Studies into angiopoietin-1 and tie receptor signalling during endothelial responses to acute inflammation

Endothelial dysfunction is a major component of the systemic inflammatory response syndrome (SIRS) triggered by major injury including burns. Angiopoietin-1, a key regulator of angiogenesis operates through two different receptors, Tie1 and Tie2. Identifying specific roles of each receptor in mediating the protective effects of Ang1 is essential for designing drug therapy for pathological inflammatory responses. In vitro models of endothelial permeability, survival and adhesion molecule expression have been established to study the effects of Ang-1 on Tie receptor deficient HUVEC generated by SiRNA techniques. Tie receptor knock-down was highly effective in HUVEC, and subsequent experiments using these cells proved the hypothesis that Tie2 is the principal receptor mediating Ang-1 induced endothelial survival and reduced endothelial permeability. In addition, absent Tie1 was found to increase baseline endothelial permeability and apoptosis in HUVEC, whilst the full anti-apoptotic effect of VEGF was shown to require both Tiel and Tie2, adding to other data indicating a novel form of heterodimeric transactivation between the two receptors. Using the developed cell adhesion molecule (CAM) assay, experiments using naive HUVEC quantitated the anti-inflammatory effects of Ang-1 following stimulation by key pro-inflammatory cytokines such as Il-1. Moreover, preliminary experiments using plasma from patients with SIRS demonstrated the usefulness of the inflammatory CAM assay as a model for studying endothelial inflammatory responses in humans. Finally, experiments combining SIRS plasma with Ang-1 demonstrated a possible role for Ang-1 in the inhibition of SIRS plasma induced CAM expression.