Maintenance Of Intestinal Stem Cells Research Articles

Impaired Wnt/\u03b2-catenin pathway leads to dysfunction of intestinal regeneration during necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating neonatal disease characterized by acute intestinal injury. Intestinal stem cell (ISC) renewal is required for gut regeneration in response to acute injury. The Wnt/β-catenin pathway is essential for intestinal renewal and ISC maintenance. We found that ISC expression, Wnt activity and intestinal regeneration were all decreased in both mice with experimental NEC and in infants with acute active NEC. Moreover, intestinal organoids derived from NEC-injured intestine of both mice and humans failed to maintain proliferation and presented more differentiation. Administration of Wnt7b reversed these changes and promoted growth of intestinal organoids. Additionally, administration of exogenous Wnt7b rescued intestinal injury, restored ISC, and reestablished intestinal epithelial homeostasis in mice with NEC. Our findings demonstrate that during NEC, Wnt/β-catenin signaling is decreased, ISC activity is impaired, and intestinal regeneration is defective. Administration of Wnt resulted in the maintenance of intestinal epithelial homeostasis and avoidance of NEC intestinal injury.

Radiation mitigation of the intestinal acute radiation injury in mice by 1-[(4-nitrophenyl)sulfonyl]-4-phenylpiperazine.

The objective of the study was to identify the mechanism of action for a radiation mitigator of the gastrointestinal (GI) acute radiation syndrome (ARS), identified in an unbiased high‐throughput screen. We used mice irradiated with a lethal dose of radiation and treated with daily injections of the radiation mitigator 1‐[(4‐nitrophenyl)sulfonyl]‐4‐phenylpiperazine to study its effects on key pathways involved in intestinal stem cell (ISC) maintenance. RNASeq, quantitative reverse transcriptase‐polymerase chain reaction, and immunohistochemistry were performed to identify pathways engaged after drug treatment. Target validation was performed with competition assays, reporter cells, and in silico docking. 1‐[(4‐Nitrophenyl)sulfonyl]‐4‐phenylpiperazine activates Hedgehog signaling by binding to the transmembrane domain of Smoothened, thereby expanding the ISC pool, increasing the number of regenerating crypts and preventing the GI‐ARS. We conclude that Smoothened is a target for radiation mitigation in the small intestine that could be explored for use in radiation accidents as well as to mitigate normal tissue toxicity during and after radiotherapy of the abdomen.

CIRCling the wagons to protect intestinal stem cells.

Innate lymphoid cell–derived cytokine IL-13 promotes the maintenance of intestinal stem cells through stabilization of β-catenin. The circular RNA circPan3 regulates mRNA encoding the cytokine receptor subunit IL-13Rα and downstream IL-13 signaling to stabilize the β-catenin pathway in intestinal stem cells.

Arid1a is essential for intestinal stem cells through Sox9 regulation

Inactivating mutations of Arid1a, a subunit of the Switch/sucrose nonfermentable chromatin remodeling complex, have been reported in multiple human cancers. Intestinal deletion of Arid1a has been reported to induce colorectal cancer in mice; however, its functional role in intestinal homeostasis remains unclear. We investigated the functional role of Arid1a in intestinal homeostasis in mice. We found that intestinal deletion of Arid1a results in loss of intestinal stem cells (ISCs), decreased Paneth and goblet cells, disorganized crypt-villous structures, and increased apoptosis in adult mice. Spheroids did not develop from intestinal epithelial cells deficient for Arid1a Lineage-tracing experiments revealed that Arid1a deletion in Lgr5+ ISCs leads to impaired self-renewal of Lgr5+ ISCs but does not perturb intestinal homeostasis. The Wnt signaling pathway, including Wnt agonists, receptors, and target genes, was strikingly down-regulated in Arid1a-deficient intestines. We found that Arid1a directly binds to the Sox9 promoter to support its expression. Remarkably, overexpression of Sox9 in intestinal epithelial cells abrogated the above phenotypes, although Sox9 overexpression in intestinal epithelial cells did not restore the expression levels of Wnt agonist and receptor genes. Furthermore, Sox9 overexpression permitted development of spheroids from Arid1a-deficient intestinal epithelial cells. In addition, deletion of Arid1a concomitant with Sox9 overexpression in Lgr5+ ISCs restores self-renewal in Arid1a-deleted Lgr5+ ISCs. These results indicate that Arid1a is indispensable for the maintenance of ISCs and intestinal homeostasis in mice. Mechanistically, this is mainly mediated by Sox9. Our data provide insights into the molecular mechanisms underlying maintenance of ISCs and intestinal homeostasis.

Cellular Plasticity of Defa4Cre-Expressing Paneth Cells in Response to Notch Activation and Intestinal Injury.

Background & AimsLoss of leucine-rich repeat-containing G-protein–coupled receptor 5–positive crypt base columnar cells provides permissive conditions for different facultative stem cell populations to dedifferentiate and repopulate the stem cell compartment. In this study, we used a defensin α4-Cre recombinase (Defa4Cre) line to define the potential of Paneth cells to dedifferentiate and contribute to intestinal stem cell (ISC) maintenance during normal homeostasis and after intestinal injury.MethodsSmall intestine and enteroids from Defa4Cre;Rosa26 tandem dimer Tomato (tdTomato), a red fluoresent protein, (or Rosa26 Enhanced Yellow Fluorescent Protein (EYFP)) reporter, Notch gain-of-function (Defa4Cre;Rosa26 Notch Intracellular Domain (NICD)-ires-nuclear Green Fluorescent Protein (nGFP) and Defa4Cre;Rosa26reverse tetracycline transactivator–ires Enhanced Green Fluorescent Protein (EGFP);TetONICD), A Disintegrin and Metalloproteinase domain-containing protein 10 (ADAM10) loss-of-function (Defa4Cre;ADAM10flox/flox), and Adenomatous polyposis coli (APC) inactivation (Defa4Cre;APCflox/flox) mice were analyzed. Doxorubicin treatment was used as an acute intestinal injury model. Lineage tracing, proliferation, and differentiation were assessed in vitro and in vivo.ResultsDefa4Cre-expressing cells are fated to become mature Paneth cells and do not contribute to ISC maintenance during normal homeostasis in vivo. However, spontaneous lineage tracing was observed in enteroids, and fluorescent-activated cell sorter–sorted Defa4Cre-marked cells showed clonogenic enteroid growth. Notch activation in Defa4Cre-expressing cells caused dedifferentiation to multipotent ISCs in vivo and was required for adenoma formation. ADAM10 deletion had no significant effect on crypt homeostasis. However, after acute doxorubicin-induced injury, Defa4Cre-expressing cells contributed to regeneration in an ADAM10–Notch–dependent manner.ConclusionsOur studies have shown that Defa4Cre-expressing Paneth cells possess cellular plasticity, can dedifferentiate into multipotent stem cells upon Notch activation, and can contribute to intestinal regeneration in an acute injury model.

Human 3D Gastrointestinal Microtissue Barrier Function As a Predictor of Drug-Induced Diarrhea

Drug-induced gastrointestinal toxicities (GITs) rank among the most common clinical side effects. Preclinical efforts to reduce incidence are limited by inadequate predictivity of in vitro assays. Recent breakthroughs in in vitro culture methods support intestinal stem cell maintenance and continual differentiation into the epithelial cell types resident in the intestine. These diverse cells self-assemble into microtissues with in vivo-like architecture. Here, we evaluate human GI microtissues grown in transwell plates that allow apical and/or basolateral drug treatment and 96-well throughput. Evaluation of assay utility focused on predictivity for diarrhea because this adverse effect correlates with intestinal barrier dysfunction which can be measured in GI microtissues using transepithelial electrical resistance (TEER). A validation set of widely prescribed drugs was assembled and tested for effects on TEER. When the resulting TEER inhibition potencies were adjusted for clinical exposure, a threshold was identified that distinguished drugs that induced clinical diarrhea from those that lack this liability. Microtissue TEER assay predictivity was further challenged with a smaller set of drugs whose clinical development was limited by diarrhea that was unexpected based on 1-month animal studies. Microtissue TEER accurately predicted diarrhea for each of these drugs. The label-free nature of TEER enabled repeated quantitation with sufficient precision to develop a mathematical model describing the temporal dynamics of barrier damage and recovery. This human 3D GI microtissue is the first in vitro assay with validated predictivity for diarrhea-inducing drugs. It should provide a platform for lead optimization and offers potential for dose schedule exploration.

Asymmetric cell division-dominant neutral drift model for normal intestinal stem cell homeostasis

The normal intestinal epithelium is continuously regenerated at a rapid rate from actively cycling Lgr5-expressing intestinal stem cells (ISCs) that reside at the crypt base. Recent mathematical modeling based on several lineage-tracing studies in mice shows that the symmetric cell division-dominant neutral drift model fits well with the observed in vivo growth of ISC clones and suggests that symmetric divisions are central to ISC homeostasis. However, other studies suggest a critical role for asymmetric cell division in the maintenance of ISC homeostasis in vivo. Here, we show that the stochastic branching and Moran process models with both a symmetric and asymmetric division mode not only simulate the stochastic growth of the ISC clone in silico but also closely fit the in vivo stem cell dynamics observed in lineage-tracing studies. In addition, the proposed model with highest probability for asymmetric division is more consistent with in vivo observations reported here and by others. Our in vivo studies of mitotic spindle orientations and lineage-traced progeny pairs indicate that asymmetric cell division is a dominant mode used by ISCs under normal homeostasis. Therefore, we propose the asymmetric cell division-dominant neutral drift model for normal ISC homeostasis. NEW & NOTEWORTHY The prevailing mathematical model suggests that intestinal stem cells (ISCs) divide symmetrically. The present study provides evidence that asymmetric cell division is the major contributor to ISC maintenance and thus proposes an asymmetric cell division-dominant neutral drift model. Consistent with this model, in vivo studies of mitotic spindle orientation and lineage-traced progeny pairs indicate that asymmetric cell division is the dominant mode used by ISCs under normal homeostasis.

The Krüppel-Like Factors and Control of Energy Homeostasis.

Nutrient handling by higher organisms is a complex process that is regulated at the transcriptional level. Studies over the past 15 years have highlighted the critical importance of a family of transcriptional regulators termed the Krüppel-like factors (KLFs) in metabolism. Within an organ, distinct KLFs direct networks of metabolic gene targets to achieve specialized functions. This regulation is often orchestrated in concert with recruitment of tissue-specific transcriptional regulators, particularly members of the nuclear receptor family. Upon nutrient entry into the intestine, gut, and liver, KLFs control a range of functions from bile synthesis to intestinal stem cell maintenance to effect nutrient acquisition. Subsequently, coordinated KLF activity across multiple organs distributes nutrients to sites of storage or liberates them for use in response to changes in nutrient status. Finally, in energy-consuming organs like cardiac and skeletal muscle, KLFs tune local metabolic programs to precisely match substrate uptake, flux, and use, particularly via mitochondrial function, with energetic demand; this is achieved in part via circulating mediators, including glucocorticoids and insulin. Here, we summarize current understanding of KLFs in regulation of nutrient absorption, interorgan circulation, and tissue-specific use.

A growth factor-free culture system underscores the coordination between Wnt and BMP signaling in Lgr5+ intestinal stem cell maintenance

Lgr5+ intestinal stem cells (ISCs) drive the fast renewal of intestinal epithelium. Several signaling pathways have been shown to regulate ISC fates. However, it is unclear what are the essential signals to sustain the ISC self-renewal. Here we show that coordination between Wnt and BMP signaling activity is necessary and sufficient to maintain Lgr5+ ISCs self-renewal. The key function of R-spondin1 is to achieve a high activity of Wnt signaling in the organoid culture. Using the GSK3 inhibitor CHIR-99021 and the BMP type I receptor inhibitor LDN-193189, we can maintain Lgr5+ ISCs without growth factors in vitro. Our results define the basic signaling pathways sustaining Lgr5+ ISCs and set up a convenient and economical culture system for their in vitro expansion. This work also set up an example for growth factor-free culture of other adult stem cells.

Telomeric epigenetic response mediated by Gadd45a regulates stem cell aging and lifespan.

Progressive attrition of telomeres triggers DNA damage response (DDR) and limits the regenerative capacity of adult stem cells during mammalian aging. Intriguingly, telomere integrity is not only determined by telomere length but also by the epigenetic status of telomeric/sub-telomeric regions. However, the functional interplay between DDR induced by telomere shortening and epigenetic modifications in aging remains unclear. Here, we show that deletion of Gadd45a improves the maintenance and function of intestinal stem cells (ISCs) and prolongs lifespan of telomerase-deficient mice (G3Terc-/-). Mechanistically, Gadd45a facilitates the generation of a permissive chromatin state for DDR signaling by inducing base excision repair-dependent demethylation of CpG islands specifically at sub-telomeric regions of short telomeres. Deletion of Gadd45a promotes chromatin compaction in sub-telomeric regions and attenuates DDR initiation at short telomeres of G3Terc-/- ISCs. Treatment with a small molecule inhibitor of base excision repair reduces DDR and improves the maintenance and function of G3Terc-/- ISCs. Taken together, our study proposes a therapeutic approach to enhance stem cell function and prolong lifespan by targeting epigenetic modifiers.

ASCL2 expression contributes to gastric tumor migration and invasion by downregulating miR223 and inducing EMT.

Achaete-scute homolog 2 (ASCL2), a basic helix-loop-helix transcription factor, serves an essential role in the maintenance of adult intestinal stem cells and the growth of gastric cancer (GC). However, the function of ASCL2 in the metastasis of GC is poorly understood. The present study aimed to evaluate the effect of ASCL2 expression on gastric tumor metastasis. ASCL2 protein expression was detected in 32 cases of gastric metastasis and its relevant primary tumors using western blotting and immunohistochemistry. The data suggested that the expression of ASCL2 was highest in metastatic tumors, among adjacent normal tissues, primary gastric tumors and gastric metastatic tumors. Furthermore, ASCL2-overexpressing GC cell lines MKN1-ASCL2 and SNU16-ASCL2 were established. An in vitro assay suggested that microRNA 223 (miR223) expression was downregulated following ASCL2 overexpression, and that the expression of the epithelium-associated protein E-cadherin was significantly decreased, while a series of mesenchyme-associated proteins, including zinc finger E-box-binding homeobox 1 (Zeb-1), twist-related protein 1, integrin, vimentin, 72 kDa type IV collagenase and matrix metalloproteinase-9 were upregulated in ASCL2-overexpressing cells. Overexpression of miR223 attenuated the epithelial-mesenchymal transition (EMT)-promoting effect induced by ASCL2 expression. In addition, the results of the chromatin immunoprecipitation and luciferase reporter gene assays indicated that ASCL2 was able to interact with the promoter of pre-miR223, and to inhibit the maturation of miR223, which may interact with the 3′ untranslated region of Zeb-1 and inhibit EMT in tumor cells. The results of the present study demonstrated that ASCL2 was able to downregulate the expression level of miR223, contribute to EMT and promote gastric tumor metastasis, which indicated that ASCL2 may serve as a therapeutic target in the treatment of GC.

Abstract 1143: Prox1 and Notch mark distinct colorectal cancer stem cell populations

Abstract Colorectal cancer (CRC) is one of the leading causes of cancer-related morbidity and mortality. Signaling pathways, such as the Wnt and Notch pathways, are essential for the maintenance and differentiation of wild-type intestinal stem cells. We have shown that the Prox1 transcription promotes expansion of the colorectal cancer stem cell pool and that a subpopulation of the Prox1+ CRC cells display stem cell activity. Because of these results we have further analyzed the role of Prox1 in the regulation of CRC stem cell. Here, we report that Prox1 regulates CRC stem-like cells via bidirectional interaction with Notch1 during CRC initiation and progression. Using genetic in vivo models and ex vivo 3D organoid cultures, we show that Notch inhibition decreases the number of Lgr5+ stem cells whereas it increases expression of the Prox1. Although Notch inhibition led to increased proliferation of the Prox1 positive cells, it did not affect their ability to give rise to differentiated Prox1 negative progeny. Ectopic overexpression of the active fragment of Notch1 suppressed Prox1 expression and inhibited stem cell activity in the CRC cells. On the other hand, the PROX1-NuRD complex suppressed the Notch signaling pathway and Prox1 deletion increased Notch target gene expression and promoter activity, indicating reciprocal regulation between Prox1 and Notch1. Thus, although Prox1 and Notch suppress each other in colorectal cancer cells, Prox1+ cells can function as a stem cell population without the need for Notch pathway activity. Citation Format: Jenny Högström, Sarika Heino, Pauliina Kallio, Marianne Lähde, Veli-Matti Leppänen, Seppo Kaijalainen, Diego Balboa, Timo Otonkoski, Sylvie Robine, Zoltan Wiener, Kari Alitalo. Prox1 and Notch mark distinct colorectal cancer stem cell populations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1143.

Fasting Activates Fatty Acid Oxidation to Enhance Intestinal Stem Cell Function during Homeostasis and Aging

Diet has a profound effect on tissue regeneration in diverse organisms, and low caloric states such as intermittent fasting have beneficial effects on organismal health and age-associated loss of tissue function. The role of adult stem and progenitor cells in responding to short-term fasting and whether such responses improve regeneration are not well studied. Here we show that a 24hr fast augments intestinal stem cell (ISC) function in young and aged mice by inducing a fatty acid oxidation (FAO) program and that pharmacological activation of this program mimics many effects of fasting. Acute genetic disruption of Cpt1a, the rate-limiting enzyme in FAO, abrogates ISC-enhancing effects of fasting, but long-term Cpt1a deletion decreases ISC numbers and function,implicating a role for FAO in ISC maintenance. Thesefindings highlight a role for FAO in mediating pro-regenerative effects of fasting in intestinal biology, and they may represent a viable strategy for enhancing intestinal regeneration.

The POU/Oct Transcription Factor Nubbin Controls the Balance of Intestinal Stem Cell Maintenance and Differentiation by Isoform-Specific Regulation.

SummaryDrosophila POU/Oct transcription factors are required for many developmental processes, but their putative regulation of adult stem cell activity has not been investigated. Here, we show that Nubbin (Nub)/Pdm1, homologous to mammalian OCT1/POU2F1 and related to OCT4/POU5F1, is expressed in gut epithelium progenitor cells. We demonstrate that the nub-encoded protein isoforms, Nub-PB and Nub-PD, play opposite roles in the regulation of intestinal stem cell (ISC) maintenance and differentiation. Depletion of Nub-PB in progenitor cells increased ISC proliferation by derepression of escargot expression. Conversely, loss of Nub-PD reduced ISC proliferation, suggesting that this isoform is necessary for ISC maintenance, analogous to mammalian OCT4/POU5F1 functions. Furthermore, Nub-PB is required in enteroblasts to promote differentiation, and it acts as a tumor suppressor of Notch RNAi-driven hyperplasia. We suggest that a dynamic and well-tuned expression of Nub isoforms in progenitor cells is required for maintaining gut epithelium homeostasis.

Sox9‐independent Control of Intestinal Paneth Cell Differentiation and Function

The genetic and signaling mechanisms controlling the generation and function of differentiated cell types are of continued interest. The intestinal Paneth cell (PC) is a post‐mitotic and dedicated secretory cell type with reported functions in supporting intestinal stem cell (ISC) maintenance in the crypt stem cell niche, and in secreting antimicrobial peptides to protect the crypt from potentially pathogenic luminal microbiota. Previous studies have reported a near‐complete loss of PCs (as defined by morphological and marker‐based criteria) in epithelium where the transcription factor Sox9 is genetically ablated, leading to the proposition that Sox9 is required for PC differentiation. Currently, however, the mechanisms through which Sox9 controls PC differentiation are not known. We have found evidence in Sox9 knockout (KO) small intestine (SI) that cells at the crypt base frequently express PC‐markers such as Lysozyme (Lyz) and Cryptdin, exhibit apical granules, and are post‐mitotic, all of which are features indicative of PC differentiation. The numbers of Lyz+ cells are highest in the distal Sox9 KO SI but are significantly reduced relative to control, and are essentially absent in the proximal SI, suggesting that regionally patterned signals may drive PC differentiation independent of Sox9. Apical granularity and expression levels of Lyz/Cryptdin are also altered, suggesting that while Sox9 KO ISCs can initiate PC differentiation, they are unable to reach full maturity. Antibody and qPCR based detection of PC gene products (including secreted antimicrobials, growth factors, and transcriptional regulators proposed to drive PC differentiation downstream of Sox9) are maintained in Sox9 KO cultured intestinal organoids and are elevated in organoids treated with pharmacological agents that drive the PC differentiation program. These results indicate that Sox9‐deficient ‘Paneth‐like’ cells are continually generated in culture and can be pushed toward PC differentiation with factors known to stimulate the PC differentiation program. We conclude that Sox9 is not required for the activation of at least sub‐sets of gene products associated with PC differentiation and function. Ongoing experiments are designed to investigate Sox9‐ dependent and independent pathways toward PC fate, and to characterize the functionality of Sox9−/− ‘Paneth‐like’ cells compared to controls.Support or Funding InformationRO1 DK091427‐05F32 DK115016‐01This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Wingless/Wnt Signaling in Intestinal Development, Homeostasis, Regeneration and Tumorigenesis: A Drosophila Perspective.

In mammals, the Wnt/β-catenin signal transduction pathway regulates intestinal stem cell maintenance and proliferation, whereas Wnt pathway hyperactivation, resulting primarily from the inactivation of the tumor suppressor Adenomatous polyposis coli (APC), triggers the development of the vast majority of colorectal cancers. The Drosophila adult gut has recently emerged as a powerful model to elucidate the mechanisms by which Wingless/Wnt signaling regulates intestinal development, homeostasis, regeneration, and tumorigenesis. Herein, we review recent insights on the roles of Wnt signaling in Drosophila intestinal physiology and pathology.

The Force Is Strong with This One: Metabolism (Over)powers Stem Cell Fate.

Compared to their differentiated progeny, stem cells are often characterized by distinct metabolic landscapes that emphasize anaerobic glycolysis and a lower fraction of mitochondrial carbohydrate oxidation. Until recently, the metabolic program of stem cells had been thought to be a byproduct of the environment, rather than an intrinsic feature determined by the cell itself. However, new studies highlight the impact of metabolic behavior on the maintenance and function of intestinal stem cells and hair follicle stem cells. This Review summarizes and discusses the evidence that metabolism is not a mere consequence of, but rather influential on stem cell fate.

Casein kinase 1‐epsilon or 1‐delta required for Wnt‐mediated intestinal stem cell maintenance

The intestinal epithelium holds an immense regenerative capacity mobilized by intestinal stem cells (ISCs), much of it supported by Wnt pathway activation. Several unique regulatory mechanisms ensuring optimal levels of Wnt signaling have been recognized in ISCs. Here, we identify another Wnt signaling amplifier, CKIε, which is specifically upregulated in ISCs and is essential for ISC maintenance, especially in the absence of its close isoform CKIδ. Co-ablation of CKIδ/ε in the mouse gut epithelium results in rapid ISC elimination, with subsequent growth arrest, crypt-villous shrinking, and rapid mouse death. Unexpectedly, Wnt activation is preserved in all CKIδ/ε-deficient enterocyte populations, with the exception of Lgr5+ ISCs, which exhibit Dvl2-dependent Wnt signaling attenuation. CKIδ/ε-depleted gut organoids cease proliferating and die rapidly, yet survive and resume self-renewal upon reconstitution of Dvl2 expression. Our study underscores a unique regulation mode of the Wnt pathway in ISCs, possibly providing new means of stem cell enrichment for regenerative medicine.

Dual roles of yes-associated protein (YAP) in colorectal cancer.

Yes-associated protein (YAP) is a downstream effector molecule of a newly emerging tumour suppressor pathway called the Hippo pathway. YAP is a transcriptional co-activator and mis-expressed in various cancers, including colorectal cancer (CRC). Accumulating studies show that the high expression of nuclear YAP is linked with tumour progression and decreased survival. Nuclear YAP can interact with other transcription factors to promote cancer cell proliferation, apoptosis, metastasis and maintenance of stemness. Therefore, YAP has the potential to be a tumour biomarker or therapeutic target for CRC. However, recently, a number of studies have supported a contradictory role for YAP as a tumour suppressor, demonstrating inhibition of the tumorigenesis of CRC, involvement in promoting cell apoptosis, and inhibiting the maintenance of intestinal stem cells and inflammatory activity. In these studies, high expression of YAP was highly correlated with worse survival in CRC. In this review, we will comprehensively summarize and analyse these paradoxical reports, and discuss both the oncogenic and tumour suppressor functions of YAP in the differential status of CRC progression. Further investigation into the mechanisms responsible for the dual function of YAP will be of great value in the prevention, early diagnosis, and therapy of CRC.

Intrinsic Autophagy Is Required for the Maintenance of Intestinal Stem Cells and for Irradiation-Induced Intestinal Regeneration

Autophagy is a lysosomal degradation pathway with important roles in physiological homeostasis and disease. However, the role of autophagy in intestinal stem cells (ISCs) is unclear. Here, we show that intrinsic autophagy in ISCs is important for ISC homeostasis. Mice lacking autophagy protein 5 (ATG5) in intestinal epithelial cells (iECs) (Villin-Cre: Atg5fl/fl, hereafter Atg5ΔIEC mice) or in all iECs except Paneth cells (Ah-Cre: Atg5fl/fl mice) had significantly fewer ISCs than did control mice and showed impaired ISC-dependent intestinal recovery after irradiation. Crypt ISCs from Atg5ΔIEC mice had significantly higher reactive oxygen species (ROS) levels than did those from control mice. A ROS-inducing reagent decreased the ISC number and impaired ISC regenerative capacity exvivo, and treating Atg5ΔIEC mice with an antioxidant rescued their defects. Our results show that intrinsic autophagy supports ISC maintenance by reducing excessive ROS. Optimizing autophagy may lead to autophagy-based therapies for intestinal injuries.