Expression and functional characterization of bovine receptor activator of NF-κB ligand (RANKL)

Receptor activator of nuclear factor Kappa-B Ligand (RANKL) is a member of the tumor necrosis factor ligand (TNF) family involved in immune responses and immunomodulation. Expressed in various cells types around the body, RANKL plays a crucial role in bone remodeling and development of the thymus, lymph nodes and mammary glands. Research in other species demonstrates that RANKL is required for the development of microfold cells (M cells) in the gut, however limited information specific to cattle is available. Cloning and expression of bovine RANKL (BoRANKL) was carried out and bioactivity of the protein was demonstrated in the induction of osteoclast differentiation from both bovine and ovine bone marrow cells. The effects of BoRANKL on particle uptake in bovine enteroids was also assessed. The production of cross-reactive bovine RANKL protein will enable further investigations into cell differentiation using the available ruminant organoid systems, and their role in investigating host-pathogen interactions in cattle and sheep.

Patient-derived Colonoids From Disease-spared Tissue Retain Inflammatory Bowel Disease-specific Transcriptomic Signatures

BACKGROUND AND AIMS

A key histopathological feature of inflammatory bowel disease is damage to the mucosa, including breakdown of the epithelial barrier. Human enteroids and colonoids are a critical bench-to-bedside tool for studying the epithelium in inflammatory bowel disease. The goal of the current study was to define transcriptional differences in healthy versus diseased subjects that are sustained in enteroids and colonoids, including from disease-spared tissue.

METHODS

Biopsies and matching enteroid or colonoid cultures from pediatric patients with ileal Crohn disease (N = 6) and control subjects (N = 17) were subjected to RNA sequencing followed by bioinformatic and machine learning analyses. Late passage enteroids were exposed to cytokines to assess durable transcriptional differences.

RESULTS

We observed substantial overlap of pathways upregulated in Crohn disease in enteroids and ileal biopsies, as well as colonoids and rectal biopsies. KEGG pathways for cytokine-cytokine receptor interaction, chemokine signaling, protein export, and Toll-like receptor signaling were upregulated in both ileal and rectal biopsies, as well as enteroids and colonoids. In vitro cytokine exposure reactivated genes previously increased in biopsies. Machine learning predicted biopsy location (100% accuracy) and donor disease status (83% accuracy). A random forest classifier generated using ileal enteroids identified rectal colonoids from ileal Crohn disease subjects with 80% accuracy.

CONCLUSION

We confirmed transcriptional profiles of Crohn disease biopsies are expressed in enteroids and colonoids. Furthermore, transcriptomic data from disease-spared rectal tissue can identify patients with ileal Crohn disease. Our data support the use of patient enteroids and colonoids as critical translational tools for the study of inflammatory bowel disease.

Culture of equine intestinal epithelial stem cells after delayed tissue storage for future applications

BACKGROUND

Equine intestinal epithelial stem cells (ISCs) serve as potential targets to treat horses with severe intestinal injury. The ability to isolate and store ISCs from intestinal biopsies creates an opportunity for both in vitro experiments to study ISC dynamics in a variety of intestinal diseases, and, in the future, utilize these cells as a possible therapy. If biopsies could be successfully stored prior to processing for ISCs, this would increase the availability of sample repositories for future experimental and therapeutic use. However, delayed culture of equine ISCs following prolonged sample storage has not been described. The objective of this study was to describe the isolation and culture of equine ISCs following delayed tissue storage. Small intestinal full thickness biopsies were collected post euthanasia. Fresh tissue was immediately processed or stored at 4 °C for 24, 48 and 72 h (H) before processing. Intestinal stem cells (crypts) were dissociated and cultured. Size, growth efficiency and proliferation potential were compared between resultant enteroids ("mini-guts") derived from each storage timepoint. In a separate study, growth efficiency of cryopreserved crypts was compared to cryopreserved enteroid fragments to investigate prolonged storage techniques.

RESULTS

Intestinal crypts were successfully isolated and cultured from all timepoints. At 72H post initial collection, the intestine was friable with epithelial sloughing; resultant dissociation yielded more partial crypts. Enteroids grown from crypts isolated at 72H were smaller with less proliferative potential (bud units, (median 6.5, 3.75-14.25)) than control (median 25, 15-28, p < 0.0001). No statistical differences were noted from tissues stored for 24H compared to control. Following cryopreservation, growth efficiency improved when cells were stored as enteroid fragments (median 81.6%, 66.2-109) compared to crypts (median 21.2%, 20-21.5, p = 0.01). The main limitations included a small sample size and lack of additional functional assays on enteroids.

CONCLUSIONS

Equine ISCs can be isolated and cultured after prolonged tissue storage. Resultant enteroids had minimal differences even after 24-48H of whole tissue storage. This suggests that ISCs could be isolated for several days from samples properly stored after procedures, including surgery or necropsy, and used to create ISC repositories for study or therapy of equine intestinal diseases.

Generation of equine enteroids and enteroid-derived 2D monolayers that are responsive to microbial mimics

Enteroid cultures are three-dimensional in vitro models that reflect the cellular composition and architecture of the small intestine. One limitation with the enteroid conformation is the enclosed lumen, making it difficult to expose the apical surface of the epithelium to experimental treatments. The present study was therefore conducted to generate cultures of equine enteroids and to develop methods for culture of enteroid-derived cells on a two-dimensional plane, enabling easy access to the apical surface of the epithelium. Equine enteroids were established from small intestinal crypts within 7-9 days of culture. Transcriptional analysis of cell type markers confirmed the presence of enterocytes, stem-, Paneth-, proliferative-, enteroendocrine-, goblet- and tuft cells. This cellular composition was maintained over multiple passages, showing that the enteroids can be kept for prolonged periods. The transfer from 3D enteroids to 2D monolayers slightly modified the relative expression levels of the cell type markers, indicating a decrease of goblet- and Paneth cells in the monolayers. Stimulation with the TLR2, 3 and 4 agonists Pam3CSK4, Poly I:C and LPS, respectively, induced the pro-inflammatory cytokines TNF-α and IL-8, while the TLR5 agonist FliC only induced TNF-α. In addition, an up-regulation of TGF-β, IL-33 and IFN-β was recorded after exposure to lipofected Poly I:C that also affected the monolayer integrity. Thus, the equine enteroid-derived 2D monolayers described in the present study show both genetic and functional similarities with the equine intestine making it an interesting in vitro model for studies demanding access to the apical surface, e.g. in studies of host-microbe interactions.

Creating a More Perfect Union: Modeling Intestinal Bacteria-Epithelial Interactions Using Organoids

Intestinal organoids have become indispensable tools for many gastrointestinal researchers, advancing their studies of nontransformed intestinal epithelial cells, and their roles in an array of diseases, including inflammatory bowel disease and colon cancer. In many cases. these diseases, as well as many enteric infections, reflect pathogenic interactions between bacteria and the gut epithelium. The complexity of studying this microbe-epithelial interface in vivo has led to significant focus on modeling this cross-talk using organoid models. Considering how quickly the organoid field is advancing, it can be difficult to keep up to date with the latest techniques, as well as their respective strengths and weaknesses. This review addresses the advantages of using organoids derived from adult stem cells and the recently identified differences that biopsy location and patient age can have on organoids and their interactions with microbes. Several approaches to introducing bacteria in a relevant (apical) manner (ie, microinjecting 3-dimensional spheroids, polarity-reversed organoids, and 2-dimensional monolayers) also are addressed, as are the key readouts that can be obtained using these models. Lastly, the potential for new approaches, such as air-liquid interface, to facilitate studying bacterial interactions with important but understudied epithelial subsets such as goblet cells and their products, is evaluated.

Establishing Human Intestinal Enteroid/Organoid Lines from Preterm Infant and Adult Tissue

Self-organizing mini-intestines cultured ex vivo from intestinal biopsy/resected samples, termed intestinal organoids or enteroids, present a unique opportunity for mechanistic investigation of health and disease of the intestinal epithelium. These patient-derived epithelial cultures are nontransformed, retain the genetic background of the patient, maintain regional specificity, differentiate into all major cell types of the intestinal epithelium, and are physiologically active. The biological relevance of human intestinal enteroids also circumvents the need for animal models for studies on the human gastrointestinal epithelium. Coculture with human endogenous microbes allows for exciting new studies on microbial-host interactions.While the popularity of organoids/enteroids for human research has risen drastically over the past decade, existing work and published methods are primarily limited to adult tissue. Here, we describe a concise and effective method for the establishment neonatal enteroids (including preterm and term) from surgically resected tissue or biopsy material. While the protocol works on adult tissue/biopsies, it has been specifically adopted and optimised for neonatal tissue. We detail the procedure at each stage ranging from human tissue collection and extraction of stem cells from the tissue, to passaging and general maintenance of organoid/enteroid lines, and how to freeze and revive lines as needed.

A Millifluidic Perfusion Cassette for Studying the Pathogenesis of Enteric Infections Using Ex-Vivo Organoids

To generate physiologically-relevant experimental models, the study of enteric diarrheal diseases is turning increasingly to advanced in vitro models that combine ex vivo, stem cell-derived "organoid" cell lines with bioengineered culture environments that expose them to mechanical stimuli, such as fluid flow. However, such approaches require considerable technical expertise with both microfabrication and organoid culture, and are, therefore, inaccessible to many researchers. For this reason, we have developed a perfusion system that is simple to fabricate, operate, and maintain. Its dimensions approximate the volume and cell culture area of traditional 96-well plates and allow the incorporation of fastidious primary, stem cell-derived cell lines with only minimal adaptation of their established culture techniques. We show that infections with enteroaggregative E. coli and norovirus, common causes of infectious diarrhea, in the system display important differences from static models, and in some ways better recreate the pathophysiology of in vivo infections. Furthermore, commensal strains of bacteria can be added alongside the pathogens to simulate the effects of a host microbiome on the infectious process. For these reasons, we believe that this perfusion system is a powerful, yet easily accessible tool for studying host-pathogen interactions in the human intestine.

Culture of rabbit caecum organoids by reconstituting the intestinal stem cell niche in vitro with pharmacological inhibitors or L-WRN conditioned medium

Intestinal organoids are self-organized 3-dimensional (3D) structures formed by a single layer of polarized epithelial cells. This innovative in vitro model is highly relevant to study physiology of the intestinal epithelium and its role in nutrition and barrier function. However, this model has never been developed in rabbits, while it would have potential applications for biomedical and veterinary research. Here, we cultured rabbit caecum organoids with either pharmacological inhibitors (2Ki medium) or L-WRN cells conditioned medium (L-WRN CM) to reconstitute the intestinal stem cell niche in vitro. Large spherical organoids were obtained with the 2Ki medium and this morphology was associated with a high level of proliferation and stem cells markers gene expression. In contrast, organoids cultured with L-WRN CM had a smaller diameter; a greater cell height and part of them were not spherical. When the L-WRN CM was used at low concentration (5%) for two days, the gene expression of stem cells and proliferation markers were very low, while absorptive and secretory cells markers and antimicrobial peptides were elevated. Epithelial cells within organoids were polarized in 3D cultures with 2Ki medium or L-WRN CM (apical side towards the lumen). We cultured dissociated organoid cells in 2D monolayers, which allowed accessibility to the apical compartment. Under these conditions, actin stress fibers were observed with the 2Ki medium, while perijonctionnal localization of actin was observed with the L-WRN CM suggesting, in 2D cultures as well, a higher differentiation level in the presence of L-WRN CM. In conclusion, rabbit caecum organoids cultured with the 2Ki medium were more proliferative and less differentiated than organoids cultured with L-WRN CM. We propose that organoids cultured with the 2Ki medium could be used to rapidly generate in vitro a large number of rabbit intestinal epithelial stem cells while organoids cultured with the L-WRN CM used at low concentration represent a suitable model to study differentiated rabbit epithelium.

Intestinal Enteroid Culture for Human Astroviruses

Human astroviruses (HAstV) are non-enveloped, positive-sense single stranded RNA viruses that typically cause gastroenteritis in children, the elderly and among immunocompromised individuals. Some HAstV species have also been implicated in neurological diseases. It is important to study these viruses to understand the pathogenesis and develop therapeutics. Here we describe HAstV infection in epithelium-only human intestinal enteroids (HIE) isolated from biopsy-derived intestinal crypts. Although different HAstV clades have been propagated in transformed immortalized cell lines such as A549, Caco-2, HEK293T and Huh7.5, we chose HIE because they better mimic the human intestine and thus are more physiologically relevant. Additionally, HIE support the replication of all HAstV clades including clinical samples, thus making HIE a valuable potential universal model to study HAstV biology.

Precision-based modeling approaches for necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in premature infants and remains stubbornly difficult to treat in many cases. Much of our understanding of NEC pathogenesis has been gained through the study of highly translational animal models. However, most models of NEC are limited by their overall complexity and by the fact that they do not incorporate human tissue. To address these limitations, investigators have recently developed precision-based ex vivo models of NEC, also termed ‘NEC-in-a-dish’ models, which provide the opportunity to increase our understanding of this disease and for drug discovery. These approaches involve exposing intestinal cells from either humans or animals with or without NEC to a combination of environmental and microbial factors associated with NEC pathogenesis. This Review highlights the current progress in the field of NEC model development, introduces NEC-in-a-dish models as a means to understand NEC pathogenesis and examines the fundamental questions that remain unanswered in NEC research. By answering these questions, and through a renewed focus on precision model development, the research community may finally achieve enduring success in improving the outcome of patients with this devastating disease.

Summary: Much of our understanding of necrotizing enterocolitis (NEC) pathogenesis has been achieved through animal models. Here, we discuss the development of advanced precision-based models to improve outcomes for patients with NEC.

Generation of small intestinal organoids for experimental intestinal physiology

Human intestinal organoids (HIOs) derived from pluripotent stem cells were first described almost a decade ago as a method to differentiate intestinal tissue containing both epithelium and supporting mesenchymal cells. The original protocol documents a directed differentiation approach to first induce definitive endoderm from pluripotent stem cells, followed by hindgut specification, resulting in the self-organization of 3D hindgut spheroids. These hindgut spheroids are then embedded in a basement membrane extracellular matrix (ECM) such as Matrigel and mature into HIOs over about 4 weeks in culture. Since the initial HIO protocol was published, the methods to generate HIOs have been updated over time including revisions to the directed differentiation protocol and implementation of new culture methods for spheroids such as embedding in alginate or polyethylene glycol hydrogels as defined alternatives to Matrigel. Additionally, HIOs have been utilized for new applications such as co-culture with bacteria. This protocol compiles the most up to date information on HIO generation and presents alternative experimental applications.

In Vivo Human PSC-Derived Intestinal Organoids to Study Stem Cell Maintenance

Human intestinal organoids (HIOs), derived from pluripotent stem cells, are a new tool to gain insights in gastrointestinal development, physiology, and associated diseases. Herein, we present a method for renal transplantation of HIOs in immunocompromised mice and subsequent analysis to study intestinal epithelial cell proliferation. In addition, we describe how to generate enteroids from transplanted HIOs. The method highlights the specific steps to successful engraftment and provides insight into the study of human intestinal stem cells.

Two- and Three-Dimensional Bioengineered Human Intestinal Tissue Models for Cryptosporidium

Conventional cell cultures utilizing transformed or immortalized cell lines or primary human epithelial cells have played a fundamental role in furthering our understanding of Cryptosporidium infection. However, they remain inadequate with respect to their inability to emulate in vivo conditions, support long-term growth, and complete the life cycle of the parasite. Previously, we developed a 3D silk scaffold-based model using transformed human intestinal epithelial cells (IECs). This model supported C. parvum infection for up to 2 weeks and resulted in completion of the life cycle of the parasite. However, transformed IECs are not representative of primary human IEC.Human intestinal enteroids (HIEs) are cultures derived from crypts that contain Lgr5+ stem cells isolated from human biopsies or surgical intestinal tissues; these established multicellular cultures can be induced to differentiate into enterocytes, enteroendocrine cells, goblet cells, Paneth cells, and tuft cells. HIEs better represent human intestinal structure and function than immortalized IEC lines. Recently, significant progress has been made in the development of technologies to culture HIEs in vitro. When grown in a 3D matrix, HIEs provide a spatial organization resembling the native human intestinal epithelium. Additionally, they can be dissociated and grown as monolayers in tissue culture plates, permeable supports or silk scaffolds that enable mechanistic studies of pathogen infections. They can also be co-cultured with other human cells such as macrophages and myofibroblasts. The HIEs grown in these novel culture systems recapitulate the physiology, the 3D architecture, and functional diversity of native intestinal epithelium and provide a powerful and promising new tool to study Cryptosporidium-host cell interactions and screen for interventions ex vivo. In this chapter, we describe the 3D silk scaffold-based model using transformed IEC co-cultured with human intestinal myofibroblasts and 2D and 3D HIE-derived models of Cryptosporidium, also co-cultured with human intestinal myofibroblasts.

Enteroendocrine Progenitor Cell-Enriched miR-7 Regulates Intestinal Epithelial Proliferation in an Xiap-Dependent Manner

BACKGROUND & AIMS

The enteroendocrine cell (EEC) lineage is important for intestinal homeostasis. It was recently shown that EEC progenitors contribute to intestinal epithelial growth and renewal, but the underlying mechanisms remain poorly understood. MicroRNAs are under-explored along the entire EEC lineage trajectory, and comparatively little is known about their contributions to intestinal homeostasis.

METHODS

We leverage unbiased sequencing and eight different mouse models and sorting methods to identify microRNAs enriched along the EEC lineage trajectory. We further characterize the functional role of EEC progenitor-enriched miRNA, miR-7, by in vivo dietary study as well as ex vivo enteroid in mice.

RESULTS

First, we demonstrate that miR-7 is highly enriched across the entire EEC lineage trajectory and is the most enriched miRNA in EEC progenitors relative to Lgr5+ intestinal stem cells. Next, we show in vivo that in EEC progenitors miR-7 is dramatically suppressed under dietary conditions that favor crypt division and suppress EEC abundance. We then demonstrate by functional assays in mouse enteroids that miR-7 exerts robust control of growth, as determined by budding (proxy for crypt division), EdU and PH3 staining, and likely regulates EEC abundance also. Finally, we show by single-cell RNA sequencing analysis that miR-7 regulates Xiap in progenitor/stem cells and we demonstrate in enteroids that the effects of miR-7 on mouse enteroid growth depend in part on Xiap and Egfr signaling.

CONCLUSIONS

This study demonstrates for the first time that EEC progenitor cell-enriched miR-7 is altered by dietary perturbations and that it regulates growth in enteroids via intact Xiap and Egfr signaling.

Human Intestinal Enteroids With Inducible Neurogenin-3 Expression as a Novel Model of Gut Hormone Secretion

BACKGROUND & AIMS

Enteroendocrine cells (EECs) are specialized epithelial cells that produce molecules vital for intestinal homeostasis, but because of their limited numbers, in-depth functional studies have remained challenging. Human intestinal enteroids (HIEs) that are derived from intestinal crypt stem cells are biologically relevant in an in vitro model of the intestinal epithelium. HIEs contain all intestinal epithelial cell types; however, similar to the intestine, HIEs spontaneously produce few EECs, which limits their study.

METHODS

To increase the number of EECs in HIEs, we used lentivirus transduction to stably engineer jejunal HIEs with doxycycline-inducible expression of neurogenin-3 (NGN3), a transcription factor that drives EEC differentiation (tetNGN3-HIEs). We examined the impact of NGN3 induction on EECs by quantifying the increase in the enterochromaffin cells and other EEC subtypes. We functionally assessed secretion of serotonin and EEC hormones in response to norepinephrine and rotavirus infection.

RESULTS

Treating tetNGN3-HIEs with doxycycline induced a dose-dependent increase of chromogranin A (ChgA)-positive and serotonin-positive cells, showing increased enterochromaffin cell differentiation. Despite increased ChgA-positive cells, other differentiated cell types of the epithelium remained largely unchanged by gene expression and immunostaining. RNA sequencing of doxycycline-induced tetNGN3-HIEs identified increased expression of key hormones and enzymes associated with several other EEC subtypes. Doxycycline-induced tetNGN3-HIEs secreted serotonin, monocyte chemoattractant protein-1, glucose-dependent insulinotropic peptide, peptide YY, and ghrelin in response to norepinephrine and rotavirus infection, further supporting the presence of multiple EEC types.

CONCLUSIONS

We have combined HIEs and inducible-NGN3 expression to establish a flexible in vitro model system for functional studies of EECs in enteroids and advance the molecular and physiological investigation of EECs.

Derivation of adult canine intestinal organoids for translational research in gastroenterology

Background

Large animal models, such as the dog, are increasingly being used for studying diseases including gastrointestinal (GI) disorders. Dogs share similar environmental, genomic, anatomical, and intestinal physiologic features with humans. To bridge the gap between commonly used animal models, such as rodents, and humans, and expand the translational potential of the dog model, we developed a three-dimensional (3D) canine GI organoid (enteroid and colonoid) system. Organoids have recently gained interest in translational research as this model system better recapitulates the physiological and molecular features of the tissue environment in comparison with two-dimensional cultures.

Results

Organoids were derived from tissue of more than 40 healthy dogs and dogs with GI conditions, including inflammatory bowel disease (IBD) and intestinal carcinomas. Adult intestinal stem cells (ISC) were isolated from whole jejunal tissue as well as endoscopically obtained duodenal, ileal, and colonic biopsy samples using an optimized culture protocol. Intestinal organoids were comprehensively characterized using histology, immunohistochemistry, RNA in situ hybridization, and transmission electron microscopy, to determine the extent to which they recapitulated the in vivo tissue characteristics. Physiological relevance of the enteroid system was defined using functional assays such as optical metabolic imaging (OMI), the cystic fibrosis transmembrane conductance regulator (CFTR) function assay, and Exosome-Like Vesicles (EV) uptake assay, as a basis for wider applications of this technology in basic, preclinical and translational GI research. We have furthermore created a collection of cryopreserved organoids to facilitate future research.

Conclusions

We establish the canine GI organoid systems as a model to study naturally occurring intestinal diseases in dogs and humans, and that can be used for toxicology studies, for analysis of host-pathogen interactions, and for other translational applications.

Electronic supplementary material

The online version of this article (10.1186/s12915-019-0652-6) contains supplementary material, which is available to authorized users.

Cellular Plasticity of Defa4Cre-Expressing Paneth Cells in Response to Notch Activation and Intestinal Injury

BACKGROUND & AIMS

Loss of leucine-rich repeat-containing G-protein-coupled receptor 5-positive crypt base columnar cells provides permissive conditions for different facultative stem cell populations to dedifferentiate and repopulate the stem cell compartment. In this study, we used a defensin α4-Cre recombinase (Defa4Cre) line to define the potential of Paneth cells to dedifferentiate and contribute to intestinal stem cell (ISC) maintenance during normal homeostasis and after intestinal injury.

METHODS

Small intestine and enteroids from Defa4^Cre;Rosa26 tandem dimer Tomato (tdTomato), a red fluoresent protein, (or Rosa26 Enhanced Yellow Fluorescent Protein (EYFP)) reporter, Notch gain-of-function (Defa4^Cre;Rosa26 Notch Intracellular Domain (NICD)-ires-nuclear Green Fluorescent Protein (nGFP) and Defa4^Cre;Rosa26^{reverse tetracycline transactivator-ires} Enhanced Green Fluorescent Protein (EGFP);TetO^NICD), A Disintegrin and Metalloproteinase domain-containing protein 10 (ADAM10) loss-of-function (Defa4^Cre;ADAM10^flox/flox), and Adenomatous polyposis coli (APC) inactivation (Defa4^Cre;APC^flox/flox) mice were analyzed. Doxorubicin treatment was used as an acute intestinal injury model. Lineage tracing, proliferation, and differentiation were assessed in vitro and in vivo.

RESULTS

Defa4^Cre-expressing cells are fated to become mature Paneth cells and do not contribute to ISC maintenance during normal homeostasis in vivo. However, spontaneous lineage tracing was observed in enteroids, and fluorescent-activated cell sorter-sorted Defa4^Cre-marked cells showed clonogenic enteroid growth. Notch activation in Defa4^Cre-expressing cells caused dedifferentiation to multipotent ISCs in vivo and was required for adenoma formation. ADAM10 deletion had no significant effect on crypt homeostasis. However, after acute doxorubicin-induced injury, Defa4^Cre-expressing cells contributed to regeneration in an ADAM10-Notch-dependent manner.

CONCLUSIONS

Our studies have shown that Defa4^Cre-expressing Paneth cells possess cellular plasticity, can dedifferentiate into multipotent stem cells upon Notch activation, and can contribute to intestinal regeneration in an acute injury model.

Interleukin 22 Expands Transit-Amplifying Cells While Depleting Lgr5+ Stem Cells via Inhibition of Wnt and Notch Signaling

BACKGROUND & AIMS

Epithelial regeneration is essential for homeostasis and repair of the mucosal barrier. In the context of infectious and immune-mediated intestinal disease, interleukin (IL) 22 is thought to augment these processes. We sought to define the mechanisms by which IL22 promotes mucosal healing.

METHODS

Intestinal stem cell cultures and mice were treated with recombinant IL22. Cell proliferation, death, and differentiation were assessed in vitro and in vivo by morphometric analysis, quantitative reverse transcriptase polymerase chain reaction, and immunohistochemistry.

RESULTS

IL22 increased the size and number of proliferating cells within enteroids but decreased the total number of enteroids. Enteroid size increases required IL22-dependent up-regulation of the tight junction cation and water channel claudin-2, indicating that enteroid enlargement reflected paracellular flux-induced swelling. However, claudin-2 did not contribute to IL22-dependent enteroid loss, depletion of Lgr5+ stem cells, or increased epithelial proliferation. IL22 induced stem cell apoptosis but, conversely, enhanced proliferation within and expanded numbers of transit-amplifying cells. These changes were associated with reduced wnt and notch signaling, both in vitro and in vivo, as well as skewing of epithelial differentiation, with increases in Paneth cells and reduced numbers of enteroendocrine cells.

CONCLUSIONS

IL22 promotes transit-amplifying cell proliferation but reduces Lgr5+ stem cell survival by inhibiting notch and wnt signaling. IL22 can therefore promote or inhibit mucosal repair, depending on whether effects on transit-amplifying or stem cells predominate. These data may explain why mucosal healing is difficult to achieve in some inflammatory bowel disease patients despite markedly elevated IL22 production.

The LPA2 receptor agonist Radioprotectin-1 spares Lgr5-positive intestinal stem cells from radiation injury in murine enteroids

Rapidly proliferating cells are highly sensitive to ionizing radiation and can undergo apoptosis if the oxidative and genotoxic injury exceed the defensive and regenerative capacity of the cell. Our earlier work has established the antiapoptotic action of the growth factor-like lipid mediator lysophosphatidic acid (LPA). Activation of the LPA₂ GPCR has been hypothesized to elicit antiapoptotic and regenerative actions of LPA. Based on this hypothesis we developed a novel nonlipid agonist of LPA₂, which we designated Radioprotectin-1 (RP-1). We tested RP-1 at the six murine LPA GPCR subtypes using the transforming growth factor alpha shedding assay and found that it had a 25 nM EC₅₀ that is similar to that of LPA18:1 at 32 nM. RP-1 effectively reduced apoptosis induced by γ-irradiation and the radiomimetic drug Adriamycin only in cells that expressed LPA₂ either endogenously or after transfection. RP-1 reduced γ-H2AX levels in irradiated mouse embryonic fibroblasts transduced with the human LPA₂ GPCR but was ineffective in vector transduced MEF control cells and significantly increased clonogenic survival after γ-irradiation. γ-Irradiation induced the expression of lpar2 transcripts that was further enhanced by RP-1 exposure within 30 min after irradiation. RP-1 decreased the mortality of C57BL/6 mice in models of the hematopoietic and gastrointestinal acute radiation syndromes. Using Lgr5-EGFP-CreER;Tdtomato^flox transgenic mice, we found that RP-1 increased the survival and growth of intestinal enteroids via the enhanced survival of Lgr5⁺ intestinal stem cells. Taken together, our results suggest that the LPA₂-specific agonist RP-1 exerts its radioprotective and radiomitigative action through specific activation of the upregulated LPA₂ GPCR in Lgr5⁺ stem cells.

Quantitative Analysis of Intestinal Stem Cell Dynamics Using Microfabricated Cell Culture Arrays

Regeneration of intestinal epithelium is fueled by a heterogeneous population of rapidly proliferating stem cells (ISCs) found in the base of the small intestine and colonic crypts. ISCs populations can be enriched by fluorescence-activated cell sorting (FACS) based on expression of combinatorial cell surface markers, and fluorescent transgenes. Conventional ISC culture is performed by embedding single ISCs or whole crypt units in a matrix and culturing in conditions that stimulate or repress key pathways to recapitulate ISC niche signaling. Cultured ISCs form organoid, which are spherical, epithelial monolayers that are self-renewing, self-patterning, and demonstrate the full complement of intestinal epithelial cell lineages. However, this conventional "bulk" approach to studying ISC biology is often semiquantitative, low throughput, and masks clonal effects and ISC phenotypic heterogeneity. Our group has recently reported the construction, long-term biocompatibility, and use of microfabricated cell raft arrays (CRA) for high-throughput analysis of single ISCs and organoids. CRAs are composed of thousands of indexed and independently retrievable microwells, which in combination with time-lapse microscopy and/or gene-expression analyses are a powerful tool for studying clonal ISC dynamics and micro-niches. In this protocol, we describe how CRAs are used as an adaptable experimental platform to study the effect of exogenous factors on clonal stem cell behavior.

WRN conditioned media is sufficient for in vitro propagation of intestinal organoids from large farm and small companion animals

Recent years have seen significant developments in the ability to continuously propagate organoids derived from intestinal crypts. These advancements have been applied to mouse and human samples providing models for gastrointestinal tissue development and disease. We adapt these methods for the propagation of intestinal organoids (enteroids) from various large farm and small companion (LF/SC) animals, including cat, dog, cow, horse, pig, sheep and chicken. We show that LF/SC enteroids propagate and expand in L-WRN conditioned media containing signaling factors Wnt3a, R-spondin-3, and Noggin (WRN). Multiple successful isolations were achieved for each species, and the growth of LF/SC enteroids was maintained to high passage number. LF/SC enteroids expressed crypt stem cell marker LGR5 and low levels of mesenchymal marker VIM. Labeling with EdU also showed distinct regions of cell proliferation within the enteroids marking crypt-like regions. The ability to grow and maintain LF/SC enteroid cell lines provides additional models for the study of gastrointestinal developmental biology as well as platforms for the study of host-pathogen interactions between intestinal cells and zoonotic enteric pathogens of medical importance.

Summary: Culturing methods for the propagation of crypt-derived mouse and human enteroids are applicable to large farm and small companion animals, demonstrating conservation of the crypt signaling microenvironment.

Alcohol Injury Damages Intestinal Stem Cells

BACKGROUND

Alcohol consumption is associated with intestinal injury including intestinal leakiness and the risk of developing progressive gastrointestinal cancer. Alcoholics have disruption of intestinal barrier dysfunction that persists weeks after stopping alcohol intake, and this occurs in spite of the fact that intestinal epithelial cells turn over every 3 to 5 days. The renewal and functional regulation of the intestinal epithelium largely relies on intestinal stem cells (ISCs). Chronic inflammation and tissue damage in the intestine can injure stem cells including accumulation of mutations that may result in ISC dysfunction and transformation. ISCs are a key element in intestinal function and pathology; however, very little is known about the effects of alcohol on ISCs. We hypothesize that dysregulation of ISCs is one mechanism by which alcohol induces long-lasting intestinal damage.

METHODS

In Vivo: Small intestinal samples from alcohol- and control-fed mice were assessed for ISC markers (Lgr5 and Bmi1) and the changes of the β-catenin signaling using immunofluorescent microscopy, Western blotting, and RT-PCR. Ex Vivo: Organoids were generated from small intestine tissue and subsequently exposed to alcohol and analyzed for ISC markers, β-catenin signaling.

RESULTS

Chronic alcohol consumption significantly decreased the expression of stem cell markers, Bmi1 in the small intestine of the alcohol-fed mice and also resulted in dysregulation of the β-catenin signaling-an essential regulator of its target gene Lgr5 and ISC function. Exposure of small intestine-derived organoids to 0.2% alcohol significantly reduced the growth of the organoids, including budding, and total surface area of the organoid cultures. Alcohol also significantly decreased the expression of Lgr5, p-β-catenin (ser552), and Bmi1 in the organoid model.

CONCLUSIONS

Both chronic alcohol feeding and acute exposure of alcohol resulted in ISC dysregulation which might be one mechanism for alcohol-induced long-lasting intestinal damage.

A novel culture system for adult porcine intestinal crypts

Porcine models are useful for investigating therapeutic approaches to short bowel syndrome and potentially to intestinal stem cell (ISC) transplantation. Whereas techniques for the culture and genetic manipulation of ISCs from mice and humans are well established, similar methods for porcine stem cells have not been reported. Jejunal crypts were isolated from murine, human, and juvenile and adult porcine small intestine, suspended in Matrigel, and co-cultured with syngeneic intestinal subepithelial myofibroblasts (ISEMFs) or cultured without feeder cells in various culture media. Media containing epidermal growth factor, noggin, and R-spondin 1 (ENR medium) were supplemented with various combinations of Wnt3a- or ISEMF-conditioned medium (CM) and with glycogen synthase kinase 3 inhibitor (GSK3i), and their effects were studied on cultured crypts. Cell lineage differentiation was assessed by immunohistochemistry and quantitative polymerase chain reaction. Cultured porcine cells were serially passaged and transduced with a lentiviral vector. Whereas ENR medium supported murine enteroid growth, it did not sustain porcine crypts beyond 5 days. Supplementation of Wnt3a-CM and GSK3i resulted in the formation of complex porcine enteroids with budding extensions. These enteroids contained a mixture of stem and differentiated cells and were successfully passaged in the presence of GSK3i. Crypts grown in media supplemented with porcine ISEMF-CM formed spheroids that were less well differentiated than enteroids. Enteroids and spheroids were transfected with a lentivirus with high efficiency. Thus, our method maintains juvenile and adult porcine crypt cells long-term in culture. Porcine enteroids and spheroids can be successfully passaged and transduced by using lentiviral vectors.

A whole new ball game: Stem cell-derived epithelia in the study of host-microbe interactions

Recent advances in developmental and stem cell biology have resulted in techniques that enable the generation and maintenance of complex epithelium in vitro. While these models have been utilized to study host development and disease, a renewed appreciation of host-microbe interactions has sparked interest in employing these new techniques to study microbes at the epithelial interface. Here we review the current advances in host-microbe interactions that have resulted from experiments using these complex epithelia. Furthermore we highlight aspects of these techniques that warrant further development to facilitate the study of host-microbe interactions.