Glycogen Exocytosis from Cultured Pompe Skin Fibroblasts

Abstract

Objective: Pompe disease is a progressive form of muscular dystrophy caused by a deficiency in the lysosomal enzyme α-glucosidase (GAA), and leads to the accumulation of glycogen in affected cells. Enzyme replacement therapy is approved to treat infantile-onset Pompe disease, but this is not completely effective, necessitating the development of new therapeutic strategies. Exocytosis involves the fusion of intracellular vesicles with the cell surface and the release of vesicular content, and is a mechanism that could be used in Pompe disease to remove stored glycogen from affected cells. The exocytosis of storage material from Pompe patient cells into circulation could result in glycogen degradation by other amylases (i.e. not GAA) and this could be developed in the future as a new or adjunct therapeutic strategy. Methods: A sensitive mass spectrometry assay was used to quantify glycogen in cell extracts and the culture media from confluent Pompe skin fibroblasts. Results: Four percent of vesicular glycogen was exocytosed after 2 hours in culture. This natural process of glycogen exocytosis was enhanced in sub-confluent Pompe cells, which released >80% of glycogen after 2 hours in culture. Conclusion: Under appropriate conditions exocytosis can release most of the stored glycogen in Pompe skin fibroblasts, identifying a potential target for therapeutic intervention.