Mechanisms of early hemato-endothelial development from human pluripotent stem cells

Abstract

Hemogenic endothelium is a highly specialized population of vascular endothelial cells that produces hematopoietic stem cells (HSCs) during embryonic development. This process, referred to as the endothelial-to-hematopoietic transition (EHT), is critical to establish a functional hematopoietic system that persists throughout adulthood. The underlying genetic and cell signaling mechanisms that regulate human EHT remain poorly defined. Human pluripotent stem cells, including embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) provide a well-defined cellular platform that can be used to study these mechanisms. In this work, functional human hemogenic endothelium was identified and isolated from the earliest hemato-endothelial cells differentiated from hESCs. Analysis of hemogenic endothelial cells at a single-cell resolution found hESC-derived hemogenic endothelium was transcriptionally distinct from vascular endothelial cells lacking hematopoietic potential. Novel genetic markers distinguishing human hemogenic endothelium are also presented. Contributions from the aryl hydrocarbon receptor (AHR), an important cell signaling molecule in HSC biology, were also assessed at the level of human EHT. Small molecule inhibition and gene deletion of AHR significantly improved functional hematopoietic stem and progenitor cell development from hESCs. Importantly, a novel role for AHR in the development of hESC-derived innate lymphoid cells is also presented. Collectively, this dissertation identifies and describes key transcriptional and signaling mechanisms that support human EHT. This information will be useful to optimize the development of HSCs and other hematopoietic lineages that are suitable for future clinical application.