Cell lineage identification and stem cell culture in a porcine model for the study of intestinal epithelial regeneration

Culture media and format alter cellular composition and barrier integrity of porcine colonoid-derived monolayers

Intestinal organoid technology has revolutionized our approach to in vitro cell culture due in part to their three-dimensional structures being more like the native tissue from which they were derived with respect to cellular composition and architecture. For this reason, organoids are becoming the new gold standard for undertaking intestinal epithelial cell research. Unfortunately, their otherwise advantageous three-dimensional geometry prevents easy access to the apical epithelium, which is a major limitation when studying interactions between dietary or microbial components and host tissues. To overcome this problem, we developed porcine colonoid-derived monolayers cultured on both permeable Transwell inserts and tissue culture treated polystyrene plates. We found that seeding density and culture format altered the expression of genes encoding markers of specific cell types (stem cells, colonocytes, goblets, and enteroendocrine cells), and barrier maturation (tight junctions). Additionally, we found that changes to the formulation of the culture medium altered the cellular composition of colonoids and of monolayers derived from them, resulting in cultures with an increasingly differentiated phenotype that was similar to that of their tissue of origin.

Comparison of the effects of normothermic machine perfusion and cold storage preservation on porcine intestinal allograft regenerative potential and viability

Intestinal transplantation (IT) is the final treatment option for intestinal failure. Static cold storage (CS) is the standard preservation method used for intestinal allografts. However, CS and subsequent transplantation induce ischemia-reperfusion injury (IRI). Severe IRI impairs epithelial barrier function, including loss of intestinal stem cells (ISC), critical to epithelial regeneration. Normothermic machine perfusion (NMP) preservation of kidney and liver allografts minimizes CS-associated IRI; however, it has not been used clinically for IT. We hypothesized that intestine NMP would induce less epithelial injury and better protect the intestine's regenerative ability when compared with CS. Full-length porcine jejunum and ileum were procured, stored at 4 °C, or perfused at 34 °C for 6 hours (T6), and transplanted. Histology was assessed following procurement (T0), T6, and 1 hour after reperfusion. Real-time quantitative reverse transcription polymerase chain reaction, immunofluorescence, and crypt culture measured ISC viability and proliferative potential. A greater number of NMP-preserved intestine recipients survived posttransplant, which correlated with significantly decreased tissue injury following 1-hour reperfusion in NMP compared with CS samples. Additionally, ISC gene expression, spheroid area, and cellular proliferation were significantly increased in NMP-T6 compared with CS-T6 intestine. NMP appears to reduce IRI and improve graft regeneration with improved ISC viability and proliferation.

A matter of differentiation: equine enteroids as a model for the in vivo intestinal epithelium

Epithelial damage due to gastrointestinal disorders frequently causes severe disease in horses. To study the underlying pathophysiological processes, we aimed to establish equine jejunum and colon enteroids (eqJE, eqCE) mimicking the in vivo epithelium. Therefore, enteroids were cultivated in four different media for differentiation and subsequently characterized histomorphologically, on mRNA and on protein level in comparison to the native epithelium of the same donor horses to identify ideal culture conditions for an in vitro model system. With increasing enterocyte differentiation, the enteroids showed a reduced growth rate as well as a predominantly spherical morphology and less budding compared to enteroids in proliferation medium. Combined or individual withdrawal of stem cell niche pathway components resulted in lower mRNA expression levels of stem cell markers and concomitant differentiation of enterocytes, goblet cells and enteroendocrine cells. For eqCE, withdrawal of Wnt alone was sufficient for the generation of differentiated enterocytes with a close resemblance to the in vivo epithelium. Combined removal of Wnt, R-spondin and Noggin and the addition of DAPT stimulated differentiation of eqJE at a similar level as the in vivo epithelium, particularly with regard to enterocytes. In summary, we successfully defined a medium composition that promotes the formation of eqJE and eqCE consisting of multiple cell types and resembling the in vivo epithelium. Our findings emphasize the importance of adapting culture conditions to the respective species and the intestinal segment. This in vitro model will be used to investigate the pathological mechanisms underlying equine gastrointestinal disorders in future studies.

Paneth cell ontogeny in term and preterm ovine models

Introduction

Paneth cells are critically important to intestinal health, including protecting intestinal stem cells, shaping the intestinal microbiome, and regulating host immunity. Understanding Paneth cell biology in the immature intestine is often modeled in rodents with little information in larger mammals such as sheep. Previous studies have only established the distribution pattern of Paneth cells in healthy adult sheep. Our study aimed to examine the ontogeny, quantification, and localization of Paneth cells in fetal and newborn lambs at different gestational ages and with perinatal transient asphyxia. We hypothesized that ovine Paneth cell distribution at birth resembles the pattern seen in humans (highest concentrations in the ileum) and that ovine Paneth cell density is gestation-dependent.

Methods

Intestinal samples were obtained from 126-127 (preterm, with and without perinatal transient asphyxia) and 140-141 (term) days gestation sheep. Samples were quantified per crypt in at least 100 crypts per animal and confirmed as Paneth cells through in immunohistochemistry.

Results

Paneth cells had significantly higher density in the ileum compared to the jejunum and were absent in the colon.

Discussion

Exposure to perinatal transient asphyxia acutely decreased Paneth cell numbers. These novel data support the possibility of utilizing ovine models for understanding Paneth cell biology in the fetus and neonate.

Adult Animal Stem Cell-Derived Organoids in Biomedical Research and the One Health Paradigm

Preclinical biomedical research is limited by the predictiveness of in vivo and in vitro models. While in vivo models offer the most complex system for experimentation, they are also limited by ethical, financial, and experimental constraints. In vitro models are simplified models that do not offer the same complexity as living animals but do offer financial affordability and more experimental freedom; therefore, they are commonly used. Traditional 2D cell lines cannot fully simulate the complexity of the epithelium of healthy organs and limit scientific progress. The One Health Initiative was established to consolidate human, animal, and environmental health while also tackling complex and multifactorial medical problems. Reverse translational research allows for the sharing of knowledge between clinical research in veterinary and human medicine. Recently, organoid technology has been developed to mimic the original organ's epithelial microstructure and function more reliably. While human and murine organoids are available, numerous other organoids have been derived from traditional veterinary animals and exotic species in the last decade. With these additional organoid models, species previously excluded from in vitro research are becoming accessible, therefore unlocking potential translational and reverse translational applications of animals with unique adaptations that overcome common problems in veterinary and human medicine.

Host-microbiota interaction in intestinal stem cell homeostasis

Intestinal stem cells (ISCs) play a pivotal role in gut physiology by governing intestinal epithelium renewal through the precise regulation of proliferation and differentiation. The gut microbiota interacts closely with the epithelium through myriad of actions, including immune and metabolic interactions, which translate into tight connections between microbial activity and ISC function. Given the diverse functions of the gut microbiota in affecting the metabolism of macronutrients and micronutrients, dietary nutrients exert pronounced effects on host-microbiota interactions and, consequently, the ISC fate. Therefore, understanding the intricate host-microbiota interaction in regulating ISC homeostasis is imperative for improving gut health. Here, we review recent advances in understanding host-microbiota immune and metabolic interactions that shape ISC function, such as the role of pattern-recognition receptors and microbial metabolites, including lactate and indole metabolites. Additionally, the diverse regulatory effects of the microbiota on dietary nutrients, including proteins, carbohydrates, vitamins, and minerals (e.g. iron and zinc), are thoroughly explored in relation to their impact on ISCs. Thus, we highlight the multifaceted mechanisms governing host-microbiota interactions in ISC homeostasis. Insights gained from this review provide strategies for the development of dietary or microbiota-based interventions to foster gut health.

Characterization of the Small Intestine in the Southern White-breasted Hedgehog (Erinaceus concolor) Using Histological, Histochemical, Immunohistochemical, and Scanning Electron Microscopic Techniques

The present study was designed to investigate the microscopic features of the small intestine in the southern white-breasted hedgehog (Erinaceus concolor). The histochemical profile of the small intestine was investigated using periodic acid Schiff (PAS), alcian blue (AB, pH 2.5), and aldehyde fuchsin. The expression of SOX9 was also evaluated immunohistochemically, and the detailed morphology of intestinal mucosa was studied by using a scanning electron microscope. The intestinal wall was composed of the tunica mucosa, tunica submucosa, tunica muscularis, and tunica serosa. Plica circulares and muscularis mucosa were present only in the duodenum. The jejunal villi were the tallest and the ileal villi were the shortest. From the duodenum to the ileum, the population density of goblet cells decreased significantly. The goblet cells throughout the small intestine reacted positively with PAS and AB. The expression rate of SOX9 was not statistically different between the three parts of the small intestine (p > 0.05). In conclusion, despite the general characteristics of the small intestine in this species of hedgehog, there were some differences when compared with other mammalian and rodent species. These findings provide a baseline for future detailed research on the digestive system of the hedgehog species and other mammalian species.

3D sheep rumen epithelial structures driven from single cells in vitro

Ruminants play a vital economic role as livestock, providing high-quality protein for humans. At present, 3D-cultured ruminant abomasum and intestinal organoids have been successfully established to study host and pathogen interaction. The rumen is a unique digestive organ of ruminants that occupies 70% of the volume of the digestive tract and its microbiota can decompose lignocellulose to support animal growth. Here we report a method for culturing rumen epithelial organoids. We found that single rumen epithelial cells form self-organized 3D structures representative of typical stratified squamous epithelium, which is similar to rumen epithelium. EGF, Noggin, Wnt3a, IGF-1, and FGF-10 significantly enhanced the seeding efficiency of organoids. Moreover, the inclusion of CHIR-99021, A83-01, SB202190, and Y-27632 is crucial for organoid formation and maintenance. Importantly, we demonstrate that rumen epithelial cells retain their ability to form organoids after passage, cryopreservation, and resuscitation. The rumen epithelial organoids express rumen cell type-specific genes, uptake fatty acids, and generate 2D cultures. In summary, our data demonstrate that it is feasible to establish organoids from single rumen epithelial cells, which is a novel in vitro system that may reduce the use of experimental animals.

Paneth cells in farm animals: current status and future direction

A healthy intestine plays an important role in the growth and development of farm animals. In small intestine, Paneth cells are well known for their regulation of intestinal microbiota and intestinal stem cells (ISCs). Although there has been a lot of studies and reviews on human and murine Paneth cells under intestinal homeostasis or disorders, little is known about Paneth cells in farm animals. Most farm animals possess Paneth cells in their small intestine, as identified by various staining methods, and Paneth cells of various livestock species exhibit noticeable differences in cell shape, granule number, and intestinal distribution. Paneth cells in farm animals and their antimicrobial peptides (AMPs) are susceptible to multiple factors such as dietary nutrients and intestinal infection. Thus, the comprehensive understanding of Paneth cells in different livestock species will contribute to the improvement of intestinal health. This review first summarizes the current status of Paneth cells in pig, cattle, sheep, horse, chicken and rabbit, and points out future directions for the investigation of Paneth cells in the reviewed animals.

Evaluation of porcine intestinal organoids as an in vitro model for mammalian orthoreovirus 3 infection

BACKGROUND

Mammalian orthoreovirus type 3 (MRV3), which is responsible for gastroenteritis in many mammalian species including pigs, has been isolated from piglets with severe diarrhea. However, the use of pig-derived cells as an infection model for swine-MRV3 has rarely been studied.

OBJECTIVES

This study aims to establish porcine intestinal organoids (PIOs) and examine their susceptibility as an in vitro model for intestinal MRV3 infection.

METHODS

PIOs were isolated and established from the jejunum of a miniature pig. Established PIOs were characterized using polymerase chain reaction (PCR) and immunofluorescence assays (IFAs) to confirm the expression of small intestine-specific genes and proteins, such as Lgr5, LYZI, Mucin-2, ChgA, and Villin. The monolayered PIOs and three-dimensional (3D) PIOs, obtained through their distribution to expose the apical surface, were infected with MRV3 for 2 h, washed with Dulbecco's phosphate-buffered saline, and observed. Viral infection was confirmed using PCR and IFA. We performed quantitative real-time reverse transcription-PCR to assess changes in viral copy numbers and gene expressions linked to intestinal epithelial genes and antiviral activity.

RESULTS

The established PIOs have molecular characteristics of intestinal organoids. Infected PIOs showed delayed proliferation with disruption of structures. In addition, infection with MRV3 altered the gene expression linked to intestinal epithelial cells and antiviral activity, and these effects were observed in both 2D and 3D models. Furthermore, viral copy numbers in the supernatant of both models increased in a time-dependent manner.

CONCLUSIONS

We suggest that PIOs can be an in vitro model to study the infection mechanism of MRV3 in detail, facilitating pharmaceutical development.

A LGR5 reporter pig model closely resembles human intestine for improved study of stem cells in disease

Intestinal epithelial stem cells (ISCs) are responsible for intestinal epithelial barrier renewal; thereby, ISCs play a critical role in intestinal pathophysiology research. While transgenic ISC reporter mice are available, advanced translational studies lack a large animal model. This study validates ISC isolation in a new porcine Leucine Rich Repeat Containing G Protein-Coupled Receptor 5 (LGR5) reporter line and demonstrates the use of these pigs as a novel colorectal cancer (CRC) model. We applied histology, immunofluorescence, fluorescence-activated cell sorting, flow cytometry, gene expression quantification, and 3D organoid cultures to whole tissue and single cells from the duodenum, jejunum, ileum, and colon of LGR5-H2B-GFP and wild-type pigs. Ileum and colon LGR5-H2B-GFP, healthy human, and murine biopsies were compared by mRNA fluorescent in situ hybridization (FISH). To model CRC, adenomatous polyposis coli (APC) mutation was induced by CRISPR/Cas9 editing in porcine LGR5-H2B-GFP colonoids. Crypt-base, green fluorescent protein (GFP) expressing cells co-localized with ISC biomarkers. LGR5-H2B-GFPhi cells had significantly higher LGR5 expression (p < .01) and enteroid forming efficiency (p < .0001) compared with LGR5-H2B-GFPmed/lo/neg cells. Using FISH, similar LGR5, OLFM4, HOPX, LYZ, and SOX9 expression was identified between human and LGR5-H2B-GFP pig crypt-base cells. LGR5-H2B-GFP/APCnull colonoids had cystic growth in WNT/R-spondin-depleted media and significantly upregulated WNT/β-catenin target gene expression (p < .05). LGR5+ ISCs are reproducibly isolated in LGR5-H2B-GFP pigs and used to model CRC in an organoid platform. The known anatomical and physiologic similarities between pig and human, and those shown by crypt-base FISH, underscore the significance of this novel LGR5-H2B-GFP pig to translational ISC research.

Evaluation of Potential Probiotic Properties of Limosilactobacillus fermentum Derived from Piglet Feces and Influence on the Healthy and E. coli-Challenged Porcine Intestine

In this work, we evaluated the probiotic properties of Limosilactobacillus fermentum strains (FL1, FL2, FL3, FL4) isolated from feces of healthy piglets. The in vitro auto-aggregation, hydrophobicity, biofilm-forming capacity, survival in the gastrointestinal tract, antimicrobial activity and anti-oxidation capacity were evaluated. Four strains were resistant to simulated gastrointestinal conditions, including low pH, pepsin, trypsin and bile salts. They also maintained strong self-aggregation and cell surface hydrophobicity. Limosilactobacillus fermentum FL4, which had the strongest adhesion ability and antimicrobial effect on Enterotoxigenic Escherichia coli K88 (ETEC K88), was then tested in porcine intestinal organoid models. The in vitro experiments in basal-out and apical-out organoids demonstrated that L. fermentum FL4 adhered to the apical surfaces more efficiently than basolateral surfaces, had the ability to activate the Wnt/β-catenin pathway to protect the mucosal barrier integrity, stimulated the proliferation and differentiation of the intestinal epithelium, and repaired ETEC K88-induced damage. Moreover, L. fermentum FL4 inhibited inflammatory responses induced by ETEC K88 through the reduced expression of pro-inflammatory cytokines (TNF-α, IL-1β and IFN-γ) and higher levels of anti-inflammatory cytokines (TGF-β and IL-10). These results show that L. fermentum FL4 isolated from feces of healthy Tunchang piglets has the potential to be used as an anti-inflammatory probiotic and for mitigation of intestinal damage in piglets.

Early weaning causes small intestinal atrophy by inhibiting the activity of intestinal stem cells: involvement of Wnt/β-catenin signaling

BACKGROUND

Early weaning and shorter breastfeeding duration are applied by a proportion of young mothers, especially in the social spheres of poverty-stricken areas. Early childhood is a critical period for intestinal development, which is driven by intestinal stem cells (ISCs). However, how early weaning practice affects the function of ISCs to mediate intestinal development remains unclear.

METHODS

We established an excellent early weaning mice model that has significant intestinal atrophy and growth arrest symptoms to explore the responses of ISCs to early weaning. The primary and passaged intestinal organoids from the suckling or early weaning mice were cultured to explore the underlying mechanism of early weaning affecting the ISCs.

RESULTS

Early weaning depressed the self-renewal of ISCs and attenuated the activity of ISCs-driven intestinal epithelial regeneration and crypt expansion in vivo and ex-vivo. Further results showed that early weaning retarded the differentiation of ISCs into transit-amplifying cells and Paneth cells, and accelerated the apoptosis of villous epithelial cells, jointly leading to intestinal epithelial atrophy. Mechanistically, early weaning inhibited Wnt signaling in ISCs, while an exogenous Wnt amplifier restored ISCs' function in ex-vivo.

CONCLUSION

Our findings indicate that early weaning depresses the activity of ISCs via attenuating Wnt/β-catenin signaling and triggers the proinflammatory cytokines TNF-α, IL-1β, IL-6, and IL-17 in jejunum, thereby impeding ISCs-driven epithelial regeneration and intestinal growth, which may provide a basal theory for the development of infant nutrients targeting stem cells to alleviate early weaning-induced intestinal problems.

Regional epithelial cell diversity in the small intestine of pigs

Understanding regional distribution and specialization of small intestinal epithelial cells is crucial for developing methods to control appetite, stress, and nutrient uptake in swine. To establish a better understanding of specific epithelial cells found across different regions of the small intestine in pigs, we utilized single-cell RNA sequencing (scRNA-seq) to recover and analyze epithelial cells from duodenum, jejunum, and ileum. Cells identified included crypt cells, enterocytes, BEST4 enterocytes, goblet cells, and enteroendocrine (EE) cells. EE cells were divided into two subsets based on the level of expression of the EE lineage commitment gene, NEUROD1. NEUROD1hi EE cells had minimal expression of hormone-encoding genes and were dissimilar to EE cells in humans and mice, indicating a subset of EE cells unique to pigs. Recently discovered BEST4 enterocytes were detected in both crypts and villi throughout the small intestine via in situ staining, unlike in humans, where BEST4 enterocytes are found only in small intestinal villi. Proximal-to-distal gradients of expression were noted for hormone-encoding genes in EE cells and nutrient transport genes in enterocytes via scRNA-seq, demonstrating regional specialization. Regional gene expression in EE cells and enterocytes was validated via quantitative PCR (qPCR) analysis of RNA isolated from epithelial cells of different small intestinal locations. Though many genes had similar patterns of regional expression when assessed by qPCR of total epithelial cells, some regional expression was only detected via scRNA-seq, highlighting advantages of scRNA-seq to deconvolute cell type-specific regional gene expression when compared to analysis of bulk samples. Overall, results provide new information on regional localization and transcriptional profiles of epithelial cells in the pig small intestine.

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.

Calpain-1: a Novel Antiviral Host Factor Identified in Porcine Small Intestinal Mucus

The thick mucus layer covering of the intestinal epithelium has received increasing attention, owing to its protective role in intestinal infection. However, the exact mechanisms by which the mucus increases intestinal resistance against viral infection remain largely unclear. Here, we identify prominent antiviral activity of the small intestinal mucus and extracted total mucus proteins, as evidenced by their inhibitory effects against porcine epidemic diarrhea virus (PEDV) infection. Of all the extracted mucus proteins, mucin 2 and fraction III (~70 kDa) exhibited potent antiviral activity. We further evaluated the antiviral effects of three candidate factors in fraction III and found that calpain-1 contributed substantially to its antiviral activity. In vivo studies demonstrated that oral administration of calpain-1 provided effective protection against intestinal PEDV infection. As a calcium-activated cysteine protease, calpain-1 inhibited viral invasion by binding to and hydrolyzing the S1 domain of the viral spike protein. The region between amino acids 297 and 337 in the b domain of PEDV S1 protein was critical for calpain-1-mediated hydrolysis. Further investigation indicated that calpain-1 could be produced by goblet cells between intestinal epithelia. Taken together, the results of our study revealed calpain-1 to be a novel antiviral protein in porcine small intestinal mucus, suggesting that calpain-1 has potential for defending against intestinal infections.

The phenotype of the gut region is more stably retained than developmental stage in piglet intestinal organoids

Intestinal organoids are innovative in vitro tools to study the digestive epithelium. The objective of this study was to generate jejunum and colon organoids from suckling and weaned piglets in order to determine the extent to which organoids retain a location-specific and a developmental stage-specific phenotype. Organoids were studied at three time points by gene expression profiling for comparison with the transcriptomic patterns observed in crypts in vivo. In addition, the gut microbiota and the metabolome were analyzed to characterize the luminal environment of epithelial cells at the origin of organoids. The location-specific expression of 60 genes differentially expressed between jejunum and colon crypts from suckling piglets was partially retained (48%) in the derived organoids at all time point. The regional expression of these genes was independent of luminal signals since the major differences in microbiota and metabolome observed in vivo between the jejunum and the colon were not reproduced in vitro. In contrast, the regional expression of other genes was erased in organoids. Moreover, the developmental stage-specific expression of 30 genes differentially expressed between the jejunum crypts of suckling and weaned piglets was not stably retained in the derived organoids. Differentiation of organoids was necessary to observe the regional expression of certain genes while it was not sufficient to reproduce developmental stage-specific expression patterns. In conclusion, piglet intestinal organoids retained a location-specific phenotype while the characteristics of developmental stage were erased in vitro. Reproducing more closely the luminal environment might help to increase the physiological relevance of intestinal organoids.

Alternatives to animal models and their application in the discovery of species susceptibility to SARS-CoV-2 and other respiratory infectious pathogens: A review

The emergence of the coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inspired rapid research efforts targeting the host range, pathogenesis and transmission mechanisms, and the development of antiviral strategies. Genetically modified mice, rhesus macaques, ferrets, and Syrian golden hamsters have been frequently used in studies of pathogenesis and efficacy of antiviral compounds and vaccines. However, alternatives to in vivo experiments, such as immortalized cell lines, primary respiratory epithelial cells cultured at an air-liquid interface, stem/progenitor cell-derived organoids, or tissue explants, have also been used for isolation of SARS-CoV-2, investigation of cytopathic effects, and pathogen-host interactions. Moreover, initial proof-of-concept studies for testing therapeutic agents can be performed with these tools, showing that animal-sparing cell culture methods could significantly reduce the need for animal models in the future, following the 3R principles of replace, reduce, and refine. So far, only few studies using animal-derived primary cells or tissues have been conducted in SARS-CoV-2 research, although natural infection has been shown to occur in several animal species. Therefore, the need for in-depth investigations on possible interspecies transmission routes and differences in susceptibility to SARS-CoV-2 is urgent. This review gives an overview of studies employing alternative culture systems like primary cell cultures, tissue explants, or organoids for investigations of the pathophysiology and reverse zoonotic potential of SARS-CoV-2 in animals. In addition, future possibilities of SARS-CoV-2 research in animals, including previously neglected methods like the use of precision-cut lung slices, will be outlined.

Porcine Intestinal Organoids: Overview of the State of the Art

The intestinal tract is a crucial part of the body for growth and development, and its dysregulation can cause several diseases. The lack of appropriate in vitro models hampers the development of effective preventions and treatments against these intestinal tract diseases. Intestinal organoids are three-dimensional (3D) polarized structures composed of different types of cells capable of self-organization and self-renewal, resembling their organ of origin in architecture and function. Porcine intestinal organoids (PIOs) have been cultured and are used widely in agricultural, veterinary, and biomedical research. Based on the similarity of the genomic sequence, anatomic morphology, and drug metabolism with humans and the difficulty in obtaining healthy human tissue, PIOs are also considered ideal models relative to rodents. In this review, we summarize the current knowledge on PIOs, emphasizing their culturing, establishment and development, and applications in the study of host–microbe interactions, nutritional development, drug discovery, and gene editing potential.

Use of Translational, Genetically Modified Porcine Models to Ultimately Improve Intestinal Disease Treatment

For both human and veterinary patients, non-infectious intestinal disease is a major cause of morbidity and mortality. To improve treatment of intestinal disease, large animal models are increasingly recognized as critical tools to translate the basic science discoveries made in rodent models into clinical application. Large animal intestinal models, particularly porcine, more closely resemble human anatomy, physiology, and disease pathogenesis; these features make them critical to the pre-clinical study of intestinal disease treatments. Previously, large animal model use has been somewhat precluded by the lack of genetically altered large animals to mechanistically investigate non-infectious intestinal diseases such as colorectal cancer, cystic fibrosis, and ischemia-reperfusion injury. However, recent advances and increased availability of gene editing technologies has led to both novel use of large animal models in clinically relevant intestinal disease research and improved testing of potential therapeutics for these diseases.

Electrical Stimulation-Mediated Tissue Healing in Porcine Intervertebral Disc Under Mechanically Dynamic Organ Culture Conditions

STUDY DESIGN

Porcine intervertebral discs (IVDs) were excised and then drilled to simulate degeneration before being electrically stimulated for 21 days while undergoing mechanical loading. The discs were then analyzed for gene expression and morphology to assess regeneration.

OBJECTIVE

The purpose of this study was to investigate the effectiveness of the electrical stimulation of IVD treatment as an early intervention method in halting the progression of degenerative disc disease using an ex-vivo porcine model.

SUMMARY OF BACKGROUND DATA

Treatments for degenerative disc disease are limited in their efficacy and tend to treat the symptoms of the disease rather than repairing the degenerated disc itself. There is a dire need for an early intervention treatment that not only halts the progression of the disease but contributes to reviving the degenerated disc.

METHODS

Lumbar IVDs were extracted from a mature pig within 1 hour of death and were drilled with a 1.5 mm bit to simulate degenerative disc disease. Four IVDs at a time were then cultured in a dynamic bioreactor system under mechanical loading for 21 days, two with and two without the electrical stimulation treatment. The IVDs were assessed using histological analysis, magnetic resonance imaging, and quantitative reverse transcriptase polymerase chain reaction to quantify the effectiveness of the treatment on the degenerated discs.

RESULTS

IVDs with electrical stimulation treatment exhibited extensive annular regeneration and prevented herniation of the nucleus pulposus (NP). In contrast, the untreated group of IVDs were unable to maintain tissue integrity and exhibited NP herniation through multiple layers of the annulus fibrosus. Gene expression showed an increase of extracellular matrix markers and antiinflammatory cytokine interleukin-4 (IL-4), while decreasing in pro-inflammatory markers and pain markers in electrically stimulated IVDs when compared to the untreated group.

CONCLUSION

The direct electrical stimulation application in NP of damaged IVDs can be a viable option to regenerate damaged NP and annulus fibrosus tissues.

Farm and Companion Animal Organoid Models in Translational Research: A Powerful Tool to Bridge the Gap Between Mice and Humans

Animal organoid models derived from farm and companion animals have great potential to contribute to human health as a One Health initiative, which recognize a close inter-relationship among humans, animals and their shared environment and adopt multi-and trans-disciplinary approaches to optimize health outcomes. With recent advances in organoid technology, studies on farm and companion animal organoids have gained more attention in various fields including veterinary medicine, translational medicine and biomedical research. Not only is this because three-dimensional organoids possess unique characteristics from traditional two-dimensional cell cultures including their self-organizing and self-renewing properties and high structural and functional similarities to the originating tissue, but also because relative to conventional genetically modified or artificially induced murine models, companion animal organoids can provide an excellent model for spontaneously occurring diseases which resemble human diseases. These features of companion animal organoids offer a paradigm-shifting approach in biomedical research and improve translatability of in vitro studies to subsequent in vivo studies with spontaneously diseased animals while reducing the use of conventional animal models prior to human clinical trials. Farm animal organoids also could play an important role in investigations of the pathophysiology of zoonotic and reproductive diseases by contributing to public health and improving agricultural production. Here, we discuss a brief history of organoids and the most recent updates on farm and companion animal organoids, followed by discussion on their potential in public health, food security, and comparative medicine as One Health initiatives. We highlight recent evolution in the culturing of organoids and their integration with organ-on-a-chip systems to overcome current limitations in in vitro studies. We envision multidisciplinary work integrating organoid culture and organ-on-a-chip technology can contribute to improving both human and animal health.

Calcium-sensing receptor is not expressed in the absorptive enterocytes of weaned piglets

The calcium-sensing receptor (CaSR) is a kokumi receptor that plays an essential role in nutrient sensing and animal physiology, growth, and development. Pig CaSR (pCaSR) was identified and characterized in the intestine. However, further research is still needed to confirm the expression of CaSR in the epithelial cells isolated from weaned piglets. In this study, primary enterocytes were isolated and characterized from the ileum of weaned piglets by the Weiser distended intestinal sac technique and fluorescence-activated cell sorting (FACS) based on sucrase-isomaltase (SI) as an enterocyte-specific marker. The expression of CaSR was investigated in both primary enterocytes and the intestinal porcine enterocyte cell line-j2 (IPEC-J2) by droplet digital polymerase chain reaction (ddPCR), immunofluorescence staining, and Western blotting. Results demonstrated that porcine enterocytes could be obtained using FACS with the SI as the enterocyte-specific marker and that pCaSR is not expressed in both porcine ileal enterocytes and IPEC-J2 cells, which specifically identified the expression of pCaSR in ileal enterocytes with sensitive and specific approaches.

Changes in progenitors and differentiated epithelial cells of neonatal piglets

This study aimed to assess the changes of small intestinal morphology, progenitors, differentiated epithelial cells, and potential mechanisms in neonatal piglets. Hematoxylin and eosin staining of samples from 36 piglets suggested that dramatic changes were observed in the jejunum crypts depth and crypt fission index of neonatal piglets (P < 0.001). The number of intestinal stem cells (ISC) tended to increase (P < 0.10), and a decreased number of enteroendocrine cells appeared in the jejunal crypt on d 7 (P < 0.05). Furthermore, the mRNA expression of jejunal chromogranin A (ChgA) was down-regulated in d 7 piglets (P < 0.05). There was an up-regulation of the adult ISC marker gene of SPARC related modular calcium binding 2 (Smoc2), and Wnt/β-catenin target genes on d 7 (P < 0.05). These results were further verified in vitro enteroid culture experiments. A mass of hollow spheroids was cultured from the fetal intestine of 0-d-old piglets (P < 0.001), whereas substantial organoids with budding and branching structures were cultured from the intestine of 7-d-old piglets (P < 0.001). The difference was reflected by the organoid budding efficiency, crypt domains per organoid, and the surface area of the organoid. Furthermore, spheroids on d 0 had more Ki67-positive cells and enteroendocrine cells (P < 0.05) and showed a decreasing trend in the ISC and goblet cells (P < 0.10). Moreover, the mRNA expression of spheroids differed markedly from that of organoids, with low expression of intestinal differentiation gene (Lysozyme; P < 0.05), epithelial-specific markers (Villin, E-cadherin; P < 0.05), and adult ISC markers (leucine-rich repeat-containing G protein-coupled receptor 5 [Lgr5], Smoc2; P < 0.001), and up-regulation of fetal marker (connexin 43 [Cnx43]; P < 0.05). The mRNA expression of relevant genes was up-regulated, and involved in Wnt/β-catenin, epidermal growth factor (EGF), Notch, and bone morphogenetic protein (BMP) signaling on d 7 organoids (P < 0.05). Spheroids displayed low differentiated phenotype and high proliferation, while organoids exhibited strong differentiation potential. These results indicated that the conversion from the fetal progenitors (spheroids) to adult ISC (normal organoids) might largely be responsible for the fast development of intestinal epithelial cells in neonatal piglets.

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

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

Porcine Intestinal Apical-Out Organoid Model for Gut Function Study

Simple Summary

Pigs have been used in various animal model studies on the gastrointestinal tract (GIT) across both animal science and biomedical science fields. Recently, intestinal organoids have been used as a research tool for the GIT, and they have also been applied to farm animals, including pigs. However, to our knowledge, no functional studies of the porcine intestine using intestinal organoids have been conducted to date. In the present study, we developed two porcine intestinal organoid models (basal-out and apical-out organoids) and compared their characteristics. We also confirmed the possibility of conducting research related to intestinal functions, such as nutrient uptake and gut barrier function. The present study suggests that porcine intestinal organoids can be used as potential models for future GIT mechanism studies, such as host–microbe interactions, harmful ingredient tests, and nutritional research.

Abstract

Pig models provide valuable research information on farm animals, veterinary, and biomedical sciences. Experimental pig gut models are used in studies on physiology, nutrition, and diseases. Intestinal organoids are powerful tools for investigating intestinal functions such as nutrient uptake and gut barrier function. However, organoids have a basal-out structure and need to grow in the extracellular matrix, which causes difficulties in research on the intestinal apical membrane. We established porcine intestinal organoids from jejunum tissues and developed basal-out and apical-out organoids using different sub-culture methods. Staining and quantitative real-time PCR showed the difference in axis change of the membrane and gene expression of epithelial cell marker genes. To consider the possibility of using apical-out organoids for intestinal function, studies involving fatty acid uptake and disruption of the epithelial barrier were undertaken. Fluorescence fatty acid was more readily absorbed in apical-out organoids than in basal-out organoids within the same time. To determine whether apical-out organoids form a functional barrier, a fluorescent dextran diffusion assay was performed. Hence, we successfully developed porcine intestinal organoid culture systems and showed that the porcine apical-out organoid model is ideal for the investigation of the intestinal environment. It can be used in future studies related to the intestine across various research fields.

Current Perspectives on Gastrointestinal Models to Assess Probiotic-Pathogen Interactions

There are different models available that mimic the human intestinal epithelium and are thus available for studying probiotic and pathogen interactions in the gastrointestinal tract. Although, in vivo models make it possible to study the overall effects of a probiotic on a living subject, they cannot always be conducted and there is a general commitment to reduce the use of animal models. Hence, in vitro methods provide a more rapid tool for studying the interaction between probiotics and pathogens; as well as being ethically superior, faster, and less expensive. The in vitro models are represented by less complex traditional models, standard 2D models compromised of culture plates as well as Transwell inserts, and newer 3D models like organoids, enteroids, as well as organ-on-a-chip. The optimal model selected depends on the research question. Properly designed in vitro and/or in vivo studies are needed to examine the mechanism(s) of action of probiotics on pathogens to obtain physiologically relevant results.

Robust differentiation of human enteroendocrine cells from intestinal stem cells

Enteroendocrine (EE) cells are the most abundant hormone-producing cells in humans and are critical regulators of energy homeostasis and gastrointestinal function. Challenges in converting human intestinal stem cells (ISCs) into functional EE cells, ex vivo, have limited progress in elucidating their role in disease pathogenesis and in harnessing their therapeutic potential. To address this, we employed small molecule targeting of the endocannabinoid receptor signaling pathway, JNK, and FOXO1, known to mediate endodermal development and/or hormone production, together with directed differentiation of human ISCs from the duodenum and rectum. We observed marked induction of EE cell differentiation and gut-derived expression and secretion of SST, 5HT, GIP, CCK, GLP-1 and PYY upon treatment with various combinations of three small molecules: rimonabant, SP600125 and AS1842856. Robust differentiation strategies capable of driving human EE cell differentiation is a critical step towards understanding these essential cells and the development of cell-based therapeutics.

Escherichia coli Nissle 1917 Enhances Efficacy of Oral Attenuated Human Rotavirus Vaccine in a Gnotobiotic Piglet Model

Human rotavirus (HRV) infection is a major cause of viral gastroenteritis in young children worldwide. Current oral vaccines perform poorly in developing countries where efficacious vaccines are needed the most. Therefore, an alternative affordable strategy to enhance efficacy of the current RV vaccines is necessary. This study evaluated the effects of colonization of neonatal gnotobiotic (Gn) pigs with Escherichia coli Nissle (EcN) 1917 and Lacticaseibacillus rhamnosus GG (LGG) probiotics on immunogenicity and protective efficacy of oral attenuated (Att) HRV vaccine. EcN-colonized pigs had reduced virulent HRV (VirHRV) shedding and decreased diarrhea severity compared with the LGG-colonized group. They also had enhanced HRV-specific IgA antibody titers in serum and antibody secreting cell numbers in tissues pre/post VirHRV challenge, HRV-specific IgA antibody titers in intestinal contents, and B-cell subpopulations in tissues post VirHRV challenge. EcN colonization also enhanced T-cell immune response, promoted dendritic cells and NK cell function, reduced production of proinflammatory cytokines/Toll like receptor (TLR), and increased production of immunoregulatory cytokines/TLR expression in various tissues pre/post VirHRV challenge. Thus, EcN probiotic adjuvant with AttHRV vaccine enhances the immunogenicity and protective efficacy of AttHRV to a greater extent than LGG and it can be used as a safe and economical oral vaccine adjuvant.

Multiomic analysis defines the first microRNA atlas across all small intestinal epithelial lineages and reveals novel markers of almost all major cell types

MicroRNA-mediated regulation is critical for the proper development and function of the small intestinal (SI) epithelium. However, it is not known which microRNAs are expressed in each of the cell types of the SI epithelium. To bridge this important knowledge gap, we performed comprehensive microRNA profiling in all major cell types of the mouse SI epithelium. We used flow cytometry and fluorescence-activated cell sorting with multiple reporter mouse models to isolate intestinal stem cells, enterocytes, goblet cells, Paneth cells, enteroendocrine cells, tuft cells, and secretory progenitors. We then subjected these cell populations to small RNA-sequencing. The resulting atlas revealed highly enriched microRNA markers for almost every major cell type (https://sethupathy-lab.shinyapps.io/SI_miRNA/). Several of these lineage-enriched microRNAs (LEMs) were observed to be embedded in annotated host genes. We used chromatin-run-on sequencing to determine which of these LEMs are likely cotranscribed with their host genes. We then performed single-cell RNA-sequencing to define the cell type specificity of the host genes and embedded LEMs. We observed that the two most enriched microRNAs in secretory progenitors are miR-1224 and miR-672, the latter of which we found is deleted in hominin species. Finally, using several in vivo models, we established that miR-152 is a Paneth cell-specific microRNA.NEW & NOTEWORTHY In this study, first, microRNA atlas (and searchable web server) across all major small intestinal epithelial cell types is presented. We have demonstrated microRNAs that uniquely mark several lineages, including enteroendocrine and tuft. Identification of a key marker of mouse secretory progenitor cells, miR-672, which we show is deleted in humans. We have used several in vivo models to establish miR-152 as a specific marker of Paneth cells, which are highly understudied in terms of microRNAs.

Assessing Intestinal Health. In Vitro and Ex vivo Gut Barrier Models of Farm Animals: Benefits and Limitations

Animal performance is determined by the functionality and health of the gastrointestinal tract (GIT). Complex mechanisms and interactions are involved in the regulation of GIT functionality and health. The understanding of these relationships could be crucial for developing strategies to improve animal production yields. The concept of "gut health" is not well defined, but this concept has begun to play a very important role in the field of animal science. However, a clear definition of GIT health and the means by which to measure it are lacking. In vitro and ex vivo models can facilitate these studies, creating well-controlled and repeatable conditions to understand how to improve animal gut health. Over the years, several models have been developed and used to study the beneficial or pathogenic relationships between the GIT and the external environment. This review aims to describe the most commonly used animals' in vitro or ex vivo models and techniques that are useful for better understanding the intestinal health of production animals, elucidating their benefits and limitations.

HOPX+ injury-resistant intestinal stem cells drive epithelial recovery after severe intestinal ischemia

Intestinal ischemia is a life-threatening emergency with mortality rates of 50%-80% due to epithelial cell death and resultant barrier loss. Loss of the epithelial barrier occurs in conditions including intestinal volvulus and neonatal necrotizing enterocolitis. Survival depends on effective epithelial repair; crypt-based intestinal epithelial stem cells (ISCs) are the source of epithelial renewal in homeostasis and after injury. Two ISC populations have been described: 1) active ISC [aISC; highly proliferative; leucine-rich-repeat-containing G protein-coupled receptor 5 (LGR5⁺)-positive or sex-determining region Y-box 9 -antigen Ki67-positive (SOX9⁺Ki67⁺)] and 2) reserve ISC [rISC; less proliferative; homeodomain-only protein X positive (HOPX⁺)]. The contributions of these ISCs have been evaluated both in vivo and in vitro using a porcine model of mesenteric vascular occlusion to understand mechanisms that modulate ISC recovery responses following ischemic injury. In our previously published work, we observed that rISC conversion to an activated state was associated with decreased HOPX expression during in vitro recovery. In the present study, we wanted to evaluate the direct role of HOPX on cellular proliferation during recovery after injury. Our data demonstrated that during early in vivo recovery, injury-resistant HOPX⁺ cells maintain quiescence. Subsequent early regeneration within the intestinal crypt occurs around 2 days after injury, a period in which HOPX expression decreased. When HOPX was silenced in vitro, cellular proliferation of injured cells was promoted during recovery. This suggests that HOPX may serve a functional role in ISC-mediated regeneration after injury and could be a target to control ISC proliferation.NEW & NOTEWORTHY This paper supports that rISCs are resistant to ischemic injury and likely an important source of cellular renewal following near-complete epithelial loss. Furthermore, we have evidence that HOPX controls ISC activity state and may be a critical signaling pathway during ISC-mediated repair. Finally, we use multiple novel methods to evaluate ISCs in a translationally relevant large animal model of severe intestinal injury and provide evidence for the potential role of rISCs as therapeutic targets.

Establishment of porcine and monkey colonic organoids for drug toxicity study

Pig and monkey are widely used models for exploration of human diseases and evaluation of drug efficiency and toxicity, but high cost limits their uses. Organoids have been shown to be promising models for drug test as they reasonably preserve tissue structure and functions. However, colonic organoids of pig and monkey are not yet established. Here, we report a culture medium to support the growth of porcine and monkey colonic organoids. Wnt signaling and PGE2 are important for long-term expansion of the organoids, and their withdrawal results in lineage differentiation to mature cells. Furthermore, we observe that porcine colonic organoids are closer to human colonic organoids in terms of drug toxicity response. Successful establishment of porcine and monkey colonic organoids would facilitate the mechanistic investigation of the homeostatic regulation of the intestine of these animals and is useful for drug development and toxicity studies.

Intestinal organoid-based 2D monolayers mimic physiological and pathophysiological properties of the pig intestine

Gastrointestinal infectious diseases remain an important issue for human and animal health. Investigations on gastrointestinal infectious diseases are classically performed in laboratory animals leading to the problem that species-specific models are scarcely available, especially when it comes to farm animals. The 3R principles of Russel and Burch were achieved using intestinal organoids of porcine jejunum. These organoids seem to be a promising tool to generate species-specific in vitro models of intestinal epithelium. 3D Organoids were grown in an extracellular matrix and characterized by qPCR. Organoids were also seeded on permeable filter supports in order to generate 2D epithelial monolayers. The organoid-based 2D monolayers were characterized morphologically and were investigated regarding their potential to study physiological transport properties and pathophysiological processes. They showed a monolayer structure containing different cell types. Moreover, their functional activity was demonstrated by their increasing transepithelial electrical resistance over 18 days and by an active glucose transport and chloride secretion. Furthermore, the organoid-based 2D monolayers were also confronted with cholera toxin derived from Vibrio cholerae as a proof of concept. Incubation with cholera toxin led to an increase of short-circuit current indicating an enhanced epithelial chloride secretion, which is a typical characteristic of cholera infections. Taken this together, our model allows the investigation of physiological and pathophysiological mechanisms focusing on the small intestine of pigs. This is in line with the 3R principle and allows the reduction of classical animal experiments.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Minipig

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the minipig used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Porcine small intestinal organoids as a model to explore ETEC-host interactions in the gut

Small intestinal organoids, or enteroids, represent a valuable model to study host–pathogen interactions at the intestinal epithelial surface. Much research has been done on murine and human enteroids, however only a handful studies evaluated the development of enteroids in other species. Porcine enteroid cultures have been described, but little is known about their functional responses to specific pathogens or their associated virulence factors. Here, we report that porcine enteroids respond in a similar manner as in vivo gut tissues to enterotoxins derived from enterotoxigenic Escherichia coli, an enteric pathogen causing postweaning diarrhoea in piglets. Upon enterotoxin stimulation, these enteroids not only display a dysregulated electrolyte and water balance as shown by their swelling, but also secrete inflammation markers. Porcine enteroids grown as a 2D-monolayer supported the adhesion of an F4⁺ ETEC strain. Hence, these enteroids closely mimic in vivo intestinal epithelial responses to gut pathogens and are a promising model to study host–pathogen interactions in the pig gut. Insights obtained with this model might accelerate the design of veterinary therapeutics aimed at improving gut health.

Effect of dietary crude protein level on growth performance, blood characteristics, and indicators of intestinal health in weanling pigs

An experiment was conducted to test the hypothesis that reducing crude protein (CP) in starter diets for pigs reduces post-weaning diarrhea and improves intestinal health. In total, 180 weanling pigs were allotted to 3 diets containing 22, 19, or 16% CP. Fecal scores were visually assessed every other day. Blood samples were collected from 1 pig per pen on days 1, 6, 13, 20, and 27, and 1 pig per pen was euthanized on day 12. Results indicated that reducing dietary CP reduced (P < 0.01) overall average daily gain, gain to feed ratio, final body weight, and fecal scores of pigs. Pigs fed the 16% CP diet had reduced (P < 0.01) serum albumin compared with pigs fed other diets. Blood urea nitrogen, haptoglobin, interleukin-1β, and interleukin-6 concentrations in serum were greatest (P < 0.01) on day 13, whereas tumor necrosis factor-α and interleukin-10 concentrations were greatest (P < 0.01) on day 6. Villus height in the jejunum increased (P < 0.05) and crypt depth in the ileum was reduced (P < 0.01) if the 19% CP diet was fed to pigs compared with the 22% CP diet. A reduction (P < 0.05) in mRNA abundance of interferon-γ, chemokine ligand 10, occludin, trefoil factor-2, trefoil factor-3, and mucin 2 was observed when pigs were fed diets with 16% CP. In conclusion, reducing CP in diets for weanling pigs reduces fecal score and expression of genes associated with inflammation.

In vitro models replicating the human intestinal epithelium for absorption and metabolism studies: A systematic review

Absorption, distribution, metabolism and excretion (ADME) studies represent a fundamental step in the early stages of drug discovery. In particular, the absorption of orally administered drugs, which occurs at the intestinal level, has gained attention since poor oral bioavailability often led to failures for new drug approval. In this context, several in vitro preclinical models have been recently developed and optimized to better resemble human physiology in the lab and serve as an animal alternative to accomplish the 3Rs principles. However, numerous models are ineffective in recapitulating the key features of the human small intestine epithelium and lack of prediction potential for drug absorption and metabolism during the preclinical stage. In this review, we provide an overview of in vitro models aimed at mimicking the intestinal barrier for pharmaceutical screening. After briefly describing how the human small intestine works, we present i) conventional 2D synthetic and cell-based systems, ii) 3D models replicating the main features of the intestinal architecture, iii) micro-physiological systems (MPSs) reproducing the dynamic stimuli to which cells are exposed in the native microenvironment. In this review, we will highlight the benefits and drawbacks of the leading intestinal models used for drug absorption and metabolism studies.

Adverse Effects of Heat Stress on the Intestinal Integrity and Function of Pigs and the Mitigation Capacity of Dietary Antioxidants: A Review

Heat stress (HS) significantly affects the performance of pigs by its induced stressors such as inflammation, hypoxia and oxidative stress (OS), which mightily strain the intestinal integrity and function of pigs. As heat stress progresses, several mechanisms in the intestinal epithelium involved in the absorption of nutrients and its protective functions are altered. Changes in these mechanisms are mainly driven by cellular oxidative stress, which promotes disruption of intestinal homeostasis, leading to intestinal permeability, emphasizing intestinal histology and morphology with little possibility of recovering even after exposure to HS. Identification and understanding of these altered mechanisms are crucial for providing appropriate intervention strategies. Therefore, it is this papers' objective to review the important components for intestinal integrity that are negatively affected by HS and its induced stressors. With due consideration to the amelioration of such effects through nutritional intervention, this work will also look into the capability of dietary antioxidants in mitigating such adverse effects and maintaining the intestine's integrity and function upon the pigs' exposure to high environmental temperature.

Meta-analysis identifies the effect of dietary multi-enzyme supplementation on gut health of pigs

Gut health though is not well defined the role of gastrointestinal tract is vital if an animal must perform well. Apart from digestion, secretion, and absorption gut is harbored with consortium of microbiota which plays a key role in one's health. Enzymes, one of the alternatives for antibiotics with beneficial effects on digestion and consistency of food and its effect on gut health. The effect of enzyme supplementation on gut health is not well established and the objective of this meta-analysis is to investigate if the enzyme supplement has influence on gut. This meta-analysis includes 1221 experiments which has single enzyme studies and or studies with multiple enzyme complexes but not challenged. The ratio of Lactobacillus and E. coli is related to ADFI which showed comparatively lower negative correlation coefficient, with - 0.052 and - 0.035, respectively, whose I2 values are below 25%, showing that these studies show a significantly lower level of heterogeneity. Correlation between villus height, crypt depth, their ratio and fatty acid is also assessed, and it showed that when the animal is supplemented with two enzyme complexes resulted in positive gut health rather than the single or more than two enzymes.

Porcine colonoids and enteroids keep the memory of their origin during regeneration

The development of alternative in vitro culture methods has increased in the last decade as three-dimensional organoids of various tissues, including those of the small and large intestines. Due to their multicellular composition, organoids offer advantages over traditionally used immortalized or primary cell lines. However, organoids must be accurate models of their tissues of origin. This study compared gene expression profiles with respect to markers of specific cell types (stem cells, enterocytes, goblet, and enteroendocrine cells) and barrier maturation (tight junctions) of colonoid and enteroid cultures with their tissues of origin and colonoids with enteroids. Colonoids derived from three healthy pigs formed multilobed structures with a monolayer of cells similar to the crypt structures in colonic tissue. Colonoid and enteroid gene expression signatures were more similar to those found for the tissues of their origin than to each other. However, relative to their derived tissues, organoids had increased gene expression levels of stem cell markers Sox9 and Lgr5 encoding sex-determining region Y-box 9 and leucine-rich repeat-containing G protein-coupled rector 5, respectively. In contrast, expression levels of Occl and Zo1 encoding occludin and zonula occludens 1, respectively, were decreased. Expression levels of the cell lineage markers Atoh1, Cga, and Muc2 encoding atonal homolog 1, chromogranin A, and mucin 2, respectively, were decreased in colonoids, whereas Sglt1 and Apn encoding sodium-glucose transporter 1 and aminopeptidase A, respectively, were decreased in enteroids. These results indicate colonoid and enteroid cultures were predominantly comprised of undifferentiated cell types with decreased barrier maturation relative to their tissues of origin.

Intestinal Co-culture System to Study TGR5 Agonism and Gut Restriction

The activation of the Takeda G-protein receptor 5 (TGR5, also known as the G protein-coupled bile acid receptor 1, GPBAR1) in enteroendocrine L-cells results in secretion of the anti-diabetic hormone Glucagon-Like Peptide 1 (GLP-1) into systemic circulation. Consequently, recent research has focused on identification and development of TGR5 agonists as type 2 diabetes therapeutics. However, the clinical application of TGR5 agonists has been hampered by side effects of these compounds that primarily result from their absorption into circulation. Here we describe an in vitro screening protocol to evaluate the TGR5 agonism, GLP-1 secretion, and gut-restricted properties of small molecules. The protocol involves differentiating gut epithelial and endocrine cells together in transwells to assess both the pharmacodynamics of TGR5 agonists and the toxicity of compounds to the intestinal monolayer. As a proof of concept, we demonstrate the use of the protocol in evaluating properties of naturally occurring bile acid metabolites that are potent TGR5 agonists. This protocol is adapted from Chaudhari et al. (2021).

Inside-out chicken enteroids with leukocyte component as a model to study host-pathogen interactions

Mammalian three-dimensional (3D) enteroids mirror in vivo intestinal organisation and are powerful tools to investigate intestinal cell biology and host-pathogen interactions. We have developed complex multilobulated 3D chicken enteroids from intestinal embryonic villi and adult crypts. These avian enteroids develop optimally in suspension without the structural support required to produce mammalian enteroids, resulting in an inside-out enteroid conformation with media-facing apical brush borders. Histological and transcriptional analyses show these enteroids comprise of differentiated intestinal epithelial cells bound by cell-cell junctions, and notably, include intraepithelial leukocytes and an inner core of lamina propria leukocytes. The advantageous polarisation of these enteroids has enabled infection of the epithelial apical surface with Salmonella Typhimurium, influenza A virus and Eimeria tenella without the need for micro-injection. We have created a comprehensive model of the chicken intestine which has the potential to explore epithelial and leukocyte interactions and responses in host-pathogen, food science and pharmaceutical research.

Organoids: a promising new in vitro platform in livestock and veterinary research

Organoids are self-organizing, self-renewing three-dimensional cellular structures that resemble organs in structure and function. They can be derived from adult stem cells, embryonic stem cells, or induced pluripotent stem cells. They contain most of the relevant cell types with a topology and cell-to-cell interactions resembling that of the in vivo tissue. The widespread and increasing adoption of organoid-based technologies in human biomedical research is testament to their enormous potential in basic, translational- and applied-research. In a similar fashion there appear to be ample possibilities for research applications of organoids from livestock and companion animals. Furthermore, organoids as in vitro models offer a great possibility to reduce the use of experimental animals. Here, we provide an overview of studies on organoids in livestock and companion animal species, with focus on the methods developed for organoids from a variety of tissues/organs from various animal species and on the applications in veterinary research. Current limitations, and ongoing research to address these limitations, are discussed. Further, we elaborate on a number of fields of research in animal nutrition, host-microbe interactions, animal breeding and genomics, and animal biotechnology, in which organoids may have great potential as an in vitro research tool.

Alteration of Colonic Mucin Composition and Cytokine Expression in Acute Swine Dysentery

Swine dysentery (SD) is an enteric disease associated with strongly β-hemolytic Brachyspira spp. that cause mucohemorrhagic diarrhea primarily in grower-finisher pigs. We characterized alteration of colonic mucin composition and local cytokine expression in the colon of pigs with acute SD after B. hyodysenteriae (Bhyo) infection and fed either a diet containing 30% distillers dried grains with solubles (DDGS) or a control diet. Colonic tissue samples from 9 noninoculated pigs (Control, N = 4; DDGS, N = 5) and 10 inoculated pigs experiencing acute SD (Bhyo, N = 4; Bhyo-DDGS, N = 6) were evaluated. At the apex of the spiral colon, histochemical staining with high-iron diamine-Alcian blue revealed increased sialomucin (P = .008) and decreased sulfomucin (P = .027) in Bhyo pigs relative to controls, with a dietary effect for sulfomucin. Noninoculated pigs fed DDGS had greater expression of sulfomucin (P = .002) compared to pigs fed the control diet. Immunohistochemically, there was de novo expression of mucin 5AC (MUC5AC) in the Bhyo group while mucin 2 (MUC2) expression was not significantly different between groups. RNA in situ hybridization to detect the pro-inflammatory cytokine IL-1β often showed increased expression in the Bhyo group although without statistical significance, and this was not correlated with MUC5AC or MUC2 expression, suggesting IL-1β is not a major regulator of their secretion in acute SD. Expression of the anti-inflammatory cytokine TGF-β1 was significantly suppressed in the Bhyo group compared to controls (P = .005). This study reveals mucin and cytokine alterations in the colon of pigs with experimentally induced SD and related dietary effects of DDGS.

Models to evaluate the barrier properties of mucus during drug diffusion

Mucus is widely disseminated in the nasal cavity, oral cavity, respiratory tract, eyes, gastrointestinal tract, and reproductive tract to prevent the invasion of pathogenic bacteria and toxins. The mucus layer through its continuous secretion can prevent the passage of macromolecular substances such as pathogenic bacteria and toxins, thereby reducing the occurrence of inflammation. Without a doubt, mucus also hinders oral absorption. The physiological and biochemical properties of intestinal mucus and the different types of mucus barrier models need to be predominated. To find ways to increase the bioavailability of drugs in the future, this article summarizes mucus composition, barrier properties, mucus models, and mucoadhesive/mucopenetrating particles to highlight the information they can afford. Collectively, the review seeks to provide a state-of-the-art roadmap for researchers who must contend with this critical barrier to drug delivery.

Intestinal organoids in farm animals

In livestock species, the monolayer of epithelial cells covering the digestive mucosa plays an essential role for nutrition and gut barrier function. However, research on farm animal intestinal epithelium has been hampered by the lack of appropriate in vitro models. Over the past decade, methods to culture livestock intestinal organoids have been developed in pig, bovine, rabbit, horse, sheep and chicken. Gut organoids from farm animals are obtained by seeding tissue-derived intestinal epithelial stem cells in a 3-dimensional culture environment reproducing in vitro the stem cell niche. These organoids can be generated rapidly within days and are formed by a monolayer of polarized epithelial cells containing the diverse differentiated epithelial progeny, recapitulating the original structure and function of the native epithelium. The phenotype of intestinal organoids is stable in long-term culture and reflects characteristics of the digestive segment of origin. Farm animal intestinal organoids can be amplified in vitro, cryopreserved and used for multiple experiments, allowing an efficient reduction of the use of live animals for experimentation. Most of the studies using livestock intestinal organoids were used to investigate host-microbe interactions at the epithelial surface, mainly focused on enteric infections with viruses, bacteria or parasites. Numerous other applications of farm animal intestinal organoids include studies on nutrient absorption, genome editing and bioactive compounds screening relevant for agricultural, veterinary and biomedical sciences. Further improvements of the methods used to culture intestinal organoids from farm animals are required to replicate more closely the intestinal tissue complexity, including the presence of non-epithelial cell types and of the gut microbiota. Harmonization of the methods used to culture livestock intestinal organoids will also be required to increase the reproducibility of the results obtained in these models. In this review, we summarize the methods used to generate and cryopreserve intestinal organoids in farm animals, present their phenotypes and discuss current and future applications of this innovative culture system of the digestive epithelium.

Harmonization of Protocols for Multi-Species Organoid Platforms to Study the Intestinal Biology of Toxoplasma gondii and Other Protozoan Infections

The small intestinal epithelium is the primary route of infection for many protozoan parasites. Understanding the mechanisms of infection, however, has been hindered due to the lack of appropriate models that recapitulate the complexity of the intestinal epithelium. Here, we describe an in vitro platform using stem cell-derived intestinal organoids established for four species that are important hosts of Apicomplexa and other protozoa in a zoonotic context: human, mouse, pig and chicken. The focus was set to create organoid-derived monolayers (ODMs) using the transwell system amenable for infection studies, and we provide straightforward guidelines for their generation and differentiation from organ-derived intestinal crypts. To this end, we reduced medium variations to an absolute minimum, allowing generation and differentiation of three-dimensional organoids for all four species and the subsequent generation of ODMs. Quantitative RT-PCR, immunolabeling with antibodies against marker proteins as well as transepithelial-electrical resistance (TEER) measurements were used to characterize ODM's integrity and functional state. These experiments show an overall uniform generation of monolayers suitable for Toxoplasma gondii infection, although robustness in terms of generation of stable TEER levels and cell differentiation status varies from species to species. Murine duodenal ODMs were then infected with T. gondii and/or Giardia duodenalis, two parasites that temporarily co-inhabit the intestinal niche but have not been studied previously in cellular co-infection models. T. gondii alone did not alter TEER values, integrity and transcriptional abundance of tight junction components. In contrast, in G. duodenalis-infected ODMs all these parameters were altered and T. gondii had no apparent influence on the G. duodenalis-triggered phenotype. In conclusion, we provide robust protocols for the generation, differentiation and characterization of intestinal organoids and ODMs from four species. We show their applications for comparative studies on parasite-host interactions during the early phase of a T. gondii infection but also its use for co-infections with other relevant intestinal protozoans.

Escherichia coli Nissle 1917 administered as a dextranomar microsphere biofilm enhances immune responses against human rotavirus in a neonatal malnourished pig model colonized with human infant fecal microbiota

Human rotavirus (HRV) is a leading cause of diarrhea in children. It causes significant morbidity and mortality, especially in low- and middle-income countries (LMICs), where HRV vaccine efficacy is low. The probiotic Escherichia coli Nissle (EcN) 1917 has been widely used in the treatment of enteric diseases in humans. However, repeated doses of EcN are required to achieve maximum beneficial effects. Administration of EcN on a microsphere biofilm could increase probiotic stability and persistence, thus maximizing health benefits without repeated administrations. Our aim was to investigate immune enhancement by the probiotic EcN adhered to a dextranomar microsphere biofilm (EcN biofilm) in a neonatal, malnourished piglet model transplanted with human infant fecal microbiota (HIFM) and infected with rotavirus. To create malnourishment, pigs were fed a reduced amount of bovine milk. Decreased HRV fecal shedding and protection from diarrhea were evident in the EcN biofilm treated piglets compared with EcN suspension and control groups. Moreover, EcN biofilm treatment enhanced natural killer cell activity in blood mononuclear cells (MNCs). Increased frequencies of activated plasmacytoid dendritic cells (pDC) in systemic and intestinal tissues and activated conventional dendritic cells (cDC) in blood and duodenum were also observed in EcN biofilm as compared with EcN suspension treated pigs. Furthermore, EcN biofilm treated pigs had increased frequencies of systemic activated and resting/memory antibody forming B cells and IgA+ B cells in the systemic tissues. Similarly, the mean numbers of systemic and intestinal HRV-specific IgA antibody secreting cells (ASCs), as well as HRV-specific IgA antibody titers in serum and small intestinal contents, were increased in the EcN biofilm treated group. In summary EcN biofilm enhanced innate and B cell immune responses after HRV infection and ameliorated diarrhea following HRV challenge in a malnourished, HIFM pig model.