The angiopoietin-Tie2 signaling axis in systemic inflammation

Systemic inflammation is a hallmark of commonly encountered diseases ranging from bacterial sepsis to sterile syndromes such as major trauma. Derangements in the host vasculature contribute to the cardinal manifestations of sepsis in profound ways. Recent studies of control pathways regulating the vascular endothelium have illuminated how this single cell layer toggles between quiescence and activation to affect the development of shock and multiorgan dysfunction. This article focuses on one such control pathway, the Tie2 receptor and its ligands the angiopoietins, to describe a growing body of genetic, biochemical, mechanistic, and human studies that implicate Tie2 as a critical switch. In health, activated Tie2 maintains the endothelium in a quiescent state characterized by dynamic barrier function and antiadhesion against circulating leukocytes. In sepsis and related diseases, expression of the angiopoietins becomes markedly imbalanced and Tie2 signaling is greatly attenuated. These rapid molecular changes potentiate pathophysiologic responses throughout the body, resulting in injurious vascular leakage and organ inflammation. The Tie2 axis, therefore,may be a promising avenue for future translational studies.