HLHS is characterised by underdevelopment of the left side of the heart, resulting in impaired systemic circulation. Although genetic factors are known to contribute to HLHS, they do not fully explain why the condition develops or why its severity differs between patients. In this study, we aimed to understand whether HLHS cardiomyocytes are already different before any external challenge, whether they react differently when stimulated, and whether these differences could make them more vulnerable during heart development. Using human induced pluripotent stem cells, we generated patient-specific cardiomyocytes to investigate molecular and functional changes associated with the disease.
Single-cell transcriptomic analyses revealed widespread changes in gene expression in HLHS cardiomyocytes, particularly affecting pathways involved in cardiac development, contraction, metabolism, and cellular stress responses. We also observed reduced activity in several transcription factor networks that normally help coordinate cardiac development and function. Functional experiments further demonstrated that HLHS cardiomyocytes exhibit an exaggerated response to endothelin-1–induced stress, including increased expression of the cardiac stress marker proBNP.
Together, our results indicate that cardiomyocytes in HLHS are intrinsically more vulnerable and less able to adapt to developmental stress. These findings support a multifactorial disease model in which genetic susceptibility and environmental or developmental stressors jointly contribute to disease progression. Future studies using larger patient cohorts will help to identify shared molecular features and advance our understanding of HLHS pathogenesis.