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

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.

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.

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.

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.