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Complex I assembly into supercomplexes determines differential mitochondrial ROS production in neurons and astrocytes. Proc Natl Acad Sci U S A 2016; 113:13063-13068. [PMID: 27799543 DOI: 10.1073/pnas.1613701113] [Citation(s) in RCA: 276] [Impact Index Per Article: 34.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Neurons depend on oxidative phosphorylation for energy generation, whereas astrocytes do not, a distinctive feature that is essential for neurotransmission and neuronal survival. However, any link between these metabolic differences and the structural organization of the mitochondrial respiratory chain is unknown. Here, we investigated this issue and found that, in neurons, mitochondrial complex I is predominantly assembled into supercomplexes, whereas in astrocytes the abundance of free complex I is higher. The presence of free complex I in astrocytes correlates with the severalfold higher reactive oxygen species (ROS) production by astrocytes compared with neurons. Using a complexomics approach, we found that the complex I subunit NDUFS1 was more abundant in neurons than in astrocytes. Interestingly, NDUFS1 knockdown in neurons decreased the association of complex I into supercomplexes, leading to impaired oxygen consumption and increased mitochondrial ROS. Conversely, overexpression of NDUFS1 in astrocytes promoted complex I incorporation into supercomplexes, decreasing ROS. Thus, complex I assembly into supercomplexes regulates ROS production and may contribute to the bioenergetic differences between neurons and astrocytes.
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Heterogeneous Cellular Distribution of Glutamate Dehydrogenase in Brain and in Non-neural Tissues. Neurochem Res 2014; 39:500-15. [DOI: 10.1007/s11064-013-1235-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2013] [Revised: 12/27/2013] [Accepted: 12/30/2013] [Indexed: 01/30/2023]
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3
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Stelmashook EV, Isaev NK, Lozier ER, Goryacheva ES, Khaspekov LG. Role of Glutamine in Neuronal Survival and Death During Brain Ischemia and Hypoglycemia. Int J Neurosci 2011; 121:415-22. [DOI: 10.3109/00207454.2011.570464] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Abstract
Mechanisms involved in hepatic encephalopathy still remain to be defined. Nonetheless, it is well recognized that ammonia is a major factor in its pathogenesis, and that the astrocyte represents a major target of its CNS toxicity. In vivo and in vitro studies have shown that ammonia evokes oxidative/nitrosative stress, mitochondrial abnormalities (the mitochondrial permeability transition, MPT) and astrocyte swelling, a major component of the brain edema associated with fulminant hepatic failure. How ammonia brings about these changes in astrocytes is not well understood. It has long been accepted that the conversion of glutamate to glutamine, catalyzed by glutamine synthetase, a cytoplasmic enzyme largely localized to astrocytes in brain, represented the principal means of cerebral ammonia detoxification. Yet, the "benign" aspect of glutamine synthesis has been questioned. This article highlights evidence that, at elevated levels, glutamine is indeed a noxious agent. We also propose a mechanism by which glutamine executes its toxic effects in astrocytes, the "Trojan horse" hypothesis. Much of the newly synthesized glutamine is subsequently metabolized in mitochondria by phosphate-activated glutaminase, yielding glutamate and ammonia. In this manner, glutamine (the Trojan horse) is transported in excess from the cytoplasm to mitochondria serving as a carrier of ammonia. We propose that it is the glutamine-derived ammonia within mitochondria that interferes with mitochondrial function giving rise to excessive production of free radicals and induction of the MPT, two phenomena known to bring about astrocyte dysfunction, including cell swelling. Future therapeutic approaches might include controlling excessive transport of newly synthesized glutamine to mitochondria and its subsequent hydrolysis.
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Affiliation(s)
- Jan Albrecht
- Department of Neurotoxicology, M. Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland.
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5
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Abstract
Astrocyte swelling represents the major factor responsible for the brain edema associated with fulminant hepatic failure (FHF). The edema may be of such magnitude as to increase intracranial pressure leading to brain herniation and death. Of the various agents implicated in the generation of astrocyte swelling, ammonia has had the greatest amount of experimental support. This article reviews mechanisms of ammonia neurotoxicity that contribute to astrocyte swelling. These include oxidative stress and the mitochondrial permeability transition (MPT). The involvement of glutamine in the production of cell swelling will be highlighted. Evidence will be provided that glutamine induces oxidative stress as well as the MPT, and that these events are critical in the development of astrocyte swelling in hyperammonemia.
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Affiliation(s)
- M D Norenberg
- Veterans Affairs Medical Center, Miami, Florida 33101, USA. mnorenbe@med,miami.edu
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6
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Norenberg MD, Rama Rao KV, Jayakumar AR. Ammonia neurotoxicity and the mitochondrial permeability transition. J Bioenerg Biomembr 2005; 36:303-7. [PMID: 15377862 DOI: 10.1023/b:jobb.0000041758.20071.19] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Ammonia is a neurotoxin that predominantly affects astrocytes. Disturbed mitochondrial function and oxidative stress, factors implicated in the induction of the mitochondrial permeability transition (MPT), appear to be involved in the mechanism of ammonia neurotoxicity. We have recently shown that ammonia induces the MPT in cultured astrocytes. To elucidate the mechanisms of the MPT, we examined the role of oxidative stress and glutamine, a byproduct of ammonia metabolism. The ammonia-induced MPT was blocked by antioxidants, suggesting a causal role of oxidative stress. Direct application of glutamine (4.5-7.0 mM) to cultured astrocytes increased free radical production and induced the MPT. Treatment of astrocytes with the mitochondrial glutaminase inhibitor, 6-diazo-5-oxo-L-norleucine, completely blocked free radical formation and the MPT, suggesting that high ammonia concentrations in mitochondria resulting from glutamine hydrolysis may be responsible for the effects of glutamine. These studies suggest that oxidative stress and glutamine play major roles in the induction of the MPT associated with ammonia neurotoxicity.
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Affiliation(s)
- M D Norenberg
- Veterans Affairs Medical Center, Miami, Florida, USA.
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7
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Rama Rao KV, Jayakumar AR, Norenberg MD. Differential response of glutamine in cultured neurons and astrocytes. J Neurosci Res 2005; 79:193-9. [PMID: 15573403 DOI: 10.1002/jnr.20295] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Glutamine, a byproduct of ammonia detoxification, is found elevated in brain in hepatic encephalopathy (HE) and other hyperammonemic disorders. Such elevation has been implicated in some of the deleterious effects of ammonia on the central nervous system (CNS). Recent studies have shown that glutamine results in the induction of the mitochondrial permeability transition (MPT) in cultured astrocytes. We examined whether glutamine shows similar effects in cultured neurons. Both cultured astrocytes and neurons were exposed to glutamine (6.5 mM) for 24 hr and the MPT was assessed by changes in cyclosporin A (CsA)-sensitive inner mitochondrial membrane potential (DeltaPsi(m)) using the potentiometric dye tetramethylrhodamine ethyl ester (TMRE). Glutamine significantly dissipated the DeltaPsi(m) in astrocytes as demonstrated by a decrease in mitochondrial TMRE fluorescence, a process that was blocked by CsA. On the other hand, treatment of cultured neurons with glutamine had no effect on the DeltaPsi(m). Dissipation of the DeltaPsi(m) in astrocytes by glutamine was blocked by treatment with 6-diazo-5-oxo-L-norleucine (DON; 100 microM), suggesting that glutamine hydrolysis and the subsequent generation of ammonia, which has been shown previously to induce the MPT, might be involved in MPT induction by glutamine. These data indicate that astrocytes but not neurons are vulnerable to the toxic effects of glutamine. The selective induction of oxidative stress and the MPT by glutamine in astrocytes may partially explain the deleterious affects of glutamine on the CNS in the setting of hyperammonemia, as well as account for the predominant involvement of astrocytes in the pathogenesis of HE and other hyperammonemic conditions.
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Affiliation(s)
- K V Rama Rao
- Department of Pathology, University of Miami School of Medicine, Miami, FL 33101, USA
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8
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Jayakumar AR, Rama Rao KV, Schousboe A, Norenberg MD. Glutamine-induced free radical production in cultured astrocytes. Glia 2004; 46:296-301. [PMID: 15048852 DOI: 10.1002/glia.20003] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Ammonia is a neurotoxin implicated in the pathogenesis of hepatic encephalopathy, Reye's syndrome, inborn errors of the urea cycle, glutaric aciduria, and other metabolic encephalopathies. Brain ammonia is predominantly metabolized to glutamine in astrocytes by glutamine synthetase. While the synthesis of glutamine has generally been viewed as the principal means of ammonia detoxification, this presumed beneficial effect has been questioned as growing evidence suggest that some of the deleterious effects of ammonia may be mediated by glutamine rather than ammonia per se. Since ammonia is known to induce the production of free radicals in cultured astrocytes, we investigated whether such production might be mediated by glutamine. Treatment of astrocytes with glutamine (4.5 mM) increased free radical production at 2-3 min (95%; P < 0.05), as well as at 1 and 3 h (42% and 49%, respectively; P < 0.05). Similarly treated cultured neurons failed to generate free radicals. Free radical production by glutamine was blocked by the antioxidants deferoxamine (40 microM) and alpha-phenyl-N-tert-butyl-nitrone (250 microM), as well as by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (500 microM). Free radical production was also blocked by 6-diazo-5-oxo-L-norleucine (1 mM), an inhibitor of glutaminase, suggesting that ammonia released by glutamine hydrolysis may be responsible for the generation of free radicals. Additionally, the mitochondrial permeability transition inhibitor, cyclosporin A, blocked free radical production by glutamine. The results indicate that astrocytes, but not neurons, generate free radicals following glutamine exposure. Glutamine-induced oxidative and/or nitrosative stress may represent a key mechanism in ammonia neurotoxicity.
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Affiliation(s)
- Arumugam R Jayakumar
- Department of Pathology, University of Miami School of Medicine, Miami, Florida 33101, USA
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9
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Rama Rao KV, Jayakumar AR, Norenberg MD. Induction of the mitochondrial permeability transition in cultured astrocytes by glutamine. Neurochem Int 2003; 43:517-23. [PMID: 12742099 DOI: 10.1016/s0197-0186(03)00042-1] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Ammonia is a toxin that has been strongly implicated in the pathogenesis of hepatic encephalopathy (HE), and astrocytes appear to be the principal target of ammonia toxicity. Glutamine, a byproduct of ammonia metabolism, has been implicated in some of the deleterious effects of ammonia on the CNS. We have recently shown that ammonia induces the mitochondrial permeability transition (MPT) in cultured astrocytes, but not in neurons. We therefore determined whether glutamine is also capable of inducing the MPT in cultured astrocytes. Astrocytes were treated with glutamine (4.5 mM) for various time periods and the MPT was assessed by changes in 2-deoxyglucose (2-DG) mitochondrial permeability, calcein fluorescence assay, and by changes in cyclosporin A (CsA)-sensitive inner mitochondrial membrane potential (deltapsi(m)) using the potentiometric dye, JC-1. Astrocytes treated with glutamine significantly increased 2-DG permeability (120%, P<0.01), decreased mitochondrial calcein fluorescence, and concomitantly dissipated the deltapsi(m). All of these effects were blocked by CsA. These data indicate that glutamine induces the MPT in cultured astrocytes. The induction of the MPT by glutamine in astrocytes, and the subsequent development of mitochondrial dysfunction, may partially explain the deleterious affects of glutamine on the CNS in the setting of hyperammonemia.
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Affiliation(s)
- K V Rama Rao
- Veterans Affairs Medical Center and Department of Pathology (D-33), P.O. Box 016960, University of Miami School of Medicine, Miami, FL 33101, USA
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10
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Burbaeva GS, Turishcheva MS, Vorobyeva EA, Savushkina OK, Tereshkina EB, Boksha IS. Diversity of glutamate dehydrogenase in human brain. Prog Neuropsychopharmacol Biol Psychiatry 2002; 26:427-35. [PMID: 11999891 DOI: 10.1016/s0278-5846(01)00273-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Three forms of glutamate dehydrogenase (GDH, EC 1.4.1.3) are purified from human brain tissue. Two of them, named GDH I (consisting of 58+/-1-kDa subunit) and GDH II (consisting of 56+/-1 -kDa subunit), are readily solubilized and the third one, GDH III (consisting of 56+/-1-kDa subunit), is a membrane-associated (particulate bound) isoform. Kinetic constants were determined for GDH III. These GDH forms were found to differ in hydrophobicity as indicated by different affinity to Phenyl-Sepharose. All three GDH forms showed microheterogeneity on two-dimensional (2-D) gel electrophoresis. Specific polyclonal antibodies, which enable to determine the levels of immunoreactivities of all the GDH forms in human brain extracts by enzyme-chemiluminescent amplified (ECL)-Western immunoblotting, were obtained.
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Affiliation(s)
- Gulnur Sh Burbaeva
- Laboratory of Neurochemistry, Mental Health Research Center RAMS, Moscow, Russia.
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11
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Schmitt A, Kugler P. Cellular and regional expression of glutamate dehydrogenase in the rat nervous system: non-radioactive in situ hybridization and comparative immunocytochemistry. Neuroscience 1999; 92:293-308. [PMID: 10392851 DOI: 10.1016/s0306-4522(98)00740-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In the central nervous system glutamate dehydrogenase appears to be strongly involved in the metabolism of transmitter glutamate and plays a role in the pathogenesis of neurodegenerative disorders. In order to identify unequivocally the neural cell types expressing this enzyme, non-radioactive in situ hybridization, using a complementary RNA probe and oligonucleotide probes, was applied to sections of the rat central nervous system and, for comparison with peripheral neural cells, to cervical spinal ganglia. The results were complemented by immunocytochemical studies using a polyclonal antibody against purified glutamate dehydrodenase. Glutamate dehydrogenase messenger RNA was detectable at varying amounts in neurons and glial cells (i.e. astrocytes, oligodendrocytes, Bergmann glia, ependymal cells, epithelial cells of the plexus choroideus) throughout the central nervous system and in neurons and satellite cells of spinal ganglia. In some neuronal populations (e.g., pyramidal cells of the hippocampus, motoneurons of the spinal cord and spinal ganglia neurons) messenger RNA-labelling was higher than in other central nervous system neurons. This is remarkable because the immunostaining of neurons in the central nervous system regions studied was at best weak, whereas a predominantly high level of immunoreactivity was detected in astrocytes (and Bergmann glia). Thus, in neurons of the central nervous system, the detected levels of glutamate dehydrogenase messenger RNA and protein seem to be at variance whereas in peripheral neurons of spinal ganglia both in situ hybridization labelling and immunostaining are intense.
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Affiliation(s)
- A Schmitt
- Institute of Anatomy, University of Würzburg, Germany
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12
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Martin M, Portais JC, Voisin P, Rousse N, Canioni P, Merle M. Comparative Analysis of 13C-Enriched Metabolites Released in the Medium of Cerebellar and Cortical Astrocytes Incubated with [1-13C]Glucose. ACTA ACUST UNITED AC 1995. [DOI: 10.1111/j.1432-1033.1995.tb20750.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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13
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Rothe F, Brosz M, Storm-Mathisen J. Quantitative ultrastructural localization of glutamate dehydrogenase in the rat cerebellar cortex. Neuroscience 1995; 64:iii-xvi. [PMID: 7753371 DOI: 10.1016/0306-4522(94)e0200-n] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Glutamate dehydrogenase is one of the main enzymes involved in the formation and metabolism of the neurotransmitter glutamate. In the present study we investigated the enzyme ultrastructurally in the cerebellar cortex, a region rich in well defined glutamatergic neurons, by pre-embedding immunocytochemical staining (peroxidase-antiperoxidase), as well as by post-embedding immunogold labelling employing a new system for quantitation and for specificity testing under the conditions of the immunocytochemical procedure. A new antiserum against immunologically purified bovine liver glutamate dehydrogenase or antibodies isolated from this by affinity chromatography were used in rats fixed by perfusion with aldehydes. The pre-embedding method displayed peroxidase reaction preferentially in mitochondria of astroglial cells (including the Bergmann glia). Mitochondria of neuronal tissue elements were usually free of peroxidase-reaction product. Extra-mitochondrial staining was not observed. The post-embedding immunogold method was employed to overcome penetration problems and allow semiquantitative analysis of localization and specificity. The highest densities of gold particles were found over the mitochondria in astroglial cell elements (including the Bergmann glia). Mitochondria in cell bodies of Bergmann glia had a lower particle density than those in astrocytic processes. In the latter, analysis of frequency distribution revealed no evidence of a population of mitochondria lacking glutamate dehydrogenase, but suggested the presence of populations with different levels of immunoreactivity. Comparison with the labelling of embedded bovine liver glutamate dehydrogenase indicated that the enzyme constitutes a high proportion (10%) of the total matrix protein of these mitochondria. A weaker but significant labelling was found in oligodendrocytes of the white matter. The labelling of mitochondria in neuronal elements including glutamatergic mossy fibre terminals was of the order of 15% of that in astroglial mitochondria. No difference was detected between glutamatergic neurons (mossy and parallel fibres, granular cells) and non-glutamatergic neurons (Purkinje cells). The particle density over non-mitochondrial areas was very close to background over empty resin. The results, obtained with different methods of tissue and antibody preparation, agree to show that the present form of glutamate dehydrogenase is restricted to mitochondria and preferentially localized in astrocytes.
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Affiliation(s)
- F Rothe
- Institute of Medical Neurobiology, Medical Faculty, University of Magdeburg, Germany
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14
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Rothe F, Brosz M, Storm-Mathisen J. Quantitative ultrastructural localization of glutamate dehydrogenase in the rat cerebellar cortex. Neuroscience 1994; 62:1133-46. [PMID: 7531302 DOI: 10.1016/0306-4522(94)90349-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Glutamate dehydrogenase is one of the main enzymes involved in the formation and metabolism of the neurotransmitter glutamate. In the present study we investigated the enzyme ultrastructurally in the cerebellar cortex, a region rich in well defined glutamatergic neurons, by pre-embedding immunocytochemical staining (peroxidase-antiperoxidase), as well as by post-embedding immunogold labelling employing a new system for quantitation and for specificity testing under the conditions of the immunocytochemical procedure. A new antiserum against immunologically purified bovine liver glutamate dehydrogenase or antibodies isolated from this by affinity chromatography were used in rats fixed by perfusion with aldehydes. The pre-embedding method displayed peroxidase reaction preferentially in mitochondria of astroglial cells (including the Bergmann glia). Mitochondria of neuronal tissue elements were usually free of peroxidase-reaction product. Extra-mitochondrial staining was not observed. The post-embedding immunogold method was employed to overcome penetration problems and allow semiquantitative analysis of localization and specificity. The highest densities of gold particles were found over the mitochondria in astroglial cell elements (including the Bergmann glia). Mitochondria in cell bodies of Bergmann glia had a lower particle density than those in astrocytic processes. In the latter, analysis of frequency distribution revealed no evidence of a population of mitochondria lacking glutamate dehydrogenase, but suggested the presence of populations with different levels of immunoreactivity. Comparison with the labelling of embedded bovine liver glutamate dehydrogenase indicated that the enzyme constitutes a high proportion (10%) of the total matrix protein of these mitochondria. A weaker but significant labelling was found in oligodendrocytes of the white matter. The labelling of mitochondria in neuronal elements including glutamatergic mossy fibre terminals was of the order of 15% of that in astroglial mitochondria. No difference was detected between glutamatergic neurons (mossy and parallel fibres, granular cells) and non-glutamatergic neurons (Purkinje cells). The particle density over non-mitochondrial areas was very close to background over empty resin. The results, obtained with different methods of tissue and antibody preparation, agree to show that the present form of glutamate dehydrogenase is restricted to mitochondria and preferentially localized in astrocytes.
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Affiliation(s)
- F Rothe
- Institute of Medical Neurobiology, Medical Faculty, University of Magdeburg, Germany
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15
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Rao VL, Murthy CR. Uptake and metabolism of glutamate and aspartate by astroglial and neuronal preparations of rat cerebellum. Neurochem Res 1993; 18:647-54. [PMID: 8099717 DOI: 10.1007/bf00966777] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Astrocytes, neuronal perikarya and synaptosomes were prepared from rat cerebellum. Kinetics of high and low affinity uptake systems of glutamate and aspartate, nominal rates of 14CO2 production from [U-14C]glutamate, [U-14C]aspartate and [1-14C]glutamate and activities of enzymes of glutamate metabolism were studied in these preparations. The rate of uptake and the nomial rate of production of 14CO2 from these amino acids was higher in the astroglia than neuronal perikarya and synaptosomes. Activities of glutamine synthetase and glutamate dehydrogenase were higher in astrocytes than in neuronal perikarya and synaptosomes. Activities of glutaminase and glutamic acid decarboxylase were observed to be highest in neuronal perikarya and synaptosomes respectively. These results are in agreement with the postulates of theory of metabolic compartmentation of glutamate while others (presence of glutaminase in astrocytes and glutamine synthetase in synaptosomes) are not. Results of this study also indicated that (i) at high extracellular concentrations, glutamate/aspartate uptake may be predominantly into astrocytes while at low extracellular concentrations, it would be into neurons (ii) production of alpha-ketoglutarate from glutamate is chiefly by way of transamination but not by oxidative deamination in these three preparations and (iii) there are topographical differences glutamate metabolism within the neurons.
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Affiliation(s)
- V L Rao
- School of Life Sciences, University of Hyderabad, India
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16
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Kugler P. Enzymes involved in glutamatergic and GABAergic neurotransmission. INTERNATIONAL REVIEW OF CYTOLOGY 1993; 147:285-336. [PMID: 7901176 DOI: 10.1016/s0074-7696(08)60771-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- P Kugler
- Department of Anatomy, University of Würzburg, Germany
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17
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Rao VL, Murthy CR. Hyperammonemic alterations in the metabolism of glutamate and aspartate in rat cerebellar astrocytes. Neurosci Lett 1992; 138:107-10. [PMID: 1357596 DOI: 10.1016/0304-3940(92)90483-n] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Pathophysiological concentrations of ammonia, both in vivo and in vitro, suppressed the production of 14CO2 from 14C-labelled glutamate and aspartate in astrocytes isolated from the rat cerebellum. Suppression of 14CO2 production with (aminooxy)acetic acid but not with glutamic acid diethyl ester indicated that transamination plays a major role in the oxidation of glutamate carbons. Activities of the enzymes, aspartate amino-transferase, alanine aminotransferase and glutaminase were decreased while those of glutamate dehydrogenase and glutamine synthetase were enhanced in the cerebellar astrocytes during hyperammonemic states. These results suggest an impairment of astrocytic glutamate metabolism during hyperammonemia.
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Affiliation(s)
- V L Rao
- School of Life Sciences, University of Hyderabad, India
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Yudkoff M, Nissim I, Hertz L, Pleasure D, Erecinska M. Chapter 18: Nitrogen metabolism: neuronal-astroglial relationships. PROGRESS IN BRAIN RESEARCH 1992; 94:213-24. [PMID: 1363141 DOI: 10.1016/s0079-6123(08)61752-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/25/2023]
Affiliation(s)
- M Yudkoff
- Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia
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19
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Fressinaud C, Weinrauder H, Delaunoy JP, Tholey G, Labourdette G, Sarliève LL. Glutamine synthetase expression in rat oligodendrocytes in culture: regulation by hormones and growth factors. J Cell Physiol 1991; 149:459-68. [PMID: 1683875 DOI: 10.1002/jcp.1041490315] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Glutamine synthetase (GS, EC 6.3.1.2.) has long been considered as a protein specific for astrocytes in the brain, but recently GS immunoreactivity has been reported in oligodendrocytes both in mixed primary glial cell cultures and in vivo. We have investigated its expression and regulation in "pure" oligodendrocyte cultures. "Pure" oligodendrocyte secondary cultures were derived from newborn rat brain primary cultures enriched in oligodendrocytes as described by Besnard et al. (1987) and were grown in chemically defined medium. These cultures contain more than 90% galactocerebroside-positive oligodendrocytes and produce "myelin" membranes (Fressinaud et al., 1990) after 6-10 days in subcultures (30-35 days, total time in culture). The presence of GS in oligodendrocytes from both primary glial cell cultures and "pure" oligodendrocyte cultures was confirmed by double immunostaining with a rabbit antisheep GS and guinea pig antirat brain myelin 2', 3'-cyclic nucleotide 3'-phosphodiesterase. In "pure" oligodendrocyte cultures, about half of cells were labeled with anti-GS antibody. Furthermore, on the immunoblot performed with a rabbit antisheep GS, the GS protein in "pure" oligodendrocyte secondary cultures was visualized as a single band with an apparent molecular mass of about 43 kDa. In contrast, two protein bands for GS were observed in cultured astrocytes. On the immunoblot performed with a rabbit antichick GS, two immunopositive protein bands were observed: a major one migrating as the purified adult chick brain GS and a minor one with a lower molecular mass. Two similar immunoreactive bands were also observed in pure rat astrocyte cultures. Compared to pure rat astrocyte cultures, "pure" oligodendrocyte cultures of the same age displayed an unexpectedly high GS specific activity that could not be explained by astrocytic contamination of the cultures (less than 5%). As for cultured astrocytes, treatment of oligodendrocyte cultures with dibutyryl-adenosine 3':5'-cyclic monophosphate, triiodothyronine, or hydrocortisone increased significantly GS specific activity. Interestingly, epidermal growth factor, basic fibroblast growth factor, and platelet-derived growth factor that increase the GS activity in astrocytes do not affect this activity in oligodendrocytes. Thus we confirm the finding of Warringa et al. (1988) that GS is also expressed in oligodendrocytes. We show that its activity is regulated similarly in astrocytes and oligodendrocytes by hormones, but that it is regulated differently by growth factors in these two cell types.
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Affiliation(s)
- C Fressinaud
- Centre de Neurochimie du CNRS, Strasbourg, France
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20
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Rao VL, Murthy CR. Hyperammonemic alterations in the uptake and release of glutamate and aspartate by rat cerebellar preparations. Neurosci Lett 1991; 130:49-52. [PMID: 1684234 DOI: 10.1016/0304-3940(91)90224-h] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Release and uptake of neurotransmitter amino acids, glutamate and aspartate, were studied in the synaptosomes, astrocytes and in the perikarya of granule neurons isolated from the cerebella of normal and hyperammonemic rats. During acute hyperammonemia, depolarization-induced release of both the amino acids from the synaptosomes was elevated. The Vmax values of high-affinity uptake systems were elevated without alterations in the Km values for these two amino acids during acute hyperammonemic states. In the case of the low-affinity uptake system of these two amino acids, there was a decrease in the Km values without alterations in the Vmax values. These results are discussed in relation to the mechanism of ammonia toxicity.
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Affiliation(s)
- V L Rao
- School of Life Sciences, University of Hyderabad, India
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Tansey FA, Farooq M, Cammer W. Glutamine synthetase in oligodendrocytes and astrocytes: new biochemical and immunocytochemical evidence. J Neurochem 1991; 56:266-72. [PMID: 1670954 DOI: 10.1111/j.1471-4159.1991.tb02591.x] [Citation(s) in RCA: 119] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The results of recent immunocytochemical experiments suggest that glutamine synthetase (GS) in the rat CNS may not be confined to astrocytes. In the present study, GS activity was assayed in oligodendrocytes isolated from bovine brain and in oligodendrocytes, astrocytes, and neurons isolated from rat forebrain, and the results were compared with new immunochemical data. Among the cells isolated from rat brain, astrocytes had the highest specific activities of GS, followed by oligodendrocytes. Oligodendrocytes isolated from white matter of bovine brain had GS specific activities almost fivefold higher than those in white matter homogenates. Immunocytochemical staining also showed the presence of GS in both oligodendrocytes and astrocytes in bovine forebrain, in three white-matter regions of rat brain, and in Vibratome sections as well as paraffin sections.
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Affiliation(s)
- F A Tansey
- Department of Neurology, Albert Einstein College of Medicine, Bronx, New York 10461
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22
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Yudkoff M, Nissim I, Hertz L. Precursors of glutamic acid nitrogen in primary neuronal cultures: studies with 15N. Neurochem Res 1990; 15:1191-6. [PMID: 2097513 DOI: 10.1007/bf01208579] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We utilized gas chromatography-mass spectrometry to study the transfer of 15N from [2-15N]glutamine, [15N]leucine, [15N]alanine, or 15NH4Cl to [15N]glutamate and [15N]aspartate in cultured cerebrocortical GABA-ergic neurons from the mouse. Initial rates of 15N appearance (atom % excess) were somewhat higher with 2mM [2-15N]glutamine as a precursor than with 1mM [15N]leucine or 1mM [15N]alanine, but initial net formation (nmol [15N]glutamate/mg protein.min-1) was roughly comparable with all precursors. At steady-state 15N labeling was about two times greater with 2mM [2-15N]glutamine as precursor. The subsequent transfer of 15N from glutamate to aspartate was extremely rapid, the labelling pattern of these two amino acid pools being virtually indistinguishable. We observed little reductive amination of 2-oxo-glutarate to yield [15N]glutamate in the presence of 0.3mM 15NH4Cl. Reductive amination through glutamate dehydrogenase was much more prominent at a concentration of 3.0mM 15NH4Cl. Glutamate formation via reductive amination was unaffected by inclusion of 1mM 2-oxo-glutarate in the incubation medium. These results indicate that glutamate synthesis in cultured GABA-ergic neurons is derived not only from the glutaminase reaction, but also from transamination reactions in which both leucine and alanine are efficient N donors. Reductive amination of 2-oxo-glutarate in the glutamate dehydrogenase pathway plays a relatively minor role at lower concentrations of extracellular ammonia but becomes quite active at 3mM ammonia.
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Affiliation(s)
- M Yudkoff
- Division of Metabolism, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia 19104
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Affiliation(s)
- M Erecińska
- Department of Pharmacology, University of Pennsylvania, School of Medicine, Philadelphia 19104-6084
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24
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Lai JC, Murthy CR, Cooper AJ, Hertz E, Hertz L. Differential effects of ammonia and beta-methylene-DL-aspartate on metabolism of glutamate and related amino acids by astrocytes and neurons in primary culture. Neurochem Res 1989; 14:377-89. [PMID: 2569676 DOI: 10.1007/bf01000042] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The effects of ammonium chloride (3 mM) and beta-methylene-DL-aspartate (BMA; 5 mM) (an inhibitor of aspartate aminotransferase, a key enzyme of the malate-aspartate shuttle (MAS] on the metabolism of glutamate and related amino acids were studied in primary cultures of astrocytes and neurons. Both ammonia and BMA inhibited 14CO2 production from [U-14C]- and [1-14C]glutamate by astrocytes and neurons and their effects were partially additive. Acute treatment of astrocytes with ammonia (but not BMA) increased astrocytic glutamine. Acute treatment of astrocytes with ammonia or BMA decreased astrocytic glutamate and aspartate (both are key components of the MAS). Acute treatment of neurons with ammonia decreased neuronal aspartate and glutamine and did not apparently affect the efflux of aspartate from neurons. However, acute BMA treatment of neurons led to decreased neuronal glutamate and glutamine and apparently reduced the efflux of aspartate and glutamine from neurons. The data are consistent with the notion that both ammonia and BMA may inhibit the MAS although BMA may also directly inhibit cellular glutamate uptake. Additionally, these results also suggest that ammonia and BMA exert differential effects on astroglial and neuronal glutamate metabolism.
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Affiliation(s)
- J C Lai
- Department of Biochemistry, Cornell University Medical College, New York, NY 10021
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25
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Ratnakumari L, Murthy CR. Activities of pyruvate dehydrogenase, enzymes of citric acid cycle, and aminotransferases in the subcellular fractions of cerebral cortex in normal and hyperammonemic rats. Neurochem Res 1989; 14:221-8. [PMID: 2725822 DOI: 10.1007/bf00971314] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Activity levels of pyruvate dehydrogenase, enzymes of citric acid cycle, aspartate and alanine aminotransferases were estimated in mitochondria, synaptosomes and cytosol isolated from brains of normal rats and those injected with acute and subacute doses of ammonium acetate. In mitochondria isolated from animals treated with acute dose of ammonium acetate, there was an elevation in the activities of pyruvate, isocitrate and succinate dehydrogenases while the activities of malate dehydrogenase (malate----oxaloacetate), aspartate and alanine aminotransferases were suppressed. In subacute conditions a similar profile of change was noticed excepting that there was an elevation in the activity of alpha-ketoglutarate dehydrogenase in mitochondria. In the synaptosomes isolated from animals administered with acute dose of ammonium acetate, there was an increase in the activities of pyruvate, isocitrate, alpha-ketoglutarate and succinate dehydrogenases while the changes in the activities of malate dehydrogenase, aspartate and alanine amino transferases were suppressed. In the subacute toxicity similar changes were observed in this fraction except that the activity of malate dehydrogenase (oxaloacetate----malate) was enhanced. In the cytosol, pyruvate dehydrogenase and other enzymes of citric acid cycle except malate dehydrogenase were enhanced in both acute and subacute ammonia toxicity though their activities are lesser than that of mitochondria. In this fraction malate dehydrogenase (oxaloacetate----malate) was enhanced while activities of malate dehydrogenase (malate----oxaloacetate), aspartate and alanine aminotransferases were suppressed in both the conditions. Based on these results it is concluded that the decreased activities of malate dehydrogenase (malate----oxaloacetate) in mitochondria and of aspartate aminotransferase in mitochondria and cytosol may be responsible for the disruption of malate-aspartate shuttle in hyperammonemic state.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L Ratnakumari
- School of Life Sciences, University of Hyderabad, India
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26
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Yudkoff M, Nissim I, Pleasure D. Astrocyte metabolism of [15N]glutamine: implications for the glutamine-glutamate cycle. J Neurochem 1988; 51:843-50. [PMID: 2900878 DOI: 10.1111/j.1471-4159.1988.tb01820.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The metabolism of glutamine was studied in cultured astrocytes by incubating these cells with [2-15N]-glutamine and using gas chromatography-mass spectrometry to quantitate the transfer of 15N to other amino acids. We found that astrocytes simultaneously synthesize and consume [2-15N]glutamine, with the respective synthetic and utilization rates being approximately equal (ca. 13.0 nmol min-1 mg protein-1). Considerable 15N was transferred to alanine and a significant amount to the essential amino acids leucine, tyrosine, and phenylalanine, the latter process denoting active reamination of cognate ketoacids. A net export of alanine into the medium was noted. Astrocyte glutamine utilization appeared to be mediated via both the phosphate-activated glutaminase (PAG) pathway and the glutamine aminotransferase pathway, the activity of which was about half that of PAG. The glutamine concentration in the incubation medium determined whether net synthesis or utilization of this amino acid occurred. When glutamine was omitted from the medium, net synthesis occurred. When it was present at a high (5 mM) level, net consumption was observed. At a physiologic (0.5 mM) concentration, neither net synthesis nor consumption was noted, although the 15N data indicated that glutamine was actively metabolized. An implication of this work is that astrocytes clearly are capable of both synthesizing and utilizing glutamine, and current concepts of a glutamate-glutamine cycle functioning stoichiometrically between astrocytes and neurons may be an oversimplification.
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Affiliation(s)
- M Yudkoff
- Division of Biochemical Development and Molecular Disease, Children's Hospital of Philadelphia, PA 19104
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27
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Silverman SJ, Vemuri MC, Lipsky RH. Differences in nuclear proteins of neurons, astrocytes and C-6 glioma cells. Neurochem Int 1988; 12:513-8. [DOI: 10.1016/0197-0186(88)90036-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/24/1987] [Indexed: 11/30/2022]
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28
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Albrecht J, Wysmyk-Cybula U, Rafałowska U. Cerebral oxygen consumption in experimental hepatic encephalopathy: different responses in astrocytes, neurons, and synaptosomes. Exp Neurol 1987; 97:418-22. [PMID: 3609222 DOI: 10.1016/0014-4886(87)90102-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Oxygen consumption was measured polarographically in fractions enriched in astrocytes or neurons, and in synaptosomes derived from rats in which two subsequent stages of acute hepatic encephalopathy were induced by thioacetamide treatment. A 30% decrease of oxygen consumption was noted in astrocytes from animals with coma, well in agreement with the decrease of whole cerebral oxygen consumption and the increase of whole brain ammonia. In contrast, at the same stage the oxygen consumption in neurons was increased by some 35%, whereas synaptosomes remained unaffected. The results are in keeping with the view that astrocytes are the cells whose metabolism is primarily affected during hepatic encephalopathy. On the other hand, they support recent pathophysiologic evidence that ammonia-induced neuronal dysfunction is not a consequence of impaired energy metabolism in the nerve cells.
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Tholey G, Ghandour MS, Bloch S, Ledig M, Mandel P. Glutamine synthetase and energy metabolism enzymes in cultivated chick neurons and astrocytes: modulation by serum and hydrocortisone. Brain Res 1987; 428:73-81. [PMID: 2880646 DOI: 10.1016/0165-3806(87)90084-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Primary cultures of astroglial cells and of neurons obtained from chick embryos were grown in culture medium with and without serum added. The expression of glutamine synthetase (GS) in the cultured nerve cells was investigated immunocytochemically and biochemically. The cellular localization of GS in cerebellar tissue sections and in cerebral cortex of chick embryos was investigated by immunohistochemical staining. In tissue sections the enzyme is only present in astrocytes and their processes; neurons and their structures do not express the enzyme. In contrast, in pure neuronal primary cultures, a high level of GS was detected by biochemical and immunochemical methods. Thus, our results clearly indicate the presence of GS in pure neuronal cell cultures and its absence in this type of cells in vivo. Removal of serum from the culture medium enhanced GS levels in primary astrocyte cultures, but was without effect on GS activity in neurons. Addition of calf serum to the culture medium induces a two-fold increase of cellular lactate dehydrogenase (LDH) activity in neurons by increasing specifically the M subunit containing isoenzymes. The sensitivity of chick astroglial cells and neurons toward the GS inducing effect of hydrocortisone and modulation of its effect by serum was also investigated. Differences in the sensitivity of the two types of nerve cells in culture toward the GS inducing effect of hydrocortisone, and the effect of serum could be demonstrated.
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Schünzel G, Wolf G, Rothe F, Seidler E. Histophotometric evaluation of glutamate dehydrogenase activity of the rat hippocampal formation during postnatal development, with special reference to the glutamate transmitter metabolism. Cell Mol Neurobiol 1986; 6:31-42. [PMID: 2872962 DOI: 10.1007/bf00742974] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Transmitter glutamate/aspartate synthesis is known to proceed along different metabolic pathways. In this light, the functional relevance of glutamate dehydrogenase in postnatally maturing glutamatergic/aspartatergic structures was studied by means of quantitative enzyme histochemistry. The basic requirements concerning the kinetics and calibration of the histochemical glutamate dehydrogenase reaction used were proved to be met in order to obtain valid quantitative data. The histochemically demonstrable activity of glutamate dehydrogenase (EC 1.4.1.3) in the hippocampal formation of the rat increased markedly during postnatal development. On day 30, the distribution pattern observed was similar to that in adult animals. While the enzyme activity rose within cell body layers from day 0 to day 30 by 240-285%, the increase in neuropil layers was found to be up to 830%. Maximum values were seen in the stratum lacunosum-moleculare of CA1 and CA3 and the stratum moleculare of the dentate fascia on day 30. Since the hippocampal neuropil is supposed to be copiously provided with glutamatergic (and aspartatergic?) structures which become functional in rats during the first weeks of postnatal life, the increase in enzyme activity is discussed to be primarily a consequence of maturing synaptic systems using glutamate and/or aspartate as transmitters.
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31
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Subbalakshmi GY, Murthy CR. Differential response of enzymes of glutamate metabolism in neuronal perikarya and synaptosomes in acute hyperammonemia in rat. Neurosci Lett 1985; 59:121-6. [PMID: 2864671 DOI: 10.1016/0304-3940(85)90225-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Activity levels of the enzymes of glutamate metabolism were determined in the neuronal perikarya and synaptosomes isolated from the cerebral cortex of normal and hyperammonemic rats. In neuronal perikarya, the activities of glutamate dehydrogenase, aspartate, alanine aminotransferases and glutamine synthetase were elevated in hyperammonemic states. In synaptosomes, glutamate dehydrogenase and aspartate aminotransferase were suppressed, while glutamine synthetase and glutaminase were elevated. These results suggested the involvement of neuronal perikarya in ammonia detoxification at least in acute hyperammonemic states.
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