title: Activation of the UPR protects against cigarette smoke-induced RPE apoptosis through up-regulation of Nrf2.
abstract: Recent studies have revealed a role of endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) in the regulation of RPE cell activity and survival. Herein, we examined the mechanisms by which the UPR modulates apoptotic signaling in human RPE cells challenged with cigarette smoking extract (CSE). Our results show that CSE exposure induced a dose- and time-dependent increase in ER stress markers, enhanced reactive oxygen species (ROS), mitochondrial fragmentation, and apoptosis of RPE cells. These changes were prevented by the anti-oxidant NAC or chemical chaperone TMAO, suggesting a close interaction between oxidative and ER stress in CSE-induced apoptosis. To decipher the role of the UPR, overexpression or down-regulation of XBP1 and CHOP genes was manipulated by adenovirus or siRNA. Overexpressing XBP1 protected against CSE-induced apoptosis by reducing CHOP, p-p38, and caspase-3 activation. In contrast, XBP1 knockdown sensitized the cells to CSE-induced apoptosis, which is likely through a CHOP-independent pathway. Surprisingly, knockdown of CHOP reduced p-eIF2α and Nrf2 resulting in a marked increase in caspase-3 activation and apoptosis. Furthermore, Nrf2 inhibition increased ER stress and exacerbated cell apoptosis, while Nrf2 overexpression reduced CHOP and protected RPE cells. Our data suggest that although CHOP may function as a pro-apoptotic gene during ER stress, it is also required for Nrf2 up-regulation and RPE cell survival. In addition, enhancing Nrf2 and XBP1 activity may help reduce oxidative and ER stress and protect RPE cells from cigarette smoke-induced damage.
authors.affiliation: From the Department of Ophthalmology/Ross Eye Institute, School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York 14215, SUNY Eye Institute, The State University of New York, Buffalo, New York 14215, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China, and.
authors.forename: Chuangxin
authors.initials: C
authors.lastname: Huang
authors.affiliation: From the Department of Ophthalmology/Ross Eye Institute, School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York 14215, SUNY Eye Institute, The State University of New York, Buffalo, New York 14215.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Wang
authors.affiliation: From the Department of Ophthalmology/Ross Eye Institute, School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York 14215, SUNY Eye Institute, The State University of New York, Buffalo, New York 14215, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China, and.
authors.forename: Jacey H
authors.initials: JH
authors.lastname: Ma
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China, and.
authors.forename: Chenjin
authors.initials: C
authors.lastname: Jin
authors.affiliation: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, 510060 China, and.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Yu
authors.affiliation: From the Department of Ophthalmology/Ross Eye Institute, School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York 14215, SUNY Eye Institute, The State University of New York, Buffalo, New York 14215, Department of Biochemistry, School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York 14215 xzhang38@buffalo.edu.
authors.forename: Sarah X
authors.initials: SX
authors.lastname: Zhang
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000502:physiology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008744:Methylamines / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D055213:Retinal Pigment Epithelium / Q000166:cytology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012906:Smoke; D014026:Nicotiana / Q000737:chemistry*; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D056811:Unfolded Protein Response / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation; D000071717:X-Box Binding Protein 1
chemical_list: C497249:DDIT3 protein, human; D004268:DNA-Binding Proteins; D016166:Free Radical Scavengers; D008744:Methylamines; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D017382:Reactive Oxygen Species; D000071701:Regulatory Factor X Transcription Factors; D012906:Smoke; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D051742:Transcription Factor CHOP; C005855:trimethyloxamine; D000111:Acetylcysteine
keywords: RPE; apoptosis; cigarette smoke; nuclear factor 2 (erythroid-derived 2-like factor) (NFE2L2) (Nrf2); oxidative stress; unfolded protein response (UPR)