Characterization of virulence factors of mouse-adapted Helicobacter pylori strain SS1 and effects on gastric hydrophobicity

Genomic and vaccine preclinical studies reveal a novel mouse-adapted Helicobacter pylori model for the hpEastAsia genotype in Southeast Asia

Introduction. Helicobacter pylori infection is a major global health concern, linked to the development of various gastrointestinal diseases, including gastric cancer. To study the pathogenesis of H. pylori and develop effective intervention strategies, appropriate animal pathogen models that closely mimic human infection are essential.Gap statement. This study focuses on the understudied hpEastAsia genotype in Southeast Asia, a region marked by a high H. pylori infection rate. No mouse-adapted model strains has been reported previously. Moreover, it recognizes the urgent requirement for vaccines in developing countries, where overuse of antimicrobials is fuelling the emergence of resistance.Aim. This study aims to establish a novel mouse-adapted H. pylori model specific to the hpEastAsia genotype prevalent in Southeast Asia, focusing on comparative genomic and histopathological analysis of pathogens coupled with vaccine preclinical studies.Methodology. We collected and sequenced the whole genome of clinical strains of H. pylori from infected patients in Vietnam and performed comparative genomic analyses of H. pylori strains in Southeast Asia. In parallel, we conducted preclinical studies to assess the pathogenicity of the mouse-adapted H. pylori strain and the protective effect of a new spore-vectored vaccine candidate on male Mlac:ICR mice and the host immune response in a female C57BL/6 mouse model.Results. Genome sequencing and comparison revealed unique and common genetic signatures, antimicrobial resistance genes and virulence factors in strains HP22 and HP34; and supported clarithromycin-resistant HP34 as a representation of the hpEastAsia genotype in Vietnam and Southeast Asia. HP34-infected mice exhibited gastric inflammation, epithelial erosion and dysplastic changes that closely resembled the pathology observed in human H. pylori infection. Furthermore, comprehensive immunological characterization demonstrated a robust host immune response, including both mucosal and systemic immune responses. Oral vaccination with candidate vaccine formulations elicited a significant reduction in bacterial colonization in the model.Conclusion. Our findings demonstrate the successful development of a novel mouse-adapted H. pylori model for the hpEastAsia genotype in Vietnam and Southeast Asia. Our research highlights the distinctive genotype and pathogenicity of clinical H. pylori strains in the region, laying the foundation for targeted interventions to address this global health burden.

A Mouse Model of Helicobacter pylori Infection

Infection with Helicobacter pylori (H. pylori) is of great distress because of its vital role in the pathogenesis of chronic gastritis, peptic ulcers, and in the multi-step carcinogenic process of gastric cancer. The increasing antibiotic resistance pattern of H. pylori worldwide has prompted the World Health Organization to put this organism in the priority pathogens list. To study the disease biology, evaluation of drugs, treatment outcome and to come up with probable vaccination strategies, competent animal models that reproduce the signature of human infection are essential. Initial reports about animal colonization with H. pylori have shown significant heterogeneity, to such an extent that Barry Marshall, Nobel laureate for the discovery of H. pylori , infected himself with the bacterium to show its involvement in acute gastric illness. A paradigm-shift discovery of the H. pylori mouse-adapted strain SS1 has opened the avenues of research regarding the organism and its pathogenicity. Although the mouse model of H. pylori infection is being utilized all over the world, there are certain issues that need awareness and specific information to achieve successful, consistent colonization with symptoms resembling human. This chapter details an established and reliable protocol for the development of a competent mouse model for H. pylori infection leading to various gastro-intestinal diseases.

Quantum changes in Helicobacter pylori gene expression accompany host-adaptation

Helicobacter pylori is a highly successful gastric pathogen. High genomic plasticity allows its adaptation to changing host environments. Complete genomes of H. pylori clinical isolate UM032 and its mice-adapted serial derivatives 298 and 299, generated using both PacBio RS and Illumina MiSeq sequencing technologies, were compared to identify novel elements responsible for host-adaptation. The acquisition of a jhp0562-like allele, which encodes for a galactosyltransferase, was identified in the mice-adapted strains. Our analysis implies a new β-1,4-galactosyltransferase role for this enzyme, essential for Le^y antigen expression. Intragenomic recombination between babA and babB genes was also observed. Further, we expanded on the list of candidate genes whose expression patterns have been mediated by upstream homopolymer-length alterations to facilitate host adaption. Importantly, greater than four-fold reduction of mRNA levels was demonstrated in five genes. Among the down-regulated genes, three encode for outer membrane proteins, including BabA, BabB and HopD. As expected, a substantial reduction in BabA protein abundance was detected in mice-adapted strains 298 and 299 via Western analysis. Our results suggest that the expression of Le^y antigen and reduced outer membrane protein expressions may facilitate H. pylori colonisation of mouse gastric epithelium.

Axisymmetric Drop Shape Analysis (ADSA): An Outline

Drop shape techniques for the measurement of interfacial tension are powerful, versatile and flexible. The shape of the drop/bubble depends on the balance between surface tension and external forces, e.g. gravity. This balance is reflected mathematically in the Laplace equation of capillarity. Axisymmetric Drop Shape Analysis (ADSA) is a commonly used drop shape technique. A streamlined version of the development of ADSA over the past several decades is presented to illustrate its validity and range of utility. Several configurations of interest will be considered and presented systematically. Shape and surface tension will be linked to a shape parameter based on proper concepts of differential geometry. The resulting shape parameter will be shown to allow determination of the range of applicability of such a drop shape method.

Helicobacter pylori-induced IL-1β secretion in innate immune cells is regulated by the NLRP3 inflammasome and requires the cag pathogenicity island

Infection with the gram-negative bacterium Helicobacter pylori is the most prevalent chronic bacterial infection, affecting ∼50% of the world's population, and is the main risk factor of gastric cancer. The proinflammatory cytokine IL-1β plays a crucial role in the development of gastric tumors and polymorphisms in the IL-1 gene cluster leading to increased IL-1β production have been associated with increased risk for gastric cancer. To be active, pro-IL-1β must be cleaved by the inflammasome, an intracellular multiprotein complex implicated in physiological and pathological inflammation. Recently, H. pylori was postulated to activate the inflammasome in murine bone marrow-derived dendritic cells; however, the molecular mechanisms as well as the bacterial virulence factor acting as signal 2 activating the inflammasome remain elusive. In this study, we analyzed the inflammasome complex regulating IL-1β upon H. pylori infection as well as the molecular mechanisms involved. Our results indicate that H. pylori-induced IL-1β secretion is mediated by activation of the nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 inflammasome. We also show that reactive oxygen species, potassium efflux, and lysosomal destabilization are the main cellular mechanisms responsible of nucleotide-binding oligomerization domain family, pyrin domain-containing 3 inflammasome activation upon H. pylori infection, and identify vacuolating cytotoxin A and cag pathogenicity island as the bacterial virulence determinants involved. Moreover, in vivo experiments indicate an important role for the inflammasome in the onset and establishment of H. pylori infection and in the subsequent inflammatory response of the host.

Caveolin-1 protects B6129 mice against Helicobacter pylori gastritis

Caveolin-1 (Cav1) is a scaffold protein and pathogen receptor in the mucosa of the gastrointestinal tract. Chronic infection of gastric epithelial cells by Helicobacter pylori (H. pylori) is a major risk factor for human gastric cancer (GC) where Cav1 is frequently down-regulated. However, the function of Cav1 in H. pylori infection and pathogenesis of GC remained unknown. We show here that Cav1-deficient mice, infected for 11 months with the CagA-delivery deficient H. pylori strain SS1, developed more severe gastritis and tissue damage, including loss of parietal cells and foveolar hyperplasia, and displayed lower colonisation of the gastric mucosa than wild-type B6129 littermates. Cav1-null mice showed enhanced infiltration of macrophages and B-cells and secretion of chemokines (RANTES) but had reduced levels of CD25⁺ regulatory T-cells. Cav1-deficient human GC cells (AGS), infected with the CagA-delivery proficient H. pylori strain G27, were more sensitive to CagA-related cytoskeletal stress morphologies (“humming bird”) compared to AGS cells stably transfected with Cav1 (AGS/Cav1). Infection of AGS/Cav1 cells triggered the recruitment of p120 RhoGTPase-activating protein/deleted in liver cancer-1 (p120RhoGAP/DLC1) to Cav1 and counteracted CagA-induced cytoskeletal rearrangements. In human GC cell lines (MKN45, N87) and mouse stomach tissue, H. pylori down-regulated endogenous expression of Cav1 independently of CagA. Mechanistically, H. pylori activated sterol-responsive element-binding protein-1 (SREBP1) to repress transcription of the human Cav1 gene from sterol-responsive elements (SREs) in the proximal Cav1 promoter. These data suggested a protective role of Cav1 against H. pylori-induced inflammation and tissue damage. We propose that H. pylori exploits down-regulation of Cav1 to subvert the host's immune response and to promote signalling of its virulence factors in host cells.

Infection with the bacterium Helicobacter pylori (H. pylori) mainly affects children in the developing countries who are at risk to progress to gastric cancer (GC) as adults after many years of persistent infection, especially with strains which are positive for the oncogenic virulence factor CagA. Eradication of H. pylori by antibiotics is a treatment of choice but may also alter the susceptibility to allergies and other tumor types. Thus, novel diagnostic or prognostic markers are needed which detect early molecular changes in the stomach mucosa during the transition of chronic inflammation to cancer. In our study, we found that the tumor suppressor caveolin-1 (Cav1) is reduced upon infection with H. pylori, and CagA was sufficient but not necessary for this down-regulation. Loss of Cav1 was caused by H. pylori-dependent activation of sterol-responsive element-binding protein-1 (SREBP1), and this event abolished the interaction of Cav1 with p120 RhoGTPase-activating protein/deleted in liver cancer-1 (p120RhoGAP/DLC1), a second bona fide tumor suppressor in gastric tissue. Conclusively, Cav1 and DLC1 may constitute novel molecular markers in the H. pylori-infected gastric mucosa before neoplastic transformation of the epithelium.

Transcriptional profiling of gastric epithelial cells infected with wild type or arginase-deficient Helicobacter pylori

Background

Helicobacter pylori causes acute and chronic gastric inflammation induced by proinflammatory cytokines and chemokines secreted by cells of the gastric mucosa, including gastric epithelial cells. Previous studies have demonstrated that the bacterial arginase, RocF, is involved in inhibiting T cell proliferation and CD3ζ expression, suggesting that arginase could be involved in a more general dampening of the immune response, perhaps by down-regulation of certain pro-inflammatory mediators.

Results

Global transcriptome analysis was performed on AGS gastric epithelial cells infected for 16 hours with a wild type Helicobacter pylori strain 26695, an arginase mutant (rocF-) or a rocF⁺ complemented strain. H. pylori infection triggered altered host gene expression in genes involved in cell movement, death/growth/proliferation, and cellular function and maintenance. While the wild type strain stimulates host inflammatory pathways, the rocF- mutant induced significantly more expression of IL-8. The results of the microarray were verified using real-time PCR, and the differential levels of protein expression were confirmed by ELISA and Bioplex analysis. MIP-1B was also significantly secreted by AGS cells after H. pylori rocF- mutant infection, as determined by Bioplex. Even though not explored in this manuscript, the impact that the results presented here may have on the development of gastritis, warrant further research to understand the underlying mechanisms of the relationship between H. pylori RocF and IL-8 induction.

Conclusions

We conclude that H. pylori arginase modulates multiple host signaling and metabolic pathways of infected gastric epithelial cells. Arginase may play a critical role in anti-inflammatory host responses that could contribute to the ability of H. pylori to establish chronic infections.

Helicobacter pylori phagosome maturation in primary human macrophages

Background

Helicobacter pylori (H. pylori) is a micro-aerophilic, spiral-shaped, motile bacterium that is the principal cause of gastric and duodenal ulcers in humans and is a major risk factor for the development of gastric cancer. Despite provoking a strong innate and adaptive immune response in the host, H. pylori persists in the gastric mucosa, avoiding eradication by macrophages and other phagocytic cells, which are recruited to the site of infection. Here we have characterised the critical degradative process of phagosome maturation in primary human macrophages for five genotypically and phenotypically distinct clinical strains of H. pylori.

Results

All of the H. pylori strains examined showed some disruption to the phagosome maturation process, when compared to control E. coli. The early endosome marker EEA1 and late endosome marker Rab7 were retained on H. pylori phagosomes, while the late endosome-lysosome markers CD63, LAMP-1 and LAMP-2 were acquired in an apparently normal manner. Acquisition of EEA1 by H. pylori phagosomes appeared to occur by two distinct, strain specific modes. H. pylori strains that were negative for the cancer associated virulence factor CagA were detected in phagosomes that recruited large amounts of EEA1 relative to Rab5, compared to CagA positive strains. There were also strain specific differences in the timing of Rab7 acquisition which correlated with differences in the rate of intracellular trafficking of phagosomes and the timing of megasome formation. Megasomes were observed for all of the H. pylori strains examined.

Conclusions

H. pylori appeared to disrupt the normal process of phagosome maturation in primary human macrophages, appearing to block endosome fission. This resulted in the formation of a hybrid phagosome-endosome-lysosome compartment, which we propose has reduced degradative capacity. Reduced killing by phagocytes is consistent with the persistence of H. pylori in the host, and would contribute to the chronic stimulation of the inflammatory immune response, which underlies H. pylori-associated disease.

Helicobacter pylori promotes hepatic fibrosis in the animal model

Helicobacter pylori infection has been reported to be very common in patients with chronic liver diseases, including cirrhosis. To elucidate the pathological effect of H. pylori infection on the progression of hepatic fibrosis, C57BL/6 mice and Sprague-Dawley rats were orally inoculated with H. pylori, and hepatic fibrosis was induced with carbon tetrachloride (CCl(4)) administration. We observed the histopathological changes and the presence of H. pylori genes by PCR in the liver. Significant increase in the fibrotic score as well as in serum alanine aminotransferase and aspartate aminotransferase levels was shown in the CCl(4)+H. pylori group compared with that in the CCl(4)-treated group. Compared with the CCl(4)-treated group, alpha-smooth muscle actin and transforming growth factor-beta1 were enhanced; however, senescence marker protein-30, a multifunctional protein protecting hepatocytes against oxidative stress and apoptosis, was suppressed in the CCl(4)+H. pylori group. The 16S rRNA (400 bp) was demonstrated by PCR for H. pylori genes from genomic DNA extracted from the liver, and H. pylori-infected mice showed 93.8% (15 of 16) seropositivity by contrast with seronegativity in all H. pylori-noninfected mice. In addition, immunohistochemical study against H. pylori showed positive antigen fragments in the liver of the infected groups. Consequently, our data suggest that H. pylori infection could be an important contributing infectious factor to the development of liver cirrhosis.

Helicobacter pylori activates myosin light-chain kinase to disrupt claudin-4 and claudin-5 and increase epithelial permeability

Helicobacter pylori is a spiral, gram-negative bacterium that specifically and persistently infects the human stomach. In some individuals, H. pylori-induced chronic gastritis may progress to gastroduodenal ulcers and gastric cancer. Currently, the host-microbe interactions that determine the clinical outcome of infection are not well defined. H. pylori strains capable of disrupting the gastric epithelial barrier may increase the likelihood of developing serious disease. In this study, H. pylori strain SS1 increased gastric, but not small intestinal, permeability in C57BL/6 mice. H. pylori strain SS1 was able to directly increase paracellular permeability, in the absence of host inflammatory cells, by disrupting the tight-junctional proteins occludin, claudin-4, and claudin-5 in confluent nontransformed epithelial cells. H. pylori SS1 also reduced claudin-4 protein levels in human gastric AGS cells. The ability of H. pylori SS1 to increase permeability appeared to be independent of the well-characterized virulence factors vacuolating cytotoxin and CagA protein. H. pylori activated myosin light-chain kinase in epithelial cells to phosphorylate myosin light chain and increase permeability by disrupting claudin-4 and claudin-5. The bacterial factor responsible for increasing epithelial permeability was heat sensitive, membrane bound, and required apical contact with monolayers. In conclusion, disruptions of the tight junctions observed in this study implicate host cell signaling pathways, including the phosphorylation of myosin light chain and the regulation of tight-junctional proteins claudin-4 and claudin-5, in the pathogenesis of H. pylori infection.

Analysis of gene expression profile in gastric cancer cells stimulated with Helicobacter pylori isogenic strains

To understand the biological processes within host cells induced by VacA, isogenic strains of Helicobacter pylori (NCTC 11638 or 11638-DeltavacA) were used to stimulate gastric cancer cells SGC7901, and differentially expressed genes in host cells were identified using cDNA microarray technology. More than 300 genes were found to alter their mRNA expression at different time points, among which 68 were related to the cytoskeleton, 87 were associated with cell cycle, cell death and proliferation, IL8 expression was also found to be up-regulated. Cells co-cultured with broth-culture supernatant (BCS) of NCTC 11638 showed more alteration in microtubule cytoskeleton morphology, as observed by laser scanning confocal microscopy, and a lower apoptosis rate, detected by flow cytometry, compared with those co-cultured with BCS of 11638-DeltavacA. The supernatants of cells co-cultured with NCTC 11638 showed significantly higher IL8 expression than those co-cultured with 11638-DeltavacA. It is concluded that VacA disrupts cytoskeletal architecture by influencing the expression of cytoskeleton-associated genes. VacA breaks the balance between cell proliferation and cell death by inducing the maladjustment of genes related to cell cycle. VacA is also able to induce the inflammatory response.

Helicobacter pylori disrupts STAT1-mediated gamma interferon-induced signal transduction in epithelial cells

Infection with Helicobacter pylori is chronic despite a vigorous mucosal immune response characterized by gastric T-helper type 1 cell expansion and gamma interferon (IFN-gamma) production. IFN-gamma signals by activation and nuclear translocation of signal transducer and activator of transcription 1 (STAT1); however, the effect of H. pylori infection on IFN-gamma-STAT1 signaling is unknown. We infected human gastric (MKN45 and AGS) and laryngeal (HEp-2) epithelial cell lines with type 1 and type 2 H. pylori strains and then stimulated them with IFN-gamma. Western blotting of whole-cell protein extracts revealed that infection with live, but not heat-killed, H. pylori time-dependently decreased IFN-gamma-induced STAT1 tyrosine phosphorylation. Electrophoretic mobility shift assay of nuclear protein extracts demonstrated that H. pylori infection reduced IFN-gamma-induced STAT1 DNA binding. STAT1 was unable to translocate from the cytoplasm to the nucleus in H. pylori-infected HEp-2 cells examined by immunofluorescence, and reverse transcription-PCR showed that IFN-gamma-induced interferon regulatory factor 1 expression was inhibited. These effects were independent of the cagA, cagE, and VacA status of the infecting H. pylori strain. Furthermore, neither H. pylori culture supernatants nor conditioned medium from H. pylori-infected MKN45 cells inhibited IFN-gamma-induced STAT1 tyrosine phosphorylation, suggesting that inhibition is independent of a soluble epithelial or bacterial factor but is dependent on bacterial contact with epithelial cells. H. pylori disruption of IFN-gamma-STAT1 signaling in epithelial cells may represent a mechanism by which the bacterium modifies mucosal immune responses to promote its survival in the human host.

Helicobacter pylori infection interferes with epithelial Stat6-mediated interleukin-4 signal transduction independent of cagA, cagE, or VacA

Helicobacter pylori is a bacterial pathogen evolved to chronically colonize the gastric epithelium, evade immune clearance by the host, and cause gastritis, peptic ulcers, and even gastric malignancies in some infected humans. In view of the known ability of this bacterium to manipulate gastric epithelial cell signal transduction cascades, we determined the effects of H. pylori infection on epithelial IL-4-Stat6 signal transduction. HEp-2 and MKN45 epithelial cells were infected with H. pylori strains LC11 or 8823 (type 1; cagA(+)/cagE(+)/VacA(+)), LC20 (type 2; cagA(-), cagE(-), VacA(-)), and cagA, cagE, and vacA isogenic mutants of strain 8823, with some cells receiving subsequent treatment with the Th2 cytokine IL-4, a known Stat6 activator. Immunofluorescence showed a disruption of Stat6-induced nuclear translocation by IL-4 in LC11-infected HEp-2 cells. IL-4-inducible Stat6 DNA binding in HEp-2 and MKN45 cells was abrogated by infection, but MKN45 cell viability was unaffected. A decrease in IL-4-mediated Stat6 tyrosine phosphorylation in nuclear and whole cell lysates was also observed following infection with strains LC11 and LC20, while neither strain altered IL-4 receptor chain alpha or Janus kinase 1 protein expression. Furthermore, parental strain 8823 and its isogenic cagA, cagE, and vacA mutants also suppressed IL-4-induced Stat6 tyrosine phosphorylation to comparable degrees. Thus, H. pylori did not directly activate Stat6, but blocked the IL-4-induced activation of epithelial Stat6. This may represent an evolutionarily conserved strategy to disrupt a Th2 response and evade the host immune system, allowing for successful chronic infection.