Abstract 13797: Elevated Circulating Angiopoietin-2 Induced by Hepatic Overexpression Leads to Differential Effects on Lung Vascular Inflammation and Leak in Endotoxin-Injured Mice
BACKGROUND: Acute lung injury (ALI) is a life-threatening condition for which there is currently no specific treatment. The constitutive activation of the endothelial cell-selective Tie2 receptor is necessary to maintain lung vascular quiescence, which is mediated in part by the actions of two opposing ligands, Angiopoietin (Angpt)-1 and -2. Elevated levels of circulating Angpt-2 have been reported in experimental and clinical ALI; however, it remains unclear whether Angpt-2 plays a causative or protective role in ALI, because Angpt-2 has been reported to be a context-dependent partial agonist of Tie2.
HYPOTHESIS: Elevated circulating levels of Angpt-2 cause increased susceptibility to endotoxin-induced lung vascular injury.
METHODS AND RESULTS: Human Angpt-2 was conditionally expressed with a liver-specific promoter using a tetracycline-based binary transgenic mouse system. Elevated plasma levels of hAngpt-2 (>9000 pg/mL) were confirmed in binary transgenic (BT) mice following dietary removal of doxycycline. In contrast, single transgenic (ST-tTA) littermate controls exhibited only background levels of hAngpt-2 (≤ 30 pg/mL). Acute lung injury was induced via intratracheal delivery of lipopolysaccharide (LPS; 1mg/kg), and mice were euthanized at 3 h, 6 h, 24 h, 48 h, and 72 h (n=7-14/group). Bronchoalveolar lavage (BAL) neutrophil and monocyte/macrophage cell counts were significantly higher (p<0.05) in BT versus ST-tTA mice 48 h after LPS challenge. Inflammatory cytokines IL-6, IL-1β, and MCP-1 were significantly higher in the lung BAL fluid of BT vs. ST-tTA controls, at 6 h post LPS. In contrast, vascular leak was attenuated in BT mice, as evidenced by decreased extravasation of plasma proteins IgM (p<0.01, 24 h; p=0.1, 48 h) and albumin (p<0.001, 24h; p<0.05, 48 h) into the lung air space. In BT mice, tail vein injection of an anti-hAngpt2 aptamer-based inhibitor (0.1 mg/kg) just prior to LPS challenge decreased total cell counts (p<0.1), but increased IgM (p<0.01) and albumin (p<0.1) levels in BAL at 48 h, relative to mice that received a scrambled-sequence non-functional aptamer.
CONCLUSION: High circulating levels of hAngpt-2 lead to dynamic and opposing effects on lung vascular inflammation and permeability in LPS-injured mice.
- © 2013 by American Heart Association, Inc.