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Carretero VJ, Ramos E, Segura-Chama P, Hernández A, Baraibar AM, Álvarez-Merz I, Muñoz FL, Egea J, Solís JM, Romero A, Hernández-Guijo JM. Non-Excitatory Amino Acids, Melatonin, and Free Radicals: Examining the Role in Stroke and Aging. Antioxidants (Basel) 2023; 12:1844. [PMID: 37891922 PMCID: PMC10603966 DOI: 10.3390/antiox12101844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 09/23/2023] [Accepted: 09/26/2023] [Indexed: 10/29/2023] Open
Abstract
The aim of this review is to explore the relationship between melatonin, free radicals, and non-excitatory amino acids, and their role in stroke and aging. Melatonin has garnered significant attention in recent years due to its diverse physiological functions and potential therapeutic benefits by reducing oxidative stress, inflammation, and apoptosis. Melatonin has been found to mitigate ischemic brain damage caused by stroke. By scavenging free radicals and reducing oxidative damage, melatonin may help slow down the aging process and protect against age-related cognitive decline. Additionally, non-excitatory amino acids have been shown to possess neuroprotective properties, including antioxidant and anti-inflammatory in stroke and aging-related conditions. They can attenuate oxidative stress, modulate calcium homeostasis, and inhibit apoptosis, thereby safeguarding neurons against damage induced by stroke and aging processes. The intracellular accumulation of certain non-excitatory amino acids could promote harmful effects during hypoxia-ischemia episodes and thus, the blockade of the amino acid transporters involved in the process could be an alternative therapeutic strategy to reduce ischemic damage. On the other hand, the accumulation of free radicals, specifically mitochondrial reactive oxygen and nitrogen species, accelerates cellular senescence and contributes to age-related decline. Recent research suggests a complex interplay between melatonin, free radicals, and non-excitatory amino acids in stroke and aging. The neuroprotective actions of melatonin and non-excitatory amino acids converge on multiple pathways, including the regulation of calcium homeostasis, modulation of apoptosis, and reduction of inflammation. These mechanisms collectively contribute to the preservation of neuronal integrity and functions, making them promising targets for therapeutic interventions in stroke and age-related disorders.
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Affiliation(s)
- Victoria Jiménez Carretero
- Department of Pharmacology and Therapeutic, Teófilo Hernando Institute, Faculty of Medicine, Universidad Autónoma de Madrid, Av. Arzobispo Morcillo 4, 28029 Madrid, Spain
| | - Eva Ramos
- Department of Pharmacology and Toxicology, Faculty of Veterinary Medicine, Complutense University of Madrid, 28040 Madrid, Spain
| | - Pedro Segura-Chama
- Investigador por México-CONAHCYT, Instituto Nacional de Psiquiatría "Ramón de la Fuente Muñiz", Calzada México-Xochimilco 101, Huipulco, Tlalpan, Mexico City 14370, Mexico
| | - Adan Hernández
- Institute of Neurobiology, Universidad Nacional Autónoma of México, Juriquilla, Santiago de Querétaro 76230, Querétaro, Mexico
| | - Andrés M Baraibar
- Department of Neurosciences, Universidad del País Vasco UPV/EHU, Achucarro Basque Center for Neuroscience, Barrio Sarriena, s/n, 48940 Leioa, Spain
| | - Iris Álvarez-Merz
- Department of Pharmacology and Therapeutic, Teófilo Hernando Institute, Faculty of Medicine, Universidad Autónoma de Madrid, Av. Arzobispo Morcillo 4, 28029 Madrid, Spain
| | - Francisco López Muñoz
- Faculty of Health Sciences, University Camilo José Cela, C/Castillo de Alarcón 49, Villanueva de la Cañada, 28692 Madrid, Spain
- Neuropsychopharmacology Unit, Hospital 12 de Octubre Research Institute (i + 12), Avda. Córdoba, s/n, 28041 Madrid, Spain
| | - Javier Egea
- Molecular Neuroinflammation and Neuronal Plasticity Research Laboratory, Hospital Universitario Santa Cristina, Health Research Institute, Hospital Universitario de la Princesa, 28006 Madrid, Spain
| | - José M Solís
- Neurobiology-Research Service, Hospital Ramón y Cajal, Carretera de Colmenar Viejo, Km. 9, 28029 Madrid, Spain
| | - Alejandro Romero
- Department of Pharmacology and Toxicology, Faculty of Veterinary Medicine, Complutense University of Madrid, 28040 Madrid, Spain
| | - Jesús M Hernández-Guijo
- Department of Pharmacology and Therapeutic, Teófilo Hernando Institute, Faculty of Medicine, Universidad Autónoma de Madrid, Av. Arzobispo Morcillo 4, 28029 Madrid, Spain
- Ramón y Cajal Institute for Health Research (IRYCIS), Hospital Ramón y Cajal, Carretera de Colmenar Viejo, Km. 9, 28029 Madrid, Spain
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2
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Ito S, Yagi R, Ogata S, Masuda T, Saito T, Saido T, Ohtsuki S. Proteomic alterations in the brain and blood-brain barrier during brain Aβ accumulation in an APP knock-in mouse model of Alzheimer's disease. Fluids Barriers CNS 2023; 20:66. [PMID: 37705104 PMCID: PMC10500766 DOI: 10.1186/s12987-023-00466-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Accepted: 09/02/2023] [Indexed: 09/15/2023] Open
Abstract
BACKGROUND Blood-brain barrier (BBB) dysfunction is supposed to be an early event in the development of Alzheimer's disease (AD). This study aimed to investigate the relationship between BBB alterations and AD progression in terms of amyloid-β peptide (Aβ) accumulation in the brains of humanized amyloid precursor protein knock-in (APP-KI) mice. METHODS Brain Aβ accumulation was examined using immunohistochemical analysis. Alterations in differentially expressed proteins were determined using sequential window acquisition of all theoretical fragment ion mass spectroscopy (SWATH-MS)-based quantitative proteomics, and Metascape, STRING, Gene Ontology, and KEGG were used for network analyses of altered biological pathways and processes. Statistical significance was determined using the unpaired two-tailed Student's t-test and Welch's t-test for two groups and one-way analysis of variance followed by Tukey's test for more than two groups. Correlations between two groups were determined using Pearson's correlation analysis. RESULTS Brain Aβ accumulation in APP-KI mice was detectable at 2 months, increased significantly at 5 months, and remained elevated at 12 months of age. The levels of differentially expressed proteins in isolated brain capillaries were higher in younger mice, whereas those in the brain were higher in older mice. Network analyses indicated changes in basement membrane-associated and ribosomal proteins in the brain capillaries. There were no significant changes in key proteins involved in drug or Aβ transport at the BBB. In contrast, solute carrier transporter levels in astrocytes, microglia, and neurons were altered in the brain of older mice. Moreover, the levels of the lipid transporters Apoe and Apoj were upregulated in both the brain and isolated brain capillaries after Aβ accumulation. CONCLUSIONS Our results suggest that changes in the brain occurred after advanced Aβ accumulation, whereas initial Aβ accumulation was sufficient to cause alterations in the BBB. These findings may help elucidate the role of BBB alterations in AD progression and predict the distribution of drugs across the BBB in the brain of patients with AD.
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Affiliation(s)
- Shingo Ito
- Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan.
- Department of Pharmaceutical Microbiology, Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan.
| | - Ryotaro Yagi
- Department of Pharmaceutical Microbiology, Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan
| | - Seiryo Ogata
- Department of Pharmaceutical Microbiology, Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan
- Department of Environmental Medicine and Molecular Toxicology, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan
| | - Takeshi Masuda
- Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan
- Department of Pharmaceutical Microbiology, Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan
| | - Takashi Saito
- Department of Neurocognitive Science, Institute of Brain Science, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, 467-8601, Japan
- Laboratory for Proteolytic Neuroscience, RIKEN Center for Brain Science, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - Takaomi Saido
- Laboratory for Proteolytic Neuroscience, RIKEN Center for Brain Science, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - Sumio Ohtsuki
- Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan
- Department of Pharmaceutical Microbiology, Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Chuo-ku, Kumamoto, 862-0973, Japan
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3
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Hamilton A, Eliasson L, Knudsen JG. Amino acids and the changing face of the α-cell. Peptides 2023:171039. [PMID: 37295651 DOI: 10.1016/j.peptides.2023.171039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 05/31/2023] [Accepted: 06/05/2023] [Indexed: 06/12/2023]
Abstract
Glucagon has long been defined by its glucogenic action and as a result α-cells have been characterised based largely on their interaction with glucose. Recent findings have challenged this preconception, bringing to the fore the significant role glucagon plays in amino acid breakdown and underlining the importance of amino acids in glucagon secretion. The challenge that remains is defining the mechanism that underlie these effects - understanding which amino acids are most important, how they act on the α-cell and how their actions integrate with other fuels such as glucose and fatty acids. This review will describe the current relationship between amino acids and glucagon and how we can use this knowledge to redefine the α-cell.
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Affiliation(s)
- Alexander Hamilton
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Denmark; Department of Clinical Sciences in Malmö, Islet Cell Exocytosis, Lund University Diabetes Centre, Lund University, Malmö, Sweden.
| | - Lena Eliasson
- Department of Clinical Sciences in Malmö, Islet Cell Exocytosis, Lund University Diabetes Centre, Lund University, Malmö, Sweden.
| | - Jakob G Knudsen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Denmark.
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Zielińska M, Albrecht J, Popek M. Dysregulation of Astrocytic Glutamine Transport in Acute Hyperammonemic Brain Edema. Front Neurosci 2022; 16:874750. [PMID: 35733937 PMCID: PMC9207324 DOI: 10.3389/fnins.2022.874750] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 05/17/2022] [Indexed: 11/13/2022] Open
Abstract
Acute liver failure (ALF) impairs ammonia clearance from blood, which gives rise to acute hyperammonemia and increased ammonia accumulation in the brain. Since in brain glutamine synthesis is the only route of ammonia detoxification, hyperammonemia is as a rule associated with increased brain glutamine content (glutaminosis) which correlates with and contributes along with ammonia itself to hyperammonemic brain edema-associated with ALF. This review focuses on the effects of hyperammonemia on the two glutamine carriers located in the astrocytic membrane: Slc38a3 (SN1, SNAT3) and Slc7a6 (y + LAT2). We emphasize the contribution of the dysfunction of either of the two carriers to glutaminosis- related aspects of brain edema: retention of osmotically obligated water (Slc38a3) and induction of oxidative/nitrosative stress (Slc7a6). The changes in glutamine transport link glutaminosis- evoked mitochondrial dysfunction to oxidative-nitrosative stress as formulated in the “Trojan Horse” hypothesis.
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Hamdani EH, Popek M, Frontczak-Baniewicz M, Utheim TP, Albrecht J, Zielińska M, Chaudhry FA. Perturbation of astroglial Slc38 glutamine transporters by NH 4 + contributes to neurophysiologic manifestations in acute liver failure. FASEB J 2021; 35:e21588. [PMID: 34169573 DOI: 10.1096/fj.202001712rr] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 03/17/2021] [Accepted: 03/25/2021] [Indexed: 02/07/2023]
Abstract
Ammonia is considered the main pathogenic toxin in hepatic encephalopathy (HE). However, the molecular mechanisms involved have been disputed. As altered glutamatergic and GABAergic neurotransmission has been reported in HE, we investigated whether four members of the solute carrier 38 (Slc38) family of amino acid transporters-involved in the replenishment of glutamate and GABA-contribute to ammonia neurotoxicity in HE. We show that ammonium ion exerts multiple actions on the Slc38 transporters: It competes with glutamine for the binding to the system N transporters Slc38a3 and Slc38a5, consequently inhibiting bidirectional astroglial glutamine transport. It also competes with H+ , Na+ , and K+ for uncoupled permeation through the same transporters, which may perturb astroglial intracellular pH, membrane potential, and K+ -buffering. Knockdown of Slc38a3 in mice results in cerebral cortical edema and disrupted neurotransmitter synthesis mimicking events contributing to HE development. Finally, in a mouse model of acute liver failure (ALF), we demonstrate the downregulation of Slc38a3 protein, impeded astroglial glutamine release, and cytotoxic edema. Altogether, we demonstrate contribution of Slc38 transporters to the ammonia-induced impairment of glutamine recycling between astrocytes and neurons, a phenomenon underlying acute ammonia neurotoxicity in the setting of ALF.
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Affiliation(s)
- El Hassan Hamdani
- Department of Molecular Medicine, University of Oslo (UiO), Oslo, Norway.,Institute of Behavioural Science, Oslo Metropolitan University, Oslo, Norway
| | - Mariusz Popek
- Neurotoxicology Department, Mossakowski Medical Research Institute PAS, Warsaw, Poland
| | | | - Tor Paaske Utheim
- Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.,Department of Plastic and Reconstructive Surgery, Oslo University Hospital, Oslo, Norway
| | - Jan Albrecht
- Neurotoxicology Department, Mossakowski Medical Research Institute PAS, Warsaw, Poland
| | - Magdalena Zielińska
- Neurotoxicology Department, Mossakowski Medical Research Institute PAS, Warsaw, Poland
| | - Farrukh Abbas Chaudhry
- Department of Molecular Medicine, University of Oslo (UiO), Oslo, Norway.,Department of Plastic and Reconstructive Surgery, Oslo University Hospital, Oslo, Norway
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Álvarez-Merz I, Luengo JG, Muñoz MD, Hernández-Guijo JM, Solís JM. Hypoxia-induced depression of synaptic transmission becomes irreversible by intracellular accumulation of non-excitatory amino acids. Neuropharmacology 2021; 190:108557. [PMID: 33848510 DOI: 10.1016/j.neuropharm.2021.108557] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 03/10/2021] [Accepted: 04/02/2021] [Indexed: 10/21/2022]
Abstract
The intracellular accumulation of some amino acids (AAs), mainly glutamine, can contribute to brain edema observed during liver failure. We recently demonstrated that individual applications of high concentrations (10 mM) of some non-excitatory AAs increase the electrical resistance of hippocampal slices, indicating cell swelling. Therefore, we pondered whether an AA mixture's application might cause cell swelling at a physiological concentration range. In rat hippocampal slices, we carried out extra- and intracellular electrophysiological recordings and AAs analysis to address this question. We applied a mixture of 19 AAs at their plasmatic concentrations (Plasma solution: Ala, Gly, Gln, His, Ser, Tau, Thr, Arg, Leu, Met, Pro, Val, Asn, Cys, Phe, Ile, Lys, Tyr, and Trp). This solution was afterward divided into two according to the individual AAs at 10 mM concentration inducing synaptic potentiation (Plasma1, containing the first seven AAs of Plasma) or not (Plasma2, with the remaining AAs). Plasma application increased evoked field potentials requiring extracellular chloride. This effect was mimicked by the Plasma1 but not the Plasma2 solution. Plasma1-induced potentiation was independent of changes in release probability, basic electrophysiological membrane properties, and NMDAR activation. AAs in Plasma1 act cooperatively to accumulate intracellularly and to induce synaptic potentiation. In the presence of Plasma1, the reversible synaptic depression caused by a 40-min hypoxia period turned into an irreversible disappearance of synaptic potentials through an NMDAR-dependent mechanism. The presence of a system A transport inhibitor did not block Plasma1-mediated effects. These results indicate that cell swelling, induced by the accumulation of non-excitotoxic AAs through unidentified transporters, might foster deleterious effects produced by hypoxia-ischemia episodes.
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Affiliation(s)
- Iris Álvarez-Merz
- Servicio de Neurobiología-Investigación, Hospital Universitario Ramón y Cajal, IRYCIS, 28034, Madrid, Spain; Departamento de Farmacología y Terapeútica, ITH, Facultad de Medicina, Universidad Autónoma de Madrid, IRYCIS, Avda. Arzobispo Morcillo 4, 28029, Madrid, Spain
| | - Javier G Luengo
- Servicio de Neurobiología-Investigación, Hospital Universitario Ramón y Cajal, IRYCIS, 28034, Madrid, Spain; Departamento de Farmacología y Terapeútica, ITH, Facultad de Medicina, Universidad Autónoma de Madrid, IRYCIS, Avda. Arzobispo Morcillo 4, 28029, Madrid, Spain
| | - María-Dolores Muñoz
- Unidad de Neurología Experimental, Hospital Universitario Ramón y Cajal, IRYCIS, Madrid, 28034, Spain
| | - Jesús M Hernández-Guijo
- Departamento de Farmacología y Terapeútica, ITH, Facultad de Medicina, Universidad Autónoma de Madrid, IRYCIS, Avda. Arzobispo Morcillo 4, 28029, Madrid, Spain
| | - José M Solís
- Servicio de Neurobiología-Investigación, Hospital Universitario Ramón y Cajal, IRYCIS, 28034, Madrid, Spain.
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Popek M, Bobula B, Sowa J, Hess G, Frontczak-Baniewicz M, Albrecht J, Zielińska M. Physiology and Morphological Correlates of Excitatory Transmission are Preserved in Glutamine Transporter SN1-Depleted Mouse Frontal Cortex. Neuroscience 2020; 446:124-136. [DOI: 10.1016/j.neuroscience.2020.08.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 07/16/2020] [Accepted: 08/14/2020] [Indexed: 01/22/2023]
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8
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Qureshi T, Bjørkmo M, Nordengen K, Gundersen V, Utheim TP, Watne LO, Storm-Mathisen J, Hassel B, Chaudhry FA. Slc38a1 Conveys Astroglia-Derived Glutamine into GABAergic Interneurons for Neurotransmitter GABA Synthesis. Cells 2020; 9:E1686. [PMID: 32668809 PMCID: PMC7407890 DOI: 10.3390/cells9071686] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 07/06/2020] [Accepted: 07/08/2020] [Indexed: 12/17/2022] Open
Abstract
GABA signaling is involved in a wide range of neuronal functions, such as synchronization of action potential firing, synaptic plasticity and neuronal development. Sustained GABA signaling requires efficient mechanisms for the replenishment of the neurotransmitter pool of GABA. The prevailing theory is that exocytotically released GABA may be transported into perisynaptic astroglia and converted to glutamine, which is then shuttled back to the neurons for resynthesis of GABA-i.e., the glutamate/GABA-glutamine (GGG) cycle. However, an unequivocal demonstration of astroglia-to-nerve terminal transport of glutamine and the contribution of astroglia-derived glutamine to neurotransmitter GABA synthesis is lacking. By genetic inactivation of the amino acid transporter Solute carrier 38 member a1 (Slc38a1)-which is enriched on parvalbumin+ GABAergic neurons-and by intraperitoneal injection of radiolabeled acetate (which is metabolized to glutamine in astroglial cells), we show that Slc38a1 mediates import of astroglia-derived glutamine into GABAergic neurons for synthesis of GABA. In brain slices, we demonstrate the role of Slc38a1 for the uptake of glutamine specifically into GABAergic nerve terminals for the synthesis of GABA depending on demand and glutamine supply. Thus, while leaving room for other pathways, our study demonstrates a key role of Slc38a1 for newly formed GABA, in harmony with the existence of a GGG cycle.
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Affiliation(s)
- Tayyaba Qureshi
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway; (T.Q.); (M.B.); (K.N.); (V.G.); (J.S.-M.)
| | - Mona Bjørkmo
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway; (T.Q.); (M.B.); (K.N.); (V.G.); (J.S.-M.)
| | - Kaja Nordengen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway; (T.Q.); (M.B.); (K.N.); (V.G.); (J.S.-M.)
| | - Vidar Gundersen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway; (T.Q.); (M.B.); (K.N.); (V.G.); (J.S.-M.)
| | - Tor Paaske Utheim
- Department of Plastic and Reconstructive Surgery, Oslo University Hospital, 0424 Oslo, Norway;
| | - Leiv Otto Watne
- Department of Geriatric Medicine, Oslo University Hospital, 0424 Oslo, Norway;
| | - Jon Storm-Mathisen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway; (T.Q.); (M.B.); (K.N.); (V.G.); (J.S.-M.)
| | - Bjørnar Hassel
- Department of Neurohabilitation, Oslo University Hospital and University of Oslo, 0424 Oslo, Norway;
| | - Farrukh Abbas Chaudhry
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway; (T.Q.); (M.B.); (K.N.); (V.G.); (J.S.-M.)
- Department of Plastic and Reconstructive Surgery, Oslo University Hospital, 0424 Oslo, Norway;
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9
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Anand AC, Nandi B, Acharya SK, Arora A, Babu S, Batra Y, Chawla YK, Chowdhury A, Chaoudhuri A, Eapen EC, Devarbhavi H, Dhiman R, Datta Gupta S, Duseja A, Jothimani D, Kapoor D, Kar P, Khuroo MS, Kumar A, Madan K, Mallick B, Maiwall R, Mohan N, Nagral A, Nath P, Panigrahi SC, Pawar A, Philips CA, Prahraj D, Puri P, Rastogi A, Saraswat VA, Saigal S, Shalimar, Shukla A, Singh SP, Verghese T, Wadhawan M. Indian National Association for the Study of the Liver Consensus Statement on Acute Liver Failure (Part 1): Epidemiology, Pathogenesis, Presentation and Prognosis. J Clin Exp Hepatol 2020; 10:339-376. [PMID: 32655238 PMCID: PMC7335721 DOI: 10.1016/j.jceh.2020.04.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 04/12/2020] [Indexed: 12/12/2022] Open
Abstract
Acute liver failure (ALF) is an infrequent, unpredictable, potentially fatal complication of acute liver injury (ALI) consequent to varied etiologies. Etiologies of ALF as reported in the literature have regional differences, which affects the clinical presentation and natural course. In this part of the consensus article designed to reflect the clinical practices in India, disease burden, epidemiology, clinical presentation, monitoring, and prognostication have been discussed. In India, viral hepatitis is the most frequent cause of ALF, with drug-induced hepatitis due to antituberculosis drugs being the second most frequent cause. The clinical presentation of ALF is characterized by jaundice, coagulopathy, and encephalopathy. It is important to differentiate ALF from other causes of liver failure, including acute on chronic liver failure, subacute liver failure, as well as certain tropical infections which can mimic this presentation. The disease often has a fulminant clinical course with high short-term mortality. Death is usually attributable to cerebral complications, infections, and resultant multiorgan failure. Timely liver transplantation (LT) can change the outcome, and hence, it is vital to provide intensive care to patients until LT can be arranged. It is equally important to assess prognosis to select patients who are suitable for LT. Several prognostic scores have been proposed, and their comparisons show that indigenously developed dynamic scores have an edge over scores described from the Western world. Management of ALF will be described in part 2 of this document.
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Key Words
- ACLF, acute on chronic liver failure
- AFLP, acute fatty liver of pregnancy
- AKI, Acute kidney injury
- ALF, Acute liver failure
- ALFED, Acute Liver Failure Early Dynamic
- ALT, alanine transaminase
- ANA, antinuclear antibody
- AP, Alkaline phosphatase
- APTT, activated partial thromboplastin time
- ASM, alternative system of medicine
- ASMA, antismooth muscle antibody
- AST, aspartate transaminase
- ATN, Acute tubular necrosis
- ATP, adenosine triphosphate
- ATT, anti-TB therapy
- AUROC, Area under the receiver operating characteristics curve
- BCS, Budd-Chiari syndrome
- BMI, body mass index
- CBF, cerebral blood flow
- CBFV, cerebral blood flow volume
- CE, cerebral edema
- CHBV, chronic HBV
- CLD, chronic liver disease
- CNS, central nervous system
- CPI, clinical prognostic indicator
- CSF, cerebrospinal fluid
- DAMPs, Damage-associated molecular patterns
- DILI, drug-induced liver injury
- EBV, Epstein-Barr virus
- ETCO2, End tidal CO2
- GRADE, Grading of Recommendations Assessment Development and Evaluation
- HAV, hepatitis A virus
- HBV, Hepatitis B virus
- HELLP, hemolysis
- HEV, hepatitis E virus
- HLH, Hemophagocytic lymphohistiocytosis
- HSV, herpes simplex virus
- HV, hepatic vein
- HVOTO, hepatic venous outflow tract obstruction
- IAHG, International Autoimmune Hepatitis Group
- ICH, intracerebral hypertension
- ICP, intracerebral pressure
- ICU, intensive care unit
- IFN, interferon
- IL, interleukin
- IND-ALF, ALF of indeterminate etiology
- INDILI, Indian Network for DILI
- KCC, King's College Criteria
- LC, liver cirrhosis
- LDLT, living donor liver transplantation
- LT, liver transplantation
- MAP, mean arterial pressure
- MHN, massive hepatic necrosis
- MPT, mitochondrial permeability transition
- MUAC, mid-upper arm circumference
- NAPQI, n-acetyl-p-benzo-quinone-imine
- NPV, negative predictive value
- NWI, New Wilson's Index
- ONSD, optic nerve sheath diameter
- PAMPs, pathogen-associated molecular patterns
- PCR, polymerase chain reaction
- PELD, Pediatric End-Stage Liver Disease
- PPV, positive predictive value
- PT, prothrombin time
- RAAS, renin–angiotensin–aldosterone system
- SHF, subacute hepatic failure
- SIRS, systemic inflammatory response syndrome
- SNS, sympathetic nervous system
- TB, tuberculosis
- TCD, transcranial Doppler
- TGF, tumor growth factor
- TJLB, transjugular liver biopsy
- TLR, toll-like receptor
- TNF, tumor necrosis factor
- TSFT, triceps skin fold thickness
- US, ultrasound
- USALF, US Acute Liver Failure
- VZV, varicella-zoster virus
- WD, Wilson disease
- Wilson disease (WD)
- YP, yellow phosphorus
- acute liver failure
- autoimmune hepatitis (AIH)
- drug-induced liver injury
- elevated liver enzymes, low platelets
- sALI, severe acute liver injury
- viral hepatitis
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Affiliation(s)
- Anil C. Anand
- Department of Gastroenterology, Kaliga Institute of Medical Sciences, Bhubaneswar, 751024, India
| | - Bhaskar Nandi
- Department of Gastroenterology, Sarvodaya Hospital and Research Centre, Faridababd, Haryana, India
| | - Subrat K. Acharya
- Department of Gastroenterology and Hepatology, KIIT University, Patia, Bhubaneswar, Odisha, 751 024, India
| | - Anil Arora
- Institute of Liver Gastroenterology &Pancreatico Biliary Sciences, Sir Ganga Ram Hospital, Rajinder Nagar, New Delhi, 110 060, India
| | - Sethu Babu
- Department of Gastroenterology, Krishna Institute of Medical Sciences, Hyderabad 500003, India
| | - Yogesh Batra
- Department of Gastroenterology, Indraprastha Apollo Hospital, SaritaVihar, New Delhi, 110 076, India
| | - Yogesh K. Chawla
- Department of Gastroenterology, Kalinga Institute of Medical Sciences (KIMS), Kushabhadra Campus (KIIT Campus-5), Patia, Bhubaneswar, Odisha, 751 024, India
| | - Abhijit Chowdhury
- Department of Hepatology, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education & Research, Kolkata, 700020, India
| | - Ashok Chaoudhuri
- Hepatology and Liver Transplant, Institute of Liver & Biliary Sciences, D-1 Vasant Kunj, New Delhi, India
| | - Eapen C. Eapen
- Department of Hepatology, Christian Medical College, Vellore, India
| | - Harshad Devarbhavi
- Department of Gastroenterology and Hepatology, St. John's Medical College Hospital, Bangalore, 560034, India
| | - RadhaKrishan Dhiman
- Department of Hepatology, Post graduate Institute of Medical Education and Research, Chandigarh, 160 012, India
| | - Siddhartha Datta Gupta
- Department of Pathology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, 110 029, India
| | - Ajay Duseja
- Department of Hepatology, Post graduate Institute of Medical Education and Research, Chandigarh, 160 012, India
| | - Dinesh Jothimani
- Institute of Liver Disease and Transplantation, Dr Rela Institute and Medical Centre, Chrompet, Chennai, 600044, India
| | | | - Premashish Kar
- Department of Gastroenterology and Hepatology, Max Super Speciality Hospital, Vaishali, Ghaziabad, Uttar Pradesh, 201 012, India
| | - Mohamad S. Khuroo
- Department of Gastroenterology, Dr Khuroo’ S Medical Clinic, Srinagar, Kashmir, India
| | - Ashish Kumar
- Institute of Liver Gastroenterology &Pancreatico Biliary Sciences, Sir Ganga Ram Hospital, Rajinder Nagar, New Delhi, 110 060, India
| | - Kaushal Madan
- Gastroenterology and Hepatology, Max Smart Super Specialty Hospital, Saket, New Delhi, India
| | - Bipadabhanjan Mallick
- Department of Gastroenterology, Kalinga Institute of Medical Sciences, Bhubaneswar, 751024, India
| | - Rakhi Maiwall
- Hepatology Incharge Liver Intensive Care, Institute of Liver & Biliary Sciences, D-1 Vasant Kunj, New Delhi, India
| | - Neelam Mohan
- Department of Pediatric Gastroenterology, Hepatology & Liver Transplantation, Medanta – the Medicity Hospital, Sector – 38, Gurgaon, Haryana, India
| | - Aabha Nagral
- Department of Gastroenterology, Apollo and Jaslok Hospital & Research Centre, 15, Dr Deshmukh Marg, Pedder Road, Mumbai, Maharashtra, 400 026, India
| | - Preetam Nath
- Department of Gastroenterology, Kaliga Institute of Medical Sciences, Bhubaneswar, 751024, India
| | - Sarat C. Panigrahi
- Department of Gastroenterology, Kaliga Institute of Medical Sciences, Bhubaneswar, 751024, India
| | - Ankush Pawar
- Liver & Digestive Diseases Institute, Fortis Escorts Hospital, Okhla Road, New Delhi, 110 025, India
| | - Cyriac A. Philips
- The Liver Unit and Monarch Liver Lab, Cochin Gastroenterology Group, Ernakulam Medical Centre, Kochi, 682028, Kerala, India
| | - Dibyalochan Prahraj
- Department of Gastroenterology, Kaliga Institute of Medical Sciences, Bhubaneswar, 751024, India
| | - Pankaj Puri
- Department of Hepatology and Gastroenterology, Fortis Escorts Liver & Digestive Diseases Institute (FELDI), Fortis Escorts Hospital, Delhi, India
| | - Amit Rastogi
- Department of Liver Transplantation, Medanta – the MedicityHospital, Sector – 38, Gurgaon, Haryana, India
| | - Vivek A. Saraswat
- Department of Gastroenterology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raibareli Road, Lucknow, Uttar Pradesh, 226 014, India
| | - Sanjiv Saigal
- Department of Hepatology, Department of Liver Transplantation, India
| | - Shalimar
- Department of Gastroenterology and Human Nutrition Unit, All India Institute of Medical Sciences, New Delhi, 29, India
| | - Akash Shukla
- Department of Gastroenterology, LTM Medical College & Sion Hospital, India
| | - Shivaram P. Singh
- Department of Gastroenterology, SCB Medical College, Cuttack, Dock Road, Manglabag, Cuttack, Odisha, 753 007, India
| | - Thomas Verghese
- Department of Gastroenterology, Government Medical College, Kozikhode, India
| | - Manav Wadhawan
- Institute of Liver & Digestive Diseases and Head of Hepatology & Liver Transplant (Medicine), BLK Super Speciality Hospital, Delhi, India
| | - The INASL Task-Force on Acute Liver Failure
- Department of Gastroenterology, Kaliga Institute of Medical Sciences, Bhubaneswar, 751024, India
- Department of Gastroenterology, Sarvodaya Hospital and Research Centre, Faridababd, Haryana, India
- Department of Gastroenterology and Hepatology, KIIT University, Patia, Bhubaneswar, Odisha, 751 024, India
- Institute of Liver Gastroenterology &Pancreatico Biliary Sciences, Sir Ganga Ram Hospital, Rajinder Nagar, New Delhi, 110 060, India
- Department of Gastroenterology, Krishna Institute of Medical Sciences, Hyderabad 500003, India
- Department of Gastroenterology, Indraprastha Apollo Hospital, SaritaVihar, New Delhi, 110 076, India
- Department of Gastroenterology, Kalinga Institute of Medical Sciences (KIMS), Kushabhadra Campus (KIIT Campus-5), Patia, Bhubaneswar, Odisha, 751 024, India
- Department of Hepatology, School of Digestive and Liver Diseases, Institute of Post Graduate Medical Education & Research, Kolkata, 700020, India
- Hepatology and Liver Transplant, Institute of Liver & Biliary Sciences, D-1 Vasant Kunj, New Delhi, India
- Department of Hepatology, Christian Medical College, Vellore, India
- Department of Gastroenterology and Hepatology, St. John's Medical College Hospital, Bangalore, 560034, India
- Department of Hepatology, Post graduate Institute of Medical Education and Research, Chandigarh, 160 012, India
- Department of Pathology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, 110 029, India
- Institute of Liver Disease and Transplantation, Dr Rela Institute and Medical Centre, Chrompet, Chennai, 600044, India
- Gleneagles Global Hospitals, Hyderabad, Telangana, India
- Department of Gastroenterology and Hepatology, Max Super Speciality Hospital, Vaishali, Ghaziabad, Uttar Pradesh, 201 012, India
- Department of Gastroenterology, Dr Khuroo’ S Medical Clinic, Srinagar, Kashmir, India
- Gastroenterology and Hepatology, Max Smart Super Specialty Hospital, Saket, New Delhi, India
- Department of Gastroenterology, Kalinga Institute of Medical Sciences, Bhubaneswar, 751024, India
- Hepatology Incharge Liver Intensive Care, Institute of Liver & Biliary Sciences, D-1 Vasant Kunj, New Delhi, India
- Department of Pediatric Gastroenterology, Hepatology & Liver Transplantation, Medanta – the Medicity Hospital, Sector – 38, Gurgaon, Haryana, India
- Department of Gastroenterology, Apollo and Jaslok Hospital & Research Centre, 15, Dr Deshmukh Marg, Pedder Road, Mumbai, Maharashtra, 400 026, India
- Liver & Digestive Diseases Institute, Fortis Escorts Hospital, Okhla Road, New Delhi, 110 025, India
- The Liver Unit and Monarch Liver Lab, Cochin Gastroenterology Group, Ernakulam Medical Centre, Kochi, 682028, Kerala, India
- Department of Hepatology and Gastroenterology, Fortis Escorts Liver & Digestive Diseases Institute (FELDI), Fortis Escorts Hospital, Delhi, India
- Department of Liver Transplantation, Medanta – the MedicityHospital, Sector – 38, Gurgaon, Haryana, India
- Department of Gastroenterology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raibareli Road, Lucknow, Uttar Pradesh, 226 014, India
- Department of Hepatology, Department of Liver Transplantation, India
- Department of Gastroenterology and Human Nutrition Unit, All India Institute of Medical Sciences, New Delhi, 29, India
- Department of Gastroenterology, LTM Medical College & Sion Hospital, India
- Department of Gastroenterology, SCB Medical College, Cuttack, Dock Road, Manglabag, Cuttack, Odisha, 753 007, India
- Department of Gastroenterology, Government Medical College, Kozikhode, India
- Institute of Liver & Digestive Diseases and Head of Hepatology & Liver Transplant (Medicine), BLK Super Speciality Hospital, Delhi, India
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10
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Dong W, Todd AC, Bröer A, Hulme SR, Bröer S, Billups B. PKC-Mediated Modulation of Astrocyte SNAT3 Glutamine Transporter Function at Synapses in Situ. Int J Mol Sci 2018; 19:ijms19040924. [PMID: 29561757 PMCID: PMC5979592 DOI: 10.3390/ijms19040924] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Revised: 03/07/2018] [Accepted: 03/15/2018] [Indexed: 01/13/2023] Open
Abstract
Astrocytes are glial cells that have an intimate physical and functional association with synapses in the brain. One of their main roles is to recycle the neurotransmitters glutamate and gamma-aminobutyric acid (GABA), as a component of the glutamate/GABA-glutamine cycle. They perform this function by sequestering neurotransmitters and releasing glutamine via the neutral amino acid transporter SNAT3. In this way, astrocytes regulate the availability of neurotransmitters and subsequently influence synaptic function. Since many plasma membrane transporters are regulated by protein kinase C (PKC), the aim of this study was to understand how PKC influences SNAT3 glutamine transport in astrocytes located immediately adjacent to synapses. We studied SNAT3 transport by whole-cell patch-clamping and fluorescence pH imaging of single astrocytes in acutely isolated brainstem slices, adjacent to the calyx of the Held synapse. Activation of SNAT3-mediated glutamine transport in these astrocytes was reduced to 77 ± 6% when PKC was activated with phorbol 12-myristate 13-acetate (PMA). This effect was very rapid (within ~20 min) and eliminated by application of bisindolylmaleimide I (Bis I) or 7-hydroxystaurosporine (UCN-01), suggesting that activation of conventional isoforms of PKC reduces SNAT3 function. In addition, cell surface biotinylation experiments in these brain slices show that the amount of SNAT3 in the plasma membrane is reduced by a comparable amount (to 68 ± 5%) upon activation of PKC. This indicates a role for PKC in dynamically controlling the trafficking of SNAT3 transporters in astrocytes in situ. These data demonstrate that PKC rapidly regulates the astrocytic glutamine release mechanism, which would influence the glutamine availability for adjacent synapses and control levels of neurotransmission.
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Affiliation(s)
- Wuxing Dong
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
| | - Alison C Todd
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
- Centre for Discovery Brain Sciences, School of Biomedical Sciences, University of Edinburgh, Edinburgh EH8 9XD, UK.
| | - Angelika Bröer
- Research School of Biology, The Australian National University, Linnaeus Way 134, Canberra ACT 2601, Australia.
| | - Sarah R Hulme
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
| | - Stefan Bröer
- Research School of Biology, The Australian National University, Linnaeus Way 134, Canberra ACT 2601, Australia.
| | - Brian Billups
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, 131 Garran Road, Canberra ACT 2601, Australia.
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11
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Bakouh N, Bellanca S, Nyboer B, Moliner Cubel S, Karim Z, Sanchez CP, Stein WD, Planelles G, Lanzer M. Iron is a substrate of the Plasmodium falciparum chloroquine resistance transporter PfCRT in Xenopus oocytes. J Biol Chem 2017; 292:16109-16121. [PMID: 28768767 DOI: 10.1074/jbc.m117.805200] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Revised: 08/01/2017] [Indexed: 01/01/2023] Open
Abstract
The chloroquine resistance transporter of the human malaria parasite Plasmodium falciparum, PfCRT, is an important determinant of resistance to several quinoline and quinoline-like antimalarial drugs. PfCRT also plays an essential role in the physiology of the parasite during development inside erythrocytes. However, the function of this transporter besides its role in drug resistance is still unclear. Using electrophysiological and flux experiments conducted on PfCRT-expressing Xenopus laevis oocytes, we show here that both wild-type PfCRT and a PfCRT variant associated with chloroquine resistance transport both ferrous and ferric iron, albeit with different kinetics. In particular, we found that the ability to transport ferrous iron is reduced by the specific polymorphisms acquired by the PfCRT variant as a result of chloroquine selection. We further show that iron and chloroquine transport via PfCRT is electrogenic. If these findings in the Xenopus model extend to P. falciparum in vivo, our data suggest that PfCRT might play a role in iron homeostasis, which is essential for the parasite's development in erythrocytes.
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Affiliation(s)
- Naziha Bakouh
- From INSERM, Centre de Recherche des Cordeliers, Unité 1138, CNRS ERL8228, Université Pierre et Marie Curie and Université Paris-Descartes, Paris 75006, France
| | - Sebastiano Bellanca
- the Center of Infectious Diseases, Parasitology, Heidelberg University Hospital, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Britta Nyboer
- the Center of Infectious Diseases, Parasitology, Heidelberg University Hospital, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Sonia Moliner Cubel
- the Center of Infectious Diseases, Parasitology, Heidelberg University Hospital, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Zoubida Karim
- INSERM, UMR1149, CNRS ERL 8252, Université Paris Diderot Paris 75890, France, and
| | - Cecilia P Sanchez
- the Center of Infectious Diseases, Parasitology, Heidelberg University Hospital, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Wilfred D Stein
- Biological Chemistry, Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Gabrielle Planelles
- From INSERM, Centre de Recherche des Cordeliers, Unité 1138, CNRS ERL8228, Université Pierre et Marie Curie and Université Paris-Descartes, Paris 75006, France,
| | - Michael Lanzer
- the Center of Infectious Diseases, Parasitology, Heidelberg University Hospital, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany,
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12
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Kim J, Okamoto H, Huang Z, Anguiano G, Chen S, Liu Q, Cavino K, Xin Y, Na E, Hamid R, Lee J, Zambrowicz B, Unger R, Murphy AJ, Xu Y, Yancopoulos GD, Li WH, Gromada J. Amino Acid Transporter Slc38a5 Controls Glucagon Receptor Inhibition-Induced Pancreatic α Cell Hyperplasia in Mice. Cell Metab 2017; 25:1348-1361.e8. [PMID: 28591637 PMCID: PMC8206958 DOI: 10.1016/j.cmet.2017.05.006] [Citation(s) in RCA: 134] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 03/09/2017] [Accepted: 05/21/2017] [Indexed: 12/22/2022]
Abstract
Glucagon supports glucose homeostasis by stimulating hepatic gluconeogenesis, in part by promoting the uptake and conversion of amino acids into gluconeogenic precursors. Genetic disruption or pharmacologic inhibition of glucagon signaling results in elevated plasma amino acids and compensatory glucagon hypersecretion involving expansion of pancreatic α cell mass. Recent findings indicate that hyperaminoacidemia triggers pancreatic α cell proliferation via an mTOR-dependent pathway. We confirm and extend these findings by demonstrating that glucagon pathway blockade selectively increases expression of the sodium-coupled neutral amino acid transporter Slc38a5 in a subset of highly proliferative α cells and that Slc38a5 controls the pancreatic response to glucagon pathway blockade; most notably, mice deficient in Slc38a5 exhibit markedly decreased α cell hyperplasia to glucagon pathway blockade-induced hyperaminoacidemia. These results show that Slc38a5 is a key component of the feedback circuit between glucagon receptor signaling in the liver and amino-acid-dependent regulation of pancreatic α cell mass in mice.
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Affiliation(s)
- Jinrang Kim
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA
| | - Haruka Okamoto
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA
| | - ZhiJiang Huang
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA
| | - Guillermo Anguiano
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA
| | - Shiuhwei Chen
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA
| | - Qing Liu
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA
| | - Katie Cavino
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA
| | - Yurong Xin
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA
| | - Erqian Na
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA
| | - Rachid Hamid
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA
| | - Joseph Lee
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA
| | | | - Roger Unger
- Touchstone Center for Diabetes Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA
| | | | - Yan Xu
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA
| | | | - Wen-Hong Li
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA.
| | - Jesper Gromada
- Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591, USA.
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13
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Todd AC, Marx MC, Hulme SR, Bröer S, Billups B. SNAT3-mediated glutamine transport in perisynaptic astrocytesin situis regulated by intracellular sodium. Glia 2017; 65:900-916. [DOI: 10.1002/glia.23133] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 01/12/2017] [Accepted: 02/08/2017] [Indexed: 01/16/2023]
Affiliation(s)
- Alison C. Todd
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
- Centre for Integrative Physiology, School of Biomedical Sciences; University of Edinburgh; Edinburgh EH8 9XD United Kingdom
| | - Mari-Carmen Marx
- Department of Pharmacology; University of Cambridge; Tennis Court Road Cambridge CB2 1BT United Kingdom
| | - Sarah R. Hulme
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
| | - Stefan Bröer
- Research School of Biology; The Australian National University; Linnaeus Way 134 Canberra ACT 2601 Australia
| | - Brian Billups
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research; The Australian National University; 131 Garran Road Canberra ACT 2601 Australia
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14
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Wang Y, Fu L, Cui M, Wang Y, Xu Y, Li M, Mi J. Amino acid transporter SLC38A3 promotes metastasis of non-small cell lung cancer cells by activating PDK1. Cancer Lett 2017; 393:8-15. [PMID: 28202352 DOI: 10.1016/j.canlet.2017.01.036] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 01/25/2017] [Accepted: 01/25/2017] [Indexed: 12/22/2022]
Abstract
BACKGROUND Tumor metastasis is a finely-tuned pathological process coupled to metabolic reprogramming that includes both glutamine and glucose. The solute carrier SLC38A3, a member of amino acid/polyamine/organocation (APC) superfamily, is an l-glutamine transporter. It is not clear whether SLC38A3 involves the metastasis of NSCLC (non small cell lung cancer). METHODS The scratch test and transwell assay were used to determine the ability of NSCLC to migrate. Cellular amino acids content was determined by mass spectrometry. The cellular response to glutamine/histidine deficiency was evaluated in A549 cells. The expression of SLC38A3 was assayed in clinical NSCLC and paratumor tissues by histoimmunochemistry staining. A nude mouse model of NSCLC metastasis was developed by tail vein injection of tumor cells. RESULTS SLC38A3 was upregulated in metastatic NSCLC cells and its expression was correlated with prognosis of NSCLC patients. SLC38A3 overexpression promoted epithelial - mesenchymal transition (EMT) and migration of HCC827 and A549 human lung adenocarcinoma cells, and accelerated tumor metastasis in mice. We found that SLC38A3 decreased the cellular concentrations of glutamine and histidine, and the deficiency of glutamine or histidine activated PDK1/AKT signaling that in turn, triggered NSCLC metastasis. CONCLUSIONS SLC38A3 activated PDK1/AKT signaling and promoted metastasis of NSCLC through regulating glutamine and histidine transport, suggesting SLC38A3 as a potential therapeutic target for treatment of NSCLC.
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Affiliation(s)
- Yanhui Wang
- Department of Biochemistry & Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China; Dalian Medical University Institute of Cancer Stem Cell, China.
| | - Li Fu
- Department of Biochemistry & Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China; Dalian Medical University Institute of Cancer Stem Cell, China.
| | - Minqing Cui
- Department of Biochemistry & Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China.
| | - Yongbin Wang
- Department of Biochemistry & Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China.
| | - Yan Xu
- Department of Biochemistry & Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China.
| | - Molin Li
- Dalian Medical University Institute of Cancer Stem Cell, China.
| | - Jun Mi
- Department of Biochemistry & Molecular Cell Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, China.
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15
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Abstract
Glycine, besides exerting essential metabolic functions, is an important inhibitory neurotransmitter in caudal areas of the central nervous system and also a positive neuromodulator at excitatory glutamate-mediated synapses. Glial cells provide metabolic support to neurons and modulate synaptic activity. Six transporters belonging to three solute carrier families (SLC6, SLC38, and SLC7) are capable of transporting glycine across the glial plasma membrane. The unique glial glycine-selective transporter GlyT1 (SLC6) is the main regulator of synaptic glycine concentrations, assisted by the neuronal GlyT2. The five additional glycine transporters ATB0,+, SNAT1, SNAT2, SNAT5, and LAT2 display broad amino acid specificity and have differential contributions to glial glycine transport. Glial glycine transporters are divergent in sequence but share a similar architecture displaying the 5 + 5 inverted fold originally characterized in the leucine transporter LeuT. The availability of protein crystals solved at high resolution for prokaryotic and, more recently, eukaryotic homologues of this superfamily has advanced significantly our understanding of the mechanism of glycine transport.
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16
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Rodríguez A, Ortega A. Glutamine/Glutamate Transporters in Glial Cells: Much More Than Participants of a Metabolic Shuttle. ADVANCES IN NEUROBIOLOGY 2017; 16:169-183. [PMID: 28828610 DOI: 10.1007/978-3-319-55769-4_8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Glial glutamine and glutamate transporters play an important role in glial/neuronal interactions. An excellent model to establish the role of these membrane proteins is the cerebellum. The most abundant glutamatergic synapse in the central nervous system is present in the molecular layer of the cerebellar cortex, and it is entirely wrapped by Bergmann glial cells. The recycling of glutamate involves glutamate and glutamine transporters enriched in these radial glial processes. The functional properties of amino acid glial transporters allow, in an activity-dependent manner, the conformation of protein complexes important for the adequate support of glutamatergic neurotransmission. A detailed description of the most important features of glial glutamate and glutamine transporters follows, and a working model of the molecular mechanisms by which these glutamate and glutamine binding proteins interact, and by these means might modulate cerebellar glutamatergic transactions, is presented.
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Affiliation(s)
- Angelina Rodríguez
- Facultad de Ciencias Naturales, Universidad Autónoma de Querétaro, Centro Universitario, Querétaro, México
| | - Arturo Ortega
- Departamento de Toxicología, Cinvestav-IPN, Apartado Postal 14-740, México, DF, 07360, México.
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17
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Rubio-Aliaga I, Wagner CA. Regulation and function of the SLC38A3/SNAT3 glutamine transporter. Channels (Austin) 2016; 10:440-52. [PMID: 27362266 DOI: 10.1080/19336950.2016.1207024] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Affiliation(s)
- Isabel Rubio-Aliaga
- a Institute of Physiology, the National Center for Competence in Research NCCR Kidney, University of Zurich , Zurich , Switzerland
| | - Carsten A Wagner
- a Institute of Physiology, the National Center for Competence in Research NCCR Kidney, University of Zurich , Zurich , Switzerland
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18
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The Glutamine Transporters and Their Role in the Glutamate/GABA-Glutamine Cycle. ADVANCES IN NEUROBIOLOGY 2016; 13:223-257. [PMID: 27885631 DOI: 10.1007/978-3-319-45096-4_8] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Glutamine is a key amino acid in the CNS, playing an important role in the glutamate/GABA-glutamine cycle (GGC). In the GGC, glutamine is transferred from astrocytes to neurons, where it will replenish the inhibitory and excitatory neurotransmitter pools. Different transporters participate in this neural communication, i.e., the transporters responsible for glutamine efflux from astrocytes and influx into the neurons, such as the members of the SNAT, LAT, y+LAT, and ASC families of transporters. The SNAT family consists of the transporter isoforms SNAT3 and SNAT5 that are related to efflux from the astrocytic compartment, and SNAT1 and SNAT2 that are associated with glutamine uptake into the neuronal compartment. The isoforms SNAT7 and SNAT8 do not have their role completely understood, but they likely also participate in the GGC. The isoforms LAT2 and y+LAT2 facilitate the exchange of neutral amino acids and cationic amino acids (y+LAT2 isoform) and have been associated with glutamine efflux from astrocytes. ASCT2 is a Na+-dependent antiporter, the participation of which in the GGC also remains to be better characterized. All these isoforms are tightly regulated by transcriptional and translational mechanisms, which are induced by several determinants such as amino acid deprivation, hormones, pH, and the activity of different signaling pathways. Dysfunctional glutamine transporter activity has been associated with the pathophysiological mechanisms of certain neurologic diseases, such as Hepatic Encephalopathy and Manganism. However, there might also be other neuropathological conditions associated with an altered GGC, in which glutamine transporters are dysfunctional. Hence, it appears to be of critical importance that the physiological and pathological aspects of glutamine transporters are thoroughly investigated.
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19
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Tavoulari S, Margheritis E, Nagarajan A, DeWitt DC, Zhang YW, Rosado E, Ravera S, Rhoades E, Forrest LR, Rudnick G. Two Na+ Sites Control Conformational Change in a Neurotransmitter Transporter Homolog. J Biol Chem 2015; 291:1456-71. [PMID: 26582198 DOI: 10.1074/jbc.m115.692012] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Indexed: 12/13/2022] Open
Abstract
In LeuT, a prokaryotic homolog of neurotransmitter transporters, Na(+) stabilizes outward-open conformational states. We examined how each of the two LeuT Na(+) binding sites contributes to Na(+)-dependent closure of the cytoplasmic pathway using biochemical and biophysical assays of conformation. Mutating either of two residues that contribute to the Na2 site completely prevented cytoplasmic closure in response to Na(+), suggesting that Na2 is essential for this conformational change, whereas Na1 mutants retained Na(+) responsiveness. However, mutation of Na1 residues also influenced the Na(+)-dependent conformational change in ways that varied depending on the position mutated. Computational analyses suggest those mutants influence the ability of Na1 binding to hydrate the substrate pathway and perturb an interaction network leading to the extracellular gate. Overall, the results demonstrate that occupation of Na2 stabilizes outward-facing conformations presumably through a direct interaction between Na(+) and transmembrane helices 1 and 8, whereas Na(+) binding at Na1 influences conformational change through a network of intermediary interactions. The results also provide evidence that N-terminal release and helix motions represent distinct steps in cytoplasmic pathway opening.
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Affiliation(s)
| | | | - Anu Nagarajan
- the Computational Structural Biology Section, NINDS, National Institutes of Health, Rockville, Maryland 20852
| | - David C DeWitt
- Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520 and
| | | | | | | | - Elizabeth Rhoades
- Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520 and
| | - Lucy R Forrest
- the Computational Structural Biology Section, NINDS, National Institutes of Health, Rockville, Maryland 20852
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Kirischuk S, Héja L, Kardos J, Billups B. Astrocyte sodium signaling and the regulation of neurotransmission. Glia 2015; 64:1655-66. [DOI: 10.1002/glia.22943] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 10/28/2015] [Indexed: 02/01/2023]
Affiliation(s)
- Sergei Kirischuk
- University Medical Center of the Johannes Gutenberg University Mainz, Institute of Physiology; Mainz Germany
| | - László Héja
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences; Budapest Hungary
| | - Julianna Kardos
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences; Budapest Hungary
| | - Brian Billups
- Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University; Acton ACT Australia
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Loss of function mutation of the Slc38a3 glutamine transporter reveals its critical role for amino acid metabolism in the liver, brain, and kidney. Pflugers Arch 2015; 468:213-27. [PMID: 26490457 DOI: 10.1007/s00424-015-1742-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Revised: 09/29/2015] [Accepted: 10/02/2015] [Indexed: 01/10/2023]
Abstract
Glutamine, the most abundant amino acid in mammals, is critical for cell and organ functions. Its metabolism depends on the ability of cells to take up or release glutamine by transporters located in the plasma membrane. Several solute carrier (SLC) families transport glutamine, but the SLC38 family has been thought to be mostly responsible for glutamine transport. We demonstrate that despite the large number of glutamine transporters, the loss of Snat3/Slc38a3 glutamine transporter has a major impact on the function of organs expressing it. Snat3 mutant mice were generated by N-ethyl-N-nitrosurea (ENU) mutagenesis and showed stunted growth, altered amino acid levels, hypoglycemia, and died around 20 days after birth. Hepatic concentrations of glutamine, glutamate, leucine, phenylalanine, and tryptophan were highly reduced paralleled by downregulation of the mTOR pathway possibly linking reduced amino acid availability to impaired growth and glucose homeostasis. Snat3-deficient mice had altered urea levels paralleled by dysregulation of the urea cycle, gluconeogenesis, and glutamine synthesis. Mice were ataxic with higher glutamine but reduced glutamate and gamma-aminobutyric acid (GABA) levels in brain consistent with a major role of Snat3 in the glutamine-glutamate cycle. Renal ammonium excretion was lower, and the expression of enzymes and amino acid transporters involved in ammoniagenesis were altered. Thus, SNAT3 is a glutamine transporter required for amino acid homeostasis and determines critical functions in various organs. Despite the large number of glutamine transporters, loss of Snat3 cannot be compensated, suggesting that this transporter is a major route of glutamine transport in the liver, brain, and kidney.
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22
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Butterworth RF. Pathogenesis of hepatic encephalopathy and brain edema in acute liver failure. J Clin Exp Hepatol 2015; 5:S96-S103. [PMID: 26041966 PMCID: PMC4442857 DOI: 10.1016/j.jceh.2014.02.004] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2013] [Accepted: 02/07/2014] [Indexed: 12/12/2022] Open
Abstract
Neuropathologic investigations in acute liver failure (ALF) reveal significant alterations to neuroglia consisting of swelling of astrocytes leading to cytotoxic brain edema and intracranial hypertension as well as activation of microglia indicative of a central neuroinflammatory response. Increased arterial ammonia concentrations in patients with ALF are predictors of patients at risk for the development of brain herniation. Molecular and spectroscopic techniques in ALF reveal alterations in expression of an array of genes coding for neuroglial proteins involved in cell volume regulation and mitochondrial function as well as in the transport of neurotransmitter amino acids and in the synthesis of pro-inflammatory cytokines. Liver-brain pro-inflammatory signaling mechanisms involving transduction of systemically-derived cytokines, ammonia neurotoxicity and exposure to increased brain lactate have been proposed. Mild hypothermia and N-Acetyl cysteine have both hepato-protective and neuro-protective properties in ALF. Potentially effective anti-inflammatory agents aimed at control of encephalopathy and brain edema in ALF include etanercept and the antibiotic minocycline, a potent inhibitor of microglial activation. Translation of these potentially-interesting findings to the clinic is anxiously awaited.
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Key Words
- ALF, acute liver failure
- ATP, adenosine triphosphate
- BBB, blood-brain barrier
- CCL2, chemokine ligand-2
- CMRO2, cerebral metabolic rate for oxygen
- CNS, central nervous system
- EEG, electroencephalography
- GABA, gamma-aminobutyric acid
- GFAP, glial fibrillary acidic protein
- IgG, immunoglobulin
- MRS, magnetic resonance spectroscopy
- NAC, N-Acetyl cysteine
- NMDA, N-methyl-d-aspartate
- SIRS, systemic inflammatory response syndrome
- SNATs, several neutral amino acid transport systems
- TLP, translocator protein
- TNFα, tumor necrosis factor alpha
- acute liver failure
- hepatic encephalopathy
- intracranial hypertension
- microglial activation
- neuroinflammation
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Affiliation(s)
- Roger F. Butterworth
- Neuroscience Research Unit, Hopital St-Luc (CHUM) and Department of Medicine, University of Montreal, Montreal, QC H2W 3J4, Canada,Address for correspondence: Roger F. Butterworth, Neuroscience Research Unit, Hospital St-Luc (CHUM) and Department of Medicine, University of Montreal, 1058 St Denis, Montreal, QC H2W 3J4, Canada. Tel.: +1 902 929 2470.
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Butterworth RF. Pathophysiology of brain dysfunction in hyperammonemic syndromes: The many faces of glutamine. Mol Genet Metab 2014; 113:113-7. [PMID: 25034052 DOI: 10.1016/j.ymgme.2014.06.003] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2014] [Revised: 06/16/2014] [Accepted: 06/16/2014] [Indexed: 12/31/2022]
Abstract
Ineffective hepatic clearance of excess ammonia in the form of urea, as occurs in urea cycle enzymopathies (UCDs) and in liver failure, leads to increases in circulating and tissue concentrations of glutamine and a positive correlation between brain glutamine and the severity of neurological symptoms. Studies using 1H/13C Nuclear Magnetic Resonance (NMR) spectroscopy reveal increased de novo synthesis of glutamine in the brain in acute liver failure (ALF) but increases of synthesis rates per se do not correlate with either the severity of encephalopathy or brain edema. Skeletal muscle becomes primarily responsible for removal of excess ammonia in liver failure and in UCDs, an adaptation that results from a post-translational induction of the glutamine synthetase (GS) gene. The importance of muscle in ammonia removal in hyperammonemia accounts for the resurgence of interest in maintaining adequate dietary protein and the use of agents aimed at the stimulation of muscle GS. Alternative or additional metabolic and regulatory pathways that impact on brain glutamine homeostasis in hyperammonemia include (i) glutamine deamination by the two isoforms of glutaminase, (ii) glutamine transamination leading to the production of the putative neurotoxin alpha-ketoglutaramate and (iii) alterations of high affinity astrocytic glutamine transporters (SNATs). Findings of reduced expression of the glutamine transporter SNAT-5 (responsible for glutamine clearance from the astrocyte) in ALF raise the possibility of "glutamine trapping" within these cells. Such a trapping mechanism could contribute to cytotoxic brain edema and to the imbalance between excitatory and inhibitory neurotransmission in this disorder.
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Affiliation(s)
- Roger F Butterworth
- Dept. of Medicine, University of Montreal and Neuroscience Research Unit, St-Luc Hospital (CHUM), Montreal, Qc, Canada
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Pochini L, Scalise M, Galluccio M, Indiveri C. Membrane transporters for the special amino acid glutamine: structure/function relationships and relevance to human health. Front Chem 2014; 2:61. [PMID: 25157349 PMCID: PMC4127817 DOI: 10.3389/fchem.2014.00061] [Citation(s) in RCA: 176] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 07/16/2014] [Indexed: 12/26/2022] Open
Abstract
Glutamine together with glucose is essential for body's homeostasis. It is the most abundant amino acid and is involved in many biosynthetic, regulatory and energy production processes. Several membrane transporters which differ in transport modes, ensure glutamine homeostasis by coordinating its absorption, reabsorption and delivery to tissues. These transporters belong to different protein families, are redundant and ubiquitous. Their classification, originally based on functional properties, has recently been associated with the SLC nomenclature. Function of glutamine transporters is studied in cells over-expressing the transporters or, more recently in proteoliposomes harboring the proteins extracted from animal tissues or over-expressed in microorganisms. The role of the glutamine transporters is linked to their transport modes and coupling with Na+ and H+. Most transporters share specificity for other neutral or cationic amino acids. Na+-dependent co-transporters efficiently accumulate glutamine while antiporters regulate the pools of glutamine and other amino acids. The most acknowledged glutamine transporters belong to the SLC1, 6, 7, and 38 families. The members involved in the homeostasis are the co-transporters B0AT1 and the SNAT members 1, 2, 3, 5, and 7; the antiporters ASCT2, LAT1 and 2. The last two are associated to the ancillary CD98 protein. Some information on regulation of the glutamine transporters exist, which, however, need to be deepened. No information at all is available on structures, besides some homology models obtained using similar bacterial transporters as templates. Some models of rat and human glutamine transporters highlight very similar structures between the orthologs. Moreover the presence of glycosylation and/or phosphorylation sites located at the extracellular or intracellular faces has been predicted. ASCT2 and LAT1 are over-expressed in several cancers, thus representing potential targets for pharmacological intervention.
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Affiliation(s)
- Lorena Pochini
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria Arcavacata di Rende, Italy
| | - Mariafrancesca Scalise
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria Arcavacata di Rende, Italy
| | - Michele Galluccio
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria Arcavacata di Rende, Italy
| | - Cesare Indiveri
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria Arcavacata di Rende, Italy
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Expression of the System N transporter (SNAT5/SN2) during development indicates its plausible role in glutamatergic neurotransmission. Neurochem Int 2014; 73:166-71. [DOI: 10.1016/j.neuint.2013.11.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 11/20/2013] [Accepted: 11/27/2013] [Indexed: 01/09/2023]
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Jenstad M, Chaudhry FA. The Amino Acid Transporters of the Glutamate/GABA-Glutamine Cycle and Their Impact on Insulin and Glucagon Secretion. Front Endocrinol (Lausanne) 2013; 4:199. [PMID: 24427154 PMCID: PMC3876026 DOI: 10.3389/fendo.2013.00199] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Accepted: 12/16/2013] [Indexed: 12/21/2022] Open
Abstract
Intercellular communication is pivotal in optimizing and synchronizing cellular responses to keep homeostasis and to respond adequately to external stimuli. In the central nervous system (CNS), glutamatergic and GABAergic signals are postulated to be dependent on the glutamate/GABA-glutamine cycle for vesicular loading of neurotransmitters, for inactivating the signal and for the replenishment of the neurotransmitters. Islets of Langerhans release the hormones insulin and glucagon, but share similarities with CNS cells in for example transcriptional control of development and differentiation, and chromatin methylation. Interestingly, CNS proteins involved in secretion of the neurotransmitters and emitting their responses as well as the regulation of these processes, are also found in islet cells. Moreover, high levels of glutamate, GABA, and glutamine and their respective vesicular and plasma membrane transporters have been shown in the islet cells and there is emerging support for these amino acids and their transporters playing important roles in the maturation and secretion of insulin and glucagon. In this review, we will discuss the feasibility of recent data in the field in relation to the biophysical properties of the transporters (Slc1, Slc17, Slc32, and Slc38) and physiology of hormone secretion in islets of Langerhans.
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Affiliation(s)
- Monica Jenstad
- Institute for Medical Informatics, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, University of Oslo, Oslo, Norway
- *Correspondence: Monica Jenstad, Institute for Medical Informatics, Oslo University Hospital, Radiumhospitalet, PO Box 4953 Nydalen, Oslo NO-0424, Norway e-mail:
| | - Farrukh Abbas Chaudhry
- Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
- The Biotechnology Centre of Oslo, University of Oslo, Oslo, Norway
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Peng L, Guo C, Wang T, Li B, Gu L, Wang Z. Methodological limitations in determining astrocytic gene expression. Front Endocrinol (Lausanne) 2013; 4:176. [PMID: 24324456 PMCID: PMC3839565 DOI: 10.3389/fendo.2013.00176] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Accepted: 10/31/2013] [Indexed: 01/15/2023] Open
Abstract
Traditionally, astrocytic mRNA and protein expression are studied by in situ hybridization (ISH) and immunohistochemically. This led to the concept that astrocytes lack aralar, a component of the malate-aspartate-shuttle. At least similar aralar mRNA and protein expression in astrocytes and neurons isolated by fluorescence-assisted cell sorting (FACS) reversed this opinion. Demonstration of expression of other astrocytic genes may also be erroneous. Literature data based on morphological methods were therefore compared with mRNA expression in cells obtained by recently developed methods for determination of cell-specific gene expression. All Na,K-ATPase-α subunits were demonstrated by immunohistochemistry (IHC), but there are problems with the cotransporter NKCC1. Glutamate and GABA transporter gene expression was well determined immunohistochemically. The same applies to expression of many genes of glucose metabolism, whereas a single study based on findings in bacterial artificial chromosome (BAC) transgenic animals showed very low astrocytic expression of hexokinase. Gene expression of the equilibrative nucleoside transporters ENT1 and ENT2 was recognized by ISH, but ENT3 was not. The same applies to the concentrative transporters CNT2 and CNT3. All were clearly expressed in FACS-isolated cells, followed by biochemical analysis. ENT3 was enriched in astrocytes. Expression of many nucleoside transporter genes were shown by microarray analysis, whereas other important genes were not. Results in cultured astrocytes resembled those obtained by FACS. These findings call for reappraisal of cellular nucleoside transporter expression. FACS cell yield is small. Further development of cell separation methods to render methods more easily available and less animal and cost consuming and parallel studies of astrocytic mRNA and protein expression by ISH/IHC and other methods are necessary, but new methods also need to be thoroughly checked.
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Affiliation(s)
- Liang Peng
- Department of Clinical Pharmacology, China Medical University, Shenyang, China
- *Correspondence: Liang Peng, College of Basic Medical Sciences, China Medical University, No. 92 Beier Road, Heping District, Shenyang 110001, China e-mail:
| | - Chuang Guo
- Institute of Neuroscience, College of Life and Health Sciences, Northeastern University, Shenyang, China
| | - Tao Wang
- Institute of Neuroscience, College of Life and Health Sciences, Northeastern University, Shenyang, China
| | - Baoman Li
- Department of Clinical Pharmacology, China Medical University, Shenyang, China
| | - Li Gu
- Department of Clinical Pharmacology, China Medical University, Shenyang, China
| | - Zhanyou Wang
- Institute of Neuroscience, College of Life and Health Sciences, Northeastern University, Shenyang, China
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28
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The SLC38 family of sodium-amino acid co-transporters. Pflugers Arch 2013; 466:155-72. [PMID: 24193407 DOI: 10.1007/s00424-013-1393-y] [Citation(s) in RCA: 157] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Revised: 10/16/2013] [Accepted: 10/20/2013] [Indexed: 12/13/2022]
Abstract
Transporters of the SLC38 family are found in all cell types of the body. They mediate Na(+)-dependent net uptake and efflux of small neutral amino acids. As a result they are particularly expressed in cells that grow actively, or in cells that carry out significant amino acid metabolism, such as liver, kidney and brain. SLC38 transporters occur in membranes that face intercellular space or blood vessels, but do not occur in the apical membrane of absorptive epithelia. In the placenta, they play a significant role in the transfer of amino acids to the foetus. Members of the SLC38 family are highly regulated in response to amino acid depletion, hypertonicity and hormonal stimuli. SLC38 transporters play an important role in amino acid signalling and have been proposed to act as transceptors independent of their transport function. The structure of SLC38 transporters is characterised by the 5 + 5 inverted repeat fold, which is observed in a wide variety of transport proteins.
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29
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Nissen-Meyer LSH, Chaudhry FA. Protein Kinase C Phosphorylates the System N Glutamine Transporter SN1 (Slc38a3) and Regulates Its Membrane Trafficking and Degradation. Front Endocrinol (Lausanne) 2013; 4:138. [PMID: 24106489 PMCID: PMC3788335 DOI: 10.3389/fendo.2013.00138] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Accepted: 09/16/2013] [Indexed: 01/11/2023] Open
Abstract
The system N transporter SN1 (also known as SNAT3) is enriched on perisynaptic astroglial cell membranes. SN1 mediates electroneutral and bidirectional glutamine transport, and regulates the intracellular as well as the extracellular concentrations of glutamine. We hypothesize that SN1 participates in the glutamate/γ-aminobutyric acid (GABA)-glutamine cycle and regulates the amount of glutamine supplied to the neurons for replenishment of the neurotransmitter pools of glutamate and GABA. We also hypothesize that its activity on the plasma membrane is regulated by protein kinase C (PKC)-mediated phosphorylation and that SN1 activity has an impact on synaptic plasticity. This review discusses reports on the regulation of SN1 by PKC and presents a consolidated model for regulation and degradation of SN1 and the subsequent functional implications. As SN1 function is likely also regulated by PKC-mediated phosphorylation in peripheral organs, the same mechanisms may, thus, have impact on e.g., pH regulation in the kidney, urea formation in the liver, and insulin secretion in the pancreas.
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Affiliation(s)
- Lise Sofie H. Nissen-Meyer
- The Biotechnology Centre, University of Oslo, Oslo, Norway
- The Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
- *Correspondence: Lise Sofie H. Nissen-Meyer and Farrukh Abbas Chaudhry, The Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1110 Blindern, 0317 Oslo, Norway e-mail: ;
| | - Farrukh Abbas Chaudhry
- The Biotechnology Centre, University of Oslo, Oslo, Norway
- The Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
- *Correspondence: Lise Sofie H. Nissen-Meyer and Farrukh Abbas Chaudhry, The Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1110 Blindern, 0317 Oslo, Norway e-mail: ;
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Wang Q, Tiffen J, Bailey CG, Lehman ML, Ritchie W, Fazli L, Metierre C, Feng YJ, Li E, Gleave M, Buchanan G, Nelson CC, Rasko JEJ, Holst J. Targeting amino acid transport in metastatic castration-resistant prostate cancer: effects on cell cycle, cell growth, and tumor development. J Natl Cancer Inst 2013; 105:1463-73. [PMID: 24052624 DOI: 10.1093/jnci/djt241] [Citation(s) in RCA: 129] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND L-type amino acid transporters (LATs) uptake neutral amino acids including L-leucine into cells, stimulating mammalian target of rapamycin complex 1 signaling and protein synthesis. LAT1 and LAT3 are overexpressed at different stages of prostate cancer, and they are responsible for increasing nutrients and stimulating cell growth. METHODS We examined LAT3 protein expression in human prostate cancer tissue microarrays. LAT function was inhibited using a leucine analog (BCH) in androgen-dependent and -independent environments, with gene expression analyzed by microarray. A PC-3 xenograft mouse model was used to study the effects of inhibiting LAT1 and LAT3 expression. Results were analyzed with the Mann-Whitney U or Fisher exact tests. All statistical tests were two-sided. RESULTS LAT3 protein was expressed at all stages of prostate cancer, with a statistically significant decrease in expression after 4-7 months of neoadjuvant hormone therapy (4-7 month mean = 1.571; 95% confidence interval = 1.155 to 1.987 vs 0 month = 2.098; 95% confidence interval = 1.962 to 2.235; P = .0187). Inhibition of LAT function led to activating transcription factor 4-mediated upregulation of amino acid transporters including ASCT1, ASCT2, and 4F2hc, all of which were also regulated via the androgen receptor. LAT inhibition suppressed M-phase cell cycle genes regulated by E2F family transcription factors including critical castration-resistant prostate cancer regulatory genes UBE2C, CDC20, and CDK1. In silico analysis of BCH-downregulated genes showed that 90.9% are statistically significantly upregulated in metastatic castration-resistant prostate cancer. Finally, LAT1 or LAT3 knockdown in xenografts inhibited tumor growth, cell cycle progression, and spontaneous metastasis in vivo. CONCLUSION Inhibition of LAT transporters may provide a novel therapeutic target in metastatic castration-resistant prostate cancer, via suppression of mammalian target of rapamycin complex 1 activity and M-phase cell cycle genes.
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Affiliation(s)
- Qian Wang
- Affiliations of authors: Origins of Cancer Laboratory (QW, JT, JH) and Gene & Stem Cell Therapy Program (QW, JT, CGB, WR, CM, YF, JEJR, JH), Centenary Institute, Camperdown, Australia; Sydney Medical School, University of Sydney, Sydney, Australia (QW, JT, CGB, WR, CM, YF, JEJR, JH); Vancouver Prostate Centre, Department of Urologic Sciences, University of British Columbia, Vancouver, BC, Canada (MLL, LF, EL, MG, CCN); Cancer Biology Group, Basil Hetzel Institute for Translational Health Research, University of Adelaide, Adelaide, Australia (GB); Australian Prostate Cancer Research Centre-Queensland, Queensland University of Technology, Brisbane, Australia (CCN, MLL); Cell and Molecular Therapies, Royal Prince Alfred Hospital, Camperdown, Australia (JEJR)
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Sidoryk-Wegrzynowicz M, Aschner M. Role of astrocytes in manganese mediated neurotoxicity. BMC Pharmacol Toxicol 2013; 14:23. [PMID: 23594835 PMCID: PMC3637816 DOI: 10.1186/2050-6511-14-23] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Accepted: 04/10/2013] [Indexed: 01/08/2023] Open
Abstract
Astrocytes are responsible for numerous aspects of metabolic support, nutrition, control of the ion and neurotransmitter environment in central nervous system (CNS). Failure by astrocytes to support essential neuronal metabolic requirements plays a fundamental role in the pathogenesis of brain injury and the ensuing neuronal death. Astrocyte-neuron interactions play a central role in brain homeostasis, in particular via neurotransmitter recycling functions. Disruption of the glutamine (Gln)/glutamate (Glu) -γ-aminobutyric acid (GABA) cycle (GGC) between astrocytes and neurons contributes to changes in Glu-ergic and/or GABA-ergic transmission, and is associated with several neuropathological conditions, including manganese (Mn) toxicity. In this review, we discuss recent advances in support of the important roles for astrocytes in normal as well as neuropathological conditions primarily those caused by exposure to Mn.
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Martínez-Lozada Z, Guillem AM, Flores-Méndez M, Hernández-Kelly LC, Vela C, Meza E, Zepeda RC, Caba M, Rodríguez A, Ortega A. GLAST/EAAT1-induced glutamine release via SNAT3 in Bergmann glial cells: evidence of a functional and physical coupling. J Neurochem 2013; 125:545-54. [PMID: 23418736 DOI: 10.1111/jnc.12211] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Revised: 10/11/2012] [Accepted: 02/15/2013] [Indexed: 01/26/2023]
Abstract
Glutamate, the major excitatory transmitter in the vertebrate brain, is removed from the synaptic cleft by a family of sodium-dependent glutamate transporters profusely expressed in glial cells. Once internalized, it is metabolized by glutamine synthetase to glutamine and released to the synaptic space through sodium-dependent neutral amino acid carriers of the N System (SNAT3/slc38a3/SN1, SNAT5/slc38a5/SN2). Glutamine is then taken up by neurons completing the so-called glutamate/glutamine shuttle. Despite of the fact that this coupling was described decades ago, it is only recently that the biochemical framework of this shuttle has begun to be elucidated. Using the established model of cultured cerebellar Bergmann glia cells, we sought to characterize the functional and physical coupling of glutamate uptake and glutamine release. A time-dependent Na⁺-dependent glutamate/aspartate transporter/EAAT1-induced System N-mediated glutamine release could be demonstrated. Furthermore, D-aspartate, a specific glutamate transporter ligand, was capable of enhancing the co-immunoprecipitation of Na⁺-dependent glutamate/aspartate transporter and Na⁺-dependent neutral amino acid transporter 3, whereas glutamine tended to reduce this association. Our results suggest that glial cells surrounding glutamatergic synapses may act as sensors of neuron-derived glutamate through their contribution to the neurotransmitter turnover.
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Affiliation(s)
- Zila Martínez-Lozada
- Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México D.F, México
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Häberle J, Shahbeck N, Ibrahim K, Schmitt B, Scheer I, O'Gorman R, Chaudhry FA, Ben-Omran T. Glutamine supplementation in a child with inherited GS deficiency improves the clinical status and partially corrects the peripheral and central amino acid imbalance. Orphanet J Rare Dis 2012; 7:48. [PMID: 22830360 PMCID: PMC3495849 DOI: 10.1186/1750-1172-7-48] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Accepted: 07/06/2012] [Indexed: 11/10/2022] Open
Abstract
Glutamine synthetase (GS) is ubiquitously expressed in mammalian organisms and is a key enzyme in nitrogen metabolism. It is the only known enzyme capable of synthesising glutamine, an amino acid with many critical roles in the human organism. A defect in GLUL, encoding for GS, leads to congenital systemic glutamine deficiency and has been described in three patients with epileptic encephalopathy. There is no established treatment for this condition.Here, we describe a therapeutic trial consisting of enteral and parenteral glutamine supplementation in a four year old patient with GS deficiency. The patient received increasing doses of glutamine up to 1020 mg/kg/day. The effect of this glutamine supplementation was monitored clinically, biochemically, and by studies of the electroencephalogram (EEG) as well as by brain magnetic resonance imaging and spectroscopy.Treatment was well tolerated and clinical monitoring showed improved alertness. Concentrations of plasma glutamine normalized while levels in cerebrospinal fluid increased but remained below the lower reference range. The EEG showed clear improvement and spectroscopy revealed increasing concentrations of glutamine and glutamate in brain tissue. Concomitantly, there was no worsening of pre-existing chronic hyperammonemia.In conclusion, supplementation of glutamine is a safe therapeutic option for inherited GS deficiency since it corrects the peripheral biochemical phenotype and partially also improves the central biochemical phenotype. There was some clinical improvement but the patient had a long standing severe encephalopathy. Earlier supplementation with glutamine might have prevented some of the neuronal damage.
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Affiliation(s)
- Johannes Häberle
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland.
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Hamdani EH, Gudbrandsen M, Bjørkmo M, Chaudhry FA. The system N transporter SN2 doubles as a transmitter precursor furnisher and a potential regulator of NMDA receptors. Glia 2012; 60:1671-83. [PMID: 22821889 DOI: 10.1002/glia.22386] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 06/14/2012] [Accepted: 06/15/2012] [Indexed: 12/28/2022]
Abstract
Activation of NMDA receptor requires two co-agonists, glutamate and glycine. Despite its intrinsic role in brain functions molecular mechanisms involved in glutamate replenishment and identification of the origin of glycine have eluded characterization. We have performed direct measurements of glycine flux by SN2 (Slc38a5; also known as SNAT5), executed extensive electrophysiological characterization as well as implemented ratiometric analyses to show that SN2 transport resembles SN1 in mechanism but differ in functional implications. We report that rat SN2 mediates electroneutral and bidirectional transport of glutamine and glycine at perisynaptic astroglial membranes. Sophisticated coupled and uncoupled movements of H(+) differentially associate with glutamine and glycine transport by SN2 and regulate pH(i) and the release mode of the transporter. Consequently, SN2 doubles as a transmitter precursor furnisher and a potential regulator of NMDA receptors.
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Affiliation(s)
- El Hassan Hamdani
- The Biotechnology Center and Center for Molecular Biology and Neuroscience, University of Oslo, Blindern, Oslo, Norway
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35
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Visualization of glutamine transporter activities in living cells using genetically encoded glutamine sensors. PLoS One 2012; 7:e38591. [PMID: 22723868 PMCID: PMC3375291 DOI: 10.1371/journal.pone.0038591] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Accepted: 05/08/2012] [Indexed: 11/19/2022] Open
Abstract
Glutamine plays a central role in the metabolism of critical biological molecules such as amino acids, proteins, neurotransmitters, and glutathione. Since glutamine metabolism is regulated through multiple enzymes and transporters, the cellular glutamine concentration is expected to be temporally dynamic. Moreover, differentiation in glutamine metabolism between cell types in the same tissue (e.g. neuronal and glial cells) is often crucial for the proper function of the tissue as a whole, yet assessing cell-type specific activities of transporters and enzymes in such heterogenic tissue by physical fractionation is extremely challenging. Therefore, a method of reporting glutamine dynamics at the cellular level is highly desirable. Genetically encoded sensors can be targeted to a specific cell type, hence addressing this knowledge gap. Here we report the development of Föster Resonance Energy Transfer (FRET) glutamine sensors based on improved cyan and yellow fluorescent proteins, monomeric Teal Fluorescent Protein (mTFP)1 and venus. These sensors were found to be specific to glutamine, and stable to pH-changes within a physiological range. Using cos7 cells expressing the human glutamine transporter ASCT2 as a model, we demonstrate that the properties of the glutamine transporter can easily be analyzed with these sensors. The range of glutamine concentration change in a given cell can also be estimated using sensors with different affinities. Moreover, the mTFP1-venus FRET pair can be duplexed with another FRET pair, mAmetrine and tdTomato, opening up the possibility for real-time imaging of another molecule. These novel glutamine sensors will be useful tools to analyze specificities of glutamine metabolism at the single-cell level.
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36
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Mechanism of proton/substrate coupling in the heptahelical lysosomal transporter cystinosin. Proc Natl Acad Sci U S A 2012; 109:E210-7. [PMID: 22232659 DOI: 10.1073/pnas.1115581109] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Secondary active transporters use electrochemical gradients provided by primary ion pumps to translocate metabolites or drugs "uphill" across membranes. Here we report the ion-coupling mechanism of cystinosin, an unusual eukaryotic, proton-driven transporter distantly related to the proton pump bacteriorhodopsin. In humans, cystinosin exports the proteolysis-derived dimeric amino acid cystine from lysosomes and is impaired in cystinosis. Using voltage-dependence analysis of steady-state and transient currents elicited by cystine and neutralization-scanning mutagenesis of conserved protonatable residues, we show that cystine binding is coupled to protonation of a clinically relevant aspartate buried in the membrane. Deuterium isotope substitution experiments are consistent with an access of this aspartate from the lysosomal lumen through a deep proton channel. This aspartate lies in one of the two PQ-loop motifs shared by cystinosin with a set of eukaryotic membrane proteins of unknown function and is conserved in about half of them, thus suggesting that other PQ-loop proteins may translocate protons.
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37
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Abstract
Glutamine (Gln) is found abundantly in the central nervous system (CNS) where it participates in a variety of metabolic pathways. Its major role in the brain is that of a precursor of the neurotransmitter amino acids: the excitatory amino acids, glutamate (Glu) and aspartate (Asp), and the inhibitory amino acid, γ-amino butyric acid (GABA). The precursor-product relationship between Gln and Glu/GABA in the brain relates to the intercellular compartmentalization of the Gln/Glu(GABA) cycle (GGC). Gln is synthesized from Glu and ammonia in astrocytes, in a reaction catalyzed by Gln synthetase (GS), which, in the CNS, is almost exclusively located in astrocytes (Martinez-Hernandez et al., 1977). Newly synthesized Gln is transferred to neurons and hydrolyzed by phosphate-activated glutaminase (PAG) to give rise to Glu, a portion of which may be decarboxylated to GABA or transaminated to Asp. There is a rich body of evidence which indicates that a significant proportion of the Glu, Asp and GABA derived from Gln feed the synaptic, neurotransmitter pools of the amino acids. Depolarization-induced-, calcium- and PAG activity-dependent releases of Gln-derived Glu, GABA and Asp have been observed in CNS preparations in vitro and in the brain in situ. Immunocytochemical studies in brain slices have documented Gln transfer from astrocytes to neurons as well as the location of Gln-derived Glu, GABA and Asp in the synaptic terminals. Patch-clamp studies in brain slices and astrocyte/neuron co-cultures have provided functional evidence that uninterrupted Gln synthesis in astrocytes and its transport to neurons, as mediated by specific carriers, promotes glutamatergic and GABA-ergic transmission. Gln entry into the neuronal compartment is facilitated by its abundance in the extracellular spaces relative to other amino acids. Gln also appears to affect neurotransmission directly by interacting with the NMDA class of Glu receptors. Transmission may also be modulated by alterations in cell membrane polarity related to the electrogenic nature of Gln transport or to uncoupled ion conductances in the neuronal or glial cell membranes elicited by Gln transporters. In addition, Gln appears to modulate the synthesis of the gaseous messenger, nitric oxide (NO), by controlling the supply to the cells of its precursor, arginine. Disturbances of Gln metabolism and/or transport contribute to changes in Glu-ergic or GABA-ergic transmission associated with different pathological conditions of the brain, which are best recognized in epilepsy, hepatic encephalopathy and manganese encephalopathy.
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Protein kinase C-mediated phosphorylation of a single serine residue on the rat glial glutamine transporter SN1 governs its membrane trafficking. J Neurosci 2011; 31:6565-75. [PMID: 21525297 DOI: 10.1523/jneurosci.3694-10.2011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Molecular mechanisms involved in the replenishment of the fast neurotransmitters glutamate and GABA are poorly understood. Glutamine sustains their generation. However, glutamine formation from the recycled transmitters is confined to glial processes and requires facilitators for its translocation across the glial and neuronal membranes. Indeed, glial processes are enriched with the system N transporter SN1 (Slc38a3), which, by bidirectional transport, maintains steady extracellular glutamine levels and thereby furnishes neurons with the primary precursor for fast neurotransmitters. We now demonstrate that SN1 is phosphorylated by protein kinase Cα (PKCα) and PKCγ. Electrophysiological characterization shows that phosphorylation reduces V(max) dramatically, whereas no significant effects are seen on the K(m). Phosphorylation occurs specifically at a single serine residue (S52) in the N-terminal rat (Rattus norvegicus) SN1 and results in sequestration of the protein into intracellular reservoirs. Prolonged activation of PKC results in partial degradation of SN1. These results provide the first demonstration of phosphorylation of SN1 and regulation of its activity at the plasma membrane. Interestingly, membrane trafficking of SN1 resembles that of the glutamate transporter GLT and the glutamate-aspartate transporter GLAST: it involves the same PKC isoforms and occurs in the same glial processes. This suggests that the glutamate/GABA-glutamine cycle may be modified at two key points by similar signaling events and unmasks a prominent role for PKC-dependent phosphorylation. Our data suggest that extracellular glutamine levels may be fine-tuned by dynamic regulation of glial SN1 activity, which may impact on transmitter generation, contribute to defining quantal size, and have profound effects on synaptic plasticity.
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The C-terminal domain of the neutral amino acid transporter SNAT2 regulates transport activity through voltage-dependent processes. Biochem J 2011; 434:287-96. [PMID: 21158741 DOI: 10.1042/bj20100507] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
SNAT (sodium-coupled neutral amino acid transporter) 2 belongs to the SLC38 (solute carrier 38) family of solute transporters. Transport of one amino acid molecule into the cell is driven by the co-transport of one Na(+) ion. The functional significance of the C-terminus of SNAT2, which is predicted to be located in the extracellular space, is currently unknown. In the present paper, we removed 13 amino acid residues from the SNAT2 C-terminus and studied the effect of this deletion on transporter function. The truncation abolished amino acid transport currents at negative membrane potentials (<0 mV), as well as substrate uptake. However, transport currents were observed at positive membrane potentials demonstrating that transport was accelerated while the driving force decreased. Membrane expression levels were normal in the truncated transporter. SNAT2(Del C-ter) (13 residues deleted from the C-terminus) showed 3-fold higher apparent affinity for alanine, and 2-fold higher Na(+) affinity compared with wild-type SNAT2, suggesting that the C-terminus is not required for high-affinity substrate and Na(+) interaction with SNAT2. The pH sensitivity of amino acid transport was retained partially after the truncation. In contrast with the truncation after TM (transmembrane domain) 11, the deletion of TM11 resulted in an inactive transporter, most probably due to a defect in cell surface expression. Taken together, the results demonstrate that the C-terminal domain of SNAT2 is an important voltage regulator that is required for a normal amino acid translocation process at physiological membrane potentials. However, the C-terminus appears not to be involved in the regulation of membrane expression.
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Solbu TT, Bjørkmo M, Berghuis P, Harkany T, Chaudhry FA. SAT1, A Glutamine Transporter, is Preferentially Expressed in GABAergic Neurons. Front Neuroanat 2010; 4:1. [PMID: 20161990 PMCID: PMC2820376 DOI: 10.3389/neuro.05.001.2010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Accepted: 12/30/2009] [Indexed: 11/13/2022] Open
Abstract
Subsets of GABAergic neurons are able to maintain high frequency discharge patterns, which requires efficient replenishment of the releasable pool of GABA. Although glutamine is considered a preferred precursor of GABA, the identity of transporters involved in glutamine uptake by GABAergic neurons remains elusive. Molecular analyses revealed that SAT1 (Slc38a1) features system A characteristics with a preferential affinity for glutamine, and that SAT1 mRNA expression is associated with GABAergic neurons. By generating specific antibodies against SAT1 we show that this glutamine carrier is particularly enriched in GABAergic neurons. Cellular SAT1 distribution resembles that of GAD67, an essential GABA synthesis enzyme, suggesting that SAT1 can be involved in translocating glutamine into GABAergic neurons to facilitate inhibitory neurotransmitter generation.
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Affiliation(s)
- Tom Tallak Solbu
- The Biotechnology Centre of Oslo, University of Oslo Oslo, Norway
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41
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Bröer S, Schneider HP, Bröer A, Deitmer JW. Mutation of asparagine 76 in the center of glutamine transporter SNAT3 modulates substrate-induced conductances and Na+ binding. J Biol Chem 2009; 284:25823-31. [PMID: 19596860 PMCID: PMC2757984 DOI: 10.1074/jbc.m109.031013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2009] [Revised: 07/08/2009] [Indexed: 11/06/2022] Open
Abstract
The glutamine transporter SLC38A3 (SNAT3) plays an important role in the release of glutamine from brain astrocytes and the uptake of glutamine into hepatocytes. It is related to the vesicular GABA (gamma-aminobutyric acid) transporter and the SLC36 family of proton-amino acid cotransporters. The transporter carries out electroneutral Na+-glutamine cotransport-H+ antiport. In addition, substrate-induced uncoupled cation currents are observed. Mutation of asparagine 76 to glutamine or histidine in predicted transmembrane helix 1 abolished all substrate-induced currents. Mutation of asparagine 76 to aspartate rendered the transporter Na+-independent and resulted in a gain of a large substrate-induced chloride conductance in the absence of Na+. Thus, a single residue is critical for coupled and uncoupled ion flows in the glutamine transporter SNAT3. Homology modeling of SNAT3 along the structure of the related benzyl-hydantoin permease from Microbacterium liquefaciens reveals that Asn-76 is likely to be located in the center of the membrane close to the translocation pore and forms part of the predicted Na+ -binding site.
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Affiliation(s)
- Stefan Bröer
- From the Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia and
| | - Hans-Peter Schneider
- the Abteilung für Allgemeine Zoologie, Fachbereich Biologie, Technische Universität Kaiserslautern, Erwin-Schrödinger Strasse, D-67653 Kaiserslautern, Germany
| | - Angelika Bröer
- From the Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia and
| | - Joachim W. Deitmer
- the Abteilung für Allgemeine Zoologie, Fachbereich Biologie, Technische Universität Kaiserslautern, Erwin-Schrödinger Strasse, D-67653 Kaiserslautern, Germany
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42
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Blot A, Billups D, Bjørkmo M, Quazi AZ, Uwechue NM, Chaudhry FA, Billups B. Functional expression of two system A glutamine transporter isoforms in rat auditory brainstem neurons. Neuroscience 2009; 164:998-1008. [PMID: 19751803 PMCID: PMC2789247 DOI: 10.1016/j.neuroscience.2009.09.015] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Revised: 08/26/2009] [Accepted: 09/04/2009] [Indexed: 01/11/2023]
Abstract
Glutamine plays multiple roles in the CNS, including metabolic functions and production of the neurotransmitters glutamate and GABA. It has been proposed to be taken up into neurons via a variety of membrane transport systems, including system A, which is a sodium-dependent electrogenic amino acid transporter system. In this study, we investigate glutamine transport by application of amino acids to individual principal neurons of the medial nucleus of the trapezoid body (MNTB) in acutely isolated rat brain slices. A glutamine transport current was studied in patch-clamped neurons, which had the electrical and pharmacological properties of system A: it was sodium-dependent, had a non-reversing current-voltage relationship, was activated by proline, occluded by N-(methylamino)isobutyric acid (MeAIB), and was unaffected by 2-aminobicyclo-[2.2.1]-heptane-2-carboxylic acid (BCH). Additionally, we examined the expression of different system A transporter isoforms using immunocytochemical staining with antibodies raised against system A transporter 1 and 2 (SAT1 and SAT2). Our results indicate that both isoforms are expressed in MNTB principal neurons, and demonstrate that functional system A transporters are present in the plasma membrane of neurons. Since system A transport is highly regulated by a number of cellular signaling mechanisms and glutamine then goes on to activate other pathways, the study of these transporters in situ gives an indication of the mechanisms of neuronal glutamine supply as well as points of regulation of neurotransmitter production, cellular signaling and metabolism in the native neuronal environment.
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Affiliation(s)
- A Blot
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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43
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Zhang Z, Albers T, Fiumera HL, Gameiro A, Grewer C. A conserved Na(+) binding site of the sodium-coupled neutral amino acid transporter 2 (SNAT2). J Biol Chem 2009; 284:25314-23. [PMID: 19589777 PMCID: PMC2757233 DOI: 10.1074/jbc.m109.038422] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Revised: 07/08/2009] [Indexed: 11/06/2022] Open
Abstract
The SLC38 family of solute transporters mediates the coupled transport of amino acids and Na(+) into or out of cells. The structural basis for this coupled transport process is not known. Here, a profile-based sequence analysis approach was used, predicting a distant relationship with the SLC5/6 transporter families. Homology models using the LeuT(Aa) and Mhp1 transporters of known structure as templates were established, predicting the location of a conserved Na(+) binding site in the center of membrane helices 1 and 8. This homology model was tested experimentally in the SLC38 member SNAT2 by analyzing the effect of a mutation to Thr-384, which is predicted to be part of this Na(+) binding site. The results show that the T384A mutation not only inhibits the anion leak current, which requires Na(+) binding to SNAT2, but also dramatically lowers the Na(+) affinity of the transporter. This result is consistent with a previous analysis of the N82A mutant transporter, which has a similar effect on anion leak current and Na(+) binding and which is also expected to form part of the Na(+) binding site. In contrast, random mutations to other sites in the transporter had little or no effect on Na(+) affinity. Our results are consistent with a cation binding site formed by transmembrane helices 1 and 8 that is conserved among the SLC38 transporters as well as among many other bacterial and plant transporter families of unknown structure, which are homologous to SLC38.
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Affiliation(s)
- Zhou Zhang
- From the College of Life and Environment Sciences, Shanghai Normal University, 100 Guilin Road, Shanghai 200234, China and
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44
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Gammelsaeter R, Jenstad M, Bredahl MKL, Gundersen V, Chaudhry FA. Complementary expression of SN1 and SAT2 in the islets of Langerhans suggests concerted action of glutamine transport in the regulation of insulin secretion. Biochem Biophys Res Commun 2009; 381:378-82. [PMID: 19233140 DOI: 10.1016/j.bbrc.2009.02.062] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Accepted: 02/11/2009] [Indexed: 11/29/2022]
Abstract
Insulin and glucagon secretion from the islets of Langerhans is highly regulated. Although an increased plasma glucose level is the major stimulus for insulin exocytosis, roles for glutamine and glutamate have been suggested. Interestingly, the islet cells display elements associated with synaptic transmission. In the central nervous system (CNS), glutamine transport by SN1 and SAT2 sustain the generation of neurotransmitter glutamate. We hypothesized that the same transporters are essential for glutamine transport into the islet cells and for subsequent formation of glutamate acting as an intracellular signaling molecule. We demonstrate that islet cells express several transporters which can mediate glutamine transport. In particular, we show pronounced expression of SN1 and SAT2 in B-cells and A-cells, respectively. The cell-specific expression of these transporters together with their functional characteristics suggest an important role for glutamine in the regulation of insulin secretion.
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Affiliation(s)
- R Gammelsaeter
- The Centre for Molecular Biology and Neuroscience, University of Oslo, N-0317 Oslo, Norway
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45
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Ramadoss J, Wu G, Cudd TA. Chronic binge ethanol-mediated acidemia reduces availability of glutamine and related amino acids in maternal plasma of pregnant sheep. Alcohol 2008; 42:657-66. [PMID: 19038697 DOI: 10.1016/j.alcohol.2008.08.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2008] [Revised: 07/29/2008] [Accepted: 08/18/2008] [Indexed: 10/21/2022]
Abstract
Heavy drinking during pregnancy can result in fetal alcohol syndrome (FAS), of which, fetal and postnatal growth retardation and central nervous system deficits are cardinal features. Although a number of mechanisms have been proposed, none fully account for these deficiencies. We have previously reported that maternal ethanol exposure (1.75 g/kg) results in transient acidemia in the mother and fetus. Alterations in pH are known to regulate glutamine homeostasis. Therefore, we hypothesized that chronic binge ethanol-mediated acidosis reduces glutamine concentrations in maternal plasma that result in decreases in the circulating levels of amino acids related to glutamine metabolism. Pregnant ewes were divided into three groups: ethanol (1.75 g/kg), saline control, and acidemia (inspired fractional carbon dioxide [CO(2)] was manipulated to mimic the maternal arterial pH pattern created by ethanol). The experiment was conducted on three consecutive days followed by four days without treatment beginning on gestational day (GD) 109, continuing to GD 132. Plasma samples were analyzed for nutrients and metabolites using HPLC and spectrophotometric methods. Maternal plasma concentrations of glutamate increased (58%), whereas glutamine, citrulline, and arginine decreased (between 14 and 53%) in response to an acute challenge after the chronic exposure in ethanol-treated ewes. No differences in these amino acid concentrations were noted between the ethanol and acidemic group subjects. Maternal plasma lactate levels increased by approximately 100% in response to ethanol, whereas glucose and urea levels did not change in any group. We conclude that maternal chronic binge ethanol consumption results in acidosis-mediated reductions in circulating levels of glutamine and related amino acids that could be responsible for neuronal deficits, altered fetal growth, development, and programming. We also speculate that the consequent increase in fetal glutamate during critical periods of brain development may contribute to the pathogenesis of FAS.
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Jenstad M, Quazi AZ, Zilberter M, Haglerød C, Berghuis P, Saddique N, Goiny M, Buntup D, Davanger S, S Haug FM, Barnes CA, McNaughton BL, Ottersen OP, Storm-Mathisen J, Harkany T, Chaudhry FA. System A transporter SAT2 mediates replenishment of dendritic glutamate pools controlling retrograde signaling by glutamate. ACTA ACUST UNITED AC 2008; 19:1092-106. [PMID: 18832333 DOI: 10.1093/cercor/bhn151] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Glutamate mediates several modes of neurotransmission in the central nervous system including recently discovered retrograde signaling from neuronal dendrites. We have previously identified the system N transporter SN1 as being responsible for glutamine efflux from astroglia and proposed a system A transporter (SAT) in subsequent transport of glutamine into neurons for neurotransmitter regeneration. Here, we demonstrate that SAT2 expression is primarily confined to glutamatergic neurons in many brain regions with SAT2 being predominantly targeted to the somatodendritic compartments in these neurons. SAT2 containing dendrites accumulate high levels of glutamine. Upon electrical stimulation in vivo and depolarization in vitro, glutamine is readily converted to glutamate in activated dendritic subsegments, suggesting that glutamine sustains release of the excitatory neurotransmitter via exocytosis from dendrites. The system A inhibitor MeAIB (alpha-methylamino-iso-butyric acid) reduces neuronal uptake of glutamine with concomitant reduction in intracellular glutamate concentrations, indicating that SAT2-mediated glutamine uptake can be a prerequisite for the formation of glutamate. Furthermore, MeAIB inhibited retrograde signaling from pyramidal cells in layer 2/3 of the neocortex by suppressing inhibitory inputs from fast-spiking interneurons. In summary, we demonstrate that SAT2 maintains a key metabolic glutamine/glutamate balance underpinning retrograde signaling by dendritic release of the neurotransmitter glutamate.
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Affiliation(s)
- Monica Jenstad
- The Biotechnology Centre of Oslo, University of Oslo, N-0317 Oslo, Norway
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Kolbaev S, Draguhn A. Glutamine-induced membrane currents in cultured rat hippocampal neurons. Eur J Neurosci 2008; 28:535-45. [DOI: 10.1111/j.1460-9568.2008.06365.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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48
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SLC9A6 mutations cause X-linked mental retardation, microcephaly, epilepsy, and ataxia, a phenotype mimicking Angelman syndrome. Am J Hum Genet 2008; 82:1003-10. [PMID: 18342287 PMCID: PMC2427207 DOI: 10.1016/j.ajhg.2008.01.013] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2007] [Revised: 12/20/2007] [Accepted: 01/09/2008] [Indexed: 12/20/2022] Open
Abstract
Linkage analysis and DNA sequencing in a family exhibiting an X-linked mental retardation (XLMR) syndrome, characterized by microcephaly, epilepsy, ataxia, and absent speech and resembling Angelman syndrome, identified a deletion in the SLC9A6 gene encoding the Na(+)/H(+) exchanger NHE6. Subsequently, other mutations were found in a male with mental retardation (MR) who had been investigated for Angelman syndrome and in two XLMR families with epilepsy and ataxia, including the family designated as having Christianson syndrome. Therefore, mutations in SLC9A6 cause X-linked mental retardation. Additionally, males with findings suggestive of unexplained Angelman syndrome should be considered as potential candidates for SLC9A6 mutations.
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49
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Obara M, Szeliga M, Albrecht J. Regulation of pH in the mammalian central nervous system under normal and pathological conditions: facts and hypotheses. Neurochem Int 2007; 52:905-19. [PMID: 18061308 DOI: 10.1016/j.neuint.2007.10.015] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Revised: 10/17/2007] [Accepted: 10/22/2007] [Indexed: 11/27/2022]
Abstract
The maintenance of pH homeostasis in the CNS is of key importance for proper execution and regulation of neurotransmission, and deviations from this homeostasis are a crucial factor in the mechanism underlying a spectrum of pathological conditions. The first few sections of the review are devoted to the brain operating under normal conditions. The article commences with an overview of how extrinsic factors modelling the brain at work: neurotransmitters, depolarising stimuli (potassium and voltage changes) and cyclic nucleotides as major signal transducing vehicles affect pH in the CNS. Further, consequences of pH alterations on the major aspects of CNS function and metabolism are outlined. Next, the major cellular events involved in the transport, sequestration, metabolic production and buffering of protons that are common to all the mammalian cells, including the CNS cells. Since CNS function reflects tight interaction between astrocytes and neurons, the pH regulatory events pertinent to either cell type are discussed: overwhelming evidence implicates astrocytes as a key player in pH homeostasis in the brain. The different classes of membrane proteins involved in proton shuttling are listed and their mechanisms of action are given. These include: the Na+/H+ exchanger, different classes of bicarbonate transporters acting in a sodium-dependent- or -independent mode, monocarboxylic acid transporters and the vacuolar-type proton ATPase. A separate section is devoted to carbonic anhydrase, which is represented by multiple isoenzymes capable of pH buffering both in the cell interior and in the extracellular space. Next, impairment of pH regulation and compensatory responses occurring in brain affected by different pathologies: hypoxia/ischemia, epilepsy, hyperammonemic encephalopathies, cerebral tumours and HIV will be described. The review is limited to facts and plausible hypotheses pertaining to phenomena directly involved in pH regulation: changes in pH that accompany metabolic stress but have no distinct implications for the pH regulatory mechanisms are not dealt with. In most cases, the vast body of knowledge derived from in vitro studies remains to be verified in in vivo settings.
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Affiliation(s)
- Marta Obara
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, 5 Pawińskiego Street, 02-106 Warsaw, Poland
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Weise A, Becker HM, Deitmer JW. Enzymatic suppression of the membrane conductance associated with the glutamine transporter SNAT3 expressed in Xenopus oocytes by carbonic anhydrase II. ACTA ACUST UNITED AC 2007; 130:203-15. [PMID: 17664347 PMCID: PMC2151638 DOI: 10.1085/jgp.200709809] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The transport activity of the glutamine/neutral amino acid transporter SNAT3 (former SN1, SLC38A3), expressed in oocytes of the frog Xenopus laevis is associated with a non-stoichiometrical membrane conductance selective for Na+ and/or H+ (Schneider, H.P., S. Bröer, A. Bröer, and J.W. Deitmer. 2007. J. Biol. Chem. 282:3788–3798). When we expressed SNAT3 in frog oocytes, the glutamine-induced membrane conductance was suppressed, when carbonic anhydrase isoform II (CAII) had been injected into the oocytes. Transport of substrate, however, was not affected by CAII. The reduction of the membrane conductance by CAII was dependent on the presence of CO2/HCO3−, and could be reversed by blocking the catalytic activity of CAII by ethoxyzolamide (10 μM). Coexpression of wild-type CAII or a N-terminal CAII mutant with SNAT3 also reduced the SNAT3- associated membrane conductance. The catalytically inactive CAII mutant V143Y coexpressed in oocytes did not affect SNAT3-associated membrane conductance. Our results reveal a new type of interaction between CAII and a transporter-associated cation conductance, and support the hypothesis that the transport of substrate and the non-stoichiometrical ion conductance are independent of each other. This study also emphasizes the importance of carbonic anhydrase activity and the presence of CO2-bicarbonate buffers for membrane transport processes.
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Affiliation(s)
- Alexandra Weise
- Abteilung für Allgemeine Zoologie, FB Biologie, Universitaet Kaiserslautern, D-67653 Kaiserslautern, Germany
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