TLR9 is important for protection against intestinal damage and for intestinal repair

Engaging natural antibody responses for the treatment of inflammatory bowel disease via phosphorylcholine-presenting nanofibres

Inflammatory bowel disease lacks a long-lasting and broadly effective therapy. Here, by taking advantage of the anti-infection and anti-inflammatory properties of natural antibodies against the small-molecule epitope phosphorylcholine (PC), we show in multiple mouse models of colitis that immunization of the animals with self-assembling supramolecular peptide nanofibres bearing PC epitopes induced sustained levels of anti-PC antibodies that were both protective and therapeutic. The strength and type of immune responses elicited by the nanofibres could be controlled through the relative valency of PC epitopes and exogenous T-cell epitopes on the nanofibres and via the addition of the adjuvant CpG. The nanomaterial-assisted induction of the production of therapeutic antibodies may represent a durable therapy for inflammatory bowel disease.

Epithelial regulation of microbiota-immune cell dynamics

The mammalian gastrointestinal tract hosts a diverse community of trillions of microorganisms, collectively termed the microbiota, which play a fundamental role in regulating tissue physiology and immunity. Recent studies have sought to dissect the cellular and molecular mechanisms mediating communication between the microbiota and host immune system. Epithelial cells line the intestine and form an initial barrier separating the microbiota from underlying immune cells, and disruption of epithelial function has been associated with various conditions ranging from infection to inflammatory bowel diseases and cancer. From several studies, it is now clear that epithelial cells integrate signals from commensal microbes. Importantly, these non-hematopoietic cells also direct regulatory mechanisms that instruct the recruitment and function of microbiota-sensitive immune cells. In this review, we discuss the central role that has emerged for epithelial cells in orchestrating intestinal immunity and highlight epithelial pathways through which the microbiota can calibrate tissue-intrinsic immune responses.

Precision medicine in inflammatory bowel disease

Inflammatory bowel disease (IBD) is an incurable disease characterized by remission-relapse cycles throughout its course. Both Crohn's disease (CD) and ulcerative colitis (UC), the two main forms of IBD, exhibit tendency to develop complications and substantial heterogeneity in terms of frequency and severity of relapse, thus posing great challenges to the clinical management for IBD. Current treatment strategies are effective in different ways in induction and maintenance therapies for IBD. Recent advances in studies of genetics, pharmacogenetics, proteomics and microbiome provide a strong driving force for identifying molecular markers of prognosis and treatment response, which should help clinicians manage IBD patients more effectively, and then, improve clinical outcomes and reduce treatment costs of patients. In this review, we summarize and discuss precision medicine in IBD, focusing on predictive markers of disease course and treatment response, and monitoring indices during therapeutic drug monitoring.

Microbial sensing in the intestine

The gut microbiota plays a key role in host health and disease, particularly through their interactions with the immune system. Intestinal homeostasis is dependent on the symbiotic relationships between the host and the diverse gut microbiota, which is influenced by the highly co-evolved immune-microbiota interactions. The first step of the interaction between the host and the gut microbiota is the sensing of the gut microbes by the host immune system. In this review, we describe the cells of the host immune system and the proteins that sense the components and metabolites of the gut microbes. We further highlight the essential roles of pattern recognition receptors (PRRs), the G protein-coupled receptors (GPCRs), aryl hydrocarbon receptor (AHR) and the nuclear receptors expressed in the intestinal epithelial cells (IECs) and the intestine-resident immune cells. We also discuss the mechanisms by which the disruption of microbial sensing because of genetic or environmental factors causes human diseases such as the inflammatory bowel disease (IBD).

Cell-penetrating TLR inhibitor peptide alleviates ulcerative colitis by the functional modulation of macrophages

Toll-like receptors (TLRs) have a crucial role not only in triggering innate responses against microbes but in orchestrating an appropriate adaptive immunity. However, deregulated activation of TLR signaling leads to chronic inflammatory conditions such as inflammatory bowel disease (IBD). In this study, we evaluated the immunomodulatory potential of a TLR inhibitor in the form of a cell-penetrating peptide using an ulcerative colitis animal model. A peptide derived from the TIR domain of the TLR adaptor molecule TIRAP that was conjugated with a cell-penetrating sequence (cpTLR-i) suppressed the induction of pro-inflammatory cytokines such as TNF-α and IL-1β in macrophages. In DSS-induced colitis mice, cpTLR-i treatment ameliorated colitis symptoms, colonic tissue damage, and mucosal inflammation. Intriguingly, cpTLR-i attenuated the induction of TNF-α-expressing proinflammatory macrophages while promoting that of regulatory macrophages expressing arginase-1 and reduced type 17 helper T cell (Th17) responses in the inflamed colonic lamina propria. An in vitro study validated that cpTLR-i enhanced the differentiation of monocyte-driven macrophages into mature macrophages with a regulatory phenotype in a microbial TLR ligand-independent manner. Furthermore, the cocultivation of CD4 T cells with macrophages revealed that cpTLR-i suppressed the activation of Th17 cells through the functional modulation of macrophages. Taken together, our data show the immunomodulatory potential of the TLR inhibitor peptide and suggest cpTLR-i as a novel therapeutic candidate for the treatment of IBD.

Activation of TLRs Triggers GLP-1 Secretion in Mice

The gastrointestinal tract constitutes a large interface with the inner body and is a crucial barrier against gut microbiota and other pathogens. As soon as this barrier is damaged, pathogen-associated molecular patterns (PAMPs) are recognized by immune system receptors, including toll-like receptors (TLRs). Glucagon-like peptide 1 (GLP-1) is an incretin that was originally involved in glucose metabolism and recently shown to be rapidly and strongly induced by luminal lipopolysaccharides (LPS) through TLR4 activation. In order to investigate whether the activation of TLRs other than TLR4 also increases GLP-1 secretion, we used a polymicrobial infection model through cecal ligation puncture (CLP) in wild-type and TLR4-deficient mice. TLR pathways were assessed by intraperitoneal injection of specific TLR agonists in mice. Our results show that CLP induces GLP-1 secretion both in wild-type and TLR4-deficient mice. CLP and TLR agonists increase gut and systemic inflammation. Thus, the activation of different TLRs increases GLP-1 secretion. This study highlights for the first time that, in addition to an increased inflammatory status, CLP and TLR agonists also strongly induce total GLP-1 secretion. Microbial-induced GLP-1 secretion is therefore not only a TLR4/LPS-cascade.

Mucosal healing and inflammatory bowel disease: Therapeutic implications and new targets

Mucosal healing (MH) is vital in maintaining homeostasis within the gut and protecting against injury and infections. Multiple factors and signaling pathways contribute in a dynamic and coordinated manner to maintain intestinal homeostasis and mucosal regeneration/repair. However, when intestinal homeostasis becomes chronically disturbed and an inflammatory immune response is constitutively active due to impairment of the intestinal epithelial barrier autoimmune disease results, particularly inflammatory bowel disease (IBD). Many proteins and signaling pathways become dysregulated or impaired during these pathological conditions, with the mechanisms of regulation just beginning to be understood. Consequently, there remains a relative lack of broadly effective therapeutics that can restore MH due to the complexity of both the disease and healing processes, so tissue damage in the gastrointestinal tract of patients, even those in clinical remission, persists. With increased understanding of the molecular mechanisms of IBD and MH, tissue damage from autoimmune disease may in the future be ameliorated by developing therapeutics that enhance the body’s own healing response. In this review, we introduce the concept of mucosal healing and its relevance in IBD as well as discuss the mechanisms of IBD and potential strategies for altering these processes and inducing MH.

Intermittent Fasting Alleviates Risk Markers in a Murine Model of Ulcerative Colitis by Modulating the Gut Microbiome and Metabolome

Clinical trials have demonstrated the health benefits of intermittent fasting (IF). However, the potential mechanism of IF in alleviating dextran sulfate sodium (DSS)-induced colitis is not fully understood. The present study was mainly designed to explore the dynamic changes in the gut microbiota and metabolome after short-term (2 weeks) or long-term (20 weeks) IF and therefore clarify the potential mechanisms by which IF ameliorates DSS-induced colitis in a murine model. Thirty-two C57BL/6 male mice were equally divided into four groups and underwent IF intervention for 2 weeks (SIF group, n = 8), 20 weeks (LIF group, n = 8), or were allowed free access to food for 2 weeks (SAL group, n = 8) or 20 weeks (LAL group, n = 8). The thirty-two C57BL/6 male mice were accepted for the diet intervention of 2 weeks of IF or fed ad libitum. Colitis was induced by drinking 2% DSS for 7 days. Our findings showed that short-term IF prominently elevates the abundance of Bacteroides, Muibaculum and Akkermansia (p < 0.001, p < 0.001, p < 0.001, respectively), and decreased the abundance of Ruminiclostridium (p < 0.05). Long-term IF, however, decreased the abundance of Akkermansia and obviously increased the abundance of Lactobacillus (p < 0.05, p < 0.001, respectively). Metabolites mainly associated with nucleoside, carbohydrate, amino acid, bile acid, fatty acid, polyol, steroid and amine metabolism were identified in the faeces using untargeted GC/MS. In particular, inosine was extremely enriched after short-term IF and long-term IF (p < 0.01, p < 0.01, respectively); butyrate, 2-methyl butyric acid and valeric acid were significantly decreased after short-term IF (p < 0.001, p < 0.001, p < 0.01, respectively); and 2-methyl butyric acid was significantly increased after long-term IF (p < 0.001). The abundance of lithocholic acid (LCA), one of the secondary bile acids, increased significantly after short-term and long-term IF based on UPLC−MS/MS (p < 0.001, p < 0.5, respectively). Of note, IF markedly mitigated DSS-induced acute colitis symptoms and down-regulated pro-inflammatory cytokines IL-1α, IL-6, keratinocyte-derived chemokine (KC) and G-CSF levels in the serum (p < 0.01, p < 0.001, p < 0.05, p < 0.001, respectively). Furthermore, a correlation analysis indicated that the disease activity index (DAI) score and serum levels of IL-1α, IL-6, KC, and G-CSF were negatively correlated with the relative abundance of Akkermansia and the faecal metabolites LCA and inosine. This study confirmed that IF altered microbiota and reprogramed metabolism, which was a promising development in the attempt to prevent DSS-induced colitis. Moreover, our findings provide new insights regarding the correlations among the mucosal barrier dysfunction, metabolome, and microbiome.

A one month high fat diet disrupts the gut microbiome and integrity of the colon inducing adiposity and behavioral despair in male Sprague Dawley rats

High-fat diet (HFD) is associated with gut microbiome dysfunction and mental disorders. However, the time-dependence as to when this occurs is unclear. We hypothesized that a short-term HFD causes colonic tissue integrity changes resulting in behavioral changes. Rats were fed HFD or low-fat diet (LFD) for a month and gut microbiome, colon, and behavior were evaluated. Behavioral despair was found in the HFD group. Although obesity was absent, the HFD group showed increased percent weight gain, epididymal fat tissue, and leptin expression. Moreover, the HFD group had increased colonic damage, decreased expression of the tight junction proteins, and higher lipopolysaccharides (LPS) in serum. Metagenomic analysis revealed that the HFD group had more Bacteroides and less S24-7 which correlated with the decreased claudin-5. Finally, HFD group showed an increase of microglia percent area, increased astrocytic projections, and decreased phospho-mTOR. In conclusion, HFD consumption in a short period is still sufficient to disrupt gut integrity resulting in LPS infiltration, alterations in the brain, and behavioral despair even in the absence of obesity.

Intestinal serotonergic system is modulated by Toll-like receptor 9

Intestinal serotonergic system is a key modulator of intestinal homeostasis; however, its regulation is still unclear. Toll-like receptor 9 (TLR9), an innate immune receptor, detects different external agents in the intestine, preserving intestinal integrity. Since little is known about TLR9 role in the intestine, our aim was to address the potential regulation between TLR9 and intestinal serotonergic system. Caco-2/TC7 cell line and intestinal tract of Tlr9^−/− mice were used in this study. Serotonin uptake studies were performed, and molecular expression of different serotonergic components was analyzed by western blot and real-time PCR. Our results show that TLR9 activation inhibits serotonin transporter activity and expression, involving p38/MAPK and ERK/MAPK intracellular pathways, and reciprocally, serotonin increases TLR9 expression. Supporting this interaction, serotonin transporter, serotonin receptors and serotonin producer enzymes were found altered in intestinal tract of Tlr9^−/− mice. We conclude that TLR9 could contribute to intestinal homeostasis by modulation of intestinal serotonergic system.

Tea Polyphenols: A Natural Antioxidant Regulates Gut Flora to Protect the Intestinal Mucosa and Prevent Chronic Diseases

The intestinal tract of a healthy human body hosts many microorganisms that are closely linked to all aspects of people’s lives. The impact of intestinal flora on host health is no longer limited to the gut but can also affect every organ in the body through various pathways. Studies have found that intestinal flora can be altered by external factors, which provides new ideas for treating some diseases. Tea polyphenols (TP), a general term for polyphenols in tea, are widely used as a natural antioxidant in various bioactive foods. In recent years, with the progress of research, there have been many experiments that provide strong evidence for the ability of TP to regulate intestinal flora. However, there are very few studies on the use of TP to modify the composition of intestinal microorganisms to maintain health or treat related diseases, and this area has not received sufficient attention. In this review, we outline the mechanisms by which TP regulates intestinal flora and the essential role in maintaining suitable health. In addition, we highlighted the protective effects of TP on intestinal mucosa by regulating intestinal flora and the preventive and therapeutic effects on certain chronic diseases, which will help further explore measures to prevent related chronic diseases.

Crosstalk Between Intestinal Serotonergic System and Pattern Recognition Receptors on the Microbiota-Gut-Brain Axis

Disruption of the microbiota-gut-brain axis results in a wide range of pathologies that are affected, from the brain to the intestine. Gut hormones released by enteroendocrine cells to the gastrointestinal (GI) tract are important signaling molecules within this axis. In the search for the language that allows microbiota to communicate with the gut and the brain, serotonin seems to be the most important mediator. In recent years, serotonin has emerged as a key neurotransmitter in the gut-brain axis because it largely contributes to both GI and brain physiology. In addition, intestinal microbiota are crucial in serotonin signaling, which gives more relevance to the role of the serotonin as an important mediator in microbiota-host interactions. Despite the numerous investigations focused on the gut-brain axis and the pathologies associated, little is known regarding how serotonin can mediate in the microbiota-gut-brain axis. In this review, we will mainly discuss serotonergic system modulation by microbiota as a pathway of communication between intestinal microbes and the body on the microbiota-gut-brain axis, and we explore novel therapeutic approaches for GI diseases and mental disorders.

Epithelial sensing of microbiota-derived signals

The gastrointestinal tract harbors trillions of microbial species, collectively termed the microbiota, which establish a symbiotic relationship with the host. Decades of research have emphasized the necessity of microbial signals in the development, maturation, and function of host physiology. However, changes in the composition or containment of the microbiota have been linked to the development of several chronic inflammatory diseases, including inflammatory bowel diseases. Intestinal epithelial cells (IECs) are in constant contact with the microbiota and are critical for maintaining intestinal homeostasis. Signals from the microbiota are directly sensed by IECs and influence intestinal health by calibrating immune cell responses and fortifying intestinal barrier function. IECs detect commensal microbes through engagement of common pattern recognition receptors or by sensing the production of microbial-derived metabolites. Deficiencies in these microbial-detecting pathways in IECs leads to impaired epithelial barrier function and altered intestinal homeostasis. This Review aims to highlight the pathways by which IECs sense microbiota-derived signals and the necessity of these detection pathways in maintaining epithelial barrier integrity.

Epithelial wound healing in inflammatory bowel diseases: the next therapeutic frontier

Patients with one of the many chronic inflammatory disorders broadly classified as inflammatory bowel disease (IBD) now have a diverse set of immunomodulatory therapies at their disposal. Despite these recent medical advances, complete sustained remission of disease remains elusive for most patients. The full healing of the damaged intestinal mucosa is the primary goal of all therapies. Achieving this requires not just a reduction of the aberrant immunological response, but also wound healing of the epithelium. No currently approved therapy directly targets the epithelium. Epithelial repair is compromised in IBD and normally facilitates re-establishment of the homeostatic barrier between the host and the microbiome. In this review, we summarize the evidence that epithelial wound healing represents an important yet underdeveloped therapeutic modality for IBD. We highlight 3 general approaches that are promising for developing a new class of epithelium-targeted therapies: epithelial stem cells, cytokines, and microbiome engineering. We also provide a frank discussion of some of the challenges that must be overcome for epithelial repair to be therapeutically leveraged. A concerted approach by the field to develop new therapies targeting epithelial wound healing will offer patients a game-changing, complementary class of medications and could dramatically improve outcomes.

Circulating Free DNA and Its Emerging Role in Autoimmune Diseases

Liquid biopsies can be used to analyse tissue-derived information, including cell-free DNA (cfDNA), circulating rare cells, and circulating extracellular vesicles in the blood or other bodily fluids, representing a new way to guide therapeutic decisions in cancer. Among the new challenges of liquid biopsy, we found clinical application in nontumour pathologies, including autoimmune diseases. Since the discovery of the presence of high levels of cfDNA in patients with systemic lupus erythaematosus (SLE) in the 1960s, cfDNA research in autoimmune diseases has mainly focused on the overall quantification of cfDNA and its association with disease activity. However, with technological advancements and the increasing understanding of the role of DNA sensing receptors in inflammation and autoimmunity, interest in cfDNA and autoimmune diseases has not expanded until recently. In this review, we provide an overview of the basic biology of cfDNA in the context of autoimmune diseases as a biomarker of disease activity, progression, and prediction of the treatment response. We discuss and integrate available information about these important aspects.

Regulation of Intestinal Barrier Function by Microbial Metabolites

The human gastrointestinal tract (GI) harbors a diverse population of microbial life that continually shapes host pathophysiological responses. Despite readily available abundant metagenomic data, the functional dynamics of gut microbiota remain to be explored in various health and disease conditions. Microbiota generate a variety of metabolites from dietary products that influence host health and pathophysiological functions. Since gut microbial metabolites are produced in close proximity to gut epithelium, presumably they have significant impact on gut barrier function and immune responses. The goal of this review is to discuss recent advances on gut microbial metabolites in the regulation of intestinal barrier function. While the mechanisms of action of these metabolites are only beginning to emerge, they mainly point to a small group of shared pathways that control gut barrier functions. Amidst expanding technology and broadening knowledge, exploitation of beneficial microbiota and their metabolites to restore pathophysiological balance will likely prove to be an extremely useful remedial tool.

Nuclear and Mitochondrial Circulating Cell-Free DNA Is Increased in Patients With Inflammatory Bowel Disease in Clinical Remission

Background: The role of cell-free DNA (cfDNA) in the pathogenesis of inflammatory bowel disease (IBD) has been recently suggested. The aim of this study was to analyze circulating cfDNA and deoxyribonuclease (DNase) activity in IBD patients in clinical remission.

Materials and Methods: Plasma and serum were obtained from 72 patients with Crohn's disease and 28 patients with ulcerative colitis. Total cfDNA, nuclear DNA (ncDNA), mitochondrial DNA (mtDNA) and DNase activity were measured.

Results: IBD patients showed higher levels of both ncDNA and mtDNA compared to healthy controls. Concentration of ncDNA was higher in males compared to females, including patients and healthy controls. However, unlike males higher amount of ncDNA was found in female IBD patients compared to healthy controls. DNase activity was significantly lower in male IBD patients compared with healthy controls. In addition, there was a negative correlation between DNase activity and ncDNA levels in male IBD patients.

Conclusions: Herein we present increased amount of circulating ncDNA and mtDNA in IBD patients in clinical remission. Thus, unlike total cfDNA, circulating ncDNA and mtDNA might not represent the optimal biomarkers of disease activity. This is also the first report on sex difference in circulating ncDNA levels, possibly associated with lower DNase activity in males.

Oral priming with oligodeoxynucleotide particles from Lactobacillus rhamnosus GG attenuates symptoms of dextran sodium sulfate-induced acute colitis in mice

Here, we investigated the effect of prophylactic oral treatment with carbonate apatite-based particles (ID35caps) containing Lactobacillus rhamnosus GG-derived immunostimulatory oligodeoxynucleotides (ID35) when used in mice with acute colitis. Mice were administered orally with control particles (carbonate apatite particles, Caps), ID35, or ID35caps for 2 days, and then were given free access to drinking water containing 3% (w/v) dextran sodium sulfate (DSS) for 5 days (Days 0-5) to induce acute colitis. Body weight change, fecal bleeding, and stool consistency were monitored and scored as a disease activity index (DAI) to assess symptoms of colitis. On Day 10, animals were euthanized and the colon length was measured to evaluate inflammatory tissue injury. Prophylactic oral treatment with ID35caps significantly suppressed DSS-induced elevation of the DAI score and shortening of the colon compared to the respective parameters in DSS-exposed mice treated with Cap or ID35. We conclude that oral priming with ID35caps attenuates symptoms and inflammatory colonic injury in a mouse model of DSS-induced acute colitis. This finding suggests that ID35caps may be a new oral agent for preventing intestinal inflammation.

The Influence of Probiotics on the Firmicutes/Bacteroidetes Ratio in the Treatment of Obesity and Inflammatory Bowel disease

The two most important bacterial phyla in the gastrointestinal tract, Firmicutes and Bacteroidetes, have gained much attention in recent years. The Firmicutes/Bacteroidetes (F/B) ratio is widely accepted to have an important influence in maintaining normal intestinal homeostasis. Increased or decreased F/B ratio is regarded as dysbiosis, whereby the former is usually observed with obesity, and the latter with inflammatory bowel disease (IBD). Probiotics as live microorganisms can confer health benefits to the host when administered in adequate amounts. There is considerable evidence of their nutritional and immunosuppressive properties including reports that elucidate the association of probiotics with the F/B ratio, obesity, and IBD. Orally administered probiotics can contribute to the restoration of dysbiotic microbiota and to the prevention of obesity or IBD. However, as the effects of different probiotics on the F/B ratio differ, selecting the appropriate species or mixture is crucial. The most commonly tested probiotics for modifying the F/B ratio and treating obesity and IBD are from the genus Lactobacillus. In this paper, we review the effects of probiotics on the F/B ratio that lead to weight loss or immunosuppression.

Thymosin alpha 1 exerts beneficial extrapulmonary effects in cystic fibrosis

Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the gene encoding for the ion channel Cystic Fibrosis Transmembrane conductance Regulator (CFTR). Long considered a lung disease for the devastating impact on the respiratory function, the recent diagnostic and therapeutic advances have shed the light on the extra-pulmonary manifestations of CF, including gastrointestinal, hepatobiliary and pancreatic symptoms. We have previously demonstrated that thymosin alpha1 (Tα1), a naturally occurring immunomodulatory peptide, displays multi-sided beneficial effects in CF that concur in ameliorating the lung inflammatory pathology. In the present study, by resorting to murine models of gut inflammation with clinical relevance for CF patients, we demonstrate that Tα1 can also have beneficial effects in extrapulmonary pathology. Specifically, Tα1 restored barrier integrity and immune homeostasis in the inflamed gut of CF mice as well as in mice with the metabolic syndrome, a disorder that may arise in CF patients with high caloric intake despite pancreatic sufficiency. The protective effects of Tα1 also extended to pancreas and liver, further emphasizing the beneficial effects of Tα1 in extra-pulmonary complications of CF. By performing wide-ranging multi-organ anti-inflammatory effects, Tα1 could potentially integrate current therapeutic approaches to tackle the complex symptomatology of CF disease.

Fasting-Mimicking Diet Modulates Microbiota and Promotes Intestinal Regeneration to Reduce Inflammatory Bowel Disease Pathology

Dietary interventions are potentially effective therapies for inflammatory bowel diseases (IBDs). We tested the effect of 4-day fasting-mimicking diet (FMD) cycles on a chronic dextran sodium sulfate (DSS)-induced murine model resulting in symptoms and pathology associated with IBD. These FMD cycles reduced intestinal inflammation, increased stem cell number, stimulated protective gut microbiota, and reversed intestinal pathology caused by DSS, whereas water-only fasting increased regenerative and reduced inflammatory markers without reversing pathology. Transplants of Lactobacillus or fecal microbiota from DSS- and FMD-treated mice reversed DSS-induced colon shortening, reduced inflammation, and increased colonic stem cells. In a clinical trial, three FMD cycles reduced markers associated with systemic inflammation. The effect of FMD cycles on microbiota composition, immune cell profile, intestinal stem cell levels and the reversal of pathology associated with IBD in mice, and the anti-inflammatory effects demonstrated in a clinical trial show promise for FMD cycles to ameliorate IBD-associated inflammation in humans.

Epithelial Toll-like receptors and their role in gut homeostasis and disease

The human gastrointestinal tract is colonized by trillions of microorganisms that interact with the host to maintain structural and functional homeostasis. Acting as the interface between the site of the highest microbial burden in the human body and the richest immune compartment, a single layer of intestinal epithelial cells specializes in nutrient absorption, stratifies microorganisms to limit colonization of tissues and shapes the responses of the subepithelial immune cells. In this Review, we focus on the expression, regulation and functions of Toll-like receptors (TLRs) in the different intestinal epithelial lineages to analyse how epithelial recognition of bacteria participates in establishing homeostasis in the gut. In particular, we elaborate on the involvement of epithelial TLR signalling in controlling crypt dynamics, enhancing epithelial barrier integrity and promoting immune tolerance towards the gut microbiota. Furthermore, we comment on the regulatory mechanisms that fine-tune TLR-driven immune responses towards pathogens and revisit the role of TLRs in epithelial repair after injury. Finally, we discuss how dysregulation of epithelial TLRs can lead to the generation of dysbiosis, thereby increasing susceptibility to colitis and tumorigenesis.

The TLR9 Agonist Cobitolimod Induces IL10-Producing Wound Healing Macrophages and Regulatory T Cells in Ulcerative Colitis

BACKGROUND AND AIMS

The topically applied Toll-like receptor 9 [TLR9] agonist cobitolimod is a first-in-class DNA-based oligonucleotide with demonstrated therapeutic efficacy in clinical trials with ulcerative colitis [UC] patients. We here characterized its anti-inflammatory mechanism in UC.

METHODS

Luminal cobitolimod administration was evaluated in an experimental dextran sodium sulfate [DSS]-induced colitis model. Cultured blood and mucosal cells from UC patients were treated with cobitolimod and analysed via microarray, quantitative real-time PCR, ELISA and flow cytometry. Intestinal slides of cobitolimod-treated UC patients were analysed by immunohistochemistry.

RESULTS

Cobitolimod administration markedly suppressed experimental colitis activity, and microarray analyses demonstrated mucosal IL10 upregulation and suppression of IL17 signalling pathways. Cobitolimod treatment was associated with significant induction of mucosal IL10+Tr1 and Treg cells and suppression of Th17 cells. TLR9 knockout mice indicated that cobitolimod requires TLR9 signalling for IL10 induction. In UC patients, mucosal TLR9 levels correlated with severity of inflammation. Cobitolimod inhibited IL17A and IL17F, but increased IL10 and FoxP3 expression in cultured intestinal UC T cells. Cobitolimod-mediated suppression of intestinal IL17+T cells was abrogated by IL10 blockade. Furthermore, cobitolimod led to heightened IL10 production by wound healing macrophages. Immunohistochemistry in intestinal biopsies of cobitolimod-treated UC patients indicated increased presence of IL10+mononuclear and regulatory T cells, as well as reduction of IL17+cells.

CONCLUSION

Activation of TLR9 via cobitolimod might represent a novel therapeutic approach in UC, as it suppresses Th17 cells and induces anti-inflammatory IL10+macrophages and regulatory T cells, thereby modifying the dysregulated intestinal cytokine balance.

PODCAST

This article has an associated podcast which can be accessed at https://academic.oup.com/ecco-jcc/pages/podcast.

TLR9 in MAFLD and NASH: At the Intersection of Inflammation and Metabolism

Toll-Like Receptor 9 (TLR9) is an ancient receptor integral to the primordial functions of inflammation and metabolism. TLR9 functions to regulate homeostasis in a healthy system under acute stress. The literature supports that overactivation of TLR9 under the chronic stress of obesity is a critical driver of the pathogenesis of NASH and NASH-associated fibrosis. Research has focused on the core contributions of the parenchymal and non-parenchymal cells in the liver, adipose, and gut compartments. TLR9 is activated by endogenous circulating mitochondrial DNA (mtDNA). Chronically elevated circulating levels of mtDNA, caused by the stress of overnutrition, are observed in obesity, metabolic dysfunction-associated fatty liver disease (MAFLD), and NASH. Clinical evidence is supportive of TLR9 overactivation as a driver of disease. The role of TLR9 in metabolism and energy regulation may have an underappreciated contribution in the pathogenesis of NASH. Antagonism of TLR9 in NASH and NASH-associated fibrosis could be an effective therapeutic strategy to target both the inflammatory and metabolic components of such a complex disease.

Limited expression of TLR9 on T cells and its functional consequences in patients with nonalcoholic fatty liver disease

Background/Aims

Toll-like receptors (TLRs) modulate T cell responses in diverse diseases. Co-stimulation of T cell activation via TLR9 induces production of interferon gamma (IFN-γ), priming of which is critical for differentiation of pro-inflammatory macrophages. These macrophages have a crucial role in nonalcoholic fatty liver disease (NAFLD). We aimed to evaluate the expression of TLR9 protein on T cells and the consequences of TLR9-mediated triggering of these cells in patients with NAFLD.

Methods

Our study included 34 patients with simple steatosis, 34 patients with nonalcoholic steatohepatitis, eight patients with NAFLD who met general diagnostic criteria but lacked histological diagnosis, and 51 control subjects. We used a synthetic TLR9 ligand to co-stimulate T cells. We measured TLR9 expression in liver and peripheral T cells and CD69 and IFN-γ as phenotypic markers of T cell activation and differentiation by flow cytometry.

Results

TLR9 expression on liver and peripheral T cells was lowest in patients with simple steatosis and was positively associated with anthropometric, biochemical, and histopathological features of NAFLD. In vitro co-stimulation of T cells from patients with simple steatosis induced a limited number of IFN-γ-producing CD8⁺ T cells. At baseline, these patients showed a low frequency of circulating type 1 CD8⁺ cells.

Conclusions

The positive associations between TLR9 and anthropometric, clinical, and histological features and the crucial role of IFN-γ-in NAFLD suggest that limited TLR9 expression and production of IFN-γ play a protective role in patients with simple steatosis.

Cell-Free Nucleic Acids and their Emerging Role in the Pathogenesis and Clinical Management of Inflammatory Bowel Disease

Cell-free nucleic acids (cfNAs) are defined as any nucleic acids that are present outside the cell. They represent valuable biomarkers in various diagnostic protocols such as prenatal diagnostics, the detection of cancer, and cardiovascular or autoimmune diseases. However, in the current literature, little is known about their implication in inflammatory bowel disease (IBD). IBD is a group of multifactorial, autoimmune, and debilitating diseases with increasing incidence worldwide. Despite extensive research, their etiology and exact pathogenesis is still unclear. Since cfNAs were observed in other autoimmune diseases and appear to be relevant in inflammatory processes, their role in the pathogenesis of IBD has also been suggested. This review provides a summary of knowledge from the available literature about cfDNA and cfRNA and the structures involving them such as exosomes and neutrophil extracellular traps and their association with IBD. Current studies showed the promise of cfNAs in the management of IBD not only as biomarkers distinguishing patients from healthy people and differentiating active from inactive disease state, but also as a potential therapeutic target. However, the detailed biological characteristics of cfNAs need to be fully elucidated in future experimental and clinical studies.

Effect of polyunsaturated fatty acids on postnatal ileum development using the fat-1 transgenic mouse model

BACKGROUND

Long-chain polyunsaturated fatty acids (LCPUFAs) play a critical role in neonatal health. We hypothesized that LCPUFAs play an essential role in priming postnatal gut development. We studied the effect of LCPUFAs on postnatal gut development using fat-1 transgenic mice, which are capable of converting n-6 to n-3 LCPUFAs, and wild-type (WT) C57BL/6 mice.

METHODS

Distal ileum sections were collected from fat-1 and WT mice on days 3, 14, and 28. Fatty acid analyses, histology, RT-qPCR and intestinal permeability were performed.

RESULTS

Fat-1 mice, relative to WT mice, showed increased n-3 LCPUFAs levels (α-linolenic acid, docosahexaenoic acid, and eicosapentaenoic acid, p < 0.05) and decreased arachidonic acid levels (p < 0.05) in the ileum. Preweaning fat-1 mice, compared to WT, showed >50% reduced muc2, Tff3, TLR9, and Camp expression (p < 0.05), markers of the innate immune response. There was a >two-fold increased expression of Fzd5 and EphB2, markers of cell differentiation (p < 0.05), and Fabp2 and 6, regulators of fatty acid transport and metabolism (p < 0.05). Despite reduced expression of tight junction genes, intestinal permeability in fat-1 was comparable to WT mice.

CONCLUSIONS

Our data support the hypothesis that fatty acid profiles early in development modulate intestinal gene expression in formative domains, such as cell differentiation, tight junctions, other innate host defenses, and lipid metabolism.

Canine primary jejunal and colonic epithelial cells predominantly express TLR5 and TLR9 but do not change TLR expression pattern after stimulation with certain Toll-like receptor ligands

The intestinal mucosa is in contact with abundant luminal antigens and coordinates immune responses to differentiate commensals from pathogens. Intestinal epithelial cells (IECs) not only represent a physical barrier but also an immunologically important cell type that recognizes microbe-associated molecular patterns via Toll-like receptors (TLR). The importance of TLR expression has been elucidated for intestinal disorders in humans, mice and dogs. However, as knowledge about canine intestinal TLRs is mainly limited to the transcriptional level, the present study analyzed the protein expression of TLR2, TLR3, TLR4, TLR5 and TLR9 by primary canine IECs in the steady state and after stimulation with TLR ligands. This exhibited TLR5 and TLR9 to be predominantly expressed in canine IECs. TLR stimulation did not result in changes of the TLR expression pattern. Further studies are needed to elucidate whether this implicates hyporesponsiveness of canine IECs towards TLR stimulation under steady state conditions.

Resveratrol Ameliorates Intestinal Barrier Defects and Inflammation in Colitic Mice and Intestinal Cells

This study is aimed to investigate the ameliorative effect of resveratrol in a dextran sodium sulfate (DSS)-induced colitis mouse model and intestinal Caco-2 cells, focusing on neutrophil infiltration and tight junction (TJ) barriers. DSS administration caused body weight loss (day8, control 104 ± 1, DSS 72 ± 2%, p < 0.05), shortening of colon length (control 5.1 ± 0.1, DSS 3.8 ± 0.1 cm, p < 0.05), pro-inflammatory cytokines increase-including interleukin (IL)-1β (control 1.0 ± 0.2, DSS 58.5 ± 29.6 arbitrary unit (AU), p < 0.05), IL-6 (control 1.0 ± 0.3, DSS 312 ± 82 AU, p < 0.05), and chemokine motif ligand 2 (CXCL-2, a murine IL-8 homologue, control 1.0 ± 0.4, DSS 696 ± 262 AU, p < 0.05), decreased TJ proteins (e.g., occludin, control 1.0 ± 0.05, DSS 0.11 ± 0.03 AU, p < 0.05), and neutrophil infiltration (control 1.2 ± 0.2, DSS 25.9 ± 1.1 cells, p < 0.05). Supplemental resveratrol (0.1% (w/w) in the diet) partially or totally reversed these symptoms (body weight change 100 ± 1, colon length 4.6 ± 0.1; IL-1β 5.9 ± 1.8, IL-6 10 ± 3, CXCL-2 14 ± 7, occludin 0.76 ± 0.06, neutrophil infiltration 9.3 ± 0.7, p < 0.05). Pretreatment of intestinal Caco-2 cells with resveratrol suppressed the TNF-α-induced production of IL-8 (control 1.00 ± 0.04, TNFα 3.40 ± 0.16, TNFα+Res 1.81 ± 0.28 AU, p < 0.05) and phosphorylation of the inflammatory signaling molecules including NF-κB, extracellular signal-regulated kinase and stress c-Jun N-terminal protein kinase. Collectively, the reduction of TJ barrier defect and IL-8 in intestinal cells, leading to reduced neutrophil infiltration into colonic tissues, appears to be one of the central mechanisms for the resveratrol-mediated effect.

Excessive endosomal TLR signaling causes inflammatory disease in mice with defective SMCR8-WDR41-C9ORF72 complex function

The SMCR8-WDR41-C9ORF72 complex is a regulator of autophagy and lysosomal function. Autoimmunity and inflammatory disease have been ascribed to loss-of-function mutations of Smcr8 or C9orf72 in mice. In humans, autoimmunity has been reported to precede amyotrophic lateral sclerosis caused by mutations of C9ORF72 However, the cellular and molecular mechanisms underlying autoimmunity and inflammation caused by C9ORF72 or SMCR8 deficiencies remain unknown. Here, we show that splenomegaly, lymphadenopathy, and activated circulating T cells observed in Smcr8 ^-/- mice were rescued by triple knockout of the endosomal Toll-like receptors (TLRs) TLR3, TLR7, and TLR9. Myeloid cells from Smcr8 ^-/- mice produced excessive inflammatory cytokines in response to endocytosed TLR3, TLR7, or TLR9 ligands administered in the growth medium and in response to TLR2 or TLR4 ligands internalized by phagocytosis. These defects likely stem from prolonged TLR signaling caused by accumulation of LysoTracker-positive vesicles and by delayed phagosome maturation, both of which were observed in Smcr8 ^-/- macrophages. Smcr8 ^-/- mice also showed elevated susceptibility to dextran sodium sulfate-induced colitis, which was not associated with increased TLR3, TLR7, or TLR9 signaling. Deficiency of WDR41 phenocopied loss of SMCR8. Our findings provide evidence that excessive endosomal TLR signaling resulting from prolonged ligand-receptor contact causes inflammatory disease in SMCR8-deficient mice.

A whole-blood RNA transcript-based gene signature is associated with the development of CTLA-4 blockade-related diarrhea in patients with advanced melanoma treated with the checkpoint inhibitor tremelimumab

BACKGROUND

Anti-CTLA-4 immune checkpoint blockade is associated with immune-related adverse events (irAEs). Grade 3-4 diarrhea/colitis is the most frequent irAE requiring treatment discontinuation. Predicting high-risk diarrhea/colitis patients may facilitate early intervention, limit irAE severity, and extend treatment duration. No biomarkers currently predict for anti-CTLA-4 immunotherapy related severe diarrhea.

METHODS

Whole-blood was collected pre-treatment and 30 days post-treatment initiation from patients with stage III or IV unresectable melanoma who received 15 mg/kg tremelimumab at 90 day intervals in two clinical trials. The discovery dataset was a phase II study that enrolled 150 patients between December 2005 and November 2006. The validation dataset was a phase III study that enrolled 210 patients between March 2006 and July 2007. RT-PCR was performed for 169 genes associated with inflammation, immunity, CTLA-4 pathway and melanoma. Gene expression was correlated with grade 0-1 versus grade 2-4 diarrhea/colitis development.

RESULTS

Pre-treatment blood obtained from the discovery dataset (N = 150) revealed no gene predictive of diarrhea/colitis development (p < 0.05). A 16-gene signature (CARD12, CCL3, CCR3, CXCL1, F5, FAM210B, GADD45A, IL18bp, IL2RA, IL5, IL8, MMP9, PTGS2, SOCS3, TLR9 and UBE2C) was identified from 30 days post-tremelimumab initiation blood that discriminated patients developing grade 0-1 from grade 2-4 diarrhea/colitis. The 16-gene signature demonstrated an AUC of 0.814 (95% CI 0.743 to 0.873, p < 0.0001), sensitivity 42.9%, specificity 99.2%, positive predictive value (PPV) 90.0%, and negative predictive value (NPV) 91.4%. In the validation dataset (N = 210), the 16-gene signature discriminated patients developing grade 0-1 from grade 2-4 diarrhea/colitis with an AUC 0.785 (95% CI 0.723 to 0.838, p < 0.0001), sensitivity 57.1%, specificity 84.4%, PPV 57.1% and NPV 84.4%.

CONCLUSION

This study identifies a whole-blood mRNA signature predictive of a clinically relevant irAE in patients treated with immune checkpoint blockade. We hypothesize that immune system modulation induced by immune checkpoint blockade results in peripheral blood gene expression changes that are detectable prior to clinical onset of severe diarrhea. Assessment of peripheral blood gene expression changes in patients receiving anti-PD-1/PD-L1 immunotherapy, or combination anti-CTLA4 and anti-PD-1/PD-L1 immunotherapy, is warranted to provide early on-treatment mechanistic insights and identify clinically relevant predictive biomarkers.

TRIAL REGISTRATION

Clinicaltrials.gov , NCT00257205 , registered 22 November 2005.

A Map of Toll-like Receptor Expression in the Intestinal Epithelium Reveals Distinct Spatial, Cell Type-Specific, and Temporal Patterns

Signaling by Toll-like receptors (TLRs) on intestinal epithelial cells (IECs) is critical for intestinal homeostasis. To visualize epithelial expression of individual TLRs in vivo, we generated five strains of reporter mice. These mice revealed that TLR expression varied dramatically along the length of the intestine. Indeed, small intestine (SI) IECs expressed low levels of multiple TLRs that were highly expressed by colonic IECs. TLR5 expression was restricted to Paneth cells in the SI epithelium. Intestinal organoid experiments revealed that TLR signaling in Paneth cells or colonic IECs induced a core set of host defense genes, but this set did not include antimicrobial peptides, which instead were induced indirectly by inflammatory cytokines. This comprehensive blueprint of TLR expression and function in IECs reveals unexpected diversity in the responsiveness of IECs to microbial stimuli, and together with the associated reporter strains, provides a resource for further study of innate immunity.

Mitochondrial DNA Is a Pro-Inflammatory Damage-Associated Molecular Pattern Released During Active IBD

Background

Due to common evolutionary origins, mitochondrial DNA (mtDNA) shares many similarities with immunogenic bacterial DNA. MtDNA is recognized as a pro-inflammatory damage-associated molecular pattern (DAMP) with a pathogenic role in several inflammatory diseases. We hypothesised that mtDNA is released during active disease, serving as a key pro-inflammatory factor in inflammatory bowel disease (IBD).

Methods

Between 2014 and 2015, we collected plasma separated within 2 hours of sampling from 97 prospectively recruited IBD patients (67 ulcerative colitis [UC] and 30 Crohn's disease [CD]) and 40 non-IBD controls. We measured circulating mtDNA using quantitative polymerase chain reaction (amplifying mitochondria COXIII/ND2 genes) and also in mouse colitis induced by dextran sulfate-sodium (DSS). We used a mass spectometry approach to detect free plasma mitochondrial formylated peptides. Furthermore, we examined for mitochondrial damage using electron microscopy (EM) and TLR9 expression, the target for mtDNA, in human intestinal IBD mucosa.

Results

Plasma mtDNA levels were increased in UC and CD (both P < 0.0001) compared with non-IBD controls. These levels were significantly correlated to blood (C-reactive protein, albumin, white cell count), clinical and endoscopic markers of severity, and disease activity. In active UC, we identified 5 mitochondrial formylated peptides (the most abundant being fMMYALF with known chemoattractant function) in plasma. We observed mitochondrial damage in inflamed UC mucosa and significantly higher fecal MtDNA levels (vs non-IBD controls [P < 0.0001]), which supports gut mucosal mitochondrial DAMP release as the primary source. In parallel, plasma mtDNA levels increased during induction of acute DSS colitis and were associated with more severe colitis (P < 0.05). In active IBD, TLR9+ lamina propria inflammatory cells were significantly higher in UC and CD compared with controls (P < 0.05).

Conclusions

We present the first evidence to show that mtDNA is released during active IBD. MtDNA is a potential mechanistic biomarker, and our data point to mtDNA-TLR9 as a therapeutic target in IBD. 10.1093/ibd/izy095_videoizy095.video5776747659001.

Microbial Factors in Inflammatory Diseases and Cancers

The intestinal microbes form a symbiotic relationship with their human host to harvest energy for themselves and their host and to shape the immune system of their host. However, alteration of this relationship, which is named as a dysbiosis, has been associated with the development of different inflammatory diseases and cancers. It is found that metabolites, cellular components, and virulence factors derived from the gut microbiota interact with the host locally or systemically to modulate the dysbiosis and the development of these diseases. In this book chapter, we discuss the role of these microbial factors in regulating the host signaling pathways, the composition and load of the gut microbiota, the co-metabolism of the host and the microbiota, the host immune system, and physiology. In particular, we highlight how each microbial factor can contribute in the manifestation of many diseases such as cancers, Inflammatory Bowel Diseases, obesity, type-2 diabetes, non-alcoholic fatty liver diseases, nonalcoholic steatohepatitis, and cardiovascular diseases.

Changes of KEAP1/NRF2 and IKB/NF-κB Expression Levels Induced by Cell-Free DNA in Different Cell Types

Cell-free DNA (cfDNA) is a circulating DNA of nuclear and mitochondrial origin mainly derived from dying cells. Recent studies have shown that cfDNA is a stress signaling DAMP (damage-associated molecular pattern) molecule. We report here that the expression profiles of cfDNA-induced factors NRF2 and NF-κB are distinct depending on the target cell's type and the GC-content and oxidation rate of the cfDNA. Stem cells (MSC) have shown higher expression of NRF2 without inflammation in response to cfDNA. In contrast, inflammatory response launched by NF-κB was dominant in differentiated cells HUVEC, MCF7, and fibroblasts, with a possibility of transition to massive apoptosis. In each cell type examined, the response for oxidized cfDNA was more acute with higher peak intensity and faster resolution than that for nonoxidized cfDNA. GC-rich nonoxidized cfDNA evoked a weaker and prolonged response with proinflammatory component (NF-κB) as predominant. The exploration of apoptosis rates after adding cfDNA showed that cfDNA with moderately increased GC-content and lightly oxidized DNA promoted cell survival in a hormetic manner. Novel potential therapeutic approaches are proposed, which depend on the current cfDNA content: either preconditioning with low doses of cfDNA before a planned adverse impact or eliminating (binding, etc.) cfDNA when its content has already become high.

Chitin protects the gut epithelial barrier in a protochordate model of DSS-induced colitis

The gastrointestinal tract of Ciona intestinalis, a solitary tunicate that siphon-filters water, shares similarities with its mammalian counterpart. The Ciona gut exhibits other features that are unique to protochordates, including certain immune molecules, and other characteristics, e.g. chitin-rich mucus, which appears to be more widespread than considered previously. Exposure of Ciona to dextran sulphate sodium (DSS) induces a colitis-like phenotype similar to that seen in other systems, and is characterized by alteration of epithelial morphology and infiltration of blood cells into lamina propria-like regions. DSS treatment also influences the production and localization of a secreted immune molecule shown previously to co-localize to chitin-rich mucus in the gut. Resistance to DSS is enhanced by exposure to exogenous chitin microparticles, suggesting that endogenous chitin is critical to barrier integrity. Protochordates, such as Ciona, retain basic characteristics found in other more advanced chordates and can inform us of uniquely conserved signals shaping host-microbiota interactions in the absence of adaptive immunity. These simpler model systems may also reveal factors and processes that modulate recovery from colitis, the role gut microbiota play in the onset of the disease, and the rules that help govern the reestablishment and maintenance of gut homeostasis.

Purified rutin and rutin-rich asparagus attenuates disease severity and tissue damage following dextran sodium sulfate-induced colitis

SCOPE

This study investigated the effects of cooked whole asparagus (ASP) versus its equivalent level of purified flavonoid glycoside, rutin (RUT), on dextran sodium sulfate (DSS)-induced colitis and subsequent colitis recovery in mice.

METHODS AND RESULTS

C57BL/6 male mice were fed an AIN-93G basal diet (BD), or BD supplemented with 2% cooked ASP or 0.025% RUT for 2 wks prior to and during colitis induction with 2% DSS in water for 7 days, followed by 5 days colitis recovery. In colitic mice, both ASP and RUT upregulated mediators of improved barrier integrity and enhanced mucosal injury repair (e.g. Muc1, IL-22, Rho-A, Rac1, and Reg3γ), increased the proportion of mouse survival, and improved disease activity index. RUT had the greatest effect in attenuating DSS-induced colonic damage indicated by increased crypt and goblet cell restitution, reduced colonic myeloperoxidase, as well as attenuated DSS-induced microbial dysbiosis (reduced Enterobacteriaceae and Bacteroides, and increased unassigned Clostridales, Oscillospira, Lactobacillus, and Bifidobacterium).

CONCLUSION

These findings demonstrate that dietary cooked ASP and its flavonoid glycoside, RUT, may be useful in attenuating colitis severity by modulating the colonic microenvironment resulting in reduced colonic inflammation, promotion of colonic mucosal injury repair, and attenuation of colitis-associated microbial dysbiosis.

Biphasic Ccl20 regulation by Toll-like receptor 9 through the activation of ERK-AP-1 and non-canonical NF-κB signaling pathways

BACKGROUND

Chemokines play key roles in immune homeostasis and inflammatory response. Considering the role of Ccl20 and Toll-like receptor 9 (TLR9) in gut homeostasis and inflammatory bowel disease (IBD), regulation of Ccl20 by bacterial DNA, the TLR9 ligand, merits in-depth studies.

METHODS

We analyzed Ccl20 expression in various epithelial cell (EC) lines by q-PCR and ELISA. In-vivo expression was investigated in isolated murine colonocytes by immunoblotting. Transcriptional regulation of Ccl20 was studied by reporter assays, gene knock-down, electrophoretic mobility shift assay and chromatin immunoprecipitation. Activation of upstream kinases was checked by immunoblotting.

RESULTS

We showed low levels of Ccl20 expression in mouse colonic ECs, but marked induction by in vivo treatment with bacterial DNA. This corroborated with persistent Ccl20 induction in different EC lines. We found involvement of MAP-kinases during the early hours after stimulation, and a novel AP-1site (-252bp) regulated the expression in colonic ECs. More importantly, mutually exclusive transcriptional regulation by AP-1 (cjun/cfos) and non-canonical NF-κB (RelB/p52) downstream of MEK-ERK and NIK-IKK-α-NF-κB2 (p100) phosphorylation, respectively was responsible for persistent Ccl20 expression in the colonic cells, while canonical NF-κB isoforms played no role.

CONCLUSIONS

Persistent Ccl20 induction by TLR9 in colonic ECs involves early and delayed activation of two independent signaling pathways. This is the first report of non-canonical NF-κB activation and Ccl20 expression in the colonic ECs by TLR9.

GENERAL SIGNIFICANCE

Our study will help to better understand immune regulation by Ccl20 in the intestine and may be exploited for future development of novel therapeutics against IBD.

Toll-like receptors in the pathogenesis of autoimmune diseases: recent and emerging translational developments

Autoinflammatory diseases are defined as the loss of self-tolerance in which an inflammatory response to self-antigens occurs, which are a significant global burden. Toll-like receptors are key pattern recognition receptors, which integrate signals leading to the activation of transcription factors and ultimately proinflammatory cytokines. Recently, it has become apparent that these are at the nexus of autoinflammatory diseases making them viable and attractive drug targets. The aim of this review was to evaluate the role of innate immunity in autoinflammatory conditions alongside the role of negative regulation while suggesting possible therapeutic targets.

Toll-like receptors: promising therapeutic targets for inflammatory diseases

The health of living organisms is constantly challenged by bacterial and viral threats. The recognition of pathogenic microorganisms by diverse receptors triggers a variety of host defense mechanisms, leading to their eradication. Toll-like receptors (TLRs), which are type I transmembrane proteins, recognize specific signatures of the invading microbes and activate a cascade of downstream signals inducing the secretion of inflammatory cytokines, chemokines, and type I interferons. The TLR response not only counteracts the pathogens but also initiates and shapes the adaptive immune response. Under normal conditions, inflammation is downregulated after the removal of the pathogen and cellular debris. However, a dysfunctional TLR-mediated response maintains a chronic inflammatory state and leads to local and systemic deleterious effects in host cells and tissues. Such inappropriate TLR response has been attributed to the development and progression of multiple diseases such as cancer, autoimmune, and inflammatory diseases. In this review, we discuss the emerging role of TLRs in the pathogenesis of inflammatory diseases and how targeting of TLRs offers a promising therapeutic strategy for the prevention and treatment of various inflammatory diseases. Additionally, we highlight a number of TLR-targeting agents that are in the developmental stage or in clinical trials.

When Insult Is Added to Injury: Cross Talk between ILCs and Intestinal Epithelium in IBD

Inflammatory bowel disease (IBD) is characterized by an impairment of the integrity of the mucosal epithelial barrier, which causes exacerbated inflammation of the intestine. The intestinal barrier is formed by different specialized epithelial cells, which separate the intestinal lumen from the lamina propria. In addition to its crucial role in protecting the body from invading pathogens, the intestinal epithelium contributes to intestinal homeostasis by its biochemical properties and communication to underlying immune cells. Innate lymphoid cells (ILCs) are a recently described population of lymphocytes that have been implicated in both mucosal homeostasis and inflammation. Recent findings indicate a critical feedback loop in which damaged epithelium activates these innate immune cells to restore epithelial barrier function. This review will focus on the signalling pathways between damaged epithelium and ILCs involved in repair of the epithelial barrier and tissue homeostasis and the relationship of these processes with the control of IBD.

Molecular mechanisms of regulation of Toll-like receptor signaling

TLRs play a critical role in the detection of microbes and endogenous "alarmins" to initiate host defense, yet they can also contribute to the development and progression of inflammatory and autoimmune diseases. To avoid pathogenic inflammation, TLR signaling is subject to multilayer regulatory control mechanisms, including cooperation with coreceptors, post-translational modifications, cleavage, cellular trafficking, and interactions with negative regulators. Nucleic acid-sensing TLRs are particularly interesting in this regard, as they can both recognize host-derived structures and require internalization of their ligand as a result of intracellular sequestration of the nucleic acid-sensing TLRs. This review summarizes the regulatory mechanisms of TLRs, including regulation of their access to ligands, receptor folding, intracellular trafficking, and post-translational modifications, as well as how altered control mechanism could contribute to inflammatory and autoimmune disorders.

An Inducible, Large-Intestine-Specific Transgenic Mouse Model for Colitis and Colitis-Induced Colon Cancer Research

BACKGROUND

Animal models are an important tool to understand intestinal biology. Our laboratory previously generated C57BL/6-Tg(Car1-cre)5Flt transgenic mice (CAC) with large-intestine-specific Cre recombinase (Cre) expression as a model to study colon health.

AIM

To expand the utility of the CAC mouse model by determining the impact of chemically induced colitis on CAC transgene expression.

METHODS

CAC mice were crossed to Rosa reporter mice (Rosa26R (flox/flox) ) with a lox-STOP-lox signal controlling β-galactosidase (βgal) expression and then further crossed with Apc(CKO/CKO) mice in some experiments to delete Apc alleles (Apc (Δ580) ). Initially, 8-week-old CAC(Tg/WT);Rosa26R (flox/WT) ;Apc (Δ580/WT) mice were treated with dextran sulfate sodium (DSS) in drinking water (5 days, 0, 0.65, 1.35, or 2.0 %). Colon tissue damage and βgal labeling were analyzed 10 day after stopping DSS. Next, 8-week-old CAC(Tg/WT);Rosa26R(flox/flox) mice were treated with 0 or 1.35 % DSS, and colonic βgal labeling was assessed at 30 day post-DSS treatment. Finally, 10-week-old CAC(Tg/WT);Apc (Δ580/WT) mice were treated with DSS (0 or 2 %) for 5 days and colonic tumors were analyzed at 20 weeks.

RESULTS

CAC(Tg/WT);Rosa26R (flox/WT) ;Apc (Δ580/WT) mice had a DSS dose-dependent increase in colon epithelial damage that correlated with increased epithelial βgal labeling at 10 days (r (2) = 0.9, β = 0.75). The βgal labeling in CAC(Tg/WT);Rosa26R(flox/flox) mice colon remained high at 30 days, especially in the crypts of the healed ulcer. DSS also increased colon tumor incidence and multiplicity in CAC(Tg/WT);Apc (Δ580/WT) mice.

CONCLUSIONS

DSS-mediated epithelial damage induces a persistent, Cre-mediated recombination of floxed alleles in CAC mice. This enables the examination of gene function in colon epithelium during experimental colitis and colitis-induced colon cancer.

TLR9 stability and signaling are regulated by phosphorylation and cell stress

Innate sensing of pathogens elicits protective immune responses through pattern recognition receptors, including Toll-like receptors. Although signaling by Toll-like receptors is regulated at multiple steps, including localization, trafficking, proteolytic cleavage, and phosphorylation, the significance of post-translational modifications and cellular stress response on Toll-like receptor stability and signaling is still largely unknown. In the present study, we investigated the role of cytoplasmic tyrosine motifs in Toll-like receptor-9 stability, proteolytic cleavage, and signaling. We demonstrated that tyrosine phosphorylation is essential for mouse Toll-like receptor-9 protein stability and signaling. Upon inhibition of tyrosine kinases with piceatannol, Toll-like receptor-9 tyrosine phosphorylation induced by CpG deoxyribonucleic acid was inhibited, which correlated with decreased signaling. Furthermore, inhibition of Src kinases with 1-tert-Butyl-3-(4-chlorophenyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine also inhibited response to CpG deoxyribonucleic acid. Toll-like receptor-9 protein stability was also sensitive to autophagy, the cellular stress response pathway, and infection by a deoxyribonucleic acid virus. Whereas autophagy induced by rapamycin or low serum levels caused a preferential loss of the mature p80 proteolytic cleavage product, infection with herpes simplex virus-1 and induction of cell stress with tunicamycin caused preferential loss of full-length Toll-like receptor-9, which is localized to the endoplasmic reticulum. Our data reveal new information about the stability and signaling of Toll-like receptor-9 and suggest that immune evasion mechanisms may involve targeted loss of innate sensing receptors.

TLR9 regulates adipose tissue inflammation and obesity-related metabolic disorders

OBJECTIVE

Recent studies have revealed a link between Toll-like receptor (TLR) signaling and the adipose tissue inflammation associated with obesity. Although TLR9 is known to play an important role in inflammation and innate immunity, its role in mediating adipose tissue inflammation has not yet been investigated. Thus, the objective of this study was to determine the role of TLR9 in regulating immune cells in visceral adipose tissue and maintaining the metabolic homeostasis.

METHODS

Wild-type and TLR9-deficient mice were fed with a high-fat diet, and the body weight gain, glucose tolerance, insulin sensitivity, and adipose tissue inflammation were examined.

RESULTS

TLR9-deficient mice gained significantly more weight and body fat under a high-fat diet than wild-type mice and exhibited more severe glucose intolerance and insulin resistance. We also found a dramatic increase of M1 macrophages as well as TH 1 cells in the adipose tissue of TLR9-deficient mice compared to wild-type mice. Furthermore, the levels of various proinflammatory cytokines and chemokines were higher in TLR9-deficient mice.

CONCLUSIONS

TLR9 signaling is involved in regulating adipose tissue inflammation and controlling obesity and the metabolic syndrome.

The Endoplasmic Reticulum Stress Sensor IRE1α in Intestinal Epithelial Cells Is Essential for Protecting against Colitis

Intestinal epithelial cells (IECs) have critical roles in maintaining homeostasis of intestinal epithelium. Endoplasmic reticulum (ER) stress is implicated in intestinal epithelium homeostasis and inflammatory bowel disease; however, it remains elusive whether IRE1α, a major sensor of ER stress, is directly involved in these processes. We demonstrate here that genetic ablation of Ire1α in IECs leads to spontaneous colitis in mice. Deletion of IRE1α in IECs results in loss of goblet cells and failure of intestinal epithelial barrier function. IRE1α deficiency induces cell apoptosis through induction of CHOP, the pro-apoptotic protein, and sensitizes cells to lipopolysaccharide, an endotoxin from bacteria. IRE1α deficiency confers upon mice higher susceptibility to chemical-induced colitis. These results suggest that IRE1α functions to maintain the intestinal epithelial homeostasis and plays an important role in defending against inflammation bowel diseases.