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Zheng X, Li H, Hu Z, Su D, Yang J. Structural and functional characterization of an achromatopsia-associated mutation in a phototransduction channel. Commun Biol 2022; 5:190. [PMID: 35233102 PMCID: PMC8888761 DOI: 10.1038/s42003-022-03120-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 02/03/2022] [Indexed: 12/30/2022] Open
Abstract
Numerous missense mutations in cyclic nucleotide-gated (CNG) channels cause achromatopsia and retinitis pigmentosa, but the underlying pathogenic mechanisms are often unclear. We investigated the structural basis and molecular/cellular effects of R410W, an achromatopsia-associated, presumed loss-of-function mutation in human CNGA3. Cryo-EM structures of the Caenorhabditis elegans TAX-4 CNG channel carrying the analogous mutation, R421W, show that most apo channels are open. R421, located in the gating ring, interacts with the S4 segment in the closed state. R421W disrupts this interaction, destabilizes the closed state, and stabilizes the open state. CNGA3_R410W/CNGB3 and TAX4_R421W channels are spontaneously active without cGMP and induce cell death, suggesting cone degeneration triggered by spontaneous CNG channel activity as a possible cause of achromatopsia. Our study sheds new light on CNG channel allosteric gating, provides an impetus for a reevaluation of reported loss-of-function CNG channel missense disease mutations, and has implications for mutation-specific treatment of retinopathy.
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Affiliation(s)
- Xiangdong Zheng
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Huan Li
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Zhengshan Hu
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Deyuan Su
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA
| | - Jian Yang
- Department of Biological Sciences, Columbia University, New York, NY, 10027, USA.
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2
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Structure of the human cone photoreceptor cyclic nucleotide-gated channel. Nat Struct Mol Biol 2022; 29:40-46. [PMID: 34969976 PMCID: PMC8776609 DOI: 10.1038/s41594-021-00699-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Accepted: 11/09/2021] [Indexed: 11/08/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels transduce light-induced chemical signals into electrical signals in retinal cone and rod photoreceptors. Structures of native CNG channels, which are heterotetramers formed by CNGA and CNGB subunits, have not been obtained. In the present study, we report a high-resolution cryo-electron microscopy structure of the human cone CNG channel in the apo closed state. The channel contains three CNGA3 and one CNGB3 subunits. Arg403 in the pore helix of CNGB3 projects into an asymmetric selectivity filter and forms hydrogen bonds with two pore-lining backbone carbonyl oxygens. Arg442 in S6 of CNGB3 protrudes into and occludes the pore below the hydrophobic cavity gate previously observed in homotetrameric CNGA channels. It is interesting that Arg403Gln is a disease mutation, and Arg442 is replaced by glutamine in some animal species with dichromatic or monochromatic vision. These and other unique structural features and the disease link conferred by CNGB3 indicate a critical role of CNGB3 in shaping cone photoresponses.
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3
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Spitschan M, Garbazza C, Kohl S, Cajochen C. Sleep and circadian phenotype in people without cone-mediated vision: a case series of five CNGB3 and two CNGA3 patients. Brain Commun 2021; 3:fcab159. [PMID: 34447932 PMCID: PMC8385249 DOI: 10.1093/braincomms/fcab159] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/14/2021] [Indexed: 01/28/2023] Open
Abstract
Light exposure entrains the circadian clock through the intrinsically photosensitive retinal ganglion cells, which sense light in addition to the cone and rod photoreceptors. In congenital achromatopsia (prevalence 1:30-50 000), the cone system is non-functional, resulting in severe light avoidance and photophobia at daytime light levels. How this condition affects circadian and neuroendocrine responses to light is not known. In this case series of genetically confirmed congenital achromatopsia patients (n = 7; age 30-72 years; 6 women, 1 male), we examined survey-assessed sleep/circadian phenotype, self-reported visual function, sensitivity to light and use of spectral filters that modify chronic light exposure. In all but one patient, we measured rest-activity cycles using actigraphy over 3 weeks and measured the melatonin phase angle of entrainment using the dim-light melatonin onset. Owing to their light sensitivity, congenital achromatopsia patients used filters to reduce retinal illumination. Thus, congenital achromatopsia patients experienced severely attenuated light exposure. In aggregate, we found a tendency to a late chronotype. We found regular rest-activity patterns in all patients and normal phase angles of entrainment in participants with a measurable dim-light melatonin onset. Our results reveal that a functional cone system and exposure to daytime light intensities are not necessary for regular behavioural and hormonal entrainment, even when survey-assessed sleep and circadian phenotype indicated a tendency for a late chronotype and sleep problems in our congenital achromatopsia cohort.
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Affiliation(s)
- Manuel Spitschan
- Department of Experimental Psychology, University of Oxford, Oxford, OX2 6GG, UK
- Centre for Chronobiology, Psychiatry Hospital of the University of Basel (UPK), CH-4002 Basel, Switzerland
- Transfaculty Research Platform Molecular and Cognitive Neurosciences (MCN), University of Basel, CH-4055 Basel, Switzerland
| | - Corrado Garbazza
- Centre for Chronobiology, Psychiatry Hospital of the University of Basel (UPK), CH-4002 Basel, Switzerland
- Transfaculty Research Platform Molecular and Cognitive Neurosciences (MCN), University of Basel, CH-4055 Basel, Switzerland
| | - Susanne Kohl
- Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, D-72076 Tübingen, Germany
| | - Christian Cajochen
- Centre for Chronobiology, Psychiatry Hospital of the University of Basel (UPK), CH-4002 Basel, Switzerland
- Transfaculty Research Platform Molecular and Cognitive Neurosciences (MCN), University of Basel, CH-4055 Basel, Switzerland
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4
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Ribeiro J, Procyk CA, West EL, O'Hara-Wright M, Martins MF, Khorasani MM, Hare A, Basche M, Fernando M, Goh D, Jumbo N, Rizzi M, Powell K, Tariq M, Michaelides M, Bainbridge JWB, Smith AJ, Pearson RA, Gonzalez-Cordero A, Ali RR. Restoration of visual function in advanced disease after transplantation of purified human pluripotent stem cell-derived cone photoreceptors. Cell Rep 2021; 35:109022. [PMID: 33882303 PMCID: PMC8065177 DOI: 10.1016/j.celrep.2021.109022] [Citation(s) in RCA: 46] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 01/08/2021] [Accepted: 03/31/2021] [Indexed: 12/19/2022] Open
Abstract
Age-related macular degeneration and other macular diseases result in the loss of light-sensing cone photoreceptors, causing irreversible sight impairment. Photoreceptor replacement may restore vision by transplanting healthy cells, which must form new synaptic connections with the recipient retina. Despite recent advances, convincing evidence of functional connectivity arising from transplanted human cone photoreceptors in advanced retinal degeneration is lacking. Here, we show restoration of visual function after transplantation of purified human pluripotent stem cell-derived cones into a mouse model of advanced degeneration. Transplanted human cones elaborate nascent outer segments and make putative synapses with recipient murine bipolar cells (BCs), which themselves undergo significant remodeling. Electrophysiological and behavioral assessments demonstrate restoration of surprisingly complex light-evoked retinal ganglion cell responses and improved light-evoked behaviors in treated animals. Stringent controls exclude alternative explanations, including material transfer and neuroprotection. These data provide crucial validation for photoreceptor replacement therapy and for the potential to rescue cone-mediated vision.
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Affiliation(s)
- Joana Ribeiro
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | | | - Emma L West
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | | | - Monica F Martins
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | | | - Aura Hare
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Mark Basche
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Milan Fernando
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Debbie Goh
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Neeraj Jumbo
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Matteo Rizzi
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Kate Powell
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Menahil Tariq
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | | | | | - Alexander J Smith
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Rachael A Pearson
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | | | - Robin R Ali
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK; Kellogg Eye Centre, University of Michigan, 1000 Wall St., Ann Arbor, MI 48105, USA.
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5
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Andersen MKG, Kessel L. Ametropia and Emmetropization in CNGB3 Achromatopsia. Invest Ophthalmol Vis Sci 2021; 62:10. [PMID: 33560291 PMCID: PMC7873492 DOI: 10.1167/iovs.62.2.10] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Accepted: 01/18/2021] [Indexed: 11/24/2022] Open
Abstract
Purpose Emmetropization is the process of adjusting ocular growth to the focal plane in order to achieve a clear image. Chromatic light may be involved as a cue to guide this process. Achromats are color blind and lack normal cone function; they are often described as being hyperopic, indicating a failure to emmetropize. We aim to describe the refraction and refractive development in a population of genetically characterized achromats. Methods Refractive error data were collected retrospectively from 28 medical records of CNGB3 c.1148delC homozygous achromats. The distribution of spherical equivalent refractive error (SER) and spherical error was analyzed in adults. The refractive development in children was analyzed by documenting astigmatic refractive error and calculating median SER in 1-year age groups and by analyzing the individual development when possible. Results The distribution of SER and spherical error resembled a Gaussian distribution, indicating that emmetropization was disturbed in achromats, but we found indication of some decrease in SER during the first years of childhood. The prevalence of refractive errors was high and broadly distributed. Astigmatic refractive errors were frequent but did not seem to increase with age. Conclusions Refractive development in achromats is more complicated than a complete failure to emmetropize. The spread of refractive errors is larger than previously documented. Results presented here support the theory that chromatic cues and cone photoreceptors may play a role in emmetropization in humans but that it is not essential.
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Affiliation(s)
| | - Line Kessel
- Department of Ophthalmology, Copenhagen University Hospital, Rigshospitalet-Glostrup, Glostrup, Denmark
- Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
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6
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Jacobson MA, Jones LJ, Colussi DJ, Tanaka JC. High-Throughput Ca 2+ Flux Assay To Monitor Cyclic Nucleotide-Gated Channel Activity and Characterize Achromatopsia Mutant Channel Function. ACS Chem Neurosci 2019; 10:3662-3670. [PMID: 31290651 DOI: 10.1021/acschemneuro.9b00231] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Cone photoreceptor cyclic-nucleotide gated channels (CNG) are tetrameric proteins composed of subunits from CNGA3 and CNGB3. These channels transduce light information into electrical signals carried by both Na+ and Ca2+ ions. More than 100 mutations in the CNGA3 gene are associated with the inherited retinal disorder, achromatopsia 2 (ACHM2), which results in attenuation or loss of color vision, daylight blindness, and reduced visual acuity. Classical techniques to measure CNG channel function utilize patch clamp electrophysiology measuring Na currents in the absence of divalent cations, yet intracellular Ca2+ regulates both light and dark adaptation in photoreceptors. We developed a fluorescence-based, high-throughput Ca2+ flux assay using yellow fluorescent protein (YFP) tagged CNGA3 channels expressed in HEK293 cells which allow monitoring for folding defects in mutant channels. The cell permeant cGMP analog, 8-(4-chlorophenylthio)-cGMP (CPT-cGMP), was used to activate Ca2+ flux. The assay was validated using wild-type CNGA3 homomeric and heteromeric channels and ACHM2-associated homomeric mutant CNG channels, CNGA3-R427C, CNGA3-E590K, and CNGA3-L633P. Additionally, we examined two naturally occurring canine mutations causing day-blindness previously studied by patch clamp. We compared the CPT-cGMP K0.5 values of the channels with patch clamp values from previous studies. The assay provides a screen for modulation of gating and/or rescue of trafficking and/or misfolding defects in ACHM2-associated CNG channels. Importantly, the calcium flux assay is advantageous compared to patch clamp as it allows the ability to monitor CNG channel activity in the presence of calcium.
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Affiliation(s)
- Marlene A Jacobson
- Department of Pharmaceutical Sciences, School of Pharmacy , Temple University , Philadelphia , Pennsylvania 19140 , United States
- Moulder Center for Drug Discovery Research, School of Pharmacy , Temple University , Philadelphia , Pennsylvania 19140 , United States
| | - Laura J Jones
- Department of Biology, College of Science and Technology , Temple University , Philadelphia , Pennsylvania 19122 , United States
| | - Dennis J Colussi
- Department of Pharmaceutical Sciences, School of Pharmacy , Temple University , Philadelphia , Pennsylvania 19140 , United States
- Moulder Center for Drug Discovery Research, School of Pharmacy , Temple University , Philadelphia , Pennsylvania 19140 , United States
| | - Jacqueline C Tanaka
- Department of Biology, College of Science and Technology , Temple University , Philadelphia , Pennsylvania 19122 , United States
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A new approach based on targeted pooled DNA sequencing identifies novel mutations in patients with Inherited Retinal Dystrophies. Sci Rep 2018; 8:15457. [PMID: 30337596 PMCID: PMC6194132 DOI: 10.1038/s41598-018-33810-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Accepted: 10/04/2018] [Indexed: 01/28/2023] Open
Abstract
Inherited retinal diseases (IRD) are a heterogeneous group of diseases that mainly affect the retina; more than 250 genes have been linked to the disease and more than 20 different clinical phenotypes have been described. This heterogeneity both at the clinical and genetic levels complicates the identification of causative mutations. Therefore, a detailed genetic characterization is important for genetic counselling and decisions regarding treatment. In this study, we developed a method consisting on pooled targeted next generation sequencing (NGS) that we applied to 316 eye disease related genes, followed by High Resolution Melting and copy number variation analysis. DNA from 115 unrelated test samples was pooled and samples with known mutations were used as positive controls to assess the sensitivity of our approach. Causal mutations for IRDs were found in 36 patients achieving a detection rate of 31.3%. Overall, 49 likely causative mutations were identified in characterized patients, 14 of which were first described in this study (28.6%). Our study shows that this new approach is a cost-effective tool for detection of causative mutations in patients with inherited retinopathies.
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8
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Vinberg F, Chen J, Kefalov VJ. Regulation of calcium homeostasis in the outer segments of rod and cone photoreceptors. Prog Retin Eye Res 2018; 67:87-101. [PMID: 29883715 DOI: 10.1016/j.preteyeres.2018.06.001] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 05/30/2018] [Accepted: 06/04/2018] [Indexed: 12/11/2022]
Abstract
Calcium plays important roles in the function and survival of rod and cone photoreceptor cells. Rapid regulation of calcium in the outer segments of photoreceptors is required for the modulation of phototransduction that drives the termination of the flash response as well as light adaptation in rods and cones. On a slower time scale, maintaining proper calcium homeostasis is critical for the health and survival of photoreceptors. Decades of work have established that the level of calcium in the outer segments of rods and cones is regulated by a dynamic equilibrium between influx via the transduction cGMP-gated channels and extrusion via rod- and cone-specific Na+/Ca2+, K+ exchangers (NCKXs). It had been widely accepted that the only mechanism for extrusion of calcium from rod outer segments is via the rod-specific NCKX1, while extrusion from cone outer segments is driven exclusively by the cone-specific NCKX2. However, recent evidence from mice lacking NCKX1 and NCKX2 have challenged that notion and have revealed a more complex picture, including a NCKX-independent mechanism in rods and two separate NCKX-dependent mechanisms in cones. This review will focus on recent findings on the molecular mechanisms of extrusion of calcium from the outer segments of rod and cone photoreceptors, and the functional and structural changes in photoreceptors when normal extrusion is disrupted.
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Affiliation(s)
- Frans Vinberg
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, USA; John A. Moran Eye Center, University of Utah, Salt Lake City, UT, USA
| | - Jeannie Chen
- Zilkha Neurogenetic Institute, Department of Physiology and Neuroscience, University of Southern California Keck School of Medicine, Los Angeles, CA, USA
| | - Vladimir J Kefalov
- Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, USA.
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9
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Zhang Z, Aung ZT, Simmons DG, Dawson PA. Molecular analysis of sequence and splice variants of the human SLC13A4 sulfate transporter. Mol Genet Metab 2017; 121:35-42. [PMID: 28385533 DOI: 10.1016/j.ymgme.2017.03.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Revised: 03/31/2017] [Accepted: 03/31/2017] [Indexed: 11/22/2022]
Abstract
The solute linked carrier 13A4 gene (SLC13A4) is abundantly expressed in the human and mouse placenta where it is proposed to transport nutrient sulfate to the fetus. In mice, targeted disruption of placental Slc13a4 leads to severe and lethal fetal phenotypes, however the involvement of SLC13A4 in human development is unknown. A search of the NCBI and Ensembl gene databases identified two alternatively spliced SLC13A4 mRNA transcripts and 98 SLC13A4 gene variants, including 85 missense, 4 splice site, 5 frameshift and 2 nonsense variants, as well as 2 in-frame deletions. We examined the relative abundance of the two SLC13A4 mRNA transcripts and then compared the sulfate transport function and plasma membrane expression of both isoforms as well as 6 sequence variants that predict disrupted SLC13A4 protein structure and function. SLC13A4 mRNA variant 1 has three additional nucleotides CAG compared to SLC13A4 mRNA variant 2 as a result of alternative splicing at the 5'-end of exon 6. Using qRT-PCR, we show a 4-fold higher abundance of SLC13A4 mRNA variant 1 compared to variant 2 in term human placentas and cultured BeWo and JEG-3 cell lines. The corresponding SLC13A4 protein isoforms 1 and 2 were found to have similar sulfate uptake activity and apical membrane expression in cultured MDCK cells. In addition, sulfate uptake into MDCK cells was similar between SLC13A4 isoform 1 and four missense variants N300S, F310C, E360Q and I570V, whereas V513M and frameshift variant L72Sfs led to partial (≈75% decrease) and complete loss-of-function, respectively. Localisation of these variants in MDCK cells showed N300S, E360Q, V513M and I570V expression on the apical plasma membrane, L72Sfs intracellularly and F310C on both apical and basolateral membranes. Our finding of partial and complete loss-of-function variants warrants further studies of the potential involvement of SLC13A4 in fetal pathophysiology.
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Affiliation(s)
- Zhe Zhang
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Zin Thu Aung
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - David G Simmons
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Paul A Dawson
- Mater Research Institute, University of Queensland, Woolloongabba, Queensland, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia.
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10
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Contribution of the cyclic nucleotide gated channel subunit, CNG-3, to olfactory plasticity in Caenorhabditis elegans. Sci Rep 2017; 7:169. [PMID: 28279024 PMCID: PMC5427828 DOI: 10.1038/s41598-017-00126-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 02/08/2017] [Indexed: 11/08/2022] Open
Abstract
In Caenorhabditis elegans, the AWC neurons are thought to deploy a cGMP signaling cascade in the detection of and response to AWC sensed odors. Prolonged exposure to an AWC sensed odor in the absence of food leads to reversible decreases in the animal’s attraction to that odor. This adaptation exhibits two stages referred to as short-term and long-term adaptation. Previously, the protein kinase G (PKG), EGL-4/PKG-1, was shown necessary for both stages of adaptation and phosphorylation of its target, the beta-type cyclic nucleotide gated (CNG) channel subunit, TAX-2, was implicated in the short term stage. Here we uncover a novel role for the CNG channel subunit, CNG-3, in short term adaptation. We demonstrate that CNG-3 is required in the AWC for adaptation to short (thirty minute) exposures of odor, and contains a candidate PKG phosphorylation site required to tune odor sensitivity. We also provide in vivo data suggesting that CNG-3 forms a complex with both TAX-2 and TAX-4 CNG channel subunits in AWC. Finally, we examine the physiology of different CNG channel subunit combinations.
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11
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He C, Altshuler-Keylin S, Daniel D, L'Etoile ND, O'Halloran D. The cyclic nucleotide gated channel subunit CNG-1 instructs behavioral outputs in Caenorhabditis elegans by coincidence detection of nutritional status and olfactory input. Neurosci Lett 2016; 632:71-8. [PMID: 27561605 DOI: 10.1016/j.neulet.2016.08.037] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Revised: 08/19/2016] [Accepted: 08/21/2016] [Indexed: 12/26/2022]
Abstract
In mammals, olfactory subsystems have been shown to express seven-transmembrane G-protein-coupled receptors (GPCRs) in a one-receptor-one-neuron pattern, whereas in Caenorhabditis elegans, olfactory sensory neurons express multiple G-protein coupled odorant receptors per olfactory sensory neuron. In both mammalian and C. elegans olfactory sensory neurons (OSNs), the process of olfactory adaptation begins within the OSN; this process of negative feedback within the mammalian OSN has been well described in mammals and enables activated OSNs to desensitize their response cell autonomously while attending to odors detected by separate OSNs. However, the mechanism that enables C. elegans to adapt to one odor and attend to another odor sensed by the same olfactory sensory neuron remains unclear. We found that the cyclic nucleotide gated channel subunit CNG-1 is required to promote cross adaptation responses between distinct olfactory cues. This change in sensitivity to a pair of odorants after persistent stimulation by just one of these odors is modulated by the internal nutritional state of the animal, and we find that this response is maintained across a diverse range of food sources for C. elegans. We also reveal that CNG-1 integrates food related cues for exploratory motor output, revealing that CNG-1 functions in multiple capacities to link nutritional information with behavioral output. Our data describes a novel model whereby CNG channels can integrate the coincidence detection of appetitive and olfactory information to set olfactory preferences and instruct behavioral outputs.
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Affiliation(s)
- Chao He
- Department of Biological Sciences, The George Washington University, Science and Engineering Hall 6000, 800 22nd St N.W., Washington DC, 20052, USA; Institute for Neuroscience, The George Washington University, 636 Ross Hall, 2300 I St. NW, Washington DC, 20052, USA
| | - Svetlana Altshuler-Keylin
- UCSF Diabetes Center, Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, Department of Cell and Tissue Biology, University of California, San Francisco, CA 94143, USA
| | - David Daniel
- Department of Biological Sciences, The George Washington University, Science and Engineering Hall 6000, 800 22nd St N.W., Washington DC, 20052, USA; Institute for Neuroscience, The George Washington University, 636 Ross Hall, 2300 I St. NW, Washington DC, 20052, USA
| | - Noelle D L'Etoile
- Kavli Institute for Fundamental Neuroscience, Department of Cell and Tissue Biology, UCSF, 513 Parnassus Avenue HSW 717, UCSF, USA
| | - Damien O'Halloran
- Department of Biological Sciences, The George Washington University, Science and Engineering Hall 6000, 800 22nd St N.W., Washington DC, 20052, USA; Institute for Neuroscience, The George Washington University, 636 Ross Hall, 2300 I St. NW, Washington DC, 20052, USA.
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12
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Giblin JP, Comes N, Strauss O, Gasull X. Ion Channels in the Eye: Involvement in Ocular Pathologies. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2015; 104:157-231. [PMID: 27038375 DOI: 10.1016/bs.apcsb.2015.11.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.
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Affiliation(s)
- Jonathan P Giblin
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Nuria Comes
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | | | - Xavier Gasull
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
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13
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Meighan PC, Peng C, Varnum MD. Inherited macular degeneration-associated mutations in CNGB3 increase the ligand sensitivity and spontaneous open probability of cone cyclic nucleotide-gated channels. Front Physiol 2015; 6:177. [PMID: 26106334 PMCID: PMC4460308 DOI: 10.3389/fphys.2015.00177] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 05/25/2015] [Indexed: 11/13/2022] Open
Abstract
Cyclic nucleotide gated (CNG) channels are a critical component of the visual transduction cascade in the vertebrate retina. Mutations in the genes encoding these channels have been associated with a spectrum of inherited retinal disorders. To gain insight into their pathophysiological mechanisms, we have investigated the functional consequences of several CNGB3 mutations, previously associated with macular degeneration (Y469D and L595F) or complete achromatopsia (S156F, P309L, and G558C), by expressing these subunits in combination with wild-type CNGA3 in Xenopus oocytes and characterizing them using patch-clamp recordings in the inside-out configuration. These mutations did not prevent the formation of functional heteromeric channels, as indicated by sensitivity to block by L-cis-diltiazem. With the exception of S156F, each of the mutant channels displayed electrophysiological properties reflecting enhanced channel activity at physiological concentrations of cGMP (i.e., a gain-of-function phenotype). The increased channel activity produced by these mutations resulted from either increased functional expression levels, or increased sensitivity to cyclic nucleotides. Furthermore, L595F increased the spontaneous open probability in the absence of activating ligand, signifying a ligand independent gain-of-function change. In addition to the CNGB3 disease-associate mutations, we characterized the effects of several common CNGB3 and CNGA3 single-nucleotide polymorphisms (SNPs) on heteromeric CNGA3+CNGB3 channel function. Two of the SNPs examined (A3-T153M, and B3-W234C) produced decreased ligand sensitivity for heteromeric CNG channels. These changes may contribute to background disease susceptibility when combined with other genetic or non-genetic factors. Together, these studies help to define the underlying molecular phenotype for mutations relating to CNG channel disease pathogenesis.
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Affiliation(s)
- Peter C Meighan
- Department of Integrative Physiology and Neuroscience, Program in Neuroscience, Washington State University Pullman, WA, USA
| | - Changhong Peng
- Department of Integrative Physiology and Neuroscience, Program in Neuroscience, Washington State University Pullman, WA, USA
| | - Michael D Varnum
- Department of Integrative Physiology and Neuroscience, Program in Neuroscience, Washington State University Pullman, WA, USA ; Center for Integrated Biotechnology, Washington State University Pullman, WA, USA
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14
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Development of pro-apoptotic peptides as potential therapy for peritoneal endometriosis. Nat Commun 2014; 5:4478. [PMID: 25047118 PMCID: PMC4109024 DOI: 10.1038/ncomms5478] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 06/22/2014] [Indexed: 11/08/2022] Open
Abstract
Endometriosis is a common gynaecological disease associated with pelvic pain and infertility. Current treatments include oral contraceptives combined with nonsteroidal anti-inflammatory drugs or surgery to remove lesions, all of which provide a temporary but not complete cure. Here we identify an endometriosis-targeting peptide that is internalized by cells, designated z13, using phage display. As most endometriosis occurs on organ surfaces facing the peritoneum, we subtracted a phage display library with female mouse peritoneum tissue and selected phage clones by binding to human endometrial epithelial cells. Proteomics analysis revealed the z13 receptor as the cyclic nucleotide-gated channel β3, a sorting pathway protein. We then linked z13 with an apoptosis-inducing peptide and with an endosome-escaping peptide. When these peptides were co-administered into the peritoneum of baboons with endometriosis, cells in lesions selectively underwent apoptosis with no effect on neighbouring organs. Thus, this study presents a strategy that could be useful to treat peritoneal endometriosis in humans.
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15
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Seim I, Fang X, Xiong Z, Lobanov AV, Huang Z, Ma S, Feng Y, Turanov AA, Zhu Y, Lenz TL, Gerashchenko MV, Fan D, Hee Yim S, Yao X, Jordan D, Xiong Y, Ma Y, Lyapunov AN, Chen G, Kulakova OI, Sun Y, Lee SG, Bronson RT, Moskalev AA, Sunyaev SR, Zhang G, Krogh A, Wang J, Gladyshev VN. Genome analysis reveals insights into physiology and longevity of the Brandt's bat Myotis brandtii. Nat Commun 2014; 4:2212. [PMID: 23962925 PMCID: PMC3753542 DOI: 10.1038/ncomms3212] [Citation(s) in RCA: 182] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Accepted: 06/26/2013] [Indexed: 11/20/2022] Open
Abstract
Bats account for one-fifth of mammalian species, are the only mammals with powered flight, and are among the few animals that echolocate. The insect-eating Brandt’s bat (Myotis brandtii) is the longest-lived bat species known to date (lifespan exceeds 40 years) and, at 4–8 g adult body weight, is the most extreme mammal with regard to disparity between body mass and longevity. Here we report sequencing and analysis of the Brandt’s bat genome and transcriptome, which suggest adaptations consistent with echolocation and hibernation, as well as altered metabolism, reproduction and visual function. Unique sequence changes in growth hormone and insulin-like growth factor 1 receptors are also observed. The data suggest that an altered growth hormone/insulin-like growth factor 1 axis, which may be common to other long-lived bat species, together with adaptations such as hibernation and low reproductive rate, contribute to the exceptional lifespan of the Brandt’s bat. Bats account for 20 per cent of all mammals, these are the only mammals with powered flight, and are among the few animals that echolocate. Here, Seim et al. sequence the genome of the long-lived (>40 years) Brandt’s bat, Myotis brandtii and provide clues to its evolution, longevity and other traits.
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Affiliation(s)
- Inge Seim
- 1] Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA [2] Department of Bioinspired Science, Ewha Womans University, Seoul 120-750, South Korea [3]
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16
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Tanaka N, Delemotte L, Klein ML, Komáromy AM, Tanaka JC. A cyclic nucleotide-gated channel mutation associated with canine daylight blindness provides insight into a role for the S2 segment tri-Asp motif in channel biogenesis. PLoS One 2014; 9:e88768. [PMID: 24586388 PMCID: PMC3931646 DOI: 10.1371/journal.pone.0088768] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Accepted: 01/15/2014] [Indexed: 11/19/2022] Open
Abstract
Cone cyclic nucleotide-gated channels are tetramers formed by CNGA3 and CNGB3 subunits; CNGA3 subunits function as homotetrameric channels but CNGB3 exhibits channel function only when co-expressed with CNGA3. An aspartatic acid (Asp) to asparagine (Asn) missense mutation at position 262 in the canine CNGB3 (D262N) subunit results in loss of cone function (daylight blindness), suggesting an important role for this aspartic acid residue in channel biogenesis and/or function. Asp 262 is located in a conserved region of the second transmembrane segment containing three Asp residues designated the Tri-Asp motif. This motif is conserved in all CNG channels. Here we examine mutations in canine CNGA3 homomeric channels using a combination of experimental and computational approaches. Mutations of these conserved Asp residues result in the absence of nucleotide-activated currents in heterologous expression. A fluorescent tag on CNGA3 shows mislocalization of mutant channels. Co-expressing CNGB3 Tri-Asp mutants with wild type CNGA3 results in some functional channels, however, their electrophysiological characterization matches the properties of homomeric CNGA3 channels. This failure to record heteromeric currents suggests that Asp/Asn mutations affect heteromeric subunit assembly. A homology model of S1-S6 of the CNGA3 channel was generated and relaxed in a membrane using molecular dynamics simulations. The model predicts that the Tri-Asp motif is involved in non-specific salt bridge pairings with positive residues of S3/S4. We propose that the D262N mutation in dogs with CNGB3-day blindness results in the loss of these inter-helical interactions altering the electrostatic equilibrium within in the S1-S4 bundle. Because residues analogous to Tri-Asp in the voltage-gated Shaker potassium channel family were implicated in monomer folding, we hypothesize that destabilizing these electrostatic interactions impairs the monomer folding state in D262N mutant CNG channels during biogenesis.
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Affiliation(s)
- Naoto Tanaka
- Department of Biology, Temple University, Philadelphia, Pennsylvania, United States of America
| | - Lucie Delemotte
- Institute of Computational and Molecular Science, Temple University, Philadelphia, Pennsylvania, United States of America
| | - Michael L. Klein
- Institute of Computational and Molecular Science, Temple University, Philadelphia, Pennsylvania, United States of America
| | - András M. Komáromy
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States of America
- Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail: (AK); (JT)
| | - Jacqueline C. Tanaka
- Department of Biology, Temple University, Philadelphia, Pennsylvania, United States of America
- * E-mail: (AK); (JT)
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Fahim AT, Khan NW, Zahid S, Schachar IH, Branham K, Kohl S, Wissinger B, Elner VM, Heckenlively JR, Jayasundera T. Diagnostic fundus autofluorescence patterns in achromatopsia. Am J Ophthalmol 2013; 156:1211-1219.e2. [PMID: 23972307 DOI: 10.1016/j.ajo.2013.06.033] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Revised: 06/23/2013] [Accepted: 06/24/2013] [Indexed: 01/10/2023]
Abstract
PURPOSE To describe the unique diagnostic fundus autofluorescence (FAF) patterns in patients with achromatopsia and the associated findings on optical coherence tomography (OCT). DESIGN Observational case series. METHODS We evaluated 10 patients with achromatopsia by means of best-corrected visual acuity (BCVA), ophthalmoscopy, Goldmann visual field, full-field electroretinography (ffERG), OCT, and FAF photography. FAF patterns were compared with patient age and foveal changes on OCT. RESULTS Patients fell into two dichotomous age groups at the time of evaluation: six patients ranged from 11 to 23 years of age, and 3 patients ranged from 52 to 63 years of age. All patients had severely reduced photopic ffERG responses, including those exhibiting preserved foveal structure on OCT. The younger patients had absent to mild foveal atrophy on OCT, and four of the six demonstrated foveal and parafoveal hyperfluorescence on FAF. In addition, a 7-month-old child with compound heterozygous mutations in CNGA3 demonstrated similar foveal hyperfluorescence. The older patients demonstrated advanced foveal atrophy and punched-out foveal hypofluorescence with discrete borders on FAF imaging corresponding to the area of outer retinal cavitation on OCT. CONCLUSIONS Foveal hyperfluorescence is an early sign of achromatopsia that can aid in clinical diagnosis. In our cohort, patients with achromatopsia demonstrated age-dependent changes in FAF, which are likely to be progressive and to correlate with foveal atrophy and cavitation on OCT. This finding may be useful in charting the natural course of the disease and in defining a therapeutic window for treatment.
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Affiliation(s)
- Abigail T Fahim
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan
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Dai G, Peng C, Liu C, Varnum MD. Two structural components in CNGA3 support regulation of cone CNG channels by phosphoinositides. ACTA ACUST UNITED AC 2013; 141:413-30. [PMID: 23530136 PMCID: PMC3607822 DOI: 10.1085/jgp.201210944] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels in retinal photoreceptors play a crucial role in vertebrate phototransduction. The ligand sensitivity of photoreceptor CNG channels is adjusted during adaptation and in response to paracrine signals, but the mechanisms involved in channel regulation are only partly understood. Heteromeric cone CNGA3 (A3) + CNGB3 (B3) channels are inhibited by membrane phosphoinositides (PIP(n)), including phosphatidylinositol 3,4,5-triphosphate (PIP(3)) and phosphatidylinositol 4,5-bisphosphate (PIP(2)), demonstrating a decrease in apparent affinity for cyclic guanosine monophosphate (cGMP). Unlike homomeric A1 or A2 channels, A3-only channels paradoxically did not show a decrease in apparent affinity for cGMP after PIP(n) application. However, PIP(n) induced an ∼2.5-fold increase in cAMP efficacy for A3 channels. The PIP(n)-dependent change in cAMP efficacy was abolished by mutations in the C-terminal region (R643Q/R646Q) or by truncation distal to the cyclic nucleotide-binding domain (613X). In addition, A3-613X unmasked a threefold decrease in apparent cGMP affinity with PIP(n) application to homomeric channels, and this effect was dependent on conserved arginines within the N-terminal region of A3. Together, these results indicate that regulation of A3 subunits by phosphoinositides exhibits two separable components, which depend on structural elements within the N- and C-terminal regions, respectively. Furthermore, both N and C regulatory modules in A3 supported PIP(n) regulation of heteromeric A3+B3 channels. B3 subunits were not sufficient to confer PIP(n) sensitivity to heteromeric channels formed with PIP(n)-insensitive A subunits. Finally, channels formed by mixtures of PIP(n)-insensitive A3 subunits, having complementary mutations in N- and/or C-terminal regions, restored PIP(n) regulation, implying that intersubunit N-C interactions help control the phosphoinositide sensitivity of cone CNG channels.
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Affiliation(s)
- Gucan Dai
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA
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19
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Liu C, Sherpa T, Varnum MD. Disease-associated mutations in CNGB3 promote cytotoxicity in photoreceptor-derived cells. Mol Vis 2013; 19:1268-81. [PMID: 23805033 PMCID: PMC3692405 DOI: 10.1167/13.9.1268] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 06/07/2013] [Indexed: 01/10/2023] Open
Abstract
Purpose To determine if achromatopsia associated F525N and T383fsX mutations in the CNGB3 subunit of cone photoreceptor cyclic nucleotide-gated (CNG) channels increases susceptibility to cell death in photoreceptor-derived cells. Methods Photoreceptor-derived 661W cells were transfected with cDNA encoding wild-type (WT) CNGA3 subunits plus WT or mutant CNGB3 subunits, and incubated with the membrane-permeable CNG channel activators 8-(4-chlorophenylthio) guanosine 3′,5′-cyclic monophosphate (CPT-cGMP) or CPT-adenosine 3′,5′-cyclic monophosphate (CPT-cAMP). Cell viability under these conditions was determined by measuring lactate dehydrogenase release. Channel ligand sensitivity was calibrated by patch-clamp recording after expression of WT or mutant channels in Xenopus oocytes. Results Coexpression of CNGA3 with CNGB3 subunits containing F525N or T383fsX mutations produced channels exhibiting increased apparent affinity for CPT-cGMP compared to WT channels. Consistent with these effects, cytotoxicity in the presence of 0.1 μM CPT-cGMP was enhanced relative to WT channels, and the increase in cell death was more pronounced for the mutation with the largest gain-of-function effect on channel gating, F525N. Increased susceptibility to cell death was prevented by application of the CNG channel blocker L-cis-diltiazem. Increased cytotoxicity was also found to be dependent on the presence of extracellular calcium. Conclusions These results indicate a connection between disease-associated mutations in cone CNG channel subunits, altered CNG channel-activation properties, and photoreceptor cytotoxicity. The rescue of cell viability via CNG channel block or removal of extracellular calcium suggests that cytotoxicity in this model depends on calcium entry through hyperactive CNG channels.
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Affiliation(s)
- Chunming Liu
- College of Optometry, Western University of Health Sciences, Pomona, CA, USA
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20
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Dai G, Varnum MD. CNGA3 achromatopsia-associated mutation potentiates the phosphoinositide sensitivity of cone photoreceptor CNG channels by altering intersubunit interactions. Am J Physiol Cell Physiol 2013; 305:C147-59. [PMID: 23552282 DOI: 10.1152/ajpcell.00037.2013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels are critical for sensory transduction in retinal photoreceptors and olfactory receptor cells; their activity is modulated by phosphoinositides (PIPn) such as phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 3,4,5-trisphosphate (PIP3). An achromatopsia-associated mutation in cone photoreceptor CNGA3, L633P, is located in a carboxyl (COOH)-terminal leucine zipper domain shown previously to be important for channel assembly and PIPn regulation. We determined the functional consequences of this mutation using electrophysiological recordings of patches excised from cells expressing wild-type and mutant CNG channel subunits. CNGA3-L633P subunits formed functional channels with or without CNGB3, producing an increase in apparent cGMP affinity. Surprisingly, L633P dramatically potentiated PIPn inhibition of apparent cGMP affinity for these channels. The impact of L633P on PIPn sensitivity depended on an intact amino (NH2) terminal PIPn regulation module. These observations led us to hypothesize that L633P enhances PIPn inhibition by altering the coupling between NH2- and COOH-terminal regions of CNGA3. A recombinant COOH-terminal fragment partially restored normal PIPn sensitivity to channels with COOH-terminal truncation, but L633P prevented this effect. Furthermore, coimmunoprecipitation of channel fragments, and thermodynamic linkage analysis, also provided evidence for NH2-COOH interactions. Finally, tandem dimers of CNGA3 subunits that specify the arrangement of subunits containing L633P and other mutations indicated that the putative interdomain interaction occurs between channel subunits (intersubunit) rather than exclusively within the same subunit (intrasubunit). Collectively, these studies support a model in which intersubunit interactions control the sensitivity of cone CNG channels to regulation by phosphoinositides. Aberrant channel regulation may contribute to disease progression in patients with the L633P mutation.
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Affiliation(s)
- Gucan Dai
- Department of Integrative Physiology and Neuroscience, Program in Neuroscience and Center for Integrated Biotechnology, Washington State University, Pullman, Washington 99164-7620, USA
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21
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Lopez-Rodriguez A, Holmgren M. Restoration of proper trafficking to the cell surface for membrane proteins harboring cysteine mutations. PLoS One 2012; 7:e47693. [PMID: 23082193 PMCID: PMC3474720 DOI: 10.1371/journal.pone.0047693] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2012] [Accepted: 09/17/2012] [Indexed: 11/18/2022] Open
Abstract
A common phenotype for many genetic diseases is that the cell is unable to deliver full-length membrane proteins to the cell surface. For some forms of autism, hereditary spherocytosis and color blindness, the culprits are single point mutations to cysteine. We have studied two inheritable cysteine mutants of cyclic nucleotide-gated channels that produce achromatopsia, a common form of severe color blindness. By taking advantage of the reactivity of cysteine’s sulfhydryl group, we modified these mutants with chemical reagents that attach moieties with similar chemistries to the wild-type amino acids’ side chains. We show that these modifications restored proper delivery to the cell membrane. Once there, the channels exhibited normal functional properties. This strategy might provide a unique opportunity to assess the chemical nature of membrane protein traffic problems.
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Affiliation(s)
- Angelica Lopez-Rodriguez
- Neurophysiology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
| | - Miguel Holmgren
- Neurophysiology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
- * E-mail: .
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22
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Defective trafficking of cone photoreceptor CNG channels induces the unfolded protein response and ER-stress-associated cell death. Biochem J 2012; 441:685-96. [PMID: 21992067 DOI: 10.1042/bj20111004] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Mutations that perturb the function of photoreceptor CNG (cyclic nucleotide-gated) channels are associated with several human retinal disorders, but the molecular and cellular mechanisms leading to photoreceptor dysfunction and degeneration remain unclear. Many loss-of-function mutations result in intracellular accumulation of CNG channel subunits. Accumulation of proteins in the ER (endoplasmic reticulum) is known to cause ER stress and trigger the UPR (unfolded protein response), an evolutionarily conserved cellular programme that results in either adaptation via increased protein processing capacity or apoptotic cell death. We hypothesize that defective trafficking of cone photoreceptor CNG channels can induce UPR-mediated cell death. To test this idea, CNGA3 subunits bearing the R563H and Q655X mutations were expressed in photoreceptor-derived 661W cells with CNGB3 subunits. Compared with wild-type, R563H and Q655X subunits displayed altered degradation rates and/or were retained in the ER. ER retention was associated with increased expression of UPR-related markers of ER stress and with decreased cell viability. Chemical and pharmacological chaperones {TUDCA (tauroursodeoxycholate sodium salt), 4-PBA (sodium 4-phenylbutyrate) and the cGMP analogue CPT-cGMP [8-(4-chlorophenylthio)-cGMP]} differentially reduced degradation and/or promoted plasma-membrane localization of defective subunits. Improved subunit maturation was concordant with reduced expression of ER-stress markers and improved viability of cells expressing localization-defective channels. These results indicate that ER stress can arise from expression of localization-defective CNG channels, and may represent a contributing factor for photoreceptor degeneration.
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Xu J, Morris L, Fliesler SJ, Sherry DM, Ding XQ. Early-onset, slow progression of cone photoreceptor dysfunction and degeneration in CNG channel subunit CNGB3 deficiency. Invest Ophthalmol Vis Sci 2011; 52:3557-66. [PMID: 21273547 DOI: 10.1167/iovs.10-6358] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
PURPOSE To investigate the progression of cone dysfunction and degeneration in CNG channel subunit CNGB3 deficiency. METHODS Retinal structure and function in CNGB3(-/-) and wild-type (WT) mice were evaluated by electroretinography (ERG), lectin cytochemistry, and correlative Western blot analysis of cone-specific proteins. Cone and rod terminal integrity was assessed by electron microscopy and synaptic protein immunohistochemical distribution. RESULTS Cone ERG amplitudes (photopic b-wave) in CNGB3(-/-) mice were reduced to approximately 50% of WT levels by postnatal day 15, decreasing further to approximately 30% of WT levels by 1 month and to approximately 20% by 12 months of age. Rod ERG responses (scotopic a-wave) were not affected in CNGB3(-/-) mice. Average CNGB3(-/-) cone densities were approximately 80% of WT levels at 1 month and declined slowly thereafter to only approximately 50% of WT levels by 12 months. Expression levels of M-opsin, cone transducin α-subunit, and cone arrestin in CNGB3(-/-) mice were reduced by 50% to 60% by 1 month and declined to 35% to 45% of WT levels by 9 months. In addition, cone opsin mislocalized to the outer nuclear layer and the outer plexiform layer in the CNGB3(-/-) retina. Cone and rod synaptic marker expression and terminal ultrastructure were normal in the CNGB3(-/-) retina. CONCLUSIONS These findings are consistent with an early-onset, slow progression of cone functional defects and cone loss in CNGB3(-/-) mice, with the cone signaling deficits arising from disrupted phototransduction and cone loss rather than from synaptic defects.
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Affiliation(s)
- Jianhua Xu
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
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24
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Carvalho LS, Xu J, Pearson RA, Smith AJ, Bainbridge JW, Morris LM, Fliesler SJ, Ding XQ, Ali RR. Long-term and age-dependent restoration of visual function in a mouse model of CNGB3-associated achromatopsia following gene therapy. Hum Mol Genet 2011; 20:3161-75. [PMID: 21576125 PMCID: PMC3140821 DOI: 10.1093/hmg/ddr218] [Citation(s) in RCA: 133] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Mutations in the CNGB3 gene account for >50% of all known cases of achromatopsia. Although of early onset, its stationary character and the potential for rapid assessment of restoration of retinal function following therapy renders achromatopsia a very attractive candidate for gene therapy. Here we tested the efficacy of an rAAV2/8 vector containing a human cone arrestin promoter and a human CNGB3 cDNA in CNGB3 deficient mice. Following subretinal delivery of the vector, CNGB3 was detected in both M- and S-cones and resulted in increased levels of CNGA3, increased cone density and survival, improved cone outer segment structure and normal subcellular compartmentalization of cone opsins. Therapy also resulted in long-term improvement of retinal function, with restoration of cone ERG amplitudes of up to 90% of wild-type and a significant improvement in visual acuity. Remarkably, successful restoration of cone function was observed even when treatment was initiated at 6 months of age; however, restoration of normal visual acuity was only possible in younger animals (e.g. 2–4 weeks old). This study represents achievement of the most substantial restoration of visual function reported to date in an animal model of achromatopsia using a human gene construct, which has the potential to be utilized in clinical trials.
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Affiliation(s)
- Livia S Carvalho
- The Department of Genetics, UCL Institute of Ophthalmology, London, UK
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25
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Ding XQ, Harry CS, Umino Y, Matveev AV, Fliesler SJ, Barlow RB. Impaired cone function and cone degeneration resulting from CNGB3 deficiency: down-regulation of CNGA3 biosynthesis as a potential mechanism. Hum Mol Genet 2009; 18:4770-80. [PMID: 19767295 DOI: 10.1093/hmg/ddp440] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The cone cyclic nucleotide-gated (CNG) channel is essential for central and color vision and visual acuity. This channel is composed of two structurally related subunits, CNGA3 and CNGB3; CNGA3 is the ion-conducting subunit, whereas CNGB3 is a modulatory subunit. Mutations in both subunits are associated with achromatopsia and progressive cone dystrophy, with mutations in CNGB3 alone accounting for 50% of all known cases of achromatopsia. However, the molecular mechanisms underlying cone diseases that result from CNGB3 deficiency are unknown. This study investigated the role of CNGB3 in cones, using CNGB3(-/-) mice. Cone dysfunction was apparent at the earliest time point examined (post-natal day 30) in CNGB3(-/-) mice. When compared with wild-type (WT) controls: photopic electroretingraphic (ERG) responses were decreased by approximately 75%, whereas scotopic ERG responses were unchanged; visual acuity was decreased by approximately 20%, whereas contrast sensitivity was unchanged; cone density was reduced by approximately 40%; photoreceptor apoptosis was detected; and outer segment disorganization was observed in some cones. Notably, CNGA3 protein and mRNA levels were significantly decreased in CNGB3(-/-) mice; in contrast, mRNA levels of S-opsin, Gnat2 and Pde6c were unchanged, relative to WT mice. Hence, we show that loss of CNGB3 reduces biosynthesis of CNGA3 and impairs cone CNG channel function. We suggest that down-regulation of CNGA3 contributes to the pathogenic mechanism by which CNGB3 mutations lead to human cone disease.
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Affiliation(s)
- Xi-Qin Ding
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
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26
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Wang Z, Jiang Y, Lu L, Huang R, Hou Q, Shi F. Molecular mechanisms of cyclic nucleotide-gated ion channel gating. J Genet Genomics 2009; 34:477-85. [PMID: 17601606 DOI: 10.1016/s1673-8527(07)60052-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Accepted: 01/08/2007] [Indexed: 01/09/2023]
Abstract
Cyclic nucleotide-gated ion channels (CNGs) are distributed most widely in the neuronal cell. Great progress has been made in molecular mechanisms of CNG channel gating in the recent years. Results of many experiments have indicated that the stoichiometry and assembly of CNG channels affect their property and gating. Experiments of CNG mutants and analyses of cysteine accessibilities show that cyclic nucleotide-binding domains (CNBD) bind cyclic nucleotides and subsequently conformational changes occurred followed by the concerted or cooperative conformational change of all four subunits during CNG gating. In order to provide theoretical assistances for further investigation on CNG channels, especially regarding the disease pathogenesis of ion channels, this paper reviews the latest progress on mechanisms of CNG channels, functions of subunits, processes of subunit assembly, and conformational changes of subunit regions during gating.
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Affiliation(s)
- Zhengchao Wang
- College of Animal Science and Technology, Nanjing Agricultural University, Nanjing 210095, China
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27
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Abstract
Cyclic nucleotide-gated (CNG) channels are ion channels which are activated by the binding of cGMP or cAMP. The channels are important cellular switches which transduce changes in intracellular concentrations of cyclic nucleotides into changes of the membrane potential and the Ca2+ concentration. CNG channels play a central role in the signal transduction pathways of vision and olfaction. Structurally, the channels belong to the superfamily of pore-loop cation channels. They share a common domain structure with hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and Eag-like K+ channels. In this chapter, we give an overview on the molecular properties of CNG channels and describe the signal transduction pathways these channels are involved in. We will also summarize recent insights into the physiological and pathophysiological role of CNG channel proteins that have emerged from the analysis of CNG channel-deficient mouse models and human channelopathies.
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Affiliation(s)
- Martin Biel
- Center for Integrated Protein Science CIPS-M and Zentrum für Pharmaforschung-Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, München, 81377, Germany.
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28
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Carroll J, Choi SS, Williams DR. In vivo imaging of the photoreceptor mosaic of a rod monochromat. Vision Res 2008; 48:2564-8. [PMID: 18499214 DOI: 10.1016/j.visres.2008.04.006] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2007] [Revised: 02/03/2008] [Accepted: 04/06/2008] [Indexed: 10/22/2022]
Abstract
Complete achromatopsia (i.e., rod monochromacy) is a congenital vision disorder in which cone function is absent or severely diminished, often due to mutations in one of two components of the cone phototransduction cascade (transducin or the cyclic-nucleotide gated channel). Previous histological data concerning cone structure are conflicting; suggesting anywhere from normal numbers of foveal cones to a complete absence of foveal cones. Here, we used an adaptive optics ophthalmoscope to obtain in vivo retinal images from a rod monochromat for whom the genetic basis of the disorder consists of a homozygous mutation in the CNGB3 gene. Behavioral data from the patient were consistent with an absence of cone function. Retinal images revealed a severely disrupted photoreceptor mosaic in the fovea and parafovea, where the size and density of the visible photoreceptors resembled that of normal rods. Imaging of additional rod monochromats to characterize differences in the photoreceptor mosaic between genetically classified patients will be required to determine which, if any, might be receptive to restorative gene therapy procedures.
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Affiliation(s)
- Joseph Carroll
- Department of Ophthalmology, Medical College of Wisconsin, The Eye Institute, 925 North 87th Street, Milwaukee, WI 53226, USA.
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29
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Function and dysfunction of CNG channels: insights from channelopathies and mouse models. Mol Neurobiol 2008; 35:266-77. [PMID: 17917115 DOI: 10.1007/s12035-007-0025-y] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Revised: 11/30/1999] [Accepted: 01/05/2007] [Indexed: 10/22/2022]
Abstract
Channels directly gated by cyclic nucleotides (CNG channels) are important cellular switches that mediate influx of Na+ and Ca2+ in response to increases in the intracellular concentration of cAMP and cGMP. In photoreceptors and olfactory receptor neurons, these channels serve as final targets for cGMP and cAMP signaling pathways that are initiated by the absorption of photons and the binding of odorants, respectively. CNG channels have been also found in other types of neurons and in non-excitable cells. However, in most of these cells, the physiological role of CNG channels has yet to be determined. CNG channels have a complex heteromeric structure. The properties of individual subunits that assemble in specific stoichiometries to the native channels have been extensively investigated in heterologous expression systems. Recently, mutations in human CNG channel genes leading to inherited diseases (so-called channelopathies) have been functionally characterized. Moreover, mouse knockout models were generated to define the role of CNG channel proteins in vivo. In this review, we will summarize recent insights into the physiological and pathophysiological role of CNG channel proteins that have emerged from genetic studies in mice and humans.
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30
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Leinders-Zufall T, Cockerham RE, Michalakis S, Biel M, Garbers DL, Reed RR, Zufall F, Munger SD. Contribution of the receptor guanylyl cyclase GC-D to chemosensory function in the olfactory epithelium. Proc Natl Acad Sci U S A 2007; 104:14507-12. [PMID: 17724338 PMCID: PMC1964822 DOI: 10.1073/pnas.0704965104] [Citation(s) in RCA: 180] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The mammalian main olfactory epithelium (MOE) recognizes and transduces olfactory cues through a G protein-coupled, cAMP-dependent signaling cascade. Additional chemosensory transduction mechanisms have been suggested but remain controversial. We show that a subset of MOE neurons expressing the orphan receptor guanylyl cyclase GC-D and the cyclic nucleotide-gated channel subunit CNGA3 employ an excitatory cGMP-dependent transduction mechanism for chemodetection. By combining gene targeting of Gucy2d, which encodes GC-D, with patch clamp recording and confocal Ca2+ imaging from single dendritic knobs in situ, we find that GC-D cells recognize the peptide hormones uroguanylin and guanylin as well as natural urine stimuli. These molecules stimulate an excitatory, cGMP-dependent signaling cascade that increases intracellular Ca2+ and action potential firing. Responses are eliminated in both Gucy2d- and Cnga3-null mice, demonstrating the essential role of GC-D and CNGA3 in the transduction of these molecules. The sensitive and selective detection of two important natriuretic peptides by the GC-D neurons suggests the possibility that these cells contribute to the maintenance of salt and water homeostasis or the detection of cues related to hunger, satiety, or thirst.
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Affiliation(s)
- Trese Leinders-Zufall
- *Department of Physiology, University of Saarland School of Medicine, 66421 Homburg/Saar, Germany
| | - Renee E. Cockerham
- Department of Anatomy and Neurobiology and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Stylianos Michalakis
- Munich Center for Integrated Protein Science and Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, 81377 Munich, Germany
| | - Martin Biel
- Munich Center for Integrated Protein Science and Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, 81377 Munich, Germany
| | - David L. Garbers
- Department of Pharmacology and the Cecil H. and Ida Green Center for Reproductive Biology Sciences, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
| | - Randall R. Reed
- Department of Molecular Biology and Genetics and Center for Sensory Biology, Johns Hopkins School of Medicine, Baltimore, MD 21205
| | - Frank Zufall
- *Department of Physiology, University of Saarland School of Medicine, 66421 Homburg/Saar, Germany
- To whom correspondence may be addressed. E-mail:
| | - Steven D. Munger
- Department of Anatomy and Neurobiology and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD 21201
- **To whom correspondence may be addressed at:
Department of Anatomy and Neurobiology, University of Maryland School of Medicine, 20 Penn Street, S251, Baltimore, MD 21201. E-mail:
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31
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Muraki-Oda S, Toyoda F, Okada A, Tanabe S, Yamade S, Ueyama H, Matsuura H, Ohji M. Functional analysis of rod monochromacy-associated missense mutations in the CNGA3 subunit of the cone photoreceptor cGMP-gated channel. Biochem Biophys Res Commun 2007; 362:88-93. [PMID: 17693388 DOI: 10.1016/j.bbrc.2007.07.152] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2007] [Accepted: 07/26/2007] [Indexed: 11/18/2022]
Abstract
Thirty-nine missense mutations, which had been identified in rod monochromacy or related disorders, in the CNGA3 subunit of cone photoreceptor cGMP-gated channels were analyzed. HEK293 cells were transfected with cDNA of the human CNGA3 subunit harboring each of these mutations in an expression vector. Patch-clamp recordings demonstrated that 32 of the 39 mutants did not show cGMP-activated current, suggesting that these 32 mutations cause a loss of function of the channels. From the remaining 7 mutants that showed cGMP-activated current, two mutations in the cyclic nucleotide-binding domain, T565M or E593K, were further studied. The half-maximal activating concentration (K(1/2)) for cGMP in the homomeric CNGA3-T565M channels (160microM) was 17.8-fold higher than that of the homomeric wild-type CNGA3 channels (9.0microM). Conversely, the K(1/2) for cGMP in the homomeric CNGA3-E593K channels (3.0microM) was 3-fold lower than that of the homomeric wild-type CNGA3 channels. These results suggest that the T565M and E593K mutations alter the apparent affinity for cGMP of the channels to cause cone dysfunction, resulting in rod monochromacy.
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Affiliation(s)
- Sanae Muraki-Oda
- Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan
| | - Futoshi Toyoda
- Department of Physiology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan
| | - Akira Okada
- Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan
| | - Shoko Tanabe
- Institute of Vision Research, 12-23 Sanbonmatsu-cho, Atsuta-ku, Nagoya 456-0032, Japan
| | - Shinichi Yamade
- Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan
| | - Hisao Ueyama
- Department of Biochemistry and Molecular Biology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan.
| | - Hiroshi Matsuura
- Department of Physiology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan
| | - Masahito Ohji
- Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan
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32
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Wiszniewski W, Lewis RA, Lupski JR. Achromatopsia: the CNGB3 p.T383fsX mutation results from a founder effect and is responsible for the visual phenotype in the original report of uniparental disomy 14. Hum Genet 2007; 121:433-9. [PMID: 17265047 DOI: 10.1007/s00439-006-0314-y] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2006] [Accepted: 12/08/2006] [Indexed: 11/29/2022]
Abstract
Achromatopsia (ACHM) or rod monochromacy is an autosomal recessive and genetically heterogeneous retinal disorder. It is characterized by a lack of color discrimination, poor visual acuity, photodysphoria, pendular infantile nystagmus, and abnormal photopic electroretinographic (ERG) recordings with preservation of rod-mediated function. Mutations in three known genes are causative; including genes for the alpha and beta subunits of the cyclic nucleotide-gated cation channel (CNGA3 and CNGB3, respectively) and cone photoreceptor transducin--GNAT2. We investigated the prevalence of mutations in achromatopsia-causing genes in a cohort of 16 families with both clinical and electrophysiologic evidence consistent with autosomal recessive transmission, including one subject with achromatopsia and maternal isodisomy for chromosome 14. The most frequent mutation, p.T383fsX in CNGB3, accounted for 75% (18/24) of disease-associated alleles; intragenic SNPs in unrelated patients revealed transmission of a common haplotype consistent with a founder effect. Homozygous p.T383fsX mutation in CNGB3 that maps to chromosome 8 was detected in a patient with achromatopsia and systemic features associated with uniparental disomy (UPD) of chromosome 14. Two novel variants, p.R223G and p.A621E were found in CNGA3. We conclude that CNGA3 and CNGB3 mutations are responsible for the substantial majority of achromatopsia. Furthermore, the CNGB3 mutation p.T383fsX is a predominant mutation, results from a founder effect, and is responsible for the ACHM in the original clinical report of UPD 14.
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Affiliation(s)
- Wojciech Wiszniewski
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
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33
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Tetreault ML, Henry D, Horrigan DM, Matthews G, Zimmerman AL. Characterization of a novel cyclic nucleotide-gated channel from zebrafish brain. Biochem Biophys Res Commun 2006; 348:441-9. [PMID: 16887101 DOI: 10.1016/j.bbrc.2006.07.074] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2006] [Accepted: 07/17/2006] [Indexed: 10/24/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels have been well characterized in the sensory receptors of vision and olfaction, but their characteristics in other tissues remain largely unknown. Here, we report characterization of a novel brain-specific CNG channel from zebrafish. Unique among CNG channels, the transcript is expressed mainly in the brain. When expressed in Xenopus oocytes, the channel's electrophysiological properties are distinct compared to CNG channels from either rods (CNGA1), olfactory receptors (CNGA2), or cones (CNGA3). The channel is less sensitive to cAMP than cGMP (K(1/2) of 280 and 7 microM, respectively), with a maximum cAMP efficacy at least 80% of that with saturating levels of cGMP. The single-channel conductance of 58pS is larger than most other CNG channels. Like other CNG channels the channel is relatively nonselective among monovalent cations. However, unlike other CNG channels, there was rundown of the macroscopic current within 30-100 min after patch excision.
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Affiliation(s)
- Michelle L Tetreault
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown Medical School, Providence, RI 02912, USA.
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34
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Pifferi S, Boccaccio A, Menini A. Cyclic nucleotide-gated ion channels in sensory transduction. FEBS Lett 2006; 580:2853-9. [PMID: 16631748 DOI: 10.1016/j.febslet.2006.03.086] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2006] [Accepted: 03/31/2006] [Indexed: 11/16/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels, directly activated by the binding of cyclic nucleotides, were first discovered in retinal rods, cones and olfactory sensory neurons. In the visual and olfactory systems, CNG channels mediate sensory transduction by conducting cationic currents carried primarily by sodium and calcium ions. In olfactory transduction, calcium in combination with calmodulin exerts a negative feedback on CNG channels that is the main molecular mechanism responsible for fast adaptation in olfactory sensory neurons. Six mammalian CNG channel genes are known and some human visual disorders are caused by mutations in retinal rod or cone CNG genes.
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Affiliation(s)
- Simone Pifferi
- International School for Advanced Studies, S.I.S.S.A., Sector of Neurobiology, Via Beirut 2-4, 34014 Trieste, Italy
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35
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Brown RL, Strassmaier T, Brady JD, Karpen JW. The pharmacology of cyclic nucleotide-gated channels: emerging from the darkness. Curr Pharm Des 2006; 12:3597-613. [PMID: 17073662 PMCID: PMC2467446 DOI: 10.2174/138161206778522100] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cyclic nucleotide-gated (CNG) ion channels play a central role in vision and olfaction, generating the electrical responses to light in photoreceptors and to odorants in olfactory receptors. These channels have been detected in many other tissues where their functions are largely unclear. The use of gene knockouts and other methods have yielded some information, but there is a pressing need for potent and specific pharmacological agents directed at CNG channels. To date there has been very little systematic effort in this direction - most of what can be termed CNG channel pharmacology arose from testing reagents known to target protein kinases or other ion channels, or by accident when researchers were investigating other intracellular pathways that may regulate the activity of CNG channels. Predictably, these studies have not produced selective agents. However, taking advantage of emerging structural information and the increasing knowledge of the biophysical properties of these channels, some promising compounds and strategies have begun to emerge. In this review we discuss progress on two fronts, cyclic nucleotide analogs as both activators and competitive inhibitors, and inhibitors that target the pore or gating machinery of the channel. We also discuss the potential of these compounds for treating certain forms of retinal degeneration.
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Affiliation(s)
- R. Lane Brown
- Neurological Sciences Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Timothy Strassmaier
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, USA
| | - James D. Brady
- Neurological Sciences Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Jeffrey W. Karpen
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, USA
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36
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Kohl S, Varsanyi B, Antunes GA, Baumann B, Hoyng CB, Jägle H, Rosenberg T, Kellner U, Lorenz B, Salati R, Jurklies B, Farkas A, Andreasson S, Weleber RG, Jacobson SG, Rudolph G, Castellan C, Dollfus H, Legius E, Anastasi M, Bitoun P, Lev D, Sieving PA, Munier FL, Zrenner E, Sharpe LT, Cremers FPM, Wissinger B. CNGB3 mutations account for 50% of all cases with autosomal recessive achromatopsia. Eur J Hum Genet 2005; 13:302-8. [PMID: 15657609 DOI: 10.1038/sj.ejhg.5201269] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Achromatopsia is a congenital, autosomal recessively inherited disorder characterized by a lack of color discrimination, low visual acuity (<0.2), photophobia, and nystagmus. Mutations in the genes for CNGA3, CNGB3, and GNAT2 have been associated with this disorder. Here, we analyzed the spectrum and prevalence of CNGB3 gene mutations in a cohort of 341 independent patients with achromatopsia. In 163 patients, CNGB3 mutations could be identified. A total of 105 achromats carried apparent homozygous mutations, 44 were compound (double) heterozygotes, and 14 patients had only a single mutant allele. The derived CNGB3 mutation spectrum comprises 28 different mutations including 12 nonsense mutations, eight insertions and/or deletions, five putative splice site mutations, and three missense mutations. Thus, the majority of mutations in the CNGB3 gene result in significantly altered and/or truncated polypeptides. Several mutations were found recurrently, in particular a 1 bp deletion, c.1148delC, which accounts for over 70% of all CNGB3 mutant alleles. In conclusion, mutations in the CNGB3 gene are responsible for approximately 50% of all patients with achromatopsia. This indicates that the CNGB3/ACHM3 locus on chromosome 8q21 is the major locus for achromatopsia in patients of European origin or descent.
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Affiliation(s)
- Susanne Kohl
- Molekulargenetisches Labor, Universitäts-Augenklinik Tübingen, Abt. Pathophysiologie des Sehens und Neuroophthalmologie, Germany.
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37
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Liu C, Varnum MD. Functional consequences of progressive cone dystrophy-associated mutations in the human cone photoreceptor cyclic nucleotide-gated channel CNGA3 subunit. Am J Physiol Cell Physiol 2005; 289:C187-98. [PMID: 15743887 DOI: 10.1152/ajpcell.00490.2004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Progressive cone dystrophies are a genetically heterogeneous group of disorders characterized by early deterioration of visual acuity and color vision, together with psychophysical and electrophysiological evidence of abnormal cone function and cone degeneration. Recently, three mutations in the gene encoding the CNGA3 subunit of cone photoreceptor cyclic nucleotide-gated (CNG) channels have been linked to progressive cone dystrophy in humans. To investigate the functional consequences of these mutations, we expressed mutant human CNGA3 subunits in Xenopus oocytes, alone or together with human CNGB3, and studied these channels using patch-clamp recording. Compared with wild-type channels, homomeric and heteromeric channels containing CNGA3-N471S or CNGA3-R563H subunits exhibited an increase in apparent affinity for cGMP and an increase in the relative agonist efficacy of cAMP compared with cGMP. In contrast, R277C subunits did not form functional homomeric or heteromeric channels. Cell surface expression levels, determined using confocal microscopy of green fluorescent protein-tagged subunits and patch-clamp recording, were significantly reduced for both R563H and R277C but unchanged for N471S. Overall, these results suggest that the plasma membrane localization and gating properties of cone CNG channels are altered by progressive cone dystrophy-associated mutations, providing evidence that supports the pathogenicity of these mutations.
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Affiliation(s)
- Chunming Liu
- Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology and Program in Neuroscience, Washington State University, PO Box 646520, Pullman, Washington 99164-6520, USA
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38
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Abstract
The normal X-chromosome-linked color-vision gene array is composed of a single long-wave-sensitive (L-) pigment gene followed by one or more middle-wave-sensitive (M-) pigment genes. The expression of these genes to form L- or M-cones is controlled by the proximal promoter and by the locus control region. The high degree of homology between the L- and M-pigment genes predisposed them to unequal recombination, leading to gene deletion or the formation of L/M hybrid genes that explain the majority of the common red-green color-vision deficiencies. Hybrid genes encode a variety of L-like or M-like pigments. Analysis of the gene order in arrays of normal and deutan subjects indicates that only the two most proximal genes of the array contribute to the color-vision phenotype. This is supported by the observation that only the first two genes of the array are expressed in the human retina. The severity of the color-vision defect is roughly related to the difference in absorption maxima (lambda(max)) between the photopigments encoded by the first two genes of the array. A single amino acid polymorphism (Ser180Ala) in the L pigment accounts for the subtle difference in normal color vision and influences the severity of red-green color-vision deficiency. Blue-cone monochromacy is a rare disorder that involves absence of L- and M-cone function. It is caused either by deletion of a critical region that regulates expression of the L/M gene array, or by mutations that inactivate the L- and M-pigment genes. Total color blindness is another rare disease that involves complete absence of all cone function. A number of mutants in the genes encoding the cone-specific alpha- and beta-subunits of the cGMP-gated cation channel as well as in the alpha-subunit of transducin have been implicated in this disorder.
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Affiliation(s)
- Samir S Deeb
- Department of Medicine, University of Washington, Seattle, USA.
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39
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Peng C, Rich ED, Varnum MD. Subunit configuration of heteromeric cone cyclic nucleotide-gated channels. Neuron 2004; 42:401-10. [PMID: 15134637 DOI: 10.1016/s0896-6273(04)00225-9] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2003] [Revised: 01/12/2004] [Accepted: 04/02/2004] [Indexed: 10/25/2022]
Abstract
Cone photoreceptor cyclic nucleotide-gated (CNG) channels are thought to be tetrameric assemblies of CNGB3 (B3) and CNGA3 (A3) subunits. We have used functional and biochemical approaches to investigate the stoichiometry and arrangement of these subunits in recombinant channels. First, tandem dimers of linked subunits were used to constrain the order of CNGB3 and CNGA3 subunits; the properties of channels formed by B3/B3+A3/A3 dimers, or A3/B3+B3/A3 dimers, closely resembled those of channels arising from B3+A3 monomers. Functional markers in B3/B3 (or A3/A3) dimers confirmed that both B3 subunits (and both A3 subunits) gained membership into the pore-forming tetramer and that like subunits were positioned adjacent to each other. Second, chemical crosslinking and co-immunoprecipitation studies using epitope-tagged monomer subunits both demonstrated the presence of two CNGB3 subunits in cone channels. Together, these data support a preferred subunit arrangement for cone CNG channels (B3-B3-A3-A3) that is distinct from the 3A:1B configuration of rod channels.
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Affiliation(s)
- Changhong Peng
- Department of Veterinary and Comparative Anatomy, Washington State University, P.O. Box 646520, Pullman, WA 99164, USA
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40
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Tränkner D, Jägle H, Kohl S, Apfelstedt-Sylla E, Sharpe LT, Kaupp UB, Zrenner E, Seifert R, Wissinger B. Molecular basis of an inherited form of incomplete achromatopsia. J Neurosci 2004; 24:138-47. [PMID: 14715947 PMCID: PMC6729583 DOI: 10.1523/jneurosci.3883-03.2004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2003] [Revised: 10/21/2003] [Accepted: 10/21/2003] [Indexed: 11/21/2022] Open
Abstract
Mutations in the genes encoding the CNGA3 and CNGB3 subunits of the cyclic nucleotide-gated (CNG) channel of cone photoreceptors have been associated with autosomal recessive achromatopsia. Here we analyze the molecular basis of achromatopsia in two siblings with residual cone function. Psychophysical and electroretinographic analyses show that the light sensitivity of the cone system is lowered, and the signal transfer from cones to secondary neurons is perturbed. Both siblings carry two mutant CNGA3 alleles that give rise to channel subunits with different single-amino acid substitutions. Heterologous expression revealed that only one mutant forms functional channels, albeit with grossly altered properties, including changes in Ca2+ blockage and permeation. Surprisingly, coexpression of this mutant subunit with CNGB3 rescues the channel phenotype, except for the Ca2+ interaction. We argue that these alterations are responsible for the perturbations in light sensitivity and synaptic transmission.
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Affiliation(s)
- Dimitri Tränkner
- Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, 52425 Jülich, Germany.
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