Let-7 microRNA–mediated regulation of IL-13 and allergic airway inflammation

Background IL-13, a cytokine secreted by TH 2 lymphocytes and other cells, critically modulates allergic inflammation and tissue remodeling in allergic asthma. Although much is known about transcriptional regulation of IL-13, posttranscriptional regulation is poorly understood. Objective Because many inflammatory pathways are known to be regulated by microRNAs, permitting a rapid and fine-tuned response, the role of microRNA-mediated regulation of IL-13 was investigated using both in vitro and in vivo studies. Methods A combination of in silico approaches and in vitro transfections in A549 cells and primary cultured T cells was used to demonstrate the involvement of let-7 in IL-13 regulation. Furthermore, intranasal delivery of let-7 microRNA mimic in mice was performed to study its effects in allergic airway inflammatory conditions. Results Using a combination of bioinformatics and molecular approaches, we demonstrate that the let-7 family of microRNAs regulates IL-13 expression. Induced levels of IL-13 in cultured T cells were inversely related to let-7 levels. In an IL-13–dependent murine model of allergic airway inflammation, we observed that inflammation was associated with a reduction in most of the members of the let-7 family. Exogenous administration of let-7 mimic to lungs of mice with allergic inflammation resulted in a decrease in IL-13 levels, resolution of airway inflammation, reduction in airway hyperresponsiveness, and attenuation of mucus metaplasia and subepithelial fibrosis. Conclusion Let-7 microRNAs inhibit IL-13 expression and represent a major regulatory mechanism for modulating IL-13 secretion in IL-13–producing cell types and thereby TH 2 inflammation.