Porin from Pseudomonas aeruginosa induces apoptosis in an epithelial cell line derived from rat seminal vesicles

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

Bacteriospermia and Male Infertility: Role of Oxidative Stress

Male infertility is one of the major challenging and prevalent diseases having diverse etiologies of which bacteriospermia play a significant role. It has been estimated that approximately 15% of all infertility cases are due to infections caused by uropathogens and in most of the cases bacteria are involved in infection and inflammation leading to the development of bacteriospermia. In response to bacterial load, excess infiltration of leukocytes in the urogenital tract occurs and concomitantly generates oxidative stress (OS). Bacteria may induce infertility either by directly interacting with sperm or by generating reactive oxygen species (ROS) and impair sperm parameters such as motility, volume, capacitation, hyperactivation. They may also induce apoptosis leading to sperm death. Acute bacteriospermia is related with another clinical condition called leukocytospermia and both compromise male fertility potential by OS-mediated damage to sperm leading to male infertility. However, bacteriospermia as a clinical condition as well as the mechanism of action remains poorly understood, necessitating further research in order to understand the role of individual bacterial species and their impact in male infertility.

The toxicity of Aspidosperma subincanum to MCF7 cells is related to modulation of oxidative status and proinflammatory pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Cancer is an inflammatory disease because carcinogenesis and tumor progression depend on intrinsic and extrinsic inflammatory pathways. Although species of the genus Aspidosperma are widely used to treat tumors, and there is ethnopharmacological evidence for traditional use of the species A. subincanum as an anti-inflammatory agent, its antineoplastic potential is unknown.

AIM OF THE STUDY

To evaluate toxic effects of the indole alkaloid-rich fraction (IAF) of A. subincanum on the MCF7 cell line and identify some of the anti-inflammatory mechanisms involved.

MATERIALS AND METHODS

Chromatographic analyses were performed by ultra-high-performance liquid chromatography with electrospray ionization mass spectrometry, and cytotoxic and antiproliferative effects of IAF were verified by MTT and clonogenic assays. Cell cycle alterations were analyzed by measuring DNA content, while propidium iodide and acridine orange staining was performed to determine the type of induced cell death. The expression of apoptosis markers and proteins involved in cell proliferation and survival pathways was analyzed by immunoblotting, RT-qPCR, and ELISAs. Interference with redox status was investigated using a DCFH-DA probe and by measuring catalase activity.

RESULTS

Chromatographic analyses showed that IAF is a complex mixture containing indole alkaloids. IAF selectively exerted toxic and antiproliferative effects, elevating the Bax/Bcl-xL ratio and inducing apoptosis in MCF7 cells. IAF decreased intracellular reactive oxygen species levels and increased catalase activity, while reducing the IL-8 level and suppressing COX-2 expression.

CONCLUSIONS

IAF induces apoptosis in MCF7 cells by suppressing COX-2 expression while reducing IL-8 levels and intracellular content of reactive oxygen species.

Bacterial Infections Affect Male Fertility: A Focus on the Oxidative Stress-Autophagy Axis

Numerous factors trigger male infertility, including lifestyle, the environment, health, medical resources and pathogenic microorganism infections. Bacterial infections of the male reproductive system can cause various reproductive diseases. Several male reproductive organs, such as the testicles, have unique immune functions that protect the germ cells from damage. In the reproductive system, immune cells can recognize the pathogen-associated molecular patterns carried by pathogenic microorganisms and activate the host's innate immune response. Furthermore, bacterial infections can lead to oxidative stress through multiple signaling pathways. Many studies have revealed that oxidative stress serves dual functions: moderate oxidative stress can help clear the invaders and maintain sperm motility, but excessive oxidative stress will induce host damage. Additionally, oxidative stress is always accompanied by autophagy which can also help maintain host homeostasis. Male reproductive system homeostasis disequilibrium can cause inflammation of the genitourinary system, influence spermatogenesis, and even lead to infertility. Here, we focus on the effect of oxidative stress and autophagy on bacterial infection in the male reproductive system, and we also explore the crosslink between oxidative stress and autophagy during this process.

Modulation of host cellular responses by gram-negative bacterial porins

The outer membrane of a gram-negative bacteria encapsulates the plasma membrane thereby protecting it from the harsh external environment. This membrane acts as a sieving barrier due to the presence of special membrane-spanning proteins called "porins." These porins are β-barrel channel proteins that allow the passive transport of hydrophilic molecules and are impermeable to large and charged molecules. Many porins form trimers in the outer membrane. They are abundantly present on the bacterial surface and therefore play various significant roles in the host-bacteria interactions. These include the roles of porins in the adhesion and virulence mechanisms necessary for the pathogenesis, along with providing resistance to the bacteria against the antimicrobial substances. They also act as the receptors for phage and complement proteins and are involved in modulating the host cellular responses. In addition, the potential use of porins as adjuvants, vaccine candidates, therapeutic targets, and biomarkers is now being exploited. In this review, we focus briefly on the structure of the porins along with their important functions and roles in the host-bacteria interactions.

OmpF porin from Yersinia ruckeri as pathogenic factor: Surface antigenic sites and biological properties

Bacterium Yersinia ruckeri as a pathogen induces causative agent of intestinal fish disease called enteric redmouth disease (ERM) is known. In this study, outer membrane OmpF porin from the Y. ruckeri (YrOmpF) has been identified as a pathogenic factor which affects host macrophage activation and life cycle of eukaryotic cells. Using synthetic peptides corresponding to the sequences of the outer loops of YrOmpF L1 loop of the porin is most involved in the structure of B epitopes on the surface of the microbial cell it was found. T epitopes of the isolated YrOmpF trimer not only by linear, but also by discontinuous determinants, which is due to the secondary structure of the protein are represented. It was shown that YrOmpF was twice more cytotoxic to THP-1 cells (human monocytes, cancer cells) in comparison with CHH-1 cells (Oncorhynchus keta cardiac muscle cell, non-cancer cells). It was found YrOmpF induce cell cycle S-phase arrest in both normal CHH-1 and cancer THP-1 cells. In the cancer cells observed effect was most pronounce. In addition, we have observed an induction of apoptosis in THP-1 cell line treated with YrOmpF for 48 h at IC₅₀ (48.6 μg/ml). Significant cytotoxic effect of YrOmpF on primary mouse peritoneal macrophages been detected as well. Of note, co-incubation of macrophages with anti-YrOmpF antibodies could decrease the amount of lactate dehydrogenase, while the number of living cells significantly increased. YrOmpF stimulates the activity of the phagocytic bactericidal systems especially of the oxygen-independent subsystem it was found. Antibodies against YrOmpF decreased MPO release and CP synthesis by peritoneal macrophages and increased their viability.

Bacterial infection of the male reproductive system causing infertility

Bacterial infections play a disruptive and hidden role in male reproductive failure. Different kinds of bacteria are often able to interfere with reproductive function in both sexes and lead to infertility. In this study, to further evaluate the role of bacterial infections in male reproduction we provided an extensive overview of so far researches investigating the effects of bacterial infections on male fertility. We searched Medline, PubMed, Scopus and Google scholar databases to identify the potentially relevant studies on bacterial infections and their implications in male infertility. All the bacteria included in this article have negative effects on the male reproductive function; however, there is ample evidence to blame bacteria such as Escherichia coli, Chlamydia trachomatis, Ureaplasma, Mycoplasma and Staphylococcus aureus for reduced fertility and deterioration of sperm parameters. More studies are needed to clarify the molecular mechanisms by which different bacteria exert their detrimental effects on male reproductive system. Getting more insight into probable mechanisms, would significantly facilitate the production of new, advanced, and effective remedies in the future. In view of all evidence, we strongly suggest increasing awareness among people and considering screening programs for patients seeking fertility both to avoid transmission and to improve fertility outcomes among them.

Outer membrane vesicles from Neisseria gonorrhoeae target PorB to mitochondria and induce apoptosis

Neisseria gonorrhoeae causes the sexually transmitted disease gonorrhoea by evading innate immunity. Colonizing the mucosa of the reproductive tract depends on the bacterial outer membrane porin, PorB, which is essential for ion and nutrient uptake. PorB is also targeted to host mitochondria and regulates apoptosis pathways to promote infections. How PorB traffics from the outer membrane of N. gonorrhoeae to mitochondria and whether it modulates innate immune cells, such as macrophages, remains unclear. Here, we show that N. gonorrhoeae secretes PorB via outer membrane vesicles (OMVs). Purified OMVs contained primarily outer membrane proteins including oligomeric PorB. The porin was targeted to mitochondria of macrophages after exposure to purified OMVs and wild type N. gonorrhoeae. This was associated with loss of mitochondrial membrane potential, release of cytochrome c, activation of apoptotic caspases and cell death in a time-dependent manner. Consistent with this, OMV-induced macrophage death was prevented with the pan-caspase inhibitor, Q-VD-PH. This shows that N. gonorrhoeae utilizes OMVs to target PorB to mitochondria and to induce apoptosis in macrophages, thus affecting innate immunity.

Neisseria gonorrhoeae causes the sexually transmitted disease gonorrhoea in more than 100 million people worldwide every year. The bacteria replicate in the reproductive tract by evading innate and adaptive immunity. In the absence of effective vaccines and the rise of antibiotic resistance, understanding the molecular interactions between innate immune cells and N. gonorrhoeae may lead to new strategies to combat bacterial growth and the symptoms of gonorrhoea. It has long been known that the N. gonorrhoeae porin, PorB, promotes bacterial survival but also targets host mitochondria in infections. The mechanism by which PorB traffics form the bacterial outer membrane to host mitochondria remains unclear. Here, we utilized proteomics and super-resolution microscopy to show that N. gonorrhoeae secretes PorB via outer membrane vesicles. These vesicles are taken up by macrophages and deliver PorB to mitochondria. Macrophages treated with N. gonorrhoeae vesicles contained damaged mitochondria and active caspase-3. A caspase inhibitor prevented apoptosis of macrophages treated with N. gonorrhoeae vesicles. This suggests that N. gonorrhoeae secretes membrane vesicles, which are readily detectable in gonorrhoea patients, to target macrophages and to promote infections.

Vibrio cholerae Porin OmpU Induces Caspase-independent Programmed Cell Death upon Translocation to the Host Cell Mitochondria

Porins, a major class of outer membrane proteins in Gram-negative bacteria, primarily act as transport channels. OmpU is one of the major porins of human pathogen, Vibrio cholerae. In the present study, we show that V. cholerae OmpU has the ability to induce target cell death. Although OmpU-mediated cell death shows some characteristics of apoptosis, such as flipping of phosphatidylserine in the membrane as well as cell size shrinkage and increased cell granularity, it does not show the caspase-3 activation and DNA laddering pattern typical of apoptotic cells. Increased release of lactate dehydrogenase in OmpU-treated cells indicates that the OmpU-mediated cell death also has characteristics of necrosis. Further, we show that the mechanism of OmpU-mediated cell death involves major mitochondrial changes in the target cells. We observe that OmpU treatment leads to the disruption of mitochondrial membrane potential, resulting in the release of cytochrome c and apoptosis-inducing factor (AIF). AIF translocates to the host cell nucleus, implying that it has a crucial role in OmpU-mediated cell death. Finally, we observe that OmpU translocates to the target cell mitochondria, where it directly initiates mitochondrial changes leading to mitochondrial membrane permeability transition and AIF release. Partial blocking of AIF release by cyclosporine A in OmpU-treated cells further suggests that OmpU may be inducing the opening of the mitochondrial permeability transition pore. All of these results lead us to the conclusion that OmpU induces cell death in target cells in a programmed manner in which mitochondria play a central role.

Macrophage Cell Death Due toSalmonella entericaSerovar Typhi and Its Acid Stress Protein Has Features of Apoptosis

Salmonella spp. have been shown to cause apoptosis of various host cell types as a part of their infection process. However, the induction of apoptosis remains to be looked into under the different host environments including acidic stress experienced by the pathogen. In order to simulate the in vivo acidic conditions, we studied the potential of S. typhi and its protein expressed under in vitro acidic conditions to induce apoptosis in macrophages. Murine macrophages were isolated and interacted with serovar Typhi and its acid stress protein for different time periods. The assessment of nucleosomal DNA, and nuclear staining with H-33342 dye and flow cytometry indicated the occurrence of characteristic features of apoptosis. Analysis of data revealed that S. typhi caused apoptotic cell death in 61% of macrophages whereas stress-induced protein alone accounted for apoptotic cell death in 45% of macrophages. The present study, for the first time demonstrates the potential of stress-induced outermembrane component of S. typhi to induce apoptosis. Identification of such factors may offer new insights for understanding the pathophysiology of the disease during the host-pathogen interactions.

Platelet-activating factor receptor initiates contact of Acinetobacter baumannii expressing phosphorylcholine with host cells

Adhesion is an initial and important step in Acinetobacter baumannii causing infections. However, the exact molecular mechanism of such a step between A. baumannii and the host cells remains unclear. Here, we demonstrated that the phosphorylcholine (ChoP)-containing outer membrane protein of A. baumannii binds to A549 cells through platelet-activating factor receptor (PAFR), resulting in activation of G protein and intracellular calcium. Upon A. baumannii expressing ChoP binding to PAFR, clathrin and β-arrestins, proteins involved in the direction of the vacuolar movement, are activated during invasion of A. baumannii. PAFR antagonism restricts the dissemination of A. baumannii in the pneumonia model. These results define a role for PAFR in A. baumannii interaction with host cells and suggest a mechanism for the entry of A. baumannii into the cytoplasm of host cells.

Acinetobacter baumannii-induced lung cell death: role of inflammation, oxidative stress and cytosolic calcium

A growing body of evidence supports the notion that susceptible Acinetobacter baumannii strain ATCC 19606 induces human epithelial cells death. However, most of the cellular and molecular mechanisms associated with this cell death remain unknown, and also the degree of the cytotoxic effects of a clinical panresistant strain compared with a susceptible strain has never been studied. Due to the role of proinflammatory cytokine release, oxidative stress and cytosolic calcium increase in the cell death-induced by other Gram-negative bacteria, we investigated whether these intracellular targets were involved in the cell death induced by clinical panresistant 113-16 and susceptible ATCC 19606 strains. Data presented here show that 113-16 and ATCC 19606 induce time-dependent cell death of lung epithelial cells involving a perturbation of cytosolic calcium homeostasis with subsequent calpain and caspase-3 activation. Prevention of this cell death by TNF-α and interleukin-6 blockers and antioxidant highlights the involvement of proinflammatory cytokines and oxidative stress in this phenomenon. These results demonstrate the involvement of calpain calcium-dependent in cell death induced by A. baumannii and the impact of proinflammatory cytokines and oxidative stress in this cell death; it is noteworthy to stress that some mechanisms are less induced by the panresistant strain.

Bacterial ortholog of mammalian translocator protein (TSPO) with virulence regulating activity

The translocator protein (TSPO), previously designated as peripheral-type benzodiazepine receptor, is a protein mainly located in the outer mitochondrial membrane of eukaryotic cells. TSPO is implicated in major physiological functions and functionally associated with other proteins such as the voltage-dependent anionic channel, also designated as mitochondrial porin. Surprisingly, a TSPO-related protein was identified in the photosynthetic bacterium Rhodobacter sphaeroides but it was initially considered as a relict of evolution. In the present study we cloned a tspO gene in Pseudomonas fluorescens MF37, a non-photosynthetic eubacterium and we used bioinformatics tools to identify TSPO in the genome of 97 other bacteria. P. fluorescens TSPO was recognized by antibodies against mouse protein and by PK 11195, an artificial ligand of mitochondrial TSPO. As in eukaryotes, bacterial TSPO appears functionally organized as a dimer and the apparent Kd for PK 11195 is in the same range than for its eukaryotic counterpart. When P. fluorescens MF37 was treated with PK 11195 (10(-5) M) adhesion to living or artificial surfaces and biofilm formation activity were increased. Conversely, the apoptotic potential of bacteria on eukaryotic cells was significantly reduced. This effect of PK11195 was abolished in a mutant of P. fluorescens MF37 deficient for its major outer membrane porin, OprF. The present results demonstrate the existence of a bacterial TSPO that shares common structural and functional characteristics with its mammalian counterpart. This protein, apparently involved in adhesion and virulence, reveals the existence of a possible new inter kingdom signalling system and suggests that the human microbiome should be involuntarily exposed to the evolutionary pressure of benzodiazepines and related molecules. This discovery also represents a promising opportunity for the development of alternative antibacterial strategies.

Anti-inflammatory effects of moxifloxacin and human beta-defensin 2 association in human lung epithelial cell line (A549) stimulated with lipopolysaccharide

Epithelia in the human airways, from the nasal aperture to the alveoli, are covered in a protective film of fluid containing a number of antimicrobial proteins. Defensins are single-chain, strongly cationic peptides and are one of the most extensively studied classes of antimicrobial peptides. Moxifloxacin (MXF) is a fluoroquinolone that acts against both Gram positive and Gram negative bacteria. In this study, we evaluated the effects of HBD2, MXF and the association MXF/HBD2 on some cytokines and on the ICAM-1 expression in LPS-stimulated A549 cells. Our results suggest that by lowering the epithelial cell-derived IL-1beta, IL-6, IL-8 and ICAM-1 expression, the MXF/HBD2 association interferes with the multifunctional cytokine network evolving during inflammatory processes of the respiratory tract; this anti-inflammatory potential could be of great value in the treatment of inflammatory disorders.

Reactive nitrogen intermediates and monokines induce caspase-3 mediated macrophage apoptosis by anaerobically stressed Salmonella typhi

A successful pathogen manipulates its host for its own benefit. After ingestion, on reaching the intestine Salmonella encounters the resident tissue macrophages. Rather than being destroyed by these professional phagocytes after internalization, Salmonella survives intracellularly. Invasive Salmonella has been reported to induce apoptosis of macrophages as a part of its infection process, which may allow it to avoid detection by the innate immune system. However, the induction of apoptosis under different host environments, including the anaerobic stress encountered by the pathogen in the gut, remains to be examined. The present study is aimed at investigating the apoptotic potential of S. enterica serovar Typhi (S. typhi) grown under anaerobic conditions simulating the in vivo situation encountered by the pathogen. Apoptotic cell death was determined by assessment of nucleosomal DNA and flow cytometric analysis. Evaluation of the data revealed that anaerobically grown S. typhi could induce apoptosis in significantly more number of macrophages compared to the bacterial cells grown under aerobic conditions. A significantly enhanced generation of reactive nitrogen intermediates and caspase-3 activity during macrophage apoptosis induced by anaerobic S. typhi correlated with the increased generation of tumour necrosis factor-alpha, interleukin (IL)-1alpha and IL-6. The results indicate that reactive nitrogen intermediates and monokines induce caspase-3 mediated apoptosis of macrophages by S. typhi under anaerobic conditions. These findings may be relevant for clearer understanding of the Salmonella-macrophage interactions and may be of clinical importance in the development of preventive intervention against the infection.

Influence of bacteria and gentamicin on cooled-stored stallion spermatozoa

This study investigated effects of bacteria from the genital tract of horses and the effect of gentamicin in semen extender on spermatozoal function in cooled-stored stallion semen. Semen was collected from healthy stallions and processed with a milk-based extender with or without gentamicin (1g/l). Pseudomonas (Ps.) aeruginosa, Staphylococcus (St.) aureus, Streptococcus (Sc.) equi subsp. equi (Sc. equi), Sc. equi subsp. zooepidemicus (Sc. zooepidemicus), Sc. dysgalactiae subsp. equisimilis (Sc. equisimilis) or culture medium alone (control) were added. Immediately after addition of bacteria and after storage at 5 degrees C for 24, 48 and 72h, motility, velocity and membrane integrity of diluted semen were determined with a CASA system. After 24h, semen with Ps. aeruginosa and Sc. equisimilis showed significantly lower motility and velocity compared to all other groups; after 72h these differences still existed for Ps. aeruginosa (p<0.05). The percentage of membrane-intact spermatozoa was significantly lower after 24h of storage in spermatozoa incubated with Sc. equisimilis and after 72h with Sc. equisimilis and Ps. aeruginosa. Addition of gentamicin to extender resulted in decreased motility and velocity in semen without addition of bacteria and did not improve motility parameters in semen with bacteria added. In conclusion, certain bacteria may have detrimental effects on semen quality during cooled-storage. These effects are not reduced by addition of gentamicin. Gentamicin can negatively affect spermatozoal function in extended semen during cooled-storage and therefore, optimal concentrations have to be tested for the respective extender medium.

Expression of Pseudomonas aeruginosa toxin ExoS effectively induces apoptosis in host cells

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that primarily infects immunocompromised individuals and patients with cystic fibrosis. Invasive strains of P. aeruginosa are known to induce apoptosis at a high frequency in HeLa cells and in many other cell lines, a process that is dependent on the ADP-ribosylation (ADPRT) activity of a type III secreted protein ExoS. In our previous report, it was proposed that P. aeruginosa secreting ExoS, upon infection, shuts down host cell survival signal pathways by inhibiting ERK1/2 and p38 activation, and it activates proapoptotic pathways through activation of JNK1/2, leading ultimately to cytochrome c release and activation of caspases. In this study, we demonstrate that the expression of ExoS in HeLa cells by eukaryotic expression vector effectively caused apoptosis in an ADPRT activity-dependent manner, indicating that ExoS alone is sufficient to trigger apoptotic death of host cells independent of any other bacterial factors. By expressing an EGFP-ExoS fusion protein, we were able to directly correlate the death of HeLa cells with the presence of intracellular ExoS and further proved the dependence of this process on both JNK activation and mitochondrial proapoptotic event. The cellular pathway responsible for the ExoS-induced cytotoxicity appears to be well conserved, since the expression of the ADPRT-competent ExoS also induced rapid cell death in the Drosophila melanogaster S2 cell lines. The presented study not only highlights the ability of ExoS ADPRT to modulate host cell signaling, eventually leading to apoptosis, but also establishes ExoS as a valuable tool, in principle, for the elucidation of apoptosis mechanisms.

Involvement of caspase-3, lipid peroxidation and TNF-alpha in causing apoptosis of macrophages by coordinately expressed Salmonella phenotype under stress conditions

Invasive Salmonella has been reported to induce apoptosis of macrophages as a part of its infection process, which may allow it to avoid detection by the innate immune system. However, the bacterial components capable of inducing apoptosis, particularly under the environments offered by the host have not been fully identified. Therefore, in the present study, attempts were made to evaluate the apoptotic potential of Salmonella enterica serovar Typhi (S. typhi) outer membrane protein expressed under stress conditions like iron, oxidative and anaerobic simulating the in vivo situations encountered by the pathogen. Analysis of data revealed that a coordinately expressed 69kDa outer membrane protein (OMP) expressed with enhanced intensity under iron, oxidative and anaerobic stress conditions caused apoptotic cell death in 51% of macrophages, whereas OMPs of S. typhi extracted under normal conditions accounted for apoptotic cell death in only 31% of macrophages. A significantly enhanced activity of caspase-3 was observed during macrophage-apoptosis induced by this protein. A significant increase in the extent of lipid peroxidation (levels of oxidant) and decrease in the activities of antioxidants was also observed which correlated with the increased generation of tumor necrosis factor-alpha, interleukine-1alpha and interleukine-6. These results suggest that caspase-3 and tumor necrosis factor-alpha in conjunction with other cytokines may induce apoptotic cell death through the up-regulation of oxidants and down-regulation of antioxidants. These findings may be relevant for the better understanding of the disease pathophysiology and for the future developments of diagnostic and preventive strategies during the host-pathogen interactions.

Outer membrane protein 38 of Acinetobacter baumannii localizes to the mitochondria and induces apoptosis of epithelial cells

Acinetobacter baumannii is an important opportunistic pathogen responsible for nosocomial infection. Despite considerable clinical and epidemiological data regarding the role of A. baumannii in nosocomial infection, the specific virulence factor or pathogenic mechanism of this organism has yet to be elucidated. This study investigated the molecular mechanism of apoptosis on the infection of human laryngeal epithelial HEp-2 cells with A. baumannii and examined the contribution of outer membrane protein 38 (Omp38) on the ability of A. baumannii to induce apoptosis of epithelial cells. A. baumannii induced apoptosis of HEp-2 cells through cell surface death receptors and mitochondrial disintegration. The Omp38-deficient mutant was not as able to induce apoptosis as the wild-type A. baumannii strain. Purified Omp38 entered the cells and was localized to the mitochondria, which led to a release of proapoptotic molecules such as cytochrome c and apoptosis-inducing factor (AIF). The activation of caspase-3, which is activated by caspase-9, degraded DNA approximately 180 bp in size, which resulted in the appearance of a characteristic DNA ladder. AIF degraded chromosomal DNA approximately 50 kb in size, which resulted in large-scale DNA fragmentation. These results demonstrate that Omp38 may act as a potential virulence factor to induce apoptosis of epithelial cells in the early stage of A. baumannii infection.

Macrophage inflammatory protein-2, neutrophil recruitment and bacterial persistence in an experimental mouse model of urinary tract infection

This study analyzed macrophage inflammatory protein-2 (MIP-2) production and neutrophil recruitment in urinary tract in response to Pseudomonas aeruginosa in an ascending model of urinary tract infection (UTI) in mice. Both planktonic and biofilm cells of P. aeruginosa were used for inducing UTI in mice. MIP-2 levels determined in urine, bladder and kidney showed maximum MIP-2 production 6 h postinfection, which correlated with neutrophil recruitment. Biofilm cells showed significantly more MIP-2 production and neutrophil recruitment. However, no correlation between bacterial numbers and neutrophil recruitment was observed in urine and kidney tissue. The role of MIP-2 and neutrophils in relation to the persistence of P. aeruginosa in the urinary tract of mice is discussed.

The porin MspA from Mycobacterium smegmatis improves growth of Mycobacterium bovis BCG

Mycobacteria are characterized by an extremely thick hydrophobic cell wall restricting the permeability for small hydrophilic compounds. Recently, a new efficient porin (MspA) has been identified in Mycobacterium smegmatis, which is lacking in slow-growing mycobacteria. Since we were interested in investigating the influence of porins on growth of slow-growing Mycobacterium bovis BCG, we inserted a 3429 bp DNA fragment from M. smegmatis carrying the mspA gene in an integrative vector and transferred it into M. bovis BCG. Expression of mspA in the BCG derivative was shown by RT-PCR and Western blot. Quantification of bacterial growth on agar plates demonstrated two- to four-fold better growth of the BCG derivative with the transferred DNA compared with the reference strain. Transposon mutagenesis proved the mspA gene to be responsible for the growth enhancement. Intracellular multiplication of the BCG derivative in the mouse macrophage cell line J774 and the human pneumocyte cell line A549 was also clearly enhanced pointing to a possible role of porins in the interaction of mycobacteria with their hosts.

The Pseudomonas aeruginosa autoinducer N-3-oxododecanoyl homoserine lactone accelerates apoptosis in macrophages and neutrophils

Quorum-sensing systems are critical regulators of the expression of virulence factors of various organisms, including Pseudomonas aeruginosa. Las and Rhl are two major quorum-sensing components, and they are regulated by their corresponding autoinducers, N-3-oxododecanoyl homoserine lactone (3-oxo-C(12)-HSL) and N-butyryl-L-homoserine lactone (C(4)-HSL). Recent progress has demonstrated the potential of quorum-sensing molecules, especially 3-oxo-C(12)-HSL, for modulation of the host immune system. Here we show the specific ability of 3-oxo-C(12)-HSL to induce apoptosis in certain types of cells. When bone marrow-derived macrophages were incubated with synthetic 3-oxo-C(12)-HSL, but when they were incubated not C(4)-HSL, significant loss of viability was observed in a concentration (12 to 50 micro M)- and incubation time (1 to 24 h)-dependent manner. The cytotoxic activity of 3-oxo-C(12)-HSL was also observed in neutrophils and monocytic cell lines U-937 and P388D1 but not in epithelial cell lines CCL-185 and HEp-2. Cells treated with 3-oxo-C(12)-HSL revealed morphological alterations indicative of apoptosis. Acceleration of apoptosis in 3-oxo-C(12)-HSL-treated cells was confirmed by multiple criteria (caspases 3 and 8, histone-associated DNA fragments, phosphatidylserine expression). Structure-activity correlation experiments demonstrated that the fine structure of 3-oxo-C(12)-HSL, the HSL backbone, and side chain length are required for maximal activity. These data suggest that Pseudomonas 3-oxo-C(12)-HSL specifically promotes induction of apoptosis, which may be associated with 3-oxo-C(12)-HSL-induced cytotoxicity in macrophages and neutrophils. Our data suggest that the quorum-sensing molecule 3-oxo-C(12)-HSL has critical roles in the pathogenesis of P. aeruginosa infection, not only in the induction of bacterial virulence factors but also in the modulation of host responses.

Bacterial components induce cytokine and intercellular adhesion molecules-1 and activate transcription factors in dermal fibroblasts

This study investigated the effect of various structural components of Gram-positive (lipotheichoic acid and protein A) and Gram-negative (porins and lipopolysaccharide) bacteria on human dermal fibroblasts. Fibroblasts are important effector cells which have a potential role in augmenting the inflammatory response in various diseases. In this study we present a profile of TNF-alpha, IL-6 and IL-8, the expression of intercellular adhesion molecules (ICAM-1) and the activation of transcriptional nuclear factor NF-kB and AP-1 in human dermal fibroblasts stimulated by bacterial surface components. Compared to the controls, increased ICAM-1, IL-6 and IL-8 gene expression after stimulation of LPS and porins at 2 and 4 h was more evident than that obtained following stimulation of LTA and PA. Gene expression was also associated with the production of cytokine proteins in culture supernatants. TNF-alpha gene expression remained undetectable. Moreover, LPS and porin treatments determined IkBalpha phosphorylation and degradation in human dermal fibroblasts and the subsequent activation of nuclear factors NF-kB and AP-1. These data suggest the importance of such stimuli in the first step of the inflammatory process, as well as the important role played by fibroblasts in skin inflammatory disease.

The functions of OmpATb, a pore-forming protein of Mycobacterium tuberculosis

The functions of OmpATb, the product of the ompATb gene of Mycobacterium tuberculosis and a putative porin, were investigated by studying a mutant with a targeted deletion of the gene, and by observing expression of the gene in wild-type M. tuberculosis H37Rv by real-time polymerase chain reaction (PCR) and immunoblotting. The loss of ompATb had no effect on growth under normal conditions, but caused a major reduction in ability to grow at reduced pH. The gene was substantially upregulated in wild-type bacteria exposed to these conditions. The mutant was impaired in its ability to grow in macrophages and in normal mice, although it was as virulent as the wild type in mice that lack T cells. Deletion of the ompATb gene reduced permeability to several small water-soluble substances. This was particularly evident at pH 5.5; at this pH, uptake of serine was minimal, suggesting that, at this pH, OmpATb might be the only functioning porin. These data indicate that OmpATb has two functions: as a pore-forming protein with properties of a porin, and in enabling M. tuberculosis to respond to reduced environmental pH. It is not known whether this second function is related to the porin-like activity at low pH or involves a completely separate role for OmpATB. The involvement with pH is likely to contribute to the ability of M. tuberculosis to overcome host defence mechanisms and grow in a mammalian host.

Pseudomonas aeruginosa outer membrane protein F is an adhesin in bacterial binding to lung epithelial cells in culture

Adherence to host cells is a crucial step by which bacteria initiate an infection but the bacterial determinants of the process are, as yet, poorly understood. In an effort to identify bacterial adhesins responsible for Pseudomonas aeruginosa binding to host cells, we identified porin F (OprF) from the outer membrane of P. aeruginosa as adhesin for human alveolar epithelial (A549) cells. Bacterial adhesion assays with (35)S-labeled wild type P. aeruginosa and its isogenic mutant strain lacking OprF showed that the mutant strain binds 43% less than the wild type to A549 cells (P<0.01). In addition, bacterial binding is significantly reduced (P<0.01) when either A549 cells were pretreated with purified OprF or if bacteria were pre-incubated with a monoclonal antibody to OprF. Finally, ligand binding experiments in which purified OprF protein was added to A549 monolayers showed saturable binding. These data indicate that OprF contributes to bacterial adherence to A549 epithelial cells and could facilitate Pseudomonas interactions with the epithelium, including colonization of the airway epithelium or the initiation of pulmonary infection.

Isolation and characterisation of the major outer membrane protein of Erwinia carotovora

The purified major outer membrane protein (37275 Da) from the psychrotrophic phytopathogen Erwinia carotovora MFCL0 was structurally characterised by MALDI-TOF mass spectrometry, N-terminal microsequencing and DNA sequence determinations, and secondary structure prediction analyses. The deduced amino acid sequence showed 76% and 72% of similarities with the Serratia marcescens and Escherichia coli OmpA proteins respectively. Dendrogram analysis allowed to point out that E. carotovora is close to the genus Serratia. After reconstitution into planar lipid bilayers, this major protein induced ion channels with a major conductance level of 630 pS in 1 M NaCl and a weak cationic selectivity. These functional and structural features allowed to identify this major outer membrane component of E. carotovora as an OmpA-like protein, i.e., a channel-forming protein which could be involved in the infection process of this phytopathogen agent.

Pseudomonas fluorescens as a potential pathogen: adherence to nerve cells

In order to determine the infectious potential of the psychrotrophic bacterium Pseudomonas fluorescens, a species closely related to the opportunistic pathogen P. aeruginosa, we investigated the binding activity of this bacterium on primary cultures of rat neonate cortical neurons and glial cells, adrenal paraneurons and NG108-15 neuroblastoma cells. Incubated at concentrations of 10(6) and 10(8) CFU/mL, P. fluorescens MF37 exhibited a high binding activity on neurons in the same range as that of P. aeruginosa PAO1. A significant, but lower, adherence of P. fluorescens was also detected on glial cells and adrenal paraneurons. In contrast, when P. fluorescens MF37 or P. aeruginosa PAO1 were incubated with neuroblastoma cells, no binding was observed. In neurons, the association of P. fluorescens with the plasma membrane occurred both on neurites and cell body. Leakage of the cytoplasmic content was frequently noted. Studies performed using the fluorescent probe Hoechst 33258 revealed that in 10% of neurons, P. fluorescens induced the appearance of densely stained clusters of DNA that was typical of an early step of apoptosis. In glial cells exposed to P. fluorescens, marked changes in the morphology of the nucleus, including fragmentation into lobular structures and aggregation of DNA, were also reminiscent of the existence of a possible apoptotic mechanism. Taken together, these results reveal that P. fluorescens can bind to nerve cells and affect their physiology and, in agreement with recent clinical observations, suggest that P. fluorescens could behave as a pathogen.

A spirochete surface protein uncouples store-operated calcium channels in fibroblasts: a novel cytotoxic mechanism

The cytotoxicity of infectious agents can be mediated by disruption of calcium signaling in target cells. Outer membrane proteins of the spirochete Treponema denticola, a periodontal pathogen, inhibit agonist-induced Ca(2+) release from internal stores in gingival fibroblasts, but the mechanism is not defined. We determined here that the major surface protein (Msp) of T. denticola perturbs calcium signaling in human fibroblasts by uncoupling store-operated channels. Msp localized in complexes on the cell surface. Ratio fluorimetry showed that in cells loaded with fura-2 or fura-C18, Msp induced cytoplasmic and near-plasma membrane Ca(2+) transients, respectively. Increased conductance was confirmed by fluorescence quenching of fura-2-loaded cells with Mn(2+) after Msp treatment. Calcium entry was blocked with anti-Msp antibodies and inhibited by chelating external Ca(2+) with EGTA. Msp pretreatment reduced the amplitude of [Ca(2+)](i) transients upon challenge with ATP or thapsigargin. In experiments using cells loaded with mag-fura-2 to report endoplasmic reticulum Ca(2+), Msp reduced Ca(2+) efflux from endoplasmic reticulum stores when ATP was used as an agonist. Msp alone did not induce Ca(2+) release from these stores. Msp inhibited store-operated influx of extracellular calcium following intracellular Ca(2+) depletion by thapsigargin and also promoted the assembly of subcortical actin filaments. This actin assembly was blocked by chelating intracellular Ca(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester. The reduced amplitude of agonist-induced transients and inhibition of store-operated Ca(2+) entry due to Msp were reversed by latrunculin B, an inhibitor of actin filament assembly. Thus, Msp retards Ca(2+) release from endoplasmic reticulum stores, and it inhibits subsequent Ca(2+) influx by uncoupling store-operated channels. Actin filament rearrangement coincident with conformational uncoupling of store-operated calcium fluxes is a novel mechanism by which surface proteins and toxins of pathogenic microorganisms may damage host cells.

Apoptotic signaling pathway activated by Helicobacter pylori infection and increase of apoptosis-inducing activity under serum-starved conditions

The enhanced gastric epithelial cell apoptosis observed during infection with Helicobacter pylori has been suggested to be of significance in the etiology of gastritis, peptic ulcers, and neoplasia. To investigate the cell death signaling induced by H. pylori infection, human gastric epithelial cells were incubated with H. pylori for up to 72 h. H. pylori infection induced the activation of caspase -8, -9, and -3 and the expression of the proapoptotic Bcl-2 family proteins Bad and Bid. The peak of the activity of the caspases occurred at 24 h. At this time, the inhibition of caspase-8 or -9 almost completely suppressed H. pylori-induced apoptosis. Inhibition of caspase-8 suppressed the expression of Bad and Bid and the subsequent activation of caspase-9 and -3. These observations indicate that H. pylori induces apoptosis through a pathway involving the sequential induction of apical caspase-8 activity, the proapoptotic proteins Bad and Bid, caspase-9 activity, and effector caspase-3 activity. Activation of the pathway was independent of CagA or vacuolating toxin. A membrane fraction of H. pylori was sufficient to activate this pathway, and treatment with proteinase K eliminated the activity. Apoptotic activity of the membrane fraction was significantly increased by incubating the bacteria under serum-starved conditions for 24 h. These observations suggest that environmental conditions in the human stomach could induce H. pylori-mediated pathogenesis, leading to a variety of clinical outcomes.

Pyelonephritogenic diffusely adhering Escherichia coli EC7372 harboring Dr-II adhesin carries classical uropathogenic virulence genes and promotes cell lysis and apoptosis in polarized epithelial caco-2/TC7 cells

Diffusely adhering Escherichia coli (DAEC) strains expressing adhesins of the Afa/Dr family bind to epithelial cells in a diffuse adherence pattern by recognizing a common receptor, the decay-accelerating factor (CD55). Recently, a novel CD55-binding adhesin, named Dr-II, was identified from the pyelonephritogenic strain EC7372. In this report, we show that despite the low level of sequence identity between Dr-II and other members of the Afa/Dr family, EC7372 induces pathophysiological effects similar to those induced by other Afa/Dr DAEC strains on the polarized epithelial cell line Caco-2/TC7. Specifically, the Dr-II adhesin was sufficient to promote CD55 and CD66e clustering around adhering bacteria and apical cytoskeleton rearrangements. Unlike other Afa/Dr DAEC strains, EC7372 expresses a functional hemolysin that promotes a rapid cellular lysis. In addition, cell death by apoptosis or necrosis was observed in EC7372-infected Caco-2/TC7 cells, depending on infection time. Our results indicate that EC7372 harbors a pathogenicity island (PAI) similar to the one described for the pyelonephritogenic strain CFT073, which carries both hly and pap operons. Cumulatively, our findings indicate that strain EC7372 can be considered a prototype of a subclass of Afa/Dr DAEC isolates that have acquired a PAI harboring several classical uropathogenic virulence genes.

Pseudomonas aeruginosa induces apoptosis in human endothelial cells

Pseudomonas aeruginosa has been shown to enter into human endothelial cells in vitro. To ascertain the effects of bacterial intracellular (IC) infection, endothelial cells were exposed to PAK and PAO-1 strains for 1 h and treated with gentamicin in culture medium for different periods. P. aeruginosa induced a significant production of superoxide and hydrogen peroxide by endothelial cells. Concentrations of IC bacteria were reduced progressively with time and no viable PAO-1 was detected at 24 h after infection. However, IC infection led to killing of 32.2%+/-2.9 and 51.8%+/-3.5 of the cells infected with PAK and PAO-1, respectively, as determined by the MTT assay. By three criteria (transmission electron microscopy, DNA electrophoresis and reactivity with annexin V) infected cells exhibited features of apoptosis. Treatment of infected cells with anti-oxidants (catalase, tocopherol and N -acetyl-L-cysteine) significantly decreased the percentage of cell death. In contrast, treatment with aminoguanidine, an inhibitor of inducible NO synthase, increased significantly the killing of PAO-1 infected cells. Based on these results we speculate that in response to P. aeruginosa infection, endothelial cells increase the production of reactive oxygen intermediates to eliminate IC pathogens, but cells do not resist the oxidative stress and die by apoptosis.

Pseudomonas aeruginosa mediated apoptosis requires the ADP-ribosylating activity of exoS

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that primarily infects immunocompromised individuals and patients with cystic fibrosis. Using a tissue culture system, invasive strains of P. aeruginosa were discovered to induce apoptosis at high frequency in HeLa and other epithelial and fibroblast cell lines. This apoptotic phenotype in the infected cells was determined by several criteria including (i) visual changes in cell morphology, (ii) induction of chromatin condensation and nuclear marginalization, (iii) the presence of a high percentage of cells with subG1 DNA content, and (iv) activation of caspase-3 activity. Induction of the type III secretion machinery, but not invasion of P. aeruginosa is required for induction of apoptosis. The apoptosis phenotype is independent of the cytoskeletal rearrangements that occur in the host cell early after infection. Mutants in P. aeruginosa exoS fail to induce apoptosis and complementation with wild-type exoS restored the apoptosis-inducing capacity, demonstrating that ExoS is the effector molecule. Analysis of exoS activity mutants shows that the ADP-ribosylating capacity of ExoS is essential for inducing the apoptotic pathway.

Homology model of surface antigen OmpC from Salmonella typhi and its functional implications

Homology based 3D structural model of the immunodominant major surface antigen OmpC from Salmonella typhi, an obligatory human pathogen, was built to understand the possible unique conformational features of its antigenic loops with respect to other immunologically cross reacting porins. The homology model was built based on the known crystal structures of the E. coli porins OmpF and PhoE. Structure based sequence alignment helped to define the structurally conserved regions (SCRs). The SCR regions of OmpC were modelled using the coordinates of corresponding regions from reference proteins. Surface exposed variable regions were modelled based on the sequence similarity and loop search in PDB. Structural refinement based on symmetry restrained energy minimization resulted in an agreeable model for the trimer of OmpC. The resulting model was compared with other porin structures, having b-barrel fold with 16 transmembrane beta-strands, and found that the variable regions are unique in terms of sequence and structure. A ranking of the loops taking into account the antigenic index, the sequence variability, the surface accessibility in the context of the trimer, and the structural variability suggests that loop 4 (151-172), loop 5 (194-218) and loop 6 (237-264) are the best ranked B-cell epitopes. The model provides possible explanations for the functional and unique immunological properties associated with the surface exposed regions and outlines the implications for structure based experimental design.

Secreted products of a nonmucoid Pseudomonas aeruginosa strain induce two modes of macrophage killing: external-ATP-dependent, P2Z-receptor-mediated necrosis and ATP-independent, caspase-mediated apoptosis

A nonmucoid clinical isolate of Pseudomonas aeruginosa, strain 808, elaborated ATP-dependent and ATP-independent types of cytotoxic factors in the growth medium. These cytotoxic factors, active against macrophages, were secreted during the exponential phase of growth in a complex medium. Commensurate with the appearance of the cytotoxic activities in the cell-free growth medium, several ATP-utilizing enzymic activities, such as adenylate kinase, nucleoside diphosphate kinase and 5'-nucleotidase (ATPase and/or phosphatase), were detected in the medium. These ATP-utilizing enzymes are believed to convert external ATP, presumably effluxed from macrophages, to various adenine nucleotides, which then activate purinergic receptors such as P2Z, leading to enhanced macrophage cell death. Pretreatment of macrophages with periodate-oxidized ATP (oATP), which is an irreversible inhibitor of P2Z receptor activation, prevented subsequent ATP-induced macrophage cell death. A second type of cytotoxic factor(s) operated in an ATP-independent manner such that it triggered activation of apoptotic processes in macrophages, leading to proteolytic conversion of procaspase-3 to active caspase-3. This cytotoxic factor(s) did not appear to act on procaspase-3 present in macrophage cytosolic extracts. Intact macrophages, when exposed to the cytotoxic factor(s) for 6-16 h, underwent apoptosis and demonstrated the presence of active caspase-3 in their cytosolic extracts. Interestingly, two redox proteins, azurin and cytochrome c(551), were detected in the cytotoxic preparation. When cell-line-derived or peritoneal macrophages or mast cells were incubated overnight with Q-Sepharose column flow-through fraction or with a mixture of azurin and cytochrome c(551), they underwent extensive cell death due to induction of apoptosis.