WNT/β-catenin signaling induces interleukin 1β expression by alveolar epithelial cells in pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease of yet unknown etiology. It is characterised by alterations of the alveolar epithelium, myofibroblast activation, and increased extracellular matrix deposition. Recently, reactivation of WNT/β-catenin signaling has been linked with IPF. The cell-specific mechanisms and mediators of WNT/β-catenin signaling in the lung, however, remain elusive. Here, we applied an unbiased gene expression screen to identify epithelial cell-specific mediators of WNT/β-catenin signaling. We found the proinflammatory cytokine interleukin (IL) 1β as one of the most upregulated genes in primary murine alveolar epithelial type (AT) II cells after WNT3a treatment. Increased transcript and protein expression of IL-1β upon WNT3a treatment was further detected in primary ATII cells by qRT-PCR (log-fold change: 2.0 +/- 0.5) and ELISA (1.8 fold increase). We observed significant IL-1β and IL-6 upregulation in bronchoalveolar lavage fluid (BALF) in bleomycin induced lung fibrosis in vivo. Importantly, primary fibrotic ATII cells secreted enhanced IL-1β and IL-6 in vitro. Furthermore, orotracheal application of recombinant WNT protein in TOPGAL reporter animals led to WNT/β-catenin activation in epithelial cells along with a significant increase in IL-1β and IL-6 in vivo (2.7-fold and 6.0-fold, respectively). Finally, we found increased WNT3a protein in fibrotic alveolar epithelium accompanied by enhanced IL-1β and IL-6 level in BALF from IPF patients. Taken together, our findings revealed that the alveolar epithelium is a relevant source of proinflammatory cytokines induced by active WNT/β-catenin. Thus, WNT/interleukin signaling represents a novel link between developmental pathway reactivation and inflammation in the development of pulmonary fibrosis