Distinct phenotypes and regenerative potentials of early endothelial progenitor cells and outgrowth endothelial progenitor cells derived from umbilical cord blood.

The capability of postnatal neovascularization makes circulating endothelial progenitor cells (EPCs) promising for regenerative medicine and tissue engineering. Using EPCs isolated from umbilical cord blood, this study aimed to clarify the transition of functional properties from early EPCs (e-EPCs) to outgrowth EPCs (og-EPCs) for potential applications in regenerative medicine. Mononuclear cells were collected from umbilical cord blood via density gradient centrifugation and further negatively selected by CD45. EPCs were sorted from mononuclear cells by the expression of CD34. e-EPCs (7 days of culture) and og-EPCs (3 weeks of culture) were characterized by morphology, intake of acetylated low-density lipoprotein, vessel-cord formation, cell surface phenotype and the expression of angiogenic genes. e-EPCs and og-EPCs were also compared for osteogenic differentiation under the stimulation of BMP-2. Chemotaxis by SDF-1 was compared among og-EPCs and the first- and second-day attached e-EPCs. Based on the expression of angiogenic genes, e-EPCs possessed few angiogenic properties in vitro and og-EPCs were angiogenic. e-EPCs, however, expressed significant CXCR4 and migrated toward the SDF-1 gradient. og-ECPs did not express CXCR4 and showed no response to SDF-1. During culture, gaining an angiogenic phenotype by og-EPCs is associated with the loss of homing potential. These contrast properties determine different potentials of e-EPCs and og-EPCs in regenerative medicine.