Microenvironmental Reprogramming by 3D Anisotropic Cardiac Extracellular Matrix Induces Nuclear Remodeling and Epigenetic Maturation of Chemically Induced Cardiomyocytes

ABSTRACT Extracellular matrix (ECM) of the heart exhibits highly organized anisotropy, which is essential for directing cellular alignment, force transmission, and tissue function. However, mechanistic pathways linking ECM alignment to nuclear and epigenetic remodeling remain poorly defined, especially in the context of direct cardiac reprogramming. Here, a 3D anisotropically aligned decellularized heart ECM (HEM) is engineered to investigate how structural and biochemical cues modulate maturation of chemically induced cardiomyocyte‐like cells (CiCMs). The alignment of HEM enhances cytoskeletal organization and perinuclear actin assembly, leading to nuclear elongation and intermembrane redistribution of emerin from the inner to the outer nuclear membrane. These changes are accompanied by upregulation of SUN1/2, key components of the LINC complex, and by a transient increase in nuclear YAP/TAZ localization. Chromatin condensation is reduced under aligned conditions, with corresponding increases in H3K4me3 and decreases in H3K9me3, indicative of a more transcriptionally permissive chromatin state. Functionally, CiCMs in aligned HEM exhibit improved sarcomere structure and t‐tubule development, enhanced responsiveness to β ‐adrenergic and muscarinic stimulation, and increased contractile force under electrical pacing. These findings reveal a mechanotransductive cascade linking cardiac ECM alignment to nuclear and chromatin remodeling, ultimately promoting functional maturation of reprogrammed cardiomyocytes in a biomimetic 3D microenvironment.