Derivation of human post-mitotic cardiomyocytes from tetraploid iPSCs

Human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (iPS-CMs) have great potential in regenerative medicine. However, iPS-CMs are immature and resemble fetal cardiomyocytes, restricting their application. Fetal cardiomyocytes in the human heart are diploid and proliferating, but gradually lose their proliferative potential during maturation. Most human cardiomyocytes eventually become tetraploid, but iPS-CMs cannot replicate this tetraploidization and remain immature with the current differentiation techniques. To overcome this problem, we fused diploid iPSCs to establish tetraploid iPSCs and differentiated them into cardiomyocytes (4N-iPS-CMs) to replicate the tetraploidy. As we expected, we found that 4N-iPS-CMs had more similar gene expression profiles, improved mitochondrial functions, contractile impedance, and resistance to a potassium blocker in post-mitotic cardiomyocytes than conventional iPS-CMs. In addition, we successfully generated 4N-iPS-CMs from two individuals to mix two different genetic backgrounds. Thus, we demonstrated a unique strategy for generating human post-mitotic cardiomyocyte-like cells by generating tetraploid iPSCs.