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Tebbe L, Kakakhel M, Al-Ubaidi MR, Naash MI. The role of syntaxins in retinal function and health. Front Cell Neurosci 2024; 18:1380064. [PMID: 38799985 PMCID: PMC11119284 DOI: 10.3389/fncel.2024.1380064] [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: 01/31/2024] [Accepted: 04/16/2024] [Indexed: 05/29/2024] Open
Abstract
The soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptor (SNARE) superfamily plays a pivotal role in cellular trafficking by facilitating membrane fusion events. These SNARE proteins, including syntaxins, assemble into complexes that actively facilitate specific membrane fusion events. Syntaxins, as integral components of the SNARE complex, play a crucial role in initiating and regulating these fusion activities. While specific syntaxins have been extensively studied in various cellular processes, including neurotransmitter release, autophagy and endoplasmic reticulum (ER)-to-Golgi protein transport, their roles in the retina remain less explored. This review aims to enhance our understanding of syntaxins' functions in the retina by shedding light on how syntaxins mediate membrane fusion events unique to the retina. Additionally, we seek to establish a connection between syntaxin mutations and retinal diseases. By exploring the intricate interplay of syntaxins in retinal function and health, we aim to contribute to the broader comprehension of cellular trafficking in the context of retinal physiology and pathology.
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Affiliation(s)
| | | | | | - Muna I. Naash
- *Correspondence: Muna I. Naash, ; Muayyad R. Al-Ubaidi,
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2
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Sun Y, Hao M, Wu H, Zhang C, Wei D, Li S, Song Z, Tao Y. Unveiling the role of CaMKII in retinal degeneration: from biological mechanism to therapeutic strategies. Cell Biosci 2024; 14:59. [PMID: 38725013 PMCID: PMC11084033 DOI: 10.1186/s13578-024-01236-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2024] [Accepted: 04/18/2024] [Indexed: 05/12/2024] Open
Abstract
Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a family of broad substrate specificity serine (Ser)/threonine (Thr) protein kinases that play a crucial role in the Ca2+-dependent signaling pathways. Its significance as an intracellular Ca2+ sensor has garnered abundant research interest in the domain of neurodegeneration. Accumulating evidences suggest that CaMKII is implicated in the pathology of degenerative retinopathies such as diabetic retinopathy (DR), age-related macular degeneration (AMD), retinitis pigmentosa (RP) and glaucoma optic neuropathy. CaMKII can induce the aberrant proliferation of retinal blood vessels, influence the synaptic signaling, and exert dual effects on the survival of retinal ganglion cells and pigment epithelial cells. Researchers have put forth multiple therapeutic agents, encompassing small molecules, peptides, and nucleotides that possess the capability to modulate CaMKII activity. Due to its broad range isoforms and splice variants therapeutic strategies seek to inhibit specifically the CaMKII are confronted with considerable challenges. Therefore, it becomes crucial to discern the detrimental and advantageous aspects of CaMKII, thereby facilitating the development of efficacious treatment. In this review, we summarize recent research findings on the cellular and molecular biology of CaMKII, with special emphasis on its metabolic and regulatory mechanisms. We delve into the involvement of CaMKII in the retinal signal transduction pathways and discuss the correlation between CaMKII and calcium overload. Furthermore, we elaborate the therapeutic trials targeting CaMKII, and introduce recent developments in the zone of CaMKII inhibitors. These findings would enrich our knowledge of CaMKII, and shed light on the development of a therapeutic target for degenerative retinopathy.
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Affiliation(s)
- Yuxin Sun
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China
- College of Medicine, Zhengzhou University, Zhengzhou, 450001, China
| | - Mengyu Hao
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China
- College of Medicine, Zhengzhou University, Zhengzhou, 450001, China
| | - Hao Wu
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China
- College of Medicine, Zhengzhou University, Zhengzhou, 450001, China
| | - Chengzhi Zhang
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China
- College of Medicine, Zhengzhou University, Zhengzhou, 450001, China
| | - Dong Wei
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China
- College of Medicine, Zhengzhou University, Zhengzhou, 450001, China
| | - Siyu Li
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China
- College of Medicine, Zhengzhou University, Zhengzhou, 450001, China
| | - Zongming Song
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China.
| | - Ye Tao
- Department of Ophthalmology, Henan Eye Hospital, Henan Provincial People's Hospital, People's Hospital of Zhengzhou University, Zhengzhou, 450003, China.
- College of Medicine, Zhengzhou University, Zhengzhou, 450001, China.
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3
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Nishad R, Betancourt-Solis M, Dey H, Heidelberger R, McNew JA. Regulation of Syntaxin3B-Mediated Membrane Fusion by T14, Munc18, and Complexin. Biomolecules 2023; 13:1463. [PMID: 37892145 PMCID: PMC10604575 DOI: 10.3390/biom13101463] [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: 08/16/2023] [Revised: 09/22/2023] [Accepted: 09/26/2023] [Indexed: 10/29/2023] Open
Abstract
Retinal neurons that form ribbon-style synapses operate over a wide dynamic range, continuously relaying visual information to their downstream targets. The remarkable signaling abilities of these neurons are supported by specialized presynaptic machinery, one component of which is syntaxin3B. Syntaxin3B is an essential t-SNARE protein of photoreceptors and bipolar cells that is required for neurotransmitter release. It has a light-regulated phosphorylation site in its N-terminal domain at T14 that has been proposed to modulate membrane fusion. However, a direct test of the latter has been lacking. Using a well-controlled in vitro fusion assay, we found that a phosphomimetic T14 syntaxin3B mutation leads to a small but significant enhancement of SNARE-mediated membrane fusion following the formation of the t-SNARE complex. While the addition of Munc18a had only a minimal effect on membrane fusion mediated by SNARE complexes containing wild-type syntaxin3B, a more significant enhancement was observed in the presence of Munc18a when the SNARE complexes contained a syntaxin3B T14 phosphomimetic mutant. Finally, we showed that the retinal-specific complexins (Cpx III and Cpx IV) inhibited membrane fusion mediated by syntaxin3B-containing SNARE complexes in a dose-dependent manner. Collectively, our results establish that membrane fusion mediated by syntaxin3B-containing SNARE complexes is regulated by the T14 residue of syntaxin3B, Munc18a, and Cpxs III and IV.
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Affiliation(s)
- Rajkishor Nishad
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
| | - Miguel Betancourt-Solis
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
- Lonza Biologics, 14905 Kirby Dr, Houston, TX 77047, USA
| | - Himani Dey
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - James A. McNew
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
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4
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Perez-Hurtado M, Dao C, Saenz AE, Heidelberger R. Syntaxin 3 is haplosufficient for long-term photoreceptor survival in the mouse retina. FRONTIERS IN OPHTHALMOLOGY 2023; 3:1208805. [PMID: 37609371 PMCID: PMC10443939 DOI: 10.3389/fopht.2023.1208805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
Biallelic loss-of-function mutations in the syntaxin 3 gene have been linked to a severe retinal dystrophy in humans that presents in early childhood. In mouse models, biallelic inactivation of the syntaxin 3 gene in photoreceptors rapidly leads to their death. What is not known is whether a monoallelic syntaxin 3 loss-of-function mutation might cause photoreceptor loss with advancing age. To address this question, we compared the outer nuclear layer of older adult mice (≈ 20 months of age) that were heterozygous for syntaxin 3 with those of similarly-aged control mice. We found that the photoreceptor layer maintains its thickness in mice that are heterozygous for syntaxin 3 relative to controls and that photoreceptor somatic counts are comparable. In addition, dendritic sprouting of the rod bipolar cell dendrites into the outer nuclear layer, which occurs following the loss of functional rod targets, was similar between genotypes. Thus, syntaxin 3 appears to be haplosufficient for photoreceptor survival, even with advancing age.
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Affiliation(s)
- Mariajose Perez-Hurtado
- Department of Neurobiology and Anatomy, McGovern Medical School at The University of Texas Health Science Center at Houston (UTHealth Houston), Houston, TX
| | - Calvin Dao
- Department of Neurobiology and Anatomy, McGovern Medical School at The University of Texas Health Science Center at Houston (UTHealth Houston), Houston, TX
| | - Amanda E. Saenz
- Department of Neurobiology and Anatomy, McGovern Medical School at The University of Texas Health Science Center at Houston (UTHealth Houston), Houston, TX
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School at The University of Texas Health Science Center at Houston (UTHealth Houston), Houston, TX
- The University of Texas MDAnderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Houston TX
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5
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Mesnard CS, Barta CL, Sladek AL, Zenisek D, Thoreson WB. Eliminating Synaptic Ribbons from Rods and Cones Halves the Releasable Vesicle Pool and Slows Down Replenishment. Int J Mol Sci 2022; 23:ijms23126429. [PMID: 35742873 PMCID: PMC9223732 DOI: 10.3390/ijms23126429] [Citation(s) in RCA: 8] [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: 05/19/2022] [Revised: 06/03/2022] [Accepted: 06/05/2022] [Indexed: 01/25/2023] Open
Abstract
Glutamate release from rod and cone photoreceptor cells involves presynaptic ribbons composed largely of the protein RIBEYE. To examine roles of ribbons in rods and cones, we studied mice in which GCamP3 replaced the B-domain of RIBEYE. We discovered that ribbons were absent from rods and cones of both knock-in mice possessing GCamP3 and conditional RIBEYE knockout mice. The mice lacking ribbons showed reduced temporal resolution and contrast sensitivity assessed with optomotor reflexes. ERG recordings showed 50% reduction in scotopic and photopic b-waves. The readily releasable pool (RRP) of vesicles in rods and cones measured using glutamate transporter anion currents (IA(glu)) was also halved. We also studied the release from cones by stimulating them optogenetically with ChannelRhodopsin2 (ChR2) while recording postsynaptic currents in horizontal cells. Recovery of the release from paired pulse depression was twofold slower in the rods and cones lacking ribbons. The release from rods at -40 mV in darkness involves regularly spaced multivesicular fusion events. While the regular pattern of release remained in the rods lacking ribbons, the number of vesicles comprising each multivesicular event was halved. Our results support conclusions that synaptic ribbons in rods and cones expand the RRP, speed up vesicle replenishment, and augment some forms of multivesicular release. Slower replenishment and a smaller RRP in photoreceptors lacking ribbons may contribute to diminished temporal frequency responses and weaker contrast sensitivity.
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Affiliation(s)
- Chris S. Mesnard
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, NE 68198, USA; (C.S.M.); (C.L.B.); (A.L.S.)
- Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198, USA
| | - Cody L. Barta
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, NE 68198, USA; (C.S.M.); (C.L.B.); (A.L.S.)
| | - Asia L. Sladek
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, NE 68198, USA; (C.S.M.); (C.L.B.); (A.L.S.)
| | - David Zenisek
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06510, USA;
| | - Wallace B. Thoreson
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, NE 68198, USA; (C.S.M.); (C.L.B.); (A.L.S.)
- Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198, USA
- Correspondence: ; Tel.: +1-402-559-4076
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6
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Janecke AR, Liu X, Adam R, Punuru S, Viestenz A, Strauß V, Laass M, Sanchez E, Adachi R, Schatz MP, Saboo US, Mittal N, Rohrschneider K, Escher J, Ganesh A, Al Zuhaibi S, Al Murshedi F, AlSaleem B, Alfadhel M, Al Sinani S, Alkuraya FS, Huber LA, Müller T, Heidelberger R, Janz R. Pathogenic STX3 variants affecting the retinal and intestinal transcripts cause an early-onset severe retinal dystrophy in microvillus inclusion disease subjects. Hum Genet 2021; 140:1143-1156. [PMID: 33974130 PMCID: PMC8263458 DOI: 10.1007/s00439-021-02284-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 04/15/2021] [Indexed: 01/12/2023]
Abstract
Biallelic STX3 variants were previously reported in five individuals with the severe congenital enteropathy, microvillus inclusion disease (MVID). Here, we provide a significant extension of the phenotypic spectrum caused by STX3 variants. We report ten individuals of diverse geographic origin with biallelic STX3 loss-of-function variants, identified through exome sequencing, single-nucleotide polymorphism array-based homozygosity mapping, and international collaboration. The evaluated individuals all presented with MVID. Eight individuals also displayed early-onset severe retinal dystrophy, i.e., syndromic-intestinal and retinal-disease. These individuals harbored STX3 variants that affected both the retinal and intestinal STX3 transcripts, whereas STX3 variants affected only the intestinal transcript in individuals with solitary MVID. That STX3 is essential for retinal photoreceptor survival was confirmed by the creation of a rod photoreceptor-specific STX3 knockout mouse model which revealed a time-dependent reduction in the number of rod photoreceptors, thinning of the outer nuclear layer, and the eventual loss of both rod and cone photoreceptors. Together, our results provide a link between STX3 loss-of-function variants and a human retinal dystrophy. Depending on the genomic site of a human loss-of-function STX3 variant, it can cause MVID, the novel intestinal-retinal syndrome reported here or, hypothetically, an isolated retinal dystrophy.
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Affiliation(s)
- Andreas R Janecke
- Department of Pediatrics I, Medical University of Innsbruck, Anichstrasse 35, 6020, Innsbruck, Austria.
- Division of Human Genetics, Medical University of Innsbruck, Innsbruck, Austria.
| | - Xiaoqin Liu
- Department of Neurobiology and Anatomy, MSB 7.046, McGovern Medical School at the University of Texas HSC (UTHealth), 6431 Fannin Street, Houston, TX, 77030, USA
| | - Rüdiger Adam
- University Children's Hospital, Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Sumanth Punuru
- Department of Neurobiology and Anatomy, MSB 7.046, McGovern Medical School at the University of Texas HSC (UTHealth), 6431 Fannin Street, Houston, TX, 77030, USA
| | - Arne Viestenz
- Department of Ophthalmology, University Medical Center Halle, Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | - Valeria Strauß
- Klinik für Kinder- und Jugendmedizin, Universitätsklinikum Halle, Halle, Germany
| | - Martin Laass
- Klinik und Poliklinik f. Kinder- u. Jugendmedizin, University of Dresden, Dresden, Germany
| | - Elizabeth Sanchez
- Department of Pulmonary Medicine, Division of Internal Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Roberto Adachi
- Department of Pulmonary Medicine, Division of Internal Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Martha P Schatz
- Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Ujwala S Saboo
- Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, USA
| | - Naveen Mittal
- Department of Department of Pediatrics, Division of Pediatric Gastroenterology, University of Texas Health Science Center, San Antonio, TX, USA
| | | | - Johanna Escher
- Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands
| | - Anuradha Ganesh
- Department of Ophthalmology, Sultan Qaboos University Hospital, Muscat, Oman
| | - Sana Al Zuhaibi
- Department of Ophthalmology, Sultan Qaboos University Hospital, Muscat, Oman
| | - Fathiya Al Murshedi
- Genetic and Developmental Medicine Clinic, Sultan Qaboos University Hospital, Muscat, Oman
| | - Badr AlSaleem
- King Fahad Medical City, Children's Specialized Hospital, Riyadh, Saudi Arabia
| | - Majid Alfadhel
- Genetics Division and Medical Genomic Research Lab, King Saud Bin Abdulaziz University for Health Sciences (KSAU-HS), Riyadh, Saudi Arabia
| | - Siham Al Sinani
- Department of Child Health, Sultan Qaboos University Hospital, Muscat, Oman
| | - Fowzan S Alkuraya
- Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
| | - Lukas A Huber
- Division of Cell Biology, Medical University of Innsbruck, Innsbruck, Austria
| | - Thomas Müller
- Department of Pediatrics I, Medical University of Innsbruck, Anichstrasse 35, 6020, Innsbruck, Austria
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, MSB 7.046, McGovern Medical School at the University of Texas HSC (UTHealth), 6431 Fannin Street, Houston, TX, 77030, USA.
| | - Roger Janz
- Department of Neurobiology and Anatomy, MSB 7.046, McGovern Medical School at the University of Texas HSC (UTHealth), 6431 Fannin Street, Houston, TX, 77030, USA
- Center for Scientific Review, National Institutes of Health, Bethesda, MD, USA
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7
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Thoreson WB. Transmission at rod and cone ribbon synapses in the retina. Pflugers Arch 2021; 473:1469-1491. [PMID: 33779813 DOI: 10.1007/s00424-021-02548-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 02/23/2021] [Accepted: 02/25/2021] [Indexed: 12/29/2022]
Abstract
Light-evoked voltage responses of rod and cone photoreceptor cells in the vertebrate retina must be converted to a train of synaptic vesicle release events for transmission to downstream neurons. This review discusses the processes, proteins, and structures that shape this critical early step in vision, focusing on studies from salamander retina with comparisons to other experimental animals. Many mechanisms are conserved across species. In cones, glutamate release is confined to ribbon release sites although rods are also capable of release at non-ribbon sites. The role of non-ribbon release in rods remains unclear. Release from synaptic ribbons in rods and cones involves at least three vesicle pools: a readily releasable pool (RRP) matching the number of membrane-associated vesicles along the ribbon base, a ribbon reserve pool matching the number of additional vesicles on the ribbon, and an enormous cytoplasmic reserve. Vesicle release increases in parallel with Ca2+ channel activity. While the opening of only a few Ca2+ channels beneath each ribbon can trigger fusion of a single vesicle, sustained release rates in darkness are governed by the rate at which the RRP can be replenished. The number of vacant release sites, their functional status, and the rate of vesicle delivery in turn govern replenishment. Along with an overview of the mechanisms of exocytosis and endocytosis, we consider specific properties of ribbon-associated proteins and pose a number of remaining questions about this first synapse in the visual system.
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Affiliation(s)
- Wallace B Thoreson
- Truhlsen Eye Institute, Departments of Ophthalmology & Visual Sciences and Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.
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Campbell JR, Li H, Wang Y, Kozhemyakin M, Hunt AJ, Liu X, Janz R, Heidelberger R. Phosphorylation of the Retinal Ribbon Synapse Specific t-SNARE Protein Syntaxin3B Is Regulated by Light via a Ca 2 +-Dependent Pathway. Front Cell Neurosci 2020; 14:587072. [PMID: 33192329 PMCID: PMC7606922 DOI: 10.3389/fncel.2020.587072] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 09/11/2020] [Indexed: 12/27/2022] Open
Abstract
Neurotransmitter release at retinal ribbon-style synapses utilizes a specialized t-SNARE protein called syntaxin3B (STX3B). In contrast to other syntaxins, STX3 proteins can be phosphorylated in vitro at T14 by Ca2+/calmodulin-dependent protein kinase II (CaMKII). This modification has the potential to modulate SNARE complex formation required for neurotransmitter release in an activity-dependent manner. To determine the extent to which T14 phosphorylation occurs in vivo in the mammalian retina and characterize the pathway responsible for the in vivo phosphorylation of T14, we utilized quantitative immunofluorescence to measure the levels of STX3 and STX3 phosphorylated at T14 (pSTX3) in the synaptic terminals of mouse retinal photoreceptors and rod bipolar cells (RBCs). Results demonstrate that STX3B phosphorylation at T14 is light-regulated and dependent upon the elevation of intraterminal Ca2+. In rod photoreceptor terminals, the ratio of pSTX3 to STX3 was significantly higher in dark-adapted mice, when rods are active, than in light-exposed mice. By contrast, in RBC terminals, the ratio of pSTX3 to STX3 was higher in light-exposed mice, when these terminals are active, than in dark-adapted mice. These results were recapitulated in the isolated eyecup preparation, but only when Ca2+ was included in the external medium. In the absence of external Ca2+, pSTX3 levels remained low regardless of light/dark exposure. Using the isolated RBC preparation, we next showed that elevation of intraterminal Ca2+ alone was sufficient to increase STX3 phosphorylation at T14. Furthermore, both the non-specific kinase inhibitor staurosporine and the selective CaMKII inhibitor AIP inhibited the Ca2+-dependent increase in the pSTX3/STX3 ratio in isolated RBC terminals, while in parallel experiments, AIP suppressed RBC depolarization-evoked exocytosis, measured using membrane capacitance measurements. Our data support a novel, illumination-regulated modulation of retinal ribbon-style synapse function in which activity-dependent Ca2+ entry drives the phosphorylation of STX3B at T14 by CaMKII, which in turn, modulates the ability to form SNARE complexes required for exocytosis.
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Affiliation(s)
- Joseph R Campbell
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Hongyan Li
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Yanzhao Wang
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Maxim Kozhemyakin
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Albert J Hunt
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Xiaoqin Liu
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Roger Janz
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
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9
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Direct Observation of Vesicle Transport on the Synaptic Ribbon Provides Evidence That Vesicles Are Mobilized and Prepared Rapidly for Release. J Neurosci 2020; 40:7390-7404. [PMID: 32847965 DOI: 10.1523/jneurosci.0605-20.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 07/23/2020] [Accepted: 08/14/2020] [Indexed: 12/12/2022] Open
Abstract
Synaptic ribbons are thought to provide vesicles for continuous release in some retinal nonspiking neurons, yet recent studies indicate that genetic removal of the ribbon has little effect on release kinetics. To investigate vesicle replenishment at synaptic ribbons, we used total internal reflection fluorescence microscopy to image synaptic vesicles and ribbons in retinal bipolar cells of goldfish (Carassius auratus) of both sexes. Analysis of vesicles released by trains of 30 ms depolarizations revealed that most releasable vesicles reside within 300 nm of the ribbon center. A single 30 ms step to 0 mV was sufficient to deplete the membrane-proximal vesicle pool, while triggering rapid stepwise movements of distal vesicles along the ribbon and toward the plasma membrane. Replenishment only becomes rate-limiting for recovery from paired-pulse depression for interstimulus intervals shorter than 250 ms. For longer interstimulus intervals, vesicle movement down the ribbon is fast enough to replenish released vesicles, but newly arrived vesicles are not release-ready. Notably, the rates of vesicle resupply and maturation of newcomers are among the fastest measured optically at any synapse. Lastly, our data show that the delay in vesicle departure increases and vesicle speed decreases with multiple stimuli. Our results support a role for ribbons in the supply of vesicles for release, provide direct measurements of vesicle movement down the ribbon, and suggest that multiple factors contribute to paired-pulse depression.SIGNIFICANCE STATEMENT Synaptic ribbons are macromolecular scaffolds that tether synaptic vesicles close to release sites in nonspiking neurons of the retina and cochlea. Because these neurons release neurotransmitter continuously, synaptic ribbons are assumed to act as platforms for supplying vesicles rapidly in the face of prolonged stimulation. Yet, ribbon synapses suffer from profound paired-pulse depression, which takes seconds to subside. We investigated the mechanistic origin of this phenomenon by directly imaging triggered vesicle movement and release at ribbon sites in retinal bipolar cells, and find that, although ribbon synapses deliver and prime vesicles faster than most conventional synapses, both vesicle absence and vesicle priming contribute to the long recovery from paired-pulse depression.
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10
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Hays CL, Grassmeyer JJ, Wen X, Janz R, Heidelberger R, Thoreson WB. Simultaneous Release of Multiple Vesicles from Rods Involves Synaptic Ribbons and Syntaxin 3B. Biophys J 2019; 118:967-979. [PMID: 31653448 DOI: 10.1016/j.bpj.2019.10.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 09/25/2019] [Accepted: 10/03/2019] [Indexed: 02/05/2023] Open
Abstract
First proposed as a specialized mode of release at sensory neurons possessing ribbon synapses, multivesicular release has since been described throughout the central nervous system. Many aspects of multivesicular release remain poorly understood. We explored mechanisms underlying simultaneous multivesicular release at ribbon synapses in salamander retinal rod photoreceptors. We assessed spontaneous release presynaptically by recording glutamate transporter anion currents (IA(glu)) in rods. Spontaneous IA(glu) events were correlated in amplitude and kinetics with simultaneously measured miniature excitatory postsynaptic currents in horizontal cells. Both measures indicated that a significant fraction of events is multiquantal, with an analysis of IA(glu) revealing that multivesicular release constitutes ∼30% of spontaneous release events. IA(glu) charge transfer increased linearly with event amplitude showing that larger events involve greater glutamate release. The kinetics of large and small IA(glu) events were identical as were rise times of large and small miniature excitatory postsynaptic currents, indicating that the release of multiple vesicles during large events is highly synchronized. Effects of exogenous Ca2+ buffers suggested that multiquantal, but not uniquantal, release occurs preferentially near Ca2+ channels clustered beneath synaptic ribbons. Photoinactivation of ribbons reduced the frequency of spontaneous multiquantal events without affecting uniquantal release frequency, showing that spontaneous multiquantal release requires functional ribbons. Although both occur at ribbon-style active zones, the absence of cross-depletion indicates that evoked and spontaneous multiquantal release from ribbons involve different vesicle pools. Introducing an inhibitory peptide into rods to interfere with the SNARE protein, syntaxin 3B, selectively reduced multiquantal event frequency. These results support the hypothesis that simultaneous multiquantal release from rods arises from homotypic fusion among neighboring vesicles on ribbons and involves syntaxin 3B.
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Affiliation(s)
- Cassandra L Hays
- Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, Nebraska; Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, Nebraska
| | - Justin J Grassmeyer
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, Nebraska; Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska
| | - Xiangyi Wen
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, Nebraska; West China Hospital, Sichuan University, Chengdu, Sichuan, P.R. China
| | - Roger Janz
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas; The University of Texas MD Anderson Cancer Center University of Texas Health Graduate School of Biomedical Sciences, Houston, Texas
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas; The University of Texas MD Anderson Cancer Center University of Texas Health Graduate School of Biomedical Sciences, Houston, Texas
| | - Wallace B Thoreson
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, Nebraska; Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska.
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Ritzau-Jost A, Jablonski L, Viotti J, Lipstein N, Eilers J, Hallermann S. Apparent calcium dependence of vesicle recruitment. J Physiol 2018; 596:4693-4707. [PMID: 29928766 DOI: 10.1113/jp275911] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 06/11/2018] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Synaptic transmission relies on the recruitment of neurotransmitter-filled vesicles to presynaptic release sites. Increased intracellular calcium buffering slows the recovery from synaptic depression, suggesting that vesicle recruitment is a calcium-dependent process. However, the molecular mechanisms of vesicle recruitment have only been investigated at some synapses. We investigate the role of calcium in vesicle recruitment at the cerebellar mossy fibre to granule cell synapse. We find that increased intracellular calcium buffering slows the recovery from depression following physiological stimulation. However, the recovery is largely resistant to perturbation of the molecular pathways previously shown to mediate calcium-dependent vesicle recruitment. Furthermore, we find two pools of vesicles with different recruitment speeds and show that models incorporating two pools of vesicles with different calcium-independent recruitment rates can explain our data. In this framework, increased calcium buffering prevents the release of intrinsically fast-recruited vesicles but does not change the vesicle recruitment rates themselves. ABSTRACT During sustained synaptic transmission, recruitment of new transmitter-filled vesicles to the release site counteracts vesicle depletion and thus synaptic depression. An elevated intracellular Ca2+ concentration has been proposed to accelerate the rate of vesicle recruitment at many synapses. This conclusion is often based on the finding that increased intracellular Ca2+ buffering slows the recovery from synaptic depression. However, the molecular mechanisms of the activity-dependent acceleration of vesicle recruitment have only been analysed at some synapses. Using physiological stimulation patterns in postsynaptic recordings and step depolarizations in presynaptic bouton recordings, we investigate vesicle recruitment at cerebellar mossy fibre boutons. We show that increased intracellular Ca2+ buffering slows recovery from depression dramatically. However, pharmacological and genetic interference with calmodulin or the calmodulin-Munc13 pathway, which has been proposed to mediate Ca2+ -dependence of vesicle recruitment, barely affects vesicle recovery from depression. Furthermore, we show that cerebellar mossy fibre boutons have two pools of vesicles: rapidly fusing vesicles that recover slowly and slowly fusing vesicles that recover rapidly. Finally, models adopting such two pools of vesicles with Ca2+ -independent recruitment rates can explain the slowed recovery from depression upon increased Ca2+ buffering. Our data do not rule out the involvement of the calmodulin-Munc13 pathway during stronger stimuli or other molecular pathways mediating Ca2+ -dependent vesicle recruitment at cerebellar mossy fibre boutons. However, we show that well-established two-pool models predict an apparent Ca2+ -dependence of vesicle recruitment. Thus, previous conclusions of Ca2+ -dependent vesicle recruitment based solely on increased intracellular Ca2+ buffering should be considered with caution.
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Affiliation(s)
- Andreas Ritzau-Jost
- Carl-Ludwig-Institute for Physiology, Faculty of Medicine, Leipzig University, Leipzig, Germany
| | - Lukasz Jablonski
- Carl-Ludwig-Institute for Physiology, Faculty of Medicine, Leipzig University, Leipzig, Germany
| | - Julio Viotti
- Carl-Ludwig-Institute for Physiology, Faculty of Medicine, Leipzig University, Leipzig, Germany.,Department of Anatomy and Embryology, Center of Anatomy, University Medical Center Göttingen, Göttingen, Germany
| | - Noa Lipstein
- Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Jens Eilers
- Carl-Ludwig-Institute for Physiology, Faculty of Medicine, Leipzig University, Leipzig, Germany
| | - Stefan Hallermann
- Carl-Ludwig-Institute for Physiology, Faculty of Medicine, Leipzig University, Leipzig, Germany
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Lipin MY, Vigh J. Quantifying the effect of light activated outer and inner retinal inhibitory pathways on glutamate release from mixed bipolar cells. Synapse 2018; 72:e22028. [PMID: 29360185 DOI: 10.1002/syn.22028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 01/19/2018] [Accepted: 01/21/2018] [Indexed: 11/12/2022]
Abstract
Inhibition mediated by horizontal and amacrine cells in the outer and inner retina, respectively, are fundamental components of visual processing. Here, our purpose was to determine how these different inhibitory processes affect glutamate release from ON bipolar cells when the retina is stimulated with full-field light of various intensities. Light-evoked membrane potential changes (ΔVm ) were recorded directly from axon terminals of intact bipolar cells receiving mixed rod and cone inputs (Mbs) in slices of dark-adapted goldfish retina. Inner and outer retinal inhibition to Mbs was blocked with bath applied picrotoxin (PTX) and NBQX, respectively. Then, control and pharmacologically modified light responses were injected into axotomized Mb terminals as command potentials to induce voltage-gated Ca2+ influx (QCa ) and consequent glutamate release. Stimulus-evoked glutamate release was quantified by the increase in membrane capacitance (ΔCm ). Increasing depolarization of Mb terminals upon removal of inner and outer retinal inhibition enhanced the ΔVm /QCa ratio equally at a given light intensity and inhibition did not alter the overall relation between QCa and ΔCm . However, relative to control, light responses recorded in the presence of PTX and PTX + NBQX increased ΔCm unevenly across different stimulus intensities: at dim stimulus intensities predominantly the inner retinal GABAergic inhibition controlled release from Mbs, whereas the inner and outer retinal inhibition affected release equally in response to bright stimuli. Furthermore, our results suggest that non-linear relationship between QCa and glutamate release can influence the efficacy of inner and outer retinal inhibitory pathways to mediate Mb output at different light intensities.
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Affiliation(s)
- Mikhail Y Lipin
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, Colorado, 80523-1617
| | - Jozsef Vigh
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, Colorado, 80523-1617
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