Extracardiac septum transversum/proepicardial endothelial cells pattern embryonic coronary arterio–venous connections

Abstract

Recent reports suggest that mammalian embryonic coronary endothelium (CoE) originates from the sinus venosus and ventricular endocardium. However, the contribution of extracardiac cells to CoE is thought to be minor and nonsignificant for coronary formation. Using classic (Wt1 Cre ) and previously undescribed (G2-Gata4 Cre ) transgenic mouse models for the study of coronary vascular development, we show that extracardiac septum transversum/ proepicardium (ST/PE)-derived endothelial cells are required for the formation of ventricular coronary arterio-venous vascular connections. Our results indicate that at least 20% of embryonic coronary arterial and capillary endothelial cells derive from the ST/PE compartment. Moreover, we show that conditional deletion of the ST/PE lineage-specific Wilms' tumor suppressor gene (Wt1) in the ST/PE ofG2-Gata4 Cre mice and in the endothelium of Tie2 Cre mice disrupts embryonic coronary transmural patterning, leading to embryonic death. Taken together, our results demonstrate that ST/PE-derived endothelial cells contribute significantly to and are required for proper coronary vascular morphogenesis.T he coronary vascular system, whose function is necessary to sustain late embryonic and postnatal cardiac function, is formed by a complex network of blood vessels, including arteries, arterioles, capillaries, venules, and veins (1). Recent reports indicate that various sources of endothelial cells contribute to the mammalian embryonic coronary system (2-4). However, the specific fate and function of these different endothelial cell pools during coronary vascular morphogenesis is the subject of intense controversy (5).Two endocardial populations have been reported to participate in the building of the embryonic coronary vascular system. The first derives from the sinus venosus endocardium, which sprouts to give rise to the nascent Apelin + coronary vasculature (2). A careful analysis of this study suggests that the sinus venosus endocardium, which is able to vascularize subepicardial and myocardial heart layers, mainly provides a cellular scaffold for the development of coronary veins (CoV). Accordingly, a second source of coronary endothelium (CoE) has been identified in the ventricular endocardium (Nfatc1 + lineage), which contributes massively to coronary arterial (CoA) endothelium (3, 6).A third disputed source of CoE is the proepicardium (PE), a structure that comprises epicardial progenitor cells. The PE protrudes from the septum transversum (ST), a folding of the lateral mesoderm that initiates the separation of thoracic and abdominal cavities in mammals (7). Although in vivo cell tracing and in vitro culture of avian PE cells clearly shows that PE cells can differentiate into CoE (8, 9), data from studies in mammals claimed the contribution of PE to CoE is minor (10-12). The so-called "epicardial" Cre constructs used in these studies are based on the expression of genes such as Gata5, Tbx18, or Wilms' tumor suppressor (Wt1) ( Table S1), all of which are expressed by both PE and...

Endocardium Minimally Contributes to Coronary Endothelium in the Embryonic Ventricular Free Walls

“…24 However, Cre-based lineage tracing in mouse studies showed that at most a small fraction of coronary vascular ECs arise from (pro)epicardium. 6,[28][29][30][31][32] In this study, although a few epicardial cells were labeled by Npr3-CreER, Npr3 + cells (including Npr3 + epicardial cells) minimally contributed to coronary vessels in the ventricular free walls. Taken together, our data are consistent with previous work suggesting the SV as the major source for coronary vessels in the ventricular free walls.…”

“…[5][6][7][8]14,[23][24][25][26][27] A consensus has emerged that there are 3 important sources for coronary vessels: proepicardium, VE, and SV. [1][2][3][4]28 Each source represents a unique developmental origin that may determine different models of coronary vessels formation. However, there is controversy over whether VE or SV is the major source for most coronary vessels.…”

WT1 in Cardiac Development and Disease

“…In addition, the same study revealed that the vessel density in matrigel plugs after subcutaneously injection, in mice lacking WT1 expression in endothelial cells, is significantly reduced compared to wild-type animals (71). Furthermore, deletion of WT1 in endothelial cells resulted in major reduction in cardiac vessel formation during mouse cardiac development supporting the presence of WT1 and the essential role of WT in cardiac endothelial cells (86).…”

Human Pluripotent Stem Cell-Derived Multipotent Vascular Progenitors of the Mesothelium Lineage Have Utility in Tissue Engineering and Repair

“…Lineage-marked descendants of mesothelium from multiple organs have been isolated and shown to have a similar potency to epicardium-derived cells (EPDCs) (Rinkevich et al, 2012). While there is some debate about the degree to which EPDCs contribute to the endothelium of the coronary vasculature (Pennisi, 2016), several studies indicate some contribution of the epicardium lineage to arterial vessels with the remainder coming from other sources (Cano et al, 2016; Chen et al, 2014a; Katz et al, 2012; Palmquist-Gomes et al, 2018; Pérez-Pomares and de la Pompa, 2011). Whether this endothelial contribution comes from EPDCs or another epicardial subtype is currently not known.…”