1
|
Idumah G, Somersalo E, Calvetti D. A spatially distributed model of brain metabolism highlights the role of diffusion in brain energy metabolism. J Theor Biol 2023; 572:111567. [PMID: 37393987 DOI: 10.1016/j.jtbi.2023.111567] [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: 10/26/2022] [Revised: 06/20/2023] [Accepted: 06/22/2023] [Indexed: 07/04/2023]
Abstract
The different active roles of neurons and astrocytes during neuronal activation are associated with the metabolic processes necessary to supply the energy needed for their respective tasks at rest and during neuronal activation. Metabolism, in turn, relies on the delivery of metabolites and removal of toxic byproducts through diffusion processes and the cerebral blood flow. A comprehensive mathematical model of brain metabolism should account not only for the biochemical processes and the interaction of neurons and astrocytes, but also the diffusion of metabolites. In the present article, we present a computational methodology based on a multidomain model of the brain tissue and a homogenization argument for the diffusion processes. In our spatially distributed compartment model, communication between compartments occur both through local transport fluxes, as is the case within local astrocyte-neuron complexes, and through diffusion of some substances in some of the compartments. The model assumes that diffusion takes place in the extracellular space (ECS) and in the astrocyte compartment. In the astrocyte compartment, the diffusion across the syncytium network is implemented as a function of gap junction strength. The diffusion process is implemented numerically by means of a finite element method (FEM) based spatial discretization, and robust stiff solvers are used to time integrate the resulting large system. Computed experiments show the effects of ECS tortuosity, gap junction strength and spatial anisotropy in the astrocyte network on the brain energy metabolism.
Collapse
Affiliation(s)
- Gideon Idumah
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, USA
| | - Erkki Somersalo
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, USA
| | - Daniela Calvetti
- Department of Mathematics, Applied Mathematics and Statistics, Case Western Reserve University, USA.
| |
Collapse
|
2
|
Kumari M, Arora P, Sharma P, Hasija Y, Rana P, D'souza MM, Chandra N, Trivedi R. Acute metabolic alterations in the hippocampus are associated with decreased acetylation after blast induced TBI. Metabolomics 2023; 19:5. [PMID: 36635559 DOI: 10.1007/s11306-022-01970-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Accepted: 12/21/2022] [Indexed: 01/14/2023]
Abstract
INTRODUCTION Blast induced Traumatic brain injury (BI-TBI) is common among military personnels as well as war affected civilians. In the war zone, people can also encounter repeated exposure of blast wave, which may affect their cognition and metabolic alterations. OBJECTIVE In this study we assess the metabolic and histological changes in the hippocampus of rats at 24 h post injury. METHOD Rats were divided into four groups: (i) Sham; (ii) Mild TBI (mi); (iii) Moderate TBI (mo); and (iv) Repetitive mild TBI (rm TBI) and then subjected to different intensities of blast exposure. Hippocampal tissues were collected after 24 h of injury for proton nuclear magnetic resonance spectroscopy (1H NMR spectroscopy) and immunohistochemical (IHC) analysis. RESULTS The metabolic alterations were found in the hippocampal tissue samples and these alterations showed significant change in glutamate, N-Acetylaspartic acid (NAA), acetate, creatine, phosphoethanolamine (PE), ethanolamine and PC/choline concentrations in rmTBI rats only. IHC studies revealed that AH3 (Acetyl histone) positive cells were decreased in rm TBI tissue samples in comparison to other TBI groups and sham rats. This might reflect an epigenetic alteration due to repeated blast exposure at 24 h post injury. Additionally, astrogliosis was observed in miTBI and moTBI hippocampal tissue while no change was observed in rmTBI tissues. CONCLUSION The present study reports altered acetylation in the presence of altered metabolism in hippocampal tissue of blast induced rmTBI at 24 h post injury. Mechanistic understanding of these intertwined processes may help in the development of better therapeutic pathways and agents for blast induced TBI in near future.
Collapse
Affiliation(s)
- Megha Kumari
- Radiological, Nuclear and Imaging Sciences (RNAIS), Institute of Nuclear Medicine and Allied Science (INMAS), DRDO, Delhi, India
- Department of Biotechnology, Delhi Technological University, Delhi, 110042, India
| | - Palkin Arora
- Radiological, Nuclear and Imaging Sciences (RNAIS), Institute of Nuclear Medicine and Allied Science (INMAS), DRDO, Delhi, India
- Department of Biochemistry, Panjab University, Chandigarh, 160014, India
| | - Priyanka Sharma
- Radiological, Nuclear and Imaging Sciences (RNAIS), Institute of Nuclear Medicine and Allied Science (INMAS), DRDO, Delhi, India
| | - Yasha Hasija
- Department of Biotechnology, Delhi Technological University, Delhi, 110042, India
| | - Poonam Rana
- Radiological, Nuclear and Imaging Sciences (RNAIS), Institute of Nuclear Medicine and Allied Science (INMAS), DRDO, Delhi, India
| | - Maria M D'souza
- Radiological, Nuclear and Imaging Sciences (RNAIS), Institute of Nuclear Medicine and Allied Science (INMAS), DRDO, Delhi, India
| | - Namas Chandra
- Center for Injury Biomechanics, New Jersey Institute of Technology, 323 Dr Martin Luther King Jr Blvd, Newark, NJ, 07102, USA
| | - Richa Trivedi
- Radiological, Nuclear and Imaging Sciences (RNAIS), Institute of Nuclear Medicine and Allied Science (INMAS), DRDO, Delhi, India.
| |
Collapse
|
3
|
Lee MH, Hwang YH, Yun CS, Han BS, Kim DY. Altered small-world property of a dynamic metabolic network in murine left hippocampus after exposure to acute stress. Sci Rep 2022; 12:3885. [PMID: 35273207 PMCID: PMC8913833 DOI: 10.1038/s41598-022-07586-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 02/18/2022] [Indexed: 11/09/2022] Open
Abstract
The acute stress response is a natural and fundamental reaction that balances the physiological conditions of the brain. To maintain homeostasis in the brain, the response is based on changes over time in hormones and neurotransmitters, which are related to resilience and can adapt successfully to acute stress. This increases the need for dynamic analysis over time, and new approaches to examine the relationship between metabolites have emerged. This study investigates whether the constructed metabolic network is a realistic or a random network and is affected by acute stress. While the metabolic network in the control group met the criteria for small-worldness at all time points, the metabolic network in the stress group did not at some time points, and the small-worldness had resilience after the fifth time point. The backbone metabolic network only met the criteria for small-worldness in the control group. Additionally, creatine had lower local efficiency in the stress group than the control group, and for the backbone metabolic network, creatine and glutamate were lower and higher in the stress group than the control group, respectively. These findings provide evidence of metabolic imbalance that may be a pre-stage of alterations to brain structure due to acute stress.
Collapse
Affiliation(s)
- Min-Hee Lee
- Institute of Human Genomic Study, College of Medicine, Korea University Ansan Hospital, Ansan, Republic of Korea
| | - Yoon Ho Hwang
- Department of Biomedical Engineering, Yonsei University, Wonju, Republic of Korea
| | - Chang-Soo Yun
- Department of Radiation Convergence Engineering, Yonsei University, Wonju, Republic of Korea
| | - Bong Soo Han
- Department of Radiation Convergence Engineering, Yonsei University, Wonju, Republic of Korea
| | - Dong Youn Kim
- Department of Biomedical Engineering, Yonsei University, Wonju, Republic of Korea.
| |
Collapse
|
4
|
González J, Pinzón A, Angarita-Rodríguez A, Aristizabal AF, Barreto GE, Martín-Jiménez C. Advances in Astrocyte Computational Models: From Metabolic Reconstructions to Multi-omic Approaches. Front Neuroinform 2020; 14:35. [PMID: 32848690 PMCID: PMC7426703 DOI: 10.3389/fninf.2020.00035] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2020] [Accepted: 07/14/2020] [Indexed: 12/12/2022] Open
Abstract
The growing importance of astrocytes in the field of neuroscience has led to a greater number of computational models devoted to the study of astrocytic functions and their metabolic interactions with neurons. The modeling of these interactions demands a combined understanding of brain physiology and the development of computational frameworks based on genomic-scale reconstructions, system biology, and dynamic models. These computational approaches have helped to highlight the neuroprotective mechanisms triggered by astrocytes and other glial cells, both under normal conditions and during neurodegenerative processes. In the present review, we evaluate some of the most relevant models of astrocyte metabolism, including genome-scale reconstructions and astrocyte-neuron interactions developed in the last few years. Additionally, we discuss novel strategies from the multi-omics perspective and computational models of other glial cell types that will increase our knowledge in brain metabolism and its association with neurodegenerative diseases.
Collapse
Affiliation(s)
- Janneth González
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá, Colombia
| | - Andrés Pinzón
- Laboratorio de Bioinformática y Biología de Sistemas, Universidad Nacional de Colombia Bogotá, Bogotá, Colombia
| | - Andrea Angarita-Rodríguez
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá, Colombia.,Laboratorio de Bioinformática y Biología de Sistemas, Universidad Nacional de Colombia Bogotá, Bogotá, Colombia
| | - Andrés Felipe Aristizabal
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá, Colombia
| | - George E Barreto
- Department of Biological Sciences, University of Limerick, Limerick, Ireland.,Health Research Institute, University of Limerick, Limerick, Ireland
| | - Cynthia Martín-Jiménez
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá, Colombia
| |
Collapse
|
5
|
McGuire JL, DePasquale EAK, Watanabe M, Anwar F, Ngwenya LB, Atluri G, Romick-Rosendale LE, McCullumsmith RE, Evanson NK. Chronic Dysregulation of Cortical and Subcortical Metabolism After Experimental Traumatic Brain Injury. Mol Neurobiol 2019; 56:2908-2921. [PMID: 30069831 PMCID: PMC7584385 DOI: 10.1007/s12035-018-1276-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 07/23/2018] [Indexed: 02/03/2023]
Abstract
Traumatic brain injury (TBI) is a leading cause of death and long-term disability worldwide. Although chronic disability is common after TBI, effective treatments remain elusive and chronic TBI pathophysiology is not well understood. Early after TBI, brain metabolism is disrupted due to unregulated ion release, mitochondrial damage, and interruption of molecular trafficking. This metabolic disruption causes at least part of the TBI pathology. However, it is not clear how persistent or pervasive metabolic injury is at later stages of injury. Using untargeted 1H-NMR metabolomics, we examined ex vivo hippocampus, striatum, thalamus, frontal cortex, and brainstem tissue in a rat lateral fluid percussion model of chronic brain injury. We found altered tissue concentrations of metabolites in the hippocampus and thalamus consistent with dysregulation of energy metabolism and excitatory neurotransmission. Furthermore, differential correlation analysis provided additional evidence of metabolic dysregulation, most notably in brainstem and frontal cortex, suggesting that metabolic consequences of injury are persistent and widespread. Interestingly, the patterns of network changes were region-specific. The individual metabolic signatures after injury in different structures of the brain at rest may reflect different compensatory mechanisms engaged to meet variable metabolic demands across brain regions.
Collapse
Affiliation(s)
- Jennifer L McGuire
- Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, 45267, USA.
| | - Erica A K DePasquale
- Graduate Program in Biomedical Informatics, University of Cincinnati, Cincinnati, OH, 45267, USA
| | - Miki Watanabe
- Division of Pathology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| | - Fatima Anwar
- Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, 45267, USA
| | - Laura B Ngwenya
- Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, 45267, USA
- Department of Neurology and Rehabilitation Medicine, University of Cincinnati, Cincinnati, OH, 45267, USA
| | - Gowtham Atluri
- Graduate Program in Biomedical Informatics, University of Cincinnati, Cincinnati, OH, 45267, USA
- Department of Electrical Engineering and Computer Science, University of Cincinnati, Cincinnati, OH, 45267, USA
| | | | - Robert E McCullumsmith
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH, 45267, USA
| | - Nathan K Evanson
- Department of Pediatrics, University of Cincinnati, Cincinnati, OH, 45267, USA
- Division of Pediatric Rehabilitation Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA
| |
Collapse
|
6
|
Mahan VL. Neurointegrity and neurophysiology: astrocyte, glutamate, and carbon monoxide interactions. Med Gas Res 2019; 9:24-45. [PMID: 30950417 PMCID: PMC6463446 DOI: 10.4103/2045-9912.254639] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Accepted: 02/15/2019] [Indexed: 12/27/2022] Open
Abstract
Astrocyte contributions to brain function and prevention of neuropathologies are as extensive as that of neurons. Astroglial regulation of glutamate, a primary neurotransmitter, is through uptake, release through vesicular and non-vesicular pathways, and catabolism to intermediates. Homeostasis by astrocytes is considered to be of primary importance in determining normal central nervous system health and central nervous system physiology - glutamate is central to dynamic physiologic changes and central nervous system stability. Gasotransmitters may affect diverse glutamate interactions positively or negatively. The effect of carbon monoxide, an intrinsic central nervous system gasotransmitter, in the complex astrocyte homeostasis of glutamate may offer insights to normal brain development, protection, and its use as a neuromodulator and neurotherapeutic. In this article, we will review the effects of carbon monoxide on astrocyte homeostasis of glutamate.
Collapse
Affiliation(s)
- Vicki L. Mahan
- Division of Pediatric Cardiothoracic Surgery in the Department of Surgery, St. Christopher's Hospital for Children/Drexel University College of Medicine, Philadelphia, PA, USA
| |
Collapse
|
7
|
Metabolomics and mitochondrial dysfunction in Alzheimer’s disease. Genes Genomics 2017. [DOI: 10.1007/s13258-016-0494-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
|
8
|
Martín-Jiménez CA, Salazar-Barreto D, Barreto GE, González J. Genome-Scale Reconstruction of the Human Astrocyte Metabolic Network. Front Aging Neurosci 2017; 9:23. [PMID: 28243200 PMCID: PMC5303712 DOI: 10.3389/fnagi.2017.00023] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 01/27/2017] [Indexed: 12/22/2022] Open
Abstract
Astrocytes are the most abundant cells of the central nervous system; they have a predominant role in maintaining brain metabolism. In this sense, abnormal metabolic states have been found in different neuropathological diseases. Determination of metabolic states of astrocytes is difficult to model using current experimental approaches given the high number of reactions and metabolites present. Thus, genome-scale metabolic networks derived from transcriptomic data can be used as a framework to elucidate how astrocytes modulate human brain metabolic states during normal conditions and in neurodegenerative diseases. We performed a Genome-Scale Reconstruction of the Human Astrocyte Metabolic Network with the purpose of elucidating a significant portion of the metabolic map of the astrocyte. This is the first global high-quality, manually curated metabolic reconstruction network of a human astrocyte. It includes 5,007 metabolites and 5,659 reactions distributed among 8 cell compartments, (extracellular, cytoplasm, mitochondria, endoplasmic reticle, Golgi apparatus, lysosome, peroxisome and nucleus). Using the reconstructed network, the metabolic capabilities of human astrocytes were calculated and compared both in normal and ischemic conditions. We identified reactions activated in these two states, which can be useful for understanding the astrocytic pathways that are affected during brain disease. Additionally, we also showed that the obtained flux distributions in the model, are in accordance with literature-based findings. Up to date, this is the most complete representation of the human astrocyte in terms of inclusion of genes, proteins, reactions and metabolic pathways, being a useful guide for in-silico analysis of several metabolic behaviors of the astrocyte during normal and pathologic states.
Collapse
Affiliation(s)
- Cynthia A Martín-Jiménez
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana Bogotá, Colombia
| | - Diego Salazar-Barreto
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana Bogotá, Colombia
| | - George E Barreto
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad JaverianaBogotá, Colombia; Instituto de Ciencias Biomédicas, Universidad Autónoma de ChileSantiago, Chile
| | - Janneth González
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana Bogotá, Colombia
| |
Collapse
|
9
|
DiNuzzo M, Giove F, Maraviglia B, Mangia S. Computational Flux Balance Analysis Predicts that Stimulation of Energy Metabolism in Astrocytes and their Metabolic Interactions with Neurons Depend on Uptake of K + Rather than Glutamate. Neurochem Res 2016; 42:202-216. [PMID: 27628293 PMCID: PMC5283516 DOI: 10.1007/s11064-016-2048-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 08/22/2016] [Accepted: 08/24/2016] [Indexed: 12/04/2022]
Abstract
Brain activity involves essential functional and metabolic interactions between neurons and astrocytes. The importance of astrocytic functions to neuronal signaling is supported by many experiments reporting high rates of energy consumption and oxidative metabolism in these glial cells. In the brain, almost all energy is consumed by the Na+/K+ ATPase, which hydrolyzes 1 ATP to move 3 Na+ outside and 2 K+ inside the cells. Astrocytes are commonly thought to be primarily involved in transmitter glutamate cycling, a mechanism that however only accounts for few % of brain energy utilization. In order to examine the participation of astrocytic energy metabolism in brain ion homeostasis, here we attempted to devise a simple stoichiometric relation linking glutamatergic neurotransmission to Na+ and K+ ionic currents. To this end, we took into account ion pumps and voltage/ligand-gated channels using the stoichiometry derived from available energy budget for neocortical signaling and incorporated this stoichiometric relation into a computational metabolic model of neuron-astrocyte interactions. We aimed at reproducing the experimental observations about rates of metabolic pathways obtained by 13C-NMR spectroscopy in rodent brain. When simulated data matched experiments as well as biophysical calculations, the stoichiometry for voltage/ligand-gated Na+ and K+ fluxes generated by neuronal activity was close to a 1:1 relationship, and specifically 63/58 Na+/K+ ions per glutamate released. We found that astrocytes are stimulated by the extracellular K+ exiting neurons in excess of the 3/2 Na+/K+ ratio underlying Na+/K+ ATPase-catalyzed reaction. Analysis of correlations between neuronal and astrocytic processes indicated that astrocytic K+ uptake, but not astrocytic Na+-coupled glutamate uptake, is instrumental for the establishment of neuron-astrocytic metabolic partnership. Our results emphasize the importance of K+ in stimulating the activation of astrocytes, which is relevant to the understanding of brain activity and energy metabolism at the cellular level.
Collapse
Affiliation(s)
- Mauro DiNuzzo
- Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 24.2.40, 2200, Copenhagen N, Denmark.
| | - Federico Giove
- Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", Rome, Italy.,Fondazione Santa Lucia IRCCS, Rome, Italy
| | - Bruno Maraviglia
- Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", Rome, Italy.,Fondazione Santa Lucia IRCCS, Rome, Italy
| | - Silvia Mangia
- Center for Magnetic Resonance Research, Department of Radiology, Univeristy of Minnesota, Minneapolis, MN, USA
| |
Collapse
|
10
|
Logica T, Riviere S, Holubiec MI, Castilla R, Barreto GE, Capani F. Metabolic Changes Following Perinatal Asphyxia: Role of Astrocytes and Their Interaction with Neurons. Front Aging Neurosci 2016; 8:116. [PMID: 27445788 PMCID: PMC4921470 DOI: 10.3389/fnagi.2016.00116] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 05/03/2016] [Indexed: 11/13/2022] Open
Abstract
Perinatal Asphyxia (PA) represents an important cause of severe neurological deficits including delayed mental and motor development, epilepsy, major cognitive deficits and blindness. The interaction between neurons, astrocytes and endothelial cells plays a central role coupling energy supply with changes in neuronal activity. Traditionally, experimental research focused on neurons, whereas astrocytes have been more related to the damage mechanisms of PA. Astrocytes carry out a number of functions that are critical to normal nervous system function, including uptake of neurotransmitters, regulation of pH and ion concentrations, and metabolic support for neurons. In this work, we aim to review metabolic neuron-astrocyte interactions with the purpose of encourage further research in this area in the context of PA, which is highly complex and its mechanisms and pathways have not been fully elucidated to this day.
Collapse
Affiliation(s)
- Tamara Logica
- Laboratorio de Citoarquitectura y Plasticidad Neuronal, Facultad de Medicina, Instituto de Investigaciones Cardiológicas Prof. Dr. Alberto C. Taquini (ININCA), UBA-CONICET, CABA Buenos Aires, Argentina
| | - Stephanie Riviere
- Laboratorio de Biología Molecular, Facultad de Medicina, Instituto de Investigaciones cardiológicas Prof. Dr. Alberto C. Taquini (ININCA), UBA-CONICET, CABA Buenos Aires, Argentina
| | - Mariana I Holubiec
- Laboratorio de Citoarquitectura y Plasticidad Neuronal, Facultad de Medicina, Instituto de Investigaciones Cardiológicas Prof. Dr. Alberto C. Taquini (ININCA), UBA-CONICET, CABA Buenos Aires, Argentina
| | - Rocío Castilla
- Laboratorio de Biología Molecular, Facultad de Medicina, Instituto de Investigaciones cardiológicas Prof. Dr. Alberto C. Taquini (ININCA), UBA-CONICET, CABA Buenos Aires, Argentina
| | - George E Barreto
- Departamento de Nutrición y Bioquímica, Facultad de Ciencias, Pontificia Universidad Javeriana Bogotá Bogotá, Colombia
| | - Francisco Capani
- Laboratorio de Citoarquitectura y Plasticidad Neuronal, Facultad de Medicina, Instituto de Investigaciones Cardiológicas Prof. Dr. Alberto C. Taquini (ININCA), UBA-CONICET, CABABuenos Aires, Argentina; Departamento de Biología, Universidad Argentina JF KennedyBuenos Aires, Argentina; Investigador Asociado, Universidad Autónoma de ChileSantiago, Chile
| |
Collapse
|
11
|
Central Role of Glutamate Metabolism in the Maintenance of Nitrogen Homeostasis in Normal and Hyperammonemic Brain. Biomolecules 2016; 6:biom6020016. [PMID: 27023624 PMCID: PMC4919911 DOI: 10.3390/biom6020016] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 03/10/2016] [Accepted: 03/15/2016] [Indexed: 12/21/2022] Open
Abstract
Glutamate is present in the brain at an average concentration—typically 10–12 mM—far in excess of those of other amino acids. In glutamate-containing vesicles in the brain, the concentration of glutamate may even exceed 100 mM. Yet because glutamate is a major excitatory neurotransmitter, the concentration of this amino acid in the cerebral extracellular fluid must be kept low—typically µM. The remarkable gradient of glutamate in the different cerebral compartments: vesicles > cytosol/mitochondria > extracellular fluid attests to the extraordinary effectiveness of glutamate transporters and the strict control of enzymes of glutamate catabolism and synthesis in well-defined cellular and subcellular compartments in the brain. A major route for glutamate and ammonia removal is via the glutamine synthetase (glutamate ammonia ligase) reaction. Glutamate is also removed by conversion to the inhibitory neurotransmitter γ-aminobutyrate (GABA) via the action of glutamate decarboxylase. On the other hand, cerebral glutamate levels are maintained by the action of glutaminase and by various α-ketoglutarate-linked aminotransferases (especially aspartate aminotransferase and the mitochondrial and cytosolic forms of the branched-chain aminotransferases). Although the glutamate dehydrogenase reaction is freely reversible, owing to rapid removal of ammonia as glutamine amide, the direction of the glutamate dehydrogenase reaction in the brain in vivo is mainly toward glutamate catabolism rather than toward the net synthesis of glutamate, even under hyperammonemia conditions. During hyperammonemia, there is a large increase in cerebral glutamine content, but only small changes in the levels of glutamate and α-ketoglutarate. Thus, the channeling of glutamate toward glutamine during hyperammonemia results in the net synthesis of 5-carbon units. This increase in 5-carbon units is accomplished in part by the ammonia-induced stimulation of the anaplerotic enzyme pyruvate carboxylase. Here, we suggest that glutamate may constitute a buffer or bulwark against changes in cerebral amine and ammonia nitrogen. Although the glutamate transporters are briefly discussed, the major emphasis of the present review is on the enzymology contributing to the maintenance of glutamate levels under normal and hyperammonemic conditions. Emphasis will also be placed on the central role of glutamate in the glutamine-glutamate and glutamine-GABA neurotransmitter cycles between neurons and astrocytes. Finally, we provide a brief and selective discussion of neuropathology associated with altered cerebral glutamate levels.
Collapse
|
12
|
Verkhratsky A, Nedergaard M, Hertz L. Why are astrocytes important? Neurochem Res 2014; 40:389-401. [PMID: 25113122 DOI: 10.1007/s11064-014-1403-2] [Citation(s) in RCA: 130] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 07/22/2014] [Accepted: 07/26/2014] [Indexed: 12/27/2022]
Abstract
Astrocytes, which populate the grey and white mater of the brain and the spinal cord are highly heterogeneous in their morphology and function. These cells are primarily responsible for homeostasis of the central nervous system (CNS). Most central synapses are surrounded by exceedingly thin astroglial perisynaptic processes, which act as "astroglial cradle" critical for genesis, maturation and maintenance of synaptic connectivity. The perisynaptic glial processes are densely packed with numerous transporters, which provide for homeostasis of ions and neurotransmitters in the synaptic cleft, for local metabolic support and for release of astroglial derived scavengers of reactive oxygen species. Through perivascular processes astrocytes contribute to blood-brain barrier and form "glymphatic" drainage system of the CNS. Furthermore astrocytes are indispensible for glutamatergic and γ-aminobutyrate-ergic synaptic transmission being the supplier of neurotransmitters precursor glutamine via an astrocytic/neuronal cycle. Pathogenesis of many neurological disorders, including neuropsychiatric and neurodegenerative diseases is defined by loss of homeostatic function (astroglial asthenia) or remodelling of astroglial homoeostatic capabilities. Astroglial cells further contribute to neuropathologies through mounting complex defensive programme generally known as reactive astrogliosis.
Collapse
Affiliation(s)
- Alexei Verkhratsky
- Faculty of Life Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PT, UK,
| | | | | |
Collapse
|
13
|
Hertz L, Rodrigues TB. Astrocytic-Neuronal-Astrocytic Pathway Selection for Formation and Degradation of Glutamate/GABA. Front Endocrinol (Lausanne) 2014; 5:42. [PMID: 24772106 PMCID: PMC3982103 DOI: 10.3389/fendo.2014.00042] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Accepted: 03/19/2014] [Indexed: 12/16/2022] Open
Affiliation(s)
- Leif Hertz
- College of Basic Medical Sciences, China Medical University, Shenyang, China
- *Correspondence: ;
| | - Tiago B. Rodrigues
- CRUK Cambridge Institute and Department of Biochemistry, University of Cambridge, Cambridge, UK
- *Correspondence: ;
| |
Collapse
|
14
|
Cooper AJL. Quantitative analysis of neurotransmitter pathways under steady state conditions - a perspective. Front Endocrinol (Lausanne) 2013; 4:179. [PMID: 24302920 PMCID: PMC3831341 DOI: 10.3389/fendo.2013.00179] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 11/04/2013] [Indexed: 11/29/2022] Open
Abstract
In a contribution to this Research Topic Erkki Somersalo and Daniela Calvetti carried out a mathematical analysis of neurotransmitter pathways in brain, modeling compartmental nitrogen flux among several major participants - ammonia, glutamine, glutamate, GABA, and selected amino acids. This analysis is important because cerebral nitrogen metabolism is perturbed in many diseases, including liver disease and inborn errors of the urea cycle. These diseases result in an elevation of blood ammonia, which is neurotoxic. Here, a brief description is provided of the discovery of cerebral metabolic compartmentation of nitrogen metabolism - a key feature of cerebral glutamate-glutamine and GABA-glutamine cycles. The work of Somersalo and Calvetti is discussed as a model for future studies of normal and pathological cerebral ammonia metabolism.
Collapse
Affiliation(s)
- Arthur J. L. Cooper
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY, USA
- *Correspondence: Arthur J. L. Cooper, Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10520, USA e-mail:
| |
Collapse
|