Idiopathic pulmonary fibrosis (IPF) is a progressive and lethal disorder characterized by fibroproliferation and excessive accumulation of extracellular matrix in the lung. Using oligonucleotide arrays, we identified osteopontin as one of the genes that significantly distinguishes IPF from normal lungs. Osteopontin was localized to alveolar epithelial cells in IPF lungs and was also significantly elevated in bronchoalveolar lavage from IPF patients. To study the fibrosis-relevant effects of osteopontin we stimulated primary human lung fibroblasts and alveolar epithelial cells (A549) with recombinant osteopontin. Osteopontin induced a significant increase of migration and proliferation in both fibroblasts and epithelial cells. Epithelial growth was inhibited by the pentapeptide Gly-Arg-Gly-Asp-Ser (GRGDS) and antibody to CD44, while fibroproliferation was inhibited by GRGDS and antibody to α_vβ₃ integrin. Fibroblast and epithelial cell migration were inhibited by GRGDS, anti-CD44, and anti-α_vβ₃. In fibroblasts, osteopontin up-regulated tissue inhibitor of metalloprotease-1 and type I collagen, and down-regulated matrix metalloprotease-1 (MMP-1) expression, while in A549 cells it caused up-regulation of MMP-7. In human IPF lungs, osteopontin colocalized with MMP-7 in alveolar epithelial cells, and application of weakest link statistical models to microarray data suggested a significant interaction between osteopontin and MMP-7. Our results provide a potential mechanism by which osteopontin secreted from the alveolar epithelium may exert a profibrotic effect in IPF lungs and highlight osteopontin as a potential target for therapeutic intervention in this incurable disease.

Fibroblast proliferation and extracellular matrix accumulation characterize idiopathic pulmonary fibrosis (IPF). We evaluated the presence of tissue inhibitor of metalloproteinase (TIMP)-1, -2, -3, and -4; collagenase-1, -2, and -3; gelatinases A and B; and membrane type 1 matrix metalloproteinase (MMP) in 12 IPF and 6 control lungs. TIMP-1 was found in interstitial macrophages and TIMP-2 in fibroblast foci. TIMP-3 revealed an intense staining mainly decorating the elastic lamina in vessels. TIMP-4 was expressed in IPF lungs by epithelial and plasma cells. TIMP-2 colocalized with Ki67 in fibroblasts, whereas TIMP-3 colocalized with p27 in inflammatory and epithelial cells. Collagenase-1 was localized in macrophages and alveolar epithelial cells, collagenase-2 was localized in a few neutrophils, and collagenase-3 was not detected. MMP-9 was found in neutrophils and subepithelial myofibroblasts. Myofibroblast expression of MMP-9 was corroborated in vitro by RT-PCR. MMP-2 was noticed in myofibroblasts, some of them close to areas of basement membrane disruption, and membrane type 1 MMP was noticed in interstitial macrophages. These findings suggest that in IPF there is higher expression of TIMPs compared with collagenases, supporting the hypothesis that a nondegrading fibrillar collagen microenvironment is prevailing.

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disorder characterized by fibroblast proliferation and extracellular matrix accumulation. However, studies on fibroblast growth rate and collagen synthesis have given contradictory results. Here we analyzed fibroblast growth rate by a formazan-based chromogenic assay; fibroblast apoptosis by in situ end labeling (ISEL) and propidium iodide staining; percent of α-smooth muscle actin ( α-SMA) positive cells by fluorescence-activated cell sorter; and α 1-(I) collagen, transforming growth factor (TGF)-β 1, collagenase-1, gelatinases A and B, and tissue inhibitor of metalloproteinase (TIMP)-1, -2, -3, and -4 expression by reverse transcriptase/polymerase chain reaction in fibroblasts derived from IPF and control lungs. Growth rate was significantly lower in IPF fibroblasts compared with controls (13.3 ± 38.5% versus 294.6 ± 57%, P < 0.0001 at 13 d). Conversely, a significantly higher percentage of apoptotic cells was observed in IPF-derived fibroblasts (ISEL: 31.9 ± 7.0% versus 15.5 ± 7.6% from controls; P < 0.008). α-SMA analysis revealed a significantly higher percentage of myofibroblasts in IPF samples (62.8 ± 25.2% versus 14.8 ± 11.7% from controls; P < 0.01). IPF fibroblasts were characterized by an increase in pro–α 1-(I) collagen, TGF-β 1, gelatinase B, and all TIMPs' gene expression, whereas collagenase-1 and gelatinase A expression showed no differences. These results suggest that fibroblasts from IPF exhibit a profibrotic secretory phenotype, with lower growth rate and increased spontaneous apoptosis.

Rationale: Fibrocytes are progenitor cells characterized by the simultaneous expression of mesenchymal, monocyte, and hematopoietic stem cell markers. We previously documented their presence in lungs of patients with idiopathic pulmonary fibrosis. However, the mechanisms involved in their migration, subsequent homing, and local role remain unclear. Matrix metalloproteinases (MMPs) facilitate cell migration and have been implicated in the pathogenesis of pulmonary fibrosis. Objectives: To evaluate the expression and role of matrix metalloproteinases in human fibrocytes. Methods: Fibrocytes were purified from CD14+ monocytes and cultured for 8 days; purity of fibrocyte cultures was 95% or greater as determined by flow cytometry. Conditioned media and total RNA were collected and the expression of MMP-1, MMP-2, MMP-7, MMP-8, and MMP-9 was evaluated by real-time polymerase chain reaction. Protein synthesis was examined using a Multiplex assay, Western blot, fluorescent immunocytochemistry, and confocal microscopy. MMP-2 and MMP-9 enzymatic activities were evaluated by gelatin zymography. Migration was assessed using collagen I–coated Boyden chambers. Stromal cell–derived factor–1α and platelet-derived growth factor–B were used as chemoattractant with or without a specific MMP-8 inhibitor. Measurements and Main Results: Fibrocytes showed gene and protein expression of MMP-2, MMP-9, MMP-8, and MMP-7. MMP-2 and MMP-9 enzymatic activities were also demonstrated by gelatin zymography. Likewise, we found colocalization of MMP-8 and MMP-7 with type I collagen in fibrocytes. Fibrocyte migration toward platelet-derived growth factor–B or Stromal cell–derived factor–1α in collagen I–coated Boyden chambers was significantly reduced by a specific MMP-8 inhibitor. Conclusions: Our findings reveal that fibrocytes express a variety of MMPs and that MMP-8 actively participates in the process of fibrocyte migration.

Rationale: Idiopathic pulmonary fibrosis (IPF) is a devastating disease characterized by epithelial phenotypic changes and fibroblast activation. Based on the temporal heterogeneity of IPF, we hypothesized that hyperplastic alveolar epithelial cells regulate the fibrotic response. Objectives: To identify novel mediators of fibrosis comparing the transcriptional signature of hyperplastic epithelial cells and conserved epithelial cells in the same lung. Methods: Laser capture microscope and microarrays analysis were used to identify differentially expressed genes in IPF lungs. Bleomycin-induced lung fibrosis was evaluated in Mmp19-deficient and wild-type (WT) mice. The role of matrix metalloproteinase (MMP)-19 was additionally studied by transfecting the human MMP19 in alveolar epithelial cells. Measurements and Main Results: Laser capture microscope followed by microarray analysis revealed a novel mediator, MMP-19, in hyperplastic epithelial cells adjacent to fibrotic regions. Mmp19−/− mice showed a significantly increased lung fibrotic response to bleomycin compared with WT mice. A549 epithelial cells transfected with human MMP19 stimulated wound healing and cell migration, whereas silencing MMP19 had the opposite effect. Gene expression microarray of transfected A549 cells showed that PTGS2 (prostaglandin–endoperoxide synthase 2) was one of the highly induced genes. PTGS2 was overexpressed in IPF lungs and colocalized with MMP-19 in hyperplastic epithelial cells. In WT mice, PTGS2 was significantly increased in bronchoalveolar lavage and lung tissues after bleomycin-induced fibrosis, but not in Mmp19−/− mice. Inhibition of Mmp-19 by siRNA resulted in inhibition of Ptgs2 at mRNA and protein levels. Conclusions: Up-regulation of MMP19 induced by lung injury may play a protective role in the development of fibrosis through the induction of PTGS2.