Studying arrhythmogenic right ventricular dysplasia with patient-specific iPSCs

Cellular reprogramming of somatic cells to patient-specific induced pluripotent stem cells (iPSCs) enables in-vitro modelling of human genetic disorders for pathogenic investigations and therapeutic screens(1–7). However, using iPSC-derived cardiomyocytes (iPSC-CMs) to model an adult-onset heart disease remains challenging due to the uncertainty regarding the ability of relatively immature iPSC-CMs to fully recapitulate adult disease phenotypes. Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited heart disease characterized by pathological fatty infiltration and cardiomyocyte loss predominantly in the right ventricle (RV)(8), which is associated with life-threatening ventricular arrhythmias. Over 50% of affected individuals have desmosome gene mutations, most commonly in PKP2 encoding plakophilin-2(9). The median age at presentation of ARVD/C is 26 years(8). We used Yamanaka’s methods(1,10) to generate iPSC lines from fibroblasts of two patients with ARVD/C and PKP2 mutations(11,12). Mutant PKP2 iPSC-CMs demonstrate abnormal plakoglobin nuclear translocation and decreased β-catenin activity(13) in cardiogenic conditions; yet these abnormal features are insufficient to reproduce the pathological phenotypes of ARVD/C in standard cardiogenic conditions. Here we show that induction of adult-like metabolic energetics from an embryonic/glycolytic state and abnormal peroxisome proliferator-activated receptor-gamma (PPARγ) activation underlie the pathogenesis of ARVD/C. By coactivating normal PPAR-alpha (PPARα)-dependent metabolism and abnormal PPARγ pathway in beating embryoid bodies (EBs) with defined media, we established an efficient ARVD/C in-vitro model within two months. This model manifests exaggerated lipogenesis and apoptosis in mutant PKP2 iPSC-CMs. iPSC-CMs with a homozygous PKP2 mutation also displayed calcium-handling deficits. Our study is the first to demonstrate that induction of adult-like metabolism plays a critical role in establishing an adult-onset disease model using patient-specific iPSCs. Using this model, we revealed crucial pathogenic insights that metabolic derangement in adult-like metabolic milieu underlies ARVD/C pathologies, enabling us to propose novel disease-modifying therapeutic strategies.