Eosinophils Restrict Diesel Exhaust Particles-induced Cell Proliferation of Lung Epithelial A549 Cells via Interleukin-13 Mediated Mechanisms: Implications for Tissue Remodeling and Fibrosis.

Abstract

Diesel exhaust particles (DEPs) affect lung physiology and cause serious damage to the lungs. A number of studies demonstrated that eosinophils play a very important role in the development of tissue remodeling and fibrosis of the lungs. However, the exact mechanism of pathogenesis of tissue remodeling and fibrosis is not known. Both in vitro and in vivo models were used in the study. HL-60 and A549 cells were also utilized in the study. 8 to 12 weeks old BALB/c mice were used for the in vivo study. Cell viability by MTT assay and RNA isolation by tri reagent was accomplished. mRNA expression of inflammatory genes was accomplished by real-time PCR or qPCR. Immunohistochemistry was done to assess the localization and expressions of proteins. One-way ANOVA followed by a post hoc test was done for the statistical analysis. Graph-Pad prism 5 software was used for statistical analysis. For the first time, we demonstrate that interleukin-13 plays a very important role in the development of tissue remodeling and fibrosis. We report that diesel exhaust particles significantly induce eosinophils cell proliferation and interleukin-13 release in in vitro culture conditions. Supernatant collected from DEP-induced eosinophils cells significantly restricts cell proliferation of epithelial cells in response to exposure to diesel exhaust particles. Furthermore, purified interleukin-13 decreases the proliferation of A549 cells, highlighting the involvement of IL- 13 in tissue remodeling. Notably, Etoricoxib (selective COX-2 inhibitor) did not inhibit the DEPtriggered release of interleukin-13, suggesting another cell signaling pathway. The in vivo exposure of DEP to the lungs of mice resulted in a high level of eosinophils degranulation as depicted by the EPX-1 immunostaining and altered level of mRNA expressions of inflammatory genes. We also found that a-SMA, fibroblast specific protein (FSP-1), has been changed in response to DEP in the mice lungs along with the mediators of inflammation. Altogether, we elucidated the mechanistic role of eosinophils and IL-13 in the DEP-triggered proliferation of lungs cells, thus providing an insight into the pathophysiology of tissue remodeling and fibrosis of lungs.