ABSTRACT
Here we investigated the impact of hypoxic environment on the angiogenic properties of early-outgrowth endothelial progenitor cells (EPCs), with particular focus on the role of secreted vascular endothelial growth factor-A (VEGF-A) and stromal derived factor-1 (SDF-1) in mediating these effects. We found that cultured EPCs secreted factors with paracrine effects on chemotaxis, migration, proliferation and tube formation of mature endothelial cells (ECs), and these properties were not affected by hypoxia. Depletion of VEGF-A did not change the ability of EPC-conditioned medium (CM) to promote EC migration and tube formation in vitro, suggesting that the pro-angiogenic paracrine effects of EPCs did not totally rely on the presence of VEGF-A. These findings were confirmed by in vivo experiments, on a mouse model of hind limb ischaemia, which showed that VEGF-depleted EPC-CM sustained tissue perfusion at the same level as complete EPC-CM. However, concomitant deletion of VEGF-A and SDF-1 in EPC-CM impaired the pro-angiogenic properties of EPC-CM, by inhibition of EC spreading in culture, tube-like structure formation on Matrigel support, in vivo neovessels formation and ischaemic hind limb regeneration. Taken together, our data demonstrate that: (i) hypoxia does not affect the capacity of EPCs to support the angiogenic process; (ii) the absence of either VEGF-A or SDF-1 from EPC-CM can be rescued by the presence of the other one, so that the overall angiogenic effects remain unchanged; and (iii) and the concomitant deletion of VEGF-A and SDF-1 from EPC-CM impairs its pro-angiogenic effect, both in vitro and in vivo. Copyright © 2016 John Wiley & Sons, Ltd.