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      17β-estradiol ameliorates oxidative stress and blue light-emitting diode-induced retinal degeneration by decreasing apoptosis and enhancing autophagy

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          Abstract

          Purpose

          This study aimed to assess the effects of 17β-estradiol (βE 2) on blue light-emitting diode (LED)-induced retinal degeneration (RD) in rats and hydrogen peroxide (H 2O 2)-induced retinal pigment epithelium cell injury in humans and elucidate the protective mechanism of βE 2 underlying these processes.

          Methods

          Female ovariectomized (OVX) rats were intravitreally injected with βE2 before blue LED exposure (3,000 lux, 2 hours). Retinal function and morphology were assayed via electroretinogram (ERG) and H&E, respectively. Cell viability was assayed using the Cell Counting Kit-8. Cell ROS were measured using dichlorofluorescein fluorescence. Apoptosis was evaluated by TUNEL and Annexin V/propidium iodide staining. Gene expression and protein expression were quantified using quantitative real-time RT-PCR, Western blotting, and immunohistochemistry. Autophagosomes were examined by electron microscopy.

          Results

          Female OVX rats were exposed to blue LED, inducing RD. βE 2 significantly prevented the reduction in the a- and b-wave ERG amplitudes and the disruption of retinal structure, the loss of photoreceptor cells, and the decrease in the thickness of the outer nuclear layer caused by blue LED exposure. βE 2 also decreased cell apoptosis in the retina in blue LED-induced RD. Additionally, βE 2 reduced ROS levels and apoptosis in H 2O 2-treated human retinal pigment epithelial (ARPE-19) cells. Furthermore, βE 2 increased the protein expression of p-Akt and Bcl-2 and decreased the protein expression of cleaved caspase-3 and Bax during blue LED-induced retinal damage and in H 2O 2-treated ARPE-19 cells. βE 2 also increased the number of autopha-gosomes and upregulated the expression of LC3-II/LC3-I and Beclin 1 in these processes.

          Conclusion

          βE 2 protects against blue LED-induced RD and H 2O 2-induced oxidative stress by acting as an antioxidant, and its protective mechanism might occur by reducing apoptosis and enhancing autophagy; βE 2 may be a novel and effective therapy for age-related macular degeneration.

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          Most cited references 53

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          Global data on visual impairment in the year 2002.

          This paper presents estimates of the prevalence of visual impairment and its causes in 2002, based on the best available evidence derived from recent studies. Estimates were determined from data on low vision and blindness as defined in the International statistical classification of diseases, injuries and causes of death, 10th revision. The number of people with visual impairment worldwide in 2002 was in excess of 161 million, of whom about 37 million were blind. The burden of visual impairment is not distributed uniformly throughout the world: the least developed regions carry the largest share. Visual impairment is also unequally distributed across age groups, being largely confined to adults 50 years of age and older. A distribution imbalance is also found with regard to gender throughout the world: females have a significantly higher risk of having visual impairment than males. Notwithstanding the progress in surgical intervention that has been made in many countries over the last few decades, cataract remains the leading cause of visual impairment in all regions of the world, except in the most developed countries. Other major causes of visual impairment are, in order of importance, glaucoma, age-related macular degeneration, diabetic retinopathy and trachoma.
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            Molecular mechanisms of light-induced photoreceptor apoptosis and neuroprotection for retinal degeneration.

            Human retinal dystrophies and degenerations and light-induced retinal degenerations in animal models are sharing an important feature: visual cell death by apoptosis. Studying apoptosis may thus provide an important handle to understand mechanisms of cell death and to develop potential rescue strategies for blinding retinal diseases. Apoptosis is the regulated elimination of individual cells and constitutes an almost universal principle in developmental histogenesis and organogenesis and in the maintenance of tissue homeostasis in mature organs. Here we present an overview on molecular and cellular mechanisms of apoptosis and summarize recent developments. The classical concept of apoptosis being initiated and executed by endopeptidases that cleave proteins at aspartate residues (Caspases) can no longer be held in its strict sense. There is an increasing number of caspase-independent pathways, involving apoptosis inducing factor, endonuclease G, poly-(ADP-ribose) polymerase-1, proteasomes, lysosomes and others. Similarly, a considerable number and diversity of pro-apoptotic stimuli is being explored. We focus on apoptosis pathways in our model: light-damage induced by short exposures to bright white light and highlight those essential conditions known so far in the apoptotic death cascade. In our model, the visual pigment rhodopsin is the essential mediator of the initial death signal. The rate of rhodopsin regeneration defines damage threshold in different strains of mice. This rate depends on the level of the pigment epithelial protein RPE65, which in turn depends on the amino acid (leucine or methionine) encoded at position 450. Activation of the pro-apoptotic transcription factor AP-1 constitutes an essential death signal. Inhibition of rhodopsin regeneration as well as suppression of AP-1 confers complete protection in our system. Furthermore, we describe observations in other light-damage systems as well as characteristics of animal models for RP with particular emphasis on rescue strategies. There is a vast array of different neuroprotective cytokines that are applied in light-damage and RP animal models and show diverging efficacy. Some cytokines protect against light damage as well as against RP in animal models. At present, the mechanisms of neuroprotective/anti-apoptotic action represent a "black box" which needs to be explored. Even though acute light damage and RP animal models show different characteristics in many respects, we hope to gain insights into apoptotic mechanisms for both conditions by studying light damage and comparing results with those obtained in animal models. In our view, future directions may include the investigation of different apoptotic pathways in light damage (and inherited animal models). Emphasis should also be placed on mechanisms of removal of dead cells in apoptosis, which appears to be more important than initially recognized. In this context, a stimulating concept concerns age-related macular degeneration, where an insufficiency of macrophages removing debris that results from cell death and photoreceptor turnover might be an important pathogenetic event. In acute light damage, the appearance of macrophages as well as phagocytosis by the retinal pigment epithelium are a consistent and conspicuous feature, which lends itself to the study of removal of cellular debris in apoptosis. We are aware of the many excellent reviews and the earlier work paving the way to our current knowledge and understanding of retinal degeneration, photoreceptor apoptosis and neuroprotection. However, we limited this review mainly to work published in the last 7-8 years and we apologize to all the researchers which have contributed to the field but are not cited here.
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              Physiological functions of Atg6/Beclin 1: a unique autophagy-related protein.

              The most striking morphological feature of eukaryotic cells is the presence of various membrane-enclosed compartments. These compartments, including organelles and transient transport intermediates, are not static. Rather, dynamic exchange of proteins and membrane is needed to maintain cellular homeostasis. One of the most dramatic examples of membrane mobilization is seen during the process of macroautophagy. Macroautophagy is the primary cellular pathway for degradation of long-lived proteins and organelles. In response to environmental cues, such as starvation or other types of stress, the cell produces a unique membrane structure, the phagophore. The phagophore sequesters cytoplasm as it forms a double-membrane cytosolic vesicle, an autophagosome. Upon completion, the autophagosome fuses with a lysosome or a vacuole in yeast, which delivers hydrolases that break down the inner autophagosome membrane along with its cargo, and the resulting macromolecules are released back into the cytosol for reuse. Autophagy is therefore a recycling process, allowing cells to survive periods of nutrient limitation; however, it has a wider physiological role, participating in development and aging, and also in protection against pathogen invasion, cancer and certain neurodegenerative diseases. In many cases, the role of autophagy is identified through studies of an autophagy-related protein, Atg6/Beclin 1. This protein is part of a lipid kinase complex, and recent studies suggest that it plays a central role in coordinating the cytoprotective function of autophagy and in opposing the cellular death process of apoptosis. Here, we summarize our current knowledge of Atg6/Beclin 1 in different model organisms and its unique function in the cell.
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                Author and article information

                Journal
                Drug Des Devel Ther
                Drug Des Devel Ther
                Drug Design, Development and Therapy
                Drug Design, Development and Therapy
                Dove Medical Press
                1177-8881
                2018
                04 September 2018
                : 12
                : 2715-2730
                Affiliations
                [1 ]Department of Ophthalmology, Shanghai Tenth People’s Hospital Affiliated with Tongji University, Shanghai, People’s Republic of China, dryujing@ 123456aliyun.com , curiec@ 123456sina.cn
                [2 ]Department of Ophthalmology, Nanchang University, Nanchang, People’s Republic of China
                [3 ]Department of Clinical Laboratory, Shanghai Tenth People’s Hospital Affiliated with Tongji University, Shanghai, People’s Republic of China
                [4 ]Department of Ophthalmology, Ninghai First Hospital, Zhejiang, People’s Republic of China, dryujing@ 123456aliyun.com
                Author notes
                Correspondence: Jing Yu; Chengda Ren, Department of Ophthalmology, Shanghai Tenth People’s Hospital Affiliated with Tongji University, 301 Middle Yanchang Road, Shanghai 200072, People’s Republic of China, Tel +86 21 6630 1362, Email dryujing@ 123456aliyun.com ; curiec@ 123456sina.cn
                [*]

                These authors contributed equally to this work

                Article
                dddt-12-2715
                10.2147/DDDT.S176349
                6129027
                © 2018 Wei et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

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