Adult ‘endothelial progenitor cells’: Renewing vasculature

Abstract

During embryogenesis, endothelial progenitor cells participate in the initial processes of primitive blood vessel formation ( vasculogenesis). It has become evident that progenitors to vascular endothelial cells also exist in the adult. Endothelial progenitors normally reside in the adult bone marrow but may become mobilized into circulation by cytokine or angiogenic growth factor signals from the periphery, enter extravascular tissue, and promote de novo vessel formation by virtue of physically integrating into vessels and/or supplying growth factors ( adult vasculogenesis). For that reason, autologous endothelial progenitors, mobilized in situ or transplanted, has become a major target of therapeutic revascularization approaches to ischemic disease and endothelial injury. Moreover, endothelial progenitors represent a potential target of strategies to block tumor growth. Cell factsEndothelial progenitor cells • are progenitors to vascular endothelial cells that exist in adult life • are circulating, mononuclear blood cells capable of assuming an adherent, endothelial-like phenotype in angiogenic conditions • normally reside in the vascular niche of the bone marrow • in healthy subjects, the basal population of circulating endothelial progenitors is very low, i.e. few thousand cells/ml blood; resident endothelial progenitors in the bone marrow can become actively mobilized into the circulation by angiogenic cytokines or drugs • possess properties of embryonic angioblasts, i.e. the capability to form endothelial capillary tubes de novo, and a high proliferation capacity • can enter extravascular tissue to specifically migrate and incorporate into sites of active angiogenesis in regenerating tissue or tumors • in situ recruited or grafted endothelial progenitors contribute to neovascularization of ischemic tissues