The Role of PGE2 in Alveolar Epithelial and Lung Microvascular Endothelial Crosstalk

Endothelialized Bronchioalveolar Lung Organoids Model Endothelial Cell Responses to Injury

Organoid three-dimensional systems are powerful platforms to study development and disease. Recently, the complexity of lung organoid models derived from adult mouse and human stem cells has increased substantially in terms of cellular composition and structural complexity. However, a murine lung organoid system with a clear integrated endothelial compartment is still missing. Here, we describe a novel method that adds another level of intricacy to our published bronchioalveolar lung organoid (BALO) model by microinjection of FACS-sorted lung endothelial cells (ECs) into differentiated organoid cultures. Before microinjection, ECs obtained from the lung homogenate of young mice expressed typical EC markers such as CD31 and vascular endothelial cadherin and showed tube formation capacity. Following microinjection, ECs surrounded the BALO's alveolar-like compartment, aligning with type I and type II alveolar epithelial cells, as demonstrated by confocal and electron microscopy. Notably, expression of Car4 and Aplnr was as well detected, suggesting the presence of EC microvascular phenotypes in the cultured ECs. Moreover, upon epithelial cell injury by LPS and influenza A virus, endothelialized BALOs released proinflammatory cytokines, leading to the upregulation ICAM-1 (intercellular adhesion molecule 1) in ECs. In summary, we characterized for the first time an organoid model that incorporates ECs into the alveolar structures of lung organoids, not only increasing our previous model's cellular and structural complexity but also providing a suitable niche to model lung endothelium responses to injury ex vivo.

Effects of early treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) on the bronchoalveolar lavage proteome and oxylipids during bovine respiratory syncytial virus (BRSV) infection

Non-steroidal anti-inflammatory drugs (NSAID) are not recommended for use against pneumonia in humans, but are commonly utilised against bovine respiratory disease. This study aimed to determine if the use of NSAIDs in the early phase of bovine respiratory syncytial virus (BRSV)-infection limits pulmonary inflammation. Four to nine-week old calves were infected with BRSV by aerosol and were treated with either meloxicam intravenously on day (D)4 (n = 5, MEL), acetylsalicylat-DL-lysin intravenously on D4 and D5 (n = 5, ASA), or were left untreated as controls (n = 5, CTR). Clinical signs were monitored daily until necropsy on D7, BRSV-RNA was detected in nasal swabs and bronchoalveolar lavage (BAL) by RT-qPCR, inflammatory cells and proteins were identified in BAL by cytology and label-free quantitative mass spectrometry-based proteomics, respectively, and oxylipids were quantified in BAL and plasma by liquid chromatography tandem mass spectrometry with triple quadrupole mass detectors. The calves developed mild to moderate signs of respiratory disease and, with the exception of one MEL-treated and one ASA-treated calf, limited lung lesions. None of the treatments had a significant effect on virus replication, clinical signs or lung lesion extent. Relative to controls, both treatments initially induced a downregulation of proteins in BAL. Immunoglobulin (Ig)-related proteins, such as the Ig kappa and lambda locus and the joining chain of IgA and IgM, were downregulated in MEL-treated calves compared to controls. In addition, meloxicam induced an increased neutrophil influx in BAL in response to BRSV, possibly related to a reduction in plasma prostaglandin, and to a downregulation of The Liver X Receptor/ Retinoid X Receptor (LXR/RXR), the Farnesoid X Receptor (FXR)/RXR and the 24-Dehydrocholesterol Reductase (DHC24) signalling pathways in the lung. The risk of NSAIDs to increase neutrophil activity during stimulation with BRSV or other toll-like receptor 4 agonists needs to be investigated further. Since augmented neutrophil responses can be detrimental, the results of the present study do not support the use of NSAIDs to prevent the clinical expression of BRSV-infection.

Eosinophil-Epithelial Cell Interactions in Asthma

BACKGROUND

Eosinophils have numerous roles in type 2 inflammation depending on their activation states in the blood and airway or after encounter with inflammatory mediators. Airway epithelial cells have a sentinel role in the lung and, by instructing eosinophils, likely have a foundational role in asthma pathogenesis.

SUMMARY

In this review, we discuss various topics related to eosinophil-epithelial cell interactions in asthma, including the influence of eosinophils and eosinophil products, e.g., granule proteins, on epithelial cell function, expression, secretion, and plasticity; the effects of epithelial released factors, including oxylipins, cytokines, and other mediators on eosinophils, e.g., on their activation, expression, and survival; possible mechanisms of eosinophil-epithelial cell adhesion; and the role of intra-epithelial eosinophils in asthma.

KEY MESSAGES

We suggest that eosinophils and their products can have both injurious and beneficial effects on airway epithelial cells in asthma and that there are bidirectional interactions and signaling between eosinophils and airway epithelial cells in asthma.

Novel insights into the potential applications of stem cells in pulmonary hypertension therapy

Pulmonary hypertension (PH) refers to a group of deadly lung diseases characterized by vascular lesions in the microvasculature and a progressive increase in pulmonary vascular resistance. The prevalence of PH has increased over time. Currently, the treatment options available for PH patients have limited efficacy, and none of them can fundamentally reverse pulmonary vascular remodeling. Stem cells represent an ideal seed with proven efficacy in clinical studies focusing on liver, cardiovascular, and nerve diseases. Since the potential therapeutic effect of mesenchymal stem cells (MSCs) on PH was first reported in 2006, many studies have demonstrated the efficacy of stem cells in PH animal models and suggested that stem cells can help slow the deterioration of lung tissue. Existing PH treatment studies basically focus on the paracrine action of stem cells, including protein regulation, exosome pathway, and cell signaling; however, the specific mechanisms have not yet been clarified. Apoptotic and afunctional pulmonary microvascular endothelial cells (PMVECs) and alveolar epithelial cells (AECs) are two fundamental promoters of PH although they have not been extensively studied by researchers. This review mainly focuses on the supportive communication and interaction between PMVECs and AECs as well as the potential restorative effect of stem cells on their injury. In the future, more studies are needed to prove these effects and explore more radical cures for PH.

Pharmacokinetics and Biodistribution of 16,16 dimethyl Prostaglandin E2 in Non-Irradiated and Irradiated Mice and Non-Irradiated Non-Human Primates

Exposure to high-dose ionizing radiation can lead to life-threatening injuries and mortality. Bone marrow is the most sensitive organ to radiation damage, resulting in the hematopoietic acute radiation syndrome (H-ARS) with the potential sequelae of infection, hemorrhage, anemia, and death if untreated. The development of medical countermeasures (MCMs) to protect or mitigate radiation injury is a medical necessity. In our well-established murine model of H-ARS we have demonstrated that the prostaglandin E2 (PGE2) analog 16,16 dimethyl-PGE2 (dmPGE2) has survival efficacy as both a radioprotectant and radiomitigator. The purpose of this study was to investigate the pharmacokinetics (PK) and biodistribution of dmPGE2 when used as a radioprotector in irradiated and non-irradiated inbred C57BL/6J mice, PK in irradiated and non-irradiated Jackson Diversity Outbred (JDO) mice, and the PK profile of dmPGE2 in non-irradiated non-human primates (NHPs). The C57BL/6J and JDO mice each received a single subcutaneous (SC) dose of 35 ug of dmPGE2 and were randomized to either receive radiation 30 min later or remain non-irradiated. Plasma and tissue PK profiles were established. The NHP were dosed with 0.1 mg/kg by SC administration and the PK profile in plasma was established. The concentration time profiles were analyzed by standard non-compartmental analysis and the metrics of AUC0-Inf, AUC60-480 (AUC from 60-480 min), Cmax, and t1/2 were evaluated. AUC60-480 represents the postirradiation time frame and was used to assess radiation effect. Overall, AUC0-Inf, Cmax, and t1/2 were numerically similar between strains (C57BL/6J and JDO) when combined, regardless of exposure status (AUC0-Inf: 112.50 ng·h/ml and 114.48 ng·h/ml, Cmax: 44.53 ng/ml and 63.96 ng/ml; t1/2: 1.8 h and 1.1 h, respectively). PK metrics were numerically lower in irradiated C57BL/6J mice than in non-irradiated mice [irradiation ratio: irradiated values/non-irradiated values = 0.71 for AUC60-480 (i.e., 29% lower), and 0.6 for t1/2]. In JDO mice, the radiation ratio was 0.53 for AUC60-480 (i.e., 47% lower), and 1.7 h for t1/2. The AUC0-Inf, Cmax, and t1/2 of the NHPs were 29.20 ng·h/ml, 7.68 ng/ml, and 3.26 h, respectively. Despite the numerical differences seen between irradiated and non-irradiated groups in PK parameters, the effect of radiation on PK can be considered minimal based on current data. The biodistribution in C57BL/6J mice showed that dmPGE2 per gram of tissue was highest in the lungs, regardless of exposure status. The radiation ratio for the different tissue AUC60-480 in C57BL/6J mice ranged between 0.5-1.1 (50% lower to 10% higher). Spleen, liver and bone marrow showed close to twice lower exposures after irradiation, whereas heart had a 10% higher exposure. Based on the clearance values from mice and NHP, the estimated allometric scaling coefficient was 0.81 (95% CI: 0.75, 0.86). While slightly higher than the current literature estimates of 0.75, this scaling coefficient can be considered a reasonable estimate and can be used to scale dmPGE2 dosing from animals to humans for future trials.

The role of ROS-pyroptosis in PM2.5 induced air-blood barrier destruction

Fine particulate matter (PM2.5) has attracted increasing attention due to its health-threatening effects. Although numerous studies have investigated the impact of PM2.5 on lung injuries, the specific mechanisms underlying the damage to the air-blood barrier after exposure to PM2.5 remain unclear. In this study, we established an in vitro co-culture system using lung epithelial cells and capillary endothelial cells. Our findings indicated that the tight junction (TJ) proteins were up-regulated in the co-cultured system compared to the monolayer-cultured cells, suggesting the establishment of a more closely connected in vitro system. Following exposure to PM2.5, we observed damage to the air-blood barrier in vitro. Concurrently, PM2.5 exposure induced significant oxidative stress and activated the NLRP3 inflammasome-mediated pyroptosis pathway. When oxidative stress was inhibited, we observed a decrease in pyroptosis and an increase in TJ protein levels. Additionally, disulfiram reversed the adverse effects of PM2.5, effectively suppressing pyroptosis and ameliorating air-blood barrier dysfunction. Our results indicate that the oxidative stress-pyroptosis pathway plays a critical role in the disruption of the air-blood barrier induced by PM2.5 exposure. Disulfiram may represent a promising therapeutic option for mitigating PM2.5-related lung damage.

Development of biomimetic co-culture and tri-culture models to mimic the complex structure of the alveolar-capillary barrier

Alveoli are the functional area of respiratory system where the gaseous exchanges take place at level of the alveolar-capillary barrier. The development of safe and effective therapeutic approaches for treating lung disease is currently limited due to the lack of realistic preclinical models for their testing and validation. In this work, tissue engineering approaches were exploited to develop a biomimetic platform that provide an appropriate mimicking of the extracellular environment and the multicellular architecture of human alveoli. Here, we propose the implementation of two biomimetic in vitro models to reproduce the features of the main anatomic portions of the physiological alveolar-capillary barrier. First, a co-culture barrier model was obtained by integrating an electrospun polycaprolactone-gelatin (PCL-Gel) membrane in a modified transwell insert (PCL-Gel TW) to mimic the alveolar basement membrane (coded as thin model). Alveolar epithelial (A549) and lung microvascular endothelial (HULEC-5a) cells were cultured on the apical and basolateral side of the PCL-Gel membrane, respectively, under physiologic air-liquid interface (ALI) conditions for 7 days. The ALI condition promoted the expression of type I and type II alveolar epithelial cell markers and the secretion of mucus in A549 cells. Increased cell viability and barrier properties in co-cultures of A549 and HULEC-5a compared to mono-cultures revealed the effectiveness of the model to reproduce in vitro physiological-relevant features of the alveolar-capillary barrier. The second portion of the alveolar-capillary barrier was developed implementing a tri-culture model (coded as thick model) including a type I collagen (COLL) hydrogel formulated to host lung fibroblasts (MRC-5). The thick barrier model was implemented by seeding HULEC-5a on the basolateral side of PCL-Gel TW and then pouring sequentially MRC-5-laden COLL hydrogel and A549 cells on the apical side of the electrospun membrane. The thick model was maintained up to 7 days at ALI and immunofluorescence staining of tight and adherent junctions demonstrated the formation of a tight barrier. Lastly, the ability of models to emulate pathological inflammatory conditions was validated by exposing the apical compartment of the PCL-Gel TW to lipopolysaccharide (LPS). The damage of A549 tight junctions, the increase of barrier permeability and IL-6 pro-inflammatory cytokine release was observed after 48 h exposure to LPS.

New Onset Anemia, Worsened Plasma Creatinine Concentration, and Hyperviscosity in a Patient With a Monoclonal IgM Paraprotein

A 76-year-old female followed closely for five years with IgM monoclonal gammopathy of uncertain significance developed anemia, worsened plasma creatinine concentration, and markedly elevated serum viscosity. This case illustrates the scope of pathology that can be caused by elevated blood viscosity. Our patient's anemia was a homeostatic response to normalize systemic vascular resistance and resulted from activation of the systemic vascular resistance response. The elevated plasma creatinine resulted from decreased renal perfusion because of elevated blood viscosity. Recent insights in hemorheology (the study of blood flow) are discussed, namely the recent identification of preferential blood flow patterns and erythrocyte autoregulation of deformability. These insights confirm that blood viscosity is part of the "milieu intérieur."

Dysregulation of metabolic pathways in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disorder of unknown origin and the most common interstitial lung disease. It progresses with the recruitment of fibroblasts and myofibroblasts that contribute to the accumulation of extracellular matrix (ECM) proteins, leading to the loss of compliance and alveolar integrity, compromising the gas exchange capacity of the lung. Moreover, while there are therapeutics available, they do not offer a cure. Thus, there is a pressing need to identify better therapeutic targets. With the advent of transcriptomics, proteomics, and metabolomics, the cellular mechanisms underlying disease progression are better understood. Metabolic homeostasis is one such factor and its dysregulation has been shown to impact the outcome of IPF. Several metabolic pathways involved in the metabolism of lipids, protein and carbohydrates have been implicated in IPF. While metabolites are crucial for the generation of energy, it is now appreciated that metabolites have several non-metabolic roles in regulating cellular processes such as proliferation, signaling, and death among several other functions. Through this review, we succinctly elucidate the role of several metabolic pathways in IPF. Moreover, we also discuss potential therapeutics which target metabolism or metabolic pathways.

PGE2 Produced by Exogenous MSCs Promotes Immunoregulation in ARDS Induced by Highly Pathogenic Influenza A through Activation of the Wnt-β-Catenin Signaling Pathway

Acute respiratory distress syndrome is an acute respiratory failure caused by cytokine storms; highly pathogenic influenza A virus infection can induce cytokine storms. The innate immune response is vital in this cytokine storm, acting by activating the transcription factor NF-κB. Tissue injury releases a danger-associated molecular pattern that provides positive feedback for NF-κB activation. Exogenous mesenchymal stem cells can also modulate immune responses by producing potent immunosuppressive substances, such as prostaglandin E2. Prostaglandin E2 is a critical mediator that regulates various physiological and pathological processes through autocrine or paracrine mechanisms. Activation of prostaglandin E2 results in the accumulation of unphosphorylated β-catenin in the cytoplasm, which subsequently reaches the nucleus to inhibit the transcription factor NF-κB. The inhibition of NF-κB by β-catenin is a mechanism that reduces inflammation.

Effects of hypoxia on bronchial and alveolar epithelial cells linked to pathogenesis in chronic lung disorders

Introduction: Chronic lung disorders involve pathological alterations in the lung tissue with hypoxia as a consequence. Hypoxia may influence the release of inflammatory mediators and growth factors including vascular endothelial growth factor (VEGF) and prostaglandin (PG)E2. The aim of this work was to investigate how hypoxia affects human lung epithelial cells in combination with profibrotic stimuli and its correlation to pathogenesis.

Methods: Human bronchial (BEAS-2B) and alveolar (hAELVi) epithelial cells were exposed to either hypoxia (1% O2) or normoxia (21% O2) during 24 h, with or without transforming growth factor (TGF)-β1. mRNA expression of genes and proteins related to disease pathology were analysed with qPCR, ELISA or immunocytochemistry. Alterations in cell viability and metabolic activity were determined.

Results: In BEAS-2B and hAELVi, hypoxia significantly dowregulated genes related to fibrosis, mitochondrial stress, oxidative stress, apoptosis and inflammation whereas VEGF receptor 2 increased. Hypoxia increased the expression of Tenascin-C, whereas both hypoxia and TGF-β1 stimuli increased the release of VEGF, IL-6, IL-8 and MCP-1 in BEAS-2B. In hAELVi, hypoxia reduced the release of fibroblast growth factor, epidermal growth factor, PGE2, IL-6 and IL-8, whereas TGF-β1 stimulus significantly increased the release of PGE2 and IL-6. TGF-β1 stimulated BEAS-2B cells showed a decreased release of VEGF-A and IL-8, while TGF-β1 stimulated hAELVi cells showed a decreased release of PGE2 and IL-8 during hypoxia compared to normoxia. Metabolic activity was significantly increased by hypoxia in both epithelial cell types.

Discussion: In conclusion, our data indicate that bronchial and alveolar epithelial cells respond differently to hypoxia and profibrotic stimuli. The bronchial epithelium appears more responsive to changes in oxygen levels and remodelling processes compared to the alveoli, suggesting that hypoxia may be a driver of pathogenesis in chronic lung disorders.

A multiplex inhalation platform to model in situ like aerosol delivery in a breathing lung-on-chip

Prolonged exposure to environmental respirable toxicants can lead to the development and worsening of severe respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD) and fibrosis. The limited number of FDA-approved inhaled drugs for these serious lung conditions has led to a shift from in vivo towards the use of alternative in vitro human-relevant models to better predict the toxicity of inhaled particles in preclinical research. While there are several inhalation exposure models for the upper airways, the fragile and dynamic nature of the alveolar microenvironment has limited the development of reproducible exposure models for the distal lung. Here, we present a mechanistic approach using a new generation of exposure systems, the Cloud α AX12. This novel in vitro inhalation tool consists of a cloud-based exposure chamber (VITROCELL) that integrates the breathing ^AXLung-on-chip system (AlveoliX). The ultrathin and porous membrane of the AX12 plate was used to create a complex multicellular model that enables key physiological culture conditions: the air-liquid interface (ALI) and the three-dimensional cyclic stretch (CS). Human-relevant cellular models were established for a) the distal alveolar-capillary interface using primary cell-derived immortalized alveolar epithelial cells (^AXiAECs), macrophages (THP-1) and endothelial (HLMVEC) cells, and b) the upper-airways using Calu3 cells. Primary human alveolar epithelial cells (^AXhAEpCs) were used to validate the toxicity results obtained from the immortalized cell lines. To mimic in vivo relevant aerosol exposures with the Cloud α AX12, three different models were established using: a) titanium dioxide (TiO2) and zinc oxide nanoparticles b) polyhexamethylene guanidine a toxic chemical and c) an anti-inflammatory inhaled corticosteroid, fluticasone propionate (FL). Our results suggest an important synergistic effect on the air-blood barrier sensitivity, cytotoxicity and inflammation, when air-liquid interface and cyclic stretch culture conditions are combined. To the best of our knowledge, this is the first time that an in vitro inhalation exposure system for the distal lung has been described with a breathing lung-on-chip technology. The Cloud α AX12 model thus represents a state-of-the-art pre-clinical tool to study inhalation toxicity risks, drug safety and efficacy.

Clinical Translation of Engineered Pulmonary Vascular Models

Diseases in pulmonary vasculature remain a major cause of morbidity and mortality worldwide. Numerous pre-clinical animal models were developed to understand lung vasculature during diseases and development. However, these systems are typically limited in their ability to represent human pathophysiology for the study of disease and drug mechanisms. In recent years, a growing number of studies have focused on developing in vitro experimental platforms that mimic human tissues/organs. In this chapter, we discuss the key components involved in developing engineered pulmonary vascular modeling systems and provide perspectives on ways to improve the translational potential of existing models.

A New Immortalized Human Alveolar Epithelial Cell Model to Study Lung Injury and Toxicity on a Breathing Lung-On-Chip System

The evaluation of inhalation toxicity, drug safety and efficacy assessment, as well as the investigation of complex disease pathomechanisms, are increasingly relying on in vitro lung models. This is due to the progressive shift towards human-based systems for more predictive and translational research. While several cellular models are currently available for the upper airways, modelling the distal alveolar region poses several constraints that make the standardization of reliable alveolar in vitro models relatively difficult. In this work, we present a new and reproducible alveolar in vitro model, that combines a human derived immortalized alveolar epithelial cell line (^AXiAEC) and organ-on-chip technology mimicking the lung alveolar biophysical environment (^AXlung-on-chip). The latter mimics key features of the in vivo alveolar milieu: breathing-like 3D cyclic stretch (10% linear strain, 0.2 Hz frequency) and an ultrathin, porous and elastic membrane. ^AXiAECs cultured on-chip were characterized for their alveolar epithelial cell markers by gene and protein expression. Cell barrier properties were examined by TER (Transbarrier Electrical Resistance) measurement and tight junction formation. To establish a physiological model for the distal lung, ^AXiAECs were cultured for long-term at air-liquid interface (ALI) on-chip. To this end, different stages of alveolar damage including inflammation (via exposure to bacterial lipopolysaccharide) and the response to a profibrotic mediator (via exposure to Transforming growth factor β1) were analyzed. In addition, the expression of relevant host cell factors involved in SARS-CoV-2 infection was investigated to evaluate its potential application for COVID-19 studies. This study shows that ^AXiAECs cultured on the ^AXlung-on-chip exhibit an enhanced in vivo-like alveolar character which is reflected into: 1) Alveolar type 1 (AT1) and 2 (AT2) cell specific phenotypes, 2) tight barrier formation (with TER above 1,000 Ω cm²) and 3) reproducible long-term preservation of alveolar characteristics in nearly physiological conditions (co-culture, breathing, ALI). To the best of our knowledge, this is the first time that a primary derived alveolar epithelial cell line on-chip representing both AT1 and AT2 characteristics is reported. This distal lung model thereby represents a valuable in vitro tool to study inhalation toxicity, test safety and efficacy of drug compounds and characterization of xenobiotics.

Antiviral Activity of a Cyclic Pro-Pro-β3-HoPhe-Phe Tetrapeptide against HSV-1 and HAdV-5

The core of Cyclolinopeptide A (CLA, cyclo(LIILVPPFF)), responsible for its high immunosuppressive activity, contains a Pro-Pro-Phe-Phe sequence. A newly synthesized cyclic tetrapeptide, cyclo(Pro-Pro-β3-HoPhe-Phe) (denoted as 4B8M) bearing the active sequence of CLA, was recently shown to exhibit a wide array of anti-inflammatory properties in mouse models. In this investigation, we demonstrate that the peptide significantly inhibits the replication of human adenovirus C serotype 5 (HAdV-5) and Herpes simplex virus type-1 (HSV-1) in epithelial lung cell line A-549, applying Cidofovir and Acyclovir as reference drugs. Based on a previously established mechanism of its action, we propose that the peptide may inhibit virus replication by the induction of PGE2 acting via EP2/EP4 receptors in epithelial cells. In summary, we reveal a new, antiviral property of this anti-inflammatory peptide.

A transcriptomics-guided drug target discovery strategy identifies receptor ligands for lung regeneration

Currently, there is no pharmacological treatment targeting defective tissue repair in chronic disease. Here, we used a transcriptomics-guided drug target discovery strategy using gene signatures of smoking-associated chronic obstructive pulmonary disease (COPD) and from mice chronically exposed to cigarette smoke, identifying druggable targets expressed in alveolar epithelial progenitors, of which we screened the function in lung organoids. We found several drug targets with regenerative potential, of which EP and IP prostanoid receptor ligands had the most profound therapeutic potential in restoring cigarette smoke-induced defects in alveolar epithelial progenitors in vitro and in vivo. Mechanistically, we found, using single-cell RNA sequencing analysis, that circadian clock and cell cycle/apoptosis signaling pathways were differentially expressed in alveolar epithelial progenitor cells in patients with COPD and in a relevant model of COPD, which was prevented by prostaglandin E2 or prostacyclin mimetics. We conclude that specific targeting of EP and IP receptors offers therapeutic potential for injury to repair in COPD.

Aryl Hydrocarbon Receptor (AhR) Limits the Inflammatory Responses in Human Lung Adenocarcinoma A549 Cells via Interference with NF-κB Signaling

Apart from its role in the metabolism of carcinogens, the aryl hydrocarbon receptor (AhR) has been suggested to be involved in the control of inflammatory responses within the respiratory tract. However, the mechanisms responsible for this are only partially known. In this study, we used A549 cell line, as a human model of lung alveolar type II (ATII)-like cells, to study the functional role of the AhR in control of inflammatory responses. Using IL-1β as an inflammation inducer, we found that the induction of cyclooxygenase-2 and secretion of prostaglandins, as well as expression and release of pro-inflammatory cytokines, were significantly higher in the AhR-deficient A549 cells. This was linked with an increased nuclear factor-κB (NF-κB) activity, and significantly enhanced phosphorylation of its regulators, IKKα/β, and their target IκBα, in the AhR-deficient A549 cells. In line with this, when we mimicked the exposure to a complex mixture of airborne pollutants, using an organic extract of reference diesel exhaust particle mixture, an exacerbated inflammatory response was observed in the AhR-deficient cells, as compared with wild-type A549 cells. Together, the present results indicate that the AhR may act as a negative regulator of the inflammatory response in the A549 model, via a direct modulation of NF-κB signaling. Its role(s) in the control of inflammation within the lung alveoli exposed to airborne pollutants, especially those which simultaneously activate the AhR, thus deserve further attention.

A20 Is Increased in Fetal Lung in a Sheep LPS Model of Chorioamnionitis

Chorioamnionitis is associated with an increased risk of preterm birth and aggravates adverse outcomes such as BPD. Development of BPD is associated with chronic inflammatory reactions and oxidative stress in the airways which may be antenatally initiated by chorioamnionitis. A20 is an immunomodulatory protein involved in the negative feedback regulation of inflammatory reactions and is a possible regulator protein in oxidative stress reactions. The influence of chorioamnionitis on A20 gene regulation in the fetal lung is unknown. We characterized the influence of LPS and proinflammatory cytokines on A20 expression in human lung endothelial (HPMEC-ST1.6R) and epithelial (A549) cells in vitro by real-time PCR and/or western blotting and used a sheep model of LPS-induced chorioamnionitis for in vivo studies. To study the functional role of A20, endogenous A20 was overexpressed in HPMEC-ST1.6R and A549 cells. LPS induced proinflammatory cytokines in HPMEC-ST1.6R and A549 cells. Both LPS and/or proinflammatory cytokines elevated A20 at transcriptional and translational levels. Intra-amniotic LPS transiently increased IL-1β, IL-6, IL-8, and TNF-α mRNA levels in fetal lamb lungs, associated with an increase in A20 mRNA and protein levels. Overexpression of A20 reduced proinflammatory cytokines in vitro. Repeated LPS exposure induced LPS tolerance for proinflammatory cytokines and A20 in vitro and in vivo. Antenatal inflammation induced a transient increase in proinflammatory cytokines in the preterm fetal lung. The expression of proinflammatory cytokines increased expression of A20. Elevated A20 may have a protective role by downregulating chorioamnionitis-triggered fetal lung inflammation. A20 may be a novel target for pharmacological interventions to prevent chorioamnionitis-induced airway inflammation and lung damage, which can result in BPD later in life.

SUCNR1 Is Expressed in Human Placenta and Mediates Angiogenesis: Significance in Gestational Diabetes

Placental hypervascularization has been reported in pregnancy-related pathologies such as gestational diabetes mellitus (GDM). Nevertheless, the underlying causes behind this abnormality are not well understood. In this study, we addressed the expression of SUCNR1 (cognate succinate receptor) in human placental endothelial cells and hypothesized that the succinate-SUCNR1 axis might play a role in the placental hypervascularization reported in GDM. We measured significantly higher succinate levels in placental tissue lysates from women with GDM relative to matched controls. In parallel, SUCNR1 protein expression was upregulated in GDM tissue lysates as well as in isolated diabetic fetoplacental arterial endothelial cells (FpECAds). A positive correlation of SUCNR1 and vascular endothelial growth factor (VEGF) protein levels in tissue lysates indicated a potential link between the succinate-SUCNR1 axis and placental angiogenesis. In our in vitro experiments, succinate prompted hallmarks of angiogenesis in human umbilical vein endothelial cells (HUVECs) such as proliferation, migration and spheroid sprouting. These results were further validated in fetoplacental arterial endothelial cells (FpECAs), where succinate induced endothelial tube formation. VEGF gene expression was increased in response to succinate in both HUVECs and FpECAs. Yet, knockdown of SUCNR1 in HUVECs led to suppression of VEGF gene expression and abrogated the migratory ability and wound healing in response to succinate. In conclusion, our data underline SUCNR1 as a promising metabolic target in human placenta and as a potential driver of enhanced placental angiogenesis in GDM.

Development of an In Vitro Airway Epithelial-Endothelial Cell Culture Model on a Flexible Porous Poly(Trimethylene Carbonate) Membrane Based on Calu-3 Airway Epithelial Cells and Lung Microvascular Endothelial Cells

Due to the continuing high impact of lung diseases on society and the emergence of new respiratory viruses, such as SARS-CoV-2, there is a great need for in vitro lung models that more accurately recapitulate the in vivo situation than current models based on lung epithelial cell cultures on stiff membranes. Therefore, we developed an in vitro airway epithelial–endothelial cell culture model based on Calu-3 human lung epithelial cells and human lung microvascular endothelial cells (LMVECs), cultured on opposite sides of flexible porous poly(trimethylene carbonate) (PTMC) membranes. Calu-3 cells, cultured for two weeks at an air–liquid interface (ALI), showed good expression of the tight junction (TJ) protein Zonula Occludens 1 (ZO-1). LMVECs cultured submerged for three weeks were CD31-positive, but the expression was diffuse and not localized at the cell membrane. Barrier functions of the Calu-3 cell cultures and the co-cultures with LMVECs were good, as determined by electrical resistance measurements and fluorescein isothiocyanate-dextran (FITC-dextran) permeability assays. Importantly, the Calu-3/LMVEC co-cultures showed better cell viability and barrier function than mono-cultures. Moreover, there was no evidence for epithelial- and endothelial-to-mesenchymal transition (EMT and EndoMT, respectively) based on staining for the mesenchymal markers vimentin and α-SMA, respectively. These results indicate the potential of this new airway epithelial–endothelial model for lung research. In addition, since the PTMC membrane is flexible, the model can be expanded by introducing cyclic stretch for enabling mechanical stimulation of the cells. Furthermore, the model can form the basis for biomimetic airway epithelial–endothelial and alveolar–endothelial models with primary lung epithelial cells.

Inhibition of p38 MAPK Mitigates Lung Ischemia Reperfusion Injury by Reducing Blood-Air Barrier Hyperpermeability

Background: Lung ischemia reperfusion injury (LIRI) is a complex pathophysiological process activated by lung transplantation and acute lung injury. The p38 mitogen-activated protein kinase (MAPK) is involved in breakdown of the endothelial barrier during LIRI, but the mechanism is still unclear. Therefore, we investigated the function of p38 MAPK in LIRI in vivo and in vitro.

Methods: Sprague–Dawley rats were subjected to ischemia reperfusion with or without pretreatment with a p38 MAPK inhibitor. Lung injury was assessed using hematoxylin and eosin staining, and pulmonary blood–air barrier permeability was evaluated using Evans blue staining. A rat pulmonary microvascular endothelial cell line was infected with lentiviral expressing short hairpin (sh)RNA targeting p38 MAPK and then cells were subjected to oxygen/glucose deprivation and reoxygenation (OGD/R). Markers of endothelial destruction were measured by western blot and immunofluorescence.

Results:In vivo LIRI models showed structural changes indicative of lung injury and hyperpermeability of the blood–air barrier. Inhibiting p38 MAPK mitigated these effects. Oxygen/glucose deprivation and reoxygenation promoted hyperpermeability of the endothelial barrier in vitro, but knockdown of p38 MAPK attenuated cell injury; maintained endothelial barrier integrity; and partially reversed injury-induced downregulation of permeability protein AQP1, endothelial protective protein eNOS, and junction proteins ZO-1 and VE-cadherin while downregulating ICAM-1, a protein involved in destroying the endothelial barrier, and ET-1, a protein involved in endothelial dysfunction.

Conclusion: Inhibition of p38 MAPK alleviates LIRI by decreasing blood–air hyperpermeability. Blocking p38 MAPK may be an effective treatment against acute lung injury.

Cyclooxgenase-2 is induced by SARS-CoV-2 infection but does not affect viral entry or replication

Identifying drugs that regulate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and its symptoms has been a pressing area of investigation during the coronavirus disease 2019 (COVID-19) pandemic. Nonsteroidal anti-inflammatory drugs (NSAIDs), which are frequently used for the relief of pain and inflammation, could modulate both SARS-CoV-2 infection and the host response to the virus. NSAIDs inhibit the enzymes cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), which mediate the production of prostaglandins (PGs). PGE2, one of the most abundant PGs, has diverse biological roles in homeostasis and inflammatory responses. Previous studies have shown that NSAID treatment or inhibition of PGE2 receptor signaling leads to upregulation of angiotensin-converting enzyme 2 (ACE2), the cell entry receptor for SARS-CoV-2, thus raising concerns that NSAIDs could increase susceptibility to infection. COX/PGE2 signaling has also been shown to regulate the replication of many viruses, but it is not yet known whether it plays a role in SARS-CoV-2 replication. The purpose of this study was to dissect the effect of NSAIDs on COVID-19 in terms of SARS-CoV-2 entry and replication. We found that SARS-CoV-2 infection induced COX-2 upregulation in diverse human cell culture and mouse systems. However, suppression of COX-2/PGE2 signaling by two commonly used NSAIDs, ibuprofen and meloxicam, had no effect on ACE2 expression, viral entry, or viral replication. Our findings suggest that COX-2 signaling driven by SARS-CoV-2 may instead play a role in regulating the lung inflammation and injury observed in COVID-19 patients.

Macromolecular biomarkers of chronic obstructive pulmonary disease in exhaled breath condensate

Biomarkers provide important diagnostic and prognostic information on heterogeneous diseases such as chronic obstructive pulmonary disease (COPD). However, finding a suitable specimen for clinical analysis of biomarkers for COPD is challenging. Exhaled breath condensate (EBC) sampling is noninvasive, rapid, cost-effective and easily repeatable. EBC sampling has also provided recent progress in the identification of biological macromolecules, such as lipids, proteins and DNA in EBC samples, which has increased its utility for clinical scientists. In this article, we review applications involving EBC sampling for the analysis of COPD biomarkers and discuss its future potential.

The novel immunomodulatory biologic LMWF5A for pharmacological attenuation of the "cytokine storm" in COVID-19 patients: a hypothesis

BACKGROUND

A common complication of viral pulmonary infections, such as in the ongoing COVID-19 pandemic, is a phenomenon described as a "cytokine storm". While poorly defined, this hyperinflammatory response results in diffuse alveolar damage. The low molecular weight fraction of commercial human serum albumin (LMWF5A), a novel biologic in development for osteoarthritis, demonstrates beneficial in vitro immunomodulatory effects complimentary to addressing inflammation, thus, we hypothesize that LMWF5A could improve the clinical outcomes of COVID-19 by attenuating hyperinflammation and the potential development of a cytokine storm.

PRESENTATION OF THE HYPOTHESIS

A variety of human in vitro immune models indicate that LMWF5A reduces the production of pro-inflammatory cytokines implicated in cytokine storm associated with COVID-19. Furthermore, evidence suggests LMWF5A also promotes the production of mediators required for resolving inflammation and enhances the barrier function of endothelial cultures.

TESTING THE HYPOTHESIS

A randomized controlled trial, to evaluate the safety and efficacy of nebulized LMWF5A in adults with Acute Respiratory Distress Syndrome (ARDS) secondary to COVID-19 infection, was developed and is currently under review by the Food and Drug Administration.

IMPLICATIONS OF HYPOTHESIS

If successful, this therapy may attenuate the cytokine storm observed in these patients and potentially reduce mortality, increase ventilation free days, improve oxygenation parameters and consequently lessen the burden on patients and the intensive care unit.

CONCLUSIONS

In conclusion, in vitro findings suggest that the immunomodulatory effects of LMWF5A make it a viable candidate for treating cytokine storm and restoring homeostasis to the immune response in COVID-19.

Lung regeneration: a tale of mice and men

The respiratory system is the main site of gas exchange with the external environment in complex terrestrial animals. Within the trachea and lungs are multiple different tissue niches each consisting of a myriad of cells types with critical roles in air conduction, gas exchange, providing important niche specific cell-cell interactions, connection to the cardiovascular system, and immune surveillance. How the respiratory system responds to external insults and executes the appropriate regenerative response remains challenging to study given the plethora of cell and tissue interactions for this to occur properly. This review will examine the various cell types and tissue niches found within the respiratory system and provide a comparison between mouse and human lungs and trachea to highlight important similarities and differences. Defining the critical gaps in knowledge in human lung and tracheal regeneration is critical for future development of therapies directed towards respiratory diseases.

Nitrite attenuates mitochondrial impairment and vascular permeability induced by ischemia-reperfusion injury in the lung

Primary graft dysfunction (PGD) is directly related to ischemia-reperfusion (I/R) injury and a major obstacle in lung transplantation (LTx). Nitrite (NO2-), which is reduced in vivo to form nitric oxide (NO), has recently emerged as an intrinsic signaling molecule with a prominent role in cytoprotection against I/R injury. Using a murine model, we provide the evidence that nitrite mitigated I/R-induced injury by diminishing infiltration of immune cells in the alveolar space, reducing pulmonary edema, and improving pulmonary function. Ultrastructural studies support severe mitochondrial impairment in the lung undergoing I/R injury, which was significantly protected by nitrite treatment. Nitrite also abrogated the increased pulmonary vascular permeability caused by I/R. In vitro, hypoxia-reoxygenation (H/R) exacerbated cell death in lung epithelial and microvascular endothelial cells. This contributed to mitochondrial dysfunction as characterized by diminished complex I activity and mitochondrial membrane potential but increased mitochondrial reactive oxygen species (mtROS). Pretreatment of cells with nitrite robustly attenuated mtROS production through modulation of complex I activity. These findings illustrate a potential novel mechanism in which nitrite protects the lung against I/R injury by regulating mitochondrial bioenergetics and vascular permeability.

Inhibiting eicosanoid degradation exerts antifibrotic effects in a pulmonary fibrosis mouse model and human tissue

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a disease with high 5-year mortality and few therapeutic options. Prostaglandin (PG) E₂ exhibits antifibrotic properties and is reduced in bronchoalveolar lavage from patients with IPF. 15-Prostaglandin dehydrogenase (15-PGDH) is the key enzyme in PGE₂ metabolism under the control of TGF-β and microRNA 218.

OBJECTIVE

We sought to investigate the expression of 15-PGDH in IPF and the therapeutic potential of a specific inhibitor of this enzyme in a mouse model and human tissue.

METHODS

In vitro studies, including fibrocyte differentiation, regulation of 15-PGDH, RT-PCR, and Western blot, were performed using peripheral blood from healthy donors and patients with IPF and A549 cells. Immunohistochemistry, immunofluorescence, 15-PGDH activity assays, and in situ hybridization as well as ex vivo IPF tissue culture experiments were done using healthy donor and IPF lungs. Therapeutic effects of 15-PGDH inhibition were studied in the bleomycin mouse model of pulmonary fibrosis.

RESULTS

We demonstrate that 15-PGDH shows areas of increased expression in patients with IPF. Inhibition of this enzyme increases PGE₂ levels and reduces collagen production in IPF precision cut lung slices and in the bleomycin model. Inhibitor-treated mice show amelioration of lung function, decreased alveolar epithelial cell apoptosis, and fibroblast proliferation. Pulmonary fibrocyte accumulation is also decreased by inhibitor treatment in mice, similar to PGE₂ that inhibits fibrocyte differentiation from blood of healthy donors and patients with IPF. Finally, microRNA 218-5p, which is downregulated in patients with IPF, suppressed 15-PGDH expression in vivo and in vitro.

CONCLUSIONS

These findings highlight the role of 15-PGDH in IPF and suggest 15-PGDH inhibition as a promising therapeutic approach.

De novo lung biofabrication: clinical need, construction methods, and design strategy

Chronic lung disease is the 4th leading cause of death in the United States. Due to a shortage of donor lungs, alternative approaches to support failing, native lungs have been attempted, including mechanical ventilation and various forms of artificial lungs. However, each of these support methods causes significant complications when used for longer than a few days and are thus not capable of long-term support. For artificial lungs, complications arise due to interactions between the artificial materials of the device and the blood of the recipient. A potential new approach is the fabrication of lungs from biological materials, such that the gas exchange membranes provide a more biomimetic blood-contacting interface. Recent advancements with three-dimensional, soft-tissue biofabrication methods and the engineering of thin, basement membranes demonstrate the potential of fabricating a lung scaffold from extracellular matrix materials. This scaffold could then be seeded with endothelial and epithelial cells, matured within a bioreactor, and transplanted. In theory, this fully biological lung could provide improved, long-term biocompatibility relative to artificial lungs, but significant work is needed to perfect the organ design and construction methods. Like artificial lungs, biofabricated lungs do not need to follow the shape and structure of a native lung, allowing for simpler manufacture. However, various functional requirements must still be met, including stable, efficient gas exchange for a period of years. Design decisions depend on the disease state, how the organ is implanted, and the latest biofabrication methods available in a rapidly evolving field.

Microvesicles derived from human Wharton's Jelly mesenchymal stem cells ameliorate acute lung injury partly mediated by hepatocyte growth factor

Several studies have highlighted the underlying role of mesenchymal stem cells microvesicles (MSC-MVs) in acute lung injury (ALI). Hepatocyte growth factor (HGF) derived from MSC-MVs is partly involved in their therapeutic effects; however, the detailed mechanism remains unclear. MVs were isolated from human Wharton's Jelly MSCs. The rat model of ALI was established by intratracheal instillation of bleomycin (BLM). A co-culture model of alveolar epithelial cells or pulmonary endothelial cells and MSC-MVs was utilized. Total protein content in bronchoalveolar lavage fluid (BALF) was determined by bicinchoninic acid method. White blood cell (WBC) and neutrophil in BALF were counted. ELISA was used for the determination of cytokines and HGF in BALF. Apoptosis was determined by TUNEL assay and Annexin V-FITC/PI staining as well as caspase-3 activity detection. HE and Masson staining of lung tissues was used for histopathology analysis. The expression of HGF and proteins involved in the PI3K/AKT/mTOR pathway were measured by quantitative Real-Time PCR (qRT-PCR) and western blotting. Treatment with MSC-MVs significantly inhibited BLM-induced apoptosis and fibrosis in lung tissues and PI3K/AKT/mTOR activation, which was reversed by HGF mRNA deficient MVs. Intriguingly, these effects were completely abrogated by PI3K inhibitor. The therapeutic effect of MSC-MVs in ALI was partly mediated through HGF mRNA.

Butyrate ameliorates allergic airway inflammation by limiting eosinophil trafficking and survival

BACKGROUND

Lung eosinophilia is a hallmark of asthma, and eosinophils are believed to play a crucial role in the pathogenesis of allergic inflammatory diseases. Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are produced in high amounts in the gastrointestinal tract by commensal bacteria and can be absorbed into the bloodstream. Although there is recent evidence that SCFAs are beneficial in allergic asthma models, the effect on eosinophils has remained elusive.

OBJECTIVE

The role of SCFAs was investigated in human eosinophil function and a mouse model of allergic asthma.

METHODS

Eosinophils were purified from self-reported allergic or healthy donors. Migration, adhesion to the endothelium, and eosinophil survival were studied in vitro. Ca²⁺ flux, apoptosis, mitochondrial membrane potential, and expression of surface markers were determined by using flow cytometry and in part by using real-time PCR. Allergic airway inflammation was assessed in vivo in an ovalbumin-induced asthma model by using invasive spirometry.

RESULTS

For the first time, we observed that SCFAs were able to attenuate human eosinophils at several functional levels, including (1) adhesion to the endothelium, (2) migration, and (3) survival. These effects were independent from GPR41 and GPR43 but were accompanied by histone acetylation and mimicked by trichostatin A, a pan-histone deacetylase inhibitor. In vivo butyrate ameliorated allergen-induced airway and lung eosinophilia, reduced type 2 cytokine levels in bronchial fluid, and improved airway hyperresponsiveness in mice.

CONCLUSION

These in vitro and in vivo findings highlight the importance of SCFAs, especially butyrate as a promising therapeutic agent in allergic inflammatory diseases.

Cellular and Molecular Heterogeneity Associated with Vessel Formation Processes

The microvasculature heterogeneity is a complex subject in vascular biology. The difficulty of building a dynamic and interactive view among the microenvironments, the cellular and molecular heterogeneities, and the basic aspects of the vessel formation processes make the available knowledge largely fragmented. The neovascularisation processes, termed vasculogenesis, angiogenesis, arteriogenesis, and lymphangiogenesis, are important to the formation and proper functioning of organs and tissues both in the embryo and the postnatal period. These processes are intrinsically related to microvascular cells, such as endothelial and mural cells. These cells are able to adjust their activities in response to the metabolic and physiological requirements of the tissues, by displaying a broad plasticity that results in a significant cellular and molecular heterogeneity. In this review, we intend to approach the microvasculature heterogeneity in an integrated view considering the diversity of neovascularisation processes and the cellular and molecular heterogeneity that contribute to microcirculatory homeostasis. For that, we will cover their interactions in the different blood-organ barriers and discuss how they cooperate in an integrated regulatory network that is controlled by specific molecular signatures.

Novel mechanisms regulating endothelial barrier function in the pulmonary microcirculation

The pulmonary epithelial and vascular endothelial cell layers provide two sequential physical and immunological barriers that together form a semi-permeable interface and prevent alveolar and interstitial oedema formation. In this review, we focus specifically on the continuous endothelium of the pulmonary microvascular bed that warrants strict control of the exchange of gases, fluid, solutes and circulating cells between the plasma and the interstitial space. The present review provides an overview of emerging molecular mechanisms that permit constant transcellular exchange between the vascular and interstitial compartment, and cause, prevent or reverse lung endothelial barrier failure under experimental conditions, yet with a clinical perspective. Based on recent findings and at times seemingly conflicting results we discuss emerging paradigms of permeability regulation by altered ion transport as well as shifts in the homeostasis of sphingolipids, angiopoietins and prostaglandins.

Injured lung endothelium: mechanisms of self-repair and agonist-assisted recovery (2017 Grover Conference Series)

The lung endothelium is vulnerable to both exogenous and endogenous insults, so a properly coordinated efficient repair system is essential for the timely recovery of the lung after injury. The agents that cause endothelial injury and dysfunction fall into a broad range from mechanical forces such as pathological cyclic stretch and shear stress to bacterial pathogens and their virulent components, vasoactive agonists including thrombin and histamine, metabolic causes including high glucose and oxidized low-density lipoprotein (OxLDL), circulating microparticles, and inflammatory cytokines. The repair mechanisms employed by endothelial cells (EC) can be broadly categorized into three groups: (1) intrinsic mechanism of recovery regulated by the cross-talk between small GTPases as exemplified by Rap1-mediated EC barrier recovery from Rho-mediated thrombin-induced EC hyperpermeability; (2) agonist-assisted recovery facilitated by the activation of Rac and Rap1 with subsequent inhibition of Rho signaling as observed with many barrier protective agonists including oxidized phospholipids, sphingosine 1-phosphate, prostacyclins, and hepatocyte growth factor; and (3) self-recovery of EC by the secretion of growth factors and other pro-survival bioactive compounds including anti-inflammatory molecules such as lipoxins during the resolution of inflammation. In this review, we will discuss the molecular and cellular mechanisms of pulmonary endothelium repair that is critical for the recovery from various forms of lung injuries.