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Schmidt SG, Nygaard A, Mindell JA, Loland CJ. Exploring the K + binding site and its coupling to transport in the neurotransmitter:sodium symporter LeuT. eLife 2024; 12:RP87985. [PMID: 38271216 PMCID: PMC10945697 DOI: 10.7554/elife.87985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2024] Open
Abstract
The neurotransmitter:sodium symporters (NSSs) are secondary active transporters that couple the reuptake of substrate to the symport of one or two sodium ions. One bound Na+ (Na1) contributes to the substrate binding, while the other Na+ (Na2) is thought to be involved in the conformational transition of the NSS. Two NSS members, the serotonin transporter (SERT) and the Drosophila dopamine transporter (dDAT), also couple substrate uptake to the antiport of K+ by a largely undefined mechanism. We have previously shown that the bacterial NSS homologue, LeuT, also binds K+, and could therefore serve as a model protein for the exploration of K+ binding in NSS proteins. Here, we characterize the impact of K+ on substrate affinity and transport as well as on LeuT conformational equilibrium states. Both radioligand binding assays and transition metal ion FRET (tmFRET) yielded similar K+ affinities for LeuT. K+ binding was specific and saturable. LeuT reconstituted into proteoliposomes showed that intra-vesicular K+ dose-dependently increased the transport velocity of [3H]alanine, whereas extra-vesicular K+ had no apparent effect. K+ binding induced a LeuT conformation distinct from the Na+- and substrate-bound conformation. Conservative mutations of the Na1 site residues affected the binding of Na+ and K+ to different degrees. The Na1 site mutation N27Q caused a >10-fold decrease in K+ affinity but at the same time a ~3-fold increase in Na+ affinity. Together, the results suggest that K+ binding to LeuT modulates substrate transport and that the K+ affinity and selectivity for LeuT is sensitive to mutations in the Na1 site, pointing toward the Na1 site as a candidate site for facilitating the interaction with K+ in some NSSs.
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Affiliation(s)
- Solveig G Schmidt
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Andreas Nygaard
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Joseph A Mindell
- Membrane Transport Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Claus J Loland
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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2
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Cherian A, Divya KP. Cerebral creatine deficiency: Black cat in the coal cellar. Acta Neurol Belg 2021; 121:1859-1861. [PMID: 32681499 DOI: 10.1007/s13760-020-01437-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2020] [Accepted: 07/03/2020] [Indexed: 11/24/2022]
MESH Headings
- Brain/diagnostic imaging
- Brain/metabolism
- Brain Diseases, Metabolic, Inborn/diagnosis
- Brain Diseases, Metabolic, Inborn/diagnostic imaging
- Brain Diseases, Metabolic, Inborn/metabolism
- Child, Preschool
- Creatine/deficiency
- Creatine/metabolism
- Humans
- Magnetic Resonance Spectroscopy
- Male
- Mental Retardation, X-Linked/diagnosis
- Mental Retardation, X-Linked/diagnostic imaging
- Mental Retardation, X-Linked/metabolism
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
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Affiliation(s)
- Ajith Cherian
- Department of Neurology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, 695011, India
| | - K P Divya
- Department of Neurology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, 695011, India.
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Peng M, Ren J, Jing Y, Jiang X, Xiao Q, Huang J, Tao Y, Lei L, Wang X, Yang Z, Yang Z, Zhan Q, Lin C, Jin G, Zhang X, Zhang L. Tumour-derived small extracellular vesicles suppress CD8+ T cell immune function by inhibiting SLC6A8-mediated creatine import in NPM1-mutated acute myeloid leukaemia. J Extracell Vesicles 2021; 10:e12168. [PMID: 34807526 PMCID: PMC8607980 DOI: 10.1002/jev2.12168] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Revised: 10/11/2021] [Accepted: 11/08/2021] [Indexed: 12/13/2022] Open
Abstract
Acute myeloid leukaemia (AML) carrying nucleophosmin (NPM1) mutations has been defined as a distinct entity of acute leukaemia. Despite remarkable improvements in diagnosis and treatment, the long-term outcomes for this entity remain unsatisfactory. Emerging evidence suggests that leukaemia, similar to other malignant diseases, employs various mechanisms to evade killing by immune cells. However, the mechanism of immune escape in NPM1-mutated AML remains unknown. In this study, both serum and leukemic cells from patients with NPM1-mutated AML impaired the immune function of CD8+ T cells in a co-culture system. Mechanistically, leukemic cells secreted miR-19a-3p into the tumour microenvironment (TME) via small extracellular vesicles (sEVs), which was controlled by the NPM1-mutated protein/CCCTC-binding factor (CTCF)/poly (A)-binding protein cytoplasmic 1 (PABPC1) signalling axis. sEV-related miR-19a-3p was internalized by CD8+ T cells and directly repressed the expression of solute-carrier family 6 member 8 (SLC6A8; a creatine-specific transporter) to inhibit creatine import. Decreased creatine levels can reduce ATP production and impair CD8+ T cell immune function, leading to immune escape by leukemic cells. In summary, leukemic cell-derived sEV-related miR-19a-3p confers immunosuppression to CD8+ T cells by targeting SLC6A8-mediated creatine import, indicating that sEV-related miR-19a-3p might be a promising therapeutic target for NPM1-mutated AML.
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Affiliation(s)
- Meixi Peng
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Jun Ren
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Yipei Jing
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Xueke Jiang
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Qiaoling Xiao
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Junpeng Huang
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Yonghong Tao
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Li Lei
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Xin Wang
- Department of HematologyThe First Affiliated Hospital of Chongqing Medical UniversityChongqingChina
| | - Zailin Yang
- Department of Clinical Laboratory The Third Affiliated Hospital of Chongqing Medical UniversityChongqingChina
- Chongqing University Cancer HospitalChongqingChina
| | - Zesong Yang
- Department of HematologyThe First Affiliated Hospital of Chongqing Medical UniversityChongqingChina
| | - Qian Zhan
- The Center for Clinical Molecular Medical detectionThe First Affiliated Hospital of Chongqing Medical UniversityChongqingChina
| | - Can Lin
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
| | - Guoxiang Jin
- Guangdong Provincial People's HospitalGuangdong Academy of Medical SciencesGuangzhouChina
| | - Xian Zhang
- Immunology ProgramMemorial Sloan Kettering Cancer CenterNew YorkNew YorkUSA
| | - Ling Zhang
- Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of EducationSchool of Laboratory MedicineChongqing Medical UniversityChongqingChina
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4
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Ghirardini E, Calugi F, Sagona G, Di Vetta F, Palma M, Battini R, Cioni G, Pizzorusso T, Baroncelli L. The Role of Preclinical Models in Creatine Transporter Deficiency: Neurobiological Mechanisms, Biomarkers and Therapeutic Development. Genes (Basel) 2021; 12:genes12081123. [PMID: 34440297 PMCID: PMC8392480 DOI: 10.3390/genes12081123] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 07/22/2021] [Accepted: 07/23/2021] [Indexed: 12/12/2022] Open
Abstract
Creatine (Cr) Transporter Deficiency (CTD) is an X-linked metabolic disorder, mostly caused by missense mutations in the SLC6A8 gene and presenting with intellectual disability, autistic behavior, and epilepsy. There is no effective treatment for CTD and patients need lifelong assistance. Thus, the research of novel intervention strategies is a major scientific challenge. Animal models are an excellent tool to dissect the disease pathogenetic mechanisms and drive the preclinical development of therapeutics. This review illustrates the current knowledge about Cr metabolism and CTD clinical aspects, with a focus on mainstay diagnostic and therapeutic options. Then, we discuss the rodent models of CTD characterized in the last decade, comparing the phenotypes expressed within clinically relevant domains and the timeline of symptom development. This analysis highlights that animals with the ubiquitous deletion/mutation of SLC6A8 genes well recapitulate the early onset and the complex pathological phenotype of the human condition. Thus, they should represent the preferred model for preclinical efficacy studies. On the other hand, brain- and cell-specific conditional mutants are ideal for understanding the basis of CTD at a cellular and molecular level. Finally, we explain how CTD models might provide novel insight about the pathogenesis of other disorders, including cancer.
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MESH Headings
- Animals
- Biomarkers/metabolism
- Brain Diseases, Metabolic, Inborn/metabolism
- Brain Diseases, Metabolic, Inborn/pathology
- Brain Diseases, Metabolic, Inborn/therapy
- Central Nervous System/pathology
- Creatine/deficiency
- Creatine/metabolism
- Disease Models, Animal
- Humans
- Mental Retardation, X-Linked/metabolism
- Mental Retardation, X-Linked/pathology
- Mental Retardation, X-Linked/therapy
- Mice
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
- Rats
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Affiliation(s)
- Elsa Ghirardini
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
| | - Francesco Calugi
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Giulia Sagona
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Federica Di Vetta
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Biology, University of Pisa, I-56126 Pisa, Italy
| | - Martina Palma
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Roberta Battini
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Department of Clinical and Experimental Medicine, University of Pisa, I-56126 Pisa, Italy
| | - Giovanni Cioni
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Department of Clinical and Experimental Medicine, University of Pisa, I-56126 Pisa, Italy
| | - Tommaso Pizzorusso
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Laura Baroncelli
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Correspondence:
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5
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Hall CHT, Lee JS, Murphy EM, Gerich ME, Dran R, Glover LE, Abdulla ZI, Skelton MR, Colgan SP. Creatine Transporter, Reduced in Colon Tissues From Patients With Inflammatory Bowel Diseases, Regulates Energy Balance in Intestinal Epithelial Cells, Epithelial Integrity, and Barrier Function. Gastroenterology 2020; 159:984-998.e1. [PMID: 32433978 PMCID: PMC7891846 DOI: 10.1053/j.gastro.2020.05.033] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 05/04/2020] [Accepted: 05/11/2020] [Indexed: 01/03/2023]
Abstract
BACKGROUND & AIMS Patients with inflammatory bowel diseases (IBDs) have intestinal barrier dysfunction. Creatine regulates energy distribution within cells and reduces the severity of colitis in mice. We studied the functions of the creatine transporter solute carrier family 6 member 8 (SLC6A8, also called CRT) in intestinal epithelial cells (IECs) and mice, and we measured levels in mucosal biopsies from patients with IBD. METHODS Colon biopsy specimens from patients with IBD (30 with Crohn's disease and 27 with ulcerative colitis) and 30 patients without IBD (control individuals) and colon tissues from mice (with and without disruption of Crt) were analyzed by immunofluorescence, immunoblots, and/or quantitative reverse-transcription polymerase chain reaction (qRT-PCR). CRT was knocked down or overexpressed in T84 cells, which were analyzed by immunofluorescence, immunoblots, high-performance liquid chromatography (to measure creatine levels), qRT-PCR, transepithelial electrical resistance, barrier function, actin localization, wound healing, mitochondrial oxygen consumption, and glycolysis extracellular acidification rate assays. Organoids from colon cells of CRT-knockout mice and control mice were analyzed by qRT-PCR, immunoblot, and transepithelial electrical resistance. RESULTS CRT localized around tight junctions (TJs) of T84 IECs. In analyses of IECs with CRT knockdown or overexpression, we found that CRT regulates intracellular creatine, barrier formation, and wound healing. CRT-knockout organoids also had diminished barrier formation. In the absence of adequate creatine, IECs transition toward a stressed, glycolysis-predominant form of metabolism; this resulted in leaky TJs and mislocalization of actin and TJ proteins. Colon tissues from patients with IBD had reduced levels of CRT messenger RNA compared with those from control individuals. CONCLUSIONS In an analysis of IEC cell lines and colonoids derived from CRT-knockout mice, we found that CRT regulates energy balance in IECs and thereby epithelial integrity and barrier function. Mucosal biopsy specimens from patients with ulcerative colitis and inactive Crohn's disease have lower levels of CRT, which might contribute to the reduced barrier function observed in patients with IBD.
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Affiliation(s)
- Caroline H T Hall
- Division of Gastroenterology, Hepatology and Nutrition, Children's Hospital Colorado, Aurora, Colorado; Mucosal Inflammation Program, University of Colorado, Aurora, Colorado
| | - J Scott Lee
- Mucosal Inflammation Program, University of Colorado, Aurora, Colorado; Division of Gastroenterology and Hepatology, University of Colorado, Aurora, Colorado
| | - Emily M Murphy
- Division of Gastroenterology, Hepatology and Nutrition, Children's Hospital Colorado, Aurora, Colorado; Mucosal Inflammation Program, University of Colorado, Aurora, Colorado; Division of Gastroenterology and Hepatology, University of Colorado, Aurora, Colorado
| | - Mark E Gerich
- Mucosal Inflammation Program, University of Colorado, Aurora, Colorado; Division of Gastroenterology and Hepatology, University of Colorado, Aurora, Colorado
| | - Rachael Dran
- Mucosal Inflammation Program, University of Colorado, Aurora, Colorado; Division of Gastroenterology and Hepatology, University of Colorado, Aurora, Colorado
| | - Louis E Glover
- Mucosal Inflammation Program, University of Colorado, Aurora, Colorado; Division of Gastroenterology and Hepatology, University of Colorado, Aurora, Colorado; School of Biochemistry and Immunology, Trinity College Dublin, Ireland
| | - Zuhair I Abdulla
- Department of Pediatrics, University of Cincinnati, Cincinnati, Ohio; Division of Neurology, Cincinnati Children's Research Foundation, Cincinnati, Ohio
| | - Matthew R Skelton
- Department of Pediatrics, University of Cincinnati, Cincinnati, Ohio; Division of Neurology, Cincinnati Children's Research Foundation, Cincinnati, Ohio
| | - Sean P Colgan
- Mucosal Inflammation Program, University of Colorado, Aurora, Colorado; Division of Gastroenterology and Hepatology, University of Colorado, Aurora, Colorado.
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6
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Li J, Zhao Z, Tajkhorshid E. Locking Two Rigid-body Bundles in an Outward-Facing Conformation: The Ion-coupling Mechanism in a LeuT-fold Transporter. Sci Rep 2019; 9:19479. [PMID: 31862903 PMCID: PMC6925253 DOI: 10.1038/s41598-019-55722-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 12/02/2019] [Indexed: 01/26/2023] Open
Abstract
Secondary active transporters use electrochemical gradient of ions to fuel the "uphill" translocation of the substrate following the alternating-access model. The coupling of ions to conformational dynamics of the protein remains one of the least characterized aspects of the transporter function. We employ extended molecular dynamics (MD) simulations to examine the Na+-binding effects on the structure and dynamics of a LeuT-fold, Na+-coupled secondary transporter (Mhp1) in its major conformational states, i.e., the outward-facing (OF) and inward-facing (IF) states, as well as on the OF ↔ IF state transition. Microsecond-long, unbiased MD simulations illustrate that Na+ stabilizes an OF conformation favorable for substrate association, by binding to a highly conserved site at the interface between the two helical bundles and restraining their relative position and motion. Furthermore, a special-protocol biased simulation for state transition suggests that Na+ binding hinders the OF ↔ IF transition. These synergistic Na+-binding effects allosterically couple the ion and substrate binding sites and modify the kinetics of state transition, collectively increasing the lifetime of an OF conformation with high substrate affinity, thereby facilitating substrate recruitment from a low-concentration environment. Based on the similarity between our findings for Mhp1 and experimental reports on LeuT, we propose that this model may represent a general Na+-coupling mechanism among LeuT-fold transporters.
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Affiliation(s)
- Jing Li
- NIH Center for Macromolecular Modeling and Bioinformatics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, 60637, United States
| | - Zhiyu Zhao
- NIH Center for Macromolecular Modeling and Bioinformatics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States
| | - Emad Tajkhorshid
- NIH Center for Macromolecular Modeling and Bioinformatics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States.
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States.
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States.
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, United States.
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Gorshkov K, Wang AQ, Sun W, Fisher E, Frigeni M, Singleton M, Thorne N, Class B, Huang W, Longo N, Do MT, Ottinger EA, Xu X, Zheng W. Phosphocyclocreatine is the dominant form of cyclocreatine in control and creatine transporter deficiency patient fibroblasts. Pharmacol Res Perspect 2019; 7:e00525. [PMID: 31859463 PMCID: PMC6924099 DOI: 10.1002/prp2.525] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 08/20/2019] [Accepted: 08/29/2019] [Indexed: 12/26/2022] Open
Abstract
Creatine transporter deficiency (CTD) is a metabolic disorder resulting in cognitive, motor, and behavioral deficits. Cyclocreatine (cCr), a creatine analog, has been explored as a therapeutic strategy for the treatment of CTD. We developed a rapid, selective, and accurate HILIC ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to simultaneously quantify the intracellular concentrations of cCr, creatine (Cr), creatine-d3 (Cr-d3), phosphocyclocreatine (pcCr), and phosphocreatine (pCr). Using HILIC-UPLC-MS/MS, we measured cCr and Cr-d3 uptake and their conversion to the phosphorylated forms in primary human control and CTD fibroblasts. Altogether, the data demonstrate that cCr enters cells and its dominant intracellular form is pcCr in both control and CTD patient cells. Therefore, cCr may replace creatine as a therapeutic strategy for the treatment of CTD.
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Affiliation(s)
- Kirill Gorshkov
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Amy Q. Wang
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Wei Sun
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Ethan Fisher
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Marta Frigeni
- Division of Medical GeneticsDepartment of PediatricsUniversity of UtahSalt Lake CityUTUSA
| | - Marc Singleton
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Natasha Thorne
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Bradley Class
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Wenwei Huang
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Nicola Longo
- Division of Medical GeneticsDepartment of PediatricsUniversity of UtahSalt Lake CityUTUSA
- Associated Regional and University Pathologists (ARUP) LaboratoriesSalt Lake CityUTUSA
| | | | - Elizabeth A. Ottinger
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Xin Xu
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
| | - Wei Zheng
- National Center for Advancing Translational SciencesNational Institutes of HealthBethesdaMDUSA
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LeVine MV, Terry DS, Khelashvili G, Siegel ZS, Quick M, Javitch JA, Blanchard SC, Weinstein H. The allosteric mechanism of substrate-specific transport in SLC6 is mediated by a volumetric sensor. Proc Natl Acad Sci U S A 2019; 116:15947-15956. [PMID: 31324743 PMCID: PMC6689989 DOI: 10.1073/pnas.1903020116] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Neurotransmitter:sodium symporters (NSSs) in the SLC6 family terminate neurotransmission by coupling the thermodynamically favorable transport of ions to the thermodynamically unfavorable transport of neurotransmitter back into presynaptic neurons. Results from many structural, functional, and computational studies on LeuT, a bacterial NSS homolog, have provided critical insight into the mechanism of sodium-coupled transport, but the mechanism underlying substrate-specific transport rates is still not understood. We present a combination of molecular dynamics simulations, single-molecule fluorescence resonance energy transfer (smFRET) imaging, and measurements of Na+ binding and substrate transport that reveals an allosteric substrate specificity mechanism. In this mechanism, residues F259 and I359 in the substrate binding pocket couple the binding of substrate to Na+ release from the Na2 site by allosterically modulating the stability of a partially open, inward-facing state. We propose a model for transport selectivity in which residues F259 and I359 act as a volumetric sensor that inhibits the transport of bulky amino acids.
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Affiliation(s)
- Michael V LeVine
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065;
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medicine, New York, NY 10021
| | - Daniel S Terry
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medicine, New York, NY 10021
| | - Zarek S Siegel
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medicine, New York, NY 10021
| | - Matthias Quick
- Department of Psychiatry, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032
- Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY 10032
| | - Jonathan A Javitch
- Department of Psychiatry, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032
- Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY 10032
- Department of Pharmacology, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032
| | - Scott C Blanchard
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065;
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medicine, New York, NY 10021
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9
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Navratna V, Gouaux E. Insights into the mechanism and pharmacology of neurotransmitter sodium symporters. Curr Opin Struct Biol 2019; 54:161-170. [PMID: 30921707 DOI: 10.1016/j.sbi.2019.03.011] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 03/07/2019] [Accepted: 03/08/2019] [Indexed: 12/17/2022]
Abstract
Neurotransmitter sodium symporters (NSS) belong to the SLC6 family of solute carriers and play an essential role in neurotransmitter homeostasis throughout the body. In the past decade, structural studies employing bacterial orthologs of NSSs have provided insight into the mechanism of neurotransmitter transport. While the overall architecture of SLC6 transporters is conserved among species, in comparison to the bacterial homologs, the eukaryotic SLC6 family members harbor differences in amino acid sequence and molecular structure, which underpins their functional and pharmacological diversity, as well as their ligand specificity. Here, we review the structures and mechanisms of eukaryotic NSSs, focusing on the molecular basis for ligand recognition and on transport mechanism.
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Affiliation(s)
- Vikas Navratna
- Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Eric Gouaux
- Vollum Institute, Oregon Health & Science University, Portland, OR, United States; Howard Hughes Medical Institute, Oregon Health & Science University, Portland, OR, United States.
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10
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Abstract
INTRODUCTION The creatine kinase circuit is central to the regulation of high-energy phosphate metabolism and the maintenance of cellular energy turnover. This circuit is fuelled by creatine, an amino acid derivative that can be obtained from a diet containing animal products, and by synthesis in the body de novo. A recent retrospective study conducted in a cohort of 287 pregnant women determined that maternal excreted levels of creatine may be associated with fetal growth. This prospective study aims to overcome some of the limitations associated with the previous study and thoroughly characterise creatine homeostasis throughout gestation in a low-risk pregnant population. METHODS AND ANALYSIS This study is recruiting women with a singleton low-risk pregnancy who are attending Monash Health, in Melbourne, Australia. Maternal blood and urine samples, along with dietary surveys, are collected at five time points during pregnancy and then at delivery. Cord blood and placenta (including membranes and cord) are collected at birth. A biobank of tissue samples for future research is being established. Primary outcome measures will include creatine, creatine kinase and associated metabolites in antenatal bloods and urine, cord bloods and placenta, along with molecular analysis of the creatine transporter (SLC6A8) and synthesising enzymes L - arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT) in placental tissues. Secondary outcome measures include dietary protein intake over pregnancy and any associations with maternal creatine, pregnancy events and birth outcomes. ETHICS AND DISSEMINATION Ethical approval was granted in August 2015 from Monash Health (Ref: 14140B) and Monash University (Ref: 7785). Study outcomes will be disseminated at international conferences and published in peer-reviewed scientific journals. TRIAL REGISTRATION NUMBER ACTRN12618001558213; Pre-results.
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Affiliation(s)
- Deborah L De Guingand
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
| | - Stacey J Ellery
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
| | - Miranda L Davies-Tuck
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
| | - Hayley Dickinson
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
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11
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Joncquel-Chevalier Curt M, Bout MA, Fontaine M, Kim I, Huet G, Bekri S, Morin G, Moortgat S, Moerman A, Cuisset JM, Cheillan D, Vamecq J. Functional assessment of creatine transporter in control and X-linked SLC6A8-deficient fibroblasts. Mol Genet Metab 2018; 123:463-471. [PMID: 29478817 DOI: 10.1016/j.ymgme.2018.02.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 02/15/2018] [Accepted: 02/15/2018] [Indexed: 01/01/2023]
Abstract
Creatine transporter is currently the focus of renewed interest with emerging roles in brain neurotransmission and physiology, and the bioenergetics of cancer metastases. We here report on amendments of a standard creatine uptake assay which might help clinical chemistry laboratories to extend their current range of measurements of creatine and metabolites in body fluids to functional enzyme explorations. In this respect, short incubation times and the use of a stable-isotope-labeled substrate (D3-creatine) preceded by a creatine wash-out step from cultured fibroblast cells by removal of fetal bovine serum (rich in creatine) from the incubation medium are recommended. Together, these measures decreased, by a first order of magnitude, creatine concentrations in the incubation medium at the start of creatine-uptake studies and allowed to functionally discriminate between 4 hemizygous male and 4 heterozygous female patients with X-linked SLC6A8 deficiency, and between this cohort of eight patients and controls. The functional assay corroborated genetic diagnosis of SLC6A8 deficiency. Gene anomalies in our small cohort included splicing site (c.912G > A [p.Ile260_Gln304del], c.778-2A > G and c.1495 + 2 T > G), substitution (c.407C > T) [p.Ala136Val] and deletion (c.635_636delAG [p.Glu212Valfs*84] and c.1324delC [p.Gln442Lysfs*21]) variants with reduced creatine transporter function validating their pathogenicity, including that of a previously unreported c.1324delC variant. The present assay adaptations provide an easy, reliable and discriminative manner for exploring creatine transporter activity and disease variations. It might apply to drug testing or other evaluations in the genetic and metabolic horizons covered by the emerging functions of creatine and its transporter, in a way, however, requiring and completed by additional studies on female patients and blood-brain barrier permeability properties of selected compounds. As a whole, the proposed assay of creatine transporter positively adds to currently existing measurements of this transporter activity, and determining on a large scale the extent of its exact suitability to detect female patients should condition in the future its transfer in clinical practice.
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MESH Headings
- Adolescent
- Brain Diseases, Metabolic, Inborn/genetics
- Brain Diseases, Metabolic, Inborn/metabolism
- Brain Diseases, Metabolic, Inborn/pathology
- Case-Control Studies
- Child
- Child, Preschool
- Cohort Studies
- Creatine/deficiency
- Creatine/genetics
- Creatine/metabolism
- Female
- Fibroblasts/metabolism
- Fibroblasts/pathology
- Follow-Up Studies
- Humans
- Infant
- Male
- Mental Retardation, X-Linked/genetics
- Mental Retardation, X-Linked/metabolism
- Mental Retardation, X-Linked/pathology
- Mutation
- Nerve Tissue Proteins/deficiency
- Nerve Tissue Proteins/genetics
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/genetics
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
- Prognosis
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Affiliation(s)
- Marie Joncquel-Chevalier Curt
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Marie-Adélaïde Bout
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Monique Fontaine
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Isabelle Kim
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Guillemette Huet
- Cell Culture Department, Center of Biology-Pathology, CHRU Lille, F-59000 Lille, France
| | - Soumeya Bekri
- Inserm U1245, UNIROUEN, Normandie Univ, Normandy Centre for Genomic and Personalized Medicine, France.Department of Metabolic Biochemistry, Rouen University Hospital, Rouen, France
| | - Gilles Morin
- EA 4666, Département de génétique, Université de Picardie-Jules-Verne, CHU d'Amiens, 80054 Amiens, France
| | - Stéphanie Moortgat
- Centre de Génétique Humaine, Institut de Pathologie et de Génétique, Charleroi, Gosselies, Belgium
| | - Alexandre Moerman
- Service de Génétique Clinique Guy Fontaine, Hôpital Jeanne de Flandre, CHRU Lille, 59037 Lille, France
| | - Jean-Marie Cuisset
- Service de Neurologie Infantile, Hôpital Roger Salengro, CHRU Lille, 59037 Lille, France
| | - David Cheillan
- Hospices Civils de Lyon, Service de Biochimie et Biologie Moléculaire Grand Est, Centre de Biologie et de Pathologie Est, 69677 Bron, France and Université de Lyon, INSERM U1060, CarMen; Medical Reference Center for Inherited Metabolic Diseases, Jeanne de Flandre Hospital, CHRU Lille, France
| | - Joseph Vamecq
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France; Inserm, Lille, France; Université de Lyon, INSERM U1060 CarMeN, Lyon, France.; Univ. Lille, RADEME - Maladies RAres du Développement et du Métabolisme : du phénotype au génotype et à la Fonction, Lille, EA 7364, France.
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12
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Terry DS, Kolster RA, Quick M, LeVine MV, Khelashvili G, Zhou Z, Weinstein H, Javitch JA, Blanchard SC. A partially-open inward-facing intermediate conformation of LeuT is associated with Na + release and substrate transport. Nat Commun 2018; 9:230. [PMID: 29335402 PMCID: PMC5768729 DOI: 10.1038/s41467-017-02202-y] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2017] [Accepted: 11/12/2017] [Indexed: 12/20/2022] Open
Abstract
Neurotransmitter:sodium symporters (NSS), targets of antidepressants and psychostimulants, clear neurotransmitters from the synaptic cleft through sodium (Na+)-coupled transport. Substrate and Na+ are thought to be transported from the extracellular to intracellular space through an alternating access mechanism by coordinated conformational rearrangements in the symporter that alternately expose the binding sites to each side of the membrane. However, the mechanism by which the binding of ligands coordinates conformational changes occurring on opposite sides of the membrane is not well understood. Here, we report the use of single-molecule fluorescence resonance energy transfer (smFRET) techniques to image transitions between distinct conformational states on both the extracellular and intracellular sides of the prokaryotic NSS LeuT, including partially open intermediates associated with transport activity. The nature and functional context of these hitherto unidentified intermediate states shed new light on the allosteric mechanism that couples substrate and Na+ symport by the NSS family through conformational dynamics.
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Affiliation(s)
- Daniel S Terry
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
| | - Rachel A Kolster
- Department of Psychiatry, Division of Molecular Therapeutics, Columbia University College of Physicians and Surgeons and New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY, 10032, USA
| | - Matthias Quick
- Department of Psychiatry, Division of Molecular Therapeutics, Columbia University College of Physicians and Surgeons and New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY, 10032, USA
| | - Michael V LeVine
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medicine, 1305 York Avenue, New York, NY, 10021, USA
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medicine, 1305 York Avenue, New York, NY, 10021, USA
| | - Zhou Zhou
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medicine, 1305 York Avenue, New York, NY, 10021, USA
| | - Jonathan A Javitch
- Department of Psychiatry, Division of Molecular Therapeutics, Columbia University College of Physicians and Surgeons and New York State Psychiatric Institute, 1051 Riverside Drive, New York, NY, 10032, USA.
- Department of Pharmacology, Columbia University College of Physicians and Surgeons, 1051 Riverside Drive, New York, NY, 10032, USA.
| | - Scott C Blanchard
- Department of Physiology and Biophysics, Weill Cornell Medicine, 1300 York Avenue, New York, NY, 10065, USA.
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13
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Dijkstra AA, Lin LC, Nana AL, Gaus SE, Seeley WW. Von Economo Neurons and Fork Cells: A Neurochemical Signature Linked to Monoaminergic Function. Cereb Cortex 2018; 28:131-144. [PMID: 27913432 PMCID: PMC6075576 DOI: 10.1093/cercor/bhw358] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Revised: 09/29/2016] [Indexed: 12/13/2022] Open
Abstract
The human anterior cingulate and frontoinsular cortices are distinguished by 2 unique Layer 5 neuronal morphotypes, the von Economo neurons (VENs) and fork cells, whose biological identity remains mysterious. Insights could impact research on diverse neuropsychiatric diseases to which these cells have been linked. Here, we leveraged the Allen Brain Atlas to evaluate mRNA expression of 176 neurotransmitter-related genes and identified vesicular monoamine transporter 2 (VMAT2), gamma-aminobutyric acid (GABA) receptor subunit θ (GABRQ), and adrenoreceptor α-1A (ADRA1A) expression in human VENs, fork cells, and a minority of neighboring Layer 5 neurons. We confirmed these results using immunohistochemistry or in situ hybridization. VMAT2 and GABRQ expression was absent in mouse cerebral cortex. Although VMAT2 is known to package monoamines into synaptic vesicles, in VENs and fork cells its expression occurs in the absence of monoamine-synthesizing enzymes or reuptake transporters. Thus, VENs and fork cells may possess a novel, uncharacterized mode of cortical monoaminergic function that distinguishes them from most other mammalian Layer 5 neurons.
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Affiliation(s)
- Anke A Dijkstra
- Memory and Aging Center, Department of Neurology, University of California, San Francisco
| | - Li-Chun Lin
- Memory and Aging Center, Department of Neurology, University of California, San Francisco
| | - Alissa L Nana
- Memory and Aging Center, Department of Neurology, University of California, San Francisco
| | - Stephanie E Gaus
- Memory and Aging Center, Department of Neurology, University of California, San Francisco
| | - William W Seeley
- Memory and Aging Center, Department of Neurology, University of California, San Francisco
- Department of Pathology, University of California, San Francisco, San Francisco, CA 94143, USA
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14
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Cameron JM, Levandovskiy V, Roberts W, Anagnostou E, Scherer S, Loh A, Schulze A. Variability of Creatine Metabolism Genes in Children with Autism Spectrum Disorder. Int J Mol Sci 2017; 18:ijms18081665. [PMID: 28758966 PMCID: PMC5578055 DOI: 10.3390/ijms18081665] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 07/19/2017] [Accepted: 07/25/2017] [Indexed: 12/23/2022] Open
Abstract
Creatine deficiency syndrome (CDS) comprises three separate enzyme deficiencies with overlapping clinical presentations: arginine:glycine amidinotransferase (GATM gene, glycine amidinotransferase), guanidinoacetate methyltransferase (GAMT gene), and creatine transporter deficiency (SLC6A8 gene, solute carrier family 6 member 8). CDS presents with developmental delays/regression, intellectual disability, speech and language impairment, autistic behaviour, epileptic seizures, treatment-refractory epilepsy, and extrapyramidal movement disorders; symptoms that are also evident in children with autism. The objective of the study was to test the hypothesis that genetic variability in creatine metabolism genes is associated with autism. We sequenced GATM, GAMT and SLC6A8 genes in 166 patients with autism (coding sequence, introns and adjacent untranslated regions). A total of 29, 16 and 25 variants were identified in each gene, respectively. Four variants were novel in GATM, and 5 in SLC6A8 (not present in the 1000 Genomes, Exome Sequencing Project (ESP) or Exome Aggregation Consortium (ExAC) databases). A single variant in each gene was identified as non-synonymous, and computationally predicted to be potentially damaging. Nine variants in GATM were shown to have a lower minor allele frequency (MAF) in the autism population than in the 1000 Genomes database, specifically in the East Asian population (Fisher’s exact test). Two variants also had lower MAFs in the European population. In summary, there were no apparent associations of variants in GAMT and SLC6A8 genes with autism. The data implying there could be a lower association of some specific GATM gene variants with autism is an observation that would need to be corroborated in a larger group of autism patients, and with sub-populations of Asian ethnicities. Overall, our findings suggest that the genetic variability of creatine synthesis/transport is unlikely to play a part in the pathogenesis of autism spectrum disorder (ASD) in children.
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Affiliation(s)
- Jessie M Cameron
- Genetics and Genome Biology, Peter Gilgan Center for Research and Learning, Toronto, ON M5G 0A4, Canada.
| | - Valeriy Levandovskiy
- Genetics and Genome Biology, Peter Gilgan Center for Research and Learning, Toronto, ON M5G 0A4, Canada.
| | - Wendy Roberts
- Department of Paediatrics, University of Toronto, Toronto, ON M5S 1A1, Canada.
- Holland Bloorview Kids Rehabilitation Hospital, 150 Kigour Rd, Toronto, ON M4G 1R8, Canada.
| | - Evdokia Anagnostou
- Department of Paediatrics, University of Toronto, Toronto, ON M5S 1A1, Canada.
- Holland Bloorview Kids Rehabilitation Hospital, 150 Kigour Rd, Toronto, ON M4G 1R8, Canada.
| | - Stephen Scherer
- Genetics and Genome Biology, Peter Gilgan Center for Research and Learning, Toronto, ON M5G 0A4, Canada.
- The Centre for Applied Genomics and Genetics and Genome Biology, the Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
- McLaughlin Centre and Department of Molecular Genetics, 686 Bay Street, 13th Floor, Peter Gilgan Center for Research and Learning, Toronto, ON M5G 0A4, Canada.
| | - Alvin Loh
- Department of Paediatrics, University of Toronto, Toronto, ON M5S 1A1, Canada.
- Surrey Place Center, 2 Surrey Place, Toronto, ON M5S 2C2, Canada.
| | - Andreas Schulze
- Genetics and Genome Biology, Peter Gilgan Center for Research and Learning, Toronto, ON M5G 0A4, Canada.
- Department of Paediatrics, University of Toronto, Toronto, ON M5S 1A1, Canada.
- Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada.
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15
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Tang X, Liu H, Chen Q, Wang X, Xiong Y, Zhao P. Genome-Wide Identification, Characterization and Expression Analysis of the Solute Carrier 6 Gene Family in Silkworm (Bombyx mori). Int J Mol Sci 2016; 17:ijms17101675. [PMID: 27706106 PMCID: PMC5085708 DOI: 10.3390/ijms17101675] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 09/26/2016] [Indexed: 11/16/2022] Open
Abstract
The solute carrier 6 (SLC6) gene family, initially known as the neurotransmitter transporters, plays vital roles in the regulation of neurotransmitter signaling, nutrient absorption and motor behavior. In this study, a total of 16 candidate genes were identified as SLC6 family gene homologs in the silkworm (Bombyx mori) genome. Spatio-temporal expression patterns of silkworm SLC6 gene transcripts indicated that these genes were highly and specifically expressed in midgut, brain and gonads; moreover, these genes were expressed primarily at the feeding stage or adult stage. Levels of expression for most midgut-specific and midgut-enriched gene transcripts were down-regulated after starvation but up-regulated after re-feeding. In addition, we observed that expression levels of these genes except for BmSLC6-15 and BmGT1 were markedly up-regulated by a juvenile hormone analog. Moreover, brain-enriched genes showed differential expression patterns during wandering and mating processes, suggesting that these genes may be involved in modulating wandering and mating behaviors. Our results improve our understanding of the expression patterns and potential physiological functions of the SLC6 gene family, and provide valuable information for the comprehensive functional analysis of the SLC6 gene family.
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Affiliation(s)
- Xin Tang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400715, China.
| | - Huawei Liu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400715, China.
| | - Quanmei Chen
- Department of Biochemistry and Molecular Biology, Chongqing Medical University, Chongqing 400016, China.
| | - Xin Wang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400715, China.
- Chongqing Engineering and Technology Research Center for Novel Silk Materials, Chongqing 400715, China.
| | - Ying Xiong
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400715, China.
| | - Ping Zhao
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400715, China.
- Chongqing Engineering and Technology Research Center for Novel Silk Materials, Chongqing 400715, China.
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16
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Romer SH, Seedle K, Turner SM, Li J, Baccei ML, Crone SA. Accessory respiratory muscles enhance ventilation in ALS model mice and are activated by excitatory V2a neurons. Exp Neurol 2016; 287:192-204. [PMID: 27456268 DOI: 10.1016/j.expneurol.2016.05.033] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 05/09/2016] [Accepted: 05/26/2016] [Indexed: 02/06/2023]
Abstract
Inspiratory accessory respiratory muscles (ARMs) enhance ventilation when demands are high, such as during exercise and/or pathological conditions. Despite progressive degeneration of phrenic motor neurons innervating the diaphragm, amyotrophic lateral sclerosis (ALS) patients and rodent models are able to maintain ventilation at early stages of disease. In order to assess the contribution of ARMs to respiratory compensation in ALS, we examined the activity of ARMs and ventilation throughout disease progression in SOD1G93A ALS model mice at rest using a combination of electromyography and unrestrained whole body plethysmography. Increased ARM activity, accompanied by increased ventilation, is observed beginning at the onset of symptoms. However, ARM recruitment fails to occur at rest at late stages of disease, even though the same ARMs are used for other behaviors. Using a chemogenetic approach, we demonstrate that a glutamatergic class of neurons in the brainstem and spinal cord, the V2a class, is sufficient to drive increased ARM activity at rest in healthy mice. Additionally, we reveal pathology in the medial reticular formation of the brainstem of SOD1G93A mice using immunohistochemistry and confocal imaging. Both spinal and brainstem V2a neurons degenerate in ALS model mice, accompanied by regional activation of astrocytes and microglia. These results establish inspiratory ARM recruitment as one of the compensatory mechanisms that maintains breathing at early stages of disease and indicate that V2a neuron degeneration may contribute to ARM failure at late stages of disease.
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Affiliation(s)
- Shannon H Romer
- Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229
| | - Kari Seedle
- Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229
| | - Sarah M Turner
- Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229
| | - Jie Li
- Pain Research Center, Dept. of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267
| | - Mark L Baccei
- Pain Research Center, Dept. of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267
| | - Steven A Crone
- Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229; Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229.
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17
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Hanna-El-Daher L, Braissant O. Creatine synthesis and exchanges between brain cells: What can be learned from human creatine deficiencies and various experimental models? Amino Acids 2016; 48:1877-95. [PMID: 26861125 DOI: 10.1007/s00726-016-2189-0] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 01/27/2016] [Indexed: 12/11/2022]
Abstract
While it has long been thought that most of cerebral creatine is of peripheral origin, the last 20 years has provided evidence that the creatine synthetic pathway (AGAT and GAMT enzymes) is expressed in the brain together with the creatine transporter (SLC6A8). It has also been shown that SLC6A8 is expressed by microcapillary endothelial cells at the blood-brain barrier, but is absent from surrounding astrocytes, raising the concept that the blood-brain barrier has a limited permeability for peripheral creatine. The first creatine deficiency syndrome in humans was also discovered 20 years ago (GAMT deficiency), followed later by AGAT and SLC6A8 deficiencies, all three diseases being characterized by creatine deficiency in the CNS and essentially affecting the brain. By reviewing the numerous and latest experimental studies addressing creatine transport and synthesis in the CNS, as well as the clinical and biochemical characteristics of creatine-deficient patients, our aim was to delineate a clearer view of the roles of the blood-brain and blood-cerebrospinal fluid barriers in the transport of creatine and guanidinoacetate between periphery and CNS, and on the intracerebral synthesis and transport of creatine. This review also addresses the question of guanidinoacetate toxicity for brain cells, as probably found under GAMT deficiency.
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MESH Headings
- Amidinotransferases/deficiency
- Amidinotransferases/genetics
- Amidinotransferases/metabolism
- Amino Acid Metabolism, Inborn Errors/genetics
- Amino Acid Metabolism, Inborn Errors/metabolism
- Amino Acid Metabolism, Inborn Errors/pathology
- Animals
- Blood-Brain Barrier/metabolism
- Blood-Brain Barrier/pathology
- Brain Diseases, Metabolic, Inborn/genetics
- Brain Diseases, Metabolic, Inborn/metabolism
- Brain Diseases, Metabolic, Inborn/pathology
- Capillaries/metabolism
- Capillaries/pathology
- Creatine/biosynthesis
- Creatine/deficiency
- Creatine/genetics
- Creatine/metabolism
- Developmental Disabilities/genetics
- Developmental Disabilities/metabolism
- Developmental Disabilities/pathology
- Disease Models, Animal
- Endothelial Cells/metabolism
- Endothelial Cells/pathology
- Guanidinoacetate N-Methyltransferase/deficiency
- Guanidinoacetate N-Methyltransferase/genetics
- Guanidinoacetate N-Methyltransferase/metabolism
- Humans
- Intellectual Disability/genetics
- Intellectual Disability/metabolism
- Intellectual Disability/pathology
- Language Development Disorders/genetics
- Language Development Disorders/metabolism
- Language Development Disorders/pathology
- Mental Retardation, X-Linked/genetics
- Mental Retardation, X-Linked/metabolism
- Mental Retardation, X-Linked/pathology
- Movement Disorders/congenital
- Movement Disorders/genetics
- Movement Disorders/metabolism
- Movement Disorders/pathology
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/metabolism
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/genetics
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
- Speech Disorders/genetics
- Speech Disorders/metabolism
- Speech Disorders/pathology
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Affiliation(s)
- Layane Hanna-El-Daher
- Service of Biomedicine, Neurometabolic Unit, Lausanne University Hospital, 1011, Lausanne, Switzerland
| | - Olivier Braissant
- Service of Biomedicine, Neurometabolic Unit, Lausanne University Hospital, 1011, Lausanne, Switzerland.
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18
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Fairweather SJ, Bröer A, Subramanian N, Tumer E, Cheng Q, Schmoll D, O'Mara ML, Bröer S. Molecular basis for the interaction of the mammalian amino acid transporters B0AT1 and B0AT3 with their ancillary protein collectrin. J Biol Chem 2015; 290:24308-25. [PMID: 26240152 PMCID: PMC4591816 DOI: 10.1074/jbc.m115.648519] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 07/19/2015] [Indexed: 12/19/2022] Open
Abstract
Many solute carrier 6 (SLC6) family transporters require ancillary subunits to modify their expression and activity. The main apical membrane neutral amino acid transporters in mouse intestine and kidney, B(0)AT1 and B(0)AT3, require the ancillary protein collectrin or ACE2 for plasma membrane expression. Expression and activity of SLC6 neurotransmitter transporters are modulated by interaction with syntaxin 1A. Utilizing monocarboxylate-B(0)AT1/3 fusion constructs, we discovered that collectrin is also necessary for B(0)AT1 and B(0)AT3 catalytic function. Syntaxin 1A and syntaxin 3 inhibit the membrane expression of B(0)AT1 by competing with collectrin for access. A mutagenesis screening approach identified residues on trans-membrane domains 1α, 5, and 7 on one face of B(0)AT3 as a key region involved in interaction with collectrin. Mutant analysis established residues that were involved in collectrin-dependent functions as follows: plasma membrane expression of B(0)AT3, catalytic activation, or both. These results identify a potential binding site for collectrin and other SLC6 ancillary proteins.
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Affiliation(s)
| | | | - Nandhitha Subramanian
- Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia and
| | | | - Qi Cheng
- From the Research School of Biology and
| | - Dieter Schmoll
- the Sanofi-Aventis Deutschland GmbH, Industriepark Hoechst, Frankfurt am Main 65926, Germany
| | - Megan L O'Mara
- Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia and
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19
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Loo JM, Scherl A, Nguyen A, Man FY, Weinberg E, Zeng Z, Saltz L, Paty PB, Tavazoie SF. Extracellular metabolic energetics can promote cancer progression. Cell 2015; 160:393-406. [PMID: 25601461 DOI: 10.1016/j.cell.2014.12.018] [Citation(s) in RCA: 262] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Revised: 09/25/2014] [Accepted: 11/19/2014] [Indexed: 12/12/2022]
Abstract
Colorectal cancer primarily metastasizes to the liver and globally kills over 600,000 people annually. By functionally screening 661 microRNAs (miRNAs) in parallel during liver colonization, we have identified miR-551a and miR-483 as robust endogenous suppressors of liver colonization and metastasis. These miRNAs convergently target creatine kinase, brain-type (CKB), which phosphorylates the metabolite creatine, to generate phosphocreatine. CKB is released into the extracellular space by metastatic cells encountering hepatic hypoxia and catalyzes production of phosphocreatine, which is imported through the SLC6A8 transporter and used to generate ATP—fueling metastatic survival. Combinatorial therapeutic viral delivery of miR-551a and miR-483-5p through single-dose adeno-associated viral (AAV) delivery significantly suppressed colon cancer metastasis, as did CKB inhibition with a small-molecule inhibitor. Importantly, human liver metastases express higher CKB and SLC6A8 levels and reduced miR-551a/miR-483 levels relative to primary tumors. We identify the extracellular space as an important compartment for malignant energetic catalysis and therapeutic targeting.
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Affiliation(s)
- Jia Min Loo
- Laboratory of Systems Cancer Biology, Rockefeller University, New York, NY 10065, USA
| | - Alexis Scherl
- Laboratory of Systems Cancer Biology, Rockefeller University, New York, NY 10065, USA
| | - Alexander Nguyen
- Laboratory of Systems Cancer Biology, Rockefeller University, New York, NY 10065, USA
| | - Fung Ying Man
- Laboratory of Systems Cancer Biology, Rockefeller University, New York, NY 10065, USA
| | - Ethan Weinberg
- Laboratory of Systems Cancer Biology, Rockefeller University, New York, NY 10065, USA
| | - Zhaoshi Zeng
- Department of Surgery, Memorial-Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Leonard Saltz
- Department of Medicine, Memorial-Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Philip B Paty
- Department of Surgery, Memorial-Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Sohail F Tavazoie
- Laboratory of Systems Cancer Biology, Rockefeller University, New York, NY 10065, USA.
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20
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Wang H, Goehring A, Wang KH, Penmatsa A, Ressler R, Gouaux E. Structural basis for action by diverse antidepressants on biogenic amine transporters. Nature 2013; 503:141-5. [PMID: 24121440 PMCID: PMC3904662 DOI: 10.1038/nature12648] [Citation(s) in RCA: 118] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2013] [Accepted: 09/11/2013] [Indexed: 12/18/2022]
Abstract
The biogenic amine transporters (BATs) regulate endogenous neurotransmitter concentrations and are targets for a broad range of therapeutic agents including selective serotonin reuptake inhibitors (SSRIs), serotonin-noradrenaline reuptake inhibitors (SNRIs) and tricyclic antidepressants (TCAs). Because eukaryotic BATs are recalcitrant to crystallographic analysis, our understanding of the mechanism of these inhibitors and antidepressants is limited. LeuT is a bacterial homologue of BATs and has proven to be a valuable paradigm for understanding relationships between their structure and function. However, because only approximately 25% of the amino acid sequence of LeuT is in common with that of BATs, and as LeuT is a promiscuous amino acid transporter, it does not recapitulate the pharmacological properties of BATs. Indeed, SSRIs and TCAs bind in the extracellular vestibule of LeuT and act as non-competitive inhibitors of transport. By contrast, multiple studies demonstrate that both TCAs and SSRIs are competitive inhibitors for eukaryotic BATs and bind to the primary binding pocket. Here we engineered LeuT to harbour human BAT-like pharmacology by mutating key residues around the primary binding pocket. The final LeuBAT mutant binds the SSRI sertraline with a binding constant of 18 nM and displays high-affinity binding to a range of SSRIs, SNRIs and a TCA. We determined 12 crystal structures of LeuBAT in complex with four classes of antidepressants. The chemically diverse inhibitors have a remarkably similar mode of binding in which they straddle transmembrane helix (TM) 3, wedge between TM3/TM8 and TM1/TM6, and lock the transporter in a sodium- and chloride-bound outward-facing open conformation. Together, these studies define common and simple principles for the action of SSRIs, SNRIs and TCAs on BATs.
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Affiliation(s)
- Hui Wang
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239
| | - April Goehring
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239
| | - Kevin H Wang
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239
| | - Aravind Penmatsa
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239
| | - Ryan Ressler
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239
| | - Eric Gouaux
- Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239
- Howard Hughes Medical Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239
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21
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Abstract
LeuT-like fold Na-dependent secondary active transporters form a large family of integral membrane proteins that transport various substrates against their concentration gradient across lipid membranes, using the free energy stored in the downhill concentration gradient of sodium ions. These transporters play an active role in synaptic transmission, the delivery of key nutrients, and the maintenance of osmotic pressure inside the cell. It is generally believed that binding of an ion and/or a substrate drives the conformational dynamics of the transporter. However, the exact mechanism for converting ion binding into useful work has yet to be established. Using a multi-dimensional path sampling (string-method) followed by all-atom free energy simulations, we established the principal thermodynamic and kinetic components governing the ion-dependent conformational dynamics of a LeuT-like fold transporter, the sodium/benzyl-hydantoin symporter Mhp1, for an entire conformational cycle. We found that inward-facing and outward-facing states of Mhp1 display nearly the same free energies with an ion absent from the Na2 site conserved across the LeuT-like fold transporters. The barrier separating an apo-state from inward-facing or outward-facing states of the transporter is very low, suggesting stochastic gating in the absence of ion/substrate bound. In contrast, the binding of a Na2 ion shifts the free energy stabilizing the outward-facing state and promoting substrate binding. Our results indicate that ion binding to the Na2 site may also play a key role in the intracellular thin gate dynamics modulation by altering its interactions with the transmembrane helix 5 (TM5). The Potential of Mean Force (PMF) computations for a substrate entrance displays two energy minima that correspond to the locations of the main binding site S1 and proposed allosteric S2 binding site. However, it was found that substrate's binds to the site S1 ∼5 kcal/mol more favorable than that to the site S2 for all studied bound combinations of ions and a substrate.
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Affiliation(s)
- Chunfeng Zhao
- Center for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Sergei Yu. Noskov
- Center for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Canada
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22
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Comeaux MS, Wang J, Wang G, Kleppe S, Zhang VW, Schmitt ES, Craigen WJ, Renaud D, Sun Q, Wong LJ. Biochemical, molecular, and clinical diagnoses of patients with cerebral creatine deficiency syndromes. Mol Genet Metab 2013; 109:260-8. [PMID: 23660394 DOI: 10.1016/j.ymgme.2013.04.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Revised: 04/02/2013] [Accepted: 04/03/2013] [Indexed: 01/09/2023]
Abstract
Cerebral creatine deficiency syndromes (CCDS) are a group of inborn errors of creatine metabolism that involve AGAT and GAMT for creatine biosynthesis disorders and SLC6A8 for creatine transporter (CT1) deficiency. Deficiencies in the three enzymes can be distinguished by intermediate metabolite levels, and a definitive diagnosis relies on the presence of deleterious mutations in the causative genes. Mutations and unclassified variants were identified in 41 unrelated patients, and 22 of these mutations were novel. Correlation of sequencing and biochemical data reveals that using plasma guanidinoacetate (GAA) as a biomarker has 100% specificity for both AGAT and GAMT deficiencies, but AGAT deficiency has decreased sensitivity in this assay. Furthermore, the urine creatine:creatinine ratio is an effective screening test with 100% specificity in males suspected of having creatine transporter deficiency. This test has a high false-positive rate due to dietary factors or dilute urine samples and lacks sensitivity in females. We conclude that biochemical screening for plasma GAA and measuring of the urine creatine:creatinine ratio should be performed for suspected CCDS patients prior to sequencing. Also, based on the results of this study, we feel that sequencing should only be considered if a patient has abnormal biochemical results on repeat testing.
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MESH Headings
- Amidinotransferases/blood
- Amidinotransferases/chemistry
- Amidinotransferases/deficiency
- Amidinotransferases/genetics
- Amidinotransferases/metabolism
- Amino Acid Metabolism, Inborn Errors/diagnosis
- Amino Acid Metabolism, Inborn Errors/genetics
- Amino Acid Metabolism, Inborn Errors/metabolism
- Brain Diseases, Metabolic, Inborn/diagnosis
- Brain Diseases, Metabolic, Inborn/genetics
- Brain Diseases, Metabolic, Inborn/metabolism
- Creatine/deficiency
- Creatine/genetics
- Creatine/metabolism
- Creatinine/urine
- Developmental Disabilities/diagnosis
- Developmental Disabilities/genetics
- Developmental Disabilities/metabolism
- Female
- Guanidinoacetate N-Methyltransferase/blood
- Guanidinoacetate N-Methyltransferase/deficiency
- Guanidinoacetate N-Methyltransferase/genetics
- Guanidinoacetate N-Methyltransferase/metabolism
- Humans
- Intellectual Disability/diagnosis
- Intellectual Disability/genetics
- Intellectual Disability/metabolism
- Language Development Disorders/diagnosis
- Language Development Disorders/genetics
- Language Development Disorders/metabolism
- Male
- Membrane Transport Proteins/genetics
- Mental Retardation, X-Linked/diagnosis
- Mental Retardation, X-Linked/genetics
- Mental Retardation, X-Linked/metabolism
- Models, Molecular
- Movement Disorders/congenital
- Movement Disorders/diagnosis
- Movement Disorders/genetics
- Movement Disorders/metabolism
- Mutation
- Phenotype
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/genetics
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
- Protein Conformation
- Speech Disorders/diagnosis
- Speech Disorders/genetics
- Speech Disorders/metabolism
- Syndrome
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Affiliation(s)
- Matthew S Comeaux
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
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23
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Mondal S, Khelashvili G, Shi L, Weinstein H. The cost of living in the membrane: a case study of hydrophobic mismatch for the multi-segment protein LeuT. Chem Phys Lipids 2013; 169:27-38. [PMID: 23376428 PMCID: PMC3631462 DOI: 10.1016/j.chemphyslip.2013.01.006] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Revised: 01/15/2013] [Accepted: 01/15/2013] [Indexed: 12/27/2022]
Abstract
Many observations of the role of the membrane in the function and organization of transmembrane (TM) proteins have been explained in terms of hydrophobic mismatch between the membrane and the inserted protein. For a quantitative investigation of this mechanism in the lipid-protein interactions of functionally relevant conformations adopted by a multi-TM segment protein, the bacterial leucine transporter (LeuT), we employed a novel method, Continuum-Molecular Dynamics (CTMD), that quantifies the energetics of hydrophobic mismatch by combining the elastic continuum theory of membrane deformations with an atomistic level description of the radially asymmetric membrane-protein interface from MD simulations. LeuT has been serving as a model for structure-function studies of the mammalian neurotransmitter:sodium symporters (NSSs), such as the dopamine and serotonin transporters, which are the subject of intense research in the field of neurotransmission. The membrane models in which LeuT was embedded for these studies were composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid, or 3:1 mixture of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) lipids. The results show that deformation of the host membrane alone is not sufficient to alleviate the hydrophobic mismatch at specific residues of LeuT. The calculations reveal significant membrane thinning and water penetration due to the specific local polar environment produced by the charged K288 of TM7 in LeuT, that is membrane-facing deep inside the hydrophobic milieu of the membrane. This significant perturbation is shown to result in unfavorable polar-hydrophobic interactions at neighboring hydrophobic residues in TM1a and TM7. We show that all the effects attributed to the K288 residue (membrane thinning, water penetration, and the unfavorable polar-hydrophobic interactions at TM1a and TM7), are abolished in calculations with the K288A mutant. The involvement of hydrophobic mismatch is somewhat different in the functionally distinct conformations (outward-open, occluded, inward-open) of LeuT, and the differences are shown to connect to structural elements (e.g., TM1a) known to play key roles in transport. This finding suggests a mechanistic hypothesis for the enhanced transport activity observed for the K288A mutant, suggesting that the unfavorable hydrophobic-hydrophilic interactions hinder the motion of TM1a in the functionally relevant conformational transition to the inward-open state. Various extents of such unfavorable interactions, involving exposure to the lipid environment of adjacent hydrophobic and polar residues, are common in multi-segment transmembrane proteins, and must be considered to affect functionally relevant conformational transitions.
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Affiliation(s)
- Sayan Mondal
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065
| | - Lei Shi
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065
- The HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, NY 10065
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065
- The HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, NY 10065
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24
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Koldsø H, Christiansen AB, Sinning S, Schiøtt B. Comparative modeling of the human monoamine transporters: similarities in substrate binding. ACS Chem Neurosci 2013; 4:295-309. [PMID: 23421681 PMCID: PMC3582297 DOI: 10.1021/cn300148r] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Accepted: 10/24/2012] [Indexed: 11/30/2022] Open
Abstract
The amino acid compositions of the substrate binding pockets of the three human monoamine transporters are compared as is the orientation of the endogenous substrates, serotonin, dopamine, and norepinephrine, bound in these. Through a combination of homology modeling, induced fit dockings, molecular dynamics simulations, and uptake experiments in mutant transporters, we propose a common binding mode for the three substrates. The longitudinal axis of the substrates is similarly oriented with these, forming an ionic interaction between the ammonium group and a highly conserved aspartate, Asp98 (serotonin transporter, hSERT), Asp79 (dopamine transporter, hDAT), and Asp75 (norepinephrine transporter, hNET). The 6-position of serotonin and the para-hydroxyl groups of dopamine and norepinephrine were found to face Ala173 in hSERT, Gly153 in hDAT, and Gly149 in hNET. Three rotations of the substrates around the longitudinal axis were identified. In each mode, an aromatic hydroxyl group of the substrates occupied equivalent volumes of the three binding pockets, where small changes in amino acid composition explains the differences in selectivity. Uptake experiments support that the 5-hydroxyl group of serotonin and the meta-hydroxyl group norepinephrine and dopamine are placed in the hydrophilic pocket around Ala173, Ser438, and Thr439 in hSERT corresponding to Gly149, Ser419, Ser420 in hNET and Gly153 Ser422 and Ala423 in hDAT. Furthermore, hDAT was found to possess an additional hydrophilic pocket around Ser149 to accommodate the para-hydroxyl group. Understanding these subtle differences between the binding site compositions of the three transporters is imperative for understanding the substrate selectivity, which could eventually aid in developing future selective medicines.
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Affiliation(s)
- Heidi Koldsø
- Center for Insoluble Protein
Structures (inSPIN) and Interdisciplinary Nanoscience
Center (iNANO), Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus
C, Denmark
| | - Anja B. Christiansen
- Laboratory of
Molecular Neurobiology,
Centre for Psychiatric Research, Aarhus University Hospital, Skovagervej 2, 8240 Risskov, Denmark
| | - Steffen Sinning
- Laboratory of
Molecular Neurobiology,
Centre for Psychiatric Research, Aarhus University Hospital, Skovagervej 2, 8240 Risskov, Denmark
| | - Birgit Schiøtt
- Center for Insoluble Protein
Structures (inSPIN) and Interdisciplinary Nanoscience
Center (iNANO), Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus
C, Denmark
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25
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Simmler LD, Buser TA, Donzelli M, Schramm Y, Dieu LH, Huwyler J, Chaboz S, Hoener MC, Liechti ME. Pharmacological characterization of designer cathinones in vitro. Br J Pharmacol 2013; 168:458-70. [PMID: 22897747 PMCID: PMC3572571 DOI: 10.1111/j.1476-5381.2012.02145.x] [Citation(s) in RCA: 503] [Impact Index Per Article: 45.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 07/30/2012] [Accepted: 08/08/2012] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Designer β-keto amphetamines (e.g. cathinones, 'bath salts' and 'research chemicals') have become popular recreational drugs, but their pharmacology is poorly characterized. EXPERIMENTAL APPROACH We determined the potencies of cathinones to inhibit DA, NA and 5-HT transport into transporter-transfected HEK 293 cells, DA and 5-HT efflux from monoamine-preloaded cells, and monoamine receptor binding affinity. KEY RESULTS Mephedrone, methylone, ethylone, butylone and naphyrone acted as non-selective monoamine uptake inhibitors, similar to cocaine. Mephedrone, methylone, ethylone and butylone also induced the release of 5-HT, similar to 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) and other entactogens. Cathinone, methcathinone and flephedrone, similar to amphetamine and methamphetamine, acted as preferential DA and NA uptake inhibitors and induced the release of DA. Pyrovalerone and 3,4-methylenedioxypyrovalerone (MDPV) were highly potent and selective DA and NA transporter inhibitors but unlike amphetamines did not evoke the release of monoamines. The non-β-keto amphetamines are trace amine-associated receptor 1 ligands, whereas the cathinones are not. All the cathinones showed high blood-brain barrier permeability in an in vitro model; mephedrone and MDPV exhibited particularly high permeability. CONCLUSIONS AND IMPLICATIONS Cathinones have considerable pharmacological differences that form the basis of their suggested classification into three groups. The predominant action of all cathinones on the DA transporter is probably associated with a considerable risk of addiction.
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Affiliation(s)
- L D Simmler
- Division of Clinical Pharmacology and Toxicology, Departments of Biomedicine and Internal Medicine, University Hospital and University of Basel, Basel, Switzerland
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26
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Valayannopoulos V, Bakouh N, Mazzuca M, Nonnenmacher L, Hubert L, Makaci FL, Chabli A, Salomons GS, Mellot-Draznieks C, Brulé E, de Lonlay P, Toulhoat H, Munnich A, Planelles G, de Keyzer Y. Functional and electrophysiological characterization of four non-truncating mutations responsible for creatine transporter (SLC6A8) deficiency syndrome. J Inherit Metab Dis 2013; 36:103-12. [PMID: 22644605 DOI: 10.1007/s10545-012-9495-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2012] [Revised: 04/24/2012] [Accepted: 05/03/2012] [Indexed: 12/27/2022]
Abstract
Intellectual disability coupled with epilepsy are clinical hallmarks of the creatine (Cr) transporter deficiency syndrome resulting from mutations in the SLC6A8 gene. So far characterization of pathogenic mutations of SLC6A8 has been limited to Cr uptake. The aim of our study was to characterize the electrogenic and pharmacological properties of non truncating SLC6A8 mutations identified in patients presenting variable clinical severity. Electrophysiological and pharmacological properties of four mutants (including two novel ones) were studied in X. laevis oocyte expression system. Creatine uptake was assessed with [(14)C]-Cr in X. laevis and patients' fibroblasts. Subcellular localization was determined by immunofluorescence and western blot. All mutants were properly targeted to the plasma membrane in both systems. Mutations led to the complete loss of both electrogenic and transport activities in X. laevis and Cr uptake in patients' fibroblasts. Among the Cr analogs tested, guanidinopropionate induced an electrogenic activity with the normal SLC6A8 transporter similar to creatine whereas a phosphocreatine derivative, PCr-Mg-CPLX, resulted in partial activity. SLC6A8 mutants displayed no electrogenic activity with all Cr analogs tested in X. laevis oocytes. Although the mutations altered various domains of SLC6A8 Cr uptake and electrogenic properties were completely inhibited and could not be dissociated. Besides the metabolic functions of Cr, the loss of SLC6A8 electrogenic activity, demonstrated here for the first time, may also play a role in the altered brain functions of the patients.
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Affiliation(s)
- Vassili Valayannopoulos
- INSERM U781 and Paris-Descartes University, Necker-Enfants Malades Hospital, 149 rue de Sèvres, 75743 Paris cedex 15, France
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27
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Mercimek-Mahmutoglu S, Al-Thihli K, Roland E. Is low serum creatine kinase a nonspecific screening marker for creatine deficiency syndromes? Mol Genet Metab 2012; 106:251-2. [PMID: 22551696 DOI: 10.1016/j.ymgme.2012.04.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Accepted: 04/09/2012] [Indexed: 10/28/2022]
MESH Headings
- Biomarkers/blood
- Brain Diseases, Metabolic, Inborn/diagnosis
- Brain Diseases, Metabolic, Inborn/genetics
- Brain Diseases, Metabolic, Inborn/metabolism
- Child, Preschool
- Creatine/deficiency
- Creatine/genetics
- Creatine/metabolism
- Creatine Kinase/blood
- Guanidinoacetate N-Methyltransferase/metabolism
- Humans
- Infant
- Male
- Membrane Transport Proteins/genetics
- Mental Retardation, X-Linked/diagnosis
- Mental Retardation, X-Linked/genetics
- Mental Retardation, X-Linked/metabolism
- Mutation
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/genetics
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
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28
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Iqbal F, Item CB, Ratschmann R, Ali M, Plas E, Bodamer O. Molecular analysis of guanidinoacetate-n-methyltransferase (GAMT) and creatine transporter (SLC6A8) gene by using denaturing high pressure liquid chromatography (DHPLC) as a possible source of human male infertility. Pak J Pharm Sci 2011; 24:75-79. [PMID: 21190923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The creatine/phosphocreatine system is essential for cellular phosphate coupled energy storage and production, particularly in tissues subject to high metabolic demands. Male factor infertility is a common condition with unknown etiology in most of the cases. Sperm abnormalities could possibly lead to infertility. As sperm motility depends on intact mitochondrial function and energy levels. Thus reduced intracellular creatine stores may contribute to decreased sperm motility leading to male infertility as creatine /phosphocreatine system plays major role in making and breaking of ATP, thus in energy kinetics. We developed and validated a denaturing high performance liquid chromatograph (DHPLC) method for the molecular analysis of SLC6A8 and GAMT genes involve in creatine biosynthesis and transport as a possible source of human male infertility by analyzing DNA from 64, clinically confirmed, infertile men. No mutation/polymorphism was detected in the exonic regions of both genes in all the patients and in fertile healthy controls indicating that SLC6A8 and GAMT genes may not be directly involved in human male infertility.
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Affiliation(s)
- Furhan Iqbal
- Institute of Pure and Applied Biology, Zoology Division. Bahauddin Zakariya University, Multan, Pakistan.
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29
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Pánek J. A comparative computational analysis of protein sequences and literature mining classify 'orphan' neurotransmitter transporters. J Theor Biol 2008; 254:301-7. [PMID: 18621060 DOI: 10.1016/j.jtbi.2008.06.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2007] [Revised: 04/30/2008] [Accepted: 06/06/2008] [Indexed: 11/19/2022]
Abstract
Various sources of protein data, such as knowledgebases and scientific literature, are currently available, as are numerous tools for their analysis. The matter becomes one of choosing the tools that are most appropriate for the specific task and for the specific proteins. A combination of standard and alternative tools may lead to biologically significant results. Here, a computational classification of proteins is made using standard multiple sequence alignment in combination with an alternative method for analysis of hydropathy distribution in proteins. Both of these methods are applied to the Na+/Cl--dependent neurotransmitter symporters (NSSs), resulting in two alternative classifications. The classifications are validated and interpreted biologically by literature and knowledgebase annotation mining, producing a consensus classification. The classification leads to the identification and functional characterization of three families of largely structurally and functionally uncharacterized orphan NSSs. The literature and knowledgebase annotations are mined to functionally characterize the NSSs in these families. The presented work also demonstrates that, in specific cases, the analysis of the hydropathy distribution in proteins is capable of revealing functional properties of proteins.
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Affiliation(s)
- Josef Pánek
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
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30
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Shi L, Quick M, Zhao Y, Weinstein H, Javitch JA. The mechanism of a neurotransmitter:sodium symporter--inward release of Na+ and substrate is triggered by substrate in a second binding site. Mol Cell 2008; 30:667-77. [PMID: 18570870 DOI: 10.1016/j.molcel.2008.05.008] [Citation(s) in RCA: 306] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Revised: 01/17/2008] [Accepted: 05/13/2008] [Indexed: 01/24/2023]
Abstract
Eukaryotic neurotransmitter:sodium symporters (NSSs), targets for antidepressants and psychostimulants, terminate neurotransmission by sodium-driven reuptake. The crystal structure of LeuT(Aa), a prokaryotic NSS homolog, revealed an occluded state in which one leucine and two Na(+) ions are bound, but provided limited clues to the molecular mechanism of transport. Using steered molecular dynamics simulations, we explored the substrate translocation pathway of LeuT. We identified a second substrate binding site located in the extracellular vestibule comprised of residues shown recently to participate in binding tricyclic antidepressants. Binding and flux experiments showed that the two binding sites can be occupied simultaneously. The substrate in the secondary site allosterically triggers intracellular release of Na(+) and substrate from the primary site, thereby functioning as a "symport effector." Because tricyclic antidepressants bind differently to this secondary site, they do not promote substrate release from the primary site and thus act as symport uncouplers and inhibit transport.
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Affiliation(s)
- Lei Shi
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA
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31
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Jin C, Navarro HA, Page K, Carroll FI. Synthesis and monoamine transporter binding properties of 2beta-[3'-(substituted benzyl)isoxazol-5-yl]- and 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes. Bioorg Med Chem 2008; 16:6682-8. [PMID: 18556210 PMCID: PMC2597627 DOI: 10.1016/j.bmc.2008.05.073] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Revised: 05/28/2008] [Accepted: 05/29/2008] [Indexed: 10/22/2022]
Abstract
A series of 2beta-[3'-(substituted benzyl)isoxazol-5-yl]- and 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes were prepared and evaluated for affinities at dopamine, serotonin, and norepinephrine transporters using competitive radioligand binding assays. The 2beta-[3'-(substituted benzyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes (3a-h) showed high binding affinities for the dopamine transporter (DAT). The IC(50) values ranged from 5.9 to 22nM. On the other hand, the 2beta-[3'-methyl-4'-(substituted phenyl)isoxazol-5-yl]-3beta-(substituted phenyl)tropanes (4a-h), with IC(50) values ranging from 65 to 173nM, were approximately 3- to 25-fold less potent than the corresponding 2beta-[3'-(substituted benzyl)isoxazol]tropanes. All tested compounds were selective for the DAT relative to the norepinephrine transporter (NET) and serotonin transporter (5-HTT). 3Beta-(4-Methylphenyl)-2beta-[3'-(4-fluorobenzyl)isoxazol-5-yl]tropane (3b) with IC(50) of 5.9nM at the DAT and K(i)s of 454 and 113nM at the NET and 5-HTT, respectively, was the most potent and DAT-selective analog. Molecular modeling studies suggested that the rigid conformation of the isoxazole side chain in 4a-h might play an important role on their low DAT binding affinities.
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Affiliation(s)
- Chunyang Jin
- Organic and Medicinal Chemistry, Research Triangle Institute, PO Box 12194, Research Triangle Park, NC 27709-2194, USA
| | - Hernán A. Navarro
- Organic and Medicinal Chemistry, Research Triangle Institute, PO Box 12194, Research Triangle Park, NC 27709-2194, USA
| | - Kevin Page
- Organic and Medicinal Chemistry, Research Triangle Institute, PO Box 12194, Research Triangle Park, NC 27709-2194, USA
| | - F. Ivy Carroll
- Organic and Medicinal Chemistry, Research Triangle Institute, PO Box 12194, Research Triangle Park, NC 27709-2194, USA
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Abstract
The Drosophila melanogaster photoreceptor cell has long served as a model system for researchers focusing on how animal sensory neurons receive information from their surroundings and translate this information into chemical and electrical messages. Electroretinograph (ERG) analysis of Drosophila mutants has helped to elucidate some of the genes involved in the visual transduction pathway downstream of the photoreceptor cell, and it is now clear that photoreceptor cell signaling is dependent upon the proper release and recycling of the neurotransmitter histamine. While the neurotransmitter transporters responsible for clearing histamine, and its metabolite carcinine, from the synaptic cleft have remained unknown, a strong candidate for a transporter of either substrate is the uncharacterized inebriated protein. The inebriated gene (ine) encodes a putative neurotransmitter transporter that has been localized to photoreceptor cells in Drosophila and mutations in ine result in an abnormal ERG phenotype in Drosophila. Loss-of-function mutations in ebony, a gene required for the synthesis of carcinine in Drosophila, suppress components of the mutant ine ERG phenotype, while loss-of-function mutations in tan, a gene necessary for the hydrolysis of carcinine in Drosophila, have no effect on the ERG phenotype in ine mutants. We also show that by feeding wild-type flies carcinine, we can duplicate components of mutant ine ERGs. Finally, we demonstrate that treatment with H3 receptor agonists or inverse agonists rescue several components of the mutant ine ERG phenotype. Here, we provide pharmacological and genetic epistatic evidence that ine encodes a carcinine neurotransmitter transporter. We also speculate that the oscillations observed in mutant ine ERG traces are the result of the aberrant activity of a putative H3 receptor. During signaling in the nervous system, individual nerve cells transfer information to one another by a complex process called synaptic transmission. This communication involves the release of a specific neurotransmitter into the synaptic cleft, which then triggers signaling in the downstream neuron by binding to and activating specific cell surface receptors. In order to terminate the neuronal signal, the neurotransmitter must be rapidly removed from the synaptic cleft. This is done by two mechanisms: the neurotransmitter can be degraded or modified, or the transmitter can be taken up by the presynaptic neuron and packaged into vesicles for reuse. In the compound eye of the fruitfly D. melanogaster, the photoreceptor cell responds to light and releases histamine into the synaptic cleft. This signal is terminated by the removal of histamine from the synapse and the enzymatic conversion of histamine to carcinine. We have shown that it is not sufficient just to modify the histamine neurotransmitter, but it is also important to remove carcinine from the photoreceptor synapse. The failure to adequately remove carcinine results in defects in the visual transduction process. Moreover, the work suggests that carcinine itself modulates vision by regulating histamine release into the synapse.
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Affiliation(s)
- Brendan A Gavin
- Department of Biology, Dartmouth College, Hanover, New Hampshire, United States of America
| | - Susan E Arruda
- Department of Biology, Franklin Pierce College, Rindge, New Hampshire, United States of America
| | - Patrick J Dolph
- Department of Biology, Dartmouth College, Hanover, New Hampshire, United States of America
- * To whom correspondence should be addressed. E-mail:
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Abstract
LeuT is a bacterial amino acid transporter belonging to a large family of membrane proteins, including the neurotransmitter transporters that are targets for antidepressant drugs. The high-resolution structure of LeuT has provided an important model for understanding structure and function in this family. Two recent papers found that LeuT can bind tricyclic antidepressants, raising the possibility that it may also serve as a model for the pharmacological properties of neurotransmitter transporters.
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Affiliation(s)
- Gary Rudnick
- Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520-8066, USA.
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Zomot E, Bendahan A, Quick M, Zhao Y, Javitch JA, Kanner BI. Mechanism of chloride interaction with neurotransmitter:sodium symporters. Nature 2007; 449:726-30. [PMID: 17704762 DOI: 10.1038/nature06133] [Citation(s) in RCA: 178] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2007] [Accepted: 08/01/2007] [Indexed: 01/20/2023]
Abstract
Neurotransmitter:sodium symporters (NSS) have a critical role in regulating neurotransmission and are targets for psychostimulants, anti-depressants and other drugs. Whereas the non-homologous glutamate transporters mediate chloride conductance, in the eukaryotic NSS chloride is transported together with the neurotransmitter. In contrast, transport by the bacterial NSS family members LeuT, Tyt1 and TnaT is chloride independent. The crystal structure of LeuT reveals an occluded binding pocket containing leucine and two sodium ions, and is highly relevant for the neurotransmitter transporters. However, the precise role of chloride in neurotransmitter transport and the location of its binding site remain elusive. Here we show that introduction of a negatively charged amino acid at or near one of the two putative sodium-binding sites of the GABA (gamma-aminobutyric acid) transporter GAT-1 from rat brain (also called SLC6A1) renders both net flux and exchange of GABA largely chloride independent. In contrast to wild-type GAT-1, a marked stimulation of the rate of net flux, but not of exchange, was observed when the internal pH was lowered. Equivalent mutations introduced in the mouse GABA transporter GAT4 (SLC6A11) and the human dopamine transporter DAT (SLC6A3) also result in chloride-independent transport, whereas the reciprocal mutations in LeuT and Tyt1 render substrate binding and/or uptake by these bacterial NSS chloride dependent. Our data indicate that the negative charge, provided either by chloride or by the transporter itself, is required during binding and translocation of the neurotransmitter, probably to counterbalance the charge of the co-transported sodium ions.
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Affiliation(s)
- Elia Zomot
- Department of Biochemistry, Hebrew University Hadassah Medical School, POB 12272, Jerusalem 91120, Israel
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35
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Abstract
Tricyclic antidepressants exert their pharmacological effect-inhibiting the reuptake of serotonin, norepinephrine, and dopamine-by directly blocking neurotransmitter transporters (SERT, NET, and DAT, respectively) in the presynaptic membrane. The drug-binding site and the mechanism of this inhibition are poorly understood. We determined the crystal structure at 2.9 angstroms of the bacterial leucine transporter (LeuT), a homolog of SERT, NET, and DAT, in complex with leucine and the antidepressant desipramine. Desipramine binds at the inner end of the extracellular cavity of the transporter and is held in place by a hairpin loop and by a salt bridge. This binding site is separated from the leucine-binding site by the extracellular gate of the transporter. By directly locking the gate, desipramine prevents conformational changes and blocks substrate transport. Mutagenesis experiments on human SERT and DAT indicate that both the desipramine-binding site and its inhibition mechanism are probably conserved in the human neurotransmitter transporters.
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Affiliation(s)
- Zheng Zhou
- Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Juan Zhen
- Departments of Psychiatry and Pharmacology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Nathan K. Karpowich
- Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Regina M. Goetz
- Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Christopher J. Law
- Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Maarten E. A. Reith
- Departments of Psychiatry and Pharmacology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
- Corresponding authors: , (212) 263-8267, , (212) 263-8634
| | - Da-Neng Wang
- Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
- Corresponding authors: , (212) 263-8267, , (212) 263-8634
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Singh SK, Yamashita A, Gouaux E. Antidepressant binding site in a bacterial homologue of neurotransmitter transporters. Nature 2007; 448:952-6. [PMID: 17687333 DOI: 10.1038/nature06038] [Citation(s) in RCA: 346] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2007] [Accepted: 06/21/2007] [Indexed: 01/11/2023]
Abstract
Sodium-coupled transporters are ubiquitous pumps that harness pre-existing sodium gradients to catalyse the thermodynamically unfavourable uptake of essential nutrients, neurotransmitters and inorganic ions across the lipid bilayer. Dysfunction of these integral membrane proteins has been implicated in glucose/galactose malabsorption, congenital hypothyroidism, Bartter's syndrome, epilepsy, depression, autism and obsessive-compulsive disorder. Sodium-coupled transporters are blocked by a number of therapeutically important compounds, including diuretics, anticonvulsants and antidepressants, many of which have also become indispensable tools in biochemical experiments designed to probe antagonist binding sites and to elucidate transport mechanisms. Steady-state kinetic data have revealed that both competitive and noncompetitive modes of inhibition exist. Antagonist dissociation experiments on the serotonin transporter (SERT) have also unveiled the existence of a low-affinity allosteric site that slows the dissociation of inhibitors from a separate high-affinity site. Despite these strides, atomic-level insights into inhibitor action have remained elusive. Here we screen a panel of molecules for their ability to inhibit LeuT, a prokaryotic homologue of mammalian neurotransmitter sodium symporters, and show that the tricyclic antidepressant (TCA) clomipramine noncompetitively inhibits substrate uptake. Cocrystal structures show that clomipramine, along with two other TCAs, binds in an extracellular-facing vestibule about 11 A above the substrate and two sodium ions, apparently stabilizing the extracellular gate in a closed conformation. Off-rate assays establish that clomipramine reduces the rate at which leucine dissociates from LeuT and reinforce our contention that this TCA inhibits LeuT by slowing substrate release. Our results represent a molecular view into noncompetitive inhibition of a sodium-coupled transporter and define principles for the rational design of new inhibitors.
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Affiliation(s)
- Satinder K Singh
- The Vollum Institute, Oregon Health and Science University, 3181 S.W. Sam Jackson Road, Portland, Oregon 97239, USA
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37
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Forrest LR, Tavoulari S, Zhang YW, Rudnick G, Honig B. Identification of a chloride ion binding site in Na+/Cl -dependent transporters. Proc Natl Acad Sci U S A 2007; 104:12761-6. [PMID: 17652169 PMCID: PMC1937540 DOI: 10.1073/pnas.0705600104] [Citation(s) in RCA: 169] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The recent determination of the crystal structure of the leucine transporter from Aquifex aeolicus (aaLeuT) has provided significant insights into the function of neurotransmitter:sodium symporters. Transport by aaLeuT is Cl(-) independent, whereas many neurotransmitter:sodium symporters from higher organisms depend on Cl(-) ions. However, the only Cl(-) ion identified in the aaLeuT structure interacts with nonconserved residues in extracellular loops, and thus the relevance of this binding site is unclear. Here, we use calculations of pK(A)s and homology modeling to predict the location of a functionally important Cl(-) binding site in serotonin transporter and other Cl(-)-dependent transporters. We validate our model through the site-directed mutagenesis of residues predicted to coordinate the Cl(-) ion and through the observation of sequence conservation patterns in other Cl(-)-dependent transporters. The proposed site is located midway across the membrane and is formed by residues from transmembrane helices 2, 6, and 7. It is close to the Na1 sodium binding site, thus providing an explanation for the coupling of Cl(-) and Na(+) ions during transport. Other implications of the model are also discussed.
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Affiliation(s)
- Lucy R. Forrest
- *Howard Hughes Medical Institute, Center for Computational Biology and Bioinformatics, and Department of Biochemistry and Molecular Biophysics, Columbia University, 1130 St. Nicholas Avenue, Room 815, New York, NY 10032; and
| | - Sotiria Tavoulari
- Department of Pharmacology, Yale University, 333 Cedar Street, New Haven, CT 06520-8066
| | - Yuan-Wei Zhang
- Department of Pharmacology, Yale University, 333 Cedar Street, New Haven, CT 06520-8066
| | - Gary Rudnick
- Department of Pharmacology, Yale University, 333 Cedar Street, New Haven, CT 06520-8066
| | - Barry Honig
- *Howard Hughes Medical Institute, Center for Computational Biology and Bioinformatics, and Department of Biochemistry and Molecular Biophysics, Columbia University, 1130 St. Nicholas Avenue, Room 815, New York, NY 10032; and
- To whom correspondence should be addressed. E-mail:
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Mellott TJ, Kowall NW, Lopez-Coviella I, Blusztajn JK. Prenatal choline deficiency increases choline transporter expression in the septum and hippocampus during postnatal development and in adulthood in rats. Brain Res 2007; 1151:1-11. [PMID: 17399691 PMCID: PMC1952662 DOI: 10.1016/j.brainres.2007.03.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 02/16/2007] [Accepted: 03/02/2007] [Indexed: 11/19/2022]
Abstract
Supplementation of maternal diet with the essential nutrient, choline, during the second half of pregnancy in rats causes long-lasting improvements in spatial memory in the offspring and protects them from the memory decline characteristic of old age. In contrast, prenatal choline deficiency is associated with poor performance in certain cognitive tasks. The mechanism by which choline influences learning and memory remains unclear; however, it may involve changes to the hippocampal cholinergic system. Previously, we showed that the hippocampi of prenatally [embryonic days (E) 11-17] choline-deficient animals have increased synthesis of acetylcholine (ACh) from choline transported by the high-affinity choline transporter (CHT) and reduced ACh content relative to the control and to the E11-17 choline-supplemented rats. In the current study, we found that, during postnatal period [postnatal days (P) 18-480], prenatal choline deficiency increased the expression of CHT mRNA in the septum and CHT mRNA and protein levels in the hippocampus and altered the pattern of CHT immunoreactivity in the dentate gyrus. CHT immunoreactivity was more prominent in the inner molecular layer in prenatally choline-deficient rats compared to controls and prenatally choline-supplemented animals. In addition, in all groups, we observed a population of hilar interneurons that were CHT-immunoreactive. These neurons are the likely source of the hippocampal CHT mRNA as their number correlated with the levels of this mRNA. The abundance of hippocampal CHT mRNA rose between P1 and P24 and then declined reaching 60% of the P1 value by P90. These data show that prenatal availability of choline alters its own metabolism (i.e., CHT expression). While the upregulated CHT expression during the period of prenatal choline deficiency may be considered as a compensatory mechanism that could enhance ACh synthesis when choline supply is low, the persistent upregulation of CHT expression subsequent to the brief period of prenatal deprivation of choline in utero might be beneficial during choline deficiency in adulthood.
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Affiliation(s)
- Tiffany J. Mellott
- Department of Pathology and Laboratory Medicine, Boston University School of Medicine, Boston, MA 02118, USA
| | - Neil W. Kowall
- Department of Pathology and Laboratory Medicine, Boston University School of Medicine, Boston, MA 02118, USA
- Geriatric Research Education Clinical Center, Veterans Affairs Medical Center, Bedford, MA 01730, USA
| | - Ignacio Lopez-Coviella
- Department of Pathology and Laboratory Medicine, Boston University School of Medicine, Boston, MA 02118, USA
| | - Jan Krzysztof Blusztajn
- Department of Pathology and Laboratory Medicine, Boston University School of Medicine, Boston, MA 02118, USA
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Verrico CD, Miller GM, Madras BK. MDMA (Ecstasy) and human dopamine, norepinephrine, and serotonin transporters: implications for MDMA-induced neurotoxicity and treatment. Psychopharmacology (Berl) 2007; 189:489-503. [PMID: 16220332 DOI: 10.1007/s00213-005-0174-5] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2005] [Accepted: 08/17/2005] [Indexed: 01/20/2023]
Abstract
RATIONALE 3,4-Methylenedioxymethamphetamine (MDMA, designated as "Ecstasy" if illicitly marketed in tablet form) induces significant decrements in neuronal serotonin (5-HT) markers in humans, nonhuman primates, and rats as a function of dosing and dosing regimen. In rats, MDMA-mediated effects are attributed, in part, to selective high-affinity transport of MDMA into 5-HT neurons by the 5-HT transporter (SERT), followed by extensive 5-HT release. OBJECTIVES To clarify whether SERT-selective effects of MDMA at human monoamine transporters can account for the reported MDMA-induced selective toxicity of serotonin neurons in primate brain. METHODS We investigated the interaction of [(3)H](+/-, RS)- (+, S)- and (-, R)-MDMA with the human SERT, dopamine (DA) transporter (DAT), and norepinephrine (NE) transporter (NET) in stably transfected human embryo kidney (HEK)-293 cells. RESULTS The human DAT, NET, and SERT actively transported [(3)H]RS(+/-)-MDMA saturably, stereoselectively, and in a temperature-, concentration-, and transporter-dependent manner. MDMA exhibited the highest affinity for the NET>>SERT>or=DAT, the same rank order for MDMA inhibition of [(3)H]DA, [(3)H]NE, and [(3)H]5-HT transport and stimulated release of the [(3)H]monoamines, which differed from reports derived from rodent monoamine transporters. The extent of MDMA-induced release of 5-HT was higher compared with release of DA or NE. CONCLUSIONS The affinity of MDMA for the human SERT in transfected cells does not clarify the apparent selective toxicity of MDMA for serotonin neurons, although conceivably, its higher efficacy for stimulating 5-HT release may be a distinguishing factor. The findings highlight the need to investigate MDMA effects in DAT-, SERT-, and NET-expressing neurons in the primate brain and the therapeutic potential of NET or DAT inhibitors, in addition to SERT-selective inhibitors, for alleviating the pharmacological effects of MDMA.
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Affiliation(s)
- Christopher D Verrico
- Department of Psychiatry, Division of Neurochemistry, New England Primate Research Center, Harvard Medical School, 1 Pine Hill Drive, Southborough, MA 01772-9102, USA
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40
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Tachikawa M, Hosoya KI, Ohtsuki S, Terasaki T. A novel relationship between creatine transport at the blood-brain and blood-retinal barriers, creatine biosynthesis, and its use for brain and retinal energy homeostasis. Subcell Biochem 2007; 46:83-98. [PMID: 18652073 DOI: 10.1007/978-1-4020-6486-9_5] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Evidence is increasing that the creatine/phosphocreatine shuttle system plays an essential role in energy homeostasis in the brain and retina to ensure proper development and function. Thus, our understanding of the mechanism of creatine supply and creatine usage in the brain and retina and of creatine supplementation in patients with creatine deficiency syndromes is an important step towards improved therapeutic strategies for brain and retinal disorders. Our recent research provides novel molecular-anatomical evidence that (i) at the blood-brain barrier and the inner blood-retinal barrier, the creatine transporter (CRT/SLC6AS) functions as a major pathway for supplying creatine to the brain and retina, and that (ii) local creatine is preferentially synthesized in the glial cells, e.g., oligodendrocytes, astrocytes, and Müller cells, in the brain and retina. Thus, the blood-brain barrier and inner blood-retinal barrier play important roles not only in supplying energy sources (glucose and lactate), but also in supplying an energy 'buffer' (creatine). These findings lead to the novel insight that the creatine/phosphocreatine shuttle system is based on an intricate relationship between the blood-brain barrier, inner blood-retinal barrier, glia, and neurons (photoreceptor cells) to maintain and ensure energy homeostasis in the brain and retina.
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Affiliation(s)
- Masanori Tachikawa
- Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama 930-0194, Japan
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41
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Harrington AM, Hutson JM, Southwell BR. High affinity choline transporter immunoreactivity in rat ileum myenteric nerves. Cell Tissue Res 2006; 327:421-31. [PMID: 17093920 DOI: 10.1007/s00441-006-0332-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2006] [Accepted: 08/16/2006] [Indexed: 11/24/2022]
Abstract
Recently, an antibody against the choline transporter (CHT), an essential molecule involved in ACh uptake, was used to label cholinergic nerves in the central nervous system; however, the enteric nervous system (ENS) was not examined. The present study localised CHT immunoreactivity (CHT-IR) within the rat ileum ENS and determined whether it colocalised with immunoreactivity for markers of cholinergic, tachykinergic and nitrergic circuitry. Segments of rat ileum were fixed, prepared for sectioning or whole-mounts and incubated with anti-CHT antisera followed by a fluorescent secondary antibody. Samples were double-labelled with antibodies to nitric oxide synthase, substance P (SP), common choline acetyltransferase (cChAT) and vesicular acetylcholine transporter (VAChT). CHT-IR was present in varicosities of nerve fibres in the myenteric plexus and muscle layers of rat ileum. In the myenteric ganglia, CHT-IR was found in nerve fibres and the cytoplasm of some nerve cell bodies. In the myenteric ganglia, no CHT/cChAT-immunoreactive neurons were present. A small number of CHT/SP-immunoreactive neurons and CHT/SP-immunoreactive nerve fibres clustered around unlabelled neurons. CHT-IR colocalised with VAChT-IR in the myenteric plexus but only half of the CHT-immunoreactive myenteric nerve fibres were VAChT-immunoreactive and half of VAChT-immunoreactive fibres were CHT-immunoreactive. In the circular muscle, 75% of CHT-immunoreactive fibres were VAChT-immunoreactive. Thus, the anti-CHT antiserum labels neurons and nerve fibres in the rat ENS. It does not label cholinergic cChAT-immunoreactive neurons, although it does immunostain cholinergic VAChT-immunoreactive nerve fibres and a population of nerves that are not VAChT-immunoreactive.
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Affiliation(s)
- Andrea M Harrington
- Gut Motility Laboratory, Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, Australia
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42
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Hara T, Bansal A, DeGrado TR. Choline transporter as a novel target for molecular imaging of cancer. Mol Imaging 2006; 5:498-509. [PMID: 17150162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023] Open
Abstract
Abnormalities of choline processing in cancer cells have been used as a basis for imaging of cancer with positron emission tomography and magnetic resonance spectroscopy. In this study, the transport mechanism for choline was investigated in cultured PC-3 prostate cancer cells. Furthermore, tritiated hemicholinium 3 (HC-3), a well-known inhibitor of choline transport, was studied as a prototypic molecular imaging probe in PC-3 cells and 9L glioma-bearing rats. [(3)H]Choline uptake by PC-3 cells was found to have both facilitative and nonfacilitative components. Facilitative transport was characterized by partial sodium dependence and intermediate affinity (K(M) = 9.7 +/- 0.8 microM). HC-3 inhibited choline with a K(I) of 10.5+/- 2.2 microM. Ouabain (1 mM) caused a 94% reduction in choline uptake. At physiologic choline concentration, phosphocholine was the rapid and predominant metabolic fate. The binding of [(3)H]HC-3 to PC-3 cells was rapid and specific (competitively blocked with unlabeled HC-3). Biodistribution of [(3)H]HC-3 in 9L glioma-bearing rats showed the ranking of uptake to be kidney > lung > tumor > liver > skeletal muscle congruent with blood > brain. In comparison with [(14)C]choline, [(3)H]HC-3 showed over twofold higher tumor uptake and favorable uptake ratios of tumor to blood, tumor to muscle, tumor to lung, and tumor to liver. The data demonstrate the quantitative importance of an intermediate-affinity, partially sodium-dependent choline transport system on choline processing in PC-3 cancer cells. The biodistribution properties of [(3)H]HC-3 in tumor-bearing rats encourage the development of molecular imaging probes based on choline transporter binding ligands.
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Affiliation(s)
- Toshihiko Hara
- Department of Radiology, Indiana University Department of Medicine, Indianapolis, IN 46202, USA
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Shojaiefard M, Christie DL, Lang F. Stimulation of the creatine transporter SLC6A8 by the protein kinases SGK1 and SGK3. Biochem Biophys Res Commun 2006; 334:742-6. [PMID: 16036218 DOI: 10.1016/j.bbrc.2005.06.164] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Accepted: 06/24/2005] [Indexed: 11/19/2022]
Abstract
Creatine binds phosphate thus serving energy storage. Cellular creatine uptake is accomplished by the Na+,Cl-, creatine transporter CreaT (SLC6A8). The present study explored the regulation of SLC6A8 by the serum and glucocorticoid inducible kinase SGK1, a kinase upregulated during ischemia. In Xenopus oocytes expressing SLC6A8 but not in water injected oocytes creatine induced a current which was significantly enhanced by coexpression of wild type SGK1 and constitutively active (S422D)SGK1, but not inactive (K127N)SGK1. Kinetic analysis revealed that (S422D)SGK1 enhanced maximal current without significantly altering affinity. The effect of SGK1 was mimicked by the constitutively active isoform (S419D)SGK3 but not by inactive (K119N)SGK3, wild type isoform SGK2 or constitutively active related kinase (T308D,S473D)PKB. In conclusion, the kinases SGK1 and SGK3 increase SLC6A8 activity by increasing the maximal transport rate of the carrier. Deranged SGK1 and/or SGK3 dependent regulation of SLC6A8 may affect energy storage particularly in skeletal muscle, heart, and neurons.
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Quick M, Yano H, Goldberg NR, Duan L, Beuming T, Shi L, Weinstein H, Javitch JA. State-dependent conformations of the translocation pathway in the tyrosine transporter Tyt1, a novel neurotransmitter:sodium symporter from Fusobacterium nucleatum. J Biol Chem 2006; 281:26444-54. [PMID: 16798738 DOI: 10.1074/jbc.m602438200] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The gene of a novel prokaryotic member (Tyt1) of the neurotransmitter:sodium symporter (NSS) family has been cloned from Fusobacterium nucleatum. In contrast to eukaryotic and some prokaryotic NSSs, which contain 12 transmembrane domains (TMs), Tyt1 contains only 11 TMs, a characteristic shared by approximately 70% of prokaryotic NSS homologues. Nonetheless upon heterologous expression in an engineered Escherichia coli host, Tyt1 catalyzes robust Na+-dependent, highly selective l-tyrosine transport. Genetic engineering of Tyt1 variants devoid of cysteines or with individually retained endogenous cysteines at positions 18 or 238, at the cytoplasmic ends of TM1 and TM6, respectively, preserved normal transport activity. Whereas cysteine-less Tyt1 was resistant to the inhibitory effect of sulfhydryl-alkylating reagents, N-ethylmaleimide inhibited transport by Tyt1 variants containing either one or both of the endogenous cysteines, and this inhibition was altered by the substrates sodium and tyrosine, consistent with substrate-induced dynamics in the transport pathway. Our findings support a binding model of Tyt1 function in which an ordered sequence of substrate-induced structural changes reflects distinct conformational states of the transporter. This work identifies Tyt1 as the first functional bacterial NSS member putatively consisting of only 11 TMs and shows that Tyt1 is a suitable model for the study of NSS dynamics with relevance to structure/function relationships of human NSSs, including the dopamine, norepinephrine, serotonin, and gamma-aminobutyric acid transporters.
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Affiliation(s)
- Matthias Quick
- Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA
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Clark AJ, Rosenberg EH, Almeida LS, Wood TC, Jakobs C, Stevenson RE, Schwartz CE, Salomons GS. X-linked creatine transporter (SLC6A8) mutations in about 1% of males with mental retardation of unknown etiology. Hum Genet 2006; 119:604-10. [PMID: 16738945 DOI: 10.1007/s00439-006-0162-9] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2005] [Accepted: 02/21/2006] [Indexed: 10/24/2022]
Abstract
Mutations in the creatine transporter gene, SLC6A8 (MIM 30036), located in Xq28, have been found in families with X-linked mental retardation (XLMR) as well as in males with idiopathic mental retardation (MR). In order to estimate the frequency of such mutations in the MR population, a screening of 478 males with MR of unknown cause was undertaken. All 13 exons of SLC6A8 were sequenced using genomic DNA. Six novel potentially pathogenic mutations were identified that were not encountered in at least 588 male control chromosomes: two deletions (p.Asn336del, p.Ile347del) and a splice site alteration (c.1016+2C>T) are considered pathogenic based on the nature of the variant. A mutation (p.Arg391Trp) should be considered pathogenic owing to its localization in a highly conserved region. Two other missense variants (p.Lys4Arg, p.Gly26Arg) are not conserved but were not observed in over 300 male control chromosomes. Their pathogenicity is uncertain. A missense variant (p.Val182Met), was classified as a polymorphism based on a normal creatine/creatinine (Cr:Crn) ratio and cerebral creatine signal in proton magnetic resonance spectroscopy (H-MRS) in the patient. Furthermore, we found 14 novel intronic and neutral variants that were not encountered in at least 280 male control chromosomes and should be considered as unclassified variants. Our findings of a minimum of four pathogenic mutations and two potentially pathogenic mutations indicate that about 1% of males with MR of unknown etiology might have a SLC6A8 mutation. Thus, DNA sequence analysis and/or a Cr:Crn urine screen is warranted in any male with MR of unknown cause.
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Affiliation(s)
- Amy J Clark
- J.C. Self Research Institute, Greenwood Genetic Center, 1 Gregor Mendel Circle, Greenwood, SC 29646, USA
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Rosenberg EH, Muñoz CM, Degrauw TJ, Jakobs CN, Salomons GS. Overexpression of wild-type creatine transporter (SLC6A8) restores creatine uptake in primary SLC6A8-deficient fibroblasts. J Inherit Metab Dis 2006; 29:345-6. [PMID: 16763899 DOI: 10.1007/s10545-006-0271-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
In the study reported, we prove that mutations in the SLC6A8 gene are responsible for SLC6A8 deficiency, a cerebral creatine deficiency syndrome (CCDS), since overexpression of the wild-type SLC6A8 open reading frame (ORF) restores the creatine uptake profile in SLC6A8-deficient fibroblasts.
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Affiliation(s)
- Efraim H Rosenberg
- Department of Clinical Chemistry, Metabolic Unit, VU University Medical Center, De Boelelaan 1118, 1081 HV, Amsterdam, The Netherlands
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Geldenhuys WJ, Lockman PR, Philip AE, McAfee JH, Miller BL, McCurdy CR, Allen DD. Inhibition of choline uptake by N-cyclohexylcholine, a high affinity ligand for the choline transporter at the blood-brain barrier. J Drug Target 2005; 13:259-66. [PMID: 16051538 DOI: 10.1080/10611860500139222] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The blood-brain barrier (BBB) choline transporter (CHT) may have utility as a drug delivery vector for drugs that act in the central nervous system. Previous studies suggested the importance of hydrophobic moieties on the cationic nitrogen of choline for improved affinity for this transporter. In a pilot study, we therefore designed five novel N-cycloalkyl derivatives of choline, one of which showed promising inhibition properties. This choline analogue had a cyclohexyl (UMBB-5) moiety substituting one of the methyl groups attached to the cationic nitrogen in choline. In situ experimental data were obtained from in situ rat brain perfusion studies. The binding affinity for the BBB-choline transporter found for UMBB-5 was K(i)=1.9 microM. Comparative molecular field analysis (CoMFA) suggested that the cyclohexyl moiety orientates towards a steric favourable area. Taken together, the results of these in situ and in silico studies provide further evidence or restrictions that occur with binding to this brain drug delivery vector.
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Affiliation(s)
- Werner J Geldenhuys
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Science Centre, Amarillo, TX 79106, USA
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