Epicardial slices: a 3D organotypic model for the study of epicardial activation and differentiation

The epicardium constitutes an untapped reservoir for cardiac regeneration. Upon myocardial injury, the adult epicardium re-activates the embryonic program, leading to epithelial-to-mesenchymal transition, migration and differentiation. Despite some successes in harnessing the epicardial therapeutic potential by thymosin {beta}4 (T{beta}4) pre-treatment, further translational advancements are hampered by the paucity of representative experimental models. Here we apply innovative protocols to obtain living 3D organotypic slices from porcine hearts, encompassing the epicardial/myocardial interface. In culture, our slices preserve the in vivo architecture and functionality, presenting a continuous epicardium overlaying a healthy and connected myocardium. Upon T{beta}4 treatment of the slices, the epicardial cells become activated upregulating embryonic and EMT genes and invading the myocardium where they differentiate towards the mesenchymal lineage. Our 3D organotypic model enables to investigate the reparative potential of the adult epicardium, offering a new tool to explore ex vivo the complex 3D interactions occurring within the native heart environment.