Understanding heart development and maturation in health and disease

The heart's function depends upon highly regulated alternative splicing programs that underlie the transition between fetal and adult states and the maintenance of cardiac physiology. Disruption of this regulation, therefore, contributes to cardiomyopathies and heart failure. In my master's thesis project, I differentiated human induced pluripotent stem cells (hiPSCs) into major cardiac cell types to investigate the cell type-specific and stress-regulated cardiac splicing events. An RBM24 isoform that contains a “poison” exon was identified, whose inclusion restricts its expression under basal conditions in a cardiomyocyte-specific manner and is dynamically suppressed under doxorubicin-induced apoptosis. This switch enhances RBM24 and P21 protein levels, supporting a protective role against apoptosis, suggesting a splicing-dependent adaptive mechanism to cardiotoxic stress. In parallel, an alternative splicing-based fluorescent reporter system (SCN5A-pSLED) was engineered to distinguish fetal-like from mature hiPSC-derived cardiomyocytes based on the developmental SCN5A exon 6A/6B switch. After designing, the construct was tested in HEK-293 cells, and its responsiveness to MBNL1 expression demonstrated the feasibility of the process for monitoring splicing-driven maturation. These findings define a novel cardiomyocyte-specific regulatory mechanism relevant to stress adaptation and provide a tool that could evaluate cardiomyocyte maturity, thereby furthering the understanding of cardiac alternative splicing in physiology and disease.