TIE Receptors

TIE1 and TIE2 receptor tyrosine kinases (RTK) form a distinct RTK subfamily with a unique extracellular structure consisting of epidermal growth factor, immunoglobulin, and fibronectin type III domains. Together with their corresponding angiopoietin growth factors (ANGPT1, ANGPT2, ANGPT4, also abbreviated as ANG) ligands, the TIE receptors form an endothelial specific signaling pathway with important functions in the regulation of lymphatic and cardiovascular development and vascular homeostasis. Angiopoietin growth factors (ANG1, ANG2, and ANG4 in humans) are ligands for TIE2, while TIE1 is an orphan receptor. In addition to the vascular endothelial growth factor (VEGF) receptor pathway, the ANG-TIE system is a second endothelial cell specific ligand-receptor signalling system necessary for embryonic cardiovascular and lymphatic development. The ANG-TIE system also regulates postnatal angiogenesis, vessel remodelling, vascular permeability and inflammation to maintain vascular homoeostasis in adult physiology.