Clara cells attenuate the inflammatory response through regulation of macrophage behavior

The multiple facets of the club cell in the pulmonary epithelium

The non-ciliated bronchiolar cell, also referred to as "club cell", serves as a significant multifunctional component of the airway epithelium. While the club cell is a prominent epithelial type found in rodents, it is restricted to the bronchioles in humans. Despite these differences, the club cell's importance remains undisputed in both species due to its multifunctionality as a regulatory cell in lung inflammation and a stem cell in lung epithelial regeneration. The objective of this review is to examine different aspects of club cell morphology and physiology in the lung epithelium, under both normal and pathological conditions, to provide a comprehensive understanding of its importance in the respiratory system.

CC16 augmentation reduces exaggerated COPD-like disease in Cc16-deficient mice

Low Club Cell 16 kDa protein (CC16) plasma levels are linked to accelerated lung function decline in patients with chronic obstructive pulmonary disease (COPD). Cigarette smoke-exposed (CS-exposed) Cc16-/- mice have exaggerated COPD-like disease associated with increased NF-κB activation in their lungs. It is unclear whether CC16 augmentation can reverse exaggerated COPD in CS-exposed Cc16-/- mice and whether increased NF-κB activation contributes to the exaggerated COPD in CS-exposed Cc16-/- lungs. CS-exposed WT and Cc16-/- mice were treated with recombinant human CC16 (rhCC16) or an NF-κB inhibitor versus vehicle beginning at the midpoint of the exposures. COPD-like disease and NF-κB activation were measured in the lungs. RhCC16 limited the progression of emphysema, small airway fibrosis, and chronic bronchitis-like disease in WT and Cc16-/- mice partly by reducing pulmonary inflammation (reducing myeloid leukocytes and/or increasing regulatory T and/or B cells) and alveolar septal cell apoptosis, reducing NF-κB activation in CS-exposed Cc16-/- lungs, and rescuing the reduced Foxj1 expression in CS-exposed Cc16-/- lungs. IMD0354 treatment reduced exaggerated lung inflammation and rescued the reduced Foxj1 expression in CS-exposed Cc16-/- mice. RhCC16 treatment reduced NF-κB activation in luciferase reporter A549 cells. Thus, rhCC16 treatment limits COPD progression in CS-exposed Cc16-/- mice partly by inhibiting NF-κB activation and represents a potentially novel therapeutic approach for COPD.

Secretoglobins in the big picture of immunoregulation in airway diseases

The proteins of the secretoglobin (SCGB) family are expressed by secretory tissues of barrier organs. They are embedded in immunoregulatory and anti-inflammatory processes of airway diseases. This review particularly illustrates the immune regulation of SCGBs by cytokines and their implication in the pathophysiology of airway diseases. The biology of SCGBs is a complex topic of increasing importance, as they are highly abundant in the respiratory tract and can also be detected in malignant tissues and as elements of immune control. In addition, SCGBs react to cytokines, they are embedded in Th1 and Th2 immune responses, and they are expressed in a manner dependent on cell maturation. The big picture of the SCGB family identifies these factors as critical elements of innate immune control at the epithelial barriers and highlights their potential for diagnostic assessment of epithelial activity. Some members of the SCGB family have so far only been superficially examined, but have high potential for translational research.

A decline in club cell secretory proteins in lung transplantation is associated with release of natural killer cells exosomes leading to chronic rejection

BACKGROUND

In human lung transplant recipients, a decline in club cell secretory protein (CCSP) in bronchoalveolar lavage fluid has been associated with chronic lung allograft dysfunction (CLAD) as well as the induction of exosomes and immune responses that lead to CLAD. However, the mechanisms by which CCSP decline contributes to CLAD remain unknown.

METHODS

To define the mechanisms leading to CCSP decline and chronic rejection, we employed two mouse models: 1) chronic rejection after orthotopic single lung transplantation and 2) anti-major histocompatibility complex (MHC) class I-induced obliterative airway disease.

RESULTS

In the chronic rejection mouse model, we detected circulating exosomes with donor MHC (H2b) and lung self-antigens and also development of antibodies to H2b and lung self-antigens and then a decline in CCSP. Furthermore, DBA2 mice that received injections of these exosomes developed antibodies to donor MHC and lung self-antigens. In the chronic rejection mouse model, natural killer (NK) and CD8 T cells were the predominant graft-infiltrating cells on day 14 of rejection followed by exosomes containing NK cell-associated and cytotoxic molecules on day 14 and 28. When NK cells were depleted, exosomes with NK cell-associated and cytotoxic molecules as well as fibrosis decreased.

CONCLUSIONS

Induction of exosomes led to immune responses to donor MHC and lung self-antigens, resulting in CCSP decline, leading to NK cell infiltration and release of exosomes from NK cells. These results suggest a novel role for exosomes derived from NK cells in the pathogenesis of chronic lung allograft rejection.

Network-Based Integrated Analysis of Transcriptomic Studies in Dissecting Gene Signatures for LPS-Induced Acute Lung Injury

Acute lung injury (ALI) is a type of serious clinical syndrome leading to morbidity and mortality. However, the precise pathogenesis of ALI remains elusive. Here, we implemented an integrative meta-analysis of six GEO microarray studies with 76 samples in the ALI mouse model. A total of 958 differentially expressed genes (DEGs) were identified in LPS relative to normal samples. Then, a network-based meta-analysis was used to mine core DEGs and to unfold the interactions among these genes. We found that Ebi3 was the top upregulated genes in the LPS-induced ALI. GO, KEGG, and GSEA analyses were performed for functional annotation. qRT-PCR revealed augmented expression of six candidate genes (Stat1, Syk, Jak3, Rac2, Ripk1, and Traf6) in the established ALI mouse model with LPS exposure. Taken together, our study investigated comprehensively hub DEGs and their networks for LPS-stimulated ALI, which might afford an additional approach to determine biomarkers and therapeutic targets and explore the molecular pathophysiology toward ALI.

Role and mechanisms of autophagy in lung metabolism and repair

Mammalian lungs are metabolically active organs that frequently encounter environmental insults. Stress responses elicit protective autophagy in epithelial barrier cells and the supportive niche. Autophagy promotes the recycling of damaged intracellular organelles, denatured proteins, and other biological macromolecules for reuse as components required for lung cell survival. Autophagy, usually induced by metabolic defects, regulates cellular metabolism. Autophagy is a major adaptive response that protects cells and organisms from injury. Endogenous region-specific stem/progenitor cell populations are found in lung tissue, which are responsible for epithelial repair after lung damage. Additionally, glucose and fatty acid metabolism is altered in lung stem/progenitor cells in response to injury-related lung fibrosis. Autophagy deregulation has been observed to be involved in the development and progression of other respiratory diseases. This review explores the role and mechanisms of autophagy in regulating lung metabolism and epithelial repair.

Immune-Associated Proteins Are Enriched in Lung Tissue-Derived Extracellular Vesicles during Allergen-Induced Eosinophilic Airway Inflammation

Studying the proteomes of tissue-derived extracellular vesicles (EVs) can lead to the identification of biomarkers of disease and can provide a better understanding of cell-to-cell communication in both healthy and diseased tissue. The aim of this study was to apply our previously established tissue-derived EV isolation protocol to mouse lungs in order to determine the changes in the proteomes of lung tissue-derived EVs during allergen-induced eosinophilic airway inflammation. A mouse model for allergic airway inflammation was used by sensitizing the mice intraperitoneal with ovalbumin (OVA), and one week after the final sensitization, the mice were challenged intranasal with OVA or PBS. The animals were sacrificed 24 h after the final challenge, and their lungs were removed and sliced into smaller pieces that were incubated in culture media with DNase I and Collagenase D for 30 min at 37 °C. Vesicles were isolated from the medium by ultracentrifugation and bottom-loaded iodixanol density cushions, and the proteomes were determined using quantitative mass spectrometry. More EVs were present in the lungs of the OVA-challenged mice compared to the PBS-challenged control mice. In total, 4510 proteins were quantified in all samples. Among them, over 1000 proteins were significantly altered (fold change >2), with 614 proteins being increased and 425 proteins being decreased in the EVs from OVA-challenged mice compared to EVs from PBS-challenged animals. The associated cellular components and biological processes were analyzed for the altered EV proteins, and the proteins enriched during allergen-induced airway inflammation were mainly associated with gene ontology (GO) terms related to immune responses. In conclusion, EVs can be isolated from mouse lung tissue, and the EVs’ proteomes undergo changes in response to allergen-induced airway inflammation. This suggests that the composition of lung-derived EVs is altered in diseases associated with inflammation of the lung, which may have implications in type-2 driven eosinophilic asthma pathogenesis.

Clara cell 16 KDa protein mitigates house dust mite-induced airway inflammation and damage via regulating airway epithelial cell apoptosis in a manner dependent on HMGB1-mediated signaling inhibition

Background

House dust mite (HDM) inhalation can cause airway epithelial damage which is implicated in the process of airway inflammation in asthma. High mobility group box 1 (HMGB1) is critically required for cellular damage and apoptosis as an important endogenous danger signal. Recently, Clara cell 16KDa protein (CC16) has been identified to exert anti-inflammatory and immunomodulatory influence in various injury-related diseases model. However, little is known about its ability to protect against airway epithelial injury in allergic asthma. This study was aimed to clarify the protective roles of CC16 on airway epithelia in HDM-induced asthma and the regulation of HMGB1 by CC16.

Methods

Mice were sensitized and challenged by HDM extract and administrated intranasally with CC16 (5 μg/g or 10 μg/g) or saline in the challenged period. The BEAS-2B human airway epithelial cell line were cultured with CC16 or the control vehicle and then exposed to HDM. Knockdown or overexpression of HMGB1 was induced by cell transfection or intratracheal injection of recombinant adenovirus.

Results

CC16 treatment decreased airway inflammation and histological damage of airway epithelium dose-dependently in HDM-induced asthma model. Airway epithelia apoptosis upon HDM stimulation was noticeably abrogated by CC16 in vivo and in vitro. In addition, upregulation of HMGB1 expression and its related signaling were also detected under HDM conditions, while silencing HMGB1 significantly inhibited the apoptosis of BEAS-2B cells. Furthermore, the activity of HMGB1-mediated signaling was restrained after CC16 treatment whereas HMGB1 overexpression abolished the protective effect of CC16 on HDM-induced airway epithelia apoptosis.

Conclusions

Our data confirm that CC16 attenuates HDM-mediated airway inflammation and damage via suppressing airway epithelial cell apoptosis in a HMGB1-dependent manner, suggesting the role of CC16 as a potential protective option for HDM-induced asthma.

Lung organoids, useful tools for investigating epithelial repair after lung injury

Organoids are derived from stem cells or organ-specific progenitors. They display structures and functions consistent with organs in vivo. Multiple types of organoids, including lung organoids, can be generated. Organoids are applied widely in development, disease modelling, regenerative medicine, and other multiple aspects. Various human pulmonary diseases caused by several factors can be induced and lead to different degrees of lung epithelial injury. Epithelial repair involves the participation of multiple cells and signalling pathways. Lung organoids provide an excellent platform to model injury to and repair of lungs. Here, we review the recent methods of cultivating lung organoids, applications of lung organoids in epithelial repair after injury, and understanding the mechanisms of epithelial repair investigated using lung organoids. By using lung organoids, we can discover the regulatory mechanisms related to the repair of lung epithelia. This strategy could provide new insights for more effective management of lung diseases and the development of new drugs.

Exogenous Clara cell protein 16 attenuates silica particles-induced inflammation in THP-1 macrophages by down-regulating NF-κB and caspase-1 activation

Inhalation of silica particles leads to pulmonary inflammatory responses. Clara cell protein 16 (CC16) has been reported to played a protective role in inflammatory lung diseases. However, its role on silica particles-induced inflammation has not been fully clarified. In this study, THP-1 macrophages were exposed to 75 μg/cm² silica particles with or without 2 μg/mL exogenous CC16 (recombinant CC16, rCC16) for 24 hr. The production of inflammatory cytokines, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α and IL-6, in the cell supernatants of different groups was detected through ELISA kits and real-time RT-PCR, respectively. The nuclear translocation of nuclear factor (NF)-κB, protein levels of pro-IL-1β, the nucleotide-binding domain-like receptor protein 3 (NLRP3) and caspase-1 were evaluated via immunofluorescence or western blot. Results showed that, at 75 μg/cm² silica particle concentration, the treatment of rCC16 significantly decreased IL-1β, TNF-α and IL-6 protein release and mRNA levels in THP-1 macrophages. Compared to those only exposed to silica particles, THP-1 macrophages exposed to both silica particles and rCC16 showed significantly lower nuclear levels and higher cytosol levels of NF-κB p65, as well as lower co-localization coefficients through immunofluorescence. Additionally, the administration of rCC16 significantly attenuated the increase of pro-IL-1β, NLRP3 and caspase-1 levels induced by silica particle exposure. Our results suggested that exogenous CC16 could inhibit silica particles-induced inflammation in THP-1 macrophages, mainly through suppressing NF-κB pathway and caspase-1 activation.

Identification of robust genetic signatures associated with lipopolysaccharide-induced acute lung injury onset and astaxanthin therapeutic effects by integrative analysis of RNA sequencing data and GEO datasets

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening clinical conditions predominantly arising from uncontrolled inflammatory reactions. It has been found that the administration of astaxanthin (AST) can exert protective effects against lipopolysaccharide (LPS)-induced ALI; however, the robust genetic signatures underlying LPS induction and AST treatment remain obscure. Here we performed a statistical meta-analysis of five publicly available gene expression datasets from LPS-induced ALI mouse models, conducted RNA-sequencing (RNA-seq) to screen differentially expressed genes (DEGs) in response to LPS administration and AST treatment, and integrative analysis to determine robust genetic signatures associated with LPS-induced ALI onset and AST administration. Both the meta-analyses and our experimental data identified a total of 198 DEGs in response to LPS administration, and 11 core DEGs (Timp1, Ly6i, Cxcl13, Irf7, Cxcl5, Ccl7, Isg15, Saa3, Saa1, Tgtp1, and Gbp11) were identified to be associated with AST therapeutic effects. Further, the 11 core DEGs were verified by quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC), and functional enrichment analysis revealed that these genes are primarily associated with neutrophils and chemokines. Collectively, these findings unearthed the robust genetic signatures underlying LPS administration and the molecular targets of AST for ameliorating ALI/ARDS which provide directions for further research.

The rCC16 Protein Protects Against LPS-Induced Cell Apoptosis and Inflammatory Responses in Human Lung Pneumocytes

Objective

Our previous clinical study showed that low lung levels of CC16 strongly influence the occurrence and development of ARDS. The aim of the present study was to evaluate the therapeutic effect of rCC16 on LPS-induced inflammation in A549 cells and to determine its mechanism.

Methods

Cell apoptosis and inflammation was induced by LPS stimulation. The cytotoxic effect of rCC16 was evaluated using the MTT assay. Cytokine levels were determined using enzyme-linked immunosorbent assays. The molecular mechanism of rCC16 was investigated by analyzing relevant signaling pathways.

Results

The LPS treatment of A549 cells significantly decreased cell viability, increased the levels of the apoptotic proteins Bax, Bak and Cleaved Caspase-3, the secretion of inflammatory cytokines, and the expression levels of TLR4, p-NF/κB, MAPK proteins. While the levels of Bcl-2, p-AKT, p-mTOR, p-ERK1/2, NF/κB, p-AMPK, and p-p38 were significantly decreased in LPS-treated A549 cells. Our experimental results also confirmed that rCC16 inhibited LPS-induced apoptosis, promoted A549 cell proliferation by activating the PI3K/AKT/mTOR/ERK1/2 pathway, and inhibited the release of certain inflammatory factors, especially HMGB1, through dephosphorylation and inactivation of the TLR4/NF-κB/AMPK signaling pathways.

Conclusion

These results highlight the potential utility of CC16 as an important cytokine for the prevention or treatment of inflammation and show that CC16 may play an important role in the future clinical treatment of ARDS.

Neonatal endotoxin stimulation is associated with a long-term bronchiolar epithelial expression of innate immune and anti-allergic markers that attenuates the allergic response

Allergic asthma is the most common phenotype of the pathology, having an early-onset in childhood and producing a Th2-driven airways remodeling process that leads to symptoms and pathophysiological changes. The avoidance of aeroallergen exposure in early life has been shown to prevent asthma, but without repeated success and with the underlying preventive mechanisms at the beginning of asthma far to be fully recognized. In the present study, we aimed to evaluate if neonatal LPS-induced boost in epithelial host defenses contribute to prevent OVA-induced asthma in adult mice. To this, we focused on the response of bronchiolar club cells (CC), which are highly specialized in maintaining the epithelial homeostasis in the lung. In these cells, neonatal LPS administration increased the expression of TLR4 and TNFα, as well as the immunodulatory/antiallergic proteins: club cell secretory protein (CCSP) and surfactant protein D (SP-D). LPS also prevented mucous metaplasia of club cells and reduced the epidermal growth factor receptor (EGFR)-dependent mucin overproduction, with mice displaying normal breathing patterns after OVA challenge. Furthermore, the overexpression of the epithelial Th2-related molecule TSLP was blunted, and normal TSLP and IL-4 levels were found in the bronchoalveolar lavage. A lower eosinophilia was detected in LPS-pretreated mice, along with an increase in phagocytes and regulatory cells (CD4+CD25+FOXP3+ and CD4+IL-10+), together with higher levels of IL-12 and TNFα. In conclusion, our study demonstrates stable asthma-preventive epithelial effects promoted by neonatal LPS stimulation, leading to the presence of regulatory cells in the lung. These anti-allergic dynamic mechanisms would be overlaid in the epithelium, favored by an adequate epidemiological environment, during the development of asthma.

The role of the non-ciliated bronchiolar cell in tolerance to inhaled vanadium of the bronchiolar epithelium

The Non-Ciliated Bronchiolar Cell (NCBC) is responsible for the defense and maintenance of the bronchiolar epithelium. Several cellular defense mechanisms have been associated with an increase in the secretion of CC16 and changes in the phenotype of the cell; these mechanisms could be linked to tolerance to the damage due to exposure to inhaled Particulate Matter (PM) of the epithelium. These defense mechanisms have not been sufficiently explored. In this article, we studied the response of the NCBC to inhaled vanadium, an element which adheres to PM. This response was measured by the changes in the phenotype of the NCBC and the secretion of CC16 in a mouse model. Mice were exposed in two phases to different vanadium concentrations; 1.27 mg/m³ in the first phase and 2.56 mg/m³ in the second phase. Mice were sacrificed on the 2nd, 4th, 5th, 6th and 8th weeks. In the second phase, we observed the following: sloughing of the NCBC, hyperplasia and small inflammatory foci remained without changes and that the expression of CC16 was higher in this phase than in phase I. We also observed a change in the phenotype with a slow decrease in both phases. The increase in the secretion of CC16 and the phenotype reversion could be due to the anti-inflammatory activity of CC16. The changes observed in the second phase could be attributed to the tolerance to inhaled vanadium.

Organoid models in lung regeneration and cancer

Improper regeneration is associated with lung diseases including lung cancer. Lung cancer is one of the leading causes of death worldwide, with nearly 2 million new cases diagnosed each year. The diagnosis is often too late for successful therapeutic intervention. Lung cancer shows substantial phenotypic and genetic heterogeneity between individuals, making it difficult to model in animals. Organoids, derived from regional stem/progenitor cells in lung epithelia, have attracted extensive interest in both research studies and the clinic, because of their great potential for use in cancer treatment. Various lung cancer organoids have been established to recapitulate the tissue architecture of primary lung tumors and maintain the genomic alterations of the original tumors during long-term expansion in vitro. In this review, we summarize the current data on lung epithelial regeneration by regional endogenous stem/progenitor cells, describe the development of organoid technology, and present its applications in lung cancer research. Furthermore, recent challenges and future directions to improve organoid technologies for lung cancer treatment are discussed.

Modeling radiation-induced lung injury: lessons learned from whole thorax irradiation

Models of thoracic irradiation have been developed as clinicians and scientists have attempted to decipher the events that led up to the pulmonary toxicity seen in human subjects following radiation treatment. The most common model is that of whole thorax irradiation (WTI), applied in a single dose. Mice, particularly the C57BL/6J strain, has been frequently used in these investigations, and has greatly informed our current understanding of the initiation and progression of radiation-induced lung injury (RILI). In this review, we highlight the sequential progression and dynamic nature of RILI, focusing primarily on the vast array of information that has been gleaned from the murine model. Ample evidence indicates a wide array of biological responses that can be seen following irradiation, including DNA damage, oxidative stress, cellular senescence and inflammation, all triggered by the initial exposure to ionizing radiation (IR) and heterogeneously maintained throughout the temporal progression of injury, which manifests as acute pneumonitis and later fibrosis. It appears that the early responses of specific cell types may promote further injury, disrupting the microenvironment and preventing a return to homeostasis, although the exact mechanisms driving these responses remains somewhat unclear. Attempts to either prevent or treat RILI in preclinical models have shown some success by targeting these disparate radiobiological processes. As our understanding of the dynamic cellular responses to radiation improves through the use of such models, so does the likelihood of preventing or treating RILI.

Development of a Novel AOP for Cyp2F2-Mediated Lung Cancer in Mice

Traditional methods for carcinogenicity testing rely heavily on the rodent bioassay as the standard for identification of tumorigenic risk. As such, identification of species-specific outcomes and/or metabolism are a frequent argument for regulatory exemption. One example is the association of tumor formation in the mouse lung after exposure to Cyp2F2 ligands. The adverse outcome pathway (AOP) framework offers a theoretical platform to address issues of species specificity that is consistent, transparent, and capable of integrating data from new approach methodologies as well as traditional data streams. A central premise of the AOP concept is that pathway progression from the molecular initiating event (MIE) implies a definable “response-response” (R-R) relationship between each key event (KE) that drives the pathway towards a specific adverse outcome (AO). This article describes an AOP for lung cancer in the mouse from an MIE of Cyp2F2-specific reactive metabolite formation, advancing through KE that include protein and/or nucleic acid adducts, diminished Club Cell 10 kDa (CC10) protein expression, hyperplasia of CC10 deficient Club cells, and culminating in the AO of mixed-cell tumor formation in the distal airways. This tumor formation is independent of route of exposure and our AOP construct is based on overlapping mechanistic events for naphthalene, styrene, ethyl benzene, isoniazid, and fluensulfone in the mouse. This AOP is intended to accelerate the explication of an apparent mouse-specific outcome and serve as a starting point for a quantitative analysis of mouse-human differences in susceptibility to the tumorigenic effects of Cyp2F2 ligands.

Allele-specific expression identified rs2509956 as a novel long-distance cis-regulatory SNP for SCGB1A1, an important gene for multiple pulmonary diseases

SCGB1A1 (secretoglobin family 1A member 1) is an important protein for multiple pulmonary diseases, especially asthma, chronic obstructive pulmonary disease, and lung cancer. One single-nucleotide polymorphism (SNP) at 5'-untranslated region of SCGB1A1, rs3741240, has been suggested to be associated with reduced protein expression and further asthma susceptibility. However, it was still unclear whether there were other cis-regulatory elements for SCGB1A1 that might further contribute to pulmonary diseases. Allele-specific expression (ASE) is a novel approach to identify the functional region in human genome. In the present study, we measured ASE on rs3741240 in lung tissues and observed a consistent excess of G allele over A (P < 10^-6), which indicated that this SNP or the one(s) in linkage disequilibrium (LD) could regulate SCGB1A1 expression. By analyzing 1000 Genomes Project data for Chinese, one SNP locating ~10.2 kb away and downstream of SCGB1A1, rs2509956, was identified to be in strong LD with rs3741240. Reporter gene assay confirmed that both SNPs could regulate gene expression in the lung cell. By chromosome conformation capture, it was verified that the region surrounding rs2509956 could interact with SCGB1A1 promoter region and act as an enhancer. Through chromatin immunoprecipitation and overexpression assay, the related transcription factor RELA (RELA proto-oncogene, NF-kB subunit) was recognized to bind the region spanning rs2509956. Our work identified a novel long-distance cis-regulatory SNP for SCGB1A1, which might contribute to multiple pulmonary diseases.

An obligatory role for club cells in preventing obliterative bronchiolitis in lung transplants

Obliterative bronchiolitis (OB) is a poorly understood airway disease characterized by the generation of fibrotic bronchiolar occlusions. In the lung transplant setting, OB is a pathological manifestation of bronchiolitis obliterans syndrome (BOS), which is a major impediment to long-term recipient survival. Club cells play a key role in bronchiolar epithelial repair, but whether they promote lung transplant tolerance through preventing OB remains unclear. We determined if OB occurs in mouse orthotopic lung transplants following conditional transgene-targeted club cell depletion. In syngeneic lung transplants club cell depletion leads to transient epithelial injury followed by rapid club cell-mediated repair. In contrast, allogeneic lung transplants develop severe OB lesions and poorly regenerate club cells despite immunosuppression treatment. Lung allograft club cell ablation also triggers the recognition of alloantigens, and pulmonary restricted self-antigens reported associated with BOS development. However, CD8+ T cell depletion restores club cell reparative responses and prevents OB. In addition, ex-vivo analysis reveals a specific role for alloantigen-primed effector CD8+ T cells in preventing club cell proliferation and maintenance. Taken together, we demonstrate a vital role for club cells in maintaining lung transplant tolerance and propose a new model to identify the underlying mechanisms of OB.

Club Cell Secretory Protein Deficiency Leads to Altered Lung Function

RATIONALE

CC16 (club cell secretory protein-16), a member of the secretoglobin family, is one of the most abundant proteins in normal airway secretions and has been described as a serum biomarker for obstructive lung diseases.

OBJECTIVES

To determine whether low CC16 is a marker for airway pathology or is implicated in the pathophysiology of progressive airway damage in these conditions.

METHODS

Using human data from the birth cohort of the Tucson Children's Respiratory Study, we examined the relation of circulating CC16 levels with pulmonary function and responses to bronchial methacholine challenge from childhood up to age 32 years. In wild-type and CC16-/- mice, we set out to comprehensively examine pulmonary physiology, inflammation, and remodeling in the naive airway.

MEASUREMENTS AND MAIN RESULTS

We observed that Tucson Children's Respiratory Study participants in the lowest tertile of serum CC16 had significant deficits in their lung function and enhanced airway hyperresponsiveness to methacholine challenge from 11 years throughout young adult life. Similarly, CC16-/- mice had significant deficits in lung function and enhanced airway hyperresponsiveness to methacholine as compared with wild-type mice, which were independent of inflammation and mucin production. As compared with wild-type mice, CC16-/- mice had significantly elevated gene expression of procollagen type I, procollagen type III, and α-smooth muscle actin, areas of pronounced collagen deposition and significantly enhanced smooth muscle thickness.

CONCLUSIONS

Our findings support clinical observations by providing evidence that lack of CC16 in the lung results in dramatically altered pulmonary function and structural alterations consistent with enhanced remodeling.

Club cell protein 16 (Cc16) deficiency increases inflamm-aging in the lungs of mice

Low serum CC16 levels are associated with accelerated lung function decline in human population studies, but it is not known whether low serum CC16 levels contribute to lung function decline, or are an epiphenomenon. We tested the hypothesis that unchallenged Cc16-/- mice develop accelerated rates of pulmonary function test abnormalities and pulmonary pathologies over time compared with unchallenged WT mice. Respiratory mechanics, airspace enlargement, and small airway fibrosis were measured in unchallenged wild-type (WT) versus Cc16-/- mice over 6-18 months of age. Lung leukocyte counts and lung levels of metalloproteinases (Mmps), cytokines, oxidative stress, cellular senescence markers (p19 and p21), and lung cell apoptosis, and serum C-reactive protein (CRP) levels were measured in age-matched WT versus Cc16-/- mice. Unchallenged Cc16-/- mice developed greater increases in lung compliance, airspace enlargement, and small airway fibrosis than age-matched WT mice over 6-18 months of age. Cc16-/- mice had greater: (1) lung leukocyte counts; (2) lung levels of Ccl2, Ccl-5, interleukin-10, Mmp-2, and Mmp-9; (3) pulmonary oxidative stress levels, (4) alveolar septal cell apoptosis and staining for p16 and p21; and (5) serum CRP levels. Unchallenged Cc16-/- mice had greater nuclear factor-κB (NF-κB) activation in their lungs than age-matched WT mice, but similar lung levels of secretory phospholipase-A2 activity. Cc16 deficiency in mice leads spontaneously to an accelerated lung aging phenotype with exaggerated pulmonary inflammation and COPD-like lung pathologies associated with increased activation of NF- κB in the lung. CC16 augmentation strategies may reduce lung aging in CC16-deficient individuals.

Pulmonary IL-1β expression in early life causes permanent changes in lung structure and function in adulthood

Chorioamnionitis, mechanical ventilation, oxygen therapy, and postnatal infection promote inflammation in the newborn lung. The long-term consequences of pulmonary inflammation during infancy have not been well characterized. The aim of this study was to examine the impact of inflammation during the late saccular to alveolar stages of lung development on lung structure and function in adulthood. To induce IL-1β expression in the pulmonary epithelium of mice with a tetracycline-inducible human IL-1β transgene, doxycycline was administered via intraperitoneal injections to bitransgenic pups and their littermate controls on postnatal days (PN) 0, 0.5, and 1. Lung structure, inflammation, and airway reactivity were studied in adulthood. IL-1β production in early life resulted in increased numbers of macrophages and neutrophils on PN21, but inflammation subsided by PN42. Permanent changes in alveolar structure, i.e., larger alveoli and thicker alveolar walls, were present from PN21 to PN84. Lack of alveolar septation thus persisted after IL-1β production and inflammation had ceased. Early IL-1β production caused goblet cell hyperplasia, enhanced calcium-activated chloride channel 3 (CLCA3) protein expression, and increased airway reactivity in response to methacholine on PN42. Lymphoid follicles were present adjacent to small airways in the lungs of adult bitransgenic mice, and levels of the B cell chemoattractant CXC-motif ligand (CXCL) 13 were elevated in the lungs of bitransgenic mice compared with controls. In conclusion, IL-1β-induced pulmonary inflammation in early life causes a chronic lung disease in adulthood.

IL-13 in LPS-Induced Inflammation Causes Bcl-2 Expression to Sustain Hyperplastic Mucous cells

Exposure to lipopolysaccharides (LPS) causes extensive neutrophilic inflammation in the airways followed by mucous cell hyperplasia (MCH) that is sustained by the anti-apoptotic protein, Bcl-2. To identify inflammatory factor(s) that are responsible for Bcl-2 expression, we established an organ culture system consisting of airway epithelial tissue from the rat nasal midseptum. The highest Muc5AC and Bcl-2 expression was observed when organ cultures were treated with brochoalveolar lavage (BAL) fluid harvested from rats 10 h post LPS instillation. Further, because BAL harvested from rats depleted of polymorphonuclear cells compared to controls showed increased Bcl-2 expression, analyses of cytokine levels in lavages identified IL-13 as an inducer of Bcl-2 expression. Ectopic IL-13 treatment of differentiated airway epithelial cells increased Bcl-2 and MUC5AC expression in the basal and apical regions of the cells, respectively. When Bcl-2 was blocked using shRNA or a small molecule inhibitor, ABT-263, mucous cell numbers were reduced due to increased apoptosis that disrupted the interaction of Bcl-2 with the pro-apoptotic protein, Bik. Furthermore, intranasal instillation of ABT-263 reduced the LPS-induced MCH in bik +/+ but not bik -/- mice, suggesting that Bik mediated apoptosis in hyperplastic mucous cells. Therefore, blocking Bcl-2 function could be useful in reducing IL-13 induced mucous hypersecretion.

Depletion of club cells attenuates bleomycin-induced lung injury and fibrosis in mice

Background

The role of bronchiolar epithelial cells in the pathogenesis of pulmonary fibrosis has not been clarified. We previously demonstrated DNA damage in murine bronchioles in the early stages of bleomycin-induced pulmonary fibrosis that subsequently extended to alveolar cells at the advanced stages of the disease. Club cells are progenitor cells for bronchioles and are known to play protective roles against lung inflammation and damage. The aim of the present study was to elucidate the role of club cells in the development of pulmonary fibrosis.

Methods

C57BL/6 J mice received naphthalene intraperitoneally on day −2 to deplete club cells and were given intratracheal bleomycin or a vehicle on day 0. Lung tissues were obtained on days 1, 7, and 14, and bronchoalveolar lavage was performed on day 14. Bronchiolar epithelial cells sampled by laser capture microdissection were analyzed by gene expression microarray analysis on day 14.

Results

Club cell depletion induced by naphthalene protected mice from bleomycin-induced lung injury and fibrosis. Bleomycin-triggered bronchiolar TGF-β1 expression was reduced. Gene expression microarray analysis revealed that genes associated with inflammatory response and chemokine activity were downregulated in the bleomycin-injured bronchiolar epithelium with club cell injury compared to that in bronchiolar epithelium without cell injury.

Conclusions

Club cells are involved in the development of lung injury and fibrosis.

Label-free LC-MS/MS shotgun proteomics to investigate the anti-inflammatory effect of rCC16

Clara cell protein (CC16) is an anti-inflammatory protein, which is expressed in the airway epithelium. It is involved in the development of airway inflammatory diseases, including chronic obstructive pulmonary disease and asthma. However, the exact molecular mechanism underlying its anti‑inflammatory action remains to be fully elucidated. The aim of the present study was to define the protein profiles of the anti‑inflammatory effect of CC16 in lipopolysaccharide (LPS)‑treated rat tracheal epithelial (RTE) cells using shotgun proteomics. Protein extracts were obtained from control RTE cells, RTE cells treated with LPS and RTE cells treated with LPS and recombinant CC16 (rCC16). Subsequent label‑free quantification and bioinformatics analyses identified 12 proteins that were differentially expressed in the three treatment groups as a cluster of five distinct groups according to their molecular functions. Five of the twelve proteins were revealed to be associated with the cytoskeleton: Matrix metalloproteinase‑9, myosin heavy chain 10, actin‑related protein‑3 homolog, elongation factor 1‑α‑1 (EF‑1‑α‑1), and acidic ribosomal phosphoprotein P0. Five of the twelve proteins were associated with cellular proliferation: DNA‑dependent protein kinase catalytic subunit, EF‑1‑α‑1, tyrosine 3‑monooxygenase, caspase recruitment domain (CARD) protein 12 and adenosylhomocysteinase (SAHH) 3. Three proteins were associated with gene regulation: EF‑1‑α‑1, SAHH 3 and acidic ribosomal phosphoprotein P0. Three proteins were associated with inflammation: Tyrosine 3‑monooxygenase, CARD protein 12 and statin‑related protein. ATPase (H+‑transporting, V1 subunit A, isoform 1) was revealed to be associated with energy metabolism, and uridine diphosphate glycosyltransferase 1 family polypeptide A8 with drug metabolism and detoxification. The identified proteins were further validated using reverse transcription‑quantitative polymerase chain reaction. These protein profiles, and their interacting protein network, may facilitate the elucidation of the molecular mechanisms underlying the anti‑inflammatory effects of CC16.

Club Cell Protein 16 (CC16) Augmentation: A Potential Disease-modifying Approach for Chronic Obstructive Pulmonary Disease (COPD)

INTRODUCTION

Club cell protein 16 (CC16) is the most abundant protein in bronchoalveolar lavage fluid. CC16 has anti-inflammatory properties in smoke-exposed lungs, and chronic obstructive pulmonary disease (COPD) is associated with CC16 deficiency. Herein, we explored whether CC16 is a therapeutic target for COPD.

AREAS COVERED

We reviewed the literature on the factors that regulate airway CC16 expression, its biologic functions and its protective activities in smoke-exposed lungs using PUBMED searches. We generated hypotheses on the mechanisms by which CC16 limits COPD development, and discuss its potential as a new therapeutic approach for COPD.

EXPERT OPINION

CC16 plasma and lung levels are reduced in smokers without airflow obstruction and COPD patients. In COPD patients, airway CC16 expression is inversely correlated with severity of airflow obstruction. CC16 deficiency increases smoke-induced lung pathologies in mice by its effects on epithelial cells, leukocytes, and fibroblasts. Experimental augmentation of CC16 levels using recombinant CC16 in cell culture systems, plasmid and adenoviral-mediated over-expression of CC16 in epithelial cells or smoke-exposed murine airways reduces inflammation and cellular injury. Additional studies are necessary to assess the efficacy of therapies aimed at restoring airway CC16 levels as a new disease-modifying therapy for COPD patients.

Explanation of Metastasis by Homeostatic Inflammation

If inflammation caused by either non-self or self molecules can disseminate throughout the body and inflammatory sites actively allow entry of circulating tumor cells and assist regrowth, then circulating tumor cells metastasize to the sites of inflammation. However, disrupted sites of homeostatic inflammation do not necessarily guarantee metastatic spread and subsequent regrowth.

Pharmacokinetics of leptin in female mice

Pharmacokinetics of leptin in mammals has received limited attention and only one study has examined more than two time points and this was in ob/ob mice. This study is the first to observe the distribution of leptin over a time course in female mice. A physiologic dose (12 ng) of radiolabelled leptin was injected in adult female mice via the lateral tail vein and tissues were dissected out and measured for radioactivity over a time course up to two hours. Major targets for administered leptin included the liver, kidneys, gastrointestinal tract and the skin while the lungs had high concentrations of administered leptin per gram of tissue. Leptin was also found to enter the lumen of the digestive tract intact from the plasma. Very little of the dose (<1 %) was recovered from the brain at any time. Consequently we confirm that the brain is not a major target for leptin from the periphery, although it may be very sensitive to leptin that does get to the hypothalamus. Several of the major targets (GI tract, skin and lungs) for leptin form the interface for the body with the environment, and given the ability of leptin to modulate immune function, this may represent a priming effect for tissues to respond to damage and infection.

Secretoglobin and Transferrin Expression in Bronchoalveolar Lavage Fluid of Horses with Chronic Respiratory Disease

Background

Lower expression of secretoglobin and transferrin has been found in the bronchoalveolar lavage fluid (BALF) of a small number of horses with experimentally induced signs of recurrent airway obstruction (RAO) compared to healthy controls.

Hypothesis/Objectives

Secretoglobin and transferrin BALF expression will be similarly decreased in horses with naturally occurring clinical signs of RAO and in horses with experimentally induced clinical signs of RAO as compared to healthy controls and intermediate in horses with inflammatory airway disease (IAD).

Animals

Recurrent airway obstruction‐affected and control horses were subjected to an experimental hay exposure trial to induce signs of RAO. Client‐owned horses with a presumptive diagnosis of RAO and controls from the same stable environments were recruited.

Methods

Pulmonary function and BALF were evaluated from control and RAO‐affected research horses during an experimental hay exposure trial (n = 5 in each group) and from client‐owned horses (RAO‐affected horses, n = 17; IAD‐affected horses, n = 19; healthy controls, n = 5). The concentrations of secretoglobin and transferrin in BALF were assessed using Western blots.

Results

Naturally occurring and experimentally induced RAO horses had similar decreases in BALF transferrin expression, but secretoglobin expression was most decreased in naturally occurring RAO. Secretoglobin and transferrin expression were both lower in BALF of RAO‐affected horses than in IAD‐affected and control horses.

Conclusions and Clinical Importance

Secretoglobin and transferrin expression is decreased in BALF of RAO‐affected horses after both experimental and natural exposure. Secretoglobin and transferrin likely play clinically relevant roles in the pathophysiology of RAO, and may thus be used as biomarkers of the disease.

Relation between circulating CC16 concentrations, lung function, and development of chronic obstructive pulmonary disease across the lifespan: a prospective study

BACKGROUND

Low concentrations of the anti-inflammatory protein CC16 (approved symbol SCGB1A1) in serum have been associated with accelerated decline in forced expiratory volume in 1 s (FEV1) in patients with chronic obstructive pulmonary disease (COPD). We investigated whether low circulating CC16 concentrations precede lung function deficits and incidence of COPD in the general population.

METHODS

We assessed longitudinal data on CC16 concentrations in serum and associations with decline in FEV1 and incidence of airflow limitation for adults who were free from COPD at baseline in the population-based Tucson Epidemiological Study of Airway Obstructive Disease ([TESAOD] n=960, mean follow-up 14 years), European Community Respiratory Health Survey ([ECRHS-Sp] n=514, 11 years), and Swiss Cohort Study on Air Pollution and Lung Diseases in Adults ([SAPALDIA] n=167, 8 years) studies. Additionally, we measured circulating CC16 concentrations in samples from children aged 4-6 years in the Tucson Children's Respiratory Study (n=427), UK Manchester Asthma and Allergy Study (n=481), and the Swedish Barn/children, Allergy, Milieu, Stockholm, Epidemiological survey (n=231) birth cohorts to assess whether low CC16 concentrations in childhood were predictive for subsequent lung function.

FINDINGS

After adjustment for sex, age, height, smoking status and intensity, pack-years, asthma, and FEV1 at baseline, we found an inverse association between CC16 concentration and decline in FEV1 in adults in TESAOD (4·4 mL/year additional FEV1 decline for each SD decrease in baseline CC16 concentration, p=0·0014) and ECRHS-Sp (2·4 mL/year, p=0·023); the effect in SAPALDIA was marginal (4·5 mL/year, p=0·052). Low CC16 concentration at baseline was also associated with increased risk of incident stage 2 airflow limitation (ratio of FEV1 to forced expiratory volume [FEV1/FVC] less than 70% plus FEV1 % predicted less than 80%) in TESAOD and ECRHS-Sp. In children, the lowest tertile of CC16 concentrations was associated with a subsequent FEV1 deficit of 68 mL up to age 16 years (p=0·0001), which was confirmed in children who had never smoked by age 16 years (-71 mL, p<0·0001).

INTERPRETATION

Low concentrations of CC16 in serum are associated with reduced lung function in childhood, accelerated lung function decline in adulthood, and development of moderate airflow limitation in the general adult population.

FUNDING

National Heart, Lung, and Blood Institute and European Union Seventh Framework Programme.

Protective role for club cell secretory protein-16 (CC16) in the development of COPD

Club cell secretory protein-16 (CC16) is the major secreted product of airway club cells, but its role in the pathogenesis of chronic obstructive pulmonary disease (COPD) is unclear. We measured CC16 airway expression in humans with and without COPD and CC16 function in a cigarette smoke (CS)-induced COPD murine model. Airway CC16 expression was measured in COPD patients, smokers without COPD and non-smokers. We exposed wildtype (WT) and CC16(-/-)mice to CS or air for up to 6 months, and measured airway CC16 expression, pulmonary inflammation, alveolar septal cell apoptosis, airspace enlargement, airway mucin 5AC (MUC5AC) expression, small airway remodelling and pulmonary function. Smokers and COPD patients had reduced airway CC16 immunostaining that decreased with increasing COPD severity. Exposing mice to CS reduced airway CC16 expression. CC16(-/-) mice had greater CS-induced emphysema, airway remodelling, pulmonary inflammation, alveolar cell apoptosis, airway MUC5AC expression, and more compliant lungs than WT mice. These changes were associated with increased nuclear factor-κB (NF-κB) activation in CC16(-/-) lungs. CS-induced acute pulmonary changes were reversed by adenoviral-mediated over-expression of CC16. CC16 protects lungs from CS-induced injury by reducing lung NF-κB activation. CS-induced airway CC16 deficiency increases CS-induced pulmonary inflammation and injury and likely contributes to the pathogenesis of COPD.

Recombinant rat CC16 protein inhibits LPS-induced MMP-9 expression via NF-κB pathway in rat tracheal epithelial cells

Clara cell protein (CC16) is a well-known anti-inflammatory protein secreted by the epithelial Clara cells of the airways. It is involved in the development of airway inflammatory diseases such as chronic obstructive pulmonary disease and asthma. Previous studies suggest that CC16 gene transfer suppresses expression of interleukin (IL)-8 in bronchial epithelial cells. However, its role in the function of these cells during inflammation is not well understood. In this study, we evaluated the effect of CC16 on the expression of matrix metalloproteinase (MMP)-9 in lipopolysaccharide (LPS)-stimulated rat tracheal epithelial cells and its underlying molecular mechanisms. We generated recombinant rat CC16 protein (rCC16) which was bioactive in inhibiting the activity of phospholipase A2. rCC16 inhibited LPS-induced MMP-9 expression at both mRNA and protein levels in a concentration-dependent (0-2 µg/mL) manner, as demonstrated by real time RT-PCR, ELISA, and zymography assays. Gene transcription and DNA binding studies demonstrated that rCC16 suppressed LPS-induced NF-κB activation and its binding of gene promoters as identified by luciferase reporter and gel mobility shift assays, respectively. Western blotting and immunofluorescence staining analyses further revealed that rCC16 concentration dependently inhibited the effects of LPS on nuclear increase and cytosol reduction of NF-κB, on the phosphorylation and reduction of NF-κB inhibitory IκBα, and on p38 MAPK-dependent NF-κB activation by phosphorylation at Ser276 of its p65 subunit. These data indicate that inhibition of LPS-mediated NF-κB activation by rCC16 involves both translocation- and phosphorylation-dependent signaling pathways. When the tracheal epithelial cells were pretreated with chlorpromazine, an inhibitor of clathrin-mediated endocytosis, cellular uptake of rCC16 and its inhibition of LPS-induced NF-κB nuclear translocation and also MMP-9 production were significantly abolished. Taken together, our data suggest that clathrin-mediated uptake of rCC16 suppresses LPS-mediated inflammatory MMP-9 production through inactivation of NF-κB and p38 MAPK pathways in tracheal epithelial cells.

Repression of CC16 by cigarette smoke (CS) exposure

Club (Clara) Cell Secretory Protein (CCSP, or CC16) is produced mainly by non-ciliated airway epithelial cells including bronchiolar club cells and the change of its expression has been shown to associate with the progress and severity of Chronic Obstructive Pulmonary Disease (COPD). In an animal model, the lack of CC16 renders the animal susceptible to the tumorigenic effect of a major CS carcinogen. A recent population-based Tucson Epidemiological Study of Airway Obstructive Diseases (TESAOD) has indicated that the low serum CC16 concentration is closely linked with the smoke-related mortality, particularly that driven by the lung cancer. However, the study of CC16 expression in well-defined smoke exposure models has been lacking, and there is no experimental support for the potential causal link between CC16 and CS-induced pathophysiological changes in the lung. In the present study, we have found that airway CC16 expression was significantly repressed in COPD patients, in monkey CS exposure model, and in CS-induced mouse model of COPD. Additionally, the lack of CC16 exacerbated airway inflammation and alveolar loss in the mouse model. Therefore, CC16 may play an important protective role in CS-related diseases.

Gene expression in whole lung and pulmonary macrophages reflects the dynamic pathology associated with airway surface dehydration

Background

Defects in airway mucosal defense, including decreased mucus clearance, contribute to the pathogenesis of human chronic obstructive pulmonary diseases. Scnn1b-Tg mice, which exhibit chronic airway surface dehydration from birth, can be used as a model to study the pathogenesis of muco-obstructive lung disease across developmental stages. To identify molecular signatures associated with obstructive lung disease in this model, gene expression analyses were performed on whole lung and purified lung macrophages collected from Scnn1b-Tg and wild-type (WT) littermates at four pathologically relevant time points. Macrophage gene expression at 6 weeks was evaluated in mice from a germ-free environment to understand the contribution of microbes to disease development.

Results

Development- and disease-specific shifts in gene expression related to Scnn1b over-expression were revealed in longitudinal analyses. While the total number of transgene-related differentially expressed genes producing robust signals was relatively small in whole lung (n = 84), Gene Set Enrichment Analysis (GSEA) revealed significantly perturbed biological pathways and interactions between normal lung development and disease initiation/progression. Purified lung macrophages from Scnn1b-Tg mice exhibited numerous robust and dynamic gene expression changes. The expression levels of Classically-activated (M1) macrophage signatures were significantly altered at post-natal day (PND) 3 when Scnn1b-Tg mice lung exhibit spontaneous bacterial infections, while alternatively-activated (M2) macrophage signatures were more prominent by PND 42, producing a mixed M1-M2 activation profile. While differentially-regulated, inflammation-related genes were consistently identified in both tissues in Scnn1b-Tg mice, there was little overlap between tissues or across time, highlighting time- and tissue-specific responses. Macrophages purified from adult germ-free Scnn1b-Tg mice exhibited signatures remarkably similar to non-germ-free counterparts, indicating that the late-phase macrophage activation profile was not microbe-dependent.

Conclusions

Whole lung and pulmonary macrophages respond independently and dynamically to local stresses associated with airway mucus stasis. Disease-specific responses interact with normal developmental processes, influencing the final state of disease in this model. The robust signatures observed in Scnn1b-Tg lung macrophages highlight their critical role in disease pathogenesis. These studies emphasize the importance of region-, cell-type-, and time-dependent analyses to fully dissect the natural history of disease and the consequences of disease on normal lung development.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-726) contains supplementary material, which is available to authorized users.

Club cell protein 16 and disease progression in chronic obstructive pulmonary disease

RATIONALE

Club (Clara) cell protein 16 (CC-16) is a protein that is synthesized predominantly in the lungs and is detectable in serum. Its expression decreases with lung injury and smoking, and is thus a marker of bronchial cell dysfunction.

OBJECTIVES

To evaluate the possibility of using serum CC-16 as a biomarker for disease progression in chronic obstructive pulmonary disease (COPD).

METHODS

We measured serum CC-16 levels from 4,724 subjects with mild-to-moderate airflow limitation in the Lung Health Study. Using a linear regression model, we determined the relationship of serum CC-16 concentrations to decline in lung function over 9 years. In addition, to determine whether CC-16 plays a major role in the pathogenesis of mild COPD, we exposed CC-16-deficient (-/-) mice to 6 months of cigarette smoke.

MEASUREMENTS AND MAIN RESULTS

Reduced serum concentrations of CC-16 were associated with accelerated decline in FEV1 over 9 years (P < 0.0001), and this association persisted after adjustments for age, sex, race, smoking status, airway reactivity, body mass index, and baseline FEV1 (P = 0.0002). However, CC-16(-/-) mice did not demonstrate an enhanced risk of emphysema or small airway remodeling in response to cigarette smoke.

CONCLUSIONS

Serum CC-16 is associated with disease progression, and may assist in the identification of "rapid progressors." However, the absence of CC-16 does not appear to modify the risk of cigarette-related COPD in mice.

Neonatal hyperoxic exposure persistently alters lung secretoglobins and annexin A1

Altered functions of the lung epithelial surface likely contribute to the respiratory morbidities in infants with bronchopulmonary dysplasia (BPD). Infants with BPD exhibit decreased expressions of secretoglobins (SCGBs), including Clara cell secretory protein (CCSP). Expression of lung SCGB and annexin A1 (ANXA1) is persistently altered in CCSP knockout mice suggesting that CCSP indirectly influences innate immune responses. The present studies tested the hypothesis that neonatal hyperoxic exposure induces deficits in CCSP expression that are associated with persistent alterations in lung SCGB and ANXA1 expression. Newborn C3H/HeN mice were exposed to room air (RA) or 85% O2 from birth and were sacrificed at 14 d or returned to RA for 14 d. Neonatal hyperoxia followed by RA recovery was associated with decreased lung CCSP and SCGB3A1 protein but not mRNA expression. Hyperoxia-induced alterations in the charge characteristics of ANXA1 were unchanged by RA recovery and were associated with elevated lung macrophage numbers. These findings support a model in which hyperoxia-induced alterations in Clara cell function influence lung innate immune function through effects on immunomodulatory proteins. Studies to determine the mechanism(s) by which CCSP alterations affect SCGBs, ANXA1, and innate immune responses in BPD are warranted.

Increased susceptibility to pulmonary Pseudomonas infection in Splunc1 knockout mice

The airway epithelium is the first line of host defense against pathogens. The short palate, lung, and nasal epithelium clone (SPLUNC)1 protein is secreted in respiratory tracts and is a member of the bacterial/permeability increasing (BPI) fold-containing protein family, which shares structural similarities with BPI-like proteins. On the basis of its homology with BPIs and restricted expression of SPLUNC1 in serous cells of submucosal glands and surface epithelial cells of the upper respiratory tract, SPLUNC1 is thought to possess antimicrobial activity in host defense. SPLUNC1 is also reported to have surfactant properties, which may contribute to anti-biofilm defenses. The objective of this study was to determine the in vivo functions of SPLUNC1 following Pseudomonas aeruginosa infection and to elucidate the underlying mechanism by using a knockout (KO) mouse model with a genetic ablation of Splunc1. Splunc1 KO mice showed accelerated mortality and increased susceptibility to P. aeruginosa infection with significantly decreased survival rates, increased bacterial burdens, exaggerated tissue injuries, and elevated proinflammatory cytokine levels as compared with those of their wild-type littermates. Increased neutrophil infiltration in Splunc1 KO mice was accompanied by elevated chemokine levels, including Cxcl1, Cxcl2, and Ccl20. Furthermore, the expression of several epithelial secretory proteins and antimicrobial molecules was considerably suppressed in the lungs of Splunc1 KO mice. The deficiency of Splunc1 in mouse airway epithelium also results in increased biofilm formation of P. aeruginosa. Taken together, our results support that the ablation of Splunc1 in mouse airways affects the mucociliary clearance, resulting in decreased innate immune response during Pseudomonas-induced respiratory infection.

Club cell secretory protein improves survival in a murine obliterative bronchiolitis model

Club cell secretory protein (CCSP) is an indirect phospholipase A2 inhibitor with some immunosuppressive and antiproliferative properties that is expressed in bronchiolar Club cells. In our murine bone marrow transplant (BMT) model of obliterative bronchiolitis (OB), CCSP is diminished; however, its role is unknown. To determine the role of CCSP, B6 wild-type (WT) or CCSP-deficient (CCSP(-/-)) mice were lethally conditioned and given allogeneic bone marrow with a sublethal dose of allogeneic splenic T cells to induce OB. We found that CCSP(-/-) mice demonstrated a higher mortality following BMT-induced OB compared with WT mice. Mice were analyzed 60 days post-BMT for protein expression, pulmonary function, and histology. CCSP levels were reduced in WT mice with BMT-induced OB, and lower levels correlated to decreased lung compliance. CCSP(-/-) had a higher degree of injury and fibrosis as measured by hydroxy proline, along with an increased lung resistance and the inflammatory markers, leukotriene B4 and CXCL1. Replacement with recombinant intravenous CCSP partially reversed the weight loss and improved survival in the CCSP(-/-) mice. In addition, CCSP replacement improved histology and decreased inflammatory cells and markers. These findings indicate that CCSP has a regulatory role in OB and may have potential as a preventive therapy.

Fetal exposure of rhesus macaques to bisphenol a alters cellular development of the conducting airway by changing epithelial secretory product expression

BACKGROUND

Bisphenol A (BPA) exposure early in life results in organizational changes in reproductive organs, but the effect of BPA on conducting airway cellular maturation has not been studied. Late gestation is characterized by active differentiation of secretory cells in the lung epithelium.

OBJECTIVE

We evaluated the hypothesis that BPA exposure disrupts epithelial secretory cell development in the fetal conducting airway of the rhesus macaque.

METHODS

We exposed animals to BPA during either the second (early term) or the third (late term) trimester. There were four treatment groups: a) sham control early term, b) sham control late term, c) BPA early term (BPA-early), and d) BPA late term (BPA-late). Because cellular maturation occurs nonuniformly in the lung, we defined mRNA and protein expression by airway level using microdissection.

RESULTS

BPA exposure of the dam during late term significantly accelerated secretory cell maturation in the proximal airways of the fetus; both Clara cell secretory protein (CCSP) and MUC5AC/5B mRNA and protein expression increased.

CONCLUSIONS

BPA exposure during late gestation accelerates secretory cell maturation in the proximal conducting airways. We identified a critical window of fetal susceptibility for BPA effects on lung epithelial cell maturation in the third trimester. This is of environmental health importance because increases in airway mucins are hallmarks of a number of childhood lung diseases that may be affected by BPA exposure.

Loss of Cftr function exacerbates the phenotype of Na(+) hyperabsorption in murine airways

Airway surface hydration depends on the balance between transepithelial Na(+) absorption and Cl(-) secretion. In adult mice, absence of functional cystic fibrosis transmembrane conductance regulator (Cftr) fails to recapitulate human cystic fibrosis (CF) lung disease. In contrast, overexpression of the epithelial Na(+) channel β subunit in transgenic mice (βENaC-Tg) produces unregulated Na(+) hyperabsorption and results in CF-like airway surface dehydration, mucus obstruction, inflammation, and increased neonatal mortality. To investigate whether the combination of airway Na(+) hyperabsorption and absent Cftr-mediated Cl(-) secretion resulted in more severe lung pathology, we generated double-mutant ΔF508 CF/βENaC-Tg mice. Survival of ΔF508 CF/βENaC-Tg mice was reduced compared with βENaC-Tg or ΔF508 CF mice. Absence of functional Cftr did not affect endogenous or transgenic ENaC currents but produced reduced basal components of Cl(-) secretion and tracheal cartilaginous defects in both ΔF508 CF and ΔF508 CF/βENaC-Tg mice. Neonatal ΔF508 CF/βENaC-Tg mice exhibited higher neutrophilic pulmonary inflammation and club cell (Clara cell) necrosis compared with βENaC-Tg littermates. Neonatal ΔF508 CF/βENaC-Tg mice also exhibited spontaneous bacterial infections, but the bacterial burden was similar to that of βENaC-Tg littermates. Adult ΔF508 CF/βENaC-Tg mice exhibited pathological changes associated with eosinophilic crystalline pneumonia, a phenotype not observed in age-matched βENaC-Tg mice. Collectively, these data suggest that the combined abnormalities in Na(+) absorption and Cl(-) secretion produce more severe lung disease than either defect alone. Airway cartilage abnormalities, airway cell necrosis, and exaggerated neutrophil infiltration likely interact with defective mucus clearance caused by βENaC overexpression and absent CFTR-mediated Cl(-) secretion to produce the increased neonatal mortality observed in ΔF508 CF/βENaC-Tg mice.

Cellular differentiation and proliferation in the ovine lung during gestation and early postnatal development

This study investigates epithelial cell differentiation and proliferation in specific anatomical regions of the ovine lung during prenatal and postnatal development. Immunohistochemistry was used to identify ciliated epithelial cells, Clara cells, neuroepithelial bodies and type II pneumocytes in the lungs of preterm (67, 127 and 140 days of gestation), full-term (147 days) and postnatal (9, 16 and 91 days old) lambs. Differentiation of ciliated epithelial cells was seen at 67 days of gestation and at term for Clara cells. Neuroepithelial bodies were first detected at 127 days of gestation. From 16 to 91 days of age there was a significant (P <0.05) increase in beta-tubulin (present in ciliated epithelial cells) and Clara cell protein (present in Clara cells) in multiple regions of the lung. Detection of Ki67, a marker of proliferation, in preterm lambs showed a reduction in proliferation index in multiple anatomical regions of the lung between 70 days of gestation and term. Cell proliferation increased following parturition, and then decreased between 16 and 91 days of age, with the largest reduction occurring in the alveolar compartment. Knowledge of which cells are present at specific times of lung development provides valuable information on the anatomy of the ovine lung, improving its use as a model for ovine and human neonatal disease. In addition, the antibodies used here will be valuable for future studies requiring the identification and quantification of respiratory epithelial cell phenotypes in the sheep lung.

Cell-specific oxidative stress and cytotoxicity after wildfire coarse particulate matter instillation into mouse lung

Our previous work has shown that coarse particulate matter (PM(10-2.5)) from wildfire smoke is more toxic to lung macrophages on an equal dose (by mass) basis than coarse PM isolated from normal ambient air, as evidenced by decreased numbers of macrophages in lung lavage fluid 6 and 24hours after PM instillation into mouse lungs in vivo and by cytotoxicity to a macrophage cell line observed directly in vitro. We hypothesized that pulmonary macrophages from mice instilled with wildfire coarse PM would undergo more cytotoxicity than macrophages from controls, and that there would be an increase in oxidative stress in their lungs. Cytotoxicity was quantified as decreased viable macrophages and increased percentages of dead macrophages in the bronchoalveolar lavage fluid (BALF) of mice instilled with wildfire coarse PM. At 1hour after PM instillation, we observed both decreased numbers of viable macrophages and increased dead macrophage percentages as compared to controls. An increase in free isoprostanes, an indicator of oxidative stress, from control values of 28.1±3.2pg/mL to 83.9±12.2pg/mL was observed a half-hour after PM instillation. By 1hour after PM instillation, isoprostane values had returned to 30.4±7.6pg/mL, not significantly different from control concentrations. Lung sections from mice instilled with wildfire coarse PM showed rapid Clara cell responses, with decreased intracellular staining for the Clara cell secretory protein CCSP 1hour after wildfire PM instillation. In conclusion, very rapid cytotoxicity occurs in pulmonary macrophages and oxidative stress responses are seen 0.5-1hour after wildfire coarse PM instillation. These results define early cellular and biochemical events occurring in vivo and support the hypothesis that oxidative stress-mediated macrophage toxicity plays a key role in the initial response of the mouse lung to wildfire PM exposure.

Genes of innate immunity and the biological response to inhaled ozone

Ambient ozone has a significant impact on human health. We have made considerable progress in understanding the fundamental mechanisms that regulate the biological response to ozone. It is increasingly clear that genes of innate immunity play a central role in both infectious and noninfectious lung disease. The biological response to ambient ozone provides a clinically relevant environmental exposure that allows us to better understand the role of innate immunity in noninfectious airways disease. In this brief review, we focus on (1) specific cell types in the lung modified by ozone, (2) ozone and oxidative stress, (3) the relationship between genes of innate immunity and ozone, (4) the role of extracellular matrix in reactive airways disease, and (5) the effect of ozone on the adaptive immune system. We summarize recent advances in understanding the mechanisms that ozone contributes to environmental airways disease.

Alleviation of lung inflammatory responses by adeno-associated virus 2/9 vector carrying CC10 in OVA-sensitized mice

Asthma is a chronic airway inflammatory disease characterized by eosinophilic infiltration and airway hyperresponsiveness. The over-activated Th2 and lung epithelium cells express many different cytokines, and chemokines mainly contribute to the severity of lung inflammation. Clara cell 10 kD protein (CC10) is highly expressed in airway epithelium cells and exhibits anti-inflammatory and immunomodulatory effects. Adeno-associated virus (AAV) 2/9 vector, composed of AAV2 rep and AAV9 cap genes, can efficiently and specifically target lung epithelium cells. Thus, AAV2/9 vector might carry therapeutic potential gene sequences for the treatment of asthma. This study tested whether AAV2/9 vector carrying CC10 could reduce inflammatory and asthmatic responses in OVA-induced asthmatic mouse model. The results showed that AAV2/9-CC10 vector virus significantly reduced airway hyperresponsiveness, CCL11, interleukin (IL)-4, IL-5, IL-6, IL-13, and eosinophilia in the lungs of sensitized mice. CC10 level in OVA-sensitized mice was rescued with the administration of AAV2/9-CC10 vector virus. Lung tissue remodeling, including collagen deposition and goblet cell hyperplasia, was also alleviated. However, serum levels of OVA-specific IgG1 and IgE as well as Th2 cytokine levels in OVA-stimulated splenocyte culture supernatants were at the comparable levels to the sensitized control group. The results demonstrate that AAV2/9-CC10 vector virus relieved local inflammatory and asthmatic responses in lung. Therefore, we propose that AAV2/9-CC10 vector virus guaranteed sufficient CC10 expression and had an anti-inflammatory effect in asthmatic mice. It might be applied as a novel therapeutic approach for asthma.

Epithelial clara cell injury occurs in bronchiolitis obliterans syndrome after human lung transplantation

Bronchiolitis obliterans syndrome (BOS) is a condition of progressive airflow obstruction that affects a majority of lung transplant recipients and limits long-term posttransplant survival. Although epithelial injury appears central to the development of BOS, little is known regarding the specific epithelial cell types that are affected in this condition. We hypothesized that BOS would involve preferential injury to the secretory Clara cells that function in innate defense and epithelial repair. To test this hypothesis, we assessed tissue transcript, tissue protein and lung fluid protein expression of Clara cell secretory protein (CCSP), a marker for Clara cells, in lung transplant recipients with BOS, BOS-free patients and in donor controls. Our results demonstrate that CCSP tissue transcript and protein expression are significantly reduced in lung transplant recipients with BOS compared to BOS-free or donor controls. In addition, we demonstrate that CCSP protein levels are significantly reduced in the lung fluid of patients with BOS compared to BOS-free controls, in cross-sectional and longitudinal analysis. Collectively, these complementary results illustrate that BOS involves a selective alteration in the distribution and function of bronchiolar Clara cells.

Lipopolysaccharide-induced cyclooxygenase-2 expression in mouse transformed Clara cells

BACKGROUND/AIMS

Exacerbation of innate immune responses can contribute to development of acute lung injury. Multiple cell populations, including the bronchiolar epithelium, coordinate these inflammatory responses. Clara cells, non-ciliated epithelial cells, are located in the distal airways in humans and conducting airways in mice. These cells actively participate in innate immune responses but their precise contributions remain poorly defined.

METHODS

To test the hypothesis that E. coli lipopolysaccaride (LPS) treatment stimulates production of pro-inflammatory mediators in mouse transformed Clara cells (MTCC), MTCC were treated with E. coli lipopolysaccaride (LPS).

RESULTS

LPS increased COX-2 expression and stimulated production of prostaglandins, including prostaglandin E(2) (PGE(2)). Enhanced mitogen activated protein kinase (MAPK) activation, nuclear factor-κB (NFκB) activation, and chemokine production were observed in MTCC in response to LPS treatment.

CONCLUSIONS

While the role for Clara cells in the regulation of host defense and the progression of acute lung injury needs further characterization, our data suggests the importance of this unique cell population in the pathogenesis of LPS-induced acute lung injury.

RNA-Seq quantification of the human small airway epithelium transcriptome

Background

The small airway epithelium (SAE), the cell population that covers the human airway surface from the 6^th generation of airway branching to the alveoli, is the major site of lung disease caused by smoking. The focus of this study is to provide quantitative assessment of the SAE transcriptome in the resting state and in response to chronic cigarette smoking using massive parallel mRNA sequencing (RNA-Seq).

Results

The data demonstrate that 48% of SAE expressed genes are ubiquitous, shared with many tissues, with 52% enriched in this cell population. The most highly expressed gene, SCGB1A1, is characteristic of Clara cells, the cell type unique to the human SAE. Among other genes expressed by the SAE are those related to Clara cell differentiation, secretory mucosal defense, and mucociliary differentiation. The high sensitivity of RNA-Seq permitted quantification of gene expression related to infrequent cell populations such as neuroendocrine cells and epithelial stem/progenitor cells. Quantification of the absolute smoking-induced changes in SAE gene expression revealed that, compared to ubiquitous genes, more SAE-enriched genes responded to smoking with up-regulation, and those with the highest basal expression levels showed most dramatic changes. Smoking had no effect on SAE gene splicing, but was associated with a shift in molecular pattern from Clara cell-associated towards the mucus-secreting cell differentiation pathway with multiple features of cancer-associated molecular phenotype.

Conclusions

These observations provide insights into the unique biology of human SAE by providing quantit-ative assessment of the global transcriptome under physiological conditions and in response to the stress of chronic cigarette smoking.