Gang Wang

The epicardium makes essential cellular and paracrine contributions to the growth of the fetal myocardium and the formation of the coronary vasculature. However, whether the epicardium has similar roles postnatally in the normal and injured heart remains enigmatic. Here, we have investigated this question using genetic fate-mapping approaches in mice. In uninjured postnatal heart, epicardial cells were quiescent. Myocardial infarction increased epicardial cell proliferation and stimulated formation of epicardium-derived cells (EPDCs), which remained in a thickened layer on the surface of the heart. EPDCs did not adopt cardiomyocyte or coronary EC fates, but rather differentiated into mesenchymal cells expressing fibroblast and smooth muscle cell markers. In vitro and in vivo assays demonstrated that EPDCs secreted paracrine factors that strongly promoted angiogenesis. In a myocardial infarction model, EPDC-conditioned medium reduced infarct size and improved heart function. Our findings indicate that epicardium modulates the cardiac injury response by conditioning the subepicardial environment, potentially offering a new therapeutic strategy for cardiac protection.

UNLABELLED: With the advent of induced pluripotent stem cell (iPSC) technology, it is now feasible to generate iPSCs with a defined genotype or disease state. When coupled with direct differentiation to a defined lineage, such as hepatic endoderm (HE), iPSCs would revolutionize the way we study human liver biology and generate efficient "off the shelf" models of human liver disease. Here, we show the "proof of concept" that iPSC lines representing both male and female sexes and two ethnic origins can be differentiated to HE at efficiencies of between 70%-90%, using a method mimicking physiological relevant condition. The iPSC-derived HE exhibited hepatic morphology and expressed the hepatic markers albumin and E-cadherin, as assessed by immunohistochemistry. They also expressed alpha-fetoprotein, hepatocyte nuclear factor-4a, and a metabolic marker, cytochrome P450 7A1 (Cyp7A1), demonstrating a definitive endodermal lineage differentiation. Furthermore, iPSC-derived hepatocytes produced and secreted the plasma proteins, fibrinogen, fibronectin, transthyretin, and alpha-fetoprotein, an essential feature for functional HE. Additionally iPSC-derived HE supported both CYP1A2 and CYP3A4 metabolism, which is essential for drug and toxicology testing. CONCLUSION: This work is first to demonstrate the efficient generation of hepatic endodermal lineage from human iPSCs that exhibits key attributes of hepatocytes, and the potential application of iPSC-derived HE in studying human liver biology. In particular, iPSCs from individuals representing highly polymorphic variants in metabolic genes and different ethnic groups will provide pharmaceutical development and toxicology studies a unique opportunity to revolutionize predictive drug toxicology assays and allow the creation of in vitro hepatic disease models.