Changes at small intestine induced by food-fish contaminated with ciguatoxins.

Ciguateric syndrome is a food poisoning associated with the consumption of some species of fish that have accumulated ciguatoxins (CTXs) in their tissues. The effects of the syndrome occur with nervous imbalances which have been described for quite some time, and mentioned in sailing literature for centuries. In the last decade, research has been focused on the implementation of analytical methods for toxin identification and the study of action modes of CTXs to design effective treatments. However, an important aspect is to determine the damage that CTXs caused in the organs of affected individuals. In this work, the damages observed in tissues of mice, mainly in the small intestine, were analyzed. The animals were fed with CTX-contaminated fish muscle at concentrations 10-times below the median lethal dose (LD50) for 10 weeks. The analysis of tissues derived from the oral treatment resulted in an increased occurrence of Paneth cells, presence of lymphoid tissue infiltrating the mucosa and fibrous lesions in the mucosal layer of the small intestine. A decreasing weight in animals fed with toxic muscle was observed.

Microbiota and angiogenesis in the intestinal vasculature.

The gut microbiota is responsible for several metabolic functions, producing various metabolites with numerous roles for the host. The gut microbiota plays a key role in constructing the microvascular network in the intestinal villus, depending on the Paneth cells, strategically positioned to coordinate the development of both the microbiota and the microvasculature. The gut microbiota secretes several molecules and chemokines involved in the induction of the secretion of pro-angiogenic factors.

Establishment of a 3D organoid culture model for the investigation of adult slow-cycling putative intestinal stem cells.

The study of intestinal stem cells is a prerequisite for the development of therapies aimed at regenerating the gut. To enable investigation of adult slow-cycling H2B-GFP-retaining putative small intestinal (SI) stem cells in vitro, we have developed a three-dimensional (3D) SI organoid culture model based on the Tet-Op histone 2 B (H2B)-green fluorescent protein (GFP) fusion protein (Tet-Op-H2B-GFP) transgenic mouse. SI crypts were isolated from 6- to 12-week-old Tet-Op-H2B-GFP transgenic mice and cultured with appropriate growth factors and an animal-derived matrix (Matrigel). For in vitro transgene expression, doxycycline was added to the culture medium for 24 h. By pulse-chase experiments, H2B-GFP expression and retention were assessed through direct GFP fluorescence observations, both by confocal and fluorescence microscopy and by immunohistochemistry. The percentages of H2B-GFP-retaining putative SI stem cells and H2B-GFP-retaining Paneth cells persisting in organoids were determined by scoring relevant GFP-positive cells. Our results indicate that 24 h exposure to doxycycline (pulse) induced ubiquitous expression of H2B-GFP in the SI organoids. During subsequent culture, in the absence of doxycycline (chase), there was a gradual loss (due to cell division) of H2B-GFP. At 6-day chase, slow-cycling H2B-GFP-retaining putative SI stem cells and H2B-GFP-retaining Paneth cells were detected in the SI organoids. The developed culture model allows detection of slow-cycling H2B-GFP-retaining putative SI stem cells and will enable the study of self-renewal and regeneration for further characterization of these cells.

IFN-γ stimulates Paneth cell secretion through necroptosis mTORC1 dependent.

Immune mediators affect multiple biological functions of intestinal epithelial cells (IECs) and, like Paneth and Paneth-like cells, play an important role in intestinal epithelial homeostasis. IFN-γ a prototypical proinflammatory cytokine disrupts intestinal epithelial homeostasis. However, the mechanism underlying the process remains unknown. In this study, using in vivo and in vitro models we demonstrate that IFN-γ is spontaneously secreted in the small intestine. Furthermore, we observed that this cytokine stimulates mitochondrial activity, ROS production, and Paneth and Paneth-like cell secretion. Paneth and Paneth-like secretion downstream of IFN-γ, as identified here, is mTORC1 and necroptosis-dependent. Thus, our findings revealed that the pleiotropic function of IFN-γ also includes the regulation of Paneth cell function in the homeostatic gut.

Intestinal Epithelial Axin1 Deficiency Protects Against Colitis via Altered Gut Microbiota.

Intestinal homeostasis is maintained by specialized host cells and the gut microbiota. Wnt/ß-catenin signaling is essential for gastrointestinal development and homeostasis, and its dysregulation has been implicated in inflammation and colorectal cancer. Axin1 negatively regulates activated Wnt/ß-catenin signaling, but little is known regarding its role in regulating host-microbial interactions in health and disease. Here, we aim to demonstrate that intestinal Axin1 determines gut homeostasis and host response to inflammation. Axin1 expression was analyzed in human inflammatory bowel disease datasets. To explore the effects and mechanism of intestinal Axin1 in regulating intestinal homeostasis and colitis, we generated new mouse models with Axin1 conditional knockout in intestinal epithelial cell (IEC; Axin1 ΔIEC) and Paneth cell (PC; Axin1 ΔPC) to compare with control (Axin1 LoxP; LoxP: locus of X-over, P1) mice. We found increased Axin1 expression in the colonic epithelium of human inflammatory bowel disease (IBD). Axin1 ΔIEC mice exhibited altered goblet cell spatial distribution, PC morphology, reduced lysozyme expression, and enriched Akkermansia muciniphila (A. muciniphila). The absence of intestinal epithelial and PC Axin1 decreased susceptibility to dextran sulfate sodium (DSS)-induced colitis in vivo. Axin1 ΔIEC and Axin1 ΔPC mice became more susceptible to DSS-colitis after cohousing with control mice. Treatment with A. muciniphila reduced DSS-colitis severity. Antibiotic treatment did not change the IEC proliferation in the Axin1 Loxp mice. However, the intestinal proliferative cells in Axin1 ΔIEC mice with antibiotic treatment were reduced compared with those in Axin1 ΔIEC mice without treatment. These data suggest non-colitogenic effects driven by the gut microbiome. In conclusion, we found that the loss of intestinal Axin1 protects against colitis, likely driven by epithelial Axin1 and Axin1-associated A. muciniphila. Our study demonstrates a novel role of Axin1 in mediating intestinal homeostasis and the microbiota. Further mechanistic studies using specific Axin1 mutations elucidating how Axin1 modulates the microbiome and host inflammatory response will provide new therapeutic strategies for human IBD.

Cadmium modulates intestinal Wnt/ß-catenin signaling ensuing intestinal barrier disruption and systemic inflammation.

The intricate architecture of the intestinal epithelium, crucial for nutrient absorption, is constantly threatened by environmental factors. The epithelium undergoes rapid turnover, which is essential for maintaining homeostasis, under the control of intestinal stem cells (ISCs). The central regulator, Wnt/ß-catenin signaling plays a key role in intestinal integrity and turnover. Despite its significance, the impact of environmental factors on this pathway has been largely overlooked. This study, for the first time, investigates the influence of Cd on the intestinal Wnt signaling pathway using a mouse model. In this study, male BALB/c mice were administered an environmentally relevant Cd dose (0.98 mg/kg) through oral gavage to investigate the intestinal disruption and Wnt signaling pathway. Various studies, including histopathology, immunohistochemistry, RT-PCR, western blotting, ELISA, intestinal permeability assay, and flow cytometry, were conducted to study Cd-induced changes in the intestine. The canonical Wnt signaling pathway experienced significant downregulation as a result of sub-chronic Cd exposure, which caused extensive damage throughout the small intestine. Increased intestinal permeability and a skewed immune response were also observed. To confirm that Wnt signaling downregulation is the key driver of Cd-induced gastrointestinal toxicity, mice were co-exposed to LiCl (a recognized Wnt activator) and Cd. The results clearly showed that the harmful effects of Cd could be reversed, which is strong evidence that Cd mostly damages the intestine through the Wnt/ß-catenin signalling axis. In conclusion, this research advances the current understanding of the role of Wnt/ß catenin signaling in gastrointestinal toxicity caused by diverse environmental pollutants.

The loss of antioxidant activities impairs intestinal epithelium homeostasis by altering lipid metabolism.

Reactive oxygens species (ROS) are common byproducts of metabolic reactions and could be at the origin of many diseases of the elderly. Here we investigated the role of ROS in the renewal of the intestinal epithelium in mice lacking catalase (CAT) and/or nicotinamide nucleotide transhydrogenase (NNT) activities. Cat-/- mice have delayed intestinal epithelium renewal and were prone to develop necrotizing enterocolitis upon starvation. Interestingly, crypts lacking CAT showed fewer intestinal stem cells (ISC) and lower stem cell activity than wild-type. In contrast, crypts lacking NNT showed a similar number of ISCs as wild-type but increased stem cell activity, which was also impaired by the loss of CAT. No alteration in the number of Paneth cells (PCs) was observed in crypts of either Cat-/- or Nnt-/- mice, but they showed an evident decline in the amount of lysozyme. Cat deficiency caused fat accumulation in crypts, and a fall in the remarkable high amount of adipose triglyceride lipase (ATGL) in PCs. Notably, the low levels of ATGL in the intestine of Cat -/- mice increased after a treatment with the antioxidant N-acetyl-L-cysteine. Supporting a role of ATGL in the regulation of ISC activity, its inhibition halt intestinal organoid development. These data suggest that the reduction in the renewal capacity of intestine originates from fatty acid metabolic alterations caused by peroxisomal ROS.

Effect of GVHD on the gut and intestinal microflora.

Graft-versus-host disease (GVHD) is one of the most important cause of death in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). The gastrointestinal tract is one of the most common sites affected by GVHD. However, there is no gold standard clinical practice for diagnosing gastrointestinal GVHD (GI-GVHD), and it is mainly diagnosed by the patient's clinical symptoms and related histological changes. Additionally, GI-GVHD causes intestinal immune system disorders, damages intestinal epithelial tissue such as intestinal epithelial cells((IEC), goblet, Paneth, and intestinal stem cells, and disrupts the intestinal epithelium's physical and chemical mucosal barriers. The use of antibiotics and diet alterations significantly reduces intestinal microbial diversity, further reducing bacterial metabolites such as short-chain fatty acids and indole, aggravating infection, and GI-GVHD. gut microbe diversity can be restored by fecal microbiota transplantation (FMT) to treat refractory GI-GVHD. This review article focuses on the clinical diagnosis of GI-GVHD and the effect of GVHD on intestinal flora and its metabolites.

Research progress on the relationship between Paneth cells-susceptibility genes, intestinal microecology and inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a disorder of the immune system and intestinal microecosystem caused by environmental factors in genetically susceptible people. Paneth cells (PCs) play a central role in IBD pathogenesis, especially in Crohn's disease development, and their morphology, number and function are regulated by susceptibility genes. In the intestine, PCs participate in the formation of the stem cell microenvironment by secreting antibacterial particles and play a role in helping maintain the intestinal microecology and intestinal mucosal homeostasis. Moreover, PC proliferation and maturation depend on symbiotic flora in the intestine. This paper describes the interactions among susceptibility genes, PCs and intestinal microecology and their effects on IBD occurrence and development.

Axin1's mystique in manipulating microbiome amidst colitis.

Classically, Axin1 is considered a regulator of Wnt/ß-catenin signaling. However, Axin1's roles in host-microbial interactions have been unknown. Our recent study has demonstrated that deletion of intestinal epithelial Axin1 in epithelial cells and Paneth cells protects the host against colitis by enhancing Akkermansia muciniphila. Loss of intestinal epithelial or Paneth cell Axin1 results in increased Wnt/ß-catenin signaling, proliferation, and cell migration. This is associated with morphologically altered goblet and Paneth cells, including increased Muc2 and decreased lysozyme. Axin1 deletion specifically enriched Akkermansia muciniphila. Akkermansia muciniphila in Axin1 knockout mice is the driver of protection against DSS-induced inflammation. Here, we feature several significant conceptual changes, such as differences between Axin1 and Axin2, Axin1 in innate immunity and microbial homeostasis, and Axin1 reduction of Akkermansia muciniphila. We discuss an important trend in the field related to Paneth cells and tissue-specific Axin1 manipulation of microbiome in health and inflammation.

Gut commensal bacteria exacerbate toxoplasmosis associated with TgSheepCHn5 (ToxoDB#2) and TgRedpandaCHn1 (ToxoDB#20) through Th1 immune response.

Oral infection of mice with several strains of Toxoplasma gondii results in intestinal pathological lesions, which contributes to the invasion of this parasite. However, the exact mechanism is unclear, and only a few strains have been explored. Here, T. gondii TgSheepCHn5 and TgRedpandaCHn1 strains from sheep and red panda were evaluated. The TgSheepCHn5 and TgRedpandaCHn1 strains induced intestinal lesions, loss of Paneth cells, and gut commensal bacteria dysbiosis in Swiss Webster mice. The lesions and loss of Paneth cells were dependent on IFN-γ and gut commensal bacteria during T. gondii infection. Deleting IFN-γ or gut commensal bacteria suppressed the Th1 immune response, alleviated the lesions and parasite loading, and upregulated the number of Paneth cells. Loss of IFN-γ production accelerated mice death, whereas the deletion of gut commensal bacteria enhanced the survival time of the host. The Th1 cell immune responses have positive and negative effects on toxoplasmosis, resistance to T. gondii infection, and acceleration intestine lesions. Adjustment of Th1 cell responses and gut commensal bacteria may be effective treatments for toxoplasmosis.

The dimerized pentraxin-like domain of the adhesion G protein-coupled receptor 112 (ADGRG4) suggests function in sensing mechanical forces.

Adhesion G protein-coupled receptors (aGPCRs) feature large extracellular regions with modular domains that often resemble protein classes of various function. The pentraxin (PTX) domain, which is predicted by sequence homology within the extracellular region of four different aGPCR members, is well known to form pentamers and other oligomers. Oligomerization of GPCRs is frequently reported and mainly driven by interactions of the seven-transmembrane region and N or C termini. While the functional importance of dimers is well-established for some class C GPCRs, relatively little is known about aGPCR multimerization. Here, we showcase the example of ADGRG4, an orphan aGPCR that possesses a PTX-like domain at its very N-terminal tip, followed by an extremely long stalk containing serine-threonine repeats. Using X-ray crystallography and biophysical methods, we determined the structure of this unusual PTX-like domain and provide experimental evidence for a homodimer equilibrium of this domain which is Ca2+-independent and driven by intermolecular contacts that differ vastly from the known soluble PTXs. The formation of this dimer seems to be conserved in mammalian ADGRG4 indicating functional relevance. Our data alongside of theoretical considerations lead to the hypothesis that ADGRG4 acts as an in vivo sensor for shear forces in enterochromaffin and Paneth cells of the small intestine.

Breastfeeding lifespan control of growth, maintenance, and metabolism of small intestinal epithelium.

Gastrointestinal epithelial cells respond to milk-born molecules throughout breastfeeding, influencing growth, and development. The rapid renewal of the small intestine depends on the proliferation in the crypt that drives cell fates. We used early weaning model to investigate immediate and late effects of breastfeeding on proliferation, differentiation of jejunal epithelial cells. Wistar rats were either allowed to suckle (S) until 21 postnatal days or submitted to early weaning (EW) at 15 days. By comparing ages (18, 60, and 120 days), we found that EW decreased Ki67 indices and villi height at 18 and 60 days (p < 0.05), and at 120 days they were similar between diets. Proliferative reduction and augmented expression of Cdkn1b (p27 gene) were parallel. In the stem cell niche, EW increased the number and activity (Defa24) of Paneth cells at 18 and 60 days (p < 0.05), and Lgr5 and Ascl2 genes showed inverted responses between ages. Among target cells, EW decreased goblet cell number at 18 and 60 days (p < 0.05) and increased it at 120 days (p < 0.05), whereas enteroendocrine marker genes were differentially altered. EW reduced enterocytes density at 18 days (p < 0.05), and at 120 days this population was decreased (vs. 60 days). Among cell fate crypt-controlling genes, Notch and Atoh1 were the main targets of EW. Metabolically, intraperitoneal glucose tolerance was immediately reduced (18 days), being reverted until 120 days (p < 0.05). Currently, we showed that breastfeeding has a lifespan influence on intestinal mucosa and on its stem cell compartment. We suggest that, although jejunum absorptive function is granted after early weaning, the long lasting changes in gene expression might prime the mucosa with a different sensitivity to gut disorders that still have to be further explored.

Infection of porcine enteroids and 2D differentiated intestinal epithelial cells with rotavirus A to study cell tropism and polarized immune response.

Intestinal epithelial cell interactions with enteric pathogens have been incompletely elucidated owing to the lack of model systems that recapitulate the cellular diversity, architecture and functionality of the intestine. To analyze rotavirus (RV) infection and the subsequent innate immune response, we established cultures of differentiated porcine intestinal epithelial cells in three different variations: basolateral-out enteroids, apical-out enteroids and two-dimensional (2D) filter-grown intestinal epithelial cells. Application of specific antibodies for fluorescent staining indicated that enteroids and enteroid-derived cell cultures contain multiple intestinal epithelial cell types. Infection studies indicated that both apical-out enteroids and 2D intestinal epithelial cells are susceptible to porcine RV infection. However, 2D intestinal epithelial cells are more useful for a detailed characterization and comparison of apical and basolateral infection than apical-out enteroids. Virus-induced apoptosis was observed in apical-out enteroids at 24 h post infection but not at earlier time points after infection. RV infected not only enterocytes but also goblet cells and Paneth cells in apical-out enteroids and 2D intestinal epithelial cells. Interestingly, despite the lack of significant differences in the efficiency of infection after apical and basolateral infection of 2D intestinal epithelial cells, stronger innate immune and inflammatory responses were observed after basolateral infection as compared to infection via the apical route. Therefore, apical-out enteroids and 2D intestinal epithelial cells provide useful primary cell culture models that can be extended to analyze invasion and replication strategies of agents implicated in enteric diseases or to study immune and inflammatory responses of the host induced by enteric pathogens.

Crohn's disease: Why the ileum?

Crohn's disease (CD) is an inflammatory bowel disease characterized by immune-mediated flares affecting any region of the intestine alternating with remission periods. In CD, the ileum is frequently affected and about one third of patients presents with a pure ileal type. Moreover, the ileal type of CD presents epidemiological specificities like a younger age at onset and often a strong link with smoking and genetic susceptibility genes. Most of these genes are associated with Paneth cell dysfunction, a cell type found in the intestinal crypts of the ileum. Besides, a Western-type diet is associated in epidemiological studies with CD onset and increasing evidence shows that diet can modulate the composition of bile acids and gut microbiota, which in turn modulates the susceptibility of the ileum to inflammation. Thus, the interplay between environmental factors and the histological and anatomical features of the ileum is thought to explain the specific transcriptome profile observed in CD ileitis. Indeed, both immune response and cellular healing processes harbour differences between ileal and non-ileal CD. Taken together, these findings advocate for a dedicated therapeutic approach to managing ileal CD. Currently, interventional pharmacological studies have failed to clearly demonstrate distinct response profiles according to disease site. However, the high rate of stricturing disease in ileal CD requires the identification of new therapeutic targets to significantly change the natural history of this debilitating disease.

Cross talk between Paneth and tuft cells drives dysbiosis and inflammation in the gut mucosa.

Gut microbiota imbalance (dysbiosis) is increasingly associated with pathological conditions, both within and outside the gastrointestinal tract. Intestinal Paneth cells are considered to be guardians of the gut microbiota, but the events linking Paneth cell dysfunction with dysbiosis remain unclear. We report a three-step mechanism for dysbiosis initiation. Initial alterations in Paneth cells, as frequently observed in obese and inflammatorybowel diseases patients, cause a mild remodeling of microbiota, with amplification of succinate-producing species. SucnR1-dependent activation of epithelial tuft cells triggers a type 2 immune response that, in turn, aggravates the Paneth cell defaults, promoting dysbiosis and chronic inflammation. We thus reveal a function of tuft cells in promoting dysbiosis following Paneth cell deficiency and an unappreciated essential role of Paneth cells in maintaining a balanced microbiota to prevent inappropriate activation of tuft cells and deleterious dysbiosis. This succinate-tuft cell inflammation circuit may also contribute to the chronic dysbiosis observed in patients.

Identification of Differentiated Intestinal Epithelial Cells Using Immunostaining and Fluorescence Microscopy.

Immunofluorescence imaging enables visualization of a wide range of molecules in diverse cells and tissues. Determining the localization and endogenous protein levels in cells using immunostaining can be highly informative for researchers studying cell structure and function. The small intestinal epithelium is composed of numerous cell types including absorptive enterocytes, mucus-producing goblet cells, lysozyme positive Paneth cells, proliferative stem cells, chemosensing tuft cells, and hormone-producing enteroendocrine cells. Each cell type in the small intestine has unique functions and structures that are critical for maintaining intestinal homeostasis and identifiable by immunofluorescence labeling. In this chapter we provide a detailed protocol and representative images of immunostaining of paraffin-embedded mouse small intestinal tissue. The method highlights antibodies and micrographs that identify differentiated cell types. These details are important because quality immunofluorescence imaging can provide novel insights and a greater understanding of healthy and disease states.

Differentiated Epithelial Cells of the Gut.

The intestine is a prime example of self-renewal where stem cells give rise to progenitor cells called transit-amplifying cells which differentiate into more specialized cells. There are two intestinal lineages: the absorptive (enterocytes and microfold cells) and the secretory (Paneth cells, enteroendocrine, goblet cells, and tuft cells). Each of these differentiated cell types has a role in creating an "ecosystem" to maintain intestinal homeostasis. Here, we summarize the main roles of each cell type.

Paneth cell development in the neonatal gut: pathway regulation, development, and relevance to necrotizing enterocolitis.

Paneth cells (PCs) are intestinal epithelial cells (IECs) that contain eosinophilic granules, which are located in Lieberkühn crypts. An increasing number of animal and human experiments have indicated that PCs are involved in the progression of a variety of intestinal as well as systemic inflammatory responses including necrotizing enterocolitis (NEC). NEC is an enteric acquired disease with high mortality that usually occurs in premature infants and neonates, however the underlying mechanisms remain unclear. In this review, we summarize the features of PCs, including their immune function, association with gut microbiota and intestinal stem cells, and their mechanism of regulating IEC death to explore the possible mechanisms by which PCs affect NEC.