Therapeutic ultrasound ameliorates pulmonary fibrosis through inhibiting TGF-β/SMAD-mediated epithelial mesenchymal transition

Abstract

Abstract Background Idiopathic pulmonary fibrosis (IPF) is a progressive pulmonary interstitial inflammatory disease with no effective treatment. Lung epithelial injury and dysfunction are the core of initiating the pathogenic process. Following injury to the lung epithelium, inflammatory cell recruitment, fibroblast proliferation and extracellular matrix expansion ultimately lead to tissue fibrosis. Chronic inflammatory microenvironment is closely related to the development of epithelial mesenchymal transition (EMT). Moreover, EMT may be the main source of pathogenic myofibroblasts in the process of pulmonary fibrosis. There is increasing evidence that therapeutic ultrasound (TUS) can alleviate the inflammatory response. This study aimed to investigate that effects of TUS on EMT and fibrosis in bleomycin (BLM)-induced model. Methods Pulmonary fibrosis was induced in mice by intratracheal instillation of bleomycin. The mice were treated with TUS for 14d. After the mice were sacrificed, lung tissues were collected for analysis. The lungs were analyzed histopathologically using hematoxylin and eosin and Masson’s trichrome staining. The fibrosis was characterized by hydroxyproline (Hyp) content, immunofluorescence and western blotting for α-SMA and Collagen I. The levels of inflammatory cytokines (TNF-α, IL-6, IL-1, and TGF-β) were measured with ELISA. The protein levels of Vimentin, E-cadherin, p-SMAD2, SMAD2, p-SMAD3, SMAD3 were examined by western blotting. Results Treatment with TUS attenuated the degree of pulmonary fibrosis, which downregulated the content of Hyp and the expression levels of α-SMA and Collagen I in lungs and reduced the inflammatory cytokines levels. TUS reversed mesenchymal-like changes in the BLM-induced mice. The results confirmed that the expression of the epithelial marker, E-cadherin, increased after TUS treatment, while expression of the mesenchymal markers, Vimentin, and α-SMA decreased after the treatment. Furthermore, TUS reduced expression of TGF-β1 and the phosphorylation of SMAD2/3. Conclusions These findings suggested that TUS therapy had anti-fibrotic activity and could be used for IPF.