Inhibition of angiogenesis: a new function for angiotensinogen and des(angiotensin I)angiotensinogen.

Angiotensinogen (AGT) can be schematically considered to consist of a combination of an angiotensin I (Ang I) function, located at the N-terminal end, and the presence of a serpin (serine protease inhibitor) structure at the opposite end. des(Ang I)AGT, which accounts for more than 97% of the molecule, apparently has no function. Several serpins (antithrombin, maspin, pigment epithelial-derived factor, and kallistatin) have been recently shown to exert an antiangiogenic activity, suggesting a common mechanism of endothelial cell proliferation and migration.

In situ hybridization and immunogold localization of vascular endothelial growth factor receptor-2 on the pericytes of the chick chorioallantoic membrane.

This paper describes the expression of VEGF and of VEGFR-2 in the vasculature of the chorioallantoic membrane (CAM) as revealed by in situ hybridization and immunoelectron microscopy. Results showed that VEGFR-2 is expressed in both the endothelial cells and the pericytes, while VEGF in the chorionic epithelial cells. VEGF may therefore be released to promote both angiogenesis, by initiating an angiogenic response by endothelial cells expressing VEGFR-2, and the recruitment of pericytes along the capillary wall, playing also a crucial role in maturation and stabilization of the CAM blood vessels.

Angiotensinogen and its cleaved derivatives inhibit angiogenesis.

The members of the serine protease inhibitor (serpin) family, which share a common tertiary structure and a role as serin protease inhibitors, are involved in a variety of newly discovered functions. For example, antithrombin III exerts a strong antiangiogenic activity. Angiotensinogen, the renin substrate, has a folded structure and is a member of the noninhibitory serpin subfamily.