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1.  Role of Breast Regression Protein–39 in the Pathogenesis of Cigarette Smoke–Induced Inflammation and Emphysema 
The exaggerated expression of chitinase-like protein YKL-40, the human homologue of breast regression protein–39 (BRP-39), was reported in a number of diseases, including chronic obstructive pulmonary disease (COPD). However, the in vivo roles of YKL-40 in normal physiology or in the pathogenesis of specific diseases such as COPD remain poorly understood. We hypothesized that BRP-39/YKL-40 plays an important role in the pathogenesis of cigarette smoke (CS)–induced emphysema. To test this hypothesis, 10-week-old wild-type and BRP-39 null mutant mice (BRP-39−/−) were exposed to room air (RA) and CS for up to 10 months. The expression of BRP-39 was significantly induced in macrophages, airway epithelial cells, and alveolar Type II cells in the lungs of CS-exposed mice compared with RA-exposed mice, at least in part via an IL-18 signaling–dependent pathway. The null mutation of BRP-39 significantly reduced CS-induced bronchoalveolar lavage and tissue inflammation. However, CS-induced epithelial cell apoptosis and alveolar destruction were further enhanced in the absence of BRP-39. Consistent with these findings in mice, the tissue expression of YKL-40 was significantly increased in the lungs of current smokers compared with the lungs of ex-smokers or nonsmokers. In addition, serum concentrations of YKL-40 were significantly higher in smokers with COPD than in nonsmokers or smokers without COPD. These studies demonstrate a novel regulatory role of BRP-39/YKL-40 in CS-induced inflammation and emphysematous destruction. These studies also underscore that maintaining physiologic concentrations of YKL-40 in the lung is therapeutically important in preventing excessive inflammatory responses or emphysematous alveolar destruction.
doi:10.1165/rcmb.2010-0081OC
PMCID: PMC3135840  PMID: 20656949
YKL-40/BRP-39; COPD; emphysema; cigarette smoke
2.  Endogenous IL-11 Signaling Is Essential in Th2- and IL-13–Induced Inflammation and Mucus Production 
IL-11 and IL-11 receptor (R)α are induced by Th2 cytokines. However, the role(s) of endogenous IL-11 in antigen-induced Th2 inflammation has not been fully defined. We hypothesized that IL-11, signaling via IL-11Rα, plays an important role in aeroallergen-induced Th2 inflammation and mucus metaplasia. To test this hypothesis, we compared the responses induced by the aeroallergen ovalbumin (OVA) in wild-type (WT) and IL-11Rα–null mutant mice. We also generated and defined the effects of an antagonistic IL-11 mutein on pulmonary Th2 responses. Increased levels of IgE, eosinophilic tissue and bronchoalveolar lavage (BAL) inflammation, IL-13 production, and increased mucus production and secretion were noted in OVA-sensitized and -challenged WT mice. These responses were at least partially IL-11 dependent because each was decreased in mice with null mutations of IL-11Rα. Importantly, the administration of the IL-11 mutein to OVA-sensitized mice before aerosol antigen challenge also caused a significant decrease in OVA-induced inflammation, mucus responses, and IL-13 production. Intraperitoneal administration of the mutein to lung-specific IL-13–overexpressing transgenic mice also reduced BAL inflammation and airway mucus elaboration. These studies demonstrate that endogenous IL-11R signaling plays an important role in antigen-induced sensitization, eosinophilic inflammation, and airway mucus production. They also demonstrate that Th2 and IL-13 responses can be regulated by interventions that manipulate IL-11 signaling in the murine lung.
doi:10.1165/rcmb.2008-0053OC
PMCID: PMC2586049  PMID: 18617680
IL-11; mutein; airway inflammation; mucus; IL-13
3.  P21 Regulates TGF-β1–Induced Pulmonary Responses via a TNF-α–Signaling Pathway 
Transforming growth factor (TGF)-β1 is an essential regulatory cytokine that has been implicated in the pathogenesis of diverse facets of the injury and repair responses in the lung. The types of responses that it elicits can be appreciated in studies from our laboratory that demonstrated that the transgenic (Tg) overexpression of TGF-β1 in the murine lung causes epithelial apoptosis followed by fibrosis, inflammation, and parenchymal destruction. Because a cyclin-dependent kinase inhibitor, p21, is a key regulator of apoptosis, we hypothesized that p21 plays an important role in the pathogenesis of TGF-β1–induced tissue responses. To test this hypothesis we evaluated the effect of TGF-β1 on the expression of p21 in the murine lung. We also characterized the effects of transgenic TGF-β1 in mice with wild-type and null mutant p21 loci. These studies demonstrate that TGF-β1 is a potent stimulator of p21 expression in the epithelial cells and macrophages in the murine lung. They also demonstrate that TGF-β1–induced lung inflammation, fibrosis, myofibroblast accumulation, and alveolar destruction are augmented in the absence of p21, and that these alterations are associated with exaggerated levels of apoptosis and caspase-3 activation. Finally, our studies further demonstrated that TGF-β1 induces p21 via a TNF-α–signaling pathway and that p21 is a negative modulator of TGF-β1–induced TNF-α expression. Collectively, our studies demonstrate that p21 regulates TGF-β1–induced apoptosis, inflammation, fibrosis, and alveolar remodeling by interacting with TNF-α–signaling pathways.
doi:10.1165/rcmb.2007-0276OC
PMCID: PMC2258454  PMID: 17932374
TGF-β; p21; apoptosis; fibrosis; emphysema
4.  RIG-like Helicase Innate Immunity Inhibits Vascular Endothelial Growth Factor Tissue Responses via a Type I IFN–dependent Mechanism 
Rationale: Vascular endothelial growth factor (VEGF) regulates vascular, inflammatory, remodeling, and cell death responses. It plays a critical role in normal pulmonary physiology, and VEGF excess and deficiency have been implicated in the pathogenesis of asthma and chronic obstructive pulmonary disease, respectively. Although viruses are an important cause of chronic obstructive pulmonary disease exacerbations and innate responses play an important role in these exacerbations, the effects of antiviral responses on VEGF homeostasis have not been evaluated.
Objectives: We hypothesized that antiviral innate immunity regulates VEGF tissue responses.
Methods: We compared the effects of transgenic VEGF165 in mice treated with viral pathogen–associated molecular pattern polyinosinic:polycytidylic acid [poly(I:C)], mice treated with live virus, and control mice.
Measurements and Main Results: Transgenic VEGF stimulated angiogenesis, edema, inflammation, and mucin accumulation. Each of these was abrogated by poly(I:C). These inhibitory effects were dose dependent, noted when poly(I:C) was administered before and after transgene activation, and mediated by a Toll-like receptor-3–independent and RIG-like helicase (RLH)– and type I IFN receptor–dependent pathway. VEGF stimulated the expression of VEGF receptor-1 and poly(I:C) inhibited this stimulation. Poly(I:C) also inhibited the ability of VEGF to activate extracellular signal–regulated kinase-1, Akt, focal adhesion kinase, and endothelial nitric oxide synthase, and aeroallergen-induced adaptive helper T-cell type 2 inflammation. Influenza and respiratory syncytial virus also inhibited VEGF-induced angiogenesis.
Conclusions: These studies demonstrate that poly(I:C) and respiratory viruses inhibit VEGF-induced tissue responses and adaptive helper T-cell type 2 inflammation and highlight the importance of a RLH- and type I IFN receptor–dependent pathway(s) in these regulatory events. They define a novel link between VEGF and antiviral and RLH innate immune responses and a novel pathway that regulates pulmonary VEGF activity.
doi:10.1164/rccm.201008-1276OC
PMCID: PMC3114061  PMID: 21278304
RIG-like helicase; mitochondrial antiviral signaling molecule; influenza virus; chronic obstructive pulmonary disease
5.  Role of breast regression protein 39 (BRP-39)/chitinase 3-like-1 in Th2 and IL-13–induced tissue responses and apoptosis 
The Journal of Experimental Medicine  2009;206(5):1149-1166.
Mouse breast regression protein 39 (BRP-39; Chi3l1) and its human homologue YKL-40 are chitinase-like proteins that lack chitinase activity. Although YKL-40 is expressed in exaggerated quantities and correlates with disease activity in asthma and many other disorders, the biological properties of BRP-39/YKL-40 have only been rudimentarily defined. We describe the generation and characterization of BRP-39−/− mice, YKL-40 transgenic mice, and mice that lack BRP-39 and produce YKL-40 only in their pulmonary epithelium. Studies of these mice demonstrated that BRP-39−/− animals have markedly diminished antigen-induced Th2 responses and that epithelial YKL-40 rescues the Th2 responses in these animals. The ability of interleukin13 to induce tissue inflammation and fibrosis was also markedly diminished in the absence of BRP-39. Mechanistic investigations demonstrated that BRP-39 and YKL-40 play an essential role in antigen sensitization and immunoglobulin E induction, stimulate dendritic cell accumulation and activation, and induce alternative macrophage activation. These proteins also inhibit inflammatory cell apoptosis/cell death while inhibiting Fas expression, activating protein kinase B/AKT, and inducing Faim 3. These studies establish novel regulatory roles for BRP-39/YKL-40 in the initiation and effector phases of Th2 inflammation and remodeling and suggest that these proteins are therapeutic targets in Th2- and macrophage-mediated disorders.
doi:10.1084/jem.20081271
PMCID: PMC2715037  PMID: 19414556
6.  Semaphorin 7A plays a critical role in TGF-β1–induced pulmonary fibrosis 
The Journal of Experimental Medicine  2007;204(5):1083-1093.
Semaphorin (SEMA) 7A regulates neuronal and immune function. In these studies, we tested the hypothesis that SEMA 7A is also a critical regulator of tissue remodeling. These studies demonstrate that SEMA 7A and its receptors, plexin C1 and β1 integrins, are stimulated by transforming growth factor (TGF)-β1 in the murine lung. They also demonstrate that SEMA 7A plays a critical role in TGF-β1–induced fibrosis, myofibroblast hyperplasia, alveolar remodeling, and apoptosis. TGF-β1 stimulated SEMA 7A via a largely Smad 3–independent mechanism and stimulated SEMA 7A receptors, matrix proteins, CCN proteins, fibroblast growth factor 2, interleukin 13 receptor components, proteases, antiprotease, and apoptosis regulators via Smad 2/3–independent and SEMA 7A–dependent mechanisms. SEMA 7A also played an important role in the pathogenesis of bleomycin-induced pulmonary fibrosis. TGF-β1 and bleomycin also activated phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB)/AKT via SEMA 7A–dependent mechanisms, and PKB/AKT inhibition diminished TGF-β1–induced fibrosis. These observations demonstrate that SEMA 7A and its receptors are induced by TGF-β1 and that SEMA 7A plays a central role in a PI3K/PKB/AKT-dependent pathway that contributes to TGF-β1–induced fibrosis and remodeling. They also demonstrate that the effects of SEMA 7A are not specific for transgenic TGF-β1, highlighting the importance of these findings for other fibrotic stimuli.
doi:10.1084/jem.20061273
PMCID: PMC2118575  PMID: 17485510
7.  Transgenic Modeling of Transforming Growth Factor-β1 
Inflammation and tissue remodeling with pathologic fibrosis are common consequences of Th2 responses in the lung and other organs. Interleukin (IL)-13 and transforming growth factor-β1 (TGF-β1) are frequently coexpressed in these responses and are believed to play important roles in the pathogenesis of Th2-induced pathologies. To shed light on the mechanisms of these responses, overexpression transgenic approaches were used to selectively target each of these cytokines to the murine lung. IL-13 proved to be a potent stimulator of eosinophilic inflammation, mucus metaplasia, tissue fibrosis, and alveolar remodeling. CC chemokines, specific chemokine receptors (CCR2, CCR1), adenosine metabolism, vascular endothelial growth factor, and IL-11 contributed to the genesis of these responses. IL-13 also induced tissue fibrosis, at least in part, via its ability to induce and activate TGF-β1. In the TGF-β1 transgenic mouse, epithelial apoptosis preceded the onset of tissue fibrosis and alveolar remodeling. In addition, chemical (Z-VAD-fmk) and genetic (null mutations of early growth response gene 1) interventions blocked apoptosis and ameliorated TGF-β1–induced fibrosis and alveolar restructuring. These studies define an IL-13–TGF-β1 pathway of tissue remodeling that regulates inflammation, mucus metaplasia, apoptosis, vascular responses, and fibrosis in the lung. They also highlight the intimate relationship between apoptosis and fibrosis induced by TGF-β1. By defining the complexities of this pathway, these studies highlight sites at which therapies can be directed to control these important responses.
doi:10.1513/pats.200602-017AW
PMCID: PMC2658706  PMID: 16799085
asthma; fibrosis; interleukin-13; transforming growth factor-β; 1; transgenic
8.  Adenosine metabolism and murine strain–specific IL-4–induced inflammation, emphysema, and fibrosis 
Journal of Clinical Investigation  2006;116(5):1274-1283.
To define the factors that control the tissue effects of IL-4, we compared the effects of Tg IL-4 in Balb/c and C57BL/6 mice. In the former, IL-4 caused modest eosinophilic inflammation and mild airway fibrosis and did not shorten survival. In C57BL/6 mice, IL-4 caused profound eosinophilic inflammation, airway fibrosis, emphysematous alveolar destruction, and premature death. These differences could not be accounted for by changes in Th2 or Th1 cytokines, receptor components, STAT6 activation, MMPs, or cathepsins. In contrast, in C57BL/6 mice, alveolar remodeling was associated with decreased levels of tissue inhibitors of metalloproteinase 2, -3, and -4 and α1-antitrypsin, and fibrosis was associated with increased levels of total and bioactive TGF-β1. Impressive differences in adenosine metabolism were also appreciated, with increased tissue adenosine levels and A1, A2B, and A3 adenosine receptor expression and decreased adenosine deaminase (ADA) activity in C57BL/6 animals. Treatment with ADA also reduced the inflammation, fibrosis, and emphysematous destruction and improved the survival of C57BL/6 Tg animals. These studies demonstrate that genetic influences control IL-4 effector pathways in the murine lung. They also demonstrate that IL-4 has different effects on adenosine metabolism in Balb/c and C57BL/6 mice and that these differences contribute to the different responses that IL-4 induces in these inbred animals.
doi:10.1172/JCI26372
PMCID: PMC1451205  PMID: 16670768
9.  ERK1/2 mitogen-activated protein kinase selectively mediates IL-13–induced lung inflammation and remodeling in vivo 
Journal of Clinical Investigation  2005;116(1):163-173.
IL-13 dysregulation plays a critical role in the pathogenesis of a variety of inflammatory and remodeling diseases. In these settings, STAT6 is believed to be the canonical signaling molecule mediating the tissue effects of IL-13. Signaling cascades involving MAPKs have been linked to inflammation and remodeling. We hypothesized that MAPKs play critical roles in effector responses induced by IL-13 in the lung. We found that Tg IL-13 expression in the lung led to potent activation of ERK1/2 but not JNK1/2 or p38. ERK1/2 activation also occurred in mice with null mutations of STAT6. Systemic administration of the MAPK/ERK kinase 1 (MEK1) inhibitor PD98059 or use of Tg mice in which a dominant-negative MEK1 construct was expressed inhibited IL-13–induced inflammation and alveolar remodeling. There were associated decreases in IL-13–induced chemokines (MIP-1α/CCL-3, MIP-1β/CCL-4, MIP-2/CXCL-1, RANTES/CCL-5), MMP-2, -9, -12, and -14, and cathepsin B and increased levels of α1-antitrypsin. IL-13–induced tissue and molecular responses were noted that were equally and differentially dependent on ERK1/2 and STAT6 signaling. Thus, ERK1/2 is activated by IL-13 in the lung in a STAT6-independent manner where it contributes to IL-13–induced inflammation and remodeling and is required for optimal IL-13 stimulation of specific chemokines and proteases as well as the inhibition of specific antiproteases. ERK1/2 regulators may be useful in the treatment of IL-13–induced diseases and disorders.
doi:10.1172/JCI25711
PMCID: PMC1319220  PMID: 16374521
10.  Role of CCR5 in IFN-γ–induced and cigarette smoke–induced emphysema 
Journal of Clinical Investigation  2005;115(12):3460-3472.
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-γ–induced inflammation and remodeling in a murine emphysema model. IFN-γ 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-γ–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-γ–dependent pathway(s), and a null mutation of CCR5 decreased these responses. These studies demonstrate that IFN-γ is a potent stimulator of CC and CXC chemokines and highlight the importance of CCR5 in the pathogenesis of IFN-γ–induced and cigarette smoke–induced inflammation, tissue remodeling, and emphysema. They also demonstrate that CCR5 is required for optimal IFN-γ stimulation of its own ligands, other chemokines, MMPs, caspases, and cell death regulators and the inhibition of antiproteases.
doi:10.1172/JCI24858
PMCID: PMC1280966  PMID: 16284650
11.  Early Growth Response Gene 1–mediated Apoptosis Is Essential for Transforming Growth Factor β1–induced Pulmonary Fibrosis 
Fibrosis and apoptosis are juxtaposed in pulmonary disorders such as asthma and the interstitial diseases, and transforming growth factor (TGF)-β1 has been implicated in the pathogenesis of these responses. However, the in vivo effector functions of TGF-β1 in the lung and its roles in the pathogenesis of these responses are not completely understood. In addition, the relationships between apoptosis and other TGF-β1–induced responses have not been defined. To address these issues, we targeted bioactive TGF-β1 to the murine lung using a novel externally regulatable, triple transgenic system. TGF-β1 produced a transient wave of epithelial apoptosis that was followed by mononuclear-rich inflammation, tissue fibrosis, myofibroblast and myocyte hyperplasia, and septal rupture with honeycombing. Studies of these mice highlighted the reversibility of this fibrotic response. They also demonstrated that a null mutation of early growth response gene (Egr)-1 or caspase inhibition blocked TGF-β1–induced apoptosis. Interestingly, both interventions markedly ameliorated TGF-β1–induced fibrosis and alveolar remodeling. These studies illustrate the complex effects of TGF-β1 in vivo and define the critical role of Egr-1 in the TGF-β1 phenotype. They also demonstrate that Egr-1–mediated apoptosis is a prerequisite for TGF-β1–induced fibrosis and remodeling.
doi:10.1084/jem.20040104
PMCID: PMC2211975  PMID: 15289506
asthma; pulmonary fibrosis; fibrosis reversibility; airway remodeling
12.  New insights into the pathogenesis of asthma 
Journal of Clinical Investigation  2003;111(3):291-297.
doi:10.1172/JCI200317748
PMCID: PMC151878  PMID: 12569150
13.  Overlapping and enzyme-specific contributions of matrix metalloproteinases-9 and -12 in IL-13–induced inflammation and remodeling 
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.
doi:10.1172/JCI14136
PMCID: PMC150413  PMID: 12189240
14.  Interleukin-13 Induces Tissue Fibrosis by Selectively Stimulating and Activating Transforming Growth Factor β1 
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.
PMCID: PMC2195954  PMID: 11560996
lung; plasmin; matrix metalloproteinase-9; CD44; asthma

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