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      Environmental stress impairs photoreceptor outer segment (POS) phagocytosis and degradation and induces autofluorescent material accumulation in hiPSC-RPE cells

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          Abstract

          Retinal pigment epithelium (RPE) cell dysfunction is central to the pathogenesis of age-related macular degeneration (AMD), a leading cause of adult blindness. Aging, the single biggest risk factor for AMD development, favors increase in RPE autofluorescent material due to accumulation of POS-digestion by-products through lysosomal dysfunction and impaired POS degradation. Apart from aging, environmental agents affect lysosomal function in multiple model systems and are implicated in AMD. Iron (Fe) overload and cigarette smoke exposure are the two environmental factors that are known to affect the lysosomal pathway and impact RPE cell health. However, the impact of Fe and cigarette smoke, on POS processing and its consequence for autofluorescent material accumulation in human RPE cells are yet to be established. Human induced pluripotent stem cell (hiPSC)-derived RPE, which phagocytoses and degrades POS in culture and can be derived from control individuals (no history/susceptibility for retinal disease), provides a model system to investigate the singular effect of excess Fe and/or cigarette smoke on POS processing by RPE cells. Using at least three distinct control hiPSC lines, we show that, compared to untreated hiPSC-RPE cells, POS uptake is reduced in both Fe (ferric ammonium citrate or FAC) and FAC + CSE (cigarette smoke extract)-treated hiPSC-RPE cells. Furthermore, exposure of hiPSC-RPE cultures to FAC + CSE leads to reduced levels of active cathepsin-D (CTSD), a lysosomal enzyme involved in POS processing, and causes delayed degradation of POS. Notably, delayed degradation of POS over time (2 weeks) in hiPSC-RPE cells exposed to Fe and CSE was sufficient to increase autofluorescent material build-up in these cells. Given that inefficient POS processing-mediated autofluorescent material accumulation in RPE cells has already been linked to AMD development, our results implicate a causative role of environmental agents, like Fe and cigarette smoke, in AMD.

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          The retinal pigment epithelium in health and disease.

          Retinal pigment epithelial cells (RPE) constitute a simple layer of cuboidal cells that are strategically situated behind the photoreceptor (PR) cells. The inconspicuousness of this monolayer contrasts sharply with its importance [1]. The relationship between the RPE and PR cells is crucial to sight; this is evident from basic and clinical studies demonstrating that primary dysfunctioning of the RPE can result in visual cell death and blindness. RPE cells carry out many functions including the conversion and storage of retinoid, the phagocytosis of shed PR outer segment membrane, the absorption of scattered light, ion and fluid transport and RPE-PR apposition. The magnitude of the demands imposed on this single layer of cells in order to execute these tasks, will become apparent to the reader of this review as will the number of clinical disorders that take origin from these cells.
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            Modeling early retinal development with human embryonic and induced pluripotent stem cells.

            Human pluripotent stem cells have the potential to provide comprehensive model systems for the earliest stages of human ontogenesis. To serve in this capacity, these cells must undergo a targeted, stepwise differentiation process that follows a normal developmental timeline. Here we demonstrate the ability of both human embryonic stem cells (hESCs) and induced pluripotent stem (iPS) cells to meet these requirements for human retinogenesis. Upon differentiation, hESCs initially yielded a highly enriched population of early eye field cells. Thereafter, a subset of cells acquired features of advancing retinal differentiation in a sequence and time course that mimicked in vivo human retinal development. Application of this culture method to a human iPS cell line also generated retina-specific cell types at comparable times in vitro. Lastly, altering endogenous signaling during differentiation affected lineage-specific gene expression in a manner consistent with established mechanisms of early neural and retinal cell fate determination. These findings should aid in the investigation of the molecular events governing retinal specification from human pluripotent stem cells.
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              The US twin study of age-related macular degeneration: relative roles of genetic and environmental influences.

              Age-related macular degeneration (AMD) is the leading cause of irreversible blindness among older individuals in many parts of the world. The relative importance of genes and environment in the etiology of this major public health problem is not well understood. To investigate the impact of genetic and environmental factors. Living twins in the National Academy of Sciences-National Research Council World War II Veteran Twin Registry born between 1917 and 1927. Twins were surveyed for the known presence of macular degeneration. Enrolled twins underwent a standardized examination and fundus photography. Age-related macular degeneration evaluation was completed for 840 elderly male twins, 210 monozygotic and 181 dizygotic complete twin pairs, both concordant and discordant for presence or absence of AMD, and 58 singletons. A bivariate twin model incorporating initial screening ascertainment and age effects was employed to partition variation in liability to AMD and signs of maculopathy into additive genetic, common environment, and unique environment components. Heritability of AMD grade and signs of maculopathy based on clinical examination and fundus photographs. Of the 840 twins, 331 had no signs of maculopathy and 241 had early signs, while 162 had intermediate AMD and 106 had advanced AMD. Heritability (additive genetic) estimates were significant for overall AMD grade (0.46) and for intermediate (0.67) and advanced (0.71) AMD. Significant unique environmental proportions of variance were also observed for these AMD variables (0.37, 0.19, and 0.24, respectively). Shared or common environmental contributions were not significant (0.05-0.17). For specific macular drusen and retinal pigment epithelial characteristics, significant genetic (0.26-0.71) and unique environmental (0.28-0.64) proportions of variance were detected. Genetic factors play a substantial role in the etiology of AMD and associated macular characteristics, explaining 46% to 71% of the variation in the overall severity of the disease. Environmental factors unique to each twin also contribute to the occurrence of this disease. This quantification of relative genetic and environmental contributions to the development of AMD should guide future research on this important cause of blindness.
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                Author and article information

                Contributors
                +585-276-3000 , ruchira_singh@urmc.rochester.edu
                Journal
                Cell Death Discov
                Cell Death Discov
                Cell Death Discovery
                Nature Publishing Group UK (London )
                2058-7716
                16 May 2019
                16 May 2019
                2019
                : 5
                : 96
                Affiliations
                [1 ]ISNI 0000 0004 1936 9174, GRID grid.16416.34, Department of Ophthalmology (Flaum Eye Institute), , University of Rochester, ; Rochester, NY USA
                [2 ]ISNI 0000 0004 1936 9174, GRID grid.16416.34, Department of Biomedical Genetics, , University of Rochester, ; Rochester, NY USA
                [3 ]ISNI 0000 0004 1936 9174, GRID grid.16416.34, UR Stem Cell and Regenerative Medicine Institute, ; Rochester, NY USA
                [4 ]ISNI 0000 0004 1936 9174, GRID grid.16416.34, Center for Visual Science, , University of Rochester, ; Rochester, NY USA
                [5 ]ISNI 0000 0004 1936 9174, GRID grid.16416.34, Present Address: Department of Pathology and Lab Medicine, , University of Rochester, ; Rochester, NY USA
                Article
                171
                10.1038/s41420-019-0171-9
                6522536
                31123602
                464a2efe-49ae-4f5b-a8c7-8e9eb5434e4e
                © The Author(s) 2019

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 5 March 2019
                : 19 March 2019
                : 21 March 2019
                Funding
                Funded by: FundRef https://doi.org/10.13039/100000009, Foundation for the National Institutes of Health (Foundation for the National Institutes of Health, Inc.);
                Award ID: NIH-1R01EY028167
                Award Recipient :
                Categories
                Article
                Custom metadata
                © The Author(s) 2019

                stem cells,pluripotent stem cells
                stem cells, pluripotent stem cells

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