Keratinocyte growth factor protects against Clara cell injury induced by naphthalene

Exposure to polyhexamethyleneguanidine phosphate in early life dampens pulmonary damage compared to adult mice

Polyhexamethyleneguanidine phosphate (PHMG-P) is a biocide of guanidine family that can cause a fatal lung damage if exposed directly to the lungs. No reports exist regarding the toxicity of PHMG-P in neonatal animals. Therefore, this study aimed to determine PHMG-P toxicity in neonatal and 8-week-old mice after they were intranasally instilled with 1.5 mg/kg, 3 mg/kg, and 4.5 mg/kg PHMG-P. PHMG-P lung exposure resulted in more severe pulmonary toxicity in adult mice than in newborn mice. In the high-dose group of newborn mice, a minimal degree of inflammatory cell infiltration and fibrosis in the lung were detected, whereas more severe pathological lesions including granulomatous inflammation, fibrosis, and degeneration of the bronchiolar epithelium were observed in adult mice. At day 4, C-C motif chemokine ligand 2 (CCL2), a potent chemokine for monocytes, was upregulated but recovered to normal levels at day 15 in newborn mice. However, increased CCL2 and IL-6 levels were sustained at day 15 in adult mice. When comparing the differentially expressed genes of newborn and adult mice through RNA-seq analysis, there were expression changes in several genes associated with inflammation in neonates that were similar or different from those in adults. Although no significant lung damage occurred in newborns, growth inhibition was observed which was not reversed until the end of the experiment. Further research is needed to determine how growth inhibition from neonatal exposure to PHMG-P affects adolescent and young adult health.

Longitudinal association of polycyclic aromatic hydrocarbons and genetic risk with lung function

To quantify the association of polycyclic aromatic hydrocarbons (PAHs) and the polygenic risk score (PRS) with lung function decline, we developed a repeated-measures study with 4681 observations from baseline and 6-year follow-up of the Wuhan-Zhuhai cohort. Lung function and urinary monohydroxylated PAH metabolites (OH-PAHs) were measured for each observation. The PRS was derived from 246 lung function-associated genetic variants weighted by the effect size of the decreasing ratio of forced expiratory volume in 1 s by forced vital capacity (FEV1/FVC). Linear mixed models were used to estimate the longitudinal exposure-response relationships between OH-PAHs and lung function, and to evaluate the interactions between OH-PAHs and PRS on the longitudinal change of lung function. We found that each 1-unit increase in log-transformed values of 9-hydroxyfluorene, 2-hydroxyfluorene, 4-hydroxyphenanthrene, 9-hydroxyphenanthrene, 2-hydroxyphenanthrene, 1-hydroxyphenanthrene, 1-hydroxypyrene, low molecular weight OH-PAHs (ΣLMW-OH-PAHs), and total OH-PAHs (ΣOH-PAHs) was associated with an annual change in FEV1/FVC of -0.140, -0.112, -0.260, -0.300, -0.159, -0.220, -0.145, -0.156, and -0.177 %/year, respectively. Interactions on the annual decline of FEV1/FVC were detected between ΣLMW-OH-PAHs and PRS (-0.010 %/year, 95% confidence interval -0.018 to -0.001, Pint = 0.0228), and between ΣOH-PAHs and PRS (-0.010 %/year, -0.018 to -0.001, Pint = 0.0203). These results indicated that specific and total urinary OH-PAHs were associated with the longitudinal FEV1/FVC decline, and ΣLMW-OH-PAHs as well as ΣOH-PAHs interacted with PRS on the annual decline of FEV1/FVC.

Lung epithelial cell-derived C3 protects against pneumonia-induced lung injury

The complement component C3 is a fundamental plasma protein for host defense, produced largely by the liver. However, recent work has demonstrated the critical importance of tissue-specific C3 expression in cell survival. Here, we analyzed the effects of local versus peripheral sources of C3 expression in a model of acute bacterial pneumonia induced by Pseudomonas aeruginosa. Whereas mice with global C3 deficiency had severe pneumonia-induced lung injury, those deficient only in liver-derived C3 remained protected, comparable to wild-type mice. Human lung transcriptome analysis showed that secretory epithelial cells, such as club cells, express high levels of C3 mRNA. Mice with tamoxifen-induced C3 gene ablation from club cells in the lung had worse pulmonary injury compared with similarly treated controls, despite maintaining normal circulating C3 levels. Last, in both the mouse pneumonia model and cultured primary human airway epithelial cells, we showed that stress-induced death associated with C3 deficiency parallels that seen in Factor B deficiency rather than C3a receptor deficiency. Moreover, C3-mediated reduction in epithelial cell death requires alternative pathway component Factor B. Thus, our findings suggest that a pathway reliant on locally derived C3 and Factor B protects the lung mucosal barrier.

Effect of Club cell secretory proteins on the association of tobacco smoke and PAH co-exposure with lung function decline: A longitudinal observation of Chinese coke oven workers

BACKGROUND

Exposure to polycyclic aromatic hydrocarbons (PAH) and tobacco smoke is associated with epithelial damage and reduced lung function. Club cell secretory protein (CC16) is a known biomarker for lung epithelial cells. However, the potential relationships between PAH and tobacco smoke exposure, CC16 levels, and reduced lung function remain unclear.

OBJECTIVES

This longitudinal study aimed to explore the potential role of CC16 in the association of tobacco smoke and PAH co-exposure with lung function.

METHODS

We enrolled 313 workers from a coking plant in China in 2014 and followed them up in 2019. The concentrations of PAH and nicotine metabolites in urine were determined using high-performance liquid chromatography (HPLC) with a fluorescence detector and HPLC-tandem mass spectrometry, respectively. The plasma CC16 concentration was determined using an enzyme-linked immunosorbent assay.

RESULTS

An analysis of the generalized estimating equation showed that each 1-unit increase in log-transformation of the last tertile of trans-3'-hydroxycotinine (3HC) was associated with a 3.30 ng/ml decrease in CC16. Restricted cubic spline analysis revealed a significant nonlinear dose-effect association between cotinine (COT) and CC16 (P_nonlinear = 0.018). In the low- CC16 subgroup, we found a significant association between total nicotine metabolites and forced vital capacity (FVC%) (β: 1.45, 95% CI: 2.87, -0.03), and the associations of nicotine (NIC), COT, and 3HC with FVC% were all of marginal significance. High levels of total hydroxyl polycyclic aromatic hydrocarbons (ΣOH-PAH) and NIC in the urine had an interactive effect on the decline of CC16 (P < 0.05). Cross-lagged panel analysis indicated that the decrease in CC16 preceded the decrease in FVC%. CC16 mediated the association between elevated nicotine metabolites and decreased FVC% in the low- CC16 subgroup.

CONCLUSIONS

CC16 plays an essential role in the association of PAH and tobacco smoke exposure with reduced lung function. Coke oven workers with low plasma CC16 levels are more likely to experience decreased lung function after tobacco smoke exposure.

Neonatal lung-derived SSEA-1+ cells exhibited distinct stem/progenitor characteristics and organoid developmental potential

Stem/progenitor cells, because of their self-renewal and multiple cell type differentiation abilities, have good potential in regenerative medicine. We previously reported a lung epithelial cell population that expressed the stem cell marker SSEA-1 was abundant in neonatal but scarce in adult mice. In the current study, neonatal and adult mouse-derived pulmonary SSEA-1⁺ cells were isolated for further characterization. The results showed that neonatal-derived pulmonary SSEA-1⁺ cells highly expressed lung development-associated genes and had enhanced organoid generation ability compared with the adult cells. Neonatal pulmonary SSEA-1⁺ cells generated airway-like and alveolar-like organoids, suggesting multilineage cell differentiation ability. Organoid generation of neonatal but not adult pulmonary SSEA-1⁺ cells was enhanced by fibroblast growth factor 7 (FGF 7). Furthermore, neonatal pulmonary SSEA-1⁺ cells colonized and developed in decellularized and injured lungs. These results suggest the potential of lung-derived neonatal-stage SSEA-1⁺ cells with enhanced stem/progenitor activity and shed light on future lung engineering applications.

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Pulmonary SSEA-1⁺ cells are abundant in neonatal and scarce in adult stages

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The stem/progenitor activity of pulmonary SSEA-1⁺ cells is enhanced in neonatal stage

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Neonatal pulmonary SSEA-1⁺ cells developed into airway- and alveolar-like organoids

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FGF7 regulates alveolar epithelium development of neonatal pulmonary SSEA-1⁺ cells

R-Spondin2, a Positive Canonical WNT Signaling Regulator, Controls the Expansion and Differentiation of Distal Lung Epithelial Stem/Progenitor Cells in Mice

The lungs have a remarkable ability to regenerate damaged tissues caused by acute injury. Many lung diseases, especially chronic lung diseases, are associated with a reduced or disrupted regeneration potential of the lungs. Therefore, understanding the underlying mechanisms of the regenerative capacity of the lungs offers the potential to identify novel therapeutic targets for these diseases. R-spondin2, a co-activator of WNT/β-catenin signaling, plays an important role in embryonic murine lung development. However, the role of Rspo2 in adult lung homeostasis and regeneration remains unknown. The aim of this study is to determine Rspo2 function in distal lung stem/progenitor cells and adult lung regeneration. In this study, we found that robust Rspo2 expression was detected in different epithelial cells, including airway club cells and alveolar type 2 (AT2) cells in the adult lungs. However, Rspo2 expression significantly decreased during the first week after naphthalene-induced airway injury and was restored by day 14 post-injury. In ex vivo 3D organoid culture, recombinant RSPO2 promoted the colony formation and differentiation of both club and AT2 cells through the activation of canonical WNT signaling. In contrast, Rspo2 ablation in club and AT2 cells significantly disrupted their expansion capacity in the ex vivo 3D organoid culture. Furthermore, mice lacking Rspo2 showed significant defects in airway regeneration after naphthalene-induced injury. Our results strongly suggest that RSPO2 plays a key role in the adult lung epithelial stem/progenitor cells during homeostasis and regeneration, and therefore, it may be a potential therapeutic target for chronic lung diseases with reduced regenerative capability.

CARM1 regulates senescence during airway epithelial cell injury in COPD pathogenesis

Chronic obstructive pulmonary disease (COPD) is a life-threatening lung disease. Although cigarette smoke was considered the main cause of development, the heterogeneous nature of the disease leaves it unclear whether other factors contribute to the predisposition or impaired regeneration response observed. Recently, epigenetic modification has emerged to be a key player in the pathogenesis of COPD. The addition of methyl groups to arginine residues in both histone and nonhistone proteins by protein arginine methyltransferases (PRMTs) is an important posttranslational epigenetic modification event regulating cellular proliferation, differentiation, apoptosis, and senescence. Here, we hypothesize that coactivator-associated arginine methyltransferase-1 (CARM1) regulates airway epithelial cell injury in COPD pathogenesis by controlling cellular senescence. Using the naphthalene (NA)-induced mouse model of airway epithelial damage, we demonstrate that loss of CC10-positive club cells is accompanied by a reduction in CARM1-expressing cells of the airway epithelium. Furthermore, Carm1 haploinsuffficent mice showed perturbed club cell regeneration following NA treatment. In addition, CARM1 reduction led to decreased numbers of antisenescent sirtuin 1-expressing cells accompanied by higher p21, p16, and β-galactosidase-positive senescent cells in the mouse airway following NA treatment. Importantly, CARM1-silenced human bronchial epithelial cells showed impaired wound healing and higher β-galactosidase activity. These results demonstrate that CARM1 contributes to airway repair and regeneration by regulating airway epithelial cell senescence.

A systems immunology approach identifies the collective impact of 5 miRs in Th2 inflammation

Allergic asthma is a chronic inflammatory disease dominated by a CD4+ T helper 2 (Th2) cell signature. The immune response amplifies in self-enforcing loops, promoting Th2-driven cellular immunity and leaving the host unable to terminate inflammation. Posttranscriptional mechanisms, including microRNAs (miRs), are pivotal in maintaining immune homeostasis. Since an altered expression of various miRs has been associated with T cell-driven diseases, including asthma, we hypothesized that miRs control mechanisms ensuring Th2 stability and maintenance in the lung. We isolated murine CD4+ Th2 cells from allergic inflamed lungs and profiled gene and miR expression. Instead of focusing on the magnitude of miR differential expression, here we addressed the secondary consequences for the set of molecular interactions in the cell, the interactome. We developed the Impact of Differential Expression Across Layers, a network-based algorithm to prioritize disease-relevant miRs based on the central role of their targets in the molecular interactome. This method identified 5 Th2-related miRs (mir27b, mir206, mir106b, mir203, and mir23b) whose antagonization led to a sharp reduction of the Th2 phenotype. Overall, a systems biology tool was developed and validated, highlighting the role of miRs in Th2-driven immune response. This result offers potentially novel approaches for therapeutic interventions.

Cholesterol metabolism promotes B-cell positioning during immune pathogenesis of chronic obstructive pulmonary disease

The development of chronic obstructive pulmonary disease (COPD) pathogenesis remains unclear, but emerging evidence supports a crucial role for inducible bronchus-associated lymphoid tissue (iBALT) in disease progression. Mechanisms underlying iBALT generation, particularly during chronic CS exposure, remain to be defined. Oxysterol metabolism of cholesterol is crucial to immune cell localization in secondary lymphoid tissue. Here, we demonstrate that oxysterols also critically regulate iBALT generation and the immune pathogenesis of COPD In both COPD patients and cigarette smoke (CS)-exposed mice, we identified significantly upregulated CH25H and CYP7B1 expression in airway epithelial cells, regulating CS-induced B-cell migration and iBALT formation. Mice deficient in CH25H or the oxysterol receptor EBI2 exhibited decreased iBALT and subsequent CS-induced emphysema. Further, inhibition of the oxysterol pathway using clotrimazole resolved iBALT formation and attenuated CS-induced emphysema in vivo therapeutically. Collectively, our studies are the first to mechanistically interrogate oxysterol-dependent iBALT formation in the pathogenesis of COPD, and identify a novel therapeutic target for the treatment of COPD and potentially other diseases driven by the generation of tertiary lymphoid organs.

Urinary polycyclic aromatic hydrocarbon metabolites, Club cell secretory protein and lung function

BACKGROUND

Exposure to polycyclic aromatic hydrocarbons (PAHs) has been associated with lung function decline. However, the underlying mechanisms for the association remain unclear.

OBJECTIVES

To explore potential role of a lung epithelial biomarker, Club cell secretory protein (CC16), in associations between PAH exposures and lung function decline.

METHODS

We investigated 3384 adults from the Wuhan-Zhuhai cohort, and followed up at three years after first examination. Linear mixed models was used to quantify dose-response relationships between urinary monohydroxylated PAH metabolites (OH-PAHs) and lung function, as well as OH-PAHs and plasma CC16. Mediation analysis was conducted to investigate role of CC16 in the association between OH-PAHs and lung function. We also estimated the relationships between OH-PAHs and lung function change in three years among participants with different levels of CC16.

RESULTS

Each 1-unit increase of log-transformed total urinary high and low molecular weight OH-PAHs (∑HMW OH-PAH and ∑LMW OH-PAHs) were associated with a 22.59 and 25.25ml reduction of FEV₁ respectively, while∑HMW OH-PAH was associated with a 30.38ml reduction of FVC. Moreover, these negative associations between OH-PAHs and lung function levels were significant only among low CC16 group (<15.83ng/ml). CC16 concentration decreased monotonically with increased high molecular weight OH-PAHs (∑HMW OH-PAHs) when ∑HMW OH-PAH concentration was over 0.67μg/mmol Cr. CC16 mediated 22.13% of the association between ∑HMW OH-PAH and FVC among individuals with higher ∑HMW OH-PAH. After three years of follow-up, subjects with low level of plasma CC16 had a significant decline of FVC when exposed to high level of ∑HMW OH-PAH.

CONCLUSIONS

CC16 play an important role in the association between high molecular weight PAHs and FVC. Individuals with low plasma CC16 level might suffer a decline in lung function when exposed to high level of high molecular weight PAHs.

Irritant-induced asthma to hypochlorite in mice due to impairment of the airway barrier

Inhalation of commonly present irritants, such as chlorine and chlorine derivatives, can cause adverse respiratory effects, including irritant-induced asthma (IIA). We hypothesize that due to airway barrier impairment, exposure to hypochlorite (ClO^-) can result in airway hypersensitivity. C57Bl/6 mice received an intra-peritoneal (i.p.) injection of the airway damaging agent naphthalene (NA, 200 mg/kg body weight) or vehicle (mineral oil, MO). In vivo micro-computed tomography (CT) images of the lungs were acquired before and at regular time points after the i.p.

TREATMENT

After a recovery period of 14 days an intranasal (i.n.) challenge with 0.003% active chlorine (in ClO^-) or vehicle (distilled water, H₂O) was given, followed by assessment of the breathing frequency. One day later, pulmonary function, along with pulmonary inflammation was determined. Lung permeability was assessed by means of total broncho-alveolar lavage (BAL) protein content and plasma surfactant protein (SP)-D levels. In vivo micro-CT imaging revealed enlargement of the lungs and airways early after NA treatment, with a return to normal at day 14. When challenged i.n. with ClO^-, NA-pretreated mice immediately responded with a sensory irritant response. Twenty-four hours later, NA/ClO^- mice showed airway hyperreactivity (AHR), accompanied by a neutrophilic and eosinophilic inflammation. NA administration followed by ClO^- induced airway barrier impairment, as shown by increased BAL protein and plasma SP-D concentrations; histology revealed epithelial denudation. These data prove that NA-induced lung impairment renders the lungs of mice more sensitive to an airway challenge with ClO^-, confirming the hypothesis that incomplete barrier repair, followed by irritant exposure results in airway hypersensitivity.

ω-3 Polyunsaturated fatty acids accelerate airway repair by activating FFA4 in club cells

A G protein-coupled receptor (GPCR) named free fatty acid receptor 4 (FFA4, also known as GPR120) was found to act as a GPCR for ω-3 polyunsaturated fatty acids. Its expression has been reported in lung epithelial club cells. We investigated whether supplementation of the ω-3 fatty acids benefits lung health. Omacor (7.75 mg/kg), clinically prescribed preparation of ω-3 fatty acids, and FFA4-knockout mice were utilized in a naphthalene-induced mouse model of acute airway injury (1 injection of 30 mg/kg ip). Naphthalene injection induced complete destruction of bronchiolar epithelial cells within a day. Appearance of bronchiolar epithelial cells was observed after 21 days in control mice. It was found, however, that supplementation of Omacor accelerated the recovery. The appearance of bronchiolar epithelial cells was observed between 7 and 14 days after naphthalene injury in Omacor-treated mice. In isolated club cells, ω-3 fatty acids were found to stimulate cell proliferation and migration but to inhibit cell differentiation. With the use of pharmacological tools and FFA4-knockout mice, FFA4 was found to be responsible for ω-3 fatty acids-induced proliferation in vitro in club cells. Furthermore, accelerated recovery from naphthalene-induced airway injury in Omacor-treated mice was not observed in FFA4-knockout mice in vivo. Present findings indicate that ω-3 fatty acids-induced proliferation of bronchiole epithelial cells through FFA4 is responsible for Omacor-induced accelerated recovery from airway injury. Therefore, intermittent administration of Omacor needs to be tested for acute airway injury because ω-3 fatty acids stimulate proliferation but inhibit differentiation of club cells.

Distal airways are protected from goblet cell metaplasia by diminished expression of IL-13 signalling components

BACKGROUND

Increased mucus production is a critical factor impairing lung function in patients suffering from bronchial asthma, the most common chronic inflammatory lung disease worldwide.

OBJECTIVE

This study aimed at investigating whether goblet cell (GC) metaplasia and mucus production are differentially regulated in proximal and distal airways.

METHODS

Female Balb/c mice were sensitized to ovalbumin (OVA) and challenged with an OVA-aerosol on two consecutive days for 1 week (acute) or 12 weeks (chronic). Real-time RT-PCR analysis was applied on microdissected airways.

RESULTS

In acutely and chronically OVA-challenged mice, GC metaplasia and mucus production were observed in proximal but not in distal airways. In contrast, inflammation reflected by the infiltration of eosinophils and expression of the TH2-type cytokines IL-4 and IL-13 was increased in both proximal and distal airways. Abundance of IL-13Rα1 was lower in distal airways of healthy control mice. Under acute and chronic OVA-exposure, activation of IL-13Rα1-dependent signalling cascade, reflected by Spdef and Foxo3A transcription factors, was attenuated in distal compared to proximal airways.

CONCLUSION AND CLINICAL RELEVANCE

These data indicate that distal airways might be less sensitive to IL-13-induced GC metaplasia and mucus production through lower expression of IL-13Rα1 and attenuated activation of downstream signalling. This might represent a protective strategy to prevent mucus plugging of distal airways and thus impaired ventilation of attached alveoli.

Bronchoalveolar sublineage specification of pluripotent stem cells: effect of dexamethasone plus cAMP-elevating agents and keratinocyte growth factor

Respiratory progenitors can be efficiently generated from pluripotent stem cells (PSCs). However, further targeted differentiation into bronchoalveolar sublineages is still in its infancy, and distinct specifying effects of key differentiation factors are not well explored. Focusing on airway epithelial Clara cell generation, we analyzed the effect of the glucocorticoid dexamethasone plus cAMP-elevating agents (DCI) on the differentiation of murine embryonic and induced pluripotent stem cells (iPSCs) into bronchoalveolar epithelial lineages, and whether keratinocyte growth factor (KGF) might further influence lineage decisions. We demonstrate that DCI strongly induce expression of the Clara cell marker Clara cell secretory protein (CCSP). While KGF synergistically supports the inducing effect of DCI on alveolar markers with increased expression of surfactant protein (SP)-C and SP-B, an inhibitory effect on CCSP expression was shown. In contrast, neither KGF nor DCI seem to have an inducing effect on ciliated cell markers. Furthermore, the use of iPSCs from transgenic mice with CCSP promoter-dependent lacZ expression or a knockin of a YFP reporter cassette in the CCSP locus enabled detection of derivatives with Clara cell typical features. Collectively, DCI was shown to support bronchoalveolar specification of mouse PSCs, in particular Clara-like cells, and KGF to inhibit bronchial epithelial differentiation. The targeted in vitro generation of Clara cells with their important function in airway protection and regeneration will enable the evaluation of innovative cellular therapies in animal models of lung diseases.

Angiogenesis and vascular remodeling in chronic airway diseases

Asthma and chronic obstructive pulmonary disease remain a global health problem, with increasing morbidity and mortality. Despite differences in the causal agents, both diseases exhibit various degrees of inflammatory changes, structural alterations of the airways leading to airflow limitation. The existence of transient disease phenotypes which overlap both diseases and which progressively decline the lung function has complicated the search for an effective therapy. Important characteristics of chronic airway diseases include airway and vascular remodeling, of which the molecular mechanisms are complex and poorly understood. Recently, we and others have shown that airway smooth muscle (ASM) cells are not only structural and contractile components of airways, rather they bear capabilities of producing large number of pro-inflammatory and mitogenic factors. Increase in size and number of blood vessels both inside and outside the smooth muscle layer as well as hyperemia of bronchial vasculature are contributing factors in airway wall remodeling in patients with chronic airway diseases, proposing for the ongoing mechanisms like angiogenesis and vascular dilatation. We believe that vascular changes directly add to the airway narrowing and hyper-responsiveness by exudation and transudation of proinflammatory mediators, cytokines and growth factors; facilitating trafficking of inflammatory cells; causing oedema of the airway wall and promoting ASM accumulation. One of the key regulators of angiogenesis, vascular endothelial growth factor in concerted action with other endothelial mitogens play pivotal role in regulating bronchial angiogenesis. In this review article we address recent advances in pulmonary angiogenesis and remodelling that contribute in the pathogenesis of chronic airway diseases.

Cigarette smoke-induced disruption of bronchial epithelial tight junctions is prevented by transforming growth factor-β

The airway epithelium constitutes an essential immunological and cytoprotective barrier to inhaled insults, such as cigarette smoke, environmental particles, or viruses. Although bronchial epithelial integrity is crucial for airway homeostasis, defective epithelial barrier function contributes to chronic obstructive pulmonary disease (COPD). Tight junctions at the apical side of epithelial cell-cell contacts determine epithelial permeability. Cigarette smoke exposure, the major risk factor for COPD, is suggested to impair tight junction integrity; however, detailed mechanisms thereof remain elusive. We investigated whether cigarette smoke extract (CSE) and transforming growth factor (TGF)-β1 affected tight junction integrity. Exposure of human bronchial epithelial cells (16HBE14o(-)) and differentiated primary human bronchial epithelial cells (pHBECs) to CSE significantly disrupted tight junction integrity and barrier function. Specifically, CSE decreased transepithelial electrical resistance (TEER) and tight junction-associated protein levels. Zonula occludens (ZO)-1 and ZO-2 protein levels were significantly reduced and dislocated from the cell membrane, as observed by fractionation and immunofluorescence analysis. These findings were reproduced in isolated bronchi exposed to CSE ex vivo, as detected by real-time quantitative reverse-transcriptase PCR and immunohistochemistry. Combined treatment of 16HBE14o(-) cells or pHBECs with CSE and TGF-β1 restored ZO-1 and ZO-2 levels. TGF-β1 cotreatment restored membrane localization of ZO-1 and ZO-2 protein and prevented CSE-mediated TEER decrease. In conclusion, CSE led to the disruption of tight junctions of human bronchial epithelial cells, and TGF-β1 counteracted this CSE-induced effect. Thus, TGF-β1 may serve as a protective factor for bronchial epithelial cell homeostasis in diseases such as COPD.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Mechanistic insights into the contribution of epithelial damage to airway remodeling. Novel therapeutic targets for asthma

It has been suggested that an inherent airway epithelial repair defect is the root cause of airway remodeling in asthma. However, the relationship between airway epithelial injury and repair, airway remodeling, and airway hyperresponsiveness (AHR) has not been directly examined. We investigated the contribution of epithelial damage and repair to the development of airway remodeling and AHR using a validated naphthalene (NA)-induced murine model of airway injury. In addition, we examined the endogenous versus exogenous role of the epithelial repair peptide trefoil factor 2 (TFF2) in disease pathogenesis. A single dose of NA (200 mg/kg in 10 ml/kg body weight corn oil [CO] vehicle, intraperitoneally) was administered to mice. Control mice were treated with CO (10 ml/kg body weight, intraperitoneally). At 12, 24, 48, and 72 hours after NA or CO injection, AHR and various measures of airway remodeling were examined by invasive plethysmography and morphometric analyses, respectively. TFF2-deficient mice and intranasal treatment were used to examine the role of the epithelial repair peptide. NA treatment induced denudation and apoptosis of airway epithelial cells, goblet cell metaplasia, elevated AHR, and increased levels of endogenous TFF2. Airway epithelial changes peaked at 12 hours after NA treatment, whereas airway remodeling changes were observed from 48 hours. TFF2 was protective against epithelial damage and induced remodeling and was found to mediate organ protection via a platelet-derived growth factor-associated mechanism. Our findings directly demonstrate the contribution of epithelial damage to airway remodeling and AHR and suggest that preventing airway epithelial damage and promoting epithelial repair may have therapeutic implications for asthma treatment.

Repair of naphthalene-induced acute tracheal injury by basal cells depends on β-catenin

OBJECTIVES

Little is known about the role of Wnt/β-catenin in postnatal airway homeostasis and basal cell function. This study aimed to investigate the role of Wnt signaling in the self-renewal of basal cells and the involvement of β-catenin in tracheal repair after naphthalene-induced injury.

METHODS

Mice were treated with naphthalene and injected with 4-hydroxytamoxifen. Injury and repair of the tracheal epithelium after naphthalene-mediated secretory cell depletion was assessed by a immunohistochemical study. The involvement of Wnt and β-catenin signaling in basal cell proliferation was investigated during in vitro expansion.

RESULTS

Immunohistochemical analysis of tracheal epithelium in wild-type mice showed a reduction in the number of Clara cell secretory protein (CCSP+) and forkhead box transcription factor (Fox-J1+) cells on days 2 to 5 after naphthalene-induced injury; this cell population was regenerated by day 10. After flush labeling, bromodeoxyuridine-positive (BrdU+) cells and Ki67+ cells were observed in tracheal epithelium on days 2 to 5 but not on days 10 and 21. Confocal microscopy visualizing K5+ and BrdU+ cells showed that Wnt3a promotes proliferation of K5+ cells. Immunohistochemical analysis of K5+ and CCSP+ in tracheal epithelial cells from wild-type littermate and K5-Cre-mediated β-catenin knock-out mice showed that on day 3, the number of CCSP+ cells was decreased in all mice. On day 10, CCSP+ cells were present in wild-type littermate mice but absent in conditional knock-out mice.

CONCLUSIONS

Basal cells serve as stem cells in the tracheal epithelium, regenerating and maintaining tracheal epithelial cells in a mouse model of tracheal injury. β-Catenin is required for proliferation and self-renewal of tracheal epithelial cells.

Aerosol delivery of kinase-deficient Akt1 attenuates Clara cell injury induced by naphthalene in the lungs of dual luciferase mice

Conventional lung cancer therapies are associated with poor survival rates; therefore, new approaches such as gene therapy are required for treating cancer. Gene therapies for treating lung cancer patients can involve several approaches. Among these, aerosol gene delivery is a potentially more effective approach. In this study, Akt1 kinase-deficient (KD) and wild-type (WT) Akt1 were delivered to the lungs of CMV-LucR-cMyc-IRES-LucF dual reporter mice through a nose only inhalation system using glucosylated polyethylenimine and naphthalene was administrated to the mice via intraperitoneal injection. Aerosol delivery of Akt1 WT and naphthalene treatment increased protein levels of downstream substrates of Akt signaling pathway while aerosol delivery of Akt1 KD did not. Our results showed that naphthalene affected extracellular signal-regulated kinase (ERK) protein levels, ERK-related signaling, and induced Clara cell injury. However, Clara cell injury induced by naphthalene was considerably attenuated in mice exposed to Akt1 KD. Furthermore, a dual luciferase activity assay showed that aerosol delivery of Akt1 WT and naphthalene treatment enhanced cap-dependent protein translation, while reduced cap-dependent protein translation was observed after delivering Akt1 KD. These studies demonstrated that our aerosol delivery is compatible for in vivo gene delivery.

Nerve growth factor induces type III collagen production in chronic allergic airway inflammation

BACKGROUND

Excessive extracellular matrix deposition occurs as a result of repetitive injury-repair cycles and plays a central role in the pathogenesis of chronic inflammatory diseases, such as allergic asthma. The molecular mechanism leading to aberrant collagen deposition is not fully understood.

OBJECTIVE

We sought to test the hypothesis that increased nerve growth factor (NGF) production contributes to collagen deposition in the airways during chronic allergic airway inflammation.

METHODS

Antibody-blocking experiments were performed in an in vivo model for chronic allergic airway inflammation (allergic asthma), which is accompanied by matrix deposition in the subepithelial compartment of the airways, to study the profibrotic effect of NGF. The signaling pathways were delineated with in vivo and in vitro studies in primary lung fibroblasts.

RESULTS

Functional blocking of NGF in chronically affected mice markedly prevented subepithelial fibrosis. Transgenic overexpression of NGF in murine airways resulted in altered airway wall morphology with increased peribronchial collagen deposition and impaired lung physiology in the absence of inflammation. NGF exerted a direct effect on collagen expression in murine lung fibroblasts, which was mainly mediated through the activation of the receptor tropomyosin-related kinase A. NGF-induced collagen expression was dependent on downstream activation of p38 mitogen-activated protein kinase independent of the TGF-β1/mothers against decapentaplegic homolog (SMAD) pathway.

CONCLUSION

The results of this study demonstrate that NGF exerts profibrotic activities in the airways by inducing type III collagen production in fibroblasts independently of TGF-β1.

A single DH gene segment is sufficient for the establishment of an asthma phenotype in a murine model of allergic airway inflammation

BACKGROUND

We have previously shown that the allergic sensitization to ovalbumin does not represent a superantigen-like immune response. In gene-targeted mice (ΔD-iD) with a single modified Diversity gene segment (D(H)) of the immunoglobulin heavy chain, enriched for charged amino acids, the asthma phenotype in a murine model was markedly alleviated compared to wild-type animals.

OBJECTIVE

We now sought to determine whether the confinement to a single D(H) gene segment alone leads to a reduced allergic phenotype.

METHODS

We examined another gene-targeted mouse strain (ΔD-DFL) with a single D(H) gene segment which encodes for neutral amino acids, thus reflecting the preferential repertoire in wild-type mice. Mice were sensitized intraperitoneally to ovalbumin.

RESULTS

Despite the constraint to a single D(H) gene segment, ΔD-DFL mice mounted high total and allergen-specific IgG(1) and IgE serum levels after sensitization to ovalbumin. The affinity constants of allergen-specific IgG(1) antibodies did not differ between ΔD-DFL and wild type. Following challenge with aerosolized allergen, a marked local T(H)2 cytokine response and an eosinophilic airway inflammation developed. Quantitative histology revealed increased mucus production and intense goblet cell metaplasia which were identical to those in wild type. Moreover, ΔD-DFL mice developed an airway hyperreactivity to methacholine and to the specific allergen, which both did not differ from those in wild-type animals.

CONCLUSION

A single D(H) gene segment is sufficient for the establishment of the asthma phenotype in a murine model of allergic airway inflammation. Thus, the allergic phenotype depends on the amino acid composition and not on the diversity of the classical antigen-binding site.

Molecular model of naphthalene-induced DNA damage in the murine lung

Airway epithelial damage and repair represents a novel therapeutic target in asthma and chronic obstructive pulmonary disease. An established mouse model of airway epithelial damage involves the Clara cell cytotoxicity of parenterally administered naphthalene, an important environmental toxicant with genotoxic and carcinogenic potential. The objective of the current study was to investigate naphthalene-induced toxicity and to identify and quantify DNA double-strand breaks in a murine naphthalene model of airway epithelial damage. Male C57/BL6 mice were injected with 200 mg/kg naphthalene and culled at 12-, 24-, 48- and 72-h time points. Lung function and bronchoalveolar lavage was performed and the lungs were dissected for histological analysis and for quantitation of DNA double-strand breaks using γH2AX as a molecular marker. Mice injected with naphthalene had increased epithelial denudation, bronchoalveolar lavage fluid cellularity and reactivity to nebulized methacholine chloride as compared to corn oil vehicle controls. Histological changes were most pronounced at the 12- and 24-h time points. DNA double-strand breaks, quantitated as the number of γH2AX foci per cell, were highest at the 24- and 48-h time points. All parameters had decreased at the 72-h time point, consistent with airway re-epithelization and cellular repair. Our findings indicate a time-dependent accumulation of γH2AX foci in mouse airway epithelial cells following administration of naphthalene. Naphthalene airway epithelial injury constitutes a model of DNA double-strand breaks in mice, which can be adapted as a suitable model for further investigation of genotoxic damage for evaluating the efficacy of potential therapeutics.

Airway trefoil factor expression during naphthalene injury and repair

While the role of trefoil factors (TFF) in the maintenance of epithelial integrity in the gastrointestinal tract is well known, their involvement in wound healing in the conducting airway is less well understood. We defined the pattern of expression of TFF1, TFF2, and TFF3 in the airways of mice during repair of both severe (300 mg/kg) and moderate (200 mg/kg) naphthalene-induced Clara cell injury. Quantitative real-time PCR for tff messenger RNA expression and immunohistochemistry for protein expression were applied to airway samples obtained by microdissection of airway trees or to fixed lung tissue from mice at 6 and 24 h and 4 and 7 days after exposure to either naphthalene or an oil (vehicle) control. All three TFF were expressed in normal whole lung and airways. TFF2 was the most abundant and was enriched in airways. Injury of the airway epithelium by 300 mg/kg naphthalene caused a significant induction of tff1 gene expression at 24 h, 4 days, and 7 days. In contrast, tff2 was decreased in the high-dose group at 24 h and 4 days but returned to baseline levels by 7 days. tff3 gene expression was not significantly changed at any time point. Protein localization via immunohistochemistry did not directly correlate with the gene expression measurements. TFF1 and TFF2 expression was most intense in the degenerating Clara cells in the injury target zone at 6 and 24 h. Following the acute injury phase, TFF1 and TFF2 were localized to the luminal apices of repairing epithelial cells and to the adjacent mesenchyme in focal regions that correlated with bifurcations and the bronchoalveolar duct junction. The temporal pattern of increases in TFF1, TFF2, and TFF3 indicate a role in cell death as well as proliferation, migration, and differentiation phases of airway epithelial repair.

Pulmonary effects of keratinocyte growth factor in newborn rats exposed to hyperoxia

Acute lung injury and compromised alveolar development characterize bronchopulmonary dysplasia (BPD) of the premature neonate. High levels of keratinocyte growth factor (KGF), a cell-cell mediator with pleiotrophic lung effects, are associated with low BPD risk. KGF decreases mortality in hyperoxia-exposed newborn rodents, a classic model of injury-induced impaired alveolarization, although the pulmonary mechanisms of this protection are poorly defined. These were explored through in vitro and in vivo approaches in the rat. Hyperoxia decreased by 30% the rate of wound closure of a monolayer of fetal alveolar epithelial cells, due to cell death, which was overcome by recombinant human KGF (100 ng/ml). In rat pups exposed to >95% O2 from birth, increased viability induced by intraperitoneal injection of KGF (2 microg/g body wt) every other day was associated with prevention of neutrophil influx in bronchoalveolar lavage (BAL), prevention of decreases in whole lung DNA content and cell proliferation rate, partial prevention of apoptosis increase, and a markedly increased proportion of surfactant protein B-immunoreactive cells in lung parenchyma. Increased lung antioxidant capacity is likely to be due in part to enhanced CAAT/enhancer binding protein alpha expression. By contrast, KGF neither corrected changes induced by hyperoxia in parameters of lung morphometry that clearly indicated impaired alveolarization nor had any significant effect on tissue or BAL surfactant phospholipids. These findings evidence KGF alveolar epithelial cell protection, enhancing effects on alveolar repair capacity, and anti-inflammatory effects in the injured neonatal lung that may account, at least in part, for its ability to reduce mortality. They argue in favor of a therapeutic potential of KGF in the injured neonatal lung.

Acute damage by naphthalene triggers expression of the neuroendocrine marker PGP9.5 in airway epithelial cells

Protein Gene Product 9.5 (PGP9.5) is highly expressed in nervous tissue. Recently PGP9.5 expression has been found to be upregulated in the pulmonary epithelium of smokers and in non-small cell lung cancer, suggesting that it also plays a role in carcinogen-inflicted lung epithelial injury and carcinogenesis. We investigated the expression of PGP9.5 in mice in response to two prominent carcinogens found in tobacco smoke: Naphthalene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). By immunostaining, we found that PGP9.5 protein was highly expressed throughout the airway epithelium in the days immediately following a single injection of naphthalene. In contrast, PGP9.5 was exclusively confined to neurons and neuroendocrine cells in the control and NNK-exposed lungs. Furthermore, we investigated the expression of PGP9.5 mRNA in the lungs by quantitative RT-PCR (qPCR). PGP9.5 mRNA expression was highly upregulated in the days immediately following naphthalene injection and gradually returning to that of control mice 5 days after naphthalene injection. In contrast, exposure to NNK did not result in a significant increase in PGP9.5 mRNA 10 weeks after exposure. No increased expression of two other neuroendocrine markers was found in the non-neuroendocrine epithelial cells after naphthalene exposure. In contrast, immunostaining for the cell cycle regulator p27(Kip1), which has previously been associated with PGP9.5 in lung cancer cells, revealed transient downregulation of p27(Kip1) in naphthalene exposed airways compared to controls, indicating that the rise in PGP9.5 in the airway epithelium is related to downregulation of p27(Kip1). This study is the first to specifically identify the carcinogen naphthalene as an inducer of PGP9.5 expression in non-neuroendocrine epithelium after acute lung injury and further strengthens the accumulating evidence of PGP9.5 as a central player in lung epithelial damage and early carcinogenesis.