Lymphoid tissue and emphysema in the lungs of transgenic mice inducibly expressing tumor necrosis factor-alpha

SNP-SNP positive interaction between MMP2 and MMP12 increases the risk of COPD

Determining SNP-SNP interaction of the disease has become important for further investigation of pathogenesis and experimental research. Although many studies have been published on the effect of MMPs gene polymorphisms on chronic obstructive pulmonary disease (COPD), there is a lack of information on SNP-SNP and SNP-environment interactions. This study aimed to investigate the interaction between the polymorphisms of MMP1, MMP2, MMP9 and MMP12 genes and its combined effect with smoking on the risk of developing COPD. Totally 181 COPD patients and 292 healthy individuals were involved. Blood samples from the participants were tested for genotyping and data were collected through questionnaires. Genotyping was performed with nested allele-specific polymerase chain reaction (AS-PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). SNP-SNP and SNP-environment interactions were investigated using multifactor dimensionality reduction and logistic regression analysis. The result showed that participants with high nicotine dependence and heavy smokers had a higher risk of COPD than non-smokers. Also, G/G genotype (cOR = 5.83; 95% CI, 1.19-28.4, p = 0.029) of MMP2 rs243864 and T/T genotype (cOR = 1.79; 95% CI, 1.16-2.76, p = 0.008) of MMP12 rs652438 independently contributes to the susceptibility of COPD. For SNP-SNP interaction, the positive interaction between rs243864 G/G genotype of MMP2 and rs652438 T/T genotype of MMP12 was found, and the combination of risk genotypes has a high risk of COPD (OR = 12.92; 95% CI, 1.46-114.4, p = 0.021). Moreover, the combination of T/T genotype of MMP12 rs652438 and smoking-related factors increases the risk of COPD approximately 4.5 to 6-fold. The results suggests that there is a combination of MMP2, MMP12, and smoking-related factors may increase the risk of developing COPD.

Apoptosis inhibitor of macrophage (AIM)/CD5L is involved in the pathogenesis of COPD

BACKGROUND

Alveolar macrophages (AMs) and AM-produced matrix metalloprotease (MMP)-12 are known to play critical roles in the pathogenesis of chronic obstructive pulmonary disease (COPD). The apoptosis inhibitor of the macrophages (AIM)/CD5 molecule-like (CD5L) is a multifunctional protein secreted by the macrophages that mainly exists in the blood in a combined form with the immunoglobulin (Ig)M pentamer. Although AIM has both facilitative and suppressive roles in various diseases, its role in COPD remains unclear.

METHODS

We investigated the role of AIM in COPD pathogenesis using porcine pancreas elastase (PPE)-induced and cigarette smoke-induced emphysema mouse models and an in vitro model using AMs. We also analyzed the differences in the blood AIM/IgM ratio among nonsmokers, healthy smokers, and patients with COPD and investigated the association between the blood AIM/IgM ratio and COPD exacerbations and mortality in patients with COPD.

RESULTS

Emphysema formation, inflammation, and cell death in the lungs were attenuated in AIM-/- mice compared with wild-type (WT) mice in both PPE- and cigarette smoke-induced emphysema models. The PPE-induced increase in MMP-12 was attenuated in AIM-/- mice at both the mRNA and protein levels. According to in vitro experiments using AMs stimulated with cigarette smoke extract, the MMP-12 level was decreased in AIM-/- mice compared with WT mice. This decrease was reversed by the addition of recombinant AIM. Furthermore, an analysis of clinical samples showed that patients with COPD had a higher blood AIM/IgM ratio than healthy smokers. Additionally, the blood AIM/IgM ratio was positively associated with disease severity in patients with COPD. A higher AIM/IgM ratio was also associated with a shorter time to the first COPD exacerbation and higher all-cause and respiratory mortality.

CONCLUSIONS

AIM facilitates the development of COPD by upregulating MMP-12. Additionally, a higher blood AIM/IgM ratio was associated with poor prognosis in patients with COPD.

TRIAL REGISTRATION

This clinical study, which included nonsmokers, healthy smokers, and smokers with COPD, was approved by the Ethics Committee of the Hokkaido University Hospital (012-0075, date of registration: September 5, 2012). The Hokkaido COPD cohort study was approved by the Ethics Committee of the Hokkaido University School of Medicine (med02-001, date of registration: December 25, 2002).

Blocking tumor necrosis factor-α delays progression of chronic obstructive pulmonary disease in rats through inhibiting MAPK signaling pathway and activating SOCS3/TRAF1

The present study was conducted in order to study the detailed molecular mechanism of tumor necrosis factor (TNF)-α in chronic obstructive pulmonary disease (COPD). The rats were treated with cigarette smoke (CS) and lipopolysaccharide (LPS) to establish the COPD model. Next, the changes in lung injury in COPD rats with TNF-α knockdown was tested. Meanwhile, the regulation of TNF-α on MAPK pathway and its downstream molecules (SOCS3/TRAF1) was determined by western blotting. On this basis, the activation of MAPK and inhibition of SOCS3/TRAF1 was also examined. Subsequently, the lung function was tested with the plethysmograph, the cells of bronchoalveolar lavage fluid was counted and classified. Furthermore, lung tissue sections were stained with hematoxylin and eosin to verify whether the treatment of MAPK pathway and downstream molecules affected the effect of TNF-α knockdown on COPD. The present study showed that TNF-α knockdown could alleviate the decrease in the function and inflammatory injury of the lungs of rats with COPD. Western blot analysis verified that TNF-α knockdown could inhibit the activation of MAPK pathway and increase the expression of SOCS3/TRAF1. The following experimental results showed that the relief of lung injury caused by TNF-α knockdown could be deteriorated by activating MAPK pathway. It was also found that the symptom of COPD was decreased following transfection with sh-TNF-α but worsened by SOCS3/TRAF1 knockdown. Overall, TNF-α knockdown inhibited the activation of MAPK pathway and increased the expression of SOCS3/TRAF1, thus delaying the process of COPD.

Asthmatic condition induced the activity of exosome secretory pathway in rat pulmonary tissues

BACKGROUND

The recent studies highlighted the critical role of exosomes in the regulation of inflammation. Here, we investigated the dynamic biogenesis of the exosomes in the rat model of asthma.

RESULTS

Our finding showed an increase in the expression of IL-4 and the suppression of IL-10 in asthmatic lung tissues compared to the control samples (p < 0.05). Along with the promotion of IL-4, the protein level of TNF-α was induced, showing an active inflammatory status in OVA-sensitized rats. According to our data, the promotion of asthmatic responses increased exosome biogenesis indicated by increased CD63 levels and acetylcholine esterase activity compared to the normal condition (p < 0.05).

CONCLUSION

Data suggest that the stimulation of inflammatory response in asthmatic rats could simultaneously increase the paracrine activity of pulmonary cells via the exosome biogenesis. Exosome biogenesis may correlate with the inflammatory response.

Downregulation of epithelial DUOX1 in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a chronic respiratory disease characterized by small airway remodeling and alveolar emphysema due to environmental stresses such as cigarette smoking (CS). Oxidative stress is commonly implicated in COPD pathology, but recent findings suggest that one oxidant-producing NADPH oxidase homolog, dual oxidase 1 (DUOX1), is downregulated in the airways of patients with COPD. We evaluated lung tissue sections from patients with COPD for small airway epithelial DUOX1 protein expression, in association with measures of lung function and small airway and alveolar remodeling. We also addressed the impact of DUOX1 for lung tissue remodeling in mouse models of COPD. Small airway DUOX1 levels were decreased in advanced COPD and correlated with loss of lung function and markers of emphysema and remodeling. Similarly, DUOX1 downregulation in correlation with extracellular matrix remodeling was observed in a genetic model of COPD, transgenic SPC-TNF-α mice. Finally, development of subepithelial airway fibrosis in mice due to exposure to the CS-component acrolein, or alveolar emphysema induced by administration of elastase, were in both cases exacerbated in Duox1-deficient mice. Collectively, our studies highlight that downregulation of DUOX1 may be a contributing feature of COPD pathogenesis, likely related to impaired DUOX1-mediated innate injury responses involved in epithelial homeostasis.

Epithelial cell-specific loss of function of Miz1 causes a spontaneous COPD-like phenotype and up-regulates Ace2 expression in mice

Cigarette smoking, the leading cause of chronic obstructive pulmonary disease (COPD), has been implicated as a risk factor for severe disease in patients infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here we show that mice with lung epithelial cell-specific loss of function of Miz1, which we identified as a negative regulator of nuclear factor κB (NF-κB) signaling, spontaneously develop progressive age-related changes resembling COPD. Furthermore, loss of Miz1 up-regulates the expression of Ace2, the receptor for SARS-CoV-2. Concomitant partial loss of NF-κB/RelA prevented the development of COPD-like phenotype in Miz1-deficient mice. Miz1 protein levels are reduced in the lungs from patients with COPD, and in the lungs of mice exposed to chronic cigarette smoke. Our data suggest that Miz1 down-regulation-induced sustained activation of NF-κB-dependent inflammation in the lung epithelium is sufficient to induce progressive lung and airway destruction that recapitulates features of COPD, with implications for COVID-19.

TNF-Induced Interstitial Lung Disease in a Murine Arthritis Model: Accumulation of Activated Monocytes, Conventional Dendritic Cells, and CD21+/CD23- B Cell Follicles Is Prevented with Anti-TNF Therapy

Interstitial lung disease (ILD) is a well-known extra-articular manifestation of rheumatoid arthritis (RA). RA-associated ILD (RA-ILD) exists on a wide spectrum, with variable levels of inflammatory and fibrotic activity, although all subtypes are regarded as irreversible pathologic conditions. In both articular and pulmonary manifestations, TNF is a significant pathogenic factor. Whereas anti-TNF therapy alleviates joint pathologic conditions, it exacerbates fibrotic RA-ILD. The TNF-transgenic (TNF-Tg) murine model of RA develops both inflammatory arthritis and an ILD that mimics a cellular nonspecific interstitial pneumonia pattern dominated by an interstitial accumulation of inflammatory cells with minimal-to-absent fibrosis. Given the model's potential to elucidate the genesis of inflammatory RA-ILD, we aim to achieve the following: 1) characterize the cellular accumulations in TNF-Tg lungs, and 2) assess the reversibility of inflammatory ILD following anti-TNF therapy known to resolve TNF-Tg inflammatory arthritis. TNF-Tg mice with established disease were randomized to anti-TNF or placebo therapy and evaluated with imaging, histology, and flow cytometric analyses, together with wild-type controls. Flow cytometry of TNF-Tg versus wild-type lungs revealed significant increases in activated monocytes, conventional dendritic cells, and CD21+/CD23- B cells that are phenotypically distinct from the B cells in inflamed nodes, which are known to accumulate in joint-draining lymph nodes. In contrast to human RA-ILD, anti-TNF treatment significantly alleviated both joint and lung inflammation. These results identify a potential role for activated monocytes, conventional dendritic cells, and CD21+/CD23- B cells in the genesis of RA-ILD, which exist in a previously unknown, reversible, prefibrotic stage of the disease.

Chronic Inflammation Directs an Olfactory Stem Cell Functional Switch from Neuroregeneration to Immune Defense

Although olfactory mucosa possesses long-lived horizontal basal stem cells (HBCs) and remarkable regenerative capacity, the function of human olfactory neuroepithelium is significantly impaired in chronic inflammatory rhinosinusitis. Here, we show that, while inflammation initially damages olfactory neurons and activates HBC-mediated regeneration, continued inflammation locks HBCs in an undifferentiated state. Global gene expression in mouse HBCs reveals broad upregulation of NF-κB-regulated cytokines and chemokines including CCL19, CCL20, and CXCL10, accompanied by enhancement of "stemness"-related transcription factors. Loss-of-function studies identify an NF-κB-dependent role of HBCs in amplifying inflammatory signaling, contributing to macrophage and T cell local proliferation. Chronically activated HBCs signal macrophages to maintain immune defense and prevent Treg development. In diseased human olfactory tissue, activated HBCs in a P63⁺ undifferentiated state similarly contribute to inflammation through chemokine production. These observations establish a mechanism of chronic rhinosinusitis-associated olfactory loss, caused by a functional switch of neuroepithelial stem cells from regeneration to immune defense.

Restrictive lung disease in TNF-transgenic mice: correlation of pulmonary function testing and micro-CT imaging

Purpose: Micro-computed tomography (µCT) is increasingly being used on animal models as a minimally-invasive longitudinal outcome measure of pulmonary disease progression. However, while imaging can elucidate macroscopic structural changes over the whole lung, µCT is unable to describe the mechanical changes and functional impairments imposed by progressive disease, which can only be measured via pulmonary function tests (PFTs). The tumor necrosis factor-transgenic (TNF-Tg) mouse model of rheumatoid arthritis (RA) develops pulmonary pathology that mimics many aspects of the inflammatory interstitial lung disease (ILD) seen in a subset of patients with RA. Prior studies using µCT imaging of these mice found increased pulmonary density, characteristic of restrictive disease; however, there have been conflicting reports in the literature regarding the obstructive versus restrictive phenotype of this model. Our study looks to 1) define the functional impairments and 2) characterize the restrictive/obstructive nature of the disease found in this model. Materials and Methods: In this study, we performed PFTs at end-stage ILD, and paired these findings with µCT results, correlating radiology to functional parameters. TNF-Tg and WT littermates of both sexes underwent µCT imaging and PFT testing at 5.5 months-old. Spearman's correlation analyses were performed comparing lung tissue volume (LTV) to PFT parameters of gas exchange and tissue stiffness. Results: Compared to WT, TNF-Tg mice had impaired gas exchange capacity, increased respiratory resistance, and reduced lung compliance, elastance, and inspiratory capacity, indicating increased tissue stiffness and compromised pulmonary function. LTV was also consistently higher in TNF-Tg lungs. Conclusions: These findings demonstrate that: 1) TNF-Tg mice display a restrictive pathology, and 2) in vivo µCT is a valid outcome measure to infer changes in pulmonary mechanical and functional parameters.

Alpha-1-Antitrypsin Ameliorates Pristane Induced Diffuse Alveolar Hemorrhage in Mice

Diffuse alveolar hemorrhage (DAH) is a fatal complication in patients with lupus. DAH can be induced in B6 mice by an intraperitoneal injection of pristane. Since human alpha-1-antitrypsin (hAAT) is an anti-inflammatory and immuno-regulatory protein, we investigated the protective effect of hAAT against pristane-induced DAH in B6 mice and hAAT transgenic (hAAT-Tg) mice. We first showed that hAAT Tg expression lowers TNF-α production in B cells, as well as CD4+ T cells in untreated mice. Conversely, the frequency of regulatory CD4+CD25+ and CD4+CD25-IL-10+ cells was significantly higher in hAAT-Tg than in B6 mice. This confirmed the anti-inflammatory effect of hAAT that was observed even at steady state. One week after a pristane injection, the frequency of peritoneal Ly6C^hi inflammatory monocytes and neutrophils in hAAT-Tg mice was significantly lower than that in B6 mice. Importantly, pristane-induced DAH was completely prevented in hAAT-Tg mice and this was associated with a modulation of anti- to pro-inflammatory myeloid cell ratio/balance. We also showed that treatment with hAAT decreased the severity of DAH in B6 mice. These results showed for the first time that hAAT has a therapeutic potential for the treatment of DAH.

Impact of one versus two doses of mesenchymal stromal cells on lung and cardiovascular repair in experimental emphysema

Background

A single administration of mesenchymal stromal cells (MSCs) has been shown to reduce lung inflammation in experimental elastase-induced emphysema; however, effects were limited in terms of lung-tissue repair and cardiac function improvement. We hypothesized that two doses of MSCs could induce further lung and cardiovascular repair by mitigating inflammation and remodeling in a model of emphysema induced by multiple elastase instillations. We aimed to comparatively investigate the effects of one versus two doses of MSCs, administered 1 week apart, in a murine model of elastase-induced emphysema.

Methods

C57BL/6 mice were randomly divided into control (CTRL) and emphysema (E) groups. Mice in the E group received porcine pancreatic elastase (0.2 IU, 50 μL) intratracheally once weekly for four consecutive weeks; the CTRL animals received sterile saline (50 μL) using the same protocol. Three hours after the last instillation, the E group was further randomized to receive either saline (SAL) or murine MSCs (10⁵ cells) intratracheally, in one or two doses (1 week apart). Fourteen days later, mice were euthanized, and all data analyzed.

Results

Both one and two doses of MSCs improved lung mechanics, reducing keratinocyte-derived chemokine and transforming growth factor-β levels in lung homogenates, total cell and macrophage counts in bronchoalveolar lavage fluid (BALF), and collagen fiber content in airways and blood vessels, as well as increasing vascular endothelial growth factor in lung homogenates and elastic fiber content in lung parenchyma. However, only the two-dose group exhibited reductions in tumor necrosis factor-α in lung tissue, BALF neutrophil and lymphocyte count, thymus weight, and total cellularity, as well as CD8⁺ cell counts and cervical lymph node CD4⁺ and CD8⁺ T cell counts, as well as further increased elastic fiber content in the lung parenchyma and reduced severity of pulmonary arterial hypertension.

Conclusions

Two doses of MSCs enhanced lung repair and improvement in cardiac function, while inducing T cell immunosuppression, mainly of CD8⁺ cells, in elastase-induced emphysema.

Neutrophilic Inflammation in the Immune Responses of Chronic Obstructive Pulmonary Disease: Lessons from Animal Models

Chronic obstructive pulmonary disease (COPD) is a major cause of mortality worldwide, which is characterized by chronic bronchitis, destruction of small airways, and enlargement/disorganization of alveoli. It is generally accepted that the neutrophilic airway inflammation observed in the lungs of COPD patients is intrinsically linked to the tissue destruction and alveolar airspace enlargement, leading to disease progression. Animal models play an important role in studying the underlying mechanisms of COPD as they address questions involving integrated whole body responses. This review aims to summarize the current animal models of COPD, focusing on their advantages and disadvantages on immune responses and neutrophilic inflammation. Also, we propose a potential new animal model of COPD, which may mimic the most characteristics of human COPD pathogenesis, including persistent moderate-to-high levels of neutrophilic inflammation.

Copper Deficiency in the Lungs of TNF-α Transgenic Mice

Tumor necrosis factor (TNF)-α is a well-known pro-inflammatory cytokine. Increased expression of Tnf-α is a feature of inflammatory lung diseases, such as asthma, emphysema, fibrosis, and smoking-induced chronic obstructive pulmonary disease (COPD). Using a mouse line with lung-specific Tnf-α overexpression (SPC-TNF-α) to mimic TNF-α-associated lung diseases, we investigated the role of chronic inflammation in the homeostasis of lung trace elements. We performed a quantitative survey of micronutrients and biometals, including copper (Cu), zinc (Zn), and selenium (Se), in the transgenic mice tissues. We also examined the expression of Cu-dependent proteins in the inflammatory lung tissue to determine whether they were affected by the severe Cu deficiency, including cuproenzymes, Cu transporters, and Cu chaperones. We found consistent lung-specific reduction of the metal Cu, with a mean decrease of 70%; however, Zn and Se were unaffected in all other tissues. RT-PCR showed that two Cu enzymes associated with lung pathology were downregulated: amine oxidase, Cu containing 3 (Aoc3) and lysyl oxidase (Lox). Two factors, vascular endothelial growth factor (Vegf) and focal adhesion kinase (Fak), related with Cu deficiency treatment, showed decreased expression in the transgenic inflammatory lung. We concluded that Cu deficiency occurs following chronic TNF-α-induced lung inflammation and this likely plays an essential role in the inflammation-induced lung damage. These results suggest the restoration of lung Cu status as a potential strategy in both treatment and prevention of chronic lung inflammation and related disorders.

Tumor necrosis factor-α driven inflammation in alpha-1 antitrypsin deficiency: a new model of pathogenesis and treatment

Alpha-1 antitrypsin (AAT) deficiency (AATD) has traditionally been thought of as a genetic disorder characterized by lung destruction and early emphysema in a low AAT, and high neutrophil elastase (NE) environment in the lungs of affected individuals. Recently, a growing body of evidence has emerged to support the hypothesis that tumor necrosis factor alpha (TNF-α) is essential in the pathogenesis of both genetic AATD and non-genetic chronic obstructive pulmonary disease (COPD). Reports have highlighted the importance of TNF-α driven immune cell dysfunction in the development of lung disease in AATD. The authors discuss the role of AAT as a key modulator of TNF-α signaling firstly in the setting of AATD and secondly in other conditions where AAT augmentation therapy has potential utility as a novel therapy.

The Effect of Cigarette Smoke Exposure on the Development of Inflammation in Lungs, Gut and Joints of TNFΔARE Mice

The inflammatory cytokine TNF-α is a central mediator in many immune-mediated diseases, such as Crohn’s disease (CD), spondyloarthritis (SpA) and chronic obstructive pulmonary disease (COPD). Epidemiologic studies have shown that cigarette smoking (CS) is a prominent common risk factor in these TNF-dependent diseases. We exposed TNF^ΔARE mice; in which a systemic TNF-α overexpression leads to the development of inflammation; to 2 or 4 weeks of air or CS. We investigated the effect of deregulated TNF expression on CS-induced pulmonary inflammation and the effect of CS exposure on the initiation and progression of gut and joint inflammation. Upon 2 weeks of CS exposure, inflammation in lungs of TNF^ΔARE mice was significantly aggravated. However, upon 4 weeks of CS-exposure, this aggravation was no longer observed. TNF^ΔARE mice have no increases in CD4+ and CD8+ T cells and a diminished neutrophil response in the lungs after 4 weeks of CS exposure. In the gut and joints of TNF^ΔARE mice, 2 or 4 weeks of CS exposure did not modulate the development of inflammation. In conclusion, CS exposure does not modulate gut and joint inflammation in TNF^ΔARE mice. The lung responses towards CS in TNF^ΔARE mice however depend on the duration of CS exposure.

Animal models of chronic obstructive pulmonary disease

Animal models of disease have always been welcomed by the scientific community because they provide an approach to the investigation of certain aspects of the disease in question. Animal models of COPD cannot reproduce the heterogeneity of the disease and usually only manage to represent the disease in its milder stages. Moreover, airflow obstruction, the variable that determines patient diagnosis, not always taken into account in the models. For this reason, models have focused on the development of emphysema, easily detectable by lung morphometry, and have disregarded other components of the disease, such as airway injury or associated vascular changes. Continuous, long-term exposure to cigarette smoke is considered the main risk factor for this disease, justifying the fact that the cigarette smoke exposure model is the most widely used. Some variations on this basic model, related to exposure time, the association of other inducers or inhibitors, exacerbations or the use of transgenic animals to facilitate the identification of pathogenic pathways have been developed. Some variations or heterogeneity of this disease, then, can be reproduced and models can be designed for resolving researchers' questions on disease identification or treatment responses.

Inhibition of elastase-pulmonary emphysema in dominant-negative MafB transgenic mice

Alveolar macrophages (AMs) play important roles in the pathogenesis of chronic obstructive pulmonary disease (COPD). We previously demonstrated upregulation of the transcription factor MafB in AMs of mice exposed to cigarette smoke. The aim of this study was to elucidate the roles of MafB in the development of pulmonary emphysema. Porcine pancreatic elastase was administered to wild-type (WT) and dominant-negative (DN)-MafB transgenic (Tg) mice in which MafB activity was suppressed only in macrophages. We measured the mean linear intercept and conducted cell differential analysis of bronchoalveolar lavage (BAL) cells, surface marker analysis using flow cytometry, and immunohistochemical staining using antibodies to matrix metalloproteinase (MMP)-9 and MMP-12. Airspace enlargement of the lungs was suppressed significantly in elastase-treated DN-MafB Tg mice compared with treated WT mice. AMs with projected pseudopods were decreased in DN-MafB Tg mice. The number of cells intermediately positive for F4/80 and weakly or intermediately positive for CD11b, which are considered cell subsets of matured AMs, decreased in the BAL of DN-MafB Tg mice. Furthermore, MMP-9 and -12 were significantly downregulated in BAL cells of DN-MafB Tg mice. Because MMPs exacerbate emphysema, MafB may be involved in pulmonary emphysema development through altered maturation of macrophages and MMP expression.

Animal models in chronic obstructive pulmonary disease-an overview

ABSTRACT Chronic obstructive pulmonary disease (COPD) is characterized by progressive airway obstruction resultant from an augmented inflammatory response of the respiratory tract to noxious particles and gases. Previous reports present a number of different hypotheses about the etiology and pathophysiology of COPD. The generating mechanisms of the disease are subject of much speculation, and a series of questions and controversies among experts still remain. In this context, several experimental models have been proposed in order to broaden the knowledge on the pathophysiological characteristics of the disease, as well as the search for new therapeutic approaches for acute or chronically injured lung tissue. This review aims to present the main experimental models of COPD, more specifically emphysema, as well as to describe the main characteristics, advantages, disadvantages, possibilities of application, and potential contribution of each of these models for the knowledge on the pathophysiological aspects and to test new treatment options for obstructive lung diseases.

Chemokines and chemokine receptors: positioning cells for host defense and immunity

Chemokines are chemotactic cytokines that control the migratory patterns and positioning of all immune cells. Although chemokines were initially appreciated as important mediators of acute inflammation, we now know that this complex system of approximately 50 endogenous chemokine ligands and 20 G protein-coupled seven-transmembrane signaling receptors is also critical for the generation of primary and secondary adaptive cellular and humoral immune responses. Recent studies demonstrate important roles for the chemokine system in the priming of naive T cells, in cell fate decisions such as effector and memory cell differentiation, and in regulatory T cell function. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the organismic level in homeostasis, in acute inflammation, and during the generation and regulation of adoptive primary and secondary immune responses in the lymphoid system and peripheral nonlymphoid tissue.

Mesenchymal stem cell therapy in lung disorders: pathogenesis of lung diseases and mechanism of action of mesenchymal stem cell

Lung disorders such as asthma, acute respiratory distress syndrome (ARDS), chronic obstructive lung disease (COPD), and interstitial lung disease (ILD) show a few common threads of pathogenic mechanisms: inflammation, aberrant immune activity, infection, and fibrosis. Currently no modes of effective treatment are available for ILD or emphysema. Being anti-inflammatory, immunomodulatory, and regenerative in nature, the administration of mesenchymal stem cells (MSCs) has shown the capacity to control immune dysfunction and inflammation in the lung. The intravenous infusion of MSCs, the common mode of delivery, is followed by their entrapment in lung vasculature before MSCs reach to other organ systems thus indicating the feasible and promising approach of MSCs therapy for lung diseases. In this review, we discuss the mechanistic basis for MSCs therapy for asthma, ARDS, COPD, and ILD.

B-lymphocyte lineage cells and the respiratory system

Adaptive humoral immune responses in the airways are mediated by B cells and plasma cells that express highly evolved and specific receptors and produce immunoglobulins of most isotypes. In some cases, such as autoimmune diseases or inflammatory diseases caused by excessive exposure to foreign antigens, these same immune cells can cause disease by virtue of overly vigorous responses. This review discusses the generation, differentiation, signaling, activation, and recruitment pathways of B cells and plasma cells, with special emphasis on unique characteristics of subsets of these cells functioning within the respiratory system. The primary sensitization events that generate B cells responsible for effector responses throughout the airways usually occur in the upper airways, tonsils, and adenoid structures that make up the Waldeyer ring. On secondary exposure to antigen in the airways, antigen-processing dendritic cells migrate into secondary lymphoid organs, such as lymph nodes, that drain the upper and lower airways, and further B-cell expansion takes place at those sites. Antigen exposure in the upper or lower airways can also drive expansion of B-lineage cells in the airway mucosal tissue and lead to the formation of inducible lymphoid follicles or aggregates that can mediate local immunity or disease.

Macrophage heterogeneity in respiratory diseases

Macrophages are among the most abundant cells in the respiratory tract, and they can have strikingly different phenotypes within this environment. Our knowledge of the different phenotypes and their functions in the lung is sketchy at best, but they appear to be linked to the protection of gas exchange against microbial threats and excessive tissue responses. Phenotypical changes of macrophages within the lung are found in many respiratory diseases including asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. This paper will give an overview of what macrophage phenotypes have been described, what their known functions are, what is known about their presence in the different obstructive and restrictive respiratory diseases (asthma, COPD, pulmonary fibrosis), and how they are thought to contribute to the etiology and resolution of these diseases.

Overexpression of tumor necrosis factor-α in the lungs alters immune response, matrix remodeling, and repair and maintenance pathways

Increased production of tumor necrosis factor (TNF)-α and matrix metalloproteinases (MMPs) is a feature of inflammatory lung diseases, including emphysema and fibrosis, but the divergent pathological characteristics that result indicate involvement of other processes in disease pathogenesis. Transgenic mice overexpressing TNF-α in type II alveolar epithelial cells under the control of the surfactant protein (SP)-C promoter develop pulmonary inflammation and emphysema but are resistant to induction of fibrosis by administration of bleomycin or transforming growth factor-β. To study the molecular mechanisms underlying the development of this phenotype, we used a microarray approach to characterize the pulmonary transcriptome of SP-C/TNF-α mice and wild-type littermates. Four-month-old SP-C/TNF-α mice displayed pronounced pulmonary inflammation, airspace enlargement, increased MMP-2 and MMP-9 levels, and altered expression of 2332 probes. The functional assessment of genes with increased expression revealed enrichment of inflammatory/immune responses and proteases, whereas genes involved in protease inhibition, angiogenesis, cross-linking of basement membrane proteins, and myofibroblast differentiation were predominantly decreased. Comparison with multiple lung disease models identified a set of genes unique to the SP-C/TNF-α model and revealed that lack of extracellular matrix production distinguished SP-C/TNF-α mice from fibrosis models. Activation of inflammatory and proteolytic pathways and disruption of maintenance and repair processes are central features of emphysema in this TNF-overexpression model. Impairment of myofibroblast differentiation and extracellular matrix production may underlie resistance to induction of fibrosis.

Association between the tumour necrosis factor-α-308G/A polymorphism and chronic obstructive pulmonary disease: an update

BACKGROUND AND OBJECTIVE

Previous studies have suggested that the -308A allele in the tumour necrosis factor-α (TNF-α) gene promoter (rs1800629) may be a potential risk factor for COPD. However, more recent findings have been inconsistent. In the present study, a meta-analysis was performed to assess the association between the TNF-α-308G/A single nucleotide polymorphism (SNP) and the risk of COPD.

METHODS

Published studies were retrieved from PubMed, EMBASE and other databases. All studies assessing the association between the TNF-α-308G/A SNP and the risk of COPD were assessed. Pooled ORs with 95% CIs were calculated.

RESULTS

In the 36 studies that met the inclusion criteria, 4975 patients and 6518 control subjects had been genotyped. The overall results showed that the association between the TNF-α-308G/A SNP and the risk of COPD was statistically significant for Asians (OR = 2.36, 95% CI: 1.84-3.02, P < 0.0001) but not for Caucasians (OR = 1.07, 95% CI: 0.91-1.25, P = 0.438). As smoking is one of the most important risk factors for COPD, a second meta-analysis that included only smokers (3018 patients and 2749 control subjects) was performed. This analysis confirmed that the association between the TNF-α-308G/A SNP and COPD was statistically significant for Asians (OR = 1.72, 95% CI: 1.14-2.61, P = 0.011) but not for Caucasians (OR = 1.16, 95% CI: 0.86-1.56, P = 0.33).

CONCLUSIONS

This meta-analysis suggests that the TNF-α-308A genotype is associated with an increased risk of COPD in Asian but not Caucasian populations. Further studies are necessary to evaluate the relationship between TNF-α polymorphisms and the risk of COPD.

Mesenchymal stem cell transplantation increases expression of vascular endothelial growth factor in papain-induced emphysematous lungs and inhibits apoptosis of lung cells

BACKGROUND

Pulmonary emphysema is characterized by loss of alveolar structures. We have found that bone marrow (BM) mesenchymal stem cell (MSC) transplantation ameliorates papain-induced pulmonary emphysema. However, the underlying mechanism is not completely understood. It has been shown that blocking the vascular endothelial growth factor (VEGF) signaling pathway leads to apoptosis of lung cells and pulmonary emphysema, and MSC are capable of secreting VEGF. We hypothesized that MSC transplantation may have a protective effect on pulmonary emphysema by increasing VEGF-A expression and inhibiting apoptosis of lung cells.

METHODS

We examined the morphology and expression of VEGF-A in rat lung after papain treatment and MSC transplantation. We also used a co-culture system in which MSC and cells prepared from papain-treated lungs or control lungs were cultured together. The levels of VEGF-A in cells and culture medium were determined, and apoptosis of cultured lung cells was evaluated.

RESULTS

VEGF-A expression in rat lungs was decreased after papain treatment, which was partly rescued by MSC transplantation. MSC production of VEGF-A was increased when MSC were co-cultured with cells prepared from papain-treated lungs. Furthermore, the apoptosis of papain-treated lung cells was inhibited when co-cultured with MSC. The induction of MSC production of VEGF-A by papain-treated lung cells was inhibited by adding anti-tumor necrosis factor (TNF)-alpha antibody to the medium.

CONCLUSIONS

The protective effect of MSC transplantation on pulmonary emphysema may be partly mediated by increasing VEGF-A expression and inhibiting the apoptosis of lung cells. TNF-alpha released from papain-treated lung cells induces MSC to secret VEGF-A.

Regulation of inducible BALT formation and contribution to immunity and pathology

Inducible bronchus-associated lymphoid tissue (iBALT) is an organized tertiary lymphoid structure that is not pre-programmed but develops in response to infection or under chronic inflammatory conditions. Emerging research has shown that iBALT provides a niche for T-cell priming and B-cell education to assist in the clearance of infectious agents, highlighting the prospect that iBALT may be engineered and harnessed to enhance protective immunity against respiratory pathogens. Although iBALT formation is associated with several canonical factors of secondary lymphoid organogenesis such as lymphotoxin-α and the homeostatic chemokines, CXCL13, CCL19, and CCL21, these cytokines are not mandatory for its formation, even though they influence its organization and function. Similarly, lymphoid tissue-inducer cells are not a requisite of iBALT formation. In contrast, dendritic cells are emerging as pivotal players required to form and sustain the presence of iBALT. Regulatory T cells appear to be able to attenuate the development of iBALT, although the underlying mechanisms remain ill-defined. In this review, we discuss facets unique to iBALT induction, the cellular subsets, and molecular cues that govern this process, and the contribution of this ectopic structure toward the generation of immune responses in the pulmonary compartment.

A genetic model of chronic rhinosinusitis-associated olfactory inflammation reveals reversible functional impairment and dramatic neuroepithelial reorganization

Inflammatory sinus and nasal disease is a common cause of human olfactory loss. To explore the mechanisms underlying rhinosinusitis-associated olfactory loss, we have generated a transgenic mouse model of olfactory inflammation, in which tumor necrosis factor alpha (TNF-alpha) expression is induced in a temporally controlled manner specifically within the olfactory epithelium (OE). Like the human disease, TNF-alpha expression leads to a progressive infiltration of inflammatory cells into the OE. Using this model, we have defined specific phases of the pathologic process. An initial loss of sensation without significant disruption is observed, followed by a striking reorganization of the sensory neuroepithelium. An inflamed and disrupted state is sustained chronically by continued induction of cytokine expression. After prolonged maintenance in a deficient state, there is a dramatic recovery of function and a normal histologic appearance when TNF-alpha expression is extinguished. Although obstruction of airflow is also a contributing factor in human rhinosinusitis, this in vivo model demonstrates for the first time that direct effects of inflammation on OE structure and function are important mechanisms of olfactory dysfunction. These features mimic essential aspects of chronic rhinosinusitis-associated olfactory loss, and illuminate underlying cellular and molecular aspects of the disease. This manipulable model also serves as a platform for developing novel therapeutic interventions.

TNF-alpha inhibitors in asthma and COPD: we must not throw the baby out with the bath water

Tumor necrosis factor (TNF)-alpha, a pleiotropic cytokine that exerts a variety of effects, such as growth promotion, growth inhibition, angiogenesis, cytotoxicity, inflammation, and immunomodulation, has been implicated in several inflammatory conditions. It plays a significant role in many inflammatory diseases of lungs. Given that there is significant literature supporting the pathobiologic role of TNF-alpha in asthma, mainly in severe refractory asthma, and COPD, TNF-alpha inhibitors (infliximab, golimumab and etanercept) are now regarded as the potential new medications in asthma and COPD management. The studies reported in literature indicate that TNF-alpha inhibitors are effective in a relatively small subgroup of patients with severe asthma, possibly defined by an increased TNF axis, but they seem to be ineffective in COPD, although an observational study demonstrated that TNF-alpha inhibitors were associated with a reduction in the rate of COPD hospitalisation among patients with COPD receiving these agents to treat their rheumatoid arthritis. These findings require a smart approach because there is still good reason to target TNF-alpha, perhaps in a more carefully selected patient group. TNF-alpha treatment should, therefore, not be thrown out, or abandoned. Indeed, since severe asthma and COPD are heterogeneous diseases that have characteristics that occur with different phenotypes that remained poorly characterized and little known about the underlying pathobiology contributing to them, it is likely that definition of these phenotypes and choice of the right outcome measure will allow us to understand which kind of patients can benefit from TNF-alpha inhibitors.

Intranasal organic dust exposure-induced airway adaptation response marked by persistent lung inflammation and pathology in mice

Organic dust exposure in agricultural environments results in an inflammatory response that attenuates over time, but repetitive exposures can result in chronic respiratory disease. Animal models to study these mechanisms are limited. This study investigated the effects of single vs. repetitive dust-induced airway inflammation in mice by intranasal exposure method. Mice were exposed to swine facility dust extract (DE) or saline once and once daily for 1 and 2 wk. Dust exposure resulted in increased bronchoalveolar lavage fluid neutrophils and macrophages after single and repetitive exposures. Lavage fluid TNFalpha, IL-6, keratinocyte chemoattractant, and macrophage inflammatory protein-2 were significantly increased after single and repetitive dust exposures, but were dampened in 2-wk dust-exposed mice compared with single exposure. Dust exposure induced PKCalpha and -epsilon activation in isolated tracheal epithelial cells but were dampened with repetitive exposures. Ex vivo stimulation of alveolar macrophages from 2-wk animals demonstrated reduced cytokine responsiveness and phagocytic ability. Significant lung pathology occurred with development of mixed mononuclear cellular aggregates (T and B lymphocytes, phagocytes) after repetitive dust exposure, a novel observation. Airway hyperresponsiveness to methacholine occurred after single dust exposure but resolved after 2 wk. Collectively, intranasal exposure to DE results in significant lung inflammatory and pathological responses marked by a modulated innate immune response to single and repetitive dust exposures that is associated with PKC activity.

Airway and lung pathology due to mucosal surface dehydration in {beta}-epithelial Na+ channel-overexpressing mice: role of TNF-{alpha} and IL-4R{alpha} signaling, influence of neonatal development, and limited efficacy of glucocorticoid treatment

Overexpression of the epithelial Na(+) channel beta subunit (Scnn1b gene, betaENaC protein) in transgenic (Tg) mouse airways dehydrates mucosal surfaces, producing mucus obstruction, inflammation, and neonatal mortality. Airway inflammation includes macrophage activation, neutrophil and eosinophil recruitment, and elevated KC, TNF-alpha, and chitinase levels. These changes recapitulate aspects of complex human obstructive airway diseases, but their molecular mechanisms are poorly understood. We used genetic and pharmacologic approaches to identify pathways relevant to the development of Scnn1b-Tg mouse lung pathology. Genetic deletion of TNF-alpha or its receptor, TNFR1, had no measurable effect on the phenotype. Deletion of IL-4Ralpha abolished transient mucous secretory cell (MuSC) abundance and eosinophilia normally observed in neonatal wild-type mice. Similarly, IL-4Ralpha deficiency decreased MuSC and eosinophils in neonatal Scnn1b-Tg mice, which correlated with improved neonatal survival. However, chronic lung pathology in adult Scnn1b-Tg mice was not affected by IL-4Ralpha status. Prednisolone treatment ablated eosinophilia and MuSC in adult Scnn1b-Tg mice, but did not decrease mucus plugging or neutrophilia. These studies demonstrate that: 1) normal neonatal mouse airway development entails an IL-4Ralpha-dependent, transient abundance of MuSC and eosinophils; 2) absence of IL-4Ralpha improved neonatal survival of Scnn1b-Tg mice, likely reflecting decreased formation of asphyxiating mucus plugs; and 3) in Scnn1b-Tg mice, neutrophilia, mucus obstruction, and airspace enlargement are IL-4Ralpha- and TNF-alpha-independent, and only MuSC and eosinophilia are sensitive to glucocorticoids. Thus, manipulation of multiple pathways will likely be required to treat the complex pathogenesis caused by airway surface dehydration.

The role of interleukin-1beta in murine cigarette smoke-induced emphysema and small airway remodeling

Interleukin-1beta (IL-1beta), a proinflammatory cytokine, is elevated in cigarette smokers. To determine whether IL-1beta plays a role in the pathogenesis of cigarette smoke-induced emphysema and small airway remodeling, IL-1 receptor knockout (IL1RKO), TNF-alpha receptor knockout (TNFRKO), or C57Bl/6 (control) mice were exposed to cigarette smoke acutely or for up to 6 months. With a single acute exposure, smoke elevated IL-1beta in C57Bl/6 mice. IL1RKO mice were protected against acute smoke-mediated increases in lavage inflammatory cells and matrix breakdown. In C57Bl/6 mice, acute smoke-mediated increases in inflammatory cells, serum IL-1beta, and serum TNF-alpha were blocked by z-VAD-fmk, a pan-caspase inhibitor, or z-WEHD-fmk, a caspase-1 (IL-1-converting enzyme, [ICE]) inhibitor. With 6 months of exposure, IL-1beta was no longer increased, but IL-18 was elevated. After 6 months of exposure, IL1RKO mice were 65% protected against emphysema, whereas TNFRKO mice were 83% protected. Both strains were completely protected against small airway remodeling. Lavage desmosine, hydroxyproline, and hyaluronan, matrix breakdown markers, were elevated in C57 but not IL1RKO mice. We conclude that IL-1beta plays a significant role in induction of murine emphysema and small airway remodeling, and is comparable to TNF-alpha in its effects. The protective effects of caspase inhibitors appear to be related to inhibition of ICE and raise the question of whether models that ameliorate emphysema with caspase inhibitors are really blocking IL-1beta (and IL-18) activation rather than blocking apoptosis.

Inflammation and the aging process: devil or angel

Inflammation is often viewed as a pathologic mechanism leading to tissue damage and interference with function, such as the process of chronic tissue scarring or fibrosis. However, it is important to note that inflammation is a crucial component of normal tissue repair as well as being fundamental to the body's defense against infection. Considering inflammation as a "causative agent in aging" belies the underlying mechanisms whereby the acute inflammatory response is necessary for survival, and efforts to reduce and control the inflammatory response leave the host susceptible to infectious agents and improper healing. Chronic inflammation inevitably has initiating mechanisms that include immune, autoimmune, and metabolic pathways, leading to the activation and presence of the host-protective response. It is more appropriate to target the underlying initiating conditions than the inflammatory process that ensues and treat the basic mechanisms of disease rather than interfere in a very important protective mechanism of the host.

Mechanisms of cigarette smoke-induced COPD: insights from animal models

Cigarette smoke-induced animal models of chronic obstructive pulmonary disease support the protease-antiprotease hypothesis of emphysema, although which cells and proteases are the crucial actors remains controversial. Inhibition of either serine or metalloproteases produces significant protection against emphysema, but inhibition is invariably accompanied by decreases in the inflammatory response to cigarette smoke, suggesting that these inhibitors do more than just prevent matrix degradation. Direct anti-inflammatory interventions are also effective against the development of emphysema, as are antioxidant strategies; the latter again decrease smoke-induced inflammation. There is increasing evidence for autoimmunity, perhaps directed against matrix components, as a driving force in emphysema. There is intriguing but controversial animal model evidence that failure to repair/failure of lung maintenance also plays a role in the pathogenesis of emphysema. Cigarette smoke produces small airway remodeling in laboratory animals, possibly by direct induction of fibrogenic growth factors in the airway wall, and also produces pulmonary hypertension, at least in part through direct upregulation of vasoactive mediators in the intrapulmonary arteries. Smoke exposure causes goblet cell metaplasia and excess mucus production in the small airways and proximal trachea, but these changes are not good models of either chronic bronchitis or acute exacerbations. Emphysema, small airway remodeling, pulmonary hypertension, and mucus production appear to be at least partially independent processes that may require different therapeutic approaches.

Haemophilus influenzae lysate induces aspects of the chronic obstructive pulmonary disease phenotype

Nontypeable Haemophilus influenzae (NTHi) commonly colonizes the lower airways of patients with chronic obstructive pulmonary disease (COPD). Whether it contributes to COPD progression is unknown. Here, we determined which aspects of the COPD phenotype can be induced by repetitive exposure to NTHi products. Mice were exposed weekly to an aerosolized NTHi lysate, and inflammation was evaluated by measurement of cells and cytokines in bronchoalveolar lavage fluid (BALF) and immunohistochemical staining; structural changes were evaluated histochemically by periodic acid fluorescent Schiff's reagent, Masson's trichrome, and Picrosirius red staining; mucin gene expression was measured by quantitative RT-PCR; and the role of TNF-alpha was examined by transgenic airway overexpression and use of an inhibitory antibody. NTHi lysate induced rapid activation of NF-kappaB in airway cells and increases of inflammatory cytokines and neutrophils in BALF. Repetitive exposure induced infiltration of macrophages, CD8+ T cells, and B cells around airways and blood vessels, and collagen deposition in airway and alveolar walls, but airway mucin staining and gel-forming mucin transcripts were not increased. Transgenic overexpression of TNF-alpha caused BALF neutrophilia and inflammatory cell infiltration around airways, but not fibrosis, and TNF-alpha neutralization did not reduce BALF neutrophilia in response to NTHi lysate. In conclusion, NTHi products elicit airway inflammation in mice with a cellular and cytokine profile similar to that in COPD, and cause airway wall fibrosis but not mucous metaplasia. TNF-alpha is neither required for inflammatory cell recruitment nor sufficient for airway fibrosis. Colonization by NTHi may contribute to the pathogenesis of small airways disease in patients with COPD.

Relationships between early inflammatory response to bleomycin and sensitivity to lung fibrosis: a role for dipeptidyl-peptidase I and tissue inhibitor of metalloproteinase-3?

RATIONALE

Different sensitivities to profibrotic compounds such as bleomycin are observed among mouse strains.

OBJECTIVES

To identify genetic factors contributing to the outcome of lung injury.

METHODS

Physiological comparison of C57BL/6 (sensitive) and BALB/c (resistant) mice challenged by intratracheal bleomycin instillation revealed several early differences: global gene expression profiles were thus established from lungs derived from the two strains, in the absence of any bleomycin administration.

MEASUREMENTS AND MAIN RESULTS

Expression of 25 genes differed between the two strains. Among them, two molecules, not previously associated with pulmonary fibrosis, were identified. The first corresponded to dipeptidyl-peptidase I (DPPI), a cysteine peptidase (also known as cathepsin C) essential for the activation of serine proteinases produced by immune/inflammatory cells. The second corresponded to tissue inhibitor of matrix metalloproteinase-3, which also inhibits members of the ADAM (a disintegrin and metalloproteinase) family, such as the tumor necrosis factor-converting enzyme. In functional studies performed in the bleomycin-induced lung fibrosis model, the level of expression of these two genes was closely correlated with specific early events associated with lung fibrosis, namely activation of polymorphonuclear neutrophil-derived serine proteases and tumor necrosis factor-alpha-dependent inflammatory syndrome. Surprisingly, genetic deletion of DPPI in the context of a C57BL/6 genetic background did not protect against bleomycin-mediated fibrosis, suggesting additional function(s) for this key enzyme.

CONCLUSIONS

This study highlights the importance of the early inflammatory events that follow bleomycin instillation in the development of lung fibrosis, and describes for the first time the roles that DPPI and tissue inhibitor of matrix metalloproteinase-3 may play in this process.

Current concepts in mechanisms of emphysema

Over the last 10 years, there has been a remarkable degree of progress in our understanding of the pathophysiological mechanisms involved in the genesis of emphysema. This review attempts to summarize these data.

Soluble TNF mediates the transition from pulmonary inflammation to fibrosis

Background

Fibrosis, the replacement of functional tissue with excessive fibrous tissue, can occur in all the main tissues and organ systems, resulting in various pathological disorders. Idiopathic Pulmonary Fibrosis is a prototype fibrotic disease involving abnormal wound healing in response to multiple sites of ongoing alveolar epithelial injury.

Methodology/Principal Findings

To decipher the role of TNF and TNF-mediated inflammation in the development of fibrosis, we have utilized the bleomycin-induced animal model of Pulmonary Fibrosis and a series of genetically modified mice lacking components of TNF signaling. Transmembrane TNF expression is shown to be sufficient to elicit an inflammatory response, but inadequate for the transition to the fibrotic phase of the disease. Soluble TNF expression is shown to be crucial for lymphocyte recruitment, a prerequisite for TGF-b1 expression and the development of fibrotic lesions. Moreover, through a series of bone marrow transfers, the necessary TNF expression is shown to originate from the non-hematopoietic compartment further localized in apoptosing epithelial cells.

Conclusions

These results suggest a primary detrimental role of soluble TNF in the pathologic cascade, separating it from the beneficial role of transmembrane TNF, and indicate the importance of assessing the efficacy of soluble TNF antagonists in the treatment of Idiopathic Pulmonary Fibrosis.

Expression of the reverse tetracycline-transactivator gene causes emphysema-like changes in mice

The doxycycline-inducible, gene regulatory system allows tight control of transgene expression for the study of organ development and disease pathogenesis. Multiple recent reports have employed this model to investigate various lung diseases including emphysema. For our study, we used this transgenic system to test whether prolonged, lung-specific, overexpression of the serine protease urokinase plasminogen activator (uPA) would result in alveolar wall destruction. Double transgenic mice were generated that possessed: (1) the rat Clara cell secretory protein promoter controlling the reverse tetracycline transactivator gene (CCSP:rtTA) and (2) the tetracycline operator controlling the murine uPA cDNA (tet[O]:muPA). Mice were treated with doxycycline beginning at age 6 wk to initiate uPA overexpression. Single transgenic and wild-type animals served as controls. A second group of double transgenic and control animals were maintained off of doxycycline. At ages 10, 18, and 30 wk, the mice underwent measurements of alveolar size, lung compliance, and total lung capacity. We found that, although the uPA overexpressing mice demonstrated an emphysema phenotype, similar abnormalities occurred in the CCSP-rtTA control animals. These CCSP-rtTA-related alterations occurred even without doxycycline exposure. Evaluation of a second transgenic line possessing the human surfactant protein C promoter controlling rtTA expression also exhibited lung abnormalities consistent with emphysema. These findings indicate that pulmonary epithelial expression of rtTA alone causes an emphysema phenotype in mice. Therefore, when using this system to study emphysema pathogenesis, the inclusion of proper controls is essential for accurate data interpretation.

Matrix metalloproteinases in destructive pulmonary pathology

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that have a number of important physiological roles including remodelling of the extracellular matrix, facilitating cell migration, cleaving cytokines, and activating defensins. However, excess MMP activity may lead to tissue destruction. The biology of MMP and the role of these proteases in normal pulmonary immunity are reviewed, and evidence that implicates excess MMP activity in causing matrix breakdown in chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), sarcoidosis, and tuberculosis is discussed. Evidence from both clinical studies and animal models showing that stromal and inflammatory cell MMP expression leads to immunopathology is examined, and the mechanisms by which excess MMP activity may be targeted to improve clinical outcomes are discussed.

Selective phosphodiesterase-4 inhibitors in chronic obstructive lung disease

PURPOSE OF REVIEW

Chronic obstructive pulmonary disease (COPD) is a disease state characterized by airflow limitation that is usually progressive. In addition, an abnormal inflammatory response of the lungs to noxious particles or gases can be seen throughout the airways, parenchyma, and pulmonary vasculature. So far, anti-inflammatory medications (eg, inhaled corticosteroids) have failed to show a major effect on the decline of lung function in COPD patients. Novel anti-inflammatory therapies such as selective phosphodiesterase 4 (PDE4) inhibitors are in clinical development. Their potential role in the management of COPD is described in this review.

RECENT FINDINGS

Some of the selective PDE4 inhibitors have demonstrated in vitro and in vivo anti-inflammatory activity on cells commonly linked to airway inflammation in COPD, such as neutrophils. While these agents seem to offer only a modest improvement in lung function compared with other bronchodilators, their anti-inflammatory effects appear to provide some substantial benefits in reducing exacerbations and improving health-related quality of life.

SUMMARY

Based on the available data, the second generation of selective PDE4 inhibitors will likely provide additional therapeutic options for the management of COPD. These agents may become an important tool in the treatment of this disease, since they target three important components of COPD: airway obstruction, inflammation, and structural changes.

Pulmonary dendritic cells

Dendritic cells (DCs) are leukocytes that are emerging as chief orchestrators of immune responses. The crucial task of DCs is the continuous surveillance of antigen-exposed sites throughout the body, and their unique responsibility is to decide whether to present sampled antigen in an immunogenic or tolerogenic way. Any misstep can either lead to a flawed immune defense or to allergy, even autoimmunity. It comes as no surprise that the lungs become increasingly the subject of DC-related investigations, as they represent a vast interface between the body and the outer world. This constitutes an enormous challenge for the immune system: "firing up" immune responses inappropriately could have devastating results for the fragile gas exchange structures. Evidence accumulates that DCs play a pivotal role in maintaining the delicate balance between tolerance and active immune response in our respiratory system. The exponentially growing body of DC-related publications is a big challenge. This article aims to provide researchers and clinicians with an up-to-date view on DC biology and its relevance to pulmonary medicine. A developing trend in the field of DCs is the shift from fundamental immunologic research toward exciting clinical insights and applications. For the pulmonary clinician, this heralds the dawn of promising therapies in various domains such as infections, allergy, and cancer.

Tumor necrosis factor-alpha overexpression in lung disease: a single cause behind a complex phenotype

RATIONALE

Tumor necrosis factor alpha (TNF-alpha) has been implicated as a key cytokine in many inflammatory lung diseases. These effects are currently unclear, because a transgenic mouse overexpressing TNF-alpha in the lung has been shown in separate studies to produce elements of both emphysema and pulmonary fibrosis.

OBJECTIVES

We sought to elucidate the phenotypic effects of TNF-alpha overexpression in a mouse model.

MEASUREMENTS

We established the phenotype by measuring lung impedance and thoracic gas volume, and using micro-computed tomography and histology.

MAIN RESULTS

We found that airways resistance in this mouse was not different to control mice, but that lung tissue dampening, elastance, and hysteresivity were significantly elevated. Major heterogeneous abnormalities of the parenchyma were also apparent in histologic sections and in micro-computed tomography images of the lung. These changes included airspace enlargement, loss of small airspaces, increased collagen, and thickened pleural septa. We also found significant increases in lung and chest cavity volumes in the TNF-alpha-overexpressing mice.

CONCLUSIONS

We conclude that TNF-alpha overexpression causes pathologic changes consistent with both emphysema and pulmonary fibrosis combined with a general lung inflammation, and consequently does not model any single human disease. Our study thus confirms the pleiotropic effects of TNF-alpha, which has been implicated in multiple inflammatory disorders, and underscores the necessity of using a wide range of investigative techniques to link gene expression and phenotype in animal models of disease.

Proteases and emphysema

PURPOSE OF REVIEW

The protease-antiprotease theory of emphysema is widely accepted, but exactly which cells/proteases play a role continues to be a controversial subject.

RECENT FINDINGS

Reports in humans show increased metalloproteinase activity in emphysema, but the exact role of metalloproteinases remains unclear. In laboratory animals, neutrophils turn out to be crucial, and neutrophil influx correlates well with measurements of matrix destruction. Neutrophil influx is linked to metalloproteinase activity, and in mice MMP12-induced release of tumor necrosis factor-alpha drives neutrophil infiltration. Serine elastase inhibitors, knockout of neutrophil elastase, and interference with tumor necrosis factor-alpha signaling all provide significant protection against smoke-induced emphysema, but metalloproteinase inhibitors may yield greater protection. In genetically modified mice, emphysema can be produced by overexpression of mediators such as tumor necrosis factor-alpha, interferon-gamma, or interleukin-13, and these models show evidence of metalloproteinase, cysteine protease, and serine protease attack with complicated relationships among these mediators. Collagen breakdown also appears to be important in the genesis of emphysema. Pro-apoptotic agents produce emphysema as well, possibly via an elastolytic pathway.

SUMMARY

The idea that a single protease or a single type of inflammatory cell is responsible for human emphysema is unlikely to be true; rather, there are complex interactions among proteases, and between proteases and other mediators. The problem at this time is attempting to sort out the numerous candidate effector agents and to determine which of the animal models are relevant to human disease, since there may be considerable discrepancies in the types of proteases and their roles between laboratory animals and humans. There is now good evidence from animal models that antiproteolytic therapy can be of benefit in ameliorating cigarette smoke-induced emphysema.

Interleukin-1beta causes pulmonary inflammation, emphysema, and airway remodeling in the adult murine lung

The production of the inflammatory cytokine interleukin (IL)-1 is increased in lungs of patients with chronic obstructive pulmonary disease (COPD) or asthma. To characterize the in vivo actions of IL-1 in the lung, transgenic mice were generated in which human IL-1beta was expressed in the lung epithelium with a doxycycline-inducible system controlled by the rat Clara cell secretory protein (CCSP) promoter. Induction of IL-1beta expression in the lungs of adult mice caused pulmonary inflammation characterized by neutrophil and macrophage infiltrates. IL-1beta caused distal airspace enlargement, consistent with emphysema. IL-1beta caused disruption of elastin fibers in alveolar septa and fibrosis in airway walls and in the pleura. IL-1beta increased the thickness of conducting airways, enhanced mucin production, and caused lymphocytic aggregates in the airways. Decreased immunostaining for the winged helix transcription factor FOXA2 was associated with goblet cell hyperplasia in IL-1beta-expressing mice. The production of the neutrophil attractant CXC chemokines KC (CXCL1) and MIP-2 (CXCL2), and of matrix metalloproteases MMP-9 and MMP-12, was increased by IL-1beta. Chronic production of IL-1beta in respiratory epithelial cells of adult mice causes lung inflammation, enlargement of distal airspaces, mucus metaplasia, and airway fibrosis in the adult mouse.

Application of microarray technology in pulmonary diseases

Microarrays are a powerful tool that have multiple applications both in clinical and cell biology arenas of common lung diseases. To exemplify how this tool can be useful, in this review, we will provide an overview of the application of microarray technology in research relevant to common lung diseases and present some of the future perspectives.