Figure 1.

Vascular quiescence and the Angiopoietin-Tie2 axis. Expression of the receptor tyrosine kinase Tie2 is heavily enriched in the endothelium. Tie2 is activated by Angpt-1 which is secreted by platelets and peri-endothelial cells. In the context of inflammation, Angpt-2 antagonizes Angpt-1. Tie1 is an orphan receptor homolog of Tie2 whose intact expression enhances Tie2 activation. A transmembrane tyrosine phosphatase VE-PTP deactivates Tie2. Downstream of activated Tie2, a PI3K signaling cascade culminates in defense of barrier function by signaling members of the Rho family of GTPases as depicted. Inhibition of the inflammatory transcription factor NF-κB suppresses the expression of key adhesion molecules. Other potential receptors of angiopoietins, such as integrins, are not depicted for simplicity.