Ca2+ from ER, ROS overproduction and finally HLECs death. Sodium selenite also activated the mRNA expressions of passive DNA demethylation pathway enzymes such as Dnmt1, Dnmt3a, and Dnmt3b, and active DNA demethylation pathway enzyme, Tet1 leading to DNA demethylation in the Keap1 promoter of HLECs. This demethylated Keap1 promoter results in overexpression of Keap1 mRNA and protein. Overexpression Keap1 protein suppresses the Nrf2 protein through ERAD leading to suppression of Nrf2/Keap1 dependent antioxidant protection in the HLECs treated with sodium selenite. As an outcome, the cellular redox status is altered towards lens oxidation and results in cataract formation. •Selenite induces cataract in suckling rats through ROS production and cell death.•Selenite induces ER-Ca2+ release in human lens epithelial cells (HLECs).•Selenite induces ER stress and unfolded protein response in HLECs.•Selenite suppresses Nrf2/Keap1 dependent antioxidant protection in HLECs.•Selenite induces loss of promoter DNA methylation in human Keap1 gene.