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 CD34(lo/-) fraction. HUVEC were initially resistant when exposed to hypoxia (1.5% O(2)) 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 cocultures of human dermal fibroblasts (hDFs). In contrast, an acute exposure to low oxygen tensions (1.5% O(2) for 24 h) followed by reoxygenation did not adversely affect the capacity of these cells to both proliferate and form vascular tubules in vitro.These studies therefore provide a model system to study the influences of the microenvironmental niche and modification of this niche on vascular tubule formation in vitro from HPP-ECFC.

Transcriptional profiling of human cord blood CD133+ and cultured bone marrow mesenchymal stem cells in response to hypoxia.

Umbilical cord blood (UCB) and bone marrow (BM)-derived stem and progenitor cells possess two characteristics required for successful tissue regeneration: extensive proliferative capacity and the ability to differentiate into multiple cell lineages. Within the normal BM and in pathological conditions, areas of hypoxia may have a role in maintaining stem cell fate or determining the fine equilibrium between their proliferation and differentiation. In this study, the transcriptional profiles and proliferation and differentiation potential of UCB CD133(+) cells and BM mesenchymal cells (BMMC) exposed to normoxia and hypoxia were analyzed and compared. Both progenitor cell populations responded to hypoxic stimuli by stabilizing the hypoxia inducible factor (HIF)-1alpha protein. Short exposures to hypoxia increased the clonogenic myeloid capacity of UCB CD133(+) cells and promoted a significant increase in BMMC number. The differentiation potential of UCB CD133(+) clonogenic myeloid cells was unaltered by short exposures to hypoxia. In contrast, the chondrogenic differentiation potential of BMMCs was enhanced by hypoxia, whereas adipogenesis and osteogenesis were unaltered. When their transcriptional profiles were compared, 183 genes in UCB CD133(+) cells and 45 genes in BMMC were differentially regulated by hypoxia. These genes included known hypoxia-responsive targets such as BNIP3, PGK1, ENO2, and VEGFA, and other genes not previously described to be regulated by hypoxia. Several of these genes, namely CDTSPL, CCL20, LSP1, NEDD9, TMEM45A, EDG-1, and EPHA3 were confirmed to be regulated by hypoxia using quantitative reverse transcriptase polymerase chain reaction. These results, therefore, provide a global view of the signaling and regulatory network that controls oxygen sensing in human adult stem/progenitor cells derived from hematopoietic tissues.