Role of endothelial progenitor cells in vascular development, homestatic maintenance of blood vessels and in injury-mediated reparative response

The blood vasculature is a closed circulatory system formed by arteries, veins and capillaries; the inner layer of these vessels is formed by a single layer of endothelial cells. Endothelial cells are specialized according to the specific needs of the tissues that they supply. The vascular system derives from the differentiation of mesodermal stem cells into angioblasts, embryonic endothelial progenitors. Endothelial progenitor cells (EPCs) are also present in adult life. Two types of EPCs have been reported: one of nonhematopoietic origin, endothelial colony forming cell (ECFC) able to generate endothelial cells, resident in vessel wall and present at low levels in peripheral blood and directly participating to the regeneration of endothelium following injury or ischemic damage; another of hematopoietic origin, called myeloid angiogenic cells (MACs), resident in bone marrow, generating monocytic cells, supporting angiogenesis through paracrine mechanisms. ECFCs play a role in reparative processes. ECFCs display a hierarchy of clonal proliferative potential and display a pronounced postnatal vascularization ability in vivo. For these properties, ECFCs represent a promising cell source for revascularization of damaged tissue. The use of ECFC for therapeutic use is still an embryonic field, but the therapeutic use of these cells holds great promise for the future.