Evidence for conserved function of γ-glutamyltranspeptidase in Helicobacter genus

Novel therapeutic regimens against Helicobacter pylori: an updated systematic review

Helicobacter pylori (H. pylori) is a strict microaerophilic bacterial species that exists in the stomach, and H. pylori infection is one of the most common chronic bacterial infections affecting humans. Eradicating H. pylori is the preferred method for the long-term prevention of complications such as chronic gastritis, peptic ulcers, gastric mucosa-associated lymphoid tissue lymphoma, and gastric cancer. However, first-line treatment with triple therapy and quadruple therapy has been unable to cope with increasing antibacterial resistance. To provide an updated review of H. pylori infections and antibacterial resistance, as well as related treatment options, we searched PubMed for articles published until March 2024. The key search terms were "H. pylori", "H. pylori infection", "H. pylori diseases", "H. pylori eradication", and "H. pylori antibacterial resistance." Despite the use of antimicrobial agents, the annual decline in the eradication rate of H. pylori continues. Emerging eradication therapies, such as the development of the new strong acid blocker vonoprazan, probiotic adjuvant therapy, and H. pylori vaccine therapy, are exciting. However, the effectiveness of these treatments needs to be further evaluated. It is worth mentioning that the idea of altering the oxygen environment in gastric juice for H. pylori to not be able to survive is a hot topic that should be considered in new eradication plans. Various strategies for eradicating H. pylori, including antibacterials, vaccines, probiotics, and biomaterials, are continuously evolving. A novel approach involving the alteration of the oxygen concentration within the growth environment of H. pylori has emerged as a promising eradication strategy.

CsMYB73 negatively regulates theanine accumulation mediated by CsGGT2 and CsGGT4 in tea shoots (Camellia sinensis)

Theanine metabolism is a necessary biological process during the planting and production of tea that determines tea quality. There is currently little knowledge about the transcriptional regulation of theanine metabolism in tea plants. In this study, we demonstrated that γ-glutamyl-transpeptidase CsGGT4, as a homologous protein of the theanine hydrolase CsGGT2, exhibited a higher theanine synthesis catalytic efficiency. Homology modeling and molecular docking showed that differential protein structures between CsGGT2 and CsGGT4 implied their different biological functions in tea plants. Theanine content correlated significantly with the expression of CsGGT2, CsGGT4 and the transcription factor CsMYB73 in tea shoots from different seasons. Additionally, CsMYB73 was confirmed to act as a nucleus-localized transcription factor (TF), directly interacts with the CsGGT2 and CsGGT4 promoters, serving as an activator of CsGGT2 and a suppressor of CsGGT4. Consequently, this leads to a negative association with theanine accumulation in tea shoots. Furthermore, the continuous increase in CsMYB73 produced a significantly increase in CsGGT2 expression and inhibited CsGGT4 expression. The present study reveals that the degradation of theanine has been observed to increase, concomitantly with the inhibition of theanine synthesis, resulting in a significant decline in the accumulation of theanine in tea shoots during the process of seasonal greening in 'Huangkui' leaves. This study contributes to the broader comprehension of the intricate transcriptional regulatory hierarchy that governs the metabolism of theanine in tea shoots, offering novel approaches for managing tea plantations and enhancing tea quality.

Helicobacter pylori and Its Role in Gastric Cancer

Gastric cancer is a challenging public health concern worldwide and remains a leading cause of cancer-related mortality. The primary risk factor implicated in gastric cancer development is infection with Helicobacter pylori. H. pylori induces chronic inflammation affecting the gastric epithelium, which can lead to DNA damage and the promotion of precancerous lesions. Disease manifestations associated with H. pylori are attributed to virulence factors with multiple activities, and its capacity to subvert host immunity. One of the most significant H. pylori virulence determinants is the cagPAI gene cluster, which encodes a type IV secretion system and the CagA toxin. This secretion system allows H. pylori to inject the CagA oncoprotein into host cells, causing multiple cellular perturbations. Despite the high prevalence of H. pylori infection, only a small percentage of affected individuals develop significant clinical outcomes, while most remain asymptomatic. Therefore, understanding how H. pylori triggers carcinogenesis and its immune evasion mechanisms is critical in preventing gastric cancer and mitigating the burden of this life-threatening disease. This review aims to provide an overview of our current understanding of H. pylori infection, its association with gastric cancer and other gastric diseases, and how it subverts the host immune system to establish persistent infection.

Helicobacter pylori Virulence Factors-Mechanisms of Bacterial Pathogenicity in the Gastric Microenvironment

Gastric cancer constitutes one of the most prevalent malignancies in both sexes; it is currently the fourth major cause of cancer-related deaths worldwide. The pathogenesis of gastric cancer is associated with the interaction between genetic and environmental factors, among which infection by Helicobacter pylori (H. pylori) is of major importance. The invasion, survival, colonization, and stimulation of further inflammation within the gastric mucosa are possible due to several evasive mechanisms induced by the virulence factors that are expressed by the bacterium. The knowledge concerning the mechanisms of H. pylori pathogenicity is crucial to ameliorate eradication strategies preventing the possible induction of carcinogenesis. This review highlights the current state of knowledge and the most recent findings regarding H. pylori virulence factors and their relationship with gastric premalignant lesions and further carcinogenesis.

Distinct transcriptome signatures of Helicobacter suis and Helicobacter heilmannii strains upon adherence to human gastric epithelial cells

The porcine Helicobacter suis and canine-feline H. heilmannii are gastric Helicobacter species with zoonotic potential. However, little is known about the pathogenesis of human infections with these Helicobacter species. To gain more insight into the interactions of both zoonotic Helicobacter species with human gastric epithelial cells, we investigated bacterial genes that are differentially expressed in a H. suis and H. heilmannii strain after adhesion to the human gastric epithelial cell line MKN7. In vitro Helicobacter-MKN7 binding assays were performed to obtain bacterial RNA for sequencing analysis. H. suis and H. heilmannii bacteria attached to the gastric epithelial cells (i.e. cases) as well as unbound bacteria (i.e. controls) were isolated, after which prokaryotic RNA was purified and sequenced. Differentially expressed genes were identified using the DESeq2 package and SARTools pipeline in R. A list of 134 (83 up-regulated and 51 down-regulated) and 143 (60 up-regulated and 83 down-regulated) differentially expressed genes (p_adj ≤ 0.01; fold change ≥ 2) were identified for the adherent H. suis and H. heilmannii strains, respectively. According to BLASTp analyses, only 2 genes were commonly up-regulated and 4 genes commonly down-regulated in both pathogens. Differentially expressed genes of the H. suis and H. heilmannii strains belonged to multiple functional classes, indicating that adhesion of both strains to human gastric epithelial cells evokes pleiotropic adaptive responses. Our results suggest that distinct pathways are involved in human gastric colonization of H. suis and H. heilmannii. Further research is needed to elucidate the clinical significance of these findings.

Mechanisms of persistence, innate immune activation and immunomodulation by the gastric pathogen Helicobacter pylori

The gastric bacterium Helicobacter pylori efficiently evades innate immune detection and persistently colonizes its human host. Understanding the genetic determinants that H. pylori uses to establish and maintain persistence, along with their cellular targets, is key to our understanding of the pathogenesis of this extraordinarily successful bacterial colonizer of the human stomach. This review highlights recent advances in elucidating innate immune recognition of H. pylori, its interactions with myeloid cells and the consequences that this very local infection has for immune responses at extragastric sites in models of allergy, autoimmunity and parasitic infection. The human-specific, gram-negative gastric colonizer and carcinogen H. pylori represents the prototype of a persistent bacterial pathogen. It is transmitted during early childhood, typically from mother to infant, and is believed to persist in its human host from the cradle to the grave. The tremendous success of H. pylori in infecting and colonizing half of the world's population, and in continuously accompanying humans since they migrated out of Africa over 60000 years ago, can largely be attributed to its ability to manipulate the host immune system to its own advantage, and to thereby ensure its own persistence and chronicity. In his final years as an active PI, Stanley Falkow increasingly recognized the need to understand bacterial persistence strategies as a prerequisite of understanding the pathogenesis of chronic bacterial infections, and, inspired in large part by Denise Monack's work on Salmonella persistence, many of our discussions at the time revolved around this topic. Multiple labs have since made important contributions to our understanding of innate immune detection of H. pylori, the types and polarization of adaptive immune responses that ensue, the ability of H. pylori to skew such immune responses to its advantage, and its ability to manipulate the host immune system with far-reaching, even systemic consequences. This review attempts to cover some of these topics, with a particular focus on the most recent contributions by researchers in the field.

Activity and Functional Importance of Helicobacter pylori Virulence Factors

Helicobacter pylori is a very successful Gram-negative pathogen colonizing the stomach of humans worldwide. Infections with this bacterium can generate pathologies ranging from chronic gastritis and peptic ulceration to gastric cancer. The best characterized H. pylori virulence factors that cause direct cell damage include an effector protein encoded by the cytotoxin-associated gene A (CagA), a type IV secretion system (T4SS) encoded in the cag-pathogenicity island (cag PAI), vacuolating cytotoxin A (VacA), γ-glutamyl transpeptidase (GGT), high temperature requirement A (HtrA, a serine protease) and cholesterol glycosyl-transferase (CGT). Since these H. pylori factors are either surface-exposed, secreted or translocated, they can directly interact with host cell molecules and are able to hijack cellular functions. Studies on these bacterial factors have progressed substantially in recent years. Here, we review the current status in the characterization of signaling cascades by these factors in vivo and in vitro, which comprise the disruption of cell-to-cell junctions, induction of membrane rearrangements, cytoskeletal dynamics, proliferative, pro-inflammatory, as well as, pro-apoptotic and anti-apoptotic responses or immune evasion. The impact of these signal transduction modules in the pathogenesis of H. pylori infections is discussed.

Helicobacter pylori VacA Targets Myeloid Cells in the Gastric Lamina Propria To Promote Peripherally Induced Regulatory T-Cell Differentiation and Persistent Infection

Helicobacter pylori has coexisted with humans for at least 60.000 years and has evolved persistence strategies that allow it to evade host immunity and colonize its host for life. The VacA protein is expressed by all H. pylori strains and is required for high-level persistent infection in experimental mouse models. Here, we show that VacA targets myeloid cells in the gastric mucosa to create a tolerogenic environment that facilitates regulatory T-cell differentiation, while suppressing effector T-cell priming and functionality. Tregs that are induced in the periphery during H. pylori infection can be found not only in the stomach but also in the lungs of infected mice, where they are likely to affect immune responses to allergens.

The gastric bacterium Helicobacter pylori causes a persistent infection that is directly responsible for gastric ulcers and gastric cancer in some patients and protective against allergic and other immunological disorders in others. The two outcomes of the Helicobacter-host interaction can be modeled in mice that are infected as immunocompetent adults and as neonates, respectively. Here, we have investigated the contribution of the Helicobacter immunomodulator VacA to H. pylori-specific local and systemic immune responses in both models. We found that neonatally infected mice are colonized at higher levels than mice infected as adults and fail to generate effector T-cell responses to the bacteria; rather, T-cell responses in neonatally infected mice are skewed toward Foxp3-positive (Foxp3⁺) regulatory T cells that are neuropilin negative and express RORγt. We found these peripherally induced regulatory T cells (pTregs) to be enriched, in a VacA-dependent manner, not only in the gastric mucosa but also in the lungs of infected mice. Pulmonary pTreg accumulation was observed in mice that have been infected neonatally with wild-type H. pylori but not in mice that have been infected as adults or mice infected with a VacA null mutant. Finally, we traced VacA to gastric lamina propria myeloid cells and show that it suppressed interleukin-23 (IL-23) expression by dendritic cells and induced IL-10 and TGF-β expression in macrophages. Taken together, the results are consistent with the idea that H. pylori creates a tolerogenic environment through its immunomodulator VacA, which skews T-cell responses toward Tregs, favors H. pylori persistence, and affects immunity at distant sites.

Comparative genomics analysis to differentiate metabolic and virulence gene potential in gastric versus enterohepatic Helicobacter species

Background

The genus Helicobacter are gram-negative, microaerobic, flagellated, mucus-inhabiting bacteria associated with gastrointestinal inflammation and classified as gastric or enterohepatic Helicobacter species (EHS) according to host species and colonization niche. While there are over 30 official species, little is known about the physiology and pathogenic mechanisms of EHS, which account for most in the genus, as well as what genetic factors differentiate gastric versus EHS, given they inhabit different hosts and colonization niches. The objective of this study was to perform a whole-genus comparative analysis of over 100 gastric versus EHS genomes in order to identify genetic determinants that distinguish these Helicobacter species and provide insights about their evolution/adaptation to different hosts, colonization niches, and mechanisms of virulence.

Results

Whole-genome phylogeny organized Helicobacter species according to their presumed gastric or EHS classification. Analysis of orthologs revealed substantial heterogeneity in physiological and virulence-related genes between gastric and EHS genomes. Metabolic reconstruction predicted that unlike gastric species, EHS appear asaccharolytic and dependent on amino/organic acids to fuel metabolism. Additionally, gastric species lack de novo biosynthetic pathways for several amino acids and purines found in EHS and instead rely on environmental uptake/salvage pathways. Comparison of virulence factor genes between gastric and EHS genomes identified overlapping yet distinct profiles and included canonical cytotoxins, outer membrane proteins, secretion systems, and survival factors.

Conclusions

The major differences in predicted metabolic function suggest gastric species and EHS may have evolved for survival in the nutrient-rich stomach versus the nutrient-devoid environments, respectively. Contrasting virulence factor gene profiles indicate gastric species and EHS may utilize different pathogenic mechanisms to chronically infect hosts and cause inflammation and tissue damage. The findings from this study provide new insights into the genetic differences underlying gastric versus EHS and support the need for future experimental studies to characterize these pathogens.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5171-2) contains supplementary material, which is available to authorized users.

Gamma-glutamyltranspeptidase expression by Helicobacter saguini, an enterohepatic Helicobacter species isolated from cotton top tamarins with chronic colitis

BACKGROUND

Helicobacter saguini is a novel enterohepatic Helicobacter species isolated from captive cotton top tamarins with chronic colitis and colon cancer. Monoassociated H. saguini infection in gnotobiotic IL-10^-/- mice causes typhlocolitis and dysplasia; however, the virulent mechanisms of this species are unknown. Gamma-glutamyltranspeptidase (GGT) is an enzymatic virulence factor expressed by pathogenic Helicobacter and Campylobacter species that inhibits host cellular proliferation and promotes inflammatory-mediated gastrointestinal pathology. The aim of this study was to determine if H. saguini expresses an enzymatically active GGT homologue with virulence properties.

EXPERIMENTAL PROCEDURES

Two putative GGT paralogs (HSGGT1 and HSGGT2) identified in the H. saguini genome were bioinformatically analysed to predict enzymatic functionality and virulence potential. An isogenic knockout mutant strain and purified recombinant protein of HSGGT1 were created to study enzymatic activity and virulence properties by in vitro biochemical and cell culture experiments.

RESULTS

Bioinformatic analysis predicted that HSGGT1 has enzymatic functionality and is most similar to the virulent homologue expressed by Helicobacter bilis, whereas HSGGT2 contains putatively inactivating mutations. An isogenic knockout mutant strain and recombinant HSGGT1 protein were successfully created and demonstrated that H. saguini has GGT enzymatic activity. Recombinant HSGGT1 protein and sonicate from wild-type but not mutant H. saguini inhibited gastrointestinal epithelial and lymphocyte cell proliferation without evidence of cell death. The antiproliferative effect by H. saguini sonicate or recombinant HSGGT1 protein could be significantly prevented with glutamine supplementation or the GGT-selective inhibitor acivicin. Recombinant HSGGT1 protein also induced proinflammatory gene expression in colon epithelial cells.

CONCLUSIONS

This study shows that H. saguini may express GGT as a potential virulence factor and supports further in vitro and in vitro studies into how GGT expression by enterohepatic Helicobacter species influences the pathogenesis of gastrointestinal inflammatory diseases.

Direct Manipulation of T Lymphocytes by Proteins of Gastrointestinal Bacterial Pathogens

Gastrointestinal bacterial infection represents a significant threat to human health, as well as a burden on food animal production and welfare. Although there is advanced knowledge about the molecular mechanisms underlying pathogenesis, including the development of immune responses to these pathogens, gaps in knowledge persist. It is well established that gastrointestinal bacterial pathogens produce a myriad of proteins that affect the development and effectiveness of innate immune responses. However, relatively few proteins that directly affect lymphocytes responsible for humoral or cell-mediated immunity and memory have been identified. Here, we review factors produced by gastrointestinal bacterial pathogens that have direct T cell interactions and what is known about their functions and mechanisms of action. T cell-interacting bacterial proteins that have been identified to date mainly target three major T cell responses: activation and expansion, chemotaxis, or apoptosis. Further, the requirement for more focused studies to identify and understand additional mechanisms used by bacteria to directly affect the T cell immune response and how these may contribute to pathogenesis is highlighted. Increased knowledge in this area will help to drive development of better interventions in prevention and treatment of gastrointestinal bacterial infection.

Metabolism of Glutathione S-Conjugates: Multiple Pathways

Many potentially toxic electrophilic xenobiotics and some endogenous compounds are detoxified by conversion to the corresponding glutathione S-conjugate, which is metabolized to the N-acetylcysteine S-conjugate (mercapturate) and excreted. Some mercapturate pathway components, however, are toxic. Bioactivation (toxification) may occur when the glutathione S-conjugate (or mercapturate) is converted to a cysteine S-conjugate that undergoes a β-lyase reaction. If the sulfhydryl-containing fragment produced in this reaction is reactive, toxicity may ensue. Some drugs and halogenated workplace/environmental contaminants are bioactivated by this mechanism. On the other hand, cysteine S-conjugate β-lyases occur in nature as a means of generating some biologically useful sulfhydryl-containing compounds.

Helicobacter saguini, a Novel Helicobacter Isolated from Cotton-Top Tamarins with Ulcerative Colitis, Has Proinflammatory Properties and Induces Typhlocolitis and Dysplasia in Gnotobiotic IL-10-/- Mice

A urease-negative, fusiform, novel bacterium named Helicobacter saguini was isolated from the intestines and feces of cotton-top tamarins (CTTs) with chronic colitis. Helicobacter sp. was detected in 69% of feces or intestinal samples from 116 CTTs. The draft genome sequence, obtained by Illumina MiSeq sequencing, for H. saguini isolate MIT 97-6194-5, consisting of ∼2.9 Mb with a G+C content of 35% and 2,704 genes, was annotated using the NCBI Prokaryotic Genomes Automatic Annotation Pipeline. H. saguini contains homologous genes of known virulence factors found in other enterohepatic helicobacter species (EHS) and H. pylori These include flagellin, γ-glutamyl transpeptidase (ggt), collagenase, the secreted serine protease htrA, and components of a type VI secretion system, but the genome does not harbor genes for cytolethal distending toxin (cdt). H. saguini MIT 97-6194-5 induced significant levels of interleukin-8 (IL-8) in HT-29 cell culture supernatants by 4 h, which increased through 24 h. mRNAs for the proinflammatory cytokines IL-1β, tumor necrosis factor alpha (TNF-α), IL-10, and IL-6 and the chemokine CXCL1 were upregulated in cocultured HT-29 cells at 4 h compared to levels in control cells. At 3 months postinfection, all H. saguini-monoassociated gnotobiotic C57BL/129 IL-10(-/-) mice were colonized and had seroconverted to H. saguini antigen with a significant Th1-associated increase in IgG2c (P < 0.0001). H. saguini induced a significant typhlocolitis, associated epithelial defects, mucosa-associated lymphoid tissue (MALT) hyperplasia, and dysplasia. Inflammatory cytokines IL-22, IL-17a, IL-1β, gamma interferon (IFN-γ), and TNF-α, as well as inducible nitric oxide synthase (iNOS) were significantly upregulated in the cecal tissues of infected mice. The expression of the DNA damage response molecule γ-H2AX was significantly higher in the ceca of H. saguini-infected gnotobiotic mice than in the controls. This model using a nonhuman primate Helicobacter sp. can be used to study the pathogenic potential of EHS isolated from primates with naturally occurring inflammatory bowel disease (IBD) and colon cancer.

Helicobacter pylori γ-Glutamyltranspeptidase Induces Tolerogenic Human Dendritic Cells by Activation of Glutamate Receptors

Helicobacter pylori infection is characterized by chronic persistence of the bacterium. Different virulence factors, including H. pylori γ-glutamyltranspeptidase (gGT), have been reported to induce tolerogenicity by reprogramming dendritic cells (DCs). gGT is present in all bacterial isolates, indicating an important role for gGT in the course of infection. In the current study, we have analyzed the effect of H. pylori gGT on human DCs and the subsequent adaptive immune response. We show that glutamate produced due to H. pylori gGT enzymatic activity tolerizes DCs by inhibiting cAMP signaling and dampening IL-6 secretion in response to the infection. Together, our results provide a novel molecular mechanism by which H. pylori manipulates the host's immune response to persist within its host.

Oral glutathione supplementation drastically reduces Helicobacter-induced gastric pathologies

Helicobacter (H.) suis causes gastric pathologies in both pigs and humans. Very little is known on the metabolism of this bacterium and its impact on the host. In this study, we have revealed the importance of the glutamate-generating metabolism, as shown by a complete depletion of glutamine (Gln) in the medium during H. suis culture. Besides Gln, H. suis can also convert glutathione (GSH) to glutamate, and both reactions are catalyzed by the H. suis γ-glutamyltranspeptidase (GGT). Both for H. pylori and H. suis, it has been hypothesized that the degradation of Gln and GSH may lead to a deficiency for the host, possibly initiating or promoting several pathologies. Therefore the in vivo effect of oral supplementation with Gln and GSH was assessed. Oral supplementation with Gln was shown to temper H. suis induced gastritis and epithelial (hyper)proliferation in Mongolian gerbils. Astonishingly, supplementation of the feed with GSH, another GGT substrate, resulted in inflammation and epithelial proliferation levels returning to baseline levels of uninfected controls. This indicates that Gln and GSH supplementation may help reducing tissue damage caused by Helicobacter infection in both humans and pigs, highlighting their potential as a supportive therapy during and after Helicobacter eradication therapy.

Infection with Helicobacter bilis but not Helicobacter hepaticus was Associated with Extrahepatic Cholangiocarcinoma

BACKGROUND AND AIMS

The biliary tract cancer or cholangiocarcinoma (CCA) represents the sixth leading cause of gastrointestinal tumors in the Western world, and mortality varies across the world, with regions such as Chile, Thailand, Japan, and northeastern India presenting the highest rates. CCA may develop in the bile duct, gallbladder, or ampulla of Vater; and risk factors include obesity, parity, genetic background, geographical and environmental factors. Inflammation induced by bacterial infections might play a role in the pathogenesis of CCA. In this work, we investigated whether there is an association between extrahepatic cholangiocarcinoma (ECCA) and infection with S. typhi, H. hepaticus, or H. bilis in a Mexican population.

METHODS

A total of 194 patients were included and divided into 91 patients with benign biliary pathology (controls) and 103 with ECCA (cases). Tumor samples were taken during endoscopic retrograde cholangiopancreatography by biliary brushing, followed by DNA extraction and PCR testing for infections.

RESULTS

We found that 44/103 cases were positive for H. bilis, compared with 19/91 controls (p = 0.002; OR 2.83, 95% CI 1.49-5.32), and when analyzed by sub-site, H. bilis infection was significantly more associated with cancer in the common bile duct (p = 0.0005; OR 3.56, 95% CI 1.77-7.17). In contrast, H. hepaticus infection was not different between cases (17/103) and controls (13/91) (p = 0.82; OR 1.19, 95% CI 0.54-2.60). None of the samples were positive for S. typhi infection.

CONCLUSION

In conclusion, infection with H. bilis but neither H. Hepaticus nor S. typhi was significantly associated with ECCA, particularly with tumors located in the common bile duct.

Helicobacter pylori γ-glutamyltranspeptidase impairs T-lymphocyte function by compromising metabolic adaption through inhibition of cMyc and IRF4 expression

Helicobacter pylori (H. pylori) is a human-specific pathogen that has evolved to cope with the immune response elicited against the infection. We previously reported that H. pylori γ-glutamyltranspeptidase (gGT) impairs T-lymphocyte proliferation and thus might act as immune regulatory factor. In this study, we analysed the underlying mechanism and its implications for H. pylori persistence. We found that H. pylori gGT compromised T-cell proliferation, activation and effector cytokine expression by specifically depriving the extracellular space of glutamine. When assessing signalling cascades and transcription factors affected by H. pylori gGT, we found that expression of cMyc and IRF4, both required for metabolic adaptation of T-lymphocytes, was highly sensitive to extracellular glutamine levels and downregulated upon gGT treatment. Moreover, we could confirm decreased IRF4 expression in T-lymphocytes infiltrating the stomach of infected individuals. Thus, our results suggest that H. pylori gGT-mediated glutamine deprivation in the gastric mucosa may suppress T-cell function thereby contributing to bacterial persistence.

Role of Campylobacter jejuni gamma-glutamyl transpeptidase on epithelial cell apoptosis and lymphocyte proliferation

Background

A gamma-glutamyl transpeptidase (GGT) is produced by up to 31% of strains of Campylobacter jejuni isolates. C. jejuni GGT is close to Helicobacter pylori GGT suggesting a conserved activity but unlike the latter, C. jejuni GGT has not been studied extensively. In line with the data available for H. pylori, our objectives were to purify C. jejuni GGT from the bacteria, and to evaluate its inhibitory and proapoptotic activities on epithelial cells and human lymphocytes.

Methods

C. jejuni GGT was purified from culture supernatants by chromatography. After verification of the purity by using mass spectrometry of the purified enzyme, its action on two epithelial cell lines and human lymphocytes was investigated. Cell culture as well as flow cytometry experiments were developed for these purposes.

Results

This study demonstrated that C. jejuni GGT is related to Helicobacter GGTs and inhibits the proliferation of epithelial cells with no proapoptotic activity. C. jejuni GGT also inhibits lymphocyte proliferation by causing a cell cycle arrest in the G0/G1 phase. These effects are abolished in the presence of a specific pharmacological inhibitor of GGT.

Conclusion

C. jejuni GGT activity is comparable to that of other Epsilonproteobacteria GGTs and more generally to Helicobacter bilis (inhibition of epithelial cell and lymphocyte proliferation, however with no proapoptotic activity). It could therefore be considered as a pathogenicity factor and promote, via the inhibition of lymphocyte proliferation, the persistence of the bacteria in the host. These observations are consistent with a role of this enzyme in the pathophysiology of chronic infections associated with C. jejuni.

Comparative genomics of unintrogressed Campylobacter coli clades 2 and 3

BACKGROUND

Campylobacter jejuni and C. coli share a multitude of risk factors associated with human gastrointestinal disease, yet their phylogeny differs significantly. C. jejuni is scattered into several lineages, with no apparent linkage, whereas C. coli clusters into three distinct phylogenetic groups (clades) of which clade 1 has shown extensive genome-wide introgression with C. jejuni, yet the other two clades (2 and 3) have less than 2% of C. jejuni ancestry. We characterized a C. coli strain (76339) with four novel multilocus sequence type alleles (ST-5088) and having the capability to express gamma-glutamyltranspeptidase (GGT); an accessory feature in C. jejuni. Our aim was to further characterize unintrogressed C. coli clades 2 and 3, using comparative genomics and with additional genome sequences available, to investigate the impact of horizontal gene transfer in shaping the accessory and core gene pools in unintrogressed C. coli.

RESULTS

Here, we present the first fully closed C. coli clade 3 genome (76339). The phylogenomic analysis of strain 76339, revealed that it belonged to clade 3 of unintrogressed C. coli. A more extensive respiratory metabolism among unintrogressed C. coli strains was found compared to introgressed C. coli (clade 1). We also identified other genes, such as serine proteases and an active sialyltransferase in the lipooligosaccharide locus, not present in C. coli clade 1 and we further propose a unique scenario for the evolution of Campylobacter ggt.

CONCLUSIONS

We propose new insights into the evolution of the accessory genome of C. coli clade 3 and C. jejuni. Also, in silico analysis of the gene content revealed that C. coli clades 2 and 3 have genes associated with infection, suggesting they are a potent human pathogen, and may currently be underreported in human infections due to niche separation.

Helicobacter pylori gamma-glutamyl transpeptidase and its pathogenic role

Helicobacter pylori (H. pylori) gamma-glutamyl transpeptidase (GGT) is a bacterial virulence factor that converts glutamine into glutamate and ammonia, and converts glutathione into glutamate and cysteinylglycine. H. pylori GGT causes glutamine and glutathione consumption in the host cells, ammonia production and reactive oxygen species generation. These products induce cell-cycle arrest, apoptosis, and necrosis in gastric epithelial cells. H. pylori GGT may also inhibit apoptosis and induce gastric epithelial cell proliferation through the induction of cyclooxygenase-2, epidermal growth factor-related peptides, inducible nitric oxide synthase and interleukin-8. H. pylori GGT induces immune tolerance through the inhibition of T cell-mediated immunity and dendritic cell differentiation. The effect of GGT on H. pylori colonization and gastric persistence are also discussed.

Effects of Helicobacter suis γ-glutamyl transpeptidase on lymphocytes: modulation by glutamine and glutathione supplementation and outer membrane vesicles as a putative delivery route of the enzyme

Helicobacter (H.) suis colonizes the stomach of the majority of pigs as well as a minority of humans worldwide. Infection causes chronic inflammation in the stomach of the host, however without an effective clearance of the bacteria. Currently, no information is available about possible mechanisms H. suis utilizes to interfere with the host immune response. This study describes the effect on various lymphocytes of the γ-glutamyl transpeptidase (GGT) from H. suis. Compared to whole cell lysate from wild-type H. suis, lysate from a H. suis ggt mutant strain showed a decrease of the capacity to inhibit Jurkat T cell proliferation. Incubation of Jurkat T cells with recombinantly expressed H. suis GGT resulted in an impaired proliferation, and cell death was shown to be involved. A similar but more pronounced inhibitory effect was also seen on primary murine CD4(+) T cells, CD8(+) T cells, and CD19(+) B cells. Supplementation with known GGT substrates was able to modulate the observed effects. Glutamine restored normal proliferation of the cells, whereas supplementation with reduced glutathione strengthened the H. suis GGT-mediated inhibition of proliferation. H. suis GGT treatment abolished secretion of IL-4 and IL-17 by CD4(+) T cells, without affecting secretion of IFN-γ. Finally, H. suis outer membrane vesicles (OMV) were identified as a possible delivery route of H. suis GGT to lymphocytes residing in the deeper mucosal layers. Thus far, this study is the first to report that the effects on lymphocytes of this enzyme, not only important for H. suis metabolism but also for that of other Helicobacter species, depend on the degradation of two specific substrates: glutamine and reduced glutatione. This will provide new insights into the pathogenic mechanisms of H. suis infection in particular and infection with gastric helicobacters in general.

Helicobacter bilis gamma-glutamyltranspeptidase enhances inflammatory stress response via oxidative stress in colon epithelial cells

Helicobacter bilis (H. bilis) infection is associated with cases of inflammatory bowel Disease, thyphlocolitis, hepatitis and cholecystitis. However, little is known about the bacterial virulence determinants or the molecular mechanisms involved. Recently, H. bilis γ-glutamyltranspeptidase (HBgGT) was shown to be a virulence factor decreasing host cell viability. Bacterial gGTs play a key role in synthesis and degradation of glutathione and enables the bacteria to utilize extracellular glutamine and glutathione as sources of glutamate. gGT-mediated loss of cell viability has so far been linked to DNA damage via oxidative stress, but the signaling cascades involved herein have not been described. In this study, we identified enhanced ROS production induced by HBgGT as a central factor involved in the activation of the oxidative stress response cascades, which finally activate CREB, AP-1 and NF-κB in H. bilis infected colon cancer cells. IL-8, an important pro-inflammatory chemokine that is a common downstream target of these transcription factors, was up-regulated upon H. bilis infection in an HBgGT dependent manner. Moreover, the induction of these signaling responses and inflammatory cytokine production in host cells could be linked to HBgGT-mediated glutamine deprivation. This study implicates for the first time HBgGT as an important regulator of signaling cascades regulating inflammation in H. bilis infected host epithelial cells that could be responsible for induction of inflammatory disorders by the bacterium.

Contingency nature of Helicobacter bizzozeronii oxygen-insensitive NAD(P)H-nitroreductase (HBZC1_00960) and its role in metronidazole resistance

Genomic analysis of a metronidazole resistant H. bizzozeronii strain revealed a frame length extension of the oxygen-insensitive NAD(P)H-nitroreductase HBZC1_00960 (RdxA), associated with the disruption of the C-terminal cysteine-containing conserved region (IACLXALGK). This was the result of the extension (from C8 to C9) of a simple sequence cytosine repeat (SSCR) located in the 3' of the gene. A 3' SSCR is also present in the rdxA homolog of H. heilmannii sensu stricto, but not in H. pylori. We showed that in the majority of in vitro spontaneous H. bizzozeronii metronidazole resistant mutants, the extension of the 3' SSCR of rdxA was the only mutation observed. In addition, we observed that H. bizzozeronii ΔrdxA mutant strain showed the same MIC value of metronidazole observed in the spontaneous mutants. These data indicate that loss of function mutations in rdxA and in particular the disruption of the conserved region IACLXALGK is associated with reduced susceptibility to metronidazole in H. bizzozeronii. Slipped-strand mispairing of the SSCR located in the 3' of the H. bizzozeronii rdxA appears to be the main mechanism. We also observed that H. bizzozeronii acquires resistance to metronidazole at high mutation rate, and that serial passages in vitro without selection induced an increased level of susceptibility. In conclusion, contrary to what was previously described in H. pylori, the H. bizzozeronii rdxA appears to be a contingency gene which undergoes phase variation. The contingency nature of rdxA should be carefully considered when metronidazole is used in the treatment of H. heilmannii-associated gastritis.

Helicobacter spp. other than H. pylori

Significant advances have been made over the last 12 months in the understanding of the biology of non-H. pylori Helicobacter species (NHPH). Several studies have investigated the association between NHPH and human disease, including Crohn's disease, lithiasis, liver disease, coronary disease, gastritis, and pyoderma gangrenosum-like ulcers. Novel Helicobacter taxa were identified in new vertebrate hosts, and new methodologies in the fields of identification of Helicobacter spp. and evaluation of antibiotic resistance were described. The genome of the first human-derived gastric NHPH strain (Helicobacter bizzozeronii CIII-1) was sequenced, and several studies elucidated functions of different genes in NHPH. A number of important investigations regarding pathogenesis and immunopathobiology of NHPH infections have been published including the description of a new urease in Helicobacter mustelae. Finally, the effects of the gut microbiota and probiotics on NHPH infections were investigated.

Pathogenesis of Helicobacter pylori infection

Although Helicobacter pylori infection is highly prevalent in the global human population, the majority of infected individuals remain asymptomatic. A complex combination of host, environmental, and bacterial factors are considered to determine susceptibility and severity of outcome in the subset of individuals that develop clinical disease. These factors collectively determine the ability of H. pylori to colonize the gastric mucosa and profoundly influence the nature of the interaction that ensues. Many studies over the last year provide new insight into H. pylori virulence strategies and the activities of critical bacterial determinants that modulate the host environment. These latter include the secreted proteins CagA and VacA and adhesins BabA and OipA, which directly interact with host tissues. Observations from several studies extend the functional repertoire of CagA and the cag type IV secretion system in particular, providing further mechanistic understanding of how these important determinants engage and activate host signalling pathways important in the development of disease.