Single Cell Analysis of Human Colonoids Exposed to Uranium-Bearing Dust.

BACKGROUND: Uranium exposure remains an important environmental legacy and physiological health concern, with hundreds of abandoned uranium mines located in the Southwestern United States largely impacting underserved indigenous communities. The negative effects of heavy metals on barrier permeability and inhibition of intestinal epithelial healing have been described; however, transcriptomic changes within the intestinal epithelial cells and impacts on lineage differentiation are largely unknown. OBJECTIVES: Herein, we sought to determine the molecular and cellular changes that occur in the colon in response to uranium bearing dust (UBD) exposure. METHODS: Human colonoids from three biologically distinct donors were acutely exposed to UBD then digested for single cell RNA sequencing to define the molecular changes that occur to specific identities of colonic epithelial cells. Validation in colonoids was assessed using morphological and imaging techniques. RESULTS: Human colonoids acutely exposed to UBD exhibited disrupted proliferation and hyperplastic differentiation of the secretory lineage cell, enteroendocrine cells (EEC). Single-cell RNA sequencing also showed more EEC subtypes present in UBD-exposed colonoids. DISCUSSION: These findings highlight the significance of crypt-based proliferative cells and secretory cell differentiation using human colonoids to model major colonic responses to uranium-bearing particulate dust exposure. https://doi.org/10.1289/EHP13855.

In Vivo Tissue Distribution of Polystyrene or Mixed Polymer Microspheres and Metabolomic Analysis after Oral Exposure in Mice.

BACKGROUND: Global plastic use has consistently increased over the past century with several different types of plastics now being produced. Much of these plastics end up in oceans or landfills leading to a substantial accumulation of plastics in the environment. Plastic debris slowly degrades into microplastics (MPs) that can ultimately be inhaled or ingested by both animals and humans. A growing body of evidence indicates that MPs can cross the gut barrier and enter into the lymphatic and systemic circulation leading to accumulation in tissues such as the lungs, liver, kidney, and brain. The impacts of mixed MPs exposure on tissue function through metabolism remains largely unexplored. OBJECTIVES: This study aims to investigate the impacts of polymer microspheres on tissue metabolism in mice by assessing the microspheres ability to translocate across the gut barrier and enter into systemic circulation. Specifically, we wanted to examine microsphere accumulation in different organ systems, identify concentration-dependent metabolic changes, and evaluate the effects of mixed microsphere exposures on health outcomes. METHODS: To investigate the impact of ingested microspheres on target metabolic pathways, mice were exposed to either polystyrene (5µm) microspheres or a mixture of polymer microspheres consisting of polystyrene (5µm), polyethylene (1-4µm), and the biodegradability and biocompatible plastic, poly-(lactic-co-glycolic acid) (5µm). Exposures were performed twice a week for 4 weeks at a concentration of either 0, 2, or 4mg/week via oral gastric gavage. Tissues were collected to examine microsphere ingress and changes in metabolites. RESULTS: In mice that ingested microspheres, we detected polystyrene microspheres in distant tissues including the brain, liver, and kidney. Additionally, we report on the metabolic differences that occurred in the colon, liver, and brain, which showed differential responses that were dependent on concentration and type of microsphere exposure. DISCUSSION: This study uses a mouse model to provide critical insight into the potential health implications of the pervasive issue of plastic pollution. These findings demonstrate that orally consumed polystyrene or mixed polymer microspheres can accumulate in tissues such as the brain, liver, and kidney. Furthermore, this study highlights concentration-dependent and polymer type-specific metabolic changes in the colon, liver, and brain after plastic microsphere exposure. These results underline the mobility within and between biological tissues of MPs after exposure and emphasize the importance of understanding their metabolic impact. https://doi.org/10.1289/EHP13435.

Uranium-bearing dust induces differentiation and expansion of enteroendocrine cells in human colonoids.

Chronic exposure to environmental toxins and heavy metals has been associated with intestinal inflammation, increased susceptibility to pathogen-induced diseases, and higher incidences of colorectal cancer, all of which have been steadily increasing in prevalence for the past 40 years. The negative effects of heavy metals on barrier permeability and inhibition of intestinal epithelial healing have been described; however, transcriptomic changes within the intestinal epithelial cells and impacts on lineage differentiation are largely unknown. Uranium exposure remains an important environmental legacy and physiological health concern, with hundreds of abandoned uranium mines located in the Southwestern United States largely impacting underserved indigenous communities. Herein, using human colonoids, we defined the molecular and cellular changes that occur in response to uranium bearing dust (UBD) exposure. We used single cell RNA sequencing to define the molecular changes that occur to specific identities of colonic epithelial cells. We demonstrate that this environmental toxicant disrupts proliferation and induces hyperplastic differentiation of secretory lineage cells, particularly enteroendocrine cells (EEC). EECs respond to UBD exposure with increased differentiation into de novo EEC sub-types not found in control colonoids. This UBD-induced EEC differentiation does not occur via canonical transcription factors NEUROG3 or NEUROD1. These findings highlight the significance of crypts-based proliferative cells and secretory cell differentiation as major colonic responses to heavy metal-induced injury.

Integrating 4-D light-sheet fluorescence microscopy and genetic zebrafish system to investigate ambient pollutants-mediated toxicity.

Ambient air pollutants, including PM2.5 (aerodynamic diameter d ~2.5 µm), PM10 (d ~10 µm), and ultrafine particles (UFP: d < 0.1 µm) impart both short- and long-term toxicity to various organs, including cardiopulmonary, central nervous, and gastrointestinal systems. While rodents have been the principal animal model to elucidate air pollution-mediated organ dysfunction, zebrafish (Danio rerio) is genetically tractable for its short husbandry and life cycle to study ambient pollutants. Its electrocardiogram (ECG) resembles that of humans, and the fluorescent reporter-labeled tissues in the zebrafish system allow for screening a host of ambient pollutants that impair cardiovascular development, organ regeneration, and gut-vascular barriers. In parallel, the high spatiotemporal resolution of light-sheet fluorescence microscopy (LSFM) enables investigators to take advantage of the transparent zebrafish embryos and genetically labeled fluorescent reporters for imaging the dynamic cardiac structure and function at a single-cell resolution. In this context, our review highlights the integrated strengths of the genetic zebrafish system and LSFM for high-resolution and high-throughput investigation of ambient pollutants-mediated cardiac and intestinal toxicity.

Inflammatory macrophages prevent colonic goblet and enteroendocrine cell differentiation through Notch signaling.

Inflammatory macrophages in the intestine are a key pathogenic factor driving inflammatory bowel disease (IBD). Here, we report the role of inflammatory macrophage-mediated notch signaling on secretory lineage differentiation in the intestinal epithelium. Utilizing IL-10-deficient (Il10-/-) mice, a model of spontaneous colitis, we found an increase in Notch activity in the colonic epithelium as well as an increase in intestinal macrophages expressing Notch ligands, which are increased in macrophages upon inflammatory stimuli. Furthermore, a co-culture system of inflammatory macrophages and intestinal stem and proliferative cells during differentiation reduced goblet and enteroendocrine cells. This was recapitulated when utilizing a Notch agonist on human colonic organoids (colonoids). In summary, our findings indicate that inflammatory macrophages upregulate notch ligands that activate notch signaling in ISC via cell-cell interactions, which in turn inhibits secretory lineage differentiation in the gastrointestinal (GI) tract.

In Vivo Tissue Distribution of Microplastics and Systemic Metabolomic Alterations After Gastrointestinal Exposure.

Global plastic use has consistently increased over the past century with several different types of plastics now being produced. Much of these plastics end up in oceans or landfills leading to a substantial accumulation of plastics in the environment. Plastic debris slowly degrades into microplastics (MPs) that can ultimately be inhaled or ingested by both animals and humans. A growing body of evidence indicates that MPs can cross the gut barrier and enter into the lymphatic and systemic circulation leading to accumulation in tissues such as the lungs, liver, kidney, and brain. The impacts of mixed MPs exposure on tissue function through metabolism remains largely unexplored. To investigate the impact of ingested MPs on target metabolomic pathways, mice were subjected to either polystyrene microspheres or a mixed plastics (5 µm) exposure consisting of polystyrene, polyethylene and the biodegradability and biocompatible plastic, poly-(lactic-co-glycolic acid). Exposures were performed twice a week for four weeks at a dose of either 0, 2, or 4 mg/week via oral gastric gavage. Our findings demonstrate that, in mice, ingested MPs can pass through the gut barrier, be translocated through the systemic circulation, and accumulate in distant tissues including the brain, liver, and kidney. Additionally, we report on the metabolomic changes that occur in the colon, liver and brain which show differential responses that are dependent on dose and type of MPs exposure. Lastly, our study provides proof of concept for identifying metabolomic alterations associated with MPs exposure and adds insight into the potential health risks that mixed MPs contamination may pose to humans.

Intestinal Enteroendocrine Cells: Present and Future Druggable Targets.

Enteroendocrine cells are specialized secretory lineage cells in the small and large intestines that secrete hormones and peptides in response to luminal contents. The various hormones and peptides can act upon neighboring cells and as part of the endocrine system, circulate systemically via immune cells and the enteric nervous system. Locally, enteroendocrine cells have a major role in gastrointestinal motility, nutrient sensing, and glucose metabolism. Targeting the intestinal enteroendocrine cells or mimicking hormone secretion has been an important field of study in obesity and other metabolic diseases. Studies on the importance of these cells in inflammatory and auto-immune diseases have only recently been reported. The rapid global increase in metabolic and inflammatory diseases suggests that increased understanding and novel therapies are needed. This review will focus on the association between enteroendocrine changes and metabolic and inflammatory disease progression and conclude with the future of enteroendocrine cells as potential druggable targets.

Photoaging of polystyrene microspheres causes oxidative alterations to surface physicochemistry and enhances airway epithelial toxicity.

Microplastics represent an emerging environmental contaminant, with large gaps in our understanding of human health impacts. Furthermore, environmental factors may modify the plastic chemistry, further altering the toxic potency. Ultraviolet (UV) light is one such unavoidable factor for airborne microplastic particulates and a known modifier of polystyrene surface chemistry. As an experimental model, we aged commercially available polystyrene microspheres for 5 weeks with UV radiation, then compared the cellular responses in A549 lung cells with both pristine and irradiated particulates. Photoaging altered the surface morphology of irradiated microspheres and increased the intensities of polar groups on the near-surface region of the particles as indicated by scanning electron microscopy and by fitting of high-resolution X-ray photoelectron spectroscopy C 1s spectra, respectively. Even at low concentrations (1-30 µg/ml), photoaged microspheres at 1 and 5 µm in diameter exerted more pronounced biological responses in the A549 cells than was caused by pristine microspheres. High-content imaging analysis revealed S and G2 cell cycle accumulation and morphological changes, which were also more pronounced in A549 cells treated with photoaged microspheres, and further influenced by the size, dose, and time of exposures. Polystyrene microspheres reduced monolayer barrier integrity and slowed regrowth in a wound healing assay in a manner dependent on dose, photoaging, and size of the microsphere. UV-photoaging generally enhanced the toxicity of polystyrene microspheres in A549 cells. Understanding the influence of weathering and environmental aging, along with size, shape, and chemistry, on microplastics biocompatibility may be an essential consideration for incorporation of different plastics in products.

Efficient RNA and RNA-protein co-detection in 3D colonoids by whole-mount staining.

Here, we describe a protocol to visualize RNA oligos and proteins independently or together using a combination of fluorescence in situ hybridization (FISH) and immunofluorescence in human colonoids, expanding on previously published research. Whole-mount staining is used to preserve the colonoid structure and fix onto glass slides. We describe procedures for efficient plating, fixation, and preservation of the colonoids. This workflow can be adapted to 3D organoid models from other tissues or organisms. For complete details on the use and execution of this protocol, please refer to In et al. (2020).

Ulcerative Colitis: Novel Epithelial Insights Provided by Single Cell RNA Sequencing.

Ulcerative Colitis (UC) is a chronic inflammatory disease of the intestinal tract for which a definitive etiology is yet unknown. Both genetic and environmental factors have been implicated in the development of UC. Recently, single cell RNA sequencing (scRNA-seq) technology revealed cell subpopulations contributing to the pathogenesis of UC and brought new insight into the pathways that connect genome to pathology. This review describes key scRNA-seq findings in two major studies by Broad Institute and University of Oxford, investigating the transcriptomic landscape of epithelial cells in UC. We focus on five major findings: (1) the identification of BEST4 + cells, (2) colonic microfold (M) cells, (3) detailed comparison of the transcriptomes of goblet cells, and (4) colonocytes and (5) stem cells in health and disease. In analyzing the two studies, we identify the commonalities and differences in methodologies, results, and conclusions, offering possible explanations, and validated several cell cluster markers. In systematizing the results, we hope to offer a framework that the broad scientific GI community and GI clinicians can use to replicate or corroborate the extensive new findings that RNA-seq offers.

Non-autophagy Role of Atg5 and NBR1 in Unconventional Secretion of IL-12 Prevents Gut Dysbiosis and Inflammation.

Intestinal myeloid cells play a critical role in balancing intestinal homeostasis and inflammation. Here, we report that expression of the autophagy-related 5 [Atg5] protein in myeloid cells prevents dysbiosis and excessive intestinal inflammation by limiting IL-12 production. Mice with a selective genetic deletion of Atg5 in myeloid cells [Atg5ΔMye] showed signs of dysbiosis preceding colitis, and exhibited severe intestinal inflammation upon colitis induction that was characterised by increased IFNγ production. The exacerbated colitis was linked to excess IL-12 secretion from Atg5-deficient myeloid cells and gut dysbiosis. Restoration of the intestinal microbiota or genetic deletion of IL-12 in Atg5ΔMye mice attenuated the intestinal inflammation in Atg5ΔMye mice. Additionally, Atg5 functions to limit IL-12 secretion through modulation of late endosome [LE] acidity. Last, the autophagy cargo receptor NBR1, which accumulates in Atg5-deficient cells, played a role by delivering IL-12 to LE. In summary, Atg5 expression in intestinal myeloid cells acts as an anti-inflammatory brake to regulate IL-12, thus preventing dysbiosis and uncontrolled IFNγ-driven intestinal inflammation.

Chronic Inflammation in Ulcerative Colitis Causes Long-Term Changes in Goblet Cell Function.

BACKGROUND & AIMS: One of the features of ulcerative colitis (UC) is a defect in the protective mucus layer. This has been attributed to a reduced number of goblet cells (GCs). However, it is not known whether abnormal GC mucus secretion also contributes to the reduced mucus layer. Our aims were to investigate whether GC secretion was abnormal in UC and exists as a long-term effect of chronic inflammation. METHODS: Colonoids were established from intestinal stem cells of healthy subjects (HS) and patients with UC. Colonoids were maintained as undifferentiated (UD) or induced to differentiate (DF) and studied as three-dimensional or monolayers on Transwell filters. Total RNA was extracted for quantitative real-time polymerase chain reaction analysis. Carbachol and prostaglandin E2 mediated mucin stimulation was examined by MUC2 IF/confocal microscopy and transmission electron microscopy. RESULTS: Colonoids from UC patients can be propagated over many passages; however, they exhibit a reduced rate of growth and transepithelial electrical resistance compared with HS. Differentiated UC colonoid monolayers form a thin and non-continuous mucus layer. UC colonoids have increased expression of secretory lineage markers ATOH1 and SPDEF, along with MUC2 positive GCs, but failed to secrete mucin in response to the cholinergic agonist carbachol and prostaglandin E2, which caused increased secretion in HS. Exposure to tumor necrosis factor α (5 days) reduced the number of GCs, with a greater percentage decrease in UC colonoids compared with HS. CONCLUSIONS: Chronic inflammation in UC causes long-term changes in GCs, leading to abnormal mucus secretion. This continued defect in GC mucus secretion may contribute to the recurrence in UC.

Human Breast Milk Enhances Intestinal Mucosal Barrier Function and Innate Immunity in a Healthy Pediatric Human Enteroid Model.

Breastfeeding has been associated with long lasting health benefits. Nutrients and bioactive components of human breast milk promote cell growth, immune development, and shield the infant gut from insults and microbial threats. The molecular and cellular events involved in these processes are ill defined. We have established human pediatric enteroids and interrogated maternal milk's impact on epithelial cell maturation and function in comparison with commercial infant formula. Colostrum applied apically to pediatric enteroid monolayers reduced ion permeability, stimulated epithelial cell differentiation, and enhanced tight junction function by upregulating occludin. Breast milk heightened the production of antimicrobial peptide α-defensin 5 by goblet and Paneth cells, and modulated cytokine production, which abolished apical release of pro-inflammatory GM-CSF. These attributes were not found in commercial infant formula. Epithelial cells exposed to breast milk elevated apical and intracellular pIgR and enabled maternal IgA translocation. Proteomic data revealed a breast milk-induced molecular pattern associated with tissue remodeling and homeostasis. Using a novel ex vivo pediatric enteroid model, we have identified distinct cellular and molecular events involved in human milk-mediated improvement of human intestinal physiology and immunity.

SARS-COV-2 induced Diarrhea is inflammatory, Ca 2+ Dependent and involves activation of calcium activated Cl channels.

Diarrhea occurs in 2-50% of cases of COVID-19 (∼8% is average across series). The diarrhea does not appear to account for the disease mortality and its contribution to the morbidity has not been defined, even though it is a component of Long Covid or post-infectious aspects of the disease. Even less is known about the pathophysiologic mechanism of the diarrhea. To begin to understand the pathophysiology of COVID-19 diarrhea, we exposed human enteroid monolayers obtained from five healthy subjects and made from duodenum, jejunum, and proximal colon to live SARS-CoV-2 and virus like particles (VLPs) made from exosomes expressing SARS-CoV-2 structural proteins (Spike, Nucleocapsid, Membrane and Envelope). Results: 1) Live virus was exposed apically for 90 min, then washed out and studied 2 and 5 days later. SARS-Cov-2 was taken up by enteroids and live virus was present in lysates and in the apical>>basolateral media of polarized enteroids 48 h after exposure. This is the first demonstration of basolateral appearance of live virus after apical exposure. High vRNA concentration was detected in cell lysates and in the apical and basolateral media up to 5 days after exposure. 2) Two days after viral exposure, cytokine measurements of media showed significantly increased levels of IL-6, IL-8 and MCP-1. 3) Two days after viral exposure, mRNA levels of ACE2, NHE3 and DRA were reduced but there was no change in mRNA of CFTR. NHE3 protein was also decreased. 4) Live viral studies were mimicked by some studies with VLP exposure for 48 h. VLPs with Spike-D614G bound to the enteroid apical surface and was taken up; this resulted in decreased mRNA levels of ACE2, NHE3, DRA and CFTR. 4) VLP effects were determined on active anion secretion measured with the Ussing chamber/voltage clamp technique. S-D614G acutely exposed to apical surface of human ileal enteroids did not alter the short-circuit current (Isc). However, VLPS-D614G exposure to enteroids that were pretreated for ∼24 h with IL-6 plus IL-8 induced a concentration dependent increase in Isc indicating stimulated anion secretion, that was delayed in onset by ∼8 min. The anion secretion was inhibited by apical exposure to a specific calcium activated Cl channel (CaCC) inhibitor (AO1) but not by a specific CFTR inhibitor (BP027); was inhibited by basolateral exposure to the K channel inhibit clortimazole; and was prevented by pretreatment with the calcium buffer BAPTA-AM. 5) The calcium dependence of the VLP-induced increase in Isc was studied in Caco-2/BBe cells stably expressing the genetically encoded Ca2+ sensor GCaMP6s. 24 h pretreatment with IL-6/IL-8 did not alter intracellular Ca2+. However, in IL-6/IL-8 pretreated cells, VLP S-D614G caused appearance of Ca 2+ waves and an overall increase in intracellular Ca 2+ with a delay of ∼10 min after VLP addition. We conclude that the diarrhea of COVID-19 appears to an example of a calcium dependent inflammatory diarrhea that involves both acutely stimulated Ca2+ dependent anion secretion (stimulated Isc) that involves CaCC and likely inhibition of neutral NaCl absorption (decreased NHE3 protein and mRNA and decreased DRA mRNA).

Human Epithelial Stem Cell-Derived Colonoid Monolayers as a Model to Study Shiga Toxin-Producing Escherichia coli-Host Interactions.

Human intestinal organoid cultures established from crypt-derived stem cells truly revolutionized our approach to study intestinal epithelial physiology and pathologies as they can be propagated indefinitely and preserve the genetic signature of the donor and the gut segment specificity in culture. Here we describe human stem cell-derived colonoid monolayers as a reliable and reproducible model to study Shiga toxin-producing Escherichia coli (STEC) infection and STEC-caused pathologies of the whole colonic epithelium comprising a mixture of colonocytes, goblet, enteroendocrine, and other rare cells present in human colonic epithelial tissue.

Epithelial WNT2B and Desert Hedgehog Are Necessary for Human Colonoid Regeneration after Bacterial Cytotoxin Injury.

Intestinal regeneration and crypt hyperplasia after radiation or pathogen injury relies on Wnt signaling to stimulate stem cell proliferation. Mesenchymal Wnts are essential for homeostasis and regeneration in mice, but the role of epithelial Wnts remains largely uncharacterized. Using the enterohemorrhagic E. coli-secreted cytotoxin EspP to induce injury to human colonoids, we evaluated a simplified, epithelial regeneration model that lacks mesenchymal Wnts. Here, we demonstrate that epithelial-produced WNT2B is upregulated following injury and essential for regeneration. Hedgehog signaling, specifically activation via the ligand Desert Hedgehog (DHH), but not Indian or Sonic Hedgehog, is another driver of regeneration and modulates WNT2B expression. These findings highlight the importance of epithelial WNT2B and DHH in regulating human colonic regeneration after injury.

Mucus layer modeling of human colonoids during infection with enteroaggragative E. coli.

EAEC is a common cause of diarrheal illness worldwide. Pathogenesis is believed to occur in the ileum and colon, where the bacteria adhere and form a robust aggregating biofilm. Among the multiple virulence factors produced by EAEC, the Pic serine protease has been implicated in bacterial colonization by virtue of its mucinolytic activity. Hence, a potential role of Pic in mucus barrier disruption during EAEC infection has been long postulated. In this study, we used human colonoids comprising goblet cells and a thick mucin barrier as an intestinal model to investigate Pic's roles during infection with EAEC. We demonstrated the ability of purified Pic, but not a protease defective Pic mutant to degrade MUC2. Western blot and confocal microscopy analysis revealed degradation of the MUC2 layer in colonoids infected with EAEC, but not with its isogenic EAECpic mutant. Wild-type and MUC2-knockdown colonoids infected with EAEC strains exposed a differential biofilm distribution, greater penetration of the mucus layer and increased colonization of the colonic epithelium by Wild-type EAEC than its isogenic Pic mutant. Higher secretion of pro-inflammatory cytokines was seen in colonoids infected with EAEC than EAECpic. Although commensal E. coli expressing Pic degraded MUC2, it did not show improved mucus layer penetration or colonization of the colonic epithelium. Our study demonstrates a role of Pic in MUC2 barrier disruption in the human intestine and shows that colonoids are a reliable system to study the interaction of pathogens with the mucus layer.

Cholinergic-induced anion secretion in murine jejunal enteroids involves synergy between muscarinic and nicotinic pathways.

Acetylcholine induces robust electrogenic anion secretion in mammalian intestine and it has long been hypothesized that it mediates the epithelial response through the M3 and, to a lesser extent, the M1 muscarinic receptors in the mouse. However, nicotinic receptors have recently been identified in intestinal enterocytes by quantitative real-time (qRT)-PCR/RNAseq, although any direct influence on intestinal transport has not been identified. We tested the hypothesis that cholinergic-induced anion secretion in the intestine is a result of both muscarinic and nicotinic pathways that are intrinsic to the intestinal epithelia. We developed a method to generate mouse jejunal enteroid monolayers which were used to measure active electrogenic anion secretion by the Ussing chamber/voltage-clamp technique. Here, we show that the cholinergic agonist carbachol (CCh) and the muscarinic agonist bethanechol (BCh) stimulate short-lived, concentration-dependent anion secretion in the epithelial cell-only enteroid monolayers. The muscarinic antagonist atropine completely inhibited CCh- and BCh-induced secretion, while the nicotinic antagonist hexamethonium reduced the CCh response by ~45%. While nicotine alone did not alter anion secretion, it increased the BCh-induced increase in short-circuit current in a concentration-dependent manner; this synergy was prevented by pretreatment with hexamethonium. In addition to being sensitive to hexamethonium, monolayers express both classes of cholinergic receptor by qRT-PCR, including 13 of 16 nicotinic receptor subunits. Our findings indicate that an interaction between muscarinic and nicotinic agonists synergistically stimulates anion secretion in mouse jejunal epithelial cells and identify a role for epithelial nicotinic receptors in anion secretion.

Human Colonoid Monolayers to Study Interactions Between Pathogens, Commensals, and Host Intestinal Epithelium.

Human 3-dimensional (3D) enteroid or colonoid cultures derived from crypt base stem cells are currently the most advanced ex vivo model of the intestinal epithelium. Due to their closed structures and significant supporting extracellular matrix, 3D cultures are not ideal for host-pathogen studies. Enteroids or colonoids can be grown as epithelial monolayers on permeable tissue culture membranes to allow manipulation of both luminal and basolateral cell surfaces and accompanying fluids. This enhanced luminal surface accessibility facilitates modeling bacterial-host epithelial interactions such as the mucus-degrading ability of enterohemorrhagic E. coli (EHEC) on colonic epithelium. A method for 3D culture fragmentation, monolayer seeding, and transepithelial electrical resistance (TER) measurements to monitor the progress towards confluency and differentiation are described. Colonoid monolayer differentiation yields secreted mucus that can be studied by the immunofluorescence or immunoblotting techniques. More generally, enteroid or colonoid monolayers enable a physiologically-relevant platform to evaluate specific cell populations that may be targeted by pathogenic or commensal microbiota.