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

Background: Diesel exhaust particulates (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 remodelling and fibrosis of lungs. However, the exact mechanism of pathogenesis of tissue remodelling and fibrosis is not known. Methods: Both in vitro and in vivo models were used in the study. HL-60 and A549 cells were used in the study. Balb/C mice of 8 to 12 weeks old were used for in vivo study. Cell viability by MTT assay, RNA isolation by tri reagent was accomplished. mRNA expression of inflammatory genes were accomplished by real time PCR or qPCR. Immunohistochemistry was done to asses the localization and expressions of proteins. One way ANOVA followed by post hoc test were done for the statistical analysis. Graph-Pad Prism software was used for statistical analysis. Results: We for the first time demonstrate that, Interleukin-13 plays a very important role in the development of tissue remodelling 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 restrict cell proliferation of epithelial cells in response to exposure of diesel exhast particles. Furthermore, purified interleukin-13 decreases the proliferation of A549 cells, highliting the involvement of IL-13 in tissue remodeling. Notably, Etoricoxib (selective COX-2 inhibitor) did not inhibit DEP-triggered release of interleukin-13, suggesting another cell signalling pathway. The in vivo exposer of DEP to the lungs of mice, resulted in 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 inside in the pathophysiology of tissue remodelling and fibrosis of lungs.

Epithelial barrier hypothesis and the development of allergic and autoimmune diseases

“…Fukuoka et al demonstrated that DEP disrupted TJs, thus leading to increased permeability of nasal epithelial cells [24] and facilitating the entry of allergens into subepithelial tissues causing the exacerbation of antigenspecific IgE-bearing mast-cell-mediated immediate allergic responses. Both in vitro and in vivo studies demonstrate that DEPs trigger the proliferation of eosinophils and increase secretion of interleukin (IL)-13 on lung epithelial cells causing fibrosis and tissue remodelling in the lungs [63]. Moreover, DEP stimulation on the primary human nasal epithelium modifies the basal secretome leading to inflammation with effusion of fluids [64,65].…”