STEM CELL AND HYPOXIA-BASED APPROACHES TO ENGINEERING BLOOD VESSELS
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The success of tissue regenerative therapies is contingent upon functional and multicellular vasculature within the redeveloping tissue. Endothelial cells (ECs), which comprise the vasculature’s inner lining, are intrinsically able to form nascent networks; however, without recruitment of pericytes, supporting cells that surround microvessel endothelium, these endothelial-only structures regress. To reconstruct a typical in vivo microvascular architecture, distinct cell sources of ECs and pericytes have traditionally been used within naturally occurring extracellular matrices (ECMs). However, the limited clinically-relevant human cell sources and inherent chemical and physical properties of natural materials hamper the translational potential of these approaches. Human pluripotent stem cells (hPSCs) are an unlimited source of progenitors from which vascular cells may be derived. Controlled and robust differentiation of hPSCs toward vascular lineages is critical for the advancement and future of patient-specific vascular therapeutics. In this work, we first derived a bicellular vascular population of ECs and pericytes, termed early vascular cells (EVCs), from hPSCs that undergoes vascular morphogenesis in a synthetic matrix to form networks that integrate with host vasculature. Next, we found that low oxygen environments enhance endothelial lineage commitment in EVCs. Subsequently, we compared arterial and venous ECs to an adult stem cell population, endothelial colony forming cells (ECFCs), revealing that ECFCs deposited abundant ECM; mature ECs only produced these ECM proteins under hypoxic conditions via hypoxia-inducible factors 1α and 2α. Finally, we found that EVCs differentiated under low oxygen conditions could produce copious amounts of collagen IV and fibronectin as well as angiogenic growth factors. EVCs differentiated under atmospheric conditions did not demonstrate such abundant ECM expression. Collectively, these findings reveal that control over microenvironmental cues via appropriate signaling molecules is able to robustly produce critical cells of the vasculature, which may in turn serve as novel therapies for vascular diseases or be incorporated into engineered tissue.