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

Targeting the PTN/PTPRZ1-ROS Pathway to Promote Bone Regeneration

Background: Osteoporosis is a global health problem that significantly decreases patients' quality of life and causes tremendous medical burdens. Therefore, exploring effective targeting strategies for osteoporosis treatment is crucial. Previous studies have indicated that pleiotrophin (PTN) was a secretory factor involved in several biological processes, such as angiogenesis, neural development, and abnormal osteogenic functions in osteoporosis. However, the roles of PTN in osteogenics and the mechanisms remain unclear. Methods: In this study, we explored the effects and mechanisms of PTN in regulating osteogenic functions using real-time quantitative PCR, immunofluorescence, ALP detection, a TUNEL assay, RNA sequencing, and phosphorylation quantitative proteomics. Fracture-healing experiments in osteoporosis rats were also conducted to evaluate the osteogenic functions of PTN in vivo. Results: We found that PTN significantly inhibited apoptosis and promoted the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs). Further experiments showed that PTN regulated the biological functions of rBMSCs by promoting antioxidant functions and reducing cellular reactive oxygen species (ROS), thereby protecting rBMSCs from accumulated ROS. Additionally, we found that PTN binds to the PTPRZ1 receptor, inducing intracellular PLCG1 phosphorylation and NCOA3 nuclear translocation, which regulate the downstream antioxidant functions of rBMSCs. Additionally, we verified that PTN effectively promoted fracture healing in osteoporotic animals. Conclusions: This study elucidates the mechanisms by which PTN promotes osteogenesis and verifies this effect in vivo, offering an effective target for osteoporosis treatment.

Unveiling the pathogenic mechanisms of Clostridium perfringens toxins and virulence factors

Clostridium perfringens causes multiple diseases in humans and animals. Its pathogenic effect is supported by a broad and heterogeneous arsenal of toxins and other virulence factors associated with a specific host tropism. Molecular approaches have indicated that most C. perfringens toxins produce membrane pores, leading to osmotic cell disruption and apoptosis. However, identifying mechanisms involved in cell tropism and selective toxicity effects should be studied more. The differential presence and polymorphisms of toxin-encoding genes and genes encoding other virulence factors suggest that molecular mechanisms might exist associated with host preference, receptor binding, and impact on the host; however, this information has not been reviewed in detail. Therefore, this review aims to clarify the current state of knowledge on the structural features and mechanisms of action of the major toxins and virulence factors of C. perfringens and discuss the impact of genetic diversity of toxinotypes in tropism for several hosts.

An autopsy case of gas gangrene, massive intravascular hemolysis, and cytokine storm due to Clostridium perfringens type A infection

Clostridium perfringens bacteremia is a rare but rapidly fatal condition, especially in patients exhibiting massive intravascular hemolysis (MIH), gas gangrene, and septic shock. Herein, we present an autopsy case of C. perfringens septicemia exhibiting MIH, gas gangrene, and cytokine storm. The patient was an 84-year-old female with a history of biliary reconstruction surgery for congenital biliary dilatation. She developed MIH, elevated inflammatory mediator levels, thrombocytopenia, and coagulopathy. She went into shock within 1 h of the presentation and died within a few hours. Rapid progression was associated with the transformation of liver abscesses into gas-filled abscesses on computed tomography scan, suggesting the rapid outgrowth of gas-producing bacteria. The patient was finally diagnosed with MIH and gas gangrene due to C. perfringens infection based on the presence of this bacterium in the blood and bile. On autopsy, gas gangrene was observed in almost all organs, originating from the bile duct. Polymerase chain reactions targeting C. perfringens toxins identified the isolated bacterium as C. perfringens type A expressing α-toxin (CPA), perfringolysin O (PFO), and collagenase (ColA). Elevated interleukin 6 and tumor necrosis factor-α expression levels were observed in the serum, and such proinflammatory responses were partially mediated by Toll-like receptor 2. This study elucidated the association between the toxin profiles of clinically isolated C. perfringens and the host cytokine responses in the patient.

Review of advances in molecular structure and biological function of alpha toxin of Clostridium perfringens

Alpha toxin has become the subject of research in recent years. The objective of this article was to review and summarize recent research on the molecular structure and biological function of the alpha toxin of Clostridium perfringens. This includes the work of our research team, as well as that of other researchers. Clostridium perfringens is an anaerobic, spore-forming, Gram-positive bacillus. It can cause various intestinal diseases, such as gas gangrene, food poisoning, non-foodborne diarrhea, and enteritis. Clostridium perfringens can be classified into 5 toxinotypes A, B, C, D, and E, based on the production of major toxins. Each type of C. perfringens produces alpha toxin, which is one of the most important lethal and dermonecrotic toxins and is considered a primary virulence factor. Alpha toxin is a multifunctional metalloenzyme with phospholipase C and sphingomyelinase activities that simultaneously hydrolyze phosphatidylcholine and sphingomyelin. It can therefore destroy the integrity of cell membranes and eventually cause cell lysis. The clinical effects of alpha toxins are characterized by cytotoxicity, hemolytic activity, lethality, skin necrosis, platelet aggregation, and increased vascular permeability. Future research will concentrate on the pathogenesis of a lpha toxin exposure, clarifying the interaction between alpha toxin and the cell membrane and investigating the mechanism of activating platelet function. This research will have substantial theoretical and practical value in controlling disease progression, identifying targeted therapeutic sites, and reducing the toxic effects of vaccines.

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.

Anti-tumor Effects of Recombinant Clostridium α-Toxin on Breast Cancer: An In Vitro and In Vivo Study

Cancer is the second leading cause of death worldwide, surpassed only by cardiovascular diseases. This study investigated the anticancer effects of recombinant Clostridium α-toxin on breast cancer, both in vitro and in vivo. The entire coding sequence of a codon-optimized α-toxin was designed, cloned into the pET28a (+) vector, and expressed as recombinant α-toxin in Escherichia coli (E. coli) BL 21(DE3) cells transformed with the recombinant plasmid. The recombinant α-toxin was purified using Ni²⁺ affinity chromatography, and its accuracy and purity were confirmed through sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis. The anticancer effects of purified α-toxin were then assessed in vitro and animal models against MCF-7 breast cancer cells. Protein analysis confirmed the presence of a 48 kDa band corresponding to the recombinant α-toxin. Additionally, the IC₅₀ values of α-toxin against MCF-7 cells at 24, 48, and 72 h were 407.3±2.392 μg/mL, 287.3±5.411 μg/mL, and 258.1±4.671 μg/mL, respectively. In vivo, results demonstrated a significant reduction in mean cancer nodule size following α-toxin treatment (p<0.001). These findings suggest that α-toxin may serve as a promising candidate for breast cancer therapy.

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.

Clostridium perfringens phospholipase C impairs innate immune response by inducing integrated stress response and mitochondrial-induced epigenetic modifications

Clostridium perfringens, a rod-shaped, gram-positive, anaerobic, spore-forming bacterium is one of the most widely occurring bacterial pathogens, associated with a spectrum of diseases in humans. A major virulence factor during its infection is the enzyme phospholipase C encoded by the plc gene, known as Clostridium perfringens phospholipase C (CpPLC). The present study was designed to understand the role of CpPLC in inducing survival mechanisms and mitochondrial-induced epigenetic changes in a human lymphocyte cell culture model. Following exposure to CpPLC, a significant generation of mitochondrial reactive oxygen species was observed, which coincided with the changes in the expression of vital components of MAP/ERK/RTK signaling cascade that regulates the downstream cellular functions. These disturbances further led to alterations in the mitochondrial genome and functioning. This was supported by the observed upregulation in the expression of mitochondrial fission genes Drp1, Fis1, and Mff, and mitochondrial fusion genes MFN1, MFN2, and OPA1 following CpPLC exposure. CpPLC exposed cells showed upregulation of OMA1, DELE1, and HRI genes involved in the integrated stress response (ISR), which suggests that it may induce the ISR that provides a pro-survival mechanism to the host cell. CpPLC also initiated immune patho-physiologic mechanisms including mitochondrial-induced epigenetic modifications through a mitochondrial-ROS driven signaling pathway. Interestingly, epigenetic machinery not only play a pivotal role in lymphocyte homeostasis by contributing to cell-fate decisions but thought to be one of the mechanisms by which intracellular pathogens survive within the host cells. Importantly, the impairment of mtDNA repair among the CpPLC exposed cells, induced alterations within mtDNA methylation, and led to the deregulation of MT-CO1, MT-ND6, MT-ATPase 6, and MT-ATPase8 gene expression profiles that are important for mitochondrial bioenergetics and subsequent metabolic pathways. This was further confirmed by the changes in the activity of mitochondrial electron chain complexes (complex I, II, III, IV and V). The altered mtDNA methylation profile was also found to be closely associated with the varied expression of mitomiRs and their targets. CpPLC exposed cells showed up-regulation of miR24 expression and down-regulation of miR34a, miR150, and miR155, while the increased expression of mitomiR target genes i.e. of K-Ras, MYC, EGFR, and NF-kβ was also observed in these cells. Altogether, our findings provide novel insights into the derailment of redox signaling machinery in CpPLC treated lymphocytes and its role in the induction of survival mechanisms and mitochondrial-induced epigenetic modifications.

Clostridium perfringens Epsilon-Toxin Impairs the Barrier Function in MDCK Cell Monolayers in a Ca2+-Dependent Manner

Epsilon-toxin produced by Clostridium perfringens significantly contributes to the pathogeneses of enterotoxemia in ruminants and multiple sclerosis in humans. Epsilon-toxin forms a heptameric oligomer in the host cell membrane, promoting cell disruption. Here, we investigate the effect of epsilon-toxin on epithelial barrier functions. Epsilon-toxin impairs the barrier integrity of Madin-Darby Canine Kidney (MDCK) cells, as demonstrated by decreased transepithelial electrical resistance (TEER), increased paracellular flux marker permeability, and the decreased cellular localization of junctional proteins, such as occludin, ZO-1, and claudin-1. U73122, an endogenous phospholipase C (PLC) inhibitor, inhibited the decrease in TEER and the increase in the permeability of flux marker induced by epsilon-toxin. The application of epsilon-toxin to MDCK cells resulted in the biphasic formation of 1,2-diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP₃). U73122 blocked the formation of DAG and IP₃ induced by the toxin. Epsilon-toxin also specifically activated endogenous PLC-γ1. Epsilon-toxin dose-dependently increased the cytosolic calcium ion concentration ([Ca²⁺]i). The toxin-induced elevation of [Ca²⁺]i was inhibited by U73122. Cofilin is a key regulator of actin cytoskeleton turnover and tight-junction (TJ) permeability regulation. Epsilon-toxin caused cofilin dephosphorylation. These results demonstrate that epsilon-toxin induces Ca²⁺ influx through activating the phosphorylation of PLC-γ1 and then causes TJ opening accompanied by cofilin dephosphorylation.

Molecular structure and function of the carboxy-terminus of the alpha-toxin from Clostridium perfringens type A

In order to interpret the molecular structure and biological characteristics of Clostridium perfringens alpha-toxin (CPA), the CPA251-370 gene was cloned and the 120 amino acid carboxy terminal of CPA (CPA251-370) was obtained. The secondary and three-dimensional (3D) structures of CPA251-370 were predicted. The secondary structure of CPA251-370 consisted primarily of 35.48% β-sheets and 44.35% random coils. Compared with the CPA toxin consisting of 10 α-helices and eight β-sheets, the 3D structure of CPA251-370 only contained eight β-sheets. The circular dichroism (CD) spectrum detection showed that the CD spectrum of CPA251-370 changed slightly compared with the CD spectrum of CPA. Biological activity assays showed that CPA251-370 had lost the phospholipase C (PLC) activity and haemolytic activity of CPA. More importantly, the mice immunized with CPA251-370 were protected against a challenge with 1 MLD C. perfringens type A strain C57-1. This study laid a solid foundation for explaining the relationship between molecular structure and biological characteristics of CPA in the future. Our research also provides CPA251-370 as a candidate strains for genetic engineering subunit vaccines of C. perfringens type A.

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.

Study of the Structure and Biological Activity of the Amino-Terminus of the α-Toxin from Clostridium welchii Type A

To explore the biological activity of Clostridium welchii α-toxin (CPA), the Asp56 residue of CPA was mutated to glycine (CPA D56G) by site-directed mutagenesis, and the 250 amino acid amino-terminal phospholipase C (PLC)-containing domain of CPA (PLC1-250) was isolated. The secondary and three-dimensional (3D) structures of CPA D56G and PLC1-250 were predicted, and the results showed that the secondary structures of CPA D56G and PLC1-250 were composed of α-helices and random coils. The 3D structures of CPA D56G and PLC1-250 were similar to the 3D structures of CPA. The circular dichroism (CD) spectrum of CPA D56G differed from the CD spectrum of CPA, but the CD spectrum of PLC1-250 was similar to the CD spectrum of CPA. Biological activity assays showed that CPA D56G lost the PLC activity of CPA and that mice immunized with CPA D56G were protected against a challenge with 1 MLD C. welchii type A strain C57-1. In addition, PLC1-250 contained the PLC activity of CPA. This study laid a solid foundation for future studies on the relationship between the molecular structure and biological function of CPA and its molecular mechanism. Our study also provided CPA D56G as a candidate strain for engineering a CPA subunit vaccine for C. welchii type A.

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.

Protein Toxins That Utilize Gangliosides as Host Receptors

Subsets of protein toxins utilize gangliosides as host receptors. Gangliosides are preferred receptors due to their extracellular localization on the eukaryotic cell and due to their essential nature in host physiology. Glycosphingolipids, including gangliosides, are mediators of signal transduction within and between eukaryotic cells. Protein toxins possess AB structure-function organization, where the A domain encodes a catalytic function for the posttranslational modification of a host macromolecule, including proteins and nucleic acids, and a B domain, which encodes host receptor recognition, including proteins and glycosphingolipids, alone or in combination. Protein toxins use similar strategies to bind glycans by pockets and loops, generally employing hydrogen bonding and aromatic stacking to stabilize interactions with sugars. In some cases, glycan binding facilitates uptake, while in other cases, cross-linking or a second receptor is necessary to stimulate entry. The affinity that protein toxins have for host glycans is necessary for tissue targeting, but not always sufficient to cause disease. In addition to affinity for binding the glycan, the lipid moiety also plays an important role in productive uptake and tissue tropism. Upon endocytosis, the protein toxin must escape to another intracellular compartment or into cytosol to modify a host substrate, modulating host signaling, often resulting in cytotoxic or apoptotic events in the cell, and a unique morbidity for the organism. The study of protein toxins that utilize gangliosides as host receptors has illuminated numerous eukaryotic cellular processes, identified the basis for developing interventions to prevent disease through vaccines and control bacterial diseases through therapies. In addition, subsets of these protein toxins have been utilized as therapeutic agents to treat numerous human inflictions.

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.

Lipidomic profile of GM95 cell death induced by Clostridium perfringens alpha-toxin

Clostridium perfringens alpha-toxin (ATX) is considered as a prototype of cytotoxic bacterial phospholipases C, and is the major virulence factor in C. perfringens-induced gas gangrene. It is known that, depending on the dose, ATX causes membrane disruption and cytolysis or only limited hydrolysis of its substrates. In the latter case, toxin activity leads to the unregulated generation of bioactive lipids that can ultimately induce cell death. We have characterized apoptosis and necrosis in highly ATX-sensitive, ganglioside-deficient cells exposed to different concentrations of ATX and we have studied the lipidomic profile of cells treated with ATX as compared to native cells to detect the main changes in the lipidomic profile and the possible involvement of lipid signals in cell death. ATX causes both apoptosis and necrosis, depending on dose and time. ATX activates cell death, stimulating the release of cytochrome C from mitochondria and the consequent activation of caspases-3. Moreover GM95 cells treated with ATX showed important lipidomic alterations, among them we detected a general decrease in several phospholipid species and important changes in lipids involved in programmed cell death e.g. ceramide. The data suggest two different mechanisms of cell death caused by ATX, one leading to (mainly saturated) glycerophospholipid hydrolysis related to an increase in diacylglycerols and associated to membrane damage and necrosis, and a second mechanism involving chiefly sphingomyelin hydrolysis and generation of proapoptotic lipidic mediators such as ceramide, N-acylethanolamine and saturated non-esterified fatty acids.

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.

Membrane-Binding Mechanism of Clostridium perfringens Alpha-Toxin

Clostridium perfringens alpha-toxin is a key mediator of gas gangrene, which is a life-threatening infection that manifests as fever, pain, edema, myonecrosis, and gas production. Alpha-toxin possesses phospholipase C and sphingomyelinase activities. The toxin is composed of an N-terminal domain (1-250 aa, N-domain), which is the catalytic site, and a C-terminal domain (251-370 aa, C-domain), which is the membrane-binding site. Immunization of mice with the C-domain of alpha-toxin prevents the gas gangrene caused by C. perfringens, whereas immunization with the N-domain has no effect. The central loop domain (55-93 aa), especially H….SW(84)Y(85)….G, plays an important role in the interaction with ganglioside GM1a. The toxin binds to lipid rafts in the presence of a GM1a/TrkA complex, and metabolites from phosphatidylcholine to diacylglycerol through the enzymatic activity of alpha-toxin itself. These membrane dynamics leads to the activation of endogenous PLCγ-1 via TrkA. In addition, treatment with alpha-toxin leads to the formation of diacylglycerol at membrane rafts in ganglioside-deficient DonQ cells; this in turn triggers endocytosis and cell death. This article summarizes the current the membrane-binding mechanism of alpha-toxin in detail.