101
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Kim SR, Jang YP, Sparrow JR. Photooxidation of RPE lipofuscin bisretinoids enhances fluorescence intensity. Vision Res 2009; 50:729-36. [PMID: 19800359 DOI: 10.1016/j.visres.2009.09.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Revised: 09/15/2009] [Accepted: 09/18/2009] [Indexed: 11/24/2022]
Abstract
Light-related cycling of chemically reactive vitamin A aldehyde leads to the formation autofluorescent bis-retinoid pigments that accumulate as lipofuscin in retinal pigment epithelial cells. The amassing of these diretinoid compounds is implicated in the pathogenesis of age-related macular degeneration and in some inherited forms of retinal degeneration. For all of these fluorophores, extended conjugation systems confer absorbance maxima in the visible spectrum. We report that an increase in fluorescence emission can accompany photoxidation of the bisretinoids A2E and all-trans-retinal dimer. These findings are relevant to the quantification of RPE lipofuscin based on inference from fluorescence intensity.
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Affiliation(s)
- So Ra Kim
- Department of Ophthalmology, Columbia University, 630 W 168th Street, New York, NY 10032, USA
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102
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Time-resolved fluorescence resonance energy transfer and surface plasmon resonance-based assays for retinoid and transthyretin binding to retinol-binding protein 4. Anal Biochem 2009; 392:162-8. [DOI: 10.1016/j.ab.2009.05.038] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Revised: 05/15/2009] [Accepted: 05/23/2009] [Indexed: 11/20/2022]
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103
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Vasireddy V, Jablonski MM, Khan NW, Wang XF, Sahu P, Sparrow JR, Ayyagari R. Elovl4 5-bp deletion knock-in mouse model for Stargardt-like macular degeneration demonstrates accumulation of ELOVL4 and lipofuscin. Exp Eye Res 2009; 89:905-12. [PMID: 19682985 DOI: 10.1016/j.exer.2009.07.021] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Revised: 07/28/2009] [Accepted: 07/29/2009] [Indexed: 11/29/2022]
Abstract
The mechanism underlying photoreceptor degeneration in autosomal dominant Stargardt-like macular degeneration (STGD3) due to mutations in the elongation of very long chain fatty acids-4 (ELOVL4) gene is not fully understood. To evaluate the pathological events associated with STGD3, we used a mouse model that mimics the human STGD3 phenotype and studied the progression of retinal degeneration. Morphological changes in the retina of Elovl4 5-bp deletion knock-in mice (E_mut(+/-)) were evaluated at 22 months of age. The localization of ELOVL4, and the expression pattern of inner retinal tissue marker proteins, and ubiquitin were determined by immunofluorescence labeling of retinal sections. Levels of the retinal pigment epithelium (RPE) lipofuscin fluorophores were measured by quantitative HPLC. Morphological evaluation of the retina revealed an accumulation of RPE debris in the subretinal space. A significant increase in the amount of ELOVL4 was observed in the outer plexiform layer in E_mut(+/-) mice compared to controls. Apart from the accumulation of ELOVL4, E_mut(+/-) mice also exhibited high expression of ubiquitin in the retina. Analysis of lipofuscin fluorophores in the RPE showed a significant elevation of A2E and compounds of the all-trans-retinal dimer series in retinas from four and ten month old E_mut(+/-) mice compared to wild-type littermates. These observations suggest that abnormal accumulation of ELOVL4 protein and lipofuscin may lead to photoreceptor degeneration in E_mut(+/-) mice.
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104
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Chrispell JD, Feathers KL, Kane MA, Kim CY, Brooks M, Khanna R, Kurth I, Hübner CA, Gal A, Mears AJ, Swaroop A, Napoli JL, Sparrow JR, Thompson DA. Rdh12 activity and effects on retinoid processing in the murine retina. J Biol Chem 2009; 284:21468-77. [PMID: 19506076 PMCID: PMC2755871 DOI: 10.1074/jbc.m109.020966] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Revised: 06/04/2009] [Indexed: 11/06/2022] Open
Abstract
RDH12 mutations are responsible for early-onset autosomal recessive retinal dystrophy, which results in profound retinal pathology and severe visual handicap in patients. To investigate the function of RDH12 within the network of retinoid dehydrogenases/reductases (RDHs) present in retina, we studied the retinal phenotype of Rdh12-deficient mice. In vivo rates of all-trans-retinal reduction and 11-cis-retinal formation during recovery from bleaching were similar in Rdh12-deficient and wild-type mice matched for an Rpe65 polymorphism that impacts visual cycle efficiency. However, retinal homogenates from Rdh12-deficient mice exhibited markedly decreased capacity to reduce exogenous retinaldehydes in vitro. Furthermore, in vivo levels of the bisretinoid compound diretinoid-pyridinium-ethanolamine (A2E) were increased in Rdh12-deficient mice of various genetic backgrounds. Conversely, in vivo levels of retinoic acid and total retinol were significantly decreased. Rdh12 transcript levels in wild-type mice homozygous for the Rpe65-Leu(450) polymorphism were greater than in Rpe65-Met(450) mice and increased during postnatal development in wild-type mice and Nrl-deficient mice having an all-cone retina. Rdh12-deficient mice did not exhibit increased retinal degeneration relative to wild-type mice at advanced ages, when bred on the light-sensitive BALB/c background, or when heterozygous for a null allele of superoxide dismutase 2 (Sod2(+/-)). Our findings suggest that a critical function of RDH12 is the reduction of all-trans-retinal that exceeds the reductive capacity of the photoreceptor outer segments.
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Affiliation(s)
| | - Kecia L. Feathers
- Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105
| | - Maureen A. Kane
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720
| | - Chul Y. Kim
- Departments of Ophthalmology and Pathology and Cell Biology, Columbia University, New York, New York 10032
| | - Matthew Brooks
- Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105
- Neurobiology-Neurodegeneration and Repair Laboratory, NEI, National Institutes of Health, Bethesda, Maryland 20892
| | - Ritu Khanna
- Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105
| | - Ingo Kurth
- Institute of Human Genetics, University of Hamburg-Eppendorf, D-20251 Hamburg, Germany
| | - Christian A. Hübner
- Department of Clinical Chemistry, Friedrich-Schiller-Universität, D-07747 Jena, Germany
| | - Andreas Gal
- Institute of Human Genetics, University of Hamburg-Eppendorf, D-20251 Hamburg, Germany
| | - Alan J. Mears
- Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105
- University of Ottawa Eye Institute and Ottawa Health Research Institute, Ottawa, Ontario K1Y 4E9, Canada, and
| | - Anand Swaroop
- Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105
- Neurobiology-Neurodegeneration and Repair Laboratory, NEI, National Institutes of Health, Bethesda, Maryland 20892
| | - Joseph L. Napoli
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720
| | - Janet R. Sparrow
- Departments of Ophthalmology and Pathology and Cell Biology, Columbia University, New York, New York 10032
| | - Debra A. Thompson
- From the Departments of Biological Chemistry and
- Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105
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105
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Sparrow JR, Wu Y, Kim CY, Zhou J. Phospholipid meets all-trans-retinal: the making of RPE bisretinoids. J Lipid Res 2009; 51:247-61. [PMID: 19666736 DOI: 10.1194/jlr.r000687] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The lipid phase of the photoreceptor outer segment membrane is essential to the photon capturing and signaling functions of rhodopsin. Rearrangement of phospholipids in the bilayer accompanies the formation of the active intermediates of rhodopsin following photon absorption. Furthermore, evidence for the formation of a condensation product between the photolyzed chromophore all-trans-retinal and phosphatidylethanolamine indicates that phospholipid may also participate in the movement of the retinoid in the membrane. The downside of these interactions is the formation of bisretinoid-phosphatidylethanolamine compounds that accumulate in retinal pigment epithelial cells with age and that are particularly abundant in some retinal disorders. The propensity of these compounds to negatively impact on the cells has been linked to the pathogenesis of some retinal disorders including juvenile onset recessive Stargardt disease and age-related macular degeneration.
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Affiliation(s)
- Janet R Sparrow
- Department of Ophthalmology, Columbia University, New York, NY 10032, USA.
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106
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Maeda A, Golczak M, Maeda T, Palczewski K. Limited roles of Rdh8, Rdh12, and Abca4 in all-trans-retinal clearance in mouse retina. Invest Ophthalmol Vis Sci 2009; 50:5435-43. [PMID: 19553623 DOI: 10.1167/iovs.09-3944] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
PURPOSE Although the retinoid cycle is essential for vision, all-trans-retinal and the side products of this cycle are toxic. Delayed clearance of all-trans-retinal causes accumulation of its condensation products, A2E, and all-trans-retinal dimer (RALdi), both associated with human macular degeneration. The protective roles were examined of the all-trans-RDHs, Rdh8 and Rdh12, and the ATP-binding cassette transporter Abca4, retinoid cycle enzymes involved in all-trans-retinal clearance. METHODS Mice genetically engineered to lack Rdh8, Rdh12, and Abca4, either singly or in various combinations, were investigated because all-trans-retinal clearance is achieved by all-trans-RDHs and Abca4. Knockout mice were evaluated by spectral-domain optical coherence tomography (SD-OCT), electroretinography, retinal morphology, and visual retinoid profiling with HPLC and MS. ARPE19 cells were examined to evaluate A2E and RALdi oxidation and toxicity induced by exposure to UV and blue light. RESULTS Rdh8(-/-)Abca4(-/-) and Rdh8(-/-)Rdh12(-/-)Abca4(-/-) mice displayed slowly progressive, severe retinal degeneration under room light conditions. Intense light-induced acute retinal degeneration was detected by SD-OCT in Rdh8(-/-)Rdh12(-/-)Abca4(-/-) mice. Amounts of A2E in the RPE correlated with diminished all-trans-retinal clearance, and the highest A2E amounts were found in Rdh8(-/-)Rdh12(-/-)Abca4(-/-) mice. However oxidized A2E was not found in any of these mice, and A2E oxidation was not induced by blue light and UV illumination of A2E-loaded ARPE19 cells. Of interest, addition of all-trans-retinal did activate retinoic acid receptors in cultured cells. CONCLUSIONS Rdh8, Rdh12, and Abca4 all protect the retina and reduce A2E production by facilitating all-trans-retinal clearance. Delayed all-trans-retinal clearance contributes more than A2E oxidation to light-induced cellular toxicity.
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Affiliation(s)
- Akiko Maeda
- Department of Pharmacology, , School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4965, USA.
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107
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Cella W, Greenstein VC, Zernant-Rajang J, Smith TR, Barile G, Allikmets R, Tsang SH. G1961E mutant allele in the Stargardt disease gene ABCA4 causes bull's eye maculopathy. Exp Eye Res 2009; 89:16-24. [PMID: 19217903 PMCID: PMC2742677 DOI: 10.1016/j.exer.2009.02.001] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2008] [Revised: 12/16/2008] [Accepted: 02/04/2009] [Indexed: 02/08/2023]
Abstract
The aim of this study was to characterize the pathological and functional consequences of the G1961E mutant allele in the Stargardt disease gene ABCA4. Data from 15 patients were retrospectively reviewed and all the patients had at least one G1961E mutation. Comprehensive ophthalmic examination, full-field and pattern electroretinograms, and fundus autofluorescence (FAF) imaging were performed on all patients. Microperimetry, spectral-domain optical coherence tomography (OCT), and fluorescein angiography were performed in selected cases. Genetic screening was performed using the ABCR400 micro-array that currently detects 496 distinct ABCA4 variants. All patients had normal full-field scotopic and photopic electroretinograms (ERGs) and abnormal pattern electroretinograms (PERGs) performed on both eyes, and all the fundi had bull's eye maculopathy without retinal flecks on FAF. On OCT, 1 patient had disorganization of photoreceptor outer segment, 2 had outer nuclear layer (ONL) thinning likely due to photoreceptor atrophy proximal to the foveal center, and 3 had additional retinal pigment epithelium (RPE) atrophy. On microperimetry, 6 patients had eccentric superior fixation and amongst this group, 5 had an absolute scotoma in the foveal area. DNA analysis revealed that 3 patients were homozygous G1961E/G1961E and the rest were compound heterozygotes for G1961E and other ABCA4 mutations. The G1961E allele in either homozygosity or heterozygosity is associated with anatomical and functional pathologies limited to the parafoveal region and a trend to delayed onset of symptoms, relative to other manifestations of ABCA4 mutations. Our observations support the hypothesis that the G1961E allele contributes to localized macular changes rather than generalized retinal dysfunction, and is a cause of bull's eye maculopathy in either the homozygosity or heterozygosity state. In addition, genetic testing provides precise diagnosis of the underlying maculopathy, and current non-invasive imaging techniques could be used to detect photoreceptor damage at the earliest clinical onset of the disease.
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Affiliation(s)
- Wener Cella
- Department of Ophthalmology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
| | - Vivienne C. Greenstein
- Department of Ophthalmology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
- Department of Ophthalmology, School of Medicine, New York University, NYU Langone Medical Center, 550 First Avenue, New York, NY 10016, USA
| | - Jana Zernant-Rajang
- Department of Ophthalmology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
| | - Theodore R. Smith
- Department of Ophthalmology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
| | - Gaetano Barile
- Department of Ophthalmology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
| | - Rando Allikmets
- Department of Ophthalmology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
- Department of Pathology & Cell Biology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
| | - Stephen H. Tsang
- Department of Ophthalmology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
- Department of Pathology & Cell Biology, Columbia University, 160 Fort Washington Avenue, New York, NY, 10032, USA
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108
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Wu Y, Fishkin NE, Pande A, Pande J, Sparrow JR. Novel lipofuscin bisretinoids prominent in human retina and in a model of recessive Stargardt disease. J Biol Chem 2009; 284:20155-66. [PMID: 19478335 DOI: 10.1074/jbc.m109.021345] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Bisretinoid adducts accumulate as lipofuscin in retinal pigment epithelial (RPE) cells of the eye and are implicated in the pathology of inherited and age-related macular degeneration. Characterization of the bisretinoids A2E and the all-trans-retinal dimer series has shown that these pigments form from reactions in photoreceptor cell outer segments that involve all-trans-retinal, the product of photoisomerization of the visual chromophore 11-cis-retinal. Here we have identified two related but previously unknown RPE lipofuscin compounds. By high performance liquid chromatography-electrospray ionization-tandem mass spectrometry, we determined that the first of these compounds is a phosphatidyl-dihydropyridine bisretinoid; to indicate this structure and its formation from two vitamin A-aldehyde (A2), we will refer to it as A2-dihydropyridine-phosphatidylethanolamine (A2-DHP-PE). The second pigment, A2-dihydropyridine-ethanolamine, forms from phosphate hydrolysis of A2-DHP-PE. The structure of A2-DHP-PE was corroborated by Fourier transform infrared spectroscopy, and density functional theory confirmed the presence of a dihydropyridine ring. This lipofuscin pigment is a fluorescent compound with absorbance maxima at approximately 490 and 330 nm, and it was identified in human, mouse, and bovine eyes. We found that A2-DHP-PE forms in reaction mixtures of all-trans-retinal and phosphatidylethanolamine, and in mouse eyecups we observed an age-related accumulation. As compared with wild-type mice, A2-DHP-PE is more abundant in mice with a null mutation in Abca4 (ATP-binding cassette transporter 4), the gene causative for recessive Stargardt macular degeneration. Efforts to clarify the composition of RPE lipofuscin are important because these compounds are targets of gene-based and drug therapies that aim to alleviate ABCA4-related retinal disease.
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Affiliation(s)
- Yalin Wu
- Department of Ophthalmology, Columbia University, New York, New York 10032, USA
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109
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Marmorstein AD, Cross HE, Peachey NS. Functional roles of bestrophins in ocular epithelia. Prog Retin Eye Res 2009; 28:206-26. [PMID: 19398034 DOI: 10.1016/j.preteyeres.2009.04.004] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
There are four members of the bestrophin family of proteins in the human genome, of which two are known to be expressed in the eye. The gene BEST1 (formerly VMD2) which encodes the protein bestrophin-1 (Best1) was first identified in 1998. Mutations in this gene have now been associated with four clinically distinguishable human eye diseases, collectively referred to as "bestrophinopathies". Over the last decade, laboratories have sought to understand how Best1 mutations could result in eye diseases that range in presentation from macular degeneration to nanophthalmos. The majority of our knowledge comes from studies that have sought to understand how Best1 mutations or dysfunction could induce the classical symptoms of the most common of these diseases: Best vitelliform macular dystrophy (BVMD). BVMD is a dominant trait that is characterized electrophysiologically by a diminished electrooculogram light peak with a normal clinical electroretinogram. This together with the localization of Best1 to the retinal pigment epithelium (RPE) basolateral plasma membrane and data from heterologous expression studies, have led to the proposal that Best1 generates the light peak, and that bestrophins are a family of Ca(2+) activated Cl(-) channels (CaCCs). However, data from Best1 knock-out and knock-in mice, coupled with the recent discovery of a recessive bestrophinopathy suggest that Best1 does not generate the light peak. Recently Best2 was found to be expressed in non-pigmented epithelia in the ciliary body. However, aqueous dynamics in Best2 knock-out mice do not support a role for Best2 as a Cl(-) channel. Thus, the purported CaCC function of the bestrophins and how loss of this function relates to clinical disease needs to be reassessed. In this article, we examine data obtained from tissue-type and animal models and discuss the current state of bestrophin research, what roles Best1 and Best2 may play in ocular epithelia and ocular electrophysiology, and how perturbation of these functions may result in disease.
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Affiliation(s)
- Alan D Marmorstein
- Department of Ophthalmology and Vision Science, University of Arizona, Tucson, AZ 85711, USA.
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110
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Maeda A, Maeda T, Golczak M, Chou S, Desai A, Hoppel CL, Matsuyama S, Palczewski K. Involvement of all-trans-retinal in acute light-induced retinopathy of mice. J Biol Chem 2009; 284:15173-83. [PMID: 19304658 DOI: 10.1074/jbc.m900322200] [Citation(s) in RCA: 193] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Exposure to bright light can cause visual dysfunction and retinal photoreceptor damage in humans and experimental animals, but the mechanism(s) remain unclear. We investigated whether the retinoid cycle (i.e. the series of biochemical reactions required for vision through continuous generation of 11-cis-retinal and clearance of all-trans-retinal, respectively) might be involved. Previously, we reported that mice lacking two enzymes responsible for clearing all-trans-retinal, namely photoreceptor-specific ABCA4 (ATP-binding cassette transporter 4) and RDH8 (retinol dehydrogenase 8), manifested retinal abnormalities exacerbated by light and associated with accumulation of diretinoid-pyridinium-ethanolamine (A2E), a condensation product of all-trans-retinal and a surrogate marker for toxic retinoids. Now we show that these mice develop an acute, light-induced retinopathy. However, cross-breeding these animals with lecithin:retinol acyltransferase knock-out mice lacking retinoids within the eye produced progeny that did not exhibit such light-induced retinopathy until gavaged with the artificial chromophore, 9-cis-retinal. No significant ocular accumulation of A2E occurred under these conditions. These results indicate that this acute light-induced retinopathy requires the presence of free all-trans-retinal and not, as generally believed, A2E or other retinoid condensation products. Evidence is presented that the mechanism of toxicity may include plasma membrane permeability and mitochondrial poisoning that lead to caspase activation and mitochondria-associated cell death. These findings further understanding of the mechanisms involved in light-induced retinal degeneration.
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Affiliation(s)
- Akiko Maeda
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
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111
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Damek-Poprawa M, Diemer T, Lopes VS, Lillo C, Harper DC, Marks MS, Wu Y, Sparrow JR, Rachel RA, Williams DS, Boesze-Battaglia K. Melanoregulin (MREG) modulates lysosome function in pigment epithelial cells. J Biol Chem 2009; 284:10877-89. [PMID: 19240024 DOI: 10.1074/jbc.m808857200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Melanoregulin (MREG), the product of the Mreg(dsu) gene, is a small highly charged protein, hypothesized to play a role in organelle biogenesis due to its effect on pigmentation in dilute, ashen, and leaden mutant mice. Here we provide evidence that MREG is required in lysosome-dependent phagosome degradation. In the Mreg(-/-) mouse, we show that loss of MREG function results in phagosome accumulation due to delayed degradation of engulfed material. Over time, the Mreg(-/-) mouse retinal pigment epithelial cells accumulate the lipofuscin component, A2E. MREG-deficient human and mouse retinal pigment epithelial cells exhibit diminished activity of the lysosomal hydrolase, cathepsin D, due to defective processing. Moreover, MREG localizes to small intracellular vesicles and associates with the endosomal phosphoinositide, phosphatidylinositol 3,5-biphosphate. Collectively, these studies suggest that MREG is required for lysosome maturation and support a role for MREG in intracellular trafficking.
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Affiliation(s)
- Monika Damek-Poprawa
- Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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112
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The role of the photoreceptor ABC transporter ABCA4 in lipid transport and Stargardt macular degeneration. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:573-83. [PMID: 19230850 DOI: 10.1016/j.bbalip.2009.02.004] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 02/04/2009] [Accepted: 02/05/2009] [Indexed: 12/26/2022]
Abstract
ABCA4 is a member of the ABCA subfamily of ATP binding cassette (ABC) transporters that is expressed in rod and cone photoreceptors of the vertebrate retina. ABCA4, also known as the Rim protein and ABCR, is a large 2,273 amino acid glycoprotein organized as two tandem halves, each containing a single membrane spanning segment followed sequentially by a large exocytoplasmic domain, a multispanning membrane domain and a nucleotide binding domain. Over 500 mutations in the gene encoding ABCA4 are associated with a spectrum of related autosomal recessive retinal degenerative diseases including Stargardt macular degeneration, cone-rod dystrophy and a subset of retinitis pigmentosa. Biochemical studies on the purified ABCA4 together with analysis of abca4 knockout mice and patients with Stargardt disease have implicated ABCA4 as a retinylidene-phosphatidylethanolamine transporter that facilitates the removal of potentially reactive retinal derivatives from photoreceptors following photoexcitation. Knowledge of the genetic and molecular basis for ABCA4 related retinal degenerative diseases is being used to develop rationale therapeutic treatments for this set of disorders.
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113
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Zhou J, Kim SR, Westlund BS, Sparrow JR. Complement activation by bisretinoid constituents of RPE lipofuscin. Invest Ophthalmol Vis Sci 2008; 50:1392-9. [PMID: 19029031 DOI: 10.1167/iovs.08-2868] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Studies implicate activation of complement among the processes involved in the pathogenesis of age-related macular degeneration (AMD). Questions pertain to the trigger(s) responsible for the complement-associated events. The authors previously reported that photooxidation products of A2E can activate complement. Here they have further explored these events. METHODS In vitro assays using human serum as a source of complement were used, and the C3 split product iC3b was measured by enzyme immunoassay. Serum was placed in contact with ARPE-19 cells and polarized human fetal retinal pigment epithelium that had accumulated A2E and were irradiated (430 nm). Serum was also incubated in wells precoated with bisretinoid pigments of lipofuscin and their oxidized forms. iC3b generation in normal human serum (NHS) was compared with that in factor B-depleted and C1q-depleted human serum. RESULTS iC3b levels were elevated in NHS placed in contact with A2E-laden retinal pigment epithelium that were irradiated to generate A2E photooxidation products. iC3b was also increased in serum incubated in wells precoated with peroxy-A2E, the lipofuscin pigment all-trans-retinal dimer, and oxidized forms of all-trans-retinal dimer. Substitution of NHS with factor B-depleted sera abrogated these increases in iC3b. Complement activation was also suppressed by the addition of C-reactive protein and by a C3 cleavage inhibitor. CONCLUSIONS The authors suggest that bisretinoid pigments of retinal pigment epithelial lipofuscin, subsequent to photoactivation and cleavage, serve to activate complement. Complement activation by this mechanism is dependent on the alternative pathway and can be modulated by an inhibitor of C3 cleavage. These events in the setting of complement dysregulation could contribute to the chronic inflammation that underlies AMD pathogenesis.
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Affiliation(s)
- Jilin Zhou
- Department of Ophthalmology, Columbia University, New York, New York 10032, USA
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114
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Maeda A, Maeda T, Golczak M, Palczewski K. Retinopathy in mice induced by disrupted all-trans-retinal clearance. J Biol Chem 2008; 283:26684-93. [PMID: 18658157 DOI: 10.1074/jbc.m804505200] [Citation(s) in RCA: 227] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The visual (retinoid) cycle is a fundamental metabolic process in vertebrate retina responsible for production of 11-cis-retinal, the chromophore of rhodopsin and cone pigments. 11-cis-Retinal is bound to opsins, forming visual pigments, and when the resulting visual chromophore 11-cis-retinylidene is photoisomerized to all-trans-retinylidene, all-trans-retinal is released from these receptors. Toxic byproducts of the visual cycle formed from all-trans-retinal often are associated with lipofuscin deposits in the retinal pigmented epithelium (RPE), but it is not clear whether aberrant reactions of the visual cycle participate in RPE atrophy, leading to a rapid onset of retinopathy. Here we report that mice lacking both the ATP-binding cassette transporter 4 (Abca4) and enzyme retinol dehydrogenase 8 (Rdh8), proteins critical for all-trans-retinal clearance from photoreceptors, developed severe RPE/photoreceptor dystrophy at an early age. This phenotype includes lipofuscin, drusen, and basal laminar deposits, Bruch's membrane thickening, and choroidal neovascularization. Importantly, the severity of visual dysfunction and retinopathy was exacerbated by light but attenuated by treatment with retinylamine, a visual cycle inhibitor that slows the flow of all-trans-retinal through the visual cycle. These findings provide direct evidence that aberrant production of toxic condensation byproducts of the visual cycle in mice can lead to rapid, progressive retinal degeneration.
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Affiliation(s)
- Akiko Maeda
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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Radu RA, Yuan Q, Hu J, Peng JH, Lloyd M, Nusinowitz S, Bok D, Travis GH. Accelerated accumulation of lipofuscin pigments in the RPE of a mouse model for ABCA4-mediated retinal dystrophies following Vitamin A supplementation. Invest Ophthalmol Vis Sci 2008; 49:3821-9. [PMID: 18515570 DOI: 10.1167/iovs.07-1470] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
PURPOSE Dietary supplementation with vitamin A is sometimes prescribed as a treatment for retinitis pigmentosa, a group of inherited retinal degenerations that cause progressive blindness. Loss-of-function mutations in the ABCA4 gene are responsible for a subset of recessive retinitis pigmentosa. Other mutant alleles of ABCA4 cause the related diseases, recessive cone-rod dystrophy, and recessive Stargardt macular degeneration. Mice with a knockout mutation in the abca4 gene massively accumulate toxic lipofuscin pigments in the retinal pigment epithelium. Treatment of these mice with fenretinide, an inhibitor of vitamin A delivery to the eye, blocks formation of these toxic pigments. Here the authors tested the hypothesis that dietary supplementation with vitamin A may accelerate lipofuscin pigment formation in abca4(-/-) mice. METHODS Wild-type and abca4(-/-) mice were fed normal or vitamin A-supplemented diets. Tissues from these mice were analyzed biochemically for retinoids and lipofuscin pigments. Eyes from these mice were analyzed morphologically for lipofuscin in the retinal pigment epithelium and for degeneration of photoreceptors. Visual function in these mice was analyzed by electroretinography. RESULTS Mice that received vitamin A supplementation had dramatically higher levels of retinyl esters in the liver and retinal pigment epithelium. Lipofuscin pigments were significantly increased by biochemical and morphologic analysis in wild-type and abca4(-/-) mice fed the vitamin A-supplemented diet. Photoreceptor degeneration was observed in 11-month-old albino, but not pigmented, abca4(-/-) mice on both diets. CONCLUSIONS Vitamin A supplementation should be avoided in patients with ABCA4 mutations or other retinal or macular dystrophies associated with lipofuscin accumulation in the retinal pigment epithelium.
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Affiliation(s)
- Roxana A Radu
- Department of Ophthalmology, University of California at Los Angeles School of Medicine, Los Angeles, California, USA
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Ng KP, Gugiu B, Renganathan K, Davies MW, Gu X, Crabb JS, Kim SR, Rózanowska MB, Bonilha VL, Rayborn ME, Salomon RG, Sparrow JR, Boulton ME, Hollyfield JG, Crabb JW. Retinal pigment epithelium lipofuscin proteomics. Mol Cell Proteomics 2008; 7:1397-405. [PMID: 18436525 DOI: 10.1074/mcp.m700525-mcp200] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lipofuscin accumulates with age in the retinal pigment epithelium (RPE) in discrete granular organelles and may contribute to age-related macular degeneration. Because previous studies suggest that lipofuscin contains protein that may impact pathogenic mechanisms, we pursued proteomics analysis of lipofuscin. The composition of RPE lipofuscin and its mechanisms of pathogenesis are poorly understood in part because of the heterogeneity of isolated preparations. We purified RPE lipofuscin granules by treatment with proteinase K or SDS and showed by light, confocal, and transmission electron microscopy that the purified granules are free of extragranular material and associated membranes. Crude and purified lipofuscin preparations were quantitatively compared by (i) LC MS/MS proteomics analyses, (ii) immunoanalyses of oxidative protein modifications, (iii) amino acid analysis, (iv) HPLC of bisretinoids, and (v) assaying phototoxicity to RPE cells. From crude lipofuscin preparations 186 proteins were identified, many of which appeared to be modified. In contrast, very little protein ( approximately 2% (w/w) by amino acid analysis) and no identifiable protein were found in the purified granules, which retained full phototoxicity to cultured RPE cells. Our analyses showed that granules in purified and crude lipofuscin preparations exhibit no statistically significant differences in diameter or circularity or in the content of the bisretinoids A2E, isoA2E, and all-trans-retinal dimer-phosphatidylethanolamine. The finding that the purified granules contain minimal protein yet retain phototoxic activity suggests that RPE lipofuscin pathogenesis is largely independent of associated protein. The purified granules also exhibited oxidative protein modifications, including nitrotyrosine generated from reactive nitrogen oxide species and carboxyethylpyrrole and iso[4]levuglandin E(2) adducts generated from reactive lipid fragments. This finding is consistent with previous studies demonstrating RPE lipofuscin to be a potent generator of reactive oxygen species and supports the hypothesis that such species, including reactive fragments from lipids and retinoids, contribute to the mechanisms of RPE lipofuscin pathogenesis.
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Affiliation(s)
- Kwok-Peng Ng
- Cole Eye Institute and Lerner Research Institute, Cleveland Clinic Foundation, Case Western Reserve University, Cleveland, Ohio 44195, USA
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Olsen TW. The Minnesota Grading System using fundus autofluorescence of eye bank eyes: a correlation to age-related macular degeneration (an AOS thesis). TRANSACTIONS OF THE AMERICAN OPHTHALMOLOGICAL SOCIETY 2008; 106:383-401. [PMID: 19277247 PMCID: PMC2646441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
PURPOSE To establish a grading system of eye bank eyes using fundus autofluorescence (FAF) and identify a methodology that correlates FAF to age-related macular degeneration (AMD) with clinical correlation to the Age-Related Eye Disease Study (AREDS). METHODS Two hundred sixty-two eye bank eyes were evaluated using a standardized analysis of FAF. Measurements were taken with the confocal scanning laser ophthalmoscope (cSLO). First, high-resolution, digital, stereoscopic, color images were obtained and graded according to AREDS criteria. With the neurosensory retina removed, mean FAF values were obtained from cSLO images using software analysis that excludes areas of atrophy and other artifact, generating an FAF value from a grading template. Age and AMD grade were compared to FAF values. An internal fluorescence reference standard was tested. RESULTS Standardization of the cSLO machine demonstrated that reliable data could be acquired after a 1-hour warm-up. Images obtained prior to 1 hour had falsely elevated levels of FAF. In this initial analysis, there was no statistical correlation of age to mean FAF. There was a statistically significant decrease in FAF from AREDS grade 1, 2 to 3, 4 (P < .0001). An internal fluorescent standard may serve as a quantitative reference. CONCLUSIONS The Minnesota Grading System (MGS) of FAF (MGS-FAF) establishes a standardized methodology for grading eye bank tissue to quantify FAF compounds in the retinal pigment epithelium and correlate these findings to the AREDS. Future studies could then correlate specific FAF to the aging process, histopathology AMD phenotypes, and other maculopathies, as well as to analyze the biochemistry of autofluorescent fluorophores.
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Affiliation(s)
- Timothy W Olsen
- Department of Ophthalmology, Emory University, Atlanta, Georgia, USA
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