Hypoxia-Inducible Factor (HIF)-1α Promotes Inflammation and Injury Following Aspiration-Induced Lung Injury in Mice.

Acid aspiration-induced lung injury is a common disease in the intensive care unit (ICU) and acute respiratory distress syndrome (ARDS). Hypoxia-inducible factor (HIF)-1α is a major transcription factor responsible for regulating the cellular response to changes in oxygen tension. A clear understanding of the function of HIF-1α in lung inflammatory response is currently lacking. Here, we sought to determine the role of HIF-1α in type 2 alveolar epithelial cells (AEC) in the generation of the acute inflammatory response following gastric aspiration (GA). GA led to profound hypoxia at very early time points following GA. This correlated to a robust increase in HIF-1α, tissue albumin and pro-inflammatory mediators following GA in AECs. The extent of lung injury and the release of pro/anti-inflammatory cytokines were significantly reduced in HIF-1α (-/-) mice. Finally, we report that HIF-1α upregulation of the acute inflammatory response is dependent on NF-κB following GA.

Double-Stranded RNA Interacts With Toll-Like Receptor 3 in Driving the Acute Inflammatory Response Following Lung Contusion.

OBJECTIVES: Lung contusion is a major risk factor for the development of acute respiratory distress syndrome. We set to determine the role of toll-like receptor 3 and the binding of double-stranded RNA in the pathogenesis of sterile injury following lung contusion. DESIGN: Toll-like receptor 3 expression was analyzed in postmortem lung samples from patients with lung contusion. Unilateral lung contusion was induced in toll-like receptor 3 (-/-), TIR-domain-containing adapter-inducing interferon-ß (-/-), and wild-type mice. Subsequently, lung injury and inflammation were evaluated. Apoptotic indices, phagocytic activity, and phenotypic characterization of the macrophages were determined. Double-stranded RNA in bronchoalveolar lavage and serum samples following lung contusion was measured. A toll-like receptor 3/double-stranded RNA ligand inhibitor was injected into wild-type mice prior to lung contusion. MEASUREMENTS AND MAIN RESULTS: Toll-like receptor 3 expression was higher in patients and wild-type mice with lung contusion. The degree of lung injury, inflammation, and macrophage apoptosis was reduced in toll-like receptor 3 (-/-), TIR-domain-containing adapter-inducing interferon-ß (-/-), and wild-type mice with toll-like receptor 3 antibody neutralization. Alveolar macrophages from toll-like receptor 3 (-/-) mice had a lower early apoptotic index, a predominant M2 phenotype and increased surface translocation of toll-like receptor 3 from the endosome to the surface. When compared with viral activation pathways, lung injury in lung contusion demonstrated increased p38 mitogen-activated protein kinases, extracellular signal-regulated kinase 1/2 phosphorylation with inflammasome activation without a corresponding increase in nuclear factor-κB or type-1 interferon production. Additionally, pretreatment with toll-like receptor 3/double-stranded RNA ligand inhibitor led to a reduction in injury, inflammation, and macrophage apoptosis. CONCLUSIONS: We conclude that the interaction of double-stranded RNA from injured cells with toll-like receptor 3 drives the acute inflammatory response following lung contusion.