Induction of NF-kappaB nuclear translocation in human respiratory epithelial cells by group A streptococci

Network pharmacology-based exploration identified the antiviral efficacy of Quercetin isolated from mulberry leaves against enterovirus 71 via the NF-κB signaling pathway

Introduction: Mulberry leaf (ML) is known for its antibacterial and anti-inflammatory properties, historically documented in "Shen Nong's Materia Medica". This study aimed to investigate the effects of ML on enterovirus 71 (EV71) using network pharmacology, molecular docking, and in vitro experiments. Methods: We successfully pinpointed shared targets between mulberry leaves (ML) and the EV71 virus by leveraging online databases. Our investigation delved into the interaction among these identified targets, leading to the identification of pivotal components within ML that possess potent anti-EV71 properties. The ability of these components to bind to the targets was verified by molecular docking. Moreover, bioinformatics predictions were used to identify the signaling pathways involved. Finally, the mechanism behind its anti-EV71 action was confirmed through in vitro experiments. Results: Our investigation uncovered 25 active components in ML that targeted 231 specific genes. Of these genes, 29 correlated with the targets of EV71. Quercetin, a major ingredient in ML, was associated with 25 of these genes. According to the molecular docking results, Quercetin has a high binding affinity to the targets of ML and EV71. According to the KEGG pathway analysis, the antiviral effect of Quercetin against EV71 was found to be closely related to the NF-κB signaling pathway. The results of immunofluorescence and Western blotting showed that Quercetin significantly reduced the expression levels of VP1, TNF-α, and IL-1β in EV71-infected human rhabdomyosarcoma cells. The phosphorylation level of NF-κB p65 was reduced, and the activation of NF-κB signaling pathway was suppressed by Quercetin. Furthermore, our results showed that Quercetin downregulated the expression of JNK, ERK, and p38 and their phosphorylation levels due to EV71 infection. Conclusion: With these findings in mind, we can conclude that inhibiting the NF-κB signaling pathway is a critical mechanism through which Quercetin exerts its anti-EV71 effectiveness.

Crocetin Improves Dengue Virus-Induced Liver Injury

Dengue virus (DENV) infection is one of the most widespread mosquito-borne viral infections. Liver injury is commonly observed in severe DENV infection, and the present study aimed to examine the efficacy of crocetin treatment in an immunocompetent mouse model of DENV infection exhibiting liver injury. The efficacy of crocetin treatment in DENV-induced liver injury was assessed via both transaminase levels and histopathology analysis. A real-time polymerase chain reaction array was then used to describe the expression of 84 apoptosis-related genes. Using real-time RT-PCR and Western blot analysis, the gene expressions of host factors were investigated. Additionally, the effect of crocetin in NF-kB signaling during DENV infection was studied. We did not observe any significant reduction in virus production when DENV-infected mice were treated with crocetin. However, DENV-infected mice treated with crocetin showed reduced DENV-induced apoptosis. The real-time polymerase chain reaction array revealed pro-inflammatory cytokine expressions to be significantly reduced in the crocetin-treated DENV-infected mice. We also found that crocetin could effectively modulate antioxidant status in DENV-infected mice. Moreover, crocetin demonstrated the ability to reduce the nuclear translocation of NF-kB in DENV-infected mice. Our results suggest that crocetin treatment does not inhibit DENV replication in the liver of DENV-infected mice; however, we did find that crocetin improves host responses that reduce liver injury.

Group A Streptococcus-Mediated Host Cell Signaling

In the past decade, the field of the cellular microbiology of group A Streptococcus (S. pyogenes) infection has made tremendous advances and touched upon several important aspects of pathogenesis, including receptor biology, invasive and evasive phenomena, inflammasome activation, strain-specific autophagic bacterial killing, and virulence factor-mediated programmed cell death. The noteworthy aspect of S. pyogenes-mediated cell signaling is the recognition of the role of M protein in a variety of signaling events, starting with the targeting of specific receptors on the cell surface and on through the induction and evasion of NETosis, inflammasome, and autophagy/xenophagy to pyroptosis and apoptosis. Variations in reports on S. pyogenes-mediated signaling events highlight the complex mechanism of pathogenesis and underscore the importance of the host cell and S. pyogenes strain specificity, as well as in vitro/in vivo experimental parameters. The severity of S. pyogenes infection is, therefore, dependent on the virulence gene expression repertoire in the host environment and on host-specific dynamic signaling events in response to infection. Commonly known as an extracellular pathogen, S. pyogenes finds host macrophages as safe havens wherein it survives and even multiplies. The fact that endothelial cells are inherently deficient in autophagic machinery compared to epithelial cells and macrophages underscores the invasive nature of S. pyogenes and its ability to cause severe systemic diseases. S. pyogenes is still one of the top 10 causes of infectious mortality. Understanding the orchestration of dynamic host signaling networks will provide a better understanding of the increasingly complex mechanism of S. pyogenes diseases and novel ways of therapeutically intervening to thwart severe and often fatal infections.

Group A Streptococcus M1T1 Intracellular Infection of Primary Tonsil Epithelial Cells Dampens Levels of Secreted IL-8 Through the Action of SpyCEP

Streptococcus pyogenes (Group A Streptococcus; GAS) commonly causes pharyngitis in children and adults, with severe invasive disease and immune sequelae being an infrequent consequence. The ability of GAS to invade the host and establish infection likely involves subversion of host immune defenses. However, the signaling pathways and innate immune responses of epithelial cells to GAS are not well-understood. In this study, we utilized RNAseq to characterize the inflammatory responses of primary human tonsil epithelial (TEpi) cells to infection with the laboratory-adapted M6 strain JRS4 and the M1T1 clinical isolate 5448. Both strains induced the expression of genes encoding a wide range of inflammatory mediators, including IL-8. Pathway analysis revealed differentially expressed genes between mock and JRS4- or 5448-infected TEpi cells were enriched in transcription factor networks that regulate IL-8 expression, such as AP-1, ATF-2, and NFAT. While JRS4 infection resulted in high levels of secreted IL-8, 5448 infection did not, suggesting that 5448 may post-transcriptionally dampen IL-8 production. Infection with 5448ΔcepA, an isogenic mutant lacking the IL-8 protease SpyCEP, resulted in IL-8 secretion levels comparable to JRS4 infection. Complementation of 5448ΔcepA and JRS4 with a plasmid encoding 5448-derived SpyCEP significantly reduced IL-8 secretion by TEpi cells. Our results suggest that intracellular infection with the pathogenic GAS M1T1 clone induces a strong pro-inflammatory response in primary tonsil epithelial cells, but modulates this host response by selectively degrading the neutrophil-recruiting chemokine IL-8 to benefit infection.

Galectin-3 Inhibits Galectin-8/Parkin-Mediated Ubiquitination of Group A Streptococcus

Group A streptococcus (GAS) is an important human pathogen that causes a wide variety of cutaneous and systemic infections. Although originally thought to be an extracellular bacterium, numerous studies have demonstrated that GAS can trigger internalization into nonimmune cells to escape from immune surveillance or antibiotic-mediated killing. Epithelial cells possess a defense mechanism involving autophagy-mediated targeting and killing of GAS within lysosome-fused autophagosomes. In endothelial cells, in contrast, we previously showed that autophagy is not sufficient for GAS killing. In the present study, we showed higher galectin-3 (Gal-3) expression and lower Gal-8 expression in endothelial cells than in epithelial cells. The recruitment of Gal-3 to GAS is higher and the recruitment of Gal-8 to GAS is lower in endothelial cells than in epithelial cells. We further showed that Gal-3 promotes GAS replication and diminishes the recruitment of Gal-8 and ubiquitin, the latter of which is a critical protein for autophagy sequestration. After knockdown of Gal-3 in endothelial cells, the colocalization of Gal-8, parkin, and ubiquitin-decorated GAS is significantly increased, as is the interaction of Gal-8 and parkin, an E3 ligase. Furthermore, inhibition of Gal-8 in epithelial cells attenuates recruitment of parkin; both Gal-8 and parkin contribute to ubiquitin recruitment and GAS elimination. Animal studies confirmed that Gal-3-knockout mice develop less-severe skin damage and that GAS replication can be detected only in the air pouch and not in organs and endothelial cells. These results demonstrate that Gal-3 inhibits ubiquitin recruitment by blocking Gal-8 and parkin recruitment, resulting in GAS replication in endothelial cells.

In epithelial cells, GAS can be efficiently killed within the lysosome-fused autophaosome compartment. However, we previously showed that, in spite of LC-3 recruitment, the autophagic machinery is not sufficient for GAS killing in endothelial cells. In this report, we provide the first evidence that Gal-3, highly expressed in endothelial cells, blocks the tagging of ubiquitin to GAS by inhibiting recruitment of Gal-8 and parkin, leading to an enhancement of GAS replication. We also provide the first demonstration that Gal-8 can interact with parkin, the critical E3 ligase, for resistance to intracellular bacteria by facilitating the decoration of bacteria with ubiquitin chains. Our findings reveal that differential levels of Gal-3 and Gal-8 expression and recruitment to GAS between epithelial cells and endothelial cells may contribute to the different outcomes of GAS elimination or survival and growth of GAS in these two types of cells.

Phytochemical-rich medicinal plant extracts suppress bacterial antigens-induced inflammation in human tonsil epithelial cells

BACKGROUND

Pharyngitis is an inflammatory condition of the pharynx and associated structures commonly caused by the Group A streptococci (GAS). There is a growing interest in discovering plant-based anti-inflammatory compounds as potential alternatives to conventional drugs. This study evaluated anti-inflammatory activity of phytochemical-rich extracts prepared from 12 herbal plants using human tonsil epithelial cells (HTonEpiC) in vitro.

METHODS

The HTonEpiC were induced by a mixture of lipoteichoic acid (LTA) and peptidoglycan (PGN) (10 µg/mL; bacterial antigens) for 4 h and then exposed to ethanol extracts (EE) or aqueous extracts (AE) for 20 h. The secretion of four pro-inflammatory cytokines was measured using enzyme-linked immunosorbent assays (ELISA). Total phenolic and total flavonoid contents of the extracts were determined using spectrophotometric methods.

RESULTS

The herbal plant extracts (≤5 µg/mL) were not cytotoxic to HTonEpiC. The extracts exhibited a broad range of reduction (1.2%-92.6%) of secretion of interleukin-8 (IL-8), human beta defensin-2 (hBD-2), epithelial-derived neutrophil activating protein-78 (ENA-78), and granulocyte chemotactic protein-2 (GCP-2). Both EE and AE of clove, ginger, and echinacea flower and EE from danshen root significantly inhibited the pro-inflammatory cytokine production as induced by LTA and PGN in HTonEpiCs at the concentrations of 1 and 5 µg/mL.

DISCUSSION

Our observations indicate that danshen root, clove, ginger, and echinacea flower extracts exhibit an anti-inflammatory effect in HTonEpiCs. The most efficacious extracts from danshen root, clove, ginger and echinacea flowers have potential to be used as natural sources for developing phytotherapeutic products in the management of painful inflammation due to streptococcal pharyngitis.

Streptolysin S Promotes Programmed Cell Death and Enhances Inflammatory Signaling in Epithelial Keratinocytes during Group A Streptococcus Infection

Streptococcus pyogenes, or group A Streptococcus (GAS), is a pathogen that causes a multitude of human diseases from pharyngitis to severe infections such as toxic shock syndrome and necrotizing fasciitis. One of the primary virulence factors produced by GAS is the peptide toxin streptolysin S (SLS). In addition to its well-recognized role as a cytolysin, recent evidence has indicated that SLS may influence host cell signaling pathways at sublytic concentrations during infection. We employed an antibody array-based approach to comprehensively identify global host cell changes in human epithelial keratinocytes in response to the SLS toxin. We identified key SLS-dependent host responses, including the initiation of specific programmed cell death and inflammatory cascades with concomitant downregulation of Akt-mediated cytoprotection. Significant signaling responses identified by our array analysis were confirmed using biochemical and protein identification methods. To further demonstrate that the observed SLS-dependent host signaling changes were mediated primarily by the secreted toxin, we designed a Transwell infection system in which direct bacterial attachment to host cells was prevented, while secreted factors were allowed access to host cells. The results using this approach were consistent with our direct infection studies and reveal that SLS is a bacterial toxin that does not require bacterial attachment to host cells for activity. In light of these findings, we propose that the production of SLS by GAS during skin infection promotes invasive outcomes by triggering programmed cell death and inflammatory cascades in host cells to breach the keratinocyte barrier for dissemination into deeper tissues.

The innate immune response elicited by Group A Streptococcus is highly variable among clinical isolates and correlates with the emm type

Group A Streptococcus (GAS) infections remain a significant health care problem due to high morbidity and mortality associated with GAS diseases, along with their increasing worldwide prevalence. Macrophages play a key role in the control and clearance of GAS infections. Moreover, pro-inflammatory cytokines production and GAS persistence and invasion are related. In this study we investigated the correlation between the GAS clinical isolates genotypes, their known clinical history, and their ability to modulate innate immune response. We constituted a collection of 40 independent GAS isolates representative of the emm types currently prevalent in France and responsible for invasive (57.5%) and non-invasive (42.5%) clinical manifestations. We tested phagocytosis and survival in mouse bone marrow-derived macrophages and quantified the pro-inflammatory mediators (IL-6, TNF-α) and type I interferon (INF-β) production. Invasive emm89 isolates were more phagocytosed than their non-invasive counterparts, and emm89 isolates more than the other isolates. Regarding the survival, differences were observed depending on the isolate emm type, but not between invasive and non-invasive isolates within the same emm type. The level of inflammatory mediators produced was also emm type-dependent and mostly invasiveness status independent. Isolates of the emm1 type were able to induce the highest levels of both pro-inflammatory cytokines, whereas emm89 isolates induced the earliest production of IFN-β. Finally, even within emm types, there was a variability of the innate immune responses induced, but survival and inflammatory mediator production were not linked.

Kallistatin modulates immune cells and confers anti-inflammatory response to protect mice from group A streptococcal infection

Group A streptococcus (GAS) infection may cause severe life-threatening diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Despite the availability of effective antimicrobial agents, there has been a worldwide increase in the incidence of invasive GAS infection. Kallistatin (KS), originally found to be a tissue kallikrein-binding protein, has recently been shown to possess anti-inflammatory properties. However, its efficacy in microbial infection has not been explored. In this study, we transiently expressed the human KS gene by hydrodynamic injection and investigated its anti-inflammatory and protective effects in mice via air pouch inoculation of GAS. The results showed that KS significantly increased the survival rate of GAS-infected mice. KS treatment reduced local skin damage and bacterial counts compared with those in mice infected with GAS and treated with a control plasmid or saline. While there was a decrease in immune cell infiltration of the local infection site, cell viability and antimicrobial factors such as reactive oxygen species actually increased after KS treatment. The efficiency of intracellular bacterial killing in neutrophils was directly enhanced by KS administration. Several inflammatory cytokines, including tumor necrosis factor alpha, interleukin 1β, and interleukin 6, in local infection sites were reduced by KS. In addition, KS treatment reduced vessel leakage, bacteremia, and liver damage after local infection. Therefore, our study demonstrates that KS provides protection in GAS-infected mice by enhancing bacterial clearance, as well as reducing inflammatory responses and organ damage.

Staphylococcus aureus regulates secretion of interleukin-6 and monocyte chemoattractant protein-1 through activation of nuclear factor kappaB signaling pathway in human osteoblasts

OBJECTIVE

Activation of nuclear factor kappaB by diverse bacteria regulates the secretion of chemokines and cytokines. Staphylococcus aureus (S. aureus)-infected osteoblasts can significantly increase the secretion of interleukin-6 and monocyte chemoattractant protein-1. The aim of this study was to investigate whether S. aureus can activate nuclear factor kappaB in human osteoblasts, and whether the activation of nuclear factor kappaB by S. aureus regulates the secretion of interleukin-6 and monocyte chemoattractant protein-1.

METHODS

Immunoblot and electrophoretic mobility shift assay were used to detect the degradation of IκBa and activation of nuclear factor kappaB in human osteoblasts in response to S. aureus, respectively. Enzyme-linked immunosorbent assay was used to measure the secretion of interleukin-6 and monocyte chemoattractant protein-1 in the supernatants. Lastly, carbobenzoxyl-l-leucinyl-l-leucinyl-l-leucinal, an inhibitor of the nuclear factor kappaB, was used to determine if activation of nuclear factor kappaB by S. aureus in human osteoblasts regulates the secretions of interleukin-6 and monocyte chemoattractant protein-1.

RESULTS

Our results for the first time demonstrated that S. aureus can induce the degradation of IκBa and activation of nuclear factor kappaB in human osteoblasts in a time and dose-dependent manner. In addition, inhibition of nuclear factor kappaB by carbobenzoxyl-l-leucinyl-l-leucinyl-l-leucinal suppressed the secretion of interleukin-6 and monocyte chemoattractant protein-1 in the supernatants of S. aureus-infected human osteoblasts in a dose-dependent manner.

CONCLUSION

These findings suggest that S. aureus can activate nuclear factor kappaB in human osteoblasts, and subsequently regulate the secretion of interleukin-6 and monocyte chemoattractant protein-1. The nuclear factor kappaB transcription factor regulates a number of genes involved in a wide variety of biological processes. Further study of the effects of nuclear factor kappaB activation on S. aureus-infected human osteoblast may provide us new insights into discovery of the immune mechanisms in osteomyelitis.

Dextromethorphan efficiently increases bactericidal activity, attenuates inflammatory responses, and prevents group a streptococcal sepsis

Group A streptococcus (GAS) is an important human pathogen that causes a wide spectrum of diseases, ranging from mild throat and skin infections to severe invasive diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. Dextromethorphan (DM), a dextrorotatory morphinan and a widely used antitussive drug, has recently been reported to possess anti-inflammatory properties. In this study, we investigated the potential protective effect of DM in GAS infection using an air pouch infection mouse model. Our results showed that DM treatment increased the survival rate of GAS-infected mice. Bacterial numbers in the air pouch were lower in mice treated with DM than in those infected with GAS alone. The bacterial elimination efficacy was associated with increased cell viability and bactericidal activity of air-pouch-infiltrating cells. Moreover, DM treatment prevented bacterial dissemination in the blood and reduced serum levels of the proinflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and IL-1β and the chemokines monocyte chemotactic protein 1 (MCP-1), macrophage inflammatory protein 2 (MIP-2), and RANTES. In addition, GAS-induced mouse liver injury was reduced by DM treatment. Taken together, DM can increase bacterial killing and reduce inflammatory responses to prevent sepsis in GAS infection. The consideration of DM as an adjunct treatment in combination with antibiotics against bacterial infection warrants further study.

Attachment of Staphylococcus aureus is required for activation of nuclear factor kappa B in human osteoblasts

Nuclear factor kappa B (NF-κB) plays a prominent role in the pathogenesis of infectious diseases. Staphylococcus aureus (S. aureus), which can attach to and invade human osteoblasts, is the most common causative agent of osteomyelitis. To determine whether S. aureus can activate NF-κB in human osteoblasts and explore the possible factors of activation in response to infection, we used flow cytometry, enzyme-linked immunosorbent assay, immunoblots, and electrophoretic mobility shift assays to quantify the invasion of bacteria, to measure the interleukin-6 (IL-6) of culture supernatants, and to investigate the IκBα degradation and NF-κB activation in human osteoblasts. Moreover, we explored the possible factors responsible for the activation of NF-κB by preventing S. aureus from physically touching human osteoblasts or inhibiting the invasion of S. aureus into human osteoblasts under co-culture conditions, by incubating proteinase K-treated or ultraviolet-killed S. aureus with human osteoblasts and by treating human osteoblasts with peptidoglycan (PGN) or lipoteichoic acid (LTA). We found that S. aureus induced the IκBα degradation and NF-κB activation, which could regulate IL-6 secretion in the culture supernatants of human osteoblasts in response to infection. In addition, the maximal IκBα degradation and NF-κB activation in human osteoblasts occurred prior to the maximal invasion of S. aureus. It was the attachment not invasion or the secreted soluble factor(s), PGN, LTA of S. aureus, that could induce the IκBα degradation and NF-κB activation in human osteoblasts. These results indicated that S. aureus can activate NF-κB in human osteoblasts and that the attachment of S. aureus is required for this activation in response to infection.

Calcium-dependent viral internalization is required for adenovirus type 7 induction of IL-8 protein

The host response to adenovirus (Ad) infection involves induction of cytokines in lung epithelia. We have demonstrated induction of the lung neutrophil chemokine interleukin-8 (IL-8) by Ad7, a major lung pathogen, in A549 lung epithelial cells and lung tissue through activation of the Erk signaling pathway. However, the mechanism of IL-8 induction is still unclear. In this paper, we first showed that Ad7 viral gene expression is not essential for IL-8 induction as psoralen-UV inactivation of Ad7 did not affect IL-8 mRNA induction or IL-8 protein induction in A549 cells. We then inhibited internalization of Ad7 by treatment of A549 cells with EGTA in calcium-free medium during exposure to Ad7. We verified that this treatment inhibited Ad internalization by confocal microscopy, FACS analysis and Ad E1A and fiber mRNA expression. Preventing internalization by calcium depletion did not inhibit Erk activation by Ad7. However, calcium-dependent internalization was required for IL-8 protein production in Ad7 exposed cells. This is not likely due to an effect of calcium depletion on downstream Erk signaling or IL-8 protein production since calcium depletion did not block IL-8 protein production stimulated by PMA, and because addition of EGTA subsequent to Ad7 internalization also did not prevent Ad induction of IL-8. These studies indicate that Ad7 internalization is calcium-dependent and is required for IL-8 protein induction upon Ad7 infection. Ad7 induction of Erk is independent of calcium and does not require virus internalization.

Streptococcus pyogenes induces epithelial inflammatory responses through NF-kappaB/MAPK signaling pathways

Innate immunity involves a cascade of inflammatory events, resulting in the secretion of chemokines and cytokines to recruit mediator cells in adaptive immunity. To study epithelial inflammatory responses initiated by Streptococcus pyogenes infection, we investigated chemotaxis ability in the supernatant of infected human respiratory epithelial HEp-2 cells. Our results showed that these supernatants showed significantly increased ability to attract monocytes, implying the release of inflammatory chemoattractants into the medium. Expression of interleukin (IL)-8 and IL-6 in HEp-2 cells was significantly increased at both the mRNA and protein levels after infection with S. pyogenes. Electrophoretic mobility shift and reporter-gene assays demonstrated that the transcription factors NF-kappaB and AP-1, regulated by mitogen-activated protein (MAP) kinase, were activated after streptococcal infection. The increases in mRNAs for IL-8 and IL-6 were abrogated by addition of NF-kappaB and MAP kinase inhibitors, suggesting that the upregulation of IL-8 and IL-6 is mediated through NF-kappaB and MAP kinase signaling pathways. Taken together, our results indicate that S. pyogenes infection of epithelial cells induces the secretion of pro-inflammatory chemokines/cytokines through activation of NF-kappaB and MAP kinase signaling pathways. These early innate responses initiated by S. pyogenes-infected respiratory epithelial cells may recruit immune cells to the airway and induce inflammation.

Carboplatin induces apoptotic cell death through downregulation of constitutively active nuclear factor-κB in human HPV-18 E6-positive HEp-2 cells

Because the role of nuclear factor kappaB (NF-kappaB) is in cellular growth control and neoplasia, we explored the status of NF-kappaB and investigated its role in survival of human HPV-18 E6-positive HEp-2 cells. We observed accumulation of p65 in the nucleus. Moreover, without any external stimulus constitutive NF-kappaB DNA binding and transactivation activity were detected in HEp-2 cells. Treatment with NF-kappaB inhibitor curcumin (diferuloylmethane) and transient transfection of the mutant form of IkappaBalpha, IkappaBalpha super repressor (IkappaBalpha-SR), suppressed constitutive NF-kappaB activity as well as proliferation, suggesting that constitutive NF-kappaB activity is required for the survival of HEp-2 cells. Carboplatin treatment downregulated constitutive NF-kappaB activity and prevented nuclear retention of p65. Further, carboplatin also suppressed the constitutive IkappaBalpha phosphorylation leading to stabilization of IkappaBalpha protein in the cells. Carboplatin inhibited NF-kappaB binding to its response element present in Bcl-2 promoter resulting in downregulation of antiapoptotic Bcl-2 protein. Thus, our results for the first time indicate that constitutive NF-kappaB has a significant role in the survival of HPV-18 E6-positive HEp-2 cells. Moreover, inactivation of NF-kappaB is one of the mechanisms underlying the induction of carboplatin-mediated apoptosis in HPV-18 E6-positive cancer cells.