Apoptotic cell clearance by macrophages and neighbouring tissue cells induces hepatocyte growth factor (HGF) secretion. HGF plays a key role in alveolar epithelial regeneration and reconstruction after lung injury. Direct in vivo exposure to apoptotic cells enhances HGF production, resulting in attenuation of pulmonary injury.We investigated the direct effect of in vivo exposure to apoptotic cells in bleomycin-stimulated lungs (2 days old) on HGF induction. Furthermore, sequential changes of bleomycin-induced HGF production following apoptotic cell instillation related to the changes in inflammatory and fibrotic responses were assessed.At 2 h after apoptotic cell instillation into bleomycin-stimulated lungs, the levels of HGF mRNA and protein production, and apoptotic cell clearance by alveolar macrophages were enhanced. Furthermore, HGF induction persistently increased following apoptotic cell instillation up to 21 days after bleomycin treatment. Apoptotic cell instillation attenuated bleomycin-induced proinflammatory mediator production, inflammatory cell recruitment and total protein levels. Apoptotic cell instillation also induced antiapoptotic and antifibrotic effects. These antiinflammatory and antiapoptotic effects could be reversed by co-administration of HGFneutralising antibody.These findings indicate that in vivo exposure to apoptotic cells enhances transcriptional HGF production in bleomycin-stimulated lungs, resulting in attenuation of lung injury and fibrosis.

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Src tyrosine kinases (TKs) are signaling proteins involved in cell signaling pathways toward cytoskeletal, membrane and nuclear targets. In the present study, using a selective Src TK inhibitor, PP1, we investigated the roles of Src TKs in the key pulmonary responses, NF-κB activation, and integrin signaling during acute lung injury in BALB/C mice intratracheally treated with LPS. LPS resulted in c-Src phosphorylation in lung tissue and the phospho-c-Src was predominantly localized in recruited neutrophils and alveolar macrophages. PP1 inhibited LPS-induced increases in total protein content in bronchoalveolar lavage fluid, neutrophil recruitment, and increases in the production or activity of TNF-α and matrix metalloproteinase-9. PP1 also blocked LPS-induced NF-κB activation, and phosphorylation and degradation of IκB-α. The inhibition of NF-κB activation by PP1 correlated with a depression of LPS-induced integrin signaling, which included increases in the phosphorylations of integrin β3, and of the focal adhesion kinase (FAK) family members, FAK and Pyk2, in lung tissue, and reductions in the fibrinogen-binding activity of alveolar macrophages. Moreover, treatment with anti-αv, anti-β3, or Arg-Gly-Asp-Ser (RGDS), inhibited LPS-induced NF-κB activation. Taken together, our findings suggest that Src TKs play a critical role in LPS-induced activations of NF-κB and integrin (αvβ3) signaling during acute lung injury. Therefore, Src TK inhibition may provide a potential means of ameliorating inflammatory cascade-associated lung injury.

Background: Synthetic peptides containing the RGD sequence inhibit integrin-related functions in different cell systems. Here, we investigated the effects of synthetic Arg-Gly-Asp-Ser (RGDS) peptide on key inflammatory responses to intratracheal (i.t.) lipopolysaccharide (LPS) treatment and on the integrin signaled mitogen-activated protein (MAP) kinase pathway during the development of acute lung injury.

These results indicate that NAC can expedite the resolution of LPS-induced pulmonary inflammation through the inhibition of RhoA activity and the enhancement of apoptotic cell clearance.