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      Screening and Characterization of Drugs That Protect Corneal Endothelial Cells Against Unfolded Protein Response and Oxidative Stress

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          Abstract

          Purpose

          To screen for and characterize compounds that protect corneal endothelial cells against unfolded protein response (UPR) and oxidative stress.

          Methods

          Bovine corneal endothelial cells (BCECs) were treated for 48 hours with 640 compounds from a Food and Drug Administration (FDA)-approved drug library and then challenged with thapsigargin or H 2O 2 to induce UPR or oxidative stress, respectively. Cell viability was measured using the CellTiter-Glo survival assay. Selected “hits” were subjected to further dose-response testing, and their ability to modulate expression of UPR and oxidative stress markers was assessed by RT-PCR, Western blot, and measurement of protein carbonyl and 8-hydroxydeoxyguanosine (8-OHdG) adducts in immortalized human corneal endothelial cells (iHCECs).

          Results

          Forty-one drugs at 20 μM and 55 drugs at 100 μM increased survival of H 2O 2-challenged cells, and 8 drugs at 20 μM and 2 drugs at 100 μM increased survival of thapsigargin-challenged cells, compared with untreated control cells. Nicergoline, ergothioneine, nimesulide, oxotremorine, and mefenamic acid increased survival of both H 2O 2- and thapsigargin-challenged cells. Oxotremorine altered DNA damage inducible 3 ( CHOP) gene expression, glucose-regulated protein 78 kDa (GRP78) and activating transcription factor 4 (ATF4) protein expression, and protein carbonyl and 8-OHdG levels. Mefenamic acid altered GRP78 protein expression and protein carbonyl and 8-OHdG levels.

          Conclusions

          Oxotremorine and mefenamic acid are potential survival factors for corneal endothelial cells under UPR and oxidative stress. The described assay can be further expanded to screen additional drugs for potential therapeutic effect in corneal endothelial diseases such as Fuchs' endothelial corneal dystrophy.

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          Most cited references31

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          Endoplasmic reticulum stress in liver disease.

          The unfolded protein response (UPR) is activated upon the accumulation of misfolded proteins in the endoplasmic reticulum (ER) that are sensed by the binding immunoglobulin protein (BiP)/glucose-regulated protein 78 (GRP78). The accumulation of unfolded proteins sequesters BiP so it dissociates from three ER-transmembrane transducers leading to their activation. These transducers are inositol requiring (IRE) 1α, PKR-like ER kinase (PERK), and activating transcription factor (ATF) 6α. PERK phosphorylates eukaryotic initiation factor 2 alpha (eIF2α) resulting in global mRNA translation attenuation, and concurrently selectively increases the translation of several mRNAs, including the transcription factor ATF4, and its downstream target CHOP. IRE1α has kinase and endoribonuclease (RNase) activities. IRE1α autophosphorylation activates the RNase activity to splice XBP1 mRNA, to produce the active transcription factor sXBP1. IRE1α activation also recruits and activates the stress kinase JNK. ATF6α transits to the Golgi compartment where it is cleaved by intramembrane proteolysis to generate a soluble active transcription factor. These UPR pathways act in concert to increase ER content, expand the ER protein folding capacity, degrade misfolded proteins, and reduce the load of new proteins entering the ER. All of these are geared toward adaptation to resolve the protein folding defect. Faced with persistent ER stress, adaptation starts to fail and apoptosis occurs, possibly mediated through calcium perturbations, reactive oxygen species, and the proapoptotic transcription factor CHOP. The UPR is activated in several liver diseases; including obesity associated fatty liver disease, viral hepatitis, and alcohol-induced liver injury, all of which are associated with steatosis, raising the possibility that ER stress-dependent alteration in lipid homeostasis is the mechanism that underlies the steatosis. Hepatocyte apoptosis is a pathogenic event in several liver diseases, and may be linked to unresolved ER stress. If this is true, restoration of ER homeostasis prior to ER stress-induced cell death may provide a therapeutic rationale in these diseases. Herein we discuss each branch of the UPR and how they may impact hepatocyte function in different pathologic states. Copyright © 2010 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
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            Tumor necrosis factor alpha (TNFalpha) induces the unfolded protein response (UPR) in a reactive oxygen species (ROS)-dependent fashion, and the UPR counteracts ROS accumulation by TNFalpha.

            Accumulation of unfolded proteins in the endoplasmic reticulum (ER) causes ER overload, resulting in ER stress. To cope with ER stress, mammalian cells trigger a specific response known as the unfolded protein response (UPR). Although recent studies have indicated cross-talk between ER stress and oxidative stress, the mechanistic link is not fully understood. By using murine fibrosarcoma L929 cells, in which tumor necrosis factor (TNF) alpha induces accumulation of reactive oxygen species (ROS) and cell death, we show that TNFalpha induces the UPR in a ROS-dependent fashion. In contrast to TNFalpha, oxidative stresses by H2O2 or arsenite only induce eukaroytic initiation factor 2alpha phosphorylation, but not activation of PERK- or IRE1-dependent pathways, indicating the specificity of downstream signaling induced by various oxidative stresses. Conversely, the UPR induced by tunicamycin substantially suppresses TNFalpha-induced ROS accumulation and cell death by inhibiting reduction of cellular glutathione levels. Collectively, some, but not all, oxidative stresses induce the UPR, and pre-emptive UPR counteracts TNFalpha-induced ROS accumulation.
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              Evidence of oxidative stress in the pathogenesis of fuchs endothelial corneal dystrophy.

              Fuchs endothelial corneal dystrophy (FECD) is a progressive, blinding disease characterized by corneal endothelial (CE) cell apoptosis. Corneal transplantation is the only measure currently available to restore vision in these patients. Despite the identification of some genetic factors, the pathophysiology of FECD remains unclear. In this study, we observed a decrease in the antioxidant response element-driven antioxidants in FECD corneal endothelium. We further demonstrated that nuclear factor erythroid 2-related factor 2, a transcription factor known to bind the antioxidant response element and activate antioxidant defense, is down-regulated in FECD endothelium. Importantly, we detected significantly higher levels of oxidative DNA damage and apoptosis in FECD endothelium compared with normal controls and pseudophakic bullous keratopathy (iatrogenic CE cell loss) specimens. A marker of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine, colocalized to mitochondria, indicating that the mitochondrial genome is the specific target of oxidative stress in FECD. Oxidative DNA damage was not detected in pseudophakic bullous keratopathy corneas, whereas it colocalized with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells in FECD samples. Ex vivo, oxidative stress caused characteristic morphological changes and apoptosis of CE, suggestive of findings that characterize FECD in vivo. Together, these data suggest that suboptimal nuclear factor erythroid 2-related factor 2-regulated defenses may account for oxidant-antioxidant imbalance in FECD, which in turn leads to oxidative DNA damage and apoptosis. This study provides evidence that oxidative stress plays a key role in FECD pathogenesis.
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                Author and article information

                Journal
                Invest Ophthalmol Vis Sci
                Invest. Ophthalmol. Vis. Sci
                iovs
                iovs
                IOVS
                Investigative Ophthalmology & Visual Science
                The Association for Research in Vision and Ophthalmology
                0146-0404
                1552-5783
                February 2017
                : 58
                : 2
                : 892-900
                Affiliations
                [1 ]Wilmer Eye Institute, Johns Hopkins Medical Institutions, Baltimore, Maryland, United States
                [2 ]Department of Ophthalmology & Visual Science, Catholic University of Korea, Seoul, Korea
                [3 ]Department of Ophthalmology, University of Tokyo, Tokyo, Japan
                [4 ]Departments of Molecular Biology and Genetics, Neuroscience, and Institute of Genetic Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland, United States
                [5 ]Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, United States
                Author notes
                Correspondence: Albert S. Jun, Wilmer Eye Institute, Johns Hopkins Medical Institutions, 600 N. Broadway, Wilmer-Woods 376, Baltimore, MD 21287, USA; aljun@ 123456jhmi.edu .

                ECK and TT contributed equally to the work presented here and should therefore be regarded as equivalent authors.

                Article
                iovs-58-01-35 IOVS-16-20147
                10.1167/iovs.16-20147
                5295784
                28159976
                f630b82b-8a55-4147-a8be-9cf1c06e28b2

                This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

                History
                : 18 June 2016
                : 2 January 2017
                Categories
                Cornea

                drug screening,corneal endothelial cells,unfolded protein response,oxidative stress,fuchs' endothelial corneal dystrophy

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