Implications of molecular contacts and signaling initiated by Neisseria gonorrhoeae

Basic Methods for Examining Neisseria gonorrhoeae Interactions with Host Cells In Vitro

The obligate human pathogen Neisseria gonorrhoeae colonizes primarily the mucosal columnar epithelium of the male urethra and the female endocervix. In addition, gonococci can infect the anorectal, pharyngeal, and gingival mucosae and epithelial cells of the conjunctiva. More rarely, the organism can disseminate through the bloodstream, which can involve interactions with other host cell types, including blood vessel endothelial cells and innate immune cells such as dendritic cells, macrophages, and neutrophils. "Disseminated gonococcal infection" is a serious condition with various manifestations resulting from the seeding of organs and tissues with the pathogen. The host response to gonococcal infection is inflammatory. Knowledge of the biology of gonococcal interactions has been served well through the use of a wide variety of ex vivo models using host tissues and eukaryotic cell monocultures. These models have helped identify bacterial surface adhesins and invasins and the corresponding cell surface receptors that play roles in gonococcal pathogenesis. Furthermore, they have been useful for understanding virulence mechanisms as well as innate and adaptive immune responses. In this chapter, readers are provided with protocols for examining the basic interactions between gonococci and a representative human cell line.

Effect of lipopolysaccharide on the expression of inflammatory mRNAs and microRNAs in the mouse oviduct

Infection with Gram-negative bacteria is a major cause of aberrant inflammation in the oviduct; consequences can include tubal-based infertility and/or ectopic pregnancy. Understanding the inflammatory response is necessary for the development of novel treatment options that counter inflammation-induced infertility. The aim of the present study was to determine the effect of intraperitoneal (i.p.) administration of Escherichia coli-derived lipopolysaccharide (LPS) on the acute expression of inflammatory mRNAs and microRNAs (miRNAs) in the oviduct. On the day of oestrus, 6- to 8-week-old CD1 mice were injected i.p. with 0, 2 or 10µg LPS in 100μL phosphate-buffered saline. Mice were killed 24h later and the oviducts collected for gene expression analyses. The effect of treatment on the expression of mRNAs and miRNAs was evaluated by one-way analysis of variance (ANOVA), with treatment means of differentially expressed (P<0.05) transcripts separated using Scheffé's test. LPS treatment affected 49 of 179 targeted inflammatory mRNAs and 51 of 578 miRNAs (P<0.05). The identity of differentially expressed miRNAs predicted as regulators of chemokine and interleukin ligand mRNAs was then extracted using the microRNA.org database. The results of the present study indicate that systemic treatment with LPS induces a robust inflammatory response in the oviducts of mice, and identify key mRNAs and putative miRNAs modulating this effect.

Neisseria gonorrhoeae infection causes DNA damage and affects the expression of p21, p27, and p53 in non-tumor epithelial cells

The constant shedding and renewal of epithelial cells maintain the protection of epithelial barriers. Interference with the processes of host cell-cycle regulation and barrier integrity permits the bacterial pathogen Neisseria gonorrhoeae to effectively colonize and invade epithelial cells. Here, we show that a gonococcal infection causes DNA damage in human non-tumor vaginal VK2/E6E7 cells with an increase of 700 DNA strand breaks per cell per hour as detected by an alkaline DNA unwinding assay. Infected cells exhibited elevated levels of DNA double-strand breaks, as indicated by a more than 50% increase in cells expressing DNA damage-response protein 53BP1-positive foci that co-localized with phosphorylated histone H2AX (γH2AX). Furthermore, infected cells abolished their expression of the tumor protein p53 and induced an increase in the expression of cyclin-dependent kinase inhibitors p21 and p27 to 2.6-fold and 4.2-fold of controls, respectively. As shown by live-cell microscopy, flow cytometry assays, and BrdU incorporation assays, gonococcal infection slowed the host cell-cycle progression mainly by impairing progression through the G2 phase. Our findings show new cellular players that are involved in the control of the human cell cycle during gonococcal infection and the potential of bacteria to cause cellular abnormalities.

Cyclic regulation of apoptotic gene expression in the mouse oviduct

The oviduct is a dynamic structure whose function relies upon cyclic changes in the morphology of both ciliated and secretory luminal epithelial cells. Unfortunately, infection of these epithelial cells by sexually transmitted pathogens can lead to pelvic inflammatory disease, ectopic pregnancies and infertility. The disruption of normal, cyclic apoptosis in the oviducal epithelium appears to be a causal factor of oviducal pathology and therefore, these pathways represent a potential target for diagnosis and therapeutic intervention. The objective of this study was to determine the pattern of expression for apoptotic genes in the oviduct of the naturally cycling mouse, generating fundamental information that can be applied to the development of animal models for research and the identification of targets for disease intervention. Whole oviducts were collected from regular cycling mice killed at 1p.m. on each day of the oestrous cycle and the expression of 84 apoptotic genes determined by targeted PCR super-array. Intact and cleaved caspases were then evaluated by western blotting. The expression of mRNA for genes classified as pro-apoptotic (Bad, Bak1 and Bok) and anti-apoptotic (Bag3, Bnip2 and Xiap) was regulated by day (P < 0.05). Differences in the temporal expression of several p53-related genes (Trp53bp2, Trp53inp1 and Trp73), those specific to the TNF superfamily (Tnfrsf10 and Tnfsf10b) and one caspase (Casp14) were also observed (P < 0.05). The cleaved forms of Caspases-3, -6 and -12 were all detected throughout the oestrous cycle. These results represent the first pathway-wide analysis of apoptotic gene expression in the murine oviduct.

Imaging of disease dynamics during meningococcal sepsis

Neisseria meningitidis is a human pathogen that causes septicemia and meningitis with high mortality. The disease progression is rapid and much remains unknown about the disease process. The understanding of disease development is crucial for development of novel therapeutic strategies and vaccines against meningococcal disease. The use of bioluminescent imaging combined with a mouse disease model allowed us to investigate the progression of meningococcal sepsis over time. Injection of bacteria in blood demonstrated waves of bacterial clearance and growth, which selected for Opa-expressing bacteria, indicating the importance of this bacterial protein. Further, N. meningitidis accumulated in the thyroid gland, while thyroid hormone T4 levels decreased. Bacteria reached the mucosal surfaces of the upper respiratory tract, which required expression of the meningococcal PilC1 adhesin. Surprisingly, PilC1 was dispensable for meningococcal growth in blood and for crossing of the blood-brain barrier, indicating that the major role of PilC1 is to interact with mucosal surfaces. This in vivo study reveals disease dynamics and organ targeting during meningococcal disease and presents a potent tool for further investigations of meningococcal pathogenesis and vaccines in vivo. This might lead to development of new strategies to improve the outcome of meningococcal disease in human patients.

Neisseria gonorrhoeae infection causes a G1 arrest in human epithelial cells

Pathogenic bacteria can modulate and interfere with human cell cycle progression. Here we study the human pathogen Neisseria gonorrhoeae and its ability to influence and affect the cell cycle in two human target cell lines. We found that bacteria adhere equally well to cells synchronized into the different cell cycle phases of G1, S, and G2, but were unable to adhere to cells in M phase or G0 phase. In addition, using Western blot and/or flow cytometry analysis we demonstrate that bacterial infection for 24 h results in decreased levels of the cell cycle regulatory proteins cyclin B1, cyclin D1, and cyclin E. Further studies in N. gonorrhoeae-infected epithelial cells involving analysis of DNA content, bromodeoxyuridine (BrdU) incorporation, quantification of late mitotic cells and analysis of nuclear phenotype provide compelling evidence that a 24 h gonococcal infection arrests the cells in early G1 phase of the cell cycle. In summary, we present data showing that MS11 P+ strain of N. gonorrhoeae can down-regulate cyclins, important modulators of the cell cycle, and result in a G1 arrest.

Type IV pili function upstream of the Dif chemotaxis pathway in Myxococcus xanthus EPS regulation

The developmental bacterium Myxococcus xanthus utilizes gliding motility to aggregate during the formation of multicellular fruiting bodies. The social (S) component of M. xanthus gliding motility requires at least two extracellular surface structures, type IV pili (Tfp) and the fibril polysaccharide or exopolysaccharide (EPS). Retraction of Tfp is proposed to power S motility and EPS from neighbouring cells is suggested to provide an anchor and trigger for Tfp retraction. The production of EPS in M. xanthus is regulated in part by the Dif chemosensory pathway; however, the input signal for the Dif pathway in EPS regulation remains to be uncovered. Using a genetic approach combined with quantitative and qualitative analysis, we demonstrate here that Tfp function upstream of the Dif proteins in regulating EPS production. The requirement of Tfp for the production of EPS was verified using various classes of Tfp mutants. Construction and examination of double and triple mutants indicated that mutations in dif are epistatic to those in pil. Furthermore, extracellular complementation between various Tfp and dif mutants suggests that Tfp, instead of being signals, may constitute the sensor or part of the sensor responsible for mediating signal input into the Dif pathway. We propose that S motility involves a regulatory loop in which EPS triggers Tfp retraction and Tfp provide proximity signals to the Dif pathway to modulate EPS production.

Infection of human fallopian tube epithelial cells with Neisseria gonorrhoeae protects cells from tumor necrosis factor alpha-induced apoptosis

Following infection with Neisseria gonorrhoeae, bacteria may ascend into the Fallopian tubes (FT) and induce salpingitis, a major cause of infertility. In the FT, interactions between mucosal epithelial cells and gonococci are pivotal events in the pathogen's infection cycle and the inflammatory response. In the current study, primary FT epithelial cells were infected in vitro with different multiplicities of infection (MOI) of Pil+ Opa+ gonococci. Bacteria showed a dose-dependent association with cells and induced the secretion of tumor necrosis factor alpha (TNF-alpha). A significant finding was that gonococcal infection (MOI = 1) induced apoptosis in approximately 30% of cells, whereas increasing numbers of bacteria (MOI = 10 to 100) did not induce apoptosis. Apoptosis was observed in only 11% of cells with associated bacteria, whereas >84% of cells with no adherent bacteria were apoptotic. TNF-alpha was a key contributor to apoptosis, since (i) culture supernatants from cells infected with gonococci (MOI = 1) induced apoptosis in naïve cultures, suggesting that a soluble factor was responsible; (ii) gonococcal infection-induced apoptosis was inhibited with anti-TNF-alpha antibodies; and (iii) the addition of exogenous TNF-alpha induced apoptosis, which was inhibited by the presence of increasing numbers of bacteria (MOI = 10 to 100). These data suggest that TNF-alpha-mediated apoptosis of FT epithelial cells is likely a primary host defense mechanism to prevent pathogen colonization. However, epithelial cell-associated gonococci have evolved a mechanism to protect the cells from undergoing TNF-alpha-mediated apoptosis, and this modulation of the host innate response may contribute to establishment of infection. Understanding the antiapoptotic mechanisms used by Neisseria gonorrhoeae will inform the pathogenesis of salpingitis and could suggest new intervention strategies for prevention and treatment of the disease.

Neisseria meningitidis: an overview of the carriage state

During periods of endemic disease, about 10 % of the general population harbour Neisseria meningitidis in the nasopharynx. Since N. meningitidis is a strict human pathogen and most patients have not been in contact with other cases, asymptomatic carriers are presumably the major source of the pathogenic strains. Most carrier isolates are shown to lack capsule production. The capsule deficient state of meningococcal strains in the nasopharynx may aid evasion of the human immune defence and hence be selected to survive nasopharyngeal colonization. Carriage itself can be an immunizing process resulting in systemic protective antibody responses. Frequent nasopharyngeal colonization with related bacteria like Neisseria lactamica improves natural immunity to meningococci by the formation of cross-reacting antibodies. While most meningococcal strains recovered from patients belong to a limited number of clonal groups worldwide, strains isolated from carriers comprise numerous genotypes, with only a small proportion of the strains representing invasive clones. During the carriage state, co-colonization with other pathogenic and non-pathogenic bacteria may lead to genetic exchange, which may result in the emergence of new meningococcal clones. The high diversity of meningococcal carrier strains, compared with hypervirulent strains, supports the idea that transmissibility, not invasion, is essential in the life cycle of N. meningitidis.

An Update on Vaginal Microbicides

In response to an increasing prevalence of sexually transmitted diseases, especially AIDS, efforts to prevent further infections have been heightened. One of those approaches has been the development of topical microbicidal agents or microbicides. These are compounds designed to protect the body's mucosal surfaces from infection by sexually transmitted disease-causing pathogens. Numerous candidates are currently in preclinical stages; however, only a handful have been tested for safety, and even fewer are ready for clinical efficacy trials. In this update, we describe some of the specific features of microbicide research and development, including preclinical screening algorithms, candidate's ideal properties, examples of compounds presently in the pipeline, and future prospects.