A reserve stem cell population in small intestine renders Lgr5-positive cells dispensable

Paneth cell development in the neonatal gut: pathway regulation, development, and relevance to necrotizing enterocolitis

Paneth cells (PCs) are intestinal epithelial cells (IECs) that contain eosinophilic granules, which are located in Lieberkühn crypts. An increasing number of animal and human experiments have indicated that PCs are involved in the progression of a variety of intestinal as well as systemic inflammatory responses including necrotizing enterocolitis (NEC). NEC is an enteric acquired disease with high mortality that usually occurs in premature infants and neonates, however the underlying mechanisms remain unclear. In this review, we summarize the features of PCs, including their immune function, association with gut microbiota and intestinal stem cells, and their mechanism of regulating IEC death to explore the possible mechanisms by which PCs affect NEC.

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.

Exploiting the Receptor-Binding Domains of R-Spondin 1 to Target Leucine-Rich Repeat-Containin G-Coupled Protein Receptor 5-Expressing Stem Cells in Ovarian Cancer

Leucine-rich repeat-containing G-protein-coupled receptor (LGR5) and LGR6 mark epithelial stem cells in normal tissues and tumors. They are expressed by stem cells in the ovarian surface and fallopian tube epithelia from which ovarian cancer arises. High-grade serous ovarian cancer is unique in expressing unusually high levels of LGR5 and LGR6 mRNA. R-spondins are the natural ligands for LGR5 and LGR6 to which they bind with nanomolar affinity. To target stem cells in ovarian cancer, we used the sortase reaction to site-specifically conjugate the potent cytotoxin monomethyl auristatin E (MMAE) via a protease sensitive linker to the two furin-like domains of RSPO1 (Fu1-Fu2) that mediate its binding to LGR5 and LGR6 and their co-receptors Zinc And Ring Finger 3 and Ring Finger Protein 43 via a protease-cleavable linker. An immunoglobulin Fc domain added to the N-terminal end served to dimerize the receptor-binding domains so that each molecule carries two MMAE. The resulting molecule, FcF2-MMAE, demonstrated: 1) selective LGR5-dependent low nanomolar cytotoxicity against ovarian cancer cells in vitro; 2) selectivity that was dependent on binding to both the LGR receptors and ubiquitin ligase co-receptors; 3) favorable stability and plasma pharmacokinetic properties when administered intravenously with an elimination half-life of 29.7 hours; 4) selective inhibition of LGR5-rich as opposed to isogenic LGR5-poor tumors in vivo; and, 5) therapeutic efficacy in three aggressive wild-type human ovarian cancer xenograft models. These results demonstrate the successful use of the Fu1-Fu2 domain of RSPO1 as a drug carrier and the ability of FcF2-MMAE to target cells in tumors that express stem cell markers. SIGNIFICANCE STATEMENT: FcF2-MMAE is a novel cancer therapeutic that exploits the high-affinity binding domains of RSPO1 to target monomethyl auristatin E to tumor stem cells that express LGR5. FcF2-MMAE has low nanomolar LGR5-dependent cytotoxicity in vitro, favorable pharmacokinetics, and differential efficacy in an isogenic LGR5-poor versus LGR5-rich ovarian cancer xenograft model when given on a weekly schedule.

Modulation of Wnt-β-catenin signaling with antibodies: therapeutic opportunities and challenges

Since the recognition that mutations in components of the Wnt-β-catenin pathway underlie some human cancers, considerable attention has been dedicated to developing therapeutic modalities to block its activity. Despite numerous efforts, no drug directly inhibiting Wnt signaling is currently clinically available. Conversely, activating the Wnt pathway in a specific manner has recently been made possible with new molecules mimicking the activity of Wnt proteins, thus offering new possibilities for controlling tissue stem cell activity and for the rational treatment of various degenerative conditions. We describe the landscape of antibody modalities that modulate the Wnt-β-catenin pathway, and detail the advances and challenges in both cancer and regenerative medicine drug development.

Dangerous liaisons: how helminths manipulate the intestinal epithelium

Intestinal helminths remain highly pervasive throughout the animal kingdom by modulating multiple aspects of the host immune response. The intestinal epithelium functions as a physical barrier as well as a sentinel innate immune tissue with the ability to sense and respond to infectious agents. Although helminths form intimate interactions with the epithelium, comprehensive knowledge about host-helminth interactions at this dynamic interface is lacking. In addition, little is known about the ability of helminths to directly shape the fate of this barrier tissue. Here, we review the diverse pathways by which helminths regulate the epithelium and highlight the emerging field of direct helminth regulation of intestinal stem cell (ISC) fate and function.

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.

Impact of enteric bacterial infections at and beyond the epithelial barrier

The mucosal lining of the gut has co-evolved with a diverse microbiota over millions of years, leading to the development of specialized mechanisms to actively limit the invasion of pathogens. However, some enteric microorganisms have adapted against these measures, developing ways to hijack or overcome epithelial micro-integrity mechanisms. This breach of the gut barrier not only enables the leakage of host factors out of circulation but can also initiate a cascade of detrimental systemic events as microbiota, pathogens and their affiliated secretions passively leak into extra-intestinal sites. Under normal circumstances, gut damage is rapidly repaired by intestinal stem cells. However, with substantial and deep perturbation to the gut lining and the systemic dissemination of gut contents, we now know that some enteric infections can cause the impairment of host regenerative processes. Although these local and systemic aspects of enteric disease are often studied in isolation, they heavily impact one another. In this Review, by examining the journey of enteric infections from initial establishment to systemic sequelae and how, or if, the host can successfully repair damage, we will tie together these complex interactions to provide a holistic overview of the impact of enteric infections at and beyond the epithelial barrier.

From organoids to bedside: Advances in modeling, decoding and targeting of colorectal cancer

Patient derived organoids closely resemble the biology of tissues and tumors. They are enabling ex vivo modeling of human diseases and dissecting key features of tumor biology like anatomical diversity or inter- and intra-tumoral heterogeneity. In the last years, organoids were established as models for drug discovery and explored to guide clinical decision making. In this review, we discuss the recent developments in organoid based research, elaborating on the developments in colorectal cancer as a prime example. We focus our review on the role of organoids to decode cancer cell dynamics and tumor microenvironmental complexity with the underlying bi-directional crosstalk. Additionally, advancements in the development of living biobanks, screening approaches, organoid based precision medicine and challenges of co-clinical trials are highlighted. We discuss ongoing efforts to overcome challenges that the field faces and indicate potential future directions.

Insights into radiation carcinogenesis based on dose-rate effects in tissue stem cells

PURPOSE

Increasing epidemiological and biological evidence suggests that radiation exposure enhances cancer risk in a dose-dependent manner. This can be attributed to the 'dose-rate effect,' where the biological effect of low dose-rate radiation is lower than that of the same dose at a high dose-rate. This effect has been reported in epidemiological studies and experimental biology, although the underlying biological mechanisms are not completely understood. In this review, we aim to propose a suitable model for radiation carcinogenesis based on the dose-rate effect in tissue stem cells.

METHODS

We surveyed and summarized the latest studies on the mechanisms of carcinogenesis. Next, we summarized the radiosensitivity of intestinal stem cells and the role of dose-rate in the modulation of stem-cell dynamics after irradiation.

RESULTS

Consistently, driver mutations can be detected in most cancers from past to present, supporting the hypothesis that cancer progression is initiated by the accumulation of driver mutations. Recent reports demonstrated that driver mutations can be observed even in normal tissues, which suggests that the accumulation of mutations is a necessary condition for cancer progression. In addition, driver mutations in tissue stem cells can cause tumors, whereas they are not sufficient when they occur in non-stem cells. For non-stem cells, tissue remodeling induced by marked inflammation after the loss of tissue cells is important in addition to the accumulation of mutations. Therefore, the mechanism of carcinogenesis differs according to the cell type and magnitude of stress. In addition, our results indicated that non-irradiated stem cells tend to be eliminated from three-dimensional cultures of intestinal stem cells (organoids) composed of irradiated and non-irradiated stem cells, supporting the stem-cell competition.

CONCLUSIONS

We propose a unique scheme in which the dose-rate dependent response of intestinal stem cells incorporates the concept of the threshold of stem-cell competition and context-dependent target shift from stem cells to whole tissue. The concept highlights four key issues that should be considered in radiation carcinogenesis: i.e. accumulation of mutations; tissue reconstitution; stem-cell competition; and environmental factors like epigenetic modifications.

Primary Cilium Identifies a Quiescent Cell Population in the Human Intestinal Crypt

Primary cilia are sensory antennae located at the cell surface which mediate a variety of extracellular signals involved in development, tissue homeostasis, stem cells and cancer. Primary cilia are found in an extensive array of vertebrae cells but can only be generated when cells become quiescent. The small intestinal epithelium is a rapidly self-renewing tissue organized into a functional unit called the crypt–villus axis, containing progenitor and differentiated cells, respectively. Terminally differentiated villus cells are notoriously devoid of primary cilia. We sought to determine if intestinal crypts contain a quiescent cell population that could be identified by the presence of primary cilia. Here we show that primary cilia are detected in a subset of cells located deep in the crypts slightly above a Paneth cell population. Using a normal epithelial proliferative crypt cell model, we show that primary cilia assembly and activity correlate with a quiescent state. These results provide further evidence for the existence of a quiescent cell population in the human small intestine and suggest the potential for new modes of regulation in stem cell dynamics.

Molecular and cellular basis of the dose-rate-dependent adverse effects of radiation exposure in animal models. Part I: Mammary gland and digestive tract

While epidemiological data are available for the dose and dose-rate effectiveness factor (DDREF) for human populations, animal models have contributed significantly to providing quantitative data with mechanistic insights. The aim of the current review is to compile both the in vitro experiments with reference to the dose-rate effects of DNA damage and repair, and the animal studies, specific to rodents, with reference to the dose-rate effects of cancer development. In particular, the review focuses especially on the results pertaining to underlying biological mechanisms and discusses their possible involvement in the process of radiation-induced carcinogenesis. Because the concept of adverse outcome pathway (AOP) together with the key events has been considered as a clue to estimate radiation risks at low doses and low dose-rates, the review scrutinized the dose-rate dependency of the key events related to carcinogenesis, which enables us to unify the underlying critical mechanisms to establish a connection between animal experimental studies with human epidemiological studies.

Temporal static and dynamic imaging of skeletal muscle in vivo

A major challenge in the study of living systems is understanding how tissues and organs are established, maintained during homeostasis, reconstituted following injury or deteriorated during disease. Most of the studies that interrogate in vivo cell biological properties of cell populations within tissues are obtained through static imaging approaches. However, in vertebrates, little is known about which, when, and how extracellular and intracellular signals are dynamically integrated to regulate cell behaviour and fates, due largely to technical challenges. Intravital imaging of cellular dynamics in mammalian models has exposed surprising properties that have been missed by conventional static imaging approaches. Here we highlight some selected examples of intravital imaging in mouse intestinal stem cells, hematopoietic stem cells, hair follicle stem cells, and neural stem cells in the brain, each of which have distinct features from an anatomical and niche-architecture perspective. Intravital imaging of mouse skeletal muscles is comparatively less advanced due to several technical constraints that will be discussed, yet this approach holds great promise as a complementary investigative method to validate findings obtained by static imaging, as well as a method for discovery.

Dissection of gastric homeostasis in vivo facilitates permanent capture of isthmus-like stem cells in vitro

The glandular stomach is composed of two regenerative compartments termed corpus and antrum, and our understanding of the transcriptional networks that maintain these tissues is incomplete. Here we show that cell types with equivalent functional roles in the corpus and antrum share similar transcriptional states including the poorly characterized stem cells of the isthmus region. To further study the isthmus, we developed a monolayer two-dimensional (2D) culture system that is continually maintained by Wnt-responsive isthmus-like cells capable of differentiating into several gastric cell types. Importantly, 2D cultures can be converted into conventional three-dimensional organoids, modelling the plasticity of gastric epithelial cells in vivo. Finally, we utilized the 2D culture system to show that Sox2 is both necessary and sufficient to generate enterochromaffin cells. Together, our data provide important insights into gastric homeostasis, establish a tractable culture system to capture isthmus cells and uncover a role for Sox2 in enterochromaffin cells.

ONECUT2 regulates RANKL-dependent enterocyte and microfold cell differentiation in the small intestine; a multi-omics study

Microfold (M) cells reside in the intestinal epithelium of Peyer's patches (PP). Their unique ability to take up and transport antigens from the intestinal lumen to the underlying lymphoid tissue is key in the regulation of the gut-associated immune response. Here, we applied a multi-omics approach to investigate the molecular mechanisms that drive M cell differentiation in mouse small intestinal organoids. We generated a comprehensive profile of chromatin accessibility changes and transcription factor dynamics during in vitro M cell differentiation, allowing us to uncover numerous cell type-specific regulatory elements and associated transcription factors. By using single-cell RNA sequencing, we identified an enterocyte and M cell precursor population. We used our newly developed computational tool SCEPIA to link precursor cell-specific gene expression to transcription factor motif activity in cis-regulatory elements, uncovering high expression of and motif activity for the transcription factor ONECUT2. Subsequent in vitro and in vivo perturbation experiments revealed that ONECUT2 acts downstream of the RANK/RANKL signalling axis to support enterocyte differentiation, thereby restricting M cell lineage specification. This study sheds new light on the mechanism regulating cell fate balance in the PP, and it provides a powerful blueprint for investigation of cell fate switches in the intestinal epithelium.

Injury-induced interleukin-1 alpha promotes Lgr5 hair follicle stem cells de novo regeneration and proliferation via regulating regenerative microenvironment in mice

BACKGROUND

The hair follicles (HFs) are barely regenerated after loss in injuries in mammals as well as in human beings. Recent studies have shown that the regenerative ability of HFs is age-related; however, the relationship between this phenomenon and the stem cell niche remains unclear. This study aimed to find a key secretory protein that promotes the HFs regeneration in the regenerative microenvironment.

METHODS

To explore why age affects HFs de novo regeneration, we established an age-dependent HFs regeneration model in leucine-rich repeat G protein-coupled receptor 5 (Lgr5) + /mTmG mice. Proteins in tissue fluids were analyzed by high-throughput sequencing. The role and mechanism of candidate proteins in HFs de novo regeneration and hair follicle stem cells (HFSCs) activation were investigated through in vivo experiments. The effects of candidate proteins on skin cell populations were investigated by cellular experiments.

RESULTS

Mice under 3-week-old (3W) could regenerate HFs and Lgr5 HFSCs, which were highly correlated with the immune cells, cytokines, IL-17 signaling pathway, and IL-1α level in the regeneration microenvironment. Additionally, IL-1α injection induced de novo regeneration of HFs and Lgr5 HFSCs in 3W mouse model with a 5 mm wound, as well as promoted activation and proliferation of Lgr5 HFSCs in 7-week-old (7W) mice without wound. Dexamethasone and TEMPOL inhibited the effects of IL-1α. Moreover, IL-1α increased skin thickness and promoted the proliferation of human epidermal keratinocyte line (HaCaT) and skin-derived precursors (SKPs) in vivo and in vitro, respectively.

CONCLUSIONS

In conclusion, injury-induced IL-1α promotes HFs regeneration by modulating inflammatory cells and oxidative stress-induced Lgr5 HFSCs regeneration as well as promoting skin cell populations proliferation. This study uncovers the underlying molecular mechanisms enabling HFs de novo regeneration in an age-dependent model.

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.

Regulation and functions of cell division in the intestinal tissue

In multicellular organisms, epithelial cells are key elements of tissue organization. In developing epithelial tissues, cellular proliferation and differentiation are under the tight regulation of morphogenetic programs to ensure correct organ formation and functioning. In these processes, proliferation rates and division orientation regulate the speed, timing and direction of tissue expansion but also its proper patterning. Moreover, tissue homeostasis relies on spatio-temporal modulations of daughter cell behavior and arrangement. These aspects are particularly crucial in the intestine, which is one of the most proliferative tissues in adults, making it a very attractive adult organ system to study the role of cell division on epithelial morphogenesis and organ function. Although epithelial cell division has been the subject of intense research for many years in multiple models, it still remains in its infancy in the context of the intestinal tissue. In this review, we focus on the current knowledge on cell division and regulatory mechanisms at play in the intestinal epithelial tissue, as well as their importance in developmental biology and physiopathology.

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.

Senescent cells perturb intestinal stem cell differentiation through Ptk7 induced noncanonical Wnt and YAP signaling

Cellular senescence and the senescence-associated secretory phenotype (SASP) are implicated in aging and age-related disease, and SASP-related inflammation is thought to contribute to tissue dysfunction in aging and diseased animals. However, whether and how SASP factors influence the regenerative capacity of tissues remains unclear. Here, using intestinal organoids as a model of tissue regeneration, we show that SASP factors released by senescent fibroblasts deregulate stem cell activity and differentiation and ultimately impair crypt formation. We identify the secreted N-terminal domain of Ptk7 as a key component of the SASP that activates non-canonical Wnt / Ca2+ signaling through FZD7 in intestinal stem cells (ISCs). Changes in cytosolic [Ca2+] elicited by Ptk7 promote nuclear translocation of YAP and induce expression of YAP/TEAD target genes, impairing symmetry breaking and stem cell differentiation. Our study discovers secreted Ptk7 as a factor released by senescent cells and provides insight into the mechanism by which cellular senescence contributes to tissue dysfunction in aging and disease.

Multi-Lineage Human Endometrial Organoids on Acellular Amniotic Membrane for Endometrium Regeneration

Asherman's syndrome is an endometrial regeneration disorder resulting from injury to the endometrial basal layer, causing the formation of scar tissue in the uterus and cervix. This usually leads to uterine infertility, menstrual disorders, and placental abnormalities. While stem cell therapy has shown extensive progress in repairing the damaged endometrium and preventing intrauterine adhesion, issues of low engraftment rates, rapid senescence, and the risk of tumorigenesis remain to be resolved for efficient and effective application of this technology in endometrial repair. This study addressed these challenges by developing a co-culture system to generate multi-lineage endometrial organoids (MLEOs) comprising endometrial epithelium organoids (EEOs) and endometrial mesenchymal stem cells (eMSCs). The efficacy of these MLEOs was investigated by seeding them on a biocompatible scaffold, the human acellular amniotic membrane (HAAM), to create a biological graft patch, which was subsequently transplanted into an injury model of the endometrium in rats. The results indicated that the MLEOs on the HAAM patch facilitated endometrial angiogenesis, regeneration, and improved pregnancy outcomes. The MLEOs on the HAAM patch could serve as a promising strategy for treating endometrial injury and preventing Asherman's syndrome.

Trends and Potential of Machine Learning and Deep Learning in Drug Study at Single-Cell Level

Cancer treatments always face challenging problems, particularly drug resistance due to tumor cell heterogeneity. The existing datasets include the relationship between gene expression and drug sensitivities; however, the majority are based on tissue-level studies. Study drugs at the single-cell level are perspective to overcome minimal residual disease caused by subclonal resistant cancer cells retained after initial curative therapy. Fortunately, machine learning techniques can help us understand how different types of cells respond to different cancer drugs from the perspective of single-cell gene expression. Good modeling using single-cell data and drug response information will not only improve machine learning for cell-drug outcome prediction but also facilitate the discovery of drugs for specific cancer subgroups and specific cancer treatments. In this paper, we review machine learning and deep learning approaches in drug research. By analyzing the application of these methods on cancer cell lines and single-cell data and comparing the technical gap between single-cell sequencing data analysis and single-cell drug sensitivity analysis, we hope to explore the trends and potential of drug research at the single-cell data level and provide more inspiration for drug research at the single-cell level. We anticipate that this review will stimulate the innovative use of machine learning methods to address new challenges in precision medicine more broadly.

RNF43 induces the turnover of protease-activated receptor 2 in colon cancer

Post-translational modification of G-protein coupled receptors (GPCRs) plays a central role in tissue hemostasis and cancer. The molecular mechanism of post-translational regulation of protease-activated receptors (PARs), a subgroup of GPCRs is yet understudied. Here we show that the cell-surface transmembrane E3 ubiquitin ligase ring finger 43 (RNF43) is a negative feedback regulator of PAR₂ , impacting PAR₂ -induced signaling and colon cancer growth. RNF43 co-associates with PAR₂ , promoting its membrane elimination and degradation as shown by reduced cell surface biotinylated PAR₂ levels and polyubiquitination. PAR₂ degradation is rescued by R-spondin2 in the presence of leucine-rich repeat-containing G-protein-coupled receptor5 (LGR5). In fact, PAR₂ acts jointly with LGR5, as recapitulated by increased β-catenin levels, transcriptional activity, phospho-LRP6, and anchorage-independent colony growth in agar. Animal models of the chemically induced AOM/DSS colon cancer of wt versus Par2/f2rl1 KO mice as also the 'spleen-liver' colon cancer metastasis, allocated a central role for PAR₂ in colon cancer growth and development. RNF43 is abundantly expressed in the Par2/f2rl1 KO-treated AOM/DSS colon tissues while its level is very low to nearly null in colon cancer adenocarcinomas of the wt mice. The same result is obtained in the 'spleen-liver' model of spleen-inoculated cells, metastasized to the liver. High RNF43 expression is observed in the liver upon shRNA -Par2 silencing. "Limited-dilution-assay" performed in mice in-vivo, assigned PAR₂ as a member of the cancer stem cell niche compartment. Collectively, we elucidate an original regulation of PAR₂ oncogene, a member of cancer stem cells, by RNF43 ubiquitin ligase. It impacts β-catenin signaling and colon cancer growth.

Role of Wnt signaling in the maintenance and regeneration of the intestinal epithelium

The intestinal epithelium plays a key role in digestion and protection against external pathogens. This tissue presents a high cellular turnover with the epithelium being completely renewed every 5days, driven by intestinal stem cells (ISCs) residing in the crypt bases. To sustain this dynamic renewal of the intestinal epithelium, the maintenance, proliferation, and differentiation of ISCs must be precisely controlled. One of the central pathways supporting ISC maintenance and dynamics is the Wnt pathway. In this chapter, we examine the role of Wnt signaling in intestinal epithelial homeostasis and tissue regeneration, including mechanisms regulating ISC identity and fine-tuning of Wnt pathway activation. We extensively discuss the contribution of the stem cell niche in maintaining Wnt signaling in the intestinal crypts that support ISC functions. The integration of these findings highlights the complex interplay of multiple niche signals and cellular components sustaining ISC behavior and maintenance, which together supports the immense plasticity of the intestinal epithelium.

Bacteroides fragilis strain ZY-312 promotes intestinal barrier integrity via upregulating the STAT3 pathway in a radiation-induced intestinal injury mouse model

Radiation-induced intestinal injury is characterized by intestinal barrier impairment. However, the therapeutic effects of probiotics for intestinal epithelial barrier repair in a mouse model of radiation-induced intestinal injury remain unclear. Previously, we isolated a strain of Bacteroides fragilis from the feces of a healthy infant and named it as B. fragilis strain ZY-312 (B. fragilis). In this study, we showed that B. fragilis can ameliorate radiation-induced intestinal injury in mice, manifested by decreased weight loss, intestinal length shortening, and intestinal epithelial cell (IEC) shedding. Moreover, we found that B. fragilis promoted IEC proliferation, stem cell regeneration, mucus secretion, and tight junction integrity by upregulating the STAT3 signaling pathway, through an experimental verification in Stat3 ^△IEC mice (STAT3 defects in intestinal epithelial cells). Thus, the underlying protective mechanism of B. fragilis in radiation-induced intestinal injury is related to IEC proliferation, stem cell regeneration, goblet cell secretion, and tight junction repair via activation of the STAT3 signaling pathway. In addition, the therapeutic effects of B. fragilis were studied to provide new insights into its application as a functional and clinical drug for radiation-induced intestinal injury after radiotherapy.

Embryogenic stem cell-derived intestinal crypt fission directs de novo crypt genesis

Intestinal epithelial replenishment is fueled by continuously dividing intestinal stem cells (ISCs) resident at the crypt niche. However, the cell type(s) enabling replenishment upon damage and subsequent loss of whole crypts remain largely unclear. Using Set domain-containing protein 4 (Setd4), we identify a small population with reserve stem cell characteristics in the mouse intestine. Upon irradiation-induced injury, Setd4-expressing (Setd4⁺) cells survive radiation exposure and then activate to produce Sca-1-expressing cell types to restore the epithelial wall and regenerate crypts de novo via crypt fission. Setd4⁺ cells are confirmed to originate from the early fetal period, subsequently contributing to the development of embryonic gut and the establishment of postnatal crypts. Setd4⁺ cells are therefore represented as both originators and key regenerators of the intestine.

c-MAF coordinates enterocyte zonation and nutrient uptake transcriptional programs

Small intestinal villi are structural and functional units present in higher vertebrates and uniquely adapted to nutrient absorption. Villus enterocytes are organized in transcriptional "zones" dedicated to specialized tasks such as absorption of specific nutrients. We report that the transcription factor c-MAF is expressed in differentiated lower and mid-villus enterocytes and is a target of BMP signaling. Maf inactivation perturbed the villus zonation program by increasing carbohydrate-related transcripts while suppressing transcripts linked to amino-acid and lipid absorption. The formation of cytoplasmic lipid droplets, shuttling dietary fat to chylomicrons, was impaired upon Maf loss indicating its role in dietary lipid handling. Maf inactivation under homeostatic conditions expanded tuft cells and led to compensatory gut lengthening, preventing weight loss. However, delayed Maf-/- enterocyte maturation impaired weight recovery after acute intestinal injury, resulting in reduced survival. Our results identify c-MAF as a regulator of the intestinal villus zonation program, while highlighting the importance of coordination between stem/progenitor and differentiation programs for intestinal regeneration.

Age disparities in intestinal stem cell quantities: a possible explanation for preterm infant susceptibility to necrotizing enterocolitis

PURPOSE

Preterm infants are more susceptible to necrotizing enterocolitis (NEC) than term Queryinfants. This may be due to a relative paucity of Lgr5⁺ or Bmi1⁺-expressing intestinal stem cells (ISCs) which are responsible for promoting intestinal recovery after injury. We hypothesized that the cellular markers of Lgr5⁺ and Bmi1⁺, which represent the two distinct ISC populations, would be lower in younger mice compared to older mice. In addition, we hypothesized that experimental NEC would result in a greater loss of Lgr5⁺ expression compared to Bmi1⁺ expression.

METHODS

Transgenic mice with EGFP-labeled Lgr5 underwent euthanasia at 10 different time points from E15 to P56 (n = 8-11/group). Lgr5⁺-expressing ISCs were quantified by GFP ELISA and Bmi1⁺ was assessed by qPCR. In addition, Lgr5^EGFP mice underwent experimental NEC via formula feeding and hypoxic and hypothermic stress. Additional portions of the intestine underwent immunostaining with anti-GFP or anti-Bmi1⁺ antibodies to confirm ELISA and PCR results. For statistical analysis, p < 0.05 was significant.

RESULTS

Lgr5⁺ and Bmi1⁺expression was lowest in embryonal and early postnatal mice and increased with age in all segments of the intestine. Experimental NEC was associated with loss of Lgr5⁺-expressing ISCs but no significant change in Bmi1⁺ expression.

CONCLUSION

Lgr5⁺ and Bmi1⁺ expression increase with age. Lgr5⁺-expressing ISCs are lower following experimental necrotizing enterocolitis while Bmi1⁺ expression remains relatively unchanged. Developing a targeted medical therapy to protect the low population of ISCs in preterm infants may promote tissue recovery and regeneration after injury from NEC.

Colon tumour cell death causes mTOR dependence by paracrine P2X4 stimulation

Solid cancers exhibit a dynamic balance between cell death and proliferation ensuring continuous tumour maintenance and growth1,2. Increasing evidence links enhanced cancer cell apoptosis to paracrine activation of cells in the tumour microenvironment initiating tissue repair programs that support tumour growth3,4, yet the direct effects of dying cancer cells on neighbouring tumour epithelia and how this paracrine effect potentially contributes to therapy resistance are unclear. Here we demonstrate that chemotherapy-induced tumour cell death in patient-derived colorectal tumour organoids causes ATP release triggering P2X4 (also known as P2RX4) to mediate an mTOR-dependent pro-survival program in neighbouring cancer cells, which renders surviving tumour epithelia sensitive to mTOR inhibition. The induced mTOR addiction in persisting epithelial cells is due to elevated production of reactive oxygen species and subsequent increased DNA damage in response to the death of neighbouring cells. Accordingly, inhibition of the P2X4 receptor or direct mTOR blockade prevents induction of S6 phosphorylation and synergizes with chemotherapy to cause massive cell death induced by reactive oxygen species and marked tumour regression that is not seen when individually applied. Conversely, scavenging of reactive oxygen species prevents cancer cells from becoming reliant on mTOR activation. Collectively, our findings show that dying cancer cells establish a new dependency on anti-apoptotic programs in their surviving neighbours, thereby creating an opportunity for combination therapy in P2X4-expressing epithelial tumours.

The Impacts of Iron Overload and Ferroptosis on Intestinal Mucosal Homeostasis and Inflammation

Intestinal homeostasis is maintained through the interplay of the intestinal mucosa, local and systemic immune factors, and the microbial content of the gut. Iron is a trace mineral in most organisms, including humans, which is essential for growth, systemic metabolism and immune response. Paradoxically, excessive iron intake and/or high iron status can be detrimental to iron metabolism in the intestine and lead to iron overload and ferroptosis-programmed cell death mediated by iron-dependent lipid peroxidation within cell membranes, which contributes to several intestinal diseases. In this review, we comprehensively review recent findings on the impacts of iron overload and ferroptosis on intestinal mucosal homeostasis and inflammation and then present the progress of iron overload and ferroptosis-targeting therapy in intestinal diseases. Understanding the involved mechanisms can provide a new understanding of intestinal disease pathogenesis and facilitate advanced preventive and therapeutic strategies for intestinal dysfunction and diseases.

Establishment of a chemical tongue injury-recovery mouse model

Tongue epithelium is one of the most proliferative and regenerative epithelia in our body. However, tongue stem cell research is hampered partly by the lack of optimal animal models to study tongue injury, repair, and regeneration. Here, we establish a novel chemically induced tongue injury-recovery mouse model. Focal application of sodium hydroxide for a limited time led to the denudation of suprabasal layers, leaving the basal layer. Time course study revealed that tongue epithelial cells robustly proliferate over one week after the tongue injury. Importantly, we demonstrated that our novel mouse model could be employed in the lineage tracing of the tongue stem cells under the injury and repair process and further showed that tongue stem cells proliferate faster and generate larger clones in the injury condition than in the steady state condition. Our data indicate the development of a novel chemically induced tongue injury-recovery mouse model for tongue stem cell research, which will significantly facilitate the preclinical study for the pathogenesis and treatment of caustic ingestion.

Transit-amplifying cells control R-spondins in the mouse crypt to modulate intestinal stem cell proliferation

Intestinal epithelium regenerates rapidly through proliferation of intestinal stem cells (ISCs), orchestrated by potent mitogens secreted within the crypt niche. However, mechanisms regulating these mitogenic factors remain largely unknown. Here, we demonstrate that transit-amplifying (TA) cells, marked by unconventional prefoldin RPB5 interactor (URI), control R-spondin production to guide ISC proliferation. Genetic intestinal URI ablation in mice injures TA cells, reducing their survival capacity, leading to an inflamed tissue and subsequently decreasing R-spondin levels, thereby causing ISC quiescence and disruption of intestinal structure. R-spondin supplementation or restoration of R-spondin levels via cell death inhibition by c-MYC elimination or the suppression of inflammation reinstates ISC proliferation in URI-depleted mice. However, selective c-MYC and p53 suppression are required to fully restore TA cell survival and differentiation capacity and preserve complete intestinal architecture. Our data reveal an unexpected role of TA cells, which represent a signaling platform instrumental for controlling inflammatory cues and R-spondin production, essential for maintaining ISC proliferation and tissue regeneration.

Autophagic state prospectively identifies facultative stem cells in the intestinal epithelium

The intestinal epithelium exhibits a rapid and efficient regenerative response to injury. Emerging evidence supports a model where plasticity of differentiated cells, particularly those in the secretory lineages, contributes to epithelial regeneration upon ablation of injury-sensitive stem cells. However, such facultative stem cell activity is rare within secretory populations. Here, we ask whether specific functional properties predict facultative stem cell activity. We utilize in vivo labeling combined with ex vivo organoid formation assays to evaluate how cell age and autophagic state contribute to facultative stem cell activity within secretory lineages. Strikingly, we find that cell age (time elapsed since cell cycle exit) does not correlate with secretory cell plasticity. Instead, high autophagic vesicle content predicts plasticity and resistance to DNA damaging injury independently of cell lineage. Our findings indicate that autophagic status prior to injury serves as a lineage-agnostic marker for the prospective identification of facultative stem cells.

The impact of targeted ablation of one row of outer hair cells and Deiters' cells on cochlear amplification

The mammalian cochlea contains three rows of outer hair cells (OHCs) that amplify the basilar membrane traveling wave with high gain and exquisite tuning. The pattern of OHC loss caused by typical methods of producing hearing loss in animal models (noise, ototoxic exposure, or aging) is variable and not consistent along the length of the cochlea. Thus, it is difficult to use these approaches to understand how forces from multiple OHCs summate to create normal cochlear amplification. Here, we selectively removed the third row of OHCs and Deiters' cells in adult mice and measured cochlear amplification. In the mature cochlear epithelia, expression of the Wnt target gene Lgr5 is restricted to the third row of Deiters' cells, the supporting cells directly underneath the OHCs. Diphtheria toxin administration to Lgr5DTR-EGFP/+ mice selectively ablated the third row of Deiters' cells and the third row of OHCs. Basilar membrane vibration in vivo demonstrated disproportionately lower reduction in cochlear amplification by about 13.5 dB. On a linear scale, this means that the 33% reduction in OHC number led to a 79% reduction in gain. Thus, these experimental data describe the impact of reducing the force of cochlear amplification by a specific amount. Furthermore, these data argue that because OHC forces progressively and sequentially amplify the traveling wave as it travels to its peak, the loss of even a relatively small number of OHCs, when evenly distributed longitudinally, will cause a substantial reduction in cochlear amplification.NEW & NOTEWORTHY Normal cochlear physiology involves force production from three rows of outer hair cells to amplify and tune the traveling wave. Here, we used a genetic approach to target and ablate the third row of outer hair cells in the mouse cochlea and found it reduced cochlear amplification by 79%. This means that the loss of even a relatively small number of OHCs, when evenly distributed, causes a substantial reduction in cochlear amplification.

Identification of Quiescent LGR5+ Stem Cells in the Human Colon

BACKGROUND & AIMS

In the mouse intestinal epithelium, Lgr5⁺ stem cells are vulnerable to injury, owing to their predominantly cycling nature, and their progenies de-differentiate to replenish the stem cell pool. However, how human colonic stem cells behave in homeostasis and during regeneration remains unknown.

METHODS

Transcriptional heterogeneity among colonic epithelial cells was analyzed by means of single-cell RNA sequencing analysis of human and mouse colonic epithelial cells. To trace the fate of human colonic stem or differentiated cells, we generated LGR5-tdTomato, LGR5-iCasase9-tdTomato, LGR5-split-Cre, and KRT20-ERCreER knock-in human colon organoids via genome engineering. p27⁺ dormant cells were further visualized with the p27-mVenus reporter. To analyze the dynamics of human colonic stem cells in vivo, we orthotopically xenotransplanted fluorescence-labeled human colon organoids into immune-deficient mice. The cell cycle dynamics in xenograft cells were evaluated using 5-ethynyl-2'-deoxyuridine pulse-chase analysis. The clonogenic capacity of slow-cycling human stem cells or differentiated cells was analyzed in the context of homeostasis, LGR5 ablation, and 5-fluorouracil-induced mucosal injury.

RESULTS

Single-cell RNA sequencing analysis illuminated the presence of nondividing LGR5⁺ stem cells in the human colon. Visualization and lineage tracing of slow-cycling LGR5⁺p27⁺ cells and orthotopic xenotransplantation validated their homeostatic lineage-forming capability in vivo, which was augmented by 5-FU-induced mucosal damage. Transforming growth factor-β signaling regulated the quiescent state of LGR5⁺ cells. Despite the plasticity of differentiated KRT20⁺ cells, they did not display clonal growth after 5-FU-induced injury, suggesting that occupation of the niche environment by LGR5⁺p27⁺ cells prevented neighboring differentiated cells from de-differentiating.

CONCLUSIONS

Our results highlight the quiescent nature of human LGR5⁺ colonic stem cells and their contribution to post-injury regeneration.

Combining single-cell sequencing data to construct a prognostic signature to predict survival, immune microenvironment, and immunotherapy response in gastric cancer patients

Background and objective

Gastric cancer (GC) represents a major factor inducing global cancer-associated deaths, but specific biomarkers and therapeutic targets for GC are lacking at present. Therefore, the present work focused on developing an immune-related genetic signature at the single-cell level for categorizing GC cases and predicting patient prognostic outcome, immune status as well as treatment response.

Methods

Single-cell RNA-sequencing (scRNA-seq) data were combined with bulk RNA-seq data in GC patients for subsequent analyses. Differences in overall survival (OS), genomic alterations, immune status, together with estimated immunotherapeutic outcomes were measured between different groups.

Results

Nine cell types were identified by analyzing scRNA-seq data from GC patients, and marker genes of immune cells were also selected for subsequent analysis. In addition, an immune-related signature was established to predict OS while validating the prediction power for GC patients. Afterwards, a nomogram with high accuracy was constructed for improving our constructed signature’s clinical utility. The low-risk group was featured by high tumor mutation burden (TMB), increased immune activation, and microsatellite instability-high (MSI-H), which were related to the prolonged OS and used in immunotherapy. By contrast, high-risk group was associated with microsatellite stability (MSS), low TMB and immunosuppression, which might be more suitable for targeted therapy. Meanwhile, the risk score generated by our signature was markedly related to the cancer stem cell (CSC) index. In addition, the immunotherapeutic response prediction accuracy of our signature was validated in an external dataset IMvigor210 cohort.

Conclusion

A signature was constructed according to scRNA-seq data analysis. The signature-screened low- and high-risk patients had different prognoses, immune statuses and enriched functions and pathways. Such results shed more lights on immune status of GC, prognosis assessment, and development of efficient immunotherapeutic treatments.

Organoids as a Model System for Studying Notch Signaling in Intestinal Epithelial Homeostasis and Intestinal Cancer

Organoid culture is an approach that allows three-dimensional growth for stem cells to self-organize and develop multicellular structures. Intestinal organoids have been widely used to study cellular or molecular processes in stem cell and cancer research. These cultures possess the ability to maintain cellular complexity as well as recapitulate many properties of the human intestinal epithelium, thereby providing an ideal in vitro model to investigate cellular and molecular signaling pathways. These include, but are not limited to, the mechanisms required for maintaining balanced populations of epithelial cells. Notch signaling is one of the major pathways of regulating stem cell functions in the gut, driving proliferation and controlling cell fate determination. Notch also plays an important role in regulating tumor progression and metastasis. Understanding how Notch pathway regulates epithelial regeneration and differentiation by using intestinal organoids is critical for studying both homeostasis and pathogenesis of intestinal stem cells that can lead to discoveries of new targets for drug development to treat intestinal diseases. In addition, use of patient-derived organoids can provide effective personalized medicine. This review summarizes the current literature regarding epithelial Notch pathways regulating intestinal homeostasis and regeneration, highlighting the use of organoid cultures and their potential therapeutic applications.

Ectopically Localized Epithelial Cell Clumps in Ulcers Are Derived from Reserved Crypt Stem Cells in a Mouse Model of Ulcerative Colitis

BACKGROUND

We previously reported that clumps of a few epithelial cells were scattered in ulcer regions in a dextran sulfate sodium (DSS)-induced mouse model of ulcerative colitis (UC).

AIMS

To determine the ectopically localized epithelial clumps might be derived from stem cells or their daughter progenitor cells.

METHODS

Female BALB/c mice were administered DSS in drinking water for 6 days, followed by withdrawal of DSS for 6 days. Histological and immunohistochemical examinations were conducted in the distal region and proximal region of the colorectum to determine expression of stem cell markers in the epithelial clumps.

RESULTS

Similar to the characteristics of UC, the ulcers were more severe in the distal region close to the anus than in the proximal region of the colorectum. Quantitative analyses revealed that the epithelial clumps appeared in relation to the severity of the ulcer, and they expressed the cell adhesion molecules E-cadherin and β-catenin. Among stem cell markers, the epithelial clumps primarily expressed +5 cell marker Dll1 as reserved intestinal stem cells, followed by +4 cell marker Bmi1 and crypt stem cell marker Lgr5 in that order. Nuclear expression of Sox9, but not nuclear β-catenin, was identified in the clumps.

CONCLUSION

The present results suggest that most epithelial clumps comprised crypt-derived, reserved stem cells, which might have potential for mucosal healing.

Spotlighting adult stem cells: advances, pitfalls, and challenges

The existence of stem cells (SCs) at the tip of the cellular differentiation hierarchy has fascinated the scientific community ever since their discovery in the early 1950s to 1960s. Despite the remarkable success of the SC theory and the development of SC-based treatments, fundamental features of SCs remain enigmatic. Recent advances in single-cell lineage tracing, live imaging, and genomic technologies have allowed capture of life histories and transcriptional signatures of individual cells, leaving SCs much less space to 'hide'. Focusing on epithelial SCs and comparing them to other SCs, we discuss new paradigms of the SC niche, dynamics, and pathology, highlighting key open questions in SC biology that need to be resolved for harnessing SC potential in regenerative medicine.

Pleiotropic effects of DCLK1 in cancer and cancer stem cells

Doublecortin-like kinase 1 (DCLK1), a protein molecule, has been identified as a tumor stem cell marker in the cancer cells of gastrointestinal, pancreas, and human colon. DCLK1 expression in cancers, such as breast carcinoma, lung carcinoma, hepatic cell carcinoma, tuft cells, and human cholangiocarcinoma, has shown a way to target the DCLK1 gene and downregulate its expression. Several studies have discussed the inhibition of tumor cell proliferation along with neoplastic cell arrest when the DCLK1 gene, which is expressed in both cancer and normal cells, was targeted successfully. In addition, previous studies have shown that DCLK1 plays a vital role in various cancer metastases. The correlation of DCLK1 with numerous stem cell receptors, signaling pathways, and genes suggests its direct or an indirect role in promoting tumorigenesis. Moreover, the impact of DCLK1 was found to be related to the functioning of an oncogene. The downregulation of DCLK1 expression by using targeted strategies, such as embracing the use of siRNA, miRNA, CRISPR/Cas9 technology, nanomolecules, specific monoclonal antibodies, and silencing the pathways regulated by DCLK1, has shown promising results in both in vitro and in vivo studies on gastrointestinal (GI) cancers. In this review, we will discuss about the present understanding of DCLK1 and its role in the progression of GI cancer and metastasis.

Clone wars: From molecules to cell competition in intestinal stem cell homeostasis and disease

The small intestine is among the fastest self-renewing tissues in adult mammals. This rapid turnover is fueled by the intestinal stem cells residing in the intestinal crypt. Wnt signaling plays a pivotal role in regulating intestinal stem cell renewal and differentiation, and the dysregulation of this pathway leads to cancer formation. Several studies demonstrate that intestinal stem cells follow neutral drift dynamics, as they divide symmetrically to generate other equipotent stem cells. Competition for niche space and extrinsic signals in the intestinal crypt is the governing mechanism that regulates stemness versus cell differentiation, but the underlying molecular mechanisms are still poorly understood, and it is not yet clear how this process changes during disease. In this review, we highlight the mechanisms that regulate stem cell homeostasis in the small intestine, focusing on Wnt signaling and its regulation by RNF43 and ZNRF3, key inhibitors of the Wnt pathway. Furthermore, we summarize the evidence supporting the current model of intestinal stem cell regulation, highlighting the principles of neutral drift at the basis of intestinal stem cell homeostasis. Finally, we discuss recent studies showing how cancer cells bypass this mechanism to gain a competitive advantage against neighboring normal cells.

Stem cells in the gut rapidly renew themselves through processes that cancer cells co-opt to trigger tumor development. Gabriele Colozza from the Institute of Molecular Biotechnology in Vienna, Austria, and colleagues review how a network of critical molecular signals and competition for limited space help to regulate the dynamics of stem cells in the intestines. The correct balance between self-renewal and differentiation is tightly controlled by the so-called Wnt signaling pathway and its inhibitors. Competition between dividing cells in the intestinal crypts, the locations between finger-like protrusions in the gut where stem cells are found, provides another protective mechanism against runaway stem cell growth. However, intestinal cancer cells, thanks to their activating mutations, bypass these safeguards to gain a survival advantage. Drugs that target these ‘super-competitive’ behaviors could therefore help combat tumor proliferation.

Ablating Lgr5-expressing prostatic stromal cells activates the ERK-mediated mechanosensory signaling and disrupts prostate tissue homeostasis

Functional implication of stromal heterogeneity in the prostate remains incompletely understood. Using lineage tracing and light-sheet imaging, we show that some fibroblast cells at the mouse proximal prostatic ducts and prostatic urethra highly express Lgr5. Genetic ablation of these anatomically restricted stromal cells, but not nonselective ablation of prostatic stromal cells, rapidly induces prostate epithelial turnover and dedifferentiation that are reversed following spontaneous restoration of the Lgr5+ stromal cells. RNA sequencing (RNA-seq) analysis indicates that ablating the Lgr5+ stromal cells activates a mechanosensory response. Ablating the Lgr5+ stromal cells impairs the control of prostatic ductal outlet, increases prostate tissue stiffness, and activates the mitogen-activated protein kinase (MAPK). Suppressing MAPK overrides the elevated epithelial proliferation. In summary, the Lgr5+ stromal cells regulate prostate tissue homeostasis and maintain its functional integrity in a long-distance manner. Our study implies that the cells at organ junctions most likely control organ homeostasis by sustaining a balanced mechanoforce.

Modification of Diet to Reduce the Stemness and Tumorigenicity of Murine and Human Intestinal Cells

Scope

Black raspberries (BRBs) have colorectal cancer (CRC) chemo‐preventative effects. As CRC originates from an intestinal stem cell (ISC) this study has investigated the impact of BRBs on normal and mutant ISCs.

Methods and results

Mice with an inducible Apc^fl mutation in either the ISC (Lgr5CreER^T2) or intestinal crypt (AhCre/VillinCreER^T2) are fed a control or 10% BRB‐supplemented diet. This study uses immunohistochemistry, gene expression analysis, and organoid culture to evaluate the effect of BRBs on intestinal homeostasis. RNAscope is performed for ISC markers on CRC adjacent normal colonic tissue pre and post BRB intervention from patients. 10% BRB diet has no overt effect on murine intestinal homeostasis, despite a reduced stem cell number. Following Apc ISC deletion, BRB diet extends lifespan and reduces tumor area. In the AhCre model, BRB diet attenuates the “crypt‐progenitor” phenotype and reduces ISC marker gene expression. In ex vivo culture BRBs reduce the self‐renewal capacity of murine and human Apc deficient organoids. Finally, the study observes a reduction in ISC marker gene expression in adjacent normal crypts following introduction of BRBs to the human bowel.

Conclusion

BRBs play a role in CRC chemoprevention by protectively regulating the ISC compartment and further supports the use of BRBs in CRC prevention.

Lymphangiocrine signals are required for proper intestinal repair after cytotoxic injury

The intestinal epithelium undergoes continuous renewal and has an exceptional capacity to regenerate after injury. Maintenance and proliferation of intestinal stem cells (ISCs) are regulated by their surrounding niche, largely through Wnt signaling. However, it remains unclear which niche cells produce signals during different injury states, and the role of endothelial cells (ECs) as a component of the ISC niche during homeostasis and after injury has been underappreciated. Here, we show that lymphatic endothelial cells (LECs) reside in proximity to crypt epithelial cells and secrete molecules that support epithelial renewal and repair. LECs are an essential source of Wnt signaling in the small intestine, as loss of LEC-derived Rspo3 leads to a lower number of stem and progenitor cells and hinders recovery after cytotoxic injury. Together, our findings identify LECs as an essential niche component for optimal intestinal recovery after cytotoxic injury.

Dynamic and adaptive cancer stem cell population admixture in colorectal neoplasia

Intestinal homeostasis is underpinned by LGR5+ve crypt-base columnar stem cells (CBCs), but following injury, dedifferentiation results in the emergence of LGR5-ve regenerative stem cell populations (RSCs), characterized by fetal transcriptional profiles. Neoplasia hijacks regenerative signaling, so we assessed the distribution of CBCs and RSCs in mouse and human intestinal tumors. Using combined molecular-morphological analysis, we demonstrate variable expression of stem cell markers across a range of lesions. The degree of CBC-RSC admixture was associated with both epithelial mutation and microenvironmental signaling disruption and could be mapped across disease molecular subtypes. The CBC-RSC equilibrium was adaptive, with a dynamic response to acute selective pressure, and adaptability was associated with chemoresistance. We propose a fitness landscape model where individual tumors have equilibrated stem cell population distributions along a CBC-RSC phenotypic axis. Cellular plasticity is represented by position shift along this axis and is influenced by cell-intrinsic, extrinsic, and therapeutic selective pressures.

Ribosome impairment regulates intestinal stem cell identity via ZAKɑ activation

The small intestine is a rapidly proliferating organ that is maintained by a small population of Lgr5-expressing intestinal stem cells (ISCs). However, several Lgr5-negative ISC populations have been identified, and this remarkable plasticity allows the intestine to rapidly respond to both the local environment and to damage. However, the mediators of such plasticity are still largely unknown. Using intestinal organoids and mouse models, we show that upon ribosome impairment (driven by Rptor deletion, amino acid starvation, or low dose cyclohexamide treatment) ISCs gain an Lgr5-negative, fetal-like identity. This is accompanied by a rewiring of metabolism. Our findings suggest that the ribosome can act as a sensor of nutrient availability, allowing ISCs to respond to the local nutrient environment. Mechanistically, we show that this phenotype requires the activation of ZAKɑ, which in turn activates YAP, via SRC. Together, our data reveals a central role for ribosome dynamics in intestinal stem cells, and identify the activation of ZAKɑ as a critical mediator of stem cell identity.

Intestinal stem cells are responsible for replenishing cells within the high-turnover intestinal epithelium. Here they show that ribosome dynamics affect intestinal stem cell identity through a mechanism that is triggered by changes in nutrient availability.

Intestinal Epithelial Regeneration in Response to Ionizing Irradiation

The intestinal epithelium consists of a single layer of cells yet contains multiple types of terminally differentiated cells, which are generated by the active proliferation of intestinal stem cells located at the bottom of intestinal crypts. However, during events of acute intestinal injury, these active intestinal stem cells undergo cell death. Gamma irradiation is a widely used colorectal cancer treatment, which, while therapeutically efficacious, has the side effect of depleting the active stem cell pool. Indeed, patients frequently experience gastrointestinal radiation syndrome while undergoing radiotherapy, in part due to active stem cell depletion. The loss of active intestinal stem cells in intestinal crypts activates a pool of typically quiescent reserve intestinal stem cells and induces dedifferentiation of secretory and enterocyte precursor cells. If not for these cells, the intestinal epithelium would lack the ability to recover from radiotherapy and other such major tissue insults. New advances in lineage-tracing technologies allow tracking of the activation, differentiation, and migration of cells during regeneration and have been successfully employed for studying this in the gut. This study aims to depict a method for the analysis of cells within the mouse intestinal epithelium following radiation injury.

The Hippo–YAP/TAZ Signaling Pathway in Intestinal Self-Renewal and Regeneration After Injury

The Hippo pathway and its downstream effectors, the transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), control stem cell fate and cell proliferation and differentiation and are essential for tissue self-renewal and regeneration. YAP/TAZ are the core components of the Hippo pathway and they coregulate transcription when localized in the nucleus. The intestinal epithelium undergoes well-regulated self-renewal and regeneration programs to maintain the structural and functional integrity of the epithelial barrier. This prevents luminal pathogen attack, and facilitates daily nutrient absorption and immune balance. Inflammatory bowel disease (IBD) is characterized by chronic relapsing inflammation of the entire digestive tract. Impaired mucosal healing is a prominent biological feature of IBD. Intestinal self-renewal is primarily dependent on functional intestinal stem cells (ISCs), especially Lgr5⁺ crypt base columnar (CBC) cells and transient-amplifying (TA) cells in the crypt base. However, intestinal wound healing is a complicated process that is often associated with epithelial cells, and mesenchymal and immune cells in the mucosal microenvironment. Upon intestinal injury, nonproliferative cells rapidly migrate towards the wound bed to reseal the damaged epithelium, which is followed by cell proliferation and differentiation. YAP is generally localized in the nucleus of Lgr5⁺ CBC cells, where it transcriptionally regulates the expression of the ISC marker Lgr5 and plays an important role in intestinal self-renewal. YAP/TAZ are the primary mechanical sensors of the cellular microenvironment. Their functions include expanding progenitor and stem cell populations, reprogramming differentiated cells into a primitive state, and mediating the regenerative function of reserve stem cells. Thus, YAP/TAZ play extremely crucial roles in epithelial repair after damage. This review provides an overview of the Hippo–YAP/TAZ signaling pathway and the processes of intestinal self-renewal and regeneration. In particular, we summarize the roles of YAP/TAZ in the phases of intestinal self-renewal and regeneration to suggest a potential strategy for IBD treatment.

Aquaporins in Cancer Biology

Aquaporins (AQPs) are a family of transmembrane water channel proteins, which were initially characterized as a novel protein family that plays a vital role in transcellular and transepithelial water movement. AQP1, AQP2, AQP4, AQP5, and AQP8 are primarily water selective, whereas AQP3, AQP7, AQP9, and AQP10 (called “aqua-glyceroporins”) also transport glycerol and other small solutes. Recently, multiple reports have suggested that AQPs have important roles in cancer cell growth, migration, invasion, and angiogenesis, each of which is important in human carcinogenesis. Here, we review recent data concerning the involvement of AQPs in tumor growth, angiogenesis, and metastasis and explore the expression profiles from various resected cancer samples to further dissect the underlying molecular mechanisms. Moreover, we discuss the potential role of AQPs during the development of genomic instability and performed modeling to describe the integration of binding between AQPs with various SH3 domain binning adaptor molecules. Throughout review and discussion of numerous reports, we have tried to provide key evidence that AQPs play key roles in tumor biology, which may provide a unique opportunity in designing a novel class of anti-tumor agents.

ADAMTS18+ villus tip telocytes maintain a polarized VEGFA signaling domain and fenestrations in nutrient-absorbing intestinal blood vessels

The small intestinal villus tip is the first point of contact for lumen-derived substances including nutrients and microbial products. Electron microscopy studies from the early 1970s uncovered unusual spatial organization of small intestinal villus tip blood vessels: their exterior, epithelial-facing side is fenestrated, while the side facing the villus stroma is non-fenestrated, covered by pericytes and harbors endothelial nuclei. Such organization optimizes the absorption process, however the molecular mechanisms maintaining this highly specialized structure remain unclear. Here we report that perivascular LGR5⁺ villus tip telocytes (VTTs) are necessary for maintenance of villus tip endothelial cell polarization and fenestration by sequestering VEGFA signaling. Mechanistically, unique VTT expression of the protease ADAMTS18 is necessary for VEGFA signaling sequestration through limiting fibronectin accumulation. Therefore, we propose a model in which LGR5⁺ ADAMTS18⁺ telocytes are necessary to maintain a “just-right” level and location of VEGFA signaling in intestinal villus blood vasculature to ensure on one hand the presence of sufficient endothelial fenestrae, while avoiding excessive leakiness of the vessels and destabilization of villus tip epithelial structures.

The molecular mechanisms ensuring the specialized structure of small intestinal villus tip blood vessels are incompletely understood. Here the authors show that ADAMTS18⁺ telocytes maintain a “just-right” level and location of VEGFA signaling on intestinal villus blood vessels, thereby ensuring the presence of endothelial fenestrae for nutrient absorption, while avoiding excessive leakiness and destabilization of villus tip epithelial structures.