Human mature endothelial cells modulate peripheral blood mononuclear cells differentiation toward an endothelial phenotype

ABSTRACT. Circulating endothelial progenitor cells (EPCs) can contribute to neovascularization, even if the mechanisms by which they interact with mature endothelial cells remain unclear. The interactions between human coronary artery endothelial cells (HCAECs) and peripheral blood mononuclear cells (PBMCs) during their early differentiation towards an EPC phenotype were investigated. A coculture model, in which the two cell types share the same culture medium in the absence of any exogenous angiogenic stimulus, was used. The role of hypoxiawas assessed by pretreating HCAECs with 3% O2 before co-culture setting. Since we have previously shown that both adherent and suspended PBMCs display a significant increase in endothelial marker expression within the 2nd day of culture in an angiogenic environment, the role of HCAECs on early PBMC differentiationwas evaluated in both adherent and suspended cell fractions. A 3-day co-culture period increased the expression of VEGF-R2, VE-cadherin, αvβ3- and α5-integrin in both the adherent and suspended PBMCs, assessed by cytofluorimetric analysis, and upregulated VEGF-R1 mRNA assessed by real-time RT-PCR. HCAECs influenced PBMC adhesion, transendothelial migration and cell organization on Matrigel. Hypoxia modulated either PBMC differentiation or their functional properties. These data strongly suggest that endothelium may support the differentiation of PBMCs into EPCs.