AIMS: Human embryonic stem cells (hESCs) can be used to generate scalable numbers of cardiomyocytes for studying cardiac biology, disease modeling, drug screens, and potentially for regenerative therapies. A fluorescence-based reporter line will significantly enhance our capacities to visualize the derivation, survival and function of hESC-derived cardiomyocytes. Our goal was to develop a reporter cell line for real-time monitoring of live hESC-derived cardiomyocytes.

METHODS AND RESULTS: We used CRISPR/Cas9 to knock an mCherry reporter gene into the MYH6 locus of hESC lines, H1 and H9, enabling real-time monitoring of the generation of cardiomyocytes. MYH6:mCherry+ cells express atrial or ventricular markers and display a range of cardiomyocyte action potential morphologies. At 20 days of differentiation, MYH6:mCherry+ cells show features characteristic of human cardiomyocytes and can be used successfully to monitor drug-induced cardiotoxicity and oleic acid-induced cardiac arrhythmia.

CONCLUSION: We created two MYH6:mCherry hESC reporter lines, and documented the application of these lines for disease modeling relevant to cardiomyocyte biology.

TRANSLATIONAL PERSPECTIVE: Cardiovascular disease is a leading cause of death in the world. Moreover, 90% of pharmaceutical compounds eventually fail and are withdrawn from the market primarily due to drug-induced cardiovascular toxicity. Thus, it is compelling needed to establish a platform to overcome this hurdle. We here report to generate a fluorescence-based cardiomyocyte reporter, the benefit of studying underlying mechanism of heart disease as well as providing a platform for cardiotoxicity screening.