1. Autophagy and mistargeting of therapeutic enzyme in skeletal muscle in Pompe disease.
- Author
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Fukuda T, Ahearn M, Roberts A, Mattaliano RJ, Zaal K, Ralston E, Plotz PH, and Raben N
- Subjects
- Age Factors, Animals, Autophagy genetics, CHO Cells, Cricetinae, Cricetulus, Endocytosis genetics, Endocytosis physiology, Glucan 1,4-alpha-Glucosidase metabolism, Glycogen metabolism, Glycogen Storage Disease Type II genetics, Glycogen Storage Disease Type II metabolism, Humans, Lysosomal-Associated Membrane Protein 1 metabolism, Lysosomes metabolism, Mice, Mice, Knockout, Muscle Fibers, Skeletal metabolism, Muscle Fibers, Skeletal pathology, Muscle, Skeletal pathology, Receptor, IGF Type 2 metabolism, Recombinant Proteins genetics, Recombinant Proteins metabolism, Autophagy physiology, Glucan 1,4-alpha-Glucosidase genetics, Glycogen Storage Disease Type II therapy, Muscle, Skeletal metabolism
- Abstract
Enzyme replacement therapy (ERT) became a reality for patients with Pompe disease, a fatal cardiomyopathy and skeletal muscle myopathy caused by a deficiency of glycogen-degrading lysosomal enzyme acid alpha-glucosidase (GAA). The therapy, which relies on receptor-mediated endocytosis of recombinant human GAA (rhGAA), appears to be effective in cardiac muscle, but less so in skeletal muscle. We have previously shown a profound disturbance of the lysosomal degradative pathway (autophagy) in therapy-resistant muscle of GAA knockout mice (KO). Our findings here demonstrate a progressive age-dependent autophagic buildup in addition to enlargement of glycogen-filled lysosomes in multiple muscle groups in the KO. Trafficking and processing of the therapeutic enzyme along the endocytic pathway appear to be affected by the autophagy. Confocal microscopy of live single muscle fibers exposed to fluorescently labeled rhGAA indicates that a significant portion of the endocytosed enzyme in the KO was trapped as a partially processed form in the autophagic areas instead of reaching its target--the lysosomes. A fluid-phase endocytic marker was similarly mistargeted and accumulated in vesicular structures within the autophagic areas. These findings may explain why ERT often falls short of reversing the disease process and point toward new avenues for the development of pharmacological intervention.
- Published
- 2006
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