Helicobacter pylori exhibits a fur-dependent acid tolerance response

Helicobacter pylori outer membrane vesicles induce astrocyte reactivity through nuclear factor-κappa B activation and cause neuronal damage in vivo in a murine model

BACKGROUND

Helicobacter pylori (Hp) infects the stomach of 50% of the world's population. Importantly, chronic infection by this bacterium correlates with the appearance of several extra-gastric pathologies, including neurodegenerative diseases. In such conditions, brain astrocytes become reactive and neurotoxic. However, it is still unclear whether this highly prevalent bacterium or the nanosized outer membrane vesicles (OMVs) they produce, can reach the brain, thus affecting neurons/astrocytes. Here, we evaluated the effects of Hp OMVs on astrocytes and neurons in vivo and in vitro.

METHODS

Purified OMVs were characterized by mass spectrometry (MS/MS). Labeled OMVs were administered orally or injected into the mouse tail vein to study OMV-brain distribution. By immunofluorescence of tissue samples, we evaluated: GFAP (astrocytes), βIII tubulin (neurons), and urease (OMVs). The in vitro effect of OMVs in astrocytes was assessed by monitoring NF-κB activation, expression of reactivity markers, cytokines in astrocyte-conditioned medium (ACM), and neuronal cell viability.

RESULTS

Urease and GroEL were prominent proteins in OMVs. Urease (OMVs) was present in the mouse brain and its detection coincided with astrocyte reactivity and neuronal damage. In vitro, OMVs induced astrocyte reactivity by increasing the intermediate filament proteins GFAP and vimentin, the plasma membrane α_Vβ₃ integrin, and the hemichannel connexin 43. OMVs also produced neurotoxic factors and promoted the release of IFNγ in a manner dependent on the activation of the transcription factor NF-κB. Surface antigens on reactive astrocytes, as well as secreted factors in response to OMVs, were shown to inhibit neurite outgrowth and damage neurons.

CONCLUSIONS

OMVs administered orally or injected into the mouse bloodstream reach the brain, altering astrocyte function and promoting neuronal damage in vivo. The effects of OMVs on astrocytes were confirmed in vitro and shown to be NF-κB-dependent. These findings suggest that Hp could trigger systemic effects by releasing nanosized vesicles that cross epithelial barriers and access the CNS, thus altering brain cells.

Consumption of a Gelatin Supplemented with the Probiotic Strain Limosilactobacillus fermentum UCO-979C Prevents Helicobacter pylori Infection in a Young Adult Population Achieved

Helicobacter pylori is a bacterium associated with various gastrointestinal diseases of high worldwide prevalence. Since probiotics are an emerging alternative to managing infection by this pathogenic bacterium, the present work evaluated, in a randomized double-blind study controlled by a placebo, if consuming Limosilactobacillus fermentum UCO-979C prevents H. pylori infection in humans. Participants consumed either L. fermentum UCO-979C-supplemented gelatin (67 participants) or placebo-supplemented gelatin (64 participants) once a day, five days per week for 12 weeks. H. pylori infection in the participants was controlled before and after the intervention detecting H. pylori antigens in stools. Regarding H. pylori-infected participants before the study, 100% remained infected at the end of the study in the placebo group, while 96.7% of those receiving the probiotic remained infected after the intervention. Most importantly, of the non-infected participants, 34.2% became infected and 65.8% remained non-infected in the placebo group, while 2.7% became infected and 97.3% remained as non-infected individuals in the intervened group. Therefore, consuming the L. fermentum UCO-979C strain significantly reduced H. pylori infection, demonstrating a 92.6% efficacy in avoiding infection by this pathogen in non-infected individuals; thus, this probiotic is an excellent candidate to prevent H. pylori infections in non-infected individuals.

Delineation of the pH-Responsive Regulon Controlled by the Helicobacter pylori ArsRS Two-Component System

Helicobacter pylori encounters a wide range of pH within the human stomach. In a comparison of H. pylori cultured in vitro under neutral or acidic conditions, about 15% of genes are differentially expressed, and corresponding changes are detectable for many of the encoded proteins. The ArsRS two-component system (TCS), comprised of the sensor kinase ArsS and its cognate response regulator ArsR, has an important role in mediating pH-responsive changes in H. pylori gene expression. In this study, we sought to delineate the pH-responsive ArsRS regulon and further define the role of ArsR in pH-responsive gene expression. We compared H. pylori strains containing an intact ArsRS system with an arsS null mutant or strains containing site-specific mutations of a conserved aspartate residue (D52) in ArsR, which is phosphorylated in response to signals relayed by the cognate sensor kinase ArsS. We identified 178 genes that were pH-responsive in strains containing an intact ArsRS system but not in ΔarsS or arsR mutants. These constituents of the pH-responsive ArsRS regulon include genes involved in acid acclimatization (ureAB, amidases), oxidative stress responses (katA, sodB), transcriptional regulation related to iron or nickel homeostasis (fur, nikR), and genes encoding outer membrane proteins (including sabA, alpA, alpB, hopD [labA], and horA). When comparing H. pylori strains containing an intact ArsRS TCS with arsRS mutants, each cultured at neutral pH, relatively few genes are differentially expressed. Collectively, these data suggest that ArsRS-mediated gene regulation has an important role in H. pylori adaptation to changing pH conditions.

The histone-like protein HU has a role in gene expression during the acid adaptation response in Helicobacter pylori

BACKGROUND

Gastritis, ulcers, and gastric malignancy have been linked to human gastric epithelial colonization by Helicobacter pylori. Characterization of the mechanisms by which H. pylori adapts to the human stomach environment is of crucial importance to understand H. pylori pathogenesis.

MATERIAL AND METHODS

In an effort to extend our knowledge of these mechanisms, we used proteomic analysis and qRT-PCR to characterize the role of the histone-like protein HU in the response of H. pylori to low pH.

RESULTS

Proteomic analysis revealed that genes involved in chemotaxis, oxidative stress, or metabolism are under control of the HU protein. Also, expression of the virulence factors Ggt and NapA is affected by the null mutation of hup gene both at neutral and acid pH, as evidenced by qRT-PCR analysis.

CONCLUSIONS

Those results showed that H. pylori gene expression is altered by shift to low pH, thus confirming that acid exposure leads to profound changes in genomic expression, and suggest that the HU protein is a regulator that may help the bacterium adapt to the acid stress. In accordance with previous reports, we found that the HU protein participates in gene expression regulation when the microorganism is exposed to acid stress. Such transcriptional regulation underlies protein accumulation in the H. pylori cell.

Metal-responsive promoter DNA compaction by the ferric uptake regulator

Short-range DNA looping has been proposed to affect promoter activity in many bacterial species and operator configurations, but only few examples have been experimentally investigated in molecular detail. Here we present evidence for a metal-responsive DNA condensation mechanism controlled by the Helicobacter pylori ferric uptake regulator (Fur), an orthologue of the widespread Fur family of prokaryotic metal-dependent regulators. H. pylori Fur represses the transcription of the essential arsRS acid acclimation operon through iron-responsive oligomerization and DNA compaction, encasing the arsR transcriptional start site in a repressive macromolecular complex. A second metal-dependent regulator NikR functions as nickel-dependent anti-repressor at this promoter, antagonizing the binding of Fur to the operator elements responsible for the DNA condensation. The results allow unifying H. pylori metal ion homeostasis and acid acclimation in a mechanistically coherent model, and demonstrate, for the first time, the existence of a selective metal-responsive DNA compaction mechanism controlling bacterial transcriptional regulation.

The Fur protein regulates transcription of bacterial genes in response to metal ions. Here, the authors show that the Fur protein from Helicobacter pylori represses transcription by iron-responsive oligomerization and DNA compaction, encasing the transcriptional start site in a macromolecular complex.

A Mycobacterium avium subsp. paratuberculosis Predicted Serine Protease Is Associated with Acid Stress and Intraphagosomal Survival

The ability to maintain intra-cellular pH is crucial for bacteria and other microbes to survive in diverse environments, particularly those that undergo fluctuations in pH. Mechanisms of acid resistance remain poorly understood in mycobacteria. Although, studies investigating acid stress in M. tuberculosis are gaining traction, few center on Mycobacterium avium subsp. paratuberculosis (MAP), the etiological agent of chronic enteritis in ruminants. We identified a MAP acid stress response network involved in macrophage infection. The central node of this network was MAP0403, a predicted serine protease that shared an 86% amino acid identity with MarP in M. tuberculosis. Previous studies confirmed MarP as a serine protease integral to maintaining intra-bacterial pH and survival in acid in vitro and in vivo. We show that MAP0403 is upregulated in infected macrophages and MAC-T cells that coincided with phagosome acidification. Treatment of mammalian cells with bafilomcyin A1, a potent inhibitor of phagosomal vATPases, diminished MAP0403 transcription. MAP0403 expression was also noted in acidic medium. A surrogate host, M. smegmatis mc(2) 155, was designed to express MAP0403 and when exposed to either macrophages or in vitro acid stress had increased bacterial cell viability, which corresponds to maintenance of intra-bacterial pH in acidic (pH = 5) conditions, compared to the parent strain. These data suggest that MAP0403 may be the equivalent of MarP in MAP. Future studies confirming MAP0403 as a serine protease and exploring its structure and possible substrates are warranted.

The DNA-binding protein HU has a regulatory role in the acid stress response mechanism in Helicobacter pylori

BACKGROUND

Bacterial genomes are compacted by association with histone-like proteins to form a complex known as bacterial chromatin. The histone-like protein HU is capable of binding and bending the DNA molecule, a function related to compaction, protection, and regulation of gene expression. In Helicobacter pylori, HU is the only histone-like protein described so far. Proteomic analysis from our laboratory showed that this protein is overexpressed under acidic stress.

MATERIALS AND METHODS

We used a purified recombinant wild-type protein and two mutant proteins with the amino acid substitutions K3A/S27D and K62R/V63N/P64A to characterize the function of the N-terminal domain and the flexible arm of HU.

RESULTS

In vitro assays for DNA protection, bending, and compaction were performed. We also designed a H. pylori hup::cat mutant strain to study the role of HU in the acid stress response. HUwt protein binds DNA and promotes its bending and compaction. Compared with the wild-type protein, both mutant proteins have less affinity for DNA and an impaired bending and compaction ability. By using qRT-PCR, we confirmed overexpression of two genes related to acid stress response (ureA and speA). Such overexpression was abolished in the hup::cat strain, which shows an acid-sensitive phenotype.

CONCLUSIONS

Altogether, we have shown that HUwt -DNA complex formation is favored under acidic pH and that the complex protects DNA from endonucleolytic cleavage and oxidative stress damage. We also showed that the amino-terminal domain of HU is relevant to DNA-protein complex formation and that the flexible arm of HU is involved in the bending and compaction activities of HU.

Characterization of the arginine decarboxylase gene (ORF HP0422, speA) involved in acid tolerance in Helicobacter pylori

BACKGROUND

Helicobacter pylori is a motile microaerophilic bacterium that colonizes the human stomach. H. pylori infection triggers gastric diseases, such as gastritis, peptic ulcer and gastric cancer. Stomach represents a barrier for microorganism colonization, particularly because of its high hydrochloric acid concentration. The main mechanism developed by H. pylori to maintain intracellular pH homeostasis in this environment is the urease activity. However, urease negative strains can be also isolated from clinical samples, suggesting that H. pylori presents other components involved in acid resistance.

OBJECTIVE

Here, we present some evidence that the arginine decarboxylase gene (speA) in H. pylori could be involved in an acid adaptation mechanism similar to the one in Enterobacteriaceae, which is dependent on the presence of arginine.

METHODS

Indeed, speA mRNA and protein expression are acutely induced by acid stress.

RESULTS

Moreover, we showed that H. pylori uses arginine in an acid response mechanism required for its growth in acid conditions.

CONCLUSION

Altogether, these results provide novel information regarding the H. pylori physiology and acid response mechanism.

Arginine 66 residue of Fur is required for the regulatory function of this protein in the acid adaptation mechanism of Helicobacter pylori

BACKGROUND

Helicobacter pylori colonizes the gastric mucosa and must survive the acid pH of that environment. Like other enteric bacterial pathogens, including Salmonella enterica, H. pylori develops an acid tolerance response that is dependent on the function of the transcriptional regulator protein Fur.

OBJECTIVE

To explore by site-directed mutagenesis whether two particular amino acid residues in the amino acid sequence of the H. pylori Fur protein, arginine 66 and histidine 99, are involved in the acid response mechanism in this bacterium.

MATERIALS AND METHODS

Complementation assays in Escherichia coli H1780 (fur null mutant) both with plasmids carrying the H. pylori fur gene bearing substitution mutations R66A or H99A or R66A/H99A and with the H. pylori Fur-R66A mutant were conducted. Wild-type and mutated Fur proteins from H. pylori were assayed by using the fiu::lacZ reporter gene in the E. coli H1780 heterologous system at various pH and iron concentrations.

RESULTS

Both bacterial growth and repression of the reporter gene were impaired under acid conditions in E. coli H1780 complemented with pUC19-fur-R66A. Also, in the H. pylori Fur-R66 strain bacterial growth and speA gene expression were impaired under acid conditions.

CONCLUSIONS

Arginine 66 but not histidine 99 in H. pylori Fur is required for the regulatory function of the Fur protein in the acid adaptation mechanism of the bacterium.