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Markussen KH, Corti M, Byrne BJ, Kooi CWV, Sun RC, Gentry MS. The multifaceted roles of the brain glycogen. J Neurochem 2024; 168:728-743. [PMID: 37554056 PMCID: PMC10901277 DOI: 10.1111/jnc.15926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 07/04/2023] [Accepted: 07/07/2023] [Indexed: 08/10/2023]
Abstract
Glycogen is a biologically essential macromolecule that is directly involved in multiple human diseases. While its primary role in carbohydrate storage and energy metabolism in the liver and muscle is well characterized, recent research has highlighted critical metabolic and non-metabolic roles for glycogen in the brain. In this review, the emerging roles of glycogen homeostasis in the healthy and diseased brain are discussed with a focus on advancing our understanding of the role of glycogen in the brain. Innovative technologies that have led to novel insights into glycogen functions are detailed. Key insights into how cellular localization impacts neuronal and glial function are discussed. Perturbed glycogen functions are observed in multiple disorders of the brain, including where it serves as a disease driver in the emerging category of neurological glycogen storage diseases (n-GSDs). n-GSDs include Lafora disease (LD), adult polyglucosan body disease (APBD), Cori disease, Glucose transporter type 1 deficiency syndrome (G1D), GSD0b, and late-onset Pompe disease (PD). They are neurogenetic disorders characterized by aberrant glycogen which results in devastating neurological and systemic symptoms. In the most severe cases, rapid neurodegeneration coupled with dementia results in death soon after diagnosis. Finally, we discuss current treatment strategies that are currently being developed and have the potential to be of great benefit to patients with n-GSD. Taken together, novel technologies and biological insights have resulted in a renaissance in brain glycogen that dramatically advanced our understanding of both biology and disease. Future studies are needed to expand our understanding and the multifaceted roles of glycogen and effectively apply these insights to human disease.
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Affiliation(s)
- Kia H. Markussen
- Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, USA
| | - Manuela Corti
- Department of Pediatrics, Powell Gene Therapy Center, College of Medicine, University of Florida, USA
| | - Barry J. Byrne
- Department of Pediatrics, Powell Gene Therapy Center, College of Medicine, University of Florida, USA
| | - Craig W. Vander Kooi
- Department of Biochemistry & Molecular Biology, College of Medicine, University of Florida, USA
- Center for Advanced Spatial Biomolecule Research, University of Florida
- Lafora Epilepsy Cure Initiative
| | - Ramon C. Sun
- Department of Biochemistry & Molecular Biology, College of Medicine, University of Florida, USA
- Center for Advanced Spatial Biomolecule Research, University of Florida
- Lafora Epilepsy Cure Initiative
| | - Matthew S. Gentry
- Department of Biochemistry & Molecular Biology, College of Medicine, University of Florida, USA
- Center for Advanced Spatial Biomolecule Research, University of Florida
- Lafora Epilepsy Cure Initiative
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Xu G, Wong M, Li Q, Park D, Cheng Z, Lebrilla CB. Unveiling the metabolic fate of monosaccharides in cell membranes with glycomic and glycoproteomic analyses. Chem Sci 2019; 10:6992-7002. [PMID: 31588266 PMCID: PMC6676465 DOI: 10.1039/c9sc01653h] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 06/10/2019] [Indexed: 12/12/2022] Open
Abstract
Cell membrane protein glycosylation is dependent on the metabolic state of the cell as well as exogenous nutrients available. Although the metabolism and interconversion of monosaccharides have been well-studied, their incorporation into cell surface glycans and their corresponding glycoproteins remains relatively unknown. In this study, we developed a method to investigate quantitatively the incorporation pathways of dietary saccharides into specific glycans and glycoproteins on the cell membrane by treating intestinal Caco-2 and hepatic KKU-M213 cells with 13C-labeled monosaccharides and characterizing the resulting cell surface glycans and glycopeptides by LC-MS/MS. Time-course studies using uniformly labeled glucose revealed that the rate of incorporation was both glycan-specific and protein-dependent. Comparative studies using different dietary saccharides and multiple cell lines revealed the variance of monosaccharide utilization and interconversion in different tissues and organisms. The robust isotope-labeling and glycan profiling methods can provide a useful tool for differentiating glycosylation pathways and enhance the understanding of how dietary sugar intake affects health.
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Affiliation(s)
- Gege Xu
- Department of Chemistry , University of California , One Shields Avenue Davis , Davis , CA 95616 , USA .
| | - Maurice Wong
- Department of Chemistry , University of California , One Shields Avenue Davis , Davis , CA 95616 , USA .
| | - Qiongyu Li
- Department of Chemistry , University of California , One Shields Avenue Davis , Davis , CA 95616 , USA .
| | - Dayoung Park
- Department of Chemistry , University of California , One Shields Avenue Davis , Davis , CA 95616 , USA .
| | - Zhi Cheng
- Department of Chemistry , University of California , One Shields Avenue Davis , Davis , CA 95616 , USA .
| | - Carlito B Lebrilla
- Department of Chemistry , University of California , One Shields Avenue Davis , Davis , CA 95616 , USA . .,Department of Biochemistry and Molecular Medicine , University of California , Davis , CA 95616 , USA.,Foods for Health Institute , University of California , Davis , CA 95616 , USA
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Brewer MK, Gentry MS. Brain Glycogen Structure and Its Associated Proteins: Past, Present and Future. ADVANCES IN NEUROBIOLOGY 2019; 23:17-81. [PMID: 31667805 PMCID: PMC7239500 DOI: 10.1007/978-3-030-27480-1_2] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
This chapter reviews the history of glycogen-related research and discusses in detail the structure, regulation, chemical properties and subcellular distribution of glycogen and its associated proteins, with particular focus on these aspects in brain tissue.
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Affiliation(s)
- M Kathryn Brewer
- Department of Molecular and Cellular Biochemistry, Epilepsy and Brain Metabolism Center, Lafora Epilepsy Cure Initiative, and Center for Structural Biology, University of Kentucky College of Medicine, Lexington, KY, USA
| | - Matthew S Gentry
- Department of Molecular and Cellular Biochemistry, Epilepsy and Brain Metabolism Center, Lafora Epilepsy Cure Initiative, and Center for Structural Biology, University of Kentucky College of Medicine, Lexington, KY, USA.
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4
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Lin S, Voyton C, Morris MT, Ackroyd PC, Morris JC, Christensen KA. pH regulation in glycosomes of procyclic form Trypanosoma brucei. J Biol Chem 2017; 292:7795-7805. [PMID: 28348078 DOI: 10.1074/jbc.m117.784173] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Indexed: 01/17/2023] Open
Abstract
Here we report the use of a fluorescein-tagged peroxisomal targeting sequence peptide (F-PTS1, acetyl-C{K(FITC)}GGAKL) for investigating pH regulation of glycosomes in live procyclic form Trypanosoma brucei When added to cells, this fluorescent peptide is internalized within vesicular structures, including glycosomes, and can be visualized after 30-60 min. Using F-PTS1 we are able to observe the pH conditions inside glycosomes in response to starvation conditions. Previous studies have shown that in the absence of glucose, the glycosome exhibits mild acidification from pH 7.4 ± 0.2 to 6.8 ± 0.2. Our results suggest that this response occurs under proline starvation as well. This pH regulation is found to be independent from cytosolic pH and requires a source of Na+ ions. Glycosomes were also observed to be more resistant to external pH changes than the cytosol; placement of cells in acidic buffers (pH 5) reduced the pH of the cytosol by 0.8 ± 0.1 pH units, whereas glycosomal pH decreases by 0.5 ± 0.1 pH units. This observation suggests that regulation of glycosomal pH is different and independent from cytosolic pH regulation. Furthermore, pH regulation is likely to work by an active process, because cells depleted of ATP with 2-deoxyglucose and sodium azide were unable to properly regulate pH. Finally, inhibitor studies with bafilomycin and EIPA suggest that both V-ATPases and Na+/H+ exchangers are required for glycosomal pH regulation.
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Affiliation(s)
- Sheng Lin
- From the Departments of Chemistry and
| | - Charles Voyton
- From the Departments of Chemistry and.,the Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602
| | - Meredith T Morris
- Genetics and Biochemistry, Clemson University, Clemson, South Carolina 29634 and
| | - P Christine Ackroyd
- the Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602
| | - James C Morris
- Genetics and Biochemistry, Clemson University, Clemson, South Carolina 29634 and
| | - Kenneth A Christensen
- the Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602
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Oligschlaeger Y, Miglianico M, Chanda D, Scholz R, Thali RF, Tuerk R, Stapleton DI, Gooley PR, Neumann D. The recruitment of AMP-activated protein kinase to glycogen is regulated by autophosphorylation. J Biol Chem 2015; 290:11715-28. [PMID: 25792737 PMCID: PMC4416872 DOI: 10.1074/jbc.m114.633271] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Indexed: 12/17/2022] Open
Abstract
The mammalian AMP-activated protein kinase (AMPK) is an obligatory αβγ heterotrimeric complex carrying a carbohydrate-binding module (CBM) in the β-subunit (AMPKβ) capable of attaching AMPK to glycogen. Nonetheless, AMPK localizes at many different cellular compartments, implying the existence of mechanisms that prevent AMPK from glycogen binding. Cell-free carbohydrate binding assays revealed that AMPK autophosphorylation abolished its carbohydrate-binding capacity. X-ray structural data of the CBM displays the central positioning of threonine 148 within the binding pocket. Substitution of Thr-148 for a phospho-mimicking aspartate (T148D) prevents AMPK from binding to carbohydrate. Overexpression of isolated CBM or β1-containing AMPK in cellular models revealed that wild type (WT) localizes to glycogen particles, whereas T148D shows a diffuse pattern. Pharmacological AMPK activation and glycogen degradation by glucose deprivation but not forskolin enhanced cellular Thr-148 phosphorylation. Cellular glycogen content was higher if pharmacological AMPK activation was combined with overexpression of T148D mutant relative to WT AMPK. In summary, these data show that glycogen-binding capacity of AMPKβ is regulated by Thr-148 autophosphorylation with likely implications in the regulation of glycogen turnover. The findings further raise the possibility of regulated carbohydrate-binding function in a wider variety of CBM-containing proteins.
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Affiliation(s)
- Yvonne Oligschlaeger
- From the Department of Molecular Genetics, CARIM School of Cardiovascular Diseases, Maastricht University, 6200 MD Maastricht, The Netherlands
| | - Marie Miglianico
- From the Department of Molecular Genetics, CARIM School of Cardiovascular Diseases, Maastricht University, 6200 MD Maastricht, The Netherlands
| | - Dipanjan Chanda
- From the Department of Molecular Genetics, CARIM School of Cardiovascular Diseases, Maastricht University, 6200 MD Maastricht, The Netherlands
| | - Roland Scholz
- the Institute of Cell Biology, ETH Zurich, 8093 Zurich, Switzerland, and
| | - Ramon F Thali
- the Institute of Cell Biology, ETH Zurich, 8093 Zurich, Switzerland, and
| | - Roland Tuerk
- the Institute of Cell Biology, ETH Zurich, 8093 Zurich, Switzerland, and
| | | | - Paul R Gooley
- Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Dietbert Neumann
- From the Department of Molecular Genetics, CARIM School of Cardiovascular Diseases, Maastricht University, 6200 MD Maastricht, The Netherlands, the Institute of Cell Biology, ETH Zurich, 8093 Zurich, Switzerland, and
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Ichikawa M, Scott DA, Losfeld ME, Freeze HH. The metabolic origins of mannose in glycoproteins. J Biol Chem 2014; 289:6751-6761. [PMID: 24407290 DOI: 10.1074/jbc.m113.544064] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Mannose in N-glycans is derived from glucose through phosphomannose isomerase (MPI, Fru-6-P ↔ Man-6-P) whose deficiency causes a congenital disorder of glycosylation (CDG)-Ib (MPI-CDG). Mannose supplements improve patients' symptoms because exogenous mannose can also directly contribute to N-glycan synthesis through Man-6-P. However, the quantitative contributions of these and other potential pathways to glycosylation are still unknown. We developed a sensitive GC-MS-based method using [1,2-(13)C]glucose and [4-(13)C]mannose to measure their contribution to N-glycans synthesized under physiological conditions (5 mm glucose and 50 μm mannose). Mannose directly provides ∼10-45% of the mannose found in N-glycans, showing up to a 100-fold preference for mannose over exogenous glucose based on their exogenous concentrations. Normal human fibroblasts normally derive 25-30% of their mannose directly from exogenous mannose, whereas MPI-deficient CDG fibroblasts with reduced glucose flux secure 80% of their mannose directly. Thus, both MPI activity and exogenous mannose concentration determine the metabolic flux into the N-glycosylation pathway. Using various stable isotopes, we found that gluconeogenesis, glycogen, and mannose salvaged from glycoprotein degradation do not contribute mannose to N-glycans in fibroblasts under physiological conditions. This quantitative assessment of mannose contribution and its metabolic fate provides information that can help bolster therapeutic strategies for treating glycosylation disorders with exogenous mannose.
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Affiliation(s)
- Mie Ichikawa
- Human Genetics Program, Sanford-Burnham Medical Research Institute, La Jolla, California 92037
| | - David A Scott
- Cancer Research Center, Sanford-Burnham Medical Research Institute, La Jolla, California 92037
| | - Marie-Estelle Losfeld
- Human Genetics Program, Sanford-Burnham Medical Research Institute, La Jolla, California 92037
| | - Hudson H Freeze
- Human Genetics Program, Sanford-Burnham Medical Research Institute, La Jolla, California 92037.
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7
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Martínez VS, Dietmair S, Quek LE, Hodson MP, Gray P, Nielsen LK. Flux balance analysis of CHO cells before and after a metabolic switch from lactate production to consumption. Biotechnol Bioeng 2012; 110:660-6. [PMID: 22991240 DOI: 10.1002/bit.24728] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Revised: 08/16/2012] [Accepted: 09/07/2012] [Indexed: 11/06/2022]
Abstract
Mammalian cell cultures typically exhibit an energy inefficient phenotype characterized by the consumption of large quantities of glucose and the concomitant production of large quantities of lactate. Under certain conditions, mammalian cells can switch to a more energy efficient state during which lactate is consumed. Using a metabolic model derived from a mouse genome scale model we performed flux balance analysis of Chinese hamster ovary cells before and after a metabolic switch from lactate production (in the presence of glucose) to lactate consumption (after glucose depletion). Despite a residual degree of freedom after accounting for measurements, the calculated flux ranges and associated errors were narrow enough to enable investigation of metabolic changes across the metabolic switch. Surprisingly, the fluxes through the lower part of the TCA cycle from oxoglutarate to malate were very similar (around 60 µmol/gDW/h) for both phases. A detailed analysis of the energy metabolism showed that cells consuming lactate have an energy efficiency (total ATP produced per total C-mol substrate consumed) six times greater than lactate producing cells.
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Affiliation(s)
- Verónica S Martínez
- Australian Institute for Bioengineering and Nanotechnology-AIBN, The University of Queensland, Brisbane, QLD 4072, Australia
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8
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Freeze HH. Towards a therapy for phosphomannomutase 2 deficiency, the defect in CDG-Ia patients. BIOCHIMICA ET BIOPHYSICA ACTA 2009; 1792:835-40. [PMID: 19339218 PMCID: PMC2783247 DOI: 10.1016/j.bbadis.2009.01.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Revised: 01/08/2009] [Accepted: 01/15/2009] [Indexed: 11/22/2022]
Abstract
Phosphomannomutase (PMM2, Mannose-6-P--> Mannose-1-P) deficiency is the most frequent glycosylation disorder affecting the N-glycosylation pathway. There is no therapy for the hundreds of patients who suffer from this disorder. This review describes previous attempts at therapeutic interventions and introduces perspectives emerging from the drawing boards. Two approaches aim to increase Mannose-1-P: small membrane permeable molecules that increase the availability or/and metabolic flux of precursors into the impaired glycosylation pathway; and, phosphomannomutase enhancement and/or replacement therapy. Glycosylation-deficient cell and animal models are needed to determine which individual or combined approaches improve glycosylation and may be suitable for preclinical evaluation.
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Affiliation(s)
- Hudson H Freeze
- Sanford Children's Health Research Center, Burnham Institute for Medical Research, 10901 N. Torrey Pines Rd, La Jolla, CA 92037, USA.
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9
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Rosa SC, Gonçalves J, Judas F, Mobasheri A, Lopes C, Mendes AF. Impaired glucose transporter-1 degradation and increased glucose transport and oxidative stress in response to high glucose in chondrocytes from osteoarthritic versus normal human cartilage. Arthritis Res Ther 2009; 11:R80. [PMID: 19490621 PMCID: PMC2714130 DOI: 10.1186/ar2713] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Revised: 04/29/2009] [Accepted: 06/02/2009] [Indexed: 12/04/2022] Open
Abstract
Introduction Disorders that affect glucose metabolism, namely diabetes mellitus (DM), may favor the development and/or progression of osteoarthritis (OA). Thus far, little is known regarding the ability of chondrocytes to adjust to variations in the extracellular glucose concentration, resulting from hypoglycemia and hyperglycemia episodes, and so, to avoid deleterious effects resulting from deprivation or intracellular accumulation of glucose. The aim of this study was to compare the ability of normal and OA chondrocytes to regulate their glucose transport capacity in conditions of insufficient or excessive extracellular glucose and to identify the mechanisms involved and eventual deleterious consequences, namely the production of reactive oxygen species (ROS). Methods Chondrocytes, isolated from normal and OA human cartilage, were maintained in high-density monolayer cultures, in media without or with 10 or 30 mM glucose. Glucose transport was measured as the uptake of 2-deoxy-D-glucose (2-DG). Glucose transporter-1 (GLUT-1) mRNA and protein content were evaluated by real-time RT-PCR and western blot, respectively. ROS production was measured with 2',7'-dichlorodihydrofluorescein diacetate. Results Basal and IL-1β-induced 2-DG uptake, including the affinity (1.066 ± 0.284 and 1.49 ± 0.59 mM) and maximal velocity (0.27 ± 0.08 and 0.33 ± 0.08 nmol/μg protein/hour), and GLUT-1 content were identical in normal and OA chondrocytes. Glucose deprivation increased 2-DG uptake and GLUT-1 protein both in normal and OA chondrocytes. Exposure to high glucose (30 mM) for 18 or 48 hours decreased those parameters in normal but not in OA chondrocytes. GLUT-1 mRNA levels were unaffected by high glucose, either in normal or OA chondrocytes. The high glucose-induced reduction in GLUT-1 protein in normal chondrocytes was reversed by treatment with a lysosome inhibitor. High glucose induced ROS production, which lasted significantly longer in OA than in normal chondrocytes. Conclusions Normal human chondrocytes adjust to variations in the extracellular glucose concentration by modulating GLUT-1 synthesis and degradation which involves the lysosome pathway. Although capable of adjusting to glucose deprivation, OA chondrocytes exposed to high glucose were unable downregulate GLUT-1, accumulating more glucose and producing more ROS. Impaired GLUT-1 downregulation may constitute an important pathogenic mechanism by which conditions characterized by hyperglycemia, like DM, can promote degenerative changes in chondrocytes that can facilitate the progression of OA.
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Affiliation(s)
- Susana C Rosa
- Center for Neurosciences and Cell Biology, and Faculty of Pharmacy, University of Coimbra, 3004-517 Coimbra, Portugal.
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10
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Metabolic discrimination of select list agents by monitoring cellular responses in a multianalyte microphysiometer. SENSORS 2009; 9:2117-33. [PMID: 22574003 PMCID: PMC3345856 DOI: 10.3390/s90302117] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Revised: 03/15/2009] [Accepted: 03/17/2009] [Indexed: 11/23/2022]
Abstract
Harnessing the potential of cells as complex biosensors promises the potential to create sensitive and selective detectors for discrimination of biodefense agents. Here we present toxin detection and suggest discrimination using cells in a multianalyte microphysiometer (MMP) that is capable of simultaneously measuring flux changes in four extracellular analytes (acidification rate, glucose uptake, oxygen uptake, and lactate production) in real-time. Differential short-term cellular responses were observed between botulinum neurotoxin A and ricin toxin with neuroblastoma cells, alamethicin and anthrax protective antigen with RAW macrophages, and cholera toxin, muscarine, 2,4-dinitro-phenol, and NaF with CHO cells. These results and the post exposure dynamics and metabolic recovery observed in each case suggest the usefulness of cell-based detectors to discriminate between specific analytes and classes of compounds in a complex matrix, and furthermore to make metabolic inferences on the cellular effects of the agents. This may be particularly valuable for classifying unknown toxins.
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Temple KA, Basko X, Allison MB, Brady MJ. Uncoupling of 3T3-L1 gene expression from lipid accumulation during adipogenesis. FEBS Lett 2007; 581:469-74. [PMID: 17239864 PMCID: PMC1803685 DOI: 10.1016/j.febslet.2007.01.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2006] [Revised: 01/03/2007] [Accepted: 01/05/2007] [Indexed: 11/18/2022]
Abstract
Adipocyte differentiation comprises altered gene expression and increased triglyceride storage. To investigate the interdependency of these two events, 3T3-L1 cells were differentiated in the presence of glucose or pyruvate. All adipocytic proteins examined were similarly increased between the two conditions. In contrast, 3T3-L1 adipocytes differentiated with glucose exhibited significant lipid accumulation, which was largely suppressed in the presence of pyruvate. Subsequent addition of glucose to the latter cells restored lipid accumulation and acute rates of insulin-stimulated lipogenesis. These data indicate that extracellular energy is required for induction of adipocytic proteins, while only glucose sustained the parallel increase in triglyceride storage.
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Affiliation(s)
- Karla A. Temple
- Department of Medicine and Committee on Molecular Metabolism and Nutrition, The University of Chicago, Chicago, Illinois 60637, USA
| | - Xheni Basko
- Department of Medicine and Committee on Molecular Metabolism and Nutrition, The University of Chicago, Chicago, Illinois 60637, USA
| | - Margaret B. Allison
- Department of Medicine and Committee on Molecular Metabolism and Nutrition, The University of Chicago, Chicago, Illinois 60637, USA
| | - Matthew J. Brady
- Department of Medicine and Committee on Molecular Metabolism and Nutrition, The University of Chicago, Chicago, Illinois 60637, USA
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Erion MD, van Poelje PD, Dang Q, Kasibhatla SR, Potter SC, Reddy MR, Reddy KR, Jiang T, Lipscomb WN. MB06322 (CS-917): A potent and selective inhibitor of fructose 1,6-bisphosphatase for controlling gluconeogenesis in type 2 diabetes. Proc Natl Acad Sci U S A 2005; 102:7970-5. [PMID: 15911772 PMCID: PMC1138262 DOI: 10.1073/pnas.0502983102] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
In type 2 diabetes, the liver produces excessive amounts of glucose through the gluconeogenesis (GNG) pathway and consequently is partly responsible for the elevated glucose levels characteristic of the disease. In an effort to find safe and efficacious GNG inhibitors, we targeted the AMP binding site of fructose 1,6-bisphosphatase (FBPase). The hydrophilic nature of AMP binding sites and their widespread use for allosteric regulation of enzymes in metabolic pathways has historically made discovery of AMP mimetics suitable for drug development difficult. By using a structure-based drug design strategy, we discovered a series of compounds that mimic AMP but bear little structural resemblance. The lead compound, MB05032, exhibited high potency and specificity for human FBPase. Oral delivery of MB05032 was achieved by using the bisamidate prodrug MB06322 (CS-917), which is converted to MB05032 in two steps through the action of an esterase and a phosphoramidase. MB06322 inhibited glucose production from a variety of GNG substrates in rat hepatocytes and from bicarbonate in male Zucker diabetic fatty rats. Analysis of liver GNG pathway intermediates confirmed FBPase as the site of action. Oral administration of MB06322 to Zucker diabetic fatty rats led to a dose-dependent decrease in plasma glucose levels independent of insulin levels and nutritional status. Glucose lowering occurred without signs of hypoglycemia or significant elevations in plasma lactate or triglyceride levels. The findings suggest that potent and specific FBPase inhibitors represent a drug class with potential to treat type 2 diabetes through inhibition of GNG.
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Affiliation(s)
- Mark D Erion
- Department of Biochemistry, Metabasis Therapeutics, Inc., 9390 Towne Centre Drive, Building 300, San Diego, CA 92121, USA.
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13
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Getty-Kaushik L, Richard AMT, Corkey BE. Free fatty acid regulation of glucose-dependent intrinsic oscillatory lipolysis in perifused isolated rat adipocytes. Diabetes 2005; 54:629-37. [PMID: 15734837 DOI: 10.2337/diabetes.54.3.629] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Free fatty acids (FFAs) and glycerol oscillate in plasma. This study examined intrinsic lipolytic oscillations within adipocytes. Rat adipocytes were perifused with Krebs-Ringer bicarbonate buffer: 1) +/- 2 mmol/l glucose; 2) +1 micromol/l isoproterenol +/- 2 mmol/l glucose; 3) + increasing oleate; and 4) + increasing percent BSA. At 2 mmol/l glucose, there were 9 +/- 1 glycerol, FFAs, and lactate pulses per hour with a pulse duration of 5 +/- 1 min. Lipolytic stimulation caused a 50-80% increase in the amplitude of lipolytic oscillations. Removal of glucose caused a 40-70% decrease in the amplitude of lipolytic oscillations and disturbed the pulsatility. Exogenous FFAs suppressed lipolysis and oscillatory amplitude, possibly because of increased cytosolic long-chain coenzyme A (LC-CoA). Increasing percent BSA increased stimulated lipolysis and oscillatory amplitude, possibly because of decreased intracellular LC-CoA. These data show, for the first time, intrinsic lipolytic oscillations, which are glucose dependent and modulated by FFAs. We hypothesize that lipolytic oscillations are driven by oscillatory glucose metabolism, which leads to oscillatory relief of LC-CoA inhibition of triglyceride lipase(s). The results contribute to the understanding of physiological and biochemical regulators of lipolysis, such as glucose and FFAs. Lipolytic oscillations may be beneficial in the delivery of FFAs to liver, pancreas, and other tissues.
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Affiliation(s)
- Lisa Getty-Kaushik
- Obesity Research Center, Department of Molecular Medicine, Boston Medical Center, EBRC 840, 650 Albany St., Boston, MA 02118, USA
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14
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Kitzman HH, McMahon RJ, Aslanian AM, Fadia PM, Frost SC. Differential regulation of GRP78 and GLUT1 expression in 3T3-L1 adipocytes. Mol Cell Biochem 1996; 162:51-8. [PMID: 8905625 DOI: 10.1007/bf00250995] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We tested the hypothesis that the constitutive glucose transporter (GLUT1) in 3T3-L1 adipocytes belongs to the family of glucose-regulated proteins which are transcriptionally regulated by glucose deprivation. Using cDNA probes for both GRP78 (BiP) and GLUT1, we show that the level of GRP78 mRNA increased by 15-fold within 24 h of glucose deprivation with little change in GLUT1 mRNA. The elevated GRP78 mRNA in turn led to a time-dependent increase in GRP78 protein. While glucose deprivation did not alter the expression of the normal glycoform of GLUT1, a lower molecular weight glycoform accumulated with extended deprivation. Mannose and fructose, but not galactose, prevented the induction of GRP78 and accumulation of the abnormal GLUT1. Because GRP78 acts as a chaperone in other cell systems, we also sought evidence to support this activity in 3T3-L1 adipocytes. Using the technique of co-immunoprecipitation, we demonstrate that GRP78 bound several proteins unique to the glucose-deprived state. No deprivation-specific proteins could be detected in association with GLUT1. These data lead us to conclude that GLUT1 does not display characteristics of the glucose-regulated proteins, at least in 3T3-L1 adipocytes, a widely used model for differentiation, hormone action, and nutrient control. However, the mechanisms for activating traditional members of this family appear intact.
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Affiliation(s)
- H H Kitzman
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville 32610, USA
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