The intestinal epithelium tuft cells: specification and function

Gaps in our understanding of how vagal afferents to the small intestinal mucosa detect luminal stimuli

Vagal afferents to the gastrointestinal tract are crucial for the regulation of food intake, signaling negative feedback that contributes to satiation and positive feedback that produces appetition and reward. Vagal afferents to the small intestinal mucosa contribute to this regulation by sensing luminal stimuli and reporting this information to the brain. These afferents respond to mechanical, chemical, thermal, pH, and osmolar stimuli, as well as to bacterial products and immunogens. Surprisingly, little is known about how these stimuli are transduced by vagal mucosal afferents or how their transduction is organized among these afferents' terminals. Furthermore, the effects of stimulus concentration ranges or physiological stimuli on vagal activity have not been examined for some of these stimuli. Also, detection of luminal stimuli has rarely been examined in rodents, which are most frequently used for studying small intestinal innervation. Here we review what is known about stimulus detection by vagal mucosal afferents and illustrate the complexity of this detection using nutrients as an exemplar. The accepted model proposes that nutrients bind to taste receptors on enteroendocrine cells (EECs), which excite them, causing the release of hormones that stimulate vagal mucosal afferents. However, evidence reviewed here suggests that although this model accounts for many aspects of vagal signaling about nutrients, it cannot account for all aspects. A major goal of this review is therefore to evaluate what is known about nutrient absorption and detection and, based on this evaluation, identify candidate mucosal cells and structures that could cooperate with EECs and vagal mucosal afferents in stimulus detection.

Loss of Elp3 blocks intestinal tuft cell differentiation via an mTORC1-Atf4 axis

Intestinal tuft cells are critical for anti-helminth parasite immunity because they produce IL-25, which triggers IL-13 secretion by activated group 2 innate lymphoid cells (ILC2s) to expand both goblet and tuft cells. We show that epithelial Elp3, a tRNA-modifying enzyme, promotes tuft cell differentiation and is consequently critical for IL-25 production, ILC2 activation, goblet cell expansion and control of Nippostrongylus brasiliensis helminth infection in mice. Elp3 is essential for the generation of intestinal immature tuft cells and for the IL-13-dependent induction of glycolytic enzymes such as Hexokinase 1 and Aldolase A. Importantly, loss of epithelial Elp3 in the intestine blocks the codon-dependent translation of the Gator1 subunit Nprl2, an mTORC1 inhibitor, which consequently enhances mTORC1 activation and stabilizes Atf4 in progenitor cells. Likewise, Atf4 overexpression in mouse intestinal epithelium blocks tuft cell differentiation in response to intestinal helminth infection. Collectively, our data define Atf4 as a negative regulator of tuft cells and provide insights into promotion of intestinal type 2 immune response to parasites through tRNA modifications.

Gallnut tannic acid alleviates gut damage induced by Salmonella pullorum in broilers by enhancing barrier function and modulating microbiota

Pullorum disease (PD) is a bacterial infection caused by Salmonella pullorum (S. pullorum) that affects poultry. It is highly infectious and often fatal. Antibiotics are currently the mainstay of prophylactic and therapeutic treatments for PD, but their use can lead to the development of resistance in pathogenic bacteria and disruption of the host's intestinal flora. We added neomycin sulfate and different doses of tannic acid (TA) to the drinking water of chicks at 3 days of age and infected them with PD by intraperitoneal injection of S. pullorum at 9 days of age. We analyzed intestinal histopathological changes and the expression of immune-related genes and proteins by using the plate smear method, histological staining, real-time fluorescence quantitative PCR, ELISA kits, and 16S rRNA Analysis of intestinal flora. The results demonstrate that S. pullorum induces alterations in the immune status and impairs the functionality of the liver and intestinal barrier. We found that tannic acid significantly ameliorated S. pullorum-induced liver and intestinal damage, protected the intestinal physical and chemical barriers, restored the intestinal immune barrier function, and regulated the intestinal flora. Our results showed that TA has good anti-diarrhoeal, growth-promoting, immune-regulating, intestinal barrier-protecting and intestinal flora-balancing effects, and the best effect was achieved at an additive dose of 0.2%.

Roles of airway and intestinal epithelia in responding to pathogens and maintaining tissue homeostasis

Epithelial cells form a resilient barrier and orchestrate defensive and reparative mechanisms to maintain tissue stability. This review focuses on gut and airway epithelia, which are positioned where the body interfaces with the outside world. We review the many signaling pathways and mechanisms by which epithelial cells at the interface respond to invading pathogens to mount an innate immune response and initiate adaptive immunity and communicate with other cells, including resident microbiota, to heal damaged tissue and maintain homeostasis. We compare and contrast how airway and gut epithelial cells detect pathogens, release antimicrobial effectors, collaborate with macrophages, Tregs and epithelial stem cells to mount an immune response and orchestrate tissue repair. We also describe advanced research models for studying epithelial communication and behaviors during inflammation, tissue injury and disease.

Trends in 3D models of inflammatory bowel disease

Inflammatory bowel disease (IBD) encompasses a set of chronic inflammatory conditions, namely Crohn's disease and ulcerative colitis. Despite all advances in the management of IBD, a definitive cure is not available, largely due to a lack of a holistic understanding of its etiology and pathophysiology. Several in vitro, in vivo, and ex vivo models have been developed over the past few decades in order to abbreviate remaining gaps. The establishment of reliable and predictable in vitro intestinal inflammation models may indeed provide valuable tools to expedite and validate the development of therapies for IBD. Three-dimensional (3D) models provide a more accurate representation of the different layers of the intestine, contributing to a stronger impact on drug screening and research on intestinal inflammation, and bridging the gap between in vitro and in vivo research. This work provides a critical overview on the state-of-the-art on existing 3D models of intestinal inflammation and discusses the remaining challenges, providing insights on possible pathways towards achieving IBD mimetic models. We also address some of the main challenges faced by implementing cell culture models in IBD research while bearing in mind clinical translational aspects.

Lab-on-chip technologies for exploring the gut-immune axis in metabolic disease

The continued rise in metabolic diseases such as obesity and type 2 diabetes mellitus poses a global health burden, necessitating further research into factors implicated in the onset and progression of these diseases. Recently, the gut-immune axis, with diet as a main regulator, has been identified as a possible role player in their development. Translation of conventional 2D in vitro and animal models is however limited, while human studies are expensive and preclude individual mechanisms from being investigated. Lab-on-chip technology therefore offers an attractive new avenue to study gut-immune interactions. This review provides an overview of the influence of diet on gut-immune interactions in metabolic diseases and a critical analysis of the current state of lab-on-chip technology to study this axis. While there has been progress in the development of "immuno-competent" intestinal lab-on-chip models, with studies showing the ability of the technology to provide mechanical cues, support longer-term co-culture of microbiota and maintain in vivo-like oxygen gradients, platforms which combine all three and include intestinal and immune cells are still lacking. Further, immune cell types and inclusion of microenvironment conditions which enable in vivo-like immune cell dynamics as well as host-microbiome interactions are limited. Future model development should focus on combining these conditions to create an environment capable of hosting more complex microbiota and immune cells to allow further study into the effects of diet and related metabolites on the gut-immune ecosystem and their role in the prevention and development of metabolic diseases in humans.

Paneth-like cells produced from OLFM4+ stem cells support OLFM4+ stem cell growth in advanced colorectal cancer

Tumor tissues consist of heterogeneous cells that originate from stem cells; however, their cell fate determination program remains incompletely understood. Using patient-derived organoids established from patients with advanced colorectal cancer (CRC), we evaluated the potential of olfactomedin 4 (OLFM4)+ stem cells to produce a bifurcated lineage of progenies with absorptive and secretory properties. In the early phases of organoid reconstruction, OLFM4+ cells preferentially gave rise to secretory cells. Additionally, we found that Paneth-like cells, which do not exist in the normal colon, were induced in response to Notch signaling inhibition. Video recordings of single OLFM4+ cells revealed that organoids containing Paneth-like cells were effectively propagated and that their selective ablation led to organoid collapse. In tumor tissues, Paneth-like cells were identified only in the region where tumor cells lost cell adhesion. These findings indicate that Paneth-like cells are directly produced by OLFM4+ stem cells and that their interaction contributes to tumor formation by providing niche factors. This study reveals the importance of the cell fate specification program for building a complete tumor cellular ecosystem, which might be targeted with novel therapeutics.

Enteroendocrine cell regulation of the gut-brain axis

Enteroendocrine cells (EECs) are an essential interface between the gut and brain that communicate signals about nutrients, pain, and even information from our microbiome. EECs are hormone-producing cells expressed throughout the gastrointestinal epithelium and have been leveraged by pharmaceuticals like semaglutide (Ozempic, Wegovy), terzepatide (Mounjaro), and retatrutide (Phase 2) for diabetes and weight control, and linaclotide (Linzess) to treat irritable bowel syndrome (IBS) and visceral pain. This review focuses on role of intestinal EECs to communicate signals from the gut lumen to the brain. Canonically, EECs communicate information about the intestinal environment through a variety of hormones, dividing EECs into separate classes based on the hormone each cell type secretes. Recent studies have revealed more diverse hormone profiles and communication modalities for EECs including direct synaptic communication with peripheral neurons. EECs known as neuropod cells rapidly relay signals from gut to brain via a direct communication with vagal and primary sensory neurons. Further, this review discusses the complex information processing machinery within EECs, including receptors that transduce intraluminal signals and the ion channel complement that govern initiation and propagation of these signals. Deeper understanding of EEC physiology is necessary to safely treat devastating and pervasive conditions like irritable bowel syndrome and obesity.

Enteric Nervous System: Identification of a Novel Neuronal Sensory Network in the Duodenal Epithelium

The communication between the intestinal epithelium and the enteric nervous system has been considered indirect. Mechanical or chemical stimuli activate enteroendocrine cells inducing hormone secretion, which act on sub-epithelial nerve ends, activating the enteric nervous system. However, we identified an epithelial cell that expresses NKAIN4, a neuronal protein associated with the β-subunit of Na+/K+-ATPase. This cell overexpresses Na+/K+-ATPase and ouabain-insensitive Na+-ATPase, enzymes involved in active sodium transport. NKAIN4-positive cells also express neuronal markers as NeuN, acetylcholine-esterase, acetylcholine-transferase, α3- and α7-subunits of ACh receptors, glutamic-decarboxylase, and serotonin-receptor-7, suggesting they are neurons. NKAIN4-positive cells show a polarized shape with an oval body, an apical process finished in a knob-like terminal in contact with the lumen, a basal cilia body at the base of the apical extension, and basal axon-like soma projections connecting sub-epithelial nerve terminals, lymphoid nodules, glial cells, and enterochromaffin cells, forming a network that reaches the epithelial surface. We also showed, using retrograde labeling and immunofluorescence, that these cells receive afferent signals from the enteric nervous system. Finally, we demonstrated that acetylcholine activates NKAIN4-positive cells inducing Ca2+ mobilization and probably serotonin secretion in enterochromaffin cells. NKAIN4-positive cells are neurons that would form a part of a duodenal sensory network for physiological or noxious luminal stimuli.

DCLK1 and tuft cells: Immune-related functions and implications for cancer immunotherapy

DCLK1, a tuft cell marker, is widely expressed in various tumors. Its high expression levels are closely linked to malignant tumor progression, making it a potential tumor-related marker. Recent studies have shed light on the critical roles of DCLK1 and tuft cells in the immune response and the maintenance of epithelial homeostasis, as well as targeted immune escape mechanisms in the tumor microenvironment. This review aims to comprehensively examine the current understanding of immune-related functions mediated by DCLK1 and tuft cells in epithelial tissues, including the roles of relevant cells and important factors involved. Additionally, this review will discuss recent advances in anti-tumor immunity mediated by DCLK1/tuft cells and their potential as immunotherapeutic targets. Furthermore, we will consider the potential impact of DCLK1 targeted therapy in cancer immunotherapy, particularly DCLK1 kinase inhibitors as potential therapeutic drugs in anti-tumor immunity, providing a new perspective and reference for future research.

Analysis of cell-specific transcriptional responses in human colon tissue using CIBERSORTx

Diet is an important determinant of overall health, and has been linked to the risk of various cancers. To understand the mechanisms involved, transcriptomic responses from human intervention studies are very informative. However, gene expression analysis of human biopsy material only represents the average profile of a mixture of cell types that can mask more subtle, but relevant cell-specific changes. Here, we use the CIBERSORTx algorithm to generate single-cell gene expression from human multicellular colon tissue. We applied the CIBERSORTx to microarray data from the PHYTOME study, which investigated the effects of different types of meat on transcriptional and biomarker changes relevant to colorectal cancer (CRC) risk. First, we used single-cell mRNA sequencing data from healthy colon tissue to generate a novel signature matrix in CIBERSORTx, then we determined the proportions and gene expression of each separate cell type. After comparison, cell proportion analysis showed a continuous upward trend in the abundance of goblet cells and stem cells, and a continuous downward trend in transit amplifying cells after the addition of phytochemicals in red meat products. The dietary intervention influenced the expression of genes involved in the growth and division of stem cells, the metabolism and detoxification of enterocytes, the translation and glycosylation of goblet cells, and the inflammatory response of innate lymphoid cells. These results show that our approach offers novel insights into the heterogeneous gene expression responses of different cell types in colon tissue during a dietary intervention.

Tuft Cells: Detectors, Amplifiers, Effectors and Targets in Parasite Infection

Tuft cells have recently emerged as the focus of intense interest following the discovery of their chemosensory role in the intestinal tract, and their ability to activate Type 2 immune responses to helminth parasites. Moreover, they populate a wide range of mucosal tissues and are intimately connected to immune and neuronal cells, either directly or through the release of pharmacologically active mediators. They are now recognised to fulfil both homeostatic roles, in metabolism and tissue integrity, as well as acting as the first sensors of parasite infection, immunity to which is lost in their absence. In this review we focus primarily on the importance of tuft cells in the intestinal niche, but also link to their more generalised physiological role and discuss their potential as targets for the treatment of gastrointestinal disorders.

Nano- and micro-polystyrene plastics interfered the gut barrier function mediated by exosomal miRNAs in rats

Microplastics (MPs) are widely distributed in the global environment, entering and accumulating in organisms in various ways and posing health threats. MPs can damage intestine; however, the mechanism by which MPs cause intestinal damage in rats is unclear. Here, rats were exposed to 50 nm PS-NPs or 5 μm PS-MPs for 4 weeks to evaluate the possible effects on intestinal barrier function and exosomal miRNAs expressions. The results showed that PS-NPs or PS-MPs disrupted the gut microbiota and affected gut barrier function at the biological level. In addition, PS-NPs and PS-MPs altered the composition of exosomal miRNAs in the intestinal and serum. Both PS-NPs and PS-MPs decreased the expression of miR-126a-3p in the intestinal and serum exosomes, which is an important signalling molecule involved in MPs induced gut barrier function disorder. More importantly, both in vitro and in vivo experiments indicated that miR-126a-3p was closely related to oxidative damage of intestinal cells through the PI3K-Akt pathway and eventually promote cell apoptosis by regulating the target gene of PIK3R2. Our study suggested that PS-NPs and PS-MPs could affect rat intestinal barrier function through an exosomal miRNA mediated pathway.

Single-Cell RNA Sequencing (scRNA-seq) Identifies L1CAM as a Key Mediator between Epithelial Tuft Cell and Innate Lymphoid Cell in the Colon of Hnrnp I Knockout Mice

(1) Background: Knockout (KO) of heterogeneous nuclear ribonucleoprotein I (Hnrnp I) in mouse intestinal epithelial cells (IECs) induced a severe inflammatory response in the colon, followed by hyperproliferation. This study aimed to investigate the epithelial lineage dynamics and cell-cell communications that underlie inflammation and colitis. (2) Methods: Single cells were isolated from the colons of wildtype (WT) and KO mice and used in scRNA-seq. Whole colons were collected for immunofluorescence staining and cytokine assays. (3) Results: from scRNA-seq, the number of DCLK1 + colonic tuft cells was significantly higher in the Hnrnp I KO mice compared to the WT mice. This was confirmed by immunofluorescent staining of DCLK1. The DCLK1 + colonic tuft cells in KO mice developed unique communications with lymphocytes via interactions between surface L1 cell adhesion molecule (L1CAM) and integrins. In the KO mice colons, a significantly elevated level of inflammatory cytokines IL4, IL6, and IL13 were observed, which marks type-2 immune responses directed by group 2 innate lymphoid cells (ILC2s). (4) Conclusions: This study demonstrates one critical cellular function of colonic tuft cells, which facilitates type-2 immune responses by communicating with ILC2s via the L1CAM-integrins interaction. This communication promotes pro-inflammatory signaling pathways in ILC2, leading to the increased secretion of inflammatory cytokines.

Hypoxia Primes Human ISCs for Interleukin-Dependent Rescue of Stem Cell Activity

BACKGROUND AND AIMS

Hypoxia in the intestinal epithelium can be caused by acute ischemic events or chronic inflammation in which immune cell infiltration produces inflammatory hypoxia starving the mucosa of oxygen. The epithelium has the capacity to regenerate after some ischemic and inflammatory conditions suggesting that intestinal stem cells (ISCs) are highly tolerant to acute and chronic hypoxia; however, the impact of hypoxia on human ISC (hISC) function has not been reported. Here we present a new microphysiological system (MPS) to investigate how hypoxia affects hISCs from healthy donors and test the hypothesis that prolonged hypoxia modulates how hISCs respond to inflammation-associated interleukins (ILs).

METHODS

hISCs were exposed to <1.0% oxygen in the MPS for 6, 24, 48, and 72 hours. Viability, hypoxia-inducible factor 1a (HIF1a) response, transcriptomics, cell cycle dynamics, and response to cytokines were evaluated in hISCs under hypoxia. HIF stabilizers and inhibitors were screened to evaluate HIF-dependent responses.

RESULTS

The MPS enables precise, real-time control and monitoring of oxygen levels at the cell surface. Under hypoxia, hISCs maintain viability until 72 hours and exhibit peak HIF1a at 24 hours. hISC activity was reduced at 24 hours but recovered at 48 hours. Hypoxia induced increases in the proportion of hISCs in G1 and expression changes in 16 IL receptors. Prolyl hydroxylase inhibition failed to reproduce hypoxia-dependent IL-receptor expression patterns. hISC activity increased when treated IL1β, IL2, IL4, IL6, IL10, IL13, and IL25 and rescued hISC activity caused by 24 hours of hypoxia.

CONCLUSIONS

Hypoxia pushes hISCs into a dormant but reversible proliferative state and primes hISCs to respond to a subset of ILs that preserves hISC activity. These findings have important implications for understanding intestinal epithelial regeneration mechanisms caused by inflammatory hypoxia.

Tuft cells - the immunological interface and role in disease regulation

Tuft cells, also known as taste chemosensory cells, accumulate during parasite colonization or infection and have powerful immunomodulatory effects on substances that could be detrimental, as well as possible anti-inflammatory or antibacterial effects. Tuft cells are the primary source of interleukin (IL)-25. They trigger extra Innate lymphoid type-2 cells (ILC2) in the intestinal lamina propria to create cytokines (type 2); for instance, IL-13, which leads to an increase in IL-25. As tuft cells can produce biological effector molecules, such as IL-25 and eicosanoids involved in allergy (for example, cysteinyl leukotrienes and prostaglandin D₂) and the neurotransmitter acetylcholine. Following parasite infection, tuft cells require transient receptor potential cation channel subfamily M member 5 (TRPM5)-dependent chemosensation to produce responses. Secretory tuft cells provide a physical mucus barrier against the external environment and therefore have vital defensive roles against diseases by supporting tissue maintenance and repair. In addition to recent research on tuft cells, more studies are required to understand the distribution, cell turnover, molecular characteristics, responses in various species, involvement in immunological function across tissues, and most importantly, the mechanism involved in the control of various diseases.

Is Candida albicans a contributor to cancer? A critical review based on the current evidence

The association between Candida albicans (C. albicans) and cancer has been noticed for decades. Whether C. albicans infection is a complication of cancer status or as a contributor to cancer development remains to be discussed. This review systematically summarized the up-to-date knowledge about associations between C. albicans and various types of cancer, and discussed the role of C. albicans in cancer development. Most of the current clinical and animal evidence support the relationship between C. albicans and oral cancer development. However, there is insufficient evidence to demonstrate the role of C. albicans in other types of cancer. Moreover, this review explored the underlying mechanisms for C. albicans promoting cancer. It was hypothesized that C. albicans may promote cancer progression by producing carcinogenic metabolites, inducing chronic inflammation, remodeling immune microenvironment, activating pro-cancer signals, and synergizing with bacteria.

A new microphysiological system shows hypoxia primes human ISCs for interleukin-dependent rescue of stem cell activity

Background & Aims

Hypoxia in the intestinal epithelium can be caused by acute ischemic events or conditions like Inflammatory Bowel Disease (IBD) where immune cell infiltration produces 'inflammatory hypoxia', a chronic condition that starves the mucosa of oxygen. Epithelial regeneration after ischemia and IBD suggests intestinal stem cells (ISCs) are highly tolerant to acute and chronic hypoxia; however, the impact of acute and chronic hypoxia on human ISC (hISC) properties have not been reported. Here we present a new microphysiological system (MPS) to investigate how hypoxia affects hISCs isolated from healthy human tissues. We then test the hypothesis that some inflammation-associated interleukins protect hISCs during prolonged hypoxia.

Methods

hISCs were exposed to <1.0% oxygen in the MPS for 6-, 24-, 48- & 72hrs. Viability, HIF1α response, transcriptomics, cell cycle dynamics, and hISC response to cytokines were evaluated.

Results

The novel MPS enables precise, real-time control and monitoring of oxygen levels at the cell surface. Under hypoxia, hISCs remain viable until 72hrs and exhibit peak HIF1α at 24hrs. hISCs lose stem cell activity at 24hrs that recovers at 48hrs of hypoxia. Hypoxia increases the proportion of hISCs in G1 and regulates hISC capacity to respond to multiple inflammatory signals. Hypoxia induces hISCs to upregulate many interleukin receptors and hISCs demonstrate hypoxia-dependent cell cycle regulation and increased organoid forming efficiency when treated with specific interleukins.

Conclusions

Hypoxia primes hISCs to respond differently to interleukins than hISCs in normoxia through a transcriptional response. hISCs slow cell cycle progression and increase hISC activity when treated with hypoxia and specific interleukins. These findings have important implications for epithelial regeneration in the gut during inflammatory events.

An update on the biological characteristics and functions of tuft cells in the gut

The intestine is a powerful digestive system and one of the most sophisticated immunological organs. Evidence shows that tuft cells (TCs), a kind of epithelial cell with distinct morphological characteristics, play a significant role in various physiological processes. TCs can be broadly categorized into different subtypes depending on different molecular criteria. In this review, we discuss its biological properties and role in maintaining homeostasis in the gastrointestinal tract. We also emphasize its relevance to the immune system and highlight its powerful influence on intestinal diseases, including inflammations and tumors. In addition, we provide fresh insights into future clinical diagnostic and therapeutic strategies related to TCs.

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.

The critical roles and therapeutic implications of tuft cells in cancer

Tuft cells are solitary chemosensory epithelial cells with microvilli at the top, which are found in hollow organs such as the gastrointestinal tract, pancreas, and lungs. Recently, an increasing number of studies have revealed the chemotactic abilities and immune function of the tuft cells, and numerous efforts have been devoted to uncovering the role of tuft cells in tumors. Notably, accumulating evidence has shown that the specific genes (POU2F3, DCLK1) expressed in tuft cells are involved in vital processes related with carcinogenesis and cancer development. However, the interaction between the tuft cells and cancer remains to be further elucidated. Here, based on an introduction of biological functions and specific markers of the tuft cells, we have summarized the functional roles and potential therapeutic implications of tuft cells in cancers, including pancreatic cancer, lung cancer, gastric cancer, colon cancer, and liver cancer, which is in the hope of inspiring the future research in validating tuft cells as novel strategies for cancer therapies.

Duodenal cholinergic tuft cell number is increased in functional dyspepsia

BACKGROUND

Low-grade duodenal inflammation has recently been identified in patients with functional dyspepsia (FD). Chemosensory tuft cells were reported to be associated with gastrointestinal diseases. We therefore assessed duodenal tuft cell density and microinflammation in patients with FD to determine whether these measures could serve as useful biomarkers, and also correlated tuft cell density and microinflammation in FD patients.

METHODS

Duodenal biopsy specimens were obtained from patients with FD and from controls. Tuft cells, eosinophils, and mast cells were immunochemically stained with specific antibodies. Tuft cells were identified by immunostaining for doublecortin-like kinase 1 (DCLK1); cholinergic tuft cells were assessed by double staining for choline acetyltransferase (ChAT) and DCLK1. Immune-type tuft cells were assessed by IL-25 mRNA expression using real-time PCR.

KEY RESULTS

The density of intramucosal eosinophils and mast cells was significantly higher in the duodenum of FD patients than in controls. The density of tuft cells was significantly higher in the duodenum of FD patients compared with controls, and significantly correlated with eosinophil density in the duodenum of FD patients and controls. Moreover, a fraction of ChAT-positive cells was DCLK1 positive; all duodenal DCLK1+ tuft cells were ChAT-immunoreactive in FD and in control subjects.

CONCLUSIONS AND INFERENCES

Cholinergic tuft cell density was higher in the duodenum of patients with FD and significantly correlated with eosinophil density. Further studies are needed to investigate the pathophysiological significance of tuft cells in FD and may provide valuable clues to the pathophysiology of FD.

Intestinal immune responses to commensal and pathogenic protozoa

The physical barrier of the intestine and associated mucosal immunity maintains a delicate homeostatic balance between the host and the external environment by regulating immune responses to commensals, as well as functioning as the first line of defense against pathogenic microorganisms. Understanding the orchestration and characteristics of the intestinal mucosal immune response during commensal or pathological conditions may provide novel insights into the mechanisms underlying microbe-induced immunological tolerance, protection, and/or pathogenesis. Over the last decade, our knowledge about the interface between the host intestinal mucosa and the gut microbiome has been dominated by studies focused on bacterial communities, helminth parasites, and intestinal viruses. In contrast, specifically how commensal and pathogenic protozoa regulate intestinal immunity is less well studied. In this review, we provide an overview of mucosal immune responses induced by intestinal protozoa, with a major focus on the role of different cell types and immune mediators triggered by commensal (Blastocystis spp. and Tritrichomonas spp.) and pathogenic (Toxoplasma gondii, Giardia intestinalis, Cryptosporidium parvum) protozoa. We will discuss how these various protozoa modulate innate and adaptive immune responses induced in experimental models of infection that benefit or harm the host.

Micro(nano)plastics in food system: potential health impacts on human intestinal system

Micro(nano)plastics (MNPs) in human food system have been broadly recognized by researchers and have drawn an increasing public attention to their potential health risks, particularly the risk to the intestinal system regarding the long-term exposure to MNPs through food consumption. This study aims to review the environmental properties (formation and composition) of MNPs and MNPs pollution in human food system following the order of food production, food processing and food consumption. The current analytic and identical technologies utilized by researchers are also summarized in this review. In fact, parts of commonly consumed food raw materials, processed food and the way to take in food all become the possible sources for human MNPs ingestion. In addition, the available literatures investigating MNPs-induced intestinal adverse effect are discussed from in vitro models and in vivo mammalian experiments, respectively. Particle translocation, cytotoxicity, damaged gut barrier, intestinal inflammation as well as microbial alteration are mostly reported. Moreover, the practical remediation strategies for MNPs pollution are also illustrated in the last section. This review is expected to provide a research insight for foodborne MNPs and arouse more public awareness of MNPs pollution in food and potential risk for human intestinal health.

Intestinal cellular heterogeneity and disease development revealed by single-cell technology

The intestinal epithelium is responsible for food digestion and nutrient absorption and plays a critical role in hormone secretion, microorganism defense, and immune response. These functions depend on the integral single-layered intestinal epithelium, which shows diversified cell constitution and rapid self-renewal and presents powerful regeneration plasticity after injury. Derailment of homeostasis of the intestine epithelium leads to the development of diseases, most commonly including enteritis and colorectal cancer. Therefore, it is important to understand the cellular characterization of the intestinal epithelium at the molecular level and the mechanisms underlying its homeostatic maintenance. Single-cell technologies allow us to gain molecular insights at the single-cell level. In this review, we summarize the single-cell RNA sequencing applications to understand intestinal cell characteristics, spatiotemporal evolution, and intestinal disease development.

Influence of Foods and Nutrition on the Gut Microbiome and Implications for Intestinal Health

Food components in our diet provide not only necessary nutrients to our body but also substrates for the mutualistic microbial flora in our gastrointestinal tract, termed the gut microbiome. Undigested food components are metabolized to a diverse array of metabolites. Thus, what we eat shapes the structure, composition, and function of the gut microbiome, which interacts with the gut epithelium and mucosal immune system and maintains intestinal homeostasis in a healthy state. Alterations of the gut microbiome are implicated in many diseases, such as inflammatory bowel disease (IBD). There is growing interest in nutritional therapy to target the gut microbiome in IBD. Investigations into dietary effects on the composition changes in the gut microbiome flourished in recent years, but few focused on gut physiology. This review summarizes the current knowledge regarding the impacts of major food components and their metabolites on the gut and health consequences, specifically within the GI tract. Additionally, the influence of the diet on the gut microbiome-host immune system interaction in IBD is also discussed. Understanding the influence of the diet on the interaction of the gut microbiome and the host immune system will be useful in developing nutritional strategies to maintain gut health and restore a healthy microbiome in IBD.

Digestive stability and transport ability changes of β-lactoglobulin–catechin complexes by M cell model in vitro

The current research on interaction between catechin and protein has focused on non-covalent crosslinking, however, the mechanism of free radical-induced crosslinking between catechin and β-lactoglobulin (BLG) is not known. In this study, BLG bound to four catechins [epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG)]. The structure change of complex was investigated by circular dichroism spectroscopy, ultraviolet-visible (UV-vis) spectroscopy and Acid and 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence spectroscopy. M cell model was constructed to evaluate the transintestinal epithelial transport capacity of complex digestive products. The results showed that catechins were covalently bound to BLG by C-S and C-N bonds and their binding content was EGCG&gt;EGC&gt;ECG&gt;EC. Moreover, catechins could change the secondary structure of BLG, with the decrease of α-helix and reduction of the irregular coilings, which leads to the loose spatial structure of the protein. Moreover, the catechin could enhance further the digestibility of BLG. Transport capacity of digestive products of M cell model was about twice of that of the Caco-2 cell model, indicating that M cell model had better antigen transport capacity. The difference between groups indicated that the transport efficiency of digestive products was decreased with the presence of catechin, in which BLG-EGCG and BLG-EGC groups were transported more strong than those of BLG-EC and BLG-ECG groups. The transport efficiency of BLG-catechin complexes were lower than that of BLG, indicating that catechin had the protective and repair roles on intestinal barrier permeability.

Differential gene expression in iPSC-derived human intestinal epithelial cell layers following exposure to two concentrations of butyrate, propionate and acetate

Intestinal epithelial cells and the intestinal microbiota are in a mutualistic relationship that is dependent on communication. This communication is multifaceted, but one aspect is communication through compounds produced by the microbiota such as the short-chain fatty acids (SCFAs) butyrate, propionate and acetate. Studying the effects of SCFAs and especially butyrate in intestinal epithelial cell lines like Caco-2 cells has been proven problematic. In contrast to the in vivo intestinal epithelium, Caco-2 cells do not use butyrate as an energy source, leading to a build-up of butyrate. Therefore, we used human induced pluripotent stem cell derived intestinal epithelial cells, grown as a cell layer, to study the effects of butyrate, propionate and acetate on whole genome gene expression in the cells. For this, cells were exposed to concentrations of 1 and 10 mM of the individual short-chain fatty acids for 24 h. Unique gene expression profiles were observed for each of the SCFAs in a concentration-dependent manner. Evaluation on both an individual gene level and pathway level showed that butyrate induced the biggest effects followed by propionate and then acetate. Several known effects of SCFAs on intestinal cells were confirmed, such as effects on metabolism and immune responses. The changes in metabolic pathways in the intestinal epithelial cell layers in this study demonstrate that there is a switch in energy homeostasis, this is likely associated with the use of SCFAs as an energy source by the induced pluripotent stem cell derived intestinal epithelial cells similar to in vivo intestinal tissues where butyrate is an important energy source.

OCA-T1 and OCA-T2 are coactivators of POU2F3 in the tuft cell lineage

Tuft cells are a rare chemosensory lineage that coordinates immune and neural responses to foreign pathogens in mucosal tissues1. Recent studies have also revealed tuft-cell-like human tumours2,3, particularly as a variant of small-cell lung cancer. Both normal and neoplastic tuft cells share a genetic requirement for the transcription factor POU2F3 (refs. 2,4), although the transcriptional mechanisms that generate this cell type are poorly understood. Here we show that binding of POU2F3 to the uncharacterized proteins C11orf53 and COLCA2 (renamed here OCA-T1/POU2AF2 and OCA-T2/POU2AF3, respectively) is critical in the tuft cell lineage. OCA-T1 and OCA-T2 are paralogues of the B-cell-specific coactivator OCA-B; all three proteins are encoded in a gene cluster and contain a conserved peptide that binds to class II POU transcription factors and a DNA octamer motif in a bivalent manner. We demonstrate that binding between POU2F3 and OCA-T1 or OCA-T2 is essential in tuft-cell-like small-cell lung cancer. Moreover, we generated OCA-T1-deficient mice, which are viable but lack tuft cells in several mucosal tissues. These findings reveal that the POU2F3-OCA-T complex is the master regulator of tuft cell identity and a molecular vulnerability of tuft-cell-like small-cell lung cancer.

Structural and Functional Thymic Biomarkers Are Involved in the Pathogenesis of Thymic Epithelial Tumors: An Overview

The normal human thymus originates from the third branchial cleft as two paired anlages that descend into the thorax and fuse on the midline of the anterior–superior mediastinum. Alongside the epithelial and lymphoid components, different types of lymphoid accessory cells, stromal mesenchymal and endothelial cells migrate to, or develop in, the thymus. After reaching maximum development during early postnatal life, the human thymus decreases in size and lymphocyte output drops with age. However, thymic immunological functions persist, although they deteriorate progressively. Several major techniques were fundamental to increasing the knowledge of thymic development and function during embryogenesis, postnatal and adult life; these include immunohistochemistry, immunofluorescence, flow cytometry, in vitro colony assays, transplantation in mice models, fetal organ cultures (FTOC), re-aggregated thymic organ cultures (RTOC), and whole-organ thymic scaffolds. The thymic morphological and functional characterization, first performed in the mouse, was then extended to humans. The purpose of this overview is to provide a report on selected structural and functional biomarkers of thymic epithelial cells (TEC) involved in thymus development and lymphoid cell maturation, and on the historical aspects of their characterization, with particular attention being paid to biomarkers also involved in Thymic Epithelial Tumor (TET) pathogenesis. Moreover, a short overview of targeted therapies in TET, based on currently available experimental and clinical data and on potential future advances will be proposed.

Enteroendocrine System and Gut Barrier in Metabolic Disorders

With the continuous rise in the worldwide prevalence of obesity and type 2 diabetes, developing therapies regulating body weight and glycemia has become a matter of great concern. Among the current treatments, evidence now shows that the use of intestinal hormone analogs (e.g., GLP1 analogs and others) helps to control glycemia and reduces body weight. Indeed, intestinal endocrine cells produce a large variety of hormones regulating metabolism, including appetite, digestion, and glucose homeostasis. Herein, we discuss how the enteroendocrine system is affected by local environmental and metabolic signals. These signals include those arising from unbalanced diet, gut microbiota, and the host metabolic organs and their complex cross-talk with the intestinal barrier integrity.

Recent advance of <i>in vitro</i> models in natural phytochemicals absorption and metabolism

Natural phytochemicals absorption and metabolic process are mainly in the human gut. Simulating the absorption and metabolism of natural phytochemicals in vitro to predict the rate and degree of absorption of natural phytochemicals provides convenience for many researchers. However, in this process, many physiological factors <i>in vitro</i> are affected, such as stomach and intestinal juice composition, pH, intestinal transmission rate and so on. In recent years, the research methods have gradually improved to make these models more suitable for the natural phytochemicals absorption process, <i>in vitro</i> simulation models have become an essential means to study natural phytochemicals absorption. Therefore, this paper introduces the advantages and disadvantages of commonly used <i>in vitro</i> simulation models of natural phytochemicals absorption and metabolism, as well as briefly introduces the working principle of each model. To provide a theoretical basis for simulating natural phytochemicals absorption <i>in vitro</i> and development and utilization of natural phytochemicals.

Sox9, Hopx, and survivin and tuft cell marker DCLK1 expression in normal canine intestine and in intestinal adenoma and adenocarcinoma

Self-renewal of the intestinal epithelium originates from stem cells located at the crypt base. Upregulation of various stem cell markers in intestinal epithelial neoplasms indicates a potential role of stem cells in tumorigenesis. In this study, the immunoreactivity of potential intestinal stem cell markers ( Sry box transcription factor 9 [Sox9], homeodomain-only protein [Hopx], survivin) and tuft cell marker doublecortin-like kinase 1 (DCLK1) in normal canine intestine and intestinal epithelial neoplasms was investigated. Formalin-fixed paraffin-embedded (FFPE) small and large intestine as well as intestinal neoplasms (55 colorectal adenomas [CRAs], 17 small intestinal adenocarcinomas [SICs], and 12 colorectal adenocarcinomas [CRCs]) were analyzed immunohistologically. Potential stem cell markers Sox9, Hopx, and survivin were detected in the crypts of normal canine small and large intestine. DCLK1+ tuft cells were present in decreasing numbers along the crypt-villus axis of the jejunum and rarely detectable in large intestine. In canine intestinal epithelial tumors, nuclear Sox9 immunoreactivity was detectable in 84.9% (CRA), 80% (CRC), and 77% of epithelial neoplastic cells (SIC). Hopx and survivin were expressed within cytoplasm and nuclei of neoplastic cells in benign and malignant tumors. DCLK1 showed a cytoplasmic reaction within neoplastic cells. The combined score of Hopx, DCLK1, and survivin varied among the examined cases. Overall, malignant tumors showed lower DCLK1 scores but higher Hopx scores in comparison with benign tumors. For survivin, no differences were detectable. In conclusion, stem cell markers Sox9, Hopx, and survivin were detectable at the crypt base and the immunoreactivity of Sox9, DCLK1, survivin, and Hopx was increased in canine intestinal adenomas and adenocarcinomas compared with normal mucosa.

Mechanisms of uptake and transport of particulate formulations in the small intestine

Micro- and nano-scale particulate formulations are widely investigated towards improving the oral bioavailability of both biologics and drugs with low solubility and/or low intestinal permeability. Particulate formulations harnessing physiological intestinal transport pathways have recently yielded remarkably high oral bioavailabilities, illustrating the need for better understanding the specific pathways underpinning particle small intestinal absorption and the relative role of intestinal cells. Mechanistic knowledge has been hampered by the well acknowledged limitations of current in vitro, in vivo and ex vivo models relevant to the human intestinal physiology and the lack of standardization in studies reporting absorption data. Here we review the relevant literature and critically discusses absorption pathways with a focus on the role of specific intestinal epithelial and immune cells. We conclude that while Microfold (M) cells are a valid target for oral vaccines, enterocytes play a greater role in the systemic bioavailability of orally administrated particulate formulations, particularly within the sub-micron size range. We also comment on less-reported mechanisms such as paracellular permeability of particles, persorption due to cell damage and uptake by migratory immune cells.

Identification of cholinergic cells with chemosensory traits in the porcine uterus

Chemosensory cells are specialized epithelial cells that act as sentinels near body entry sites. The majority of these cells express a cholinergic phenotype and utilize the taste signaling system to monitor the mucosal environment for potentially harmful substances, triggering protective reflexes. We report the identification of cells with a putative chemosensory role in the uterus. Presumptive chemosensory cells were immunoreactive to key components of the taste transduction, including the transient receptor potential channel M5 (TRPM5) and the phospholipase Cβ2 (PLCB2). These cells localized to endometrial glandular and luminal epithelia, while absent from myometrium and perimetrium. Double immunofluorescence revealed co-expression of chemosensory cell markers with the acetylcholine (ACh) synthesizing enzyme, choline acetyltransferase (ChAT). Further, we investigated the regional distribution and expression of chemosensory cells at different stages of the estrous cycle. Uteri were collected postmortem from gilts and stages of the ovarian cycle were determined macroscopically. The uteri were classified into three groups: prepubertal (PB), follicular (FOL), or luteal (LUT). The number of ChAT-immunoreactive cells was increased in the luminal epithelium in the caudal compartment compared to the cranial region of the uterine horn, and at the LUT compared to PB and FOL stages. An increase in ChAT protein abundance in LUT uterine homogenates was noted, although not followed by an increase in ACh content. In summary, our study has identified a hitherto unrecognized cholinergic cell in the uterus that has chemosensory traits and may be involved in a multitude of biological processes.

Tuft Cells Increase Following Ovine Intestinal Parasite Infections and Define Evolutionarily Conserved and Divergent Responses

Helminth parasite infections of humans and livestock are a global health and economic problem. Resistance of helminths to current drug treatment is an increasing problem and alternative control approaches, including vaccines, are needed. Effective vaccine design requires knowledge of host immune mechanisms and how these are stimulated. Mouse models of helminth infection indicate that tuft cells, an unusual type of epithelial cell, may 'sense' infection in the small intestine and trigger a type 2 immune response. Currently nothing is known of tuft cells in immunity in other host species and in other compartments of the gastrointestinal (GI) tract. Here we address this gap and use immunohistochemistry and single cell RNA-sequencing to detail the presence and gene expression profile of tuft cells in sheep following nematode infections. We identify and characterize tuft cells in the ovine abomasum (true stomach of ruminants) and show that they increase significantly in number following infection with the globally important nematodes Teladorsagia circumcincta and Haemonchus contortus. Ovine abomasal tuft cells show enriched expression of tuft cell markers POU2F3, GFI1B, TRPM5 and genes involved in signaling and inflammatory pathways. However succinate receptor SUCNR1 and free fatty acid receptor FFAR3, proposed as 'sensing' receptors in murine tuft cells, are not expressed, and instead ovine tuft cells are enriched for taste receptor TAS2R16 and mechanosensory receptor ADGRG6. We also identify tuft cell sub-clusters at potentially different stages of maturation, suggesting a dynamic process not apparent from mouse models of infection. Our findings reveal a tuft cell response to economically important parasite infections and show that while tuft cell effector functions have been retained during mammalian evolution, receptor specificity has diverged. Our data advance knowledge of host-parasite interactions in the GI mucosa and identify receptors that may potentiate type 2 immunity for optimized control of parasitic nematodes.

Inhibition of DCLK1 with DCLK1-IN-1 Suppresses Renal Cell Carcinoma Invasion and Stemness and Promotes Cytotoxic T-Cell-Mediated Anti-Tumor Immunity

Simple Summary

In this study, we found that the novel small molecule kinase inhibitor DCLK1-IN-1 not only inhibited DCLK1 phosphorylation, stemness, and EMT-related properties of RCC cells but also revealed its potential as an immunotherapy agent and potential combination therapy with anti-PD1 against RCC in immune co-culture experiments.

Abstract

The approval of immune checkpoint inhibitors has expanded treatment options for renal cell carcinoma (RCC), but new therapies that target RCC stemness and promote anti-tumor immunity are needed. Previous findings demonstrate that doublecortin-like kinase 1 (DCLK1) regulates stemness and is associated with RCC disease progression. Herein, we demonstrate that small-molecule kinase inhibitor DCLK1-IN-1 strongly inhibits DCLK1 phosphorylation and downregulates pluripotency factors and cancer stem cell (CSC) or epithelial-mesenchymal transition (EMT)-associated markers including c-MET, c-MYC, and N-Cadherin in RCC cell lines. Functionally, DCLK1-IN-1 treatment resulted in significantly reduced colony formation, migration, and invasion. Additionally, assays using floating or Matrigel spheroid protocols demonstrated potent inhibition of stemness. An analysis of clinical populations showed that DCLK1 predicts RCC survival and that its expression is correlated with reduced CD8+ cytotoxic T-cell infiltration and increases in M2 immunosuppressive macrophage populations. The treatment of RCC cells with DCLK1-IN-1 significantly reduced the expression of immune checkpoint ligand PD-L1, and co-culture assays using peripheral blood monocytes (PBMCs) or T-cell expanded PBMCs demonstrated a significant increase in immune-mediated cytotoxicity alone or in combination with anti-PD1 therapy. Together, these findings demonstrate broad susceptibility to DCLK1 kinase inhibition in RCC using DCLK1-IN-1 and provide the first direct evidence for DCLK1-IN-1 as an immuno-oncology agent.

DCLK1 and its interaction partners: An effective therapeutic target for colorectal cancer

Doublecortin-like kinase protein 1 (DCLK1) is a microtubule-associated protein with a C-terminal serine/threonine kinase domain. Its expression was first reported in radial glial cells, where it serves an essential role in early neurogenesis, and since then, other functions of the DCLK1 protein have also been identified. Initially considered to be a marker of quiescent gastrointestinal and pancreatic stem cells, DCLK1 has recently been identified in the gastrointestinal tract as a marker of tuft cells. It has also been implicated in different types of cancer, where it regulates several vital pathways, such as Kras signaling. However, its underlying molecular mechanisms remain unclear. The present review discusses the different roles of DCLK1 and its interactions with other proteins that are homologically similar to DCLK1 to develop a novel therapeutic strategy to target cancer cells more accurately.

Type 2 immunity in intestinal homeostasis and inflammatory bowel disease

Type 2 immune responses commonly emerge during allergic reactions or infections with helminth parasites. Most of the cytokines associated with type 2 immune responses are IL-4, IL-5, and IL13, which are mainly produced by T helper 2 cells (T_H2), eosinophils, basophils, mast cells, and group 2 innate lymphoid cells (ILC2s). Over the course of evolution, humans have developed type 2 immune responses to fight infections and to protect tissues from the potential collateral damage caused by inflammation. For example, worm parasites induce potent type 2 immune responses, which are needed to simultaneously clear the pathogen and to promote tissue repair following injury. Due to the strong type 2 immune responses induced by helminths, which can promote tissue repair in the damaged epithelium, their use has been suggested as a possible treatment for inflammatory bowel disease (IBD); however, the role of type 2 immune responses in the initiation and progression of IBD is not fully understood. In this review, we discuss the molecular and cellular mechanisms that regulate type 2 immune responses during intestinal homeostasis, and we briefly discuss the scarce evidence linking type 2 immune responses with the aetiology of IBD.

An MST4-pβ-CateninThr40 Signaling Axis Controls Intestinal Stem Cell and Tumorigenesis

Elevated Wnt/β-catenin signaling has been commonly associated with tumorigenesis especially colorectal cancer (CRC). Here, an MST4-pβ-cateninThr40 signaling axis essential for intestinal stem cell (ISC) homeostasis and CRC development is uncovered. In response to Wnt3a stimulation, the kinase MST4 directly phosphorylates β-catenin at Thr40 to block its Ser33 phosphorylation by GSK3β. Thus, MST4 mediates an active process that prevents β-catenin from binding to and being degraded by β-TrCP, leading to accumulation and full activation of β-catenin. Depletion of MST4 causes loss of ISCs and inhibits CRC growth. Mice bearing either MST4T178E mutation with constitutive kinase activity or β-cateninT40D mutation mimicking MST4-mediated phosphorylation show overly increased ISCs/CSCs and exacerbates CRC. Furthermore, the MST4-pβ-cateninThr40 axis is upregulated and correlated with poor prognosis of human CRC. Collectively, this work establishes a previously undefined machinery for β-catenin activation, and further reveals its function in stem cell and tumor biology, opening new opportunities for targeted therapy of CRC.

Microplastic: A potential threat to human and animal health by interfering with the intestinal barrier function and changing the intestinal microenvironment

Plastics are widely used in many fields due to their stable physical and chemical properties, and their global production and usage increase significantly every year, which leads to the accumulation of microplastics in the entire ecosystem. Numerous studies have shown that microplastics (MPs) have harmful effects on living organisms. This review aims to provide a comprehensive conclusion of the current knowledge of the impacts of MPs on the stability of the gut microenvironment, especially on the gut barrier. Studies showed that exposure to MPs could cause oxidative damage and inflammation in the gut, as well as the destruction of the gut epithelium, reduction of the mucus layer, microbial disorders, and immune cell toxicity. Although there are few reports directly related to humans, we hoped that this review could bring together more and more evidence that exposure to MPs results in disturbances of the intestinal microenvironment. Therefore, it is necessary to investigate their threats to human health further.

Cell differentiation is disrupted by MYO5B loss through Wnt/Notch imbalance

Functional loss of myosin Vb (MYO5B) induces a variety of deficits in intestinal epithelial cell function and causes a congenital diarrheal disorder, microvillus inclusion disease (MVID). The impact of MYO5B loss on differentiated cell lineage choice has not been investigated. We quantified the populations of differentiated epithelial cells in tamoxifen-induced, epithelial cell–specific MYO5B-knockout (VilCre^ERT2 Myo5b^fl/fl) mice utilizing digital image analysis. Consistent with our RNA-sequencing data, MYO5B loss induced a reduction in tuft cells in vivo and in organoid cultures. Paneth cells were significantly increased by MYO5B deficiency along with expansion of the progenitor cell zone. We further investigated the effect of lysophosphatidic acid (LPA) signaling on epithelial cell differentiation. Intraperitoneal LPA significantly increased tuft cell populations in both control and MYO5B-knockout mice. Transcripts for Wnt ligands were significantly downregulated by MYO5B loss in intestinal epithelial cells, whereas Notch signaling molecules were unchanged. Additionally, treatment with the Notch inhibitor dibenzazepine (DBZ) restored the populations of secretory cells, suggesting that the Notch pathway is maintained in MYO5B-deficient intestine. MYO5B loss likely impairs progenitor cell differentiation in the small intestine in vivo and in vitro, partially mediated by Wnt/Notch imbalance. Notch inhibition and/or LPA treatment may represent an effective therapeutic approach for treatment of MVID.

Brg1 is required to maintain colorectal cancer stem cells

Tumor cells capable of self-renewal and continuous production of progeny cells are called tumor stem cells (TSCs) and are considered to be potential therapeutic targets. However, the mechanisms underlying the survival and function of TSCs are not fully understood. We previously reported that chromatin remodeling regulator Brg1 is essential for intestinal stem cells in mice and Dclk1 is an intestinal TSC marker. In this study, we investigated the role of Brg1 in Dclk1⁺ intestinal tumor cells for the maintenance of intestinal tumors in mice. Specific ablation of Brg1 in Dclk1⁺ intestinal tumor cells reduced intestinal tumors in Apc^Min mice, and continuous ablation of Brg1 maintained the reduction of intestinal tumors. Lineage tracing in the context of Brg1 ablation in Dclk1⁺ intestinal tumor cells revealed that Brg1-null Dclk1⁺ intestinal tumor cells did not give rise to their descendent tumor cells, indicating that Brg1 is essential for the self-renewal of Dclk1⁺ intestinal tumor cells. Five days after Brg1 ablation, we observed increased apoptosis in Dclk1⁺ tumor cells. Furthermore, Brg1 was crucial for the stemness of intestinal tumor cells in a spheroid culture system. BRG1 knockdown also impaired cell proliferation and increased apoptosis in human colorectal cancer (CRC) cells. Microarray analysis revealed that apoptosis-related genes were upregulated and stem cell-related genes were downregulated in human CRC cells by BRG1 suppression. Consistently, high BRG1 expression correlated with poor disease-specific survival in human CRC patients. These data indicate that Brg1 plays a crucial role in intestinal TSCs in mice by inhibiting apoptosis and is critical for cell survival and stem cell features in human CRC cells. Thus, BRG1 represents a new therapeutic target for human CRC. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Prostaglandin regulation of type 2 inflammation: From basic biology to therapeutic interventions

Type 2 immunity is critical for the protective and repair responses that mediate resistance to parasitic helminth infection. This immune response also drives aberrant inflammation during atopic diseases. Prostaglandins are a class of critical lipid mediators that are released during type 2 inflammation and are integral in controlling the initiation, activation, maintenance, effector functions, and resolution of Type 2 inflammation. In this review, we explore the roles of the different prostaglandin family members and the receptors they bind to during allergen‐ and helminth‐induced Type 2 inflammation and the mechanism through which prostaglandins promote or suppress Type 2 inflammation. Furthermore, we discuss the potential role of prostaglandins produced by helminth parasites in the regulation of host–pathogen interactions, and how prostaglandins may regulate the inverse relationship between helminth infection and allergy. Finally, we discuss opportunities to capitalize on our understanding of prostaglandin pathways to develop new therapeutic options for humans experiencing Type 2 inflammatory disorders that have a significant prostaglandin‐driven component including allergic rhinitis and asthma.

Molecular phenotyping reveals the identity of Barrett's esophagus and its malignant transition

The origin of human metaplastic states and their propensity for cancer is poorly understood. Barrett's esophagus is a common metaplastic condition that increases the risk for esophageal adenocarcinoma, and its cellular origin is enigmatic. To address this, we harvested tissues spanning the gastroesophageal junction from healthy and diseased donors, including isolation of esophageal submucosal glands. A combination of single-cell transcriptomic profiling, in silico lineage tracing from methylation, open chromatin and somatic mutation analyses, and functional studies in organoid models showed that Barrett's esophagus originates from gastric cardia through c-MYC and HNF4A-driven transcriptional programs. Furthermore, our data indicate that esophageal adenocarcinoma likely arises from undifferentiated Barrett's esophagus cell types even in the absence of a pathologically identifiable metaplastic precursor, illuminating early detection strategies.

Decreased number of colonic tuft cells in quiescent ulcerative colitis patients

BACKGROUND

Colonic tuft cells are epithelial chemosensory cells involved in barrier integrity, modulation of inflammatory responses and gut homeostasis. Recent evidence indicates an involvement of tuft cells in ulcerative colitis pathogenesis, though mechanisms remain largely unknown.Here, we quantified the colonic tuft cell population in patients with quiescent ulcerative colitis as compared to patients without identified colonic disease (controls).

METHODS

In this retrospective study, we obtained endoscopic colonic sigmoid biopsies from 14 patients with quiescent ulcerative colitis and from 17 controls. In a blinded central-reading design, we identified tuft cells by immunohistochemistry using a cyclooxygenase-1 antibody as a marker and performed a simple counting by visual inspection. Poisson regression was employed for statistics and results were adjusted for gender, age and smoking status.

RESULTS

Ulcerative colitis patients demonstrated a 55% reduced tuft cell count in colonic mucosa compared with the control group (95% confidence limit: range 31-71%, P = 0.0002). Ulcerative colitis patients had a mean tuft cells count of 46 tuft cells/mm2 (95% CI, 36-59), while controls demonstrated a mean of 104 tuft cells/mm2 (95% CI, 79-136). No interactions of other covariates, such as age, smoking status, total duration of ulcerative colitis disease and duration of clinical remission prior to study inclusion were detected between ulcerative colitis patients and controls.

CONCLUSION

Quiescent ulcerative colitis patients have a relatively low number of colonic tuft cells. Further studies are warranted to explore the potential involvement of tuft cells in ulcerative colitis pathogenesis.

Clump sequencing exposes the spatial expression programs of intestinal secretory cells

Single-cell RNA sequencing combined with spatial information on landmark genes enables reconstruction of spatially-resolved tissue cell atlases. However, such approaches are challenging for rare cell types, since their mRNA contents are diluted in the spatial transcriptomics bulk measurements used for landmark gene detection. In the small intestine, enterocytes, the most common cell type, exhibit zonated expression programs along the crypt-villus axis, but zonation patterns of rare cell types such as goblet and tuft cells remain uncharacterized. Here, we present ClumpSeq, an approach for sequencing small clumps of attached cells. By inferring the crypt-villus location of each clump from enterocyte landmark genes, we establish spatial atlases for all epithelial cell types in the small intestine. We identify elevated expression of immune-modulatory genes in villus tip goblet and tuft cells and heterogeneous migration patterns of enteroendocrine cells. ClumpSeq can be applied for reconstructing spatial atlases of rare cell types in other tissues and tumors.

Adhesion receptor ADGRG2/GPR64 is in the GI-tract selectively expressed in mature intestinal tuft cells

Objective

GPR64/ADGRG2 is an orphan Adhesion G protein-coupled receptor (ADGR) known to be mainly expressed in the parathyroid gland and epididymis. This investigation aimed to delineate the cellular expression of GPR64 throughout the body with focus on the gastrointestinal (GI) tract.

Methods

Transgenic Gpr64^mCherry reporter mice were histologically examined throughout the body and reporter protein expression in intestinal tuft cells was confirmed by specific cell ablation. The GPCR repertoire of intestinal Gpr64^mCherry-positive tuft cells was analyzed by quantitative RT-PCR analysis and in situ hybridization. The Gpr64^mCherry was crossed into the general tuft cell reporter Trpm5^GFP to generate small intestinal organoids for time-lapse imaging. Intestinal tuft cells were isolated from small intestine, FACS-purified and transcriptionally compared using RNA-seq analysis.

Results

Expression of the Gpr64^mCherry reporter was identified in multiple organs and specifically in olfactory microvillous cells, enteric nerves, and importantly in respiratory and GI tuft cells. In the small intestine, cell ablation targeting Gpr64-expressing epithelial cells eliminated tuft cells. Transcriptional analysis of small intestinal Gpr64^mCherry -positive tuft cells confirmed expression of Gpr64 and the chemo-sensors Sucnr1, Gprc5c, Drd3, and Gpr41/Ffar3. Time-lapse studies of organoids from Trpm5^GFP:Gpr64^mCherry mice revealed sequential expression of initially Trpm5^GFP and subsequently also Gpr64^mCherry in maturing intestinal tuft cells. RNA-seq analysis of small intestinal tuft cells based on these two markers demonstrated a dynamic change in expression of transcription factors and GPCRs from young to mature tuft cells.

Conclusions

GPR64 is expressed in chemosensory epithelial cells across a broad range of tissues; however, in the GI tract, GPR64 is remarkably selectively expressed in mature versus young immunoregulatory tuft cells.

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GPR64-RFP is expressed mainly in chemosensory epithelial cells, including tuft cells.

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Maturing intestinal tuft cells initially express Trpm5 and subsequently Gpr64.

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Mature intestinal Gpr64+ tuft cells express Sucnr1, Gprc5c, Drd3, and Gpr41/Ffar3.

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RNAseq analysis reveals dynamic transcriptional change of mature vs. young tuft cells.

Crossing the barriers: Revisiting the gut feeling in rheumatoid arthritis

To avoid autoimmunity, it is essential to keep the balance between the defence against pathogens and the maintenance of tolerance to self-antigens. Mucosal inflammation may lead to breakdown of tolerance and activation of autoreactive cells. Growing evidence suggests a major contribution of gut microbiota to the onset of chronic, autoimmune inflammatory diseases including rheumatoid arthritis (RA). RA patients show significant differences in the composition of gut microbiota compared to healthy controls, and in murine arthritis models certain bacteria can induce inflammatory Th17 responses or autoantibody production. The gut microbiota plays an important role in regulating the balance between immunogenic and tolerogenic immune responses. The intestinal barrier is the site of the body where most host-microbiota interaction takes place. Certain microbiota or their metabolites can cause a break in homeostasis by affecting the intestinal barrier integrity and permeability. However, an intact intestinal barrier is essential to separate the intestinal epithelium from toxins, microorganisms, and antigens in the gut lumen. This review will focus on the correlation between a leaky gut and the onset of arthritis. Furthermore, it will be discussed how targeting the intestinal barrier function by dietary changes might provide an opportunity to modulate the development of RA.