1
|
Rodríguez-Campuzano AG, Hernández-Kelly LC, Ortega A. DNA Methylation-Dependent Gene Expression Regulation of Glutamate Transporters in Cultured Radial Glial Cells. Mol Neurobiol 2022; 59:1912-1924. [PMID: 35032319 DOI: 10.1007/s12035-022-02746-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 01/11/2022] [Indexed: 11/26/2022]
Abstract
Exposure to xenobiotics has a significant impact in brain physiology that could be liked to an excitotoxic process induced by a massive release of the main excitatory neurotransmitter, L-glutamate. Overstimulation of extra-synaptic glutamate receptors, mainly of the N-methyl-D-aspartate subtype leads to a disturbance of intracellular calcium homeostasis that is critically involved in neuronal death. Hence, glutamate extracellular levels are tightly regulated through its uptake by glial glutamate transporters. It has been observed that glutamate regulates its own removal, both in the short-time frame via a transporter-mediated decrease in the uptake, and in the long-term through the transcriptional control of its gene expression, a process mediated by glutamate receptors that involves the Ca2+/diacylglycerol-dependent protein kinase and the transcription factor Ying Yang 1. Taking into consideration that this transcription factor is a member of the Polycomb complex and thus, part of repressive and activating chromatin remodeling factors, it might direct the interaction of DNA methyltransferases or dioxygenases of methylated cytosines to their target sequences. Here we explored the role of dynamic DNA methylation in the expression and function of glial glutamate transporters. To this end, we used the well-characterized models of primary cultures of chick cerebellar Bergmann glia cells and a human retina-derived Müller glia cell line. A time and dose-dependent increase in global DNA methylation was evident upon glutamate exposure. Under hypomethylation conditions, the glial glutamate transporter protein levels and uptake activity were increased. These results favor the notion that a dynamic DNA methylation program triggered by glutamate in glial cells modulates one of its major functions: glutamate removal.
Collapse
Affiliation(s)
- Ada G Rodríguez-Campuzano
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Av. IPN 2508, Zacatenco Ciudad de México, 07360, México
| | - Luisa C Hernández-Kelly
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Av. IPN 2508, Zacatenco Ciudad de México, 07360, México
| | - Arturo Ortega
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Av. IPN 2508, Zacatenco Ciudad de México, 07360, México.
| |
Collapse
|
2
|
Hernández-Melchor D, Ramírez-Martínez L, Cid L, Palafox-Gómez C, López-Bayghen E, Ortega A. EAAT1-dependent slc1a3 Transcriptional Control depends on the Substrate Translocation Process. ASN Neuro 2022; 14:17590914221116574. [PMID: 35903937 PMCID: PMC9340397 DOI: 10.1177/17590914221116574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Glutamate, the major excitatory neurotransmitter in the vertebrate brain, is removed from the synaptic cleft by a family of sodium-dependent transporters expressed in neurons and glial cells. The bulk of glutamate uptake activity occurs in glial cells through the sodium-dependent glutamate/aspartate transporter (EAAT1/GLAST) and glutamate transporter 1 (EAAT2/GLT-1). EAAT1/GLAST is the predominant transporter within the cerebellum. It is highly enriched in Bergmann glial cells that span the cerebellar cortex and wrap the most abundant glutamatergic synapses in the central nervous system, the synapse formed by the parallel fibers and the Purkinje cells. In the past years, it has become evident that Bergmann glial cells are involved in glutamatergic transmission. Glutamate transporters are tightly regulated due to their essential role in tripartite synapses. Glutamate regulates EAAT1/GLAST function and gene expression in a receptor-dependent and receptor-independent manner. Through the use of the non-metabolizable EAAT1/GLAST ligand, D-Aspartate, and the well-established chick cerebellar Bergmann glia primary culture, in this contribution, we demonstrate that EAAT1/GLAST down-regulates its expression and function at the transcriptional level through the activation of a signaling pathway that includes the phosphatidyl inositol 3 kinase (PI3K), the Ca2+/diacylglycerol dependent protein kinase PKC and the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB). These results favor the notion of an activity-dependent fine-tuning of glutamate recycling and its synaptic transactions through glial cells. Summary statement EAAT1/GLAST down-regulates its expression and function at the transcriptional level by activating a signaling pathway that includes PI3K, PKC and NF-κB, favoring the notion of an activity-dependent fine-tuning of glutamate recycling and its synaptic transactions through glial cells.
Collapse
Affiliation(s)
- Dinorah Hernández-Melchor
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México
- Science, Technology and Society Program. Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México
| | - Leticia Ramírez-Martínez
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México
| | - Luis Cid
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México
| | - Cecilia Palafox-Gómez
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México
| | - Esther López-Bayghen
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México
| | - Arturo Ortega
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México City, México
| |
Collapse
|
3
|
Rapid Regulation of Glutamate Transport: Where Do We Go from Here? Neurochem Res 2022; 47:61-84. [PMID: 33893911 PMCID: PMC8542062 DOI: 10.1007/s11064-021-03329-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 04/08/2021] [Accepted: 04/13/2021] [Indexed: 01/03/2023]
Abstract
Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). A family of five Na+-dependent transporters maintain low levels of extracellular glutamate and shape excitatory signaling. Shortly after the research group of the person being honored in this special issue (Dr. Baruch Kanner) cloned one of these transporters, his group and several others showed that their activity can be acutely (within minutes to hours) regulated. Since this time, several different signals and post-translational modifications have been implicated in the regulation of these transporters. In this review, we will provide a brief introduction to the distribution and function of this family of glutamate transporters. This will be followed by a discussion of the signals that rapidly control the activity and/or localization of these transporters, including protein kinase C, ubiquitination, glutamate transporter substrates, nitrosylation, and palmitoylation. We also include the results of our attempts to define the role of palmitoylation in the regulation of GLT-1 in crude synaptosomes. In some cases, the mechanisms have been fairly well-defined, but in others, the mechanisms are not understood. In several cases, contradictory phenomena have been observed by more than one group; we describe these studies with the goal of identifying the opportunities for advancing the field. Abnormal glutamatergic signaling has been implicated in a wide variety of psychiatric and neurologic disorders. Although recent studies have begun to link regulation of glutamate transporters to the pathogenesis of these disorders, it will be difficult to determine how regulation influences signaling or pathophysiology of glutamate without a better understanding of the mechanisms involved.
Collapse
|
4
|
Jiménez-Torres C, Hernández-Kelly LC, Najimi M, Ortega A. Bisphenol A exposure disrupts aspartate transport in HepG2 cells. J Biochem Mol Toxicol 2020; 34:e22516. [PMID: 32363662 DOI: 10.1002/jbt.22516] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 03/17/2020] [Accepted: 04/22/2020] [Indexed: 01/01/2023]
Abstract
The liver is the organ responsible for bisphenol A (BPA) metabolism, an environmental chemical agent. Exposure to this toxin is associated with liver abnormalities and dysfunction. An important role played by excitatory amino acid transporters (EAATs) of the slc1 gene family has been reported in liver injuries. To gain insight into a plausible effect of BPA exposure in the liver glutamate/aspartate transport, using the human hepatoblastoma cell line HepG2, we report a BPA-dependent dynamic regulation of SLC1A3 and SLC1A2. Through the use of radioactive [3 H]- d-aspartate uptake experiments and immunochemical approaches, we characterized time and dose-dependent regulation of the protein levels and function of these transporters after acute exposure to BPA. An increase in nuclear Yin Yang 1 was found. These results suggest an important involvement of the EAATs in liver physiology and its disruption after acute BPA exposure.
Collapse
Affiliation(s)
- Catya Jiménez-Torres
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del IPN, Ciudad de México, México
| | - Luisa C Hernández-Kelly
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del IPN, Ciudad de México, México
| | - Mustapha Najimi
- Hepato-Gastroenterolgy Research Pole, Laboratory of Pediatric Hepatology and Cell Therapy, Institut de Recherche Expérimentale et Clinique (IREC), Université́ Catholique de Louvain, Brussels, Belgium
| | - Arturo Ortega
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del IPN, Ciudad de México, México
| |
Collapse
|
5
|
Mahmoud S, Gharagozloo M, Simard C, Gris D. Astrocytes Maintain Glutamate Homeostasis in the CNS by Controlling the Balance between Glutamate Uptake and Release. Cells 2019; 8:E184. [PMID: 30791579 PMCID: PMC6406900 DOI: 10.3390/cells8020184] [Citation(s) in RCA: 322] [Impact Index Per Article: 64.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 02/15/2019] [Accepted: 02/19/2019] [Indexed: 01/26/2023] Open
Abstract
Glutamate is one of the most prevalent neurotransmitters released by excitatory neurons in the central nervous system (CNS); however, residual glutamate in the extracellular space is, potentially, neurotoxic. It is now well-established that one of the fundamental functions of astrocytes is to uptake most of the synaptically-released glutamate, which optimizes neuronal functions and prevents glutamate excitotoxicity. In the CNS, glutamate clearance is mediated by glutamate uptake transporters expressed, principally, by astrocytes. Interestingly, recent studies demonstrate that extracellular glutamate stimulates Ca2+ release from the astrocytes' intracellular stores, which triggers glutamate release from astrocytes to the adjacent neurons, mostly by an exocytotic mechanism. This released glutamate is believed to coordinate neuronal firing and mediate their excitatory or inhibitory activity. Therefore, astrocytes contribute to glutamate homeostasis in the CNS, by maintaining the balance between their opposing functions of glutamate uptake and release. This dual function of astrocytes represents a potential therapeutic target for CNS diseases associated with glutamate excitotoxicity. In this regard, we summarize the molecular mechanisms of glutamate uptake and release, their regulation, and the significance of both processes in the CNS. Also, we review the main features of glutamate metabolism and glutamate excitotoxicity and its implication in CNS diseases.
Collapse
Affiliation(s)
- Shaimaa Mahmoud
- Program of Immunology, Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada.
| | - Marjan Gharagozloo
- Program of Immunology, Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada.
| | - Camille Simard
- Program of Immunology, Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada.
| | - Denis Gris
- Program of Immunology, Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, QC J1H 5N4, Canada.
| |
Collapse
|
6
|
Dong W, Todd AC, Bröer A, Hulme SR, Bröer S, Billups B. PKC-Mediated Modulation of Astrocyte SNAT3 Glutamine Transporter Function at Synapses in Situ. Int J Mol Sci 2018; 19:ijms19040924. [PMID: 29561757 PMCID: PMC5979592 DOI: 10.3390/ijms19040924] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Revised: 03/07/2018] [Accepted: 03/15/2018] [Indexed: 01/13/2023] Open
Abstract
Astrocytes are glial cells that have an intimate physical and functional association with synapses in the brain. One of their main roles is to recycle the neurotransmitters glutamate and gamma-aminobutyric acid (GABA), as a component of the glutamate/GABA-glutamine cycle. They perform this function by sequestering neurotransmitters and releasing glutamine via the neutral amino acid transporter SNAT3. In this way, astrocytes regulate the availability of neurotransmitters and subsequently influence synaptic function. Since many plasma membrane transporters are regulated by protein kinase C (PKC), the aim of this study was to understand how PKC influences SNAT3 glutamine transport in astrocytes located immediately adjacent to synapses. We studied SNAT3 transport by whole-cell patch-clamping and fluorescence pH imaging of single astrocytes in acutely isolated brainstem slices, adjacent to the calyx of the Held synapse. Activation of SNAT3-mediated glutamine transport in these astrocytes was reduced to 77 ± 6% when PKC was activated with phorbol 12-myristate 13-acetate (PMA). This effect was very rapid (within ~20 min) and eliminated by application of bisindolylmaleimide I (Bis I) or 7-hydroxystaurosporine (UCN-01), suggesting that activation of conventional isoforms of PKC reduces SNAT3 function. In addition, cell surface biotinylation experiments in these brain slices show that the amount of SNAT3 in the plasma membrane is reduced by a comparable amount (to 68 ± 5%) upon activation of PKC. This indicates a role for PKC in dynamically controlling the trafficking of SNAT3 transporters in astrocytes in situ. These data demonstrate that PKC rapidly regulates the astrocytic glutamine release mechanism, which would influence the glutamine availability for adjacent synapses and control levels of neurotransmission.
Collapse
Affiliation(s)
- Wuxing Dong
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
| | - Alison C Todd
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
- Centre for Discovery Brain Sciences, School of Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK.
| | - Angelika Bröer
- Research School of Biology, The Australian National University, Linnaeus Way 134, Canberra ACT 2601, Australia.
| | - Sarah R Hulme
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
| | - Stefan Bröer
- Research School of Biology, The Australian National University, Linnaeus Way 134, Canberra ACT 2601, Australia.
| | - Brian Billups
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
| |
Collapse
|
7
|
|
8
|
Glia plasma membrane transporters: Key players in glutamatergic neurotransmission. Neurochem Int 2016; 98:46-55. [DOI: 10.1016/j.neuint.2016.04.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 03/07/2016] [Accepted: 04/06/2016] [Indexed: 12/27/2022]
|
9
|
Abstract
L-Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system and plays important roles in a wide variety of brain functions, but it is also a key player in the pathogenesis of many neurological disorders. The control of glutamate concentrations is critical to the normal functioning of the central nervous system, and in this review we discuss how glutamate transporters regulate glutamate concentrations to maintain dynamic signaling mechanisms between neurons. In 2004, the crystal structure of a prokaryotic homolog of the mammalian glutamate transporter family of proteins was crystallized and its structure determined. This has paved the way for a better understanding of the structural basis for glutamate transporter function. In this review we provide a broad perspective of this field of research, but focus primarily on the more recent studies with a particular emphasis on how our understanding of the structure of glutamate transporters has generated new insights.
Collapse
|
10
|
Sidoryk-Wegrzynowicz M, Lee E, Aschner M. Mechanism of Mn(II)-mediated dysregulation of glutamine-glutamate cycle: focus on glutamate turnover. J Neurochem 2012; 122:856-67. [PMID: 22708868 DOI: 10.1111/j.1471-4159.2012.07835.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Manganese (Mn) has been implicated in the impairment of the glutamate-glutamine cycling (GGC) by deregulation of Glu and glutamine (Gln) turnover in astrocytes. Here, we have examined possible mechanisms involved in the Mn(II)-mediated disruption of Glu turnover, including those related to protein degradation, such as the proteasomal and lysosomal machinery. Our study revealed that lysosome but not proteasomal inhibition is responsible for down-regulation of the Glu transporter after Mn(II) treatment. Because protein kinase C (PKC) activation leads to the down-regulation of Glu carriers, and Mn(II) increases PKC activity, we hypothesized that the PKC signaling contributes to the Mn(II)-mediated disruption of Glu turnover. Our results show that PKC activation causes a decrease in Glu uptake and that inhibition of PKC reverses Mn(II)-dependent down-regulation of Glu influx as well as glutamate transporter 1 (GLT1) and glutamate-aspartate transporter (GLAST) protein level. Co-immunoprecipitation studies show association of GLT1 with the PKCδ and PKCα isoforms and Mn(II)-induced specific increase in PKCδ-GLT1 interaction. In addition, astrocytes transfected with shRNA against PKCδ show decreased sensitivity to Mn(II) compared with those transfected with control shRNA or shRNA targeted against PKCα. Taken together, these findings demonstrate that PKCδ signaling is involved in the Mn(II)-induced deregulation of Glu turnover in astrocytes.
Collapse
|
11
|
López-Bayghen E, Ortega A. Glial glutamate transporters: New actors in brain signaling. IUBMB Life 2011; 63:816-23. [DOI: 10.1002/iub.536] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Accepted: 06/10/2011] [Indexed: 01/10/2023]
|
12
|
Castro-Coronel Y, Del Razo LM, Huerta M, Hernandez-Lopez A, Ortega A, López-Bayghen E. Arsenite Exposure Downregulates EAAT1/GLAST Transporter Expression in Glial Cells. Toxicol Sci 2011; 122:539-50. [DOI: 10.1093/toxsci/kfr126] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
13
|
Bull ND, Wood JP, Osborne NN, Barnett NL. Protein Kinase C-Mediated Modulation of Glutamate Transporter Activity in Rat Retina. Curr Eye Res 2009; 32:123-31. [PMID: 17364745 DOI: 10.1080/02713680601139200] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
It has previously been shown that inhibitors of protein kinase C (PKC) attenuate retinal glutamate uptake in situ. The aim of the current study was to determine whether PKCdelta-mediated inhibition differentially reduces the transport of glutamate into retinal Müller cells when compared with retinal neurons. The influence of two different types of PKC inhibitors on the uptake of [3H]D-aspartate was therefore compared in the intact retina, mixed retinal cultures, and Müller cell-enriched retinal cultures. It was found that 25 microM of the pan-isoform PKC inhibitor, chelerythrine, reduced [3H]D-aspartate uptake by 78%, 71%, and 68% in isolated retinas, mixed neuronal/glial cultures, and Müller cell-enriched cultures, respectively. Importantly, 20 microM of the PKCdelta-selective inhibitor rottlerin also reduced the uptake of D-aspartate to similar extents in all three systems, and the reductions were statistically similar to those found for the pan-specific PKC inhibitor. Neither pan-isoform nor PKCdelta-selective activators stimulated glutamate uptake in either culture system or the intact retina. The current results suggest that specific PKC inhibitors are quantitatively similar in reducing the uptake of glutamate into retinal neurons and Müller cells.
Collapse
Affiliation(s)
- Natalie D Bull
- Vision, Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland, Brisbane, QLD 4072, Australia
| | | | | | | |
Collapse
|
14
|
Etomidate reduces glutamate uptake in rat cultured glial cells: involvement of PKA. Br J Pharmacol 2008; 155:925-33. [PMID: 19002104 DOI: 10.1038/bjp.2008.336] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE Glutamate is the main excitatory neurotransmitter in the vertebrate CNS. Removal of the transmitter from the synaptic cleft by glial and neuronal glutamate transporters (GLTs) has an important function in terminating glutamatergic neurotransmission and neurological disorders. Five distinct excitatory amino-acid transporters have been characterized, among which the glial transporters excitatory amino-acid transporter 1 (EAAT1) (glutamate aspartate transporter) and EAAT2 (GLT1) are most important for the removal of extracellular glutamate. The purpose of this study was to describe the effect of the commonly used anaesthetic etomidate on glutamate uptake in cultures of glial cells. EXPERIMENTAL APPROACH The activity of the transporters was determined electrophysiologically using the whole cell configuration of the patch-clamp recording technique. KEY RESULTS Glutamate uptake was suppressed by etomidate (3-100 microM) in a time- and concentration-dependent manner with a half-maximum effect occurring at 2.4+/-0.6 microM. Maximum inhibition was approximately 50% with respect to the control. Etomidate led to a significant decrease of V(max) whereas the K(m) of the transporter was unaffected. In all cases, suppression of glutamate uptake was reversible within a few minutes upon washout. Furthermore, both GF 109203X, a nonselective inhibitor of PKs, and H89, a selective blocker of PKA, completely abolished the inhibitory effect of etomidate. CONCLUSION AND IMPLICATIONS Inhibition of glutamate uptake by etomidate at clinically relevant concentrations may affect glutamatergic neurotransmission by increasing the glutamate concentration in the synaptic cleft and may compromise patients suffering from acute or chronic neurological disorders such as CNS trauma or epilepsy.
Collapse
|
15
|
Adolph O, Köster S, Räth M, Georgieff M, Weigt HU, Engele J, Senftleben U, Föhr KJ. Rapid increase of glial glutamate uptake via blockade of the protein kinase A pathway. Glia 2007; 55:1699-707. [PMID: 17886291 DOI: 10.1002/glia.20583] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Glutamate is the main excitatory neurotransmitter in the vertebrate central nervous system. Removal of this transmitter from the synaptic cleft by glial and neuronal transporter systems plays an important role in terminating glutamatergic neurotransmission. The effects of different activators and blockers of PKA and PKC on glutamate uptake were studied in primary glial cells cultivated from the rat cortex using the patch-clamp recording technique and immunocytochemical methods. GF 109203X enhances glutamate-induced membrane currents in a concentration- and time-dependent manner. After pre-application for 40 s the maximal transport capacity was increased by 30-80%. The estimated Km-value of the transport system did not change after drug application and the enhanced glutamate uptake was reversible within a few minutes upon washout. Activators and blockers of the PKC pathway did not affect glutamate uptake, whereas H89, a selective blocker of PKA, mimicked the effects of GF 109203X, indicating involvement of the protein kinase A pathway. The GF 109203X-induced increase in transport capacity is likely to be mediated by GLAST since the GLT-1 selective blocker dihydrokainate was unable to block basal or stimulated glutamate uptake. Furthermore, the increase in transport activity may well be based on an increase in cell surface expression of the transporter protein since preincubation with cytochalasin-B, a protein that blocks actin polymerization, almost completely abolished the effect of GF 109203X and H89. These results indicate that GF 109203X and H89 enhance glial glutamate uptake via blockade of the PKA. The described effect may affect glutamatergic neurotransmission by reducing the glutamate concentration in the synaptic cleft.
Collapse
Affiliation(s)
- Oliver Adolph
- Department of Anesthesiology, University Hospital of Ulm, Steinhoevelstrasse 9, 89075 Ulm, Germany.
| | | | | | | | | | | | | | | |
Collapse
|
16
|
Rajamanickam J, Palmada M, Lang F, Boehmer C. EAAT4 phosphorylation at the SGK1 consensus site is required for transport modulation by the kinase. J Neurochem 2007; 102:858-66. [PMID: 17442044 DOI: 10.1111/j.1471-4159.2007.04585.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
EAAT4 (SLC1A6) is a Purkinje-Cell-specific post-synaptic excitatory amino acid transporter that plays a major role in clearing synaptic glutamate. EAAT4 abundance and function is known to be modulated by the serum and glucocorticoid inducible kinase (SGK) 1 but the precise mechanism of kinase action has not been defined yet. The present work aims to identify the molecular mechanism of EAAT4 modulation by the kinase. The EAAT4 sequence bears two putative SGK1 consensus sites (at Thr40 and Thr504) at the amino and carboxy terminus that are conserved among species. Expression studies in Xenopus oocytes demonstrated that EAAT4-mediated [(3)H] glutamate uptake and cell surface abundance are enhanced by co-expression of SGK1. Disruption of the SGK1 phosphorylation site at threonine 40 ((T40A)EAAT4) or of both phosphorylation sites ((T40AT504A)EAAT4) abrogated the effect of SGK1 on transporter function and expression. SGK1 modulates several transport proteins via inhibition of the ubiquitin ligase Nedd4-2. Co-expression of Nedd4-2 inhibited wild-type EAAT4 but not the (T40AT504A)EAAT4 mutant. Besides, RNA interference-mediated reduction of endogenous Nedd4-2 (xNedd4-2) expression increased the activity of the transporter. In conclusion, maximal glutamate transport modulation by SGK1 is accomplished by direct EAAT4 stimulation and to a lesser extent by inhibition of intrinsic Nedd4-2.
Collapse
|
17
|
Rosas S, Vargas MA, López-Bayghen E, Ortega A. Glutamate‐dependent transcriptional regulation of GLAST/EAAT1: a role for YY1. J Neurochem 2007; 101:1134-44. [PMID: 17394550 DOI: 10.1111/j.1471-4159.2007.04517.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Glutamate is the major excitatory transmitter in the vertebrate brain and its extracellular levels are tightly regulated to prevent excitotoxic effects. The Na(+)-dependent glutamate/aspartate transporter GLAST/EAAT1 is regulated in the short and in the long term by glutamate. A receptors-independent change in its membrane translocation rate, accounts for an acute modulation in GLAST/EAAT1 transport. In contrast, activation of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate subtype of glutamate receptors represses the transcription of the chick glast gene. A glutamate responsive element has been mapped to the promoter region of this gene containing a bonafide binding site for the transcription factor Ying-Yang 1. Using cultured chick cerebellar Bergmann glia cells, glutamate elicited a time and dose-dependent increase in Ying-Yang 1 DNA binding consistent with the negative response generated in a reporter gene construct controlled for Ying-Yang 1. Over-expression of this transcription factor leads to a substantial reduction in GLAST/EAAT1 transporter uptake and an important decrease in mRNA levels, all associated with the transcriptional repression of the chick glast promoter activity. These results provide evidence for an involvement of Ying-Yang 1 in the transcriptional response to glutamate in glial cells and favor the notion of a relevant role of this factor in GLAST/EAAT1 transcriptional control.
Collapse
Affiliation(s)
- Sandra Rosas
- Departamento de Genética y Biología Molecular y Departamento de Biomedicina Molecular, Centro de Investigación y de Estudios Avanzados Campus Zacatenco, México City, México
| | | | | | | |
Collapse
|
18
|
LEE AVEN, RAYFIELD ANDREW, HRYCIW DEANNEH, MA THEINGIAUNG, WANG DONGSHENG, POW DAVID, BROER STEFAN, YUN CHRIS, PORONNIK PHILIP. Na+-H+ exchanger regulatory factor 1 is a PDZ scaffold for the astroglial glutamate transporter GLAST. Glia 2007; 55:119-29. [PMID: 17048262 PMCID: PMC2773615 DOI: 10.1002/glia.20439] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Glutamate is a key neurotransmitter and its levels in the synaptic cleft are tightly regulated by reuptake mechanisms that primarily involve transporters in astrocytes. This requires that the glutamate transporters be spatially constrained to effect maximum glutamate transport. GLAST (EAAT1) is the predominant astroglial transporter and contains a class I PDZ-binding consensus (ETKM) in its C-terminus. The epithelial Na(+)/H(+) exchanger regulatory factors NHERF1 and NHERF2 are PDZ proteins that contain two tandem PDZ domains and a C-terminal domain that binds members of the ERM (ezrin-radixin-moesin) family of membrane-cytoskeletal adaptors. NHERF proteins have been extensively characterized in renal epithelia and their expression in brain has recently been reported; however, their function in the brain remains unknown. The aims of the current study were to (1) determine the distribution of NHERF1/2 in the rodent brain and (2) investigate whether GLAST was a physiological ligand for NHERF1/2. Immunohistochemistry revealed that NHERF1 expression was widespread in rat brain (abundant in cerebellum, cerebral cortex, hippocampus, and thalamus) and primarily restricted to astrocytes whereas NHERF2 expression was primarily restricted to endothelial cells of blood vessels and capillaries. Importantly, NHERF1 distribution closely matched that of GLAST and confocal imaging demonstrated co-localization of the two proteins. Co-immunoprecipitation demonstrated that GLAST, NHERF1, and ezrin associate in vivo. In vitro binding assays showed that GLAST bound directly to the PDZ1 domain of NHERF1 via the C-terminal ETKM motif of GLAST. These findings implicate the GLAST-NHERF1 complex in the regulation of glutamate homeostasis in astrocytes.
Collapse
Affiliation(s)
- AVEN LEE
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
| | - ANDREW RAYFIELD
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
| | - DEANNE H. HRYCIW
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
| | - THEINGI AUNG MA
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
| | - DONGSHENG WANG
- Department of Medicine, Emory University, Atlanta, Georgia 30322
| | - DAVID POW
- School of Biomedical Sciences and HMRI, University of Newcastle, New South Wales 2308, Australia
| | - STEFAN BROER
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australian Capital Territory 0200, Australia
| | - CHRIS YUN
- Department of Medicine, Emory University, Atlanta, Georgia 30322
| | - PHILIP PORONNIK
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
- Correspondence to: Philip Poronnik, School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
| |
Collapse
|
19
|
Ramírez-Sotelo G, López-Bayghen E, Hernández-Kelly LCR, Arias-Montaño JA, Bernabé A, Ortega A. Regulation of the Mouse Na+-Dependent Glutamate/Aspartate Transporter GLAST: Putative Role of an AP-1 DNA Binding Site. Neurochem Res 2006; 32:73-80. [PMID: 17151912 DOI: 10.1007/s11064-006-9227-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2006] [Accepted: 11/10/2006] [Indexed: 11/30/2022]
Abstract
Appropriate removal of L: -glutamate from the synaptic cleft is important for prevention of the excitotoxic effects of this neurotransmitter. The Na+-dependent glutamate/aspartate transporter GLAST is regulated in the short term, by a transporter-dependent decrease in uptake activity while in the long term, a receptor's-dependent decrease in GLAST protein levels leads to a severe reduction in glutamate uptake. The promoter region of the mouse glast gene harbors an Activator Protein-1 site (AP-1). To gain insight into the molecular mechanisms triggered by Glu-receptors activation involved in GLAST regulation, we took advantage of the neonatal mouse cerebellar prisms model. We characterized the glutamate uptake activity; the glutamate-dependent effect on GLAST protein levels and over the interaction of nuclear proteins with a mouse glast promoter AP-1 probe. A time and dose dependent decrease in transporter activity matching with a decrease in GLAST levels was recorded upon glutamate treatment. Moreover, a significant increase in glast AP-1 DNA binding was found. Pharmacological experiments established that both effects are mediated through alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors, favoring the notion of the critical involvement of glutamate in the regulation of its binding partners: receptors and transporters.
Collapse
Affiliation(s)
- Guadalupe Ramírez-Sotelo
- Departamento de Genética y Biología Molecular, Cinvestav Campus Zacatenco, Apartado Postal 14-740, Mexico, D.F. 07000, Mexico
| | | | | | | | | | | |
Collapse
|
20
|
Nickell J, Salvatore MF, Pomerleau F, Apparsundaram S, Gerhardt GA. Reduced plasma membrane surface expression of GLAST mediates decreased glutamate regulation in the aged striatum. Neurobiol Aging 2006; 28:1737-48. [PMID: 16959378 DOI: 10.1016/j.neurobiolaging.2006.07.015] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2006] [Revised: 06/30/2006] [Accepted: 07/17/2006] [Indexed: 10/24/2022]
Abstract
Extracellular L-glutamate poses a severe excitotoxic threat to neurons and glia when unregulated, therefore low synaptic levels of this neurotransmitter must be maintained via a rapid and robust transport system. A recent study from our laboratory showed a reduced glutamate uptake rate in the striatum of the aged Fischer 344 (F344) rat, yet the mechanism underlying this phenomenon is unknown. The current study utilized in vivo electrochemical recordings, immunoblotting and biotinylation in young (6 months), late-middle aged (18 months) and aged (24 months) F344 rats to elucidate the potential role that glutamate transporters (GLT-1, GLAST, and EAAC1) may play in this mechanism. Here we show that the time necessary to clear glutamate from the late-middle aged and aged striatum is significantly prolonged in comparison to the young striatum. In addition, an analysis of various sub-regions of the striatum revealed a marked dorsoventral gradient in terms of glutamate clearance times in the aged striatum, a phenomenon which was not present in the striatum of the animals of the remaining age groups. We also found that the decreased glutamate clearance time observed in the late-middle aged and aged rats is not due to a decrease in the production of total transporter protein among these three transporters. Rather, a significant reduction in the amount of GLAST expressed on the plasma membrane surface in the aged animals (approximately 55% when compared to young rats) may contribute to this phenomenon. These age-related alterations in extracellular l-glutamate regulation may be key contributors to the increased susceptibility of the aged brain to excitotoxic insults such as stroke and hypoxia.
Collapse
Affiliation(s)
- Justin Nickell
- Department of Anatomy and Neurobiology, Center for Sensor Technology, University of Kentucky Chandler Medical Center, Lexington, KY 40536-0098, USA.
| | | | | | | | | |
Collapse
|
21
|
Abstract
Glutamate is the primary excitatory neurotransmitter in the central nervous system. During synaptic activity, glutamate is released into the synaptic cleft and binds to glutamate receptors on the pre- and postsynaptic membrane as well as on neighboring astrocytes in order to start a number of intracellular signaling cascades. To allow for an efficient signaling to occur, glutamate levels in the synaptic cleft have to be maintained at very low levels. This process is regulated by glutamate transporters, which remove excess extracellular glutamate via a sodium-potassium coupled uptake mechanism. When extracellular glutamate levels rise to about normal, glutamate overactivates glutamate receptors, triggering a multitude of intracellular events in the postsynaptic neuron, which ultimately results in neuronal cell death. This phenomenon is known as excitotoxicity and is the underlying mechanisms of a number of neurodegenerative diseases. A dysfunction of the glutamate transporter is thought to contribute to cell death during excitotoxicity. Therefore, efforts have been made to understand the regulation of glutamate transporter function. Transporter activity can be regulated in different ways, including through gene expression, transporter protein targeting and trafficking and through posttranslational modifications of the transporter protein. The identification of these mechanisms has helped to understand the role of glutamate transporters during pathology and will aid in the development of therapeutic strategies with the transporter as a desirable target.
Collapse
Affiliation(s)
- R Sattler
- Department of Neurology, Johns Hopkins University, 600 N Wolfe Street, Meyer 6-109, Baltimore, MD 21287, USA
| | | |
Collapse
|
22
|
Shen Y, Linden DJ. Long-term potentiation of neuronal glutamate transporters. Neuron 2005; 46:715-22. [PMID: 15924858 DOI: 10.1016/j.neuron.2005.04.033] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2004] [Revised: 02/02/2005] [Accepted: 04/28/2005] [Indexed: 01/21/2023]
Abstract
Persistent, use-dependent modulation of synaptic strength has been demonstrated for fast synaptic transmission mediated by glutamate and has been hypothesized to underlie persistent behavioral changes ranging from memory to addiction. Glutamate released at synapses is sequestered by the action of excitatory amino acid transporters (EAATs) in glia and postsynaptic neurons. So, the efficacy of glutamate transporter function is crucial for regulating glutamate spillover to adjacent presynaptic and postsynaptic receptors and the consequent induction of plastic or excitotoxic processes. Here, we report that tetanic stimulation of cerebellar climbing fiber-Purkinje cell synapses results in long-term potentiation (LTP) of a climbing fiber-evoked glutamate transporter current recorded in Purkinje cells. This LTP is postsynaptically expressed and requires activation of an mGluR1/PKC cascade. Together with a simultaneously induced long-term depression (LTD) of postsynaptic AMPA receptors, this might reflect an integrated antiexcitotoxic cellular response to strong climbing fiber synaptic activation, as occurs following an ischemic episode.
Collapse
Affiliation(s)
- Ying Shen
- Department of Neuroscience, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205, USA
| | | |
Collapse
|
23
|
Susarla BTS, Seal RP, Zelenaia O, Watson DJ, Wolfe JH, Amara SG, Robinson MB. Differential regulation of GLAST immunoreactivity and activity by protein kinase C: evidence for modification of amino and carboxyl termini. J Neurochem 2005; 91:1151-63. [PMID: 15569258 DOI: 10.1111/j.1471-4159.2004.02791.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Many neurotransmitter transporters, including the GLT-1 and EAAC1 subtypes of the glutamate transporter, are regulated by protein kinase C (PKC) and these effects are associated with changes in cell surface expression. In the present study, the effects of PKC activation on the glutamate aspartate transporter (GLAST) subtype of glutamate transporter were examined in primary astrocyte cultures. Acute (30 min) exposure to the phorbol 12-myristate 13-acetate (PMA) increased (approximately 20%) transport activity but had the opposite effect on both total and cell surface immunoreactivity. Chronic treatment (6 or 24 h) with PMA had no effect on transport activity but caused an even larger decrease in total and cell surface immunoreactivity. This loss of immunoreactivity was observed using antibodies directed against three different cytoplasmic epitopes, and was blocked by the PKC antagonist, bisindolylmaleimide II. We provide biochemical and pharmacological evidence that the activity observed after treatment with PMA is mediated by GLAST. Two different flag-tagged variants of the human homolog of GLAST were introduced into astrocytes using lentiviral vectors. Although treatment with PMA caused a loss of transporter immunoreactivity, flag immunoreactivity did not change in amount or size. Together, these studies suggest that activation of PKC acutely up-regulates GLAST activity, but also results in modification of several different intracellular epitopes so that they are no longer recognized by anti-GLAST antibodies. We found that exposure of primary cultures of neurons/astrocytes to transient hypoxia/glucose deprivation also caused a loss of GLAST immunoreactivity that was attenuated by the PKC antagonist, bisindolylmaleimide II, suggesting that some acute insults previously thought to cause a loss of GLAST protein may mimic the phenomenon observed in the present study.
Collapse
Affiliation(s)
- Bala T S Susarla
- Department of Pediatrics, University of Pennsylvania and Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | | | | | | | | | | | | |
Collapse
|
24
|
Schousboe A, Sarup A, Bak LK, Waagepetersen HS, Larsson OM. Role of astrocytic transport processes in glutamatergic and GABAergic neurotransmission. Neurochem Int 2004; 45:521-7. [PMID: 15186918 DOI: 10.1016/j.neuint.2003.11.001] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2003] [Accepted: 11/10/2003] [Indexed: 10/26/2022]
Abstract
The fine tuning of both glutamatergic and GABAergic neurotransmission is to a large extent dependent upon optimal function of astrocytic transport processes. Thus, glutamate transport in astrocytes is mandatory to maintain extrasynaptic glutamate levels sufficiently low to prevent excitotoxic neuronal damage. In GABA synapses hyperactivity of astroglial GABA uptake may lead to diminished GABAergic inhibitory activity resulting in seizures. As a consequence of this the expression and functional activity of astrocytic glutamate and GABA transport is regulated in a number of ways at transcriptional, translational and post-translational levels. This opens for a number of therapeutic strategies by which the efficacy of excitatory and inhibitory neurotransmission may be manipulated.
Collapse
Affiliation(s)
- A Schousboe
- Department of Pharmacology, The Danish University of Pharmaceutical Sciences, Neuroscience Research Center, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
| | | | | | | | | |
Collapse
|
25
|
Wang Z, Li W, Mitchell CK, Carter-Dawson L. Activation of protein kinase C reduces GLAST in the plasma membrane of rat Müller cells in primary culture. Vis Neurosci 2004; 20:611-9. [PMID: 15088714 DOI: 10.1017/s0952523803206039] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In this study, a Müller cell culture preparation from young rats was used to investigate the regulation of GLAST transport activity in native cells. Immunohistochemical analysis confirmed GLAST to be the predominant glutamate transporter expressed by the cells through five passages. [3H]-glutamate uptake assays showed the typical Na+-dependent glutamate transport which was blocked by L-(-)-threo-3-hydroxyaspartate (L-THA), a competitive inhibitor. Glutamate transport was decreased significantly in Müller cells exposed to phorbol-12-myristate-13-acetate (PMA), a protein kinase C (PKC) activator. A similar effect on [3H]-D-aspartate (nonmetabolizable glutamate analog) uptake ruled out the possibility that the decrease was a consequence of altered metabolism. However, PMA did not affect Na+-dependent [3H]-glycine transport, indicating the absence of a nonspecific change in the electrochemical gradients. The PMA effect on glutamate uptake was evidenced by partial blocking with a specific PKC inhibitor, bisindolymaleimide II (Bis II). Activation of PKC did not change the Km, but the Vmax was significantly reduced. Image analysis of Müller cells with biotinylated cell membranes immunolabeled with GLAST shows a reduction of GLAST in the plasma membrane. In conclusion, these data show that rat Müller cells in primary cultures express GLAST and that PKC activation affects GLAST transport activity by decreasing cell surface expression.
Collapse
Affiliation(s)
- Zhiqing Wang
- Department of Ophthalmology and Visual Science, The University of Texas-Houston Medical School, Houston 77030, USA
| | | | | | | |
Collapse
|
26
|
Bernabé A, Méndez JA, Hernández-Kelly LCR, Ortega A. Regulation of the Na+-dependent glutamate/aspartate transporter in rodent cerebellar astrocytes. Neurochem Res 2004; 28:1843-9. [PMID: 14649726 DOI: 10.1023/a:1026171724963] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The regulation of the Na+-dependent glutamate/aspartate transporter system GLAST expressed in rat and mouse cerebellar and cortical astrocytic cultures was examined. Pretreatment of the cerebellar cells with L-glutamate and 12-O-tetradecanoyl-phorbol-13-acetate (TPA), a known Ca2+/diacylglicerol-dependent protein kinase (PKC) activator, produced a decrease in [3H]-D-aspartate uptake. This reduction was dose- and time-dependent and sensitive to PKC inhibitors. Furthermore, the L-glutamate-dependent [3H]-D-aspartate uptake decrease is a non-receptor dependent process, because neither of the agonists or antagonists were effective in mimicking or reverting the effect. Interestingly, transportable substrates could reproduce the L-glutamate effect. In sharp contrast, in cortical astrocytes, both L-glutamate and TPA pre-exposure result in an augmentation of the [3H]-D-aspartate uptake. These findings suggest that the Na+-dependent glutamate uptake GLAST undergoes a region-specific regulation.
Collapse
Affiliation(s)
- Alfonso Bernabé
- Departamento de Genética y Biología Molecular, Cinvestav-IPN, Apartado Postal 14-740 México, DF, 07000, México
| | | | | | | |
Collapse
|
27
|
López-Bayghen E, Aguirre A, Ortega A. Transcriptional regulation through glutamate receptors: Involvement of tyrosine kinases. J Neurosci Res 2004; 74:717-25. [PMID: 14635222 DOI: 10.1002/jnr.10807] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Glutamate receptors play a key role in neuronal plasticity, learning and memory, and in several neuropathologies. Short-term and long-term changes in synaptic efficacy are triggered by glutamate. Although an enhanced glutamate-dependent tyrosine phosphorylation has been described in several systems, its role in membrane-to-nuclei signaling is unclear. Taking advantage of the fact that the gene encoding the chick kainate-binding protein undergoes a glutamate-dependent transcriptional regulation via an activator protein-1 (AP-1) site, we evaluated the involvement of tyrosine kinases in this process. We describe here the participation of receptor and non-receptor tyrosine kinases in the signaling cascade triggered by glutamate. Our results suggest that in Bergmann glia cells, glutamate receptors transactivate receptor tyrosine kinases, favoring the idea of a complex network of signals activated by this excitatory neurotransmitter that results in regulation of gene expression.
Collapse
Affiliation(s)
- Esther López-Bayghen
- Departamento de Genética y Biología Molecular, Cinvestav-IPN, México, D.F., México
| | | | | |
Collapse
|
28
|
Figiel M, Maucher T, Rozyczka J, Bayatti N, Engele J. Regulation of glial glutamate transporter expression by growth factors. Exp Neurol 2003; 183:124-35. [PMID: 12957496 DOI: 10.1016/s0014-4886(03)00134-1] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Injuries to the brain result in the decline of glial glutamate transporter expression within hours and a recovery after several days. One consequence of this disturbed expression seems to consist in the temporary accumulation of toxic extracellular glutamate levels followed by secondary neuronal cell death. Whereas evidence exists that the decline in glutamate transporter expression results from a loss of neuronal PACAP influences on astroglia, the mechanism(s) inducing the reexpression of glial glutamate transporters is presently unknown. We now demonstrate that the injury-induced growth factors EGF, TGFalpha, FGF-2, and PDGF all promote the expression of the glutamate transporters GLT-1 and/or GLAST in cultured cortical astroglia. In contrast, similar stimulatory influences were absent with GDNF and BDNF, growth factors not affected by brain injuries. The effects of EGF, TGFalpha, FGF-2, and PDGF on glial glutamate transport were only partly redundant and involved distinctly different signaling pathways. Unlike EGF, TGFalpha, and FGF-2, PDGF promoted GLT-1, but not GLAST expression and further failed to increase the maximal velocity of sodium-dependent glutamate uptake. Moreover, FGF-2 only affected glial glutamate transport when the RAF-MEK-ERK signaling pathway was concomitantly inhibited with PD98059. Depending on the extracellular growth factor and glutamate transporter subtype, the observed stimulatory effects required the activation of PKA, PKC, and/or AKT. We suggest that after brain injury, reactive processes may limit secondary neuronal cell death by promoting glial glutamate transport. The detailed knowledge of these compensatory mechanisms will eventually allow us to therapeutically interfere with glutamate-associated neuronal cell death in the brain.
Collapse
Affiliation(s)
- Maciej Figiel
- Anatomie und Zellbiologie, Universität Ulm, 89069 Ulm, Germany
| | | | | | | | | |
Collapse
|
29
|
Susarla BTS, Robinson MB. Rottlerin, an inhibitor of protein kinase Cdelta (PKCdelta), inhibits astrocytic glutamate transport activity and reduces GLAST immunoreactivity by a mechanism that appears to be PKCdelta-independent. J Neurochem 2003; 86:635-45. [PMID: 12859677 DOI: 10.1046/j.1471-4159.2003.01886.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Protein kinase C (PKC) regulates the activity and/or cell surface expression of several different neurotransmitter transporters, including subtypes of glutamate transporters. In the present study, the effects of pharmacological inhibitors of PKC were studied in primary astrocyte cultures that express the glutamate aspartate transporter (GLAST) subtype of glutamate transporter. We found that general inhibitors of PKC, bisindolylmaleimide I (Bis I), bisindolylmaleimide II (Bis II), staurosporine and an inhibitor of classical PKCs, Gö6976, had no effect on Na+-dependent glutamate transport activity. However, rottlerin, a putative specific inhibitor of PKCdelta, decreased transport activity with an IC50 value (less than 10 micro m) that is comparable to that reported for inhibition of PKCdelta. The effect of rottlerin was very rapid (maximal effect within 5 min) and was due to a decrease in the capacity (Vmax) for transport. Rottlerin also caused a drastic loss of GLAST immunoreactivity within 5 min, suggesting that rottlerin accelerates GLAST degradation/proteolysis. Rottlerin had no effect on cell surface or total expression of the transferrin receptor, providing evidence that the effect on GLAST cannot be attributed to a non-specific internalization/degradation of plasma membrane proteins. Down-regulation of PKCdelta with chronic phorbol ester treatment did not block rottlerin-mediated inhibition of transport activity. These results suggest a novel mechanism for regulation of the GLAST subtype of glutamate transporter and indicate that there is a rottlerin target that is capable of controlling the levels of GLAST by controlling the rate of degradation or limited proteolysis. It appears that the target for rottlerin may not be PKCdelta.
Collapse
Affiliation(s)
- Bala T S Susarla
- Departments of Pediatrics and Pharmacology, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania 19104-4318, USA
| | | |
Collapse
|
30
|
Schousboe A. Role of astrocytes in the maintenance and modulation of glutamatergic and GABAergic neurotransmission. Neurochem Res 2003; 28:347-52. [PMID: 12608708 DOI: 10.1023/a:1022397704922] [Citation(s) in RCA: 150] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The functional activity in the brain is primarily composed of an interplay between excitation and inhibition. In any given region the output is based upon a complex processing of incoming signals that require both excitatory and inhibitory units. Moreover, these units must be regulated and balanced such that an integrated and finely tuned response is generated. In each of these units or synapses the activity depends on biosynthesis, release, receptor interaction, and inactivation of the neurotransmitter in question; thus, it is easily understood that each of these processes needs to be highly regulated and controlled. It is interesting to note that in case of the most prevailing neurotransmitters, glutamate and GABA, which mediate excitation and inhibition, respectively, the inactivation process is primarily maintained by highly efficient, high-affinity transport systems capable of maintaining transmembrane concentration gradients of these amino acids of 10(4)-10(5)-fold. The demonstration of the presence of transporters for glutamate and GABA in both neuronal and astrocytic elements naturally raises the question of the functional importance of the astrocytes in the regulation of the level of the neurotransmitters in the synaptic cleft and hence for the activity of excitatory and inhibitory neurotransmission. Obviously, this discussion has important implications for the understanding of the role of astrocytes in disease states in which imbalances between excitation and inhibition are a triggering factor, for example, epilepsy and neurodegeneration.
Collapse
Affiliation(s)
- Arne Schousboe
- Department of Pharmacology, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
| |
Collapse
|
31
|
Gamboa C, Ortega A. Insulin-like growth factor-1 increases activity and surface levels of the GLAST subtype of glutamate transporter. Neurochem Int 2002; 40:397-403. [PMID: 11821146 DOI: 10.1016/s0197-0186(01)00106-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Glutamate uptake systems are the primary mechanisms involved in excitatory amino acids clearance, their regulation is extremely important for proper neuronal function. Using cultured chick cerebellar Bergmann glia cells, the involvement of receptor tyrosine kinases in glutamate uptake was studied. Treatment of the cells with insulin-like growth factor-1 but not epidermal growth factor or neuronal growth factor, induces a dose and time dependent increase in [(3)H]-D-aspartate uptake that is sensitive to wortmannin, an inhibitor of phosphatidylinositol 3-kinase. Saturation experiments show a significant increase in V(max), suggesting that the amount of transporter molecules at the cell membrane under insulin-like growth factor-1 treatment is augmented. This interpretation was strengthen by equilibrium-binding experiments and by the fact that the increase in [(3)H]-D-aspartate uptake was not dependent on protein synthesis. The present studies suggest that insulin-like growth factor-1 signaling is involved in modulation of glutamate transporter cell surface expression.
Collapse
Affiliation(s)
- Citlalli Gamboa
- Departamento de Genética y Biologija Molecular, Centro de Investigación y de Estudios, Avanzados del Instituto Politécnico Nacional, Apartado Postal 14-740, México D.F 07000, Mexico
| | | |
Collapse
|
32
|
Abstract
The activity of biogenic amine and amino acid neurotransmitters is limited by presynaptic and astrocytic Na(+)-dependent transport systems. Their functional importance is underscored by the observation that these transporters are the targets of broad classes of psychotherapeutic agents, including antidepressants and stimulants. Early studies suggested that the activity of these transporters can be fine tuned by a number of different signaling pathways. In the past five years, several groups have provided compelling evidence that changing the cell surface availability of these transporters contributes to this fine tuning. This regulated trafficking can result in rapid (within minutes) increases or decreases in the plasma membrane expression of these transporters and is independent of transcriptional or translational control mechanisms. Many of the same signaling molecules, including protein kinase C (PKC), tyrosine kinase, phosphatidylinositol 3-kinase (P13-K), and protein phosphatase, regulate the transporters for different neurotransmitters. In addition to these classical receptor activated pathways, transporter substrates also regulate activity and cell surface expression of these transporters. In fact, some of the transporters form complexes with signaling molecules. Given the functional and genetic similarities of these transporters, it is not surprising that the same signaling molecules regulate their trafficking, but except for the molecules, the actual effects on individual transporters are remarkably different. It is as if the same musical notes have been rearranged into several different melodies.
Collapse
Affiliation(s)
- Michael B Robinson
- Department of Pediatrics, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
| |
Collapse
|
33
|
Gegelashvili G, Robinson MB, Trotti D, Rauen T. Regulation of glutamate transporters in health and disease. PROGRESS IN BRAIN RESEARCH 2001; 132:267-86. [PMID: 11544995 DOI: 10.1016/s0079-6123(01)32082-4] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- G Gegelashvili
- Department of Pharmacology, Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen Ø, Denmark.
| | | | | | | |
Collapse
|
34
|
Abstract
Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.
Collapse
Affiliation(s)
- N C Danbolt
- Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1105, Blindern, N-0317, Oslo, Norway
| |
Collapse
|
35
|
Gadea A, López-Colomé AM. Glial transporters for glutamate, glycine, and GABA III. Glycine transporters. J Neurosci Res 2001; 64:218-22. [PMID: 11319765 DOI: 10.1002/jnr.1069] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Glial cells possess transport systems for the three major amino acid neurotransmitters glutamate, gamma-aminobutyric acid (GABA) and glycine, involved in the arrest of neurotransmission mediated by these compounds. Two glycine transporters have been cloned: GLYT1, mainly expressed by glial cells and shown to colocalize with NMDA receptors, and GLYT2, exclusively expressed by neurons and colocalized with the inhibitory glycine receptors. The way in which the regulation of extracellular glycine concentration by glial glycine transporters affects physiological and pathological conditions is discussed. The presence, differential pharmacology and specific regulation of glycine transporters in glial cells strongly support an important role for glia in the modulation of both, excitatory and inhibitory neurotransmission.
Collapse
Affiliation(s)
- A Gadea
- Instituto de Fisiología Celular, Departamento de Neurociencias, UNAM, México
| | | |
Collapse
|
36
|
Toimela TA, Tähti H. Effects of mercuric chloride exposure on the glutamate uptake by cultured retinal pigment epithelial cells. Toxicol In Vitro 2001; 15:7-12. [PMID: 11259864 DOI: 10.1016/s0887-2333(00)00057-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The cytotoxicity of mercuric chloride and the effects of mercuric chloride on glutamate and calcium uptake and the factors regulating glutamate uptake were studied in retinal pigment epithelium (RPE) cell cultures. RPE cells isolated from pig eyes and human RPE cell line (D407) cells were cultured to confluency and further subcultured according to the test protocol in question. The cytotoxicity caused by 15 min of exposure to mercuric chloride (0.01--1000 microM) was evaluated by WST-1 assay based on the activity of mitochondrial dehydrogenases. [(3)H]Glutamate uptake was measured after the cells were exposed to 0.1--100 microM mercuric chloride and the selected regulators of protein kinase C (PKC) pathway: PKC activator SC10, PKC inhibitor chelerythrine chloride, phospholipase A(2)/C inhibitor manoalide, tyrosine kinase inhibitor lavendustin A, competitive NMDA receptor antagonist AP7 and IP(3) receptor antagonist heparin. Intracellular calcium was monitored with Fluo-3 probe starting immediately after the exposure to 1--1000 microM mercuric chloride. Mercuric chloride showed concentration-dependent effects on cell viability, on glutamate uptake and on intracellular calcium concentration. The results give some support to the concept that glutamate uptake is affected by PKC. The PKC inhibitor chelerythrine chloride decreased glutamate uptake by 25%, but the PKC activator SC10 could partly prevent the inhibitory effect of mercuric chloride. Lavendustin A, manoalide and heparin had smaller, but statistically significant, effects. All these substances act on mediators which can regulate the activity of PKC. However, PKC is not likely to be the only regulator of glutamate uptake. The rise observed in [Ca(2+)](i) may initiate various cellular events during mercury intoxication.
Collapse
Affiliation(s)
- T A Toimela
- Tampere University Medical School, FIN-33014 University of Tampere, Finland
| | | |
Collapse
|
37
|
Abstract
The gene expression regulation of the Na+-dependent high affinity glutamate/aspartate transporter GLAST expressed in cultured Bergmann glia cells from chick cerebellum was studied. A 679 bp fragment of the chick GLAST cDNA was cloned and sequenced. Specific PCR primers were used to quantify chick GLAST mRNA levels. Treatment of the cells with the Ca2+/diacylglycerol dependent protein kinase C (PKC) activator, phorbol 12-tetradecanoyl-13-acetate (TPA) produced a decrease in transporter mRNA levels, without an effect in its mRNA half life, suggesting a transcriptional down regulation. Activation of the cAMP pathway results in a transient decrease in GLAST mRNA levels, in contrast with the TPA effect. These findings suggest that GLAST expression is under control of distinct signaling pathways.
Collapse
Affiliation(s)
- M Espinoza-Rojo
- Departamento de Genética y Biología Molecular, Cinvestav-IPN, México DF, México
| | | | | |
Collapse
|
38
|
González MI, Ortega A. Regulation of high-affinity glutamate uptake activity in Bergmann glia cells by glutamate. Brain Res 2000; 866:73-81. [PMID: 10825482 DOI: 10.1016/s0006-8993(00)02226-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The effect of glutamate receptor activation on the high-affinity sodium-dependent glutamate transport expressed in chick Bergmann glia cells was examined. Pre-exposure to glutamate produced a time- and dose-dependent decrease in 3H-labeled D-aspartate uptake. This effect could not be reproduced by selective glutamate receptor agonists. Furthermore, it was insensitive to both ionotropic and metabotropic glutamate receptor antagonists. Replacement of extracellular sodium ions with choline in the preincubation media, abolished the reduction of the uptake. When the cells were pre-exposed to competitive transportable inhibitors of the transporter, such as D-aspartate, DL-threo-hydroxyaspartate (DL-THA), and aspartate-beta-hydroxamate (ABH), the glutamate effect was mimicked. From saturation experiments, it was found that the reduction on the uptake, after glutamate treatment, is related to an increase in K(m). Interestingly, the effect is blocked by staurosporine, a Ca(2+)/diacylglycerol-dependent protein kinase (PKC) inhibitor. The present findings suggest that glutamate regulates its transport in a non-receptor fashion, a phenomena that is most probably linked to changes induced by the translocation process of the substrate through the transporter.
Collapse
Affiliation(s)
- M I González
- Departamento de Genética y Biología Molecular, Cinvestav-IPN, Apartado Postal 14-740, DF 07000, México, Mexico
| | | |
Collapse
|
39
|
|
40
|
Gadea A, López E, López-Colomé AM. The adenylate cyclase inhibitor MDL-12330A has a non-specific effect on glycine transport in Müller cells from the retina. Brain Res 1999; 838:200-4. [PMID: 10446333 DOI: 10.1016/s0006-8993(99)01683-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Müller glial cells express two transport systems for glycine (Gly): one with low affinity and another identified as GLYT1 with high affinity. The latter colocalizes with NMDA receptors in the CNS. Gly is considered as an obligatory coagonist at NMDA receptors, and, hence, the Gly transport system could contribute to the modulation of glutamate (Glu) excitatory transmission in the vertical pathways of the retina. For this reason, the regulation of Gly transport by cAMP was studied. We report here a non-specific effect of MDL-12330A, a compound reported to inhibit adenylate cyclase (AC), on Gly transport in Müller glia. This effect might be due to a toxic action on the cells, decreasing cell viability, and not to a specific inhibition of the adenylate cyclase. Non-specific effects of this drug should be considered when the participation of cAMP in any biological process is studied. We have clearly demonstrated that cAMP does not participate in the regulation of Gly transport in Müller glia.
Collapse
Affiliation(s)
- A Gadea
- Instituto de Fisiología Celular, Departamento de Neurociencias, UNAM, Apartado Postal 70-253, 04510, D.F., Mexico
| | | | | |
Collapse
|
41
|
Aguilera P, Ortega A. Stat3 participates in the metabotropic glutamate signaling pathway in Bergmann glial cells. Neurochem Res 1999; 24:981-6. [PMID: 10478936 DOI: 10.1023/a:1021044424103] [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: 11/12/2022]
Abstract
Purkinje cells establish a glutamatergic synapse with the parallel fibers in the cerebellum. Bergmann glial cells surround this synapse. The transcription factor Stat3, highly expressed in cerebellum, is present in cultures of chick Bergmann glia. Treatment of these cells with L-glutamate induces the tyrosine-phosphorylation of Stat3. The maximal phosphorylation was observed after 15 min and by 30 min returned to basal levels. This effect correlated with Stat3 translocation to nucleus and the appearance of a retarded band in gel mobility shift assays. The effects observed with L-glutamate were mediated through metabotropic glutamate receptors. These results further support the notion that glial cells respond to L-glutamate through changes in the existing proteins and also in gene expression regulation.
Collapse
Affiliation(s)
- P Aguilera
- Departamento de Genética y Biología Molecular, CINVESTAV-IPN, México DF, Mexico
| | | |
Collapse
|
42
|
González MI, López-Colom AM, Ortega A. Sodium-dependent glutamate transport in Müller glial cells: regulation by phorbol esters. Brain Res 1999; 831:140-5. [PMID: 10411993 DOI: 10.1016/s0006-8993(99)01438-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The regulation of the Na(+)-dependent high affinity glutamate/aspartate transporter system expressed in cultured Müller glia cells from chick retina was studied. Treatment of the cells with the Ca(2+)/diacylglycerol dependent protein kinase C (PKC) activator, phorbol 12-tetradecanoil-13-acetate (TPA) produced a decrease in [(3)H]D-aspartate uptake which was reversed by staurosporine and partially by H7 [1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochoride], two PKC inhibitors. Long-term treatment with TPA resulted in a drastic decrease in the uptake activity, correlated with a substantial fall in the expression of the transporter protein. These findings suggest that PKC is involved in transport modulation at two different levels: phosphorylation and transporter expression in retinal Müller glial cells.
Collapse
Affiliation(s)
- M I González
- Departamento de Genética y Biología Molecular, CINVESTAV-IPN, Apartado Postal 14-740, México D.F. 07000, Mexico
| | | | | |
Collapse
|
43
|
Liachenko S, Tang P, Somogyi GT, Xu Y. Concentration-dependent isoflurane effects on depolarization-evoked glutamate and GABA outflows from mouse brain slices. Br J Pharmacol 1999; 127:131-8. [PMID: 10369465 PMCID: PMC1566008 DOI: 10.1038/sj.bjp.0702543] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The synaptic concentrations of glutamate and gamma-aminobutyric acid (GABA) are modulated by their release and re-uptake. The effects of general anaesthetics on these two processes remain unclear. This study evaluates the effects of isoflurane, a clinically important anaesthetic, on glutamate and GABA release and re-uptake in superfused mouse cerebrocortical slices. Experiments consisted of two 1.5-min exposures to 40 mM KCl in 30 min intervals. During the second exposure, different concentrations of isoflurane with and without 0.3 mM L-transpyrrolidine-2,4-dicarboxylic acid (PDC, a competitive inhibitor of glutamate uptake transporter) or 1 mM nipecotic acid (a competitive inhibitor of GABA uptake transporter) were introduced. The ratios of the second to first KCl-evoked increases in glutamate and GABA were used to determine the isoflurane concentration-response curves. The results can be described as a sum of two independent processes, corresponding to the inhibitions of release and re-uptake, respectively. The EC50 values for the inhibitions of release and re-uptake were 295+/-16 and 805+/-43 microM for glutamate, and 229+/-13 and 520+/-25 microM for GABA, respectively. Addition of PDC did not significantly affect glutamate release but shifted the re-uptake curve to the left (EC50= 315+/-20 microM). Nipecotic acid completely blocked GABA uptake, rendering isoflurane inhibition of GABA re-uptake undetectable. Our data suggest that isoflurane inhibits both the release and re-uptake of neurotransmitters and that the inhibitions occur at different EC50's. For GABA, both EC50's are within the clinical concentration range. The net anaesthetic effect on extracellular concentrations of neurotransmitters, particularly GABA, depends on the competition between inhibition of release and that of re-uptake.
Collapse
Affiliation(s)
- Serguei Liachenko
- Department of Anaesthesiology and Critical Care Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, U.S.A
| | - Pei Tang
- Department of Anaesthesiology and Critical Care Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, U.S.A
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, U.S.A
| | - George T Somogyi
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, U.S.A
| | - Yan Xu
- Department of Anaesthesiology and Critical Care Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, U.S.A
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, U.S.A
- Author for correspondence:
| |
Collapse
|