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Voelz C, Schaack LEM, Kogel V, Beyer C, Seitz J, Trinh S. Reversibility of Endoplasmic Reticulum Stress Markers During Long-Term Glucose Starvation in Astrocytes. J Mol Neurosci 2024; 74:53. [PMID: 38750341 PMCID: PMC11096255 DOI: 10.1007/s12031-024-02223-5] [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: 12/14/2023] [Accepted: 04/10/2024] [Indexed: 05/18/2024]
Abstract
Previous studies have demonstrated a brain volume decrease linked to long-term starvation in patients with anorexia nervosa (AN). Food intake is critically diminished in this disorder, leading to one of the highest mortality rates within the psychiatric disease spectrum. As reported in animal models, astrocytes seem to be the most affected cell type in AN. In a recently established primary cell culture model, an elevated unfolded protein response (UPR) was observed in long-term glucose semi-starved astrocytes. A well-functioning protein machinery is essential for every cell, and prolonged UPR will lead to cell death. As a nucleic acid stress-sensing pathway with the activator located in the endoplasmic reticulum, the regulation of the cGAS-STING pathway (cyclic GMP-AMP synthase/stimulator of interferon genes) was additionally investigated in the starvation context. In the current study, a glucose semi-starvation protocol of 15 days, during which cells were supplied with 2 mM glucose in the medium, was prolonged with an additional 6-day long recovery period. Our findings showed that increased UPR mRNA expression was reversible after re-establishing the standard glucose concentration of 25 mM. Furthermore, we were able to verify the presence of cGAS and STING in astrocytes with a characteristic presence of cGAS in the astrocyte nucleus during starvation. A correlation between STING and the glial fibrillary acidic protein (GFAP) could be established, hinting at a conditional presence of STING with a specific astrocyte phenotype.
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Affiliation(s)
- Clara Voelz
- Institute of Neuroanatomy, RWTH Aachen University, Aachen, Germany.
| | - Lena E M Schaack
- Institute of Neuroanatomy, RWTH Aachen University, Aachen, Germany
| | - Vanessa Kogel
- Institute of Neuroanatomy, RWTH Aachen University, Aachen, Germany
| | - Cordian Beyer
- Institute of Neuroanatomy, RWTH Aachen University, Aachen, Germany
| | - Jochen Seitz
- Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, University of Duisburg-Essen, Essen, Germany
| | - Stefanie Trinh
- Institute of Neuroanatomy, RWTH Aachen University, Aachen, Germany
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β-lapachone-mediated WST1 Reduction as Indicator for the Cytosolic Redox Metabolism of Cultured Primary Astrocytes. Neurochem Res 2023; 48:2148-2160. [PMID: 36811754 PMCID: PMC10182120 DOI: 10.1007/s11064-023-03878-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 01/25/2023] [Accepted: 01/26/2023] [Indexed: 02/24/2023]
Abstract
Electron cycler-mediated extracellular reduction of the water-soluble tetrazolium salt 1 (WST1) is frequently used as tool for the determination of cell viability. We have adapted this method to monitor by determining the extracellular WST1 formazan accumulation the cellular redox metabolism of cultured primary astrocytes via the NAD(P)H-dependent reduction of the electron cycler β-lapachone by cytosolic NAD(P)H:quinone oxidoreductase 1 (NQO1). Cultured astrocytes that had been exposed to β-lapachone in concentrations of up to 3 µM remained viable and showed an almost linear extracellular accumulation of WST1 formazan for the first 60 min, while higher concentrations of β-lapachone caused oxidative stress and impaired cell metabolism. β-lapachone-mediated WST1 reduction was inhibited by the NQO1 inhibitors ES936 and dicoumarol in a concentration-dependent manner, with half-maximal inhibition observed at inhibitor concentrations of about 0.3 µM. β-lapachone-mediated WST1 reduction depended strongly on glucose availability, while mitochondrial substrates such as lactate, pyruvate or ketone bodies allowed only residual β-lapachone-mediated WST1 reduction. Accordingly, the mitochondrial respiratory chain inhibitors antimycin A and rotenone hardly affected astrocytic WST1 reduction. Both NADH and NADPH are known to supply electrons for reactions catalysed by cytosolic NQO1. Around 60% of the glucose-dependent β-lapachone-mediated WST1 reduction was prevented by the presence of the glucose-6-phosphate dehydrogenase inhibitor G6PDi-1, while the glyceraldehyde-3-phosphate dehydrogenase inhibitor iodoacetate had only little inhibitory potential. These data suggest that pentose phosphate pathway-generated NADPH, and not glycolysis-derived NADH, is the preferred electron source for cytosolic NQO1-catalysed reductions in cultured astrocytes.
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Distinct and Dynamic Transcriptome Adaptations of iPSC-Generated Astrocytes after Cytokine Stimulation. Cells 2022; 11:cells11172644. [PMID: 36078052 PMCID: PMC9455058 DOI: 10.3390/cells11172644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Revised: 08/19/2022] [Accepted: 08/22/2022] [Indexed: 11/17/2022] Open
Abstract
Astrocytes (ACs) do not only play a role in normal neurogenesis and brain homeostasis, but also in inflammatory and neurodevelopmental disorders. We studied here the different patterns of inflammatory activation triggered by cytokines in human induced pluripotent stem cell (iPSC)-derived ACs. An optimized differentiation protocol provided non-inflamed ACs. These cells reacted to TNFα with a rapid translocation of NFκB, while AC precursors showed little response. Transcriptome changes were quantified at seven time points (2–72 h) after stimulation with TNFα, IFNγ or TNFα plus IFNγ. TNFα triggered a strong response within 2 h. It peaked from 12–24 h and reverted towards the ground state after 72 h. Activation by IFNγ was also rapid, but the response pattern differed from that of TNFα. For instance, several chemokines up-regulated by TNFα were not affected by IFNγ. Instead, MHC-II-related antigen presentation was drastically enhanced. The combination of the two cytokines led to a stronger and more persistent response. For instance, TRIB3 up-regulation by the combination of TNFα plus IFNγ may have slowed NFκB inactivation. Additionally, highly synergistic regulation was observed for inflammation modifiers, such as CASP4, and for STAT1-controlled genes. The combination of the cytokines also increased oxidative stress markers (e.g., CHAC1), led to phenotypic changes in ACs and triggered markers related to cell death. In summary, these data demonstrate that there is a large bandwidth of pro-inflammatory AC states, and that single markers are not suitable to describe AC activation or their modulation in disease, development and therapy.
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Bastian C, Zerimech S, Nguyen H, Doherty C, Franke C, Faris A, Quinn J, Baltan S. Aging astrocytes metabolically support aging axon function by proficiently regulating astrocyte-neuron lactate shuttle. Exp Neurol 2022; 357:114173. [PMID: 35863500 DOI: 10.1016/j.expneurol.2022.114173] [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: 02/07/2022] [Revised: 06/23/2022] [Accepted: 07/14/2022] [Indexed: 11/19/2022]
Abstract
The astrocyte-neuron lactate shuttle (ANLS) is an essential metabolic support system that uptakes glucose, stores it as glycogen in astrocytes, and provides glycogen-derived lactate for axonal function. Aging intrinsically increases the vulnerability of white matter (WM) to injury. Therefore, we investigated the regulation of this shuttle to understand vascular-glial metabolic coupling to support axonal function during aging in two different WM tracts. Aging astrocytes displayed larger cell bodies and thicker horizontal processes in contrast to thinner vertically oriented processes of young astrocytes. Aging axons recovered less following aglycemia in mouse optic nerves (MONs) compared to young axons, although providing lactate during aglycemia equally supported young and aging axonal function. Incubating MONs in high glucose to upregulate glycogen stores in astrocytes delayed loss of function during aglycemia and improved recovery in both young and aging axons. Providing lactate during recovery from aglycemia unmasked a metabolic switch from glucose to lactate in aging axons. Young and aging corpus callosum consisting of a mixture of myelinated and unmyelinated axons sustained their function fully when lactate was available during aglycemia and surprisingly showed a greater resilience to aglycemia compared to fully myelinated axons of optic nerve. We conclude that lactate is a universal substrate for axons independent of their myelination content and age.
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Affiliation(s)
- Chinthasagar Bastian
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Sarah Zerimech
- Anesthesia and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, United States of America
| | - Hung Nguyen
- Anesthesia and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, United States of America
| | - Christine Doherty
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Caroline Franke
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Anna Faris
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - John Quinn
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Selva Baltan
- Anesthesia and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, United States of America; Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America.
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Kogel V, Trinh S, Gasterich N, Beyer C, Seitz J. Long-Term Glucose Starvation Induces Inflammatory Responses and Phenotype Switch in Primary Cortical Rat Astrocytes. J Mol Neurosci 2021; 71:2368-2382. [PMID: 33580474 PMCID: PMC8585803 DOI: 10.1007/s12031-021-01800-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 01/15/2021] [Indexed: 12/18/2022]
Abstract
Astrocytes are the most abundant cell type in the brain and crucial to ensure the metabolic supply of neurons and their synapse formation. Overnutrition as present in patients suffering from obesity causes astrogliosis in the hypothalamus. Other diseases accompanied by malnutrition appear to have an impact on the brain and astrocyte function. In the eating disorder anorexia nervosa (AN), patients suffer from undernutrition and develop volume reductions of the cerebral cortex, associated with reduced astrocyte proliferation and cell count. Although an effect on astrocytes and their function has already been shown for overnutrition, their role in long-term undernutrition remains unclear. The present study used primary rat cerebral cortex astrocytes to investigate their response to chronic glucose starvation. Cells were grown with a medium containing a reduced glucose concentration (2 mM) for 15 days. Long-term glucose starvation increased the expression of a subset of pro-inflammatory genes and shifted the primary astrocyte population to the pro-inflammatory A1-like phenotype. Moreover, genes encoding for proteins involved in the unfolded protein response were elevated. Our findings demonstrate that astrocytes under chronic glucose starvation respond with an inflammatory reaction. With respect to the multiple functions of astrocytes, an association between elevated inflammatory responses due to chronic starvation and alterations found in the brain of patients suffering from undernutrition seems possible.
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Affiliation(s)
- Vanessa Kogel
- Institute of Neuroanatomy, RWTH Aachen University, 52074, Aachen, Germany.
| | - Stefanie Trinh
- Institute of Neuroanatomy, RWTH Aachen University, 52074, Aachen, Germany
| | - Natalie Gasterich
- Institute of Neuroanatomy, RWTH Aachen University, 52074, Aachen, Germany
| | - Cordian Beyer
- Institute of Neuroanatomy, RWTH Aachen University, 52074, Aachen, Germany
| | - Jochen Seitz
- Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, University Hospital, RWTH Aachen University, 52074, Aachen, Germany
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Ehrke E, Steinmeier J, Stapelfeldt K, Dringen R. The Menadione-Mediated WST1 Reduction by Cultured Astrocytes Depends on NQO1 Activity and Cytosolic Glucose Metabolism. Neurochem Res 2021; 46:88-99. [PMID: 31902045 DOI: 10.1007/s11064-019-02930-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 12/03/2019] [Accepted: 12/05/2019] [Indexed: 01/07/2023]
Abstract
The reduction of water-soluble tetrazolium salts (WSTs) is frequently used to determine the metabolic integrity and the viability of cultured cells. Recently, we have reported that the electron cycler menadione can efficiently connect intracellular oxidation reactions in cultured astrocytes with the extracellular reduction of WST1 and that this menadione cycling reaction involves an enzyme. The enzymatic reaction involved in the menadione-dependent WST1 reduction was found strongly enriched in the cytosolic fraction of cultured astrocytes and is able to efficiently use both NADH and NADPH as electron donors. In addition, the reaction was highly sensitive towards dicoumarol with Kic values in the low nanomolar range, suggesting that the NAD(P)H:quinone oxidoreductase 1 (NQO1) catalyzes the menadione-dependent WST1 reduction in astrocytes. Also, in intact astrocytes, dicoumarol inhibited the menadione-dependent WST1 reduction in a concentration-dependent manner with half-maximal inhibition observed at around 50 nM. Moreover, the menadione-dependent WST1 reduction by viable astrocytes was strongly affected by the availability of glucose. In the absence of glucose only residual WST1 reduction was observed, while a concentration-dependent increase in WST1 reduction was found during a 30 min incubation with maximal WST1 reduction already determined in the presence of 0.5 mM glucose. Mannose could fully replace glucose as substrate for astrocytic WST1 reduction, while other hexoses, lactate and the mitochondrial substrate β-hydroxybutyrate failed to provide electrons for the cell-dependent WST1 reduction. These results demonstrate that the menadione-mediated WST1 reduction involves cytosolic NQO1 activity and that this process is strongly affected by the availability of glucose as metabolic substrate.
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Affiliation(s)
- Eric Ehrke
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
- Center for Environmental Research and Sustainable Technology (UFT), University of Bremen, Bremen, Germany
| | - Johann Steinmeier
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
- Center for Environmental Research and Sustainable Technology (UFT), University of Bremen, Bremen, Germany
| | - Karsten Stapelfeldt
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
- Institute for Biophysics, University of Bremen, Bremen, Germany
| | - Ralf Dringen
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany.
- Center for Environmental Research and Sustainable Technology (UFT), University of Bremen, Bremen, Germany.
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7
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Pedro JR, Moura LIF, Valério-Fernandes Â, Baptista FI, Gaspar JM, Pinheiro BS, Lemos C, Kaufmann FN, Morgado C, Silva-Santos CSD, Tavares I, Ferreira SG, Carvalho E, Ambrósio AF, Cunha RA, Duarte JMN, Köfalvi A. Transient gain of function of cannabinoid CB 1 receptors in the control of frontocortical glucose consumption in a rat model of Type-1 diabetes. Brain Res Bull 2020; 161:106-115. [PMID: 32428627 DOI: 10.1016/j.brainresbull.2020.05.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 04/23/2020] [Accepted: 05/04/2020] [Indexed: 12/31/2022]
Abstract
Here we aimed to unify some previous controversial reports on changes in both cannabinoid CB1 receptor (CB1R) expression and glucose metabolism in the forebrain of rodent models of diabetes. We determined how glucose metabolism and its modulation by CB1R ligands evolve in the frontal cortex of young adult male Wistar rats, in the first 8 weeks of streptozotocin-induced type-1 diabetes (T1D). We report that frontocortical CB1R protein density was biphasically altered in the first month of T1D, which was accompanied with a reduction of resting glucose uptake ex vivo in acute frontocortical slices that was normalized after eight weeks in T1D. This early reduction of glucose uptake in slices was also restored by ex vivo treatment with both the non-selective CB1R agonists, WIN55212-2 (500 nM) and the CB1R-selective agonist, ACEA (3 μM) while it was exacerbated by the CB1R-selective antagonist, O-2050 (500 nM). These results suggest a gain-of-function for the cerebrocortical CB1Rs in the control of glucose uptake in diabetes. Although insulin and IGF-1 receptor protein densities remained unaffected, phosphorylated GSKα and GSKβ levels showed different profiles 2 and 8 weeks after T1D induction in the frontal cortex. Altogether, the biphasic response in frontocortical CB1R density within a month after T1D induction resolves previous controversial reports on forebrain CB1R levels in T1D rodent models. Furthermore, this study also hints that cannabinoids may be useful to alleviate impaired glucoregulation in the diabetic cortex.
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Affiliation(s)
- Joana Reis Pedro
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal
| | - Liane I F Moura
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal
| | - Ângela Valério-Fernandes
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal; Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal
| | - Filipa I Baptista
- Coimbra Institute for Clinical and Biomedical Research, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal
| | - Joana M Gaspar
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal
| | - Bárbara S Pinheiro
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal
| | - Cristina Lemos
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal
| | | | - Carla Morgado
- Department of Biomedicine, Faculty of Medicine, University of Porto, Porto, Portugal
| | - Carla S da Silva-Santos
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal
| | - Isaura Tavares
- Department of Biomedicine, Faculty of Medicine, University of Porto, Porto, Portugal; Instituto de Biologia Molecular e Celular, Universidade do Porto, Portugal; I3S Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Portugal
| | - Samira G Ferreira
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal
| | - Eugénia Carvalho
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal; Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal; The Portuguese Diabetes Association (APDP), Lisbon, Portugal; Arkansas Children's Research Institute, and Department of Geriatrics, University of Arkansas for Medical Sciences, Arkansas 72205, United States
| | - António F Ambrósio
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal; Coimbra Institute for Clinical and Biomedical Research, Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; Association for Innovation and Biomedical Research on Light and Image (AIBILI), 3000-548 Coimbra, Portugal
| | - Rodrigo A Cunha
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal; Faculty of Medicine, University of Coimbra, 3004-504 Coimbra, Portugal
| | - João M N Duarte
- Department of Experimental Medical Science, Faculty of Medicine, Lund University, Lund, Sweden; Wallenberg Centre for Molecular Medicine, Lund University, Lund, Sweden
| | - Attila Köfalvi
- CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal; Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal.
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Coggan JS, Keller D, Calì C, Lehväslaiho H, Markram H, Schürmann F, Magistretti PJ. Norepinephrine stimulates glycogenolysis in astrocytes to fuel neurons with lactate. PLoS Comput Biol 2018; 14:e1006392. [PMID: 30161133 PMCID: PMC6160207 DOI: 10.1371/journal.pcbi.1006392] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 09/27/2018] [Accepted: 07/24/2018] [Indexed: 12/20/2022] Open
Abstract
The mechanism of rapid energy supply to the brain, especially to accommodate the heightened metabolic activity of excited states, is not well-understood. We explored the role of glycogen as a fuel source for neuromodulation using the noradrenergic stimulation of glia in a computational model of the neural-glial-vasculature ensemble (NGV). The detection of norepinephrine (NE) by the astrocyte and the coupled cAMP signal are rapid and largely insensitive to the distance of the locus coeruleus projection release sites from the glia, implying a diminished impact for volume transmission in high affinity receptor transduction systems. Glucosyl-conjugated units liberated from glial glycogen by NE-elicited cAMP second messenger transduction winds sequentially through the glycolytic cascade, generating robust increases in NADH and ATP before pyruvate is finally transformed into lactate. This astrocytic lactate is rapidly exported by monocarboxylate transporters to the associated neuron, demonstrating that the astrocyte-to-neuron lactate shuttle activated by glycogenolysis is a likely fuel source for neuromodulation and enhanced neural activity. Altogether, the energy supply for both astrocytes and neurons can be supplied rapidly by glycogenolysis upon neuromodulatory stimulus. Although efficient compared to computers, the human brain utilizes energy at 10-fold the rate of other organs by mass. How the brain is supplied with sufficient on-demand energy to support its activity in the absence of neuronal storage capacity remains unknown. Neurons are not capable of meeting their own energy requirements, instead energy supply in the brain is managed by an oligocellular cartel composed of neurons, glia and the local vasculature (NGV), wherein glia can provide the ergogenic metabolite lactate to the neuron in a process called the astrocyte-to-neuron shuttle (ANLS). The only means of energy storage in the brain is glycogen, a polymerized form of glucose that is localized largely to astrocytes, but its exact role and conditions of use are not clear. In this computational model we show that neuromodulatory stimulation by norepinephrine induces astrocytes to recover glucosyl subunits from glycogen for use in a glycolytic process that favors the production of lactate. The ATP and NADH produced support metabolism in the astrocyte while the lactate is exported to feed the neuron. Thus, rapid energy demands by both neurons and glia in a stimulated brain can be met by glycogen mobilization.
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Affiliation(s)
- Jay S. Coggan
- Blue Brain Project, École Polytechnique Fédérale de Lausanne (EPFL), Geneva, Switzerland
- * E-mail: (JSC); (PJM)
| | - Daniel Keller
- Blue Brain Project, École Polytechnique Fédérale de Lausanne (EPFL), Geneva, Switzerland
| | - Corrado Calì
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia
| | - Heikki Lehväslaiho
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia
| | - Henry Markram
- Blue Brain Project, École Polytechnique Fédérale de Lausanne (EPFL), Geneva, Switzerland
| | - Felix Schürmann
- Blue Brain Project, École Polytechnique Fédérale de Lausanne (EPFL), Geneva, Switzerland
| | - Pierre J. Magistretti
- Blue Brain Project, École Polytechnique Fédérale de Lausanne (EPFL), Geneva, Switzerland
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia
- * E-mail: (JSC); (PJM)
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Gentry MS, Guinovart JJ, Minassian BA, Roach PJ, Serratosa JM. Lafora disease offers a unique window into neuronal glycogen metabolism. J Biol Chem 2018; 293:7117-7125. [PMID: 29483193 DOI: 10.1074/jbc.r117.803064] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Lafora disease (LD) is a fatal, autosomal recessive, glycogen-storage disorder that manifests as severe epilepsy. LD results from mutations in the gene encoding either the glycogen phosphatase laforin or the E3 ubiquitin ligase malin. Individuals with LD develop cytoplasmic, aberrant glycogen inclusions in nearly all tissues that more closely resemble plant starch than human glycogen. This Minireview discusses the unique window into glycogen metabolism that LD research offers. It also highlights recent discoveries, including that glycogen contains covalently bound phosphate and that neurons synthesize glycogen and express both glycogen synthase and glycogen phosphorylase.
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Affiliation(s)
- Matthew S Gentry
- Lafora Epilepsy Cure Initiative, Lexington, Kentucky 40503; Department of Biochemistry and Molecular Biology, Lexington, Kentucky 40503; University of Kentucky Epilepsy Research Center (EpiC), University of Kentucky, Lexington, Kentucky 40503.
| | - Joan J Guinovart
- Lafora Epilepsy Cure Initiative, Lexington, Kentucky 40503; Institute for Research in Biomedicine (IRB Barcelona), Barcelona Institute of Science and Technology, 08028 Barcelona, Spain; Biomedical Research Networking Center in Diabetes and Associated Metabolic Disorders (CIBERDEM), 28029 Madrid, Spain; Department of Biochemistry and Molecular Biomedicine, University of Barcelona, 08028 Barcelona, Spain
| | - Berge A Minassian
- Lafora Epilepsy Cure Initiative, Lexington, Kentucky 40503; Department of Pediatrics and Dallas Children's Medical Center, University of Texas Southwestern, Dallas, Texas 75390-9063; Department of Pediatrics, The Hospital for Sick Children Research Institute, University of Toronto, Toronto, Ontario M5G 0A4, Canada
| | - Peter J Roach
- Lafora Epilepsy Cure Initiative, Lexington, Kentucky 40503; Department of Biochemistry and Molecular Biology, Center for Diabetes and Metabolic Diseases and Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana 46202
| | - Jose M Serratosa
- Lafora Epilepsy Cure Initiative, Lexington, Kentucky 40503; Laboratory of Neurology, IIS-Jimenez Diaz Foundation, UAM, 28045 Madrid, Spain; Biomedical Research Networking Center on Rare Diseases (CIBERER), 28029 Madrid, Spain
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10
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Metabolism of Mannose in Cultured Primary Rat Neurons. Neurochem Res 2017; 42:2282-2293. [DOI: 10.1007/s11064-017-2241-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 03/16/2017] [Accepted: 03/17/2017] [Indexed: 10/19/2022]
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11
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The Protein Tyrosine Kinase Inhibitor Tyrphostin 23 Strongly Accelerates Glycolytic Lactate Production in Cultured Primary Astrocytes. Neurochem Res 2016; 41:2607-2618. [PMID: 27278759 DOI: 10.1007/s11064-016-1972-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 05/29/2016] [Accepted: 06/01/2016] [Indexed: 02/07/2023]
Abstract
Tyrphostin 23 (T23) is a well-known inhibitor of protein tyrosine kinases. To investigate potential acute effects of T23 on the viability and the glucose metabolism of brain cells, we exposed cultured primary rat astrocytes to T23 for up to 4 h. While the viability and the morphology of the cultured astrocytes were not acutely affected by the presence of T23 in concentrations of up to 300 µM, this compound caused a rapid, time- and concentration-dependent increase in glucose consumption and lactate release. Maximal effects on glycolytic flux were found for incubations with 100 µM T23 for 2 h which doubled both glucose consumption and lactate production. The stimulation of glycolytic flux by T23 was reversible, completely abolished upon removal of the compound and not found in presence of other known inhibitors of endocytosis. Structurally related compounds such as tyrphostin 25 and catechol or modulators of AMP kinase activity did neither affect the basal nor the T23-stimulated lactate production by astrocytes. In contrast, the presence of the phosphatase inhibitor vanadate completely abolished the stimulation by T23 of astrocytic lactate production in a concentration-dependent manner. These data suggest that T23-sensitive phosphorylation/dephosphorylation events are involved in the regulation of astrocytic glycolysis.
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Westhaus A, Blumrich EM, Dringen R. The Antidiabetic Drug Metformin Stimulates Glycolytic Lactate Production in Cultured Primary Rat Astrocytes. Neurochem Res 2015; 42:294-305. [PMID: 26433380 DOI: 10.1007/s11064-015-1733-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 09/25/2015] [Accepted: 09/26/2015] [Indexed: 12/11/2022]
Abstract
Metformin is the most frequently used drug for the treatment of type 2 diabetes in humans. However, only little is known about effects of metformin on brain metabolism. To investigate potential metabolic consequences of an exposure of brain cells to metformin, we incubated rat astrocyte-rich primary cultures with this compound. Metformin in concentrations of up to 30 mM did not acutely compromise the viability of astrocytes, but caused a time- and concentration-dependent increase in cellular glucose consumption and lactate production. For acute incubations in the hour range, the presence of 10 mM metformin doubled the glycolytic flux, while already 1 mM metformin doubled glycolytic flux during incubation for 24 h. In addition to metformin, also other guanidino compounds increased astrocytic lactate production. After 4 h of incubation, half-maximal stimulation of glycolysis was observed for metformin, guanidine and phenformin at concentrations of around 3 mM, 3 mM and 30 µM, respectively. The acute stimulation of glycolytic lactate production by metformin was persistent after removal of extracellular metformin and was also observed, if glucose was absent from the incubation medium or replaced by other hexoses. The metformin-induced stimulation of glycolytic flux was not prevented by compound C, an inhibitor of AMP-dependent protein kinase, nor was it additive to the stimulation of glycolytic flux caused by respiratory chain inhibitors. These data demonstrate that the antidiabetic drug metformin has the potential to strongly activate glycolytic lactate production in brain astrocytes.
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Affiliation(s)
- Adrian Westhaus
- Centre for Biomolecular Interactions Bremen, University of Bremen, PO. Box 330440, 28334, Bremen, Germany
| | - Eva Maria Blumrich
- Centre for Biomolecular Interactions Bremen, University of Bremen, PO. Box 330440, 28334, Bremen, Germany.,Centre for Environmental Research and Sustainable Technology, Leobener Strasse, 28359, Bremen, Germany
| | - Ralf Dringen
- Centre for Biomolecular Interactions Bremen, University of Bremen, PO. Box 330440, 28334, Bremen, Germany. .,Centre for Environmental Research and Sustainable Technology, Leobener Strasse, 28359, Bremen, Germany.
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13
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Saez I, Duran J, Sinadinos C, Beltran A, Yanes O, Tevy MF, Martínez-Pons C, Milán M, Guinovart JJ. Neurons have an active glycogen metabolism that contributes to tolerance to hypoxia. J Cereb Blood Flow Metab 2014; 34:945-55. [PMID: 24569689 PMCID: PMC4050236 DOI: 10.1038/jcbfm.2014.33] [Citation(s) in RCA: 142] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Revised: 01/28/2014] [Accepted: 01/29/2014] [Indexed: 01/08/2023]
Abstract
Glycogen is present in the brain, where it has been found mainly in glial cells but not in neurons. Therefore, all physiologic roles of brain glycogen have been attributed exclusively to astrocytic glycogen. Working with primary cultured neurons, as well as with genetically modified mice and flies, here we report that-against general belief-neurons contain a low but measurable amount of glycogen. Moreover, we also show that these cells express the brain isoform of glycogen phosphorylase, allowing glycogen to be fully metabolized. Most importantly, we show an active neuronal glycogen metabolism that protects cultured neurons from hypoxia-induced death and flies from hypoxia-induced stupor. Our findings change the current view of the role of glycogen in the brain and reveal that endogenous neuronal glycogen metabolism participates in the neuronal tolerance to hypoxic stress.
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Affiliation(s)
- Isabel Saez
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona, Spain
- Department of Biochemistry and Molecular Biology, University of Barcelona, Barcelona, Spain
| | - Jordi Duran
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Barcelona, Spain
| | | | - Antoni Beltran
- Metabolomics Platform, CIBERDEM, Reus, Spain
- Center for Omic Sciences (COS), Universitat Rovira i Virgili, Reus, Spain
- Institut d'Investigació Biomédica Pere Virgili (IISPV), Reus, Spain
| | - Oscar Yanes
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Barcelona, Spain
- Metabolomics Platform, CIBERDEM, Reus, Spain
- Center for Omic Sciences (COS), Universitat Rovira i Virgili, Reus, Spain
- Institut d'Investigació Biomédica Pere Virgili (IISPV), Reus, Spain
| | - María F Tevy
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona, Spain
| | | | - Marco Milán
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
| | - Joan J Guinovart
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona, Spain
- Department of Biochemistry and Molecular Biology, University of Barcelona, Barcelona, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Barcelona, Spain
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14
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Stobart JL, Anderson CM. Multifunctional role of astrocytes as gatekeepers of neuronal energy supply. Front Cell Neurosci 2013; 7:38. [PMID: 23596393 PMCID: PMC3622037 DOI: 10.3389/fncel.2013.00038] [Citation(s) in RCA: 171] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Accepted: 03/26/2013] [Indexed: 01/01/2023] Open
Abstract
Dynamic adjustments to neuronal energy supply in response to synaptic activity are critical for neuronal function. Glial cells known as astrocytes have processes that ensheath most central synapses and express G-protein-coupled neurotransmitter receptors and transporters that respond to neuronal activity. Astrocytes also release substrates for neuronal oxidative phosphorylation and have processes that terminate on the surface of brain arterioles and can influence vascular smooth muscle tone and local blood flow. Membrane receptor or transporter-mediated effects of glutamate represent a convergence point of astrocyte influence on neuronal bioenergetics. Astrocytic glutamate uptake drives glycolysis and subsequent shuttling of lactate from astrocytes to neurons for oxidative metabolism. Astrocytes also convert synaptically reclaimed glutamate to glutamine, which is returned to neurons for glutamate salvage or oxidation. Finally, astrocytes store brain energy currency in the form of glycogen, which can be mobilized to produce lactate for neuronal oxidative phosphorylation in response to glutamatergic neurotransmission. These mechanisms couple synaptically driven astrocytic responses to glutamate with release of energy substrates back to neurons to match demand with supply. In addition, astrocytes directly influence the tone of penetrating brain arterioles in response to glutamatergic neurotransmission, coordinating dynamic regulation of local blood flow. We will describe the role of astrocytes in neurometabolic and neurovascular coupling in detail and discuss, in turn, how astrocyte dysfunction may contribute to neuronal bioenergetic deficit and neurodegeneration. Understanding the role of astrocytes as a hub for neurometabolic and neurovascular coupling mechanisms is a critical underpinning for therapeutic development in a broad range of neurodegenerative disorders characterized by chronic generalized brain ischemia and brain microvascular dysfunction.
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Affiliation(s)
- Jillian L Stobart
- Division of Neurodegenerative Disorders, Department of Pharmacology and Therapeutics, St. Boniface Hospital Research, University of Manitoba Winnipeg, MB, Canada ; Department of Nuclear Medicine, Institute of Pharmacology and Toxicology, University of Zürich Zürich, Switzerland
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15
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Kreft M, Lukšič M, Zorec TM, Prebil M, Zorec R. Diffusion of D-glucose measured in the cytosol of a single astrocyte. Cell Mol Life Sci 2013; 70:1483-92. [PMID: 23224430 PMCID: PMC11113596 DOI: 10.1007/s00018-012-1219-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Revised: 11/18/2012] [Accepted: 11/22/2012] [Indexed: 01/26/2023]
Abstract
Astrocytes interact with neurons and endothelial cells and may mediate exchange of metabolites between capillaries and nerve terminals. In the present study, we investigated intracellular glucose diffusion in purified astrocytes after local glucose uptake. We used a fluorescence resonance energy transfer (FRET)-based nano sensor to monitor the time dependence of the intracellular glucose concentration at specific positions within the cell. We observed a delay in onset and kinetics in regions away from the glucose uptake compared with the region where we locally super-fused astrocytes with the D-glucose-rich solution. We propose a mathematical model of glucose diffusion in astrocytes. The analysis showed that after gradual uptake of glucose, the locally increased intracellular glucose concentration is rapidly spread throughout the cytosol with an apparent diffusion coefficient (D app) of (2.38 ± 0.41) × 10(-10) m(2) s(-1) (at 22-24 °C). Considering that the diffusion coefficient of D-glucose in water is D = 6.7 × 10(-10) m(2) s(-1) (at 24 °C), D app determined in astrocytes indicates that the cytosolic tortuosity, which hinders glucose molecules, is approximately three times higher than in aqueous solution. We conclude that the value of D app for glucose measured in purified rat astrocytes is consistent with the view that cytosolic diffusion may allow glucose and glucose metabolites to traverse from the endothelial cells at the blood-brain barrier to neurons and neighboring astrocytes.
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Affiliation(s)
- Marko Kreft
- LN-MCP, Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Zaloška cesta 4, 1000, Ljubljana, Slovenia.
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16
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Pérezleón JA, Osorio-Paz I, Francois L, Salceda R. Immunohistochemical localization of glycogen synthase and GSK3β: control of glycogen content in retina. Neurochem Res 2013; 38:1063-9. [PMID: 23512644 DOI: 10.1007/s11064-013-1017-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 03/04/2013] [Accepted: 03/12/2013] [Indexed: 11/30/2022]
Abstract
Glycogen has an important role in energy handling in several brain regions. In the brain, glycogen is localized in astrocytes and its role in several normal and pathological processes has been described, whereas in the retina, glycogen metabolism has been scarcely investigated. The enzyme glycogen phosphorylase has been located in retinal Müller cells; however the cellular location of glycogen synthase (GS) and its regulatory partner, glycogen synthase kinase 3β (GSK3β), has not been investigated. Our aim was to localize these enzymes in the rat retina by immunofluorescence techniques. We found both GS and GSK3β in Müller cells in the synaptic layers, and within the inner segments of photoreceptor cells. The presence of these enzymes in Müller cells suggests that glycogen could be regulated within the retina as in other tissues. Indeed, we showed that glycogen content in the whole retina in vitro was increased by high glucose concentrations, glutamate, and insulin. In contrast, retina glycogen levels were not modified by norepinephrine nor by depolarization with high KCl concentrations. Insulin also induced an increase in glycogen content in cultured Müller cells. The effect of insulin in both, whole retina and cultured Müller cells was blocked by inhibitors of phosphatidyl-inositol 3-kinase, strongly suggesting that glycogen content in retina is modulated by the insulin signaling pathway. The expression of GS and GSK3β in the synaptic layers and photoreceptor cells suggests an important role of GSK3β regulating glycogen synthase in neurons, which opens multiple feasible roles of insulin within the retina.
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Affiliation(s)
- Jorge Alberto Pérezleón
- Departamento de Ciencias Químico Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, Anillo PRONAF y Estocolmo s/n, Colonia PRONAF, 31330 Ciudad Juárez, Chihuahua, Mexico.
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17
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Choi HB, Gordon GRJ, Zhou N, Tai C, Rungta RL, Martinez J, Milner TA, Ryu JK, McLarnon JG, Tresguerres M, Levin LR, Buck J, MacVicar BA. Metabolic communication between astrocytes and neurons via bicarbonate-responsive soluble adenylyl cyclase. Neuron 2012; 75:1094-104. [PMID: 22998876 DOI: 10.1016/j.neuron.2012.08.032] [Citation(s) in RCA: 201] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/23/2012] [Indexed: 11/17/2022]
Abstract
Astrocytes are proposed to participate in brain energy metabolism by supplying substrates to neurons from their glycogen stores and from glycolysis. However, the molecules involved in metabolic sensing and the molecular pathways responsible for metabolic coupling between different cell types in the brain are not fully understood. Here we show that a recently cloned bicarbonate (HCO₃⁻) sensor, soluble adenylyl cyclase (sAC), is highly expressed in astrocytes and becomes activated in response to HCO₃⁻ entry via the electrogenic NaHCO₃ cotransporter (NBC). Activated sAC increases intracellular cAMP levels, causing glycogen breakdown, enhanced glycolysis, and the release of lactate into the extracellular space, which is subsequently taken up by neurons for use as an energy substrate. This process is recruited over a broad physiological range of [K⁺](ext) and also during aglycemic episodes, helping to maintain synaptic function. These data reveal a molecular pathway in astrocytes that is responsible for brain metabolic coupling to neurons.
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Affiliation(s)
- Hyun B Choi
- Brain Research Centre, Department of Psychiatry, University of British Columbia, Vancouver, BC V6T 2B5, Canada
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18
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Kreft M, Bak LK, Waagepetersen HS, Schousboe A. Aspects of astrocyte energy metabolism, amino acid neurotransmitter homoeostasis and metabolic compartmentation. ASN Neuro 2012; 4:e00086. [PMID: 22435484 PMCID: PMC3338196 DOI: 10.1042/an20120007] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 03/06/2012] [Accepted: 03/21/2012] [Indexed: 02/08/2023] Open
Abstract
Astrocytes are key players in brain function; they are intimately involved in neuronal signalling processes and their metabolism is tightly coupled to that of neurons. In the present review, we will be concerned with a discussion of aspects of astrocyte metabolism, including energy-generating pathways and amino acid homoeostasis. A discussion of the impact that uptake of neurotransmitter glutamate may have on these pathways is included along with a section on metabolic compartmentation.
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Key Words
- amino acid
- astrocyte
- compartmentation
- energy
- metabolism
- α-kg, α-ketoglutarate
- aat, aspartate aminotransferase
- cfp, cyan fluorescence protein
- dab, diaminobenzidine
- fret, fluorescence resonance energy transfer
- [glc]i, intracellular glucose concentration
- gaba, γ-aminobutyric acid
- gaba-t, gaba aminotransferase
- gdh, glutamate dehydrogenase
- glut, glucose transporter
- gp, glycogen phosphorylase
- gs, glutamine synthetase
- gsk3, gs kinase 3
- pag, phosphate-activated glutaminase
- pi3k, phosphoinositide 3-kinase
- pkc, protein kinase c
- tca, tricarboxylic acid
- yfp, yellow fluorescence protein
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Affiliation(s)
- Marko Kreft
- *LNMCP, Institute of Pathophysiology, Faculty of Medicine and CPAE, Department of Biology, Biotechnical Faculty, University of Ljubljana and Celica Biomedical Center, Slovenia
| | - Lasse K Bak
- †Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Helle S Waagepetersen
- †Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Arne Schousboe
- †Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
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19
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β2-adrenergic receptor and astrocyte glucose metabolism. J Mol Neurosci 2012; 48:456-63. [PMID: 22399228 DOI: 10.1007/s12031-012-9742-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2012] [Accepted: 02/27/2012] [Indexed: 12/19/2022]
Abstract
Astrocyte glucose metabolism functions to maintain brain activity in both normal and stress conditions. Dysregulation of astrocyte glucose metabolism relates to development of neuronal disease, such as multiple sclerosis and Alzheimer's disease. In response to acute stress, beta2-adrenergic receptor is activated and initiates multiple signaling events mediated by Gs, Gi, arrestin, or other effectors depending on specific cellular contexts. In astrocytes, beta2-adrenergic receptor promotes glucose uptake through GLUT1 and accelerates glycogen degradation via coupling to Gs and second messenger cAMP-dependent pathway. Beta2-adrenergic receptor may regulate other steps in astrocyte glucose metabolism, such as lactate production or transduction. Inappropriate regulation of beta2-adrenergic receptor activity can disrupt normal glucose metabolism, and leads to accelerate neuronal disease development. It was demonstrated that the absence of beta2-adrenergic receptor in astrocytes occurred in multiple sclerosis patients, and the increased beta2-adrenergic receptor activity relates to Alzheimer's disease. A clear view of beta2-adrenergic receptor-mediated signaling pathways in regulating astrocyte glucose metabolism could help us to develop neuronal diseases treatment by targeting to the beta2-adrenergic receptor.
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20
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Control of glycogen content in retina: allosteric regulation of glycogen synthase. PLoS One 2012; 7:e30822. [PMID: 22363495 PMCID: PMC3281881 DOI: 10.1371/journal.pone.0030822] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Accepted: 12/26/2011] [Indexed: 02/03/2023] Open
Abstract
Retinal tissue is exceptional because it shows a high level of energy metabolism. Glycogen content represents the only energy reserve in retina, but its levels are limited. Therefore, elucidation of the mechanisms controlling glycogen content in retina will allow us to understand retina response under local energy demands that can occur under normal and pathological conditions. Thus, we studied retina glycogen levels under different experimental conditions and correlated them with glucose-6-phosphate (G-6-P) content and glycogen synthase (GS) activity. Glycogen and G-6-P content were studied in ex vivo retinas from normal, fasted, streptozotocin-treated, and insulin-induced hypoglycemic rats. Expression levels of GS and its phosphorylated form were also analyzed. Ex vivo retina from normal rats showed low G-6-P (14±2 pmol/mg protein) and glycogen levels (43±3 nmol glycosyl residues/mg protein), which were increased 6 and 3 times, respectively, in streptozotocin diabetic rats. While no changes in phosphorylated GS levels were observed in any condition tested, a positive correlation was found between G-6-P levels with GS activity and glycogen content. The results indicated that in vivo, retina glycogen may act as an immediately accessible energy reserve and that its content was controlled primarily by G-6-P allosteric activation of GS. Therefore, under hypoglycemic situations retina energy supply is strongly compromised and could lead to the alterations observed in type 1 diabetes.
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Abstract
Astrocytes are glial cells, which play a significant role in a number of processes, including the brain energy metabolism. Their anatomical position between blood vessels and neurons make them an interface for effective glucose uptake from blood. After entering astrocytes, glucose can be involved in different metabolic pathways, e.g. in glycogen production. Glycogen in the brain is localized mainly in astrocytes and is an important energy source in hypoxic conditions and normal brain functioning. The portion of glucose metabolized into glycogen molecules in astrocytes is as high as 40%. It is thought that the release of gliotransmitters (such as glutamate, neuroactive peptides and ATP) into the extracellular space by regulated exocytosis supports a significant part of communication between astrocytes and neurons. On the other hand, neurotransmitter action on astrocytes has a significant role in brain energy metabolism. Therefore, understanding the astrocytes energy metabolism may help understanding neuron-astrocyte interactions.
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Affiliation(s)
- Mateja Prebil
- Laboratory of Neuroendocrinology and Molecular Cell Physiology, Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Slovenia
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22
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Changes in cytosolic glucose level in ATP stimulated live astrocytes. Biochem Biophys Res Commun 2011; 405:308-13. [PMID: 21237134 DOI: 10.1016/j.bbrc.2011.01.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Accepted: 01/07/2011] [Indexed: 11/24/2022]
Abstract
Astrocytes which lie between brain capillaries and neuronal terminals are the primary site of glucose uptake and have a key role in coupling synaptic activity to glucose utilization in the central nervous system (CNS). We used a fluorescence resonance energy transfer (FRET) based approach to monitor cytosolic glucose in astrocytes. We determined the effect of increasing extracellular glucose concentrations on FRET ratio as a measure of increased cytosolic glucose in astrocytes. By briefly raising extracellular glucose concentration, astrocytes responded promptly by increased cytosolic glucose levels, which was manifested by decreased time-dependent FRET ratio. The FRET ratio fall-time recorded at low extracellular D-glucose concentration change (from 0 to 0.5 mM) was 53 s, whereas 17 s was recorded by raising extracellular concentration of D-glucose from 0 to 10 mM, which is likely due to facilitated d-glucose entry along the increased D-glucose gradient across the plasmalemma. The relationship between the extracellular glucose concentration and the FRET ratio change is limited to the maximal ratio change, where the D-glucose plasma membrane permeability is balanced by the cytosolic utilization. We measured the effect of extracellular ATP, an important extracellular messenger for astrocyte-to-astrocyte communication, on intracellular glucose concentration. The results show that stimulation of astrocytes with ATP (1 mM) decreases cytosolic glucose concentration with a time constant of ∼145 s. The mechanism of this change is discussed.
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23
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Seifert TS, Brassard P, Jørgensen TB, Hamada AJ, Rasmussen P, Quistorff B, Secher NH, Nielsen HB. Cerebral non-oxidative carbohydrate consumption in humans driven by adrenaline. J Physiol 2008; 587:285-93. [PMID: 19015195 DOI: 10.1113/jphysiol.2008.162073] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
During brain activation, the decrease in the ratio between cerebral oxygen and carbohydrate uptake (6 O(2)/(glucose + (1)/(2) lactate); the oxygen-carbohydrate index, OCI) is attenuated by the non-selective beta-adrenergic receptor antagonist propranolol, whereas OCI remains unaffected by the beta(1)-adrenergic receptor antagonist metroprolol. These observations suggest involvement of a beta(2)-adrenergic mechanism in non-oxidative metabolism for the brain. Therefore, we evaluated the effect of adrenaline (0.08 microg kg(-1) min(-1) i.v. for 15 min) and noradrenaline (0.5, 0.1 and 0.15 microg kg(-1) min(-1) i.v. for 20 min) on the arterial to internal jugular venous concentration differences (a-v diff) of O(2), glucose and lactate in healthy humans. Adrenaline (n = 10) increased the arterial concentrations of O(2), glucose and lactate (P < 0.05) and also increased the a-v diff for glucose from 0.6 +/- 0.1 to 0.8 +/- 0.2 mM (mean +/- s.d.; P < 0.05). The a-v diff for lactate shifted from a net cerebral release to an uptake and OCI was lowered from 5.1 +/- 1.5 to 3.6 +/- 0.4 (P < 0.05) indicating an 8-fold increase in the rate of non-oxidative carbohydrate uptake during adrenaline infusion (P < 0.01). Conversely, noradrenaline (n = 8) did not affect the OCI despite an increase in the a-v diff for glucose (P < 0.05). These results support that non-oxidative carbohydrate consumption for the brain is driven by a beta(2)-adrenergic mechanism, giving neurons an abundant provision of energy when plasma adrenaline increases.
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Affiliation(s)
- Thomas S Seifert
- Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, Faculty of Health Sciences, University of Copenhagen, Denmark.
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24
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Gailliot MT. Unlocking the Energy Dynamics of Executive Functioning: Linking Executive Functioning to Brain Glycogen. PERSPECTIVES ON PSYCHOLOGICAL SCIENCE 2008; 3:245-63. [DOI: 10.1111/j.1745-6924.2008.00077.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Past work suggests that executive functioning relies on glucose as a depletable energy, such that executive functioning uses a relatively large amount of glucose and is impaired when glucose is low. Glucose from the bloodstream is one energy source for the brain, and glucose stored in the brain as glycogen is another. A review of the literature on glycogen suggests that executive functioning uses it in much the same way as glucose, such that executive functioning uses glycogen and is impaired when glycogen is low. Findings on stress, physical persistence, glucose tolerance, diabetes, sleep, heat, and other topics provide general support for this view.
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25
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Effect of Diabetes on Glycogen Metabolism in Rat Retina. Neurochem Res 2008; 33:1301-8. [DOI: 10.1007/s11064-007-9583-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2007] [Accepted: 12/26/2007] [Indexed: 10/22/2022]
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Abstract
The brain contains glycogen but at low concentration compared with liver and muscle. In the adult brain, glycogen is found predominantly in astrocytes. Astrocyte glycogen content is modulated by a number of factors including some neurotransmitters and ambient glucose concentration. Compelling evidence indicates that astrocyte glycogen breaks down during hypoglycemia to lactate that is transferred to adjacent neurons or axons where it is used aerobically as fuel. In the case of CNS white matter, this source of energy can extend axon function for 20 min or longer. Likewise, during periods of intense neural activity when energy demand exceeds glucose supply, astrocyte glycogen is degraded to lactate, a portion of which is transferred to axons for fuel. Astrocyte glycogen, therefore, offers some protection against hypoglycemic neural injury and ensures that neurons and axons can maintain their function during very intense periods of activation. These emerging principles about the roles of astrocyte glycogen contradict the long held belief that this metabolic pool has little or no functional significance.
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Affiliation(s)
- Angus M Brown
- School of Biomedical Sciences, Queens Medical Centre, University of Nottingham, Nottingham, NG7 2UH, United Kingdom
- Department of Neurology, University of Washington, Seattle, Washington, USA
| | - Bruce R Ransom
- School of Biomedical Sciences, Queens Medical Centre, University of Nottingham, Nottingham, NG7 2UH, United Kingdom
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27
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Verleysdonk S, Kistner S, Pfeiffer-Guglielmi B, Wellard J, Lupescu A, Laske J, Lang F, Rapp M, Hamprecht B. Glycogen metabolism in rat ependymal primary cultures: regulation by serotonin. Brain Res 2005; 1060:89-99. [PMID: 16202983 DOI: 10.1016/j.brainres.2005.08.045] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Revised: 08/18/2005] [Accepted: 08/19/2005] [Indexed: 10/25/2022]
Abstract
Ependymal primary cultures are a model for studying ependymal energy metabolism. Intracellular glycogen is built up in the cultures dependent on culture age and the presence of glucose and glutamate. This energy store is mobilized upon glucose withdrawal, stimulation with isoproterenol, forskolin or serotonin and after uncoupling of oxidative phosphorylation from ATP production. Serotonin regulates ependymal glycogen metabolism predominantly via 5-HT receptor (5-HTR) 7, which elicits an increase in the level of ependymal cyclic AMP. Although the most abundant mRNAs for serotonin receptors are those of 5-HTR 2B and 5-HTR 3A, ependymal cells in primary culture do not respond to serotonin with an increase in their concentration of cytosolic calcium ions. The mRNAs of 5-HTRs 1A, 6, 1B, 5B, 7, 1/2C and 5A are also detectable in order of decreasing abundance. The mRNAs for 5-HTRs 1D, 1F, 3B and 4 are absent from the cultured cells. The ability of serotonin to mobilize ependymal glycogen depends on the culture age and the time allowed for glycogen buildup. During glycogen buildup time, glutamate is consumed by the cells. An increased ability of 5-HT to mobilize ependymal glycogen stores is noticed after the depletion of glutamate from the glycogen buildup medium. In ependymal primary cultures, cilia are colocalized with glycogen phosphorylase isozyme BB, while the MM isoform is not expressed. It is known from the literature that an increase in the concentration of cytosolic cAMP in ependymal cells leads to a decrease in ciliary beat frequency. Therefore, the present data point towards a function for ependymal glycogen other than supplying energy for the movement of cilia.
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Affiliation(s)
- Stephan Verleysdonk
- Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, D-72076 Tübingen, Germany.
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Massengale JL, Gasche Y, Chan PH. Carbohydrate source influences gelatinase production by mouse astrocytes in vitro. Glia 2002; 38:240-5. [PMID: 11968061 DOI: 10.1002/glia.10070] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Molecular mediators of ischemic brain injury include intercellular adhesion molecule-1 (ICAM-1) and matrix metalloproteinase-9 (MMP-9), involved in the alteration of blood-brain barrier permeability and induced in astroglial cultures by tumor necrosis factor-alpha (TNF-alpha). Hyperglycemia is known to aggravate in vivo ischemic brain damage, while treatment with sorbitol shows benefit in reducing vasogenic brain edema. This study investigated whether a culture medium carbohydrate source could alter the astrocyte production of MMP-9 and ICAM-1 in vitro. The growth of astrocytes in 12.5 mM glucose, 25 mM glucose, or 25 mM sorbitol for 14 days did not alter cellular release of lactate dehydrogenase, uptake of Trypan blue, or surface expression of glial fibrillary acidic protein (GFAP). ICAM-1 levels were similar in astrocytes grown in glucose or sorbitol both under basal conditions and after TNF-alpha stimulation for 48 h. In contrast, levels of proMMP-9 released from astrocytes cultured for 14 days in 25 mM sorbitol reached only 55-28% of those obtained from cultures in 25 mM glucose after stimulation with 1,000 U/ml (P = 0.05) or 5,000 U/ml (P < 0.025) TNF-alpha, respectively. Limiting the duration of pre-stimulation sorbitol exposure to 48 h resulted in lower proMMP-9 levels than in glucose cultures after 5,000, but not 1,000, U/ml TNF-alpha, and differences were not significant when sorbitol exposure was further reduced to 24 h. Incubation in mixed glucose/sorbitol media did not affect the release of proMMP-9. These findings suggest that MMP-9 production may be increased in astrocytes as a consequence of glucose metabolism, which can be avoided by growth in sorbitol alone.
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Affiliation(s)
- Justin L Massengale
- Department of Neurosurgery, Program in Neurosciences, Stanford University School of Medicine, California 94305-5487, USA
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Brown AM, Wender R, Ransom BR. Metabolic substrates other than glucose support axon function in central white matter. J Neurosci Res 2001; 66:839-43. [PMID: 11746409 DOI: 10.1002/jnr.10081] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We tested the hypothesis that non-glucose energy sources can support axon function in the rat optic nerve. Axon function was assessed by monitoring the stimulus-evoked compound action potential (CAP). CAP was maintained at full amplitude for 2 hr in 10 mM glucose. 20 mM lactate, 20 mM pyruvate, 10 mM fructose, or 10 mM mannose supported axon function as effectively as did glucose, and 10 mM glutamine provided partial support, but beta-hydroxybutyrate, octanoate, sorbitol, alanine, aspartate, and glutamate failed to support axon function. Our results indicated that a variety of compounds can sustain function in CNS myelinated axons. Axons probably use lactate, pyruvate, and glutamine directly as energy substrates, whereas mannose and fructose could be shuttled through astrocytes to lactate, which is then exported to axons.
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Affiliation(s)
- A M Brown
- Department of Neurology, Box 356465, University of Washington School of Medicine, Seattle, WA 98195, USA.
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Prothmann C, Wellard J, Berger J, Hamprecht B, Verleysdonk S. Primary cultures as a model for studying ependymal functions: glycogen metabolism in ependymal cells. Brain Res 2001; 920:74-83. [PMID: 11716813 DOI: 10.1016/s0006-8993(01)03021-9] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Ependymal cells form a single-layered, ciliated epithelium at the interface between the cerebrospinal fluid and the brain parenchyma. Although their morphology has been studied in detail, ependymal functions remain largely speculative. We have established and characterized a previously described cell culture model to investigate ependymal glycogen metabolism. During growth in minimal medium lacking many non-essential amino acids including L-glutamate, but containing glucose at physiological concentration, the cells contained negligible amounts of glycogen (7+/-3 nmol glucosyl residues/mg protein) despite the presence of insulin. However, during a period of 24 h, the cells accumulated glycogen to very high levels after transferal to a medium containing insulin, glucose at a 5-fold higher concentration, and all proteinogenic amino acids except L-asparagine and L-serine (990+/-112 nmol glucosyl residues/mg protein). Omission of insulin resulted in a 50% reduction in glycogen accumulation. Upon glucose deprivation, glycogen was degraded with a half-life of 21 min. The ependymal primary cultures contained 80+/-5 mU glycogen phosphorylase (Pho)/mg protein and stained positively with antibodies raised against this enzyme. Astroglial cultures built up less glycogen and had less Pho activity under identical conditions. Ependymal glycogen was mobilized by noradrenaline and serotonin. Our results indicate that ependymal cells maintain glycogen as a functional energy store, subject to rapid turnover dependent on the availability of energy substrates and the presence of appropriate signal molecules. Thus ependymocytes appear to be active players in the multitude of processes resulting in normal brain function, and ependymal primary cultures are suggested as a suitable model for studying the role of ependymal cells in these processes.
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Affiliation(s)
- C Prothmann
- Physiologisch-chemisches Institut der Universität, Hoppe-Seyler-Str. 4, D-72076, Tübingen, Germany
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31
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Briski KP, Marshall ES. Induction of ependymal, glial, and neuronal transactivation by intraventricular administration of the SGLT1 Na+-D-glucose cotransporter inhibitor phlorizin. Neurochem Res 2001; 26:783-92. [PMID: 11565609 DOI: 10.1023/a:1011655901032] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Reports that food intake is stimulated by intracerebroventricular (i.c.v.) administration of the SGLT1 Na+-D-glucose cotransport inhibitor, phlorizin, suggest that decreased central glucose uptake is a stimulus for compensatory motor activity underlying restoration of energy imbalance. In order to identify central cell populations that are functionally responsive to decreased SGLT1 function in the brain, the present study utilized immunocytochemical techniques to demonstrate cellular expression of the inducible activator protein-1 transcription factor, Fos, following i.c.v. delivery of phlorizin. Groups of adult male rats were treated with phlorizin at a dose of 10, 50, or 250 microg/animal, then sacrificed 2 hr later by transcardial perfusion. Ependymal expression of Fos-immunoreactivity (-ir) was observed throughout most of the cerebroventricular system, except the medullary fourth ventricle, at each dose examined. Higher doses of the transport inhibitor elicited immunostaining of periventricular glia, characterized by cytoplasmic glial fibrillary acidic protein-ir, underlying the lateral, third, and rostral fourth ventricles and cerebral aqueduct. These doses also resulted in the transcriptional activation of neurons in discrete brain sites, including the rostral medial preoptic area, median preoptic n., preoptic and hypothalamic periventricular n., subfornical organ, thalamic medial habenular and paraventricular n., hypothalamic paraventricular, ventromedial, and arcuate n., and n. of the solitary tract. These results show that nonexcitable cells located throughout much of the central neuroaxis and discrete populations of neurons in the brain are genomically responsive to pharmacological inhibition of central SGLT1 function. Evidence for the functional responsiveness of these cell types to manipulation of energy-dependent glucose transport suggests that cellular uptake of this metabolic fuel may serve as an indicator of central energy substrate availability, and that alterations in glucose uptake via this specific mechanism may be the source of regulatory signals involved in the maintenance of energy homeostasis.
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Affiliation(s)
- K P Briski
- Department of Basic Pharmaceutical Sciences, College of Pharmacy, University of Louisiana at Monroe, 71209-0470, USA.
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32
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Kussmaul L, Hamprecht B, Dringen R. The detoxification of cumene hydroperoxide by the glutathione system of cultured astroglial cells hinges on hexose availability for the regeneration of NADPH. J Neurochem 1999; 73:1246-53. [PMID: 10461918 DOI: 10.1046/j.1471-4159.1999.0731246.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ability of astroglia-rich primary cultures derived from the brains of newborn rats to detoxify exogenously applied cumene hydroperoxide (CHP) was analyzed as a model to study glutathione-mediated peroxide detoxification by astrocytes. Under the conditions used, 200 microM CHP disappeared from the incubation buffer with a half-time of approximately 10 min. The half-time of CHP in the incubation buffer was found strongly elevated (a) in cultures depleted of glutathione by a preincubation with buthionine sulfoximine, an inhibitor of glutathione synthesis, (b) in the presence of mercaptosuccinate, an inhibitor of glutathione peroxidase, and (c) in the absence of glucose, a precursor for the regeneration of NADPH. The involvement of glutathione peroxidase in the clearance of CHP was confirmed by the rapid increase in the level of GSSG after application of CHP. The restoration of the initial high ratio of GSH to GSSG depended on the presence of glucose during the incubation. The high capacity of astroglial cells to clear CHP and to restore the initial ratio of GSH to GSSG was fully maintained when glucose was replaced by mannose. In addition, fructose and galactose at least partially substituted for glucose, whereas exogenous isocitrate and malate were at best marginally able to replace glucose during peroxide detoxification and regeneration of GSH. These results demonstrate that CHP is detoxified rapidly by astroglial cells via the glutathione system. This metabolic process strongly depends on the availability of glucose or mannose as hydride donors for the regeneration of the NADPH that is required for the reduction of GSSG by glutathione reductase.
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Affiliation(s)
- L Kussmaul
- Physiologisch-chemisches Institut der Universität, Tübingen, Germany
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33
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Abstract
Studies using primary cultures of astrocytes have made essential contributions to the understanding of astrocytic functions and neuronal-astrocytic interactions. The purposes of this article are to (i) outline principles and methodologies used in the preparation of such cultures and caveats for the interpretation of the observations made; (ii) summarize astrocytic functions in turnover of the amino acid transmitters glutamate and gamma-aminobutyric acid (GABA), in energy metabolism and in Na+,K+-ATPase-catalyzed processes and emphasize the degree to which the observations have been confirmed in intact tissue; (iii) describe regulations of astrocytic functions by transmitters and by calcium channel activity; and (iv) indicate suggestions for future functional studies using astrocytes in primary cultures and emphasize that some of the conclusions about neuronal-astrocytic interactions reached on the basis of studies in cultured cells and confirmed in intact tissue may not yet have been completely integrated into general neuroscience knowledge.
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Affiliation(s)
- L Hertz
- Department of Pharmacology, University of Saskatchewan, Saskatoon, Canada
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34
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Paspalas CD, Papadopoulos GC. Ultrastructural evidence for combined action of noradrenaline and vasoactive intestinal polypeptide upon neurons, astrocytes, and blood vessels of the rat cerebral cortex. Brain Res Bull 1998; 45:247-59. [PMID: 9510417 DOI: 10.1016/s0361-9230(97)00327-4] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The intracortical organization of the noradrenaline (NA) and vasoactive intestinal polypeptide (VIP) systems provides ample opportunity for functional convergence, and accumulated evidence indicates that NA and VIP share certain cellular actions upon both neuronal and nonneuronal cortical elements. In the present study, a double immunolabeling method was combined with a silver-gold intensification procedure to examine the ultrastructural relationships of the NA coeruleocortical afferents and the intrinsic VIP neurons with three main constituents of the cortex: neurons, astrocytes, and blood vessels. Electron microscopy of singly or doubly labeled material indicated that NA and VIP boutons are engaged in a variety of anatomical relationships with both neuronal and nonneuronal elements. Dendritic shafts and perikarya of nonpyramidal neurons, some of which are VIP positive, receive combined NA and VIP synapses. A significant number of cortical microvessels are in intimate contact with NA or VIP profiles. NA axons often form perivascular loops, and VIP dendritic shafts of large diameter are frequently observed to bend around the vessel circumference. Serial section examination demonstrates that some NA boutons are directly apposed to the capillary wall at sites of glial end-feet discontinuities, whereas VIP boutons contact astrocytic sleeves of capillaries but never cross the perivascular astroglial barrier. Some VIP dendrites containing coated vesicles make intimate contact with the capillary basal lamina. Astrocytic perikarya, mainly in the supragranular layers, are also directly apposed to NA and/or VIP elements. These complex anatomical relationships provide a structural basis for the known interactions between NA and VIP in the control of cortical metabolism and function.
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Affiliation(s)
- C D Paspalas
- Department of Anatomy and Histology, Faculty of Veterinary Medicine, Aristotle University of Thessaloniki, Greece
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Schmoll D, Führmann E, Gebhardt R, Hamprecht B. Significant amounts of glycogen are synthesized from 3-carbon compounds in astroglial primary cultures from mice with participation of the mitochondrial phosphoenolpyruvate carboxykinase isoenzyme. EUROPEAN JOURNAL OF BIOCHEMISTRY 1995; 227:308-15. [PMID: 7851401 DOI: 10.1111/j.1432-1033.1995.tb20390.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The incorporation was studied of the gluconeogenic substrates lactate, alanine, aspartate and glutamate into glycogen of astroglial primary cultures derived from mouse brain. The incorporation was inhibited by 3-mercaptopicolinate, an inhibitor of one of the characteristic gluconeogenic enzymes, phosphoenolpyruvate carboxykinase. Only the mitochondrial isoenzyme of phosphoenolpyruvate carboxykinase was detectable in the astroglial primary cultures. After the incubation of glucose-starved cells with medium containing a mixture of [6-3H]glucose and [U-14C]glucose, the newly synthesized glycogen showed a 3H/14C ratio which was approximately 15% less than the isotope ratio for the medium. The decrease of the isotope ratio was not significantly inhibited by 3-mercaptopicolinate, indicating a cycling of approximately 15% of the glucose to the level of the triose phosphates before its incorporation into astroglial glycogen. During the initial phase of glycogen resynthesis, the contribution of the gluconeogenic substrates appeared to be higher. This was in agreement with the accumulation of fructose 2,6-bisphosphate during refeeding. A participation of gluconeogenic substrates in glycogen metabolism was also detectable when the glycogen content was not changing significantly.
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Affiliation(s)
- D Schmoll
- Physiologisch-chemisches Institut, Universität Tübingen, Germany
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36
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O'Dowd BS, Gibbs ME, Sedman GL, Ng KT. Astrocytes implicated in the energizing of intermediate memory processes in neonate chicks. BRAIN RESEARCH. COGNITIVE BRAIN RESEARCH 1994; 2:93-102. [PMID: 7833696 DOI: 10.1016/0926-6410(94)90006-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Day-old chicks trained in a single trial passive avoidance task develop three sequentially dependent stages of discrimination memory. The second intermediate stage is made up of two phases: the initial A phase being susceptible to inhibition of oxidative metabolism in the tricarboxcylic acid (TCA) system with 2,4-dinitrophenol (DNP), and a second DNP-insensitive B phase. The studies reported in this paper found that doses of the metabolic toxins fluoroacetate (0.2 mM) and fluorocitrate (0.1 mM) previously reported to disrupt the astrocytic TCA cycle only, also disrupt the A (but not the B) phase of intermediate memory, suggesting an interaction between the astrocytic and neuronal oxidative systems may be required to meet the metabolic demands of this earlier phase. The B phase, on the other hand, was not expressed in the presence of the glycolytic inhibitor iodoacetate (1 mM), suggesting that glycolysis (known to be more efficient in astrocytes) and glycogenolysis (which may be exclusive to astrocytes) may support this second phase of intermediate memory. In this regard, the rise in forebrain noradrenaline levels previously reported to occur before the appearance of the B phase is particularly relevant. Given that noradrenaline has been shown to be capable of enhancing glycogenolysis in astrocyte-enriched cell cultures, it is conceivable that noradrenaline exerts an effect on memory by stimulating the glycolytic system in astrocytes, thereby providing energy or metabolites (e.g. pyruvate) needed to sustain the cellular processes operating during the B phase of intermediate memory.
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Affiliation(s)
- B S O'Dowd
- La Trobe University, Bundoora, Vic., Australia
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37
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O'Dowd BS, Gibbs ME, Ng KT, Hertz E, Hertz L. Astrocytic glycogenolysis energizes memory processes in neonate chicks. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1994; 78:137-41. [PMID: 8004768 DOI: 10.1016/0165-3806(94)90018-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In previous pharmaco-behavioural experiments, we have shown that three sequential stages can be distinguished in discrimination memory for a single trial passive avoidance experience in neonate chicks: a short-term (STM) stage, available for 10 min following learning; an intermediate (ITM) stage, operating between 20 and 50 min (ITMB) post-learning; and a long-term (LTM) stage formed by 60 min after learning. The ITM stage can be divided into two parts: a first phase (ITMA) which is susceptible to inhibition by the uncoupler of oxidative phosphorylation (and thus of oxidative metabolism), 2,4-dinitrophenol (DNP), and a second DNP-insensitive phase (ITMB). ITMA occurs between 20 and 30 min post-training and ITMB between 30 and 50 min. In the present study we have shown: (1) that day-old chicks trained in the passive avoidance task and immediately thereafter injected with the glycolytic inhibitor iodoacetate show retention deficits that are first evident 30 min post-training, and (2) that glycogenolysis, i.e. breakdown of glycogen, a high-molecular carbohydrate energy store localized in astrocytes, occurs in the forebrains of trained, but otherwise untreated birds, between 35 and 55 min after learning. These findings strongly suggest that glycolysis, including astrocytically localized glycogenolysis, is essential to provide energy for active processes occurring during ITMB and that these processes are indispensable for subsequent development of long-term memory.
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Affiliation(s)
- B S O'Dowd
- Psychology Department, La Trobe University, Bundoora, Melbourne, Vic., Australia
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38
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Dringen R, Gebhardt R, Hamprecht B. Glycogen in astrocytes: possible function as lactate supply for neighboring cells. Brain Res 1993; 623:208-14. [PMID: 8221102 DOI: 10.1016/0006-8993(93)91429-v] [Citation(s) in RCA: 430] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In order to contribute to the elucidation of the function of astrocyte glycogen in brain, studies on the fate of the glucosyl residues of glycogen were carried out on astroglia-rich primary cultures derived from the brains of newborn rats. On glucose deprivation astroglial cells rapidly deplete their glycogen. In contrast to the situation with hepatocytes, only lactate, but not glucose, is detectable in the medium surrounding the astroglial cells. Besides glucose, astroglial cultures can also use mannose as a substrate for the synthesis of glycogen and the generation of lactate. Although mannose-fed astroglial cells contain glucose-6-phosphate, they do not release a measurable amount of glucose into the culture medium. Instead of glucose the astroglial cells release high amounts of lactate into the culture medium. Gluconolactone or 2-deoxyglucose which prevent glycogen breakdown in astroglial cells after glucose deprivation, allow to discriminate between lactate generated from glycogen and lactate from other sources. The amount of lactate found in the medium in the absence of gluconolactone (or 2-deoxyglucose) exceeds the amount found in the presence of either compound by the lactate equivalents calculated to be contained in the cellular glycogen. In conclusion, glycogen in astrocytes can be considered as a store for lactate rather than for glucose.
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Affiliation(s)
- R Dringen
- Physiologisch-chemisches Institut der Universität, Tübingen Germany
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