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 screens1–7. 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-29. The median age at presentation of ARVD/C is 26 years8. We used Yamanaka’s methods1,10 to generate iPSC lines from fibroblasts of two patients with ARVD/C and PKP2 mutations11,12. Mutant PKP2 iPSC-CMs demonstrate abnormal plakoglobin nuclear translocation and decreased β-catenin activity13 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.

Background Brugada syndrome (BrS) primarily associates with loss of sodium channel function. Previous studies showed features consistent with sodium current (INa) deficit in patients carrying desmosomal mutations, diagnosed with arrhythmogenic cardiomyopathy (AC; or arrhythmogenic right ventricular cardiomyopathy, ARVC). Experimental models showed correlation between loss of expression of desmosomal protein plakophilin-2 (PKP2), and reduced INa. We hypothesized that PKP2 variants that reduce INa could yield a BrS phenotype, even without overt structural features. Methods and Results We searched for PKP2 variants in genomic DNA of 200 patients with BrS diagnosis, no signs of AC, and no mutations in BrS-related genes SCN5A, CACNa1c, GPD1L and MOG1. We identified 5 cases of single amino acid substitutions. Mutations were tested in HL-1-derived cells endogenously expressing NaV1.5 but made deficient in PKP2 (PKP2-KD). Loss of PKP2 caused decreased INa and NaV1.5 at site of cell contact. These deficits were restored by transfection of wild-type PKP2 (PKP2-WT), but not of BrS-related PKP2 mutants. Human induced pluripotent stem cell cardiomyocytes (hIPSC-CMs) from a patient with PKP2 deficit showed drastically reduced INa. The deficit was restored by transfection of WT, but not BrS-related PKP2. Super-resolution microscopy in murine PKP2-deficient cardiomyocytes related INa deficiency to reduced number of channels at the intercalated disc, and increased separation of microtubules from the cell-end. Conclusions This is the first systematic retrospective analysis of a patient group to define the co-existence of sodium channelopathy and genetic PKP2 variations. PKP2 mutations may be a molecular substrate leading to the diagnosis of BrS.

BackgroundDevelopmental, physiological and tissue engineering studies critical to the development of successful myocardial regeneration therapies require new ways to effectively visualize and isolate large numbers of fluorescently labeled, functional cardiomyocytes.Methodology/Principal FindingsHere we describe methods for the clonal expansion of engineered hESCs and make available a suite of lentiviral vectors for that combine Blasticidin, Neomycin and Puromycin resistance based drug selection of pure populations of stem cells and cardiomyocytes with ubiquitous or lineage-specific promoters that direct expression of fluorescent proteins to visualize and track cardiomyocytes and their progenitors. The phospho-glycerate kinase (PGK) promoter was used to ubiquitously direct expression of histone-2B fused eGFP and mCherry proteins to the nucleus to monitor DNA content and enable tracking of cell migration and lineage. Vectors with T/Brachyury and α-myosin heavy chain (αMHC) promoters targeted fluorescent or drug-resistance proteins to early mesoderm and cardiomyocytes. The drug selection protocol yielded 96% pure cardiomyocytes that could be cultured for over 4 months. Puromycin-selected cardiomyocytes exhibited a gene expression profile similar to that of adult human cardiomyocytes and generated force and action potentials consistent with normal fetal cardiomyocytes, documenting these parameters in hESC-derived cardiomyocytes and validating that the selected cells retained normal differentiation and function.Conclusion/SignificanceThe protocols, vectors and gene expression data comprise tools to enhance cardiomyocyte production for large-scale applications.

Various types of cardiomyocytes undergo changes in automaticity and electrical properties during fetal heart development. Human embryonic stem cell-derived cardiomyocytes (hESC-CMs), like fetal cardiomyocytes, are electrophysiologically immature and exhibit automaticity. We used hESC-CMs to investigate developmental changes in mechanisms of automaticity and to determine whether electrophysiological maturation is driven by an intrinsic developmental clock and/or is regulated by interactions with non-cardiomyocytes in embryoid bodies (EBs). We isolated pure populations of hESC-CMs from EBs by lentivirus-engineered Puromycin resistance at various stages of differentiation. Using pharmacological agents, calcium (Ca 2+ ) imaging, and intracellular recording techniques, we found that intracellular Ca 2+ -cycling mechanisms developed early and contributed to dominant automaticity throughout hESC-CM differentiation. Sarcolemmal ion channels evolved later upon further differentiation within EBs and played an increasing role in controlling automaticity and electrophysiological properties of hESC-CMs. In contrast to the development of intracellular Ca 2+ -handling proteins, ion channel development and electrophysiological maturation of hESC-CMs did not occur when hESC-CMs were isolated from EBs early and maintained in culture without further interaction with non-cardiomyocytes. Adding back non-cardiomyocytes to early-isolated hESC-CMs rescued the arrest of electrophysiological maturation, indicating that non-cardiomyocytes in EBs drive electrophysiological maturation of early hESC-CMs. Non-cardiomyocytes in EBs contain most cell types present in the embryonic heart that are known to infl uence early cardiac development. Our study is the fi rst to demonstrate that non-cardiomyocytes infl uence electrophysiological maturation of early hESC-CMs in cultures. Defi ning the nature of these extrinsic signals will aid in the directed maturation of immature hESC-CMs to mitigate arrhythmogenic risks of cell-based therapies.