Lgr5+ intestinal stem cells are required for organoid survival after genotoxic injury

Progenitors and mature cells can maintain the intestinal epithelium by dedifferentiation and facultative intestinal stem cell (fISC) function when active ISCs (aISCs) are lost to damage. Here, we sought to model fISC activation in intestinal organoids with doxorubicin (DXR), a chemotherapeutic known to ablate Lgr5+ aISCs in vivo. We identified low and high doses of DXR compatible with long-term organoid survival. Similar fISC gene activation was observed between organoids treated with low vs high DXR, despite significantly decreased survival at the higher dose. aISCs exhibit dose-dependent loss after DXR but survive at doses compatible with organoid survival. We ablated residual aISCs after DXR using a Lgr52A-DTR allele and observed that aISC survival of the initial genotoxic insult is required for organoid survival following DXR. These results suggest that while typical fISC genes are activated by DXR injury in organoids, functional stemness remains dependent on the aISC pool. Our data establish a reproducible model of DXR injury in intestinal organoids and reveal differences in in vitro responses to an established in vivo damage modality.

Circadian regulation of cancer stem cells and the tumor microenvironment during metastasis

The circadian clock regulates daily rhythms of numerous physiological activities through tightly coordinated modulation of gene expression and biochemical functions. Circadian disruption is associated with enhanced tumor formation and metastasis via dysregulation of key biological processes and modulation of cancer stem cells (CSCs) and their specialized microenvironment. Here, we review how the circadian clock influences CSCs and their local tumor niches in the context of different stages of tumor metastasis. Identifying circadian therapeutic targets could facilitate the development of new treatments that leverage circadian modulation to ablate tumor-resident CSCs, inhibit tumor metastasis and enhance response to current therapies.

Minimum intervention oral care - incentivising preventive management of high-needs/high caries-risk patients using phased courses of treatment

This paper demonstrates how person-focused, prevention-based, risk/needs-related, team-delivered, minimum intervention oral care (MIOC) principles and approaches can be integrated into the dental profession for the delivery of environmentally sustainable, optimal care to high-needs and high caries-risk/susceptibility patients. It highlights the potential for NHS remuneration for prevention-based, phased, personalised care pathways/plans (PCPs) within a reformed NHS dental contract system. It emphasises the importance of comprehensive and longitudinal patient risk/susceptibility assessments, prevention and stabilisation of the oral environment before considering more complex, definitive restorative work. This paper forms the first of several components of a suite of educational/information materials needed to instil confidence and implementation protocols within primary care clinical oral health care teams delivering MIOC through phased PCPs, especially when managing patients with high needs and/or disease susceptibility.

Serrated colorectal cancer: preclinical models and molecular pathways

Serrated lesions are histologically heterogeneous, and detection can be challenging as these lesions have subtle features that may be missed by endoscopy. Furthermore, while approximately 30% of colorectal cancers (CRCs) arise from serrated lesions, only 8-10% of invasive serrated CRCs exhibit serrated morphology at presentation, suggesting potential loss of apparent characteristics with increased malignancy. Thus, understanding the genetic basis driving serrated CRC initiation and progression is critical to improve diagnosis and identify therapeutic biomarkers and targets to guide disease management. This review discusses the preclinical models of serrated CRCs reported to date and how these systems have been used to provide mechanistic insights into tumor initiation, progression, and novel treatment targets.

A Mutation-driven oncofetal regression fuels phenotypic plasticity in colorectal cancer

Targeting cancer stem cells (CSCs) is crucial for effective cancer treatment 1 . However, the molecular mechanisms underlying resistance to LGR5 + CSCs depletion in colorectal cancer (CRC) 2,3 remain largely elusive. Here, we unveil the existence of a primitive cell state dubbed the oncofetal (OnF) state, which works in tandem with the LGR5 + stem cells (SCs) to fuel tumor evolution in CRC. OnF cells emerge early during intestinal tumorigenesis and exhibit features of lineage plasticity. Normally suppressed by the Retinoid X Receptor (RXR) in mature SCs, the OnF program is triggered by genetic deletion of the gatekeeper APC. We demonstrate that diminished RXR activity unlocks an epigenetic circuity governed by the cooperative action of YAP and AP1, leading to OnF reprogramming. This high-plasticity state is inherently resistant to conventional chemotherapies and its adoption by LGR5 + CSCs enables them to enter a drug-tolerant state. Furthermore, through phenotypic tracing and ablation experiments, we uncover a functional redundancy between the OnF and stem cell (SC) states and show that targeting both cellular states is essential for sustained tumor regression in vivo . Collectively, these findings establish a mechanistic foundation for developing effective combination therapies with enduring impact on CRC treatment.

Unveiling the Influence of Tumor Microenvironment and Spatial Heterogeneity on Temozolomide Resistance in Glioblastoma Using an Advanced Human In Vitro Model of the Blood-Brain Barrier and Glioblastoma

Glioblastoma (GBM) is the most common primary malignant brain cancer in adults with a dismal prognosis. Temozolomide (TMZ) is the first-in-line chemotherapeutic; however, resistance is frequent and multifactorial. While many molecular and genetic factors have been linked to TMZ resistance, the role of the solid tumor morphology and the tumor microenvironment, particularly the blood-brain barrier (BBB), is unknown. Here, the authors investigate these using a complex in vitro model for GBM and its surrounding BBB. The model recapitulates important clinical features such as a dense tumor core with tumor cells that invade along the perivascular space; and a perfusable BBB with a physiological permeability and morphology that is altered in the presence of a tumor spheroid. It is demonstrated that TMZ sensitivity decreases with increasing cancer cell spatial organization, and that the BBB can contribute to TMZ resistance. Proteomic analysis with next-generation low volume sample workflows of these cultured microtissues revealed potential clinically relevant proteins involved in tumor aggressiveness and TMZ resistance, demonstrating the utility of complex in vitro models for interrogating the tumor microenvironment and therapy validation.

Gastric epithelial stem cells in development, homeostasis and regeneration

The stem/progenitor cell pool is indispensable for the development, homeostasis and regeneration of the gastric epithelium, owing to its defining ability to self-renew whilst supplying the various functional epithelial lineages needed to digest food efficiently. A detailed understanding of the intricacies and complexities surrounding the behaviours and roles of these stem cells offers insights, not only into the physiology of gastric epithelial development and maintenance, but also into the pathological consequences following aberrations in stem cell regulation. Here, we provide an insightful synthesis of the existing knowledge on gastric epithelial stem cell biology, including the in vitro and in vivo experimental techniques that have advanced such studies. We highlight the contributions of stem/progenitor cells towards patterning the developing stomach, specification of the differentiated cell lineages and maintenance of the mature epithelium during homeostasis and following injury. Finally, we discuss gaps in our understanding and identify key research areas for future work.

The Helicobacter pylori CagA oncoprotein disrupts Wnt/PCP signaling and promotes hyperproliferation of pyloric gland base cells

Helicobacter pylori strains that deliver the oncoprotein CagA into gastric epithelial cells are the major etiologic agents of upper gastric diseases including gastric cancer. CagA promotes gastric carcinogenesis through interactions with multiple host proteins. Here, we show that CagA also disrupts Wnt-dependent planar cell polarity (Wnt/PCP), which orients cells within the plane of an epithelium and coordinates collective cell behaviors such as convergent extension to enable epithelial elongation during development. Ectopic expression of CagA in Xenopus laevis embryos impaired gastrulation, neural tube formation, and axis elongation, processes driven by convergent extension movements that depend on the Wnt/PCP pathway. Mice specifically expressing CagA in the stomach epithelium had longer pyloric glands and mislocalization of the tetraspanin proteins VANGL1 and VANGL2 (VANGL1/2), which are critical components of Wnt/PCP signaling. The increased pyloric gland length was due to hyperproliferation of cells at the gland base, where Lgr5⁺ stem and progenitor cells reside, and was associated with fewer differentiated enteroendocrine cells. In cultured human gastric epithelial cells, the N terminus of CagA interacted with the C-terminal cytoplasmic tails of VANGL1/2, which impaired Wnt/PCP signaling by inducing the mislocalization of VANGL1/2 from the plasma membrane to the cytoplasm. Thus, CagA may contribute to the development of gastric cancer by subverting a Wnt/PCP-dependent mechanism that restrains pyloric gland stem cell proliferation and promotes enteroendocrine differentiation.

Proteasome inhibitor bortezomib stabilizes and activates p53 in hematopoietic stem/progenitors and double-negative T cells in vivo

We have previously shown that proteasome inhibitor bortezomib stabilizes p53 in stem and progenitor cells within gastrointestinal tissues. Here, we characterize the effect of bortezomib treatment on primary and secondary lymphoid tissues in mice. We find that bortezomib stabilizes p53 in significant fractions of hematopoietic stem and progenitor cells in the bone marrow, including common lymphoid and myeloid progenitors, granulocyte-monocyte progenitors, and dendritic cell progenitors. The stabilization of p53 is also observed in multipotent progenitors and hematopoietic stem cells, albeit at lower frequencies. In the thymus, bortezomib stabilizes p53 in CD4-CD8- T cells. Although there is less p53 stabilization in secondary lymphoid organs, cells in the germinal center of the spleen and Peyer's patch accumulate p53 in response to bortezomib. Bortezomib induces the upregulation of p53 target genes and p53 dependent/independent apoptosis in the bone marrow and thymus, suggesting that cells in these organs are robustly affected by proteasome inhibition. Comparative analysis of cell percentages in the bone marrow indicates expanded stem and multipotent progenitor pools in p53R172H mutant mice compared with p53 wild-type mice, suggesting a critical role for p53 in regulating the development and maturation of hematopoietic cells in the bone marrow. We propose that progenitors along the hematopoietic differentiation pathway express relatively high levels of p53 protein, which under steady-state conditions is constantly degraded by Mdm2 E3 ligase; however, these cells rapidly respond to stress to regulate stem cell renewal and consequently maintain the genomic integrity of hematopoietic stem/progenitor cell populations.

The East of England dental trauma service

BACKGROUND

Current evidence suggests traumatic dental injuries can be difficult to manage in primary care due to uncommon occurrence and challenging patient presentations. Such factors may contribute to general dental practitioners lacking experience and confidence in the assessment, treatment and management of traumatic dental injuries. Furthermore, there are anecdotal accounts of patients presenting to accident and emergency (A&E) services with a traumatic dental injury, which could be placing avoidable strain on secondary care services. For these reasons, a novel primary care-led dental trauma service has been established in the East of England.

METHODS

This brief report shares our experiences of establishing this dental trauma service, titled 'Think T's'. It aims to provide effective trauma care across an entire region by a dedicated team of experienced clinicians from primary care settings to reduce inappropriate attendance to secondary care services and upskill colleagues in dental traumatology.

FINDINGS AND CONCLUSIONS

Since its inception, the dental trauma service has been public-facing and has managed referrals from a range of sources which include general medical practitioners, A&E clinicians and ambulance services. The service has been well received and has been seeking to integrate with the Directory of Services as well as NHS 111.

Cell transcriptomic atlas of the non-human primate Macaca fascicularis

Studying tissue composition and function in non-human primates (NHPs) is crucial to understand the nature of our own species. Here we present a large-scale cell transcriptomic atlas that encompasses over 1 million cells from 45 tissues of the adult NHP Macaca fascicularis. This dataset provides a vast annotated resource to study a species phylogenetically close to humans. To demonstrate the utility of the atlas, we have reconstructed the cell-cell interaction networks that drive Wnt signalling across the body, mapped the distribution of receptors and co-receptors for viruses causing human infectious diseases, and intersected our data with human genetic disease orthologues to establish potential clinical associations. Our M. fascicularis cell atlas constitutes an essential reference for future studies in humans and NHPs.

A constant pool of Lgr5+ intestinal stem cells is required for intestinal homeostasis

Lgr5⁺ crypt base columnar cells, the operational intestinal stem cells (ISCs), are thought to be dispensable for small intestinal (SI) homeostasis. Using a Lgr5-2A-DTR (diphtheria toxin receptor) model, which ablates Lgr5⁺ cells with near-complete efficiency and retains endogenous levels of Lgr5 expression, we show that persistent depletion of Lgr5⁺ ISCs in fact compromises SI epithelial integrity and reduces epithelial turnover in vivo. In vitro, Lgr5-2A-DTR SI organoids are unable to establish or survive when Lgr5⁺ ISCs are continuously eliminated by adding DT to the media. However, transient exposure to DT at the start of culture allows organoids to form, and the rate of outgrowth reduces with the increasing length of DT presence. Our results indicate that intestinal homeostasis requires a constant pool of Lgr5⁺ ISCs, which is supplied by rapidly reprogrammed non-Lgr5⁺ crypt populations when preexisting Lgr5⁺ ISCs are ablated.

Lgr5 Marks Adult Progenitor Cells Contributing to Skeletal Muscle Regeneration and Sarcoma Formation

Regeneration of adult skeletal muscle is driven largely by resident satellite cells, a stem cell population increasingly considered to display a high degree of molecular heterogeneity. In this study, we find that Lgr5, a receptor for Rspo and a potent mediator of Wnt/β-catenin signaling, marks a subset of activated satellite cells that contribute to muscle regeneration. Lgr5 is found to be rapidly upregulated in purified myogenic progenitors following acute cardiotoxin-induced injury. In vivo lineage tracing using our Lgr5-2ACre^ERT2R26tdTomato^LSL reporter mouse model shows that Lgr5⁺ cells can reconstitute damaged muscle fibers following muscle injury, as well as replenish the quiescent satellite cell pool. Moreover, conditional mutation in Lgr52ACre^ERT2;Kras^G12D;Trp53^flox/flox mice drives undifferentiated pleomorphic sarcoma formation in adult mice, thereby substantiating Lgr5⁺ cells as a cell of origin of sarcomas. Our findings provide the groundwork for developing Rspo/Wnt-signaling-based therapeutics to potentially enhance regenerative outcomes of skeletal muscles in degenerative muscle diseases.

Neonatal Wnt-dependent Lgr5 positive stem cells are essential for uterine gland development

Wnt signaling is critical for directing epithelial gland development within the uterine lining to ensure successful gestation in adults. Wnt-dependent, Lgr5-expressing stem/progenitor cells are essential for the development of glandular epithelia in the intestine and stomach, but their existence in the developing reproductive tract has not been investigated. Here, we employ Lgr5-2A-EGFP/CreERT2/DTR mouse models to identify Lgr5-expressing cells in the developing uterus and to evaluate their stem cell identity and function. Lgr5 is broadly expressed in the uterine epithelium during embryogenesis, but becomes largely restricted to the tips of developing glands after birth. In-vivo lineage tracing/ablation/organoid culture assays identify these gland-resident Lgr5^high cells as Wnt-dependent stem cells responsible for uterine gland development. Adjacent Lgr5^neg epithelial cells within the neonatal glands function as essential niche components to support the function of Lgr5^high stem cells ex-vivo. These findings constitute a major advance in our understanding of uterine development and lay the foundations for investigating potential contributions of Lgr5⁺ stem/progenitor cells to uterine disorders.

Uterine gland development is essential for successful embryo implantation, decidua formation and placental development. Here the authors demonstrate that neonatal Wnt-dependent Lgr5 expressing stem/progenitor cells at the tips of developing glands are indispensable for uterine gland development.

Frizzled-7 Is Required for Wnt Signaling in Gastric Tumors with and Without Apc Mutations

A subset of patients with gastric cancer have mutations in genes that participate in or regulate Wnt signaling at the level of ligand (Wnt) receptor (Fzd) binding. Moreover, increased Fzd expression is associated with poor clinical outcome. Despite these findings, there are no in vivo studies investigating the potential of targeting Wnt receptors for treating gastric cancer, and the specific Wnt receptor transmitting oncogenic Wnt signaling in gastric cancer is unknown. Here, we use inhibitors of Wnt/Fzd (OMP-18R5/vantictumab) and conditional gene deletion to test the therapeutic potential of targeting Wnt signaling in preclinical models of intestinal-type gastric cancer and ex vivo organoid cultures. Pharmacologic targeting of Fzd inhibited the growth of gastric adenomas in vivo. We identified Fzd7 to be the predominant Wnt receptor responsible for transmitting Wnt signaling in human gastric cancer cells and mouse models of gastric cancer, whereby Fzd7-deficient cells were retained in gastric adenomas but were unable to respond to Wnt signals and consequently failed to proliferate. Genetic deletion of Fzd7 or treatment with vantictumab was sufficient to inhibit the growth of gastric adenomas with or without mutations to Apc. Vantictumab is currently in phase Ib clinical trials for advanced pancreatic, lung, and breast cancer. Our data extend the scope of patients that may benefit from this therapeutic approach as we demonstrate that this drug will be effective in treating patients with gastric cancer regardless of APC mutation status. SIGNIFICANCE: The Wnt receptor Fzd7 plays an essential role in gastric tumorigenesis irrespective of Apc mutation status, therefore targeting Wnt/Fzd7 may be of therapeutic benefit to patients with gastric cancer.

RSPO2 inhibition of RNF43 and ZNRF3 governs limb development independently of LGR4/5/6

The four R-spondin secreted ligands (RSPO1-RSPO4) act via their cognate LGR4, LGR5 and LGR6 receptors to amplify WNT signalling^1-3. Here we report an allelic series of recessive RSPO2 mutations in humans that cause tetra-amelia syndrome, which is characterized by lung aplasia and a total absence of the four limbs. Functional studies revealed impaired binding to the LGR4/5/6 receptors and the RNF43 and ZNRF3 transmembrane ligases, and reduced WNT potentiation, which correlated with allele severity. Unexpectedly, however, the triple and ubiquitous knockout of Lgr4, Lgr5 and Lgr6 in mice did not recapitulate the known Rspo2 or Rspo3 loss-of-function phenotypes. Moreover, endogenous depletion or addition of exogenous RSPO2 or RSPO3 in triple-knockout Lgr4/5/6 cells could still affect WNT responsiveness. Instead, we found that the concurrent deletion of rnf43 and znrf3 in Xenopus embryos was sufficient to trigger the outgrowth of supernumerary limbs. Our results establish that RSPO2, without the LGR4/5/6 receptors, serves as a direct antagonistic ligand to RNF43 and ZNRF3, which together constitute a master switch that governs limb specification. These findings have direct implications for regenerative medicine and WNT-associated cancers.

Genomic and Epigenomic Profiling of High-Risk Intestinal Metaplasia Reveals Molecular Determinants of Progression to Gastric Cancer

Intestinal metaplasia (IM) is a pre-malignant condition of the gastric mucosa associated with increased gastric cancer (GC) risk. We performed (epi)genomic profiling of 138 IMs from 148 cancer-free patients, recruited through a 10-year prospective study. Compared with GCs, IMs exhibit low mutational burdens, recurrent mutations in certain tumor suppressors (FBXW7) but not others (TP53, ARID1A), chromosome 8q amplification, and shortened telomeres. Sequencing identified more IM patients with active Helicobacter pylori infection compared with histopathology (11%-27%). Several IMs exhibited hypermethylation at DNA methylation valleys; however, IMs generally lack intragenic hypomethylation signatures of advanced malignancy. IM patients with shortened telomeres and chromosomal alterations were associated with subsequent dysplasia or GC; conversely patients exhibiting normal-like epigenomic patterns were associated with regression.

Wnt Signaling in Adult Epithelial Stem Cells and Cancer

Wnt/β-catenin signaling is integral to the homeostasis and regeneration of many epithelial tissues due to its critical role in adult stem cell regulation. It is also implicated in many epithelial cancers, with mutations in core pathway components frequently present in patient tumors. In this chapter, we discuss the roles of Wnt/β-catenin signaling and Wnt-regulated stem cells in homeostatic, regenerative and cancer contexts of the intestines, stomach, skin, and liver. We also examine the sources of Wnt ligands that form part of the stem cell niche. Despite the diversity in characteristics of various tissue stem cells, the role(s) of Wnt/β-catenin signaling is generally coherent in maintaining stem cell fate and/or promoting proliferation. It is also likely to play similar roles in cancer stem cells, making the pathway a salient therapeutic target for cancer. While promising progress is being made in the field, deeper understanding of the functions and signaling mechanisms of the pathway in individual epithelial tissues will expedite efforts to modulate Wnt/β-catenin signaling in cancer treatment and tissue regeneration.

The Central Role of Wnt Signaling and Organoid Technology in Personalizing Anticancer Therapy

The Wnt pathway is at the heart of organoid technology, which is set to revolutionize the cancer field. We can now predetermine a patient's response to any given anticancer therapy by exposing tumor organoids established from the patient's own tumor. This cutting-edge biomedical platform translates to patients being treated with the correct drug at the correct dose from the outset, a truly personalized and precise medical approach. A high throughput drug screen on organoids also allows drugs to be tested in limitless combinations. More recently, the tumor cells that are resistant to the therapy given to a patient were selected in culture using the patient's organoids. The resistant tumor organoids were then screened empirically to identify drugs that will kill the resistant cells. This information allows diagnosis in real-time to either prevent tumor recurrence or effectively treat the recurring tumor. Furthermore, the ability to culture stem cell-derived epithelium as organoids has enabled us to begin to understand how a stem cell becomes a cancer cell or to pin-point the genetic alteration that underlies a given genetic syndrome. Here we summarize these advances and the central role of Wnt signaling, and identify the next challenges for organoid technology.

Loss of the Wnt receptor frizzled 7 in the mouse gastric epithelium is deleterious and triggers rapid repopulation in vivo

The gastric epithelium consists of tubular glandular units, each containing several differentiated cell types, and populations of stem cells, which enable the stomach to secrete the acid, mucus and various digestive enzymes required for its function. Very little is known about which cell signalling pathways are required for homeostasis of the gastric epithelium. Many diseases, such as cancer, arise as a result of deregulation of signalling pathways that regulate homeostasis of the diseased organ. Therefore, it is important to understand the biology of how normal conditions are maintained in a tissue to help inform the mechanisms driving disease in that same tissue, and to identify potential points of therapeutic intervention. Wnt signalling regulates several cell functions, including proliferation, differentiation and migration, and plays a crucial role during homeostasis of several tissues, including the intestinal epithelium. Wnt3a is required in the culture medium of gastric organoids, suggesting it is also important for the homeostasis of the gastric epithelium, but this has not been investigated in vivo. Here, we show that the Wnt receptor frizzled 7 (Fzd7), which is required for the homeostasis of the intestine, is expressed in the gastric epithelium and is required for gastric organoid growth. Gastric-specific loss of Fzd7 in the adult gastric epithelium of mice is deleterious and triggers rapid epithelial repopulation, which we believe is the first observation of this novel function for this tissue. Taken together, these data provide functional evidence of a crucial role for Wnt signalling, via the Fzd7 receptor, during homeostasis of the gastric epithelium.

Editors’ choice: Wnt signalling regulates homeostasis of the gastric epithelium via the Fzd7 receptor, which could be a target for therapeutic intervention in gastric cancer.

Lgr5-expressing chief cells drive epithelial regeneration and cancer in the oxyntic stomach

The daily renewal of the corpus epithelium is fuelled by adult stem cells residing within tubular glands, but the identity of these stem cells remains controversial. Lgr5 marks homeostatic stem cells and 'reserve' stem cells in multiple tissues. Here, we report Lgr5 expression in a subpopulation of chief cells in mouse and human corpus glands. Using a non-variegated Lgr5-2A-CreERT2 mouse model, we show by lineage tracing that Lgr5-expressing chief cells do not behave as corpus stem cells during homeostasis, but are recruited to function as stem cells to effect epithelial renewal following injury by activating Wnt signalling. Ablation of Lgr5⁺ cells severely impairs epithelial homeostasis in the corpus, indicating an essential role for these Lgr5⁺ cells in maintaining the homeostatic stem cell pool. We additionally define Lgr5⁺ chief cells as a major cell-of-origin of gastric cancer. These findings reveal clinically relevant insights into homeostasis, repair and cancer in the corpus.

Inactivation of TGFβ receptors in stem cells drives cutaneous squamous cell carcinoma

Melanoma patients treated with oncogenic BRAF inhibitors can develop cutaneous squamous cell carcinoma (cSCC) within weeks of treatment, driven by paradoxical RAS/RAF/MAPK pathway activation. Here we identify frequent TGFBR1 and TGFBR2 mutations in human vemurafenib-induced skin lesions and in sporadic cSCC. Functional analysis reveals these mutations ablate canonical TGFβ Smad signalling, which is localized to bulge stem cells in both normal human and murine skin. MAPK pathway hyperactivation (through Braf(V600E) or Kras(G12D) knockin) and TGFβ signalling ablation (through Tgfbr1 deletion) in LGR5(+ve) stem cells enables rapid cSCC development in the mouse. Mutation of Tp53 (which is commonly mutated in sporadic cSCC) coupled with Tgfbr1 deletion in LGR5(+ve) cells also results in cSCC development. These findings indicate that LGR5(+ve) stem cells may act as cells of origin for cSCC, and that RAS/RAF/MAPK pathway hyperactivation or Tp53 mutation, coupled with loss of TGFβ signalling, are driving events of skin tumorigenesis.

Organoids as an in vitro model of human development and disease

The in vitro organoid model is a major technological breakthrough that has already been established as an essential tool in many basic biology and clinical applications. This near-physiological 3D model facilitates an accurate study of a range of in vivo biological processes including tissue renewal, stem cell/niche functions and tissue responses to drugs, mutation or damage. In this Review, we discuss the current achievements, challenges and potential applications of this technique.

Mutant p53 accumulates in cycling and proliferating cells in the normal tissues of p53 R172H mutant mice

The tumour suppressor p53 is regulated primarily at the protein level. In normal tissues its levels are maintained at a very low level by the action of specific E3 ligases and the ubiquitin proteosome pathway. The mutant p53 protein contributes to transformation, metastasis and drug resistance. High levels of mutant p53 can be found in tumours and the accumulation of mutant p53 has previously been reported in pathologically normal cells in human skin. We show for the first time that similarly elevated levels of mutant p53 can be detected in apparently normal cells in a mutant p53 knock-in mouse model. In fact, in the small intestine, mutant p53 spontaneously accumulates in a manner dependent on gene dosage and cell type. Mutant p53 protein is regulated similarly to wild type p53, which can accumulate rapidly after induction by ionising radiation or Mdm2 inhibitors, however, the clearance of mutant p53 protein is much slower than wild type p53. The accumulation of the protein in the murine small intestine is limited to the cycling, crypt base columnar cells and proliferative zone and is lost as the cells differentiate and exit the cell cycle. Loss of Mdm2 results in even higher levels of p53 expression but p53 is still restricted to proliferating cells in the small intestine. Therefore, the small intestine of these p53 mutant mice is an experimental system in which we can dissect the molecular pathways leading to p53 accumulation, which has important implications for cancer prevention and therapy.

Quantifying Lgr5-positive stem cell behaviour in the pyloric epithelium

Using in-vivo lineage tracing data we quantified clonal expansion as well as proliferation and differentiation of the Lgr5-positive stem cell population in pyloric gastric glands. Fitting clone expansion models, we estimated that there are five effective Lgr5-positive cells able to give rise to monoclonal glands by replacing each other following a pattern of neutral drift dynamics. This analysis is instrumental to assess stem cell performance; however, stem cell proliferation is not quantified by clone expansion analysis. We identified a suitable mathematical model to quantify proliferation and differentiation of the Lgr5-positive population. As expected for populations in steady-state, the proliferation rate of the Lgr5-positive population was equal to its rate of differentiation. This rate was significantly faster than the rate at which effective cells are replaced, estimated by modelling clone expansion/contraction. This suggests that the majority of Lgr5-positive cell divisions serve to renew epithelial cells and only few result in the effective replacement of a neighbour to effect expansion to the entire gland. The application of the model under altered situations with uncoupled differentiation and proliferation was demonstrated. This methodology represents a valuable tool for quantifying stem cell performance in homeostasis and importantly for deciphering altered stem cell behaviour in disease.

Stemming Colorectal Cancer Growth and Metastasis: HOXA5 Forces Cancer Stem Cells to Differentiate

Wnt signaling drives colorectal cancer stem cells, but effective therapeutics targeting these cells and their signaling pathways are lacking. In this issue of Cancer Cell, Ordóñez-Morán and colleagues describe a promising therapeutic intervention for colorectal cancers that selectively induces cancer stem cell differentiation through HOXA5 expression and Wnt signaling inhibition.

E-cadherin can limit the transforming properties of activating β-catenin mutations

Wnt pathway deregulation is a common characteristic of many cancers. Only colorectal cancer predominantly harbours mutations in APC, whereas other cancer types (hepatocellular carcinoma, solid pseudopapillary tumours of the pancreas) have activating mutations in β-catenin (CTNNB1). We have compared the dynamics and the potency of β-catenin mutations in vivo. Within the murine small intestine (SI), an activating mutation of β-catenin took much longer to achieve Wnt deregulation and acquire a crypt-progenitor cell (CPC) phenotype than Apc or Gsk3 loss. Within the colon, a single activating mutation of β-catenin was unable to drive Wnt deregulation or induce the CPC phenotype. This ability of β-catenin mutation to differentially transform the SI versus the colon correlated with higher expression of E-cadherin and a higher number of E-cadherin:β-catenin complexes at the membrane. Reduction in E-cadherin synergised with an activating mutation of β-catenin resulting in a rapid CPC phenotype within the SI and colon. Thus, there is a threshold of β-catenin that is required to drive transformation, and E-cadherin can act as a buffer to sequester mutated β-catenin.

Frizzled7 functions as a Wnt receptor in intestinal epithelial Lgr5(+) stem cells

The mammalian adult small intestinal epithelium is a rapidly self-renewing tissue that is maintained by a pool of cycling stem cells intermingled with Paneth cells at the base of crypts. These crypt base stem cells exclusively express Lgr5 and require Wnt3 or, in its absence, Wnt2b. However, the Frizzled (Fzd) receptor that transmits these Wnt signals is unknown. We determined the expression profile of Fzd receptors in Lgr5(+) stem cells, their immediate daughter cells, and Paneth cells. Here we show Fzd7 is enriched in Lgr5(+) stem cells and binds Wnt3 and Wnt2b. Conditional deletion of the Fzd7 gene in adult intestinal epithelium leads to stem cell loss in vivo and organoid death in vitro. Crypts of conventional Fzd7 knockout mice show decreased basal Wnt signaling and impaired capacity to regenerate the epithelium following deleterious insult. These observations indicate that Fzd7 is required for robust Wnt-dependent processes in Lgr5(+) intestinal stem cells.

Snai1 regulates cell lineage allocation and stem cell maintenance in the mouse intestinal epithelium

Snail family members regulate epithelial-to-mesenchymal transition (EMT) during invasion of intestinal tumours, but their role in normal intestinal homeostasis is unknown. Studies in breast and skin epithelia indicate that Snail proteins promote an undifferentiated state. Here, we demonstrate that conditional knockout of Snai1 in the intestinal epithelium results in apoptotic loss of crypt base columnar stem cells and bias towards differentiation of secretory lineages. In vitro organoid cultures derived from Snai1 conditional knockout mice also undergo apoptosis when Snai1 is deleted. Conversely, ectopic expression of Snai1 in the intestinal epithelium in vivo results in the expansion of the crypt base columnar cell pool and a decrease in secretory enteroendocrine and Paneth cells. Following conditional deletion of Snai1, the intestinal epithelium fails to produce a proliferative response following radiation-induced damage indicating a fundamental requirement for Snai1 in epithelial regeneration. These results demonstrate that Snai1 is required for regulation of lineage choice, maintenance of CBC stem cells and regeneration of the intestinal epithelium following damage.

Ex vivo culture of the intestinal epithelium: strategies and applications

Limited pools of resident adult stem cells are critical effectors of epithelial renewal in the intestine throughout life. Recently, significant progress has been made regarding the isolation and in vitro propagation of fetal and adult intestinal stem cells in mammals. It is now possible to generate ever-expanding, three-dimensional epithelial structures in culture that closely parallel the in vivo epithelium of the intestine. Growing such organotypic epithelium ex vivo facilitates a detailed description of endogenous niche factors or stem-cell characteristics, as they can be monitored in real time. Accordingly, this technology has already greatly contributed to our understanding of intestinal adult stem-cell renewal and differentiation. Transplanted organoids have also been proven to readily integrate into, and effect the long-term repair of, mouse colonic epithelia in vivo, establishing the organoid culture as a promising tool for adult stem cell/gene therapy. In another exciting development, novel genome-editing techniques have been successfully employed to functionally repair disease loci in cultured intestinal stem cells from human patients with a hereditary defect. It is anticipated that this technology will be instrumental in exploiting the regenerative medicine potential of human intestinal stem cells for treating human disorders in the intestinal tract and for creating near-physiological ex vivo models of human gastrointestinal disease.

Leucine-rich repeat-containing G-protein-coupled Receptor 5 marks short-term hematopoietic stem and progenitor cells during mouse embryonic development

Lgr5 is a marker for proliferating stem cells in adult intestine, stomach, and hair follicle. However, Lgr5 is not expressed in adult hematopoietic stem and progenitor cells (HSPCs). Whether Lgr5 is expressed in the embryonic and fetal HSPCs that undergo rapid proliferation is unknown. Here we report the detection of Lgr5 expression in HSPCs in the aorta-gonad-mesonephros (AGM) and fetal liver. We also found that a portion of Lgr5(+) cells expressed the Runx1 gene that is critical for the ontogeny of HSPCs. A small portion of Lgr5(+) cells also expressed HSPC surface markers c-Kit and CD34 in AGM or CD41 in fetal liver. Furthermore, the majority of Lgr5(+) cells expressed Ki67, indicating their proliferating state. Transplantation of fetal liver-derived Lgr5-GFP(+) cells (E12.5) demonstrated that Lgr5-GFP(+) cells were able to reconstitute myeloid and lymphoid lineages in adult recipients, but the engraftment was short-term (4-8 weeks) and 20-fold lower compared with the Lgr5-GFP(-) control. Our data show that Lgr5-expressing cells mark short-term hematopoietic stem and progenitor cells, consistent with the role of Lgr5 in supporting HSPCs rapid proliferation during embryonic and fetal development.

Epithelial stem cells and intestinal cancer

The mammalian intestine is comprised of an epithelial layer that serves multiple functions in order to maintain digestive activity as well as intestinal homeostasis. This epithelial layer contains highly proliferative stem cells which facilitate its characteristic rapid regeneration. How these stem cells contribute to tissue repair and normal homeostasis are actively studied, and while we have a greater understanding of the molecular mechanisms and cellular locations that underlie stem cell regulation in this tissue, much still remains undiscovered. This review describes epithelial stem cells in both intestinal and non-intestinal tissues, as well as the strategies that have been used to further characterize the cells. Through a discussion of the current understanding of intestinal self-renewal and tissue regeneration in response to injury, we focus on how dysregulation of critical signaling pathways results in potentially oncogenic aberrations, and highlight issues that should be addressed in order for effective intestinal cancer therapies to be devised.

Preparation for and physiological responses to competing in the Marathon des Sables: a case report

A case study into the preparation and physiological responses of competing in the Marathon des Sables (MDS) was conducted by preparing a male competitor for, and monitoring him during, his first attempt at the race. The aims of this case report were to (a) prepare and monitor an ex-Olympic, male rower (S1) during the 2010 race and; (b) compare his physiological responses and race performance to that of the current MDS record holder (S2). S1 (age 37 y; body mass 94.0 kg; height 1.92 m; VO(2peak) 66.0 ml·kg⁻¹·min⁻¹) and S2 (age 37 y; body mass 60.8 kg; height 1.68 m; VO(2peak) 65.9 ml·kg⁻¹·min⁻¹) completed a heat test and S1 subsequently underwent 7 d of heat acclimation prior to the MDS. Gastro-intestinal temperature (Tgi) and heart rate (HR) were measured for S1 during Stages 2, 4, and 5 of the MDS and pre- and post-stage body mass, and urine specific gravity were measured for all stages. Race time and average speeds were collected for S1 and S2. Total race times for S1 and S2 were 25:29:35 and 19:45:08 h:min:s. S1's mean (± 1 SD) percentage HR range (%HRR=[HR-HRmin]/[HRmax-HRmin]x100) was 66.1 ± 13.4% and Tgi ranged between 36.63-39.65°C. The results provide a case report on the physiological responses of a highly aerobically-trained, but novice ultra-endurance runner competing in the MDS, and allow for a comparison with an elite performer.

Ovarian LGR5 is critical for successful pregnancy

Leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) is expressed in many organs, including female reproductive organs, and is a stem cell marker in the stomach and intestinal epithelium, hair follicles, and ovarian surface epithelium. Despite ongoing studies, the definitive physiological functions of Lgr5 remain unclear. We utilized mice with conditional deletion of Lgr5 (Lgr5(d/d)) in the female reproductive organs by progesterone receptor-Cre (Pgr(Cre)) to determine Lgr5's functions during pregnancy. Only 30% of plugged Lgr5(d/d) females delivered live pups, and their litter sizes were lower. We found that pregnancy failure in Lgr5(d/d) females was due to insufficient ovarian progesterone (P4) secretion that compromised decidualization, terminating pregnancy. The drop in P4 levels was reflected in elevated levels of P4-metabolizing enzyme 20α-hydroxysteroid dehydrogenase in corpora lutea (CL) inactivated of Lgr5. Of interest, P4 supplementation rescued decidualization failure and supported pregnancy to full term in Lgr5(d/d) females. These results provide strong evidence that Lgr5 is critical to normal CL function, unveiling a new role of LGR5 in the ovary.

LGR5 positivity defines stem-like cells in colorectal cancer

Like normal colorectal epithelium, colorectal carcinomas (CRCs) are organized hierarchically and include populations of cells with stem-like properties. Leucine-rich-repeat-containing G-protein-coupled receptor 5 (LGR5) is associated with these stem cells in normal colorectal epithelium; however, the precise function of LGR5 in CRC remains largely unknown. Here, we analyzed the functional and molecular consequences of short hairpin RNA-mediated silencing of LGR5 in CRC cell lines SW480 and HT-29. Additionally, we exposed Lgr5-EGFP-IRES-CreERT2 mice to azoxymethane/dextrane sodium sulfate (AOM/DSS), which induces inflammation-driven colon tumors. Tumors were then flow-sorted into fractions of epithelial cells that expressed high or low levels of Lgr5 and were molecularly characterized using gene expression profiling and array comparative genomic hybridization. Silencing of LGR5 in SW480 CRC cells resulted in a depletion of spheres but did not affect adherently growing cells. Spheres expressed higher levels of several stem cell-associated genes than adherent cells, including LGR5. Silencing of LGR5 reduced proliferation, migration and colony formation in vitro and tumorigenicity in vivo. In accordance with these results, NOTCH signaling was downregulated upon LGR5 silencing. In AOM/DSS-induced colon tumors, Lgr5 high cells showed higher levels of several stem cell-associated genes and higher Wnt signaling than Lgr5 low tumor cells and Lgr5 high normal colon cells. Array comparative genomic hybridization revealed no genomic imbalances in either tumor cell fraction. Our data elucidate mechanisms that define the role of LGR5 as a marker for stem-like cells in CRC.

Lgr proteins in epithelial stem cell biology

The ultimate success of global efforts to exploit adult stem cells for regenerative medicine will depend heavily on the availability of robust, highly selective stem cell surface markers that facilitate the isolation of stem cells from human tissues. Any subsequent expansion or manipulation of isolated stem cells will also require an intimate knowledge of the mechanisms that regulate these cells, to ensure maintenance of their regenerative capacities and to minimize the risk of introducing undesirable growth traits that could pose health risks for patients. A subclass of leucine-rich repeat-containing G-protein-coupled receptor (Lgr) proteins has recently gained prominence as adult stem cell markers with crucial roles in maintaining stem cell functions. Here, we discuss the major impact that their discovery has had on our understanding of adult stem cell biology in various self-renewing tissues and in accelerating progress towards the development of effective stem cell therapies.