Isthmin-1 is a Key Regulator of Induced Pluripotent Stem Cell–Derived Cardiomyocytes Maturation through Activation of p53 Signaling

Abstract Aims Human induced pluripotent stem cell–derived cardiomyocytes (iPSC-CMs) exhibit an immature structural and metabolic phenotype that limits their utility for cardiac disease modeling and regenerative therapy. Although multiple extrinsic strategies have been proposed to enhance iPSC-CM maturation, intrinsic molecular regulators governing this process remain incompletely defined. This study aimed to identify and characterize a novel molecular factor that promotes cardiomyocyte maturation. Methods and Results Cross-species transcriptomic analyses comparing adult versus fetal hearts and hypertrophic cardiomyopathy versus healthy myocardium identified Isthmin-1 (ISM1) as a conserved maturation-associated gene. In human iPSC-CMs, ISM1 overexpression enhanced sarcomere organization, mitochondrial oxidative phosphorylation, ATP production, and calcium-handling properties, whereas ISM1 knockdown impaired these maturation features. RNA sequencing revealed global transcriptional reprogramming toward an adult-like state, characterized by suppression of cell-cycle–related gene programs and activation of oxidative metabolic pathways. KEGG pathway enrichment, GSVA, and GSEA consistently identified p53 signaling as the most significantly activated pathway in ISM1-overexpressing iPSC-CMs. Mechanistically, ISM1 directly interacted with p53, enhanced its protein stability, promoted nuclear localization, and increased transcription of p53 downstream targets involved in metabolic remodeling and cell-cycle exit. Pharmacological inhibition of p53 abolished ISM1-induced structural and metabolic maturation, demonstrating that ISM1 promotes cardiomyocyte maturation in a p53-dependent manner. Conclusions ISM1 is a previously unrecognized molecular driver of cardiomyocyte maturation that promotes structural, metabolic, and functional maturation of iPSC-CMs through activation of p53-dependent transcriptional programs. These findings provide new mechanistic insight into cardiomyocyte maturation and identify ISM1 as a promising target for improving the maturity of stem cell–derived cardiomyocytes. Graphical Abstract