Abstract
The epicardium constitutes an untapped reservoir for cardiac regeneration. Upon heart injury, the adult epicardium re-activates, leading to epithelial-to-mesenchymal transition (EMT), migration, and differentiation. While interesting mechanistic and therapeutic findings arose from lower vertebrates and rodent models, the introduction of an experimental system representative of large mammals would undoubtedly facilitate translational advancements. Here, we apply innovative protocols to obtain living 3D organotypic epicardial 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 thymosin β4 treatment of the slices, the epicardial cells become activated, upregulating epicardial and EMT genes, resulting in epicardial cell mobilization and differentiation into epicardial-derived mesenchymal cells. Our 3D organotypic model enables to investigate the reparative potential of the adult epicardium, offering an advanced tool to explore ex vivo the complex 3D interactions occurring within the native heart environment.
Highlights
The epicardium plays a crucial role in the embryo during heart development[1]
Even in the absence of an ischemic stimulus, Tβ4 treatment resulted in epicardial cells activation leading to the overexpression of epicardial transcription factors and epithelial-to-mesenchymal transition (EMT) markers in the slices, enhancing the epicardial cell motility and differentiation
In order to maintain a viable epicardial cell monolayer, we developed an alternative protocol that protects the epicardium while ensuring the myocardium alignment
Summary
The epicardium plays a crucial role in the embryo during heart development[1]. Lineage tracing studies indicate that the embryonic epicardium is a major source of cardiac fibroblasts[2], cardiac adipose tissue[3], vascular smooth muscle cells, and pericytes of the coronary vasculature[4]. In response to injury, such as myocardial infarction (MI), the adult epicardium is able to retrace the embryonic gene expression, upregulating transcription factors such as Wilms’ tumor 1 (WT1) and T box 18 (Tbx18)[5,6,7] In this context, epicardial cells undergo epithelial-to-mesenchymal transition (EMT) and start migrating into the myocardium, contributing to remodeling, re-vascularization, and repair through differentiation and paracrine stimulation[8,9]. Despite some clinical evidence of the human newborn hearts’ recovery capacity[11], the role of the epicardium in human adult heart repair has been largely investigated through primary or progenitor-derived cell culture experiments[12,13,14] These valuable systems do not replicate the multicellular complexity of the tissue and the interaction with the extracellular matrix (ECM), which play a critical role in the epicardial-mediated repair[15]. A robust and comprehensive model of the epicardial physiological environment is needed to help unveil the adult epicardial cell potential in large mammals
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