Lung microvascular endothelium is enriched with progenitor cells that exhibit vasculogenic capacity

Abstract

Endothelial progenitor cells (EPCs) have been isolated postnatally from bone marrow, blood, and both the intima and adventitia of conduit vessels. However, it is unknown whether EPCs can be isolated from the lung microcirculation. Thus we sought to determine whether the microvasculature possesses EPCs capable of de novo vasculogenesis. Rat pulmonary artery (PAEC) and microvascular (PMVEC) endothelial cells were isolated and selected by using a single-cell clonogenic assay. Whereas the majority of PAECs (approximately 60%) were fully differentiated, the majority of PMVECs (approximately 75%) divided, with approximately 50% of the single cells giving rise to large colonies (>2,000 cells/colony). These highly proliferative cells exhibited the capacity to reconstitute the entire proliferative hierarchy of PMVECs, unveiling the existence of resident microvascular endothelial progenitor cells (RMEPCs). RMEPCs expressed endothelial cell markers (CD31, CD144, endothelial nitric oxide synthase, and von Willenbrand factor) and progenitor cell antigens (CD34 and CD309) but did not express the leukocyte marker CD45. Consistent with their origin, RMEPCs interacted with Griffonia simplicifolia and displayed restrictive barrier properties. In vitro and in vivo Matrigel assays revealed that RMEPCs possess vasculogenic capacity, forming ultrastructurally normal de novo vessels. Thus the pulmonary microcirculation is enriched with EPCs that display vasculogenic competence while maintaining functional endothelial microvascular specificity.

Evidence of Dysfunction of Endothelial Progenitors in Pulmonary Arterial Hypertension

“…The late-outgrowth cells isolated from patients with BMPRII mutations demonstrated clear differences in angiogenic capacity and proliferation in response to serum. Interestingly, this is similar to the phenotypic descriptions of alterations in pulmonary microvascular endothelial cells that have been previously described in PAH (25,31).…”

“…Rat pulmonary microvascular endothelial cells postulated to arise from stem cells have demonstrated the capacity to reconstitute the entire proliferative hierarchy of the microvasculature (31). In humans a fraction of human aortic endothelial cells has long been known to demonstrate proliferative characteristics strikingly similar to those of stem cells (32) and more pertinently a hyperproliferative phenotype in idiopathic PAH endothelial cells has been identified (33).…”

The isolation and culture of endothelial colony-forming cells from human and rat lungs

“…Recently, three papers have demonstrated the existence of endothelial progenitor-like cells with a high potential for proliferation in the peripheral microvasculature of rat 19,20 and mouse 21 lungs.…”

“…The cells were cultured in DMEM supplemented with 10% fetal bovine serum (FBS) and antibiotics and observed to demonstrate ECFC-like phenotype, on the basis of both expression of surface antigens and functional behaviours such as uptake of low-density lipoprotein (LDL), maintenance of high barrier resistance, in vitro and in vivo vasculogenesis in Matrigel 20 . Weich and colleagues 21,22 , on the other hand, selected out CD31+ cells from mouse peripheral lung microvasculature by successively using magnetic and fluorescence-activated cell sorting (MACS and FACS).…”

Actin Cytoskeleton Regulates Stretch-Activated Ca2+ Influx in Human Pulmonary Microvascular Endothelial Cells

“…The expression of endothelial markers platelet EC adhesion molecule-1 (CD31) and Tie-2 was confirmed by immunofluorescent staining (data not shown). The HPMVECs were stained with the lectins Griffonia simplicifolia and Helix pomatia, which recognize microvascular and macrovascular endothelial cells, respectively (27,28). Staining with FITC-conjugated Griffonia simplicifolia but not with FITC-labeled Helix pomatia was observed (data not shown).…”