Background Idiopathic pulmonary fibrosis (IPF) is a diffuse parenchymal lung disease characterized by exuberant deposition of extracellular matrix (ECM) proteins in the lung interstitium, which contributes to substantial morbidity and mortality in IPF patients. Matrix metalloproteinases (MMPs) are a large family of zinc-dependent endopeptidases, many of which have been implicated in the regulation of ECM degradation in lung fibrosis. However, the roles of MMP-2 and -9 (also termed gelatinases A and B) have not yet been explored in lung fibrosis in detail. Methods AdTGF-β1 was applied via orotracheal routes to the lungs of WT, MMP-2 KO, MMP-9 KO and MMP-2/-9 dKO mice on day 0 to induce lung fibrosis. Using hydroxyproline assay, FlexiVent based lung function measurement, histopathology, western blot and ELISA techniques, we analyzed MMP-2 and MMP-9 levels in BAL fluid and lung, collagen contents in lung and lung function in mice on day 14 and 21 post-treatment. Result IPF lung homogenates exhibited significantly increased levels of MMP-2 and MMP-9, relative to disease controls. Enzymatically active MMP-2 and MMP-9 was increased in lungs of mice exposed to adenoviral TGF-β1, suggesting a role for these metalloproteinases in lung fibrogenesis. However, we found that neither MMP-2 or MMP-9 nor combined MMP-2/-9 deletion had any effect on experimental lung fibrosis in mice. Conclusion Together, our data strongly suggest that both gelatinases MMP-2 and MMP-9 play only a subordinate role in experimental lung fibrosis in mice.

The current study has been funded by the Bundesministerium für Bildung und Forschung supporting the German Center for Lung Research (Deutsches Zentrum für Lungenforschung).

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease (ILD) associated with high morbidity and mortality. Patients with ILD frequently develop an acute exacerbation of their disease, which may be triggered by viral and/or bacterial infections. Prostaglandin E2 (PGE2) is an eicosanoid released in a cyclooxygenase-2 (COX2) dependent manner and is considered to contribute to regulation of lung fibrosis. However, its role in infection-induced exacerbation of lung fibrosis is poorly defined. We found significantly increased levels of PGE2 in lung tissue of patients with ILD. Increased levels of PGE2 were also found in lung tissue of mice with AdTGF-β1 induced lung fibrosis and even more so in S. pneumoniae exacerbated lung fibrosis. Type II alveolar epithelial cells (AT II cells) and alveolar macrophages (AM) contributed to PGE2 release during exacerbating fibrosis. Application of Parecoxib to inhibit PGE2 synthesis ameliorated lung fibrosis, while intratracheal application of PGE2 worsened lung fibrosis in mice. Both interventions had no effect on S. pneumoniae exacerbated lung fibrosis. Together, we found that the COX2/PGE2 axis has dual roles in fibrosis that may offset each other: PGE2 helps resolve infection/attenuate inflammation in fibrosis exacerbation but accentuates TGF-b/AT II cell-mediated fibrosis. These data support the efficacy of COX/PGE2 interventions in the setting of non-exacerbating lung fibrosis.

Idiopathic pulmonary fibrosis (IPF) is an irreversible, age-related diffuse parenchymal lung disease of poorly defined etiology. Many patients with IPF demonstrate distinctive lymphocytic interstitial infiltrations within remodeled lung tissue with uncertain pathogenetic relevance. Histopathological examination of explant lung tissue of patients with IPF revealed accentuated lymphoplasmacellular accumulations in close vicinity to, or even infiltrating, remodeled lung tissue. Similarly, we found significant accumulations of B cells interfused with T cells within remodeled lung tissue in two murine models of adenoviral TGF-β1 or bleomycin (BLM)-induced lung fibrosis. Such B cell accumulations coincided with significantly increased lung collagen deposition, lung histopathology, and worsened lung function in wild-type (WT) mice. Surprisingly, B cell–deficient µMT knockout mice exhibited similar lung tissue remodeling and worsened lung function upon either AdTGF-β1 or BLM as for WT mice. Comparative transcriptomic profiling of sorted B cells collected from lungs of AdTGF-β1– and BLM-exposed WT mice identified a large set of commonly regulated genes, but with significant enrichment observed for Gene Ontology terms apparently not related to lung fibrogenesis. Collectively, although we observed B cell accumulations in lungs of IPF patients as well as two experimental models of lung fibrosis, comparative profiling of characteristic features of lung fibrosis between WT and B cell–deficient mice did not support a major involvement of B cells in lung fibrogenesis in mice.