title: Methylglyoxal induces endoplasmic reticulum stress and DNA demethylation in the Keap1 promoter of human lens epithelial cells and age-related cataracts.
abstract: Age-related cataracts are a leading cause of blindness. Previously, we have demonstrated the association of the unfolded protein response with various cataractogenic stressors. However, DNA methylation alterations leading to suppression of lenticular antioxidant protection remains unclear. Here, we report the methylglyoxal-mediated sequential events responsible for Keap1 promoter DNA demethylation in human lens epithelial cells, because Keap1 is a negative regulatory protein that regulates the Nrf2 antioxidant protein. Methylglyoxal induces endoplasmic reticulum stress and activates the unfolded protein response leading to overproduction of reactive oxygen species before human lens epithelial cell death. Methylglyoxal also suppresses Nrf2 and DNA methyltransferases but activates the DNA demethylation pathway enzyme TET1. Bisulfite genomic DNA sequencing confirms the methylglyoxal-mediated Keap1 promoter DNA demethylation leading to overexpression of Keap1 mRNA and protein. Similarly, bisulfite genomic DNA sequencing shows that human clear lenses (n = 15) slowly lose 5-methylcytosine in the Keap1 promoter throughout life, at a rate of 1% per year. By contrast, diabetic cataractous lenses (n = 21) lose an average of 90% of the 5-methylcytosine regardless of age. Overexpressed Keap1 protein is responsible for decreasing Nrf2 by proteasomal degradation, thereby suppressing Nrf2-dependent stress protection. This study demonstrates for the first time the associations of unfolded protein response activation, Nrf2-dependent antioxidant system failure, and loss of Keap1 promoter methylation because of altered active and passive DNA demethylation pathway enzymes in human lens epithelial cells by methylglyoxal. As an outcome, the cellular redox balance is altered toward lens oxidation and cataract formation.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, NE 68198, USA.
authors.forename: Periyasamy
authors.initials: P
authors.lastname: Palsamy
authors.affiliation: Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198, USA.
authors.forename: Keshore R
authors.initials: KR
authors.lastname: Bidasee
authors.affiliation: Department of Ophthalmology, Keio University, Tokyo 1698582, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ayaki
authors.affiliation: Vision Cooperative Research Centre, Brien Holden Vision Institute, Sydney 2052, Australia; Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Augusteyn
authors.affiliation: Department of Laboratory Medicine and Pathology, University of California at Irvine, Irvine, CA 92697, USA.
authors.forename: Jefferson Y
authors.initials: JY
authors.lastname: Chan
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, NE 68198, USA. Electronic address: tshinohara@unmc.edu.
authors.forename: Toshimichi
authors.initials: T
authors.lastname: Shinohara
mesh_terms: D000375:Aging / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002386:Cataract / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D019175:DNA Methylation / Q000187:drug effects / Q000502:physiology*; D003921:Diabetes Mellitus, Experimental; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects / Q000502:physiology*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D007908:Lens, Crystalline / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011401:Promoter Regions, Genetic; D011765:Pyruvaldehyde / Q000378:metabolism* / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D056811:Unfolded Protein Response / Q000187:drug effects
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; C431364:KEAP1 protein, human; D000072019:Kelch-Like ECH-Associated Protein 1; D011765:Pyruvaldehyde
keywords: Cataracts; DNA methylation; ER stress; Free radicals; Keap1 promoter demethylation; Methylglyoxal; Nrf2-dependent antioxidant protection; Unfolded protein response
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