Mechanism of cell damage and repair in acute lung injury

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The first study was performed to examine the putative role of high-mobility group box (HMGB) protein in the pathogenesis of acute lung injury. Observations were made 1) in 21 septic patients with acute lung injury and 15 patients with normal lung function, and 2) in a mouse model, 24 h after intratracheal instillation of lipopolysaccharide. The concentrations of HMGB 1 were increased in plasma and lung epithelial lining fluid of patients with acute lung injury and mice instilled with lipopolysaccharide. Lipopolysaccharide-induced acute lung injury was mitigated by anti-HMGB1 antibody. Although this protein was not detected in the plasma of control humans or mice, the concentrations of HMGB 1 in lung epithelial lining fluid or in bronchoalveolar lavage fluid were unexpectedly high. The nuclear expression of HMGB 1 was apparent in epithelial cells surrounding terminal bronchioles in normal mice, while its nuclear and cytoplasmic expression was observed in alveolar macrophages in lipopoly … More saccharide-instilled mice. Lung instillation of HMGB2 did not cause as much inflammation as HMGB 1. Extracellular HMGB 1 may play a key role in the pathogenesis of clinical and experimental acute lung injury. However, its expression in normal airways is noteworthy, and suggests that it also plays a physiologic role in the lung. And the second study was about Fas/FasL system. Alveolar epithelial cell death plays a crucial role in the progression of acute lung injury. We have demonstrated up-regulation of Fas expression on alveolar epithelial cells, and soluble Fas ligand secretion from inflammatory cells upon acute lung injury. Here we show that the lipopolysaccharide-stimulated human monocyte cell line THP-1 releases Fas ligand, and that conditioned medium from lipopolysaccharide-stimulated THP-1 cells induces apoptosis of the human pulmonary adenocarcinoma cell line A549. Activation of caspase-3 and -8 is associated with the apoptosis. Gene targeting on Fas in A549 cells by specific small interfering RNA impairs apoptosis induced by conditioned medium from activated THP-1, while that on Fas ligand in THP-1 cells impairs the apoptosis-inducing activity of the conditioned medium produced by lipopolysaccharide-stimulated cells. These results suggest that Fas ligand released by monocytes causes alveolar epithelial cell death through a Fas-dependent apoptotic mechanism in the development of acute lung injury. Less