Modeling Glycogen Storage Diseases with Human Induced Pluripotent Stem Cells

The ability to establish patient-specific human induced pluripotent stem cells (hiPSCs) offers a new paradigm for disease modeling and personalized therapies. Glycogen storage diseases type II (Pompe disease) and type IIb (Danon disease) are skeletal and cardiac myopathies caused by deficiency of glycogen-degrading lysosomal enzyme acid alpha-glucosidase (GAA) and Lysosomal-Associated Membrane Protein 2 (LAMP2), respectively. We aimed to establish patient/disease-specific hiPSCs models of infantile Pompe and Danon cardiomyopathies.

Dermal fibroblasts were obtained from two infants with Pompe disease and a patient with Danon disease, reprogrammed to generate hiPSCs and differentiated into the cardiac lineage. GAA activity measurement revealed negligible levels in Pompe-originated cells. LAMP2-specific immunostaining confirmed its absence in Danon hiPSCs-derived cardiomyocytes (hiPSC-CMs). Various staining and imaging methods revealed the presence of enlarged glycogen-containing lysosomes and "glycogen lakes" in Pompe hiPSC-CMs. Also, autophagic build-up was noted in Pompe hiPSC-CMs, suggesting a mechanistic role for abnormal autophagy in the disease. In Danon hiPSC-CMs, immunostaining and transmission electron microscopy showed intracellular autophagosome accumulation. Also, western blot analysis showed higher LC3-II:LC3-I ratio upon protein starvation suggesting earlier increased autophagosome formation. Pompe hiPSC-CM electrical recordings and ca²⁺ imaging showed electrophysiological impairments. Force measurement preliminary results from Pompe and Danon hiPSC-CM-derived engineered heart tissue showed active force similar to the control. Treatment with recombinant human GAA restored its activity and prevented/reversed glycogen storage in Pompe hiPSC-CMs. However, it failed to clear the abnormal autophagic build-up.

This study highlights hiPSCs modeling unique potential for providing patient-specific mechanistic insights into the pathogenesis and treatment of metabolic disorders and inherited cardiomyopathies.