Notch signalling regulates asymmetric division and inter-conversion between lgr5 and bmi1 expressing intestinal stem cells

Critical Signaling Transduction Pathways and Intestinal Barrier: Implications for Pathophysiology and Therapeutics

The intestinal barrier is a sum of the functions and structures consisting of the intestinal mucosal epithelium, mucus, intestinal flora, secretory immunoglobulins, and digestive juices. It is the first-line defense mechanism that resists nonspecific infections with powerful functions that include physical, endocrine, and immune defenses. Health and physiological homeostasis are greatly dependent on the sturdiness of the intestinal barrier shield, whose dysfunction can contribute to the progression of numerous types of intestinal diseases. Disorders of internal homeostasis may also induce barrier impairment and form vicious cycles during the response to diseases. Therefore, the identification of the underlying mechanisms involved in intestinal barrier function and the development of effective drugs targeting its damage have become popular research topics. Evidence has shown that multiple signaling pathways and corresponding critical molecules are extensively involved in the regulation of the barrier pathophysiological state. Ectopic expression or activation of signaling pathways plays an essential role in the process of shield destruction. Although some drugs, such as molecular or signaling inhibitors, are currently used for the treatment of intestinal diseases, their efficacy cannot meet current medical requirements. In this review, we summarize the current achievements in research on the relationships between the intestinal barrier and signaling pathways. The limitations and future perspectives are also discussed to provide new horizons for targeted therapies for restoring intestinal barrier function that have translational potential.

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.

Lactobacillus rhamnosus GG Promotes Recovery of the Colon Barrier in Septic Mice through Accelerating ISCs Regeneration

Disruption of the intestinal barrier is both the cause and result of sepsis. The proliferation and differentiation of intestinal stem cells (ISCs) promote the regenerative nature of intestinal epithelial cells, repairing the injured intestinal mucosal barrier; however, it is uncertain whether the recovery effects mediated by the ISCs are related to the gut microbiota. This research found that the survival rate of septic mice was improved with a Lactobacillus rhamnosus GG (LGG) treatment. Furthermore, an increased proliferation and decreased apoptosis in colon epithelial cells were observed in the LGG-treated septic mice. In vitro, we found that a LGG supernatant was effective in maintaining the colonoid morphology and proliferation under the damage of TNF-α. Both in the mice colon and the colonoid, the LGG-induced barrier repair process was accompanied by an increased expression of Lgr5⁺ and lysozyme⁺ cells. This may be attributed to the upregulation of the IL-17, retinol metabolism, NF-kappa B and the MAPK signaling pathways, among which, Tnfaip3 and Nfkbia could be used as two potential biomarkers for LGG in intestinal inflammation therapy. In conclusion, our finding suggests that LGG protects a sepsis-injured intestinal barrier by promoting ISCs regeneration, highlighting the protective mechanism of oral probiotic consumption in sepsis.

Distinct but interchangeable subpopulations of colorectal cancer cells with different growth fates and drug sensitivity

Dynamic changes in cell properties lead to intratumor heterogeneity; however, the mechanisms of nongenetic cellular plasticity remain elusive. When the fate of each cell from colorectal cancer organoids was tracked through a clonogenic growth assay, the cells showed a wide range of growth ability even within the clonal organoids, consisting of distinct subpopulations; the cells generating large spheroids and the cells generating small spheroids. The cells from the small spheroids generated only small spheroids (S-pattern), while the cells from the large spheroids generated both small and large spheroids (D-pattern), both of which were tumorigenic. Transition from the S-pattern to the D-pattern occurred by various extrinsic triggers, in which Notch signaling and Musashi-1 played a key role. The S-pattern spheroids were resistant to chemotherapy and transited to the D-pattern upon drug treatment through Notch signaling. As the transition is linked to the drug resistance, it can be a therapeutic target.

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.

A gut-centric view of aging: Do intestinal epithelial cells contribute to age-associated microbiota changes, inflammaging, and immunosenescence?

Intestinal epithelial cells (IECs) serve as both a physical and an antimicrobial barrier against the microbiota, as well as a conduit for signaling between the microbiota and systemic host immunity. As individuals age, the balance between these systems undergoes a myriad of changes due to age-associated changes to the microbiota, IECs themselves, immunosenescence, and inflammaging. In this review, we discuss emerging data related to age-associated loss of intestinal barrier integrity and posit that IEC dysfunction may play a central role in propagating age-associated alterations in microbiota composition and immune homeostasis.

Panoramic view of microRNAs in regulating cancer stem cells

Cancer stem cells (CSCs) are a subgroup of tumor cells, possessing the abilities of self-renewal and generation of heterogeneous tumor cell lineages. They are believed to be responsible for tumor initiation, metastasis, as well as chemoresistance in human malignancies. MicroRNAs (miRNAs) are small noncoding RNAs that play essential roles in various cellular activities including CSC initiation and CSC-related properties. Mature miRNAs with ∼22 nucleotides in length are generated from primary miRNAs via its precursors by miRNA-processing machinery. Extensive studies have demonstrated that mature miRNAs modulate CSC initiation and stemness features by regulating multiple pathways and targeting stemness-related factors. Meanwhile, both miRNA precursors and miRNA-processing machinery can also affect CSC properties, unveiling a new insight into miRNA function. The present review summarizes the roles of mature miRNAs, miRNA precursors, and miRNA-processing machinery in regulating CSC properties with a specific focus on the related molecular mechanisms, and also outlines the potential application of miRNAs in cancer diagnosis, predicting prognosis, as well as clinical therapy.

The role of intestinal stem cell within gut homeostasis: Focusing on its interplay with gut microbiota and the regulating pathways

Intestinal stem cells (ISCs) play an important role in maintaining intestinal homeostasis via promoting a healthy gut barrier. Within the stem cell niche, gut microbiota linking the crosstalk of dietary influence and host response has been identified as a key regulator of ISCs. Emerging insights from recent research reveal that ISC and gut microbiota interplay regulates epithelial self-renewal. This article reviews the recent knowledge on the key role of ISC in their local environment (stem cell niche) associating with gut microbiota and their metabolites as well as the signaling pathways. The current progress of intestinal organoid culture is further summarized. Subsequently, the key challenges and future directions are discussed.

Asymmetric Cell Division and Tumor Heterogeneity

Asymmetric cell division (ACD) gives rise to two daughter cells with different fates after mitosis and is a fundamental process for generating cell diversity and for the maintenance of the stem cell population. The cancer stem cell (CSC) theory suggests that CSCs with dysregulated self-renewal and asymmetric cell division serve as a source of intra-tumoral heterogeneity. This heterogeneity complicates the diagnosis and treatment of cancer patients, because CSCs can give rise to aggressive clones that are metastatic and insensitive to multiple drugs, or to dormant tumor cells that are difficult to detect. Here, we review the regulatory mechanisms and biological significance of asymmetric division in tumor cells, with a focus on ACD-induced tumor heterogeneity in early tumorigenesis and cancer progression. We will also discuss how dissecting the relationship between ACD and cancer may help us find new approaches for combatting this heterogeneity.

Glycans that regulate Notch signaling in the intestine

Intestinal homeostasis is key to the maintenance of good health. The small intestine plays important roles in absorption, digestion, hormonal and immune functions. Crypt base columnar (CBC) stem cells residing at the bottom of crypts are nurtured by Paneth cells, and together create the stem cell niche, the foundation of intestinal homeostasis. CBC stem cells replicate to replenish their number, or differentiate into a variety of epithelial cells with specialized functions. Notch signaling is a cell-cell signaling pathway that regulates both the proliferation and differentiation of CBC stem cells. NOTCH1 and NOTCH2 stimulated by canonical Notch ligands DLL1 and DLL4 mediate Notch signaling in the intestine that, in concert with other signaling pathways including the WNT and BMP pathways, determines cell fates. Importantly, interactions between Notch receptors and canonical Notch ligands are regulated by O-glycans linked to Ser/Thr in epidermal growth factor-like (EGF) repeats of the Notch receptor extracellular domain (NECD). The O-glycans attached to NECD are key regulators of the strength of Notch signaling. Imbalances in Notch signaling result in altered cell fate decisions and may lead to cancer in the intestine. In this review, we summarize the impacts of mutations in Notch pathway members on intestinal development and homeostasis, with a focus on the glycosyltransferases that transfer O-glycans to EGF repeats of NOTCH1, NOTCH2, DLL1 and DLL4.

Single-cell RNA Sequencing Reveals How the Aryl Hydrocarbon Receptor Shapes Cellular Differentiation Potency in the Mouse Colon

Despite recent progress recognizing the importance of aryl hydrocarbon receptor (Ahr)-dependent signaling in suppressing colon tumorigenesis, its role in regulating colonic crypt homeostasis remains unclear. To assess the effects of Ahr on intestinal epithelial cell heterogeneity and functional phenotypes, we utilized single-cell transcriptomics and advanced analytic strategies to generate a high-quality atlas for colonic intestinal crypts from wild-type and intestinal-specific Ahr knockout mice. Here we observed the promotive effects of Ahr deletion on Foxm1-regulated genes in crypt-associated canonical epithelial cell types and subtypes of goblet cells and deep crypt-secretory cells. We also show that intestinal Ahr deletion elevated single-cell entropy (a measure of differentiation potency or cell stemness) and RNA velocity length (a measure of the rate of cell differentiation) in noncycling and cycling Lgr5⁺ stem cells. In general, intercellular signaling cross-talk via soluble and membrane-bound factors was perturbed in Ahr-null colonocytes. Taken together, our single-cell RNA sequencing analyses provide new evidence of the molecular function of Ahr in modulating putative stem cell driver genes, cell potency lineage decisions, and cell-cell communication in vivo. PREVENTION RELEVANCE: Our mouse single-cell RNA sequencing analyses provide new evidence of the molecular function of Ahr in modulating colonic stemness and cell-cell communication in vivo. From a cancer prevention perspective, Ahr should be considered a therapeutic target to recalibrate remodeling of the intestinal stem cell niche.

Valproic acid protects intestinal organoids against radiation via NOTCH signaling

Radiotherapy is a leading treatment for various types of cancer. However, exposure to high-dose ionizing radiation causes acute gastrointestinal injury and gastrointestinal syndrome. This has significant implications for human health, and therefore, radioprotection is a major area of research. Radiation induces the loss of intestinal stem cells; hence, the protection of stem cells expressing LGR5 (a marker of intestinal epithelial stem cells) is a key strategy for the prevention of radiation-induced injury. In this study, we identified valproic acid (VPA) as a potent radioprotector using an intestinal organoid culture system. VPA treatment increased the number of LGR5+ stem cells and organoid regeneration after irradiation. N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT, an inhibitor of NOTCH signaling) blocked the radioprotective effects of VPA, indicating that NOTCH signaling is a likely mechanism underlying the observed effects of VPA. In addition, VPA acted as a radiosensitizer via the inhibition of histone deacetylase (HDAC) in a colorectal cancer organoid. These results demonstrate that VPA exerts strong protective effects on LGR5+ stem cells via NOTCH signaling and that the inhibition of NOTCH signaling reduces these protective effects, providing a basis for the improved management of radiation injury.

Microenvironmental regulation of intestinal stem cells in the inflamed intestine

The rapid renewal of intestinal epithelium during homeostasis requires balanced proliferation and differentiation of intestinal stem cells (ISCs) at the base of crypt. Upon intestinal inflammation, the vigorous expansion of surviving ISCs is responsible for epithelial repair. However, it is not well depicted how ISCs adapt to the inflammatory conditions within intestinal tissue and support epithelial repair. In the intestinal inflammation, niche cells around ISCs along with their secreted niche factors can facilitate the regeneration of ISCs via niche signals. Additionally, the growth of ISCs can respond to inflammatory cells, inflammatory cytokines, and inflammatory signals. Understanding the adaptive mechanism of ISCs in supporting intestinal epithelial regeneration during inflammation is a focus on the treatment for patients with intestinal inflammation. Here, we aim to present an overview of how ISCs adapt to the acute inflammation to support intestinal repair, with a focus on the roles and interaction of niche signals.

Strontium regulates stem cell fate during osteogenic differentiation through asymmetric cell division

Strontium, a popular osteogenic component, has been incorporated into various types of orthopaedic biomaterials to enhance bone regeneration. Strontium performs dual effects in promoting bone formation and inhibiting bone resorption. Previous studies have focused on the effects of strontium ions (Sr²⁺) in regulating stem cell behavior to initiate regenerative capacity. However, its mechanisms for regulating the fate and homeostasis of stem cells have not been fully elucidated. In this study, the promotive effect of Sr²⁺ on the osteogenic differentiation of mesenchymal stem cells was confirmed both in vitro and in vivo. Interestingly, in response to Sr²⁺ treatment, stem cells performed asymmetric cell division to balance stemness maintenance and osteogenic differentiation. In initiating osteogenic differentiation, Sr²⁺ maintained more cells in the cell cycle by upregulating the population of S and G2/M phase cells, and this increase in the cell population contributed to enhanced osteogenic differentiation. The divided cells with different cell fates were observed, with one daughter cell maintained stemness, while the other committed to osteogenic lineage. Further investigation revealed that Sr²⁺ activated noncanonical Wnt signaling to regulate the expression and distribution of the Par complex, thus regulating cell division. As a result, the daughter cells committed to different cell fates due to the discriminately activation of osteogenic transcription factors caused by asymmetrically distributed Par3 and aPKC. The results of this study could facilitate the design of biomaterials for bone regeneration by providing a better understanding of cell fate determination regulated by strontium.

Self-organization of organoids from endoderm-derived cells

Organoids constitute biological systems which are used to model organ development, homeostasis, regeneration, and disease in vitro and hold promise for use in therapy. Reflecting in vivo development, organoids form from tissue cells or pluripotent stem cells. Cues provided from the media and individual cells promote self-organization of these uniform starting cells into a structure, with emergent differentiated cells, morphology, and often functionality that resemble the tissue of origin. Therefore, organoids provide a complement to two-dimensional in vitro culture and in vivo animal models of development, providing the experimental control and flexibility of in vitro methods with the three-dimensional context of in vivo models, with fewer ethical restraints than human or animal work. However, using organoids, we are only just beginning to understand on the cellular level how the external conditions and signaling between individual cells promote the emergence of cells and structures. In this review, we focus specifically on organoids derived from endodermal tissues: the starting conditions of the cells, signaling mechanisms, and external media that allow the emergence of higher order self-organization.

Gut bacteria signaling to mitochondria in intestinal inflammation and cancer

The gastrointestinal microbiome plays a pivotal role in physiological homeostasis of the intestine as well as in the pathophysiology of diseases including inflammatory bowel diseases (IBD) and colorectal cancer (CRC). Emerging evidence suggests that gut microbiota signal to the mitochondria of mucosal cells, including epithelial cells and immune cells. Gut microbiota signaling to mitochondria has been shown to alter mitochondrial metabolism, activate immune cells, induce inflammasome signaling, and alter epithelial barrier function. Both dysbiosis of the gut microbiota and mitochondrial dysfunction are associated with chronic intestinal inflammation and CRC. This review discusses mitochondrial metabolism of gut mucosal cells, mitochondrial dysfunction, and known gut microbiota-mediated mitochondrial alterations during IBD and CRC.

The pluripotency network in colorectal cancer pathogenesis and prognosis: an update

Stemness characteristics are defining properties of cancer initiating cells and are associated with the ability to metastasize and survive in hostile environments. Establishment of the stem cell network depends on the action of a set of core transcription factors that work in concert with other ancillary proteins that are also important during embryonic development. New data consolidate the role of core pluripotency transcription factors OCT4, SOX2 and NANOG as adverse prognostic factors in colorectal cancer. mRNA-binding proteins LIN28 and Musashi, that are associated with stemness, and epigenetic modifiers such as de-acetylase SIRT1 may also have prognostic value in colorectal cancer. This paper provides an update of the stem cell factors in the pathogenesis and prognosis of colorectal cancer.

Unraveling the journey of cancer stem cells from origin to metastasis

Cancer biology research over recent decades has given ample evidence for the existence of self-renewing and drug-resistant populations within heterogeneous tumors, widely recognized as cancer stem cells (CSCs). However, a lack of clear understanding about the origin, existence, maintenance, and metastatic roles of CSCs limit efforts towards the development of CSC-targeted therapy. In this review, we describe novel avenues of current CSC biology. In addition to cell fusion and horizontal gene transfer, CSCs are originated by mutations in somatic or differentiated cancer cells, resulting in de-differentiation and reprogramming. Recent studies also provided evidence for the existence of distinct or heterogeneous CSC populations within a single heterogeneous tumor. Our analysis of the literature also opens the doors for a novel hypothesis that CSC populations with specific phenotypes, metabolic profiles, and clonogenic potential metastasize to specific organs.

Reserve Stem Cells in Intestinal Homeostasis and Injury

Renewal of the intestinal epithelium occurs approximately every week and requires a careful balance between cell proliferation and differentiation to maintain proper lineage ratios and support absorptive, secretory, and barrier functions. We review models used to study the mechanisms by which intestinal stem cells (ISCs) fuel the rapid turnover of the epithelium during homeostasis and might support epithelial regeneration after injury. In anatomically defined zones of the crypt stem cell niche, phenotypically distinct active and reserve ISC populations are believed to support homeostatic epithelial renewal and injury-induced regeneration, respectively. However, other cell types previously thought to be committed to differentiated states might also have ISC activity and participate in regeneration. Efforts are underway to reconcile the proposed relatively strict hierarchical relationships between reserve and active ISC pools and their differentiated progeny; findings from models provide evidence for phenotypic plasticity that is common among many if not all crypt-resident intestinal epithelial cells. We discuss the challenges to consensus on ISC nomenclature, technical considerations, and limitations inherent to methodologies used to define reserve ISCs, and the need for standardized metrics to quantify and compare the relative contributions of different epithelial cell types to homeostatic turnover and post-injury regeneration. Increasing our understanding of the high-resolution genetic and epigenetic mechanisms that regulate reserve ISC function and cell plasticity will help refine these models and could affect approaches to promote tissue regeneration after intestinal injury.

Mature enteroendocrine cells contribute to basal and pathological stem cell dynamics in the small intestine

Lgr5-expressing intestinal stem cells (ISCs) maintain continuous and rapid generation of the intestinal epithelium. Here, we present evidence that dedifferentiation of committed enteroendocrine cells (EECs) contributes to maintenance of the epithelium under both basal conditions and in response to injury. Lineage-tracing studies identified a subset of EECs that reside at +4 position for more than 2 wk, most of which were BrdU-label-retaining cells. Under basal conditions, cells derived from these EECs grow from the bottom of the crypt to generate intestinal epithelium according to neutral drift kinetics that is consistent with dedifferentiation of mature EECs to ISCs. The lineage tracing of EECs demonstrated reserve stem cell properties in response to radiation-induced injury with the generation of reparative EEC-derived epithelial patches. Finally, the enterochromaffin (EC) cell was the predominant EEC type participating in these stem cell dynamics. These results provide novel insights into the +4 reserve ISC hypothesis, stem cell dynamics of the intestinal epithelium, and in the development of EC-derived small intestinal tumors. NEW & NOTEWORTHY The current manuscript demonstrating that a subset of mature enteroendocrine cells (EECs), predominantly enterochromaffin cells, dedifferentiates to fully functional intestinal stem cells (ISCs) is novel, timely, and important. These cells dedifferentiate to ISCs not only in response to injury but also under basal homeostatic conditions. These novel findings provide a mechanism in which a specified cell can dedifferentiate and contribute to normal tissue plasticity as well as the development of EEC-derived intestinal tumors under pathologic conditions.

JAK/STAT-1 Signaling Is Required for Reserve Intestinal Stem Cell Activation during Intestinal Regeneration Following Acute Inflammation

The intestinal epithelium serves as an essential barrier to the outside world and is maintained by functionally distinct populations of rapidly cycling intestinal stem cells (CBC ISCs) and slowly cycling, reserve ISCs (r-ISCs). Because disruptions in the epithelial barrier can result from pathological activation of the immune system, we sought to investigate the impact of inflammation on ISC behavior during the regenerative response. In a murine model of αCD3 antibody-induced small-intestinal inflammation, r-ISCs proved highly resistant to injury, while CBC ISCs underwent apoptosis. Moreover, r-ISCs were induced to proliferate and functionally contribute to intestinal regeneration. Further analysis revealed that the inflammatory cytokines interferon gamma and tumor necrosis factor alpha led to r-ISC activation in enteroid culture, which could be blocked by the JAK/STAT inhibitor, tofacitinib. These results highlight an important role for r-ISCs in response to acute intestinal inflammation and show that JAK/STAT-1 signaling is required for the r-ISC regenerative response.

Alcohol Feeding in Mice Promotes Colonic Hyperpermeability and Changes in Colonic Organoid Stem Cell Fate

BACKGROUND

Alcohol increases intestinal permeability to proinflammatory microbial products that promote liver disease, even after a period of sobriety. We sought to test the hypothesis that alcohol affects intestinal stem cells using an in vivo model and ex vivo organoids generated from jejunum and colon from mice fed chronic alcohol.

METHODS

Mice were fed a control or an alcohol diet. Intestinal permeability, liver steatosis-inflammation, and stool short-chain fatty acids (SCFAs) were measured. Jejunum and colonic organoids and tissue were stained for stem cell, cell lineage, and apical junction markers with assessment of mRNA by PCR and RNA-seq. ChIP-PCR analysis was carried out for Notch1 using an antibody specific for acetylated histone 3.

RESULTS

Alcohol-fed mice exhibited colonic (but not small intestinal) hyperpermeability, steatohepatitis, and decreased butyrate/total SCFA ratio in stool. Stem cell, cell lineage, and apical junction marker staining in tissue or organoids from jejunum tissue were not impacted by alcohol. Only chromogranin A (Chga) was increased in jejunum organoids by qPCR. However, colonic tissue and organoid staining exhibited an alcohol-induced significant decrease in cytokeratin 20+  (Krt20+) absorptive lineage enterocytes, a decrease in occludin and E-cadherin apical junction proteins, an increase in Chga, and an increase in the Lgr5 stem cell marker. qPCR revealed an alcohol-induced decrease in colonic organoid and tissue Notch1, Hes1, and Krt20 and increased Chga, supporting an alteration in stem cell fate due to decreased Notch1 expression. Colonic tissue ChIP-PCR revealed alcohol feeding suppressed Notch1 mRNA expression (via deacetylation of histone H3) and decreased Notch1 tissue staining.

CONCLUSIONS

Data support a model for alcohol-induced colonic hyperpermeability via epigenetic effects on Notch1, and thus Hes1, suppression through a mechanism involving histone H3 deacetylation at the Notch1 locus. This decreased enterocyte and increased enteroendocrine cell colonic stem cell fate and decreased apical junctional proteins leading to hyperpermeability.

Brief Report: Interleukin-17A-Dependent Asymmetric Stem Cell Divisions Are Increased in Human Psoriasis: A Mechanism Underlying Benign Hyperproliferation

The balance between asymmetric and symmetric stem cell (SC) divisions is key to tissue homeostasis, and dysregulation of this balance has been shown in cancers. We hypothesized that the balance between asymmetric cell divisions (ACDs) and symmetric cell divisions (SCDs) would be dysregulated in the benign hyperproliferation of psoriasis. We found that, while SCDs were increased in squamous cell carcinoma (SCC) (human and murine), ACDs were increased in the benign hyperproliferation of psoriasis (human and murine). Furthermore, while sonic hedgehog (linked to human cancer) and pifithrinα (p53 inhibitor) promoted SCDs, interleukin (IL)-1α and amphiregulin (associated with benign epidermal hyperproliferation) promoted ACDs. While there was dysregulation of the ACD:SCD ratio, no change in SC frequency was detected in epidermis from psoriasis patients, or in human keratinocytes treated with IL-1α or amphiregulin. We investigated the mechanism whereby immune alterations of psoriasis result in ACDs. IL17 inhibitors are effective new therapies for psoriasis. We found that IL17A increased ACDs in human keratinocytes. Additionally, studies in the imiquimod-induced psoriasis-like mouse model revealed that ACDs in psoriasis are IL17A-dependent. In summary, our studies suggest an association between benign hyperproliferation and increased ACDs. This work begins to elucidate the mechanisms by which immune alteration can induce keratinocyte hyperproliferation. Altogether, this work affirms that a finely tuned balance of ACDs and SCDs is important and that manipulating this balance may constitute an effective treatment strategy for hyperproliferative diseases. Stem Cells 2017;35:2001-2007.

The Research Progress on Intestinal Stem Cells and Its Relationship with Intestinal Microbiota

The intestine is home to trillions of microorganisms, and the vast diversity within this gut microbiota exists in a balanced state to protect the intestinal mucosal barrier. Research into the association of the intestinal microbiota with health and disease (including diet, nutrition, obesity, inflammatory bowel disease, and cancer) continues to expand, with the field advancing at a rapid rate. Intestinal stem cells (ISCs) are the fundamental component of the mucosal barrier; they undergo continuous proliferation to replace the epithelium, which is also intimately involved in intestinal diseases. The intestinal microbiota, such as Lactobacillus, communicates with ISCs both directly and indirectly to regulate the proliferation and differentiation of ISCs. Moreover, Salmonella infection significantly decreased the expression of intestinal stem cell markers Lgr5 and Bmi1. However, the detailed interaction of intestinal microbiota and ISCs are still unclear. This review considers the progress of research on the model and niches of ISCs, as well as the complex interplay between the gut microbiota and ISCs, which will be crucial for explaining the mechanisms of intestinal diseases related to imbalances in the intestinal microbiota and ISCs.

A Notch positive feedback in the intestinal stem cell niche is essential for stem cell self-renewal

The intestinal epithelium is the fastest regenerative tissue in the body, fueled by fast‐cycling stem cells. The number and identity of these dividing and migrating stem cells are maintained by a mosaic pattern at the base of the crypt. How the underlying regulatory scheme manages this dynamic stem cell niche is not entirely clear. We stimulated intestinal organoids with Notch ligands and inhibitors and discovered that intestinal stem cells employ a positive feedback mechanism via direct Notch binding to the second intron of the Notch1 gene. Inactivation of the positive feedback by CRISPR/Cas9 mutation of the binding sequence alters the mosaic stem cell niche pattern and hinders regeneration in organoids. Dynamical system analysis and agent‐based multiscale stochastic modeling suggest that the positive feedback enhances the robustness of Notch‐mediated niche patterning. This study highlights the importance of feedback mechanisms in spatiotemporal control of the stem cell niche.

Time- and cell-resolved dynamics of redox-sensitive Nrf2, HIF and NF-κB activities in 3D spheroids enriched for cancer stem cells

Cancer cells have an altered redox status, with changes in intracellular signaling pathways. The knowledge of how such processes are regulated in 3D spheroids, being well-established tumor models, is limited. To approach this question we stably transfected HCT116 cells with a pTRAF reporter that enabled time- and cell-resolved activity monitoring of three redox-regulated transcription factors Nrf2, HIF and NF-κB in spheroids enriched for cancer stem cells. At the first day of spheroid formation, these transcription factors were activated and thereafter became repressed. After about a week, both HIF and Nrf2 were reactivated within the spheroid cores. Further amplifying HIF activation in spheroids by treatment with DMOG resulted in a dominant quiescent stem-cell-like phenotype, with high resistance to stress-inducing treatments. Auranofin, triggering oxidative stress and Nrf2 activation, had opposite effects with increased differentiation and proliferation. These novel high-resolution insights into spatiotemporal activation patterns demonstrate a striking coordination of redox regulated transcription factors within spheroids not occurring in conventional cell culture models.

Environmental Impact on Intestinal Stem Cell Functions in Mucosal Homeostasis and Tumorigenesis

Multiple cell compartments at or near the base of the intestinal crypt have been identified as contributing intestinal stem cells for homeostasis of the rapidly turning over intestinal mucosa and cells that can initiate tumor development upon appropriate genetic changes. There is a strong literature establishing the importance of the frequently dividing Lgr5+ crypt base columnar cells as the fundamental cell in providing these stem cell-associated functions, but there are also clear data that more quiescent cells from other compartments can be mobilized to provide these stem cell functions upon compromise of Lgr5+ cells. We review the data that vitamin D, a pleiotropic hormone, is essential for Lgr5 stem cell functions by signaling through the vitamin D receptor. Moreover, we discuss the implications of this role of vitamin D and its impact on relatively long-lived stem cells in regards to the fact that virtually all the data on normal functioning of mouse Lgr5 stem cells is derived from mice exposed to vitamin D levels well above those that characterize the human population. Thus, there are still many questions regarding how dietary and environmental factors influence the complement of cells providing stem cell functions and the mechanisms by which this is determined, and the importance of this in human colorectal tumor development. J. Cell. Biochem. 118: 943-952, 2017. © 2016 Wiley Periodicals, Inc.