Angiopoietin-1 Protein

Alkaline phosphatase (ALPP) is plasma membrane bound glycoprotein involved in energy production. Human ALKP is classified into four tissue specific forms or isozymes, according to the site where it is expressed: placenta, intestine, liver, bone, kidney and germ cell. During pregnancy, serum ALPP levels increase progressively, reaching its highest value in the third trimester, mostly due to addition of placental isoenzyme. This usually results in doubling in the total ALPP level.Angiopoietin-1 (ANG-1) is a secreted glycoprotein that plays a critical role in the development and maintenance of the vascular system. It contains a N-terminal coiled-coil region and a C-terminal fibrinogen-like domain separated by a short flexible region. Angiopoietin-1 binds and activates the receptor tyrosine kinase Tie-2, and its association into tetramers is important for full Tie-2 activation. Angiopoietin-1 ligation of Tie-2 on vascular endothelial cells (EC) induces the development and branching of blood vessels. In confluent EC (i.e. in homeostasis), multimeric Angiopoietin-1 enhances vascular integrity by promoting the in trans homotypic association of Tie-2 between EC or with the substratum. In addition, Angiopoietin-1 suppresses several VEGF-induced effects on the vasculature including endothelial permeability, stretch-induced release of Angiopoietin-2, and up-regulation of the leukocyte adhesion molecules VCAM-1, ICAM-1, and E-Selectin. Angiopoietin-1 also interacts with a variety of integrins and the extracellular matrix independently of Tie-2. These interactions support the adhesion, migration and stress resistance of EC, fibroblasts, and myocytes. Angiopoietin-1 can protect against pulmonary arterial hypertension, reduce the extent of fibrosis and remodeling in infarcted diabetic myocardium, and enhance tumor progression and metastasis.