Receptor-activated Smad localization in Bleomycin-induced pulmonary fibrosis

¹ GlaxosmithKline, Japan
² GlaxoSmithKline, Japan

^* To whom correspondence should be addressed. E-mail: satoshi.asano{at}gsk.com.

Accepted 23 March 2006

	Abstract

Background: Recent advances in fibrosis biology have identified transforming growth factor (TGF)-beta type I receptors-mediated activation of Smads is a central player in the development of fibrosis. To date, however, there have been few studies examining the receptor-activated Smads protein (R-Smads: Smad2 and 3) localization and distribution during the fibrosis progression.

Aims: To histopathologically assess the time course change of the Smads protein localization and distribution 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 hematoxylin-eosin stain or Masson's trichrome stain, and scored. TGF-beta1, Smad 3 and phosphorylated Smad 2 localizations in lung tissues were determined by immunohistochemistry.

Results: The Bleomycin treatment led to significant pulmonary fibrotic changes accompanied by marked increase in TGF-beta1 expression in infiltrating macrophages. With fibrosis progressing (day 7-14), a marked increases in Smad3- and pSmad2-positive cells were observed. There were intense Smad3- and pSmad2-positive signals localized 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: Our time course data of TGF-beta1 and R-Smads indicate that progressive enhancement of TGF-beta1 signaling via R-Smad is activated in the process of fibrosis progression.

Key Words: Smad proteins, TGF-beta1, pulmonary fibrosis