Tight Junctions, the Epithelial Barrier, and Toll-like Receptor-4 During Lung Injury

Lipopolysaccharide induces retention of E-cadherin in the endoplasmic reticulum and promotes hybrid epithelial-to-mesenchymal transition of human embryonic stem cells-derived expandable lung epithelial cells

BACKGROUND

Lipopolysaccharide (LPS)-induced inflammation of lung tissues triggers irreversible alterations in the lung parenchyma, leading to fibrosis and pulmonary dysfunction. While the molecular and cellular responses of immune and connective tissue cells in the lungs are well characterized, the specific epithelial response remains unclear due to the lack of representative cell models. Recently, we introduced human embryonic stem cell-derived expandable lung epithelial (ELEP) cells as a novel model for studying lung injury and regeneration.

METHODS

ELEPs were derived from the CCTL 14 human embryonic stem cell line through activin A-mediated endoderm specification, followed by further induction toward pulmonary epithelium using FGF2 and EGF. ELEPs exhibit a high proliferation rate and express key structural and molecular markers of alveolar progenitors, such as NKX2-1. The effects of Escherichia coli LPS serotype O55:B5 on the phenotype and molecular signaling of ELEPs were analyzed using viability and migration assays, mRNA and protein levels were determined by qRT-PCR, western blotting, and immunofluorescent microscopy.

RESULTS

We demonstrated that purified LPS induces features of a hybrid epithelial-to-mesenchymal transition in pluripotent stem cell-derived ELEPs, triggers the unfolded protein response, and upregulates intracellular β-catenin level through retention of E-cadherin within the endoplasmic reticulum.

CONCLUSIONS

Human embryonic stem cell-derived ELEPs provide a biologically relevant, non-cancerous lung cell model to investigate molecular responses to inflammatory stimuli and address epithelial plasticity. This approach offers novel insights into the fine molecular processes underlying lung injury and repair.

Impact of maternal microplastic exposure on offspring lung structure and function: Insights into transcriptional misregulation and the TGF-β/α-SMA pathway

The "Developmental Origins of Health and Disease" (DOHaD) theory suggests that prenatal exposure to harmful environmental factors may impair fetal tissue development, increasing the risk of diseases later in life. This study investigated the effects of prenatal exposure to polystyrene microplastics (PS-MPs) on offspring lung development. Pregnant Sprague-Dawley rats were randomly assigned to receive PS-MPs in drinking water until delivery, with a control group receiving standard water. Offspring were assessed at 7 and 120 d after birth without further PS-MPs exposure. Histopathological examination at 7 d revealed PS-MPs deposits, alveolar collapse, and inflammation in lung tissue. Gene expression analysis showed disruptions in tight junctions, transcriptional regulation, and transforming growth factor-beta (TGF-β) pathways. By day 120, lung dysfunction and structural changes, consistent with emphysema were observed. These findings demonstrate that prenatal PS-MPs exposure adversely affects lung development potentially increasing the risk of respiratory diseases. Public health measures should address the potential hazards of microplastics to fetal health.

Mesenchymal stem cells protect the integrity of the alveolar epithelial barrier through extracellular vesicles by inhibiting MAPK-mediated necroptosis

BACKGROUND

Alveolar‒capillary barrier disruption is a hallmark of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). The contribution of necroptosis to the compromised alveolar-barrier in ALI remains unclear. Mesenchymal stem cells (MSCs) may contribute to tissue repair in ALI and ARDS. Here we evaluated the efficacy and explored the molecular mechanisms of menstrual blood-derived endometrial stem cells (MenSCs) and MenSC-derived extracellular vesicles (MenSC-EVs) in ALI-induced alveolar epithelial barrier dysfunction.

METHODS

Human lung epithelial cells were stimulated with endotoxin and treated with MenSCs or MenSC-EVs, and their barrier properties were evaluated. Lipopolysaccharide (LPS)-injured mice were treated with MenSCs or MSC-EVs, and the degree of lung injury and the alveolar epithelial barrier of the lung tissue were assessed.

RESULTS

We found that MenSCs reduced lung injury and restored alveolar-barrier integrity in lung tissue. In vitro, MenSCs reduced paracellular permeability and restored barrier integrity in human lung epithelial cells. MenSC-EVs replicated all these MenSC-mediated changes. Mechanistic research revealed that MenSCs inhibited MAPK signaling and necroptosis. JNK inhibition SP600125, and ERK inhibition U0126 or inhibition of necroptosis with Nec-1 or GSK872 diminished the beneficial anti-epithelial barrier dysfunction effects of MenSCs or MenSC-EVs.

CONCLUSIONS

Our results suggest that human menstrual blood-derived endometrial stem cells mitigate lung injury and improve alveolar barrier properties by inhibiting MAPK-mediated necroptosis through extracellular vesicles, supporting the application of MenSCs or MenSC-derived extracellular vesicles to treat ALI or ARDS.

AhR Activation at the Air-Blood Barrier Alters Systemic microRNA Release After Inhalation of Particulate Matter Containing Environmentally Persistent Free Radicals

Particulate matter containing environmentally persistent free radicals (EPFRs) is formed when organic pollutants are incompletely burned and adsorb to the surface of particles containing redox-active metals. Our prior studies showed that in mice, EPFR inhalation impaired vascular relaxation in a dose- and endothelium-dependent manner. We also observed that activation of the aryl hydrocarbon receptor (AhR) in the alveolar type-II (AT-II) cells that form the air-blood interface stimulates the release of systemic factors that promote endothelial dysfunction in vessels peripheral to the lung. AhR is a recognized regulator of microRNA (miRNA) biogenesis, and miRNA control diverse signaling pathways. We thus hypothesized that systemic EPFR-induced vascular endothelial dysfunction is initiated via AhR activation in AT-II cells, resulting in a systemic release of miRNA. Using a combustion reactor, we generated EPFR of two free radical concentrations-EPFRlo (1016-17 radicals/g particles) and EPFR (1018-19 radicals/g)-and exposed mice by inhalation. EFPR inhalation resulted in changes in a distinct array of miRNA in the plasma, and these miRNAs are linked to multiple systemic effects, including cardiovascular diseases and dysregulation of cellular and molecular pathways associated with cardiovascular dysfunction. We identified 17 miRNA in plasma that were altered dependent upon both AhR activation in AT-II cells and ~ 280 ug/m3 EPFR exposure. Using Ingenuity Pathway Analysis, we found that 5 of these miRNAs have roles in modulating endothelin-1 and endothelial nitric oxide signaling, known regulators of endothelial function. Furthermore, EPFR exposure reduced the expression of lung adherens and gap junction proteins in control mice but not AT-II-AhR deficient mice, and reductions in barrier function may facilitate miRNA release from the lungs. In summary, our findings support that miRNA may be systemic mediators promoting endothelial dysfunction mediated via EPFR-induced AhR activation at the air-blood interface.

Characteristics, triggers, treatments, and experimental models of neonatal acute respiratory distress syndrome

Neonatal acute respiratory distress syndrome (NARDS) is a severe and potentially life-threatening form of lung injury recently defined by the International Neonatal ARDS Consensus. It is marked by extensive lung inflammation and damage to the alveolar epithelium and vascular endothelium. NARDS can be triggered by direct inflammatory exposures, such as pneumonia and aspiration, and indirect exposures, including sepsis, necrotizing enterocolitis, and chorioamnionitis. This review provides clinicians and researchers with the latest insights on NARDS. We adopt a cross-disciplinary approach to discuss the diagnostic criteria, pathobiology, triggers, epidemiology, and treatments of NARDS. In addition, we summarize existing clinical studies and advanced preclinical models that help address current knowledge gaps. Future research should focus on standardizing the Montreux consensus definition of NARDS in preclinical and clinical studies, identifying biomarkers, developing prediction models, and exploring novel therapies for affected infants.

In vitro models to study viral-induced asthma exacerbation: a short review for a key issue

Asthma is a heterogenous inflammatory bronchial disease involving complex mechanisms, several inflammatory pathways, and multiples cell-type networks. Bronchial inflammation associated to asthma is consecutive to multiple aggressions on epithelium, such as microbiologic, pollutant, and antigenic agents, which are responsible for both T2 and non-T2 inflammatory responses and further airway remodeling. Because asthma physiopathology involves multiple crosstalk between several cell types from different origins (epithelial, mesenchymal, and immune cells) and numerous cellular effectors, no single and/or representative in vitro model is suitable to study the overall of this disease. In this short review, we present and discuss the advantages and limitations of different in vitro models to decipher different aspects of virus-related asthma physiopathology and exacerbation.

De-coding the complex role of microbial metabolites in cancer

The human microbiome, an intricate ecosystem of trillions of microbes residing across various body sites, significantly influences cancer, a leading cause of morbidity and mortality worldwide. Recent studies have illuminated the microbiome's pivotal role in cancer development, either through direct cellular interactions or by secreting bioactive compounds such as metabolites. Microbial metabolites contribute to cancer initiation through mechanisms such as DNA damage, epithelial barrier dysfunction, and chronic inflammation. Furthermore, microbial metabolites exert dual roles on cancer progression and response to therapy by modulating cellular metabolism, gene expression, and signaling pathways. Understanding these complex interactions is vital for devising new therapeutic strategies. This review highlights microbial metabolites as promising targets for cancer prevention and treatment, emphasizing their impact on therapy responses and underscoring the need for further research into their roles in metastasis and therapy resistance.

Crosstalk between ROS-inflammatory gene expression axis in the progression of lung disorders

A significant number of deaths and disabilities worldwide are brought on by inflammatory lung diseases. Many inflammatory lung disorders, including chronic respiratory emphysema, resistant asthma, resistance to steroids, and coronavirus-infected lung infections, have severe variants for which there are no viable treatments; as a result, new treatment alternatives are needed. Here, we emphasize how oxidative imbalance contributes to the emergence of provocative lung problems that are challenging to treat. Endogenic antioxidant systems are not enough to avert free radical-mediated damage due to the induced overproduction of ROS. Pro-inflammatory mediators are then produced due to intracellular signaling events, which can harm the tissue and worsen the inflammatory response. Overproduction of ROS causes oxidative stress, which causes lung damage and various disease conditions. Invasive microorganisms or hazardous substances that are inhaled repeatedly can cause an excessive amount of ROS to be produced. By starting signal transduction pathways, increased ROS generation during inflammation may cause recurrent DNA damage and apoptosis and activate proto-oncogenes. This review provides information about new targets for conducting research in related domains or target factors to prevent, control, or treat such inflammatory oxidative stress-induced inflammatory lung disorders.

Exposure to toluene diisocyanate induces dysbiosis of gut-lung homeostasis: Involvement of gut microbiota

Toluene diisocyanate (TDI) is a major industrial compound that induces occupational asthma with steroid-resistant properties. Recent studies suggest that the gastrointestinal tract may be an effective target for the treatment of respiratory diseases. However, the alterations of the gut-lung axis in TDI-induced asthma remain unexplored. Therefore, in this study, a model of stable occupational asthma caused by TDI exposure was established to detect the alteration of the gut-lung axis. Exposure to TDI resulted in dysbiosis of the gut microbiome, with significant decreases in Barnesiella_intestinihominis, Faecalicoccus_pleomorphus, Lactobacillus_apodemi, and Lactobacillus_intestinalis, but increases in Alistipes_shahii and Odoribacter_laneus. The largest change in abundance was in Barnesiella_intestinihominis, which decreased from 12.14 per cent to 6.18 per cent. The histopathological abnormalities, including shorter length of intestinal villi, thinner thickness of muscularis, reduced number of goblet cells and inflammatory cell infiltration, were found in TDI-treated mice compared to control mice. In addition, increased permeability (evidenced by significantly reduced levels of ZO-1, Occludin and Claudin-1) and activation of TLR4/NF-κB signaling were observed in the intestine of these TDI-exposed mice. Concurrently, exposure to TDI resulted in airway hyperresponsiveness, overt cytokine production (e.g., IL-4, IL-5, IL-13, IL-25, and IL-33), and elevated IgE level within the respiratory tract. The expression of tight junction proteins is reduced and TLR4/NF-κB signaling is activated in the lung following TDI treatment. In addition, correlation analyses showed that changes in the gut microbiota were correlated with TDI exposure-induced airway inflammation. In conclusion, the present study suggests that the immune gut-lung axis may be involved in the development of TDI-induced asthma, which may have implications for potential interventions against steroid-resistant asthma.

Terpenoids, a Rising Star in Bioactive Constituents for Alleviating Food Allergy: A Review about the Potential Mechanism, Preparation, and Application

Food allergies affect approximately 2.5% of the global population, with a notable increase in prevalence observed each year. Terpenoids, a class of natural bioactive constituents, have been widely utilized in the management of immune- and inflammation-related disorders, and their potential in alleviating food allergies is increasingly being recognized. This article summarizes various terpenoids derived from plant, fungal, and marine sources. Among them, triterpenoids, such as oleanolic acid, ursolic acid, and lupeol, possess the highest proportion and bioactivity in alleviating food allergy. Additionally, the mechanisms by which terpenoids may mitigate allergic diseases were categorically outlined, focusing on their roles in epithelial mucosal barrier function, immunomodulatory effects during the sensitization phase, inhibition of effector cells, oxidative stress, and regulation of microbial homeostasis. Finally, the advantages and limitations of natural extraction and artificial synthesis methods were compared, and the application of terpenoids in the food industry were also discussed. This article serves as a useful reference for the development of methods or functional foods based on terpenoids, which could represent a promising avenue for alleviating food allergy.

Subway Fine Particles (PM2.5 )-Induced Pro-Inflammatory Response Triggers Airway Epithelial Barrier Damage Through the TLRs/NF-κB-Dependent Pathway In Vitro

Subways are widely used in major cities around the world, and subway fine particulate matter (PM2.5) is the main source of daily PM2.5 exposure for urban residents. Exposure to subway PM2.5 leads to acute inflammatory damage in humans, which has been confirmed in mouse in vivo studies. However, the concrete mechanism by which subway PM2.5 causes airway damage remains obscure. In this study, we found that subway PM2.5 triggered release of pro-inflammatory cytokines such as interleukin 17E, tumor necrosis factor α, transforming growth factor β, and thymic stromal lymphopoietin from human bronchial epithelial cells (BEAS-2B) in a dose-effect relationship. Subsequently, supernatant recovered from the subway PM2.5 group significantly increased expression of the aforementioned cytokines in BEAS-2B cells compared with the subway PM2.5 group. Additionally, tight junctions (TJs) of BEAS-2B cells including zonula occludens-1, E-cadherin, and occludin were decreased by subway PM2.5 in a dose-dependent manner. Moreover, supernatant recovered from the subway PM2.5 group markedly decreased the expression of these TJs compared with the control group. Furthermore, inhibitors of toll-like receptors (TLRs) and nuclear factor-kappa B (NF-κB), as well as chelate resins (e.g., chelex) and deferoxamine, remarkably ameliorated the observed changes of cytokines and TJs caused by subway PM2.5 in BEAS-2B cells. Therefore, these results suggest that subway PM2.5 induced a decline of TJs after an initial ascent of cytokine expression, and subway PM2.5 altered expression of both cytokines and TJs by activating TLRs/NF-κB-dependent pathway in BEAS-2B cells. The metal components of subway PM2.5 may contribute to the airway epithelial injury.

Human placental mesenchymal stem cells transplantation repairs the alveolar epithelial barrier to alleviate lipopolysaccharides-induced acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are accompanied by high mortality rates and few effective treatments. Transplantation of human placental mesenchymal stem cells (hPMSCs) may attenuate ALI and the mechanism is still unclear. Our study aimed to elucidate the potential protective effect and therapeutic mechanism of hPMSCs against lipopolysaccharide (LPS)-induced ALI, An ALI model was induced by tracheal instillation of LPS into wild-type (WT) and angiotensin-converting enzyme 2 (ACE2) knockout (KO) male mice, followed by injection of hPMSCs by tail vein. Treatment with hPMSCs improved pulmonary histopathological injury, reduced pulmonary injury scores, decreased leukocyte count and protein levels in bronchoalveolar lavage fluid(BALF), protected the damaged alveolar epithelial barrier, and reversed LPS-induced upregulation of pro-inflammatory factors Interleukin-6 (IL-6) and Tumor necrosis factor-α(TNF-α) and downregulation of anti-inflammatory factor Interleukin-6(IL-10) in BALF. Moreover, administration of hPMSCs inhibited Angiotensin (Ang)II activation and promoted the expression levels of ACE2 and Ang (1-7) in ALI mice. Pathological damage, inflammation levels, and disruption of alveolar epithelial barrier in ALI mice were elevated after the deletion of ACE2 gene, and the Renin angiotensin system (RAS) imbalance was exacerbated. The therapeutic effect of hPMSCs was significantly reduced in ACE2 KO mice. Our findings suggest that ACE2 plays a key role in hPMSCs repairing the alveolar epithelial barrier to protect against ALI, laying a new foundation for the clinical treatment of ALI.

Ameliorating lipopolysaccharide induced acute lung injury with Lianhua Qingke: focus on pulmonary endothelial barrier protection

Background

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) has long posed challenges in clinical practice, lacking established preventive and therapeutic approaches. Lianhua Qingke (LHQK), a patented traditional Chinese medicine (TCM), has been found to have anti-inflammatory effects for ameliorating ALI/ARDS induced by lipopolysaccharide (LPS). This study aimed to investigate the effects and potential mechanisms of LHQK on endothelial protection in LPS-induced ALI/ARDS in vivo and in LPS-induced human pulmonary microvascular endothelial cells (HPMECs) injury in vitro.

Methods

In the animal experiment, we induced an ALI/ARDS model by intratracheal injection of LPS (5 mg/mL). LHQK (3.7 g/kg/d for low dose and 7.4 g/kg/d for high dose) or dexamethasone (DEX) (5 mg/kg/d) was administered to mice 3 days prior to LPS treatment. In the in vitro experiments, HPMECs were pretreated with LHQK at concentrations of 125 and 250 µg/mL for 2 hours before being stimulated with LPS (10 µg/mL). We employed lung function test, measurement of lung index, hematoxylin and eosin (H&E) staining, bronchoalveolar lavage fluid (BALF) cell counts, and inflammatory cytokine levels to assess the therapeutic effect of LHQK. Additionally, the extravasation assay of fluorescein isothiocyanate-dextran (FITC-dextran) dye and the transmembrane electrical resistance (TEER) assay were used to evaluate endothelial barrier. Barrier integrity and relevant protein validation were assessed using immunofluorescence (IF) and Western blot analyses. Furthermore, network pharmacology analysis and cellular level screening were employed to predict and screen the active ingredients of LHQK.

Results

Compared to the LPS group, LHQK significantly improved lung function, mitigated lung pathological injuries, reduced inflammatory cells and inflammatory cytokines [tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6] levels in BALF, and inhibited the expression of vascular cell adhesion molecule-1 (VCAM-1), attenuated LPS-induced pulmonary oedema and FITC-dextran permeability, and enhanced the expression of vascular endothelial-cadherin (VE-cadherin) and occludin. In vitro, LHQK attenuated LPS-induced HPMECs injury by elevating TEER values and enhancing VE-cadherin and occludin protein levels. Finally, network pharmacology analysis and cellular level validation identified potential active ingredients of LHQK.

Conclusions

In summary, LHQK can mitigate LPS-induced inflammatory infiltration, pulmonary edema, and pulmonary vascular endothelial barrier dysfunction in the context of ALI/ARDS. This is achieved by decreasing the levels of VCAM-1, and increasing the expression levels of barrier-associated junctions, such as VE-cadherin and occludin. Consequently, LHQK exhibits promising therapeutic potential in preventing the progression of ALI/ARDS.

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.

Application of a derivative of human defensin 5 to treat ionizing radiation-induced enterogenic infection

Enterogenic infection is a common complication for patients with radiation injury and requires efficient therapeutics in the clinic. Herein, we evaluated the promising drug candidate T7E21RHD5, which is a peptide derived from intestinal Paneth cell-secreted human defensin 5. Oral administration of this peptide alleviated the diarrhea symptoms of mice that received total abdominal irradiation (TAI, γ-ray, 12 Gy) and improved survival. Pathologic analysis revealed that T7E21RHD5 elicited an obvious mitigation of ionizing radiation (IR)-induced epithelial damage and ameliorated the reduction in the levels of claudin, zonula occluden 1 and occludin, three tight junction proteins in the ileum. Additionally, T7E21RHD5 regulated the gut microbiota in TAI mice by remodeling β diversity, manifested as a reversal of the inverted proportion of Bacteroidota to Firmicutes caused by IR. T7E21RHD5 treatment also decreased the abundance of pathogenic Escherichia-Shigella but significantly increased the levels of Alloprevotella and Prevotellaceae_NK3B31, two short-chain fatty acid-producing bacterial genera in the gut. Accordingly, the translocation of enterobacteria and lipopolysaccharide to the blood, as well as the infectious inflammatory responses in the intestine after TAI, was all suppressed by T7E21RHD5 administration. Hence, this versatile antimicrobial peptide possesses promising application prospects in the treatment of IR-induced enterogenic infection.