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Castiglione GM, Chiu YLI, Gutierrez EDA, Van Nynatten A, Hauser FE, Preston M, Bhattacharyya N, Schott RK, Chang BSW. Convergent evolution of dim light vision in owls and deep-diving whales. Curr Biol 2023; 33:4733-4740.e4. [PMID: 37776863 DOI: 10.1016/j.cub.2023.09.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2023] [Revised: 08/21/2023] [Accepted: 09/05/2023] [Indexed: 10/02/2023]
Abstract
Animals with enhanced dim-light sensitivity are at higher risk of light-induced retinal degeneration when exposed to bright light conditions.1,2,3,4 This trade-off is mediated by the rod photoreceptor sensory protein, rhodopsin (RHO), and its toxic vitamin A chromophore by-product, all-trans retinal.5,6,7,8 Rod arrestin (Arr-1) binds to RHO and promotes sequestration of excess all-trans retinal,9,10 which has recently been suggested as a protective mechanism against photoreceptor cell death.2,11 We investigated Arr-1 evolution in animals at high risk of retinal damage due to periodic bright-light exposure of rod-dominated retinas. Here, we find the convergent evolution of enhanced Arr-1/RHO all-trans-retinal sequestration in owls and deep-diving whales. Statistical analyses reveal a parallel acceleration of Arr-1 evolutionary rates in these lineages, which is associated with the introduction of a rare Arr-1 mutation (Q69R) into the RHO-Arr-1 binding interface. Using in vitro assays, we find that this single mutation significantly enhances RHO-all-trans-retinal sequestration by ∼30%. This functional convergence across 300 million years of evolutionary divergence suggests that Arr-1 and RHO may play an underappreciated role in the photoprotection of the eye, with potentially vast clinical significance.
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Affiliation(s)
- Gianni M Castiglione
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Ophthalmology & Visual Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada; Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada; Evolutionary Studies, Vanderbilt University, Nashville, TN 37235, USA.
| | - Yan L I Chiu
- Department of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada
| | - Eduardo de A Gutierrez
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
| | - Alexander Van Nynatten
- Department of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada; Department of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
| | - Frances E Hauser
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada; Department of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
| | - Matthew Preston
- Department of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada
| | - Nihar Bhattacharyya
- Department of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada; Institute of Ophthalmology, University College London, London EC1V 2PD, UK
| | - Ryan K Schott
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada; Department of Biology and Centre for Vision Research, York University, Toronto, ON M3J 1P3, Canada; Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA
| | - Belinda S W Chang
- Department of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada; Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada.
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2
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Bocchero U, Pahlberg J. Origin of Discrete and Continuous Dark Noise in Rod Photoreceptors. eNeuro 2023; 10:ENEURO.0390-23.2023. [PMID: 37973380 PMCID: PMC10687842 DOI: 10.1523/eneuro.0390-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 11/02/2023] [Indexed: 11/19/2023] Open
Abstract
The detection of a single photon by a rod photoreceptor is limited by two sources of physiological noise, called discrete and continuous noise. Discrete noise occurs as intermittent current deflections with a waveform very similar to that of the single-photon response to real light and is thought to be produced by spontaneous activation of rhodopsin. Continuous noise occurs as random and continuous fluctuations in outer-segment current and is usually attributed to some intermediate in the phototransduction cascade. To confirm the origin of these noise sources, we have recorded from retinas of mouse lines with rods having reduced levels of rhodopsin, transducin, or phosphodiesterase. We show that the rate of discrete noise is diminished in proportion to the decrease in rhodopsin concentration, and that continuous noise is independent of transducin concentration but clearly elevated when the level of phosphodiesterase is reduced. Our experiments provide new molecular evidence that discrete noise is indeed produced by rhodopsin itself, and that continuous noise is generated by spontaneous activation of phosphodiesterase resulting in random fluctuations in outer-segment current.
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Affiliation(s)
- Ulisse Bocchero
- Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510
| | - Johan Pahlberg
- Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510
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Poria D, Kolesnikov AV, Lee TJ, Salom D, Palczewski K, Kefalov VJ. Investigating the Role of Rhodopsin F45L Mutation in Mouse Rod Photoreceptor Signaling and Survival. eNeuro 2023; 10:ENEURO.0330-22.2023. [PMID: 36823167 PMCID: PMC9997694 DOI: 10.1523/eneuro.0330-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 01/16/2023] [Accepted: 01/24/2023] [Indexed: 02/25/2023] Open
Abstract
Rhodopsin is the critical receptor molecule which enables vertebrate rod photoreceptor cells to detect a single photon of light and initiate a cascade of molecular events leading to visual perception. Recently, it has been suggested that the F45L mutation in the transmembrane helix of rhodopsin disrupts its dimerization in vitro To determine whether this mutation of rhodopsin affects its signaling properties in vivo, we generated knock-in mice expressing the rhodopsin F45L mutant. We then examined the function of rods in the mutant mice versus wild-type controls, using in vivo electroretinography and transretinal and single cell suction recordings, combined with morphologic analysis and spectrophotometry. Although we did not evaluate the effect of the F45L mutation on the state of dimerization of the rhodopsin in vivo, our results revealed that F45L-mutant mice exhibit normal retinal morphology, normal rod responses as measured both in vivo and ex vivo, and normal rod dark adaptation. We conclude that the F45L mutation does not affect the signaling properties of rhodopsin in its natural setting.
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Affiliation(s)
- Deepak Poria
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, CA 92697
| | - Alexander V Kolesnikov
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, CA 92697
| | - Tae Jun Lee
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, MO 63110
| | - David Salom
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, CA 92697
| | - Krzysztof Palczewski
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, CA 92697
- Department of Chemistry, University of California, Irvine, CA 92697
- Department of Physiology and Biophysics, University of California, Irvine, CA 92697
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697
| | - Vladimir J Kefalov
- Department of Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, CA 92697
- Department of Physiology and Biophysics, University of California, Irvine, CA 92697
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Sirés A, Pazo-González M, López-Soriano J, Méndez A, de la Rosa EJ, de la Villa P, Comella JX, Hernández-Sánchez C, Solé M. The Absence of FAIM Leads to a Delay in Dark Adaptation and Hampers Arrestin-1 Translocation upon Light Reception in the Retina. Cells 2023; 12:cells12030487. [PMID: 36766830 PMCID: PMC9914070 DOI: 10.3390/cells12030487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 01/14/2023] [Accepted: 01/29/2023] [Indexed: 02/05/2023] Open
Abstract
The short and long isoforms of FAIM (FAIM-S and FAIM-L) hold important functions in the central nervous system, and their expression levels are specifically enriched in the retina. We previously described that Faim knockout (KO) mice present structural and molecular alterations in the retina compatible with a neurodegenerative phenotype. Here, we aimed to study Faim KO retinal functions and molecular mechanisms leading to its alterations. Electroretinographic recordings showed that aged Faim KO mice present functional loss of rod photoreceptor and ganglion cells. Additionally, we found a significant delay in dark adaptation from early adult ages. This functional deficit is exacerbated by luminic stress, which also caused histopathological alterations. Interestingly, Faim KO mice present abnormal Arrestin-1 redistribution upon light reception, and we show that Arrestin-1 is ubiquitinated, a process that is abrogated by either FAIM-S or FAIM-L in vitro. Our results suggest that FAIM assists Arrestin-1 light-dependent translocation by a process that likely involves ubiquitination. In the absence of FAIM, this impairment could be the cause of dark adaptation delay and increased light sensitivity. Multiple retinal diseases are linked to deficits in photoresponse termination, and hence, investigating the role of FAIM could shed light onto the underlying mechanisms of their pathophysiology.
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Affiliation(s)
- Anna Sirés
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
| | - Mateo Pazo-González
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Department of Systems Biology, Facultad de Medicina, Universidad de Alcalá, 28871 Alcalá de Henares, Spain
| | - Joaquín López-Soriano
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
| | - Ana Méndez
- Department of Physiological Sciences, School of Medicine, Campus Universitari de Bellvitge, University of Barcelona, 08907 Barcelona, Spain
- Institut de Neurociències, Campus Universitari de Bellvitge, University of Barcelona, 08907 Barcelona, Spain
- Institut d’Investigació Biomèdica de Bellvitge (IDIBELL), Campus Universitari de Bellvitge, University of Barcelona, 08907 Barcelona, Spain
| | - Enrique J. de la Rosa
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, 28029 Madrid, Spain
| | - Pedro de la Villa
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Department of Systems Biology, Facultad de Medicina, Universidad de Alcalá, 28871 Alcalá de Henares, Spain
| | - Joan X. Comella
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
| | - Catalina Hernández-Sánchez
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, 28029 Madrid, Spain
| | - Montse Solé
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
- Correspondence:
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Guo X, Cui Y, Irwin DM, Liu Y. Accelerated evolution of dim-light vision-related arrestin in deep-diving amniotes. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.1069088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Arrestins are key molecules involved in the signaling of light-sensation initiated by visual pigments in retinal photoreceptor cells. Vertebrate photoreceptor cells have two types of arrestins, rod arrestin, which is encoded by SAG and is expressed in both rods and cones, and cone arrestin, encoded by ARR3 in cones. The arrestins can bind to visual pigments, and thus regulate either dim-light vision via interactions with rhodopsin or bright-light vision together with cone visual pigments. After adapting to terrestrial life, several amniote lineages independently went back to the sea and evolved deep-diving habits. Interestingly, the rhodopsins in these species exhibit specialized phenotypes responding to rapidly changing dim-light environments. However, little is known about whether their rod arrestin also experienced adaptive evolution associated with rhodopsin. Here, we collected SAG coding sequences from >250 amniote species, and examined changes in selective pressure experienced by the sequences from deep-diving taxa. Divergent patterns of evolution of SAG were observed in the penguin, pinniped and cetacean clades, suggesting possible co-adaptation with rhodopsin. After verifying pseudogenes, the same analyses were performed for cone arrestin (ARR3) in deep-diving species and only sequences from cetacean species, and not pinnipeds or penguins, have experienced changed selection pressure compared to other species. Taken together, this evidence for changes in selective pressures acting upon arrestin genes strengthens the suggestion that rapid dim-light adaptation for deep-diving amniotes require SAG, but not ARR3.
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Kolesnikov AV, Luu J, Jin H, Palczewski K, Kefalov VJ. Deletion of Protein Phosphatase 2A Accelerates Retinal Degeneration in GRK1- and Arr1-Deficient Mice. Invest Ophthalmol Vis Sci 2022; 63:18. [PMID: 35861670 PMCID: PMC9315073 DOI: 10.1167/iovs.63.8.18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose Light detection in retinal rod photoreceptors is initiated by activation of the visual pigment rhodopsin. A critical, yet often-overlooked, step enabling efficient perception of light is rhodopsin dephosphorylation mediated by protein phosphatase 2A (PP2A). PP2A deficiency has been reported to impair rhodopsin regeneration after phosphorylation by G protein receptor kinase 1 (GRK1) and binding of arrestin (Arr1), thereby delaying rod dark adaptation. However, its effects on the viability of photoreceptors in the absence of GRK1 and Arr1 remain unclear. Here, we investigated the effects of PP2A deficiency in the absence of GRK1 or Arr1, both of which have been implicated in Oguchi disease, a form of night blindness. Methods Rod-specific mice lacking the predominant catalytic Cα-subunit of PP2A were crossed with the Grk1−/− or Arr1−/− strains to obtain double knockout lines. Rod photoreceptor viability was analyzed in histological cross-sections of the retina stained with hematoxylin and eosin, and rod function was evaluated by ex vivo electroretinography. Results PP2A deficiency alone did not impair photoreceptor viability up to 12 months of age. Retinal degeneration was more pronounced in rods lacking GRK1 compared to rods lacking Arr1, and degeneration was accelerated in both Grk1−/− or Arr1−/− strains where PP2A was also deleted. In Arr1−/− mice, rod maximal photoresponse amplitudes were reduced by 80% at 3 months, and this diminution was enhanced further with concomitant PP2A deficiency. Conclusions These results suggest that although PP2A is not required for the survival of rods, its deletion accelerates the degeneration induced by the absence of either GRK1 or Arr1.
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Affiliation(s)
- Alexander V Kolesnikov
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California, United States
| | - Jennings Luu
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California, United States.,Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, United States
| | - Hui Jin
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, United States
| | - Krzysztof Palczewski
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California, United States.,Department of Physiology & Biophysics, University of California, Irvine, California, United States.,Department of Chemistry, University of California, Irvine, California, United States.,Department of Molecular Biology and Biochemistry, University of California, Irvine, California, United States
| | - Vladimir J Kefalov
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California, United States.,Department of Physiology & Biophysics, University of California, Irvine, California, United States
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Ancient whale rhodopsin reconstructs dim-light vision over a major evolutionary transition: Implications for ancestral diving behavior. Proc Natl Acad Sci U S A 2022; 119:e2118145119. [PMID: 35759662 PMCID: PMC9271160 DOI: 10.1073/pnas.2118145119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Cetaceans are fully aquatic mammals that descended from terrestrial ancestors, an iconic evolutionary transition characterized by adaptations for underwater foraging via breath-hold diving. Although the evolutionary history of this specialized behavior is challenging to reconstruct, coevolving sensory systems may offer valuable clues. The dim-light visual pigment, rhodopsin, which initiates phototransduction in the rod photoreceptors of the eye, has provided insight into the visual ecology of depth in several aquatic vertebrate lineages. Here, we use ancestral sequence reconstruction and protein resurrection experiments to quantify light-activation metrics in rhodopsin pigments from ancestors bracketing the cetacean terrestrial-to-aquatic transition. By comparing multiple reconstruction methods on a broadly sampled cetartiodactyl species tree, we generated highly robust ancestral sequence estimates. Our experimental results provide direct support for a blue-shift in spectral sensitivity along the branch separating cetaceans from terrestrial relatives. This blue-shift was 14 nm, resulting in a deep-sea signature (λmax = 486 nm) similar to many mesopelagic-dwelling fish. We also discovered that the decay rates of light-activated rhodopsin increased in ancestral cetaceans, which may indicate an accelerated dark adaptation response typical of deeper-diving mammals. Because slow decay rates are thought to help sequester cytotoxic photoproducts, this surprising result could reflect an ecological trade-off between rod photoprotection and dark adaptation. Taken together, these ancestral shifts in rhodopsin function suggest that some of the first fully aquatic cetaceans could dive into the mesopelagic zone (>200 m). Moreover, our reconstructions indicate that this behavior arose before the divergence of toothed and baleen whales.
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8
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Jain S, Sekhar A. Elucidating the mechanisms underlying protein conformational switching using NMR spectroscopy. JOURNAL OF MAGNETIC RESONANCE OPEN 2022; 10-11:100034. [PMID: 35586549 PMCID: PMC7612731 DOI: 10.1016/j.jmro.2022.100034] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
How proteins switch between various ligand-free and ligand-bound structures has been a key biophysical question ever since the postulation of the Monod-Wyman-Changeux and Koshland-Nemethy-Filmer models over six decades ago. The ability of NMR spectroscopy to provide structural and kinetic information on biomolecular conformational exchange places it in a unique position as an analytical tool to interrogate the mechanisms of biological processes such as protein folding and biomolecular complex formation. In addition, recent methodological developments in the areas of saturation transfer and relaxation dispersion have expanded the scope of NMR for probing the mechanics of transitions in systems where one or more states constituting the exchange process are sparsely populated and 'invisible' in NMR spectra. In this review, we highlight some of the strategies available from NMR spectroscopy for examining the nature of multi-site conformational exchange, using five case studies that have employed NMR, either in isolation, or in conjunction with other biophysical tools.
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Kawamura S, Tachibanaki S. Molecular basis of rod and cone differences. Prog Retin Eye Res 2021; 90:101040. [PMID: 34974196 DOI: 10.1016/j.preteyeres.2021.101040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2021] [Revised: 12/22/2021] [Accepted: 12/27/2021] [Indexed: 12/15/2022]
Abstract
In the vertebrate retina, rods and cones both detect light, but they are different in functional aspects such as light sensitivity and time resolution, for example, and in some of cell biological aspects. For functional aspects, both photoreceptors are known to share a common mechanism, phototransduction cascade, consisting of a series of enzyme reactions to convert a photon-capture signal to an electrical signal. To understand the mechanisms of the functional differences between rods and cones at the molecular level, we compared biochemically each of the reactions in the phototransduction cascade between rods and cones using the cells isolated and purified from carp retina. Although proteins in the cascade are functionally similar between rods and cones, their activities together with their expression levels are mostly different between these photoreceptors. In general, reactions to generate a response are slightly less effective, as a total, in cones than in rods, but each of the reactions for termination and recovery of a response are much more effective in cones. These findings explain lower light sensitivity and briefer light responses in cones than in rods. In addition, our considerations suggest that a Ca2+-binding protein, S-modulin or recoverin, has a currently unnoticed role in shaping light responses. With comparison of the expression levels of proteins and/or mRNAs using purified cells, several proteins were found to be specifically or predominantly expressed in cones. These proteins would be of interest for future studies on the difference between rods and cones.
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Affiliation(s)
- Satoru Kawamura
- Graduate School of Frontier Biosciences, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan.
| | - Shuji Tachibanaki
- Graduate School of Frontier Biosciences, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan.
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Rod Photoreceptors Avoid Saturation in Bright Light by the Movement of the G Protein Transducin. J Neurosci 2021; 41:3320-3330. [PMID: 33593858 DOI: 10.1523/jneurosci.2817-20.2021] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 01/21/2021] [Accepted: 01/26/2021] [Indexed: 11/21/2022] Open
Abstract
Rod photoreceptors can be saturated by exposure to bright background light, so that no flash superimposed on the background can elicit a detectable response. This phenomenon, called increment saturation, was first demonstrated psychophysically by Aguilar and Stiles and has since been shown in many studies to occur in single rods. Recent experiments indicate, however, that rods may be able to avoid saturation under some conditions of illumination. We now show in ex vivo electroretinogram and single-cell recordings that in continuous and prolonged exposure even to very bright light, the rods of mice from both sexes recover as much as 15% of their dark current and that responses can persist for hours. In parallel to recovery of outer segment current is an ∼10-fold increase in the sensitivity of rod photoresponses. This recovery is decreased in transgenic mice with reduced light-dependent translocation of the G protein transducin. The reduction in outer-segment transducin together with a novel mechanism of visual-pigment regeneration within the rod itself enable rods to remain responsive over the whole of the physiological range of vision. In this way, rods are able to avoid an extended period of transduction channel closure, which is known to cause photoreceptor degeneration.SIGNIFICANCE STATEMENT Rods are initially saturated in bright light so that no flash superimposed on the background can elicit a detectable response. Frederiksen and colleagues show in whole retina and single-cell recordings that, if the background light is prolonged, rods slowly recover and can continue to produce significant responses over the entire physiological range of vision. Response recovery occurs by translocation of the G protein transducin from the rod outer to the inner segment, together with a novel mechanism of visual-pigment regeneration within the rod itself. Avoidance of saturation in bright light may be one of the principal mechanisms the retina uses to keep rod outer-segment channels from ever closing for too long a time, which is known to produce photoreceptor degeneration.
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Luo DG, Silverman D, Frederiksen R, Adhikari R, Cao LH, Oatis JE, Kono M, Cornwall MC, Yau KW. Apo-Opsin and Its Dark Constitutive Activity across Retinal Cone Subtypes. Curr Biol 2020; 30:4921-4931.e5. [PMID: 33065015 PMCID: PMC8561704 DOI: 10.1016/j.cub.2020.09.062] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 08/08/2020] [Accepted: 09/18/2020] [Indexed: 11/22/2022]
Abstract
Retinal rod and cone photoreceptors mediate vision in dim and bright light, respectively, by transducing absorbed photons into neural electrical signals. Their phototransduction mechanisms are essentially identical. However, one difference is that, whereas a rod visual pigment remains stable in darkness, a cone pigment has some tendency to dissociate spontaneously into apo-opsin and retinal (the chromophore) without isomerization. This cone-pigment property is long known but has mostly been overlooked. Importantly, because apo-opsin has weak constitutive activity, it triggers transduction to produce electrical noise even in darkness. Currently, the precise dark apo-opsin contents across cone subtypes are mostly unknown, as are their dark activities. We report here a study of goldfish red (L), green (M), and blue (S) cones, finding with microspectrophotometry widely different apo-opsin percentages in darkness, being ∼30% in L cones, ∼3% in M cones, and negligible in S cones. L and M cones also had higher dark apo-opsin noise than holo-pigment thermal isomerization activity. As such, given the most likely low signal amplification at the pigment-to-transducin/phosphodiesterase phototransduction step, especially in L cones, apo-opsin noise may not be easily distinguishable from light responses and thus may affect cone vision near threshold.
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Affiliation(s)
- Dong-Gen Luo
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Daniel Silverman
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Biochemistry, Cellular and Molecular Biology Graduate Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Rikard Frederiksen
- Jules Stein Eye Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Rajan Adhikari
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118, USA
| | - Li-Hui Cao
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - John E Oatis
- Department of Ophthalmology, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Masahiro Kono
- Department of Ophthalmology, Medical University of South Carolina, Charleston, SC 29425, USA
| | - M Carter Cornwall
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118, USA
| | - King-Wai Yau
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Accelerated evolution and positive selection of rhodopsin in Tibetan loaches living in high altitude. Int J Biol Macromol 2020; 165:2598-2606. [PMID: 33470199 DOI: 10.1016/j.ijbiomac.2020.10.151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 10/16/2020] [Accepted: 10/19/2020] [Indexed: 11/22/2022]
Abstract
Rhodopsin (RH1), the temperature-sensitive visual pigment, attained cold adaptation by functional trade-offs between protein stability and activity. Recent studies suggested convergent selection pressures drove cold adaptation of rhodopsin in high altitude catfishes through nonparallel molecular mechanisms. Here, we tested whether the similar shift occurred in RH1 of Tibetan loaches on the Qinghai-Tibet Plateau (QTP) by investigating the molecular evolution and potential effect on function of RH1. We sequenced RH1 from 27 Triplophysa species, and four lowland loaches and combined these data with published sequences. Tests using a series of models of molecular evolution resulted in strong evidence for accelerated evolution and positive selection in Triplophysa RH1. Three positively selected sites were near key functional domains modulating nonspectral properties of rhodopsin, substitutions of which were likely to compensate for cold-induced decrease in rhodopsin kinetics in cold environments. Moreover, although accelerated evolutionary rates in Tibetan loaches was convergent with those in high altitude catfishes, the sites under positive selection were nonoverlapping. Our findings provide evidence for convergent shift in selection pressures of RH1 in high altitude fish during the ecological transition to cold environment of the QTP.
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Abstract
The retina is famous for its ability to operate under a broad range of light intensities. This is partly due to the presence of two types of photoreceptor cells, rods and cones. Rods are used mostly for dim light vision, and cones are used for bright light and colour vision. These cells are also able to adapt to a broad range of light intensities using light- and dark-adaptation mechanisms. Dark adaptation is used by the vertebrate retina to increase its visual sensitivity when moving from a brightly lit environment to a dark environment. The brighter the surrounding light, the longer it takes for the retina to adapt to the dark. Most retina biologists have studied dark adaptation by exposing animals to a 90% bleach, meaning that 90% of the light-sensing proteins in these photoreceptor cells have been activated, followed by transfer of these animals to a dark room and analysis of their light sensitivity using electrophysiological methods. In this report, we introduce the basic elements of the visual system and describe how the system might operate during dark adaptation. We also introduce a novel role for cAMP-mediated phosphorylation of G protein-coupled receptor kinase 1 (GRK1), a major kinase in visual signalling.
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14
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Abstract
The visual phototransduction cascade begins with a cis-trans photoisomerization of a retinylidene chromophore associated with the visual pigments of rod and cone photoreceptors. Visual opsins release their all-trans-retinal chromophore following photoactivation, which necessitates the existence of pathways that produce 11-cis-retinal for continued formation of visual pigments and sustained vision. Proteins in the retinal pigment epithelium (RPE), a cell layer adjacent to the photoreceptor outer segments, form the well-established "dark" regeneration pathway known as the classical visual cycle. This pathway is sufficient to maintain continuous rod function and support cone photoreceptors as well although its throughput has to be augmented by additional mechanism(s) to maintain pigment levels in the face of high rates of photon capture. Recent studies indicate that the classical visual cycle works together with light-dependent processes in both the RPE and neural retina to ensure adequate 11-cis-retinal production under natural illuminances that can span ten orders of magnitude. Further elucidation of the interplay between these complementary systems is fundamental to understanding how cone-mediated vision is sustained in vivo. Here, we describe recent advances in understanding how 11-cis-retinal is synthesized via light-dependent mechanisms.
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15
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Functional Imaging of the Outer Retinal Complex using High Fidelity Imaging Retinal Densitometry. Sci Rep 2020; 10:4494. [PMID: 32161284 PMCID: PMC7066170 DOI: 10.1038/s41598-020-60660-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 01/29/2020] [Indexed: 11/30/2022] Open
Abstract
We describe a new technique, high fidelity Imaging Retinal Densitometry (IRD), which probes the functional integrity of the outer retinal complex. We demonstrate the ability of the technique to map visual pigment optical density and synthesis rates in eyes with and without macular disease. A multispectral retinal imaging device obtained precise measurements of retinal reflectance over space and time. Data obtained from healthy controls and 5 patients with intermediate AMD, before and after photopigment bleaching, were used to quantify visual pigment metrics. Heat maps were plotted to summarise the topography of rod and cone pigment kinetics and descriptive statistics conducted to highlight differences between those with and without AMD. Rod and cone visual pigment synthesis rates in those with AMD (v = 0.043 SD 0.019 min−1 and v = 0.119 SD 0.046 min−1, respectively) were approximately half those observed in healthy controls (v = 0.079 SD 0.024 min−1 for rods and v = 0.206 SD 0.069 min−1 for cones). By mapping visual pigment kinetics across the central retina, high fidelity IRD provides a unique insight into outer retinal complex function. This new technique will improve the phenotypic characterisation, diagnosis and treatment monitoring of various ocular pathologies, including AMD.
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16
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Kolesnikov AV, Chrispell JD, Osawa S, Kefalov VJ, Weiss ER. Phosphorylation at Serine 21 in G protein-coupled receptor kinase 1 (GRK1) is required for normal kinetics of dark adaption in rod but not cone photoreceptors. FASEB J 2019; 34:2677-2690. [PMID: 31908030 DOI: 10.1096/fj.201902535r] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 11/25/2019] [Accepted: 12/05/2019] [Indexed: 12/22/2022]
Abstract
Timely recovery of the light response in photoreceptors requires efficient inactivation of photoactivated rhodopsin. This process is initiated by phosphorylation of its carboxyl terminus by G protein-coupled receptor kinase 1 (GRK1). Previously, we showed that GRK1 is phosphorylated in the dark at Ser21 in a cAMP-dependent manner and dephosphorylated in the light. Results in vitro indicate that dephosphorylation of Ser21 increases GRK1 activity, leading to increased phosphorylation of rhodopsin. This creates the possibility of light-dependent regulation of GRK1 activity and its efficiency in inactivating the visual pigment. To address the functional role of GRK1 phosphorylation in rods and cones in vivo, we generated mutant mice in which Ser21 is substituted with alanine (GRK1-S21A), preventing dark-dependent phosphorylation of GRK1. GRK1-S21A mice had normal retinal morphology, without evidence of degeneration. The function of dark-adapted GRK1-S21A rods and cones was also unaffected, as demonstrated by the normal amplitude and kinetics of their responses obtained by ex vivo and in vivo ERG recordings. In contrast, rod dark adaptation following exposure to bright bleaching light was significantly delayed in GRK1-S21A mice, suggesting that the higher activity of this kinase results in enhanced rhodopsin phosphorylation and therefore delays its regeneration. In contrast, dark adaptation of cones was unaffected by the S21A mutation. Taken together, these data suggest that rhodopsin phosphorylation/dephosphorylation modulates the recovery of rhodopsin to the ground state and rod dark adaptation. They also reveal a novel role for cAMP-dependent phosphorylation of GRK1 in regulating the dark adaptation of rod but not cone photoreceptors.
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Affiliation(s)
- Alexander V Kolesnikov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, MO, USA
| | - Jared D Chrispell
- Department of Cell Biology and Physiology, The University of North Carolina, Lineberger Comprehensive Cancer Center, Chapel Hill, NC, USA
| | - Shoji Osawa
- Department of Cell Biology and Physiology, The University of North Carolina, Lineberger Comprehensive Cancer Center, Chapel Hill, NC, USA
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, MO, USA
| | - Ellen R Weiss
- Department of Cell Biology and Physiology, The University of North Carolina, Lineberger Comprehensive Cancer Center, Chapel Hill, NC, USA
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17
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Zhang J, Choi EH, Tworak A, Salom D, Leinonen H, Sander CL, Hoang TV, Handa JT, Blackshaw S, Palczewska G, Kiser PD, Palczewski K. Photic generation of 11- cis-retinal in bovine retinal pigment epithelium. J Biol Chem 2019; 294:19137-19154. [PMID: 31694912 DOI: 10.1074/jbc.ra119.011169] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2019] [Revised: 10/25/2019] [Indexed: 12/19/2022] Open
Abstract
Photoisomerization of the 11-cis-retinal chromophore of rod and cone visual pigments to an all-trans-configuration is the initiating event for vision in vertebrates. The regeneration of 11-cis-retinal, necessary for sustained visual function, is an endergonic process normally conducted by specialized enzyme systems. However, 11-cis-retinal also can be formed through reverse photoisomerization from all-trans-retinal. A nonvisual opsin known as retinal pigment epithelium (RPE)-retinal G-protein-coupled receptor (RGR) was previously shown to mediate visual chromophore regeneration in photic conditions, but conflicting results have cast doubt on its role as a photoisomerase. Here, we describe high-level production of 11-cis-retinal from RPE membranes stimulated by illumination at a narrow band of wavelengths. This activity was associated with RGR and enhanced by cellular retinaldehyde-binding protein (CRALBP), which binds the 11-cis-retinal produced by RGR and prevents its re-isomerization to all-trans-retinal. The activity was recapitulated with cells heterologously expressing RGR and with purified recombinant RGR. Using an RGR variant, K255A, we confirmed that a Schiff base linkage at Lys-255 is critical for substrate binding and isomerization. Single-cell RNA-Seq analysis of the retina and RPE tissue confirmed that RGR is expressed in human and bovine RPE and Müller glia, whereas mouse RGR is expressed in RPE but not in Müller glia. These results provide key insights into the mechanisms of physiological retinoid photoisomerization and suggest a novel mechanism by which RGR, in concert with CRALBP, regenerates the visual chromophore in the RPE under sustained light conditions.
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Affiliation(s)
- Jianye Zhang
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California 92697
| | - Elliot H Choi
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California 92697.,Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Aleksander Tworak
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California 92697
| | - David Salom
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California 92697
| | - Henri Leinonen
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California 92697
| | - Christopher L Sander
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California 92697.,Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106
| | - Thanh V Hoang
- Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - James T Handa
- Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287
| | - Seth Blackshaw
- Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.,Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287
| | | | - Philip D Kiser
- Department of Physiology and Biophysics, University of California, Irvine, California 92697.,Research Service, Veterans Affairs Long Beach Healthcare System, Long Beach, California 90822
| | - Krzysztof Palczewski
- Gavin Herbert Eye Institute, Department of Ophthalmology, University of California, Irvine, California 92697
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18
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Leinonen H, Choi EH, Gardella A, Kefalov VJ, Palczewski K. A Mixture of U.S. Food and Drug Administration-Approved Monoaminergic Drugs Protects the Retina From Light Damage in Diverse Models of Night Blindness. Invest Ophthalmol Vis Sci 2019; 60:1442-1453. [PMID: 30947334 PMCID: PMC6736410 DOI: 10.1167/iovs.19-26560] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Purpose The purpose of this study was to test the extent of light damage in different models of night blindness and apply these paradigms in testing the therapeutic efficacy of combination therapy by drugs acting on the Gi, Gs, and Gq protein-coupled receptors. Methods Acute bright light exposure was used to test susceptibility to light damage in mice lacking the following crucial phototransduction proteins: rod transducin (GNAT1), cone transducin (GNAT2), visual arrestin 1 (ARR1), and rhodopsin kinase 1 (GRK1). Mice were intraperitoneally injected with either vehicle or drug combination consisting of metoprolol (β1-receptor antagonist), bromocriptine (dopamine family-2 receptor agonist) and tamsulosin (α1-receptor antagonist) before bright light exposure. Light damage was primarily assessed with optical coherence tomography and inspection of cone population in retinal whole mounts. Retinal inflammation was assessed in a subset of experiments using autofluorescence imaging by scanning laser ophthalmoscopy and by postmortem inspection of microglia and astrocyte activity. Results The Gnat1−/− mice showed slightly increased susceptibility to rod light damage, whereas the Gnat2−/− mice were very resistant. The Arr1−/− and Grk1−/− mice were sensitive for both rod and cone light damage and showed robust retinal inflammation 7 days after bright light exposure. Pretreatment with metoprolol + bromocriptine + tamsulosin rescued the retina in all genetic backgrounds, starting at doses of 0.2 mg/kg metoprolol, 0.02 mg/kg bromocriptine, and 0.01 mg/kg tamsulosin in the Gnat1−/− mice. The therapeutic drug doses increased in parallel with light-damage severity. Conclusions Our results suggest that congenital stationary night blindness and Oguchi disease patients can be at an elevated risk of the toxic effects of bright light. Furthermore, systems pharmacology drug regimens that stimulate Gi signaling and attenuate Gs and Gq signaling present a promising disease-modifying therapy for photoreceptor degenerative diseases.
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Affiliation(s)
- Henri Leinonen
- Gavin Herbert Eye Institute and the Department of Ophthalmology, University of California-Irvine, Irvine, California, United States.,Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, United States
| | - Elliot H Choi
- Gavin Herbert Eye Institute and the Department of Ophthalmology, University of California-Irvine, Irvine, California, United States.,Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, United States
| | - Anthony Gardella
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, Ohio, United States
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University, St. Louis, Missouri, United States
| | - Krzysztof Palczewski
- Gavin Herbert Eye Institute and the Department of Ophthalmology, University of California-Irvine, Irvine, California, United States.,Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio, United States
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19
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Abstract
G protein-coupled receptor (GPCR) signaling is crucial for many physiological processes. A signature of such pathways is high amplification, a concept originating from retinal rod phototransduction, whereby one photoactivated rhodopsin molecule (Rho*) was long reported to activate several hundred transducins (GT*s), each then activating a cGMP-phosphodiesterase catalytic subunit (GT*·PDE*). This high gain at the Rho*-to-GT* step has been challenged more recently, but estimates remain dispersed and rely on some nonintact rod measurements. With two independent approaches, one with an extremely inefficient mutant rhodopsin and the other with WT bleached rhodopsin, which has exceedingly weak constitutive activity in darkness, we obtained an estimate for the electrical effect from a single GT*·PDE* molecular complex in intact mouse rods. Comparing the single-GT*·PDE* effect to the WT single-photon response, both in Gcaps-/- background, gives an effective gain of only ∼12-14 GT*·PDE*s produced per Rho*. Our findings have finally dispelled the entrenched concept of very high gain at the receptor-to-G protein/effector step in GPCR systems.
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20
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Castiglione GM, Schott RK, Hauser FE, Chang BSW. Convergent selection pressures drive the evolution of rhodopsin kinetics at high altitudes via nonparallel mechanisms. Evolution 2018; 72:170-186. [DOI: 10.1111/evo.13396] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/02/2017] [Indexed: 01/01/2023]
Affiliation(s)
- Gianni M. Castiglione
- Department of Cell & Systems Biology; University of Toronto; Toronto Ontario M5S 3G5 Canada
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
| | - Ryan K. Schott
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
| | - Frances E. Hauser
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
| | - Belinda S. W. Chang
- Department of Cell & Systems Biology; University of Toronto; Toronto Ontario M5S 3G5 Canada
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
- Centre for the Analysis of Genome Evolution and Function; University of Toronto; Toronto Ontario M5S 3B2 Canada
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21
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Dephosphorylation by protein phosphatase 2A regulates visual pigment regeneration and the dark adaptation of mammalian photoreceptors. Proc Natl Acad Sci U S A 2017; 114:E9675-E9684. [PMID: 29078372 DOI: 10.1073/pnas.1712405114] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Resetting of G-protein-coupled receptors (GPCRs) from their active state back to their biologically inert ground state is an integral part of GPCR signaling. This "on-off" GPCR cycle is regulated by reversible phosphorylation. Retinal rod and cone photoreceptors arguably represent the best-understood example of such GPCR signaling. Their visual pigments (opsins) are activated by light, transduce the signal, and are then inactivated by a GPCR kinase and arrestin. Although pigment inactivation by phosphorylation is well understood, the enzyme(s) responsible for pigment dephosphorylation and the functional significance of this reaction remain unknown. Here, we show that protein phosphatase 2A (PP2A) acts as opsin phosphatase in both rods and cones. Elimination of PP2A substantially slows pigment dephosphorylation, visual chromophore recycling, and ultimately photoreceptor dark adaptation. These findings demonstrate that visual pigment dephosphorylation regulates the dark adaptation of photoreceptors and provide insights into the role of this reaction in GPCR signaling.
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22
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Joachimsthaler A, Tsai TI, Kremers J. Electrophysiological Studies on The Dynamics of Luminance Adaptation in the Mouse Retina. Vision (Basel) 2017; 1:vision1040023. [PMID: 31740648 PMCID: PMC6835873 DOI: 10.3390/vision1040023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 10/11/2017] [Accepted: 10/15/2017] [Indexed: 12/31/2022] Open
Abstract
To date, most studies involving in vivo electroretinography in mice are performed on steady state adapted animals. In this study, we focused on the dynamics of adaptation to high and low light levels in the mouse retina. Two flash electroretinogram (ERG) protocols and one flicker ERG protocol were employed. In the two flash ERG protocols, the animals were adapted to either 25 or 40 cd/m2 white light and ERGs were recorded for up to 15 min of adaptation. Afterwards, flash ERGs were recorded for up to 45 min of dark adaptation. Amplitudes of the flash ERG increased during light adaptation, while implicit times of the different wave components decreased. During subsequent dark adaptation, the amplitudes further increased. The increase in a-to-b-wave ratio indicated adaptational processes at the photoreceptor synapse. In the flicker ERG protocol, the responses to 12 Hz sinusoidal luminance modulation during the adaptation to 25 cd/m2 and a 1 cd/m2 mean luminances were recorded. The amplitudes of the first harmonic components in the flicker protocol decreased during light adaptation but increased during dark adaptation. This is at odds with the changes in the flash ERG, indicating that adaptation may be different in different retinal pathways.
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Affiliation(s)
- Anneka Joachimsthaler
- Department of Ophthamlology, University Hospital Erlangen, 91054 Erlangen, Germany
- Department of Biology, Animal Physiology, FAU Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Tina I. Tsai
- Department of Ophthamlology, University Hospital Erlangen, 91054 Erlangen, Germany
- Department of Biology, Animal Physiology, FAU Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Jan Kremers
- Department of Ophthamlology, University Hospital Erlangen, 91054 Erlangen, Germany
- Correspondence:
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23
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Hanneken A, Neikirk T, Johnson J, Kono M. Biochemical Measurements of Free Opsin in Macular Degeneration Eyes: Examining the 11- CIS Retinal Deficiency Hypothesis of Delayed Dark Adaptation (An American Ophthalmological Society Thesis). TRANSACTIONS OF THE AMERICAN OPHTHALMOLOGICAL SOCIETY 2017; 115:T1. [PMID: 28900371 PMCID: PMC5572981] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
PURPOSE To test the hypothesis that delayed dark adaptation in patients with macular degeneration is due to an excess of free unliganded opsin (apo-opsin) and a deficiency of the visual chromophore, 11-cis retinal, in rod outer segments. METHODS A total of 50 human autopsy eyes were harvested from donors with and without macular degeneration within 2-24 hrs. postmortem. Protocols were developed which permitted dark adaptation of normal human eyes after death and enucleation. Biochemical methods of purifying rod outer segments were optimized and the concentration of rhodopsin and apo-opsin was measured with UV-visible scanning spectroscopy. The presence of apo-opsin was calculated by measuring the difference in the rhodopsin absorption spectra before and after the addition of 11-cis retinal. RESULTS A total of 20 normal eyes and 16 eyes from donors with early, intermediate and advanced stages of macular degeneration were included in the final analysis. Dark adaptation was achieved by harvesting whole globes in low light, transferring into dark (light-proof) canisters and dissecting the globes using infrared light and image converters for visualization. Apo-opsin was readily detected in positive controls after the addition of 11-cis retinal. Normal autopsy eyes showed no evidence of apo-opsin. Eyes with macular degeneration also showed no evidence of apo-opsin, regardless of the severity of disease. CONCLUSIONS Methods have been developed to study dark adaptation in human autopsy eyes. Eyes with age-related macular degeneration do not show a deficiency of 11-cis retinal or an excess of apo-opsin within rod outer segments.
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The role of retinol dehydrogenase 10 in the cone visual cycle. Sci Rep 2017; 7:2390. [PMID: 28539612 PMCID: PMC5443843 DOI: 10.1038/s41598-017-02549-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 04/12/2017] [Indexed: 11/18/2022] Open
Abstract
Pigment regeneration is critical for the function of cone photoreceptors in bright and rapidly-changing light conditions. This process is facilitated by the recently-characterized retina visual cycle, in which Müller cells recycle spent all-trans-retinol visual chromophore back to 11-cis-retinol. This 11-cis-retinol is oxidized selectively in cones to the 11-cis-retinal used for pigment regeneration. However, the enzyme responsible for the oxidation of 11-cis-retinol remains unknown. Here, we sought to determine whether retinol dehydrogenase 10 (RDH10), upregulated in rod/cone hybrid retinas and expressed abundantly in Müller cells, is the enzyme that drives this reaction. We created mice lacking RDH10 either in cone photoreceptors, Müller cells, or the entire retina. In vivo electroretinography and transretinal recordings revealed normal cone photoresponses in all RDH10-deficient mouse lines. Notably, their cone-driven dark adaptation both in vivo and in isolated retina was unaffected, indicating that RDH10 is not required for the function of the retina visual cycle. We also generated transgenic mice expressing RDH10 ectopically in rod cells. However, rod dark adaptation was unaffected by the expression of RDH10 and transgenic rods were unable to use cis-retinol for pigment regeneration. We conclude that RDH10 is not the dominant retina 11-cis-RDH, leaving its primary function in the retina unknown.
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