Brain glycogen serves as a critical glucosamine cache required for protein glycosylation.

Glycosylation defects are a hallmark of many nervous system diseases. However, the molecular and metabolic basis for this pathology is not fully understood. In this study, we found that N-linked protein glycosylation in the brain is metabolically channeled to glucosamine metabolism through glycogenolysis. We discovered that glucosamine is an abundant constituent of brain glycogen, which functions as a glucosamine reservoir for multiple glycoconjugates. We demonstrated the enzymatic incorporation of glucosamine into glycogen by glycogen synthase, and the release by glycogen phosphorylase by biochemical and structural methodologies, in primary astrocytes, and in vivo by isotopic tracing and mass spectrometry. Using two mouse models of glycogen storage diseases, we showed that disruption of brain glycogen metabolism causes global decreases in free pools of UDP-N-acetylglucosamine and N-linked protein glycosylation. These findings revealed fundamental biological roles of brain glycogen in protein glycosylation with direct relevance to multiple human diseases of the central nervous system.

Genetic loss of AMPK-glycogen binding destabilises AMPK and disrupts metabolism.

OBJECTIVE: Glycogen is a major energy reserve in liver and skeletal muscle. The master metabolic regulator AMP-activated protein kinase (AMPK) associates with glycogen via its regulatory ß subunit carbohydrate-binding module (CBM). However, the physiological role of AMPK-glycogen binding in energy homeostasis has not been investigated in vivo. This study aimed to determine the physiological consequences of disrupting AMPK-glycogen interactions. METHODS: Glycogen binding was disrupted in mice via whole-body knock-in (KI) mutation of either the AMPK ß1 (W100A) or ß2 (W98A) isoform CBM. Systematic whole-body, tissue and molecular phenotyping was performed in KI and respective wild-type (WT) mice. RESULTS: While ß1 W100A KI did not affect whole-body metabolism or exercise capacity, ß2 W98A KI mice displayed increased adiposity and impairments in whole-body glucose handling and maximal exercise capacity relative to WT. These KI mutations resulted in reduced total AMPK protein and kinase activity in liver and skeletal muscle of ß1 W100A and ß2 W98A, respectively, versus WT mice. ß1 W100A mice also displayed loss of fasting-induced liver AMPK total and α-specific kinase activation relative to WT. Destabilisation of AMPK was associated with increased fat deposition in ß1 W100A liver and ß2 W98A skeletal muscle versus WT. CONCLUSIONS: These results demonstrate that glycogen binding plays critical roles in stabilising AMPK and maintaining cellular, tissue and whole-body energy homeostasis.

Indirect Assessment of Skeletal Muscle Glycogen Content in Professional Soccer Players before and after a Match through a Non-Invasive Ultrasound Technology.

Skeletal muscle glycogen (SMG) stores in highly glycolytic activities regulate muscle contraction by controlling calcium release and uptake from sarcoplasmic reticulum, which could affect muscle contraction. Historically, the assessment of SMG was performed through invasive and non-practical muscle biopsies. In this study we have utilized a novel methodology to assess SMG through a non-invasive high-frequency ultrasound. Nine MLS professional soccer players (180.4 ± 5.9 cm; 72.4 ± 9.3 kg; 10.4% ± 0.7% body fat) participated. All followed the nutritional protocol 24 h before the official match as well as performing the same practice program the entire week leading to the match. The SMG decreased from 80 ± 8.6 to 63.9 ± 10.2; p = 0.005 on MuscleSound® score (0-100) representing a 20% ± 10.4% decrease in muscle glycogen after match. Inter-individual differences in both starting glycogen content (65-90) and in percentage decrease in glycogen after the match (between 6.2% and 44.5%). Some players may not start the match with adequate SMG while others' SMG decreased significantly throughout the game. Adequate pre-match SMG should be achieved during half-time and game-play in order to mitigate the decrease in glycogen. Further and more ample studies are needed before the application of this technology.

A thermodynamic function of glycogen in brain and muscle.

Brain and muscle glycogen are generally thought to function as local glucose reserves, for use during transient mismatches between glucose supply and demand. However, quantitative measures show that glucose supply is likely never rate-limiting for energy metabolism in either brain or muscle under physiological conditions. These tissues nevertheless do utilize glycogen during increased energy demand, despite the availability of free glucose, and despite the ATP cost of cycling glucose through glycogen polymer. This seemingly wasteful process can be explained by considering the effect of glycogenolysis on the amount of energy obtained from ATP (ΔG'ATP). The amount of energy obtained from ATP is reduced by elevations in inorganic phosphate (Pi). Glycogen utilization sequesters Pi in the glycogen phosphorylase reaction and in downstream phosphorylated glycolytic intermediates, thereby buffering Pi elevations and maximizing energy yield at sites of rapid ATP consumption. This thermodynamic effect of glycogen may be particularly important in the narrow, spatially constrained astrocyte processes that ensheath neuronal synapses and in cells such as astrocytes and myocytes that release Pi from phosphocreatine during energy demand. The thermodynamic effect may also explain glycolytic super-compensation in brain when glycogen is not available, and aspects of exercise physiology in muscle glycogen phosphorylase deficiency (McArdle disease).

Individualized Breakfast Programs or Glycogen Super-Compensation: Which Is the Better Performing Strategy? Insights from an Italian Soccer Referees Cohort.

The role of soccer referees has grown in importance in the last decades, as has attention to their performance, which may be influenced and improved with specific and evolved training programs. Today, multiple specialists are working as a team in order to develop effective training programs. Moreover, for athletes, it is becoming more and more important to be attentive to nutrition. By considering such items, in this study, we aimed to investigate the nutritional habits of a group of referees belonging to the Italian Soccer Referees' Association (on behalf of AIA-FIGC). Our main aim was to spread a "culture of nutrition" in refereeing, starting with a survey on referees' breakfast attitudes and in order to disseminate such a "culture", we chose top-level elite referees who were younger subjects (despite the average 4 years' experience). Therefore, we enrolled 31 subjects (aged 22.74 ± 1.79, BMI 22.30 ± 1.53) and asked them about their breakfast habits. Then, for measuring their performance, we used the conventional fitness test named Yo-Yo (YYiR1), performed in three different sessions (test 1, test 2, test 3). Test 1 was carried out without any nutritional indications, test 2 was given after individualized breakfast suggestions by a designed dietician, and test 3 after an individualized glycogen super-compensation strategy. The Wilcoxon statistical analysis indicates that following an individualized breakfast strategy may enhance referees' performance (p < 0.0001), whereas no significant effects were observed with the glycogen super-compensation option. However, further studies will be necessary to better address this topic and clarify whether high-carbohydrates (high-CHO) intake may be useful in other sports.

Glycogen in Astrocytes and Neurons: Physiological and Pathological Aspects.

Brain glycogen is stored mainly in astrocytes, although neurons also have an active glycogen metabolism. Glycogen has gained relevance as a key player in brain function. In this regard, genetically modified animals have allowed researchers to unravel new roles of this polysaccharide in the brain. Remarkably, mice in which glycogen synthase is abolished in the brain, and thus devoid of brain glycogen, are viable, thereby indicating that the polysaccharide in this organ is not a requirement for survival. While there was growing evidence supporting a role of glycogen in learning and memory, these animals have now confirmed that glycogen participates in these two processes.The association of epilepsy with brain glycogen has also attracted attention. Analysis of genetically modified mice indicates that the relation between brain glycogen and epilepsy is complex. While the formation of glycogen aggregates clearly underlies epilepsy, as in Lafora Disease (LD), the absence of glycogen also favors the occurrence of seizures.LD is a rare genetic condition that affects children. It is characterized by epileptic seizures and neurodegeneration, and it develops rapidly until finally causing death. Research into this disease has unveiled new aspects of glycogen metabolism. Animal models of LD accumulate polyglucosan bodies formed by aberrant glycogen aggregates, called Lafora bodies (LBs). The abolition of glycogen synthase (GS) prevents the formation of LBs and the development of LD, thereby indicating that glycogen accumulation underlies this disease and the associated symptoms, and thus establishing a clear relation between the accumulation of glycogen aggregates and the incidence of seizures.Although it was initially accepted that LBs were essentially neuronal, it is now evident that astrocytes also accumulate polyglucosan aggregates in LD. However, the appearance and composition of these deposits differs from that observed in neurons. Of note, the astrocytic aggregates in LD models show remarkable similarities with corpora amylacea (CA), a type of polyglucosan aggregate observed in the brains of aged mice and humans. The abolition of GS in mice also impedes the formation of CA with age and at the same time prevents the formation of a number of protein aggregates associated with aging. Therefore CA may play a role in age-related neurological decline.

Contemporary Nutrition Interventions to Optimize Performance in Middle-Distance Runners.

Middle-distance runners utilize the full continuum of energy systems throughout training, and given the infinite competition tactical scenarios, this event group is highly complex from a performance intervention point of view. However, this complexity results in numerous potential periodized nutrition interventions to optimize middle-distance training adaptation and competition performance. Middle-distance race intensity is extreme, with 800- to 5,000-m races being at ∼95% to 130% of VO2max. Accordingly, elite middle-distance runners have primarily Type IIa/IIx fiber morphology and rely almost exclusively on carbohydrate (primarily muscle glycogen) metabolic pathways for producing adenosine triphosphate. Consequently, the principle nutritional interventions that should be emphasized are those that optimize muscle glycogen contents to support high glycolytic flux (resulting in very high lactate values, of >20 mmol/L in some athletes) with appropriate buffering capabilities, while optimizing power to weight ratios, all in a macro- and microperiodized manner. From youth to elite level, middle-distance athletes have arduous racing schedules (10-25 races/year), coupled with excessive global travel, which can take a physical and emotional toll. Accordingly, proactive and integrated nutrition planning can have a profound recovery effect over a long race season, as well as optimizing recovery during rounds of championship racing. Finally, with evidence-based implementation and an appropriate risk/reward assessment, several ergogenic aids may have an adaptive and/or performance-enhancing effect in the middle-distance athlete. Given that elite middle-distance athletes undertake ∼400 to 800 training sessions with 10-25 races/year, there are countless opportunities to implement various periodized acute and chronic nutrition-based interventions to optimize performance.

The dynamic life of the glycogen granule.

Glycogen, the primary storage form of glucose, is a rapid and accessible form of energy that can be supplied to tissues on demand. Each glycogen granule, or "glycosome," is considered an independent metabolic unit composed of a highly branched polysaccharide and various proteins involved in its metabolism. In this Minireview, we review the literature to follow the dynamic life of a glycogen granule in a multicompartmentalized system, i.e. the cell, and how and where glycogen granules appear and the factors governing its degradation. A better understanding of the importance of cellular compartmentalization as a regulator of glycogen metabolism is needed to unravel its role in brain energetics.

Histochemical and immunohistochemical examination of odontoblasts (petroblasts) in petrodentine formation of lungfish.

OBJECTIVE: Petrodentine, the core of the lungfish tooth plate, is a well-mineralized tissue similar to mammalian enamel and analogous to enameloid in fish teeth. Petrodentine is formed solely by petroblasts, which are specialized odontoblasts, whereas enameloid is a composite tissue produced by both odontoblasts and dental epithelial cells. To clarify the details of petrodentine formation, petroblasts were investigated using histochemical and immunohistochemical techniques. METHODS: Extant lungfish (Lepidosiren paradoxa) were used in this study. Tooth plates during the stage of petrodentine formation were observed by means of histochemistry and immunohistochemistry. Commercial kits were used to detect enzyme activity. Correlative sections were immunostained using antibodies against selected peptides. Routine staining such as periodic acid-Schiff (PAS) reaction to identify glycogen and Elastica van Gieson staining for the detection of elastic fibers in histological sections were performed. In addition, conventional transmission electron microscopy was used for observing the fine structure. RESULTS: Petroblasts showed marked acid and alkaline phosphatase activities, and positive immunoreactivities against anti-nestin, anti-V-ATPase, and anti-Ca2+-ATPase, during the maturation stage, but in the matrix formation stage, reactions were much weaker than that of the maturation stage. During the maturation stage, petroblasts showed intense PAS reactivity, and glycogen particles were observed in petroblasts by transmission electron microscopy. Glucose transporter 1-immunoreactivity was observed in petroblasts in the matrix formation stage and the initial to mid part of the maturation stage. CONCLUSIONS: The results in this study suggested that petroblasts have two functional stages, matrix formation and maturation, and glycogen plays an important role in the modulation of petroblasts.

Single Muscle Fiber Proteomics Reveals Fiber-Type-Specific Features of Human Muscle Aging.

Skeletal muscle is a key tissue in human aging, which affects different muscle fiber types unequally. We developed a highly sensitive single muscle fiber proteomics workflow to study human aging and show that the senescence of slow and fast muscle fibers is characterized by diverging metabolic and protein quality control adaptations. Whereas mitochondrial content declines with aging in both fiber types, glycolysis and glycogen metabolism are upregulated in slow but downregulated in fast muscle fibers. Aging mitochondria decrease expression of the redox enzyme monoamine oxidase A. Slow fibers upregulate a subset of actin and myosin chaperones, whereas an opposite change happens in fast fibers. These changes in metabolism and sarcomere quality control may be related to the ability of slow, but not fast, muscle fibers to maintain their mass during aging. We conclude that single muscle fiber analysis by proteomics can elucidate pathophysiology in a sub-type-specific manner.

Survival, physical and physiological changes of Taenia hydatigena eggs under different conditions of water stress.

Taenia hydatigena eggs were investigated for morphological and physiological changes under water stress conditions. Fresh eggs were exposed at 31%, 47% and 89% of relative humidity (RH), and survival, size and ultrastructural changes were accounted up to 365 days of exposition. The article shows how each RH environment affects the vitality of the eggs. Results of this study suggest that T. hydatigena eggs have mechanisms to withstand water stress, indicating that the eggs clustering improves protection against desiccation, and that endogenous metabolism using triacylglycerols play an important role in the maintenance of embryo vitality under low, medium and high relative humidity conditions. This contributes to understanding the water stress resistance mechanism in eggs belonging to Taeniidae family. The findings shown herein have provided a basis to better comprehend basic biology and epidemiology of the cysticercosis caused by T. hydatigena.

Glycogen: Multiple Roles in the CNS.

The historically neurocentric view of astrocytes as Styrofoam cushioning that rigidly clad neurons within the brain parenchyma has been superseded in the past 30 years by an increasing appreciation of the myriad roles astrocytes contribute to supporting physiological brain function. It is widely recognized that the continuous support provided by astrocytes, from prenatal development to maturity, is vital for neuronal function. Indeed, the numerous and diverse roles furnished by astrocytes contrasts with the vital but restricted transmission of action potentials that is the neuron's primary role. An emerging role for astrocytes is that of providing energy substrate in the form of glycogen-derived lactate to neurons. This role was established during periods of limited glucose availability but has been extended to encompass one of the most important physiological brain functions, learning and memory. In this context glycogen metabolism is integral to the consolidation of learning into long-term retention of memories, a process vital to the higher functioning of the human brain.

Genetic models rule out a major role of beta cell glycogen in the control of glucose homeostasis.

AIMS/HYPOTHESIS: Glycogen accumulation occurs in beta cells of diabetic patients and has been proposed to partly mediate glucotoxicity-induced beta cell dysfunction. However, the role of glycogen metabolism in beta cell function and its contribution to diabetes pathophysiology remain poorly understood. We investigated the function of beta cell glycogen by studying glucose homeostasis in mice with (1) defective glycogen synthesis in the pancreas; and (2) excessive glycogen accumulation in beta cells. METHODS: Conditional deletion of the Gys1 gene and overexpression of protein targeting to glycogen (PTG) was accomplished by Cre-lox recombination using pancreas-specific Cre lines. Glucose homeostasis was assessed by determining fasting glycaemia, insulinaemia and glucose tolerance. Beta cell mass was determined by morphometry. Glycogen was detected histologically by periodic acid-Schiff's reagent staining. Isolated islets were used for the determination of glycogen and insulin content, insulin secretion, immunoblots and gene expression assays. RESULTS: Gys1 knockout (Gys1 (KO)) mice did not exhibit differences in glucose tolerance or basal glycaemia and insulinaemia relative to controls. Insulin secretion and gene expression in isolated islets was also indistinguishable between Gys1 (KO) and controls. Conversely, despite effective glycogen overaccumulation in islets, mice with PTG overexpression (PTG(OE)) presented similar glucose tolerance to controls. However, under fasting conditions they exhibited lower glycaemia and higher insulinaemia. Importantly, neither young nor aged PTG(OE) mice showed differences in beta cell mass relative to age-matched controls. Finally, a high-fat diet did not reveal a beta cell-autonomous phenotype in either model. CONCLUSIONS/INTERPRETATION: Glycogen metabolism is not required for the maintenance of beta cell function. Glycogen accumulation in beta cells alone is not sufficient to trigger the dysfunction or loss of these cells, or progression to diabetes.

Rat skeletal muscle glycogen degradation pathways reveal differential association of glycogen-related proteins with glycogen granules

Glycogenin, glycogen-debranching enzyme (GDE) and glycogen phosphorylase (GP) are important enzymes that contribute to glycogen particle metabolism. In Long-Evans Hooded rat whole muscle homogenates prepared from extensor digitorum longus (EDL, fast-twitch) and soleus (SOL, oxidative, predominantly slow twitch), it was necessary to include alfa-amylase, which releases glucosyl units from glycogen, to detect glycogenin but not GDE or GP. Up to ∼12 % of intramuscular glycogen pool was broken down using either in vitro electrical stimulation or leaving muscle at room temperature >3 h (delayed, post-mortem). Electrical stimulation did not reveal glycogenin unless alfa-amylase was added, although in post-mortem muscle ∼50 and ∼30 % of glycogenin in EDL and SOL muscles, respectively, was detected compared to the amount detected with alfa-amylase treatment. Single muscle fibres were dissected from fresh or post-mortem EDL muscles, mechanically skinned to remove surface membrane and the presence of glycogenin, GDE and GP as freely diffusible proteins (i.e. cytoplasmic localization) compared by Western blotting. Diffusibility of glycogenin (∼20 %) and GP (∼60 %) was not different between muscles, although GDE increased from ∼15 % diffusible in fresh muscle to ∼60 % in post-mortem muscle. Under physiologically relevant circumstances, in rat muscle and within detection limits: (1) The total cellular pool of glycogenin is always associated with glycogen granules, (2) GDE is associated with glycogen granules with over half the total pool associated with the outer tiers of glycogen, (3) GP is only ever weakly associated with glycogen granules and (4) addition of alfa-amylase is necessary in order to detect glycogenin, but not GDE or GP

ACTN3 genotype and modulation of skeletal muscle response to exercise in human subjects.

α-Actinin-3 is a Z-disc protein expressed only in type II muscle fibers. A polymorphism in the ACTN3 gene (R577X) results in lack of α-actinin-3 in XX genotype. The prevalence of the mutated X-allele is lower among power/sprint oriented athletes compared with controls, indicating that the lack of α-actinin-3 is detrimental in these sports, but a mechanistic link has not been established. Results from Actn3-knockout (KO) mouse model suggest that α-actinin-3 may affect muscle mass and muscle glycogen levels. In the present investigation we examined muscle fiber type composition, cross-sectional fiber area (CSA), and muscle glycogen levels at baseline in 143 human subjects with different ACTN3 genotypes. In addition, hypertrophy signaling and glycogen utilization in response to sprint exercise were studied in a subset of subjects. Glycogen utilization was analyzed in separate pools of type I and type II fibers. No differences in fiber type composition, CSA, or muscle glycogen levels were observed at baseline across the ACTN3 genotypes. However, the sprint exercise-induced increase in phosphorylation of mTOR and p70S6k was smaller in XX than in RR+RX (P = 0.03 and P = 0.01, respectively), indicating a less pronounced activation of hypertrophy signaling in XX. Glycogen utilization during sprint exercise varied across ACTN3 genotypes in type II fibers (P = 0.03) but not in type I fibers (P = 0.38). The present results are in accordance with findings from the KO mice and reinforce the hypothesis that ACTN3 genotype-associated differences in muscle mass and glycogen utilization provide a mechanistic explanation for the modulation of human performance by the ACTN3 genotype.

Do skeletal muscle properties recover following repeat onabotulinum toxin A injections?

Onabotulinum toxin A (BTX-A) is a frequently used treatment modality to relax spastic muscles by preventing acetylcholine release at the motor nerve endings. Although considered safe, previous studies have shown that BTX-A injections cause muscle atrophy and deterioration in target and non-target muscles. Ideally, muscles should fully recover following BTX-A treatments, so that muscle strength and performance are not affected in the long-term. However, systematic, long-term data on the recovery of muscles exposed to BTX-A treatments are not available, thus practice guidelines on the frequency and duration of BTX-A injections, and associated recovery protocols, are based on clinical experience with little evidence-based information. Therefore, the purpose of this study was to investigate muscle recovery following a six months, monthly BTX-A injection (3.5 U/kg) protocol. Twenty seven skeletally mature NZW rabbits were divided into 5 groups: Control (n=5), zero month recovery - BTX-A+0M (n=5), one month recovery - BTX-A+1M (n=5), three months recovery - BTX-A+3M (n=5), and six months recovery - BTX-A+6M (n=7). Knee extensor strength, muscle mass and percent contractile material in injected and contralateral non-injected muscles was measured at each point of recovery. Strength and muscle mass were partially and completely recovered in injected and contralateral non-injected muscles for BTX-A+6M group animals, respectively. The percent of contractile material partially recovered in the injected, but did not recover in the contralateral non-injected muscles. We conclude from these results that neither target nor non-target muscles fully recover within six months of a BTX-A treatment protocol and that clinical studies on muscle recovery should be pursued.

Recovery in soccer : part ii-recovery strategies.

In the formerly published part I of this two-part review, we examined fatigue after soccer matchplay and recovery kinetics of physical performance, and cognitive, subjective and biological markers. To reduce the magnitude of fatigue and to accelerate the time to fully recover after completion, several recovery strategies are now used in professional soccer teams. During congested fixture schedules, recovery strategies are highly required to alleviate post-match fatigue, and then to regain performance faster and reduce the risk of injury. Fatigue following competition is multifactorial and mainly related to dehydration, glycogen depletion, muscle damage and mental fatigue. Recovery strategies should consequently be targeted against the major causes of fatigue. Strategies reviewed in part II of this article were nutritional intake, cold water immersion, sleeping, active recovery, stretching, compression garments, massage and electrical stimulation. Some strategies such as hydration, diet and sleep are effective in their ability to counteract the fatigue mechanisms. Providing milk drinks to players at the end of competition and a meal containing high-glycaemic index carbohydrate and protein within the hour following the match are effective in replenishing substrate stores and optimizing muscle-damage repair. Sleep is an essential part of recovery management. Sleep disturbance after a match is common and can negatively impact on the recovery process. Cold water immersion is effective during acute periods of match congestion in order to regain performance levels faster and repress the acute inflammatory process. Scientific evidence for other strategies reviewed in their ability to accelerate the return to the initial level of performance is still lacking. These include active recovery, stretching, compression garments, massage and electrical stimulation. While this does not mean that these strategies do not aid the recovery process, the protocols implemented up until now do not significantly accelerate the return to initial levels of performance in comparison with a control condition. In conclusion, scientific evidence to support the use of strategies commonly used during recovery is lacking. Additional research is required in this area in order to help practitioners establish an efficient recovery protocol immediately after matchplay, but also for the following days. Future studies could focus on the chronic effects of recovery strategies, on combinations of recovery protocols and on the effects of recovery strategies inducing an anti-inflammatory or a pro-inflammatory response.

More than a store: regulatory roles for glycogen in skeletal muscle adaptation to exercise.

The glycogen content of muscle determines not only our capacity for exercise but also the signaling events that occur in response to exercise. The result of the shift in signaling is that frequent training in a low-glycogen state results in improved fat oxidation during steady-state submaximal exercise. This review will discuss how the amount or localization of glycogen particles can directly or indirectly result in this differential response to training. The key direct effect discussed is carbohydrate binding, whereas the indirect effects include the metabolic shift toward fat oxidation, the increase in catecholamines, and osmotic stress. Although our understanding of the role of glycogen in response to training has expanded exponentially over the past 5 years, there are still many questions remaining as to how stored carbohydrate affects the muscular adaptation to exercise.

Glycogen and its metabolism: some new developments and old themes.

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.