Multi-disciplinary Insights from the First European Forum on Visceral Myopathy 2022 Meeting.

Visceral myopathy is a rare, life-threatening disease linked to identified genetic mutations in 60% of cases. Mostly due to the dearth of knowledge regarding its pathogenesis, effective treatments are lacking. The disease is most commonly diagnosed in children with recurrent or persistent disabling episodes of functional intestinal obstruction, which can be life threatening, often requiring long-term parenteral or specialized enteral nutritional support. Although these interventions are undisputedly life-saving as they allow affected individuals to avoid malnutrition and related complications, they also seriously compromise their quality of life and can carry the risk of sepsis and thrombosis. Animal models for visceral myopathy, which could be crucial for advancing the scientific knowledge of this condition, are scarce. Clearly, a collaborative network is needed to develop research plans to clarify genotype-phenotype correlations and unravel molecular mechanisms to provide targeted therapeutic strategies. This paper represents a summary report of the first 'European Forum on Visceral Myopathy'. This forum was attended by an international interdisciplinary working group that met to better understand visceral myopathy and foster interaction among scientists actively involved in the field and clinicians who specialize in care of people with visceral myopathy.

Activation of Hedgehog Signaling Promotes Development of Mouse and Human Enteric Neural Crest Cells, Based on Single-Cell Transcriptome Analyses.

BACKGROUND & AIMS: It has been a challenge to develop fully functioning cells from human pluripotent stem cells (hPSCs). We investigated how activation of hedgehog signaling regulates derivation of enteric neural crest (NC) cells from hPSCs. METHODS: We analyzed transcriptomes of mouse and hPSC-derived enteric NCs using single-cell RNA sequencing (scRNA-seq) to identify the changes in expression associated with lineage differentiation. Intestine tissues were collected from Tg(GBS-GFP), Sufuf/f; Wnt1-cre, Ptch1+/-, and Gli3Δ699/Δ699 mice and analyzed by flow cytometry and immunofluorescence for levels of messenger RNAs encoding factors in the hedgehog signaling pathway during differentiation of enteric NCs. Human NC cells (HNK-1+p75NTR+) were derived from IMR90 and UE02302 hPSC lines. hPSCs were incubated with a hedgehog agonist (smoothened agonist [SAG]) and antagonists (cyclopamine) and analyzed for differentiation. hPSC-based innervated colonic organoids were derived from these hPSC lines and analyzed by immunofluorescence and neuromuscular coupling assay for expression of neuronal subtype markers and assessment of the functional maturity of the hPSC-derived neurons, respectively. RESULTS: Single-cell RNA sequencing analysis showed that neural fate acquisition by human and mouse enteric NC cells requires reduced expression of NC- and cell cycle-specific genes and up-regulation of neuronal or glial lineage-specific genes. Activation of the hedgehog pathway was associated with progression of mouse enteric NCs to the more mature state along the neuronal and glial lineage differentiation trajectories. Activation of the hedgehog pathway promoted development of cultured hPSCs into NCs of greater neurogenic potential by activating expression of genes in the neurogenic lineage. The hedgehog agonist increased differentiation of hPSCs into cells of the neuronal lineage by up-regulating expression of GLI2 target genes, including INSM1, NHLH1, and various bHLH family members. The hedgehog agonist increased expression of late neuronal markers and neuronal activities in hPSC-derived neurons. CONCLUSIONS: In enteric NCs from humans and mice, activation of hedgehog signaling promotes differentiation into neurons by promoting cell-state transition, expression of genes in the neurogenic lineage, and functional maturity of enteric neurons.

IL-13-induced intestinal secretory epithelial cell antigen passages are required for IgE-mediated food-induced anaphylaxis.

BACKGROUND: Food-induced anaphylaxis (FIA) is an IgE-dependent immune response that can affect multiple organs and lead to life-threatening complications. The processes by which food allergens cross the mucosal surface and are delivered to the subepithelial immune compartment to promote the clinical manifestations associated with food-triggered anaphylaxis are largely unexplored. OBJECTIVE: We sought to define the processes involved in the translocation of food allergens across the mucosal epithelial surface to the subepithelial immune compartment in FIA. METHODS: Two-photon confocal and immunofluorescence microscopy was used to visualize and trace food allergen passage in a murine model of FIA. A human colon cancer cell line, RNA silencing, and pharmacologic approaches were used to identify the molecular regulation of intestinal epithelial allergen uptake and translocation. Human intestinal organoid transplants were used to demonstrate the conservation of these molecular processes in human tissues. RESULTS: Food allergens are sampled by using small intestine (SI) epithelial secretory cells (termed secretory antigen passages [SAPs]) that are localized to the SI villous and crypt region. SAPs channel food allergens to lamina propria mucosal mast cells through an IL-13-CD38-cyclic adenosine diphosphate ribose (cADPR)-dependent process. Blockade of IL-13-induced CD38/cADPR-dependent SAP antigen passaging in mice inhibited induction of clinical manifestations of FIA. IL-13-CD38-cADPR-dependent SAP sampling of food allergens was conserved in human intestinal organoids. CONCLUSION: We identify that SAPs are a mechanism by which food allergens are channeled across the SI epithelium mediated by the IL-13/CD38/cADPR pathway, regulate the onset of FIA reactions, and are conserved in human intestine.

CD44 plays a functional role in Helicobacter pylori-induced epithelial cell proliferation.

The cytotoxin-associated gene (Cag) pathogenicity island is a strain-specific constituent of Helicobacter pylori (H. pylori) that augments cancer risk. CagA translocates into the cytoplasm where it stimulates cell signaling through the interaction with tyrosine kinase c-Met receptor, leading cellular proliferation. Identified as a potential gastric stem cell marker, cluster-of-differentiation (CD) CD44 also acts as a co-receptor for c-Met, but whether it plays a functional role in H. pylori-induced epithelial proliferation is unknown. We tested the hypothesis that CD44 plays a functional role in H. pylori-induced epithelial cell proliferation. To assay changes in gastric epithelial cell proliferation in relation to the direct interaction with H. pylori, human- and mouse-derived gastric organoids were infected with the G27 H. pylori strain or a mutant G27 strain bearing cagA deletion (∆CagA::cat). Epithelial proliferation was quantified by EdU immunostaining. Phosphorylation of c-Met was analyzed by immunoprecipitation followed by Western blot analysis for expression of CD44 and CagA. H. pylori infection of both mouse- and human-derived gastric organoids induced epithelial proliferation that correlated with c-Met phosphorylation. CagA and CD44 co-immunoprecipitated with phosphorylated c-Met. The formation of this complex did not occur in organoids infected with ∆CagA::cat. Epithelial proliferation in response to H. pylori infection was lost in infected organoids derived from CD44-deficient mouse stomachs. Human-derived fundic gastric organoids exhibited an induction in proliferation when infected with H. pylori that was not seen in organoids pre-treated with a peptide inhibitor specific to CD44. In the well-established Mongolian gerbil model of gastric cancer, animals treated with CD44 peptide inhibitor Pep1, resulted in the inhibition of H. pylori-induced proliferation and associated atrophic gastritis. The current study reports a unique approach to study H. pylori interaction with the human gastric epithelium. Here, we show that CD44 plays a functional role in H. pylori-induced epithelial cell proliferation.

Glutamine and alanyl-glutamine promote crypt expansion and mTOR signaling in murine enteroids.

L-glutamine (Gln) is a key metabolic fuel for intestinal epithelial cell proliferation and survival and may be conditionally essential for gut homeostasis during catabolic states. We show that L-alanyl-L-glutamine (Ala-Gln), a stable Gln dipeptide, protects mice against jejunal crypt depletion in the setting of dietary protein and fat deficiency. Separately, we show that murine crypt cultures (enteroids) derived from the jejunum require Gln or Ala-Gln for maximal expansion. Once expanded, enteroids deprived of Gln display a gradual atrophy of cryptlike domains, with decreased epithelial proliferation, but stable proportions of Paneth and goblet cell differentiation, at 24 h. Replenishment of enteroid medium with Gln selectively activates mammalian target of rapamycin (mTOR) signaling pathways, rescues proliferation, and promotes crypt regeneration. Gln deprivation beyond 48 h leads to destabilization of enteroids but persistence of EGFP-Lgr5-positive intestinal stem cells with the capacity to regenerate enteroids upon Gln rescue. Collectively, these findings indicate that Gln deprivation induces a reversible quiescence of intestinal stem cells and provides new insights into nutritional regulation of intestinal epithelial homeostasis.

Isolation and characterization of intestinal stem cells based on surface marker combinations and colony-formation assay.

BACKGROUND & AIMS: Identification of intestinal stem cells (ISCs) has relied heavily on the use of transgenic reporters in mice, but this approach is limited by mosaic expression patterns and difficult to directly apply to human tissues. We sought to identify reliable surface markers of ISCs and establish a robust functional assay to characterize ISCs from mouse and human tissues. METHODS: We used immunohistochemistry, real-time reverse-transcription polymerase chain reaction, and fluorescence-activated cell sorting (FACS) to analyze intestinal epithelial cells isolated from mouse and human intestinal tissues. We compared different combinations of surface markers among ISCs isolated based on expression of Lgr5-green fluorescent protein. We developed a culture protocol to facilitate the identification of functional ISCs from mice and then tested the assay with human intestinal crypts and putative ISCs. RESULTS: CD44(+)CD24(lo)CD166(+) cells, isolated by FACS from mouse small intestine and colon, expressed high levels of stem cell-associated genes. Transit-amplifying cells and progenitor cells were then excluded based on expression of GRP78 or c-Kit. CD44(+)CD24(lo)CD166(+) GRP78(lo/-) putative stem cells from mouse small intestine included Lgr5-GFP(hi) and Lgr5-GFP(med/lo) cells. Incubation of these cells with the GSK inhibitor CHIR99021 and the E-cadherin stabilizer Thiazovivin resulted in colony formation by 25% to 30% of single-sorted ISCs. CONCLUSIONS: We developed a culture protocol to identify putative ISCs from mouse and human tissues based on cell surface markers. CD44(+)CD24(lo)CD166(+), GRP78(lo/-), and c-Kit(-) facilitated identification of putative stem cells from the mouse small intestine and colon, respectively. CD44(+)CD24(-/lo)CD166(+) also identified putative human ISCs. These findings will facilitate functional studies of mouse and human ISCs.

Intestinal stem cells remain viable after prolonged tissue storage.

Intestinal stem cells (ISCs) are responsible for renewal of the epithelium both during normal homeostasis and following injury. As such, they have significant therapeutic potential. However, whether ISCs can survive tissue storage is unknown. We hypothesize that, although the majority of epithelial cells might die, ISCs would remain viable for at least 24 h at 4 °C. To explore this hypothesis, jejuna of C57Bl6/J or Lgr5-LacZ mice were removed and either processed immediately or placed in phosphate-buffered saline at 4 °C. Delayed isolation of epithelium was performed after 24, 30, or 48 h storage. At the light microscope level, despite extensive apoptosis of villus epithelial cells, small intestinal crypts remained morphologically intact for 30 h and ISCs were identifiable via Lgr5-LacZ positivity. Electron microscopy showed that ISCs retained high integrity for 24 h. When assessed by flow cytometry, ISCs were more resistant to degeneration than the rest of the epithelium, including neighboring Paneth cells, with higher viability across all time points. Cultured isolated crypts showed no loss of capacity to form complex enteroids after 24 h tissue storage, with efficiencies after 7 days of culture remaining above 80 %. By 30 h storage, efficiencies declined but budding capability was retained. We conclude that, with delay in isolation, ISCs remain viable and retain their proliferative capacity. In contrast, the remainder of the epithelium, including the Paneth cells, exhibits degeneration and programmed cell death. If these findings are recapitulated in human tissue, storage at 4 °C might offer a valuable temporal window for the harvesting of crypts or ISCs for therapeutic application.

Gut Microbiota Remodeling and Intestinal Adaptation to Lipid Malabsorption After Enteroendocrine Cell Loss in Adult Mice.

BACKGROUND & AIMS: Enteroendocrine cells (EECs) and their hormones are essential regulators of whole-body energy homeostasis. EECs sense luminal nutrients and microbial metabolites and subsequently secrete various hormones acting locally or at a distance. Impaired development of EECs during embryogenesis is life-threatening in newborn mice and humans due to compromised nutrient absorption. However, the physiological importance of the EEC system in adult mice has yet to be directedly studied. Herein, we aimed to determine the long-term consequences of a total loss of EECs in healthy adults on energy metabolism, intestinal transcriptome, and microbiota. METHODS: We depleted intestinal EECs by tamoxifen treatment of adult Neurog3fl/fl; Villin-CreERT2 male mice. We studied intestinal cell differentiation, food efficiency, lipid absorption, microbiota composition, fecal metabolites, and transcriptomic responses in the proximal and distal small intestines of mice lacking EECs. We also determined the high-fat diet-induced transcriptomic changes in sorted Neurog3eYFP/+ EECs. RESULTS: Induction of EEC deficiency in adults is not life-threatening unless fed with a high-fat diet. Under a standard chow diet, mice lose 10% of weight due to impaired food efficiency. Blood concentrations of cholesterol, triglycerides, and free fatty acids are reduced, and lipid absorption is impaired and delayed in the distal small intestine. Genes controlling lipogenesis, carbohydrate metabolism, and neoglucogenesis are upregulated. Microbiota composition is rapidly altered after EECs depletion and is characterized by decreased α-diversity. Bacteroides and Lactobacillus were progressively enriched, whereas Lachnospiraceae declined without impacting fecal short-chain fatty acid concentrations. CONCLUSIONS: EECs are dispensable for survival in adult male mice under a standard chow diet. The absence of EECs impairs intestinal lipid absorption, leading to transcriptomic and metabolic adaptations and remodeling of the gut microbiota.

In vivo development of immune tissue in human intestinal organoids transplanted into humanized mice.

Human intestinal organoids (HIOs) derived from pluripotent stem cells provide a valuable model for investigating human intestinal organogenesis and physiology, but they lack the immune components required to fully recapitulate the complexity of human intestinal biology and diseases. To address this issue and to begin to decipher human intestinal-immune crosstalk during development, we generated HIOs containing immune cells by transplanting HIOs under the kidney capsule of mice with a humanized immune system. We found that human immune cells temporally migrate to the mucosa and form cellular aggregates that resemble human intestinal lymphoid follicles. Moreover, after microbial exposure, epithelial microfold cells are increased in number, leading to immune cell activation determined by the secretion of IgA antibodies in the HIO lumen. This in vivo HIO system with human immune cells provides a framework for future studies on infection- or allergen-driven intestinal diseases.

Development of functional resident macrophages in human pluripotent stem cell-derived colonic organoids and human fetal colon.

Most organs have tissue-resident immune cells. Human organoids lack these immune cells, which limits their utility in modeling many normal and disease processes. Here, we describe that pluripotent stem cell-derived human colonic organoids (HCOs) co-develop a diverse population of immune cells, including hemogenic endothelium (HE)-like cells and erythromyeloid progenitors that undergo stereotypical steps in differentiation, resulting in the generation of functional macrophages. HCO macrophages acquired a transcriptional signature resembling human fetal small and large intestine tissue-resident macrophages. HCO macrophages modulate cytokine secretion in response to pro- and anti-inflammatory signals and were able to phagocytose and mount a robust response to pathogenic bacteria. When transplanted into mice, HCO macrophages were maintained within the colonic organoid tissue, established a close association with the colonic epithelium, and were not displaced by the host bone-marrow-derived macrophages. These studies suggest that HE in HCOs gives rise to multipotent hematopoietic progenitors and functional tissue-resident macrophages.

The omega-6 fatty acid derivative 15-deoxy-Δ¹²,¹4-prostaglandin J2 is involved in neuroprotection by enteric glial cells against oxidative stress.

Increasing evidence suggests that enteric glial cells (EGCs) are critical for enteric neuron survival and functions. In particular, EGCs exert direct neuroprotective effects mediated in part by the release of glutathione. However, other glial factors such as those identified as regulating the intestinal epithelial barrier and in particular the omega-6 fatty acid derivative 15-deoxy-Δ¹²,¹4-prostaglandin J2 (15d-PGJ2) could also be involved in EGC-mediated neuroprotection. Therefore, our study aimed to assess the putative role of EGC-derived 15d-PGJ2 in their neuroprotective effects. We first showed that pretreatment of primary cultures of enteric nervous system(ENS)or humann euroblastoma cells (SH-SY5Y)with 15d-PGJ2 dose dependently prevented hydrogen peroxide neurotoxicity. Furthermore, neuroprotective effects of EGCs were significantly inhibited following genetic invalidation in EGCs of the key enzyme involved in 15d-PGJ2 synthesis, i.e. L-PGDS. We next showed that 15d-PGJ2 effects were mediated by an Nrf2 dependent pathway but were not blocked by PPARγ inhibitor (GW9662) in SH-SY5Y cells and enteric neurons. Finally, 15d-PGJ2 induced a significant increase in glutamate cysteine ligase expression and intracellular glutathione in SH cells and enteric neurons. In conclusion, we identified 15d-PGJ2 as a novel glial-derived molecule with neuroprotective effects in the ENS. This study further supports the concept that omega-6 derivatives such as 15d-PGJ2 might be used in preventive and/or therapeutic strategies for the treatment of enteric neuropathies.

Enteric glia protect against Shigella flexneri invasion in intestinal epithelial cells: a role for S-nitrosoglutathione.

BACKGROUND: Enteric glial cells (EGCs) are important regulators of intestinal epithelial barrier (IEB) functions. EGC-derived S-nitrosoglutathione (GSNO) has been shown to regulate IEB permeability. Whether EGCs and GSNO protect the IEB during infectious insult by pathogens such as Shigella flexneri is not known. METHODS: S flexneri effects were characterised using in vitro coculture models of Caco-2 cells and EGCs (or GSNO), ex vivo human colonic mucosa, and in vivo ligated rabbit intestinal loops. The effect of EGCs on S flexneri-induced changes in the invasion area and the inflammatory response were analysed by combining immunohistochemical, ELISA and PCR methods. Expression of small G-proteins was analysed by western blot. Expression of ZO-1 and localisation of bacteria were analysed by fluorescence microscopy. RESULTS: EGCs significantly reduced barrier lesions and inflammatory response induced by S flexneri in Caco-2 monolayers. The EGC-mediated effects were reproduced by GSNO, but not by reduced glutathione, and pharmacological inhibition of pathways involved in GSNO synthesis reduced EGC protecting effects. Furthermore, expression of Cdc42 and phospho-PAK in Caco-2 monolayers was significantly reduced in the presence of EGCs or GSNO. In addition, changes in ZO-1 expression and distribution induced by S flexneri were prevented by EGCs and GSNO. Finally, GSNO reduced S flexneri-induced lesions of the IEB in human mucosal colonic explants and in a rabbit model of shigellosis. CONCLUSION: These results highlight a major protective function of EGCs and GSNO in the IEB against S flexneri attack. Consequently, this study lays the scientific basis for using GSNO to reduce barrier susceptibility to infectious or inflammatory challenge.

Intestinal Organoids: New Tools to Comprehend the Virulence of Bacterial Foodborne Pathogens.

Foodborne diseases cause high morbidity and mortality worldwide. Understanding the relationships between bacteria and epithelial cells throughout the infection process is essential to setting up preventive and therapeutic solutions. The extensive study of their pathophysiology has mostly been performed on transformed cell cultures that do not fully mirror the complex cell populations, the in vivo architectures, and the genetic profiles of native tissues. Following advances in primary cell culture techniques, organoids have been developed. Such technological breakthroughs have opened a new path in the study of microbial infectious diseases, and thus opened onto new strategies to control foodborne hazards. This review sheds new light on cellular messages from the host-foodborne pathogen crosstalk during in vitro organoid infection by the foodborne pathogenic bacteria with the highest health burden. Finally, future perspectives and current challenges are discussed to provide a better understanding of the potential applications of organoids in the investigation of foodborne infectious diseases.

UNC45A deficiency causes microvillus inclusion disease-like phenotype by impairing myosin VB-dependent apical trafficking.

Variants in the UNC45A cochaperone have been recently associated with a syndrome combining diarrhea, cholestasis, deafness, and bone fragility. Yet the mechanism underlying intestinal failure in UNC45A deficiency remains unclear. Here, biallelic variants in UNC45A were identified by next-generation sequencing in 6 patients with congenital diarrhea. Corroborating in silico prediction, variants either abolished UNC45A expression or altered protein conformation. Myosin VB was identified by mass spectrometry as client of the UNC45A chaperone and was found misfolded in UNC45AKO Caco-2 cells. In keeping with impaired myosin VB function, UNC45AKO Caco-2 cells showed abnormal epithelial morphogenesis that was restored by full-length UNC45A, but not by mutant alleles. Patients and UNC45AKO 3D organoids displayed altered luminal development and microvillus inclusions, while 2D cultures revealed Rab11 and apical transporter mislocalization as well as sparse and disorganized microvilli. All those features resembled the subcellular abnormalities observed in duodenal biopsies from patients with microvillus inclusion disease. Finally, microvillus inclusions and shortened microvilli were evidenced in enterocytes from unc45a-deficient zebrafish. Taken together, our results provide evidence that UNC45A plays an essential role in epithelial morphogenesis through its cochaperone function of myosin VB and that UNC45A loss causes a variant of microvillus inclusion disease.

Enteric glia promote intestinal mucosal healing via activation of focal adhesion kinase and release of proEGF.

Wound healing of the gastrointestinal mucosa is essential for the maintenance of gut homeostasis and integrity. Enteric glial cells play a major role in regulating intestinal barrier function, but their role in mucosal barrier repair remains unknown. The impact of conditional ablation of enteric glia on dextran sodium sulfate (DSS)-induced mucosal damage and on healing of diclofenac-induced mucosal ulcerations was evaluated in vivo in GFAP-HSVtk transgenic mice. A mechanically induced model of intestinal wound healing was developed to study glial-induced epithelial restitution. Glial-epithelial signaling mechanisms were analyzed by using pharmacological inhibitors, neutralizing antibodies, and genetically engineered intestinal epithelial cells. Enteric glial cells were shown to be abundant in the gut mucosa, where they associate closely with intestinal epithelial cells as a distinct cell population from myofibroblasts. Conditional ablation of enteric glia worsened mucosal damage after DSS treatment and significantly delayed mucosal wound healing following diclofenac-induced small intestinal enteropathy in transgenic mice. Enteric glial cells enhanced epithelial restitution and cell spreading in vitro. These enhanced repair processes were reproduced by use of glial-conditioned media, and soluble proEGF was identified as a secreted glial mediator leading to consecutive activation of epidermal growth factor receptor and focal adhesion kinase signaling pathways in intestinal epithelial cells. Our study shows that enteric glia represent a functionally important cellular component of the intestinal epithelial barrier microenvironment and that the disruption of this cellular network attenuates the mucosal healing process.

Modeling Gastrointestinal Diseases Using Organoids to Understand Healing and Regenerative Processes.

The gastrointestinal tract is a continuous series of organs from the mouth to the esophagus, stomach, intestine and anus that allows digestion to occur. These organs are frequently associated with chronic stress and injury during life, subjecting these tissues to frequent regeneration and to the risk of developing disease-associated cancers. The possibility of generating human 3D culture systems, named organoids, that resemble histologically and functionally specific organs, has opened up potential applications in the analysis of the cellular and molecular mechanisms involved in epithelial wound healing and regenerative therapy. Here, we review how during normal development homeostasis takes place, and the role of the microenvironmental niche cells in the intestinal stem cell crypt as an example. Then, we introduce the notion of a perturbed niche during disease conditions affecting the esophageal-stomach junction and the colon, and describe the potential applications of organoid models in the analysis of human gastrointestinal disease mechanisms. Finally, we highlight the perspectives of organoid-based regenerative therapy to improve the repair of the epithelial barrier.

Intestinal multicellular organoids to study colorectal cancer.

Modeling colorectal cancer (CRC) using organoids has burgeoned in the last decade, providing enhanced in vitro models to study the development and possible treatment options for this type of cancer. In this review, we describe both normal and CRC intestinal organoid models and their utility in the cancer research field. Besides highlighting studies that develop epithelial CRC organoid models, i.e. organoids without tumor microenvironment (TME) cellular components, we emphasize on the need for TME in CRC modeling, to help reduce translational disparities in this area. Also, we discuss the utilization of CRC organoids derived from pluripotent stem cells, as well as their potential to be used in cancer research. Finally, limitations and challenges in the current CRC organoids field, are discussed.

Intestinal Stem Cell-on-Chip to Study Human Host-Microbiota Interaction.

The gut is a tubular organ responsible for nutrient absorption and harbors our intestinal microbiome. This organ is composed of a multitude of specialized cell types arranged in complex barrier-forming crypts and villi covered by a mucosal layer controlling nutrient passage and protecting from invading pathogens. The development and self-renewal of the intestinal epithelium are guided by niche signals controlling the differentiation of specific cell types along the crypt-villus axis in the epithelium. The emergence of microphysiological systems, or organ-on-chips, has paved the way to study the intestinal epithelium within a dynamic and controlled environment. In this review, we describe the use of organ-on-chip technology to control and guide these differentiation processes in vitro. We further discuss current applications and forthcoming strategies to investigate the mechanical processes of intestinal stem cell differentiation, tissue formation, and the interaction of the intestine with the microbiota in the context of gastrointestinal diseases.

PGI2 Inhibits Intestinal Epithelial Permeability and Apoptosis to Alleviate Colitis.

BACKGROUND & AIMS: Inflammatory bowel diseases (IBDs) that encompass both ulcerative colitis and Crohn's disease are a major public health problem with an etiology that has not been fully elucidated. There is a need to improve disease outcomes and preventive measures by developing new effective and lasting treatments. Although polyunsaturated fatty acid metabolites play an important role in the pathogenesis of several disorders, their contribution to IBD is yet to be understood. METHODS: Polyunsaturated fatty acids metabolite profiles were established from biopsy samples obtained from Crohn's disease, ulcerative colitis, or control patients. The impact of a prostaglandin I2 (PGI2) analog on intestinal epithelial permeability was tested in vitro using Caco-2 cells and ex vivo using human or mouse explants. In addition, mice were treated with PGI2 to observe dextran sulfate sodium (DSS)-induced colitis. Tight junction protein expression, subcellular location, and apoptosis were measured in the different models by immunohistochemistry and Western blotting. RESULTS: A significant reduction of PGI2 in IBD patient biopsies was identified. PGI2 treatment reduced colonic inflammation, increased occludin expression, decreased caspase-3 cleavage and intestinal permeability, and prevented colitis development in DSS-induced mice. Using colonic explants from mouse and human control subjects, the staurosporine-induced increase in paracellular permeability was prevented by PGI2. PGI2 also induced the membrane location of occludin and reduced the permeability observed in colonic biopsies from IBD patients. CONCLUSIONS: The present study identified a PGI2 defect in the intestinal mucosa of IBD patients and demonstrated its protective role during colitis.