Abstract 97: Epigenetic Signatures Contribute to the Superior Endothelial Cell Identity in Human Induced Pluripotent Stem Cells Derived From Endothelial Cells

Abstract

Human induced pluripotent stem cells (iPSCs) can be derived from multiple types of somatic cells by transient overexpression of four Yamanaka factors. Epigenetic memory of the tissue of origin is seen in early passage iPSCs, which may interfere the directed differentiation towards target lineages in disease modeling and drug discovery. Here we derived human iPSC from three types of somatic cells of the same individuals: fibroblast (FB-iPSCs), endothelial cells (EC-iPSCs) and cardiac progenitor cells (CPC-iPSCs). We then differentiated them into endothelial cells by using sequential administration of Activin, BMP4, bFGF and vEGF. EC-iPSCs show higher EC differentiation propensity and EC-specific markers (PECAM1 and NOS3) gene expression in early passage iPSCs than FB-iPSCs and CPC-iPSCs. In vivo, EC-iPSC-ECs display significantly greater revascularization capacity than those of FB-iPSCs and CPC-iPSCs when transplanted to the hindlimb ischemic mice. In addition, transplanted EC-iPSC-ECs were recovered with a higher percentage of CD31+ population and higher EC-specific markers (PECAM1, KDR and ICAM) gene expression by using single cell qPCR. In vitro, EC-iPSC-ECs exhibit better endothelial cell character maintenance along with extensive culturing and passaging. Several chromatin signatures, including H3K27ac, H3K4me1 and p300 were found highly enriched in ECs and EC-iPSCs, but not in human embryonic stem cells (ESCs). Gene ontology analysis indicates that the differentially enriched regions are primarily associated with angiogenesis and vascular development, reflecting the residual epigenetic signatures in EC-iPSCs. Finally EC-specific enhancer markers undergo dynamic changes during the process of EC fate commitment and differentiation, though the majority of them sustain conserved pattern in EC-iPSCs, CPC-iPSCs and FB-iPSCs. In conclusion, these results highlight that the residual epigenetic signatures of tissue of origin may affect lineage differentiation propensity in early-passage human iPSCs.