Quercetin-Induced Enhancement of Nasal Epithelial Cells' Ability to Produce Clara Cell 10-kD Protein In Vitro and In Vivo

Background: Quercetin, a polyphenolic flavonoid found in various plants and foods, is known to have antioxidant, antiviral and anticancer effects. Although quercetin is well known to exert anti-inflammatory and anti-allergic effects, the precise mechanisms by which quercetin favorably modifies the clinical status of allergic diseases, such as allergic rhinitis (AR), remain unclear. The present study examined whether quercetin could modulate the production of the endogenous anti-inflammatory molecule, Clara cell 10-kD protein (CC10), in vitro and in vivo. Methods: Human nasal epithelial cells (1 × 10⁵ cells/mL) were stimulated with 20 ng/mL of tumor necrosis factor-alpha (TNF) in the presence of quercetin for 24 h. CC10 levels in culture supernatants were examined by ELISA. Sprague Dawley rats were sensitised with toluene 2,4-diisocyanate (TDI) by intranasal instillation of 10% TDI in ethyl acetate at a volume of 5.0 μL once daily for five days. This sensitisation procedure was repeated after an interval of two days. The rats were treated with different dosages of quercetin once daily for five days starting on the 5th day following the second sensitization. Nasal allergy-like symptoms induced by the bilateral application of 5.0 μL of 10% TDI were assessed by counting sneezing and nasal-rubbing behaviours for 10 min immediately after the TDI nasal challenge. The levels of CC10 in nasal lavage fluids obtained 6 h after TDI nasal challenge were examined using ELISA. Results: The treatment of cells with low doses of quercetin (<2.5 μM) scarcely affected TNF-induced CC10 production from nasal epithelial cells. However, the ability of nasal epithelial cells to produce CC10 after TNF stimulation significantly increased on treatment with quercetin doses (>5.0 μM). The oral administration of quercetin (>25 mg/kg) for five days significantly increased the CC10 content in nasal lavage fluids and attenuated the nasal symptoms induced by the TDI nasal challenge. Conclusions: Quercetin inhibits AR development by increasing the ability of nasal epithelial cells to produce CC10.

Club Cell Secretory Protein in Lung Disease: Emerging Concepts and Potential Therapeutics

Club cell secretory protein (CCSP), also known as secretoglobin 1A1 (gene name SCGB1A1), is one of the most abundant proteins in the lung, primarily produced by club cells of the distal airway epithelium. At baseline, CCSP is found in large concentrations in lung fluid specimens and can also be detected in the blood and urine. Obstructive lung diseases are generally associated with reduced CCSP levels, thought to be due to decreased CCSP production or club cell depletion. Conversely, several restrictive lung diseases have been found to have increased CCSP levels both in the lung and in the circulation, likely related to club cell dysregulation as well as increasedlung permeability. Recent studies demonstrate multiple mechanisms by which CCSP dampens acute and chronic lung inflammation. Given these anti-inflammatory effects, CCSP represents a novel potential therapeutic modality in lung disease.

Emerging role of an immunomodulatory protein secretoglobin 3A2 in human diseases

Secretoglobin (SCGB) 3A2 was first identified in 2001 as a protein exhibiting similarities in amino acid sequence and gene structure to SCGB1A1, a multi-functional cytokine-like molecule highly expressed in airway epithelial Club cells that was the first identified and extensively studied member of the SCGB gene superfamily. SCGB3A2 is a small secretory protein of ~10 kDa that forms a dimer and a tetramer. SCGB3A2 is predominantly expressed in airway epithelial Club cells, and has anti-inflammatory, growth factor, anti-fibrotic, and anti-cancer activities that influence various lung diseases. This review summarizes the current understanding of SCGB3A2 biological functions and its role in human diseases with emphasis on its mechanisms of actions and signaling pathway.

Circulating Secretoglobin Family 1A Member 1 (SCGB1A1) Levels as a Marker of Biomass Smoke Induced Chronic Obstructive Pulmonary Disease

Secretoglobin family 1A member 1 (SCGB1A1) alternatively known as club cell protein 16 is a protective pneumo-protein. Decreased serum levels of SCGB1A1 have been associated with tobacco smoke induced chronic obstructive pulmonary disease (TS-COPD). Exposure to biomass smoke (BMS) is an important COPD risk factor among women in low and lower-middle income countries. Therefore, in a cross-sectional study (n = 50/group; total 200 subjects) we assessed serum SCGB1A1 levels in BMS-COPD subjects (11 male, 39 female) compared to TS-COPD (all male) along with TS-CONTROL (asymptomatic smokers, all male) and healthy controls (29 male, 21 female) in an Indian population. Normal and chronic bronchitis like bronchial mucosa models developed at the air–liquid interface using human primary bronchial epithelial cells (3 donors, and three replicates per donor) were exposed to cigarette smoke condensate (CSC; 0.25, 0.5, and 1%) to assess SCGB1A1 transcript expression and protein secretion. Significantly (p < 0.0001) decreased serum SCGB1A1 concentrations (median, interquartile range, ng/mL) were detected in both BMS-COPD (1.6; 1.3–2.4) and TS-COPD (1.8; 1.4–2.5) subjects compared to TS-CONTROL (3.3; 2.9–3.5) and healthy controls (5.1; 4.5–7.2). The levels of SCGB1A1 were positively correlated (r = 0.7–0.8; p < 0.0001) with forced expiratory volume in 1 s, forced vital capacity, their ratios, and exercise capacity. The findings are also consistent within the BMS-COPD sub-group as well. Significantly (p < 0.03) decreased SCGB1A1 concentrations were detected with severity of COPD, dyspnea, quality of life, and mortality indicators. In vitro studies demonstrated significantly (p < 0.05) decreased SCGB1A1 transcript and/or protein levels following CSC exposure. Circulating SCGB1A1 levels may therefore also be considered as a potent marker of BMS-COPD and warrant studies in larger independent cohorts.

Roles of Clara cell 10-kD protein and type 2 innate lymphoid cells in allergic rhinitis

This study examined the potential roles of CC10 (Clara cell 10-kD protein) and ILC2s (type 2 innate lymphoid cells) in allergic rhinitis (AR). After ovalbumin was used to construct the AR model, microarray analysis was performed to reveal the key differentially expressed genes. The phenotypic changes of nasal mucosa were examined by H&E staining. Western blot analysis, qRT-PCR, ELISA and immunohistochemistry were performed to identify the levels of cytokines. The lineage markers (CD127 and CD117) of ILC2s were detected using immunofluorescence. The microarray analysis and qRT-PCR results showed that CC10 overexpression inhibited the expression of A20, BAFF, and IL-4 R in vivo. Also, CC10 overexpression was found to ameliorate the damage of nasal mucosa in AR mice. Investigations revealed that the ILC2s were activated in AR mice and AR patients with high levels of IgE, IgG1, IL-4, IL-5, IL-13, IL-25, and IL-33. Moreover, CD127+ was found to activate ILC2s. However, CC10 overexpression suppressed the activation of ILC2s. In conclusion, this research suggested that CC10 could suppress the activation of ILC2s to attenuate the damage of nasal mucosa and that CD127+ may be a biomarker of the activation of ILC2s in AR mice and AR patients.

Aryl Hydrocarbon Receptor is Essential in the Control of Lung Club Cell Homeostasis

Background

Club cells play an important role in maintaining lung homeostasis and aryl hydrocarbon receptor (AhR) is known to be important in xenobiotic metabolism, but its role in regulating club cells is currently unknown.

Methods

To this end, mice with club cell-specific AhR deficiency were generated and evaluated in a model of antigen (ovalbumin, OVA)-induced airway inflammation for the number of infiltrating inflammatory cells, the levels of cytokines and CC10 and Notch signaling by standard methods.

Results

After OVA sensitization and challenge, Scgb1a1-Cre; Ahr^flox/flox mice showed aggravated levels of pulmonary inflammation with increased levels of inflammatory cells and cytokines 1 day after challenge as compared to those seen in their littermate controls, but in contrast to the littermate controls, no significant change in the levels of CC10 and SP-D was noted in Scgb1a1-Cre; Ahr^flox/flox mice. Surprisingly, 7 days after the challenge, while, as expected, wild-type mice recovered from acute inflammation, significantly increased lymphocytic infiltration was noted in Scgb1a1-Cre; Ahr^flox/flox mice, suggesting their defective mechanism of recovery. Mechanistically, this was due, in part, to the decreased Notch1 signaling and expression of its downstream gene, HES5, while AhR was shown to positively regulate Notch1 expression via its transactivating activity targeting the xenobiotic response element in the promoter region of Notch1 gene.

Conclusion

Under the condition of pulmonary inflammation, AhR is critical in controlling lung club cell homeostasis via targeting Notch1 signaling and the generation of anti-inflammatory mediators.

Crystalline silica particles cause rapid NLRP3-dependent mitochondrial depolarization and DNA damage in airway epithelial cells

BACKGROUND

Respirable crystalline silica causes lung carcinomas and many thousand future cancer cases are expected in e.g. Europe. Critical questions are how silica causes genotoxicity in the respiratory epithelium and if new cases can be avoided by lowered permissible exposure levels. In this study we investigate early DNA damaging effects of low doses of silica particles in respiratory epithelial cells in vitro and in vivo in an effort to understand low-dose carcinogenic effects of silica particles.

RESULTS

We find DNA damage accumulation already after 5-10 min exposure to low doses (5 μg/cm²) of silica particles (Min-U-Sil 5) in vitro. DNA damage was documented as increased levels of γH2AX, pCHK2, by Comet assay, AIM2 induction, and by increased DNA repair (non-homologous end joining) signaling. The DNA damage response (DDR) was not related to increased ROS levels, but to a NLRP3-dependent mitochondrial depolarization. Particles in contact with the plasma membrane elicited a Ser198 phosphorylation of NLRP3, co-localization of NLRP3 to mitochondria and depolarization. FCCP, a mitochondrial uncoupler, as well as overexpressed NLRP3 mimicked the silica-induced depolarization and the DNA damage response. A single inhalation of 25 μg silica particles gave a similar rapid DDR in mouse lung. Biomarkers (CC10 and GPRC5A) indicated an involvement of respiratory epithelial cells.

CONCLUSIONS

Our findings demonstrate a novel mode of action (MOA) for silica-induced DNA damage and mutagenic double strand breaks in airway epithelial cells. This MOA seems independent of particle uptake and of an involvement of macrophages. Our study might help defining models for estimating exposure levels without DNA damaging effects.

The Club Cell Marker SCGB1A1 Downstream of FOXA2 is Reduced in Asthma

Human SCGB1A1 protein has been shown to be significantly reduced in BAL, sputum, and serum from humans with asthma as compared with healthy individuals. However, the mechanism of this reduction and its functional impact have not been entirely elucidated. By mining online datasets, we found that the mRNA of SCGB1A1 was significantly repressed in brushed human airway epithelial cells from individuals with asthma, and this repression appeared to be associated with reduced expression of FOXA2. Consistently, both Scgb1A1 and FoxA2 were downregulated in an ovalbumin-induced mouse model of asthma. Furthermore, compared with wild-type mice, Scgb1a1 knockout mice had increased airway hyperreactivity and inflammation when they were exposed to ovalbumin, confirming the antiinflammatory role of Scgb1a1 in protection against asthma phenotypes. To search for potential asthma-related stimuli of SCGB1A1 repression, we tested T-helper cell type 2 cytokines. Both IL-4 and IL-13 repressed epithelial expression of SCGB1A1 and FOXA2. Importantly, infection of epithelial cells with human rhinovirus similarly reduced expression of these two genes, which suggests that FOXA2 may be the common regulator of SCGB1A1. To establish the causal role of reduced FOXA2 in SCGB1A1 repression, we demonstrated that FOXA2 was required for SCGB1A1 expression at baseline. FOXA2 overexpression was sufficient to drive promoter activity and expression of SCGB1A1 and was also able to restore the repressed SCGB1A1 expression in IL-13-treated or rhinovirus-infected cells. Taken together, these findings suggest that low levels of epithelial SCGB1A1 in asthma are caused by reduced FOXA2 expression.

Spatiotemporal Expression of Three Secretoglobin Proteins, SCGB1A1, SCGB3A1, and SCGB3A2, in Mouse Airway Epithelia

Secretoglobins (SCGBs) are cytokine-like small molecular weight secreted proteins with largely unknown biological functions. Three SCGB proteins, SCGB1A1, SCGB3A1, and SCGB3A2, are predominantly expressed in lung airways. To gain insight into the possible functional relationships among the SCGBs, their protein and mRNA expression patterns were examined in lungs during gestation and in adult mice, using Scgb3a1-null and Scgb3a2-null mice as negative controls, by immunohistochemistry and by qRT-PCR analysis, respectively. The three SCGBs exhibited unique spatiotemporal expression patterns during embryogenesis. The lack of Scgb3a1 or Scgb3a2 did not affect expression of the other Scgb genes as determined by mRNA measurements. Moreover, the lack of Scgb3a1 or Scgb3a2 did not affect development of the pulmonary neuroepithelial bodies during embryogenesis, while the lack of Scgb3a2 may have resulted in slightly fewer ciliated cells than in the wild-type. These results suggest that SCGB1A1, SCGB3A1, and SCGB3A2 each may possess its own unique biological function.

Clara Cell 10 kDa Protein Alleviates Murine Hepatitis Virus Strain 3-Induced Fulminant Hepatitis by Inhibiting Fibrinogen-Like Protein 2 Expression

Background: Fulminant hepatitis (FH) is a serious threat to human life, accompanied by massive and rapid necroinflammation. Kupffer cells, the major immune cell population involved in innate immune responses, are considered to be central for FH. Fibrinogen-like protein 2 (Fgl2) is a pro-coagulant protein that is substantially induced in macrophages upon viral infection, and Fgl2 depletion represses murine hepatitis virus strain 3 (MHV-3) infection. Clara cell 10 kDa (CC10) protein is a secretory protein with anti-inflammatory properties in allergic rhinitis and asthma. However, its mechanisms of action and pathogenic roles in other disease are still unclear. In this study, we aimed to determine the role of CC10 in FH and the regulation of Fgl2 by CC10.

Methods: A mouse FH model was established by peritoneal injection of MHV-3. The mice received CC10 protein through tail vein injection before viral infection. Survival rate, liver function, liver histology, fibrin deposition, and necrosis were examined. The regulatory effect of CC10 on Fgl2 expression was investigated using THP-1 cells and mouse peritoneal macrophages in vitro.

Results: In the mouse FH model induced by MHV-3, the survival rate increased from 0 to 12.5% in the CC10 group compared to that in the saline-only control group. Meanwhile, the levels of ALT and AST in serum were significantly decreased and liver damage was reduced. Furthermore, hepatic Fgl2, TNF-α, and IL-1β expression was obviously downregulated together with fibrin deposition, and hepatocyte apoptosis was reduced after administration of CC10 protein. In vitro, CC10 was found to significantly inhibit the expression of Fgl2 in IFN-γ-treated THP-1 cells and MHV-3-infected mouse peritoneal macrophages by western blot and real-time PCR. However, there was no direct interaction between CC10 and Fgl2 as shown by co-immunoprecipitation. Microarray investigations suggested that HMG-box transcription factor 1 (HBP1) was significantly low in CC10-treated and IFN-γ-primed THP-1 cells. HBP1-siRNA treatment abrogated the inhibitory effect of CC10 on Fgl2 expression in Human Umbilical Vein Endothelial cells (HUVECs).

Conclusion:CC10 protects against MHV-3-induced FH via suppression of Fgl2 expression in macrophages. Such effects may be mediated by the transcription factor HBP1.

Is blaCTX-M-1 Riding the Same Plasmid Among Horses in Sweden and France?

A predominance of the blaCTX-M-1/IncHI1 plasmid combination in horses has been reported in Czech-Republic, Denmark, and The Netherlands. To clarify a possible specific plasmid epidemiology of blaCTX-M-1 in horses in a European perspective, a collection of 74 extended-spectrum beta-lactamase-producing Escherichia coli recovered from diseased horses in France and Sweden during the period 2009-2014 was investigated in respect of their genetic relatedness, plasmid content, and molecular features. Overall, 80% of E. coli isolates from diseased horses harbored blaCTX-M-1 on large IncHI1 plasmids with plasmid sequence type (pST) 2 and pST9 more prevalent in Sweden and France, respectively. In French isolates, IncI1/pST3 plasmids were also identified. The CTX-M-1-producing E. coli belonged principally to the clonal complex 10. ST641, together with its single locus variant, and ST1730 constituted two other major groups. The rep-PCR clustering highlighted a clonal dissemination of E. coli CTX-M-1 producers in different regions of the same country and during several years. The STs found in our isolates were also reported in The Netherlands, suggesting a common source of contamination in Europe, although only further cooperative investigation will clarify this issue. On the other hand, the spread of IncI1/pST3 plasmids among horses constitutes another worrisome issue considering their successful spread in other animal hosts such as chicken or bovines. Monitoring evolution and propagation of antimicrobial resistance in equine environment is a priority to avoid further propagation of antimicrobial resistance mechanisms threatening human and animal health.

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.

Postnatal development of the bronchiolar club cells of distal airways in the mouse lung: stereological and molecular biological studies

Club (Clara) cells are nonciliated secretory epithelial cells present in bronchioles of distal pulmonary airways. So far, no information is available on the postnatal differentiation of club cells by a combination of molecular biological, biochemical, and stereological approaches in the murine lung. Therefore, the present study was designed to investigate the changes in the club cell secretory proteins (CC10, surfactant proteins A, B and D) and club cell abundance within the epithelium of bronchioles of distal airways during the postnatal development of the mouse lung. Perfusion-fixed murine lungs of three developmental stages (newborn, 15-day-old and adult) were used. Frozen, unfixed lungs were used for cryosectioning and subsequent laser-assisted microdissection of bronchiolar epithelial cells and RT-PCR analyses. High resolution analyses of the three-dimensional structures and composition of lung airways were obtained by scanning electron microscopy. Finally, using design-based stereology, the total and average club cell volume and the volume of secretory granules were quantified by light and transmission electron microscopy. Our results reveal that murine club cells are immature at birth and differentiate postnatally. Further, increase of the club cell volume and number of intracellular granules are closely correlated to the total lung volume enlargement. However, secretory granule density was only increased within the first 15 days of postnatal development. The differentiation is accompanied by a decrease in glycogen content, and a close positive relationship between CC10 expression and secretory granule abundance. Taken together, our data are consistent with the concept that the morphological and functional differentiation of club cells is a postnatal phenomenon.

Association between CC10 +38A/G polymorphism and asthma risk: A meta-analysis

OBJECTIVES

A number of studies conducted to assess the association between Clara cell 10-kDa protein (CC10) +38A/G polymorphism and susceptibility to asthma have yielded inconsistent and inconclusive results. In the present study, the possible association was assessed by a meta-analysis.

METHODS

Relevant articles were identified for the period ranging from Jan 1998 up to March 2013. Pooled odds ratios (OR) with 95% confidence intervals (CI) were appropriately derived from fixed effects or random-effects models.

RESULTS

Ten case-control studies with a total of 1529 asthma cases and 2399 controls were included in this meta-analysis. The association between CC10 +38A/G polymorphism and asthma risk was determined in dominant model, recessive model, additive model, and codominant model. In dominant model, CC10 +38A/G polymorphism seemed to be associated with elevated asthma risk (OR = 1.62; 95% CI, 1.23-2.12; P = 0.0005). Subgroup analyses by ethnicity also found significant associations between this polymorphism and asthma risk in Asians and Caucasians. RESULTS from other genetic models further identified this possible association.

CONCLUSION

This meta-analysis suggests that CC10 +38A/G polymorphism confers asthma risk.

Phylogenetic relationships among Perissodactyla: secretoglobin 1A1 gene duplication and triplication in the Equidae family

Secretoglobin family 1A member 1 (SCGB 1A1) is a small anti-inflammatory and immunomodulatory protein that is abundantly secreted in airway surface fluids. We recently reported the existence of three distinct SCGB1A1 genes in the domestic horse genome as opposed to the single gene copy consensus present in other mammals. The origin of SCGB1A1 gene triplication and the evolutionary relationship of the three genes amongst Equidae family members are unknown. For this study, SCGB1A1 genomic data were collected from various Equus individuals including E. caballus, E. przewalskii, E. asinus, E. grevyi, and E. quagga. Three SCGB1A1 genes in E. przewalskii, two SCGB1A1 genes in E. asinus, and a single SCGB1A1 gene in E. grevyi and E. quagga were identified. Sequence analysis revealed that the non-synonymous nucleotide substitutions between the different equid genes coded for 17 amino acid changes. Most of these changes localized to the SCGB 1A1 central cavity that binds hydrophobic ligands, suggesting that this area of SCGB 1A1 evolved to accommodate diverse molecular interactions. Three-dimensional modeling of the proteins revealed that the size of the SCGB 1A1 central cavity is larger than that of SCGB 1A1A. Altogether, these findings suggest that evolution of the SCGB1A1 gene may parallel the separation of caballine and non-caballine species amongst Equidae, and may indicate an expansion of function for SCGB1A1 gene products.