CCAAT/Enhancer-Binding Protein δ Is a Critical Mediator of Lipopolysaccharide-Induced Acute Lung Injury

Although inflammation plays a central role in the pathogenesis of acute lung injury, the molecular mechanisms underlying inflammatory responses in acute lung injury are poorly understood, and therapeutic options remain limited. CCAAT/enhancer-binding proteins, C/EBPβ and C/EBPδ, are expressed in the lung and have been implicated in the regulation of inflammatory mediators. However, their functions in lung pathobiological characteristics are not well characterized. Herein, we show that C/EBPβ and C/EBPδ are activated in mouse lung after intrapulmonary deposition of lipopolysaccharide (LPS). Mice carrying a targeted deletion of the C/EBPδ gene displayed significant attenuation of the lung permeability index (lung vascular leak of albumin), lung neutrophil accumulation (myeloperoxidase activity), and neutrophils in bronchial alveolar lavage fluids compared with wild-type mice. These phenotypes were consistent with morphological evaluation of lung, which showed reduced inflammatory cell influx and minimal intra-alveolar hemorrhage. Moreover, mutant mice expressed considerably less tumor necrosis factor-α, IL-6, and macrophage inflammatory protein-2 in bronchial alveolar lavage fluids in LPS-injured lung compared with wild-type mice. In contrast, C/EBPβ deficiency had no effect on LPS-induced lung injury. By using small-interfering RNA-mediated knockdown for C/EBPδ, we demonstrate, for the first time to our knowledge, that C/EBPδ plays a critical role for the tumor necrosis factor-α, IL-6, and macrophage inflammatory protein-2 production in LPS-stimulated alveolar macrophages. These findings demonstrate that C/EBPδ, but not C/EBPβ, plays an important role in LPS-induced lung inflammatory responses and injury.