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Drulis‐Fajdasz D, Krzystyniak A, Puścian A, Pytyś A, Gostomska‐Pampuch K, Pudełko‐Malik N, Wiśniewski JŁ, Młynarz P, Miazek A, Wójtowicz T, Włodarczyk J, Duś‐Szachniewicz K, Gizak A, Wiśniewski JR, Rakus D. Glycogen phosphorylase inhibition improves cognitive function of aged mice. Aging Cell 2023; 22:e13928. [PMID: 37522798 PMCID: PMC10497847 DOI: 10.1111/acel.13928] [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: 11/30/2022] [Revised: 05/31/2023] [Accepted: 06/23/2023] [Indexed: 08/01/2023] Open
Abstract
Inhibition of glycogen breakdown blocks memory formation in young animals, but it stimulates the maintenance of the long-term potentiation, a cellular mechanism of memory formation, in hippocampal slices of old animals. Here, we report that a 2-week treatment with glycogen phosphorylase inhibitor BAY U6751 alleviated memory deficits and stimulated neuroplasticity in old mice. Using the 2-Novel Object Recognition and Novel Object Location tests, we discovered that the prolonged intraperitoneal administration of BAY U6751 improved memory formation in old mice. This was accompanied by changes in morphology of dendritic spines in hippocampal neurons, and by "rejuvenation" of hippocampal proteome. In contrast, in young animals, inhibition of glycogen degradation impaired memory formation; however, as in old mice, it did not alter significantly the morphology and density of cortical dendritic spines. Our findings provide evidence that prolonged inhibition of glycogen phosphorolysis improves memory formation of old animals. This could lead to the development of new strategies for treatment of age-related memory deficits.
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Affiliation(s)
| | - Adam Krzystyniak
- Laboratory of Cell BiophysicsNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Alicja Puścian
- Nencki‐EMBL Partnership for Neural Plasticity and Brain Disorders – BRAINCITYNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Agata Pytyś
- Laboratory of Cell BiophysicsNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Kinga Gostomska‐Pampuch
- Department of Biochemistry and ImmunochemistryWroclaw Medical UniversityWroclawPoland
- Biochemical Proteomics Group, Department of Proteomics and Signal TransductionMax Planck Institute of BiochemistryMartinsriedGermany
| | - Natalia Pudełko‐Malik
- Department of Biochemistry, Molecular Biology and Biotechnology, Faculty of ChemistryWroclaw University of Science and TechnologyWroclawPoland
| | - Jerzy Ł. Wiśniewski
- Department of Biochemistry, Molecular Biology and Biotechnology, Faculty of ChemistryWroclaw University of Science and TechnologyWroclawPoland
| | - Piotr Młynarz
- Department of Biochemistry, Molecular Biology and Biotechnology, Faculty of ChemistryWroclaw University of Science and TechnologyWroclawPoland
| | - Arkadiusz Miazek
- Laboratory of Tumor ImmunologyHirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of SciencesWroclawPoland
| | - Tomasz Wójtowicz
- Laboratory of Cell BiophysicsNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Jakub Włodarczyk
- Laboratory of Cell BiophysicsNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Kamila Duś‐Szachniewicz
- Department of Clinical and Experimental PathologyInstitute of General and Experimental Pathology, Wroclaw Medical UniversityWroclawPoland
| | - Agnieszka Gizak
- Department of Molecular Physiology and NeurobiologyUniversity of WroclawWroclawPoland
| | - Jacek R. Wiśniewski
- Biochemical Proteomics Group, Department of Proteomics and Signal TransductionMax Planck Institute of BiochemistryMartinsriedGermany
| | - Dariusz Rakus
- Department of Molecular Physiology and NeurobiologyUniversity of WroclawWroclawPoland
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2
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Vezzoli E, Calì C, De Roo M, Ponzoni L, Sogne E, Gagnon N, Francolini M, Braida D, Sala M, Muller D, Falqui A, Magistretti PJ. Ultrastructural Evidence for a Role of Astrocytes and Glycogen-Derived Lactate in Learning-Dependent Synaptic Stabilization. Cereb Cortex 2021; 30:2114-2127. [PMID: 31807747 PMCID: PMC7174989 DOI: 10.1093/cercor/bhz226] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Revised: 08/17/2019] [Accepted: 08/28/2019] [Indexed: 12/12/2022] Open
Abstract
Long-term memory formation (LTM) is a process accompanied by energy-demanding structural changes at synapses and increased spine density. Concomitant increases in both spine volume and postsynaptic density (PSD) surface area have been suggested but never quantified in vivo by clear-cut experimental evidence. Using novel object recognition in mice as a learning task followed by 3D electron microscopy analysis, we demonstrate that LTM induced all aforementioned synaptic changes, together with an increase in the size of astrocytic glycogen granules, which are a source of lactate for neurons. The selective inhibition of glycogen metabolism in astrocytes impaired learning, affecting all the related synaptic changes. Intrahippocampal administration of l-lactate rescued the behavioral phenotype, along with spine density within 24 hours. Spine dynamics in hippocampal organotypic slices undergoing theta burst-induced long-term potentiation was similarly affected by inhibition of glycogen metabolism and rescued by l-lactate. These results suggest that learning primes astrocytic energy stores and signaling to sustain synaptic plasticity via l-lactate.
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Affiliation(s)
- E Vezzoli
- Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Saudi Arabia.,Dipartimento di Bioscienze, Università degli Studi di Milano, 20133 Milano, Italy.,Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università degli Studi di Milano, 20133 Milano, Italy
| | - C Calì
- Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Saudi Arabia
| | - M De Roo
- Department of Basic Neuroscience, University of Geneva Medical School, 1206 Geneva, Switzerland
| | - L Ponzoni
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università degli Studi di Milano, 20133 Milano, Italy
| | - E Sogne
- Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Saudi Arabia
| | - N Gagnon
- Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Saudi Arabia
| | - M Francolini
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università degli Studi di Milano, 20133 Milano, Italy
| | - D Braida
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università degli Studi di Milano, 20133 Milano, Italy
| | - M Sala
- CNR, Institute of Neuroscience, 20129 Milano, Italy
| | - D Muller
- Department of Basic Neuroscience, University of Geneva Medical School, 1206 Geneva, Switzerland
| | - A Falqui
- Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Saudi Arabia
| | - P J Magistretti
- Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST), 23955-6900 Thuwal, Saudi Arabia
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3
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Fink K, Velebit J, Vardjan N, Zorec R, Kreft M. Noradrenaline-induced l-lactate production requires d-glucose entry and transit through the glycogen shunt in single-cultured rat astrocytes. J Neurosci Res 2021; 99:1084-1098. [PMID: 33491223 DOI: 10.1002/jnr.24783] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 12/07/2020] [Accepted: 12/10/2020] [Indexed: 12/21/2022]
Abstract
During cognitive efforts mediated by local neuronal networks, approximately 20% of additional energy is required; this is mediated by chemical messengers such as noradrenaline (NA). NA targets astroglial aerobic glycolysis, the hallmark of which is the end product l-lactate, a fuel for neurons. Biochemical studies have revealed that astrocytes exhibit a prominent glycogen shunt, in which a portion of d-glucose molecules entering the cytoplasm is transiently incorporated into glycogen, a buffer and source of d-glucose during increased energy demand. Here, we studied single astrocytes by measuring cytosolic L-lactate ([lac]i ) with the FRET nanosensor Laconic. We examined whether NA-induced increase in [lac]i is influenced by: (a) 2-deoxy-d-glucose (2-DG, 3 mM), a molecule that enters the cytosol and inhibits the glycolytic pathway; (b) 1,4-dideoxy-1,4-imino-d-arabinitol (DAB, 300 µM), a potent inhibitor of glycogen phosphorylase and glycogen degradation; and (c) 3-nitropropionic acid (3-NPA, 1 mM), an inhibitor of the Krebs cycle. The results of these pharmacological experiments revealed that d-glucose uptake is essential for the NA-induced increase in [lac]i , and that this exclusively arises from glycogen degradation, indicating that most, if not all, d-glucose molecules in NA-stimulated cells transit the glycogen shunt during glycolysis. Moreover, under the defined transmembrane d-glucose gradient, the glycolytic intermediates were not only used to produce l-lactate, but also to significantly support oxidative phosphorylation, as demonstrated by an elevation in [lac]i when Krebs cycle was inhibited. We conclude that l-lactate production via aerobic glycolysis is an essential energy pathway in NA-stimulated astrocytes; however, oxidative metabolism is important at rest.
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Affiliation(s)
- Katja Fink
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia
| | - Jelena Velebit
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia.,Celica Biomedical, Ljubljana, Slovenia
| | - Nina Vardjan
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia.,Celica Biomedical, Ljubljana, Slovenia
| | - Robert Zorec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia.,Celica Biomedical, Ljubljana, Slovenia
| | - Marko Kreft
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology, University of Ljubljana, Ljubljana, Slovenia.,Celica Biomedical, Ljubljana, Slovenia.,Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia
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Klunda T, Hricovíni M, Šesták S, Kóňa J, Poláková M. Selective Golgi α-mannosidase II inhibitors: N-alkyl substituted pyrrolidines with a basic functional group. NEW J CHEM 2021. [DOI: 10.1039/d1nj01176f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Enzymatic assays, molecular modeling and NMR studies of novel 1,4-dideoxy-1,4-imino-l-lyxitols provided new information on the GH38 family enzyme inhibitors and their selectivity.
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Affiliation(s)
- Tomáš Klunda
- Institute of Chemistry
- Center for Glycomics
- Slovak Academy of Sciences
- SK-845 38 Bratislava
- Slovakia
| | - Michal Hricovíni
- Institute of Chemistry
- Center for Glycomics
- Slovak Academy of Sciences
- SK-845 38 Bratislava
- Slovakia
| | - Sergej Šesták
- Institute of Chemistry
- Center for Glycomics
- Slovak Academy of Sciences
- SK-845 38 Bratislava
- Slovakia
| | - Juraj Kóňa
- Institute of Chemistry
- Center for Glycomics
- Slovak Academy of Sciences
- SK-845 38 Bratislava
- Slovakia
| | - Monika Poláková
- Institute of Chemistry
- Center for Glycomics
- Slovak Academy of Sciences
- SK-845 38 Bratislava
- Slovakia
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5
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Jiang X, Challiss J, Glynn P. β1-adrenoceptor-stimulated lactate production in cultured astrocytes is predominantly glycogen-independent. Biochem Pharmacol 2020; 177:114035. [PMID: 32413424 DOI: 10.1016/j.bcp.2020.114035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Accepted: 05/06/2020] [Indexed: 10/24/2022]
Abstract
Noradrenaline (NA) promotes breakdown of the glucose-polymer, glycogen, and hence enhances glycolytic production of lactate in astrocytes. Here, in cultured rat cerebrocortical astrocytes, we examined the contributions of different adrenoceptor subtypes to NA-modulated glucose metabolism, and the relationship of NA-induced glycogenolysis to lactate production. Stimulation of astrocytic glucose metabolism by NA was mediated predominantly via β1-adrenoceptors and cAMP. Constitutive β 1-adrenoceptor activity - in the absence of exogenous NA - contributed to the basal rate of glycogen turnover. Although mRNAs encoding both β 1- and β 2-adrenoceptors were detected in these astrocytes, β 2-adrenoceptors contributed little to NA-induced modulation of glucose metabolism. Activation of α2- and α 1-adrenoceptors in these cells decreased cAMP and increased cytosolic Ca2+, respectively, but did not modulate NA-induced glycogenolysis: α 2-adrenoceptors because glycogenolysis was induced maximally by NA concentrations that only began to inhibit cAMP production; and α 1-adrenoceptors possibly because of desensitisation and depletion of Ca2+ stores. Under basal conditions, astrocytes converted glucose to extracellular lactate in near stoichiometric manner. When glucose-starved astrocytes were given fresh glucose-containing medium, lactate accumulation displayed a brief lag period before attaining a steady-state rate. During this lag period NA, acting at β 1-adrenoceptors, increased the rate of lactate accumulation both in the absence and presence of an inhibitor of glycogen turnover. At the steady-state, the rate of glucose incorporation into accumulated glycogen was ~ 5% of that into lactate, but NA enhanced lactate output by 20-50%: this further indicates that NA, via β 1-adrenoceptors and cAMP, can enhance astrocytic lactate production independently of its effect on glycogen turnover.
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Affiliation(s)
- Xianguo Jiang
- Department of Molecular and Cell Biology, University of Leicester, Leicester, LE1 9HN, UK
| | - John Challiss
- Department of Molecular and Cell Biology, University of Leicester, Leicester, LE1 9HN, UK
| | - Paul Glynn
- Department of Molecular and Cell Biology, University of Leicester, Leicester, LE1 9HN, UK.
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Jensen R, Nielsen J, Ørtenblad N. Inhibition of glycogenolysis prolongs action potential repriming period and impairs muscle function in rat skeletal muscle. J Physiol 2020; 598:789-803. [PMID: 31823376 DOI: 10.1113/jp278543] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 12/06/2019] [Indexed: 12/22/2022] Open
Abstract
KEY POINTS Muscle glycogen content is associated with muscle function, but the physiological link between the two is poorly understood. This study investigated the effects of inhibiting glycogenolysis, while maintaining high overall energy status, on different aspects of muscle function. We demonstrate here that Na+ ,K+ -ATPase activity depends on glycogenolytically derived ATP regardless of high global ATP, with a decrease in activity leading to reduced force production and accelerated fatigue development. The results support the concept of compartmentalized energy transfer with glycogen metabolism playing a crucial role in intramuscular ATP resynthesis and ion regulation. This study gives specific insights into muscular function and may help towards a better understanding of glycogen storage diseases and muscle fatigue. ABSTRACT Skeletal muscle glycogen content is associated with muscle function and fatigability. However, little is known about the physiological link between glycogen content and muscle function. Here we aimed to investigate the importance of glycogenolytically derived ATP per se on muscle force and action potential (AP) repriming period, i.e. the time before a second AP can be produced (indicative of Na+ ,K+ -ATPase activity). Single fibres from rat extensor digitorum longus muscles were isolated and mechanically skinned in order to investigate force production and the AP repriming period while global ATP and PCr concentrations were kept high. The importance of glycogenolytically derived ATP was studied by inhibition of glycogen phosphorylase (1,4-dideoxy-1,4-imino-d-arabinitol (DAB; 2 mm) or CP-316,819 (CP; 10 µm)) or glycogen removal (amyloglucosidase, 20 U ml-1 ). Tetanic force decreased by (mean (SD)) 21 (15)% (P < 0.001) and 76 (28)% (DAB) or 94 (6)% (CP, P < 0.001) in well-polarized and partially depolarized fibres, respectively. In depolarized fibres, twitch force decreased by 16 (10)% and 55 (26)% with DAB and CP, respectively, with no effect in well-polarized fibres (84 (10)%, P = 0.14). There was no effect of glycogen phosphorylase inhibition on repriming period in well-polarized fibres (median (25th, 75th percentile): 5 (4, 5) vs. 4 (4, 5) ms, P = 0.26), while the repriming period was prolonged from 6 (5, 7) to 8 (7, 10) ms (P = 0.01) in partially depolarized fibres. In line with this, glycogen removal increased repriming period from 5 (5, 6) to 6 (5, 7) ms (P = 0.003) in depolarized fibres. Together, these data strongly indicate that blocking glycogenolysis attenuates Na+ ,K+ -ATPase activity, which in turn increases the repriming period and reduces force, demonstrating a functional link between glycogenolytically derived ATP and force production.
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Affiliation(s)
- Rasmus Jensen
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Joachim Nielsen
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Niels Ørtenblad
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
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Yang W, Zhang C, Li Y, Jin A, Sun Y, Yang X, Wang B, Guo W. Phosphorylase Kinase β Represents a Novel Prognostic Biomarker and Inhibits Malignant Phenotypes of Liver Cancer Cell. Int J Biol Sci 2019; 15:2596-2606. [PMID: 31754332 PMCID: PMC6854366 DOI: 10.7150/ijbs.33278] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Accepted: 08/15/2019] [Indexed: 12/24/2022] Open
Abstract
Glycogen phosphorylase kinase β-subunit (PHKB) is a regulatory subunit of phosphorylase kinase (PHK), involving in the activation of glycogen phosphorylase (GP) and the regulation of glycogen breakdown. Emerging evidence suggests that PHKB plays a role in tumor progression. However, the function of PHKB in HCC progression remains elusive. Here, our study revealed that the expression of PHKB significantly decreased in HCC tissues, and the low expression of PHKB could serve as an independent indicator for predicting poor prognosis in HCC. Functional experiments showed that PHKB knockdown significantly promoted cell proliferation both in vitro and in vivo, whereas PHKB overexpression resulted in opposing effects. Additionally, in vitro assays revealed that the over (or high) expression of PHKB greatly hindered HCC cell invasion and increased apoptosis rates. Also, we found that the over (or high) expression of PHKB effectively suppressed the epithelial-mesenchymal transition, which was further confirmed by our clinical data. Intriguingly, the biological function of PHKB in HCC was independent of glycogen metabolism. Mechanically, PHKB could inhibit AKT and STAT3 signaling pathway activation in HCC. Collectively, our data demonstrate that PHKB acts as a novel prognostic indicator for HCC, which exerts its suppression function via inactivating AKT and STAT3. Our data might provide novel insights into progression and facilitate the development of a new therapeutic strategy for HCC.
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Affiliation(s)
- Wenjing Yang
- Department of Laboratory Medicine, Zhongshan Hospital, Fudan University, 136 Yi Xue Yuan Road, Shanghai 200032, P. R. China
| | - Chunyan Zhang
- Department of Laboratory Medicine, Zhongshan Hospital, Fudan University, 136 Yi Xue Yuan Road, Shanghai 200032, P. R. China
| | - Yihao Li
- Department of Laboratory Medicine, Zhongshan Hospital, Fudan University, 136 Yi Xue Yuan Road, Shanghai 200032, P. R. China
| | - Anli Jin
- Department of Laboratory Medicine, Zhongshan Hospital, Fudan University, 136 Yi Xue Yuan Road, Shanghai 200032, P. R. China
| | - Yunfan Sun
- Department of Liver Surgery, Liver Cancer Institute, Zhongshan Hospital, Fudan University; Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Shanghai 200032, P. R. China
| | - Xinrong Yang
- Department of Liver Surgery, Liver Cancer Institute, Zhongshan Hospital, Fudan University; Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Shanghai 200032, P. R. China
| | - Beili Wang
- Department of Laboratory Medicine, Zhongshan Hospital, Fudan University, 136 Yi Xue Yuan Road, Shanghai 200032, P. R. China
| | - Wei Guo
- Department of Laboratory Medicine, Zhongshan Hospital, Fudan University, 136 Yi Xue Yuan Road, Shanghai 200032, P. R. China
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Barr D, Szennyes E, Bokor É, Al-Oanzi ZH, Moffatt C, Kun S, Docsa T, Sipos Á, Davies MP, Mathomes RT, Snape TJ, Agius L, Somsák L, Hayes JM. Identification of C-β-d-Glucopyranosyl Azole-Type Inhibitors of Glycogen Phosphorylase That Reduce Glycogenolysis in Hepatocytes: In Silico Design, Synthesis, in Vitro Kinetics, and ex Vivo Studies. ACS Chem Biol 2019; 14:1460-1470. [PMID: 31243960 DOI: 10.1021/acschembio.9b00172] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Several C-β-d-glucopyranosyl azoles have recently been uncovered as among the most potent glycogen phosphorylase (GP) catalytic site inhibitors discovered to date. Toward further exploring their translational potential, ex vivo experiments have been performed for their effectiveness in reduction of glycogenolysis in hepatocytes. New compounds for these experiments were predicted in silico where, for the first time, effective ranking of GP catalytic site inhibitor potencies using the molecular mechanics-generalized Born surface area (MM-GBSA) method has been demonstrated. For a congeneric training set of 27 ligands, excellent statistics in terms of Pearson (RP) and Spearman (RS) correlations (both 0.98), predictive index (PI = 0.99), and area under the receiver operating characteristic curve (AU-ROC = 0.99) for predicted versus experimental binding affinities were obtained, with ligand tautomeric/ionization states additionally considered using density functional theory (DFT). Seven 2-aryl-4(5)-(β-d-glucopyranosyl)-imidazoles and 2-aryl-4-(β-d-glucopyranosyl)-thiazoles were subsequently synthesized, and kinetics experiments against rabbit muscle GPb revealed new potent inhibitors with best Ki values in the low micromolar range (5c = 1.97 μM; 13b = 4.58 μM). Ten C-β-d-glucopyranosyl azoles were then tested ex vivo in mouse primary hepatocytes. Four of these (5a-c and 9d) demonstrated significant reduction of glucagon stimulated glycogenolysis (IC50 = 30-60 μM). Structural and predicted physicochemical properties associated with their effectiveness were analyzed with permeability related parameters identified as crucial factors. The most effective ligand series 5 contained an imidazole ring, and the calculated pKa (Epik: 6.2; Jaguar 5.5) for protonated imidazole suggests that cellular permeation through the neutral state is favored, while within the cell, there is predicted more favorable binding to GP in the protonated form.
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Affiliation(s)
- Daniel Barr
- School of Physical Sciences & Computing, University of Central Lancashire, Preston PR1 2HE, United Kingdom
| | - Eszter Szennyes
- Department of Organic Chemistry, University of Debrecen, POB 400, H-4002 Debrecen, Hungary
| | - Éva Bokor
- Department of Organic Chemistry, University of Debrecen, POB 400, H-4002 Debrecen, Hungary
| | - Ziad H. Al-Oanzi
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Colin Moffatt
- Health & Life Sciences, De Montfort University, Gateway House, Leicester LE1 9BH, United Kingdom
| | - Sándor Kun
- Department of Organic Chemistry, University of Debrecen, POB 400, H-4002 Debrecen, Hungary
| | - Tibor Docsa
- Department of Medical Chemistry, Medical and Health Science Centre, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary
| | - Ádám Sipos
- Department of Medical Chemistry, Medical and Health Science Centre, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary
| | - Matthew P. Davies
- School of Physical Sciences & Computing, University of Central Lancashire, Preston PR1 2HE, United Kingdom
| | - Rachel T. Mathomes
- School of Pharmacy & Biomedical Sciences, University of Central Lancashire, Preston PR1 2HE, United Kingdom
| | - Timothy J. Snape
- School of Pharmacy & Biomedical Sciences, University of Central Lancashire, Preston PR1 2HE, United Kingdom
| | - Loranne Agius
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - László Somsák
- Department of Organic Chemistry, University of Debrecen, POB 400, H-4002 Debrecen, Hungary
| | - Joseph M. Hayes
- School of Pharmacy & Biomedical Sciences, University of Central Lancashire, Preston PR1 2HE, United Kingdom
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9
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Díaz-Lobo M, Concia AL, Gómez L, Clapés P, Fita I, Guinovart JJ, Ferrer JC. Inhibitory properties of 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) derivatives acting on glycogen metabolising enzymes. Org Biomol Chem 2018; 14:9105-9113. [PMID: 27714243 DOI: 10.1039/c6ob01543c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Glycogen synthase (GS) and glycogen phosphorylase (GP) are the key enzymes that control, respectively, the synthesis and degradation of glycogen, a multi-branched glucose polymer that serves as a form of energy storage in bacteria, fungi and animals. An abnormal glycogen metabolism is associated with several human diseases. Thus, GS and GP constitute adequate pharmacological targets to modulate cellular glycogen levels by means of their selective inhibition. The compound 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) is a known potent inhibitor of GP. We studied the inhibitory effect of DAB, its enantiomer LAB, and 29 DAB derivatives on the activity of rat muscle glycogen phosphorylase (RMGP) and E. coli glycogen synthase (EcGS). The isoform 4 of sucrose synthase (SuSy4) from Solanum tuberosum L. was also included in the study for comparative purposes. Although these three enzymes possess highly conserved catalytic site architectures, the DAB derivatives analysed showed extremely diverse inhibitory potential. Subtle changes in the positions of crucial residues in their active sites are sufficient to discriminate among the structural differences of the tested inhibitors. For the two Leloir-type enzymes, EcGS and SuSy4, which use sugar nucleotides as donors, the inhibitory potency of the compounds analysed was synergistically enhanced by more than three orders of magnitude in the presence of ADP and UDP, respectively. Our results are consistent with a model in which these compounds bind to the subsite in the active centre of the enzymes that is normally occupied by the glucosyl residue which is transferred between donor and acceptor substrates. The ability to selectively inhibit the catalytic activity of the key enzymes of the glycogen metabolism may represent a new approach for the treatment of disorders of the glycogen metabolism.
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Affiliation(s)
- Mireia Díaz-Lobo
- Departament de Bioquímica i Biomedicina Molecular, Universitat de Barcelona, Av. Diagonal 645, E-08028, Barcelona, Spain. and Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, E-08028, Barcelona, Spain and CIBER de Diabetes y Enfermedades Metabólicas (CIBERDEM), Madrid, Spain
| | - Alda Lisa Concia
- Department of Biological Chemistry and Molecular Modeling, Instituto de Química Avanzada de Cataluña, IQAC-CSIC, Barcelona, Spain
| | - Livia Gómez
- Department of Biological Chemistry and Molecular Modeling, Instituto de Química Avanzada de Cataluña, IQAC-CSIC, Barcelona, Spain
| | - Pere Clapés
- Department of Biological Chemistry and Molecular Modeling, Instituto de Química Avanzada de Cataluña, IQAC-CSIC, Barcelona, Spain
| | - Ignacio Fita
- Institut de Biologia Molecular de Barcelona (IBMB-CSIC), Baldiri Reixac 10, E-08028, Barcelona, Spain
| | - Joan J Guinovart
- Departament de Bioquímica i Biomedicina Molecular, Universitat de Barcelona, Av. Diagonal 645, E-08028, Barcelona, Spain. and Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, E-08028, Barcelona, Spain and CIBER de Diabetes y Enfermedades Metabólicas (CIBERDEM), Madrid, Spain
| | - Joan C Ferrer
- Departament de Bioquímica i Biomedicina Molecular, Universitat de Barcelona, Av. Diagonal 645, E-08028, Barcelona, Spain.
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Fernández-Novell JM, Díaz-Lobo M. Immunochemical Study of the Effect of F 2Glc on Glycogen Synthase Translocation and Glycogen Synthesis in Isolated Rat Hepatocytes. Appl Biochem Biotechnol 2017; 184:909-918. [PMID: 28918449 DOI: 10.1007/s12010-017-2597-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 09/06/2017] [Indexed: 10/18/2022]
Abstract
The compound 2-deoxy-2-fluoro-α-D-glucopyranosyl fluoride (F2Glc), which is a nonmetabolized superior glucose analogue, is a potent inhibitor of glycogen phosphorylase and pharmacological properties are reported. Glycogen phosphorylase (GP) and glycogen synthase (GS) are responsible of the degradation and synthesis, respectively, of glycogen which is a polymer of glucose units that provides a readily available source of energy in mammals. GP and GS are two key enzymes that modulate cellular glucose and glycogen levels; therefore, these proteins are suggested as potential targets for the treatment of diseases related to glycogen metabolism disorders. We studied by Western Blot technique that F2Glc decreased GP activity, and we also showed that F2Glc did not affect GS activity and its translocation from a uniform cytosolic distribution to the hepatocyte periphery, which is crucial for glycogen synthesis, using immunoblotting and immunofluorescence labeling techniques. F2Glc specifically inhibits glycogenolysis pathway and permits a greater deposition of glycogen. These observations open up the possibility of further develop drugs that act specifically on GP. The ability to selectively inhibit GP, which is a key enzyme for the release of glucose from the hepatic glycogen reserve, may represent a new approach for the treatment of hyperglycemia in type 2 diabetes.
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Affiliation(s)
- J M Fernández-Novell
- Department of Biochemistry and Molecular Biomedicine, Faculty of Biology, University of Barcelona, Avda. Diagonal 643, Edifici Prevosti, Planta (-2), 08028, Barcelona, Spain.
| | - M Díaz-Lobo
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Barcelona, Spain
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11
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Zois CE, Harris AL. Glycogen metabolism has a key role in the cancer microenvironment and provides new targets for cancer therapy. J Mol Med (Berl) 2016; 94:137-54. [PMID: 26882899 PMCID: PMC4762924 DOI: 10.1007/s00109-015-1377-9] [Citation(s) in RCA: 160] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 12/21/2015] [Accepted: 12/28/2015] [Indexed: 12/13/2022]
Abstract
Metabolic reprogramming is a hallmark of cancer cells and contributes to their adaption within the tumour microenvironment and resistance to anticancer therapies. Recently, glycogen metabolism has become a recognised feature of cancer cells since it is upregulated in many tumour types, suggesting that it is an important aspect of cancer cell pathophysiology. Here, we provide an overview of glycogen metabolism and its regulation, with a focus on its role in metabolic reprogramming of cancer cells under stress conditions such as hypoxia, glucose deprivation and anticancer treatment. The various methods to detect glycogen in tumours in vivo as well as pharmacological modulators of glycogen metabolism are also reviewed. Finally, we discuss the therapeutic value of targeting glycogen metabolism as a strategy for combinational approaches in cancer treatment.
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Affiliation(s)
- Christos E Zois
- Molecular Oncology Laboratories, Department of Oncology, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford University, Oxford, OX3 9DS, UK.
| | - Adrian L Harris
- Molecular Oncology Laboratories, Department of Oncology, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford University, Oxford, OX3 9DS, UK.
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12
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Donnier-Maréchal M, Vidal S. Glycogen phosphorylase inhibitors: a patent review (2013 - 2015). Expert Opin Ther Pat 2016; 26:199-212. [PMID: 26666989 DOI: 10.1517/13543776.2016.1131268] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
INTRODUCTION Control of glycemia is crucial in the treatment of type 2 diabetes complications. Glycogen phosphorylase (GP) releases glucose from the liver into the blood stream. Design of potent GP inhibitors is a therapeutic strategy in the context of type 2 diabetes. AREAS COVERED Glucose-based inhibitors have found potential applications since they now reach low nanomolar Ki values. Another set of patents disclose cholic acid/7-aza-indole conjugates for targeted drug delivery to the liver. A series of benzazepinones have also been reported as potent GP inhibitors. In vitro data are reported for GP inhibition but the in vivo biological data at the cellular or animal levels are often missing, even though the literature reported for these molecules is also discussed. EXPERT OPINION A structural analogy between glucose-based GP inhibitors and C-glucosides targeting sodium glucose co-transporter 2 (SGLT2) is intriguing. Cholic acid/7-aza-indole conjugates are promising in vivo drug delivery systems to the liver. Benzazepinones were very recently described and no associated literature is available, making it very difficult to comment at present. While industry has slowed down on GP inhibitors design, academic groups are pursuing investigations and have provided potential drug candidates which will resuscitate the interest for GP, including its potential for targeting cancer.
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Affiliation(s)
- Marion Donnier-Maréchal
- a Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Laboratoire de Chimie Organique 2-Glycochimie, UMR 5246 , CNRS and Université Claude Bernard Lyon 1 , Villeurbanne , France
| | - Sébastien Vidal
- a Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Laboratoire de Chimie Organique 2-Glycochimie, UMR 5246 , CNRS and Université Claude Bernard Lyon 1 , Villeurbanne , France
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13
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Role of glycogen phosphorylase in liver glycogen metabolism. Mol Aspects Med 2015; 46:34-45. [PMID: 26519772 DOI: 10.1016/j.mam.2015.09.002] [Citation(s) in RCA: 94] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 09/11/2015] [Indexed: 02/05/2023]
Abstract
Liver glycogen is synthesized after a meal in response to an increase in blood glucose concentration in the portal vein and endocrine and neuroendocrine signals, and is degraded to glucose between meals to maintain blood glucose homeostasis. Glycogen degradation and synthesis during the diurnal cycle are mediated by changes in the activities of phosphorylase and glycogen synthase. Phosphorylase is regulated by phosphorylation of serine-14. Only the phosphorylated form of liver phosphorylase (GPa) is catalytically active. Interconversion between GPa and GPb (unphosphorylated) is dependent on the activities of phosphorylase kinase and of phosphorylase phosphatase. The latter comprises protein phosphatase-1 in conjunction with a glycogen-targeting protein (G-subunit) of the PPP1R3 family. At least two of six G-subunits (GL and PTG) expressed in liver are involved in GPa dephosphorylation. GPa to GPb interconversion is dependent on the conformational state of phosphorylase which can be relaxed (R) or tense (T) depending on the concentrations of allosteric effectors such as glucose, glucose 6-phosphate and adenine nucleotides and on the acetylation state of lysine residues. The G-subunit, GL, encoded by PPP1R3B gene is expressed at high levels in liver and can function as a phosphorylase phosphatase and a synthase phosphatase and has an allosteric binding site for GPa at the C-terminus which inhibits synthase phosphatase activity. GPa to GPb conversion is a major upstream event in the regulation of glycogen synthesis by glucose, its downstream metabolites and extracellular signals such as insulin and neurotransmitters.
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Zois CE, Favaro E, Harris AL. Glycogen metabolism in cancer. Biochem Pharmacol 2014; 92:3-11. [PMID: 25219323 DOI: 10.1016/j.bcp.2014.09.001] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 08/29/2014] [Accepted: 09/04/2014] [Indexed: 12/30/2022]
Abstract
Since its identification more than 150 years ago, there has been an extensive characterisation of glycogen metabolism and its regulatory pathways in the two main glycogen storage organs of the body, i.e. liver and muscle. In recent years, glycogen metabolism has also been demonstrated to be upregulated in many tumour types, suggesting it is an important aspect of cancer cell pathophysiology. Here, we provide an overview of glycogen metabolism and its regulation, with a focus on its role in metabolic reprogramming of cancer cells. The various methods to detect glycogen in tumours in vivo are also reviewed. Finally, we discuss the targeting of glycogen metabolism as a strategy for cancer treatment.
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Affiliation(s)
- Christos E Zois
- Molecular Oncology Laboratories, Oxford University, Department of Oncology, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
| | - Elena Favaro
- Cell Death and Metabolism, Danish Cancer Society Research Center, Strandboulevarden 49, 2100 Copenhagen, Denmark.
| | - Adrian L Harris
- Molecular Oncology Laboratories, Oxford University, Department of Oncology, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
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Zani F, Breasson L, Becattini B, Vukolic A, Montani JP, Albrecht U, Provenzani A, Ripperger JA, Solinas G. PER2 promotes glucose storage to liver glycogen during feeding and acute fasting by inducing Gys2 PTG and G L expression. Mol Metab 2013; 2:292-305. [PMID: 24049741 DOI: 10.1016/j.molmet.2013.06.006] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Revised: 06/17/2013] [Accepted: 06/21/2013] [Indexed: 01/14/2023] Open
Abstract
The interplay between hepatic glycogen metabolism and blood glucose levels is a paradigm of the rhythmic nature of metabolic homeostasis. Here we show that mice lacking a functional PER2 protein (Per2 (Brdm1) ) display reduced fasting glycemia, altered rhythms of hepatic glycogen accumulation, and altered rhythms of food intake. Per2 (Brdm1) mice show reduced hepatic glycogen content and altered circadian expression during controlled fasting and refeeding. Livers from Per2 (Brdm1) mice display reduced glycogen synthase protein levels during refeeding, and increased glycogen phosphorylase activity during fasting. The latter is explained by PER2 action on the expression of the adapter proteins PTG and GL, which target the protein phosphatase-1 to glycogen to decrease glycogen phosphorylase activity. Finally, PER2 interacts with genomic regions of Gys2, PTG, and G L . These results indicate an important role for PER2 in the hepatic transcriptional response to feeding and acute fasting that promotes glucose storage to liver glycogen.
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Affiliation(s)
- Fabio Zani
- Laboratory of Metabolic Stress Biology, Division of Physiology, Department of Medicine, University of Fribourg, 1700 Fribourg, Switzerland
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Melancon BJ, Hopkins CR, Wood MR, Emmitte KA, Niswender CM, Christopoulos A, Conn PJ, Lindsley CW. Allosteric modulation of seven transmembrane spanning receptors: theory, practice, and opportunities for central nervous system drug discovery. J Med Chem 2012; 55:1445-64. [PMID: 22148748 DOI: 10.1021/jm201139r] [Citation(s) in RCA: 183] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Bruce J Melancon
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, United States
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17
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Torres TP, Sasaki N, Donahue EP, Lacy B, Printz RL, Cherrington AD, Treadway JL, Shiota M. Impact of a glycogen phosphorylase inhibitor and metformin on basal and glucagon-stimulated hepatic glucose flux in conscious dogs. J Pharmacol Exp Ther 2011; 337:610-20. [PMID: 21363927 DOI: 10.1124/jpet.110.177899] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The effects of a glycogen phosphorylase inhibitor (GPI) and metformin (MT) on hepatic glucose fluxes (μmol · kg(-1) · min(-1)) in the presence of basal and 4-fold basal levels of plasma glucagon were investigated in 18-h fasted conscious dogs. Compared with the vehicle treatment, GPI infusion suppressed net hepatic glucose output (NHGO) completely (-3.8 ± 1.3 versus 9.9 ± 2.8) despite increased glucose 6-phosphate (G-6-P) neogenesis from gluconeogenic precursors (8.1 ± 1.1 versus 5.5 ± 1.1). MT infusion did not alter those parameters. In response to a 4-fold rise in plasma glucagon levels, in the vehicle group, plasma glucose levels were increased 2-fold, and NHGO was increased (43.9 ± 5.7 at 10 min and 22.7 ± 3.4 at steady state) without altering G-6-P neogenesis (3.7 ± 1.5 and 5.5 ± 0.5, respectively). In the GPI group, there was no increase in NHGO due to decreased glucose-6-phosphatase flux associated with reduced G-6-P concentration. A lower G-6-P concentration was the result of increased net glycogenesis without altering G-6-P neogenesis. In the MT group, the increment in NHGO (22.2 ± 4.4 at 10 min and 12.1 ± 3.6 at steady state) was approximately half of that of the vehicle group. The lesser NHGO was associated with reduced glucose-6-phosphatase flux but a rise in G-6-P concentration and only a small incorporation of plasma glucose into glycogen. In conclusion, the inhibition of glycogen phosphorylase a activity decreases basal and glucagon-induced NHGO via redirecting glucose 6-phosphate flux from glucose toward glycogen, and MT decreases glucagon-induced NHGO by inhibiting glucose-6-phosphatase flux and thereby reducing glycogen breakdown.
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Affiliation(s)
- Tracy P Torres
- Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 2215 Garland Ave., Nashville, TN 37232-0615, USA
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18
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Elbein AD, Pastuszak I, Tackett AJ, Wilson T, Pan YT. Last step in the conversion of trehalose to glycogen: a mycobacterial enzyme that transfers maltose from maltose 1-phosphate to glycogen. J Biol Chem 2010; 285:9803-9812. [PMID: 20118231 DOI: 10.1074/jbc.m109.033944] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We show that Mycobacterium smegmatis has an enzyme catalyzing transfer of maltose from [(14)C]maltose 1-phosphate to glycogen. This enzyme was purified 90-fold from crude extracts and characterized. Maltose transfer required addition of an acceptor. Liver, oyster, or mycobacterial glycogens were the best acceptors, whereas amylopectin had good activity, but amylose was a poor acceptor. Maltosaccharides inhibited the transfer of maltose from [(14)C]maltose-1-P to glycogen because they were also acceptors of maltose, and they caused production of larger sized radioactive maltosaccharides. When maltotetraose was the acceptor, over 90% of the (14)C-labeled product was maltohexaose, and no radioactivity was in maltopentaose, demonstrating that maltose was transferred intact. Stoichiometry showed that 0.89 micromol of inorganic phosphate was produced for each micromole of maltose transferred to glycogen, and 56% of the added maltose-1-P was transferred to glycogen. This enzyme has been named alpha1,4-glucan:maltose-1-P maltosyltransferase (GMPMT). Transfer of maltose to glycogen was inhibited by micromolar amounts of inorganic phosphate or arsenate but was only slightly inhibited by millimolar concentrations of glucose-1-P, glucose-6-P, or inorganic pyrophosphate. GMPMT was compared with glycogen phosphorylase (GP). GMPMT catalyzed transfer of [(14)C]maltose-1-P, but not [(14)C]glucose-1-P, to glycogen, whereas GP transferred radioactivity from glucose-1-P but not maltose-1-P. GMPMT and GP were both inhibited by 1,4-dideoxy-1,4-imino-d-arabinitol, but only GP was inhibited by isofagomine. Because mycobacteria that contain trehalose synthase accumulate large amounts of glycogen when grown in high concentrations of trehalose, we propose that trehalose synthase, maltokinase, and GMPMT represent a new pathway of glycogen synthesis using trehalose as the source of glucose.
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Affiliation(s)
- Alan D Elbein
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205
| | - Irena Pastuszak
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205
| | - Alan J Tackett
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205.
| | - Tyler Wilson
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205
| | - Yuan T Pan
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205
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Disruption of the allosteric phosphorylase a regulation of the hepatic glycogen-targeted protein phosphatase 1 improves glucose tolerance in vivo. Cell Signal 2009; 21:1123-34. [DOI: 10.1016/j.cellsig.2009.03.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2009] [Accepted: 03/02/2009] [Indexed: 11/17/2022]
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Robust glycogen shunt activity in astrocytes: Effects of glutamatergic and adrenergic agents. Neuroscience 2008; 158:284-92. [PMID: 19000744 DOI: 10.1016/j.neuroscience.2008.09.058] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Revised: 08/15/2008] [Accepted: 09/20/2008] [Indexed: 11/23/2022]
Abstract
The significance and functional roles of glycogen shunt activity in the brain are largely unknown. It represents the fraction of metabolized glucose that passes through glycogen molecules prior to entering the glycolytic pathway. The present study was aimed at elucidating this pathway in cultured astrocytes from mouse exposed to agents such as a high [K+], D-aspartate and norepinephrine (NE) known to affect energy metabolism in response to neurotransmission. Glycogen shunt activity was assessed employing [1,6-13C]glucose, and the glycogen phosphorylase inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) to block glycogen degradation. The label intensity in lactate, reflecting glycolytic activity, was determined by mass spectrometry. In the presence of NE a substantial glycogen shunt activity was observed, accounting for almost 40% of overall glucose metabolism. Moreover, when no metabolic stimulant was applied, a compensatory increase in glycolytic activity was seen when the shunt was inhibited by DAB. Actually the labeling in lactate exceeded that obtained when glycolysis and glycogen shunt both were operational, i.e. supercompensation. A similar phenomenon was seen when astrocytes were exposed to D-aspartate. In addition to glycolysis, tricarboxylic acid (TCA) cycle activity was monitored, analyzing labeling by mass spectrometry in glutamate which equilibrates with alpha-ketoglutarate. Both an elevated [K+] and D-aspartate induced an increased TCA cycle activity, which was altered when glycogen degradation was inhibited. Thus, the present study provides evidence that manipulation of glycogen metabolism affects both glycolysis and TCA cycle metabolism. Altogether, the results reveal a highly complex interaction between glycogenolysis and glycolysis, with the glycogen shunt playing a significant role in astrocytic energy metabolism.
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Metabolic control analysis: a tool for designing strategies to manipulate metabolic pathways. J Biomed Biotechnol 2008; 2008:597913. [PMID: 18629230 PMCID: PMC2447884 DOI: 10.1155/2008/597913] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2007] [Revised: 01/16/2008] [Accepted: 03/26/2008] [Indexed: 02/06/2023] Open
Abstract
The traditional experimental approaches used for changing the flux or the concentration of a particular metabolite of a metabolic pathway have been mostly based on the inhibition or over-expression of the presumed rate-limiting step. However, the attempts to manipulate a metabolic pathway by following such approach have proved to be unsuccessful. Metabolic Control Analysis (MCA) establishes how to determine, quantitatively, the degree of control that a given enzyme exerts on flux and on the concentration of metabolites, thus substituting the intuitive, qualitative concept of rate limiting step. Moreover, MCA helps to understand (i) the underlying mechanisms by which a given enzyme exerts high or low control and (ii) why the control of the pathway is shared by several pathway enzymes and transporters. By applying MCA it is possible to identify the steps that should be modified to achieve a successful alteration of flux or metabolite concentration in pathways of biotechnological (e.g., large scale metabolite production) or clinical relevance (e.g., drug therapy). The different MCA experimental approaches developed for the determination of the flux-control distribution in several pathways are described. Full understanding of the pathway properties when is working under a variety of conditions can help to attain a successful manipulation of flux and metabolite concentration.
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Abstract
Conversion of glucose into glycogen is a major pathway that contributes to the removal of glucose from the portal vein by the liver in the postprandial state. It is regulated in part by the increase in blood-glucose concentration in the portal vein, which activates glucokinase, the first enzyme in the pathway, causing an increase in the concentration of glucose 6-P (glucose 6-phosphate), which modulates the phosphorylation state of downstream enzymes by acting synergistically with other allosteric effectors. Glucokinase is regulated by a hierarchy of transcriptional and post-transcriptional mechanisms that are only partially understood. In the fasted state, glucokinase is in part sequestered in the nucleus in an inactive state, complexed to a specific regulatory protein, GKRP (glucokinase regulatory protein). This reserve pool is rapidly mobilized to the cytoplasm in the postprandial state in response to an elevated concentration of glucose. The translocation of glucokinase between the nucleus and cytoplasm is modulated by various metabolic and hormonal conditions. The elevated glucose 6-P concentration, consequent to glucokinase activation, has a synergistic effect with glucose in promoting dephosphorylation (inactivation) of glycogen phosphorylase and inducing dephosphorylation (activation) of glycogen synthase. The latter involves both a direct ligand-induced conformational change and depletion of the phosphorylated form of glycogen phosphorylase, which is a potent allosteric inhibitor of glycogen synthase phosphatase activity associated with the glycogen-targeting protein, GL [hepatic glycogen-targeting subunit of PP-1 (protein phosphatase-1) encoded by PPP1R3B]. Defects in both the activation of glucokinase and in the dephosphorylation of glycogen phosphorylase are potential contributing factors to the dysregulation of hepatic glucose metabolism in Type 2 diabetes.
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Gillies RJ, Robey I, Gatenby RA. Causes and consequences of increased glucose metabolism of cancers. J Nucl Med 2008; 49 Suppl 2:24S-42S. [PMID: 18523064 DOI: 10.2967/jnumed.107.047258] [Citation(s) in RCA: 453] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
In this review we examine the mechanisms (causes) underlying the increased glucose consumption observed in tumors within a teleological context (consequences). In other words, we will ask not only "How do cancers have high glycolysis?" but also, "Why?" We believe that the insights gained from answering the latter question support the conclusion that elevated glucose consumption is a necessary component of carcinogenesis. Specifically we propose that glycolysis is elevated because it produces acid, which provides an evolutionary advantage to cancer cells vis-à-vis normal parenchyma into which they invade.
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Inhibition of the interaction between protein phosphatase 1 glycogen-targeting subunit and glycogen phosphorylase increases glycogen synthesis in primary rat hepatocytes. Biochem J 2008; 412:359-66. [DOI: 10.1042/bj20071483] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
In Type 2 diabetes, increased glycogenolysis contributes to the hyperglycaemic state, therefore the inhibition of GP (glycogen phosphorylase), a key glycogenolytic enzyme, is one of the possibilities to lower plasma glucose levels. Following this strategy, a number of GPis (GP inhibitors) have been described. However, certain critical issues are associated with their mode of action, e.g. an impairment of muscle function. The interaction between GP and the liver glycogen targeting subunit (termed GL) of PP1 (protein phosphatase 1) has emerged as a new potential anti-diabetic target, as the disruption of this interaction should increase glycogen synthesis, potentially providing an alternative approach to counteract the enhanced glycogenolysis without inhibiting GP activity. We identified an inhibitor of the GL–GP interaction (termed GL–GPi) and characterized its mechanism of action in comparison with direct GPis. In primary rat hepatocytes, at elevated glucose levels, the GL–GPi increased glycogen synthesis similarly to direct GPis. Direct GPis significantly reduced the cellular GP activity, caused a dephosphorylation of the enzyme and decreased the amounts of GP in the glycogen-enriched fraction; the GL–GPi did not influence any of these parameters. Both mechanisms increased glycogen accumulation at elevated glucose levels. However, at low glucose levels, only direct GPis led to increased glycogen amounts, whereas the GL–GPi allowed the mobilization of glycogen because it did not block the activity of GP. Due to this characteristic, GL–GPi in comparison with GPis could offer an advantageous risk/benefit profile circumventing the potential downsides of a complete prevention of glycogen breakdown while retaining glucose- lowering efficacy, suggesting that inhibition of the GL–GP interaction may provide an attractive novel approach for rebalancing the disturbed glycogen metabolism in diabetic patients.
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Walls AB, Sickmann HM, Brown A, Bouman SD, Ransom B, Schousboe A, Waagepetersen HS. Characterization of 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) as an inhibitor of brain glycogen shunt activity. J Neurochem 2008; 105:1462-70. [PMID: 18221367 DOI: 10.1111/j.1471-4159.2008.05250.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The pharmacological properties of 1,4-dideoxy-1,4-imino-d-arabinitol (DAB), a potent inhibitor of glycogen phosphorylase and synthase activity in liver preparations, were characterized in different brain tissue preparations as a prerequisite for using it as a tool to investigate brain glycogen metabolism. Its inhibitory effect on glycogen phosphorylase was studied in homogenates of brain tissue and astrocytes and IC50-values close to 400 nM were found. However, the concentration of DAB needed for inhibition of glycogen shunt activity, i.e. glucose metabolism via glycogen, in intact astrocytes was almost three orders of magnitude higher. Additionally, such complete inhibition required a pre-incubation period, a finding possibly reflecting a limited permeability of the astrocytic membrane. DAB did not affect the accumulation of 2-deoxyglucose-6-phosphate indicating that the transport of DAB is not mediated by the glucose transporter. DAB had no effect on enzymes involving glucose-6-phosphate, i.e. glucose-6-phosphate dehydrogenase, phosphoglucoisomerase and hexokinase. Furthermore, DAB was evaluated in a functional preparation of the isolated mouse optic nerve, in which its presence severely reduced the ability to sustain evoked compound action potentials in the absence of glucose, a condition in which glycogen serves as an important energy substrate. Based on the experimental findings, DAB can be used to evaluate glycogen shunt activity and its functional importance in intact brain tissue and cells at a concentration of 300-1000 muM and a pre-incubation period of 1 h.
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Affiliation(s)
- Anne B Walls
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark
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Abstract
Type-2 diabetes is associated with impaired glucose clearance by the liver in the postprandial state, and with elevated glucose production in the post-absorptive state. New targets within the liver are currently being investigated for development of antihyperglycaemic drugs for type-2 diabetes. They include glucokinase, which catalyses the first step in glucose metabolism, the glucagon receptor, and enzymes of gluconeogenesis and/or glycogenolysis such as glucose 6-phosphatase, fructose 1,6-bisphosphatase and glycogen phosphorylase. Preclinical studies with candidate drugs on animal models or cell-based assays suggest that these targets have the potential for pharmacological glycaemic control. Data from clinical studies is awaited. Further work is required for better understanding of the implications of targeting these sites in terms of possible side-effects or tachyphylaxis. The advantage of combined targeting of two or more sites within the liver for minimizing side-effects and tachyphylaxis caused by single-site targeting is discussed.
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Affiliation(s)
- Loranne Agius
- Institute of Cellular Medicine, School of Clinical Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.
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Poucher SM, Freeman S, Loxham SJG, Convey G, Bartlett JB, De Schoolmeester J, Teague J, Walker M, Turnbull AV, Charles AD, Carey F, Berg S. An assessment of the in vivo efficacy of the glycogen phosphorylase inhibitor GPi688 in rat models of hyperglycaemia. Br J Pharmacol 2007; 152:1239-47. [PMID: 17934512 DOI: 10.1038/sj.bjp.0707502] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE Studies in cultured hepatocytes demonstrate glycogen synthase (GS) activation with glycogen phosphorylase (GP) inhibitors. The current study investigated whether these phenomena occurred in vivo using a novel GP inhibitor. EXPERIMENTAL APPROACH An allosteric GP inhibitor, GPi688, was evaluated against both glucagon-mediated hyperglycaemia and oral glucose challenge-mediated hyperglycaemia to determine the relative effects against GP and GS in vivo. KEY RESULTS In rat primary hepatocytes, GPi688 inhibited glucagons-mediated glucose output in a concentration dependent manner. Additionally GP activity was reduced and GS activity increased seven-fold. GPi688 inhibited glucagon-mediated hyperglycaemia in both Wistar (65%) & obese Zucker (100%) rats and demonstrated a long duration of action in the Zucker rat. The in vivo efficacy in the glucagon challenge model could be predicted by the equation; % glucagon inhibition=56.9+34.3[log ([free plasma]/rat IC50)], r=0.921). GPi688 also reduced the blood glucose of obese Zucker rats after a 7 h fast by 23%. In an oral glucose tolerance test in Zucker rats, however, GPi688 was less efficacious (7% reduction) than a glycogen synthase kinase-3 (GSK-3) inhibitor (22% reduction), despite also observing activation (by 45%) of GS in vivo. CONCLUSIONS AND IMPLICATIONS Although GP inhibition can inhibit hyperglycaemia mediated by increased glucose production, the degree of GS activation induced by allosteric GP inhibitors in vivo, although discernible, is insufficient to increase glucose disposal. The data suggests that GP inhibitors might be more effective clinically against fasting rather than prandial hyperglycaemic control.
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Affiliation(s)
- S M Poucher
- Cardiovascular & Gastrointestinal Discovery Department, AstraZeneca Pharmaceuticals, Alderley Park, Macclesfield, Cheshire, UK.
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29
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Hampson LJ, Arden C, Agius L, Ganotidis M, Kosmopoulou MN, Tiraidis C, Elemes Y, Sakarellos C, Leonidas DD, Oikonomakos NG. Bioactivity of glycogen phosphorylase inhibitors that bind to the purine nucleoside site. Bioorg Med Chem 2007; 14:7835-45. [PMID: 16908161 DOI: 10.1016/j.bmc.2006.07.060] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 07/25/2006] [Accepted: 07/28/2006] [Indexed: 11/25/2022]
Abstract
The bioactivity in hepatocytes of glycogen phosphorylase inhibitors that bind to the active site, the allosteric activator site and the indole carboxamide site has been described. However, the pharmacological potential of the purine nucleoside inhibitor site has remained unexplored. We report the chemical synthesis and bioactivity in hepatocytes of four new olefin derivatives of flavopiridol (1-4) that bind to the purine site. Flavopiridol and 1-4 counteracted the activation of phosphorylase in hepatocytes caused by AICAR (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside), which is metabolised to an AMP analogue. Unlike an indole carboxamide inhibitor, the analogues 1 and 4 suppressed the basal rate of glycogenolysis in hepatocytes by allosteric inhibition rather than by inactivation of phosphorylase, and accordingly caused negligible stimulation of glycogen synthesis. However, they counteracted the stimulation of glycogenolysis by dibutyryl cAMP by both allosteric inhibition and inactivation of phosphorylase. Cumulatively, the results show key differences between purine site and indole carboxamide site inhibitors in terms of (i) relative roles of dephosphorylation of phosphorylase-a as compared with allosteric inhibition, (ii) counteraction of the efficacy of the inhibitors on glycogenolysis by dibutyryl-cAMP and (iii) stimulation of glycogen synthesis.
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Affiliation(s)
- Laura J Hampson
- School of Clinical Medical Sciences-Diabetes, Newcastle University, The Medical School, Newcastle upon Tyne NE2 4HH, UK
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30
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Oikonomakos NG, Tiraidis C, Leonidas DD, Zographos SE, Kristiansen M, Jessen CU, Nørskov-Lauritsen L, Agius L. Iminosugars as Potential Inhibitors of Glycogenolysis: Structural Insights into the Molecular Basis of Glycogen Phosphorylase Inhibition. J Med Chem 2006; 49:5687-701. [PMID: 16970395 DOI: 10.1021/jm060496g] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Iminosugars DAB (5), isofagomine (9), and several N-substituted derivatives have been identified as potent inhibitors of liver glycogen phosphorylase a (IC(50) = 0.4-1.2 microM) and of basal and glucagon-stimulated glycogenolysis (IC(50) = 1-3 microM). The X-ray structures of 5, 9, and its N-3-phenylpropyl analogue 8 in complex with rabbit muscle glycogen phosphorylase (GPb) shows that iminosugars bind tightly at the catalytic site in the presence of the substrate phosphate and induce conformational changes that characterize the R-state conformation of the enzyme. Charged nitrogen N1 is within hydrogen-bonding distance with the carbonyl oxygen of His377 (5) and in ionic contact with the substrate phosphate oxygen (8 and 9). Our findings suggest that the inhibitors function as oxocarbenium ion transition-state analogues. The conformational change to the R state provides an explanation for previous findings that 5, unlike inhibitors that favor the T state, promotes phosphorylation of GPb in hepatocytes with sequential inactivation of glycogen synthase.
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Affiliation(s)
- Nikos G Oikonomakos
- Institute of Organic and Pharmaceutical Chemistry, The National Hellenic Research Foundation, Athens 11635, Greece.
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31
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Petsalakis EI, Chrysina ED, Tiraidis C, Hadjiloi T, Leonidas DD, Oikonomakos NG, Aich U, Varghese B, Loganathan D. Crystallographic studies on N-azidoacetyl-β-d-glucopyranosylamine, an inhibitor of glycogen phosphorylase: Comparison with N-acetyl-β-d-glucopyranosylamine. Bioorg Med Chem 2006; 14:5316-24. [PMID: 16616506 DOI: 10.1016/j.bmc.2006.03.044] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Revised: 03/20/2006] [Accepted: 03/24/2006] [Indexed: 11/25/2022]
Abstract
N-acetyl-beta-D-glucopyranosylamine (NAG) is a potent inhibitor (Ki=32 microM) of glycogen phosphorylase b (GPb), and has been employed as a lead compound for the structure-based design of new analogues, in an effort to utilize its potential as a hypoglycaemic agent. Replacement of the acetamido group by azidoacetamido group resulted in an inhibitor, N-azidoacetyl-beta-D-glucopyranosylamine (azido-NAG), with a Ki value of 48.7 microM, in the direction of glycogen synthesis. In order to elucidate the mechanism of inhibition, we determined the ligand structure in complex with GPb at 2.03 A resolution, and the structure of the fully acetylated derivative in the free form. The molecular packing of the latter is stabilized by a number of bifurcated hydrogen bonds of which the one involving a bifurcated C-H...N...H-C type hydrogen bonding is rather unique in organic azides. Azido-NAG can be accommodated in the catalytic site of T-state GPb at approximately the same position as that of NAG and stabilizes the T-state conformation of the 280 s loop by making several favourable contacts to residues of this loop. The difference observed in the Ki values of the two analogues can be interpreted in terms of desolvation effects, subtle structural changes of protein residues and changes in water structure.
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Affiliation(s)
- Evangelia I Petsalakis
- Institute of Organic and Pharmaceutical Chemistry, The National Hellenic Research Foundation, 48, Vas. Constantinou Ave., 116 35 Athens, Greece
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32
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Hadjiloi T, Tiraidis C, Chrysina ED, Leonidas DD, Oikonomakos NG, Tsipos P, Gimisis T. Binding of oxalyl derivatives of β-d-glucopyranosylamine to muscle glycogen phosphorylase b. Bioorg Med Chem 2006; 14:3872-82. [PMID: 16464598 DOI: 10.1016/j.bmc.2006.01.045] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2005] [Revised: 01/13/2006] [Accepted: 01/17/2006] [Indexed: 11/29/2022]
Abstract
Five oxalyl derivatives of beta-d-glucopyranosylamine were synthesized as potential inhibitors of glycogen phosphorylase (GP). The compounds 1-4 were competitive inhibitors of rabbit muscle GPb (with respect to alpha-d-glucose-1-phosphate) with K(i) values of 0.2-1.4 mM, while compound 5 was not effective up to a concentration of 10 mM. In order to elucidate the structural basis of their inhibition, we analysed the structures of compounds 1-4 in complex with GPb at 1.93-1.96 Angstrom resolution. The complex structures reveal that the inhibitors can be accommodated at the catalytic site at approximately the same position as alpha-d-glucose and stabilize the T-state conformation of the 280 s loop by making several favourable contacts to Asp283 and Asn284 of this loop. Comparison with the lead compound N-acetyl-beta-d-glucopyranosylamine (6) shows that the hydrogen bonding interaction of the amide nitrogen with the main-chain carbonyl oxygen of His377 is not present in these complexes. The differences observed in the K(i) values of the four analogues can be interpreted in terms of subtle conformational changes of protein residues and shifts of water molecules in the vicinity of the catalytic site, variations in van der Waals interactions, conformational entropy and desolvation effects.
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Affiliation(s)
- Theodoros Hadjiloi
- Institute of Organic and Pharmaceutical Chemistry, The National Hellenic Research Foundation, 48 Vas. Constantinou Ave., 11635 Athens, Greece
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33
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Arden C, Green AR, Hampson LJ, Aiston S, Härndahl L, Greenberg CC, Brady MJ, Freeman S, Poucher SM, Agius L. Increased sensitivity of glycogen synthesis to phosphorylase-a and impaired expression of the glycogen-targeting protein R6 in hepatocytes from insulin-resistant Zucker fa/fa rats. FEBS J 2006; 273:1989-99. [PMID: 16640562 DOI: 10.1111/j.1742-4658.2006.05215.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Hepatic insulin resistance in the leptin-receptor defective Zucker fa/fa rat is associated with impaired glycogen synthesis and increased activity of phosphorylase-a. We investigated the coupling between phosphorylase-a and glycogen synthesis in hepatocytes from fa/fa rats by modulating the concentration of phosphorylase-a. Treatment of hepatocytes from fa/fa rats and Fa/? controls with a selective phosphorylase inhibitor caused depletion of phosphorylase-a, activation of glycogen synthase and stimulation of glycogen synthesis. The flux-control coefficient of phosphorylase on glycogen synthesis was glucose dependent and at 10 mm glucose was higher in fa/fa than Fa/? hepatocytes. There was an inverse correlation between the activities of glycogen synthase and phosphorylase-a in both fa/fa and Fa/? hepatocytes. However, fa/fa hepatocytes had a higher activity of phosphorylase-a, for a corresponding activity of glycogen synthase. This defect was, in part, normalized by expression of the glycogen-targeting protein, PTG. Hepatocytes from fa/fa rats had normal expression of the glycogen-targeting proteins G(L) and PTG but markedly reduced expression of R6. Expression of R6 protein was increased in hepatocytes from Wistar rats after incubation with leptin and insulin. Diminished hepatic R6 expression in the leptin-receptor defective fa/fa rat may be a contributing factor to the elevated phosphorylase activity and/or its high control strength on glycogen synthesis.
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MESH Headings
- Animals
- Carrier Proteins/antagonists & inhibitors
- Carrier Proteins/biosynthesis
- Carrier Proteins/physiology
- Cells, Cultured
- Diabetes Mellitus, Type 2/enzymology
- Diabetes Mellitus, Type 2/genetics
- Disease Models, Animal
- Female
- Glycogen/biosynthesis
- Glycogen/metabolism
- Glycogen/physiology
- Hepatocytes/enzymology
- Insulin/chemistry
- Insulin Resistance/genetics
- Intracellular Signaling Peptides and Proteins
- Leptin/chemistry
- Male
- Obesity/enzymology
- Obesity/genetics
- Phosphoprotein Phosphatases/antagonists & inhibitors
- Phosphoprotein Phosphatases/biosynthesis
- Phosphoprotein Phosphatases/metabolism
- Phosphorylase a/chemistry
- Phosphorylase a/physiology
- Protein Subunits/antagonists & inhibitors
- Protein Subunits/biosynthesis
- Protein Subunits/metabolism
- Rats
- Rats, Wistar
- Rats, Zucker
- Receptors, Cell Surface/deficiency
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/physiology
- Receptors, Leptin
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Affiliation(s)
- Catherine Arden
- School of Clinical Medical Sciences--Diabetes, University of Newcastle upon Tyne, UK
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34
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Abstract
Scientists and science in the pharmaceutical industry rely heavily on the more academically orientated basic research carried out at Universities, for first of all training, but also as a source of new ideas and approaches to drug discovery. Progress in the discovery and development of novel therapeutics benefits from a healthy alliance with, and the output from, more basic research institutions, and the reverse is also true, with many advances in understanding of physiological and pathological processes being as the result of the application of novel targeted molecules. To illustrate this, some examples related to the themes of this meeting from my experiences in three different companies will be described. The first involves a metabolic angle in the unravelling of the mechanism of the novel anti-anginal agent ranolazine. The second describes the application of detailed knowledge of insulin structure and action to then use recombinant approaches to design novel molecules to be able to offer the Type I (insulin-dependent) diabetic patient therapies allowing a more physiological treatment regime, and also the further application of learned technology to then discover a means of harnessing the potential of GLP-1 (glucagon-like polypeptide 1) for treating Type II (non-insulin-dependent) diabetes. The last illustrates how findings of novel binding sites on glycogen phosphorylase and glucokinase as the result of drug discovery programmes have led to increased understanding of these key metabolic enzymes and also potential new therapies for Type II diabetes.
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35
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Aiston S, Hampson LJ, Arden C, Iynedjian PB, Agius L. The role of protein kinase B/Akt in insulin-induced inactivation of phosphorylase in rat hepatocytes. Diabetologia 2006; 49:174-82. [PMID: 16341839 DOI: 10.1007/s00125-005-0068-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/24/2005] [Accepted: 07/28/2005] [Indexed: 11/30/2022]
Abstract
AIMS/HYPOTHESIS An insulin signalling pathway leading from activation of protein kinase B (PKB, also known as Akt) to phosphorylation (inactivation) of glycogen synthase kinase-3 (GSK-3) and activation of glycogen synthase is well characterised. However, in hepatocytes, inactivation of GSK-3 is not the main mechanism by which insulin stimulates glycogen synthesis. We therefore tested whether activation of PKB causes inactivation of glycogen phosphorylase. MATERIALS AND METHODS We used a conditionally active form of PKB, produced using recombinant adenovirus, to test the role of acute PKB activation in the control of glycogen phosphorylase and glycogen synthesis in hepatocytes. RESULTS Conditional activation of PKB mimicked the inactivation of phosphorylase, the activation of glycogen synthase, and the stimulation of glycogen synthesis caused by insulin. In contrast, inhibition of GSK-3 caused activation of glycogen synthase but did not mimic the stimulation of glycogen synthesis by insulin. PKB activation and GSK-3 inhibition had additive effects on the activation of glycogen synthase, indicating convergent mechanisms downstream of PKB involving inactivation of either phosphorylase or GSK-3. Glycogen synthesis correlated inversely with the activity of phosphorylase-a, irrespective of whether this was modulated by insulin, by PKB activation or by a selective phosphorylase ligand, supporting an essential role for phosphorylase inactivation in the glycogenic action of insulin in hepatocytes. CONCLUSIONS/INTERPRETATION In hepatocytes, the acute activation of PKB, but not the inhibition of GSK-3, mimics the stimulation of glycogen synthesis by insulin. This is explained by a pathway downstream of PKB leading to inactivation of phosphorylase, activation of glycogen synthase, and stimulation of glycogen synthesis, independent of the GSK-3 pathway.
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Affiliation(s)
- S Aiston
- School of Clinical Medical Sciences-Diabetes, University of Newcastle upon Tyne, NE2 4HH, Newcastle upon Tyne, UK
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36
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Watson KA, Chrysina ED, Tsitsanou KE, Zographos SE, Archontis G, Fleet GWJ, Oikonomakos NG. Kinetic and crystallographic studies of glucopyranose spirohydantoin and glucopyranosylamine analogs inhibitors of glycogen phosphorylase. Proteins 2005; 61:966-83. [PMID: 16222658 DOI: 10.1002/prot.20653] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Glycogen phosphorylase (GP) is currently exploited as a target for inhibition of hepatic glycogenolysis under high glucose conditions. Spirohydantoin of glucopyranose and N-acetyl-beta-D-glucopyranosylamine have been identified as the most potent inhibitors of GP that bind at the catalytic site. Four spirohydantoin and three beta-D-glucopyranosylamine analogs have been designed, synthesized and tested for inhibition of GP in kinetic experiments. Depending on the functional group introduced, the K(i) values varied from 16.5 microM to 1200 microM. In order to rationalize the kinetic results, we determined the crystal structures of the analogs in complex with GP. All the inhibitors bound at the catalytic site of the enzyme, by making direct and water-mediated hydrogen bonds with the protein and by inducing minor movements of the side chains of Asp283 and Asn284, of the 280s loop that blocks access of the substrate glycogen to the catalytic site, and changes in the water structure in the vicinity of the site. The differences observed in the Ki values of the analogs can be interpreted in terms of variations in hydrogen bonding and van der Waals interactions, desolvation effects, ligand conformational entropy, and displacement of water molecules on ligand binding to the catalytic site.
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Affiliation(s)
- Kimberly A Watson
- Laboratory of Molecular Biophysics, University of Oxford, Oxford, United Kingdom
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37
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Anagnostou E, Kosmopoulou MN, Chrysina ED, Leonidas DD, Hadjiloi T, Tiraidis C, Zographos SE, Györgydeák Z, Somsák L, Docsa T, Gergely P, Kolisis FN, Oikonomakos NG. Crystallographic studies on two bioisosteric analogues, N-acetyl-beta-D-glucopyranosylamine and N-trifluoroacetyl-beta-D-glucopyranosylamine, potent inhibitors of muscle glycogen phosphorylase. Bioorg Med Chem 2005; 14:181-9. [PMID: 16213146 DOI: 10.1016/j.bmc.2005.08.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2005] [Accepted: 08/02/2005] [Indexed: 10/25/2022]
Abstract
Structure-based inhibitor design has led to the discovery of a number of potent inhibitors of glycogen phosphorylase b (GPb), N-acyl derivatives of beta-D-glucopyranosylamine, that bind at the catalytic site of the enzyme. The first good inhibitor in this class of compounds, N-acetyl-beta-D-glucopyranosylamine (NAG) (K(i) = 32 microM), has been previously characterized by biochemical, biological and crystallographic experiments at 2.3 angstroms resolution. Bioisosteric replacement of the acetyl group by trifluoroacetyl group resulted in an inhibitor, N-trifluoroacetyl-beta-D-glucopyranosylamine (NFAG), with a K(i) = 75 microM. To elucidate the structural basis of its reduced potency, we determined the ligand structure in complex with GPb at 1.8 angstroms resolution. To compare the binding mode of N-trifluoroacetyl derivative with that of the lead molecule, we also determined the structure of GPb-NAG complex at a higher resolution (1.9 angstroms). NFAG can be accommodated in the catalytic site of T-state GPb at approximately the same position as that of NAG and stabilize the T-state conformation of the 280 s loop by making several favourable contacts to Asn284 of this loop. The difference observed in the K(i) values of the two analogues can be interpreted in terms of subtle conformational changes of protein residues and shifts of water molecules in the vicinity of the catalytic site, variations in van der Waals interaction, and desolvation effects.
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Affiliation(s)
- Eleni Anagnostou
- Institute of Organic and Pharmaceutical Chemistry, The National Hellenic Research Foundation, 48, Vas. Constantinou Ave. 116 35 Athens, Greece
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38
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Chrysina ED, Kosmopoulou MN, Tiraidis C, Kardakaris R, Bischler N, Leonidas DD, Hadady Z, Somsak L, Docsa T, Gergely P, Oikonomakos NG. Kinetic and crystallographic studies on 2-(beta-D-glucopyranosyl)-5-methyl-1, 3, 4-oxadiazole, -benzothiazole, and -benzimidazole, inhibitors of muscle glycogen phosphorylase b. Evidence for a new binding site. Protein Sci 2005; 14:873-88. [PMID: 15741340 PMCID: PMC2253430 DOI: 10.1110/ps.041216105] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
In an attempt to identify leads that would enable the design of inhibitors with enhanced affinity for glycogen phosphorylase (GP), that might control hyperglycaemia in type 2 diabetes, three new analogs of beta-D-glucopyranose, 2-(beta-D-glucopyranosyl)-5-methyl-1, 3, 4-oxadiazole, -benzothiazole, and -benzimidazole were assessed for their potency to inhibit GPb activity. The compounds showed competitive inhibition (with respect to substrate Glc-1-P) with K(i) values of 145.2 (+/-11.6), 76 (+/-4.8), and 8.6 (+/-0.7) muM, respectively. In order to establish the mechanism of this inhibition, crystallographic studies were carried out and the structures of GPb in complex with the three analogs were determined at high resolution (GPb-methyl-oxadiazole complex, 1.92 A; GPb-benzothiazole, 2.10 A; GPb-benzimidazole, 1.93 A). The complex structures revealed that the inhibitors can be accommodated in the catalytic site of T-state GPb with very little change of the tertiary structure, and provide a rationalization for understanding variations in potency of the inhibitors. In addition, benzimidazole bound at the new allosteric inhibitor or indole binding site, located at the subunit interface, in the region of the central cavity, and also at a novel binding site, located at the protein surface, far removed (approximately 32 A) from the other binding sites, that is mostly dominated by the nonpolar groups of Phe202, Tyr203, Val221, and Phe252.
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Affiliation(s)
- Evangelia D Chrysina
- Institute of Organic and Pharmaceutical Chemistry, The National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 116 35 Athens, Greece
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39
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Hampson LJ, Agius L. Increased potency and efficacy of combined phosphorylase inactivation and glucokinase activation in control of hepatocyte glycogen metabolism. Diabetes 2005; 54:617-23. [PMID: 15734835 DOI: 10.2337/diabetes.54.3.617] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucokinase and phosphorylase both have a high control strength over hepatocyte glycogen metabolism and are potential therapeutic targets for type 2 diabetes. We tested whether combined phosphorylase inactivation and glucokinase activation is a more effective strategy for controlling hepatic glycogen metabolism than single-site targeting. Activation of glucokinase by enzyme overexpression combined with selective dephosphorylation of phosphorylase-a by an indole carboxamide that favors the T conformation of phosphorylase caused a greater stimulation of glycogen synthesis than the sum of either treatment alone. This result is explained by the complementary roles of elevated glucose-6-phosphate (G6P; a positive modulator) and depleted phosphorylase-a (a negative modulator) in activating glycogen synthase and also by synergistic inactivation of phosphorylase-a by glucokinase activation and the indole carboxamide. Inactivation of phosphorylase-a by the indole carboxamide was counteracted by 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside, which is metabolized to an AMP analog; this effect was reversed by G6P. Our findings provide further evidence for the inverse roles of G6P and AMP in regulating the activation state of hepatic phosphorylase. It is proposed that dual targeting of glucokinase and phosphorylase-a enables improved potency and efficacy in controlling hepatic glucose metabolism.
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Affiliation(s)
- Laura J Hampson
- School of Clinical Medical Sciences-Diabetes, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, NE2 4HH, U.K
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40
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Green AR, Aiston S, Greenberg CC, Freeman S, Poucher SM, Brady MJ, Agius L. The Glycogenic Action of Protein Targeting to Glycogen in Hepatocytes Involves Multiple Mechanisms Including Phosphorylase Inactivation and Glycogen Synthase Translocation. J Biol Chem 2004; 279:46474-82. [PMID: 15322104 DOI: 10.1074/jbc.m405660200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Expression of the glycogen-targeting protein PTG promotes glycogen synthase activation and glycogen storage in various cell types. In this study, we tested the contribution of phosphorylase inactivation to the glycogenic action of PTG in hepatocytes by using a selective inhibitor of phosphorylase (CP-91149) that causes dephosphorylation of phosphorylase a and sequential activation of glycogen synthase. Similar to CP-91194, graded expression of PTG caused a concentration-dependent inactivation of phosphorylase and activation of glycogen synthase. The latter was partially counter-acted by the expression of muscle phosphorylase and was not additive with the activation by CP-91149, indicating that it is in part secondary to the inactivation of phosphorylase. PTG expression caused greater stimulation of glycogen synthesis and translocation of glycogen synthase than CP-91149, and the translocation of synthase could not be explained by accumulation of glycogen, supporting an additional role for glycogen synthase translocation in the glycogenic action of PTG. The effects of PTG expression on glycogen synthase and glycogen synthesis were additive with the effects of glucokinase expression, confirming the complementary roles of depletion of phosphorylase a (a negative modulator) and elevated glucose 6-phosphate (a positive modulator) in potentiating the activation of glycogen synthase. PTG expression mimicked the inactivation of phosphorylase caused by high glucose and counteracted the activation caused by glucagon. The latter suggests a possible additional role for PTG on phosphorylase kinase inactivation.
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Affiliation(s)
- Andrew R Green
- Department of Diabetes, School of Clinical Medical Sciences, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom
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41
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Aiston S, Green A, Mukhtar M, Agius L. Glucose 6-phosphate causes translocation of phosphorylase in hepatocytes and inactivates the enzyme synergistically with glucose. Biochem J 2004; 377:195-204. [PMID: 13678417 PMCID: PMC1223839 DOI: 10.1042/bj20031191] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2003] [Accepted: 09/18/2003] [Indexed: 01/21/2023]
Abstract
The role of glucose 6-P (glucose 6-phosphate) in regulating the activation state of glycogen synthase and its translocation is well documented. In the present study, we investigated the effects of glucose 6-P on the activation state and compartmentation of phosphorylase in hepatocytes. Glucose 6-P levels were modulated in hepatocytes by glucokinase overexpression or inhibition with 5-thioglucose and the effects of AMP were tested using AICAR (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside), which is metabolized to an AMP analogue. Inhibition of glucokinase partially counteracted the effect of glucose both on the inactivation of phosphorylase and on the translocation of phosphorylase a from a soluble to a particulate fraction. The increase in glucose 6-P caused by glucokinase overexpression caused translocation of phosphorylase a to the pellet and had additive effects with glucose on inactivation of phosphorylase. It decreased the glucose concentration that caused half-maximal inactivation from 20 to 11 mM, indicating that it acts synergistically with glucose. AICAR activated phosphorylase and counteracted the effect of glucose 6-P on phosphorylase inactivation. However, it did not counteract translocation of phosphorylase by glucose 6-P. Glucose 6-P and AICAR had opposite effects on the activation state of glycogen synthase, but they had additive effects on translocation of the enzyme to the pellet. There was a direct correlation between the translocation of phosphorylase a and of glycogen synthase to the pellet, suggesting that these enzymes translocate in tandem. In conclusion, glucose 6-P causes both translocation of phosphorylase and inactivation, indicating a more complex role in the regulation of glycogen metabolism than can be explained from regulation of glycogen synthase alone.
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Affiliation(s)
- Susan Aiston
- Department of Diabetes, School of Clinical Medical Sciences, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK
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Tavridou A, Agius L. Phosphorylase regulates the association of glycogen synthase with a proteoglycogen substrate in hepatocytes. FEBS Lett 2003; 551:87-91. [PMID: 12965209 DOI: 10.1016/s0014-5793(03)00902-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Changes in the glucosylation state of the glycogen primer, glycogenin, or its association with glycogen synthase are potential sites for regulation of glycogen synthesis. In this study we found no evidence for hormonal control of the glucosylation state of glycogenin in hepatocytes. However, using a modified glycogen synthase assay that separates the product into acid-soluble (glycogen) and acid-insoluble (proteoglycogen) fractions we found that insulin and glucagon increase and decrease, respectively, the association of glycogen synthase with an acid-insoluble substrate. The latter fraction had a higher affinity for UDP-glucose and accounted for between 5 and 21% of total activity depending on hormonal conditions. Phosphorylase overexpression mimicked the effect of glucagon. It is concluded that phosphorylase activation or overexpression causes dissociation of glycogen synthase from proteoglycogen causing inhibition of initiation of glycogen synthesis.
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Affiliation(s)
- Anna Tavridou
- School of Clinical Medical Sciences-Diabetes, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK
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Aiston S, Coghlan MP, Agius L. Inactivation of phosphorylase is a major component of the mechanism by which insulin stimulates hepatic glycogen synthesis. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:2773-81. [PMID: 12823547 DOI: 10.1046/j.1432-1033.2003.03648.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Multiple signalling pathways are involved in the mechanism by which insulin stimulates hepatic glycogen synthesis. In this study we used selective inhibitors of glycogen synthase kinase-3 (GSK-3) and an allosteric inhibitor of phosphorylase (CP-91149) that causes dephosphorylation of phosphorylase a, to determine the relative contributions of inactivation of GSK-3 and dephosphorylation of phosphorylase a as alternative pathways in the stimulation of glycogen synthesis by insulin in hepatocytes. GSK-3 inhibitors (SB-216763 and Li+) caused a greater activation of glycogen synthase than insulin (90% vs. 40%) but a smaller stimulation of glycogen synthesis (30% vs. 150%). The contribution of GSK-3 inactivation to insulin stimulation of glycogen synthesis was estimated to be less than 20%. Dephosphorylation of phosphorylase a with CP-91149 caused activation of glycogen synthase and translocation of the protein from a soluble to a particulate fraction and mimicked the stimulation of glycogen synthesis by insulin. The stimulation of glycogen synthesis by phosphorylase inactivation cannot be explained by either inhibition of glycogen degradation or activation of glycogen synthase alone and suggests an additional role for translocation of synthase. Titrations with the phosphorylase inactivator showed that stimulation of glycogen synthesis by insulin can be largely accounted for by inactivation of phosphorylase over a wide range of activities of phosphorylase a. We conclude that a signalling pathway involving dephosphorylation of phosphorylase a leading to both activation and translocation of glycogen synthase is a critical component of the mechanism by which insulin stimulates hepatic glycogen synthesis. Selective inactivation of phosphorylase can mimic insulin stimulation of hepatic glycogen synthesis.
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Affiliation(s)
- Susan Aiston
- School of Clinical Medical Sciences, University of Newcastle upon Tyne, The Medical School, Newcastle upon Tyne, UK
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Aiston S, Andersen B, Agius L. Glucose 6-phosphate regulates hepatic glycogenolysis through inactivation of phosphorylase. Diabetes 2003; 52:1333-9. [PMID: 12765941 DOI: 10.2337/diabetes.52.6.1333] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
High glucose concentration suppresses hepatic glycogenolysis by allosteric inhibition and dephosphorylation (inactivation) of phosphorylase-a. The latter effect is attributed to a direct effect of glucose on the conformation of phosphorylase-a. Although glucose-6-phosphate (G6P), like glucose, stimulates dephosphorylation of phosphorylase-a by phosphorylase phosphatase, its physiological role in regulating glycogenolysis in intact hepatocytes has not been tested. We show in this study that metabolic conditions associated with an increase in G6P, including glucokinase overexpression and incubation with octanoate or dihydroxyacetone, cause inactivation of phosphorylase. The latter conditions also inhibit glycogenolysis. The activity of phosphorylase-a correlated inversely with the G6P concentration within the physiological range. The inhibition of glycogenolysis and inactivation of phosphorylase-a caused by 10 mmol/l glucose can be at least in part counteracted by inhibition of glucokinase with 5-thioglucose, which lowers G6P. In conclusion, metabolic conditions that alter the hepatic G6P content affect glycogen metabolism not only through regulation of glycogen synthase but also through regulation of the activation state of phosphorylase. Dysregulation of G6P in diabetes by changes in activity of glucokinase or glucose 6-phosphatase may be a contributing factor to impaired suppression of glycogenolysis by hyperglycemia.
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Affiliation(s)
- Susan Aiston
- Department of Diabetes, School of Clinical Medical Sciences, University of Newcastle upon Tyne, The Medical School, Newcastle upon Tyne NE2 4HH, U.K
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