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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Biophysical Analysis of the Human Erythrocyte Glucose Transporter: a Dissertation

Graybill, Christopher A. 05 October 2005 (has links)
Hydrodynamic analysis and electron microscopy of GLUT1/lipid/detergent micelles and freeze fracture electron microscopy of GLUT1 proteoliposomes support the hypothesis that the glucose transporter is a multimeric (probably tetrameric) complex of GLUT1 proteins. Some detergents (e.g. octylglucoside) maintain the multimeric complex while other detergents (e.g. CHAPS and dodecylmaltoside) promote the dissociation of GLUT1 oligomers into smaller aggregation states (dimers or monomers). GLUT1 does not appear to exchange rapidly between protein/lipid/detergent micelles but is able to self-associate in the plane of the lipid bilayer. Quantitatively deglycosylated GLUT1 displays aberrant electrophoretic mobility, but each protein band contains full-length GLUT1 and the less mobile species, when treated with additional detergent and reductant, converts to the more mobile species. Preliminary structural analysis suggests that denaturing detergent- and thiol chemistry-related changes of α-helical content may mirror mobility shifts. Limited proteolysis of membrane-resident GLUT1 (± ligands) releases membrane-spanning α-helical domains suggesting that (i) some bilayer-resident helices are highly solvent exposed; (ii) membrane-spanning domains 1, 2, & 4 and 7, 8, & 10 are destabilized upon ligand binding; and (iii) helix packing compares well with high-resolution structures of prokaryotic transporters from the same superfamily. Results are consistent with a central, hydrophilic, translocation pathway comprised of amphipathic, membrane-spanning domains that alter associations upon ligand/substrate binding. We have resolved technical difficulties (heterogeneity, lipid/detergent removal, glycosylation, small molecule contamination) associated with GLUT1 analysis by mass spectrometry; and we map global conformational changes between sugar uptake and sugar efflux.
2

Role of Protein Kinase Map4k4 in Energy Metabolism: A Dissertation

Danai, Laura V. 29 April 2015 (has links)
Systemic glucose regulation is essential for human survival as low or chronically high glucose levels can be detrimental to the health of an individual. Glucose levels are highly regulated via inter-organ communication networks that alter metabolic function to maintain euglycemia. For example, when nutrient levels are low, pancreatic α-cells secrete glucagon, which signals to the liver to promote glycogen breakdown and glucose production. In times of excess nutrient intake, pancreatic β-cells release insulin. Insulin signals to the liver to suppress hepatic glucose production, and signals to the adipose tissue and the skeletal muscle to take up excess glucose via insulin-regulated glucose transporters. Defects in this inter-organ communication network including insulin resistance can result in glucose deregulation and ultimately the onset of type-2 diabetes (T2D). To identify novel regulators of insulin-mediated glucose transport, our laboratory performed an siRNA-mediated gene-silencing screen in cultured adipocytes and measured insulin-mediated glucose transport. Gene silencing of Mitogen-activated protein kinase kinase kinase kinase 4 (Map4k4), a Sterile-20-related serine/threonine protein kinase, enhanced insulin-stimulated glucose transport, suggesting Map4k4 inhibits insulin action and glucose transport. Thus, for the first part of my thesis, I explore the role of Map4k4 in cultured adipose cells and show that Map4k4 also represses lipid synthesis independent of its effects on glucose transport. Map4k4 inhibits lipid synthesis in a Mechanistic target of rapamycin complex 1 (mTORC1)- and Sterol regulatory element-binding transcription factor 1 (Srebp-1)-dependent mechanism and not via a c-Jun NH2-terminal kinase (Jnk)-dependent mechanism. For the second part of my thesis, I explore the metabolic function of Map4k4 in vivo. Using mice with loxP sites flanking the Map4k4 allele and a ubiquitously expressed tamoxifen-activated Cre, we inducibly ablated Map4k4 expression in adult mice and found significant improvements in metabolic health indicated by improved fasting glucose and whole-body insulin action. To assess the role of Map4k4 in specific metabolic tissues responsible for systemic glucose regulation, we employed tissue-specific knockout mice to deplete Map4k4 in adipose tissue using an adiponectin-cre transgene, liver using an albumin-cre transgene, and skeletal muscle using a Myf5-cre transgene. Ablation of Map4k4 expression in adipose tissue or liver had no impact on whole body glucose homeostasis or insulin resistance. However, we surprisingly found that Map4k4 depletion in Myf5-positive tissues, which include skeletal muscles, largely recapitulates the metabolic phenotypes observed in systemic Map4k4 knockout mice, restoring obesity-induced glucose intolerance and insulin resistance. Furthermore these metabolic changes were associated with enhanced insulin signaling to Akt in the visceral adipose tissue, a tissue that is nearly devoid of Myf5-positive cells and does not display changes in Map4k4 expression. Thus, these results indicate that Map4k4 in Myf5-positive cells, most likely skeletal muscle cells, inhibits whole-body insulin action and these effects may be mediated via an indirect effect on the visceral adipose tissue. The results presented here provide evidence for Map4k4 as a potential therapeutic target for the treatment of insulin resistance and T2D.

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