Clostridium perfringens alpha-toxin induces the release of IL-8 through a dual pathway via TrkA in A549 cells

Arginine alleviates Clostridium perfringens α toxin-induced intestinal injury in vivo and in vitro via the SLC38A9/mTORC1 pathway

Introduction

Clostridium perfringens α toxin is a main virulence factor responsible for gut damage in animals. Arginine is a functional amino acid exhibiting significant immunoregulatory activities. However, the effects and immunoregulatory mechanisms of arginine supplementation on α toxin-induced intestinal injury remain unclear.

Methods

In vivo, 256 male Arbor Acres chickens were randomly assigned to a 2×2 factorial arrangement, involving diet treatments (with or without 0.3% arginine supplementation) and immunological stress (with or without α toxin challenge). In vitro, IEC-6 cells were treated with or without arginine in the presence or absence of α toxin. Moreover, IEC-6 cells were transfected with siRNA targeting mTOR and SLC38A9 to explore the underlying mechanisms.

Results and discussion

The results showed that in vivo, arginine supplementation significantly alleviated the α toxin-induced growth performance impairment, decreases in serum immunoglobulin (Ig)A and IgG levels, and intestinal morphology damage. Arginine supplementation also significantly reduced the α toxin-induced increase in jejunal proinflammatory cytokines interleukin (IL)-1β, IL-6 and IL-17 mRNA expression. Clostridium perfringens α toxin significantly decreased jejunal mechanistic target of rapamycin (mTOR) and solute carrier family 38 member 9 (SLC38A9) mRNA expression, while arginine supplementation significantly increased mTOR and SLC38A9 mRNA expression. In vitro, arginine pretreatment mitigated the α toxin-induced decrease in cell viability and the increase in cytotoxicity and apoptosis. Arginine pretreatment also alleviated the α toxin-induced upregulation of mRNA expression of inflammation-related cytokines IL-6, C-X-C motif chemokine ligand (CXCL)10, CXCL11 and transforming growth factor-β (TGF-β), as well as apoptosis-related genes B-cell lymphoma-2 associated X protein (Bax), B-cell lymphoma-2 (Bcl-2), B-cell lymphoma-extra large (Bcl-XL) and cysteinyl aspartate specific proteinase 3 (Caspase-3) and the ratio of Bax to Bcl-2. Arginine pretreatment significantly increased the α toxin-induced decrease in mTOR, SLC38A9, eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4EBP1) and ribosomal protein S6 kinase (S6K) mRNA expression. Knockdown SLC38A9 and mTOR largely abrogated the positive effects of arginine pretreatment on α toxin-induced intracellular changes. Furthermore, SLC38A9 silencing abolished the increased mTOR mRNA expression caused by arginine pretreatment. In conclusion, arginine administration attenuated α toxin-induced intestinal injury in vivo and in vitro, which could be associated with the downregulation of inflammation via regulating SLC38A9/mTORC1 pathway.

Clostridium perfringens α toxin damages the immune function, antioxidant capacity and intestinal health and induces PLCγ1/AMPK/mTOR pathway-mediated autophagy in broiler chickens

Clostridium perfringens α toxin is generated by all types of C. perfringens and is closely related to necrotic enteritis in poultry. This study was conducted to investigate the effects of α toxin on immune function, antioxidant capacity, intestinal health and the underlying mechanisms in broiler chickens. A total of 144 twenty-day-old broiler chickens were randomly assigned to four treatments. On d 21, the birds were intraperitoneally injected with PBS (control group) or α toxin at 0.025, 0.1 or 0.4 U/kg of body weight. Samples were collected at 3 h and 24 h post injection (p.i.). Results showed that α toxin challenge linearly decreased the average daily gain during the 3 days after infection and decreased plasma IgA and IgM levels 3 h p.i. Plasma diamine oxidase and d-lactate levels were linearly elevated by α toxin challenge at 3 h p.i. and 24 h p.i. Alpha toxin challenge linearly decreased plasma and jejunal mucosal catalase, glutathione peroxidase and total superoxide dismutase activities at 3 h p.i. and linearly decreased glutathione peroxidase and total superoxide dismutase activities at 24 h p.i. The ileal villus height to crypt depth ratio decreased linearly with increasing α toxin levels at 3 h p.i. and 24 h p.i. Alpha toxin challenge linearly elevated jejunal IL-1β, IL-6, IL-8 and tumor necrosis factor α mRNA expression at 3 h p.i. Additionally, α toxin challenge linearly reduced the jejunal claudin-1, claudin-3 and zonula occludens 1 mRNA expression at 3 h p.i. and the claudin-3, occludin and zonula occludens 1 mRNA expression at 24 h p.i. What's more, α toxin linearly increased the jejunal PLCγ1, AMPKα1 and ATG5 mRNA expression and linearly decreased the mTOR mRNA expression. In conclusion, C. perfringens α toxin challenge decreased body weight gain, impaired immune function, antioxidant capacity and intestinal health, and induced PLCγ1/AMPK/mTOR pathway-mediated autophagy. The recommended intraperitoneal injection dose for moderate injury was 0.1 U/kg of body weight and the recommended sampling time was 3 h p.i. in broiler chickens.

Phospholipase C: underrated players in microbial infections

During bacterial infections, one or more virulence factors are required to support the survival, growth, and colonization of the pathogen within the host, leading to the symptomatic characteristic of the disease. The outcome of bacterial infections is determined by several factors from both host as well as pathogen origin. Proteins and enzymes involved in cellular signaling are important players in determining the outcome of host-pathogen interactions. phospholipase C (PLCs) participate in cellular signaling and regulation by virtue of their ability to hydrolyze membrane phospholipids into di-acyl-glycerol (DAG) and inositol triphosphate (IP3), which further causes the activation of other signaling pathways involved in various processes, including immune response. A total of 13 PLC isoforms are known so far, differing in their structure, regulation, and tissue-specific distribution. Different PLC isoforms have been implicated in various diseases, including cancer and infectious diseases; however, their roles in infectious diseases are not clearly understood. Many studies have suggested the prominent roles of both host and pathogen-derived PLCs during infections. PLCs have also been shown to contribute towards disease pathogenesis and the onset of disease symptoms. In this review, we have discussed the contribution of PLCs as a determinant of the outcome of host-pathogen interaction and pathogenesis during bacterial infections of human importance.

Bacterial phospholipases C with dual activity: phosphatidylcholinesterase and sphingomyelinase

Bacterial phospholipases and sphingomyelinases are lipolytic esterases that are structurally and evolutionarily heterogeneous. These enzymes play crucial roles as virulence factors in several human and animal infectious diseases. Some bacterial phospholipases C (PLCs) have both phosphatidylcholinesterase and sphingomyelinase C activities. Among them, Listeria  monocytogenes PlcB, Clostridium perfringens PLC, and Pseudomonas aeruginosa PlcH are the most deeply understood. In silico predictions of substrates docking with these three bacterial enzymes provide evidence that they interact with different substrates at the same active site. This review discusses structural aspects, substrate specificity, and the mechanism of action of those bacterial enzymes on target cells and animal infection models to shed light on their roles in pathogenesis.

Inhibition of ssc-microRNA-140-5p ameliorates the Clostridium perfringens beta2 toxin-induced inflammatory response in IPEC-J2 cells via the ERK1/2 and JNK pathways by targeting VEGFA

Piglet diarrhea and even death due to Clostridium perfringens (C. perfringens) type C infection have led to huge economic losses in the pig industry worldwide. C. perfringens beta2 (CPB2) toxin is the main virulence factor for this pathogen. MiR-140-5p can exacerbate toxin-induced toxicity of toxin to cells by promoting oxidative stress. However, the role of pig miR-140-5p (ssc-miR-140-5p) in piglet diarrhea caused by C. perfringens type C has not been studied. Here, we study investigated the function of ssc-miR-140-5p by generating an in vitro CPB2-induced injury model in intestinal porcine epithelial (IPEC-J2) cells. Our results revealed that transfection with an ssc-miR-140-5p inhibitor significantly increased the viability of CPB2-induced IPEC-J2 cells, decrease the release of lactate dehydrogenase (LDH) and reactive oxygen species (ROS), and inhibit inflammatory responses and apoptosis. In addition, vascular endothelial growth factor A (VEGFA) was identified as a direct target of ssc-miR-140-5p by luciferase reporter assay. Western blot analysis showed that inhibition of ssc-miR-140-5p could activate the ERK1/2 signaling pathway and inhibit the JNK signaling pathway. In summary, we showed that down-regulation of ssc-miR-140-5p ameliorated CPB2-induced inflammatory responses in IPEC-J2 cells via the ERK1/2 and JNK signaling pathways by targeting VEGFA.

Identification and Characterization of MAPK Signaling Pathway Genes and Associated lncRNAs in the Ileum of Piglets Infected by Clostridium perfringens Type C

Clostridium perfringens type C (C. perfringens type C) is one of the main microbial pathogens responsible for piglet diarrhea worldwide, causing substantial economic losses for pig-rearing industries. The mitogen-activated protein kinase (MAPK) signaling pathway is a key regulator of inflammatory bowel disease, especially necrotic enteritis. However, whether and how the MAPK signaling pathway is involved in regulating the process of piglet diarrhea when challenged by C. perfringens type C are still unknown. Here, we screened 38 differentially expressed genes (DEGs) in piglets' ileum tissues experimentally infected with C. perfringens type C that were enriched in the Sus scrofa MAPK signaling pathway, based on our previous transcriptome data. Of these DEGs, 12 genes (TRAF2, MAPK8, and GADD45G, among others) were upregulated whereas 26 genes (MAPK1, TP53, and CHUK, among others) were downregulated in the infected group. Our results showed that MAPK1, TP53, MAPK8, MYC, and CHUK were in the core nodes of the PPI network. Additionally, we obtained 35 lncRNAs from the sequencing data, which could be trans-targeted to MAPK signaling pathway genes and were differentially expressed in the ileum tissues infected with C. perfringens. We used qRT-PCR to verify the expression levels of genes and lncRNAs related to the MAPK signaling pathway; their expression patterns were consistent with RNA sequencing data. Our results provide strong support for deeply exploring the role of the MAPK signaling pathway in diarrhea caused by C. perfringens type C.

Inflammasome Activation Induced by Perfringolysin O of Clostridium perfringens and Its Involvement in the Progression of Gas Gangrene

Clostridium perfringens (C. perfringens) is Gram-positive anaerobic, spore-forming rod-shaped bacterial pathogen that is widely distributed in nature. This bacterium is known as the causative agent of a foodborne illness and of gas gangrene. While the major virulence factors are the α-toxin and perfringolysin O (PFO) produced by type A strains of C. perfringens, the precise mechanisms of how these toxins induce the development of gas gangrene are still not well understood. In this study, we analyzed the host responses to these toxins, including inflammasome activation, using mouse bone marrow-derived macrophages (BMDMs). Our results demonstrated, for the first time, that C. perfringens triggers the activation of caspase-1 and release of IL-1β through PFO-mediated inflammasome activation via a receptor of the Nod-like receptor (NLR) family, pyrin-domain containing 3 protein (NLRP3). The PFO-mediated inflammasome activation was not induced in the cultured myocytes. We further analyzed the functional roles of the toxins in inducing myonecrosis in a mouse model of gas gangrene. Although the myonecrosis was found to be largely dependent on the α-toxin, PFO also induced myonecrosis to a lesser extent, again through the mediation of NLRP3. These results suggest that C. perfringens triggers inflammatory responses via PFO-mediated inflammasome activation via NLRP3, and that this axis contributes in part to the progression of gas gangrene. Our findings provide a novel insight into the molecular mechanisms underlying the pathogenesis of gas gangrene caused by C. perfringens.

Histotoxic Clostridial Infections

The pathogenesis of clostridial myonecrosis or gas gangrene involves an interruption to the blood supply to the infected tissues, often via a traumatic wound, anaerobic growth of the infecting clostridial cells, the production of extracellular toxins, and toxin-mediated cell and tissue damage. This review focuses on host-pathogen interactions in Clostridium perfringens-mediated and Clostridium septicum-mediated myonecrosis. The major toxins involved are C. perfringens α-toxin, which has phospholipase C and sphingomyelinase activity, and C. septicum α-toxin, a β-pore-forming toxin that belongs to the aerolysin family. Although these toxins are cytotoxic, their effects on host cells are quite complex, with a range of intracellular cell signaling pathways induced by their action on host cell membranes.

Clostridium perfringens α-toxin impairs granulocyte colony-stimulating factor receptor-mediated granulocyte production while triggering septic shock

During bacterial infection, granulocyte colony-stimulating factor (G-CSF) is produced and accelerates neutrophil production from their progenitors. This process, termed granulopoiesis, strengthens host defense, but Clostridium perfringens α-toxin impairs granulopoiesis via an unknown mechanism. Here, we tested whether G-CSF accounts for the α-toxin-mediated impairment of granulopoiesis. We find that α-toxin dramatically accelerates G-CSF production from endothelial cells in response to Toll-like receptor 2 (TLR2) agonists through activation of the c-Jun N-terminal kinase (JNK) signaling pathway. Meanwhile, α-toxin inhibits G-CSF-mediated cell proliferation of Ly-6G+ neutrophils by inducing degradation of G-CSF receptor (G-CSFR). During sepsis, administration of α-toxin promotes lethality and tissue injury accompanied by accelerated production of inflammatory cytokines in a TLR4-dependent manner. Together, our results illustrate that α-toxin disturbs G-CSF-mediated granulopoiesis by reducing the expression of G-CSFR on neutrophils while augmenting septic shock due to excess inflammatory cytokine release, which provides a new mechanism to explain how pathogenic bacteria modulate the host immune system.

Concurrent Host-Pathogen Transcriptional Responses in a Clostridium perfringens Murine Myonecrosis Infection

To obtain an insight into host-pathogen interactions in clostridial myonecrosis, we carried out comparative transcriptome analysis of both the bacterium and the host in a murine Clostridium perfringens infection model, which is the first time that such an investigation has been conducted. Analysis of the host transcriptome from infected muscle tissues indicated that many genes were upregulated compared to the results seen with mock-infected mice. These genes were enriched for host defense pathways, including Toll-like receptor (TLR) and Nod-like receptor (NLR) signaling components. Real-time PCR confirmed that host TLR2 and NLRP3 inflammasome genes were induced in response to C. perfringens infection. Comparison of the transcriptome of C. perfringens cells from the infected tissues with that from broth cultures showed that host selective pressure induced a global change in C. perfringens gene expression. A total of 33% (923) of C. perfringens genes were differentially regulated, including 10 potential virulence genes that were upregulated relative to their expression in vitro These genes encoded putative proteins that may be involved in the synthesis of cell wall-associated macromolecules, in adhesion to host cells, or in protection from host cationic antimicrobial peptides. This report presents the first successful expression profiling of coregulated transcriptomes of bacterial and host genes during a clostridial myonecrosis infection and provides new insights into disease pathogenesis and host-pathogen interactions.IMPORTANCEClostridium perfringens is the causative agent of traumatic clostridial myonecrosis, or gas gangrene. In this study, we carried out transcriptional analysis of both the host and the bacterial pathogen in a mouse myonecrosis infection. The results showed that in comparison to mock-infected control tissues, muscle tissues from C. perfringens-infected mice had a significantly altered gene expression profile. In particular, the expression of many genes involved in the innate immune system was upregulated. Comparison of the expression profiles of C. perfringens cells isolated from the infected tissues with those from equivalent broth cultures identified many potential virulence genes that were significantly upregulated in vivo These studies have provided a new understanding of the range of factors involved in host-pathogen interactions in a myonecrosis infection.

Delta-toxin from Clostridium perfringens perturbs intestinal epithelial barrier function in Caco-2 cell monolayers

Clostridium perfringens delta-toxin is a β-barrel-pore-forming toxin (β-PFT) and a presumptive virulence factor of type B and C strains, which are causative organisms of fatal intestinal diseases in animals. We showed previously that delta-toxin causes cytotoxicity via necrosis in sensitive cells. Here, we examined the effect of delta-toxin on intestinal membrane integrity. Delta-toxin led to a reduction in transepithelial electrical resistance (TEER) and increased the permeability of fluorescence isothiocyanate-conjugated dextran in human intestinal epithelial Caco-2 cells without changing the tight junction proteins, such as zonula occludens-1 (ZO-1), occludin, and claudin-1. On the other hand, delta-toxin reduced the cellular levels of adherence junction protein E-cadherin before cell injury. A disintegrin and metalloprotease (ADAM) 10 facilitates E-cadherin cleavage and was identified as the cellular receptor for alpha-toxin, a β-PFT produced by Staphylococcus aureus. ADAM10 inhibitor (GI254023X) blocked the toxin-induced decrease in TEER and cleavage of E-cadherin. Delta-toxin enhanced ADAM10 activity in a dose- and time-dependent manner. Furthermore, delta-toxin colocalized with ADAM10. These results indicated that ADAM10 plays a key role in delta-toxin-induced intestinal injury.

Scarless surgery for a huge liver cyst: A case report

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Fenestration is the definitive treatment for symptomatic/complicated liver cysts.

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NOTES, which has been reported recently, enables surgery without scars.

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Multiple clinical and technological barriers impede further progress with NOTES.

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Our safe and unique method enables minimally invasive surgery with small incisions.

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This “scarless surgery” is expected to yield some clinical benefits.

Introduction

Symptomatic or complicated liver cysts sometimes require surgical intervention and laparoscopic fenestration is the definitive treatment for these cysts. We performed minimally invasive surgery, hybrid natural orifice transluminal endoscopic surgery (NOTES) without scarring, for a huge liver cyst.

Presentation of case

An 82-year-old female presented with a month-long history of right upper abdominal pain. We diagnosed her condition as a huge liver cyst by morphological studies. She denied any history of abdominal trauma. Her serum CEA and CA19-9 were normal and a serum echinococcus serologic test was negative. Laparoscopic fenestration, using a hybrid NOTES procedure via a transvaginal approach, was performed for a huge liver cyst because we anticipated difficulty with an umbilical approach, such as single incision laparoscopic surgery (SILS). Her post-operative course was uneventful and she was discharged from our hospital three days after surgery. Pain killers were not required during and after hospitalization. No recurrence of the liver cyst or bulging was detected by clinical examination two years later.

Discussion

A recent trend of laparoscopic procedure has been towards minimizing the number of incisions to achieve less invasiveness. This hybrid NOTES, with a small incision for abdominal access, along with vaginal access, enabled painless operation for a huge liver cyst.

Conclusion

We report a huge liver cyst treated by hybrid NOTES. This approach is safe, less invasive, and may be the first choice for a huge liver cyst.

Clostridium perfringens α-toxin impairs erythropoiesis by inhibition of erythroid differentiation

Clostridium perfringens α-toxin induces hemolysis of erythrocytes from various species, but it has not been elucidated whether the toxin affects erythropoiesis. In this study, we treated bone marrow cells (BMCs) from mice with purified α-toxin and found that TER119⁺ erythroblasts were greatly decreased by the treatment. A variant α-toxin defective in enzymatic activities, phospholipase C and sphingomyelinase, had no effect on the population of erythroblasts, demonstrating that the decrease in erythroblasts was dependent of its enzymatic activities. α-Toxin reduced the CD71⁺TER119⁺ and CD71^–TER119⁺ cell populations but not the CD71⁺TER119⁻ cell population. In addition, α-toxin decreased the number of colony-forming unit erythroid colonies but not burst-forming unit erythroid colonies, indicating that α-toxin preferentially reduced mature erythroid cells compared with immature cells. α-Toxin slightly increased annexinV⁺ cells in TER119⁺ cells. Additionally, simultaneous treatment of BMCs with α-toxin and erythropoietin greatly attenuated the reduction of TER119⁺ erythroblasts by α-toxin. Furthermore, hemin-induced differentiation of human K562 erythroleukemia cells was impaired by α-toxin, whereas the treatment exhibited no apparent cytotoxicity. These results suggested that α-toxin mainly inhibited erythroid differentiation. Together, our results provide new insights into the biological activities of α-toxin, which might be important to understand the pathogenesis of C. perfringens infection.

Bacterial Sphingomyelinases and Phospholipases as Virulence Factors

Bacterial sphingomyelinases and phospholipases are a heterogeneous group of esterases which are usually surface associated or secreted by a wide variety of Gram-positive and Gram-negative bacteria. These enzymes hydrolyze sphingomyelin and glycerophospholipids, respectively, generating products identical to the ones produced by eukaryotic enzymes which play crucial roles in distinct physiological processes, including membrane dynamics, cellular signaling, migration, growth, and death. Several bacterial sphingomyelinases and phospholipases are essential for virulence of extracellular, facultative, or obligate intracellular pathogens, as these enzymes contribute to phagosomal escape or phagosomal maturation avoidance, favoring tissue colonization, infection establishment and progression, or immune response evasion. This work presents a classification proposal for bacterial sphingomyelinases and phospholipases that considers not only their enzymatic activities but also their structural aspects. An overview of the main physiopathological activities is provided for each enzyme type, as are examples in which inactivation of a sphingomyelinase- or a phospholipase-encoding gene impairs the virulence of a pathogen. The identification of sphingomyelinases and phospholipases important for bacterial pathogenesis and the development of inhibitors for these enzymes could generate candidate vaccines and therapeutic agents, which will diminish the impacts of the associated human and animal diseases.

Involvement of cholesterol in Campylobacter jejuni cytolethal distending toxin-induced pathogenesis

AIM

The aim of this study was to investigate whether cholesterol plays a pivotal role in cytolethal distending toxin (CDT) mediated pathogenic effects in hosts.

MATERIALS & METHODS

The molecular mechanisms underlying cholesterol sequestering conferred resistance to CDT-induced DNA double-strand breaks (DSBs) and cell cycle arrest were investigated. Histopathological analysis was conducted for evaluating CDT-induced intestinal inflammation in mouse.

RESULTS

CDT actions were attenuated by treatment of cells with methyl-β-cyclodextrin (MβCD). Severe intestinal inflammation induced by CDT treatment was observed in high-cholesterol diet-fed mice, but not in normal diet-fed mice, indicating that cholesterol is essential for CDT intoxication.

CONCLUSION

Our findings demonstrate a molecular link between Campylobacter jejuni CDT and cholesterol, which is crucial to facilitate CDT-induced pathogenesis in hosts.

Inflammatory responses to a Clostridium perfringens type A strain and α-toxin in primary intestinal epithelial cells of chicken embryos

The causative pathogen of necrotic enteritis is the Gram-positive bacterium Clostridium perfringens. Its main cell wall component, peptidoglycan (PGN), can be recognized by Toll-like receptor 2 and nucleotide-binding oligomerization domain (NOD). Consequently, the immune response is initiated via activation of nuclear factor kappa B (NF-κB) signalling pathway. An in vitro study was conducted to investigate chicken intestinal inflammatory responses to C. perfringens type A and one of its virulence factors, α-toxin. In primary intestinal epithelial cells, C. perfringens as well as commercially available PGN and α-toxin challenge upregulated mRNA expression of interleukin (IL)-6, IL-8 and inducible nitric oxide synthase (iNOS) with a dosage-dependent manner at 3 h post infection (p.i.; P ≤ 0.001). Time-course effects of three stimulators at high concentration were further examined. C. perfringens infection elevated IL-6, IL-8 and iNOS levels from 1 h to 9 h p.i., while PGN treatment increased IL-6 and IL-8 expression at 1 h and 3 h p.i. (P < 0.05). Bacterial and PGN treatments induced NOD1 expression at 6 h p.i. and only bacterial infection boosted NF-κB p65 expression at 6 h and 9 h p.i. (P < 0.05). α-Toxin treatment upregulated IL-6 and IL-8 expression throughout infection, as well as iNOS, TNF-α and NF-κB p65 expression at later hours p.i. (P < 0.05). In conclusion, both C. perfringens and α-toxin challenge induced intense cytokine expression associated with NF-κB activation in chicken intestinal epithelial cells. The receptors for the recognition of PGN component of C. perfringens need further investigation.

Clostridium perfringens Alpha-Toxin Induces Gm1a Clustering and Trka Phosphorylation in the Host Cell Membrane

Clostridium perfringens alpha-toxin elicits various immune responses such as the release of cytokines, chemokines, and superoxide via the GM1a/TrkA complex. Alpha-toxin possesses phospholipase C (PLC) hydrolytic activity that contributes to signal transduction in the pathogenesis of gas gangrene. Little is known about the relationship between lipid metabolism and TrkA activation by alpha-toxin. Using live-cell fluorescence microscopy, we monitored transbilayer movement of diacylglycerol (DAG) with the yellow fluorescent protein-tagged C1AB domain of protein kinase C-γ (EYFP-C1AB). DAG accumulated at the marginal region of the plasma membrane in alpha toxin-treated A549 cells, which also exhibited GM1a clustering and TrkA phosphorylation. Annexin V binding assays showed that alpha-toxin induced the exposure of phosphatidylserine on the outer leaflet of the plasma membrane. However, H148G, a variant toxin which binds cell membrane and has no enzymatic activity, did not induce DAG translocation, GM1a clustering, or TrkA phosphorylation. Alpha-toxin also specifically activated endogenous phospholipase Cγ-1 (PLCγ-1), a TrkA adaptor protein, via phosphorylation. U73122, an endogenous PLC inhibitor, and siRNA for PLCγ-1 inhibited the formation of DAG and release of IL-8. GM1a accumulation and TrkA phosphorylation in A549 cells treated with alpha-toxin were also inhibited by U73122. These results suggest that the flip-flop motion of hydrophobic lipids such as DAG leads to the accumulation of GM1a and TrkA. We conclude that the formation of DAG by alpha-toxin itself (first step) and activation of endogenous PLCγ-1 (second step) leads to alterations in membrane dynamics, followed by strong phosphorylation of TrkA.

The pore-forming α-toxin from clostridium septicum activates the MAPK pathway in a Ras-c-Raf-dependent and independent manner

Clostridium septicum is the causative agent of atraumatic gas gangrene, with α-toxin, an extracellular pore-forming toxin, essential for disease. How C. septicum modulates the host’s innate immune response is poorly defined, although α-toxin-intoxicated muscle cells undergo cellular oncosis, characterised by mitochondrial dysfunction and release of reactive oxygen species. Nonetheless, the signalling events that occur prior to the initiation of oncosis are poorly characterised. Our aims were to characterise the ability of α-toxin to activate the host mitogen activated protein kinase (MAPK) signalling pathway both in vitro and in vivo. Treatment of Vero cells with purified α-toxin activated the extracellular-signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 arms of the MAPK pathway and stimulated the release of TNF-α in a dose-dependent manner. Studies using inhibitors of all three MAPK components suggested that activation of ERK occurred in a Ras-c-Raf dependent manner, whereas activation of JNK and p38 occurred by a Ras-independent mechanism. Toxin-mediated activation was dependent on efficient receptor binding and pore formation and on an influx of extracellular calcium ions. In the mouse myonecrosis model we showed that the MAPK pathway was activated in tissues of infected mice, implying that it has an important role in the disease process.

Clostridium perfringens phospholipase C induced ROS production and cytotoxicity require PKC, MEK1 and NFκB activation

Clostridium perfringens phospholipase C (CpPLC), also called α-toxin, is the most toxic extracellular enzyme produced by this bacteria and is essential for virulence in gas gangrene. At lytic concentrations, CpPLC causes membrane disruption, whereas at sublytic concentrations this toxin causes oxidative stress and activates the MEK/ERK pathway, which contributes to its cytotoxic and myotoxic effects. In the present work, the role of PKC, ERK 1/2 and NFκB signalling pathways in ROS generation induced by CpPLC and their contribution to CpPLC-induced cytotoxicity was evaluated. The results demonstrate that CpPLC induces ROS production through PKC, MEK/ERK and NFκB pathways, the latter being activated by the MEK/ERK signalling cascade. Inhibition of either of these signalling pathways prevents CpPLC's cytotoxic effect. In addition, it was demonstrated that NFκB inhibition leads to a significant reduction in the myotoxicity induced by intramuscular injection of CpPLC in mice. Understanding the role of these signalling pathways could lead towards developing rational therapeutic strategies aimed to reduce cell death during a clostridialmyonecrosis.

Hemoglobin receptor protein from Porphyromonas gingivalis induces interleukin-8 production in human gingival epithelial cells through stimulation of the mitogen-activated protein kinase and NF-κB signal transduction pathways

Periodontitis is an inflammatory disease of polymicrobial origin affecting the tissues supporting the tooth. The oral anaerobic bacterium Porphyromonas gingivalis, which is implicated as an important pathogen for chronic periodontitis, triggers a series of host inflammatory responses that promote the destruction of periodontal tissues. Among the virulence factors of P. gingivalis, hemoglobin receptor protein (HbR) is a major protein found in culture supernatants. In this study, we investigated the roles of HbR in the production of inflammatory mediators. We found that HbR induced interleukin-8 (IL-8) production in the human gingival epithelial cell line Ca9-22. p38 mitogen-activated protein kinase (MAPK) and extracellular signal-related kinase 1/2 (Erk1/2) were activated in HbR-stimulated Ca9-22 cells. Inhibitors of p38 MAPK (SB203580) and Erk1/2 (PD98059) blocked HbR-induced IL-8 production. Additionally, HbR stimulated the translocation of NF-κB-p65 to the nucleus, consistent with enhancement of IL-8 expression by activation of the NF-κB pathway. In addition, small interfering RNA (siRNA) targeting activating transcription factor 2 (ATF-2) or cyclic AMP-response element-binding protein (CREB) inhibited HbR-induced IL-8 production. Moreover, pretreatment with SB203580 and PD98059 reduced HbR-induced phosphorylation of CREB and ATF-2, respectively. Combined pretreatment with an inhibitor of NF-κB (BAY11-7082) and SB203580 was more efficient in inhibiting the ability of HbR to induce IL-8 production than pretreatment with either BAY11-7082 or SB203580 alone. Thus, in Ca9-22 cells, the direct activation of p38 MAPK and Erk1/2 by HbR caused the activation of the transcription factors ATF-2, CREB, and NF-κB, thus resulting in the induction of IL-8 production.

Thymosin beta-4 promotes mesenchymal stem cell proliferation via an interleukin-8-dependent mechanism

Mesenchymal stem cells (MSCs) hold great promise for the field of tissue regeneration. Because only a limited number of MSCs can be obtained from each donor site, it is important to establish standard methods for MSC expansion using growth and trophic factors. Thymosin β4 (Tβ4) is a novel trophic factor that has antimicrobial effects and the potential to promote tissue repair. Tβ4 is a ubiquitous, naturally-occurring peptide in the wound bed. Therefore, the relationship between Tβ4 and MSCs, especially adjacent adipose tissue-derived stem cells (ASCs), merits consideration. Exogenous Tβ4 treatment enhanced the proliferation of human ASCs, resulting in prominent nuclear localization of PCNA immunoreactivity. In addition, exogenous Tβ4 also increased IL-8 secretion and blocking of IL-8 with neutralizing antibodies decreased Tβ4-induced ASC proliferation, suggesting that IL-8 is a critical mediator of Tβ4-enhanced proliferation. Moreover, Tβ4 activated phosphorylation of ERK1/2 and increased the nuclear translocation of NF-κB. These observation provide that Tβ4 promotes the expansion of human ASCs via an IL-8-dependent mechanism that involves the ERK and NF-κB pathways. Therefore, Tβ4 could be used as a tool for MSC expansion in cell therapeutics.

Clostridium perfringens alpha-toxin recognizes the GM1a-TrkA complex

Clostridium perfringens alpha-toxin is the major virulence factor in the pathogenesis of gas gangrene. Alpha-toxin is a 43-kDa protein with two structural domains; the N-domain contains the catalytic site and coordinates the divalent metal ions, and the C-domain is a membrane-binding site. The role of the exposed loop region (72-93 residues) in the N-domain, however, has been unclear. Here we show that this loop contains a ganglioside binding motif (H … SXWY … G) that is the same motif seen in botulinum neurotoxin and directly binds to a specific conformation of the ganglioside Neu5Acα2-3(Galβ1-3GalNAcβ1-4)Galβ1-4Glcβ1Cer (GM1a) through a carbohydrate moiety. Confocal microscopy analysis using fluorescently labeled BODIPY-GM1a revealed that the toxin colocalized with GM1a and induced clustering of GM1a on the cell membranes. Alpha-toxin was only slightly toxic in β1,4-N-acetylgalactosaminyltransferase knock-out mice, which lack the a-series gangliosides that contain GM1a, but was highly toxic in α2,8-sialyltransferase knock-out mice, which lack both b-series and c-series gangliosides, similar to the control mice. Moreover, experiments with site-directed mutants indicated that Trp-84 and Tyr-85 in the exposed alpha-toxin loop play an important role in the interaction with GM1a and subsequent activation of TrkA. These results suggest that binding of alpha-toxin to GM1a facilitates the activation of the TrkA receptor and induces a signal transduction cascade that promotes the release of chemokines. Therefore, we conclude that GM1a is the primary cellular receptor for alpha-toxin, which can be a potential target for drug developed against this pathogen.