Understanding angiogenesis: a clue for understanding vascular malformations.

Vasculogenesis is defined by the differentiation of mesodermal precursors into endothelial cells, and angiogenesis by the formation of new vessels from preexisting vessels. Growth factors initiate cellular differentiation but also induce endothelial migration and proliferation; extracellular proteolysis is essential for disassembly and reassembly of endothelial cells to their environmental matrix and allow their migration to elongate the arterial tree. The coagulation and fibrinolysis system, metalloproteinases and adhesion molecules are critical during this step. The balance between pro- and antiangiogenic factors regulates angiogenesis. Ongoing studies dissecting angiogenesis mechanisms offer a new perspective to our understanding of vascular malformations.