Abstract
Idiopathic pulmonary fibrosis (IPF) is a progressive disease characterized by fibrosis and abnormal vascularity. IL-13, a profibrotic cytokine that plays a role in IPF, functions through the Jak/STAT pathway after binding to the IL-13 receptor α1 (IL-13Rα1)/IL-4Rα complex. IL-13 also binds to IL-13Rα2, which has been thought to function as a nonsignaling decoy receptor, although possible signaling roles of this receptor have been proposed. CXCR3 and its IFN-inducible ligands-CXCL9, CXCL10, and CXCL11-have been implicated in vascular remodeling and fibroblast motility during the development of IPF. In this study, CXCR3 expression was demonstrated in cultured pulmonary fibroblasts from wild-type BALB/c mice and was found to be necessary for the IL-13-mediated gene and protein up-regulation of IL-13Rα2. In fibroblasts from CXCR3-deficient mice, STAT6 activation was prolonged. This study is the first to demonstrate the expression of CXCR3 in fibroblasts and its association with the expression of IL-13Rα2. Taken together, the results from this study point strongly to a requirement for CXCR3 for IL-13-mediated IL-13Rα2 gene expression. Understanding the function of CXCR3 in IL-13-mediated lung injury may lead to novel approaches to combat the development of pulmonary fibrosis, whether by limiting the effects of IL-13 or by manipulation of angiostatic pathways. The elucidation of the complex relationship between these antifibrotic receptors and manipulation of the CXCR3-mediated regulation of IL-13Rα2 may represent a novel therapeutic modality in cases of acute lung injury or chronic inflammation that may progress to fibrosis.