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McKenna MC, Sonnewald U, Waageptersen HS, White HS. A tribute to Arne Schousboe's contributions to neurochemistry and his innovative and enduring research in GABA, glutamate, and brain energy metabolism. J Neurochem 2024. [PMID: 39183580 DOI: 10.1111/jnc.16207] [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: 07/19/2024] [Revised: 08/06/2024] [Accepted: 08/06/2024] [Indexed: 08/27/2024]
Abstract
This is a tribute to Arne Schousboe, Professor Emeritus at the University of Copenhagen, an eminent neurochemist and neuroscientist who was a leader in the fields of GABA, glutamate, and brain energy metabolism. Arne was known for his keen intellect, his wide-ranging expertise in neurochemistry and neuropharmacology of GABA and glutamate and brain energy metabolism. Arne was also known for his strong leadership, his warm and engaging personality and his enjoyment of fine wine and great food shared with friends, family, and colleagues. Sadly, Arne passed away on February 27, 2024, after a short illness. He is survived by his wife Inger Schousboe, his two children, and three wonderful grandchildren. His death is a tremendous loss to the neuroscience community. He will be greatly missed by his friends, family, and colleagues. Some of the highlights of Arne's career are described in this tribute.
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Affiliation(s)
- Mary C McKenna
- Department of Pediatrics and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Ursula Sonnewald
- Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
| | | | - H Steve White
- Department of Pharmacy, University of Washington, Seattle, Washington, USA
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2
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Gondáš E, Baranovičová E, Šofranko J, Murín R. Hyperglycemia Stimulates the Irreversible Catabolism of Branched-Chain Amino Acids and Generation of Ketone Bodies by Cultured Human Astrocytes. Biomedicines 2024; 12:1803. [PMID: 39200266 PMCID: PMC11351101 DOI: 10.3390/biomedicines12081803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2024] [Revised: 07/22/2024] [Accepted: 08/06/2024] [Indexed: 09/02/2024] Open
Abstract
Astrocytes are considered to possess a noticeable role in brain metabolism and, as a partners in neuron-glia cooperation, to contribute to the synthesis, bioconversion, and regulation of the flux of substrates for neuronal metabolism. With the aim of investigating to what extent human astrocytes are metabolizing amino acids and by which compounds are they enriching their surroundings, we employed a metabolomics analysis of their culture media by 1H-NMR. In addition, we compared the composition of media with either 5 mM or 25 mM glucose. The quantitative analysis of culture media by 1H-NMR revealed that astrocytes readily dispose from their milieu glutamine, branched-chain amino acids, and pyruvate with significantly high rates, while they enrich the culture media with lactate, branched-chain keto acids, citrate, acetate, ketone bodies, and alanine. Hyperglycemia suppressed the capacity of astrocytes to release branched-chain 2-oxo acids, while stimulating the generation of ketone bodies. Our results highlight the active involvement of astrocytes in the metabolism of several amino acids and the regulation of key metabolic intermediates. The observed metabolic activities of astrocytes provide valuable insights into their roles in supporting neuronal function, brain metabolism, and intercellular metabolic interactions within the brain. Understanding the complex metabolic interactions between astrocytes and neurons is essential for elucidating brain homeostasis and the pathophysiology of neurological disorders. The observed metabolic activities of astrocytes provide hints about their putative metabolic roles in brain metabolism.
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Affiliation(s)
- Eduard Gondáš
- Department of Pharmacology, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Malá Hora 4D, 036 01 Martin, Slovakia;
- Department of Medical Biochemistry, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Malá Hora 4D, 036 01 Martin, Slovakia;
| | - Eva Baranovičová
- Biomedical Center Martin, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Malá Hora 4D, 036 01 Martin, Slovakia;
| | - Jakub Šofranko
- Department of Medical Biochemistry, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Malá Hora 4D, 036 01 Martin, Slovakia;
| | - Radovan Murín
- Department of Medical Biochemistry, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Malá Hora 4D, 036 01 Martin, Slovakia;
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Dienel GA, Schousboe A, McKenna MC, Rothman DL. A tribute to Leif Hertz: The historical context of his pioneering studies of the roles of astrocytes in brain energy metabolism, neurotransmission, cognitive functions, and pharmacology identifies important, unresolved topics for future studies. J Neurochem 2024; 168:461-495. [PMID: 36928655 DOI: 10.1111/jnc.15812] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Revised: 03/10/2023] [Accepted: 03/13/2023] [Indexed: 03/18/2023]
Abstract
Leif Hertz, M.D., D.Sc. (honōris causā) (1930-2018), was one of the original and noteworthy participants in the International Conference on Brain Energy Metabolism (ICBEM) series since its inception in 1993. The biennial ICBEM conferences are organized by neuroscientists interested in energetics and metabolism underlying neural functions; they have had a high impact on conceptual and experimental advances in these fields and on promoting collaborative interactions among neuroscientists. Leif made major contributions to ICBEM discussions and understanding of metabolic and signaling characteristics of astrocytes and their roles in brain function. His studies ranged from uptake of K+ from extracellular fluid and its stimulation of astrocytic respiration, identification, and regulation of enzymes specifically or preferentially expressed in astrocytes in the glutamate-glutamine cycle of excitatory neurotransmission, a requirement for astrocytic glycogenolysis for fueling K+ uptake, involvement of glycogen in memory consolidation in the chick, and pharmacology of astrocytes. This tribute to Leif Hertz highlights his major discoveries, the high impact of his work on astrocyte-neuron interactions, and his unparalleled influence on understanding the cellular basis of brain energy metabolism. His work over six decades has helped integrate the roles of astrocytes into neurotransmission where oxidative and glycogenolytic metabolism during neurotransmitter glutamate turnover are key aspects of astrocytic energetics. Leif recognized that brain astrocytic metabolism is greatly underestimated unless the volume fraction of astrocytes is taken into account. Adjustment for pathway rates expressed per gram tissue for volume fraction indicates that astrocytes have much higher oxidative rates than neurons and astrocytic glycogen concentrations and glycogenolytic rates during sensory stimulation in vivo are similar to those in resting and exercising muscle, respectively. These novel insights are typical of Leif's astute contributions to the energy metabolism field, and his publications have identified unresolved topics that provide the neuroscience community with challenges and opportunities for future research.
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Affiliation(s)
- Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, 72205, USA
- Department of Cell Biology and Physiology, University of New Mexico, Albuquerque, New Mexico, 87131, USA
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Mary C McKenna
- Department of Pediatrics and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland, 21201, USA
| | - Douglas L Rothman
- Department of Radiology, Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, 06520, USA
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Harders AR, Spellerberg P, Dringen R. Exogenous Substrates Prevent the Decline in the Cellular ATP Content of Primary Rat Astrocytes During Glucose Deprivation. Neurochem Res 2024; 49:1188-1199. [PMID: 38341839 PMCID: PMC10991069 DOI: 10.1007/s11064-024-04104-0] [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: 11/29/2023] [Revised: 01/04/2024] [Accepted: 01/05/2024] [Indexed: 02/13/2024]
Abstract
Brain astrocytes are well known for their broad metabolic potential. After glucose deprivation, cultured primary astrocytes maintain a high cellular ATP content for many hours by mobilizing endogenous substrates, but within 24 h the specific cellular ATP content was lowered to around 30% of the initial ATP content. This experimental setting was used to test for the potential of various exogenous substrates to prevent a loss in cellular ATP in glucose deprived astrocytes. The presence of various extracellular monocarboxylates, purine nucleosides or fatty acids prevented the loss of ATP from glucose-deprived astrocytes. Of the 20 proteinogenic amino acids, only alanine, aspartate, glutamate, glutamine, lysine or proline maintained high ATP levels in starved astrocytes. Among these amino acids, proline was found to be the most potent one to prevent the ATP loss. The astrocytic consumption of proline as well as the ability of proline to maintain a high cellular ATP content was prevented in a concentration-dependent manner by the proline dehydrogenase inhibitor tetrahydro-2-furoic acid. Analysis of the concentration-dependencies obtained by considering the different carbon content of the applied substrates revealed that fatty acids and proline are more potent than glucose and monocarboxylates as exogenous substrates to prevent ATP depletion in glucose-deprived astrocytes. These data demonstrate that cultured astrocytes can utilise a wide range of extracellular substrates as fuels to support mitochondrial ATP regeneration and identify proline as potent exogenous substrate for the energy metabolism of starved astrocytes.
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Affiliation(s)
- Antonia Regina Harders
- Centre for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
- Centre for Environmental Research and Sustainable Technologies, University of Bremen, Bremen, Germany
| | - Paul Spellerberg
- Centre for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
| | - Ralf Dringen
- Centre for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany.
- Centre for Environmental Research and Sustainable Technologies, University of Bremen, Bremen, Germany.
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Andersen JV, Schousboe A. Glial Glutamine Homeostasis in Health and Disease. Neurochem Res 2023; 48:1100-1128. [PMID: 36322369 DOI: 10.1007/s11064-022-03771-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 08/25/2022] [Accepted: 09/27/2022] [Indexed: 11/05/2022]
Abstract
Glutamine is an essential cerebral metabolite. Several critical brain processes are directly linked to glutamine, including ammonia homeostasis, energy metabolism and neurotransmitter recycling. Astrocytes synthesize and release large quantities of glutamine, which is taken up by neurons to replenish the glutamate and GABA neurotransmitter pools. Astrocyte glutamine hereby sustains the glutamate/GABA-glutamine cycle, synaptic transmission and general brain function. Cerebral glutamine homeostasis is linked to the metabolic coupling of neurons and astrocytes, and relies on multiple cellular processes, including TCA cycle function, synaptic transmission and neurotransmitter uptake. Dysregulations of processes related to glutamine homeostasis are associated with several neurological diseases and may mediate excitotoxicity and neurodegeneration. In particular, diminished astrocyte glutamine synthesis is a common neuropathological component, depriving neurons of an essential metabolic substrate and precursor for neurotransmitter synthesis, hereby leading to synaptic dysfunction. While astrocyte glutamine synthesis is quantitatively dominant in the brain, oligodendrocyte-derived glutamine may serve important functions in white matter structures. In this review, the crucial roles of glial glutamine homeostasis in the healthy and diseased brain are discussed. First, we provide an overview of cellular recycling, transport, synthesis and metabolism of glutamine in the brain. These cellular aspects are subsequently discussed in relation to pathological glutamine homeostasis of hepatic encephalopathy, epilepsy, Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis. Further studies on the multifaceted roles of cerebral glutamine will not only increase our understanding of the metabolic collaboration between brain cells, but may also aid to reveal much needed therapeutic targets of several neurological pathologies.
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Affiliation(s)
- Jens V Andersen
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
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Yoon JH, Hwang J, Son SU, Choi J, You SW, Park H, Cha SY, Maeng S. How Can Insulin Resistance Cause Alzheimer's Disease? Int J Mol Sci 2023; 24:3506. [PMID: 36834911 PMCID: PMC9966425 DOI: 10.3390/ijms24043506] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 01/17/2023] [Accepted: 01/27/2023] [Indexed: 02/12/2023] Open
Abstract
Alzheimer's disease (AD) is a neurodegenerative disorder associated with cognitive decline. Despite worldwide efforts to find a cure, no proper treatment has been developed yet, and the only effective countermeasure is to prevent the disease progression by early diagnosis. The reason why new drug candidates fail to show therapeutic effects in clinical studies may be due to misunderstanding the cause of AD. Regarding the cause of AD, the most widely known is the amyloid cascade hypothesis, in which the deposition of amyloid beta and hyperphosphorylated tau is the cause. However, many new hypotheses were suggested. Among them, based on preclinical and clinical evidence supporting a connection between AD and diabetes, insulin resistance has been pointed out as an important factor in the development of AD. Therefore, by reviewing the pathophysiological background of brain metabolic insufficiency and insulin insufficiency leading to AD pathology, we will discuss how can insulin resistance cause AD.
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Affiliation(s)
- Ji Hye Yoon
- Age-Tech Service Convergence Major, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
| | - JooHyun Hwang
- Age-Tech Service Convergence Major, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
| | - Sung Un Son
- Department of Comprehensive Health Science, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
| | - Junhyuk Choi
- Age-Tech Service Convergence Major, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
| | - Seung-Won You
- Department of Comprehensive Health Science, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
| | - Hyunwoo Park
- Department of Comprehensive Health Science, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
- Health Park Co., Ltd., Seoul 02447, Republic of Korea
| | - Seung-Yun Cha
- Department of Comprehensive Health Science, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
| | - Sungho Maeng
- Age-Tech Service Convergence Major, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
- Department of Comprehensive Health Science, Graduate School of East–West Medical Science, Kyung Hee University, Yongin-si 17104, Republic of Korea
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Kruyer A, Kalivas PW, Scofield MD. Astrocyte regulation of synaptic signaling in psychiatric disorders. Neuropsychopharmacology 2023; 48:21-36. [PMID: 35577914 PMCID: PMC9700696 DOI: 10.1038/s41386-022-01338-w] [Citation(s) in RCA: 28] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/05/2022] [Revised: 04/27/2022] [Accepted: 05/01/2022] [Indexed: 02/07/2023]
Abstract
Over the last 15 years, the field of neuroscience has evolved toward recognizing the critical role of astroglia in shaping neuronal synaptic activity and along with the pre- and postsynapse is now considered an equal partner in tripartite synaptic transmission and plasticity. The relative youth of this recognition and a corresponding deficit in reagents and technologies for quantifying and manipulating astroglia relative to neurons continues to hamper advances in understanding tripartite synaptic physiology. Nonetheless, substantial advances have been made and are reviewed herein. We review the role of astroglia in synaptic function and regulation of behavior with an eye on how tripartite synapses figure into brain pathologies underlying behavioral impairments in psychiatric disorders, both from the perspective of measures in postmortem human brains and more subtle influences on tripartite synaptic regulation of behavior in animal models of psychiatric symptoms. Our goal is to provide the reader a well-referenced state-of-the-art understanding of current knowledge and predict what we may discover with deeper investigation of tripartite synapses using reagents and technologies not yet available.
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Affiliation(s)
- Anna Kruyer
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC, USA
| | - Peter W Kalivas
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC, USA.
- Ralph H. Johnson Veterans Affairs Medical Center, Charleston, SC, USA.
| | - Michael D Scofield
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC, USA.
- Department of Anesthesia & Perioperative Medicine, Medical University of South Carolina, Charleston, SC, USA.
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Eraso‐Pichot A, Pouvreau S, Olivera‐Pinto A, Gomez‐Sotres P, Skupio U, Marsicano G. Endocannabinoid signaling in astrocytes. Glia 2023; 71:44-59. [PMID: 35822691 PMCID: PMC9796923 DOI: 10.1002/glia.24246] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 06/28/2022] [Accepted: 07/04/2022] [Indexed: 01/07/2023]
Abstract
The study of the astrocytic contribution to brain functions has been growing in popularity in the neuroscience field. In the last years, and especially since the demonstration of the involvement of astrocytes in synaptic functions, the astrocyte field has revealed multiple functions of these cells that seemed inconceivable not long ago. In parallel, cannabinoid investigation has also identified different ways by which cannabinoids are able to interact with these cells, modify their functions, alter their communication with neurons and impact behavior. In this review, we will describe the expression of different endocannabinoid system members in astrocytes. Moreover, we will relate the latest findings regarding cannabinoid modulation of some of the most relevant astroglial functions, namely calcium (Ca2+ ) dynamics, gliotransmission, metabolism, and inflammation.
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Affiliation(s)
- Abel Eraso‐Pichot
- U1215 Neurocentre MagendieInstitut national de la santé et de la recherche médicale (INSERM)BordeauxFrance,University of BordeauxBordeauxFrance
| | - Sandrine Pouvreau
- U1215 Neurocentre MagendieInstitut national de la santé et de la recherche médicale (INSERM)BordeauxFrance,University of BordeauxBordeauxFrance
| | - Alexandre Olivera‐Pinto
- U1215 Neurocentre MagendieInstitut national de la santé et de la recherche médicale (INSERM)BordeauxFrance,University of BordeauxBordeauxFrance
| | - Paula Gomez‐Sotres
- U1215 Neurocentre MagendieInstitut national de la santé et de la recherche médicale (INSERM)BordeauxFrance,University of BordeauxBordeauxFrance
| | - Urszula Skupio
- U1215 Neurocentre MagendieInstitut national de la santé et de la recherche médicale (INSERM)BordeauxFrance,University of BordeauxBordeauxFrance
| | - Giovanni Marsicano
- U1215 Neurocentre MagendieInstitut national de la santé et de la recherche médicale (INSERM)BordeauxFrance,University of BordeauxBordeauxFrance
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Tefera TW, Steyn FJ, Ngo ST, Borges K. CNS glucose metabolism in Amyotrophic Lateral Sclerosis: a therapeutic target? Cell Biosci 2021; 11:14. [PMID: 33431046 PMCID: PMC7798275 DOI: 10.1186/s13578-020-00511-2] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Accepted: 12/04/2020] [Indexed: 12/11/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disorder primarily characterized by selective degeneration of both the upper motor neurons in the brain and lower motor neurons in the brain stem and the spinal cord. The exact mechanism for the selective death of neurons is unknown. A growing body of evidence demonstrates abnormalities in energy metabolism at the cellular and whole-body level in animal models and in people living with ALS. Many patients with ALS exhibit metabolic changes such as hypermetabolism and body weight loss. Despite these whole-body metabolic changes being observed in patients with ALS, the origin of metabolic dysregulation remains to be fully elucidated. A number of pre-clinical studies indicate that underlying bioenergetic impairments at the cellular level may contribute to metabolic dysfunctions in ALS. In particular, defects in CNS glucose transport and metabolism appear to lead to reduced mitochondrial energy generation and increased oxidative stress, which seem to contribute to disease progression in ALS. Here, we review the current knowledge and understanding regarding dysfunctions in CNS glucose metabolism in ALS focusing on metabolic impairments in glucose transport, glycolysis, pentose phosphate pathway, TCA cycle and oxidative phosphorylation. We also summarize disturbances found in glycogen metabolism and neuroglial metabolic interactions. Finally, we discuss options for future investigations into how metabolic impairments can be modified to slow disease progression in ALS. These investigations are imperative for understanding the underlying causes of metabolic dysfunction and subsequent neurodegeneration, and to also reveal new therapeutic strategies in ALS.
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Affiliation(s)
- Tesfaye Wolde Tefera
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, 4072, Australia.
| | - Frederik J Steyn
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia.,Center for Clinical Research, The University of Queensland, Brisbane, Australia
| | - Shyuan T Ngo
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, 4072, Australia.,Center for Clinical Research, The University of Queensland, Brisbane, Australia
| | - Karin Borges
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia
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Schousboe A. Astrocytic Metabolism Focusing on Glutamate Homeostasis: A Short Review Dedicated to Vittorio Gallo. Neurochem Res 2019; 45:522-525. [PMID: 31617053 DOI: 10.1007/s11064-019-02888-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 10/04/2019] [Accepted: 10/09/2019] [Indexed: 01/25/2023]
Abstract
A large number of studies have during the last several decades shown that astrocytes play a significant role in brain energy metabolism accounting for a considerable part of the oxygen uptake and the corresponding oxidative metabolism of glucose and lactate. Interestingly, it has become clear that in addition to these two major energy substrates, glutamate may be considered as an important alternative energy substrate and this is tightly coupled to its role as an excitatory neurotransmitter. Hence, this short review will link these events and provide an account of the role that Vittorio Gallo came to play as he coauthored a publication which demonstrated the usefulness of cultured cerebellar granule cells for studies of glutamate neurotransmission. Just by chance this study was published the same year that my own group published a similar study of glutamate uptake and release in a corresponding preparation of cultured neurons and astrocytes from cerebellum and cerebral cortex. Thus, it is a pleasure to dedicate this account of the role of astrocytes in glutamate neurotransmission to Vittorio Gallo whom I have had the pleasure of knowing for more than three decades.
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Affiliation(s)
- Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen Ø, Denmark.
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11
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Weckmann K, Deery MJ, Howard JA, Feret R, Asara JM, Dethloff F, Filiou MD, Labermaier C, Maccarrone G, Lilley KS, Mueller M, Turck CW. Ketamine's Effects on the Glutamatergic and GABAergic Systems: A Proteomics and Metabolomics Study in Mice. MOLECULAR NEUROPSYCHIATRY 2018; 5:42-51. [PMID: 31019917 DOI: 10.1159/000493425] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Accepted: 08/31/2018] [Indexed: 12/15/2022]
Abstract
Ketamine, a noncompetitive, voltage-dependent N-Methyl-D-aspartate receptor (NMDAR) antagonist, has been shown to have a rapid antidepressant effect and is used for patients experiencing treatment-resistant depression. We carried out a time-dependent targeted mass spectrometry-based metabolomics profiling analysis combined with a quantitative based on in vivo 15N metabolic labeling proteome comparison of ketamine- and vehicle-treated mice. The metabolomics and proteomics datasets were used to further elucidate ketamine's mode of action on the gamma-aminobutyric acid (GABA)ergic and glutamatergic systems. In addition, myelin basic protein levels were analyzed by Western Blot. We found altered GABA, glutamate and glutamine metabolite levels and ratios as well as increased levels of putrescine and serine - 2 positive modulators of the NMDAR. In addition, GABA receptor (GABAR) protein levels were reduced, whereas the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunit Gria2 protein levels were increased upon ketamine treatment. The significantly altered metabolite and protein levels further significantly correlated with the antidepressant-like behavior, which was assessed using the forced swim test. In conclusion and in line with previous research, our data indicate that ketamine impacts the AMPAR subunit Gria2 and results in decreased GABAergic inhibitory neurotransmission leading to increased excitatory neuronal activity.
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Affiliation(s)
- Katja Weckmann
- Max Planck Institute of Psychiatry, Department of Translational Research in Psychiatry, Munich, Germany.,Institute for Pathobiochemistry, University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Michael J Deery
- Cambridge Centre for Proteomics, Cambridge System Biology Centre, University of Cambridge, Cambridge, United Kingdom
| | - Julie A Howard
- Cambridge Centre for Proteomics, Cambridge System Biology Centre, University of Cambridge, Cambridge, United Kingdom
| | - Renata Feret
- Cambridge Centre for Proteomics, Cambridge System Biology Centre, University of Cambridge, Cambridge, United Kingdom
| | - John M Asara
- Division of Signal Transduction, Beth Israel Deaconess Medical Center and Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA
| | - Frederik Dethloff
- Max Planck Institute of Psychiatry, Department of Translational Research in Psychiatry, Munich, Germany
| | - Michaela D Filiou
- Department of Biological Applications and Technology, School of Health Sciences, University of Ioannina, Ioannina, Greece
| | - Christiana Labermaier
- Max Planck Institute of Psychiatry, Department of Translational Research in Psychiatry, Munich, Germany
| | - Giuseppina Maccarrone
- Max Planck Institute of Psychiatry, Department of Translational Research in Psychiatry, Munich, Germany
| | - Kathryn S Lilley
- Cambridge Centre for Proteomics, Cambridge System Biology Centre, University of Cambridge, Cambridge, United Kingdom
| | - Marianne Mueller
- Experimental Psychiatry, Department of Psychiatry and Psychotherapy and Focus Program Translational Neuroscience, Johannes Gutenberg University Medical Center, Mainz, Germany
| | - Christoph W Turck
- Max Planck Institute of Psychiatry, Department of Translational Research in Psychiatry, Munich, Germany
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Kölker S. Metabolism of amino acid neurotransmitters: the synaptic disorder underlying inherited metabolic diseases. J Inherit Metab Dis 2018; 41:1055-1063. [PMID: 29869166 DOI: 10.1007/s10545-018-0201-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 05/09/2018] [Accepted: 05/14/2018] [Indexed: 10/14/2022]
Abstract
Amino acids are involved in various metabolic pathways and some of them also act as neurotransmitters. Since biosynthesis of L-glutamate and γ-aminobutyric acid (GABA) requires 2-oxoglutarate while 3-phosphoglycerate is the precursor of L-glycine and D-serine, evolutionary selection of these amino acid neurotransmitters might have been driven by their capacity to provide important information about the glycolytic pathway and Krebs cycle. Synthesis and recycling of amino acid neurotransmitters as well as composition and function of their receptors are often compromised in inherited metabolic diseases. For instance, increased plasma L-phenylalanine concentrations impair cerebral biosynthesis of protein and bioamines in phenylketonuria, while elevated cerebral L-phenylalanine directly acts via ionotropic glutamate receptors. In succinic semialdehyde dehydrogenase deficiency, the neurotransmitter GABA and neuromodulatory γ-hydroxybutyric acid are elevated. Chronic hyperGABAergic state results in progressive downregulation of GABAA and GABAB receptors and impaired mitophagy. In glycine encephalopathy, the neurological phenotype is precipitated by L-glycine acting both via cortical NMDA receptors and glycine receptors in spinal cord and brain stem neurons. Serine deficiency syndromes are biochemically characterized by decreased biosynthesis of L-serine, an important neurotrophic factor, and the neurotransmitters D-serine and L-glycine. Supplementation with L-serine and L-glycine has a positive effect on seizure frequency and spasticity, while neurocognitive development can only be improved if treatment starts in utero or immediately postnatally. With novel techniques, the study of synaptic dysfunction in inherited metabolic diseases has become an emerging research field. More and better therapies are needed for these difficult-to-treat diseases.
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Affiliation(s)
- Stefan Kölker
- Division of Pediatric Neurology and Metabolic Medicine, Centre for Pediatric and Adolescent Medicine, University Hospital Heidelberg, Im Neuenheimer Feld 430, 69120, Heidelberg, Germany.
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13
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Sharma R, Razdan K, Bansal Y, Kuhad A. Rollercoaster ride of kynurenines: steering the wheel towards neuroprotection in Alzheimer's disease. Expert Opin Ther Targets 2018; 22:849-867. [PMID: 30223691 DOI: 10.1080/14728222.2018.1524877] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
INTRODUCTION Alzheimer's disease (AD) is associated with cerebral cognitive deficits exhibiting two cardinal hallmarks: accruement of extracellular amyloid plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. The currently accessible therapeutic armamentarium merely provides symptomatic relief. Therefore, the cry for prospective neuroprotective strategies seems to be the need of the hour. Areas covered: This review comprehensively establishes correlation between kynurenine pathway (KP) metabolites and AD with major emphasis on its two functionally contrasting neuroactive metabolites i.e. kynurenic acid (KYNA) and quinolinic acid (QUIN) and enlists various clinical studies which hold a potential for future therapeutics in AD. Also, major hypotheses of AD and mechanisms underlying them have been scrutinized with the aim to brush up the readers with basic pathology of AD. Expert opinion: KP is unique in itself as it holds two completely different domains i.e. neurotoxic QUIN and neuroprotective KYNA and disrupted equilibrium between the two has a hand in neurodegeneration. KYNA has long been demonstrated to be neuroprotective but lately being disparaged for cognitive side effects. But we blaze a trail by amalgamating the pharmacological mechanistic studies of KYNA in kinship with α7nAChRs, NMDARs and GABA which lends aid in favour of KA.
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Affiliation(s)
- Radhika Sharma
- a Pharmacology Research Laboratory , University Institute of Pharmaceutical Sciences, UGC-Centre of Advanced Study, Panjab University , Chandigarh , India
| | - Karan Razdan
- b Pharmaceutics division , University Institute of Pharmaceutical Sciences, UGC-Centre of Advanced Study, Panjab University , Chandigarh , India
| | - Yashika Bansal
- a Pharmacology Research Laboratory , University Institute of Pharmaceutical Sciences, UGC-Centre of Advanced Study, Panjab University , Chandigarh , India
| | - Anurag Kuhad
- a Pharmacology Research Laboratory , University Institute of Pharmaceutical Sciences, UGC-Centre of Advanced Study, Panjab University , Chandigarh , India
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14
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Jaber SM, Bordt EA, Bhatt NM, Lewis DM, Gerecht S, Fiskum G, Polster BM. Sex differences in the mitochondrial bioenergetics of astrocytes but not microglia at a physiologically relevant brain oxygen tension. Neurochem Int 2018; 117:82-90. [PMID: 28888963 PMCID: PMC5839942 DOI: 10.1016/j.neuint.2017.09.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Revised: 08/14/2017] [Accepted: 09/05/2017] [Indexed: 11/22/2022]
Abstract
Biological sex is thought to influence mitochondrial bioenergetic function. Previous respiration measurements examining brain mitochondrial sex differences were made at atmospheric oxygen using isolated brain mitochondria. Oxygen is 160 mm Hg (21%) in the atmosphere, while the oxygen tension in the brain generally ranges from ∼5 to 45 mm Hg (∼1-6% O2). This study tested the hypothesis that sex and/or brain physiological oxygen tension influence the mitochondrial bioenergetic properties of primary rat cortical astrocytes and microglia. Oxygen consumption was measured with a Seahorse XF24 cell respirometer in an oxygen-controlled environmental chamber. Strikingly, male astrocytes had a higher maximal respiration than female astrocytes when cultured and assayed at 3% O2. Three percent O2 yielded a low physiological dissolved O2 level of ∼1.2% (9.1 mm Hg) at the cell monolayer during culture and 1.2-3.0% O2 during assays. No differences in bioenergetic parameters were observed between male and female astrocytes at 21% O2 (dissolved O2 of ∼19.7%, 150 mm Hg during culture) or between either of these cell populations and female astrocytes at 3% O2. In contrast to astrocytes, microglia showed no sex differences in mitochondrial bioenergetic parameters at either oxygen level, regardless of whether they were non-stimulated or activated to a proinflammatory state. There were also no O2- or sex-dependent differences in proinflammatory TNF-α or IL-1β cytokine secretion measured at 18 h activation. Overall, results reveal an intriguing sex variance in astrocytic maximal respiration that requires additional investigation. Findings also demonstrate that sex differences can be masked by conducting experiments at non-physiological O2.
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Affiliation(s)
- Sausan M Jaber
- Department of Anesthesiology, and the Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA; Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA
| | - Evan A Bordt
- Department of Anesthesiology, and the Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA
| | - Niraj M Bhatt
- Department of Anesthesiology, and the Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA
| | - Daniel M Lewis
- Department of Chemical and Biomolecular Engineering, Institute for NanoBioTechnology, Johns Hopkins University, 3400 North Charles Street, Shaffer Hall 200C, Baltimore, MD 21218, USA
| | - Sharon Gerecht
- Department of Chemical and Biomolecular Engineering, Institute for NanoBioTechnology, Johns Hopkins University, 3400 North Charles Street, Shaffer Hall 200C, Baltimore, MD 21218, USA; Department of Materials Science and Engineering, Johns Hopkins University, 3400 North Charles Street, Shaffer Hall 200C, Baltimore, MD 21218, USA
| | - Gary Fiskum
- Department of Anesthesiology, and the Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA; Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA
| | - Brian M Polster
- Department of Anesthesiology, and the Center for Shock, Trauma and Anesthesiology Research (STAR), University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA; Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 685 W. Baltimore ST., MSTF 5-34, Baltimore, MD, 21201, USA.
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15
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Jalloh I, Helmy A, Howe DJ, Shannon RJ, Grice P, Mason A, Gallagher CN, Murphy MP, Pickard JD, Menon DK, Carpenter TA, Hutchinson PJ, Carpenter KLH. A Comparison of Oxidative Lactate Metabolism in Traumatically Injured Brain and Control Brain. J Neurotrauma 2018; 35:2025-2035. [PMID: 29690859 PMCID: PMC6098406 DOI: 10.1089/neu.2017.5459] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Metabolic abnormalities occur after traumatic brain injury (TBI). Glucose is conventionally regarded as the major energy substrate, although lactate can also be an energy source. We compared 3-13C lactate metabolism in TBI with "normal" control brain and muscle, measuring 13C-glutamine enrichment to assess tricarboxylic acid (TCA) cycle metabolism. Microdialysis catheters in brains of nine patients with severe TBI, five non-TBI brain surgical patients, and five resting muscle (non-TBI) patients were perfused (24 h in brain, 8 h in muscle) with 8 mmol/L sodium 3-13C lactate. Microdialysate analysis employed ISCUS and nuclear magnetic resonance. In TBI, with 3-13C lactate perfusion, microdialysate glucose concentration increased nonsignificantly (mean +11.9%, p = 0.463), with significant increases (p = 0.028) for lactate (+174%), pyruvate (+35.8%), and lactate/pyruvate ratio (+101.8%). Microdialysate 13C-glutamine fractional enrichments (median, interquartile range) were: for C4 5.1 (0-11.1) % in TBI and 5.7 (4.6-6.8) % in control brain, for C3 0 (0-5.0) % in TBI and 0 (0-0) % in control brain, and for C2 2.9 (0-5.7) % in TBI and 1.8 (0-3.4) % in control brain. 13C-enrichments were not statistically different between TBI and control brain, showing both metabolize 3-13C lactate via TCA cycle, in contrast to muscle. Several patients with TBI exhibited 13C-glutamine enrichment above the non-TBI control range, suggesting lactate oxidative metabolism as a TBI "emergency option."
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Affiliation(s)
- Ibrahim Jalloh
- 1 Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom
| | - Adel Helmy
- 1 Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom
| | - Duncan J Howe
- 2 Department of Chemistry, University of Cambridge , Cambridge, United Kingdom
| | - Richard J Shannon
- 1 Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom
| | - Peter Grice
- 2 Department of Chemistry, University of Cambridge , Cambridge, United Kingdom
| | - Andrew Mason
- 2 Department of Chemistry, University of Cambridge , Cambridge, United Kingdom
| | - Clare N Gallagher
- 1 Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom .,3 Division of Neurosurgery, Department of Clinical Neurosciences, University of Calgary , Calgary, Ontario, Canada
| | - Michael P Murphy
- 4 MRC Mitochondrial Biology Unit, University of Cambridge , Cambridge, United Kingdom
| | - John D Pickard
- 1 Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom .,5 Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom
| | - David K Menon
- 5 Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom .,6 Division of Anaesthesia, Department of Medicine, University of Cambridge , Cambridge, United Kingdom
| | - T Adrian Carpenter
- 5 Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom
| | - Peter J Hutchinson
- 1 Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom .,5 Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom
| | - Keri L H Carpenter
- 1 Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom .,5 Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge , Cambridge, United Kingdom
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16
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Silverman RB. Design and Mechanism of GABA Aminotransferase Inactivators. Treatments for Epilepsies and Addictions. Chem Rev 2018; 118:4037-4070. [PMID: 29569907 DOI: 10.1021/acs.chemrev.8b00009] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
When the brain concentration of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) diminishes below a threshold level, the excess neuronal excitation can lead to convulsions. This imbalance in neurotransmission can be corrected by inhibition of the enzyme γ-aminobutyric acid aminotransferase (GABA-AT), which catalyzes the conversion of GABA to the excitatory neurotransmitter l-glutamic acid. It also has been found that raising GABA levels can antagonize the rapid elevation and release of dopamine in the nucleus accumbens, which is responsible for the reward response in addiction. Therefore, the design of new inhibitors of GABA-AT, which increases brain GABA levels, is an important approach to new treatments for epilepsy and addiction. This review summarizes findings over the last 40 or so years of mechanism-based inactivators (unreactive compounds that require the target enzyme to catalyze their conversion to the inactivating species, which inactivate the enzyme prior to their release) of GABA-AT with emphasis on their catalytic mechanisms of inactivation, presented according to organic chemical mechanism, with minimal pharmacology, except where important for activity in epilepsy and addiction. Patents, abstracts, and conference proceedings are not covered in this review. The inactivation mechanisms described here can be applied to the inactivations of a wide variety of unrelated enzymes.
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Affiliation(s)
- Richard B Silverman
- Department of Chemistry, Department of Molecular Biosciences, Chemistry of Life Processes Institute, Center for Molecular Innovation and Drug Discovery, Center for Developmental Therapeutics , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208-3113 , United States
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17
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Naseri M, Parham A, Moghimi A. The effect of sodium thiopental as a GABA mimetic drug in neonatal period on expression of GAD65 and GAD67 genes in hippocampus of newborn and adult male rats. IRANIAN JOURNAL OF BASIC MEDICAL SCIENCES 2017; 20:996-1001. [PMID: 29085593 PMCID: PMC5651466 DOI: 10.22038/ijbms.2017.9264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Objective(s): Development of the nervous system in human and most animals is continued after the birth. Critical role of this period in generation and specialization of the neuronal circuits is confirmed in numerous studies. Any pharmacological intervention in this period may result in structural, functional or behavioral abnormalities. In this study, sodium thiopental a GABA mimetic drug was administrated to newborn rats and their GAD65 and GAD67 expression in hippocampus was evaluated before and after puberty. Materials and Methods: Newborn male Wistar rats were received sodium thiopental (35 mg/kg) daily for 11 days (from 4 to 14 days after birth). Expression of GAD65 and GAD67 in their hippocampus was compared with control groups in 15 and 45 days after birth with RT-qPCR method. Results: Significant down regulation of GAD65 and GAD67 gene expression was observed in treated rats compared with control group in 45 days after birth animals. But no significant difference was shown between experimental and control groups 15 days after birth animals. Conclusion: The effect of sodium thiopental on GAD65 and GAD67 expression only at adult rats showed a latent period of influence which can be attributed to dosage or intension of sodium thiopental neurotoxicity. Significant down regulation of GAD65 and GAD67 showed unwanted effect of sodium thiopental as GABA mimetic drug in critical period of development.
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Affiliation(s)
- Masoud Naseri
- Division of Physiology, Department of Basic Sciences, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran
| | - Abbas Parham
- Division of Physiology, Department of Basic Sciences, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran.,Embryonic and Stem Cell Biology and Biotechnology Research Group, Institute of Biotechnology, Ferdowsi University of Mashhad, Mashhad, Iran
| | - Ali Moghimi
- Rayan Center for Neuroscience and Behavior, Department of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
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18
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da Silva GSF, Sabino JPJ, Rajani V, Alvares TS, Pagliardini S, Branco LGS, Funk GD. Excitatory Modulation of the preBötzinger Complex Inspiratory Rhythm Generating Network by Endogenous Hydrogen Sulfide. Front Physiol 2017; 8:452. [PMID: 28713283 PMCID: PMC5492353 DOI: 10.3389/fphys.2017.00452] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 06/14/2017] [Indexed: 12/18/2022] Open
Abstract
Hydrogen Sulfide (H2S) is one of three gasotransmitters that modulate excitability in the CNS. Global application of H2S donors or inhibitors of H2S synthesis to the respiratory network has suggested that inspiratory rhythm is modulated by exogenous and endogenous H2S. However, effects have been variable, which may reflect that the RTN/pFRG (retrotrapezoid nucleus, parafacial respiratory group) and the preBötzinger Complex (preBötC, critical for inspiratory rhythm generation) are differentially modulated by exogenous H2S. Importantly, site-specific modulation of respiratory nuclei by H2S means that targeted, rather than global, manipulation of respiratory nuclei is required to understand the role of H2S signaling in respiratory control. Thus, our aim was to test whether endogenous H2S, which is produced by cystathionine-β-synthase (CBS) in the CNS, acts specifically within the preBötC to modulate inspiratory activity under basal (in vitro/in vivo) and hypoxic conditions (in vivo). Inhibition of endogenous H2S production by bath application of the CBS inhibitor, aminooxyacetic acid (AOAA, 0.1-1.0 mM) to rhythmic brainstem spinal cord (BSSC) and medullary slice preparations from newborn rats, or local application of AOAA into the preBötC (slices only) caused a dose-dependent decrease in burst frequency. Unilateral injection of AOAA into the preBötC of anesthetized, paralyzed adult rats decreased basal inspiratory burst frequency, amplitude and ventilatory output. AOAA in vivo did not affect the initial hypoxia-induced (10% O2, 5 min) increase in ventilatory output, but enhanced the secondary hypoxic respiratory depression. These data suggest that the preBötC inspiratory network receives tonic excitatory modulation from the CBS-H2S system, and that endogenous H2S attenuates the secondary hypoxic respiratory depression.
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Affiliation(s)
- Glauber S. F. da Silva
- Department of Physiology, Faculty of Medicine and Dentistry, Women and Children's Health Research Institute, Neuroscience and Mental Health Institute, University of AlbertaEdmonton, AB, Canada
- Department of Morphology and Animal Physiology, Sao Paulo State UniversityJaboticabal, Brazil
| | - João P. J. Sabino
- Department of Physiology, Faculty of Medicine and Dentistry, Women and Children's Health Research Institute, Neuroscience and Mental Health Institute, University of AlbertaEdmonton, AB, Canada
- Department of Biophysics and Physiology, Federal University of PiauiTeresina, Brazil
| | - Vishaal Rajani
- Department of Physiology, Faculty of Medicine and Dentistry, Women and Children's Health Research Institute, Neuroscience and Mental Health Institute, University of AlbertaEdmonton, AB, Canada
| | - Tucaauê S. Alvares
- Department of Physiology, Faculty of Medicine and Dentistry, Women and Children's Health Research Institute, Neuroscience and Mental Health Institute, University of AlbertaEdmonton, AB, Canada
| | - Silvia Pagliardini
- Department of Physiology, Faculty of Medicine and Dentistry, Women and Children's Health Research Institute, Neuroscience and Mental Health Institute, University of AlbertaEdmonton, AB, Canada
| | - Luiz G. S. Branco
- Department of Physiology, Faculty of Dentistry of Ribeirao Preto, University of Sao PauloRibeirao Preto, Brazil
| | - Gregory D. Funk
- Department of Physiology, Faculty of Medicine and Dentistry, Women and Children's Health Research Institute, Neuroscience and Mental Health Institute, University of AlbertaEdmonton, AB, Canada
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19
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Haroon E, Fleischer CC, Felger JC, Chen X, Woolwine BJ, Patel T, Hu XP, Miller AH. Conceptual convergence: increased inflammation is associated with increased basal ganglia glutamate in patients with major depression. Mol Psychiatry 2016; 21:1351-7. [PMID: 26754953 PMCID: PMC4940313 DOI: 10.1038/mp.2015.206] [Citation(s) in RCA: 158] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 10/08/2015] [Accepted: 10/30/2015] [Indexed: 01/19/2023]
Abstract
Inflammation and altered glutamate metabolism are two pathways implicated in the pathophysiology of depression. Interestingly, these pathways may be linked given that administration of inflammatory cytokines such as interferon-α to otherwise non-depressed controls increased glutamate in the basal ganglia and dorsal anterior cingulate cortex (dACC) as measured by magnetic resonance spectroscopy (MRS). Whether increased inflammation is associated with increased glutamate among patients with major depression is unknown. Accordingly, we conducted a cross-sectional study of 50 medication-free, depressed outpatients using single-voxel MRS, to measure absolute glutamate concentrations in basal ganglia and dACC. Multivoxel chemical shift imaging (CSI) was used to explore creatine-normalized measures of other metabolites in basal ganglia. Plasma and cerebrospinal fluid (CSF) inflammatory markers were assessed along with anhedonia and psychomotor speed. Increased log plasma C-reactive protein (CRP) was significantly associated with increased log left basal ganglia glutamate controlling for age, sex, race, body mass index, smoking status and depression severity. In turn, log left basal ganglia glutamate was associated with anhedonia and psychomotor slowing measured by the finger-tapping test, simple reaction time task and the Digit Symbol Substitution Task. Plasma CRP was not associated with dACC glutamate. Plasma and CSF CRP were also associated with CSI measures of basal ganglia glutamate and the glial marker myoinositol. These data indicate that increased inflammation in major depression may lead to increased glutamate in the basal ganglia in association with glial dysfunction and suggest that therapeutic strategies targeting glutamate may be preferentially effective in depressed patients with increased inflammation as measured by CRP.
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Affiliation(s)
- E Haroon
- Emory Behavioral Immunology Program, Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA, USA
- Emory Biomedical Imaging Technology Center, Wallace H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
- Winship Cancer Center, Department of Hematology and Oncology, Emory University School of Medicine, Atlanta, GA, USA
| | - C C Fleischer
- Emory Biomedical Imaging Technology Center, Wallace H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - J C Felger
- Emory Behavioral Immunology Program, Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA, USA
- Winship Cancer Center, Department of Hematology and Oncology, Emory University School of Medicine, Atlanta, GA, USA
| | - X Chen
- Emory Biomedical Imaging Technology Center, Wallace H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - B J Woolwine
- Emory Behavioral Immunology Program, Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA, USA
- Winship Cancer Center, Department of Hematology and Oncology, Emory University School of Medicine, Atlanta, GA, USA
| | - T Patel
- Department of Anesthesiology, Emory University School of Medicine, Atlanta, GA, USA
| | - X P Hu
- Emory Biomedical Imaging Technology Center, Wallace H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - A H Miller
- Emory Behavioral Immunology Program, Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, GA, USA
- Winship Cancer Center, Department of Hematology and Oncology, Emory University School of Medicine, Atlanta, GA, USA
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20
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McKenna MC, Stridh MH, McNair LF, Sonnewald U, Waagepetersen HS, Schousboe A. Glutamate oxidation in astrocytes: Roles of glutamate dehydrogenase and aminotransferases. J Neurosci Res 2016; 94:1561-1571. [PMID: 27629247 DOI: 10.1002/jnr.23908] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Revised: 07/22/2016] [Accepted: 08/05/2016] [Indexed: 12/11/2022]
Abstract
The cellular distribution of transporters and enzymes related to glutamate metabolism led to the concept of the glutamate-glutamine cycle. Glutamate is released as a neurotransmitter and taken up primarily by astrocytes ensheathing the synapses. The glutamate carbon skeleton is transferred back to the presynaptic neurons as the nonexcitatory amino acid glutamine. The cycle was initially thought to function with a 1:1 ratio between glutamate released and glutamine taken up by neurons. However, studies of glutamate metabolism in astrocytes have shown that a considerable proportion of glutamate undergoes oxidative degradation; thus, quantitative formation of glutamine from the glutamate taken up is not possible. Oxidation of glutamate is initiated by transamination catalyzed by an aminotransferase, or oxidative deamination catalyzed by glutamate dehydrogenase (GDH). We discuss methods available to elucidate the enzymes that mediate this conversion. Methods include pharmacological tools such as the transaminase inhibitor aminooxyacetic acid, studies using GDH knockout mice, and siRNA-mediated knockdown of GDH in astrocytes. Studies in brain slices incubated with [15 N]glutamate demonstrated activity of GDH in astrocytes in situ. These results, in conjunction with reports in the literature, support the conclusion that GDH is active in astrocytes both in culture and in vivo and that this enzyme plays a significant role in glutamate oxidation. Oxidative metabolism of glutamate, primarily mediated by GDH, but also by transamination by aspartate aminotransferase, provides considerably more energy than is required to maintain the activity of the high-affinity glutamate transporters needed for efficient removal of glutamate from the synaptic cleft. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Mary C McKenna
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland. .,Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland.
| | - Malin H Stridh
- Department of Drug Design and Pharmacology, Faculty of Health and Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Laura F McNair
- Department of Drug Design and Pharmacology, Faculty of Health and Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Ursula Sonnewald
- Department of Drug Design and Pharmacology, Faculty of Health and Medicine, University of Copenhagen, Copenhagen, Denmark.,Department of Neuroscience, Faculty of Medicine, University of Science and Technology, Trondheim, Norway
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medicine, University of Copenhagen, Copenhagen, Denmark
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21
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Pearson-Leary J, Osborne DM, McNay EC. Role of Glia in Stress-Induced Enhancement and Impairment of Memory. Front Integr Neurosci 2016; 9:63. [PMID: 26793072 PMCID: PMC4707238 DOI: 10.3389/fnint.2015.00063] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Accepted: 12/05/2015] [Indexed: 12/20/2022] Open
Abstract
Both acute and chronic stress profoundly affect hippocampally-dependent learning and memory: moderate stress generally enhances, while chronic or extreme stress can impair, neural and cognitive processes. Within the brain, stress elevates both norepinephrine and glucocorticoids, and both affect several genomic and signaling cascades responsible for modulating memory strength. Memories formed at times of stress can be extremely strong, yet stress can also impair memory to the point of amnesia. Often overlooked in consideration of the impact of stress on cognitive processes, and specifically memory, is the important contribution of glia as a target for stress-induced changes. Astrocytes, microglia, and oligodendrocytes all have unique contributions to learning and memory. Furthermore, these three types of glia express receptors for both norepinephrine and glucocorticoids and are hence immediate targets of stress hormone actions. It is becoming increasingly clear that inflammatory cytokines and immunomodulatory molecules released by glia during stress may promote many of the behavioral effects of acute and chronic stress. In this review, the role of traditional genomic and rapid hormonal mechanisms working in concert with glia to affect stress-induced learning and memory will be emphasized.
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Affiliation(s)
- Jiah Pearson-Leary
- Department of Anesthesiology and Critical Care Medicine, Children's Hospital of Philadelphia Philadelphia, PA, USA
| | | | - Ewan C McNay
- Behavioral Neuroscience and Biology, University at Albany Albany, NY, USA
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22
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23
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Abstract
Transient multienzyme and/or multiprotein complexes (metabolons) direct substrates toward specific pathways and can significantly influence the metabolism of glutamate and glutamine in the brain. Glutamate is the primary excitatory neurotransmitter in brain. This neurotransmitter has essential roles in normal brain function including learning and memory. Metabolism of glutamate involves the coordinated activity of astrocytes and neurons and high affinity transporter proteins that are selectively distributed on these cells. This chapter describes known and possible metabolons that affect the metabolism of glutamate and related compounds in the brain, as well as some factors that can modulate the association and dissociation of such complexes, including protein modifications by acylation reactions (e.g., acetylation, palmitoylation, succinylation, SUMOylation, etc.) of specific residues. Development of strategies to modulate transient multienzyme and/or enzyme-protein interactions may represent a novel and promising therapeutic approach for treatment of diseases involving dysregulation of glutamate metabolism.
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24
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A Tribute to Mary C. McKenna: Glutamate as Energy Substrate and Neurotransmitter-Functional Interaction Between Neurons and Astrocytes. Neurochem Res 2015; 42:4-9. [PMID: 26721512 DOI: 10.1007/s11064-015-1813-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 12/16/2015] [Accepted: 12/18/2015] [Indexed: 10/22/2022]
Abstract
Glutamate metabolism in the brain is extremely complex not only involving a large variety of enzymes but also a tight partnership between neurons and astrocytes, the latter cells being in control of de novo synthesis of glutamate. This review provides an account of the processes involved, i.e. pyruvate carboxylation and recycling as well as the glutamate-glutamine cycle, focusing on the many seminal contributions from Dr. Mary McKenna. The ramification of the astrocytic end feet allowing contact and control of hundreds of thousands of synapses at the same time obviously puts these cells in a prominent position to regulate neural activity. Additionally, the astrocytes take active part in the neurotransmission processes by releasing a variety of gliotransmitters including glutamate. Hence, the term "the tripartite synapse", in which there is an active and dynamic interplay between the pre- and post-synaptic neurons and the ensheathing astrocytes, has been coined. The studies of Mary McKenna and her colleagues over several decades have been of paramount importance for the elucidation of compartmentation in astrocytes and synaptic terminals and the intricate metabolic processes underlying the glutamatergic neurotransmission process.
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Nissen JD, Pajęcka K, Stridh MH, Skytt DM, Waagepetersen HS. Dysfunctional TCA-Cycle Metabolism in Glutamate Dehydrogenase Deficient Astrocytes. Glia 2015. [DOI: 10.1002/glia.22895] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Jakob D. Nissen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Kamilla Pajęcka
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Malin H. Stridh
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Dorte M. Skytt
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Helle S. Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
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Wei L, Xue R, Zhang P, Wu Y, Li X, Pei F. (1)H NMR-Based Metabolomics and Neurotoxicity Study of Cerebrum and Cerebellum in Rats Treated with Cinnabar, a Traditional Chinese Medicine. OMICS-A JOURNAL OF INTEGRATIVE BIOLOGY 2015; 19:490-8. [PMID: 26110755 DOI: 10.1089/omi.2015.0042] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Cinnabar, an important traditional Chinese mineral medicine, has been widely used as a Chinese patent medicine ingredient for sedative therapy. Nevertheless, the neurotoxic effects of cinnabar have also been noted. In this study, (1)H NMR-based metabolomics, combined with multivariate pattern recognition, were applied to investigate the neurotoxic effects of cinnabar after intragastrical administration (dosed at 2 and 5 g/kg body weight) on male Wistar rats. The metabolite variations induced by cinnabar were characterized by increased levels of glutamate, glutamine, myo-inositol, and choline, as well as decreased levels of GABA, taurine, NAA, and NAAG in tissue extracts of the cerebellum and cerebrum. These findings suggested that cinnabar induced glutamate excitotoxicity, neuronal cell loss, osmotic state changes, membrane fluidity disruption, and oxidative injury in the brain. We also show here that there is a dose- and time-dependent neurotoxicity of cinnabar, and that cerebellum was more sensitive to cinnabar induction than cerebrum. This work illustrates the utility and reliability of (1)H NMR-based metabolomics approach for examining the potential neurotoxic effects of cinnabar and other traditional Chinese medicines.
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Affiliation(s)
- Lai Wei
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun, People's Republic of China
| | - Rong Xue
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun, People's Republic of China
| | - Panpan Zhang
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun, People's Republic of China
| | - Yijie Wu
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun, People's Republic of China
| | - Xiaojing Li
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun, People's Republic of China
| | - Fengkui Pei
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun, People's Republic of China
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Voss CM, Pajęcka K, Stridh MH, Nissen JD, Schousboe A, Waagepetersen HS. AMPK Activation Affects Glutamate Metabolism in Astrocytes. Neurochem Res 2015; 40:2431-42. [PMID: 25846006 DOI: 10.1007/s11064-015-1558-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 03/09/2015] [Accepted: 03/12/2015] [Indexed: 12/20/2022]
Abstract
Mammalian AMP-activated protein kinase (AMPK) functions as a metabolic switch. It is composed of 3 different subunits and its activation depends on phosphorylation of a threonine residue (Thr172) in the α-subunit. This phosphorylation can be brought about by 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR) which in the cells is converted to a monophosphorylated nucleotide mimicking the effect of AMP. We show that the preparation of cultured astrocytes used for metabolic studies expresses AMPK, which could be phosphorylated by exposure of the cells to AICAR. The effect of AMPK activation on glutamate metabolism in astrocytes was studied using primary cultures of these cells from mouse cerebral cortex during incubation in media containing 2.5 mM glucose and 100 µM [U-(13)C]glutamate. The metabolism of glutamate including a detailed analysis of its metabolic pathways involving the tricarboxylic acid (TCA) cycle was studied using high-performance liquid chromatography analysis supplemented with gas chromatography-mass spectrometry technology. It was found that AMPK activation had profound effects on the pathways involved in glutamate metabolism since the entrance of the glutamate carbon skeleton into the TCA cycle was reduced. On the other hand, glutamate uptake into the astrocytes as well as its conversion to glutamine catalyzed by glutamine synthetase was not affected by AMPK activation. Interestingly, synthesis and release of citrate, which are hallmarks of astrocytic function, were affected by a reduction of the flux of glutamate derived carbon through the malic enzyme and pyruvate carboxylase catalyzed reactions. Finally, it was found that in the presence of glutamate as an additional substrate, glucose metabolism monitored by the use of tritiated deoxyglucose was unaffected by AMPK activation. Accordingly, the effects of AMPK activation appeared to be specific for certain key processes involved in glutamate metabolism.
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Affiliation(s)
- Caroline M Voss
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Kamilla Pajęcka
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
- Department of Clinical Medicine, The Department of Endocrinology and Diabetes, University of Aarhus, 8000, Århus, Denmark
| | - Malin H Stridh
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Jakob D Nissen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark.
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Bejarano E, Rodríguez-Navarro JA. Autophagy and amino acid metabolism in the brain: implications for epilepsy. Amino Acids 2014; 47:2113-26. [DOI: 10.1007/s00726-014-1822-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Accepted: 07/31/2014] [Indexed: 12/31/2022]
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Hertz L, Peng L, Song D. Ammonia, like K(+), stimulates the Na(+), K(+), 2 Cl(-) cotransporter NKCC1 and the Na(+),K(+)-ATPase and interacts with endogenous ouabain in astrocytes. Neurochem Res 2014; 40:241-57. [PMID: 24929663 DOI: 10.1007/s11064-014-1352-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 05/31/2014] [Accepted: 06/03/2014] [Indexed: 12/12/2022]
Abstract
Brain edema during hepatic encephalopathy or acute liver failure as well as following brain ischemia has a multifactorial etiology, but it is a dangerous and occasionally life-threatening complication because the brain is enclosed in the rigid skull. During ischemia the extracellular K(+) concentration increases to very high levels, which when energy becomes available during reperfusion stimulate NKCC1, a cotransporter driven by the transmembrane ion gradients established by the Na(+),K(+)-ATPase and accumulating Na(+), K(+) and 2 Cl(-) together with water. This induces pronounced astrocytic swelling under pathologic conditions, but NKCC1 is probably also activated, although to a lesser extent, during normal brain function. Redistribution of ions and water between extra- and intracellular phases does not create brain edema, which in addition requires uptake across the blood-brain barrier. During hepatic encephalopathy and acute liver failure a crucial factor is the close resemblance between K(+) and NH4(+) in their effects not only on NKCC1 and Na(+),K(+)-ATPase but also on Na(+),K(+)-ATPase-induced signaling by endogenous ouabains. These in turn activate production of ROS and nitrosactive agents which slowly sensitize NKCC1, explaining why cell swelling and brain edema generally are delayed under hyperammonemic conditions, although very high ammonia concentrations can cause immediate NKCC1 activation.
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Affiliation(s)
- Leif Hertz
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University, No. 92 Beier Road, Heping District, Shenyang, People's Republic of China
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Tani H, Dulla CG, Farzampour Z, Taylor-Weiner A, Huguenard JR, Reimer RJ. A local glutamate-glutamine cycle sustains synaptic excitatory transmitter release. Neuron 2014; 81:888-900. [PMID: 24559677 DOI: 10.1016/j.neuron.2013.12.026] [Citation(s) in RCA: 135] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/19/2013] [Indexed: 01/02/2023]
Abstract
Biochemical studies suggest that excitatory neurons are metabolically coupled with astrocytes to generate glutamate for release. However, the extent to which glutamatergic neurotransmission depends on this process remains controversial because direct electrophysiological evidence is lacking. The distance between cell bodies and axon terminals predicts that glutamine-glutamate cycle is synaptically localized. Hence, we investigated isolated nerve terminals in brain slices by transecting hippocampal Schaffer collaterals and cortical layer I axons. Stimulating with alternating periods of high frequency (20 Hz) and rest (0.2 Hz), we identified an activity-dependent reduction in synaptic efficacy that correlated with reduced glutamate release. This was enhanced by inhibition of astrocytic glutamine synthetase and reversed or prevented by exogenous glutamine. Importantly, this activity dependence was also revealed with an in-vivo-derived natural stimulus both at network and cellular levels. These data provide direct electrophysiological evidence that an astrocyte-dependent glutamate-glutamine cycle is required to maintain active neurotransmission at excitatory terminals.
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Affiliation(s)
- Hiroaki Tani
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Chris G Dulla
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - Zoya Farzampour
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA; Graduate Program in Neuroscience, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Amaro Taylor-Weiner
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
| | - John R Huguenard
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA; Graduate Program in Neuroscience, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Richard J Reimer
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA; Graduate Program in Neuroscience, Stanford University School of Medicine, Stanford, CA 94305, USA; Neurology Service, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304, USA.
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31
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Resmini E, Santos A, Gómez-Anson B, López-Mourelo O, Pires P, Vives-Gilabert Y, Crespo I, Portella MJ, de Juan-Delago M, Webb SM. Hippocampal dysfunction in cured Cushing's syndrome patients, detected by (1) H-MR-spectroscopy. Clin Endocrinol (Oxf) 2013; 79:700-7. [PMID: 23594250 DOI: 10.1111/cen.12224] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 02/13/2013] [Accepted: 04/14/2013] [Indexed: 01/12/2023]
Abstract
BACKGROUND Proton magnetic resonance spectroscopy ((1) H-MRS) is a sensitive, noninvasive imaging technique capable of measuring brain metabolites in vivo. Chronic exposure to endogenous hypercortisolism in Cushing's syndrome (CS) is associated with negative effects on memory and hippocampal volumes, even after biochemical cure. OBJECTIVE To investigate metabolites in the hippocampi of CS patients and controls, using (1) H-MRS. PATIENTS AND METHODS Eighteen right-handed cured CS patients (age 44·8 ± 12·5 years, 12·6 ± 3·8 years of education) and 18 right-handed healthy controls, matched for age (40·0 ± 11·9) and years of education (14·4 ± 3·8), underwent 3-Tesla magnetic resonance imaging (3T MRI) and (1) H-MRS including the head of each hippocampus. Concentrations of Glu (Glutamate), Glx (Glutamate + Glutamine), NAA (N-Acetyl-aspartate), total NAA (N-Acetyl-aspartate + N-Acetyl-aspartyl-Glutamate), Cho (Glycerophosphocholine and Phosphocholine compounds), Cr (Creatine) and MI (mionositol) were measured (mmol/l). Hippocampal volumes (mm(3) ) were additionally calculated using an automated procedure (FreeSurfer). RESULTS CS patients had lower NAA than controls in the left and right hippocampus (5·2 ± 1·0 vs 6·1 ± 0·7, P < 0·05; 4·9 ± 0·8 vs 6·1 ± 0·6, P < 0·001, respectively), and lower total NAA on the right side (5·7 ± 0·9 vs 6·3 ± 0·9, P < 0·05), suggesting neuronal dysfunction/loss. CS patients had higher Glx than controls in both hippocampi (10·4 ± 1·9 vs 8·6 ± 1·4, P < 0·01; 9·9 ± 1·6 vs 8·9 ± 1·3, P < 0·05, respectively), suggesting glial proliferation, as a repair mechanism after neuronal dysfunction. No differences were found in the other brain metabolites, and there were no differences in left (3815·78 ± 502·96) and right (3980·75 ± 369·44) total hippocampal volumes between CS patients and controls (3945·08 ± 408·90 and 4108·39 ± 365·11, respectively). CONCLUSION Persistently abnormal metabolites are evidenced in the hippocampi of CS patients despite endocrine cure. These functional alterations could be early markers of glucocorticoid neurotoxicity, preceding hippocampal volume reduction.
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Affiliation(s)
- Eugenia Resmini
- Endocrinology/Medicine Department, Hospital Sant Pau, Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBER-ER, Unidad 747), IIB-Sant Pau, ISCIII and Universitat Autònoma de Barcelona (UAB), Barcelona, Spain
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Possible involvement of TLRs and hemichannels in stress-induced CNS dysfunction via mastocytes, and glia activation. Mediators Inflamm 2013; 2013:893521. [PMID: 23935250 PMCID: PMC3713603 DOI: 10.1155/2013/893521] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Revised: 05/16/2013] [Accepted: 06/11/2013] [Indexed: 12/13/2022] Open
Abstract
In the central nervous system (CNS), mastocytes and glial cells (microglia, astrocytes and oligodendrocytes) function as sensors of neuroinflammatory conditions, responding to stress triggers or becoming sensitized to subsequent proinflammatory challenges. The corticotropin-releasing hormone and glucocorticoids are critical players in stress-induced mastocyte degranulation and potentiation of glial inflammatory responses, respectively. Mastocytes and glial cells express different toll-like receptor (TLR) family members, and their activation via proinflammatory molecules can increase the expression of connexin hemichannels and pannexin channels in glial cells. These membrane pores are oligohexamers of the corresponding protein subunits located in the cell surface. They allow ATP release and Ca2+ influx, which are two important elements of inflammation. Consequently, activated microglia and astrocytes release ATP and glutamate, affecting myelinization, neuronal development, and survival. Binding of ligands to TLRs induces a cascade of intracellular events leading to activation of several transcription factors that regulate the expression of many genes involved in inflammation. During pregnancy, the previous responses promoted by viral infections and other proinflammatory conditions are common and might predispose the offspring to develop psychiatric disorders and neurological diseases. Such disorders could eventually be potentiated by stress and might be part of the etiopathogenesis of CNS dysfunctions including autism spectrum disorders and schizophrenia.
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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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Magnetic resonance spectroscopy and molecular studies in ornithine transcarbamylase deficiency novel mutation c.802A>G in exon 8 (p.Met268Val). Neurol Neurochir Pol 2013; 47:283-9. [DOI: 10.5114/ninp.2013.35488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Whitelaw BS, Robinson MB. Inhibitors of glutamate dehydrogenase block sodium-dependent glutamate uptake in rat brain membranes. Front Endocrinol (Lausanne) 2013; 4:123. [PMID: 24062726 PMCID: PMC3775299 DOI: 10.3389/fendo.2013.00123] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Accepted: 08/30/2013] [Indexed: 02/02/2023] Open
Abstract
We recently found evidence for anatomic and physical linkages between the astroglial Na(+)-dependent glutamate transporters (GLT-1/EAAT2 and GLAST/EAAT1) and mitochondria. In these same studies, we found that the glutamate dehydrogenase (GDH) inhibitor, epigallocatechin-monogallate (EGCG), inhibits both glutamate oxidation and Na(+)-dependent glutamate uptake in astrocytes. In the present study, we extend this finding by exploring the effects of EGCG on Na(+)-dependent l-[(3)H]-glutamate (Glu) uptake in crude membranes (P2) prepared from rat brain cortex. In this preparation, uptake is almost exclusively mediated by GLT-1. EGCG inhibited l-[(3)H]-Glu uptake in cortical membranes with an IC50 value of 230 μM. We also studied the effects of two additional inhibitors of GDH, hexachlorophene (HCP) and bithionol (BTH). Both of these compounds also caused concentration-dependent inhibition of glutamate uptake in cortical membranes. Pre-incubating with HCP for up to 15 min had no greater effect than that observed with no pre-incubation, showing that the effects occur rapidly. HCP decreased the V max for glutamate uptake without changing the K m, consistent with a non-competitive mechanism of action. EGCG, HCP, and BTH also inhibited Na(+)-dependent transport of d-[(3)H]-aspartate (Asp), a non-metabolizable transporter substrate, and [(3)H]-γ-aminobutyric acid (GABA). In contrast to the forebrain, glutamate uptake in crude cerebellar membranes (P2) is likely mediated by GLAST (EAAT1). Therefore, the effects of these compounds were examined in cerebellar membranes. In this region, none of these compounds had any effect on uptake of either l-[(3)H]-Glu or d-[(3)H]-Asp, but they all inhibited [(3)H]-GABA uptake. Together these studies suggest that GDH is preferentially required for glutamate uptake in forebrain as compared to cerebellum, and GDH may be required for GABA uptake as well. They also provide further evidence for a functional linkage between glutamate transport and mitochondria.
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Affiliation(s)
- Brendan S. Whitelaw
- Children’s Hospital of Philadelphia Research Institute, Philadelphia, PA, USA
| | - Michael B. Robinson
- Children’s Hospital of Philadelphia Research Institute, Philadelphia, PA, USA
- Departments of Pediatrics and Pharmacology, University of Pennsylvania, Philadelphia, PA, USA
- *Correspondence: Michael B. Robinson, Department of Pediatrics, University of Pennsylvania, 502N Abramson Pediatric Research Building, 3615 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA e-mail:
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Rothman DL, De Feyter HM, Maciejewski PK, Behar KL. Is there in vivo evidence for amino acid shuttles carrying ammonia from neurons to astrocytes? Neurochem Res 2012; 37:2597-612. [PMID: 23104556 DOI: 10.1007/s11064-012-0898-7] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 09/27/2012] [Accepted: 10/03/2012] [Indexed: 10/27/2022]
Abstract
The high in vivo flux of the glutamate/glutamine cycle puts a strong demand on the return of ammonia released by phosphate activated glutaminase from the neurons to the astrocytes in order to maintain nitrogen balance. In this paper we review several amino acid shuttles that have been proposed for balancing the nitrogen flows between neurons and astrocytes in the glutamate/glutamine cycle. All of these cycles depend on the directionality of glutamate dehydrogenase, catalyzing reductive glutamate synthesis (forward reaction) in the neuron in order to capture the ammonia released by phosphate activated glutaminase, while catalyzing oxidative deamination of glutamate (reverse reaction) in the astrocytes to release ammonia for glutamine synthesis. Reanalysis of results from in vivo experiments using (13)N and (15)N labeled ammonia and (15)N leucine in rats suggests that the maximum flux of the alanine/lactate or branched chain amino acid/branched chain amino acid transaminase shuttles between neurons and astrocytes are approximately 3-5 times lower than would be required to account for the ammonia transfer from neurons to astrocytes needed for glutamine synthesis (amide nitrogen) to sustain the glutamate/glutamine cycle. However, in the rat brain both the total ammonia fixation rate by glutamate dehydrogenase and the total branched chain amino acid transaminase activity are sufficient to support a branched chain amino acid/branched chain keto acid shuttle, as proposed by Hutson and coworkers, which would support the de novo synthesis of glutamine in the astrocyte to replace the ~20 % of neurotransmitter glutamate that is oxidized. A higher fraction of the nitrogen needs of total glutamate neurotransmitter cycling could be supported by hybrid cycles in which glutamate and tricarboxylic acid cycle intermediates act as a nitrogen shuttle. A limitation of all in vivo studies in animals conducted to date is that none have shown transfer of nitrogen for glutamine amide synthesis, either as free ammonia or via an amino acid from the neurons to the astrocytes. Future work will be needed, perhaps using methods for selectively labeling nitrogen in neurons, to conclusively establish the rate of amino acid nitrogen shuttles in vivo and their coupling to the glutamate/glutamine cycle.
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Affiliation(s)
- Douglas L Rothman
- Department of Diagnostic Radiology and Biomedical Engineering, Magnetic Resonance Research Center, Yale University School of Medicine, 300 Cedar Street, P.O. Box 208043, New Haven, CT 06520-8043, USA.
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McKenna MC. Substrate competition studies demonstrate oxidative metabolism of glucose, glutamate, glutamine, lactate and 3-hydroxybutyrate in cortical astrocytes from rat brain. Neurochem Res 2012; 37:2613-26. [PMID: 23079895 DOI: 10.1007/s11064-012-0901-3] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Revised: 10/01/2012] [Accepted: 10/03/2012] [Indexed: 01/14/2023]
Abstract
It is well established that astrocytes can utilize many substrates to support oxidative energy metabolism; however, use of energy substrates in the presence of other substrates, as would occur in vivo, has not been systematically evaluated. Substrate competition studies were used to determine changes in the rates of (14)CO(2) production since little is known about the interaction of energy substrates in astrocytes. The rates of (14)CO(2) production from 1 mM D-[6-(14)C]glucose, L-[U-(14)C]glutamate, L-[U-(14)C]glutamine, D-3-hydroxy[3-(14)C]butyrate, L-[U-(14)C]lactate and L-[U-(14)C]malate by primary cultures of astrocytes from rat brain were determined to be 1.17 ± 0.19, 85.30 ± 12.25, 28.04 ± 2.84, 13.55 ± 4.56, 14.84 ± 2.40 and 5.20 ± 1.20 nmol/h/mg protein (mean ± SEM), respectively. The rate of (14)CO(2) production from glutamate oxidation was higher than that of the other substrates Addition of unlabeled glutamate significantly decreased the rates of (14)CO(2) production from all other substrates studied; however, glutamate oxidation was not altered by the addition of any of the other substrates. The rate of (14)CO(2) production of glutamine was decreased by glutamate, but not altered by other substrates. The rate of (14)CO(2) production from glucose was significantly decreased by the addition of unlabeled glutamate, glutamine or lactate, but not by 3-hydroxybutyrate or malate. Addition of unlabeled glucose did not significantly alter the (14)CO(2) production from any other substrate. (14)CO(2) production from lactate was decreased by the addition of unlabeled glutamine or glutamate and increased by addition of malate. The (14)CO(2) production from malate was decreased by the addition of unlabeled glutamate or lactate, but was not altered by the other substrates. The substrate utilization for oxidative energy metabolism in astrocytes is very different than the profile previously reported for synaptic terminals. These studies demonstrate the potential use of multiple substrates including glucose, glutamate, glutamine, lactate and 3-hydroxybutyrate as energy substrates for astrocytes. The data also provide evidence of interactions of substrates and multiple compartments of TCA cycle activity in cultured astrocytes.
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Affiliation(s)
- Mary C McKenna
- Department of Pediatrics and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA.
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Glutamine in the pathogenesis of acute hepatic encephalopathy. Neurochem Int 2012; 61:575-80. [DOI: 10.1016/j.neuint.2012.01.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Revised: 01/11/2012] [Accepted: 01/12/2012] [Indexed: 01/28/2023]
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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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40
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Skytt DM, Klawonn AM, Stridh MH, Pajęcka K, Patruss Y, Quintana-Cabrera R, Bolaños JP, Schousboe A, Waagepetersen HS. siRNA knock down of glutamate dehydrogenase in astrocytes affects glutamate metabolism leading to extensive accumulation of the neuroactive amino acids glutamate and aspartate. Neurochem Int 2012; 61:490-7. [PMID: 22542772 DOI: 10.1016/j.neuint.2012.04.014] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2012] [Revised: 04/02/2012] [Accepted: 04/11/2012] [Indexed: 11/27/2022]
Abstract
Glutamate is the most abundant excitatory neurotransmitter in the brain and astrocytes are key players in sustaining glutamate homeostasis. Astrocytes take up the predominant part of glutamate after neurotransmission and metabolism of glutamate is necessary for a continuous efficient removal of glutamate from the synaptic area. Glutamate may either be amidated by glutamine synthetase or oxidatively metabolized in the mitochondria, the latter being at least to some extent initiated by oxidative deamination by glutamate dehydrogenase (GDH). To explore the particular importance of GDH for astrocyte metabolism we have knocked down GDH in cultured cortical astrocytes employing small interfering RNA (siRNA) achieving a reduction of the enzyme activity by approximately 44%. The astrocytes were incubated for 2h in medium containing either 1.0mM [(15)NH(4)(+)] or 100 μM [(15)N]glutamate. For those exposed to [(15)N]glutamate an additional 100 μM was added after 1h. Metabolic mapping was performed from isotope incorporation measured by mass spectrometry into relevant amino acids of cell extracts and media. The contents of the amino acids were measured by HPLC. The (15)N incorporation from [(15)NH(4)(+)] into glutamate, aspartate and alanine was decreased in astrocytes exhibiting reduced GDH activity. However, the reduced GDH activity had no effect on the cellular contents of these amino acids. This supports existing in vivo and in vitro studies that GDH is predominantly working in the direction of oxidative deamination and not reductive amination. In contrast, when exposing the astrocytes to [(15)N]glutamate, the reduced GDH activity led to an increased (15)N incorporation into glutamate, aspartate and alanine and a large increase in the content of glutamate and aspartate. Surprisingly, this accumulation of glutamate and net-synthesis of aspartate were not reflected in any alterations in either the glutamine content or labeling, but a slight increase in mono labeling of glutamine in the medium. We suggest that this extensive net-synthesis of aspartate due to lack of GDH activity is occurring via the concerted action of AAT and the part of TCA cycle operating from α-ketoglutarate to oxaloacetate, i.e. the truncated TCA cycle.
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Affiliation(s)
- Dorte M Skytt
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
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41
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Biochemical and structural characterization of mouse mitochondrial aspartate aminotransferase, a newly identified kynurenine aminotransferase-IV. Biosci Rep 2012; 31:323-32. [PMID: 20977429 DOI: 10.1042/bsr20100117] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Mammalian mAspAT (mitochondrial aspartate aminotransferase) is recently reported to have KAT (kynurenine aminotransferase) activity and plays a role in the biosynthesis of KYNA (kynurenic acid) in rat, mouse and human brains. This study concerns the biochemical and structural characterization of mouse mAspAT. In this study, mouse mAspAT cDNA was amplified from mouse brain first stand cDNA and its recombinant protein was expressed in an Escherichia coli expression system. Sixteen oxo acids were tested for the co-substrate specificity of mouse mAspAT and 14 of them were shown to be capable of serving as co-substrates for the enzyme. Structural analysis of mAspAT by macromolecular crystallography revealed that the cofactor-binding residues of mAspAT are similar to those of other KATs. The substrate-binding residues of mAspAT are slightly different from those of other KATs. Our results provide a biochemical and structural basis towards understanding the overall physiological role of mAspAT in vivo and insight into controlling the levels of endogenous KYNA through modulation of the enzyme in the mouse brain.
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42
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Bauer DE, Jackson JG, Genda EN, Montoya MM, Yudkoff M, Robinson MB. The glutamate transporter, GLAST, participates in a macromolecular complex that supports glutamate metabolism. Neurochem Int 2012; 61:566-74. [PMID: 22306776 DOI: 10.1016/j.neuint.2012.01.013] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 01/11/2012] [Accepted: 01/12/2012] [Indexed: 01/25/2023]
Abstract
GLAST is the predominant glutamate transporter in the cerebellum and contributes substantially to glutamate transport in forebrain. This astroglial glutamate transporter quickly binds and clears synaptically released glutamate and is principally responsible for ensuring that synaptic glutamate concentrations remain low. This process is associated with a significant energetic cost. Compartmentalization of GLAST with mitochondria and proteins involved in energy metabolism could provide energetic support for glutamate transport. Therefore, we performed immunoprecipitation and co-localization experiments to determine if GLAST might co-compartmentalize with proteins involved in energy metabolism. GLAST was immunoprecipitated from rat cerebellum and subunits of the Na(+)/K(+) ATPase, glycolytic enzymes, and mitochondrial proteins were detected. GLAST co-localized with mitochondria in cerebellar tissue. GLAST also co-localized with mitochondria in fine processes of astrocytes in organotypic hippocampal slice cultures. From these data, we hypothesized that mitochondria participate in a macromolecular complex with GLAST to support oxidative metabolism of transported glutamate. To determine the functional metabolic role of this complex, we measured CO(2) production from radiolabeled glutamate in cultured astrocytes and compared it to overall glutamate uptake. Within 15 min, 9% of transported glutamate was converted to CO(2). This CO(2) production was blocked by inhibitors of glutamate transport and glutamate dehydrogenase, but not by an inhibitor of glutamine synthetase. Our data support a model in which GLAST exists in a macromolecular complex that allows transported glutamate to be metabolized in mitochondria to support energy production.
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Affiliation(s)
- Deborah E Bauer
- Children's Hospital of Philadelphia Research Institute, University of Pennsylvania, Philadelphia, PA 19104, United States
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43
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Abstract
Glutamine (Gln) is found abundantly in the central nervous system (CNS) where it participates in a variety of metabolic pathways. Its major role in the brain is that of a precursor of the neurotransmitter amino acids: the excitatory amino acids, glutamate (Glu) and aspartate (Asp), and the inhibitory amino acid, γ-amino butyric acid (GABA). The precursor-product relationship between Gln and Glu/GABA in the brain relates to the intercellular compartmentalization of the Gln/Glu(GABA) cycle (GGC). Gln is synthesized from Glu and ammonia in astrocytes, in a reaction catalyzed by Gln synthetase (GS), which, in the CNS, is almost exclusively located in astrocytes (Martinez-Hernandez et al., 1977). Newly synthesized Gln is transferred to neurons and hydrolyzed by phosphate-activated glutaminase (PAG) to give rise to Glu, a portion of which may be decarboxylated to GABA or transaminated to Asp. There is a rich body of evidence which indicates that a significant proportion of the Glu, Asp and GABA derived from Gln feed the synaptic, neurotransmitter pools of the amino acids. Depolarization-induced-, calcium- and PAG activity-dependent releases of Gln-derived Glu, GABA and Asp have been observed in CNS preparations in vitro and in the brain in situ. Immunocytochemical studies in brain slices have documented Gln transfer from astrocytes to neurons as well as the location of Gln-derived Glu, GABA and Asp in the synaptic terminals. Patch-clamp studies in brain slices and astrocyte/neuron co-cultures have provided functional evidence that uninterrupted Gln synthesis in astrocytes and its transport to neurons, as mediated by specific carriers, promotes glutamatergic and GABA-ergic transmission. Gln entry into the neuronal compartment is facilitated by its abundance in the extracellular spaces relative to other amino acids. Gln also appears to affect neurotransmission directly by interacting with the NMDA class of Glu receptors. Transmission may also be modulated by alterations in cell membrane polarity related to the electrogenic nature of Gln transport or to uncoupled ion conductances in the neuronal or glial cell membranes elicited by Gln transporters. In addition, Gln appears to modulate the synthesis of the gaseous messenger, nitric oxide (NO), by controlling the supply to the cells of its precursor, arginine. Disturbances of Gln metabolism and/or transport contribute to changes in Glu-ergic or GABA-ergic transmission associated with different pathological conditions of the brain, which are best recognized in epilepsy, hepatic encephalopathy and manganese encephalopathy.
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44
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McKenna MC. Glutamate dehydrogenase in brain mitochondria: do lipid modifications and transient metabolon formation influence enzyme activity? Neurochem Int 2011; 59:525-33. [PMID: 21771624 DOI: 10.1016/j.neuint.2011.07.003] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2011] [Revised: 06/30/2011] [Accepted: 07/03/2011] [Indexed: 11/17/2022]
Abstract
Metabolism of glutamate, the primary excitatory neurotransmitter in brain, is complex and of paramount importance to overall brain function. Thus, understanding the regulation of enzymes involved in formation and disposal of glutamate and related metabolites is crucial to understanding glutamate metabolism. Glutamate dehydrogenase (GDH) is a pivotal enzyme that links amino acid metabolism and TCA cycle activity in brain and other tissues. The allosteric regulation of GDH has been extensively studied and characterized. Less is known about the influence of lipid modifications on GDH activity, and the participation of GDH in transient heteroenzyme complexes (metabolons) that can greatly influence metabolism by altering kinetic parameters and lead to channeling of metabolites. This review summarizes evidence for palmitoylation and acylation of GDH, information on protein binding, and information regarding the participation of GDH in transient heteroenzyme complexes. Recent studies suggest that a number of other proteins can bind to GDH altering activity and overall metabolism. It is likely that these modifications and interactions contribute additional levels of regulation of GDH activity and glutamate metabolism.
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Affiliation(s)
- Mary C McKenna
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
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45
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Had-Aissouni L. Toward a new role for plasma membrane sodium-dependent glutamate transporters of astrocytes: maintenance of antioxidant defenses beyond extracellular glutamate clearance. Amino Acids 2011; 42:181-97. [DOI: 10.1007/s00726-011-0863-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Accepted: 02/17/2011] [Indexed: 01/17/2023]
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46
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Gwak YS, Hulsebosch CE. GABA and central neuropathic pain following spinal cord injury. Neuropharmacology 2011; 60:799-808. [PMID: 21216257 DOI: 10.1016/j.neuropharm.2010.12.030] [Citation(s) in RCA: 149] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 12/02/2010] [Accepted: 12/22/2010] [Indexed: 12/31/2022]
Abstract
Spinal cord injury induces maladaptive synaptic transmission in the somatosensory system that results in chronic central neuropathic pain. Recent literature suggests that glial-neuronal interactions are important modulators in synaptic transmission following spinal cord injury. Neuronal hyperexcitability is one of the predominant phenomenon caused by maladaptive synaptic transmission via altered glial-neuronal interactions after spinal cord injury. In the somatosensory system, spinal inhibitory neurons counter balance the enhanced synaptic transmission from peripheral input. For a decade, the literature suggests that hypofunction of GABAergic inhibitory tone is an important factor in the enhanced synaptic transmission that often results in neuronal hyperexcitability in dorsal horn neurons following spinal cord injury. Neurons and glial cells synergistically control intracellular chloride ion gradients via modulation of chloride transporters, extracellular glutamate and GABA concentrations via uptake mechanisms. Thus, the intracellular "GABA-glutamate-glutamine cycle" is maintained for normal physiological homeostasis. However, hyperexcitable neurons and glial activation after spinal cord injury disrupts the balance of chloride ions, glutamate and GABA distribution in the spinal dorsal horn and results in chronic neuropathic pain. In this review, we address spinal cord injury induced mechanisms in hypofunction of GABAergic tone that results in chronic central neuropathic pain. This article is part of a Special Issue entitled 'Synaptic Plasticity & Interneurons'.
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Affiliation(s)
- Young S Gwak
- Department of Neuroscience & Cell Biology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1043, USA.
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47
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Pardo B, Rodrigues TB, Contreras L, Garzón M, Llorente-Folch I, Kobayashi K, Saheki T, Cerdan S, Satrústegui J. Brain glutamine synthesis requires neuronal-born aspartate as amino donor for glial glutamate formation. J Cereb Blood Flow Metab 2011; 31:90-101. [PMID: 20736955 PMCID: PMC3049464 DOI: 10.1038/jcbfm.2010.146] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The glutamate-glutamine cycle faces a drain of glutamate by oxidation, which is balanced by the anaplerotic synthesis of glutamate and glutamine in astrocytes. De novo synthesis of glutamate by astrocytes requires an amino group whose origin is unknown. The deficiency in Aralar/AGC1, the main mitochondrial carrier for aspartate-glutamate expressed in brain, results in a drastic fall in brain glutamine production but a modest decrease in brain glutamate levels, which is not due to decreases in neuronal or synaptosomal glutamate content. In vivo (13)C nuclear magnetic resonance labeling with (13)C(2)acetate or (1-(13)C) glucose showed that the drop in brain glutamine is due to a failure in glial glutamate synthesis. Aralar deficiency induces a decrease in aspartate content, an increase in lactate production, and lactate-to-pyruvate ratio in cultured neurons but not in cultured astrocytes, indicating that Aralar is only functional in neurons. We find that aspartate, but not other amino acids, increases glutamate synthesis in both control and aralar-deficient astrocytes, mainly by serving as amino donor. These findings suggest the existence of a neuron-to-astrocyte aspartate transcellular pathway required for astrocyte glutamate synthesis and subsequent glutamine formation. This pathway may provide a mechanism to transfer neuronal-born redox equivalents to mitochondria in astrocytes.
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Affiliation(s)
- Beatriz Pardo
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa UAM-CSIC, and CIBER de Enfermedades Raras, Universidad Autónoma de Madrid, Madrid, Spain
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48
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Murín R, Mohammadi G, Kowtharapu BS, Leibfritz D, Hamprecht B. Metabolism of [U-(13)C]aspartate by astroglial cultures: nuclear magnetic resonance analysis of the culture media. Neurochem Res 2010; 35:2053-61. [PMID: 21107687 DOI: 10.1007/s11064-010-0326-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/11/2010] [Indexed: 11/29/2022]
Abstract
In brain the amino acid L-aspartate serves roles as: (1) putative transmitter, (2) protein precursor, (3) donor of atoms for the biosynthesis of pyrimidine and purine bases, and (4) fuel for energy metabolism. Astrocytes dominate aspartate clearance in brain, and in culture they take up aspartate and quickly metabolize it. In brain, only astrocytes were shown to express the enzymes for de novo pyrimidine biosynthesis. To gain more details about the spectrum of metabolites generated from aspartate and subsequently released by cultured astrocytes a (13)C-nuclear magnetic resonance analysis was performed of [U-(13)C]aspartate supplemented incubation media exposed to astroglial cultures. The results show that astrocytes readily metabolize aspartate and release into their culture media (13)C-isotopomers of lactate, glutamine, citrate and alanine. Despite the presence in astroglial cells of two tandem enzymes of pyrimidine biosynthesis and their mRNAs, pyrimidine nucleotide-related heterocyclic compounds such as dihydroorotate and orotate could not be detected in the culture media.
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Affiliation(s)
- Radovan Murín
- Interfaculty Institute for Biochemistry, University of Tuebingen, Hoppe-Seyler-Str 4, 72076 Tuebingen, Germany
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49
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Han Q, Cai T, Tagle DA, Li J. Structure, expression, and function of kynurenine aminotransferases in human and rodent brains. Cell Mol Life Sci 2010; 67:353-68. [PMID: 19826765 PMCID: PMC2867614 DOI: 10.1007/s00018-009-0166-4] [Citation(s) in RCA: 170] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Revised: 09/27/2009] [Accepted: 09/29/2009] [Indexed: 01/12/2023]
Abstract
Kynurenine aminotransferases (KATs) catalyze the synthesis of kynurenic acid (KYNA), an endogenous antagonist of N-methyl-D: -aspartate and alpha 7-nicotinic acetylcholine receptors. Abnormal KYNA levels in human brains are implicated in the pathophysiology of schizophrenia, Alzheimer's disease, and other neurological disorders. Four KATs have been reported in mammalian brains, KAT I/glutamine transaminase K/cysteine conjugate beta-lyase 1, KAT II/aminoadipate aminotransferase, KAT III/cysteine conjugate beta-lyase 2, and KAT IV/glutamic-oxaloacetic transaminase 2/mitochondrial aspartate aminotransferase. KAT II has a striking tertiary structure in N-terminal part and forms a new subgroup in fold type I aminotransferases, which has been classified as subgroup Iepsilon. Knowledge regarding KATs is vast and complex; therefore, this review is focused on recent important progress of their gene characterization, physiological and biochemical function, and structural properties. The biochemical differences of four KATs, specific enzyme activity assays, and the structural insights into the mechanism of catalysis and inhibition of these enzymes are discussed.
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Affiliation(s)
- Qian Han
- Department of Biochemistry, Virginia Tech, Blacksburg, VA 24061 USA
| | - Tao Cai
- OIIB, NIDCR, National Institutes of Health, Bethesda MD, 20892-4322 USA
| | - Danilo A. Tagle
- Neuroscience Center, NINDS, National Institutes of Health, Bethesda, MD 2089-29525 USA
| | - Jianyong Li
- Department of Biochemistry, Virginia Tech, Blacksburg, VA 24061 USA
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50
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Gallagher CN, Carpenter KLH, Grice P, Howe DJ, Mason A, Timofeev I, Menon DK, Kirkpatrick PJ, Pickard JD, Sutherland GR, Hutchinson PJ. The human brain utilizes lactate via the tricarboxylic acid cycle: a 13C-labelled microdialysis and high-resolution nuclear magnetic resonance study. ACTA ACUST UNITED AC 2009; 132:2839-49. [PMID: 19700417 DOI: 10.1093/brain/awp202] [Citation(s) in RCA: 155] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Energy metabolism in the human brain is not fully understood. Classically, glucose is regarded as the major energy substrate. However, lactate (conventionally a product of anaerobic metabolism) has been proposed to act as an energy source, yet whether this occurs in man is not known. Here we show that the human brain can indeed utilize lactate as an energy source via the tricarboxylic acid cycle. We used a novel combination of (13)C-labelled cerebral microdialysis both to deliver (13)C substrates into the brain and recover (13)C metabolites from the brain, and high-resolution (13)C nuclear magnetic resonance. Microdialysis catheters were placed in the vicinity of focal lesions and in relatively less injured regions of brain, in patients with traumatic brain injury. Infusion with 2-(13)C-acetate or 3-(13)C-lactate produced (13)C signals for glutamine C4, C3 and C2, indicating tricarboxylic acid cycle operation followed by conversion of glutamate to glutamine. This is the first direct demonstration of brain utilization of lactate as an energy source in humans.
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Affiliation(s)
- Clare N Gallagher
- Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge, UK
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