Phospholipase Cϵ plays a crucial role in neutrophilic inflammation accompanying acute lung injury through augmentation of CXC chemokine production from alveolar epithelial cells

Abstract

Background: We have shown that phospholipase Cϵ (PLCϵ), an effector of Ras and Rap1 small GTPases, plays pivotal roles in inflammation and inflammation-associated carcinogenesis by augmenting proinflammatory cytokine production from epithelial cells of various organs. The purpose of this study is to analyze its role in neutrophilic alveolar inflammation accompanying acute lung injury (ALI), focusing on that in alveolar epithelial cells (AECs), which are known to make a major contribution to the pathogenesis of ALI. Methods: We examine the effect of the PLCϵ genotypes on the development of ALI induced by intratracheal administration of lipopolysaccharide (LPS) to PLCϵ wild-type (PLCϵ +/+ ) and knockout (PLCϵ ΔX/ΔX ) mice. Pathogenesis of ALI is analyzed by histological examination of lung inflammation and measurements of the levels of various cytokines, in particular neutrophil-attracting chemokines such as Cxcl5, by quantitative reverse transcription-polymerase chain reaction and immunostaining. Primary cultures of AECs, established from PLCϵ +/+ and PLCϵ ΔX/ΔX mice, are used to analyze the roles of PLCϵ, protein kinase D (PKD) and nuclear factor-κB (NF-κB) in augmentation of LPS-induced Cxcl5 expression. Results: Compared to PLCϵ +/+ mice, PLCϵ ΔX/ΔX mice exhibit marked alleviation of lung inflammation as shown by great reduction in lung wet/dry weight ratios, accumulation of inflammatory cells in the alveolar space and thickening of alveolar walls as well as the number of neutrophils and the protein concentration in bronchoalveolar lavage fluid. Also, LPS-induced expression of the CXC family of chemokines, in particular Cxcl5, is substantially diminished in the total lung and AECs of PLCϵ ΔX/ΔX mice. Moreover, LPS-induced Cxcl5 expression in primary cultured AECs is markedly suppressed on the PLCϵ ΔX/ΔX background (p < 0.05 versus PLCϵ +/+ AECs), which is accompanied by the reduction in phosphorylation of inhibitor κB (IκB), PKD and nuclear translocation of NF-κB p65. Also, it is suppressed by the treatment with inhibitors of PKD and IκB kinase, suggesting the involvement of the PLCϵ-PKD-IκB-NF-κB pathway. Conclusions: PLCϵ-mediated augmentation of the production of the CXC family of chemokines, in particular Cxcl5, in AECs plays a crucial role in neutrophilic alveolar inflammation accompanying ALI, suggesting that PLCϵ may be a potential molecular target for the treatment of acute respiratory distress syndrome.