Comparison between endothelial progenitor cells and human umbilical vein endothelial cells on neovascularization in an adipogenesis mouse model

Volume stability and growth of tissue engineered adipose tissue equivalents using adipose-derived stem cells (ASCs) rely strongly on angiogenesis and neovascularization to support the maintenance of cells. An attractive cellular approach is based on coimplantation of endothelial cells to create a vascular network. Endothelial progenitor cells (EPCs) are a promising cell population, since they can be easily isolated from autologous human peripheral blood and thus represent a clinically feasible option. We have previously shown in in vitro and semi-in vivo studies that ASCs exert beneficial effects on EPCs in terms of enhanced tube formation and formation of blood vessels, respectively. In this study, we investigated the in vivo effects of coimplantation on endothelial cell-mediated neovascularization and ASC-mediated adipose tissue formation. For this purpose, human ASCs and human EPCs (or HUVECs as direct comparison to EPCs) were suspended alone or in coculture in fibrin and subcutaneously injected into the back of athymic nude mice and explanted after 1, 3 or 6 months. Our results show that monocultures of EPCs or HUVECs were not able to perform vasculogenesis and constructs exhibited complete resorption already after 1 month. However, a remarkable difference between EPCs and HUVECs was detected when coimplanted with ASCs. While coimplanted HUVECs gave rise to a stable neovasculature which was characterized by perfusion with erythrocytes, coimplanted EPCs showed no ability to form vascular structures. In the case of HUVEC-derived neovasculature, coimplanted ASCs displayed perivascular properties by stabilizing these neovessels. However, formation of human adipose tissue was independent of coimplanted endothelial cells. Our results indicate that HUVECs are superior to EPCs in terms of promoting in vivo neovascularization and recruiting perivascular cells for vessel stabilization when coimplanted with ASCs.