Pulmonary epithelial barrier function: some new players and mechanisms

GLUT1 Promotes NLRP3 Inflammasome Activation of Airway Epithelium in Lipopolysaccharide-Induced Acute Lung Injury

Acute lung injury (ALI) is a devastating clinical syndrome caused by different factors, with high morbidity and mortality. Lung injury and inflammation caused by lipopolysaccharide (LPS) can be modulated by NLRP3 inflammasome activation, yet its exact function within the airway epithelium is still unknown. Meanwhile, glucose transporter protein 1 (GLUT1) contributes to a number of inflammatory illnesses, including ALI. The present study aimed to assess GLUT1's function in NLRP3 inflammasome activation of airway epithelium in LPS-induced acute lung injury. BALB/c mice and BEAS-2B cells were exposed to LPS (5 mg/kg and 200 μg/mL, respectively), with or without GLUT1 antagonists (WZB117 or BAY876). LPS up-regulated pulmonary expression of NLRP3 and GLUT1 in mice, which could be blocked by WZB117 or BAY876. Pharmacological inhibition of GLUT1 in vivo significantly attenuated lung tissue damage, neutrophil accumulation, and proinflammatory factors release (TNF-α, IL-6, and IL-1β) in LPS-exposed mice. Meanwhile, the activation markers of NLRP3 inflammasome (ASC, caspase-1, IL-1β, and IL-18) induced by LPS were also suppressed. In cultured BEAS-2B cells, LPS induced an increase in GLUT1 expression and triggered activation of the NLRP3 inflammasome, both of which were inhibited by GLUT1 antagonists. These results illustrate that GLUT1 participates in LPS-induced ALI and promotes the activation of the NLRP3 inflammasome in airway epithelial cells.

Exposure to Environmental Toxins: Potential Implications for Stroke Risk via the Gut- and Lung-Brain Axis

Recent evidence indicates that exposure to environmental toxins, both short-term and long-term, can increase the risk of developing neurological disorders, including neurodegenerative diseases (i.e., Alzheimer's disease and other dementias) and acute brain injury (i.e., stroke). For stroke, the latest systematic analysis revealed that exposure to ambient particulate matter is the second most frequent stroke risk after high blood pressure. However, preclinical and clinical stroke investigations on the deleterious consequences of environmental pollutants are scarce. This review examines recent evidence of how environmental toxins, absorbed along the digestive tract or inhaled through the lungs, affect the host cellular response. We particularly address the consequences of environmental toxins on the immune response and the microbiome at the gut and lung barrier sites. Additionally, this review highlights findings showing the potential contribution of environmental toxins to an increased risk of stroke. A better understanding of the biological mechanisms underlying exposure to environmental toxins has the potential to mitigate stroke risk and other neurological disorders.

Serine protease Rv2569c facilitates transmission of Mycobacterium tuberculosis via disrupting the epithelial barrier by cleaving E-cadherin

Epithelial cells function as the primary line of defense against invading pathogens. However, bacterial pathogens possess the ability to compromise this barrier and facilitate the transmigration of bacteria. Nonetheless, the specific molecular mechanism employed by Mycobacterium tuberculosis (M.tb) in this process is not fully understood. Here, we investigated the role of Rv2569c in M.tb translocation by assessing its ability to cleave E-cadherin, a crucial component of cell-cell adhesion junctions that are disrupted during bacterial invasion. By utilizing recombinant Rv2569c expressed in Escherichia coli and subsequently purified through affinity chromatography, we demonstrated that Rv2569c exhibited cell wall-associated serine protease activity. Furthermore, Rv2569c was capable of degrading a range of protein substrates, including casein, fibrinogen, fibronectin, and E-cadherin. We also determined that the optimal conditions for the protease activity of Rv2569c occurred at a temperature of 37°C and a pH of 9.0, in the presence of MgCl2. To investigate the function of Rv2569c in M.tb, a deletion mutant of Rv2569c and its complemented strains were generated and used to infect A549 cells and mice. The results of the A549-cell infection experiments revealed that Rv2569c had the ability to cleave E-cadherin and facilitate the transmigration of M.tb through polarized A549 epithelial cell layers. Furthermore, in vivo infection assays demonstrated that Rv2569c could disrupt E-cadherin, enhance the colonization of M.tb, and induce pathological damage in the lungs of C57BL/6 mice. Collectively, these results strongly suggest that M.tb employs the serine protease Rv2569c to disrupt epithelial defenses and facilitate its systemic dissemination by crossing the epithelial barrier.

Ezrin Contributes to the Damage of Airway Epithelial Barrier Related to Diabetes Mellitus

Background

Diabetes mellitus predisposes individuals to respiratory infections. The airway epithelial barrier provides defense against inhaled antigens and pathogens. Ezrin, is a component of the membrane-cytoskeleton that maintains the cellular morphology, intercellular adhesion, and barrier function of epithelial cells. This study aimed to explore the role of ezrin in airway epithelial barrier damage and correlate its expression and activation with diabetes mellitus.

Methods

This study was performed in a murine model of diabetes mellitus and with human bronchial epithelial BEAS-2B cells using real-time PCR, Western blotting, immunohistochemical and immunofluorescence staining. Ezrin was knocked down in BEAS-2B cells using siRNA. Ezrin phosphorylation levels were measured to determine activation status. The integrity of the airway epithelial barrier was assessed in vivo by characterizing morphological structure, and in vitro in BEAS-2B cells by measuring tight junction protein expression, transepithelial electrical resistance (TER) and permeability.

Results

We demonstrated that ezrin expression levels were lower in the lung tissue and airway epithelium of diabetic mice than those in control mice. The morphological structure of the airway epithelium was altered in diabetic mice. High glucose levels downregulated the expression and distribution of ezrin and connexin 43, reduced the expression of tight junction proteins, and altered the epithelial barrier characteristics of BEAS-2B cells. Ezrin knockdown had effects similar to those of high glucose levels. Moreover, a specific inhibitor of ezrin Thr567 phosphorylation (NSC305787) inhibited epithelial barrier formation.

Conclusion

These results demonstrate that ezrin expression and activation are associated with airway epithelial damage in diabetes mellitus. These findings provide new insights into the molecular pathogenesis of pulmonary infections in diabetes mellitus and may lead to novel therapeutic interventions for airway epithelial barrier damage.

Molecular Mechanisms Responsible for the Therapeutic Potential of Mesenchymal Stem Cell-Derived Exosomes in the Treatment of Lung Fibrosis

Mesenchymal stem cell-derived exosomes (MSC-Exos) are nano-sized extracellular vesicles which contain various MSC-sourced anti-fibrotic, immunoregulatory and angio-modulatory proteins (growth factors, immunoregulatory cytokines, chemokines), lipids, and nucleic acids (messenger RNA and microRNAs). Due to their lipid envelope, MSC-Exos easily by-pass all barriers in the body and deliver their cargo directly in target cells, modulating their viability, proliferation, phenotype and function. The results obtained in recently published experimental studies demonstrated beneficial effects of MSC-Exos in the treatment of lung fibrosis. MSC-Exos reduced activation of fibroblasts and prevented their differentiation in myofibroblasts. By delivering MSC-sourced immunoregulatory factors in lung-infiltrated monocytes and T cells, MSC-Exos modulate their function, alleviating on-going inflammation and fibrosis. MSC-Exos may also serve as vehicles for the target delivery of anti-fibrotic and immunomodulatory agents, enabling enhanced attenuation of lung fibrosis. Although numerous pre-clinical studies have demonstrated the therapeutic potential of MSC-Exos in the treatment of pulmonary fibrosis, there are several challenges that currently hinder their clinical implementation. Therefore, in this review article, we summarized current knowledge and we discussed future perspectives regarding molecular and cellular mechanisms which were responsible for the anti-fibrotic, anti-inflammatory and immunoregulatory properties of MSC-Exos, paving the way for their clinical use in the treatment of lung fibrosis.

Bacteriophage therapy for the treatment of Mycobacterium tuberculosis infections in humanized mice

The continuing emergence of new strains of antibiotic-resistant bacteria has renewed interest in phage therapy; however, there has been limited progress in applying phage therapy to multi-drug resistant Mycobacterium tuberculosis (Mtb) infections. In this study, we show that bacteriophage strains D29 and DS6A can efficiently lyse Mtb H37Rv in 7H10 agar plates. However, only phage DS6A efficiently kills H37Rv in liquid culture and in Mtb-infected human primary macrophages. We further show in subsequent experiments that, after the humanized mice were infected with aerosolized H37Rv, then treated with DS6A intravenously, the DS6A treated mice showed increased body weight and improved pulmonary function relative to control mice. Furthermore, DS6A reduces Mtb load in mouse organs with greater efficacy in the spleen. These results demonstrate the feasibility of developing phage therapy as an effective therapeutic against Mtb infection.

Liquid application dosing alters the physiology of air-liquid interface (ALI) primary human bronchial epithelial cell/lung fibroblast co-cultures and in vitro testing relevant endpoints

Differentiated primary human bronchial epithelial cell (dpHBEC) cultures grown under air-liquid interface (ALI) conditions exhibit key features of the human respiratory tract and are thus critical for respiratory research as well as efficacy and toxicity testing of inhaled substances (e.g., consumer products, industrial chemicals, and pharmaceuticals). Many inhalable substances (e.g., particles, aerosols, hydrophobic substances, reactive substances) have physiochemical properties that challenge their evaluation under ALI conditions in vitro. Evaluation of the effects of these methodologically challenging chemicals (MCCs) in vitro is typically conducted by "liquid application," involving the direct application of a solution containing the test substance to the apical, air-exposed surface of dpHBEC-ALI cultures. We report that the application of liquid to the apical surface of a dpHBEC-ALI co-culture model results in significant reprogramming of the dpHBEC transcriptome and biological pathway activity, alternative regulation of cellular signaling pathways, increased secretion of pro-inflammatory cytokines and growth factors, and decreased epithelial barrier integrity. Given the prevalence of liquid application in the delivery of test substances to ALI systems, understanding its effects provides critical infrastructure for the use of in vitro systems in respiratory research as well as in the safety and efficacy testing of inhalable substances.

Pathogenicity and virulence of Aspergillus fumigatus

Pulmonary infections caused by the mould pathogen Aspergillus fumigatus are a major cause of morbidity and mortality globally. Compromised lung defences arising from immunosuppression, chronic respiratory conditions or more recently, concomitant viral or bacterial pulmonary infections are recognised risks factors for the development of pulmonary aspergillosis. In this review, we will summarise our current knowledge of the mechanistic basis of pulmonary aspergillosis with a focus on emerging at-risk populations.

Mycobacterium tuberculosis Rv1987 protein attenuates inflammatory response and consequently alters microbiota in mouse lung

Introduction

Healthy lung microbiota plays an important role in preventing Mycobacterium tuberculosis (Mtb) infections by activating immune cells and stimulating production of T-helper cell type 1 cytokines. The dynamic stability of lung microbiota relies mostly on lung homeostasis. In our previous studies, we found that Mtb virulence factor, Rv1987 protein, can mediate host immune response and enhance mycobacterial survival in host lung. However, the alteration of lung microbiota and the contribution of lung microbiota dysbiosis to mycobacterial evasion in this process are not clear so far.

Methods

M. smegmatis which does not contain the ortholog of Rv1987 protein was selected as a model strain to study the effects of Rv1987 on host lung microbiota. The lung microbiota, immune state and metabolites of mice infected by M. smegmatis overexpressing Rv1987 protein (MS1987) were detected and analyzed.

Results

The results showed that Rv1987 inhibited inflammatory response in mouse lung and anaerobic bacteria and Proteobacteria, Bacteroidota, Actinobacteriota and Acidobacteriota bacteria were enriched in the lung tissues correspondingly. The immune alterations and microbiota dysbiosis affected host metabolic profiles, and some of significantly altered bacteria in MS1987-infected mouse lung, such as Delftia acidovorans, Ralstonia pickettii and Escherichia coli, led to anti-inflammatory responses in mouse lung. The secretory metabolites of these altered bacteria also influenced mycobacterial growth and biofilm formation directly.

Conclusion

All these results suggested that Rv1987 can attenuate inflammatory response and alter microbiota in the lung, which in turn facilitates mycobacterial survival in the host.

Microphysiological Models of Lung Epithelium-Alveolar Macrophage Co-Cultures to Study Chronic Lung Disease

The interactions between immune cells and epithelial cells influence the progression of many respiratory diseases, such as chronic obstructive pulmonary disease (COPD). In vitro models allow for the examination of cells in controlled environments. However, these models lack the complex 3D architecture and vast multicellular interactions between the lung resident cells and infiltrating immune cells that can mediate cellular response to insults. In this study, three complementary microphysiological systems are presented to delineate the effects of cigarette smoke and respiratory disease on the lung epithelium. First, the Transwell system allows the co-culture of pulmonary immune and epithelial cells to evaluate cellular and monolayer phenotypic changes in response to cigarette smoke exposure. Next, the human and mouse precision-cut lung slices system provides a physiologically relevant model to study the effects of chronic insults like cigarette smoke with the dissection of specific interaction of immune cell subtypes within the structurally complex tissue environment. Finally, the lung-on-a-chip model provides an adaptable system for live imaging of polarized epithelial tissues that mimic the in vivo environment of the airways. Using a combination of these models, a complementary approach is provided to better address the intricate mechanisms of lung disease.

Lung Microbiome as a Treatable Trait in Chronic Respiratory Disorders

Once thought to be a sterile environment, it is now established that lungs are populated by various microorganisms that participate in maintaining lung function and play an important role in shaping lung immune surveillance. Although our comprehension of the molecular and metabolic interactions between microbes and lung cells is still in its infancy, any event causing a persistent qualitative or quantitative variation in the composition of lung microbiome, termed "dysbiosis", has been virtually associated with many respiratory diseases. A deep understanding of the composition and function of the "healthy" lung microbiota and how dysbiosis can cause or participate in disease progression will be pivotal in finding specific therapies aimed at preventing diseases and restoring lung function. Here, we review lung microbiome dysbiosis in different lung pathologies and the mechanisms by which these bacteria can cause or contribute to the severity of the disease. Furthermore, we describe how different respiratory disorders can be caused by the same pathogen, and that the real pathogenetic mechanism is not only dependent by the presence and amount of the main pathogen but can be shaped by the interaction it can build with other bacteria, fungi, and viruses present in the lung. Understanding the nature of this bacteria crosstalk could further our understanding of each respiratory disease leading to the development of new therapeutic strategies.

Lung cancer associated with combustion particles and fine particulate matter (PM2.5) - The roles of polycyclic aromatic hydrocarbons (PAHs) and the aryl hydrocarbon receptor (AhR)

Air pollution is the leading cause of lung cancer after tobacco smoking, contributing to 20% of all lung cancer deaths. Increased risk associated with living near trafficked roads, occupational exposure to diesel exhaust, indoor coal combustion and cigarette smoking, suggest that combustion components in ambient fine particulate matter (PM2.5), such as polycyclic aromatic hydrocarbons (PAHs), may be central drivers of lung cancer. Activation of the aryl hydrocarbon receptor (AhR) induces expression of xenobiotic-metabolizing enzymes (XMEs) and increase PAH metabolism, formation of reactive metabolites, oxidative stress, DNA damage and mutagenesis. Lung cancer tissues from smokers and workers exposed to high combustion PM levels contain mutagenic signatures derived from PAHs. However, recent findings suggest that ambient air PM2.5 exposure primarily induces lung cancer development through tumor promotion of cells harboring naturally acquired oncogenic mutations, thus lacking typical PAH-induced mutations. On this background, we discuss the role of AhR and PAHs in lung cancer development caused by air pollution focusing on the tumor promoting properties including metabolism, immune system, cell proliferation and survival, tumor microenvironment, cell-to-cell communication, tumor growth and metastasis. We suggest that the dichotomy in lung cancer patterns observed between smoking and outdoor air PM2.5 represent the two ends of a dose-response continuum of combustion PM exposure, where tumor promotion in the peripheral lung appears to be the driving factor at the relatively low-dose exposures from ambient air PM2.5, whereas genotoxicity in the central airways becomes increasingly more important at the higher combustion PM levels encountered through smoking and occupational exposure.

Biomimetic Human Lung Alveolar Interstitium Chip with Extended Longevity

Determining the mechanistic causes of lung diseases, developing new treatments thereof, and assessing toxicity whether from chemical exposures or engineered nanomaterials would benefit significantly from a preclinical human lung alveolar interstitium model of physiological relevance. The existing preclinical models have limitations because they fail to replicate the key anatomical and physiological characteristics of human alveoli. Thus, a human lung alveolar interstitium chip was developed to imitate key alveolar microenvironmental factors including an electrospun nanofibrous membrane as the analogue of the basement membrane for co-culture of epithelial cells with fibroblasts embedded in 3D collagenous gels, physiologically relevant interstitial matrix stiffness, interstitial fluid flow, and 3D breathing-like mechanical stretch. The biomimetic chip substantially improved the epithelial barrier function compared to transwell models. Moreover, the chip having a gel made of a collagen I-fibrin blend as the interstitial matrix sustained the interstitium integrity and further enhanced the epithelial barrier, resulting in a longevity that extended beyond eight weeks. The assessment of multiwalled carbon nanotube toxicity on the chip was in line with the animal study.

Establishment of a porcine bronchial epithelial cell line and its application to study innate immunity in the respiratory epithelium

In vitro culture models that precisely mirror the porcine respiratory epithelium are needed to gain insight into how pathogens and host interact. In this study, a new porcine bronchial epithelial cell line, designated as PBE cells, was established from the respiratory tract of a neonatal pig. PBE cells assumed a cobblestone-epithelial like morphology with close contacts between the cells when they reached confluence. The PBE cell line was characterized in terms of its expression of pattern recognition receptors (PRRs) and its ability to respond to the activation of the Toll-like receptor 3 (TLR3) and TLR4 signaling pathways, which are key PRRs involved in the defense of the respiratory epithelium against pathogens. PBE cells stimulated with poly(I:C) were able to up-regulate the expression of IFN-β, IFN-λ1 (IL-29), IFN-λ3 (IL-28B), the antiviral factors Mx1, OAS1, and PKR, as well as the viral PRRs RIG-1 and MDA5. The expression kinetics studies of immune factors in PBE cells allow us to speculate that this cell line can be a useful in vitro tool to investigate treatments that help to potentiate antiviral immunity in the respiratory epithelium of the porcine host. In addition, poly(I:C) and LPS treatments increased the expression of the inflammatory cytokines TNF-α, IL-6, IL-8, and MCP-1/CCL2 and differentially modulated the expression of negative regulators of the TLR signaling pathways. Then, PBE cells may also allow the evaluation of treatments that can regulate TLR3- and TLR4-mediated inflammatory injury in the porcine airway, thereby protecting the host against harmful overresponses.

Advanced approaches to overcome biological barriers in respiratory and systemic routes of administration for enhanced nucleic acid delivery to the lung

INTRODUCTION

Numerous delivery strategies, primarily novel nucleic acid delivery carriers, have been developed and explored to enable therapeutically relevant lung gene therapy. However, its clinical translation is yet to be achieved despite over 30 years of efforts, which is attributed to the inability to overcome a series of biological barriers that hamper efficient nucleic acid transfer to target cells in the lung.

AREAS COVERED

This review is initiated with the fundamentals of nucleic acid therapy and a brief overview of previous and ongoing efforts on clinical translation of lung gene therapy. We then walk through the nature of biological barriers encountered by nucleic acid carriers administered via respiratory and/or systemic routes. Finally, we introduce advanced strategies developed to overcome those barriers to achieve therapeutically relevant nucleic acid delivery efficiency in the lung.

EXPERT OPINION

We are now stepping close to the clinical translation of lung gene therapy, thanks to the discovery of novel delivery strategies that overcome biological barriers via comprehensive preclinical studies. However, preclinical findings should be cautiously interpreted and validated to ultimately realize meaningful therapeutic outcomes with newly developed delivery strategies in humans. In particular, individual strategies should be selected, tailored, and implemented in a manner directly relevant to specific therapeutic applications and goals.

Effects of sevoflurane on lung epithelial permeability in experimental models of acute respiratory distress syndrome

BACKGROUND

Preclinical studies in acute respiratory distress syndrome (ARDS) have suggested that inhaled sevoflurane may have lung-protective effects and clinical trials are ongoing to assess its impact on major clinical outcomes in patients with ARDS. However, the underlying mechanisms of these potential benefits are largely unknown. This investigation focused on the effects of sevoflurane on lung permeability changes after sterile injury and the possible associated mechanisms.

METHODS

To investigate whether sevoflurane could decrease lung alveolar epithelial permeability through the Ras homolog family member A (RhoA)/phospho-Myosin Light Chain 2 (Ser19) (pMLC)/filamentous (F)-actin pathway and whether the receptor for advanced glycation end-products (RAGE) may mediate these effects. Lung permeability was assessed in RAGE^-/- and littermate wild-type C57BL/6JRj mice on days 0, 1, 2, and 4 after acid injury, alone or followed by exposure at 1% sevoflurane. Cell permeability of mouse lung epithelial cells was assessed after treatment with cytomix (a mixture of TNFɑ, IL-1β, and IFNγ) and/or RAGE antagonist peptide (RAP), alone or followed by exposure at 1% sevoflurane. Levels of zonula occludens-1, E-cadherin, and pMLC were quantified, along with F-actin immunostaining, in both models. RhoA activity was assessed in vitro.

RESULTS

In mice after acid injury, sevoflurane was associated with better arterial oxygenation, decreased alveolar inflammation and histological damage, and non-significantly attenuated the increase in lung permeability. Preserved protein expression of zonula occludens-1 and less increase of pMLC and actin cytoskeletal rearrangement were observed in injured mice treated with sevoflurane. In vitro, sevoflurane markedly decreased electrical resistance and cytokine release of MLE-12 cells, which was associated with higher protein expression of zonula occludens-1. Improved oxygenation levels and attenuated increase in lung permeability and inflammatory response were observed in RAGE^-/- mice compared to wild-type mice, but RAGE deletion did not influence the effects of sevoflurane on permeability indices after injury. However, the beneficial effect of sevoflurane previously observed in wild-type mice on day 1 after injury in terms of higher PaO₂/FiO₂ and decreased alveolar levels of cytokines was not found in RAGE^-/- mice. In vitro, RAP alleviated some of the beneficial effects of sevoflurane on electrical resistance and cytoskeletal rearrangement, which was associated with decreased cytomix-induced RhoA activity.

CONCLUSIONS

Sevoflurane decreased injury and restored epithelial barrier function in two in vivo and in vitro models of sterile lung injury, which was associated with increased expression of junction proteins and decreased actin cytoskeletal rearrangement. In vitro findings suggest that sevoflurane may decrease lung epithelial permeability through the RhoA/pMLC/F-actin pathway.

Degradation of EGFR on lung epithelial cells by neutrophil elastase contributes to the aggravation of pneumococcal pneumonia

Streptococcus pneumoniae is the main cause of bacterial pneumonia. S. pneumoniae infection has been shown to cause elastase, an intracellular host defense factor, to leak from neutrophils. However, when neutrophil elastase (NE) leaks into the extracellular environment, it can degrade host cell surface proteins such as epidermal growth factor receptor (EGFR) and potentially disrupt the alveolar epithelial barrier. In this study, we hypothesized that NE degrades the extracellular domain of EGFR in alveolar epithelial cells and inhibits alveolar epithelial repair. Using SDS-PAGE, we showed that NE degraded the recombinant EGFR extracellular domain and its ligand EGF, and that the degradation of these proteins was counteracted by NE inhibitors. Furthermore, we confirmed the degradation by NE of EGFR expressed in alveolar epithelial cells in vitro. We show intracellular uptake of EGF and EGFR signaling were downregulated in alveolar epithelial cells exposed to NE, and found cell proliferation was inhibited in these cells These negative effects of NE on cell proliferation were abolished by NE inhibitors. Finally, we confirmed the degradation of EGFR by NE in vivo. Fragments of the extracellular domain of EGFR were detected in bronchoalveolar lavage fluid from pneumococcal pneumonia mice, and the percentage of cells positive for a cell proliferation marker Ki67 in lung tissue was reduced. In contrast, administration of an NE inhibitor decreased EGFR fragments in bronchoalveolar lavage fluid and increased the percentage of Ki67-positive cells. These findings suggest that degradation of EGFR by NE could inhibit the repair of alveolar epithelium and cause severe pneumonia.

Single-cell transcriptomes reveal heterogeneity of chlorine-induced mice acute lung injury and the inhibitory effect of pentoxifylline on ferroptosis

To investigate the effect of pentoxifylline (PTX) on Chlorine (Cl₂)-induced acute lung injury (ALI) by single-cell RNA sequencing (scRNA-seq). Female BALB/c mice were exposed to Cl₂ at 400 ppm for 15 min. H&E staining was used to observe the degree of lung injury. scRNA-seq was conducted to analysis of normal and Cl₂-exposed mice lung tissues. Immunofluorescence was used to observe genes of interest. Thirty-two mice were randomly divided into four groups: Control, Cl₂, Cl₂+Fer-1, Cl₂+PTX. TEM, WB and ELISA were used to detect ferroptosis-related indicators. The 5, 8, 10, 12, 16, 20 clusters were epithelial cells and 4, 15, 18, 19, 21 clusters were endothelial cells. Pseudo-time analysis revealed the differentiation trajectory of epithelial cells and key regulatory genes (Gclc, Bpifa1, Dnah5 and Dnah9) during the process of injury. Cell-cell communication analysis identified several important receptor-ligand complexes (Nrp1-Vegfa, Nrp2-Vegfa, Flt1-Vegfa and Flt4-Vegfa). Ferroptosis were found up-regulated in epithelial and endothelial cells by GSVA analysis. Highly expressed genes to which closely related ferroptosis were found by SCENIC analysis. PTX could significantly decrease the levels of MDA and abnormal high expression of solute carrier family 7 member 11 (SLC7A11, the key transporter of cystine) as well as increase the expression of GSH/GSSG and glutathione peroxidase 4 (GPX4) (p < 0.05). This study revealed novel molecular features of Cl₂-induced ALI. PTX may be a potential specific drug by inhibiting the process of ferroptosis in epithelial and endothelial cells.

Mechanical Regulation of Oral Epithelial Barrier Function

Epithelial cell function is modulated by mechanical forces imparted by the extracellular environment. The transmission of forces onto the cytoskeleton by modalities such as mechanical stress and matrix stiffness is necessary to address by the development of new experimental models that permit finely tuned cell mechanical challenges. Herein, we developed an epithelial tissue culture model, named the 3D Oral Epi-mucosa platform, to investigate the role mechanical cues in the epithelial barrier. In this platform, low-level mechanical stress (0.1 kPa) is applied to oral keratinocytes, which lie on 3D fibrous collagen (Col) gels whose stiffness is modulated by different concentrations or the addition of other factors such as fibronectin (FN). Our results show that cells lying on intermediate Col (3 mg/mL; stiffness = 30 Pa) demonstrated lower epithelial leakiness compared with soft Col (1.5 mg/mL; stiffness = 10 Pa) and stiff Col (6 mg/mL; stiffness = 120 Pa) gels, indicating that stiffness modulates barrier function. In addition, the presence of FN reversed the barrier integrity by inhibiting the interepithelial interaction via E-cadherin and Zonula occludens-1. Overall, the 3D Oral Epi-mucosa platform, as a new in vitro system, will be utilized to identify new mechanisms and develop future targets involved in mucosal diseases.

A Monoclonal Human Alveolar Epithelial Cell Line ("Arlo") with Pronounced Barrier Function for Studying Drug Permeability and Viral Infections

In the development of orally inhaled drug products preclinical animal models regularly fail to predict pharmacological as well as toxicological responses in humans. Models based on human cells and tissues are potential alternatives to animal experimentation allowing for the isolation of essential processes of human biology and making them accessible in vitro. Here, the generation of a novel monoclonal cell line "Arlo," derived from the polyclonal human alveolar epithelium lentivirus immortalized cell line hAELVi via single-cell printing, and its characterization as a model for the human alveolar epithelium as well as a building block for future complex in vitro models is described. "Arlo" is systematically compared in vitro to primary human alveolar epithelial cells (hAEpCs) as well as to the polyclonal hAELVi cell line. "Arlo" cells show enhanced barrier properties with high transepithelial electrical resistance (TEER) of ≈3000 Ω cm2 and a potential difference (PD) of ≈30 mV under air-liquid interface (ALI) conditions, that can be modulated. The cells grow in a polarized monolayer and express genes relevant to barrier integrity as well as homeostasis as is observed in hAEpCs. Successful productive infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a proof-of-principle study offers an additional, attractive application of "Arlo" beyond biopharmaceutical experimentation.

Liquid Application Dosing Alters the Physiology of Air-Liquid Interface Primary Bronchial Epithelial Cultures and In vitro Testing Relevant Endpoints

Differentiated Primary human bronchial epithelial cell (dpHBEC) cultures grown under air-liquid interface (ALI) conditions exhibit key features of the human respiratory tract and are thus critical for respiratory research as well as efficacy and toxicity testing of inhaled substances (e.g., consumer products, industrial chemicals, and pharmaceuticals). Many inhalable substances (e.g., particles, aerosols, hydrophobic substances, reactive substances) have physiochemical properties that challenge their evaluation under ALI conditions in vitro. Evaluation of the effects of these methodologically challenging chemicals (MCCs) in vitro is typically conducted by "liquid application," involving the direct application of a solution containing the test substance to the apical, air-exposed surface of dpHBEC-ALI cultures. We report that the application of liquid to the apical surface of a dpHBEC-ALI co-culture model results in significant reprogramming of the dpHBEC transcriptome and biological pathway activity, alternative regulation of cellular signaling pathways, increased secretion of pro-inflammatory cytokines and growth factors, and decreased epithelial barrier integrity. Given the prevalence of liquid application in the delivery of test substances to ALI systems, understanding its effects provides critical infrastructure for the use of in vitro systems in respiratory research as well as in the safety and efficacy testing of inhalable substances.

Bacteriophage therapy for the treatment of Mycobacterium tuberculosis infections in humanized mice

The continuing emergence of new strains of antibiotic-resistant bacteria has renewed interest in phage therapy; however, there has been limited progress in applying phage therapy to multi-drug resistant Mycobacterium tuberculosis (Mtb) infections. In this study, we tested three bacteriophage strains for their Mtb-killing activities and found that two of them efficiently lysed Mtb H37Rv in 7H10 agar plates. However, only phage DS6A efficiently killed H37Rv in liquid culture and in Mtb-infected human primary macrophages. In subsequent experiments, we infected humanized mice with aerosolized H37Rv, then treated these mice with DS6A intravenously to test its in vivo efficacy. We found that DS6A treated mice showed increased body weight and improved pulmonary function relative to control mice. Furthermore, DS6A reduced Mtb load in mouse organs with greater efficacy in the spleen. These results demonstrated the feasibility of developing phage therapy as an effective therapeutic against Mtb infection.

The lung employs an intrinsic surfactant-mediated inflammatory response for viral defense

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) causes an acute respiratory distress syndrome (ARDS) that resembles surfactant deficient RDS. Using a novel multi-cell type, human induced pluripotent stem cell (hiPSC)-derived lung organoid (LO) system, validated against primary lung cells, we found that inflammatory cytokine/chemokine production and interferon (IFN) responses are dynamically regulated autonomously within the lung following SARS-CoV-2 infection, an intrinsic defense mechanism mediated by surfactant proteins (SP). Single cell RNA sequencing revealed broad infectability of most lung cell types through canonical (ACE2) and non-canonical (endocytotic) viral entry routes. SARS-CoV-2 triggers rapid apoptosis, impairing viral dissemination. In the absence of surfactant protein B (SP-B), resistance to infection was impaired and cytokine/chemokine production and IFN responses were modulated. Exogenous surfactant, recombinant SP-B, or genomic correction of the SP-B deletion restored resistance to SARS-CoV-2 and improved viability.

Maresin-2 promotes mucosal repair and has therapeutic potential when encapsulated in thermostable nanoparticles

Resolution of inflammation and mucosal wound healing are crucial processes required to re-establish homeostasis following injury of mucosal tissues. Maresin-2 (MaR2), a lipid specialized pro-resolving mediator derived from omega-3 polyunsaturated fatty acid, has been reported to promote resolution of inflammation. However, a potential role for MaR2 in regulating mucosal repair remains undefined. Using lipidomic analyses, we demonstrate biosynthesis of MaR2 in healing intestinal mucosal wounds in vivo. Importantly, administration of exogenous MaR2 promoted mucosal repair following dextran sulfate sodium-induced colitis or biopsy-induced colonic mucosal injury. Functional analyses revealed that MaR2 promotes mucosal wound repair by driving intestinal epithelial migration through activation of focal cell-matrix adhesion signaling in primary human intestinal epithelial cells. Because of its labile nature, MaR2 is easily degradable and requires ultracold storage to maintain functionality. Thus, we created thermostable polylactic acid MaR2 nanoparticles that retain biological activity following extended storage at 4 °C or above. Taken together, these results establish MaR2 as a potent pro-repair lipid mediator with broad therapeutic potential for use in promoting mucosal repair in inflammatory diseases.

Alpha-1 antitrypsin limits neutrophil extracellular trap disruption of airway epithelial barrier function

Neutrophil extracellular traps contribute to lung injury in cystic fibrosis and asthma, but the mechanisms are poorly understood. We sought to understand the impact of human NETs on barrier function in primary human bronchial epithelial and a human airway epithelial cell line. We demonstrate that NETs disrupt airway epithelial barrier function by decreasing transepithelial electrical resistance and increasing paracellular flux, partially by NET-induced airway cell apoptosis. NETs selectively impact the expression of tight junction genes claudins 4, 8 and 11. Bronchial epithelia exposed to NETs demonstrate visible gaps in E-cadherin staining, a decrease in full-length E-cadherin protein and the appearance of cleaved E-cadherin peptides. Pretreatment of NETs with alpha-1 antitrypsin (A1AT) inhibits NET serine protease activity, limits E-cadherin cleavage, decreases bronchial cell apoptosis and preserves epithelial integrity. In conclusion, NETs disrupt human airway epithelial barrier function through bronchial cell death and degradation of E-cadherin, which are limited by exogenous A1AT.

Filaggrin and cytokines in respiratory samples of preterm infants at risk for respiratory viral infection

Respiratory viral infections (RVIs) are frequent in preterm infants possibly inducing long-term impact on respiratory morbidity. Immune response and respiratory barriers are key defense elements against viral insults in premature infants admitted to Neonatal Intensive Care Units (NICUs). Our main goals were to describe the local immune response in respiratory secretions of preterm infants with RVIs during NICU admission and to evaluate the expression and synthesis of lung barrier regulators, both in respiratory samples and in vitro models. Samples from preterm infants that went on to develop RVIs had lower filaggrin gene and protein levels at a cellular level were compared to never-infected neonates (controls). Filaggrin, MIP-1α/CCL3 and MCP-1 levels were higher in pre-infection supernatants compared to controls. Filaggrin, HIF-1α, VEGF, RANTES/CCL5, IL-17A, IL-1β, MIP-1α and MIP-1β/CCL5 levels were higher during and after infection. ROC curve and logistic regression analysis shows that these molecules could be used as infection risk biomarkers. Small airway epithelial cells stimulated by poly:IC presented reduced filaggrin gene expression and increased levels in supernatant. We conclude that filaggrin gene and protein dysregulation is a risk factor of RVI in newborns admitted at the NICU.

Interleukin-11 receptor subunit α-1 is required for maximal airway responsiveness to methacholine after acute exposure to ozone

Interleukin (IL)-11, a multifunctional cytokine, contributes to numerous biological processes, including adipogenesis, hematopoiesis, and inflammation. Asthma, a respiratory disease, is notably characterized by reversible airway obstruction, persistent lung inflammation, and airway hyperresponsiveness (AHR). Nasal insufflation of IL-11 causes AHR in wild-type mice while lung inflammation induced by antigen sensitization and challenge, which mimics features of atopic asthma in humans, is attenuated in mice genetically deficient in IL-11 receptor subunit α-1 (IL-11Rα1-deficient mice), a transmembrane receptor that is required conjointly with glycoprotein 130 to transduce IL-11 signaling. Nevertheless, the contribution of IL-11Rα1 to characteristics of nonatopic asthma is unknown. Thus, based on the aforementioned observations, we hypothesized that genetic deficiency of IL-11Rα1 attenuates lung inflammation and increases airway responsiveness after acute inhalation exposure to ozone (O3), a criteria pollutant and nonatopic asthma stimulus. Accordingly, 4 and/or 24 h after cessation of exposure to filtered room air or O3, we assessed lung inflammation and airway responsiveness in wild-type and IL-11Rα1-deficient mice. With the exception of bronchoalveolar lavage macrophages and adiponectin, which were significantly increased and decreased, respectively, in O3-exposed IL-11Rα1-deficient as compared with O3-exposed wild-type mice, no other genotype-related differences in lung inflammation indices that we quantified were observed in O3-exposed mice. However, airway responsiveness to acetyl-β-methylcholine chloride (methacholine) was significantly diminished in IL-11Rα1-deficient as compared with wild-type mice after O3 exposure. In conclusion, these results demonstrate that IL-11Rα1 minimally contributes to lung inflammation but is required for maximal airway responsiveness to methacholine in a mouse model of nonatopic asthma.

The emerging role of histone deacetylase 1 in allergic diseases

Histone deacetylase 1 (HDAC1) is a unique member of the classes I HDACs and helps to regulate acute and chronic adaptation to environmental stimuli such as allergen, stress. Allergic diseases are complex diseases resulting from the effect of multiple genetic and interacting foreign substances. Epigenetics play an important role in both pathological and immunomodulatory conditions of allergic diseases. To be consistent with this role, recent evidence strongly suggests that histone deacetylase 1 (HDAC1) plays a critical role in allergic response. HDAC1 expression is stimulated by allergen and attributes to increase T helper 2 (Th2) cytokine levels, decrease Th1/Th17 cells and anti-inflammatory cytokine Interleukin-10 (IL-10), and TWIK-related potassium channel-1 (Trek-1) expression. This review focuses on the contribution of HDAC1 and the regulatory role in characterizing allergic endotypes with common molecular pathways and understanding allergic multimorbidity relationships, as well as addressing their potential as therapeutic targets for these conditions.

Alternatives to animal models and their application in the discovery of species susceptibility to SARS-CoV-2 and other respiratory infectious pathogens: A review

The emergence of the coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inspired rapid research efforts targeting the host range, pathogenesis and transmission mechanisms, and the development of antiviral strategies. Genetically modified mice, rhesus macaques, ferrets, and Syrian golden hamsters have been frequently used in studies of pathogenesis and efficacy of antiviral compounds and vaccines. However, alternatives to in vivo experiments, such as immortalized cell lines, primary respiratory epithelial cells cultured at an air-liquid interface, stem/progenitor cell-derived organoids, or tissue explants, have also been used for isolation of SARS-CoV-2, investigation of cytopathic effects, and pathogen-host interactions. Moreover, initial proof-of-concept studies for testing therapeutic agents can be performed with these tools, showing that animal-sparing cell culture methods could significantly reduce the need for animal models in the future, following the 3R principles of replace, reduce, and refine. So far, only few studies using animal-derived primary cells or tissues have been conducted in SARS-CoV-2 research, although natural infection has been shown to occur in several animal species. Therefore, the need for in-depth investigations on possible interspecies transmission routes and differences in susceptibility to SARS-CoV-2 is urgent. This review gives an overview of studies employing alternative culture systems like primary cell cultures, tissue explants, or organoids for investigations of the pathophysiology and reverse zoonotic potential of SARS-CoV-2 in animals. In addition, future possibilities of SARS-CoV-2 research in animals, including previously neglected methods like the use of precision-cut lung slices, will be outlined.

Acinetobacter baumannii Outer Membrane Protein A Induces Pulmonary Epithelial Barrier Dysfunction and Bacterial Translocation Through The TLR2/IQGAP1 Axis

Pulmonary epithelial barrier dysfunction is a critical pathophysiological process in pneumonia and associated invasive infections, such as those caused by Acinetobacter baumannii. However, the mechanisms underlying A. baumannii-induced pulmonary epithelial barrier dysfunction and bacterial translocation remain unclear. In this study, lungs of mice and A549 human epithelial cell monolayers were challenged with the A. baumannii wild-type strain and an outer membrane protein A (ompA) deletion strain. In addition, epithelial cells in culture were treated with purified OmpA protein or transfected with a eukaryotic expression vector encoding ompA (pCMV-ompA). Bacterial translocation across cell monolayers and intrapulmonary burden were measured, barrier function was evaluated in vivo and in vitro; cell migration ability was determined. The specific inhibitors C29 and JSH-23 were used to suppress the activity of Toll-like receptor 2 (TLR2) and of NF-κB, respectively. IQ-GTPase-activating protein 1 (IQGAP1) small interfering RNA was used to knock down endogenous IQGAP1 expression. In this work, we show that OmpA from A. baumannii increased the production of pro-inflammatory cytokines, remodeled the cytoskeleton, and internalized intercellular adherens junctions (AJs); these changes eventually induced pulmonary epithelial barrier dysfunction to promote bacterial translocation. IQGAP1-targeting small interfering RNA and chemical inhibition of TLR2 or NF-κB prevented high permeability of the pulmonary epithelial barrier. TLR2/NF-κB signaling was involved in OmpA-induced inflammation, IQGAP1-mediated OmpA-induced opening of the pulmonary epithelial barrier via cytoskeleton dynamic remodeling, and cellular redistribution of the major AJ protein, E-cadherin. These observations indicate that A. baumannii uses OmpA to overcome epithelial defences and cross the pulmonary epithelial barrier.

DUSP3 regulates phosphorylation-mediated degradation of occludin and is required for maintaining epithelial tight junction

Background

Tight junctions (TJ) are multi-protein complexes that hold epithelial cells together and form structural and functional barriers for maintaining proper biological activities. Dual specificity phosphatase 3 (DUSP3), a suppressor of multiple protein tyrosine (Tyr) kinases, is decreased in lung cancer tissues. Here we demonstrated the role of DUSP3 in regulation of epithelial TJ.

Methods

Barrier functions of TJ were examined in wild-type or DUSP3-deficient lung epithelial cells. Animal and clinical data were analyzed for the association between DUSP3 deficiency and lung cancer progression. Proximity ligation assay, immunoblotting, and phosphatase assay were performed to study the effect of DUSP3 on the TJ protein occludin (OCLN). Mutations of Tyr residues on OCLN showed the role of Tyr phosphorylation in regulating OCLN.

Results

Compared to those of the DUSP3-expressing cells, we found the expression and distribution of ZO-1, a TJ-anchoring molecule, were abnormal in DUSP3-deficient cells. OCLN had an increased phosphorylation level in DUSP3-deficient cells. We identified that OCLN is a direct substrate of DUSP3. DUSP3 regulated OCLN ubiquitination and degradation through decreasing OCLN tyrosine phosphorylation directly or through suppressing focal adhesion kinase, the OCLN kinase.

Conclusion

Our study revealed that DUSP3 is an important TJ regulatory protein and its decrease may be involved in progression of epithelial cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00826-x.

3D Lung-on-Chip Model Based on Biomimetically Microcurved Culture Membranes

A comparatively straightforward approach to accomplish more physiological realism in organ-on-a-chip (OoC) models is through substrate geometry. There is increasing evidence that the strongly, microscale curved surfaces that epithelial or endothelial cells experience when lining small body lumens, such as the alveoli or blood vessels, impact their behavior. However, the most commonly used cell culture substrates for modeling of these human tissue barriers in OoCs, ion track-etched porous membranes, provide only flat surfaces. Here, we propose a more realistic culture environment for alveolar cells based on biomimetically microcurved track-etched membranes. They recreate the mainly spherical geometry of the cells’ native microenvironment. In this feasibility study, the membranes were given the shape of hexagonally arrayed hemispherical microwells by an innovative combination of three-dimensional (3D) microfilm (thermo)forming and ion track technology. Integrated in microfluidic chips, they separated a top from a bottom cell culture chamber. The microcurved membranes were seeded by infusion with primary human alveolar epithelial cells. Despite the pronounced topology, the cells fully lined the alveoli-like microwell structures on the membranes’ top side. The confluent curved epithelial cell monolayers could be cultured successfully at the air−liquid interface for 14 days. Similarly, the top and bottom sides of the microcurved membranes were seeded with cells from the Calu-3 lung epithelial cell line and human lung microvascular endothelial cells, respectively. Thereby, the latter lined the interalveolar septum-like interspace between the microwells in a network-type fashion, as in the natural counterpart. The coculture was maintained for 11 days. The presented 3D lung-on-a-chip model might set the stage for other (micro)anatomically inspired membrane-based OoCs in the future.

Mucosal immune responses to infection and vaccination in the respiratory tract

The lungs are constantly exposed to inhaled debris, allergens, pollutants, commensal or pathogenic microorganisms, and respiratory viruses. As a result, innate and adaptive immune responses in the respiratory tract are tightly regulated and are in continual flux between states of enhanced pathogen clearance, immune-modulation, and tissue repair. New single-cell-sequencing techniques are expanding our knowledge of airway cellular complexity and the nuanced connections between structural and immune cell compartments. Understanding these varied interactions is critical in treatment of human pulmonary disease and infections and in next-generation vaccine design. Here, we review the innate and adaptive immune responses in the lung and airways following infection and vaccination, with particular focus on influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The ongoing SARS-CoV-2 pandemic has put pulmonary research firmly into the global spotlight, challenging previously held notions of respiratory immunity and helping identify new populations at high risk for respiratory distress.

The Ability of Resveratrol to Attenuate Ovalbumin-Mediated Allergic Asthma Is Associated With Changes in Microbiota Involving the Gut-Lung Axis, Enhanced Barrier Function and Decreased Inflammation in the Lungs

Asthma is a chronic respiratory disease highly prevalent worldwide. Recent studies have suggested a role for microbiome-associated gut-lung axis in asthma development. In the current study, we investigated if Resveratrol (RES), a plant-based polyphenol, can attenuate ovalbumin (OVA)-induced murine allergic asthma, and if so, the role of microbiome in the gut-lung axis in this process. We found that RES attenuated allergic asthma with significant improvements in pulmonary functions in OVA-exposed mice when tested using plethysmography for frequency (F), mean volume (MV), specific airway resistance (sRaw), and delay time(dT). RES treatment also suppressed inflammatory cytokines in the lungs. RES modulated lung microbiota and caused an abundance of Akkermansia muciniphila accompanied by a reduction of LPS biosynthesis in OVA-treated mice. Furthermore, RES also altered gut microbiota and induced enrichment of Bacteroides acidifaciens significantly in the colon accompanied by an increase in butyric acid concentration in the colonic contents from OVA-treated mice. Additionally, RES caused significant increases in tight junction proteins and decreased mucin (Muc5ac) in the pulmonary epithelium of OVA-treated mice. Our results demonstrated that RES may attenuate asthma by inducing beneficial microbiota in the gut-lung axis and through the promotion of normal barrier functions of the lung.

Sex-Specific Differences in Resolution of Airway Inflammation in Fat-1 Transgenic Mice Following Repetitive Agricultural Dust Exposure

In agriculture industries, workers are at increased risk for developing pulmonary diseases due to inhalation of agricultural dusts, particularly when working in enclosed confinement facilities. Agricultural dusts inhalation leads to unresolved airway inflammation that precedes the development and progression of lung disease. We have previously shown beneficial effects of the omega-3 polyunsaturated fatty acid (ω-3 PUFA) DHA in protecting against the negative inflammatory effects of repetitive dust exposure in the lung. Dietary manipulation of pulmonary disease risk is an attractive and timely approach given the contribution of an increased ω-6 to ω-3 PUFA ratio to low grade inflammation and chronic disease in the Western diet. To prevent any confounding factors that comes with dietary supplementation of ω-3 PUFA (different sources, purity, dose, and duration), we employed a Fat-1 transgenic mouse model that convert ω-6 PUFA to ω-3 PUFA, leading to a tissue ω-6 to ω-3 PUFA ratio of approximately 1:1. Building on our initial findings, we hypothesized that attaining elevated tissue levels of ω-3 PUFA would attenuate agricultural dust-induced lung inflammation and its resolution. To test this hypothesis, we compared wild-type (WT) and Fat-1 transgenic mice in their response to aqueous extracts of agricultural dust (DE). We also used a soluble epoxide hydrolase inhibitor (sEH) to potentiate the effects of ω-3 PUFA, since sEH inhibitors have been shown to stabilize the anti-inflammatory P450 metabolites derived from both ω-3 and ω-6 PUFA and promote generation of specialized pro-resolving lipid mediators from ω-3 PUFA. Over a three-week period, mice were exposed to a total of 15 intranasal instillations of DE obtained from swine confinement buildings in the Midwest. We observed genotype and sex-specific differences between the WT vs. Fat-1 transgenic mice in response to repetitive dust exposure, where three-way ANOVA revealed significant main effects of treatment, genotype, and sex. Also, Fat-1 transgenic mice displayed reduced lymphoid aggregates in the lung following DE exposure as compared to WT animals exposed to DE, suggesting improved resilience to the DE-induced inflammatory effects. Overall, our data implicate a protective role of ω-3 FA in the lung following repetitive dust exposure.

Novel regulators of airway epithelial barrier function during inflammation: potential targets for drug repurposing

INTRODUCTION

Endogenous inflammatory signaling molecules resulting from deregulated immune responses, can impair airway epithelial barrier function and predispose individuals with airway inflammatory diseases to exacerbations and lung infections. Targeting the specific endogenous factors disrupting the airway barrier therefore has the potential to prevent disease exacerbations without affecting the protective immune responses.

AREAS COVERED

Here, we review the endogenous factors and specific mechanisms disrupting airway epithelial barrier during inflammation and reflect on whether these factors can be specifically targeted by repurposed existing drugs. Literature search was conducted using PubMed, drug database of US FDA and European Medicines Agency until and including September 2021.

EXPERT OPINION

IL-4 and IL-13 signaling are the major pathways disrupting the airway epithelial barrier during airway inflammation. However, blocking IL-4/IL-13 signaling may adversely affect protective immune responses and increase susceptibility of host to infections. An alternate approach to modulate airway epithelial barrier function involves targeting specific downstream component of IL-4/IL-13 signaling or different inflammatory mediators responsible for regulation of airway epithelial barrier. Airway epithelium-targeted therapy using inhibitors of HDAC, HSP90, MIF, mTOR, IL-17A and VEGF may be a potential strategy to prevent airway epithelial barrier dysfunction in airway inflammatory diseases.

Pseudomonas aeruginosa Triggered Exosomal Release of ADAM10 Mediates Proteolytic Cleavage in Trans

Pneumonia is a life-threatening disease often caused by infection with Streptococcus pneumoniae and Pseudomonas aeruginosa. Many of the mediators (e.g., TNF, IL-6R) and junction molecules (e.g., E-cadherin) orchestrating inflammatory cell recruitment and loss of barrier integrity are proteolytically cleaved through a disintegrin and metalloproteinases (ADAMs). We could show by Western blot, surface expression analysis and measurement of proteolytic activity in cell-based assays, that ADAM10 in epithelial cells is upregulated and activated upon infection with Pseudomonas aeruginosa and Exotoxin A (ExoA), but not upon infection with Streptococcus pneumoniae. Targeting ADAM10 by pharmacological inhibition or gene silencing, we demonstrated that this activation was critical for cleavage of E-cadherin and modulated permeability and epithelial integrity. Stimulation with heat-inactivated bacteria revealed that the activation was based on the toxin repertoire rather than the interaction with the bacterial particle itself. Furthermore, calcium imaging experiments showed that the ExoA action was based on the induction of calcium influx. Investigating the extracellular vesicles and their proteolytic activity, we could show that Pseudomonas aeruginosa triggered exosomal release of ADAM10 and proteolytic cleavage in trans. This newly described mechanism could constitute an essential mechanism causing systemic inflammation in patients suffering from Pseudomonas aeruginosa-induced pneumonia stimulating future translational studies.

Gene Therapy for Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a devastating clinical syndrome that leads to acute respiratory failure and accounts for over 70,000 deaths per year in the United States alone, even prior to the COVID-19 pandemic. While its molecular details have been teased apart and its pathophysiology largely established over the past 30 years, relatively few pharmacological advances in treatment have been made based on this knowledge. Indeed, mortality remains very close to what it was 30 years ago. As an alternative to traditional pharmacological approaches, gene therapy offers a highly controlled and targeted strategy to treat the disease at the molecular level. Although there is no single gene or combination of genes responsible for ARDS, there are a number of genes that can be targeted for upregulation or downregulation that could alleviate many of the symptoms and address the underlying mechanisms of this syndrome. This review will focus on the pathophysiology of ARDS and how gene therapy has been used for prevention and treatment. Strategies for gene delivery to the lung, such as barriers encountered during gene transfer, specific classes of genes that have been targeted, and the outcomes of these approaches on ARDS pathogenesis and resolution will be discussed.

Human microphysiological models of airway and alveolar epithelia

Human organ-on-a-chip models are powerful tools for preclinical research that can be used to study the mechanisms of disease and evaluate new targets for therapeutic intervention. Lung-on-a-chip models have been one of the most well-characterized designs in this field and can be altered to evaluate various types of respiratory disease and to assess treatment candidates prior to clinical testing. These systems are capable of overcoming the flaws of conventional two-dimensional (2-D) cell culture and in vivo animal testing due to their ability to accurately recapitulate the in vivo microenvironment of human tissue with tunable material properties, microfluidic integration, delivery of precise mechanical and biochemical cues, and designs with organ-specific architecture. In this review, we first describe an overview of currently available lung-on-a-chip designs. We then present how recent innovations in human stem cell biology, tissue engineering, and microfabrication can be used to create more predictive human lung-on-a-chip models for studying respiratory disease. Finally, we discuss the current challenges and future directions of lung-on-a-chip designs for in vitro disease modeling with a particular focus on immune and multiorgan interactions.

Honokiol alleviates LPS-induced acute lung injury by inhibiting NLRP3 inflammasome-mediated pyroptosis via Nrf2 activation in vitro and in vivo

Background

Honokiol (HKL) has been reported to ameliorate lipopolysaccharide (LPS)-induced acute lung injury (ALI). However, its potential mechanism of its protective effects remains unclear. In this study, the protective mechanism of HKL on LPS-induced ALI was explored in vivo and in vitro.

Methods

In vivo, the SD rats were intratracheally instilled with LPS (5 mg/kg) to establish an acute lung injury model and then treated with HKL (1.25/2.5/5 mg/kg) or ML385 (30 mg/kg) intraperitoneally. In vitro, the human bronchial epithelial cell line (BEAS-2B) was stimulated with LPS and ATP to induce pyroptosis and treated with HKL (12.5/25/50 μM). Small interfering RNA (siRNA) technique was used to knockdown Nrf2 in BEAS-2B cells. The protein and mRNA expression levels of Nrf2, HO-1, NLRP3, ASC, CASP1, and GSDMD in cells and lung tissues were detected by western blot and real time-PCR. The expression levels of interleukin (IL)-1β, IL-18, MPO, MDA, and SOD in bronchoalveolar lavage fluid (BALF) and supernatant were determined by ELISA. The degree of pathological injury of lung tissue was evaluated by H&E staining.

Results

The results showed that HKL could alleviate oxidative stress and inflammatory responses by regulating the levels of MPO, MDA, SOD, IL-1β, IL-18 in supernatant. And it could also inhibit the expression levels of NLRP3, ASC, CASP1, GSDMD via activation of Nrf2 in BEAS-2B cells. Further studies revealed that HKL could attenuate the pathological injury in LPS-induced ALI rats, and the molecular mechanism was consistent with the results in vitro.

Conclusions

Our study demonstrated that HKL could alleviate LPS-induced ALI by reducing the oxidative stress and inhibiting NLRP3 inflammasome-mediated pyroptosis, which was partly dependent on the Nrf2 activation.

Graphical Abstract

Recent advances in human respiratory epithelium models for drug discovery

The respiratory epithelium is intimately associated with the pathophysiologies of highly infectious viral contagions and chronic illnesses such as chronic obstructive pulmonary disorder, presently the third leading cause of death worldwide with a projected economic burden of £1.7 trillion by 2030. Preclinical studies of respiratory physiology have almost exclusively utilised non-humanised animal models, alongside reductionistic cell line-based models, and primary epithelial cell models cultured at an air-liquid interface (ALI). Despite their utility, these model systems have been limited by their poor correlation to the human condition. This has undermined the ability to identify novel therapeutics, evidenced by a 15% chance of success for medicinal respiratory compounds entering clinical trials in 2018. Consequently, preclinical studies require new translational efficacy models to address the problem of respiratory drug attrition. This review describes the utility of the current in vivo (rodent), ex vivo (isolated perfused lungs and precision cut lung slices), two-dimensional in vitro cell-line (A549, BEAS-2B, Calu-3) and three-dimensional in vitro ALI (gold-standard and co-culture) and organoid respiratory epithelium models. The limitations to the application of these model systems in drug discovery research are discussed, in addition to perspectives of the future innovations required to facilitate the next generation of human-relevant respiratory models.

Improving Anti-Inflammatory Effect of Luteolin with Nano-Micelles in the Bacteria-Induced Lung Infection

The effective therapy for lung infectious diseases became more and more difficult since the severe antibiotic resistance of pathogenic microorganisms, it is urgent to develop new antimicrobial agents. Luteolin has been reported to play a crucial part in host immune responses. However, the clinical use of luteolin is impeded due to its hydrophobicity and low oral bioavailability. In this study, we formulated luteolin-loaded Methoxy poly(ethylene glycol)-poly(lactide) micelles (luteolin/MPEG-PLA), to improve the bioavailability of luteolin in lung infectious diseases. The results showed that luteolin/MPEG-PLA treatment could reduce the adhesion of Klebsiella pneumoniae (K. pneumoniae) to lung epithelial cells and enhance the germicidal ability of macrophages against K. pneumoniae compared to untreated group. Meanwhile, luteolin/MPEG-PLA showed stronger adhesion resistance of epithelial cells and germicidal ability of macrophages compared with free luteolin. In vivo study, luteolin/MPEG-PLA administration significantly promoted the clearance of bacteria and reduced inflammatory infiltration of lung tissue in K. pneumoniae induced lung infectious mice model. Further studies showed that treatment with luteolin/MPEG-PLA reduced the mRNA expression of LPS-induced inflammatory cytokines and chemokines in macrophages significantly. In general, luteolin/MPEG-PLA can enhance the anti-bacterial ability of lung epithelial cells and macrophages, and has a stronger therapeutic effect than free luteolin in bacterial-induced lung infection. Luteolin/MPEG-PLA may be an excellent potential drug for bacterial-induced lung infectious diseases treatment.

Impact of Probiotic Bacteria on Respiratory Allergy Disorders

Respiratory allergy is a common disease with an increased prevalence worldwide. The effective remedy is still unknown, and a new therapeutic approach is highly desirable. The review elaborates the influence of probiotic bacteria on respiratory allergy prevention and treatment with particular emphasis on the impact of the current methods of their administration – oral and intranasal. The background of the respiratory allergy is complex thus, we focused on the usefulness of probiotics in the alleviation of different allergy factors, in particular involved in pathomechanism, local hypersensitive evidence and the importance of epithelial barrier. In this review, we have shown that (1) probiotic strains may vary in modulatory potential in respiratory allergy, (2) probiotic bacteria are beneficial in oral and intranasal administration, (3) recombinant probiotic bacteria can modulate the course of respiratory allergy.

Epithelial Barrier Integrity Profiling: Combined Approach Using Cellular Junctional Complex Imaging and Transepithelial Electrical Resistance

A core aspect of epithelial cell function is barrier integrity. A loss of barrier integrity is a feature of a number of respiratory diseases, including asthma, allergic rhinitis, and chronic obstructive pulmonary disease. Restoration of barrier integrity is a target for respiratory disease drug discovery. Traditional methods for assessing barrier integrity have their limitations. Transepithelial electrical resistance (TEER) and dextran permeability methods can give poor in vitro assay robustness. Traditional junctional complex imaging approaches are labor-intensive and tend to be qualitative but not quantitative. To provide a robust and quantitative assessment of barrier integrity, high-content imaging of junctional complexes was combined with TEER. A scalable immunofluorescent high-content imaging technique, with automated quantification of junctional complex proteins zonula occludens-1 and occludin, was established in 3D pseudostratified primary human bronchial epithelial cells cultured at an air-liquid interface. Ionic permeability was measured using TEER on the same culture wells.The improvements to current technologies include the design of a novel 24-well holder to enable scalable in situ confocal cell imaging without Transwell membrane excision, the development of image analysis pipelines to quantify in-focus junctional complex structures in each plane of a Z stack, and the enhancement of the TEER data analysis process to enable statistical evaluation of treatment effects on barrier integrity. This novel approach was validated by demonstrating measurable changes in barrier integrity in cells grown under conditions known to perturb epithelial cell function.

In Vitro Models for Studying Respiratory Host-Pathogen Interactions

Respiratory diseases and lower respiratory tract infections are among the leading cause of death worldwide and, especially given the recent severe acute respiratory syndrome coronavirus-2 pandemic, are of high and prevalent socio-economic importance. In vitro models, which accurately represent the lung microenvironment, are of increasing significance given the ethical concerns around animal work and the lack of translation to human disease, as well as the lengthy time to market and the attrition rates associated with clinical trials. This review gives an overview of the biological and immunological components involved in regulating the respiratory epithelium system in health, disease, and infection. The evolution from 2D to 3D cell biology and to more advanced technological integrated models for studying respiratory host-pathogen interactions are reviewed and provide a reference point for understanding the in vitro modeling requirements. Finally, the current limitations and future perspectives for advancing this field are presented.

The Epithelial-Immune Crosstalk in Pulmonary Fibrosis

Interactions between the lung epithelium and the immune system involve a tight regulation to prevent inappropriate reactions and have been connected to several pulmonary diseases. Although the distal lung epithelium and local immunity have been implicated in the pathogenesis and disease course of idiopathic pulmonary fibrosis (IPF), consequences of their abnormal interplay remain less well known. Recent data suggests a two-way process, as illustrated by the influence of epithelial-derived periplakin on the immune landscape or the effect of macrophage-derived IL-17B on epithelial cells. Additionally, damage associated molecular patterns (DAMPs), released by damaged or dying (epithelial) cells, are augmented in IPF. Next to “sterile inflammation”, pathogen-associated molecular patterns (PAMPs) are increased in IPF and have been linked with lung fibrosis, while outer membrane vesicles from bacteria are able to influence epithelial-macrophage crosstalk. Finally, the advent of high-throughput technologies such as microbiome-sequencing has allowed for the identification of a disease-specific microbial environment. In this review, we propose to discuss how the interplays between the altered distal airway and alveolar epithelium, the lung microbiome and immune cells may shape a pro-fibrotic environment. More specifically, it will highlight DAMPs-PAMPs pathways and the specificities of the IPF lung microbiome while discussing recent elements suggesting abnormal mucosal immunity in pulmonary fibrosis.

Proteases, Mucus, and Mucosal Immunity in Chronic Lung Disease

Dysregulated protease activity has long been implicated in the pathogenesis of chronic lung diseases and especially in conditions that display mucus obstruction, such as chronic obstructive pulmonary disease, cystic fibrosis, and non-cystic fibrosis bronchiectasis. However, our appreciation of the roles of proteases in various aspects of such diseases continues to grow. Patients with muco-obstructive lung disease experience progressive spirals of inflammation, mucostasis, airway infection and lung function decline. Some therapies exist for the treatment of these symptoms, but they are unable to halt disease progression and patients may benefit from novel adjunct therapies. In this review, we highlight how proteases act as multifunctional enzymes that are vital for normal airway homeostasis but, when their activity becomes immoderate, also directly contribute to airway dysfunction, and impair the processes that could resolve disease. We focus on how proteases regulate the state of mucus at the airway surface, impair mucociliary clearance and ultimately, promote mucostasis. We discuss how, in parallel, proteases are able to promote an inflammatory environment in the airways by mediating proinflammatory signalling, compromising host defence mechanisms and perpetuating their own proteolytic activity causing structural lung damage. Finally, we discuss some possible reasons for the clinical inefficacy of protease inhibitors to date and propose that, especially in a combination therapy approach, proteases represent attractive therapeutic targets for muco-obstructive lung diseases.

Alveolar epithelial glycocalyx shedding aggravates the epithelial barrier and disrupts epithelial tight junctions in acute respiratory distress syndrome

The main pathophysiological mechanism of acute respiratory distress syndrome (ARDS) invovles the increase in alveolar barrier permeability that is primarily caused by epithelial glycocalyx and tight junction (TJ) protein destruction. This study was performed to explore the effects of the alveolar epithelial glycocalyx on the epithelial barrier, specifically on TJ proteins, in ARDS. We used C57BL/6 mice and human lung epithelial cell models of lipopolysaccharide (LPS)-induced ARDS. Changes in alveolar permeability were evaluated via pulmonary histopathology analysis and by measuring the wet/dry weight ratio of the lungs. Degradation of heparan sulfate (HS), an important component of the epithelial glycocalyx, and alterations in levels of the epithelial TJ proteins (occludin, zonula occludens 1, and claudin 4) were assessed via ELISA, immunofluorescence analysis, and western blotting analysis. Real-time quantitative polymerase chain reaction was used to detect the mRNA of the TJ protein. Changes in glycocalyx and TJ ultrastructures in alveolar epithelial cells were evaluated through electron microscopy. In vivo and in vitro, LPS increased the alveolar permeability and led to HS degradation and TJ damage. After LPS stimulation, the expression of the HS-degrading enzyme heparanase (HPA) in the alveolar epithelial cells was increased. The HPA inhibitor N-desulfated/re-N-acetylated heparin alleviated LPS-induced HS degradation and reduced TJ damage. In vitro, recombinant HPA reduced the expression of the TJ protein zonula occludens-1 (ZO-1) and inhibited its mRNA expression in the alveolar epithelial cells. Taken together, our results demonstrate that shedding of the alveolar epithelial glycocalyx aggravates the epithelial barrier and damages epithelial TJ proteins in ARDS, with the underlying mechanism involving the effect of HPA on ZO-1.