Brg1 inhibits E-cadherin expression in lung epithelial cells and disrupts epithelial integrity

CTNNAL1 promotes the structural integrity of bronchial epithelial cells through the RhoA/ROCK1 pathway

Adhesion molecules play critical roles in maintaining the structural integrity of the airway epithelium in airways under stress. Previously, we reported that catenin alpha-like 1 (CTNNAL1) is downregulated in an asthma animal model and upregulated at the edge of human bronchial epithelial cells (HBECs) after ozone stress. In this work, we explore the potential role of CTNNAL1 in the structural adhesion of HBECs and its possible mechanism. We construct a CTNNAL1 ‒/‒ mouse model with CTNNAL1-RNAi recombinant adeno-associated virus (AAV) in the lung and a CTNNAL1-silencing cell line stably transfected with CTNNAL1-siRNA recombinant plasmids. Hematoxylin and eosin (HE) staining reveals that CTNNAL1 ‒/‒ mice have denuded epithelial cells and structural damage to the airway. Silencing of CTNNAL1 in HBECs inhibits cell proliferation and weakens extracellular matrix adhesion and intercellular adhesion, possibly through the action of the cytoskeleton. We also find that the expressions of the structural adhesion-related molecules E-cadherin, integrin β1, and integrin β4 are significantly decreased in ozone-treated cells than in vector control cells. In addition, our results show that the expression levels of RhoA/ROCK1 are decreased after CTNNAL1 silencing. Treatment with Y27632, a ROCK inhibitor, abolished the expressions of adhesion molecules induced by ozone in CTNNAL1-overexpressing HBECs. Overall, the findings of the present study suggest that CTNNAL1 plays a critical role in maintaining the structural integrity of the airway epithelium under ozone challenge, and is associated with epithelial cytoskeleton dynamics and the expressions of adhesion-related molecules via the RhoA/ROCK1 pathway.

HMGB1 coordinates with Brahma-related gene 1 to promote epithelial-mesenchymal transition via the PI3K/Akt/mTOR pathway in BEAS-2B cells

High mobility group protein B1 (HMGB1), a highly conserved non-histone nuclear protein, is highly expressed in fibrotic diseases; however, the role of HMGB1 in pulmonary fibrosis has not been fully elucidated. In this study, an epithelial-mesenchymal transition (EMT) model was constructed using transforming growth factor-β1 (TGF-β1) to stimulate BEAS-2B cells in vitro, and HMGB1 was knocked down or overexpressed to observe its effects on cell proliferation, migration and EMT. Meanwhile, string system, immunoprecipitation and immunofluorescence analyses were applied to identify and examine the relationship between HMGB1 and its potential interacting protein Brahma-related gene 1 (BRG1), and to explore the mechanism of interaction between HMGB1 and BRG1 in EMT. The results indicate that exogenous increase in HMGB1 promotes cell proliferation and migration and facilitates EMT by enhancing the PI3K/Akt/mTOR signaling pathway, whereas silencing HMGB1 has the opposite effect. Mechanistically, HMGB1 exerts these functions by interacting with BRG1, which may enhance BRG1 function and activate the PI3K/Akt/mTOR signaling pathway, thereby promoting EMT. These results suggest that HMGB1 is important for EMT and is a potential therapeutic target for the treatment of pulmonary fibrosis.

Knockdown of Brg1 reduced mucus secretion in HDM stimulated airway inflammation

BACKGROUND

The Brg1 (Brahma-related gene 1) is an important chromatin remodeling factor protein. The Brg1 protein can promote the transcriptional activation or inhibit target genes through regulating ATP hydrolysis which rearranges the nucleosomes position and the histone DNA interaction. In this study, we explored the role of Brg1 in house dust mite (HDM) stimulated airway inflammation.

METHODS

The wild-type C57BL/6 mice (wild-type, WT) and alveolar epithelial cells specifically knockout Brg1 mice (Brg1^fl/fl) were selected as the experimental subjects. HDM was used to stimulate human bronchial epithelial cells (16HBE) to construct an model of airway inflammation in vitro. The asthma group was established with HDM, and the control group was treated with normal saline. Wright's staining for the detection of differential counts of inflammatory cells in bronchoalveolar lavage fluid (BALF). Invasive lung function was used to assess the airway compliance. Hematoxylin and eosin (HE) staining and periodic acid-schiff (PAS) staining were used to detect mucus secretion. Immunohistochemistry was used to measure mucin glycoprotein 5AC (MUC5AC) protein expression in airway epithelium. Western blotting was used to detect the MUC5AC and JAK1/2-STAT6 proteins in mouse lung tissues and 16HBE cells. Co-immunoprecipitation (Co-IP) and Chromatin Immunoprecipitation (CHIP) were used to detect whether Brg1 could regulate the JAK1/2-STAT6 signaling pathway.

RESULTS

The airway inflammation, pulmonary ventilation resistance, airway mucus secretion, MUC5AC and IL-13 in BALF and MUC5AC protein expression in lung tissue of Brg1 knockout mice stimulated by HDM were lower than those of wild-type mice. The expression of MUC5AC protein in HDM stimulated Brg1 knockdown 16HBE cells was significantly lower than that in the control group. In vivo and in vitro, it was found that the activation of JAK1/2-STAT6 signal pathway in mouse lung tissue or 16HBE cells was inhibited after knockdown of Brg1 gene. The Co-IP and CHIP results showed that Brg1 could bind to the JAK1/2 promoter region and regulate the expression of JAK1/2 gene.

CONCLUSION

The Brg1 may promote the secretion of airway mucus stimulated by HDM through regulating the JAK1/2-STAT6 pathway. Knockdown of Brg1 reduced mucus secretion in HDM stimulated airway inflammation.

Glycyrrhizic Acid Attenuates Pulmonary Fibrosis of Silicosis by Inhibiting the Interaction between HMGB1 and BRG1 through PI3K/Akt/mTOR Pathway

Purpose: High mobility group protein 1 (HMGB1) is a highly conserved DNA-binding nuclear protein that participates in the occurrence and development of silicosis. HMGB1 binds to its specific receptor and activates phosphatidylinositol 3-kinase (PI3K)/protein kinase B, (PKB; Akt)/mammalian target of rapamycin (mTOR) pathway. Brahma-related genes 1 (BRG1; SMARCA4) is the core subunit of SWI/SNF. HMGB1 activates the Akt pathway through BRG1 to promote the proliferation of prostate cancer. Glycyrrhizic acid is a new pharmacological inhibitor of HMGB1, which may inhibit the occurrence and development of silicosis. We speculate that glycyrrhizic acid inhibits the interaction between HMGB1 and BRG1 through the PI3K/Akt/mTOR pathway to affect the progression of silicosis. Methods: We carried out an in vitro study and stimulated A549 with TGF-β1 to establish an epithelial–mesenchymal transition (EMT) model, knocked down the HMGB1 and BRG1 genes in cells, observed the expression of EMT markers, and detected the interaction between HMGB1 and BRG1 by co-immunoprecipitation. In vivo, we injected glycyrrhizic acid into the mouse silicosis model to inhibit the expression of HMGB1. Results: Both HMGB1 and BRG1 were highly expressed in the process of EMT. After knocking down HMGB1 and BRG1, the process of EMT was inhibited through the PI3K/Akt/mTOR pathway, and their expressions were influenced by each other. HMGB1 and BRG1 interact with each other in A549 cells. HMGB1 and BRG1 are also highly expressed in the mouse silicosis model, and glycyrrhizic acid can inhibit the expression of HMGB1/BRG1 through the PI3K/Akt/mTOR pathway. Conclusion: Glycyrrhizic acid can inhibit the interaction between HMGB1 and BRG1 through the PI3K/Akt/mTOR pathway to affect the progression of silicosis.

Neutrophil Extracellular Traps (NETs) in Severe SARS-CoV-2 Lung Disease

Neutrophil extracellular traps (NETs), built from mitochondrial or nuclear DNA, proteinases, and histones, entrap and eliminate pathogens in the course of bacterial or viral infections. Neutrophils’ activation and the formation of NETs have been described as major risk factors for acute lung injury, multi-organ damage, and mortality in COVID-19 disease. NETs-related lung injury involves both epithelial and endothelial cells, as well as the alveolar-capillary barrier. The markers for NETs formation, such as circulating DNA, neutrophil elastase (NE) activity, or myeloperoxidase-DNA complexes, were found in lung specimens of COVID-19 victims, as well as in sera and tracheal aspirates obtained from COVID-19 patients. DNA threads form large conglomerates causing local obstruction of the small bronchi and together with NE are responsible for overproduction of mucin by epithelial cells. Various components of NETs are involved in the pathogenesis of cytokine storm in SARS-CoV-2 pulmonary disease. NETs are responsible for the interplay between inflammation and thrombosis in the affected lungs. The immunothrombosis, stimulated by NETs, has a poor prognostic significance. Better understanding of the role of NETs in the course of COVID-19 can help to develop novel approaches to the therapeutic interventions in this condition.

Targeting neutrophil extracellular traps in severe acute pancreatitis treatment

Severe acute pancreatitis (SAP) is a critical abdominal disease associated with high death rates. A systemic inflammatory response promotes disease progression, resulting in multiple organ dysfunction. The functions of neutrophils in the pathology of SAP have been presumed traditionally to be activation of chemokine and cytokine cascades accompanying the inflammatory process. Recently, since their discovery, a new type of antimicrobial mechanism, neutrophil extracellular traps (NETs), and their role in SAP, has attracted widespread attention from the scientific community. Significantly different from phagocytosis and degranulation, NETs kill extracellular microorganisms by releasing DNA fibers decorated with granular proteins. In addition to their strong antimicrobial functions, NETs participate in the pathophysiological process of many noninfectious diseases. In SAP, NETs injure normal tissues under inflammatory stress, which is associated with the activation of inflammatory cells, to cause an inflammatory cascade, and SAP products also trigger NET formation. Thus, due to the interaction between NET generation and SAP, a treatment targeting NETs might become a key point in SAP therapy. In this review, we summarize the mechanism of NETs in protecting the host from pathogen invasion, the stimulus that triggers NET formation, organ injury associated with SAP involving NETs, methods to interrupt the harmful effects of NETs, and different therapeutic strategies to preserve the organ function of patients with SAP by targeting NETs.

BRG1 protects the heart from acute myocardial infarction by reducing oxidative damage through the activation of the NRF2/HO1 signaling pathway

Brahma-related gene 1 (BRG1) regulates the chromatin structure and expression of cardiac genes. Although BRG1 is downregulated in adult cardiomyocytes, it is reactivated during cardiac stress. The role of BRG1 in acute myocardial infarction (AMI) has not been clearly defined. This study assessed the protective role of BRG1 in AMI using cell cultures and an animal model and explored the underlying molecular events. The results showed that in the peri-infarct zone, expression of BRG1 protein was significantly increased relative to the sham group, which was accompanied by NRF2 and HO1 upregulation and KEAP1 downregulation. BRG1 overexpression through adenoviral intramyocardial injection into AMI mice reduced the infarct size and improved cardiac functions with upregulation of NRF2 and its target HO1 and attenuated oxidative damage and cell apoptosis. However, shRNA-mediated Brg1 knockdown had the opposite effects. These results were further confirmed in cultured primary neonatal rat cardiomyocytes (NRCMs) with oxygen-glucose deprivation (OGD). Moreover, the selective NRF2 inhibitor brusatol could partially reverse cardiomyocyte antioxidant ability and BRG1 overexpression-induced cardiac protection in vitro. In addition, co-immunoprecipitation and immunofluorescence data showed that BRG1 overexpression significantly promoted the BRG1/NRF2 co-localization in cardiomyocytes. The chromatin immunoprecipitation-qPCR revealed BRG1 interaction with the Ho1 promoter and BRG1 overexpression could induce BRG1 binding to the Ho1 promoter during the OGD. In conclusion, this study demonstrated that BRG1 upregulation during AMI in vitro and in vivo increased the NRF2 level and NRF2 nuclear accumulation for HO1 expression to alleviate cardiac myocyte oxidative stress and upregulate cardiomyocyte viability. The BRG1-NRF2-HO1 pathway may represent a novel therapeutic target in the prevention of cardiac dysfunction in AMI patients.

Qi-Xian Decoction Upregulated E-cadherin Expression in Human Lung Epithelial Cells and Ovalbumin-Challenged Mice by Inhibiting Reactive Oxygen Species-Mediated Extracellular-Signal-Regulated Kinase (ERK) Activation

Background

Loss of the epithelial barrier is characterized by a reduction in E-cadherin expression and is a hallmark of asthma. Qi-xian decoction (QXT) is a Chinese medicinal formula that has been used to effectively treat asthma. This study aimed to investigate the effect of QXT on E-cadherin expression in human lung epithelial 16HBE cells and ovalbumin-challenged mice and to explore the underlying molecular mechanism.

Material/Methods

Ovalbumin (OVA)-induced mice were used as a model of asthma. Real-time PCR and Western blotting were utilized to examine mRNA and protein levels. Lung tissue reactive oxygen species (ROS) levels were evaluated using dichloro-dihydro-fluorescein diacetate (DCFH-DA). Serum superoxide dismutase (SOD) and the total antioxidant capacity (TAOC) were measured via enzyme-linked immunosorbent assay (ELISA)-based analyses. 16HBE cells were utilized to explore the effect of QXT or hydrogen peroxide (H₂O₂) on the expression of E-cadherin in vitro.

Results

We found that QXT treatment increased E-cadherin expression and decreased extracellular-signal-regulated kinase (ERK) phosphorylation levels in the lung tissues of OVA-challenged mice. QXT also downregulated ROS levels and increased serum SOD and TAOC levels in OVA-challenged mice. In vitro studies demonstrated that increased ROS generation induced by H₂O₂ resulted in decreased E-cadherin expression levels in 16HBE cells, which was attenuated by inhibition of ERK signaling. Moreover, the H₂O₂-induced downregulation of E-cadherin expression, increased ROS generation, and ERK activation in 16HBE cells were restored by treatment with QXT water or ethanol extract.

Conclusions

These data demonstrate that one mechanism by which QXT protects against asthma is to restore E-cadherin expression in vivo and in vitro by inhibiting ROS-mediated ERK activation.

Stratification of asthma phenotypes by airway proteomic signatures

BACKGROUND

Stratification by eosinophil and neutrophil counts increases our understanding of asthma and helps target therapy, but there is room for improvement in our accuracy in prediction of treatment responses and a need for better understanding of the underlying mechanisms.

OBJECTIVE

We sought to identify molecular subphenotypes of asthma defined by proteomic signatures for improved stratification.

METHODS

Unbiased label-free quantitative mass spectrometry and topological data analysis were used to analyze the proteomes of sputum supernatants from 246 participants (206 asthmatic patients) as a novel means of asthma stratification. Microarray analysis of sputum cells provided transcriptomics data additionally to inform on underlying mechanisms.

RESULTS

Analysis of the sputum proteome resulted in 10 clusters (ie, proteotypes) based on similarity in proteomic features, representing discrete molecular subphenotypes of asthma. Overlaying granulocyte counts onto the 10 clusters as metadata further defined 3 of these as highly eosinophilic, 3 as highly neutrophilic, and 2 as highly atopic with relatively low granulocytic inflammation. For each of these 3 phenotypes, logistic regression analysis identified candidate protein biomarkers, and matched transcriptomic data pointed to differentially activated underlying mechanisms.

CONCLUSION

This study provides further stratification of asthma currently classified based on quantification of granulocytic inflammation and provided additional insight into their underlying mechanisms, which could become targets for novel therapies.

Brg1 aggravates airway inflammation in asthma via inhibition of the PI3K/Akt/mTOR pathway

The PI3K/Akt/mTOR pathway is thought to be closely associated with airway inflammation and is regulated by various upstream proteins. Brahma-related gene 1 (Brg1) plays an important role in chromatin remodeling and facilitates recruitment of essential transcription factors, leading to regulation of gene expression. Thus, the present study aimed at evaluating the anti-inflammatory role of Brg1 on house dust mite (HDM)-induced asthma through regulating the PI3K/Akt/mTOR pathway. The Brg^fl/fl mice were crossbred with the SFTPC-Cre mice to generate bronchial epithelial cell specific Brg1 knockout mice, and LY294002 was used to inhibit PI3K. Western blot, immunofluorescence, immunoprecipitation, and immunohistochemical staining were used to detect the expression of proteins. An increase in Brg1 and a decrease in the PI3K/Akt/mTOR pathway activity were detected in asthmatic mice, but not in control mice. When Brg1 was knocked out, the asthma severity was ameliorated and the PI3K/Akt/mTOR pathway was activated. However, this protective effect could be suppressed by LY294002. Additionally, we observed that Brg1 was co-localized and co-immunoprecipitated with PI3K, using immunofluorescence and immunoprecipitation assays. Our results suggest that Brg1 might play an essential role in maintaining airway inflammation and affect the PI3K/Akt/mTOR pathway in asthma.