Pediatric dilated cardiomyopathy caused by <scp>TNNT2</scp> ‐ <scp>R151W</scp> mutation: Modeling and rescue in patient‐derived <scp>i</scp> nduced pluripotent stem cells and engineered heart tissue

Abstract Dilated cardiomyopathy (DCM) is the most prevalent pediatric cardiomyopathy and has a poor prognosis. Although heart transplantation is the only curative option, the severe donor shortage in Japan underscores an urgent need for alternative therapies. Here, we generated induced pluripotent stem cell (iPSC) lines from two unrelated children with the same TNNT2‐R151W mutation. We then investigated the cellular characteristics of the cardiomyocytes derived from these iPSC lines (R151W iPSC‐CMs) and evaluated their contractile function in pillar‐based engineered heart tissue (EHT). We also assessed the therapeutic potential of overexpressing wild‐type TNNT2 in patient‐derived iPSCs (wtTNNT2‐OE‐iPSCs). R151W‐iPSC‐CMs exhibited pronounced sarcomere disarray, attenuated Ca 2+ transient amplitude, prolonged time to peak, and delayed decay tau. These characteristics are indicative of failing myocardium and were restored in wtTNNT2‐OE‐iPSC‐CMs. Pillar‐based EHT assays revealed a substantial decrease in contractile force in R151W‐EHTs compared to wtTNNT2‐OE‐EHTs, which is suggestive of the systolic dysfunction observed clinically in DCM. Collectively, these results provide the first functional evidence that the TNNT2‐R151W mutation leads to pediatric DCM by causing sarcomere insufficiency and disturbances in Ca 2+ handling. Our patient‐specific iPSC‐EHT platform faithfully recapitulates key features of pediatric DCM and could offer a robust system for mechanistic studies and drug testing. Furthermore, phenotypic rescue upon overexpression of wild‐type TNNT2 suggests that this allele is amenable to a gene replacement approach aimed at restoring wild‐type function in TNNT2‐mutant cardiomyopathies.