Abstract 20051: Divergent Actions of Circulating Angiopoietin-2 on Vascular Inflammation and Leak in a Mouse Model of Acute Lung Injury

Abstract

Introduction: Angiopoietin-2 (Angpt2) is a partial agonist/antagonist of the vascular-stabilizing endothelial Tie2 receptor. In both animal models and patients with acute lung injury (ALI), Angpt2 circulating levels are elevated; however, it remains unclear whether these elevated levels contribute to, or protect against, the lung inflammation and vascular leak associated with ALI. Objective: To evaluate the biological consequences of elevated circulating Angpt2 levels in a mouse model of endotoxin-induced ALI. Methods and Results: Transgenic mice (Angpt2OVR) with elevated circulating levels of human (h)Angpt2, via conditional hepatocyte-specific overexpression, were examined at several timepoints (from 3 h to 72 h) following lipopolysaccharide (LPS)-induced ALI (n=7-14 mice/genotype group/timepoint). Bronchoalveolar lavage (BAL) neutrophil and inflammatory cytokine levels were significantly higher (P<0.05) in Angpt2OVR versus littermate controls at 48 h and 6 h post LPS, respectively. In contrast, vascular leak, evidenced by decreased BAL IgM and albumin levels at 24 and 48 h, was attenuated in Angpt2OVR mice. Systemic Angpt2 overexpression showed no net detriment or benefit for survival following LPS-induced injury (n=37-38 mice/group). Tail vein injection of an anti-hAngpt2-neutralizing aptamer (versus non-functional scrambled-sequence control; n=12-13 mice/group), reversed the pro-inflammatory and anti-leak effects observed at 48 h in LPS-injured Angpt2OVR mice. Transcript profiling, via PCR array, was also conducted to probe the effects of Angpt2 neutralization on the lung tissue expression of 84 genes involved in vascular biology. Angpt2 neutralization via aptamer caused alterations in multiple genes linked to angiogenesis, vascular tone, inflammation, apoptosis, cell adhesion, coagulation, and platelet activation (P<0.05 versus scrambled control, n=4/group). Conclusions: Angpt2 exerts differential effects on lung inflammation and permeability under pathological conditions in vivo. These data establish novel context-dependent actions of Angpt2, and suggest elevated circulating levels may help regulate multiple pathways necessary to fine-tune the vascular response to lung injury.