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Identification of SLC38A7 (SNAT7) Protein as a Glutamine Transporter Expressed in Neurons
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
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2011 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, no 23, 20500-20511 p.Article in journal (Refereed) Published
Abstract [en]

The SLC38 family of transporters has in total 11 members in humans and they encode amino acid transporters called sodium-coupled amino acid transporters (SNAT). To date, five SNATs have been characterized and functionally subdivided into systems A (SLC38A1, SLC38A2, and SLC38A4) and N (SLC38A3 and SLC38A5) showing the highest transport for glutamine and alanine. Here we present identification of a novel glutamine transporter encoded by the Slc38a7 gene, which we propose should be named SNAT7. This transporter has L-glutamine as the preferred substrate but also transports other amino acids with polar side chains, as well as L-histidine and L-alanine. The expression pattern and substrate profile for SLC38A7 shows highest similarity to the known system N transporters. Therefore, we propose that SLC38A7 is a novel member of this system. We used in situ hybridization and immunohistochemistry with a custom-made antibody to show that SLC38A7 is expressed in all neurons, but not in astrocytes, in the mouse brain. SLC38A7 is unique in being the first system N transporter expressed in GABAergic and also other neurons. The preferred substrate and axonal localization of SLC38A7 close to the synaptic cleft indicates that SLC38A7 could have an important function for the reuptake and recycling of glutamate.

Place, publisher, year, edition, pages
2011. Vol. 286, no 23, 20500-20511 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-155238DOI: 10.1074/jbc.M110.162404ISI: 000291267600037OAI: oai:DiVA.org:uu-155238DiVA: diva2:425352
Available from: 2011-06-21 Created: 2011-06-20 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Functional Characterization of Centrally Expressed Solute Carriers and G Protein-Coupled Receptors
Open this publication in new window or tab >>Functional Characterization of Centrally Expressed Solute Carriers and G Protein-Coupled Receptors
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Transmembrane proteins are gatekeepers of the cells; controlling the transport of substrates as well as communicating signals among cells and between the organelles and cytosol. Solute carriers (SLC) and G protein-coupled receptors (GPCR) are the largest family of membrane transporters and membrane receptors respectively. The overall aim of this thesis was to provide a basic understanding of some of the novel SLCs and GPCRs with emphasis on expression, transport property, evolution and probable function.

The first part of the thesis directs towards the study of some novel solute carriers. In an initial study, we provided an overall picture of the sequence relationship and tissue expression of 14 diverse atypical SLCs confirming some of their evolutionary conservation and highly specific expression pattern. The focus then was on the SLC17 family (mainly vesicular proteins) and a novel member named Slc17a9. This study revealed that SLC17 family could be divided into four main phylogenetic clades which were all present before the divergence of the insect lineage with Slc17a9 having the most restricted evolutionary history. Detailed expression study of Slc17a9 in the mouse brain suggests that it is also expressed in some regions important for purinergic neurotransmission. Further, we deorphanised an aminoacid transporter Slc38a7 which was expressed in a majority of neurons in the CNS and showed that it preferably mediate transport of L–glutamine and L–histidine.

The second part of the thesis focuses on the study of two GPCRs belonging to the Rhodopsin superfamily, Gpr162 and Gpr153. A phylogenetic analysis revealed that both Gpr153 and Gpr162 originated from a common ancestor before the radiation of the mammalian lineage. Expression study revealed that Gpr162 had a predominant expression in the CNS and relatively lower expression in the other tissue tested whereas Gpr153 had a more widespread and similar expression pattern in both CNS and peripheral tissues. The functional studies of the two GPCRs were done using the antisense oligodeoxynucleotide knockdown rat model. These studies provided evidence linking the orphan Gpr162 gene with the regulation of food intake– related behaviour whereas Gpr153 gene caused only a slight reduction in food intake.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 51 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 689
Keyword
GPCR, SLC, Gpr153, Gpr162, Slc17, Slc38
National Category
Neurosciences
Research subject
Neuroscience
Identifiers
urn:nbn:se:uu:diva-156832 (URN)978-91-554-8120-9 (ISBN)
Public defence
2011-09-22, B42, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2011-09-01 Created: 2011-08-09 Last updated: 2011-11-03Bibliographically approved
2. Characterization of Amino Acid Transporters in the Brain: Molecular and Functional Studies of Members within the Solute Carrier Families SLC38 and SLC6
Open this publication in new window or tab >>Characterization of Amino Acid Transporters in the Brain: Molecular and Functional Studies of Members within the Solute Carrier Families SLC38 and SLC6
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solute carriers (SLCs) comprise the largest group of transporters in humans and there are currently 52 SLC families. They are embedded in cellular membranes and transport numerous molecules; defects in many of the genes encoding SLCs have been connected to pathological conditions, and several SLCs are potential drug targets.

The SLC38 family has in total eleven members in humans and they encode transporters called SNATs. In paper I and paper II, we reported molecular and functional characterization of Slc38a7 and Slc38a8, two of the previous orphan members in the family which we suggested to be named SNAT7 and SNAT8, respectively. Using in situ hybridization and immunohistochemistry, these transporters showed similar expression pattern and localized to neurons in the brain For functional characterization proteins were overexpressed in X. laevis oocytes and an Uptake Assay and electrophysiological recordings showed preferred transport of L-glutamine, L-histidine, L-alanine, L-asparagine, L-aspartate and L-arginine for SNAT7. A similar pattern was seen for SNAT8 in a slightly different order of affinities. We classified SNAT7 as a system N transporter and SNAT8 as belonging to system A, and suggests that SNAT7 and SNAT8 could play a role in the glutamine/glutamate(GABA) cycle (GGC) in the brain.

Furthermore, we studied the vesicular B0AT3 (Slc6a17) transporter in paper III, and the sodium-coupled amino acid transporter B0AT2 (Slc6a15) in paper IV. Tissue expression studies showed similar localization of Slc6a17 and Slc6a15 mRNA using in situ hybridization and real-time PCR. In paper III, vesicular localization of B0AT2 was shown in both excitatory and inhibitory neurons. When challenging the monoaminergic system with drugs both Slc6a17 and Slc6a15 were upregulated. Suggested roles for the transporters are thereby in synaptic remodeling by regulating the availability of free amino acids used as precursors needed in neurotransmitter synthesis. Moreover, in paper IV, immunohistochemistry showed B0AT3 localization to neurons, astrocytes and epithelial cells of the choroid plexus. Leucine injections caused a smaller reduction of food intake as well as higher neuronal activation in the paraventricular hypothalamic nucleus in Slc6a15 KO mice, compared with wild type mice. This suggests B0AT2 involvement in the anorexigenic effects of leucine.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 55 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 960
Keyword
Amino acid transporter, Solute Carrier, Glutamine, Leucine, SNAT, B0AT
National Category
Neurosciences
Research subject
Neuroscience
Identifiers
urn:nbn:se:uu:diva-212610 (URN)978-91-554-8832-1 (ISBN)
Public defence
2014-02-14, B/B22, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2014-01-23 Created: 2013-12-12 Last updated: 2014-02-10

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