1
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Lo HH, Munkongcharoen T, Muijen RM, Gurung R, Umredkar AG, Baker MD. Application of near infra-red laser light increases current threshold in optic nerve consistent with increased Na +-dependent transport. Pflugers Arch 2024; 476:847-859. [PMID: 38421407 PMCID: PMC11033230 DOI: 10.1007/s00424-024-02932-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 02/06/2024] [Accepted: 02/22/2024] [Indexed: 03/02/2024]
Abstract
Increases in the current threshold occur in optic nerve axons with the application of infra-red laser light, whose mechanism is only partly understood. In isolated rat optic nerve, laser light was applied near the site of electrical stimulation, via a flexible fibre optic. Paired applications of light produced increases in threshold that were reduced on the second application, the response recovering with increasing delays, with a time constant of 24 s. 3-min duration single applications of laser light gave rise to a rapid increase in threshold followed by a fade, whose time-constant was between 40 and 50 s. After-effects were sometimes apparent following the light application, where the resting threshold was reduced. The increase in threshold was partially blocked by 38.6 mM Li+ in combination with 5 μ M bumetanide, a manoeuvre increasing refractoriness and consistent with axonal depolarization. Assessing the effect of laser light on the nerve input resistance ruled out a previously suggested fall in myelin resistance as contributing to threshold changes. These data appear consistent with an axonal membrane potential that partly relies on temperature-dependent electroneutral Na+ influx, and where fade in the response to the laser may be caused by a gradually diminishing Na+ pump-induced hyperpolarization, in response to falling intracellular [Na+].
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Affiliation(s)
- Hin Heng Lo
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Tawan Munkongcharoen
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Rosa M Muijen
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Ritika Gurung
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Anjali G Umredkar
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Mark D Baker
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK.
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2
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Jiang Q, Sherlock DN, Guyader J, Loor JJ. Abundance of Amino Acid Transporters and mTOR Pathway Components in the Gastrointestinal Tract of Lactating Holstein Cows. Animals (Basel) 2023; 13:ani13071189. [PMID: 37048445 PMCID: PMC10093496 DOI: 10.3390/ani13071189] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Revised: 03/25/2023] [Accepted: 03/27/2023] [Indexed: 03/31/2023] Open
Abstract
Data from non-ruminants indicate that amino acid (AA) transport into cells can regulate mTOR pathway activity and protein synthesis. Whether mTOR is expressed in the ruminant gastrointestinal tract (GIT) and how it may be related to AA transporters and the AA concentrations in the tissue is unknown. Ruminal papillae and the epithelia of the duodenum, jejunum, and ileum collected at slaughter from eight clinically healthy Holstein in mid-lactation were used. Metabolites and RNA were extracted from tissue for liquid chromatography–mass spectrometry and RT-qPCR analysis. The glycine and asparagine concentrations in the rumen were greater than those in the intestine (p < 0.05), but the concentrations of other AAs were greater in the small intestine than those in the rumen. Among the 20 AAs identified, the concentrations of glutamate, alanine, and glycine were the greatest. The mRNA abundances of AKT1 and MTOR were greater in the small intestine than those in the rumen (p < 0.05). Similarly, the SLC1A1, SLC6A6, SLC7A8, SLC38A1, SLC38A7, and SLC43A2 mRNA abundances were greater (p < 0.05) in the small intestine than those in the rumen. The mRNA abundances of SLC1A5, SLC3A2, and SLC7A5 were greater in the rumen than those in the small intestine (p < 0.05). Overall, the present study provides fundamental data on the relationship between mTOR pathway components and the transport of AAs in different sections of the gastrointestinal tract.
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Affiliation(s)
- Qianming Jiang
- Department of Animal Sciences, University of Illinois, Urbana, IL 61801, USA
| | | | - Jessie Guyader
- Evonik Operations GmbH, Hanau-Wolfgang, 63457 Essen, Germany
| | - Juan J. Loor
- Department of Animal Sciences, University of Illinois, Urbana, IL 61801, USA
- Division of Nutritional Sciences, University of Illinois, Urbana, IL 61801, USA
- Correspondence:
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3
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Smirnova EV, Rakitina TV, Ziganshin RH, Saratov GA, Arapidi GP, Belogurov AA, Kudriaeva AA. Identification of Myelin Basic Protein Proximity Interactome Using TurboID Labeling Proteomics. Cells 2023; 12:cells12060944. [PMID: 36980286 PMCID: PMC10047773 DOI: 10.3390/cells12060944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/14/2023] [Accepted: 03/16/2023] [Indexed: 03/30/2023] Open
Abstract
Myelin basic protein (MBP) is one of the key structural elements of the myelin sheath and has autoantigenic properties in multiple sclerosis (MS). Its intracellular interaction network is still partially deconvoluted due to the unfolded structure, abnormally basic charge, and specific cellular localization. Here we used the fusion protein of MBP with TurboID, an engineered biotin ligase that uses ATP to convert biotin to reactive biotin-AMP that covalently attaches to nearby proteins, to determine MBP interactome. Despite evident benefits, the proximity labeling proteomics technique generates high background noise, especially in the case of proteins tending to semi-specific interactions. In order to recognize unique MBP partners, we additionally mapped protein interaction networks for deaminated MBP variant and cyclin-dependent kinase inhibitor 1 (p21), mimicking MBP in terms of natively unfolded state, size and basic amino acid clusters. We found that in the plasma membrane region, MBP is colocalized with adhesion proteins occludin and myelin protein zero-like protein 1, solute carrier family transporters ZIP6 and SNAT1, Eph receptors ligand Ephrin-B1, and structural components of the vesicle transport machinery-synaptosomal-associated protein 23 (SNAP23), vesicle-associated membrane protein 3 (VAMP3), protein transport protein hSec23B and cytoplasmic dynein 1 heavy chain 1. We also detected that MBP potentially interacts with proteins involved in Fe2+ and lipid metabolism, namely, ganglioside GM2 activator protein, long-chain-fatty-acid-CoA ligase 4 (ACSL4), NADH-cytochrome b5 reductase 1 (CYB5R1) and metalloreductase STEAP3. Assuming the emerging role of ferroptosis and vesicle cargo docking in the development of autoimmune neurodegeneration, MBP may recruit and regulate the activity of these processes, thus, having a more inclusive role in the integrity of the myelin sheath.
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Affiliation(s)
- Evgeniya V Smirnova
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
| | - Tatiana V Rakitina
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
| | - Rustam H Ziganshin
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
| | - George A Saratov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
- Phystech School of Biological and Medical Physics, Moscow Institute of Physics and Technology (National Research University), 141701 Dolgoprudny, Russia
| | - Georgij P Arapidi
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
- Phystech School of Biological and Medical Physics, Moscow Institute of Physics and Technology (National Research University), 141701 Dolgoprudny, Russia
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, 119435 Moscow, Russia
| | - Alexey A Belogurov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
- Department of Biological Chemistry, Evdokimov Moscow State University of Medicine and Dentistry, Ministry of Health of Russian Federation, 127473 Moscow, Russia
| | - Anna A Kudriaeva
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia
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Castillo-Castrejon M, Yamaguchi K, Rodel RL, Erickson K, Kramer A, Hirsch NM, Rolloff K, Jansson T, Barbour LA, Powell TL. Effect of type 2 diabetes mellitus on placental expression and activity of nutrient transporters and their association with birth weight and neonatal adiposity. Mol Cell Endocrinol 2021; 532:111319. [PMID: 33989714 PMCID: PMC8206039 DOI: 10.1016/j.mce.2021.111319] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 05/06/2021] [Accepted: 05/07/2021] [Indexed: 11/19/2022]
Abstract
AIMS Infants born to women with Type 2 Diabetes Mellitus (T2DM) are at risk of being born large for gestational age due to excess fetal fat accretion. Placental nutrient transport determines fetal nutrient availability, impacting fetal growth. The aims of the study were to evaluate the effect of T2DM on placental insulin signaling, placental nutrient transporters and neonatal adiposity. METHODS Placentas were collected from BMI-matched normoglycemic controls (NGT, n = 9) and T2DM (n = 9) women. Syncytiotrophoblast microvillous (MVM) and basal (BM) plasma membranes were isolated. Expression of glucose (GLUT1, -4), fatty acid (FATP2, -4, -6, FAT/CD36), amino acid (SNAT1, -2, -4, LAT1, -2) transporters, insulin signaling, and System A transporter activity was determined. Neonatal fat mass (%) was measured in a subset of neonates born to T2DM women. RESULTS GLUT1 protein expression was increased (p = 0.001) and GLUT4 decreased (p = 0.006) in BM from T2DM. MVM FATP6 expression was increased (p = 0.02) and correlated with birth weight in both T2DM and NGT groups (r = 0.65, p = 0.02). BM FATP6 expression was increased (p = 0.01) in T2DM. In MVM of T2DM placentas, SNAT1 expression was increased (p = 0.05) and correlated with birth weight (r = 0.84, p = 0.004); SNAT2 was increased (p = 0.01), however System A transporter activity was not different between groups. MVM LAT1 expression was increased (p = 0.01) in T2DM and correlated with birth weight (r = 0.59, p = 0.04) and neonatal fat mass (r = 0.76, p = 0.06). CONCLUSION In pregnancies complicated by T2DM placental protein expression of transporters for glucose, amino acids and fatty acids is increased, which may contribute to increased fetal growth and neonatal adiposity.
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Affiliation(s)
- Marisol Castillo-Castrejon
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA.
| | - Kyohei Yamaguchi
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA; Department of Obstetrics and Gynecology, Mie University, Mie, Japan
| | - Rachel L Rodel
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Kathryn Erickson
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Anita Kramer
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Nicole M Hirsch
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Kristy Rolloff
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Thomas Jansson
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Linda A Barbour
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA; Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Theresa L Powell
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA; Department of Pediatrics, Section of Neonatology, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
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5
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Song J, Liu Y, Guan X, Zhang X, Yu W, Li Q. A Novel Ferroptosis-Related Biomarker Signature to Predict Overall Survival of Esophageal Squamous Cell Carcinoma. Front Mol Biosci 2021; 8:675193. [PMID: 34291083 PMCID: PMC8287967 DOI: 10.3389/fmolb.2021.675193] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 06/11/2021] [Indexed: 01/06/2023] Open
Abstract
Esophageal squamous cell carcinoma (ESCC) accounts for the main esophageal cancer (ESCA) type, which is also associated with the greatest malignant grade and low survival rates worldwide. Ferroptosis is recently discovered as a kind of programmed cell death, which is indicated in various reports to be involved in the regulation of tumor biological behaviors. This work focused on the comprehensive evaluation of the association between ferroptosis-related gene (FRG) expression profiles and prognosis in ESCC patients based on The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO). ALOX12, ALOX12B, ANGPTL7, DRD4, MAPK9, SLC38A1, and ZNF419 were selected to develop a novel ferroptosis-related gene signature for GEO and TCGA cohorts. The prognostic risk model exactly classified patients who had diverse survival outcomes. In addition, this study identified the ferroptosis-related signature as a factor to independently predict the risk of ESCC. Thereafter, we also constructed the prognosis nomogram by incorporating clinical factors and risk score, and the calibration plots illustrated good prognostic performance. Moreover, the association of the risk score with immune checkpoints was observed. Collectively, the proposed ferroptosis-related gene signature in our study is effective and has a potential clinical application to predict the prognosis of ESCC.
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Affiliation(s)
- Jiahang Song
- Cardiovascular Center, The Second Affiliated Hospital of Nanjing Medical University, Nanjing, China.,Department of Radiation Oncology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Yanhu Liu
- Cardiovascular Center, The Second Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Xiang Guan
- Cardiovascular Center, The Second Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Xun Zhang
- Cardiovascular Center, The Second Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Wenda Yu
- Cardiovascular Center, The Second Affiliated Hospital of Nanjing Medical University, Nanjing, China
| | - Qingguo Li
- Cardiovascular Center, The Second Affiliated Hospital of Nanjing Medical University, Nanjing, China.,Department of Cardiovascular Surgery, The Affiliated Hospital of Qinghai University, Xining, China
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6
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Maternal supplementation with uridine influences fatty acid and amino acid constituents of offspring in a sow-piglet model. Br J Nutr 2020; 125:743-756. [PMID: 32792039 DOI: 10.1017/s0007114520003165] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
To investigate the cumulative effects of maternal supplementation with nucleotides in the form of uridine (UR) on fatty acid and amino acid constituents of neonatal piglets, fifty-two sows in late gestation were assigned randomly into the control (CON) group (fed a basal diet) or UR group (fed a basal diet with 150 g/t UR). Samples of neonates were collected during farrowing. Results showed that supplementing with UR in sows' diet significantly decreased the birth mortality of pigs (P = 0·05), and increased serum total cholesterol, HDL and LDL of neonatal piglets (P < 0·05). Moreover, the amino acid profile of serum and liver of neonatal piglets was affected by the addition of UR in sows' diets (P < 0·05). Furthermore, an up-regulation of mRNA expression of energy metabolism-related genes, including fatty acid elongase 5, fatty acid desaturase 1, hormone-sensitive lipase and cholesterol-7a-hydroxylase, was observed in the liver of neonates from the UR group. Additionally, a decrease in placental gene expression of excitatory amino acid transporters 2, excitatory amino acid transporter 3 and neutral AA transporter 1 in the UR group was concurrently observed (P < 0·05), and higher protein expression of phosphorylated protein kinase B, raptor, PPARα and PPARγ in placenta from the UR group was also observed (P < 0·05). Together, these results showed that maternal UR supplementation could regulate placental nutrient transport, largely in response to an alteration of mTORC1-PPAR signalling, thus regulating the nutrition metabolism of neonatal piglets and improving reproductive performance.
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7
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Chen X, Lan T, Wang Y, He Y, Wu Z, Tian Y, Li Y, Bai M, Zhou W, Zhang H, Cheng K, Xie P. Entorhinal cortex-based metabolic profiling of chronic restraint stress mice model of depression. Aging (Albany NY) 2020; 12:3042-3052. [PMID: 32074509 PMCID: PMC7041782 DOI: 10.18632/aging.102798] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2019] [Accepted: 01/22/2020] [Indexed: 02/07/2023]
Abstract
Despite that millions of people suffer from major depressive disorder (MDD), the mechanism underlying MDD remains elusive. Recently, it has been reported that entorhinal cortex (EC) functions on the regulation of depressive-like phenotype relying on the stimulation of glutamatergic afferent from EC to hippocampus. Based on this, we used liquid chromatography-tandem mass spectrometry method to explore metabolic alterations in the EC of mice after exposed to chronic restraint stress (CRS). Molecular validation was conducted via the application of western blot and RT-qPCR. Through this study, we found significant upregulation of glutamate, ornithine aspartic acid, 5-hydroxytryptophan, L-tyrosine and norepinephrine in CRS group, accompanied with downregulation of homovanillic acid. Focusing on these altered metabolic pathways in EC, we found that gene levels of GAD1, GLUL and SNAT1 were increased. Upregulation of SERT and EAAT2 in protein expression level were also validated, while no significant changes were found in TH, AADC, MAOA, VMAT2, GAD1, GLUL and SNAT1. Our findings firstly provide evidence about the alteration of metabolites and related molecules in the EC of mice model of depression, implying the potential mechanism in MDD pathology.
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Affiliation(s)
- Xi Chen
- Department of Neurology, Yongchuan Hospital of Chongqing Medical University, Chongqing 402460, China.,Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
| | - Tianlan Lan
- Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China.,College of Biomedical Engineering, Chongqing Medical University, Chongqing 400016, China
| | - Yue Wang
- Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China.,Institute of Neuroscience, Basic Medical College, Chongqing Medical University, Chongqing 400016, China
| | - Yong He
- Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
| | - Zhonghao Wu
- Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China.,College of Biomedical Engineering, Chongqing Medical University, Chongqing 400016, China
| | - Yu Tian
- Department of Neurology, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China.,Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
| | - Yan Li
- Department of Neurology, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China.,Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
| | - Mengge Bai
- Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
| | - Wei Zhou
- Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
| | - Hanping Zhang
- Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
| | - Ke Cheng
- Department of Neurology, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China.,Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience, Basic Medical College, Chongqing Medical University, Chongqing 400016, China
| | - Peng Xie
- Department of Neurology, Yongchuan Hospital of Chongqing Medical University, Chongqing 402460, China.,Department of Neurology, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China.,Chongqing Key Laboratory of Neurobiology, Chongqing 400016, China.,Institute of Neuroscience and the Collaborative Innovation Center for Brain Science, Chongqing Medical University, Chongqing 400016, China
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Soper A, Juarez-Fernandez G, Aso H, Moriwaki M, Yamada E, Nakano Y, Koyanagi Y, Sato K. Various plus unique: Viral protein U as a plurifunctional protein for HIV-1 replication. Exp Biol Med (Maywood) 2017; 242:850-858. [PMID: 28346011 DOI: 10.1177/1535370217697384] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome, encodes four accessory genes, one of which is viral protein U (Vpu). Recently, the study of Vpu has been of great interest. For instance, various cellular proteins are degraded (e.g. CD4) and down-modulated (e.g. tetherin) by Vpu. Vpu also antagonizes the function of tetherin and inhibits NF-κB. Moreover, Vpu is a viroporin forming ion channels and may represent a promising target for anti-HIV-1 drugs. In this review, we summarize the domains/residues that are responsible for Vpu's functions, describe the current understanding of the role of Vpu in HIV-1-infected cells, and review the effect of Vpu on HIV-1 in replication and pathogenesis. Future investigations that simultaneously assess a combination of Vpu functions are required to clearly delineate the most important functions for viral replication. Impact statement Viral protein U (Vpu) is a unique protein encoded by human immunodeficiency virus type 1 (HIV-1) and related lentiviruses, playing multiple roles in viral replication and pathogenesis. In this review, we briefly summarize the most up-to-date knowledge of HIV-1 Vpu.
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Affiliation(s)
- Andrew Soper
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan
| | - Guillermo Juarez-Fernandez
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan
| | - Hirofumi Aso
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan.,2 Faculty of Pharmaceutical Sciences, Kyoto University, Kyoto 6068501, Japan
| | - Miyu Moriwaki
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan.,3 Graduate School of Biostudies, Kyoto University, Kyoto 6068315, Japan
| | - Eri Yamada
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan
| | - Yusuke Nakano
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan
| | - Yoshio Koyanagi
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan
| | - Kei Sato
- 1 Laboratory of Systems Virology, Department of Biosystems Science, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 6068507, Japan.,4 CREST, Japan Science and Technology Agency, Saitama 3220012, Japan
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9
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N-Glycosylation influences transport, but not cellular trafficking, of a neuronal amino acid transporter SNAT1. Biochem J 2016; 473:4227-4242. [DOI: 10.1042/bcj20160724] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 09/12/2016] [Accepted: 09/20/2016] [Indexed: 11/17/2022]
Abstract
SNAT1 is a system N/A neutral amino acid transporter that primarily expresses in neurons and mediates the transport of l-glutamine (Gln). Gln is an important amino acid involved in multiple cellular functions and also is a precursor for neurotransmitters, glutamate and GABA. In the present study, we demonstrated that SNAT1 is an N-glycoprotein expressed in neurons. We identified three glycosylation sites at asparagine residues 251, 257 and 310 in SNAT1 protein, and that the first two are the primary sites. The biotinylation and confocal immunofluorescence analysis showed that the glycosylation-impaired mutants and deglycosylated SNAT1 were equally capable of expressing on the cell surface. However, l-Gln and 3H-labeled methyl amino isobutyrate (MeAIB) was significantly compromised in N-glycosylation-impaired mutants and deglycosylated SNAT1 when compared with the wild-type control. Taken together, these results suggest that SNAT1 is an N-glycosylated protein with three de novo glycosylation sites and N-glycosylation of SNAT1 may play an important role in the transport of substrates across the cell membrane.
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10
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Chen C, Wang J, Cai R, Yuan Y, Guo Z, Grewer C, Zhang Z. Identification of a Disulfide Bridge in Sodium-Coupled Neutral Amino Acid Transporter 2(SNAT2) by Chemical Modification. PLoS One 2016; 11:e0158319. [PMID: 27355203 PMCID: PMC4927162 DOI: 10.1371/journal.pone.0158319] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 06/14/2016] [Indexed: 12/02/2022] Open
Abstract
Sodium-coupled neutral amino acid transporter 2 (SNAT2) belongs to solute carrier 38 (SLC38) family of transporters, which is ubiquitously expressed in mammalian tissues and mediates transport of small, neutral amino acids, exemplified by alanine(Ala, A). Yet structural data on SNAT2, including the relevance of intrinsic cysteine residues on structure and function, is scarce, in spite of its essential roles in many tissues. To better define the potential of intrinsic cysteines to form disulfide bonds in SNAT2, mutagenesis experiments and thiol-specific chemical modifications by N-ethylmaleimide (NEM) and methoxy-polyethylene glycol maleimide (mPEG-Mal, MW 5000) were performed, with or without the reducing regent dithiothreitol (DTT) treatment. Seven single mutant transporters with various cysteine (Cys, C) to alanine (Ala, A) substitutions, and a C245,279A double mutant were introduced to SNAT2 with a hemagglutinin (HA) tag at the C-terminus. The results showed that the cells expressing C245A or C279A were labeled by one equivalent of mPEG-Mal in the presence of DTT, while wild-type or all the other single Cys to Ala mutants were modified by two equivalents of mPEG-Mal. Furthermore, the molecular weight of C245,279A was not changed in the presence or absence of DTT treatment. The results suggest a disulfide bond between Cys245 and Cys279 in SNAT2 which has no effect on cell surface trafficking, as well as transporter function. The proposed disulfide bond may be important to delineate proximity in the extracellular domain of SNAT2 and related proteins.
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Affiliation(s)
- Chen Chen
- College of Life Science and Biopharmacy, Shenyang Pharmaceutical University, Shenyang 110015, People’s Republic of China
| | - Jiahong Wang
- College of Life Science and Biopharmacy, Shenyang Pharmaceutical University, Shenyang 110015, People’s Republic of China
| | - Ruiping Cai
- College of Life Science and Biopharmacy, Shenyang Pharmaceutical University, Shenyang 110015, People’s Republic of China
| | - Yanmeng Yuan
- College of Life Science and Biopharmacy, Shenyang Pharmaceutical University, Shenyang 110015, People’s Republic of China
| | - Zhanyun Guo
- Institute of Protein Research, College of Life Sciences and Technology, Tongji University, Shanghai 200092, People’s Republic of China
| | - Christof Grewer
- Departments of Chemistry and Biological Sciences, Binghamton University, Binghamton, New York, 13902, United States of America
| | - Zhou Zhang
- College of Life Science and Biopharmacy, Shenyang Pharmaceutical University, Shenyang 110015, People’s Republic of China
- * E-mail:
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11
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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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12
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Matheson NJ, Sumner J, Wals K, Rapiteanu R, Weekes MP, Vigan R, Weinelt J, Schindler M, Antrobus R, Costa ASH, Frezza C, Clish CB, Neil SJD, Lehner PJ. Cell Surface Proteomic Map of HIV Infection Reveals Antagonism of Amino Acid Metabolism by Vpu and Nef. Cell Host Microbe 2015; 18:409-23. [PMID: 26439863 PMCID: PMC4608997 DOI: 10.1016/j.chom.2015.09.003] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 08/30/2015] [Accepted: 09/10/2015] [Indexed: 11/24/2022]
Abstract
Critical cell surface immunoreceptors downregulated during HIV infection have previously been identified using non-systematic, candidate approaches. To gain a comprehensive, unbiased overview of how HIV infection remodels the T cell surface, we took a distinct, systems-level, quantitative proteomic approach. >100 plasma membrane proteins, many without characterized immune functions, were downregulated during HIV infection. Host factors targeted by the viral accessory proteins Vpu or Nef included the amino acid transporter SNAT1 and the serine carriers SERINC3/5. We focused on SNAT1, a β-TrCP-dependent Vpu substrate. SNAT1 antagonism was acquired by Vpu variants from the lineage of SIVcpz/HIV-1 viruses responsible for pandemic AIDS. We found marked SNAT1 induction in activated primary human CD4+ T cells, and used Consumption and Release (CoRe) metabolomics to identify alanine as an endogenous SNAT1 substrate required for T cell mitogenesis. Downregulation of SNAT1 therefore defines a unique paradigm of HIV interference with immunometabolism. Unbiased global analysis of T cell surface proteome remodeling during HIV infection >100 proteins downregulated, including Nef targets SERINC3/5 and Vpu target SNAT1 β-TrCP-dependent SNAT1 downregulation acquired by pandemic SIVcpz/HIV-1 viruses Uptake of exogenous alanine by SNAT1 critical for primary CD4+ T cell mitogenesis
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Affiliation(s)
- Nicholas J Matheson
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK.
| | - Jonathan Sumner
- Department of Infectious Diseases, King's College London School of Medicine, Guy's Hospital, London SE1 9RT, UK
| | - Kim Wals
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK
| | - Radu Rapiteanu
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK
| | - Michael P Weekes
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK
| | - Raphael Vigan
- Department of Infectious Diseases, King's College London School of Medicine, Guy's Hospital, London SE1 9RT, UK
| | - Julia Weinelt
- Department of Infectious Diseases, King's College London School of Medicine, Guy's Hospital, London SE1 9RT, UK
| | - Michael Schindler
- Helmholtz Center Munich, Institute of Virology, 85764 Neuherberg, Germany; Institute of Medical Virology and Epidemiology of Viral Diseases, University Clinic Tübingen, 72076 Tübingen, Germany
| | - Robin Antrobus
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK
| | - Ana S H Costa
- MRC Cancer Unit, Hutchison/MRC Research Centre, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XZ, UK
| | - Christian Frezza
- MRC Cancer Unit, Hutchison/MRC Research Centre, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XZ, UK
| | - Clary B Clish
- The Broad Institute of the Massachusetts Institute of Technology and Harvard, Cambridge, MA 02142, USA
| | - Stuart J D Neil
- Department of Infectious Diseases, King's College London School of Medicine, Guy's Hospital, London SE1 9RT, UK
| | - Paul J Lehner
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge CB2 0XY, UK.
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13
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Hägglund MGA, Hellsten SV, Bagchi S, Philippot G, Löfqvist E, Nilsson VCO, Almkvist I, Karlsson E, Sreedharan S, Tafreshiha A, Fredriksson R. Transport of L-glutamine, L-alanine, L-arginine and L-histidine by the neuron-specific Slc38a8 (SNAT8) in CNS. J Mol Biol 2014; 427:1495-1512. [PMID: 25451601 DOI: 10.1016/j.jmb.2014.10.016] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 09/30/2014] [Accepted: 10/17/2014] [Indexed: 11/19/2022]
Abstract
Glutamine transporters are important for regulating levels of glutamate and GABA in the brain. To date, six members of the SLC38 family (SNATs) have been characterized and functionally subdivided them into System A (SNAT1, SNAT2 and SNAT4) and System N (SNAT3, SNAT5 and SNAT7). Here we present the first functional characterization of SLC38A8, one of the previous orphan transporters from the family, and we suggest that the encoded protein should be named SNAT8 to adhere with the SNAT nomenclature. We show that SLC38A8 has preference for transporting L-glutamine, L-alanine, L-arginine, L-histidine and L-aspartate using a Na+-dependent transport mechanism and that the functional characteristics of SNAT8 have highest similarity to the known System A transporters. We also provide a comprehensive central nervous system expression profile in mouse brain for the Slc38a8 gene and the SNAT8 protein. We show that Slc38a8 (SNAT8) is expressed in all neurons, both excitatory and inhibitory, in mouse brain using in situ hybridization and immunohistochemistry. Furthermore, proximity ligation assay shows highly similar subcellular expression of SNAT7 and SNAT8. In conclusion, the neuronal SLC38A8 has a broad amino acid transport profile and is the first identified neuronal System A transporter. This suggests a key role of SNAT8 in the glutamine/glutamate (GABA) cycle in the brain.
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Affiliation(s)
- Maria G A Hägglund
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Sofie V Hellsten
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Sonchita Bagchi
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Gaëtan Philippot
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Erik Löfqvist
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Victor C O Nilsson
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Ingrid Almkvist
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Edvin Karlsson
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Smitha Sreedharan
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Atieh Tafreshiha
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Robert Fredriksson
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
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14
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Schiöth HB, Roshanbin S, Hägglund MGA, Fredriksson R. Evolutionary origin of amino acid transporter families SLC32, SLC36 and SLC38 and physiological, pathological and therapeutic aspects. Mol Aspects Med 2013; 34:571-85. [PMID: 23506890 DOI: 10.1016/j.mam.2012.07.012] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Accepted: 06/25/2012] [Indexed: 10/27/2022]
Abstract
About 25% of all solute carriers (SLCs) are likely to transport amino acids as their primary substrate. One of the major phylogenetic clusters of amino acid transporters from the SLC family is the β-family, which is part of the PFAM APC clan. The β-family includes three SLC families, SLC32, SLC36 and SLC38 with one, four and eleven members in humans, respectively. The most well characterized genes within these families are the vesicular inhibitory amino acid transporter (VIAAT, SLC32A1), PAT1 (SLC36A1), PAT2 (SLC36A2), PAT4 (SLC36A4), SNAT1 (SLC38A1), SNAT2 (SLC38A2), SNAT3 (SLC38A3), and SNAT4 (SLC38A4). Here we review the structural characteristics and functional role of these transporters. We also mined the complete protein sequence datasets for nine different genomes to clarify the evolutionary history of the β-family of transporters. We show that all three main branches of the this family are found as far back as green algae suggesting that genes from these families existed in the early eukaryote before the split of animals and plants and that they are present in most animal species. We also address the potential of further drug development within this field highlighting the important role of these transporters in neurotransmission and transport of amino acids as nutrients.
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Affiliation(s)
- Helgi B Schiöth
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Uppsala, Sweden.
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15
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Abstract
The eye is a highly protected organ, and designing an effective therapy is often considered a challenging task. The anatomical and physiological barriers result in low ocular bioavailability of drugs. Due to these constraints, less than 5% of the administered dose is absorbed from the conventional ophthalmic dosage forms. Further, physicochemical properties such as lipophilicity, molecular weight and charge modulate the permeability of drug molecules. Vision-threatening diseases such as glaucoma, diabetic macular edema, cataract, wet and dry age-related macular degeneration, proliferative vitreoretinopathy, uveitis, and cytomegalovirus retinitis alter the pathophysiological and molecular mechanisms. Understanding these mechanisms may result in the development of novel treatment modalities. Recently, transporter/receptor targeted prodrug approach has generated significant interest in ocular drug delivery. These transporters and receptors are involved in the transport of essential nutrients, vitamins, and xenobiotics across biological membranes. Several influx transporters (peptides, amino acids, glucose, lactate and nucleosides/nucleobases) and receptors (folate and biotin) have been identified on conjunctiva, cornea, and retina. Structural and functional delineation of these transporters will enable more drugs targeting the posterior segment to be successfully delivered topically. Prodrug derivatization targeting transporters and receptors expressed on ocular tissues has been the subject of intense research. Several prodrugs have been designed to target these transporters and enhance the absorption of poorly permeating parent drug. Moreover, this approach might be used in gene delivery to modify cellular function and membrane receptors. This review provides comprehensive information on ocular drug delivery, with special emphasis on the use of transporters and receptors to improve drug bioavailability.
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16
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Padmanabhan Iyer R, Gu S, Nicholson BJ, Jiang JX. Identification of a disulfide bridge important for transport function of SNAT4 neutral amino acid transporter. PLoS One 2013; 8:e56792. [PMID: 23451088 PMCID: PMC3579933 DOI: 10.1371/journal.pone.0056792] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Accepted: 01/14/2013] [Indexed: 11/23/2022] Open
Abstract
SNAT4 is a member of system N/A amino acid transport family that primarily expresses in liver and muscles and mediates the transport of L-alanine. However, little is known about the structure and function of the SNAT family of transporters. In this study, we showed a dose-dependent inhibition in transporter activity of SNAT4 with the treatment of reducing agents, dithiothreitol (DTT) and Tris(2-carboxyethyl)phosphine (TCEP), indicating the possible involvement of disulfide bridge(s). Mutation of residue Cys-232, and the two highly conserved residues Cys-249 and Cys-321, compromised the transport function of SNAT4. However, this reduction was not caused by the decrease of SNAT4 on the cell surface since the cysteine-null mutant generated by replacing all five cysteines with alanine was equally capable of being expressed on the cell surface as wild-type SNAT4. Interestingly, by retaining two cysteine residues, 249 and 321, a significant level of L-alanine uptake was restored, indicating the possible formation of disulfide bond between these two conserved residues. Biotinylation crosslinking of free thiol groups with MTSEA-biotin provided direct evidence for the existence of a disulfide bridge between Cys-249 and Cys-321. Moreover, in the presence of DTT or TCEP, transport activity of the mutant retaining Cys-249 and Cys-321 was reduced in a dose-dependent manner and this reduction is gradually recovered with increased concentration of H2O2. Disruption of the disulfide bridge also decreased the transport of L-arginine, but to a lesser degree than that of L-alanine. Together, these results suggest that cysteine residues 249 and 321 form a disulfide bridge, which plays an important role in substrate transport but has no effect on trafficking of SNAT4 to the cell surface.
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Affiliation(s)
- Rugmani Padmanabhan Iyer
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas, United States of America
| | - Sumin Gu
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas, United States of America
| | - Bruce J. Nicholson
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas, United States of America
| | - Jean X. Jiang
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas, United States of America
- * E-mail:
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17
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Rosario FJ, Kanai Y, Powell TL, Jansson T. Mammalian target of rapamycin signalling modulates amino acid uptake by regulating transporter cell surface abundance in primary human trophoblast cells. J Physiol 2012; 591:609-25. [PMID: 23165769 DOI: 10.1113/jphysiol.2012.238014] [Citation(s) in RCA: 139] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Abnormal fetal growth increases the risk for perinatal complications and predisposes for the development of obesity, diabetes and cardiovascular disease later in life. Emerging evidence suggests that changes in placental amino acid transport directly contribute to altered fetal growth. However, the molecular mechanisms regulating placental amino acid transport are largely unknown. Here we combined small interfering (si) RNA-mediated silencing approaches with protein expression/localization and functional studies in cultured primary human trophoblast cells to test the hypothesis that mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) regulate amino acid transporters by post-translational mechanisms. Silencing raptor (inhibits mTORC1) or rictor (inhibits mTORC2) markedly decreased basal System A and System L amino acid transport activity but had no effect on growth factor-stimulated amino acid uptake. Simultaneous inhibition of mTORC1 and 2 completely inhibited both basal and growth factor-stimulated amino acid transport activity. In contrast, mTOR inhibition had no effect on serotonin transport. mTORC1 or mTORC2 silencing markedly decreased the plasma membrane expression of specific System A (SNAT2, SLC38A2) and System L (LAT1, SLC7A5) transporter isoforms without affecting global protein expression. In conclusion, mTORC1 and mTORC2 regulate human trophoblast amino acid transporters by modulating the cell surface abundance of specific transporter isoforms. This is the first report showing regulation of amino acid transport by mTORC2. Because placental mTOR activity and amino acid transport are decreased in human intrauterine growth restriction our data are consistent with the possibility that dysregulation of placental mTOR plays an important role in the development of abnormal fetal growth.
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Affiliation(s)
- Fredrick J Rosario
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, Mail Code 7836, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
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18
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Gokulgandhi MR, Barot M, Bagui M, Pal D, Mitra AK. Transporter-targeted lipid prodrugs of cyclic cidofovir: a potential approach for the treatment of cytomegalovirus retinitis. J Pharm Sci 2012; 101:3249-63. [PMID: 22499243 DOI: 10.1002/jps.23140] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 02/25/2012] [Accepted: 03/16/2012] [Indexed: 01/24/2023]
Abstract
Cidofovir (CDF) and its cyclic analogue (cCDF) have shown potential in vitro and in vivo antiviral activity against cytomegalovirus (CMV) retinitis. However, hydrophilic nature of CDF may affect cell permeation across lipophilic epithelium and thus limit its effectiveness in the treatment of CMV retinitis. In the present study, we have tested a novel hypothesis, which involves chemical derivatization of cCDF into lipophilic transporter-targeted prodrug [via conjugation with different carbon chain length of lipid raft and targeting moiety (biotin) for sodium-dependent multivitamin transporter (SMVT)]. We have synthesized and characterized three derivatives of cCDF including biotin B-C2-cCDF, B-C6-cCDF, and B-C12-cCDF. Physicochemical properties such as solubility, partition coefficient (n-octanol/water and ocular tissue), bioreversion kinetics, and interaction with SMVT transporter have been determined. Among these novel conjugates, B-C12-cCDF has shown higher interaction to SMVT transporter with lowest half maximal inhibitory concentration value, higher cellular accumulation, and high tissue partitioning. Improvement in physicochemical properties, lipophilicity, and interaction with transporter was observed in the trend of increasing the lipid chain length, that is, B-C12-cCDF > B-C6-cCDF > B-C2-cCDF. These results indicate that transporter-targeted lipid analogue of cCDF exhibits improved cellular accumulation along with higher transporter affinity and hence could be a viable strategy for the treatment of CMV retinitis.
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Affiliation(s)
- Mitan R Gokulgandhi
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, Missouri 64108, USA
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19
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Rosario FJ, Schumacher MA, Jiang J, Kanai Y, Powell TL, Jansson T. Chronic maternal infusion of full-length adiponectin in pregnant mice down-regulates placental amino acid transporter activity and expression and decreases fetal growth. J Physiol 2012; 590:1495-509. [PMID: 22289908 DOI: 10.1113/jphysiol.2011.226399] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Maternal adiponectin levels are inversely correlated to birth weight, suggesting that maternal adiponectin limits fetal growth. We hypothesized that full-length adiponectin (fADN) infusion in pregnant mice down-regulates placental amino acid transporters and decreases fetal growth. Starting at embryonic day (E) 14.5, fADN (0.62 ± 0.02 μg (g body weight)(−1) day(−1), n = 7) or vehicle (control, n = 9) were infused in pregnant C57/BL6 mice by mini-osmotic pump. At E18.5, dams were killed and placental homogenates and trophoblast plasma membrane (TPM) vesicles were prepared. Infusion of fADN elevated maternal serum fADN by 4-fold and decreased fetal weights by 18%. Adiponectin receptor 2, but not adiponectin receptor 1, was expressed in TPM. fADN infusion decreased TPM System A (–56%, P < 0.001) and System L amino acid transporter activity (–50%, P < 0.03). TPM protein expression of SNAT1, 2 and 4 (System A amino acid transporter isoforms) and LAT1 and LAT2, but not CD98, (System L amino acid transporter isoforms) was down-regulated by fADN infusion. To identify possible mechanisms underlying these changes we determined the phosphorylation of proteins in signalling pathways known to regulate placental amino acid transporters. fADN decreased phosphorylation of insulin receptor substrate-1 (Tyr-608), Akt (Thr-308 and Ser-473), S6 kinase 1 (Thr-389), eukaryotic initiation factor 4E binding protein 1 (Thr-37/46 and Thr-70) and ribosomal protein S6 (Ser-235/236) and increased the phosphorylation of peroxisome proliferator-activated receptor α (PPARα) (Ser-21) in the placenta. These data suggest that maternal adiponectin decreases fetal growth by down-regulation of placental amino acid transporters, which limits fetal nutrient availability. This effect may be mediated by inhibition of insulin/IGF-I and mTOR signalling pathways, which are positive regulators of placental amino acid transporters. We have identified a novel physiological mechanism by which the endocrine functions of maternal adipose tissue influence fetal growth.
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Affiliation(s)
- Fredrick J Rosario
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, Mail Code 7836, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
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20
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Shi Q, Padmanabhan R, Villegas CJ, Gu S, Jiang JX. Membrane topological structure of neutral system N/A amino acid transporter 4 (SNAT4) protein. J Biol Chem 2011; 286:38086-38094. [PMID: 21917917 DOI: 10.1074/jbc.m111.220277] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Members of system N/A amino acid transporter (SNAT) family mediate transport of neutral amino acids, including l-alanine, l-glutamine, and l-histidine, across the plasma membrane and are involved in a variety of cellular functions. By using chemical labeling, glycosylation, immunofluorescence combined with molecular modeling approaches, we resolved the membrane topological structure of SNAT4, a transporter expressed predominantly in liver. To analyze the orientation using the chemical labeling and biotinylation approach, the "Cys-null" mutant of SNAT4 was first generated by mutating all five endogenous cysteine residues. Based on predicted topological structures, a single cysteine residue was introduced individually into all possible nontransmembrane domains of the Cys-null mutant. The cells expressing these mutants were labeled with N-biotinylaminoethyl methanethiosulfonate, a membrane-impermeable cysteine-directed reagent. We mapped the orientations of N- and C-terminal domains. There are three extracellular loop domains, and among them, the second loop domain is the largest that spans from amino acid residue ∼242 to ∼335. The orientation of this domain was further confirmed by the identification of two N-glycosylated residues, Asn-260 and Asn-264. Together, we showed that SNAT4 contains 10 transmembrane domains with extracellular N and C termini and a large N-glycosylated, extracellular loop domain. This is the first report concerning membrane topological structure of mammalian SNAT transporters, which will provide important implications for our understanding of structure-function of the members in this amino acid transporter family.
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Affiliation(s)
- Qian Shi
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900
| | - Rugmani Padmanabhan
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900
| | - Carla J Villegas
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900
| | - Sumin Gu
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900
| | - Jean X Jiang
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900.
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21
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Hägglund MGA, Sreedharan S, Nilsson VCO, Shaik JHA, Almkvist IM, Bäcklin S, Wrange Ö, Fredriksson R. Identification of SLC38A7 (SNAT7) protein as a glutamine transporter expressed in neurons. J Biol Chem 2011; 286:20500-11. [PMID: 21511949 PMCID: PMC3121473 DOI: 10.1074/jbc.m110.162404] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Revised: 04/15/2011] [Indexed: 12/16/2022] Open
Abstract
The SLC38 family of transporters has in total 11 members in humans and they encode amino acid transporters called sodium-coupled amino acid transporters (SNAT). To date, five SNATs have been characterized and functionally subdivided into systems A (SLC38A1, SLC38A2, and SLC38A4) and N (SLC38A3 and SLC38A5) showing the highest transport for glutamine and alanine. Here we present identification of a novel glutamine transporter encoded by the Slc38a7 gene, which we propose should be named SNAT7. This transporter has L-glutamine as the preferred substrate but also transports other amino acids with polar side chains, as well as L-histidine and L-alanine. The expression pattern and substrate profile for SLC38A7 shows highest similarity to the known system N transporters. Therefore, we propose that SLC38A7 is a novel member of this system. We used in situ hybridization and immunohistochemistry with a custom-made antibody to show that SLC38A7 is expressed in all neurons, but not in astrocytes, in the mouse brain. SLC38A7 is unique in being the first system N transporter expressed in GABAergic and also other neurons. The preferred substrate and axonal localization of SLC38A7 close to the synaptic cleft indicates that SLC38A7 could have an important function for the reuptake and recycling of glutamate.
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Affiliation(s)
- Maria G. A. Hägglund
- From the Department of Neuroscience, Functional Pharmacology, Uppsala University, 75124 Uppsala, Sweden and
| | - Smitha Sreedharan
- From the Department of Neuroscience, Functional Pharmacology, Uppsala University, 75124 Uppsala, Sweden and
| | - Victor C. O. Nilsson
- From the Department of Neuroscience, Functional Pharmacology, Uppsala University, 75124 Uppsala, Sweden and
| | - Jafar H. A. Shaik
- From the Department of Neuroscience, Functional Pharmacology, Uppsala University, 75124 Uppsala, Sweden and
| | - Ingrid M. Almkvist
- From the Department of Neuroscience, Functional Pharmacology, Uppsala University, 75124 Uppsala, Sweden and
| | - Sofi Bäcklin
- From the Department of Neuroscience, Functional Pharmacology, Uppsala University, 75124 Uppsala, Sweden and
| | - Örjan Wrange
- the Department of Cell and Molecular Biology, Karolinska Institute, 17177 Stockholm, Sweden
| | - Robert Fredriksson
- From the Department of Neuroscience, Functional Pharmacology, Uppsala University, 75124 Uppsala, Sweden and
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Yu WL, Cong WM, Zhang Y, Chen Y, Wang F, Yu G. Overexpression of ATA1/SLC38A1 predicts future recurrence and death in Chinese patients with hilar cholangiocarcinoma. J Surg Res 2010; 171:663-8. [PMID: 20605601 DOI: 10.1016/j.jss.2010.03.049] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2009] [Revised: 03/12/2010] [Accepted: 03/23/2010] [Indexed: 01/26/2023]
Abstract
System A amino acid transporter is a Na+-dependent active transport system, mediating the uptake of amino acids, dysregulation of which has been found to be associated with malignant transformation in mammalian cells. However, the role of ATA1 in hilar cholangiocarcinoma is unclear. Here, we investigated ATA1 expression and determined its clinical significance in hilar cholangiocarcinoma. Tissue microarray blocks containing tumor specimens obtained from 48 patients were constructed. Expression of ATA1 in these specimens was analyzed using immunohistochemical studies. ATA1 overexpression was observed in 22 cases (44.9%). Overexpression of ATA1 was significantly associated with lymph node metastases. ATA1 expression has a significant correlation with recurrence and poor survival in univariate analyses. Multivariate analyses revealed that ATA1 was an independent predictor for future recurrence in patients with cholangiocarcinoma. Increased expression of ATA1 is frequent in human hilar cholangiocarcinoma and significantly correlated with the progression of cholangiocarcinoma, suggesting the importance of ATA1 in cancer development and progression. ATA1 expression may be used to predict recurrence and death and can serve as a promising target for therapy of this malignancy.
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Affiliation(s)
- Wen-long Yu
- Department of Surgery, Eastern Hepatobiliary Hospital, Shanghai, People's Republic of China
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23
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Ernst C, Dumoulin P, Cabot S, Erickson J, Turecki G. SNAT1 and a family with high rates of suicidal behavior. Neuroscience 2009; 162:415-22. [DOI: 10.1016/j.neuroscience.2009.05.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 05/03/2009] [Accepted: 05/06/2009] [Indexed: 10/20/2022]
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24
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Grewal S, Defamie N, Zhang X, De Gois S, Shawki A, Mackenzie B, Chen C, Varoqui H, Erickson JD. SNAT2 amino acid transporter is regulated by amino acids of the SLC6 gamma-aminobutyric acid transporter subfamily in neocortical neurons and may play no role in delivering glutamine for glutamatergic transmission. J Biol Chem 2009; 284:11224-36. [PMID: 19240036 PMCID: PMC2670127 DOI: 10.1074/jbc.m806470200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 02/06/2009] [Indexed: 01/24/2023] Open
Abstract
System A transporters SNAT1 and SNAT2 mediate uptake of neutral alpha-amino acids (e.g. glutamine, alanine, and proline) and are expressed in central neurons. We tested the hypothesis that SNAT2 is required to support neurotransmitter glutamate synthesis by examining spontaneous excitatory activity after inducing or repressing SNAT2 expression for prolonged periods. We stimulated de novo synthesis of SNAT2 mRNA and increased SNAT2 mRNA stability and total SNAT2 protein and functional activity, whereas SNAT1 expression was unaffected. Increased endogenous SNAT2 expression did not affect spontaneous excitatory action-potential frequency over control. Long term glutamine exposure strongly repressed SNAT2 expression but increased excitatory action-potential frequency. Quantal size was not altered following SNAT2 induction or repression. These results suggest that spontaneous glutamatergic transmission in pyramidal neurons does not rely on SNAT2. To our surprise, repression of SNAT2 activity was not limited to System A substrates. Taurine, gamma-aminobutyric acid, and beta-alanine (substrates of the SLC6 gamma-aminobutyric acid transporter family) repressed SNAT2 expression more potently (10x) than did System A substrates; however, the responses to System A substrates were more rapid. Since ATF4 (activating transcription factor 4) and CCAAT/enhancer-binding protein are known to bind to an amino acid response element within the SNAT2 promoter and mediate induction of SNAT2 in peripheral cell lines, we tested whether either factor was similarly induced by amino acid deprivation in neurons. We found that glutamine and taurine repressed the induction of both transcription factors. Our data revealed that SNAT2 expression is constitutively low in neurons under physiological conditions but potently induced, together with the taurine transporter TauT, in response to depletion of neutral amino acids.
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Affiliation(s)
- Sukhjeevan Grewal
- Neuroscience Center, Louisiana State University Health Science Center, New Orleans, Louisiana 70112, USA
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25
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Umapathy NS, Dun Y, Martin PM, Duplantier JN, Roon P, Prasad P, Smith SB, Ganapathy V. Expression and function of system N glutamine transporters (SN1/SN2 or SNAT3/SNAT5) in retinal ganglion cells. Invest Ophthalmol Vis Sci 2008; 49:5151-60. [PMID: 18689705 DOI: 10.1167/iovs.08-2245] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
PURPOSE Glutamine transport is essential for the glutamate-glutamine cycle, which occurs between neurons and glia. System N, consisting of SN1 (SNAT3) and SN2 (SNAT5), is the principal mediator of glutamine transport in retinal Müller cells. Mediators of glutamine transport in retinal ganglion cells were investigated. METHODS The relative contributions of various transport systems for glutamine uptake (systems N, A, L, y+L, ASCT, and ATB(0,+)) were examined in RGC-5 cells based on differential features of the individual transport systems. mRNA for the genes encoding members of these transport systems were analyzed by RT-PCR. Based on these data, SN1 and SN2 were analyzed in mouse retina, RGC-5 cells, and primary mouse ganglion cells (GCs) by in situ hybridization (ISH), immunofluorescence (IF), and Western blotting. RESULTS Three transport systems--N, A, and L--participated in glutamine uptake in RGC-5 cells. System N was the principal contributor; systems A and L contributed considerably less. ISH and IF revealed SN1 and SN2 expression in the ganglion, inner nuclear, and photoreceptor cell layers. SN1 and SN2 colocalized with the ganglion cell marker Thy 1.2 and with the Müller cell marker vimentin, confirming their presence in both retinal cell types. SN1 and SN2 proteins were detected in primary mouse GCs. CONCLUSIONS These findings suggest that in addition to its role in glutamine uptake in retinal glial cells, system N contributes significantly to glutamine uptake in ganglion cells and, hence, contributes to the retinal glutamate-glutamine cycle.
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Affiliation(s)
- Nagavedi S Umapathy
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA
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26
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Subtoxic chlorpyrifos treatment resulted in differential expression of genes implicated in neurological functions and development. Arch Toxicol 2008; 83:319-33. [PMID: 18668222 DOI: 10.1007/s00204-008-0346-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2008] [Accepted: 07/16/2008] [Indexed: 10/21/2022]
Abstract
Chlorpyrifos (CPF), a commonly used organophosphorus insecticide, induces acetylcholinesterase inhibition and cholinergic toxicity. Subtoxic exposure to CPF has long-term adverse effects on synaptic function/development and behavioral performance. To gain insight into the possible mechanism(s) of these observations, this study aims to investigate gene expression changes in the forebrain of rats treated with subtoxic CPF doses using DNA microarrays. Statistical analysis revealed that CPF treatment resulted in differential expression of 277 genes. Gene ontology and pathway analyses revealed that these genes have important roles in nervous system development and functions including axon guidance, dorso-ventral axis formation, long-term potentiation, synaptic transmission, and insulin signaling. The results of biological associated network analysis showed that Gsk3b is highly connected in several of these networks suggesting its potential role in cellular response to CPF exposure/neurotoxicity. These findings might serve as the basis for future mechanistic analysis of the long-term adverse effects of subtoxic CPF exposure.
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27
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Hariharan S, Janoria KG, Gunda S, Zhu X, Pal D, Mitra AK. Identification and functional expression of a carrier-mediated riboflavin transport system on rabbit corneal epithelium. Curr Eye Res 2006; 31:811-24. [PMID: 17050273 DOI: 10.1080/02713680600899655] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
PURPOSE To investigate the functional expression of a carrier-mediated transport mechanism for riboflavin (vitamin B2) across cultured rabbit primary corneal epithelial cells (rPCECs) and intact rabbit cornea. The secondary objective was to understand the physiological significance behind the presence of such a transport system for riboflavin on the apical side of the corneal epithelium. METHODS rPCECs and freshly excised rabbit corneas were selected as in vitro and ex vivo models, respectively. Transport and uptake characteristics of [3H]riboflavin were determined at various time points, concentrations, temperatures, and pH. Substrate specificity, energy, and ion dependence studies were carried out to characterize the translocation mechanism. Rabbit tear analysis was done with liquid chromatography/tandem mass spectrometry (LC-MS/MS) to understand the physiological relevance of this transporter. RESULTS The uptake process in rPCECs was found to be concentration dependent and saturable at higher concentrations. The process was also independent of pH, Na+, and Cl- but dependent on energy and temperature. Unlabeled riboflavin and its structural analogues caused significant inhibition, whereas unrelated vitamins did not interfere with the process. Transport of [3H]riboflavin across rabbit cornea was also saturable at higher concentration and energy dependent but Na+ independent. Substrate specificity studies across intact rabbit cornea produced results similar to the uptake studies in cultured rPCECs. LC-MS/MS analysis of rabbit tears showed the presence of riboflavin. CONCLUSIONS Results suggest the presence of a specialized, high-affinity transport mechanism for riboflavin that is expressed on the apical side of rabbit corneal epithelium and may in turn be responsible for influx of riboflavin from tears to cornea.
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Affiliation(s)
- Sudharshan Hariharan
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, Missouri 64112-2499, USA
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28
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Richert L, Liguori MJ, Abadie C, Heyd B, Mantion G, Halkic N, Waring JF. GENE EXPRESSION IN HUMAN HEPATOCYTES IN SUSPENSION AFTER ISOLATION IS SIMILAR TO THE LIVER OF ORIGIN, IS NOT AFFECTED BY HEPATOCYTE COLD STORAGE AND CRYOPRESERVATION, BUT IS STRONGLY CHANGED AFTER HEPATOCYTE PLATING. Drug Metab Dispos 2006; 34:870-9. [PMID: 16473918 DOI: 10.1124/dmd.105.007708] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Isolated primary human hepatocytes are a well accepted system for evaluating pharmacological and toxicological effects in humans. However, questions remain regarding how culturing affects the liver-specific functions of the hepatocytes. In addition, cryopreservation could also potentially affect the differentiation state of the hepatocytes. The first aim of the present study was to compare gene expression in freshly isolated primary hepatocytes to that of the liver of origin and to evaluate the expression changes occurring after cryopreservation/thawing, both when maintained in suspension and after plating. The second aim of the present study was to evaluate gene expression in hepatocytes after cold storage of suspensions up to 24 h compared with freshly isolated hepatocytes in suspension. Our results show that the gene expression in freshly isolated human hepatocytes in suspension after isolation is similar to that of the liver of origin. Furthermore, gene expression in primary human hepatocytes in suspension is not affected by hepatocyte cold storage and cryopreservation. However, the gene expression is profoundly affected in monolayer cultures after plating. Specifically, gene expression changes were observed in cultured relative to suspensions of human hepatocytes that are involved in cellular processes such as phase I/II metabolism, basolateral and canalicular transport systems, fatty acid and lipid metabolism, apoptosis, and proteasomal protein recycling. An oxidative stress response may be partially involved in these changes in gene expression. Taken together, these results may aid in the interpretation of data collected from human hepatocyte experiments and suggest additional utility for cold storage and cryopreservation of hepatocytes.
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Affiliation(s)
- Lysiane Richert
- Laboratoire de Biologie Cellulaire, EA3921 Optimisation Métabolique et Cellulaire, UFR des Sciences Médicales et Pharmaceutiques, Place Saint-Jacques, 25030 Besançon cedex, France.
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29
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Gu S, Villegas CJ, Jiang JX. Differential Regulation of Amino Acid Transporter SNAT3 by Insulin in Hepatocytes. J Biol Chem 2005; 280:26055-62. [PMID: 15899884 DOI: 10.1074/jbc.m504401200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The liver is a metabolism and transfer center of amino acids as well as the prime target organ of insulin. In this report, we characterized the regulation of system N/A transporter 3 (SNAT3) in the liver of dietary-restricted mice and in hepatocytes treated with serum starvation and insulin. The expression of SNAT3 was up-regulated in dietary-restricted mice. The expression of SNAT3 protein was detected on the plasma membrane of hepatocyte-like H2.35 cells with a half-life of 6-8 h. When H2.35 cells were depleted of serum, the expression of SNAT3 was increased. An increased concentration of insulin, however, suppressed SNAT3 expression. Interestingly, the down-regulation of SNAT3 expression by insulin was blocked by the specific phosphoinositide 3-kinase inhibitor LY294002 and mammalian target of rapamycin inhibitor, but not by MAPK inhibitor PD98059, suggesting that insulin exerts its effect on SNAT3 through phosphoinositide 3-kinase-mammalian target of rapamycin signaling. Surface biotinylation assay showed an increased level of SNAT3 on the cell surface after 0.5 h of insulin treatment, although no effect was observed after 24 h of treatment. Consistently, the transport of the substrate l-histidine was increased with short, but not long, treatment by insulin in both H2.35- and SNAT3-transfected COS-7 cells. The L-histidine uptake was inhibited significantly by L-histidine followed by 2-endoamino-bicycloheptane-2-carboxylic acid and L-cysteine and to a lesser extent by L-alanine and aminoisobutyric acid, but was not inhibited by alpha-(methylamino)isobutyric acid, implying that uptake of L-histidine in H2.35 cells is primarily mediated by system N transporters. In conclusion, differential regulation of SNAT3 by insulin and serum starvation reinforces the functional significance of this transporter in liver physiology.
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Affiliation(s)
- Sumin Gu
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA
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30
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Akerman M, Shaked-Mishan P, Mazareb S, Volpin H, Zilberstein D. Novel motifs in amino acid permease genes from Leishmania. Biochem Biophys Res Commun 2005; 325:353-66. [PMID: 15522240 DOI: 10.1016/j.bbrc.2004.09.212] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2004] [Indexed: 11/29/2022]
Abstract
Eight amino acid permease genes from the protozoan parasite Leishmania donovani (AAPLDs) were cloned, sequenced, and shown to be expressed in promastigotes. Seven of these belong to the amino acid transporter-1 and one to the amino acid polyamino-choline superfamilies. Using these sequences as well as known and characterized amino acid permease genes from all kingdoms, a training set was established and used to search for motifs, using the MEME motif discovery tool. This study revealed two motifs that are specific to the genus Leishmania, four to the family trypanosomatidae, and a single motif that is common between trypanosomatidae and mammalian systems A1 and N. Interestingly, most of these motifs are clustered in two regions of 50-60 amino acids. Blast search analyses indicated a close relationship between the L. donovani and Trypanosoma brucei amino acid permeases. The results of this work describe the cloning of the first amino acid permease genes in parasitic protozoa and contribute to the understanding of amino acid permease evolution in these organisms. Furthermore, the identification of genus-specific motifs in these proteins might be useful to better understand parasite physiology within its hosts.
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Affiliation(s)
- Martin Akerman
- Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
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31
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Sáenz DA, Goldin AP, Minces L, Chianelli M, Sarmiento MIK, Rosenstein RE. Effect of melatonin on the retinal glutamate/glutamine cycle in the golden hamster retina. FASEB J 2004; 18:1912-3. [PMID: 15448109 DOI: 10.1096/fj.04-2062fje] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Glutamate is the main excitatory neurotransmitter in the retina, but it is neurotoxic when present in excessive amounts. The metabolic dependence of glutamatergic neurons upon glia via the glutamate/glutamine cycle to provide the precursor for neurotransmitter glutamate is well established. Since melatonin has been shown to be neuroprotective in several systems, in the present report, its effect on the glutamate/glutamine cycle activity was examined in the golden hamster retina. Melatonin (0.1-10 nM) significantly increased retinal glutamine synthetase activity but it did not affect L-glutamine release. A characterization of the hamster retinal L-glutamine uptake mechanism was performed. This mechanism was partly Na+-dependent, and it was significantly inhibited by 2-aminobicyclo (2, 2, 1) heptane 2-carboxylic acid (BCH, a selective antagonists for the L-type system) and by alpha-(methylamino)-isobutyric acid (MeAIB, substrate characteristic for the A -type transporter) suggesting the coexistence of these transport systems in the hamster retina. Melatonin (0.1-10 nM) significantly increased total glutamine uptake as well as the BCH and the MeAIB-insensitive transporters activity. On the other hand, melatonin significantly decreased retinal glutaminase activity. On the basis of these results, it might be presumed that hamster retinal glutamate/glutamine cycle activity is regulated by physiological concentrations of melatonin. Furthermore, these findings suggest that a treatment with melatonin could be considered as a new approach to handling glutamate-mediated neuronal degeneration.
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Affiliation(s)
- Daniel A Sáenz
- Laboratorio de Neuroquímica Retiniana y Oftalmología Experimental, Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, CONICET, Buenos Aires, Argentina
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32
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Gandhi MD, Pal D, Mitra AK. Identification and functional characterization of a Na(+)-independent large neutral amino acid transporter (LAT2) on ARPE-19 cells. Int J Pharm 2004; 275:189-200. [PMID: 15081149 DOI: 10.1016/j.ijpharm.2004.01.035] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2003] [Revised: 01/27/2004] [Accepted: 01/27/2004] [Indexed: 12/21/2022]
Abstract
The objective of this study was to investigate the presence of a large neutral amino acid transporter on the ARPE-19 cell line. ARPE-19 cells were grown on 24-well plates for uptake studies. Uptake characteristics of [3H]L-phenylalanine (L-Phe) were determined at various concentrations and pH at 37 degrees C. Inhibition studies were conducted in presence of L- and D-amino acids, metabolic inhibitors, like ouabain, sodium azide, and in presence of sodium-free medium, to delineate the mechanism of uptake. RT-PCR was carried out on total RNA isolated from the ARPE-19 cells. Presence of Na(+)-free buffer did reduce the uptake rate. Hence, all experiments were carried out in Na(+)-free medium to delineate the sodium-independent uptake mechanism. Uptake of L-Phe on ARPE cells was found to be saturable with a Km = 89.35 +/- 14 microM, Vmax = 58.9 +/- 2.5 pmol min(-1) mg protein(-1), and Kd = 0.108 +/- 0.04 microl min(-1) mg protein(-1). Dose-dependent inhibition was observed with increasing concentrations of unlabeled L-Phe. Uptake also was found to be energy independent. Significant inhibition of [3H]L-Phe was observed with large neutral aromatic and aliphatic amino acids as well as small neutral amino acids. System L-specific inhibitor BCH produced partial inhibition of uptake. Neither acidic nor basic amino acids altered the uptake rate. Results obtained were predominantly characteristic of LAT2, particularly with respect to substrate selectivity and pH dependence. Bands for LAT2 were detected by RT-PCR in the ARPE cell line. This study provides biochemical evidence of the presence of a Na(+)-independent, facilitative transport system, LAT2, on the ARPE-19 cells.
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Affiliation(s)
- Mohit D Gandhi
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri Kansas City, 5005 Rockhill Road, Kansas City, MO 64110-2499, USA
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33
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Mackenzie B, Erickson JD. Sodium-coupled neutral amino acid (System N/A) transporters of the SLC38 gene family. Pflugers Arch 2004; 447:784-95. [PMID: 12845534 DOI: 10.1007/s00424-003-1117-9] [Citation(s) in RCA: 375] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2003] [Revised: 05/16/2003] [Accepted: 05/16/2003] [Indexed: 01/04/2023]
Abstract
The sodium-coupled neutral amino acid transporters (SNAT) of the SLC38 gene family resemble the classically-described System A and System N transport activities in terms of their functional properties and patterns of regulation. Transport of small, aliphatic amino acids by System A subtypes (SNAT1, SNAT2, and SNAT4) is rheogenic and pH sensitive. The System N subtypes SNAT3 and SNAT5 also countertransport H(+), which may be key to their operation in reverse, and have narrower substrate profiles than do the System A subtypes. Glutamine emerges as a favored substrate throughout the family, except for SNAT4. The SLC38 transporters undoubtedly play many physiological roles including the transfer of glutamine from astrocyte to neuron in the CNS, ammonia detoxification and gluconeogenesis in the liver, and the renal response to acidosis. Probing their regulation has revealed additional roles, and recent work has considered SLC38 transporters as therapeutic targets in neoplasia.
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Affiliation(s)
- Bryan Mackenzie
- Membrane Biology Program and Renal Division, Brigham and Women's Hospital and Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
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34
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Dolińska M, Zabłocka B, Sonnewald U, Albrecht J. Glutamine uptake and expression of mRNA's of glutamine transporting proteins in mouse cerebellar and cerebral cortical astrocytes and neurons. Neurochem Int 2004; 44:75-81. [PMID: 12971909 DOI: 10.1016/s0197-0186(03)00123-2] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The relative roles of the three sodium-dependent transport systems: A, ASC and N in the uptake of [3H]Gln, and the compatibility of the uptake characteristics with the expression of mRNAs coding for the Gln transporting molecules, were examined in primary cultures of astrocytes and neurons derived from mouse cerebellum, a glutaminergic system-enriched structure, and in cerebral cortex. Gln uptake activity (Vmax) was higher in cerebellar astrocytes or neurons than in their cerebral cortical counterparts. The N-methylamino-isobutyric acid (MeAiB)- and pH-sensitive, system A-mediated component of the uptake, and the uptake of [14C]MeAiB itself, was much more active in neurons than in astrocytes derived from either region. Also, the expression of mRNA for GlnT (SAT1), a system A isoform specific for Gln, was only expressed in neurons derived from both structures, while an alanine (Ala)-preferring system A transporter, SAT2, was expressed in neurons and astrocytes from either region. System ASC-mediated Gln uptake and expression of ASCT2 mRNA were in both structures more pronounced in astrocytes than in neurons, consistent with the postulated role of ASCT2 in the efflux of de novo synthesized Gln from astrocytes. System N-mediated (threonine+MeAiB-inhibitable) Gln uptake showed comparable activities in all four types of cells, which is compatible with the ubiquitous expression of NAT2 mRNA-a mouse brain-specific N-system isoform.
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Affiliation(s)
- Monika Dolińska
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawiñskiego St. 5, Warsaw 02-106, Poland
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35
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Zhou F, Tanaka K, Soares MJ, You G. Characterization of an organic anion transport system in a placental cell line. Am J Physiol Endocrinol Metab 2003; 285:E1103-9. [PMID: 12902320 DOI: 10.1152/ajpendo.00182.2003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transporters within the placenta play a crucial role in the distribution of nutrients and xenobiotics across the maternal-fetal interface. An organic anion transport system was identified on the apical membrane of the rat placenta cell line HRP-1, a model for the placenta barrier. The apical uptake of 3H-labeled organic anion estrone sulfate in HRP-1 cells was saturable (Km = 4.67 microM), temperature and Na+ dependent, Li+ tolerant, and pH sensitive. The substrate specificity of the transport system includes various steroid sulfates, such as beta-estradiol 3,17-disulfate, 17 beta-estradiol 3-sulfate, and dehydroepiandrosterone 3-sulfate (DHEAS) but does not include taurocholate, p-aminohippuric acid (PAH), and tetraethylammonium. Preincubation of HRP-1 cells with 8-bromo-cAMP (a cAMP analog) and forskolin (an adenylyl cyclase activator) acutely stimulated the apical transport activity. This stimulation was further enhanced in the presence of IBMX (a phosphodiesterase inhibitor). Together these data show that the apical membrane of HRP-1 cells expresses an organic anion transport system that is regulated by cellular cAMP levels. This transport system appears to be different from the known taurocholate-transporting organic anion-transporting polypeptides and PAH-transporting organic anion transporters, both of which also mediate the transport of estrone sulfate and DHEAS.
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Affiliation(s)
- Fanfan Zhou
- Department of Pharmaceutics, Rutgers, The State University of New Jersey, 160 Frelinghuysen Rd., Piscataway, NJ 08854, USA
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Dolińska M, Dybel A, Zabłocka B, Albrecht J. Glutamine transport in C6 glioma cells shows ASCT2 system characteristics. Neurochem Int 2003; 43:501-7. [PMID: 12742097 DOI: 10.1016/s0197-0186(03)00040-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Previous studies from this laboratory have shown that glutamine (Gln) uptake in a rat astrocytoma-derived C6 cell line shows characteristics similar with the uptake of a model ASC system substrate, threonine, whose pH-dependence and partial tolerance of Li(+) substitution for Na(+) resemble the ASCT2 variant of the system. In support of the previous findings, RT-PCR analysis revealed that C6 cells strongly express ASCT2 mRNA, but not at all GlnT mRNA or NAT2 mRNA, the A and N system variants specifically engaged in Gln transport in normal CNS. Other features of Gln transport in C6 cells indicating the involvement of ASCT2 system included its resistance to ouabain and stimulation of Gln efflux from the cells in the presence of excess Gln or cysteine (Cys), demonstrating that the system operates in the exchange mode. Replacement of NaCl in the incubation medium with isoosmotic sucrose did neither significantly affect the kinetics, nor any other major characteristics of Gln or Thr transport, including its pH-dependence, inhibition by ASCT system substrates or resistance to the model system A substrate-N-methylamino-isobutyric acid (MeAiB).
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Affiliation(s)
- Monika Dolińska
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawińskiego St. 5, 02-106 Warsaw, Poland
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Mackenzie B, Schäfer MKH, Erickson JD, Hediger MA, Weihe E, Varoqui H. Functional properties and cellular distribution of the system A glutamine transporter SNAT1 support specialized roles in central neurons. J Biol Chem 2003; 278:23720-30. [PMID: 12684517 DOI: 10.1074/jbc.m212718200] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glutamine, the preferred precursor for neurotransmitter glutamate and GABA, is likely to be the principal substrate for the neuronal System A transporter SNAT1 in vivo. We explored the functional properties of SNAT1 (the product of the rat Slc38a1 gene) by measuring radiotracer uptake and currents associated with SNAT1 expression in Xenopus oocytes and determined the neuronal-phenotypic and cellular distribution of SNAT1 by confocal laser-scanning microscopy alongside other markers. We found that SNAT1 mediates transport of small, neutral, aliphatic amino acids including glutamine (K0.5 approximately 0.3 mm), alanine, and the System A-specific analogue 2-(methylamino)isobutyrate. Amino acid transport is driven by the Na+ electrochemical gradient. The voltage-dependent binding of Na+ precedes that of the amino acid in a simultaneous transport mechanism. Li+ (but not H+) can substitute for Na+ but results in reduced Vmax. In the absence of amino acid, SNAT1 mediates Na+-dependent presteady-state currents (Qmax approximately 9 nC) and a nonsaturable cation leak with selectivity Na+, Li+ >> H+, K+. Simultaneous flux and current measurements indicate coupling stoichiometry of 1 Na+ per 1 amino acid. SNAT1 protein was detected in somata and proximal dendrites but not nerve terminals of glutamatergic and GABAergic neurons throughout the adult CNS. We did not detect SNAT1 expression in astrocytes but detected its expression on the luminal membranes of the ependyma. The functional properties and cellular distribution of SNAT1 support a primary role for SNAT1 in glutamine transport serving the glutamate/GABA-glutamine cycle in central neurons. Localization of SNAT1 to certain dopaminergic neurons of the substantia nigra and cholinergic motoneurons suggests that SNAT1 may play additional specialized roles, providing metabolic fuel (via alpha-ketoglutarate) or precursors (cysteine, glycine) for glutathione synthesis.
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Affiliation(s)
- Bryan Mackenzie
- Membrane Biology Program and Renal Division, Brigham & Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
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38
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Gu S, Langlais P, Liu F, Jiang JX. Mouse system-N amino acid transporter, mNAT3, expressed in hepatocytes and regulated by insulin-activated and phosphoinositide 3-kinase-dependent signalling. Biochem J 2003; 371:721-31. [PMID: 12537539 PMCID: PMC1223327 DOI: 10.1042/bj20030049] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2003] [Accepted: 01/22/2003] [Indexed: 11/17/2022]
Abstract
Amino acid transporters are essential for normal cell function and physiology. In the present study, we report the identification and functional and regulatory characterization of a mouse system-N amino acid transporter, mNAT3. Expression of mNAT3 in Xenopus oocytes revealed that the strongest transport activities were preferred for L-alanine. In addition, mNAT3 is an Na(+)- and pH-dependent low-affinity transporter and it partially tolerates substitution of Na(+) by Li(+). mNAT3 has been found to be expressed predominantly in the liver, where it is localized to the plasma membrane of hepatocytes, with the strongest expression in those cells adjacent to the central vein, decreasing gradually towards the portal tract. Treatment of mouse hepatocyte-like H2.35 cells with insulin led to a significant increase in the expression of mNAT3, and this stimulation was associated closely with an increase in the uptake of L-alanine. Interestingly, this insulin-induced stimulatory effect on mNAT3 expression was attenuated by the phosphoinositide 3-kinase inhibitor LY294002, but not by the mitogen-activated protein kinase inhibitor PD98059, although both kinases were fully activated by insulin. The results suggest that insulin-mediated regulation of mNAT3 is likely to be mediated through a phosphoinositide 3-kinase-dependent signalling pathway. The unique expression pattern and insulin-mediated regulatory properties of mNAT3 suggest that this transporter may play an important role in liver physiology.
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Affiliation(s)
- Sumin Gu
- Department of Biochemistry, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA
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Abstract
The most common optic neuropathy is glaucomatous optic neuropathy, distinguished by a distinctive and progressive excavation of the optic nerve head without significant pallor of the remaining neuroretinal rim. Neuroprotection is a novel strategy for treating disorders that affect the nervous system by preventing death of neurons. In glaucomatous optic neuropathy, the neurons that die are retinal ganglion cells. This article reviews the recent basic science relevant to neuroprotection, particularly with respect to retinal ganglion cell death in glaucomatous and other optic neuropathies.
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Affiliation(s)
- Francine B Wein
- Department of Ophthalmology, McGill University Health Center, Montreal, Canada
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Brown AM, Wender R, Ransom BR. Metabolic substrates other than glucose support axon function in central white matter. J Neurosci Res 2001; 66:839-43. [PMID: 11746409 DOI: 10.1002/jnr.10081] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We tested the hypothesis that non-glucose energy sources can support axon function in the rat optic nerve. Axon function was assessed by monitoring the stimulus-evoked compound action potential (CAP). CAP was maintained at full amplitude for 2 hr in 10 mM glucose. 20 mM lactate, 20 mM pyruvate, 10 mM fructose, or 10 mM mannose supported axon function as effectively as did glucose, and 10 mM glutamine provided partial support, but beta-hydroxybutyrate, octanoate, sorbitol, alanine, aspartate, and glutamate failed to support axon function. Our results indicated that a variety of compounds can sustain function in CNS myelinated axons. Axons probably use lactate, pyruvate, and glutamine directly as energy substrates, whereas mannose and fructose could be shuttled through astrocytes to lactate, which is then exported to axons.
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Affiliation(s)
- A M Brown
- Department of Neurology, Box 356465, University of Washington School of Medicine, Seattle, WA 98195, USA.
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