1
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Heigl T, Netzer MA, Zanetti L, Ganglberger M, Fernández-Quintero ML, Koschak A. Characterization of two pathological gating-charge substitutions in Cav1.4 L-type calcium channels. Channels (Austin) 2023; 17:2192360. [PMID: 36943941 PMCID: PMC10038055 DOI: 10.1080/19336950.2023.2192360] [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: 11/07/2022] [Accepted: 03/14/2023] [Indexed: 03/23/2023] Open
Abstract
Cav1.4 L-type calcium channels are predominantly expressed at the photoreceptor terminals and in bipolar cells, mediating neurotransmitter release. Mutations in its gene, CACNA1F, can cause congenital stationary night-blindness type 2 (CSNB2). Due to phenotypic variability in CSNB2, characterization of pathological variants is necessary to better determine pathological mechanism at the site of action. A set of known mutations affects conserved gating charges in the S4 voltage sensor, two of which have been found in male CSNB2 patients. Here, we describe two disease-causing Cav1.4 mutations with gating charge neutralization, exchanging an arginine 964 with glycine (RG) or arginine 1288 with leucine (RL). In both, charge neutralization was associated with a reduction channel expression also reflected in smaller ON gating currents. In RL channels, the strong decrease in whole-cell current densities might additionally be explained by a reduction of single-channel currents. We further identified alterations in their biophysical properties, such as a hyperpolarizing shift of the activation threshold and an increase in slope factor of activation and inactivation. Molecular dynamic simulations in RL substituted channels indicated water wires in both, resting and active, channel states, suggesting the development of omega (ω)currents as a new pathological mechanism in CSNB2. This sum of the respective channel property alterations might add to the differential symptoms in patients beside other factors, such as genomic and environmental deviations.
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Affiliation(s)
- Thomas Heigl
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Innsbruck, Austria
| | - Michael A. Netzer
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Innsbruck, Austria
| | - Lucia Zanetti
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Innsbruck, Austria
| | - Matthias Ganglberger
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Innsbruck, Austria
| | - Monica L. Fernández-Quintero
- Institute of General, Inorganic and Theoretical Chemistry, Center for Chemistry and Biomedicine, University of Innsbruck, Innsbruck, Austria
- Division of Pharmacology and Toxicology, Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | - Alexandra Koschak
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Innsbruck, Austria
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2
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Muangkram Y, Himeno Y, Amano A. Clarifying the composition of the ATP consumption factors required for maintaining ion homeostasis in mouse rod photoreceptors. Sci Rep 2023; 13:14161. [PMID: 37644037 PMCID: PMC10465610 DOI: 10.1038/s41598-023-40663-y] [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: 04/11/2023] [Accepted: 08/16/2023] [Indexed: 08/31/2023] Open
Abstract
To date, no effective treatment has been established for photoreceptor loss due to energy imbalances, but numerous therapeutic approaches have reported some success in slowing photoreceptor degeneration by downregulating energy demand. However, the detailed mechanisms remain unclear. This study aimed to clarify the composition of ATP consumption factors in photoreceptors in darkness and in light. We introduced mathematical formulas for ionic current activities combined with a phototransduction model to form a new mathematical model for estimating the energy expenditure of each ionic current. The proposed model included various ionic currents identified in mouse rods using a gene expression database incorporating an available electrophysiological recording of each specific gene. ATP was mainly consumed by Na+/K+-ATPase and plasma membrane Ca2+-ATPase pumps to remove excess Na+ and Ca2+. The rod consumed 7 [Formula: see text] 107 molecules of ATP s-1, where 65% was used to remove ions from the cyclic nucleotide-gated channel and 20% from the hyperpolarization-activated current in darkness. Increased light intensity raised the energy requirements of the complex phototransduction cascade mechanisms. Nevertheless, the overall energy consumption was less than that in darkness due to the significant reduction in ATPase activities, where the hyperpolarization-activated current proportion increased to 83%. A better understanding of energy demand/supply may provide an effective tool for investigating retinal pathophysiological changes and analyzing novel therapeutic treatments related to the energy consumption of photoreceptors.
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Affiliation(s)
- Yuttamol Muangkram
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga, Japan.
| | - Yukiko Himeno
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga, Japan
| | - Akira Amano
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga, Japan
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3
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Laird JG, Kopel A, Lankford CK, Baker SA. Mouse all-cone retina models of Cav1.4 synaptopathy. Front Mol Neurosci 2023; 16:1155955. [PMID: 37181655 PMCID: PMC10174292 DOI: 10.3389/fnmol.2023.1155955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 04/03/2023] [Indexed: 05/16/2023] Open
Abstract
The voltage-gated calcium channel, Cav1.4 is localized to photoreceptor ribbon synapses and functions both in molecular organization of the synapse and in regulating release of synaptic vesicles. Mutations in Cav1.4 subunits typically present as either incomplete congenital stationary night blindness or a progressive cone-rod dystrophy in humans. We developed a cone-rich mammalian model system to further study how different Cav1.4 mutations affect cones. RPE65 R91W KI; Nrl KO "Conefull" mice were crossed to Cav1.4 α1F or α2δ4 KO mice to generate the "Conefull:α1F KO" and "Conefull:α2δ4 KO" lines. Animals were assessed using a visually guided water maze, electroretinogram (ERG), optical coherence tomography (OCT), and histology. Mice of both sexes and up to six-months of age were used. Conefull: α1F KO mice could not navigate the visually guided water maze, had no b-wave in the ERG, and the developing all-cone outer nuclear layer reorganized into rosettes at the time of eye opening with degeneration progressing to 30% loss by 2-months of age. In comparison, the Conefull: α2δ4 KO mice successfully navigated the visually guided water maze, had a reduced amplitude b-wave ERG, and the development of the all-cone outer nuclear layer appeared normal although progressive degeneration with 10% loss by 2-months of age was observed. In summary, new disease models for studying congenital synaptic diseases due to loss of Cav1.4 function have been created.
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Affiliation(s)
| | | | | | - Sheila A. Baker
- Department of Biochemistry and Molecular Biology, University of Iowa, Iowa City, IA, United States
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4
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Seitter H, Obkircher J, Grabher P, Hartl J, Zanetti L, Lux UT, Fotakis G, Fernández-Quintero ML, Kaserer T, Koschak A. A novel calcium channel Cavβ 2 splice variant with unique properties predominates in the retina. J Biol Chem 2023; 299:102972. [PMID: 36738788 PMCID: PMC10074810 DOI: 10.1016/j.jbc.2023.102972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 01/15/2023] [Accepted: 01/17/2023] [Indexed: 02/05/2023] Open
Abstract
Cavβ subunits are essential for surface expression of voltage-gated calcium channel complexes and crucially modulate biophysical properties like voltage-dependent inactivation. Here, we describe the discovery and characterization of a novel Cavβ2 variant with distinct features that predominates in the retina. We determined spliced exons in retinal transcripts of the Cacnb2 gene, coding for Cavβ2, by RNA-Seq data analysis and quantitative PCR. We cloned a novel Cavβ2 splice variant from mouse retina, which we are calling β2i, and investigated biophysical properties of calcium currents with this variant in a heterologous expression system as well as its intrinsic membrane interaction when expressed alone. Our data showed that β2i predominated in the retina with expression in photoreceptors and bipolar cells. Furthermore, we observed that the β2i N-terminus exhibited an extraordinary concentration of hydrophobic residues, a distinct feature not seen in canonical variants. The biophysical properties resembled known membrane-associated variants, and β2i exhibited both a strong membrane association and a propensity for clustering, which depended on hydrophobic residues in its N-terminus. We considered available Cavβ structure data to elucidate potential mechanisms underlying the observed characteristics but resolved N-terminus structures were lacking and thus, precluded clear conclusions. With this description of a novel N-terminus variant of Cavβ2, we expand the scope of functional variation through N-terminal splicing with a distinct form of membrane attachment. Further investigation of the molecular mechanisms underlying the features of β2i could provide new angles on the way Cavβ subunits modulate Ca2+ channels at the plasma membrane.
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Affiliation(s)
- Hartwig Seitter
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria.
| | - Jana Obkircher
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria
| | - Patricia Grabher
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria
| | - Julia Hartl
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria
| | - Lucia Zanetti
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria
| | - Uwe Thorsten Lux
- Department of Biology, Animal Physiology/Neurobiology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Georgios Fotakis
- Institute of Bioinformatics, Medical University of Innsbruck, Innsbruck, Austria
| | | | - Teresa Kaserer
- Department of Pharmaceutical Chemistry, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria
| | - Alexandra Koschak
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria.
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5
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Hessenberger M, Haddad S, Obermair GJ. Pathophysiological Roles of Auxiliary Calcium Channel α 2δ Subunits. Handb Exp Pharmacol 2023; 279:289-316. [PMID: 36598609 DOI: 10.1007/164_2022_630] [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] [Indexed: 01/05/2023]
Abstract
α2δ proteins serve as auxiliary subunits of voltage-gated calcium channels, which are essential components of excitable cells such as skeletal and heart muscles, nerve cells of the brain and the peripheral nervous system, as well as endocrine cells. Over the recent years, α2δ proteins have been identified as critical regulators of synaptic functions, including the formation and differentiation of synapses. These functions require signalling mechanisms which are partly independent of calcium channels. Hence, in light of these features it is not surprising that the genes encoding for the four α2δ isoforms have recently been linked to neurological and neurodevelopmental disorders including epilepsy, autism spectrum disorders, schizophrenia, and depressive and bipolar disorders. Despite the increasing number of identified disease-associated mutations, the underlying pathophysiological mechanisms are only beginning to emerge. However, a thorough understanding of the pathophysiological role of α2δ proteins ideally serves two purposes: first, it will contribute to our understanding of general pathological mechanisms in synaptic disorders. Second, it may support the future development of novel and specific treatments for brain disorders. In this context, it is noteworthy that the antiepileptic and anti-allodynic drugs gabapentin and pregabalin both act via binding to α2δ proteins and are among the top sold drugs for treating neuropathic pain. In this book chapter, we will discuss recent developments in our understanding of the functions of α2δ proteins, both as calcium channel subunits and as independent regulatory entities. Furthermore, we present and summarize recently identified and likely pathogenic mutations in the genes encoding α2δ proteins and discuss potential underlying pathophysiological consequences at the molecular and structural level.
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Affiliation(s)
- Manuel Hessenberger
- Division Physiology, Department Pharmacology, Physiology and Microbiology, Karl Landsteiner University of Health Sciences, Krems, Austria
| | - Sabrin Haddad
- Division Physiology, Department Pharmacology, Physiology and Microbiology, Karl Landsteiner University of Health Sciences, Krems, Austria
- Institute of Physiology, Medical University of Innsbruck, Innsbruck, Austria
| | - Gerald J Obermair
- Division Physiology, Department Pharmacology, Physiology and Microbiology, Karl Landsteiner University of Health Sciences, Krems, Austria.
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6
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Abstract
Voltage-gated Ca2+ (Cav) channels play pivotal roles in regulating gene transcription, neuronal excitability, and neurotransmitter release. To meet the spatial and temporal demands of visual signaling, Cav channels exhibit unusual properties in the retina compared to their counterparts in other areas of the nervous system. In this article, we review current concepts regarding the specific subtypes of Cav channels expressed in the retina, their intrinsic properties and forms of modulation, and how their dysregulation could lead to retinal disease.
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Affiliation(s)
- Brittany Williams
- Department of Cell Biology & Physiology, Carolina Institute for Developmental Disabilities, and Neuroscience Center, University of North Carolina, Chapel Hill, North Carolina, USA
| | - J Wesley Maddox
- Department of Neuroscience, University of Texas, Austin, Texas, USA;
| | - Amy Lee
- Department of Neuroscience, University of Texas, Austin, Texas, USA;
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7
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Ablinger C, Eibl C, Geisler SM, Campiglio M, Stephens GJ, Missler M, Obermair GJ. α 2δ-4 and Cachd1 Proteins Are Regulators of Presynaptic Functions. Int J Mol Sci 2022; 23:9885. [PMID: 36077281 PMCID: PMC9456004 DOI: 10.3390/ijms23179885] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 08/15/2022] [Accepted: 08/24/2022] [Indexed: 11/17/2022] Open
Abstract
The α2δ auxiliary subunits of voltage-gated calcium channels (VGCC) were traditionally regarded as modulators of biophysical channel properties. In recent years, channel-independent functions of these subunits, such as involvement in synapse formation, have been identified. In the central nervous system, α2δ isoforms 1, 2, and 3 are strongly expressed, regulating glutamatergic synapse formation by a presynaptic mechanism. Although the α2δ-4 isoform is predominantly found in the retina with very little expression in the brain, it was recently linked to brain functions. In contrast, Cachd1, a novel α2δ-like protein, shows strong expression in brain, but its function in neurons is not yet known. Therefore, we aimed to investigate the presynaptic functions of α2δ-4 and Cachd1 by expressing individual proteins in cultured hippocampal neurons. Both α2δ-4 and Cachd1 are expressed in the presynaptic membrane and could rescue a severe synaptic defect present in triple knockout/knockdown neurons that lacked the α2δ-1-3 isoforms (α2δ TKO/KD). This observation suggests that presynaptic localization and the regulation of synapse formation in glutamatergic neurons is a general feature of α2δ proteins. In contrast to this redundant presynaptic function, α2δ-4 and Cachd1 differentially regulate the abundance of presynaptic calcium channels and the amplitude of presynaptic calcium transients. These functional differences may be caused by subtle isoform-specific differences in α1-α2δ protein-protein interactions, as revealed by structural homology modelling. Taken together, our study identifies both α2δ-4 and Cachd1 as presynaptic regulators of synapse formation, differentiation, and calcium channel functions that can at least partially compensate for the loss of α2δ-1-3. Moreover, we show that regulating glutamatergic synapse formation and differentiation is a critical and surprisingly redundant function of α2δ and Cachd1.
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Affiliation(s)
- Cornelia Ablinger
- Institute of Physiology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Clarissa Eibl
- Division Physiology, Department of Pharmacology, Physiology and Microbiology, Karl Landsteiner University of Health Sciences, 3500 Krems, Austria
| | - Stefanie M. Geisler
- Department Pharmacology and Toxicology, University of Innsbruck, 6020 Innsbruck, Austria
| | - Marta Campiglio
- Institute of Physiology, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Gary J. Stephens
- Reading School of Pharmacy, University of Reading, Reading RG6 6UB, UK
| | - Markus Missler
- Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, 48149 Münster, Germany
| | - Gerald J. Obermair
- Institute of Physiology, Medical University Innsbruck, 6020 Innsbruck, Austria
- Division Physiology, Department of Pharmacology, Physiology and Microbiology, Karl Landsteiner University of Health Sciences, 3500 Krems, Austria
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8
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Koschak A, Fernandez-Quintero ML, Heigl T, Ruzza M, Seitter H, Zanetti L. Cav1.4 dysfunction and congenital stationary night blindness type 2. Pflugers Arch 2021; 473:1437-1454. [PMID: 34212239 PMCID: PMC8370969 DOI: 10.1007/s00424-021-02570-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Revised: 04/14/2021] [Accepted: 04/18/2021] [Indexed: 12/04/2022]
Abstract
Cav1.4 L-type Ca2+ channels are predominantly expressed in retinal neurons, particularly at the photoreceptor terminals where they mediate sustained Ca2+ entry needed for continuous neurotransmitter release at their ribbon synapses. Cav1.4 channel gating properties are controlled by accessory subunits, associated regulatory proteins, and also alternative splicing. In humans, mutations in the CACNA1F gene encoding for Cav1.4 channels are associated with X-linked retinal disorders such as congenital stationary night blindness type 2. Mutations in the Cav1.4 protein result in a spectrum of altered functional channel activity. Several mouse models broadened our understanding of the role of Cav1.4 channels not only as Ca2+ source at retinal synapses but also as synaptic organizers. In this review, we highlight different structural and functional phenotypes of Cav1.4 mutations that might also occur in patients with congenital stationary night blindness type 2. A further important yet mostly neglected aspect that we discuss is the influence of alternative splicing on channel dysfunction. We conclude that currently available functional phenotyping strategies should be refined and summarize potential specific therapeutic options for patients carrying Cav1.4 mutations. Importantly, the development of new therapeutic approaches will permit a deeper understanding of not only the disease pathophysiology but also the physiological function of Cav1.4 channels in the retina.
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MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Animals
- Calcium Channel Agonists/pharmacology
- Calcium Channels, L-Type/genetics
- Calcium Channels, L-Type/metabolism
- Eye Diseases, Hereditary/genetics
- Eye Diseases, Hereditary/metabolism
- Genetic Diseases, X-Linked/genetics
- Genetic Diseases, X-Linked/metabolism
- Humans
- Mutation/physiology
- Myopia/genetics
- Myopia/metabolism
- Night Blindness/genetics
- Night Blindness/metabolism
- Retina/drug effects
- Retina/metabolism
- Synapses/drug effects
- Synapses/genetics
- Synapses/metabolism
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Affiliation(s)
- Alexandra Koschak
- Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82/III, 6020, Innsbruck, Austria.
| | - Monica L Fernandez-Quintero
- Institute of General, Inorganic and Theoretical Chemistry, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82/III, 6020, Innsbruck, Austria
| | - Thomas Heigl
- Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82/III, 6020, Innsbruck, Austria
| | - Marco Ruzza
- Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82/III, 6020, Innsbruck, Austria
| | - Hartwig Seitter
- Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82/III, 6020, Innsbruck, Austria
| | - Lucia Zanetti
- Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82/III, 6020, Innsbruck, Austria
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Rashwan R, Hunt DM, Carvalho LS. The role of voltage-gated ion channels in visual function and disease in mammalian photoreceptors. Pflugers Arch 2021; 473:1455-1468. [PMID: 34255151 DOI: 10.1007/s00424-021-02595-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 05/31/2021] [Accepted: 06/10/2021] [Indexed: 12/26/2022]
Abstract
Light activation of the classical light-sensing retinal neurons, the photoreceptors, results in a graded change in membrane potential that ultimately leads to a reduction in neurotransmitter release to the post-synaptic retinal neurons. Photoreceptors show striking powers of adaptation, and for visual processing to function optimally, they must adjust their gain to remain responsive to different levels of ambient light intensity. The presence of a tightly controlled balance of inward and outward currents modulated by several different types of ion channels is what gives photoreceptors their remarkably dynamic operating range. Part of the resetting and modulation of this operating range is controlled by potassium and calcium voltage-gated channels, which are involved in setting the dark resting potential and synapse signal processing, respectively. Their essential contribution to visual processing is further confirmed in patients suffering from cone dystrophy with supernormal rod response (CDSRR) and congenital stationary night blindness type 2 (CSNB2), both conditions that lead to irreversible vision loss. This review will discuss these two types of voltage-gated ion channels present in photoreceptors, focussing on their structure and physiology, and their role in visual processing. It will also discuss the use and benefits of knockout mouse models to further study the function of these channels and what routes to potential treatments could be applied for CDSRR and CSNB2.
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Affiliation(s)
- Rabab Rashwan
- Lions Eye Institute, Nedlands, Western Australia, 6009, Australia
- Department of Microbiology and Immunology, Faculty of Medicine, Minia University, Minia, Egypt
| | - David M Hunt
- Lions Eye Institute, Nedlands, Western Australia, 6009, Australia
- Centre for Ophthalmology and Vision Science, The University of Western Australia, Perth, Western Australia, 6009, Australia
- School of Biological Sciences, University of Western Australia, Nedlands, Western Australia, 6009, Australia
| | - Livia S Carvalho
- Lions Eye Institute, Nedlands, Western Australia, 6009, Australia.
- Centre for Ophthalmology and Vision Science, The University of Western Australia, Perth, Western Australia, 6009, Australia.
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10
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Kessi M, Chen B, Peng J, Yan F, Yang L, Yin F. Calcium channelopathies and intellectual disability: a systematic review. Orphanet J Rare Dis 2021; 16:219. [PMID: 33985586 PMCID: PMC8120735 DOI: 10.1186/s13023-021-01850-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Accepted: 05/04/2021] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Calcium ions are involved in several human cellular processes including corticogenesis, transcription, and synaptogenesis. Nevertheless, the relationship between calcium channelopathies (CCs) and intellectual disability (ID)/global developmental delay (GDD) has been poorly investigated. We hypothesised that CCs play a major role in the development of ID/GDD and that both gain- and loss-of-function variants of calcium channel genes can induce ID/GDD. As a result, we performed a systematic review to investigate the contribution of CCs, potential mechanisms underlying their involvement in ID/GDD, advancements in cell and animal models, treatments, brain anomalies in patients with CCs, and the existing gaps in the knowledge. We performed a systematic search in PubMed, Embase, ClinVar, OMIM, ClinGen, Gene Reviews, DECIPHER and LOVD databases to search for articles/records published before March 2021. The following search strategies were employed: ID and calcium channel, mental retardation and calcium channel, GDD and calcium channel, developmental delay and calcium channel. MAIN BODY A total of 59 reports describing 159 cases were found in PubMed, Embase, ClinVar, and LOVD databases. Variations in ten calcium channel genes including CACNA1A, CACNA1C, CACNA1I, CACNA1H, CACNA1D, CACNA2D1, CACNA2D2, CACNA1E, CACNA1F, and CACNA1G were found to be associated with ID/GDD. Most variants exhibited gain-of-function effect. Severe to profound ID/GDD was observed more for the cases with gain-of-function variants as compared to those with loss-of-function. CACNA1E, CACNA1G, CACNA1F, CACNA2D2 and CACNA1A associated with more severe phenotype. Furthermore, 157 copy number variations (CNVs) spanning calcium genes were identified in DECIPHER database. The leading genes included CACNA1C, CACNA1A, and CACNA1E. Overall, the underlying mechanisms included gain- and/ or loss-of-function, alteration in kinetics (activation, inactivation) and dominant-negative effects of truncated forms of alpha1 subunits. Forty of the identified cases featured cerebellar atrophy. We identified only a few cell and animal studies that focused on the mechanisms of ID/GDD in relation to CCs. There is a scarcity of studies on treatment options for ID/GDD both in vivo and in vitro. CONCLUSION Our results suggest that CCs play a major role in ID/GDD. While both gain- and loss-of-function variants are associated with ID/GDD, the mechanisms underlying their involvement need further scrutiny.
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Affiliation(s)
- Miriam Kessi
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
- Kilimanjaro Christian Medical University College, Moshi, Tanzania
- Mawenzi Regional Referral Hospital, Moshi, Tanzania
| | - Baiyu Chen
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Jing Peng
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Fangling Yan
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Lifen Yang
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China
| | - Fei Yin
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, 410008, Hunan, China.
- Hunan Intellectual and Developmental Disabilities Research Center, Changsha, Hunan, China.
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11
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Schöpf CL, Ablinger C, Geisler SM, Stanika RI, Campiglio M, Kaufmann WA, Nimmervoll B, Schlick B, Brockhaus J, Missler M, Shigemoto R, Obermair GJ. Presynaptic α 2δ subunits are key organizers of glutamatergic synapses. Proc Natl Acad Sci U S A 2021; 118:e1920827118. [PMID: 33782113 PMCID: PMC8040823 DOI: 10.1073/pnas.1920827118] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
In nerve cells the genes encoding for α2δ subunits of voltage-gated calcium channels have been linked to synaptic functions and neurological disease. Here we show that α2δ subunits are essential for the formation and organization of glutamatergic synapses. Using a cellular α2δ subunit triple-knockout/knockdown model, we demonstrate a failure in presynaptic differentiation evidenced by defective presynaptic calcium channel clustering and calcium influx, smaller presynaptic active zones, and a strongly reduced accumulation of presynaptic vesicle-associated proteins (synapsin and vGLUT). The presynaptic defect is associated with the downscaling of postsynaptic AMPA receptors and the postsynaptic density. The role of α2δ isoforms as synaptic organizers is highly redundant, as each individual α2δ isoform can rescue presynaptic calcium channel trafficking and expression of synaptic proteins. Moreover, α2δ-2 and α2δ-3 with mutated metal ion-dependent adhesion sites can fully rescue presynaptic synapsin expression but only partially calcium channel trafficking, suggesting that the regulatory role of α2δ subunits is independent from its role as a calcium channel subunit. Our findings influence the current view on excitatory synapse formation. First, our study suggests that postsynaptic differentiation is secondary to presynaptic differentiation. Second, the dependence of presynaptic differentiation on α2δ implicates α2δ subunits as potential nucleation points for the organization of synapses. Finally, our results suggest that α2δ subunits act as transsynaptic organizers of glutamatergic synapses, thereby aligning the synaptic active zone with the postsynaptic density.
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Affiliation(s)
- Clemens L Schöpf
- Institute of Physiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria
| | - Cornelia Ablinger
- Institute of Physiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria
| | - Stefanie M Geisler
- Institute of Physiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria
- Department of Pharmacology and Toxicology, University of Innsbruck, A-6020 Innsbruck, Austria
| | - Ruslan I Stanika
- Division of Physiology, Karl Landsteiner University of Health Sciences, A-3500 Krems, Austria
| | - Marta Campiglio
- Institute of Physiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria
| | - Walter A Kaufmann
- Institute of Science and Technology Austria, A-3400 Klosterneuburg, Austria
| | - Benedikt Nimmervoll
- Institute of Physiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria
| | - Bettina Schlick
- Institute of Physiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria
| | - Johannes Brockhaus
- Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms University, 48149 Münster, Germany
| | - Markus Missler
- Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms University, 48149 Münster, Germany
| | - Ryuichi Shigemoto
- Institute of Science and Technology Austria, A-3400 Klosterneuburg, Austria
| | - Gerald J Obermair
- Institute of Physiology, Medical University of Innsbruck, A-6020 Innsbruck, Austria;
- Division of Physiology, Karl Landsteiner University of Health Sciences, A-3500 Krems, Austria
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12
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Leahy KE, Wright T, Grudzinska Pechhacker MK, Audo I, Tumber A, Tavares E, MacDonald H, Locke J, VandenHoven C, Zeitz C, Heon E, Buncic JR, Vincent A. Optic Atrophy and Inner Retinal Thinning in CACNA1F-related Congenital Stationary Night Blindness. Genes (Basel) 2021; 12:genes12030330. [PMID: 33668843 PMCID: PMC7996180 DOI: 10.3390/genes12030330] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 02/06/2021] [Accepted: 02/20/2021] [Indexed: 12/25/2022] Open
Abstract
Hemizygous pathogenic variants in CACNA1F lead to defective signal transmission from retinal photoreceptors to bipolar cells and cause incomplete congenital stationary night blindness in humans. Although the primary defect is at the terminal end of first-order neurons (photoreceptors), there is limited knowledge of higher-order neuronal changes (inner retinal) in this disorder. This study aimed to investigate inner retinal changes in CACNA1F-retinopathy by analyzing macular ganglion cell layer-inner plexiform layer (GCL-IPL) thickness and optic disc pallor in 22 subjects with molecularly confirmed CACNA1F-retinopathy. Detailed ocular phenotypic data including distance and color vision, refraction and electroretinogram (ERG) were collected. Distance vision was universally reduced (mean: 0.42 LogMAR), six had abnormal color vision and myopia was common (n = 15; mean: −6.32 diopters). Mean GCL-IPL thickness was significantly lower in patients (55.00 µm) compared to age-matched controls (n = 87; 84.57 µm; p << 0.001). The GCL-IPL thickness correlated with scotopic standard (p = 0.04) and bright-flash (p = 0.014) ERG b/a ratios and photopic b-wave amplitudes (p = 0.05). Twenty-one patients had some degree of disc pallor (bilateral in 19). Fifteen putative disease-causing, including five novel variants were identified. This study establishes macular inner retinal thinning and optic atrophy as characteristic features of CACNA1F-retinopathy, which are independent of myopia and could impact potential future treatment strategies.
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Affiliation(s)
- Kate E Leahy
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON M5T 3A9, Canada;
| | - Tom Wright
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON M5T 3A9, Canada;
- Kensington Eye Institute, Toronto, ON M5T 3A9, Canada
| | - Monika K Grudzinska Pechhacker
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON M5T 3A9, Canada;
| | - Isabelle Audo
- INSERM, CNRS, Institut de la Vision, Sorbonne Université, 75012 Paris, France; (I.A.); (C.Z.)
- CHNO des Quinze-Vingts, DHU Sight Restore, INSERM-DGOS CIC 1423, 75012 Paris, France
- Institute of Ophthalmology, University College of London, London EC1V 9EL, UK
| | - Anupreet Tumber
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
| | - Erika Tavares
- Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada;
| | - Heather MacDonald
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada
- Department of Genetic Counselling, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
| | - Jeff Locke
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
| | - Cynthia VandenHoven
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
| | - Christina Zeitz
- INSERM, CNRS, Institut de la Vision, Sorbonne Université, 75012 Paris, France; (I.A.); (C.Z.)
| | - Elise Heon
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON M5T 3A9, Canada;
- Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada;
| | - J Raymond Buncic
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON M5T 3A9, Canada;
| | - Ajoy Vincent
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada; (K.E.L.); (M.K.G.P.); (A.T.); (H.M.); (J.L.); (C.V.); (E.H.); (J.R.B.)
- Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, ON M5T 3A9, Canada;
- Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada;
- Correspondence: ; Tel.: +1-416-813-1500
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13
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Geisler SM, Benedetti A, Schöpf CL, Schwarzer C, Stefanova N, Schwartz A, Obermair GJ. Phenotypic Characterization and Brain Structure Analysis of Calcium Channel Subunit α 2δ-2 Mutant (Ducky) and α 2δ Double Knockout Mice. Front Synaptic Neurosci 2021; 13:634412. [PMID: 33679366 PMCID: PMC7933509 DOI: 10.3389/fnsyn.2021.634412] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Accepted: 01/11/2021] [Indexed: 01/19/2023] Open
Abstract
Auxiliary α2δ subunits of voltage-gated calcium channels modulate channel trafficking, current properties, and synapse formation. Three of the four isoforms (α2δ-1, α2δ-2, and α2δ-3) are abundantly expressed in the brain; however, of the available knockout models, only α2δ-2 knockout or mutant mice display an obvious abnormal neurological phenotype. Thus, we hypothesize that the neuronal α2δ isoforms may have partially specific as well as redundant functions. To address this, we generated three distinct α2δ double knockout mouse models by crossbreeding single knockout (α2δ-1 and -3) or mutant (α2δ-2/ducky) mice. Here, we provide a first phenotypic description and brain structure analysis. We found that genotypic distribution of neonatal litters in distinct α2δ-1/-2, α2δ-1/-3, and α2δ-2/-3 breeding combinations did not conform to Mendel's law, suggesting premature lethality of single and double knockout mice. Notably, high occurrences of infant mortality correlated with the absence of specific α2δ isoforms (α2Δ-2 > α2δ-1 > α2δ-3), and was particularly observed in cages with behaviorally abnormal parenting animals of α2δ-2/-3 cross-breedings. Juvenile α2δ-1/-2 and α2δ-2/-3 double knockout mice displayed a waddling gate similar to ducky mice. However, in contrast to ducky and α2δ-1/-3 double knockout animals, α2δ-1/-2 and α2δ-2/-3 double knockout mice showed a more severe disease progression and highly impaired development. The observed phenotypes within the individual mouse lines may be linked to differences in the volume of specific brain regions. Reduced cortical volume in ducky mice, for example, was associated with a progressively decreased space between neurons, suggesting a reduction of total synaptic connections. Taken together, our findings show that α2δ subunits differentially regulate premature survival, postnatal growth, brain development, and behavior, suggesting specific neuronal functions in health and disease.
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Affiliation(s)
- Stefanie M. Geisler
- Institute of Physiology, Medical University Innsbruck, Innsbruck, Austria
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Ariane Benedetti
- Institute of Physiology, Medical University Innsbruck, Innsbruck, Austria
| | - Clemens L. Schöpf
- Institute of Physiology, Medical University Innsbruck, Innsbruck, Austria
| | - Christoph Schwarzer
- Department of Pharmacology, Medical University Innsbruck, Innsbruck, Austria
| | - Nadia Stefanova
- Division of Neurobiology, Department of Neurology, Medical University Innsbruck, Innsbruck, Austria
| | - Arnold Schwartz
- Department of Pharmacology and Systems Physiology, College of Medicine, University of Cincinnati, Cincinnati, OH, United States
| | - Gerald J. Obermair
- Institute of Physiology, Medical University Innsbruck, Innsbruck, Austria
- Division Physiology, Karl Landsteiner University of Health Sciences, Krems an der Donau, Austria
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14
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Function of cone and cone-related pathways in Ca V1.4 IT mice. Sci Rep 2021; 11:2732. [PMID: 33526839 PMCID: PMC7851161 DOI: 10.1038/s41598-021-82210-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Accepted: 01/11/2021] [Indexed: 11/09/2022] Open
Abstract
CaV1.4 L-type calcium channels are predominantly expressed in photoreceptor terminals playing a crucial role for synaptic transmission and, consequently, for vision. Human mutations in the encoding gene are associated with congenital stationary night blindness type-2. Besides rod-driven scotopic vision also cone-driven photopic responses are severely affected in patients. The present study therefore examined functional and morphological changes in cones and cone-related pathways in mice carrying the CaV1.4 gain-of function mutation I756T (CaV1.4-IT) using multielectrode array, patch-clamp and immunohistochemical analyses. CaV1.4-IT ganglion cell responses to photopic stimuli were seen only in a small fraction of cells indicative of a major impairment in the cone pathway. Though cone photoreceptors underwent morphological rearrangements, they retained their ability to release glutamate. Our functional data suggested a postsynaptic cone bipolar cell defect, supported by the fact that the majority of cone bipolar cells showed sprouting, while horizontal cells maintained contacts with cones and cone-to-horizontal cell input was preserved. Furthermore a reduction of basal Ca2+ influx by a calcium channel blocker was not sufficient to rescue synaptic transmission deficits caused by the CaV1.4-IT mutation. Long term treatments with low-dose Ca2+ channel blockers might however be beneficial reducing Ca2+ toxicity without major effects on ganglion cells responses.
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15
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Kaehler K, Seitter H, Sandbichler AM, Tschugg B, Obermair GJ, Stefanova N, Koschak A. Assessment of the Retina of Plp-α-Syn Mice as a Model for Studying Synuclein-Dependent Diseases. Invest Ophthalmol Vis Sci 2021; 61:12. [PMID: 32503050 PMCID: PMC7415298 DOI: 10.1167/iovs.61.6.12] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Purpose Synucleinopathies such as multiple system atrophy (MSA) and Parkinson's disease are associated with a variety of visual symptoms. Functional and morphological retinal aberrations are therefore supposed to be valuable biomarkers for these neurodegenerative diseases. This study examined the retinal morphology and functionality resulting from human α-synuclein (α-Syn) overexpression in the transgenic Plp-α-Syn mouse model. Methods Immunohistochemistry on retinal sections and whole-mounts was performed on 8- to 11-week-old and 12-month-old Plp-α-Syn mice and C57BL/6N controls. Quantitative RT-PCR experiments were performed to study the expression of endogenous and human α-Syn and tyrosine hydroxylase (TH). We confirmed the presence of human α-Syn in the retina in western blot analyses. Multi-electrode array (MEA) analyses from light-stimulated whole-mounted retinas were used to investigate their functionality. Results Biochemical and immunohistochemical analyses showed human α-Syn in the retina of Plp-α-Syn mice. We found distinct staining in different retinal cell layers, most abundantly in rod bipolar cells of the peripheral retina. In the periphery, we also observed a trend toward a decline in the number of retinal ganglion cells. The number of TH+ neurons was unaffected in this human α-Syn overexpression model. MEA recordings showed that Plp-α-Syn retinas were functional but exhibited mild alterations in dim light conditions. Conclusions Together, these findings implicate an impairment of retinal neurons in the Plp-α-Syn mouse. The phenotype partly relates to retinal deficits reported in MSA patients. We further propose the suitability of the Plp-α-Syn retina as a biological model to study synuclein-mediated mechanisms.
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16
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Williams B, Lopez JA, Maddox JW, Lee A. Functional impact of a congenital stationary night blindness type 2 mutation depends on subunit composition of Ca v1.4 Ca 2+ channels. J Biol Chem 2020; 295:17215-17226. [PMID: 33037074 DOI: 10.1074/jbc.ra120.014138] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 09/17/2020] [Indexed: 12/30/2022] Open
Abstract
Voltage-gated Cav1 and Cav2 Ca2+ channels are comprised of a pore-forming α1 subunit (Cav1.1-1.4, Cav2.1-2.3) and auxiliary β (β1-4) and α2δ (α2δ-1-4) subunits. The properties of these channels vary with distinct combinations of Cav subunits and alternative splicing of the encoding transcripts. Therefore, the impact of disease-causing mutations affecting these channels may depend on the identities of Cav subunits and splice variants. Here, we analyzed the effects of a congenital stationary night blindness type 2 (CSNB2)-causing mutation, I745T (IT), in Cav1.4 channels typical of those in human retina: Cav1.4 splice variants with or without exon 47 (Cav1.4+ex47 and Cav1.4Δex47, respectively), and the auxiliary subunits, β2X13 and α2δ-4. We find that IT caused both Cav1.4 splice variants to activate at significantly more negative voltages and with slower deactivation kinetics than the corresponding WT channels. These effects of the IT mutation, along with unexpected alterations in ion selectivity, were generally larger in channels lacking exon 47. The weaker ion selectivity caused by IT led to hyperpolarizing shifts in the reversal potential and large outward currents that were evident in channels containing the auxiliary subunits β2X13 and α2δ-4 but not in those with β2A and α2δ-1. We conclude that the IT mutation stabilizes channel opening and alters ion selectivity of Cav1.4 in a manner that is strengthened by exclusion of exon 47 and inclusion of β2X13 and α2δ-4. Our results reveal complex actions of IT in modifying the properties of Cav1.4 channels, which may influence the pathological consequences of this mutation in retinal photoreceptors.
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Affiliation(s)
- Brittany Williams
- Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, Iowa Neuroscience Institute, Pappajohn Biomedical Institute, University of Iowa, Iowa City, Iowa USA; Interdisciplinary Graduate Program in Neuroscience, University of Iowa, Iowa City, Iowa USA
| | - Josue A Lopez
- Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, Iowa Neuroscience Institute, Pappajohn Biomedical Institute, University of Iowa, Iowa City, Iowa USA
| | - J Wesley Maddox
- Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, Iowa Neuroscience Institute, Pappajohn Biomedical Institute, University of Iowa, Iowa City, Iowa USA
| | - Amy Lee
- Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, Iowa Neuroscience Institute, Pappajohn Biomedical Institute, University of Iowa, Iowa City, Iowa USA.
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17
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Sensing through Non-Sensing Ocular Ion Channels. Int J Mol Sci 2020; 21:ijms21186925. [PMID: 32967234 PMCID: PMC7554890 DOI: 10.3390/ijms21186925] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 09/17/2020] [Accepted: 09/18/2020] [Indexed: 12/12/2022] Open
Abstract
Ion channels are membrane-spanning integral proteins expressed in multiple organs, including the eye. In the eye, ion channels are involved in various physiological processes, like signal transmission and visual processing. A wide range of mutations have been reported in the corresponding genes and their interacting subunit coding genes, which contribute significantly to an array of blindness, termed ocular channelopathies. These mutations result in either a loss- or gain-of channel functions affecting the structure, assembly, trafficking, and localization of channel proteins. A dominant-negative effect is caused in a few channels formed by the assembly of several subunits that exist as homo- or heteromeric proteins. Here, we review the role of different mutations in switching a “sensing” ion channel to “non-sensing,” leading to ocular channelopathies like Leber’s congenital amaurosis 16 (LCA16), cone dystrophy, congenital stationary night blindness (CSNB), achromatopsia, bestrophinopathies, retinitis pigmentosa, etc. We also discuss the various in vitro and in vivo disease models available to investigate the impact of mutations on channel properties, to dissect the disease mechanism, and understand the pathophysiology. Innovating the potential pharmacological and therapeutic approaches and their efficient delivery to the eye for reversing a “non-sensing” channel to “sensing” would be life-changing.
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18
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Ablinger C, Geisler SM, Stanika RI, Klein CT, Obermair GJ. Neuronal α 2δ proteins and brain disorders. Pflugers Arch 2020; 472:845-863. [PMID: 32607809 PMCID: PMC7351808 DOI: 10.1007/s00424-020-02420-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 06/08/2020] [Accepted: 06/12/2020] [Indexed: 01/31/2023]
Abstract
α2δ proteins are membrane-anchored extracellular glycoproteins which are abundantly expressed in the brain and the peripheral nervous system. They serve as regulatory subunits of voltage-gated calcium channels and, particularly in nerve cells, regulate presynaptic and postsynaptic functions independently from their role as channel subunits. α2δ proteins are the targets of the widely prescribed anti-epileptic and anti-allodynic drugs gabapentin and pregabalin, particularly for the treatment of neuropathic pain conditions. Recently, the human genes (CACNA2D1-4) encoding for the four known α2δ proteins (isoforms α2δ-1 to α2δ-4) have been linked to a large variety of neurological and neuropsychiatric disorders including epilepsy, autism spectrum disorders, bipolar disorders, schizophrenia, and depressive disorders. Here, we provide an overview of the hitherto identified disease associations of all known α2δ genes, hypothesize on the pathophysiological mechanisms considering their known physiological roles, and discuss the most immanent future research questions. Elucidating their specific physiological and pathophysiological mechanisms may open the way for developing entirely novel therapeutic paradigms for treating brain disorders.
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Affiliation(s)
- Cornelia Ablinger
- Institute of Physiology, Medical University Innsbruck, 6020, Innsbruck, Austria
| | - Stefanie M Geisler
- Department of Pharmacology and Toxicology, University of Innsbruck, 6020, Innsbruck, Austria
| | - Ruslan I Stanika
- Division Physiology, Karl Landsteiner University of Health Sciences, 3500, Krems, Austria
| | - Christian T Klein
- Department of Life Sciences, IMC University of Applied Sciences, 3500, Krems, Austria
| | - Gerald J Obermair
- Institute of Physiology, Medical University Innsbruck, 6020, Innsbruck, Austria.
- Division Physiology, Karl Landsteiner University of Health Sciences, 3500, Krems, Austria.
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19
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Wang S, Cortes CJ. Interactions with PDZ proteins diversify voltage-gated calcium channel signaling. J Neurosci Res 2020; 99:332-348. [PMID: 32476168 DOI: 10.1002/jnr.24650] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2020] [Revised: 04/29/2020] [Accepted: 05/07/2020] [Indexed: 11/12/2022]
Abstract
Voltage-gated Ca2+ (CaV ) channels are crucial for neuronal excitability and synaptic transmission upon depolarization. Their properties in vivo are modulated by their interaction with a variety of scaffolding proteins. Such interactions can influence the function and localization of CaV channels, as well as their coupling to intracellular second messengers and regulatory pathways, thus amplifying their signaling potential. Among these scaffolding proteins, a subset of PDZ (postsynaptic density-95, Drosophila discs-large, and zona occludens)-domain containing proteins play diverse roles in modulating CaV channel properties. At the presynaptic terminal, PDZ proteins enrich CaV channels in the active zone, enabling neurotransmitter release by maintaining a tight and vital link between channels and vesicles. In the postsynaptic density, these interactions are essential in regulating dendritic spine morphology and postsynaptic signaling cascades. In this review, we highlight the studies that demonstrate dynamic regulations of neuronal CaV channels by PDZ proteins. We discuss the role of PDZ proteins in controlling channel activity, regulating channel cell surface density, and influencing channel-mediated downstream signaling events. We highlight the importance of PDZ protein regulations of CaV channels and evaluate the link between this regulatory effect and human disease.
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Affiliation(s)
- Shiyi Wang
- Department of Cell Biology, Duke University, Durham, NC, USA.,Department of Neurology, Duke University, Durham, NC, USA
| | - Constanza J Cortes
- Department of Neurology, Duke University, Durham, NC, USA.,Department of Cell, Developmental and Integrative Biology, University of Alabama Birmingham, Birmingham, AL, USA
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20
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Kalpachidou T, Makrygiannis AK, Pavlakis E, Stylianopoulou F, Chalepakis G, Stamatakis A. Behavioural effects of extracellular matrix protein Fras1 depletion in the mouse. Eur J Neurosci 2020; 53:3905-3919. [DOI: 10.1111/ejn.14759] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 03/21/2020] [Accepted: 04/17/2020] [Indexed: 12/18/2022]
Affiliation(s)
- Theodora Kalpachidou
- Biology‐Biochemistry Lab Faculty of Nursing School of Health Sciences National and Kapodistrian University of Athens Athens Greece
| | | | | | - Fotini Stylianopoulou
- Biology‐Biochemistry Lab Faculty of Nursing School of Health Sciences National and Kapodistrian University of Athens Athens Greece
| | | | - Antonios Stamatakis
- Biology‐Biochemistry Lab Faculty of Nursing School of Health Sciences National and Kapodistrian University of Athens Athens Greece
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21
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Schlegel DK, Glasauer SMK, Mateos JM, Barmettler G, Ziegler U, Neuhauss SCF. A New Zebrafish Model for CACNA2D4-Dysfunction. Invest Ophthalmol Vis Sci 2020; 60:5124-5135. [PMID: 31834350 DOI: 10.1167/iovs.19-26759] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose Mutations in CACNA2D4, encoding the α2δ4 subunit of retinal voltage-gated calcium channels (Cav), cause a rare type of retinal dysfunction in human, mainly affecting cone vision. Here, we investigate the role of CACNA2D4 in targeting of Cav, its influence on cone-mediated signal transmission, and the cellular and subcellular changes upon loss of α2δ4 by exploiting the advantages of the cone-dominant zebrafish as model system. Methods We identified two zebrafish CACNA2D4 paralogs (cacna2d4a and cacna2d4b), analyzed their expression by RNA in situ hybridization and introduced truncating frameshift mutations through CRISPR/Cas9-mediated mutagenesis. We analyzed retinal function and morphology of the single and double mutant lines by electroretinography, immunohistochemistry, light- and electron microscopy. Results Knockout of cacna2d4b reduces the expression of Cacna1fa, the pore-forming subunit of retinal Cav1.4, whereas loss of cacna2d4a did not. Only knockout of both paralogs impaired cone-mediated ERG b-wave amplitude. The number of "floating" ribbons is increased in double-KO, while retinal morphology and expression of postsynaptic mGluR6b remain largely unaffected. Both Cacna1fa and Ribeyeb show ectopic punctate expression in cacna2d4b-KO and double-KO photoreceptors. Conclusions We find that increasing the expression of Cav at the synaptic membrane is an evolutionarily conserved function of Cacna2d4b. Yet, since both paralogs participate in cone synaptic transmission, we propose partial subfunctionalization in zebrafish. Similar to human patients, our double KO zebrafish model shows mild cone dysfunction, which was not associated with signs of retinal degeneration. Therefore, cacna2d4-KO zebrafish is a suitable model to study the pathophysiological mechanisms underlying CACNA2D4 dysfunction in human.
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Affiliation(s)
- Domino K Schlegel
- Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland.,Life Science Zurich Graduate School, Ph.D. Program in Molecular Life Sciences, Zurich, Switzerland
| | - Stella M K Glasauer
- Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland.,Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California, United States.,Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, United States
| | - José M Mateos
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Gery Barmettler
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Urs Ziegler
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
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22
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Ko GYP. Circadian regulation in the retina: From molecules to network. Eur J Neurosci 2020; 51:194-216. [PMID: 30270466 PMCID: PMC6441387 DOI: 10.1111/ejn.14185] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Revised: 08/16/2018] [Accepted: 08/20/2018] [Indexed: 12/14/2022]
Abstract
The mammalian retina is the most unique tissue among those that display robust circadian/diurnal oscillations. The retina is not only a light sensing tissue that relays light information to the brain, it has its own circadian "system" independent from any influence from other circadian oscillators. While all retinal cells and retinal pigment epithelium (RPE) possess circadian oscillators, these oscillators integrate by means of neural synapses, electrical coupling (gap junctions), and released neurochemicals (such as dopamine, melatonin, adenosine, and ATP), so the whole retina functions as an integrated circadian system. Dysregulation of retinal clocks not only causes retinal or ocular diseases, it also impacts the circadian rhythm of the whole body, as the light information transmitted from the retina entrains the brain clock that governs the body circadian rhythms. In this review, how circadian oscillations in various retinal cells are integrated, and how retinal diseases affect daily rhythms.
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Affiliation(s)
- Gladys Y-P Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas
- Texas A&M Institute for Neuroscience, Texas A&M University, College Station, Texas
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Kinoshita J, Hasan N, Bell BA, Peachey NS. Reduced expression of the nob8 gene does not normalize the distribution or function of mGluR6 in the mouse retina. Mol Vis 2019; 25:890-901. [PMID: 32025181 PMCID: PMC6982428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Accepted: 12/30/2019] [Indexed: 11/21/2022] Open
Abstract
Purpose The Grm6nob8 mouse carries a missense mutation in the Grm6 gene (p.Met66Leu), and exhibits a reduced b-wave of the electroretinogram (ERG), abnormal localization of metabotropic glutamate receptor 6 (mGluR6) to the depolarizing bipolar cell (DBC) soma, and a reduced level of mGluR6 at the DBC dendritic tips. Although the underlying mechanism remains unknown, one possible explanation is that DBCs cannot efficiently traffic the mutant mGluR6. In that scenario, reducing the total amount of mutant mGluR6 protein might normalize localization, and thus, improve the ERG phenotype as well. The second purpose of this study was to determine whether the abnormal cellular distribution of mutant mGluR6 in Grm6nob8 retinas might induce late onset DBC degeneration. Methods We crossed Grm6nob8 animals with Grm6nob3 mice, which carry a null mutation in Grm6, to generate Grm6nob3/nob8 compound heterozygotes. We used western blotting to measure the total mGluR6 content, and immunohistochemistry to document mGluR6 localization within DBCs. In addition, we examined outer retinal function with ERG and retinal architecture in vivo with spectral domain optical coherence tomography (SD-OCT). Results The retinal content of mGluR6 was reduced in the retinas of the Grm6nob3/nob8 compound heterozygotes compared to the Grm6nob8 homozygotes. The cellular distribution of mGluR6 in the Grm6nob3/nob8 compound heterozygotes matched that of the Grm6nob8 homozygotes, with extensive expression throughout the DBC cell body and limited expression at the DBC dendritic tips. The dark-adapted ERG b-waves of the Grm6nob3/nob8 mice were reduced in comparison to those of the Grm6nob8 homozygotes at postnatal day 21 and 28. The overall ERG waveforms obtained from 4- through 68-week old Grm6nob8 mice were in general agreement for dark- and light-adapted conditions. The maximum response and sensitivity of the dark-adapted ERG b-wave did not change statistically significantly with age. SD-OCT revealed the maintained laminar structure of the retina, including a clear inner nuclear layer (INL) at each age examined (from 11 to 57 weeks old), although the INL in the mice older than 39 weeks of age was somewhat thinner than that seen at 11 weeks. Conclusions Mislocalization of mutant mGluR6 is not normalized by reducing the total mGluR6. Mislocalized mutant mGluR6 does not trigger substantial loss of DBCs.
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Affiliation(s)
| | - Nazarul Hasan
- Department of Biochemistry & Molecular Genetics, University of Louisville, Louisville, KY
| | | | - Neal S. Peachey
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH
- Research Service, Louis Stokes Cleveland VA Medical Center, Cleveland, OH
- Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH
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24
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Pangrsic T, Singer JH, Koschak A. Voltage-Gated Calcium Channels: Key Players in Sensory Coding in the Retina and the Inner Ear. Physiol Rev 2019; 98:2063-2096. [PMID: 30067155 DOI: 10.1152/physrev.00030.2017] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Calcium influx through voltage-gated Ca (CaV) channels is the first step in synaptic transmission. This review concerns CaV channels at ribbon synapses in primary sense organs and their specialization for efficient coding of stimuli in the physical environment. Specifically, we describe molecular, biochemical, and biophysical properties of the CaV channels in sensory receptor cells of the retina, cochlea, and vestibular apparatus, and we consider how such properties might change over the course of development and contribute to synaptic plasticity. We pay particular attention to factors affecting the spatial arrangement of CaV channels at presynaptic, ribbon-type active zones, because the spatial relationship between CaV channels and release sites has been shown to affect synapse function critically in a number of systems. Finally, we review identified synaptopathies affecting sensory systems and arising from dysfunction of L-type, CaV1.3, and CaV1.4 channels or their protein modulatory elements.
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Affiliation(s)
- Tina Pangrsic
- Synaptic Physiology of Mammalian Vestibular Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen and Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine , Göttingen, Germany ; Department of Biology, University of Maryland , College Park, Maryland ; and Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck , Innsbruck , Austria
| | - Joshua H Singer
- Synaptic Physiology of Mammalian Vestibular Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen and Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine , Göttingen, Germany ; Department of Biology, University of Maryland , College Park, Maryland ; and Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck , Innsbruck , Austria
| | - Alexandra Koschak
- Synaptic Physiology of Mammalian Vestibular Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen and Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine , Göttingen, Germany ; Department of Biology, University of Maryland , College Park, Maryland ; and Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck , Innsbruck , Austria
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Dai X, Pang S, Wang J, FitzMaurice B, Pang J, Chang B. Photoreceptor degeneration in a new Cacna1f mutant mouse model. Exp Eye Res 2018; 179:106-114. [PMID: 30445045 DOI: 10.1016/j.exer.2018.11.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Revised: 10/17/2018] [Accepted: 11/12/2018] [Indexed: 02/06/2023]
Abstract
The Cacna1f gene encodes the α1F subunit of an L-type voltage-gated calcium channel, Cav1.4. In photoreceptor synaptic terminals, Cav1.4 channels mediate glutamate release and postsynaptic responses associated with visual signal transmission. We have discovered a new Cacna1f mutation in nob9 mice, which display more severe phenotypes than do nob2 mice. To characterize the nob9 phenotype at different ages, we examined the murine fundus, applied retinal optical coherence tomography, measured flash electroretinograms (ERGs) in vivo, and analyzed the retinal histology in vitro. After identifying the X-linked recessive inheritance trait, we sequenced Cacna1f as the candidate gene. Mutations in this gene were detected by polymerase chain reaction (PCR) and confirmed by restriction fragment length polymorphism. Morphologically, an early-onset of retinal disorder was detected, and the degeneration of the outer plexiform layers progressed rapidly. Moreover, the mutant mice showed drastically reduced scotopic ERGs with increasing age. In 14-month-old nob9 retinas, immunostaining of cone opsins demonstrated a reduction in the number of short-wavelength opsins (S-opsins) to 54% of wild-type levels, and almost no middle-wavelength opsins (M-opsins) were observed. No cone ERGs could be detected from residual cones, in which S-opsins abnormally migrated to inner segments of the photoreceptors. The mutations of the Cacna1f gene in nob9 mice involved both a single nucleotide G to A transition and a 10-nucleotide insertion, the latter resulting in a frame-shift mutation in exon 14.
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Affiliation(s)
- Xufeng Dai
- School of Ophthalmology and Optometry, The Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, 325027, China; Department of Ophthalmology, University of Florida, Gainesville, FL, 32610, USA
| | - Shiyi Pang
- The Jackson Laboratory, Bar Harbor, ME, 04609, USA; College of Medicine, University of Florida, Gainesville, FL, 32610, USA
| | - Jieping Wang
- The Jackson Laboratory, Bar Harbor, ME, 04609, USA
| | | | - Jijing Pang
- School of Ophthalmology and Optometry, The Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, 325027, China; Department of Ophthalmology, University of Florida, Gainesville, FL, 32610, USA; College of Medicine, University of Florida, Gainesville, FL, 32610, USA; Eye Research Institute, Xiamen Eye Center of Xiamen University, Xiamen, 361001, China.
| | - Bo Chang
- The Jackson Laboratory, Bar Harbor, ME, 04609, USA.
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Kerov V, Laird JG, Joiner ML, Knecht S, Soh D, Hagen J, Gardner SH, Gutierrez W, Yoshimatsu T, Bhattarai S, Puthussery T, Artemyev NO, Drack AV, Wong RO, Baker SA, Lee A. α 2δ-4 Is Required for the Molecular and Structural Organization of Rod and Cone Photoreceptor Synapses. J Neurosci 2018; 38:6145-6160. [PMID: 29875267 PMCID: PMC6031576 DOI: 10.1523/jneurosci.3818-16.2018] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 05/10/2018] [Accepted: 05/31/2018] [Indexed: 11/21/2022] Open
Abstract
α2δ-4 is an auxiliary subunit of voltage-gated Cav1.4 L-type channels that regulate the development and mature exocytotic function of the photoreceptor ribbon synapse. In humans, mutations in the CACNA2D4 gene encoding α2δ-4 cause heterogeneous forms of vision impairment in humans, the underlying pathogenic mechanisms of which remain unclear. To investigate the retinal function of α2δ-4, we used genome editing to generate an α2δ-4 knock-out (α2δ-4 KO) mouse. In male and female α2δ-4 KO mice, rod spherules lack ribbons and other synaptic hallmarks early in development. Although the molecular organization of cone synapses is less affected than rod synapses, horizontal and cone bipolar processes extend abnormally in the outer nuclear layer in α2δ-4 KO retina. In reconstructions of α2δ-4 KO cone pedicles by serial block face scanning electron microscopy, ribbons appear normal, except that less than one-third show the expected triadic organization of processes at ribbon sites. The severity of the synaptic defects in α2δ-4 KO mice correlates with a progressive loss of Cav1.4 channels, first in terminals of rods and later cones. Despite the absence of b-waves in electroretinograms, visually guided behavior is evident in α2δ-4 KO mice and better under photopic than scotopic conditions. We conclude that α2δ-4 plays an essential role in maintaining the structural and functional integrity of rod and cone synapses, the disruption of which may contribute to visual impairment in humans with CACNA2D4 mutations.SIGNIFICANCE STATEMENT In the retina, visual information is first communicated by the synapse formed between photoreceptors and second-order neurons. The mechanisms that regulate the structural integrity of this synapse are poorly understood. Here we demonstrate a role for α2δ-4, a subunit of voltage-gated Ca2+ channels, in organizing the structure and function of photoreceptor synapses. We find that presynaptic Ca2+ channels are progressively lost and that rod and cone synapses are disrupted in mice that lack α2δ-4. Our results suggest that alterations in presynaptic Ca2+ signaling and photoreceptor synapse structure may contribute to vision impairment in humans with mutations in the CACNA2D4 gene encoding α2δ-4.
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Affiliation(s)
- Vasily Kerov
- Department of Molecular Physiology and Biophysics
| | | | | | - Sharmon Knecht
- Department of Biological Structure, University of Washington, Seattle, Washington 98195, and
| | - Daniel Soh
- Department of Molecular Physiology and Biophysics
| | | | | | | | - Takeshi Yoshimatsu
- Department of Biological Structure, University of Washington, Seattle, Washington 98195, and
| | - Sajag Bhattarai
- Department of Ophthalmology and Institute for Vision Research
| | - Teresa Puthussery
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239
| | | | - Arlene V Drack
- Department of Ophthalmology and Institute for Vision Research
| | - Rachel O Wong
- Department of Biological Structure, University of Washington, Seattle, Washington 98195, and
| | - Sheila A Baker
- Department of Biochemistry,
- Department of Ophthalmology and Institute for Vision Research
| | - Amy Lee
- Department of Molecular Physiology and Biophysics,
- Department of Otolaryngology-Head and Neck Surgery
- Department of Neurology, University of Iowa, Iowa City, Iowa 52242
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Gong N, Park J, Luo ZD. Injury-induced maladaptation and dysregulation of calcium channel α 2 δ subunit proteins and its contribution to neuropathic pain development. Br J Pharmacol 2018; 175:2231-2243. [PMID: 28646556 PMCID: PMC5980513 DOI: 10.1111/bph.13930] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Revised: 06/05/2017] [Accepted: 06/12/2017] [Indexed: 01/12/2023] Open
Abstract
Voltage-gated calcium channels (VGCCs) play important roles in physiological functions including the modulation of neurotransmitter release, neuronal network activities, intracellular signalling pathways and gene expression. Some pathological conditions, including nerve injuries, can cause the dysregulation of VGCCs and their subunits. This in turn can lead to a functional maladaptation of VGCCs and their subunits, which can contribute to the development of disorders such as pain sensations. This review has summarized recent findings related to maladaptive changes in the dysregulated VGCC α2 δ1 subunit (Cav α2 δ1 ) with a focus on exploring the mechanisms underlying the contribution of Cav α2 δ1 to pain signal transduction. At least under neuropathic pain conditions, the dysregulated Cav α2 δ1 can modulate VGCC functions as well as other plasticity changes. The latter includes abnormal excitatory synaptogenesis resulting from its interactions with injury-induced extracellular matrix glycoprotein molecule thrombospondins, which is independent of the VGCC functions. Blocking Cav α2 δ1 with gabapentinoids can reverse neuropathic pain significantly with relatively mild side effects, but only in a small population of neuropathic pain patients due to reasons yet to be explored. There are emerging data suggesting that early preventive treatment with gabapentinoids can prevent aberrant excitatory synapse formation and the development of chronic pain. If these findings are confirmed clinically, this could be an attractive approach for neuropathic pain management. LINKED ARTICLES This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.
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Affiliation(s)
- Nian Gong
- Department of Anesthesiology & Perioperative CareSchool of Medicine, University of California IrvineIrvineCAUSA
| | - John Park
- Department of Pharmacology, School of MedicineUniversity of California IrvineIrvineCAUSA
| | - Z David Luo
- Department of Anesthesiology & Perioperative CareSchool of Medicine, University of California IrvineIrvineCAUSA
- Department of Pharmacology, School of MedicineUniversity of California IrvineIrvineCAUSA
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Waldner DM, Bech-Hansen NT, Stell WK. Channeling Vision: Ca V1.4-A Critical Link in Retinal Signal Transmission. BIOMED RESEARCH INTERNATIONAL 2018; 2018:7272630. [PMID: 29854783 PMCID: PMC5966690 DOI: 10.1155/2018/7272630] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 02/15/2018] [Indexed: 01/09/2023]
Abstract
Voltage-gated calcium channels (VGCC) are key to many biological functions. Entry of Ca2+ into cells is essential for initiating or modulating important processes such as secretion, cell motility, and gene transcription. In the retina and other neural tissues, one of the major roles of Ca2+-entry is to stimulate or regulate exocytosis of synaptic vesicles, without which synaptic transmission is impaired. This review will address the special properties of one L-type VGCC, CaV1.4, with particular emphasis on its role in transmission of visual signals from rod and cone photoreceptors (hereafter called "photoreceptors," to the exclusion of intrinsically photoreceptive retinal ganglion cells) to the second-order retinal neurons, and the pathological effects of mutations in the CACNA1F gene which codes for the pore-forming α1F subunit of CaV1.4.
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Affiliation(s)
- D. M. Waldner
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - N. T. Bech-Hansen
- Department of Medical Genetics and Department of Surgery, Alberta Children's Hospital Research Institute, and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - W. K. Stell
- Department of Cell Biology and Anatomy and Department of Surgery, Hotchkiss Brain Institute, and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
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29
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Waldner DM, Giraldo Sierra NC, Bonfield S, Nguyen L, Dimopoulos IS, Sauvé Y, Stell WK, Bech-Hansen NT. Cone dystrophy and ectopic synaptogenesis in a Cacna1f loss of function model of congenital stationary night blindness (CSNB2A). Channels (Austin) 2018; 12:17-33. [PMID: 29179637 PMCID: PMC5972796 DOI: 10.1080/19336950.2017.1401688] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Revised: 10/22/2017] [Accepted: 10/31/2017] [Indexed: 01/05/2023] Open
Abstract
Congenital stationary night blindness 2A (CSNB2A) is an X-linked retinal disorder, characterized by phenotypically variable signs and symptoms of impaired vision. CSNB2A is due to mutations in CACNA1F, which codes for the pore-forming α1F subunit of a L-type voltage-gated calcium channel, Cav1.4. Mouse models of CSNB2A, used for characterizing the effects of various Cacna1f mutations, have revealed greater severity of defects than in human CSNB2A. Specifically, Cacna1f-knockout mice show an apparent lack of visual function, gradual retinal degeneration, and disruption of photoreceptor synaptic terminals. Several reports have also noted cone-specific disruptions, including axonal abnormalities, dystrophy, and cell death. We have explored further the involvement of cones in our 'G305X' mouse model of CSNB2A, which has a premature truncation, loss-of-function mutation in Cacna1f. We show that the expression of genes for several phototransduction-related cone markers is down-regulated, while that of several cellular stress- and damage-related markers is up-regulated; and that cone photoreceptor structure and photopic visual function - measured by immunohistochemistry, optokinetic response and electroretinography - deteriorate progressively with age. We also find that dystrophic cone axons establish synapse-like contacts with rod bipolar cell dendrites, which they normally do not contact in wild-type retinas - ectopically, among rod cell bodies in the outer nuclear layer. These data support a role for Cav1.4 in cone synaptic development, cell viability, and synaptic transmission of cone-dependent visual signals. Although our novel finding of cone-to-rod-bipolar cell contacts in this mouse model of a retinal channelopathy may challenge current views of the role of Cav1.4 in photopic vision, it also suggests a potential new target for restorative therapy.
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Affiliation(s)
- D. M. Waldner
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - N. C. Giraldo Sierra
- Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - S. Bonfield
- Department of Neuroscience, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - L. Nguyen
- Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - I. S. Dimopoulos
- Department of Ophthalmology and Visual Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Y. Sauvé
- Department of Ophthalmology and Visual Sciences, University of Alberta, Edmonton, Alberta, Canada
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
| | - W. K. Stell
- Department of Cell Biology and Anatomy and Department of Surgery, Hotchkiss Brain Institute, and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - N. T. Bech-Hansen
- Department of Medical Genetics, and Department of Surgery, Alberta Children's Hospital Research Institute, and Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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α2δ2 Controls the Function and Trans-Synaptic Coupling of Cav1.3 Channels in Mouse Inner Hair Cells and Is Essential for Normal Hearing. J Neurosci 2017; 36:11024-11036. [PMID: 27798183 DOI: 10.1523/jneurosci.3468-14.2016] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 09/03/2016] [Indexed: 11/21/2022] Open
Abstract
The auxiliary subunit α2δ2 modulates the abundance and function of voltage-gated calcium channels. Here we show that α2δ2 mRNA is expressed in neonatal and mature hair cells. A functional α2δ2-null mouse, the ducky mouse (du), showed elevated auditory brainstem response click and frequency-dependent hearing thresholds. Otoacoustic emissions were not impaired pointing to normal outer hair cell function. Peak Ca2+ and Ba2+ currents of mature du/du inner hair cells (IHCs) were reduced by 30-40%, respectively, and gating properties, such as the voltage of half-maximum activation and voltage sensitivity, were altered, indicating that Cav1.3 channels normally coassemble with α2δ2 at IHC presynapses. The reduction of depolarization-evoked exocytosis in du/du IHCs reflected their reduced Ca2+ currents. Ca2+- and voltage-dependent K+ (BK) currents and the expression of the pore-forming BKα protein were normal. Cav1.3 and Cavβ2 protein expression was unchanged in du/du IHCs, forming clusters at presynaptic ribbons. However, the close apposition of presynaptic Cav1.3 clusters with postsynaptic glutamate receptor GluA4 and PSD-95 clusters was significantly impaired in du/du mice. This implies that, in addition to controlling the expression and gating properties of Cav1.3 channels, the largely extracellularly localized α2δ2 subunit moreover plays a so far unknown role in mediating trans-synaptic alignment of presynaptic Ca2+ channels and postsynaptic AMPA receptors. SIGNIFICANCE STATEMENT Inner hair cells possess calcium channels that are essential for transmitting sound information into synaptic transmitter release. Voltage-gated calcium channels can coassemble with auxiliary subunit α2δ isoforms 1-4. We found that hair cells of the mouse express the auxiliary subunit α2δ2, which is needed for normal hearing thresholds. Using a mouse model with a mutant, nonfunctional α2δ2 protein, we showed that the α2δ2 protein is necessary for normal calcium currents and exocytosis in inner hair cells. Unexpectedly, the α2δ2 protein is moreover required for the optimal spatial alignment of presynaptic calcium channels and postsynaptic glutamate receptor proteins across the synaptic cleft. This suggests that α2δ2 plays a novel role in organizing the synapse.
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Seitter H, Koschak A. Relevance of tissue specific subunit expression in channelopathies. Neuropharmacology 2017; 132:58-70. [PMID: 28669898 DOI: 10.1016/j.neuropharm.2017.06.029] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Revised: 06/22/2017] [Accepted: 06/28/2017] [Indexed: 12/27/2022]
Abstract
Channelopathies are a diverse group of human disorders that are caused by mutations in genes coding for ion channels or channel-regulating proteins. Several dozen channelopathies have been identified that involve both non-excitable cells as well as electrically active tissues like brain, skeletal and smooth muscle or the heart. In this review, we start out from the general question which ion channel genes are expressed tissue-selectively. We mined the human gene expression database Human Protein Atlas (HPA) for tissue-enriched ion channel genes and found 85 genes belonging to the ion channel families. Most of these genes were enriched in brain, testis and muscle and a complete list of the enriched ion channel genes is provided. We further focused on the tissue distribution of voltage-gated calcium channel (VGCC) genes including different brain areas and the retina based on the human gene expression from the FANTOM5 dataset. The expression data is complemented by an overview of the tissue-dependent aspects of L-type calcium channel (LTCC) function, dysfunction and pharmacology, as well as of their splice variants. Finally, we focus on the pathology of tissue-restricted LTCC channelopathies and their treatment options. This article is part of the Special Issue entitled 'Channelopathies.'
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Affiliation(s)
- Hartwig Seitter
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, Innrain 80-82/III, 6020 Innsbruck, Austria
| | - Alexandra Koschak
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, Innrain 80-82/III, 6020 Innsbruck, Austria.
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Kerov V, Lee A. Degrading vision with too much Ca(2+). Channels (Austin) 2016; 9:221-2. [PMID: 26542625 DOI: 10.1080/19336950.2015.1089073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Affiliation(s)
- Vasily Kerov
- a Departments of Molecular Physiology & Biophysics , Otolaryngology-Head and Neck Surgery, and Neurology, University of Iowa ; Iowa City , IA USA
| | - Amy Lee
- a Departments of Molecular Physiology & Biophysics , Otolaryngology-Head and Neck Surgery, and Neurology, University of Iowa ; Iowa City , IA USA
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Dinet V, Ciccotosto GD, Delaunay K, Borras C, Ranchon-Cole I, Kostic C, Savoldelli M, El Sanharawi M, Jonet L, Pirou C, An N, Abitbol M, Arsenijevic Y, Behar-Cohen F, Cappai R, Mascarelli F. Amyloid Precursor-Like Protein 2 deletion-induced retinal synaptopathy related to congenital stationary night blindness: structural, functional and molecular characteristics. Mol Brain 2016; 9:64. [PMID: 27267879 PMCID: PMC4897877 DOI: 10.1186/s13041-016-0245-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 05/30/2016] [Indexed: 12/03/2022] Open
Abstract
Background Amyloid precursor protein knockout mice (APP-KO) have impaired differentiation of amacrine and horizontal cells. APP is part of a gene family and its paralogue amyloid precursor-like protein 2 (APLP2) has both shared as well as distinct expression patterns to APP, including in the retina. Given the impact of APP in the retina we investigated how APLP2 expression affected the retina using APLP2 knockout mice (APLP2-KO). Results Using histology, morphometric analysis with noninvasive imaging technique and electron microscopy, we showed that APLP2-KO retina displayed abnormal formation of the outer synaptic layer, accompanied with greatly impaired photoreceptor ribbon synapses in adults. Moreover, APLP2-KO displayed a significant decease in ON-bipolar, rod bipolar and type 2 OFF-cone bipolar cells (36, 21 and 63 %, respectively). Reduction of the number of bipolar cells was accompanied with disrupted dendrites, reduced expression of metabotropic glutamate receptor 6 at the dendritic tips and alteration of axon terminals in the OFF laminae of the inner plexiform layer. In contrast, the APP-KO photoreceptor ribbon synapses and bipolar cells were intact. The APLP2-KO retina displayed numerous phenotypic similarities with the congenital stationary night blindness, a non-progressive retinal degeneration disease characterized by the loss of night vision. The pathological phenotypes in the APLP2-KO mouse correlated to altered transcription of genes involved in pre- and postsynatic structure/function, including CACNA1F, GRM6, TRMP1 and Gα0, and a normal scotopic a-wave electroretinogram amplitude, markedly reduced scotopic electroretinogram b-wave and modestly reduced photopic cone response. This confirmed the impaired function of the photoreceptor ribbon synapses and retinal bipolar cells, as is also observed in congenital stationary night blindness. Since congenital stationary night blindness present at birth, we extended our analysis to retinal differentiation and showed impaired differentiation of different bipolar cell subtypes and an altered temporal sequence of development from OFF to ON laminae in the inner plexiform layer. This was associated with the altered expression patterns of bipolar cell generation and differentiation factors, including MATH3, CHX10, VSX1 and OTX2. Conclusions These findings demonstrate that APLP2 couples retina development and synaptic genes and present the first evidence that APLP2 expression may be linked to synaptic disease. Electronic supplementary material The online version of this article (doi:10.1186/s13041-016-0245-z) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Virginie Dinet
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Giuseppe D Ciccotosto
- Department of Pathology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, Australia
| | - Kimberley Delaunay
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Céline Borras
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Isabelle Ranchon-Cole
- Laboratoire de Biophysique Sensorielle, Université Clermont 1, Clermont-Ferrand, France
| | - Corinne Kostic
- Unit of Gene Therapy & Stem Cell Biology, University of Lausanne, Jules-Gonin Eye Hospital, Lausanne, Switzerland
| | - Michèle Savoldelli
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Mohamed El Sanharawi
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Laurent Jonet
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Caroline Pirou
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Na An
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Marc Abitbol
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Yvan Arsenijevic
- Unit of Gene Therapy & Stem Cell Biology, University of Lausanne, Jules-Gonin Eye Hospital, Lausanne, Switzerland
| | - Francine Behar-Cohen
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France
| | - Roberto Cappai
- Department of Pathology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, Australia
| | - Frédéric Mascarelli
- Centre de Recherche des Cordeliers, Université Paris Descartes, Université Pierre et Marie Curie, Paris, France.
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Giblin JP, Comes N, Strauss O, Gasull X. Ion Channels in the Eye: Involvement in Ocular Pathologies. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2015; 104:157-231. [PMID: 27038375 DOI: 10.1016/bs.apcsb.2015.11.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.
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Affiliation(s)
- Jonathan P Giblin
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Nuria Comes
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | | | - Xavier Gasull
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
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Congenital stationary night blindness: An analysis and update of genotype–phenotype correlations and pathogenic mechanisms. Prog Retin Eye Res 2015; 45:58-110. [DOI: 10.1016/j.preteyeres.2014.09.001] [Citation(s) in RCA: 207] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 09/25/2014] [Accepted: 09/30/2014] [Indexed: 01/18/2023]
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Abstract
Across the nervous system, neurons form highly stereotypic patterns of synaptic connections that are designed to serve specific functions. Mature wiring patterns are often attained upon the refinement of early, less precise connectivity. Much work has led to the prevailing view that many developing circuits are sculpted by activity-dependent competition among converging afferents, which results in the elimination of unwanted synapses and the maintenance and strengthening of desired connections. Studies of the vertebrate retina, however, have recently revealed that activity can play a role in shaping developing circuits without engaging competition among converging inputs that differ in their activity levels. Such neurotransmission-mediated processes can produce stereotypic wiring patterns by promoting selective synapse formation rather than elimination. We discuss how the influence of transmission may also be limited by circuit design and further highlight the importance of transmission beyond development in maintaining wiring specificity and synaptic organization of neural circuits.
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Knoflach D, Schicker K, Glösmann M, Koschak A. Gain-of-function nature of Cav1.4 L-type calcium channels alters firing properties of mouse retinal ganglion cells. Channels (Austin) 2015; 9:298-306. [PMID: 26274509 PMCID: PMC4826138 DOI: 10.1080/19336950.2015.1078040] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 07/22/2015] [Accepted: 07/22/2015] [Indexed: 10/25/2022] Open
Abstract
Proper function of Cav1.4 L-type calcium channels is crucial for neurotransmitter release in the retina. Our understanding about how different levels of Cav1.4 channel activity affect retinal function is still limited. In the gain-of-function mouse model Cav1.4-IT we expected a reduction in the photoreceptor dynamic range but still transmission toward retinal ganglion cells. A fraction of Cav1.4-IT ganglion cells responded to light stimulation in multielectrode array recordings from whole-mounted retinas, but showed a significantly delayed response onset. Another significant number of cells showed higher activity in darkness. In addition to structural remodeling observed at the first retinal synapse of Cav1.4-IT mice the functional data suggested a loss of contrast enhancement, a fundamental feature of our visual system. In fact, Cav1.4-IT mouse retinas showed a decline in spatial response and changes in their contrast sensitivity profile. Photoreceptor degeneration was obvious from the nodular structure of cone axons and enlarged pedicles which partly moved toward the outer nuclear layer. Loss of photoreceptors was also expressed as reduced expression of proteins involved in chemical and electrical transmission, as such metabotropic glutamate receptor mGluR6 and the gap junction protein Connexin 36. Such gross changes in retinal structure and function could also explain the diminished visual performance of CSNB2 patients. The expression pattern of the plasma-membrane calcium ATPase 1 which participates in the maintenance of the intracellular calcium homeostasis in photoreceptors was changed in Cav1.4-IT mice. This might be part of a protection mechanism against increased calcium influx, as this is suggested for Cav1.4-IT channels.
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Affiliation(s)
- Dagmar Knoflach
- Medical University Vienna, Center for Physiology and Pharmacology; Department of Neurophysiology and -pharmacology; Vienna, Austria
| | - Klaus Schicker
- Medical University Vienna, Center for Physiology and Pharmacology; Department of Neurophysiology and -pharmacology; Vienna, Austria
| | | | - Alexandra Koschak
- Medical University Vienna, Center for Physiology and Pharmacology; Department of Neurophysiology and -pharmacology; Vienna, Austria
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology; Innsbruck, Austria
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Geisler S, Schöpf CL, Obermair GJ. Emerging evidence for specific neuronal functions of auxiliary calcium channel α₂δ subunits. Gen Physiol Biophys 2014; 34:105-118. [PMID: 25504062 DOI: 10.4149/gpb_2014037] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 11/06/2014] [Indexed: 11/08/2022]
Abstract
In nerve cells the ubiquitous second messenger calcium regulates a variety of vitally important functions including neurotransmitter release, gene regulation, and neuronal plasticity. The entry of calcium into cells is tightly regulated by voltage-gated calcium channels, which consist of a heteromultimeric complex of a pore forming α₁, and the auxiliary β and α₂δ subunits. Four genes (Cacna2d1-4) encode for the extracellular membrane-attached α₂δ subunits (α₂δ-1 to α₂δ-4), out of which three isoforms (α₂δ-1 to -3) are strongly expressed in the central nervous system. Over the years a wealth of studies has demonstrated the classical role of α₂δ subunits in channel trafficking and calcium current modulation. Recent studies in specialized neuronal cell systems propose roles of α₂δ subunits beyond the classical view and implicate α₂δ subunits as important regulators of synapse formation. These findings are supported by the identification of novel human disease mutations associated with α₂δ subunits and by the fact that α₂δ subunits are the target of the anti-epileptic and anti-allodynic drugs gabapentin and pregabalin. Here we review the recently emerging evidence for specific as well as redundant neuronal roles of α₂δ subunits and discuss the mechanisms for establishing and maintaining specificity.
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Affiliation(s)
- Stefanie Geisler
- Division of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Clemens L Schöpf
- Division of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, 6020 Innsbruck, Austria
| | - Gerald J Obermair
- Division of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, 6020 Innsbruck, Austria
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Lee A, Wang S, Williams B, Hagen J, Scheetz TE, Haeseleer F. Characterization of Cav1.4 complexes (α11.4, β2, and α2δ4) in HEK293T cells and in the retina. J Biol Chem 2014; 290:1505-21. [PMID: 25468907 DOI: 10.1074/jbc.m114.607465] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
In photoreceptor synaptic terminals, voltage-gated Cav1.4 channels mediate Ca(2+) signals required for transmission of visual stimuli. Like other high voltage-activated Cav channels, Cav1.4 channels are composed of a main pore-forming Cav1.4 α1 subunit and auxiliary β and α2δ subunits. Of the four distinct classes of β and α2δ, β2 and α2δ4 are thought to co-assemble with Cav1.4 α1 subunits in photoreceptors. However, an understanding of the functional properties of this combination of Cav subunits is lacking. Here, we provide evidence that Cav1.4 α1, β2, and α2δ4 contribute to Cav1.4 channel complexes in the retina and describe their properties in electrophysiological recordings. In addition, we identified a variant of β2, named here β2X13, which, along with β2a, is present in photoreceptor terminals. Cav1.4 α1, β2, and α2δ4 were coimmunoprecipitated from lysates of transfected HEK293 cells and mouse retina and were found to interact in the outer plexiform layer of the retina containing the photoreceptor synaptic terminals, by proximity ligation assays. In whole-cell patch clamp recordings of transfected HEK293T cells, channels (Cav1.4 α1 + β2X13) containing α2δ4 exhibited weaker voltage-dependent activation than those with α2δ1. Moreover, compared with channels (Cav1.4 α1 + α2δ4) with β2a, β2X13-containing channels exhibited greater voltage-dependent inactivation. The latter effect was specific to Cav1.4 because it was not seen for Cav1.2 channels. Our results provide the first detailed functional analysis of the Cav1.4 subunits that form native photoreceptor Cav1.4 channels and indicate potential heterogeneity in these channels conferred by β2a and β2X13 variants.
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Affiliation(s)
- Amy Lee
- From the Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, University of Iowa, Iowa City, Iowa 52242
| | - Shiyi Wang
- From the Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, University of Iowa, Iowa City, Iowa 52242
| | - Brittany Williams
- From the Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, University of Iowa, Iowa City, Iowa 52242
| | - Jussara Hagen
- From the Departments of Molecular Physiology and Biophysics, Otolaryngology Head-Neck Surgery, and Neurology, University of Iowa, Iowa City, Iowa 52242
| | - Todd E Scheetz
- the Departments of Ophthalmology and Visual Sciences and Biomedical Engineering, University of Iowa, Iowa City, Iowa 52242, and
| | - Françoise Haeseleer
- the Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195
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Burtscher V, Schicker K, Novikova E, Pöhn B, Stockner T, Kugler C, Singh A, Zeitz C, Lancelot ME, Audo I, Leroy BP, Freissmuth M, Herzig S, Matthes J, Koschak A. Spectrum of Cav1.4 dysfunction in congenital stationary night blindness type 2. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1838:2053-65. [PMID: 24796500 PMCID: PMC4065569 DOI: 10.1016/j.bbamem.2014.04.023] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 04/11/2014] [Accepted: 04/23/2014] [Indexed: 11/26/2022]
Abstract
Defective retinal synaptic transmission in patients affected with congenital stationary night blindness type 2 (CSNB2) can result from different dysfunction phenotypes in Cav1.4 L-type calcium channels. Here we investigated two prototypical Cav1.4 variants from either end of the functional spectrum. Using whole-cell and single-channel patch-clamp techniques, we provide analysis of the biophysical characteristics of the point mutation L860P and the C-terminal truncating mutation R1827X. L860P showed a typical loss-of-function phenotype attributed to a reduced number of functional channels expressed at the plasma membrane as implied by gating current and non-stationary noise analyses. This phenotype can be rationalized, because the inserted proline is predicted to break an amphipatic helix close to the transmembrane segment IIIS1 and thus to reduce channel stability and promote misfolding. In fact, L860P was subject to an increased turnover. In contrast, R1827X displayed an apparent gain-of-function phenotype, i.e., due to a hyperpolarizing shift of the IV-curve and increased single-channel activity. However, truncation also resulted in the loss of functional C-terminal modulation and thus unmasked calcium-dependent inactivation. Thus R1827X failed to support continuous calcium influx. Current inactivation curtails the dynamic range of photoreceptors (e.g., when adapting to variation in illumination). Taken together, the analysis of two representative mutations that occur in CSNB2 patients revealed fundamental differences in the underlying defect. These may explain subtle variations in the clinical manifestation and must be taken into account, if channel function is to be restored by pharmacochaperones or related approaches.
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Affiliation(s)
- Verena Burtscher
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Klaus Schicker
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Elena Novikova
- University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany
| | - Birgit Pöhn
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Thomas Stockner
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Pharmacology, Währingerstrasse 13A, 1090 Wien, Austria
| | - Christof Kugler
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Anamika Singh
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, Innrain 80-82/III, 6020 Innsbruck, Austria
| | - Christina Zeitz
- INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France
| | - Marie-Elise Lancelot
- INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France
| | - Isabelle Audo
- INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France; Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts, INSERM-DHOS CIC 503, Paris F-75012, France; UCL-Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Bart Peter Leroy
- Dept of Ophthalmology & Center for Medical Genetics, Ghent University Hospital & Ghent University, 9000 Ghent, Belgium
| | - Michael Freissmuth
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Pharmacology, Währingerstrasse 13A, 1090 Wien, Austria
| | - Stefan Herzig
- University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany
| | - Jan Matthes
- University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany
| | - Alexandra Koschak
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria.
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Simms BA, Zamponi GW. Neuronal voltage-gated calcium channels: structure, function, and dysfunction. Neuron 2014; 82:24-45. [PMID: 24698266 DOI: 10.1016/j.neuron.2014.03.016] [Citation(s) in RCA: 420] [Impact Index Per Article: 42.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Voltage-gated calcium channels are the primary mediators of depolarization-induced calcium entry into neurons. There is great diversity of calcium channel subtypes due to multiple genes that encode calcium channel α1 subunits, coassembly with a variety of ancillary calcium channel subunits, and alternative splicing. This allows these channels to fulfill highly specialized roles in specific neuronal subtypes and at particular subcellular loci. While calcium channels are of critical importance to brain function, their inappropriate expression or dysfunction gives rise to a variety of neurological disorders, including, pain, epilepsy, migraine, and ataxia. This Review discusses salient aspects of voltage-gated calcium channel function, physiology, and pathophysiology.
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Affiliation(s)
- Brett A Simms
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, AB T2N 4N1, Canada
| | - Gerald W Zamponi
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, AB T2N 4N1, Canada.
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Schmitz F. Presynaptic [Ca(2+)] and GCAPs: aspects on the structure and function of photoreceptor ribbon synapses. Front Mol Neurosci 2014; 7:3. [PMID: 24567702 PMCID: PMC3915146 DOI: 10.3389/fnmol.2014.00003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Accepted: 01/15/2014] [Indexed: 12/21/2022] Open
Abstract
Changes in intracellular calcium ions [Ca2+] play important roles in photoreceptor signaling. Consequently, intracellular [Ca2+] levels need to be tightly controlled. In the light-sensitive outer segments (OS) of photoreceptors, Ca2+ regulates the activity of retinal guanylate cyclases thus playing a central role in phototransduction and light-adaptation by restoring light-induced decreases in cGMP. In the synaptic terminals, changes of intracellular Ca2+ trigger various aspects of neurotransmission. Photoreceptors employ tonically active ribbon synapses that encode light-induced, graded changes of membrane potential into modulation of continuous synaptic vesicle exocytosis. The active zones of ribbon synapses contain large electron-dense structures, synaptic ribbons, that are associated with large numbers of synaptic vesicles. Synaptic coding at ribbon synapses differs from synaptic coding at conventional (phasic) synapses. Recent studies revealed new insights how synaptic ribbons are involved in this process. This review focuses on the regulation of [Ca2+] in presynaptic photoreceptor terminals and on the function of a particular Ca2+-regulated protein, the neuronal calcium sensor protein GCAP2 (guanylate cyclase-activating protein-2) in the photoreceptor ribbon synapse. GCAP2, an EF-hand-containing protein plays multiple roles in the OS and in the photoreceptor synapse. In the OS, GCAP2 works as a Ca2+-sensor within a Ca2+-regulated feedback loop that adjusts cGMP levels. In the photoreceptor synapse, GCAP2 binds to RIBEYE, a component of synaptic ribbons, and mediates Ca2+-dependent plasticity at that site. Possible mechanisms are discussed.
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Affiliation(s)
- Frank Schmitz
- Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Medical School Homburg/Saar, Saarland University Saarland, Germany
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Regus-Leidig H, Atorf J, Feigenspan A, Kremers J, Maw MA, Brandstätter JH. Photoreceptor degeneration in two mouse models for congenital stationary night blindness type 2. PLoS One 2014; 9:e86769. [PMID: 24466230 PMCID: PMC3897778 DOI: 10.1371/journal.pone.0086769] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 12/17/2013] [Indexed: 02/02/2023] Open
Abstract
Light-dependent conductance changes of voltage-gated Cav1.4 channels regulate neurotransmitter release at photoreceptor ribbon synapses. Mutations in the human CACNA1F gene encoding the α1F subunit of Cav1.4 channels cause an incomplete form of X-linked congenital stationary night blindness (CSNB2). Many CACNA1F mutations are loss-of-function mutations resulting in non-functional Cav1.4 channels, but some mutations alter the channels’ gating properties and, presumably, disturb Ca2+ influx at photoreceptor ribbon synapses. Notably, a CACNA1F mutation (I745T) was identified in a family with an uncommonly severe CSNB2-like phenotype, and, when expressed in a heterologous system, the mutation was shown to shift the voltage-dependence of channel activation, representing a gain-of-function. To gain insight into the pathomechanism that could explain the severity of this disorder, we generated a mouse model with the corresponding mutation in the murine Cacna1f gene (I756T) and compared it with a mouse model carrying a loss-of-function mutation (ΔEx14–17) in a longitudinal study up to eight months of age. In ΔEx14–17 mutants, the b-wave in the electroretinogram was absent, photoreceptor ribbon synapses were abnormal, and Ca2+ responses to depolarization of photoreceptor terminals were undetectable. In contrast, I756T mutants had a reduced scotopic b-wave, some intact rod ribbon synapses, and a strong, though abnormal, Ca2+ response to depolarization. Both mutants showed a progressive photoreceptor loss, but degeneration was more severe and significantly enhanced in the I756T mutants compared to the ΔEx14–17 mutants.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
| | - Jenny Atorf
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Andreas Feigenspan
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
| | - Jan Kremers
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Marion A. Maw
- Department of Biochemistry, University of Otago, Dunedin, New Zealand
- * E-mail: (MAM); (JHB)
| | - Johann Helmut Brandstätter
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
- * E-mail: (MAM); (JHB)
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