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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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2
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Bastian C, Zerimech S, Nguyen H, Doherty C, Franke C, Faris A, Quinn J, Baltan S. Aging astrocytes metabolically support aging axon function by proficiently regulating astrocyte-neuron lactate shuttle. Exp Neurol 2022; 357:114173. [PMID: 35863500 PMCID: PMC11218845 DOI: 10.1016/j.expneurol.2022.114173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 06/23/2022] [Accepted: 07/14/2022] [Indexed: 11/19/2022]
Abstract
The astrocyte-neuron lactate shuttle (ANLS) is an essential metabolic support system that uptakes glucose, stores it as glycogen in astrocytes, and provides glycogen-derived lactate for axonal function. Aging intrinsically increases the vulnerability of white matter (WM) to injury. Therefore, we investigated the regulation of this shuttle to understand vascular-glial metabolic coupling to support axonal function during aging in two different WM tracts. Aging astrocytes displayed larger cell bodies and thicker horizontal processes in contrast to thinner vertically oriented processes of young astrocytes. Aging axons recovered less following aglycemia in mouse optic nerves (MONs) compared to young axons, although providing lactate during aglycemia equally supported young and aging axonal function. Incubating MONs in high glucose to upregulate glycogen stores in astrocytes delayed loss of function during aglycemia and improved recovery in both young and aging axons. Providing lactate during recovery from aglycemia unmasked a metabolic switch from glucose to lactate in aging axons. Young and aging corpus callosum consisting of a mixture of myelinated and unmyelinated axons sustained their function fully when lactate was available during aglycemia and surprisingly showed a greater resilience to aglycemia compared to fully myelinated axons of optic nerve. We conclude that lactate is a universal substrate for axons independent of their myelination content and age.
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Affiliation(s)
- Chinthasagar Bastian
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Sarah Zerimech
- Anesthesia and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, United States of America
| | - Hung Nguyen
- Anesthesia and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, United States of America
| | - Christine Doherty
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Caroline Franke
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Anna Faris
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - John Quinn
- Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America
| | - Selva Baltan
- Anesthesia and Perioperative Medicine, Oregon Health and Science University, Portland, OR 97239, United States of America; Department of Neurosciences, Cleveland Clinic Foundation, Cleveland, OH 441952, United States of America.
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Capturing the third dimension in drug discovery: Spatially-resolved tools for interrogation of complex 3D cell models. Biotechnol Adv 2021; 55:107883. [PMID: 34875362 DOI: 10.1016/j.biotechadv.2021.107883] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 11/22/2021] [Accepted: 11/30/2021] [Indexed: 02/07/2023]
Abstract
Advanced three-dimensional (3D) cell models have proven to be capable of depicting architectural and microenvironmental features of several tissues. By providing data of higher physiological and pathophysiological relevance, 3D cell models have been contributing to a better understanding of human development, pathology onset and progression mechanisms, as well as for 3D cell-based assays for drug discovery. Nonetheless, the characterization and interrogation of these tissue-like structures pose major challenges on the conventional analytical methods, pushing the development of spatially-resolved technologies. Herein, we review recent advances and pioneering technologies suitable for the interrogation of multicellular 3D models, while capable of retaining biological spatial information. We focused on imaging technologies and omics tools, namely transcriptomics, proteomics and metabolomics. The advantages and shortcomings of these novel methodologies are discussed, alongside the opportunities to intertwine data from the different tools.
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Muddapu VR, Chakravarthy VS. Influence of energy deficiency on the subcellular processes of Substantia Nigra Pars Compacta cell for understanding Parkinsonian neurodegeneration. Sci Rep 2021; 11:1754. [PMID: 33462293 PMCID: PMC7814067 DOI: 10.1038/s41598-021-81185-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 12/23/2020] [Indexed: 01/29/2023] Open
Abstract
Parkinson's disease (PD) is the second most prominent neurodegenerative disease around the world. Although it is known that PD is caused by the loss of dopaminergic cells in substantia nigra pars compacta (SNc), the decisive cause of this inexorable cell loss is not clearly elucidated. We hypothesize that "Energy deficiency at a sub-cellular/cellular/systems level can be a common underlying cause for SNc cell loss in PD." Here, we propose a comprehensive computational model of SNc cell, which helps us to understand the pathophysiology of neurodegeneration at the subcellular level in PD. The aim of the study is to see how deficits in the supply of energy substrates (glucose and oxygen) lead to a deficit in adenosine triphosphate (ATP). The study also aims to show that deficits in ATP are the common factor underlying the molecular-level pathological changes, including alpha-synuclein aggregation, reactive oxygen species formation, calcium elevation, and dopamine dysfunction. The model suggests that hypoglycemia plays a more crucial role in leading to ATP deficits than hypoxia. We believe that the proposed model provides an integrated modeling framework to understand the neurodegenerative processes underlying PD.
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Affiliation(s)
- Vignayanandam Ravindernath Muddapu
- grid.417969.40000 0001 2315 1926Computational Neuroscience Lab, Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Sardar Patel Road, Chennai, 600036 Tamil Nadu India
| | - V. Srinivasa Chakravarthy
- grid.417969.40000 0001 2315 1926Computational Neuroscience Lab, Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Sardar Patel Road, Chennai, 600036 Tamil Nadu India
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5
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Ding X, Peng D. Transient Global Amnesia: An Electrophysiological Disorder Based on Cortical Spreading Depression-Transient Global Amnesia Model. Front Hum Neurosci 2020; 14:602496. [PMID: 33363460 PMCID: PMC7753037 DOI: 10.3389/fnhum.2020.602496] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 11/17/2020] [Indexed: 01/09/2023] Open
Abstract
Transient global amnesia (TGA) is a benign memory disorder with etiologies that have been debated for a long time. The prevalence of stressful events before a TGA attack makes it hard to overlook these precipitating factors, given that stress has the potential to organically effect the brain. Cortical spreading depression (CSD) was proposed as a possible cause decades ago. Being a regional phenomenon, CSD seems to affect every aspect of the micro-mechanism in maintaining the homeostasis of the central nervous system (CNS). Corresponding evidence regarding hemodynamic and morphological changes from TGA and CSD have been accumulated separately, but the resemblance between the two has not been systematically explored so far, which is surprising especially considering that CSD had been confirmed to cause secondary damage in the human brain. Thus, by deeply delving into the anatomic and electrophysiological properties of the CNS, the CSD-TGA model may render insights into the basic pathophysiology behind the façade of the enigmatic clinical presentation.
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Affiliation(s)
- Xuejiao Ding
- Department of Neurology, China-Japan Friendship Hospital, Beijing, China
- Graduate School of Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Dantao Peng
- Department of Neurology, China-Japan Friendship Hospital, Beijing, China
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Dewan N, Shukla V, Rehni AK, Koronowski KB, Klingbeil KD, Stradecki‐Cohan H, Garrett TJ, Rundek T, Perez‐Pinzon MA, Dave KR. Exposure to recurrent hypoglycemia alters hippocampal metabolism in treated streptozotocin-induced diabetic rats. CNS Neurosci Ther 2020; 26:126-135. [PMID: 31282100 PMCID: PMC6930817 DOI: 10.1111/cns.13186] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2019] [Revised: 05/31/2019] [Accepted: 06/04/2019] [Indexed: 12/13/2022] Open
Abstract
AIMS Exposure to recurrent hypoglycemia (RH) is common in diabetic patients receiving glucose-lowering therapies and is implicated in causing cognitive impairments. Despite the significant effect of RH on hippocampal function, the underlying mechanisms are currently unknown. Our goal was to determine the effect of RH exposure on hippocampal metabolism in treated streptozotocin-diabetic rats. METHODS Hyperglycemia was corrected by insulin pellet implantation. Insulin-treated diabetic (ITD) rats were exposed to mild/moderate RH once a day for 5 consecutive days. RESULTS The effect of RH on hippocampal metabolism revealed 65 significantly altered metabolites in the RH group compared with controls. Several significant differences in metabolite levels belonging to major pathways (eg, Krebs cycle, gluconeogenesis, and amino acid metabolism) were discovered in RH-exposed ITD rats when compared to a control group. Key glycolytic enzymes including hexokinase, phosphofructokinase, and pyruvate kinase were affected by RH exposure. CONCLUSION Our results demonstrate that the exposure to RH leads to metabolomics alterations in the hippocampus of insulin-treated streptozotocin-diabetic rats. Understanding how RH affects hippocampal metabolism may help attenuate the adverse effects of RH on hippocampal functions.
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Affiliation(s)
- Neelesh Dewan
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Vibha Shukla
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Ashish K. Rehni
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Kevin B. Koronowski
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
- Neuroscience ProgramUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Kyle D. Klingbeil
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Holly Stradecki‐Cohan
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
- Neuroscience ProgramUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Timothy J. Garrett
- Southeast Center for Integrated Metabolomics, Clinical and Translational Science InstituteUniversity of FloridaGainesvilleFloridaUSA
| | - Tatjana Rundek
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
- Evelyn F. McKnight Brain InstituteUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Miguel A. Perez‐Pinzon
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
- Neuroscience ProgramUniversity of Miami School of MedicineMiamiFloridaUSA
- Evelyn F. McKnight Brain InstituteUniversity of Miami School of MedicineMiamiFloridaUSA
| | - Kunjan R. Dave
- Peritz Scheinberg Cerebral Vascular Disease Research LaboratoriesUniversity of Miami School of MedicineMiamiFloridaUSA
- Department of NeurologyUniversity of Miami School of MedicineMiamiFloridaUSA
- Neuroscience ProgramUniversity of Miami School of MedicineMiamiFloridaUSA
- Evelyn F. McKnight Brain InstituteUniversity of Miami School of MedicineMiamiFloridaUSA
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7
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Astrocytic pyruvate carboxylation: Status after 35 years. J Neurosci Res 2019; 97:890-896. [DOI: 10.1002/jnr.24402] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 01/11/2019] [Accepted: 02/05/2019] [Indexed: 12/24/2022]
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8
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Rehni AK, Dave KR. Impact of Hypoglycemia on Brain Metabolism During Diabetes. Mol Neurobiol 2018; 55:9075-9088. [PMID: 29637442 PMCID: PMC6179939 DOI: 10.1007/s12035-018-1044-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2018] [Accepted: 03/27/2018] [Indexed: 12/24/2022]
Abstract
Diabetes is a metabolic disease afflicting millions of people worldwide. A substantial fraction of world's total healthcare expenditure is spent on treating diabetes. Hypoglycemia is a serious consequence of anti-diabetic drug therapy, because it induces metabolic alterations in the brain. Metabolic alterations are one of the central mechanisms mediating hypoglycemia-related functional changes in the brain. Acute, chronic, and/or recurrent hypoglycemia modulate multiple metabolic pathways, and exposure to hypoglycemia increases consumption of alternate respiratory substrates such as ketone bodies, glycogen, and monocarboxylates in the brain. The aim of this review is to discuss hypoglycemia-induced metabolic alterations in the brain in glucose counterregulation, uptake, utilization and metabolism, cellular respiration, amino acid and lipid metabolism, and the significance of other sources of energy. The present review summarizes information on hypoglycemia-induced metabolic changes in the brain of diabetic and non-diabetic subjects and the manner in which they may affect brain function.
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Affiliation(s)
- Ashish K Rehni
- Cerebral Vascular Disease Research Laboratories, University of Miami Miller School of Medicine, Miami, FL, 33136, USA
- Department of Neurology, University of Miami Miller School of Medicine, 1420 NW 9th Ave, NRB/203E, Miami, FL, 33136, USA
| | - Kunjan R Dave
- Cerebral Vascular Disease Research Laboratories, University of Miami Miller School of Medicine, Miami, FL, 33136, USA.
- Department of Neurology, University of Miami Miller School of Medicine, 1420 NW 9th Ave, NRB/203E, Miami, FL, 33136, USA.
- Neuroscience Program, University of Miami Miller School of Medicine, Miami, FL, 33136, USA.
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9
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Oligodendrocytes: Development, Physiology and Glucose Metabolism. ADVANCES IN NEUROBIOLOGY 2018; 13:275-294. [PMID: 27885633 DOI: 10.1007/978-3-319-45096-4_10] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The glutamate-glutamine cycle is an outstanding example of how essential neuronal-glial interactions are for brain function. For several decades, this and other metabolic cycles in the brain have only included neurons and astrocytes but not oligodendrocytes, the myelinating cells of the central nervous system (CNS). Recent data revealed that oligodendrocytes are highly metabolically active cells in the brain and, therefore, should not be ignored. Using 13C-labelled glucose in combination with nuclear magnetic resonance spectroscopy (MRS) and/or mass spectrometry (MS) it is possible to characterize metabolic functions in primary oligodendrocyte cultures. Mature rat oligodendrocytes avidly metabolize glucose in the cytosol and pyruvate derived from glucose in mitochondria. Moreover, they seem to have the ability of performing anaplerosis from pyruvate, which might enable them to synthesize metabolites de novo and transfer them to neighbouring cells. All these original findings highlight the importance of investigating oligodendrocyte metabolism separately from that of astrocytes and neurons to be able to discern the roles played by the individual partners. This is of particular importance in the white matter where the number of oligodendrocytes is considerable. The present book chapter provides some background on oligodendrocyte biology and physiology and summarizes the not very extensive information published on glucose metabolism in oligodendrocytes.
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Cerdán S. Twenty-seven Years of Cerebral Pyruvate Recycling. Neurochem Res 2017; 42:1621-1628. [PMID: 28101749 DOI: 10.1007/s11064-017-2173-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/02/2017] [Accepted: 01/02/2017] [Indexed: 10/20/2022]
Abstract
Cerebral pyruvate recycling is a metabolic pathway deriving carbon skeletons and reducing equivalents from mitochondrial oxaloacetate and malate, to the synthesis of mitochondrial and cytosolic pyruvate, lactate and alanine. The pathway allows both, to provide the tricarboxylic acid cycle with pyruvate molecules produced from alternative substrates to glucose and, to generate reducing equivalents necessary for the operation of NADPH requiring processes. At the cellular level, pyruvate recycling involves the activity of malic enzyme, or the combined activities of phosphoenolpyruvate carboxykinase and pyruvate kinase, as well as of those transporters of the inner mitochondrial membrane exchanging the corresponding intermediates. Its cellular localization between the neuronal or astrocytic compartments of the in vivo brain has been controversial, with evidences favoring either a primarily neuronal or glial localizations, more recently accepted to occur in both environments. This review provides a brief history on the detection and characterization of the pathway, its relations with the early developments of cerebral high resolution 13C NMR, and its potential neuroprotective functions under hypoglycemic conditions or ischemic redox stress.
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Affiliation(s)
- Sebastián Cerdán
- Instituto de Investigaciones Biomédicas "Alberto Sols" CSIC/UAM, c/ Arturo Duperier 4, 28029, Madrid, Spain.
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11
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Kim AY, Jeong KH, Lee JH, Kang Y, Lee SH, Baik EJ. Glutamate dehydrogenase as a neuroprotective target against brain ischemia and reperfusion. Neuroscience 2016; 340:487-500. [PMID: 27845178 DOI: 10.1016/j.neuroscience.2016.11.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 11/02/2016] [Accepted: 11/06/2016] [Indexed: 01/13/2023]
Abstract
Deregulation of glutamate homeostasis is associated with degenerative neurological disorders. Glutamate dehydrogenase (GDH) is important for glutamate metabolism and plays a central role in expanding the pool of tricarboxylic acid (TCA) cycle intermediate alpha-ketoglutarate (α-KG), which improves overall bioenergetics. Under high energy demand, maintenance of ATP production results in functionally active mitochondria. Here, we tested whether the modulation of GDH activity can rescue ischemia/reperfusion-induced neuronal death in an in vivo mouse model of middle artery occlusion and an in vitro oxygen/glucose depletion model. Iodoacetate, an inhibitor of glycolysis, was also used in a model of energy failure, remarkably depleting ATP and α-KG. To stimulate GDH activity, the GDH activator 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid and potential activator beta-lapachone were used. The GDH activators restored α-KG and ATP levels in the injury models and provided potent neuroprotection. We also found that beta-lapachone increased glutamate utilization, accompanied by a reduction in extracellular glutamate. Thus, our hypothesis that mitochondrial GDH activators increase α-KG production as an alternative energy source for use in the TCA cycle under energy-depleted conditions was confirmed. Our results suggest that increasing GDH-mediated glutamate oxidation represents a new therapeutic intervention for neurodegenerative disorders, including stoke.
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Affiliation(s)
- A Young Kim
- Department of Physiology, Ajou University School of Medicine, Suwon 16499, Republic of Korea; Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Kyeong-Hoon Jeong
- Gachon University of Medicine and Science, Incheon 406-840, Republic of Korea
| | - Jae Ho Lee
- Department of Biochemistry, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Yup Kang
- Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Soo Hwan Lee
- Department of Physiology, Ajou University School of Medicine, Suwon 16499, Republic of Korea
| | - Eun Joo Baik
- Department of Physiology, Ajou University School of Medicine, Suwon 16499, Republic of Korea; Chronic Inflammatory Disease Research Center, Ajou University School of Medicine, Suwon 16499, Republic of Korea.
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12
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β-Hydroxybutyrate in the Brain: One Molecule, Multiple Mechanisms. Neurochem Res 2016; 42:35-49. [DOI: 10.1007/s11064-016-2099-2] [Citation(s) in RCA: 123] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 10/31/2016] [Accepted: 11/02/2016] [Indexed: 12/16/2022]
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13
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Kennedy BE, Hundert AS, Goguen D, Weaver ICG, Karten B. Presymptomatic Alterations in Amino Acid Metabolism and DNA Methylation in the Cerebellum of a Murine Model of Niemann-Pick Type C Disease. THE AMERICAN JOURNAL OF PATHOLOGY 2016; 186:1582-97. [PMID: 27083515 DOI: 10.1016/j.ajpath.2016.02.012] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2014] [Revised: 02/08/2016] [Accepted: 02/16/2016] [Indexed: 10/21/2022]
Abstract
The fatal neurodegenerative disorder Niemann-Pick type C (NPC) is caused in most cases by mutations in NPC1, which encodes the late endosomal NPC1 protein. Loss of NPC1 disrupts cholesterol trafficking from late endosomes to the endoplasmic reticulum and plasma membrane, causing cholesterol accumulation in late endosomes/lysosomes. Neurons are particularly vulnerable to this cholesterol trafficking defect, but the pathogenic mechanisms through which NPC1 deficiency causes neuronal dysfunction remain largely unknown. Herein, we have investigated amino acid metabolism in cerebella of NPC1-deficient mice at different stages of NPC disease. Imbalances in amino acid metabolism were evident from increased branched chain amino acid and asparagine levels and altered expression of key enzymes of glutamine/glutamate metabolism in presymptomatic and early symptomatic NPC1-deficient cerebellum. Increased levels of several amino acid intermediates of one-carbon metabolism indicated disturbances in folate and methylation pathways. Alterations in DNA methylation were apparent in decreased expression of DNA methyltransferase 3a and methyl-5'-cytosine-phosphodiester-guanine-domain binding proteins, reduced 5-methylcytosine immunoreactivity in the molecular and Purkinje cell layers, demethylation of genome-wide repetitive LINE-1 elements, and hypermethylation in specific promoter regions of single-copy genes in NPC1-deficient cerebellum at early stages of the disease. Alterations in amino acid metabolism and epigenetic changes in the cerebellum at presymptomatic stages of NPC disease represent previously unrecognized mechanisms of NPC pathogenesis.
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Affiliation(s)
- Barry E Kennedy
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Amos S Hundert
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Donna Goguen
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Ian C G Weaver
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada.
| | - Barbara Karten
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
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14
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Amaral AI, Hadera MG, Tavares JM, Kotter MRN, Sonnewald U. Characterization of glucose-related metabolic pathways in differentiated rat oligodendrocyte lineage cells. Glia 2016; 64:21-34. [PMID: 26352325 PMCID: PMC4832329 DOI: 10.1002/glia.22900] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Accepted: 07/22/2015] [Indexed: 12/24/2022]
Abstract
Although oligodendrocytes constitute a significant proportion of cells in the central nervous system (CNS), little is known about their intermediary metabolism. We have, therefore, characterized metabolic functions of primary oligodendrocyte precursor cell cultures at late stages of differentiation using isotope-labelled metabolites. We report that differentiated oligodendrocyte lineage cells avidly metabolize glucose in the cytosol and pyruvate derived from glucose in the mitochondria. The labelling patterns of metabolites obtained after incubation with [1,2-(13)C]glucose demonstrated that the pentose phosphate pathway (PPP) is highly active in oligodendrocytes (approximately 10% of glucose is metabolized via the PPP as indicated by labelling patterns in phosphoenolpyruvate). Mass spectrometry and magnetic resonance spectroscopy analyses of metabolites after incubation of cells with [1-(13)C]lactate or [1,2-(13)C]glucose, respectively, demonstrated that anaplerotic pyruvate carboxylation, which was thought to be exclusive to astrocytes, is also active in oligodendrocytes. Using [1,2-(13)C]acetate, we show that oligodendrocytes convert acetate into acetyl CoA which is metabolized in the tricarboxylic acid cycle. Analysis of labelling patterns of alanine after incubation of cells with [1,2-(13)C]acetate and [1,2-(13)C]glucose showed catabolic oxidation of malate or oxaloacetate. In conclusion, we report that oligodendrocyte lineage cells at late differentiation stages are metabolically highly active cells that are likely to contribute considerably to the metabolic activity of the CNS.
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Affiliation(s)
- Ana I. Amaral
- Anne McLaren LaboratoryWellcome Trust‐Medical Research Council Cambridge Stem Cell Institute and Department of Clinical Neurosciences, University of CambridgeCambridgeCB2 0SZUnited Kingdom
| | - Mussie G. Hadera
- Department of Neuroscience, Faculty of MedicineNorwegian University of Science and TechnologyTrondheim7491Norway
| | - Joana M. Tavares
- Anne McLaren LaboratoryWellcome Trust‐Medical Research Council Cambridge Stem Cell Institute and Department of Clinical Neurosciences, University of CambridgeCambridgeCB2 0SZUnited Kingdom
| | - Mark R. N. Kotter
- Anne McLaren LaboratoryWellcome Trust‐Medical Research Council Cambridge Stem Cell Institute and Department of Clinical Neurosciences, University of CambridgeCambridgeCB2 0SZUnited Kingdom
| | - Ursula Sonnewald
- Department of Neuroscience, Faculty of MedicineNorwegian University of Science and TechnologyTrondheim7491Norway
- Department of Drug Design and Pharmacology, Faculty of Health and Medical SciencesUniversity of CopenhagenCopenhagen2100Denmark
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A Tribute to Mary C. McKenna: Glutamate as Energy Substrate and Neurotransmitter-Functional Interaction Between Neurons and Astrocytes. Neurochem Res 2015; 42:4-9. [PMID: 26721512 DOI: 10.1007/s11064-015-1813-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 12/16/2015] [Accepted: 12/18/2015] [Indexed: 10/22/2022]
Abstract
Glutamate metabolism in the brain is extremely complex not only involving a large variety of enzymes but also a tight partnership between neurons and astrocytes, the latter cells being in control of de novo synthesis of glutamate. This review provides an account of the processes involved, i.e. pyruvate carboxylation and recycling as well as the glutamate-glutamine cycle, focusing on the many seminal contributions from Dr. Mary McKenna. The ramification of the astrocytic end feet allowing contact and control of hundreds of thousands of synapses at the same time obviously puts these cells in a prominent position to regulate neural activity. Additionally, the astrocytes take active part in the neurotransmission processes by releasing a variety of gliotransmitters including glutamate. Hence, the term "the tripartite synapse", in which there is an active and dynamic interplay between the pre- and post-synaptic neurons and the ensheathing astrocytes, has been coined. The studies of Mary McKenna and her colleagues over several decades have been of paramount importance for the elucidation of compartmentation in astrocytes and synaptic terminals and the intricate metabolic processes underlying the glutamatergic neurotransmission process.
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Gebril HM, Avula B, Wang YH, Khan IA, Jekabsons MB. (13)C metabolic flux analysis in neurons utilizing a model that accounts for hexose phosphate recycling within the pentose phosphate pathway. Neurochem Int 2015; 93:26-39. [PMID: 26723542 DOI: 10.1016/j.neuint.2015.12.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Revised: 12/16/2015] [Accepted: 12/18/2015] [Indexed: 11/25/2022]
Abstract
Glycolysis, mitochondrial substrate oxidation, and the pentose phosphate pathway (PPP) are critical for neuronal bioenergetics and oxidation-reduction homeostasis, but quantitating their fluxes remains challenging, especially when processes such as hexose phosphate (i.e., glucose/fructose-6-phosphate) recycling in the PPP are considered. A hexose phosphate recycling model was developed which exploited the rates of glucose consumption, lactate production, and mitochondrial respiration to infer fluxes through the major glucose consuming pathways of adherent cerebellar granule neurons by replicating [(13)C]lactate labeling from metabolism of [1,2-(13)C2]glucose. Flux calculations were predicated on a steady-state system with reactions having known stoichiometries and carbon atom transitions. Non-oxidative PPP activity and consequent hexose phosphate recycling, as well as pyruvate production by cytoplasmic malic enzyme, were optimized by the model and found to account for 28 ± 2% and 7.7 ± 0.2% of hexose phosphate and pyruvate labeling, respectively. From the resulting fluxes, 52 ± 6% of glucose was metabolized by glycolysis, compared to 19 ± 2% by the combined oxidative/non-oxidative pentose cycle that allows for hexose phosphate recycling, and 29 ± 8% by the combined oxidative PPP/de novo nucleotide synthesis reactions. By extension, 62 ± 6% of glucose was converted to pyruvate, the metabolism of which resulted in 16 ± 1% of glucose oxidized by mitochondria and 46 ± 6% exported as lactate. The results indicate a surprisingly high proportion of glucose utilized by the pentose cycle and the reactions synthesizing nucleotides, and exported as lactate. While the in vitro conditions to which the neurons were exposed (high glucose, no lactate or other exogenous substrates) limit extrapolating these results to the in vivo state, the approach provides a means of assessing a number of metabolic fluxes within the context of hexose phosphate recycling in the PPP from a minimal set of measurements.
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Affiliation(s)
- Hoda M Gebril
- Department of Biology, Shoemaker Hall, University of Mississippi, University, MS 38677, USA.
| | - Bharathi Avula
- National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
| | - Yan-Hong Wang
- National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
| | - Ikhlas A Khan
- Department of Biomedical Sciences and National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, MS 38677, USA.
| | - Mika B Jekabsons
- Department of Biology, Shoemaker Hall, University of Mississippi, University, MS 38677, USA.
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Olsen GM, Sonnewald U. Glutamate: Where does it come from and where does it go? Neurochem Int 2015; 88:47-52. [DOI: 10.1016/j.neuint.2014.11.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Revised: 10/30/2014] [Accepted: 11/03/2014] [Indexed: 11/15/2022]
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Sá JV, Duarte TM, Carrondo MJT, Alves PM, Teixeira AP. Metabolic Flux Analysis: A Powerful Tool in Animal Cell Culture. CELL ENGINEERING 2015. [DOI: 10.1007/978-3-319-10320-4_16] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Sonnewald U. Glutamate synthesis has to be matched by its degradation - where do all the carbons go? J Neurochem 2014; 131:399-406. [PMID: 24989463 DOI: 10.1111/jnc.12812] [Citation(s) in RCA: 120] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 06/24/2014] [Accepted: 06/28/2014] [Indexed: 01/11/2023]
Abstract
The central process in energy production is the oxidation of acetyl-CoA to CO2 by the tricarboxylic acid (TCA, Krebs, citric acid) cycle. However, this cycle functions also as a biosynthetic pathway from which intermediates leave to be converted primarily to glutamate, GABA, glutamine and aspartate and to a smaller extent to glucose derivatives and fatty acids in the brain. When TCA cycle ketoacids are removed, they must be replaced to permit the continued function of this essential pathway, by a process termed anaplerosis. Since the TCA cycle cannot act as a carbon sink, anaplerosis must be coupled with cataplerosis; the exit of intermediates from the TCA cycle. The role of anaplerotic reactions for cellular metabolism in the brain has been studied extensively. However, the coupling of this process with cataplerosis and the roles that both pathways play in the regulation of amino acid, glucose, and fatty acid homeostasis have not been emphasized. The concept of a linkage between anaplerosis and cataplerosis should be underscored, because the balance between these two processes is essential. The hypothesis that cataplerosis in the brain is achieved by exporting the lactate generated from the TCA cycle intermediates into the blood and perivascular area is presented. This shifts the generally accepted paradigm of lactate generation as simply derived from glycolysis to that of oxidation and might present an alternative explanation for aerobic glycolysis. Intermediates leave the tricarboxylic acid cycle and must be replaced by a process termed anaplerosis that must be coupled to cataplerosis. We hypothesize that cataplerosis is achieved by exporting the lactate generated from the cycle into the blood and perivascular area. This shifts the paradigm of lactate generation as solely derived from glycolysis to that of oxidation and might present an alternative explanation for aerobic glycolysis.
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Affiliation(s)
- Ursula Sonnewald
- Department of Neuroscience, Faculty of Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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Dos Reis EA, Rieger E, de Souza SS, Rasia-Filho AA, Wannmacher CMD. Effects of a co-treatment with pyruvate and creatine on dendritic spines in rat hippocampus and posterodorsal medial amygdala in a phenylketonuria animal model. Metab Brain Dis 2013; 28:509-17. [PMID: 23430365 DOI: 10.1007/s11011-013-9389-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 02/11/2013] [Indexed: 12/13/2022]
Abstract
Phenylketonuria (PKU) is the most frequent aminoacidopathy that damage the central nervous system and is characterized by neural injury, mental retardation and accumulation of phenylalanine and its metabolites in plasma and tissues. So far, the only effective protection against brain injury is the administration of special phenylalanine-free diets. Animals with lesions in the hippocampus and amygdala had behavioral impairments indicating the importance of the integrity of these brain structures in learning and memory tasks which are disability characteristics of patients affected by PKU. In the present study we aimed to test the effect of the combination of two energetic and antioxidant compounds-pyruvate and creatine (intraperitoneal injections of 0.2 mg/g of body weight and 0.4 mg/g of body weight, respectively, treatment from the 7th to the 28th postnatal day)-in animals subjected to a chronic model of PKU. To assess likely effects, the density of dendritic spines in the hippocampal CA1 region and in the posterodorsal medial amygdala of 60-day-old male rats were analyzed under confocal microscopy. Present results showed that the co-treatment with pyruvate and creatine prevented the reduction in dendritic spine density in the stratum radiatum of the CA1 hippocampal field and in the posterodorsal medial amygdala of PKU animals. If this can also occur in PKU patients, it is possible that creatine and pyruvate may help to prevent brain damage in patients under specific diet.
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Affiliation(s)
- Eleonora Araújo Dos Reis
- Departamento de Bioquímica, Programa de Pós-Graduação em Ciências Biológicas: Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
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Magi S, Arcangeli S, Castaldo P, Nasti AA, Berrino L, Piegari E, Bernardini R, Amoroso S, Lariccia V. Glutamate-induced ATP synthesis: relationship between plasma membrane Na+/Ca2+ exchanger and excitatory amino acid transporters in brain and heart cell models. Mol Pharmacol 2013; 84:603-14. [PMID: 23913256 DOI: 10.1124/mol.113.087775] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
It is known that glutamate (Glu), the major excitatory amino acid in the central nervous system, can be an essential source for cell energy metabolism. Here we investigated the role of the plasma membrane Na(+)/Ca(2+) exchanger (NCX) and the excitatory amino acid transporters (EAATs) in Glu uptake and recycling mechanisms leading to ATP synthesis. We used different cell lines, such as SH-SY5Y neuroblastoma, C6 glioma and H9c2 as neuronal, glial, and cardiac models, respectively. We first observed that Glu increased ATP production in SH-SY5Y and C6 cells. Pharmacological inhibition of either EAAT or NCX counteracted the Glu-induced ATP synthesis. Furthermore, Glu induced a plasma membrane depolarization and an intracellular Ca(2+) increase, and both responses were again abolished by EAAT and NCX blockers. In line with the hypothesis of a mutual interplay between the activities of EAAT and NCX, coimmunoprecipitation studies showed a physical interaction between them. We expanded our studies on EAAT/NCX interplay in the H9c2 cells. H9c2 expresses EAATs but lacks endogenous NCX1 expression. Glu failed to elicit any significant response in terms of ATP synthesis, cell depolarization, and Ca(2+) increase unless a functional NCX1 was introduced in H9c2 cells by stable transfection. Moreover, these responses were counteracted by EAAT and NCX blockers, as observed in SH-SY5Y and C6 cells. Collectively, these data suggest that plasma membrane EAAT and NCX are both involved in Glu-induced ATP synthesis, with NCX playing a pivotal role.
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Affiliation(s)
- Simona Magi
- Department of Biomedical Sciences and Public Health, School of Medicine, University Politecnica of Marche, Ancona, Italy (S.M., S.Ar., P.C., A.A.N., S.Am., V.L.); Department of Experimental Medicine, Second University of Naples, Naples, Italy (L.B., E.P.); and Department of Clinical and Molecular Biomedicine, School of Medicine, University of Catania, Catania, Italy (R.B.)
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Amaral AI. Effects of hypoglycaemia on neuronal metabolism in the adult brain: role of alternative substrates to glucose. J Inherit Metab Dis 2013; 36:621-34. [PMID: 23109064 DOI: 10.1007/s10545-012-9553-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2012] [Revised: 10/02/2012] [Accepted: 10/11/2012] [Indexed: 12/22/2022]
Abstract
Hypoglycaemia is characterized by decreased blood glucose levels and is associated with different pathologies (e.g. diabetes, inborn errors of metabolism). Depending on its severity, it might affect cognitive functions, including impaired judgment and decreased memory capacity, which have been linked to alterations of brain energy metabolism. Glucose is the major cerebral energy substrate in the adult brain and supports the complex metabolic interactions between neurons and astrocytes, which are essential for synaptic activity. Therefore, hypoglycaemia disturbs cerebral metabolism and, consequently, neuronal function. Despite the high vulnerability of neurons to hypoglycaemia, important neurochemical changes enabling these cells to prolong their resistance to hypoglycaemia have been described. This review aims at providing an overview over the main metabolic effects of hypoglycaemia on neurons, covering in vitro and in vivo findings. Recent studies provided evidence that non-glucose substrates including pyruvate, glycogen, ketone bodies, glutamate, glutamine, and aspartate, are metabolized by neurons in the absence of glucose and contribute to prolong neuronal function and delay ATP depletion during hypoglycaemia. One of the pathways likely implicated in the process is the pyruvate recycling pathway, which allows for the full oxidation of glutamate and glutamine. The operation of this pathway in neurons, particularly after hypoglycaemia, has been re-confirmed recently using metabolic modelling tools (i.e. Metabolic Flux Analysis), which allow for a detailed investigation of cellular metabolism in cultured cells. Overall, the knowledge summarized herein might be used for the development of potential therapies targeting neuronal protection in patients vulnerable to hypoglycaemic episodes.
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Affiliation(s)
- Ana I Amaral
- Anne McLaren Laboratory for Regenerative Medicine, Department of Clinical Neurosciences, MRC Centre for Stem Cell Biology and Regenerative Medicine, University of Cambridge, West Forvie Building, Robinson Way, CB2 0SZ Cambridge, UK.
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Shetty PK, Galeffi F, Turner DA. Cellular Links between Neuronal Activity and Energy Homeostasis. Front Pharmacol 2012; 3:43. [PMID: 22470340 PMCID: PMC3308331 DOI: 10.3389/fphar.2012.00043] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 02/24/2012] [Indexed: 12/20/2022] Open
Abstract
Neuronal activity, astrocytic responses to this activity, and energy homeostasis are linked together during baseline, conscious conditions, and short-term rapid activation (as occurs with sensory or motor function). Nervous system energy homeostasis also varies during long-term physiological conditions (i.e., development and aging) and with adaptation to pathological conditions, such as ischemia or low glucose. Neuronal activation requires increased metabolism (i.e., ATP generation) which leads initially to substrate depletion, induction of a variety of signals for enhanced astrocytic function, and increased local blood flow and substrate delivery. Energy generation (particularly in mitochondria) and use during ATP hydrolysis also lead to considerable heat generation. The local increases in blood flow noted following neuronal activation can both enhance local substrate delivery but also provides a heat sink to help cool the brain and removal of waste by-products. In this review we highlight the interactions between short-term neuronal activity and energy metabolism with an emphasis on signals and factors regulating astrocyte function and substrate supply.
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Affiliation(s)
- Pavan K Shetty
- Neurosurgery and Neurobiology, Research and Surgery Services, Durham VA Medical Center, Duke University Durham, NC, USA
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Amaral AI, Teixeira AP, Håkonsen BI, Sonnewald U, Alves PM. A comprehensive metabolic profile of cultured astrocytes using isotopic transient metabolic flux analysis and C-labeled glucose. FRONTIERS IN NEUROENERGETICS 2011; 3:5. [PMID: 21941478 PMCID: PMC3171112 DOI: 10.3389/fnene.2011.00005] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/04/2010] [Accepted: 08/04/2011] [Indexed: 12/21/2022]
Abstract
Metabolic models have been used to elucidate important aspects of brain metabolism in recent years. This work applies for the first time the concept of isotopic transient 13C metabolic flux analysis (MFA) to estimate intracellular fluxes in primary cultures of astrocytes. This methodology comprehensively explores the information provided by 13C labeling time-courses of intracellular metabolites after administration of a 13C-labeled substrate. Cells were incubated with medium containing [1-13C]glucose for 24 h and samples of cell supernatant and extracts collected at different time points were then analyzed by mass spectrometry and/or high performance liquid chromatography. Metabolic fluxes were estimated by fitting a carbon labeling network model to isotopomer profiles experimentally determined. Both the fast isotopic equilibrium of glycolytic metabolite pools and the slow labeling dynamics of TCA cycle intermediates are described well by the model. The large pools of glutamate and aspartate which are linked to the TCA cycle via reversible aminotransferase reactions are likely to be responsible for the observed delay in equilibration of TCA cycle intermediates. Furthermore, it was estimated that 11% of the glucose taken up by astrocytes was diverted to the pentose phosphate pathway. In addition, considerable fluxes through pyruvate carboxylase [PC; PC/pyruvate dehydrogenase (PDH) ratio = 0.5], malic enzyme (5% of the total pyruvate production), and catabolism of branched-chained amino acids (contributing with ∼40% to total acetyl-CoA produced) confirmed the significance of these pathways to astrocytic metabolism. Consistent with the need of maintaining cytosolic redox potential, the fluxes through the malate–aspartate shuttle and the PDH pathway were comparable. Finally, the estimated glutamate/α-ketoglutarate exchange rate (∼0.7 μmol mg prot−1 h−1) was similar to the TCA cycle flux. In conclusion, this work demonstrates the potential of isotopic transient MFA for a comprehensive analysis of energy metabolism.
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Affiliation(s)
- Ana I Amaral
- Instituto de Tecnologia Química e Biológica - Universidade Nova de Lisboa Oeiras, Portugal
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