Identification of functional endothelial progenitor cells suitable for the treatment of ischemic tissue using human umbilical cord blood

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Abstract
Umbilical cord blood (UCB) has been used as a potential source of various kinds of stem cells, including hematopoietic stem cells, mesenchymal stem cells, and endothelial progenitor cells (EPCs), for a variety of cell therapies. Recently, EPCs were introduced for restoring vascularization in ischemic tissues. An appropriate procedure for isolating EPCs from UCB is a key issue for improving therapeutic efficacy and eliminating the unexpected expansion of nonessential cells. Here we report a novel method for isolating EPCs from UCB by a combination of negative immunoselection and cell culture techniques. In addition, we divided EPCs into 2 subpopulations according to the aldehyde dehydrogenase (ALDH) activity. We found that EPCs with low ALDH activity (Alde-Low) possess a greater ability to proliferate and migrate compared to those with high ALDH activity (Alde-High). Moreover, hypoxia-inducible factor proteins are up-regulated and VEGF, CXCR4, and GLUT-1 mRNAs are increased in Alde-Low EPCs under hypoxic conditions, while the response was not significant in Alde-High EPCs. In fact, the introduction of Alde-Low EPCs significantly reduced tissue damage in ischemia in a mouse flap model. Thus, the introduction of Alde-Low EPCs may be a potential strategy for inducing rapid neovascularization and subsequent regeneration of ischemic tissues.