Non-junctional roles of desmosome proteins in the pathogenesis of arrhythmogenic cardiomyopathy

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PROJECT SUMMARY Cardiovascular diseases remain the major cause of death in the US. Recent advances in reprogramming somatic cells from cardiac patients into induced pluripotent stem cells (iPSCs) enables in vitro modeling of human cardiac diseases for pathogenic studies and therapeutic screens. Traditionally, weakened desmosome junctions are considered the main pathogenic mechanism for Arrhythmogenic Cardiomyopathy (AC), caused by mutations in five desmosome component proteins. Pathological hallmarks of AC are progressive fibro-fatty replacement of cardiomyocytes (CMs) with increased CM apoptosis primarily in the RV, leading to sudden death in the young. We have established a novel method to induce adult-like, fatty acid oxidation-dominant metabolism of primitive CMs derived from iPSCs (iPSC-CMs) and established the first metabolic maturation- based in vitro cardiac disease model for elucidation of novel pathogenic insights for human AC (Nature, 2013). We showed that abnormal PPARγ activation after normal PPARα-mediated metabolic maturation in AC CMs resulted in exaggerated lipogenesis, apoptosis, sodium channel deficits and defective Ca2+ handling in CMs with desmosome mutations, recapitulating the pathological signatures of AC hearts. Using our AC model and samples from pathological human AC hearts, we show here that plakoglobin is a key component of Insulin-p85 metabolic signaling complex. Desmosome mutations lead to faster plakoglobin degradation, reduce PI3K/Akt activation, and hyperactivate GSK3β, which downregulate a microRNA (miR) cluster leading to subsequent abnormal PPARγ activation and CM apoptosis. Importantly, we used genetic and cellular methods to confirm the clinically relevance of our pathogenic pathways in human AC hearts and in mouse models of AC. We propose here to further elucidate the dysregulated and non-junctional signaling networks caused by plakoglobin deficits, to study how plakophilin-2 deficits deregulate additional signaling pathways, and to find clinically safe therapeutic agents for treating AC using both in vitro iPSC-CM based models and mouse models of AC.