The bone marrow constitutes a reservoir of pericyte progenitors

Adult bone marrow is a rich reservoir of hematopoietic and mesenchymal stem and progenitor cells. Mobilization and recruitment of bone marrow-derived cells to injured or ischemic tissue or tumors endorse the initiation and maintenance of angiogenic processes in the adult by incorporating endothelial progenitor cells (EPC) into the developing vasculature and by recruiting accessory hematopoietic cells. Recent data have now revealed that the origin of bone marrow-derived vascular cells is not restricted to endothelial cells but also includes pericytes--the perivascular support cells. Several laboratories have now reported the existence of pericyte progenitor cells, and these cells, like EPC, can be mobilized and recruited to the remodeling vasculature under ischemic conditions and in tumors. This review focuses on pericytes in vessel formation and on recent discoveries about their bone marrow origin in the adult.