The Intestinal Epithelium: Central Coordinator of Mucosal Immunity

Gut Microbiota: A Perspective for Psychiatrists

There is mounting evidence that the trillions of microbes that inhabit our gut are a substantial contributing factor to mental health and, equally, to the progression of neuropsychiatric disorders. The extraordinary complexity of the gut ecosystem, and how it interacts with the intestinal epithelium to manifest physiological changes in the brain to influence mood and behaviour, has been the subject of intense scientific scrutiny over the last 2 decades. To further complicate matters, we each harbour a unique microbiota community that is subject to change by a number of factors including diet, exercise, stress, health status, genetics, medication, and age, amongst others. The microbiota-gut-brain axis is a dynamic matrix of tissues and organs including the gastrointestinal (GI) microbiota, immune cells, gut tissue, glands, the autonomic nervous system (ANS), and the brain that communicate in a complex multidirectional manner through a number of anatomically and physiologically distinct systems. Long-term perturbations to this homeostatic environment may contribute to the progression of a number of disorders by altering physiological processes including hypothalamic-pituitary-adrenal axis activation, neurotransmitter systems, immune function, and the inflammatory response. While an appropriate, co-ordinated physiological response, such as an immune or stress response, is necessary for survival, a dysfunctional response can be detrimental to the host, contributing to the development of a number of central nervous system disorders.

Changes in dietary fiber intake in mice reveal associations between colonic mucin O-glycosylation and specific gut bacteria

The colonic mucus layer, comprised of highly O-glycosylated mucins, is vital to mediating host-gut microbiota interactions, yet the impact of dietary changes on colonic mucin O-glycosylation and its associations with the gut microbiota remains unexplored. Here, we used an array of omics techniques including glycomics to examine the effect of dietary fiber consumption on the gut microbiota, colonic mucin O-glycosylation and host physiology of high-fat diet-fed C57BL/6J mice. The high-fat diet group had significantly impaired glucose tolerance and altered liver proteome, gut microbiota composition, and short-chain fatty acid production compared to normal chow diet group. While dietary fiber inclusion did not reverse all high fat-induced modifications, it resulted in specific changes, including an increase in the relative abundance of bacterial families with known fiber digesters and a higher propionate concentration. Conversely, colonic mucin O-glycosylation remained similar between the normal chow and high-fat diet groups, while dietary fiber intervention resulted in major alterations in O-glycosylation. Correlation network analysis revealed previously undescribed associations between specific bacteria and mucin glycan structures. For example, the relative abundance of the bacterium Parabacteroides distasonis positively correlated with glycan structures containing one terminal fucose and correlated negatively with glycans containing two terminal fucose residues or with both an N-acetylneuraminic acid and a sulfate residue. This is the first comprehensive report of the impact of dietary fiber on the colonic mucin O-glycosylation and associations of these mucosal glycans with specific gut bacteria.

Human intestinal dendritic cell and macrophage subsets in coeliac disease

Dendritic cells (DC) and macrophages (Mϕ) constitute the most abundant antigen presenting cells in the human intestinal mucosa. In resting conditions, they are essential to maintain the mechanisms of immune tolerance toward food antigens and commensals, at the time that they keep the capacity to initiate and maintain antigen-specific pro-inflammatory immune responses toward invading pathogens. Nevertheless, this delicate equilibrium between immunity and tolerance is not perfect, like in coeliac disease (CD), where DC and Mϕ drive the development of antigen-specific immune responses toward dietary gluten peptides. In this review, we provide therefore a comprehensive discussion about CD pathogenesis, the human intestinal immune system and the biology of intestinal DC and Mϕ both in resting conditions and in CD. Last, but not least, we discuss about all the remaining issues pending to be studied regarding DC and Mϕ contribution toward CD pathogenesis. This may allow the identification of unique and specific factors which may be useful in the clinical practice, as well as identify new therapeutic targets in order to reestablish the loss intestinal homeostasis in CD.

Epithelial cell dysfunction in coeliac disease

The intestinal epithelium limits host-luminal interactions and maintains gut homeostasis. Breakdown of the epithelial barrier and villous atrophy are hallmarks of coeliac disease. Besides the well characterized immune-mediated epithelial damage induced in coeliac mucosa, constitutional changes and early gluten direct effects disturb intestinal epithelial cells. The subsequent modifications in key epithelial signaling pathways leads to outnumbered immature epithelial cells that, in turn, facilitate epithelial dysfunction, promote crypt hyperplasia, and increase intestinal permeability. Consequently, underlying immune cells have a greater access to gluten, which boosts the proinflammatory immune response against gluten and positively feedback the epithelial damage loop. Gluten-free diet is an indispensable treatment for coeliac disease patients, but additional therapies are under development, including those that reinforce intestinal epithelial healing. In this chapter, we provide an overview of intestinal epithelial cell disturbances that develop during gluten intake in coeliac disease mucosa.

Immunoglobulin Receptors Expression in Indian Colon Cancer Patients and Healthy Subjects Using a Noninvasive Approach and Flowcytometry

Background:

Isolation of viable colonocytes from human stool is a noninvasive and convenient approach that can be used for diagnostic, screening, management, and research on various gastrointestinal (GI) diseases including colon cancer. Limited studies are available globally and for the first time in this article, we have reported the immunoglobulin (Ig) (IgA and IgG) receptors concentration on viable colonocytes for Indian colon cancer patients using this noninvasive approach.

Materials and Methods:

Viable colonocytes from stool were isolated by the Somatic Cell Sampling and Recovery method (Noninvasive Technology, USA) and processed for the assessment of Igs (IgA and IgG) receptors expression using standard immunophenotyping and flow cytometry.

Results:

IgA and IgG receptor expression was measured and reported on these viable colonocytes. There was a significant difference in the expression of IgA and IgG receptors on viable colonocytes between colon cancer patients and healthy individuals.

Conclusion:

This noninvasive technique is a promising approach for the detection of molecular and immunological markers that will help clinicians in the diagnosis, screening, monitoring, and management of different GI diseases including colon cancer.

Gut Microbiota as a Trigger for Metabolic Inflammation in Obesity and Type 2 Diabetes

The gut microbiota has been linked to the development of obesity and type 2 diabetes (T2D). The underlying mechanisms as to how intestinal microbiota may contribute to T2D are only partly understood. It becomes progressively clear that T2D is characterized by a chronic state of low-grade inflammation, which has been linked to the development of insulin resistance. Here, we review the current evidence that intestinal microbiota, and the metabolites they produce, could drive the development of insulin resistance in obesity and T2D, possibly by initiating an inflammatory response. First, we will summarize major findings about immunological and gut microbial changes in these metabolic diseases. Next, we will give a detailed view on how gut microbial changes have been implicated in low-grade inflammation. Lastly, we will critically discuss clinical studies that focus on the interaction between gut microbiota and the immune system in metabolic disease. Overall, there is strong evidence that the tripartite interaction between gut microbiota, host immune system and metabolism is a critical partaker in the pathophysiology of obesity and T2D.

Anti‑inflammatory mechanism of berberine on lipopolysaccharide‑induced IEC‑18 models based on comparative transcriptomics

Intestinal surface epithelial cells (IECs) have long been considered as an effective barrier for maintaining water and electrolyte balance, and are involved in the mechanism of nutrient absorption. When intestinal inflammation occurs, it is often accompanied by IEC malfunction. Berberine (BBR) is an isoquinoline alkaloid found in numerous types of medicinal plants, which has been clinically used in China to treat symptoms of gastrointestinal pathogenic bacterial infection, especially bacteria‑induced diarrhea and inflammation. In the present study, IEC‑18 rat intestinal epithelial cells were treated with lipopolysaccharide (LPS) to establish an in vitro model of epithelial cell inflammation, and the cells were subsequently treated with BBR in order to elucidate the anti‑inflammatory mechanism. Transcriptome data were then searched to find the differentially expressed genes (DEGs) compared between two of the treatment groups (namely, the LPS and LPS+BBR groups), and DEGs were analyzed using Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Weighted Gene Correlation Network Analysis and Interactive Pathways Explorer to identify the functions and pathways enriched with DEGs. Finally, reverse transcription‑quantitative PCR was used to verify the transcriptome data. These experiments revealed that, comparing between the LPS and LPS+BBR groups, the functions and pathways enriched in DEGs were 'DNA replication', 'cell cycle', 'apoptosis', 'leukocyte migration' and the 'NF‑κB and AP‑1 pathways'. The results revealed that BBR is able to restrict DNA replication, inhibit the cell cycle and promote apoptosis. It can also inhibit the classic inflammatory pathways, such as those mediated by NF‑κB and AP‑1, and the expression of various chemokines to prevent the migration of leukocytes. According to transcriptomic data, BBR can exert its anti‑inflammatory effects by regulating a variety of cellular physiological activities, including cell cycle, apoptosis, inflammatory pathways and leukocyte migration.

Human-origin Lactobacillus salivarius AR809 protects against immunosuppression in S. aureus-induced pharyngitis via Akt-mediated NF-κB and autophagy signaling pathways

Lactobacillus salivarius AR809 is a newly discovered probiotic strain from a healthy human pharynx and has potential ability to adhere to the pharyngeal epithelium and inhibit Staphylococcus aureus (S. aureus)-induced inflammatory response. Pharyngeal spray administration of AR809 exhibited protective effects in a S. aureus-induced mouse model of pharyngitis. The inhibitory effect and underlying molecular mechanism of AR809 on S. aureus-stimulated pharyngitis were further investigated. AR809 significantly increased phagocytosis and bactericidal activity, reduced the production of inflammatory mediators (intracellular reactive oxygen species (ROS), prostaglandin E2 (PGE2), cyclooxygenase-2 (COX-2), nitric oxide (NO), inducible NOS (iNOS)) and the expression of inflammatory cytokines (tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)), and induced macrophages to adopt the M2 phenotype. AR809 also attenuated S. aureus-induced phosphorylations of protein kinase B (Akt) and rapamycin (mTOR), and elevated the autophagic protein (light chain 3 from II (LC3-II) and Beclin-1) level. Furthermore, AR809 inhibited nuclear transcription factor kappa-B (NF-κB) activation by suppressing the nuclear translocation of NF-κB p65. Likewise, 740Y-P (a PI3K activator) decreased the anti-inflammatory effect of AR809 against S. aureus-induced inflammatory response, while AR809 treatments with wortmannin (a PI3K inhibitor) markedly reversed this inflammatory response. AR809 prevents S. aureus-induced pharyngeal inflammatory response, possibly by regulating TLR/PI3K/Akt/mTOR signalling pathway-related autophagy and TLR/PI3K/Akt/IκB/NF-κB pathway activity, and therefore has potential for use in preventing pharyngitis and other inflammatory diseases.

The Gut Microbiota at the Service of Immunometabolism

The gut microbiota is implicated in immune system functions. Regulation of the metabolic processes occurring in immune cells is crucial for the maintenance of homeostasis and immunopathogenesis. Emerging data demonstrate that the gut microbiota is an actor in immunometabolism, notably through the effect of metabolites such as short-chain fatty acids, bile acids, and tryptophan metabolites. In this Perspective, we discuss the impact of the gut microbiota on the intracellular metabolism of the different subtypes of immune cells, including intestinal epithelial cells. Besides the effects on health, we discuss the potential consequences in infection context and inflammatory bowel diseases.

Distinctive probiotic features share common TLR2-dependent signalling in intestinal epithelial cells

The underlying mechanisms of probiotics and postbiotics are not well understood, but it is known that both affect the adaptive and innate immune responses. In addition, there is a growing concept that some probiotic strains have common core mechanisms that provide certain health benefits. Here, we aimed to elucidate the signalization of the probiotic bacterial strains Lactobacillus paragasseri K7, Limosilactobacillus fermentum L930BB, Bifidobacterium animalis subsp. animalis IM386 and Lactiplantibacillus plantarum WCFS1. We showed in in vitro experiments that the tested probiotics exhibit common TLR2- and TLR10-dependent downstream signalling cascades involving inhibition of NF-κB signal transduction. Under inflammatory conditions, the probiotics activated phosphatidylinositol 3-kinase (PI3K)/Akt anti-apoptotic pathways and protein kinase C (PKC)-dependent pathways, which led to regulation of the actin cytoskeleton and tight junctions. These pathways contribute to the regeneration of the intestinal epithelium and modulation of the mucosal immune system, which, together with the inhibition of canonical TLR signalling, promote general immune tolerance. With this study we identified shared probiotic mechanisms and were the first to pinpoint the role of anti-inflammatory probiotic signalling through TLR10.

Gastrointestinal stress as innate defence against microbial attack

The human gastrointestinal (GI) tract has been bestowed with the most difficult task of protecting the underlying biological compartments from the resident commensal flora and the potential pathogens in transit through the GI tract. It has a unique environment in which several defence tactics are at play while maintaining homeostasis and health. The GI tract shows myriad number of environmental extremes, which includes pH variations, anaerobic conditions, nutrient limitations, elevated osmolarity etc., which puts a check to colonization and growth of nonfriendly microbial strains. The GI tract acts as a highly selective barrier/platform for ingested food and is the primary playground for balance between the resident and uninvited organisms. This review focuses on antimicrobial defense mechanisms of different sections of human GI tract. In addition, the protective mechanisms used by microbes to combat the human GI defence systems are also discussed. The ability to survive this innate defence mechanism determines the capability of probiotic or pathogen strains to confer health benefits or induce clinical events respectively.

Pathophysiology and protective approaches of gut injury in critical illness

The gut is a complex organ that has played an important role in digestion, absorption, endocrine functions, and immunity. The gut mucosal barriers consist of the immunologic barrier and nonimmunologic barrier. During critical illnesses, the gut is susceptible to injury due to the induction of intestinal hyperpermeability. Gut hyperpermeability and barrier dysfunction may lead to systemic inflammatory response syndrome. Additionally, gut microbiota are altered during critical illnesses. The etiology of such microbiome alterations in critical illnesses is multifactorial. The interaction or systemic host defense modulation between distant organs and the gut microbiome is increasingly studied in disease research. No treatment modality exists to significantly enhance the gut epithelial integrity, permeability, or mucus layer in critically ill patients. However, multiple helpful approaches including clinical and preclinical strategies exist. Enteral nutrition is associated with an increased mucosal barrier in animal and human studies. The trophic effects of enteral nutrition might help to maintain the intestinal physiology, prevent atrophy of gut villi, reduce intestinal permeability, and protect against ischemia-reperfusion injury. The microbiome approach such as the use of probiotics, fecal microbial transplantation, and selective decontamination of the digestive tract has been suggested. However, its evidence does not have a high quality. To promote rapid hypertrophy of the small bowel, various factors have been reported, including the epidermal growth factor, membrane permeant inhibitor of myosin light chain kinase, mucus surrogate, pharmacologic vagus nerve agonist, immune-enhancing diet, and glucagon-like peptide-2 as preclinical strategies. However, the evidence remains unclear.

GPA peptide inhibits NLRP3 inflammasome activation to ameliorate colitis through AMPK pathway

Ulcerative colitis (UC) is a chronic and idiopathic inflammatory disease that affects the colon, resulting in immune dysregulation and the production of large amounts of pro-inflammatory cytokines. Pyroptosis and NLRP3 inflammasome are associated with various kinds of inflammatory diseases including colitis. The purpose of this study is to investigate the protective effects and regulatory mechanism of Gly-Pro-Ala (GPA) peptide on DSS-induced colitis. In vivo, we find GPA peptide could exert anti-inflammatory effects on DSS-induced mice colitis, and its anti-inflammatory effects are abolished in NLRP3^-/- mice. In macrophage, GPA suppresses the assembly of NLRP3 inflammasome and GSDMD cleavage. Furthermore, GPA maintains mitochondrial homeostasis through inhibiting ROS, mtDNA and NLRP3 mitochondrial localization, with other signals related to NLRP3 inflammasome unaffected. Furthermore, the inhibitory effects of GPA on reactive oxygen species (ROS) are found to be achieved by increasing AMPK phosphorylation. Our results suggest that GPA inhibits NLRP3 inflammasome activation through increasing AMPK phosphorylation to suppress ROS, and can be applied in the prevention of colitis through targeting NLRP3.

Modulating the gut-liver axis and the pivotal role of the faecal microbiome in cirrhosis

Cirrhosis is associated with intestinal dysbiosis, with specific alterations in the gut microbiota linked to particular aetiologies and manifestations of the disease. We review the role of the gut microbiome and the importance of the intestinal barrier in cirrhosis, provide an overview of the terminology and techniques relevant to this emerging area, and discuss the latest developments in therapies targeting the gut-liver axis.

The Link between Oral and Gut Microbiota in Inflammatory Bowel Disease and a Synopsis of Potential Salivary Biomarkers

The objective of this review is to provide recent evidence for the oral–gut axis connection and to discuss gastrointestinal (GI) immune response, inflammatory bowel disease (IBD) pathogenesis, and potential salivary biomarkers for determining GI health. IBD affects an estimated 1.3% of the US adult population. While genetic predisposition and environment play a role, abnormal immune activity and microbiota dysbiosis within the gastrointestinal tract are also linked in IBD pathogenesis. It has been inferred that a reduced overall richness of bacterial species as well as colonization of opportunistic bacteria induce systemic inflammation in the GI tract. Currently, there is supporting evidence that both oral and gut microbiota may be related to the development of IBD. Despite this, there are currently no curative therapies for IBD, and diagnosis requires samples of blood, stool, and invasive diagnostic imaging techniques. Considering the relative ease of collection, emerging evidence of association with non-oral diseases may imply that saliva microbiome research may have the potential for gut diagnostic or prognostic value. This review demonstrates a link between saliva and intestinal profiles in IBD patients, suggesting that saliva sampling has the potential to serve as a non-invasive biomarker for gut diseases such as IBD in the oral–gut axis.

MicroRNAs Regulate Intestinal Immunity and Gut Microbiota for Gastrointestinal Health: A Comprehensive Review

MicroRNAs are small non-coding RNAs regulating gene expression at the post-transcriptional level. The regulation of microRNA expression in the gut intestine is gradually recognized as one of the crucial contributors of intestinal homeostasis and overall health. Recent studies indicated that both the microRNAs endogenous in the gut intestine and exogenous from diets could play influential roles in modulating microbial colonization and intestinal immunity. In this review, we discuss the biological functions of microRNAs in regulating intestinal homeostasis by modulating intestinal immune responses and gut microbiota. We particularly focus on addressing the microRNA-dependent communication and interactions among microRNA, gut microbiota, and intestinal immune system. Besides, we also summarize the roles of diet-derived microRNAs in host-microbiome homeostasis and their benefits on intestinal health. A better understanding of the relationships among intestinal disorders, microRNAs, and other factors influencing intestinal health can facilitate the application of microRNA-based therapeutics for gastrointestinal diseases.

Improvement of intestinal stem cells and barrier function via energy restriction in middle-aged C57BL/6 mice

This study aimed to reveal the impact of energy restriction on the intestine via structural and molecular changes in terms of intestinal stem cell (ISC) function, ISC niche, intestinal epithelial barrier function, and intestinal immune function. Female C57BL/6J mice, aged 12 months, fed a commercial chow were used in this study. The ISC function, ISC niche, intestinal epithelial barrier function, and intestinal immune function were assessed. Energy restriction reversed aging-induced intestinal shortening and made the crypts shallower. The intestinal epithelial cells isolated from the intestine showed a significant increase in the expression levels of stem cell-associated genes in small intestinal epithelial cells as detected by flow cytometry. Despite the increase in the number of stem cells and the expression levels of markers, no increase or decrease was found in the enteroid complexity of the small intestine and colonic enteroid formation in vitro. The colonic mucous layer was measured in mice of the energy restricted (ER)-treated group to investigate the epithelial barrier function in the colon. The results revealed that the barrier was more complete. The fluorescence intensity of tight junction markers claudin-2 and zonula occludens-1 increased and the mRNA expression profiles of monocyte chemotactic protein 1 and interleukin-6 decreased in the colon of mice in the ER-treated group. The beneficial effects of ER on the colon in terms of the integrity of the mucosal barrier and alleviation of inflammation were confirmed, thus highlighting the importance of modulating the intestinal function in developing effective antiaging dietary interventions.

Gut microbiota derived metabolites contribute to intestinal barrier maturation at the suckling-to-weaning transition

In suckling mammals, the onset of solid food ingestion is coincident with the maturation of the gut barrier. This ontogenic process is driven by the colonization of the intestine by the microbiota. However, the mechanisms underlying the microbial regulation of the intestinal development in early life are not fully understood. Here, we studied the co-maturation of the microbiota (composition and metabolic activity) and of the gut barrier at the suckling-to-weaning transition by using a combination of experiments in vivo (suckling rabbit model), ex vivo (Ussing chambers) and in vitro (epithelial cell lines and organoids). The microbiota composition, its metabolic activity, para-cellular epithelial permeability and the gene expression of key components of the gut barrier shifted sharply at the onset of solid food ingestion in vivo, despite milk was still predominant in the diet at that time. We found that cecal content sterile supernatant (i.e. containing a mixture of metabolites) obtained after the onset of solid food ingestion accelerated the formation of the epithelial barrier in Caco-2 cells in vitro and our results suggested that these effects were driven by the bacterial metabolite butyrate. Moreover, the treatment of organoids with cecal content sterile supernatant partially replicated in vitro the effects of solid food ingestion on the epithelial barrier in vivo. Altogether, our results show that the metabolites produced by the microbiota at the onset of solid food ingestion contribute to the maturation of the gut barrier at the suckling-to-weaning transition. Targeting the gut microbiota metabolic activity during this key developmental window might therefore be a promising strategy to promote intestinal homeostasis.

Changes in colonic microbiotas in rat after long-term exposure to low dose of okadaic acid

Okadaic acid (OA), one of the most important phycotoxins, is widely distributed around the world, concerning diarrheic shellfish poisoning (DSP), and even colorectal cancer. Here, we found that long-term exposure of OA at a low dose (80 μg kg^-1 body weight) had certain effects on colonic microbiotas and tract in rat. In the OA-exposed rat, colonic epithelium layer was damaged, and relative abundance of some microbiotas were significantly changed, especially genera in Clostridiales. However, no intestinal inflammation or significant disease was observed. Combined with the increase in relative abundance of some genera in Clostridiales induced by OA in the fermentation experiment, we proposed that OA could cause damage to the intestinal epithelium and increase the relative abundance of pathogenic bacteria, thereby increasing the probability of contact between intestinal epithelium and pathogenic bacteria and leading to an easier pathogenicity.

Probiotic Bacillus amyloliquefaciens H57 ameliorates subclinical necrotic enteritis in broiler chicks by maintaining intestinal mucosal integrity and improving feed efficiency

Subclinical necrotic enteritis (NE) was induced in broiler chicks using a high dose of Eimeria spp. vaccine in the drinking water on day 9, and Clostridium perfringens (Cp) culture mixed in the feed on days 14 and 15. The aim was to evaluate the effects of probiotic Bacillus amyloliquefaciens strain H57 (H57) in preventing NE in chicks. Day-old Ross 308, male broilers were weighed and randomly assigned to 6 treatment groups (6 replicate cages/treatment and 8 birds/cage). Birds in group 1 (control) were fed the basal wheat-soybean diet without H57 or NE infection; in group 2 (Eimeria) were treated with Eimeria alone; in group 3 (Cp) were treated with Cp alone; in group 4 (NE) received both Eimeria and Cp; in group 5 (NE-H57) received NE infection and H57; and group 6 (H57) received H57. The basal diet of chicks in groups 5 and 6 was supplemented with H57 at a density of 2 × 108 spores/g feed from 1 D of age. On day 21, there were no significant treatment effects on BW and feed intake between control and H57 birds. However, on day 21, the feed conversion ratio of NE-H57 birds was significantly improved when compared with NE birds (1.28 vs. 1.36; P < 0.001). Birds challenged with NE had a higher occurrence of pasty vent than birds infected with either Eimeria, Cp, or NE-H57 (41 vs. 27 vs. 29 vs. 19%, respectively; P < 0.001). Intestinal lesion scores of NE birds were also higher than those of Eimeria, Cp, and NE-H57 birds (5.67 vs. 2.56 vs. 2.78 vs. 2.10, respectively; P < 0.001) and correlated with pasty vent (Pearson's r = 0.56; P < 0.001). Microscopic evaluation showed mucosal damage and necrosis in NE birds. In contrast, villi from NE-H57 birds were normal, with no damage or infiltration with Eimeria or Cp. H57 appears to be effective in challenged birds, as it maintained epithelial barrier integrity and improved feed efficiency.

Paneth cells promote angiogenesis and regulate portal hypertension in response to microbial signals

BACKGROUND & AIMS

Paneth cells (PCs) synthesize and secrete antimicrobial peptides that are key mediators of host-microbe interactions, establishing a balance between intestinal microflora and enteric pathogens. We observed that their number increases in experimental portal hypertension and aimed to investigate the mechanisms by which these cells can contribute to the regulation of portal pressure.

METHODS

We first treated Math1^Lox/LoxVilcreERT2 mice with tamoxifen to induce the complete depletion of intestinal PCs. Subsequently, we performed partial portal vein or bile duct ligation. We then studied the effects of these interventions on hemodynamic parameters, proliferation of blood vessels and the expression of genes regulating angiogenesis. Intestinal organoids were cultured and exposed to different microbial products to study the composition of their secreted products (by proteomics) and their effects on the proliferation and tube formation of endothelial cells (ECs). In vivo confocal laser endomicroscopy was used to confirm the findings on blood vessel proliferation.

RESULTS

Portal hypertension was significantly attenuated in PC-depleted mice compared to control mice and was associated with a decrease in portosystemic shunts. Depletion of PCs also resulted in a significantly decreased density of blood vessels in the intestinal wall and mesentery. Furthermore, we observed reduced expression of intestinal genes regulating angiogenesis in Paneth cell depleted mice using arrays and next generation sequencing. Tube formation and wound healing responses were significantly decreased in ECs treated with conditioned media from PC-depleted intestinal organoids exposed to intestinal microbiota-derived products. Proteomic analysis of conditioned media in the presence of PCs revealed an increase in factors regulating angiogenesis and additional metabolic processes. In vivo endomicroscopy showed decreased vascular proliferation in the absence of PCs.

CONCLUSIONS

These results suggest that in response to intestinal flora and microbiota-derived factors, PCs secrete not only antimicrobial peptides, but also pro-angiogenic signaling molecules, thereby promoting intestinal and mesenteric angiogenesis and regulating portal hypertension.

LAY SUMMARY

Paneth cells are present in the lining of the small intestine. They prevent the passage of bacteria from the intestine into the blood circulation by secreting substances to fight bacteria. In this paper, we discovered that these substances not only act against bacteria, but also increase the quantity of blood vessels in the intestine and blood pressure in the portal vein. This is important, because high blood pressure in the portal vein may result in several complications which could be targeted with novel approaches.

Exploiting disease-induced changes for targeted oral delivery of biologics and nanomedicines in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic and progressive disorder with destructive inflammation in the gastrointestinal tract (GIT). Biologics have changed the management of IBD, but have serious limitations, which is associated with their systemic administration via injection. Oral administration is the most accepted route of drug administration. However, the physiological barriers of the GIT pose significant challenges for oral administration of biologics, making this route of administration currently unavailable. The status of tissue barriers to oral drug delivery is altered in IBD. This may bring more challenges, but also present opportunities for oral delivery of biologics. This article provides an overview of disease-induced alterations of GIT barriers in IBD and discusses challenges, opportunities and commonly-utilised strategies for oral delivery of complex therapeutics, including biologics and nanomedicines.

Immune System Modulations by Products of the Gut Microbiota

The gut microbiota, which consists of all bacteria, viruses, fungus, and protozoa living in the intestine, and the immune system have co-evolved in a symbiotic relationship since the origin of the immune system. The bacterial community forming the microbiota plays an important role in the regulation of multiple aspects of the immune system. This regulation depends, among other things, on the production of a variety of metabolites by the microbiota. These metabolites range from small molecules to large macro-molecules. All types of immune cells from the host interact with these metabolites resulting in the activation of different pathways, which result in either positive or negative responses. The understanding of these pathways and their modulations will help establish the microbiota as a therapeutic target in the prevention and treatment of a variety of immune-related diseases.

MiR-339 attenuates LPS-induced intestinal epithelial cells inflammatory responses and apoptosis by targeting TLR4

BACKGROUND

Intestinal epithelial cells are important for defending against pathogen infection. LPS is an endotoxin that is highly antigenic and cytotoxic produced by bacteria. LPS disrupts the intestine epithelium integrity and induced the intestinal epithelial cell inflammation and apoptosis. Our previous study has predicted the function of exosome miRNAs through bioinformatics analysis, and we found that miR-339 had a potential function in cell inflammation response. To our knowledge, no published paper has demonstrated the miR-339 function in protecting the intestine epithelium against bacterial infection.

OBJECTIVE

The objective of this study is to evaluate the miR-339 function in regulating intestinal epithelial cells to defend against bacterial infection through biological experiments and bioinformatics analyses.

METHODS

Through the miR-339 transfection experiment and TLR4 interfering experiment, we evaluated the function of miR-339 and TLR4 in the process of inflammatory responses and apoptosis. Through Bioinformatics analyses and dual-luciferase reporter experiment, we identified the target gene of miR-339.

RESULTS

miR-339 attenuates LPS-induced intestinal epithelial cells inflammatory responses through the TLR4/NF-κB signaling pathway and inhibited LPS-induced apoptosis through the P53 signaling pathway. TLR4 is the target gene of miR-339. TLR4 reduced LPS-induced proinflammatory responses and apoptosis.

CONCLUSIONS

In conclusion, miR-339 protected the intestine epithelial cells from LPS-induced cell inflammation and apoptosis through targeting TLR4. This study expanded our understanding of how miRNAs and genes work collaboratively in regulating intestinal epithelial cells to defend against bacterial infection.

Fluoride-Induced Alteration in the Diversity and Composition of Bacterial Microbiota in Mice Colon

Fluoride, as an environmental toxin, causes damage to intestinal mucosa. It may promote pathogen infection by increasing the intestinal mucosa permeability. In this study, the colonic fecal samples from the control group (C group, 0 mg/L NaF for 60 days) and the fluoride group (F group, 100 mg/L NaF for 60 days) were subjected to high-throughput 16S rRNA sequencing to verify the effects of fluoride on the colonic flora of animals. Results revealed a total of 253 operative taxonomical units (OTUs) in two groups, and 22 unique OTUs occurred in the F group. Fluoride increased the microbiota diversity and species richness of the colon. Concretely, the abundance of the Tenericutes was increased at the level of the phyla in the F group. In addition, in the F group, significant differences at the genus level were observed in Faecalibaculum, Alloprevotella, [Eubacterium]_xylanophilum_group, Prevotellaceae_UCG-001, and Ruminiclostridium_9, compared to the C group. Among them, except for the reduction in Faecalibaculum, the other four bacteria were increased in the F group. In summary, the intestinal microbial composition of mice was reconstituted by the presence of fluoride, and the significantly changing bacteria may partly account for the pathogenesis of fluoride-induced intestinal dysfunction.

Cutibacterium acnes regulates the epidermal barrier properties of HPV-KER human immortalized keratinocyte cultures

Our skin provides a physical barrier to separate the internal part of our body from the environment. Maintenance of complex barrier functions is achieved through anatomical structures in the skin, the stratified squamous epithelium specialized junctional organelles, called tight junctions (TJs). Several members of our microbial communities are known to affect the differentiation state and function of the colonized organ. Whether and how interactions between skin cells and cutaneous microbes, including Cutibacterium acnes (C. acnes), modify the structure and/or function of our skin is currently only partly understood. Thus, in our studies, we investigated whether C. acnes may affect the epidermal barrier using in vitro model systems. Real-time cellular analysis showed that depending on the keratinocyte differentiation state, the applied C. acnes strains and their dose, the measured impedance values change, together with the expression of selected TJ proteins. These may reflect barrier alterations, which can be partially restored upon antibiotic–antimycotic treatment. Our findings suggest that C. acnes can actively modify the barrier properties of cultured keratinocytes, possibly through alteration of tight cell-to-cell contacts. Similar events may play important roles in our skin, in the maintenance of cutaneous homeostasis.

Protective action of Bacillus clausii probiotic strains in an in vitro model of Rotavirus infection

Rotavirus is the most common cause of acute gastroenteritis (AGE) in young children. Bacillus clausii (B. clausii) is a spore-forming probiotic that is able to colonize the gut. A mixture of four B. clausii strains (O/C, T, SIN and N/R) is commonly used for the treatment of AGE, and it has been demonstrated that it can reduce the duration and severity of diarrhea in children with AGE. Few studies have sought to characterize the mechanisms responsible for such beneficial effects. Intestinal effects of probiotics are likely to be strain-specific. We conducted a series of in vitro experiments investigating the activities of this mixture of B. clausii strains on biomarkers of mucosal barrier integrity and immune function in a cellular model of Rotavirus infection. B. clausii protected enterocytes against Rotavirus-induced decrease in trans-epithelial electrical resistance, and up-regulated expression of mucin 5AC and tight junction proteins (occludin and zonula occludens-1), all of which are important for effective mucosal barrier function. B. clausii also inhibited reactive oxygen species production and release of pro-inflammatory cytokines (interleukin-8 and interferon-β) in Rotavirus-infected cells, and down-regulated pro-inflammatory Toll-like receptor 3 pathway gene expression. Such mechanisms likely contributed to the observed protective effects of B. clausii against reduced cell proliferation and increased apoptosis in Rotavirus-infected enterocytes.

Innate Lymphoid Cell-Epithelial Cell Modules Sustain Intestinal Homeostasis

The intestines have the essential but challenging mission of absorbing nutrients, restricting damage from food-derived toxins, promoting colonization by symbionts, and expelling pathogens. These processes are often incompatible with each other and must therefore be prioritized in view of the most crucial contemporary needs of the host. Recent work has shown that tissue-resident innate lymphoid cells (ILCs) constitute a central sensory module allowing adaptation of intestinal organ function to changing environmental input. Here, we propose a conceptual framework positing that the various types of ILC act in distinct modules with intestinal epithelial cells, collectively safeguarding organ function. Such homeostasis-promoting circuitry has high potential to be plumbed for new therapeutic approaches to the treatment of immune-mediated inflammatory diseases.

Regulation of Intestinal Epithelial Barrier and Immune Function by Activated T Cells

BACKGROUND & AIMS

Communication between T cells and the intestinal epithelium is altered in many diseases, causing T-cell activation, depletion, or recruitment, and disruption of the epithelium. We hypothesize that activation of T cells regulates epithelial barrier function by targeting the assembly of the tight junction complex.

METHODS

In a 3-dimensional and 2-dimensional co-culture model of activated T cells subjacent to the basolateral surface of an epithelial monolayer, the pore, leak, and unrestricted pathways were evaluated using transepithelial resistance and flux of fluorescently labeled tracers. T cells were acutely and chronically activated by cross-linking the T-cell receptor. Tight junction assembly and expression were measured using quantitative polymerase chain reaction, immunoblot, and immunofluorescence confocal microscopy.

RESULTS

Co-culture with acutely and chronically activated T cells decreased the magnitude of ion flux through the pore pathway, which was maintained in the presence of acutely activated T cells. Chronically activated T cells after 30 hours induced a precipitous increase in the magnitude of both ion and molecular flux, resulting in an increase in the unrestricted pathway, destruction of microvilli, expansion in cell surface area, and cell death. These fluctuations in permeability were the result of changes in the assembly and expression of tight junction proteins, cell morphology, and viability. Co-culture modulated the expression of immune mediators in the epithelium and T cells.

CONCLUSIONS

Bidirectional communication between T cells and epithelium mediates a biphasic response in barrier integrity that is facilitated by the balance between structural proteins partitioning in the mobile lateral phase vs the tight junction complex and cell morphology.

Coeliac Disease Pathogenesis: The Uncertainties of a Well-Known Immune Mediated Disorder

Coeliac disease is a common small bowel enteropathy arising in genetically predisposed individuals and caused by ingestion of gluten in the diet. Great advances have been made in understanding the role of the adaptive immune system in response to gluten peptides. Despite detailed knowledge of these adaptive immune mechanisms, the complete series of pathogenic events responsible for development of the tissue lesion remains less certain. This review contributes to the field by discussing additional mechanisms which may also contribute to pathogenesis. These include the production of cytokines such as interleukin-15 by intestinal epithelial cells and local antigen presenting cells as a pivotal event in the disease process. A subset of unconventional T cells called gamma/delta T cells are also persistently expanded in the coeliac disease (CD) small intestinal epithelium and recent analysis has shown that these cells contribute to pathogenic inflammation. Other unconventional T cell subsets may play a local immunoregulatory role and require further study. It has also been suggested that, in addition to activation of pathogenic T helper cells by gluten peptides, other peptides may directly interact with the intestinal mucosa, further contributing to the disease process. We also discuss how myofibroblasts, a major source of tissue transglutaminase and metalloproteases, may play a key role in intestinal tissue remodeling. Contribution of each of these factors to pathogenesis is discussed to enhance our view of this complex disorder and to contribute to a wider understanding of chronic immune-mediated disease.

Stromal Cells in the Pathogenesis of Inflammatory Bowel Disease

Up till now, research on inflammatory bowel disease [IBD] has mainly been focused on the immune cells present in the gastrointestinal tract. However, recent insights indicate that stromal cells also play an important and significant role in IBD pathogenesis. Stromal cells in the intestines regulate both intestinal epithelial and immune cell homeostasis. Different subsets of stromal cells have been found to play a role in other inflammatory diseases [e.g. rheumatoid arthritis], and these various stromal subsets now appear to carry out also specific functions in the inflamed gut in IBD. Novel potential therapies for IBD utilize, as well as target, these pathogenic stromal cells. Injection of mesenchymal stromal cells [MSCs] into fistula tracts of Crohn's disease patients is already approved and used in clinical settings. In this review we discuss the current knowledge of the role of stromal cells in IBD pathogenesis. We further outline recent attempts to modify the stromal compartment in IBD with agents that target or replace the pathogenic stroma.

Intestinal Epithelial Cells Express Immunomodulatory ISG15 During Active Ulcerative Colitis and Crohn's Disease

BACKGROUND AND AIMS

Intestinal epithelial cells [IECs] secrete cytokines that recruit immune cells to the mucosa and regulate immune responses that drive inflammation in inflammatory bowel disease [IBD]. However, experiments in patient-derived IEC models are still scarce. Here, we aimed to investigate how innate immunity and IEC-specific pattern recognition receptor [PRR] signalling can be involved in an enhanced type I interferon [IFN] gene signature observed in colon epithelium of patients with active IBD, with a special focus on secreted ubiquitin-like protein ISG15.

METHODS

Gene and protein expression in whole mucosa biopsies and in microdissected human colonic epithelial lining, in HT29 human intestinal epithelial cells and primary 3D colonoids treated with PRR-ligands and cytokines, were detected by transcriptomics, in situ hybridisation, immunohistochemistry, western blots, and enzyme-linked immunosorbent assay [ELISA]. Effects of IEC-secreted cytokines were examined in human peripheral blood mononuclear cells [PBMCs] by multiplex chemokine profiling and ELISA.

RESULTS

The type I IFN gene signature in human mucosal biopsies was mimicked in Toll-like receptor TLR3 and to some extent tumour necrosis factor [TNF]-treated human IECs. In intestinal biopsies, ISG15 expression correlated with expression of the newly identified receptor for extracellular ISG15, LFA-1 integrin. ISG15 was expressed and secreted from HT29 cells and primary 3D colonoids through both JAK1-pSTAT-IRF9-dependent and independent pathways. In experiments using PBMCs, we show that ISG15 releases IBD-relevant proinflammatory cytokines such as CXCL1, CXCL5, CXCL8, CCL20, IL1, IL6, TNF, and IFNγ.

CONCLUSIONS

ISG15 is secreted from primary IECs upon extracellular stimulation, and mucosal ISG15 emerges as an intriguing candidate for immunotherapy in IBD.

Manipulation of epithelial integrity and mucosal immunity by host and microbiota-derived metabolites

The human intestinal tract contains a large number of microbes, their metabolites, and potentially harmful food antigens. The intestinal epithelium separates the mucosa where immune cells are located from luminal microbes by expressing various factors that assemble into physical and chemical barriers. In addition to epithelial cells, immune cells are essential for enforcing mucosal barriers through production of inflammatory and anti-inflammatory mediators. Intestinal microbiota, represented by gut ecological communities of living microorganisms, influences maturation and homeostasis of host immune system and contributes to the maintenance of the epithelial integrity with small molecules derived from their metabolism, termed metabolites. In turn, immune cells receive signals from microbiota, and may play key role in maintenance of a healthy bacterial composition and reinforcement of epithelial barrier functions, leading to the establishment of a host-bacterial mutualism. Alterations in the microbiota community and metabolome profiles are observed in patients with various disorders including inflammatory bowel disease. In this review, we will discuss physiological functions of the microbiota and its metabolites in regulating host immune system and reinforcing epithelial barrier functions. Further understanding of these processes will aid in identification of novel therapeutic targets and subsequent development of therapeutic interventions in a range of chronic inflammatory diseases.

A Human 2D Primary Organoid-Derived Epithelial Monolayer Model to Study Host-Pathogen Interaction in the Small Intestine

Gut organoids are stem cell derived 3D models of the intestinal epithelium that are useful for studying interactions between enteric pathogens and their host. While the organoid model has been used for both bacterial and viral infections, this is a closed system with the luminal side being inaccessible without microinjection or disruption of the organoid polarization. In order to overcome this and simplify their applicability for transepithelial studies, permeable membrane based monolayer approaches are needed. In this paper, we demonstrate a method for generating a monolayer model of the human fetal intestinal polarized epithelium that is fully characterized and validated. Proximal and distal small intestinal organoids were used to generate 2D monolayer cultures, which were characterized with respect to epithelial cell types, polarization, barrier function, and gene expression. In addition, viral replication and bacterial translocation after apical infection with enteric pathogens Enterovirus A71 and Listeria monocytogenes were evaluated, with subsequent monitoring of the pro-inflammatory host response. This human 2D fetal intestinal monolayer model will be a valuable tool to study host-pathogen interactions and potentially reduce the use of animals in research.

Germ-free and microbiota-associated mice yield small intestinal epithelial organoids with equivalent and robust transcriptome/proteome expression phenotypes

Intestinal epithelial organoids established from gut tissue have become a widely used research tool. However, it remains unclear how environmental cues, divergent microbiota composition and other sources of variation before, during and after establishment confound organoid properties, and how these properties relate to the original tissue. While environmental influences cannot be easily addressed in human organoids, mice offer a controlled assay-system. Here, we probed the effect of donor microbiota differences, previously identified as a confounding factor in murine in vivo studies, on organoids. We analysed the proteomes and transcriptomes of primary organoid cultures established from two colonised and one germ-free mouse colony of C57BL/6J genetic background, and compared them to their tissue of origin and commonly used cell lines. While an imprint of microbiota-exposure was observed on the proteome of epithelial samples, the long-term global impact of donor microbiota on organoid expression patterns was negligible. Instead, stochastic culture-to-culture differences accounted for a moderate variability between independently established organoids. Integration of transcriptome and proteome datasets revealed an organoid-typic expression signature comprising 14 transcripts and 10 proteins that distinguished organoids across all donors from murine epithelial cell lines and fibroblasts and closely mimicked expression patterns in the gut epithelium. This included the inflammasome components ASC, Naip1-6, Nlrc4 and Caspase-1, which were highly expressed in all organoids compared to the reference cell line m-ICc12 or mouse embryonic fibroblasts. Taken together, these results reveal that the donor microbiota has little effect on the organoid phenotype and suggest that organoids represent a more suitable culture model than immortalised cell lines, in particular for studies of intestinal epithelial inflammasomes.

Review article: impact of cigarette smoking on intestinal inflammation-direct and indirect mechanisms

BACKGROUND

The inflammatory bowel diseases, Crohn's disease and ulcerative colitis are related multifactorial diseases. Their pathogenesis is influenced by each individual's immune system, the environmental factors within exposome and genetic predisposition. Smoking habit is the single best-established environmental factor that influences disease phenotype, behaviour and response to therapy.

AIM

To assess current epidemiological, experimental and clinical evidence that may explain how smoking impacts on the pathogenesis of inflammatory bowel disease.

METHODS

A Medline search for 'cigarette smoking', in combination with terms including 'passive', 'second-hand', 'intestinal inflammation', 'Crohn's disease', 'ulcerative colitis', 'colitis'; 'intestinal epithelium', 'immune system', 'intestinal microbiota', 'tight junctions', 'mucus', 'goblet cells', 'Paneth cells', 'autophagy'; 'epigenetics', 'genes', 'DNA methylation', 'histones', 'short noncoding/long noncoding RNAs'; 'carbon monoxide/CO' and 'nitric oxide/NO' was performed.

RESULTS

Studies found evidence of direct and indirect effects of smoking on various parameters, including oxidative damage, impairment of intestinal barrier and immune cell function, epigenetic and microbiota composition changes, that contribute to the pathogenesis of inflammatory bowel disease.

CONCLUSIONS

Cigarette smoking promotes intestinal inflammation by affecting the function and interactions among intestinal epithelium, immune system and microbiota/microbiome.

Hypoxia and Innate Immunity: Keeping Up with the HIFsters

Recent years have witnessed an emergence of interest in understanding metabolic changes associated with immune responses, termed immunometabolism. As oxygen is central to all aerobic metabolism, hypoxia is now recognized to contribute fundamentally to inflammatory and immune responses. Studies from a number of groups have implicated a prominent role for oxygen metabolism and hypoxia in innate immunity of healthy tissue (physiologic hypoxia) and during active inflammation (inflammatory hypoxia). This inflammatory hypoxia emanates from a combination of recruited inflammatory cells (e.g., neutrophils, eosinophils, and monocytes), high rates of oxidative metabolism, and the activation of multiple oxygen-consuming enzymes during inflammation. These localized shifts toward hypoxia have identified a prominent role for the transcription factor hypoxia-inducible factor (HIF) in the regulation of innate immunity. Such studies have provided new and enlightening insight into our basic understanding of immune mechanisms, and extensions of these findings have identified potential therapeutic targets. In this review, we summarize recent literature around the topic of innate immunity and mucosal hypoxia with a focus on transcriptional responses mediated by HIF.

More than sugar in the milk: human milk oligosaccharides as essential bioactive molecules in breast milk and current insight in beneficial effects

Human milk is the gold standard for newborn infants. Breast milk not only provides nutrients, it also contains bioactive components that guide the development of the infant's intestinal immune system, which can have a lifelong effect. The bioactive molecules in breast milk regulate microbiota development, immune maturation and gut barrier function. Human milk oligosaccharides (hMOs) are the most abundant bioactive molecules in human milk and have multiple beneficial functions such as support of growth of beneficial bacteria, anti-pathogenic effects, immune modulating effects, and stimulation of intestine barrier functions. Here we critically review the current insight into the benefits of bioactive molecules in mother milk that contribute to neonatal development and focus on current knowledge of hMO-functions on microbiota and the gastrointestinal immune barrier. hMOs produced via genetically engineered microorganisms are now applied in infant formulas to mimic the nutritional composition of breast milk as closely as possible, and their prospects and scientific challenges are discussed in depth.

Epithelium intrinsic vitamin A signaling co-ordinates pathogen clearance in the gut via IL-18

Intestinal epithelial cells (IECs) are at the forefront of host-pathogen interactions, coordinating a cascade of immune responses to protect against pathogens. Here we show that IEC-intrinsic vitamin A signaling restricts pathogen invasion early in the infection and subsequently activates immune cells to promote pathogen clearance. Mice blocked for retinoic acid receptor (RAR) signaling selectively in IECs (stop^ΔIEC) showed higher Salmonella burden in colonic tissues early in the infection that associated with higher luminal and systemic loads of the pathogen at later stages. Higher pathogen burden in stop^ΔIEC mice correlated with attenuated mucosal interferon gamma (IFNγ) production by underlying immune cells. We found that, at homeostasis, the intestinal epithelium of stop^ΔIEC mice produced significantly lower amounts of interleukin 18 (IL-18), a potent inducer of IFNγ. Regulation of IL-18 by vitamin A was also observed in a dietary model of vitamin A supplementation. IL-18 reconstitution in stop^ΔIEC mice restored resistance to Salmonella by promoting epithelial cell shedding to eliminate infected cells and limit pathogen invasion early in infection. Further, IL-18 augmented IFNγ production by underlying immune cells to restrict pathogen burden and systemic spread. Our work uncovers a critical role for vitamin A in coordinating a biphasic immune response to Salmonella infection by regulating IL-18 production by IECs.

Epithelial cells line the intestinal lumen, forming a barrier between the body and dietary and microbial contents in the lumen. Apart from absorbing nutrients from diet, these epithelial cells help mediate a stable, symbiotic relationship between commensal bacteria and the immune cells. During infection, they help co-ordinate the immune response to counter the infection. How dietary micronutrients, such as vitamin A, inform epithelial cell function during infection is poorly understood. Using a model where epithelial cells in the gut cannot respond to vitamin A signals, we find that epithelial vitamin A signaling promotes resistance to Salmonella infection. We show that, vitamin A increases the production of a key cytokine, interleukin 18, by epithelial cells. IL-18 promotes shedding of infected epithelial cells to reduce the pathogen invasion while also inducing the production of interferon gamma by immune cells to mediate pathogen clearance. Thus, epithelial cells dynamically respond to dietary vitamin A to regulate interleukin 18 production and potentiate resistance to infection.

Intestinal Permeability, Inflammation and the Role of Nutrients

The interaction between host and external environment mainly occurs in the gastrointestinal tract, where the mucosal barrier has a critical role in many physiologic functions ranging from digestion, absorption, and metabolism. This barrier allows the passage and absorption of nutrients, but at the same time, it must regulate the contact between luminal antigens and the immune system, confining undesirable products to the lumen. Diet is an important regulator of the mucosal barrier, and the cross-talk among dietary factors, the immune system, and microbiota is crucial for the modulation of intestinal permeability and for the maintenance of gastrointestinal tract (GI) homeostasis. In the present review, we will discuss the role of a number of dietary nutrients that have been proposed as regulators of inflammation and epithelial barrier function. We will also consider the metabolic function of the microbiota, which is capable of elaborating the diverse nutrients and synthesizing products of great interest. Better knowledge of the influence of dietary nutrients on inflammation and barrier function can be important for the future development of new therapeutic approaches for patients with mucosal barrier dysfunction, a critical factor in the pathogenesis of many GI and non-GI diseases.

Ulcerative colitis: understanding its cellular pathology could provide insights into novel therapies

Dynamic interactions between the gastrointestinal epithelium and the mucosal immune system normally contribute to ensuring intestinal homeostasis and optimal immunosurveillance, but destabilisation of these interactions in genetically predisposed individuals can lead to the development of chronic inflammatory diseases. Ulcerative colitis is one of the main types of inflammatory diseases that affect the bowel, but its pathogenesis has yet to be completely defined. Several genetic factors and other inflammation-related genes are implicated in mediating the inflammation and development of the disease. Some susceptibility loci associated with increased risk of ulcerative colitis are found to be implicated in mucosal barrier function. Different biomarkers that cause damage to the colonic mucosa can be detected in patients, including perinuclear ANCA, which is also useful in distinguishing ulcerative colitis from other colitides. The choice of treatment for ulcerative colitis depends on disease severity. Therapeutic strategies include anti-tumour necrosis factor alpha (TNF-α) monoclonal antibodies used to block the production of TNF-α that mediates intestinal tract inflammation, an anti-adhesion drug that prevents lymphocyte infiltration from the blood into the inflamed gut, inhibitors of JAK1 and JAK3 that suppress the innate immune cell signalling and interferons α/β which stimulate the production of anti-inflammatory cytokines, as well as faecal microbiota transplantation. Although further research is still required to fully dissect the pathophysiology of ulcerative colitis, understanding its cellular pathology and molecular mechanisms has already proven beneficial and it has got the potential to identify further novel, effective targets for therapy and reduce the burden of this chronic disease.

Mechanisms of Endogenous HIV-1 Reactivation by Endocervical Epithelial Cells

Pharmacological HIV-1 reactivation to reverse latent infection has been extensively studied. However, HIV-1 reactivation also occurs naturally, as evidenced by occasional low-level viremia ("viral blips") during antiretroviral treatment (ART). Clarifying where blips originate from and how they happen could provide clues to stimulate latency reversal more effectively and safely or to prevent viral rebound following ART cessation. We studied HIV-1 reactivation in the female genital tract, a dynamic anatomical target for HIV-1 infection throughout all disease stages. We found that primary endocervical epithelial cells from several women reactivated HIV-1 from latently infected T cells. The endocervical cells' HIV-1 reactivation capacity further increased upon Toll-like receptor 3 stimulation with poly(I·C) double-stranded RNA or infection with herpes simplex virus 2 (HSV-2). Notably, acyclovir did not eliminate HSV-2-induced HIV-1 reactivation. While endocervical epithelial cells secreted large amounts of several cytokines and chemokines, especially tumor necrosis factor alpha (TNF-α), CCL3, CCL4, and CCL20, their HIV-1 reactivation capacity was almost completely blocked by TNF-α neutralization alone. Thus, immunosurveillance activities by columnar epithelial cells in the endocervix can cause endogenous HIV-1 reactivation, which may contribute to viral blips during ART or rebound following ART interruption.IMPORTANCE A reason that there is no universal cure for HIV-1 is that the virus can hide in the genome of infected cells in the form of latent proviral DNA. This hidden provirus is protected from antiviral drugs until it eventually reactivates to produce new virions. It is not well understood where in the body or how this reactivation occurs. We studied HIV-1 reactivation in the female genital tract, which is often the portal of HIV-1 entry and which remains a site of infection throughout the disease. We found that the columnar epithelial cells lining the endocervix, the lower part of the uterus, are particularly effective in reactivating HIV-1 from infected T cells. This activity was enhanced by certain microbial stimuli, including herpes simplex virus 2, and blocked by antibodies against the inflammatory cytokine TNF-α. Avoiding HIV-1 reactivation could be important for maintaining a functional HIV-1 cure when antiviral therapy is stopped.

Intestinal restriction of Salmonella Typhimurium requires caspase-1 and caspase-11 epithelial intrinsic inflammasomes

We investigated the role of the inflammasome effector caspases-1 and -11 during Salmonella enterica serovar Typhimurium infection of murine intestinal epithelial cells (IECs). Salmonella burdens were significantly greater in the intestines of caspase-1/11 deficient (Casp1/11^−/−), Casp1^−/− and Casp11^−/− mice, as compared to wildtype mice. To determine if this reflected IEC-intrinsic inflammasomes, enteroid monolayers were derived and infected with Salmonella. Casp11^−/− and wildtype monolayers responded similarly, whereas Casp1^−/− and Casp1/11^−/− monolayers carried significantly increased intracellular burdens, concomitant with marked decreases in IEC shedding and death. Pretreatment with IFN-γ to mimic inflammation increased caspase-11 levels and IEC death, and reduced Salmonella burdens in Casp1^−/− monolayers, while high intracellular burdens and limited cell shedding persisted in Casp1/11^−/− monolayers. Thus caspase-1 regulates inflammasome responses in IECs at baseline, while proinflammatory activation of IECs reveals a compensatory role for caspase-11. These results demonstrate the importance of IEC-intrinsic canonical and non-canonical inflammasomes in host defense against Salmonella.

Intestinal epithelial cells (IECs) are located at the interface between the gut lumen and the mucosal immune system and form the first layer of defense against the invasive enteric pathogen Salmonella enterica serovar Typhimurium. To prevent Salmonella, and other pathogens from establishing a foothold in the gut, the host mobilizes the inflammasome to selectively eject infected/compromised IECs from the epithelial layer into the intestinal lumen. This involves the activation of the inflammatory caspases; caspase-1 and -11. The individual contributions of each caspase to intestinal host defense, as well as the importance of IEC-intrinsic inflammasomes have not been previously defined, due to the lack of Casp1^−/− mice as well as appropriate IEC-intrinsic defense models. Here, we determined that both caspases contribute to controlling Salmonella pathogen burdens and IEC shedding in the mouse intestine. Caspase-1 appears to play a larger role at baseline since caspase-11 expression must be first induced through proinflammatory signalling. Our data also highlights that IEC-intrinsic caspase activation is sufficient for infection-induced cell shedding and that the intestinal epithelium is a key site for inflammasome-mediated immune defense.

Human Intestinal Mononuclear Phagocytes in Health and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is a complex immune-mediated disease of the gastrointestinal tract that increases morbidity and negatively influences the quality of life. Intestinal mononuclear phagocytes (MNPs) have a crucial role in maintaining epithelial barrier integrity while controlling pathogen invasion by activating an appropriate immune response. However, in genetically predisposed individuals, uncontrolled immune activation to intestinal flora is thought to underlie the chronic mucosal inflammation that can ultimately result in IBD. Thus, MNPs are involved in fine-tuning mucosal immune system responsiveness and have a critical role in maintaining homeostasis or, potentially, the emergence of IBD. MNPs include monocytes, macrophages and dendritic cells, which are functionally diverse but highly complementary. Despite their crucial role in maintaining intestinal homeostasis, specific functions of human MNP subsets are poorly understood, especially during diseases such as IBD. Here we review the current understanding of MNP ontogeny, as well as the recently identified human intestinal MNP subsets, and discuss their role in health and IBD.

The Role of Tissue-resident T Cells in Stress Surveillance and Tissue Maintenance

While forming a minor population in the blood and lymphoid compartments, T cells are significantly enriched within barrier tissues. In addition to providing protection against infection, these tissue-resident T cells play critical roles in tissue homeostasis and repair. T cells in the epidermis and intestinal epithelium produce growth factors and cytokines that are important for the normal turnover and maintenance of surrounding epithelial cells and are additionally required for the efficient recognition of, and response to, tissue damage. A role for tissue-resident T cells is emerging outside of the traditional barrier tissues as well, with recent research indicating that adipose tissue-resident T cells are required for the normal maintenance and function of the adipose tissue compartment. Here we review the functions of tissue-resident T cells in the epidermis, intestinal epithelium, and adipose tissue, and compare the mechanisms of their activation between these sites.

Pravastatin Alleviates Radiation Proctitis by Regulating Thrombomodulin in Irradiated Endothelial Cells

Although radiotherapy plays a crucial in the management of pelvic tumors, its toxicity on surrounding healthy tissues such as the small intestine, colon, and rectum is one of the major limitations associated with its use. In particular, proctitis is a major clinical complication of pelvic radiotherapy. Recent evidence suggests that endothelial injury significantly affects the initiation of radiation-induced inflammation. The damaged endothelial cells accelerate immune cell recruitment by activating the expression of endothelial adhesive molecules, which participate in the development of tissue damage. Pravastatin, a cholesterol lowering drug, exerts persistent anti-inflammatory and anti-thrombotic effects on irradiated endothelial cells and inhibits the interaction of leukocytes and damaged endothelial cells. Here, we aimed to investigate the effects of pravastatin on radiation-induced endothelial damage in human umbilical vein endothelial cell and a murine proctitis model. Pravastatin attenuated epithelial damage and inflammatory response in irradiated colorectal lesions. In particular, pravastatin improved radiation-induced endothelial damage by regulating thrombomodulin (TM) expression. In addition, exogenous TM inhibited leukocyte adhesion to the irradiated endothelial cells. Thus, pravastatin can inhibit endothelial damage by inducing TM, thereby alleviating radiation proctitis. Therefore, we suggest that pharmacological modulation of endothelial TM may limit intestinal inflammation after irradiation.

Risk of Gastrointestinal Adverse Events in Cancer Patients Treated With Immune Checkpoint Inhibitor Plus Chemotherapy: A Systematic Review and Meta-Analysis

Background: The combination of immune checkpoint inhibitors (ICIs) and chemotherapy can improve clinical outcomes in the treatment of various tumors, but may also be associated with more adverse events (AEs). We performed a systematic review and meta-analysis to characterize the risk of gastrointestinal AEs in cancer patients treated with ICI plus chemotherapy.

Methods: This review was based on comprehensive search through PubMed, EMBASE, and the Cochrane Library for randomized controlled trials (RCTs) that reported gastrointestinal AEs following the use of ICI plus chemotherapy. Literature screening, data extraction, and quality evaluation were performed by two individual reviewers. Revman (version 5.3) was used for meta-analysis. Risk ratios (RR) with 95% confidence interval (CI) were calculated. Meta-analysis was conducted according to different types of ICIs [programmed death 1 (PD-1), programmed death ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors].

Results: After a full-text review, 10 trials involving 5,142 patients were included in the study. Compared with chemotherapy alone, PD-1 inhibitor plus chemotherapy significantly increased the risk of diarrhea (RR = 1.38, 95% CI, 1.13–1.68, P = 0.001; I² = 0%) and colitis (RR = 2.90, 95% CI, 1.02–8.21, P = 0.050; I² = 0%), PD-L1 inhibitor plus chemotherapy significantly increased the risk of nausea (RR = 1.17, 95% CI, 1.02-1.35, P = 0.020; I² = 0%), while CTLA-4 inhibitor plus chemotherapy significantly increased the risk of decreased appetite (RR = 1.49, 95% CI, 1.17–1.90, P = 0.001; I² = 0%), diarrhea (RR = 2.23, 95% CI, 1.90–2.63, P < 0.00001; I² = 0%), and colitis (RR = 28.39, 95% CI, 5.59–144.24, P < 0.001; I² = 0%).

Conclusions: This meta-analysis demonstrated that ICI plus chemotherapy is associated with a higher risk of gastrointestinal AEs. However, combining different ICIs may lead to diverse gastrointestinal toxicities. Clinicians should be aware of these AEs in the application of ICI plus chemotherapy.

Defatted Rice Bran Supplementation in Diets of Finishing Pigs: Effects on Physiological, Intestinal Barrier, and Oxidative Stress Parameters

Simple Summary

Most studies on dietary fiber mainly focus on the digestibility of feed nutrients and microbial flora, etc. However, insufficient attention has been paid to the regulation of immune and oxidative stress of the intestinal tract by dietary fiber. This study investigated the effects of varying levels of defatted rice bran replacing corn on physiological, intestinal barrier, and oxidative stress parameters in finishing pigs. Based on the current findings, a high diet of rice bran will not only reduce the level of inflammatory factors in the peripheral blood of finishing pigs, but also enhance the healthy level of the colon through mucin2 and keap1-Nrf2 pathways. Our results can be used as reference for dietary rice bran to improve intestinal health in finishing pigs.

Abstract

Rice bran is a waste product with low cost and high fiber content, giving it an added advantage over corn and soybean meal, which have to be purchased and always at a relatively higher cost. Under the background of increased attention to sustainable agriculture, it is significant to find alternative uses for this byproduct. A total of 35 finishing pigs were allotted to five dietary treatments: a control group with basal diet and four experimental diets where corn was equivalently substituted by 7%, 14%, 21%, and 28% defatted rice bran (DFRB), respectively. With increasing levels of DFRB, the neutrophil to lymphocyte ratio (NLR) linearly decreased (p < 0.05). In the jejunum, the mRNA level of nuclear factor erythroid-2 related factor-2 (Nrf2) exhibited a quadratic response (p < 0.01) with incremental levels of DFRB. In the colon, the mRNA levels of mucin 2 (MUC2), Nrf2, and NAD(P)H: quinone oxidoreductase 1 (NQO1) were upregulated (linear, p < 0.05) and heme oxygenase-1 (HO-1) was upregulated (linear, p < 0.01). Overall, using DFRB to replace corn decreased the inflammatory biomarkers of serum and showed potential function in modulating the intestinal barrier by upregulating the mRNA expression levels of MUC2 and downregulating that of Nrf2, NQO1, and HO-1 in the colon.

When Rhythms Meet the Blues: Circadian Interactions with the Microbiota-Gut-Brain Axis

The microbiota-gut-brain axis encompasses a bidirectional mode of communication between the microorganisms residing in our gut, and our brain function and behavior. The composition of the gut microbiota is subject to diurnal variation and is entrained by host circadian rhythms. In turn, a diverse microbiota is essential for optimal regulation of host circadian pathways. Disruption of the cyclical nature of this microbe-host interaction profoundly influences disease pathology and severity. This review aims to summarize current knowledge on this bidirectional relationship. Indeed, the past few years have revealed promising data regarding the relationship between the microbiota-gut-brain axis and circadian rhythms and how they act in concert to influence disease, but further research needs to be done to examine how they coalesce to modulate severity of, and risk for, certain diseases. Moreover, there is a need for a greater understanding of the molecular mechanisms underlying the close relationship between circadian-microbiome-brain interactions.