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De Marchi F, Venkatesan S, Saraceno M, Mazzini L, Grossini E. Acetyl-L-carnitine and Amyotrophic Lateral Sclerosis: Current Evidence and Potential use. CNS & NEUROLOGICAL DISORDERS DRUG TARGETS 2024; 23:588-601. [PMID: 36998125 DOI: 10.2174/1871527322666230330083757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 01/26/2023] [Accepted: 01/31/2023] [Indexed: 04/01/2023]
Abstract
BACKGROUND The management of neurodegenerative diseases can be frustrating for clinicians, given the limited progress of conventional medicine in this context. AIM For this reason, a more comprehensive, integrative approach is urgently needed. Among various emerging focuses for intervention, the modulation of central nervous system energetics, oxidative stress, and inflammation is becoming more and more promising. METHODS In particular, electrons leakage involved in the mitochondrial energetics can generate reactive oxygen-free radical-related mitochondrial dysfunction that would contribute to the etiopathology of many disorders, such as Alzheimer's and other dementias, Parkinson's disease, multiple sclerosis, stroke, and amyotrophic lateral sclerosis (ALS). RESULTS In this context, using agents, like acetyl L-carnitine (ALCAR), provides mitochondrial support, reduces oxidative stress, and improves synaptic transmission. CONCLUSION This narrative review aims to update the existing literature on ALCAR molecular profile, tolerability, and translational clinical potential use in neurodegeneration, focusing on ALS.
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Affiliation(s)
- Fabiola De Marchi
- ALS Center, Neurology Unit, Department of Translational Medicine, University of Piemonte Orientale 28100 Novara, Italy
| | - Sakthipriyan Venkatesan
- Laboratory of Physiology, Department of Translational Medicine, University of Piemonte Orientale 28100, Novara, Italy
| | - Massimo Saraceno
- ALS Center, Neurology Unit, Department of Translational Medicine, University of Piemonte Orientale 28100 Novara, Italy
| | - Letizia Mazzini
- ALS Center, Neurology Unit, Department of Translational Medicine, University of Piemonte Orientale 28100 Novara, Italy
| | - Elena Grossini
- Laboratory of Physiology, Department of Translational Medicine, University of Piemonte Orientale 28100, Novara, Italy
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Justs KA, Sempertegui S, Riboul DV, Oliva CD, Durbin RJ, Crill S, Stawarski M, Su C, Renden RB, Fily Y, Macleod GT. Mitochondrial phosphagen kinases support the volatile power demands of motor nerve terminals. J Physiol 2023; 601:5705-5732. [PMID: 37942946 PMCID: PMC10841428 DOI: 10.1113/jp284872] [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: 04/12/2023] [Accepted: 10/17/2023] [Indexed: 11/10/2023] Open
Abstract
Motor neurons are the longest neurons in the body, with axon terminals separated from the soma by as much as a meter. These terminals are largely autonomous with regard to their bioenergetic metabolism and must burn energy at a high rate to sustain muscle contraction. Here, through computer simulation and drawing on previously published empirical data, we determined that motor neuron terminals in Drosophila larvae experience highly volatile power demands. It might not be surprising then, that we discovered the mitochondria in the motor neuron terminals of both Drosophila and mice to be heavily decorated with phosphagen kinases - a key element in an energy storage and buffering system well-characterized in fast-twitch muscle fibres. Knockdown of arginine kinase 1 (ArgK1) in Drosophila larval motor neurons led to several bioenergetic deficits, including mitochondrial matrix acidification and a faster decline in the cytosol ATP to ADP ratio during axon burst firing. KEY POINTS: Neurons commonly fire in bursts imposing highly volatile demands on the bioenergetic machinery that generates ATP. Using a computational approach, we built profiles of presynaptic power demand at the level of single action potentials, as well as the transition from rest to sustained activity. Phosphagen systems are known to buffer ATP levels in muscles and we demonstrate that phosphagen kinases, which support such phosphagen systems, also localize to mitochondria in motor nerve terminals of fruit flies and mice. By knocking down phosphagen kinases in fruit fly motor nerve terminals, and using fluorescent reporters of the ATP:ADP ratio, lactate, pH and Ca2+ , we demonstrate a role for phosphagen kinases in stabilizing presynaptic ATP levels. These data indicate that the maintenance of phosphagen systems in motor neurons, and not just muscle, could be a beneficial initiative in sustaining musculoskeletal health and performance.
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Affiliation(s)
- Karlis A. Justs
- Integrative Biology and Neuroscience Graduate Program, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Sergio Sempertegui
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, FL, 33431, USA
| | - Danielle V. Riboul
- Integrative Biology and Neuroscience Graduate Program, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Carlos D. Oliva
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Ryan J. Durbin
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557
| | - Sarah Crill
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Michal Stawarski
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Chenchen Su
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Robert B. Renden
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557
| | - Yaouen Fily
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Gregory T. Macleod
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
- Institute for Human Health & Disease Intervention, Florida Atlantic University, Jupiter, FL 33458, USA
- Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, FL 33458, USA
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3
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Quiñones-Frías MC, Ocken DM, Rodal A. High-resolution imaging of presynaptic ER networks in Atlastin mutants. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.01.555994. [PMID: 37693578 PMCID: PMC10491308 DOI: 10.1101/2023.09.01.555994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/12/2023]
Abstract
The endoplasmic reticulum (ER) is a continuous organelle that extends to the periphery of neurons and regulates many neuronal functions including neurite outgrowth, neurotransmission, and synaptic plasticity. Mutations in proteins that control ER shape are linked to the neurodegenerative disorder Hereditary Spastic Paraplegia (HSP). However, the ultrastructure and dynamics of the neuronal ER have been under-investigated, particularly at presynaptic terminals. Here we developed new super-resolution and live imaging methods in D. melanogaster larval motor neurons to investigate ER structure at presynaptic terminals from wild-type animals, and in null mutants of the HSP gene Atlastin. Previous studies indicated diffuse localization of an ER lumen marker at Atlastin mutant presynaptic terminals, which was attributed to ER fragmentation. By contrast, we found using an ER membrane marker that the ER in Atlastin mutants formed robust networks. Further, our high-resolution imaging results suggest that overexpression of luminal ER proteins in Atlastin mutants causes their progressive displacement to the cytosol at synapses, perhaps due to proteostatic stress and/or changes in ER membrane integrity. Remarkably, these luminal ER proteins remain correctly localized in cell bodies, axons, and other cell types such as body wall muscles, suggesting that ER tubules at synapses have unique structural and functional characteristics. This displacement phenotype has not been reported in numerous studies of Atlastin in non-neuronal cells, emphasizing the importance of conducting experiments in neurons when investigating the mechanisms leading to upper motor neuron dysfunction in HSP.
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Affiliation(s)
| | - Dina M. Ocken
- Department of Biology, Brandeis University, Waltham, MA
| | - Avital Rodal
- Department of Biology, Brandeis University, Waltham, MA
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4
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He K, Han Y, Li X, Hernandez RX, Riboul DV, Feghhi T, Justs KA, Mahneva O, Perry S, Macleod GT, Dickman D. Physiologic and Nanoscale Distinctions Define Glutamatergic Synapses in Tonic vs Phasic Neurons. J Neurosci 2023; 43:4598-4611. [PMID: 37221096 PMCID: PMC10286941 DOI: 10.1523/jneurosci.0046-23.2023] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Revised: 05/05/2023] [Accepted: 05/11/2023] [Indexed: 05/25/2023] Open
Abstract
Neurons exhibit a striking degree of functional diversity, each one tuned to the needs of the circuitry in which it is embedded. A fundamental functional dichotomy occurs in activity patterns, with some neurons firing at a relatively constant "tonic" rate, while others fire in bursts, a "phasic" pattern. Synapses formed by tonic versus phasic neurons are also functionally differentiated, yet the bases of their distinctive properties remain enigmatic. A major challenge toward illuminating the synaptic differences between tonic and phasic neurons is the difficulty in isolating their physiological properties. At the Drosophila neuromuscular junction, most muscle fibers are coinnervated by two motor neurons: the tonic "MN-Ib" and phasic "MN-Is." Here, we used selective expression of a newly developed botulinum neurotoxin transgene to silence tonic or phasic motor neurons in Drosophila larvae of either sex. This approach highlighted major differences in their neurotransmitter release properties, including probability, short-term plasticity, and vesicle pools. Furthermore, Ca2+ imaging demonstrated ∼2-fold greater Ca2+ influx at phasic neuron release sites relative to tonic, along with an enhanced synaptic vesicle coupling. Finally, confocal and super-resolution imaging revealed that phasic neuron release sites are organized in a more compact arrangement, with enhanced stoichiometry of voltage-gated Ca2+ channels relative to other active zone scaffolds. These data suggest that distinctions in active zone nano-architecture and Ca2+ influx collaborate to differentially tune glutamate release at tonic versus phasic synaptic subtypes.SIGNIFICANCE STATEMENT "Tonic" and "phasic" neuronal subtypes, based on differential firing properties, are common across many nervous systems. Using a recently developed approach to selectively silence transmission from one of these two neurons, we reveal specialized synaptic functional and structural properties that distinguish these specialized neurons. This study provides important insights into how input-specific synaptic diversity is achieved, which could have implications for neurologic disorders that involve changes in synaptic function.
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Affiliation(s)
- Kaikai He
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
- USC Neuroscience Graduate Program, Los Angeles, California 90089
| | - Yifu Han
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
- USC Neuroscience Graduate Program, Los Angeles, California 90089
| | - Xiling Li
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
- USC Neuroscience Graduate Program, Los Angeles, California 90089
| | - Roberto X Hernandez
- Integrative Biology and Neuroscience Graduate Program, Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
- International Max Planck Research School for Brain and Behavior, Jupiter, Florida 33458
| | - Danielle V Riboul
- Integrative Biology Graduate Program, Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
| | - Touhid Feghhi
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431
| | - Karlis A Justs
- Integrative Biology and Neuroscience Graduate Program, Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
| | - Olena Mahneva
- Wilkes Honors College, Florida Atlantic University, Jupiter, Florida 33458
| | - Sarah Perry
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
| | - Gregory T Macleod
- Wilkes Honors College, Florida Atlantic University, Jupiter, Florida 33458
- Institute for Human Health and Disease Intervention, Florida Atlantic University, Jupiter, Florida 33458
| | - Dion Dickman
- Department of Neurobiology, University of Southern California, Los Angeles, California 90089
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5
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Pérez-Moreno JJ, Smith RC, Oliva MK, Gallo F, Ojha S, Müller KH, O’Kane CJ. Drosophila SPG12 ortholog, reticulon-like 1, governs presynaptic ER organization and Ca2+ dynamics. J Cell Biol 2023; 222:e202112101. [PMID: 36952540 PMCID: PMC10072275 DOI: 10.1083/jcb.202112101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 01/01/2023] [Accepted: 02/24/2023] [Indexed: 03/25/2023] Open
Abstract
Neuronal endoplasmic reticulum (ER) appears continuous throughout the cell. Its shape and continuity are influenced by ER-shaping proteins, mutations in which can cause distal axon degeneration in Hereditary Spastic Paraplegia (HSP). We therefore asked how loss of Rtnl1, a Drosophila ortholog of the human HSP gene RTN2 (SPG12), which encodes an ER-shaping protein, affects ER organization and the function of presynaptic terminals. Loss of Rtnl1 depleted ER membrane markers at Drosophila presynaptic motor terminals and appeared to deplete narrow tubular ER while leaving cisternae largely unaffected, thus suggesting little change in resting Ca2+ storage capacity. Nevertheless, these changes were accompanied by major reductions in activity-evoked Ca2+ fluxes in the cytosol, ER lumen, and mitochondria, as well as reduced evoked and spontaneous neurotransmission. We found that reduced STIM-mediated ER-plasma membrane contacts underlie presynaptic Ca2+ defects in Rtnl1 mutants. Our results show the importance of ER architecture in presynaptic physiology and function, which are therefore potential factors in the pathology of HSP.
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Affiliation(s)
| | | | - Megan K. Oliva
- Department of Genetics, University of Cambridge, Cambridge, UK
| | - Filomena Gallo
- Development and Neuroscience, Cambridge Advanced Imaging Centre, Cambridge, UK
| | - Shainy Ojha
- Department of Genetics, University of Cambridge, Cambridge, UK
| | - Karin H. Müller
- Development and Neuroscience, Cambridge Advanced Imaging Centre, Cambridge, UK
| | - Cahir J. O’Kane
- Department of Genetics, University of Cambridge, Cambridge, UK
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6
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O'Connor K, Spendiff S, Lochmüller H, Horvath R. Mitochondrial Mutations Can Alter Neuromuscular Transmission in Congenital Myasthenic Syndrome and Mitochondrial Disease. Int J Mol Sci 2023; 24:ijms24108505. [PMID: 37239850 DOI: 10.3390/ijms24108505] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 04/28/2023] [Accepted: 05/02/2023] [Indexed: 05/28/2023] Open
Abstract
Congenital myasthenic syndromes (CMS) are a group of rare, neuromuscular disorders that usually present in childhood or infancy. While the phenotypic presentation of these disorders is diverse, the unifying feature is a pathomechanism that disrupts neuromuscular transmission. Recently, two mitochondrial genes-SLC25A1 and TEFM-have been reported in patients with suspected CMS, prompting a discussion about the role of mitochondria at the neuromuscular junction (NMJ). Mitochondrial disease and CMS can present with similar symptoms, and potentially one in four patients with mitochondrial myopathy exhibit NMJ defects. This review highlights research indicating the prominent roles of mitochondria at both the pre- and postsynapse, demonstrating the potential for mitochondrial involvement in neuromuscular transmission defects. We propose the establishment of a novel subcategorization for CMS-mitochondrial CMS, due to unifying clinical features and the potential for mitochondrial defects to impede transmission at the pre- and postsynapse. Finally, we highlight the potential of targeting the neuromuscular transmission in mitochondrial disease to improve patient outcomes.
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Affiliation(s)
- Kaela O'Connor
- Children's Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Centre for Neuromuscular Disease, University of Ottawa Brain and Mind Research Institute, Ottawa, ON K1H 8M5, Canada
| | - Sally Spendiff
- Children's Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada
| | - Hanns Lochmüller
- Children's Hospital of Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada
- Division of Neurology, Department of Medicine, The Ottawa Hospital, Ottawa, ON K1H 8L6, Canada
- Brain and Mind Research Institute, University of Ottawa, Ottawa, ON K1H 8M5, Canada
- Department of Neuropediatrics and Muscle Disorders, Faculty of Medicine, Medical Center-University of Freiburg, 79104 Freiburg, Germany
- Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Barcelona Institute of Science and Technology (BIST), 08028 Barcelona, Catalonia, Spain
| | - Rita Horvath
- Department of Clinical Neurosciences, University of Cambridge, Cambridge CB3 0FD, UK
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7
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Bademosi AT, Decet M, Kuenen S, Calatayud C, Swerts J, Gallego SF, Schoovaerts N, Karamanou S, Louros N, Martin E, Sibarita JB, Vints K, Gounko NV, Meunier FA, Economou A, Versées W, Rousseau F, Schymkowitz J, Soukup SF, Verstreken P. EndophilinA-dependent coupling between activity-induced calcium influx and synaptic autophagy is disrupted by a Parkinson-risk mutation. Neuron 2023; 111:1402-1422.e13. [PMID: 36827984 PMCID: PMC10166451 DOI: 10.1016/j.neuron.2023.02.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 11/09/2022] [Accepted: 01/31/2023] [Indexed: 02/26/2023]
Abstract
Neuronal activity causes use-dependent decline in protein function. However, it is unclear how this is coupled to local quality control mechanisms. We show in Drosophila that the endocytic protein Endophilin-A (EndoA) connects activity-induced calcium influx to synaptic autophagy and neuronal survival in a Parkinson disease-relevant fashion. Mutations in the disordered loop, including a Parkinson disease-risk mutation, render EndoA insensitive to neuronal stimulation and affect protein dynamics: when EndoA is more flexible, its mobility in membrane nanodomains increases, making it available for autophagosome formation. Conversely, when EndoA is more rigid, its mobility reduces, blocking stimulation-induced autophagy. Balanced stimulation-induced autophagy is required for dopagminergic neuron survival, and a variant in the human ENDOA1 disordered loop conferring risk to Parkinson disease also blocks nanodomain protein mobility and autophagy both in vivo and in human-induced dopaminergic neurons. Thus, we reveal a mechanism that neurons use to connect neuronal activity to local autophagy and that is critical for neuronal survival.
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Affiliation(s)
- Adekunle T Bademosi
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium; Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia Campus, Brisbane, QLD 4072, Australia
| | - Marianna Decet
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium
| | - Sabine Kuenen
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium
| | - Carles Calatayud
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium
| | - Jef Swerts
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium
| | - Sandra F Gallego
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium
| | - Nils Schoovaerts
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium
| | - Spyridoula Karamanou
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Leuven 3000, Belgium
| | - Nikolaos Louros
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; Switch Laboratory, Department of Cellular and Molecular Medicine, KU Leuven, Leuven 3000, Belgium
| | - Ella Martin
- VIB-VUB Center for Structural Biology, Brussels 1050, Belgium; Department of Structural Biology Brussels, Vrije Universiteit Brussel, Brussels 1050, Belgium
| | - Jean-Baptiste Sibarita
- Interdisciplinary Institute for Neuroscience, University of Bordeaux, F-33000 Bordeaux, France
| | - Katlijn Vints
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium; VIB Bio Core, KU Leuven, Leuven 3000, Belgium
| | - Natalia V Gounko
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium; VIB Bio Core, KU Leuven, Leuven 3000, Belgium
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia Campus, Brisbane, QLD 4072, Australia; School of Biomedical Sciences, The University of Queensland, St Lucia Campus, Brisbane, QLD 4072, Australia
| | - Anastassios Economou
- KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Leuven 3000, Belgium
| | - Wim Versées
- VIB-VUB Center for Structural Biology, Brussels 1050, Belgium; Department of Structural Biology Brussels, Vrije Universiteit Brussel, Brussels 1050, Belgium
| | - Frederic Rousseau
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; Switch Laboratory, Department of Cellular and Molecular Medicine, KU Leuven, Leuven 3000, Belgium
| | - Joost Schymkowitz
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; Switch Laboratory, Department of Cellular and Molecular Medicine, KU Leuven, Leuven 3000, Belgium
| | | | - Patrik Verstreken
- VIB-KU Leuven Center for Brain & Disease Research, Leuven 3000, Belgium; KU Leuven, Department of Neurosciences, Leuven Brain Institute, Mission Lucidity, Leuven 3000, Belgium.
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8
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Walters GC, Usachev YM. Mitochondrial calcium cycling in neuronal function and neurodegeneration. Front Cell Dev Biol 2023; 11:1094356. [PMID: 36760367 PMCID: PMC9902777 DOI: 10.3389/fcell.2023.1094356] [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: 11/10/2022] [Accepted: 01/12/2023] [Indexed: 01/26/2023] Open
Abstract
Mitochondria are essential for proper cellular function through their critical roles in ATP synthesis, reactive oxygen species production, calcium (Ca2+) buffering, and apoptotic signaling. In neurons, Ca2+ buffering is particularly important as it helps to shape Ca2+ signals and to regulate numerous Ca2+-dependent functions including neuronal excitability, synaptic transmission, gene expression, and neuronal toxicity. Over the past decade, identification of the mitochondrial Ca2+ uniporter (MCU) and other molecular components of mitochondrial Ca2+ transport has provided insight into the roles that mitochondrial Ca2+ regulation plays in neuronal function in health and disease. In this review, we discuss the many roles of mitochondrial Ca2+ uptake and release mechanisms in normal neuronal function and highlight new insights into the Ca2+-dependent mechanisms that drive mitochondrial dysfunction in neurologic diseases including epilepsy, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. We also consider how targeting Ca2+ uptake and release mechanisms could facilitate the development of novel therapeutic strategies for neurological diseases.
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Affiliation(s)
- Grant C. Walters
- Department of Neuroscience and Pharmacology, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA, United States
| | - Yuriy M. Usachev
- Department of Neuroscience and Pharmacology, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA, United States
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9
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Lopez-Manzaneda M, Fuentes-Moliz A, Tabares L. Presynaptic Mitochondria Communicate With Release Sites for Spatio-Temporal Regulation of Exocytosis at the Motor Nerve Terminal. Front Synaptic Neurosci 2022; 14:858340. [PMID: 35645766 PMCID: PMC9133601 DOI: 10.3389/fnsyn.2022.858340] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 04/07/2022] [Indexed: 11/13/2022] Open
Abstract
Presynaptic Ca2+ regulation is critical for accurate neurotransmitter release, vesicle reloading of release sites, and plastic changes in response to electrical activity. One of the main players in the regulation of cytosolic Ca2+ in nerve terminals is mitochondria, which control the size and spread of the Ca2+ wave during sustained electrical activity. However, the role of mitochondria in Ca2+ signaling during high-frequency short bursts of action potentials (APs) is not well known. Here, we studied spatial and temporal relationships between mitochondrial Ca2+ (mCa2+) and exocytosis by live imaging and electrophysiology in adult motor nerve terminals of transgenic mice expressing synaptophysin-pHluorin (SypHy). Our results show that hot spots of exocytosis and mitochondria are organized in subsynaptic functional regions and that mitochondria start to uptake Ca2+ after a few APs. We also show that mitochondria contribute to the regulation of the mode of fusion (synchronous and asynchronous) and the kinetics of release and replenishment of the readily releasable pool (RRP) of vesicles. We propose that mitochondria modulate the timing and reliability of neurotransmission in motor nerve terminals during brief AP trains.
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10
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Serrat R, Oliveira-Pinto A, Marsicano G, Pouvreau S. Imaging mitochondrial calcium dynamics in the central nervous system. J Neurosci Methods 2022; 373:109560. [PMID: 35320763 DOI: 10.1016/j.jneumeth.2022.109560] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 03/04/2022] [Accepted: 03/06/2022] [Indexed: 12/28/2022]
Abstract
Mitochondrial calcium handling is a particularly active research area in the neuroscience field, as it plays key roles in the regulation of several functions of the central nervous system, such as synaptic transmission and plasticity, astrocyte calcium signaling, neuronal activity… In the last few decades, a panel of techniques have been developed to measure mitochondrial calcium dynamics, relying mostly on photonic microscopy, and including synthetic sensors, hybrid sensors and genetically encoded calcium sensors. The goal of this review is to endow the reader with a deep knowledge of the historical and latest tools to monitor mitochondrial calcium events in the brain, as well as a comprehensive overview of the current state of the art in brain mitochondrial calcium signaling. We will discuss the main calcium probes used in the field, their mitochondrial targeting strategies, their key properties and major drawbacks. In addition, we will detail the main roles of mitochondrial calcium handling in neuronal tissues through an extended report of the recent studies using mitochondrial targeted calcium sensors in neuronal and astroglial cells, in vitro and in vivo.
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Affiliation(s)
- Roman Serrat
- Institut National de la Santé et de la Recherche Médicale (INSERM), U1215 NeuroCentre Magendie, France; University of Bordeaux, Bordeaux 33077, France
| | - Alexandre Oliveira-Pinto
- Institut National de la Santé et de la Recherche Médicale (INSERM), U1215 NeuroCentre Magendie, France; University of Bordeaux, Bordeaux 33077, France
| | - Giovanni Marsicano
- Institut National de la Santé et de la Recherche Médicale (INSERM), U1215 NeuroCentre Magendie, France; University of Bordeaux, Bordeaux 33077, France
| | - Sandrine Pouvreau
- Institut National de la Santé et de la Recherche Médicale (INSERM), U1215 NeuroCentre Magendie, France; University of Bordeaux, Bordeaux 33077, France.
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11
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Newman ZL, Bakshinskaya D, Schultz R, Kenny SJ, Moon S, Aghi K, Stanley C, Marnani N, Li R, Bleier J, Xu K, Isacoff EY. Determinants of synapse diversity revealed by super-resolution quantal transmission and active zone imaging. Nat Commun 2022; 13:229. [PMID: 35017509 PMCID: PMC8752601 DOI: 10.1038/s41467-021-27815-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Accepted: 12/06/2021] [Indexed: 01/23/2023] Open
Abstract
Neural circuit function depends on the pattern of synaptic connections between neurons and the strength of those connections. Synaptic strength is determined by both postsynaptic sensitivity to neurotransmitter and the presynaptic probability of action potential evoked transmitter release (Pr). Whereas morphology and neurotransmitter receptor number indicate postsynaptic sensitivity, presynaptic indicators and the mechanism that sets Pr remain to be defined. To address this, we developed QuaSOR, a super-resolution method for determining Pr from quantal synaptic transmission imaging at hundreds of glutamatergic synapses at a time. We mapped the Pr onto super-resolution 3D molecular reconstructions of the presynaptic active zones (AZs) of the same synapses at the Drosophila larval neuromuscular junction (NMJ). We find that Pr varies greatly between synapses made by a single axon, quantify the contribution of key AZ proteins to Pr diversity and find that one of these, Complexin, suppresses spontaneous and evoked transmission differentially, thereby generating a spatial and quantitative mismatch between release modes. Transmission is thus regulated by the balance and nanoscale distribution of release-enhancing and suppressing presynaptic proteins to generate high signal-to-noise evoked transmission.
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Affiliation(s)
- Zachary L Newman
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Dariya Bakshinskaya
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Ryan Schultz
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Samuel J Kenny
- Department of Chemistry, University of California, Berkeley, CA, 94720, USA
| | - Seonah Moon
- Department of Chemistry, University of California, Berkeley, CA, 94720, USA
| | - Krisha Aghi
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Cherise Stanley
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Nadia Marnani
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Rachel Li
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Julia Bleier
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Ke Xu
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
- Department of Chemistry, University of California, Berkeley, CA, 94720, USA
- Molecular Biophysics and Integrated BioImaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Ehud Y Isacoff
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA.
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA.
- Molecular Biophysics and Integrated BioImaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
- Weill Neurohub, University of California Berkeley, Berkeley, CA, 94720, USA.
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12
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Krill JL, Dawson-Scully K. Characterization of a novel stimulus-induced glial calcium wave in Drosophila larval peripheral segmental nerves and its role in PKG-modulated thermoprotection. J Neurogenet 2021; 35:221-235. [PMID: 34309496 DOI: 10.1080/01677063.2021.1941945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Insects, as poikilotherms, have adaptations to deal with wide ranges in temperature fluctuation. Allelic variations in the foraging gene that encodes a cGMP dependent protein kinase, were discovered to have effects on behavior in Drosophila by Dr. Marla Sokolowski in 1980. This single gene has many pleiotropic effects and influences feeding behavior, metabolic storage, learning and memory and has been shown to affect stress tolerance. PKG regulation affects motoneuronal thermotolerance in Drosophila larvae as well as adults. While the focus of thermotolerance studies has been on the modulation of neuronal function, other cell types have been overlooked. Because glia are vital to neuronal function and survival, we wanted to determine if glia play a role in thermotolerance as well. In our investigation, we discovered a novel calcium wave at the larval NMJ and set out to characterize the wave's dynamics and the potential mechanism underlying the wave prior to determining what effect, if any, PKG modulation has on the thermotolerance of glia cells. Using pharmacology, we determined that calcium buffering mechanisms of the mitochondria and endoplasmic reticulum play a role in the propagation of our novel glial calcium wave. By coupling pharmacology with genetic manipulation using RNA interference (RNAi), we found that PKG modulation in glia alters thermoprotection of function as well as glial calcium wave dynamics.
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Affiliation(s)
- Jennifer L Krill
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida
| | - Ken Dawson-Scully
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida
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13
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Datta S, Jaiswal M. Mitochondrial calcium at the synapse. Mitochondrion 2021; 59:135-153. [PMID: 33895346 DOI: 10.1016/j.mito.2021.04.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 03/28/2021] [Accepted: 04/13/2021] [Indexed: 12/15/2022]
Abstract
Mitochondria are dynamic organelles, which serve various purposes, including but not limited to the production of ATP and various metabolites, buffering ions, acting as a signaling hub, etc. In recent years, mitochondria are being seen as the central regulators of cellular growth, development, and death. Since neurons are highly specialized cells with a heavy metabolic demand, it is not surprising that neurons are one of the most mitochondria-rich cells in an animal. At synapses, mitochondrial function and dynamics is tightly regulated by synaptic calcium. Calcium influx during synaptic activity causes increased mitochondrial calcium influx leading to an increased ATP production as well as buffering of synaptic calcium. While increased ATP production is required during synaptic transmission, calcium buffering by mitochondria is crucial to prevent faulty neurotransmission and excitotoxicity. Interestingly, mitochondrial calcium also regulates the mobility of mitochondria within synapses causing mitochondria to halt at the synapse during synaptic transmission. In this review, we summarize the various roles of mitochondrial calcium at the synapse.
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Affiliation(s)
- Sayantan Datta
- Tata Institute of Fundamental Research, Hyderabad, India
| | - Manish Jaiswal
- Tata Institute of Fundamental Research, Hyderabad, India.
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14
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Aponte-Santiago NA, Littleton JT. Synaptic Properties and Plasticity Mechanisms of Invertebrate Tonic and Phasic Neurons. Front Physiol 2020; 11:611982. [PMID: 33391026 PMCID: PMC7772194 DOI: 10.3389/fphys.2020.611982] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 11/24/2020] [Indexed: 12/15/2022] Open
Abstract
Defining neuronal cell types and their associated biophysical and synaptic diversity has become an important goal in neuroscience as a mechanism to create comprehensive brain cell atlases in the post-genomic age. Beyond broad classification such as neurotransmitter expression, interneuron vs. pyramidal, sensory or motor, the field is still in the early stages of understanding closely related cell types. In both vertebrate and invertebrate nervous systems, one well-described distinction related to firing characteristics and synaptic release properties are tonic and phasic neuronal subtypes. In vertebrates, these classes were defined based on sustained firing responses during stimulation (tonic) vs. transient responses that rapidly adapt (phasic). In crustaceans, the distinction expanded to include synaptic release properties, with tonic motoneurons displaying sustained firing and weaker synapses that undergo short-term facilitation to maintain muscle contraction and posture. In contrast, phasic motoneurons with stronger synapses showed rapid depression and were recruited for short bursts during fast locomotion. Tonic and phasic motoneurons with similarities to those in crustaceans have been characterized in Drosophila, allowing the genetic toolkit associated with this model to be used for dissecting the unique properties and plasticity mechanisms for these neuronal subtypes. This review outlines general properties of invertebrate tonic and phasic motoneurons and highlights recent advances that characterize distinct synaptic and plasticity pathways associated with two closely related glutamatergic neuronal cell types that drive invertebrate locomotion.
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Affiliation(s)
- Nicole A. Aponte-Santiago
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
- Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, San Francisco, CA, United States
| | - J. Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
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15
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Yang CH, Lee KH, Ho WK, Lee SH. Inter-spike mitochondrial Ca 2+ release enhances high frequency synaptic transmission. J Physiol 2020; 599:1567-1594. [PMID: 33140422 DOI: 10.1113/jp280351] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Accepted: 10/27/2020] [Indexed: 01/03/2023] Open
Abstract
KEY POINTS Presynaptic mitochondria not only absorb but also release Ca2+ during high frequency stimulation (HFS) when presynaptic [Ca2+ ] is kept low (<500 nm) by high cytosolic Ca2+ buffer or strong plasma membrane calcium clearance mechanisms under physiological external [Ca2+ ]. Mitochondrial Ca2+ release (MCR) does not alter the global presynaptic Ca2+ transients. MCR during HFS enhances short-term facilitation and steady state excitatory postsynaptic currents by increasing vesicular release probability. The intra-train MCR may provide residual calcium at interspike intervals, and thus support high frequency neurotransmission at central glutamatergic synapses. ABSTRACT Emerging evidence indicates that mitochondrial Ca2+ buffering contributes to local regulation of synaptic transmission. It is unknown, however, whether mitochondrial Ca2+ release (MCR) occurs during high frequency synaptic transmission. Confirming the previous notion that 2 μm tetraphenylphosphonium (TPP+ ) is a specific inhibitor of the mitochondrial Na+ /Ca2+ exchanger (mNCX), we studied the role of MCR via mNCX in short-term plasticity during high frequency stimulation (HFS) at the calyx of Held synapse of the rat. TPP+ reduced short-term facilitation (STF) and steady state excitatory postsynaptic currents during HFS at mature calyx synapses under physiological extracellular [Ca2+ ] ([Ca2+ ]o = 1.2 mm), but not at immature calyx or at 2 mm [Ca2+ ]o . The inhibitory effects of TPP+ were stronger at synapses with morphologically complex calyces harbouring many swellings and at 32°C than at simple calyx synapses and at room temperature. These effects of TPP+ on STF were well correlated with those on the presynaptic mitochondrial [Ca2+ ] build-up during HFS. Mitochondrial [Ca2+ ] during HFS was increased by TPP+ at mature calyces under 1.2 mm [Ca2+ ]o , and further enhanced at 32°C, but not under 2 mm [Ca2+ ]o or at immature calyces. The close correlation of the effects of TPP+ on mitochondrial [Ca2+ ] with those on STF suggests that mNCX contributes to STF at the calyx of Held synapses. The intra-train MCR enhanced vesicular release probability without altering global presynaptic [Ca2+ ]. Our results suggest that MCR during HFS elevates local [Ca2+ ] near synaptic sites at interspike intervals to enhance STF and to support stable synaptic transmission under physiological [Ca2+ ]o .
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Affiliation(s)
- Che Ho Yang
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea
| | - Kyu-Hee Lee
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea
| | - Won-Kyung Ho
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea.,Department of Brain and Cognitive Science, Seoul National University, Seoul, Republic of Korea
| | - Suk-Ho Lee
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea.,Department of Brain and Cognitive Science, Seoul National University, Seoul, Republic of Korea
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16
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Activity-Dependent Global Downscaling of Evoked Neurotransmitter Release across Glutamatergic Inputs in Drosophila. J Neurosci 2020; 40:8025-8041. [PMID: 32928887 DOI: 10.1523/jneurosci.0349-20.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 09/01/2020] [Accepted: 09/04/2020] [Indexed: 12/11/2022] Open
Abstract
Within mammalian brain circuits, activity-dependent synaptic adaptations, such as synaptic scaling, stabilize neuronal activity in the face of perturbations. Stability afforded through synaptic scaling involves uniform scaling of quantal amplitudes across all synaptic inputs formed on neurons, as well as on the postsynaptic side. It remains unclear whether activity-dependent uniform scaling also operates within peripheral circuits. We tested for such scaling in a Drosophila larval neuromuscular circuit, where the muscle receives synaptic inputs from different motoneurons. We used motoneuron-specific genetic manipulations to increase the activity of only one motoneuron and recordings of postsynaptic currents from inputs formed by the different motoneurons. We discovered an adaptation which caused uniform downscaling of evoked neurotransmitter release across all inputs through decreases in release probabilities. This "presynaptic downscaling" maintained the relative differences in neurotransmitter release across all inputs around a homeostatic set point, caused a compensatory decrease in synaptic drive to the muscle affording robust and stable muscle activity, and was induced within hours. Presynaptic downscaling was associated with an activity-dependent increase in Drosophila vesicular glutamate transporter expression. Activity-dependent uniform scaling can therefore manifest also on the presynaptic side to produce robust and stable circuit outputs. Within brain circuits, uniform downscaling on the postsynaptic side is implicated in sleep- and memory-related processes. Our results suggest that evaluation of such processes might be broadened to include uniform downscaling on the presynaptic side.SIGNIFICANCE STATEMENT To date, compensatory adaptations which stabilise target cell activity through activity-dependent global scaling have been observed only within central circuits, and on the postsynaptic side. Considering that maintenance of stable activity is imperative for the robust function of the nervous system as a whole, we tested whether activity-dependent global scaling could also manifest within peripheral circuits. We uncovered a compensatory adaptation which causes global scaling within a peripheral circuit and on the presynaptic side through uniform downscaling of evoked neurotransmitter release. Unlike in central circuits, uniform scaling maintains functionality over a wide, rather than a narrow, operational range, affording robust and stable activity. Activity-dependent global scaling therefore operates on both the presynaptic and postsynaptic sides to maintain target cell activity.
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17
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Lnenicka GA. Crayfish and Drosophila NMJs. Neurosci Lett 2020; 732:135110. [PMID: 32497734 DOI: 10.1016/j.neulet.2020.135110] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Revised: 05/27/2020] [Accepted: 05/29/2020] [Indexed: 01/06/2023]
Abstract
Many synaptic studies have utilized the experimental advantages of the Arthropod NMJ and the most prominent preparations have been the crayfish and Drosophila larval NMJs. Early cellular studies in the crayfish established the framework for later molecular studies in Drosophila. The two neuromuscular systems are compared including the advantages presented by each preparation for cellular analysis. Beginning with the early work in the crayfish, research developments are followed in the areas of structure/function relationships, activity-dependent synaptic plasticity/development and synaptic homeostasis. A reoccurring theme in these studies is the regulation of active zone structure and function. Early studies in the crayfish focused on the role of active zone number/size and possible functional heterogeneity in regulating transmitter release. Recent studies in Drosophila have begun to characterize this heterogeneity using new approaches that combine imaging of transmitter release, Ca2+ influx and molecular composition for individual active zones.
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Affiliation(s)
- Gregory A Lnenicka
- Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, United States.
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18
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Proportional Downscaling of Glutamatergic Release Sites by the General Anesthetic Propofol at Drosophila Motor Nerve Terminals. eNeuro 2020; 7:ENEURO.0422-19.2020. [PMID: 32019872 PMCID: PMC7053172 DOI: 10.1523/eneuro.0422-19.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 01/21/2020] [Accepted: 01/24/2020] [Indexed: 01/12/2023] Open
Abstract
Propofol is the most common general anesthetic used for surgery in humans, yet its complete mechanism of action remains elusive. In addition to potentiating inhibitory synapses in the brain, propofol also impairs excitatory neurotransmission. We use electrophysiological recordings from individual glutamatergic boutons in male and female larval Drosophila melanogaster motor nerve terminals to characterize this effect. We recorded from two bouton types, which have distinct presynaptic physiology and different average numbers of release sites or active zones. We show that a clinically relevant dose of propofol (3 μm) impairs neurotransmitter release similarly at both bouton types by decreasing the number of active release sites by half, without affecting release probability. In contrast, an analog of propofol has no effect on glutamate release. Coexpressing a truncated syntaxin1A protein in presynaptic boutons completely blocked this effect of propofol. Overexpressing wild-type syntaxin1A in boutons also conferred a level of resistance by increasing the number of active release sites to a physiological ceiling set by the number of active zones or T-bars, and in this way counteracting the effect of propofol. These results point to the presynaptic release machinery as a target for the general anesthetic. Proportionally equivalent effects of propofol on the number of active release sites across the different bouton types suggests that glutamatergic circuits that involve smaller boutons with fewer release sites may be more vulnerable to the presynaptic effects of the drug.
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19
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Neuronal Glutamatergic Synaptic Clefts Alkalinize Rather Than Acidify during Neurotransmission. J Neurosci 2020; 40:1611-1624. [PMID: 31964719 DOI: 10.1523/jneurosci.1774-19.2020] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 01/14/2020] [Accepted: 01/15/2020] [Indexed: 12/11/2022] Open
Abstract
The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of neurotransmitters and protons from synaptic vesicles, and is supported by direct data from sensory ribbon-type synapses. However, it is unclear whether acidification occurs at non-ribbon-type synapses. Here we used genetically encoded fluorescent pH indicators to examine cleft pH at conventional neuronal synapses. At the neuromuscular junction of female Drosophila larvae, we observed alkaline spikes of over 1 log unit during fictive locomotion in vivo. Ex vivo, single action potentials evoked alkalinizing pH transients of only ∼0.01 log unit, but these transients summated rapidly during burst firing. A chemical pH indicator targeted to the cleft corroborated these findings. Cleft pH transients were dependent on Ca2+ movement across the postsynaptic membrane, rather than neurotransmitter release per se, a result consistent with cleft alkalinization being driven by the Ca2+/H+ antiporting activity of the plasma membrane Ca2+-ATPase at the postsynaptic membrane. Targeting the pH indicators to the microenvironment of the presynaptic voltage gated Ca2+ channels revealed that alkalinization also occurred within the cleft proper at the active zone and not just within extrasynaptic regions. Application of the pH indicators at the mouse calyx of Held, a mammalian central synapse, similarly revealed cleft alkalinization during burst firing in both males and females. These findings, made at two quite different non-ribbon type synapses, suggest that cleft alkalinization during neurotransmission, rather than acidification, is a generalizable phenomenon across conventional neuronal synapses.SIGNIFICANCE STATEMENT Neurotransmission is highly sensitive to the pH of the extracellular milieu. This is readily evident in the neurological symptoms that accompany systemic acid/base imbalances. Imaging data from sensory ribbon-type synapses show that neurotransmission itself can acidify the synaptic cleft, likely due to the corelease of protons and glutamate. It is not clear whether the same phenomenon occurs at conventional neuronal synapses due to the difficulties in collecting such data. If it does occur, it would provide for an additional layer of activity-dependent modulation of neurotransmission. Our findings of alkalinization, rather than acidification, within the cleft of two different neuronal synapses encourages a reassessment of the scope of activity-dependent pH influences on neurotransmission and short-term synaptic plasticity.
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20
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The Impact of Kinases in Amyotrophic Lateral Sclerosis at the Neuromuscular Synapse: Insights into BDNF/TrkB and PKC Signaling. Cells 2019; 8:cells8121578. [PMID: 31817487 PMCID: PMC6953086 DOI: 10.3390/cells8121578] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 11/19/2019] [Accepted: 12/03/2019] [Indexed: 12/14/2022] Open
Abstract
Brain-derived neurotrophic factor (BDNF) promotes neuron survival in adulthood in the central nervous system. In the peripheral nervous system, BDNF is a contraction-inducible protein that, through its binding to tropomyosin-related kinase B receptor (TrkB), contributes to the retrograde neuroprotective control done by muscles, which is necessary for motor neuron function. BDNF/TrkB triggers downstream presynaptic pathways, involving protein kinase C, essential for synaptic function and maintenance. Undeniably, this reciprocally regulated system exemplifies the tight communication between nerve terminals and myocytes to promote synaptic function and reveals a new view about the complementary and essential role of pre and postsynaptic interplay in keeping the synapse healthy and strong. This signaling at the neuromuscular junction (NMJ) could establish new intervention targets across neuromuscular diseases characterized by deficits in presynaptic activity and muscle contractility and by the interruption of the connection between nervous and muscular tissues, such as amyotrophic lateral sclerosis (ALS). Indeed, exercise and other therapies that modulate kinases are effective at delaying ALS progression, preserving NMJs and maintaining motor function to increase the life quality of patients. Altogether, we review synaptic activity modulation of the BDNF/TrkB/PKC signaling to sustain NMJ function, its and other kinases’ disturbances in ALS and physical and molecular mechanisms to delay disease progression.
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21
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Wong HTC, Zhang Q, Beirl AJ, Petralia RS, Wang YX, Kindt K. Synaptic mitochondria regulate hair-cell synapse size and function. eLife 2019; 8:e48914. [PMID: 31609202 PMCID: PMC6879205 DOI: 10.7554/elife.48914] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Accepted: 10/13/2019] [Indexed: 11/21/2022] Open
Abstract
Sensory hair cells in the ear utilize specialized ribbon synapses. These synapses are defined by electron-dense presynaptic structures called ribbons, composed primarily of the structural protein Ribeye. Previous work has shown that voltage-gated influx of Ca2+ through CaV1.3 channels is critical for hair-cell synapse function and can impede ribbon formation. We show that in mature zebrafish hair cells, evoked presynaptic-Ca2+ influx through CaV1.3 channels initiates mitochondrial-Ca2+ (mito-Ca2+) uptake adjacent to ribbons. Block of mito-Ca2+ uptake in mature cells depresses presynaptic-Ca2+ influx and impacts synapse integrity. In developing zebrafish hair cells, mito-Ca2+ uptake coincides with spontaneous rises in presynaptic-Ca2+ influx. Spontaneous mito-Ca2+ loading lowers cellular NAD+/NADH redox and downregulates ribbon size. Direct application of NAD+ or NADH increases or decreases ribbon size respectively, possibly acting through the NAD(H)-binding domain on Ribeye. Our results present a mechanism where presynaptic- and mito-Ca2+ couple to confer proper presynaptic function and formation.
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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
- Animals, Genetically Modified
- Calcium/metabolism
- Calcium Channel Agonists/pharmacology
- Calcium Channel Blockers/pharmacology
- Calcium Channels, L-Type/genetics
- Calcium Channels, L-Type/metabolism
- Calcium Signaling
- Cell Size
- Embryo, Nonmammalian
- Evoked Potentials, Auditory/physiology
- Eye Proteins/chemistry
- Eye Proteins/genetics
- Eye Proteins/metabolism
- Gene Expression
- Hair Cells, Auditory/cytology
- Hair Cells, Auditory/drug effects
- Hair Cells, Auditory/metabolism
- Isradipine/pharmacology
- Mitochondria/drug effects
- Mitochondria/metabolism
- Mitochondria/ultrastructure
- NAD/metabolism
- Oxidation-Reduction
- Protein Binding
- Protein Interaction Domains and Motifs
- Ruthenium Compounds/pharmacology
- Synapses/drug effects
- Synapses/metabolism
- Synapses/ultrastructure
- Synaptic Transmission
- Zebrafish
- Zebrafish Proteins/agonists
- Zebrafish Proteins/antagonists & inhibitors
- Zebrafish Proteins/chemistry
- Zebrafish Proteins/genetics
- Zebrafish Proteins/metabolism
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Affiliation(s)
- Hiu-tung C Wong
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
- National Institutes of Health-Johns Hopkins University Graduate Partnership ProgramNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Qiuxiang Zhang
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Alisha J Beirl
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Ronald S Petralia
- Advanced Imaging CoreNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Ya-Xian Wang
- Advanced Imaging CoreNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
| | - Katie Kindt
- Section on Sensory Cell Development and FunctionNational Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesdaUnited States
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22
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Devine MJ, Kittler JT. Mitochondria at the neuronal presynapse in health and disease. Nat Rev Neurosci 2019; 19:63-80. [PMID: 29348666 DOI: 10.1038/nrn.2017.170] [Citation(s) in RCA: 350] [Impact Index Per Article: 70.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Synapses enable neurons to communicate with each other and are therefore a prerequisite for normal brain function. Presynaptically, this communication requires energy and generates large fluctuations in calcium concentrations. Mitochondria are optimized for supplying energy and buffering calcium, and they are actively recruited to presynapses. However, not all presynapses contain mitochondria; thus, how might synapses with and without mitochondria differ? Mitochondria are also increasingly recognized to serve additional functions at the presynapse. Here, we discuss the importance of presynaptic mitochondria in maintaining neuronal homeostasis and how dysfunctional presynaptic mitochondria might contribute to the development of disease.
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Affiliation(s)
- Michael J Devine
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
| | - Josef T Kittler
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
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23
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González-Mariscal I, Montoro RA, O'Connell JF, Kim Y, Gonzalez-Freire M, Liu QR, Alfaras I, Carlson OD, Lehrmann E, Zhang Y, Becker KG, Hardivillé S, Ghosh P, Egan JM. Muscle cannabinoid 1 receptor regulates Il-6 and myostatin expression, governing physical performance and whole-body metabolism. FASEB J 2019; 33:5850-5863. [PMID: 30726112 DOI: 10.1096/fj.201801145r] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Sarcopenic obesity, the combination of skeletal muscle mass and function loss with an increase in body fat, is associated with physical limitations, cardiovascular diseases, metabolic stress, and increased risk of mortality. Cannabinoid receptor type 1 (CB1R) plays a critical role in the regulation of whole-body energy metabolism because of its involvement in controlling appetite, fuel distribution, and utilization. Inhibition of CB1R improves insulin secretion and insulin sensitivity in pancreatic β-cells and hepatocytes. We have now developed a skeletal muscle-specific CB1R-knockout (Skm-CB1R-/-) mouse to study the specific role of CB1R in muscle. Muscle-CB1R ablation prevented diet-induced and age-induced insulin resistance by increasing IR signaling. Moreover, muscle-CB1R ablation enhanced AKT signaling, reducing myostatin expression and increasing IL-6 secretion. Subsequently, muscle-CB1R ablation increased myogenesis through its action on MAPK-mediated myogenic gene expression. Consequently, Skm-CB1R-/- mice had increased muscle mass and whole-body lean/fat ratio in obesity and aging. Muscle-CB1R ablation improved mitochondrial performance, leading to increased whole-body muscle energy expenditure and improved physical endurance, with no change in body weight. These results collectively show that CB1R in muscle is sufficient to regulate whole-body metabolism and physical performance and is a novel target for the treatment of sarcopenic obesity. -González-Mariscal, I., Montoro, R. A., O'Connell, J. F., Kim, Y., Gonzalez-Freire, M., Liu, Q.-R., Alfaras, I., Carlson, O. D., Lehrmann, E., Zhang, Y., Becker, K. G., Hardivillé, S., Ghosh, P., Egan, J. M. Muscle cannabinoid 1 receptor regulates Il-6 and myostatin expression, governing physical performance and whole-body metabolism.
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Affiliation(s)
- Isabel González-Mariscal
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
| | - Rodrigo A Montoro
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
| | - Jennifer F O'Connell
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
| | - Yoo Kim
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
| | - Marta Gonzalez-Freire
- Translational Gerontology Branch, National Institute on Aging (NIA), National Institutes of Health, Baltimore, Maryland, USA
| | - Qing-Rong Liu
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
| | - Irene Alfaras
- Translational Gerontology Branch, National Institute on Aging (NIA), National Institutes of Health, Baltimore, Maryland, USA
| | - Olga D Carlson
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
| | - Elin Lehrmann
- Laboratory of Genetics and Genomics, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Yongqing Zhang
- Laboratory of Genetics and Genomics, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Kevin G Becker
- Laboratory of Genetics and Genomics, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
| | - Stéphan Hardivillé
- Unité Propre de Recherche (UMR) 8576-Unité de Glycobiologie Structurale et Fonctionelle (UGSF), Centre National de la Recherche (CNRS), Université Lille, Lille, France
| | - Paritosh Ghosh
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
| | - Josephine M Egan
- Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (NIH), Baltimore, Maryland, USA
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Oswald MC, Brooks PS, Zwart MF, Mukherjee A, West RJ, Giachello CN, Morarach K, Baines RA, Sweeney ST, Landgraf M. Reactive oxygen species regulate activity-dependent neuronal plasticity in Drosophila. eLife 2018; 7:39393. [PMID: 30540251 PMCID: PMC6307858 DOI: 10.7554/elife.39393] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 12/12/2018] [Indexed: 12/11/2022] Open
Abstract
Reactive oxygen species (ROS) have been extensively studied as damaging agents associated with ageing and neurodegenerative conditions. Their role in the nervous system under non-pathological conditions has remained poorly understood. Working with the Drosophila larval locomotor network, we show that in neurons ROS act as obligate signals required for neuronal activity-dependent structural plasticity, of both pre- and postsynaptic terminals. ROS signaling is also necessary for maintaining evoked synaptic transmission at the neuromuscular junction, and for activity-regulated homeostatic adjustment of motor network output, as measured by larval crawling behavior. We identified the highly conserved Parkinson’s disease-linked protein DJ-1β as a redox sensor in neurons where it regulates structural plasticity, in part via modulation of the PTEN-PI3Kinase pathway. This study provides a new conceptual framework of neuronal ROS as second messengers required for neuronal plasticity and for network tuning, whose dysregulation in the ageing brain and under neurodegenerative conditions may contribute to synaptic dysfunction.
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Affiliation(s)
- Matthew Cw Oswald
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | - Paul S Brooks
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | | | - Amrita Mukherjee
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | - Ryan Jh West
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom.,Department of Biology, University of York, York, United Kingdom
| | - Carlo Ng Giachello
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Khomgrit Morarach
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | - Richard A Baines
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Sean T Sweeney
- Department of Biology, University of York, York, United Kingdom
| | - Matthias Landgraf
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
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25
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Xing X, Wu CF. Inter-relationships among physical dimensions, distal-proximal rank orders, and basal GCaMP fluorescence levels in Ca 2+ imaging of functionally distinct synaptic boutons at Drosophila neuromuscular junctions. J Neurogenet 2018; 32:195-208. [PMID: 30322321 DOI: 10.1080/01677063.2018.1504043] [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] [Indexed: 12/15/2022]
Abstract
GCaMP imaging is widely employed for investigating neuronal Ca2+ dynamics. The Drosophila larval neuromuscular junction (NMJ) consists of three distinct types of motor terminals (type Ib, Is and II). We investigated whether variability in synaptic bouton sizes and GCaMP expression levels confound interpretations of GCaMP readouts, in inferring the intrinsic Ca2+ handling properties among these functionally distinct synapses. Analysis of large data sets accumulated over years established the wide ranges of bouton sizes and GCaMP baseline fluorescence, with large overlaps among synaptic categories. We showed that bouton size and GCaMP baseline fluorescence were not confounding factors in determining the characteristic frequency responses among type Ib, Is and II synapses. More importantly, the drastic phenotypes that hyperexcitability mutations manifest preferentially in particular synaptic categories, were not obscured by bouton heterogeneity in physical size and GCaMP expression level. Our data enabled an extensive analysis of the distal-proximal gradient of GCaMP responses upon genetic and pharmacological manipulations. The results illustrate the conditions that disrupt or enhance the distal-proximal gradients. For example, stimulus frequencies just above the threshold level produced the steepest gradient in low Ca2+ (0.1 mM) saline, while supra-threshold stimulation flattened the gradient. Moreover, membrane hyperexcitability mutations (eag1 Sh120 and parabss1) and mitochondrial inhibition by dinitrophenol (DNP) disrupted the gradient. However, a novel distal-proximal gradient of decay kinetics appeared after long-term DNP incubation. We performed focal recording to assess the failure rates in transmission at low Ca2+ levels, which yielded indications of a mild distal-proximal gradient in release probability.
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Affiliation(s)
- Xiaomin Xing
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Chun-Fang Wu
- a Department of Biology , University of Iowa , Iowa City , IA , USA
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26
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Ormerod KG, Jung J, Mercier AJ. Modulation of neuromuscular synapses and contraction in Drosophila 3rd instar larvae. J Neurogenet 2018; 32:183-194. [PMID: 30303434 DOI: 10.1080/01677063.2018.1502761] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Over the past four decades, Drosophila melanogaster has become an increasingly important model system for studying the modulation of chemical synapses and muscle contraction by cotransmitters and neurohormones. This review describes how advantages provided by Drosophila have been utilized to investigate synaptic modulation, and it discusses key findings from investigations of cotransmitters and neurohormones that act on body wall muscles of 3rd instar Drosophila larvae. These studies have contributed much to our understanding of how neuromuscular systems are modulated by neuropeptides and biogenic amines, but there are still gaps in relating these peripheral modulatory effects to behavior.
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Affiliation(s)
- Kiel G Ormerod
- a Department of Biology , Massachusetts Institute of Technology , Cambridge , MA , USA
| | - JaeHwan Jung
- b Department of Biological Sciences , Brock University , St. Catharines , Canada
| | - A Joffre Mercier
- b Department of Biological Sciences , Brock University , St. Catharines , Canada
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Abstract
While readers of Journal of Neurogenetics may be familiar with Harold Atwood's work with Drosophila, most may know little of his previous work on crustacean neuromuscular systems that prepared him to utilise Drosophila neuromuscular junctions. Here, I will give brief overviews of his academic career, one line of his research that persisted throughout his career and his entry to the Drosophila field. This is not a review paper. Finally, I will relate my experiences with Atwood since 1967 as an undergraduate, Postdoctoral Fellow, and Faculty member and finish with some personal anecdotal observations.
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Affiliation(s)
- Milton P Charlton
- a Physiology Department , University of Toronto , Toronto , Ontario , Canada
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28
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Zhao T, Hao Y, Kaplan JM. Axonal Mitochondria Modulate Neuropeptide Secretion Through the Hypoxic Stress Response in Caenorhabditis elegans. Genetics 2018; 210:275-285. [PMID: 30049781 PMCID: PMC6116974 DOI: 10.1534/genetics.118.301014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2018] [Accepted: 07/25/2018] [Indexed: 12/13/2022] Open
Abstract
Neurons are highly dependent on mitochondrial function, and mitochondrial damage has been implicated in many neurological and neurodegenerative diseases. Here we show that axonal mitochondria are necessary for neuropeptide secretion in Caenorhabditis elegans and that oxidative phosphorylation, but not mitochondrial calcium uptake, is required for secretion. Oxidative phosphorylation produces cellular ATP, reactive oxygen species, and consumes oxygen. Disrupting any of these functions could inhibit neuropeptide secretion. We show that blocking mitochondria transport into axons or decreasing mitochondrial function inhibits neuropeptide secretion through activation of the hypoxia inducible factor HIF-1 Our results suggest that axonal mitochondria modulate neuropeptide secretion by regulating transcriptional responses induced by metabolic stress.
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Affiliation(s)
- Tongtong Zhao
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
| | - Yingsong Hao
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
| | - Joshua M Kaplan
- Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
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29
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Unraveling Synaptic GCaMP Signals: Differential Excitability and Clearance Mechanisms Underlying Distinct Ca 2+ Dynamics in Tonic and Phasic Excitatory, and Aminergic Modulatory Motor Terminals in Drosophila. eNeuro 2018; 5:eN-NWR-0362-17. [PMID: 29464198 PMCID: PMC5818553 DOI: 10.1523/eneuro.0362-17.2018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Revised: 01/27/2018] [Accepted: 02/02/2018] [Indexed: 11/21/2022] Open
Abstract
GCaMP is an optogenetic Ca2+ sensor widely used for monitoring neuronal activities but the precise physiological implications of GCaMP signals remain to be further delineated among functionally distinct synapses. The Drosophila neuromuscular junction (NMJ), a powerful genetic system for studying synaptic function and plasticity, consists of tonic and phasic glutamatergic and modulatory aminergic motor terminals of distinct properties. We report a first simultaneous imaging and electric recording study to directly contrast the frequency characteristics of GCaMP signals of the three synapses for physiological implications. Different GCaMP variants were applied in genetic and pharmacological perturbation experiments to examine the Ca2+ influx and clearance processes underlying the GCaMP signal. Distinct mutational and drug effects on GCaMP signals indicate differential roles of Na+ and K+ channels, encoded by genes including paralytic (para), Shaker (Sh), Shab, and ether-a-go-go (eag), in excitability control of different motor terminals. Moreover, the Ca2+ handling properties reflected by the characteristic frequency dependence of the synaptic GCaMP signals were determined to a large extent by differential capacity of mitochondria-powered Ca2+ clearance mechanisms. Simultaneous focal recordings of synaptic activities further revealed that GCaMPs were ineffective in tracking the rapid dynamics of Ca2+ influx that triggers transmitter release, especially during low-frequency activities, but more adequately reflected cytosolic residual Ca2+ accumulation, a major factor governing activity-dependent synaptic plasticity. These results highlight the vast range of GCaMP response patterns in functionally distinct synaptic types and provide relevant information for establishing basic guidelines for the physiological interpretations of presynaptic GCaMP signals from in situ imaging studies.
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30
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Lu Z, Chouhan AK, Borycz JA, Lu Z, Rossano AJ, Brain KL, Zhou Y, Meinertzhagen IA, Macleod GT. High-Probability Neurotransmitter Release Sites Represent an Energy-Efficient Design. Curr Biol 2016; 26:2562-2571. [PMID: 27593375 DOI: 10.1016/j.cub.2016.07.032] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Revised: 06/06/2016] [Accepted: 07/12/2016] [Indexed: 01/22/2023]
Abstract
Nerve terminals contain multiple sites specialized for the release of neurotransmitters. Release usually occurs with low probability, a design thought to confer many advantages. High-probability release sites are not uncommon, but their advantages are not well understood. Here, we test the hypothesis that high-probability release sites represent an energy-efficient design. We examined release site probabilities and energy efficiency at the terminals of two glutamatergic motor neurons synapsing on the same muscle fiber in Drosophila larvae. Through electrophysiological and ultrastructural measurements, we calculated release site probabilities to differ considerably between terminals (0.33 versus 0.11). We estimated the energy required to release and recycle glutamate from the same measurements. The energy required to remove calcium and sodium ions subsequent to nerve excitation was estimated through microfluorimetric and morphological measurements. We calculated energy efficiency as the number of glutamate molecules released per ATP molecule hydrolyzed, and high-probability release site terminals were found to be more efficient (0.13 versus 0.06). Our analytical model indicates that energy efficiency is optimal (∼0.15) at high release site probabilities (∼0.76). As limitations in energy supply constrain neural function, high-probability release sites might ameliorate such constraints by demanding less energy. Energy efficiency can be viewed as one aspect of nerve terminal function, in balance with others, because high-efficiency terminals depress significantly during episodic bursts of activity.
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Affiliation(s)
- Zhongmin Lu
- Integrative Biology and Neuroscience Graduate Program, Department of Biological Sciences and Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Amit K Chouhan
- School of Psychology and Neuroscience, University of St Andrews, St Andrews KY16 9AJ, Scotland, UK
| | - Jolanta A Borycz
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Zhiyuan Lu
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Adam J Rossano
- Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
| | - Keith L Brain
- Institute of Clinical Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - You Zhou
- Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
| | - Ian A Meinertzhagen
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Gregory T Macleod
- Department of Biological Sciences and Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA.
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31
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The influence of postsynaptic structure on missing quanta at the Drosophila neuromuscular junction. BMC Neurosci 2016; 17:53. [PMID: 27459966 PMCID: PMC4962461 DOI: 10.1186/s12868-016-0290-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 07/20/2016] [Indexed: 11/10/2022] Open
Abstract
Background Synaptic transmission requires both pre- and post-synaptic elements for neural communication. The postsynaptic structure contributes to the ability of synaptic currents to induce voltage changes in postsynaptic cells. At the Drosophila neuromuscular junction (NMJ), the postsynaptic structure, known as the subsynaptic reticulum (SSR), consists of elaborate membrane folds that link the synaptic contacts to the muscle, but its role in synaptic physiology is poorly understood. Results In this study, we investigate the role of the SSR with simultaneous intra- and extra-cellular recordings that allow us to identify the origin of spontaneously occurring synaptic events. We compare data from Type 1b and 1s synaptic boutons, which have naturally occurring variations of the SSR, as well as from genetic mutants that up or down-regulate SSR complexity. We observed that some synaptic currents do not result in postsynaptic voltage changes, events we called ‘missing quanta’. The frequency of missing quanta is positively correlated with SSR complexity in both natural and genetically-induced variants. Rise-time and amplitude data suggest that passive membrane properties contribute to the observed differences in synaptic effectiveness. Conclusion We conclude that electrotonic decay within the postsynaptic structure contributes to the phenomenon of missing quanta. Further studies directed at understanding the role of the SSR in synaptic transmission and the potential for regulating ‘missing quanta’ will yield important information about synaptic transmission at the Drosophila NMJ.
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Kwon SK, Sando R, Lewis TL, Hirabayashi Y, Maximov A, Polleux F. LKB1 Regulates Mitochondria-Dependent Presynaptic Calcium Clearance and Neurotransmitter Release Properties at Excitatory Synapses along Cortical Axons. PLoS Biol 2016; 14:e1002516. [PMID: 27429220 PMCID: PMC4948842 DOI: 10.1371/journal.pbio.1002516] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Accepted: 06/21/2016] [Indexed: 12/24/2022] Open
Abstract
Individual synapses vary significantly in their neurotransmitter release properties, which underlie complex information processing in neural circuits. Presynaptic Ca2+ homeostasis plays a critical role in specifying neurotransmitter release properties, but the mechanisms regulating synapse-specific Ca2+ homeostasis in the mammalian brain are still poorly understood. Using electrophysiology and genetically encoded Ca2+ sensors targeted to the mitochondrial matrix or to presynaptic boutons of cortical pyramidal neurons, we demonstrate that the presence or absence of mitochondria at presynaptic boutons dictates neurotransmitter release properties through Mitochondrial Calcium Uniporter (MCU)-dependent Ca2+ clearance. We demonstrate that the serine/threonine kinase LKB1 regulates MCU expression, mitochondria-dependent Ca2+ clearance, and thereby, presynaptic release properties. Re-establishment of MCU-dependent mitochondrial Ca2+ uptake at glutamatergic synapses rescues the altered neurotransmitter release properties characterizing LKB1-null cortical axons. Our results provide novel insights into the cellular and molecular mechanisms whereby mitochondria control neurotransmitter release properties in a bouton-specific way through presynaptic Ca2+ clearance.
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Affiliation(s)
- Seok-Kyu Kwon
- Columbia University Medical Center, Department of Neuroscience, Mortimer B. Zuckerman Mind Brain Behavior Institute, Kavli Institute for Brain Science, New York, New York, United States of America
| | - Richard Sando
- The Scripps Research Institute, Dorris Neuroscience Center, La Jolla, California, United States of America
| | - Tommy L. Lewis
- Columbia University Medical Center, Department of Neuroscience, Mortimer B. Zuckerman Mind Brain Behavior Institute, Kavli Institute for Brain Science, New York, New York, United States of America
| | - Yusuke Hirabayashi
- Columbia University Medical Center, Department of Neuroscience, Mortimer B. Zuckerman Mind Brain Behavior Institute, Kavli Institute for Brain Science, New York, New York, United States of America
| | - Anton Maximov
- The Scripps Research Institute, Dorris Neuroscience Center, La Jolla, California, United States of America
| | - Franck Polleux
- Columbia University Medical Center, Department of Neuroscience, Mortimer B. Zuckerman Mind Brain Behavior Institute, Kavli Institute for Brain Science, New York, New York, United States of America
- * E-mail:
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Astroglial glutamate transporters coordinate excitatory signaling and brain energetics. Neurochem Int 2016; 98:56-71. [PMID: 27013346 DOI: 10.1016/j.neuint.2016.03.014] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Revised: 03/15/2016] [Accepted: 03/17/2016] [Indexed: 12/22/2022]
Abstract
In the mammalian brain, a family of sodium-dependent transporters maintains low extracellular glutamate and shapes excitatory signaling. The bulk of this activity is mediated by the astroglial glutamate transporters GLT-1 and GLAST (also called EAAT2 and EAAT1). In this review, we will discuss evidence that these transporters co-localize with, form physical (co-immunoprecipitable) interactions with, and functionally couple to various 'energy-generating' systems, including the Na(+)/K(+)-ATPase, the Na(+)/Ca(2+) exchanger, glycogen metabolizing enzymes, glycolytic enzymes, and mitochondria/mitochondrial proteins. This functional coupling is bi-directional with many of these systems both being regulated by glutamate transport and providing the 'fuel' to support glutamate uptake. Given the importance of glutamate uptake to maintaining synaptic signaling and preventing excitotoxicity, it should not be surprising that some of these systems appear to 'redundantly' support the energetic costs of glutamate uptake. Although the glutamate-glutamine cycle contributes to recycling of neurotransmitter pools of glutamate, this is an over-simplification. The ramifications of co-compartmentalization of glutamate transporters with mitochondria for glutamate metabolism are discussed. Energy consumption in the brain accounts for ∼20% of the basal metabolic rate and relies almost exclusively on glucose for the production of ATP. However, the brain does not possess substantial reserves of glucose or other fuels. To ensure adequate energetic supply, increases in neuronal activity are matched by increases in cerebral blood flow via a process known as 'neurovascular coupling'. While the mechanisms for this coupling are not completely resolved, it is generally agreed that astrocytes, with processes that extend to synapses and endfeet that surround blood vessels, mediate at least some of the signal that causes vasodilation. Several studies have shown that either genetic deletion or pharmacologic inhibition of glutamate transport impairs neurovascular coupling. Together these studies strongly suggest that glutamate transport not only coordinates excitatory signaling, but also plays a pivotal role in regulating brain energetics.
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Deshpande M, Rodal AA. The Crossroads of Synaptic Growth Signaling, Membrane Traffic and Neurological Disease: Insights from Drosophila. Traffic 2015; 17:87-101. [PMID: 26538429 DOI: 10.1111/tra.12345] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 10/29/2015] [Accepted: 10/29/2015] [Indexed: 12/13/2022]
Abstract
Neurons require target-derived autocrine and paracrine growth factors to maintain proper identity, innervation, homeostasis and survival. Neuronal growth factor signaling is highly dependent on membrane traffic, both for the packaging and release of the growth factors themselves, and for regulation of intracellular signaling by their transmembrane receptors. Here, we review recent findings from the Drosophila larval neuromuscular junction (NMJ) that illustrate how specific steps of intracellular traffic and inter-organelle interactions impinge on signaling, particularly in the bone morphogenic protein, Wingless and c-Jun-activated kinase pathways, regulating elaboration and stability of NMJ arbors, construction of synapses and synaptic transmission and homeostasis. These membrane trafficking and signaling pathways have been implicated in human motor neuron diseases including amyotrophic lateral sclerosis and hereditary spastic paraplegia, highlighting their importance for neuronal health and survival.
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Affiliation(s)
| | - Avital A Rodal
- Department of Biology, Brandeis University, Waltham, MA, USA
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35
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Marland JRK, Hasel P, Bonnycastle K, Cousin MA. Mitochondrial Calcium Uptake Modulates Synaptic Vesicle Endocytosis in Central Nerve Terminals. J Biol Chem 2015; 291:2080-6. [PMID: 26644474 PMCID: PMC4732196 DOI: 10.1074/jbc.m115.686956] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Indexed: 12/15/2022] Open
Abstract
Presynaptic calcium influx triggers synaptic vesicle (SV) exocytosis and modulates subsequent SV endocytosis. A number of calcium clearance mechanisms are present in central nerve terminals that regulate intracellular free calcium levels both during and after stimulation. During action potential stimulation, mitochondria rapidly accumulate presynaptic calcium via the mitochondrial calcium uniporter (MCU). The role of mitochondrial calcium uptake in modulating SV recycling has been debated extensively, but a definitive conclusion has not been achieved. To directly address this question, we manipulated the expression of the MCU channel subunit in primary cultures of neurons expressing a genetically encoded reporter of SV turnover. Knockdown of MCU resulted in ablation of activity-dependent mitochondrial calcium uptake but had no effect on the rate or extent of SV exocytosis. In contrast, the rate of SV endocytosis was increased in the absence of mitochondrial calcium uptake and slowed when MCU was overexpressed. MCU knockdown did not perturb activity-dependent increases in presynaptic free calcium, suggesting that SV endocytosis may be controlled by calcium accumulation and efflux from mitochondria in their immediate vicinity.
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Affiliation(s)
- Jamie Roslin Keynes Marland
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Philip Hasel
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Katherine Bonnycastle
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Michael Alan Cousin
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
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36
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Harris KP, Littleton JT. Transmission, Development, and Plasticity of Synapses. Genetics 2015; 201:345-75. [PMID: 26447126 PMCID: PMC4596655 DOI: 10.1534/genetics.115.176529] [Citation(s) in RCA: 119] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 05/28/2015] [Indexed: 01/03/2023] Open
Abstract
Chemical synapses are sites of contact and information transfer between a neuron and its partner cell. Each synapse is a specialized junction, where the presynaptic cell assembles machinery for the release of neurotransmitter, and the postsynaptic cell assembles components to receive and integrate this signal. Synapses also exhibit plasticity, during which synaptic function and/or structure are modified in response to activity. With a robust panel of genetic, imaging, and electrophysiology approaches, and strong evolutionary conservation of molecular components, Drosophila has emerged as an essential model system for investigating the mechanisms underlying synaptic assembly, function, and plasticity. We will discuss techniques for studying synapses in Drosophila, with a focus on the larval neuromuscular junction (NMJ), a well-established model glutamatergic synapse. Vesicle fusion, which underlies synaptic release of neurotransmitters, has been well characterized at this synapse. In addition, studies of synaptic assembly and organization of active zones and postsynaptic densities have revealed pathways that coordinate those events across the synaptic cleft. We will also review modes of synaptic growth and plasticity at the fly NMJ, and discuss how pre- and postsynaptic cells communicate to regulate plasticity in response to activity.
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Affiliation(s)
- Kathryn P Harris
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - J Troy Littleton
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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Central presynaptic terminals are enriched in ATP but the majority lack mitochondria. PLoS One 2015; 10:e0125185. [PMID: 25928229 PMCID: PMC4416033 DOI: 10.1371/journal.pone.0125185] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 03/10/2015] [Indexed: 11/19/2022] Open
Abstract
Synaptic neurotransmission is known to be an energy demanding process. At the presynapse, ATP is required for loading neurotransmitters into synaptic vesicles, for priming synaptic vesicles before release, and as a substrate for various kinases and ATPases. Although it is assumed that presynaptic sites usually harbor local mitochondria, which may serve as energy powerhouse to generate ATP as well as a presynaptic calcium depot, a clear role of presynaptic mitochondria in biochemical functioning of the presynapse is not well-defined. Besides a few synaptic subtypes like the mossy fibers and the Calyx of Held, most central presynaptic sites are either en passant or tiny axonal terminals that have little space to accommodate a large mitochondrion. Here, we have used imaging studies to demonstrate that mitochondrial antigens poorly co-localize with the synaptic vesicle clusters and active zone marker in the cerebral cortex, hippocampus and the cerebellum. Confocal imaging analysis on neuronal cultures revealed that most neuronal mitochondria are either somatic or distributed in the proximal part of major dendrites. A large number of synapses in culture are devoid of any mitochondria. Electron micrographs from neuronal cultures further confirm our finding that the majority of presynapses may not harbor resident mitochondria. We corroborated our ultrastructural findings using serial block face scanning electron microscopy (SBFSEM) and found that more than 60% of the presynaptic terminals lacked discernible mitochondria in the wild-type mice hippocampus. Biochemical fractionation of crude synaptosomes into mitochondria and pure synaptosomes also revealed a sparse presence of mitochondrial antigen at the presynaptic boutons. Despite a low abundance of mitochondria, the synaptosomal membranes were found to be highly enriched in ATP suggesting that the presynapse may possess alternative mechanism/s for concentrating ATP for its function. The potential mechanisms including local glycolysis and the possible roles of ATP-binding synaptic proteins such as synapsins, are discussed.
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Ueda A, Wu CF. The role of cAMP in synaptic homeostasis in response to environmental temperature challenges and hyperexcitability mutations. Front Cell Neurosci 2015; 9:10. [PMID: 25698925 PMCID: PMC4313691 DOI: 10.3389/fncel.2015.00010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 01/08/2015] [Indexed: 11/13/2022] Open
Abstract
Homeostasis is the ability of physiological systems to regain functional balance following environment or experimental insults and synaptic homeostasis has been demonstrated in various species following genetic or pharmacological disruptions. Among environmental challenges, homeostatic responses to temperature extremes are critical to animal survival under natural conditions. We previously reported that axon terminal arborization in Drosophila larval neuromuscular junctions (NMJs) is enhanced at elevated temperatures; however, the amplitude of excitatory junctional potentials (EJPs) remains unaltered despite the increase in synaptic bouton numbers. Here we determine the cellular basis of this homeostatic adjustment in larvae reared at high temperature (HT, 29°C). We found that synaptic current focally recorded from individual synaptic boutons was unaffected by rearing temperature (<15°C to >30°C). However, HT rearing decreased the quantal size (amplitude of spontaneous miniature EJPs, or mEJPs), which compensates for the increased number of synaptic releasing sites to retain a normal EJP size. The quantal size decrease is accounted for by a decrease in input resistance of the postsynaptic muscle fiber, indicating an increase in membrane area that matches the synaptic growth at HT. Interestingly, a mutation in rutabaga (rut) encoding adenylyl cyclase (AC) exhibited no obvious changes in quantal size or input resistance of postsynaptic muscle cells after HT rearing, suggesting an important role for rut AC in temperature-induced synaptic homeostasis in Drosophila. This extends our previous finding of rut-dependent synaptic homeostasis in hyperexcitable mutants, e.g., slowpoke (slo). In slo larvae, the lack of BK channel function is partially ameliorated by upregulation of presynaptic Shaker (Sh) IA current to limit excessive transmitter release in addition to postsynaptic glutamate receptor recomposition that reduces the quantal size.
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Affiliation(s)
- Atsushi Ueda
- Department of Biology, University of Iowa Iowa City, IA, USA
| | - Chun-Fang Wu
- Department of Biology, University of Iowa Iowa City, IA, USA
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Pendin D, Greotti E, Filadi R, Pozzan T. Spying on organelle Ca²⁺ in living cells: the mitochondrial point of view. J Endocrinol Invest 2015; 38:39-45. [PMID: 25245340 DOI: 10.1007/s40618-014-0178-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Accepted: 09/15/2014] [Indexed: 01/04/2023]
Abstract
Over the past years, the use of genetically encoded Ca(2+) indicators (GECIs), derived from aequorin and green fluorescent protein, has profoundly transformed the study of Ca(2+) homeostasis in living cells leading to novel insights into functional aspects of Ca(2+) signalling. Particularly relevant for a deeper understanding of these key aspects of cell pathophysiology has been the possibility of imaging changes in Ca(2+) concentration not only in the cytoplasm, but also inside organelles. In this review, we will provide an overview of the ongoing developments in the use of GECIs, with particular focus on mitochondrially targeted probes. Indeed, due to recent advances in organelle Ca(2+) imaging with GECIs, mitochondria are now at the centre of renewed interest: they play key roles both in the physiology of the cell and in multiple pathological conditions relevant to human health.
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Affiliation(s)
- D Pendin
- Department of Biomedical Sciences, University of Padua, viale G. Colombo 3, 35131, Padua, Italy.
- Neuroscience Institute, National Research Council, viale G. Colombo 3, 35131, Padua, Italy.
| | - E Greotti
- Department of Biomedical Sciences, University of Padua, viale G. Colombo 3, 35131, Padua, Italy
- Neuroscience Institute, National Research Council, viale G. Colombo 3, 35131, Padua, Italy
| | - R Filadi
- Department of Biomedical Sciences, University of Padua, viale G. Colombo 3, 35131, Padua, Italy
| | - T Pozzan
- Department of Biomedical Sciences, University of Padua, viale G. Colombo 3, 35131, Padua, Italy
- Neuroscience Institute, National Research Council, viale G. Colombo 3, 35131, Padua, Italy
- Venetian Institute of Molecular Medicine, Via G. Orus 2, 35129, Padua, Italy
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40
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Wong CO, Chen K, Lin YQ, Chao Y, Duraine L, Lu Z, Yoon WH, Sullivan JM, Broadhead GT, Sumner CJ, Lloyd TE, Macleod GT, Bellen HJ, Venkatachalam K. A TRPV channel in Drosophila motor neurons regulates presynaptic resting Ca2+ levels, synapse growth, and synaptic transmission. Neuron 2014; 84:764-77. [PMID: 25451193 DOI: 10.1016/j.neuron.2014.09.030] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/10/2014] [Indexed: 12/30/2022]
Abstract
Presynaptic resting Ca(2+) influences synaptic vesicle (SV) release probability. Here, we report that a TRPV channel, Inactive (Iav), maintains presynaptic resting [Ca(2+)] by promoting Ca(2+) release from the endoplasmic reticulum in Drosophila motor neurons, and is required for both synapse development and neurotransmission. We find that Iav activates the Ca(2+)/calmodulin-dependent protein phosphatase calcineurin, which is essential for presynaptic microtubule stabilization at the neuromuscular junction. Thus, loss of Iav induces destabilization of presynaptic microtubules, resulting in diminished synaptic growth. Interestingly, expression of human TRPV1 in Iav-deficient motor neurons rescues these defects. We also show that the absence of Iav causes lower SV release probability and diminished synaptic transmission, whereas Iav overexpression elevates these synaptic parameters. Together, our findings indicate that Iav acts as a key regulator of synaptic development and function by influencing presynaptic resting [Ca(2+)].
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Affiliation(s)
- Ching-On Wong
- Department of Integrative Biology and Pharmacology, University of Texas School of Medicine, 6431 Fannin Street, Houston, TX 77030, USA
| | - Kuchuan Chen
- Graduate Program in Developmental Biology, Baylor College of Medicine, 1250 Moursund Street, Suite N1125.14, Mailstop NR-1125, Houston, TX 77030, USA
| | - Yong Qi Lin
- Howard Hughes Medical Institute; Departments of Molecular and Human Genetics and Neuroscience, Baylor College of Medicine, 1250 Moursund Street, Suite N1125.14, Mailstop NR-1125, Houston, TX 77030, USA
| | - Yufang Chao
- Department of Integrative Biology and Pharmacology, University of Texas School of Medicine, 6431 Fannin Street, Houston, TX 77030, USA
| | - Lita Duraine
- Howard Hughes Medical Institute; Departments of Molecular and Human Genetics and Neuroscience, Baylor College of Medicine, 1250 Moursund Street, Suite N1125.14, Mailstop NR-1125, Houston, TX 77030, USA
| | - Zhongmin Lu
- Integrative Biology and Neuroscience program, Florida Atlantic University and Max Planck Florida Institute, 5353 Parkside Drive, Jupiter, FL 33458, USA
| | - Wan Hee Yoon
- Howard Hughes Medical Institute; Departments of Molecular and Human Genetics and Neuroscience, Baylor College of Medicine, 1250 Moursund Street, Suite N1125.14, Mailstop NR-1125, Houston, TX 77030, USA
| | - Jeremy M Sullivan
- Department of Neurology, Johns Hopkins University School of Medicine, 855 North Wolfe Street, Baltimore, MD 21231, USA
| | - Geoffrey T Broadhead
- Department of Integrative Biology and Pharmacology, University of Texas School of Medicine, 6431 Fannin Street, Houston, TX 77030, USA
| | - Charlotte J Sumner
- Department of Neurology, Johns Hopkins University School of Medicine, 855 North Wolfe Street, Baltimore, MD 21231, USA; Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, Baltimore, MD 21231, USA
| | - Thomas E Lloyd
- Department of Neurology, Johns Hopkins University School of Medicine, 855 North Wolfe Street, Baltimore, MD 21231, USA; Department of Neuroscience, Johns Hopkins University School of Medicine, 855 North Wolfe Street, Baltimore, MD 21231, USA
| | - Gregory T Macleod
- Department of Physiology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA
| | - Hugo J Bellen
- Graduate Program in Developmental Biology, Baylor College of Medicine, 1250 Moursund Street, Suite N1125.14, Mailstop NR-1125, Houston, TX 77030, USA; Howard Hughes Medical Institute; Departments of Molecular and Human Genetics and Neuroscience, Baylor College of Medicine, 1250 Moursund Street, Suite N1125.14, Mailstop NR-1125, Houston, TX 77030, USA
| | - Kartik Venkatachalam
- Department of Integrative Biology and Pharmacology, University of Texas School of Medicine, 6431 Fannin Street, Houston, TX 77030, USA; Graduate Program in Developmental Biology, Baylor College of Medicine, 1250 Moursund Street, Suite N1125.14, Mailstop NR-1125, Houston, TX 77030, USA; Graduate Programs in Cell and Regulatory Biology (CRB) and Neuroscience, Graduate School of Biomedical Sciences, University of Texas School of Medicine, Houston, TX 77030.
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41
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Knodel MM, Geiger R, Ge L, Bucher D, Grillo A, Wittum G, Schuster CM, Queisser G. Synaptic bouton properties are tuned to best fit the prevailing firing pattern. Front Comput Neurosci 2014; 8:101. [PMID: 25249970 PMCID: PMC4158995 DOI: 10.3389/fncom.2014.00101] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 08/07/2014] [Indexed: 11/25/2022] Open
Abstract
The morphology of presynaptic specializations can vary greatly ranging from classical single-release-site boutons in the central nervous system to boutons of various sizes harboring multiple vesicle release sites. Multi-release-site boutons can be found in several neural contexts, for example at the neuromuscular junction (NMJ) of body wall muscles of Drosophila larvae. These NMJs are built by two motor neurons forming two types of glutamatergic multi-release-site boutons with two typical diameters. However, it is unknown why these distinct nerve terminal configurations are used on the same postsynaptic muscle fiber. To systematically dissect the biophysical properties of these boutons we developed a full three-dimensional model of such boutons, their release sites and transmitter-harboring vesicles and analyzed the local vesicle dynamics of various configurations during stimulation. Here we show that the rate of transmission of a bouton is primarily limited by diffusion-based vesicle movements and that the probability of vesicle release and the size of a bouton affect bouton-performance in distinct temporal domains allowing for an optimal transmission of the neural signals at different time scales. A comparison of our in silico simulations with in vivo recordings of the natural motor pattern of both neurons revealed that the bouton properties resemble a well-tuned cooperation of the parameters release probability and bouton size, enabling a reliable transmission of the prevailing firing-pattern at diffusion-limited boutons. Our findings indicate that the prevailing firing-pattern of a neuron may determine the physiological and morphological parameters required for its synaptic terminals.
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Affiliation(s)
- Markus M Knodel
- Bernstein Group Detailed Modeling of Signal Processing in Neurons, University of Heidelberg and University of Frankfurt Heidelberg/Frankfurt, Germany ; Department of Simulation and Modeling, Goethe Center for Scientific Computing, University of Frankfurt Frankfurt, Germany
| | - Romina Geiger
- Bernstein Center for Computational Neuroscience Heidelberg-Mannheim Heidelberg/Mannheim, Germany ; Department of Neurobiology, Interdisciplinary Center for Neurosciences, University of Heidelberg Heidelberg, Germany
| | - Lihao Ge
- Bernstein Center for Computational Neuroscience Heidelberg-Mannheim Heidelberg/Mannheim, Germany ; Department of Neurobiology, Interdisciplinary Center for Neurosciences, University of Heidelberg Heidelberg, Germany
| | - Daniel Bucher
- Bernstein Group Detailed Modeling of Signal Processing in Neurons, University of Heidelberg and University of Frankfurt Heidelberg/Frankfurt, Germany ; Department of Neurobiology, Interdisciplinary Center for Neurosciences, University of Heidelberg Heidelberg, Germany ; Development Unit, European Molecular Biology Laboratory Heidelberg, Germany
| | - Alfio Grillo
- Department of Simulation and Modeling, Goethe Center for Scientific Computing, University of Frankfurt Frankfurt, Germany ; Department of Mathematical Sciences, Polythecnic of Turin Turin, Italy
| | - Gabriel Wittum
- Bernstein Group Detailed Modeling of Signal Processing in Neurons, University of Heidelberg and University of Frankfurt Heidelberg/Frankfurt, Germany ; Department of Simulation and Modeling, Goethe Center for Scientific Computing, University of Frankfurt Frankfurt, Germany
| | - Christoph M Schuster
- Bernstein Group Detailed Modeling of Signal Processing in Neurons, University of Heidelberg and University of Frankfurt Heidelberg/Frankfurt, Germany ; Bernstein Center for Computational Neuroscience Heidelberg-Mannheim Heidelberg/Mannheim, Germany ; Department of Neurobiology, Interdisciplinary Center for Neurosciences, University of Heidelberg Heidelberg, Germany
| | - Gillian Queisser
- Bernstein Group Detailed Modeling of Signal Processing in Neurons, University of Heidelberg and University of Frankfurt Heidelberg/Frankfurt, Germany ; Bernstein Center for Computational Neuroscience Heidelberg-Mannheim Heidelberg/Mannheim, Germany ; Department of Computational Neuroscience, Goethe Center for Scientific Computing, University of Frankfurt Frankfurt, Germany
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42
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Expression of multiple transgenes from a single construct using viral 2A peptides in Drosophila. PLoS One 2014; 9:e100637. [PMID: 24945148 PMCID: PMC4063965 DOI: 10.1371/journal.pone.0100637] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 05/29/2014] [Indexed: 01/29/2023] Open
Abstract
Expression of multiple reporter or effector transgenes in the same cell from a single construct is increasingly necessary in various experimental paradigms. The discovery of short, virus-derived peptide sequences that mediate a ribosome-skipping event enables generation of multiple separate peptide products from one mRNA. Here we describe methods and vectors to facilitate easy production of polycistronic-like sequences utilizing these 2A peptides tailored for expression in Drosophila both in vitro and in vivo. We tested the separation efficiency of different viral 2A peptides in cultured Drosophila cells and in vivo and found that the 2A peptides from porcine teschovirus-1 (P2A) and Thosea asigna virus (T2A) worked best. To demonstrate the utility of this approach, we used the P2A peptide to co-express the red fluorescent protein tdTomato and the genetically-encoded calcium indicator GCaMP5G in larval motorneurons. This technique enabled ratiometric calcium imaging with motion correction allowing us to record synaptic activity at the neuromuscular junction in an intact larval preparation through the cuticle. The tools presented here should greatly facilitate the generation of 2A peptide-mediated expression of multiple transgenes in Drosophila.
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43
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Pollari E, Goldsteins G, Bart G, Koistinaho J, Giniatullin R. The role of oxidative stress in degeneration of the neuromuscular junction in amyotrophic lateral sclerosis. Front Cell Neurosci 2014; 8:131. [PMID: 24860432 PMCID: PMC4026683 DOI: 10.3389/fncel.2014.00131] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 04/27/2014] [Indexed: 12/12/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is characterized by the progressive loss of motoneurons and degradation of the neuromuscular junctions (NMJ). Consistent with the dying-back hypothesis of motoneuron degeneration the decline in synaptic function initiates from the presynaptic terminals in ALS. Oxidative stress is a major contributory factor to ALS pathology and affects the presynaptic transmitter releasing machinery. Indeed, in ALS mouse models nerve terminals are sensitive to reactive oxygen species (ROS) suggesting that oxidative stress, along with compromised mitochondria and increased intracellular Ca(2+) amplifies the presynaptic decline in NMJ. This initial dysfunction is followed by a neurodegeneration induced by inflammatory agents and loss of trophic support. To develop effective therapeutic approaches against ALS, it is important to identify the mechanisms underlying the initial pathological events. Given the role of oxidative stress in ALS, targeted antioxidant treatments could be a promising therapeutic approach. However, the complex nature of ALS and failure of monotherapies suggest that an antioxidant therapy should be accompanied by anti-inflammatory interventions to enhance the restoration of the redox balance.
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Affiliation(s)
- Eveliina Pollari
- Molecular Brain Research Laboratory, Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland Kuopio, Finland ; Experimental Neurology - Laboratory of Neurobiology, Department of Neurosciences, Vesalius Research Center, KULeuven - University of Leuven Leuven, Belgium
| | - Gundars Goldsteins
- Molecular Brain Research Laboratory, Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland Kuopio, Finland
| | - Geneviève Bart
- Cell Biology Laboratory, Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland Kuopio, Finland
| | - Jari Koistinaho
- Molecular Brain Research Laboratory, Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland Kuopio, Finland
| | - Rashid Giniatullin
- Cell Biology Laboratory, Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland Kuopio, Finland ; Laboratory of Neurobiology, Department of Physiology, Kazan Federal University Kazan, Russia
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44
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Titlow JS, Rice J, Majeed ZR, Holsopple E, Biecker S, Cooper RL. Anatomical and genotype-specific mechanosensory responses in Drosophila melanogaster larvae. Neurosci Res 2014; 83:54-63. [PMID: 24768745 DOI: 10.1016/j.neures.2014.04.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 04/08/2014] [Accepted: 04/09/2014] [Indexed: 11/27/2022]
Abstract
Afferent neurons commonly exhibit a somatotopic arrangement in the central nervous system that organizes spatially discrete sensory input. We are interested in how that spatial input gets integrated into motor commands. With resources for screening genes and neural circuits, and given that the cells and ion channels that transduce tactile stimuli in Drosophila larvae are remarkably well-characterized, larval mechanosensation is an ideal system for investigating how specific behaviors emerge from localized sensory input. We observed that crawling larvae are more reactive to a 20mN tactile stimulus on the head than on the tail or abdomen. Behavioral responses that were evoked by the stimuli also depended on where the stimulus was delivered. Differences in relative sensitivity were observed in different genotypes, e.g., a null white mutant and hypomorphic smn mutant are significantly more reactive to tail touches than Canton-S larvae. Responses were inhibited by silencing chemical transmission in a combination of multidendritic and chordotonal neurons, but not by inhibiting any specific subset of neurons. Extracellular recordings from segmental nerves revealed that sensory-evoked responses exhibit spike-timing dependence at the neural circuit level. Tactile stimuli reduced endogenous firing frequency and increased bursting periods when applied during periods of motor activity. The same stimulus initiated bursts of activity when applied during inactive periods. Together, these data depict the spatial and temporal complexity of mechanosensation as it applies to action selection, and provide a foundation for addressing how neural circuits in the CNS adjust their activity to afferent input.
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Affiliation(s)
- Josh S Titlow
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA.
| | - Jordan Rice
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA; Transylvania University, Lexington, KY 40508, USA
| | - Zana R Majeed
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA; Department of Biology, College of Science, University of Salahaddin, Erbil, Iraq
| | - Emily Holsopple
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Stephanie Biecker
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
| | - Robin L Cooper
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA
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45
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Abstract
Homeostatic plasticity functions within the nervous system to maintain normal neural functions, such as neurotransmission, within predefined optimal ranges. The defined output of these neuronal processes is referred to as the set point, which is the value that the homeostatic system defends against fluctuations. Currently, it is unknown how stable homeostatic set points are within the nervous system. In the present study we used the CM9 neuromuscular junctions (NMJs) in the adult Drosophila to investigate the stability of the set point of synaptic homeostasis across the lifespan of the fly. At the fly NMJ, it is believed that the depolarization of the muscle by neurotransmitter during an action potential, represented by the EPSP, is a homeostatic set point that is precisely maintained via changes in synaptic vesicle release. We find that the amplitude of the EPSP abruptly increases during middle age and that this enhanced EPSP is maintained into late life, consistent with an age-dependent change to the homeostatic set point of the synapse during middle age. In support of this, comparison of the homeostatic response at the young versus the old synapse shows that the magnitude of the homeostatic response at the older synapse is significantly larger than the response at the young NMJ, appropriate for a synapse at which the set point has been increased. Our data demonstrate that the amplitude of the EPSP at the Drosophila NMJ increases during aging and that the homeostatic signaling system adjusts its response to accommodate the new set point.
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46
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Gertner DM, Desai S, Lnenicka GA. Synaptic excitation is regulated by the postsynaptic dSK channel at the Drosophila larval NMJ. J Neurophysiol 2014; 111:2533-43. [PMID: 24671529 DOI: 10.1152/jn.00903.2013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the mammalian central nervous system, the postsynaptic small-conductance Ca(2+)-dependent K(+) (SK) channel has been shown to reduce postsynaptic depolarization and limit Ca(2+) influx through N-methyl-d-aspartate receptors. To examine further the role of the postsynaptic SK channel in synaptic transmission, we studied its action at the Drosophila larval neuromuscular junction (NMJ). Repetitive synaptic stimulation produced an increase in postsynaptic membrane conductance leading to depression of excitatory postsynaptic potential amplitude and hyperpolarization of the resting membrane potential (RMP). This reduction in synaptic excitation was due to the postsynaptic Drosophila SK (dSK) channel; synaptic depression, increased membrane conductance and RMP hyperpolarization were reduced in dSK mutants or after expressing a Ca(2+) buffer in the muscle. Ca(2+) entering at the postsynaptic membrane was sufficient to activate dSK channels based upon studies in which the muscle membrane was voltage clamped to prevent opening voltage-dependent Ca(2+) channels. Increasing external Ca(2+) produced an increase in resting membrane conductance and RMP that was not seen in dSK mutants or after adding the glutamate-receptor blocker philanthotoxin. Thus it appeared that dSK channels were also activated by spontaneous transmitter release and played a role in setting membrane conductance and RMP. In mammals, dephosphorylation by protein phosphatase 2A (PP2A) increased the Ca(2+) sensitivity of the SK channel; PP2A appeared to increase the sensitivity of the dSK channel since PP2A inhibitors reduced activation of the dSK channel by evoked synaptic activity or increased external Ca(2+). It is proposed that spontaneous and evoked transmitter release activate the postsynaptic dSK channel to limit synaptic excitation and stabilize synapses.
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Affiliation(s)
- Daniel M Gertner
- Department of Biological Sciences, University at Albany, Albany, New York
| | - Sunil Desai
- Department of Biological Sciences, University at Albany, Albany, New York
| | - Gregory A Lnenicka
- Department of Biological Sciences, University at Albany, Albany, New York
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47
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Ivannikov MV, Macleod GT. Mitochondrial free Ca²⁺ levels and their effects on energy metabolism in Drosophila motor nerve terminals. Biophys J 2014; 104:2353-61. [PMID: 23746507 DOI: 10.1016/j.bpj.2013.03.064] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Revised: 02/24/2013] [Accepted: 03/25/2013] [Indexed: 01/29/2023] Open
Abstract
Mitochondrial Ca²⁺ uptake exerts dual effects on mitochondria. Ca²⁺ accumulation in the mitochondrial matrix dissipates membrane potential (ΔΨm), but Ca²⁺ binding of the intramitochondrial enzymes accelerates oxidative phosphorylation, leading to mitochondrial hyperpolarization. The levels of matrix free Ca²⁺ ([Ca²⁺]m) that trigger these metabolic responses in mitochondria in nerve terminals have not been determined. Here, we estimated [Ca²⁺]m in motor neuron terminals of Drosophila larvae using two methods: the relative responses of two chemical Ca²⁺ indicators with a 20-fold difference in Ca²⁺ affinity (rhod-FF and rhod-5N), and the response of a low-affinity, genetically encoded ratiometric Ca²⁺ indicator (D4cpv) calibrated against known Ca²⁺ levels. Matrix pH (pHm) and ΔΨm were monitored using ratiometric pericam and tetramethylrhodamine ethyl ester probe, respectively, to determine when mitochondrial energy metabolism was elevated. At rest, [Ca²⁺]m was 0.22 ± 0.04 μM, but it rose to ~26 μM (24.3 ± 3.4 μM with rhod-FF/rhod-5N and 27.0 ± 2.6 μM with D4cpv) when the axon fired close to its endogenous frequency for only 2 s. This elevation in [Ca²⁺]m coincided with a rapid elevation in pHm and was followed by an after-stimulus ΔΨm hyperpolarization. However, pHm decreased and no ΔΨm hyperpolarization was observed in response to lower levels of [Ca²⁺]m, up to 13.1 μM. These data indicate that surprisingly high levels of [Ca²⁺]m are required to stimulate presynaptic mitochondrial energy metabolism.
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Affiliation(s)
- Maxim V Ivannikov
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.
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48
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Rossano AJ, Chouhan AK, Macleod GT. Genetically encoded pH-indicators reveal activity-dependent cytosolic acidification of Drosophila motor nerve termini in vivo. J Physiol 2013; 591:1691-706. [PMID: 23401611 PMCID: PMC3624846 DOI: 10.1113/jphysiol.2012.248377] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Accepted: 01/04/2013] [Indexed: 01/27/2023] Open
Abstract
All biochemical processes, including those underlying synaptic function and plasticity, are pH sensitive. Cytosolic pH (pH(cyto)) shifts are known to accompany nerve activity in situ, but technological limitations have prevented characterization of such shifts in vivo. Genetically encoded pH-indicators (GEpHIs) allow for tissue-specific in vivo measurement of pH. We expressed three different GEpHIs in the cytosol of Drosophila larval motor neurons and observed substantial presynaptic acidification in nerve termini during nerve stimulation in situ. SuperEcliptic pHluorin was the most useful GEpHI for studying pH(cyto) shifts in this model system. We determined the resting pH of the nerve terminal cytosol to be 7.30 ± 0.02, and observed a decrease of 0.16 ± 0.01 pH units when the axon was stimulated at 40 Hz for 4 s. Realkalinization occurred upon cessation of stimulation with a time course of 20.54 ± 1.05 s (τ). The chemical pH-indicator 2,7-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein corroborated these changes in pH(cyto). Bicarbonate-derived buffering did not contribute to buffering of acid loads from short (≤ 4 s) trains of action potentials but did buffer slow (~60 s) acid loads. The magnitude of cytosolic acid transients correlated with cytosolic Ca(2+) increase upon stimulation, and partial inhibition of the plasma membrane Ca(2+)-ATPase, a Ca(2+)/H(+) exchanger, attenuated pH(cyto) shifts. Repeated stimulus trains mimicking motor patterns generated greater cytosolic acidification (~0.30 pH units). Imaging through the cuticle of intact larvae revealed spontaneous pH(cyto) shifts in presynaptic termini in vivo, similar to those seen in situ during fictive locomotion, indicating that presynaptic pH(cyto) shifts cannot be dismissed as artifacts of ex vivo preparations.
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Affiliation(s)
- Adam J Rossano
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
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Shutov LP, Kim MS, Houlihan PR, Medvedeva YV, Usachev YM. Mitochondria and plasma membrane Ca2+-ATPase control presynaptic Ca2+ clearance in capsaicin-sensitive rat sensory neurons. J Physiol 2013; 591:2443-62. [PMID: 23381900 DOI: 10.1113/jphysiol.2012.249219] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The central processes of primary nociceptors form synaptic connections with the second-order nociceptive neurons located in the dorsal horn of the spinal cord. These synapses gate the flow of nociceptive information from the periphery to the CNS, and plasticity at these synapses contributes to centrally mediated hyperalgesia and allodynia. Although exocytosis and synaptic plasticity are controlled by Ca(2+) at the release sites, the mechanisms underlying presynaptic Ca(2+) signalling at the nociceptive synapses are not well characterized. We examined the presynaptic mechanisms regulating Ca(2+) clearance following electrical stimulation in capsaicin-sensitive nociceptors using a dorsal root ganglion (DRG)/spinal cord neuron co-culture system. Cytosolic Ca(2+) concentration ([Ca(2+)]i) recovery following electrical stimulation was well approximated by a monoexponential function with a ∼2 s. Inhibition of sarco-endoplasmic reticulum Ca(2+)-ATPase did not affect presynaptic [Ca(2+)]i recovery, and blocking plasmalemmal Na(+)/Ca(2+) exchange produced only a small reduction in the rate of [Ca(2+)]i recovery (∼12%) that was independent of intracellular K(+). However, [Ca(2+)]i recovery in presynaptic boutons strongly depended on the plasma membrane Ca(2+)-ATPase (PMCA) and mitochondria that accounted for ∼47 and 40%, respectively, of presynaptic Ca(2+) clearance. Measurements using a mitochondria-targeted Ca(2+) indicator, mtPericam, demonstrated that presynaptic mitochondria accumulated Ca(2+) in response to electrical stimulation. Quantitative analysis revealed that the mitochondrial Ca(2+) uptake is highly sensitive to presynaptic [Ca(2+)]i elevations, and occurs at [Ca(2+)]i levels as low as ∼200-300 nm. Using RT-PCR, we detected expression of several putative mitochondrial Ca(2+) transporters in DRG, such as MCU, Letm1 and NCLX. Collectively, this work identifies PMCA and mitochondria as the major regulators of presynaptic Ca(2+) signalling at the first sensory synapse, and underlines the high sensitivity of the mitochondrial Ca(2+) uniporter in neurons to cytosolic Ca(2+).
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Affiliation(s)
- Leonid P Shutov
- Y. M. Usachev: Department of Pharmacology, University of Iowa Carver College of Medicine, 2-340F BSB, 51 Newton Road, Iowa City, IA 52242, USA
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Akerboom J, Chen TW, Wardill TJ, Tian L, Marvin JS, Mutlu S, Calderón NC, Esposti F, Borghuis BG, Sun XR, Gordus A, Orger MB, Portugues R, Engert F, Macklin JJ, Filosa A, Aggarwal A, Kerr RA, Takagi R, Kracun S, Shigetomi E, Khakh BS, Baier H, Lagnado L, Wang SSH, Bargmann CI, Kimmel BE, Jayaraman V, Svoboda K, Kim DS, Schreiter ER, Looger LL. Optimization of a GCaMP calcium indicator for neural activity imaging. J Neurosci 2012; 32:13819-40. [PMID: 23035093 PMCID: PMC3482105 DOI: 10.1523/jneurosci.2601-12.2012] [Citation(s) in RCA: 887] [Impact Index Per Article: 73.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Revised: 07/25/2012] [Accepted: 08/01/2012] [Indexed: 01/14/2023] Open
Abstract
Genetically encoded calcium indicators (GECIs) are powerful tools for systems neuroscience. Recent efforts in protein engineering have significantly increased the performance of GECIs. The state-of-the art single-wavelength GECI, GCaMP3, has been deployed in a number of model organisms and can reliably detect three or more action potentials in short bursts in several systems in vivo. Through protein structure determination, targeted mutagenesis, high-throughput screening, and a battery of in vitro assays, we have increased the dynamic range of GCaMP3 by severalfold, creating a family of "GCaMP5" sensors. We tested GCaMP5s in several systems: cultured neurons and astrocytes, mouse retina, and in vivo in Caenorhabditis chemosensory neurons, Drosophila larval neuromuscular junction and adult antennal lobe, zebrafish retina and tectum, and mouse visual cortex. Signal-to-noise ratio was improved by at least 2- to 3-fold. In the visual cortex, two GCaMP5 variants detected twice as many visual stimulus-responsive cells as GCaMP3. By combining in vivo imaging with electrophysiology we show that GCaMP5 fluorescence provides a more reliable measure of neuronal activity than its predecessor GCaMP3. GCaMP5 allows more sensitive detection of neural activity in vivo and may find widespread applications for cellular imaging in general.
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Affiliation(s)
- Jasper Akerboom
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Tsai-Wen Chen
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Trevor J. Wardill
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Lin Tian
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Jonathan S. Marvin
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Sevinç Mutlu
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
- Champalimaud Neuroscience Programme, Champalimaud Centre for the Unknown, Doca de Pedrouços, 1400-038 Lisboa, Portugal
| | - Nicole Carreras Calderón
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
- Medical Research Council Laboratory of Molecular Biology, Cambridge, CB2 0QH United Kingdom
- Department of Chemistry, University of Puerto Rico–Río Piedras, San Juan, Puerto Rico 00931
| | - Federico Esposti
- Medical Research Council Laboratory of Molecular Biology, Cambridge, CB2 0QH United Kingdom
| | - Bart G. Borghuis
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06511
| | - Xiaonan Richard Sun
- Department of Molecular Biology and Princeton Neuroscience Institute, Princeton University, Princeton, New Jersey 08544
| | - Andrew Gordus
- Howard Hughes Medical Institute, Laboratory of Neural Circuits and Behavior, The Rockefeller University, New York, New York 10065
| | - Michael B. Orger
- Champalimaud Neuroscience Programme, Champalimaud Centre for the Unknown, Doca de Pedrouços, 1400-038 Lisboa, Portugal
- Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138
| | - Ruben Portugues
- Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138
| | - Florian Engert
- Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138
| | - John J. Macklin
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Alessandro Filosa
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, University of California, San Francisco, San Francisco, California 94158
| | - Aman Aggarwal
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India, and
| | - Rex A. Kerr
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Ryousuke Takagi
- Department of Physiology, University of California, Los Angeles, Los Angeles, California 90095
| | - Sebastian Kracun
- Department of Physiology, University of California, Los Angeles, Los Angeles, California 90095
| | - Eiji Shigetomi
- Department of Physiology, University of California, Los Angeles, Los Angeles, California 90095
| | - Baljit S. Khakh
- Department of Physiology, University of California, Los Angeles, Los Angeles, California 90095
| | - Herwig Baier
- Department of Physiology, Programs in Neuroscience, Genetics, and Developmental Biology, University of California, San Francisco, San Francisco, California 94158
| | - Leon Lagnado
- Medical Research Council Laboratory of Molecular Biology, Cambridge, CB2 0QH United Kingdom
| | - Samuel S.-H. Wang
- Department of Molecular Biology and Princeton Neuroscience Institute, Princeton University, Princeton, New Jersey 08544
| | - Cornelia I. Bargmann
- Howard Hughes Medical Institute, Laboratory of Neural Circuits and Behavior, The Rockefeller University, New York, New York 10065
| | - Bruce E. Kimmel
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Vivek Jayaraman
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Karel Svoboda
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Douglas S. Kim
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
| | - Eric R. Schreiter
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
- Department of Chemistry, University of Puerto Rico–Río Piedras, San Juan, Puerto Rico 00931
| | - Loren L. Looger
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia 20147
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