Testoni, GiorgiaDuran, JordiGarcía-Rocha, MarVilaplana, FranciscoSerrano, Antonio L.Sebastián, DavidLópez Soldado, IlianaSullivan, Mitchell A.Slebe Concha, Juan Felipe, 1981-Vilaseca, MartaMuñoz Cánoves, Pura, 1962-Guinovart, Joan J. (Joan Josep), 1947-2019-03-152019-03-152017Testoni G, Duran J, García-Rocha M, Vilaplana F, Serrano AL, Sebastián D et al. Lack of glycogenin causes glycogen accumulation and muscle function impairment. Cell Metab. 2017 Jul 5;26(1):256-266.e4. DOI: 10.1016/j.cmet.2017.06.0081550-4131http://hdl.handle.net/10230/36843Glycogenin is considered essential for glycogen synthesis, as it acts as a primer for the initiation of the polysaccharide chain. Against expectations, glycogenin-deficient mice (Gyg KO) accumulate high amounts of glycogen in striated muscle. Furthermore, this glycogen contains no covalently bound protein, thereby demonstrating that a protein primer is not strictly necessary for the synthesis of the polysaccharide in vivo. Strikingly, in spite of the higher glycogen content, Gyg KO mice showed lower resting energy expenditure and less resistance than control animals when subjected to endurance exercise. These observations can be attributed to a switch of oxidative myofibers toward glycolytic metabolism. Mice overexpressing glycogen synthase in the muscle showed similar alterations, thus indicating that this switch is caused by the excess of glycogen. These results may explain the muscular defects of GSD XV patients, who lack glycogenin-1 and show high glycogen accumulation in muscle.application/pdfeng© Elsevier This is the published version of an article http://dx.doi.org/10.1016/j.cmet.2017.06.008 that appeared in the journal Cell metabolism. It is published in an Open Archive under an Elsevier user license. Details of this licence are available here: https://www.elsevier.com/about/our-business/policies/open-access-licenses/elsevier-user-licenseinfo:eu-repo/semantics/articlehttp://dx.doi.org/10.1016/j.cmet.2017.06.008GlycogeninGlycogenGSD XVGlycogen storage disease XVGlycogenosisExerciseMuscle performancePriming proteinOxidative metabolismMitochondrial respirationinfo:eu-repo/semantics/openAccess