Description
The Angiopoietins are a family of growth factors which bind to the endothelial receptor tyrosine kinase Tie2. Two of the Angs, Ang-1 and Ang-4, activate the Tie2 receptor, whereas Ang-2 and Ang-3 inhibit Ang-1-induced Tie2 phosphorylation. Ang-1 is a secreted growth factor which enhances endothelial cell survival and capillary morphogenesis, also it limits capillary permeability. Ang-2 is a natural inhibitor of Ang-1 because it binds the same receptor but fails to activate it. When ambient levels of VEGF are high Ang-2 destabilizes capillary integrity, facilitating sprouting, but when VEGF levels are low it causes vessel regression. Preliminary data suggests angiopoietins are implicated in deregulated vessel growth in Wilms' kidney tumors and in vascular remodeling after nephrotoxicity. Existing data suggests that during vascular development VEGF-A and Angiopoietins not only have different roles, but also complementary and coordinated roles