Three-dimensional cardiac organoid formation accelerates the functional maturation of human induced pluripotent stem cell-derived cardiomyocytes

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs) offer a promising source for heart regeneration, disease modeling, and drug screening. Recent developments in organoid technology have made it possible to study how hiPSC-derived CMs interact together, and this culture system mimics the tissue environment and behavior of the cardiac cells in our body. However, the similarities and differences between conventional 2-dimensional (2D) culture and 3-dimensional (3D) organoid culture systems for CM differentiation have been incompletely elucidated. To study how the individual microenvironment formed by each culture system affects the properties of CMs differentiated from hiPSCs, we conducted a comparative study between 2D monolayer and direct 3D cardiac organoid (hiCO) differentiation from hiPSCs throughout the sequential differentiation stages. Although identical differentiation cues were applied to hiPSCs, the 3D differentiation system strongly exhibited higher mesoderm commitment and cardiac induction than 2D monolayer differentiation. In the late stage of differentiation, the 3D hiCOs showed a higher frequency of a mature myofibrillar isoform switching in sarcomere structure of differentiated CMs than was observed in monolayer culture, although over 94% of cardiac troponin T-positive cells resulted at the end point of differentiation in both systems. Furthermore, the accelerated structural maturation in 3D hiCOs resulted in increased expression of cardiac-specific ion channel genes and Ca2+ transient properties, with a high signal amplitude and rapid contractility. The present study provides details surrounding the 2D and 3D culture methods for CM differentiation from iPSCs, and focuses on 3D cell culture as an improved strategy for approaching and applying cardiac maturation.