Bidirectional role of IL-6 signal in pathogenesis of lung fibrosis

Abstract

BackgroundVarious signals are known to participate in the pathogenesis of lung fibrosis. Our aim was to determine which signal is predominantly mobilized in the early inflammatory phase and thereafter modulates the development of lung fibrosis.MethodsMice received a single dose of 3 mg/kg body weight of bleomycin (BLM) and were sacrificed at designated days post-instillation (dpi). Lung homogenates and sections from mice in the early inflammatory phase were subjected to phospho-protein array analysis and immunofluorescence studies, respectively. Bronchoalveolar lavage fluid (BALF) from mice was subjected to an enzyme-linked immunosorbent assay (EIA) for interleukin (IL)-6 and evaluation of infiltrated cell populations. The effects of endogenous and exogenous IL-6 on the BLM-induced apoptotic signal in A549 cells and type 2 pneumocytes were elucidated. In addition, the effect of IL-6-neutralizing antibody on BLM-induced lung injury was evaluated.ResultsPhospho-protein array revealed that BLM induced phosphorylation of molecules downstream of the IL-6 receptor such as Stat3 and Akt in the lung at 3 dpi. At 3 dpi, immunofluorescence studies showed that signals of phospho-Stat3 and -Akt were localized in type 2 pneumocytes, and that BLM-induced IL-6-like immunoreactivity was predominantly observed in type 2 pneumocytes. Activation of caspases in BLM-treated A549 cells and type 2 pneumocytes was augmented by application of IL-6-neutralizing antibody, a PI3K inhibitor or a Stat3 inhibitor. EIA revealed that BLM-induced IL-6 in BALF was biphasic, with the first increase from 0.5 to 3 dpi followed by the second increase from 8 to 10 dpi. Blockade of the first increase of IL-6 by IL-6-neutralizing antibody enhanced apoptosis of type 2 pneumocytes and neutrophilic infiltration and markedly accelerated fibrosis in the lung. In contrast, blockade of the second increase of IL-6 by IL-6-neutralizing antibody ameliorated lung fibrosis.ConclusionsThe present study demonstrated that IL-6 could play a bidirectional role in the pathogenesis of lung fibrosis. In particular, upregulation of IL-6 at the early inflammatory stage of BLM-injured lung has antifibrotic activity through regulating the cell fate of type 2 pneumocytes in an autocrine/paracrine manner.Electronic supplementary materialThe online version of this article (doi:10.1186/s12931-015-0261-z) contains supplementary material, which is available to authorized users.

Amnion Epithelial Cells Promote Lung Repair via Lipoxin A4

“…Conversely, we found significant reduction in Th1 drivers IL-6 and IL-2 by day 7, suggesting a repression of inflammatory responses. This is supported by an earlier report that showed blocking IL-6 at days 8, 9, and 10 after bleomycin instillation can ameliorate lung fibrosis [35]. Surprisingly, we observed a transient reduction in IL-10 levels on day 5, which contradicts a previous finding by Manuelpillai and colleagues that described an increase in IL-10 levels following hAEC treatment in a mouse model of liver fibrosis [36].…”

Antifibrotic effects of cyclosporine A on TGF‐β1–treated lung fibroblasts and lungs from bleomycin‐treated mice: role of hypoxia‐inducible factor‐1α

“…Freshly cut lung sections (5 μm thick) placed on poly‐L‐lysine–coated slides were stained with hematoxylin and eosin (H&E) or Masson's trichrome to visualize inflammatory or fibrotic lesions. Semi‐quantitative elucidation of lung fibrotic changes was performed according to Ashcroft and coworkers’ method with a modification (16). In brief, under ×100 magnification, the grade of lung fibrosis was scored on a scale of 0–8 (17) by examining 10 randomly selected fields in each section (>4 sections/group), and the average score was calculated.…”

“…In a mouse model with a single intratracheal administration of BLM, acute alveolitis and interstitial inflammation accompanied by accumulation of leukocytes and pulmonary edema were induced within 1 wk, and fibrotic lung lesions were clearly observed in patches at 7 dpi, which is termed the early fibrotic stage. BLM‐induced fibrotic responses, including the synthesis of such profibrotic proteins as αSMA and collagen, subsequently progressed, and large parts of alveoli were obliterated with fibrous masses at 14 dpi (16, 30). Consistent with previous findings, up‐regulation of αSMA in the lung was typically detected at 7 dpi, the level of which increased at least until 14 dpi (Supplemental Fig.…”

Separate roles of IL‐6 and oncostatin M in mouse macrophage polarization in vitro and in vivo

“…Gp130 cytokines are elevated during chronic inflammatory lung disease, including IL‐6, Leukemia Inhibitory Factor (LIF), Oncostatin M (OSM), IL‐11 and IL‐31, and these cytokines may participate in immune cell skewing within the lung microenvironment . Recently, IL‐6 and OSM have been implicated in macrophage polarization in vitro .…”