Increased transforming growth factor beta 1 expression mediates ozone-induced airway fibrosis in mice

Abstract

Ozone (O₃), a commonly encountered environmental pollutant, has been shown to induce pulmonary fibrosis in different animal models; the underlying mechanism, however, remains elusive. To investigate the molecular mechanism underlying O₃-induced pulmonary fibrosis, 6- to 8-week-old C57BL/6 male mice were exposed to a cyclic O₃ exposure protocol consisting of 2 days of filtered air and 5 days of O₃ exposure (0.5 ppm, 8 h/day) for 5 and 10 cycles with or without intraperitoneal injection of IN-1233, a specific inhibitor of the type 1 receptor of transforming growth factor beta (TGF-β), the most potent profibrogenic cytokine. The results showed that O₃ exposure for 5 or 10 cycles increased the TGF-β protein level in the epithelial lining fluid (ELF), associated with an increase in the expression of plasminogen activator inhibitor 1 (PAI-1), a TGF-β-responsive gene that plays a critical role in the development of fibrosis under various pathological conditions. Cyclic O₃ exposure also increased the deposition of collagens and alpha smooth muscle actin (α-SMA) in airway walls. However, these fibrotic changes were not overt until after 10 cycles of O₃ exposure. Importantly, blockage of the TGF-β signaling pathway with IN-1233 suppressed O₃-induced Smad2/3 phosphorylation, PAI-1 expression, as well as collagens and α-SMA deposition in the lung. Our data demonstrate for the first time that O₃ exposure increases TGF-β expression and activates TGF-β signaling pathways, which mediates O₃-induced lung fibrotic responses in vivo.

Keywords::

• Ozone
• TGF-β
• PAI-1
• airway fibrosis

Acknowledgement

The authors would like to thank the following people for their technical assistance with ozone exposure and sample collection/processing: Jo Anne Balanay, Wentan Huang, and Kishor Gangani.

Declaration of interest

The work was supported by grants from National Institute of Environmental Health Sciences R01 ES011831 (RML) and P01 ES011617 (EMP, MF, and CB), National Heart, Lung, and Blood Institute R01 HL088141 (RML) and R01 HL54696 (EMP), and the American Lung Association (RML).