Tranilast Inhibits Pulmonary Fibrosis by Suppressing TGFβ/SMAD2 Pathway

Abstract

Purpose

Idiopathic pulmonary fibrosis (IPF) is characterized by the accumulation of extracellular matrix (ECM) protein in the lungs. Transforming growth factor (TGF) β-induced ECM protein synthesis contributes to the development of IPF. Tranilast, an anti-allergy drug, suppresses TGFβ expression and inhibits interstitial renal fibrosis in animal models. However, the beneficial effects of tranilast or its mechanism as a therapy for pulmonary fibrosis have not been clarified.

Methods

We investigated the in vitro effect of tranilast on ECM production and TGFβ/SMAD2 pathway in TGFβ2-stimulated A549 human alveolar epithelial cells, using quantitative polymerase chain reaction, Western blotting, and immunofluorescence. In vitro observations were validated in the lungs of a murine pulmonary fibrosis model, which we developed by intravenous injection of bleomycin.

Results

Treatment with tranilast suppressed the expression of ECM proteins, such as fibronectin and type IV collagen, and attenuated SMAD2 phosphorylation in TGFβ2-stimulated A549 cells. In addition, based on a wound healing assay in these cells, tranilast significantly inhibited cell motility, with foci formation that comprised of ECM proteins. Histological analyses revealed that the administration of tranilast significantly attenuated lung fibrosis in mice. Furthermore, tranilast treatment significantly reduced levels of TGFβ, collagen, fibronectin, and phosphorylated SMAD2 in pulmonary fibrotic tissues in mice.

Conclusion

These findings suggest that tranilast inhibits pulmonary fibrosis by suppressing TGFβ/SMAD2-mediated ECM protein production, presenting tranilast as a promising and novel anti-fibrotic agent for the treatment of IPF.

Keywords:

• tranilast
• idiopathic pulmonary fibrosis
• TGFβ
• SMAD2

Acknowledgments

This study was supported by Japan Society for the Promotion of Science KAKENHI Grant Number 26461200. This study was partially supported by Ministry of Health, Labour and Welfare of Japan awarded to the Study Group on Diffuse Pulmonary Disorders, Scientific Research/Research on intractable diseases, Grant for Cross-disciplinary Collaboration, Grant from Institute for Environmental & Gender-specific Medicine, and President’s Grant for Interfaculty Collaboration, Juntendo University.

Abbreviations

IPF, idiopathic pulmonary fibrosis; ECM, extracellular matrix; TGF, transforming growth factor; EMT, epithelial–mesenchymal transition; BLM, bleomycin; CMC, carboxymethylcellulose; HE, hematoxylin-eosin; MT, Masson trichrome; FFR, focus formation ratio; qPCR, quantitative polymerase chain reaction; TGFβRI, TGFβ receptor inhibitor.

Data Sharing Statement

Not applicable.

Consent for Publication

Not applicable.

Ethics Approval and Consent to Participate

The Institutional Review Board at the Juntendo University School of Medicine approved the procedures. (No. 290,031).

Disclosure

The authors declare no conflicts of interest for this work.