1
|
Prech S, Groschner LN, Borst A. An open platform for visual stimulation of insects. PLoS One 2024; 19:e0301999. [PMID: 38635686 PMCID: PMC11025907 DOI: 10.1371/journal.pone.0301999] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Accepted: 03/26/2024] [Indexed: 04/20/2024] Open
Abstract
To study how the nervous system processes visual information, experimenters must record neural activity while delivering visual stimuli in a controlled fashion. In animals with a nearly panoramic field of view, such as flies, precise stimulation of the entire visual field is challenging. We describe a projector-based device for stimulation of the insect visual system under a microscope. The device is based on a bowl-shaped screen that provides a wide and nearly distortion-free field of view. It is compact, cheap, easy to assemble, and easy to operate using the included open-source software for stimulus generation. We validate the virtual reality system technically and demonstrate its capabilities in a series of experiments at two levels: the cellular, by measuring the membrane potential responses of visual interneurons; and the organismal, by recording optomotor and fixation behavior of Drosophila melanogaster in tethered flight. Our experiments reveal the importance of stimulating the visual system of an insect with a wide field of view, and we provide a simple solution to do so.
Collapse
Affiliation(s)
- Stefan Prech
- Max Planck Institute for Biological Intelligence, Martinsried, Germany
| | - Lukas N. Groschner
- Max Planck Institute for Biological Intelligence, Martinsried, Germany
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Graz, Austria
| | - Alexander Borst
- Max Planck Institute for Biological Intelligence, Martinsried, Germany
| |
Collapse
|
2
|
Abstract
How neurons detect the direction of motion is a prime example of neural computation: Motion vision is found in the visual systems of virtually all sighted animals, it is important for survival, and it requires interesting computations with well-defined linear and nonlinear processing steps-yet the whole process is of moderate complexity. The genetic methods available in the fruit fly Drosophila and the charting of a connectome of its visual system have led to rapid progress and unprecedented detail in our understanding of how neurons compute the direction of motion in this organism. The picture that emerged incorporates not only the identity, morphology, and synaptic connectivity of each neuron involved but also its neurotransmitters, its receptors, and their subcellular localization. Together with the neurons' membrane potential responses to visual stimulation, this information provides the basis for a biophysically realistic model of the circuit that computes the direction of visual motion.
Collapse
Affiliation(s)
- Alexander Borst
- Max Planck Institute for Biological Intelligence, Martinsried, Germany; ,
| | - Lukas N Groschner
- Max Planck Institute for Biological Intelligence, Martinsried, Germany; ,
| |
Collapse
|
3
|
Abstract
Nonlinear, multiplication-like operations carried out by individual nerve cells greatly enhance the computational power of a neural system1–3, but our understanding of their biophysical implementation is scant. Here we pursue this problem in the Drosophila melanogaster ON motion vision circuit4,5, in which we record the membrane potentials of direction-selective T4 neurons and of their columnar input elements6,7 in response to visual and pharmacological stimuli in vivo. Our electrophysiological measurements and conductance-based simulations provide evidence for a passive supralinear interaction between two distinct types of synapse on T4 dendrites. We show that this multiplication-like nonlinearity arises from the coincidence of cholinergic excitation and release from glutamatergic inhibition. The latter depends on the expression of the glutamate-gated chloride channel GluClα8,9 in T4 neurons, which sharpens the directional tuning of the cells and shapes the optomotor behaviour of the animals. Interacting pairs of shunting inhibitory and excitatory synapses have long been postulated as an analogue approximation of a multiplication, which is integral to theories of motion detection10,11, sound localization12 and sensorimotor control13. Release from shunting inhibition and coincident excitation implement a multiplication-like synaptic interaction in motion-sensing neurons of Drosophila melanogaster.
Collapse
Affiliation(s)
| | | | - Birte Zuidinga
- Max Planck Institute of Neurobiology, Martinsried, Germany
| | | |
Collapse
|
4
|
Vrontou E, Groschner LN, Szydlowski S, Brain R, Krebbers A, Miesenböck G. Response competition between neurons and antineurons in the mushroom body. Curr Biol 2021; 31:4911-4922.e4. [PMID: 34610272 PMCID: PMC8612741 DOI: 10.1016/j.cub.2021.09.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 08/03/2021] [Accepted: 09/03/2021] [Indexed: 11/04/2022]
Abstract
The mushroom bodies of Drosophila contain circuitry compatible with race models of perceptual choice. When flies discriminate odor intensity differences, opponent pools of αβ core Kenyon cells (on and off αβc KCs) accumulate evidence for increases or decreases in odor concentration. These sensory neurons and “antineurons” connect to a layer of mushroom body output neurons (MBONs) which bias behavioral intent in opposite ways. All-to-all connectivity between the competing integrators and their MBON partners allows for correct and erroneous decisions; dopaminergic reinforcement sets choice probabilities via reciprocal changes to the efficacies of on and off KC synapses; and pooled inhibition between αβc KCs can establish equivalence with the drift-diffusion formalism known to describe behavioral performance. The response competition network gives tangible form to many features envisioned in theoretical models of mammalian decision making, but it differs from these models in one respect: the principal variables—the fill levels of the integrators and the strength of inhibition between them—are represented by graded potentials rather than spikes. In pursuit of similar computational goals, a small brain may thus prioritize the large information capacity of analog signals over the robustness and temporal processing span of pulsatile codes. Mushroom body output neurons respond with excitation to odor on- and offset On and off responses reflect the convergence of oppositely tuned Kenyon cells (KCs) Opponent KCs compete by eliciting inhibitory feedback from a common interneuron pool KCs and interneurons communicate through graded potentials rather than spikes
Collapse
Affiliation(s)
- Eleftheria Vrontou
- Centre for Neural Circuits and Behaviour, University of Oxford, Tinsley Building, Mansfield Road, Oxford OX1 3SR, UK
| | - Lukas N Groschner
- Centre for Neural Circuits and Behaviour, University of Oxford, Tinsley Building, Mansfield Road, Oxford OX1 3SR, UK
| | - Susanne Szydlowski
- Centre for Neural Circuits and Behaviour, University of Oxford, Tinsley Building, Mansfield Road, Oxford OX1 3SR, UK
| | - Ruth Brain
- Centre for Neural Circuits and Behaviour, University of Oxford, Tinsley Building, Mansfield Road, Oxford OX1 3SR, UK
| | - Alina Krebbers
- Centre for Neural Circuits and Behaviour, University of Oxford, Tinsley Building, Mansfield Road, Oxford OX1 3SR, UK
| | - Gero Miesenböck
- Centre for Neural Circuits and Behaviour, University of Oxford, Tinsley Building, Mansfield Road, Oxford OX1 3SR, UK.
| |
Collapse
|
5
|
Abstract
All an animal can do to infer the state of its environment is to observe the sensory-evoked activity of its own neurons. These inferences about the presence, quality, or similarity of objects are probabilistic and inform behavioral decisions that are often made in close to real time. Neural systems employ several strategies to facilitate sensory discrimination: Biophysical mechanisms separate the neuronal response distributions in coding space, compress their variances, and combine information from sequential observations. We review how these strategies are implemented in the olfactory system of the fruit fly. The emerging principles of odor discrimination likely apply to other neural circuits of similar architecture.
Collapse
Affiliation(s)
- Lukas N Groschner
- Centre for Neural Circuits and Behavior, University of Oxford, Oxford OX1 3SR, United Kingdom;
| | - Gero Miesenböck
- Centre for Neural Circuits and Behavior, University of Oxford, Oxford OX1 3SR, United Kingdom;
| |
Collapse
|
6
|
Podlaski WF, Seeholzer A, Groschner LN, Miesenböck G, Ranjan R, Vogels TP. Mapping the function of neuronal ion channels in model and experiment. eLife 2017; 6. [PMID: 28267430 PMCID: PMC5340531 DOI: 10.7554/elife.22152] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Accepted: 01/28/2017] [Indexed: 11/13/2022] Open
Abstract
Ion channel models are the building blocks of computational neuron models. Their biological fidelity is therefore crucial for the interpretation of simulations. However, the number of published models, and the lack of standardization, make the comparison of ion channel models with one another and with experimental data difficult. Here, we present a framework for the automated large-scale classification of ion channel models. Using annotated metadata and responses to a set of voltage-clamp protocols, we assigned 2378 models of voltage- and calcium-gated ion channels coded in NEURON to 211 clusters. The IonChannelGenealogy (ICGenealogy) web interface provides an interactive resource for the categorization of new and existing models and experimental recordings. It enables quantitative comparisons of simulated and/or measured ion channel kinetics, and facilitates field-wide standardization of experimentally-constrained modeling.
Collapse
Affiliation(s)
- William F Podlaski
- Centre for Neural Circuits and Behaviour, University of Oxford, Oxford, United Kingdom.,Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Alexander Seeholzer
- School of Computer and Communication Sciences, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.,School of Life Sciences, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland.,Brain Mind Institute, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | - Lukas N Groschner
- Centre for Neural Circuits and Behaviour, University of Oxford, Oxford, United Kingdom.,Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Gero Miesenböck
- Centre for Neural Circuits and Behaviour, University of Oxford, Oxford, United Kingdom.,Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Rajnish Ranjan
- Blue Brain Project, École Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Tim P Vogels
- Centre for Neural Circuits and Behaviour, University of Oxford, Oxford, United Kingdom.,Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| |
Collapse
|
7
|
Abstract
Mitochondrial Ca(2+) uptake regulates mitochondrial function and contributes to cell signaling. Accordingly, quantifying mitochondrial Ca(2+) signals and elaborating the mechanisms that accomplish mitochondrial Ca(2+) uptake are essential to gain our understanding of cell biology. Here, we describe the benefits and drawbacks of various established old and new techniques to assess dynamic changes of mitochondrial Ca(2+) concentration ([Ca(2+)]mito) in a wide range of applications.
Collapse
Affiliation(s)
- András T Deak
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria
| | | | | | | | | | | | | |
Collapse
|
8
|
Zhang Q, Chibalina MV, Bengtsson M, Groschner LN, Ramracheya R, Rorsman NJG, Leiss V, Nassar MA, Welling A, Gribble FM, Reimann F, Hofmann F, Wood JN, Ashcroft FM, Rorsman P. Na+ current properties in islet α- and β-cells reflect cell-specific Scn3a and Scn9a expression. J Physiol 2014; 592:4677-96. [PMID: 25172946 PMCID: PMC4253470 DOI: 10.1113/jphysiol.2014.274209] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Mouse pancreatic β- and α-cells are equipped with voltage-gated Na+ currents that inactivate over widely different membrane potentials (half-maximal inactivation (V0.5) at −100 mV and −50 mV in β- and α-cells, respectively). Single-cell PCR analyses show that both α- and β-cells have Nav1.3 (Scn3) and Nav1.7 (Scn9a) α subunits, but their relative proportions differ: β-cells principally express Nav1.7 and α-cells Nav1.3. In α-cells, genetically ablating Scn3a reduces the Na+ current by 80%. In β-cells, knockout of Scn9a lowers the Na+ current by >85%, unveiling a small Scn3a-dependent component. Glucagon and insulin secretion are inhibited in Scn3a−/− islets but unaffected in Scn9a-deficient islets. Thus, Nav1.3 is the functionally important Na+ channel α subunit in both α- and β-cells because Nav1.7 is largely inactive at physiological membrane potentials due to its unusually negative voltage dependence of inactivation. Interestingly, the Nav1.7 sequence in brain and islets is identical and yet the V0.5 for inactivation is >30 mV more negative in β-cells. This may indicate the presence of an intracellular factor that modulates the voltage dependence of inactivation.
Collapse
Affiliation(s)
- Quan Zhang
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Margarita V Chibalina
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Martin Bengtsson
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Lukas N Groschner
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Reshma Ramracheya
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Nils J G Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Veronika Leiss
- Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany Institut für Pharmakologie und Toxikologie, Eberhard-Karls Universität, Wilhelmstr. 56, 72074, Tübingen, Germany
| | - Mohammed A Nassar
- Molecular Nociception Group, University College London (UCL), Gower Street, London, WC1E 6BT, UK Biomedical Science, University of Sheffield, Sheffield, S10 2TN, UK
| | - Andrea Welling
- Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany
| | - Fiona M Gribble
- Cambridge Institute for Medical Research, University of Cambridge School of Clinical Medicine, Wellcome Trust/MRC Building, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0XY, UK
| | - Frank Reimann
- Cambridge Institute for Medical Research, University of Cambridge School of Clinical Medicine, Wellcome Trust/MRC Building, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0XY, UK
| | - Franz Hofmann
- Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany FOR 923, Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany
| | - John N Wood
- Molecular Nociception Group, University College London (UCL), Gower Street, London, WC1E 6BT, UK
| | - Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK Department of Neuroscience and Physiology, Sahlgren's Academy, University of Göteborg, Box 430, SE40530, Göteborg, Sweden
| |
Collapse
|
9
|
Deak AT, Blass S, Khan MJ, Groschner LN, Waldeck-Weiermair M, Hallström S, Graier WF, Malli R. IP3-mediated STIM1 oligomerization requires intact mitochondrial Ca2+ uptake. J Cell Sci 2014; 127:2944-55. [PMID: 24806964 PMCID: PMC4077590 DOI: 10.1242/jcs.149807] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Mitochondria contribute to cell signaling by controlling store-operated Ca2+ entry (SOCE). SOCE is activated by Ca2+ release from the endoplasmic reticulum (ER), whereupon stromal interacting molecule 1 (STIM1) forms oligomers, redistributes to ER–plasma-membrane junctions and opens plasma membrane Ca2+ channels. The mechanisms by which mitochondria interfere with the complex process of SOCE are insufficiently clarified. In this study, we used an shRNA approach to investigate the direct involvement of mitochondrial Ca2+ buffering in SOCE. We demonstrate that knockdown of either of two proteins that are essential for mitochondrial Ca2+ uptake, the mitochondrial calcium uniporter (MCU) or uncoupling protein 2 (UCP2), results in decelerated STIM1 oligomerization and impaired SOCE following cell stimulation with an inositol-1,4,5-trisphosphate (IP3)-generating agonist. Upon artificially augmented cytosolic Ca2+ buffering or ER Ca2+ depletion by sarcoplasmic or endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitors, STIM1 oligomerization did not rely on intact mitochondrial Ca2+ uptake. However, MCU-dependent mitochondrial sequestration of Ca2+ entering through the SOCE pathway was essential to prevent slow deactivation of SOCE. Our findings show a stimulus-specific contribution of mitochondrial Ca2+ uptake to the SOCE machinery, likely through a role in shaping cytosolic Ca2+ micro-domains.
Collapse
Affiliation(s)
- Andras T Deak
- The Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010-Graz, Austria
| | - Sandra Blass
- The Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010-Graz, Austria
| | - Muhammad J Khan
- The Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010-Graz, Austria
| | - Lukas N Groschner
- The Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010-Graz, Austria
| | - Markus Waldeck-Weiermair
- The Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010-Graz, Austria
| | - Seth Hallström
- The Institute of Physiological Chemistry, Center of Physiological Medicine, Medical University of Graz, 8010-Graz, Austria
| | - Wolfgang F Graier
- The Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010-Graz, Austria
| | - Roland Malli
- The Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010-Graz, Austria
| |
Collapse
|
10
|
Vishnu N, Jadoon Khan M, Karsten F, Groschner LN, Waldeck-Weiermair M, Rost R, Hallström S, Imamura H, Graier WF, Malli R. ATP increases within the lumen of the endoplasmic reticulum upon intracellular Ca2+ release. Mol Biol Cell 2014; 25:368-79. [PMID: 24307679 PMCID: PMC3907277 DOI: 10.1091/mbc.e13-07-0433] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 11/19/2013] [Accepted: 11/22/2013] [Indexed: 01/02/2023] Open
Abstract
Multiple functions of the endoplasmic reticulum (ER) essentially depend on ATP within this organelle. However, little is known about ER ATP dynamics and the regulation of ER ATP import. Here we describe real-time recordings of ER ATP fluxes in single cells using an ER-targeted, genetically encoded ATP sensor. In vitro experiments prove that the ATP sensor is both Ca(2+) and redox insensitive, which makes it possible to monitor Ca(2+)-coupled ER ATP dynamics specifically. The approach uncovers a cell type-specific regulation of ER ATP homeostasis in different cell types. Moreover, we show that intracellular Ca(2+) release is coupled to an increase of ATP within the ER. The Ca(2+)-coupled ER ATP increase is independent of the mode of Ca(2+) mobilization and controlled by the rate of ATP biosynthesis. Furthermore, the energy stress sensor, AMP-activated protein kinase, is essential for the ATP increase that occurs in response to Ca(2+) depletion of the organelle. Our data highlight a novel Ca(2+)-controlled process that supplies the ER with additional energy upon cell stimulation.
Collapse
Affiliation(s)
- Neelanjan Vishnu
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Muhammad Jadoon Khan
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Felix Karsten
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Lukas N. Groschner
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Markus Waldeck-Weiermair
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Rene Rost
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Seth Hallström
- Institute of Physiological Chemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Hiromi Imamura
- Precursory Research for Embryonic Science, Japan Science and Technology Agency, Tokyo 102-0075, Japan
| | - Wolfgang F. Graier
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| | - Roland Malli
- Institute of Molecular Biology and Biochemistry, Center of Physiological Medicine, Medical University of Graz, 8010 Graz, Austria
| |
Collapse
|
11
|
Abstract
Pancreatic β-cells are the only cells capable of lowering blood glucose by secreting insulin. The β-cell continuously adjusts its secretory activity to substrate availability in order to keep blood glucose levels within the physiological range--a process called metabolism-secretion coupling. Glucose is readily taken up by the β-cell and broken down into intermediates that fuel oxidative metabolism inside the mitochondria to generate ATP. The resulting increase in the ATP/ADP ratio causes closure of plasma membrane KATP channels, thereby depolarizing the cell and triggering the opening of voltage-gated Ca²⁺ channels. Consequential oscillations of cytosolic Ca²⁺ not only mediate the exocytosis of insulin granules but are also relayed to other subcellular compartments including the mitochondria, where Ca²⁺ is required to accelerate mitochondrial metabolism in response to nutrient stimulation. The mitochondrial Ca²⁺ uptake machinery plays a fundamental role in this feed-forward mechanism that guarantees sustained insulin secretion and, thus, represents a promising therapeutic target for type 2 diabetes.
Collapse
Affiliation(s)
- Lukas N Groschner
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria
| | - Muhammad Rizwan Alam
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria
| | - Wolfgang F Graier
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Graz, Austria.
| |
Collapse
|
12
|
Pessentheiner AR, Pelzmann HJ, Walenta E, Schweiger M, Groschner LN, Graier WF, Kolb D, Uno K, Miyazaki T, Nitta A, Rieder D, Prokesch A, Bogner-Strauss JG. NAT8L (N-acetyltransferase 8-like) accelerates lipid turnover and increases energy expenditure in brown adipocytes. J Biol Chem 2013; 288:36040-51. [PMID: 24155240 PMCID: PMC3861652 DOI: 10.1074/jbc.m113.491324] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
NAT8L (N-acetyltransferase 8-like) catalyzes the formation of N-acetylaspartate (NAA) from acetyl-CoA and aspartate. In the brain, NAA delivers the acetate moiety for synthesis of acetyl-CoA that is further used for fatty acid generation. However, its function in other tissues remained elusive. Here, we show for the first time that Nat8l is highly expressed in adipose tissues and murine and human adipogenic cell lines and is localized in the mitochondria of brown adipocytes. Stable overexpression of Nat8l in immortalized brown adipogenic cells strongly increases glucose incorporation into neutral lipids, accompanied by increased lipolysis, indicating an accelerated lipid turnover. Additionally, mitochondrial mass and number as well as oxygen consumption are elevated upon Nat8l overexpression. Concordantly, expression levels of brown marker genes, such as Prdm16, Cidea, Pgc1α, Pparα, and particularly UCP1, are markedly elevated in these cells. Treatment with a PPARα antagonist indicates that the increase in UCP1 expression and oxygen consumption is PPARα-dependent. Nat8l knockdown in brown adipocytes has no impact on cellular triglyceride content, lipogenesis, or oxygen consumption, but lipolysis and brown marker gene expression are increased; the latter is also observed in BAT of Nat8l-KO mice. Interestingly, the expression of ATP-citrate lyase is increased in Nat8l-silenced adipocytes and BAT of Nat8l-KO mice, indicating a compensatory mechanism to sustain the acetyl-CoA pool once Nat8l levels are reduced. Taken together, our data show that Nat8l impacts on the brown adipogenic phenotype and suggests the existence of the NAT8L-driven NAA metabolism as a novel pathway to provide cytosolic acetyl-CoA for lipid synthesis in adipocytes.
Collapse
Affiliation(s)
- Ariane R. Pessentheiner
- From the Institute for Genomics and Bioinformatics, Graz University of Technology, Petergasse 14, 8010 Graz, Austria, ,the Institute of Biochemistry, Graz University of Technology, Petergasse 12, 8010 Graz, Austria
| | - Helmut J. Pelzmann
- From the Institute for Genomics and Bioinformatics, Graz University of Technology, Petergasse 14, 8010 Graz, Austria, ,the Institute of Biochemistry, Graz University of Technology, Petergasse 12, 8010 Graz, Austria
| | - Evelyn Walenta
- From the Institute for Genomics and Bioinformatics, Graz University of Technology, Petergasse 14, 8010 Graz, Austria
| | - Martina Schweiger
- the Institute for Molecular Biosciences, University of Graz, Heinrichstrasse 31, 8010 Graz, Austria
| | | | | | - Dagmar Kolb
- Institute of Cell Biology, Histology, and Embryology, Medical University of Graz, Harrachgasse 21, 8010 Graz, Austria, ,the Core Facility Ultrastructure Analysis, Center for Medical Research, Medical University of Graz, Stiftingtalstrasse 24, 8010 Graz, Austria
| | - Kyosuke Uno
- the Department of Pharmaceutical Therapy and Neuropharmacology, Faculty of Pharmaceutical Sciences, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan, and
| | - Toh Miyazaki
- the Department of Pharmaceutical Therapy and Neuropharmacology, Faculty of Pharmaceutical Sciences, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan, and
| | - Atsumi Nitta
- the Department of Pharmaceutical Therapy and Neuropharmacology, Faculty of Pharmaceutical Sciences, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan, and
| | - Dietmar Rieder
- the Division of Bioinformatics, Biocenter, Innsbruck Medical University, Innrain 80, 6020 Innsbruck, Austria
| | - Andreas Prokesch
- From the Institute for Genomics and Bioinformatics, Graz University of Technology, Petergasse 14, 8010 Graz, Austria, ,the Institute of Biochemistry, Graz University of Technology, Petergasse 12, 8010 Graz, Austria
| | - Juliane G. Bogner-Strauss
- From the Institute for Genomics and Bioinformatics, Graz University of Technology, Petergasse 14, 8010 Graz, Austria, ,the Institute of Biochemistry, Graz University of Technology, Petergasse 12, 8010 Graz, Austria, , To whom correspondence should be addressed: Petersgasse 14/5, 8010 Graz, Austria. Tel.: 43-316-873-5337; E-mail:
| |
Collapse
|
13
|
Zhang Q, Ramracheya R, Lahmann C, Tarasov A, Bengtsson M, Braha O, Braun M, Brereton M, Collins S, Galvanovskis J, Gonzalez A, Groschner LN, Rorsman NJG, Salehi A, Travers ME, Walker JN, Gloyn AL, Gribble F, Johnson PRV, Reimann F, Ashcroft FM, Rorsman P. Role of KATP channels in glucose-regulated glucagon secretion and impaired counterregulation in type 2 diabetes. Cell Metab 2013; 18:871-82. [PMID: 24315372 PMCID: PMC3851686 DOI: 10.1016/j.cmet.2013.10.014] [Citation(s) in RCA: 166] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 07/05/2013] [Accepted: 10/31/2013] [Indexed: 01/03/2023]
Abstract
Glucagon, secreted by pancreatic islet α cells, is the principal hyperglycemic hormone. In diabetes, glucagon secretion is not suppressed at high glucose, exacerbating the consequences of insufficient insulin secretion, and is inadequate at low glucose, potentially leading to fatal hypoglycemia. The causal mechanisms remain unknown. Here we show that α cell KATP-channel activity is very low under hypoglycemic conditions and that hyperglycemia, via elevated intracellular ATP/ADP, leads to complete inhibition. This produces membrane depolarization and voltage-dependent inactivation of the Na(+) channels involved in action potential firing that, via reduced action potential height and Ca(2+) entry, suppresses glucagon secretion. Maneuvers that increase KATP channel activity, such as metabolic inhibition, mimic the glucagon secretory defects associated with diabetes. Low concentrations of the KATP channel blocker tolbutamide partially restore glucose-regulated glucagon secretion in islets from type 2 diabetic organ donors. These data suggest that impaired metabolic control of the KATP channels underlies the defective glucose regulation of glucagon secretion in type 2 diabetes.
Collapse
Affiliation(s)
- Quan Zhang
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Forbes JM, Ke BX, Nguyen TV, Henstridge DC, Penfold SA, Laskowski A, Sourris KC, Groschner LN, Cooper ME, Thorburn DR, Coughlan MT. Deficiency in mitochondrial complex I activity due to Ndufs6 gene trap insertion induces renal disease. Antioxid Redox Signal 2013; 19:331-43. [PMID: 23320803 DOI: 10.1089/ars.2012.4719] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
AIMS Defects in the activity of enzyme complexes of the mitochondrial respiratory chain are thought to be responsible for several disorders, including renal impairment. Gene mutations that result in complex I deficiency are the most common oxidative phosphorylation disorders in humans. To determine whether an abnormality in mitochondrial complex I per se is associated with development of renal disease, mice with a knockdown of the complex I gene, Ndufs6 were studied. RESULTS Ndufs6 mice had a partial renal cortical complex I deficiency; Ndufs6gt/gt, 32% activity and Ndufs6gt/+, 83% activity compared with wild-type mice. Both Ndufs6gt/+ and Ndufs6gt/gt mice exhibited hallmarks of renal disease, including albuminuria, urinary excretion of kidney injury molecule-1 (Kim-1), renal fibrosis, and changes in glomerular volume, with decreased capacity to generate mitochondrial ATP and superoxide from substrates oxidized via complex I. However, more advanced renal defects in Ndufs6gt/gt mice were observed in the context of a disruption in the inner mitochondrial electrochemical potential, 3-nitrotyrosine-modified mitochondrial proteins, increased urinary excretion of 15-isoprostane F2t, and up-regulation of antioxidant defence. Juvenile Ndufs6gt/gt mice also exhibited signs of early renal impairment with increased urinary Kim-1 excretion and elevated circulating cystatin C. INNOVATION We have identified renal impairment in a mouse model of partial complex I deficiency, suggesting that even modest deficits in mitochondrial respiratory chain function may act as risk factors for chronic kidney disease. CONCLUSION These studies identify for the first time that complex I deficiency as the result of interruption of Ndufs6 is an independent cause of renal impairment.
Collapse
Affiliation(s)
- Josephine M Forbes
- Glycation, Nutrition and Metabolism Laboratory, Baker IDI Heart & Diabetes Institute, Melbourne, Australia
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Waldeck-Weiermair M, Deak AT, Groschner LN, Alam MR, Jean-Quartier C, Malli R, Graier WF. Molecularly distinct routes of mitochondrial Ca2+ uptake are activated depending on the activity of the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA). J Biol Chem 2013; 288:15367-79. [PMID: 23592775 PMCID: PMC3663555 DOI: 10.1074/jbc.m113.462259] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The transfer of Ca2+ across the inner mitochondrial membrane is an important physiological process linked to the regulation of metabolism, signal transduction, and cell death. While the definite molecular composition of mitochondrial Ca2+ uptake sites remains unknown, several proteins of the inner mitochondrial membrane, that are likely to accomplish mitochondrial Ca2+ fluxes, have been described: the novel uncoupling proteins 2 and 3, the leucine zipper-EF-hand containing transmembrane protein 1 and the mitochondrial calcium uniporter. It is unclear whether these proteins contribute to one unique mitochondrial Ca2+ uptake pathway or establish distinct routes for mitochondrial Ca2+ sequestration. In this study, we show that a modulation of Ca2+ release from the endoplasmic reticulum by inhibition of the sarco/endoplasmatic reticulum ATPase modifies cytosolic Ca2+ signals and consequently switches mitochondrial Ca2+ uptake from an uncoupling protein 3- and mitochondrial calcium uniporter-dependent, but leucine zipper-EF-hand containing transmembrane protein 1-independent to a leucine zipper-EF-hand containing transmembrane protein 1- and mitochondrial calcium uniporter-mediated, but uncoupling protein 3-independent pathway. Thus, the activity of sarco/endoplasmatic reticulum ATPase is significant for the mode of mitochondrial Ca2+ sequestration and determines which mitochondrial proteins might actually accomplish the transfer of Ca2+ across the inner mitochondrial membrane. Moreover, our findings herein support the existence of distinct mitochondrial Ca2+ uptake routes that might be essential to ensure an efficient ion transfer into mitochondria despite heterogeneous cytosolic Ca2+ rises.
Collapse
Affiliation(s)
- Markus Waldeck-Weiermair
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010 Graz, Austria
| | | | | | | | | | | | | |
Collapse
|
16
|
Deak AT, Groschner LN, Alam MR, Seles E, Bondarenko AI, Graier WF, Malli R. The endocannabinoid N-arachidonoyl glycine (NAGly) inhibits store-operated Ca2+ entry by preventing STIM1-Orai1 interaction. J Cell Sci 2012; 126:879-88. [PMID: 23239024 DOI: 10.1242/jcs.118075] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The endocannabiniod anandamide (AEA) and its derivate N-arachidonoyl glycine (NAGly) have a broad spectrum of physiological effects, which are induced by both binding to receptors and receptor-independent modulations of ion channels and transporters. The impact of AEA and NAGly on store-operated Ca(2+) entry (SOCE), a ubiquitous Ca(2+) entry pathway regulating many cellular functions, is unknown. Here we show that NAGly, but not AEA reversibly hinders SOCE in a time- and concentration-dependent manner. The inhibitory effect of NAGly on SOCE was found in the human endothelial cell line EA.hy926, the rat pancreatic β-cell line INS-1 832/13, and the rat basophilic leukemia cell line RBL-2H3. NAGly diminished SOCE independently from the mode of Ca(2+) depletion of the endoplasmic reticulum, whereas it had no effect on Ca(2+) entry through L-type voltage-gated Ca(2+) channels. Enhanced Ca(2+) entry was effectively hampered by NAGly in cells overexpressing the key molecular constituents of SOCE, stromal interacting molecule 1 (STIM1) and the pore-forming subunit of SOCE channels, Orai1. Fluorescence microscopy revealed that NAGly did not affect STIM1 oligomerization, STIM1 clustering, or the colocalization of STIM1 with Orai1, which were induced by Ca(2+) depletion of the endoplasmic reticulum. In contrast, independently from its slow depolarizing effect on mitochondria, NAGly instantly and strongly diminished the interaction of STIM1 with Orai1, indicating that NAGly inhibits SOCE primarily by uncoupling STIM1 from Orai1. In summary, our findings revealed the STIM1-Orai1-mediated SOCE machinery as a molecular target of NAGly, which might have many implications in cell physiology.
Collapse
Affiliation(s)
- Andras T Deak
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, Graz, Austria
| | | | | | | | | | | | | |
Collapse
|
17
|
Alam MR, Groschner LN, Parichatikanond W, Kuo L, Bondarenko AI, Rost R, Waldeck-Weiermair M, Malli R, Graier WF. Mitochondrial Ca2+ uptake 1 (MICU1) and mitochondrial Ca2+ uniporter (MCU) contribute to metabolism-secretion coupling in clonal pancreatic β-cells. J Biol Chem 2012. [DOI: 10.1074/jbc.a112.392084] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
|
18
|
Alam MR, Groschner LN, Parichatikanond W, Kuo L, Bondarenko AI, Rost R, Waldeck-Weiermair M, Malli R, Graier WF. Mitochondrial Ca2+ uptake 1 (MICU1) and mitochondrial ca2+ uniporter (MCU) contribute to metabolism-secretion coupling in clonal pancreatic β-cells. J Biol Chem 2012; 287:34445-54. [PMID: 22904319 PMCID: PMC3464549 DOI: 10.1074/jbc.m112.392084] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
In pancreatic β-cells, uptake of Ca2+ into mitochondria facilitates metabolism-secretion coupling by activation of various matrix enzymes, thus facilitating ATP generation by oxidative phosphorylation and, in turn, augmenting insulin release. We employed an siRNA-based approach to evaluate the individual contribution of four proteins that were recently described to be engaged in mitochondrial Ca2+ sequestration in clonal INS-1 832/13 pancreatic β-cells: the mitochondrial Ca2+ uptake 1 (MICU1), mitochondrial Ca2+ uniporter (MCU), uncoupling protein 2 (UCP2), and leucine zipper EF-hand-containing transmembrane protein 1 (LETM1). Using a FRET-based genetically encoded Ca2+ sensor targeted to mitochondria, we show that a transient knockdown of MICU1 or MCU diminished mitochondrial Ca2+ uptake upon both intracellular Ca2+ release and Ca2+ entry via L-type channels. In contrast, knockdown of UCP2 and LETM1 exclusively reduced mitochondrial Ca2+ uptake in response to either intracellular Ca2+ release or Ca2+ entry, respectively. Therefore, we further investigated the role of MICU1 and MCU in metabolism-secretion coupling. Diminution of MICU1 or MCU reduced mitochondrial Ca2+ uptake in response to d-glucose, whereas d-glucose-triggered cytosolic Ca2+ oscillations remained unaffected. Moreover, d-glucose-evoked increases in cytosolic ATP and d-glucose-stimulated insulin secretion were diminished in MICU1- or MCU-silenced cells. Our data highlight the crucial role of MICU1 and MCU in mitochondrial Ca2+ uptake in pancreatic β-cells and their involvement in the positive feedback required for sustained insulin secretion.
Collapse
Affiliation(s)
- Muhammad Rizwan Alam
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010 Graz, Austria
| | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Abstract
Lining the inner surface of the circulatory system, the vascular endothelium accomplishes a vast variety of specialized functions. Even slight alterations of these functions are implicated in the development of certain cardiovascular diseases that represent major causes of morbidity and mortality in developed countries. Endothelial mitochondria are essential to the functional integrity of the endothelial cell as they integrate a wide range of cellular processes including Ca²⁺ handling, redox signaling and apoptosis, all of which are closely interrelated. Growing evidence supports the notion that impairment of mitochondrial signaling in the endothelium is an early event and a causative factor in the development of diseases such as atherosclerosis or diabetic complications. In this review, we want to outline the significance of mitochondria in both physiology and pathology of the vascular endothelium.
Collapse
Affiliation(s)
- Lukas N. Groschner
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010 Graz, Austria
| | - Markus Waldeck-Weiermair
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010 Graz, Austria
| | - Roland Malli
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010 Graz, Austria
| | - Wolfgang F. Graier
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010 Graz, Austria
| |
Collapse
|