Abstract 13848: Establishing an Optogenetic in vitro Model to Study Atrial Fibrillation Based on Human Engineered Heart Tissue

Abstract

Introduction: Atrial fibrillation (AF) is a type of sustained cardiac tachyarrhythmia in which the atrial rate can reach up to 300-600 beats per minute (BPM). The elucidation of the mechanisms of AF and the search for new therapeutic methods is hampered by a lack of suitable in vitro models. In previous studies, chronic optical tachypacing induced arrhythmia vulnerability in ventricular-like human engineered heart tissue (EHT). Here, we aimed to optimize an AF in vitro model based on optogenetics, EHT and a novel optogenetic pacing platform. Methods: Human induced pluripotent stem cells (hiPSC) stably expressing Volvox-Channelrhodopsin-1 (VChR1) were differentiated into atrial-like cardiomyocytes (CM) by treatment with 1 μM retinoic acid (RA) at the cardiac induction stage. CMs were used to cast fibrin-based 24-well format EHTs. The expression of atrial/ventricular markers was validated by qPCR, and action potential (AP) recordings with atrial-specific channel inhibitors were performed on at least one-month-old EHTs. A novel custom-designed circuit board with a programmable microcontroller and 24 RGB addressable light-emitting diodes (LED) was used for optical tachypacing. 25-30 days old EHTs were stimulated by 90 s bursts of blue light pulses (5 Hz), separated by 10 s breaks for 35-40 days. Non-paced and paced EHTs were characterized regarding contractility and gene expression. Results: EHTs had a high expression of atrial mRNA markers and displayed atrial-like AP. A flexible and straightforward optogenetic tool was built to make chronic tachypacing feasible. Using this novel platform, EHTs were successfully paced at 5 Hz for up to 40 days. Compared with non-paced EHTs, paced EHTs showed a different spontaneous contractility profile, higher expression of stress genes, and released more troponin I into the medium. Conclusions: We have successfully generated an in vitro model to mimic the status of atria with a high frequency (300 BPM) during AF. Paced EHTs displayed stress signs, partially resembling the changes of atria in AF. In the future, we could utilize this model to study the underlying mechanisms and assess proarrhythmic and antiarrhythmic drug effects.