TLR2 contributes to trigger immune response of pleural mesothelial cells against Mycobacterium bovis BCG and M. tuberculosis infection

Toll-like Receptor 2 Mediates VEGF Overexpression and Mesothelial Hyperpermeability in Tuberculous Pleural Effusion

Toll-like receptor (TLR) is essential for the immune response to Mycobacterium tuberculosis (MTB) infection. However, the mechanism whereby TLR mediates the MTB-induced pleural mesothelial hyperpermeability in tuberculous pleural effusion (TBPE) remains unclear. Pleural effusion size and pleural fluid levels of vascular endothelial growth factor (VEGF) and soluble TLR2 (sTLR2) in patients with TBPE (n = 36) or transudative pleural effusion (TPE, n = 16) were measured. The effects of MTB H37Ra (MTBRa) on pleural mesothelial permeability and the expression of VEGF and zonula occludens (ZO)-1 in human pleural mesothelial cells (PMCs) were assessed. Levels of VEGF and sTLR2 were significantly elevated in TBPE compared to TPE. Moreover, effusion VEGF levels correlated positively, while sTLR2 values correlated negatively, with pleural effusion size in TBPE. In human PMCs, MTBRa substantially activated JNK/AP-1 signaling and upregulated VEGF expression, whereas knockdown of TLR2 remarkably inhibited MTBRa-induced JNK phosphorylation and VEGF overexpression. Additionally, both MTBRa and VEGF markedly reduced ZO-1 expression and induced pleural mesothelial permeability, while TLR2 silencing or pretreatment with anti-VEGF antibody significantly attenuated the MTBRa-triggered effects. Collectively, TLR2 mediates VEGF overproduction and downregulates ZO-1 expression in human PMCs, leading to mesothelial hyperpermeability in TBPE. Targeting TLR2/VEGF pathway may confer a potential treatment strategy for TBPE.

Novel 3D organotypic co-culture model of pleura

Pleural mesothelial cells are the predominant cell type in the pleural cavity, but their role in the pathogenesis of pleural diseases needs to be further elucidated. 3D organotypic models are an encouraging approach for an in vivo understanding of molecular disease development. The aim of the present study was to develop a 3D organotypic model of the pleural mesothelium. Specimens of human pleura parietalis were obtained from patients undergoing surgery at the University Hospital Leipzig, Germany. 3D co-culture model of pleura was established from human pleural mesothelial cells and fibroblasts. The model was compared to human pleura tissue by phase-contrast and light microscopy, immunochemistry and -fluorescence as well as solute permeation test. Histological assessment of the 3D co-culture model displayed the presence of both cell types mimicking the morphology of the human pleura. Vimentin and Cytokeratin, PHD1 showed a similar expression pattern in pleural biopsies and 3D model. Expression of Ki-67 indicates the presence of proliferating cells. Tight junctional marker ZO-1 was found localized at contact zones between mesothelial cells. Each of these markers were expressed in both the 3D co-culture model and human biopsies. Permeability of 3D organotypic co-culture model of pleura was found to be higher for 70 kDa-Dextran and no significant difference was seen in the permeability for small dextran (4 kDa). In summary, the presented 3D organoid of pleura functions as a robust assay for pleural research serving as a precise reproduction of the in vivo morphology and microenvironment.

Mycobacterium tuberculosis Rv2387 Facilitates Mycobacterial Survival by Silencing TLR2/p38/JNK Signaling

Mycobacterium tuberculosis (Mtb) can evade antimicrobial immunity and persist within macrophages by interfering with multiple host cellular functions through its virulence factors, causing latent tuberculosis. The Rv2387 protein has been identified as a putative effector that potentially participates in Mtb pathogenicity. To explore the role of the Rv2387 protein in host–mycobacteria interactions, we established recombinant M. smegmatis strains and RAW264.7 cell lines that stably express the Rv2387 protein. We found that this protein suppresses mycobacteria infection-induced macrophage apoptosis by inactivating caspase-3/-8, thus facilitating the intracellular survival of mycobacteria. In addition, Rv2387 inhibits the production of inflammatory cytokines in macrophages by specifically suppressing TLR2-dependent stimulation of p38 and JNK MAPK pathways. Moreover, we further determined that the Rv2387 protein conferred a growth advantage over recombinant M. smegmatis and suppressed the inflammatory response in a mouse infection model. Overall, these data suggested that Rv2387 facilitates mycobacteria to escape host immunity and might be an essential virulence factor in Mtb.

Anaphylatoxins Enhance Recruitment of Nonclassical Monocytes via Chemokines Produced by Pleural Mesothelial Cells in Tuberculous Pleural Effusion

In the present study, we sought to elucidate the mechanisms by which monocytes migrate into the pleural space in the presence of anaphylatoxins in tuberculous pleural effusion (TPE). Monocytes in both pleural effusion and blood were counted, and their phenotypic characteristics were analyzed. Activation of the complement system was detected in TPE. The effects of Mpt64 and anaphylatoxins on the production of chemokines in pleural mesothelial cells (PMCs) were measured. The chemoattractant activity of chemokines produced by PMCs for monocytes was observed. Levels of CD14⁺CD16⁺ monocytes were significantly higher in TPE than in blood. Three pathways of the complement system were activated in TPE. C3a-C3aR1, C5a-C5aR1, CCL2-CCR2, CCL7-CCR2, and CX3CL1-CX3CR1 were coexpressed in PMCs and monocytes isolated from TPE. Moreover, we initially found that Mpt64 stimulated the expression of C3a and C5a in PMCs. C3a and C5a not only induced CCL2, CCL7, and CX3CL1 expression in PMCs but also stimulated production of IL-1β, IL-17, and IL-27 in monocytes. C3a and C5a stimulated PMCs to secrete CCL2, CCL7, and CX3CL1, which recruited CD14⁺CD16⁺ monocytes to the pleural cavity. As a result, the infiltration of CD14⁺CD16⁺ monocytes engaged in the pathogenesis of TPE by excessive production of inflammatory cytokines.

Proteomics analysis of HSV-1-induced alterations in mouse brain microvascular endothelial cells

Herpes simplex virus 1 (HSV-1) is a predominant cause of herpes simplex encephalitis (HSE), leading to a high mortality rate and severe neurological sequelae worldwide. HSE is typically accompanied by the blood-brain barrier (BBB) disruption, but the underlying mechanisms are unclear. To explore the disruption mechanisms of the BBB, quantitative analysis of the cellular proteome was carried out to investigate the proteomic changes that occur after infection. In this study, bEnd.3 cells were infected with HSV-1, followed by liquid chromatography-tandem mass spectrometry. A total of 6761 proteins were identified in three independent mass spectrometry analyses. Compared to the uninfected cells, 386 and 293 differentially expressed proteins were markedly upregulated or downregulated, respectively. Bioinformatic analysis showed that the activator protein-1 factor, including Fos, Jun, and ATF family proteins and cell adhesion molecules were significantly changed. Further validation of the changes observed for these proteins was carried out by western blotting and quantitative real-time PCR. Transendothelial electrical resistance (TEER) studies were performed to explore the effects of ATF3, Fra1, or JunB overexpression on the function of bEnd.3 cells. Characterization of the differential expression of these proteins in bEnd.3 cells will facilitate further exploration of BBB disruption upon HSV-1 infection.

Inhibition of NADPH Oxidase 4 (NOX4) Signaling Attenuates Tuberculous Pleural Fibrosis

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase [NOX] enzymes serve several hemostatic and host defense functions in various lung diseases, but the role of NOX4 signaling in tuberculous pleurisy is not well understood. The role of NOX4 signaling in tuberculous pleural fibrosis was studied using invitro pleural mesothelial cell (PMC) experiments and a murine model of Mycobacterium bovis bacillus Calmette–Guérin (BCG) pleural infection. The production of NOX4 reactive oxygen species (NOX4–ROS) and the epithelial mesenchymal transition (EMT) in PMCs were both induced by heat-killed mycobacterium tuberculosis (HKMT). In cultured PMCs, HKMT-induced collagen-1 synthesis and EMT were blocked by pretreatment with small interfering RNA (siRNA) NOX4. Moreover, NOX4–ROS production and subsequent fibrosis were reduced by treatment with losartan and the toll-like receptor 4 (TLR4) inhibitor TAK-242. The HKMT-induced EMT and intracellular ROS production were mediated by NOX4 via the activation of extracellular signal-regulated kinase (ERK) signaling. Finally, in a BCG-induced pleurisy model, recruitment of inflammatory pleural cells, release of inflammatory cytokines, and thickened mesothelial fibrosis were attenuated by SiNOX4 compared to SiCon. Our study identified that HKMT-induced pleural fibrosis is mediated by NOX4–ERK–ROS via TLR4 and Angiotensin II receptor type1 (AT1R). There results suggest that NOX4 may be a novel therapeutic target for intervention in tuberculous pleural fibrosis.