ABSTRACT
Influenza infection exacerbates chronic pulmonary diseases, including idiopathic pulmonary fibrosis. A central pathway in the pathogenesis of idiopathic pulmonary fibrosis is epithelial injury leading to activation of transforming growth factor ß (TGFß). The mechanism and functional consequences of influenza-induced activation of epithelial TGFß are unclear. Influenza stimulates toll-like receptor 3 (TLR3), which can increase RhoA activity, a key event prior to activation of TGFß by the αvß6 integrin. We hypothesized that influenza would stimulate TLR3 leading to activation of latent TGFß via αvß6 integrin in epithelial cells. Using H1152 (IC50 6.1 µm) to inhibit Rho kinase and 6.3G9 to inhibit αvß6 integrins, we demonstrate their involvement in influenza (A/PR/8/34 H1N1) and poly(I:C)-induced TGFß activation. We confirm the involvement of TLR3 in this process using chloroquine (IC50 11.9 µm) and a dominant negative TLR3 construct (pZERO-hTLR3). Examination of lungs from influenza-infected mice revealed augmented levels of collagen deposition, phosphorylated Smad2/3, αvß6 integrin, and apoptotic cells. Finally, we demonstrate that αvß6 integrin-mediated TGFß activity following influenza infection promotes epithelial cell death in vitro and enhanced collagen deposition in vivo and that this response is diminished in Smad3 knock-out mice. These data show that H1N1 and poly(I:C) can induce αvß6 integrin-dependent TGFß activity in epithelial cells via stimulation of TLR3 and suggest a novel mechanism by which influenza infection may promote collagen deposition in fibrotic lung disease.
