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

Background: 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.

Methods: 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.

Results: 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.

Conclusion: 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.