Figure 1.

Schematic overview of the principal stages of angiogenesis. (1) In quiescent capillaries, endothelial cells form tight contacts with each other and with neighboring pericytes. Both cell types are embedded in the shared basement membrane. (2) Angiogenic sprouting requires local degradation of extracellular components of the basement membrane by endothelial-cell-derived proteases, loosening of the cell–cell and cell–matrix contacts, endothelial cell proliferation, migration, and formation of a nonlumenized sprout. Factors secreted by the endothelial cells attract pericytes that contribute to stabilization of the newly formed vessel. (3) Maturation of capillaries involves re-establishment of cell–cell contacts, lumen formation, secretion of new basement membrane, and recruitment of pericytes.