TGF-β and Smad3 Signaling Link Inflammation to Chronic Fibrogenesis

Abstract

Transient adenovirus-mediated gene transfer of IL-1β (AdIL-1β), a proinflammatory cytokine, induces marked inflammation and severe and progressive fibrosis in rat lungs. This is associated with an increase in TGF-β1 concentration in bronchoalveolar lavage (BAL) fluid. TGF-β1 is a key cytokine in the process of fibrogenesis, using intracellular signaling pathways involving Smad2 and Smad3. In this study we investigate whether inflammation induced by IL-1β is able to independently induce lung fibrosis in mice deficient in the Smad3 gene. Seven days after AdIL-1β administration, similar levels of IL-1β transgene are seen in BAL in both wild-type (WT) and knockout (KO) mice, and BAL cell profiles demonstrated a similar marked neutrophilic inflammation. Phospho-Smad2 staining was positive in areas of inflammation in both WT and KO mice at day 7. By day 35 after transient IL-1β expression, WT mice showed marked fibrosis in peribronchial areas, quantified by picrosirius red staining and morphometry. However, there was no evidence of fibrosis or collagen accumulation in IL-1β-treated KO mice, and peribronchial areas were not different from KO mice treated with the control adenovector. TGF-β1 and phospho-Smad2 were strongly positive at day 35 in fibrotic areas observed in WT mice, but no such staining was detectable in KO mice. The IL-1β-induced chronic fibrotic response in mouse lungs is dependent on Smad3. KO and WT animals demonstrated a similar inflammatory response to overexpression of IL-1β indicating that inflammation must link to the Smad3 pathway, likely through TGF-β, to induce progressive fibrosis.

Matrix Metalloproteinase 3 Is a Mediator of Pulmonary Fibrosis

“…32,33 Although multiple complex signaling pathways are likely to contribute to end-stage tissue fibrosis, a prominent role of TGF-␤ in both experimental animal and human studies has been established. 28,29,49,50 Among its various properties, TGF-␤ has been shown to induce myofibroblast differentiation, EMT in pulmonary epithelial cells, and extracellular matrix gene transcription promoting collagen and fibronectin deposition. As noted above, however, there was no difference in the TGF-␤ levels in BALF between wild-type and MMP-3-null mice at early or later time points after bleomycin administration, despite considerable differences in physiological and histological measures of fibrosis.…”

TGF-β1 Induces Progressive Pleural Scarring and Subpleural Fibrosis

“…Transient overexpression of active TGF-␤1 in rat lungs by adenoviral gene transfer causes progressive lung fibrosis without major inflammation, characterized by extensive deposition of extracellular matrix proteins such as collagen and fibronectin and by accumulation of myofibroblasts (20). In contrast, adenovector-mediated overexpression of IL-1␤ induces a severe inflammatory response in the lung followed by progressive fibrosis, likely mediated through endogenous up-regulation of TGF-␤1 (21,24). The profibrotic effects of TGF-␤ do not only apply to bronchial and alveolar epithelial cells but also to mesothelial cells (28).…”

“…Collagen amount was analyzed on paraffin sections stained with Picrosirius Red (20 times) as previously described (23,24). Briefly, 25 random fields for each animal were digitized under polarized transmission illumination.…”

Treatment with CA-074Me, a Cathepsin B inhibitor, reduces lung interstitial inflammation and fibrosis in a rat model of polymyositis

“…28 TGF-b1 links inflammation to fibrogenesis and is one of the key mediators in the fibrotic process. [29][30][31][32] It has been observed that integrinb6 knockout mice develop lung inflammation but not pulmonary fibrosis after bleomycin exposure because of the absence of activation of latent TGF-b by integrin-b6. 33 As a downstream mediator of TGF-b1, connective tissue growth factor has a crucial role in TGF-b-induced connective tissue cell proliferation and organic ECM deposition.…”