Bacterial Genotoxin-Induced DNA Damage and Modulation of the Host Immune Microenvironment

MNDA, a PYHIN factor involved in transcriptional regulation and apoptosis control in leukocytes

Inflammation control is critical during the innate immune response. Such response is triggered by the detection of molecules originating from pathogens or damaged host cells by pattern-recognition receptors (PRRs). PRRs subsequently initiate intra-cellular signalling through different pathways, resulting in i) the production of inflammatory cytokines, including type I interferon (IFN), and ii) the initiation of a cascade of events that promote both immediate host responses as well as adaptive immune responses. All human PYRIN and HIN-200 domains (PYHIN) protein family members were initially proposed to be PRRs, although this view has been challenged by reports that revealed their impact on other cellular mechanisms. Of relevance here, the human PYHIN factor myeloid nuclear differentiation antigen (MNDA) has recently been shown to directly control the transcription of genes encoding factors that regulate programmed cell death and inflammation. While MNDA is mainly found in the nucleus of leukocytes of both myeloid (neutrophils and monocytes) and lymphoid (B-cell) origin, its subcellular localization has been shown to be modulated in response to genotoxic agents that induce apoptosis and by bacterial constituents, mediators of inflammation. Prior studies have noted the importance of MNDA as a marker for certain forms of lymphoma, and as a clinical prognostic factor for hematopoietic diseases characterized by defective regulation of apoptosis. Abnormal expression of MNDA has also been associated with altered levels of cytokines and other inflammatory mediators. Refining our comprehension of the regulatory mechanisms governing the expression of MNDA and other PYHIN proteins, as well as enhancing our definition of their molecular functions, could significantly influence the management and treatment strategies of numerous human diseases. Here, we review the current state of knowledge regarding PYHIN proteins and their role in innate and adaptive immune responses. Emphasis will be placed on the regulation, function, and relevance of MNDA expression in the control of gene transcription and RNA stability during cell death and inflammation.

Overview of Bacterial Protein Toxins from Pathogenic Bacteria: Mode of Action and Insights into Evolution

Bacterial protein toxins are secreted by certain bacteria and are responsible for mild to severe diseases in humans and animals. They are among the most potent molecules known, which are active at very low concentrations. Bacterial protein toxins exhibit a wide diversity based on size, structure, and mode of action. Upon recognition of a cell surface receptor (protein, glycoprotein, and glycolipid), they are active either at the cell surface (signal transduction, membrane damage by pore formation, or hydrolysis of membrane compound(s)) or intracellularly. Various bacterial protein toxins have the ability to enter cells, most often using an endocytosis mechanism, and to deliver the effector domain into the cytosol, where it interacts with an intracellular target(s). According to the nature of the intracellular target(s) and type of modification, various cellular effects are induced (cell death, homeostasis modification, cytoskeleton alteration, blockade of exocytosis, etc.). The various modes of action of bacterial protein toxins are illustrated with representative examples. Insights in toxin evolution are discussed.

Genotoxin-producing Salmonella enterica induces tissue-specific types of DNA damage and DNA damage response outcomes

Introduction

Typhoid toxin-expressing Salmonella enterica causes DNA damage in the intestinal mucosa in vivo, activating the DNA damage response (DDR) in the absence of inflammation. To understand whether the tissue microenvironment constrains the infection outcome, we compared the immune response and DDR patterns in the colon and liver of mice infected with a genotoxigenic strain or its isogenic control strain.

Methods

In situ spatial transcriptomic and immunofluorescence have been used to assess DNA damage makers, activation of the DDR, innate immunity markers in a multiparametric analysis.

Result

The presence of the typhoid toxin protected from colonic bacteria-induced inflammation, despite nuclear localization of p53, enhanced co-expression of type-I interferons (IfnbI) and the inflammasome sensor Aim2, both classic features of DNA-break-induced DDR activation. These effects were not observed in the livers of either infected group. Instead, in this tissue, the inflammatory response and DDR were associated with high oxidative stress-induced DNA damage.

Conclusions

Our work highlights the relevance of the tissue microenvironment in enabling the typhoid toxin to suppress the host inflammatory response in vivo.

Intratumoural microbiota: a new frontier in cancer development and therapy

Human microorganisms, including bacteria, fungi, and viruses, play key roles in several physiological and pathological processes. Some studies discovered that tumour tissues once considered sterile actually host a variety of microorganisms, which have been confirmed to be closely related to oncogenesis. The concept of intratumoural microbiota was subsequently proposed. Microbiota could colonise tumour tissues through mucosal destruction, adjacent tissue migration, and hematogenic invasion and affect the biological behaviour of tumours as an important part of the tumour microenvironment. Mechanistic studies have demonstrated that intratumoural microbiota potentially promote the initiation and progression of tumours by inducing genomic instability and mutations, affecting epigenetic modifications, promoting inflammation response, avoiding immune destruction, regulating metabolism, and activating invasion and metastasis. Since more comprehensive and profound insights about intratumoral microbiota are continuously emerging, new methods for the early diagnosis and prognostic assessment of cancer patients have been under examination. In addition, interventions based on intratumoural microbiota show great potential to open a new chapter in antitumour therapy, especially immunotherapy, although there are some inevitable challenges. Here, we aim to provide an extensive review of the concept, development history, potential sources, heterogeneity, and carcinogenic mechanisms of intratumoural microorganisms, explore the potential role of microorganisms in tumour prognosis, and discuss current antitumour treatment regimens that target intratumoural microorganisms and the research prospects and limitations in this field.

Selective pks+ Escherichia coli strains induce cell cycle arrest and apoptosis in colon cancer cell line

pks+ Escherichia coli (E. coli) triggers genomic instability in normal colon cells which leads to colorectal cancer (CRC) tumorigenesis. Previously, we reported a significant presentation of pks+ E. coli strains in CRC patients' biopsies as compared to healthy cohorts. In this work, using an in vitro infection model, we further explored the ability of these strains in modulating cell cycle arrest and activation of apoptotic mediators in both primary colon epithelial cells (PCE) and CRC cells (HCT-116). Sixteen strains, of which eight tumours and the matching non-malignant tissues, respectively, from eight pks+ E. coli CRC patients were subjected to BrDU staining and cell cycle analysis via flow cytometry, while a subset of these strains underwent analysis of apoptotic mediators including caspase proteins, cellular reactive oxygen species (cROS) and mitochondrial membrane potential (MMP) via spectrophotometry as well as proinflammatory cytokines via flow cytometry. Data revealed that all strains exerted S-phase cell cycle blockade in both cells and G2/M phase in PCE cells only. Moreover, more significant upregulation of Caspase 9, cROS, proinflammatory cytokines and prominent downregulation of MMP were detected in HCT-116 cells indicating the potential role of pks related bacterial toxin as anticancer agent as compared to PCE cells which undergo cellular senescence leading to cell death without apparent upregulation of apoptotic mediators. These findings suggest the existence of discrepancies underlying the mechanism of action of pks+ E. coli on both cancer and normal cell lines. This work propounds the rationale to further understand the mechanism underlying pks+ E. coli-mediated CRC tumorigenesis and cancer killing.

Senescent Markers Expressed by Periodontal Ligament-Derived Stem Cells (PDLSCs) Harvested from Patients with Periodontitis Can Be Rejuvenated by RG108

Periodontal ligament (PDL) has become an elective source of mesenchymal stem cells (PDLSCs) in dentistry. This research aimed to compare healthy PDLSCs (hPDLSCs) and periodontitis PDLSCs (pPDLSCs) to ascertain any possible functional differences owing to their milieux of origin. Cells were tested in terms of colony-forming unit efficiency; multi differentiating capacity; immunophenotype, stemness, and senescent state were studied by flow cytometry, immunofluorescence, and β-galactosidase staining; gene expression using RT-PCR. Both hPDLSCs and pPDLSCs were comparable in terms of their immunophenotype and multilineage differentiation capabilities, but pPDLSCs showed a senescent phenotype more frequently. Thus, a selective small molecule inhibitor of DNA methyltransferase (DNMT), RG108, known for its effect on senescence, was used to possibly reverse this phenotype. RG108 did not affect the proliferation and apoptosis of PDLSCs, and it showed little effect on hPDLSCs, while a significant reduction of both p16 and p21 was detected along with an increase of SOX2 and OCT4 in pPDLSCs after treatment at 100 μM RG108. Moreover, the subset of PDLSCs co-expressing OCT4 and p21 decreased, and adipogenic potential increased in pPDLSCs after treatment. pPDLSCs displayed a senescent phenotype that could be reversed, opening new perspectives for the treatment of periodontitis.

P. aeruginosa interactions with other microbes in biofilms during co-infection

This review addresses the topic of biofilms, including their development and the interaction between different counterparts. There is evidence that various diseases, such as cystic fibrosis, otitis media, diabetic foot wound infections, and certain cancers, are promoted and aggravated by the presence of polymicrobial biofilms. Biofilms are composed by heterogeneous communities of microorganisms protected by a matrix of polysaccharides. The different types of interactions between microorganisms gives rise to an increased resistance to antimicrobials and to the host's defense mechanisms, with the consequent worsening of disease symptoms. Therefore, infections caused by polymicrobial biofilms affecting different human organs and systems will be discussed, as well as the role of the interactions between the gram-negative bacteria Pseudomonas aeruginosa, which is at the base of major polymicrobial infections, and other bacteria, fungi, and viruses in the establishment of human infections and diseases. Considering that polymicrobial biofilms are key to bacterial pathogenicity, it is fundamental to evaluate which microbes are involved in a certain disease to convey an appropriate and efficacious antimicrobial therapy.

Clostridioides difficile Toxin B Induced Senescence: A New Pathologic Player for Colorectal Cancer?

Clostridioides difficile (C. difficile) is responsible for a high percentage of gastrointestinal infections and its pathological activity is due to toxins A and B. C. difficile infection (CDI) is increasing worldwide due to the unstoppable spread of C. difficile in the anthropized environment and the progressive human colonization. The ability of C. difficile toxin B to induce senescent cells and the direct correlation between CDI, irritable bowel syndrome (IBS), and inflammatory bowel diseases (IBD) could cause an accumulation of senescent cells with important functional consequences. Furthermore, these senescent cells characterized by long survival could push pre-neoplastic cells originating in the colon towards the complete neoplastic transformation in colorectal cancer (CRC) by the senescence-associated secretory phenotype (SASP). Pre-neoplastic cells could appear as a result of various pro-carcinogenic events, among which, are infections with bacteria that produce genotoxins that generate cells with high genetic instability. Therefore, subjects who develop IBS and/or IBD after CDI should be monitored, especially if they then have further CDI relapses, waiting for the availability of senolytic and anti-SASP therapies to resolve the pro-carcinogenic risk due to accumulation of senescent cells after CDI followed by IBS and/or IBD.

Cortactin: A universal host cytoskeletal target of Gram-negative and Gram-positive bacterial pathogens

Pathogenic bacteria possess a great potential of causing infectious diseases and represent a serious threat to human and animal health. Understanding the molecular basis of infection development can provide new valuable strategies for disease prevention and better control. In host-pathogen interactions, actin-cytoskeletal dynamics play a crucial role in the successful adherence, invasion, and intracellular motility of many intruding microbial pathogens. Cortactin, a major cellular factor that promotes actin polymerization and other functions, appears as a central regulator of host-pathogen interactions and different human diseases including cancer development. Various important microbes have been reported to hijack cortactin signaling during infection. The primary regulation of cortactin appears to proceed via serine and/or tyrosine phosphorylation events by upstream kinases, acetylation, and interaction with various other host proteins, including the Arp2/3 complex, filamentous actin, the actin nucleation promoting factor N-WASP, focal adhesion kinase FAK, the large GTPase dynamin-2, the guanine nucleotide exchange factor Vav2, and the actin-stabilizing protein CD2AP. Given that many signaling factors can affect cortactin activities, several microbes target certain unique pathways, while also sharing some common features. Here we review our current knowledge of the hallmarks of cortactin as a major target for eminent Gram-negative and Gram-positive bacterial pathogens in humans.

Vibrational spectroscopy for decoding cancer microbiota interactions: Current evidence and future perspective

The role of human microbiota in cancer initiation and progression is recognized in recent years. In order to investigate the interactions between cancer cells and microbes, a systematic analysis using various emerging techniques is required. Owing to the label-free, non-invasive and molecular fingerprinting characteristics, vibrational spectroscopy is uniquely suited to decode and understand the relationship and interactions between cancer and the microbiota at the molecular level. In this review, we first provide a quick overview of the fundamentals of vibrational spectroscopic techniques, namely Raman and infrared spectroscopy. Next, we discuss the emerging evidence underscoring utilities of these spectroscopic techniques to study cancer or microbes separately, and share our perspective on how vibrational spectroscopy can be employed at the intersection of the two fields. Finally, we envision the potential opportunities in exploiting vibrational spectroscopy not only in basic cancer-microbiome research but also in its clinical translation, and discuss the challenges in the bench to bedside translation.

The Role of Cyclomodulins and Some Microbial Metabolites in Bacterial Microecology and Macroorganism Carcinogenesis

A number of bacteria that colonize the human body produce toxins and effectors that cause changes in the eukaryotic cell cycle—cyclomodulins and low-molecular-weight compounds such as butyrate, lactic acid, and secondary bile acids. Cyclomodulins and metabolites are necessary for bacteria as adaptation factors—which are influenced by direct selection—to the ecological niches of the host. In the process of establishing two-way communication with the macroorganism, these compounds cause limited damage to the host, despite their ability to disrupt key processes in eukaryotic cells, which can lead to pathological changes. Possible negative consequences of cyclomodulin and metabolite actions include their potential role in carcinogenesis, in particular, with the ability to cause DNA damage, increase genome instability, and interfere with cancer-associated regulatory pathways. In this review, we aim to examine cyclomodulins and bacterial metabolites as important factors in bacterial survival and interaction with the host organism to show their heterogeneous effect on oncogenesis depending on the surrounding microenvironment, pathological conditions, and host genetic background.

Blood biomarkers representing maternal-fetal interface tissues used to predict early-and late-onset preeclampsia but not COVID-19 infection

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Endothelial dysfunction misleads blood marker discovery by differential expression.

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Blood-derived surrogate transcriptome of target-tissue avoids the false discovery.

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ITGA5 implies polymicrobial infection of maternal-fetal interface in preeclampsia.

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ITGA5 and IRF6 implies viral co-infection in early-onset preeclampsia.

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ITGA5, IRF6, and P2RX7 differ imminent preeclampsia from COVID-19 infection.

Background

A well-known blood biomarker (soluble fms-like tyrosinase-1 [sFLT-1]) for preeclampsia, i.e., a pregnancy disorder, was found to predict severe COVID-19, including in males. True biomarker may be masked by more-abrupt changes related to endothelial instead of placental dysfunction. This study aimed to identify blood biomarkers that represent maternal-fetal interface tissues for predicting preeclampsia but not COVID-19 infection.

Methods

The surrogate transcriptome of tissues was determined by that in maternal blood, utilizing four datasets (n = 1354) which were collected before the COVID-19 pandemic. Applying machine learning, a preeclampsia prediction model was chosen between those using blood transcriptome (differentially expressed genes [DEGs]) and the blood-derived surrogate for tissues. We selected the best predictive model by the area under the receiver operating characteristic (AUROC) using a dataset for developing the model, and well-replicated in datasets both with and without an intervention. To identify eligible blood biomarkers that predicted any-onset preeclampsia from the datasets but that were not positive in the COVID-19 dataset (n = 47), we compared several methods of predictor discovery: (1) the best prediction model; (2) gene sets of standard pipelines; and (3) a validated gene set for predicting any-onset preeclampsia during the pandemic (n = 404). We chose the most predictive biomarkers from the best method with the significantly largest number of discoveries by a permutation test. The biological relevance was justified by exploring and reanalyzing low- and high-level, multiomics information.

Results

A prediction model using the surrogates developed for predicting any-onset preeclampsia (AUROC of 0.85, 95 % confidence interval [CI] 0.77 to 0.93) was the only that was well-replicated in an independent dataset with no intervention. No model was well-replicated in datasets with a vitamin D intervention. None of the blood biomarkers with high weights in the best model overlapped with blood DEGs. Blood biomarkers were transcripts of integrin-α5 (ITGA5), interferon regulatory factor-6 (IRF6), and P2X purinoreceptor-7 (P2RX7) from the prediction model, which was the only method that significantly discovered eligible blood biomarkers (n = 3/100 combinations, 3.0 %; P =.036). Most of the predicted events (73.70 %) among any-onset preeclampsia were cluster A as defined by ITGA5 (Z-score ≥ 1.1), but were only a minority (6.34 %) among positives in the COVID-19 dataset. The remaining were predicted events (26.30 %) among any-onset preeclampsia or those among COVID-19 infection (93.66 %) if IRF6 Z-score was ≥-0.73 (clusters B and C), in which none was the predicted events among either late-onset preeclampsia (LOPE) or COVID-19 infection if P2RX7 Z-score was <0.13 (cluster C). Greater proportions of predicted events among LOPE were cluster A (82.85 % vs 70.53 %) compared to early-onset preeclampsia (EOPE). The biological relevance by multiomics information explained the biomarker mechanism, polymicrobial infection in any-onset preeclampsia by ITGA5, viral co-infection in EOPE by ITGA5-IRF6, a shared prediction with COVID-19 infection by ITGA5-IRF6-P2RX7, and non-replicability in datasets with a vitamin D intervention by ITGA5.

Conclusions

In a model that predicts preeclampsia but not COVID-19 infection, the important predictors were genes in maternal blood that were not extremely expressed, including the proposed blood biomarkers. The predictive performance and biological relevance should be validated in future experiments.

DNA-double strand breaks enhance the expression of major histocompatibility complex class II through the ATM-NF-κΒ-IRF1-CIITA pathway

Major histocompatibility complex class II (MHC II) is important for the adaptive immune response because MHC II presents processed antigens to a cluster of differentiation 4 (CD4)-positive T-cells. Conventional doses of chemotherapeutic agents induce tumor cell death by causing DNA double-strand breaks (DSBs). However, cellular responses caused by sub-lethal doses of chemotherapeutic agents are poorly understood. In this study, using low doses of chemotherapeutic agents, we showed that DSBs enhanced the expression of MHC II on cells that originate from antigen-presenting cells (APCs). These agents induced the MHC class II transactivator (CIITA), the master regulator of MHC II, and interferon regulatory factor 1 (IRF1), a transcription factor for CIITA. Short hairpin RNA against IRF1 suppressed chemotherapeutic agent-induced CIITA expression, whereas exogenous expression of IRF1 induced CIITA. Inhibition of ataxia-telangiectasia mutated (ATM), a DSB-activated kinase, suppressed induction of IRF1, CIITA, and MHC II. Similar results were observed by inhibiting NF-κB, a downstream target of ATM. These results suggest that DSBs induce MHC II activity via the ATM-NF-κB-IRF1-CIITA pathway in cells that intrinsically present antigens. Additionally, chemotherapeutic agents induced T-cell regulatory molecules. Our findings suggest that chemotherapeutic agents enhance the antigen presentation activity of APCs for T-cell activation.

Neutralization of typhoid toxin by alpaca-derived, single-domain antibodies targeting the PltB and CdtB subunits

Typhoid toxin is secreted by the typhoid fever-causing bacterial pathogen Salmonella enterica serovar Typhi and has tropism for immune cells and brain endothelial cells. Here, we generated a camelid single-domain antibody (VHH) library from typhoid toxoid-immunized alpacas and identified 41 VHHs selected on the glycan receptor-binding PltB and nuclease CdtB. VHHs exhibiting potent in vitro neutralizing activities from each sequence-based family were epitope binned via competition enzyme-linked immunosorbent assays (ELISAs), leading to 6 distinct VHHs, 2 anti-PltBs (T2E7 and T2G9), and 4 anti-CdtB VHHs (T4C4, T4C12, T4E5, and T4E8), whose in vivo neutralizing activities and associated toxin-neutralizing mechanisms were investigated. We found that T2E7, T2G9, and T4E5 effectively neutralized typhoid toxin in vivo, as demonstrated by 100% survival of mice administered a lethal dose of typhoid toxin and with little to no typhoid toxin-mediated upper motor function defect. Cumulatively, these results highlight the potential of the compact antibodies to neutralize typhoid toxin by targeting the glycan-binding and/or nuclease subunits.

From DNA Damage to Cancer Progression: Potential Effects of Cytolethal Distending Toxin

Cytolethal distending toxin (CDT), one of the most important genotoxins, is produced by several gram-negative bacteria and is involved in bacterial pathogenesis. Recent studies have shown that bacteria producing this peculiar genotoxin target host DNA, which potentially contributes to development of cancer. In this review, we highlighted the recent studies focusing on the idea that CDT leads to DNA damage, and the cells with inappropriately repaired DNA continue cycling, resulting in cancer development. Understanding the detailed mechanisms of genotoxins that cause DNA damage might be useful for targeting potential markers that drive cancer progression and help to discover new therapeutic strategies to prevent diseases caused by pathogens.

Chronic exposure to Cytolethal Distending Toxin (CDT) promotes a cGAS-dependent type I interferon response

The Cytolethal Distending Toxin (CDT) is a bacterial genotoxin produced by pathogenic bacteria causing major foodborne diseases worldwide. CDT activates the DNA Damage Response and modulates the host immune response, but the precise relationship between these outcomes has not been addressed so far. Here, we show that chronic exposure to CDT in HeLa cells or mouse embryonic fibroblasts promotes a strong type I interferon (IFN) response that depends on the cytoplasmic DNA sensor cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS) through the recognition of micronuclei. Indeed, despite active cell cycle checkpoints and in contrast to other DNA damaging agents, cells exposed to CDT reach mitosis where they accumulate massive DNA damage, resulting in chromosome fragmentation and micronucleus formation in daughter cells. These mitotic phenotypes are observed with CDT from various origins and in cancer or normal cell lines. Finally, we show that CDT exposure in immortalized normal colonic epithelial cells is associated to cGAS protein loss and low type I IFN response, implying that CDT immunomodulatory function may vary depending on tissue and cell type. Thus, our results establish a direct link between CDT-induced DNA damage, genetic instability and the cellular immune response that may be relevant in the context of natural infection associated to chronic inflammation or carcinogenesis.

Bacterial Toxins Are a Never-Ending Source of Surprises: From Natural Born Killers to Negotiators

The idea that bacterial toxins are not only killers but also execute more sophisticated roles during bacteria-host interactions by acting as negotiators has been highlighted in the past decades. Depending on the toxin, its cellular target and mode of action, the final regulatory outcome can be different. In this review, we have focused on two families of bacterial toxins: genotoxins and pore-forming toxins, which have different modes of action but share the ability to modulate the host's immune responses, independently of their capacity to directly kill immune cells. We have addressed their immuno-suppressive effects with the perspective that these may help bacteria to avoid clearance by the host's immune response and, concomitantly, limit detrimental immunopathology. These are optimal conditions for the establishment of a persistent infection, eventually promoting asymptomatic carriers. This immunomodulatory effect can be achieved with different strategies such as suppression of pro-inflammatory cytokines, re-polarization of the immune response from a pro-inflammatory to a tolerogenic state, and bacterial fitness modulation to favour tissue colonization while preventing bacteraemia. An imbalance in each of those effects can lead to disease due to either uncontrolled bacterial proliferation/invasion, immunopathology, or both.

Intestinal Inflammation and Altered Gut Microbiota Associated with Inflammatory Bowel Disease Render Mice Susceptible to Clostridioides difficile Colonization and Infection

Clostridioides difficile is a noteworthy pathogen in patients with inflammatory bowel disease (IBD). Patients with IBD who develop concurrent C. difficile infection (CDI) experience increased morbidity and mortality. IBD is associated with intestinal inflammation and alterations of the gut microbiota, both of which can diminish colonization resistance to C. difficile. Here, we describe the development of a mouse model to explore the role that IBD-induced changes of the gut microbiome play in susceptibility to C. difficile. Helicobacter hepaticus, a normal member of the mouse gut microbiota, triggers pathological inflammation in the distal intestine akin to human IBD in mice that lack intact interleukin 10 (IL-10) signaling. We demonstrate that mice with H. hepaticus-induced IBD were susceptible to C. difficile colonization in the absence of other perturbations, such as antibiotic treatment. Concomitant IBD and CDI were associated with significantly worse disease than observed in animals with colitis alone. Development of IBD resulted in a distinct intestinal microbiota community compared to that of non-IBD controls. Inflammation played a critical role in the susceptibility of animals with IBD to C. difficile colonization, as mice colonized with an isogenic mutant of H. hepaticus that triggers an attenuated intestinal inflammation maintained full colonization resistance. These studies with a novel mouse model of IBD and CDI emphasize the importance of host responses and alterations of the gut microbiota in susceptibility to C. difficile colonization and infection in the setting of IBD.

Bacterial genotoxins induce T cell senescence

Several types of pathogenic bacteria produce genotoxins that induce DNA damage in host cells. Accumulating evidence suggests that a central function of these genotoxins is to dysregulate the host's immune response, but the underlying mechanisms remain unclear. To address this issue, we investigated the effects of the most widely expressed bacterial genotoxin, the cytolethal distending toxin (CDT), on T cells-the key mediators of adaptive immunity. We show that CDT induces premature senescence in activated CD4 T cells in vitro and provide evidence suggesting that infection with genotoxin-producing bacteria promotes T cell senescence in vivo. Moreover, we demonstrate that genotoxin-induced senescent CD4 T cells assume a senescence-associated secretory phenotype (SASP) which, at least partly, is orchestrated by the ATM-p38 signaling axis. These findings provide insight into the immunomodulatory properties of bacterial genotoxins and uncover a putative link between bacterial infections and T cell senescence.

Influence of the microenvironment on modulation of the host response by typhoid toxin

Bacterial genotoxins cause DNA damage in eukaryotic cells, resulting in activation of the DNA damage response (DDR) in vitro. These toxins are produced by Gram-negative bacteria, enriched in the microbiota of inflammatory bowel disease (IBD) and colorectal cancer (CRC) patients. However, their role in infection remains poorly characterized. We address the role of typhoid toxin in modulation of the host-microbial interaction in health and disease. Infection with a genotoxigenic Salmonella protects mice from intestinal inflammation. We show that the presence of an active genotoxin promotes DNA fragmentation and senescence in vivo, which is uncoupled from an inflammatory response and unexpectedly associated with induction of an anti-inflammatory environment. The anti-inflammatory response is lost when infection occurs in mice with acute colitis. These data highlight a complex context-dependent crosstalk between bacterial-genotoxin-induced DDR and the host immune response, underlining an unexpected role for bacterial genotoxins.

The Active Subunit of the Cytolethal Distending Toxin, CdtB, Derived From Both Haemophilus ducreyi and Campylobacter jejuni Exhibits Potent Phosphatidylinositol-3,4,5-Triphosphate Phosphatase Activity

Human lymphocytes exposed to Aggregatibacter actinomycetemcomitans (Aa) cytolethal distending toxin (Cdt) undergo cell cycle arrest and apoptosis. In previous studies, we demonstrated that the active Cdt subunit, CdtB, is a potent phosphatidylinositol (PI) 3,4,5-triphosphate phosphatase. Moreover, AaCdt-treated cells exhibit evidence of PI-3-kinase (PI-3K) signaling blockade characterized by reduced levels of PIP3, pAkt, and pGSK3β. We have also demonstrated that PI-3K blockade is a requisite of AaCdt-induced toxicity in lymphocytes. In this study, we extended our observations to include assessment of Cdts from Haemophilus ducreyi (HdCdt) and Campylobacter jejuni (CjCdt). We now report that the CdtB subunit from HdCdt and CjCdt, similar to that of AaCdt, exhibit potent PIP3 phosphatase activity and that Jurkat cells treated with these Cdts exhibit PI-3K signaling blockade: reduced levels of pAkt and pGSK3β. Since non-phosphorylated GSK3β is the active form of this kinase, we compared Cdts for dependence on GSK3β activity. Two GSK3β inhibitors were employed, LY2090314 and CHIR99021; both inhibitors blocked the ability of Cdts to induce cell cycle arrest. We have previously demonstrated that AaCdt induces increases in the CDK inhibitor, p21^CIP1/WAF1, and, further, that this was a requisite for toxin-induced cell death via apoptosis. We now demonstrate that HdCdt and CjCdt also share this requirement. It is also noteworthy that p21^CIP1/WAF1 was not involved in the ability of the three Cdts to induce cell cycle arrest. Finally, we demonstrate that, like AaCdt, HdCdt is dependent upon the host cell protein, cellugyrin, for its toxicity (and presumably internalization of CdtB); CjCdt was not dependent upon this protein. The implications of these findings as they relate to Cdt’s molecular mode of action are discussed.

Eutopic endometrium from women with endometriosis and chlamydial endometritis share immunological cell types and DNA repair imbalance: A transcriptome meta-analytical perspective

The aim of this study was to identify the key similarities between the eutopic endometrium of women with endometriosis and chlamydia-induced endometritis taking into account tissue microenvironment heterogeneity, transcript gene profile, and enriched pathways. A meta-analysis of whole transcriptome microarrays was performed using publicly available data, including samples containing both glandular and stromal endometrial components. Control samples were obtained from women without any reported pathological condition. Only samples obtained during the proliferative menstrual phase were included. Cellular tissue heterogeneity was predicted using a method that integrates gene set enrichment and deconvolution approaches. The batch effect was estimated by principal variant component analysis and removed using an empirical Bayes method. Differentially expressed genes were identified using an adjusted p-value < 0.05 and fold change = 1.5. The protein-protein interaction network was built using the STRING database and interaction score over 400. The Molecular Signatures Database was used to analyse the functional enrichment analysis. Both conditions showed similarities in cell types in the microenvironment, particularly CD4⁺ and CD8⁺ Tem cells, NKT cells, Th2 cells, basophils, and eosinophils. With regards to the regulation of cellular senescence and DNA integrity/damage checkpoint, which are commonly enriched pathways, 21 genes were down-regulated and directly related to DNA repair. Compared to the endometriosis samples, some chlamydial endometritis samples presented a lack of enriched immune pathways. Our results suggest that both conditions show similar distributions of microenvironment cell types, the downregulation of genes involved in DNA repair and cell cycle control, and pathways involved in immune response evasion.

The CDT of Helicobacter hepaticus induces pro-survival autophagy and nucleoplasmic reticulum formation concentrating the RNA binding proteins UNR/CSDE1 and P62/SQSTM1

Humans are frequently exposed to bacterial genotoxins of the gut microbiota, such as colibactin and cytolethal distending toxin (CDT). In the present study, whole genome microarray-based identification of differentially expressed genes was performed in vitro on HT29 intestinal cells while following the ectopic expression of the active CdtB subunit of Helicobacter hepaticus CDT. Microarray data showed a CdtB-dependent upregulation of transcripts involved in positive regulation of autophagy concomitant with the downregulation of transcripts involved in negative regulation of autophagy. CdtB promotes the activation of autophagy in intestinal and hepatic cell lines. Experiments with cells lacking autophagy related genes, ATG5 and ATG7 infected with CDT- and colibactin-producing bacteria revealed that autophagy protects cells against the genotoxin-induced apoptotic cell death. Autophagy induction could also be associated with nucleoplasmic reticulum (NR) formation following DNA damage induced by these bacterial genotoxins. In addition, both genotoxins promote the accumulation of the autophagic receptor P62/SQSTM1 aggregates, which colocalized with foci concentrating the RNA binding protein UNR/CSDE1. Some of these aggregates were deeply invaginated in NR in distended nuclei together or in the vicinity of UNR-rich foci. Interestingly, micronuclei-like structures and some vesicles containing chromatin and γH2AX foci were found surrounded with P62/SQSTM1 and/or the autophagosome marker LC3. This study suggests that autophagy and P62/SQSTM1 regulate the abundance of micronuclei-like structures and are involved in cell survival following the DNA damage induced by CDT and colibactin. Similar effects were observed in response to DNA damaging chemotherapeutic agents, offering new insights into the context of resistance of cancer cells to therapies inducing DNA damage.

Cancer trigger or remedy: two faces of the human microbiome

Currently, increasing attention cancer treatment has focused on molecularly targeted therapies and more recently on immunotherapies targeting immune checkpoints. However, even such advanced treatment may be ineffective. The reasons for this are sought, inter alia, in the human microbiome. In our intestines, there are bacteria that are beneficial to us, but pathogenic microorganisms may also be present. Microbial imbalance (dysbiosis) is now perceived as one of the gateways to cancer. However, it is feasible to use bacteria and their metabolites to restore the natural, beneficial microbiome during oncological treatment. Akkermansia mucinifila, Enterococcus hirae, or Faecalibacterium prausnitzii are bacteria that exhibit this beneficial potential. Greater benefits of therapy can be observed in cancer patients enriched in these bacterial species and treated with anti-PD-1, anti-PD-L1, or anti-CTLA-4 monoclonal antibodies. In this review, we present issues related to the role of bacteria in carcinogenesis and their therapeutic potential "supporting" modern anti-cancer therapies.Key Points• Bacteria can be directly or indirectly a cancer trigger.• Bacterial metabolites regulate the pathways associated with carcinogenesis.• Intestinal bacteria activate the immune system to fight cancer.

Genetic damage in lymphocytes of lung cancer patients is correlated to the composition of the respiratory tract microbiome

Recent findings indicate that the microbiome may have significant impact on the development of lung cancer by its effects on inflammation, dysbiosis or genome damage. The aim of this study was to compare the sputum microbiome of lung cancer (LC) patients with the chromosomal aberration (CA) and micronuclei (MN) frequency in peripheral blood lymphocytes. In the study, the taxonomic composition of the sputum microbiome of 66 men with untreated LC were compared with 62 control subjects with respect to CA and MN frequency and centromere fluorescence in situ hybridisation analysis. Results showed a significant increase in CA (4.11 ± 2.48% versus 2.08 ± 1.18%) and MN (1.53 ± 0.67% versus 0.87 ± 0.49%) frequencies, respectively, in LC patients as compared to control subjects. The higher frequency of centromeric positive MN of LC patients was mainly due to aneuploidy. A significant increase in Streptococcus, Bacillus, Gemella and Haemophilus in LC patients was detected, in comparison to the control subjects while 18 bacterial genera were significantly reduced, which indicates a decrease in the beta diversity in the microbiome of LC patients. Although, the CA frequency in LC patients is significantly associated with an increased presence of the genera Bacteroides, Lachnoanaerobaculum, Porphyromonas, Mycoplasma and Fusobacterium in their sputum, and a decrease for the genus Granulicatella after application of false discovery rate correction, significance was not any more present. The decrease of MN frequency of LC patients is significantly associated with an increase in Megasphaera genera and Selenomonas bovis. In conclusion, a significant difference in beta diversity of microbiome between LC and control subjects and association between the sputum microbiome composition and genome damage of LC patients was detected, thus supporting previous studies suggesting an etiological connection between the airway microbiome and LC.

The Microbiome and Cancer: Creating Friendly Neighborhoods and Removing the Foes Within

The human body is colonized by the microbial cells that are estimated to be as abundant as human cells, yet their genome is roughly 100 times the human genome, providing significantly more genetic diversity. The past decade has observed an explosion of interest in examining the existence of microbiota in the human body and understanding its role in various diseases including inflammatory bowel disease, neurologic diseases, cardiovascular disorders, and cancer. Many studies have demonstrated differential community composition between normal tissue and cancerous tissue, paving the way for investigations focused on deciphering the cause-and-effect relationships between specific microbes and initiation and progression of various cancers. Also, evolving are the strategies to alter tumor-associated dysbiosis and move it toward eubiosis with holistic approaches to change the entire neighborhood or to neutralize pathogenic strains. In this review, we discuss important pathogenic bacteria and the underlying mechanisms by which they affect cancer progression. We summarize key microbiota alterations observed in multiple tumor niches, their association with clinical stages, and their potential use in cancer diagnosis and management. Finally, we discuss microbiota-based therapeutic approaches.

Rck of Salmonella Typhimurium Delays the Host Cell Cycle to Facilitate Bacterial Invasion

Salmonella Typhimurium expresses on its outer membrane the protein Rck which interacts with the epidermal growth factor receptor (EGFR) of the plasma membrane of the targeted host cells. This interaction activates signaling pathways, leading to the internalization of Salmonella. Since EGFR plays a key role in cell proliferation, we sought to determine the influence of Rck mediated infection on the host cell cycle. By analyzing the DNA content of uninfected and infected cells using flow cytometry, we showed that the Rck-mediated infection induced a delay in the S-phase (DNA replication phase) of the host cell cycle, independently of bacterial internalization. We also established that this Rck-dependent delay in cell cycle progression was accompanied by an increased level of host DNA double strand breaks and activation of the DNA damage response. Finally, we demonstrated that the S-phase environment facilitated Rck-mediated bacterial internalization. Consequently, our results suggest that Rck can be considered as a cyclomodulin with a genotoxic activity.

Co- and polymicrobial infections in the gut mucosa: The host-microbiota-pathogen perspective

Infections in humans occur in the context of complex niches where the pathogen interacts with both the host microenvironment and immune response, and the symbiotic microbial community. The polymicrobial nature of many human infections adds a further layer of complexity. The effect of co‐ or polymicrobial infections can result in enhanced severity due to pathogens cooperative interaction or reduced morbidity because one of the pathogens affects the fitness of the other(s). In this review, the concept of co‐infections and polymicrobial interactions in the context of the intestinal mucosa is discussed, focusing on the interplay between the host, the microbiota and the pathogenic organisms. Specifically, we will examine examples of pathogen‐cooperative versus ‐antagonistic behaviour during co‐ and polymicrobial infections. We discuss: the infection‐induced modulation of the host microenvironment and immune responses; the direct modulation of the microorganism's fitness; the potentiation of inflammatory/carcinogenic conditions by polymicrobial biofilms; and the promotion of co‐infections by microbial‐induced DNA damage. Open questions in this very exciting field are also highlighted.

Periodontal Disease and Senescent Cells: New Players for an Old Oral Health Problem?

The recent identification of senescent cells in periodontal tissues has the potential to provide new insights into the underlying mechanisms of periodontal disease etiology. DNA damage-driven senescence is perhaps one of the most underappreciated delayed consequences of persistent Gram-negative bacterial infection and inflammation. Although the host immune response rapidly protects against bacterial invasion, oxidative stress generated during inflammation can indirectly deteriorate periodontal tissues through the damage to vital cell macromolecules, including DNA. What happens to those healthy cells that reside in this harmful environment? Emerging evidence indicates that cells that survive irreparable genomic damage undergo cellular senescence, a crucial intermediate mechanism connecting DNA damage and the immune response. In this review, we hypothesize that sustained Gram-negative bacterial challenge, chronic inflammation itself, and the constant renewal of damaged tissues create a permissive environment for the abnormal accumulation of senescent cells. Based on emerging data we propose a model in which the dysfunctional presence of senescent cells may aggravate the initial immune reaction against pathogens. Further understanding of the role of senescent cells in periodontal disease pathogenesis may have clinical implications by providing more sophisticated therapeutic strategies to combat tissue destruction.

Gut Microbiota and Colon Cancer: A Role for Bacterial Protein Toxins?

Accumulating evidence indicates that the human intestinal microbiota can contribute to the etiology of colorectal cancer. Triggering factors, including inflammation and bacterial infections, may favor the shift of the gut microbiota from a mutualistic to a pro-carcinogenic configuration. In this context, certain bacterial pathogens can exert a pro-tumoral activity by producing enzymatically-active protein toxins that either directly induce host cell DNA damage or interfere with essential host cell signaling pathways involved in cell proliferation, apoptosis, and inflammation. This review is focused on those toxins that, by mimicking carcinogens and cancer promoters, could represent a paradigm for bacterially induced carcinogenesis.

Senescence and Host-Pathogen Interactions

Damage to our genomes triggers cellular senescence characterised by stable cell cycle arrest and a pro-inflammatory secretome that prevents the unrestricted growth of cells with pathological potential. In this way, senescence can be considered a powerful innate defence against cancer and viral infection. However, damage accumulated during ageing increases the number of senescent cells and this contributes to the chronic inflammation and deregulation of the immune function, which increases susceptibility to infectious disease in ageing organisms. Bacterial and viral pathogens are masters of exploiting weak points to establish infection and cause devastating diseases. This review considers the emerging importance of senescence in the host-pathogen interaction: we discuss the pathogen exploitation of ageing cells and senescence as a novel hijack target of bacterial pathogens that deploys senescence-inducing toxins to promote infection. The persistent induction of senescence by pathogens, mediated directly through virulence determinants or indirectly through inflammation and chronic infection, also contributes to age-related pathologies such as cancer. This review highlights the dichotomous role of senescence in infection: an innate defence that is exploited by pathogens to cause disease.