UC San Diego

Hypoplastic Left Heart Syndrome (HLHS) is a congenital heart defect that results in hypoplasia of the left ventricle and changes in cardiac hemodynamics during development. Cardiomyocytes derived from HLHS patients exhibit reduced contractility and diminished proliferative capacity, suggesting that disrupted mechanical loading may contribute to disease progression. While abnormal hemodynamic forces are known to influence cardiac development, their effect on nuclear structure and mechanoregulation at single-cell level remain poorly understood. The nucleus is a central mechanosensitive organelle that responds to extracellular and cytoskeletal forces through nuclear lamina, whose structural integrity depends largely on Lamin A/C (LMNA). Prior nuclear mechanobiology studies have shown that Lamin A/C responds to mechanical cues and contributes to nuclear mechanical resilience [1]. However, it remains unclear how the interplay between altered developmental hemodynamics and matrix stiffness jointly influences Lamin A/C expression, nuclear mechanoadaptation, and cellular remodeling during cardiac development, particularly in cardiomyocytes derived from the left atrial ligation (LAL) model of hypoplastic left heart syndrome. LAL causes immediate flow and wall shear stress changes in chick embryo that propagate into more serious defect with 4 to 5 days post-surgery [2]. This thesis tests the hypothesis that altered developmental hemodynamics in the chick left atrial ligation (LAL) model impair nuclear mechanoadaptation in developing cardiomyocytes, resulting in altered LAMN A/C expression and organization, as well as changes in nuclear and cellular morphology. These effects are expected to be modulated by extracellular matrix stiffness and developmental stage. To test this hypothesis nuclear morphology, cellular morphology, and Lamin A/C organization are quantified at the single-cell level across healthy and disease conditions (LAL vs control), developmental stage (HH27 vs. HH31), and substrate stiffness represented by 0.3 kPa (verry soft), 1-2 kPa (heart-like), and 40 kPa (very stiff) hydrogels. This study defines how ECM mechanics and nuclear lamina regulation intersect to shape mechanosensitive remodeling relevant to ventricular hypoplasia.