Stem cell-derived heterocellular atrial engineered cardiac tissue with comparisons to native human atrial myocardium

There is a need for robust in vitro models of human atrial tissue to empower mechanistic disease research, drug discovery, toxicity screening, and precision medicine. In the present study, we used atrial-like human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-aCM) and hiPSC-cardiac fibroblasts to produce and evaluate atrial-like engineered cardiac tissue (aECT) constructs compared with adult native human atrial myocardium. Using various techniques to evaluate ultrastructure, molecular makeup, contractile function, and electrophysiology, we compare these aECT to ventricular-like engineered cardiac tissue (vECT) and native atrial myocardium. First, aECT demonstrated a higher spontaneous beating rate, lowered IRX4 mRNA expression, and an atrial-like expression of contractile mRNA and protein with higher MYL7/MLC2a and lower MYL2/MLC2v, compared with vECT, following similar patterns exhibited by native myocardium. Second, aECT exhibited ultrastructural features like native atrial myocardium, including lower cardiomyocyte circularity, higher dimensional cardiomyocyte anisotropy (i.e., rod-shaped), higher caveolae abundance, and higher sarcomere alignment. Importantly, aECT showed contractile parameters similar to those previously observed in native atrial myocardium with minimal differences between the two in twitch force, contraction and relaxation times, and contraction kinetics. Electrophysiological data also showed that aECT exhibits atrial-like action potential morphology, with shorter action potential duration, lower APD20/80 ratio, and higher repolarization fraction. Electrophysiological data were accompanied by elevated potassium channel mRNA expressions, compared with vECT. Overall, we have generated aECT with atrial-like phenotypes, compared with vECT and native atrial myocardium, that can be leveraged for drug testing and disease modeling of atrial electroanatomical remodeling and contractile dysfunction that occurs during atrial pathology.NEW & NOTEWORTHY We demonstrate an atrial-like engineered cardiac tissue that recapitulates adult human atrial contraction for both kinetics and force production. Furthermore, we include numerous previously unmeasured ultrastructure metrics such as sarcomere alignment, cardiomyocyte anisotropy, and caveolae abundance. Our constructs may provide a human cardiac tissue platform for drug testing to identify combinatorial therapies to address atrial contractile dysfunction and diseases linked to cardiomyocyte ultrastructural defects.