Optogenetic Control of Human Induced Pluripotent Stem Cell Derived Cardiomyocytes (hiPSC-CMs)

Background and Aims:
Optogenetics approaches, utilizing light-sensitive proteins, have emerged as unique experimental paradigms to modulate neuronal excitability. We aim to evaluate whether a similar strategy could be used to control the excitable properties of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs).

Methods and Results:
HEK293 cells were stably transfected to express the light-sensitive cationic channel Channelrhodopsin2 (ChR2). These ChR2-HEK cells were then used in co-culture studies involving large-scale 2-dimentional (1cm) cell sheets and 3-dimentional engineered heart tissues (EHT), composed of hiPSC-CMs. The hypothesis in these studies was that the engineered cells would influence adjacent cardiomyocytes through electrotonic interactions.

Optical mapping system is used to study the electrophysiological properties of the multicellular (tissue) models. Optical imaging is carried out using voltage sensitive dyes (VSDs). Initial studies in the co-cultures involving the ChR2-HEK cells co-cultured with multicellular large-scale sheets of 1-3 million hiPSC-CMs, revealed the ability of flashes of monochromatic blue light to pace these cardiac-tissue preparations.

In addition, we use multicellular models to unravel electrical conduction characteristics of the models. We show how specific optical stimulation protocols can disrupt the normal conduction patterns, and induce abnormal spiral wave patterns associated with reentry mechanism of arrhythmia in the heart. Finally, we demonstrate how application of diffused illumination enables synchronous activation of the models, and how it serves as a potent optical defibrillation strategy, which is able to stop reentrant waves in the sample.

Conclusions:
The results of our initial studies demonstrate the unique potential of combining the emerging optogenetics and hiPSC technologies to derive light-controllable excitable cardiac cell that could be used for several cardiovascular research applications. Such applications include development of unique in vitro models of cardiac conduction, disease modeling, drug screening, and novel cardiac resynchronization therapy and painless optogenetic defibrillation.