On the Mechanisms of Cardiomyopathy in a Human Induced Pluripotent Stem Cell-derived Cardiomyocyte Model of Infantile-Onset Pompe Disease

Infantile onset Pompe disease, caused by the loss of lysosomal glycogen hydrolyzing enzyme acid alpha-glucosidase (GAA) activity, presents with a hypertrophic cardiomyopathy at birth. Without enzyme replacement, death occurs within 1 year of life. We have evaluated the leading hypotheses of contractile insufficiency and autophagic dysfunction as mechanisms of Pompe cardiomyopathy in a human induced pluripotent stem (iPS) cell derived cardiomyocyte (iPSC-CM) model. Pompe patient skin fibroblasts were reprogrammed into iPS cells and differentiated into cardiomyocytes that have undetectable GAA activity and pathognomonic glycogen-filled lysosomes. The iPSC-CMs were combined with a fibrin scaffold to make strips of engineered cardiac tissue (ECT). Pompe and Control ECTs had no consistent differences in contractile force or kinetics. Autophagic function was measured through inhibition and then re-establishment of lysosomal activity. Control and Pompe iPSC-CMs demonstrated no remarkable differences in autophagosomal clearance. Higher electrophoretic mobilities of protein-sodium dodecyl sulfate complexes and more basic isoelectric points were noticed in the lysosomal associated membrane proteins (LAMPs) from Pompe compared to control iPSC-CMs. We determined that these lighter and more basic LAMPs lacked golgi modification, which typically include poly-N-acetyllactosamine and sialic acids, that could be partially reproduced in Control iPSC-CMs through destruction of the golgi apparatus. No abnormalities in golgi structure were observed in Pompe iPSC-CMs. Therefore, we have identified an unknown deficit in golgi-based glycosylation that may contribute to Pompe cardiomyopathy through mechanisms shared by the congenital disorders of glycosylation or LAMP2 deficiency (Danon Disease), both of which have cardiac phenotypes similar to Pompe disease.