The impact of proliferative potential of umbilical cord-derived endothelial progenitor cells and hypoxia on vascular tubule formation in vitro.

Revascularization of the damaged tissue is pivotal to tissue repair. Here, by bringing together two in vitro model systems, we have been able to examine (1) the ability of human umbilical vein endothelial cells (HUVEC) containing a complete hierarchy of endothelial progenitors derived from the human umbilical cord to generate vascular tubules within a human stromal niche in vitro and (2) the effects of exposure to low oxygen tensions on endothelial progenitor cell proliferation and tubule formation in vitro. Our results demonstrate that high proliferative potential endothelial colony forming cells (HPP-ECFC) from cultured HUVEC preferentially contribute to vascular tubule formation in vitro and that these progenitor cells are concentrated in the CD34lo/− fraction. HUVEC were initially resistant when exposed to hypoxia (1.5% O2) for short periods (1–2 days), but sustained chronic hypoxia (4–14 days) inhibited their ability to proliferate. This was reflected by a loss in their ability to form tubules in coc...