1
|
Jeitner TM, Battaile K, Cooper AJL. Critical Evaluation of the Changes in Glutamine Synthetase Activity in Models of Cerebral Stroke. Neurochem Res 2015; 40:2544-56. [DOI: 10.1007/s11064-015-1667-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Revised: 05/14/2015] [Accepted: 05/20/2015] [Indexed: 01/04/2023]
|
2
|
Rapid Elevation of Calcium Concentration in Cultured Dorsal Spinal Cord Astrocytes by Corticosterone. Neurochem Res 2012. [DOI: 10.1007/s11064-012-0929-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
3
|
Coulter DA, Eid T. Astrocytic regulation of glutamate homeostasis in epilepsy. Glia 2012; 60:1215-26. [PMID: 22592998 PMCID: PMC3375386 DOI: 10.1002/glia.22341] [Citation(s) in RCA: 213] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Accepted: 03/16/2012] [Indexed: 12/18/2022]
Abstract
Astrocytes play a critical role in regulation of extracellular neurotransmitter levels in the central nervous system. This function is particularly prominent for the excitatory amino acid glutamate, with estimates that 80-90% of extracellular glutamate uptake in brain is through astrocytic glutamate transporters. This uptake has significance both in regulation of the potential toxic accumulation of extracellular glutamate and in normal resupply of inhibitory and excitatory synapses with neurotransmitter. This resupply of neurotransmitter is accomplished by astroglial uptake of glutamate, transformation of glutamate to glutamine by the astrocytic enzyme glutamine synthetase (GS), and shuttling of glutamine back to excitatory and inhibitory neurons via specialized transporters. Once in neurons, glutamine is enzymatically converted back to glutamate, which is utilized for synaptic transmission, either directly, or following decarboxylation to γ-aminobutyric acid. Many neurologic and psychiatric conditions, particularly epilepsy, are accompanied by the development of reactive gliosis, a pathology characterized by anatomical and biochemical plasticity in astrocytes, accompanied by proliferation of these cells. Among the biochemical changes evident in reactive astrocytes is a downregulation of several of the important regulators of the glutamine-glutamate cycle, including GS, and possibly also glutamate transporters. This downregulation may have significance in contributing both to the aberrant excitability and to the altered neuropathology characterizing epilepsy. In the present review, we provide an overview of the normal function of astrocytes in regulating extracellular glutamate homeostasis, neurotransmitter supply, and excitotoxicity. We further discuss the potential role reactive gliosis may play in the pathophysiology of epilepsy.
Collapse
Affiliation(s)
- Douglas A Coulter
- Departments of Pediatrics and Neuroscience, University of Pennsylvania School of Medicine and the Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Tore Eid
- Departments of Laboratory Medicine and Neurosurgery, Yale University School of Medicine and the Clinical Chemistry Laboratory, Yale-New Haven Hospital, New Haven, Connecticut
| |
Collapse
|
4
|
Perez EL, Lauritzen F, Wang Y, Lee TSW, Kang D, Zaveri HP, Chaudhry FA, Ottersen OP, Bergersen LH, Eid T. Evidence for astrocytes as a potential source of the glutamate excess in temporal lobe epilepsy. Neurobiol Dis 2012; 47:331-7. [PMID: 22659305 DOI: 10.1016/j.nbd.2012.05.010] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Revised: 05/07/2012] [Accepted: 05/24/2012] [Indexed: 12/26/2022] Open
Abstract
Increased extracellular brain glutamate has been implicated in the pathophysiology of human refractory temporal lobe epilepsy (TLE), but the cause of the excessive glutamate is unknown. Prior studies by us and others have shown that the glutamate degrading enzyme glutamine synthetase (GS) is deficient in astrocytes in the epileptogenic hippocampal formation in a subset of patients with TLE. We have postulated that the loss of GS in TLE leads to increased glutamate in astrocytes with elevated concentrations of extracellular glutamate and recurrent seizures as the ultimate end-points. Here we test the hypothesis that the deficiency in GS leads to increased glutamate in astrocytes. Rats were chronically infused with methionine sulfoximine (MSO, n=4) into the hippocampal formation to induce GS deficiency and recurrent seizures. A separate group of rats was infused with 0.9% NaCl (saline) as a control (n=6). At least 10days after the start of infusion, once recurrent seizures were established in the MSO-treated rats, the concentration of glutamate was assessed in CA1 of the hippocampal formation by immunogold electron microscopy. The concentration of glutamate was 47% higher in astrocytes in the MSO-treated vs. saline-treated rats (p=0.02), and the ratio of glutamate in astrocytes relative to axon terminals was increased by 74% in the MSO-treated rats (p=0.003). These data support our hypothesis that a deficiency in GS leads to increased glutamate in astrocytes. We additionally propose that the GS-deficient astrocytes in the hippocampal formation in TLE lead to elevated extracellular brain glutamate either through decreased clearance of extracellular glutamate or excessive release of glutamate into the extracellular space from these cells, or a combination of the two.
Collapse
Affiliation(s)
- Edgar L Perez
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT 06520, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Takahashi K, Saitoh A, Yamada M, Iwai T, Inagaki M, Yamada M. Dexamethasone indirectly induces Ndrg2 expression in rat astrocytes. J Neurosci Res 2011; 90:160-6. [PMID: 21928335 DOI: 10.1002/jnr.22727] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2011] [Revised: 05/17/2011] [Accepted: 06/02/2011] [Indexed: 12/16/2022]
Abstract
N-myc downstream-regulated gene 2 (Ndrg2) has been associated with cell proliferation, differentiation, and apoptosis. Ndrg2 expression in the brain is induced by glucocorticoid treatment or chronic stress in vivo. It has been postulated that glucocorticoid-induced Ndrg2 expression in astrocytes is regulated by the glucocorticoid response element half-site (GRE1/2) upstream of the Ndrg2 transcription site. Here we examined the mechanisms of dexamethasone-induced Ndrg2 expression in rat astrocytes. Ndrg2 mRNA expression in primary astrocytes was significantly increased after 24 hr of exposure to dexamethasone in a concentration-dependent manner. Dexamethasone-induced Ndrg2 mRNA and protein expression was blocked by pretreatment with RU486, a glucocorticoid receptor antagonist. Moreover, dexamethasone-induced Ndrg2 mRNA expression was reduced by pretreatment with the protein synthesis inhibitor cycloheximide. The Ndrg2 reporter assay showed that deletion of a putative GRE1/2, located upstream of Ndrg2, did not affect induction by dexamethasone. A region between -755 and -701 bp from the transcription start site was shown to regulate induction by dexamethasone using promoter constructs progressively deleted from the 5' to 3' ends. This region contained the predicted transcription factor binding sites for early B-cell factor 1 (Ebf1), nuclear factor-κB (NFκB), and paired box gene 5 (Pax5). Mutation at the NFκB- or Pax5-binding site, but not the Ebf1 binding site, abolished dexamethasone-induced promoter activation. These results indicate that Ndrg2 expression was indirectly induced by dexamethasone at the DNA level, potentially by the binding of NFκB or Pax5 to the transcription factor binding sites, and GRE1/2 was not involved in this induction.
Collapse
Affiliation(s)
- Kou Takahashi
- Department of Neuropsychopharmacology, National Institute of Mental Health, National Center of Neurology and Psychiatry, Tokyo, Japan
| | | | | | | | | | | |
Collapse
|
6
|
Pathmajeyan MS, Patel SA, Carroll JA, Seib T, Striebel JF, Bridges RJ, Chesebro B. Increased excitatory amino acid transport into murine prion protein knockout astrocytes cultured in vitro. Glia 2011; 59:1684-94. [PMID: 21766339 DOI: 10.1002/glia.21215] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Accepted: 06/16/2011] [Indexed: 11/06/2022]
Abstract
Prion protein (PrP) is expressed on a wide variety of cells and plays an important role in the pathogenesis of transmissible spongiform encephalopathies. However, its normal function remains unclear. Mice that do not express PrP exhibit deficits in spatial memory and abnormalities in excitatory neurotransmission suggestive that PrP may function in the glutamatergic synapse. Here, we show that transport of D-aspartate, a nonmetabolized L-glutamate analog, through excitatory amino acid transporters (EAATs) was faster in astrocytes from PrP knockout (PrPKO) mice than in astrocytes from C57BL/10SnJ wild-type (WT) mice. Experiments using EAAT subtype-specific inhibitors demonstrated that in both WT and PrPKO astrocytes, the majority of transport was mediated by EAAT1. Furthermore, PrPKO astrocytes were more effective than WT astrocytes at alleviating L-glutamate-mediated excitotoxic damage in both WT and PrPKO neuronal cultures. Thus, in this in vitro model, PrPKO astrocytes exerted a functional influence on neuronal survival and may therefore influence regulation of glutamatergic neurotransmission in vivo.
Collapse
Affiliation(s)
- Melissa S Pathmajeyan
- Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, NIAID, National Institute of Health, Hamilton, Montana, USA
| | | | | | | | | | | | | |
Collapse
|
7
|
Danielyan L, Zellmer S, Sickinger S, Tolstonog GV, Salvetter J, Lourhmati A, Reissig DD, Gleiter CH, Gebhardt R, Buniatian GH. Keratinocytes as depository of ammonium-inducible glutamine synthetase: age- and anatomy-dependent distribution in human and rat skin. PLoS One 2009; 4:e4416. [PMID: 19204801 PMCID: PMC2637544 DOI: 10.1371/journal.pone.0004416] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Accepted: 12/23/2008] [Indexed: 02/02/2023] Open
Abstract
In inner organs, glutamine contributes to proliferation, detoxification and establishment of a mechanical barrier, i.e., functions essential for skin, as well. However, the age-dependent and regional peculiarities of distribution of glutamine synthetase (GS), an enzyme responsible for generation of glutamine, and factors regulating its enzymatic activity in mammalian skin remain undisclosed. To explore this, GS localization was investigated using immunohistochemistry and double-labeling of young and adult human and rat skin sections as well as skin cells in culture. In human and rat skin GS was almost completely co-localized with astrocyte-specific proteins (e.g. GFAP). While GS staining was pronounced in all layers of the epidermis of young human skin, staining was reduced and more differentiated among different layers with age. In stratum basale and in stratum spinosum GS was co-localized with the adherens junction component beta-catenin. Inhibition of, glycogen synthase kinase 3beta in cultured keratinocytes and HaCaT cells, however, did not support a direct role of beta-catenin in regulation of GS. Enzymatic and reverse transcriptase polymerase chain reaction studies revealed an unusual mode of regulation of this enzyme in keratinocytes, i.e., GS activity, but not expression, was enhanced about 8-10 fold when the cells were exposed to ammonium ions. Prominent posttranscriptional up-regulation of GS activity in keratinocytes by ammonium ions in conjunction with widespread distribution of GS immunoreactivity throughout the epidermis allows considering the skin as a large reservoir of latent GS. Such a depository of glutamine-generating enzyme seems essential for continuous renewal of epidermal permeability barrier and during pathological processes accompanied by hyperammonemia.
Collapse
Affiliation(s)
- Lusine Danielyan
- Department of Clinical Pharmacology, University Hospital of Tübingen, Tübingen, Germany
| | - Sebastian Zellmer
- Institute of Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Stefan Sickinger
- Institute of Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Genrich V. Tolstonog
- Heinrich-Pette-Institute for Experimental Virology and Immunology, Hamburg, Germany
| | | | - Ali Lourhmati
- Department of Clinical Pharmacology, University Hospital of Tübingen, Tübingen, Germany
| | | | - Cristoph H. Gleiter
- Department of Clinical Pharmacology, University Hospital of Tübingen, Tübingen, Germany
| | - Rolf Gebhardt
- Institute of Biochemistry, Medical Faculty, University of Leipzig, Leipzig, Germany
| | | |
Collapse
|
8
|
Eid T, Williamson A, Lee TSW, Petroff OA, De Lanerolle NC. Glutamate and astrocytes-Key players in human mesial temporal lobe epilepsy? Epilepsia 2008; 49 Suppl 2:42-52. [DOI: 10.1111/j.1528-1167.2008.01492.x] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
9
|
Modulation of glutamatergic and GABAergic neurotransmission by corticosteroid hormones and stress. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s0921-0709(05)80029-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
|
10
|
Eid T, Thomas MJ, Spencer DD, Rundén-Pran E, Lai JCK, Malthankar GV, Kim JH, Danbolt NC, Ottersen OP, de Lanerolle NC. Loss of glutamine synthetase in the human epileptogenic hippocampus: possible mechanism for raised extracellular glutamate in mesial temporal lobe epilepsy. Lancet 2004; 363:28-37. [PMID: 14723991 DOI: 10.1016/s0140-6736(03)15166-5] [Citation(s) in RCA: 302] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
BACKGROUND High extracellular glutamate concentrations have been identified as a likely trigger of epileptic seizures in mesial temporal lobe epilepsy (MTLE), but the underlying mechanism remains unclear. We investigated whether a deficiency in glutamine synthetase, a key enzyme in catabolism of extracellular glutamate in the brain, could explain the perturbed glutamate homoeostasis in MTLE. METHODS The anteromedial temporal lobe is the focus of the seizures in MTLE, and surgical resection of this structure, including the hippocampus, leads to resolution of seizures in many cases. By means of immunohistochemistry, western blotting, and functional enzyme assays, we assessed the distribution, quantity, and activity of glutamine synthetase in the MTLE hippocampus. FINDINGS In western blots, the expression of glutamine synthetase in the hippocampus was 40% lower in MTLE than in non-MTLE samples (median 44 [IQR 30-58] vs 69 [56-87]% of maximum concentration in standard curve; p=0.043; n=8 and n=6, respectively). The enzyme activity was lower by 38% in MTLE vs non-MTLE (mean 0.0060 [SD 0.0031] vs 0.0097 [0.0042] U/mg protein; p=0.045; n=6 and n=9, respectively). Loss of glutamine synthetase was particularly pronounced in areas of the MTLE hippocampus with astroglial proliferation, even though astrocytes normally have high content of the enzyme. Quantitative immunoblotting showed no significant change in the amount of EAAT2, the predominant glial glutamate transporter in the hippocampus. INTERPRETATION A deficiency in glutamine synthetase in astrocytes is a possible molecular basis for extracellular glutamate accumulation and seizure generation in MTLE. Further studies are needed to define the cause, but the loss of glutamine synthetase may provide a new focus for therapeutic interventions in MTLE.
Collapse
Affiliation(s)
- T Eid
- Department of Neurosurgery, Yale University School of Medicine, New Haven, CT, USA.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Rao TS, Lariosa-Willingham KD, Yu N. Glutamate-dependent glutamine, aspartate and serine release from rat cortical glial cell cultures. Brain Res 2003; 978:213-22. [PMID: 12834916 DOI: 10.1016/s0006-8993(03)02841-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Glia play a pivotal role in glutaminergic excitatory neurotransmission in the central nervous system by regulating synaptic levels of glutamate and by providing glutamine as the sole precursor for the neurotransmitter pool glutamate to neurons through the glutamate-glutamine cycle. In the present investigation, we examined the influence of glutamate application on glutamine, serine and aspartate release from rat cortical glial cultures. The glial glutamate transporters rapidly cleared exogenously applied glutamate and this was accompanied by rapid increases in aspartate and glutamine, and a delayed increase in serine levels in the glial-conditioned medium. While glutamate-induced increases in glutamine and serine were sustained for up to 24 h, increases in aspartate lasted only for up to 6 h. The glutamate-induced increases in aspartate and glutamine were dependent both on the concentration and the duration of glutamate stimulus, but were largely insensitive to the inhibition of non-N-methyl-D-aspartate receptors or the metabotropic glutamate receptor 5. Inhibition of the glutamate transporter function by L-trans-pyrrolidine 2,4-dicarboxylate decreased the rate of glutamate uptake but not completely abrogated the uptake process, and this resulted in the attenuation of rate of glutamate induced glutamine synthesis. Dexamethasone treatment increased serine and glutamine levels in conditioned medium and increased glutamate induced glutamine release suggesting an upregulation of glutamine synthase activity. These results further substantiate coupling between glutamate and glutamine, and shed light on glutamate-dependent release of serine and aspartate, which may further contribute to excitatory neurotransmission.
Collapse
Affiliation(s)
- Tadimeti S Rao
- Merck Research Laboratories, 3535 General Atomics Ct, MRLSDB1, San Diego, CA 92122, USA.
| | | | | |
Collapse
|
12
|
Tsai YJ, Chen IL, Horng LY, Wu RT. Induction of differentiation in rat C6 glioma cells with Saikosaponins. Phytother Res 2002; 16:117-21. [PMID: 11933111 DOI: 10.1002/ptr.752] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The effects of saikosaponins (a, b(1), b(2), c, d), isolated from Bupleurum Radix, on the induction of differentiation in rat C6 glioma cells were studied. Saikosaponins a and d were shown to inhibit cell proliferation and alter cell morphology. In addition to cytostasis, the enzymatic activities of glutamine synthetase (GS) and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) were also noticeably increased after treatment with saikosaponin a. Nevertheless, saikosaponin d only showed an increase of GS activity, no significant changes in CNP activity were found. These results suggest that saikosaponin a can induce the differentiation of C6 glioma cells into astrocytes and/or oligodendrocytes, but saikosaponin d can only induce the differentiation of C6 glioma cells into astrocytes.
Collapse
Affiliation(s)
- Yan-Jyu Tsai
- Department of Pharmacology, Institute of Medical Research, Taipei Medical College, Taipei, Taiwan, R.O.C
| | | | | | | |
Collapse
|
13
|
Abstract
The glucocorticoid signaling pathway is responsive to a considerable number of internal and external signals and can therefore establish diverse patterns of gene expression. A glial-specific pattern, for example, is shown by the glucocorticoid-inducible gene glutamine synthetase. The enzyme is expressed at a particularly high level in glial cells, where it catalyzes the recycling of the neurotransmitter glutamate, and at a low level in most other cells, for housekeeping duties. Glial specificity of glutamine synthetase induction is achieved by the use of positive and negative regulatory elements, a glucocorticoid response element and a neural restrictive silencer element. Though not glial specific by themselves, these elements may establish a glial-specific pattern of expression through their mutual activity and their combined effect. The inductive activity of glucocorticoids is markedly repressed by the c-Jun protein, which is expressed at relatively high levels in proliferating glial cells. The signaling pathway of c-Jun is activated by the disruption of glia-neuron cell contacts, by transformation with v-src, and in proliferating retinal cells of early embryonic ages. The c-Jun protein inhibits the transcriptional activity of the glucocorticoid receptor and thus represses glutamine synthetase expression. This repressive mechanism might also affect the ability of glial cells to cope with glutamate neurotoxicity in injured tissues.
Collapse
Affiliation(s)
- L Vardimon
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
| | | | | | | | | |
Collapse
|
14
|
Brodie C, Bogi K, Acs P, Lorenzo PS, Baskin L, Blumberg PM. Protein kinase C delta (PKCdelta) inhibits the expression of glutamine synthetase in glial cells via the PKCdelta regulatory domain and its tyrosine phosphorylation. J Biol Chem 1998; 273:30713-8. [PMID: 9804846 DOI: 10.1074/jbc.273.46.30713] [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: 11/06/2022] Open
Abstract
Protein kinase C (PKC) plays an important role in the proliferation and differentiation of glial cells. In a recent study we found that overexpression of PKCdelta reduced the expression of the astrocytic marker glutamine synthetase (GS). In this study we explored the mechanisms involved in the inhibitory effect of PKCdelta on the expression of glutamine synthetase. Using PKC chimeras we first examined the role of the catalytic and regulatory domains of PKCdelta on the expression of glutamine synthetase. We found that cells stably transfected with chimeras between the regulatory domain of PKCdelta and the catalytic domains of PKCalpha or epsilon inhibited the expression of GS, similar to the inhibition exerted by overexpression of PKCdelta itself. In contrast, no significant effects were observed in cells transfected with the reciprocal PKC chimeras between the regulatory domains of PKCalpha or epsilon and the catalytic domain of PKCdelta. PKCdelta has been shown to undergo tyrosine phosphorylation in response to various activators. Tyrosine phosphorylation of PKCdelta in response to phorbol 12-myristate 13-acetate and platelet-derived growth factor occurred only in chimeras which contained the PKCdelta regulatory domain. Cells transfected with a PKCdelta mutant (PKCdelta5), in which the five putative tyrosine phosphorylation sites were mutated to phenylalanine, showed markedly diminished tyrosine phosphorylation in response to phorbol 12-myristate 13-acetate and platelet-derived growth factor and normal levels of GS. Our results indicate that the regulatory domain of PKCdelta mediates the inhibitory effect of this isoform on the expression of GS. Phosphorylation of PKCdelta on tyrosine residues in the regulatory domain is implicated in this inhibitory effect.
Collapse
Affiliation(s)
- C Brodie
- Molecular Mechanisms of Tumor Promotion Section, Laboratory of Cellular Carcinogenesis and Tumor Promotion, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | | | | | |
Collapse
|
15
|
Lie-Venema H, Hakvoort TB, van Hemert FJ, Moorman AF, Lamers WH. Regulation of the spatiotemporal pattern of expression of the glutamine synthetase gene. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1998; 61:243-308. [PMID: 9752723 DOI: 10.1016/s0079-6603(08)60829-6] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Glutamine synthetase, the enzyme that catalyzes the ATP-dependent conversion of glutamate and ammonia into glutamine, is expressed in a tissue-specific and developmentally controlled manner. The first part of this review focuses on its spatiotemporal pattern of expression, the factors that regulate its levels under (patho)physiological conditions, and its role in glutamine, glutamate, and ammonia metabolism in mammals. Glutamine synthetase protein stability is more than 10-fold reduced by its product glutamine and by covalent modifications. During late fetal development, translational efficiency increases more than 10-fold. Glutamine synthetase mRNA stability is negatively affected by cAMP, whereas glucocorticoids, growth hormone, insulin (all positive), and cAMP (negative) regulate its rate of transcription. The signal transduction pathways by which these factors may regulate the expression of glutamine synthetase are briefly discussed. The second part of the review focuses on the evolution, structure, and transcriptional regulation of the glutamine synthetase gene in rat and chicken. Two enhancers (at -6.5 and -2.5 kb) were identified in the upstream region and two enhancers (between +156 and +857 bp) in the first intron of the rat glutamine synthetase gene. In addition, sequence analysis suggests a regulatory role for regions in the 3' untranslated region of the gene. The immediate-upstream region of the chicken glutamine synthetase gene is responsible for its cell-specific expression, whereas the glucocorticoid-induced developmental appearance in the neural retina is governed by its far-upstream region.
Collapse
Affiliation(s)
- H Lie-Venema
- Department of Anatomy and Embryology, University of Amsterdam, The Netherlands
| | | | | | | | | |
Collapse
|
16
|
Brodie C, Kuperstein I, Acs P, Blumberg PM. Differential role of specific PKC isoforms in the proliferation of glial cells and the expression of the astrocytic markers GFAP and glutamine synthetase. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1998; 56:108-17. [PMID: 9602083 DOI: 10.1016/s0169-328x(98)00035-7] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In this study, we explored the role of specific protein kinase C (PKC) isoforms in glial cell proliferation and on the expression of the astrocytic markers GFAP and glutamine synthetase using C6 cells as a model. Analysis of the expression of the various PKC isoforms in control and differentiated C6 cells revealed differences in the expression of specific PKC isoforms. Undifferentiated C6 cells, which express low levels of GFAP and glutamine synthetase (GS), have high levels of PKCalpha and delta, whereas differentiated C6 cells, which express higher levels of both GFAP and GS have lower levels of PKCalpha and delta and higher levels of PKCgamma, theta and eta. Using C6 cells overexpressing specific PKC isoforms, we examined the role of these isoforms on the proliferation and differentiation of C6 cells. Cells overexpressing PKCalpha displayed a reduced level of GFAP, whereas GS expression was not affected. On the other hand, cells overexpressing PKCdelta showed reduced GS expression but little effect on GFAP. Finally, cells expressing PKCgamma displayed a marked increase in the levels of both GFAP and GS. The proliferation of C6 cells was increased in cells overexpressing PKCalpha and epsilon and decreased in cells overexpressing PKCgamma, delta and eta. The results of this study suggest that glial cell proliferation and astrocytic differentiation can be regulated by specific PKC isoforms that selectively affect cell proliferation and the expression of the two astrocytic markers GFAP and GS.
Collapse
Affiliation(s)
- C Brodie
- Molecular Mechanisms of Tumor Promotion Section, LCCTP, NCI, NIH, Bethesda, MD 20892, USA.
| | | | | | | |
Collapse
|
17
|
Spoerri PE, Grant MB, Gomez J, Vernadakis A. Endothelial cell conditioned media mediated regulation of glutamine synthetase activity in glial cells. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 1997; 104:205-8. [PMID: 9466724 DOI: 10.1016/s0165-3806(97)00173-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The responsiveness of late passage C-6 glial cells to human retinal endothelial cell-conditioned medium (HREC-CM) was examined using glutamine synthetase (GS) activity as test parameter. Treatment with 50% or 100% HREC-CM for 4-5 days slightly affected the morphology but significantly increased GS activity. Increased glial GS activity induced by vascular endothelial cells is of relevance in preventing extracellular glutamate toxicity and regulating the brain/retinal blood barrier.
Collapse
Affiliation(s)
- P E Spoerri
- Department of Medicine, University of Florida, Health Sciences Center, Gainesville 32610, USA
| | | | | | | |
Collapse
|
18
|
Niu H, Hinkle DA, Wise PM. Dexamethasone regulates basic fibroblast growth factor, nerve growth factor and S100beta expression in cultured hippocampal astrocytes. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1997; 51:97-105. [PMID: 9427511 DOI: 10.1016/s0169-328x(97)00221-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Glucocorticoids regulate hippocampal neuron survival during fetal development, in the adult, and during aging; however, the mechanisms underlying the effects are unclear. Since astrocytes contain adrenocortical receptors and synthesize and release a wide variety of growth factors, we hypothesized that glucocorticoids may alter neuron-astrocyte interactions by regulating the expression of growth factors in hippocampal astrocytes. In this study, three growth factors, which are important for hippocampal neuron development and survival, were investigated: basic fibroblast growth factor (bFGF), nerve growth factor (NGF), and S100beta. Enriched type I astrocyte cultures were treated with 1 microM dexamethasone (DEX), a synthetic glucocorticoid, for up to 120 h. Cells and culture medium were collected and total RNA and protein were measured at 6, 12, 24, 48, 72, 96 and 120 h after the initiation of hormone treatment. Growth factor mRNA levels were measured and quantified using solution hybridization-RNase protection assays and protein levels were quantified using ELISA methods. We report that DEX stimulates the bFGF mRNA levels over the 120-h treatment. In contrast, DEX suppresses NGF mRNA continuously over the same period of treatment. DEX induces a biphasic response in S100beta mRNA levels. In addition, some of the changes in gene expression are translated into parallel changes in protein levels of these growth factors. Our results demonstrate that dexamethasone can differentially regulate the expression of growth factors in hippocampal astrocytes in vitro. This suggests that one of the mechanisms through which glucocorticoids affect hippocampal functions may be by regulating the expression of astrocyte-derived growth factors.
Collapse
Affiliation(s)
- H Niu
- Department of Physiology, College of Medicine, University of Kentucky, Lexington 40536-0084, USA
| | | | | |
Collapse
|
19
|
Klegeris A, Walker DG, McGeer PL. Regulation of glutamate in cultures of human monocytic THP-1 and astrocytoma U-373 MG cells. J Neuroimmunol 1997; 78:152-61. [PMID: 9307240 DOI: 10.1016/s0165-5728(97)00094-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Glutamate, an excitatory neurotransmitter, is neurotoxic at high concentrations. Neuroglial cells, including astrocytes and microglia, play an important role in regulating its extracellular levels. Cultured human monocytic THP-1 cells increased their glutamate secretion following 18 and 68 h exposure to the inflammatory mediators zymosan, phorbol myristate acetate (PMA), lipopolysaccharide, interferon-gamma, tumor-necrosis factor-alpha and interleukin-1beta. Cultured astrocytoma U-373 MG cells increased their glutamate secretion following similar exposure to zymosan and PMA. DL-Alpha-aminopimelic acid, an inhibitor of the glutamate secretion system, reduced extracellular glutamate in both cell culture systems, while the high-affinity glutamate uptake inhibitors D-Aspartic acid, DL-threo-beta-hydroxyaspartic acid and L-trans-pyrrolidine-2,4-dicarboxylic acid increased extracellular glutamate in U-373 MG, but not THP-1 cell cultures. In co-cultures of THP-1 and U-373 MG cells, extracellular glutamate levels were increased significantly by the Alzheimer beta-amyloid peptide (1-40) and were decreased significantly by the anti-inflammatory drug dexamethasone. These data indicate that inflammatory stimuli may increase extracellular glutamate while antiinflammatory drugs decrease it.
Collapse
Affiliation(s)
- A Klegeris
- Kinsmen Laboratory of Neurological Research, University of British Columbia, Vancouver, Canada.
| | | | | |
Collapse
|
20
|
Jackson MJ, Zielke HR, Zielke CL. Induction of astrocyte argininosuccinate synthetase and argininosuccinate lyase by dibutyryl cyclic AMP and dexamethasone. Neurochem Res 1996; 21:1161-5. [PMID: 8923475 DOI: 10.1007/bf02532390] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Arginine is an intermediate in the elimination of excess nitrogen and is the substrate for nitric oxide synthesis. Arginine synthesis has been reported in brain tissue. We have studied the activity of the arginine biosynthetic enzymes argininosuccinate synthetase and argininosuccinate lyase in dexamethasone and/or dibutyryl cyclic AMP treated rat astrocyte cultures. Argininosuccinate lyase activity was stimulated by treatment with either effector and an additive effect was obtained when both agents were added simultaneously. Argininosuccinate synthetase was also increased in dexamethasone treated astrocytes. The effect of dibutyryl cyclic AMP on argininosuccinate synthetase was variable, suggesting a role for additional factors in its regulation as compared to argininosuccinate lyase. Regulation of arginine synthesis in astrocytes may be important to insure that arginine is not limiting for nitric oxide synthesis in neural tissue.
Collapse
Affiliation(s)
- M J Jackson
- Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, USA.
| | | | | |
Collapse
|
21
|
Arcuri C, Tardy M, Rolland B, Armellini R, Menghini AR, Bocchini V. Glutamine synthetase gene expression in a glioblastoma cell-line of clonal origin: regulation by dexamethasone and dibutyryl cyclic AMP. Neurochem Res 1995; 20:1133-9. [PMID: 8746797 DOI: 10.1007/bf00995375] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We investigated the expression of glutamine synthetase (GS), an enzyme involved in astroglial metabolism and marker of astroglial functional maturity, in a glioblastoma cell-line (GL-15) of clonal origin. In spite of their phenotypic immaturity, evidenced in a mosaic fashion by a poor glial fibrillary acidic protein (GFAP) expression, the level of GS-mRNA is high in GL15 cells and the considerable amount of GS biological activity can be further induced and stabilized by glucocorticoids. A correlation between the induction by dexamethasone of the GS-mRNA level and the GS biological activity suggests a transcriptional regulation of GS expression by the aforesaid hormone. Under this hormonal action, changes in cell morphology occur and they are correlated with an overexpression of the GFAP, a marker of astroglial differentiation. On the contrary, dibutyryl cyclic AMP (dbc AMP) down-regulates the GS-mRNA expression and decreases GS activity. These results suggest that GL-15 cells have a common glucocorticoid dependent mechanism able to induce GS and GFAP as well as morphological changes. However in these cells AMPc responsive elements are involved in the negative modulation of the GS expression, contrary to what occurs in normal astroglial cells.
Collapse
Affiliation(s)
- C Arcuri
- INSERM U 421, Hôpital Henri Mondor, Creteil, France
| | | | | | | | | | | |
Collapse
|