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Sensing Cardiac Electrical Activity with a Cardiomyocyte Targeted Optogenetic Voltage Indicator

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE69190 | GEO | 2015/09/02

SECONDARY ACCESSION(S): PRJNA284774

REPOSITORIES: GEO

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Project description:Direct conversion of fibroblasts to induced cardiomyocytes (iCMs) has great potential for regenerative medicine. Recent publications have reported significant progress, but the evaluation of reprogramming has relied upon non-functional measures such as flow cytometry for cardiomyocyte markers or GFP expression driven by a cardiomyocyte-specific promoter. The issue is one of practicality: the most stringent measures - electrophysiology to detect cell excitation and the presence of spontaneously contracting myocytes - are not readily quantifiable in the large numbers of cells screened in reprogramming experiments. However, excitation and contraction are linked by a third functional characteristic of cardiomyocytes: the rhythmic oscillation of intracellular calcium levels. We set out to optimize direct conversion of fibroblasts to iCMs with a quantifiable calcium reporter to rapidly assess functional transdifferentiation. We constructed a reporter system in which the calcium indicator GCaMP is driven by the cardiomyocyte-specific Troponin T promoter. Using calcium activity as our primary outcome measure, we compared several published combinations of transcription factors along with novel combinations in mouse embryonic fibroblasts. The most effective combination consisted of Hand2, Nkx2.5, Gata4, Mef2c, and Tbx5 (HNGMT). This combination is >50-fold more efficient than GMT alone and produces iCMs with cardiomyocyte marker expression, robust calcium oscillation, and spontaneous beating that persists for weeks following inactivation of reprogramming factors. HNGMT is also significantly more effective than previously published factor combinations for the transdifferentiation of adult mouse cardiac fibroblasts to iCMs. Quantification of calcium function is a convenient and effective means for the identification and evaluation of cardiomyocytes generated by direct reprogramming. Using this stringent outcome measure, we conclude that HNGMT produces iCMs more efficiently than previously published methods. Mouse embryonic fibroblasts were treated with different combinations of transcription factors to drive transdifferentiation to induced cardiomyocytes (iCMs). Putative iCMs were enriched by zeocin selection. Zeocin resistance was conferred to iCMs via the TroponinT-GCaMP5-Zeo lentiviral reporter.

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Sensing Cardiac Electrical Activity with a Cardiomyocyte Targeted Optogenetic Voltage Indicator

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