Sensing Cardiac Electrical Activity with a Cardiomyocyte Targeted Optogenetic Voltage Indicator

Rationale: Monitoring and controlling cardiomyocyte activity with optogenetic tools offers exciting possibilities for fundamental and translational cardiovascular research. Genetically encoded voltage indicators may be particularly attractive for minimal invasive and repeated assessments of cardiac excitation from the cellular to the whole heart level. Objective: To test the hypothesis that cardiomyocyte-targeted voltage-sensitive fluorescence protein 2.3 (VSFP2.3) can be exploited as optogenetic tool for the monitoring of electrical activity in isolated cardiomyocytes and the whole heart as well as function and maturity in induced pluripotent stem cell (iPSC)-derived cardiomyocytes. Methods and Results: We first generated mice with cardiomyocyte-restricted expression of VSFP2.3 and demonstrated distinct sarcolemmal localization of VSFP2.3 without any signs for associated pathologies (assessed by echocardiography). Optically recorded VSFP2.3 signals correlated well with membrane voltage measured simultaneously by patch-clamping. The utility of VSFP2.3 for human action potential recordings was confirmed by simulation of immature and mature action potentials in murine VSFP2.3 cardiomyocytes. Optical cardiograms (OCGs) could be monitored in whole hearts ex vivo and minimally invasively in vivo via fiber optics at physiological heart rate (10 Hz) and under pacing-induced arrhythmia. Finally, we reprogrammed tail-tip fibroblasts from transgenic mice and used the VSFP2.3 sensor for benchmarking functional and structural maturation in iPSC-derived cardiomyocytes. Conclusions: We introduce a novel transgenic voltage-sensor model as a new method in cardiovascular research and provide proof-of-concept for its utility in optogenetic sensing of physiological and pathological excitation in mature and immature cardiomyocytes in vitro and in vivo. Overall design: Determination of transgene (VSFP2.3) cardiotoxicity

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Chang Liao ML, de Boer TP, Mutoh H, Raad N, Richter C, Wagner E, Downie BR, Unsöld B, Arooj I, Streckfuss-Bömeke K, Döker S, Luther S, Guan K, Wagner S, Lehnart SE, Maier LS, Stühmer W, Wettwer E, van Veen T, Morlock MM, Knöpfel T, Zimmermann WH