Ang-1 maintains and, when required, restores the higher order architecture of growing blood vessels [43,44, 105, 106] . This is achieved by inhibiting apoptosis of ECs by Tie2mediated activation of PI3K/Akt signalling [107] [108] [109] . Ang-1/ Tie2 signalling is involved in angiogenesis induced by cyclic strain and hypoxia [110, 111] . Although its role is less clear, Tie1 might be involved in EC reactions to shear stress [112] . Ang-1 is a chemoattractant for ECs [83] [84] [85] , and both Ang-1 and Ang-2 have proliferative effects on those cells [98, 113] . At the end of a vascular remodelling phase, Ang-2 induces apoptosis of ECs for vessel regression in competition with the survival signal of Ang-1 [106] . This apoptotic process requires macrophages, which are recruited by Ang-2 [70, 114] .