Reischauer, S., Arnaout, R., Ramadass, R., Stainier, D. (2014) Actin Binding GFP Allows 4D In Vivo Imaging of Myofilament Dynamics in the Zebrafish Heart and the Identification of Erbb2 Signaling as a Remodeling Factor of Myofibril Architecture. Circulation research. 115(10):845-56.
Rationale: Dilated cardiomyopathy is a leading cause of congestive heart failure and a debilitating complication of anti-neoplastic therapies. Despite disparate causes for dilated cardiomyopathy, maladaptive cardiac remodeling and decreased systolic function are common clinical consequences, begging an investigation of in vivo contractile dynamics in development and disease, one that has been impossible to date. Objective: Imaging in vivo myocardial contractile filament dynamics and assess potential causes of dilated cardiomyopathy in anti-neoplastic therapies targeting Erbb2. Methods and Results: We generated a transgenic zebrafish line expressing an actin-binding GFP in cardiomyocytes, allowing in vivo imaging of myofilaments. Analysis of this line revealed architectural differences in myofibrils of the distinct cardiomyocyte subtypes. We used this model to investigate the effects of Erbb2 signaling on myofibrillar organization, since drugs targeting ERBB2 (HER2/NEU) signaling, a mainstay of breast cancer chemotherapy, cause dilated cardiomyopathy in many patients. High-resolution in vivo imaging revealed that Erbb2 signaling regulates a switch between a dense apical network of filamentous myofibrils and the assembly of basally localized myofibrils in ventricular cardiomyocytes. Conclusions: Using this novel line, we compiled a reference for myofibrillar microarchitecture among myocardial subtypes in vivo and at different developmental stages, establishing this model as a tool to analyze in vivo cardiomyocyte contractility and remodeling for a broad range of cardiovascular questions. Further, we applied this model to study Erbb2 signaling in cardiomyopathy. We show a direct link between Erbb2 activity and remodeling of myofibrils, revealing an unexpected mechanism with potentially important implications for prevention and treatment of cardiomyopathy.