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Deficiency of the myeloid differentiation primary response molecule MyD88 leads to an early and rapid development of Helicobacter-induced gastric malignancy.

ABSTRACT: Approximately 50% of the world's population is infected with Helicobacter pylori, leading to chronic inflammation, which increases the risk for gastric adenocarcinoma. MyD88 is a key adaptor molecule in inflammatory pathways involved in interleukin 1 (IL-1)/IL-18/Toll-like receptor signaling and has been shown to have divergent effects in carcinogenesis. The role of MyD88 in Helicobacter-induced gastric malignancy is unknown. Using a mouse model of Helicobacter-induced gastric cancer, we assessed the role of MyD88 in cancer development by evaluating gastric histopathology, apoptosis, proliferation, and cytokine expression. Infection of MyD88-deficient (Myd88(-/-)) mice with Helicobacter resulted in early and rapid advancement to gastric dysplasia as early as 25 weeks postinfection. The progression of Helicobacter-induced disease to precancerous and cancerous lesions in the absence of MyD88 signaling was accompanied by increased gastric epithelial apoptosis and proliferation. In addition, inflammatory cytokines, including tumor necrosis factor alpha (TNF-?), gamma interferon (IFN-?), IL-6, and IL-1? were highly expressed in association with the development of gastric dysplasia. These data suggest that MyD88 signaling retards development and progression to cancer during Helicobacter infection. This is the first study to show evidence of MyD88 protection in an infection-driven inflammation-associated cancer model.

SUBMITTER: Banerjee A

PROVIDER: S-EPMC3911874 | biostudies-other | 2014 Jan

REPOSITORIES: biostudies-other

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Deficiency of the myeloid differentiation primary response molecule MyD88 leads to an early and rapid development of Helicobacter-induced gastric malignancy.

Banerjee Anirban A Thamphiwatana Soracha S Carmona Ellese M EM Rickman Barry B Doran Kelly S KS Obonyo Marygorret M

Infection and immunity 20131028 1

Approximately 50% of the world's population is infected with Helicobacter pylori, leading to chronic inflammation, which increases the risk for gastric adenocarcinoma. MyD88 is a key adaptor molecule in inflammatory pathways involved in interleukin 1 (IL-1)/IL-18/Toll-like receptor signaling and has been shown to have divergent effects in carcinogenesis. The role of MyD88 in Helicobacter-induced gastric malignancy is unknown. Using a mouse model of Helicobacter-induced gastric cancer, we assesse ...[more]

PMID: 24166959

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Project description:BackgroundHelicobacter pylori is a human stomach pathogen, naturally-competent for DNA uptake, and prone to homologous recombination. Extensive homoplasy (i.e., phylogenetically-unlinked identical variations) observed in H. pylori genes is considered a hallmark of such recombination. However, H. pylori also exhibits a high mutation rate. The relative adaptive role of homologous recombination and mutation in species diversity is a highly-debated issue in biology. Recombination results in homoplasy. While convergent mutation can also account for homoplasy, its contribution is thought to be minor. We demonstrate here that, contrary to dogma, convergent mutation is a key contributor to Helicobacter pylori homoplasy, potentially driven by adaptive evolution of proteins.ResultsOur present genome-wide analysis shows that homoplastic nonsynonymous (amino acid replacement) changes are not typically accompanied by homoplastic synonymous (silent) variations. Moreover, the majority of the codon positions with homoplastic nonsynonymous changes also contain different (i.e. non-homoplastic) nonsynonymous changes arising from mutation only. This indicates that, to a considerable extent, nonsynonymous homoplasy is due to convergent mutations. High mutation rate or limited availability of evolvable sites cannot explain this excessive convergence, as suggested by our simulation studies. Rather, the genes with convergent mutations are overrepresented in distinct functional categories, suggesting possible selective responses to conditions such as distinct micro-niches in single hosts, and to differences in host genotype, physiology, habitat and diet.ConclusionsWe propose that mutational convergence is a key player in H. pylori's adaptation and extraordinary persistence in human hosts. High frequency of mutational convergence could be due to saturation of evolvable sites capable of responding to selection pressures, while the number of mutable residues is far from saturation. We anticipate a similar scenario of mutational vs. recombinational genome dynamics or plasticity for other naturally competent microbes where strong positive selection could favor frequent convergent mutations in adaptive protein evolution.

Project description: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.IMPORTANCEHelicobacter 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.

Dataset Information

Deficiency of the myeloid differentiation primary response molecule MyD88 leads to an early and rapid development of Helicobacter-induced gastric malignancy.

Publications

Deficiency of the myeloid differentiation primary response molecule MyD88 leads to an early and rapid development of Helicobacter-induced gastric malignancy.

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