Valproic acid suppresses Nrf2/Keap1 dependent antioxidant protection through induction of endoplasmic reticulum stress and Keap1 promoter DNA demethylation in human lens epithelial cells

• Published in: Experimental eye research 2014-04, Vol.121, p.26-34
• Main Authors: Palsamy, Periyasamy, Bidasee, Keshore R., Shinohara, Toshimichi
• Format: Article
• Language: English
• Subjects: Anticonvulsants - pharmacology; Antioxidants - metabolism; Apoptosis - drug effects; Blotting, Western; Calcium - metabolism; Catalase - metabolism; cataracts; Cells, Cultured; DNA Methylation; Endoplasmic Reticulum - drug effects; Endoplasmic Reticulum - metabolism; Epithelial Cells - drug effects; Epithelial Cells - metabolism; ER stress; Glutathione Reductase - metabolism; Humans; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Keap1 promoter demethylation; Kelch-Like ECH-Associated Protein 1; Lens, Crystalline - cytology; Lens, Crystalline - drug effects; NF-E2-Related Factor 2 - metabolism; Nrf2; Oxidative Stress - drug effects; Promoter Regions, Genetic - drug effects; Reactive Oxygen Species - metabolism; Real-Time Polymerase Chain Reaction; RNA, Messenger - metabolism; unfolded protein response; valproic acid; Valproic Acid - pharmacology
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/j.exer.2014.01.021

Recent epidemiological studies confirm the prevalence of cataract in epileptic patients. Similarly, the drugs used to treat epilepsy also show the connection with increased cataract formation. In this present study, we investigated the suppression of Nrf2/Keap1 dependent antioxidant protection through induction of endoplasmic (ER) stress and Keap1 promoter DNA demethylation in human lens epithelial cells (HLECs) treated with valproic acid (VPA), an antiepileptic drug. 20 mM VPA induces ER stress and activates the unfolded protein response (UPR) within 4 h by activating the ER stress sensor proteins, such as PERK, IRE1α, and ATF6 in HLECs. Consequently, the integrated ER stress signals, such as eIF2α, ATF4, BiP, and CHOP are altered accordingly to induce ER-Ca2+ release, reactive oxygen species (ROS) overproduction, and cell death in HLECs treated with VPA. VPA also suppresses the Nrf2, catalase, and glutathione reductase expressions with significant increases in Keap1 protein. Bisulphite genomic DNA sequencing reveals the promoter DNA demethylation in the Keap1 promoter, which results in the overexpression of Keap1 mRNA and protein in HLECs treated with 20 mM VPA. VPA also alters the expression profiles of passive DNA demethylation pathway enzymes such Dnmt1, Dnmt3a, Dnmt3b, and active DNA demethylation pathway enzyme, TET1 leading to DNA demethylation in the Keap1 promoter of HLECs. Overexpressed Keap1 decreases the Nrf2 level, thereby abolishing the Nrf2 dependent antioxidant protection. This might be responsible for lenticular proteins oxidation and cataract formation. •Valproic acid (VPA) activates ER stress mediated UPR in human lens epithelial cells.•VPA induces Ca2+ release from ER to cytoplasm in human lens epithelial cells.•VPA suppresses Nrf2 dependent antioxidant protection in human lens epithelial cells.•VPA demethylates Keap1 promoter by modifying DNA demethylation enzyme expressions.