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Lung microvascular resident endothelial progenitor cells exhibit high vasculogenic capacity

We recently cloned endothelial progenitor cells (EPCs) residing within the pulmonary microcirculation. However, it is not clear whether resident EPCs display de novo vessel formation, a sine qua non behavior of endothelial cells. We hypothesized that resident lung EPCs possess high vasculogenic capacity. Rat endothelial cells were isolated from the pulmonary artery (PAECs) and the pulmonary microcirculation (PMVECs), while resident EPCs were selected from PMVECs using a single cell clonogenic assay. An in vitro Matrigel assay revealed that PAECs organize in scattered patches, while PMVECs and EPCs form extensive, time‐dependent networks beginning as early as 8 hours post‐seeding (2, 7 and 8 networks/mm2, respectively). Vasculogenic capacity was determined by the de novo vessel formation within in vivo gel implants containing GFP‐retrovirally transfected cells. Removal of plugs after 4 days demonstrated that PMVEC and EPCs, but not PAECs, form de novo vessels. After 10 days, EPCs display high vasculogenic capacity compared to PAECs and PMVECs (11, 3, and 8 vessels/mm2, respectively). Ultrastructural analysis revealed integrity of newly formed vessels. Immunostaining confirmed the presence of GFP‐tagged cells within the intima of de novo vessels. The data indicate that lung microvascular EPCs display a uniquely high vasculogenic capacity, which is a critical determinant of vascular repair. HL66299.