Paneth Cells Respond to Inflammation and Contribute to Tissue Regeneration by Acquiring Stem-like Features through SCF/c-Kit Signaling

Intestinal secretory differentiation reflects niche-driven phenotypic and epigenetic plasticity of a common signal-responsive terminal cell

Enterocytes and four classic secretory cell types derive from intestinal epithelial stem cells. Based on morphology, location, and canonical markers, goblet and Paneth cells are considered distinct secretory types. Here, we report high overlap in their transcripts and sites of accessible chromatin, in marked contrast to those of their enteroendocrine or tuft cell siblings. Mouse and human goblet and Paneth cells express extraordinary fractions of few antimicrobial genes, which reflect specific responses to local niches. Wnt signaling retains some ATOH1+ secretory cells in crypt bottoms, where the absence of BMP signaling potently induces Paneth features. Cells that migrate away from crypt bottoms encounter BMPs and thereby acquire goblet properties. These phenotypes and underlying accessible cis-elements interconvert in post-mitotic cells. Thus, goblet and Paneth properties represent alternative phenotypic manifestations of a common signal-responsive terminal cell type. These findings reveal exquisite niche-dependent cell plasticity and cis-regulatory dynamics in likely response to antimicrobial needs.

A Lgr5-independent developmental lineage is involved in mouse intestinal regeneration

Collagenase and dispase treatment of intestinal tissue from adult mice generates cells growing in matrigel as stably replatable cystic spheroids, in addition to differentiated organoids. Contrary to classical EDTA-derived organoids, these spheroids display poor intestinal differentiation and grow independently of Rspondin, noggin and EGF. Their transcriptome strikingly resembles that of fetal intestinal spheroids, with downregulation of crypt base columnar cell (CBC) markers (Lgr5, Ascl2, Smoc2 and Olfm4). In addition, they display upregulation of inflammatory and mesenchymal genetic programs, together with robust expression of YAP target genes. Lineage tracing, cell-sorting and single cell RNA sequencing experiments demonstrate that adult spheroid-generating cells belong to a hitherto undescribed developmental lineage, independent of Lgr5-positive CBCs, and are involved in regeneration of the epithelium following CBC ablation.

c-Kit+ cells that intercalate with crypt Lgr5+ cells are distinctively multipotent in colonic epithelium renewal and repair

The colonic crypts are principally composed by Lgr5+ stem cells and deep crypt secretory (DCS) cells. c-Kit-expressing cells mark DCS cells and supply Wnt3, EGF, and Notch signals to support their neighboring crypt bottom-intermingled Lgr5+ cells. However, the role of c-Kit+ cells beyond supporting Lgr5+ cells in colonic epithelium remains unexplored. Here, we identify that c-Kit+ cells are a heterogeneous entity and possess stemness potency to differentiate into the entire spectrum of epithelial cells and renew the homeostatic colon. Intriguingly, c-Kit+ cells play a pivotal role in epithelium repair in mouse models of colitis when contemporary Lgr5+ cells are insufficient or absent. Depletion of c-Kit+ cells or inhibition of SCF/c-Kit signaling worsens, while supplementation of SCF alleviates colonic epithelium injury during colitis. Our findings unravel the fate and function of c-Kit+ cells in homeostatic colon and recovery during colonic epithelium injury which has translational implications for human inflammatory bowel diseases.

Dietary Iron Alleviates Dextran Sodium Sulfate-Induced Intestinal Injury by Regulating Regeneration of Intestinal Stem Cells in Weaned Mice

Iron deficiency is the most common comorbidity of inflammatory bowel disease (IBD), but the effect of iron supplementation on the repair processes of intestinal injury in weaned mice is unknown. This study aimed to evaluate the potential mechanism of dietary iron on intestinal injury and intestinal regeneration in the dextran sodium sulfate (DSS)-induced colitis of the weaned mouse model. The mice were fed either a control diet containing (45.00 mg/kg Fe) or iron supplemental (448.30 mg/kg Fe) diet for 14 days, followed by a 7-day oral administration of 2.5% DSS to all mice. The result showed that at day 0 of the recovery period (0 DRP), the impact of iron on the gut index and intestinal morphology was found to be more significant in weaned mice compared to adult mice. At 3 DRP, the iron diet alleviated inflammation-induced weight loss, shortening of colon length, thickening of the muscle layer, and disruption of gut morphology. At 0, 3, and 7 DRP, we found that an iron diet increased intestinal stem cell (ISC) viability and protected epithelial integrity. Furthermore, FeSO4 significantly enhanced organoid viability and increased mRNA expression of differentiation, ISC, and retinol metabolism-related marker genes in the organoids compared with the control group. Overall, this study demonstrates that the iron diet accelerates intestinal regeneration after intestinal injury in weaned mice by activating the retinol metabolic pathway to regulate the proliferation and differentiation of ISCs.

Wnt/β-catenin maintains epithelial IL-33 in the colonic stem and progenitor cell niche and drives its induction in colitis

Interleukin (IL)-33 is a key responder to intestinal injury and inflammation. In the colon, it is expressed by several cell populations, with the specific cellular source likely determining its role. The colonic epithelium expresses IL-33; however, the factors controlling its production and the specific epithelial lineage(s) expressing IL-33 are poorly understood. We recently reported that colonic epithelial IL-33 is induced by inhibition of glycogen synthase kinase-3β (GSK3β), but the signaling pathway mediating this induction is unknown. Here we tested the role of Wnt/β-catenin signaling in regulating colonic epithelial IL-33 at homeostasis and in injury-induced colitis. Transcriptomic analysis shows that epithelial IL-33 localizes to stem and progenitor cells. Ligand activation of Wnt/β-catenin signaling induced IL-33 in colonic organoid and cell cultures. Furthermore, small-molecule disruption of β-catenin interaction with cyclic AMP response element binding protein (CBP) prevented epithelial IL-33 induction. Antagonism of CBP/β-catenin signaling also prevented rapid epithelial IL-33 induction in dextran sodium sulfate (DSS)-mediated colitis, and was associated with maintenance of crypt-expressed host defense peptides. Together, these findings show β-catenin-driven production of epithelial IL-33 is an early response to colonic injury that shapes the crypt base defense response and suggest an immunoregulatory role for the stem cell niche in tissue injury.

Prostaglandin E2 and Akt Promote Stemness in Apc Mutant Dclk1+ Cells to Give Rise to Colitis-associated Cancer

BACKGROUND & AIMS

Loss of the tumor suppressor gene Apc in Lgr5+ intestinal stem cells results in aberrant Wnt signaling and colonic tumorigenesis. In the setting of injury, however, we and others have also shown that non-stem cells can give rise to colonic tumors. The mechanism by which inflammation leads to cellular plasticity and cancer, however, remains largely unknown.

METHODS

RNA expression analysis of Wnt, COX, and Akt signaling was assessed in patients with quiescent or active ulcerative colitis (UC) and patients with UC-associated neoplasia using available datasets. The role of COX signaling in colonic tumorigenesis was examined using epithelial and doublecortin-like kinase 1 (Dclk1)+ cell-specific conditional COX-1 knockout mice and pharmacologic treatment with different nonsteroidal anti-inflammatory drugs.

RESULTS

In this study, we show that prostaglandins and phospho-Akt are key inflammatory mediators that promote stemness in Apc mutant Dclk1+ cells that give rise to colorectal cancer. Moreover, prostaglandin E2 (PGE2) and Akt are increased in colitis in both mice and humans, leading to inflammation-associated dysplasia upon activation of Wnt signaling. Importantly, inhibition of epithelial-derived COX-1 by aspirin or conditional knockout in Dclk1+ cells reduced PGE2 levels and prevented the development of inflammation-associated colorectal cancer.

CONCLUSIONS

Our data shows that epithelial and Dclk1+ cell-derived COX-1 plays an important role in inflammation-associated tumorigenesis. Importantly, low-dose aspirin was effective in chemo-prevention through inhibition of COX-1 that reduced colitis-associated cancer.

Dietary and metabolic effects on intestinal stem cells in health and disease

Diet and nutritional metabolites exhibit wide-ranging effects on health and disease partly by altering tissue composition and function. With rapidly rising rates of obesity, there is particular interest in how obesogenic diets influence tissue homeostasis and risk of tumorigenesis; epidemiologically, these diets have a positive correlation with various cancers, including colorectal cancer. The gastrointestinal tract is a highly specialized, continuously renewing tissue with a fundamental role in nutrient uptake and is, in turn, influenced by diet composition and host metabolic state. Intestinal stem cells are found at the base of the intestinal crypt and can generate all mature lineages that comprise the intestinal epithelium and are uniquely influenced by host diet, metabolic by-products and energy dynamics. Similarly, tumour growth and metabolism can also be shaped by nutrient availability and host diet. In this Review, we discuss how different diets and metabolic changes influence intestinal stem cells in homeostatic and pathological conditions, as well as tumorigenesis. We also discuss how dietary changes and composition affect the intestinal epithelium and its surrounding microenvironment.

Type III interferons induce pyroptosis in gut epithelial cells and impair mucosal repair

Tissue damage and repair are hallmarks of inflammation. Despite a wealth of information on the mechanisms that govern tissue damage, mechanistic insight into how inflammation affects repair is lacking. Here, we investigated how interferons influence tissue repair after damage to the intestinal mucosa. We found that type III, not type I or type II, interferons delay epithelial cell regeneration by inducing the upregulation of Z-DNA-binding protein 1 (ZBP1). Z-nucleic acids formed following intestinal damage are sensed by ZBP1, leading to caspase-8 activation and the cleavage of gasdermin C (GSDMC). Cleaved GSDMC drives epithelial cell death by pyroptosis and delays repair of the large or small intestine after colitis or irradiation, respectively. The type III interferon/ZBP1/caspase-8/GSDMC axis is also active in patients with inflammatory bowel disease (IBD). Our findings highlight the capacity of type III interferons to delay gut repair, which has implications for IBD patients or individuals exposed to radiation therapies.

Alterations in Ileal Secretory Cells of The DSS-Induced Colitis Model Mice

Inflammatory bowel disease is triggered by abnormalities in epithelial barrier function and immunological responses, although its pathogenesis is poorly understood. The dextran sodium sulphate (DSS)-induced colitis model has been used to examine inflammation in the colon. Damage to mucosa primality occurs in the large intestine and scarcely in the small intestine. To evaluate the effect on the ileum, we histologically analyzed the inflammatory and recovery phases in DSS model mice, and 40 kDa FITC-dextran was used to investigate barrier function. In the inflammatory phase, histological damage was insignificant. However, expanded crypts, hypertrophic goblet and Paneth cells, increased mucus production and secretion were observed. The cellular morphology was restored to that of the control in the recovery phase. According to in situ hybridization and lectin histochemistry, the expression of intestinal stem cell markers, secretory cell differentiation factors, and glycosylation of secretory granules in Paneth cells differed in the DSS model. DSS-treatment did not influence the barrier function in the ileum, and FITC-dextran did not diffuse via the paracellular pathway into the mucosa. However, cells incorporating FITC appeared even under normal conditions. The number of FITC-positive Paneth cells was lower in the DSS group than the control group. Our results showed morphological and functional alterations in ileal epithelial cells, especially secretory cells, in the DSS colitis model.

Paneth Cells: Dispensable yet Irreplaceable for the Intestinal Stem Cell Niche

Intestinal stem cells replenish the epithelium throughout life by continuously generating intestinal epithelial cell types, including absorptive enterocytes, and secretory goblet, endocrine, and Paneth cells. This process is orchestrated by a symphony of niche factors required to maintain intestinal stem cells and to direct their proliferation and differentiation. Among the various mature intestinal epithelial cell types, Paneth cells are unique in their location in the stem cell zone, directly adjacent to intestinal stem cells. Although Paneth cells were first described as an epithelial cell component of the innate immune system due to their expression of anti-microbial peptides, they have been proposed to be niche cells due to their close proximity to intestinal stem cells and expression of niche factors. However, function as a niche cell has been debated since mice lacking Paneth cells retain functional stem cells that continue to replenish the intestinal epithelium. In this review, we summarize the intestinal stem cell niche, including the Notch, Wnt, growth factor, mechanical, and metabolic niche, and discuss how Paneth cells might contribute to these various components. We also present a nuanced view of the Paneth cell as a niche cell. Although not required, Paneth cells enhance stem cell function, particularly during intestinal development and regeneration. Furthermore, we suggest that Paneth cell loss induces intestinal stem cell remodeling to adjust their niche demands.

Crosstalk Within the Intestinal Epithelium: Aspects of Intestinal Absorption, Homeostasis, and Immunity

Gut health is crucial in many ways, such as in improving human health in general and enhancing production in agricultural animals. To maximize the effect of a healthy gastrointestinal tract (GIT), an understanding of the regulation of intestinal functions is needed. Proper intestinal functions depend on the activity, composition, and behavior of intestinal epithelial cells (IECs). There are various types of IECs, including enterocytes, Paneth cells, enteroendocrine cells (EECs), goblet cells, tuft cells, M cells, and intestinal epithelial stem cells (IESCs), each with unique 3D structures and IEC distributions. Although the communication between IECs and other cell types, such as immune cells and neurons, has been intensively reviewed, communication between different IECs has rarely been addressed. The present paper overviews the networks among IECs that influence intestinal functions. Intestinal absorption is regulated by incretins derived from EECs that induce nutrient transporter activity in enterocytes. EECs, Paneth cells, tuft cells, and enterocytes release signals to activate Notch signaling, which modulates IESC activity and intestinal homeostasis, including proliferation and differentiation. Intestinal immunity can be altered via EECs, goblet cells, tuft cells, and cytokines derived from IECs. Finally, tools for investigating IEC communication have been discussed, including the novel 3D intestinal cell model utilizing enteroids that can be considered a powerful tool for IEC communication research. Overall, the importance of IEC communication, especially EECs and Paneth cells, which cover most intestinal functional regulating pathways, are overviewed in this paper. Such a compilation will be helpful in developing strategies for maintaining gut health.

Regulation of the Intestinal Stem Cell Pool and Proliferation in Drosophila

Understanding the regulation of somatic stem cells, both during homeostasis and in response to environmental challenges like injury, infection, chemical exposure, and nutritional changes, is critical because their dysregulation can result in tissue degeneration or tumorigenesis. The use of models such as the Drosophila and mammalian adult intestines offers valuable insights into tissue homeostasis and regeneration, advancing our knowledge of stem cell biology and cancer development. This review highlights significant findings from recent studies, unveiling the molecular mechanisms that govern self-renewal, proliferation, differentiation, and regeneration of intestinal stem cells (ISCs). These insights not only enhance our understanding of normal tissue maintenance but also provide critical perspectives on how ISC dysfunction can lead to pathological conditions such as colorectal cancer (CRC).

Metabolic regulation of intestinal homeostasis: molecular and cellular mechanisms and diseases

Metabolism serves not only as the organism's energy source but also yields metabolites crucial for maintaining tissue homeostasis and overall health. Intestinal stem cells (ISCs) maintain intestinal homeostasis through continuous self-renewal and differentiation divisions. The intricate relationship between metabolic pathways and intestinal homeostasis underscores their crucial interplay. Metabolic pathways have been shown to directly regulate ISC self-renewal and influence ISC fate decisions under homeostatic conditions, but the cellular and molecular mechanisms remain incompletely understood. Understanding the intricate involvement of various pathways in maintaining intestinal homeostasis holds promise for devising innovative strategies to address intestinal diseases. Here, we provide a comprehensive review of recent advances in the regulation of intestinal homeostasis. We describe the regulation of intestinal homeostasis from multiple perspectives, including the regulation of intestinal epithelial cells, the regulation of the tissue microenvironment, and the key role of nutrient metabolism. We highlight the regulation of intestinal homeostasis and ISC by nutrient metabolism. This review provides a multifaceted perspective on how intestinal homeostasis is regulated and provides ideas for intestinal diseases and repair of intestinal damage.

Evaluation of the Use of Cell Lines in Studies of Selenium-Dependent Glutathione Peroxidase 2 (GPX2) Involvement in Colorectal Cancer

Hydroperoxides (ROOHs) are known as damaging agents capable of mediating mutation, while a role as signaling agents through oxidation of protein sulfhydryls that can alter cancer-related pathways has gained traction. Glutathione peroxidase 2 (GPX2) is an antioxidant enzyme that reduces ROOHs at the expense of glutathione (GSH). GPX2 is noted for a tendency of large increases or decreases in expression levels during tumorigenesis that leads to investigators focusing on its role in cancer. However, GPX2 is only one component of multiple enzyme families that metabolize ROOH, and GPX2 levels are often very low in the context of these other ROOH-reducing activities. Colorectal cancer (CRC) was selected as a case study for examining GPX2 function, as colorectal tissues and cancers are sites where GPX2 is highly expressed. A case can be made for a significant impact of changes in expression levels. There is also a link between GPX2 and NADPH oxidase 1 (NOX1) from earlier studies that is seldom addressed and is discussed, presenting data on a unique association in colon and CRC. Tumor-derived cell lines are quite commonly used for pre-clinical studies involving the role of GPX2 in CRC. Generally, selection for this type of work is limited to identifying cell lines based on high and low GPX2 expression with the standard research scheme of overexpression in low-expressing lines and suppression in high-expressing lines to identify impacted pathways. This overlooks CRC subtypes among cell lines involving a wide range of gene expression profiles and a variety of driver mutation differences, along with a large difference in GPX2 expression levels. A trend for low and high GPX2 expressing cell lines to segregate into different CRC subclasses, indicated in this report, suggests that choices based solely on GPX2 levels may provide misleading and conflicting results by disregarding other properties of cell lines and failing to factor in differences in potential protein targets of ROOHs. CRC and cell line classification schemes are presented here that were intended to assist workers in performing pre-clinical studies but are largely unnoted in studies on GPX2 and CRC. Studies are often initiated on the premise that the transition from normal to CRC is associated with upregulation of GPX2. This is probably correct. However, the source normal cells for CRC could be almost any colon cell type, some with very high GPX2 levels. These factors are addressed in this study.

Identification and Characterization of Multiple Paneth Cell Types in the Mouse Small Intestine

The small intestinal crypts harbor secretory Paneth cells (PCs) which express bactericidal peptides that are crucial for maintaining intestinal homeostasis. Considering the diverse environmental conditions throughout the course of the small intestine, multiple subtypes of PCs are expected to exist. We applied single-cell RNA-sequencing of PCs combined with deep bulk RNA-sequencing on PC populations of different small intestinal locations and discovered several expression-based PC clusters. Some of these are discrete and resemble tuft cell-like PCs, goblet cell (GC)-like PCs, PCs expressing stem cell markers, and atypical PCs. Other clusters are less discrete but appear to be derived from different locations along the intestinal tract and have environment-dictated functions such as food digestion and antimicrobial peptide production. A comprehensive spatial analysis using Resolve Bioscience was conducted, leading to the identification of different PC's transcriptomic identities along the different compartments of the intestine, but not between PCs in the crypts themselves.

Desulfovibrio vulgaris caused gut inflammation and aggravated DSS-induced colitis in C57BL/6 mice model

BACKGROUND

Sulfate-reducing bacteria (SRB) is a potential pathogen usually detected in patients with gastrointestinal diseases. Hydrogen sulfide (H2S), a metabolic byproduct of SRB, was considered the main causative agent that disrupted the morphology and function of gut epithelial cells. Associated study also showed that flagellin from Desulfovibrio vulgaris (DVF), the representative bacterium of the Desulfovibrio genus, could exacerbate colitis due to the interaction of DVF and LRRC19, leading to the secretion of pro-inflammatory cytokines. However, we still have limited understanding about the change of gut microbiota (GM) composition caused by overgrowth of SRB and its exacerbating effects on colitis.

RESULTS

In this study, we transplanted D. vulgaris into the mice treated with or without DSS, and set a one-week recovery period to investigate the impact of D. vulgaris on the mice model. The outcomes showed that transplanted D. vulgaris into the normal mice could cause the gut inflammation, disrupt gut barrier and reduce the level of short-chain fatty acids (SCFAs). Moreover, D. vulgaris also significantly augmented DSS-induced colitis by exacerbating the damage of gut barrier and the secretion of inflammatory cytokines, for instance, IL-1β, iNOS, and TNF-α. Furthermore, results also showed that D. vulgaris could markedly change GM composition, especially decrease the relative abundance of SCFAs-producing bacteria. Additionally, D. vulgaris significantly stimulated the growth of Akkermansia muciniphila probably via its metabolic byproduct, H2S, in vivo.

CONCLUSIONS

Collectively, this study indicated that transplantation of D. vulgaris could cause gut inflammation and aggravate the colitis induced by DSS.

Non-stem cell lineages as an alternative origin of intestinal tumorigenesis in the context of inflammation

According to conventional views, colon cancer originates from stem cells. However, inflammation, a key risk factor for colon cancer, has been shown to suppress intestinal stemness. Here, we used Paneth cells as a model to assess the capacity of differentiated lineages to trigger tumorigenesis in the context of inflammation in mice. Upon inflammation, Paneth cell-specific Apc mutations led to intestinal tumors reminiscent not only of those arising in patients with inflammatory bowel disease, but also of a larger fraction of human sporadic colon cancers. The latter is possibly because of the inflammatory consequences of western-style dietary habits, a major colon cancer risk factor. Machine learning methods designed to predict the cell-of-origin of cancer from patient-derived tumor samples confirmed that, in a substantial fraction of sporadic cases, the origins of colon cancer reside in secretory lineages and not in stem cells.

Notoginsenoside R1 promotes Lgr5+ stem cell and epithelium renovation in colitis mice via activating Wnt/β-Catenin signaling

Inflammatory bowel disease (IBD) is characterized by persistent damage to the intestinal barrier and excessive inflammation, leading to increased intestinal permeability. Current treatments of IBD primarily address inflammation, neglecting epithelial repair. Our previous study has reported the therapeutic potential of notoginsenoside R1 (NGR1), a characteristic saponin from the root of Panax notoginseng, in alleviating acute colitis by reducing mucosal inflammation. In this study we investigated the reparative effects of NGR1 on mucosal barrier damage after the acute injury stage of DSS exposure. DSS-induced colitis mice were orally treated with NGR1 (25, 50, 125 mg·kg-1·d-1) for 10 days. Body weight and rectal bleeding were daily monitored throughout the experiment, then mice were euthanized, and the colon was collected for analysis. We showed that NGR1 administration dose-dependently ameliorated mucosal inflammation and enhanced epithelial repair evidenced by increased tight junction proteins, mucus production and reduced permeability in colitis mice. We then performed transcriptomic analysis on rectal tissue using RNA-sequencing, and found NGR1 administration stimulated the proliferation of intestinal crypt cells and facilitated the repair of epithelial injury; NGR1 upregulated ISC marker Lgr5, the genes for differentiation of intestinal stem cells (ISCs), as well as BrdU incorporation in crypts of colitis mice. In NCM460 human intestinal epithelial cells in vitro, treatment with NGR1 (100 μM) promoted wound healing and reduced cell apoptosis. NGR1 (100 μM) also increased Lgr5+ cells and budding rates in a 3D intestinal organoid model. We demonstrated that NGR1 promoted ISC proliferation and differentiation through activation of the Wnt signaling pathway. Co-treatment with Wnt inhibitor ICG-001 partially counteracted the effects of NGR1 on crypt Lgr5+ ISCs, organoid budding rates, and overall mice colitis improvement. These results suggest that NGR1 alleviates DSS-induced colitis in mice by promoting the regeneration of Lgr5+ stem cells and intestinal reconstruction, at least partially via activation of the Wnt/β-Catenin signaling pathway. Schematic diagram of the mechanism of NGR1 in alleviating colitis. DSS caused widespread mucosal inflammation epithelial injury. This was manifested by the decreased expression of tight junction proteins, reduced mucus production in goblet cells, and increased intestinal permeability in colitis mice. Additionally, Lgr5+ ISCs were in obviously deficiency in colitis mice, with aberrant down-regulation of the Wnt/β-Catenin signaling. However, NGR1 amplified the expression of the ISC marker Lgr5, elevated the expression of genes associated with ISC differentiation, enhanced the incorporation of BrdU in the crypt and promoted epithelial restoration to alleviate DSS-induced colitis in mice, at least partially, by activating the Wnt/β-Catenin signaling pathway.

Tuft cell acetylcholine is released into the gut lumen to promote anti-helminth immunity

Upon parasitic helminth infection, activated intestinal tuft cells secrete interleukin-25 (IL-25), which initiates a type 2 immune response during which lamina propria type 2 innate lymphoid cells (ILC2s) produce IL-13. This causes epithelial remodeling, including tuft cell hyperplasia, the function of which is unknown. We identified a cholinergic effector function of tuft cells, which are the only epithelial cells that expressed choline acetyltransferase (ChAT). During parasite infection, mice with epithelial-specific deletion of ChAT had increased worm burden, fitness, and fecal egg counts, even though type 2 immune responses were comparable. Mechanistically, IL-13-amplified tuft cells release acetylcholine (ACh) into the gut lumen. Finally, we demonstrated a direct effect of ACh on worms, which reduced their fecundity via helminth-expressed muscarinic ACh receptors. Thus, tuft cells are sentinels in naive mice, and their amplification upon helminth infection provides an additional type 2 immune response effector function.

Claudin-7 is essential for the maintenance of colonic stem cell homoeostasis via the modulation of Wnt/Notch signalling

Intestinal stem cells (ISCs) play a crucial role in the continuous self-renewal and recovery of the intestinal epithelium. In previous studies, we have revealed that the specific absence of Claudin-7 (Cldn-7) in intestinal epithelial cells (IECs) can lead to the development of spontaneous colitis. However, the mechanisms by which Cldn-7 maintains homeostasis in the colonic epithelium remain unclear. Therefore, in the present study, we used IEC- and ISC-specific Cldn-7 knockout mice to investigate the regulatory effects of Cldn-7 on colonic Lgr5+ stem cells in the mediation of colonic epithelial injury and repair under physiological and inflammatory conditions. Notably, our findings reveal that Cldn-7 deletion disrupts the self-renewal and differentiation of colonic stem cells alongside the formation of colonic organoids in vitro. Additionally, these Cldn-7 knockout models exhibited heightened susceptibility to experimental colitis, limited epithelial repair and regeneration, and increased differentiation toward the secretory lineage. Mechanistically, we also established that Cldn-7 facilitates the proliferation, differentiation, and organoid formation of Lgr5+ stem cells through the maintenance of Wnt and Notch signalling pathways in the colonic epithelium. Overall, our study provides new insights into the maintenance of ISC function and colonic epithelial homoeostasis.

Detailed survey of an in vitro intestinal epithelium model by single-cell transcriptomics

The co-culture of two adult human colorectal cancer cell lines, Caco-2 and HT29, on Transwell is commonly used as an in vitro gut mimic, yet the translatability of insights from such a system to adult human physiological contexts is not fully characterized. Here, we used single-cell RNA sequencing on the co-culture to obtain a detailed survey of cell type heterogeneity in the system and conducted a holistic comparison with human physiology. We identified the intestinal stem cell-, transit amplifying-, enterocyte-, goblet cell-, and enteroendocrine-like cells in the system. In general, the co-culture was fetal intestine-like, with less variety of gene expression compared to the adult human gut. Transporters for major types of nutrients were found in the majority of the enterocytes-like cells in the system. TLR 4 was not expressed in the sample, indicating that the co-culture model is incapable of mimicking the innate immune aspect of the human epithelium.

Intestinal Mucosal Immune Barrier: A Powerful Firewall Against Severe Acute Pancreatitis-Associated Acute Lung Injury via the Gut-Lung Axis

The pathogenesis of severe acute pancreatitis-associated acute lung injury (SAP-ALI), which is the leading cause of mortality among hospitalized patients in the intensive care unit, remains incompletely elucidated. The intestinal mucosal immune barrier is a crucial component of the intestinal epithelial barrier, and its aberrant activation contributes to the induction of sustained pro-inflammatory immune responses, paradoxical intercellular communication, and bacterial translocation. In this review, we firstly provide a comprehensive overview of the composition of the intestinal mucosal immune barrier and its pivotal roles in the pathogenesis of SAP-ALI. Secondly, the mechanisms of its crosstalk with gut microbiota, which is called gut-lung axis, and its effect on SAP-ALI were summarized. Finally, a number of drugs that could enhance the intestinal mucosal immune barrier and exhibit potential anti-SAP-ALI activities were presented, including probiotics, glutamine, enteral nutrition, and traditional Chinese medicine (TCM). The aim is to offer a theoretical framework based on the perspective of the intestinal mucosal immune barrier to protect against SAP-ALI.

The loss of antioxidant activities impairs intestinal epithelium homeostasis by altering lipid metabolism

Reactive oxygens species (ROS) are common byproducts of metabolic reactions and could be at the origin of many diseases of the elderly. Here we investigated the role of ROS in the renewal of the intestinal epithelium in mice lacking catalase (CAT) and/or nicotinamide nucleotide transhydrogenase (NNT) activities. Cat-/- mice have delayed intestinal epithelium renewal and were prone to develop necrotizing enterocolitis upon starvation. Interestingly, crypts lacking CAT showed fewer intestinal stem cells (ISC) and lower stem cell activity than wild-type. In contrast, crypts lacking NNT showed a similar number of ISCs as wild-type but increased stem cell activity, which was also impaired by the loss of CAT. No alteration in the number of Paneth cells (PCs) was observed in crypts of either Cat-/- or Nnt-/- mice, but they showed an evident decline in the amount of lysozyme. Cat deficiency caused fat accumulation in crypts, and a fall in the remarkable high amount of adipose triglyceride lipase (ATGL) in PCs. Notably, the low levels of ATGL in the intestine of Cat -/- mice increased after a treatment with the antioxidant N-acetyl-L-cysteine. Supporting a role of ATGL in the regulation of ISC activity, its inhibition halt intestinal organoid development. These data suggest that the reduction in the renewal capacity of intestine originates from fatty acid metabolic alterations caused by peroxisomal ROS.

Associations of inflammatory cytokines with inflammatory bowel disease: a Mendelian randomization study

Objectives

Previous studies have confirmed a link between specific inflammatory cytokines and inflammatory bowel disease (IBD), but the causal relationship between them is not completely clear. This Mendelian Randomization (MR) study aims to evaluate the causal relationship between 18 inflammatory cytokines and inflammatory bowel disease.

Method

Two-sample Mendelian randomization utilized genetic variances associated with IBD from two extensive publicly available genome-wide association studies (GWAS) (Crohn's Disease (CD): 12,194 cases and 28,072 controls; Ulcerative Colitis (UC): 12,336 cases and 33,609 controls). The data of inflammatory cytokines was acquired from a GWAS including 8,293 healthy participants. We used inverse variance weighted method, MR-Egger, weighted median, simple model and weighted model to evaluate the causal relationship between inflammatory cytokines and IBD. Sensitivity analysis includes heterogeneity and pleiotropy analysis to evaluate the robustness of the results.

Results

The findings indicated suggestive positive associations between Interleukin-13 (IL-13) and macrophage migration inhibitory factor (MIF) with CD (odds ratio, OR: 1.101, 95%CI: 1.021-1.188, p = 0.013; OR: 1.134, 95%CI: 1.024-1.255, p = 0.015). IL-13 also displayed a significant positive correlation with UC (OR: 1.099, 95%CI: 1.018-1.186, p = 0.016). Stem cell factor (SCF) was suggested to be associated with the development of both CD and UC (OR: 1.032, 95%CI: 0.973-1.058, p = 0.012; OR: 1.038, 95%CI: 1.005-1.072, p = 0.024).

Conclusion

This study proposes that IL-13 may be a factor correlated with the etiology of IBD (CD and UC), while MIF just be specifically associated with CD. Additionally, SCF appears more likely to be involved in the downstream development of IBD (CD and UC).

Hallmarks of stemness in mammalian tissues

All adult tissues experience wear and tear. Most tissues can compensate for cell loss through the activity of resident stem cells. Although the cellular maintenance strategies vary greatly between different adult (read: postnatal) tissues, the function of stem cells is best defined by their capacity to replace lost tissue through division. We discuss a set of six complementary hallmarks that are key enabling features of this basic function. These include longevity and self-renewal, multipotency, transplantability, plasticity, dependence on niche signals, and maintenance of genome integrity. We discuss these hallmarks in the context of some of the best-understood adult stem cell niches.

The emerging roles of deep crypt secretory cells in colonic physiology

Deep crypt secretory (DCS) cells are a population of epithelial cells located at the colonic crypt base that share some similarities to Paneth and goblet cells. They were initially defined as c-Kit expressing cells, though subsequent work showed that they are more specifically marked by Reg4 in the murine colon. The best-understood function of DCS cells at present is supporting the stem cell niche by generating Notch and EGF ligands. However, as these cells also express immunoregulatory (e.g., Ccl6) and host defense (e.g., Retnlb) genes, it is likely they have additional functions in maintaining colonic health outside of maintenance of the stem niche. Recent advances in single-cell transcriptomic profiling hint at additional epithelial and immune roles that may exist for these cells and have aided in elucidating their developmental lineage. This review highlights the emerging evidence supporting a crucial role for DCS cells in intestinal physiology, the current understanding of how these cells are regulated, and their potential role(s) in colonic disease.

Recent Advances in Cell-Based In Vitro Models to Recreate Human Intestinal Inflammation

Inflammatory bowel disease causes a major burden to patients and healthcare systems, raising the need to develop effective therapies. Technological advances in cell culture, allied with ethical issues, have propelled in vitro models as essential tools to study disease aetiology, its progression, and possible therapies. Several cell-based in vitro models of intestinal inflammation have been used, varying in their complexity and methodology to induce inflammation. Immortalized cell lines are extensively used due to their long-term survival, in contrast to primary cultures that are short-lived but patient-specific. Recently, organoids and organ-chips have demonstrated great potential by being physiologically more relevant. This review aims to shed light on the intricate nature of intestinal inflammation and cover recent works that report cell-based in vitro models of human intestinal inflammation, encompassing diverse approaches and outcomes.

The origin of intestinal cancer in the context of inflammation

According to conventional views, colon cancer originates from stem cells. However, inflammation, a key risk factor for colon cancer, was shown to suppress intestinal stemness. Here, we employed Paneth cells (PCs) as a model to assess the capacity of differentiated lineages to trigger tumorigenesis in the context of inflammation. Upon inflammation, PC-specific Apc mutations led to intestinal tumors reminiscent not only of those arising in inflammatory bowel disease (IBD) patients but also of a larger fraction of sporadic colon cancers. The latter is likely due to the inflammatory consequences of Western-style dietary habits, the major colon cancer risk factor. Computational methods designed to predict the cell-of-origin of cancer confirmed that, in a substantial fraction of sporadic colon cancers the cells-of-origin are secretory lineages and not stem cells.

Genome-Wide Association Study Identifies 4 Novel Risk Loci for Small Intestinal Neuroendocrine Tumors Including a Missense Mutation in LGR5

BACKGROUND & AIMS

Small intestinal neuroendocrine tumor (SI-NET) is a rare disease, but its incidence has increased over the past 4 decades. Understanding the genetic risk factors underlying SI-NETs can help in disease prevention and may provide clinically beneficial markers for diagnosis. Here the results of the largest genome-wide association study of SI-NETs performed to date with 405 cases and 614,666 controls are reported.

METHODS

Samples from 307 patients with SI-NETs and 287,137 controls in the FinnGen study were used for the identification of SI-NET risk-associated genetic variants. The results were also meta-analyzed with summary statistics from the UK Biobank (n = 98 patients with SI-NET and n = 327,529 controls).

RESULTS

We identified 6 genome-wide significant (P < 5 × 10-8) loci associated with SI-NET risk, of which 4 (near SEMA6A, LGR5, CDKAL1, and FERMT2) are novel and 2 (near LTA4H-ELK and in KIF16B) have been reported previously. Interestingly, the top hit (rs200138614; P = 1.80 × 10-19) was a missense variant (p.Cys712Phe) in the LGR5 gene, a bona-fide marker of adult intestinal stem cells and a potentiator of canonical WNT signaling. The association was validated in an independent Finnish collection of 70 patients with SI-NETs, as well as in the UK Biobank exome sequence data (n = 92 cases and n = 392,814 controls). Overexpression of LGR5 p.Cys712Phe in intestinal organoids abolished the ability of R-Spondin1 to support organoid growth, indicating that the mutation perturbed R-Spondin-LGR5 signaling.

CONCLUSIONS

Our study is the largest genome-wide association study to date on SI-NETs and reported 4 new associated genome-wide association study loci, including a novel missense mutation (rs200138614, p.Cys712Phe) in LGR5, a canonical marker of adult intestinal stem cells.

Advanced Progression for the Heterogeneity and Homeostasis of Intestinal Stem Cells

Current understanding of the leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) in intestinal stem cells (ISCs) is well established, however, the implications of ISC heterogeneity and homeostasis are poorly understood. Prior studies have provided important evidence for the association between heterogeneity of ISC pools with pathogenesis and therapeutic response of malignant disease. Leveraging the advantages of organoids and single cell RNA sequencing (scRNA-seq), glandular development has been simulated and cell heterogeneity has been clarified. Based on this research, several potential ISCs were identified, such as LGR5 + p27 + quiescent ISCs, LGR5 + Mex3a + slowly proliferating stem cells, and CLU + reverse stem cells. We also illustrated major factors responsible for ISC homeostasis including metabolism-related (LKB1, TGR5, HMGCS2), inflammation-related (IFB-b, IFN2, TNF), and Wnt signaling-related (CREPT, Mex3a, MTG16) factors. ISCs play complex roles in intestinal tumorigenesis, chemoresistance and occasional relapse of colon cancer, which bear discussion. In this review, we focus on novel technical challenges in ISCs fate drawing upon recent research with the goals of clarifying our understanding of complex ISCs, elucidating the integrated intestinal crypt niche, and creating new opportunities for therapeutic development.

Nutrient-driven dedifferentiation of enteroendocrine cells promotes adaptive intestinal growth in Drosophila

Post-developmental organ resizing improves organismal fitness under constantly changing nutrient environments. Although stem cell abundance is a fundamental determinant of adaptive resizing, our understanding of its underlying mechanisms remains primarily limited to the regulation of stem cell division. Here, we demonstrate that nutrient fluctuation induces dedifferentiation in the Drosophila adult midgut to drive adaptive intestinal growth. From lineage tracing and single-cell RNA sequencing, we identify a subpopulation of enteroendocrine (EE) cells that convert into functional intestinal stem cells (ISCs) in response to dietary glucose and amino acids by activating the JAK-STAT pathway. Genetic ablation of EE-derived ISCs severely impairs ISC expansion and midgut growth despite the retention of resident ISCs, and in silico modeling further indicates that EE dedifferentiation enables an efficient increase in the midgut cell number while maintaining epithelial cell composition. Our findings identify a physiologically induced dedifferentiation that ensures ISC expansion during adaptive organ growth in concert with nutrient conditions.

A tissue-intrinsic IL-33/EGF circuit promotes epithelial regeneration after intestinal injury

Intestinal stem cells (ISCs) maintain the epithelial lining of the intestines, but mechanisms regulating ISCs and their niche after damage remain poorly understood. Utilizing radiation injury to model intestinal pathology, we report here that the Interleukin-33 (IL-33)/ST2 axis, an immunomodulatory pathway monitored clinically as an intestinal injury biomarker, regulates intrinsic epithelial regeneration by inducing production of epidermal growth factor (EGF). Three-dimensional imaging and lineage-specific RiboTag induction within the stem cell compartment indicated that ISCs expressed IL-33 in response to radiation injury. Neighboring Paneth cells responded to IL-33 by augmenting production of EGF, which promoted ISC recovery and epithelial regeneration. These findings reveal an unknown pathway of niche regulation and crypt regeneration whereby the niche responds dynamically upon injury and the stem cells orchestrate regeneration by regulating their niche. This regenerative circuit also highlights the breadth of IL-33 activity beyond immunomodulation and the therapeutic potential of EGF administration for treatment of intestinal injury.

Fetal Muse-based therapy prevents lethal radio-induced gastrointestinal syndrome by intestinal regeneration

BACKGROUND

Human multilineage-differentiating stress enduring (Muse) cells are nontumorigenic endogenous pluripotent-like stem cells that can be easily obtained from various adult or fetal tissues. Regenerative effects of Muse cells have been shown in some disease models. Muse cells specifically home in damaged tissues where they exert pleiotropic effects. Exposition of the small intestine to high doses of irradiation (IR) delivered after radiotherapy or nuclear accident results in a lethal gastrointestinal syndrome (GIS) characterized by acute loss of intestinal stem cells, impaired epithelial regeneration and subsequent loss of the mucosal barrier resulting in sepsis and death. To date, there is no effective medical treatment for GIS. Here, we investigate whether Muse cells can prevent lethal GIS and study how they act on intestinal stem cell microenvironment to promote intestinal regeneration.

METHODS

Human Muse cells from Wharton's jelly matrix of umbilical cord (WJ-Muse) were sorted by flow cytometry using the SSEA-3 marker, characterized and compared to bone-marrow derived Muse cells (BM-Muse). Under gas anesthesia, GIS mice were treated or not through an intravenous retro-orbital injection of 50,000 WJ-Muse, freshly isolated or cryopreserved, shortly after an 18 Gy-abdominal IR. No immunosuppressant was delivered to the mice. Mice were euthanized either 24 h post-IR to assess early small intestine tissue response, or 7 days post-IR to assess any regenerative response. Mouse survival, histological stainings, apoptosis and cell proliferation were studied and measurement of cytokines, recruitment of immune cells and barrier functional assay were performed.

RESULTS

Injection of WJ-Muse shortly after abdominal IR highly improved mouse survival as a result of a rapid regeneration of intestinal epithelium with the rescue of the impaired epithelial barrier. In small intestine of Muse-treated mice, an early enhanced secretion of IL-6 and MCP-1 cytokines was observed associated with (1) recruitment of monocytes/M2-like macrophages and (2) proliferation of Paneth cells through activation of the IL-6/Stat3 pathway.

CONCLUSION

Our findings indicate that a single injection of a small quantity of WJ-Muse may be a new and easy therapeutic strategy for treating lethal GIS.

A stromal lineage maintains crypt structure and villus homeostasis in the intestinal stem cell niche

BACKGROUND

The nutrient-absorbing villi of small intestines are renewed and repaired by intestinal stem cells (ISCs), which reside in a well-organized crypt structure. Genetic studies have shown that Wnt molecules secreted by telocytes, Gli1+ stromal cells, and epithelial cells are required for ISC proliferation and villus homeostasis. Intestinal stromal cells are heterogeneous and single-cell profiling has divided them into telocytes/subepithelial myofibroblasts, myocytes, pericytes, trophocytes, and Pdgfralow stromal cells. Yet, the niche function of these stromal populations remains incompletely understood.

RESULTS

We show here that a Twist2 stromal lineage, which constitutes the Pdgfralow stromal cell and trophocyte subpopulations, maintains the crypt structure to provide an inflammation-restricting niche for regenerating ISCs. Ablating Twist2 lineage cells or deletion of one Wntless allele in these cells disturbs the crypt structure and impairs villus homeostasis. Upon radiation, Wntless haplo-deficiency caused decreased production of anti-microbial peptides and increased inflammation, leading to defective ISC proliferation and crypt regeneration, which were partially rescued by eradication of commensal bacteria. In addition, we show that Wnts secreted by Acta2+ subpopulations also play a role in crypt regeneration but not homeostasis.

CONCLUSIONS

These findings suggest that ISCs may require different niches for villus homeostasis and regeneration and that the Twist2 lineage cells may help to maintain a microbe-restricted environment to allow ISC-mediated crypt regeneration.

Cancer cell plasticity during tumor progression, metastasis and response to therapy

Cell plasticity represents the ability of cells to be reprogrammed and to change their fate and identity, enabling homeostasis restoration and tissue regeneration following damage. Cell plasticity also contributes to pathological conditions, such as cancer, enabling cells to acquire new phenotypic and functional features by transiting across distinct cell states that contribute to tumor initiation, progression, metastasis and resistance to therapy. Here, we review the intrinsic and extrinsic mechanisms driving cell plasticity that promote tumor growth and proliferation as well as metastasis and drug tolerance. Finally, we discuss how cell plasticity could be exploited for anti-cancer therapy.

Intestinal stem cells and gut microbiota therapeutics: hype or hope?

The vital role of the intestines as the main site for the digestion and absorption of nutrients for the body continues subconsciously throughout one's lifetime, but underneath all the complex processes lie the intestinal stem cells and the gut microbiota that work together to maintain the intestinal epithelium. Intestinal stem cells (ISC) are multipotent stem cells from which all intestinal epithelial cells originate, and the gut microbiota refers to the abundant collection of various microorganisms that reside in the gastrointestinal tract. Both reside in the intestines and have many mechanisms and pathways in place with the ultimate goal of co-managing human gastrointestinal tract homeostasis. Based on the abundance of research that is focused on either of these two topics, this suggests that there are many methods by which both players affect one another. Therefore, this review aims to address the relationship between ISC and the gut microbiota in the context of regenerative medicine. Understanding the principles behind both aspects is therefore essential in further studies in the field of regenerative medicine by making use of the underlying designed mechanisms.

Sonic Hedgehog and WNT Signaling Regulate a Positive Feedback Loop Between Intestinal Epithelial and Stromal Cells to Promote Epithelial Regeneration

BACKGROUND AND AIMS

Active intestinal stem cells are prone to injury by ionizing radiation. We previously showed that upon radiation-induced injury, normally quiescent reserve intestinal stem cells (rISCs) (marked by BMI1) are activated by Musashi-1 (MSI1) and exit from the quiescent state to regenerate the intestinal epithelium. This study aims to further establish the mechanism that regulates activation of Bmi1-CreER;Rosa26eYFP (Bmi1-CreER) rISCs following γ radiation-induced injury.

METHODS

Bmi1-CreER mice were treated with tamoxifen to initiate lineage tracing of BMI1 (eYFP+) cells and exposed to 12 Gy of total body γ irradiation or sham. Intestinal tissues were collected and analyzed by immunofluorescence, Western blot, reverse-transcription quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and chromatin immunoprecipitation real-time polymerase chain reaction.

RESULTS

After irradiation, increased expression of Msi1 in eYFP+ cells was accompanied by increased expression of Axin2, a WNT marker. Promoter studies of the Msi1 gene indicated that Msi1 is a WNT target gene. Coculture of stromal cells isolated from irradiated mice stimulated Bmi1-CreER-derived organoid regeneration more effectively than those from sham mice. Expression of WNT ligands, including Wnt2b, Wnt4, Wnt5a, and Rspo3, was increased in irradiated stromal cells compared with sham-treated stromal cells. Moreover, expression of the Sonic hedgehog (SHH) effector Gli1 was increased in stromal cells from irradiated mice. This was correlated with an increased expression of SHH in epithelial cells postirradiation, indicating epithelial-stromal interaction. Finally, preinjury treatment with SHH inhibitor cyclopamine significantly reduced intestinal epithelial regeneration and Msi1 expression postirradiation.

CONCLUSIONS

Upon ionizing radiation-induced injury, intestinal epithelial cells increase SHH secretion, stimulating stromal cells to secrete WNT ligands. WNT activators induce Msi1 expression in the Bmi1-CreER cells. This stromal-epithelial interaction leads to Bmi1-CreER rISCs induction and epithelial regeneration.

Inhibition of Soluble Stem Cell Factor Promotes Intestinal Mucosal Repair

BACKGROUND

Incidences of inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, are escalating worldwide and can be considered a global public health problem. Given that the gold standard approach to IBD therapeutics focuses on reducing the severity of symptoms, there is an urgent unmet need to develop alternative therapies that halt not only inflammatory processes but also promote mucosal repair. Previous studies have identified increased stem cell factor (SCF) expression in inflamed intestinal mucosal tissues. However, the role that SCF plays in mediating intestinal inflammation and repair has not been explored.

METHODS

Changes in the expression of SCF were evaluated in the colonic tissue of healthy mice and during dextran sodium sulfate (DSS)-induced colitis. Furthermore, mucosal wound healing and colitis severity were analyzed in mice subjected to either mechanical biopsy or DSS treatment, respectively, following intestinal epithelial cell-specific deletion of SCF or anti-SCF antibody administration.

RESULTS

We report robust expression of SCF by intestinal epithelial cells during intestinal homeostasis with a switch to immune cell-produced SCF during colitis. Data from mice with intestinal epithelial cell-specific deletion of SCF highlight the importance of immune cell-produced SCF in driving the pathogenesis of colitis. Importantly, antibody-mediated neutralization of total SCF or the specific SCF248 isoform decreased immune cell infiltration and enhanced mucosal wound repair following biopsy-induced colonic injury or DSS-induced colitis.

CONCLUSIONS

These data demonstrate that SCF functions as a pro-inflammatory mediator in mucosal tissues and that specific neutralization of SCF248 could be a viable therapeutic option to reduce intestinal inflammation and promote mucosal wound repair in individuals with IBD.

Cytarabine induces cachexia with lipid malabsorption via zippering the junctions of lacteal in murine small intestine

Chemotherapy-induced cachexia causes severe metabolic abnormalities independently of cancer and reduces the therapeutic efficacy of chemotherapy. The underlying mechanism of chemotherapy-induced cachexia remains unclear. Here we investigated the cytarabine (CYT)-induced alteration in energy balance and its underlying mechanisms in mice. We compared energy balance-associated parameters among the three groups of mice: CON, CYT, and PF (pair-fed mice with the CYT group) that were intravenously administered vehicle or CYT. Weight gain, fat mass, skeletal muscle mass, grip strength, and nocturnal energy expenditure were significantly lowered in the CYT group than in the CON and PF groups. The CYT group demonstrated less energy intake than the CON group and higher respiratory quotient than the PF group, indicating that CYT induced cachexia independently from the anorexia-induced weight loss. Serum triglyceride was significantly lower in the CYT group than in the CON group, whereas the intestinal mucosal triglyceride levels and the lipid content within the small intestine enterocyte were higher after lipid loading in the CYT group than in the CON and PF groups, suggesting that CYT inhibited lipid uptake in the intestine. This was not associated with obvious intestinal damage. The CYT group showed increased zipper-like junctions of lymphatic endothelial vessel in duodenal villi compared to that in the CON and CYT groups, suggesting their imperative role in the CYT-induced inhibition of lipid uptake. CYT worsens cachexia independently of anorexia by inhibiting the intestinal lipid uptake, via the increased zipper-like junctions of lymphatic endothelial vessel.

Stiffness Restricts the Stemness of the Intestinal Stem Cells and Skews Their Differentiation Toward Goblet Cells

BACKGROUND & AIMS

Fibrosis and tissue stiffening are hallmarks of inflammatory bowel disease (IBD). We have hypothesized that the increased stiffness directly contributes to the dysregulation of the epithelial cell homeostasis in IBD. Here, we aim to determine the impact of tissue stiffening on the fate and function of the intestinal stem cells (ISCs).

METHODS

We developed a long-term culture system consisting of 2.5-dimensional intestinal organoids grown on a hydrogel matrix with tunable stiffness. Single-cell RNA sequencing provided stiffness-regulated transcriptional signatures of the ISCs and their differentiated progeny. YAP-knockout and YAP-overexpression mice were used to manipulate YAP expression. In addition, we analyzed colon samples from murine colitis models and human IBD samples to assess the impact of stiffness on ISCs in vivo.

RESULTS

We demonstrated that increasing the stiffness potently reduced the population of LGR5+ ISCs and KI-67+-proliferating cells. Conversely, cells expressing the stem cell marker, olfactomedin-4, became dominant in the crypt-like compartments and pervaded the villus-like regions. Concomitantly, stiffening prompted the ISCs to preferentially differentiate toward goblet cells. Mechanistically, stiffening increased the expression of cytosolic YAP, driving the extension of olfactomedin-4+ cells into the villus-like regions, while it induced the nuclear translocation of YAP, leading to preferential differentiation of ISCs toward goblet cells. Furthermore, analysis of colon samples from murine colitis models and patients with IBD demonstrated cellular and molecular remodeling reminiscent of those observed in vitro.

CONCLUSIONS

Collectively, our findings highlight that matrix stiffness potently regulates the stemness of ISCs and their differentiation trajectory, supporting the hypothesis that fibrosis-induced gut stiffening plays a direct role in epithelial remodeling in IBD.

Histological assessment of intestinal injury by ionizing radiation

Given the potential risk of radiological terrorism and disasters, it is essential to develop plans to prepare for such events. In these hazardous scenarios, radiation-induced gastrointestinal (GI) syndrome is one of the many manifestations that may happen after the organism is exposed to a lethal dose of ionizing radiation. Therefore, it is critical to better understand how the intestinal tissues initiate and orchestrate regeneration following severe radiation injury. In this chapter, we aimed to provide several key considerations for researchers who utilize histological assessment to study radiation-induced intestinal injury. Rigor and reproducibility are critical in experimental design and can be achieved by maintaining proper radiation administration, maintaining consistency in sample collection, and selecting and using appropriate controls. We also provided technical details of histological preparation of the intestines with tips on dissecting, cleaning, fixing, and preserving. Step-by-step descriptions of both bundling and Swiss rolling are provided with discussion on how to choose between the two approaches. In the following section, we detailed several histological assessment methods and then provided suggestions on how to use histological assessment to study cellular dynamics in the small intestines. Finally, we touched on some non-histological assessments. We hope that the information provided in this chapter will contribute to the research society of radiation-induced intestinal injury with an ultimate goal of promoting the development of radiation countermeasures against the GI acute radiation syndrome.

The emerging roles of autophagy in intestinal epithelial cells and its links to inflammatory bowel disease

Landmark genome-wide association studies (GWAS) identified that mutations in autophagy genes correlated with inflammatory bowel disease (IBD), a heterogenous disease characterised by prolonged inflammation of the gastrointestinal tract, that can reduce a person's quality of life. Autophagy, the delivery of intracellular components to the lysosome for degradation, is a critical cellular housekeeping process that removes damaged proteins and turns over organelles, recycling their amino acids and other constituents to supply cells with energy and necessary building blocks. This occurs under both basal and challenging conditions such as nutrient deprivation. An understanding of the relationship between autophagy, intestinal health and IBD aetiology has improved over time, with autophagy having a verified role in the intestinal epithelium and immune cells. Here, we discuss research that has led to an understanding that autophagy genes, including ATG16L, ATG5, ATG7, IRGM, and Class III PI3K complex members, contribute to innate immune defence in intestinal epithelial cells (IECs) via selective autophagy of bacteria (xenophagy), how autophagy contributes to the regulation of the intestinal barrier via cell junctional proteins, and the critical role of autophagy genes in intestinal epithelial secretory subpopulations, namely Paneth and goblet cells. We also discuss how intestinal stem cells can utilise autophagy. Importantly, mouse studies have provided evidence that autophagy deregulation has serious physiological consequences including IEC death and intestinal inflammation. Thus, autophagy is now established as a key regulator of intestinal homeostasis. Further research into how its cytoprotective mechanisms can prevent intestinal inflammation may provide insights into the effective management of IBD.

Maintenance of high-turnover tissues during and beyond homeostasis

Tissues with a high turnover rate produce millions of cells daily and have abundant regenerative capacity. At the core of their maintenance are populations of stem cells that balance self-renewal and differentiation to produce the adequate numbers of specialized cells required for carrying out essential tissue functions. Here, we compare and contrast the intricate mechanisms and elements of homeostasis and injury-driven regeneration in the epidermis, hematopoietic system, and intestinal epithelium-the fastest renewing tissues in mammals. We highlight the functional relevance of the main mechanisms and identify open questions in the field of tissue maintenance.

PTBP1 controls intestinal epithelial regeneration through post-transcriptional regulation of gene expression

The intestinal epithelial regeneration is driven by intestinal stem cells under homeostatic conditions. Differentiated intestinal epithelial cells, such as Paneth cells, are capable of acquiring multipotency and contributing to regeneration upon the loss of intestinal stem cells. Paneth cells also support intestinal stem cell survival and regeneration. We report here that depletion of an RNA-binding protein named polypyrimidine tract binding protein 1 (PTBP1) in mouse intestinal epithelial cells causes intestinal stem cell death and epithelial regeneration failure. Mechanistically, we show that PTBP1 inhibits neuronal-like splicing programs in intestinal crypt cells, which is critical for maintaining intestinal stem cell stemness. This function is achieved at least in part through promoting the non-productive splicing of its paralog PTBP2. Moreover, PTBP1 inhibits the expression of an AKT inhibitor PHLDA3 in Paneth cells and permits AKT activation, which presumably maintains Paneth cell plasticity and function in supporting intestinal stem cell niche. We show that PTBP1 directly binds to a CU-rich region in the 3' UTR of Phlda3, which we demonstrate to be critical for downregulating the mRNA and protein levels of Phlda3. Our results thus reveal the multifaceted in vivo regulation of intestinal epithelial regeneration by PTBP1 at the post-transcriptional level.

Genetic heterogeneity of colorectal cancer and the microbiome

In 2020, the International Agency for Research on Cancer and the World Health Organization's GLOBOCAN database ranked colorectal cancer (CRC) as the third most common cancer in the world. Most cases of CRC (> 95%) are sporadic and develop from colorectal polyps that can progress to intramucosal carcinoma and CRC. Increasing evidence is accumulating that the gut microbiota can play a key role in the initiation and progression of CRC, as well as in the treatment of CRC, acting as an important metabolic and immunological regulator. Factors that may determine the microbiota role in CRC carcinogenesis include inflammation, changes in intestinal stem cell function, impact of bacterial metabolites on gut mucosa, accumulation of genetic mutations and other factors. In this review, I discuss the major mechanisms of the development of sporadic CRC, provide detailed characteristics of the bacteria that are most often associated with CRC, and analyze the role of the microbiome and microbial metabolites in inflammation initiation, activation of proliferative activity in intestinal epithelial and stem cells, and the development of genetic and epigenetic changes in CRC. I consider long-term studies in this direction to be very important, as they open up new opportunities for the treatment and prevention of CRC.

From birth to death: The hardworking life of Paneth cell in the small intestine

Paneth cells are a group of unique intestinal epithelial cells, and they play an important role in host-microbiota interactions. At the origin of Paneth cell life, several pathways such as Wnt, Notch, and BMP signaling, affect the differentiation of Paneth cells. After lineage commitment, Paneth cells migrate downward and reside in the base of crypts, and they possess abundant granules in their apical cytoplasm. These granules contain some important substances such as antimicrobial peptides and growth factors. Antimicrobial peptides can regulate the composition of microbiota and defend against mucosal penetration by commensal and pathogenic bacteria to protect the intestinal epithelia. The growth factors derived from Paneth cells contribute to the maintenance of the normal functions of intestinal stem cells. The presence of Paneth cells ensures the sterile environment and clearance of apoptotic cells from crypts to maintain the intestinal homeostasis. At the end of their lives, Paneth cells experience different types of programmed cell death such as apoptosis and necroptosis. During intestinal injury, Paneth cells can acquire stem cell features to restore the intestinal epithelial integrity. In view of the crucial roles of Paneth cells in the intestinal homeostasis, research on Paneth cells has rapidly developed in recent years, and the existing reviews on Paneth cells have mainly focused on their functions of antimicrobial peptide secretion and intestinal stem cell support. This review aims to summarize the approaches to studying Paneth cells and introduce the whole life experience of Paneth cells from birth to death.

Perturbation of intestinal stem cell homeostasis and radiation enteritis recovery via dietary titanium dioxide nanoparticles

Small intestinal health and enteritis incidence are tightly coupled to the homeostasis of intestinal stem cells (ISCs), which are sensitive to dietary alterations. However, little is known about the impact of food additives on ISC pool. Here, we demonstrate that chronic exposure to low-dose TiO₂ NPs, a commonly used food additive, significantly hampers primary human and mouse ISC-derived organoid formation and growth by specifically attenuating Wnt signal transduction. Mechanistically, TiO₂ NPs alter the endocytic trafficking of the Wnt receptor LRP6 and prevent the nuclear entry of β-catenin. Notably, dietary TiO₂ NPs elicit modest chronic stress in healthy intestines and considerably impede the recovery of radiation enteritis by perturbing the homeostasis of ISCs in vivo. Our results identify a health concern of TiO₂ NP exposure on ISC homeostasis and radiation enteritis recovery. These findings suggest extra precaution during the treatment of radiation enteritis and provide new insights into food additive-ISC interaction.

TRIM27 maintains gut homeostasis by promoting intestinal stem cell self-renewal

Dysregulation of gut homeostasis is associated with irritable bowel syndrome (IBS), a chronic functional gastrointestinal disorder affecting approximately 11.2% of the global population. The poorly understood pathogenesis of IBS has impeded its treatment. Here, we report that the E3 ubiquitin ligase tripartite motif-containing 27 (TRIM27) is weakly expressed in IBS but highly expressed in inflammatory bowel disease (IBD), a frequent chronic organic gastrointestinal disorder. Accordingly, knockout of Trim27 in mice causes spontaneously occurring IBS-like symptoms, including increased visceral hyperalgesia and abnormal stool features, as observed in IBS patients. Mechanistically, TRIM27 stabilizes β-catenin and thus activates Wnt/β-catenin signaling to promote intestinal stem cell (ISC) self-renewal. Consistent with these findings, Trim27 deficiency disrupts organoid formation, which is rescued by reintroducing TRIM27 or β-catenin. Furthermore, Wnt/β-catenin signaling activator treatment ameliorates IBS symptoms by promoting ISC self-renewal. Taken together, these data indicate that TRIM27 is critical for maintaining gut homeostasis, suggesting that targeting the TRIM27/Wnt/β-catenin axis could be a potential treatment strategy for IBS. Our study also indicates that TRIM27 might serve as a potential biomarker for differentiating IBS from IBD.

Epithelial plasticity enhances regeneration of committed taste receptor cells following nerve injury

Taste receptor cells are taste bud epithelial cells that are dependent upon the innervating nerve for continuous renewal and are maintained by resident tissue stem/progenitor cells. Transection of the innervating nerve causes degeneration of taste buds and taste receptor cells. However, a subset of the taste receptor cells is maintained without nerve contact after glossopharyngeal nerve transection in the circumvallate papilla in adult mice. Here, we revealed that injury caused by glossopharyngeal nerve transection triggers the remaining differentiated K8-positive taste receptor cells to dedifferentiate and acquire transient progenitor cell-like states during regeneration. Dedifferentiated taste receptor cells proliferate, express progenitor cell markers (K14, Sox2, PCNA) and form organoids in vitro. These data indicate that differentiated taste receptor cells can enter the cell cycle, acquire stemness, and participate in taste bud regeneration. We propose that dedifferentiated taste receptor cells in combination with stem/progenitor cells enhance the regeneration of taste buds following nerve injury.

Glycoprotein (GP)96 Is Essential for Maintaining Intestinal Epithelial Architecture by Supporting Its Self-Renewal Capacity

BACKGROUND & AIMS

Glycoprotein (GP)96 is an endoplasmic reticulum-resident master chaperone for cell surface receptors including the Wnt co-receptors low-density lipoprotein-receptor-related protein 5/6. Intestinal epithelial cell (IEC)-specific deletion of Gp96 is embryonically lethal. However, the role of GP96 in adult intestinal tissue and especially within the intestinal stem cell (ISC) niche is unknown. Here, we investigated how GP96 loss interferes with intestinal homeostasis by compromising viability, proliferation, and differentiation of IECs.

METHODS

Tamoxifen was used to induce Cre-mediated deletion of Gp96 in GP96-Villin^creERT2 (Cre recombinase-Estrogen-Receptor Transgene 2) mice and intestinal organoids. With H&E and immunofluorescence staining we assessed alterations in intestinal morphology and the presence and localization of IEC types. Real-time polymerase chain reaction and Western blot analysis were performed to explore the molecular mechanisms underlying the severe phenotype of Gp96 KO mice and organoids.

RESULTS

IEC-specific deletion of Gp96 in adult mice resulted in a rapid degeneration of the stem cell niche, followed by complete eradication of the epithelial layer and death within a few days. These effects were owing to severe defects in ISC renewal and premature ISC differentiation, which resulted from defective Wnt and Notch signaling. Furthermore, depletion of GP96 led to massive induction of endoplasmic reticulum stress. Although effects on ISC renewal and adequate differentiation were partly reversed upon activation of Wnt/Notch signaling, viability could not be restored, indicating that reduced viability was mediated by other mechanisms.

CONCLUSIONS

Our work shows that GP96 plays a fundamental role in regulating ISC fate and epithelial regeneration and therefore is indispensable for maintaining intestinal epithelial homeostasis.