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Cai CX, Light JG, Handa JT. Quantifying the Rate of Ellipsoid Zone Loss in Stargardt Disease. Am J Ophthalmol 2018; 186:1-9. [PMID: 29126757 DOI: 10.1016/j.ajo.2017.10.032] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 10/28/2017] [Accepted: 10/30/2017] [Indexed: 01/26/2023]
Abstract
PURPOSE To determine a reliable method of using the ellipsoid zone (EZ) on optical coherence tomography (OCT) to track disease progression in Stardgardt disease (STGD). DESIGN Retrospective reliability study. METHODS STGD patients with genetically confirmed ABCA4 gene mutations seen at the Wilmer Eye Institute with follow-up visits separated by at least 12 months were identified. Spectral-domain optical coherence tomography (SD-OCT) macula volume scans centered at the fovea and fundus autofluorescence (FAF) images were obtained. The area of EZ loss was calculated from the SD-OCT and the area of retinal pigment epithelium (RPE) loss from the FAF. Scans were reanalyzed by the primary grader to assess intragrader reliability, and reanalyzed by a second grader to assess intergrader reliability. RESULTS Sixteen STGD patients (total of 31 eyes) were followed for a mean of 2 years (range 1-4.7 years). The mean rate of EZ loss, 0.31 ± 0.31 mm2/year, was similar to the average rate of RPE loss, 0.33 ± 0.38 mm2/year. The average area of EZ loss at the initial examination, 4.18 ± 1.91 mm2, was larger than the initial area of RPE loss, 2.25 ± 1.66 mm2 (P < .01). The absolute difference of the area of EZ loss on test-retest for the first grader was 0.12 ± 0.10 mm2, and between graders 0.21 ± 0.21 mm2. The intraclass correlation (ICC) of both intragrader and intergrader reliability for EZ loss was excellent at 0.99. CONCLUSIONS Tracking the area of EZ loss on SD-OCT macular volume scans longitudinally is a reliable way of monitoring disease progression in STGD. This could be used as a sensitive anatomic outcome measure in clinical trials related to STGD.
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Sasaki K, Tachikawa M, Uchida Y, Hirano S, Kadowaki F, Watanabe M, Ohtsuki S, Terasaki T. ATP-Binding Cassette Transporter A Subfamily 8 Is a Sinusoidal Efflux Transporter for Cholesterol and Taurocholate in Mouse and Human Liver. Mol Pharm 2018; 15:343-355. [DOI: 10.1021/acs.molpharmaceut.7b00679] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kazunari Sasaki
- Membrane Transport
and Drug Targeting Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan
| | - Masanori Tachikawa
- Membrane Transport
and Drug Targeting Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan
| | - Yasuo Uchida
- Membrane Transport
and Drug Targeting Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan
| | - Satoshi Hirano
- Membrane Transport
and Drug Targeting Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan
| | - Fumito Kadowaki
- Membrane Transport
and Drug Targeting Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan
| | - Michitoshi Watanabe
- Membrane Transport
and Drug Targeting Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan
| | - Sumio Ohtsuki
- Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto 860-8555, Japan
| | - Tetsuya Terasaki
- Membrane Transport
and Drug Targeting Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan
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Joyal JS, Gantner ML, Smith LEH. Retinal energy demands control vascular supply of the retina in development and disease: The role of neuronal lipid and glucose metabolism. Prog Retin Eye Res 2017; 64:131-156. [PMID: 29175509 DOI: 10.1016/j.preteyeres.2017.11.002] [Citation(s) in RCA: 91] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 11/11/2017] [Accepted: 11/15/2017] [Indexed: 12/15/2022]
Affiliation(s)
- Jean-Sébastien Joyal
- Department of Pediatrics, Pharmacology and Ophthalmology, CHU Sainte-Justine Research Center, Université de Montréal, Montreal, Qc, Canada; Department of Pharmacology and Therapeutics, McGill University, Montreal, Qc, Canada.
| | - Marin L Gantner
- The Lowy Medical Research Institute, La Jolla, United States
| | - Lois E H Smith
- Department of Ophthalmology, Harvard Medical School, Boston Children's Hospital, 300 Longwood Avenue, Boston MA 02115, United States.
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Membrane proteins structures: A review on computational modeling tools. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:2021-2039. [DOI: 10.1016/j.bbamem.2017.07.008] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Revised: 07/04/2017] [Accepted: 07/13/2017] [Indexed: 01/02/2023]
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Zhang J, Qi A, Wang X, Pan H, Mo H, Huang J, Li H, Chen Z, Wei M, Wang B. Novel compound heterozygous mutations in ABCA4 in a Chinese pedigree with Stargardt disease. Mol Vis 2016; 22:1514-1521. [PMID: 28050124 PMCID: PMC5204459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Accepted: 12/28/2016] [Indexed: 11/12/2022] Open
Abstract
PURPOSE Stargardt disease (STGD) is a common macular dystrophy in juveniles that is commonly inherited as an autosomal recessive trait. Mutations in five genes (ABCA4, PROM1, ELOVL4, BEST1, and PRPH2) have been reported to be associated with STGD. In the present study, we aimed to identify the pathogenic mutations in affected members in a Chinese STGD pedigree. METHODS One patient was selected for whole-exome sequencing. Variants in five candidate genes were identified initially, followed by several filtering steps against public and private variation databases (1000Genomes, ESP6500si, ExAC, and in-house database), as well as bioinformatic analysis of the putative pathogenic roles. Sanger sequencing was used for cosegregation analysis among all members with available DNA. RESULTS Two mutations in ABCA4 (NM_000350.2; c.5646G>A; p.Met1882Ile and NM_000350.2; c.3523-2A>G) were found using whole-exome sequencing. Cosegregation analysis confirmed all the affected members carried the compound heterozygous mutations while the other healthy members had at most one. The missense mutation was extremely rare in public databases and predicted to be deleterious. The splice-site mutation was absent from all public and private databases and was predicted to alter the splice pattern, resulting in an exon skip and a frameshift. CONCLUSIONS Using whole-exome sequencing, we found novel compound heterozygous mutations in ABCA4 in a Chinese STGD pedigree. These mutations are reported for the first time, therefore widening the mutation spectrum of Stargardt disease. The present study also illustrates the potential of whole-exome sequencing in determining the genetic cause of STGD.
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Affiliation(s)
- Jianping Zhang
- Department of Ophthalmology, Liuzhou Maternal and Child Healthcare Hospital, Liuzhou, Guangxi, China
| | - Anhui Qi
- Graduate School of Peking Union Medical College, Beijing, China,National Research Institute of Family Planning, Beijing, China
| | - Xi Wang
- National Research Institute of Family Planning, Beijing, China
| | - Hong Pan
- Graduate School of Peking Union Medical College, Beijing, China,National Research Institute of Family Planning, Beijing, China
| | - Haiming Mo
- Department of Ophthalmology, Liuzhou Maternal and Child Healthcare Hospital, Liuzhou, Guangxi, China
| | - Jiwei Huang
- Department of Ophthalmology, Liuzhou Maternal and Child Healthcare Hospital, Liuzhou, Guangxi, China
| | - Honghui Li
- Department of Ophthalmology, Liuzhou Maternal and Child Healthcare Hospital, Liuzhou, Guangxi, China
| | - Zhenwen Chen
- Department of Ophthalmology, Liuzhou Maternal and Child Healthcare Hospital, Liuzhou, Guangxi, China
| | - Meirong Wei
- Department of Ophthalmology, Liuzhou Maternal and Child Healthcare Hospital, Liuzhou, Guangxi, China
| | - Binbin Wang
- National Research Institute of Family Planning, Beijing, China
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Xue C, Raveendran M, Harris RA, Fawcett GL, Liu X, White S, Dahdouli M, Rio Deiros D, Below JE, Salerno W, Cox L, Fan G, Ferguson B, Horvath J, Johnson Z, Kanthaswamy S, Kubisch HM, Liu D, Platt M, Smith DG, Sun B, Vallender EJ, Wang F, Wiseman RW, Chen R, Muzny DM, Gibbs RA, Yu F, Rogers J. The population genomics of rhesus macaques (Macaca mulatta) based on whole-genome sequences. Genome Res 2016; 26:1651-1662. [PMID: 27934697 PMCID: PMC5131817 DOI: 10.1101/gr.204255.116] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 10/12/2016] [Indexed: 12/30/2022]
Abstract
Rhesus macaques (Macaca mulatta) are the most widely used nonhuman primate in biomedical research, have the largest natural geographic distribution of any nonhuman primate, and have been the focus of much evolutionary and behavioral investigation. Consequently, rhesus macaques are one of the most thoroughly studied nonhuman primate species. However, little is known about genome-wide genetic variation in this species. A detailed understanding of extant genomic variation among rhesus macaques has implications for the use of this species as a model for studies of human health and disease, as well as for evolutionary population genomics. Whole-genome sequencing analysis of 133 rhesus macaques revealed more than 43.7 million single-nucleotide variants, including thousands predicted to alter protein sequences, transcript splicing, and transcription factor binding sites. Rhesus macaques exhibit 2.5-fold higher overall nucleotide diversity and slightly elevated putative functional variation compared with humans. This functional variation in macaques provides opportunities for analyses of coding and noncoding variation, and its cellular consequences. Despite modestly higher levels of nonsynonymous variation in the macaques, the estimated distribution of fitness effects and the ratio of nonsynonymous to synonymous variants suggest that purifying selection has had stronger effects in rhesus macaques than in humans. Demographic reconstructions indicate this species has experienced a consistently large but fluctuating population size. Overall, the results presented here provide new insights into the population genomics of nonhuman primates and expand genomic information directly relevant to primate models of human disease.
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Affiliation(s)
- Cheng Xue
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Muthuswamy Raveendran
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - R Alan Harris
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA.,Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Gloria L Fawcett
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Xiaoming Liu
- University of Texas Health Science Center, Houston, Texas 77030, USA
| | - Simon White
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Mahmoud Dahdouli
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - David Rio Deiros
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Jennifer E Below
- University of Texas Health Science Center, Houston, Texas 77030, USA
| | - William Salerno
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Laura Cox
- Southwest National Primate Research Center, San Antonio, Texas 78227, USA
| | - Guoping Fan
- Department of Human Genetics, University of California, Los Angeles, California 90095, USA
| | - Betsy Ferguson
- Oregon National Primate Research Center, Beaverton, Oregon 97006, USA
| | - Julie Horvath
- North Carolina Museum of Natural Sciences, Raleigh, North Carolina 27601, USA.,Biological and Biomedical Sciences, North Carolina Central University, Durham, North Carolina 27707, USA.,Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708, USA
| | - Zach Johnson
- Yerkes National Primate Research Center, Atlanta, Georgia 30322, USA
| | - Sree Kanthaswamy
- California National Primate Research Center, Davis, California 95616, USA.,School of Mathematical and Natural Sciences, Arizona State University, Phoenix, Arizona 85004, USA
| | - H Michael Kubisch
- Tulane National Primate Research Center, Covington, Louisiana 70433, USA
| | - Dahai Liu
- Center for Stem Cell and Translational Medicine, Anhui University, Anhui, China 230601
| | - Michael Platt
- Department of Neurobiology, Duke University, Durham, North Carolina 27708, USA.,Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - David G Smith
- California National Primate Research Center, Davis, California 95616, USA
| | - Binghua Sun
- Center for Stem Cell and Translational Medicine, Anhui University, Anhui, China 230601
| | - Eric J Vallender
- Tulane National Primate Research Center, Covington, Louisiana 70433, USA.,New England National Primate Research Center, Southborough, Massachusetts 01772, USA
| | - Feng Wang
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Roger W Wiseman
- Wisconsin National Primate Research Center, Madison, Wisconsin 53711, USA
| | - Rui Chen
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA.,Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Donna M Muzny
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Richard A Gibbs
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA.,Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Fuli Yu
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA.,Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Jeffrey Rogers
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas 77030, USA.,Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
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57
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Lin B, Cai XB, Zheng ZL, Huang XF, Liu XL, Qu J, Jin ZB. Clinical and genetic analyses reveal novel pathogenic ABCA4 mutations in Stargardt disease families. Sci Rep 2016; 6:35414. [PMID: 27739528 PMCID: PMC5064356 DOI: 10.1038/srep35414] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Accepted: 09/27/2016] [Indexed: 12/28/2022] Open
Abstract
Stargardt disease (STGD1) is a juvenile macular degeneration predominantly inherited in an autosomal recessive pattern, characterized by decreased central vision in the first 2 decades of life. The condition has a genetic basis due to mutation in the ABCA4 gene, and arises from the deposition of lipofuscin-like substance in the retinal pigmented epithelium (RPE) with secondary photoreceptor cell death. In this study, we describe the clinical and genetic features of Stargardt patients from four unrelated Chinese cohorts. The targeted exome sequencing (TES) was carried out in four clinically confirmed patients and their family members using a gene panel comprising 164 known causative inherited retinal dystrophy (IRD) genes. Genetic analysis revealed eight ABCA4 mutations in all of the four pedigrees, including six mutations in coding exons and two mutations in adjacent intronic areas. All the affected individuals showed typical manifestations consistent with the disease phenotype. We disclose two novel ABCA4 mutations in Chinese patients with STGD disease, which will expand the existing spectrum of disease-causing variants and will further aid in the future mutation screening and genetic counseling, as well as in the understanding of phenotypic and genotypic correlations.
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Affiliation(s)
- Bing Lin
- The Eye Hospital of Wenzhou Medical University, The State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health, Wenzhou 325027, China
| | - Xue-Bi Cai
- The Eye Hospital of Wenzhou Medical University, The State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health, Wenzhou 325027, China
| | - Zhi-Li Zheng
- The Eye Hospital of Wenzhou Medical University, The State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health, Wenzhou 325027, China
| | - Xiu-Feng Huang
- The Eye Hospital of Wenzhou Medical University, The State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health, Wenzhou 325027, China
| | - Xiao-Ling Liu
- The Eye Hospital of Wenzhou Medical University, The State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health, Wenzhou 325027, China
| | - Jia Qu
- The Eye Hospital of Wenzhou Medical University, The State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health, Wenzhou 325027, China
| | - Zi-Bing Jin
- The Eye Hospital of Wenzhou Medical University, The State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health, Wenzhou 325027, China
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58
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Li J, Zhang Y, Cai X, Xia Q, Chen J, Liao Y, Liu Z, Wu Y. All-trans-retinal dimer formation alleviates the cytotoxicity of all-trans-retinal in human retinal pigment epithelial cells. Toxicology 2016; 371:41-48. [PMID: 27751755 DOI: 10.1016/j.tox.2016.10.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Accepted: 10/09/2016] [Indexed: 12/20/2022]
Abstract
Effective clearance of all-trans-retinal (atRAL) from retinal pigment epithelial (RPE) cells is important for avoiding its cytotoxicity. However, the metabolism of atRAL in RPE cells is poorly clarified. The present study was designed to analyze metabolic products of atRAL and to compare the cytotoxicity of atRAL versus its derivative all-trans-retinal dimer (atRAL-dimer) in human RPE cells. We found that all-trans-retinol (atROL) and a mixture of atRAL condensation metabolites including atRAL-dimer and A2E were generated after incubating RPE cells with atRAL for 6h, and the amount of atRAL-dimer was significantly higher than that of A2E. In the eyes of Rdh8-/- Abca4-/- mice, a mouse model with defects in retinoid cycle that displays some symbolic characteristics of age-related macular degeneration (AMD), the level of atRAL-dimer was increased compared to wild-type mice, and was even much greater than that of A2E & isomers. The cytotoxicity of atRAL-dimer was reduced compared with its precursor atRAL. The latter could provoke intracellular reactive oxygen species (ROS) overproduction, increase the mRNA expression of several oxidative stress related genes (Nrf2, HO-1, and γ-GCSh), and induce ΔΨm loss in RPE cells. By contrast, the abilities of atRAL-dimer to induce intracellular ROS and oxidative stress were much weaker versus that of concentration-matched atRAL, and atRAL-dimer exhibited no toxic effect on mitochondrial function at higher concentrations. In conclusion, the formation of atRAL-dimer during atRAL metabolic process ameliorates the cytotoxicity of atRAL by reducing oxidative stress.
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Affiliation(s)
- Jie Li
- Fujian Provincial Key Laboratory of Ophthalmology and Visual Science, Eye Institute of Xiamen University, College of Medicine, Xiamen University, Xiamen, Fujian Province, China; Taizhou First People's Hospital, Taizhou, Zhejiang Province, China
| | - Yanli Zhang
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Xianhui Cai
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, Zhejiang Province, China
| | - Qingqing Xia
- Taizhou First People's Hospital, Taizhou, Zhejiang Province, China
| | - Jingmeng Chen
- College of Medicine, Xiamen University, Xiamen, Fujian Province, China
| | - Yi Liao
- Fujian Provincial Key Laboratory of Ophthalmology and Visual Science, Eye Institute of Xiamen University, College of Medicine, Xiamen University, Xiamen, Fujian Province, China
| | - Zuguo Liu
- Fujian Provincial Key Laboratory of Ophthalmology and Visual Science, Eye Institute of Xiamen University, College of Medicine, Xiamen University, Xiamen, Fujian Province, China
| | - Yalin Wu
- Fujian Provincial Key Laboratory of Ophthalmology and Visual Science, Eye Institute of Xiamen University, College of Medicine, Xiamen University, Xiamen, Fujian Province, China.
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Abstract
Retinal photoreceptor cells contain a specialized outer segment (OS) compartment that functions in the capture of light and its conversion into electrical signals in a process known as phototransduction. In rods, photoisomerization of 11-cis to all-trans retinal within rhodopsin triggers a biochemical cascade culminating in the closure of cGMP-gated channels and hyperpolarization of the cell. Biochemical reactions return the cell to its 'dark state' and the visual cycle converts all-trans retinal back to 11-cis retinal for rhodopsin regeneration. OS are continuously renewed, with aged membrane removed at the distal end by phagocytosis and new membrane added at the proximal end through OS disk morphogenesis linked to protein trafficking. The molecular basis for disk morphogenesis remains to be defined in detail although several models have been proposed, and molecular mechanisms underlying protein trafficking are under active investigation. The aim of this Cell Science at a Glance article and the accompanying poster is to highlight our current understanding of photoreceptor structure, phototransduction, the visual cycle, OS renewal, protein trafficking and retinal degenerative diseases.
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Affiliation(s)
- Robert S Molday
- Department of Biochemistry and Molecular Biology, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3 Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9
| | - Orson L Moritz
- Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9
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Neumann J, Rose-Sperling D, Hellmich UA. Diverse relations between ABC transporters and lipids: An overview. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:605-618. [PMID: 27693344 DOI: 10.1016/j.bbamem.2016.09.023] [Citation(s) in RCA: 103] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 09/24/2016] [Accepted: 09/26/2016] [Indexed: 12/19/2022]
Abstract
It was first discovered in 1992 that P-glycoprotein (Pgp, ABCB1), an ATP binding cassette (ABC) transporter, can transport phospholipids such as phosphatidylcholine, -ethanolamine and -serine as well as glucosylceramide and glycosphingolipids. Subsequently, many other ABC transporters were identified to act as lipid transporters. For substrate transport by ABC transporters, typically a classic, alternating access model with an ATP-dependent conformational switch between a high and a low affinity substrate binding site is evoked. Transport of small hydrophilic substrates can easily be imagined this way, as the molecule can in principle enter and exit the transporter in the same orientation. Lipids on the other hand need to undergo a 180° degree turn as they translocate from one membrane leaflet to the other. Lipids and lipidated molecules are highly diverse, so there may be various ways how to achieve their flipping and flopping. Nonetheless, an increase in biophysical, biochemical and structural data is beginning to shed some light on specific aspects of lipid transport by ABC transporters. In addition, there is now abundant evidence that lipids affect ABC transporter conformation, dynamics as well as transport and ATPase activity in general. In this review, we will discuss different ways in which lipids and ABC transporters interact and how lipid translocation may be achieved with a focus on the techniques used to investigate these processes. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.
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Affiliation(s)
- Jennifer Neumann
- Institute of Pharmacy and Biochemistry, Johannes Gutenberg University Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Dania Rose-Sperling
- Institute of Pharmacy and Biochemistry, Johannes Gutenberg University Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Ute A Hellmich
- Institute of Pharmacy and Biochemistry, Johannes Gutenberg University Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany.
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61
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Genomic screening of ABCA4 and array CGH analysis underline the genetic variability of Greek patients with inherited retinal diseases. Meta Gene 2016; 8:37-43. [PMID: 27014590 PMCID: PMC4792891 DOI: 10.1016/j.mgene.2016.02.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 01/12/2016] [Accepted: 02/10/2016] [Indexed: 11/22/2022] Open
Abstract
Background Retinal dystrophies are a clinically and genetically heterogeneous group of disorders which affect more than two million people worldwide. The present study focused on the role of the ABCA4 gene in the pathogenesis of hereditary retinal dystrophies (autosomal recessive Stargardt disease, autosomal recessive cone-rod dystrophy, and autosomal recessive retinitis pigmentosa) in patients of Greek origin. Materials and methods Our cohort included 26 unrelated patients and their first degree healthy relatives. The ABCA4 mutation screening involved Sanger sequencing of all exons and flanking regions. Evaluation of novel variants included sequencing of control samples, family segregation analysis and characterization by in silico prediction tools. Twenty five patients were also screened for copy number variations by array-comparative genomic hybridization. Results Excluding known disease-causing mutations and polymorphisms, two novel variants were identified in coding and non-coding regions of ABCA4. Array-CGH analysis revealed two partial deletions of USH2A and MYO3A in two patients with nonsyndromic autosomal recessive retinitis pigmentosa. Conclusions The ABCA4 mutation spectrum in Greek patients differs from other populations. Bioinformatic tools, segregation analysis along with clinical data from the patients seemed to be crucial for the evaluation of genetic variants and particularly for the discrimination between causative and non-causative variants. Sixteen known pathological genetic variants were identified in ABCA4 gene in Greek patients with retinal dystrophies. Two novel variants were found in patients with Stargardt’s disease and cone-rod dystrophy respectively. Two reported mutations in Stargardt's patients were identified in retinitis pigmentosa and cone-rod dystrophy patients. The mutations p.Gly1961Glu and p.Ala1038Val, which are common in other populations, where also found in our cohort consisted of 26 Greek patients. Array-comparative genome hybridization revealed large deletions in two out of the 25 cases studied.
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62
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Sangermano R, Bax NM, Bauwens M, van den Born LI, De Baere E, Garanto A, Collin RWJ, Goercharn-Ramlal ASA, den Engelsman-van Dijk AHA, Rohrschneider K, Hoyng CB, Cremers FPM, Albert S. Photoreceptor Progenitor mRNA Analysis Reveals Exon Skipping Resulting from the ABCA4 c.5461-10T→C Mutation in Stargardt Disease. Ophthalmology 2016; 123:1375-85. [PMID: 26976702 DOI: 10.1016/j.ophtha.2016.01.053] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Revised: 01/29/2016] [Accepted: 01/29/2016] [Indexed: 02/06/2023] Open
Abstract
PURPOSE To elucidate the functional effect of the ABCA4 variant c.5461-10T→C, one of the most frequent variants associated with Stargardt disease (STGD1). DESIGN Case series. PARTICIPANTS Seventeen persons with STGD1 carrying ABCA4 variants and 1 control participant. METHODS Haplotype analysis of 4 homozygotes and 11 heterozygotes for c.5461-10T→C and sequence analysis of the ABCA4 gene for a homozygous proband. Fibroblasts were reprogrammed from 3 persons with STGD1 into induced pluripotent stem cells, which were differentiated into photoreceptor progenitor cells (PPCs). The effect of the c.5461-10T→C variant on RNA splicing by reverse-transcription polymerase chain reaction was analyzed using PPC mRNA. In vitro assays were performed with minigene constructs containing ABCA4 exon 39. We analyzed the natural history and ophthalmologic characteristics of 4 persons homozygous for c.5461-10T→C. MAIN OUTCOME MEASURES Haplotype and rare variant data for ABCA4, RNA splice defects, age at diagnosis, visual acuity, fundus appearance, visual field, electroretinography (ERG) results, fluorescein angiography results, and fundus autofluorescence findings. RESULTS The frequent ABCA4 variant c.5461-10T→C has a subtle effect on splicing based on prediction programs. A founder haplotype containing c.5461-10T→C was found to span approximately 96 kb of ABCA4 and did not contain other rare sequence variants. Patient-derived PPCs showed skipping of exon 39 or exons 39 and 40 in the mRNA. HEK293T cell transduction with minigenes carrying exon 39 showed that the splice defects were the result of the c.5461-10T→C variant. All 4 subjects carrying the c.5461-10T→C variant in a homozygous state showed a young age of STGD1 onset, with low visual acuity at presentation and abnormal cone ERG results. All 4 demonstrated severe cone-rod dystrophy before 20 years of age and were legally blind by 25 years of age. CONCLUSIONS The ABCA4 variant c.5461-10T→C is located on a founder haplotype lacking other disease-causing rare sequence variants. In vitro studies revealed that it leads to mRNA exon skipping and ABCA4 protein truncation. Given the severe phenotype in persons homozygous for this variant, we conclude that this variant results in the absence of ABCA4 activity.
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Affiliation(s)
- Riccardo Sangermano
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands; Radboud Institute of Molecular Life Sciences, Nijmegen, The Netherlands
| | - Nathalie M Bax
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Miriam Bauwens
- Center for Medical Genetics, Ghent University and Ghent University Hospital, Ghent, Belgium
| | | | - Elfride De Baere
- Center for Medical Genetics, Ghent University and Ghent University Hospital, Ghent, Belgium
| | - Alejandro Garanto
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands; Radboud Institute of Molecular Life Sciences, Nijmegen, The Netherlands
| | - Rob W J Collin
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands; Radboud Institute of Molecular Life Sciences, Nijmegen, The Netherlands
| | | | | | - Klaus Rohrschneider
- Universitätsaugenklinik, Ruprecht-Karls-Universität, Heidelberg, Heidelberg, Germany
| | - Carel B Hoyng
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Frans P M Cremers
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands; Radboud Institute of Molecular Life Sciences, Nijmegen, The Netherlands.
| | - Silvia Albert
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands; Radboud Institute of Molecular Life Sciences, Nijmegen, The Netherlands.
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Trapani I, Banfi S, Simonelli F, Surace EM, Auricchio A. Gene therapy of inherited retinal degenerations: prospects and challenges. Hum Gene Ther 2016; 26:193-200. [PMID: 25762209 DOI: 10.1089/hum.2015.030] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Because of its favorable anatomical and immunological characteristics, the eye has been at the forefront of translational gene therapy. Dozens of promising proofs of concept have been obtained in animal models of inherited retinal degenerations (IRDs), and some of them have been relayed to the clinic. The results from the first clinical trials for a congenital form of blindness have generated great interest and have demonstrated the safety and efficacy of intraocular administrations of viral vectors in humans. However, this progress has also generated new questions and posed challenges that need to be addressed to further expand the applicability of gene therapy in the eye, including safe delivery of viral vectors to the outer retina, treatment of dominant IRDs as well as of IRDs caused by mutations in large genes, and, finally, selection of the appropriate IRDs and patients to maximize the efficacy of gene transfer. This review summarizes the strategies that are currently being exploited to overcome these challenges and drive the clinical development of retinal gene therapy.
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Affiliation(s)
- Ivana Trapani
- 1 Telethon Institute of Genetics and Medicine (TIGEM) , Pozzuoli, Naples 80078, Italy
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Mitra RN, Zheng M, Han Z. Nanoparticle-motivated gene delivery for ophthalmic application. WILEY INTERDISCIPLINARY REVIEWS. NANOMEDICINE AND NANOBIOTECHNOLOGY 2016; 8:160-74. [PMID: 26109528 PMCID: PMC4688250 DOI: 10.1002/wnan.1356] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 05/21/2015] [Accepted: 05/23/2015] [Indexed: 12/24/2022]
Abstract
Ophthalmic gene therapy is an intellectual and intentional manipulation of desired gene expression into the specific cells of an eye for the treatment of ophthalmic (ocular) genetic dystrophies and pathological conditions. Exogenous nucleic acids such as DNA, small interfering RNA, micro RNA, and so on, are used for the purpose of managing expression of the desired therapeutic proteins in ocular tissues. The delivery of unprotected nucleic acids into the cells is limited because of exogenous and endogenous degradation modalities. Nanotechnology, a promising and sophisticated cutting edge tool, works as a protective shelter for these therapeutic nucleic acids. They can be safely delivered to the required cells in order to modulate anticipated protein expression. To this end, nanotechnology is seen as a potential and promising strategy in the field of ocular gene delivery. This review focused on current nanotechnology modalities and other promising nonviral strategies being used to deliver therapeutic genes in order to treat various devastating ocular diseases.
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Affiliation(s)
| | - Min Zheng
- Department of Ophthalmology, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Zongchao Han
- Department of Ophthalmology, University of North Carolina, Chapel Hill, NC 27599, USA
- Carolina Institute for NanoMedicine, University of North Carolina, Chapel Hill, NC 27599, USA
- Division of Molecular Pharmaceutics, Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599, USA
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Babu Gurramkonda V, Hussain Syed A, Murthy J, Chaubey G, Bhaskar Lakkakula VKS. Polymorphic variants near 1p22 and 20q11.2 loci and the risk of non-syndromic cleft lip and palate in South Indian population. Int J Pediatr Otorhinolaryngol 2015; 79:2389-93. [PMID: 26586245 DOI: 10.1016/j.ijporl.2015.10.055] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2015] [Revised: 10/28/2015] [Accepted: 10/29/2015] [Indexed: 11/29/2022]
Abstract
BACKGROUND Recent genome-wide association studies (GWAS) have reported multiple genetic risk loci for non-syndromic orofacial clefts (NSOFCs) in many populations. However, the contribution of these loci to NSOFC in India, which comprises one-fifth of the global population, is completely lacking. Our aim was to replicate the association of the SNPs located on 1p22 chromosomal loci (rs540026, rs481931) and 20q11.2 (rs13041247, rs11696257) in the aetiology of NSOFCs, in South Indian populations. METHODS The SNPs were genotyped by using KBiosciences KASPar SNP genotyping chemistry in 173 cases and 176 controls for NSOFCs in South India. To estimate the association between these SNPs and NSOFCs, chi-square test was adopted. Odds ratios (OR) with 95% confidence intervals (CI) were also calculated in order to assess the risk. RESULTS Single nucleotide polymorphisms located at chromosomal region 1p22 are not found to be associated with cleft lip with or without non-syndromic cleft palate (NSCL/P) and non-syndromic cleft palate only (NSCPO) at either the genotype or allele levels. Further, there is no LD observed between these variants. The polymorphic variants near 20q11.2 (rs13041247, rs11696257) are in complete linkage disequilibrium (LD) and are significantly associated with only NSCL/P in genotypic (p=0.013) and allelic models (p=0.029). In the genotypic model significance persisted even after Bonferroni correction (p<0.016). CONCLUSION These results suggest that 20q11.2 SNPs could play a contributory role in the pathophysiology and risk of NSCL/P, while the variations in 1p22 do not underlie the pathophysiology of NSOFCs in South Indian populations.
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Affiliation(s)
| | - Altaf Hussain Syed
- Department of Plastic Surgery, Sri Ramachandra University, Chennai, India
| | - Jyotsna Murthy
- Department of Plastic Surgery, Sri Ramachandra University, Chennai, India
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Structural Features of the ATP-Binding Cassette (ABC) Transporter ABCA3. Int J Mol Sci 2015; 16:19631-44. [PMID: 26295388 PMCID: PMC4581316 DOI: 10.3390/ijms160819631] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2015] [Revised: 07/23/2015] [Accepted: 08/07/2015] [Indexed: 12/20/2022] Open
Abstract
In this review we reported and discussed the structural features of the ATP-Binding Cassette (ABC) transporter ABCA3 and how the use of bioinformatics tools could help researchers to obtain a reliable structural model of this important transporter. In fact, a model of ABCA3 is still lacking and no crystallographic structures (of the transporter or of its orthologues) are available. With the advent of next generation sequencing, many disease-causing mutations have been discovered and many more will be found in the future. In the last few years, ABCA3 mutations have been reported to have important pediatric implications. Thus, clinicians need a reliable structure to locate relevant mutations of this transporter and make genotype/phenotype correlations of patients affected by ABCA3-related diseases. In conclusion, we strongly believe that the model preliminarily generated by these novel bioinformatics tools could be the starting point to obtain more refined models of the ABCA3 transporter.
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Sabirzhanova I, Lopes Pacheco M, Rapino D, Grover R, Handa JT, Guggino WB, Cebotaru L. Rescuing Trafficking Mutants of the ATP-binding Cassette Protein, ABCA4, with Small Molecule Correctors as a Treatment for Stargardt Eye Disease. J Biol Chem 2015; 290:19743-55. [PMID: 26092729 DOI: 10.1074/jbc.m115.647685] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Indexed: 11/06/2022] Open
Abstract
Stargardt disease is the most common form of early onset macular degeneration. Mutations in ABCA4, a member of the ATP-binding cassette (ABC) family, are associated with Stargardt disease. Here, we have examined two disease-causing mutations in the NBD1 region of ABCA4, R1108C, and R1129C, which occur within regions of high similarity with CFTR, another ABC transporter gene, which is associated with cystic fibrosis. We show that R1108C and R1129C are both temperature-sensitive processing mutants that engage the cellular quality control mechanism and show a strong interaction with the chaperone Hsp 27. Both mutant proteins also interact with HDCAC6 and are degraded in the aggresome. We also demonstrate that novel corrector compounds that are being tested as treatment for cystic fibrosis, such as VX-809, can rescue the processing of the ABCA4 mutants, particularly their expression at the cell surface, and can reduce their binding to HDAC6. Thus, our data suggest that VX-809 can potentially be developed as a new therapy for Stargardt disease, for which there is currently no treatment.
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Affiliation(s)
- Inna Sabirzhanova
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - Miquéias Lopes Pacheco
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - Daniele Rapino
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - Rahul Grover
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - James T Handa
- Department of Ophthalmology, Johns Hopkins University, Baltimore, Maryland 21231
| | - William B Guggino
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205
| | - Liudmila Cebotaru
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and Department of Ophthalmology, Johns Hopkins University, Baltimore, Maryland 21231
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Identification of Novel Mutations in ABCA4 Gene: Clinical and Genetic Analysis of Indian Patients with Stargardt Disease. BIOMED RESEARCH INTERNATIONAL 2015; 2015:940864. [PMID: 25922843 PMCID: PMC4398921 DOI: 10.1155/2015/940864] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Revised: 02/13/2015] [Accepted: 03/09/2015] [Indexed: 11/17/2022]
Abstract
Stargardt disease (STGD) is the leading cause of juvenile macular degeneration associated with progressive central vision loss, photophobia, and colour vision abnormalities. In this study, we have described the clinical and genetic features of Stargardt patients from an Indian cohort. The next generation sequencing was carried out in five clinically confirmed unrelated patients and their family members using a gene panel comprising 184 retinal specific genes. Sequencing results were analyzed by read mapping and variant calling in genes of interest, followed by their verification and interpretation. Genetic analysis revealed ABCA4 mutations in all of the five unrelated patients. Among these, four patients were found with compound heterozygous mutations and another one had homozygous mutation. All the affected individuals showed signs and symptoms consistent with the disease phenotype. We report two novel ABCA4 mutations in Indian patients with STGD disease, which expands the existing spectrum of disease-causing variants and the understanding of phenotypic and genotypic correlations. Screening for causative mutations in patients with STGD using panel of targeted gene sequencing by NGS would be a cost effective tool, might be helpful in confirming the precise diagnosis, and contributes towards the genetic counselling of asymptomatic carriers and isolated patients.
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Garcia-Cazorla À, Mochel F, Lamari F, Saudubray JM. The clinical spectrum of inherited diseases involved in the synthesis and remodeling of complex lipids. A tentative overview. J Inherit Metab Dis 2015; 38:19-40. [PMID: 25413954 DOI: 10.1007/s10545-014-9776-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Revised: 09/16/2014] [Accepted: 09/23/2014] [Indexed: 12/19/2022]
Abstract
Over one hundred diseases related to inherited defects of complex lipids synthesis and remodeling are now reported. Most of them were described within the last 5 years. New descriptions and phenotypes are expanding rapidly. While the associated clinical phenotype is currently difficult to outline, with only a few patients identified, it appears that all organs and systems may be affected. The main clinical presentations can be divided into (1) Diseases affecting the central and peripheral nervous system. Complex lipid synthesis disorders produce prominent motor manifestations due to upper and/or lower motoneuron degeneration. Motor signs are often complex, associated with other neurological and extra-neurological signs. Three neurological phenotypes, spastic paraparesis, neurodegeneration with brain iron accumulation and peripheral neuropathies, deserve special attention. Many apparently well clinically defined syndromes are not distinct entities, but rather clusters on a continuous spectrum, like for the PNPLA6-associated diseases, extending from Boucher-Neuhauser syndrome via Gordon Holmes syndrome to spastic ataxia and pure hereditary spastic paraplegia; (2) Muscular/cardiac presentations; (3) Skin symptoms mostly represented by syndromic (neurocutaneous) and non syndromic ichthyosis; (4) Retinal dystrophies with syndromic and non syndromic retinitis pigmentosa, Leber congenital amaurosis, cone rod dystrophy, Stargardt disease; (5) Congenital bone dysplasia and segmental overgrowth disorders with congenital lipomatosis; (6) Liver presentations characterized mainly by transient neonatal cholestatic jaundice and non alcoholic liver steatosis with hypertriglyceridemia; and (7) Renal and immune presentations. Lipidomics and molecular functional studies could help to elucidate the mechanism(s) of dominant versus recessive inheritance observed for the same gene in a growing number of these disorders.
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Affiliation(s)
- Àngels Garcia-Cazorla
- Department of Neurology, Neurometabolic Unit, Hospital Sant Joan de Déu and CIBERER, ISCIII, Barcelona, Spain,
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Molday RS. Insights into the Molecular Properties of ABCA4 and Its Role in the Visual Cycle and Stargardt Disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 134:415-31. [DOI: 10.1016/bs.pmbts.2015.06.008] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Lamari F, Mochel F, Saudubray JM. An overview of inborn errors of complex lipid biosynthesis and remodelling. J Inherit Metab Dis 2015; 38:3-18. [PMID: 25238787 DOI: 10.1007/s10545-014-9764-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 08/08/2014] [Accepted: 08/14/2014] [Indexed: 01/10/2023]
Abstract
In a review published in 2012, we delineated 14 inborn errors of metabolism (IEM) related to defects in biosynthesis of complex lipids, particularly phospholipids and sphingolipids (Lamari et al 2013). Given the numerous roles played by these molecules in membrane integrity, cell structure and function, this group of diseases is rapidly expanding as predicted. Almost 40 new diseases related to genetic defects in enzymes involved in the biosynthesis and remodelling of phospholipids, sphingolipids and complex fatty acids are now reported. While the clinical phenotype associated with these defects is currently difficult to outline, with only a few patients identified to date, it appears that all organs and systems may be affected - central and peripheral nervous system, eye, muscle, skin, bone, liver, immune system, etc. This chapter presents an introductive overview of this new group of IEM. More broadly, this special issue provides an update on other IEM involving complex lipids, namely dolichol and isoprenoids, glycolipids and congenital disorders of glycosylation, very long chain fatty acids and plasmalogens. Likewise, more than 100 IEM may actually lead to primary or secondary defects of complex lipids synthesis and remodelling. Because of the implication of several cellular compartments, this new group of disorders affecting the synthesis and remodelling of complex molecules challenges our current classification of IEM still largely based on cellular organelles--i.e. mitochondrial, lysosomal, peroxisomal disorders. While most of these new disorders have been identified by next generation sequencing, we wish to emphasize the promising role of lipidomics in deciphering their pathophysiology and identifying therapeutic targets.
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Affiliation(s)
- Foudil Lamari
- Bioclinic and Genetic Unit of Neurometabolic Diseases, Pitié-Salpêtrière Hospital, (APHP), Paris, 75013, France
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A polymorphic marker associated with non-syndromic cleft lip with or without cleft palate in a population in Heilongjiang Province, northern China. Arch Oral Biol 2014; 60:357-61. [PMID: 25499508 DOI: 10.1016/j.archoralbio.2014.11.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 09/24/2014] [Accepted: 11/16/2014] [Indexed: 11/21/2022]
Abstract
OBJECTIVE To further assess the roles of the ABCA4 (ATP-binding cassette, sub-family A, member 4) gene in NSCL/P, we investigated two tag SNPs in ABCA4 (rs481931 and rs560426) in a northern Chinese Han population where the prevalence of NSCL/P is high. MATERIALS AND METHODS The two SNPs were examined for association with NSCL/P in 344 patients and 324 healthy controls. Peripheral blood samples were acquired at study enrollment, and DNA samples were extracted. SNPs were genotyped using a mini-sequencing (SNAPSHOT) method. RESULTS We observed a significant correlation between the ABCA4 SNP rs560426 and NSCL/P (p=0.0041) but no evidence of association between rs481931 and NSCL/P. The G/G genotype at the rs560426 SNP in ABCA4 gene had an odd ratios of 2.39 (95%CI: 1.38-4.14, p=0.0041) compared with the A/A genotype, and a similar significance was noted in the CL/P subgroup (ORA/G=1.60, 95%CI: 1.09-2.34, ORG/G=2.96, 95%CI: 1.63-5.37 and ORG/G+A/G=1.80, 95%CI: 1.25-2.60, p=0.0007). CONCLUSIONS Our study provides further evidence regarding the roles of genetic markers in ABCA4 in NSCL/P development in this northern Chinese Han population. G allele of rs560426 may be a risk factor for developing NSCL/P.
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Li J, Cai X, Xia Q, Yao K, Chen J, Zhang Y, Naranmandura H, Liu X, Wu Y. Involvement of Endoplasmic Reticulum Stress in All-Trans-Retinal-Induced Retinal Pigment Epithelium Degeneration. Toxicol Sci 2014; 143:196-208. [DOI: 10.1093/toxsci/kfu223] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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ATP-binding cassette transporter ABCA4 and chemical isomerization protect photoreceptor cells from the toxic accumulation of excess 11-cis-retinal. Proc Natl Acad Sci U S A 2014; 111:5024-9. [PMID: 24707049 DOI: 10.1073/pnas.1400780111] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The visual cycle is a series of enzyme-catalyzed reactions which converts all-trans-retinal to 11-cis-retinal for the regeneration of visual pigments in rod and cone photoreceptor cells. Although essential for vision, 11-cis-retinal like all-trans-retinal is highly toxic due to its highly reactive aldehyde group and has to be detoxified by either reduction to retinol or sequestration within retinal-binding proteins. Previous studies have focused on the role of the ATP-binding cassette transporter ABCA4 associated with Stargardt macular degeneration and retinol dehydrogenases (RDH) in the clearance of all-trans-retinal from photoreceptors following photoexcitation. How rod and cone cells prevent the accumulation of 11-cis-retinal in photoreceptor disk membranes in excess of what is required for visual pigment regeneration is not known. Here we show that ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes. This transport function together with chemical isomerization to its all-trans isomer and reduction to all-trans-retinol by RDH can prevent the accumulation of excess 11-cis-retinal and its Schiff-base conjugate and the formation of toxic bisretinoid compounds as found in ABCA4-deficient mice and individuals with Stargardt macular degeneration. This segment of the visual cycle in which excess 11-cis-retinal is converted to all-trans-retinol provides a rationale for the unusually high content of PE and its long-chain unsaturated docosahexaenoyl group in photoreceptor membranes and adds insight into the molecular mechanisms responsible for Stargardt macular degeneration.
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Layer PG, Araki M, Vogel-Höpker A. New concepts for reconstruction of retinal and pigment epithelial tissues. EXPERT REVIEW OF OPHTHALMOLOGY 2014. [DOI: 10.1586/eop.10.42] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Affiliation(s)
| | | | - Krzysztof Palczewski
- Department of Pharmacology, School of Medicine, Case
Western Reserve University, 2109 Adelbert Road, Cleveland, Ohio 44106-4965,
United States
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Utz VM, Chappelow AV, Marino MJ, Beight CD, Sturgill-Short GM, Pauer GJT, Crowe S, Hagstrom SA, Traboulsi EI. Identification of three ABCA4 sequence variations exclusive to African American patients in a cohort of patients with Stargardt disease. Am J Ophthalmol 2013; 156:1220-1227.e2. [PMID: 24011517 DOI: 10.1016/j.ajo.2013.07.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 07/10/2013] [Accepted: 07/11/2013] [Indexed: 11/18/2022]
Abstract
PURPOSE To describe the clinical and molecular findings in ten unrelated African American patients with Stargardt disease. DESIGN Retrospective, observational case series. METHODS We reviewed the clinical histories, examinations, and genotypes of 85 patients with molecular diagnoses of Stargardt disease. Three ABCA4 sequence variations identified exclusively in African Americans were evaluated in 300 African American controls and by in silico analysis. RESULTS ABCA4 sequence changes were identified in 85 patients from 80 families, of which 11 patients identified themselves as African American. Of these 11 patients, 10 unrelated patients shared 1 of 3 ABCA4 sequence variations: c.3602T>G (p.L1201R); c.3899G>A (p.R1300Q); or c.6320G>A (p.R2107H). The minor allele frequencies in the African American control population for each variation were 7.5%, 6.3%, and 2%, respectively. This is comparable to the allele frequency in African Americans in the Exome Variant Server. In contrast, the allele frequency of all three of these variations was less than or equal to 0.05% in European Americans. Although both c.3602T>G and c.3899G>A have been reported as likely disease-causing variations, one of our control patients was homozygous for each variant, suggesting that these are nonpathogenic. In contrast, the absence of c.6320G>A in the control population in the homozygous state, combined with the results of bioinformatics analysis, support its pathogenicity. CONCLUSIONS Three ABCA4 sequence variations were identified exclusively in 10 unrelated African American patients: p.L1201R and p.R1300Q likely represent nonpathogenic sequence variants, whereas the p.R2107H substitution appears to be pathogenic. Characterization of population-specific disease alleles may have important implications for the development of genetic screening algorithms.
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Quazi F, Molday RS. Differential phospholipid substrates and directional transport by ATP-binding cassette proteins ABCA1, ABCA7, and ABCA4 and disease-causing mutants. J Biol Chem 2013; 288:34414-26. [PMID: 24097981 DOI: 10.1074/jbc.m113.508812] [Citation(s) in RCA: 156] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
ABCA1, ABCA7, and ABCA4 are members of the ABCA subfamily of ATP-binding cassette transporters that share extensive sequence and structural similarity. Mutations in ABCA1 cause Tangier disease characterized by defective cholesterol homeostasis and high density lipoprotein (HDL) deficiency. Mutations in ABCA4 are responsible for Stargardt disease, a degenerative disorder associated with severe loss in central vision. Although cell-based studies have implicated ABCA proteins in lipid transport, the substrates and direction of transport have not been firmly established. We have purified and reconstituted ABCA1, ABCA7, and ABCA4 into liposomes for fluorescent-lipid transport studies. ABCA1 actively exported or flipped phosphatidylcholine, phosphatidylserine, and sphingomyelin from the cytoplasmic to the exocytoplasmic leaflet of membranes, whereas ABCA7 preferentially exported phosphatidylserine. In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction. The same phospholipids stimulated the ATPase activity of these ABCA transporters. The transport and ATPase activities of ABCA1 and ABCA4 were reduced by 25% in the presence of 20% cholesterol. Nine ABCA1 Tangier mutants and the corresponding ABCA4 Stargardt mutants showed significantly reduced phospholipid transport activity and subcellular mislocalization. These studies provide the first direct evidence for ABCA1 and ABCA7 functioning as phospholipid transporters and suggest that this activity is an essential step in the loading of apoA-1 with phospholipids for HDL formation.
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Affiliation(s)
- Faraz Quazi
- From the Department of Biochemistry and Molecular Biology, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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80
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Mihai DM, Jiang H, Blaner WS, Romanov A, Washington I. The retina rapidly incorporates ingested C20-D₃-vitamin A in a swine model. Mol Vis 2013; 19:1677-83. [PMID: 23914132 PMCID: PMC3731456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 07/22/2013] [Indexed: 11/12/2022] Open
Abstract
PURPOSE To determine how the retina uses vitamin A for vision, we studied the flux of oral vitamin A into and out of the swine retina. METHODS We administered labeled vitamin A to swine daily for 30 days and measured the percent of the labeled vitamin A to native unlabeled vitamin A in the retinal epithelium, neuroretina, plasma, liver, lung, and kidney. RESULTS We show that during normal vitamin A homeostasis, the retina rapidly assimilates newly ingested dietary vitamin A, which replaces native vitamin A. Retinal vitamin A is turned over faster than previously thought. Provitamin A carotenoids do not significantly contribute to retinal vitamin A pools when consuming diets adequate in vitamin A. CONCLUSIONS Fast vitamin A turnover in the retina has direct implications for emerging therapies to prevent major forms of blindness based on controlling the concentrations of retinal vitamin A.
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Affiliation(s)
- Doina M. Mihai
- Department of Ophthalmology, Columbia University Medical Center New York, NY
| | - Hongfeng Jiang
- Department of Medicine, Columbia University Medical Center, New York, NY
| | - William S. Blaner
- Department of Medicine, Columbia University Medical Center, New York, NY
| | - Alexander Romanov
- Institute of Comparative Medicine, Columbia University Medical Center, New York, NY
| | - Ilyas Washington
- Department of Ophthalmology, Columbia University Medical Center New York, NY
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81
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Fujinami K, Sergouniotis PI, Davidson AE, Mackay DS, Tsunoda K, Tsubota K, Robson AG, Holder GE, Moore AT, Michaelides M, Webster AR. The clinical effect of homozygous ABCA4 alleles in 18 patients. Ophthalmology 2013; 120:2324-31. [PMID: 23769331 DOI: 10.1016/j.ophtha.2013.04.016] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Revised: 04/17/2013] [Accepted: 04/17/2013] [Indexed: 10/26/2022] Open
Abstract
PURPOSE To describe the phenotypic presentation of a cohort of individuals with homozygous disease-associated ABCA4 variants. DESIGN Retrospective case series. PARTICIPANTS Eighteen affected individuals from 13 families ascertained from a total cohort of 214 families with ABCA4-related retinal disease presenting to a single center. METHODS A detailed history was obtained, and color fundus photography, autofluorescence (AF) imaging, optical coherence tomography (OCT), and electrophysiologic assessment were performed. Phenotypes based on ophthalmoscopy, AF, and electrophysiology were assigned using previously reported characteristics. ABCA4 mutation detection was performed using the ABCR400 microarray (Asper Biotech, Tartu, Estonia) and high-throughput DNA sequencing, with direct sequencing used to assess segregation. MAIN OUTCOME MEASURES Detailed clinical, electrophysiologic, and molecular genetic findings. RESULTS Eleven disease-associated homozygous ABCA4 alleles were identified, including 1 frame shift, 2 stops, 1 intronic variant causing splice-site alteration, 2 complex missense variants, and 5 missense variants: p.Glu905fsX916, p.Arg1300X, p.Gln2220X, c.4253+4 C>T, p.Leu541Pro and p.Ala1038Val (homozygosity for complex allele), p.Val931Met and p.Arg1705Gln (complex allele), p.Arg212Cys, p.Cys1488Arg, p.Arg1640Trp, p.Gly1961Glu, and p.Leu2027Phe. Eight of these 11 homozygous alleles have not been reported previously. Six of 7 patients with homozygous null alleles had early-onset (<10 years) disease, with all 7 having a severe phenotype. Two patients with homozygous missense variants (p.Leu541Pro and p.Ala1038Val [complex], and p.Arg1640Trp) presented with a severe phenotype. Three patients with homozygous p.Gly1961Glu had adult-onset disease and a mild phenotype. One patient with homozygous p.Leu2027Phe showed a spared fovea and preserved visual acuity. CONCLUSIONS The phenotypes represented in patients identified as homozygous for presumed disease-associated ABCA4 variants gives insight into the effect of individual alleles. Null alleles have severe functional effects, and certain missense variants are similar to nulls, suggesting complete abrogation of protein function. The common alleles identified, p.Gly1961Glu and p. Leu2027Phe, both have a mild structural and functional effect on the adult retina; the latter is associated with relatively retained photoreceptor architecture and function at the fovea.
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Affiliation(s)
- Kaoru Fujinami
- UCL Institute of Ophthalmology, London, United Kingdom; Moorfields Eye Hospital, London, United Kingdom; National Institute of Sensory Organs, National Tokyo Medical Center, Tokyo, Japan; Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan
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82
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Boye SE, Boye SL, Lewin AS, Hauswirth WW. A comprehensive review of retinal gene therapy. Mol Ther 2013; 21:509-19. [PMID: 23358189 DOI: 10.1038/mt.2012.280] [Citation(s) in RCA: 204] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Blindness, although not life threatening, is a debilitating disorder for which few, if any treatments exist. Ocular gene therapies have the potential to profoundly improve the quality of life in patients with inherited retinal disease. As such, tremendous focus has been given to develop such therapies. Several factors make the eye an ideal organ for gene-replacement therapy including its accessibility, immune privilege, small size, compartmentalization, and the existence of a contralateral control. This review will provide a comprehensive summary of (i) existing gene therapy clinical trials for several genetic forms of blindness and (ii) preclinical efficacy and safety studies in a variety of animal models of retinal disease which demonstrate strong potential for clinical application. To be as comprehensive as possible, we include additional proof of concept studies using gene replacement, neurotrophic/neuroprotective, optogenetic, antiangiogenic, or antioxidative stress strategies as well as a description of the current challenges and future directions in the ocular gene therapy field to this review as a supplement.
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Affiliation(s)
- Shannon E Boye
- Department of Ophthalmology, University of Florida, Gainesville, FL, USA.
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83
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Bende P, Natarajan K, Marudhamuthu T, Madhavan J. Severity of familial isolated retinitis pigmentosa across different inheritance patterns among an Asian Indian cohort. J Pediatr Ophthalmol Strabismus 2013; 50:34-6. [PMID: 23463886 DOI: 10.3928/01913913-20121107-01] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To predict the progression to legal blindness in patients with isolated inherited retinitis pigmentosa. METHODS This retrospective study evaluated patients with isolated inherited retinitis pigmentosa for age at onset, duration of the disease, and best-corrected visual acuity in an Asian Indian cohort. The Mann–Whitney U test was used to analyze the variables. RESULTS Of 134 patients evaluated, 72% were autosomal recessive, 17% were autosomal dominant, and 11% were X-linked recessive pedigrees. Median age at onset was 8 years for X-linked recessive, 11 years for autosomal recessive, and 21 years for autosomal dominant disease, which was statistically significant. The refractive error due to axial myopia was significantly high in X-linked recessive (−3.50 diopter sphere) compared to autosomal recessive (−1 diopter sphere) and autosomal dominant (0.00 diopter sphere) cases (P < .000). Legal blindness occurred in 50% of X-linked recessive and autosomal recessive cases but in only 32% of autosomal dominant cases. CONCLUSION Identifying the gene defects involved in this cohort will help understand the phenotype variability.
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Affiliation(s)
- Purva Bende
- Department of Genetics and Molecular Biology, Vision Research Foundation, Chennai, Tamil Nadu, India
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84
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Zhong M, Kawaguchi R, Kassai M, Sun H. Retina, retinol, retinal and the natural history of vitamin A as a light sensor. Nutrients 2012; 4:2069-96. [PMID: 23363998 PMCID: PMC3546623 DOI: 10.3390/nu4122069] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Revised: 11/27/2012] [Accepted: 11/28/2012] [Indexed: 02/07/2023] Open
Abstract
Light is both the ultimate energy source for most organisms and a rich information source. Vitamin A-based chromophore was initially used in harvesting light energy, but has become the most widely used light sensor throughout evolution from unicellular to multicellular organisms. Vitamin A-based photoreceptor proteins are called opsins and have been used for billions of years for sensing light for vision or the equivalent of vision. All vitamin A-based light sensors for vision in the animal kingdom are G-protein coupled receptors, while those in unicellular organisms are light-gated channels. This first major switch in evolution was followed by two other major changes: the switch from bistable to monostable pigments for vision and the expansion of vitamin A's biological functions. Vitamin A's new functions such as regulating cell growth and differentiation from embryogenesis to adult are associated with increased toxicity with its random diffusion. In contrast to bistable pigments which can be regenerated by light, monostable pigments depend on complex enzymatic cycles for regeneration after every photoisomerization event. Here we discuss vitamin A functions and transport in the context of the natural history of vitamin A-based light sensors and propose that the expanding functions of vitamin A and the choice of monostable pigments are the likely evolutionary driving forces for precise, efficient, and sustained vitamin A transport.
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Affiliation(s)
- Ming Zhong
- Department of Physiology, Jules Stein Eye Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA.
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85
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Transporter Proteins. Mol Pharmacol 2012. [DOI: 10.1002/9781118451908.ch5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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86
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Coleman JA, Quazi F, Molday RS. Mammalian P4-ATPases and ABC transporters and their role in phospholipid transport. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1831:555-74. [PMID: 23103747 DOI: 10.1016/j.bbalip.2012.10.006] [Citation(s) in RCA: 102] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 10/16/2012] [Accepted: 10/18/2012] [Indexed: 02/08/2023]
Abstract
Transport of phospholipids across cell membranes plays a key role in a wide variety of biological processes. These include membrane biosynthesis, generation and maintenance of membrane asymmetry, cell and organelle shape determination, phagocytosis, vesicle trafficking, blood coagulation, lipid homeostasis, regulation of membrane protein function, apoptosis, etc. P(4)-ATPases and ATP binding cassette (ABC) transporters are the two principal classes of membrane proteins that actively transport phospholipids across cellular membranes. P(4)-ATPases utilize the energy from ATP hydrolysis to flip aminophospholipids from the exocytoplasmic (extracellular/lumen) to the cytoplasmic leaflet of cell membranes generating membrane lipid asymmetry and lipid imbalance which can induce membrane curvature. Many ABC transporters play crucial roles in lipid homeostasis by actively transporting phospholipids from the cytoplasmic to the exocytoplasmic leaflet of cell membranes or exporting phospholipids to protein acceptors or micelles. Recent studies indicate that some ABC proteins can also transport phospholipids in the opposite direction. The importance of P(4)-ATPases and ABC transporters is evident from the findings that mutations in many of these transporters are responsible for severe human genetic diseases linked to defective phospholipid transport. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.
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Affiliation(s)
- Jonathan A Coleman
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, B.C., Canada
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87
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Cheepala S, Hulot JS, Morgan JA, Sassi Y, Zhang W, Naren AP, Schuetz JD. Cyclic nucleotide compartmentalization: contributions of phosphodiesterases and ATP-binding cassette transporters. Annu Rev Pharmacol Toxicol 2012; 53:231-53. [PMID: 23072381 DOI: 10.1146/annurev-pharmtox-010611-134609] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Cyclic nucleotides [e.g., cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)] are ubiquitous second messengers that affect multiple cell functions from maturation of the egg to cell division, growth, differentiation, and death. The concentration of cAMP can be regulated by processes within membrane domains (local regulation) as well as throughout a cell (global regulation). The phosphodiesterases (PDEs) that degrade cAMP have well-known roles in both these processes. It has recently been discovered that ATP-binding cassette (ABC) transporters contribute to both local and global regulation of cAMP. This regulation may require the formation of macromolecular complexes. Some of these transporters are ubiquitously expressed, whereas others are more tissue restricted. Because some PDE inhibitors are also ABC transporter inhibitors, it is conceivable that the therapeutic benefits of their use result from the combined inhibition of both PDEs and ABC transporters. Deciphering the individual contributions of PDEs and ABC transporters to such drug effects may lead to improved therapeutic benefits.
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Affiliation(s)
- Satish Cheepala
- Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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88
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Nakao T, Tsujikawa M, Sawa M, Gomi F, Nishida K. Foveal sparing in patients with Japanese Stargardt's disease and good visual acuity. Jpn J Ophthalmol 2012; 56:584-8. [PMID: 22956038 DOI: 10.1007/s10384-012-0172-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2011] [Accepted: 05/28/2012] [Indexed: 11/29/2022]
Abstract
PURPOSE Patients with Stargardt's disease usually have a poor visual prognosis. However, in our clinical practice we have observed some patients with dark-red foveal pigmentation (sparing) who had good best corrected visual acuity (BCVA) despite the presence of a late-stage disease. The purpose of this study was to investigate the BCVA outcomes in Japanese patients with Stargardt's disease with foveal sparing. METHODS Eighteen consecutive patients (36 eyes) with Stargardt's disease underwent ophthalmoscopy, fluorescein angiography, fundus autofluorescence imaging, and near-infrared fundus autofluorescence (NIA) imaging. The patients were divided into two groups based on the presence or absence of foveal sparing. The presence of foveal sparing was determined based on ophthalmoscopy and NIA imaging results. The association between foveal sparing and BCVA was assessed statistically by Students' t test. RESULTS Of the 36 eyes, ten (27.8 %) had dark-red foveal sparing. The mean BCVA of the group with sparing was 0.16 ± 0.31, expressed in logarithm of the minimum angle of resolution (logMAR) units, and that of the group without sparing was 1.03 ± 0.39 logMAR units, which is a significant difference (p = 0.0000002507). CONCLUSION A subgroup of Japanese patients with late-stage Stargardt's disease and dark-red foveal sparing maintained a relatively good BCVA. The pigmentation was clearly observed using NIA and proved useful for assessing the BCVA prognosis.
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Affiliation(s)
- Takeshi Nakao
- Department of Ophthalmology, Osaka University Medical School, Osaka, Japan
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89
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Quazi F, Lenevich S, Molday RS. ABCA4 is an N-retinylidene-phosphatidylethanolamine and phosphatidylethanolamine importer. Nat Commun 2012; 3:925. [PMID: 22735453 PMCID: PMC3871175 DOI: 10.1038/ncomms1927] [Citation(s) in RCA: 196] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 05/28/2012] [Indexed: 01/26/2023] Open
Abstract
ATP-binding cassette (ABC) transporters comprise a superfamily of proteins, which actively transport a variety of compounds across cell membranes. Mammalian and most eukaryotic ABC transporters function as exporters, flipping or extruding substrates from the cytoplasmic to the extracellular or lumen side of cell membranes. Prokaryotic ABC transporters function either as exporters or importers. Here we show that ABCA4, an ABC transporter found in retinal photoreceptor cells and associated with Stargardt macular degeneration, is a novel importer that actively flips N-retinylidene-phosphatidylethanolamine from the lumen to the cytoplasmic leaflet of disc membranes, thereby facilitating the removal of potentially toxic retinoid compounds from photoreceptors. ABCA4 also actively transports phosphatidylethanolamine in the same direction. Mutations known to cause Stargardt disease decrease N-retinylidene-phosphatidylethanolamine and phosphatidylethanolamine transport activity of ABCA4. These studies provide the first direct evidence for a mammalian ABC transporter that functions as an importer and provide insight into mechanisms underlying substrate transport and the molecular basis of Stargardt disease.
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Affiliation(s)
- Faraz Quazi
- Department of Biochemistry and Molecular Biology, Centre for Macular Research, University of British Columbia, 2350 Health Sciences Mall, Vancouver, British Columbia, Canada V6T 1Z3
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90
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Boyer NP, Higbee D, Currin MB, Blakeley LR, Chen C, Ablonczy Z, Crouch RK, Koutalos Y. Lipofuscin and N-retinylidene-N-retinylethanolamine (A2E) accumulate in retinal pigment epithelium in absence of light exposure: their origin is 11-cis-retinal. J Biol Chem 2012; 287:22276-86. [PMID: 22570475 DOI: 10.1074/jbc.m111.329235] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The age-dependent accumulation of lipofuscin in the retinal pigment epithelium (RPE) has been associated with the development of retinal diseases, particularly age-related macular degeneration and Stargardt disease. A major component of lipofuscin is the bis-retinoid N-retinylidene-N-retinylethanolamine (A2E). The current model for the formation of A2E requires photoactivation of rhodopsin and subsequent release of all-trans-retinal. To understand the role of light exposure in the accumulation of lipofuscin and A2E, we analyzed RPEs and isolated rod photoreceptors from mice of different ages and strains, reared either in darkness or cyclic light. Lipofuscin levels were determined by fluorescence imaging, whereas A2E levels were quantified by HPLC and UV-visible absorption spectroscopy. The identity of A2E was confirmed by tandem mass spectrometry. Lipofuscin and A2E levels in the RPE increased with age and more so in the Stargardt model Abca4(-/-) than in the wild type strains 129/sv and C57Bl/6. For each strain, the levels of lipofuscin precursor fluorophores in dark-adapted rods and the levels and rates of increase of RPE lipofuscin and A2E were not different between dark-reared and cyclic light-reared animals. Both 11-cis- and all-trans-retinal generated lipofuscin-like fluorophores when added to metabolically compromised rod outer segments; however, it was only 11-cis-retinal that generated such fluorophores when added to metabolically intact rods. The results suggest that lipofuscin originates from the free 11-cis-retinal that is continuously supplied to the rod for rhodopsin regeneration and outer segment renewal. The physiological role of Abca4 may include the translocation of 11-cis-retinal complexes across the disk membrane.
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Affiliation(s)
- Nicholas P Boyer
- Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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91
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Oldani M, Marchi S, Giani A, Cecchin S, Rigoni E, Persi A, Podavini D, Guerrini A, Nervegna A, Staurenghi G, Bertelli M. Clinical and molecular genetic study of 12 Italian families with autosomal recessive Stargardt disease. GENETICS AND MOLECULAR RESEARCH 2012; 11:4342-50. [DOI: 10.4238/2012.october.9.3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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92
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Sparrow JR, Gregory-Roberts E, Yamamoto K, Blonska A, Ghosh SK, Ueda K, Zhou J. The bisretinoids of retinal pigment epithelium. Prog Retin Eye Res 2011; 31:121-35. [PMID: 22209824 DOI: 10.1016/j.preteyeres.2011.12.001] [Citation(s) in RCA: 286] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Revised: 12/05/2011] [Accepted: 12/14/2011] [Indexed: 02/07/2023]
Abstract
The retina exhibits an inherent autofluorescence that is imaged ophthalmoscopically as fundus autofluorescence. In clinical settings, fundus autofluorescence examination aids in the diagnosis and follow-up of many retinal disorders. Fundus autofluorescence originates from the complex mixture of bisretinoid fluorophores that are amassed by retinal pigment epithelial (RPE) cells as lipofuscin. Unlike the lipofuscin found in other cell-types, this material does not form as a result of oxidative stress. Rather, the formation is attributable to non-enzymatic reactions of vitamin A aldehyde in photoreceptor cells; transfer to RPE occurs upon phagocytosis of photoreceptor outer segments. These fluorescent pigments accumulate even in healthy photoreceptor cells and are generated as a consequence of the light capturing function of the cells. Nevertheless, the formation of this material is accelerated in some retinal disorders including recessive Stargardt disease and ELOVL4-related retinal degeneration. As such, these bisretinoid side-products are implicated in the disease processes that threaten vision. In this article, we review our current understanding of the composition of RPE lipofuscin, the structural characteristics of the various bisretinoids, their related spectroscopic features and the biosynthetic pathways by which they form. We will revisit factors known to influence the extent of the accumulation and therapeutic strategies being used to limit bisretinoid formation. Given their origin from vitamin A aldehyde, an isomer of the visual pigment chromophore, it is not surprising that the bisretinoids of retina are light sensitive molecules. Accordingly, we will discuss recent findings that implicate the photodegradation of bisretinoid in the etiology of age-related macular degeneration.
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Affiliation(s)
- Janet R Sparrow
- Department of Ophthalmology, Columbia University, 630 W. 168th Street, New York, NY 10032, USA.
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93
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Tsybovsky Y, Wang B, Quazi F, Molday RS, Palczewski K. Posttranslational modifications of the photoreceptor-specific ABC transporter ABCA4. Biochemistry 2011; 50:6855-66. [PMID: 21721517 DOI: 10.1021/bi200774w] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
ABCA4 is a photoreceptor-specific ATP-binding cassette transporter implicated in the clearance of all-trans-retinal produced in the retina during light perception. Multiple mutations in this protein have been linked to Stargardt disease and other visual disorders. Here we report the first systematic study of posttranslational modifications in native ABCA4 purified from bovine rod outer segments. Seven N-glycosylation sites were detected in exocytoplasmic domains 1 and 2 by mass spectrometry, confirming the topological model of ABCA4 proposed previously. The modifying oligosaccharides were relatively short and homogeneous, predominantly representing a high-mannose type of N-glycosylation. Five phosphorylation sites were detected in cytoplasmic domain 1, with four of them located in the linker "regulatory-like" region conserved among ABCA subfamily members. Contrary to published results, phosphorylation of ABCA4 was found to be independent of light. Using human ABCA4 mutants heterologously expressed in mammalian cells, we showed that the Stargardt disease-associated alanine mutation in the phosphorylation site at position 901 led to protein misfolding and degradation. Furthermore, replacing the S1317 phosphorylation site reduced the basal ATPase activity of ABCA4, whereas an alanine mutation in either the S1185 or T1313 phosphorylation site resulted in a significant decrease in the all-trans-retinal-stimulated ATPase activity without affecting the basal activity, protein expression, or localization. In agreement with this observation, partial dephosphorylation of native bovine ABCA4 led to reduction of both basal and stimulated ATPase activity. Thus, we present the first evidence that phosphorylation of ABCA4 can regulate its function.
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Affiliation(s)
- Yaroslav Tsybovsky
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, United States
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94
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Sun H. Membrane receptors and transporters involved in the function and transport of vitamin A and its derivatives. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:99-112. [PMID: 21704730 DOI: 10.1016/j.bbalip.2011.06.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Revised: 06/01/2011] [Accepted: 06/10/2011] [Indexed: 12/12/2022]
Abstract
The eye is the human organ most sensitive to vitamin A deficiency because of vision's absolute and heavy dependence on vitamin A for light perception. Studies of the molecular basis of vision have provided important insights into the intricate mechanistic details of the function, transport and recycling of vitamin A and its derivatives (retinoid). This review focuses on retinoid-related membrane receptors and transporters. Three kinds of mammalian membrane receptors and transporters are discussed: opsins, best known as vitamin A-based light sensors in vision; ABCA4, an ATP-dependent transporter specializes in the transport of vitamin A derivative; and STRA6, a recently identified membrane receptor that mediates cellular uptake of vitamin A. The evolutionary driving forces for their existence and the wide spectrum of human diseases associated with these proteins are discussed. Lessons learned from the study of the visual system might be useful for understanding retinoid biology and retinoid-related diseases in other organ systems as well. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.
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Affiliation(s)
- Hui Sun
- Department of Physiology, Jules Stein Eye Institute, Brian Research Institute, and Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
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95
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Abstract
Mutations to members of the A subfamily of ATP binding cassette (ABC) proteins are responsible for a number of diseases; typically they are associated with aberrant cellular lipid transport processes. Mutations to the ABCA4 protein are linked to a number of visual disorders including Stargardt's disease and retinitis pigmentosa. Over 500 disease-associated mutations in ABCA4 have been demonstrated; however, the genotype-phenotype link has not been firmly established. This shortfall is primarily because the function of ABCA4 in the visual cycle is not yet fully understood. One hypothesis suggests that ABCA4 mediates the trans-bilayer translocation of retinal-phosphatidylethanolamine conjugates to facilitate the retinal regeneration process in the visual cycle. This review examines the evidence to support, or refute, this working hypothesis on the function of this clinically important protein.
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Affiliation(s)
- Naomi Laura Pollock
- Nuffield Department of Clinical Laboratory Science, University of Oxford, Oxford, UK
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96
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Yuan Q, Blanton SH, Hecht JT. Association of ABCA4 and MAFB with non-syndromic cleft lip with or without cleft palate. Am J Med Genet A 2011; 155A:1469-71. [PMID: 21567910 DOI: 10.1002/ajmg.a.33940] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Accepted: 01/17/2011] [Indexed: 11/10/2022]
Affiliation(s)
- Qiuping Yuan
- Department of Pediatrics, University of Texas Medical School at Houston, USA
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97
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Abstract
Pseudoxanthoma elasticum (PXE), a heritable multi-system disorder, is caused by mutations in the ABCC6 gene primarily expressed in the liver. Recent analysis of cultured fibroblasts from patients with PXE has suggested compensatory alterations in the expression of the ABCA-subfamily of genes. We have now determined by quantitative RT-PCR the level of expression of Abca-family of genes in a mouse model of PXE developed by targeted ablation of Abcc6. The results indicated variable levels of mRNA for different Abca genes in the liver; however, only one of them, Abca4, was significantly, ∼6.5-fold, upregulated in the Abcc6(-/-) mice in comparison with wild-type mice. In the same mice, Abca4 was not upregulated in the eyes or the kidney, suggesting that the upregulation of Abca4 in the liver is a tissue-specific compensatory consequence of the 'knock-out' of Abcc6.
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98
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Chloroquine treatment of ARPE-19 cells leads to lysosome dilation and intracellular lipid accumulation: possible implications of lysosomal dysfunction in macular degeneration. Cell Biosci 2011; 1:10. [PMID: 21711726 PMCID: PMC3125200 DOI: 10.1186/2045-3701-1-10] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Accepted: 03/08/2011] [Indexed: 11/10/2022] Open
Abstract
Background Age-related macular degeneration (AMD) is the leading cause of vision loss in elderly people over 60. The pathogenesis is still unclear. It has been suggested that lysosomal stress may lead to drusen formation, a biomarker of AMD. In this study, ARPE-19 cells were treated with chloroquine to inhibit lysosomal function. Results Chloroquine-treated ARPE-19 cells demonstrate a marked increase in vacuolation and dense intracellular debris. These are identified as chloroquine-dilated lysosomes and lipid bodies with LAMP-2 and LipidTOX co-localization, respectively. Dilation is an indicator of lysosomal dysfunction. Chloroquine disrupts uptake of exogenously applied rhodamine-labeled dextran by these cells. This suggests a disruption in the phagocytic pathway. The increase in LAMP protein levels, as assessed by Western blots, suggests the possible involvement in autophagy. Oxidative stress with H2O2 does not induce vacuolation or lipid accumulation. Conclusion These findings suggest a possible role for lysosomes in AMD. Chloroquine treatment of RPE cells may provide insights into the cellular mechanisms underlying AMD.
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99
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Menon I, Huber T, Sanyal S, Banerjee S, Barré P, Canis S, Warren JD, Hwa J, Sakmar TP, Menon AK. Opsin is a phospholipid flippase. Curr Biol 2011; 21:149-53. [PMID: 21236677 DOI: 10.1016/j.cub.2010.12.031] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 11/17/2010] [Accepted: 12/14/2010] [Indexed: 11/19/2022]
Abstract
Polar lipids must flip-flop rapidly across biological membranes to sustain cellular life [1, 2], but flipping is energetically costly [3] and its intrinsic rate is low. To overcome this problem, cells have membrane proteins that function as lipid transporters (flippases) to accelerate flipping to a physiologically relevant rate. Flippases that operate at the plasma membrane of eukaryotes, coupling ATP hydrolysis to unidirectional lipid flipping, have been defined at a molecular level [2]. On the other hand, ATP-independent bidirectional flippases that translocate lipids in biogenic compartments, e.g., the endoplasmic reticulum, and specialized membranes, e.g., photoreceptor discs [4, 5], have not been identified even though their activity has been recognized for more than 30 years [1]. Here, we demonstrate that opsin is the ATP-independent phospholipid flippase of photoreceptor discs. We show that reconstitution of opsin into large unilamellar vesicles promotes rapid (τ<10 s) flipping of phospholipid probes across the vesicle membrane. This is the first molecular identification of an ATP-independent phospholipid flippase in any system. It reveals an unexpected activity for opsin and, in conjunction with recently available structural information on this G protein-coupled receptor [6, 7], significantly advances our understanding of the mechanism of ATP-independent lipid flip-flop.
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Affiliation(s)
- Indu Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
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100
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Fletcher EL, Jobling AI, Vessey KA, Luu C, Guymer RH, Baird PN. Animal models of retinal disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2011; 100:211-86. [PMID: 21377628 DOI: 10.1016/b978-0-12-384878-9.00006-6] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Diseases of the retina are the leading causes of blindness in the industrialized world. The recognition that animals develop retinal diseases with similar traits to humans has led to not only a dramatic improvement in our understanding of the pathogenesis of retinal disease but also provided a means for testing possible treatment regimes and successful gene therapy trials. With the advent of genetic and molecular biological tools, the association between specific gene mutations and retinal signs has been made. Animals carrying natural mutations usually in one gene now provide well-established models for a host of inherited retinal diseases, including retinitis pigmentosa, Leber congenital amaurosis, inherited macular degeneration, and optic nerve diseases. In addition, the development of transgenic technologies has provided a means by which to study the effects of these and novel induced mutations on retinal structure and function. Despite these advances, there is a paucity of suitable animal models for complex diseases, including age-related macular degeneration (AMD) and diabetic retinopathy, largely because these diseases are not caused by single gene defects, but involve complex genetics and/or exacerbation through environmental factors, epigenetic, or other modes of genetic influence. In this review, we outline in detail the available animal models for inherited retinal diseases and how this information has furthered our understanding of retinal diseases. We also examine how transgenic technologies have helped to develop our understanding of the role of isolated genes or pathways in complex diseases like AMD, diabetes, and glaucoma.
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Affiliation(s)
- Erica L Fletcher
- Department of Anatomy and Cell Biology, The University of Melbourne, Parkville, Victoria, Australia
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