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Maddox JW, Ordemann GJ, Vázquez JDLR, Huang A, Gault C, Wisner SR, Randall K, Futagi D, DeVries SH, Hoon M, Lee A. A non-conducting role of the Ca v1.4 Ca 2+ channel drives homeostatic plasticity at the cone photoreceptor synapse. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.05.570129. [PMID: 38106079 PMCID: PMC10723350 DOI: 10.1101/2023.12.05.570129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
In congenital stationary night blindness type 2 (CSNB2)-a disorder involving dysfunction of the Cav1.4 Ca2+ channel-visual impairment is relatively mild considering that Cav1.4 mediates synaptic transmission by rod and cone photoreceptors. Here, we addressed this conundrum using a Cav1.4 knockout (KO) mouse and a knock-in (KI) mouse expressing a non-conducting Cav1.4 mutant. Surprisingly, aberrant Cav3 currents were detected in cones of the KI and KO but not wild-type mice. Cone synapses, which fail to develop in KO mice, are present but enlarged in KI mice. Moreover, light responses in cone pathways and photopic visual behavior are preserved in KI but not in KO mice. In CSNB2, we propose that Cav3 channels maintain cone synaptic output provided that the Ca2+-independent role of Cav1.4 in cone synaptogenesis remains intact. Our findings reveal an unexpected form of homeostatic plasticity that relies on a non-canonical role of an ion channel.
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Affiliation(s)
- J. Wesley Maddox
- Dept of Neuroscience, University of Texas-Austin, Austin, TX 78712, USA
- These authors contributed equally
| | - Gregory J. Ordemann
- Dept of Neuroscience, University of Texas-Austin, Austin, TX 78712, USA
- These authors contributed equally
| | | | - Angie Huang
- Dept of Neuroscience, University of Texas-Austin, Austin, TX 78712, USA
| | - Christof Gault
- Dept of Neuroscience, University of Texas-Austin, Austin, TX 78712, USA
| | - Serena R. Wisner
- Dept. of Ophthalmology and Visual Sciences, University of Wisconsin- Madison, Madison, WI, 53706, USA
- Neuroscience Training Program, University of Wisconsin-Madison, Madison WI 53706 USA
| | - Kate Randall
- Dept of Neuroscience, University of Texas-Austin, Austin, TX 78712, USA
| | - Daiki Futagi
- Dept. of Ophthalmology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Steven H. DeVries
- Dept. of Ophthalmology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Mrinalini Hoon
- Dept. of Ophthalmology and Visual Sciences, University of Wisconsin- Madison, Madison, WI, 53706, USA
- McPherson Eye Research Institute, Madison WI 53706 USA
| | - Amy Lee
- Dept of Neuroscience, University of Texas-Austin, Austin, TX 78712, USA
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Townes-Anderson E, Halász É, Sugino I, Davidow AL, Frishman LJ, Fritzky L, Yousufzai FAK, Zarbin M. Injury to Cone Synapses by Retinal Detachment: Differences from Rod Synapses and Protection by ROCK Inhibition. Cells 2023; 12:1485. [PMID: 37296606 PMCID: PMC10253016 DOI: 10.3390/cells12111485] [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: 04/15/2023] [Revised: 05/22/2023] [Accepted: 05/24/2023] [Indexed: 06/12/2023] Open
Abstract
Attachment of a detached retina does not always restore vision to pre-injury levels, even if the attachment is anatomically successful. The problem is due in part to long-term damage to photoreceptor synapses. Previously, we reported on damage to rod synapses and synaptic protection using a Rho kinase (ROCK) inhibitor (AR13503) after retinal detachment (RD). This report documents the effects of detachment, reattachment, and protection by ROCK inhibition on cone synapses. Conventional confocal and stimulated emission depletion (STED) microscopy were used for morphological assessment and electroretinograms for functional analysis of an adult pig model of RD. RDs were examined 2 and 4 h after injury or two days later when spontaneous reattachment had occurred. Cone pedicles respond differently than rod spherules. They lose their synaptic ribbons, reduce invaginations, and change their shape. ROCK inhibition protects against these structural abnormalities whether the inhibitor is applied immediately or 2 h after the RD. Functional restoration of the photopic b-wave, indicating cone-bipolar neurotransmission, is also improved with ROCK inhibition. Successful protection of both rod and cone synapses with AR13503 suggests this drug will (1) be a useful adjunct to subretinal administration of gene or stem cell therapies and (2) improve recovery of the injured retina when treatment is delayed.
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Affiliation(s)
- Ellen Townes-Anderson
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA;
| | - Éva Halász
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA;
| | - Ilene Sugino
- Institute of Ophthalmology and Visual Science, Rutgers New Jersey Medical School, 90 Bergen Street, Newark, NJ 07103, USA; (I.S.); (M.Z.)
| | - Amy L. Davidow
- Department of Biostatistics, New York University School of Global Public Health, 708 Broadway, New York, NY 10003, USA;
| | - Laura J. Frishman
- Department of Vision Sciences, College of Optometry, University of Houston, Martin Luther King Blvd, Houston, TX 77204, USA;
| | - Luke Fritzky
- Cellular Imaging and Histology Core, Rutgers New Jersey Medical School, 205 South Orange Avenue, Newark, NJ 07103, USA; (L.F.); (F.A.K.Y.)
| | - Fawad A. K. Yousufzai
- Cellular Imaging and Histology Core, Rutgers New Jersey Medical School, 205 South Orange Avenue, Newark, NJ 07103, USA; (L.F.); (F.A.K.Y.)
| | - Marco Zarbin
- Institute of Ophthalmology and Visual Science, Rutgers New Jersey Medical School, 90 Bergen Street, Newark, NJ 07103, USA; (I.S.); (M.Z.)
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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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Davison A, Gierke K, Brandstätter JH, Babai N. Synaptic vesicle release during ribbon synapse formation of cone photoreceptors. Front Cell Neurosci 2022; 16:1022419. [PMID: 36406751 PMCID: PMC9672513 DOI: 10.3389/fncel.2022.1022419] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 10/20/2022] [Indexed: 08/14/2023] Open
Abstract
Mammalian cone photoreceptors enable through their sophisticated synapse the high-fidelity transfer of visual information to second-order neurons in the retina. The synapse contains a proteinaceous organelle, called the synaptic ribbon, which tethers synaptic vesicles (SVs) at the active zone (AZ) close to voltage-gated Ca2+ channels. However, the exact contribution of the synaptic ribbon to neurotransmission is not fully understood, yet. In mice, precursors to synaptic ribbons appear within photoreceptor terminals shortly after birth as free-floating spherical structures, which progressively elongate and then attach to the AZ during the following days. Here, we took advantage of the process of synaptic ribbon maturation to study their contribution to SV release. We performed whole-cell patch-clamp recordings from cone photoreceptors at three postnatal (P) development stages (P8-9, P12-13, >P30) and measured evoked SV release, SV replenishment rate, recovery from synaptic depression, domain organization of voltage-sensitive Ca2+ channels, and Ca2+-sensitivity of exocytosis. Additionally, we performed electron microscopy to determine the density of SVs at ribbon-free and ribbon-occupied AZs. Our results suggest that ribbon attachment does not organize the voltage-sensitive Ca2+ channels into nanodomains or control SV release probability. However, ribbon attachment increases SV density at the AZ, increases the pool size of readily releasable SVs available for evoked SV release, facilitates SV replenishment without changing the SV pool refilling time, and increases the Ca2+- sensitivity of glutamate release.
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Affiliation(s)
| | | | | | - Norbert Babai
- Division of Animal Physiology/Neurobiology, Department of Biology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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