Dysfunction of endocytic and autophagic pathways in a lysosomal storage disease.
OBJECTIVE
To understand the mechanisms of skeletal muscle destruction and resistance to enzyme replacement therapy in Pompe disease, a deficiency of lysosomal acid alpha-glucosidase (GAA), in which glycogen accumulates in lysosomes primarily in cardiac and skeletal muscles.


METHODS
We have analyzed compartments of the lysosomal degradative pathway in GAA-deficient myoblasts and single type I and type II muscle fibers isolated from wild-type, untreated, and enzyme replacement therapy-treated GAA knock-out mice.


RESULTS
Studies in myoblasts from GAA knock-out mice showed a dramatic expansion of vesicles of the endocytic/autophagic pathways, decreased vesicular movement in overcrowded cells, and an acidification defect in a subset of late endosomes/lysosomes. Analysis by confocal microscopy of isolated muscle fibers demonstrated that the consequences of the lysosomal glycogen accumulation are strikingly different in type I and II muscle fibers. Only type II fibers, which are the most resistant to therapy, contain large regions of autophagic buildup that span the entire length of the fibers.


CONCLUSIONS
The vastly increased autophagic buildup may be responsible for skeletal muscle damage and prevent efficient trafficking of replacement enzyme to lysosomes.
Arthritis and Rheumatism Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892-1820, USA.
Tokiko
T
Fukuda
Lindsay
L
Ewan
Martina
M
Bauer
Robert J
RJ
Mattaliano
Kristien
K
Zaal
Evelyn
E
Ralston
Paul H
PH
Plotz
Nina
N
Raben
D000367:Age Factors; D000818:Animals; D001343:Autophagy / Q000502:physiology*; D015153:Blotting, Western / Q000379:methods; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004705:Endocytosis / Q000502:physiology*; D005455:Fluorescent Antibody Technique / Q000379:methods; D005087:Glucan 1,4-alpha-Glucosidase / Q000172:deficiency; D049452:Green Fluorescent Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D016464:Lysosomal Storage Diseases / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D052118:Lysosomal-Associated Membrane Protein 1 / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission / Q000379:methods; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000648:ultrastructure; D032446:Myoblasts / Q000378:metabolism / Q000648:ultrastructure; D013997:Time Factors; D014162:Transfection / Q000379:methods; D022161:Transport Vesicles / Q000378:metabolism / Q000648:ultrastructure; D014404:Tubulin / Q000378:metabolism
D052118:Lysosomal-Associated Membrane Protein 1; D014404:Tubulin; D049452:Green Fluorescent Proteins; D005087:Glucan 1,4-alpha-Glucosidase