A Functional Human Glycogen Debranching Enzyme Encoded by a Synthetic Gene: Its Implications for Glycogen Storage Disease Type III Management

Abstract

Background: Glycogen Storage Disease type III (GSD III) is a metabolic disorder resulting from a deficiency of the Glycogen Debranching Enzyme (GDE), a large monomeric protein (approximately 170 kDa) with cytoplasmic localization and two distinct enzymatic activities: 4-α-glucantransferase and amylo-α-1,6-glucosidase. Mutations in the Agl gene, with consequent deficiency in GDE, lead to the accumulation of abnormal/toxic glycogen with shorter chains (phosphorylase limit dextrin, PLD) in skeletal and/or heart muscle and/or in the liver. Currently, there is no targeted therapy, and available treatments are symptomatic, relying on specific diets. Methods: Enzyme Replacement Therapy (ERT) might represent a potential therapeutic strategy for GSD III. Moreover, the single-gene nature of GSD III, the subcellular localization of GDE, and the type of affected tissues represent ideal conditions for exploring gene therapy approaches. Toward this direction, we designed a synthetic, codon-optimized cDNA encoding the human GDE. Results: This gene yielded high amounts of soluble, enzymatically active protein in Escherichia coli. Moreover, when transfected in Human Embryonic Kidney cells (HEK-293), it successfully encoded a functional GDE. Conclusion: These results suggest that our gene or protein might complement the missing function in GSD III patients, opening the door to further exploration of therapeutic approaches for this disease.