Toll-like receptor (TLR) 2 and TLR5, but not TLR4, are required for Helicobacter pylori-induced NF-kappa B activation and chemokine expression by epithelial cells

Current Knowledge about Gastric Microbiota with Special Emphasis on Helicobacter pylori-Related Gastric Conditions

The gastric milieu, because of its very low acidic pH, is very harsh for bacterial growth. The discovery of Helicobacter pylori (H.p.) has opened a new avenue for studies on the gastric microbiota, thus indicating that the stomach is not a sterile environment. Nowadays, new technologies of bacterial identification have demonstrated the existence of other microorganisms in the gastric habitat, which play an important role in health and disease. This bacterium possesses an arsenal of compounds which enable its survival but, at the same time, damage the gastric mucosa. Toxins, such as cytotoxin-associated gene A, vacuolar cytotoxin A, lipopolysaccharides, and adhesins, determine an inflammatory status of the gastric mucosa which may become chronic, ultimately leading to a gastric carcinoma. In the initial stage, H.p. persistence alters the gastric microbiota with a condition of dysbiosis, predisposing to inflammation. Probiotics and prebiotics exhibit beneficial effects on H.p. infection, and, among them, anti-inflammatory, antioxidant, and antibacterial activities are the major ones. Moreover, the association of probiotics with prebiotics (synbiotics) to conventional anti-H.p. therapy contributes to a more efficacious eradication of the bacterium. Also, polyphenols, largely present in the vegetal kingdom, have been demonstrated to alleviate H.p.-dependent pathologies, even including the inhibition of tumorigenesis. The gastric microbiota composition in health and disease is described. Then, cellular and molecular mechanisms of H.p.-mediated damage are clarified. Finally, the use of probiotics, prebiotics, and polyphenols in experimental models and in patients infected with H.p. is discussed.

Sustained exposure to Helicobacter pylori induces immune tolerance by desensitizing TLR6

Helicobacter pylori (H. pylori, Hp) has been designated a class I carcinogen and is closely associated with severe gastric diseases. During colonization in the gastric mucosa, H. pylori develops immune escape by inducing host immune tolerance. The gastric epithelium acts as the first line of defense against H. pylori, with Toll-like receptors (TLRs) in gastric epithelial cells being sensitive to H. pylori components and subsequently activating the innate immune system. However, the mechanism of immune tolerance induced by H. pylori through the TLR signalling pathway has not been fully elucidated. In this research, we detected the expression of TLRs and inflammatory cytokines in GES-1 cells upon sustained exposure to H. pylori or H. pylori lysate from 1 to 30 generations and in Mongolian gerbils infected with H. pylori for 5 to 90 weeks. We found that the levels of TLR6 and inflammatory cytokines first increased and then dropped during the course of H. pylori treatment in vitro and in vivo. The restoration of TLR6 potentiated the expression of IL-1β and IL-8 in GES-1 cells, which recruited neutrophils and reduced the colonization of H. pylori in the gastric mucosa of gerbils. Mechanistically, we found that persistent infection with H. pylori reduces the sensitivity of TLR6 to bacterial components and regulates the expression of inflammatory cytokines in GES-1 cells through TLR6/JNK signaling. The TLR6 agonist obviously alleviated inflammation in vitro and in vivo. Promising results suggest that TLR6 may be a potential candidate immunotherapy drug for H. pylori infection.

Essential role of Helicobacter pylori apolipoprotein N-acyltransferase (Lnt) in stomach colonization

Bacterial lipoproteins are post-translationally modified with acyl chains, anchoring these proteins to bacterial membranes. In Gram-negative bacteria, three enzymes complete the modifications. Lgt (which adds two acyl chains) and LspA (which removes the signal peptide) are essential. Lnt (which adds a third acyl chain) is not essential in certain bacteria including Francisella tularensis, Neisseria gonorrhoeae, and Acinetobacter baumannii. Deleting lnt results in mild to severe physiologic changes. We previously showed lnt is not essential for Helicobacter pylori growth in vitro. Here, the physiologic consequences of deleting lnt in H. pylori and the role of Lnt in the host response to H. pylori were examined using in vitro and in vivo models. Comparing wild-type, Δlnt, and complemented mutant H. pylori, no changes in growth rates or sensitivity to acid or antibiotics were observed. Since deleting lnt changes the number of acyl chains on lipoproteins and the number of acyl chains on lipoproteins impacts the innate immune response through Toll-like receptor 2 (TLR2) signaling, primary human gastric epithelial cells were treated with a purified lipoprotein from wild-type or lnt mutant H. pylori. Differential gene expression analysis indicated that lipoprotein from the lnt mutant induced a more robust TLR2 response. In a complementary approach, we infected wild-type and Tlr2-/- mice and found that both the wild-type and complemented mutant strains successfully colonized the animals. However, the lnt mutant strain was unable to colonize either mouse strain. These results show that lnt is essential for H. pylori colonization and identifies lipoprotein synthesis as a target for therapeutic intervention.

The role of toll-like receptors in immune tolerance induced by Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a gram-negative, microaerobic bacterium that colonizes the gastric mucosa in about half of the world's population. H. pylori infection can lead to various diseases. Chronic infection by H. pylori exposes the gastric mucosa to bacterial components such as lipopolysaccharide (LPS), outer membrane vesicles (OMVs), and several toxic proteins. Infected with H. pylori activates the release of pro-inflammatory factors and triggers inflammatory responses that damage the gastric mucosa. As the only microorganism that permanently colonizes the human stomach, H. pylori can suppress host immunity to achieve long-term colonization. Toll-like receptors (TLRs) play a crucial role in T-cell activation, promoting innate immune responses and immune tolerance during H. pylori infection. Among the 10 TLRs found in humans, TLR2, TLR4, TLR5, and TLR9 have been thoroughly investigated in relation to H. pylori-linked immune regulation. In the present review, we provide a comprehensive analysis of the various mechanisms employed by different TLRs in the induction of immune tolerance upon H. pylori infection, which will contribute to the research of pathogenic mechanism of H. pylori.

The TLR/MyD88 signalling cascade in inflammation and gastric cancer: the immune regulatory network of Helicobacter pylori

Helicobacter pylori-induced chronic gastritis represents a well-established risk factor for gastric cancer (GC). However, the mechanism by which chronic inflammation caused by H. pylori induces the development of GC is unclear. H. pylori can influence host cell signalling pathways to induce gastric disease development and mediate cancer promotion and progression. Toll-like receptors (TLRs), as pattern recognition receptors (PRRs), play a key role in the gastrointestinal innate immune response, and their signalling has been implicated in the pathogenesis of an increasing number of inflammation-associated cancers. The core adapter myeloid differentiation factor-88 (MyD88) is shared by most TLRs and functions primarily in H. pylori-triggered innate immune signalling. MyD88 is envisioned as a potential target for the regulation of immune responses and is involved in the regulation of tumourigenesis in a variety of cancer models. In recent years, the TLR/MyD88 signalling pathway has received increasing attention for its role in regulating innate and adaptive immune responses, inducing inflammatory activation and promoting tumour formation. In addition, TLR/MyD88 signalling can manipulate the expression of infiltrating immune cells and various cytokines in the tumour microenvironment (TME). In this review, we discuss the pathogenetic regulatory mechanisms of the TLR/MyD88 signalling cascade pathway and its downstream molecules in H. pylori infection-induced-associated GC. The focus is to elucidate the immunomolecular mechanisms of pathogen recognition and innate immune system activation of H. pylori in the TME of inflammation-associated GC. Ultimately, this study will provide insight into the mechanism of H. pylori-induced chronic inflammation-induced GC development and provide thoughts for GC prevention and treatment strategies.

Role of TLRs in EGFR-mediated IL-8 secretion by enteroaggregative Escherichia coli-infected cultured human intestinal epithelial cells

Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen associated with persistent diarrhea in travelers, immunocompromised patients and children worldwide. However, the pathogenesis of this organism is yet to be established. In this study, the role of Toll-like receptors (TLRs) was evaluated in epidermal growth factor receptor (EGFR)-mediated IL-8 secretion by EAEC-infected human small intestinal and colonic epithelial cells (INT-407 and HCT-15, respectively). We observed that EAEC-induced upregulation of TLR2, TLR4 and TLR5 transcripts in both types of cells, and the maximum level of these transcripts was seen in cells infected with EAEC-T8 (an invasive clinical isolate). All these TLRs made a significant contribution to the EAEC-T8-mediated EGFR activation in these cells. Furthermore, these TLRs were found to be associated with activation of the downstream effectors (ERK-1/2, PI3 kinase and Akt) and transcription factors (NF-κB, c-Jun, c-Fos and STAT-3) of EGFR-mediated signal transduction pathways. Moreover, the involvement of these TLRs was also noted in IL-8 secretion by both EAEC-T8-infected cell types. Our findings suggest that EAEC-induced upregulation of TLR2, TLR4 and TLR5 is important for the IL-8 response via EGFR-mediated signal transduction pathways in these cells.

Impact of Probiotics on the Prevention and Treatment of Gastrointestinal Diseases in the Pediatric Population

Despite the high prevalence of gastrointestinal disorders (GIDs) in infants and children, especially those categorized as functional GIDs (FGIDs), insufficient knowledge about their pathophysiology has limited both symptomatic diagnosis and the development of optimal therapies. Recent advances in the field of probiotics have made their potential use as an interesting therapeutic and preventive strategy against these disorders possible, but further efforts are still needed. In fact, there is great controversy surrounding this topic, generated by the high variety of potential probiotics strains with plausible therapeutic utility, the lack of consensus in their use as well as the few comparative studies available on probiotics that record their efficacy. Taking into account these limitations, and in the absence of clear guidelines about the dose and timeframe for successful probiotic therapy, our review aimed to evaluate current studies on potential use of probiotics for the prevention and treatment of the most common FGIDs and GIDs in the pediatric population. Furthermore, matters referring to know major action pathways and key safety recommendations for probiotic administration proposed by major pediatric health agencies shall also be discussed.

The cytosolic DNA sensor AIM2 promotes Helicobacter-induced gastric pathology via the inflammasome

Helicobacter pylori (H. pylori) infection can trigger chronic gastric inflammation perpetuated by overactivation of the innate immune system, leading to a cascade of precancerous lesions culminating in gastric cancer. However, key regulators of innate immunity that promote H. pylori-induced gastric pathology remain ill-defined. The innate immune cytosolic DNA sensor absent in melanoma 2 (AIM2) contributes to the pathogenesis of numerous autoimmune and chronic inflammatory diseases, as well as cancers including gastric cancer. We therefore investigated whether AIM2 contributed to the pathogenesis of Helicobacter-induced gastric disease. Here, we reveal that AIM2 messenger RNA and protein expression levels are elevated in H. pylori-positive versus H. pylori-negative human gastric biopsies. Similarly, chronic Helicobacter felis infection in wild-type mice augmented Aim2 gene expression levels compared with uninfected controls. Notably, gastric inflammation and hyperplasia were less severe in H. felis-infected Aim2-/- versus wild-type mice, evidenced by reductions in gastric immune cell infiltrates, mucosal thickness and proinflammatory cytokine and chemokine release. In addition, H. felis-driven proliferation and apoptosis in both gastric epithelial and immune cells were largely attenuated in Aim2-/- stomachs. These observations in Aim2-/- mouse stomachs correlated with decreased levels of inflammasome activity (caspase-1 cleavage) and the mature inflammasome effector cytokine, interleukin-1β. Taken together, this work uncovers a pathogenic role for the AIM2 inflammasome in Helicobacter-induced gastric disease, and furthers our understanding of the host immune response to a common pathogen and the complex and varying roles of AIM2 at different stages of cancerous and precancerous gastric disease.

Intersections between innate immune response and gastric cancer development

Worldwide, gastric cancer (GC) is the fifth most commonly diagnosed malignancy. It has a reduced prevalence but has maintained its poor prognosis being the fourth leading cause of deaths related to cancer. The highest mortality rates occur in Asian and Latin American countries, where cases are usually diagnosed at advanced stages. Overall, GC is viewed as the consequence of a multifactorial process, involving the virulence of the Helicobacter pylori (H. pylori) strains, as well as some environmental factors, dietary habits, and host intrinsic factors. The tumor microenvironment in GC appears to be chronically inflamed which promotes tumor progression and reduces the therapeutic opportunities. It has been suggested that inflammation assessment needs to be measured qualitatively and quantitatively, considering cell-infiltration types, availability of receptors to detect damage and pathogens, and presence or absence of aggressive H. pylori strains. Gastrointestinal epithelial cells express several Toll-like receptors and determine the first defensive line against pathogens, and have been also described as mediators of tumorigenesis. However, other molecules, such as cytokines related to inflammation and innate immunity, including immune checkpoint molecules, interferon-gamma pathway and NETosis have been associated with an increased risk of GC. Therefore, this review will explore innate immune activation in the context of premalignant lesions of the gastric epithelium and established gastric tumors.

Gastric immune homeostasis imbalance: An important factor in the development of gastric mucosal diseases

The gastric mucosal immune system is a unique immune organ independent of systemic immunity that not only maintains nutrient absorption but also plays a role in resisting the external environment. Gastric mucosal immune disorder leads to a series of gastric mucosal diseases, including autoimmune gastritis (AIG)-related diseases, Helicobacter pylori (H. pylori)-induced diseases, and various types of gastric cancer (GC). Therefore, understanding the role of gastric mucosal immune homeostasis in gastric mucosal protection and the relationship between mucosal immunity and gastric mucosal diseases is very important. This review focuses on the protective effect of gastric mucosal immune homeostasis on the gastric mucosa, as well as multiple gastric mucosal diseases caused by gastric immune disorders. We hope to offer new prospects for the prevention and treatment of gastric mucosal diseases.

Endotoxemia and Gastrointestinal Cancers: Insight into the Mechanisms Underlying a Dangerous Relationship

Lipopolysaccharide (LPS), also known as endotoxin, is a component of the membrane of gram-negative bacteria and a well-recognized marker of sepsis. In case of disruption of the intestinal barrier, as occurs with unhealthy diets, alcohol consumption, or during chronic diseases, the microbiota residing in the gastrointestinal tract becomes a crucial factor in amplifying the systemic inflammatory response. Indeed, the translocation of LPS into the bloodstream and its interaction with toll-like receptors (TLRs) triggers molecular pathways involved in cytokine release and immune dysregulation. This is a critical step in the exacerbation of many diseases, including metabolic disorders and cancer. Indeed, the role of LPS in cancer development is widely recognized, and examples include gastric tumor related to Helicobacter pylori infection and hepatocellular carcinoma, both of which are preceded by a prolonged inflammatory injury; in addition, the risk of recurrence and development of metastasis appears to be associated with endotoxemia. Here, we review the mechanisms that link the promotion and progression of tumorigenesis with endotoxemia, and the possible therapeutic interventions that can be deployed to counteract these events.

Immune Biology and Persistence of Helicobacter pylori in Gastric Diseases

Helicobacter pylori is a prevalent pathogen, which affects more than 40% of the global population. It colonizes the human stomach and persists in its host for several decades or even a lifetime, if left untreated. The persistent infection has been linked to various gastric diseases, including gastritis, peptic ulcers, and an increased risk for gastric cancer. H. pylori infection triggers a strong immune response directed against the bacterium associated with the infiltration of innate phagocytotic immune cells and the induction of a Th1/Th17 response. Even though certain immune cells seem to be capable of controlling the infection, the host is unable to eliminate the bacteria as H. pylori has developed remarkable immune evasion strategies. The bacterium avoids its killing through innate recognition mechanisms and manipulates gastric epithelial cells and immune cells to support its persistence. This chapter focuses on the innate and adaptive immune response induced by H. pylori infection, and immune evasion strategies employed by the bacterium to enable persistent infection.

Persistence Infection of TGEV Promotes Enterococcus faecalis Infection on IPEC-J2 Cells

Transmissible gastroenteritis virus (TGEV) is a coronavirus causing diarrhea with high incidence in swine herds. Its persistent infection might lead to epithelial-mesenchymal transition (EMT) of swine intestinal epithelial cells, followed by subsequent infections of other pathogens. Enterococcus faecalis (E. faecalis) is a member of the enteric microorganisms and an opportunistic pathogen. There is no report of secondary E. faecalis infection to TGEV, even though they both target to the intestinal tracts. To investigate the interactions between TGEV and E. faecalis, we set up an in vitro infection model by the swine IPEC-J2 cells. Dynamic changes of cell traits, including EMT and cell motility, were evaluated through qPCR, Western blot, electronic microscopy, scratch test, Transwell migration test and invasion test, respectively. The adhesion and invasion tests of E. faecalis were taken to verify the impact of the preceding TGEV infection. The cell morphology and molecular marker evaluation results showed that the TGEV persistent infection induced EMT on IPEC-J2 cells; increased cellular motility and invasion potential were also observed. Spontaneously, the expression levels of fibronectin (FN) and the membrane protein integrin-α5, which are dominant bacterial receptors on IPEC-J2 cells, were upgraded. It indicated that the bacteria E. faecalis adhered to IPEC-J2 cells through the FN receptor, and then invaded the cells by binding with the integrin-α5, suggesting that both molecules were critical for the adhesion and invasion of E. faecalis to IPEC-J2 cells. Additionally, it appeared that E. faecalis alone might trigger certain EMT phenomena, implying a vicious circle might occur. Generally, bacterial and viral co-infections are frustrating yet common in both human and veterinary medicines, and our observations on enteric TGEV and E. faecalis interactions, especially the diversity of bacterial invasion strategies, might provide new insights into the mechanisms of E. faecalis pathogenicity.

Influence of Helicobacter pylori oncoprotein CagA in gastric cancer: A critical-reflective analysis

Gastric cancer is the fifth most common malignancy and third leading cancer-related cause of death worldwide. Helicobacter pylori is a Gram-negative bacterium that inhabits the gastric environment of 60.3% of the world’s population and represents the main risk factor for the onset of gastric neoplasms. CagA is the most important virulence factor in H. pylori, and is a translocated oncoprotein that induces morphofunctional modifications in gastric epithelial cells and a chronic inflammatory response that increases the risk of developing precancerous lesions. Upon translocation and tyrosine phosphorylation, CagA moves to the cell membrane and acts as a pathological scaffold protein that simultaneously interacts with multiple intracellular signaling pathways, thereby disrupting cell proliferation, differentiation and apoptosis. All these alterations in cell biology increase the risk of damaged cells acquiring pro-oncogenic genetic changes. In this sense, once gastric cancer sets in, its perpetuation is independent of the presence of the oncoprotein, characterizing a “hit-and-run” carcinogenic mechanism. Therefore, this review aims to describe H. pylori- and CagA-related oncogenic mechanisms, to update readers and discuss the novelties and perspectives in this field.

Helicobacter pylori Infection Elicits Type I Interferon Response in Human Monocytes via Toll-Like Receptor 8 Signaling

Helicobacter pylori colonization and persistence could precede gastric adenocarcinoma. Elucidating immune recognition strategies of H. pylori is therefore imperative to curb chronic persistence in the human host. Toll-like receptor 7 (TLR7) and TLR8 are widely known as viral single-stranded RNA (ssRNA) sensors yet less studied in the bacteria context. Here, we investigated the involvement of these receptors in the immunity to H. pylori. Human THP-1 monocytic cells were infected with H. pylori, and the expression levels of human Toll-like receptors (TLRs) were examined. The roles of TLR7 and TLR8 in response to H. pylori infection were further investigated using receptor antagonists. Among all TLR transcripts examined, TLR8 exhibited the most prominent upregulation, followed by TLR7 in the THP-1 cells infected with H. pylori J99 or SS1 strains. H. pylori infection-mediated IFN-α and IFN-β transactivation was significantly abrogated by the TLR7/8 (but not TLR7) antagonist. Additionally, TLR7/8 antagonist treatment reduced H. pylori infection-mediated phosphorylation of interferon regulatory factor 7 (IRF7). Our study suggests a novel role of TLR8 signaling in host immunity against H. pylori through sensing live bacteria to elicit the production of type I interferon.

Innate Immunity Crosstalk with Helicobacter pylori: Pattern Recognition Receptors and Cellular Responses

Helicobacter pylori is one of the most successful gastric pathogens that has co-existed with human for centuries. H. pylori is recognized by the host immune system through human pattern recognition receptors (PRRs), such as toll-like receptors (TLRs), C-type lectin like receptors (CLRs), NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs), which activate downstream signaling pathways. Following bacterial recognition, the first responders of the innate immune system, including neutrophils, macrophages, and dendritic cells, eradicate the bacteria through phagocytic and inflammatory reaction. This review provides current understanding of the interaction between the innate arm of host immunity and H. pylori, by summarizing H. pylori recognition by PRRs, and the subsequent signaling pathway activation in host innate immune cells.

Inflammation and Gastric Cancer

Gastric cancer remains a major killer globally, although its incidence has declined over the past century. It is the fifth most common cancer and the third most common reason for cancer-related deaths worldwide. Gastric cancer is the outcome of a complex interaction between environmental, host genetic, and microbial factors. There is significant evidence supporting the association between chronic inflammation and the onset of cancer. This association is particularly robust for gastrointestinal cancers in which microbial pathogens are responsible for the chronic inflammation that can be a triggering factor for the onset of those cancers. Helicobacter pylori is the most prominent example since it is the most widespread infection, affecting nearly half of the world’s population. It is well-known to be responsible for inducing chronic gastric inflammation progressing to atrophy, metaplasia, dysplasia, and eventually, gastric cancer. This review provides an overview of the association of the factors playing a role in chronic inflammation; the bacterial characteristics which are responsible for the colonization, persistence in the stomach, and triggering of inflammation; the microbiome involved in the chronic inflammation process; and the host factors that have a role in determining whether gastritis progresses to gastric cancer. Understanding these interconnections may improve our ability to prevent gastric cancer development and enhance our understanding of existing cases.

Implications of Gut Microbiota in Epithelial-Mesenchymal Transition and Cancer Progression: A Concise Review

Simple Summary

Recently, the interactions between microbiota and the host have been reported to induce the onset and progression of human cancer via epithelial–mesenchymal transition (EMT). In contrast, some microorganisms can protect against cancer growth, indicating an anticancer therapeutic action of such microbiota. In the review, we summarize findings from the literature, exploring the underlying mechanisms by which pathogenic microorganisms induce EMT. We also highlight the potential of exploiting these complex interactions for developing new biological therapies.

Abstract

Advancement in the development of molecular sequencing platforms has identified infectious bacteria or viruses that trigger the dysregulation of a set of genes inducing the epithelial–mesenchymal transition (EMT) event. EMT is essential for embryogenesis, wound repair, and organ development; meanwhile, during carcinogenesis, initiation of the EMT can promote cancer progression and metastasis. Recent studies have reported that interactions between the host and dysbiotic microbiota in different tissues and organs, such as the oral and nasal cavities, esophagus, stomach, gut, skin, and the reproductive tract, may provoke EMT. On the other hand, it is revealed that certain microorganisms display a protective role against cancer growth, indicative of possible therapeutic function. In this review, we summarize recent findings elucidating the underlying mechanisms of pathogenic microorganisms, especially the microbiota, in eliciting crucial regulator genes that induce EMT. Such an approach may help explain cancer progression and pave the way for developing novel preventive and therapeutic strategies.

Inhibition of LPS-mediated TLR4 activation abrogates gastric adenocarcinoma-associated peritoneal metastasis

Surgical resection, the cornerstone of curative intent treatment for gastric adenocarcinoma, is associated with a high rate of infection-related post-operative complications, leading to an increased incidence of metastasis to the peritoneum. However, the mechanisms underlying this process are poorly understood. Lipopolysaccharide (LPS), an antigen from Gram-negative bacteria, represents a potential mechanism via induction of local and systemic inflammation through activation of Toll-like receptor (TLR). Here, we use both a novel ex vivo model of peritoneal metastasis and in vivo animal models to assess gastric cancer cell adhesion to peritoneum both before and after inhibition of the TLR4 pathway. We demonstrate that activation of TLR4 by either LPS or Gram-negative bacteria (E. coli) significantly increases the adherence of gastric cancer cells to human peritoneal mesothelial cells, and that this increased adherence is abrogated by inhibition of the TLR4 signal cascade and downstream TAK1 and MEK1/2 pathways. We also demonstrate that the influence of LPS on adherence extends to peritoneal tissue and metastatic spread. Furthermore, we show that loss of TLR4 at the site of metastasis reduces tumor cell adhesion, implicating the TLR4 signaling cascade in potentiating metastatic adhesion and peritoneal spread. These results identify potential therapeutic targets for the clinical management of patients undergoing resection for gastric cancer.

Induction and Regulation of the Innate Immune Response in Helicobacter pylori Infection

Gastric cancer (GC) is the fifth most common cancer and the fourth most common cause of cancer-related death worldwide. The intestinal type of GC progresses from acute to chronic gastritis, multifocal atrophic gastritis, intestinal metaplasia, dysplasia, and carcinoma. Infection of the stomach by Helicobacter pylori, a Gram-negative bacterium that infects approximately 50% of the world's population, is the causal determinant that initiates the gastric inflammation and then disease progression. In this context, the induction of the innate immune response of gastric epithelial cells and myeloid cells by H. pylori effectors plays a critical role in the outcome of the infection. However, only 1% to 3% of infected patients develop gastric adenocarcinoma, emphasizing that other mechanisms regulate the localized non-specific response, including the gastric microbiota and genetic factors. This review summarizes studies describing the factors that induce and regulate the mucosal innate immune response during H. pylori infection.

Network pharmacology to unveil the mechanism of Moluodan in the treatment of chronic atrophic gastritis

BACKGROUND

Moluodan (MLD) is a traditional Chinese patent medicine for the treatment of chronic atrophic gastritis (CAG). However, the mechanism of action (MoA) of MLD for treating CAG still remain unclear.

PURPOSE

Elucidate the MoA of MLD for treating CAG based on network pharmacology.

STUDY DESIGN

Integrate computational prediction and experimental validation based on network pharmacology.

METHODS

Computationally, compounds of MLD were scanned by LC-MS/MS and the target profiles of compounds were identified based on network-based target prediction method. Compounds in MLD were compared with western drugs used for gastritis by hierarchical clustering of target profile. Key biological functional modules of MLD were analyzed, and herb-biological functional module network was constructed to elucidate combinatorial rules of MLD herbs for CAG. Experimentally, MLD's effect on different biological functional modules were validated from both phenotypic level and molecular level in 1- Methyl-3-nitro-1-nitrosoguanidine (MNNG)-induced GES-1 cells.

RESULTS

Computational results show that the target profiles of compounds in MLD can cover most of the biomolecules reported in literature. The MoA of MLD can cover most types of MoA of western drugs for CAG. The treatment of CAG by MLD involved the regulation of various biological functional modules, e.g., inflammation/immune, cell proliferation, cell apoptosis, cell differentiation, digestion and metabolism. Experimental results show that MLD can inhibit cell proliferation, promote cell apoptosis and differentiation, reduce the inflammation level and promote lipid droplet accumulation in MNNG-induced GES-1 cells.

CONCLUSION

The network pharmacology framework integrating computational prediction and experimental validation provides a novel way for exploring the MoA of MLD.

The role of toll-like receptors in peptic ulcer disease

Helicobacter pylori (HP) is the primary etiologic factor that induces events in the immune system that lead to peptic ulcers. Toll-like receptors (TLRs) are an important part of the innate immune system, as they play pivotal roles in pathogen-associated molecular pattern (PAMP) recognition of HP as well host-associated damage-associated molecular patterns (DAMPs). Recent advancements such as COX-2 production, LPS recognition through TLR2, CagL, and CagY protein of HP activating TLR5, TLR9 activation via type IV secretion system (T4SS) using DNA transfer, TLR polymorphisms, their adaptor molecules, cytokines, and other factors play a significant role in PUD. Thus, some novel PUD treatments including Chuyou Yuyang granules, function by TLR4/NF-κB signaling pathway suppression and TNF-α and IL-18 inhibition also rely on TLR signaling. Similarly glycyrrhetinic acid (GA) treatment activates TLR-4 in Ana-1 cells not via TRIF, but via MYD88 expression, which is significantly upregulated to cure PUD. Therefore, understanding TLR signaling complexity and its resultant immune modulation after host-pathogen interactions is pivotal to drug and vaccine development for other diseases as well including cancer and recent pandemic COVID-19. In this review, we summarize the TLRs and HP interaction; its pathophysiology-related signaling pathways, polymorphisms, and pharmaceutical approaches toward PUD.

Effects of Helicobacter pylori Infection on the Oral Microbiota of Reflux Esophagitis Patients

The human oral microbiota plays a vital role in maintaining metabolic homeostasis. To explore the relationship between Helicobacter pylori (Hp) and reflux esophagitis, we collected 86 saliva samples from reflux esophagitis patients (RE group) and 106 saliva samples from healthy people (C group) for a high-throughput sequencing comparison. No difference in alpha diversity was detected between the RE and the C groups, but beta diversity of the RE group was higher than the C group. Bacteroidetes was more abundant in the RE group, whereas Firmicutes was more abundant in the C group. The linear discriminant analysis effect size analysis demonstrated that the biomarkers of the RE group were Prevotella, Veillonella, Leptotrichia, and Actinomyces, and the biomarkers of the C group were Lautropia, Gemella, Rothia, and Streptococcus. The oral microbial network structure of the C group was more complex than that of the RE group. Second, to explore the effect of Hp on the oral microbiota of RE patients, we performed the ¹⁴C-urea breath test on 45 of the 86 RE patients. We compared the oral microbiota of 33 Hp-infected reflux esophagitis patients (REHpp group) and 12 non-Hp-infected reflux esophagitis patients (REHpn group). No difference in alpha diversity was observed between the REHpn and REHpp groups, and beta diversity of the REHpp group was significantly lower than that of the REHpn group. The biomarkers in the REHpp group were Veillonella, Haemophilus, Selenomonas, Megasphaera, Oribacterium, Butyrivibrio, and Campylobacter; and the biomarker in the REHpn group was Stomatobaculum. Megasphaera was positively correlated with Veillonella in the microbial network of the REHpp group. The main finding of this study is that RE disturbs the human oral microbiota, such as increased beta diversity. Hp infection may inhibit this disorderly trend.

Pattern recognition receptors and their roles in the host response to Helicobacter pylori infection

Helicobacter pylori (H. pylori) infection is highly prevalent, affecting 4.4 billion people globally. This pathogen is a risk factor in the pathogenesis of more than 75% of worldwide cases of gastric cancer. Pattern recognition receptors are essential in the innate immune response to H. pylori infection. They recognize conserved pathogen structures and myriad alarmins released by host cells in response to microbial components, cytokines or cellular stress, thus triggering a robust proinflammatory response, which is crucial in H. pylori-induced gastric carcinogenesis. In this review, we intend to highlight the main pattern recognition receptors involved in the recognition and host response to H. pylori, as well as the main structures recognized and the subsequent inflammatory response.

Genome-Wide DNA Methylation Pattern in Whole Blood Associated With Primary Intracerebral Hemorrhage

Primary intracerebral hemorrhage (ICH) is a significant cause of morbidity and mortality throughout the world. ICH is a multifactorial disease that emerges from interactions among multiple genetic and environmental factors. DNA methylation plays an important role in the etiology of complex traits and diseases. We used the Illumina Infinium Human Methylation 850k BeadChip to detect changes in DNA methylation in peripheral blood samples from patients with ICH and healthy controls to explore DNA methylation patterns in ICH. Here, we compared genomic DNA methylation patterns in whole blood from ICH patients (n = 30) and controls (n = 34). The ICH and control groups showed significantly different DNA methylation patterns at 1530 sites (p-value < 5.92E-08), with 1377 hypermethylated sites and 153 hypomethylated sites in ICH patients compared to the methylation status in healthy controls. A total of 371 hypermethylated sites and 35 hypomethylated sites were in promoters, while 738 hypermethylated sites and 67 hypomethylated sites were in coding regions. Furthermore, the differentially methylated genes between ICH patients and controls were largely related to inflammatory pathways. Abnormalities in the DNA methylation pattern identified in the peripheral blood of ICH patients may play an important role in the development of ICH and warranted further investigation.

Vulture Genomes Reveal Molecular Adaptations Underlying Obligate Scavenging and Low Levels of Genetic Diversity

Obligate scavenging on the dead and decaying animal matter is a rare dietary specialization that in extant vertebrates is restricted to vultures. These birds perform essential ecological services, yet many vulture species have undergone recent steep population declines and are now endangered. To test for molecular adaptations underlying obligate scavenging in vultures, and to assess whether genomic features might have contributed to their population declines, we generated high-quality genomes of the Himalayan and bearded vultures, representing both independent origins of scavenging within the Accipitridae, alongside a sister taxon, the upland buzzard. By comparing our data to published sequences from other birds, we show that the evolution of obligate scavenging in vultures has been accompanied by widespread positive selection acting on genes underlying gastric acid production, and immunity. Moreover, we find evidence of parallel molecular evolution, with amino acid replacements shared among divergent lineages of these scavengers. Our genome-wide screens also reveal that both the Himalayan and bearded vultures exhibit low levels of genetic diversity, equating to around a half of the mean genetic diversity of other bird genomes examined. However, demographic reconstructions indicate that population declines began at around the Last Glacial Maximum, predating the well-documented dramatic declines of the past three decades. Taken together, our genomic analyses imply that vultures harbor unique adaptations for processing carrion, but that modern populations are genetically depauperate and thus especially vulnerable to further genetic erosion through anthropogenic activities.

Heat-killed Helicobacter pylori upregulates NKG2D ligands expression on gastric adenocarcinoma cells via Toll-like receptor 4

BACKGROUND

Natural killer (NK) cells are paramount for immunity against infectious agents and tumors. Their cytokine and cytolytic responses can be mediated by natural killer group 2, member D (NKG2D), an activating receptor whose ligands (NKG2DL) expression is induced in conditions of cell stress and malignant transformation. Since sustained expression of NKG2DL MICA is related to lower survival rates in gastric adenocarcinoma patients, and Helicobacter pylori infection contributes to tumorigenesis; we asked whether H. pylori stimulus could promote NKG2DL expression on human gastric adenocarcinoma cells.

METHODS

Heat-killed H. pylori (HKHP) was used to stimulate MKN45 cells before analysis of NKG2DL and Toll-like receptor 4 (TLR4) protein levels by flow cytometry and transcripts by real-time PCR. LPS from Rhodobacter sphaeroides and inhibitory peptide Pepinh MYD were used to inhibit TLR4/MyD88 signaling pathway to assess its participation on NKG2DL expression. NK cell-mediated cytotoxicity was measured by lactate dehydrogenase (LDH) and CD107a mobilization assays.

RESULTS

Stimulation of MKN45 cells with HKHP increased MICA, ULBP4 (another NKG2DL), and TLR4 at the protein and transcriptional levels. MICA, but not ULBP4 expression, was upregulated in a TLR4/MyD88-dependent manner. Furthermore, the presence of NKG2DL on the surface of HKHP-stimulated MKN45 cells enabled NK cell cytotoxic activation.

CONCLUSIONS

Our data indicate that induction of NKG2DL expression on gastric adenocarcinoma cells by H. pylori promotes an immune response that may ultimately contribute to either gastric tissue damage, as a consequence of persistent activation of immunity, or tumor immune evasion due to chronic NKG2DL expression.

Vaccine development against Helicobacter pylori: from ideal antigens to the current landscape

Introduction: The interest of the world scientific community for an effective vaccine against Helicobacter pylori infection arises from its high prevalence and association with many diseases. Moreover, with an immunological response that is not always effective for the eradication of the bacteria and an increasing antibiotic resistance in the treatment of this infection, the search for a vaccine and new therapeutic modalities to control this infection is urgent.Areas covered: We bring an overview of the infection worldwide, discussing its prevalence, increasing resistance to antibiotics used in its therapy, in addition to the response of the immune system to the infection registered so far. Moreover, we address the most used antigens and their respective immunological responses expected or registered up to now. Finally, we address the trials and their partial results in development for such vaccines.Expert opinion: Although several studies for the development of an effective vaccine against this pathogen are taking place, many are still in the preclinical phase or even without updated information. In this sense, taking into account the high prevalence and association with important comorbidities, the interest of the pharmaceutical industry in developing an effective vaccine against this pathogen is questioned.

Comprehensive Integration of Genome-Wide Association and Gene Expression Studies Reveals Novel Gene Signatures and Potential Therapeutic Targets for Helicobacter pylori-Induced Gastric Disease

Helicobacter pylori is a gram-negative bacterium that colonizes the human gastric mucosa and can lead to gastric inflammation, ulcers, and stomach cancer. Due to the increase in H. pylori antimicrobial resistance new methods to identify the molecular mechanisms of H. pylori-induced pathology are urgently needed. Here we utilized a computational biology approach, harnessing genome-wide association and gene expression studies to identify genes and pathways determining disease development. We mined gene expression data related to H. pylori-infection and its complications from publicly available databases to identify four human datasets as discovery datasets and used two different multi-cohort analysis pipelines to define a H. pylori-induced gene signature. An initial Helicobacter-signature was curated using the MetaIntegrator pipeline and validated in cell line model datasets. With this approach we identified cell line models that best match gene regulation in human pathology. A second analysis pipeline through NetworkAnalyst was used to refine our initial signature. This approach defined a 55-gene signature that is stably deregulated in disease conditions. The 55-gene signature was validated in datasets from human gastric adenocarcinomas and could separate tumor from normal tissue. As only a small number of H. pylori patients develop cancer, this gene-signature must interact with other host and environmental factors to initiate tumorigenesis. We tested for possible interactions between our curated gene signature and host genomic background mutations and polymorphisms by integrating genome-wide association studies (GWAS) and known oncogenes. We analyzed public databases to identify genes harboring single nucleotide polymorphisms (SNPs) associated with gastric pathologies and driver genes in gastric cancers. Using this approach, we identified 37 genes from GWA studies and 61 oncogenes, which were used with our 55-gene signature to map gene-gene interaction networks. In conclusion, our analysis defines a unique gene signature driven by H. pylori-infection at early phases and that remains relevant through different stages of pathology up to gastric cancer, a stage where H. pylori itself is rarely detectable. Furthermore, this signature elucidates many factors of host gene and pathway regulation in infection and can be used as a target for drug repurposing and testing of infection models suitability to investigate human infection.

Surfactant protein A reduces TLR4 and inflammatory cytokine mRNA levels in neonatal mouse ileum

Levels of intestinal toll-like receptor 4 (TLR4) impact inflammation in the neonatal gastrointestinal tract. While surfactant protein A (SP-A) is known to regulate TLR4 in the lung, it also reduces intestinal damage, TLR4 and inflammation in an experimental model of necrotizing enterocolitis (NEC) in neonatal rats. We hypothesized that SP-A-deficient (SP-A^-/-) mice have increased ileal TLR4 and inflammatory cytokine levels compared to wild type mice, impacting intestinal physiology. We found that ileal TLR4 and proinflammatory cytokine levels were significantly higher in infant SP-A^-/- mice compared to wild type mice. Gavage of neonatal SP-A^-/- mice with purified SP-A reduced ileal TLR4 protein levels. SP-A reduced expression of TLR4 and proinflammatory cytokines in normal human intestinal epithelial cells (FHs74int), suggesting a direct effect. However, incubation of gastrointestinal cell lines with proteasome inhibitors did not abrogate the effect of SP-A on TLR4 protein levels, suggesting that proteasomal degradation is not involved. In a mouse model of experimental NEC, SP-A^-/- mice were more susceptible to intestinal stress resembling NEC, while gavage with SP-A significantly decreased ileal damage, TLR4 and proinflammatory cytokine mRNA levels. Our data suggests that SP-A has an extrapulmonary role in the intestinal health of neonatal mice by modulating TLR4 and proinflammatory cytokines mRNA expression in intestinal epithelium.

An Overview of Helicobacter pylori Infection

Helicobacter pylori (H. pylori) represents one of the most widespread bacterial infections globally. Infection causes chronic gastritis and increases the risk of peptic ulcer disease, gastric adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma. The pioneering discovery of H. pylori by Marshall and Warren in the early 1980s has initiated fervent research into H. pylori as a pathogen ever since. This chapter aims to provide an overview of our understanding of H. pylori infection and its management, with a focus on current options for diagnosis, the challenges associated with H. pylori eradication, and the need for alternative therapeutic strategies based on furthering our understanding of host: H. pylori interactions.

Etidronate down-regulates Toll-like receptor 2 ligand-induced chemokine production by inhibiting MyD88 expression and NF-κB activation

OBJECTIVE

Pretreatment of J774.1 cells with etidronate, a non-nitrogen-containing bisphosphonate (non-NBP) used as an antibone resorptive drug, was previously reported to inhibit Toll-like receptor (TLR) 2 agonist-induced proinflammatory cytokine production. The present study aimed to examine the effects of etidronate on chemokine production by human monocytic U937 cells incubated with Pam₃Cys-Ser-(Lys)₄ (Pam₃CSK₄, a TLR2 ligand) and lipid A (a TLR4 ligand).

METHODS

U937 cells were pretreated with or without etidronate, and then incubated with or without Pam₃CSK₄ or lipid A. Levels of secreted human interleukin (IL)-8 and monocyte chemoattractant protein-1 (MCP-1) in culture supernatants and activation of nuclear factor-κB (NF-κB) p65 were measured by enzyme-linked immunosorbent assay (ELISA). Cytotoxicity was determined by measuring lactate dehydrogenase (LDH) activity in supernatants. Expression of intracellular adhesion molecule (ICAM)-1 and MyD88 was analyzed by flow cytometry and Western blot analysis, respectively.

RESULTS

Etidronate down-regulated IL-8 and MCP-1 production and NF-κB p65 activation induced by Pam₃CSK_4, but not lipid A, in U937 cells. Etidronate also inhibited MyD88 expression in U937 cells incubated with Pam₃CSK₄.

CONCLUSION

Etidronate down-regulates IL-8 and MCP-1 production in U937 cells by inhibiting both the expression of MyD88 and activation of NF-κB p65 in the TLR2, but not TLR4, pathway.

Leptospiral LPS escapes mouse TLR4 internalization and TRIF‑associated antimicrobial responses through O antigen and associated lipoproteins

Leptospirosis is a worldwide re-emerging zoonosis caused by pathogenic Leptospira spp. All vertebrate species can be infected; humans are sensitive hosts whereas other species, such as rodents, may become long-term renal carrier reservoirs. Upon infection, innate immune responses are initiated by recognition of Microbial Associated Molecular Patterns (MAMPs) by Pattern Recognition Receptors (PRRs). Among MAMPs, the lipopolysaccharide (LPS) is recognized by the Toll-Like-Receptor 4 (TLR4) and activates both the MyD88-dependent pathway at the plasma membrane and the TRIF-dependent pathway after TLR4 internalization. We previously showed that leptospiral LPS is not recognized by the human-TLR4, whereas it signals through mouse-TLR4 (mTLR4), which mediates mouse resistance to acute leptospirosis. However, although resistant, mice are known to be chronically infected by leptospires. Interestingly, the leptospiral LPS has low endotoxicity in mouse cells and is an agonist of TLR2, the sensor for bacterial lipoproteins. Here, we investigated the signaling properties of the leptospiral LPS in mouse macrophages. Using confocal microscopy and flow cytometry, we showed that the LPS of L. interrogans did not induce internalization of mTLR4, unlike the LPS of Escherichia coli. Consequently, the LPS failed to induce the production of the TRIF-dependent nitric oxide and RANTES, both important antimicrobial responses. Using shorter LPS and LPS devoid of TLR2 activity, we further found this mTLR4-TRIF escape to be dependent on both the co-purifying lipoproteins and the full-length O antigen. Furthermore, our data suggest that the O antigen could alter the binding of the leptospiral LPS to the co-receptor CD14 that is essential for TLR4-TRIF activation. Overall, we describe here a novel leptospiral immune escape mechanism from mouse macrophages and hypothesize that the LPS altered signaling could contribute to the stealthiness and chronicity of the leptospires in mice.

Leptospira interrogans is a bacterial pathogen, responsible for leptospirosis, a worldwide neglected reemerging disease. L. interrogans may cause an acute severe disease in humans, whereas rodents and other animals asymptomatically carry the leptospires in their kidneys. They can therefore excrete live bacteria in urine and contaminate the environment. Leptospires are stealth pathogens known to escape the innate immune defenses of their hosts. They are covered in lipopolysaccharide (LPS), a bacterial motif recognized in mammals through the Toll-like receptor 4 (TLR4), which triggers two different signaling pathways. We showed previously that pathogenic leptospires fully escape TLR4 recognition in humans. Here we focused on the LPS signaling in mice that are, although resistant to acute leptospirosis, chronically infected. We showed in mouse cells that the leptospiral LPS triggers only one arm of the TLR4 pathway and escapes the other, hence avoiding production of antimicrobial compounds. Removing the lipoproteins that always co-purify with the leptospiral LPS, or using shorter LPS, restores the stimulation of both pathways. This suggests a novel escape mechanism linked to the LPS and involving lipoproteins that could be instrumental for leptospires to escape the mouse defense and to allow for their chronic renal colonization.

The NF-κB Signaling Pathway, the Microbiota, and Gastrointestinal Tumorigenesis: Recent Advances

Gastrointestinal (GI) cancers, especially gastric cancer and colorectal cancer (CRC), represent a major global health burden. A large population of microorganisms residing in the GI tract regulate physiological processes, such as the immune response, metabolic balance, and homeostasis. Accumulating evidence has revealed the alteration of microbial communities in GI tumorigenesis. Experimental studies in cell lines and animal models showed the functional roles and molecular mechanisms of several bacteria in GI cancers, including Helicobacter pylori in gastric cancer as well as Fusobacterium nucleatum, Escherichia coli, Peptostreptococcus anaerobius, and Bacteroides fragilis in CRC. The transcriptional factor NF-κB plays a crucial role in the host response to microbial infection through orchestrating innate and adaptive immune functions. Moreover, NF-κB activity is linked to GI cancer initiation and development through its induction of chronic inflammation, cellular transformation and proliferation. Here, we provide an overview and discussion of modulation of the NF-κB signaling pathway by microbiota, especially infectious bacteria, in GI tumorigenesis, with a major focus on gastric cancer and CRC.

Unveiling the Crucial Role of Type IV Secretion System and Motility of Helicobacter pylori in IL-1β Production via NLRP3 Inflammasome Activation in Neutrophils

Helicobacter pylori is a gram-negative, microaerophilic, and spiral-shaped bacterium and causes gastrointestinal diseases in human. IL-1β is a representative cytokine produced in innate immune cells and is considered to be a key factor in the development of gastrointestinal malignancies. However, the mechanism of IL-1β production by neutrophils during H. pylori infection is still unknown. We designed this study to identify host and bacterial factors involved in regulation of H. pylori-induced IL-1β production in neutrophils. We found that H. pylori-induced IL-1β production is abolished in NLRP3-, ASC-, and caspase-1/11-deficient neutrophils, suggesting essential role for NLRP3 inflammasome in IL-1β response against H. pylori. Host TLR2, but not TLR4 and Nod2, was also required for transcription of NLRP3 and IL-1β as well as secretion of IL-1β. H. pylori lacking cagL, a key component of the type IV secretion system (T4SS), induced less IL-1β production in neutrophils than did its isogenic WT strain, whereas vacA and ureA were dispensable. Moreover, T4SS was involved in caspase-1 activation and IL-1β maturation in H. pylori-infected neutrophils. We also found that FlaA is essential for H. pylori-mediated IL-1β production in neutrophils, but not dendritic cells. TLR5 and NLRC4 were not required for H. pylori-induced IL-1β production in neutrophils. Instead, bacterial motility is essential for the production of IL-1β in response to H. pylori. In conclusion, our study shows that host TLR2 and NLRP3 inflammasome and bacterial T4SS and motility are essential factors for IL-1β production by neutrophils in response to H. pylori.

TLR2, TLR4 and TLR10 Shape the Cytokine and Chemokine Release of H. pylori-Infected Human DCs

Helicobacter pylori (H. pylori) is a stomach pathogen that persistently colonizes the gastric mucosa, often leading to chronic inflammation and gastric pathologies. Although infection with H. pylori is the primary risk factor for gastric cancer, the underlying mechanisms of pathogen persistence and consequential chronic inflammation are still not well understood. Conventional dendritic cells (cDCs), which are among the first immune cells to encounter H. pylori in the gastric lining, and the cytokines and chemokines they secrete, contribute to both acute and chronic inflammation. Therefore, this study aimed to unravel the contributions of specific signaling pathways within human CD1c⁺ cDCs (cDC2s) to the composition of secreted cytokines and chemokines in H. pylori infection. Here, we show that the type IV secretion system (T4SS) plays only a minor role in H. pylori-induced activation of cDC2s. In contrast, Toll-like receptor 4 (TLR4) signaling drives the secretion of inflammatory mediators, including IL-12 and IL-18, while signaling via TLR10 attenuates the release of IL-1β and other inflammatory cytokines upon H. pylori infection. The TLR2 pathway significantly blocks the release of CXCL1 and CXCL8, while it promotes the secretion of TNFα and GM-CSF. Taken together, these results highlight how specific TLR-signaling pathways in human cDC2s shape the H. pylori-induced cytokine and chemokine milieu, which plays a pivotal role in the onset of an effective immune response.

Lipopolysaccharides From Non-Helicobacter pylori Gastric Bacteria Potently Stimulate Interleukin-8 Production in Gastric Epithelial Cells

Gastric acid secretion is compromised in chronic Helicobacter pylori (H. pylori) infection allowing overgrowth of non-H. pylori gastric bacteria (NHGB) in the stomach.

Unique responses of Helicobacter pylori to exogenous hydrophobic compounds

Helicobacter pylori is a pathogen responsible for peptic ulcers and gastric cancers in human. One of the unique biological features of this bacterium is a membrane lipid composition significantly differed from that of typical Gram-negative bacteria. Due to its unique lipid composition, the responses of H. pylori to various exogenous lipophilic compounds significantly differ from the responses of typical Gram-negative bacteria to the same lipophilic compounds. For instance, some steroidal compounds are incorporated into the biomembranes of H. pylori through the intermediation of the myristoyl-phosphatidylethanolamine (PE). In addition, H. pylori shows high susceptibility to bacteriolytic action of lipids such as 3-carbonyl steroids, vitamin D, and indene compounds. These lipids are also considered to interact with myristoyl-PE of H. pylori membranes, and to ultimately confer the bactericidal action to this bacterium. In this study we summarize the lipids concerned with H. pylori and suggest the possibility of the development of chemotherapeutic medicines that act on the membrane lipid component of H. pylori.

Proregenerative Activity of IL-33 in Gastric Tissue Cells Undergoing Helicobacter Pylori-Induced Apoptosis

Interleukin (IL)-33 is a proinflammatory mediator that alerts the host immune system to disorders in tissue homeostasis. Aim. To understand the role of IL-33 in modulating gastric tissue cell growth affected by Helicobacter pylori (H. pylori). Methods. IL-33 production in guinea pigs (Caviae porcellus) experimentally infected with H. pylori was evaluated by ELISA or immunohistochemical staining. The proregenerative activity of IL-33 was evaluated using gastric epithelial cells and fibroblasts that were naive or transfected with IL-33 siRNA exposed to H. pylori glycine acid extract antigenic complex (GE), as well as by measuring cell migration, proliferation, metabolic activity and apoptosis. Animals infected by H. pylori responded with increased production of IL-33. Also, cells treated in vitro with GE released more IL-33 than cells that were unstimulated. Silencing IL-33 in cells resulted in downregulation of metabolic activity, adhesion, migration and proliferation, especially after treatment with H. pylori GE, as well as upregulation of cells apoptosis associated with caspase 3 increase and Bcl-xL decrease, suggesting proregenerative activity of IL-33. Interestingly, upregulation of cell proliferation by IL-33 was Erk independent. Our results indicate that IL-33 may protect gastric tissue from loss of homeostasis caused by deleterious effects of H. pylori components and the inflammatory response developed during infection.

Pathogenesis and clinical management of Helicobacter pylori gastric infection

Helicobacter pylori (H. pylori) is a gram-negative bacterium that infects approximately 4.4 billion individuals worldwide. However, its prevalence varies among different geographic areas, and is influenced by several factors. The infection can be acquired by means of oral-oral or fecal-oral transmission, and the pathogen possesses various mechanisms that improve its capacity of mobility, adherence and manipulation of the gastric microenvironment, making possible the colonization of an organ with a highly acidic lumen. In addition, H. pylori presents a large variety of virulence factors that improve its pathogenicity, of which we highlight cytotoxin associated antigen A, vacuolating cytotoxin, duodenal ulcer promoting gene A protein, outer inflammatory protein and gamma-glutamyl transpeptidase. The host immune system, mainly by means of a Th1-polarized response, also plays a crucial role in the infection course. Although most H. pylori-positive individuals remain asymptomatic, the infection predisposes the development of various clinical conditions as peptic ulcers, gastric adenocarcinomas and mucosa-associated lymphoid tissue lymphomas. Invasive and non-invasive diagnostic methods, each of them with their related advantages and limitations, have been applied in H. pylori detection. Moreover, bacterial resistance to antimicrobial therapy is a major challenge in the treatment of this infection, and new therapy alternatives are being tested to improve H. pylori eradication. Last but not least, the development of effective vaccines against H. pylori infection have been the aim of several research studies.

Isolation and expression of four Megalobrama amblycephala toll-like receptor genes in response to a bacterial infection

Toll-like receptors (TLRs) are a category of pattern recognition receptors (PRRs), which recognize pathogen associated molecular patterns (PAMPs) and participate in the immune responses. We identified tlr5a, tlr5b, tlr9 and tlr21 from the genome of blunt snout bream (Megalobrama amblycephala). All four tlrs were constitutively expressed in all examined tissues. After an immune bacterial challenge with Aeromonas hydrophila, their expressionwas up-regulated in lymphoid organs and tissues. Recombinant eukaryotic plasmid pEGFP-N1 was transfected into the common carp (Cyprinus carpio) EPC (epithelioma papulosum cyprini) cells for the purpose of subcellular localization. pcDNA3.1(+) recombinant eukaryotic plasmid was used to investigate the effects of overexpression of tlrs on the expression of downstream interferon-associated immune factors. The four Tlrs were distributed in the cytoplasm of transfected cells and appeared as filamentous or reticular. The expression of irf3, irf7, isg15, mx1, pkr and viperin at 0, 6, 12, 18, 24, 36, 48 and 72 h post-transfection in transfected EPC cells was quantified by qPCR. Overexpression of tlrs upregulated the expression of viperin, isg15, irf3, irf7, mx1 and pkr (in that order of magnitude). We also cloned the following promoters of irfs: Irf1-p, irf2-p, irf6-p, irf7-p, irf8-p and irf9-p. Results of the dual luciferase reporter assay suggested that tlr5a, tlr5b and tlr9 enhanced the activities of irf7-p, while tlr5b enhanced the activities of irf1-p and irf7-p. This suggests that they all play a role in the innate immunity. The experiments also indicated that TLRs activate irf3 or irf7 signaling to induce IFN secretion and subsequent upregulation of IFN-stimulated genes. These results indicate that tlrs and irfs play an important immune role in response to A. hydrophila infection in blunt snout bream, and pave the way for further studies of immune mechanisms mediated by TLRs in fish.

Comparative transcriptional analysis for Toll-like receptors, inflammatory cytokines, and apoptotic genes in response to different cytolethal-encoding and noncoding isolates of Salmonella enterica and Campylobacter jejuni from food and human stool

Diversity of Campylobacter and Salmonella strains in interaction with epithelial cells may explain distinct modes of the pathogenesis, varying from mild watery to severe inflammatory diarrhea. We analyzed impact of this diversity, in relation to carriage and expression of cytholethal distending toxin B (cdtB), on alteration of IL-8, TNF-α, TLR2, TLR4, TLR5, CASP3 mRNA and cytokine levels in HT-29 cell line. A diversity was observed for induction of genes among different strains. Great diversity in IL-8 induction was detected between cdtB⁺ and cdtB^- strains. Early analysis showed down-regulation of TNF-α, mostly among cdtB⁺ strains. Any increase or decrease in expression of TLR2 in the cdtB^-C. jejuni strains was orderly correlated with increase or decrease of TLR4 and TNF-α. Up-regulation of CASP3 was followed by upregulation of TLR2, -4 and/or TNF-α, regardless to the cdtB status. In conclusion, induction of inflammatory response could mediate by distinct C. jejuni and S. enterica strains by several ways.

Flagellin-independent effects of a Toll-like receptor 5 polymorphism in the inflammatory response to Burkholderia pseudomallei

Background

Toll-like receptors (TLRs) are sentinel receptors of the innate immune system. TLR4 detects bacterial lipopolysaccharide (LPS) and TLR5 detects bacterial flagellin. A common human nonsense polymorphism, TLR5:c.1174C>T, results in a non-functional TLR5 protein. Individuals carrying this variant have decreased mortality from melioidosis, infection caused by the flagellated Gram-negative bacterium Burkholderia pseudomallei. Although impaired flagellin-dependent signaling in carriers of TLR5:c.1174C>T is well established, this study tested the hypothesis that a functional effect of TLR5:c.1174C>T is flagellin-independent and involves LPS-TLR4 pathways.

Methodology/Principal findings

Whole blood from two independent cohorts of individuals genotyped at TLR5:c.1174C>T was stimulated with wild type or aflagellated B. pseudomallei or purified bacterial motifs followed by plasma cytokine measurements. Blood from individuals carrying the TLR5:c.1174C>T variant produced less IL-6 and IL-10 in response to an aflagellated B. pseudomallei mutant and less IL-8 in response to purified B. pseudomallei LPS than blood from individuals without the variant. TLR5 expression in THP1 cells was silenced using siRNA; these cells were stimulated with LPS before cytokine levels in cell supernatants were quantified by ELISA. In these cells following LPS stimulation, silencing of TLR5 with siRNA reduced both TNF-α and IL-8 levels. These effects were not explained by differences in TLR4 mRNA expression or NF-κB or IRF activation.

Conclusions/Significance

The effects of the common nonsense TLR5:c.1174C>T polymorphism on the host inflammatory response to B. pseudomallei may not be restricted to flagellin-driven pathways. Moreover, TLR5 may modulate TLR4-dependent cytokine production. While these results may have broader implications for the role of TLR5 in the innate immune response in melioidosis and other conditions, further studies of the mechanisms underlying these observations are required.

Toll-like receptors (TLRs) are important receptors of the innate immune system. TLR4 detects bacterial lipopolysaccharide (LPS) and TLR5 detects bacterial flagellin. A common human polymorphism in TLR5 encodes a shortened protein and blunts the immune response to flagellin. Individuals carrying this variant have decreased mortality from melioidosis, infection caused by the flagellated Gram-negative bacterium Burkholderia pseudomallei. The mechanism of protection is not known. We tested the hypothesis that the observed effect of the polymorphism is independent of flagellin and involves LPS-TLR4 pathways. We found that blood from individuals carrying the polymorphism produced lower levels of cytokines IL-6 and IL-10 in response to an aflagellated B. pseudomallei mutant and less IL-8 in response to purified B. pseudomallei LPS than blood from individuals without the variant. We further observed that in THP1 cells stimulated with LPS, silencing of TLR5 with siRNA reduced levels of both TNF-α and IL-8. These effects were not explained by differences in TLR4 mRNA expression. We conclude that the effects of the TLR5 polymorphism on the host inflammatory response to B. pseudomallei may not be restricted to flagellin-driven pathways. These results provide insights into the role of TLR5 in the innate immune response in melioidosis and other conditions.

Alpha lipoic acid and metformin alleviates experimentally induced insulin resistance and cognitive deficit by modulation of TLR2 signalling

BACKGROUND

Obesity is commonly found to be co-morbid with type 2 Diabetes Mellitus. In obese diabetic patients, TLR-2 receptor induced inflammation leads to the development of insulin resistance (IR). Furthermore, the IR is considered to be the most important cause for promoting cognitive decline which is evident in brain of patients with Alzheimer's disease related dementia (ADRD).

METHODS

In this study, the effect of α-lipoic acid (ALA) has been examined in rodent model of zymosan induced insulin resistance and cognitive deficits, targeting at TLR-2 signalling. TLR-2 agonist, Zymosan initiates inflammatory cascade, resulting in IR and cognitive dysfunction. Zymosan (50 mg/kg ip) was given to mice on 1st, 8th, 15th and 22nd day to induce IR which was confirmed by hyperglycaemia, hyperinsulinemia, hyperlipidimea, increased glycated haemoglobin and HOMA-IR. Further the cognitive performance was assessed in Morris water maze revealing cognitive deficit in zymosan treated mice.

RESULTS

Daily treatment with ALA for 28 days (50, 100, 200 mg/kg, ip) significantly improved insulin sensitivity and cognitive performance in mice by decreasing insulin resistance, corticosterone, IL-6 levels, acetylcholinesterase enzyme activity and oxidative stress in liver, cortex and hippocampus. ALA also increased adiponectin level and reduced body weight. Combination of ALA (100 mg/kg, ip) with metformin (100 mg/kg, ip) exhibited a potentiating effect in improving cognitive performance and insulin signalling.

CONCLUSION

The findings of the study supported the hypothesis that TLR-2 induced inflammation leads to insulin resistance and cognitive impairment and provides an evidence for the therapeutic effect of ALA in IR and ADRD patients.

Genetic polymorphisms in TLR1, TLR2, TLR4, and TLR10 of Helicobacter pylori-associated gastritis: a prospective cross-sectional study in Thailand

The toll-like receptors (TLRs) mediate the recognition of Helicobacter pylori and initiate the innate immune response to infection. We hypothesized those genetic polymorphisms in the TLR1, TLR2, TLR4, and TLR10 influence bacterial infection, affecting susceptibility H. pylori to disease outcomes. Genomic DNA was extracted and genotypes of TLR1 (rs4833095), TLR2 (rs3804099 and rs3804100), TLR4(rs10759932), and TLR10 (rs10004195) polymorphism were detected by the TagMan single-nucleotide epolymorphisms genotyping assay using the real-time PCR hybridization probe method. The TLR1 (rs4833095), C allele and the TLR10 (rs10004195), A allele frequency was significantly increased risk in the H. pylori infection group (odds ratio=1.76, 95% confidence interval=1.84–2.15, P=0.01 and odds ratio=1.81, 95% confidence interval=1.18–3.26, P=0.04, respectively). The TLR1 (rs4833095), C allele and TLR10 (rs10004195), A allele are susceptible TLRs polymorphisms in the Thai population. These findings suggest that TLR1 rs4833095 and TLR10 rs10004195 may play crucial roles in H. pylori susceptibility and gastric pathogenesis.

The Relationship between Toll-like Receptors and Helicobacter pylori-Related Gastropathies: Still a Controversial Topic

Innate immunity represents the first barrier against bacterial invasion. Toll-like receptors (TLRs) belong to the large family of pattern recognition receptors (PRRs), and their activation leads to the induction of inflammatory cytokines, chemokines, antigen-presenting molecules, and costimulatory molecules. Recent studies have focused on identifying the association between TLRs and Helicobacter pylori- (H. pylori-) related diseases. Therefore, this minireview focuses on assessing the role of these TLRs in the development of H. pylori-related gastropathies. Both TLR2 and TLR were found to be involved in H. pylori LPS recognition, with contradictory results most likely due to both the inability to obtain pure LPS in experimental studies and the heterogeneity of the bacterial LPS. In addition, TLR2 was found to be the most extensively expressed gene among all the TLRs in gastric tumors. High levels of TLR4 were also associated with a higher risk of gastric cancer. TLR5 was initially associated with the recognition of H. pylori flagellin, but it seems that this bacterium has developed mechanisms to escape this recognition representing an important factor involved in the persistence of this infection and subsequent carcinogenesis. TLR9, the only TLR with both anti- and proinflammatory roles, was involved in the recognition of H. pylori DNA. The dichotomous role of TLR9, promoting or suppressing the infection, depends on the gastric environment. Recently, TLR7 and TLR8 were shown to recognize purified H. pylori RNA, thereby inducing proinflammatory cytokines. TLR1 and TLR10 gene polymorphisms were associated with a higher risk for gastric cancer in H. pylori-infected individuals. Different gene polymorphisms of these TLRs were found to be associated with gastric cancer depending mostly on ethnicity. Further studies are required in order to develop preventive and therapeutic strategies against H. pylori infections based on the functions of TLRs.

Association of TLR4 Polymorphisms, Expression, and Vitamin D with Helicobacter pylori Infection

Helicobacter pylori (H. pylori) infection is the strongest recognized risk factor for gastric adenocarcinoma. Since previous observations have shown that polymorphisms in innate immune system genes, as well as vitamin D (VitD) levels, could modify the risk of infection with Helicobacterpylori (H. pylori), we analyzed the relation between single nucleotide polymorphisms (SNPs) in TLRs (TLR1, TLR2, TLR4) CD14, RUNX3 and VitD levels with H. pylori infection. A case-control study on four hundred sixty Lebanese individuals was conducted. Eleven SNPs in total were genotyped and gene expression analysis using real-time PCR was performed in white blood cells of a subsample of eight individuals. A total of 49% of the participants were affected. Although no direct association was found between the SNPs and H. pylori infection, rs4986790G>A and rs4986791T>C in TLR4 were negatively associated with VitD levels (β = −0.371, p = 5 × 10⁻³ and β = −0.4, p = 2 × 10⁻³, respectively), which was negatively associated with H. pylori infection (OR = 0.01, p < 1 × 10⁻³). TLR4 expression was 3× lower in individuals with H. pylori compared with non-infected (p = 0.01). TLR4 polymorphisms, expression, and VitD could be implicated in H. pylori infection and further development of gastric adenocarcinoma.

Mechanisms of Inflammasome Signaling, microRNA Induction and Resolution of Inflammation by Helicobacter pylori

Inflammasome-controlled transcription and subsequent cleavage-mediated activation of mature IL-1β and IL-18 cytokines exemplify a crucial innate immune mechanism to combat intruding pathogens. Helicobacter pylori represents a predominant persistent infection in humans, affecting approximately half of the population worldwide, and is associated with the development of chronic gastritis, peptic ulcer disease, and gastric cancer. Studies in knockout mice have demonstrated that the pro-inflammatory cytokine IL-1β plays a central role in gastric tumorigenesis. Infection by H. pylori was recently reported to stimulate the inflammasome both in cells of the mouse and human immune systems. Using mouse models and in vitro cultured cell systems, the bacterial pathogenicity factors and molecular mechanisms of inflammasome activation have been analyzed. On the one hand, it appears that H. pylori-stimulated IL-1β production is triggered by engagement of the immune receptors TLR2 and NLRP3, and caspase-1. On the other hand, microRNA hsa-miR-223-3p is induced by the bacteria, which controls the expression of NLRP3. This regulating effect by H. pylori on microRNA expression was also described for more than 60 additionally identified microRNAs, indicating a prominent role for inflammatory and other responses. Besides TLR2, TLR9 becomes activated by H. pylori DNA and further TLR10 stimulated by the bacteria induce the secretion of IL-8 and TNF, respectively. Interestingly, TLR-dependent pathways can accelerate both pro- and anti-inflammatory responses during H. pylori infection. Balancing from a pro-inflammation to anti-inflammation phenotype results in a reduction in immune attack, allowing H. pylori to persistently colonize and to survive in the gastric niche. In this chapter, we will pinpoint the role of H. pylori in TLR- and NLRP3 inflammasome-dependent signaling together with the differential functions of pro- and anti-inflammatory cytokines. Moreover, the impact of microRNAs on H. pylori-host interaction will be discussed, and its role in resolution of infection versus chronic infection, as well as in gastric disease development.

Importance of Toll-like Receptors in Pro-inflammatory and Anti-inflammatory Responses by Helicobacter pylori Infection

Infectious diseases have been paramount among the threats to human health and survival throughout evolutionary history. Bacterial cell-surface molecules are key factors in the microorganism-host crosstalk, as they can interact with host pattern-recognition receptors (PRRs) of the gastrointestinal mucosa. The best-studied PRRs are toll-like receptors (TLRs). Because TLRs play an important key role in host defense, they have received increasing interest in the evolutionary and population genetics literature, and their variation represents a potential target of adaptive evolution. Helicobacter pylori is one of the commensal bacteria in our body and can have pathogenic properties in a subset of infected people. The history of H. pylori research indicated that humans and bacteria co-evolved during evolution. A genome-wide association study (GWAS) has opened the way for investigating the genomic evolution of bacterial pathogens during the colonization and infection of humans. Recent GWAS research emphasized the importance of TLRs, especially TLR10 during pathogenesis in H. pylori infection. We demonstrated that TLR10, whose ligand was unknown for a long time, can recognize H. pylori LPS. Our results of H. pylori research suggest that TLR10 might play an important role to also recognize other commensal bacteria. In this review, we discuss the importance of TLRs in pro-inflammatory and anti-inflammatory responses by H. pylori infection. Especially, we highlight the TLR10 interaction with H. pylori infection, providing new insights about TLR10 signaling.