Articles de revues : « GlycoGag »

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Fujisawa, Ryuichi, Frank J. McAtee, Cynthia Favara, Stanley F. Hayes et John L. Portis. « N-Terminal Cleavage Fragment of Glycosylated Gag Is Incorporated into Murine Oncornavirus Particles ». Journal of Virology 75, n^o 22 (15 novembre 2001) : 11239–43. http://dx.doi.org/10.1128/jvi.75.22.11239-11243.2001.

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ABSTRACT Glycosylated Gag (Glycogag) is a transmembrane protein encoded by murine and feline oncornaviruses. While the protein is dispensible for virus replication, Glycogag-null mutants of a neurovirulent murine oncornavirus are slow to spread in vivo and exhibit a loss of pathogenicity. The function of this protein in the virus life cycle, however, is not understood. Glycogag is expressed at the plasma membrane of infected cells but has not been detected in virions. In the present study we have reexamined this issue and have found an N-terminal cleavage fragment of Glycogag which was pelleted by high-speed centrifugation and sedimented in sucrose density gradients at the same bouyant density as virus particles. Its association with virions was confirmed by velocity sedimentation through iodixanol, which effectively separated membrane microvesicles from virus particles. Furthermore, the apparent molecular weight of the virion-associated protein was different from that of the protein extracted from the plasma membrane, suggesting some level of specificity or selectivity of incorporation.

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Gonzalez-Enriquez, Gracia Viviana, Martha Escoto-Delgadillo, Eduardo Vazquez-Valls et Blanca Miriam Torres-Mendoza. « SERINC as a Restriction Factor to Inhibit Viral Infectivity and the Interaction with HIV ». Journal of Immunology Research 2017 (2017) : 1–9. http://dx.doi.org/10.1155/2017/1548905.

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The serine incorporator 5 (SERINC5) is a recently discovered restriction factor that inhibits viral infectivity by preventing fusion. Retroviruses have developed strategies to counteract the action of SERINC5, such as the expression of proteins like negative regulatory factor (Nef), S2, and glycosylated Gag (glycoGag). These accessory proteins downregulate SERINC5 from the plasma membrane for subsequent degradation in the lysosomes. The observed variability in the action of SERINC5 suggests the participation of other elements like the envelope glycoprotein (Env) that modulates susceptibility of the virus towards SERINC5. The exact mechanism by which SERINC5 inhibits viral fusion has not yet been determined, although it has been proposed that it increases the sensitivity of the Env by exposing regions which are recognized by neutralizing antibodies. More studies are needed to understand the role of SERINC5 and to assess its utility as a therapeutic strategy.

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Firrito, Claudia, Cinzia Bertelli, Teresa Vanzo, Ajit Chande et Massimo Pizzato. « SERINC5 as a New Restriction Factor for Human Immunodeficiency Virus and Murine Leukemia Virus ». Annual Review of Virology 5, n^o 1 (29 septembre 2018) : 323–40. http://dx.doi.org/10.1146/annurev-virology-092917-043308.

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SERINC genes encode for homologous multipass transmembrane proteins with unknown cellular function, despite being highly conserved across eukaryotes. Among the five SERINC genes found in humans, SERINC5 was shown to act as a powerful inhibitor of retroviruses. It is efficiently incorporated into virions and blocks the penetration of the viral core into target cells, by impairing the fusion process with a yet unclear mechanism. SERINC5 was also found to promote human immunodeficiency virus 1 (HIV-1) virion neutralization by antibodies, indicating a pleiotropic activity, which remains mostly unexplored. Counteracting factors have emerged independently in at least three retrovirus lineages, underscoring their fundamental importance during retrovirus evolution. Nef and S2 of primate and equine lentiviruses, and glycoGag of gammaretroviruses, act similarly by targeting SERINC5 to endosomes and excluding it from virions. Here, we discuss the features that distinguish SERINC5 from other known restriction factors, delineating a yet unique class of antiviral inhibitors.

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Cano-Ortiz, Lucía, Qinyong Gu, Patricia de Sousa-Pereira, Zeli Zhang, Catherina Chiapella, Augustin Penda Twizerimana, Chaohui Lin et al. « Feline Leukemia Virus-B Envelope Together With its GlycoGag and Human Immunodeficiency Virus-1 Nef Mediate Resistance to Feline SERINC5 ». Journal of Molecular Biology 434, n^o 6 (mars 2022) : 167421. http://dx.doi.org/10.1016/j.jmb.2021.167421.

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Diehl, William E., Mehmet H. Guney, Teresa Vanzo, Pyae P. Kyawe, Judith M. White, Massimo Pizzato et Jeremy Luban. « Influence of Different Glycoproteins and of the Virion Core on SERINC5 Antiviral Activity ». Viruses 13, n^o 7 (30 juin 2021) : 1279. http://dx.doi.org/10.3390/v13071279.

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Host plasma membrane protein SERINC5 is incorporated into budding retrovirus particles where it blocks subsequent entry into susceptible target cells. Three structurally unrelated proteins encoded by diverse retroviruses, human immunodeficiency virus type 1 (HIV-1) Nef, equine infectious anemia virus (EIAV) S2, and ecotropic murine leukemia virus (MLV) GlycoGag, disrupt SERINC5 antiviral activity by redirecting SERINC5 from the site of virion assembly on the plasma membrane to an internal RAB7+ endosomal compartment. Pseudotyping retroviruses with particular glycoproteins, e.g., vesicular stomatitis virus glycoprotein (VSV G), renders the infectivity of particles resistant to inhibition by virion-associated SERINC5. To better understand viral determinants for SERINC5-sensitivity, the effect of SERINC5 was assessed using HIV-1, MLV, and Mason-Pfizer monkey virus (M-PMV) virion cores, pseudotyped with glycoproteins from Arenavirus, Coronavirus, Filovirus, Rhabdovirus, Paramyxovirus, and Orthomyxovirus genera. SERINC5 restricted virions pseudotyped with glycoproteins from several retroviruses, an orthomyxovirus, a rhabdovirus, a paramyxovirus, and an arenavirus. Infectivity of particles pseudotyped with HIV-1, amphotropic-MLV (A-MLV), or influenza A virus (IAV) glycoproteins, was decreased by SERINC5, whether the core was provided by HIV-1, MLV, or M-PMV. In contrast, particles pseudotyped with glycoproteins from M-PMV, parainfluenza virus 5 (PIV5), or rabies virus (RABV) were sensitive to SERINC5, but only with particular retroviral cores. Resistance to SERINC5 did not correlate with reduced SERINC5 incorporation into particles, route of viral entry, or absolute infectivity of the pseudotyped virions. These findings indicate that some non-retroviruses may be sensitive to SERINC5 and that, in addition to the viral glycoprotein, the retroviral core influences sensitivity to SERINC5.

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Li, Minghua, Abdul A. Waheed, Jingyou Yu, Cong Zeng, Hui-Yu Chen, Yi-Min Zheng, Amin Feizpour et al. « TIM-mediated inhibition of HIV-1 release is antagonized by Nef but potentiated by SERINC proteins ». Proceedings of the National Academy of Sciences 116, n^o 12 (6 mars 2019) : 5705–14. http://dx.doi.org/10.1073/pnas.1819475116.

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The T cell Ig and mucin domain (TIM) proteins inhibit release of HIV-1 and other enveloped viruses by interacting with cell- and virion-associated phosphatidylserine (PS). Here, we show that the Nef proteins of HIV-1 and other lentiviruses antagonize TIM-mediated restriction. TIM-1 more potently inhibits the release of Nef-deficient relative to Nef-expressing HIV-1, and ectopic expression of Nef relieves restriction. HIV-1 Nef does not down-regulate the overall level of TIM-1 expression, but promotes its internalization from the plasma membrane and sequesters its expression in intracellular compartments. Notably, Nef mutants defective in modulating membrane protein endocytic trafficking are incapable of antagonizing TIM-mediated inhibition of HIV-1 release. Intriguingly, depletion of SERINC3 or SERINC5 proteins in human peripheral blood mononuclear cells (PBMCs) attenuates TIM-1 restriction of HIV-1 release, in particular that of Nef-deficient viruses. In contrast, coexpression of SERINC3 or SERINC5 increases the expression of TIM-1 on the plasma membrane and potentiates TIM-mediated inhibition of HIV-1 production. Pulse-chase metabolic labeling reveals that the half-life of TIM-1 is extended by SERINC5 from <2 to ∼6 hours, suggesting that SERINC5 stabilizes the expression of TIM-1. Consistent with a role for SERINC protein in potentiating TIM-1 restriction, we find that MLV glycoGag and EIAV S2 proteins, which, like Nef, antagonize SERINC-mediated diminishment of HIV-1 infectivity, also effectively counteract TIM-mediated inhibition of HIV-1 release. Collectively, our work reveals a role of Nef in antagonizing TIM-1 and highlights the complex interplay between Nef and HIV-1 restriction by TIMs and SERINCs.

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Chande, Ajit, Emilia Cristiana Cuccurullo, Annachiara Rosa, Serena Ziglio, Susan Carpenter et Massimo Pizzato. « S2 from equine infectious anemia virus is an infectivity factor which counteracts the retroviral inhibitors SERINC5 and SERINC3 ». Proceedings of the National Academy of Sciences 113, n^o 46 (1 novembre 2016) : 13197–202. http://dx.doi.org/10.1073/pnas.1612044113.

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The lentivirus equine infectious anemia virus (EIAV) encodes the small protein S2, a pathogenic determinant that is important for virus replication and disease progression in horses. No molecular function had been linked to this accessory protein. We report that S2 can replace the activity of Negative factor (Nef) in HIV-1 infectivity, being required to antagonize the inhibitory activity of Serine incorporator (SERINC) proteins on Nef-defective HIV-1. Like Nef, S2 excludes SERINC5 from virus particles and requires an ExxxLL motif predicted to recruit the clathrin adaptor, Adaptor protein 2 (AP2). Accordingly, functional endocytic machinery is essential for S2-mediated infectivity enhancement, and S2-mediated enhancement is impaired by inhibitors of clathrin-mediated endocytosis. In addition to retargeting SERINC5 to a late endosomal compartment, S2 promotes host factor degradation. Emphasizing the similarity with Nef, we show that S2 is myristoylated, and, as is compatible with a crucial role in posttranslational modification, its N-terminal glycine is required for anti-SERINC5 activity. EIAV-derived vectors devoid of S2 are less susceptible than HIV-1 to the inhibitory effect of both human and equine SERINC5. We then identified the envelope glycoprotein of EIAV as a determinant that also modulates retroviral susceptibility to SERINC5, indicating that EIAV has a bimodal ability to counteract the host factor. S2 shares no sequence homology with other retroviral factors known to counteract SERINC5. Like the primate lentivirus Nef and the gammaretrovirus glycoGag, the accessory protein from EIAV is an example of a retroviral virulence determinant that independently evolved SERINC5-antagonizing activity. SERINC5 therefore plays a critical role in the interaction of the host with diverse retrovirus pathogens.

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Ma, Yulong, Yanhui Cai, Doutong Yu, Yuting Qiao, Haiyun Guo, Zejun Gao et Li Guo. « Astrocytic Glycogen Mobilization in Cerebral Ischemia/Reperfusion Injury ». Neuroscience and Neurological Surgery 11, n^o 3 (21 février 2022) : 01–05. http://dx.doi.org/10.31579/2578-8868/228.

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Glycogen is an important energy reserve in the brain and can be rapidly degraded to maintain metabolic homeostasis during cerebral blood vessel occlusion. Recent studies have pointed out the alterations in glycogen and its underlying mechanism during reperfusion after ischemic stroke. In addition, glycogen metabolism may work as a promising therapeutic target to relieve reperfusion injury. Here, we summarize the progress of glycogen metabolism during reperfusion injury and its corresponding application in patients suffering from ischemic stroke.

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Nanware, Sanjay Shamrao, Habib Mohammed Hasmi et Dhanraj Balbhim Bhure. « Glycogen Content in Moniezia Expansa and its Host Intestine ». Indian Journal of Applied Research 4, n^o 5 (1 octobre 2011) : 651–52. http://dx.doi.org/10.15373/2249555x/may2014/206.

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Kanungo, Shibani, Kimberly Wells, Taylor Tribett et Areeg El-Gharbawy. « Glycogen metabolism and glycogen storage disorders ». Annals of Translational Medicine 6, n^o 24 (décembre 2018) : 474. http://dx.doi.org/10.21037/atm.2018.10.59.

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HORI, Keiichi, Hiroshi NARITA et Masanao SAIO. « A case of glycogen-rich clear cell carcinoma of the breast ». Nihon Rinsho Geka Gakkai Zasshi (Journal of Japan Surgical Association) 69, n^o 9 (2008) : 2173–77. http://dx.doi.org/10.3919/jjsa.69.2173.

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Ragano-Caracciolo, Maria, William K. Berlin, Mill W. Miller et John A. Hanover. « Nuclear Glycogen and Glycogen Synthase Kinase 3 ». Biochemical and Biophysical Research Communications 249, n^o 2 (août 1998) : 422–27. http://dx.doi.org/10.1006/bbrc.1998.9159.

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Frolow, Jason, et C. Louise Milligan. « Hormonal regulation of glycogen metabolism in white muscle slices from rainbow trout (Oncorhynchus mykiss Walbaum) ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 287, n^o 6 (décembre 2004) : R1344—R1353. http://dx.doi.org/10.1152/ajpregu.00532.2003.

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To test the hypothesis that cortisol and epinephrine have direct regulatory roles in muscle glycogen metabolism and to determine what those roles might be, we developed an in vitro white muscle slice preparation from rainbow trout ( Oncorhynchus mykiss Walbaum). In the absence of hormones, glycogen-depleted muscle slices obtained from exercised trout were capable of significant glycogen synthesis, and the amount of glycogen synthesized was inversely correlated with the initial postexercise glycogen content. When postexercise glycogen levels were <5 μmol/g, about 4.3 μmol/g of glycogen were synthesized, but when postexercise glycogen levels were >5 μmol/g, only about 1.7 μmol/g of glycogen was synthesized. This difference in the amount of glycogen synthesized was reflected in the degree of activation of glycogen synthase. Postexercise glycogen content also influenced the response of the muscle to 10−8 M epinephrine and 10−8 M dexamethasone (a glucocorticoid analog). At high glycogen levels (>5 μmol/g), epinephrine and dexamethasone stimulated glycogen phosphorylase activity and net glycogenolysis, whereas at low (<5 μmol/g) glycogen levels, glycogenesis and activation of glycogen synthase activity prevailed. These data clearly indicate not only is trout muscle capable of in situ glycogenesis, but the amount of glycogen synthesized is a function of initial glycogen content. Furthermore, whereas dexamethasone and epinephrine directly stimulate muscle glycogen metabolism, the net effect is dependent on initial glycogen content.

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Ryu, Hojin. « The functional roles of plant glycogen synthase kinase 3 (GSK3) in plant growth and development ». Journal of Plant Biotechnology 42, n^o 1 (31 mars 2015) : 1–5. http://dx.doi.org/10.5010/jpb.2015.42.1.1.

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Coderre, L., A. K. Srivastava et J. L. Chiasson. « Effect of hypercorticism on regulation of skeletal muscle glycogen metabolism by insulin ». American Journal of Physiology-Endocrinology and Metabolism 262, n^o 4 (1 avril 1992) : E427—E433. http://dx.doi.org/10.1152/ajpendo.1992.262.4.e427.

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The effects of hypercorticism on the regulation of glycogen metabolism by insulin in skeletal muscles was examined by using the hindlimb perfusion technique. Rats were injected daily with either saline or dexamethasone (0.4 mg.kg-1.day-1) for 14 days and were studied in the fed or fasted (24 h) state under saline or insulin (1 mU/ml) treatment. In fed controls, insulin resulted in glycogen synthase activation and in enhanced glycogen synthesis. In dexamethasone-treated animals, basal muscle glycogen concentration remained normal, but glycogen synthase activity ratio was decreased in white and red gastrocnemius and plantaris muscles. Furthermore, insulin failed to activate glycogen synthase and glycogen synthesis. In the controls, fasting was associated with decreased glycogen concentrations and with increased glycogen synthase activity ratio in all four groups of muscles (P less than 0.01). Dexamethasone treatment, however, completely abolished the decrease in muscle glycogen content as well as the augmented glycogen synthase activity ratio associated with fasting. Insulin infusion stimulated glycogen synthesis in fasted controls but not in dexamethasone-treated rats. These data therefore indicate that dexamethasone treatment inhibits the stimulatory effect of insulin on glycogen synthase activity and on glycogen synthesis. Furthermore, hypercorticism suppresses the decrease in muscle glycogen content associated with fasting.

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Kuipers, H., D. L. Costill, D. A. Porter, W. J. Fink et W. M. Morse. « Glucose feeding and exercise in trained rats : mechanisms for glycogen sparing ». Journal of Applied Physiology 61, n^o 3 (1 septembre 1986) : 859–63. http://dx.doi.org/10.1152/jappl.1986.61.3.859.

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This investigation studied the effect of an oral glucose feeding on glycogen sparing during exercise in non-glycogen-depleted and glycogen-depleted endurance-trained rats. The non-glycogen-depleted rats received via a stomach tube 2 ml of a 20% glucose solution labeled with [U-14C]glucose just prior to exercise (1 h at 25 m/min). Another group of rats ran for 40 min at higher intensity to deplete glycogen stores, after which they received the same glucose feeding and continued running for 1 h at 25 m/min. The initial 40-min run depleted glycogen in heart, skeletal muscle, and liver. In the non-glycogen-depleted rats the glucose feeding spared glycogen in the liver, primarily from the oxidation of blood-borne glucose in muscle. In the glycogen-depleted rats, muscle glycogen was repleted after the feeding, but sources other than the administered glucose also contributed to glycogen synthesis. The results suggest that glycogen depletion rather than the glucose feeding per se stimulates glycogen resynthesis in muscle during exercise in endurance-trained rats.

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Shockey Breslin, Joanette, et Robert R. Cardell. « Morphometric analysis and autoradiography of the smooth endoplasmic reticulum during glycogen deposition in the fetal mouse hepatocyte ». Proceedings, annual meeting, Electron Microscopy Society of America 48, n^o 3 (12 août 1990) : 544–45. http://dx.doi.org/10.1017/s0424820100160273.

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Analyses of adult hepatic glycogen deposition by numerous investigators have determined that the smooth endoplasmic reticulum (SER) proliferates immediately prior to glycogen deposition and during the early stages of glycogen accumulation, then decreases as glycogen levels reach their maximum, suggesting that SER participates in adult hepatic glycogen metabolism. Less is known regarding fetal hepatic glycogen synthesis and the participation of the fetal SER. The studies described here test the hypothesis that the SER functions in the synthesis of fetal hepatic glycogen. Quantitative analysis of SER and glycogen levels during hepatic glycogen synthesis tests the existence of a correlation between glycogen and SER. Newly deposited labeled glycogen is localized via autoradiography and the extent of association between labeled glycogen and SER quantified, establishing whether glycogen is necessarily deposited near membranes of SER.Fetal mouse livers were harvested at daily intervals between days 14 and 19 of gestation, immersion fixed in 2% glutaraldehyde, 2% paraformaldehyde, post-fixed in 1 % OsO4 dehydrated in EtOH and embedded in Epon 812. Semi-thin (0.5μm) and ultra-thin sections (60 nm) were prepared for morphometric analysis.2

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McNulty, P. H., C. Ng, W. X. Liu, D. Jagasia, G. V. Letsou, J. C. Baldwin et R. Soufer. « Autoregulation of myocardial glycogen concentration during intermittent hypoxia ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 271, n^o 2 (1 août 1996) : R311—R319. http://dx.doi.org/10.1152/ajpregu.1996.271.2.r311.

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During hypoxia, the heart consumes glycogen to generate ATP. Tolerance of repetitive hypoxia logically requires prompt replenishment of glycogen, a process whose regulation is not fully understood. To examine this, we imposed a defined hypoxic stimulus on the rat heart while varying its workload. In intact rats, hypoxia reduced myocardial glycogen approximately 30% and increased both the fraction of glycogen synthase in its physiologically active (GS I) form (from 0.24 +/- 0.06 to 0.82 +/- 0.07; P < 0.005) and glycogen synthesis (from 0.087 +/- 0.011 to 0.375 +/- 0.046 mumol.g-1.min-1; P < 0.005). Reducing cardiac work (with propranolol or heterotopic transplantation) reduced glycogen breakdown, glycogen synthase activation, and glycogen synthesis in parallel, stepwise fashion in intact rats. Correspondingly, hypoxia increased GS I activity in the perfused heart in vitro, but only under conditions where glycogen was consumed. This suggests myocardial glycogen synthase is activated by systemic hypoxia and catalyzes rapid posthypoxic glycogen synthesis. Hypoxic glycogen synthase activation appears to be a proportionate, wholly intrinsic response to local glycogenolysis, operating to preserve myocardial glycogen stores independent of any extracardiac mediator of carbohydrate metabolism.

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FRANCH, Jesper, Rune ASLESEN et Jørgen JENSEN. « Regulation of glycogen synthesis in rat skeletal muscle after glycogen-depleting contractile activity : effects of adrenaline on glycogen synthesis and activation of glycogen synthase and glycogen phosphorylase ». Biochemical Journal 344, n^o 1 (8 novembre 1999) : 231–35. http://dx.doi.org/10.1042/bj3440231.

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We investigated the effects of insulin and adrenaline on the rate of glycogen synthesis in skeletal muscles after electrical stimulation in vitro. The contractile activity decreased the glycogen concentration by 62%. After contractile activity, the glycogen stores were fully replenished at a constant and high rate for 3 h when 10 m-i.u./ml insulin was present. In the absence of insulin, only 65% of the initial glycogen stores was replenished. Adrenaline decreased insulin-stimulated glycogen synthesis. Surprisingly, adrenaline did not inhibit glycogen synthesis stimulated by glycogen-depleting contractile activity. In agreement with this, the fractional activity of glycogen synthase was high when adrenaline was present after exercise, whereas adrenaline decreased the fractional activity of glycogen synthase to a low level during stimulation with insulin. Furthermore, adrenaline activated glycogen phosphorylase almost completely during stimulation with insulin, whereas a much lower activation of glycogen phosphorylase was observed after contractile activity. Thus adrenaline does not inhibit contraction-stimulated glycogen synthesis.

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Talmadge, R. J., et H. Silverman. « Glyconeogenic and glycogenic enzymes in chronically active and normal skeletal muscle ». Journal of Applied Physiology 71, n^o 1 (1 juillet 1991) : 182–91. http://dx.doi.org/10.1152/jappl.1991.71.1.182.

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The chronically active (pseudomyotonic) gastrocnemius muscle in the C57B16J dy2J/dy2J mouse contains both elevated lactate and glycogen as well as fibers that have high amounts of glycogen and enhanced glyconeogenic activity. In the present study we analyze the activities of some key glyconeogenic enzymes to assess the causes of elevated muscle glycogen and to determine the pathway for glycogen synthesis from lactate. Glycogen synthase, malate dehydrogenase, phosphoenolpyruvate carboxykinase, and malic enzyme were all elevated in homogenates of the chronically active muscle. Activities of glycogen phosphorylase and fructose 1,6-bisphosphatase were decreased in whole muscle homogenates. Histochemistry demonstrated that the high-glycogen fibers were typically fast-twitch glycolytic fibers that had high glycogen synthase, glycogen phosphorylase, and malic enzyme activities. Malate dehydrogenase activity followed succinate dehydrogenase activity and did not correlate to high-glycogen fibers. Thus the high-glycogen fibers have an elevated enzymatic capacity for glycogen synthesis from lactate, and the pathway may involve use of the pyruvate kinase bypass enzymes.

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Wilson, Wayne A., Michael P. Boyer, Keri D. Davis, Michael Burke et Peter J. Roach. « The subcellular localization of yeast glycogen synthase is dependent upon glycogen content ». Canadian Journal of Microbiology 56, n^o 5 (mai 2010) : 408–20. http://dx.doi.org/10.1139/w10-027.

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The budding yeast, Saccharomyces cerevisiae , accumulates the storage polysaccharide glycogen in response to nutrient limitation. Glycogen synthase, the major form of which is encoded by the GSY2 gene, catalyzes the key regulated step in glycogen storage. Here, we utilized Gsy2p fusions to green fluorescent protein (GFP) to determine where glycogen synthase was located within cells. We demonstrated that the localization pattern of Gsy2-GFP depended upon the glycogen content of the cell. When glycogen was abundant, Gsy2-GFP was found uniformly throughout the cytoplasm, but under low glycogen conditions, Gsy2-GFP localized to discrete spots within cells. Gsy2p is known to bind to glycogen, and we propose that the subcellular distribution of Gsy2-GFP reflects the distribution of glycogen particles. In the absence of glycogen, Gsy2p translocates into the nucleus. We hypothesize that Gsy2p is normally retained in the cytoplasm through its interaction with glycogen particles. When glycogen levels are reduced, Gsy2p loses this anchor and can traffic into the nucleus.

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Shiose, Keisuke, Yosuke Yamada, Keiko Motonaga et Hideyuki Takahashi. « Muscle glycogen depletion does not alter segmental extracellular and intracellular water distribution measured using bioimpedance spectroscopy ». Journal of Applied Physiology 124, n^o 6 (1 juin 2018) : 1420–25. http://dx.doi.org/10.1152/japplphysiol.00666.2017.

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Although each gram of glycogen is well known to bind 2.7–4.0 g of water, no studies have been conducted on the effect of muscle glycogen depletion on body water distribution. We investigated changes in extracellular and intracellular water (ECW and ICW) distribution in each body segment in muscle glycogen-depletion and glycogen-recovery condition using segmental bioimpedance spectroscopy technique (BIS). Twelve male subjects consumed 7.0 g/kg body mass of indigestible (glycogen-depleted group) or digestible (glycogen-recovered group) carbohydrate for 24 h after a glycogen-depletion cycling exercise. Muscle glycogen content using 13C-magnetic resonance spectroscopy, blood hydration status, body composition, and ECW and ICW content of the arm, trunk, and leg using BIS were measured. Muscle glycogen content at the thigh muscles decreased immediately after exercise (glycogen-depleted group, 71.6 ± 12.1 to 25.5 ± 10.1 mmol/kg wet wt; glycogen-recovered group, 76.2 ± 16.4 to 28.1 ± 16.8 mmol/kg wet wt) and recovered in the glycogen-recovered group (72.7 ± 21.2 mmol/kg wet wt) but not in the glycogen-depleted group (33.2 ± 12.6 mmol/kg wet wt) 24 h postexercise. Fat-free mass decreased in the glycogen-depleted group ( P < 0.05) but not in the glycogen-recovered group 24 h postexercise. However, no changes were observed in ECW and ICW content at the leg in both groups. Our results suggested that glycogen depletion per se does not alter body water distribution as estimated via BIS. This information is valuable in assessing body composition using BIS in athletes who show variable glycogen status during training and recovery. NEW & NOTEWORTHY Segmental bioimpedance spectroscopy analysis reveals the effect of muscle glycogen depletion on body segmental water distribution in controlled conditions. Despite the significant difference in the muscle glycogen levels at the leg, no difference was observed in body resistance and the corresponding water content of the extracellular and intracellular compartments.

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Vardanis, Alexander. « Particulate glycogen of mammalian liver : specificity in binding phosphorylase and glycogen synthase ». Biochemistry and Cell Biology 70, n^o 7 (1 juillet 1992) : 523–27. http://dx.doi.org/10.1139/o92-081.

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The glycogen particle – glycogen metabolizing enzyme complex was investigated to gain some understanding of its physiological significance. Fractionations of populations of particles from mouse liver were carried out utilising open column and high performance liquid chromatography, and based either on the molecular weight of the particles or the hydrophobic interactions of the glycogen-associated proteins. The activities of glycogen phosphorylase and glycogen synthase were measured in these fractions. Fractionations were of tissue in different stages of glycogen deposition or mobilization. In animals fed ad libitum, glycogen synthase was associated with the whole spectrum of molecular weights, while the glycogen phosphorylase distribution was skewed in favour of the lower molecular weight species. Under conditions of glycogen mobilization, the phosphorylase distribution changed to include all molecular weights. The hydrophobic interaction separations demonstrated that glycogen synthase binds to a specific subpopulation of particles that is a minor proportion of the total. In general, there was a direct relationship of the total amount of phosphorylase and synthase bound during periods of mobilization and deposition, respectively. Two notable exceptions were the large amounts of glucose-6-P dependent synthase present during the early period of glycogen mobilization and the high amounts of active phosphorylase appearing shortly after food withdrawal, in spite of interim glycogen deposition from presumably already ingested food.Key words: glycogen particle, glycogenolysis, glycogenesis, glycogen phosphorylase, glycogen synthase.

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Shearer, Jane, et Terry E. Graham. « New Perspectives on the Storage and Organization of Muscle Glycogen ». Canadian Journal of Applied Physiology 27, n^o 2 (1 avril 2002) : 179–203. http://dx.doi.org/10.1139/h02-012.

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Due to its large mass, skeletal muscle contains the largest depot of stored carbohydrate in the body in the form of muscle glycogen. Readily visualized by the electron microscope, glycogen granules appear as bead-like structures localized to specific subcellular locales. Each glycogen granule is a functional unit, not only containing carbohydrate, but also enzymes and other proteins needed for its metabolism. These proteins are not static, but rather associate and dissociate depending on the carbohydrate balance in the muscle. This review examines glycogen-associated proteins, their interactions, and roles in regulating glycogen metabolism. While certain enzymes such as glycogen synthase and glycogen phosphorylase have been extensively studied, other proteins such as the glycogen initiating and targeting proteins are just beginning to be understood. Two metabolically distinct forms of glycogen, pro- and marcoglycogen have been identified that vary in their carbohydrate complement per molecule and have different sensitivities to glycogen synthesis and degradation. Glycogen regulation takes place not only by allosteric regulation of enzymes, but also due to other factors such as subcellular location, granule size, and association with various glycogen-related proteins. Keywords: glycogen-associated proteins, skeletal muscle, carbohydrate metabolism, proglycogen, macroglycogen.

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KÃ¶nig, Helmut, Elisabeth Nusser et Karl O. Stetter. « Glycogen inMethanolobusandMethanococcus ». FEMS Microbiology Letters 28, n^o 3 (juillet 1985) : 265–69. http://dx.doi.org/10.1111/j.1574-6968.1985.tb00803.x.

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Kotoulas, Othon B., Stefanos A. Kalamidas et Dimitrios J. Kondomerkos. « Glycogen autophagy ». Microscopy Research and Technique 64, n^o 1 (2004) : 10–20. http://dx.doi.org/10.1002/jemt.20046.

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Pfeiffer-Guglielmi, Brigitte, et Ralf-Peter Jansen. « The Motor Neuron-Like Cell Line NSC-34 and Its Parent Cell Line N18TG2 Have Glycogen that is Degraded Under Cellular Stress ». Neurochemical Research 46, n^o 6 (30 mars 2021) : 1567–76. http://dx.doi.org/10.1007/s11064-021-03297-y.

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AbstractBrain glycogen has a long and versatile history: Primarily regarded as an evolutionary remnant, it was then thought of as an unspecific emergency fuel store. A dynamic role for glycogen in normal brain function has been proposed later but exclusively attributed to astrocytes, its main storage site. Neuronal glycogen had long been neglected, but came into focus when sensitive technical methods allowed quantification of glycogen at low concentration range and the detection of glycogen metabolizing enzymes in cells and cell lysates. Recently, an active role of neuronal glycogen and even its contribution to neuronal survival could be demonstrated. We used the neuronal cell lines NSC-34 and N18TG2 and could demonstrate that they express the key-enzymes of glycogen metabolism, glycogen phosphorylase and glycogen synthase and contain glycogen which is mobilized on glucose deprivation and elevated potassium concentrations, but not by hormones stimulating cAMP formation. Conditions of metabolic stress, namely hypoxia, oxidative stress and pH lowering, induce glycogen degradation. Our studies revealed that glycogen can contribute to the energy supply of neuronal cell lines in situations of metabolic stress. These findings shed new light on the so far neglected role of neuronal glycogen. The key-enzyme in glycogen degradation is glycogen phosphorylase. Neurons express only the brain isoform of the enzyme that is supposed to be activated primarily by the allosteric activator AMP and less by covalent phosphorylation via the cAMP cascade. Our results indicate that neuronal glycogen is not degraded upon hormone action but by factors lowering the energy charge of the cells directly.

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Jensen, Jørgen, Einar Jebens, Erlend O. Brennesvik, Jérôme Ruzzin, Maria A. Soos, Ellen M. L. Engebretsen, Stephen O'Rahilly et Jonathan P. Whitehead. « Muscle glycogen inharmoniously regulates glycogen synthase activity, glucose uptake, and proximal insulin signaling ». American Journal of Physiology-Endocrinology and Metabolism 290, n^o 1 (janvier 2006) : E154—E162. http://dx.doi.org/10.1152/ajpendo.00330.2005.

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Insulin-stimulated glucose uptake and incorporation of glucose into skeletal muscle glycogen contribute to physiological regulation of blood glucose concentration. In the present study, glucose handling and insulin signaling in isolated rat muscles with low glycogen (LG, 24-h fasting) and high glycogen (HG, refed for 24 h) content were compared with muscles with normal glycogen (NG, rats kept on their normal diet). In LG, basal and insulin-stimulated glycogen synthesis and glycogen synthase activation were higher and glycogen synthase phosphorylation (Ser645, Ser649, Ser653, Ser657) lower than in NG. GLUT4 expression, insulin-stimulated glucose uptake, and PKB phosphorylation were higher in LG than in NG, whereas insulin receptor tyrosyl phosphorylation, insulin receptor substrate-1-associated phosphatidylinositol 3-kinase activity, and GSK-3 phosphorylation were unchanged. Muscles with HG showed lower insulin-stimulated glycogen synthesis and glycogen synthase activation than NG despite similar dephosphorylation. Insulin signaling, glucose uptake, and GLUT4 expression were similar in HG and NG. This discordant regulation of glucose uptake and glycogen synthesis in HG resulted in higher insulin-stimulated glucose 6-phosphate concentration, higher glycolytic flux, and intracellular accumulation of nonphosphorylated 2-deoxyglucose. In conclusion, elevated glycogen synthase activation, glucose uptake, and GLUT4 expression enhance glycogen resynthesis in muscles with low glycogen. High glycogen concentration per se does not impair proximal insulin signaling or glucose uptake. “Insulin resistance” is observed at the level of glycogen synthase, and the reduced glycogen synthesis leads to increased levels of glucose 6-phosphate, glycolytic flux, and accumulation of nonphosphorylated 2-deoxyglucose.

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Napit, Prabhat R., Abdulrahman Alhamyani, Khaggeswar Bheemanapally, Paul W. Sylvester et Karen P. Briski. « Sex-Dimorphic Glucocorticoid Receptor Regulation of Hypothalamic Primary Astrocyte Glycogen Metabolism : Interaction with Norepinephrine ». Neuroglia 3, n^o 4 (17 novembre 2022) : 144–57. http://dx.doi.org/10.3390/neuroglia3040010.

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Astrocyte glycogen is a critical metabolic variable that affects hypothalamic control of glucostasis. Glucocorticoid hormones regulate peripheral glycogen, but their impact on hypothalamic glycogen is not known. A hypothalamic astrocyte primary culture model was used to investigate the premise that glucocorticoids impose sex-dimorphic independent and interactive control of glycogen metabolic enzyme protein expression and glycogen accumulation. The glucocorticoid receptor (GR) agonist dexamethasone (DEX) down-regulated glycogen synthase (GS), glycogen phosphorylase (GP)–brain type (GPbb), and GP–muscle type (GPmm) proteins in glucose-supplied male astrocytes, but enhanced these profiles in female. The catecholamine neurotransmitter norepinephrine (NE) did not alter these proteins, but amplified DEX inhibition of GS and GPbb in male or abolished GR stimulation of GPmm in female. In both sexes, DEX and NE individually increased glycogen content, but DEX attenuated the magnitude of noradrenergic stimulation. Glucoprivation suppressed GS, GPbb, and GPmm in male, but not female astrocytes, and elevated or diminished glycogen in these sexes, respectively. Glucose-deprived astrocytes exhibit GR-dependent induced glycogen accumulation in both sexes, and corresponding loss (male) or attenuation (female) of noradrenergic-dependent glycogen build-up. Current evidence for GR augmentation of hypothalamic astrocyte glycogen content in each sex, yet divergent effects on glycogen enzyme proteins infers that glucocorticoids may elicit opposite adjustments in glycogen turnover in each sex. Results document GR modulation of NE stimulation of glycogen accumulation in the presence (male and female) or absence (female) of glucose. Outcomes provide novel proof that astrocyte energy status influences the magnitude of GR and NE signal effects on glycogen mass.

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Price, Thomas B., Didier Laurent, Kitt F. Petersen, Douglas L. Rothman et Gerald I. Shulman. « Glycogen loading alters muscle glycogen resynthesis after exercise ». Journal of Applied Physiology 88, n^o 2 (1 février 2000) : 698–704. http://dx.doi.org/10.1152/jappl.2000.88.2.698.

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This study compared muscle glycogen recovery after depletion of ∼50 mmol/l (ΔGly) from normal (Nor) resting levels (63.2 ± 2.8 mmol/l) with recovery after depletion of ∼50 mmol/l from a glycogen-loaded (GL) state (99.3 ± 4.0 mmol/l) in 12 healthy, untrained subjects (5 men, 7 women). To glycogen load, a 7-day carbohydrate-loading protocol increased muscle glycogen 1.6 ± 0.2-fold ( P ≤ 0.01). GL subjects then performed plantar flexion (single-leg toe raises) at 50 ± 3% of maximum voluntary contraction (MVC) to yield ΔGly = 48.0 ± 1.3 mmol/l. The Nor trial, performed on a separate occasion, yielded ΔGly = 47.5 ± 4.5 mmol/l. Interleaved natural abundance13C-31P-NMR spectra were acquired and quantified before exercise and during 5 h of recovery immediately after exercise. During the initial 15 min after exercise, glycogen recovery in the GL trial was rapid (32.9 ± 8.9 mmol ⋅ l−1 ⋅ h−1) compared with the Nor trial (15.9 ± 6.9 mmol ⋅ l−1 ⋅ h−1). During the next 45 min, GL glycogen synthesis was not as rapid as in the Nor trial (0.9 ± 2.5 mmol ⋅ l−1 ⋅ h−1for GL; 14.7 ± 3.0 mmol ⋅ l−1 ⋅ h−1for Nor; P ≤ 0.005) despite similar glucose 6-phosphate levels. During extended recovery (60–300 min), reduced GL recovery rates continued (1.3 ± 0.5 mmol ⋅ l−1 ⋅ h−1for GL; 3.9 ± 0.3 mmol ⋅ l−1 ⋅ h−1for Nor; P ≤ 0.001). We conclude that glycogen recovery from heavy exercise is controlled primarily by the remaining postexercise glycogen concentration, with only a transient synthesis period when glycogen levels are not severely reduced.

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Agius, Loranne. « Role of glycogen phosphorylase in liver glycogen metabolism ». Molecular Aspects of Medicine 46 (décembre 2015) : 34–45. http://dx.doi.org/10.1016/j.mam.2015.09.002.

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Contreras, Christopher J., Dyann M. Segvich, Krishna Mahalingan, Vimbai M. Chikwana, Terence L. Kirley, Thomas D. Hurley, Anna A. DePaoli-Roach et Peter J. Roach. « Incorporation of phosphate into glycogen by glycogen synthase ». Archives of Biochemistry and Biophysics 597 (mai 2016) : 21–29. http://dx.doi.org/10.1016/j.abb.2016.03.020.

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Montell, Eulàlia, Alexandra Arias et Anna M. Gómez-Foix. « Glycogen depletion rather than glucose 6-P increments controls early glycogen recovery in human cultured muscle ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 276, n^o 5 (1 mai 1999) : R1489—R1495. http://dx.doi.org/10.1152/ajpregu.1999.276.5.r1489.

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In glycogen-containing muscle, glycogenesis appears to be controlled by glucose 6-phosphate (6- P) provision, but after glycogen depletion, an autoinhibitory control of glycogen could be a determinant. We analyzed in cultured human muscle the contribution of glycogen depletion versus glucose 6- P in the control of glycogen recovery. Acute deglycogenation was achieved by engineering cells to overexpress glycogen phosphorylase (GP). Cells treated with AdCMV-MGP adenovirus to express 10 times higher active GP showed unaltered glycogen relative to controls at 25 mM glucose, but responded to 6-h glucose deprivation with more extensive glycogen depletion. Glycogen synthase (GS) activity ratio was double in glucose-deprived AdCMV-MGP cells compared with controls, despite identical glucose 6- P. The GS activation peak (30 min) induced by glucose reincubation dose dependently correlated with glucose 6- P concentration, which reached similar steady-state levels in both cell types. GS activation was significantly blunted in AdCMV-MGP cells, whereas it strongly correlated, with an inverse relationship, with glycogen content. An initial (0–1 h) rapid insulin-independent glycogen resynthesis was observed only in AdCMV-MGP cells, which progressed up to glycogen levels ∼150 μg glucose/mg protein; control cells, which did not deplete glycogen below this concentration, showed a 1-h lag time for recovery. In summary, acute deglycogenation, as achieved by GP overexpression, caused the activation of GS, which inversely correlated with glycogen replenishment independent of glucose 6- P. During glycogen recovery, the activation promoted by acute deglycogenation rendered GS effective for controlling glycogenesis, whereas the transient activation of GS induced by the glucose 6- P rise had no impact on the resynthesis rate. We conclude that the early insulin-independent glycogen resynthesis is dependent on the activation of GS due to GP-mediated exhaustion of glycogen rather than glucose 6- P provision.

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Allen, Tara J., et Christopher D. Hardin. « Influence of glycogen storage on vascular smooth muscle metabolism ». American Journal of Physiology-Heart and Circulatory Physiology 278, n^o 6 (1 juin 2000) : H1993—H2002. http://dx.doi.org/10.1152/ajpheart.2000.278.6.h1993.

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The role of glycogen as an oxidative substrate for vascular smooth muscle (VSM) remains controversial. To elucidate the importance of glycogen as an oxidative substrate and the influence of glycogen flux on VSM substrate selection, we systematically altered glycogen levels and measured metabolism of glucose, acetate, and glycogen. Hog carotid arteries with glycogen contents ranging from 1 to 11 μmol/g were isometrically contracted in physiological salt solution containing 5 mM [1-13C]glucose and 1 mM [1,2-13C]acetate at 37°C for 6 h. [1-13C]glucose, [1,2-13C]acetate, and glycogen oxidation were simultaneously measured with the use of a 13C-labeled isotopomer analysis of glutamate. Although oxidation of glycogen increased with the glycogen content of the tissue, glycogen oxidation contributed only ∼10% of the substrate oxidized by VSM. Whereas [1-13C]glucose flux, [3-13C]lactate production from [1-13C]glucose, and [1,2-13C]acetate oxidation were not regulated by glycogen content, [1-13C]glucose oxidation was significantly affected by the glycogen content of VSM. However, [1-13C]glucose remained the primary (∼40–50%) contributor to substrate oxidation. Therefore, we conclude that glucose is the predominate substrate oxidized by VSM, and glycogen oxidation contributes minimally to substrate oxidation.

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Henriksen, E. J., C. R. Kirby et M. E. Tischler. « Glycogen supercompensation in rat soleus muscle during recovery from nonweight bearing ». Journal of Applied Physiology 66, n^o 6 (1 juin 1989) : 2782–87. http://dx.doi.org/10.1152/jappl.1989.66.6.2782.

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The time course of glycogen changes in soleus muscle recovering from 3 days of nonweight bearing by hindlimb suspension was investigated. Within 15 min and up to 2 h, muscle glycogen decreased. Coincidentally, muscle glucose 6-phosphate and the fractional activity of glycogen phosphorylase, measured at the fresh muscle concentrations of AMP, increased. Increased fractional activity of glycogen synthase during this time was likely the result of greater glucose 6-phosphate and decreased glycogen. From 2 to 4 h, when the synthase activity remained elevated and the phosphorylase activity declined, glycogen levels increased (glycogen supercompensation). A further increase of glycogen up to 24 h did not correlate with the enzyme activities. Between 24 and 72 h, glycogen decreased to control values, possibly initiated by high phosphorylase activity at 24 h. At 12 and 24 h, the inverse relationship between glycogen concentration and the synthase activity ratio was lost, indicating that reloading transiently uncoupled glycogen control of this enzyme. These data suggest that the activities of glycogen synthase and phosphorylase, when measured at physiological effector levels, likely provide the closest approximation to the actual enzyme activities in vivo. Measurements made in this way effectively explained the majority of the changes in the soleus glycogen content during recovery from nonweight bearing.

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Kolnes, Anders J., Jesper B. Birk, Einar Eilertsen, Jorid T. Stuenæs, Jørgen F. P. Wojtaszewski et Jørgen Jensen. « Epinephrine-stimulated glycogen breakdown activates glycogen synthase and increases insulin-stimulated glucose uptake in epitrochlearis muscles ». American Journal of Physiology-Endocrinology and Metabolism 308, n^o 3 (1 février 2015) : E231—E240. http://dx.doi.org/10.1152/ajpendo.00282.2014.

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Epinephrine increases glycogen synthase (GS) phosphorylation and decreases GS activity but also stimulates glycogen breakdown, and low glycogen content normally activates GS. To test the hypothesis that glycogen content directly regulates GS phosphorylation, glycogen breakdown was stimulated in condition with decreased GS activation. Saline or epinephrine (0.02 mg/100 g rat) was injected subcutaneously in Wistar rats (∼130 g) with low (24-h-fasted), normal (normal diet), and high glycogen content (fasted-refed), and epitrochlearis muscles were removed after 3 h and incubated ex vivo, eliminating epinephrine action. Epinephrine injection reduced glycogen content in epitrochlearis muscles with high (120.7 ± 17.8 vs. 204.6 ± 14.5 mmol/kg, P < 0.01) and normal glycogen (89.5 ± 7.6 vs. 152 ± 8.1 mmol/kg, P < 0.01), but not significantly in muscles with low glycogen (90.0 ± 5.0 vs. 102.8 ± 7.8 mmol/kg, P = 0.17). In saline-injected rats, GS phosphorylation at sites 2+2a, 3a+3b, and 1b was higher and GS activity lower in muscles with high compared with low glycogen. GS sites 2+2a and 3a+3b phosphorylation decreased and GS activity increased in muscles where epinephrine decreased glycogen content; these parameters were unchanged in epitrochlearis from fasted rats where epinephrine injection did not decrease glycogen content. Incubation with insulin decreased GS site 3a+3b phosphorylation independently of glycogen content. Insulin-stimulated glucose uptake was increased in muscles where epinephrine injection decreased glycogen content. In conclusion, epinephrine stimulates glycogenolysis in epitrochlearis muscles with normal and high, but not low, glycogen content. Epinephrine-stimulated glycogenolysis decreased GS phosphorylation and increased GS activity. These data for the first time document direct regulation of GS phosphorylation by glycogen content.

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Ortmeyer, Heidi K., et Noni L. Bodkin. « Lack of defect in insulin action on hepatic glycogen synthase and phosphorylase in insulin-resistant monkeys ». American Journal of Physiology-Gastrointestinal and Liver Physiology 274, n^o 6 (1 juin 1998) : G1005—G1010. http://dx.doi.org/10.1152/ajpgi.1998.274.6.g1005.

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It is well known that an alteration in insulin activation of skeletal muscle glycogen synthase is associated with insulin resistance. To determine whether this defect in insulin action is specific to skeletal muscle, or also present in liver, simultaneous biopsies of these tissues were obtained before and during a euglycemic hyperinsulinemic clamp in spontaneously obese insulin-resistant male rhesus monkeys. The activities of glycogen synthase and glycogen phosphorylase and the concentrations of glucose 6-phosphate and glycogen were measured. There were no differences between basal and insulin-stimulated glycogen synthase and glycogen phosphorylase activities or in glucose 6-phosphate and glycogen contents in muscle. Insulin increased the activities of liver glycogen synthase ( P < 0.05) and decreased the activities of liver glycogen phosphorylase ( P ≤ 0.001). Insulin also caused a reduction in liver glucose 6-phosphate ( P = 0.05). We conclude that insulin-resistant monkeys do not have a defect in insulin action on liver glycogen synthase, although a defect in insulin action on muscle glycogen synthase is present. Therefore, tissue-specific alterations in insulin action on glycogen synthase are present in the development of insulin resistance in rhesus monkeys.

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Lynch, R. M., C. P. Kuettner et R. J. Paul. « Glycogen metabolism during tension generation and maintenance in vascular smooth muscle ». American Journal of Physiology-Cell Physiology 257, n^o 4 (1 octobre 1989) : C736—C742. http://dx.doi.org/10.1152/ajpcell.1989.257.4.c736.

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To study the regulation of glycogen utilization in vascular smooth muscle, we measured the content of glycogen and glucose 6-phosphate and the activity of the glycogen phosphorylase and glycogen debrancher enzymes in porcine carotid artery. During active contraction, the rates of glycogen phosphorylase and glycogenolysis were as high as expected. Despite this, glycogen content did not decrease to less than approximately 50% of control levels even after sustained contractions. The activity of glycogen debrancher enzyme was found to be limiting glycogen utilization at this point. Although glycogenolysis is closely coordinated with increases in oxidative metabolism concomitant with active contraction, the maximal level of tension obtained after stimulation was not substantially reduced under conditions where glycogen debrancher enzyme was limiting glycogen utilization. On the other hand, the rate of tension generation was increased in these tissues. Thus glycogen utilization is not necessary for maximal force generation per se, but may influence other muscle contractile properties. Finally, during steady-state tension maintenance, glycogen utilization is likely to be regulated by the intracellular concentrations of metabolic intermediates (glucose, glucose 6-phosphate), as it is in skeletal muscle.

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Pérez-Torrado, R., J. V. Gimeno-Alcañiz et E. Matallana. « Wine Yeast Strains Engineered for Glycogen Overproduction Display Enhanced Viability under Glucose Deprivation Conditions ». Applied and Environmental Microbiology 68, n^o 7 (juillet 2002) : 3339–44. http://dx.doi.org/10.1128/aem.68.7.3339-3344.2002.

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ABSTRACT We used metabolic engineering to produce wine yeasts with enhanced resistance to glucose deprivation conditions. Glycogen metabolism was genetically modified to overproduce glycogen by increasing the glycogen synthase activity and eliminating glycogen phosphorylase activity. All of the modified strains had a higher glycogen content at the stationary phase, but accumulation was still regulated during growth. Strains lacking GPH1, which encodes glycogen phosphorylase, are unable to mobilize glycogen. Enhanced viability under glucose deprivation conditions occurs when glycogen accumulates in the strain that overexpresses GSY2, which encodes glycogen synthase and maintains normal glycogen phosphorylase activity. This enhanced viability is observed under laboratory growth conditions and under vinification conditions in synthetic and natural musts. Wines obtained from this modified strain and from the parental wild-type strain don't differ significantly in the analyzed enological parameters. The engineered strain might better resist some stages of nutrient depletion during industrial use.

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Udoh, Uduak S., Telisha M. Swain, Ashley N. Filiano, Karen L. Gamble, Martin E. Young et Shannon M. Bailey. « Chronic ethanol consumption disrupts diurnal rhythms of hepatic glycogen metabolism in mice ». American Journal of Physiology-Gastrointestinal and Liver Physiology 308, n^o 11 (1 juin 2015) : G964—G974. http://dx.doi.org/10.1152/ajpgi.00081.2015.

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Chronic ethanol consumption has been shown to significantly decrease hepatic glycogen content; however, the mechanisms responsible for this adverse metabolic effect are unknown. In this study, we examined the impact chronic ethanol consumption has on time-of-day-dependent oscillations (rhythms) in glycogen metabolism processes in the liver. For this, male C57BL/6J mice were fed either a control or ethanol-containing liquid diet for 5 wk, and livers were collected every 4 h for 24 h and analyzed for changes in various genes and proteins involved in hepatic glycogen metabolism. Glycogen displayed a robust diurnal rhythm in the livers of mice fed the control diet, with the peak occurring during the active (dark) period of the day. The diurnal glycogen rhythm was significantly altered in livers of ethanol-fed mice, with the glycogen peak shifted into the inactive (light) period and the overall content of glycogen decreased compared with controls. Chronic ethanol consumption further disrupted diurnal rhythms in gene expression (glycogen synthase 1 and 2, glycogenin, glucokinase, protein targeting to glycogen, and pyruvate kinase), total and phosphorylated glycogen synthase protein, and enzyme activities of glycogen synthase and glycogen phosphorylase, the rate-limiting enzymes of glycogen metabolism. In summary, these results show for the first time that chronic ethanol consumption disrupts diurnal rhythms in hepatic glycogen metabolism at the gene and protein level. Chronic ethanol-induced disruption in these daily rhythms likely contributes to glycogen depletion and disruption of hepatic energy homeostasis, a recognized risk factor in the etiology of alcoholic liver disease.

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Swanson, Raymond A. « Physiologic coupling of glial glycogen metabolism to neuronal activity in brain ». Canadian Journal of Physiology and Pharmacology 70, S1 (15 mai 1992) : S138—S144. http://dx.doi.org/10.1139/y92-255.

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Brain glycogen is localized almost exclusively to glia, where it undergoes continuous utilization and resynthesis. We have shown that glycogen utilization increases during tactile stimulation of the rat face and vibrissae. Conversely, decreased neuronal activity during hibernation and anesthesia is accompanied by a marked increase in brain glycogen content. These observations support a link between neuronal activity and glial glycogen metabolism. The energetics of glycogen metabolism suggest that glial glycogen is mobilized to meet increased metabolic demands of glia rather than to serve as a substrate for neuronal activity. An advantage to the use of glycogen may be the potentially faster generation of ATP from glycogen than from glucose. Alternatively, glycogen could be utilized if glucose supply is transiently insufficient during the onset of increased metabolic activity. Brain glycogen may have a dynamic role as a buffer between the abrupt increases in focal metabolic demands that occur during normal brain activity and the compensatory changes in focal cerebral blood flow or oxidative metabolism.Key words: brain, glia, glycogen, glycolysis, hibernation.

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Roach, Peter J., Anna A. Depaoli-Roach, Thomas D. Hurley et Vincent S. Tagliabracci. « Glycogen and its metabolism : some new developments and old themes ». Biochemical Journal 441, n^o 3 (16 janvier 2012) : 763–87. http://dx.doi.org/10.1042/bj20111416.

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Glycogen is a branched polymer of glucose that acts as a store of energy in times of nutritional sufficiency for utilization in times of need. Its metabolism has been the subject of extensive investigation and much is known about its regulation by hormones such as insulin, glucagon and adrenaline (epinephrine). There has been debate over the relative importance of allosteric compared with covalent control of the key biosynthetic enzyme, glycogen synthase, as well as the relative importance of glucose entry into cells compared with glycogen synthase regulation in determining glycogen accumulation. Significant new developments in eukaryotic glycogen metabolism over the last decade or so include: (i) three-dimensional structures of the biosynthetic enzymes glycogenin and glycogen synthase, with associated implications for mechanism and control; (ii) analyses of several genetically engineered mice with altered glycogen metabolism that shed light on the mechanism of control; (iii) greater appreciation of the spatial aspects of glycogen metabolism, including more focus on the lysosomal degradation of glycogen; and (iv) glycogen phosphorylation and advances in the study of Lafora disease, which is emerging as a glycogen storage disease.

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Saez, Isabel, Jordi Duran, Christopher Sinadinos, Antoni Beltran, Oscar Yanes, María F. Tevy, Carlos Martínez-Pons, Marco Milán et Joan J. Guinovart. « Neurons Have an Active Glycogen Metabolism that Contributes to Tolerance to Hypoxia ». Journal of Cerebral Blood Flow & ; Metabolism 34, n^o 6 (26 février 2014) : 945–55. http://dx.doi.org/10.1038/jcbfm.2014.33.

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Glycogen is present in the brain, where it has been found mainly in glial cells but not in neurons. Therefore, all physiologic roles of brain glycogen have been attributed exclusively to astrocytic glycogen. Working with primary cultured neurons, as well as with genetically modified mice and flies, here we report that—against general belief—neurons contain a low but measurable amount of glycogen. Moreover, we also show that these cells express the brain isoform of glycogen Phosphorylase, allowing glycogen to be fully metabolized. Most importantly, we show an active neuronal glycogen metabolism that protects cultured neurons from hypoxia-induced death and flies from hypoxia-induced stupor. Our findings change the current view of the role of glycogen in the brain and reveal that endogenous neuronal glycogen metabolism participates in the neuronal tolerance to hypoxic stress.

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Huang, D., I. Farkas et P. J. Roach. « Pho85p, a cyclin-dependent protein kinase, and the Snf1p protein kinase act antagonistically to control glycogen accumulation in Saccharomyces cerevisiae. » Molecular and Cellular Biology 16, n^o 8 (août 1996) : 4357–65. http://dx.doi.org/10.1128/mcb.16.8.4357.

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In Saccharomyces cerevisiae, nutrient levels control multiple cellular processes. Cells lacking the SNF1 gene cannot express glucose-repressible genes and do not accumulate the storage polysaccharide glycogen. The impaired glycogen synthesis is due to maintenance of glycogen synthase in a hyperphosphorylated, inactive state. In a screen for second site suppressors of the glycogen storage defect of snf1 cells, we identified a mutant gene that restored glycogen accumulation and which was allelic with PHO85, which encodes a member of the cyclin-dependent kinase family. In cells with disrupted PHO85 genes, we observed hyperaccumulation of glycogen, activation of glycogen synthase, and impaired glycogen synthase kinase activity. In snf1 cells, glycogen synthase kinase activity was elevated. Partial purification of glycogen synthase kinase activity from yeast extracts resulted in the separation of two fractions by phenyl-Sepharose chromatography, both of which phosphorylated and inactivated glycogen synthase. The activity of one of these, GPK2, was inhibited by olomoucine, which potently inhibits cyclin-dependent protein kinases, and contained an approximately 36-kDa species that reacted with antibodies to Pho85p. Analysis of Ser-to-Ala mutations at the three potential Gsy2p phosphorylation sites in pho85 cells implicated Ser-654 and/or Thr-667 in PHO85 control of glycogen synthase. We propose that Pho85p is a physiological glycogen synthase kinase, possibly acting downstream of Snf1p.

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Shearer, Jane, Karen D. Ross, Curtis C. Hughey, Virginia L. Johnsen, Dustin S. Hittel et David L. Severson. « Exercise training does not correct abnormal cardiac glycogen accumulation in the db/db mouse model of type 2 diabetes ». American Journal of Physiology-Endocrinology and Metabolism 301, n^o 1 (juillet 2011) : E31—E39. http://dx.doi.org/10.1152/ajpendo.00525.2010.

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Substrate imbalance is a well-recognized feature of diabetic cardiomyopathy. Insulin resistance effectively limits carbohydrate oxidation, resulting in abnormal cardiac glycogen accumulation. Aims of the present study were to 1) characterize the role of glycogen-associated proteins involved in excessive glycogen accumulation in type 2 diabetic hearts and 2) determine if exercise training can attenuate abnormal cardiac glycogen accumulation. Control ( db+) and genetically diabetic ( db/db) C57BL/KsJ-lepr db/lepr db mice were subjected to sedentary or treadmill exercise regimens. Exercise training consisted of high-intensity/short-duration (10 days) and low-intensity/long-duration (6 wk) protocols. Glycogen levels were elevated by 35–50% in db/db hearts . Exercise training further increased (2- to 3-fold) glycogen levels in db/db hearts. Analysis of soluble and insoluble glycogen pools revealed no differential accumulation of one glycogen subspecies. Phosphorylation (Ser640) of glycogen synthase, an indicator of enzymatic fractional activity, was greater in db/db mice subjected to sedentary and exercise regimens. Elevated glycogen levels were accompanied by decreased phosphorylation (Thr172) of 5′-AMP-activated kinase and phosphorylation (Ser79) of its downstream substrate acetyl-CoA carboxylase. Glycogen concentration was not associated with increases in other glycogen-associated proteins, including malin and laforin. Novel observations show that exercise training does not correct diabetes-induced elevations in cardiac glycogen but, rather, precipitates further accumulation.

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Greenberg, Cynthia C., Arpad M. Danos et Matthew J. Brady. « Central Role for Protein Targeting to Glycogen in the Maintenance of Cellular Glycogen Stores in 3T3-L1 Adipocytes ». Molecular and Cellular Biology 26, n^o 1 (1 janvier 2006) : 334–42. http://dx.doi.org/10.1128/mcb.26.1.334-342.2006.

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ABSTRACT Overexpression of the protein phosphatase 1 (PP1) subunit protein targeting to glycogen (PTG) markedly enhances cellular glycogen levels. In order to disrupt the endogenous PTG-PP1 complex, small interfering RNA (siRNA) constructs against PTG were identified. Infection of 3T3-L1 adipocytes with PTG siRNA adenovirus decreased PTG mRNA and protein levels by >90%. In parallel, PTG reduction resulted in a >85% decrease in glycogen levels 4 days after infection, supporting a critical role for PTG in glycogen metabolism. Total PP1, glycogen synthase, and GLUT4 levels, as well as insulin-stimulated signaling cascades, were unaffected. However, PTG knockdown reduced glycogen-targeted PP1 protein levels, corresponding to decreased cellular glycogen synthase- and phosphorylase-directed PP1 activity. Interestingly, GLUT1 levels and acute insulin-stimulated glycogen synthesis rates were increased two- to threefold, and glycogen synthase activation in the presence of extracellular glucose was maintained. In contrast, glycogenolysis rates were markedly increased, suggesting that PTG primarily acts to suppress glycogen breakdown. Cumulatively, these data indicate that disruption of PTG expression resulted in the uncoupling of PP1 activity from glycogen metabolizing enzymes, the enhancement of glycogenolysis, and a dramatic decrease in cellular glycogen levels. Further, they suggest that reduction of glycogen stores induced cellular compensation by several mechanisms, but ultimately these changes could not overcome the loss of PTG expression.

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McNulty, P. H., A. Darling et J. M. Whiting. « Glycogen depletion contributes to ischemic preconditioning in the rat heart in vivo ». American Journal of Physiology-Heart and Circulatory Physiology 271, n^o 6 (1 décembre 1996) : H2283—H2289. http://dx.doi.org/10.1152/ajpheart.1996.271.6.h2283.

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Ischemic preconditioning depletes the myocardium of glycogen, thus blunting lactic acidosis during subsequent episodes of ischemia. Preconditioning also protects against reperfusion arrhythmias and infarction. To test whether glycogen depletion is necessary for this ischemic tolerance, we preconditioned two groups of intact rats with a series of 3-min coronary artery occlusions. In one group, preconditioning lowered the glycogen concentration of the ischemic region by approximately 50% (24.9 +/- 2.5 to 12.5 +/- 1.8 mumol/g; P < 0.01). In the other, the heart was first loaded with glycogen via glucose-insulin infusion so that preconditioning merely reduced its glycogen concentration back to normal physiological levels. Compared with nonpreconditioned control rats, preconditioned rats with both normal and subnormal glycogen concentrations were protected from reperfusion arrhythmias after a 6-min coronary occlusion (incidence: control rats, 100%; normal glycogen rats, 11%; reduced glycogen rats, 11%). In contrast, only rats with subnormal glycogen concentration after preconditioning exhibited reduced lactate formation and infarct size after a 45-min coronary occlusion [infarct size (percentage of risk area): control rats, 53 +/- 10%; normal glycogen rats, 50 +/- 16%, P = not significant; subnormal glycogen rats, 18 +/- 10%, P < 0.01]. Thus, in the intact rat, myocardial glycogen depletion appears to be necessary for the infarct-limiting, but not for the antiarrhythmic, effects of ischemic preconditioning.

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Nitschke, Silvia, Sara Petković, Saija Ahonen, Berge A. Minassian et Felix Nitschke. « Sensitive quantification of α-glucans in mouse tissues, cell cultures, and human cerebrospinal fluid ». Journal of Biological Chemistry 295, n^o 43 (13 août 2020) : 14698–709. http://dx.doi.org/10.1074/jbc.ra120.015061.

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The soluble α-polyglucan glycogen is a central metabolite enabling transient glucose storage to suit cellular energy needs. Glycogen storage diseases (GSDs) comprise over 15 entities caused by generalized or tissue-specific defects in enzymes of glycogen metabolism. In several, e.g. in Lafora disease caused by the absence of the glycogen phosphatase laforin or its interacting partner malin, degradation-resistant abnormally structured insoluble glycogen accumulates. Sensitive quantification methods for soluble and insoluble glycogen are critical to research, including therapeutic studies, in such diseases. This paper establishes methodological advancements relevant to glycogen metabolism investigations generally, and GSDs. Introducing a pre-extraction incubation method, we measure degradation-resistant glycogen in as little as 30 mg of skeletal muscle or a single hippocampus from Lafora disease mouse models. The digestion-resistant glycogen correlates with the disease-pathogenic insoluble glycogen and can readily be detected in very young mice where glycogen accumulation has just begun. Second, we establish a high-sensitivity glucose assay with detection of ATP depletion, enabling 1) quantification of α-glucans in cell culture using a medium-throughput assay suitable for assessment of candidate glycogen synthesis inhibitors, and 2) discovery of α-glucan material in healthy human cerebrospinal fluid, establishing a novel methodological platform for biomarker analyses in Lafora disease and other GSDs.

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Shiose, Keisuke, Hideyuki Takahashi et Yosuke Yamada. « Muscle Glycogen Assessment and Relationship with Body Hydration Status : A Narrative Review ». Nutrients 15, n^o 1 (29 décembre 2022) : 155. http://dx.doi.org/10.3390/nu15010155.

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Muscle glycogen is a crucial energy source for exercise, and assessment of muscle glycogen storage contributes to the adequate manipulation of muscle glycogen levels in athletes before and after training and competition. Muscle biopsy is the traditional and gold standard method for measuring muscle glycogen; alternatively, 13C magnetic resonance spectroscopy (MRS) has been developed as a reliable and non-invasive method. Furthermore, outcomes of ultrasound and bioimpedance methods have been reported to change in association with muscle glycogen conditions. The physiological mechanisms underlying this activity are assumed to involve a change in water content bound to glycogen; however, the relationship between body water and stored muscle glycogen is inconclusive. In this review, we discuss currently available muscle glycogen assessment methods, focusing on 13C MRS. In addition, we consider the involvement of muscle glycogen in changes in body water content and discuss the feasibility of ultrasound and bioimpedance outcomes as indicators of muscle glycogen levels. In relation to changes in body water content associated with muscle glycogen, this review broadens the discussion on changes in body weight and body components other than body water, including fat, during carbohydrate loading. From these discussions, we highlight practical issues regarding muscle glycogen assessment and manipulation in the sports field.

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Youn, J. H., et R. N. Bergman. « Patterns of glycogen turnover in liver characterized by computer modeling ». American Journal of Physiology-Endocrinology and Metabolism 253, n^o 4 (1 octobre 1987) : E360—E369. http://dx.doi.org/10.1152/ajpendo.1987.253.4.e360.

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We used a computer model of liver glycogen turnover to reexamine the data of Devos and Hers, who reported the time course of accumulation in and loss from glycogen of label originating in [1-14C]galactose injected at different times after the start of refeeding of 40-h fasted mice or rats. In the present study computer representation of individual glycogen molecules was utilized to account for growth and degradation of glycogen according to specific hypothetical patterns. Using this model we could predict the accumulation and localization within glycogen of labeled glucose residues and compare the predictions with the previously published data. We considered three specific hypotheses of glycogen accumulation during refeeding: 1) simultaneous, 2) sequential, and 3) accelerating growth. Hypothetical patterns of glycogen degradation were 1) ordered and 2) random degradation. The pattern of glycogen synthesis consistent with experimental data was a steadily increasing number of growing glycogen molecules, whereas during degradation glycogen molecules are exposed to degrading enzymes randomly, rather than in a specific reverse order of synthesis. These patterns predict the existence of a specific mechanism for the steadily increasing "seeding" of new glycogen molecules during synthesis.

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