Host-derived CEACAM-laden vesicles engage enterotoxigenic Escherichia coli for elimination and toxin neutralization.

Enterotoxigenic Escherichia coli (ETEC) cause hundreds of millions of diarrheal illnesses annually ranging from mildly symptomatic cases to severe, life-threatening cholera-like diarrhea. Although ETEC are associated with long-term sequelae including malnutrition, the acute diarrheal illness is largely self-limited. Recent studies indicate that in addition to causing diarrhea, the ETEC heat-labile toxin (LT) modulates the expression of many genes in intestinal epithelia, including carcinoembryonic cell adhesion molecules (CEACAMs) which ETEC exploit as receptors, enabling toxin delivery. Here, however, we demonstrate that LT also enhances the expression of CEACAMs on extracellular vesicles (EV) shed by intestinal epithelia and that CEACAM-laden EV increase in abundance during human infections, mitigate pathogen-host interactions, scavenge free ETEC toxins, and accelerate ETEC clearance from the gastrointestinal tract. Collectively, these findings indicate that CEACAMs play a multifaceted role in ETEC pathogen-host interactions, transiently favoring the pathogen, but ultimately contributing to innate responses that extinguish these common infections.

Host-derived CEACAM-laden vesicles engage enterotoxigenic E. coli for elimination and toxin neutralization.

Enterotoxigenic Escherichia coli (ETEC) cause hundreds of millions of diarrheal illnesses annually ranging from mildly symptomatic cases to severe, life-threatening cholera-like diarrhea. Although ETEC are associated with long-term sequelae including malnutrition, the acute diarrheal illness is largely self-limited. Recent studies indicate that in addition to causing diarrhea, the ETEC heat-labile toxin (LT) modulates the expression of many genes in intestinal epithelia, including carcinoembryonic cell adhesion molecules (CEACAMs) which ETEC exploit as receptors, enabling toxin delivery. Here however, we demonstrate that LT also enhances the expression of CEACAMs on extracellular vesicles (EV) shed by intestinal epithelia and that CEACAM-laden EV increase in abundance during human infections, mitigate pathogen-host interactions, scavenge free ETEC toxins, and accelerate ETEC clearance from the gastrointestinal tract. Collectively, these findings indicate that CEACAMs play a multifaceted role in ETEC pathogen-host interactions, transiently favoring the pathogen, but ultimately contributing to innate responses that extinguish these common infections.

Intestinal epigenomic alterations are associated with a dysregulated nutrient absorption phenotype in obesity.

Obesity is an epidemic with myriad health effects, but little is understood regarding individual obese phenotypes and how they may respond to therapy. Epigenetic changes associated with obesity have been detected in blood, liver, pancreas, and adipose tissues. Previous work found that dietary glucose hyperabsorption occurs in some obese subjects, but detailed transcriptional or epigenomic features of the intestine associated with this phenotype are unknown. This study evaluated differentially expressed genes and relative chromatin accessibility in intestinal organoids established from donors classified as lean, obese, or obese hyperabsorptive by body mass index and glucose transport assays. Transcriptomic analysis indicated that obese hyperabsorptive subjects have significantly upregulated dietary nutrient absorption proteins and downregulated type I interferon targets. Chromatin accessibility and transcription factor footprinting suggested that enhanced binding of HNF4G promotes the obese hyperabsorption phenotype. Quantitative PCR assessment in a larger subject cohort suggested that intestinal epithelial expression of CUBN, GIP, and SLC2A5 have high correlation with hyperabsorption. The obese hyperabsorption phenotype is characterized by transcriptional changes that support increased nutrient uptake and may be driven by differentially accessible chromatin. Recognizing unique intestinal phenotypes in obesity provides new perspective in considering therapeutic targets and options to manage the disease.

Farnesoid X receptor enhances epithelial ACE2 expression and inhibits virally induced IL-6 secretion: implications for intestinal symptoms of SARS-CoV-2.

Intestinal inflammation and diarrhea are often associated with SARS-CoV-2 infection. The angiotensin converting enzyme 2 (ACE2) receptor plays a key role in SARS-CoV-2 pathogenesis, facilitating entry of the virus into epithelial cells, while also regulating mucosal inflammatory responses. Here, we investigated roles for the nuclear bile acid receptor farnesoid X receptor (FXR) in regulating ACE2 expression and virally mediated inflammatory responses in intestinal epithelia. Human colonic or ileal enteroids and cultured T84 and Caco-2 monolayers were treated with the FXR agonists, obeticholic acid (OCA) or GW4064, or infected with live SARS-CoV-2 (2019-nCoV/USA_WA1/2020). Changes in mRNA, protein, or secreted cytokines were measured by qPCR, Western blotting, and ELISA. Treatment of undifferentiated colonic or ileal enteroids with OCA increased ACE2 mRNA by 2.1 ± 0.4-fold (n = 3; P = 0.08) and 2.3 ± 0.2-fold (n = 3; P < 0.05), respectively. In contrast, ACE2 expression in differentiated enteroids was not significantly altered. FXR activation in cultured epithelial monolayers also upregulated ACE2 mRNA, accompanied by increases in ACE2 expression and secretion. Further experiments revealed FXR activation to inhibit IL-6 release from both Caco-2 cells infected with SARS-CoV-2 and T84 cells treated with the viral mimic, polyinosinic:polycytidylic acid, by 46 ± 12% (n = 3, P < 0.05) and 35 ± 6% (n = 8; P < 0.01), respectively. By virtue of its ability to modulate epithelial ACE2 expression and inhibit virus-mediated proinflammatory cytokine release, FXR represents a promising target for the development of new approaches to prevent intestinal manifestations of SARS-CoV-2.NEW & NOTEWORTHY Activation of the nuclear bile acid receptor, farnesoid X receptor (FXR), specifically upregulates ACE2 expression in undifferentiated colonic epithelial cells and inhibits virus-induced proinflammatory cytokine release. By virtue of these actions FXR represents a promising target for the development of new approaches to prevent intestinal manifestations of SARS-CoV-2 infection.

The role of CFA/I in adherence and toxin delivery by ETEC expressing multiple colonization factors in the human enteroid model.

Enterotoxigenic Escherichia coli (ETEC) is a primary causative agent of diarrhea in travelers and young children in low-to-middle-income countries (LMICs). ETEC adhere to intestinal epithelia via colonization factors (CFs) and secrete heat-stable toxin (ST) and/or heat-labile toxin (LT), causing dysregulated cellular ion transport and water secretion. ETEC isolates often harbor genes encoding more than one CF that are targets as vaccine antigens. CFA/I is a major CF that is associated with ETEC that causes moderate-to-severe diarrhea and plays an important role in pathogenesis. The Global Enteric Multicenter Study finding that 78% of CFA/I-expressing ETEC also encode the minor CF CS21 prompted investigation of the combined role of these two CFs. Western blots and electron microscopy demonstrated growth media-dependent and strain-dependent differences in CFA/I and CS21 expression. The critical role of CFA/I in adherence by ETEC strains expressing CFA/I and CS21 was demonstrated using the human enteroid model and a series of CFA/I- and CS21-specific mutants. Furthermore, only anti-CFA/I antibodies inhibited adherence by global ETEC isolates expressing CFA/I and CS21. Delivery of ST and resulting cGMP secretion was measured in supernatants from infected enteroid monolayers, and strain-specific ST delivery and time-dependent cGMP production was observed. Interestingly, cGMP levels were similar across wildtype and CF-deficient strains, reflecting a limitation of this static aerobic infection model. Despite adherence by ETEC and delivery of ST, the enteroid monolayer integrity was not disrupted, as shown by the lack of decrease in transepithelial electrical resistance and the lack of IL-8 cytokines produced during infection. Taken together, these data demonstrate that targeting CFA/I in global clinical CFA/I-CS21 strains is sufficient for adherence inhibition, supporting a vaccine strategy that focuses on blocking major CFs. In addition, the human enteroid model has significant utility for the study of ETEC pathogenesis and evaluation of vaccine-induced functional antibody responses.

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.

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.

Evaluation of a Live Attenuated S. sonnei Vaccine Strain in the Human Enteroid Model.

Shigella is a leading cause of bacillary dysentery worldwide, responsible for high death rates especially among children under five in low-middle income countries. Shigella sonnei prevails in high-income countries and is becoming prevalent in industrializing countries, where multi-drug resistant strains have emerged, as a significant public health concern. One strategy to combat drug resistance in S. sonnei is the development of effective vaccines. There is no licensed vaccine against Shigella, and development has been hindered by the lack of an effective small-animal model. In this work, we used human enteroids, for the first time, as a model system to evaluate a plasmid-stabilized S. sonnei live attenuated vaccine strain, CVD 1233-SP, and a multivalent derivative, CVD 1233-SP::CS2-CS3, which expresses antigens from enterotoxigenic Escherichia coli. The strains were also tested for immunogenicity and protective capacity in the guinea pig model, demonstrating their ability to elicit serum and mucosal antibody responses as well as protection against challenge with wild-type S. sonnei. These promising results highlight the utility of enteroids as an innovative preclinical model to evaluate Shigella vaccine candidates, constituting a significant advance for the development of preventative strategies against this important human pathogen.

Research in a time of enteroids and organoids: how the human gut model has transformed the study of enteric bacterial pathogens.

Enteric bacterial pathogens cause significant morbidity and mortality globally. Studies in tissue culture and animal models shaped our initial understanding of these host-pathogen interactions. However, intrinsic shortcomings in these models limit their application, especially in translational applications like drug screening and vaccine development. Human intestinal enteroid and organoid models overcome some limitations of existing models and advance the study of enteric pathogens. In this review, we detail the use of human enteroids and organoids to investigate the pathogenesis of invasive bacteria Shigella, Listeria, and Salmonella, and noninvasive bacteria pathogenic Escherichia coli, Clostridium difficile, and Vibrio cholerae. We highlight how these studies confirm previously identified mechanisms and, importantly, reveal novel ones. We also discuss the challenges for model advancement, including platform engineering to integrate environmental conditions, innate immune cells and the resident microbiome, and the potential for pre-clinical testing of recently developed antimicrobial drugs and vaccines.

Phosphodiesterase 5 (PDE5) restricts intracellular cGMP accumulation during enterotoxigenic Escherichia coli infection.

Diarrhea caused by enterotoxigenic Escherichia coli (ETEC) has a continuing impact on residents and travelers in underdeveloped countries. Both heat-labile (LT) and heat-stable (ST) enterotoxins contribute to pathophysiology via induction of cyclic nucleotide synthesis, and previous investigations focused on intracellular signal transduction rather than possible intercellular second messenger signaling. We modeled ETEC infection in human jejunal enteroid/organoid monolayers (HEM) and evaluated cyclic nucleotide pools, finding that intracellular cAMP was significantly increased but also underwent apical export, whereas cGMP was minimally retained intracellularly and predominantly effluxed into the basolateral space. LT and virulence factors including EatA, EtpA, and CfaE promoted ST release and enhanced ST-stimulated cGMP production. Intracellular cGMP was regulated by MK-571-sensitive export in addition to degradation by phosphodiesterase 5. HEMs had limited ST-induced intracellular cGMP accumulation compared to T84 or Caco-2 models. Cyclic nucleotide export/degradation demonstrates additional complexity in the mechanism of ETEC infection and may redirect understanding of diarrheal onset.

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.

Enterohemorrhagic E. coli (EHEC)-Secreted Serine Protease EspP Stimulates Electrogenic Ion Transport in Human Colonoid Monolayers.

One of the characteristic manifestations of Shiga-toxin-producing Escherichia coli (E. coli) infection in humans, including EHEC and Enteroaggregative E. coli O104:H4, is watery diarrhea. However, neither Shiga toxin nor numerous components of the type-3 secretion system have been found to independently elicit fluid secretion. We used the adult stem-cell-derived human colonoid monolayers (HCM) to test whether EHEC-secreted extracellular serine protease P (EspP), a member of the serine protease family broadly expressed by diarrheagenic E. coli can act as an enterotoxin. We applied the Ussing chamber/voltage clamp technique to determine whether EspP stimulates electrogenic ion transport indicated by a change in short-circuit current (Isc). EspP stimulates Isc in HCM. The EspP-stimulated Isc does not require protease activity, is not cystic fibrosis transmembrane conductance regulator (CFTR)-mediated, but is partially Ca2+-dependent. EspP neutralization with a specific antibody reduces its potency in stimulating Isc. Serine Protease A, secreted by Enteroaggregative E. coli, also stimulates Isc in HCM, but this current is CFTR-dependent. In conclusion, EspP stimulates colonic CFTR-independent active ion transport and may be involved in the pathophysiology of EHEC diarrhea. Serine protease toxins from E. coli pathogens appear to serve as enterotoxins, potentially significantly contributing to watery diarrhea.

Molecular Basis and Differentiation-Associated Alterations of Anion Secretion in Human Duodenal Enteroid Monolayers.

BACKGROUND & AIMS: Human enteroids present a novel tool to study human intestinal ion transport physiology and pathophysiology. The present study describes the contributions of Cl- and HCO3- secretion to total cyclic adenosine monophosphate (cAMP)-stimulated electrogenic anion secretion in human duodenal enteroid monolayers and the relevant changes after differentiation. METHODS: Human duodenal enteroids derived from 4 donors were grown as monolayers and differentiated by a protocol that includes the removal of Wnt3A, R-spondin1, and SB202190 for 5 days. The messenger RNA level and protein expression of selected ion transporters and carbonic anhydrase isoforms were determined by quantitative real-time polymerase chain reaction and immunoblotting, respectively. Undifferentiated and differentiated enteroid monolayers were mounted in the Ussing chamber/voltage-current clamp apparatus, using solutions that contained as well as lacked Cl- and HCO3-/CO2, to determine the magnitude of forskolin-induced short-circuit current change and its sensitivity to specific inhibitors that target selected ion transporters and carbonic anhydrase(s). RESULTS: Differentiation resulted in a significant reduction in the messenger RNA level and protein expression of cystic fibrosis transmembrane conductance regulator, (CFTR) Na+/K+/2Cl- co-transporter 1 (NKCC1), and potassium channel, voltage gated, subfamily E, regulatory subunit 3 (KCNE3); and, conversely, increase of down-regulated-in-adenoma (DRA), electrogenic Na+/HCO3- co-transporter 1 (NBCe1), carbonic anhydrase 2 (CA2), and carbonic anhydrase 4 (CA4). Both undifferentiated and differentiated enteroids showed active cAMP-stimulated anion secretion that included both Cl- and HCO3- secretion as the magnitude of total active anion secretion was reduced after the removal of extracellular Cl- or HCO3-/CO2. The magnitude of total anion secretion in differentiated enteroids was approximately 33% of that in undifferentiated enteroids, primarily owing to the reduction in Cl- secretion with no significant change in HCO3- secretion. Anion secretion was consistently lower but detectable in differentiated enteroids compared with undifferentiated enteroids in the absence of extracellular Cl- or HCO3-/CO2. Inhibiting CFTR, NKCC1, carbonic anhydrase(s), cAMP-activated K+ channel(s), and Na+/K+-adenosine triphosphatase reduced cAMP-stimulated anion secretion in both undifferentiated and differentiated enteroids. CONCLUSIONS: Human enteroids recapitulate anion secretion physiology of small intestinal epithelium. Enteroid differentiation is associated with significant alterations in the expression of several ion transporters and carbonic anhydrase isoforms, leading to a reduced but preserved anion secretory phenotype owing to markedly reduced Cl- secretion but no significant change in HCO3- secretion.

Enterotoxigenic Escherichia coli-blood group A interactions intensify diarrheal severity.

Enterotoxigenic Escherichia coli (ETEC) infections are highly prevalent in developing countries, where clinical presentations range from asymptomatic colonization to severe cholera-like illness. The molecular basis for these varied presentations, which may involve strain-specific virulence features as well as host factors, has not been elucidated. We demonstrate that, when challenged with ETEC strain H10407, originally isolated from a case of cholera-like illness, blood group A human volunteers developed severe diarrhea more frequently than individuals from other blood groups. Interestingly, a diverse population of ETEC strains, including H10407, secrete the EtpA adhesin molecule. As many bacterial adhesins also agglutinate red blood cells, we combined the use of glycan arrays, biolayer inferometry, and noncanonical amino acid labeling with hemagglutination studies to demonstrate that EtpA is a dominant ETEC blood group A-specific lectin/hemagglutinin. Importantly, we have also shown that EtpA interacts specifically with glycans expressed on intestinal epithelial cells from blood group A individuals and that EtpA-mediated bacterial-host interactions accelerate bacterial adhesion and effective delivery of both the heat-labile and heat-stable toxins of ETEC. Collectively, these data provide additional insight into the complex molecular basis of severe ETEC diarrheal illness that may inform rational design of vaccines to protect those at highest risk.

Lipofuscin Formation Catalyzed by the Milk Protein ß-Lactoglobulin: Lysine Residues in Cycloretinal Synthesis.

Lipofuscins are toxic autofluorescent byproducts of the visual cycle. The accumulation of lipofuscins such as cycloretinal in the retina is thought to play a role in the progression of age-related macular degeneration (AMD). Intriguingly, the milk protein ß-lactoglobulin (BLG) can promote the cyclodimerization of all-trans-retinal to cycloretinal both in vitro and in vivo. Here, site-directed mutagenesis of BLG and mass spectrometric analysis with substrate analogues demonstrate that lysine residues play a key role in catalysis. It is also shown that catalytic activity necessitates the presence of a physical binding site and cannot be mediated by a peptide chain. These studies provide insight into the mechanism of the cyclodimerization process and provide a model system for biocatalysis and biosynthesis of cycloretinal in vivo. In the long term, these studies may pave the way for drug development and inhibitor design as an early treatment regimen for AMD.

Functional Coupling of Human Microphysiology Systems: Intestine, Liver, Kidney Proximal Tubule, Blood-Brain Barrier and Skeletal Muscle.

Organ interactions resulting from drug, metabolite or xenobiotic transport between organs are key components of human metabolism that impact therapeutic action and toxic side effects. Preclinical animal testing often fails to predict adverse outcomes arising from sequential, multi-organ metabolism of drugs and xenobiotics. Human microphysiological systems (MPS) can model these interactions and are predicted to dramatically improve the efficiency of the drug development process. In this study, five human MPS models were evaluated for functional coupling, defined as the determination of organ interactions via an in vivo-like sequential, organ-to-organ transfer of media. MPS models representing the major absorption, metabolism and clearance organs (the jejunum, liver and kidney) were evaluated, along with skeletal muscle and neurovascular models. Three compounds were evaluated for organ-specific processing: terfenadine for pharmacokinetics (PK) and toxicity; trimethylamine (TMA) as a potentially toxic microbiome metabolite; and vitamin D3. We show that the organ-specific processing of these compounds was consistent with clinical data, and discovered that trimethylamine-N-oxide (TMAO) crosses the blood-brain barrier. These studies demonstrate the potential of human MPS for multi-organ toxicity and absorption, distribution, metabolism and excretion (ADME), provide guidance for physically coupling MPS, and offer an approach to coupling MPS with distinct media and perfusion requirements.

Human mini-guts: new insights into intestinal physiology and host-pathogen interactions.

The development of indefinitely propagating human 'mini-guts' has led to a rapid advance in gastrointestinal research related to transport physiology, developmental biology, pharmacology, and pathophysiology. These mini-guts, also called enteroids or colonoids, are derived from LGR5+ intestinal stem cells isolated from the small intestine or colon. Addition of WNT3A and other growth factors promotes stemness and results in viable, physiologically functional human intestinal or colonic cultures that develop a crypt-villus axis and can be differentiated into all intestinal epithelial cell types. The success of research using human enteroids has highlighted the limitations of using animals or in vitro, cancer-derived cell lines to model transport physiology and pathophysiology. For example, curative or preventive therapies for acute enteric infections have been limited, mostly due to the lack of a physiological human intestinal model. However, the human enteroid model enables specific functional studies of secretion and absorption in each intestinal segment as well as observations of the earliest molecular events that occur during enteric infections. This Review describes studies characterizing these human mini-guts as a physiological model to investigate intestinal transport and host-pathogen interactions.

Enterohemorrhagic Escherichia coli reduce mucus and intermicrovillar bridges in human stem cell-derived colonoids.

BACKGROUND AND AIMS: Enterohemorrhagic E. coli (EHEC) causes over 70,000 episodes of foodborne diarrhea annually in the USA. The early sequence of events which precede life-threatening hemorrhagic colitis and hemolytic uremic syndrome are not fully understood due to the initial asymptomatic phase of the disease and the lack of a suitable animal model. The aim of this study was to determine the initial molecular events in the interaction between EHEC and human colonic epithelium. METHODS: Human colonoids derived from adult proximal colonic stem cells were developed into monolayers to study EHEC-epithelial interactions. Monolayer confluency and differentiation were monitored by transepithelial electrical resistance (TER) measurements. The monolayers were apically infected with EHEC and the progression of epithelial damage over time was assessed using biochemical and imaging approaches. RESULTS: Human colonoid cultures recapitulate the differential protein expression patterns characteristic of the crypt and surface colonocytes. Mucus-producing differentiated colonoid monolayers are preferentially colonized by EHEC. Upon colonization, EHEC forms characteristic attaching and effacing lesions on the apical surface of colonoid monolayers. Mucin 2, a main component of colonic mucus, and protocadherin 24 (PCDH24), a microvillar resident protein, are targeted by EHEC at early stages of infection. The EHEC secreted serine protease, EspP, initiates brush border damage through PCDH24 reduction. CONCLUSIONS: Human colonoid monolayers are a relevant pathophysiological model which allows the study of early molecular events during enteric infections. Colonoid monolayers provide access to both apical and basolateral surfaces, thus providing an advantage over 3D cultures to study host-pathogen interactions in a controllable and tractable manner. EHEC reduces colonic mucus and affects the brush border cytoskeleton in the absence of commensal bacteria.