Processes in angiogenesis. (1) Angiogenic factors bind to their receptors on endothelial cells and activate the signal transduction pathways. (2) Matrix metalloproteinases are activated, and they degrade the extracellular matrix. (3) Endothelial cells migrate out of the preexisting capillary wall and proliferate. (4) Integrins are expressed by endothelial cells, facilitating their adhesion to the extracellular matrix and their migration for tube formation. (5) Angiopoietin 1 binds to Tie-2 receptors and stimulates pericyte recruitment and vessel stabilization.
