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Interleukin (IL)-13 is a key mediator of tissue fibrosis caused by T helper cell type 2 inflammation. We hypothesized that the fibrogenic effects of IL-13 are mediated by transforming growth factor (TGF)-β. To test this hypothesis we compared the regulation of TGF-β in lungs from wild-type mice and CC10-IL-13 mice in which IL-13 overexpression causes pulmonary fibrosis. IL-13 selectively stimulated TGF-β1 production in transgenic animals and macrophages were the major site of TGF-β1 production and deposition in these tissues. IL-13 also activated TGF-β1 in vivo. This activation was associated with decreased levels of mRNA encoding latent TGF-β–binding protein-1 and increased mRNA encoding urinary plasminogen activator, matrix metalloproteinase (MMP)-9, and CD44. TGF-β1 activation was abrogated by the plasmin/serine protease antagonist aprotinin. It was also decreased in progeny of crosses of CC10-IL-13 mice and MMP-9 null mice but was not altered in crosses with CD44 null animals. IL-13–induced fibrosis was also significantly ameliorated by treatment with the TGF-β antagonist soluble TGFβR-Fc (sTGFβR-Fc). These studies demonstrate that IL-13 is a potent stimulator and activator of TGF-β1 in vivo. They also demonstrate that this activation is mediated by a plasmin/serine protease- and MMP-9–dependent and CD44-independent mechanism(s) and that the fibrogenic effects of IL-13 are mediated, in great extent, by this TGF-β pathway.

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IntroductionTissue remodeling responses are prominent features of inflammatory disorders of the airway and parenchyma of the lung. These responses are readily apparent in chronic obstructive pulmonary disease (COPD), asthma, and interstitial lung diseases: in which remodeling causes the alveolar septal destruction and changes in compliance that are characteristic of pulmonary emphysema (1), the subepithelial fibrosis, mucus metaplasia, and other structural alterations seen in asthmatic airway remodeling (2), and the pulmonary fibrosis that characterizes the interstitial disorders (3). Elevated levels of matrix metalloproteinases (MMPs) have been noted in patients with these disorders (4-12). In addition, studies from our laboratories and others demonstrated that MMP-12 plays an essential role in the pathogenesis of cigarette smoke-induced emphysema in mice (13) and that pretreatment with broad-spectrum MMP antagonists decreases the inflammation and airway hyperresponsiveness in murine models of asthma and the fibrosis in murine models of interstitial lung disorders (14,15). Surprisingly, little else is known about the roles that individual MMPs play in the pathogenesis of these important pulmonary disorders.IL-13 is a pleiotropic 12-kDa product of a gene on chromosome 5 at q31 that is produced in large quantities by Th2 cells and in lesser quantities by Th1 cells. IL-13 potently stimulates eosinophilic and lymphocytic inflammation and alveolar remodeling in the lung, effects that depend on the induction of various matrix metalloproteinases (MMPs).Here, we compared the remodeling and inflammatory effects of an IL-13 transgene in lungs of wild-type, MMP-9-deficient, or MMP-12-deficient mice. IL-13-induced alveolar enlargement, lung enlargement, compliance alterations, and respiratory failure and death were markedly decreased in the absence of MMP-9 or MMP-12. Moreover, IL-13 potently induced MMPs-2, -12, -13, and -14 in the absence of MMP-9, while induction of MMPs-2, -9, -13, and -14 by IL-13 was diminished in the absence of MMP-12. A deficiency in MMP-9 did not alter eosinophil, macrophage, or lymphocyte recovery, but increased the recovery of total leukocytes and neutrophils in bronchoalveolar lavage (BAL) fluids from IL-13 transgenic mice. In contrast, a deficiency in MMP-12 decreased the recovery of leukocytes, eosinophils, and macrophages, but not lymphocytes or neutrophils. These studies demonstrate that IL-13 acts via MMPs-9 and -12 to induce alveolar remodeling, respiratory failure, and death and that IL-13 induction of MMPs-2, -9, -13, and -14 is mediated at least partially by an MMP-12-dependent pathway. The also demonstrate that MMPs-9 and -12 play different roles in the generation of IL-13-induced inflammation, with MMP-9 inhibiting neutrophil accumulation and MMP-12 contributing to the accumulation of eosinophils and macrophages.

Objective Semaphorin (Sema) 7a regulates TGF- β1 induced fibrosis. Using a murine model of pulmonary fibrosis in which an inducible, bioactive form of the human TGF- β1 gene is overexpressed in the lung, we tested the hypothesis that Sema-7a exerts its pro-fibrotic effects in part by promoting the tissue accumulation of CD45+ fibrocytes. Methods Fibrosis and fibrocytes were evaluated in TGF- β1 transgenic mice in which the Sema-7a locus had been disrupted. The effect of replacement or deletion of Sema-7a on bone marrow derived cells was ascertained using bone marrow transplantation. The role of the Sema-7a receptor β1 integrin was assessed using neutralizing antibodies. The applicability of these findings to TGF-β1-driven fibrosis in humans was examined in patients with scleroderma-related interstitial lung disease. Results The appearance of fibrocytes in the lungs in TGF- β1 transgenic mice requires Sema-7a. Replacement of Sema-7a in bone marrow derived cells restores lung fibrosis and fibrocytes. Immunoneutralization of β1 integrin reduces pulmonary fibrocytes and fibrosis. Peripheral blood mononuclear cells from patients with scleroderma-related interstitial lung disease show increased mRNA for Sema-7a and the β1 integrin, with Sema-7a located on collagen producing fibrocytes and CD19+ lymphocytes. Peripheral blood fibrocyte outgrowth is enhanced in these patients. Stimulation of normal human peripheral blood mononuclear cells with recombinant Sema-7a enhances fibrocyte differentiation; these effects are attenuated by β1 integrin neutralization. Conclusion Interventions that reduce Sema-7a expression or prevent the Sema-7a - β1 integrin interaction may be ameliorative in TGF- β1-driven or fibrocyte-associated autoimmune fibroses.

IntroductionTissue remodeling responses are prominent features of inflammatory disorders of the airway and parenchyma of the lung. These responses are readily apparent in chronic obstructive pulmonary disease (COPD), asthma, and interstitial lung diseases: in which remodeling causes the alveolar septal destruction and changes in compliance that are characteristic of pulmonary emphysema (1), the subepithelial fibrosis, mucus metaplasia, and other structural alterations seen in asthmatic airway remodeling (2), and the pulmonary fibrosis that characterizes the interstitial disorders (3). Elevated levels of matrix metalloproteinases (MMPs) have been noted in patients with these disorders (4-12). In addition, studies from our laboratories and others demonstrated that MMP-12 plays an essential role in the pathogenesis of cigarette smoke-induced emphysema in mice (13) and that pretreatment with broad-spectrum MMP antagonists decreases the inflammation and airway hyperresponsiveness in murine models of asthma and the fibrosis in murine models of interstitial lung disorders (14,15). Surprisingly, little else is known about the roles that individual MMPs play in the pathogenesis of these important pulmonary disorders.IL-13 is a pleiotropic 12-kDa product of a gene on chromosome 5 at q31 that is produced in large quantities by Th2 cells and in lesser quantities by Th1 cells. IL-13 potently stimulates eosinophilic and lymphocytic inflammation and alveolar remodeling in the lung, effects that depend on the induction of various matrix metalloproteinases (MMPs).Here, we compared the remodeling and inflammatory effects of an IL-13 transgene in lungs of wild-type, MMP-9-deficient, or MMP-12-deficient mice. IL-13-induced alveolar enlargement, lung enlargement, compliance alterations, and respiratory failure and death were markedly decreased in the absence of MMP-9 or MMP-12. Moreover, IL-13 potently induced MMPs-2, -12, -13, and -14 in the absence of MMP-9, while induction of MMPs-2, -9, -13, and -14 by IL-13 was diminished in the absence of MMP-12. A deficiency in MMP-9 did not alter eosinophil, macrophage, or lymphocyte recovery, but increased the recovery of total leukocytes and neutrophils in bronchoalveolar lavage (BAL) fluids from IL-13 transgenic mice. In contrast, a deficiency in MMP-12 decreased the recovery of leukocytes, eosinophils, and macrophages, but not lymphocytes or neutrophils. These studies demonstrate that IL-13 acts via MMPs-9 and -12 to induce alveolar remodeling, respiratory failure, and death and that IL-13 induction of MMPs-2, -9, -13, and -14 is mediated at least partially by an MMP-12-dependent pathway. The also demonstrate that MMPs-9 and -12 play different roles in the generation of IL-13-induced inflammation, with MMP-9 inhibiting neutrophil accumulation and MMP-12 contributing to the accumulation of eosinophils and macrophages.

Th1 inflammation and remodeling characterized by tissue destruction frequently coexist in human diseases.To further understand the mechanisms of these responses, we defined the role(s) of CCR5 in the pathogenesis of IFN-g-induced inflammation and remodeling in a murine emphysema model. IFN-g was a potent stimulator of the CCR5 ligands macrophage inflammatory protein-1α/CCL-3 (MIP-1α/CCL-3), MIP-1β/CCL-4, and RANTES/CCL-5, among others. Antibody neutralization or null mutation of CCR5 decreased IFN-g-induced inflammation, DNA injury, apoptosis, and alveolar remodeling. These interventions decreased the expression of select chemokines, including CCR5 ligands and MMP-9, and increased levels of secretory leukocyte protease inhibitor. They also decreased the expression and/or activation of Fas, FasL, TNF, caspase-3, -8, and -9, Bid, and Bax. In accordance with these findings, cigarette smoke induced pulmonary inflammation, DNA injury, apoptosis, and emphysema via an IFN-g-dependent pathway(s), and a null mutation of CCR5 decreased these responses. These studies demonstrate that IFN-g is a potent stimulator of CC and CXC chemokines and highlight the importance of CCR5 in the pathogenesis of IFN-g-induced and cigarette smoke-induced inflammation, tissue remodeling, and emphysema. They also demonstrate that CCR5 is required for optimal IFN-g stimulation of its own ligands, other chemokines, MMPs, caspases, and cell death regulators and the inhibition of antiproteases.