1
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Wang Y, Qiu L, Wang B, Guan Z, Dong Z, Zhang J, Cao S, Yang L, Wang B, Gong Z, Zhang L, Ma W, Liu Z, Zhang D, Wang G, Yin P. Structural basis for odorant recognition of the insect odorant receptor OR-Orco heterocomplex. Science 2024; 384:1453-1460. [PMID: 38870272 DOI: 10.1126/science.adn6881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Accepted: 05/29/2024] [Indexed: 06/15/2024]
Abstract
Insects detect and discriminate a diverse array of chemicals using odorant receptors (ORs), which are ligand-gated ion channels comprising a divergent odorant-sensing OR and a conserved odorant receptor co-receptor (Orco). In this work, we report structures of the ApOR5-Orco heterocomplex from the pea aphid Acyrthosiphon pisum alone and bound to its known activating ligand, geranyl acetate. In these structures, three ApOrco subunits serve as scaffold components that cannot bind the ligand and remain relatively unchanged. Upon ligand binding, the pore-forming helix S7b of ApOR5 shifts outward from the central pore axis, causing an asymmetrical pore opening for ion influx. Our study provides insights into odorant recognition and channel gating of the OR-Orco heterocomplex and offers structural resources to support development of innovative insecticides and repellents for pest control.
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Affiliation(s)
- Yidong Wang
- Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Synthetic Biology Laboratory of the Ministry of Agriculture and Rural Affairs, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518120, China
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Liang Qiu
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Bing Wang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Zeyuan Guan
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Zhi Dong
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Jie Zhang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Song Cao
- Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Synthetic Biology Laboratory of the Ministry of Agriculture and Rural Affairs, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518120, China
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Lulu Yang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Bo Wang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Zhou Gong
- Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
| | - Liwei Zhang
- College of Grassland Science and Technology, China Agricultural University, Beijing 100193, China
| | - Weihua Ma
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Zhu Liu
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Delin Zhang
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Guirong Wang
- Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Synthetic Biology Laboratory of the Ministry of Agriculture and Rural Affairs, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518120, China
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Ping Yin
- National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan 430070, China
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2
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Pliushcheuskaya P, Kesh S, Kaufmann E, Wucherpfennig S, Schwede F, Künze G, Nache V. Similar Binding Modes of cGMP Analogues Limit Selectivity in Modulating Retinal CNG Channels via the Cyclic Nucleotide-Binding Domain. ACS Chem Neurosci 2024; 15:1652-1668. [PMID: 38579109 PMCID: PMC11027099 DOI: 10.1021/acschemneuro.3c00665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 02/28/2024] [Accepted: 03/19/2024] [Indexed: 04/07/2024] Open
Abstract
In treating retinitis pigmentosa, a genetic disorder causing progressive vision loss, selective inhibition of rod cyclic nucleotide-gated (CNG) channels holds promise. Blocking the increased Ca2+-influx in rod photoreceptors through CNG channels can potentially delay disease progression and improve the quality of life for patients. To find inhibitors for rod CNG channels, we investigated the impact of 16 cGMP analogues on both rod and cone CNG channels using the patch-clamp technique. Although modifications at the C8 position of the guanine ring did not change the ligand efficacy, modifications at the N1 and N2 positions rendered cGMP largely ineffective in activating retinal CNG channels. Notably, PET-cGMP displayed selective potential, favoring rod over cone, whereas Rp-cGMPS showed greater efficiency in activating cone over rod CNG channels. Ligand docking and molecular dynamics simulations on cyclic nucleotide-binding domains showed comparable binding energies and binding modes for cGMP and its analogues in both rod and cone CNG channels (CNGA1 vs CNGA3 subunits). Computational experiments on CNGB1a vs CNGB3 subunits showed similar binding modes albeit with fewer amino acid interactions with cGMP due to an inactivated conformation of their C-helix. In addition, no clear correlation could be observed between the computational scores and the CNG channel efficacy values, suggesting additional factors beyond binding strength determining ligand selectivity and potency. This study highlights the importance of looking beyond the cyclic nucleotide-binding domain and toward the gating mechanism when searching for selective modulators. Future efforts in developing selective modulators for CNG channels should prioritize targeting alternative channel domains.
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Affiliation(s)
- Palina Pliushcheuskaya
- Institute
for Drug Discovery, Medical Faculty, University
of Leipzig, Leipzig 04103, Germany
| | - Sandeep Kesh
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
| | - Emma Kaufmann
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
| | - Sophie Wucherpfennig
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
| | - Frank Schwede
- BIOLOG
Life Science Institute GmbH & Co KG, Bremen 28199, Germany
| | - Georg Künze
- Institute
for Drug Discovery, Medical Faculty, University
of Leipzig, Leipzig 04103, Germany
- Interdisciplinary
Center for Bioinformatics, University of
Leipzig, Leipzig 04107, Germany
- Center
for Scalable Data Analytics and Artificial Intelligence, University of Leipzig, Leipzig 04105, Germany
| | - Vasilica Nache
- Institute
of Physiology II, University Hospital Jena, Friedrich Schiller University
Jena, Jena 07743, Germany
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3
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Hu Z, Yang J. Structural basis of properties, mechanisms, and channelopathy of cyclic nucleotide-gated channels. Channels (Austin) 2023; 17:2273165. [PMID: 37905307 PMCID: PMC10761061 DOI: 10.1080/19336950.2023.2273165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 10/07/2023] [Indexed: 11/02/2023] Open
Abstract
Recent years have seen an outpouring of atomic or near atomic resolution structures of cyclic nucleotide-gated (CNG) channels, captured in closed, transition, pre-open, partially open, and fully open states. These structures provide unprecedented molecular insights into the activation, assembly, architecture, regulation, and channelopathy of CNG channels, as well as mechanistic explanations for CNG channel biophysical and pharmacological properties. This article summarizes recent advances in CNG channel structural biology, describes key structural features and elements, and illuminates a detailed conformational landscape of activation by cyclic nucleotides. The review also correlates structures with findings and properties delineated in functional studies, including nonselective monovalent cation selectivity, Ca2+ permeation and block, block by L-cis-diltiazem, location of the activation gate, lack of voltage-dependent gating, and modulation by lipids and calmodulin. A perspective on future research is also offered.
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Affiliation(s)
- Zhengshan Hu
- Department of Biological Sciences, Columbia University, New York, NY, USA
| | - Jian Yang
- Department of Biological Sciences, Columbia University, New York, NY, USA
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4
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Tolone A, Haq W, Fachinger A, Roy A, Kesh S, Rentsch A, Wucherpfennig S, Zhu Y, Groten J, Schwede F, Tomar T, Herberg FW, Nache V, Paquet-Durand F. The PKG Inhibitor CN238 Affords Functional Protection of Photoreceptors and Ganglion Cells against Retinal Degeneration. Int J Mol Sci 2023; 24:15277. [PMID: 37894958 PMCID: PMC10607377 DOI: 10.3390/ijms242015277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 09/27/2023] [Accepted: 10/11/2023] [Indexed: 10/29/2023] Open
Abstract
Hereditary retinal degeneration (RD) is often associated with excessive cGMP signalling in photoreceptors. Previous research has shown that inhibition of cGMP-dependent protein kinase G (PKG) can reduce photoreceptor loss in two different RD animal models. In this study, we identified a PKG inhibitor, the cGMP analogue CN238, which preserved photoreceptor viability and functionality in rd1 and rd10 mutant mice. Surprisingly, in explanted retinae, CN238 also protected retinal ganglion cells from axotomy-induced retrograde degeneration and preserved their functionality. Furthermore, kinase activity-dependent protein phosphorylation of the PKG target Kv1.6 was reduced in CN238-treated rd10 retinal explants. Ca2+-imaging on rd10 acute retinal explants revealed delayed retinal ganglion cell repolarization with CN238 treatment, suggesting a PKG-dependent modulation of Kv1-channels. Together, these results highlight the strong neuroprotective capacity of PKG inhibitors for both photoreceptors and retinal ganglion cells, illustrating their broad potential for the treatment of retinal diseases and possibly neurodegenerative diseases in general.
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Affiliation(s)
- Arianna Tolone
- Cell Death Mechanism Group, Institute for Ophthalmic Research, Eberhard-Karls-Universität Tübingen, 72076 Tübingen, Germany; (A.T.); (Y.Z.)
| | - Wadood Haq
- Neuroretinal Electrophysiology and Imaging, Institute for Ophthalmic Research, Eberhard-Karls-Universität Tübingen, 72076 Tübingen, Germany;
| | - Alexandra Fachinger
- Biochemistry Department, University of Kassel, 34132 Kassel, Germany; (A.F.); (F.W.H.)
| | - Akanksha Roy
- PamGene International B.V., 5211 ‘s-Hertogenbosch, The Netherlands; (A.R.); (J.G.); (T.T.)
| | - Sandeep Kesh
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743 Jena, Germany; (S.K.); (S.W.); (V.N.)
| | - Andreas Rentsch
- Biolog Life Science Institute GmbH & Co. KG, 28199 Bremen, Germany; (A.R.); (F.S.)
| | - Sophie Wucherpfennig
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743 Jena, Germany; (S.K.); (S.W.); (V.N.)
| | - Yu Zhu
- Cell Death Mechanism Group, Institute for Ophthalmic Research, Eberhard-Karls-Universität Tübingen, 72076 Tübingen, Germany; (A.T.); (Y.Z.)
| | - John Groten
- PamGene International B.V., 5211 ‘s-Hertogenbosch, The Netherlands; (A.R.); (J.G.); (T.T.)
| | - Frank Schwede
- Biolog Life Science Institute GmbH & Co. KG, 28199 Bremen, Germany; (A.R.); (F.S.)
| | - Tushar Tomar
- PamGene International B.V., 5211 ‘s-Hertogenbosch, The Netherlands; (A.R.); (J.G.); (T.T.)
| | - Friedrich W. Herberg
- Biochemistry Department, University of Kassel, 34132 Kassel, Germany; (A.F.); (F.W.H.)
| | - Vasilica Nache
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743 Jena, Germany; (S.K.); (S.W.); (V.N.)
| | - François Paquet-Durand
- Cell Death Mechanism Group, Institute for Ophthalmic Research, Eberhard-Karls-Universität Tübingen, 72076 Tübingen, Germany; (A.T.); (Y.Z.)
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5
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Inamdar SM, Lankford CK, Baker SA. Photoreceptor Ion Channels in Signaling and Disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1415:269-276. [PMID: 37440044 DOI: 10.1007/978-3-031-27681-1_39] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/14/2023]
Abstract
Photoreceptors (PRs) in the neural retina convert photon capture into an electrical signal that is communicated across a chemical synapse to second-order neurons in the retina and on through the rest of the visual pathway. This information is decoded in the visual cortex to create images. The activity of PRs depends on the concerted action of several voltage-gated ion channels that will be discussed in this chapter.
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Affiliation(s)
- Shivangi M Inamdar
- Department of Biochemistry and Molecular Biology, University of Iowa, Iowa City, IA, USA.
| | - Colten K Lankford
- Department of Biochemistry and Molecular Biology, University of Iowa, Iowa City, IA, USA
| | - Sheila A Baker
- Department of Biochemistry and Molecular Biology, University of Iowa, Iowa City, IA, USA
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6
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cGMP Analogues with Opposing Actions on CNG Channels Selectively Modulate Rod or Cone Photoreceptor Function. Pharmaceutics 2022; 14:pharmaceutics14102102. [PMID: 36297537 PMCID: PMC9612005 DOI: 10.3390/pharmaceutics14102102] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 09/23/2022] [Accepted: 09/28/2022] [Indexed: 11/09/2022] Open
Abstract
The vertebrate retina harbors rod and cone photoreceptors. Human vision critically depends on cone photoreceptor function. In the phototransduction cascade, cGMP activates distinct rod and cone isoforms of the cyclic nucleotide-gated (CNG) channel. Excessive cGMP levels initiate a pathophysiological rollercoaster, which starts with CNG channel over-activation, typically in rod photoreceptors. This triggers cell death of rods first, and then cones, and is the root cause of many blinding retinal diseases, including Retinitis pigmentosa. While targeting of CNG channels has been proposed for therapeutic purposes, thus far, it has not been possible to inhibit rod CNG channels without compromising cone function. Here, we present a novel strategy, based on cGMP analogues with opposing actions on CNG channels, which enables the selective modulation of either rod or cone photoreceptor activity. The combined treatment with the weak rod-selective CNG-channel inhibitor (Rp-8-Br-PET-cGMPS) and the cone-selective CNG-channel activator (8-pCPT-cGMP) essentially normalized rod CNG-channel function while preserving cone functionality at physiological and pathological cGMP levels. Hence, combinations of cGMP analogues with desired properties may elegantly address the isoform-specificity problem in future pharmacological therapies. Moreover, this strategy may allow for improvements in visual performance in certain light environments.
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7
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The Natural History of CNGB1-Related Retinopathy: A Longitudinal Phenotypic Analysis. Int J Mol Sci 2022; 23:ijms23126785. [PMID: 35743231 PMCID: PMC9245601 DOI: 10.3390/ijms23126785] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 06/13/2022] [Accepted: 06/15/2022] [Indexed: 02/01/2023] Open
Abstract
Cyclic nucleotide-gated channel β 1 (CNGB1) encodes a subunit of the rod cyclic nucleotide-gated channel. Pathogenic variants in CNGB1 are responsible for 4% of autosomal recessive retinitis pigmentosa (RP). Several treatment strategies show promise for treating inherited retinal degenerations, however relevant metrics of progression and sensitive clinical trial endpoints are needed to assess therapeutic efficacy. This study reports the natural history of CNGB1-related RP with a longitudinal phenotypic analysis of 33 molecularly-confirmed patients with a mean follow-up period of 4.5 ± 3.9 years (range 0-17). The mean best corrected visual acuity (BCVA) of the right eye was 0.31 ± 0.43 logMAR at baseline and 0.47 ± 0.63 logMAR at the final visit over the study period. The ellipsoid zone (EZ) length was measurable in at least one eye of 23 patients and had a mean rate of constriction of 178 ± 161 µm per year (range 1.0-661 µm), with 57% of patients having a decrease in EZ length of greater than 250 µm in a simulated two-year trial period. Hyperautofluorescent outer ring (hyperAF) area was measurable in 17 patients, with 10 patients not displaying a ring phenotype. The results support previous findings of CNGB1-related RP being a slowly progressive disease with patients maintaining visual acuity. Prospective deep phenotyping studies assessing multimodal retinal imaging and functional measures are now required to determine clinical endpoints to be used in a trial.
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8
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Das S, Popp V, Power M, Groeneveld K, Yan J, Melle C, Rogerson L, Achury M, Schwede F, Strasser T, Euler T, Paquet-Durand F, Nache V. Redefining the role of Ca 2+-permeable channels in photoreceptor degeneration using diltiazem. Cell Death Dis 2022; 13:47. [PMID: 35013127 PMCID: PMC8748460 DOI: 10.1038/s41419-021-04482-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 10/07/2021] [Accepted: 11/23/2021] [Indexed: 12/18/2022]
Abstract
Hereditary degeneration of photoreceptors has been linked to over-activation of Ca2+-permeable channels, excessive Ca2+-influx, and downstream activation of Ca2+-dependent calpain-type proteases. Unfortunately, after more than 20 years of pertinent research, unequivocal evidence proving significant and reproducible photoreceptor protection with Ca2+-channel blockers is still lacking. Here, we show that both D- and L-cis enantiomers of the anti-hypertensive drug diltiazem were very effective at blocking photoreceptor Ca2+-influx, most probably by blocking the pore of Ca2+-permeable channels. Yet, unexpectedly, this block neither reduced the activity of calpain-type proteases, nor did it result in photoreceptor protection. Remarkably, application of the L-cis enantiomer of diltiazem even led to a strong increase in photoreceptor cell death. These findings shed doubt on the previously proposed links between Ca2+ and retinal degeneration and are highly relevant for future therapy development as they may serve to refocus research efforts towards alternative, Ca2+-independent degenerative mechanisms.
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Affiliation(s)
- Soumyaparna Das
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Valerie Popp
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany
| | - Michael Power
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany.,Werner Reichardt Centre for Integrative Neuroscience (CIN), University of Tübingen, 72076, Tübingen, Germany
| | - Kathrin Groeneveld
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany.,Biomolecular Photonics Group, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany
| | - Jie Yan
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Christian Melle
- Biomolecular Photonics Group, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany
| | - Luke Rogerson
- Werner Reichardt Centre for Integrative Neuroscience (CIN), University of Tübingen, 72076, Tübingen, Germany
| | - Marlly Achury
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Frank Schwede
- BIOLOG Life Science Institute GmbH & Co KG, 28199, Bremen, Germany
| | - Torsten Strasser
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Thomas Euler
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany.,Werner Reichardt Centre for Integrative Neuroscience (CIN), University of Tübingen, 72076, Tübingen, Germany
| | | | - Vasilica Nache
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University Jena, 07743, Jena, Germany.
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9
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Xue J, Han Y, Zeng W, Jiang Y. Structural mechanisms of assembly, permeation, gating, and pharmacology of native human rod CNG channel. Neuron 2022; 110:86-95.e5. [PMID: 34699778 PMCID: PMC8738139 DOI: 10.1016/j.neuron.2021.10.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 09/15/2021] [Accepted: 10/01/2021] [Indexed: 01/07/2023]
Abstract
Mammalian cyclic nucleotide-gated (CNG) channels are nonselective cation channels activated by cGMP or cAMP and play essential roles in the signal transduction of the visual and olfactory sensory systems. CNGA1, the principal component of the CNG channel from rod photoreceptors, can by itself form a functional homotetrameric channel and has been used as the model system in the majority of rod CNG studies. However, the native rod CNG functions as a heterotetramer consisting of three A1 and one B1 subunits and exhibits different functional properties than the CNGA1 homomer. Here we present the functional analysis of human rod CNGA1/B1 heterotetramer and its cryo-EM structures in apo, cGMP-bound, cAMP-bound, and L-cis-Diltiazem-blocked states. These structures, with resolution ranging from 2.6 to 3.3 Å, elucidate the structural mechanisms underlying the 3:1 subunit stoichiometry, the asymmetrical gating upon cGMP activation, and the unique pharmacological property of the native rod CNG channel.
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Affiliation(s)
- Jing Xue
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Yan Han
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Weizhong Zeng
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Youxing Jiang
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA,Lead Contact: Youxing Jiang, Ph.D., Department of Physiology, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, Texas 75390-9040, Tel. 214 645-6027; Fax. 214 645-6042;
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10
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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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11
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Kawamura S, Tachibanaki S. Molecular basis of rod and cone differences. Prog Retin Eye Res 2021; 90:101040. [PMID: 34974196 DOI: 10.1016/j.preteyeres.2021.101040] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2021] [Revised: 12/22/2021] [Accepted: 12/27/2021] [Indexed: 12/15/2022]
Abstract
In the vertebrate retina, rods and cones both detect light, but they are different in functional aspects such as light sensitivity and time resolution, for example, and in some of cell biological aspects. For functional aspects, both photoreceptors are known to share a common mechanism, phototransduction cascade, consisting of a series of enzyme reactions to convert a photon-capture signal to an electrical signal. To understand the mechanisms of the functional differences between rods and cones at the molecular level, we compared biochemically each of the reactions in the phototransduction cascade between rods and cones using the cells isolated and purified from carp retina. Although proteins in the cascade are functionally similar between rods and cones, their activities together with their expression levels are mostly different between these photoreceptors. In general, reactions to generate a response are slightly less effective, as a total, in cones than in rods, but each of the reactions for termination and recovery of a response are much more effective in cones. These findings explain lower light sensitivity and briefer light responses in cones than in rods. In addition, our considerations suggest that a Ca2+-binding protein, S-modulin or recoverin, has a currently unnoticed role in shaping light responses. With comparison of the expression levels of proteins and/or mRNAs using purified cells, several proteins were found to be specifically or predominantly expressed in cones. These proteins would be of interest for future studies on the difference between rods and cones.
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Affiliation(s)
- Satoru Kawamura
- Graduate School of Frontier Biosciences, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan.
| | - Shuji Tachibanaki
- Graduate School of Frontier Biosciences, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Yamada-oka 1-3, Suita, Osaka, 565-0871, Japan.
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12
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Wang NK, Liu PK, Kong Y, Levi SR, Huang WC, Hsu CW, Wang HH, Chen N, Tseng YJ, Quinn PMJ, Tai MH, Lin CS, Tsang SH. Mouse Models of Achromatopsia in Addressing Temporal "Point of No Return" in Gene-Therapy. Int J Mol Sci 2021; 22:8069. [PMID: 34360834 PMCID: PMC8347118 DOI: 10.3390/ijms22158069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 07/22/2021] [Accepted: 07/25/2021] [Indexed: 12/03/2022] Open
Abstract
Achromatopsia is characterized by amblyopia, photophobia, nystagmus, and color blindness. Previous animal models of achromatopsia have shown promising results using gene augmentation to restore cone function. However, the optimal therapeutic window to elicit recovery remains unknown. Here, we attempted two rounds of gene augmentation to generate recoverable mouse models of achromatopsia including a Cnga3 model with a knock-in stop cassette in intron 5 using Easi-CRISPR (Efficient additions with ssDNA inserts-CRISPR) and targeted embryonic stem (ES) cells. This model demonstrated that only 20% of CNGA3 levels in homozygotes derived from target ES cells remained, as compared to normal CNGA3 levels. Despite the low percentage of remaining protein, the knock-in mouse model continued to generate normal cone phototransduction. Our results showed that a small amount of normal CNGA3 protein is sufficient to form "functional" CNG channels and achieve physiological demand for proper cone phototransduction. Thus, it can be concluded that mutating the Cnga3 locus to disrupt the functional tetrameric CNG channels may ultimately require more potent STOP cassettes to generate a reversible achromatopsia mouse model. Our data also possess implications for future CNGA3-associated achromatopsia clinical trials, whereby restoration of only 20% functional CNGA3 protein may be sufficient to form functional CNG channels and thus rescue cone response.
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Affiliation(s)
- Nan-Kai Wang
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Pei-Kang Liu
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
- Department of Ophthalmology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80756, Taiwan
- School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
- Institute of Biomedical Sciences, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
| | - Yang Kong
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Sarah R. Levi
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Wan-Chun Huang
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Chun-Wei Hsu
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Hung-Hsi Wang
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Nelson Chen
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Yun-Ju Tseng
- Department of Pathology & Cell Biology, Columbia University Irving Medical Center, New York, NY 10032, USA; (Y.-J.T.); (C.-S.L.)
- Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Peter M. J. Quinn
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
| | - Ming-Hong Tai
- Institute of Biomedical Sciences, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
- Center for Neuroscience, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
- Graduate Program in Marine Biotechnology, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
| | - Chyuan-Sheng Lin
- Department of Pathology & Cell Biology, Columbia University Irving Medical Center, New York, NY 10032, USA; (Y.-J.T.); (C.-S.L.)
- Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Stephen H. Tsang
- Department of Ophthalmology, Edward S. Harkness Eye Institute, Columbia University Irving Medical Center, New York, NY 10032, USA; (N.-K.W.); (P.-K.L.); (Y.K.); (S.R.L.); (W.-C.H.); (C.-W.H.); (H.-H.W.); (N.C.); (P.M.J.Q.)
- Jonas Children’s Vision Care, and Bernard and Shirlee Brown Glaucoma Laboratory, Columbia Stem Cell Initiative, Departments of Ophthalmology, Pathology and Cell Biology, Institute of Human Nutrition, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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13
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Das S, Chen Y, Yan J, Christensen G, Belhadj S, Tolone A, Paquet-Durand F. The role of cGMP-signalling and calcium-signalling in photoreceptor cell death: perspectives for therapy development. Pflugers Arch 2021; 473:1411-1421. [PMID: 33864120 PMCID: PMC8370896 DOI: 10.1007/s00424-021-02556-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 03/04/2021] [Accepted: 03/10/2021] [Indexed: 12/12/2022]
Abstract
The second messengers, cGMP and Ca2+, have both been implicated in retinal degeneration; however, it is still unclear which of the two is most relevant for photoreceptor cell death. This problem is exacerbated by the close connections and crosstalk between cGMP-signalling and calcium (Ca2+)-signalling in photoreceptors. In this review, we summarize key aspects of cGMP-signalling and Ca2+-signalling relevant for hereditary photoreceptor degeneration. The topics covered include cGMP-signalling targets, the role of Ca2+ permeable channels, relation to energy metabolism, calpain-type proteases, and how the related metabolic processes may trigger and execute photoreceptor cell death. A focus is then put on cGMP-dependent mechanisms and how exceedingly high photoreceptor cGMP levels set in motion cascades of Ca2+-dependent and independent processes that eventually bring about photoreceptor cell death. Finally, an outlook is given into mutation-independent therapeutic approaches that exploit specific features of cGMP-signalling. Such approaches might be combined with suitable drug delivery systems for translation into clinical applications.
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Affiliation(s)
- Soumyaparna Das
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Yiyi Chen
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Jie Yan
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Gustav Christensen
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Soumaya Belhadj
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - Arianna Tolone
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany
| | - François Paquet-Durand
- Institute for Ophthalmic Research, University of Tübingen, Elfriede-Aulhorn-Strasse 7, 72076, Tübingen, Germany.
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14
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Structural mechanisms of gating and selectivity of human rod CNGA1 channel. Neuron 2021; 109:1302-1313.e4. [PMID: 33651975 DOI: 10.1016/j.neuron.2021.02.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/22/2021] [Accepted: 02/03/2021] [Indexed: 11/22/2022]
Abstract
Mammalian cyclic nucleotide-gated (CNG) channels play an essential role in the signal transduction of the visual and olfactory sensory systems. Here we reveal the structural mechanism of ligand gating in human rod CNGA1 channel by determining its cryo-EM structures in both the apo closed and cGMP-bound open states. Distinct from most other members of voltage-gated tetrameric cation channels, CNGA1 forms a central channel gate in the middle of the membrane, occluding the central cavity. Structural analyses of ion binding profiles in the selectivity filters of the wild-type channel and the E365Q filter mutant allow us to unambiguously define the two Ca2+ binding sites inside the selectivity filter, providing structural insights into Ca2+ blockage and permeation in CNG channels. The structure of the E365Q mutant also reveals two alternative side-chain conformations at Q365, providing a plausible explanation for the voltage-dependent gating of CNG channel acquired upon E365 mutation.
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15
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Radojevic B, Jones K, Klein M, Mauro-Herrera M, Kingsley R, Birch DG, Bennett LD. Variable expressivity in patients with autosomal recessive retinitis pigmentosa associated with the gene CNGB1. Ophthalmic Genet 2020; 42:15-22. [PMID: 33465333 DOI: 10.1080/13816810.2020.1832532] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
PURPOSE In a cohort of eight families (11 patients) with autosomal recessive retinitis pigmentosa (arRP), we clinically characterized disease associated with mutations in CNGB1. METHODS Visual function was determined by measuring the patients' visual acuity, dark- and light-adapted perimetry, and by full-field electroretinography. Retinal structure was evaluated with spectral-domain optical coherence tomography, fundus imaging, and autofluorescence imaging. RESULTS Age of onset ranged from 4 to 49 years (mean [SD] 26 [17], median 27 years). The age at visit was 27-54 years, mean 37 (17). The range of visual acuity was logMAR -0.1 to 1.3 (Snellen 20/16 to 20/400) in the right eye and -0.1 to 0.9 (Snellen 20/16 to 20/160) in the left eye. Electrophysiological testing in five patients showed an absence of the rod response. Cone responses ranged from normal to severely reduced. The patients exhibited loss of rod vision more severe than cone vision. Funduscopic images showed widespread retinal degeneration with pigment clumping, optic disk pallor, arteriole attenuation, and a peri-foveal ring of hyper autofluorescence. Three families were tested for olfactory dysfunction and results indicated mild to complete anosmia in individuals with mutations in CNGB1. Genetic analysis revealed 6 novel variants, c.2127 C > G, p.Phe709Leu; c.1431 C > A, p.Cys477*; c.2034 G > A, p.Trp678*; c.2092 T > C, p.Cys698Arg; and c.583 + 2 T > C, c.2305-34 G > A and 3 variants that have been previously described, c.2957A>T, p.Asn986Ile; c.2544dup, p.Leu849Alafs*3; and c.2492 + 1 G > A. DISCUSSION This is the first report for six novel CNGB1 variants associated with arRP. Two families had olfactory dysfunction in patients with arRP and family members who were heterozygous for a CNGB1 mutation. Additionally, findings demonstrated variable penetrance and expressivity of disease in these patients.
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Affiliation(s)
- Bojana Radojevic
- Department of Ophthalmology, University of Oklahoma Health Sciences Center , Oklahoma City, OK, USA
| | - Kaylie Jones
- Rose-Silverthorne Retinal Degenerations Laboratory, Retina Foundation of the Southwest , Dallas, TX, USA
| | - Martin Klein
- Rose-Silverthorne Retinal Degenerations Laboratory, Retina Foundation of the Southwest , Dallas, TX, USA
| | - Margarita Mauro-Herrera
- Department of Ophthalmology, University of Oklahoma Health Sciences Center , Oklahoma City, OK, USA
| | - Ronald Kingsley
- Department of Ophthalmology, University of Oklahoma Health Sciences Center , Oklahoma City, OK, USA.,Department of Ophthalmology, Dean McGee Eye Institute , Oklahoma City, OK, USA
| | - David G Birch
- Rose-Silverthorne Retinal Degenerations Laboratory, Retina Foundation of the Southwest , Dallas, TX, USA.,Department of Ophthalmology, UT Southwestern Medical Center , Dallas, TX, USA
| | - Lea D Bennett
- Department of Ophthalmology, University of Oklahoma Health Sciences Center , Oklahoma City, OK, USA.,Department of Ophthalmology, UT Southwestern Medical Center , Dallas, TX, USA
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16
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Feketa VV, Nikolaev YA, Merriman DK, Bagriantsev SN, Gracheva EO. CNGA3 acts as a cold sensor in hypothalamic neurons. eLife 2020; 9:55370. [PMID: 32270761 PMCID: PMC7182431 DOI: 10.7554/elife.55370] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 04/08/2020] [Indexed: 11/13/2022] Open
Abstract
Most mammals maintain their body temperature around 37°C, whereas in hibernators it can approach 0°C without triggering a thermogenic response. The remarkable plasticity of the thermoregulatory system allowed mammals to thrive in variable environmental conditions and occupy a wide range of geographical habitats, but the molecular basis of thermoregulation remains poorly understood. Here we leverage the thermoregulatory differences between mice and hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus) to investigate the mechanism of cold sensitivity in the preoptic area (POA) of the hypothalamus, a critical thermoregulatory region. We report that, in comparison to squirrels, mice have a larger proportion of cold-sensitive neurons in the POA. We further show that mouse cold-sensitive neurons express the cyclic nucleotide-gated ion channel CNGA3, and that mouse, but not squirrel, CNGA3 is potentiated by cold. Our data reveal CNGA3 as a hypothalamic cold sensor and a molecular marker to interrogate the neuronal circuitry underlying thermoregulation.
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Affiliation(s)
- Viktor V Feketa
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Yale University School of Medicine, New Haven, United States.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, United States
| | - Yury A Nikolaev
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States
| | - Dana K Merriman
- Department of Biology, University of Wisconsin-Oshkosh, Oshkosh, United States
| | - Sviatoslav N Bagriantsev
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States
| | - Elena O Gracheva
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, United States.,Department of Neuroscience, Yale University School of Medicine, New Haven, United States.,Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, United States
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17
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Zhang Y, Wang S, Xu M, Pang J, Yuan Z, Zhao C. AAV-mediated human CNGB3 restores cone function in an all-cone mouse model of CNGB3 achromatopsia. J Biomed Res 2020; 34:114-121. [PMID: 32305965 DOI: 10.7555/jbr.33.20190056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Complete congenital achromatopsia is a devastating hereditary visual disorder. Mutations in the CNGB3 gene account for more than 50% of all known cases of achromatopsia. This work investigated the efficiency of subretinal (SR) delivered AAV8 (Y447, 733F) vector containing a human PR2.1 promoter and a human CNGB3 cDNA in Cngb3 -/-/ Nrl -/- mice. The Cngb3 -/-/ Nrl -/- mouse was a cone-dominant model with Cngb3 channel deficiency, which partially mimicked the all-cone foveal structure of human achromatopsia with CNGB3 mutations. Following SR delivery of the vector, AAV-mediated CNGB3 expression restored cone function which was assessed by the restoration of the cone-mediated electroretinogram (ERG) and immunohistochemistry. This therapeutic rescue resulted in long-term improvement of retinal function with the restoration of cone ERG amplitude. This study demonstrated an AAV-mediated gene therapy in a cone-dominant mouse model using a human gene construct and provided the potential to be utilized in clinical trials.
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Affiliation(s)
- Yuxin Zhang
- Department of Ophthalmology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Shanshan Wang
- Department of Ophthalmology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Miao Xu
- Department of Ophthalmology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Jijing Pang
- Department of Ophthalmology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu 210029, China;Department of Ophthalmology, University of Florida, Gainesville, FL 32610, USA
| | - Zhilan Yuan
- Department of Ophthalmology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu 210029, China
| | - Chen Zhao
- Department of Ophthalmology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu 210029, China
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18
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Hassall MM, Barnard AR, Orlans HO, McClements ME, Charbel Issa P, Aslam SA, MacLaren RE. A Novel Achromatopsia Mouse Model Resulting From a Naturally Occurring Missense Change in Cngb3. Invest Ophthalmol Vis Sci 2019; 59:6102-6110. [PMID: 30592498 DOI: 10.1167/iovs.18-24328] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose A local colony of inbred mice (129S6/SvEvTac origin), in isolation for over a decade, were found to have absent light-adapted electroretinogram (ERG) responses. We investigated the inheritance and genetic basis of this phenotype of cone photoreceptor function loss. Methods An affected 129S6/SvEvTac colony animal was outcrossed to a C57BL/6J mouse and intercrossed to investigate inheritance in the F2 generation. We performed ERG testing and targeted resequencing on genes of interest (Gnat2, Cnga3, Cngb3, Pde6c, Hcn1, Syne2). The eyes of a subset of animals underwent histologic immunostaining. Results All 129S6/SvEvTac colony animals tested lacked cone pathway function by ERG testing (n = 12), although rod pathway-based ERG responses remained unaffected. Outcross-intercross breeding showed a recessive inheritance pattern. A novel missense mutation was identified in the Cngb3 gene, which causes an amino acid substitution at a conserved residue (NM_013927)c.692G>A; p.(R231H). The recessive phenotype only affected homozygotes (χ2 = 39, P = 3.2e-10). Cones had normal morphology at postnatal day (PND) 70, but cone cell counts declined from PND 30 to PND 335 (P = 0.038), indicating progressive cone photoreceptor death. Conclusions We identified the spontaneous occurrence of a 10th model of cone photoreceptor function loss (cpfl10) in an isolated line of inbred mice. Our results indicate that this is caused by a novel missense mutation in the Cngb3 gene, with a fully recessive inheritance pattern. This mouse may provide a more appropriate background against which to assess CNGB3 achromatopsia gene therapy for missense mutations.
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Affiliation(s)
- Mark M Hassall
- Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.,Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
| | - Alun R Barnard
- Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.,Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
| | - Harry O Orlans
- Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.,Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
| | - Michelle E McClements
- Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
| | - Peter Charbel Issa
- Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.,Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
| | - Sher A Aslam
- Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.,Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
| | - Robert E MacLaren
- Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom.,Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom
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Lelle M, Otte M, Thon S, Bertinetti D, Herberg FW, Benndorf K. Chemical synthesis and biological activity of novel brominated 7-deazaadenosine-3',5'-cyclic monophosphate derivatives. Bioorg Med Chem 2019; 27:1704-1713. [PMID: 30879860 DOI: 10.1016/j.bmc.2019.03.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 03/09/2019] [Accepted: 03/11/2019] [Indexed: 11/19/2022]
Abstract
Synthetic derivatives of cyclic adenosine monophosphate, such as halogenated or other more hydrophobic analogs, are widely used compounds, to investigate diverse signal transduction pathways of eukaryotic cells. This inspired us to develop cyclic nucleotides, which exhibit chemical structures composed of brominated 7-deazaadenines and the phosphorylated ribosugar. The synthesized 8-bromo- and 7-bromo-7-deazaadenosine-3',5'-cyclic monophosphates rank among the most potent activators of cyclic nucleotide-regulated ion channels as well as cAMP-dependent protein kinase. Moreover, these substances bind tightly to exchange proteins directly activated by cAMP.
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Affiliation(s)
- Marco Lelle
- Institute of Physiology II, University Hospital Jena, Kollegiengasse 9, 07743 Jena, Germany
| | - Maik Otte
- Institute of Physiology II, University Hospital Jena, Kollegiengasse 9, 07743 Jena, Germany
| | - Susanne Thon
- Institute of Physiology II, University Hospital Jena, Kollegiengasse 9, 07743 Jena, Germany
| | - Daniela Bertinetti
- Department of Biochemistry, University of Kassel, Heinrich-Plett-Straße 40, 34132 Kassel, Germany
| | - Friedrich W Herberg
- Department of Biochemistry, University of Kassel, Heinrich-Plett-Straße 40, 34132 Kassel, Germany
| | - Klaus Benndorf
- Institute of Physiology II, University Hospital Jena, Kollegiengasse 9, 07743 Jena, Germany.
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20
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Sun W, Zhang Q. Diseases associated with mutations in CNGA3: Genotype-phenotype correlation and diagnostic guideline. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2018; 161:1-27. [PMID: 30711023 DOI: 10.1016/bs.pmbts.2018.10.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Along with the molecular and functional characterization of CNGA3, knowledge about diseases associated with CNGA3 mutations has made great progress. So far, CNGA3 mutations are not only one of the most common causes of achromatopsia and cone dystrophy or cone-rod dystrophy but also one of the most commonly mutated genes among various forms of retinopathy. Understanding the clinical characteristics of CNGA3-associated retinal diseases may help clinical practice of infants or children with related diseases. Recognizing the importance of CNGA3 in inherited retinal diseases may enhance related research in searching for functional restoration or repair of CNGA3 defects.
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Affiliation(s)
- Wenmin Sun
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China
| | - Qingjiong Zhang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.
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21
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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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22
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Iribarne M, Masai I. Neurotoxicity of cGMP in the vertebrate retina: from the initial research on rd mutant mice to zebrafish genetic approaches. J Neurogenet 2017; 31:88-101. [PMID: 28812418 DOI: 10.1080/01677063.2017.1358268] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Zebrafish are an excellent animal model for research on vertebrate development and human diseases. Sophisticated genetic tools including large-scale mutagenesis methodology make zebrafish useful for studying neuronal degenerative diseases. Here, we review zebrafish models of inherited ophthalmic diseases, focusing on cGMP metabolism in photoreceptors. cGMP is the second messenger of phototransduction, and abnormal cGMP levels are associated with photoreceptor death. cGMP concentration represents a balance between cGMP phosphodiesterase 6 (PDE6) and guanylate cyclase (GC) activities in photoreceptors. Various zebrafish cGMP metabolism mutants were used to clarify molecular mechanisms by which dysfunctions in this pathway trigger photoreceptor degeneration. Here, we review the history of research on the retinal degeneration (rd) mutant mouse, which carries a genetic mutation of PDE6b, and we also highlight recent research in photoreceptor degeneration using zebrafish models. Several recent discoveries that provide insight into cGMP toxicity in photoreceptors are discussed.
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Affiliation(s)
- Maria Iribarne
- a Okinawa Institute of Science and Technology Graduate University , Onna, Okinawa , Japan
| | - Ichiro Masai
- a Okinawa Institute of Science and Technology Graduate University , Onna, Okinawa , Japan
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Abstract
As our understanding of the genetic basis for inherited retinal disease has expanded, gene therapy has advanced into clinical development. When the gene mutations associated with inherited retinal dystrophies were identified, it became possible to create animal models in which individual gene were altered to match the human mutations. The retina of these animals were then characterized to assess whether the mutated genes produced retinal phenotypes characteristic of disease-affected patients. Following the identification of a subpopulation of patients with the affected gene and the development of techniques for the viral gene transduction of retinal cells, it has become possible to deliver a copy of the normal gene into the retinal sites of the mutated genes. When this was performed in animal models of monogenic diseases, at an early stage of retinal degeneration when the affected cells remained viable, successful gene augmentation corrected the structural and functional lesions characteristic of the specific diseases in the areas of the retina that were successfully transduced. These studies provided the essential proof-of-concept needed to advance monogenic gene therapies into clinic development; these therapies include treatments for: Leber's congenital amaurosis type 2, caused by mutations to RPE65, retinoid isomerohydrolase; choroideremia, caused by mutations to REP1, Rab escort protein 1; autosomal recessive Stargardt disease, caused by mutations to ABCA4, the photoreceptor-specific ATP-binding transporter; Usher 1B disease caused by mutations to MYO7A, myosin heavy chain 7; X-linked juvenile retinoschisis caused by mutations to RS1, retinoschisin; autosomal recessive retinitis pigmentosa caused by mutations to MERTK, the proto-oncogene tyrosine-protein kinase MER; Leber's hereditary optic neuropathy caused by mutations to ND4, mitochondrial nicotinamide adenine dinucleotide ubiquinone oxidoreductase (complex I) subunit 4 and achromatopsia, caused by mutations to CNGA3, cyclic nucleotide-gated channel alpha 3 and CNGB3, cyclic nucleotide-gated channel beta 3. This review includes a tabulated summary of treatments for these monogenic retinal dystrophies that have entered into clinical development, as well as a brief summary of the preclinical data that supported their advancement into clinical development.
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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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Nache V, Wongsamitkul N, Kusch J, Zimmer T, Schwede F, Benndorf K. Deciphering the function of the CNGB1b subunit in olfactory CNG channels. Sci Rep 2016; 6:29378. [PMID: 27405959 PMCID: PMC4942689 DOI: 10.1038/srep29378] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 06/15/2016] [Indexed: 11/29/2022] Open
Abstract
Olfactory cyclic nucleotide-gated (CNG) ion channels are key players in the signal transduction cascade of olfactory sensory neurons. The second messengers cAMP and cGMP directly activate these channels, generating a depolarizing receptor potential. Olfactory CNG channels are composed of two CNGA2 subunits and two modulatory subunits, CNGA4, and CNGB1b. So far the exact role of the modulatory subunits for channel activation is not fully understood. By measuring ligand binding and channel activation simultaneously, we show that in functional heterotetrameric channels not only the CNGA2 subunits and the CNGA4 subunit but also the CNGB1b subunit binds cyclic nucleotides and, moreover, also alone translates this signal to open the pore. In addition, we show that the CNGB1b subunit is the most sensitive subunit in a heterotetrameric channel to cyclic nucleotides and that it accelerates deactivation to a similar extent as does the CNGA4 subunit. In conclusion, the CNGB1b subunit participates in ligand-gated activation of olfactory CNG channels and, particularly, contributes to rapid termination of odorant signal in an olfactory sensory neuron.
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Affiliation(s)
- Vasilica Nache
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Nisa Wongsamitkul
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Jana Kusch
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Thomas Zimmer
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Frank Schwede
- BIOLOG Life Science Institute, Flughafendamm 9A, D-28199 Bremen, Germany
| | - Klaus Benndorf
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
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Canine CNGA3 Gene Mutations Provide Novel Insights into Human Achromatopsia-Associated Channelopathies and Treatment. PLoS One 2015; 10:e0138943. [PMID: 26407004 PMCID: PMC4583268 DOI: 10.1371/journal.pone.0138943] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 09/06/2015] [Indexed: 12/27/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) ion channels are key mediators underlying signal transduction in retinal and olfactory receptors. Genetic defects in CNGA3 and CNGB3, encoding two structurally related subunits of cone CNG channels, lead to achromatopsia (ACHM). ACHM is a congenital, autosomal recessive retinal disorder that manifests by cone photoreceptor dysfunction, severely reduced visual acuity, impaired or complete color blindness and photophobia. Here, we report the first canine models for CNGA3-associated channelopathy caused by R424W or V644del mutations in the canine CNGA3 ortholog that accurately mimic the clinical and molecular features of human CNGA3-associated ACHM. These two spontaneous mutations exposed CNGA3 residues essential for the preservation of channel function and biogenesis. The CNGA3-R424W results in complete loss of cone function in vivo and channel activity confirmed by in vitro electrophysiology. Structural modeling and molecular dynamics (MD) simulations revealed R424-E306 salt bridge formation and its disruption with the R424W mutant. Reversal of charges in a CNGA3-R424E-E306R double mutant channel rescued cGMP-activated currents uncovering new insights into channel gating. The CNGA3-V644del affects the C-terminal leucine zipper (CLZ) domain destabilizing intersubunit interactions of the coiled-coil complex in the MD simulations; the in vitro experiments showed incompetent trimeric CNGA3 subunit assembly consistent with abnormal biogenesis of in vivo channels. These newly characterized large animal models not only provide a valuable system for studying cone-specific CNG channel function in health and disease, but also represent prime candidates for proof-of-concept studies of CNGA3 gene replacement therapy for ACHM patients.
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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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Gofman Y, Schärfe C, Marks DS, Haliloglu T, Ben-Tal N. Structure, dynamics and implied gating mechanism of a human cyclic nucleotide-gated channel. PLoS Comput Biol 2014; 10:e1003976. [PMID: 25474149 PMCID: PMC4256070 DOI: 10.1371/journal.pcbi.1003976] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 10/09/2014] [Indexed: 11/18/2022] Open
Abstract
Cyclic nucleotide-gated (CNG) ion channels are nonselective cation channels, essential for visual and olfactory sensory transduction. Although the channels include voltage-sensor domains (VSDs), their conductance is thought to be independent of the membrane potential, and their gating regulated by cytosolic cyclic nucleotide-binding domains. Mutations in these channels result in severe, degenerative retinal diseases, which remain untreatable. The lack of structural information on CNG channels has prevented mechanistic understanding of disease-causing mutations, precluded structure-based drug design, and hampered in silico investigation of the gating mechanism. To address this, we built a 3D model of the cone tetrameric CNG channel, based on homology to two distinct templates with known structures: the transmembrane (TM) domain of a bacterial channel, and the cyclic nucleotide-binding domain of the mouse HCN2 channel. Since the TM-domain template had low sequence-similarity to the TM domains of the CNG channels, and to reconcile conflicts between the two templates, we developed a novel, hybrid approach, combining homology modeling with evolutionary coupling constraints. Next, we used elastic network analysis of the model structure to investigate global motions of the channel and to elucidate its gating mechanism. We found the following: (i) In the main mode of motion, the TM and cytosolic domains counter-rotated around the membrane normal. We related this motion to gating, a proposition that is supported by previous experimental data, and by comparison to the known gating mechanism of the bacterial KirBac channel. (ii) The VSDs could facilitate gating (supplementing the pore gate), explaining their presence in such 'voltage-insensitive' channels. (iii) Our elastic network model analysis of the CNGA3 channel supports a modular model of allosteric gating, according to which protein domains are quasi-independent: they can move independently, but are coupled to each other allosterically.
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Affiliation(s)
- Yana Gofman
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv, Israel
| | - Charlotta Schärfe
- Center for Bioinformatics, Quantitative Biology Center, and Department of Computer Science, Tübingen University, Tübingen, Germany
- Department of Systems Biology, Harvard University, Boston, Massachusetts, United States of America
| | - Debora S. Marks
- Department of Systems Biology, Harvard University, Boston, Massachusetts, United States of America
| | - Turkan Haliloglu
- Polymer Research Centre and Chemical Engineering Department, Bogazici University, Bebek-Istanbul, Turkey
| | - Nir Ben-Tal
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv, Israel
- * E-mail:
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Zein WM, Jeffrey BG, Wiley HE, Turriff AE, Tumminia SJ, Tao W, Bush RA, Marangoni D, Wen R, Wei LL, Sieving PA. CNGB3-achromatopsia clinical trial with CNTF: diminished rod pathway responses with no evidence of improvement in cone function. Invest Ophthalmol Vis Sci 2014; 55:6301-8. [PMID: 25205868 DOI: 10.1167/iovs.14-14860] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Ciliary neurotrophic factor (CNTF) protects rod photoreceptors from retinal degenerative disease in multiple nonhuman models. Thus far, CNTF has failed to demonstrate rod protection in trials for human retinitis pigmentosa. Recently, CNTF was found to improve cone photoreceptor function in a canine CNGB3 achromatopsia model. This study explores whether this finding translates to humans with CNGB3 achromatopsia. METHODS A five-subject, open-label Phase I/II study was initiated by implanting intraocular microcapsules releasing CNTF (nominally 20 ng/d) into one eye each of CNGB3 achromat participants. Fellow eyes served as untreated controls. Subjects were followed for 1 year. RESULTS Pupil constriction in treated eyes gave evidence of intraocular CNTF release. Additionally, scotopic ERG responses were reduced, and dark-adapted psychophysical absolute thresholds were increased, attributable to diminished rod or rod pathway activity. Optical coherence tomography revealed that the cone-rich fovea underwent structural changes as the foveal hyporeflective zone (HRZ) became diminished in CNTF-treated eyes. No objectively measurable enhancement of cone function was found by assessments of visual acuity, mesopic increment sensitivity threshold, or the photopic ERG. Careful measurements of color hue discrimination showed no change. Nonetheless, subjects reported beneficial changes of visual function in the treated eyes, including reduced light sensitivity and aversion to bright light, which may trace to decreased effective ambient light from the pupillary constriction; further they noted slowed adaptation to darkness, consistent with CNTF action on rod photoreceptors. CONCLUSIONS Ciliary neurotrophic factor did not measurably enhance cone function, which reveals a species difference between human and canine CNGB3 cones in response to CNTF. (ClinicalTrials.gov number, NCT01648452.).
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Affiliation(s)
- Wadih M Zein
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Brett G Jeffrey
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Henry E Wiley
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Amy E Turriff
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Santa J Tumminia
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Weng Tao
- Neurotech Pharmaceuticals, Inc., Cumberland, Rhode Island, United States
| | - Ronald A Bush
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, United States
| | - Dario Marangoni
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, United States Department of Biotechnology and Applied Clinical Science, University of L'Aquila, L'Aquila, Italy
| | - Rong Wen
- Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami, Miller School of Medicine, Miami, Florida, United States
| | - Lisa L Wei
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
| | - Paul A Sieving
- National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, United States
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Homozygous missense variant in the human CNGA3 channel causes cone-rod dystrophy. Eur J Hum Genet 2014; 23:473-80. [PMID: 25052312 DOI: 10.1038/ejhg.2014.136] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Revised: 06/06/2014] [Accepted: 06/18/2014] [Indexed: 12/30/2022] Open
Abstract
We assessed a large consanguineous Pakistani family (PKAB157) segregating early onset low vision problems. Funduscopic and electroretinographic evaluation of affected individuals revealed juvenile cone-rod dystrophy (CRD) with maculopathy. Other clinical symptoms included loss of color discrimination, photophobia and nystagmus. Whole-exome sequencing, segregation and haplotype analyses demonstrated that a transition variant (c.955T>C; p.(Cys319Arg)) in CNGA3 co-segregated with the CRD phenotype in family PKAB157. The ability of CNGA3 channel to influx calcium in response to agonist, when expressed either alone or together with the wild-type CNGB3 subunit in HEK293 cells, was completely abolished due to p.Cys319Arg variant. Western blotting and immunolocalization studies suggest that a decreased channel density in the HEK293 cell membrane due to impaired folding and/or trafficking of the CNGA3 protein is the main pathogenic effect of the p.Cys319Arg variant. Mutant alleles of the human cone photoreceptor cyclic nucleotide-gated channel (CNGA3) are frequently associated with achromatopsia. In rare cases, variants in CNGA3 are also associated with cone dystrophy, Leber's congenital amaurosis and oligo cone trichromacy. The identification of predicted p.(Cys319Arg) missense variant in CNGA3 expands the repertoire of the known genetic causes of CRD and phenotypic spectrum of CNGA3 alleles.
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Dai G, Sherpa T, Varnum MD. Alternative splicing governs cone cyclic nucleotide-gated (CNG) channel sensitivity to regulation by phosphoinositides. J Biol Chem 2014; 289:13680-90. [PMID: 24675082 DOI: 10.1074/jbc.m114.562272] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Precursor mRNA encoding CNGA3 subunits of cone photoreceptor cyclic nucleotide-gated (CNG) channels undergoes alternative splicing, generating isoforms differing in the N-terminal cytoplasmic region of the protein. In humans, four variants arise from alternative splicing, but the functional significance of these changes has been a persistent mystery. Heterologous expression of the four possible CNGA3 isoforms alone or with CNGB3 subunits did not reveal significant differences in basic channel properties. However, inclusion of optional exon 3, with or without optional exon 5, produced heteromeric CNGA3 + CNGB3 channels exhibiting an ∼2-fold greater shift in K1/2,cGMP after phosphatidylinositol 4,5-biphosphate or phosphatidylinositol 3,4,5-trisphosphate application compared with channels lacking the sequence encoded by exon 3. We have previously identified two structural features within CNGA3 that support phosphoinositides (PIPn) regulation of cone CNG channels: N- and C-terminal regulatory modules. Specific mutations within these regions eliminated PIPn sensitivity of CNGA3 + CNGB3 channels. The exon 3 variant enhanced the component of PIPn regulation that depends on the C-terminal region rather than the nearby N-terminal region, consistent with an allosteric effect on PIPn sensitivity because of altered N-C coupling. Alternative splicing of CNGA3 occurs in multiple species, although the exact variants are not conserved across CNGA3 orthologs. Optional exon 3 appears to be unique to humans, even compared with other primates. In parallel, we found that a specific splice variant of canine CNGA3 removes a region of the protein that is necessary for high sensitivity to PIPn. CNGA3 alternative splicing may have evolved, in part, to tune the interactions between cone CNG channels and membrane-bound phosphoinositides.
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Affiliation(s)
- Gucan Dai
- From the Department of Integrative Physiology and Neuroscience
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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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Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Catterall WA, Spedding M, Peters JA, Harmar AJ. The Concise Guide to PHARMACOLOGY 2013/14: ion channels. Br J Pharmacol 2013; 170:1607-51. [PMID: 24528239 PMCID: PMC3892289 DOI: 10.1111/bph.12447] [Citation(s) in RCA: 224] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Ion channels are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
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Affiliation(s)
- Stephen PH Alexander
- School of Life Sciences, University of Nottingham Medical SchoolNottingham, NG7 2UH, UK
- *
Author for correspondence;
| | - Helen E Benson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Elena Faccenda
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Adam J Pawson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Joanna L Sharman
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - William A Catterall
- University of Washington, School of Medicine, Department of PharmacologyBox 357280, Seattle, WA 98195-7280, USA
| | | | - John A Peters
- Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of DundeeDundee, DD1 9SY, UK
| | - Anthony J Harmar
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
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Meighan SE, Meighan PC, Rich ED, Brown RL, Varnum MD. Cyclic nucleotide-gated channel subunit glycosylation regulates matrix metalloproteinase-dependent changes in channel gating. Biochemistry 2013; 52:8352-62. [PMID: 24164424 DOI: 10.1021/bi400824x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Cyclic-nucleotide gated (CNG) channels are essential for phototransduction within retinal photoreceptors. We have demonstrated previously that the enzymatic activity of matrix metalloproteinase-2 and -9, members of the matrix metalloproteinase (MMP) family of extracellular, Ca(2+)- and Zn(2+)-dependent proteases, enhances the ligand sensitivity of both rod (CNGA1 and CNGB1) and cone (CNGA3 and CNGB3) CNG channels. Additionally, we have observed a decrease in the maximal CNG channel current (Imax) that begins late during MMP-directed gating changes. Here we demonstrate that CNG channels become nonconductive after prolonged MMP exposure. Concurrent with the loss of conductive channels is the increased relative contribution of channels exhibiting nonmodified gating properties, suggesting the presence of a subpopulation of channels that are protected from MMP-induced gating effects. CNGA subunits are known to possess one extracellular core glycosylation site, located at one of two possible positions within the turret loop near the pore-forming region. Our results indicate that CNGA glycosylation can impede MMP-dependent modification of CNG channels. Furthermore, the relative position of the glycosylation site within the pore turret influences the extent of MMP-dependent proteolysis. Glycosylation at the site found in CNGA3 subunits was found to be protective, while glycosylation at the bovine CNGA1 site was not. Relocating the glycosylation site in CNGA1 to the position found in CNGA3 recapitulated CNGA3-like protection from MMP-dependent processing. Taken together, these data indicate that CNGA glycosylation may protect CNG channels from MMP-dependent proteolysis, consistent with MMP modification of channel function having a requirement for physical access to the extracellular face of the channel.
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Affiliation(s)
- Starla E Meighan
- Program in Neuroscience, Department of Integrative Physiology and Neuroscience, ‡WWAMI Medical Education Program, and §Center for Integrated Biotechnology, Washington State University , P.O. Box 647620, Pullman, Washington 99164, United States
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Podda MV, Grassi C. New perspectives in cyclic nucleotide-mediated functions in the CNS: the emerging role of cyclic nucleotide-gated (CNG) channels. Pflugers Arch 2013; 466:1241-57. [PMID: 24142069 DOI: 10.1007/s00424-013-1373-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Revised: 09/27/2013] [Accepted: 09/28/2013] [Indexed: 01/07/2023]
Abstract
Cyclic nucleotides play fundamental roles in the central nervous system (CNS) under both physiological and pathological conditions. The impact of cAMP and cGMP signaling on neuronal and glial cell functions has been thoroughly characterized. Most of their effects have been related to cyclic nucleotide-dependent protein kinase activity. However, cyclic nucleotide-gated (CNG) channels, first described as key mediators of sensory transduction in retinal and olfactory receptors, have been receiving increasing attention as possible targets of cyclic nucleotides in the CNS. In the last 15 years, consistent evidence has emerged for their expression in neurons and astrocytes of the rodent brain. Far less is known, however, about the functional role of CNG channels in these cells, although several of their features, such as Ca(2+) permeability and prolonged activation in the presence of cyclic nucleotides, make them ideal candidates for mediators of physiological functions in the CNS. Here, we review literature suggesting the involvement of CNG channels in a number of CNS cellular functions (e.g., regulation of membrane potential, neuronal excitability, and neurotransmitter release) as well as in more complex phenomena, like brain plasticity, adult neurogenesis, and pain sensitivity. The emerging picture is that functional and dysfunctional cyclic nucleotide signaling in the CNS has to be reconsidered including CNG channels among possible targets. However, concerted efforts and multidisciplinary approaches are still needed to get more in-depth knowledge in this field.
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Affiliation(s)
- Maria Vittoria Podda
- Institute of Human Physiology, Medical School, Università Cattolica, Largo Francesco Vito 1, 00168, Rome, Italy
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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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38
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Evolution of phototransduction, vertebrate photoreceptors and retina. Prog Retin Eye Res 2013; 36:52-119. [DOI: 10.1016/j.preteyeres.2013.06.001] [Citation(s) in RCA: 257] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 06/02/2013] [Indexed: 01/12/2023]
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Schön C, Biel M, Michalakis S. Gene replacement therapy for retinal CNG channelopathies. Mol Genet Genomics 2013; 288:459-67. [DOI: 10.1007/s00438-013-0766-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 06/25/2013] [Indexed: 12/20/2022]
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Abdel-Hamid H, Chin K, Moeder W, Shahinas D, Gupta D, Yoshioka K. A suppressor screen of the chimeric AtCNGC11/12 reveals residues important for intersubunit interactions of cyclic nucleotide-gated ion channels. PLANT PHYSIOLOGY 2013; 162:1681-93. [PMID: 23735507 PMCID: PMC3707543 DOI: 10.1104/pp.113.217539] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Accepted: 06/01/2013] [Indexed: 05/23/2023]
Abstract
To investigate the structure-function relationship of plant cyclic nucleotide-gated ion channels (CNGCs), we identified a total of 29 mutant alleles of the chimeric AtCNGC11/12 gene that induces multiple defense responses in the Arabidopsis (Arabidopsis thaliana) mutant, constitutive expresser of PR genes22 (cpr22). Based on computational modeling, two new alleles, S100 (AtCNGC11/12:G459R) and S137 (AtCNGC11/12:R381H), were identified as counterparts of human CNGA3 (a human CNGC) mutants. Both mutants lost all cpr22-mediated phenotypes. Transient expression in Nicotiana benthamiana as well as functional complementation in yeast (Saccharomyces cerevisiae) showed that both AtCNGC11/12:G459R and AtCNGC11/12:R381H have alterations in their channel function. Site-directed mutagenesis coupled with fast-protein liquid chromatography using recombinantly expressed C-terminal peptides indicated that both mutations significantly influence subunit stoichiometry to form multimeric channels. This observation was confirmed by bimolecular fluorescence complementation in planta. Taken together, we have identified two residues that are likely important for subunit interaction for plant CNGCs and likely for animal CNGCs as well.
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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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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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Herguedas B, Krieger J, Greger IH. Receptor Heteromeric Assembly—How It Works and Why It Matters. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 117:361-86. [DOI: 10.1016/b978-0-12-386931-9.00013-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Abstract
Photoreceptors are exquisitely adapted to transform light stimuli into electrical signals that modulate neurotransmitter release. These cells are organized into several compartments including the unique outer segment (OS). Its whole function is to absorb light and transduce this signal into a change of membrane potential. Another compartment is the inner segment where much of metabolism and regulation of membrane potential takes place and that connects the OS and synapse. The synapse is the compartment where changes in membrane potentials are relayed to other neurons in the retina via release of neurotransmitter. The composition of the plasma membrane surrounding these compartments varies to accommodate their specific functions. In this chapter, we discuss the organization of the plasma membrane emphasizing the protein composition of each region as it relates to visual signaling. We also point out examples where mutations in these proteins cause visual impairment.
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Affiliation(s)
- Sheila A Baker
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA.
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Chen J, Sampath AP. Structure and Function of Rod and Cone Photoreceptors. Retina 2013. [DOI: 10.1016/b978-1-4557-0737-9.00014-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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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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Nache V, Zimmer T, Wongsamitkul N, Schmauder R, Kusch J, Reinhardt L, Bönigk W, Seifert R, Biskup C, Schwede F, Benndorf K. Differential regulation by cyclic nucleotides of the CNGA4 and CNGB1b subunits in olfactory cyclic nucleotide-gated channels. Sci Signal 2012; 5:ra48. [PMID: 22786723 DOI: 10.1126/scisignal.2003110] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Olfactory cyclic nucleotide-gated (CNG) ion channels are essential contributors to signal transduction of olfactory sensory neurons. The activity of the channels is controlled by the cyclic nucleotides guanosine 3',5'-monophosphate (cGMP) and adenosine 3',5'-monophosphate (cAMP). The olfactory CNG channels are composed of two CNGA2 subunits, one CNGA4 and one CNGB1b subunit, each containing a cyclic nucleotide-binding domain. Using patch-clamp fluorometry, we measured ligand binding and channel activation simultaneously and showed that cGMP activated olfactory CNG channels not only by binding to the two CNGA2 subunits but also by binding to the CNGA4 subunit. In a channel in which the CNGA2 subunits were compromised for ligand binding, cGMP binding to CNGA4 was sufficient to partly activate the channel. In contrast, in heterotetrameric channels, the CNGB1b subunit did not bind cGMP, but channels with this subunit showed activation by cAMP. Thus, the modulatory subunits participate actively in translating ligand binding to activation of heterotetrameric olfactory CNG channels and enable the channels to differentiate between cyclic nucleotides.
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Affiliation(s)
- Vasilica Nache
- Institute of Physiology II, University Hospital Jena, Friedrich-Schiller-University Jena, D-07740 Jena, Germany
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Meighan PC, Meighan SE, Rich ED, Brown RL, Varnum MD. Matrix metalloproteinase-9 and -2 enhance the ligand sensitivity of photoreceptor cyclic nucleotide-gated channels. Channels (Austin) 2012; 6:181-96. [PMID: 22699690 PMCID: PMC3431585 DOI: 10.4161/chan.20904] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Photoreceptor cyclic nucleotide-gated (CNG) channels are the principal ion channels responsible for transduction of the light-induced change in cGMP concentration into an electrical signal. The ligand sensitivity of photoreceptor CNG channels is subject to regulation by intracellular signaling effectors, including calcium-calmodulin, tyrosine kinases and phosphoinositides. Little is known, however, about regulation of channel activity by modification to extracellular regions of CNG channel subunits. Extracellular proteases MMP9 and -2 are present in the interphotoreceptor matrix adjacent to photoreceptor outer segments. Given that MMPs have been implicated in retinal dysfunction and degeneration, we hypothesized that MMP activity may alter the functional properties of photoreceptor CNG channels. For heterologously expressed rod and cone CNG channels, extracellular exposure to MMPs dramatically increased the apparent affinity for cGMP and the efficacy of cAMP. These changes to ligand sensitivity were not prevented by destabilization of the actin cytoskeleton or by disruption of integrin mediated cell adhesion, but could be attenuated by inhibition of MMP catalytic activity. MMP-mediated gating changes exhibited saturable kinetic properties consistent with enzymatic processing of the CNG channels. In addition, exposure to MMPs decreased the abundance of full-length expressed CNGA3 subunits, with a concomitant increase in putative degradation products. Similar gating effects and apparent proteolysis were observed also for native rod photoreceptor CNG channels. Furthermore, constitutive apparent proteolysis of retinal CNGA1 and retinal MMP9 levels were both elevated in aged mice compared with young mice. Together, these results provide evidence that MMP-mediated proteolysis can regulate the ligand sensitivity of CNG channels.
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Affiliation(s)
- Peter C Meighan
- Department of Veterinary and Comparative Anatomy, Program in Neuroscience, Washington State University, Pullman, USA
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AAV-mediated cone rescue in a naturally occurring mouse model of CNGA3-achromatopsia. PLoS One 2012; 7:e35250. [PMID: 22509403 PMCID: PMC3324465 DOI: 10.1371/journal.pone.0035250] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Accepted: 03/12/2012] [Indexed: 12/22/2022] Open
Abstract
Achromatopsia is a rare autosomal recessive disorder which shows color blindness, severely impaired visual acuity, and extreme sensitivity to bright light. Mutations in the alpha subunits of the cone cyclic nucleotide-gated channels (CNGA3) are responsible for about 1/4 of achromatopsia in the U.S. and Europe. Here, we test whether gene replacement therapy using an AAV5 vector could restore cone-mediated function and arrest cone degeneration in the cpfl5 mouse, a naturally occurring mouse model of achromatopsia with a CNGA3 mutation. We show that gene therapy leads to significant rescue of cone-mediated ERGs, normal visual acuities and contrast sensitivities. Normal expression and outer segment localization of both M- and S-opsins were maintained in treated retinas. The therapeutic effect of treatment lasted for at least 5 months post-injection. This study is the first demonstration of substantial, relatively long-term restoration of cone-mediated light responsiveness and visual behavior in a naturally occurring mouse model of CNGA3 achromatopsia. The results provide the foundation for development of an AAV5-based gene therapy trial for human CNGA3 achromatopsia.
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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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