Mitochondrial dysfunction caused by inactivation induced ROS production, activated the DNA damage response, and caused cardiomyocyte cell cycle arrest, ultimately resulting in lethal cardiomyopathy. Normal mitochondrial function was not required for cardiomyocyte maturation. Pharmacological inhibition of ROS or DNA damage response pathways is a potential strategy to prevent cardiac dysfunction caused by some forms of mitochondrial dysfunction.

Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited cardiac arrhythmia characterized by adrenergically triggered arrhythmias, is inadequately treated by current standard of care. Ca 2+ /calmodulin-dependent protein kinase II (CaMKII), an adrenergically activated kinase that contributes to arrhythmogenesis in heart disease models, is a candidate therapeutic target in CPVT. However, translation of CaMKII inhibition has been limited by the need for selective CaMKII inhibition in cardiomyocytes. Here we tested the hypothesis that CaMKII inhibition using a cardiomyocyte-targeted gene therapy strategy would suppress arrhythmia in CPVT mouse models. Methods:We developed AAV9-GFP-AIP, an adeno-associated viral vector in which a potent CaMKII inhibitory peptide (AIP), is fused to GFP and expressed from a cardiomyocyte selective promoter. The vector was delivered systemically. Arrhythmia burden was evaluated using invasive electrophysiology testing in adult mice. AIP was also tested on induced pluripotent stem cells (iPSC) derived from CPVT patients with different disease-causing mutations to determine the effectiveness of our proposed therapy on human iPSC-derived cardiomyocytes (iPSC-CMs) and different pathogenic genotypes.Results: AAV9-GFP-AIP was robustly expressed in the heart without significant expression in extra-cardiac tissues, including the brain. Administration of AAV9-GFP-AIP to neonatal mice with a known CPVT mutation (RYR2 R176Q/+ ) effectively suppressed ventricular arrhythmias induced by either β-adrenergic stimulation or programmed ventricular pacing, without significant proarrhythmic effect. Intravascular delivery of AAV9-GFP-AIP to adolescent mice transduced ~50% of cardiomyocytes and was effective in suppressing arrhythmia in CPVT mice. iPSC-CMs derived from two different CPVT patients with different pathogenic mutations demonstrated

Conflict of interest:MEA is a named inventor on patents claiming to treat heart disease by CaMKII inhibition. No income derives from these activities.

Current drug development efforts for the treatment of atrial fibrillation are hampered by the fact that many preclinical models have been unsuccessful in reproducing human cardiac physiology and its response to medications. In this study, we demonstrated an approach using human induced pluripotent stem cell-derived atrial and ventricular cardiomyocytes (hiPSC-aCMs and hiPSC-vCMs, respectively) coupled with a sophisticated optical mapping system for drug screening of atrial-selective compounds in vitro. We optimized differentiation of hiPSC-aCMs by modulating the WNT and retinoid signaling pathways. Characterization of the transcriptome and proteome revealed that retinoic acid pushes the differentiation process into the atrial lineage and generated hiPSC-aCMs. Functional characterization using optical mapping showed that hiPSC-aCMs have shorter action potential durations and faster Ca 2+ handling dynamics compared with hiPSC-vCMs. Furthermore, pharmacological investigation of hiPSC-aCMs captured atrial-selective effects by displaying greater sensitivity to atrialselective compounds 4-aminopyridine, AVE0118, UCL1684, and vernakalant when compared with hiPSC-vCMs. These results established that a model system incorporating hiPSC-aCMs combined with optical mapping is well-suited for preclinical drug screening of novel and targeted atrial selective compounds.