Objective— Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by fibrofatty changes of the right ventricle, ventricular arrhythmias, and sudden death. Though ARVC is currently regarded as a disease of the desmosome, desmosomal gene mutations have been identified only in half of ARVC patients, suggesting the involvement of other associated mechanisms. Rho-kinase signaling is involved in the regulation of intracellular transport and organizes cytoskeletal filaments, which supports desmosomal protein complex at the myocardial cell–cell junctions. Here, we explored whether inhibition of Rho-kinase signaling is involved in the pathogenesis of ARVC. Approach and Results— Using 2 novel mouse models with SM22α- or αMHC-restricted overexpression of dominant-negative Rho-kinase, we show that mice with Rho-kinase inhibition in the developing heart (SM22α-restricted) spontaneously develop cardiac dilatation and dysfunction, myocardial fibrofatty changes, and ventricular arrhythmias, resulting in premature sudden death, phenotypes fulfilling the criteria of ARVC in humans. Rho-kinase inhibition in the developing heart results in the development of ARVC phenotypes in dominant-negative Rho-kinase mice through 3 mechanisms: (1) reduction of cardiac cell proliferation and ventricular wall thickness, (2) stimulation of the expression of the proadipogenic noncanonical Wnt ligand, Wnt5b, and the major adipogenic transcription factor, PPARγ (peroxisome proliferator activated receptor-γ), and inhibition of Wnt/β-catenin signaling, and (3) development of desmosomal abnormalities. These mechanisms lead to the development of cardiac dilatation and dysfunction, myocardial fibrofatty changes, and ventricular arrhythmias, ultimately resulting in sudden premature death in this ARVC mouse model. Conclusions— This study demonstrates a novel crucial role of Rho-kinase inhibition during cardiac development in the pathogenesis of ARVC in mice.

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In diseased hearts, impaired muscle within the hearts is passively stretched by contractions of the more viable neighboring muscle during the contraction phase. We investigated whether in the myocardium with nonuniform contraction such passive stretch regionally generates ROS within the stretched region and exacerbates arrhythmias. In trabeculae from rat hearts, force, intracellular Ca, and membrane potential were measured. To assess regional ROS generation, the slope of the change in the 2',7'-dichlorofluorescein fluorescence (DCF) was calculated at the each pixel position along the long axis of trabeculae using DCF fluorescence images. Ca waves and arrhythmias were induced by electrical stimulation. A HO (1 mmol/L) jet regionally increased the DCF within the jet-exposed region. A blebbistatin (10 μmol/L) jet caused passive stretch of the muscle within the jet-exposed region during the contraction phase and increased the DCF within the stretched region, the velocity of Ca waves, and the number of beats after electrical stimulation (0.2 μmol/L isoproterenol), while 3 μmol/L diphenyleneiodonium (DPI), NADPH oxidase inhibitor, decreased them. A jet of a solution containing 0.2 mmol/L HO in addition to 10 µmol/L blebbistatin also increased them. A HO jet within the region where Ca waves propagated increased their velocity. In the myocardium with nonuniform contraction, passive stretch of the muscle by contractions of the neighboring muscle regionally increases ROS within the stretched region, and the regional ROS exacerbates arrhythmias by activating the propagation of Ca waves.

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