Istaroxime treatment ameliorates calcium dysregulation in a zebrafish model for Phospholamban R14del cardiomyopathy

The heterozygous phospholamban (PLN) p.Arg14del (R14del) mutation is found in patients with dilated or arrhythmogenic cardiomyopathy. The PLN R14del mutation triggers cardiac contractile dysfunction and arrhythmogenesis by affecting intracellular Ca2+ dynamics. Little is known about the physiological processes preceding PLN R14del induced cardiomyopathy, which is characterized by sub-epicardial accumulation of fibrofatty tissue, and a specific drug treatment is currently lacking. Here, we addressed these issues using a knock-in PLN R14del zebrafish model. Hearts from adult zebrafish with the R14del mutation display age-related remodeling with sub-epicardial inflammation and fibrosis. Echocardiography revealed contractile pulsus alternans before overt structural changes occurred, which correlated at the cellular level with action potential duration (APD) alternans. These functional alterations are preceded by diminished Ca2+ transient amplitudes in embryonic hearts. We found that istaroxime treatment ameliorates the in vivo Ca2+ dysregulation, rescues the cellular APD alternans, while it improves cardiac relaxation. Thus, we present novel insight into the pathophysiology of PLN R14del cardiomyopathy and identify istaroxime as a potential novel drug for its treatment.