Pericytes are adjacent to endothelial cells of blood vessels. They are the mural cells of microvessels such as arterioles, capillaries and venules, stabilizing the walls of blood vessel and participate in the regulation of blood flow. These cells also influence the proliferation, survival, migration, and maturation of endothelial cells (Shepro and Morel, 1993) and also take an active part in developmental angiogenic processes (Betsholtz et al, 2005). Pericytes form pericyte tubes free of endothelial cells, which may reflect the early participation of these cells in the process of angiogenic sprouting.
Cerebral pericytes constitute an essential component of the blood-brain barrier, which they form together with endothelial cells and astrocytes (Dohgu et al, 2005). Newly formed blood vessels appear to become independent of VEGF when covered by pericytes (Alon et al, 1995; Benjamin et al, 1998). A lack of pericytes leads to endothelial hyperplasia and abnormal vascular morphogenesis (Hellstrom et al, 2001). Genetically engineered mice that lack pericytes have been shown to develop microaneurysms at late gestation and die before birth (Lindahl et al, 1997).