TNF-α mediates macrophage-induced bystander effects through Netrin-1

Inactivation of glutathione S-transferase alpha 4 blocks Enterococcus faecalis-induced bystander effect by promoting macrophage ferroptosis

Enterococcus faecalis-infected macrophages produce 4-hydroxynonenal (4-HNE) that mediates microbiota-induced bystander effect (MIBE) leading to colorectal cancer (CRC). Glutathione S-transferase alpha 4 (Gsta4), a specific detoxifying enzyme for 4-HNE, is overexpressed in human CRC and E. faecalis-induced murine CRC. However, the roles of Gsta4 in E. faecalis-induced colitis and CRC remain unclear. Herein, we demonstrate that Gsta4 is essential for MIBE by protecting macrophages from E. faecalis-induced ferroptosis. E. faecalis OG1RFSS was used to induce colitis in Gsta4-/- and Il10-/-/Gsta4-/- mice by orogastric gavage. Ferroptosis was assessed in Gsta4-deficient murine macrophages. We found that, unlike Il10-/- mice, Gsta4-/- and Il10-/-/Gsta4-/- mice colonized with E. faecalis failed to develop colitis or CRC. Immunofluorescent staining showed a reduction of macrophages in the lamina propria of E. faecalis-colonized Il10-/-/Gsta4-/- mice, as well as decreased Gpx4 expression, indicating the occurrence of ferroptosis. Ferroptosis was further confirmed in Gsta4-deficient murine macrophages infected with E. faecalis. Moreover, Gsta4 inactivation induced the upregulation of Hmox1 and phosphorylated c-Jun while blocked Nos2 expression, leading to the accumulation of intracellular ferrous iron, lipid peroxidation and, eventually, ferroptosis. Finally, Mapk8, as a ferroptosis driver, was remarkably elevated in E. faecalis-infected Gsta4-deficient macrophages. These results suggest that Gsta4 inactivation blocks MIBE by eliminating macrophages, thereby attenuates E. faecalis-induced colitis and CRC.

Gut bacteria, host immunity, and colorectal cancer: From pathogenesis to therapy

The emergence of 16S rRNA and metagenomic sequencing has gradually revealed the close relationship between dysbiosis and colorectal cancer (CRC). Recent studies have confirmed that intestinal dysbiosis plays various roles in the occurrence, development, and therapeutic response of CRC. Perturbation of host immunity is one of the key mechanisms involved. The intestinal microbiota, or specific bacteria and their metabolites, can modulate the progression of CRC through pathogen recognition receptor signaling or via the recruitment, polarization, and activation of both innate and adaptive immune cells to reshape the protumor/antitumor microenvironment. Therefore, the administration of gut bacteria to enhance immune homeostasis represents a new strategy for the treatment of CRC. In this review, we cover recent studies that illuminate the role of gut bacteria in the progression and treatment of CRC through orchestrating the immune response, which potentially offers insights for subsequent transformative research.

Role of Gut Microbiota in Predisposition to Colon Cancer: A Narrative Review

Globally, colorectal cancer (CRC) is a leading cause of cancer-related mortality. Dietary habits, inflammation, hereditary characteristics, and gut microbiota are some of its causes. The gut microbiota, a diverse population of bacteria living in the digestive system, has an impact on a variety of parameters, including inflammation, DNA damage, and immune response. The gut microbiome has a significant role in colon cancer susceptibility. Many studies have highlighted dysbiosis, an imbalance in the gut microbiota's makeup, as a major factor in colon cancer susceptibility. Dysbiosis has the potential to produce toxic metabolites and pro-inflammatory substances, which can hasten the growth of tumours. The ability of the gut microbiota to affect the host's immune system can also influence whether cancer develops or not. By better comprehending these complex interactions between colon cancer predisposition and gut flora, new preventive and therapeutic techniques might be developed. Targeting the gut microbiome with dietary modifications, probiotics, or faecal microbiota transplantation may offer cutting-edge approaches to reducing the risk of colon cancer and improving patient outcomes. The complex connection between the makeup of the gut microbiota and the emergence of colorectal cancer is explored in this narrative review.

Genetics and Genomics of Chronic Pancreatitis with a Focus on Disease Biology and Molecular Pathogenesis

Chronic pancreatitis is a long-term fibroinflammatory condition of the pancreas with varying incidences across countries. The recent increase in its occurrence implies the involvement of genetic, hereditary, and unconventional risk factors. However, there is a lack of updated literature on recent advances in genetic polymorphisms of chronic pancreatitis. Therefore, this review aims to present recent findings on the genetic implications of chronic pancreatitis based on individual gene mechanisms and to discuss epigenetics and epistasis involved in the disease. Four mechanisms have been implicated in the pathogenesis of chronic pancreatitis, including premature activation of proteases, endoplasmic reticulum stress, ductal pathway dysfunction, and inflammatory pathway dysfunction. These mechanisms involve genes such as PRSS1, PRSS2, SPINK, CEL, PNLIP, PNLIPRP2, CFTR, CaSR, CLDN2, Alpha 1 antitrypsin, and GGT1 . Studying genetic polymorphisms on the basis of altered genes and their products may aid clinicians in identifying predispositions in patients with and without common risk factors. Further research may also identify associations between genetic predispositions and disease staging or prognosis, leading to personalized treatment protocols and precision medicine.

Colonic expression of glutathione S-transferase alpha 4 and 4-hydroxynonenal adducts is correlated with the pathology of murine colitis-associated cancer

Chronic inflammation-induced oxidative stress is an important driving force for developing colitis-associated cancer (CAC). 4-hydroxynonenal (4-HNE) is a highly reactive aldehyde derived from lipid peroxidation of ω-6 polyunsaturated fatty acids that contributes to colorectal carcinogenesis. Glutathione S-transferase alpha 4 (Gsta4) specifically conjugates glutathione to 4-HNE and thereby detoxifies 4-HNE. The correlation of these oxidative biomarkers with the pathological changes in CAC is, however, unclear. In this study, we investigated the expression of Gsta4 and 4-HNE adducts in azoxymethane/dextran sulfate sodium (AOM/DSS)-induced murine CAC, and analyzed the correlations of 4-HNE and Gsta4 with inflammatory cytokines and the pathological scores in the colon biopsies. Real-time quantitative PCR showed that expression of IL6, TNFα, and Gsta4 sequentially increased in colon tissues for mice treated with DSS for 1, 2, and 3 cycles, respectively. Moreover, immunohistochemical staining showed remarkably increased expression of 4-HNE adducts, Gsta4, TNFα, and IL6 in the colon biopsies after 3 cycles of DSS treatment. Correlation analysis demonstrated that 4-HNE adducts in the colon biopsies were positively correlated with Gsta4 expression. Additionally, the expression of Gsta4 and 4-HNE adducts were strongly correlated with the pathological changes of colon, as well as the expression of TNFα and IL6 in colon tissues. These results provide evidence for the association of oxidative biomarkers Gsta4 and 4-HNE with the pathological changes of CAC and may help developing novel histopathological biomarkers and prevention targets for CAC.

Research Progress of Intestinal Microecology in the Pathogenesis of Colorectal Adenoma and Carcinogenesis

Colorectal adenoma is a precancerous lesion that may progress to colorectal cancer. Patients with colorectal adenoma had a 4-fold higher risk of developing colorectal malignancy than the rest of the population, with approximately 80% of colorectal cancer originating from colorectal adenoma. Therefore, preventing the occurrence and progression of colorectal adenoma is crucial in reducing the risk for colorectal cancer. The human intestinal microecology is a complex system consisting of numerous microbial communities with a sophisticated structure. Interactions among intestinal microorganisms play crucial roles in maintaining normal intestinal structure, digestion, absorption, metabolism, and other functions. The colorectal system is the largest microbial bank or fermentation system in the human body. Studies suggest that intestinal microecological imbalance, one of the most important environmental factors, may play an essential role in the occurrence and development of colorectal adenoma and colorectal cancer. Based on the complexity of studying the gut microbiota ecosystem, its specific role in the occurrence and development of colorectal adenoma is yet to be elucidated. In addition, further studies are expected to provide new insights regarding the prevention and treatment of colorectal adenoma. This article reviews the relationship and mechanism of the diversity of the gut microbiota, the relevant inflammatory response, immune regulation, and metabolic changes in the presence of colorectal adenomas.

Cellular Carcinogenesis: Role of Polarized Macrophages in Cancer Initiation

Simple Summary

Inflammation is a hallmark of many cancers. Macrophages are key participants in innate immunity and important drivers of inflammation. When chronically polarized beyond normal homeostatic responses to infection, injury, or aging, macrophages can express several pro-carcinogenic phenotypes. In this review, evidence supporting polarized macrophages as endogenous sources of carcinogenesis is discussed. In addition, the depletion or modulation of macrophages by small molecule inhibitors and probiotics are reviewed as emerging strategies in cancer prevention.

Abstract

Inflammation is an essential hallmark of cancer. Macrophages are key innate immune effector cells in chronic inflammation, parainflammation, and inflammaging. Parainflammation is a form of subclinical inflammation associated with a persistent DNA damage response. Inflammaging represents low-grade inflammation due to the dysregulation of innate and adaptive immune responses that occur with aging. Whether induced by infection, injury, or aging, immune dysregulation and chronic macrophage polarization contributes to cancer initiation through the production of proinflammatory chemokines/cytokines and genotoxins and by modulating immune surveillance. This review presents pre-clinical and clinical evidence for polarized macrophages as endogenous cellular carcinogens in the context of chronic inflammation, parainflammation, and inflammaging. Emerging strategies for cancer prevention, including small molecule inhibitors and probiotic approaches, that target macrophage function and phenotype are also discussed.

Enterococcus spp.: Is It a Bad Choice for a Good Use-A Conundrum to Solve?

Since antiquity, the ubiquitous lactic acid bacteria (LAB) Enterococci, which are just as predominant in both human and animal intestinal commensal flora, have been used (and still are) as probiotics in food and feed production. Their qualities encounter several hurdles, particularly in terms of the array of virulence determinants, reflecting a notorious reputation that nearly prevents their use as probiotics. Additionally, representatives of the Enterococcus spp. genus showed intrinsic resistance to several antimicrobial agents, and flexibility to acquire resistance determinants encoded on a broad array of conjugative plasmids, transposons, and bacteriophages. The presence of such pathogenic aspects among some species represents a critical barrier compromising their use as probiotics in food. Thus, the genus neither has Generally Recognized as Safe (GRAS) status nor has it been included in the Qualified Presumption of Safety (QPS) list implying drastic legislation towards these microorganisms. To date, the knowledge of the virulence factors and the genetic structure of foodborne enterococcal strains is rather limited. Although enterococcal infections originating from food have never been reported, the consumption of food carrying virulence enterococci seems to be a risky path of transfer, and hence, it renders them poor choices as probiotics. Auspiciously, enterococcal virulence factors seem to be strain specific suggesting that clinical isolates carry much more determinants that food isolates. The latter remain widely susceptible to clinically relevant antibiotics and subsequently, have a lower potential for pathogenicity. In terms of the ideal enterococcal candidate, selected strains deemed for use in foods should not possess any virulence genes and should be susceptible to clinically relevant antibiotics. Overall, implementation of an appropriate risk/benefit analysis, in addition to the case-by-case assessment, the establishment of a strain's innocuity, and consideration for relevant guidelines, legislation, and regulatory aspects surrounding functional food development seem to be the crucial elements for industries, health-staff and consumers to accept enterococci, like other LAB, as important candidates for useful and beneficial applications in food industry and food biotechnology. The present review aims at shedding light on the world of hurdles and limitations that hampers the Enterococcus spp. genus and its representatives from being used or proposed for use as probiotics. The future of enterococci use as probiotics and legislation in this field are also discussed.

Mechanisms of Macrophage Plasticity in the Tumor Environment: Manipulating Activation State to Improve Outcomes

Macrophages are a specialized class of innate immune cells with multifaceted roles in modulation of the inflammatory response, homeostasis, and wound healing. While developmentally derived or originating from circulating monocytes, naïve macrophages can adopt a spectrum of context-dependent activation states ranging from pro-inflammatory (classically activated, M1) to pro-wound healing (alternatively activated, M2). Tumors are known to exploit macrophage polarization states to foster a tumor-permissive milieu, particularly by skewing macrophages toward a pro-tumor (M2) phenotype. These pro-tumoral macrophages can support cancer progression by several mechanisms including immune suppression, growth factor production, promotion of angiogenesis and tissue remodeling. By preventing the adoption of this pro-tumor phenotype or reprogramming these macrophages to a more pro-inflammatory state, it may be possible to inhibit tumor growth. Here, we describe types of tumor-derived signaling that facilitate macrophage reprogramming, including paracrine signaling and activation of innate immune checkpoints. We also describe intervention strategies targeting macrophage plasticity to limit disease progression and address their implications in cancer chemo- and immunotherapy.

It takes a village: microbiota, parainflammation, paligenosis and bystander effects in colorectal cancer initiation

Sporadic colorectal cancer (CRC) is a leading cause of worldwide cancer mortality. It arises from a complex milieu of host and environmental factors, including genetic and epigenetic changes in colon epithelial cells that undergo mutation, selection, clonal expansion, and transformation. The gut microbiota has recently gained increasing recognition as an additional important factor contributing to CRC. Several gut bacteria are known to initiate CRC in animal models and have been associated with human CRC. In this Review, we discuss the factors that contribute to CRC and the role of the gut microbiota, focusing on a recently described mechanism for cancer initiation, the so-called microbiota-induced bystander effect (MIBE). In this cancer mechanism, microbiota-driven parainflammation is believed to act as a source of endogenous mutation, epigenetic change and induced pluripotency, leading to the cancerous transformation of colon epithelial cells. This theory links the gut microbiota to key risk factors and common histologic features of sporadic CRC. MIBE is analogous to the well-characterized radiation-induced bystander effect. Both phenomena drive DNA damage, chromosomal instability, stress response signaling, altered gene expression, epigenetic modification and cellular proliferation in bystander cells. Myeloid-derived cells are important effectors in both phenomena. A better understanding of the interactions between the gut microbiota and mucosal immune effector cells that generate bystander effects can potentially identify triggers for parainflammation, and gain new insights into CRC prevention.

Colon Carcinogenesis: The Interplay Between Diet and Gut Microbiota

Colorectal cancer (CRC) incidence increases yearly, and is three to four times higher in developed countries compared to developing countries. The well-known risk factors have been attributed to low physical activity, overweight, obesity, dietary consumption including excessive consumption of red processed meats, alcohol, and low dietary fiber content. There is growing evidence of the interplay between diet and gut microbiota in CRC carcinogenesis. Although there appears to be a direct causal role for gut microbes in the development of CRC in some animal models, the link between diet, gut microbes, and colonic carcinogenesis has been established largely as an association rather than as a cause-and-effect relationship. This is especially true for human studies. As essential dietary factors influence CRC risk, the role of proteins, carbohydrates, fat, and their end products are considered as part of the interplay between diet and gut microbiota. The underlying molecular mechanisms of colon carcinogenesis mediated by gut microbiota are also discussed. Human biological responses such as inflammation, oxidative stress, deoxyribonucleic acid (DNA) damage can all influence dysbiosis and consequently CRC carcinogenesis. Dysbiosis could add to CRC risk by shifting the effect of dietary components toward promoting a colonic neoplasm together with interacting with gut microbiota. It follows that dietary intervention and gut microbiota modulation may play a vital role in reducing CRC risk.

Streptococcus mutans bystander-induced bioeffects following sonodynamic antimicrobial chemotherapy through sonocatalytic performance of Curcumin-Poly (Lactic-co-Glycolic Acid) on off-target cells

To assessed the Streptococcus mutans bystander-induced bioeffects following sonodynamic antimicrobial chemotherapy (SACT) by Curcumin-Poly (Lactic-co-Glycolic Acid) nanoparticles (Cur-PLGA-NPs). Cur-PLGA-NPs were synthesized and characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Attenuated Total Reflection Fourier Transform IR (ATR-FTIR) spectroscopy, as well as, determination of in vitro drug release. Following the successful synthesis and characterization of Cur-PLGA-NPs, the cell survival, intracellular ROS production, apoptotic effects, DNA fragmentation, and gene expression levels of pro-inflammatory cytokines were investigated on human gingival fibroblast (HGF) cells as off-target cells through S. mutans bystander-induced bioeffects following SACT (BCS^S). No significant cytotoxic and damage caused by the release of ROS from BCS^S were observed in HGF cells (P > 0.05). There was no DNA fragmentation and anti-proliferation effects on HGF cells. The expression levels of bFGF, TNF-α, and IL-8 genes were increased after exposure to BCS^S to 15.4-, 13.5-, and 8.7-fold, respectively (P < 0.05), while TGF-ß and IL-10 were downregulated to -4.1- and -6.8-fold, respectively (P < 0.05). It could be concluded that there were no bystander bioeffects of targeted sonocatalytic stress on off-target cells.

Cordyceps militaris induces apoptosis in ovarian cancer cells through TNF-α/TNFR1-mediated inhibition of NF-κB phosphorylation

BACKGROUND

Cordyceps militaris (L.) Fr. (C. militaris) exhibits pharmacological activities, including antitumor properties, through the regulation of the nuclear factor kappa B (NF-κB) signaling. Tumor Necrosis Factor (TNF) and TNF-α modulates cell survival and apoptosis through NF- κB signaling. However, the mechanism underlying its mode of action on the NF-κB pathway is unclear.

METHODS

Here, we analyzed the effect of C. militaris extract (CME) on the proliferation of ovarian cancer cells by confirming viability, morphological changes, migration assay. Additionally, CME induced apoptosis was determined by apoptosis assay and apoptotic body formation under TEM. The mechanisms of CME were determined through microarray, immunoblotting and immunocytochemistry.

RESULTS

CME reduced the viability of cells in a dose-dependent manner and induced morphological changes. We confirmed the decrease in the migration activity of SKOV-3 cells after treatment with CME and the consequent induction of apoptosis. Immunoblotting results showed that the CME-mediated upregulation of tumor necrosis factor receptor 1 (TNFR1) expression induced apoptosis of SKOV-3 cells via the serial activation of caspases. Moreover, CME negatively modulated NF-κB activation via TNFR expression, suggestive of the activation of the extrinsic apoptotic pathway. The binding of TNF-α to TNFR results in the disassociation of IκB from NF-κB and the subsequent translocation of the active NF-κB to the nucleus. CME clearly suppressed NF-κB translocation induced by interleukin (IL-1β) from the cytosol into the nucleus. The decrease in the expression levels of B cell lymphoma (Bcl)-xL and Bcl-2 led to a marked increase in cell apoptosis.

CONCLUSION

These results suggest that C. militaris inhibited ovarian cancer cell proliferation, survival, and migration, possibly through the coordination between TNF-α/TNFR1 signaling and NF-κB activation. Taken together, our findings provide a new insight into a novel treatment strategy for ovarian cancer using C. militaris.

Risks associated with enterococci as probiotics

Probiotics are naturally occurring microorganisms that confer health benefits by altering host commensal microbiota, modulating immunity, enhancing intestinal barrier function, or altering pain perception. Enterococci are human and animal intestinal commensals that are used as probiotics and in food production. These microorganisms, however, express many virulence traits including cytolysin, proteases, aggregation substance, capsular polysaccharide, enterococcal surface protein, biofilm formation, extracellular superoxide, intestinal translocation, and resistance to innate immunity that can lead to serious hospital-acquired infections. In addition, enterococci are facile in acquiring antibiotic resistance genes to many clinically important antibiotics encoded on a wide variety of conjugative plasmids, transposons, and bacteriophages. The pathogenicity and disease burden caused by enterococci render them poor choices as probiotics. No large, randomized, placebo-controlled clinical trials have demonstrated the safety and efficacy of any enterococcal probiotic. As a result, no enterococcal probiotic has been approved by the United States Food and Drug Administration for the treatment, cure, or amelioration of human disease. In 2007, the European Food Safety Authority concluded that enterococci do not meet the standard for "Qualified Presumption of Safety". Enterococcal strains used or proposed for use as probiotics should be carefully screened for efficacy and safety.

Microbial osteoporosis: The interplay between the gut microbiota and bones via host metabolism and immunity

The complex relationship between intestinal microbiota and host is a novel field in recent years. A large number of studies are being conducted on the relationship between intestinal microbiota and bone metabolism. Bone metabolism consisted of bone absorption and formation exists in the whole process of human growth and development. The nutrient components, inflammatory factors, and hormone environment play important roles in bone metabolism. Recently, intestinal microbiota has been found to influence bone metabolism via influencing the host metabolism, immune function, and hormone secretion. Here, we searched relevant literature on Pubmed and reviewed the effect of intestinal microbiota on bone metabolism through the three aspects, which may provide new ideas and targets for the clinical treatment of osteoporosis.

Astragalus Polysaccharide Eases G1 Phase-Correlative Bystander Effects through Mediation of TGF-βR/MAPK/ROS Signal Pathway After Carbon Ion Irradiation in BMSCs

Although Astragalus polysaccharide (APS) has been shown to have various pharmacological effects, there have been no studies concerning the inhibitory effects of APS on the radiation-induced bystander effects (RIBE). The aim of this study was to investigate whether APS could suppress RIBE damage by inhibiting cell growth, micronucleus (MN) formation and 53BP1 foci number increased in bone marrow mesenchymal stem cells (BMSCs), named bystander cells, as well as to explore its mechanism. In this study, APS decreased proliferation and colony rate of bystander cells by inducing cell cycle arrest at G1 phase via extrinsic and intrinsic DNA damage. Regarding mechanism, APS inhibited mitogen-activated protein kinase (MAPK) signal pathway by down-regulating the expression of the key proteins, phosphorylated JNK (p-JNK), phosphorylated ERK (p-ERK) but not phosphorylated P38 (p-P38), and down-regulating their downstream function protein and molecule, cyclooxygenase-2 (COX-2) and reactive oxygen species (ROS). Moreover, in bystander cells, APS inhibits expression of transforming growth factor [Formula: see text] receptor II (TGF-[Formula: see text]R II), a cell membrane receptor, resulting in lower ROS production and secretion via TGF-[Formula: see text]R-JNK/ERK-COX-2/ROS not P38 signaling. They gave a hint that the decreased RIBE damage induced by APS treatment involved TGF-[Formula: see text]R-JNK/ERK-COX-2/ROS down-regulation.

The Role of the Nuclear Factor κB Pathway in the Cellular Response to Low and High Linear Energy Transfer Radiation

Astronauts are exposed to considerable doses of space radiation during long-term space missions. As complete shielding of the highly energetic particles is impracticable, the cellular response to space-relevant radiation qualities has to be understood in order to develop countermeasures and to reduce radiation risk uncertainties. The transcription factor Nuclear Factor κB (NF-κB) plays a fundamental role in the immune response and in the pathogenesis of many diseases. We have previously shown that heavy ions with a linear energy transfer (LET) of 100–300 keV/µm have a nine times higher potential to activate NF-κB compared to low-LET X-rays. Here, chemical inhibitor studies using human embryonic kidney cells (HEK) showed that the DNA damage sensor Ataxia telangiectasia mutated (ATM) and the proteasome were essential for NF-κB activation in response to X-rays and heavy ions. NF-κB’s role in cellular radiation response was determined by stable knock-down of the NF-κB subunit RelA. Transfection of a RelA short-hairpin RNA plasmid resulted in higher sensitivity towards X-rays, but not towards heavy ions. Reverse Transcriptase real-time quantitative PCR (RT-qPCR) showed that after exposure to X-rays and heavy ions, NF-κB predominantly upregulates genes involved in intercellular communication processes. This process is strictly NF-κB dependent as the response is completely absent in RelA knock-down cells. NF-κB’s role in the cellular radiation response depends on the radiation quality.

Commensal-infected macrophages induce dedifferentiation and reprogramming of epithelial cells during colorectal carcinogenesis

The colonic microbiome contributes to the initiation of colorectal cancer through poorly characterized mechanisms. We have shown that commensal-polarized macrophages induce gene mutation, chromosomal instability, and endogenous transformation through microbiome-induced bystander effects (MIBE). In this study we show that MIBE activates Wnt/β-catenin signaling and pluripotent transcription factors associated with dedifferentiation, reprogramming, and the development of colorectal cancer stem cells (CSCs). Exposure of murine primary colon epithelial cells (YAMC) to Enterococcus faecalis-infected macrophages increased Wnt3α expression while suppressing Wnt inhibitor factor 1 (Wif1). Wnt/β-catenin activation was confirmed by increased active β-catenin and Tcf4. in vivo, active β-catenin was evident in colon biopsies from E. faecalis-colonized Il10 knockout mice compared to sham-colonized mice. This effect was mediated, in part, by 4-hydroxy-2-nonenal and tumor necrosis factor α. MIBE also activated pluripotent transcription factors c-Myc, Klf4, Oct4, and Sox2 in YAMC cells and colons from E. faecalis-colonized Il10 knockout mice. These transcription factors are associated with cellular reprogramming, dedifferentiation, and induction of colorectal CSC progenitors. In support of this was an increase in the expression of Dclk1 and CD44, two colorectal CSC markers, in YAMC cells that were exposed to MIBE. Finally, compared to normal colon biopsies and hyperplastic polyps, DCLK1 expression increased in human tubular adenomas and invasive colorectal cancers. Blocking β-catenin/TCF4 signaling using FH535 and CTNNB1-specific small interfering RNA decreased DCLK1 expression in HCT116 human colon cancer cells. These findings provide mechanism for microbiome-induced colorectal cancer and identify new potential targets for colorectal cancer prevention.

Microbiome-driven carcinogenesis in colorectal cancer: Models and mechanisms

Colorectal cancer (CRC) is a leading cause of cancer death and archetype for cancer as a genetic disease. However, the mechanisms for genetic change and their interactions with environmental risk factors have been difficult to unravel. New hypotheses, models, and methods are being used to investigate a complex web of risk factors that includes the intestinal microbiome. Recent research has clarified how the microbiome can generate genomic change in CRC. Several phenotypes among a small group of selected commensals have helped us better understand how mutations and chromosomal instability (CIN) are induced in CRC (e.g., toxin production, metabolite formation, radical generation, and immune modulation leading to a bystander effect). This review discusses recent hypotheses, models, and mechanisms by which the intestinal microbiome contributes to the initiation and progression of sporadic and colitis-associated forms of CRC. Overall, it appears the microbiome can initiate and/or promote CRC at all stages of tumorigenesis by acting as an inducer of DNA damage and CIN, regulating cell growth and death, generating epigenetic changes, and modulating host immune responses. Understanding how the microbiome interacts with other risk factors to define colorectal carcinogenesis will ultimately lead to more accurate risk prediction. A deeper understanding of CRC etiology will also help identify new targets for prevention and treatment and help accelerate the decline in mortality for this common cancer.

Identification of the long, edited dsRNAome of LPS-stimulated immune cells

Endogenous double-stranded RNA (dsRNA) must be intricately regulated in mammals to prevent aberrant activation of host inflammatory pathways by cytosolic dsRNA binding proteins. Here, we define the long, endogenous dsRNA repertoire in mammalian macrophages and monocytes during the inflammatory response to bacterial lipopolysaccharide. Hyperediting by adenosine deaminases that act on RNA (ADAR) enzymes was quantified over time using RNA-seq data from activated mouse macrophages to identify 342 Editing Enriched Regions (EERs), indicative of highly structured dsRNA. Analysis of publicly available data sets for samples of human peripheral blood monocytes resulted in discovery of 3438 EERs in the human transcriptome. Human EERs had predicted secondary structures that were significantly more stable than those of mouse EERs and were located primarily in introns, whereas nearly all mouse EERs were in 3' UTRs. Seventy-four mouse EER-associated genes contained an EER in the orthologous human gene, although nucleotide sequence and position were only rarely conserved. Among these conserved EER-associated genes were several TNF alpha-signaling genes, including Sppl2a and Tnfrsf1b, important for processing and recognition of TNF alpha, respectively. Using publicly available data and experimental validation, we found that a significant proportion of EERs accumulated in the nucleus, a strategy that may prevent aberrant activation of proinflammatory cascades in the cytoplasm. The observation of many ADAR-edited dsRNAs in mammalian immune cells, a subset of which are in orthologous genes of mouse and human, suggests a conserved role for these structured regions.

Gut microbiota imbalance and colorectal cancer

The gut microbiota acts as a real organ. The symbiotic interactions between resident micro-organisms and the digestive tract highly contribute to maintain the gut homeostasis. However, alterations to the microbiome caused by environmental changes (e.g., infection, diet and/or lifestyle) can disturb this symbiotic relationship and promote disease, such as inflammatory bowel diseases and cancer. Colorectal cancer is a complex association of tumoral cells, non-neoplastic cells and a large amount of micro-organisms, and the involvement of the microbiota in colorectal carcinogenesis is becoming increasingly clear. Indeed, many changes in the bacterial composition of the gut microbiota have been reported in colorectal cancer, suggesting a major role of dysbiosis in colorectal carcinogenesis. Some bacterial species have been identified and suspected to play a role in colorectal carcinogenesis, such as Streptococcus bovis, Helicobacter pylori, Bacteroides fragilis, Enterococcus faecalis, Clostridium septicum, Fusobacterium spp. and Escherichia coli. The potential pro-carcinogenic effects of these bacteria are now better understood. In this review, we discuss the possible links between the bacterial microbiota and colorectal carcinogenesis, focusing on dysbiosis and the potential pro-carcinogenic properties of bacteria, such as genotoxicity and other virulence factors, inflammation, host defenses modulation, bacterial-derived metabolism, oxidative stress and anti-oxidative defenses modulation. We lastly describe how bacterial microbiota modifications could represent novel prognosis markers and/or targets for innovative therapeutic strategies.

Colorectal cancer: role of commensal bacteria and bystander effects

For years the human microbiota has been implicated in the etiology of colorectal cancer (CRC). However, identifying the molecular mechanisms for how aneuploidy and chromosomal instability (CIN) arise in sporadic and colitis-associated CRC has been difficult. In this Addendum we review recent work from our laboratory that explore mechanisms by which intestinal commensals polarize colon macrophages to an M1 phenotype to generate a bystander effect (BSE) that leads to mutations, spindle malfunction, cell cycle arrest, tetraploidy, and aneuploidy in epithelial cells. BSE represents the application of a phenomenon initially described in the radiation biology field. The result of commensal-driven BSE on colon epithelial cells is aneuploidy, chromosomal instability (CIN), expression of stem cell and tumor stem cell markers and, ultimately, malignant transformation. Our findings provide a conceptual framework for integrating the microbiota with aging, cyclooxygenase (COX)-2, and inflammation as risk factors for CRC.

Potential strategies to ameliorate risk of radiotherapy-induced second malignant neoplasms

This review is aimed at the issue of radiation-induced second malignant neoplasms (SMN), which has become an important problem with the increasing success of modern cancer radiotherapy (RT). It is imperative to avoid compromising the therapeutic ratio while addressing the challenge of SMN. The dilemma is illustrated by the role of reactive oxygen species in both the mechanisms of tumor cell kill and of radiation-induced carcinogenesis. We explore the literature focusing on three potential routes of amelioration to address this challenge. An obvious approach to avoiding compromise of the tumor response is the use of radioprotectors or mitigators that are selective for normal tissues. We also explore the opportunities to avoid protection of the tumor by topical/regional radioprotection of normal tissues, although this strategy limits the scope of protection. Finally, we explore the role of the bystander/abscopal phenomenon in radiation carcinogenesis, in association with the inflammatory response. Targeted and non-targeted effects of radiation are both linked to SMN through induction of DNA damage, genome instability and mutagenesis, but differences in the mechanisms and kinetics between targeted and non-targeted effects may provide opportunities to lessen SMN. The agents that could be employed to pursue each of these strategies are briefly reviewed. In many cases, the same agent has potential utility for more than one strategy. Although the parallel problem of chemotherapy-induced SMN shares common features, this review focuses on RT associated SMN. Also, we avoid the burgeoning literature on the endeavor to suppress cancer incidence by use of antioxidants and vitamins either as dietary strategies or supplementation.

Netrin-1 as a potential target for metastatic cancer: focus on colorectal cancer

Despite advanced screening technology and cancer treatments available today, metastasis remains an ongoing major cause of cancer-related deaths worldwide. Typically, colorectal cancer is one of the cancers treatable by surgery in conjunction with chemotherapy when it is detected at an early stage. However, it still ranks as the second highest modality and mortality of cancer types in western countries, and this is mostly due to a recurrence of metastatic colorectal cancer post-resection of the primary malignancy. Colorectal cancer metastases predominantly occur in the liver and lung, and yet the molecular mechanisms that regulate these organ-specific colorectal cancer metastases are largely unknown. Therefore, the identification of any critical molecule, which triggers malignancy in colorectal cancer, would be an excellent target for treatment. Netrin-1 was initially discovered as a chemotropic neuronal guidance molecule, and has been marked as a regulator for many cancers including colorectal cancer. Here, we summarise key findings of the role of netrin-1 intrinsic to colorectal cancer cells, extrinsic to the tumour microenvironment and angiogenesis, and consequently, we evaluate netrin-1 as a potential target molecule for metastasis.

Commensal bacteria drive endogenous transformation and tumour stem cell marker expression through a bystander effect

OBJECTIVE

Commensal bacteria and innate immunity play a major role in the development of colorectal cancer (CRC). We propose that selected commensals polarise colon macrophages to produce endogenous mutagens that initiate chromosomal instability (CIN), lead to expression of progenitor and tumour stem cell markers, and drive CRC through a bystander effect.

DESIGN

Primary murine colon epithelial cells were repetitively exposed to Enterococcus faecalis-infected macrophages, or purified trans-4-hydroxy-2-nonenal (4-HNE)-an endogenous mutagen and spindle poison produced by macrophages. CIN, gene expression, growth as allografts in immunodeficient mice were examined for clones and expression of markers confirmed using interleukin (IL) 10 knockout mice colonised by E. faecalis.

RESULTS

Primary colon epithelial cells exposed to polarised macrophages or 4-hydroxy-2-nonenal developed CIN and were transformed after 10 weekly treatments. In immunodeficient mice, 8 of 25 transformed clones grew as poorly differentiated carcinomas with 3 tumours invading skin and/or muscle. All tumours stained for cytokeratins confirming their epithelial cell origin. Gene expression profiling of clones showed alterations in 3 to 7 cancer driver genes per clone. Clones also strongly expressed stem/progenitor cell markers Ly6A and Ly6E. Although not differentially expressed in clones, murine allografts positively stained for the tumour stem cell marker doublecortin-like kinase 1. Doublecortin-like kinase 1 and Ly6A/E were expressed by epithelial cells in colon biopsies for areas of inflamed and dysplastic tissue from E. faecalis-colonised IL-10 knockout mice.

CONCLUSIONS

These results validate a novel mechanism for CRC that involves endogenous CIN and cellular transformation arising through a microbiome-driven bystander effect.

Macrophage contact dependent and independent TLR4 mechanisms induce β-cell dysfunction and apoptosis in a mouse model of type 2 diabetes

Type 2 diabetes (T2D) is evolving into a global disease and patients have a systemic low-grade inflammation, yet the role of this inflammation is still not established. One plausible mechanism is enhanced expression and activity of the innate immune system. Therefore, we evaluated the expression and the function of the toll-like receptor 4 (TLR4) on pancreatic β-cells in primary mouse islets and on the murine β-cell line MIN6 in the presence or absence of macrophages. Diabetic islets have 40% fewer TLR4 positive β-cells, but twice the number of TLR4 positive macrophages as compared to healthy islets. Healthy and diabetic islets respond to a TLR4 challenge with enhanced production of cytokines (5–10-fold), while the TLR4 negative β-cell line MIN6 fails to produce cytokines. TLR4 stimulation induces β-cell dysfunction in mouse islets, measured as reduced glucose stimulated insulin secretion. Diabetic macrophages from 4-months old mice have acquired a transient enhanced capacity to produce cytokines when stimulated with LPS. Interestingly, this is lost in 6-months old diabetic mice. TLR4 activation alone does not induce apoptosis in islets or MIN-6 cells. In contrast, macrophages mediate TLR4-dependent cell-contact dependent (3-fold) as well as cell-contact independent (2-fold) apoptosis of both islets and MIN-6 cells. Importantly, diabetic macrophages have a significantly enhanced capacity to induce β-cell apoptosis compared to healthy macrophages. Taken together, the TLR4 responsiveness is elevated in the diabetic islets and mainly mediated by newly recruited macrophages. The TLR4 positive macrophages, in both a cell-contact dependent and independent manner, induce apoptosis of β-cells in a TLR4 dependent fashion and TLR4 activation directly induces β-cell dysfunction. Thus, targeting either the TLR4 pathway or the macrophages provides a novel attractive treatment regime for T2D.

Escherichia coli producing colibactin triggers premature and transmissible senescence in mammalian cells

Cellular senescence is an irreversible state of proliferation arrest evoked by a myriad of stresses including oncogene activation, telomere shortening/dysfunction and genotoxic insults. It has been associated with tumor activation, immune suppression and aging, owing to the secretion of proinflammatory mediators. The bacterial genotoxin colibactin, encoded by the pks genomic island is frequently harboured by Escherichia coli strains of the B2 phylogenetic group. Mammalian cells exposed to live pks+ bacteria exhibit DNA-double strand breaks (DSB) and undergo cell-cycle arrest and death. Here we show that cells that survive the acute bacterial infection with pks+ E. coli display hallmarks of cellular senescence: chronic DSB, prolonged cell-cycle arrest, enhanced senescence-associated β-galactosidase (SA-β-Gal) activity, expansion of promyelocytic leukemia nuclear foci and senescence-associated heterochromatin foci. This was accompanied by reactive oxygen species production and pro-inflammatory cytokines, chemokines and proteases secretion. These mediators were able to trigger DSB and enhanced SA-β-Gal activity in bystander recipient cells treated with conditioned medium from senescent cells. Furthermore, these senescent cells promoted the growth of human tumor cells. In conclusion, the present data demonstrated that the E. coli genotoxin colibactin induces cellular senescence and subsequently propel bystander genotoxic and oncogenic effects.

Colon Macrophages Polarized by Commensal Bacteria Cause Colitis and Cancer through the Bystander Effect

Intestinal commensal bacteria have recently been shown to trigger macrophages to produce diffusible clastogens (or chromosome-breaking factors) through a bystander effect (BSE) that mediates DNA damage and induces chromosomal instability in neighboring cells. Colon macrophages appear central to colon carcinogenesis and BSE through the expression of tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2). The former induces netrin-1, a regulator of intestinal epithelial cell apoptosis, and the latter generates trans-4-hydroxy-2-nonenal (4-HNE), an endogenous mutagen. To test whether colon macrophages are key effectors for BSE, we depleted these cells in interleukin-10 knockout mice colonized with Enterococcus faecalis using encapsulated liposomal clodronate (ELC), a bisphosphonate that causes macrophage apoptosis. We observed that E. faecalis polarizes colon macrophages to an M1 phenotype. In addition, depleting these cells suppressed COX-2 and TNF-α, blocked the formation of 4-HNE protein adducts, and inhibited up-regulation of netrin-1-all markers for BSE. Finally, treatment with ELC prevented colitis, β-catenin activation, and cancer formation. These results show that selected human commensals can polarize colon macrophages to the M1 phenotype and, when activated, serve as the key effector for bacterial-induced BSE. Our findings suggest that depleting M1-polarized macro-phages is a mechanism for the chemopreventive activity of bisphosphonates and that it represents a new strategy for preventing colon cancer induced by intestinal commensals.

Physically disconnected non-diffusible cell-to-cell communication between neuroblastoma SH-SY5Y and DRG primary sensory neurons

BACKGROUND

Cell-cell communication occurs via a variety of mechanisms, including long distances (hormonal), short distances (paracrine and synaptic) or direct coupling via gap junctions, antigen presentation, or ligand-receptor interactions. We evaluated the possibility of neuro-hormonal independent, non-diffusible, physically disconnected pathways for cell-cell communication using dorsal root ganglion (DRG) neurons.

METHODS

We assessed intracellular calcium ([Ca(2+)]) in primary culture DRG neurons that express ATP-sensitive P2X3, capsaicinsensitive TRPV1 receptors modulated by estradiol. Physically disconnected (dish-in-dish system; inner chamber enclosed) mouse DRG were cultured for 12 hours near: a) media alone (control 1), b) mouse DRG (control 2), c) human neuroblastoma SHSY-5Y cells (cancer intervention), or d) mouse DRG treated with KCl (apoptosis intervention).

RESULTS

Chemosensitive receptors [Ca(2+)](i) signaling did not differ between control 1 and 2. ATP (10 μM) and capsaicin (100nM) increased [Ca(2+)](i) transients to 425.86 + 49.5 nM, and 399.21 ± 44.5 nM, respectively. 17β-estradiol (100 nM) exposure reduced ATP (171.17 ± 48.9 nM) and capsaicin (175.01±34.8 nM) [Ca(2+)](i) transients. The presence of cancer cells reduced ATP- and capsaicin-induced [Ca(2+)](i) by >50% (p<0.05) and abolished the 17β-estradiol effect. By contrast, apoptotic DRG cells increased initial ATP-induced [Ca(2+)](i), flux four fold and abolished subsequent [Ca(2+)](i), responses to ATP stimulation (p<0.001). Capsaicin (100nM) induced [Ca(2+)](i) responses were totally abolished.

CONCLUSION

The local presence of apoptotic DRG or human neuroblastoma cells induced differing abnormal ATP and capsaicin-mediated [Ca(2+)](i) fluxes in normal DRG. These findings support physically disconnected, non-diffusible cell-to-cell signaling. Further studies are needed to delineate the mechanism(s) of and model(s) of communication.

Cyclooxygenase-2 generates the endogenous mutagen trans-4-hydroxy-2-nonenal in Enterococcus faecalis-infected macrophages

Infection of macrophages by the human intestinal commensal Enterococcus faecalis generates DNA damage and chromosomal instability in mammalian cells through bystander effects. These effects are characterized by clastogenesis and damage to mitotic spindles in target cells and are mediated, in part, by trans-4-hydroxy-2-nonenal (4-HNE). In this study, we investigated the role of COX and lipoxygenase (LOX) in producing this reactive aldehyde using E. faecalis-infected macrophages and interleukin (IL)-10-knockout mice colonized with this commensal. 4-HNE production by E. faecalis-infected macrophages was significantly reduced by COX and LOX inhibitors. The infection of macrophages led to decreased Cox1 and Alox5 expression whereas COX-2 and 4-HNE increased. Silencing Alox5 and Cox1 with gene-specific siRNAs had no effect on 4-HNE production. In contrast, silencing Cox2 significantly decreased 4-HNE production by E. faecalis-infected macrophages. Depleting intracellular glutathione increased 4-HNE production by these cells. Next, to confirm COX-2 as a source for 4-HNE, we assayed the products generated by recombinant human COX-2 and found 4-HNE in a concentration-dependent manner using arachidonic acid as a substrate. Finally, tissue macrophages in colon biopsies from IL-10-knockout mice colonized with E. faecalis were positive for COX-2 by immunohistochemical staining. This was associated with increased staining for 4-HNE protein adducts in surrounding stroma. These data show that E. faecalis, a human intestinal commensal, can trigger macrophages to produce 4-HNE through COX-2. Importantly, it reinforces the concept of COX-2 as a procarcinogenic enzyme capable of damaging DNA in target cells through bystander effects that contribute to colorectal carcinogenesis.