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Xiang J, Keep RF. Proton-Coupled Oligopeptide Transport (Slc15) in the Brain: Past and Future Research. Pharm Res 2023; 40:2533-2540. [PMID: 37308743 DOI: 10.1007/s11095-023-03550-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 06/06/2023] [Indexed: 06/14/2023]
Abstract
This mini-review describes the role of the solute carrier (SLC)15 family of proton-coupled oligopeptide transporters (POTs) and particularly Pept2 (Slc15A2) and PhT1 (Slc15A4) in the brain. That family transports endogenous di- and tripeptides and peptidomimetics but also a number of drugs. The review focuses on the pioneering work of David E. Smith in the field in identifying the impact of PepT2 at the choroid plexus (the blood-CSF barrier) as well as PepT2 and PhT1 in brain parenchymal cells. It also discusses recent findings and future directions in relation to brain POTs including cellular and subcellular localization, regulatory pathways, transporter structure, species differences and disease states.
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Affiliation(s)
- Jianming Xiang
- Department of Neurosurgery, University of Michigan, R5018 BSRB 109 Zina Pitcher Place, Ann Arbor, MI, 48109, USA
| | - Richard F Keep
- Department of Neurosurgery, University of Michigan, R5018 BSRB 109 Zina Pitcher Place, Ann Arbor, MI, 48109, USA.
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2
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Wang C, Chu C, Ji X, Luo G, Xu C, He H, Yao J, Wu J, Hu J, Jin Y. Biology of Peptide Transporter 2 in Mammals: New Insights into Its Function, Structure and Regulation. Cells 2022; 11:cells11182874. [PMID: 36139448 PMCID: PMC9497230 DOI: 10.3390/cells11182874] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 09/09/2022] [Accepted: 09/12/2022] [Indexed: 11/16/2022] Open
Abstract
Peptide transporter 2 (PepT2) in mammals plays essential roles in the reabsorption and conservation of peptide-bound amino acids in the kidney and in maintaining neuropeptide homeostasis in the brain. It is also of significant medical and pharmacological significance in the absorption and disposing of peptide-like drugs, including angiotensin-converting enzyme inhibitors, β-lactam antibiotics and antiviral prodrugs. Understanding the structure, function and regulation of PepT2 is of emerging interest in nutrition, medical and pharmacological research. In this review, we provide a comprehensive overview of the structure, substrate preferences and localization of PepT2 in mammals. As PepT2 is expressed in various organs, its function in the liver, kidney, brain, heart, lung and mammary gland has also been addressed. Finally, the regulatory factors that affect the expression and function of PepT2, such as transcriptional activation and posttranslational modification, are also discussed.
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Affiliation(s)
- Caihong Wang
- College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou 310032, China
- Department of Bioinformatics, College of Life Sciences, Zhejiang University, Hangzhou 310058, China
- Zhejiang Conba Pharmaceutical Limited Company, Hangzhou 310052, China
| | - Chu Chu
- College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou 310032, China
| | - Xiang Ji
- College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou 310032, China
| | - Guoliang Luo
- Zhejiang Conba Pharmaceutical Limited Company, Hangzhou 310052, China
- Zhejiang Institute of Modern Chinese Medicine and Natural Medicine, Hangzhou 310052, China
| | - Chunling Xu
- Zhejiang Conba Pharmaceutical Limited Company, Hangzhou 310052, China
- Zhejiang Institute of Modern Chinese Medicine and Natural Medicine, Hangzhou 310052, China
| | - Houhong He
- Zhejiang Conba Pharmaceutical Limited Company, Hangzhou 310052, China
- Zhejiang Institute of Modern Chinese Medicine and Natural Medicine, Hangzhou 310052, China
| | - Jianbiao Yao
- Zhejiang Conba Pharmaceutical Limited Company, Hangzhou 310052, China
- Zhejiang Institute of Modern Chinese Medicine and Natural Medicine, Hangzhou 310052, China
| | - Jian Wu
- Zhejiang Conba Pharmaceutical Limited Company, Hangzhou 310052, China
- Zhejiang Institute of Modern Chinese Medicine and Natural Medicine, Hangzhou 310052, China
| | - Jiangning Hu
- Zhejiang Conba Pharmaceutical Limited Company, Hangzhou 310052, China
- Zhejiang Institute of Modern Chinese Medicine and Natural Medicine, Hangzhou 310052, China
- Correspondence: (J.H.); (Y.J.)
| | - Yuanxiang Jin
- College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou 310032, China
- Correspondence: (J.H.); (Y.J.)
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Vacca F, Gomes AS, Murashita K, Cinquetti R, Roseti C, Barca A, Rønnestad I, Verri T, Bossi E. Functional characterization of Atlantic salmon (Salmo salar L.) PepT2 transporters. J Physiol 2022; 600:2377-2400. [PMID: 35413133 PMCID: PMC9321897 DOI: 10.1113/jp282781] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 03/16/2022] [Indexed: 11/24/2022] Open
Abstract
Abstract The high‐affinity/low‐capacity system Slc15a2 (PepT2) is responsible for the reuptake of di/tripeptides from the renal proximal tubule, but it also operates in many other tissues and organs. Information regarding PepT2 in teleost fish is limited and, to date, functional data are available from the zebrafish (Danio rerio) only. Here, we report the identification of two slc15a2 genes in the Atlantic salmon (Salmo salar) genome, namely slc15a2a and slc15a2b. The two encoded PepT2 proteins share 87% identity and resemble both structurally and functionally the canonical vertebrate PepT2 system. The mRNA tissue distribution analyses reveal a widespread distribution of slc15a2a transcripts, being more abundant in the brain and gills, while slc15a2b transcripts are mainly expressed in the kidney and the distal part of the gastrointestinal tract. The function of the two transporters was investigated by heterologous expression in Xenopus laevis oocytes and two‐electrode voltage‐clamp recordings of transport and presteady‐state currents. Both PepT2a and PepT2b in the presence of Gly‐Gln elicit pH‐dependent and Na+ independent inward currents. The biophysical and kinetic analysis of the recorded currents defined the transport properties, confirming that the two Atlantic salmon PepT2 proteins behave as high‐affinity/low‐capacity transporters. The recent structures and the previous kinetic schemes of rat and human PepT2 qualitatively account for the characteristics of the two Atlantic salmon proteins. This study is the first to report on the functional expression of two PepT2‐type transporters that operate in the same vertebrate organism as a result of (a) gene duplication process(es). Key points Two slc15a2‐type genes, slc15a2a and slc15a2b coding for PepT2‐type peptide transporters were found in the Atlantic salmon. slc15a2a
transcripts, widely distributed in the fish tissues, are abundant in the brain and gills, while slc15a2b transcripts are mainly expressed in the kidney and distal gastrointestinal tract. Amino acids involved in vertebrate Slc15 transport function are conserved in PepT2a and PepT2b proteins. Detailed kinetic analysis indicates that both PepT2a and PepT2b operate as high‐affinity transporters. The kinetic schemes and structures proposed for the mammalian models of PepT2 are suitable to explain the function of the two Atlantic salmon transporters.
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Affiliation(s)
- Francesca Vacca
- Laboratory of Cellular and Molecular Physiology, Department of Biotechnology and Life Sciences, University of Insubria, via Dunant 3, Varese, I-21100, Italy
| | - Ana S Gomes
- Department of Biological Sciences, University of Bergen, Po. Box 7803, Bergen, NO-5020, Norway
| | - Koji Murashita
- Research Center for Aquaculture Systems, National Research Institute of Aquaculture, Japan Fisheries Research and Education Agency, Minami-ise, Mie, 516-0193, Japan
| | - Raffella Cinquetti
- Laboratory of Cellular and Molecular Physiology, Department of Biotechnology and Life Sciences, University of Insubria, via Dunant 3, Varese, I-21100, Italy
| | - Cristina Roseti
- Laboratory of Cellular and Molecular Physiology, Department of Biotechnology and Life Sciences, University of Insubria, via Dunant 3, Varese, I-21100, Italy
| | - Amilcare Barca
- Laboratory of Applied Physiology, Department of Biological and Environmental Sciences and Technologies, University of Salento, via Provinciale Lecce-Monteroni, Lecce, I-73100, Italy
| | - Ivar Rønnestad
- Department of Biological Sciences, University of Bergen, Po. Box 7803, Bergen, NO-5020, Norway
| | - Tiziano Verri
- Laboratory of Applied Physiology, Department of Biological and Environmental Sciences and Technologies, University of Salento, via Provinciale Lecce-Monteroni, Lecce, I-73100, Italy
| | - Elena Bossi
- Laboratory of Cellular and Molecular Physiology, Department of Biotechnology and Life Sciences, University of Insubria, via Dunant 3, Varese, I-21100, Italy
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Takano M, Kuriyama S, Kameda N, Kawami M, Yumoto R. Effect of Corticosteroids on Peptide Transporter 2 Function and Induction of Innate Immune Response by Bacterial Peptides in Alveolar Epithelial Cells. Biol Pharm Bull 2022; 45:213-219. [PMID: 35110509 DOI: 10.1248/bpb.b21-00813] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In the lung alveolar region, the innate immune system serves as an important host defense system. We recently reported that peptide transporter 2 (PEPT2) has an essential role in the uptake of bacterial peptides and induction of innate immune response in alveolar epithelial cells. In this study, we aimed to clarify the effects of corticosteroids on PEPT2 function and PEPT2-dependent innate immune response. NCI-H441 (H441) cells were used as an in vitro model of human alveolar type II epithelial cells, and the effects of dexamethasone (DEX) and budesonide (BUD) on the transport function of PEPT2 and the innate immune response induced by bacterial peptides were examined. PEPT2 function, estimated by measuring β-alanyl-Nε-(7-amino-4-methyl-2-oxo-2H-1-benzopyran-3-acetyl)-L-lysine (β-Ala-Lys-AMCA) uptake in H441 cells, was suppressed by treatment with DEX and BUD in a concentration- and time-dependent manner. The suppression of PEPT2 function was partially recovered by a glucocorticoid receptor antagonist. The expression of PEPT2 and nucleotide-binding oligomerization domain 1 (NOD1) mRNAs was suppressed by treatment with DEX and BUD, while PEPT2 protein level was not changed by these treatment conditions. Additionally, the increased mRNA expression of interleukin (IL)-8 and the increased secretion of IL-8 into the culture medium induced by bacterial peptides were also suppressed by treatment with these corticosteroids. Taken together, these results clearly suggest that corticosteroids suppress PEPT2 function and bacterial peptide-induced innate immune response in alveolar epithelial cells. Therefore, PEPT2- and NOD1-dependent innate immune response induced by bacterial peptides in the lung alveolar region may be suppressed during the inhaled corticosteroid therapy.
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Affiliation(s)
- Mikihisa Takano
- Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical and Health Sciences, Hiroshima University
| | - Shiori Kuriyama
- Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical and Health Sciences, Hiroshima University
| | - Nanako Kameda
- Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical and Health Sciences, Hiroshima University
| | - Masashi Kawami
- Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical and Health Sciences, Hiroshima University
| | - Ryoko Yumoto
- Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical and Health Sciences, Hiroshima University
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5
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Giannaki M, Ludwig C, Heermann S, Roussa E. Regulation of electrogenic Na + /HCO 3 - cotransporter 1 (NBCe1) function and its dependence on m-TOR mediated phosphorylation of Ser 245. J Cell Physiol 2021; 237:1372-1388. [PMID: 34642952 DOI: 10.1002/jcp.30601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 09/09/2021] [Accepted: 10/01/2021] [Indexed: 11/09/2022]
Abstract
Astrocytes are pivotal responders to alterations of extracellular pH, primarily by regulation of their principal acid-base transporter, the membrane-bound electrogenic Na+ /bicarbonate cotransporter 1 (NBCe1). Here, we describe amammalian target of rapamycin (mTOR)-dependent and NBCe1-mediated astroglial response to extracellular acidosis. Using primary mouse cortical astrocytes, we investigated the effect of long-term extracellular metabolic acidosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H+ recording using the H+ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant increase of NBCe1-mediated recovery of intracellular pH from acidification in WT astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Acidosis-induced upregulation of NBCe1 activity was prevented following inhibition of mTOR signaling by rapamycin. Yet, during acidosis or following exposure of astrocytes to rapamycin, surface protein abundance of NBCe1 remained -unchanged. Mutational analysis in HeLa cells suggested that NBCe1 activity was dependent on phosphorylation state of Ser245 , a residue conserved in all NBCe1 variants. Moreover, phosphorylation state of Ser245 is regulated by mTOR and is inversely correlated with NBCe1 transport activity. Our results identify pSer245 as a novel regulator of NBCe1 functional expression. We propose that context-dependent and mTOR-mediated multisite phosphorylation of serine residues of NBCe1 is likely to be a potent mechanism contributing to the response of astrocytes to acid/base challenges during pathophysiological conditions.
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Affiliation(s)
- Marina Giannaki
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Medical Faculty, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Christina Ludwig
- Bavarian Center for Biomolecular Mass Spectrometry (BayBioMS), Technical University of Munich (TUM), Freising, Germany
| | - Stephan Heermann
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Medical Faculty, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Eleni Roussa
- Department of Molecular Embryology, Institute of Anatomy and Cell Biology, Medical Faculty, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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Viennois E, Pujada A, Zen J, Merlin D. Function, Regulation, and Pathophysiological Relevance of the POT Superfamily, Specifically PepT1 in Inflammatory Bowel Disease. Compr Physiol 2018; 8:731-760. [PMID: 29687900 DOI: 10.1002/cphy.c170032] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Mammalian members of the proton-coupled oligopeptide transporter family are integral membrane proteins that mediate the cellular uptake of di/tripeptides and peptide-like drugs and couple substrate translocation to the movement of H+ , with the transmembrane electrochemical proton gradient providing the driving force. Peptide transporters are responsible for the (re)absorption of dietary and/or bacterial di- and tripeptides in the intestine and kidney and maintaining homeostasis of neuropeptides in the brain. These proteins additionally contribute to absorption of a number of pharmacologically important compounds. In this overview article, we have provided updated information on the structure, function, expression, localization, and activities of PepT1 (SLC15A1), PepT2 (SLC15A2), PhT1 (SLC15A4), and PhT2 (SLC15A3). Peptide transporters, in particular, PepT1 are discussed as drug-delivery systems in addition to their implications in health and disease. Particular emphasis has been placed on the involvement of PepT1 in the physiopathology of the gastrointestinal tract, specifically, its role in inflammatory bowel diseases. © 2018 American Physiological Society. Compr Physiol 8:731-760, 2018.
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Affiliation(s)
- Emilie Viennois
- Institute for Biomedical Sciences, Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, USA
| | - Adani Pujada
- Institute for Biomedical Sciences, Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, USA
| | - Jane Zen
- Institute for Biomedical Sciences, Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, USA
| | - Didier Merlin
- Institute for Biomedical Sciences, Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, USA.,Veterans Affairs Medical Center, Decatur, Georgia, USA
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7
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Usefulness of kidney slices for functional analysis of apical reabsorptive transporters. Sci Rep 2017; 7:12814. [PMID: 28993647 PMCID: PMC5634478 DOI: 10.1038/s41598-017-12828-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 09/15/2017] [Indexed: 02/02/2023] Open
Abstract
Kidney plays a key role in the elimination and reabsorption of drugs and nutrients, however in vitro methods to evaluate renal disposition are limited. In the present study, we investigated usefulness of isolated kidney slice, which had been used for transport only at basolateral membrane of tubular epithelial cells, for evaluation of apical membrane transporters. As transporters that are easy to discriminate between apical and basolateral transports, apical membrane specific and sodium-dependent transporters (SGLTs and OCTNs) and pH-dependent transporters (PEPTs) are selected. Uptake of ergothioneine, carnitine and methyl-α-D-glucopyranoside, which are substrates of apical Octn1, Octn2, and Sglt1/2, respectively, by mice kidney slices showed clear Na+ dependence and reduction by selective inhibitors. In addition, sodium dependence of ergothioneine uptake was negligible in the kidney slice from Octn1-gene deficient mice. Moreover, uptake of PepT1/2 substrate glycyl-sarcosine, was higher than that in the presence of glycyl-leucine, a non-specific Pept inhibitor. The Km and IC50 values for substrates and inhibitors of each transporter were mostly comparable to those obtained in transporter-transfected cells. In conclusion, it was demonstrated that kidney slices are promising tool to study transporters expressed at the apical membranes as well as basolateral membranes of kidney tubular epithelial cells.
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8
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Di- and tripeptide transport in vertebrates: the contribution of teleost fish models. J Comp Physiol B 2016; 187:395-462. [PMID: 27803975 DOI: 10.1007/s00360-016-1044-7] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 10/12/2016] [Accepted: 10/20/2016] [Indexed: 02/06/2023]
Abstract
Solute Carrier 15 (SLC15) family, alias H+-coupled oligopeptide cotransporter family, is a group of membrane transporters known for their role in the cellular uptake of di- and tripeptides (di/tripeptides) and peptide-like molecules. Of its members, SLC15A1 (PEPT1) chiefly mediates intestinal absorption of luminal di/tripeptides from dietary protein digestion, while SLC15A2 (PEPT2) mainly allows renal tubular reabsorption of di/tripeptides from ultrafiltration, SLC15A3 (PHT2) and SLC15A4 (PHT1) possibly interact with di/tripeptides and histidine in certain immune cells, and SLC15A5 has unknown function. Our understanding of this family in vertebrates has steadily increased, also due to the surge of genomic-to-functional information from 'non-conventional' animal models, livestock, poultry, and aquaculture fish species. Here, we review the literature on the SLC15 transporters in teleost fish with emphasis on SLC15A1 (PEPT1), one of the solute carriers better studied amongst teleost fish because of its relevance in animal nutrition. We report on the operativity of the transporter, the molecular diversity, and multiplicity of structural-functional solutions of the teleost fish orthologs with respect to higher vertebrates, its relevance at the intersection of the alimentary and osmoregulative functions of the gut, its response under various physiological states and dietary solicitations, and its possible involvement in examples of total body plasticity, such as growth and compensatory growth. By a comparative approach, we also review the few studies in teleost fish on SLC15A2 (PEPT2), SLC15A4 (PHT1), and SLC15A3 (PHT2). By representing the contribution of teleost fish to the knowledge of the physiology of di/tripeptide transport and transporters, we aim to fill the gap between higher and lower vertebrates.
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Abstract
Oligopeptide transporters serve important functions in nutrition and pharmacology. In particular, these transporters help maintain the homeostasis of peptides. The peptide-transporter PEPT2 is a high-affinity and low-capacity type oligopeptide transporter from the proton-coupled oligopeptide transporter family. PEPT2 has recently received attention because of its potential application in targeted drug delivery. PEPT2 is widely distributed in kidney, central nervous system, and lung of organisms. In general, all dipeptides, tripeptides, and peptide-like drugs such as β-lactam antibiotics and angiotensin-converting enzyme inhibitors could be mediated and transported as a substrate of PEPT2. The design of many extant drugs and prodrugs is based on the substrate structure of PEPT2 to accelerate absorption via peptide transporters. Thus, this paper summarizes the substrate features of PEPT2 to promote the rational design of drugs and prodrugs that target peptide transporters.
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Affiliation(s)
- Dongxin Zhao
- School of Chemistry and Chemical Engineering, Henan University of Technology
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10
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Wang P, Li L, Zhang Z, Kan Q, Gao F, Chen S. Time-dependent activity of Na+/H+ exchanger isoform 1 and homeostasis of intracellular pH in astrocytes exposed to CoCl2 treatment. Mol Med Rep 2016; 13:4443-50. [PMID: 27035646 DOI: 10.3892/mmr.2016.5067] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 02/11/2016] [Indexed: 11/06/2022] Open
Abstract
Hypoxia causes injury to the central nervous system during stroke and has significant effects on pH homeostasis. Na+/H+ exchanger isoform 1 (NHE1) is important in the mechanisms of hypoxia and intracellular pH (pHi) homeostasis. As a well-established hypoxia-mimetic agent, CoCl2 stabilizes and increases the expression of hypoxia inducible factor‑1α (HIF-1α), which regulates several genes involved in pH balance, including NHE1. However, it is not fully understood whether NHE1 is activated in astrocytes under CoCl2 treatment. In the current study, pHi and NHE activity were analyzed using the pHi‑sensitive dye BCECF‑AM. Using cariporide (an NHE1‑specific inhibitor) and EIPA (an NHE nonspecific inhibitor), the current study demonstrated that it was NHE1, not the other NHE isoforms, that was important in regulating pHi homeostasis in astrocytes during CoCl2 treatment. Additionally, the present study observed that, during the early period of CoCl2 treatment (the first 2 h), NHE1 activity and pHi dropped immediately, and NHE1 mRNA expression was reduced compared with control levels, whereas expression levels of the NHE1 protein had not yet changed. In the later period of CoCl2 treatment, NHE1 activity and pHi significantly increased compared with the control levels, as did the mRNA and protein expression levels of NHE1. Furthermore, the cell viability and injury of astrocytes was not changed during the initial 8 h of CoCl2 treatment; their deterioration was associated with the higher levels of pHi and NHE1 activity. The current study concluded that NHE1 activity and pHi homeostasis are regulated by CoCl2 treatment in a time-dependent manner in astrocytes, and may be responsible for the changes in cell viability and injury observed under hypoxia-mimetic conditions induced by CoCl2 treatment.
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Affiliation(s)
- Peng Wang
- Department of Basic Medicine, Nursing College, Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Ling Li
- Department of Palliative and Hospice Care, The Ninth People's Hospital of Zhengzhou, Zhengzhou, Henan 450053, P.R. China
| | - Zhenxiang Zhang
- Department of Basic Medicine, Nursing College, Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Quancheng Kan
- Clinical Pharmacology Base, Department of Infectious Disease, First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Feng Gao
- Department of Neuroimmunology, Henan Academy of Medical and Pharmaceutical Sciences, Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Suyan Chen
- Department of Basic Medicine, Nursing College, Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
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11
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Na+-H+ exchanger-1 (NHE1) regulation in kidney proximal tubule. Cell Mol Life Sci 2015; 72:2061-74. [PMID: 25680790 DOI: 10.1007/s00018-015-1848-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 01/28/2015] [Accepted: 01/29/2015] [Indexed: 01/17/2023]
Abstract
The ubiquitously expressed plasma membrane Na(+)-H(+) exchanger NHE1 is a 12 transmembrane-spanning protein that directs important cell functions such as homeostatic intracellular volume and pH control. The 315 amino acid cytosolic tail of NHE1 binds plasma membrane phospholipids and multiple proteins that regulate additional, ion-translocation independent functions. This review focuses on NHE1 structure/function relationships, as well as the role of NHE1 in kidney proximal tubule functions, including pH regulation, vectorial Na(+) transport, cell volume control and cell survival. The implications of these functions are particularly critical in the setting of progressive, albuminuric kidney diseases, where the accumulation of reabsorbed fatty acids leads to disruption of NHE1-membrane phospholipid interactions and tubular atrophy, which is a poor prognostic factor for progression to end stage renal disease. This review amplifies the vital role of the proximal tubule NHE1 Na(+)-H(+) exchanger as a kidney cell survival factor.
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12
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Takano M, Horiuchi T, Sasaki Y, Kato Y, Nagai J, Yumoto R. Expression and function of PEPT2 during transdifferentiation of alveolar epithelial cells. Life Sci 2013; 93:630-6. [DOI: 10.1016/j.lfs.2013.08.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 08/10/2013] [Accepted: 08/15/2013] [Indexed: 01/25/2023]
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13
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Spanier B. Transcriptional and functional regulation of the intestinal peptide transporter PEPT1. J Physiol 2013; 592:871-9. [PMID: 23959672 DOI: 10.1113/jphysiol.2013.258889] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Dietary proteins are cleaved within the intestinal lumen to oligopeptides which are further processed to small peptides (di- and tripeptides) and free amino acids. Although the transport of amino acids is mediated by several specific amino acid transporters, the proton-coupled uptake of the more than 8000 different di- and tripeptides is performed by the high-capacity/low-affinity peptide transporter isoform PEPT1 (SLC15A1). Its wide substrate tolerance also allows the transport of a repertoire of structurally closely related compounds and drugs, which explains their high oral bioavailability and brings PEPT1 into focus for medical and pharmaceutical approaches. Although the first evidence for the interplay of nutrient supply and PEPT1 expression and function was described over 20 years ago, many aspects of the molecular processes controlling its transcription and translation and modifying its transporter properties are still awaiting discovery. The present review summarizes the recent knowledge on the factors modulating PEPT1 expression and function in Caenorhabditis elegans, Danio rerio, Mus musculus and Homo sapiens, with focus on dietary ingredients, transcription factors and functional modulators, such as the sodium-proton exchanger NHE3 and selected scaffold proteins.
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Affiliation(s)
- Britta Spanier
- Biochemistry, Technische Universität München, ZIEL Research Center of Nutrition and Food Sciences, Gregor-Mendel-Straße 2, D-85350 Freising, Germany.
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14
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Tai W, Chen Z, Cheng K. Expression profile and functional activity of peptide transporters in prostate cancer cells. Mol Pharm 2012; 10:477-87. [PMID: 22950754 DOI: 10.1021/mp300364k] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Peptide transporters are expressed predominantly in intestinal and renal epithelial cells. The functional expression of peptide transporters is also identified in other types of tissues, such as glia cells, macrophages, and the epithelia of the bile duct, the lungs, and the mammary glands. However, their presence and role are poorly understood in carcinomas. We explored the expression profile and functional activity of peptide transporters in the prostate cancer cell lines LNCaP, PC-3, and DU145. Quantitative real time RT-PCR (qRT-PCR) and Western blot were used to evaluate the expression profile of peptide transporter 1 (PEPT1), peptide transporter 2 (PEPT2), peptide histidine transporter 1 (PHT1), and peptide histidine transporter 2 (PHT2) in these cells. LNCaP expresses high levels of PEPT2 and PHT1, while PC-3 demonstrates strong expression of PEPT1 and PHT1. DU145 shows only weak expression of PEPT1 and PHT1. Functional activities were studied in these cell lines using radiolabeled glycylsarcosine ([(3)H]Gly-Sar) and l-histidine ([(3)H]-l-histidine). The uptake of [(3)H]Gly-Sar and [(3)H]-l-histidine was time- and pH-dependent. A kinetic study showed that the uptake of Gly-Sar and l-histidine is saturable over the tested concentration range. The binding affinity (K(m)) and the maximal velocity (V(max)) exhibited in the three cell lines were consistent with the expression profiles we observed in qRT-PCR and Western blot analysis. A competitive inhibition study revealed that peptide transporters in prostate cancer cells exhibited broad substrate specificity with a preference for hydrophobic dipeptides, such as Leu-Leu. Fluorescence microscopy study revealed that the fluorescent dipeptide probe d-Ala-Lys-AMCA (a substrate of peptide transporters) specifically accumulated in the cytoplasm of LNCaP and PC-3, but not DU145 cells. Inhibiting the peptide transporter activity by Gly-Sar suppressed the growth of LNCaP and PC-3 cells. Our study indicated that PC-3 cells can be established as a new cell culture model for PEPT1 study, and LNCaP can be used as a model for PEPT2 study. Moreover, our results suggested that peptide transporters are overexpressed in prostate cancer cells and can be adopted as a promising target for tumor-specific drug delivery.
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Affiliation(s)
- Wanyi Tai
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, 2464 Charlotte Street, Kansas City, Missouri 64108, United States
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15
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Anderson CMH, Thwaites DT. Hijacking solute carriers for proton-coupled drug transport. Physiology (Bethesda) 2011; 25:364-77. [PMID: 21186281 DOI: 10.1152/physiol.00027.2010] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The physiological role of mammalian solute carrier (SLC) proteins is to mediate transmembrane movement of electrolytes, nutrients, micronutrients, vitamins, and endogenous metabolites from one cellular compartment to another. Many transporters in the small intestine, kidney, and solid tumors are H(+)-coupled, driven by local H(+)-electrochemical gradients, and transport numerous drugs. These transporters include PepT1 and PepT2 (SLC15A1/2), PCFT (SLC46A1), PAT1 (SLC36A1), OAT10 (SLC22A13), OATP2B1 (SLCO2B1), MCT1 (SLC16A1), and MATE1 and MATE2-K (SLC47A1/2).
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Affiliation(s)
- Catriona M H Anderson
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
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16
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Romano A, Barca A, Kottra G, Daniel H, Storelli C, Verri T. Functional expression of SLC15 peptide transporters in rat thyroid follicular cells. Mol Cell Endocrinol 2010; 315:174-81. [PMID: 19913073 DOI: 10.1016/j.mce.2009.11.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Revised: 09/23/2009] [Accepted: 11/02/2009] [Indexed: 11/19/2022]
Abstract
Peptide transport and expression of SoLute Carrier 15 (SLC15) peptide transporters was assessed in rat thyroid tissue and a rat thyroid cell line (PC Cl3 cells). Peptide transport was studied by monitoring the uptake of the fluorophore-conjugated dipeptide beta-Ala-Lys-N(epsilon)-7-amino-4-methyl-coumarin-3-acetic acid (Ala-Lys-AMCA). Expression of SLC15-specific mRNA transcripts was analyzed by RT-PCR. Of the two SLC15 transporters expressed in thyroid follicular cells, namely PEPT2 (SLC15A2) and PHT1 (SLC15A4), only PEPT2 was involved in peptide transport at the plasma membrane, with PHT1 most likely being intracellular. Interestingly, at the mRNA level PEPT2 was up-regulated under TSH stimulation. These findings represent the first evidence that peptide transport occurs in thyroid follicular cells. SLC15 transporters could participate to recycling of peptides derived from extracellular and lysosomal thyroglobulin proteolysis, both essential steps for thyroid hormone synthesis.
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Affiliation(s)
- A Romano
- Laboratory of General Physiology, Department of Biological and Environmental Sciences and Technologies, University of Salento, via Provinciale Lecce-Monteroni, I-73100 Lecce, Italy
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17
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Rubio-Aliaga I, Daniel H. Peptide transporters and their roles in physiological processes and drug disposition. Xenobiotica 2008; 38:1022-42. [PMID: 18668438 DOI: 10.1080/00498250701875254] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
1. The peptide transporters belong to the peptide transporter (PTR) family and serve as integral membrane proteins for the cellular uptake of di- and tripeptides in the organism. By their ability also to transport peptidomimetics and other substrates with therapeutic activities or precursors of pharmacologically active agents, they are of considerable importance in pharmacology. 2. PEPT1 is the low-affinity, high-capacity transporter and is mainly expressed in the small intestine, whereas PEPT2 is the high-affinity, low-capacity transporter and has a broader distribution in the organism. 3. Targeted mouse models have revealed PEPT2 to be the dominant transporter for the reabsorption of di- and tripeptides and its pharmacological substrates in the organism, and for the removal of these substrates from the cerebrospinal fluid. Moreover, the peptide transporters undergo physiological and pharmacological regulation and, of great interest, are present in disease states where PEPT1 exhibits ectopic expression in colonic inflammation. 4. The paper reviews the structural characteristics of the peptide transporters, the structural requirements for substrates, the distribution of the peptide transporters in the organism, and finally their regulation in the organism in healthy and pathological situations.
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Affiliation(s)
- I Rubio-Aliaga
- Molecular Nutrition Unit, Technical University of Munich, Freising-Weihenstephan, Germany
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18
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Obara M, Szeliga M, Albrecht J. Regulation of pH in the mammalian central nervous system under normal and pathological conditions: facts and hypotheses. Neurochem Int 2007; 52:905-19. [PMID: 18061308 DOI: 10.1016/j.neuint.2007.10.015] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Revised: 10/17/2007] [Accepted: 10/22/2007] [Indexed: 11/27/2022]
Abstract
The maintenance of pH homeostasis in the CNS is of key importance for proper execution and regulation of neurotransmission, and deviations from this homeostasis are a crucial factor in the mechanism underlying a spectrum of pathological conditions. The first few sections of the review are devoted to the brain operating under normal conditions. The article commences with an overview of how extrinsic factors modelling the brain at work: neurotransmitters, depolarising stimuli (potassium and voltage changes) and cyclic nucleotides as major signal transducing vehicles affect pH in the CNS. Further, consequences of pH alterations on the major aspects of CNS function and metabolism are outlined. Next, the major cellular events involved in the transport, sequestration, metabolic production and buffering of protons that are common to all the mammalian cells, including the CNS cells. Since CNS function reflects tight interaction between astrocytes and neurons, the pH regulatory events pertinent to either cell type are discussed: overwhelming evidence implicates astrocytes as a key player in pH homeostasis in the brain. The different classes of membrane proteins involved in proton shuttling are listed and their mechanisms of action are given. These include: the Na+/H+ exchanger, different classes of bicarbonate transporters acting in a sodium-dependent- or -independent mode, monocarboxylic acid transporters and the vacuolar-type proton ATPase. A separate section is devoted to carbonic anhydrase, which is represented by multiple isoenzymes capable of pH buffering both in the cell interior and in the extracellular space. Next, impairment of pH regulation and compensatory responses occurring in brain affected by different pathologies: hypoxia/ischemia, epilepsy, hyperammonemic encephalopathies, cerebral tumours and HIV will be described. The review is limited to facts and plausible hypotheses pertaining to phenomena directly involved in pH regulation: changes in pH that accompany metabolic stress but have no distinct implications for the pH regulatory mechanisms are not dealt with. In most cases, the vast body of knowledge derived from in vitro studies remains to be verified in in vivo settings.
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Affiliation(s)
- Marta Obara
- Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, 5 Pawińskiego Street, 02-106 Warsaw, Poland
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19
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Xiang J, Hu Y, Smith DE, Keep RF. PEPT2-mediated transport of 5-aminolevulinic acid and carnosine in astrocytes. Brain Res 2006; 1122:18-23. [PMID: 17034769 PMCID: PMC1829310 DOI: 10.1016/j.brainres.2006.09.013] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Revised: 09/05/2006] [Accepted: 09/06/2006] [Indexed: 11/28/2022]
Abstract
5-aminolevulinic acid (ALA) and carnosine have important physiological and pathophysiological roles in the CNS. Both are substrates for the proton-coupled oligopeptide transporter PEPT2. The purpose of the current study was to determine the importance of PEPT2 in the uptake of ALA and carnosine in rat and mouse (PEPT2+/+ and PEPT2-/-) cultured neonatal astrocytes. Although neonatal astrocytes are known to express PEPT2, its quantitative importance in the transport of these compounds is not known. [14C]ALA uptake in neonatal rat astrocytes was inhibited by dipeptides, an alpha-amino containing cephalosporin (which is a PEPT2 substrate) but was not affected by a non-amino containing cephalosporin (which is not a PEPT2 substrate). Uptake was pH sensitive as expected from a proton-coupled transporter and was saturable (Vmax=715+/-29 pmol/mg/min, Km=606+/-14 microM). [3H]Carnosine uptake in neonatal rat astrocytes was inhibited by dipeptides but not by histidine (a substrate for the peptide/histidine transporters PHT1 and PHT2) and also showed saturable transport (Vmax=447+/-23 pmol/mg/min, Km=43+/-5.5 microM). Neonatal astrocytes from PEPT2-/- mice had a 62% reduction in [14C]ALA uptake and a 92% reduction in [3H]carnosine uptake compared to PEPT2+/+ mice. These results demonstrate that PEPT2 is the primary transporter responsible for the astrocytic uptake of ALA and carnosine.
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Affiliation(s)
- Jianming Xiang
- Department of Neurosurgery, University of Michigan, 5014 BSRB, Ann Arbor, MI 48109-2200, USA.
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20
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Noshiro R, Anzai N, Sakata T, Miyazaki H, Terada T, Shin HJ, He X, Miura D, Inui K, Kanai Y, Endou H. The PDZ domain protein PDZK1 interacts with human peptide transporter PEPT2 and enhances its transport activity. Kidney Int 2006; 70:275-82. [PMID: 16738539 DOI: 10.1038/sj.ki.5001522] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The proton-coupled peptide transporter PEPT2 (SLC15A2) mediates the high-affinity low-capacity transport of small peptides as well as various oral peptide-like drugs in the kidney. In contrast to its well-characterized transport properties, there is less information available on its regulatory mechanism, although the interaction of PEPT2 to the PDZ (PSD-95, DglA, and ZO-1)-domain protein PDZK1 has been preliminarily reported. To examine whether PDZK1 is a physiological partner of PEPT2 in kidneys, we started from a yeast two-hybrid screen of a human kidney cDNA library with the C-terminus of PEPT2 (PEPT2 C-terminus (PEPT2-CT)) as bait. We could identify PDZK1 as one of the positive clones. This interaction requires the PDZ motif of PEPT2-CT detected by a yeast two-hybrid assay, in vitro binding assay and co-immunoprecipitation. The binding affinities of second and third PDZ domains of PDZK1 to PEPT2-CT were measured by surface plasmon resonance. Co-immunoprecipitation using human kidney membrane fraction and localization of PEPT2 in renal apical proximal tubules revealed the physiological meaning of this interaction in kidneys. Furthermore, we clarified the mechanism of enhanced glycylsarcosine (Gly-Sar) transport activity in PEPT2-expressing HEK293 cells after the PDZK1 coexpression. This augmentation was accompanied by a significant increase in the V(max) of Gly-Sar transport via PEPT2 and it was also associated with the increased surface expression level of PEPT2. These results indicate that the PEPT2-PDZK1 interaction thus plays a physiologically important role in both oligopeptide handling as well as peptide-like drug transport in the human kidney.
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Affiliation(s)
- R Noshiro
- Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Mitaka, Tokyo, Japan
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21
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Yodoya E, Wada M, Shimada A, Katsukawa H, Okada N, Yamamoto A, Ganapathy V, Fujita T. Functional and molecular identification of sodium-coupled dicarboxylate transporters in rat primary cultured cerebrocortical astrocytes and neurons. J Neurochem 2006; 97:162-73. [PMID: 16524379 DOI: 10.1111/j.1471-4159.2006.03720.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Na+-coupled carboxylate transporters (NaCs) mediate the uptake of tricarboxylic acid cycle intermediates in mammalian tissues. Of these transporters, NaC3 (formerly known as Na+-coupled dicarboxylate transporter 3, NaDC3/SDCT2) and NaC2 (formerly known as Na+-coupled citrate transporter, NaCT) have been shown to be expressed in brain. There is, however, little information available on the precise distribution and function of both transporters in the CNS. In the present study, we investigated the functional characteristics of Na+-dependent succinate and citrate transport in primary cultures of astrocytes and neurons from rat cerebral cortex. Uptake of succinate was Na+ dependent, Li+ sensitive and saturable with a Michaelis constant (Kt) value of 28.4 microM in rat astrocytes. Na+ activation kinetics revealed that the Na+ to succinate stoichiometry was 3:1 and the concentration of Na+ necessary for half-maximal transport was 53 mM. Although uptake of citrate in astrocytes was also Na+ dependent and saturable, its Kt value was significantly higher (approximately 1.2 mM) than that of succinate. Unlabeled succinate (2 mM) inhibited Na+-dependent [14C]succinate (18 microM) and [14C]citrate (4.5 microM) transport completely, whereas unlabeled citrate inhibited Na+-dependent [14C]succinate uptake more weakly. Interestingly, N-acetyl-L-aspartate, which is the second most abundant amino acid in the nervous system, also completely inhibited Na+-dependent succinate transport in rat astrocytes. The inhibition constant (Ki) for the inhibition of [14C]succinate uptake by unlabeled succinate, N-acetyl-L-aspartate and citrate was 15.9, 155 and 764 microM respectively. In primary cultures of neurons, uptake of citrate was also Na+ dependent and saturable with a Kt value of 16.2 microM, which was different from that observed in astrocytes, suggesting that different Na+-dependent citrate transport systems are expressed in neurons and astrocytes. RT-PCR and immunocytochemistry revealed that NaC3 and NaC2 are expressed in cerebrocortical astrocytes and neurons respectively. These results are in good agreement with our previous reports on the brain distribution pattern of NaC2 and NaC3 mRNA using in situ hybridization. This is the first report of the differential expression of different NaCs in astrocytes and neurons. These transporters might play important roles in the trafficking of tricarboxylic acid cycle intermediates and related metabolites between glia and neurons.
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Affiliation(s)
- Etsuo Yodoya
- Department of Biopharmaceutics, Kyoto Pharmaceutical University, Yamashina-ku, Kyoto, Japan
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22
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Wada M, Shimada A, Fujita T. Functional characterization of Na+-coupled citrate transporter NaC2/NaCT expressed in primary cultures of neurons from mouse cerebral cortex. Brain Res 2006; 1081:92-100. [PMID: 16516867 DOI: 10.1016/j.brainres.2006.01.084] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2005] [Revised: 01/14/2006] [Accepted: 01/17/2006] [Indexed: 10/24/2022]
Abstract
Neurons are known to express a high-affinity Na+ -coupled dicarboxylate transporter(s) for uptake of tricarboxylic acid cycle intermediates, such as alpha-ketoglutarate and malate, which are precursors for neurotransmitters including glutamate and gamma-aminobutyric acid. There is, however, little information available on the molecular identity of the transporters responsible for this uptake process in neurons. In the present study, we investigated the characteristics of Na+ -dependent citrate transport in primary cultures of neurons from mouse cerebral cortex and established the molecular identity of this transport system as the Na+ -coupled citrate transporter (NaC2/NaCT). Reverse transcriptase (RT)-PCR and immunocytochemical analyses revealed that only NaC2/NaCT was expressed in mouse cerebrocortical neurons but not in astrocytes. Uptake of citrate in neurons was Na+ -dependent, Li+ -sensitive, and saturable with the Kt value of 12.3 microM. This Kt value was comparable with that in the case of Na+ -dependent succinate transport (Kt = 9.2 microM). Na+ -activation kinetics revealed that the Na+ -to-citrate stoichiometry was 3.4:1 and concentration of Na+ necessary for half-maximal activation (K0.5(Na)) was 45.7 mM. Na+ -dependent uptake of [14C]citrate (18 microM) was significantly inhibited by unlabeled citrate as well as dicarboxylates such as succinate, malate, fumarate, and alpha-ketoglutarate. This is the first report demonstrating the molecular identity of the Na+ -coupled di/tricarboxylate transport system expressed in neurons as NaC2/NaCT, which can transport the tricarboxylate citrate as well as dicarboxylates such as succinate, alpha-ketoglutarate, and malate.
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Affiliation(s)
- Miyuki Wada
- Department of Biochemical Pharmacology, Kyoto Pharmaceutical University, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan
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23
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Fujita T, Shimada A, Wada M, Miyakawa S, Yamamoto A. Functional Expression of Taurine Transporter and its Up-Regulation in Developing Neurons from Mouse Cerebral Cortex. Pharm Res 2006; 23:689-96. [PMID: 16550472 DOI: 10.1007/s11095-006-9745-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2005] [Accepted: 12/15/2005] [Indexed: 11/25/2022]
Abstract
PURPOSE In the present study, we investigate the characteristics of taurine transport in primary cultures of neurons from mouse cerebral cortex to understand the possibility that taurine might attenuate the effects of central nervous system drugs. METHODS Primary cultured neurons from mouse cerebral cortex were used to determine the transport characteristics of taurine. The expression of taurine transporter (TAUT) in mouse neurons was determined by use of reverse transcriptase-polymerase chain reaction and Western blotting. RESULTS In vitro transport of taurine in mouse cerebrocortical neurons at day 9 was Na+-dependent and saturable with a Michaelis-Menten constant (Kt) of 10.6 +/- 4.1 microM and a maximum velocity (Vmax) of 6.68 +/- 0.85 nmol/mg protein/10 min. Na+ and Cl- activation kinetics revealed that the Na+-to-Cl(-)-to-taurine stoichiometry was 2:1:1. Na+-dependent [3H]-taurine transport was competitively inhibited by beta-alanine with an inhibitory constant (Ki) of 47.4 +/- 6.5 microM. Gamma-aminobutyric acid also inhibited Na+-dependent [3H]-taurine transport with relatively low affinity (Ki = 273 +/- 71 microM). TAUT mRNA was detected in mouse primary cultured neurons, and TAUT protein was also expressed at approximately 70 kDa. Na+-dependent taurine transport activity was increased with developing neurons and corresponded with the increasing mRNA and protein level of TAUT. CONCLUSIONS The present study revealed that Na+/Cl(-)-coupled taurine transporter TAUT is responsible for taurine uptake in mouse cerebrocortical neurons, and that the expression of TAUT is increased with developing cerebrocortical neurons.
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Affiliation(s)
- Takuya Fujita
- Department of Biochemical Pharmacology, Kyoto Pharmaceutical University, Misasagi, Yamashina-ku, Kyoto, 607-8414, Japan.
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24
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Wu Q, Wada M, Shimada A, Yamamoto A, Fujita T. Functional characterization of Zn2(+)-sensitive GABA transporter expressed in primary cultures of astrocytes from rat cerebral cortex. Brain Res 2006; 1075:100-9. [PMID: 16466645 DOI: 10.1016/j.brainres.2005.12.109] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2005] [Revised: 12/26/2005] [Accepted: 12/27/2005] [Indexed: 11/26/2022]
Abstract
The extracellular levels of gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the mammalian cerebral cortex, are regulated by specific high-affinity Na(+)/Cl(-) dependent transporters (GATs). GAT1 mainly expressed in cerebrocortical neurons is thought to play an important role for clearance of GABA in the extracellular fluid, whereas there is a little information available for pharmacological importance for astrocytic GABA transporters. In the present study, we therefore described the functional characterization of GABA transport in primary cultures of astrocytes from rat cerebral cortex and the identification of GABA transporter subtype(s). GABA transport was Na(+) and Cl(-) dependent and saturable with a Michaelis constant (K(t)) of 9.3+/-2.8 microM. Na(+)- and Cl(-)- activation kinetics revealed that the Na(+)-Cl(-)-to-GABA stoichiometry was 2:1:1 and concentrations of Na(+) and Cl(-) necessary for half-maximal transport (K(0.5)(Na) and K(0.5)(Cl)) were 78+/-28 mM and 9.6+/-2.6 mM, respectively. Na(+)-dependent GABA transport was competitively inhibited by various GABA transport inhibitors, especially GAT2- or GAT3-selective inhibitor. In addition, Zn(2+), which has been reported to be a potent inhibitor of GAT3, was found to have a significantly but partially inhibitory effect on the Na(+)-dependent GABA transport in a concentration-dependent manner. Furthermore, reverse transcription-PCR and Western blot analyses revealed that GAT2 and GAT3 are expressed in primary cultures of astrocytes. These results clearly showed that zinc is a useful reagent for separating GAT3 activity from GAT1- and GAT2-activities in CNS. To our knowledge, the present study represents the first report on the inhibitory effect of zinc on the Na(+)-dependent GABA transport in rat cerebrocortical astrocytes.
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Affiliation(s)
- Qiang Wu
- Department of Biopharmaceutics, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan
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25
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Oka M, Wada M, Wu Q, Yamamoto A, Fujita T. Functional expression of metabotropic GABAB receptors in primary cultures of astrocytes from rat cerebral cortex. Biochem Biophys Res Commun 2006; 341:874-81. [PMID: 16455058 DOI: 10.1016/j.bbrc.2006.01.039] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2006] [Accepted: 01/10/2006] [Indexed: 11/25/2022]
Abstract
GABA(B) receptor subunits are widely expressed on neurons throughout the central nervous system (CNS), at both pre- and postsynaptic sites, where they mediate the late and slow component of the inhibitory response to the major inhibitory neurotransmitter GABA. Recently, GABA(B) receptors have been reported to be expressed in astrocytes and microglia in the rat CNS by immunocytochemistry. However, there are few reports available for the functional characterization of GABA(B) receptors on astrocytes. In the present study, we therefore investigated the functional expression and characteristics of GABA(B) receptors in primary cultures of astrocytes from rat cerebral cortex. In the presence of 10 microM GTP, forskolin concentration-dependently increased adenylylcyclase (AC) activity in membranes prepared from rat astrocytes. The selective GABA(B) agonist (R)-baclofen concentration-dependently reduced forskolin-stimulated AC activity in the presence of 10 microM GTP. This effect was reversed by the selective GABA(B) antagonists, CGP-55845 and CGP-54626, and was completely abolished by treatment of astrocytic membranes with pertussis toxin. In addition, RT-PCR, Western blotting, and immunocytochemistry clearly showed that metabotropic GABA(B) receptor isoforms (GABA(B)R1 and GABA(B)R2) are expressed in rat cerebrocortical astrocytes. Taken collectively, these results demonstrate that functionally active metabotropic GABA(B) receptors are expressed in rat cerebrocortical astrocytes.
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Affiliation(s)
- Michiko Oka
- Department of Biochemical Pharmacology, Kyoto Pharmaceutical University, Misasagi, Kyoto, Japan
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26
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Fujita T, Shimada A, Okada N, Yamamoto A. Functional characterization of Na+-independent choline transport in primary cultures of neurons from mouse cerebral cortex. Neurosci Lett 2006; 393:216-21. [PMID: 16239069 DOI: 10.1016/j.neulet.2005.09.069] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2005] [Revised: 09/09/2005] [Accepted: 09/27/2005] [Indexed: 11/23/2022]
Abstract
We report here the functional characteristics of Na+-independent choline transport system in primary cultures of neurons from mouse cerebral cortex. Na+-independent choline transport was saturable with a Michaelis constant (Kt) of 26.7+/-1.2 microM and a maximal velocity (Vmax) of 1.04+/-0.02 nmol/mg protein/10 min. Choline uptake was significantly influenced by extracellular pH and by membrane depolarization. This uptake system was inhibited by various organic cations including unlabeled choline, guanidine, diphenhydramine and the choline analog hemicholinium-3. However, the prototypical organic cation tetraethylammonium and cimetidine showed very little affinity for the Na+-independent choline uptake system in neurons. These results indicate that mouse cerebrocortical neurons express a Na+-independent, high-affinity choline transport system. RT-PCR revealed that choline transporter-like protein 1 (CTL1) and its spliced variant CTL1a, which have been reported to be novel Na+-independent choline transporter, are expressed in mouse cerebrocortical neurons. The Na+-independent transport properties of choline in mouse neurons is similar or identical to that of CTL1 and/or CTL1a. This choline transport system seems to have relevance not only for neuronal physiology but also for the uptake of pharmacologically important organic cation drugs.
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Affiliation(s)
- Takuya Fujita
- Department of Biochemical Pharmacology, Kyoto Pharmaceutical University, Misasagi, Kyoto 607-8414, Japan.
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27
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Xiang J, Chiang PP, Hu Y, Smith DE, Keep RF. Role of PEPT2 in glycylsarcosine transport in astrocyte and glioma cultures. Neurosci Lett 2005; 396:225-9. [PMID: 16364547 DOI: 10.1016/j.neulet.2005.11.037] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2005] [Accepted: 11/17/2005] [Indexed: 11/16/2022]
Abstract
The aims of the current study were (1) to quantify the role of PEPT2 in the uptake of glycylsarcosine (GlySar) in cultured neonatal astrocytes and (2) to examine GlySar transport and PEPT2 expression in two glioma cell lines. The uptake of [(14)C]GlySar was measured in astrocytes cultured from neonatal mouse (PEPT2(+/+) and PEPT2(-/-)) and rat, as well as rat C6 and F98 glioma cells. PEPT2 expression was examined by reverse transcription-polymerase chain reaction (RT-PCR). Neonatal astrocytes from PEPT2(-/-) mice had a 94% reduction in [(14)C]GlySar uptake compared to wild type mice and there was no saturable transport. In PEPT2(+/+) mice, [(14)C]GlySar uptake was saturable (V(max) 58 +/- 12 pmol/mg/min, K(m) 107 +/- 46 microM, K(d) 0.043 +/- 0.004 microl/mg/min). In neonatal rat astrocytes, kinetic analysis also suggested that [(14)C]GlySar uptake was via a single transporter. The inhibitor profile and pH dependence of that transport process was consistent with PEPT2. In C6 and F98 glioma cells, [(14)C]GlySar uptake was markedly reduced ( approximately 96-98%) compared to that in neonatal astrocytes and this was reflected by an absence of PEPT2 mRNA expression. These results indicate that PEPT2 is the sole transporter involved in the uptake of GlySar into neonatal cultured astrocytes. However, PEPT2 mRNA appears to be absent from two glioma cell lines.
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Affiliation(s)
- Jianming Xiang
- Department of Neurosurgery, University of Michigan, 1500 East Medical Center Drive, R5550 Kresge I, Ann Arbor, 48109-0532, USA
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Shimada A, Nakagawa Y, Morishige H, Yamamoto A, Fujita T. Functional characteristics of H+ -dependent nicotinate transport in primary cultures of astrocytes from rat cerebral cortex. Neurosci Lett 2005; 392:207-12. [PMID: 16213084 DOI: 10.1016/j.neulet.2005.09.030] [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] [Received: 03/15/2005] [Revised: 08/30/2005] [Accepted: 09/09/2005] [Indexed: 11/22/2022]
Abstract
In the present study, we report the characteristics of H(+)-coupled nicotinate transport in primary cultures of astrocytes from rat cerebral cortex. The [(3)H]nicotinate transport in rat astrocytes increased up to a pH 5.5. The nicotinic acid uptake at pH 6.0 was both energy-dependent and saturable with a Michaelis constant (K(t)) of 2.8+/-0.4 mM and the maximal uptake rate (V(max)) of 31+/-3.2 nmol/mg protein/10 min. This process was reduced by a protonophore, carbonylcyanide p-trifluoromethoxyphenylhydrazone, and a typical monocarboxylate transporter (MCT) inhibitor, alpha-cyano-4-hydroxycinnamic acid, suggesting that nicotinate uptake by rat astrocytes is mediated by H(+)-coupled monocarboxylate transport system. [(3)H]Nicotinate transport in rat astrocytes was significantly inhibited by various monocarboxylic acids such as l-lactic acid and pyruvic acid with a relatively low affinity (K(i)>10 mM). On the other hand, the uptake process of l-lactic acid was also saturable with a high-affinity component (K(t)=0.27 mM) and a low-affinity component (K(t)=35.9 mM). Reverse transcription-PCR and Western blot analyses revealed that three MCT subtypes, MCT1/Slc16a1, MCT2/Slc16a7, and MCT4/Slc16a3, were expressed in these cells. Because l-lactate reduced to 67% of the nicotinate uptake even at 10mM, it is unlikely that nicotinate uptake in rat astrocytes is mediated by MCT1 and/or MCT2. These results provide biochemical evidence of a H(+)-coupled and saturable transport system, presumed to be a low-affinity monocarboxylate transporter MCT4 or other unknown H(+)-coupled monocarboxylate transport system, for nicotinate in rat cerebrocortical astrocytes.
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Affiliation(s)
- Ayumi Shimada
- Department of Biochemical Pharmacology, Kyoto Pharmaceutical University, Japan
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