System L (SL), a basolateral amino acid transporter, transports large neutral amino acids (LNAAs) in a Na+-independent manner. Previously, we identified two isoforms of transporters: L-type amino acid transporter 1 (LAT1) and 2 (LAT2) and revealed their distinct substrate selectivity and transport properties. In this study, to establish more stable human LAT1 (hLAT1) and LAT2 (hLAT2) in vitro assay systems, we established mouse cell lines stably expressing hLAT1 (S2-LAT1) and hLAT2 (S2-LAT2). Real-time quantitative RT-PCR analysis revealed that S2-LAT1 and S2-LAT2 cells express hLAT1 and hLAT2 mRNAs at 20 - 1000-fold higher levels than those of endogenous mouse Lat1 and Lat2. S2-LAT1 and S2-LAT2 mediated [14C]L-leucine transport properties were measured and corresponded to results observed via Xenopus oocytes. Using these cells, the data demonstrate that hLAT1 and hLAT2 exhibit different characters in the acceptance of α-methyl amino acids and amino acid-related compounds with bulky side chains such as thyroid hormones and melphalan. S2-LAT1 and S2-LAT2 cells are expected to facilitate hLAT1 and hLAT2 substrate recognition research and contribute to drug development by providing an efficient assay system to screen for chemical compounds that interact with hLAT1 and hLAT2.

The Solute Carrier (SLC) superfamily is the largest group of membrane-bound transporters, currently with 456 transporters in 52 families. Much remains unknown about the tissue distribution and function of many of these transporters. The aim of this thesis was to characterize select SLCs with emphasis on tissue distribution, cellular localization, and function.       In paper I, we studied the leucine transporter B0AT2 (Slc6a15). Localization of B0AT2 and Slc6a15 in mouse brain was determined using in situ hybridization (ISH) and immunohistochemistry (IHC), localizing it to neurons, epithelial cells, and astrocytes. Furthermore, we observed a lower reduction of food intake in Slc6a15 knockout mice (KO) upon intraperitoneal injections with leucine, suggesting B0AT2 is involved in mediating the anorexigenic effects of leucine.     In paper II, we studied the postnatal, forebrain-specific deletion of Slcz1, belonging to the SLC18 family, in conditional KO mice (cKO). We observed a decreased response to diazepam and a higher neuronal activity in cortex and hippocampus of cKO mice, as well as an impairment in short-term recognition memory. Intracellular expression was found in neurons but not astrocytes with IHC, indicating SLCZ1 is implicated in neuronal regulation of locomotion and memory.    In paper III, we performed the first detailed histological analysis of PAT4, a transporter belonging to the SLC36 family, involved in the activation of mTOR complex 1 on lysosomes. We found abundant Slc36a4 mRNA and PAT4 expression in mouse brain, using ISH and IHC. We used IHC to localize PAT4 to both inhibitory and excitatory neurons and epithelial cells. We also found both intracellular- and plasmalemmal expression and partial colocalization of PAT4 with lysosomal markers.    Lastly, in paper IV, we provided the first tissue mapping of orphan transporter MCT14 (SLC16A14). Using qPCR, we detected moderate to high Slc16a14 mRNA in the central nervous system and kidney. We found widespread Slc16a14 and MCT14 in mouse brain using ISH and IHC. We also found MCT14 to have intracellular and plasmalemmal expression in mainly excitatory but also inhibitory neurons, as well as epithelial cells. We found MCT14 to be most closely related to MCT8, MCT2 and MCT9, suggesting a similar role for this transporter.

No description available.

The activity of glutamate transporters is essential for the temporal and spatial regulation of the neurotransmitter concentration in the synaptic cleft which is critical for proper neuronal signaling. Because of their role in controlling extracellular glutamate concentrations, dysfunctional glutamate transporters have been implicated in several neurodegenerative diseases and psychiatric disorders. Therefore, investigating the mechanism of substrate transport by these transporters is essential in understanding their behavior when they malfunction. A bacterial glutamate transporter homologue has been successfully crystallized revealing the molecular architecture of glutamate transporters. However, many important questions remain unanswered. In this thesis, I will address the role of D439 in the binding of Na+, and I will identify other electrogenic steps that contribute to the total electrogenicity of the transporter cycle. The role of D439 in the binding of Na+ to the transporter was explored previously in this lab. While it was proposed that the effect of D439 in Na+ binding is indirect, the results described in this thesis provides added support to this work. Here, I will show that the D439 mutation changed the pharmacology of EAAC1 such that THA was converted from a transported substrate to a competitive inhibitor. I will also show that Na+ binding to the substrate-bound mutant transporter occurred with the same affinity as that of Na+ to the substrate-bound wild-type transporter. Therefore, based on these results, D439 is not directly involved in the binding of Na+ to the substrate-bound transporter, but that its effect is rather indirect through changing the substrate binding properties. Na+ binding steps to the empty transporter and to the glutamate-bound EAAC1 contribute only 20% of the total electrogenicity of the glutamate transporter reactions cycle. While K+-induced relocation has been proposed to be electrogenic, there is no experimental evidence that supports it. In this work, I will show that the K+-induced relocation of the empty transporter is electrogenic. Moreover, the results in this work show that the K+-dependent steps are slower than the steps associated with the Na+/glutamate translocation suggesting that the K+-induced relocation determines the transporter?s properties at steady state.

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.

京都大学 / 新制・課程博士 / 博士(薬学) / 甲第23843号 / 薬博第850号 / 新制||薬||242(附属図書館) / 京都大学大学院薬学研究科薬学専攻 / (主査)教授 木村 郁夫, 教授 中山 和久, 教授 伊藤 貴浩 / 学位規則第4条第1項該当 / Doctor of Pharmaceutical Sciences / Kyoto University / DFAM

No description available.

The cyanobacterial amino acid β-N-methylamino-L-alanine (BMAA) is a neurotoxin implicated in the etiology of neurodegenerative diseases. Cyanobacteria are cosmopolitan organisms present in various environments. BMAA can cause long-term neurodegenerative alterations in rats exposed during the neonatal period, a period that corresponds to the last trimester and the first few years of life in humans. As BMAA has been reported to be bioaccumulated in the aquatic food chain and detected in mussels, crayfish and fish used for human consumption, the main aim of this thesis has been to investigate the final step in the mammalian food-chain, i.e. the transfer of BMAA into breast milk. Autoradiographic imaging and mass spectrometry analysis showed an enantiomer-selective uptake of BMAA and that the neurotoxin was transferred from lactating mice and rat, via the milk, to the brain of the nursed pups. The results show that transport of BMAA may be disproportional to dose. In addition, BMAA was found present both as free amino acid and tightly associated to proteins in rat brains. Surprisingly, however, no association to milk proteins was found. In vitro studies of murine (HC11) and human (MCF7) mammary epithelial cells suggest that BMAA can pass the human mammary epithelium into milk. Additional transport studies on human intestinal, glioblastoma and neuroblastoma cells showed that L-BMAA was consistently favored over D-BMAA and that the transport was mediated by several amino acid transporters. We also demonstrated that egg-laying quail transfer BMAA to its offspring by deposition in the eggs, particularly in the yolk but also in the albumen. Furthermore, comparative analysis of carboxyl- and methyl-labeled [14C]-BMAA suggested that BMAA was not metabolized to a large degree. Altogether, the results indicate that BMAA can be transferred from mothers, via the milk, to the brain of nursed human infants. Determinations of BMAA in mothers’ milk and cows’ milk are therefore warranted. We also propose that birds’ eggs could be an additional source of BMAA exposure in humans. It might therefore be of concern that mussels are increasingly used as feed in commercial egg production.

No description available.

Amino acids are necessary for protein synthesis and specialized metabolism in plants. Yet very little is known about how plants sense and regulate when and where to allocate amino acids to meet the demand for nitrogen in growing tissues. In particular, while characterized in yeast and mammals, no amino acid sensor has been identified in plants. Amino Acid Permease 1 (AAP1) has been previously characterized and was shown to mediate amino acid uptake from the soil. aap1 knockout plants and several EMS mutants affected in AAP1 sequence display enhanced tolerance to toxic concentrations of amino acids. Yet, two of the corresponding variant proteins appear to be functional transporters, effectively dissociating amino acid transport and phenotype. To understand this apparent discrepancy, I precisely studied AAP1 localization of expression at the plant and cellular level, and in specific tissue types of the root where AAP1 function is required for the tolerance phenotype and the amino acid uptake activity. I showed that AAP1 protein is present in the endoplasmic reticulum of the cortex in wild type plants Yet, its ectopic expression in root tip and phloem increased amino acid uptake, while expression in cortex could not. This and other of my results do not support the current model of AAP1 functioning in amino acid uptake by the root. I propose that the main effect of mutations in AAP1 is a disturbance in amino acid metabolism, possibly triggered by altered amino acid sensing. In this new model, AAP1 would be necessary for sensing amino acid status of cortex cells, possibly in the endoplasmic reticulum, and adjust amino acid metabolic activity and uptake to current availability. In effect, disruption of the sensing function, either by complete loss of AAP1 function (knockout) or by uncoupling the transport and sensing function (EMS mutants), would lead to the various characteristics of the phenotype of the aap1 mutants I observed. My main hypothesis is that AAP1 is a transporter endowed with sensing function, i.e., an amino acid transceptor. / Doctor of Philosophy / Changing environments create challenges for plants to grow under harsher, nutrient limiting conditions. Nitrogen is an essential nutrient for plant growth, used for the synthesis of amino acids and other nitrogen-containing metabolites. Amino acids are necessary for protein synthesis and other specialized metabolism – being targets for manipulation for improving agronomic traits. Protein content is a complex trait that involves many genes, possibly including amino acid transporters. In addition, the amount of nitrogen needed by and available to the plant increases or decreases depending on the environment conditions. How plants control nitrogen need and use at the molecular level is not well understood. The data presented here challenge a current model and I report how a protein (AAP1) involved in the acquisition of amino acids from the soil provides regulatory control over these processes. . This valuable information is useful for better understanding how plants use nitrogen and more precise breeding methods can be used to improve traits, such as protein content in agronomically important crops.