Investigating Inherited HCM Caused by SCO2 and PRKAG2 Mutations Using the Patients` Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Ronen Ben Jehuda1,2,3,4, Tova Hallas2,3,4, Revital Schick2,3,4, Mihaela Gherghiceanu5, Hanna Mandel6, Michael Arad7, Ofer Binah2,3,4
1 Biotechnology, Technion, Israel
2 Ruth & Bruce Rappaport Faculty of Medicine, Technion, Israel
3 Physiology, Biophysics and System Biology, Technion, Israel
4 The Rappaport Institute, Technion, Israel
5 Ultrastructure, Victor Babes National Institute of Pathology, Romania
6 Inherited Metabolic Disorders, Rambam Medical Center, Israel
7 Heart Failure Service and Heart Institute, Sheba Medical Center, Tel Hashomer, Israel

Mutations in PRKAG2 gene encoding the γ subunit of AMPK cause hypertrophic cardiomyopathy (HCM) and familial Wolff-Parkinson-White syndrome (WPW). Patients with R302Q mutation in PRKAG2 suffer from sinus bradycardia, escape rhythms, atrial fibrillation and supraventricular tachycardia. This mutation affects AMPK activity and causes elevated glycogen storage in cardiomyocytes. The link between glycogen storage and WPW syndrome, HCM and arrhythmia remains unknown. A mutation in SCO2 gene encoding for mammalian cytochrome-c oxidase, a crucial part of the mitochondrial electron transport-chain, causes HCM and infants deaths.

To investigate the pathological mechanisms underlying these HCM-causing mutations and search for novel pharmaceutical and genetic therapeutic modalities, we generated induced Pluripotent Stem Cells-derived cardiomyocytes (iPSC-CMs) from patients` somatic cells, attempting to recapitulate the disease phenotype in vitro. The diseases we explored are: (1) HCM with familial WPW caused by R302Q mutation in PRKAG2 gene. (2) Concentric HCM caused by G192S mutation in SCO2 gene. Successful reprogramming of respective patients` skin-derived fibroblasts resulted in iPSCs colonies expressing R302Q or G192S mutations. Action potentials were recorded from cardiomyocytes and extracellular electrograms from beating cardiomyocytes clusters using patch clamp and Micro Electrode Array (MEA) techniques, respectively. [Ca2+]i transients and contractions were recorded by means of fura-2 and video edge detector, respectively. The major findings were: (1) PRKAG2: mutated iPSC-CMs exhibited spontaneous delayed afterdepolarizations (DADs), slow firing rates and irregular rhythms (the latter two at the single cell and network level). Further, these phenomena were intensified with culture age, suggesting inter-relations between glycogen storage and electrophysiological abnormalities. (2) SCO2: mutated iPSC-CMs exhibited attenuated inotropic response to isoproterenol as well as DADs and irregular rhythms. Importantly, transmission electron microscopy analysis of SCO2-mutated iPSC-CMs displayed abnormal mitochondria size and morphology. Conclusions: PRKAG2 and SCO2-mutated iPSC-CMs displayed abnormal functional features resembling the clinical phenotype expressed in patients carrying the mutations.