Paneth cells and innate mucosal immunity

CNPY2 drives DSS-induced colitis via the macrophage-ROS axis

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract, driven by genetic, environmental, and immune system factors. However, its exact mechanisms remain unclear. Here, we demonstrate that CNPY2 plays a critical role in colitis by modulating macrophage activity. Mice with whole-body Cnpy2 knockout (KO) exhibited significantly reduced dextran sodium sulfate (DSS)-induced colitis compared to wild-type controls. Cnpy2 KO mice showed less mucosal barrier disruption and fewer lamina propria macrophages (LPMφs) following DSS treatment. Proinflammatory cytokine production was also diminished in the colons of Cnpy2 KO mice. Furthermore, Cnpy2 KO macrophages generated markedly lower levels of reactive oxygen species (ROS), partly through CHOP regulation. Notably, treatment with the ROS scavenger N-acetyl-L-cysteine (NAC) completely abolished DSS-induced colitis in Cnpy2 KO mice. Thus, CNPY2 exacerbates DSS-induced colitis primarily through macrophage-specific effects, with ROS upregulation being central to its pathogenic role.

Effects of high-level ghrelin on intestinal epithelial cell proliferation, nutrient transport and intestinal mucosal immune barrier in chickens

1. Chicken ghrelin (GH) plays an important role in regulating growth hormone secretion, immunity and gastrointestinal motility. This study utilised haematoxylin-eosin staining, quantitative reverse transcription PCR and western blotting to examine the effects of high-level ghrelin on the proliferation of small intestinal epithelial cells, intestinal nutrient transport and the mucosal immune barrier in chicks.2. Eighty, 17-d-old layer type chicks were randomly divided into two groups: control (C treated with sterile phosphate buffer) and the ghrelin-treated group (GH; intraperitoneally injected with 0.5 nM GH per 100 g body weight). At 1, 3 and 5 d post-injection, six chicks from each group were randomly selected for sampling of the duodenum and ileum.3. Administering GH reduced the expression of proliferating cell nuclear antigen protein in the duodenum and leucine-rich repeat-containing G protein-coupled receptor 5 mRNA in both the duodenum and ileum. In addition, GH affected villus height and ratio of villus height to crypt (H/C) depth in these sections and fatty acid binding protein 6 expression in the ileum. The relative mRNA levels of oligopeptide transporter 1, solute carrier family 3 member 1, solute carrier family 1 member 1 and solute carrier family 5 member 1 were decreased by GH.4. Birds treated with GH had a decrease in duodenal intraepithelial lymphocytes, Paneth cells and ileal goblet cells. There was a reduction in mucin 2 mRNA in goblet cells and lysozyme C and phospholipaseA2 mRNA in Paneth cells. Additionally, the relative mRNA levels of avian β-defensin 1 (AvBD1), AvBD6 and AvBD7 in the duodenum and ileum decreased with GH administration.5. The GH inhibited proliferation of chicken duodenal epithelial cells and decreased surface area available for intestinal villus absorption. This affected the transport of intestinal amino acids, glucose and bile acids and impaired the function of the mucosal immune barrier in both the duodenum and ileum.

Ontogeny and function of the intestinal epithelial and innate immune cells during early development of chicks: to explore in ovo immunomodulatory nutrition

Intestinal epithelial cells (IECs) and innate immune cells in the gastrointestinal tract (GIT) of chickens play crucial roles in pathogens defense and maintaining gut health. However, their effectiveness influenced with their developmental and functional stages during pre and post hatch periods of chick. During embryonic development, differentiation and migration of these innate immune systems are tightly regulated by diverse cellular and molecular factors. The maturation and functionality of IECs are histologically evident starting embryonic day (ED) 14. Moreover, the innate immun cells, such as dendritic cells (DCs), macrophages, natural killer (NK) cells, and gamma-delta (γδ) T cells have showed developmental expression varation, while most identified by the 3rd days of incubation and capable of responsing to their cognate ligands of pathogens by ED 17, it may not efficient during posthatch period. In modern poultry production, in ovo feeding of bioactive substances is a topic of interest to maximize the protection capability of hatched chicks by enhancing improvement on the development of innate immune systems. However, their actions and effects on each distinct innate immune involved response are inconsistent and not clearly understood. Thus, summarizing the ontogeny and function of IECs, innate immunity systems, and interaction mechanisms of in ovo feeding of bioactive substances could provide baseline information for designing targeted in ovo feeding interventions to modulate cell waise specific innate immune systems.

Identification of Key Genes in Fetal Gut Development at Single-Cell Level by Exploiting Machine Learning Techniques

The study of fetal gut development is critical due to its substantial influence on immediate neonatal and long-term adult health. Current research largely focuses on microbiome colonization, gut immunity, and barrier function, alongside the impact of external factors on these phenomena. Limited research has been dedicated to the categorization of developing fetal gut cells. Our study aimed to enhance our understanding of fetal gut development by employing advanced machine-learning techniques on single-cell sequencing data. This dataset consisted of 62,849 samples, each characterized by 33,694 distinct gene features. Four feature ranking algorithms were utilized to sort features according to their significance, resulting in four feature lists. Then, these lists were fed into an incremental feature selection method to extract essential genes, classification rules, and build efficient classifiers. Several important genes were recognized by multiple feature ranking algorithms, such as FGG, MDK, RBP1, RBP2, IGFBP7, and SPON2. These features were key in differentiating specific developing intestinal cells, including epithelial, immune, mesenchymal, and vasculature cells of the colon, duo jejunum, and ileum cells. The classification rules showed special gene expression patterns on some intestinal cell types and the efficient classifiers can be useful tools for identifying intestinal cells.

Ileal Paneth Cell Phenotype is a Cellular Biomarker for Pouch Complications in Ulcerative Colitis

BACKGROUND & AIMS

Biomarkers that integrate genetic and environmental factors and predict outcome in complex immune diseases such as inflammatory bowel disease (IBD; including Crohn's disease [CD] and ulcerative colitis [UC]) are needed. We showed that morphologic patterns of ileal Paneth cells (Paneth cell phenotype [PCP]; a surrogate for PC function) is one such cellular biomarker for CD. Given the shared features between CD and UC, we hypothesized that PCP is also associated with molecular/genetic features and outcome in UC. Because PC density is highest in the ileum, we further hypothesized that PCP predicts outcome in UC subjects who underwent total colectomy and ileal pouch-anal anastomosis (IPAA).

METHODS

Uninflamed ileal resection margins from UC subjects with colectomy and IPAA were used for PCP and transcriptomic analyses. PCP was defined using defensin 5 immunofluorescence. Genotyping was performed using Immunochip. UC transcriptomic and genotype associations of PCP were incorporated with data from CD subjects to identify common IBD-related pathways and genes that regulate PCP.

RESULTS

The prevalence of abnormal ileal PCP was 27%, comparable to that seen in CD. Combined analysis of UC and CD subjects showed that abnormal PCP was associated with transcriptomic pathways of secretory granule maturation and polymorphisms in innate immunity genes. Abnormal ileal PCP at the time of colectomy was also associated with pouch complications including de novo CD in the pouch and time to first episode of pouchitis.

CONCLUSIONS

Ileal PCP is biologically and clinically relevant in UC and can be used as a biomarker in IBD.

Transcriptome-wide association studies associated with Crohn's disease: challenges and perspectives

Crohn's disease (CD) is regarded as a lifelong progressive disease affecting all segments of the intestinal tract and multiple organs. Based on genome-wide association studies (GWAS) and gene expression data, transcriptome-wide association studies (TWAS) can help identify susceptibility genes associated with pathogenesis and disease behavior. In this review, we overview seven reported TWASs of CD, summarize their study designs, and discuss the key methods and steps used in TWAS, which affect the prioritization of susceptibility genes. This article summarized the screening of tissue-specific susceptibility genes for CD, and discussed the reported potential pathological mechanisms of overlapping susceptibility genes related to CD in a certain tissue type. We observed that ileal lipid-related metabolism and colonic extracellular vesicles may be involved in the pathogenesis of CD by performing GO pathway enrichment analysis for susceptibility genes. We further pointed the low reproducibility of TWAS associated with CD and discussed the reasons for these issues, strategies for solving them. In the future, more TWAS are needed to be designed into large-scale, unified cohorts, unified analysis pipelines, and fully classified databases of expression trait loci.

Orally-administered nanomedicine systems targeting colon inflammation for the treatment of inflammatory bowel disease: latest advances

Inflammatory bowel disease (IBD) is a chronic and idiopathic condition that results in inflammation of the gastrointestinal tract, leading to conditions such as ulcerative colitis and Crohn's disease. Commonly used treatments for IBD include anti-inflammatory drugs, immunosuppressants, and antibiotics. Fecal microbiota transplantation is also being explored as a potential treatment method; however, these drugs may lead to systemic side effects. Oral administration is preferred for IBD treatment, but accurately locating the inflamed area in the colon is challenging due to multiple physiological barriers. Nanoparticle drug delivery systems possess unique physicochemical properties that enable precise delivery to the target site for IBD treatment, exploiting the increased permeability and retention effect of inflamed intestines. The first part of this review comprehensively introduces the pathophysiological environment of IBD, covering the gastrointestinal pH, various enzymes in the pathway, transport time, intestinal mucus, intestinal epithelium, intestinal immune cells, and intestinal microbiota. The second part focuses on the latest advances in the mechanism and strategies of targeted delivery using oral nanoparticle drug delivery systems for colitis-related fields. Finally, we present challenges and potential directions for future IBD treatment with the assistance of nanotechnology.

Interleukin-9 production by type 2 innate lymphoid cells induces Paneth cell metaplasia and small intestinal remodeling

Paneth cell metaplasia (PCM) typically arises in pre-existing gastrointestinal (GI) diseases; however, the mechanistic pathway that induces metaplasia and whether PCM is initiated exclusively by disorders intrinsic to the GI tract is not well known. Here, we describe the development of PCM in a murine model of chronic myelogenous leukemia (CML) that is driven by an inducible bcr-abl oncogene. Mechanistically, CML induces a proinflammatory state within the GI tract that results in the production of epithelial-derived IL-33. The binding of IL-33 to the decoy receptor ST2 leads to IL-9 production by type 2 innate lymphoid cells (ILC2) which is directly responsible for the induction of PCM in the colon and tissue remodeling in the small intestines, characterized by goblet and tuft cell hyperplasia along with expansion of mucosal mast cells. Thus, we demonstrate that an extra-intestinal disease can trigger an ILC2/IL-9 immune circuit, which induces PCM and regulates epithelial cell fate decisions in the GI tract.

Estradiol mediates colonic epithelial protection in aged mice after stroke and is associated with shifts in the gut microbiome

The gut is a major source of bacteria and antigens that contribute to neuroinflammation after brain injury. Colonic epithelial cells (ECs) are responsible for secreting major cellular components of the innate defense system, including antimicrobial proteins (AMP) and mucins. These cells serve as a critical regulator of gut barrier function and maintain host-microbe homeostasis. In this study, we determined post-stroke host defense responses at the colonic epithelial surface in mice. We then tested if the enhancement of these epithelial protective mechanisms is beneficial in young and aged mice after stroke. AMPs were significantly increased in the colonic ECs of young males, but not in young females after experimental stroke. In contrast, mucin-related genes were enhanced in young females and contributed to mucus formation that maintains the distance between the host and gut bacteria. Bacterial community profiling was done using universal amplification of 16S rRNA gene sequences. The sex-specific colonic epithelial defense responses after stroke in young females were reversed with ovariectomy and led to a shift from a predominately mucin response to the enhanced AMP expression seen in males after stroke. Estradiol (E2) replacement prior to stroke in aged females increased mucin gene expression in the colonic ECs. Interestingly, we found that E2 treatment reduced stroke-associated neuronal hyperactivity in the insular cortex, a brain region that interacts with visceral organs such as the gut, in parallel to an increase in the composition of Lactobacillus and Bifidobacterium in the gut microbiota. This is the first study demonstrating sex differences in host defense mechanisms in the gut after brain injury.

Recent Advancements in the Development of Nanocarriers for Mucosal Drug Delivery Systems to Control Oral Absorption

Oral administration of active pharmaceutical ingredients is desirable because it is easy, safe, painless, and can be performed by patients, resulting in good medication adherence. The mucus layer in the gastrointestinal (GI) tract generally acts as a barrier to protect the epithelial membrane from foreign substances; however, in the absorption process after oral administration, it can also disturb effective drug absorption by trapping it in the biological sieve structured by mucin, a major component of mucus, and eliminating it by mucus turnover. Recently, functional nanocarriers (NCs) have attracted much attention due to their immense potential and effectiveness in the field of oral drug delivery. Among them, NCs with mucopenetrating and mucoadhesive properties are promising dosage options for controlling drug absorption from the GI tracts. Mucopenetrating and mucoadhesive NCs can rapidly deliver encapsulated drugs to the absorption site and/or prolong the residence time of NCs close to the absorption membrane, providing better medications than conventional approaches. The surface characteristics of NCs are important factors that determine their functionality, owing to the formation of various kinds of interactions between the particle surface and mucosal components. Thus, a deeper understanding of surface modifications on the biopharmaceutical characteristics of NCs is necessary to develop the appropriate mucosal drug delivery systems (mDDS) for the treatment of target diseases. This review summarizes the basic information and functions of the mucosal layer, highlights the recent progress in designing functional NCs for mDDS, and discusses their performance in the GI tract.

Pouchitis Is Associated with Paneth Cell Dysfunction and Ameliorated by Exogenous Lysosome in a Rat Model Undergoing Ileal Pouch Anal Anastomosis

BACKGROUND

Pouchitis is a common complication of restorative proctocolectomy and ileal pouch anal anastomosis (IPAA) for ulcerative colitis (UC), significantly affecting the postoperative quality of life. Paneth cells play an important role in the maintenance of gut homeostasis. This study aimed to investigate the role of Paneth cells in the pathogenesis of pouchitis.

METHOD

Endoscopic biopsies from the pouch body and terminal ileum of UC patients undergoing IPAA with or without pouchitis were obtained to analyze Paneth cell function. Acute pouchitis was induced with 5% dextran sulfate sodium (DSS) for seven consecutive days in a rat model of IPAA. The Paneth cell morphology was examined by immunofluorescence and electron microscopy. The effect of exogenous lysozyme supplementation on pouchitis was also investigated. The fecal microbiota profile after DSS and lysozyme treatment was determined by 16s rRNA ITS2 sequence analysis.

RESULT

Abnormal mucosal lysozyme expression was observed in patients with pouchitis. The rat model of pouchitis showed increased pouch inflammation, increased CD3+ and CD45+ T cell infiltration, and decreased tight junction proteins, including ZO-1 and Occludin. There is a significant deficiency of Paneth cell-derived lysozyme granules in the rat model of pouchitis. Supplementation with exogenous lysozyme significantly ameliorated pouchitis, lowering the levels of inflammatory cytokines such as TNF-α and IL-6 in the pouch tissue. 16s rRNA analysis revealed a higher Lachnospiraceae level after lysosome treatment.

CONCLUSIONS

Paneth cell dysfunction is prominent in patients and rat models of pouchitis and may be one of its causes. The decrease in Lachnospiraceae, a characteristic of dysbiosis in pouchitis, could be reserved by lysosome treatment. Lysozyme supplementation shows promise as a novel treatment strategy for pouchitis.

Differential invasiveness & expression of antimicrobial peptides in Shigella serotypes

Background & objectives

The study of Shigella pathogenesis at present is severely hampered by the lack of a relevant animal model that replicates human bacillary dysentery. Different Shigella serogroups cause varying severity of clinical illness. Ex vivo colonization of Shigella flexneri, S. dysenteriae and S. sonnei were characterized in human paediatric colonic pinch biopsies in the in vitro organ culture (IVOC) model to study the invasiveness of Shigella by gentamicin protection assay (GPA). Furthermore, the expression of antimicrobial peptides (AMPs) in response to different serotypes of Shigella was also studied in IVOC model.

Methods

IVOC explants were inoculated with 109 colony forming units of different serotypes of Shigella and recovery of bacteria studied. Histopathological analysis was carried out to study inflammatory immune responses. GPA was done to elucidate the invasiveness of different serotypes of Shigella. Secretions of AMPs were measured by enzyme-linked immunosorbent assay (ELISA). Western blotting was performed to check the expression of AMPs and nuclear factor kappa B in IVOC explants.

Results

After 24 h post-infection, the colon biopsies showed intense inflammatory reaction. In both IVOC and GPA, S. dysenteriae 1 was the most invasive as compared to S. flexneri and S. sonnei. S. sonnei was the least invasive. ELISA demonstrated that S. sonnei dampened the HBD (human β-defensin)-2 responses whereas there was augmentation by S. dysenteriae and there was a modest but non-significant increase by S. flexneri. A modest increase in HBD-3 by S. sonnei and S. flexneri was observed but was not found to be significant. However, western blotting data showed upregulation of all AMPs by all serotypes. Western blotting is more sensitive than ELISA.

Interpretation & conclusions

In the present study, differences in invasiveness and AMP production induced by different serotypes of Shigella were found. Human intestinal IVOC represents a model system to investigate early interaction between pathogenic bacteria and the human gut.

TLR5 Signaling in the Regulation of Intestinal Mucosal Immunity

Toll-like receptor 5 (TLR5) is a pattern recognition receptor that specifically recognizes flagellin and consequently plays a crucial role in the control of intestinal homeostasis by activating innate and adaptive immune responses. TLR5 overexpression, on the other hand, might disrupt the intestinal mucosal barrier, which serves as the first line of defense against harmful microbes. The intestine symbiotic bacteria, mucous layer, intestinal epithelial cells (IECs), adherens junctions (such as tight junctions and peripheral membrane proteins), the intestinal mucosal immune system, and cytokines make up the intestinal mucosal barrier. Impaired barrier function has been linked to intestinal illnesses such as inflammatory bowel disease (IBD). IBD is a persistent non-specific inflammatory illness of the digestive system with an unknown cause. It is now thought to be linked to infection, environment, genes, immune system, and the gut microbiota. The significance of immunological dysfunction in IBD has received more attention in recent years. The purpose of this paper is to explore TLR5's position in the intestinal mucosal barrier and its relevance to IBD.

Food, gut barrier dysfunction, and related diseases: A new target for future individualized disease prevention and management

Dysfunction of gut barrier is known as "leaky gut" or increased intestinal permeability. Numerous recent scientific evidences showed the association between gut dysfunction and multiple gastrointestinal tract (GI) and non-GI diseases. Research also demonstrated that food plays a crucial role to cause or remedy gut dysfunction related to diseases. We reviewed recent articles from electronic databases, mainly PubMed. The data were based on animal models, cell models, and human research in vivo and in vitro models. In this comprehensive review, our aim focused on the relationship between dietary factors, intestinal permeability dysfunction, and related diseases. This review synthesizes currently available literature and is discussed in three parts: (a) the mechanism of gut barrier and function, (b) food and dietary supplements that may promote gut health, and food or medication that may alter gut function, and (c) a table that organizes the synthesized information by general mechanisms for diseases related to leaky gut/intestinal permeability and associated dietary influences. With future research, dietary intervention could be a new target for individualized disease prevention and management.

Gut microbiota promotes stem cell differentiation through macrophage and mesenchymal niches in early postnatal development

Intestinal stem cell maturation and development coincide with gut microbiota exposure after birth. Here, we investigated how early life microbial exposure, and disruption of this process, impacts the intestinal stem cell niche and development. Single-cell transcriptional analysis revealed impaired stem cell differentiation into Paneth cells and macrophage specification upon antibiotic treatment in early life. Mouse genetic and organoid co-culture experiments demonstrated that a CD206+ subset of intestinal macrophages secreted Wnt ligands, which maintained the mesenchymal niche cells important for Paneth cell differentiation. Antibiotics and reduced numbers of Paneth cells are associated with the deadly infant disease, necrotizing enterocolitis (NEC). We showed that colonization with Lactobacillus or transfer of CD206+ macrophages promoted Paneth cell differentiation and reduced NEC severity. Together, our work defines the gut microbiota-mediated regulation of stem cell niches during early postnatal development.

Neonatal microbiota-epithelial interactions that impact infection

Despite modern therapeutic developments and prophylactic use of antibiotics during birth or in the first few months of life, enteric infections continue to be a major cause of neonatal mortality and morbidity globally. The neonatal period is characterized by initial intestinal colonization with microbiota and concurrent immune system development. It is also a sensitive window during which perturbations to the environment or host can significantly impact colonization by commensal microbes. Extensive research has demonstrated that these early life alterations to the microbiota can lead to enhanced susceptibility to enteric infections and increased systemic dissemination in newborns. Various contributing factors continue to pose challenges in prevention and control of neonatal enteric infections. These include alterations in the gut microbiota composition, impaired immune response, and effects of maternal factors. In addition, there remains limited understanding for how commensal microbes impact host-pathogen interactions in newborns. In this review, we discuss the recent recognition of initial microbiota-epithelial interactions that occur in neonates and can regulate susceptibility to intestinal infection. These studies suggest the development of neonatal prophylactic or therapeutic regimens that include boosting epithelial defense through microbiota-directed interventions.

The Role of 4-Phenylbutyric Acid in Gut Microbial Dysbiosis in a Mouse Model of Simulated Microgravity

The altered gut microbes of astronauts during space travel may contribute to health issues after their return to Earth. Previously, an association between the elevated endoplasmic reticulum (ER) stress and gut microbial dysbiosis has been described. Herein, we induced gut microbial changes in mice under a simulated microgravity environment in an established model of hindlimb unloaded (HU) mice. The intestinal metabolomic profiles under microgravity conditions using the HU model were examined, along with the potential role of 4-phenylbutyric acid (4-PBA), a potent ER stress inhibitor. For a microgravity environment, the mice were suspended in special cages individually for three weeks. Mice were sacrificed, and gut dissections were performed, followed by amplicon sequencing analysis of bacterial species via DNA extraction and 16S rRNA analysis. The results indicate that the gut bacterial communities of mice differed under gravity and microgravity conditions. Principal component analyses revealed differences in the bacterial community structure in all groups. Around 434 operational taxonomic units (OTUs) were specific to mice seen in controls, while 620 OTUs were specific to HU mice. Additionally, 321 bacterial OTUs were specific to HU mice treated with 4-PBA. When the relative abundance of taxa was analyzed, Bacteroidetes dominated the gut of control and HU mice treated with 4-PBA.. In contrast, the untreated HU mice were dominated by Firmicutes. At the genus level, a reduction in beneficial species of Akkermansia and Lactobacillus was observed in HU but not the unloaded–treated and control mice. Furthermore, an increase in the relative abundance of Lachnospiraceae and Enterorhabdus, associated with inflammation, was observed in HUmice but not in controls and unloaded-treated mice. Following treatment with 4-PBA, the ratio of Firmicutes to Bacteroidetes was restored in unloaded–treated mice, comparable to controls. Of note, beneficial microbes such as Akkermansia and Lactobacillus were observed in unloaded–treated mice but not or in lesser relative abundance in HU mice. Nonetheless, microbial diversity was reduced in unloaded–treated mice compared to controls, and future studies are needed to mitigate this finding. These may comprise the addition of pre-/pro- and postbiotic species in the diet to increase microbial diversity. Overall, the findings suggest that 4-PBA, a potent ER stress inhibitor, may have therapeutic value in treating patients on prolonged bed rest or astronauts during spaceflight.

Mucus interaction to improve gastrointestinal retention and pharmacokinetics of orally administered nano-drug delivery systems

Oral delivery of therapeutics is the preferred route of administration due to ease of administration which is associated with greater patient medication adherence. One major barrier to oral delivery and intestinal absorption is rapid clearance of the drug and the drug delivery system from the gastrointestinal (GI) tract. To address this issue, researchers have investigated using GI mucus to help maximize the pharmacokinetics of the therapeutic; while mucus can act as a barrier to effective oral delivery, it can also be used as an anchoring mechanism to improve intestinal residence. Nano-drug delivery systems that use materials which can interact with the mucus layers in the GI tract can enable longer residence time, improving the efficacy of oral drug delivery. This review examines the properties and function of mucus in the GI tract, as well as diseases that alter mucus. Three broad classes of mucus-interacting systems are discussed: mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems. For each class of system, the basis for mucus interaction is presented, and examples of materials that inform the development of these systems are discussed and reviewed. Finally, a list of FDA-approved mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems is reviewed. In summary, this review highlights the progress made in developing mucus-interacting systems, both at a research-scale and commercial-scale level, and describes the theoretical basis for each type of system.

Diet and feeding pattern modulate diurnal dynamics of the ileal microbiome and transcriptome

Compositional oscillations of the gut microbiome are essential for normal peripheral circadian rhythms, both of which are disrupted in diet-induced obesity (DIO). Although time-restricted feeding (TRF) maintains circadian synchrony and protects against DIO, its impact on the dynamics of the cecal gut microbiome is modest. Thus, other regions of the gut, particularly the ileum, the nexus for incretin and bile acid signaling, may play an important role in entraining peripheral circadian rhythms. We demonstrate the effect of diet and feeding rhythms on the ileal microbiome composition and transcriptome in mice. The dynamic rhythms of ileal microbiome composition and transcriptome are dampened in DIO. TRF partially restores diurnal rhythms of the ileal microbiome and transcriptome, increases GLP-1 release, and alters the ileal bile acid pool and farnesoid X receptor (FXR) signaling, which could explain how TRF exerts its metabolic benefits. Finally, we provide a web resource for exploration of ileal microbiome and transcriptome circadian data.

The Pathology and Physiology of Ileostomy

An ileostomy is a surgery that is commonly performed to protect low pelvic anastomoses or prevent high-risk anastomotic leakages. However, various postoperative complications remain of major concern. After an ileostomy, the distal intestinal segment is left open for an extended period and is in a non-functional state. Consequently, the intestinal mucosa, smooth muscle, and microbiota undergo significant changes that are closely related to postoperative recovery and complications. A systematic description of these changes is necessary to understand the relationship among them and take more effective measures for postoperative intervention.

Inflammatory and Microbiota-Related Regulation of the Intestinal Epithelial Barrier

The intestinal epithelial barrier (IEB) is one of the largest interfaces between the environment and the internal milieu of the body. It is essential to limit the passage of harmful antigens and microorganisms and, on the other side, to assure the absorption of nutrients and water. The maintenance of this delicate equilibrium is tightly regulated as it is essential for human homeostasis. Luminal solutes and ions can pass across the IEB via two main routes: the transcellular pathway or the paracellular pathway. Tight junctions (TJs) are a multi-protein complex responsible for the regulation of paracellular permeability. TJs control the passage of antigens through the IEB and have a key role in maintaining barrier integrity. Several factors, including cytokines, gut microbiota, and dietary components are known to regulate intestinal TJs. Gut microbiota participates in several human functions including the modulation of epithelial cells and immune system through the release of several metabolites, such as short-chain fatty acids (SCFAs). Mediators released by immune cells can induce epithelial cell damage and TJs dysfunction. The subsequent disruption of the IEB allows the passage of antigens into the mucosa leading to further inflammation. Growing evidence indicates that dysbiosis, immune activation, and IEB dysfunction have a role in several diseases, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and gluten-related conditions. Here we summarize the interplay between the IEB and gut microbiota and mucosal immune system and their involvement in IBS, IBD, and gluten-related disorders.

Western diet induces Paneth cell defects through microbiome alterations and farnesoid X receptor and type I interferon activation

Intestinal Paneth cells modulate innate immunity and infection. In Crohn's disease, genetic mutations together with environmental triggers can disable Paneth cell function. Here, we find that a western diet (WD) similarly leads to Paneth cell dysfunction through mechanisms dependent on the microbiome and farnesoid X receptor (FXR) and type I interferon (IFN) signaling. Analysis of multiple human cohorts suggests that obesity is associated with Paneth cell dysfunction. In mouse models, consumption of a WD for as little as 4 weeks led to Paneth cell dysfunction. WD consumption in conjunction with Clostridium spp. increased the secondary bile acid deoxycholic acid levels in the ileum, which in turn inhibited Paneth cell function. The process required excess signaling of both FXR and IFN within intestinal epithelial cells. Our findings provide a mechanistic link between poor diet and inhibition of gut innate immunity and uncover an effect of FXR activation in gut inflammation.

Morph-anatomic and histochemical study of ileum of goose (Alopochen egyptiacus) with special references to immune cells, mucous and serous goblet cells, telocytes, and dark and light smooth muscle fibers

The morphological characteristics of the ileum of 20 adult male Egyptian geese were determined using LM, SEM, and TEM. The mean length of the ileum in the male goose was approximately 158.71 mm, representing nearly 10.19% of the total length of the small intestine. The ileum is composed of four layers: mucosa, submucosa, muscular layer, and serosa. The mucosal layer comprises the epithelium, lamina propria, and muscularis mucosa. The mucosa forms finger-like villi and is invaginated at the bases, forming the crypts of Lieberkühn. The ileum is lined by simple columnar epithelium that contains absorptive dark and light enterocytes with two types of goblet cells (mucous and serous varieties) microfold like cells, dendritic reticulum cells, Paneth cells, and a closed type of enteroendocrine cells. The lamina propria has diffuse lymphoid tissue containing lymphocytes, macrophages, mast cells, plasma cells, and heterophils as well as telocytes. The muscularis mucosa comprises circular smooth muscle fibers extending into the core of the villi. The submucosa is a thin layer of elastic-rich connective tissue. The muscular level consists of four layers, with light and dark smooth muscle fibers. We described in detail the structure of all cellular components and histomorphometric measurements.

Endoplasmic Reticulum Stress and Intestinal Inflammation: A Perilous Union

The intestinal tract encompasses the largest mucosal surface fortified with a fine layer of intestinal epithelial cells along with highly sophisticated network of the lamina propria immune cells that are indispensable to sustain gut homeostasis. However, it can be challenging to uphold homeostasis when these cells in the intestine are perpetually exposed to insults of both endogenous and exogenous origin. The complex networking and dynamic microenvironment in the intestine demand highly functional cells ultimately burdening the endoplasmic reticulum (ER) leading to ER stress. Unresolved ER stress is one of the primary contributors to the pathogenesis of inflammatory bowel diseases (IBD). Studies also suggest that ER stress can be the primary cause of inflammation and/or the consequence of inflammation. Therefore, understanding the patterns of expression of ER stress regulators and deciphering the intricate interplay between ER stress and inflammatory pathways in intestinal epithelial cells in association with lamina propria immune cells contribute toward the development of novel therapies to tackle IBD. This review provides imperative insights into the molecular markers involved in the pathogenesis of IBD by potentiating ER stress and inflammation and briefly describes the potential pharmacological intervention strategies to mitigate ER stress and IBD. In addition, genetic mutations in the biomarkers contributing to abnormalities in the ER stress signaling pathways further emphasizes the relevance of biomarkers in potential treatment for IBD.

Regulation of autophagy by canonical and non-canonical ER stress responses

Cancer cells encounter numerous stresses that pose a threat to their survival. Tumor microenviroment stresses that perturb protein homeostasis can produce endoplasmic reticulum (ER) stress, which can be counterbalanced by triggering the unfolded protein response (UPR) which is considered the canonical ER stress response. The UPR is characterized by three major proteins that lead to specific changes in transcriptional and translational programs in stressed cells. Activation of the UPR can induce apoptosis, but also can induce cytoprotective programs such as autophagy. There is increasing appreciation for the role that UPR-induced autophagy plays in supporting tumorigenesis and cancer therapy resistance. More recently several new pathways that connect cell stresses, components of the UPR and autophagy have been reported, which together can be viewed as non-canonical ER stress responses. Here we review recent findings on the molecular mechanisms by which canonical and non-canonical ER stress responses can activate cytoprotective autophagy and contribute to tumor growth and therapy resistance. Autophagy has been identified as a druggable pathway, however the components of autophagy (ATG genes) have proven difficult to drug. It may be the case that targeting the UPR or non-canonical ER stress programs can more effectively block cytoprotective autophagy to enhance cancer therapy. A deeper understanding of these pathways could provide new therapeutic targets in cancer.

Microbe-Driven Genotoxicity in Gastrointestinal Carcinogenesis

The intestinal epithelium serves as a barrier to discriminate the outside from the inside and is in constant exchange with the luminal contents, including nutrients and the microbiota. Pathogens have evolved mechanisms to overcome the multiple ways of defense in the mucosa, while several members of the microbiota can exhibit pathogenic features once the healthy barrier integrity of the epithelium is disrupted. This not only leads to symptoms accompanying the acute infection but may also contribute to long-term injuries such as genomic instability, which is linked to mutations and cancer. While for Helicobacter pylori a link between infection and cancer is well established, many other bacteria and their virulence factors have only recently been linked to gastrointestinal malignancies through epidemiological as well as mechanistic studies. This review will focus on those pathogens and members of the microbiota that have been linked to genotoxicity in the context of gastric or colorectal cancer. We will address the mechanisms by which such bacteria establish contact with the gastrointestinal epithelium-either via an existing breach in the barrier or via their own virulence factors as well as the mechanisms by which they interfere with host genomic integrity.

The Role of the Gastrointestinal Mucus System in Intestinal Homeostasis: Implications for Neurological Disorders

Mucus is integral to gut health and its properties may be affected in neurological disease. Mucus comprises a hydrated network of polymers including glycosylated mucin proteins. We propose that factors that influence the nervous system may also affect the volume, viscosity, porosity of mucus composition and subsequently, gastrointestinal (GI) microbial populations. The gut has its own intrinsic neuronal network, the enteric nervous system, which extends the length of the GI tract and innervates the mucosal epithelium. The ENS regulates gut function including mucus secretion and renewal. Both dysbiosis and gut dysfunction are commonly reported in several neurological disorders such as Parkinson's and Alzheimer's disease as well in patients with neurodevelopmental disorders including autism. Since some microbes use mucus as a prominent energy source, changes in mucus properties could alter, and even exacerbate, dysbiosis-related gut symptoms in neurological disorders. This review summarizes existing knowledge of the structure and function of the mucus of the GI tract and highlights areas to be addressed in future research to better understand how intestinal homeostasis is impacted in neurological disorders.

The Paneth Cell: The Curator and Defender of the Immature Small Intestine

Paneth cells were first described in the late 19th century by Gustav Schwalbe and Josef Paneth as columnar epithelial cells possessing prominent eosinophilic granules in their cytoplasm. Decades later there is continued interest in Paneth cells as they play an integral role in maintaining intestinal homeostasis and modulating the physiology of the small intestine and its associated microbial flora. Paneth cells are highly specialized secretory epithelial cells located in the small intestinal crypts of Lieberkühn. The dense granules produced by Paneth cells contain an abundance of antimicrobial peptides and immunomodulating proteins that function to regulate the composition of the intestinal flora. This in turn plays a significant role in secondary regulation of the host microvasculature, the normal injury and repair mechanisms of the intestinal epithelial layer, and the levels of intestinal inflammation. These critical functions may have even more importance in the immature intestine of premature infants. While Paneth cells begin to develop in the middle of human gestation, they do not become immune competent or reach their adult density until closer to term gestation. This leaves preterm infants deficient in normal Paneth cell biology during the greatest window of susceptibility to develop intestinal pathology such as necrotizing enterocolitis (NEC). As 10% of infants worldwide are currently born prematurely, there is a significant population of infants contending with an inadequate cohort of Paneth cells. Infants who have developed NEC have decreased Paneth cell numbers compared to age-matched controls, and ablation of murine Paneth cells results in a NEC-like phenotype suggesting again that Paneth cell function is critical to homeostasis to the immature intestine. This review will provide an up to date and comprehensive look at Paneth cell ontogeny, the impact Paneth cells have on the host-microbial axis in the immature intestine, and the repercussions of Paneth cell dysfunction or loss on injury and repair mechanisms in the immature gut.

Crohn's disease

Crohn's disease is an inflammatory bowel disease that is characterized by chronic inflammation of any part of the gastrointestinal tract, has a progressive and destructive course and is increasing in incidence worldwide. Several factors have been implicated in the cause of Crohn's disease, including a dysregulated immune system, an altered microbiota, genetic susceptibility and environmental factors, but the cause of the disease remains unknown. The onset of the disease at a young age in most cases necessitates prompt but long-term treatment to prevent disease flares and disease progression with intestinal complications. Thus, earlier, more aggressive treatment with biologic therapies or novel small molecules could profoundly change the natural history of the disease and decrease complications and the need for hospitalization and surgery. Although less invasive biomarkers are in development, diagnosis still relies on endoscopy and histological assessment of biopsy specimens. Crohn's disease is a complex disease, and treatment should be personalized to address the underlying pathogenetic mechanism. In the future, disease management might rely on severity scores that incorporate prognostic factors, bowel damage assessment and non-invasive close monitoring of disease activity to reduce the severity of complications.

Enteroendocrine and tuft cells support Lgr5 stem cells on Paneth cell depletion

Cycling intestinal Lgr5⁺ stem cells are intermingled with their terminally differentiated Paneth cell daughters at crypt bottoms. Paneth cells provide multiple secreted (e.g., Wnt, EGF) as well as surface-bound (Notch ligand) niche signals. Here we show that ablation of Paneth cells in mice, using a diphtheria toxin receptor gene inserted into the P-lysozyme locus, does not affect the maintenance of Lgr5⁺ stem cells. Flow cytometry, single-cell sequencing, and histological analysis showed that the ablated Paneth cells are replaced by enteroendocrine and tuft cells. As these cells physically occupy Paneth cell positions between Lgr5 stem cells, they serve as an alternative source of Notch signals, which are essential for Lgr5⁺ stem cell maintenance. Our combined in vivo results underscore the adaptive flexibility of the intestine in maintaining normal tissue homeostasis.

Functional Changes of Paneth Cells in the Intestinal Epithelium of Mice with Obstructive Jaundice and After Internal and External Biliary Drainage

OBJECTIVE

To investigate the functional changes of Paneth cells in the intestinal epithelium of mice with obstructive jaundice (OJ) and after internal biliary drainage (ID) and external biliary drainage (ED).

METHODS

The experiment was divided into two stages. First stage: Mice were randomly assigned to two groups: (I) sham operation (SH); (II) OJ. The mice were sacrificed before the operation and on the 1st, 3rd, 5th and 7th day after the operation to collect specimens. Second stage: Mice were randomly assigned to four groups: (I) SH; (II) OJ; (III) OJ and ED; and (IV) OJ and ID. They were reoperated on day 5 for biliary drainage procedure. The specimens were collected on day 10.

RESULTS

The expressions of lysozyme and cryptdin-4 increased first and then decreased over time in group OJ, and the number of Paneth cells decreased gradually with the extension of OJ time（p<0.05. After the secondary operation on the mice to relieve OJ, the number of Paneth cells and expressions of lysozyme and cryptdin-4 in group ID increased more significantly than those in group ED（p<0.05）.

CONCLUSION

OJ could cause intestinal Paneth cells to dysfunction in mice. ID was more significant than ED in restoring the function of Paneth cells. It might be one of the mechanisms that make ID superior to ED.

Role for diet in normal gut barrier function: developing guidance within the framework of food-labeling regulations

A reduction in intestinal barrier function is currently believed to play an important role in pathogenesis of many diseases, as it facilitates passage of injurious factors such as lipopolysaccharide, peptidoglycan, whole bacteria, and other toxins to traverse the barrier to damage the intestine or enter the portal circulation. Currently available evidence in animal models and in vitro systems has shown that certain dietary interventions can be used to reinforce the intestinal barrier to prevent the development of disease. The relevance of these studies to human health is unknown. Herein, we define the components of the intestinal barrier, review available modalities to assess its structure and function in humans, and review the available evidence in model systems or perturbations in humans that diet can be used to fortify intestinal barrier function. Acknowledging the technical challenges and the present gaps in knowledge, we provide a conceptual framework by which evidence could be developed to support the notion that diet can reinforce human intestinal barrier function to restore normal function and potentially reduce the risk for disease. Such evidence would provide information on the development of healthier diets and serve to provide a framework by which federal agencies such as the US Food and Drug Administration can evaluate evidence linking diet with normal human structure/function claims focused on reducing risk of disease in the general public.

Circulating LPS and (1→3)-β-D-Glucan: A Folie à Deux Contributing to HIV-Associated Immune Activation

Immune activation is the driving force behind the occurrence of AIDS and non-AIDS events, and is only partially reduced by antiretroviral therapy (ART). Soon after HIV infection, intestinal CD4+ T cells are depleted leading to epithelial gut damage and subsequent translocation of microbes and/or their products into systemic circulation. Bacteria and fungi are the two most abundant populations of the gut microbiome. Circulating lipopolysaccharide (LPS) and (1→3)-β-D-Glucan (βDG), major components of bacterial and fungal cell walls respectively, are measured as markers of microbial translocation in the context of compromised gut barriers. While LPS is a well-known inducer of innate immune activation, βDG is emerging as a significant source of monocyte and NK cell activation that contributes to immune dysfunction. Herein, we critically evaluated recent literature to untangle the respective roles of LPS and βDG in HIV-associated immune dysfunction. Furthermore, we appraised the relevance of LPS and βDG as biomarkers of disease progression and immune activation on ART. Understanding the consequences of elevated LPS and βDG on immune activation will provide insight into novel therapeutic strategies against the occurrence of AIDS and non-AIDS events.

Roles of Autophagy-Related Genes in the Pathogenesis of Inflammatory Bowel Disease

Autophagy is an intracellular catabolic process that is essential for a variety of cellular responses. Due to its role in the maintenance of biological homeostasis in conditions of stress, dysregulation or disruption of autophagy may be linked to human diseases such as inflammatory bowel disease (IBD). IBD is a complicated inflammatory colitis disorder; Crohn’s disease and ulcerative colitis are the principal types. Genetic studies have shown the clinical relevance of several autophagy-related genes (ATGs) in the pathogenesis of IBD. Additionally, recent studies using conditional knockout mice have led to a comprehensive understanding of ATGs that affect intestinal inflammation, Paneth cell abnormality and enteric pathogenic infection during colitis. In this review, we discuss the various ATGs involved in macroautophagy and selective autophagy, including ATG16L1, IRGM, LRRK2, ATG7, p62, optineurin and TFEB in the maintenance of intestinal homeostasis. Although advances have been made regarding the involvement of ATGs in maintaining intestinal homeostasis, determining the precise contribution of autophagy has remained elusive. Recent efforts based on direct targeting of ATGs and autophagy will further facilitate the development of new therapeutic opportunities for IBD.

Deficiency in intestinal epithelial Reg4 ameliorates intestinal inflammation and alters the colonic bacterial composition

The regenerating islet-derived family member 4 (Reg4) in the gastrointestinal tract is up-regulated during intestinal inflammation. However, the physiological function of Reg4 in the inflammation is largely unknown. In the current study, the functional roles and involved mechanisms of intestinal epithelial Reg4 in intestinal inflammation were studied in healthy and inflamed states using human intestinal specimens, an intestinal conditional Reg4 knockout mouse (Reg4^ΔIEC) model and dextran sulfate sodium (DSS)-induced colitis model. We showed that the elevated serum Reg4 in pediatric intestinal failure (IF) patients were positively correlated with the serum concentrations of proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). In inflamed intestine of IF patients, the crypt base Reg4 protein was increased and highly expressed towards the luminal face. The Reg4 was indicated as a novel target of activating transcription factor 2 (ATF2) that enhanced Reg4 expression during the intestinal inflammation. In vivo, the DSS-induced colitis was significantly ameliorated in Reg4^ΔIEC mice. Reg4^ΔIEC mice altered the colonic bacterial composition and reduced the bacteria adhere to the colonic epithelium. In vitro, Reg4 was showed to promote the growth of colonic organoids, and that this occurs through a mechanism involving activation of signal transducer and activator of transcription 3 (STAT3). In conclusion, our findings demonstrated intestinal-epithelial Reg4 deficiency protects against experimental colitis and mucosal injury via a mechanism involving alteration of bacterial homeostasis and STAT3 activation.

The enteric microbiota regulates jejunal Paneth cell number and function without impacting intestinal stem cells

Paneth cells (PCs) are epithelial cells found in the small intestine, next to intestinal stem cells (ISCs) at the base of the crypts. PCs secrete antimicrobial peptides (AMPs) that regulate the commensal gut microbiota. In contrast, little is known regarding how the enteric microbiota reciprocally influences PC function. In this study, we sought to characterize the impact of the enteric microbiota on PC biology in the mouse small intestine. This was done by first enumerating jejunal PCs in germ-free (GF) versus conventionally raised (CR) mice. We next evaluated the possible functional consequences of altered PC biology in these experimental groups by assessing epithelial proliferation, ISC numbers, and the production of AMPs. We found that PC numbers were significantly increased in CR versus GF mice; however, there were no differences in ISC numbers or cycling activity between groups. Of the AMPs assessed, only Reg3γ transcript expression was significantly increased in CR mice. Intriguingly, this increase was abrogated in cultured CR versus GF enteroids, and could not be re-induced with various bacterial ligands. Our findings demonstrate the enteric microbiota regulates PC function by increasing PC numbers and inducing Reg3γ expression, though the latter effect may not involve direct interactions between bacteria and the intestinal epithelium. In contrast, the enteric microbiota does not appear to regulate jejunal ISC census and proliferation. These are critical findings for investigators using GF mice and the enteroid system to study PC and ISC biology.

Mouse intestinal niche cells express a distinct α1,2-fucosylated glycan recognized by a lectin from Burkholderia cenocepacia

In this study, we examined the distribution of fucosylated glycans in mouse intestines using a lectin, BC2LCN (N-terminal domain of the lectin BC2L-C from Burkholderia cenocepacia), as a probe. BC2LCN is specific for glycans with a terminal Fucα1,2Galβ1,3-motif and it is a useful marker for discriminating the undifferentiated status of human induced/embryonic stem cells. Apparent BC2LCN reactivity was detected in the secretory granules of goblet cells in the ileum but not those in the colon. We also found distinctive reactivity in the crypt bottom, which is known as the stem cell zone, of the colon and the ileum. Other lectins for fucosylated glycans, including Ulex europaeus agglutinin-I, Pholiota squarrosa lectin and Aleuria aurantia lectin, did not exhibit similar reactivity in the crypt bottom. Remarkably, BC2LCN-positive epithelial cells could be labeled with a niche cell marker, c-Kit/CD117. Overall, our results indicate that intestinal niche cells express distinct fucosylated glycans recognized by BC2LCN. Increasing evidence suggests that the self-renewal and proliferation of stem cells depend on specific signals derived from niche cells. Our results highlight novel molecular properties of intestinal niche cells in terms of their glycosylation, which may help to understand the regulation of intestinal stem cells. The distinct expression of glycans may reflect the functional roles of niche cells. BC2LCN is a valuable tool for investigating the functional significance of protein glycosylation in stem cell regulation.

Expression of neutrophil gelatinase-associated lipocalin (NGAL) in the gut in Crohn's disease

The antimicrobial glycoprotein neutrophil gelatinase-associated lipocalin (NGAL) is strongly expressed in several infectious, inflammatory and malignant disorders, among these inflammatory bowel disease (IBD). Fecal and serum NGAL is elevated during active IBD and we have recently shown that fecal NGAL is a novel biomarker for IBD with a test performance comparable to the established fecal biomarker calprotectin. This study examines expression of NGAL in the healthy gut and in Crohn’s disease (CD), with emphasis on the previously unexplored small intestine. Pinch biopsies were taken from active and inactive CD in jejunum, ileum and colon and from the same sites in healthy controls. Microarray gene expression showed that the NGAL gene, LCN2, was the second most upregulated among 1820 differentially expressed genes in terminal ileum comparing active CD and controls (FC 5.86, p = 0.027). Based on immunohistochemistry and in situ hybridization findings, this upregulation most likely represented increased expression in epithelial cells. Double immunofluorescence showed NGAL expression in 49% (range 19–70) of Paneth cells (PCs) in control ileum with no change during inflammation. In healthy jejunum, the NGAL expression in PCs was weak to none but markedly increased during active CD. We further found NGAL also in metaplastic PCs in colon. Finally, we show for the first time that NGAL is expressed in enteroendocrine cells in small intestine as well as in colon.

Innate Recognition of the Microbiota by TLR1 Promotes Epithelial Homeostasis and Prevents Chronic Inflammation

There is cross-talk between the intestinal epithelium and the microbiota that functions to maintain a tightly regulated microenvironment and prevent chronic inflammation. This communication is partly mediated through the recognition of bacterial proteins by host-encoded innate receptors, such as TLRs. However, studies examining the role of TLR signaling on colonic homeostasis have given variable and conflicting results. Despite its critical role in mediating immunity during enteric infection of the small intestine, TLR1-mediated recognition of microbiota-derived ligands and their influence on colonic homeostasis has not been well studied. In this study, we demonstrate that defective TLR1 recognition of the microbiome by epithelial cells results in disruption of crypt homeostasis specifically within the secretory cell compartment, including a defect in the mucus layer, ectopic Paneth cells in the colon, and an increase in the number of rapidly dividing cells at the base of the crypt. As a consequence of the perturbed epithelial barrier, we found an increase in mucosal-associated and translocated commensal bacteria and chronic low-grade inflammation characterized by an increase in lineage-negative Sca1⁺Thy1^hi innate lymphoid-like cells that exacerbate inflammation and worsen outcomes in a model of colonic injury and repair. Our findings demonstrate that sensing of the microbiota by TLR1 may provide key signals that regulate the colonic epithelium, thereby limiting inflammation through the prevention of bacterial attachment to the mucosa and exposure to the underlying immune system.

Paneth Cells during Viral Infection and Pathogenesis

Paneth cells are major secretory cells located in the crypts of Lieberk&uuml;hn in the small intestine. Our understanding of the diverse roles that Paneth cells play in homeostasis and disease has grown substantially since their discovery over a hundred years ago. Classically, Paneth cells have been characterized as a significant source of antimicrobial peptides and proteins important in host defense and shaping the composition of the commensal microbiota. More recently, Paneth cells have been shown to supply key developmental and homeostatic signals to intestinal stem cells in the crypt base. Paneth cell dysfunction leading to dysbiosis and a compromised epithelial barrier have been implicated in the etiology of Crohn&rsquo;s disease and susceptibility to enteric bacterial infection. Our understanding of the impact of Paneth cells on viral infection is incomplete. Enteric &alpha;-defensins, produced by Paneth cells, can directly alter viral infection. In addition, &alpha;-defensins and other antimicrobial Paneth cell products may modulate viral infection indirectly by impacting the microbiome. Here, we discuss recent insights into Paneth cell biology, models to study their function, and the impact, both direct and indirect, of Paneth cells on enteric viral infection.

Impact of Paneth Cell Autophagy on Inflammatory Bowel Disease

Intestinal mucosal barrier, mainly consisting of the mucus layer and epithelium, functions in absorbing nutrition as well as prevention of the invasion of pathogenic microorganisms. Paneth cell, an important component of mucosal barrier, plays a vital role in maintaining the intestinal homeostasis by producing antimicrobial materials and controlling the host-commensal balance. Current evidence shows that the dysfunction of intestinal mucosal barrier, especially Paneth cell, participates in the onset and progression of inflammatory bowel disease (IBD). Autophagy, a cellular stress response, involves various physiological processes, such as secretion of proteins, production of antimicrobial peptides, and degradation of aberrant organelles or proteins. In the recent years, the roles of autophagy in the pathogenesis of IBD have been increasingly studied. Here in this review, we mainly focus on describing the roles of Paneth cell autophagy in IBD as well as several popular autophagy-related genetic variants in Penath cell and the related therapeutic strategies against IBD.

Loss of Paneth Cell Autophagy Causes Acute Susceptibility to Toxoplasma gondii-Mediated Inflammation

The protozoan parasite Toxoplasma gondii triggers severe small intestinal immunopathology characterized by IFN-γ- and intestinal microbiota-mediated inflammation, Paneth cell loss, and bacterial dysbiosis. Paneth cells are a prominent secretory epithelial cell type that resides at the base of intestinal crypts and releases antimicrobial peptides. We demonstrate that the microbiota triggers basal Paneth cell-specific autophagy via induction of IFN-γ, a known trigger of autophagy, to maintain intestinal homeostasis. Deletion of the autophagy protein Atg5 specifically in Paneth cells results in exaggerated intestinal inflammation characterized by complete destruction of the intestinal crypts resembling that seen in pan-epithelial Atg5-deficient mice. Additionally, lack of functional autophagy in Paneth cells within intestinal organoids and T. gondii-infected mice causes increased sensitivity to the proinflammatory cytokine TNF along with increased intestinal permeability, leading to exaggerated microbiota- and IFN-γ-dependent intestinal immunopathology. Thus, Atg5 expression in Paneth cells is essential for tissue protection against cytokine-mediated immunopathology during acute gastrointestinal infection.

A slippery slope: On the origin, role and physiology of mucus

The mucosa of the gastrointestinal tract, eyes, nose, lungs, cervix and vagina is lined by epithelium interspersed with mucus-secreting goblet cells, all of which contribute to their unique functions. This mucus provides an integral defence to the epithelium against noxious agents and pathogens. However, it can equally act as a barrier to drugs and delivery systems targeting epithelial passive and active transport mechanisms. This review highlights the various mucins expressed at different mucosal surfaces on the human body, and their role in creating a mucoid architecture to protect epithelia with specialized functions. Various factors compromising the barrier properties of mucus have been discussed, with an emphasis on how disease states and microbiota can alter the physical properties of mucus. For instance, Akkermansia muciniphila, a bacterium found in higher levels in the gut of lean individuals induces the production of a thickened gut mucus layer. The aims of this article are to elucidate the different physiological, biochemical and physical properties of bodily mucus, a keen appreciation of which will help circumvent the slippery slope of challenges faced in achieving effective mucosal drug and gene delivery.

Bacterial Signaling at the Intestinal Epithelial Interface in Inflammation and Cancer

The gastrointestinal (GI) tract provides a compartmentalized interface with an enormous repertoire of immune and metabolic activities, where the multicellular structure of the mucosa has acquired mechanisms to sense luminal factors, such as nutrients, microbes, and a variety of host-derived and microbial metabolites. The GI tract is colonized by a complex ecosystem of microorganisms, which have developed a highly coevolved relationship with the host’s cellular and immune system. Intestinal epithelial pattern recognition receptors (PRRs) substantially contribute to tissue homeostasis and immune surveillance. The role of bacteria-derived signals in intestinal epithelial homeostasis and repair has been addressed in mouse models deficient in PRRs and signaling adaptors. While critical for host physiology and the fortification of barrier function, the intestinal microbiota poses a considerable health challenge. Accumulating evidence indicates that dysbiosis is associated with the pathogenesis of numerous GI tract diseases, including inflammatory bowel diseases (IBD) and colorectal cancer (CRC). Aberrant signal integration at the epithelial cell level contributes to such diseases. An increased understanding of bacterial-specific structure recognition and signaling mechanisms at the intestinal epithelial interface is of great importance in the translation to future treatment strategies. In this review, we summarize the growing understanding of the regulation and function of the intestinal epithelial barrier, and discuss microbial signaling in the dynamic host–microbe mutualism in both health and disease.