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Departments of 1Exercise Science and 2Anatomy and Cell Biology, University of Iowa, Iowa City, Iowa 52242
Submitted 8 May 2003 ; accepted in final form 30 December 2003
It appears that there are two classes of human circulating endothelial cell (EC) progenitors, CD34+ and CD34CD14+ cells. Attention has focused on CD34+ cells, yet CD34CD14+ monocytic cells are far more abundant and may represent the most common class of circulating EC progenitor. Little is known about molecular or physiological factors that regulate putative CD34CD14+ EC progenitor function, although factors secreted by other blood and cardiovascular cells to which they are exposed probably affect their behavior. Hypoxia and stretch are two important physiological stimuli known to trigger growth factors in cardiovascular cells and accordingly may modulate EC progenitors. To investigate the impact of these environmental parameters on EC progenitors, EC production in CD34CD14+ cultures was evaluated. Our data indicate that neither stretch nor hypoxia alters EC production by EC progenitors directly but do so indirectly through their effects on cardiovascular cells. Conditioned media (CM) from coronary artery smooth muscle cells inhibit EC production in culture, and this inhibition is stronger if the coronary smooth muscle cells have been subjected to cyclic stretch. In contrast, cardiomyocyte CM increases EC cell number, an effect that is potentiated if the myocytes have been subjected to hypoxia. Significantly, EC progenitor responses to CM are altered by the presence of CD34CD14 peripheral blood mononuclear cells (PBMCs). Moreover, CD34CD14 PBMCs attenuate EC progenitor responsiveness to the angiogenic factors basic fibroblast growth factor (FGF-2), vascular endothelial cell growth factor-A165, and erythropoietin while inducing EC progenitor death in the presence of transforming growth factor-
1 in vitro
cyclic stretch; hypoxia; erythropoietin; monocyte; conditioned medium
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