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Cui L, Li S, Wang S, Wu X, Liu Y, Yu W, Wang Y, Tang Y, Xia M, Li B. Major depressive disorder: hypothesis, mechanism, prevention and treatment. Signal Transduct Target Ther 2024; 9:30. [PMID: 38331979 PMCID: PMC10853571 DOI: 10.1038/s41392-024-01738-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 12/24/2023] [Accepted: 12/28/2023] [Indexed: 02/10/2024] Open
Abstract
Worldwide, the incidence of major depressive disorder (MDD) is increasing annually, resulting in greater economic and social burdens. Moreover, the pathological mechanisms of MDD and the mechanisms underlying the effects of pharmacological treatments for MDD are complex and unclear, and additional diagnostic and therapeutic strategies for MDD still are needed. The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis, but these hypothesis cannot completely explain the pathological mechanism of MDD. Even it is still hard to adopt only one hypothesis to completely reveal the pathogenesis of MDD, thus in recent years, great progress has been made in elucidating the roles of multiple organ interactions in the pathogenesis MDD and identifying novel therapeutic approaches and multitarget modulatory strategies, further revealing the disease features of MDD. Furthermore, some newly discovered potential pharmacological targets and newly studied antidepressants have attracted widespread attention, some reagents have even been approved for clinical treatment and some novel therapeutic methods such as phototherapy and acupuncture have been discovered to have effective improvement for the depressive symptoms. In this work, we comprehensively summarize the latest research on the pathogenesis and diagnosis of MDD, preventive approaches and therapeutic medicines, as well as the related clinical trials.
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Affiliation(s)
- Lulu Cui
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China
- China Medical University Centre of Forensic Investigation, Shenyang, China
| | - Shu Li
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China
- China Medical University Centre of Forensic Investigation, Shenyang, China
| | - Siman Wang
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China
- China Medical University Centre of Forensic Investigation, Shenyang, China
| | - Xiafang Wu
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China
- China Medical University Centre of Forensic Investigation, Shenyang, China
| | - Yingyu Liu
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China
- China Medical University Centre of Forensic Investigation, Shenyang, China
| | - Weiyang Yu
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China
- China Medical University Centre of Forensic Investigation, Shenyang, China
| | - Yijun Wang
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China
- China Medical University Centre of Forensic Investigation, Shenyang, China
| | - Yong Tang
- International Joint Research Centre on Purinergic Signalling/Key Laboratory of Acupuncture for Senile Disease (Chengdu University of TCM), Ministry of Education/School of Health and Rehabilitation, Chengdu University of Traditional Chinese Medicine/Acupuncture and Chronobiology Key Laboratory of Sichuan Province, Chengdu, China
| | - Maosheng Xia
- Department of Orthopaedics, The First Hospital, China Medical University, Shenyang, China.
| | - Baoman Li
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China.
- Liaoning Province Key Laboratory of Forensic Bio-evidence Sciences, Shenyang, China.
- China Medical University Centre of Forensic Investigation, Shenyang, China.
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Leek AN, Quinn JA, Krapf D, Tamkun MM. GLT-1a glutamate transporter nanocluster localization is associated with astrocytic actin and neuronal Kv2 clusters at sites of neuron-astrocyte contact. Front Cell Dev Biol 2024; 12:1334861. [PMID: 38362041 PMCID: PMC10867268 DOI: 10.3389/fcell.2024.1334861] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Accepted: 01/16/2024] [Indexed: 02/17/2024] Open
Abstract
Introduction: Astrocytic GLT-1 glutamate transporters ensure the fidelity of glutamic neurotransmission by spatially and temporally limiting glutamate signals. The ability to limit neuronal hyperactivity relies on the localization and diffusion of GLT-1 on the astrocytic surface, however, little is known about the underlying mechanisms. We show that two isoforms of GLT-1, GLT-1a and GLT-1b, form nanoclusters on the surface of transfected astrocytes and HEK-293 cells. Methods: We used both fixed and live cell super-resolution imaging of fluorescent protein and epitope tagged proteins in co-cultures of rat astrocytes and neurons. Immunofluorescence techniques were also used. GLT1 diffusion was assessed via single particle tracking and fluorescence recovery after photobleach (FRAP). Results: We found GLT-1a, but not GLT-1b, nanoclusters concentrated adjacent to actin filaments which was maintained after addition of glutamate. GLT-1a nanocluster concentration near actin filaments was prevented by expression of a cytosolic GLT-1a C-terminus, suggesting the C-terminus is involved in the localization adjacent to cortical actin. Using super-resolution imaging, we show that astrocytic GLT-1a and actin co-localize in net-like structures around neuronal Kv2.1 clusters at points of neuron/astrocyte contact. Conclusion: Overall, these data describe a novel relationship between GLT-1a and cortical actin filaments, which localizes GLT-1a near neuronal structures responsive to ischemic insult.
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Affiliation(s)
- Ashley N. Leek
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO, United States
| | - Josiah A. Quinn
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States
| | - Diego Krapf
- Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, CO, United States
| | - Michael M. Tamkun
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO, United States
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, United States
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Siemsen BM, Denton AR, Parrila-Carrero J, Hooker KN, Carpenter EA, Prescot ME, Brock AG, Westphal AM, Leath MN, McFaddin JA, Jhou TC, McGinty JF, Scofield MD. Heroin Self-Administration and Extinction Increase Prelimbic Cortical Astrocyte-Synapse Proximity and Alter Dendritic Spine Morphometrics That Are Reversed by N-Acetylcysteine. Cells 2023; 12:1812. [PMID: 37508477 PMCID: PMC10378353 DOI: 10.3390/cells12141812] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 05/09/2023] [Accepted: 07/06/2023] [Indexed: 07/30/2023] Open
Abstract
Clinical and preclinical studies indicate that adaptations in corticostriatal neurotransmission significantly contribute to heroin relapse vulnerability. In animal models, heroin self-administration and extinction produce cellular adaptations in both neurons and astrocytes within the nucleus accumbens (NA) core that are required for cue-induced heroin seeking. Specifically, decreased glutamate clearance and reduced association of perisynaptic astrocytic processes with NAcore synapses allow glutamate release from prelimbic (PrL) cortical terminals to engage synaptic and structural plasticity in NAcore medium spiny neurons. Normalizing astrocyte glutamate homeostasis with drugs like the antioxidant N-acetylcysteine (NAC) prevents cue-induced heroin seeking. Surprisingly, little is known about heroin-induced alterations in astrocytes or pyramidal neurons projecting to the NAcore in the PrL cortex (PrL-NAcore). Here, we observe functional adaptations in the PrL cortical astrocyte following heroin self-administration (SA) and extinction as measured by the electrophysiologically evoked plasmalemmal glutamate transporter 1 (GLT-1)-dependent current. We likewise observed the increased complexity of the glial fibrillary acidic protein (GFAP) cytoskeletal arbor and increased association of the astrocytic plasma membrane with synaptic markers following heroin SA and extinction training in the PrL cortex. Repeated treatment with NAC during extinction reversed both the enhanced astrocytic complexity and synaptic association. In PrL-NAcore neurons, heroin SA and extinction decreased the apical tuft dendritic spine density and enlarged dendritic spine head diameter in male Sprague-Dawley rats. Repeated NAC treatment during extinction prevented decreases in spine density but not dendritic spine head expansion. Moreover, heroin SA and extinction increased the co-registry of the GluA1 subunit of AMPA receptors in both the dendrite shaft and spine heads of PrL-NAcore neurons. Interestingly, the accumulation of GluA1 immunoreactivity in spine heads was further potentiated by NAC treatment during extinction. Finally, we show that the NAC treatment and elimination of thrombospondin 2 (TSP-2) block cue-induced heroin relapse. Taken together, our data reveal circuit-level adaptations in cortical dendritic spine morphology potentially linked to heroin-induced alterations in astrocyte complexity and association at the synapses. Additionally, these data demonstrate that NAC reverses PrL cortical heroin SA-and-extinction-induced adaptations in both astrocytes and corticostriatal neurons.
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Affiliation(s)
- Benjamin M. Siemsen
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Adam R. Denton
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC 29425, USA
| | | | - Kaylee N. Hooker
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Eilish A. Carpenter
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Meagan E. Prescot
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Ashley G. Brock
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Annaka M. Westphal
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Mary-Nan Leath
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - John A. McFaddin
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Thomas C. Jhou
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Jacqueline F. McGinty
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC 29425, USA
| | - Michael D. Scofield
- Department of Anesthesia and Perioperative Medicine, Medical University of South Carolina, Charleston, SC 29425, USA
- Department of Neuroscience, Medical University of South Carolina, Charleston, SC 29425, USA
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Conti F, Pietrobon D. Astrocytic Glutamate Transporters and Migraine. Neurochem Res 2023; 48:1167-1179. [PMID: 36583835 DOI: 10.1007/s11064-022-03849-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2022] [Revised: 12/07/2022] [Accepted: 12/17/2022] [Indexed: 12/31/2022]
Abstract
Glutamate levels and lifetime in the brain extracellular space are dinamically regulated by a family of Na+- and K+-dependent glutamate transporters, which thereby control numerous brain functions and play a role in numerous neurological and psychiatric diseases. Migraine is a neurological disorder characterized by recurrent attacks of typically throbbing and unilateral headache and by a global dysfunction in multisensory processing. Familial hemiplegic migraine type 2 (FHM2) is a rare monogenic form of migraine with aura caused by loss-of-function mutations in the α2 Na/K ATPase (α2NKA). In the adult brain, this pump is expressed almost exclusively in astrocytes where it is colocalized with glutamate transporters. Knockin mouse models of FHM2 (FHM2 mice) show a reduced density of glutamate transporters in perisynaptic astrocytic processes (mirroring the reduced expression of α2NKA) and a reduced rate of glutamate clearance at cortical synapses during neuronal activity and sensory stimulation. Here we review the migraine-relevant alterations produced by the astrocytic glutamate transport dysfunction in FHM2 mice and their underlying mechanisms, in particular regarding the enhanced brain susceptibility to cortical spreading depression (the phenomenon that underlies migraine aura and can also initiate the headache mechanisms) and the enhanced algesic response to a migraine trigger.
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Affiliation(s)
- Fiorenzo Conti
- Section of Neuroscience and Cell Biology, Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy.
- Center for Neurobiology of Aging, IRCCS INRCA, Ancona, Italy.
| | - Daniela Pietrobon
- Department of Biomedical Sciences and Padova Neuroscience Center (PNC), University of Padova, 35131, Padua, Italy.
- CNR Institute of Neuroscience, 35131, Padua, Italy.
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5
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Lee A, Klinkradt S, McCombe P, Pow D. Cloning of a new form of EAAT2/GLT-1 from human and rodent brains. Neurosci Lett 2022; 780:136637. [DOI: 10.1016/j.neulet.2022.136637] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 04/08/2022] [Accepted: 04/13/2022] [Indexed: 11/15/2022]
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6
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Taspinar N, Hacimuftuoglu A, Butuner S, Togar B, Arslan G, Taghizadehghalehjoughi A, Okkay U, Agar E, Stephens R, Turkez H, Abd El-Aty AM. Differential effects of inhibitors of PTZ-induced kindling on glutamate transporters and enzyme expression. Clin Exp Pharmacol Physiol 2021; 48:1662-1673. [PMID: 34409650 DOI: 10.1111/1440-1681.13575] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 07/31/2021] [Accepted: 08/14/2021] [Indexed: 12/01/2022]
Abstract
Epilepsy is a neurological disorder resulting from abnormal neuronal firing in the brain. Glutamate transporters and the glutamate-glutamine cycle play crucial roles in the development of seizures. In the present study, the correlation of epilepsy with glutamate transporters and enzymes was investigated. Herein, male Wistar rats were randomly allocated into four groups (six animals/group); 35 mg/kg pentylenetetrazole (PTZ) was used to induce a kindling model of epilepsy. Once the kindling model was established, animals were treated for 15 days with either valproic acid (VPA, 350 mg/kg) or ceftriaxone (CEF, 200 mg/kg) in addition to the control group receiving saline. After treatment, electrocorticography (ECoG) was performed to record the electrical activity of the cerebral cortex. The glutamate reuptake time (T80 ) was also determined in situ using an in vivo voltammetry. The expression levels of glutamate transporters and enzymes in the M1 and CA3 areas of the brain were determined using a real-time polymerase chain reaction (RT-PCR). ECoG measurements showed that the mean spike number of the PTZ + VPA and PTZ + CEF groups was significantly lower (p < 0.05) than that of the PTZ group. Compared with the PTZ group, VPA or CEF treatment decreased the glutamate reuptake time (T80 ). The expression levels of EAAC1, GLT-1, GLAST, glutamine synthetase (GS), and glutaminase were increased in the PTZ group. Treatment with VPA or CEF enhanced the expression levels of GLT-1, GLAST, EAAC1, and GS, whereas the glutaminase expression level was reduced. The current results suggest that VPA or CEF decreases seizure activity by increasing glutamate reuptake by upregulating GLT-1 and GLAST expression, implying a possible mechanism for treating epilepsy. Also, we have suggested a novel mechanism for the antiepileptic activity of VPA via decreasing glutaminase expression levels. To our knowledge, this is the first study to measure the glutamate reuptake time in situ during the seizure (i.e., real-time measurement).
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Affiliation(s)
- Numan Taspinar
- Department of Medical Pharmacology, Faculty of Medicine, Uşak University, Uşak, Turkey
| | - Ahmet Hacimuftuoglu
- Department of Medical Pharmacology, Faculty of Medicine, Atatürk University, Erzurum, Turkey
| | - Selcuk Butuner
- Department of Medical Pharmacology, Faculty of Medicine, Atatürk University, Erzurum, Turkey
| | - Basak Togar
- Department of Medical Services and Techniques, Vocational School of Health Services, Bayburt University, Bayburt, Turkey
| | - Gokhan Arslan
- Department of Physiology, Faculty of Medicine, Ondokuz Mayıs University, Samsun, Turkey
| | - Ali Taghizadehghalehjoughi
- Department of Pharmacology and Toxicology, Faculty of Veterinary Medicine, Atatürk University, Erzurum, Turkey
| | - Ufuk Okkay
- Department of Medical Pharmacology, Faculty of Medicine, Atatürk University, Erzurum, Turkey
| | - Erdal Agar
- Department of Physiology, Faculty of Medicine, Ondokuz Mayıs University, Samsun, Turkey
| | - Robert Stephens
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA
| | - Hasan Turkez
- Department of Medical Biology, Faculty of Medicine, Atatürk University, Erzurum, Turkey
| | - A M Abd El-Aty
- Department of Medical Pharmacology, Faculty of Medicine, Atatürk University, Erzurum, Turkey
- Department of Pharmacology, Faculty of Veterinary Medicine, Cairo University, Giza, Egypt
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7
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Rodríguez-Campuzano AG, Ortega A. Glutamate transporters: Critical components of glutamatergic transmission. Neuropharmacology 2021; 192:108602. [PMID: 33991564 DOI: 10.1016/j.neuropharm.2021.108602] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 04/09/2021] [Accepted: 04/27/2021] [Indexed: 02/06/2023]
Abstract
Glutamate is the major excitatory neurotransmitter in the vertebrate central nervous system. Once released, it binds to specific membrane receptors and transporters activating a wide variety of signal transduction cascades, as well as its removal from the synaptic cleft in order to avoid its extracellular accumulation and the overstimulation of extra-synaptic receptors that might result in neuronal death through a process known as excitotoxicity. Although neurodegenerative diseases are heterogenous in clinical phenotypes and genetic etiologies, a fundamental mechanism involved in neuronal degeneration is excitotoxicity. Glutamate homeostasis is critical for brain physiology and Glutamate transporters are key players in maintaining low extracellular Glutamate levels. Therefore, the characterization of Glutamate transporters has been an active area of glutamatergic research for the last 40 years. Transporter activity its regulated at different levels: transcriptional and translational control, transporter protein trafficking and membrane mobility, and through extensive post-translational modifications. The elucidation of these mechanisms has emerged as an important piece to shape our current understanding of glutamate actions in the nervous system.
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Affiliation(s)
- Ada G Rodríguez-Campuzano
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14-740, Ciudad de México, 07000, Mexico
| | - Arturo Ortega
- Departamento de Toxicología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14-740, Ciudad de México, 07000, Mexico.
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Ryan RM, Ingram SL, Scimemi A. Regulation of Glutamate, GABA and Dopamine Transporter Uptake, Surface Mobility and Expression. Front Cell Neurosci 2021; 15:670346. [PMID: 33927596 PMCID: PMC8076567 DOI: 10.3389/fncel.2021.670346] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Accepted: 03/15/2021] [Indexed: 01/31/2023] Open
Abstract
Neurotransmitter transporters limit spillover between synapses and maintain the extracellular neurotransmitter concentration at low yet physiologically meaningful levels. They also exert a key role in providing precursors for neurotransmitter biosynthesis. In many cases, neurons and astrocytes contain a large intracellular pool of transporters that can be redistributed and stabilized in the plasma membrane following activation of different signaling pathways. This means that the uptake capacity of the brain neuropil for different neurotransmitters can be dynamically regulated over the course of minutes, as an indirect consequence of changes in neuronal activity, blood flow, cell-to-cell interactions, etc. Here we discuss recent advances in the mechanisms that control the cell membrane trafficking and biophysical properties of transporters for the excitatory, inhibitory and modulatory neurotransmitters glutamate, GABA, and dopamine.
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Affiliation(s)
- Renae M. Ryan
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
| | - Susan L. Ingram
- Department of Neurological Surgery, Oregon Health & Science University, Portland, OR, United States
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9
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Zhao F, Zhang T, Shen Q, Yin K, Wang Y, Zhang G. Tak1 in the astrocytes of mediobasal hypothalamus regulates anxiety-like behavior in mice. Glia 2021; 69:609-618. [PMID: 32979244 DOI: 10.1002/glia.23916] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2020] [Revised: 09/11/2020] [Accepted: 09/14/2020] [Indexed: 12/11/2022]
Abstract
Anxiety disorder is characterized by excessive fear, anxiety, and avoidance of perceived threats in internal to oneself or the environment, however, the underlying mechanisms are less well understood. Here, we show that transforming growth factor-β-activated kinase 1 (Tak1) expressed in the astrocytes of mediobasal hypothalamus (MBH) plays a crucial role in anxiety-like behavior in mice. Our data demonstrate that deficiency of Tak1 in astrocytes increased anxiety level, but did not impact locomotor activity in mice. Astrocytic activation of Tak1 in the MBH mitigated the anxiety-like behavior, whereas suppression of Tak1 in MBH astrocytes promoted the anxiety-like behavior in mice. Collectively, these data suggest that Tak1 expressed in the MBH astrocytes could modulate the anxiety-like behavior in mice.
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Affiliation(s)
- Faming Zhao
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Wuhan, Hubei, China
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Tingting Zhang
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Wuhan, Hubei, China
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Qing Shen
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Wuhan, Hubei, China
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Kaili Yin
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Wuhan, Hubei, China
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yu Wang
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Wuhan, Hubei, China
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Guo Zhang
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Wuhan, Hubei, China
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei, China
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10
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Neurobiology, Functions, and Relevance of Excitatory Amino Acid Transporters (EAATs) to Treatment of Refractory Epilepsy. CNS Drugs 2020; 34:1089-1103. [PMID: 32926322 DOI: 10.1007/s40263-020-00764-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Epilepsy is one of the most prevalent and devastating neurological disorders characterized by episodes of unusual sensations, loss of awareness, and reoccurring seizures. The frequency and intensity of epileptic fits can vary to a great degree, with almost a third of all cases resistant to available therapies. At present, there is a major unmet need for effective and specific therapeutic intervention. Impairments of the exquisite balance between excitatory and inhibitory synaptic processes in the brain are considered key in the onset and pathophysiology of the disease. As the primary excitatory neurotransmitter in the central nervous system, glutamate has been implicated in the process, with the glutamatergic system holding center stage in the pathobiology as well as in developing disease-modifying therapies. Emerging data pinpoint impairments of glutamate clearance as one of the key causative factors in drug-resistant disease forms. Reinstatement of glutamate homeostasis using pharmacological and genetic modulation of glutamate clearance is therefore considered to be of major translational relevance. In this article, we review the neurobiological and clinical evidence suggesting complex aberrations in the activity and functions of excitatory amino acid transporters (EAATs) in epilepsy, with knock-on effects on glutamate homeostasis as a leading cause for the development of refractory forms. We consider the emerging data on pharmacological and genetic manipulations of EAATs, with reference to seizures and glutamate dyshomeostasis, and review their fundamental and translational relevance. We discuss the most recent advances in the EAATs research in human and animal models, along with numerous questions that remain open for debate and critical appraisal. Contrary to the widely held view on EAATs as a promising therapeutic target for management of refractory epilepsy as well as other neurological and psychiatric conditions related to glutamatergic hyperactivity and glutamate-induced cytotoxicity, we stress that the true relevance of EAAT2 as a target for medical intervention remains to be fully appreciated and verified. Despite decades of research, the emerging properties and functional characteristics of glutamate transporters and their relationship with neurophysiological and behavioral correlates of epilepsy challenge the current perception of this disease and fit unambiguously in neither EAATs functional deficit nor in reversal models. We stress the pressing need for new approaches and models for research and restoration of the physiological activity of glutamate transporters and synaptic transmission to achieve much needed therapeutic effects. The complex mechanism of EAATs regulation by multiple factors, including changes in the electrochemical environment and ionic gradients related to epileptic hyperactivity, impose major therapeutic challenges. As a final note, we consider the evolving views and present a cautious perspective on the key areas of future progress in the field towards better management and treatment of refractory disease forms.
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11
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Lee A, Balcar VJ, McCombe P, Pow DV. Human brain neurons express a novel splice variant of excitatory amino acid transporter 5 (hEAAT5v). J Comp Neurol 2020; 528:3134-3142. [PMID: 32173860 DOI: 10.1002/cne.24907] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 03/05/2020] [Accepted: 03/06/2020] [Indexed: 11/08/2022]
Abstract
Excitatory amino acid transporter 5 (EAAT5) is a protein that is known to be alternately spliced and to be abundantly expressed in the retina by populations of neurons including photoreceptors and bipolar cells. EAAT5 acts as a slow glutamate transporter and also as glutamate-gated chloride channel, the chloride conductance being large enough for EAAT5 to serve functionally as an "inhibitory" glutamate receptor. However, there has been a long-standing view that the classically spliced form of EAAT5 is not abundant or widespread in the brain and so it has not been extensively investigated in the literature. We recently identified a human-specific splicing form of EAAT5 that was not expressed by rodents but was shown to be a functional glutamate transporter. We have examined the expression of this form of EAAT5, hEAAT5v at the mRNA, and protein level in human brain, and show that populations of human cortical pyramidal neurons and cerebellar Purkinje cells show significant expression of hEAAT5v. Accordingly, we infer that EAAT5 may well be a player in modulating neuronal function in the human brain and propose that its localization in both glutamatergic and GABAergic neurons could be compatible with a role in influencing intracellular chloride and thereby neuronal parameters such as membrane potential rather than acting as a presynaptic glutamate transporter.
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Affiliation(s)
- Aven Lee
- UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia
| | - Vladimir J Balcar
- Discipline of Anatomy and Histology, School of Medical Sciences and Bosch Institute, Sydney Medical School, The University of Sydney, Sydney, New South Wales, Australia.,Laboratory of Neurobiology and Pathological Physiology, Institute of Animal Physiology and Genetics, Academy of Sciences of the Czech Republic, Brno, Czech Republic
| | - Pamela McCombe
- UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia
| | - David V Pow
- UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia
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12
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Suárez-Pozos E, Thomason EJ, Fuss B. Glutamate Transporters: Expression and Function in Oligodendrocytes. Neurochem Res 2020; 45:551-560. [PMID: 30628017 PMCID: PMC6616022 DOI: 10.1007/s11064-018-02708-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Revised: 12/19/2018] [Accepted: 12/22/2018] [Indexed: 12/14/2022]
Abstract
Glutamate, the main excitatory neurotransmitter of the vertebrate central nervous system (CNS), is well known as a regulator of neuronal plasticity and neurodevelopment. Such glutamate function is thought to be mediated primarily by signaling through glutamate receptors. Thus, it requires a tight regulation of extracellular glutamate levels and a fine-tuned homeostasis that, when dysregulated, has been associated with a wide range of central pathologies including neuropsychiatric, neurodevelopmental, and neurodegenerative disorders. In the mammalian CNS, extracellular glutamate levels are controlled by a family of sodium-dependent glutamate transporters belonging to the solute carrier family 1 (SLC1) that are also referred to as excitatory amino acid transporters (EAATs). The presumed main function of EAATs has been best described in the context of synaptic transmission where EAATs expressed by astrocytes and neurons effectively regulate extracellular glutamate levels so that synapses can function independently. There is, however, increasing evidence that EAATs are expressed by cells other than astrocytes and neurons, and that they exhibit functions beyond glutamate clearance. In this review, we will focus on the expression and functions of EAATs in the myelinating cells of the CNS, oligodendrocytes. More specifically, we will discuss potential roles of oligodendrocyte-expressed EAATs in contributing to extracellular glutamate homeostasis, and in regulating oligodendrocyte maturation and CNS myelination by exerting signaling functions that have traditionally been associated with glutamate receptors. In addition, we will provide some examples for how dysregulation of oligodendrocyte-expressed EAATs may be involved in the pathophysiology of neurologic diseases.
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Affiliation(s)
- Edna Suárez-Pozos
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of Medicine, Box 980709, Richmond, VA, 23298, USA
| | - Elizabeth J Thomason
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of Medicine, Box 980709, Richmond, VA, 23298, USA
| | - Babette Fuss
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of Medicine, Box 980709, Richmond, VA, 23298, USA.
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13
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Sex-dependent impaired locomotion and motor coordination in the HdhQ200/200 mouse model of Huntington's Disease. Neurobiol Dis 2019; 132:104607. [PMID: 31499139 DOI: 10.1016/j.nbd.2019.104607] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 08/02/2019] [Accepted: 09/04/2019] [Indexed: 01/08/2023] Open
Abstract
Huntington's Disease (HD) is a fatal neurodegenerative disease characterized by severe loss of medium spiny neuron (MSN) function and striatal-dependent behaviors. We report that female HdhQ200/200 mice display an earlier onset and more robust deterioration in spontaneous locomotion and motor coordination measured at 8 months of age compared to male HdhQ200/200 mice. Remarkably, HdhQ200/200 mice of both sexes exhibit comparable impaired spontaneous locomotion and motor coordination at 10 months of age and reach moribund stage by 12 months of age, demonstrating reduced life span in this model system. Histopathological analysis revealed enhanced mutant huntingtin protein aggregation in male HdhQ200/200 striatal tissue at 8 months of age compared to female HdhQ200/200. Functional analysis of calcium dynamics in MSNs of female HdhQ200/200 mice using GCaMP6m imaging revealed elevated responses to excitatory cortical-striatal stimulation suggesting increased MSN excitability. Although there was no down-regulation of the expression of common HD biomarkers (DARPP-32, enkephalin and CB1R), we measured a sex-dependent reduction of the astrocytic glutamate transporter, GLT-1, in female HdhQ200/200 mice that was not detected in male HdhQ200/200 mice when compared to respective wild-type littermates. Our study outlines a sex-dependent rapid deterioration of striatal-dependent behaviors occurring in the HdhQ200/200 mouse line that does not involve alterations in the expression of common HD biomarkers and yet includes impaired MSN function.
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14
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Cheng Z, Ou Y, Zhang L, Zhang P, Yuan X, Peng W, Wang S, Zhu X, Zhang L, Meng Y. The glutamate clearance function of adipose stromal cells-derived astrocytes. Neurosci Lett 2018; 677:94-102. [PMID: 29704575 DOI: 10.1016/j.neulet.2018.04.048] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2017] [Accepted: 04/24/2018] [Indexed: 10/17/2022]
Abstract
ADSCs-derived astrocytes qualify the morphology, ultrastructure and membrane electrical potential, which are all unique to astrocytes. But whether they have the glutamate clearance function like mature astrocytes is under exploration. ADSCs were extracted, cultured and induced into astrocytes for 48 h, 7d, 14d and 21d in vitro. Inverted phase contrast microscope was used to observe the morphology of the cells in each group. Immunocytochemistry assay, immunofluorescence assay and Western blotting were used to detect the expression of GFAP, EAAT2 and GS of the cells in each group. The cells were cultured in glutamate solution for 1, 2, 3 and 4 h respectively before the solution collected. The glutamate concentration of the solution was detected using Glutamate Colorimetric Assay Hit. ADSCs-derived astrocytes expressed GFAP, EAAT2 and GS, all of which increased gradually and reached peak when induced for 14 days. In induction for 48 h, 7d and 14d groups, the extracellular glutamate concentration decreased gradually during the cells cultured in glutamate solution for 1, 2, 3 and 4 h, among which the decrease extent was most prominent in 14d group, while the extracellular glutamate concentration had no change in uninduction and induction for 21d group. ADSCs-derived astrocytes expressed EAAT2 and GS, meanwhile had the function of clearing glutamate, which was prominent when induced into astrocytes for 7-14 days.
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Affiliation(s)
- Zanzan Cheng
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
| | - Ya Ou
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
| | - Lili Zhang
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
| | - Pingshu Zhang
- Key Laboratory of Neurological and Biological Function of Hebei Province, Tangshan 063000, Hebei Province, China; Key Laboratory of Neurology of Tangshan, Tangshan 063000, Hebei Province, China
| | - Xiaodong Yuan
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China; Key Laboratory of Neurological and Biological Function of Hebei Province, Tangshan 063000, Hebei Province, China.
| | - Wei Peng
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
| | - Shujuan Wang
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
| | - Xuhong Zhu
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
| | - Liping Zhang
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
| | - Yan Meng
- Department of Neurology, Affiliated Kailuan General Hospital of North China University of Science and Technology, Tangshan 063000, Hebei Province, China
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15
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Logan CN, LaCrosse AL, Knackstedt LA. Nucleus accumbens GLT-1a overexpression reduces glutamate efflux during reinstatement of cocaine-seeking but is not sufficient to attenuate reinstatement. Neuropharmacology 2018; 135:297-307. [PMID: 29567092 PMCID: PMC6383073 DOI: 10.1016/j.neuropharm.2018.03.022] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 03/14/2018] [Accepted: 03/17/2018] [Indexed: 12/22/2022]
Abstract
Cocaine use disorder is a chronically relapsing disease without FDA-approved treatments. Using a rodent model of cocaine relapse, we and others have previously demonstrated that the beta-lactam antibiotic ceftriaxone attenuates cue- and cocaine-primed reinstatement of cocaine-seeking. Ceftriaxone restores cocaine-induced deficits in both system xc- and GLT-1 expression and function in the nucleus accumbens core (NAc). We recently demonstrated that restoration of GLT-1 expression in the NAc is necessary for ceftriaxone to attenuate reinstatement of cocaine-seeking. Here we used an adeno-associated virus (AAV) to overexpress GLT-1a in the NAc to investigate whether such restoration is sufficient to attenuate cue- and cocaine-primed reinstatement. Rats self-administered cocaine for two weeks and received injections of either AAV-GFAP-GLT-1a or AAV-GFAP-eGFP in the NAc following the last day of self-administration. Rats then underwent three weeks of extinction training (during which time transduction and expression occurred) before undergoing a cue- or cocaine-primed reinstatement test. Microdialysis for the quantification of glutamate efflux in the NAc was conducted during the cocaine-primed test. Rats that received AAV-GFAP-GLT-1a reinstated cue-primed cocaine-seeking in a similar manner as rats that received the control AAV-GFAP-eGFP. Upregulation of GLT-1a attenuated glutamate efflux during a cocaine-primed reinstatement test, but was not sufficient to attenuate reinstatement. We confirmed that GLT-1a upregulation resulted in functional upregulation of glutamate transport and expression, without affecting sodium-independent glutamate uptake, indicating system xc-was not altered. These results indicate that upregulation of NAc GLT-1 transporters alone is not sufficient to prevent the reinstatement of cocaine-seeking and implicate additional mechanisms in regulating glutamate efflux.
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Affiliation(s)
- Carly N Logan
- Psychology Department, University of Florida, Gainesville, FL, United States.
| | - Amber L LaCrosse
- Psychology Department, University of Florida, Gainesville, FL, United States
| | - Lori A Knackstedt
- Psychology Department, University of Florida, Gainesville, FL, United States; Center for Addiction Research and Education, University of Florida, Gainesville, FL, United States
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16
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Al Awabdh S, Gupta-Agarwal S, Sheehan DF, Muir J, Norkett R, Twelvetrees AE, Griffin LD, Kittler JT. Neuronal activity mediated regulation of glutamate transporter GLT-1 surface diffusion in rat astrocytes in dissociated and slice cultures. Glia 2018; 64:1252-64. [PMID: 27189737 PMCID: PMC4915597 DOI: 10.1002/glia.22997] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Revised: 04/03/2016] [Accepted: 04/13/2016] [Indexed: 11/17/2022]
Abstract
The astrocytic GLT‐1 (or EAAT2) is the major glutamate transporter for clearing synaptic glutamate. While the diffusion dynamics of neurotransmitter receptors at the neuronal surface are well understood, far less is known regarding the surface trafficking of transporters in subcellular domains of the astrocyte membrane. Here, we have used live‐cell imaging to study the mechanisms regulating GLT‐1 surface diffusion in astrocytes in dissociated and brain slice cultures. Using GFP‐time lapse imaging, we show that GLT‐1 forms stable clusters that are dispersed rapidly and reversibly upon glutamate treatment in a transporter activity‐dependent manner. Fluorescence recovery after photobleaching and single particle tracking using quantum dots revealed that clustered GLT‐1 is more stable than diffuse GLT‐1 and that glutamate increases GLT‐1 surface diffusion in the astrocyte membrane. Interestingly, the two main GLT‐1 isoforms expressed in the brain, GLT‐1a and GLT‐1b, are both found to be stabilized opposed to synapses under basal conditions, with GLT‐1b more so. GLT‐1 surface mobility is increased in proximity to activated synapses and alterations of neuronal activity can bidirectionally modulate the dynamics of both GLT‐1 isoforms. Altogether, these data reveal that astrocytic GLT‐1 surface mobility, via its transport activity, is modulated during neuronal firing, which may be a key process for shaping glutamate clearance and glutamatergic synaptic transmission. GLIA 2016;64:1252–1264
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Affiliation(s)
- Sana Al Awabdh
- Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom
| | - Swati Gupta-Agarwal
- Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom
| | - David F Sheehan
- Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom
| | - James Muir
- Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom
| | - Rosalind Norkett
- Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom
| | - Alison E Twelvetrees
- Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom
| | - Lewis D Griffin
- Department of Computer Science, University College London, United Kingdom
| | - Josef T Kittler
- Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom
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17
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Rosenblum LT, Shamamandri-Markandaiah S, Ghosh B, Foran E, Lepore AC, Pasinelli P, Trotti D. Mutation of the caspase-3 cleavage site in the astroglial glutamate transporter EAAT2 delays disease progression and extends lifespan in the SOD1-G93A mouse model of ALS. Exp Neurol 2017; 292:145-153. [PMID: 28342750 DOI: 10.1016/j.expneurol.2017.03.014] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Revised: 03/15/2017] [Accepted: 03/22/2017] [Indexed: 12/11/2022]
Abstract
Downregulation in the astroglial glutamate transporter EAAT2 in amyotrophic lateral sclerosis (ALS) patients and mutant SOD1 mouse models of ALS is believed to contribute to the death of motor neurons by excitotoxicity. We previously reported that caspase-3 cleaves EAAT2 at a unique cleavage consensus site located in its c-terminus domain, a proteolytic cleavage that also occurs in vivo in the mutant SOD1 mouse model of ALS and leads to accumulation of a sumoylated EAAT2 C-terminus fragment (CTE-SUMO1) beginning around onset of disease. CTE-SUMO1 accumulates in PML nuclear bodies of astrocytes and causes them to alter their mature phenotypes and secrete factors toxic to motor neurons. Here, we report that mutating the caspase-3 consensus site in the EAAT2 sequence with an aspartate to asparagine mutation (D504N), thereby inhibiting caspase-3 cleavage of EAAT2, confers protection to the SOD1-G93A mouse. EAAT2-D504N knock-in mutant mice were generated and crossed with SOD1-G93A mice to assess the in vivo pathogenic relevance for ALS symptoms of EAAT2 cleavage. The mutation did not affect normal EAAT2 function nor non-ALS mice. In agreement with the timing of CTE-SUMO1 accumulation, while onset of disease was not affected, the mutation caused an extension in progression time, a delay in the development of hindlimb and forelimb muscle weakness, and a significant increase in the lifespan of SOD1-G93A mice.
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Affiliation(s)
- Lauren Taylor Rosenblum
- Jefferson Weinberg ALS Center, Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, 900 Walnut St, Philadelphia, PA 19107, USA
| | - Shashirekha Shamamandri-Markandaiah
- Jefferson Weinberg ALS Center, Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, 900 Walnut St, Philadelphia, PA 19107, USA
| | - Biswarup Ghosh
- Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, 900 Walnut St, Philadelphia, PA 19107, USA
| | - Emily Foran
- Jefferson Weinberg ALS Center, Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, 900 Walnut St, Philadelphia, PA 19107, USA
| | - Angelo C Lepore
- Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, 900 Walnut St, Philadelphia, PA 19107, USA
| | - Piera Pasinelli
- Jefferson Weinberg ALS Center, Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, 900 Walnut St, Philadelphia, PA 19107, USA
| | - Davide Trotti
- Jefferson Weinberg ALS Center, Vickie and Jack Farber Institute for Neuroscience, Department of Neuroscience, Thomas Jefferson University, 900 Walnut St, Philadelphia, PA 19107, USA.
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18
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Rose CR, Ziemens D, Untiet V, Fahlke C. Molecular and cellular physiology of sodium-dependent glutamate transporters. Brain Res Bull 2016; 136:3-16. [PMID: 28040508 DOI: 10.1016/j.brainresbull.2016.12.013] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 12/20/2016] [Accepted: 12/21/2016] [Indexed: 02/04/2023]
Abstract
Glutamate is the major excitatory transmitter in the vertebrate brain. After its release from presynaptic nerve terminals, it is rapidly taken up by high-affinity sodium-dependent plasma membrane transporters. While both neurons and glial cells express these excitatory amino acid transporters (EAATs), the majority of glutamate uptake is accomplished by astrocytes, which convert synaptically-released glutamate to glutamine or feed it into their own metabolism. Glutamate uptake by astrocytes not only shapes synaptic transmission by regulating the availability of glutamate to postsynaptic neuronal receptors, but also protects neurons from hyper-excitability and subsequent excitotoxic damage. In the present review, we provide an overview of the molecular and cellular characteristics of sodium-dependent glutamate transporters and their associated anion permeation pathways, with a focus on astrocytic glutamate transport. We summarize their functional properties and roles within tripartite synapses under physiological and pathophysiological conditions, exemplifying the intricate interactions and interrelationships between neurons and glial cells in the brain.
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Affiliation(s)
- Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Germany.
| | - Daniel Ziemens
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Germany
| | - Verena Untiet
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Germany
| | - Christoph Fahlke
- Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, Germany
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19
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Danbolt NC, Furness DN, Zhou Y. Neuronal vs glial glutamate uptake: Resolving the conundrum. Neurochem Int 2016; 98:29-45. [PMID: 27235987 DOI: 10.1016/j.neuint.2016.05.009] [Citation(s) in RCA: 158] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Revised: 05/03/2016] [Accepted: 05/17/2016] [Indexed: 12/30/2022]
Abstract
Neither normal brain function nor the pathological processes involved in neurological diseases can be adequately understood without knowledge of the release, uptake and metabolism of glutamate. The reason for this is that glutamate (a) is the most abundant amino acid in the brain, (b) is at the cross-roads between several metabolic pathways, and (c) serves as the major excitatory neurotransmitter. In fact most brain cells express glutamate receptors and are thereby influenced by extracellular glutamate. In agreement, brain cells have powerful uptake systems that constantly remove glutamate from the extracellular fluid and thereby limit receptor activation. It has been clear since the 1970s that both astrocytes and neurons express glutamate transporters. However the relative contribution of neuronal and glial transporters to the total glutamate uptake activity, however, as well as their functional importance, has been hotly debated ever since. The present short review provides (a) an overview of what we know about neuronal glutamate uptake as well as an historical description of how we got there, and (b) a hypothesis reconciling apparently contradicting observations thereby possibly resolving the paradox.
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Affiliation(s)
- N C Danbolt
- The Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
| | - D N Furness
- School of Life Sciences, Keele University, Keele, Staffs. ST5 5BG, UK
| | - Y Zhou
- The Neurotransporter Group, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
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20
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Alasmari F, Rao PSS, Sari Y. Effects of cefazolin and cefoperazone on glutamate transporter 1 isoforms and cystine/glutamate exchanger as well as alcohol drinking behavior in male alcohol-preferring rats. Brain Res 2016; 1634:150-157. [PMID: 26790351 DOI: 10.1016/j.brainres.2016.01.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2015] [Revised: 12/09/2015] [Accepted: 01/07/2016] [Indexed: 12/22/2022]
Abstract
Previously, we have reported that cefazolin and cefoperazone treatments attenuated ethanol consumption, at least in part, through upregulation of GLT-1 expression in male alcohol-preferring (P) rats. In this study, we determined the effects of these compounds on the expression of GLT-1 isoforms (GLT-1a and GLT-1b), cysteine/glutamate exchanger (xCT), which is another glial glutamate transporter co-localized with GLT-1, and glutamate/aspartate transporter (GLAST). We found that cefazolin and cefoperazone treatments decreased ethanol intake and upregulated both GLT-1 isoforms, GLT-1a and GLT-1b, in nucleus accumbens (NAc) and prefrontal cortex (PFC) compared to saline treated group. In addition, cefazolin increased the expression of xCT in NAc and PFC, while cefoperazone upregulated xCT expression only in NAc. However, we did not find any significant differences in GLAST expression between the treated and control groups. Overall, our findings suggest that cefazolin and cefoperazone may be considered as potential compounds for the treatment of ethanol dependence.
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Affiliation(s)
- Fawaz Alasmari
- Department of Pharmacology and Experimental Therapeutics, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, Toledo, OH, USA
| | - P S S Rao
- Department of Pharmacology and Experimental Therapeutics, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, Toledo, OH, USA
| | - Youssef Sari
- Department of Pharmacology and Experimental Therapeutics, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, Toledo, OH, USA.
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21
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Takahashi K, Foster JB, Lin CLG. Glutamate transporter EAAT2: regulation, function, and potential as a therapeutic target for neurological and psychiatric disease. Cell Mol Life Sci 2015; 72:3489-506. [PMID: 26033496 PMCID: PMC11113985 DOI: 10.1007/s00018-015-1937-8] [Citation(s) in RCA: 135] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 05/22/2015] [Accepted: 05/26/2015] [Indexed: 12/12/2022]
Abstract
Glutamate is the predominant excitatory neurotransmitter in the central nervous system. Excitatory amino acid transporter 2 (EAAT2) is primarily responsible for clearance of extracellular glutamate to prevent neuronal excitotoxicity and hyperexcitability. EAAT2 plays a critical role in regulation of synaptic activity and plasticity. In addition, EAAT2 has been implicated in the pathogenesis of many central nervous system disorders. In this review, we summarize current understanding of EAAT2, including structure, pharmacology, physiology, and functions, as well as disease relevancy, such as in stroke, Parkinson's disease, epilepsy, amyotrophic lateral sclerosis, Alzheimer's disease, major depressive disorder, and addiction. A large number of studies have demonstrated that up-regulation of EAAT2 protein provides significant beneficial effects in many disease models suggesting EAAT2 activation is a promising therapeutic approach. Several EAAT2 activators have been identified. Further understanding of EAAT2 regulatory mechanisms could improve development of drug-like compounds that spatiotemporally regulate EAAT2.
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Affiliation(s)
- Kou Takahashi
- Department of Neuroscience, The Ohio State University, 333 West 10th Avenue, Columbus, OH 43210 USA
| | - Joshua B. Foster
- Department of Neuroscience, The Ohio State University, 333 West 10th Avenue, Columbus, OH 43210 USA
| | - Chien-Liang Glenn Lin
- Department of Neuroscience, The Ohio State University, 333 West 10th Avenue, Columbus, OH 43210 USA
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22
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Differential regulation of two isoforms of the glial glutamate transporter EAAT2 by DLG1 and CaMKII. J Neurosci 2015; 35:5260-70. [PMID: 25834051 DOI: 10.1523/jneurosci.4365-14.2015] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The gene for EAAT2, the major astrocytic glutamate transporter, generates two carrier isoforms (EAAT2a and EAAT2b) that vary at their C termini as a consequence of alternative RNA splicing. The EAAT2b cytoplasmic C terminus contains a postsynaptic density-95/Discs large/zona occludens-1 (PDZ) ligand, which is absent in EAAT2a. To understand how the distinct C termini might affect transporter trafficking and surface localization, we generated Madin-Darby canine kidney (MDCK) cells that stably express EGFP-EAAT2a or EGFP-EAAT2b and found robust basolateral membrane expression of the EAAT2b isoform. In contrast, EAAT2a displayed a predominant distribution within intracellular vesicle compartments, constitutively cycling to and from the membrane. Addition of the PDZ ligand to EAAT2a as well as its deletion from EAAT2b confirmed the importance of the motif for cell-surface localization. Using EAAT2 constructs with an extracellular biotin acceptor tag to directly assess surface proteins, we observed significant PDZ ligand-dependent EAAT2b surface expression in cultured astrocytes, consistent with observations in cell lines. Discs large homolog 1 (DLG1; SAP97), a PDZ protein prominent in both astrocytes and MDCK cells, colocalized and coimmunoprecipitated with EAAT2b. shRNA knockdown of DLG1 expression decreased surface EAAT2b in both MDCK cells and cultured astrocytes, suggesting that the DLG scaffolding protein stabilizes EAAT2b at the surface. DLG1 can be phosphorylated by Ca(2+)/calmodulin-dependent protein kinase (CaMKII), resulting in disruption of its PDZ-mediated interaction. In murine astrocytes and acute brain slices, activation of CaMKII decreases EAAT2b surface expression but does not alter the distribution of EAAT2a. These data indicate that the surface expression and function of EAAT2b can be rapidly modulated through the disruption of its interaction with DLG1 by CaMKII activation.
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23
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O'Donovan SM, Hasselfeld K, Bauer D, Simmons M, Roussos P, Haroutunian V, Meador-Woodruff JH, McCullumsmith RE. Glutamate transporter splice variant expression in an enriched pyramidal cell population in schizophrenia. Transl Psychiatry 2015; 5:e579. [PMID: 26057049 PMCID: PMC4490284 DOI: 10.1038/tp.2015.74] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Revised: 02/02/2015] [Accepted: 03/01/2015] [Indexed: 12/27/2022] Open
Abstract
Dysregulation of the glutamate transporters EAAT1 and EAAT2 and their isoforms have been implicated in schizophrenia. EAAT1 and EAAT2 expression has been studied in different brain regions but the prevalence of astrocytic glutamate transporter expression masks the more subtle changes in excitatory amino acid transporters (EAATs) isoforms in neurons in the cortex. Using laser capture microdissection, pyramidal neurons were cut from the anterior cingulate cortex of postmortem schizophrenia (n = 20) and control (n = 20) subjects. The messenger RNA (mRNA) levels of EAAT1, EAAT2 and the splice variants EAAT1 exon9skipping, EAAT2 exon9skipping and EAAT2b were analyzed by real time PCR (RT-PCR) in an enriched population of neurons. Region-level expression of these transcripts was measured in postmortem schizophrenia (n = 25) and controls (n = 25). The relationship between selected EAAT polymorphisms and EAAT splice variant expression was also explored. Anterior cingulate cortex pyramidal cell expression of EAAT2b mRNA was increased (P < 0.001; 67%) in schizophrenia subjects compared with controls. There was no significant change in other EAAT variants. EAAT2 exon9skipping mRNA was increased (P < 0.05; 38%) at region level in the anterior cingulate cortex with no significant change in other EAAT variants at region level. EAAT2 single-nucleotide polymorphisms were significantly associated with changes in EAAT2 isoform expression. Haloperidol decanoate-treated animals, acting as controls for possible antipsychotic effects, did not have significantly altered neuronal EAAT2b mRNA levels. The novel finding that EAAT2b levels are increased in populations of anterior cingulate cortex pyramidal cells further demonstrates a role for neuronal glutamate transporter splice variant expression in schizophrenia.
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Affiliation(s)
- S M O'Donovan
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH, USA
| | - K Hasselfeld
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH, USA
| | - D Bauer
- Department of Neuroscience, Wellesley College, Wellesley, MA, USA
| | - M Simmons
- Department of Psychiatry, University of Alabama, Birmingham, AL, USA
| | - P Roussos
- Department of Psychiatry, Department of Genetics and Genomic Sciences, and Institute for Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, New York, NY, USA,James J. Peters VA Medical Center, Mental Illness Research Education and Clinical Center, Bronx, NY, USA
| | - V Haroutunian
- Department of Psychiatry and Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | | | - R E McCullumsmith
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH, USA,Department of Neuroscience, Wellesley College, Wellesley, MA, USA,Department of Psychiatry, University of Alabama, Birmingham, AL, USA,Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, CARE 5830, 231 Albert Sabin Way Cincinnati, Cincinnati, OH 45267-0583, USA. E-mail:
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Alhaddad H, Das SC, Sari Y. Effects of ceftriaxone on ethanol intake: a possible role for xCT and GLT-1 isoforms modulation of glutamate levels in P rats. Psychopharmacology (Berl) 2014; 231:4049-57. [PMID: 24687412 PMCID: PMC4176549 DOI: 10.1007/s00213-014-3545-y] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Accepted: 03/12/2014] [Indexed: 12/21/2022]
Abstract
RATIONALE Evidence suggests that glutamate transporter 1 (GLT-1) and cystine/glutamate exchanger transporter (xCT) are critical in maintaining glutamate homeostasis. We have recently demonstrated that ceftriaxone treatment induced upregulation of GLT1 levels and attenuated ethanol intake; however, less is known about the involvement of xCT on ethanol intake. In this study, we investigated the effects of ceftriaxone on the levels of xCT in both continuous and relapse-like ethanol drinking, as well as GLT-1 isoforms, and glutamate aspartate transporter (GLAST) in relapse-like ethanol intake. METHODS P rats received free choice of 15 and 30 % ethanol and water for 5 weeks and then deprived of ethanol for 2 weeks. Rats were treated with ceftriaxone (100 mg/kg, i.p.) or saline during the last 5 days of the 2-week deprivation period. After deprivation period, P rats were re-exposed to free choice of 15 and 30 % ethanol and water for nine consecutive days. A second group of P rats was given continuous ethanol access for 5 weeks, then ceftriaxone (100 mg/kg, i.p.) or saline throughout the week 6. RESULTS Ceftriaxone significantly attenuated relapse-like ethanol intake. Importantly, this effect of ceftriaxone was associated in part with upregulation of the levels of GLT-1a and GLT-1b isoforms and xCT in the prefrontal cortex (PFC) and the nucleus accumbens (NAc). There were no significant differences in GLAST expression among all groups. We also found that ceftriaxone treatment increased xCT levels in both PFC and NAc in continuous ethanol intake. CONCLUSION These findings suggest that xCT and GLT-1 isoforms might be target proteins for the treatment of alcohol dependence.
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Differential cellular expression of organic anion transporting peptides OATP1A2 and OATP2B1 in the human retina and brain: implications for carrier-mediated transport of neuropeptides and neurosteriods in the CNS. Pflugers Arch 2014; 467:1481-1493. [DOI: 10.1007/s00424-014-1596-x] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Revised: 07/28/2014] [Accepted: 08/06/2014] [Indexed: 02/07/2023]
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Rauen T, Tanui R, Grewer C. Structural and functional dynamics of Excitatory Amino Acid Transporters (EAAT). AIMS MOLECULAR SCIENCE 2014. [DOI: 10.3934/molsci.2014.3.99] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
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Grewer C, Gameiro A, Rauen T. SLC1 glutamate transporters. Pflugers Arch 2013; 466:3-24. [PMID: 24240778 DOI: 10.1007/s00424-013-1397-7] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Revised: 10/21/2013] [Accepted: 10/22/2013] [Indexed: 12/13/2022]
Abstract
The plasma membrane transporters for the neurotransmitter glutamate belong to the solute carrier 1 family. They are secondary active transporters, taking up glutamate into the cell against a substantial concentration gradient. The driving force for concentrative uptake is provided by the cotransport of Na(+) ions and the countertransport of one K(+) in a step independent of the glutamate translocation step. Due to eletrogenicity of transport, the transmembrane potential can also act as a driving force. Glutamate transporters are expressed in many tissues, but are of particular importance in the brain, where they contribute to the termination of excitatory neurotransmission. Glutamate transporters can also run in reverse, resulting in glutamate release from cells. Due to these important physiological functions, glutamate transporter expression and, therefore, the transport rate, are tightly regulated. This review summarizes recent literature on the functional and biophysical properties, structure-function relationships, regulation, physiological significance, and pharmacology of glutamate transporters. Particular emphasis is on the insight from rapid kinetic and electrophysiological studies, transcriptional regulation of transporter expression, and reverse transport and its importance for pathophysiological glutamate release under ischemic conditions.
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Affiliation(s)
- Christof Grewer
- Department of Chemistry, Binghamton University, PO Box 6000, Binghamton, 13902-6000, NY, USA,
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Macaluso A, Bernabucci M, Trabucco A, Ciolli L, Troisi F, Baldini R, Gradini R, Battaglia G, Nicoletti F, Collini S. Analgesic Effect of a Single Preoperative Dose of the Antibiotic Ceftriaxone in Humans. THE JOURNAL OF PAIN 2013; 14:604-12. [DOI: 10.1016/j.jpain.2013.01.774] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 01/18/2013] [Accepted: 01/19/2013] [Indexed: 01/14/2023]
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Sogaard R, Borre L, Braunstein TH, Madsen KL, MacAulay N. Functional modulation of the glutamate transporter variant GLT1b by the PDZ domain protein PICK1. J Biol Chem 2013; 288:20195-207. [PMID: 23697999 DOI: 10.1074/jbc.m113.471128] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dominant glutamate transporter isoform in the mammalian brain, GLT1, exists as at least three splice variants, GLT1a, GLT1b, and GLT1c. GLT1b interacts with the scaffold protein PICK1 (protein interacting with kinase C1), which is implicated in glutamatergic neurotransmission via its regulatory effect on trafficking of AMPA-type glutamate receptors. The 11 extreme C-terminal residues specific for the GLT1b variant are essential for its specific interaction with the PICK1 PDZ domain, but a functional consequence of this interaction has remained unresolved. To identify a functional effect of PICK1 on GLT1a or GLT1b separately, we employed the Xenopus laevis expression system. GLT1a and GLT1b displayed similar electrophysiological properties and EC50 for glutamate. Co-expressed PICK1 localized efficiently to the plasma membrane and resulted in a 5-fold enhancement of the leak current in GLT1b-expressing oocytes with only a minor effect on [(3)H]glutamate uptake. Three different GLT1 substrates all caused a slow TBOA-sensitive decay in the membrane current upon prolonged application, which provides support for the leak current being mediated by GLT1b itself. Leak and glutamate-evoked currents in GLT1a-expressing oocytes were unaffected by PICK1 co-expression. PKC activation down-regulated GLT1a and GLT1b activity to a similar extent, which was not affected by co-expression of PICK1. In conclusion, PICK1 may not only affect glutamatergic neurotransmission by its regulatory effect on glutamate receptors but may also affect neuronal excitability via an increased GLT1b-mediated leak current. This may be particularly relevant in pathological conditions such as amyotrophic lateral sclerosis and cerebral hypoxia, which are associated with neuronal GLT1b up-regulation.
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Affiliation(s)
- Rikke Sogaard
- Department of Cellular and Molecular Medicine, University of Copenhagen, DK-2200 Copenhagen N, Denmark
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Dumont AO, Hermans E, Goursaud S. Differential regulation of the glutamate transporter variants GLT-1a and GLT-1b in the cortex and spinal cord of transgenic rats expressing hSOD1(G93A). Neurochem Int 2013; 63:61-8. [PMID: 23665075 DOI: 10.1016/j.neuint.2013.04.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Revised: 04/22/2013] [Accepted: 04/29/2013] [Indexed: 12/11/2022]
Abstract
Altered expression and activity of GLT-1 have been characterized in amyotrophic lateral sclerosis (ALS) patients and in animal models of the disease. Data suggest that the expression of two C-terminus splice variants of GLT-1 (namely GLT-1a and GLT-1b) can be differentially regulated in this pathological context. We herein characterized the expression of GLT-1a and GLT-1b mRNA and the glutamate uptake activity in the fronto-temporal cortex and the lumbar spinal cord of transgenic rats expressing hSOD1(G93A) at various stages of the disease. We also investigated the expression and activity of the other key glutamate transporters GLAST and EAAC1. While the progression of the disease was associated with a reduction of the overall GLT-1 activity in both cortex and spinal cord, the regulation of GLT-1a and GLT-1b transcripts showed different profiles. In the cortex, GLT-1a mRNA which appears as the most abundant isoform at a pre-symptomatic stage was strongly decreased during the progression of the disease while GLT-1b mRNA increased to reach a similar level as GLT-1a at end-stage. In the lumbar spinal cord of transgenic rats, both GLT-1a and GLT-1b mRNAs, expressed at the same levels before the symptom onset, were strongly decreased in the ventral horns. While no modification of GLAST was detected, EAAC1 mRNA was highly increased at a pre-symptomatic stage in transgenic animals, explaining a higher activity of glutamate transporters at this age. These results demonstrate that glutamate transporters are differentially expressed in nervous structures of wild-type and transgenic animals although the total GLT-1 activity was constantly decreased during the disease progression.
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Affiliation(s)
- Amélie O Dumont
- Institute of Neuroscience, Group of Neuropharmacology, Université catholique de Louvain, Brussels, Belgium
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Koeglsperger T, Li S, Brenneis C, Saulnier JL, Mayo L, Carrier Y, Selkoe DJ, Weiner HL. Impaired glutamate recycling and GluN2B-mediated neuronal calcium overload in mice lacking TGF-β1 in the CNS. Glia 2013; 61:985-1002. [PMID: 23536313 DOI: 10.1002/glia.22490] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Accepted: 02/06/2013] [Indexed: 12/14/2022]
Abstract
Transforming growth factor β1 (TGF-β1) is a pleiotropic cytokine expressed throughout the CNS. Previous studies demonstrated that TGF-β1 contributes to maintain neuronal survival, but mechanistically this effect is not well understood. We generated a CNS-specific TGF-β1-deficient mouse model to investigate the functional consequences of TGF-β1-deficiency in the adult mouse brain. We found that depletion of TGF-β1 in the CNS resulted in a loss of the astrocyte glutamate transporter (GluT) proteins GLT-1 (EAAT2) and GLAST (EAAT1) and decreased glutamate uptake in the mouse hippocampus. Treatment with TGF-β1 induced the expression of GLAST and GLT-1 in cultured astrocytes and enhanced astroglial glutamate uptake. Similar to GLT-1-deficient mice, CNS-TGF-β1-deficient mice had reduced brain weight and neuronal loss in the CA1 hippocampal region. CNS-TGF-β1-deficient mice showed GluN2B-dependent aberrant synaptic plasticity in the CA1 area of the hippocampus similar to the glutamate transport inhibitor DL-TBOA and these mice were highly sensitive to excitotoxic injury. In addition, hippocampal neurons from TGF-β1-deficient mice had elevated GluN2B-mediated calcium signals in response to extrasynaptic glutamate receptor stimulation, whereas cells treated with TGF-β1 exhibited reduced GluN2B-mediated calcium signals. In summary, our study demonstrates a previously unrecognized function of TGF-β1 in the CNS to control extracellular glutamate homeostasis and GluN2B-mediated calcium responses in the mouse hippocampus.
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Affiliation(s)
- Thomas Koeglsperger
- Department of Neurology, Center for Neurologic Diseases, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
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Cao F, Yin A, Wen G, Sheikh AM, Tauqeer Z, Malik M, Nagori A, Schirripa M, Schirripa F, Merz G, Brown WT, Li X. Alteration of astrocytes and Wnt/β-catenin signaling in the frontal cortex of autistic subjects. J Neuroinflammation 2012; 9:223. [PMID: 22999633 PMCID: PMC3544729 DOI: 10.1186/1742-2094-9-223] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Accepted: 08/27/2012] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND Autism is a neurodevelopmental disorder characterized by impairments in social interaction, verbal communication and repetitive behaviors. To date the etiology of this disorder is poorly understood. Studies suggest that astrocytes play critical roles in neural plasticity by detecting neuronal activity and modulating neuronal networks. Recently, a number of studies suggested that an abnormal function of glia/astrocytes may be involved in the development of autism. However, there is yet no direct evidence showing how astrocytes develop in the brain of autistic individuals. METHODS Study subjects include brain tissue from autistic subjects, BTBR T + tfJ (BTBR) and Neuroligin (NL)-3 knock-down mice. Western blot analysis, Immunohistochemistry and confocal microscopy studies have be used to examine the density and morphology of astrocytes, as well as Wnt and β-catenin protein expression. RESULTS In this study, we demonstrate that the astrocytes in autisitcsubjects exhibit significantly reduced branching processes, total branching length and cell body sizes. We also detected an astrocytosis in the frontal cortex of autistic subjects. In addition, we found that the astrocytes in the brain of an NL3 knockdown mouse exhibited similar alterations to what we found in the autistic brain. Furthermore, we detected that both Wnt and β-catenin proteins are decreased in the frontal cortex of autistic subjects. Wnt/β-catenin pathway has been suggested to be involved in the regulation of astrocyte development. CONCLUSIONS Our findings imply that defects in astrocytes could impair neuronal plasticity and partially contribute to the development of autistic-like behaviors in both humans and mice. The alteration of Wnt/β-catenin pathway in the brain of autistic subjects may contribute to the changes of astrocytes.
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Affiliation(s)
- Fujiang Cao
- Department of Neurochemistry, NY State Institute for Basic Research in Developmental Disabilities, 1050 Forest Hill Road, Staten Island New York, NY 10314, USA
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Benediktsson AM, Marrs GS, Tu JC, Worley PF, Rothstein JD, Bergles DE, Dailey ME. Neuronal activity regulates glutamate transporter dynamics in developing astrocytes. Glia 2012; 60:175-88. [PMID: 22052455 PMCID: PMC3232333 DOI: 10.1002/glia.21249] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Accepted: 09/02/2011] [Indexed: 12/20/2022]
Abstract
Glutamate transporters (GluTs) maintain a low ambient level of glutamate in the central nervous system (CNS) and shape the activation of glutamate receptors at synapses. Nevertheless, the mechanisms that regulate the trafficking and localization of transporters near sites of glutamate release are poorly understood. Here, we examined the subcellular distribution and dynamic remodeling of the predominant GluT GLT-1 (excitatory amino acid transporter 2, EAAT2) in developing hippocampal astrocytes. Immunolabeling revealed that endogenous GLT-1 is concentrated into discrete clusters along branches of developing astrocytes that were apposed preferentially to synapsin-1 positive synapses. Green fluorescent protein (GFP)-GLT-1 fusion proteins expressed in astrocytes also formed distinct clusters that lined the edges of astrocyte processes, as well as the tips of filopodia and spine-like structures. Time-lapse three-dimensional confocal imaging in tissue slices revealed that GFP-GLT-1 clusters were dynamically remodeled on a timescale of minutes. Some transporter clusters moved within developing astrocyte branches as filopodia extended and retracted, while others maintained stable positions at the tips of spine-like structures. Blockade of neuronal activity with tetrodotoxin reduced both the density and perisynaptic localization of GLT-1 clusters. Conversely, enhancement of neuronal activity increased the size of GLT-1 clusters and their proximity to synapses. Together, these findings indicate that neuronal activity influences both the organization of GluTs in developing astrocyte membranes and their position relative to synapses.
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Meabon JS, Lee A, Meeker KD, Bekris LM, Fujimura RK, Yu CE, Watson GS, Pow DV, Sweet IR, Cook DG. Differential expression of the glutamate transporter GLT-1 in pancreas. J Histochem Cytochem 2011; 60:139-51. [PMID: 22114258 DOI: 10.1369/0022155411430095] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The glutamate uptake transporter GLT-1 is best understood for its critical role in preventing brain seizures. Increasing evidence argues that GLT-1 also modulates, and is modulated by, metabolic processes that influence glucose homeostasis. To investigate further the potential role of GLT-1 in these regards, the authors examined GLT-1 expression in pancreas and found that mature multimeric GLT-1 protein is stably expressed in the pancreas of wild-type, but not GLT-1 knockout, mice. There are three primary functional carboxyl-terminus GLT-1 splice variants, called GLT-1a, b, and c. Brain and liver express all three variants; however, the pancreas expresses GLT-1a and GLT-1b but not GLT-1c. Quantitative real time-PCR further revealed that while GLT-1a is the predominant GLT-1 splice variant in brain and liver, GLT-1b is the most abundant splice variant expressed in pancreas. Confocal microscopy and immunohistochemistry showed that GLT-1a and GLT-1b are expressed in both islet β- and α-cells. GLT-1b was also expressed in exocrine ductal domains. Finally, glutamine synthetase was coexpressed with GLT-1 in islets, which suggests that, as with liver and brain, one possible role of GLT-1 in the pancreas is to support glutamine synthesis.
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Affiliation(s)
- James S Meabon
- Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, Washington, USA
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Kim K, Lee SG, Kegelman TP, Su ZZ, Das SK, Dash R, Dasgupta S, Barral PM, Hedvat M, Diaz P, Reed JC, Stebbins JL, Pellecchia M, Sarkar D, Fisher PB. Role of excitatory amino acid transporter-2 (EAAT2) and glutamate in neurodegeneration: opportunities for developing novel therapeutics. J Cell Physiol 2011; 226:2484-93. [PMID: 21792905 DOI: 10.1002/jcp.22609] [Citation(s) in RCA: 297] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Glutamate is an essential excitatory neurotransmitter regulating brain functions. Excitatory amino acid transporter (EAAT)-2 is one of the major glutamate transporters expressed predominantly in astroglial cells and is responsible for 90% of total glutamate uptake. Glutamate transporters tightly regulate glutamate concentration in the synaptic cleft. Dysfunction of EAAT2 and accumulation of excessive extracellular glutamate has been implicated in the development of several neurodegenerative diseases including Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. Analysis of the 2.5 kb human EAAT2 promoter showed that NF-κB is an important regulator of EAAT2 expression in astrocytes. Screening of approximately 1,040 FDA-approved compounds and nutritionals led to the discovery that many β-lactam antibiotics are transcriptional activators of EAAT2 resulting in increased EAAT2 protein levels. Treatment of animals with ceftriaxone (CEF), a β-lactam antibiotic, led to an increase of EAAT2 expression and glutamate transport activity in the brain. CEF has neuroprotective effects in both in vitro and in vivo models based on its ability to inhibit neuronal cell death by preventing glutamate excitotoxicity. CEF increases EAAT2 transcription in primary human fetal astrocytes through the NF-κB signaling pathway. The NF-κB binding site at -272 position was critical in CEF-mediated EAAT2 protein induction. These studies emphasize the importance of transcriptional regulation in controlling glutamate levels in the brain. They also emphasize the potential utility of the EAAT2 promoter for developing both low and high throughput screening assays to identify novel small molecule regulators of glutamate transport with potential to ameliorate pathological changes occurring during and causing neurodegeneration.
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Affiliation(s)
- Keetae Kim
- Department of Human and Molecular Genetics, Virginia Commonwealth University, School of Medicine, Richmond, Virginia 23298, USA.
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The discovery of slowness: low-capacity transport and slow anion channel gating by the glutamate transporter EAAT5. Biophys J 2011; 100:2623-32. [PMID: 21641307 DOI: 10.1016/j.bpj.2011.04.034] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 04/15/2011] [Accepted: 04/18/2011] [Indexed: 01/12/2023] Open
Abstract
Excitatory amino acid transporters (EAATs) control the glutamate concentration in the synaptic cleft by glial and neuronal glutamate uptake. Uphill glutamate transport is achieved by the co-/countertransport of Na(+) and other ions down their concentration gradients. Glutamate transporters also display an anion conductance that is activated by the binding of Na(+) and glutamate but is not thermodynamically coupled to the transport process. Of the five known glutamate transporter subtypes, the retina-specific subtype EAAT5 has the largest conductance relative to glutamate uptake activity. Our results suggest that EAAT5 behaves as a slow-gated anion channel with little glutamate transport activity. At steady state, EAAT5 was activated by glutamate, with a K(m)= 61 ± 11 μM. Binding of Na(+) to the empty transporter is associated with a K(m) = 229 ± 37 mM, and binding to the glutamate-bound form is associated with a K(m) = 76 ± 40 mM. Using laser-pulse photolysis of caged glutamate, we determined the pre-steady-state kinetics of the glutamate-induced anion current of EAAT5. This was characterized by two exponential components with time constants of 30 ± 1 ms and 200 ± 15 ms, which is an order of magnitude slower than those observed in other glutamate transporters. A voltage-jump analysis of the anion currents indicates that the slow activation behavior is caused by two slow, rate-limiting steps in the transport cycle, Na(+) binding to the empty transporter, and translocation of the fully loaded transporter. We propose a kinetic transport scheme that includes these two slow steps and can account for the experimentally observed data. Overall, our results suggest that EAAT5 may not act as a classical high-capacity glutamate transporter in the retina; rather, it may function as a slow-gated glutamate receptor and/or glutamate buffering system.
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Expression of multiple glutamate transporter splice variants in the rodent testis. Asian J Androl 2010; 13:254-65. [PMID: 21170079 DOI: 10.1038/aja.2010.99] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Glutamate is a regulated molecule in the mammalian testis. Extracellular regulation of glutamate in the body is determined largely by the expression of plasmalemmal glutamate transporters. We have examined by PCR, western blotting and immunocytochemistry the expression of a panel of sodium-dependent plasmalemmal glutamate transporters in the rat testis. Proteins examined included: glutamate aspartate transporter (GLAST), glutamate transporter 1 (GLT1), excitatory amino acid carrier 1 (EAAC1), excitatory amino acid transporter 4 (EAAT4) and EAAT5. We demonstrate that many of the glutamate transporters in the testis are alternately spliced. GLAST is present as exon-3- and exon-9-skipping forms. GLT1 was similarly present as the alternately spliced forms GLT1b and GLT1c, whereas the abundant brain form (GLT1a) was detectable only at the mRNA level. EAAT5 was also strongly expressed, whereas EAAC1 and EAAT4 were absent. These patterns of expression were compared with the patterns of endogenous glutamate localization and with patterns of d-aspartate accumulation, as assessed by immunocytochemistry. The presence of multiple glutamate transporters in the testis, including unusually spliced forms, suggests that glutamate homeostasis may be critical in this organ. The apparent presence of many of these transporters in the testis and sperm may indicate a need for glutamate transport by such cells.
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Gebhardt FM, Mitrovic AD, Gilbert DF, Vandenberg RJ, Lynch JW, Dodd PR. Exon-skipping splice variants of excitatory amino acid transporter-2 (EAAT2) form heteromeric complexes with full-length EAAT2. J Biol Chem 2010; 285:31313-24. [PMID: 20688910 PMCID: PMC2951206 DOI: 10.1074/jbc.m110.153494] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Revised: 08/02/2010] [Indexed: 12/12/2022] Open
Abstract
The glial transporter excitatory amino acid transporter-2 (EAAT2) is the main mediator of glutamate clearance in brain. The wild-type transporter (EAAT2wt) forms trimeric membrane complexes in which each protomer functions autonomously. Several EAAT2 variants are found in control and Alzheimer-diseased human brains; their expression increases with pathological severity. These variants might alter EAAT2wt-mediated transport by abrogating membrane trafficking, or by changing the configuration or functionality of the assembled transporter complex. HEK293 cells were transfected with EAAT2wt; EAAT2b, a C-terminal variant; or either of two exon-skipping variants: alone or in combination. Surface biotinylation studies showed that only the exon-7 deletion variant was not trafficked to the membrane when transfected alone, and that all variants could reach the membrane when co-transfected with EAAT2wt. Fluorescence resonance energy transfer (FRET) studies showed that co-transfected EAAT2wt and EAAT2 splice variants were expressed in close proximity. Glutamate transporter function was measured using a whole cell patch clamp technique, or by changes in membrane potential indexed by a voltage-sensitive fluorescent dye (FMP assay): the two methods gave comparable results. Cells transfected with EAAT2wt or EAAT2b showed glutamate-dependent membrane potential changes consistent with functional expression. Cells transfected with EAAT2 exon-skipping variants alone gave no response to glutamate. Co-transfection of EAAT2wt (or EAAT2b) and splice variants in various ratios significantly raised glutamate EC(50) and decreased Hill coefficients. We conclude that exon-skipping variants form heteromeric complexes with EAAT2wt or EAAT2b that traffic to the membrane but show reduced glutamate-dependent activity. This could allow glutamate to accumulate extracellularly and promote excitotoxicity.
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Affiliation(s)
| | - Ann D. Mitrovic
- the Discipline of Pharmacology and Bosch Institute, University of Sydney, Sydney 2006, Australia
| | - Daniel F. Gilbert
- the Queensland Brain Institute and School of Biomedical Sciences, University of Queensland, Brisbane 4072 and
| | - Robert J. Vandenberg
- the Discipline of Pharmacology and Bosch Institute, University of Sydney, Sydney 2006, Australia
| | - Joseph W. Lynch
- the Queensland Brain Institute and School of Biomedical Sciences, University of Queensland, Brisbane 4072 and
| | - Peter R. Dodd
- From the School of Chemistry and Molecular Biosciences and
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Sullivan SM, Björkman ST, Miller SM, Colditz PB, Pow DV. Structural remodeling of gray matter astrocytes in the neonatal pig brain after hypoxia/ischemia. Glia 2010; 58:181-94. [PMID: 19606499 DOI: 10.1002/glia.20911] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Astrocytes play a vital role in the brain; their structural integrity and sustained function are essential for neuronal viability, especially after injury or insult. In this study, we have examined the response of astrocytes to hypoxia/ischemia (H/I), employing multiple methods (immunohistochemistry, iontophoretic cell injection, Golgi-Kopsch staining, and D-aspartate uptake) in a neonatal pig model of H/I. We have identified morphological changes in cortical gray matter astrocytes in response to H/I. Initial astrocytic changes were evident as early as 8 h post-insult, before histological evidence for neuronal damage. By 72 h post-insult, astrocytes exhibited significantly fewer processes that were shorter, thicker, and had abnormal terminal swellings, compared with astrocytes from control brains that exhibited a complex structure with multiple fine branching processes. Quantification and image analysis of astrocytes at 72 h post-insult revealed significant decreases in the average astrocyte size, from 686 microm(2) in controls to 401 microm(2) in H/I brains. Sholl analysis revealed a significant decrease (>60%) in the complexity of astrocyte branching between 5 and 20 microm from the cell body. D-Aspartate uptake studies revealed that the H/I insult resulted in impaired astrocyte function, with significantly reduced clearance of the glutamate analog, D-aspartate. These results suggest that astrocytes may be involved in the pathophysiological events of H/I brain damage at a far earlier time point than first thought. Developing therapies that prevent or reverse these astrocytic changes may potentially improve neuronal survival and thus might be a useful strategy to minimize brain damage after an H/I insult.
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Affiliation(s)
- Susan M Sullivan
- UQ Centre for Clinical Research and Perinatal Research Centre, The University of Queensland, Herston, Brisbane, Queensland 4029, Australia.
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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.
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Affiliation(s)
- Natalie D Bull
- Vision, Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland, Brisbane, QLD 4072, Australia
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41
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Bellesi M, Melone M, Gubbini A, Battistacci S, Conti F. GLT-1 upregulation impairs prepulse inhibition of the startle reflex in adult rats. Glia 2009; 57:703-13. [PMID: 18985735 DOI: 10.1002/glia.20798] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We tested the hypothesis that glutamate transporter GLT-1 (also known as EAAT2) plays a role in the regulation of prepulse inhibition (PPI) of the acoustic startle reflex, a simple form of information processing which is reduced in schizophrenia. To do this, we studied PPI in rats treated with ceftriaxone (200 mg/kg/day for 8 days), an antibiotic that selectively enhances GLT-1 expression and activity. We showed that ceftriaxone-induced GLT-1 upregulation is associated with impaired PPI of the startle, that this effect is reversed by dihydrokainate, a GLT-1 antagonist, that GLT-1 expression correlates negatively with PPI, and that PPI normalizes when GLT-1a levels return to baseline. Our data indicate that GLT-1 regulates PPI of the startle reflex.
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Affiliation(s)
- Michele Bellesi
- Dipartimento di Neuroscienze, Università Politecnica delle Marche, Ancona, Italy
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42
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Shin JW, Nguyen KTD, Pow DV, Knight T, Buljan V, Bennett MR, Balcar VJ. Distribution of glutamate transporter GLAST in membranes of cultured astrocytes in the presence of glutamate transport substrates and ATP. Neurochem Res 2009; 34:1758-66. [PMID: 19440835 DOI: 10.1007/s11064-009-9982-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Accepted: 04/20/2009] [Indexed: 11/27/2022]
Abstract
Neurotransmitter L-glutamate released at central synapses is taken up and "recycled" by astrocytes using glutamate transporter molecules such as GLAST and GLT. Glutamate transport is essential for prevention of glutamate neurotoxicity, it is a key regulator of neurotransmitter metabolism and may contribute to mechanisms through which neurons and glia communicate with each other. Using immunocytochemistry and image analysis we have found that extracellular D-aspartate (a typical substrate for glutamate transport) can cause redistribution of GLAST from cytoplasm to the cell membrane. The process appears to involve phosphorylation/dephosphorylation and requires intact cytoskeleton. Glutamate transport ligands L-trans-pyrrolidine-2,4-dicarboxylate and DL-threo-3-benzyloxyaspartate but not anti,endo-3,4-methanopyrrolidine dicarboxylate have produced similar redistribution of GLAST. Several representative ligands for glutamate receptors whether of ionotropic or metabotropic type, were found to have no effect. In addition, extracellular ATP induced formation of GLAST clusters in the cell membranes by a process apparently mediated by P2 receptors. The present data suggest that GLAST can rapidly and specifically respond to changes in the cellular environment thus potentially helping to fine-tune the functions of astrocytes.
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Affiliation(s)
- Jae-Won Shin
- Anatomy and Histology, School of Medical Sciences and Bosch Institute for Biomedical Research, The University of Sydney, Sydney, NSW 2006, Australia
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43
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Peacey E, Miller CCJ, Dunlop J, Rattray M. The four major N- and C-terminal splice variants of the excitatory amino acid transporter GLT-1 form cell surface homomeric and heteromeric assemblies. Mol Pharmacol 2009; 75:1062-73. [PMID: 19201818 PMCID: PMC2672809 DOI: 10.1124/mol.108.052829] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2008] [Accepted: 02/06/2009] [Indexed: 12/20/2022] Open
Abstract
The L-glutamate transporter GLT-1 is an abundant central nervous system (CNS) membrane protein of the excitatory amino acid transporter (EAAT) family that controls extracellular L-glutamate levels and is important in limiting excitotoxic neuronal death. Using reverse transcription-polymerase chain reaction, we have determined that four mRNAs encoding GLT-1 exist in mouse brain, with the potential to encode four GLT-1 isoforms that differ in their N and C termini. We expressed all four isoforms (termed MAST-KREK, MPK-KREK, MAST-DIETCI, and MPK-DIETCI according to amino acid sequence) in a range of cell lines and primary astrocytes and show that each isoform can reach the cell surface. In transfected human embryonic kidney (HEK) 293 or COS-7 cells, all four isoforms support high-affinity sodium-dependent L-glutamate uptake with identical pharmacological and kinetic properties. Inserting a viral epitope (tagged with V5, hemagglutinin, or FLAG) into the second extracellular domain of each isoform allowed coimmunoprecipitation and time-resolved Förster resonance energy transfer (tr-FRET) studies using transfected HEK-293 cells. Here we show for the first time that each of the four isoforms is able to combine to form homomeric and heteromeric assemblies, each of which is expressed at the cell surface of primary astrocytes. After activation of protein kinase C by phorbol ester, V5-tagged GLT-1 is rapidly removed from the cell surface of HEK-293 cells and degraded. This study provides direct biochemical evidence for oligomeric assembly of GLT-1 and reports the development of novel tools to provide insight into the trafficking of GLT-1.
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Affiliation(s)
- Eleanor Peacey
- Wolfson Centre for Age-Related Diseases, King's College London, London, United Kingdom
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González-González IM, García-Tardón N, Giménez C, Zafra F. Splice variants of the glutamate transporter GLT1 form hetero-oligomers that interact with PSD-95 and NMDA receptors. J Neurochem 2009; 110:264-74. [PMID: 19457061 DOI: 10.1111/j.1471-4159.2009.06125.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The glutamate transporter GLT1 is expressed in at least two isoforms, GLT1a and GLT1b, which differ in their C termini. As GLT1 is an oligomeric protein, we have investigated whether GLT1a and GLT1b might associate as hetero-oligomers. Differential tagging (HA-GLT1a and YFP-GLT1b) revealed that these isoforms form complexes that could be immunoprecipitated when co-expressed in heterologous systems. The association of GLT1a and GLT1b was also observed in mixed primary cultures of rat brain and in the adult rat brain, where specific antibodies for GLT1a immunoprecipitated GLT1b and vice versa. Dual immunofluorescence in mixed cultures demonstrated the partial co-localization of both isoforms in neurons and in glial cells. Because GLT1b interacts with an organizer of post-synaptic densities, PSD-95, we examined the capacity of GLT1a to associate with this protein. GLT1a was immunoprecipitated from the rat brain in protein complexes that contained not only GLT1b but also PSD-95 and NMDAR. The interaction between GLT1a with PSD-95 and NMDAR was reproduced in transfected COS7 cells and it appears to be indirect as it requires the presence of GLT1b. These results indicate that the major isoform of the glutamate transporter, GLT1a, can acquire the capacity to interact with PDZ proteins through its inclusion in hetero-oligomers containing GLT1b.
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Affiliation(s)
- Inmaculada M González-González
- Facultad de Ciencias, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid, Consejo Superior de Investigaciones Científicas, Centro de Investigación en Red de Enfermedades Raras, Madrid, Spain
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45
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Zanazzi G, Matthews G. The molecular architecture of ribbon presynaptic terminals. Mol Neurobiol 2009; 39:130-48. [PMID: 19253034 PMCID: PMC2701268 DOI: 10.1007/s12035-009-8058-z] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Accepted: 02/04/2009] [Indexed: 12/24/2022]
Abstract
The primary receptor neurons of the auditory, vestibular, and visual systems encode a broad range of sensory information by modulating the tonic release of the neurotransmitter glutamate in response to graded changes in membrane potential. The output synapses of these neurons are marked by structures called synaptic ribbons, which tether a pool of releasable synaptic vesicles at the active zone where glutamate release occurs in response to calcium influx through L-type channels. Ribbons are composed primarily of the protein, RIBEYE, which is unique to ribbon synapses, but cytomatrix proteins that regulate the vesicle cycle in conventional terminals, such as Piccolo and Bassoon, also are found at ribbons. Conventional and ribbon terminals differ, however, in the size, molecular composition, and mobilization of their synaptic vesicle pools. Calcium-binding proteins and plasma membrane calcium pumps, together with endomembrane pumps and channels, play important roles in calcium handling at ribbon synapses. Taken together, emerging evidence suggests that several molecular and cellular specializations work in concert to support the sustained exocytosis of glutamate that is a hallmark of ribbon synapses. Consistent with its functional importance, abnormalities in a variety of functional aspects of the ribbon presynaptic terminal underlie several forms of auditory neuropathy and retinopathy.
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Affiliation(s)
- George Zanazzi
- Department of Neurobiology & Behavior, State Universtiy of New York, Stony Brook, NY 11794-5230, USA
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Holmseth S, Scott HA, Real K, Lehre KP, Leergaard TB, Bjaalie JG, Danbolt NC. The concentrations and distributions of three C-terminal variants of the GLT1 (EAAT2; slc1a2) glutamate transporter protein in rat brain tissue suggest differential regulation. Neuroscience 2009; 162:1055-71. [PMID: 19328838 DOI: 10.1016/j.neuroscience.2009.03.048] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 03/11/2009] [Accepted: 03/16/2009] [Indexed: 12/13/2022]
Abstract
The neurotransmitter glutamate is inactivated by cellular uptake; mostly catalyzed by the glutamate transporter GLT1 (slc1a2, excitatory amino acid transporter [EAAT2]) subtype which is expressed at high levels in brain astrocytes and at lower levels in neurons. Three coulombs-terminal variants of GLT1 exist (GLT1a, GLT1b and GLT1c). Their cellular distributions are currently being debated (that of GLT1b in particular). Here we have made antibodies to the variants and produced pure preparations of the individual variant proteins. The immunoreactivities of each variant per amount of protein were compared to that of total GLT1 immunoisolated from Wistar rat brains. At eight weeks of age GLT1a, GLT1b and GLT1c represented, respectively 90%+/-1%, 6+/-1% and 1%+/-0.5% (mean+/-SEM) of total hippocampal GLT1. The levels of all three variants were low at birth and increased towards adulthood, but GLT1a increased relatively more than the other two. At postnatal day 14 the levels of GLT1b and GLT1c relative to total GLT1 were, respectively, 1.7+/-0.1 and 2.5+/-0.1 times higher than at eight weeks. In tissue sections, antibodies to GLT1a gave stronger labeling than antibodies to GLT1b, but the distributions of GLT1a and GLT1b were similar in that both were predominantly expressed in astroglia, cell bodies as well as their finest ramifications. GLT1b was not detected in nerve terminals in normal brain tissue. The findings illustrate the need for quantitative measurements and support the notion that the importance of the variants may not be due to the transporter molecules themselves, but rather that their expression represents the activities of different regulatory pathways.
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Affiliation(s)
- S Holmseth
- Center for Molecular Biology and Neuroscience, Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, PO Box 1105 Blindern, N 0317 Oslo, Norway
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Neuronal expression of splice variants of "glial" glutamate transporters in brains afflicted by Alzheimer's disease: unmasking an intrinsic neuronal property. Neurochem Res 2009; 34:1748-57. [PMID: 19319679 DOI: 10.1007/s11064-009-9957-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Accepted: 03/11/2009] [Indexed: 01/24/2023]
Abstract
Anomalies in glutamate homeostasis may contribute to the pathological processes involved in Alzheimer's disease (AD). Glutamate released from neurons or glial cells is normally rapidly cleared by glutamate transporters, most of which are expressed at the protein level by glial cells. However, in some patho-physiological situations, expression of glutamate transporters that are normally considered to be glial types, appears to be evoked in populations of distressed neurons. This study analysed the expression of exon-skipping forms of the three predominant excitatory amino acid (glutamate) transporters (EAATs1-3) in brains afflicted with AD. We demonstrate by immunocytochemistry in temporal cortex, the expression of these proteins particularly in limited subsets of neurons, some of which appeared to be dys-morphic. Whilst the neuronal expression of the "glial" glutamate transporters EAAT1 and EAAT2 is frequently considered to represent the abnormal and ectopic expression of such transporters, we suggest this may be a misinterpretation, since neurons such as cortical pyramidal cells normally express abundant mRNA for these EAATs (but little if any EAAT protein expression). We hypothesize instead that distressed neurons in the AD brain can turn on the translation of pre-existent mRNA pools, or suppress the degradation of alternately spliced glutamate transporter protein, leading to the "unmasking" of, rather than evoked expression of "glial" glutamate transporters in stressed neurons.
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Zagami CJ, Beart PM, Wallis N, Nagley P, O'Shea RD. Oxidative and excitotoxic insults exert differential effects on spinal motoneurons and astrocytic glutamate transporters: Implications for the role of astrogliosis in amyotrophic lateral sclerosis. Glia 2009; 57:119-35. [PMID: 18661557 DOI: 10.1002/glia.20739] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In amyotrophic lateral sclerosis (ALS) non-neuronal cells play key roles in disease etiology and loss of motoneurons via noncell-autonomous mechanisms. Reactive astrogliosis and dysfunctional transporters for L-glutamate [excitatory amino acid transporters, (EAATs)] are hallmarks of ALS pathology. Here, we describe mechanistic insights into ALS pathology involving EAAT-associated homeostasis in response to a destructive milieu, in which oxidative stress and excitotoxicity induce respectively astrogliosis and motoneuron injury. Using an in vitro neuronal-glial culture of embryonic mouse spinal cord, we demonstrate that EAAT activity was maintained initially, despite a loss of cellular viability induced by exposure to oxidative [3-morpholinosydnonimine chloride (SIN-1)] and excitotoxic [(S)-5-fluorowillardiine (FW)] conditions. This homeostatic response of EAAT function involved no change in the cell surface expression of EAAT1/2 at 0.5-4 h, but rather alterations in kinetic properties. Over this time-frame, EAAT1/2 both became more widespread across astrocytic arbors in concert with increased expression of glial fibrillary acidic protein (GFAP), although at 8-24 h there was gliotoxicity, especially with SIN-1 rather than FW. An opposite picture was found for motoneurons where FW, not SIN-1, produced early and extensive neuritic shrinkage and blebbing (> or =0.5 h) with somata loss from 2 h. We postulate that EAATs play an early homeostatic and protective role in the pathologic milieu. Moreover, the differential profiles of injury produced by oxidative and excitotoxic insults identify two distinct phases of injury which parallel important aspects of the pathology of ALS.
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Melone M, Bellesi M, Conti F. Synaptic localization of GLT-1a in the rat somatic sensory cortex. Glia 2009; 57:108-17. [DOI: 10.1002/glia.20744] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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50
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Dynamic regulation of the Kv2.1 voltage-gated potassium channel during brain ischemia through neuroglial interaction. J Neurosci 2008; 28:8529-38. [PMID: 18716211 DOI: 10.1523/jneurosci.1417-08.2008] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The physiological significance of neuroglial interactions in the CNS has been emphasized in neurological conditions such as epilepsy and brain ischemia. The Kv2.1 voltage-gated potassium channel is unique in its ability to form large clusters in the plasma membrane of neuronal cell bodies. We have previously shown that brain ischemia causes rapid dephosphorylation of Kv2.1 subunits and resultant activation of the ion channel function. However, the physiological significance of the channel clustering is unknown. Here we present evidence that clustered Kv2.1 channels in the neuronal plasma membrane are juxtaposed to axosomatic synapses and associated with astrocytic processes expressing high levels of glutamate transporters. In acute cortical slices, ischemic stress rapidly resulted in the dephosphorylation and dispersion of Kv2.1. Selective inhibition of metabolism in astrocytes was sufficient to induce Kv2.1 dephosphorylation in neurons. Interestingly, these effects were blocked by the antagonists of ionotropic glutamate receptors, indicating the involvement of glutamate as the signal mediator between astrocytes and neurons. Furthermore, the pharmacological inhibition of glial glutamate transporter GLT-1 induced the similar Kv2.1 dephosphorylation, whereas exogenous glutamate alone was not efficacious. These results suggest that ischemic stress rapidly causes the dysfunction of glutamate transporters in astrocytes and resultant accumulation of glutamate in the extracellular space. The elevated glutamate may subsequently activate ionotropic glutamate receptors and result in the dephosphorylation of Kv2.1 in neurons. These findings implicate that Kv2.1 clusters are strategically situated at neuroglial junctions to achieve the rapid modulation after ischemic stress via glutamate signaling.
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