Orchestration of dysregulated epithelial turnover by a manipulative pathogen

Identification of Desmoglein-2 as a novel target of Helicobacter pylori HtrA in epithelial cells

BACKGROUND

High temperature requirement A (HtrA) is an active serine protease secreted by the group-I carcinogen Helicobacter pylori (H. pylori). The human cell adhesion protein and tumor suppressor E-cadherin (hCdh1) expressed on the surface of gastric epithelial cells was identified as the first HtrA substrate. HtrA-mediated hCdh1 cleavage and subsequent disruption of intercellular adhesions are considered as important steps in H. pylori pathogenesis. In this study, we performed a proteomic profiling of H. pylori HtrA (HpHtrA) to decipher the complex mechanism of H. pylori interference with the epithelial barrier integrity.

RESULTS

Using a proteomic approach we identified human desmoglein-2 (hDsg2), neuropilin-1, ephrin-B2, and semaphorin-4D as novel extracellular HpHtrA substrates and confirmed the well characterized target hCdh1. HpHtrA-mediated hDsg2 cleavage was further analyzed by in vitro cleavage assays using recombinant proteins. In infection experiments, we demonstrated hDsg2 shedding from H. pylori-colonized MKN28 and NCI-N87 cells independently of pathogen-induced matrix-metalloproteases or ADAM10 and ADAM17.

CONCLUSIONS

Characterizing the substrate specificity of HpHtrA revealed efficient hDsg2 cleavage underlining the importance of HpHtrA in opening intercellular junctions. Video Abstract.

High-resolution computational modeling of immune responses in the gut

Background

Helicobacter pylori causes gastric cancer in 1–2% of cases but is also beneficial for protection against allergies and gastroesophageal diseases. An estimated 85% of H. pylori–colonized individuals experience no detrimental effects. To study the mechanisms promoting host tolerance to the bacterium in the gastrointestinal mucosa and systemic regulatory effects, we investigated the dynamics of immunoregulatory mechanisms triggered by H. pylori using a high-performance computing–driven ENteric Immunity SImulator multiscale model. Immune responses were simulated by integrating an agent-based model, ordinary, and partial differential equations.

Results

The outputs were analyzed using 2 sequential stages: the first used a partial rank correlation coefficient regression–based and the second a metamodel-based global sensitivity analysis. The influential parameters screened from the first stage were selected to be varied for the second stage. The outputs from both stages were combined as a training dataset to build a spatiotemporal metamodel. The Sobol indices measured time-varying impact of input parameters during initiation, peak, and chronic phases of infection. The study identified epithelial cell proliferation and epithelial cell death as key parameters that control infection outcomes. In silico validation showed that colonization with H. pylori decreased with a decrease in epithelial cell proliferation, which was linked to regulatory macrophages and tolerogenic dendritic cells.

Conclusions

The hybrid model of H. pylori infection identified epithelial cell proliferation as a key factor for successful colonization of the gastric niche and highlighted the role of tolerogenic dendritic cells and regulatory macrophages in modulating the host responses and shaping infection outcomes.

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-Induced DNA Damage Is a Potential Driver for Human Gastric Cancer AGS Cells

Helicobacter pylori is a major cause of gastric cancer. This study was aimed to explore the characteristic of DNA damage induced by H. pylori infection in gastric cancer AGS cells. After infection with H. pylori, the reactive oxygen species (ROS) levels in AGS cells were significantly higher than those in the uninfected cells. Cells with longer comet tails were detected after infection with H. pylori. The number of apurinic/apyrimidinic endonuclease 1- and phosphorylated H2AX-positive cells was significantly increased compared with the number of negative control cells. The expression of pChk1 and pChk2 was significantly upregulated by H. pylori infection. Cell growth was inhibited after H. pylori infection. All these results were dose dependent. The cell alterations were more significant upon infection with H. pylori at a multiplicity of infection (MOI) of 100:1 than at an MOI of 50:1. H. pylori infection can induce DNA single-strand breaks, DNA double-strand breaks, and cell cycle checkpoint activation after ROS generation in the gastric cancer cell line AGS, which is a potential driver for gastric cancer.

Hydrotalcite Can Prevent the Damaging Effects of Helicobacter Pylori on Gastric Epithelial Cells

BACKGROUND

Helicobacter pylori is a major cause of gastric diseases including gastric cancer. This study was aimed to explore whether hydrotalcite can inhibit H. pylori infection of gastric epithelial cells.

METHODS

the gastric epithelial cell line GES-1 and the gastric cancer cell line BGC823 were infected with H. pylori at multiplicities of infections (MOIs) of 50:1 and 100:1. Hydrotalcite was added to cell cultures. Cell apoptosis and cell cycle analysis were performed to measure the situation of cell growth. The main changes of cell ultrastructure were observed by transmission electron microscopy. H. pylori cell adhesion was observed by scanning electron microscopy.

RESULTS

hydrotalcite could significantly inhibit cell apoptosis of GES-1 and cell proliferation of BGC823 induced by H. pylori infection at an MOI of 50:1. Hydrotalcite treatment protected gastric cells from H. pylori infection, and H. pylori adhesion to gastric cells was reduced. However, hydrotalcite could not reverse damage induced by H. pylori infection at an MOI of 100:1.

CONCLUSION

hydrotalcite can protect gastric cells from H. pylori infection when cell damage is not serious. It can weaken the damage of cells induced by H. pylori and decrease H. pylori adhesion to gastric cells.

Helicobacter pylori and gastric cancer: factors that modulate disease risk

Helicobacter pylori is a gastric pathogen that colonizes approximately 50% of the world's population. Infection with H. pylori causes chronic inflammation and significantly increases the risk of developing duodenal and gastric ulcer disease and gastric cancer. Infection with H. pylori is the strongest known risk factor for gastric cancer, which is the second leading cause of cancer-related deaths worldwide. Once H. pylori colonizes the gastric environment, it persists for the lifetime of the host, suggesting that the host immune response is ineffective in clearing this bacterium. In this review, we discuss the host immune response and examine other host factors that increase the pathogenic potential of this bacterium, including host polymorphisms, alterations to the apical-junctional complex, and the effects of environmental factors. In addition to host effects and responses, H. pylori strains are genetically diverse. We discuss the main virulence determinants in H. pylori strains and the correlation between these and the diverse clinical outcomes following H. pylori infection. Since H. pylori inhibits the gastric epithelium of half of the world, it is crucial that we continue to gain understanding of host and microbial factors that increase the risk of developing more severe clinical outcomes.

Acetylation of apurinic/apyrimidinic endonuclease-1 regulates Helicobacter pylori-mediated gastric epithelial cell apoptosis

BACKGROUND & AIMS

Helicobacter pylori-induced gastric epithelial cell (GEC) apoptosis is a complex process that includes activation of the tumor suppressor p53. p53-mediated apoptosis involves p53 activation, bax transcription, and cytochrome c release from mitochondria. Apurinic/apyrimidinic endonuclease-1 (APE-1) regulates transcriptional activity of p53, and H pylori induce APE-1 expression in human GECs. H pylori infection increases intracellular calcium ion concentration [Ca2+]i of GECs, which induces APE-1 acetylation. We investigated the effects of H pylori infection and APE-1 acetylation on GEC apoptosis.

METHODS

AGS cells (wild-type or with suppressed APE-1), KATO III cells, and cells isolated from gastric biopsy specimens were infected with H pylori. Effects were examined by immunoblotting, real-time reverse-transcription polymerase chain reaction, immunoprecipitation, immunofluorescence microscopy, chromatin immunoprecipitation, mobility shift, DNA binding, and luciferase assays.

RESULTS

H pylori infection increased [Ca2+]i and acetylation of APE-1 in GECs, but the acetylation status of APE-1 did not affect the transcriptional activity of p53. In GECs, expression of a form of APE-1 that could not be acetylated increased total and mitochondrial levels of Bax and induced release of cytochrome c and fragmentation of DNA; expression of wild-type APE-1 reduced these apoptotic events. We identified a negative calcium response element in the human bax promoter and found that poly (adenosine diphosphate-ribose) polymerase 1 recruited the acetylated APE-1/histone deacetylase-1 repressor complex to bax nCaRE.

CONCLUSIONS

H pylori-mediated acetylation of APE-1 suppresses Bax expression; this prevents p53-mediated apoptosis when H pylori infect GECs.