Exercise capacity of mice genetically lacking muscle glycogen synthase: in mice, muscle glycogen is not essential for exercise.
ABSTRACT The glucose storage polymer glycogen is generally considered to be an important source of energy for skeletal muscle contraction and a factor in exercise endurance. A genetically modified mouse model lacking muscle glycogen was used to examine whether the absence of the polysaccharide affects the ability of mice to run on a treadmill. The MGSKO mouse has the GYS1 gene, encoding the muscle isoform of glycogen synthase, disrupted so that skeletal muscle totally lacks glycogen. The morphology of the soleus and quadriceps muscles from MGSKO mice appeared normal. MGSKO-null mice, along with wild type littermates, were exercised to exhaustion. There were no significant differences in the work performed by MGSKO mice as compared with their wild type littermates. The amount of liver glycogen consumed during exercise was similar for MGSKO and wild type animals. Fasting reduced exercise endurance, and after overnight fasting, there was a trend to reduced exercise endurance for the MGSKO mice. These studies provide genetic evidence that in mice muscle glycogen is not essential for strenuous exercise and has relatively little effect on endurance.
Article: Creatine supplementation spares muscle glycogen during high intensity intermittent exercise in rats.[show abstract] [hide abstract]
ABSTRACT: The effects of creatine (CR) supplementation on glycogen content are still debatable. Thus, due to the current lack of clarity, we investigated the effects of CR supplementation on muscle glycogen content after high intensity intermittent exercise in rats. First, the animals were submitted to a high intensity intermittent maximal swimming exercise protocol to ensure that CR-supplementation was able to delay fatigue (experiment 1). Then, the CR-mediated glycogen sparing effect was examined using a high intensity intermittent sub-maximal exercise test (fixed number of bouts; six bouts of 30-second duration interspersed by two-minute rest interval) (experiment 2). For both experiments, male Wistar rats were given either CR supplementation or placebo (Pl) for 5 days. As expected, CR-supplemented animals were able to exercise for a significant higher number of bouts than Pl. Experiment 2 revealed a higher gastrocnemius glycogen content for the CR vs. the Pl group (33.59%). Additionally, CR animals presented lower blood lactate concentrations throughout the intermittent exercise bouts compared to Pl. No difference was found between groups in soleus glycogen content. The major finding of this study is that CR supplementation was able to spare muscle glycogen during a high intensity intermittent exercise in rats.Journal of the International Society of Sports Nutrition 01/2010; 7(1):6. · 1.64 Impact Factor
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ABSTRACT: Lafora disease is the most common teenage-onset neurodegenerative disease, the main teenage-onset form of progressive myoclonus epilepsy (PME), and one of the severest epilepsies. Pathologically, a starch-like compound, polyglucosan, accumulates in neuronal cell bodies and overtakes neuronal small processes, mainly dendrites. Polyglucosan formation is catalyzed by glycogen synthase, which is activated through dephosphorylation by glycogen-associated protein phosphatase-1 (PP1). Here we remove PTG, one of the proteins that target PP1 to glycogen, from mice with Lafora disease. This results in near-complete disappearance of polyglucosans and in resolution of neurodegeneration and myoclonic epilepsy. This work discloses an entryway to treating this fatal epilepsy and potentially other glycogen storage diseases.PLoS Genetics 04/2011; 7(4):e1002037. · 8.69 Impact Factor
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ABSTRACT: Muscle glycogen storage disease 0 (GSD0) is caused by glycogen depletion in skeletal and cardiac muscles due to deficiency of glycogen synthase 1 (GYS1), which is encoded by the GYS1 gene. Only two families with this disease have been identified. We report a new muscle GSD0 patient, a Japanese girl, who had been suffering from recurrent attacks of exertional syncope accompanied by muscle weakness and pain since age 5 years until she died of cardiac arrest at age 12. Muscle biopsy at age 11 years showed glycogen depletion in all muscle fibers. Her loss of consciousness was gradual and lasted for hours, suggesting that the syncope may not be simply caused by cardiac event but probably also contributed by metabolic distress.Neuromuscular Disorders 09/2011; 22(2):162-5. · 2.80 Impact Factor