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Updated: Aug 8, 2026
Oropharyngeal Administration of Bleomycin in the Murine Model of Pulmonary Fibrosis
Published on: May 9, 2025
Receptor-activated Smad localisation in bleomycin-induced pulmonary fibrosis
Hiroyuki Higashiyama1, Daisuke Yoshimoto, Yuji Okamoto
1Department of Pharmacology, Tsukuba Research Laboratories, GlaxoSmithKline, Tsukuba, Ibaraki, Japan.
Background:
Recent advances in fibrosis biology have identified transforming growth factor (TGF)-beta type I receptor-mediated activation of Smads as playing a central part in the development of fibrosis. However, to date, there have been few studies that examined the localisation and distribution of receptor-activated Smads protein (R-Smads: Smad2 and 3) during the fibrosis progression.
Aims:
To histopathologically assess the time-course change of the localisation and distribution of the Smads protein in pulmonary fibrosis.
Methods:
Pulmonary fibrosis was induced by intranasal injection of bleomycin (0.3 U/mouse). Lungs were isolated 2, 5, 7, 9 and 14 days after bleomycin treatment. Histological changes in the lungs were evaluated by haematoxylin-eosin stain or Masson's trichrome stain, and scored. TGF-beta1, Smad3 and phosphorylated Smad2 localisations in lung tissues were determined by immunohistochemistry.
Results:
The bleomycin treatment led to considerable pulmonary fibrotic changes accompanied by marked increase in TGF-beta1 expression in infiltrating macrophages. With the progression in fibrosis (day 7-14), marked increases in Smad3-positive and pSmad2-positive cells were observed. There were intense Smad3-positive and pSmad2-positive signals localised to the nuclei of the infiltrating macrophages and to type II epithelial cells, and less intense signals in fibroblasts and hyperplastic alveolar/bronchiolar epithelial cells.
Conclusions:
The time-course data of TGF-beta1 and R-Smads indicate that progressive enhancement of TGF-beta1 signalling via R-Smad is activated in the process of fibrosis progression.
Insights
Transforming growth factor-beta (TGF-β) signaling via receptor-activated Smads (R-Smads) is key in fibrosis. This study tracked R-Smad protein localization during bleomycin-induced pulmonary fibrosis, revealing their activation in macrophages and epithelial cells.
Area of Science:
- Fibrosis biology
- Cell signaling pathways
- Pulmonary pathology
Background:
- Transforming growth factor-beta (TGF)-beta type I receptor-mediated activation of Smads is central to fibrosis.
- Limited research exists on receptor-activated Smads (R-Smads) protein localization during fibrosis progression.
Purpose of the Study:
- To histopathologically assess the time-course changes in Smads protein localization and distribution in pulmonary fibrosis.
- Investigate the role of R-Smads in the progression of lung fibrosis.
Main Methods:
- Pulmonary fibrosis induced via intranasal bleomycin in mice.
- Lung tissues collected at 2, 5, 7, 9, and 14 days post-bleomycin.
- Histological evaluation (H&E, Masson's trichrome) and immunohistochemistry for TGF-beta1, Smad3, and pSmad2.
Main Results:
- Bleomycin induced significant pulmonary fibrosis with increased TGF-beta1 in macrophages.
- Smad3 and pSmad2 positive cells increased from day 7 to 14.
- Intense Smad3 and pSmad2 signals detected in macrophage nuclei and type II epithelial cells.
Conclusions:
- Time-course data show progressive TGF-beta1 signaling via R-Smads activation during fibrosis.
- R-Smad localization provides insights into the cellular mechanisms of pulmonary fibrosis progression.
