Generation of functional human NKX2.5GFP reporter cell lines for direct reprogramming into proliferative cardiac progenitors

Abstract

The mammalian heart is the first organ formed in the embryo and is composed of four chambers: right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV), and three layers: the endocardium, the myocardium, and the pericardium. The endocardium is formed by simple squamous epithelium known as endothelium, which lines the chambers and is joined to myocardium by a thin layer of connective tissue. The pericardium is comprised of two distinct sublayers: the inner serous pericardium, which is formed by visceral pericardium or epicardium and parietal pericardium separated by pericardial cavity, and the outer fibrous pericardium made of dense connective tissue. The myocardium is the muscular layer of the heart, it is the thickest one and is located between the endocardium and the pericardium. With regard to cellular composition, the heart is principally formed by cardiomyocytes (CM), cardiac fibroblasts (cFib) , vascular smooth muscle cells (localized fundamentally within the myocardium), vascular endothelial cells (located within the myocardium and endocardium) and mesothelial cells present in the pericardium 1–3 . CM are specialized cells with a complex filament structure responsible for the control of the rhythmic beating of the heart and present heterogeneity depending on the location, morphology, and function, including atrial, ventricular, sinoatrial nodal, atrioventricular nodal, His bundle, and Purkinje fibers 4,5 .