Regulation of intestinal stem cell fate specification

Genetic disruption of the circadian gene Bmal1 in the intestinal epithelium reduces colonic inflammation

Disruption of the circadian clock is associated with the development of inflammatory bowel disease (IBD), but the underlying mechanisms remain unclear. Here, we observe that mice in the early active phase (Zeitgeber time 12, ZT12) of the circadian clock are more tolerant to dextran sodium sulfate (DSS)-induced colitis, compared to those in the early resting phase (ZT0). The expression of the circadian gene Bmal1 peaks in the early resting phase and declines in the early active phase. Bmal1 knockout in the intestinal epithelium reduces DSS-induced inflammatory symptoms. Mechanistically, BMAL1 promotes apoptosis by binding to apoptosis-related genes, including Bax, p53, and Bak1, and promotes their expression. Intriguingly, we observe circadian apoptotic rhythms in the homeostatic intestinal epithelium, while Bmal1 deletion reduces cell apoptosis. Consistently, reducing Bmal1 expression by the REV-ERBα agonist SR9009 has the best therapeutic efficacy against DSS-induced colitis at ZT0. Collectively, our data demonstrate that the Bmal1-centered circadian clock is involved in intestinal injury repair.

Development of Sheep Intestinal Organoids for Studying Deoxynivalenol-Induced Toxicity

Sheep are an important livestock species whose gastrointestinal tract is essential for overall health. Feed contaminants such as bacterial toxins and mycotoxins severely damage the sheep intestine, yet the mechanisms remain mostly elusive partially due to the lack of physiologically relevant in vitro models. Here, we investigated molecular mechanisms underlying deoxynivalenol (DON)-induced toxicity by developing intestinal organoids from isolated intestinal crypts of Hu sheep. The organoids had a central lumen and monolayer epithelium, and could be continuously passaged, cryopreserved, and resuscitated. Histological and transcriptomic analysis showed that the intestinal organoids recapitulate the cell lineages and gene expression characteristics of the original intestinal tissues. Statistical analysis indicated that DON exposure significantly inhibited organoid formation efficiency, as well as the proliferation and activity of intestinal organoid cells. RNA-seq and Western blotting analysis further revealed that DON exposure induces intestinal toxicity by inhibiting the PI3K/AKT/GSK3β/β-catenin signaling pathway. Our study provides a novel example of organoid application in toxicity studies and reveals the signaling pathway involved in DON-induced toxicity in sheep, which is of great significance for improving mitigation strategies for DON.

Effects of Hermetia illucens larvae meal and astaxanthin on intestinal histology and expression of tight junction proteins in weaned piglets

The weaning phase in piglets causes significant physiological stress, disrupts intestinal integrity and reduces productivity, necessitating strategies to improve intestinal health and nutrient absorption. While current research highlights the role of diet in mitigating these adverse effects, identifying effective dietary supplements remains a challenge. This study evaluated the effects of Hermetia illucens (HI) larvae meal and astaxanthin (AST) on the intestinal histology of weaned piglets. In a controlled experiment, 48 weaned piglets were divided into six groups and received varying levels of HI larval meal (2.5% and 5%) and AST in their diets. The methodology involved comprehensive histological examinations of the small intestine, assessing absorption area, villi elongation, crypt depth, goblet cells, enterocytes and expression of ileal tight junction (TJ) proteins. The study found that HI larval meal significantly improved nutrient absorption in the jejunum and ileum (p < 0.001), thereby enhancing feed conversion. AST supplementation increased the number of enterocytes (p < 0.001). Both HI larval meal and AST positively affected intestinal morphology and function, increasing muscularis muscle mass and villi elongation (p < 0.001 and p < 0.05, respectively). The 2.5% HI meal improved the villi length to crypt depth ratio and slightly increased the goblet cell count (both p < 0.05). Ki-67 antibody analysis showed increased cell proliferation in the duodenal and jejunal crypts, particularly with the 2.5% HI meal (p < 0.001). Insect meal did not affect TJ protein expression, indicating that it had no effect on intestinal permeability. These findings suggest that HI larval meal and AST can enhance the intestinal wellness and productivity of weaned piglets.

Loss of Nrf2 aggravates ionizing radiation-induced intestinal injury by activating the cGAS/STING pathway via Pirin

Ionizing radiation (IR)-induced intestinal injury remains a major limiting factor in abdominal radiation therapy, and its pathogenesis remains unclear. In this study, mouse models of IR-induced intestinal injury were established, and the effect of IR on nuclear factor erythroid 2-related factor 2 (Nrf2) was determined. More severe IR-induced intestinal damage was observed in Nrf2 knockout (KO) mice than in wild-type mice. Then, the negative regulation of cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) signaling by Nrf2 was examined both in vivo and in vitro after IR. This was accompanied by alterations in the intestinal neutrophil and macrophage populations in mice. Subsequently, the effect of the cGAS/STING pathway on the intestinal toxicity of IR was also investigated. Moreover, the downregulation of cGAS/STING by Nrf2 via its target gene, Pirin, was confirmed using transfection assays. A rescue experiment with Pirin was also conducted using adeno-associated virus in Nrf2 KO mice. Finally, the protective effect of calcitriol against IR-induced intestinal injury, along with increased Nrf2 and Pirin levels and decreased cGAS, pSTING, and interferon-beta levels, were observed. Taken together, our results suggest that Nrf2 alleviates IR-induced intestinal injury through Pirin-mediated inhibition of the innate immunity-related cGAS/STING pathway.

Dietary regulation of intestinal stem cells in health and disease

Diet is a critical regulator for physiological metabolism and tissue homeostasis, with a close relation to health and disease. As an important organ for digestion and absorption, the intestine comes into direct contact with many dietary components. The rapid renewal of its mucosal epithelium depends on the continuous proliferation and differentiation of intestinal stem cells (ISCs). The function and metabolism of ISCs can be controlled by a variety of dietary patterns including calorie restriction, fasting, high-fat, ketogenic, and high-sugar diets, as well as different nutrients including vitamins, amino acids, dietary fibre, and probiotics. Therefore, dietary interventions targeting ISCs may make it possible to prevent and treat intestinal disorders such as colon cancer, inflammatory bowel disease, and radiation enteritis. This review summarised recent research on the role and mechanism of diet in regulating ISCs, and discussed the potential of dietary modulation for intestinal diseases.

Paneth cells protect intestinal stem cell niche to alleviate deoxynivalenol-induced intestinal injury

Deoxynivalenol (DON) is a common toxin in grains and feeds, and DON exposure triggers severe small intestinal injury and inflammation, which harms the health of humans and livestock. DON treatment leads to a decrease in Paneth cells, whereas the role of Paneth cells in DON-induced intestinal injury is poorly understood. We utilized dithizone (40 mg/kg) to keep murine Paneth cell number at a low level. The results showed that dithizone-mediated long-term disruption of Paneth cells aggravated intestinal injury, intestinal stem cell (ISC) loss, and microbiota disorder in DON (2 mg/kg)-treated mice. Unexpectedly, the number of goblet cells and proliferative cells was boosted in mice treated with dithizone and DON. After dithizone and DON treatments, the Firmicutes/Bacteroidetes (F/B) ratio was reduced, and the increased abundance of Dubosiella and the decreased abundance of Lactobacillus were observed in mice. The functional recovery of Paneth cells by lysozyme (200 U/day) supplementation improved intestinal injury and ISC loss in mice after DON challenge. In addition, lysozyme also promoted the growth and ISC activity of intestinal organoids. Taken together, these results demonstrate the protective role of Paneth cells in DON-induced intestinal injury. Our study raises a novel target, Paneth cell, for the treatment of DON exposure.

Segregation of the stemness program from the proliferation program in intestinal stem cells

Stem cells can undergo continuous self-renewal and meanwhile retain the stemness capability to differentiate to mature functional cells. However, it is unclear whether the proliferation property can be segregated from the stemness in stem cells. The intestinal epithelium undergoes fast renewal, and the Lgr5⁺ intestinal stem cells (ISCs) are essential to maintain homeostasis. Here, we report that methyltransferase-like 3 (Mettl3), a critical enzyme for N6-methyladenosine (m6A) methylation, is required for ISCs maintenance as its deletion results in fast loss of stemness markers but has no effect on cell proliferation. We further identify four m6A-modified transcriptional factors, whose ectopic expression can restore stemness gene expression in Mettl3^-/- organoids, while their silencing leads to stemness loss. In addition, transcriptomic profiling analysis discerns 23 genes that can be segregated from the genes responsible for cell proliferation. Together, these data reveal that m6A modification sustains ISC stemness, which can be uncoupled from cell proliferation.

Chronic GPER activation prompted the proliferation of ileal stem cell in ovariectomized mice depending on Paneth cell-derived Wnt3

Menopausal women often face long-term estrogen treatment. G protein-coupled estrogen receptor (GPER) expressed in intestinal crypt was activated by estrogen therapy, but it was unclear whether chronic GPER activation during menopause had an effect on intestinal stem cells (ISCs). We tested the effect of chronic GPER activation on ISCs of ovariectomized (OVX) mice by injection of the selective GPER agonist G-1 for 28 days, or G-1 stimulation of organoids derived from crypts of OVX mice. G-1 up-regulated crypt depth, the number of Ki67+, bromodeoxyuridine+ cells and Olfm4+ ISCs, and the expression of ISCs marker genes (Lgr5, Olfm4 and Axin2). G-1 administration promoted organoid growth, increased the number of EdU+ cells per organoid and protein expression of Cyclin D1 and cyclin B1 in organoids. After G-1 treatment in vivo or in vitro, Paneth cell-derived Wnt3, Wnt3 effector β-catenin and Wnt target genes c-Myc and Cyclin D1 increased in ileum or organoids. Once blocking the secretion of Wnt3 from Paneth cells, the effects of G-1 on organoids growth, ISCs marker genes and Wnt/β-catenin signaling were abolished. G-1 did not affect the number of Paneth cells in ex vivo organoids, while activated Mmp7/cryptdin program in Paneth cells, promoted their maturation, and increased the expression of lysozyme protein. G-1 pretreatment in OVX mice inhibited radiation-induced ISCs proliferation injury and enhanced the resistance of mice to intestinal injury. In conclusion, chronic GPER activation prompted the Wnt3 synthesis in Paneth cells, thus increased the proliferation of ISCs via activation of Wnt3/β-catenin signaling in OVX mice.

Selenomethionine Alleviates DON-Induced Oxidative Stress via Modulating Keap1/Nrf2 Signaling in the Small Intestinal Epithelium

The small intestinal epithelium is regulated in response to various beneficial or harmful environmental information. Deoxynivalenol (DON), a mycotoxin widely distributed in cereal-based feeds, induces oxidative stress damage in the intestine due to the mitochondrial stress. As a functional nutrient, selenomethionine (Se-Met) is involved in synthesizing several antioxidant enzymes, yet whether it can replenish the intestinal epithelium upon DON exposure remains unknown. Therefore, the in vivo model C57BL/6 mice and the in vitro model MODE-K cells were treated with l-Se-Met and DON alone or in combination to confirm the status of intestinal stem cell (ISC)-driven epithelial regeneration. The results showed that 0.1 mg/kg body weight (BW) Se-Met reinstated the growth performance and integrity of jejunal structure and barrier function in DON-challenged mice. Moreover, Lgr5⁺ ISCs and PCNA⁺ mitotic cells in crypts were prominently increased by Se-Met in the presence of DON, concomitant with a significant increase in absorptive cells, goblet cells, and Paneth cells. Simultaneously, crypt-derived jejunal organoids from the Se-Met + DON group exhibited more significant growth advantages ex vivo. Furthermore, Se-Met-stimulated Keap1/Nrf2-dependent antioxidant system (T-AOC and GSH-Px) to inhibit the accumulation of ROS and MDA in the jejunum and serum. Moreover, Se-Met failed to rescue the DON-triggered impairment of cell antioxidant function after Nrf2 perturbation using its specific inhibitor ML385 in MODE-K cells. In conclusion, Se-Met protects ISC-driven intestinal epithelial integrity against DON-induced oxidative stress damage by modulating Keap1/Nrf2 signaling.

Intestinal cellular heterogeneity and disease development revealed by single-cell technology

The intestinal epithelium is responsible for food digestion and nutrient absorption and plays a critical role in hormone secretion, microorganism defense, and immune response. These functions depend on the integral single-layered intestinal epithelium, which shows diversified cell constitution and rapid self-renewal and presents powerful regeneration plasticity after injury. Derailment of homeostasis of the intestine epithelium leads to the development of diseases, most commonly including enteritis and colorectal cancer. Therefore, it is important to understand the cellular characterization of the intestinal epithelium at the molecular level and the mechanisms underlying its homeostatic maintenance. Single-cell technologies allow us to gain molecular insights at the single-cell level. In this review, we summarize the single-cell RNA sequencing applications to understand intestinal cell characteristics, spatiotemporal evolution, and intestinal disease development.

Research Advances of Lactoferrin in Electrostatic Spinning, Nano Self-Assembly, and Immune and Gut Microbiota Regulation

Lactoferrin (LF) is a naturally present iron-binding globulin with the structural properties of an N-lobe strongly positively charged terminus and a cage-like structure of nano self-assembly encapsulation. These unique structural properties give it potential for development in the fields of electrostatic spinning, targeted delivery systems, and the gut-brain axis. This review will provide an overview of LF's unique structure, encapsulation, and targeted transport capabilities, as well as its applications in immunity and gut microbiota regulation. First, the microstructure of LF is summarized and compared with its homologous ferritin, revealing both structural and functional similarities and differences between them. Second, the electrostatic interactions of LF and its application in electrostatic spinning are summarized. Its positive charge properties can be applied to functional environmental protection packaging materials and to improving drug stability and antiviral effects, while electrostatic spinning can promote bone regeneration and anti-inflammatory effects. Then the nano self-assembly behavior of LF is exploited as a cage-like protein to encapsulate bioactive substances to construct functional targeted delivery systems for applications such as contrast agents, antibacterial dressings, anti-cancer therapy, and gene delivery. In addition, some covalent and noncovalent interactions of LF in the Maillard reaction and protein interactions and other topics are briefly discussed. Finally, LF may affect immunological function via controlling the gut microbiota. In conclusion, this paper reviews the research advances of LF in electrostatic spinning, nano self-assembly, and immune and gut microbiota regulation, aiming to provide a reference for its application in the food and pharmaceutical fields.

Emerging Prospects for the Study of Colorectal Cancer Stem Cells using Patient-Derived Organoids

Abstract:

Human colorectal cancer (CRC) patient-derived organoids (PDOs) are a powerful ex vivo platform to directly assess the impact of molecular alterations and therapies on tumor cell proliferation, differentiation, response to chemotherapy, tumor-microenvironment interactions, and other facets of CRC biology. Next-generation sequencing studies have demonstrated that CRC is a highly heterogeneous disease with multiple distinct subtypes. PDOs are a promising new tool to study CRC due to their ability to accurately recapitulate their source tumor and thus reproduce this heterogeneity. This review summarizes the state-of-the-art for CRC PDOs in the study of cancer stem cells (CSCs) and the cancer stem cell niche. Areas of focus include the relevance of PDOs to understanding CSC-related paracrine signaling, identifying interactions between CSCs and the tumor microenvironment, and modeling CSC-driven resistance to chemotherapies and targeted therapies. Finally, we summarize current findings regarding the identification and verification of CSC targets using PDOs and their potential use in personalized medicine.

Recent advances in tissue stem cells

Stem cells are undifferentiated cells capable of self-renewal and differentiation, giving rise to specialized functional cells. Stem cells are of pivotal importance for organ and tissue development, homeostasis, and injury and disease repair. Tissue-specific stem cells are a rare population residing in specific tissues and present powerful potential for regeneration when required. They are usually named based on the resident tissue, such as hematopoietic stem cells and germline stem cells. This review discusses the recent advances in stem cells of various tissues, including neural stem cells, muscle stem cells, liver progenitors, pancreatic islet stem/progenitor cells, intestinal stem cells, and prostate stem cells, and the future perspectives for tissue stem cell research.

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.

Stem/progenitor cells in fetuses and newborns: overview of immunohistochemical markers

Microanatomy of the vast majority of human organs at birth is characterized by marked differences as compared to adult organs, regarding their architecture and the cell types detectable at histology. In preterm neonates, these differences are even more evident, due to the lower level of organ maturation and to ongoing cell differentiation. One of the most remarkable finding in preterm tissues is the presence of huge amounts of stem/progenitor cells in multiple organs, including kidney, brain, heart, adrenals, and lungs. In other organs, such as liver, the completely different burden of cell types in preterm infants is mainly related to the different function of the liver during gestation, mainly focused on hematopoiesis, a function that is taken by bone marrow after birth. Our preliminary studies showed that the antigens expressed by stem/progenitors differ significantly from one organ to the next. Moreover, within each developing human tissue, reactivity for different stem cell markers also changes during gestation, according with the multiple differentiation steps encountered by each progenitor during development. A better knowledge of stem/progenitor cells of preterms will allow neonatologists to boost preterm organ maturation, favoring the differentiation of the multiple cells types that characterize each organ in at term neonates.

Intestinal epithelial plasticity and regeneration via cell dedifferentiation

The intestinal epithelium possesses a great capacity of self-renewal under normal homeostatic conditions and of regeneration upon damages. The renewal and regenerative processes are driven by intestinal stem cells (ISCs), which reside at the base of crypts and are marked by Lgr5. As Lgr5⁺ ISCs undergo fast cycling and are vulnerable to damages, there must be other types of cells that can replenish the lost Lgr5⁺ ISCs and then regenerate the damage epithelium. In addition to Lgr5⁺ ISCs, quiescent ISCs at the + 4 position in the crypt have been proposed to convert to Lgr5⁺ ISCs during regeneration. However, this “reserve stem cell” model still remains controversial. Different from the traditional view of a hierarchical organization of the intestinal epithelium, recent works support the dynamic “dedifferentiation” model, in which various cell types within the epithelium can de-differentiate to revert to the stem cell state and then regenerate the epithelium upon tissue injury. Here, we provide an overview of the cell identity and features of two distinct models and discuss the possible mechanisms underlying the intestinal epithelial plasticity.

Generation of 3D human gastrointestinal organoids: principle and applications

The stomach and intestine are important organs for food digestion, nutrient absorption, immune protection and hormone production. Gastrointestinal diseases such as cancer and ulcer are big threats to human health. Appropriate disease models are in sore need for mechanistic understanding and drug discovery. Organoids are three-dimensional in vitro cultured structures derived from tissues and pluripotent stem cells with multiple types of cells and mimicking in vivo tissues in major aspects. They have a great potential in regenerative medicine and personalized medicine. Here, we review the major signaling pathways regulating gastrointestinal epithelial homeostasis, summarize different methods to generate human gastrointestinal organoids and highlight their applications in biological research and medical practice.

Nutritional Regulation of Gut Barrier Integrity in Weaning Piglets

Simple Summary

Weaning is a very stressful period in the piglet’s life in intensive farming: it is a sudden process occurring between three to four weeks of age, when the gastrointestinal tract (GIT) is still immature. The GIT is formed by the epithelial, immune and enteric nervous system which controls epithelial barrier integrity as well as gut functions including the transport of luminal nutrients, water and electrolytes. Early weaning is characterized by a breakdown of these gut functions, an increase in intestinal permeability and the appearance of gastrointestinal functional disorders, which can have long-lasting consequences in the pig’s life. Weaning, therefore, requires the correct level of nutrients, high quality ingredients, and management, which are directed primarily at encouraging rapid feed intake whilst reducing mortality and morbidity. This review describes the organization of the GIT and highlights the interactions between feed components and the morphology and physiology of the epithelial barrier. Novel dietary strategies focused on improving gut health are also discussed, considering the impacts of selected feed ingredients or additives on the GIT such as functional amino acids, phytochemicals and organic acids.

Abstract

Weaning is very stressful for piglets and leads to alterations in the intestinal barrier, a reduction in nutrient absorption and a higher susceptibility to intestinal diseases with heavy economic losses. This review describes the structures involved in the intestinal barrier: the epithelial barrier, immune barrier and the enteric nervous system. Here, new insights into the interactions between feed components and the physiology and morphology of the epithelial barrier are highlighted. Dietary strategies focused on improving gut health are also described including amino acids, phytochemicals and organic acids.

The Impact of Lactoferrin on the Growth of Intestinal Inhabitant Bacteria

Lactoferrin (Lf) is an iron-binding milk glycoprotein that promotes the growth of selected probiotic strains. The effect of Lf on the growth and diversification of intestinal microbiota may have an impact on several issues, including (i) strengthening the permeability of the epithelial cell monolayer, (ii) favoring the microbial antagonism that discourages the colonization and proliferation of enteric pathogens, (iii) enhancing the growth and maturation of cell-monolayer components and gut nerve fibers, and (iv) providing signals to balance the anti- and pro-inflammatory responses resulting in gut homeostasis. Given the beneficial role of probiotics, this contribution aims to review the current properties of bovine and human Lf and their derivatives in in vitro probiotic growth and Lf interplay with microbiota described in the piglet model. By using Lf as a component in pharmacological products, we may enable novel strategies that promote probiotic growth while conferring antimicrobial activity against multidrug-resistant microorganisms that cause life-threatening diseases, especially in neonates.

Identification of microRNA transcriptome reveals that miR-100 is involved in the renewal of porcine intestinal epithelial cells

MicroRNAs play important roles in various cellular processes, including differentiation, proliferation and survival. Using a pig model, this study sought to identify the miRNAs responsible for crypt-villus axis renewal of the small intestinal epithelium. Compared to the villus upper cells, there were 15 up-regulated and 41 down-regulated miRNAs in the crypt cells of the jejunum. Notably, we found that miR-100 was expressed more in the villus upper cells than in the crypt cells, suggesting an effect on intestinal epithelium differentiation. Overexpression of miR-100 increased the activity of alkaline phosphatase, confirming that miR-100 promoted IPEC-J2 cell differentiation. MiR-100 can inhibit cell proliferation as evidenced by CCK-8 and cell cycle assay results. We also showed that miR-100 significantly inhibited the migration of IPEC-J2 cells and promoted cell apoptosis through caspase-3-dependent cleavage of Bcl-2. Furthermore, FGFR3 was identified as a potential target of miR-100 by bioinformatics analysis. We confirmed that overexpression of miR-100 suppressed FGFR3 expression in IPEC-J2 cells by directly targeting the FGFR3 3'-UTR. This is the first report of miRNAs acting on the renewal of the intestinal crypt-villus axis. Our results also showed that miR-100 promotes the differentiation and apoptosis, and inhibits the proliferation and migration of enterocytes of pigs.

Nutritional Intervention for the Intestinal Development and Health of Weaned Pigs

Weaning imposes simultaneous stress, resulting in reduced feed intake, and growth rate, and increased morbidity and mortality of weaned pigs. Weaning impairs the intestinal integrity, disturbs digestive and absorptive capacity, and increases the intestinal oxidative stress, and susceptibility of diseases in piglets. The improvement of intestinal development and health is critically important for enhancing nutrient digestibility capacity and disease resistance of weaned pigs, therefore, increasing their survival rate at this most vulnerable stage, and overall productive performance during later stages. A healthy gut may include but not limited several important features: a healthy proliferation of intestinal epithelial cells, an integrated gut barrier function, a preferable or balanced gut microbiota, and a well-developed intestinal mucosa immunity. Burgeoning evidence suggested nutritional intervention are one of promising measures to enhance intestinal health of weaned pigs, although the exact protective mechanisms may vary and are still not completely understood. Previous research indicated that functional amino acids, such as arginine, cysteine, glutamine, or glutamate, may enhance intestinal mucosa immunity (i.e., increased sIgA secretion), reduce oxidative damage, stimulate proliferation of enterocytes, and enhance gut barrier function (i.e., enhanced expression of tight junction protein) of weaned pigs. A number of feed additives are marketed to assist in boosting intestinal immunity and regulating gut microbiota, therefore, reducing the negative impacts of weaning, and other environmental challenges on piglets. The promising results have been demonstrated in antimicrobial peptides, clays, direct-fed microbials, micro-minerals, milk components, oligosaccharides, organic acids, phytochemicals, and many other feed additives. This review summarizes our current understanding of nutritional intervention on intestinal health and development of weaned pigs and the importance of mechanistic studies focusing on this research area.

2D- and 3D-Based Intestinal Stem Cell Cultures for Personalized Medicine

Colorectal cancer (CRC) is one of the most common cancers that have high occurrence and death in both males and females. As various factors have been found to contribute to CRC development, personalized therapies are critical for efficient treatment. To achieve this purpose, the establishment of patient-derived tumor models is critical for diagnosis and drug test. The establishment of three-dimensional (3D) organoid cultures and two-dimensional (2D) monolayer cultures of patient-derived epithelial tissues is a breakthrough for expanding living materials for later use. This review provides an overview of the different types of 2D- and 3D-based intestinal stem cell cultures, their potential benefits, and the drawbacks in personalized medicine in treatment of the intestinal disorders.

Tankyrases maintain homeostasis of intestinal epithelium by preventing cell death

Lgr5⁺ intestinal stem cells are crucial for fast homeostatic renewal of intestinal epithelium and Wnt/β-catenin signaling plays an essential role in this process by sustaining stem cell self-renewal. The poly(ADP-ribose) polymerases tankyrases (TNKSs) mediate protein poly-ADP-ribosylation and are involved in multiple cellular processes such as Wnt signaling regulation, mitotic progression and telomere maintenance. However, little is known about the physiological function of TNKSs in epithelium homeostasis regulation. Here, using Villin-creERT2;Tnks1^-/-;Tnks2^fl/fl (DKO) mice, we observed that loss of TNKSs causes a rapid decrease of Lgr5⁺ intestinal stem cells and magnified apoptosis in small intestinal crypts, leading to intestine degeneration and increased mouse mortality. Consistently, deletion of Tnks or blockage of TNKS activity with the inhibitor XAV939 significantly inhibits the growth of intestinal organoids. We further showed that the Wnt signaling agonist CHIR99021 sustains the growth of DKO organoids, and XAV939 does not cause growth retardation of Apc^-/- organoids. Consistent with the promoting function of TNKSs in Wnt signaling, Wnt/β-catenin signaling is significantly decreased with stabilized Axin in DKO crypts. Together, our findings unravel the essential role of TNKSs-mediated protein parsylation in small intestinal homeostasis by modulating Wnt/β-catenin signaling.

Although tankyrases have been indicated to play important roles in telomere maintenance, mitosis and Wnt signaling regulation, little is known about their physiological function in intestinal epithelium. Using Villin-creERT2;Tnks1^-/-;Tnks2^fl/fl mice, which harbored conventional Tnks1 deletion and inducible intestinal epithelium-specific Tnks2 knockout, we show that tankyrases regulate adult intestinal Lgr5+ stem cells and epithelium homeostasis by preventing cell death and promoting cell proliferation.

BMP signaling in homeostasis, transformation and inflammatory response of intestinal epithelium

Intestine is the organ for food digestion, nutrient absorption and pathogen defense, in which processes intestinal epithelium plays a central role. Intestinal epithelium undergoes fast turnover, and its homeostasis is regulated by multiple signaling pathways, including Wnt, Notch, Hippo and BMP pathways. BMP signaling has been shown to negatively regulate self-renewal of Lgr5⁺ intestinal stem cells, constrains the expansion of intestinal epithelium, therefore attenuating colorectal cancer formation. BMPs and their receptors are expressed in both epithelial and mesenchymal cells, suggesting a two-way interaction between the mesenchyme and epithelium. In this review, we summarize the current understanding of the function of BMP signaling in homeostasis, cancerous transformation and inflammatory response of intestinal epithelium.

Patterning the gastrointestinal epithelium to confer regional-specific functions

The gastrointestinal (GI) tract, in simplest terms, can be described as an epithelial-lined muscular tube extending along the cephalocaudal axis from the oral cavity to the anus. Although the general architecture of the GI tract organs is conserved from end to end, the presence of different epithelial tissue structures and unique epithelial cell types within each organ enables each to perform the distinct digestive functions required for efficient nutrient assimilation. Spatiotemporal regulation of signaling pathways and downstream transcription factors controls GI epithelial morphogenesis during development to confer essential regional-specific epithelial structures and functions. Here, we discuss the fundamental functions of each GI tract organ and summarize the diversity of epithelial structures present along the cephalocaudal axis of the GI tract. Next, we discuss findings, primarily from genetic mouse models, that have defined the roles of key transcription factors during epithelial morphogenesis, including p63, SOX2, SOX15, GATA4, GATA6, HNF4A, and HNF4G. Additionally, we examine how the Hedgehog, WNT, and BMP signaling pathways contribute to defining unique epithelial features along the cephalocaudal axis of the GI tract. Lastly, we examine the molecular mechanisms controlling regionalized cytodifferentiation of organ-specific epithelial cell types within the GI tract, concentrating on the stomach and small intestine. The delineation of GI epithelial patterning mechanisms in mice has provided fundamental knowledge to guide the development and refinement of three-dimensional GI organotypic culture models such as those derived from directed differentiation of human pluripotent stem cells and those derived directly from human tissue samples. Continued examination of these pathways will undoubtedly provide vital insights into the mechanisms of GI development and disease and may afford new avenues for innovative tissue engineering and personalized medicine approaches to treating GI diseases.

A Survey of Strategies to Modulate the Bone Morphogenetic Protein Signaling Pathway: Current and Future Perspectives

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the TGF-β family of ligands and are unequivocally involved in regulating stem cell behavior. Appropriate regulation of canonical BMP signaling is critical for the development and homeostasis of numerous human organ systems, as aberrations in the BMP pathway or its regulation are increasingly associated with diverse human pathologies. In this review, we provide a wide-perspective on strategies that increase or decrease BMP signaling. We briefly outline the current FDA-approved approaches, highlight emerging next-generation technologies, and postulate prospective avenues for future investigation. We also detail how activating other pathways may indirectly modulate BMP signaling, with a particular emphasis on the relationship between the BMP and Activin/TGF-β pathways.