1
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Zhang P, Li J, Li W, Qiao S, Ou Y, Yuan X. Synaptic endocytosis in adult adipose stromal cell-derived neurons. Brain Res 2024; 1827:148746. [PMID: 38184164 DOI: 10.1016/j.brainres.2023.148746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Revised: 12/24/2023] [Accepted: 12/30/2023] [Indexed: 01/08/2024]
Abstract
Synapses are essential for facilitating the transmission of information between neurons and for executing neurophysiological processes. Following the exocytosis of neurotransmitters, the synaptic vesicle may quickly undergo endocytosis to preserve the structural integrity of the synapse. When converting adipose-derived stromal cells (ADSCs) into neurons, the ADSCs have already demonstrated comparable morphology, structure, and electrophysiological characteristics to neurons. Nevertheless, there is currently no published study on the endocytotic function of neurons that are produced from ADSCs. This study aimed to examine synaptic endocytosis in neurons derived from ADSCs by qualitatively and quantitatively analyzing the presence of Ap-2, Clathrin, Endophilin, Dynamin, and Hsc70, which are the key proteins involved in clathrin-mediated endocytosis (CME), as well as by using FM1-43 and cadmium selenide quantum dots (CdSe QDs). Additionally, single-cell RNA sequencing (scRNA-seq) was used to look at the levels of both neuronal markers and markers related to CME at the same time. The results of this study provide evidence that synapses in neurons produced from ADSCs have a role in endocytosis, mainly through the CME route.
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Affiliation(s)
- Pingshu Zhang
- Department of Neurology, Kailuan General Hospital, North China University of Science and Technology, Tangshan, China; Neurobiology Key Laboratory of HeBei, Tangshan, China
| | - Jing Li
- Radiology Department of Tangshan Maternal and Child Health Hospital, Tangshan City, Hebei Province, China
| | - Wen Li
- Department of Neurology, Kailuan General Hospital, North China University of Science and Technology, Tangshan, China; Neurobiology Key Laboratory of HeBei, Tangshan, China
| | - Sijia Qiao
- Department of Neurology, Kailuan General Hospital, North China University of Science and Technology, Tangshan, China; Neurobiology Key Laboratory of HeBei, Tangshan, China
| | - Ya Ou
- Department of Neurology, Kailuan General Hospital, North China University of Science and Technology, Tangshan, China; Neurobiology Key Laboratory of HeBei, Tangshan, China
| | - Xiaodong Yuan
- Department of Neurology, Kailuan General Hospital, North China University of Science and Technology, Tangshan, China; Neurobiology Key Laboratory of HeBei, Tangshan, China.
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2
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Nolte TM. 300-fold higher neuro- and immunotoxicity from low-redox transformation of carbamazepine. Toxicol Rep 2023; 11:319-329. [PMID: 37927955 PMCID: PMC10622881 DOI: 10.1016/j.toxrep.2023.09.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 09/19/2023] [Accepted: 09/20/2023] [Indexed: 11/07/2023] Open
Abstract
Current challenges in (eco)toxicology are in understanding the transformation of (reactive) substances, and how transformation affects toxic modes of action. Empirical assessment of transformation products of, practically an infinite number of substances, via experimentation, is impossible. Predicting transformation products for (benchmarking) compounds from conditions, facilitates risk analyses. This study applied calculus to predict transformation products of an important environmental and medicinal/toxicological marker, carbamazepine. As radicals are ubiquitous in humans and the environment, we looked into radical-mediated transformations of carbamazepine as a benchmark. We calculated proportions of their speciation states as function of redox conditions, which we took as pH and O2 concentration, describing transformation via covalent and ionic interactions. Formation of ring-contracted products with neuro-immunological activity is thermodynamically favored under anaerobic conditions and at low pH. Experimentally observed product distributions and toxicities reflect that pattern. Our predictive method may support toxicity predictions for other substances and conditions 'similar' to the current case study via interpolation. This paves the way for a more coherent, effective and easier risk assessment of transformation products.
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Affiliation(s)
- Tom M. Nolte
- Department of Environmental Science, Institute for Water and Wetland Research, Radboud, University Nijmegen, 6500 GL Nijmegen, the Netherlands
- Eidgenössische Technische Hochschule (ETH) Zurich, Laboratory of Inorganic Chemistry, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland
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3
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Unique dynamics and exocytosis properties of GABAergic synaptic vesicles revealed by three-dimensional single vesicle tracking. Proc Natl Acad Sci U S A 2021; 118:2022133118. [PMID: 33622785 DOI: 10.1073/pnas.2022133118] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Maintaining the balance between neuronal excitation and inhibition is essential for proper function of the central nervous system. Inhibitory synaptic transmission plays an important role in maintaining this balance. Although inhibitory transmission has higher kinetic demands compared to excitatory transmission, its properties are poorly understood. In particular, the dynamics and exocytosis of single inhibitory vesicles have not been investigated, due largely to both technical and practical limitations. Using a combination of quantum dots (QDs) conjugated to antibodies against the luminal domain of the vesicular GABA transporter to selectively label GABAergic (i.e., predominantly inhibitory) vesicles together with dual-focus imaging optics, we tracked the real-time three-dimensional position of single GABAergic vesicles up to the moment of exocytosis (i.e., fusion). Using three-dimensional trajectories, we found that GABAergic synaptic vesicles traveled a shorter distance prior to fusion and had a shorter time to fusion compared to synaptotagmin-1 (Syt1)-labeled vesicles, which were mostly from excitatory neurons. Moreover, our analysis revealed that GABAergic synaptic vesicles move more straightly to their release sites than Syt1-labeled vesicles. Finally, we found that GABAergic vesicles have a higher prevalence of kiss-and-run fusion than Syt1-labeled vesicles. These results indicate that inhibitory synaptic vesicles have a unique set of dynamics and exocytosis properties to support rapid synaptic inhibition, thereby maintaining a tightly regulated coordination between excitation and inhibition in the central nervous system.
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4
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Lüthy K, Mei D, Fischer B, De Fusco M, Swerts J, Paesmans J, Parrini E, Lubarr N, Meijer IA, Mackenzie KM, Lee WT, Cittaro D, Aridon P, Schoovaerts N, Versées W, Verstreken P, Casari G, Guerrini R. TBC1D24-TLDc-related epilepsy exercise-induced dystonia: rescue by antioxidants in a disease model. Brain 2020; 142:2319-2335. [PMID: 31257402 DOI: 10.1093/brain/awz175] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 04/08/2019] [Accepted: 04/25/2019] [Indexed: 11/13/2022] Open
Abstract
Genetic mutations in TBC1D24 have been associated with multiple phenotypes, with epilepsy being the main clinical manifestation. The TBC1D24 protein consists of the unique association of a Tre2/Bub2/Cdc16 (TBC) domain and a TBC/lysin motif domain/catalytic (TLDc) domain. More than 50 missense and loss-of-function mutations have been described and are spread over the entire protein. Through whole genome/exome sequencing we identified compound heterozygous mutations, R360H and G501R, within the TLDc domain, in an index family with a Rolandic epilepsy exercise-induced dystonia phenotype (http://omim.org/entry/608105). A 20-year long clinical follow-up revealed that epilepsy was self-limited in all three affected patients, but exercise-induced dystonia persisted into adulthood in two. Furthermore, we identified three additional sporadic paediatric patients with a remarkably similar phenotype, two of whom had compound heterozygous mutations consisting of an in-frame deletion I81_K84 and an A500V mutation, and the third carried T182M and G511R missense mutations, overall revealing that all six patients harbour a missense mutation in the subdomain of TLDc between residues 500 and 511. We solved the crystal structure of the conserved Drosophila TLDc domain. This allowed us to predict destabilizing effects of the G501R and G511R mutations and, to a lesser degree, of R360H and potentially A500V. Next, we characterized the functional consequences of a strong and a weak TLDc mutation (TBC1D24G501R and TBC1D24R360H) using Drosophila, where TBC1D24/Skywalker regulates synaptic vesicle trafficking. In a Drosophila model neuronally expressing human TBC1D24, we demonstrated that the TBC1D24G501R TLDc mutation causes activity-induced locomotion and synaptic vesicle trafficking defects, while TBC1D24R360H is benign. The neuronal phenotypes of the TBC1D24G501R mutation are consistent with exacerbated oxidative stress sensitivity, which is rescued by treating TBC1D24G501R mutant animals with antioxidants N-acetylcysteine amide or α-tocopherol as indicated by restored synaptic vesicle trafficking levels and sustained behavioural activity. Our data thus show that mutations in the TLDc domain of TBC1D24 cause Rolandic-type focal motor epilepsy and exercise-induced dystonia. The humanized TBC1D24G501R fly model exhibits sustained activity and vesicle transport defects. We propose that the TBC1D24/Sky TLDc domain is a reactive oxygen species sensor mediating synaptic vesicle trafficking rates that, when dysfunctional, causes a movement disorder in patients and flies. The TLDc and TBC domain mutations' response to antioxidant treatment we observed in the animal model suggests a potential for combining antioxidant-based therapeutic approaches to TBC1D24-associated disorders with previously described lipid-altering strategies for TBC domain mutations.
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Affiliation(s)
- Kevin Lüthy
- VIB-KU Leuven Center for Brain and Disease Research, Leuven, Belgium.,KU Leuven, Department of Neurosciences, Leuven Brain Institute, Leuven, Belgium
| | - Davide Mei
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Children's Hospital A. Meyer-University of Florence, Florence, Italy
| | - Baptiste Fischer
- VIB-VUB Center for Structural Biology, Brussels, Belgium.,Vrije Universiteit Brussel, Structural Biology Brussels, Brussels, Belgium
| | | | - Jef Swerts
- VIB-KU Leuven Center for Brain and Disease Research, Leuven, Belgium.,KU Leuven, Department of Neurosciences, Leuven Brain Institute, Leuven, Belgium
| | - Jone Paesmans
- VIB-VUB Center for Structural Biology, Brussels, Belgium.,Vrije Universiteit Brussel, Structural Biology Brussels, Brussels, Belgium
| | - Elena Parrini
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Children's Hospital A. Meyer-University of Florence, Florence, Italy
| | - Naomi Lubarr
- Mount Sinai Beth Israel, Department of Neurology, New York, NY, USA
| | - Inge A Meijer
- Department of Pediatrics and Neurosciences, CHU Sainte-Justine and University of Montreal, Montreal, Canada
| | | | - Wang-Tso Lee
- Department of Pediatrics, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | | | - Paolo Aridon
- Department of Experimental Biomedicine and Clinical Neurosciences, University of Palermo, Palermo, Italy
| | - Nils Schoovaerts
- VIB-KU Leuven Center for Brain and Disease Research, Leuven, Belgium.,KU Leuven, Department of Neurosciences, Leuven Brain Institute, Leuven, Belgium
| | - Wim Versées
- VIB-VUB Center for Structural Biology, Brussels, Belgium.,Vrije Universiteit Brussel, Structural Biology Brussels, Brussels, Belgium
| | - Patrik Verstreken
- VIB-KU Leuven Center for Brain and Disease Research, Leuven, Belgium.,KU Leuven, Department of Neurosciences, Leuven Brain Institute, Leuven, Belgium
| | - Giorgio Casari
- San Raffaele University, Milan, Italy.,Telethon Institute of Genetics and Medicine, Naples, Italy
| | - Renzo Guerrini
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Children's Hospital A. Meyer-University of Florence, Florence, Italy.,IRCCS Fondazione Stella Maris, Pisa, Italy
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5
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Reshetniak S, Rizzoli SO. Interrogating Synaptic Architecture: Approaches for Labeling Organelles and Cytoskeleton Components. Front Synaptic Neurosci 2019; 11:23. [PMID: 31507402 PMCID: PMC6716447 DOI: 10.3389/fnsyn.2019.00023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 08/02/2019] [Indexed: 01/06/2023] Open
Abstract
Synaptic transmission has been studied for decades, as a fundamental step in brain function. The structure of the synapse, and its changes during activity, turned out to be key aspects not only in the transfer of information between neurons, but also in cognitive processes such as learning and memory. The overall synaptic morphology has traditionally been studied by electron microscopy, which enables the visualization of synaptic structure in great detail. The changes in the organization of easily identified structures, such as the presynaptic active zone, or the postsynaptic density, are optimally studied via electron microscopy. However, few reliable methods are available for labeling individual organelles or protein complexes in electron microscopy. For such targets one typically relies either on combination of electron and fluorescence microscopy, or on super-resolution fluorescence microscopy. This review focuses on approaches and techniques used to specifically reveal synaptic organelles and protein complexes, such as cytoskeletal assemblies. We place the strongest emphasis on methods detecting the targets of interest by affinity binding, and we discuss the advantages and limitations of each method.
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Affiliation(s)
- Sofiia Reshetniak
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, Göttingen, Germany
- International Max Planck Research School for Molecular Biology, Göttingen, Germany
| | - Silvio O. Rizzoli
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, Göttingen, Germany
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6
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Richter KN, Patzelt C, Phan NTN, Rizzoli SO. Antibody-driven capture of synaptic vesicle proteins on the plasma membrane enables the analysis of their interactions with other synaptic proteins. Sci Rep 2019; 9:9231. [PMID: 31239503 PMCID: PMC6592915 DOI: 10.1038/s41598-019-45729-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Accepted: 06/13/2019] [Indexed: 01/07/2023] Open
Abstract
Many organelles from the secretory pathway fuse to the plasma membrane, to exocytose different cargoes. Their proteins are then retrieved from the plasma membrane by endocytosis, and the organelles are re-formed. It is generally unclear whether the organelle proteins colocalize when they are on the plasma membrane, or whether they disperse. To address this, we generated here a new approach, which we tested on synaptic vesicles, organelles that are known to exo- and endocytose frequently. We tagged the synaptotagmin molecules of newly exocytosed vesicles using clusters of primary and secondary antibodies targeted against the luminal domains of these molecules. The antibody clusters are too large for endocytosis, and thus sequestered the synaptotagmin molecules on the plasma membrane. Immunostainings for other synaptic molecules then revealed whether they colocalized with the sequestered synaptotagmin molecules. We suggest that such assays may be in the future extended to other cell types and other organelles.
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Affiliation(s)
- Katharina N Richter
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany.
| | - Christina Patzelt
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - Nhu T N Phan
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - Silvio O Rizzoli
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany.
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7
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Seitz KJ, Rizzoli SO. GFP nanobodies reveal recently-exocytosed pHluorin molecules. Sci Rep 2019; 9:7773. [PMID: 31123313 PMCID: PMC6533288 DOI: 10.1038/s41598-019-44262-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 05/13/2019] [Indexed: 11/21/2022] Open
Abstract
Neurotransmitter release requires vesicle recycling, which consists of exocytosis, endocytosis and the reformation of new fusion-competent vesicles. One poorly understood aspect in this cycle is the fate of the vesicle proteins after exocytosis, when they are left on the plasma membrane. Such proteins are often visualized by coupling to pH-sensitive GFP moieties (pHluorins). However, pHluorin imaging is typically limited by diffraction to spots several-fold larger than the vesicles. Here we show that pHuorin-tagged vesicle proteins can be easily detected using single-domain antibodies (nanobodies) raised against GFP. By coupling the nanobodies to chemical fluorophores that were optimal for super-resolution imaging, we could analyze the size and intensity of the groups of pHluorin-tagged proteins under a variety of conditions, in a fashion that would have been impossible based solely on the pHluorin fluorescence. We conclude that nanobody-based pHluorin detection is a promising tool for investigating post-exocytosis events in neurons.
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Affiliation(s)
- Katharina J Seitz
- Institute for Neuro- and Sensory Physiology, University Medical Center, Göttingen, Germany. .,Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany.
| | - Silvio O Rizzoli
- Institute for Neuro- and Sensory Physiology, University Medical Center, Göttingen, Germany. .,Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany.
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8
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Chanaday NL, Kavalali ET. Presynaptic origins of distinct modes of neurotransmitter release. Curr Opin Neurobiol 2018; 51:119-126. [PMID: 29597140 PMCID: PMC6066415 DOI: 10.1016/j.conb.2018.03.005] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 02/22/2018] [Accepted: 03/12/2018] [Indexed: 11/17/2022]
Abstract
Presynaptic nerve terminals release neurotransmitter synchronously, asynchronously or spontaneously. During synchronous neurotransmission release is precisely coupled to action potentials, in contrast, asynchronous release events show only loose temporal coupling to presynaptic activity whereas spontaneous neurotransmission occurs independent of presynaptic activity. The mechanisms that give rise to this diversity in neurotransmitter release modes are poorly understood. Recent studies have described several presynaptic molecular pathways controlling synaptic vesicle pool segregation and recycling, which in turn may dictate distinct modes of neurotransmitter release. In this article, we review this recent work regarding neurotransmitter release modes and their relationship to synaptic vesicle pool dynamics as well as the molecular machinery that establishes synaptic vesicle pool identity.
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Affiliation(s)
- Natali L Chanaday
- Department of Neuroscience, the University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
| | - Ege T Kavalali
- Department of Neuroscience, the University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA.
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9
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Cruz-Lopez D, Ramos D, Castilloveitia G, Schikorski T. Quintuple labeling in the electron microscope with genetically encoded enhanced horseradish peroxidase. PLoS One 2018; 13:e0200693. [PMID: 30011315 PMCID: PMC6047818 DOI: 10.1371/journal.pone.0200693] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Accepted: 07/02/2018] [Indexed: 11/25/2022] Open
Abstract
Genetic encoded multilabeling is essential for modern cell biology. In fluorescence microscopy this need has been satisfied by the development of numerous color-variants of the green fluorescent protein. In electron microscopy, however, true genetic encoded multilabeling is currently not possible. Here, we introduce combinatorial cell organelle type-specific labeling as a strategy for multilabeling. First, we created a reliable and high sensitive label by evolving the catalytic activity of horseradish peroxidase (HRP). We then built fusion proteins that targeted our new enhanced HRP (eHRP) to three cell organelles whose labeling pattern did not overlap with each other. The labeling of the endoplasmic reticulum, synaptic vesicles and the plasma membrane consequently allowed for triple labeling in the EM. The combinatorial expression of the three organelle-specific constructs increased the number of clearly distinguishable labels to seven. This strategy of multilabeling for EM closes a significant gap in our tool set and has a broad application range in cell biology.
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Affiliation(s)
- Didiana Cruz-Lopez
- Department of Neuroscience, Universidad Central del Caribe, Bayamon, Puerto Rico, United States of America
| | - Dianne Ramos
- Department of Neuroscience, Universidad Central del Caribe, Bayamon, Puerto Rico, United States of America
| | - Gloria Castilloveitia
- Department of Neuroscience, Universidad Central del Caribe, Bayamon, Puerto Rico, United States of America
| | - Thomas Schikorski
- Department of Neuroscience, Universidad Central del Caribe, Bayamon, Puerto Rico, United States of America
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10
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Riemann D, Petkova A, Dresbach T, Wallrafen R. An Optical Assay for Synaptic Vesicle Recycling in Cultured Neurons Overexpressing Presynaptic Proteins. J Vis Exp 2018:58043. [PMID: 30010661 PMCID: PMC6101998 DOI: 10.3791/58043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
At active presynaptic nerve terminals, synaptic vesicles undergo cycles of exo- and endocytosis. During recycling, the luminal domains of SV transmembrane proteins become exposed at the cell surface. One of these proteins is Synaptotagmin-1 (Syt1). An antibody directed against the luminal domain of Syt1, once added to the culture medium, is taken up during the exo-endocytotic cycle. This uptake is proportional to the amount of SV recycling and can be quantified through immunofluorescence. Here, we combine Syt1 antibody uptake with double transfection of cultured hippocampal neurons. This allows us to (1) localize presynaptic sites based on expression of recombinant presynaptic marker Synaptophysin, (2) determine their functionality using Syt1 uptake, and (3) characterize the targeting and effects of a protein of interest, GFP-Rogdi.
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Affiliation(s)
- Donatus Riemann
- Institute for Anatomy and Embryology, University Medical Centre Göttingen
| | - Andoniya Petkova
- Institute for Anatomy and Embryology, University Medical Centre Göttingen
| | - Thomas Dresbach
- Institute for Anatomy and Embryology, University Medical Centre Göttingen;
| | - Rebecca Wallrafen
- Institute for Anatomy and Embryology, University Medical Centre Göttingen
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11
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SNT-1 Functions as the Ca 2+ Sensor for Tonic and Evoked Neurotransmitter Release in Caenorhabditis Elegans. J Neurosci 2018; 38:5313-5324. [PMID: 29760174 DOI: 10.1523/jneurosci.3097-17.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Revised: 04/23/2018] [Accepted: 05/03/2018] [Indexed: 12/23/2022] Open
Abstract
Synaptotagmin-1 (Syt1) binds Ca2+ through its tandem C2 domains (C2A and C2B) and triggers Ca2+-dependent neurotransmitter release. Here, we show that snt-1, the homolog of mammalian Syt1, functions as the Ca2+ sensor for both tonic and evoked neurotransmitter release at the Caenorhabditis elegans neuromuscular junction. Mutations that disrupt Ca2+ binding in double C2 domains of SNT-1 significantly impaired tonic release, whereas disrupting Ca2+ binding in a single C2 domain had no effect, indicating that the Ca2+ binding of the two C2 domains is functionally redundant for tonic release. Stimulus-evoked release was significantly reduced in snt-1 mutants, with prolonged release latency as well as faster rise and decay kinetics. Unlike tonic release, evoked release was triggered by Ca2+ binding solely to the C2B domain. Moreover, we showed that SNT-1 plays an essential role in the priming process in different subpopulations of synaptic vesicles with tight or loose coupling to Ca2+ entry.SIGNIFICANCE STATEMENT We showed that SNT-1 in Caenorhabditis elegans regulates evoked neurotransmitter release through Ca2+ binding to its C2B domain in a similar way to Syt1 in the mouse CNS and the fly neuromuscular junction. However, the largely decreased tonic release in snt-1 mutants argues SNT-1 has a clamping function. Indeed, Ca2+-binding mutations in the C2 domains in SNT-1 significantly reduced the frequency of the miniature EPSC, indicating that SNT-1 also acts as a Ca2+ sensor for tonic release. Therefore, revealing the differential mechanisms between invertebrates and vertebrates will provide significant insights into our understanding how synaptic vesicle fusion is regulated.
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12
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Modulation of the inwardly rectifying potassium channel Kir4.1 by the pro-invasive miR-5096 in glioblastoma cells. Oncotarget 2018; 8:37681-37693. [PMID: 28445150 PMCID: PMC5514940 DOI: 10.18632/oncotarget.16949] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Accepted: 03/22/2017] [Indexed: 12/19/2022] Open
Abstract
Inwardly rectifying potassium channels (Kir), and especially the barium-sensitive Kir4.1 encoded by KCNJ10, are key regulators of glial functions. A lower expression or mislocation of Kir4.1 is detected in human brain tumors. MicroRNAs participate in the regulation of ionic channels and associated neurologic disorders. Here, we analyze effects of miR-5096 on the Kir4.1 expression and function in two glioblastoma cell lines, U87 and U251. Using whole-cell patch-clamp and western-blot analysis, we show that cell loading with miR-5096 decreases the Kir4.1 protein level and associated K+ current. Cell treatment with barium, a Kir4.1 blocker, or cell loading of miR-5096 both increase the outgrowth of filopodia in glioma cells, as observed by time-lapse microscopy. Knocking-down Kir4.1 expression by siRNA transfection similarly increased both filopodia formation and invasiveness of glioma cells as observed in Boyden chamber assay. MiR-5096 also promotes the release of extracellular vesicles by which it increases its own transfer to surrounding cells, in a Kir4.1-dependent manner in U251 but not in U87. Altogether, our results validate Kir4.1 as a miR-5096 target to promote invasion of glioblastoma cells. Our data highlight the complexity of microRNA effects and the role of K+ channels in cancer.
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13
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Babiec WE, O'Dell TJ. Novel Ca 2+-dependent mechanisms regulate spontaneous release at excitatory synapses onto CA1 pyramidal cells. J Neurophysiol 2017; 119:597-607. [PMID: 29142096 DOI: 10.1152/jn.00628.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Although long thought to simply be a source of synaptic noise, spontaneous, action potential-independent release of neurotransmitter from presynaptic terminals has multiple roles in synaptic function. We explored whether and to what extent the two predominantly proposed mechanisms for explaining spontaneous release, stochastic activation of voltage-gated Ca2+ channels (VGCCs) or activation of Ca2+-sensing receptors (CaSRs) by extracellular Ca2+, played a role in the sensitivity of spontaneous release to the level of extracellular Ca2+ concentration at excitatory synapses at CA1 pyramidal cells of the adult male mouse hippocampus. Blocking VGCCs with Cd2+ had no effect on spontaneous release, ruling out stochastic activation of VGCCs. Although divalent cation agonists of CaSRs, Co2+ and Mg2+, dramatically enhanced miniature excitatory postsynaptic current (mEPSC) frequency, potent positive and negative allosteric modulators of CaSRs had no effect. Moreover, immunoblot analysis of hippocampal lysates failed to detect CaSR expression, ruling out the CaSR. Instead, the increase in mEPSC frequency induced by Co2+ and Mg2+ was mimicked by lowering postsynaptic Ca2+ levels with BAPTA. Together, our results suggest that a reduction in intracellular Ca2+ may trigger a homeostatic-like compensatory response that upregulates spontaneous transmission at excitatory synapses onto CA1 pyramidal cells in the adult hippocampus. NEW & NOTEWORTHY We show that the predominant theories for explaining the regulation of spontaneous, action potential-independent synaptic release do not explain the sensitivity of this type of synaptic transmission to external Ca2+ concentration at excitatory synapses onto hippocampal CA1 pyramidal cells. In addition, our data indicate that intracellular Ca2+ levels in CA1 pyramidal cells regulate spontaneous release, suggesting that excitatory synapses onto CA1 pyramidal cells may express a novel, rapid form of homeostatic plasticity.
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Affiliation(s)
- Walter E Babiec
- Department of Physiology, David Geffen School of Medicine at UCLA , Los Angeles, California
| | - Thomas J O'Dell
- Department of Physiology, David Geffen School of Medicine at UCLA , Los Angeles, California.,UCLA Integrative Center for Learning and Memory, Brain Research Institute, UCLA, Los Angeles, California
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Cousin MA. A (free) radical approach reveals the physiological function of different synaptic vesicle pools. J Physiol 2017; 595:1005-1006. [PMID: 28198012 DOI: 10.1113/jp273596] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 10/18/2016] [Indexed: 11/08/2022] Open
Affiliation(s)
- Michael A Cousin
- Centre for Integrative Physiology, Hugh Robson Building, George Square, University of Edinburgh, Edinburgh, EH8 9XD, UK
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