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      Myeloid Lineage of Human Endothelial Outgrowth Cells Circulating in Blood and Vasculogenic Endothelial-Like Cells in the Diseased Vessel Wall

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          Endothelial injury is a major step in the pathogenesis of atherosclerosis. Accumulated data suggest endothelial progenitor cells can derive from various sources, including the host bone marrow, circulating blood mononuclear cells, as well as resident precursors within the vessel wall. Early experimental animal data supported a haematopoietic origin for vascular precursors, but more recently cells of myeloid lineage have been suggested as precursors of endothelial and smooth muscle cells. However, to date, little evidence exists to support a myeloid lineage-endothelial cell differentiation pathway within the vasculature of human subjects. Here, we undertook two sets of experiments aimed at determining whether (a) blood endothelial outgrowth cells (EOC) had a myeloid lineage and whether (b) chimeric endothelial-like cells within the neovasculature of gender-mismatched cardiac transplant arteriopathy subjects shared common myelomonocytic markers. We show here that in vitro blood-derived EOC and recipient-derived endothelial-like cells participating in vasculogenesis in vivo share some myeloid immunophenotypes. Additionally, these microvascular chimeric cells show no evidence of tetraploidy or cell fusion.

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          Most cited references 19

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          Redefining endothelial progenitor cells via clonal analysis and hematopoietic stem/progenitor cell principals.

          The limited vessel-forming capacity of infused endothelial progenitor cells (EPCs) into patients with cardiovascular dysfunction may be related to a misunderstanding of the biologic potential of the cells. EPCs are generally identified by cell surface antigen expression or counting in a commercially available kit that identifies "endothelial cell colony-forming units" (CFU-ECs). However, the origin, proliferative potential, and differentiation capacity of CFU-ECs is controversial. In contrast, other EPCs with blood vessel-forming ability, termed endothelial colony-forming cells (ECFCs), have been isolated from human peripheral blood. We compared the function of CFU-ECs and ECFCs and determined that CFU-ECs are derived from the hematopoietic system using progenitor assays, and analysis of donor cells from polycythemia vera patients harboring a Janus kinase 2 V617F mutation in hematopoietic stem cell clones. Further, CFU-ECs possess myeloid progenitor cell activity, differentiate into phagocytic macrophages, and fail to form perfused vessels in vivo. In contrast, ECFCs are clonally distinct from CFU-ECs, display robust proliferative potential, and form perfused vessels in vivo. Thus, these studies establish that CFU-ECs are not EPCs and the role of these cells in angiogenesis must be re-examined prior to further clinical trials, whereas ECFCs may serve as a potential therapy for vascular regeneration.
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            Vascular wall resident progenitor cells: a source for postnatal vasculogenesis.

            Here, we report the existence of endothelial precursor (EPC) and stem cells in a distinct zone of the vascular wall that are capable to differentiate into mature endothelial cells, hematopoietic and local immune cells, such as macrophages. This zone has been identified to be localized between smooth muscle and adventitial layer of human adult vascular wall. It predominantly contains CD34-positive (+) but CD31-negative (-) cells, which also express VEGFR2 and TIE2. Only few cells in this zone of the vascular wall are positive for CD45. In a ring assay using the fragments of human internal thoracic artery (HITA), we show here that the CD34+ cells of the HITA-wall form capillary sprouts ex vivo and are apparently recruited for capillary formation by tumor cells. New vessels formed by these vascular wall resident EPCs express markers for angiogenically activated endothelial cells, such as CEACAM1, and also for mature endothelial cells, such as VE-cadherin or occludin. Vascular wall areas containing EPCs are found in large and middle sized arteries and veins of all organs studied here. These data suggest the existence of a ;vasculogenic zone' in the wall of adult human blood vessels, which may serve as a source for progenitor cells for postnatal vasculogenesis, contributing to tumor vascularization and local immune response.
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              Relevance of monocytic features for neovascularization capacity of circulating endothelial progenitor cells.

              Transplantation of ex vivo expanded circulating endothelial progenitor cells (EPCs) from peripheral blood mononuclear cells improves the neovascularization after critical ischemia. However, the origin of the endothelial progenitor lineage and its characteristics have not yet been clearly defined. Therefore, we investigated whether the phenotype and functional capacity of EPCs to improve neovascularization depend on their monocytic origin. Monocytic CD14+ cells were isolated from mononuclear cells and incubated on fibronectin-coated dishes in endothelial medium in the presence of vascular endothelial growth factor. After 4 days of cultivation, adherent cells deriving from CD14+ or CD14- mononuclear cells showed equal expression of endothelial marker proteins and capacity for clonal expansion as determined by measuring endothelial colony-forming units. In addition, transplanted EPCs (5x10(5) cells) deriving from CD14+ or CD14- cells were incorporated into vascular structures of nude mice after hind-limb ischemia and significantly improved neovascularization from 0.27+/-0.12 (no cells) to 0.66+/-0.12 and 0.65+/-0.17, respectively (P<0.001; laser Doppler-derived relative blood flow). In contrast, no functional improvement of neovascularization was detected when freshly isolated CD14+ mononuclear cells without ex vivo expansion were used (0.33+/-0.17). Moreover, macrophages or dendritic cells differentiated from isolated CD14+ cells were significantly less effective in improving neovascularization than EPCs cultivated from the same starting population (P<0.01). These data demonstrate that EPCs can be generated from nonmonocytic CD14- peripheral blood mononuclear cells and exhibit a unique functional activity to improve neovascularization after hind-limb ischemia.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                October 2009
                30 June 2009
                : 46
                : 6
                : 581-591
                aDivision of Cardiovascular Diseases and Molecular Medicine Program, Mayo Clinic, Rochester, Minn., USA; bCentre for Research in Vascular Biology, BioSciences Institute, University College, Cork, Ireland
                226226 J Vasc Res 2009;46:581–591
                © 2009 S. Karger AG, Basel

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                Page count
                Figures: 7, Tables: 1, References: 31, Pages: 11
                Research Paper


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