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Ian A. Simpson - One of the best experts on this subject based on the ideXlab platform.
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Glucose Transporter glut 5 expression in microglial cells
Glia, 1997Co-Authors: Jennifer Payne, Fran Maher, Ian A. Simpson, Linda Mattice, Peter DaviesAbstract:Glut 5 is a member of a family of facilitative Glucose Transporter proteins that are involved in the transportation of Glucose and/or fructose across plasma membranes. Glut 5 is one of three isoforms expressed in brain. Using immunocytochemical and immunoblotting techniques in formalin fixed tissue, we have shown that Glut 5 is exclusively expressed in microglial cells of the human and rat brain. Our data demonstrate that unlike other microglial markers, Glut 5 can be used as a microglial marker in formalin fixed tissue.
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Glucose Transporter proteins in brain delivery of Glucose to neurons and glia
Glia, 1997Co-Authors: Susan J Vannucci, Fran Maher, Ian A. SimpsonAbstract:Glucose is the principle energy source for the mammalian brain. Delivery of Glucose from the blood to the brain requires transport across the endothelial cells of the blood-brain barrier and into the neurons and glia. The facilitative Glucose Transporter proteins mediate these processes. The primary isoforms in brain are GLUT1, detected at high concentrations as a highly glycosylated form, (55 kDa) in blood-brain barrier, and also as a less glycosylated, 45 kDa form, present in parenchyma, predominantly glia; GLUT3 in neurons; and GLUT5 in microglia. The rest of the Transporter family, GLUTs 2, 4, and 7, have also been detected in brain but at lower levels of expression and confined to more discrete regions. All of the Transporters probably contribute to cerebral Glucose utilization, as part of overall metabolism and metabolic interactions among cells. We discuss the properties, regulation, cell-specific location, and kinetic characteristics of the isoforms, their potential contributions to cerebral metabolism, and several experimental paradigms in which alterations in energetic demand and/or substrate supply affect Glucose Transporter expression.
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Glucose Transporter isoforms glut1 and glut3 transport dehydroascorbic acid
Journal of Biological Chemistry, 1997Co-Authors: Steven C Rumsey, Guo Wei Xu, Oran Kwon, Charles F Burant, Ian A. Simpson, Mark LevineAbstract:Abstract Dehydroascorbic acid (DHA) is rapidly taken up by cells and reduced to ascorbic acid (AA). Using the Xenopus laevis oocyte expression system we examined transport of DHA and AA via Glucose Transporter isoforms GLUT1–5 and SGLT1. The apparentK m of DHA transport via GLUT1 and GLUT3 was 1.1 ± 0.2 and 1.7 ± 0.3 mm, respectively. High performance liquid chromatography analysis confirmed 100% reduction of DHA to AA within oocytes. GLUT4 transport of DHA was only 2–4-fold above control and transport kinetics could not be calculated. GLUT2, GLUT5, and SGLT1 did not transport DHA and none of the isoforms transported AA. Radiolabeled sugar transport confirmed Transporter function and identity of all cDNA clones was confirmed by restriction fragment mapping. GLUT1 and GLUT3 cDNA were further verified by polymerase chain reaction. DHA transport activity in both GLUT1 and GLUT3 was inhibited by 2-deoxyGlucose, d-Glucose, and 3-O-methylGlucose among other hexoses while fructose and l-Glucose showed no inhibition. Inhibition by the endofacial inhibitor, cytochalasin B, was non-competitive and inhibition by the exofacial inhibitor, 4,6-O-ethylidene-α-Glucose, was competitive. Expressed mutant constructs of GLUT1 and GLUT3 did not transport DHA. DHA and 2-deoxyGlucose uptake by Chinese hamster ovary cells overexpressing either GLUT1 or GLUT3 was increased 2–8-fold over control cells. These studies suggest GLUT1 and GLUT3 isoforms are the specific Glucose Transporter isoforms which mediate DHA transport and subsequent accumulation of AA.
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Glucose Transporter isoforms in brain absence of glut3 from the blood brain barrier
Journal of Cerebral Blood Flow and Metabolism, 1993Co-Authors: Frances Maher, Susan J Vannucci, Ian A. SimpsonAbstract:Two Glucose Transporter (GLUT) isoforms have been identified in brain. The GLUT1 isoform is abundant in cerebral microvessels and may be present in glia and neurons, whereas GLUT3 is probably the major neuronal Glucose Transporter. This study investigates whether GLUT3 is also present in microvessels from rat, human, and canine brain, by means of antisera directed against the divergent C-terminal sequences of mouse and human GLUT3. GLUT1 was detected in whole brain as two molecular mass forms: 55 kDa in microvessels and 45 kDa in cortical neuronal/glial membranes. With the aid of the appropriate antisera to the species-specific sequences, GLUT3 was detected in rat and human cortical membranes but not in isolated rat or human microvessels. These antisera failed to detect GLUT3 in either canine cortical membranes or canine microvessels, implying additional species specificity in the C-terminal sequence.
Graeme I Bell - One of the best experts on this subject based on the ideXlab platform.
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human intestinal Glucose Transporter expression and localization of glut5
American Journal of Physiology-cell Physiology, 1992Co-Authors: Nicholas O Davidson, Charles F Burant, Gwyn W. Gould, A M L Hausman, C A Ifkovits, John B Buse, Graeme I BellAbstract:We have studied the developmental and regional expression of mRNAs encoding sodium-dependent and facilitative Glucose Transporter proteins in human fetal and adult small intestine. The abundance of...
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Glucose Transporter expression in brain cdna sequence of mouse glut3 the brain facilitative Glucose Transporter isoform and identification of sites of expression by in situ hybridization
Journal of Biological Chemistry, 1992Co-Authors: Shinya Nagamatsu, Charles F Burant, Susumu Seino, Jon M Kornhauser, Kelly E Mayo, Graeme I BellAbstract:Abstract Complementary DNAs encoding the mouse GLUT3/brain facilitative Glucose Transporter have been isolated and sequenced. The predicted amino acid sequence indicates that mouse GLUT3 is composed of 493 amino acids and has 83 and 89% identity and similarity, respectively, to the sequence of human GLUT3. In contrast to human GLUT3 mRNA, which can be readily detected by RNA blotting in all human tissues that have been examined, mouse GLUT3 mRNA was only present at significant levels in brain. In situ hybridization showed differential expression of GLUT3 mRNA in several regions of adult mouse brain. Specific expression was observed in the hippocampus, with GLUT3 mRNA levels being higher in areas CA1 to CA3 than in the dentate gyrus. It was also detected in the Purkinje cell layer of the cerebellum and in the cerebral cortex, with higher expression in the piriform cortex than in other regions of the cortex. Antisera to mouse GLUT3 immunoblotted a series of proteins of 45-50 kDa in mouse brain plasma membranes. These results are consistent with GLUT3 being a neuronal Glucose Transporter.
Scott M. Landfear - One of the best experts on this subject based on the ideXlab platform.
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phenotypic characterization of a Glucose Transporter null mutant in leishmania mexicana
Molecular and Biochemical Parasitology, 2007Co-Authors: Dayana Rodriguezcontreras, Xiuhong Feng, Kristie M Keeney, H Archie G Bouwer, Scott M. LandfearAbstract:Glucose is a major source of energy and carbon in promastigotes of Leishmania mexicana, and its uptake is mediated by three Glucose Transporters whose genes are encoded within a single cluster. A null mutant in which the Glucose Transporter gene cluster was deleted by homologous gene replacement was generated previously and shown to grow more slowly than wild type promastigotes but not to be viable as amastigotes in primary tissue culture macrophages or in axenic culture. Further phenotypic characterization demonstrates that the null mutant is unable to import Glucose, mannose, fructose, or galactose and that each of the three Glucose Transporter isoforms, LmGT1, LmGT2, and LmGT3, is capable of transporting each of these hexoses. Complementation of the null mutant with each isoform is able to restore growth in each of the four hexoses to wild type parasites. Null mutant promastigotes are reduced in size to about 2/3 the volume of wild type parasites. In addition, the null mutants are significantly more sensitive to oxidative stress than their wild type counterparts. These results underscore the importance of Glucose Transporters in the parasite life cycle and suggest reasons for their non-viability in the disease-causing amastigote stage.
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metabolic changes in Glucose Transporter deficient leishmania mexicana and parasite virulence
Journal of Biological Chemistry, 2006Co-Authors: Dayana Rodriguezcontreras, Scott M. LandfearAbstract:Abstract Leishmania mexicana are parasitic protozoa that express a variety of glycoconjugates that play important roles in their biology as well as the storage carbohydrate β-mannan, which is an essential virulence factor for survival of intracellular amastigote forms in the mammalian host. Glucose Transporter null mutants, which are viable as insect form promastigotes but not as amastigotes, do not take up Glucose and other hexoses but are still able to synthesize these glycoconjugates and β-mannan, although at reduced levels. Synthesis of these carbohydrate-containing macromolecules could be accounted for by incorporation of non-carbohydrate precursors into carbohydrates by gluconeogenesis. However, the significantly reduced level of the virulence factor β-mannan in the Glucose Transporter null mutants compared with wild-type parasites may contribute to the non-viability of these null mutants in the disease-causing amastigote stage of the life cycle.
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genetic characterization of Glucose Transporter function in leishmania mexicana
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Richard Burchmore, Dayana Rodriguezcontreras, Kathleen Mcbride, Michael P Barrett, Govind B Modi, David L Sacks, Scott M. LandfearAbstract:Both insect and mammalian life cycle stages of Leishmania mexicana take up Glucose and express all three isoforms encoded by the LmGT Glucose Transporter gene family. To evaluate Glucose Transporter function in intact parasites, a null mutant line has been created by targeted disruption of the LmGT locus that encompasses the LmGT1, LmGT2, and LmGT3 genes. This Δlmgt null mutant exhibited no detectable Glucose transport activity. The growth rate of the Δlmgt knockout in the promastigote stage was reduced to a rate comparable with that of WT cells grown in the absence of Glucose. Δlmgt cells also exhibited dramatically reduced infectivity to macrophages, demonstrating that expression of LmGT isoforms is essential for viability of amastigotes. Furthermore, WT L. mexicana were not able to grow as axenic culture form amastigotes if Glucose was withdrawn from the medium, implying that Glucose is an essential nutrient in this life cycle stage. Expression of either LmGT2 or LmGT3, but not of LmGT1, in Δlmgt null mutants significantly restored growth as promastigotes, but only LmGT3 expression substantially rescued amastigote growth in macrophages. Subcellular localization of the three isoforms was investigated in Δlmgt cells expressing individual LmGT isoforms. Using anti-LmGT antiserum and GFP-tagged LmGT fusion proteins, LmGT2 and LmGT3 were localized to the cell body, whereas LmGT1 was localized specifically to the flagellum. These results establish that each Glucose Transporter isoform has distinct biological functions in the parasite.
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differential regulation of multiple Glucose Transporter genes in leishmania mexicana
Journal of Biological Chemistry, 1998Co-Authors: Richard Burchmore, Scott M. LandfearAbstract:: We have studied the structure and expression of Glucose Transporter genes in the parasitic protozoan Leishmania mexicana. Three distinct Glucose Transporter isoforms, LmGT1, LmGT2, and LmGT3, are encoded by single copy genes that are clustered together at a single locus. Quantitation of Northern blots reveals that LmGT2 mRNA is present at approximately 15-fold higher level in promastigotes, the insect stage of the parasite life cycle, compared with amastigotes, the intracellular stage of the life cycle that lives within the mammalian host. In contrast, LmGT1 and LmGT3 mRNAs are expressed at similar levels in both life cycle stages. Transcription of the LmGT genes in promastigotes and axenically cultured amastigotes occurs at similar levels, as measured by nuclear run-on transcription. Consequently, the approximately 15-fold up-regulation of LmGT2 mRNA levels in promastigotes compared with amastigotes must be controlled at the post-transcriptional level. Measurement of LmGT2 RNA decay in promastigotes and axenic amastigotes treated with actinomycin D suggests that differential mRNA stability may play a role in regulating Glucose Transporter mRNA levels in the two life cycle stages.
Richard A Roth - One of the best experts on this subject based on the ideXlab platform.
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expression of a constitutively active akt ser thr kinase in 3t3 l1 adipocytes stimulates Glucose uptake and Glucose Transporter 4 translocation
Journal of Biological Chemistry, 1996Co-Authors: Aimee D Kohn, Scott A Summers, Morris J Birnbaum, Richard A RothAbstract:Akt is a serine/threonine kinase that requires a functional phosphatidylinositol 3-kinase to be stimulated by insulin and other growth factors. When directed to membranes by the addition of a src myristoylation sequence, Akt becomes constitutively active. In the present studies, the constitutively active Akt and a nonmyristoylated control mutant were expressed in 3T3-L1 cells that can be induced to differentiate into adipocytes. The constitutively active Akt induced Glucose uptake into adipocytes in the absence of insulin by stimulating translocation of the insulin-responsive Glucose Transporter 4 to the plasma membrane. The constitutively active Akt also increased the synthesis of the ubiquitously expressed Glucose Transporter 1. The increased Glucose influx in the 3T3-L1 adipocytes directed lipid but not glycogen synthesis. These results indicate that Akt can regulate Glucose uptake and metabolism.
Sigurd Lenzen - One of the best experts on this subject based on the ideXlab platform.
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importance of the glut2 Glucose Transporter for pancreatic beta cell toxicity of alloxan
Diabetologia, 2002Co-Authors: Matthias Elsner, Markus Tiedge, B Guldbakke, Rex Munday, Sigurd LenzenAbstract:Abstract Aims/hypothesis. We investigated the importance of the low affinity GLUT2 Glucose Transporter in the diabetogenic action of alloxan in bioengineered RINm5F insulin-producing cells with different expressions of the Transporter. Methods. GLUT2 Glucose Transporter expressing RINm5F cells were generated through stable transfection of the rat GLUT2 cDNA under the control of the cytomegalovirus promoter in the pcDNA3 vector. Viability of the cells was determined using a microtitre plate-based 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. Results. Cells expressing the GLUT2 Transporter were susceptible to alloxan toxicity due to the uptake of alloxan by this specific Glucose Transporter isoform. The extent of the toxicity of alloxan was dependent upon the GLUT2 protein expression in the cells. The lipophilic alloxan derivative, butylalloxan, was toxic also to non-transfected control cells. Expression of the GLUT2 Glucose Transporter caused only a marginal increase in the toxicity of this substance. Butylalloxan, unlike alloxan itself, is not diabetogenic in vivo although, like the latter substance, it is beta-cell toxic in vitro through its ability to generate free radicals during redox cycling with glutathione. Conclusion/interpretation. Our results are consistent with the central importance of selective uptake of alloxan through the low affinity GLUT2 Glucose Transporter for the pancreatic beta-cell toxicity and diabetogenicity of this substance. Redox cycling and the subsequent generation of oxygen free radicals leads to necrosis of pancreatic beta cells and thus to a state of insulin-dependent diabetes mellitus, well-known as alloxan diabetes in experimental diabetes research.