51
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Palczewska G, Golczak M, Williams DR, Hunter JJ, Palczewski K. Endogenous fluorophores enable two-photon imaging of the primate eye. Invest Ophthalmol Vis Sci 2014; 55:4438-47. [PMID: 24970255 DOI: 10.1167/iovs.14-14395] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
PURPOSE Noninvasive two-photon imaging of a living mammalian eye can reveal details of molecular processes in the retina and RPE. Retinyl esters and all-trans-retinal condensation products are two types of retinoid fluorophores present in these tissues. We measured the content of these two types of retinoids in monkey and human eyes to validate the potential of two-photon imaging for monitoring retinoid changes in human eyes. METHODS Two-photon microscopy (TPM) was used to visualize excised retina from monkey eyes. Retinoid composition and content in human and monkey eyes were quantified by HPLC and mass spectrometry (MS). RESULTS Clear images of inner and outer segments of rods and cones were obtained in primate eyes at different eccentricities. Fluorescence spectra from outer segments revealed a maximum emission at 480 nm indicative of retinols and their esters. In cynomolgus monkey and human retinal extracts, retinyl esters existed predominantly in the 11-cis configuration along with notable levels of 11-cis-retinol, a characteristic of cone-enriched retinas. Average amounts of di-retinoid-pyridinium-ethanolamine (A2E) in primate and human eyes were 160 and 225 pmol/eye, respectively. CONCLUSIONS These data show that human retina contains sufficient amounts of retinoids for two-photon excitation imaging. Greater amounts of 11-cis-retinyl esters relative to rodent retinas contribute to the fluorescence signal from both monkey and human eyes. These observations indicate that TPM imaging found effective in mice could detect early age- and disease-related changes in human retina.
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Affiliation(s)
| | - Marcin Golczak
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, United States
| | - David R Williams
- Center for Visual Science, University of Rochester, Rochester, New York, United States The Institute of Optics, University of Rochester, Rochester, New York, United States
| | - Jennifer J Hunter
- Center for Visual Science, University of Rochester, Rochester, New York, United States Flaum Eye Institute, University of Rochester, Rochester, New York, United States Department of Biomedical Engineering, University of Rochester, Rochester, New York, United States
| | - Krzysztof Palczewski
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, United States
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52
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Two-photon microscopy reveals early rod photoreceptor cell damage in light-exposed mutant mice. Proc Natl Acad Sci U S A 2014; 111:E1428-37. [PMID: 24706832 DOI: 10.1073/pnas.1317986111] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Atrophic age-related and juvenile macular degeneration are especially devastating due to lack of an effective cure. Two retinal cell types, photoreceptor cells and the adjacent retinal pigmented epithelium (RPE), reportedly display the earliest pathological changes. Abca4(-/-)Rdh8(-/-) mice, which mimic many features of human retinal degeneration, allowed us to determine the sequence of light-induced events leading to retinal degeneration. Using two-photon microscopy with 3D reconstruction methodology, we observed an initial strong retinoid-derived fluorescence and expansion of Abca4(-/-)Rdh8(-/-) mouse rod cell outer segments accompanied by macrophage infiltration after brief exposure of the retina to bright light. Additionally, light-dependent fluorescent compounds produced in rod outer segments were not transferred to the RPE of mice genetically defective in RPE phagocytosis. Collectively, these findings suggest that for light-induced retinopathies in mice, rod photoreceptors are the primary site of toxic retinoid accumulation and degeneration, followed by secondary changes in the RPE.
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53
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Bueno JM, Palacios R, Giakoumaki A, Gualda EJ, Schaeffel F, Artal P. Retinal cell imaging in myopic chickens using adaptive optics multiphoton microscopy. BIOMEDICAL OPTICS EXPRESS 2014; 5:664-674. [PMID: 24688804 PMCID: PMC3959843 DOI: 10.1364/boe.5.000664] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 01/30/2014] [Accepted: 01/31/2014] [Indexed: 06/03/2023]
Abstract
Abnormal eye growth induced by visual deprivation can modify the structure and density of the retinal cells. We have used an adaptive optics multiphoton microscope to image photoreceptors (PRs) and ganglion cells (GCs) at different retinal locations in unstained retinas of chicken eyes with about 10D of myopia and their normal-sighted fellow eyes. In all samples, the local averaged inter-PR distance increased with eccentricity. No significant differences in PR density were found between control and myopic eyes. GC density declined in myopic eyes compared to control eyes and the inter-cell distance increased. In normal eyes, the size of the GC cell bodies increased approximately two-fold between the area centralis and the peripheral retina. In myopic eyes, this trend was preserved but the GC bodies were larger at each retinal location, compared to control eyes. Obviously, GC morphology is changing when the retinal area is enlarged in myopic eyes.
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Affiliation(s)
- Juan M. Bueno
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Ed.34), 30100 Murcia, Spain
| | | | - Anastasia Giakoumaki
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Ed.34), 30100 Murcia, Spain
| | - Emilio J. Gualda
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Ed.34), 30100 Murcia, Spain
| | - Frank Schaeffel
- Section of Neurobiology of the Eye, Ophthalmic Research Institute, Calwerstrasse 7/1, 72076 Tuebingen, Germany
| | - Pablo Artal
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Ed.34), 30100 Murcia, Spain
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54
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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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55
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Chen Y, Palczewska G, Mustafi D, Golczak M, Dong Z, Sawada O, Maeda T, Maeda A, Palczewski K. Systems pharmacology identifies drug targets for Stargardt disease-associated retinal degeneration. J Clin Invest 2013; 123:5119-34. [PMID: 24231350 DOI: 10.1172/jci69076] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Accepted: 09/12/2013] [Indexed: 12/22/2022] Open
Abstract
A systems pharmacological approach that capitalizes on the characterization of intracellular signaling networks can transform our understanding of human diseases and lead to therapy development. Here, we applied this strategy to identify pharmacological targets for the treatment of Stargardt disease, a severe juvenile form of macular degeneration. Diverse GPCRs have previously been implicated in neuronal cell survival, and crosstalk between GPCR signaling pathways represents an unexplored avenue for pharmacological intervention. We focused on this receptor family for potential therapeutic interventions in macular disease. Complete transcriptomes of mouse and human samples were analyzed to assess the expression of GPCRs in the retina. Focusing on adrenergic (AR) and serotonin (5-HT) receptors, we found that adrenoceptor α 2C (Adra2c) and serotonin receptor 2a (Htr2a) were the most highly expressed. Using a mouse model of Stargardt disease, we found that pharmacological interventions that targeted both GPCR signaling pathways and adenylate cyclases (ACs) improved photoreceptor cell survival, preserved photoreceptor function, and attenuated the accumulation of pathological fluorescent deposits in the retina. These findings demonstrate a strategy for the identification of new drug candidates and FDA-approved drugs for the treatment of monogenic and complex diseases.
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MESH Headings
- ATP-Binding Cassette Transporters/deficiency
- ATP-Binding Cassette Transporters/genetics
- Adenine/analogs & derivatives
- Adenine/pharmacology
- Adenine/therapeutic use
- Adenylyl Cyclase Inhibitors
- Adrenergic alpha-Agonists/pharmacology
- Adrenergic alpha-Agonists/therapeutic use
- Adrenergic alpha-Antagonists/pharmacology
- Adrenergic alpha-Antagonists/therapeutic use
- Alcohol Oxidoreductases/deficiency
- Alcohol Oxidoreductases/genetics
- Animals
- Cell Survival
- Disease Models, Animal
- Doxazosin/pharmacology
- Doxazosin/therapeutic use
- Drug Evaluation, Preclinical
- Guanabenz/pharmacology
- Guanabenz/therapeutic use
- Humans
- Light/adverse effects
- Macaca fascicularis
- Macular Degeneration/congenital
- Macular Degeneration/drug therapy
- Macular Degeneration/genetics
- Macular Degeneration/prevention & control
- Mice
- Mice, Inbred BALB C
- Mice, Knockout
- Molecular Targeted Therapy
- Nerve Tissue Proteins/biosynthesis
- Nerve Tissue Proteins/genetics
- Photoreceptor Cells, Vertebrate/drug effects
- Photoreceptor Cells, Vertebrate/pathology
- Photoreceptor Cells, Vertebrate/physiology
- Photoreceptor Cells, Vertebrate/radiation effects
- Reactive Oxygen Species
- Receptor, Serotonin, 5-HT2A/biosynthesis
- Receptor, Serotonin, 5-HT2A/genetics
- Receptors, Adrenergic, alpha-2/biosynthesis
- Receptors, Adrenergic, alpha-2/genetics
- Receptors, G-Protein-Coupled/biosynthesis
- Receptors, G-Protein-Coupled/genetics
- Serotonin Antagonists/pharmacology
- Serotonin Antagonists/therapeutic use
- Signal Transduction
- Stargardt Disease
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56
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Maeda T, Lee MJ, Palczewska G, Marsili S, Tesar PJ, Palczewski K, Takahashi M, Maeda A. Retinal pigmented epithelial cells obtained from human induced pluripotent stem cells possess functional visual cycle enzymes in vitro and in vivo. J Biol Chem 2013; 288:34484-93. [PMID: 24129572 DOI: 10.1074/jbc.m113.518571] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Differentiated retinal pigmented epithelial (RPE) cells have been obtained from human induced pluripotent stem (hiPS) cells. However, the visual (retinoid) cycle in hiPS-RPE cells has not been adequately examined. Here we determined the expression of functional visual cycle enzymes in hiPS-RPE cells compared with that of isolated wild-type mouse primary RPE (mpRPE) cells in vitro and in vivo. hiPS-RPE cells appeared morphologically similar to mpRPE cells. Notably, expression of certain visual cycle proteins was maintained during cell culture of hiPS-RPE cells, whereas expression of these same molecules rapidly decreased in mpRPE cells. Production of the visual chromophore, 11-cis-retinal, and retinosome formation also were documented in hiPS-RPE cells in vitro. When mpRPE cells with luciferase activity were transplanted into the subretinal space of mice, bioluminance intensity was preserved for >3 months. Additionally, transplantation of mpRPE into blind Lrat(-/-) and Rpe65(-/-) mice resulted in the recovery of visual function, including increased electrographic signaling and endogenous 11-cis-retinal production. Finally, when hiPS-RPE cells were transplanted into the subretinal space of Lrat(-/-) and Rpe65(-/-) mice, their vision improved as well. Moreover, histological analyses of these eyes displayed replacement of dysfunctional RPE cells by hiPS-RPE cells. Together, our results show that hiPS-RPE cells can exhibit a functional visual cycle in vitro and in vivo. These cells could provide potential treatment options for certain blinding retinal degenerative diseases.
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Affiliation(s)
- Tadao Maeda
- From the Departments of Ophthalmology and Visual Sciences
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57
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Vitamin A derivatives as treatment options for retinal degenerative diseases. Nutrients 2013; 5:2646-66. [PMID: 23857173 PMCID: PMC3738993 DOI: 10.3390/nu5072646] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Revised: 06/05/2013] [Accepted: 06/13/2013] [Indexed: 11/17/2022] Open
Abstract
The visual cycle is a sequential enzymatic reaction for vitamin A, all-trans-retinol, occurring in the outer layer of the human retina and is essential for the maintenance of vision. The central source of retinol is derived from dietary intake of both retinol and pro-vitamin A carotenoids. A series of enzymatic reactions, located in both the photoreceptor outer segment and the retinal pigment epithelium, transform retinol into the visual chromophore 11-cis-retinal, regenerating visual pigments. Retina specific proteins carry out the majority of the visual cycle, and any significant interruption in this sequence of reactions is capable of causing varying degrees of blindness. Among these important proteins are Lecithin:retinol acyltransferase (LRAT) and retinal pigment epithelium-specific 65-kDa protein (RPE65) known to be responsible for esterification of retinol to all-trans-retinyl esters and isomerization of these esters to 11-cis-retinal, respectively. Deleterious mutations in these genes are identified in human retinal diseases that cause blindness, such as Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP). Herein, we discuss the pathology of 11-cis-retinal deficiency caused by these mutations in both animal disease models and human patients. We also review novel therapeutic strategies employing artificial visual chromophore 9-cis-retinoids which have been employed in clinical trials involving LCA patients.
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58
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Capozzi ME, Gordon AY, Penn JS, Jayagopal A. Molecular imaging of retinal disease. J Ocul Pharmacol Ther 2013; 29:275-86. [PMID: 23421501 DOI: 10.1089/jop.2012.0279] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Imaging of the eye plays an important role in ocular therapeutic discovery and evaluation in preclinical models and patients. Advances in ophthalmic imaging instrumentation have enabled visualization of the retina at an unprecedented resolution. These developments have contributed toward early detection of the disease, monitoring of disease progression, and assessment of the therapeutic response. These powerful technologies are being further harnessed for clinical applications by configuring instrumentation to detect disease biomarkers in the retina. These biomarkers can be detected either by measuring the intrinsic imaging contrast in tissue, or by the engineering of targeted injectable contrast agents for imaging of the retina at the cellular and molecular level. Such approaches have promise in providing a window on dynamic disease processes in the retina such as inflammation and apoptosis, enabling translation of biomarkers identified in preclinical and clinical studies into useful diagnostic targets. We discuss recently reported and emerging imaging strategies for visualizing diverse cell types and molecular mediators of the retina in vivo during health and disease, and the potential for clinical translation of these approaches.
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Affiliation(s)
- Megan E Capozzi
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-8808, USA
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59
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Maeda T, Dong Z, Jin H, Sawada O, Gao S, Utkhede D, Monk W, Palczewska G, Palczewski K. QLT091001, a 9-cis-retinal analog, is well-tolerated by retinas of mice with impaired visual cycles. Invest Ophthalmol Vis Sci 2013; 54:455-66. [PMID: 23249702 DOI: 10.1167/iovs.12-11152] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
PURPOSE Investigate whether retinas of mice with impaired retinal cycles exposed to light or kept in the dark tolerate prolonged high-dose administration of QLT091001, which contains as an active ingredient, the 9-cis-retinal precursor, 9-cis-retinyl acetate. METHODS Four- to six-week-old Lrat(-/-) and Rpe65(-/-) mice (n = 126) as well as crossbred Gnat1(-/-) mice lacking rod phototransduction (n = 110) were gavaged weekly for 6 months with 50 mg/kg QLT091001, either after being kept in the dark or after light bleaching for 30 min/wk followed by maintenance in a 12-hour light ≤ 10 lux)/12-hour dark cycle. Retinal health was monitored by spectral-domain optical coherent tomography (SD-OCT) and scanning laser ophthalmoscopy (SLO) every other month and histological, biochemical, and visual functional analyses were performed at the end of the experiment. Two-photon microscopy (TPM) was used to observe retinoid-containing retinosome structures in the RPE. RESULTS Retinal thickness and morphology examined by SD-OCT were well maintained in all strains treated with QLT091001. No significant increases of fundus autofluorescence were detected by SLO imaging of any strain. Accumulation of all-trans-retinyl esters varied with genetic background, types of administered compounds and lighting conditions but retinal health was not compromised. TPM imaging clearly revealed maintenance of retinosomes in the RPE of all mouse strains tested. CONCLUSIONS Retinas of Lrat(-/-), Rpe65(-/-), and crossbred Gnat1(-/-) mice tolerated prolonged high-dose QLT091001 treatment well.
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Affiliation(s)
- Tadao Maeda
- Department of Ophthalmology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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60
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Maeda A, Palczewski K. Retinal degeneration in animal models with a defective visual cycle. DRUG DISCOVERY TODAY. DISEASE MODELS 2013; 10:e163-e172. [PMID: 25210527 PMCID: PMC4157753 DOI: 10.1016/j.ddmod.2014.01.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Continuous generation of visual chromophore through the visual (retinoid) cycle is essential to maintain eyesight and retinal heath. Impairments in this cycle and related pathways adversely affect vision. In this review, we summarize the chemical reactions of vitamin A metabolites involved in the retinoid cycle and describe animal models of associated human diseases. Development of potential therapies for retinal disorders in these animal models is also introduced.
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Affiliation(s)
- Akiko Maeda
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106
| | - Krzysztof Palczewski
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106
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61
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Sharma R, Yin L, Geng Y, Merigan WH, Palczewska G, Palczewski K, Williams DR, Hunter JJ. In vivo two-photon imaging of the mouse retina. BIOMEDICAL OPTICS EXPRESS 2013; 4:1285-93. [PMID: 24009992 PMCID: PMC3756587 DOI: 10.1364/boe.4.001285] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 05/06/2013] [Accepted: 06/17/2013] [Indexed: 05/18/2023]
Abstract
Though in vivo two-photon imaging has been demonstrated in non-human primates, improvements in the signal-to-noise ratio (SNR) would greatly improve its scientific utility. In this study, extrinsic fluorophores, expressed in otherwise transparent retinal ganglion cells, were imaged in the living mouse eye using a two-photon fluorescence adaptive optics scanning laser ophthalmoscope. We recorded two orders of magnitude greater signal levels from extrinsically labeled cells relative to previous work done in two-photon autofluorescence imaging of primates. Features as small as single dendrites in various layers of the retina could be resolved and predictions are made about the feasibility of measuring functional response from cells. In the future, two-photon imaging in the intact eye may allow us to monitor the function of retinal cell classes with infrared light that minimally excites the visual response.
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Affiliation(s)
- Robin Sharma
- Center for Visual Science, University of Rochester, Rochester, New York 14627, USA
- The Institute of Optics, University of Rochester, Rochester, New York 14620, USA
| | - Lu Yin
- Center for Visual Science, University of Rochester, Rochester, New York 14627, USA
| | - Ying Geng
- Center for Visual Science, University of Rochester, Rochester, New York 14627, USA
- The Institute of Optics, University of Rochester, Rochester, New York 14620, USA
- Currently at: Corning Incorporated, One Riverfront Plaza, Corning, New York 14831, USA
| | - William H. Merigan
- Center for Visual Science, University of Rochester, Rochester, New York 14627, USA
- Flaum Eye Institute, University of Rochester, Rochester, New York 14642, USA
| | - Grazyna Palczewska
- Polgenix, Inc., 11000 Cedar Avenue, Suite 260, Cleveland, Ohio 44106, USA
| | - Krzysztof Palczewski
- Department of Pharmacology, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA
| | - David R. Williams
- Center for Visual Science, University of Rochester, Rochester, New York 14627, USA
- The Institute of Optics, University of Rochester, Rochester, New York 14620, USA
- Flaum Eye Institute, University of Rochester, Rochester, New York 14642, USA
| | - Jennifer J. Hunter
- Center for Visual Science, University of Rochester, Rochester, New York 14627, USA
- Flaum Eye Institute, University of Rochester, Rochester, New York 14642, USA
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62
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Abstract
The chromophore of all known visual pigments consists of 11-cis-retinal (derived from either vitamin A1 or A2) or a hydroxylated derivative, bound to a protein (opsin) via a Schiff base. Absorption of a photon results in photoisomerization of the chromophore to all-trans-retinal and conversion of the visual pigment to the signaling form. Regeneration of the 11-cis-retinal occurs in an adjacent tissue and involves several enzymes, several water-soluble retinoid-binding proteins, and intra- and intercellular diffusional processes. Rod photoreceptor cells depend completely on the output of 11-cis-retinal from adjacent retinal pigment epithelial (RPE) cells. Cone photoreceptors cells can use 11-cis-retinal from the RPE and from a second more poorly characterized cycle, which appears to involve adjacent Müller (glial) cells. Recent progress in the characterization of rod and cone visual cycle components and reactions will result in the development of approaches to the amelioration of blinding eye diseases associated with visual cycle defects.
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Affiliation(s)
- John C Saari
- Department of Ophthalmology and Biochemistry, University of Washington, Seattle, WA 91895, USA.
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63
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Gao SQ, Maeda T, Okano K, Palczewski K. A microparticle/hydrogel combination drug-delivery system for sustained release of retinoids. Invest Ophthalmol Vis Sci 2012; 53:6314-23. [PMID: 22918645 PMCID: PMC3465014 DOI: 10.1167/iovs.12-10279] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2012] [Revised: 07/18/2012] [Accepted: 08/20/2012] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To design and develop a drug-delivery system containing a combination of poly(D,L-lactide-co-glycolide) (PLGA) microparticles and alginate hydrogel for sustained release of retinoids to treat retinal blinding diseases that result from an inadequate supply of retinol and generation of 11-cis-retinal. METHODS To study drug release in vivo, either the drug-loaded microparticle-hydrogel combination was injected subcutaneously or drug-loaded microparticles were injected intravitreally into Lrat(-/-) mice. Orally administered 9-cis-retinoids were used for comparison and drug concentrations in plasma were determined by HPLC. Electroretinography (ERG) and both chemical and histologic analyses were used to evaluate drug effects on visual function and morphology. RESULTS Lrat(-/-) mice demonstrated sustained drug release from the microparticle/hydrogel combination that lasted 4 weeks after subcutaneous injection. Drug concentrations in plasma of the control group treated with the same oral dose rose to higher levels for 6-7 hours but then dropped markedly by 24 hours. Significantly increased ERG responses and a markedly improved retinal pigmented epithelium (RPE)-rod outer segment (ROS) interface were observed after subcutaneous injection of the drug-loaded delivery combination. Intravitreal injection of just 2% of the systemic dose of drug-loaded microparticles provided comparable therapeutic efficacy. CONCLUSIONS Sustained release of therapeutic levels of 9-cis-retinoids was achieved in Lrat(-/-) mice by subcutaneous injection in a microparticle/hydrogel drug-delivery system. Both subcutaneous and intravitreal injections of drug-loaded microparticles into Lrat(-/-) mice improved visual function and retinal structure.
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Affiliation(s)
| | - Tadao Maeda
- Ophthalmology, School of Medicine, Case Western Reserve University, Cleveland, Ohio
| | - Kiichiro Okano
- Ophthalmology, School of Medicine, Case Western Reserve University, Cleveland, Ohio
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64
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Abstract
The human eye is constantly exposed to sunlight and artificial lighting. Light transmission through the eye is fundamental to its unique biological functions of directing vision and circadian rhythm and therefore light absorbed by the eye must be benign. However, exposure to the very intense ambient radiation can pose a hazard particularly if the recipient is over 40 years of age. There are age-related changes in the endogenous (natural) chromophores (lipofuscin, A2E and all-trans-retinal derivatives) in the human retina that makes it more susceptible to visible light damage. Intense visible light sources that do not filter short blue visible light (400-440 nm) used for phototherapy of circadian imbalance (i.e. seasonal affective disorder) increase the risk for age-related light damage to the retina. Moreover, many drugs, dietary supplements, nanoparticles and diagnostic dyes (xenobiotics) absorb ocular light and have the potential to induce photodamage to the retina, leading to transient or permanent blinding disorders. This article will review the underlying reasons why visible light in general and short blue visible light in particular dramatically raises the risk of photodamage to the human retina.
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Affiliation(s)
- Albert R Wielgus
- Department of Ophthalmology, Duke University Medical Center, Durham, NC, USA
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65
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Masihzadeh O, Lei TC, Ammar DA, Kahook MY, Gibson EA. A multiphoton microscope platform for imaging the mouse eye. Mol Vis 2012; 18:1840-8. [PMID: 22815637 PMCID: PMC3398498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Accepted: 07/01/2012] [Indexed: 11/29/2022] Open
Abstract
PURPOSE To demonstrate the ability of multiphoton microscopy to obtain full three-dimensional high-resolution images of the intact mouse eye anterior chamber without need for enucleation. METHODS A custom multiphoton microscope was constructed and optimized for deep tissue imaging. Simultaneous two-photon autofluorescence (2PAF) and second harmonic generation (SHG) imaging were performed. A mouse holder and stereotaxic platform were designed to access different parts of the eye for imaging. A reservoir for keeping the eye moist was used during imaging sessions. RESULTS Non-invasive multiphoton images deep inside the anterior chamber of the mouse eye were obtained without the need for enucleation. The iris, corneal epithelium and endothelium, trabecular meshwork region and conjunctiva were visualized by the 2PAF and SHG signals. Identification of the anatomy was achieved by the intrinsic properties of the native tissue without any exogenous labeling. Images as deep as 600 microns into the eye were clearly demonstrated. Full three-dimensional image reconstructions of the entire anterior chamber were performed and analyzed using custom software. CONCLUSIONS Multiphoton imaging is a highly promising tool for ophthalmic research. We have demonstrated the ability to image the entire anterior chamber of the mouse eye in its native state. These results provide a foundation for future in vivo studies of the eye.
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Affiliation(s)
- Omid Masihzadeh
- Department of Bioengineering, University of Colorado Anschutz Medical Campus, Aurora, CO
| | - Tim C. Lei
- Department of Electrical Engineering, University of Colorado Denver, Denver, CO
| | - David A. Ammar
- Department of Ophthalmology, University of Colorado Hospital Eye Center, Aurora, CO
| | - Malik Y. Kahook
- Department of Ophthalmology, University of Colorado Hospital Eye Center, Aurora, CO
| | - Emily A. Gibson
- Department of Bioengineering, University of Colorado Anschutz Medical Campus, Aurora, CO
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66
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Jiang W, Napoli JL. Reorganization of cellular retinol-binding protein type 1 and lecithin:retinol acyltransferase during retinyl ester biosynthesis. BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1820:859-69. [PMID: 22498138 PMCID: PMC3366551 DOI: 10.1016/j.bbagen.2012.03.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2011] [Revised: 03/21/2012] [Accepted: 03/23/2012] [Indexed: 12/26/2022]
Abstract
BACKGROUND Cellular retinol-binding protein, type 1 (Crbp1), chaperones retinyl ester (RE) biosynthesis catalyzed by lecithin:retinol acyltransferase (LRAT). METHODS We monitored the subcellular loci of LRAT and Crbp1 before and during RE biosynthesis, and compared the results to diacylglycerol:acyltransferase type 2 (DGAT2) during triacylglycerol biosynthesis in three cell lines: COS7, CHO and HepG2. RESULTS Before initiation of RE biosynthesis, LRAT distributed throughout the endoplasmic reticulum (ER), similar to DGAT2, and Crpb1 localized with mitochondria associated membranes (MAM), surrounded by LRAT. Upon initiating RE biosynthesis in cells transfected with low amounts of vector to simulate physiological expression levels, Crpb1 remained with MAM, and both Crbp1 and MAM re-localized with LRAT. LRAT formed rings around the growing lipid droplets. LRAT activity was higher in these rings relative to the general ER. LRAT-containing rings colocalized with the lipid-droplet surface proteins, desnutrin/adipose triglyceride lipase and perilipin 2. Colocalization with lipid droplets required the 38 N-terminal amino acid residues of LRAT, and specifically K36 and R38. Formation of rings around the growing lipid droplets did not require functional microtubules. GENERAL SIGNIFICANCE These data indicate a relationship between LRAT and Crbp1 during RE biosynthesis in which MAM-associated Crpb1 and LRAT colocalize, and both surround the growing RE-containing lipid droplet. The N-terminus of LRAT, especially K36 and R38, is essential to colocalization with the lipid droplet.
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Affiliation(s)
- Weiya Jiang
- Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, College of Natural Resources, University of California, Berkeley, California 94720, USA
| | - Joseph L. Napoli
- Graduate Program in Metabolic Biology, Nutritional Sciences and Toxicology, College of Natural Resources, University of California, Berkeley, California 94720, USA
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67
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A homozygous frameshift mutation in LRAT causes retinitis punctata albescens. Ophthalmology 2012; 119:1899-906. [PMID: 22559933 DOI: 10.1016/j.ophtha.2012.02.037] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2011] [Revised: 02/21/2012] [Accepted: 02/21/2012] [Indexed: 12/13/2022] Open
Abstract
PURPOSE To determine the genetic defect and to describe the clinical characteristics in patients with retinitis punctata albescens (RPA) and fundus albipunctatus (FAP). DESIGN Case series/observational study. PARTICIPANTS We included 13 patients affected by RPA or FAP. METHODS Thirteen patients were collected from 8 families with a retinal dystrophy characterized by tiny, yellow-white dots on funduscopy, typical for FAP or RPA. All patients underwent full ophthalmologic examinations, including visual field assessment. Fundus photography, and electroretinography were performed in 12 patients, and optical coherence tomography and fundus autofluorescence were performed in 4 patients. DNA samples of all patients were screened for mutations in RLBP1 and for mutations in RDH5 in patients who did not carry mutations in RLBP1. DNA samples of 2 sibling pairs of nonconsanguineous families who carried mutations neither in RLBP1 nor in RDH5 were analyzed by genome-wide homozygosity mapping. Sequence analysis was performed of LRAT, a candidate gene in a shared homozygous region. MAIN OUTCOME MEASURES We assessed DNA sequence variants, best-corrected visual acuity, fundus appearance, visual field measurements, electroretinogram responses, optical coherence tomography, and fundus autofluorescence. RESULTS A homozygous frameshift mutation was identified in LRAT in 4 patients with RPA. Mutations in RLBP1 were identified in 7 patients with RPA and in 1 patient with FAP and cone dystrophy. One patient had compound heterozygous mutations in RDH5 and suffered from FAP with mild maculopathy. CONCLUSIONS A genetic defect was identified in LRAT as a novel cause of RPA. LRAT is therefore the fourth gene involved in the visual cycle that may cause a white-dot retinopathy. We also revealed that mutations in RLBP1 may lead to FAP with cone dystrophy.
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68
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Padayatti P, Palczewska G, Sun W, Palczewski K, Salom D. Imaging of protein crystals with two-photon microscopy. Biochemistry 2012; 51:1625-37. [PMID: 22324807 DOI: 10.1021/bi201682q] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Second-order nonlinear optical imaging of chiral crystals (SONICC), which portrays second-harmonic generation (SHG) by noncentrosymmetric crystals, is emerging as a powerful imaging technique for protein crystals in media opaque to visible light because of its high signal-to-noise ratio. Here we report the incorporation of both SONICC and two-photon excited fluorescence (TPEF) into one imaging system that allows visualization of crystals as small as ~10 μm in their longest dimension. Using this system, we then documented an inverse correlation between the level of symmetry in examined crystals and the intensity of their SHG. Moreover, because of blue-green TPEF exhibited by most tested protein crystals, we also could identify and image SHG-silent protein crystals. Our experimental data suggest that the TPEF in protein crystals is mainly caused by the oxidation of tryptophan residues. Additionally, we found that unspecific fluorescent dyes are able to bind to lysozyme crystals and enhance their detection by TPEF. We finally confirmed that the observed fluorescence was generated by a two-photon rather than a three-photon process. The capability for imaging small protein crystals in turbid or opaque media with nondamaging infrared light in a single system makes the combination of SHG and intrinsic visible TPEF a powerful tool for nondestructive protein crystal identification and characterization during crystallization trials.
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69
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Lin Y, Jones BW, Liu A, Tucker JF, Rapp K, Luo L, Baehr W, Bernstein PS, Watt CB, Yang JH, Shaw MV, Marc RE. Retinoid receptors trigger neuritogenesis in retinal degenerations. FASEB J 2012; 26:81-92. [PMID: 21940995 PMCID: PMC3250249 DOI: 10.1096/fj.11-192914] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Accepted: 09/01/2011] [Indexed: 12/25/2022]
Abstract
Anomalous neuritogenesis is a hallmark of neurodegenerative disorders, including retinal degenerations, epilepsy, and Alzheimer's disease. The neuritogenesis processes result in a partial reinnervation, new circuitry, and functional changes within the deafferented retina and brain regions. Using the light-induced retinal degeneration (LIRD) mouse model, which provides a unique platform for exploring the mechanisms underlying neuritogenesis, we found that retinoid X receptors (RXRs) control neuritogenesis. LIRD rapidly triggered retinal neuron neuritogenesis and up-regulated several key elements of retinoic acid (RA) signaling, including retinoid X receptors (RXRs). Exogenous RA initiated neuritogenesis in normal adult retinas and primary retinal cultures and exacerbated it in LIRD retinas. However, LIRD-induced neuritogenesis was partly attenuated in retinol dehydrogenase knockout (Rdh12(-/-)) mice and by aldehyde dehydrogenase inhibitors. We further found that LIRD rapidly increased the expression of glutamate receptor 2 and β Ca(2+)/calmodulin-dependent protein kinase II (βCaMKII). Pulldown assays demonstrated interaction between βCaMKII and RXRs, suggesting that CaMKII pathway regulates the activities of RXRs. RXR antagonists completely prevented and RXR agonists were more effective than RA in inducing neuritogenesis. Thus, RXRs are in the final common path and may be therapeutic targets to attenuate retinal remodeling and facilitate global intervention methods in blinding diseases and other neurodegenerative disorders.
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Affiliation(s)
- Yanhua Lin
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Bryan W. Jones
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Aihua Liu
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - James F. Tucker
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Kevin Rapp
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Ling Luo
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Wolfgang Baehr
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
- Department of Neurobiology and Anatomy, Health Science Center, and
- Department of Biology, University of Utah, Salt Lake City, Utah, USA
| | - Paul S. Bernstein
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Carl B. Watt
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Jia-Hui Yang
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Marguerite V. Shaw
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
| | - Robert E. Marc
- Department of Ophthalmology, John A. Moran Eye Center, School of Medicine
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70
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Hunter JJ, Morgan JIW, Merigan WH, Sliney DH, Sparrow JR, Williams DR. The susceptibility of the retina to photochemical damage from visible light. Prog Retin Eye Res 2012; 31:28-42. [PMID: 22085795 PMCID: PMC3242847 DOI: 10.1016/j.preteyeres.2011.11.001] [Citation(s) in RCA: 219] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 10/28/2011] [Accepted: 11/01/2011] [Indexed: 02/08/2023]
Abstract
The photoreceptor/RPE complex must maintain a delicate balance between maximizing the absorption of photons for vision and retinal image quality while simultaneously minimizing the risk of photodamage when exposed to bright light. We review the recent discovery of two new effects of light exposure on the photoreceptor/RPE complex in the context of current thinking about the causes of retinal phototoxicity. These effects are autofluorescence photobleaching in which exposure to bright light reduces lipofuscin autofluorescence and, at higher light levels, RPE disruption in which the pattern of autofluorescence is permanently altered following light exposure. Both effects occur following exposure to visible light at irradiances that were previously thought to be safe. Photopigment, retinoids involved in the visual cycle, and bisretinoids in lipofuscin have been implicated as possible photosensitizers for photochemical damage. The mechanism of RPE disruption may follow either of these paths. On the other hand, autofluorescence photobleaching is likely an indicator of photooxidation of lipofuscin. The permanent changes inherent in RPE disruption might require modification of the light safety standards. AF photobleaching recovers after several hours although the mechanisms by which this occurs are not yet clear. Understanding the mechanisms of phototoxicity is all the more important given the potential for increased susceptibility in the presence of ocular diseases that affect either the visual cycle and/or lipofuscin accumulation. In addition, knowledge of photochemical mechanisms can improve our understanding of some disease processes that may be influenced by light exposure, such as some forms of Leber's congenital amaurosis, and aid in the development of new therapies. Such treatment prior to intentional light exposures, as in ophthalmic examinations or surgeries, could provide an effective preventative strategy.
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Affiliation(s)
- Jennifer J Hunter
- Flaum Eye Institute, University of Rochester, Box 314, 601Elmwood Ave, Rochester, NY 14642, USA.
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71
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Maeda A, Golczak M, Chen Y, Okano K, Kohno H, Shiose S, Ishikawa K, Harte W, Palczewska G, Maeda T, Palczewski K. Primary amines protect against retinal degeneration in mouse models of retinopathies. Nat Chem Biol 2011; 8:170-8. [PMID: 22198730 PMCID: PMC3518042 DOI: 10.1038/nchembio.759] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Accepted: 10/07/2011] [Indexed: 12/31/2022]
Abstract
Vertebrate vision is initiated by photoisomerization of the visual pigment chromophore 11-cis-retinal and is maintained by continuous regeneration of this retinoid through a series of reactions termed the retinoid cycle. However, toxic side reaction products, especially those involving reactive aldehyde groups of the photoisomerized product, all-trans-retinal, can cause severe retinal pathology. Here we lowered peak concentrations of free all-trans-retinal with primary amine-containing Food and Drug Administration (FDA)-approved drugs that did not inhibit chromophore regeneration in mouse models of retinal degeneration. Schiff base adducts between all-trans-retinal and these amines were identified by MS. Adducts were observed in mouse eyes only when an experimental drug protected the retina from degeneration in both short-term and long-term treatment experiments. This study demonstrates a molecular basis of all-trans-retinal-induced retinal pathology and identifies an assemblage of FDA-approved compounds with protective effects against this pathology in a mouse model that shows features of Stargardt's disease and age-related retinal degeneration.
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Affiliation(s)
- Akiko Maeda
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, Ohio, USA
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72
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Abstract
Visual perception in humans occurs through absorption of electromagnetic radiation from 400 to 780 nm by photoreceptors in the retina. A photon of visible light carries a sufficient amount of energy to cause, when absorbed, a cis,trans-geometric isomerization of the 11-cis-retinal chromophore, a vitamin A derivative bound to rhodopsin and cone opsins of retinal photoreceptors. The unique biochemistry of these complexes allows us to reliably and reproducibly collect continuous visual information about our environment. Moreover, other nonconventional retinal opsins such as the circadian rhythm regulator melanopsin also initiate light-activated signaling based on similar photochemistry.
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Affiliation(s)
- Krzysztof Palczewski
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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73
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Bonilha VL, Rayborn ME, Li Y, Grossman GH, Berson EL, Hollyfield JG. Histopathology and functional correlations in a patient with a mutation in RPE65, the gene for retinol isomerase. Invest Ophthalmol Vis Sci 2011; 52:8381-92. [PMID: 21931134 DOI: 10.1167/iovs.11-7973] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Here the authors describe the structural features of the retina and retinal pigment epithelium (RPE) in postmortem donor eyes of a 56-year-old patient with a homozygous missense RPE65 mutation (Ala132Thr) and correlate the pathology with the patient's visual function last measured at age 51. METHODS Eyes were enucleated within 13.5 hours after death. Representative areas from the macula and periphery were processed for light and electron microscopy. Immunofluorescence was used to localize the distribution of RPE65, rhodopsin, and cone arrestin. The autofluorescence in the RPE was compared with that of two normal eyes from age-similar donors. RESULTS Histologic examination revealed the loss of rods and cones across most areas of the retina, attenuated retinal vessels, and RPE thinning in both eyes. A small number of highly disorganized cones were present in the macula that showed simultaneous labeling with cone arrestin and red/green or blue opsin. RPE65 immunoreactivity and RPE autofluorescence were reduced compared with control eyes in all areas studied. Rhodopsin labeling was observed in rods in the far periphery. The optic nerve showed a reduced number of axons. CONCLUSIONS The clinical findings of reduced visual acuity, constricted fields, and reduced electroretinograms (ERGs) 5 years before death correlated with the small number of cones present in the macula and the extensive loss of photoreceptors in the periphery. The absence of autofluorescence in the RPE suggests that photoreceptor cells were probably missing across the retina for extended periods of time. Possible mechanisms that could lead to photoreceptor cell death are discussed.
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Affiliation(s)
- Vera L Bonilha
- Cole Eye Institute, Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine, Cleveland, Ohio 44195, USA.
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74
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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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75
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Bueno JM, Giakoumaki A, Gualda EJ, Schaeffel F, Artal P. Analysis of the chicken retina with an adaptive optics multiphoton microscope. BIOMEDICAL OPTICS EXPRESS 2011; 2:1637-48. [PMID: 21698025 PMCID: PMC3114230 DOI: 10.1364/boe.2.001637] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Revised: 05/13/2011] [Accepted: 05/13/2011] [Indexed: 05/23/2023]
Abstract
The structure and organization of the chicken retina has been investigated with an adaptive optics multiphoton imaging microscope in a backward configuration. Non-stained flat-mounted retinal tissues were imaged at different depths, from the retinal nerve fiber layer to the outer segment, by detecting the intrinsic nonlinear fluorescent signal. From the stacks of images corresponding to the different retinal layers, volume renderings of the entire retina were reconstructed. The density of photoreceptors and ganglion cells layer were directly estimated from the images as a function of the retinal eccentricity. The maximum anatomical resolving power at different retinal eccentricities was also calculated. This technique could be used for a better characterization of retinal alterations during myopia development, and may be useful for visualization of retinal pathologies and intoxication during pharmacological studies.
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Affiliation(s)
- Juan M. Bueno
- Laboratorio de Óptica, Centro de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), 30100 Murcia, Spain
| | - Anastasia Giakoumaki
- Laboratorio de Óptica, Centro de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), 30100 Murcia, Spain
| | - Emilio J. Gualda
- Laboratorio de Óptica, Centro de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), 30100 Murcia, Spain
| | - Frank Schaeffel
- Section of Neurobiology of the Eye, Ophthalmic Research Institute, Calwerstrasse 7/1, 72076 Tuebingen, Germany
| | - Pablo Artal
- Laboratorio de Óptica, Centro de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), 30100 Murcia, Spain
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76
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Schreiber R, Taschler U, Preiss-Landl K, Wongsiriroj N, Zimmermann R, Lass A. Retinyl ester hydrolases and their roles in vitamin A homeostasis. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:113-23. [PMID: 21586336 PMCID: PMC3242165 DOI: 10.1016/j.bbalip.2011.05.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Revised: 04/28/2011] [Accepted: 05/02/2011] [Indexed: 12/16/2022]
Abstract
In mammals, dietary vitamin A intake is essential for the maintenance of adequate retinoid (vitamin A and metabolites) supply of tissues and organs. Retinoids are taken up from animal or plant sources and subsequently stored in form of hydrophobic, biologically inactive retinyl esters (REs). Accessibility of these REs in the intestine, the circulation, and their mobilization from intracellular lipid droplets depends on the hydrolytic action of RE hydrolases (REHs). In particular, the mobilization of hepatic RE stores requires REHs to maintain steady plasma retinol levels thereby assuring constant vitamin A supply in times of food deprivation or inadequate vitamin A intake. In this review, we focus on the roles of extracellular and intracellular REHs in vitamin A metabolism. Furthermore, we will discuss the tissue-specific function of REHs and highlight major gaps in the understanding of RE catabolism. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.
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77
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Kiser PD, Golczak M, Maeda A, Palczewski K. Key enzymes of the retinoid (visual) cycle in vertebrate retina. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:137-51. [PMID: 21447403 DOI: 10.1016/j.bbalip.2011.03.005] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 03/08/2011] [Accepted: 03/22/2011] [Indexed: 12/11/2022]
Abstract
A major goal in vision research over the past few decades has been to understand the molecular details of retinoid processing within the retinoid (visual) cycle. This includes the consequences of side reactions that result from delayed all-trans-retinal clearance and condensation with phospholipids that characterize a variety of serious retinal diseases. Knowledge of the basic retinoid biochemistry involved in these diseases is essential for development of effective therapeutics. Photoisomerization of the 11-cis-retinal chromophore of rhodopsin triggers a complex set of metabolic transformations collectively termed phototransduction that ultimately lead to light perception. Continuity of vision depends on continuous conversion of all-trans-retinal back to the 11-cis-retinal isomer. This process takes place in a series of reactions known as the retinoid cycle, which occur in photoreceptor and RPE cells. All-trans-retinal, the initial substrate of this cycle, is a chemically reactive aldehyde that can form toxic conjugates with proteins and lipids. Therefore, much experimental effort has been devoted to elucidate molecular mechanisms of the retinoid cycle and all-trans-retinal-mediated retinal degeneration, resulting in delineation of many key steps involved in regenerating 11-cis-retinal. Three particularly important reactions are catalyzed by enzymes broadly classified as acyltransferases, short-chain dehydrogenases/reductases and carotenoid/retinoid isomerases/oxygenases. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.
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Affiliation(s)
- Philip D Kiser
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106-4965, USA
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78
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Orban T, Palczewska G, Palczewski K. Retinyl ester storage particles (retinosomes) from the retinal pigmented epithelium resemble lipid droplets in other tissues. J Biol Chem 2011; 286:17248-58. [PMID: 21454509 DOI: 10.1074/jbc.m110.195198] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Levels of many hydrophobic cellular substances are tightly regulated because of their potential cytotoxicity. These compounds tend to self-aggregate in cytoplasmic storage depots termed lipid droplets/bodies that have well defined structures that contain additional components, including cholesterol and various proteins. Hydrophobic substances in these structures become mobilized in a specific and regulated manner as dictated by cellular requirements. Retinal pigmented epithelial cells in the eye produce retinyl ester-containing lipid droplets named retinosomes. These esters are mobilized to replenish the visual chromophore, 11-cis-retinal, and their storage ensures proper visual function despite fluctuations in dietary vitamin A intake. But it remains unclear whether retinosomes are structures specific to the eye or similar to lipid droplets in other organs/tissues that contain substances other than retinyl esters. Thus, we initially investigated the production of these lipid droplets in experimental cell lines expressing lecithin:retinol acyltransferase, a key enzyme involved in formation of retinyl ester-containing retinosomes from all-trans-retinol. We found that retinosomes and oleate-derived lipid droplets form and co-localize concomitantly, indicating their intrinsic structural similarities. Next, we isolated native retinosomes from bovine retinal pigmented epithelium and found that their protein and hydrophobic small molecular constituents were similar to those of lipid droplets reported for other experimental cell lines and tissues. These unexpected findings suggest a common mechanism for lipid droplet formation that exhibits broad chemical specificity for the hydrophobic substances being stored.
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Affiliation(s)
- Tivadar Orban
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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79
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Structural and functional characteristics in carriers of X-linked retinitis pigmentosa with a tapetal-like reflex. Retina 2011; 30:1726-33. [PMID: 20829740 DOI: 10.1097/iae.0b013e3181dde629] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PURPOSE The purpose of this study was to identify the functional and structural characteristics in three female obligate carriers of X-linked retinitis pigmentosa from the same family by using spectral domain optical coherence tomography, fundus autofluorescence, and microperimetry. METHODS Three female obligate carriers with a tapetal-like reflex, 21, 49, and 57 years of age, from a single family of X-linked retinitis pigmentosa that was seen in the ophthalmology department at the University of Illinois at Chicago, were enrolled in the study. All carriers underwent a complete ophthalmic examination. Spectral domain optical coherence tomography measurements, a macular microperimetry examination, and fundus autofluorescence testing were performed. RESULTS The spectral domain optical coherence tomography examination in all three carriers showed a normal retinal microstructure and thickness. Microperimeter testing showed subnormal retinal sensitivity in the areas of the tapetal-like reflex. Fundus autofluorescence examination showed the presence of speckled areas of enhanced autofluorescence. CONCLUSION Our study demonstrates that the carriers of X-linked retinitis pigmentosa with a tapetal-like reflex can show an enhanced reflectance on infrared images, abnormal autofluorescence properties, elevated retinal thresholds, and a normal retinal morphology within the posterior pole on spectral domain optical coherence tomography testing.
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80
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Ammar DA, Lei TC, Masihzadeh O, Gibson EA, Kahook MY. Trans-scleral imaging of the human trabecular meshwork by two-photon microscopy. Mol Vis 2011; 17:583-90. [PMID: 21386924 PMCID: PMC3049734] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Accepted: 02/18/2011] [Indexed: 12/02/2022] Open
Abstract
PURPOSE To image the native (unfixed) human trabecular meshwork (TM) through the overlying sclera using a non-invasive, non-destructive technique. METHODS Two-photon microscopic (2PM) methods, including two-photon autofluorescence (2PAF) and second harmonic generation (SHG), were used to image through the sclera of a human cadaver eye into the TM region. Multiple images were analyzed along the tissue axis (z-axis) to generate a three-dimensional (3D) model of the region. The tissue was subsequently fixed, paraffin embedded, and histological sections were photographed for comparison to the 2PM images. RESULTS 3D analysis of multiple 2PM SHG images revealed an open region deep within the TM consistent with the location of Schlemm's canal (SC). Images of the scleral spur and surrounding tissues were also obtained. The SC, TM, scleral spur, and surrounding tissue images obtained with 2PM matched with histologically stained sections of the same tissue. CONCLUSIONS 2PM imaging of the outflow system of the human eye documented collagenous structures solely from inherent optical properties. 2PM successfully imaged through the sclera into the SC/TM without the need for fixation, embedding, or histological processing. This work reveals that 2PM imaging has potential as a new metric for evaluating the aqueous outflow region of the human eye and is worthy of further exploration.
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Affiliation(s)
- David A. Ammar
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO
| | - Tim C. Lei
- Department of Electrical Engineering, University of Colorado Denver, Denver, CO
| | - Omid Masihzadeh
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO,Department of Bioengineering, University of Colorado Denver, Aurora, CO
| | - Emily A. Gibson
- Department of Bioengineering, University of Colorado Denver, Aurora, CO
| | - Malik Y. Kahook
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO
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81
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Multiphoton microscopy for ophthalmic imaging. J Ophthalmol 2011; 2011:870879. [PMID: 21274261 PMCID: PMC3022205 DOI: 10.1155/2011/870879] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Revised: 09/06/2010] [Accepted: 10/26/2010] [Indexed: 12/02/2022] Open
Abstract
We review multiphoton microscopy (MPM) including two-photon autofluorescence (2PAF), second harmonic generation (SHG), third harmonic generation (THG), fluorescence lifetime (FLIM), and coherent anti-Stokes Raman Scattering (CARS) with relevance to clinical applications in ophthalmology. The different imaging modalities are discussed highlighting the particular strength that each has for functional tissue imaging. MPM is compared with current clinical ophthalmological imaging techniques such as reflectance confocal microscopy, optical coherence tomography, and fluorescence imaging. In addition, we discuss the future prospects for MPM in disease detection and clinical monitoring of disease progression, understanding fundamental disease mechanisms, and real-time monitoring of drug delivery.
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82
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Sun H, Kawaguchi R. The membrane receptor for plasma retinol-binding protein, a new type of cell-surface receptor. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2011; 288:1-41. [PMID: 21482409 DOI: 10.1016/b978-0-12-386041-5.00001-7] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Vitamin A is essential for diverse aspects of life ranging from embryogenesis to the proper functioning of most adult organs. Its derivatives (retinoids) have potent biological activities such as regulating cell growth and differentiation. Plasma retinol-binding protein (RBP) is the specific vitamin A carrier protein in the blood that binds to vitamin A with high affinity and delivers it to target organs. A large amount of evidence has accumulated over the past decades supporting the existence of a cell-surface receptor for RBP that mediates cellular vitamin A uptake. Using an unbiased strategy, this specific cell-surface RBP receptor has been identified as STRA6, a multitransmembrane domain protein with previously unknown function. STRA6 is not homologous to any protein of known function and represents a new type of cell-surface receptor. Consistent with the diverse functions of vitamin A, STRA6 is widely expressed in embryonic development and in adult organ systems. Mutations in human STRA6 are associated with severe pathological phenotypes in many organs such as the eye, brain, heart, and lung. STRA6 binds to RBP with high affinity and mediates vitamin A uptake into cells. This review summarizes the history of the RBP receptor research, its expression in the context of known functions of vitamin A in distinct human organs, structure/function analysis of this new type of membrane receptor, pertinent questions regarding its very existence, and its potential implication in treating human diseases.
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Affiliation(s)
- Hui Sun
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California, USA
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83
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Hunter JJ, Masella B, Dubra A, Sharma R, Yin L, Merigan WH, Palczewska G, Palczewski K, Williams DR. Images of photoreceptors in living primate eyes using adaptive optics two-photon ophthalmoscopy. BIOMEDICAL OPTICS EXPRESS 2010; 2:139-48. [PMID: 21326644 PMCID: PMC3028489 DOI: 10.1364/boe.2.000139] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Revised: 12/14/2010] [Accepted: 12/14/2010] [Indexed: 05/18/2023]
Abstract
In vivo two-photon imaging through the pupil of the primate eye has the potential to become a useful tool for functional imaging of the retina. Two-photon excited fluorescence images of the macaque cone mosaic were obtained using a fluorescence adaptive optics scanning laser ophthalmoscope, overcoming the challenges of a low numerical aperture, imperfect optics of the eye, high required light levels, and eye motion. Although the specific fluorophores are as yet unknown, strong in vivo intrinsic fluorescence allowed images of the cone mosaic. Imaging intact ex vivo retina revealed that the strongest two-photon excited fluorescence signal comes from the cone inner segments. The fluorescence response increased following light stimulation, which could provide a functional measure of the effects of light on photoreceptors.
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Affiliation(s)
- Jennifer J. Hunter
- Flaum Eye Institute, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
- Center for Visual Science, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
| | - Benjamin Masella
- Institute of Optics, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
- Center for Visual Science, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
| | - Alfredo Dubra
- Flaum Eye Institute, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
- Center for Visual Science, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
| | - Robin Sharma
- Institute of Optics, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
- Center for Visual Science, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
| | - Lu Yin
- Center for Visual Science, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
| | - William H. Merigan
- Flaum Eye Institute, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
- Center for Visual Science, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
| | - Grazyna Palczewska
- Polgenix, Inc., 11000 Cedar Avenue, Suite 260, Cleveland, OH, 44106, USA
| | - Krzysztof Palczewski
- Polgenix, Inc., 11000 Cedar Avenue, Suite 260, Cleveland, OH, 44106, USA
- Department of Pharmacology, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, 44106, USA
| | - David R. Williams
- Flaum Eye Institute, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
- Institute of Optics, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
- Center for Visual Science, University of Rochester, 601 Elmwood Avenue, Rochester, NY, 14642, USA
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84
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Palczewski K. Blind dogs that can see: pharmacological treatment of Leber congenital amaurosis caused by a defective visual cycle. ACTA ACUST UNITED AC 2010; 128:1483-5. [PMID: 21060052 DOI: 10.1001/archophthalmol.2010.245] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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85
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Noninvasive multiphoton fluorescence microscopy resolves retinol and retinal condensation products in mouse eyes. Nat Med 2010; 16:1444-9. [PMID: 21076393 PMCID: PMC3057900 DOI: 10.1038/nm.2260] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Accepted: 08/03/2010] [Indexed: 12/13/2022]
Abstract
Multi–photon excitation fluorescence microscopy (MPM) can image certain molecular processes in vivo. In the eye, fluorescent retinyl esters in sub–cellular structures called retinosomes mediate regeneration of the visual chromophore, 11–cis–retinal, by the visual cycle. But harmful fluorescent condensation products were also identified previously. We report that in wild type mice, excitation with λ ~730 nm identified retinosomes in the retinal pigment epithelium, whereas excitation with λ ~910 nm revealed at least one additional retinal fluorophore. The latter fluorescence was absent in eyes of genetically modified mice lacking a functional visual cycle, but accentuated in eyes of older WT mice and mice with defective clearance of all–trans–retinal, an intermediate in the visual cycle. MPM, a noninvasive imaging modality that facilitates concurrent monitoring of retinosomes along with potentially harmful products in aging eyes, has the potential to detect early molecular changes due to age–related macular degeneration and other defects in retinoid metabolism.
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86
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87
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Retinoids for treatment of retinal diseases. Trends Pharmacol Sci 2010; 31:284-95. [PMID: 20435355 DOI: 10.1016/j.tips.2010.03.001] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2010] [Revised: 03/10/2010] [Accepted: 03/11/2010] [Indexed: 12/31/2022]
Abstract
Knowledge about retinal photoreceptor signal transduction and the visual cycle required for normal eyesight has increased exponentially over the past decade. Substantial progress in human genetics has facilitated the identification of candidate genes and complex networks underlying inherited retinal diseases. Natural mutations in animal models that mimic human diseases have been characterized and advanced genetic manipulation can now be used to generate small mammalian models of human retinal diseases. Pharmacological repair of defective visual processes in animal models not only validates their involvement in vision, but also provides great promise for the development of improved therapies for millions who are progressing towards blindness or are almost completely robbed of their eyesight.
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88
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Genead MA, Fishman GA, Lindeman M. Spectral-domain optical coherence tomography and fundus autofluorescence characteristics in patients with fundus albipunctatus and retinitis punctata albescens. Ophthalmic Genet 2010; 31:66-72. [PMID: 20450307 DOI: 10.3109/13816810903584971] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE Fundus albipunctatus is a form of congenital stationary night blindness characterized by an early onset and nonprogressive impairment of night vision and the presence of numerous dull-white punctate lesions scattered throughout the fundus, while retinitis punctata albescens patients often show similar fundus changes but manifest a severe and progressive hereditary retinal dystrophy. CONCLUSIONS In this study, we report the optical coherence tomography and fundus autofluorescence measurements in patients with these hereditary night blinding diseases.
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Affiliation(s)
- Mohamed A Genead
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, USA
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89
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Ammar DA, Lei TC, Gibson EA, Kahook MY. Two-photon imaging of the trabecular meshwork. Mol Vis 2010; 16:935-44. [PMID: 20596237 PMCID: PMC2890557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Accepted: 05/22/2010] [Indexed: 11/21/2022] Open
Abstract
PURPOSE To image the trabecular meshwork (TM) in its native unfixed state using a non-invasive, non-destructive technique. METHODS Two-photon microscopy (2PM), including two-photon excitation fluorescence (2PEF) and second harmonic generation (SHG), was used to image flat-mounted trabecular meshwork samples from human cadaver eyes. Multiple images were analyzed along the tissue axis (z-axis) to generate a three-dimensional (3D) model of the region. RESULTS A lattice of large collagen fibers (approximately 10 microm in diameter) were detected by inherent fluorescence (2PEF) and SHG. There are regions of both tightly overlapping bundles as well as fluid-filled regions visible from the surface of the TM. 3D analysis of multiple images reveals that the open regions deep in the TM penetrate the juxtacanalicular TM (JTM) and connect to the inner wall of Schlemm's canal (IWSC). These open regions may represent low-resistance fluid pathways between the anterior chamber and Schlemm's canal (SC). CONCLUSIONS 2PM imaging of the outflow system of the human eye documented collagenous structures solely from inherent optical properties, without addition of an exogenous fluorescent label. 2PM successfully imaged into the TM without the need for fixation, embedding, or histological processing. Deep penetration using advanced optical techniques revealed regions likely representing pores in the IWSC that have been documented by multiple electron microscope studies. Our work reveals that 2PM imaging has potential as a new metric for evaluating the aqueous outflow region of the human eye and is worthy of further exploration.
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Affiliation(s)
- David A. Ammar
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO
| | - Tim C. Lei
- Department of Electrical Engineering, University of Colorado Denver, Aurora, CO
| | - Emily A. Gibson
- Department of Physics, University of Colorado Denver, Aurora, CO
| | - Malik Y. Kahook
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO
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90
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Wielgus AR, Chignell CF, Ceger P, Roberts JE. Comparison of A2E cytotoxicity and phototoxicity with all-trans-retinal in human retinal pigment epithelial cells. Photochem Photobiol 2010; 86:781-91. [PMID: 20497365 DOI: 10.1111/j.1751-1097.2010.00750.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
All-trans-retinal is the precursor of A2E, a fluorophore within lipofuscin, which accumulates in human retinal pigment epithelial (hRPE) cells and contributes to age-related macular degeneration. Here we have compared the in vitro dark cytotoxicity and visible-light-mediated photoreactivity of all-trans-retinal and A2E in hRPE cells. All-trans-retinal caused distinct cytotoxicity in hRPE cells measured with cell metabolic activity (MTS) and lactate dehydrogenase release assays. Significant increases in intracellular oxidized glutathione (GSSG), extracellular GSH and GSSG levels and lipid hydroperoxide production were observed in cells incubated in the dark with 25 and 50 microM all-trans-retinal. Light modified all-trans-retinal's harmful action and decreased extracellular glutathione and hydroperoxide levels. A2E (<25 microM) did not affect cell metabolism or cytoplasmic membrane integrity in the dark or when irradiated. 25 microM A2E raised the intracellular GSSG level in hRPE cells to a much smaller extent than 25 microM all-trans-retinal. A2E did not induce glutathione efflux or hydroperoxide generation in the dark or after irradiation. These studies support our previous conclusions that although A2E may be harmful at high concentrations or when oxidized, its phototoxic properties are insignificant compared to those of all-trans-retinal. The endogenous production of A2E may serve as a protective mechanism to prevent damage to the retina by free all-trans-retinal.
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Affiliation(s)
- Albert R Wielgus
- Laboratory of Pharmacology, NIEHS, Research Triangle Park, NC, USA.
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91
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Cideciyan AV. Leber congenital amaurosis due to RPE65 mutations and its treatment with gene therapy. Prog Retin Eye Res 2010; 29:398-427. [PMID: 20399883 DOI: 10.1016/j.preteyeres.2010.04.002] [Citation(s) in RCA: 178] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Leber congenital amaurosis (LCA) is a rare hereditary retinal degeneration caused by mutations in more than a dozen genes. RPE65, one of these mutated genes, is highly expressed in the retinal pigment epithelium where it encodes the retinoid isomerase enzyme essential for the production of chromophore which forms the visual pigment in rod and cone photoreceptors of the retina. Congenital loss of chromophore production due to RPE65-deficiency together with progressive photoreceptor degeneration cause severe and progressive loss of vision. RPE65-associated LCA recently gained recognition outside of specialty ophthalmic circles due to early success achieved by three clinical trials of gene therapy using recombinant adeno-associated virus (AAV) vectors. The trials were built on multitude of basic, pre-clinical and clinical research defining the pathophysiology of the disease in human subjects and animal models, and demonstrating the proof-of-concept of gene (augmentation) therapy. Substantial gains in visual function of clinical trial participants provided evidence for physiologically relevant biological activity resulting from a newly introduced gene. This article reviews the current knowledge on retinal degeneration and visual dysfunction in animal models and human patients with RPE65 disease, and examines the consequences of gene therapy in terms of improvement of vision reported.
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Affiliation(s)
- Artur V Cideciyan
- Scheie Eye Institute, University of Pennsylvania, 51 North 39th St, Philadelphia, PA 19104, USA.
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92
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Abstract
S-palmitoylation is a conserved feature in many G protein-coupled receptors (GPCRs) involved in a broad array of signaling processes. The prototypical GPCR, rhodopsin, is S-palmitoylated on two adjacent C-terminal Cys residues at its cytoplasmic surface. Surprisingly, absence of palmitoylation has only a modest effect on in vitro or in vivo signaling. Here, we report that palmitoylation-deficient (Palm(-/-)) mice carrying two Cys to Thr and Ser mutations in the opsin gene displayed profound light-induced retinal degeneration that first involved rod and then cone cells. After brief bright light exposure, their retinas exhibited two types of deposits containing nucleic acid and invasive phagocytic macrophages. When Palm(-/-) mice were crossed with Lrat(-/-) mice lacking lecithin:retinol acyl transferase to eliminate retinoid binding to opsin and thereby rendering the eye insensitive to light, rapid retinal degeneration occurred even in 3- to 4-week-old animals. This rapid degeneration suggests that nonpalmitoylated rod opsin is unstable. Treatment of 2-week-old Palm(-/-)Lrat(-/-) mice with an artificial chromophore precursor prevented this retinopathy. In contrast, elimination of signaling to G protein in Palm(-/-)Gnat1(-/-) mice had no effect, indicating that instability of unpalmitoylated opsin lacking chromophore rather than aberrant signal transduction resulted in retinal pathology. Together, these observations provide evidence for a structural role of rhodopsin S-palmitoylation that may apply to other GPCRs as well.
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93
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Golczak M, Kiser PD, Lodowski DT, Maeda A, Palczewski K. Importance of membrane structural integrity for RPE65 retinoid isomerization activity. J Biol Chem 2010; 285:9667-9682. [PMID: 20100834 PMCID: PMC2843217 DOI: 10.1074/jbc.m109.063941] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2009] [Revised: 12/21/2009] [Indexed: 01/17/2023] Open
Abstract
Regeneration of visual chromophore in the vertebrate visual cycle involves the retinal pigment epithelium-specific protein RPE65, the key enzyme catalyzing the cleavage and isomerization of all-trans-retinyl fatty acid esters to 11-cis-retinol. Although RPE65 has no predicted membrane spanning domains, this protein predominantly associates with microsomal fractions isolated from bovine retinal pigment epithelium (RPE). We have re-examined the nature of RPE65 interactions with native microsomal membranes by using extraction and phase separation experiments. We observe that hydrophobic interactions are the dominant forces that promote RPE65 association with these membranes. These results are consistent with the crystallographic model of RPE65, which features a large lipophilic surface that surrounds the entrance to the catalytic site of this enzyme and likely interacts with the hydrophobic core of the endoplasmic reticulum membrane. Moreover, we report a critical role for phospholipid membranes in preserving the retinoid isomerization activity and physical properties of RPE65. Isomerase activity measured in bovine RPE was highly sensitive to phospholipase A(2) treatment, but the observed decline in 11-cis-retinol production did not directly reflect inhibition by products of lipid hydrolysis. Instead, a direct correlation between the kinetics of phospholipid hydrolysis and retinoid isomerization suggests that the lipid membrane structure is critical for RPE65 enzymatic activity. We also provide evidence that RPE65 operates in a multiprotein complex with retinol dehydrogenase 5 and retinal G protein-coupled receptor in RPE microsomes. Modifications in the phospholipid environment affecting interactions with these protein components may be responsible for the alterations in retinoid metabolism observed in phospholipid-depleted RPE microsomes. Thus, our results indicate that the enzymatic activity of native RPE65 strongly depends on its membrane binding and phospholipid environment.
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Affiliation(s)
| | | | | | - Akiko Maeda
- Ophthalmology and Visual Sciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
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94
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Abstract
Regeneration of visual pigments is essential for sustained visual function. Although the requirement for non-photochemical regeneration of the visual chromophore, 11-cis-retinal, was recognized early on, it was only recently that the trans to cis retinoid isomerase activity required for this process was assigned to a specific protein, a microsomal membrane enzyme called RPE65. In this review, we outline progress that has been made in the functional characterization of RPE65. We then discuss general concepts related to protein-membrane interactions and the mechanism of the retinoid isomerization reaction and describe some of the important biochemical and structural features of RPE65 with respect to its membrane-binding and enzymatic properties.
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Affiliation(s)
- Philip D Kiser
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Ave., Cleveland OH 44106-4965, USA
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95
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Gualda EJ, Bueno JM, Artal P. Wavefront optimized nonlinear microscopy of ex vivo human retinas. JOURNAL OF BIOMEDICAL OPTICS 2010; 15:026007. [PMID: 20459252 DOI: 10.1117/1.3369001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A multiphoton microscope incorporating a Hartmann-Shack (HS) wavefront sensor to control the ultrafast laser beam's wavefront aberrations has been developed. This instrument allowed us to investigate the impact of the laser beam aberrations on two-photon autofluorescence imaging of human retinal tissues. We demonstrated that nonlinear microscopy images are improved when laser beam aberrations are minimized by realigning the laser system cavity while wavefront controlling. Nonlinear signals from several human retinal anatomical features have been detected for the first time, without the need of fixation or staining procedures. Beyond the improved image quality, this approach reduces the required excitation power levels, minimizing the side effects of phototoxicity within the imaged sample. In particular, this may be important to study the physiology and function of the healthy and diseased retina.
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Affiliation(s)
- Emilio J Gualda
- Universidad de Murcia, Laboratorio de Optica, Campus de Espinardo (CiOyN), Murcia, 30100 Spain
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96
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von Lintig J, Kiser PD, Golczak M, Palczewski K. The biochemical and structural basis for trans-to-cis isomerization of retinoids in the chemistry of vision. Trends Biochem Sci 2010; 35:400-10. [PMID: 20188572 DOI: 10.1016/j.tibs.2010.01.005] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Revised: 01/08/2010] [Accepted: 01/20/2010] [Indexed: 01/20/2023]
Abstract
Recently, much progress has been made in elucidating the chemistry and metabolism of retinoids and carotenoids, as well as the structures of processing proteins related to vision. Carotenoids and their retinoid metabolites are isoprenoids, so only a limited number of chemical transformations are possible, and just a few of these occur naturally. Although there is an intriguing evolutionary conservation of the key components involved in the production and recycling of chromophores, these genes have also adapted to the specific requirements of insect and vertebrate vision. These 'ancestral footprints' in animal genomes bear witness to the common origin of the chemistry of vision, and will further stimulate research across evolutionary boundaries.
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Affiliation(s)
- Johannes von Lintig
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA.
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97
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Abstract
Vertebrate vision is maintained by the retinoid (visual) cycle, a complex enzymatic pathway that operates in the retina to regenerate the visual chromophore, 11-cis-retinal, a prosthetic group of rhodopsin that undergoes activation by light. Many different mutations in genes encoding retinoid cycle proteins can cause a variety of human blinding diseases. Two-photon microscopy is an evolving, non-invasive, and repetitive imaging technology that can be used to monitor biomolecules within the vertebrate retina at a subcellular resolution. This method has the great advantage of portraying endogenous retinoid fluorophores in their native state without the need for artificial staining. Such real-time retinal imaging permits rapid evaluation not only of various stages of retinal disease in live animal models of human retinopathies but also of the outcome from intended pharmacological therapies. Two-photon microscopy offers substantial potential for early detection of age- and disease-related changes in the eye, long before clinical or pathological manifestations become apparent.
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Affiliation(s)
- Yoshikazu Imanishi
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965, USA
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98
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Golczak M, Bereta G, Maeda A, Palczewski K. Molecular biology and analytical chemistry methods used to probe the retinoid cycle. Methods Mol Biol 2010; 652:229-45. [PMID: 20552432 PMCID: PMC4607022 DOI: 10.1007/978-1-60327-325-1_13] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The retinoid (visual) cycle is a complex enzymatic pathway essential for regeneration of the visual chromophore, 11-cis-retinal, a component of rhodopsin that undergoes activation by light in vertebrate eyes. Pathogenic mutations within genes encoding proteins involved in the retinoid cycle lead to abnormalities in retinoid homeostasis and numerous congenital blinding diseases of humans. Thus, elucidation of disease-specific changes in enzymatic activities and retinoid content of the retina can provide important insights into the mechanisms of disease initiation and progression. Here, we use the protein RPE65 as an example to describe generally applicable methods for determining the stability and enzymatic activity of proteins and their mutants involved in retinoid metabolism. Additionally, we introduce a range of analytical techniques involving high-performance liquid chromatography and mass spectrometry to detect and quantify retinoids and their derivatives in eye extracts. Biochemical protocols combined with advanced mass spectrometry should facilitate fundamental biological studies of vision.
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Affiliation(s)
- Marcin Golczak
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965, USA
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99
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Geng Y, Greenberg KP, Wolfe R, Gray DC, Hunter JJ, Dubra A, Flannery JG, Williams DR, Porter J. In vivo imaging of microscopic structures in the rat retina. Invest Ophthalmol Vis Sci 2009; 50:5872-9. [PMID: 19578019 PMCID: PMC2873188 DOI: 10.1167/iovs.09-3675] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
PURPOSE The ability to resolve single retinal cells in rodents in vivo has applications in rodent models of the visual system and retinal disease. The authors have characterized the performance of a fluorescence adaptive optics scanning laser ophthalmoscope (fAOSLO) that provides cellular and subcellular imaging of rat retina in vivo. METHODS Enhanced green fluorescent protein (eGFP) was expressed in retinal ganglion cells of normal Sprague-Dawley rats via intravitreal injections of adeno-associated viral vectors. Simultaneous reflectance and fluorescence retinal images were acquired using the fAOSLO. fAOSLO resolution was characterized by comparing in vivo images with subsequent imaging of retinal sections from the same eyes using confocal microscopy. RESULTS Retinal capillaries and eGFP-labeled ganglion cell bodies, dendrites, and axons were clearly resolved in vivo with adaptive optics. Adaptive optics correction reduced the total root mean square wavefront error, on average, from 0.30 microm to 0.05 microm (measured at 904 nm, 1.7-mm pupil). The full width at half maximum (FWHM) of the average in vivo line-spread function (LSF) was approximately 1.84 microm, approximately 82% greater than the FWHM of the diffraction-limited LSF. CONCLUSIONS With perfect aberration compensation, the in vivo resolution in the rat eye could be approximately 2x greater than that in the human eye because of its large numerical aperture (approximately 0.43). Although the fAOSLO corrects a substantial fraction of the rat eye's aberrations, direct measurements of retinal image quality reveal some blur beyond that expected from diffraction. Nonetheless, subcellular features can be resolved, offering promise for using adaptive optics to investigate the rodent eye in vivo with high resolution.
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Affiliation(s)
- Ying Geng
- Center for Visual Science, University of Rochester, Rochester, New York 14627, USA.
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100
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Bereta G, Wang B, Kiser PD, Baehr W, Jang GF, Palczewski K. A functional kinase homology domain is essential for the activity of photoreceptor guanylate cyclase 1. J Biol Chem 2009; 285:1899-908. [PMID: 19901021 DOI: 10.1074/jbc.m109.061713] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Phototransduction is carried out by a signaling pathway that links photoactivation of visual pigments in retinal photoreceptor cells to a change in their membrane potential. Upon photoactivation, the second messenger of phototransduction, cyclic GMP, is rapidly degraded and must be replenished during the recovery phase of phototransduction by photoreceptor guanylate cyclases (GCs) GC1 (or GC-E) and GC2 (or GC-F) to maintain vision. Here, we present data that address the role of the GC kinase homology (KH) domain in cyclic GMP production by GC1, the major cyclase in photoreceptors. First, experiments were done to test which GC1 residues undergo phosphorylation and whether such phosphorylation affects cyclase activity. Using mass spectrometry, we showed that GC1 residues Ser-530, Ser-532, Ser-533, and Ser-538, located within the KH domain, undergo light- and signal transduction-independent phosphorylation in vivo. Mutations in the putative Mg(2+) binding site of the KH domain abolished phosphorylation, indicating that GC1 undergoes autophosphorylation. The dramatically reduced GC activity of these mutants suggests that a functional KH domain is essential for cyclic GMP production. However, evidence is presented that autophosphorylation does not regulate GC1 activity, in contrast to phosphorylation of other members of this cyclase family.
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Affiliation(s)
- Grzegorz Bereta
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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