title: Murine muscle cell models for Pompe disease and their use in studying therapeutic approaches.
abstract: Lysosomes filled with glycogen are a major pathologic feature of Pompe disease, a fatal myopathy and cardiomyopathy caused by a deficiency of the glycogen-degrading lysosomal enzyme, acid alpha-glucosidase (GAA). To facilitate studies germane to this genetic disorder, we developed two in vitro Pompe models: myotubes derived from cultured primary myoblasts isolated from Pompe (GAA KO) mice, and myotubes derived from primary myoblasts of the same genotype that had been transduced with cyclin-dependent kinase 4 (CDK4). This latter model is endowed with extended proliferative capacity. Both models showed extremely large alkalinized, glycogen-filled lysosomes as well as impaired trafficking to lysosomes. Although both Pompe tissue culture models were derived from fast muscles and were fast myosin positive, they strongly resemble slow fibers in terms of their pathologic phenotype and their response to therapy with recombinant human GAA (rhGAA). Autophagic buildup, a hallmark of Pompe disease in fast muscle fibers, was absent, but basal autophagy was functional. To evaluate substrate deprivation as a strategy to prevent the accumulation of lysosomal glycogen, we knocked down Atg7, a gene essential for autophagosome formation, via siRNA, but we observed no effect on the extent of glycogen accumulation, thus confirming our recent observation in autophagy-deficient Pompe mice [N. Raben, V. Hill, L. Shea, S. Takikita, R. Baum, N. Mizushima, E. Ralston, P. Plotz, Suppression of autophagy in skeletal muscle uncovers the accumulation of ubiquitinated proteins and their potential role in muscle damage in Pompe disease, Hum. Mol. Genet. 17 (2008) 3897-3908] that macroautophagy is not the major route of glycogen transport to lysosomes. The in vitro Pompe models should be useful in addressing fundamental questions regarding the pathway of glycogen to the lysosomes and testing panels of small molecules that could affect glycogen biosynthesis or speed delivery of the replacement enzyme to affected lysosomes.
authors.affiliation: Arthritis and Rheumatism Branch, National Institutes of Arthritis and Musculoskeletal and Skin Diseases, NIH, Building 50 Room 1345, 50 South Drive, Bethesda, MD 20892, USA. takikitas@mail.nih.gov
authors.forename: Shoichi
authors.initials: S
authors.lastname: Takikita
authors.forename: Rachel
authors.initials: R
authors.lastname: Myerowitz
authors.forename: Kristien
authors.initials: K
authors.lastname: Zaal
authors.forename: Nina
authors.initials: N
authors.lastname: Raben
authors.forename: Paul H
authors.initials: PH
authors.lastname: Plotz
mesh_terms: D000818:Animals; D001343:Autophagy; D000071193:Autophagy-Related Protein 7; D002401:Cathepsin B / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D002478:Cells, Cultured; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D004195:Disease Models, Animal; D004705:Endocytosis; D006009:Glycogen Storage Disease Type II / Q000473:pathology* / Q000628:therapy*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000473:pathology; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D032342:Muscle Cells / Q000473:pathology*; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000473:pathology; D032446:Myoblasts / Q000201:enzymology / Q000473:pathology; D034741:RNA, Small Interfering / Q000378:metabolism; D014161:Transduction, Genetic; D000520:alpha-Glucosidases / Q000172:deficiency / Q000378:metabolism
chemical_list: C502661:Atg7 protein, mouse; D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; D051358:Cyclin-Dependent Kinase 4; D000520:alpha-Glucosidases; D002401:Cathepsin B; D002402:Cathepsin D; D000071193:Autophagy-Related Protein 7