Epidermal growth factor system regulates mucin production in airways

Emerging cell and molecular targets for treating mucus hypersecretion in asthma

Mucus provides a protective barrier that is crucial for host defense in the lungs. However, excessive or abnormal mucus can have pathophysiological consequences in many pulmonary diseases, including asthma. Patients with asthma are treated with agents that relax airway smooth muscle and reduce airway inflammation, but responses are often inadequate. In part, this is due to the inability of existing therapeutic agents to directly target mucus. Accordingly, there is a critical need to better understand how mucus hypersecretion and airway plugging are affected by the epithelial cells that synthesize, secrete, and transport mucus components. This review highlights recent advances in the biology of mucin glycoproteins with a specific focus on MUC5AC and MUC5B, the chief macromolecular components of airway mucus. An improved mechanistic understanding of key steps in mucin production and secretion will help reveal novel potential therapeutic strategies.

Submandibular Gland Pathogenesis Following SARS-CoV-2 Infection and Implications for Xerostomia

Although SARS-CoV-2 induces mucin hypersecretion in the respiratory tract, hyposalivation/xerostomia has been reported by COVID-19 patients. We evaluate the submandibular gland (SMGs) pathogenesis in SARS-CoV-2-infected K18-hACE2 mice, focusing on the impact of infection on the mucin production and structural integrity of acini, ductal system, myoepithelial cells (MECs) and telocytes. The spike protein, the nucleocapsid protein, hACE2, actin, EGF, TNF-α and IL-1β were detected by immunofluorescence, and the Egfr and Muc5b expression was evaluated. In the infected animals, significant acinar hypertrophy was observed in contrast to ductal atrophy. Nucleocapsid proteins and/or viral particles were detected in the SMG cells, mainly in the nuclear membrane-derived vesicles, confirming the nuclear role in the viral formation. The acinar cells showed intense TNF-α and IL-1β immunoexpression, and the EGF-EGFR signaling increased, together with Muc5b upregulation. This finding explains mucin hypersecretion and acinar hypertrophy, which compress the ducts. Dying MECs and actin reduction were also observed, indicating failure of contraction and acinar support, favoring acinar hypertrophy. Viral assembly was found in the dying telocytes, pointing to these intercommunicating cells as viral transmitters in SMGs. Therefore, EGF-EGFR-induced mucin hypersecretion was triggered by SARS-CoV-2 in acinar cells, likely mediated by cytokines. The damage to telocytes and MECs may have favored the acinar hypertrophy, leading to ductal obstruction, explaining xerostomia in COVID-19 patients. Thus, acinar cells, telocytes and MECs may be viral targets, which favor replication and cell-to-cell viral transmission in the SMG, corroborating the high viral load in saliva of infected individuals.

In vitro modelling of bacterial pneumonia: a comparative analysis of widely applied complex cell culture models

Bacterial pneumonia greatly contributes to the disease burden and mortality of lower respiratory tract infections among all age groups and risk profiles. Therefore, laboratory modelling of bacterial pneumonia remains important for elucidating the complex host-pathogen interactions and to determine drug efficacy and toxicity. In vitro cell culture enables for the creation of high-throughput, specific disease models in a tightly controlled environment. Advanced human cell culture models specifically, can bridge the research gap between the classical two-dimensional cell models and animal models. This review provides an overview of the current status of the development of complex cellular in vitro models to study bacterial pneumonia infections, with a focus on air-liquid interface models, spheroid, organoid, and lung-on-a-chip models. For the wide scale, comparative literature search, we selected six clinically highly relevant bacteria (Pseudomonas aeruginosa, Mycoplasma pneumoniae, Haemophilus influenzae, Mycobacterium tuberculosis, Streptococcus pneumoniae, and Staphylococcus aureus). We reviewed the cell lines that are commonly used, as well as trends and discrepancies in the methodology, ranging from cell infection parameters to assay read-outs. We also highlighted the importance of model validation and data transparency in guiding the research field towards more complex infection models.

Surfactant protein D prevents mucin overproduction in airway goblet cells via SIRPα

Mucin overproduction is a common feature of chronic airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), and exacerbates their underlying respiratory condition. Surfactant protein D (SP-D) protects against airway diseases through modulation of immune reactions, but whether it also exerts direct effects on airway epithelial cells has remained unclear. Therefore, we sought to investigate the inhibitory role of SP-D on mucin production in airway epithelial cells. We prepared air-liquid interface (ALI) cultures of human primary bronchial epithelial cells (HBECs), which recapitulated a well-differentiated human airway epithelium. Benzo(a)pyrene (BaP), a key toxicant in cigarette smoke, induced mucin 5AC (MUC5AC) production in ALI-cultured HBECs, airway secretory cell lines, and airway epithelia of mice. Then, the protective effects of SP-D against the BaP-induced mucin overproduction were examined. BaP increased MUC5AC production in ALI cultures of HBECs, and this effect was attenuated by SP-D. SP-D also suppressed the BaP-induced phosphorylation of extracellular signal-regulated kinase (ERK) and MUC5AC expression in NCI-H292 goblet-like cells, but not in NCI-H441 club-like cells. Signal regulatory protein α (SIRPα) was found to be expressed in HBECs and NCI-H292 cells but absent in NCI-H441 cells. In NCI-H292 cells, SP-D activated SH2 domain-containing tyrosine phosphatase-1 (SHP-1), downstream of SIRPα, and knockdown of SIRPα abolished the suppressive effects of SP-D on BaP-induced ERK phosphorylation and MUC5AC production. Consistent with these in vitro findings, intratracheal instillation of SP-D prevented the BaP-induced phosphorylation of ERK and Muc5ac expression in airway epithelial cells in a mouse model. SP-D acts directly on airway epithelial cells to inhibit mucin secretion through ligation of SIRPα and SHP-1-mediated dephosphorylation of ERK. Targeting of SIRPα is therefore a potential new therapeutic approach to suppression of mucin hypersecretion in chronic airway diseases such as COPD and asthma.

Localization of Sites of Osimertinib Action in Rat Intestine, Skin, and Lung by Immunohistochemistry

Osimertinib is a third-generation, irreversible tyrosine kinase inhibitor (TKI) of epidermal growth factor receptor (EGFR) that selectively inhibits both EGFR-TKI-sensitizing and EGFR T790M resistance mutations and has shown efficacy in patients with non-small-cell lung cancer. In this study, we created osimertinib-specific antibodies and developed an immunohistochemistry (IHC) for locating the sites of osimertinib action. Moreover, we located osimertinib-protein conjugates in intestinal, dermal, and lung tissues of rats, thereby using our IHC to visualize the sites of the adverse effects of osimertinib, including diarrhea, skin disorder, and interstitial pneumonia. This report is the first to elucidate the localization of the sites of action of osimertinib in the rat intestine, skin, and lung and is expected to help clarify the mechanism of osimertinib-induced adverse effects.

Regulation of the Gene Expression of Airway MUC5AC Mucin through NF-κB Signaling Pathway by Artesunate, an Antimalarial Agent

In this study, artesunate, an antimalarial agent, was investigated for its potential effect on the gene expression of airway MUC5AC mucin. The human pulmonary epithelial NCI-H292 cells were pretreated with artesunate for 30 min and then stimulated with phorbol 12-myristate 13-acetate (PMA), for the following 24 h. The effect of artesunate on PMA-induced nuclear factor kappa B (NF-kB) signaling pathway was also examined. Artesunate inhibited the glycoprotein production and mRNA expression of MUC5AC mucins, induced by PMA through the inhibition of degradation of inhibitory kappa Bα (IkBα) and NF-kB p65 nuclear translocation. These results suggest artesunate suppresses the gene expression of mucin through regulation of NF-kB signaling pathway, in human pulmonary epithelial cells.

A human model of asthma exacerbation reveals transcriptional programs and cell circuits specific to allergic asthma

Asthma is a chronic disease most commonly associated with allergy and type 2 inflammation. However, the mechanisms that link airway inflammation to the structural changes that define asthma are incompletely understood. Using a human model of allergen-induced asthma exacerbation, we compared the lower airway mucosa in allergic asthmatics and allergic non-asthmatic controls using single-cell RNA sequencing. In response to allergen, the asthmatic airway epithelium was highly dynamic and up-regulated genes involved in matrix degradation, mucus metaplasia, and glycolysis while failing to induce injury-repair and antioxidant pathways observed in controls. IL9-expressing pathogenic TH2 cells were specific to asthmatic airways and were only observed after allergen challenge. Additionally, conventional type 2 dendritic cells (DC2 that express CD1C) and CCR2-expressing monocyte-derived cells (MCs) were uniquely enriched in asthmatics after allergen, with up-regulation of genes that sustain type 2 inflammation and promote pathologic airway remodeling. In contrast, allergic controls were enriched for macrophage-like MCs that up-regulated tissue repair programs after allergen challenge, suggesting that these populations may protect against asthmatic airway remodeling. Cellular interaction analyses revealed a TH2-mononuclear phagocyte-basal cell interactome unique to asthmatics. These pathogenic cellular circuits were characterized by type 2 programming of immune and structural cells and additional pathways that may sustain and amplify type 2 signals, including TNF family signaling, altered cellular metabolism, failure to engage antioxidant responses, and loss of growth factor signaling. Our findings therefore suggest that pathogenic effector circuits and the absence of proresolution programs drive structural airway disease in response to type 2 inflammation.

Successful treatment with osimertinib for nonmucinous bronchioloalveolar carcinoma with massive bronchorrhea and respiratory failure: a case report and literature review

Background

Correct diagnosis of bronchioloalveolar carcinoma (BAC) is often delayed due to the lack of familiarity with the condition among clinicians as its sporadic nature and its symptoms are similar to other respiratory issues. Among these, acute respiratory failure (ARF) caused by massive bronchorrhea is rarely associated with BAC. Here we first reported osimertinib in the treatment of BAC with bronchorrhea and ARF.

Case Description

A 38-year-old woman presented with massive bronchorrhea and progressive dyspnea. A chest computed tomography (CT) scan showed consolidation with air bronchograms and multiple nodules in both lungs. The patient had no history of chronic pulmonary disease, diabetes mellitus, hypertension or smoke. The patient was initially diagnosed with pneumonia, but ARF developed despite the antibiotic therapy provided. Lung biopsy results revealed nonmucinous BAC. Osimertinib (80 mg daily) was prescribed and proved effective for the first time with an improved ARF and a decreased multiple nodules or consolidation in the lungs during the follow-up period.

Conclusions

It is important for physicians to recognize the typical symptoms and radiological manifestations of BAC to avoid misdiagnosis or late diagnosis. This is especially important since early diagnosis allows for immediate epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) therapy, which is a potentially beneficial treatment for patients with BAC.

Systematic Pharmacology-Based Strategy to Explore the Mechanism of Bufei Huoxue Capsule in the Treatment of Chronic Obstructive Pulmonary Disease

Objective. To explore the effects and mechanisms of Bufei Huoxue Capsule (BHC) on chronic obstructive pulmonary disease (COPD) based on network pharmacology. Methods. The effective components and related targets of BHC were collected by searching TCMSP, HERB, and ETCM databases, after which the related targets of COPD were obtained on GeneCards and OMIM databases. The common targets were imported into the STRING database and Cytoscape database to construct a target interaction network and screen core targets. Next, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed on the Metascape platform. According to the prediction results of network pharmacology, the action mechanism was further examined in an animal model of COPD. The pathological changes of lung tissue were observed by HE staining; goblet cells and mucus secretion in lung tissue were observed by AB-PAS staining, airway collagen deposition was observed by Masson staining, and the expression of NE, TGF-β1, P-EGFR/EGFR, P-ERK1/2/ERK1/2, P-JNK/JNK, and P-P38/P38MAPK protein was detected by Western blot analysis. Results. A total of 379 targets related to BHC and 7391 targets related to COPD were obtained, including 313 potential targets of BHC in treating chronic obstructive pulmonary disease, with JUN, AKT1, TNF, IL6, EGFR, MAPK1, and MAPK14 as the core targets. Through enrichment analysis, BHC may interfere with COPD by regulating the MAPK signal pathway, HIF-1 signal pathway, NF-κB signal pathway, cAMP signal pathway, cGMP-PKG signal pathway, and so on. Animal experiments showed that the BHC could reduce airway inflammatory cell infiltration, inhibit airway epithelial goblet cell proliferation, reduce mucus secretion, and improve small airway collagen fiber deposition in COPD model rats. Besides, BHC could downregulate the protein expression of NE, TGF-β1, P-EGFR, P-ERK1/2, and P-P38MAPK. Conclusion. BHC can reduce airway inflammation, inhibit mucus hypersecretion, and improve airway remodeling by regulating the MAPK signal transduction pathway.

Involvement of IKK/IkBα/NF-kB p65 Signaling into the Regulative Effect of Engeletin on MUC5AC Mucin Gene Expression in Human Airway Epithelial Cells

In this study, we examined whether engeletin exerts an effect on the gene expression of MUC5AC mucin, in human pulmonary epithelial NCI-H292 cells. The cells were pretreated with engeletin for 30 min and stimulated with phorbol 12-myristate 13-acetate (PMA), for the following 24 h. The effect of engeletin on PMA-induced nuclear factor kappa B (NF-kB) signaling pathway was also investigated. Engeletin suppressed the mRNA expression and production of MUC5AC mucin, induced by PMA through the inhibition of degradation of inhibitory kappa Bα (IkBα) and NF-kB p65 nuclear translocation. These results suggest engeletin inhibits the gene expression of mucin through regulation of NF-kB signaling pathway, in human airway epithelial cells.

Autocrine TGF-alpha is associated with Benzo(a)pyrene-induced mucus production and MUC5AC expression during allergic asthma

OBJECTS

Benzo(a)pyrene (BaP), an environmental pollutant, is present in high concentrations in urban smog and cigarette smoke and has been reported to promote high mucin 5AC (MUC5AC) expression. Epithelium-derived inflammatory cytokines are considered an important modulator of mucus oversecretion and MUC5AC overexpression. Here, we investigated whether the effect of BaP on MUC5AC overexpression was associated with cytokine autocrine activity in vivo and in vitro.

METHODS

In vivo, BALB/c mice were treated with ovalbumin (OVA) in the presence or absence of BaP. Allergy-induced mucus production was assessed by Alcian Blue Periodic acid Schiff (AB-PAS) staining. The human airway epithelial cell line NCI-H292 was used in vitro. MUC5AC and transforming growth factor (TGF)-α mRNA levels were assessed with real-time quantitative PCR. The concentration of cytokines was measured by ELISA. The MUC5AC, p-ERK, ERK, p-EGFR and EGFR proteins were detected by Western blotting in cells or by immunohistochemistry in mouse lungs. Small-interfering RNAs were used for gene silencing.

RESULTS

TGF-α was overproduced in the supernatant of NCI-H292 cells treated with BaP. Knockdown of TGF-α expression inhibited the BaP-induced increase in MUC5AC expression and subsequent activation of the EGFR-ERK signalling pathway. Knocking down aryl hydrocarbon receptor (AhR) expression or treatment with an ROS inhibitor (N-acetyl-L-cysteine) could relieve the TGF-α secretion induced by BaP in epithelial cells. In an animal study, coexposure to BaP with OVA increased mucus production, MUC5AC expression and ROS-EGFR-ERK activation in the lung as well as TGF-α levels in bronchoalveolar lavage fluid (BALF). Furthermore, the concentration of TGF-α in BALF was correlated with MUC5AC mRNA levels. Additionally, TGF-α expression was found to be positively correlated with MUC5AC expression in the airway epithelial cells of smokers. Compared with non-smoker asthma patients, TGF-α serum levels were also elevated in smoker asthma patients.

CONCLUSION

Autocrine TGF-α was associated with BaP-induced MUC5AC expression in vitro and in vivo. BaP induced TGF-α secretion by activating AhR and producing ROS, which led to activation of the EGFR-ERK pathway.

Symptomatic Radiation Pneumonitis in NSCLC Patients Receiving EGFR-TKIs and Concurrent Once-daily Thoracic Radiotherapy: Predicting the Value of Clinical and Dose-volume Histogram Parameters

BACKGROUND

The incidence of symptomatic radiation pneumonitis (RP) and its relationship with dose-volume histogram (DVH) parameters in non-small cell lung cancer (NSCLC) patients receiving epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) and concurrent once-daily thoracic radiotherapy (TRT) remain unclear. We aim to analyze the values of clinical factors and dose-volume histogram (DVH) parameters to predict the risk for symptomatic RP in these patients.

METHODS

Between 2011 and 2019, we retrospectively analyzed and identified 85 patients who had received EGFR-TKIs and once-daily TRT simultaneously (EGFR-TKIs group) and 129 patients who had received concurrent chemoradiotherapy (CCRT group). The symptomatic RP was recorded according to the Common Terminology Criteria for Adverse Event (CTCAE) criteria (grade 2 or above). Statistical analyses were performed using SPSS 26.0.

RESULTS

In total, the incidences of symptomatic (grade≥2) and severe RP (grade≥3) were 43.5% (37/85) and 16.5% (14/85) in EGFR-TKIs group vs 27.1% (35/129) and 10.1% (13/129) in CCRT group respectively. After 1:1 ratio between EGFR-TKIs group and CCRT group was matched by propensity score matching, chi-square test suggested that the incidence of symptomatic RP in the MATCHED EGFR-TKIs group was higher than that in the matched CCRT group (χ2=4.469, P=0.035). In EGFR-TKIs group, univariate and multivariate analyses indicated that the percentage of ipsilateral lung volume receiving ≥30 Gy (ilV30) [odds ratio (OR): 1.163, 95%CI: 1.036-1.306, P=0.011] and the percentage of total lung volume receiving ≥20 Gy (tlV20) (OR: 1.171, 95%CI: 1.031-1.330, P=0.015), with chronic obstructive pulmonary disease (COPD) or not (OR: 0.158, 95%CI: 0.041-0.600, P=0.007), were independent predictors of symptomatic RP. Compared to patients with lower ilV30/tlV20 values (ilV30 and tlV20<cut-off point values) and without COPD, patients with higher ilV30/tlV20 values (ilV30 and tlV20>cut-off point values) and COPD had a significantly higher risk for developing symptomatic RP, with a hazard ratio (HR) of 1.350 (95%CI: 1.190-1.531, P<0.001).

CONCLUSIONS

Patients receiving both EGFR-TKIs and once-daily TRT were more likely to develop symptomatic RP than patients receiving concurrent chemoradiotherapy. The ilV30, tlV20, and comorbidity of COPD may predict the risk of symptomatic RP among NSCLC patients receiving EGFR-TKIs and conventionally fractionated TRT concurrently.

Targeting the EGFR-ERK axis using the compatible solute ectoine to stabilize CFTR mutant F508del

Mutations in the CFTR gene lead to cystic fibrosis, a genetic disease associated with chronic infection and inflammation and ultimately respiratory failure. The most common CF-causing mutation is F508del and CFTR modulators (correctors and potentiators) are being developed to rescue its trafficking and activity defects. However, there are currently no modulators that stabilize the rescued membrane F508del-CFTR which is endocytosed and quickly degraded resulting in a shorter half-life than wild-type (WT). We previously reported that the extracellular signal-regulated kinase (ERK) MAPK pathway is involved in CFTR degradation upon cigarette smoke exposure. Interestingly, we found that ERK phosphorylation was increased in CF human bronchial epithelial (HBE) cells (CF-HBE41o- and primary CF-HBE) compared to non-CF controls, and this was likely due to signaling by the epidermal growth factor receptor (EGFR). EGFR can be activated by several ligands, and we provide evidence that amphiregulin (AREG) is important for activating this signaling axis in CF. The natural osmolyte ectoine stabilizes membrane macromolecules. We show that ectoine decreases ERK phosphorylation, increases the half-life of rescued CFTR, and increases CFTR-mediated chloride transport in combination with the CFTR corrector VX-661. Additionally, ectoine reduces production of AREG and interleukin-8 by CF primary bronchial epithelial cells. In conclusion, EGFR-ERK signaling negatively regulates CFTR and is hyperactive in CF, and targeting this axis with ectoine may prove beneficial for CF patients.

Pathophysiological relevance of sputum MUC5AC and MUC5B levels in patients with mild asthma

BACKGROUND

Airway mucus hypersecretion is an important pathophysiological feature of asthma. MUC5AC and MUC5B are the major secreted polymeric mucins in airways, and their compositions affect mucus properties. Despite the increasing appreciation of MUC5AC and MUC5B compositions in asthmatic airways, their pathophysiological relevance remains to be fully understood in humans.

METHODS

In this cross-sectional study, we prospectively enrolled newly referred steroid-untreated patients with mild asthma and healthy controls. We compared induced sputum MUC5AC and MUC5B levels between patients and controls. Subsequently, we assessed the correlation between MUC5AC and MUC5B levels and clinical indices in patients. Sputum MUC5AC and MUC5B levels were measured using enzyme-linked immunosorbent assays.

RESULTS

Sputum MUC5AC and MUC5B levels were significantly higher in patients (n = 87) than in controls (n = 22) (p = 0.0002 and p = 0.006, respectively). The ratio of sputum MUC5AC to MUC5B tended to be higher in patients than in controls (p = 0.07). Sputum MUC5AC levels significantly and positively correlated with fractional exhaled nitric oxide at expiratory flow of 50 mL/s (Spearman's rho = 0.29, p = 0.006), sputum eosinophil proportion (rho = 0.34, p = 0.0013), and airway sensitivity (rho = 0.39, p = 0.0005). By contrast, sputum MUC5B levels significantly and positively correlated with airway sensitivity (rho = 0.35, p = 0.002) and negatively correlated with airway reactivity (rho = -0.33, p = 0.004).

CONCLUSIONS

Sputum MUC5AC is increased by protein levels and involved in airway type 2/eosinophilic inflammation and airway hyperresponsiveness in steroid-untreated patients with mild asthma.

Lysophosphatidylserine Induces MUC5AC Production via the Feedforward Regulation of the TACE-EGFR-ERK Pathway in Airway Epithelial Cells in a Receptor-Independent Manner

Lysophosphatidylserine (LysoPS) is an amphipathic lysophospholipid that mediates a broad spectrum of inflammatory responses through a poorly characterized mechanism. Because LysoPS levels can rise in a variety of pathological conditions, we sought to investigate LysoPS's potential role in airway epithelial cells that actively participate in lung homeostasis. Here, we report a previously unappreciated function of LysoPS in production of a mucin component, MUC5AC, in the airway epithelial cells. LysoPS stimulated lung epithelial cells to produce MUC5AC via signaling pathways involving TACE, EGFR, and ERK. Specifically, LysoPS- dependent biphasic activation of ERK resulted in TGF-α secretion and strong EGFR phosphorylation leading to MUC5AC production. Collectively, LysoPS induces the expression of MUC5AC via a feedback loop composed of proligand synthesis and its proteolysis by TACE and following autocrine EGFR activation. To our surprise, we were not able to find a role of GPCRs and TLR2, known LyoPS receptors in LysoPS-induced MUC5AC production in airway epithelial cells, suggesting a potential receptor-independent action of LysoPS during inflammation. This study provides new insight into the potential function and mechanism of LysoPS as an emerging lipid mediator in airway inflammation.

Methods of Sputum and Mucus Assessment for Muco-Obstructive Lung Diseases in 2022: Time to “Unplug” from Our Daily Routine!

Obstructive lung diseases, such as chronic obstructive pulmonary disease, asthma, or non-cystic fibrosis bronchiectasis, share some major pathophysiological features: small airway involvement, dysregulation of adaptive and innate pulmonary immune homeostasis, mucus hyperproduction, and/or hyperconcentration. Mucus regulation is particularly valuable from a therapeutic perspective given it contributes to airflow obstruction, symptom intensity, disease severity, and to some extent, disease prognosis in these diseases. It is therefore crucial to understand the mucus constitution of our patients, its behavior in a stable state and during exacerbation, and its regulatory mechanisms. These are all elements representing potential therapeutic targets, especially in the era of biologics. Here, we first briefly discuss the composition and characteristics of sputum. We focus on mucus and mucins, and then elaborate on the different sample collection procedures and how their quality is ensured. We then give an overview of the different direct analytical techniques available in both clinical routine and more experimental settings, giving their advantages and limitations. We also report on indirect mucus assessment procedures (questionnaires, high-resolution computed tomography scanning of the chest, lung function tests). Finally, we consider ways of integrating these techniques with current and future therapeutic options. Cystic fibrosis will not be discussed given its monogenic nature.

Role of EGF Receptor Regulatory Networks in the Host Response to Viral Infections

In this review article, we will first provide a brief overview of EGF receptor (EGFR) structure and function, and its importance as a therapeutic target in epithelial carcinomas. We will then compare what is currently known about canonical EGFR trafficking pathways that are triggered by ligand binding, versus ligand-independent pathways activated by a variety of intrinsic and environmentally induced cellular stresses. Next, we will review the literature regarding the role of EGFR as a host factor with critical roles facilitating viral cell entry and replication. Here we will focus on pathogens exploiting virus-encoded and endogenous EGFR ligands, as well as EGFR-mediated trafficking and signaling pathways that have been co-opted by wild-type viruses and recombinant gene therapy vectors. We will also provide an overview of a recently discovered pathway regulating non-canonical EGFR trafficking and signaling that may be a common feature of viruses like human adenoviruses which signal through p38-mitogen activated protein kinase. We will conclude by discussing the emerging role of EGFR signaling in innate immunity to viral infections, and how viral evasion mechanisms are contributing to our understanding of fundamental EGFR biology.

ITGB4 deficiency induces mucus hypersecretion by upregulating MUC5AC in RSV-infected airway epithelial cells

Respiratory syncytial virus (RSV) infection is the main cause of bronchiolitis in children. Excessive mucus secretion is one of the primary symbols in RSV related lower respiratory tract infections (RSV-related LRTI), which is closely associated with the occurrence and development of asthma in later life. Integrin β4 (ITGB4) is down-regulated in the airway epithelial cells (AECs) of asthma patients which plays a critical role in the pathogenesis of asthma. However, whether ITGB4 is involved in the pathological processes of RSV infection remains unclear. In this study, we found that decreased expression of ITGB4 was negatively correlated with the level of MUC5AC in childhood AECs following RSV infection. Moreover, ITGB4 deficiency led to mucus hypersecretion and MUC5AC overexpression in the small airway of RSV-infected mice. MUC5AC expression was upregulated by ITGB4 in HBE cells through EGFR, ERK and c-Jun pathways. EGFR inhibitors treatment inhibited mucus hypersecretion and MUC5AC overexpression in ITGB4-deficient mice after RSV infection. Together, these results demonstrated that epithelial ITGB4 deficiency induces mucus hypersecretion by upregulating the expression of MUC5AC through EGFR/ERK/c-Jun pathway, which further associated with RSV-related LRTI.

Mucus-producing epithelial models for investigating the activity of gene delivery systems in the lung

Inhaled transfection particles have to penetrate the mucus layer lining the airways to successfully deliver their therapeutic nucleic acid payload to target cells in the underlying epithelium. However, the in vitro models used for evaluating gene carrier efficiency often disregard this viscous defensive barrier. In this study, the two mucus-secreting cell lines NCI-H292 and Calu-3 were selected to develop a series of epithelial models displaying gradual mucus production. In NCI-H292 models, a gradual increase in the MUC5AC mucin was obtained after cell exposure to inducers. In Calu-3 models, MUC5AC production increased as a function of culture duration (3, 7, 14 days) at the air-liquid interface (ALI). Six DOPC-derived cationic lipids were designed and their pDNA delivery activity was evaluated to validate these cellular models. The strongest impairment of the lipid delivery activity was observed in the Calu-3 14-d ALI model. The MUC5AC production in this model was the greatest and the mucus layer was 20 µm thick. The mucus exhibited a solid viscoelastic behaviour, and represented a major hindrance to lipoplex diffusion. The Calu-3 14-d ALI model will be highly useful for accurate evaluation of gene carriers intended for airway administration and characterization of their interactions with the mucus.

Epilobiumpyrricholophum Extract Suppresses Porcine Pancreatic Elastase and Cigarette Smoke Extract-Induced Inflammatory response in a Chronic Obstructive Pulmonary Disease Model

Chronic airway exposure to harmful substances, such as deleterious gases, cigarette smoke (CS), and particulate matter, triggers chronic obstructive pulmonary disease (COPD), characterized by impaired lung function and unbridled immune responses. Emerging epigenomic and genomic evidence suggests that excessive recruitment of alveolar macrophages and neutrophils contributes to COPD pathogenesis by producing various inflammatory mediators, such as reactive oxygen species (ROS), neutrophil elastase, interleukin (IL) 6, and IL8. Recent studies showed that Epilobium species attenuated ROS, myeloperoxidase, and inflammatory cytokine production in murine and human innate immune cells. Although the Epilobium genus exerts anti-inflammatory, antioxidant, and antimicrobial effects, the question of whether the Epilobium species regulate lung inflammation and innate immune response in COPD has not been investigated. In this study, Epilobium pyrricholophum extract (EPE) suppressed inflammatory cell recruitment and clinical symptoms in porcine pancreatic elastase and CS extract-induced COPD mice. In addition, EPE attenuated inflammatory gene expression by suppressing MAPKs and NFκB activity. Furthermore, UPLC-Q-TOF MS analyses revealed the anti-inflammatory effects of the identified phytochemical constituents of EPE. Collectively, our studies revealed that EPE represses the innate immune response and inflammatory gene expression in COPD pathogenesis in mice. These findings provide insights into new therapeutic approaches for treating COPD.

Eriodictyol Inhibits the Production and Gene Expression of MUC5AC Mucin via the IκBα-NF-κB p65 Signaling Pathway in Airway Epithelial Cells

In this study, we investigated whether eriodictyol exerts an effect on the production and gene expression of MUC5AC mucin in human pulmonary epithelial NCI-H292 cells. The cells were pretreated with eriodictyol for 30 min and then stimulated with phorbol 12-myristate 13-acetate (PMA) for 24 h. The effect of eriodictyol on PMA-induced nuclear factor kappa B (NF-κB) signaling pathway was also investigated. Eriodictyol suppressed the MUC5AC mucin production and gene expression induced by PMA via suppression of inhibitory kappa Bα degradation and NF-κB p65 nuclear translocation. These results suggest that eriodictyol inhibits mucin gene expression and production in human airway epithelial cells via regulation of the NF-κB signaling pathway.

Integrin β1 subunit regulates cellular and secreted MUC5AC and MUC5B production in NCI-H292 human lung epithelial cells

The surface of the human respiratory tract is covered with a mucus layer containing mucin 5AC (MUC5AC) and mucin 5B (MUC5B) as the main components. This layer contributes to biological defense by eliminating irritants, but excessive MUC5AC secretion by the airway epithelial cells exacerbates asthma. Therefore, regulating mucin production is important for asthma treatment. In this study, the effects of integrin β1 subunit on MUC5AC and MUC5B production were examined in NCI–H292 human lung cancer epithelial cells. When integrin β1 was overexpressed, cellular and secreted MUC5AC levels were decreased, whereas cellular MUC5B production was increased. Conversely, integrin β1 depletion using siRNA increased cellular and secreted MUC5AC production, but decreased cellular MUC5B production. Further, the activity of extracellular signal-regulated kinase (ERK), which promotes MUC5AC production, was decreased by integrin β1 overexpression and increased by its depletion. These results suggest that integrin β1 suppresses MUC5AC production and promotes MUC5B production by downregulating ERK.

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We studied the regulation of MUC5AC and MUC5B production by integrin β1 subunit.

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Integrin β1 overexpression reduced MUC5AC, but increased MUC5B levels.

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Integrin β1 depletion increased MUC5AC production and ROS level, but decreased MUC5B production.

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Integrin β1 overexpression decreased ERK activity in NCI–H292 airway cells.

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Integrin β1 downregulates ERK to suppress MUC5AC & promote MUC5B production.

Muc5ac Production Inhibited by Decreased lncRNA H19 via PI3K/Akt/NF-kB in Asthma

Introduction

LncRNAs play important roles in multiple diseases including asthma, while there are a few reports on the role of lncRNA H19 about asthma. This study aimed to investigate the roles and mechanisms of lncRNA H19 in asthma.

Methods

We detected lncRNA H19 and Muc5ac mRNA by establishing a murine asthma model and an in vitro inflammation model. Regulatory roles of lncRNA H19 in asthma were explored by lncRNA H19 overexpression or knockdown in vitro. To study its mechanisms, we detect p-NF-κB and p-Akt expression, and treated 16-HBE cells with inhibitors of PI3K. To study regulatory effects of miR-675-3p on Muc5ac, miR-675-3p mimics and inhibitors were respectively transfected into 16-HBE cells.

Results

Firstly, we established a murine asthma model and an in vitro inflammation model. We found that lncRNA H19 expression was decreased, while Muc5ac mRNA was increased in lung tissues of murine asthma model and in the in vitro inflammation model. lncRNA H19 overexpression increased Muc5ac mRNA expression and lncRNA H19 knockdown decreased Muc5ac mRNA expression in 16-HBE cells. Moreover, lncRNA H19 overexpression further increased Muc5ac expression in TNFα-induced in vitro inflammation model. lncRNA H19 knockdown decreased p-Akt and p-NF-κB expression. Inhibitors of PI3K abolished Muc5ac induced by lncRNA H19 overexpression. Although miR-675-3p was increased by lncRNA H19 overexpression, it had no regulatory effects on Muc5ac expression.

Discussion

These results demonstrated that lncRNA H19 positively regulates Muc5ac expression through PI3K/Akt /NF-κB pathway in the in vitro inflammation model. Therefore, this study indicated that decreased lncRNA H19 in asthma might play a protective role relieving mucus overproduction, and lncRNA H19 might be a potential target for asthma treatment.

Epithelial Barrier Dysfunction in Chronic Respiratory Diseases

Mucosal surfaces are lined by epithelial cells, which provide a complex and adaptive module that ensures first-line defense against external toxics, irritants, antigens, and pathogens. The underlying mechanisms of host protection encompass multiple physical, chemical, and immune pathways. In the lung, inhaled agents continually challenge the airway epithelial barrier, which is altered in chronic diseases such as chronic obstructive pulmonary disease, asthma, cystic fibrosis, or pulmonary fibrosis. In this review, we describe the epithelial barrier abnormalities that are observed in such disorders and summarize current knowledge on the mechanisms driving impaired barrier function, which could represent targets of future therapeutic approaches.

Rhinovirus Reduces the Severity of Subsequent Respiratory Viral Infections by Interferon-Dependent and -Independent Mechanisms

Coinfection by heterologous viruses in the respiratory tract is common and can alter disease severity compared to infection by individual virus strains. We previously found that inoculation of mice with rhinovirus (RV) 2 days before inoculation with a lethal dose of influenza A virus [A/Puerto Rico/8/34 (H1N1) (PR8)] provides complete protection against mortality. Here, we extended that finding to a second lethal respiratory virus, pneumonia virus of mice (PVM), and analyzed potential mechanisms of RV-induced protection. RV completely prevented mortality and weight loss associated with PVM infection. Major changes in host gene expression upon PVM infection were delayed compared to PR8. RV induced earlier recruitment of inflammatory cells, which were reduced at later times in RV-inoculated mice. Findings common to both virus pairs included the upregulated expression of mucin-associated genes and dampening of inflammation-related genes in mice that were inoculated with RV before lethal virus infection. However, type I interferon (IFN) signaling was required for RV-mediated protection against PR8 but not PVM. IFN signaling had minor effects on PR8 replication and contributed to controlling neutrophilic inflammation and hemorrhagic lung pathology in RV/PR8-infected mice. These findings, combined with differences in virus replication levels and disease severity, suggest that the suppression of inflammation in RV/PVM-infected mice may be due to early, IFN-independent suppression of viral replication, while that in RV/PR8-infected mice may be due to IFN-dependent modulation of immune responses. Thus, a mild upper respiratory viral infection can reduce the severity of a subsequent severe viral infection in the lungs through virus-dependent mechanisms.

IMPORTANCE Respiratory viruses from diverse families cocirculate in human populations and are frequently detected within the same host. Although clinical studies suggest that infection by multiple different respiratory viruses may alter disease severity, animal models in which we can control the doses, timing, and strains of coinfecting viruses are critical to understanding how coinfection affects disease severity. Here, we compared gene expression and immune cell recruitment between two pairs of viruses (RV/PR8 and RV/PVM) inoculated sequentially in mice, both of which result in reduced severity compared to lethal infection by PR8 or PVM alone. Reduced disease severity was associated with suppression of inflammatory responses in the lungs. However, differences in disease kinetics and host and viral gene expression suggest that protection by coinfection with RV may be due to distinct molecular mechanisms. Indeed, we found that antiviral cytokine signaling was required for RV-mediated protection against lethal infection by PR8 but not PVM.

Wood Smoke Particles Stimulate MUC5AC Overproduction by Human Bronchial Epithelial Cells Through TRPA1 and EGFR Signaling

Mucus hypersecretion is a pathological feature of acute inflammatory and chronic obstructive pulmonary diseases. Exposure to air pollutants can be a cause of pathological mucus overproduction, but mechanisms by which different forms of air pollutants elicit this response are not fully understood. In this study, particulate matter (PM) generated from burning pine wood and other types of biomass was used to determine mechanisms by which these forms of PM stimulate mucin gene expression and secretion by primary human bronchial epithelial cells (HBECs). Biomass PM < 2.5 μm generated from pine wood and several other fuels stimulated the expression and secretion of the gel-forming glycoprotein MUC5AC by HBECs. Muc5ac gene induction was also observed in mouse airways following subacute oropharyngeal delivery of pine wood smoke PM. In HBECs, MUC5AC was also induced by the transient receptor potential ankyrin-1 (TRPA1) agonists' coniferaldehyde, a component of pine smoke PM, and allyl isothiocyanate, and was attenuated by a TRPA1 antagonist. Additionally, inhibition of epidermal growth factor receptor (EGFR/ErbB1) and the EGFR signaling partners p38 MAPK and GSK3β also prevented MUC5AC overexpression. Collectively, our results suggest that activation of TRPA1 and EGFR, paired with alterations to p38 MAPK and GSK3β activity, plays a major role in MUC5AC overproduction by bronchial epithelial cells exposed to biomass smoke PM. These results reveal specific processes for how biomass smoke PM may impact the human respiratory system and highlight potential avenues for therapeutic manipulation of lung diseases that are affected by air pollutants.

Less airway inflammation and goblet cell metaplasia in an IL-33-induced asthma model of leptin-deficient obese mice

BACKGROUND

Obesity-associated asthma is a phenotype of severe asthma. Late-onset, non-eosinophilic and female-dominant phenotype is highly symptomatic and difficult to treat. Leptin, an adipokine, exerts an immunomodulatory effect. IL-33 associated with innate immunity induces type 2 inflammation and is present in adipose tissue. The purpose of this study was to elucidate the pathogenesis of obesity-associated asthma by focusing on the interaction between leptin and IL-33.

METHODS

In leptin-deficient obese (ob/ob) and wild-type mice, IL-33 was instilled intranasally on three consecutive days. In part of the mice, leptin was injected intraperitoneally prior to IL-33 treatment. The mice were challenged with methacholine, and airway hyperresponsiveness (AHR) was assessed by resistance (Rrs) and elastance (Ers) of the respiratory system using the forced oscillation technique. Cell differentiation, IL-5, IL-13, eotaxin, keratinocyte-derived chemokine (KC) in bronchoalveolar lavage fluid (BALF) and histology of the lung were analyzed. For the in vitro study, NCI-H292 cells were stimulated with IL-33 in the presence or absence of leptin. Mucin-5AC (MUC5AC) levels were measured using an enzyme-linked immunosorbent assay.

RESULTS

Ob/ob mice showed greater Rrs and Ers than wild-type mice. IL-33 with leptin, but not IL-33 alone, enhanced Ers rather than Rrs challenged with methacholine in ob/ob mice, whereas it enhanced Rrs alone in wild-type mice. IL-33-induced eosinophil numbers, cytokine levels in BALF, eosinophilic infiltration around the bronchi, and goblet cell metaplasia were less in ob/ob mice than in wild-type mice. However, leptin pretreatment attenuated these changes in ob/ob mice. MUC5AC levels were increased by co-stimulation with IL-33 and leptin in vitro.

CONCLUSIONS

Ob/ob mice show innate AHR. IL-33 with leptin, but not IL-33 alone, induces airway inflammation and goblet cell metaplasia and enhances AHR involving peripheral airway closure. This is presumably accelerated by mucus in ob/ob mice. These results may explain some aspects of the pathogenesis of obesity-associated asthma.

Goblet Cell Differentiation Potential in Human Corneal Limbal Epithelial Progenitor Cells In Vitro

Purpose

The existence of goblet cells has been regarded as a critical differential point to distinguish conjunctival epithelium from corneal epithelium in vivo. We tested differentiation potential of single progenitor cells from corneal limbal epithelium with growth factors in vitro.

Methods

Dissociated single cells from corneal limbal epithelium were cultured in the serum- and feeder cell–free medium containing B27 and various growth factors using nontissue culture dishes. Specific marker expression was examined in the colonies stimulated with growth factors. Differentiation of some mucosal epithelia was tested.

Results

Adherent single cells from dissociated single cells in corneal limbal epithelium did not proliferate in the serum- and feeder cell–free medium containing B27 only and formed corneal epithelium with B27 plus epidermal growth factor, while they gave rise to goblet cell with periodic acid Schiff–positive mucin and cytokeratin-3 and-12 expressing corneal epithelium with fibroblast growth factor (FGF)2 stimulation. Colonies stimulated with FGF2 expressed goblet cell specific MUC5AC and cytokeratin-7 mRNA and protein. FGF receptor 1 was a functional receptor for the differentiation to goblet cells and corneal epithelium.

Conclusions

Single corneal limbal progenitor cells give rise to goblet cells and corneal epithelium by FGF2 stimulation via FGF receptor 1 in vitro.

Kaempferol Regulates the Expression of Airway MUC5AC Mucin Gene via IκBα-NF-κB p65 and p38-p44/42-Sp1 Signaling Pathways

In the present study, kaempferol, a flavonoidal natural compound found in Polygonati Rhizoma, was investigated for its potential effect on the gene expression and production of airway MUC5AC mucin. A human respiratory epithelial NCI-H292 cells was pretreated with kaempferol for 30 min and stimulated with epidermal growth factor (EGF) or phorbol 12-myristate 13-acetate (PMA), for the following 24 h. The effect on PMA-induced nuclear factor kappa B (NF-κB) signaling pathway or EGF-induced mitogen-activated protein kinase (MAPK) signaling pathway was investigated. Kaempferol suppressed the production and gene expression of MUC5AC mucins, induced by PMA through the inhibition of degradation of inhibitory kappa Bα (IκBα), and NF-κB p65 nuclear translocation. Also, kaempferol inhibited EGF-induced gene expression and production of MUC5AC mucin through regulating the phosphorylation of EGFR, phosphorylation of p38 MAPK and extracellular signal-regulated kinase (ERK) 1/2 (p44/42), and the nuclear expression of specificity protein-1 (Sp1). These results suggest kaempferol regulates the gene expression and production of mucin through regulation of NF-κB and MAPK signaling pathways, in human airway epithelial cells.

Bisacodyl Suppresses TGF-α-Induced MUC5AC Production in NCI-H292 Cells

MUC5AC overproduction is commonly observed in chronic inflammatory lung diseases and worsens these conditions. Therefore, drugs that inhibit MUC5AC production are urgently needed. To identify novel drugs directly inhibiting MUC5AC production, 640 already approved drugs were screened. We found that the laxative bisacodyl suppressed transforming growth factor (TGF)-α-induced MUC5AC production in a concentration-dependent manner. Additionally, bisacodyl also suppressed TGF-α-induced MUC5AC mRNA expression in the same concentration range. These results suggested that bisacodyl could be a new drug for treating mucin overproduction.

Influence of Hypoxia on the Epithelial-Pathogen Interactions in the Lung: Implications for Respiratory Disease

Under normal physiological conditions, the lung remains an oxygen rich environment. However, prominent regions of hypoxia are a common feature of infected and inflamed tissues and many chronic inflammatory respiratory diseases are associated with mucosal and systemic hypoxia. The airway epithelium represents a key interface with the external environment and is the first line of defense against potentially harmful agents including respiratory pathogens. The protective arsenal of the airway epithelium is provided in the form of physical barriers, and the production of an array of antimicrobial host defense molecules, proinflammatory cytokines and chemokines, in response to activation by receptors. Dysregulation of the airway epithelial innate immune response is associated with a compromised immunity and chronic inflammation of the lung. An increasing body of evidence indicates a distinct role for hypoxia in the dysfunction of the airway epithelium and in the responses of both innate immunity and of respiratory pathogens. Here we review the current evidence around the role of tissue hypoxia in modulating the host-pathogen interaction at the airway epithelium. Furthermore, we highlight the work needed to delineate the role of tissue hypoxia in the pathophysiology of chronic inflammatory lung diseases such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease in addition to novel respiratory diseases such as COVID-19. Elucidating the molecular mechanisms underlying the epithelial-pathogen interactions in the setting of hypoxia will enable better understanding of persistent infections and complex disease processes in chronic inflammatory lung diseases and may aid the identification of novel therapeutic targets and strategies.

Ibudilast Suppresses MUC5AC Mucus Production through Inhibition of ERK1/2 Phosphorylation

Mucus hypersecretion is a hallmark of respiratory diseases, and excess airway mucus can worsen these conditions. Therefore, it is important to control the production of airway mucus in the treatment of respiratory diseases. The phosphodiesterase inhibitor ibudilast has been reported to be effective in treating sputum and postnasal drip in patients with chronic airway inflammation. On the basis of the hypothesis that ibudilast could inhibit mucus production in the airway, in the present study, we examined the effects of ibudilast on the production of MUC5AC, a major protein component of mucus. In in vitro studies using NCI-H292 cells, ibudilast suppressed MUC5AC production induced by various stimuli. In addition, ibudilast inhibited extracellular signal-regulated kinase (ERK)1/2 phosphorylation and MUC5AC gene transcription. Furthermore, it attenuated MUC5AC production and Muc5ac mRNA expression in lipopolysaccharide-treated mice in vivo. Collectively, these findings demonstrate that ibudilast has an inhibitory effect on mucus production, which could at least partly be attributed to the inhibition of ERK1/2 phosphorylation and the repression of MUC5AC gene transcription.

Bronchoconstriction: a potential missing link in airway remodelling

In asthma, progressive structural changes of the airway wall are collectively termed airway remodelling. Despite its deleterious effect on lung function, airway remodelling is incompletely understood. As one of the important causes leading to airway remodelling, here we discuss the significance of mechanical forces that are produced in the narrowed airway during asthma exacerbation, as a driving force of airway remodelling. We cover in vitro, ex vivo and in vivo work in this field, and discuss up-to-date literature supporting the idea that bronchoconstriction may be the missing link in a comprehensive understanding of airway remodelling in asthma.

Airway Epithelial Dysfunction in Asthma: Relevant to Epidermal Growth Factor Receptors and Airway Epithelial Cells

Airway epithelium plays an important role as the first barrier from external pathogens, including bacteria, viruses, chemical substances, and allergic components. Airway epithelial cells also have pivotal roles as immunological coordinators of defense mechanisms to transfer signals to immunologic cells to eliminate external pathogens from airways. Impaired airway epithelium allows the pathogens to remain in the airway epithelium, which induces aberrant immunological reactions. Dysregulated functions of asthmatic airway epithelium have been reported in terms of impaired wound repair, fragile tight junctions, and excessive proliferation, leading to airway remodeling, which contributes to aberrant airway responses caused by external pathogens. To maintain airway epithelium integrity, a family of epidermal growth factor receptors (EGFR) have pivotal roles in mechanisms of cell growth, proliferation, and differentiation. There are extensive studies focusing on the relation between EGFR and asthma pathophysiology, which describe airway remodeling, airway hypermucus secretion, as well as immunological responses of airway inflammation. Furthermore, the second EGFR family member, erythroblastosis oncogene B2 (ErbB2), has been recognized to be involved with impaired wound recovery and epithelial differentiation in asthmatic airway epithelium. In this review, the roles of the EGFR family in asthmatic airway epithelium are focused on to elucidate the pathogenesis of airway epithelial dysfunction in asthma.

Diclofenac Inhibits Phorbol Ester-Induced Gene Expression and Production of MUC5AC Mucin via Affecting Degradation of IkBα and Translocation of NF-kB p65 in NCI-H292 Cells

In this study, diclofenac, a non-steroidal anti-inflammatory drug, was investigated for its potential effect on the gene expression and production of airway MUC5AC mucin. The human respiratory epithelial NCI-H292 cells were pretreated with diclofenac for 30 min and stimulated with phorbol 12-myristate 13-acetate (PMA), for the following 24 h. The effect of diclofenac on PMA-induced nuclear factor kappa B (NF-kB) signaling pathway was also investigated. Diclofenac suppressed the production and gene expression of MUC5AC mucins, induced by PMA through the inhibition of degradation of inhibitory kappa Bα (IkBα) and NF-kB p65 nuclear translocation. These results suggest diclofenac regulates the gene expression and production of mucin through regulation of NF-kB signaling pathway, in human airway epithelial cells.

Epidermal growth factor upregulates expression of MUC5AC via TMEM16A, in chronic rhinosinusitis with nasal polyps

Background

Mucus hypersecretion and goblet cell upregulation are common features of chronic rhinosinusitis with nasal polyps (CRSwNP). Although epidermal growth factor (EGF) has been reported to stimulate the expression of MUC5AC, the major macro-molecular constituent of airway mucus, the precise mechanisms underlying the regulation of MUC5AC expression are still not fully understood. The aim of this study therefore was to investigate the role of EGF in regulation of mucin MUC5AC expression and define the involvement of transmembrane protein 16A (TMEM16A) in mediating the EGF-induced mucus overexpression.

Methods

Human nasal epithelial cells (HNECs) derived from tissue of patients with CRSwNP and control subjects were established as air-liquid interface (ALI) cultures. Differentiated cultures were treated with different concentrations of EGF for 4-24 h, and assessed for the expression of TMEM16A and MUC5AC by real-time RT-PCR, Western blotting, ELISA and immunofluorescence. Cultures pretreated for 30 min with T16Ainh-A01 (a specific TMEM16A inhibitor) or LY294002 (a phosphoinositide 3-kinase (PI3K) inhibitor) were also assessed similarly following EGF treatment.

Results

EGF treatment (10-100 ng/ml for 4-24 h) significantly increased the expression of both TMEM16A and MUC5AC mRNA and protein, as well as the percentage of TMEM16A-positive cells, MUC5AC-positive cells and cells coexpressing TMEM16A and MUC5AC in HNECs compared to control non-EGF-treated HNECs. Pretreatment of the HNECs with T16Ainh-A01 and LY294002 attenuated these EGF-induced effects.

Conclusions

This study demonstrated that EGF upregulates the expression of MUC5AC in HNECs from CRSwNP patients. Furthermore, the EGF-mediated regulation of MUC5AC expression is likely to involve a PI3K-TMEM16A signalling pathway in CRSwNP.

Airway Remodeling in Asthma

Asthma is an inflammatory disease of the airways that may result from exposure to allergens or other environmental irritants, resulting in bronchoconstriction, wheezing, and shortness of breath. The structural changes of the airways associated with asthma, broadly referred to as airway remodeling, is a pathological feature of chronic asthma that contributes to the clinical manifestations of the disease. Airway remodeling in asthma constitutes cellular and extracellular matrix changes in the large and small airways, epithelial cell apoptosis, airway smooth muscle cell proliferation, and fibroblast activation. These pathological changes in the airway are orchestrated by crosstalk of different cell types within the airway wall and submucosa. Environmental exposures to dust, chemicals, and cigarette smoke can initiate the cascade of pro-inflammatory responses that trigger airway remodeling through paracrine signaling and mechanostimulatory cues that drive airway remodeling. In this review, we explore three integrated and dynamic processes in airway remodeling: (1) initiation by epithelial cells; (2) amplification by immune cells; and (3) mesenchymal effector functions. Furthermore, we explore the role of inflammaging in the dysregulated and persistent inflammatory response that perpetuates airway remodeling in elderly asthmatics.

MUC1 contributes to goblet cell metaplasia and MUC5AC expression in response to cigarette smoke in vivo

Goblet cell metaplasia (GCM) and mucin overproduction are a hallmark of chronic rhinosinusitis (CRS) and chronic obstructive pulmonary disease (COPD). In the airways, cigarette smoke (CS) induces activation of the epidermal growth factor receptor (EGFR) leading to GCM and overexpression of the gel-forming mucin MUC5AC. Although previous studies have demonstrated that a membrane-bound mucin, MUC1, modulates the activation of CS-induced EGFR, the role of MUC1 in CS-induced GCM and mucin overproduction has not been explored. In response to CS exposure, wild-type (WT) rats displayed Muc1 translocation from the apical surface of airway epithelium to the intracellular compartment of hyperplastic intermediate cells, EGFR phosphorylation, GCM, and Muc5ac overproduction. Similarly, human CRS sinonasal tissues demonstrated hyperplasia of intermediate cells enriched with MUC1 in the intracellular compartment, which was accompanied by GCM and increased MUC5AC expression. To further evaluate the role of Muc1 in vivo, a Muc1 knockout (KO) rat (MUC in humans and Muc in animals) was developed. In contrast to WT littermates, Muc1-KO rats exhibited no activation of EGFR, and were protected from GCM and Muc5ac overproduction. Genetic knockdown of MUC1 in human lung or Muc1 knockout in primary rat airway epithelial cells led to significantly diminished EGF-induced MUC5AC production. Together, these findings suggest that MUC1-dependent EGFR activation mediates CS-induced GCM and mucin overproduction. Strategies designed to suppress MUC1-dependent EGFR activation may provide a novel therapeutic approach for treating mucin hypersecretion in CRS and COPD.

More Than Just a Barrier: The Immune Functions of the Airway Epithelium in Asthma Pathogenesis

Allergic bronchial asthma is a chronic disease of the airways that is characterized by symptoms like respiratory distress, chest tightness, wheezing, productive cough, and acute episodes of broncho-obstruction. This symptom-complex arises on the basis of chronic allergic inflammation of the airway wall. Consequently, the airway epithelium is central to the pathogenesis of this disease, because its multiple abilities directly have an impact on the inflammatory response and thus the formation of the disease. In turn, its structure and functions are markedly impaired by the inflammation. Hence, the airway epithelium represents a sealed, self-cleaning barrier, that prohibits penetration of inhaled allergens, pathogens, and other noxious agents into the body. This barrier is covered with mucus that further contains antimicrobial peptides and antibodies that are either produced or specifically transported by the airway epithelium in order to trap these particles and to remove them from the body by a process called mucociliary clearance. Once this first line of defense of the lung is overcome, airway epithelial cells are the first cells to get in contact with pathogens, to be damaged or infected. Therefore, these cells release a plethora of chemokines and cytokines that not only induce an acute inflammatory reaction but also have an impact on the alignment of the following immune reaction. In case of asthma, all these functions are impaired by the already existing allergic immune response that per se weakens the barrier integrity and self-cleaning abilities of the airway epithelium making it more vulnerable to penetration of allergens as well as of infection by bacteria and viruses. Recent studies indicate that the history of allergy- and pathogen-derived insults can leave some kind of memory in these cells that can be described as imprinting or trained immunity. Thus, the airway epithelium is in the center of processes that lead to formation, progression and acute exacerbation of asthma.

Epidermal growth factor receptor (EGFR) involvement in epithelial-derived cancers and its current antibody-based immunotherapies

The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein that is part of the family of tyrosine kinase receptors. The binding of EGFR to its cognate ligands leads to its autophosphorylation and subsequent activation of the signal transduction pathways involved in regulating cellular proliferation, differentiation, and survival. Accordingly, this receptor carries out both redundant and restricted functions in the germline development of mammals and in the maintenance of various adult tissues. Correspondingly, the loss of EGFR regulation results in many human diseases, with the most notable cancer. This receptor is overexpressed and/or mutated in multiple epithelial-derived tumors, and associated with poor prognosis and survival in cancer patients. Here, we discuss in detail the role of EGFR in specific epithelial-derived cancer pathologies; these include lung cancer, colorectal cancer, and squamous cell carcinomas. The development of multiple anticancer agents against EGFR diminished the progression and metastasis of tumors. Some of the most versatile therapeutic anti-EGFR agents include the monoclonal antibodies (mAbs), demonstrating success in clinical settings when used in combination with cytotoxic treatments, such as chemotherapy and/or radiation. We thus discuss the development and application of two of the most notable therapeutic mAbs, cetuximab, and panitumumab, currently utilized in various EGFR-related epithelial cancers.

Erlotinib Protects LPS-Induced Acute Lung Injury in Mice by Inhibiting EGFR/TLR4 Signaling Pathway

Epidermal growth factor receptor (EGFR) has been reported to initiate the inflammatory response, but its activation in lipopolysaccharide (LPS)-induced murine model of acute lung injury (ALI) remains unclear. In this study, we investigated the role of EGFR in the LPS-induced murine model of ALI and explored whether its inhibitor erlotinib could affect the progression of lung injury. We first detected the phosphorylated EGFR (p-EGFR)/EGFR ratio at different time points after LPS stimulation, and then different concentrations of erlotinib were used to treat mice at 1 h before LPS stimulation and collected samples at the time point of the highest p-EGFR/EGFR ratio. Lung injury indicators were detected and compared among groups. EGFR and toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signal transduction factors, including p-EGFR, p-AKT, p-ERK1/2, p-p65, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β), were measured with western blot. We found that the mice challenged with LPS suffered from the most serious lung injury at 24 h after LPS stimulation when the p-EGFR/EGFR ratio was relatively the highest. Erlotinib significantly diminished LPS-induced exudation of total cells, neutrophils, and proteins in BALF. Both the ELISA and western blot results showed that erlotinib attenuated the expression of TNF-α and IL-1β in LPS-induced ALI in mice. Inhibition of EGFR by erlotinib downregulated the expression of p-p65 protein level as well as blocked the activation of AKT and ERK1/2 signaling pathway. Taken together, erlotinib alleviated the LPS-induced ALI in a dose-dependent manner by suppressing EGFR activation and downregulating the NF-κB-mediated secretion of proinflammatory cytokines.

Eupatilin downregulates phorbol 12-myristate 13-acetate-induced MUC5AC expression via inhibition of p38/ERK/JNK MAPKs signal pathway in human airway epithelial cells

Chronic inflammatory airway diseases, such as chronic rhinosinusitis, chronic obstructive pulmonary disease, and asthma, are associated with excessive mucus production. Hence, the regulation of mucus production is important for the treatment of upper and lower airway diseases. Eupatilin is a pharmacologically active ingredient obtained from Artemisia asiatica Nakai (Asteraceae) and exerts potent anti-inflammatory, anti-allergic, and anti-tumor activities. In the present study, we investigated the effect of eupatilin on phorbol 12-myristate 13-acetate (PMA)-induced MUC5AC and MUC5B expression in human airway epithelial cells. We found that eupatilin treatment significantly inhibited PMA-induced mucus secretion in PAS staining. In addition, qRT-PCR results showed that eupatilin dose-dependently decreased the mRNA expression of MUC5AC in human airway epithelial cells. Western blot and immunofluorescence assay also showed that PMA-induced protein expression of MUC5AC was inhibited by eupatilin treatment. Finally, we investigated MAPKs activity after stimulation with PMA using western blot analysis in human airway epithelial cells. The results showed that eupatilin downregulated the levels of phosphorylated p38, ERK, and JNK. In summary, the anti-inflammatory activities of eupatilin, characterized as the suppression of MUC5AC expression and secretion in human airway epithelial cells, were found to be associated with the inhibition of p38/ERK/JNK MAPKs signaling pathway of MUC5AC secretion.

Suhuang Antitussive Capsules-Ameliorative Effects on LPS-Induced Sputum Obstruction in Mice Through Promoting HGF Secretion

Sputum obstruction is one of common cough complications, which is tightly associated with airway inflammation. Suhuang antitussive capsule (SH Capsule), a classic traditional Chinese medicine prescription, has been used for the treatment of post-cold cough and cough variant asthma in the long clinical application. This study aims to investigate the effects and underlying mechanisms of SH Capsule on LPS-induced sputum obstruction in mice. The results showed that SH Capsule effectively promoted the tracheal phenol red output and mucociliary clearance. SH Capsule also alleviated airway inflammation-mediated mucin 5AC (MUC5AC) level through EGFR-ERK signaling. A further in vivo analysis showed that HGF inhibitor SU11274 abrogated the effects of SH Capsule on MUC5AC, well demonstrating that HGF was required for the beneficial effects of SH Capsule on expectoration in vivo. Moreover, SH Capsule promoted HGF secretion in a colon-dependent manner, which reached lung tissues via blood circulation. Collectively, this study provided new pharmacological data for clinical use of SH Capsule, and proposed a novel mechanism by which SH Capsule was pharmacologically promising for treating sputum obstruction.

Type IV collagen reduces mucin 5AC secretion in three-dimensional cultured human primary airway epithelial cells

Mucin 5AC (MUC5AC) hypersecretion induces airway narrowing in patients with asthma, which leads to breathing problems. We investigated the regulation of MUC5AC secretion by extracellular matrix (ECM) proteins in human primary airway epithelial cells from patients with asthma. The addition of type IV collagen to three-dimensional cultured human primary airway epithelial cells, which mimics the airway surface, reduced MUC5AC secretion in the medium, while the addition of laminin increased MUC5AC secretion. Furthermore, the addition of fibronectin did not affect MUC5AC secretion. In particular, the repeated addition of a low concentration of type IV collagen demonstrated a cumulative effect on the reduction in MUC5AC secretion. Human primary cells incubated with type IV collagen showed downregulated extracellular signal-regulated kinase (ERK) activity, which induced MUC5AC hypersecretion but did not affect Akt activity. These results suggest that the addition of type IV collagen to the apical surface of primary cells downregulates MUC5AC secretion and has a cumulative effect on MUC5AC secretion which might be effected via the ERK signaling pathway.

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We studied the regulation of MUC5AC secretion by extracellular matrix proteins.

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The addition of type IV collagen reduced MUC5AC secretion in primary airway cells.

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The repeated addition of a low concentration of collagen reduced MUC5AC secretion.

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Type IV collagen induced the downregulation of ERK which induces MUC5AC secretion.

Pravastatin alleviates allergic airway inflammation in obesity-related asthma mouse model

Background: Obesity is one of the factors associated with severe, uncontrolled asthma. The effect of pravastatin on asthmatic airway inflammation in obesity has not been evaluated. Methods: C57BL/6 mice were fed a high-fat diet (HFD) to induce obesity with or without ovalbumin (OVA) sensitization and challenge. Pravastatin was administered intraperitoneally during the OVA treatment. Airway inflammation and airway hyper-responsiveness (AHR) were analyzed and lung tissues were examined. The changes in mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/Akt signaling pathways were measured in the lung tissues. Results: HFD with OVA sensitization and challenge exacerbated eosinophilic and neutrophilic airway inflammation and increased AHR compared to lean asthma mice. The levels of cytokines examined in bronchoalveolar lavage fluid (BALF) revealed that the expressions of IL-4, 5, and 17 were elevated in the obese asthmatic group and decreased after pravastatin treatment, indicating that both the Th2 and Th17 pathways were stimulated by HFD-induced obesity and OVA challenge and suppressed by pravastatin treatment. Moreover, the serum leptin and adiponectin ratio was elevated only in obese asthmatic mice and decreased with pravastatin administration. Pravastatin successfully alleviated the airway inflammation of lung tissues and AHR in both obese and lean asthmatic mice, however, treatment with pravastatin had no effects on BALF cell counts and cytokines in lean asthma mice. In lung tissues, the phosphorylation of p38 MAPK was significantly decreased in lean as well as obese asthmatic mice. Conclusions: Pravastatin treatment in obese asthmatic mice suppressed allergic airway infiltration and AHR by inhibition of Th2 and Th17-associated signaling pathways, decreasing the leptin expression and downstream p38 MAPK signaling pathways. The effect on lean asthmatic mice was different, independent of airway cell counts and cytokines.

Carbocisteine inhibits the expression of Muc5b in COPD mouse model

Background

Cigarette smoke (CS) results in chronic mucus hypersecretion and airway inflammation, contributing to COPD pathogenesis. Mucin 5B (MUC5B) and mucin 5 AC (MUC5AC) are major mucins implicated in COPD pathogenesis. Carbocisteine can reduce mucus viscosity and elasticity. Although carbocisteine decreased human elastase-induced MUC5AC expression in vitro and reduced MUC5AC expression that alleviated bacteria adhesion and improved mucus clearance in vivo, the roles of carbocisteine in inducing MUC5B expression in COPD remain unclear.

Methods

To investigate the Muc5b/Muc5ac ratio and the gene and protein levels of Muc5b in COPD and carbocisteine intervention models. C57B6J mice were used to develop COPD model by instilling intratracheally with lipopolysaccharide on days 1 and 14 and were exposed to CS for 2 hr twice a day for 12 weeks. Low and high doses of carbocisteine 112.5 and 225 mg/kg/d, respectively, given by gavage administration were applied for the treatment in COPD models for the same duration, and carboxymethylcellulose was used as control. Carbocisteine significantly attenuated inflammation in bronchoalveolar lavage fluid and pulmonary tissue, improved pulmonary function and protected against emphysema.

Results

High-dose carbocisteine significantly decreased the overproduction of Muc5b (P<0.01) and Muc5ac (P<0.001), and restored Muc5b/Muc5ac ratio in COPD model group (P<0.001). Moreover, the Muc5b/Muc5ac ratio negatively correlated with pro-inflammatory cytokines such as IL-6 and keratinocyte-derived cytokine, mean linear intercept, functional residual capacity and airway resistance, but positively correlated with dynamic compliance.

Conclusions

These findings suggest that carbocisteine attenuated Muc5b and Muc5ac secretion and restored Muc5b protein levels, which may improve mucus clearance in COPD.

Estrogen and EGFR Pathways Regulate Notch Signaling in Opposing Directions for Multi-Ciliogenesis in the Fallopian Tube

The lumen of the fallopian tube (FT) is lined with columnar epithelium composed of secretory and ciliated cells, both of which are important for reproduction. However, the molecular mechanism regulating cell fate remains controversial. In this study, we established a primary culture system using porcine fallopian tube epithelial cells (FTECs) to study the differentiation mechanism. We found that estrogen promoted the differentiation of multi-ciliated cells (MCCs) through estrogen receptor β, following the reduction of DLL1, a ligand of Notch. Meanwhile, epidermal growth factor (EGF), a regulator of epithelial homeostasis and differentiation, suppressed ciliogenesis by the activation of Notch signaling. However, the estrogen pathway did not affect the activation of the EGF pathway. Taken together, the differentiation of MMCs in FT depends on the balance of EGF and estrogen signaling, either of which inhibits or stimulates the Notch signaling pathway respectively.

VEGF and FGF-2: Promising targets for the treatment of respiratory disorders

The endothelial cells play a crucial role in the progression of angiogenesis, which causes cell re-modulation, proliferation, adhesion, migration, invasion and survival. Angiogenic factors like cytokines, cell adhesion molecules, growth factors, vasoactive peptides, proteolytic enzymes (metalloproteinases) and plasminogen activators bind to their receptors on endothelial cells and activate the signal transduction pathways like epidermal growth factor receptor (EGFR phosphatidylinositol 3-kinase and (PI3K)/AKT/mammalian target of rapamycin (mTOR) which initiate the process of angiogenesis. Cytokines that stimulate angiogenesis include direct and indirect proangiogenic markers. The direct proangiogenic group of markers consists of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (FGF-2) and hepatocyte growth factor (HGF) whereas the indirect proangiogenic markers include transforming growth factor-beta (TGF-β), interleukin 6 (IL-6), interleukin 8 (IL-8) and platelet-derived growth factor (PDGF). VEGF and FGF-2 are the strongest activators of angiogenesis which stimulate migration and proliferation of endothelial cells in existing vessels to generate and stabilize new blood vessels. VEGF is released in hypoxic conditions as an effect of the hypoxia-inducible factor (HIF-1α) and causes re-modulation and inflammation of bronchi cell. Cell re-modulation and inflammation leads to the development of various lung disorders like pulmonary hypertension, chronic obstructive pulmonary disease, asthma, fibrosis and lung cancer. This indicates that there is a firm link between overexpression of VEGF and FGF-2 with lung disorders. Various natural and synthetic drugs are available for reducing the overexpression of VEGF and FGF-2 which can be helpful in treating lung disorders. Researchers are still searching for new angiogenic inhibitors which can be helpful in the treatment of lung disorders. The present review emphasizes on molecular mechanisms and new drug discovery focused on VEGF and FGF-2 inhibitors and their role as anti-angiogenetic agents in lung disorders.

Natural inhibitors on airway mucin: Molecular insight into the therapeutic potential targeting MUC5AC expression and production

Airway mucin overproduction is the hallmark risk factor of asthma, which is associated with the reduction of lung function. An aberrant mucin expression is responsible for airway obstruction due to its high viscous characteristics. Among the mucins discovered, MUC5AC is the prime mucin of airway epithelia. Nowadays, mucins induced asthma and chronic obstructive pulmonary disease (COPD) are a great concern all over the world. This review focuses on the effects of natural compounds that can be beneficial to explore new drugs to halt MUC5AC secretion and production in airway epithelial, and also their underlying molecular mechanisms based on recent studies. Several researchers are seeking natural sources to identify a new potent MUC5AC inhibitory agent for clinical applications, because of countable limitations of existing synthetic drugs. Currently, flavonoids, glycoside and steroids like natural compounds have acquired great attention due to their anti-inflammatory and mucoregulatory effects. Most importantly, many natural compounds have shown their potential effects as the modulator of mucin expression, secretion, and production. Therefore, targeting airway MUC5AC expression and production represents an auspicious area of research for the development of drugs against various respiratory diseases.