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Xu W, Borges K. Case for supporting astrocyte energetics in glucose transporter 1 deficiency syndrome. Epilepsia 2024. [PMID: 38767952 DOI: 10.1111/epi.18013] [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: 02/01/2024] [Revised: 04/30/2024] [Accepted: 05/02/2024] [Indexed: 05/22/2024]
Abstract
In glucose transporter 1 deficiency syndrome (Glut1DS), glucose transport into brain is reduced due to impaired Glut1 function in endothelial cells at the blood-brain barrier. This can lead to shortages of glucose in brain and is thought to contribute to seizures. Ketogenic diets are the first-line treatment and, among many beneficial effects, provide auxiliary fuel in the form of ketone bodies that are largely metabolized by neurons. However, Glut1 is also the main glucose transporter in astrocytes. Here, we review data indicating that glucose shortage may also impact astrocytes in addition to neurons and discuss the expected negative biochemical consequences of compromised astrocytic glucose transport for neurons. Based on these effects, auxiliary fuels are needed for both cell types and adding medium chain triglycerides (MCTs) to ketogenic diets is a biochemically superior treatment for Glut1DS compared to classical ketogenic diets. MCTs provide medium chain fatty acids (MCFAs), which are largely metabolized by astrocytes and not neurons. MCFAs supply energy and contribute carbons for glutamine and γ-aminobutyric acid synthesis, and decanoic acid can also block α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors. MCTs do not compete with metabolism of ketone bodies mostly occurring in neurons. Triheptanoin, an anaplerotic but also gluconeogenic uneven MCT, may be another potential addition to ketogenic diets, although maintenance of "ketosis" can be difficult. Gene therapy has also targeted both endothelial cells and astrocytes. Other approaches to increase fuel delivery to the brain currently investigated include exchange of Glut1DS erythrocytes with healthy cells, infusion of lactate, and pharmacological improvement of glucose transport. In conclusion, although it remains difficult to assess impaired astrocytic energy metabolism in vivo, astrocytic energy needs are most likely not met by ketogenic diets in Glut1DS. Thus, we propose prospective studies including monitoring of blood MCFA levels to find optimal doses for add-on MCT to ketogenic diets and assessing of short- and long-term outcomes.
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Affiliation(s)
- Weizhi Xu
- School of Biomedical Sciences, University of Queensland, St Lucia, Queensland, Australia
| | - Karin Borges
- School of Biomedical Sciences, University of Queensland, St Lucia, Queensland, Australia
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2
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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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3
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Fonseca-Barriendos D, Castañeda-Cabral JL, Martínez-Cuevas F, Besio W, Valdés-Cruz A, Rocha L. Transcranial Focal Electric Stimulation Avoids P-Glycoprotein Over-Expression during Electrical Amygdala Kindling and Delays Epileptogenesis in Rats. Life (Basel) 2023; 13:1294. [PMID: 37374077 DOI: 10.3390/life13061294] [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: 04/13/2023] [Revised: 05/23/2023] [Accepted: 05/24/2023] [Indexed: 06/29/2023] Open
Abstract
Recent evidence suggests that P-glycoprotein (P-gp) overexpression mediates hyperexcitability and is associated with epileptogenesis. Transcranial focal electrical stimulation (TFS) delays epileptogenesis and inhibits P-gp overexpression after a generalized seizure. Here, first we measured P-gp expression during epileptogenesis and second, we assessed if TFS antiepileptogenic effect was related with P-gp overexpression avoidance. Male Wistar rats were implanted in right basolateral amygdala and stimulated daily for electrical amygdala kindling (EAK), P-gp expression was assessed during epileptogenesis in relevant brain areas. Stage I group showed 85% increase in P-gp in ipsilateral hippocampus (p < 0.001). Stage III group presented 58% and 57% increase in P-gp in both hippocampi (p < 0.05). Kindled group had 92% and 90% increase in P-gp in both hippocampi (p < 0.01), and 93% and 143% increase in both neocortices (p < 0.01). For the second experiment, TFS was administrated daily after each EAK stimulation for 20 days and P-gp concentration was assessed. No changes were found in the TFS group (p > 0.05). Kindled group showed 132% and 138% increase in P-gp in both hippocampi (p < 0.001) and 51% and 92% increase in both cortices (p < 0.001). Kindled + TFS group presented no changes (p > 0.05). Our experiments revealed that progression of EAK is associated with increased P-gp expression. These changes are structure-specific and dependent on seizure severity. EAK-induced P-gp overexpression would be associated with neuronal hyperexcitability and thus, epileptogenesis. P-gp could be a novel therapeutical target to avoid epileptogenesis. In accordance with this, TFS inhibited P-gp overexpression and interfered with EAK. An important limitation of the present study is that P-gp neuronal expression was not evaluated under the different experimental conditions. Future studies should be carried out to determine P-gp neuronal overexpression in hyperexcitable networks during epileptogenesis. The TFS-induced lessening of P-gp overexpression could be a novel therapeutical strategy to avoid epileptogenesis in high-risk patients.
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Affiliation(s)
- Daniel Fonseca-Barriendos
- Departamento de Farmacobiología, Centro de Investigación y de Estudios Avanzados, Ciudad de México C.P. 14330, Mexico
| | - José Luis Castañeda-Cabral
- Departamento de Biología Celular y Molecular, Centro Universitrio de Ciencias Biológicas y Agropecuaias, Universidad de Guadalajara, Zapopan C.P. 44600, Mexico
| | - Frida Martínez-Cuevas
- Departamento de Farmacobiología, Centro de Investigación y de Estudios Avanzados, Ciudad de México C.P. 14330, Mexico
| | - Walter Besio
- Department of Electrical, Computer, and Biomedical Engineering, University of Rhode Island, Kingston, RI 028881, USA
| | - Alejandro Valdés-Cruz
- Laboratorio de Neurofisiología del Control y la Regulación, Instituto Nacional de Psiquiatría "Ramón de la Fuente Muñiz", Ciudad de México C.P. 14370, Mexico
| | - Luisa Rocha
- Departamento de Farmacobiología, Centro de Investigación y de Estudios Avanzados, Ciudad de México C.P. 14330, Mexico
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4
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Affiliation(s)
- Gerald A. Dienel
- Department of Neurology University of Arkansas for Medical Sciences Little Rock Arkansas USA
- Department of Cell Biology and Physiology University of New Mexico School of Medicine Albuquerque New Mexico USA
| | - Lisa Gillinder
- Mater Hospital South Brisbane Queensland Australia
- Faculty of Medicine Mater Research Institute, University of Queensland St Lucia Queensland Australia
| | - Aileen McGonigal
- Mater Hospital South Brisbane Queensland Australia
- Faculty of Medicine Mater Research Institute, University of Queensland St Lucia Queensland Australia
| | - Karin Borges
- Faculty of Medicine School of Biomedical Sciences, University of Queensland St Lucia Queensland Australia
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5
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Dienel GA, Gillinder L, McGonigal A, Borges K. Potential new roles for glycogen in epilepsy. Epilepsia 2023; 64:29-53. [PMID: 36117414 PMCID: PMC10952408 DOI: 10.1111/epi.17412] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 09/15/2022] [Accepted: 09/15/2022] [Indexed: 01/21/2023]
Abstract
Seizures often originate in epileptogenic foci. Between seizures (interictally), these foci and some of the surrounding tissue often show low signals with 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in many epileptic patients, even when there are no radiologically detectable structural abnormalities. Low FDG-PET signals are thought to reflect glucose hypometabolism. Here, we review knowledge about metabolism of glucose and glycogen and oxidative stress in people with epilepsy and in acute and chronic rodent seizure models. Interictal brain glucose levels are normal and do not cause apparent glucose hypometabolism, which remains unexplained. During seizures, high amounts of fuel are needed to satisfy increased energy demands. Astrocytes consume glycogen as an additional emergency fuel to supplement glucose during high metabolic demand, such as during brain stimulation, stress, and seizures. In rodents, brain glycogen levels drop during induced seizures and increase to higher levels thereafter. Interictally, in people with epilepsy and in chronic epilepsy models, normal glucose but high glycogen levels have been found in the presumed brain areas involved in seizure generation. We present our new hypothesis that as an adaptive response to repeated episodes of high metabolic demand, high interictal glycogen levels in epileptogenic brain areas are used to support energy metabolism and potentially interictal neuronal activity. Glycogenolysis, which can be triggered by stress or oxidative stress, leads to decreased utilization of plasma glucose in epileptogenic brain areas, resulting in low FDG signals that are related to functional changes underlying seizure onset and propagation. This is (partially) reversible after successful surgery. Last, we propose that potential interictal glycogen depletion in epileptogenic and surrounding areas may cause energy shortages in astrocytes, which may impair potassium buffering and contribute to seizure generation. Based on these hypotheses, auxiliary fuels or treatments that support glycogen metabolism may be useful to treat epilepsy.
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Affiliation(s)
- Gerald A. Dienel
- Department of NeurologyUniversity of Arkansas for Medical SciencesLittle RockArkansasUSA
- Department of Cell Biology and PhysiologyUniversity of New Mexico School of MedicineAlbuquerqueNew MexicoUSA
| | - Lisa Gillinder
- Mater HospitalSouth BrisbaneQueenslandAustralia
- Faculty of MedicineMater Research Institute, University of QueenslandSt LuciaQueenslandAustralia
| | - Aileen McGonigal
- Mater HospitalSouth BrisbaneQueenslandAustralia
- Faculty of MedicineMater Research Institute, University of QueenslandSt LuciaQueenslandAustralia
| | - Karin Borges
- Faculty of MedicineSchool of Biomedical Sciences, University of QueenslandSt LuciaQueenslandAustralia
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6
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McNair LM, Mason GF, Chowdhury GM, Jiang L, Ma X, Rothman DL, Waagepetersen HS, Behar KL. Rates of pyruvate carboxylase, glutamate and GABA neurotransmitter cycling, and glucose oxidation in multiple brain regions of the awake rat using a combination of [2- 13C]/[1- 13C]glucose infusion and 1H-[ 13C]NMR ex vivo. J Cereb Blood Flow Metab 2022; 42:1507-1523. [PMID: 35048735 PMCID: PMC9274856 DOI: 10.1177/0271678x221074211] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Anaplerosis occurs predominately in astroglia through the action of pyruvate carboxylase (PC). The rate of PC (Vpc) has been reported for cerebral cortex (or whole brain) of awake humans and anesthetized rodents, but regional brain rates remain largely unknown and, hence, were subjected to investigation in the current study. Awake male rats were infused with either [2-13C]glucose or [1-13C]glucose (n = 27/30) for 8, 15, 30, 60 or 120 min, followed by rapid euthanasia with focused-beam microwave irradiation to the brain. Blood plasma and extracts of cerebellum, hippocampus, striatum, and cerebral cortex were analyzed by 1H-[13C]-NMR to establish 13C-enrichment time courses for glutamate-C4,C3,C2, glutamine-C4,C3, GABA-C2,C3,C4 and aspartate-C2,C3. Metabolic rates were determined by fitting a three-compartment metabolic model (glutamatergic and GABAergic neurons and astroglia) to the eighteen time courses. Vpc varied by 44% across brain regions, being lowest in the cerebellum (0.087 ± 0.004 µmol/g/min) and highest in striatum (0.125 ± 0.009) with intermediate values in cerebral cortex (0.106 ± 0.005) and hippocampus (0.114 ± 0.005). Vpc constituted 13-19% of the oxidative glucose consumption rate. Combination of cerebral cortical data with literature values revealed a positive correlation between Vpc and the rates of glutamate/glutamine-cycling and oxidative glucose consumption, respectively, consistent with earlier observations.
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Affiliation(s)
- Laura M McNair
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Graeme F Mason
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA.,Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, USA.,Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
| | - Golam Mi Chowdhury
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Lihong Jiang
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Xiaoxian Ma
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Douglas L Rothman
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, USA.,Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kevin L Behar
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, USA
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7
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Rothman DL, Dienel GA, Behar KL, Hyder F, DiNuzzo M, Giove F, Mangia S. Glucose sparing by glycogenolysis (GSG) determines the relationship between brain metabolism and neurotransmission. J Cereb Blood Flow Metab 2022; 42:844-860. [PMID: 34994222 PMCID: PMC9254033 DOI: 10.1177/0271678x211064399] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Over the last two decades, it has been established that glucose metabolic fluxes in neurons and astrocytes are proportional to the rates of the glutamate/GABA-glutamine neurotransmitter cycles in close to 1:1 stoichiometries across a wide range of functional energy demands. However, there is presently no mechanistic explanation for these relationships. We present here a theoretical meta-analysis that tests whether the brain's unique compartmentation of glycogen metabolism in the astrocyte and the requirement for neuronal glucose homeostasis lead to the observed stoichiometries. We found that blood-brain barrier glucose transport can be limiting during activation and that the energy demand could only be met if glycogenolysis supports neuronal glucose metabolism by replacing the glucose consumed by astrocytes, a mechanism we call Glucose Sparing by Glycogenolysis (GSG). The predictions of the GSG model are in excellent agreement with a wide range of experimental results from rats, mice, tree shrews, and humans, which were previously unexplained. Glycogenolysis and glucose sparing dictate the energy available to support neuronal activity, thus playing a fundamental role in brain function in health and disease.
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Affiliation(s)
- Douglas L Rothman
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA
| | - Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, AR, USA.,Department of Cell Biology and Physiology, University of New Mexico School of Medicine, Albuquerque, NM, USA
| | - Kevin L Behar
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA.,Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
| | - Fahmeed Hyder
- Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA.,Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Mauro DiNuzzo
- Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Rome, RM, Italy
| | - Federico Giove
- Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Rome, RM, Italy.,Fondazione Santa Lucia IRCCS, Rome, RM, Italy
| | - Silvia Mangia
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, USA
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8
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Young Seo G, Neal ES, Han F, Vidovic D, Nooru-Mohamed F, Dienel GA, Sullivan MA, Borges K. Brain glycogen content is increased in the acute and interictal chronic stages of the mouse pilocarpine model of epilepsy. Epilepsia Open 2022; 7:361-367. [PMID: 35377551 PMCID: PMC9159246 DOI: 10.1002/epi4.12599] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2022] [Revised: 04/01/2022] [Accepted: 04/01/2022] [Indexed: 11/30/2022] Open
Abstract
Glucose is the main brain fuel in fed conditions, while astrocytic glycogen is used as supplemental fuel when the brain is stimulated. Brain glycogen levels are decreased shortly after induced seizures in rodents, but little is known about how glycogen levels are affected interictally in chronic models of epilepsy. Reduced glutamine synthetase activity has been suggested to lead to increased brain glycogen levels in humans with chronic epilepsy. Here, we used the mouse pilocarpine model of epilepsy to investigate whether brain glycogen levels are altered, both acutely and in the chronic stage of the model. One day after pilocarpine‐induced convulsive status epilepticus (CSE), glycogen levels were higher in the hippocampal formation, cerebral cortex, and cerebellum. Opposite to expected, this was accompanied by elevated glutamine synthetase activity in the hippocampus but not the cortex. Increased interictal glycogen amounts were seen in the hippocampal formation and cerebral cortex in the chronic stage of the model (21 days post‐CSE), suggesting long‐lasting alterations in glycogen metabolism. Glycogen solubility in the cerebral cortex was unaltered in this epilepsy mouse model. Glycogen synthase kinase 3 beta (Gsk3b) mRNA levels were reduced in the hippocampal formations of mice in the chronic stage, which may underlie the elevated brain glycogen content in this model. This is the first report of elevated interictal glycogen levels in a chronic epilepsy model. Increased glycogen amounts in the brain may influence seizure susceptibility in this model, and this warrants further investigation.
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Affiliation(s)
- Gi Young Seo
- School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Elliott S Neal
- School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Felicity Han
- School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Diana Vidovic
- School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Fathima Nooru-Mohamed
- School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, AR, USA, 72205.,Department of Cell Biology and Physiology, University of New Mexico School of Medicine, Albuquerque, NM, USA, 87131
| | - Mitchell A Sullivan
- Glycation and Diabetes Group, Mater Research Institute, Translational Research Institute, The University of Queensland, Translational Research Institute, Brisbane, Queensland, 4072, Australia
| | - Karin Borges
- School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, St Lucia, QLD, 4072, Australia
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9
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Zhu Y, Sun Y, Hu J, Pan Z. Insight Into the Mechanism of Exercise Preconditioning in Ischemic Stroke. Front Pharmacol 2022; 13:866360. [PMID: 35350755 PMCID: PMC8957886 DOI: 10.3389/fphar.2022.866360] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 02/21/2022] [Indexed: 01/07/2023] Open
Abstract
Exercise preconditioning has attracted extensive attention to induce endogenous neuroprotection and has become the hotspot in neurotherapy. The training exercise is given multiple times before cerebral ischemia, effectively inducing ischemic tolerance and alleviating secondary brain damage post-stroke. Compared with other preconditioning methods, the main advantages of exercise include easy clinical operation and being readily accepted by patients. However, the specific mechanism behind exercise preconditioning to ameliorate brain injury is complex. It involves multi-pathway and multi-target regulation, including regulation of inflammatory response, oxidative stress, apoptosis inhibition, and neurogenesis promotion. The current review summarizes the recent studies on the mechanism of neuroprotection induced by exercise, providing the theoretical basis of applying exercise therapy to prevent and treat ischemic stroke. In addition, we highlight the various limitations and future challenges of translational medicine from fundamental study to clinical application.
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Affiliation(s)
- Yuanhan Zhu
- Department of Neurosurgery, Zhejiang Rongjun Hospital, Jiaxing, China
| | - Yulin Sun
- Department of Neurosurgery, Zhejiang Rongjun Hospital, Jiaxing, China
| | - Jichao Hu
- Department of Orthopedics, Zhejiang Rongjun Hospital, Jiaxing, China
| | - Zhuoer Pan
- Department of Orthopedics, Zhejiang Rongjun Hospital, Jiaxing, China
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10
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Mayorga-Weber G, Rivera FJ, Castro MA. Neuron-glia (mis)interactions in brain energy metabolism during aging. J Neurosci Res 2022; 100:835-854. [PMID: 35085408 DOI: 10.1002/jnr.25015] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Revised: 11/08/2021] [Accepted: 12/06/2021] [Indexed: 02/06/2023]
Abstract
Life expectancy in humans is increasing, resulting in a growing aging population, that is accompanied by an increased disposition to develop cognitive deterioration. Hypometabolism is one of the multiple factors related to inefficient brain function during aging. This review emphasizes the metabolic interactions between glial cells (astrocytes, oligodendrocytes, and microglia) and neurons, particularly, during aging. Glial cells provide support and protection to neurons allowing adequate synaptic activity. We address metabolic coupling from the expression of transporters, availability of substrates, metabolic pathways, and mitochondrial activity. In aging, the main metabolic exchange machinery is altered with inefficient levels of nutrients and detrimental mitochondrial activity that results in high reactive oxygen species levels and reduced ATP production, generating a highly inflammatory environment that favors deregulated cell death. Here, we provide an overview of the glial-to-neuron mechanisms, from the molecular components to the cell types, emphasizing aging as the crucial risk factor for developing neurodegenerative/neuroinflammatory diseases.
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Affiliation(s)
- Gonzalo Mayorga-Weber
- Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile
| | - Francisco J Rivera
- Center for Interdisciplinary Studies on the Nervous System (CISNe), Universidad Austral de Chile, Valdivia, Chile.,Laboratory of Stem Cells and Neuroregeneration, Instituto de Anatomía, Histología y Patología, Facultad de Medicina, Universidad Austral de Chile, Valdivia, Chile.,Institute of Molecular Regenerative Medicine, Paracelsus Medical University, Salzburg, Austria.,Spinal Cord Injury and Tissue Regeneration Center Salzburg (SCI-TReCS), Paracelsus Medical University, Salzburg, Austria
| | - Maite A Castro
- Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.,Center for Interdisciplinary Studies on the Nervous System (CISNe), Universidad Austral de Chile, Valdivia, Chile.,Janelia Research Campus, HHMI, Ashburn, VA, USA
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11
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Modeling the effect of cerebral capillary blood flow on neuronal firing. J Theor Biol 2022; 537:111018. [DOI: 10.1016/j.jtbi.2022.111018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2021] [Revised: 11/19/2021] [Accepted: 01/05/2022] [Indexed: 11/18/2022]
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12
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Gorina YV, Salmina AB, Erofeev AI, Can Z, Bolshakova AV, Balaban PM, Bezprozvanny IB, Vlasova OL. Metabolic Plasticity of Astrocytes. J EVOL BIOCHEM PHYS+ 2021. [DOI: 10.1134/s0022093021060016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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13
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Maly IV, Morales MJ, Pletnikov MV. Astrocyte Bioenergetics and Major Psychiatric Disorders. ADVANCES IN NEUROBIOLOGY 2021; 26:173-227. [PMID: 34888836 DOI: 10.1007/978-3-030-77375-5_9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Ongoing research continues to add new elements to the emerging picture of involvement of astrocyte energy metabolism in the pathophysiology of major psychiatric disorders, including schizophrenia, mood disorders, and addictions. This review outlines what is known about the energy metabolism in astrocytes, the most numerous cell type in the brain, and summarizes the recent work on how specific perturbations of astrocyte bioenergetics may contribute to the neuropsychiatric conditions. The role of astrocyte energy metabolism in mental health and disease is reviewed on the organism, organ, and cell level. Data arising from genomic, metabolomic, in vitro, and neurobehavioral studies is critically analyzed to suggest future directions in research and possible metabolism-focused therapeutic interventions.
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Affiliation(s)
- Ivan V Maly
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, State University of New York, Buffalo, NY, USA
| | - Michael J Morales
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, State University of New York, Buffalo, NY, USA
| | - Mikhail V Pletnikov
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, State University of New York, Buffalo, NY, USA.
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14
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Hu QP, Yan HX, Peng F, Feng W, Chen FF, Huang XY, Zhang X, Zhou YY, Chen YS. Genistein protects epilepsy-induced brain injury through regulating the JAK2/STAT3 and Keap1/Nrf2 signaling pathways in the developing rats. Eur J Pharmacol 2021; 912:174620. [PMID: 34752743 DOI: 10.1016/j.ejphar.2021.174620] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Revised: 10/30/2021] [Accepted: 11/03/2021] [Indexed: 01/07/2023]
Abstract
BACKGROUND Epilepsy is a common chronic neurological disease. Recurrent seizures can cause irreversible brain damage. This study aimed to explore the regulation of Genistein on JAK2/STAT3 and Keap1/Nrf2 signaling pathway and the protective effects on brain injury after epilepsy. METHODS Pentylenetetrazole (PTZ) was used to induce epilepsy in developing rats and Genistein was used for pretreatment of epilepsy. The seizure latency, grade scores and duration of the first generalized tonic-clonic seizure (GTCs) were recorded. Hippocampus tissue was sampled at 24 h post-epilepsy. Immunofluorescence staining was used to observe mature neurons, activated microglia and astrocytes in the hippocampal CA1 region. Western blot and qRT-PCR were used to determine the protein and mRNA levels of JAK2, STAT3, TNF-α, IL-1β, Keap1, Nrf2, HO-1, NQO1, caspase3, Bax and Bcl2 in the hippocampus. RESULTS Immunofluorescence showed that the number of neurons significantly decreased, and activated microglia and astrocytes significantly increased after epilepsy; Western blot and q-PCR showed that the expressions of JAK2, STAT3, TNF-α, IL-1β, Keap1, caspase3 and Bax significantly increased, while Nrf2, HO-1, NQO1 and Bcl-2 were significantly reduced after epilepsy. These effects were reversed by Genistein treatment. Moreover, Genistein was found to prolong seizure latency and reduce seizure intensity score and duration of generalized tonic-clonic seizures(GTCs) CONCLUSIONS: Genistein can activate the Keap1/Nrf2 antioxidant stress pathway and attenuate the activation of microglia and astrocytes. Genistein also inhibits the JAK2-STAT3 inflammation pathway and expression of apoptotic proteins, and increases the number of surviving neurons, thus having a protective effect on epilepsy-induced brain damage.
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Affiliation(s)
- Qing-Peng Hu
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China.
| | - Hong-Xia Yan
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China.
| | - Fang Peng
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China.
| | - Wei Feng
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China
| | - Fen-Fang Chen
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China
| | - Xiang-Yi Huang
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China
| | - Xin Zhang
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China
| | - Yang-Yu Zhou
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China
| | - Yi-Shui Chen
- Department of Pediatrics, the Second Affiliated Hospital, Hengyang Medical School, University of South China, Hengyang, Hunan, 421001, China
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15
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Shichkova P, Coggan JS, Markram H, Keller D. A Standardized Brain Molecular Atlas: A Resource for Systems Modeling and Simulation. Front Mol Neurosci 2021; 14:604559. [PMID: 34858137 PMCID: PMC8631404 DOI: 10.3389/fnmol.2021.604559] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Accepted: 10/05/2021] [Indexed: 12/12/2022] Open
Abstract
Accurate molecular concentrations are essential for reliable analyses of biochemical networks and the creation of predictive models for molecular and systems biology, yet protein and metabolite concentrations used in such models are often poorly constrained or irreproducible. Challenges of using data from different sources include conflicts in nomenclature and units, as well as discrepancies in experimental procedures, data processing and implementation of the model. To obtain a consistent estimate of protein and metabolite levels, we integrated and normalized data from a large variety of sources to calculate Adjusted Molecular Concentrations. We found a high degree of reproducibility and consistency of many molecular species across brain regions and cell types, consistent with tight homeostatic regulation. We demonstrated the value of this normalization with differential protein expression analyses related to neurodegenerative diseases, brain regions and cell types. We also used the results in proof-of-concept simulations of brain energy metabolism. The standardized Brain Molecular Atlas overcomes the obstacles of missing or inconsistent data to support systems biology research and is provided as a resource for biomolecular modeling.
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Affiliation(s)
- Polina Shichkova
- Blue Brain Project, École Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Jay S Coggan
- Blue Brain Project, École Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Henry Markram
- Blue Brain Project, École Polytechnique Fédérale de Lausanne, Geneva, Switzerland.,Laboratory of Neural Microcircuitry, Brain Mind Institute, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Daniel Keller
- Blue Brain Project, École Polytechnique Fédérale de Lausanne, Geneva, Switzerland
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16
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Sobotka L, Sobotka O. The predominant role of glucose as a building block and precursor of reducing equivalents. Curr Opin Clin Nutr Metab Care 2021; 24:555-562. [PMID: 34456247 DOI: 10.1097/mco.0000000000000786] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
PURPOSE OF REVIEW Stores of glucose (Glc) in our body are small compared with protein and lipid. Therefore, at times of famines or trauma/disease-related starvation, glucose utilization must be limited only to pathways that can only run with glucose carbon as substrate. We will try to outline how insulin resistance drives these pathways and inhibits glucose oxidation in the stressed organism. RECENT FINDINGS Glc is a basic substrate for a variety of other biomolecules like nucleic acids, amino acids, proteoglycans, mucopolysaccharides and lipids. It is essential for the formation of reducing equivalents, indispensable for anabolic, antioxidative, regulatory and immune processes. As a result, a continuous Glc turnover/cycle is essential to secure at all times the Glc requirements for nonoxidative pathways mentioned above but then requires introduction of extra glucose or other intermediates into the cycle. The production of ATP through complete Glc oxidation occurs only when Glc intake is higher than required for its nonoxidative metabolism. Insulin resistance and decreased Glc oxidation indicate that requirements of Glc for anabolic pathways are high. SUMMARY Glc is an important building block for anabolic reactions and substrate for reducing equivalents formation. Insulin resistance prevents irreversible Glc oxidation and stimulates Glc production during stress or growth. Glc is only oxidized when intake is in excess of its anabolic requirements.
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Affiliation(s)
- Lubos Sobotka
- 3rd Department of Medicine, Gerontology and Metabolism, University Hospital and Faculty of Medicine in Hradec Kralove, Charles University, Czech Republic
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17
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Cleland NRW, Al-Juboori SI, Dobrinskikh E, Bruce KD. Altered substrate metabolism in neurodegenerative disease: new insights from metabolic imaging. J Neuroinflammation 2021; 18:248. [PMID: 34711251 PMCID: PMC8555332 DOI: 10.1186/s12974-021-02305-w] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 10/21/2021] [Indexed: 12/13/2022] Open
Abstract
Neurodegenerative diseases (NDs), such as Alzheimer's disease (AD), Parkinson's disease (PD) and multiple sclerosis (MS), are relatively common and devastating neurological disorders. For example, there are 6 million individuals living with AD in the United States, a number that is projected to grow to 14 million by the year 2030. Importantly, AD, PD and MS are all characterized by the lack of a true disease-modifying therapy that is able to reverse or halt disease progression. In addition, the existing standard of care for most NDs only addresses the symptoms of the disease. Therefore, alternative strategies that target mechanisms underlying the neuropathogenesis of disease are much needed. Recent studies have indicated that metabolic alterations in neurons and glia are commonly observed in AD, PD and MS and lead to changes in cell function that can either precede or protect against disease onset and progression. Specifically, single-cell RNAseq studies have shown that AD progression is tightly linked to the metabolic phenotype of microglia, the key immune effector cells of the brain. However, these analyses involve removing cells from their native environment and performing measurements in vitro, influencing metabolic status. Therefore, technical approaches that can accurately assess cell-specific metabolism in situ have the potential to be transformative to our understanding of the mechanisms driving AD. Here, we review our current understanding of metabolism in both neurons and glia during homeostasis and disease. We also evaluate recent advances in metabolic imaging, and discuss how emerging modalities, such as fluorescence lifetime imaging microscopy (FLIM) have the potential to determine how metabolic perturbations may drive the progression of NDs. Finally, we propose that the temporal, regional, and cell-specific characterization of brain metabolism afforded by FLIM will be a critical first step in the rational design of metabolism-focused interventions that delay or even prevent NDs.
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Affiliation(s)
- Nicholas R W Cleland
- Endocrinology, Metabolism and Diabetes, Division of Endocrinology, Metabolism and Diabetes, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, USA
- School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, USA
| | - Saif I Al-Juboori
- Section of Neonatology, Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, USA
| | - Evgenia Dobrinskikh
- Section of Neonatology, Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, USA
- Division of Pulmonary Sciences and Critical Care, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, USA
| | - Kimberley D Bruce
- Endocrinology, Metabolism and Diabetes, Division of Endocrinology, Metabolism and Diabetes, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, USA.
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18
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Mahan VL. Effects of lactate and carbon monoxide interactions on neuroprotection and neuropreservation. Med Gas Res 2021; 11:158-173. [PMID: 34213499 PMCID: PMC8374456 DOI: 10.4103/2045-9912.318862] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 08/21/2020] [Accepted: 10/23/2020] [Indexed: 11/04/2022] Open
Abstract
Lactate, historically considered a waste product of anerobic metabolism, is a metabolite in whole-body metabolism needed for normal central nervous system (CNS) functions and a potent signaling molecule and hormone in the CNS. Neuronal activity signals normally induce its formation primarily in astrocytes and production is dependent on anerobic and aerobic metabolisms. Functions are dependent on normal dynamic, expansive, and evolving CNS functions. Levels can change under normal physiologic conditions and with CNS pathology. A readily combusted fuel that is sshuttled throughout the body, lactate is used as an energy source and is needed for CNS hemostasis, plasticity, memory, and excitability. Diffusion beyond the neuron active zone impacts activity of neurons and astrocytes in other areas of the brain. Barriergenesis, function of the blood-brain barrier, and buffering between oxidative metabolism and glycolysis and brain metabolism are affected by lactate. Important to neuroprotection, presence or absence is associated with L-lactate and heme oxygenase/carbon monoxide (a gasotransmitter) neuroprotective systems. Effects of carbon monoxide on L-lactate affect neuroprotection - interactions of the gasotransmitter with L-lactate are important to CNS stability, which will be reviewed in this article.
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Affiliation(s)
- Vicki L. Mahan
- Department of Surgery and Pediatrics, Drexel University College of Medicine, Philadelphia, PA, USA
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19
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Abdik E, Çakır T. Systematic investigation of mouse models of Parkinson's disease by transcriptome mapping on a brain-specific genome-scale metabolic network. Mol Omics 2021; 17:492-502. [PMID: 34370801 DOI: 10.1039/d0mo00135j] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Genome-scale metabolic networks enable systemic investigation of metabolic alterations caused by diseases by providing interpretation of omics data. Although Mus musculus (mouse) is one of the most commonly used model organisms for neurodegenerative diseases, a brain-specific metabolic network model of mice has not yet been reconstructed. Here we reconstructed the first brain-specific metabolic network model of mice, iBrain674-Mm, by a homology-based approach, which consisted of 992 reactions controlled by 674 genes and distributed over 48 pathways. We validated the newly reconstructed network model by showing that it predicts healthy resting-state metabolic phenotypes of mouse brain compatible with the literature. We later used iBrain674-Mm to interpret various experimental mouse models of Parkinson's Disease (PD) at the transcriptome level. To this end, we applied a constraint-based modelling based biomarker prediction method called TIMBR (Transcriptionally Inferred Metabolic Biomarker Response) to predict altered metabolite production from transcriptomic data. Systemic analysis of seven different PD mouse models by TIMBR showed that the neuronal levels of glutamate, lactate, creatine phosphate, neuronal acetylcholine, bilirubin and formate increased in most of the PD mouse models, whereas the levels of melatonin, epinephrine, astrocytic formate and astrocytic bilirubin decreased. Although most of the predictions were consistent with the literature, there were some inconsistencies among different PD mouse models, signifying that there is no perfect experimental model to reflect PD metabolism. The newly reconstructed brain-specific genome-scale metabolic network model of mice can make important contributions to the interpretation and development of experimental mouse models of PD and other neurodegenerative diseases.
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Affiliation(s)
- Ecehan Abdik
- Department of Bioengineering, Gebze Technical University, Kocaeli, Turkey.
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20
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Reevaluation of Astrocyte-Neuron Energy Metabolism with Astrocyte Volume Fraction Correction: Impact on Cellular Glucose Oxidation Rates, Glutamate-Glutamine Cycle Energetics, Glycogen Levels and Utilization Rates vs. Exercising Muscle, and Na +/K + Pumping Rates. Neurochem Res 2020; 45:2607-2630. [PMID: 32948935 DOI: 10.1007/s11064-020-03125-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2020] [Revised: 08/31/2020] [Accepted: 09/03/2020] [Indexed: 12/22/2022]
Abstract
Accurate quantification of cellular contributions to rates of substrate utilization in resting, activated, and diseased brain is essential for interpretation of data from studies using [18F]fluorodeoxyglucose-positron-emission tomography (FDG-PET) and [13C]glucose/magnetic resonance spectroscopy (MRS). A generally-accepted dogma is that neurons have the highest energy demands of all brain cells, and calculated neuronal rates of glucose oxidation in awake, resting brain accounts for 70-80%, with astrocytes 20-30%. However, these proportions do not take cell type volume fractions into account. To evaluate the conclusion that neuron-astrocyte glucose oxidation rates are similar when adjusted for astrocytic volume fraction (Hertz, Magn Reson Imaging 2011; 29, 1319), the present study analyzed data from 31 studies. On average, astrocytes occupy 6.1, 9.6, and 15% of tissue volume in hippocampus, cerebral cortex, and cerebellum, respectively, and regional astrocytic metabolic rates are adjusted for volume fraction by multiplying by 17.6, 11.4, and 6.8, respectively. After adjustment, astrocytic glucose oxidation rates in resting awake rat brain are 4-10 fold higher than neuronal oxidation rates. Volume-fraction adjustment also increases brain glycogen concentrations and utilization rates to be similar to or exceed exercising muscle. Ion flux calculations to evaluate sodium/potassium homeostasis during neurotransmission are not correct if astrocyte-neuron volume fractions are assumed to be equal. High rates of glucose and glycogen utilization after adjustment for volume fraction indicate that astrocytic energy demands are much greater than recognized, with most of the ATP being used for functions other than glutamate processing in the glutamate-glutamine cycle, challenging the notion that astrocytes 'feed hungry neurons'.
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21
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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.
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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
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22
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A thermodynamic function of glycogen in brain and muscle. Prog Neurobiol 2020; 189:101787. [PMID: 32151532 DOI: 10.1016/j.pneurobio.2020.101787] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 01/30/2020] [Accepted: 03/03/2020] [Indexed: 11/20/2022]
Abstract
Brain and muscle glycogen are generally thought to function as local glucose reserves, for use during transient mismatches between glucose supply and demand. However, quantitative measures show that glucose supply is likely never rate-limiting for energy metabolism in either brain or muscle under physiological conditions. These tissues nevertheless do utilize glycogen during increased energy demand, despite the availability of free glucose, and despite the ATP cost of cycling glucose through glycogen polymer. This seemingly wasteful process can be explained by considering the effect of glycogenolysis on the amount of energy obtained from ATP (ΔG'ATP). The amount of energy obtained from ATP is reduced by elevations in inorganic phosphate (Pi). Glycogen utilization sequesters Pi in the glycogen phosphorylase reaction and in downstream phosphorylated glycolytic intermediates, thereby buffering Pi elevations and maximizing energy yield at sites of rapid ATP consumption. This thermodynamic effect of glycogen may be particularly important in the narrow, spatially constrained astrocyte processes that ensheath neuronal synapses and in cells such as astrocytes and myocytes that release Pi from phosphocreatine during energy demand. The thermodynamic effect may also explain glycolytic super-compensation in brain when glycogen is not available, and aspects of exercise physiology in muscle glycogen phosphorylase deficiency (McArdle disease).
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23
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Patsatzis DG, Tingas EA, Goussis DA, Sarathy SM. Computational singular perturbation analysis of brain lactate metabolism. PLoS One 2019; 14:e0226094. [PMID: 31846455 PMCID: PMC6917278 DOI: 10.1371/journal.pone.0226094] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2019] [Accepted: 11/19/2019] [Indexed: 01/09/2023] Open
Abstract
Lactate in the brain is considered an important fuel and signalling molecule for neuronal activity, especially during neuronal activation. Whether lactate is shuttled from astrocytes to neurons or from neurons to astrocytes leads to the contradictory Astrocyte to Neuron Lactate Shuttle (ANLS) or Neuron to Astrocyte Lactate Shuttle (NALS) hypotheses, both of which are supported by extensive, but indirect, experimental evidence. This work explores the conditions favouring development of ANLS or NALS phenomenon on the basis of a model that can simulate both by employing the two parameter sets proposed by Simpson et al. (J Cereb. Blood Flow Metab., 27:1766, 2007) and Mangia et al. (J of Neurochemistry, 109:55, 2009). As most mathematical models governing brain metabolism processes, this model is multi-scale in character due to the wide range of time scales characterizing its dynamics. Therefore, we utilize the Computational Singular Perturbation (CSP) algorithm, which has been used extensively in multi-scale systems of reactive flows and biological systems, to identify components of the system that (i) generate the characteristic time scale and the fast/slow dynamics, (ii) participate to the expressions that approximate the surfaces of equilibria that develop in phase space and (iii) control the evolution of the process within the established surfaces of equilibria. It is shown that a decisive factor on whether the ANLS or NALS configuration will develop during neuronal activation is whether the lactate transport between astrocytes and interstitium contributes to the fast dynamics or not. When it does, lactate is mainly generated in astrocytes and the ANLS hypothesis is realised, while when it doesn't, lactate is mainly generated in neurons and the NALS hypothesis is realised. This scenario was tested in exercise conditions.
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Affiliation(s)
- Dimitris G. Patsatzis
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center (CCRC), Thuwal, Saudi Arabia
- Department of Mechanics, School of Applied Mathematics and Physical Sciences, National Technical University of Athens (NTUA), Athens, Greece
| | - Efstathios-Al. Tingas
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center (CCRC), Thuwal, Saudi Arabia
- Perth College, University of the Highlands and Islands, Crieff Rd, Perth PH1 2NX, United Kingdom
| | - Dimitris A. Goussis
- Department of Mechanical Engineering, Khalifa University of Science, Technology and Research (KUSTAR), Abu Dhabi, United Arab Emirates
| | - S. Mani Sarathy
- King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center (CCRC), Thuwal, Saudi Arabia
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24
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DiNuzzo M. How glycogen sustains brain function: A plausible allosteric signaling pathway mediated by glucose phosphates. J Cereb Blood Flow Metab 2019; 39:1452-1459. [PMID: 31208240 PMCID: PMC6681540 DOI: 10.1177/0271678x19856713] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Astrocytic glycogen is the sole glucose reserve of the brain. Both glycogen and glucose are necessary for basic neurophysiology and in turn for higher brain functions. In spite of low concentration, turnover and stimulation-induced degradation, any interference with normal glycogen metabolism in the brain severely affects neuronal excitability and disrupts memory formation. Here, I briefly discuss the glycogenolysis-induced glucose-sparing effect, which involves glucose phosphates as key allosteric effectors in the modulation of astrocytic and neuronal glucose uptake and phosphorylation. I further advance a novel and thus far unexplored effect of glycogenolysis that might be mediated by glucose phosphates.
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25
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Dienel GA. The “protected” glucose transport through the astrocytic endoplasmic reticulum is too slow to serve as a quantitatively‐important highway for nutrient delivery. J Neurosci Res 2019; 97:854-862. [DOI: 10.1002/jnr.24432] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Revised: 04/04/2019] [Accepted: 04/08/2019] [Indexed: 01/05/2023]
Affiliation(s)
- Gerald A. Dienel
- Department of Neurology University of Arkansas for Medical Sciences Little Rock Arkansas
- Department of Cell Biology and Physiology University of New Mexico Albuquerque New Mexico
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26
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Abstract
Glucose is the long-established, obligatory fuel for brain that fulfills many critical functions, including ATP production, oxidative stress management, and synthesis of neurotransmitters, neuromodulators, and structural components. Neuronal glucose oxidation exceeds that in astrocytes, but both rates increase in direct proportion to excitatory neurotransmission; signaling and metabolism are closely coupled at the local level. Exact details of neuron-astrocyte glutamate-glutamine cycling remain to be established, and the specific roles of glucose and lactate in the cellular energetics of these processes are debated. Glycolysis is preferentially upregulated during brain activation even though oxygen availability is sufficient (aerobic glycolysis). Three major pathways, glycolysis, pentose phosphate shunt, and glycogen turnover, contribute to utilization of glucose in excess of oxygen, and adrenergic regulation of aerobic glycolysis draws attention to astrocytic metabolism, particularly glycogen turnover, which has a high impact on the oxygen-carbohydrate mismatch. Aerobic glycolysis is proposed to be predominant in young children and specific brain regions, but re-evaluation of data is necessary. Shuttling of glucose- and glycogen-derived lactate from astrocytes to neurons during activation, neurotransmission, and memory consolidation are controversial topics for which alternative mechanisms are proposed. Nutritional therapy and vagus nerve stimulation are translational bridges from metabolism to clinical treatment of diverse brain disorders.
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Affiliation(s)
- Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences , Little Rock, Arkansas ; and Department of Cell Biology and Physiology, University of New Mexico , Albuquerque, New Mexico
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27
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Glycogenolysis in Cerebral Cortex During Sensory Stimulation, Acute Hypoglycemia, and Exercise: Impact on Astrocytic Energetics, Aerobic Glycolysis, and Astrocyte-Neuron Interactions. ADVANCES IN NEUROBIOLOGY 2019; 23:209-267. [DOI: 10.1007/978-3-030-27480-1_8] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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28
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Rothman DL, Dienel GA. Development of a Model to Test Whether Glycogenolysis Can Support Astrocytic Energy Demands of Na +, K +-ATPase and Glutamate-Glutamine Cycling, Sparing an Equivalent Amount of Glucose for Neurons. ADVANCES IN NEUROBIOLOGY 2019; 23:385-433. [PMID: 31667817 DOI: 10.1007/978-3-030-27480-1_14] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Recent studies of glycogen in brain have suggested a much more important role in brain energy metabolism and function than previously recognized, including findings of much higher than previously recognized concentrations, consumption at substantial rates compared with utilization of blood-borne glucose, and involvement in ion pumping and in neurotransmission and memory. However, it remains unclear how glycogenolysis is coupled to neuronal activity and provides support for neuronal as well as astroglial function. At present, quantitative aspects of glycogenolysis in brain functions are very difficult to assess due to its metabolic lability, heterogeneous distributions within and among cells, and extreme sensitivity to physiological stimuli. To begin to address this problem, the present study develops a model based on pathway fluxes, mass balance, and literature relevant to functions and turnover of pathways that intersect with glycogen mobilization. A series of equations is developed to describe the stoichiometric relationships between net glycogen consumption that is predominantly in astrocytes with the rate of the glutamate-glutamine cycle, rates of astrocytic and neuronal glycolytic and oxidative metabolism, and the energetics of sodium/potassium pumping in astrocytes and neurons during brain activation. Literature supporting the assumptions of the model is discussed in detail. The overall conclusion is that astrocyte glycogen metabolism is primarily coupled to neuronal function via fueling glycolytically pumping of Na+ and K+ and sparing glucose for neuronal oxidation, as opposed to previous proposals of coupling neurotransmission via glutamate transport, lactate shuttling, and neuronal oxidation of lactate.
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Affiliation(s)
- Douglas L Rothman
- Magnetic Resonance Research Center and Department of Radiology, Yale University, New Haven, CT, USA.
| | - Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, AR, USA.,Department of Cell Biology and Physiology, University of New Mexico, Albuquerque, NM, USA
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Gandini Wheeler-Kingshott CAM, Riemer F, Palesi F, Ricciardi A, Castellazzi G, Golay X, Prados F, Solanky B, D'Angelo EU. Challenges and Perspectives of Quantitative Functional Sodium Imaging (fNaI). Front Neurosci 2018; 12:810. [PMID: 30473659 PMCID: PMC6237845 DOI: 10.3389/fnins.2018.00810] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Accepted: 10/17/2018] [Indexed: 12/31/2022] Open
Abstract
Brain function has been investigated via the blood oxygenation level dependent (BOLD) effect using magnetic resonance imaging (MRI) for the past decades. Advances in sodium imaging offer the unique chance to access signal changes directly linked to sodium ions (23Na) flux across the cell membrane, which generates action potentials, hence signal transmission in the brain. During this process 23Na transiently accumulates in the intracellular space. Here we show that quantitative functional sodium imaging (fNaI) at 3T is potentially sensitive to 23Na concentration changes during finger tapping, which can be quantified in gray and white matter regions key to motor function. For the first time, we measured a 23Na concentration change of 0.54 mmol/l in the ipsilateral cerebellum, 0.46 mmol/l in the contralateral primary motor cortex (M1), 0.27 mmol/l in the corpus callosum and -11 mmol/l in the ipsilateral M1, suggesting that fNaI is sensitive to distributed functional alterations. Open issues persist on the role of the glymphatic system in maintaining 23Na homeostasis, the role of excitation and inhibition as well as volume distributions during neuronal activity. Haemodynamic and physiological signal recordings coupled to realistic models of tissue function will be critical to understand the mechanisms of such changes and contribute to meeting the overarching challenge of measuring neuronal activity in vivo.
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Affiliation(s)
- Claudia A M Gandini Wheeler-Kingshott
- NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom.,Department of Brain and Behavioural Sciences, University of Pavia, Pavia, Italy.,Brain MRI 3T Mondino Research Center, IRCCS Mondino Foundation, Pavia, Italy
| | - Frank Riemer
- NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom.,Department of Radiology, School of Clinical Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Fulvia Palesi
- Neuroradiology Unit, IRCCS Mondino Foundation, Pavia, Italy
| | - Antonio Ricciardi
- NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom.,Center for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom
| | - Gloria Castellazzi
- NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom.,Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy
| | - Xavier Golay
- NMR Research Unit, Queen Square MS Centre, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom
| | - Ferran Prados
- NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom.,Center for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom.,Universitat Oberta de Catalunya, Barcelona, Spain
| | - Bhavana Solanky
- NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, Faculty of Brain Sciences, University College London, London, United Kingdom
| | - Egidio U D'Angelo
- Department of Brain and Behavioural Sciences, University of Pavia, Pavia, Italy.,Brain Connectivity Center, IRCCS Mondino Foundation, Pavia, Italy
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30
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Winter F, Bludszuweit-Philipp C, Wolkenhauer O. Mathematical analysis of the influence of brain metabolism on the BOLD signal in Alzheimer's disease. J Cereb Blood Flow Metab 2018; 38:304-316. [PMID: 28271954 PMCID: PMC5951012 DOI: 10.1177/0271678x17693024] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI) is a standard clinical tool for the detection of brain activation. In Alzheimer's disease (AD), task-related and resting state fMRI have been used to detect brain dysfunction. It has been shown that the shape of the BOLD response is affected in early AD. To correctly interpret these changes, the mechanisms responsible for the observed behaviour need to be known. The parameters of the canonical hemodynamic response function (HRF) commonly used in the analysis of fMRI data have no direct biological interpretation and cannot be used to answer this question. We here present a model that allows relating AD-specific changes in the BOLD shape to changes in the underlying energy metabolism. According to our findings, the classic view that differences in the BOLD shape are only attributed to changes in strength and duration of the stimulus does not hold. Instead, peak height, peak timing and full width at half maximum are sensitive to changes in the reaction rate of several metabolic reactions. Our systems-theoretic approach allows the use of patient-specific clinical data to predict dementia-driven changes in the HRF, which can be used to improve the results of fMRI analyses in AD patients.
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Affiliation(s)
- Felix Winter
- 1 ASD Advanced Simulation and Design GmbH, Rostock, Germany.,2 Department of Systems Biology and Bioinformatics, Rostock University, Rostock, Germany
| | | | - Olaf Wolkenhauer
- 2 Department of Systems Biology and Bioinformatics, Rostock University, Rostock, Germany.,3 Stellenbosch Institute for Advanced Study (STIAS), Wallenberg Research Centre at Stellenbosch University, Stellenbosch, South Africa
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31
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Dienel GA, Behar KL, Rothman DL. Cellular Origin of [ 18F]FDG-PET Imaging Signals During Ceftriaxone-Stimulated Glutamate Uptake: Astrocytes and Neurons. Neuroscientist 2017; 24:316-328. [PMID: 29276856 DOI: 10.1177/1073858417749375] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Ceftriaxone stimulates astrocytic uptake of the excitatory neurotransmitter glutamate, and it is used to treat glutamatergic excitotoxicity that becomes manifest during many brain diseases. Ceftriaxone-stimulated glutamate transport was reported to drive signals underlying [18F]fluorodeoxyglucose-positron emission tomographic ([18F]FDG-PET) metabolic images of brain glucose utilization and interpreted as supportive of the notion of lactate shuttling from astrocytes to neurons. This study draws attention to critical roles of astrocytes in the energetics and imaging of brain activity, but the results are provocative because (1) the method does not have cellular resolution or provide information about downstream pathways of glucose metabolism, (2) neuronal and astrocytic [18F]FDG uptake were not separately measured, and (3) strong evidence against lactate shuttling was not discussed. Evaluation of potential metabolic responses to ceftriaxone suggests lack of astrocytic specificity and significant contributions by pre- and postsynaptic neuronal compartments. Indeed, astrocytic glycolysis may not make a strong contribution to the [18F]FDG-PET signal because partial or complete oxidation of one glutamate molecule on its uptake generates enough ATP to fuel uptake of 3 to 10 more glutamate molecules, diminishing reliance on glycolysis. The influence of ceftriaxone on energetics of glutamate-glutamine cycling must be determined in astrocytes and neurons to elucidate its roles in excitotoxicity treatment.
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Affiliation(s)
- Gerald A Dienel
- 1 Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, AR, USA.,2 Department of Cell Biology and Physiology, University of New Mexico, Albuquerque, NM, USA
| | - Kevin L Behar
- 3 Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
| | - Douglas L Rothman
- 4 Departments of Radiology and Biomedical Engineering, Yale University School of Medicine, New Haven, CT, USA
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32
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Sonnay S, Poirot J, Just N, Clerc AC, Gruetter R, Rainer G, Duarte JMN. Astrocytic and neuronal oxidative metabolism are coupled to the rate of glutamate-glutamine cycle in the tree shrew visual cortex. Glia 2017; 66:477-491. [DOI: 10.1002/glia.23259] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Revised: 10/20/2017] [Accepted: 10/24/2017] [Indexed: 01/09/2023]
Affiliation(s)
- Sarah Sonnay
- Laboratory for Functional and Metabolic Imaging (LIFMET); Ecole Polytechnique Fédérale de Lausanne (EPFL); Lausanne Switzerland
| | - Jordan Poirot
- Department of Medicine, Visual Cognition Laboratory; University of Fribourg; Fribourg Switzerland
| | | | - Anne-Catherine Clerc
- Laboratory for Functional and Metabolic Imaging (LIFMET); Ecole Polytechnique Fédérale de Lausanne (EPFL); Lausanne Switzerland
| | - Rolf Gruetter
- Laboratory for Functional and Metabolic Imaging (LIFMET); Ecole Polytechnique Fédérale de Lausanne (EPFL); Lausanne Switzerland
- Department of Radiology; University de Lausanne; Lausanne Switzerland
- Department of Radiology; University de Geneva; Geneva Switzerland
| | - Gregor Rainer
- Department of Medicine, Visual Cognition Laboratory; University of Fribourg; Fribourg Switzerland
| | - João M. N. Duarte
- Laboratory for Functional and Metabolic Imaging (LIFMET); Ecole Polytechnique Fédérale de Lausanne (EPFL); Lausanne Switzerland
- Department of Experimental Medical Science, Faculty of Medicine; Lund University; Lund Sweden
- Wallenberg Centre for Molecular Medicine, Lund University; Lund Sweden
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33
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Hertz L, Chen Y. Integration between Glycolysis and Glutamate-Glutamine Cycle Flux May Explain Preferential Glycolytic Increase during Brain Activation, Requiring Glutamate. Front Integr Neurosci 2017. [PMID: 28890689 DOI: 10.3389/fnint.2017.00018+10.3389/fnint.2017.00018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The 1988 observation by Fox et al. (1988) that brief intense brain activation increases glycolysis (pyruvate formation from glucose) much more than oxidative metabolism has been abundantly confirmed. Specifically glycolytic increase was unexpected because the amount of ATP it generates is much smaller than that formed by subsequent oxidative metabolism of pyruvate. The present article shows that preferential glycolysis can be explained by metabolic processes associated with activation of the glutamate-glutamine cycle. The flux in this cycle, which is essential for production of transmitter glutamate and GABA, equals 75% of brain glucose utilization and each turn is associated with utilization of ~1 glucose molecule. About one half of the association between cycle flux and glucose metabolism occurs during neuronal conversion of glutamine to glutamate in a process similar to the malate-aspartate shuttle (MAS) except that glutamate is supplied from glutamine, not formed from α-ketoglutarate (αKG) as during operation of conventional MAS. Regular MAS function is triggered by one oxidative process in the cytosol during glycolysis causing NAD+ reduction to NADH. Since NADH cannot cross the mitochondrial membrane (MEM) for oxidation NAD+ is re-generated by conversion of cytosolic oxaloacetate (OAA) to malate, which enters the mitochondria for oxidation and in a cyclic process regenerates cytosolic OAA. Therefore MAS as well as the "pseudo-MAS" necessary for neuronal glutamate formation can only operate together with cytosolic reduction of NAD+ to NADH. The major process causing NAD+ reduction is glycolysis which therefore also must occur during neuronal conversion of glutamine to glutamate and may energize vesicular glutamate uptake which preferentially uses glycolytically derived energy. Another major contributor to the association between glutamate-glutamine cycle and glucose utilization is the need for astrocytic pyruvate to generate glutamate. Although some oxidative metabolism occurs during glutamate formation it is only one half of that during normal tricarboxylic acid (TCA) cycle function. Glutamate's receptor stimulation leads to potassium ion (K+) release and astrocytic uptake, preferentially fueled by glycolysis and followed by release and neuronal re-accumulation. The activation-induced preferential glycolysis diminishes with continued activation and is followed by an increased ratio between oxidative metabolism and glycolysis, reflecting oxidation of generated glutamate and accumulated lactate.
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Affiliation(s)
- Leif Hertz
- Laboratory of Metabolic Brain Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical UniversityShenyang, China
| | - Ye Chen
- Henry M. Jackson FoundationBethesda, MD, United States
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34
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Hertz L, Chen Y. Integration between Glycolysis and Glutamate-Glutamine Cycle Flux May Explain Preferential Glycolytic Increase during Brain Activation, Requiring Glutamate. Front Integr Neurosci 2017; 11:18. [PMID: 28890689 PMCID: PMC5574930 DOI: 10.3389/fnint.2017.00018] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2017] [Accepted: 08/11/2017] [Indexed: 11/13/2022] Open
Abstract
The 1988 observation by Fox et al. (1988) that brief intense brain activation increases glycolysis (pyruvate formation from glucose) much more than oxidative metabolism has been abundantly confirmed. Specifically glycolytic increase was unexpected because the amount of ATP it generates is much smaller than that formed by subsequent oxidative metabolism of pyruvate. The present article shows that preferential glycolysis can be explained by metabolic processes associated with activation of the glutamate-glutamine cycle. The flux in this cycle, which is essential for production of transmitter glutamate and GABA, equals 75% of brain glucose utilization and each turn is associated with utilization of ~1 glucose molecule. About one half of the association between cycle flux and glucose metabolism occurs during neuronal conversion of glutamine to glutamate in a process similar to the malate-aspartate shuttle (MAS) except that glutamate is supplied from glutamine, not formed from α-ketoglutarate (αKG) as during operation of conventional MAS. Regular MAS function is triggered by one oxidative process in the cytosol during glycolysis causing NAD+ reduction to NADH. Since NADH cannot cross the mitochondrial membrane (MEM) for oxidation NAD+ is re-generated by conversion of cytosolic oxaloacetate (OAA) to malate, which enters the mitochondria for oxidation and in a cyclic process regenerates cytosolic OAA. Therefore MAS as well as the "pseudo-MAS" necessary for neuronal glutamate formation can only operate together with cytosolic reduction of NAD+ to NADH. The major process causing NAD+ reduction is glycolysis which therefore also must occur during neuronal conversion of glutamine to glutamate and may energize vesicular glutamate uptake which preferentially uses glycolytically derived energy. Another major contributor to the association between glutamate-glutamine cycle and glucose utilization is the need for astrocytic pyruvate to generate glutamate. Although some oxidative metabolism occurs during glutamate formation it is only one half of that during normal tricarboxylic acid (TCA) cycle function. Glutamate's receptor stimulation leads to potassium ion (K+) release and astrocytic uptake, preferentially fueled by glycolysis and followed by release and neuronal re-accumulation. The activation-induced preferential glycolysis diminishes with continued activation and is followed by an increased ratio between oxidative metabolism and glycolysis, reflecting oxidation of generated glutamate and accumulated lactate.
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Affiliation(s)
- Leif Hertz
- Laboratory of Metabolic Brain Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical UniversityShenyang, China
| | - Ye Chen
- Henry M. Jackson FoundationBethesda, MD, United States
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35
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Hertz L, Chen Y. Integration between Glycolysis and Glutamate-Glutamine Cycle Flux May Explain Preferential Glycolytic Increase during Brain Activation, Requiring Glutamate. Front Integr Neurosci 2017. [PMID: 28890689 DOI: 10.3389/fnint.2017.00018 10.3389/fnint.2017.00018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The 1988 observation by Fox et al. (1988) that brief intense brain activation increases glycolysis (pyruvate formation from glucose) much more than oxidative metabolism has been abundantly confirmed. Specifically glycolytic increase was unexpected because the amount of ATP it generates is much smaller than that formed by subsequent oxidative metabolism of pyruvate. The present article shows that preferential glycolysis can be explained by metabolic processes associated with activation of the glutamate-glutamine cycle. The flux in this cycle, which is essential for production of transmitter glutamate and GABA, equals 75% of brain glucose utilization and each turn is associated with utilization of ~1 glucose molecule. About one half of the association between cycle flux and glucose metabolism occurs during neuronal conversion of glutamine to glutamate in a process similar to the malate-aspartate shuttle (MAS) except that glutamate is supplied from glutamine, not formed from α-ketoglutarate (αKG) as during operation of conventional MAS. Regular MAS function is triggered by one oxidative process in the cytosol during glycolysis causing NAD+ reduction to NADH. Since NADH cannot cross the mitochondrial membrane (MEM) for oxidation NAD+ is re-generated by conversion of cytosolic oxaloacetate (OAA) to malate, which enters the mitochondria for oxidation and in a cyclic process regenerates cytosolic OAA. Therefore MAS as well as the "pseudo-MAS" necessary for neuronal glutamate formation can only operate together with cytosolic reduction of NAD+ to NADH. The major process causing NAD+ reduction is glycolysis which therefore also must occur during neuronal conversion of glutamine to glutamate and may energize vesicular glutamate uptake which preferentially uses glycolytically derived energy. Another major contributor to the association between glutamate-glutamine cycle and glucose utilization is the need for astrocytic pyruvate to generate glutamate. Although some oxidative metabolism occurs during glutamate formation it is only one half of that during normal tricarboxylic acid (TCA) cycle function. Glutamate's receptor stimulation leads to potassium ion (K+) release and astrocytic uptake, preferentially fueled by glycolysis and followed by release and neuronal re-accumulation. The activation-induced preferential glycolysis diminishes with continued activation and is followed by an increased ratio between oxidative metabolism and glycolysis, reflecting oxidation of generated glutamate and accumulated lactate.
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Affiliation(s)
- Leif Hertz
- Laboratory of Metabolic Brain Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical UniversityShenyang, China
| | - Ye Chen
- Henry M. Jackson FoundationBethesda, MD, United States
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36
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Sonnay S, Gruetter R, Duarte JMN. How Energy Metabolism Supports Cerebral Function: Insights from 13C Magnetic Resonance Studies In vivo. Front Neurosci 2017; 11:288. [PMID: 28603480 PMCID: PMC5445183 DOI: 10.3389/fnins.2017.00288] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Accepted: 05/04/2017] [Indexed: 12/25/2022] Open
Abstract
Cerebral function is associated with exceptionally high metabolic activity, and requires continuous supply of oxygen and nutrients from the blood stream. Since the mid-twentieth century the idea that brain energy metabolism is coupled to neuronal activity has emerged, and a number of studies supported this hypothesis. Moreover, brain energy metabolism was demonstrated to be compartmentalized in neurons and astrocytes, and astrocytic glycolysis was proposed to serve the energetic demands of glutamatergic activity. Shedding light on the role of astrocytes in brain metabolism, the earlier picture of astrocytes being restricted to a scaffold-associated function in the brain is now out of date. With the development and optimization of non-invasive techniques, such as nuclear magnetic resonance spectroscopy (MRS), several groups have worked on assessing cerebral metabolism in vivo. In this context, 1H MRS has allowed the measurements of energy metabolism-related compounds, whose concentrations can vary under different brain activation states. 1H-[13C] MRS, i.e., indirect detection of signals from 13C-coupled 1H, together with infusion of 13C-enriched glucose has provided insights into the coupling between neurotransmission and glucose oxidation. Although these techniques tackle the coupling between neuronal activity and metabolism, they lack chemical specificity and fail in providing information on neuronal and glial metabolic pathways underlying those processes. Currently, the improvement of detection modalities (i.e., direct detection of 13C isotopomers), the progress in building adequate mathematical models along with the increase in magnetic field strength now available render possible detailed compartmentalized metabolic flux characterization. In particular, direct 13C MRS offers more detailed dataset acquisitions and provides information on metabolic interactions between neurons and astrocytes, and their role in supporting neurotransmission. Here, we review state-of-the-art MR methods to study brain function and metabolism in vivo, and their contribution to the current understanding of how astrocytic energy metabolism supports glutamatergic activity and cerebral function. In this context, recent data suggests that astrocytic metabolism has been underestimated. Namely, the rate of oxidative metabolism in astrocytes is about half of that in neurons, and it can increase as much as the rate of neuronal metabolism in response to sensory stimulation.
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Affiliation(s)
- Sarah Sonnay
- Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de LausanneLausanne, Switzerland
| | - Rolf Gruetter
- Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de LausanneLausanne, Switzerland.,Department of Radiology, University of LausanneLausanne, Switzerland.,Department of Radiology, University of GenevaGeneva, Switzerland
| | - João M N Duarte
- Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de LausanneLausanne, Switzerland
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37
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Dienel GA. Lack of appropriate stoichiometry: Strong evidence against an energetically important astrocyte-neuron lactate shuttle in brain. J Neurosci Res 2017; 95:2103-2125. [PMID: 28151548 DOI: 10.1002/jnr.24015] [Citation(s) in RCA: 115] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Revised: 11/28/2016] [Accepted: 12/16/2016] [Indexed: 12/22/2022]
Abstract
Glutamate-stimulated aerobic glycolysis in astrocytes coupled with lactate shuttling to neurons where it can be oxidized was proposed as a mechanism to couple excitatory neuronal activity with glucose utilization (CMRglc ) during brain activation. From the outset, this model was not viable because it did not fulfill critical stoichiometric requirements: (i) Calculated glycolytic rates and measured lactate release rates were discordant in cultured astrocytes. (ii) Lactate oxidation requires oxygen consumption, but the oxygen-glucose index (OGI, calculated as CMRO2 /CMRglc ) fell during activation in human brain, and the small rise in CMRO2 could not fully support oxidation of lactate produced by disproportionate increases in CMRglc . (iii) Labeled products of glucose metabolism are not retained in activated rat brain, indicating rapid release of a highly labeled, diffusible metabolite identified as lactate, thereby explaining the CMRglc -CMRO2 mismatch. Additional independent lines of evidence against lactate shuttling include the following: astrocytic oxidation of glutamate after its uptake can help "pay" for its uptake without stimulating glycolysis; blockade of glutamate receptors during activation in vivo prevents upregulation of metabolism and lactate release without impairing glutamate uptake; blockade of β-adrenergic receptors prevents the fall in OGI in activated human and rat brain while allowing glutamate uptake; and neurons upregulate glucose utilization in vivo and in vitro under many stimulatory conditions. Studies in immature cultured cells are not appropriate models for lactate shuttling in adult brain because of their incomplete development of metabolic capability and astrocyte-neuron interactions. Astrocyte-neuron lactate shuttling does not make large, metabolically significant contributions to energetics of brain activation. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, and Department of Cell Biology and Physiology, University of New Mexico, Albuquerque, New Mexico
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