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

Lgr5 and stem/progenitor gene expression in gastric/gastroesophageal junction carcinoma - significance of potentially retained stemness

Background

Gastric/gastroesophageal junction (GEJ) adenocarcinomas are heterogeneous, comprising four molecularly distinct subtypes, namely EBV-positive, microsatellite instability (MSI), chromosomal instability (CIN) and genomically stable (GS) subtypes, and a part of this heterogeneity may hypothesized to be different cells-of-origin. Stem/progenitor cell hierarchy in the stomach is complex, which include the Lgr5⁽⁺⁾ gastric stem cells (GSCs).

Methods

While previous studies have focused on non-nuclear Lgr5 expression, nuclear Lgr5 expression has been reported in a subset of stem cells, and we examined nuclear Lgr5 expression in a local cohort of 95 cases of gastric/GEJ adenocarcinoma. mRNA levels for LGR5 and other stem cell marker genes were examined in the TCGA cohort.

Results

We observed nuclear Lgr5 expression in a 18/95 cases. Near mutual exclusivity was seen between nuclear Lgr5 and strong non-nuclear Lgr5. Both strong non-nuclear and nuclear Lgr5 expression tended to be seen more frequently with the intestinal histotype and approximated CIN molecular subtype. With respect to overall survival (OS), nuclear Lgr5 expression appears to be protective, with the worst survival being seen in the cases lacking nuclear Lgr5 and with low non-nuclear Lgr5 expression. When compared to other stem/progenitor cell markers, LGR5 mRNA expression clusters with other GSC marker genes, including VIL1. Higher expression of these GSC marker genes was associated with better OS.

Conclusions

Our results show that Lgr5 expression is dynamic in gastric/GEJ adenocarcinoma and heterogeneous across the several disease attributes. We postulate that this may reflect “retained stemness” in the form of Lgr5^High-GSC signature that appears to be associated with better survival.

Slow-Cycling Cancer Stem Cells Regulate Progression and Chemoresistance in Colon Cancer

Cancer chemoresistance is often attributed to the presence of cancer stem cell (CSC)-like cells, but whether they are homogeneously chemoresistant remains unclear. We previously showed that in colon tumors, a subpopulation of LGR5⁺ CSC-like cells driven by TCF1 (TCF7), a Wnt-responsive transcription factor, were responsible for tumorigenicity. Here we demonstrate that the tumorigenic subpopulation of mouse LGR5⁺ cells exists in a slow-cycling state and identify a unique 22-gene signature that characterizes these slow-cycling CSC. Seven of the signature genes are specifically expressed in slow-cycling LGR5⁺ cells from xenografted human colon tumors and are upregulated in colon cancer clinical specimens. Among these seven, four genes (APCDD1, NOTUM, PROX1, and SP5) are known to be direct Wnt target genes, and PROX1 was expressed in the invasive fronts of colon tumors. PROX1 was activated by TCF1 to induce CDKN1C and maintain a slow-cycling state in colon cancer organoids. Strikingly, PROX1 was required for recurrent growth after chemotherapeutic treatment, suggesting that inhibition of slow-cycling CSC by targeting the TCF1-PROX1-CDKN1C pathway is an effective strategy to combat refractory colon cancer in combination with conventional chemotherapy. SIGNIFICANCE: These findings illustrate the importance of a slow-cycling CSC subpopulation in colon cancer development and chemoresistance, with potential implications for the identified slow-cycling CSC signatures and the TCF1-PROX1-CDKN1C pathway as therapeutic targets.

Defining Adult Stem Cell Function at Its Simplest: The Ability to Replace Lost Cells through Mitosis

Classic studies on hematopoiesis indicate that blood cell numbers are maintained by rare, hard-wired, transplantable stem cells (SCs). Subsequent studies in other organs have implicitly assumed that all SC hierarchies follow the design of the hematopoietic system. Lineage tracing techniques have revolutionized the study of solid tissue SCs. It thus appears that key characteristics of the hematopoietic SC hierarchy (rarity of SCs, specific marker expression, quiescence, asymmetric division, and unidirectional differentiation) are not generalizable to other tissues. In light of these insights, we offer a revised, generalizable definition of SC function: the ability to replace lost tissue through cell division.

MicroRNA-222 Regulates Melanoma Plasticity

Melanoma is one of the most aggressive and highly resistant tumors. Cell plasticity in melanoma is one of the main culprits behind its metastatic capabilities. The detailed molecular mechanisms controlling melanoma plasticity are still not completely understood. Here we combine mathematical models of phenotypic switching with experiments on IgR39 human melanoma cells to identify possible key targets to impair phenotypic switching. Our mathematical model shows that a cancer stem cell subpopulation within the tumor prevents phenotypic switching of the other cancer cells. Experiments reveal that hsa-mir-222 is a key factor enabling this process. Our results shed new light on melanoma plasticity, providing a potential target and guidance for therapeutic studies.

Role of metaplasia during gastric regeneration

Spasmolytic polypeptide/trefoil factor 2 (TFF2)-expressing metaplasia (SPEM) is a mucous-secreting reparative lineage that emerges at the ulcer margin in response to gastric injury. Under conditions of chronic inflammation with parietal cell loss, SPEM has been found to emerge and evolve into neoplasia. Cluster-of-differentiation gene 44 (CD44) is known to coordinate normal and metaplastic epithelial cell proliferation. In particular, CD44 variant isoform 9 (CD44v9) associates with the cystine-glutamate transporter xCT, stabilizes the protein, and provides defense against reactive oxygen species (ROS). xCT stabilization by CD44v9 leads to defense against ROS by cystine uptake, glutathione (GSH) synthesis, and maintenance of the redox balance within the intracellular environment. Furthermore, p38 signaling is a known downstream ROS target, leading to diminished cell proliferation and migration, two vital processes of gastric epithelial repair. CD44v9 emerges during repair of the gastric epithelium after injury, where it is coexpressed with other markers of SPEM. The regulatory mechanisms for the emergence of CD44v9 and the role of CD44v9 during the process of gastric epithelial regeneration are largely unknown. Inflammation and M2 macrophage infiltration have recently been demonstrated to play key roles in the induction of SPEM after injury. The following review proposes new insights into the functional role of metaplasia in the process of gastric regeneration in response to ulceration. Our insights are extrapolated from documented studies reporting oxyntic atrophy and SPEM development and our current unpublished findings using the acetic acid-induced gastric injury model.

Generation of 3D human gastrointestinal organoids: principle and applications

The stomach and intestine are important organs for food digestion, nutrient absorption, immune protection and hormone production. Gastrointestinal diseases such as cancer and ulcer are big threats to human health. Appropriate disease models are in sore need for mechanistic understanding and drug discovery. Organoids are three-dimensional in vitro cultured structures derived from tissues and pluripotent stem cells with multiple types of cells and mimicking in vivo tissues in major aspects. They have a great potential in regenerative medicine and personalized medicine. Here, we review the major signaling pathways regulating gastrointestinal epithelial homeostasis, summarize different methods to generate human gastrointestinal organoids and highlight their applications in biological research and medical practice.

Prevention of tumor risk associated with the reprogramming of human pluripotent stem cells

Human pluripotent embryonic stem cells have two special features: self-renewal and pluripotency. It is important to understand the properties of pluripotent stem cells and reprogrammed stem cells. One of the major problems is the risk of reprogrammed stem cells developing into tumors. To understand the process of differentiation through which stem cells develop into cancer cells, investigators have attempted to identify the key factors that generate tumors in humans. The most effective method for the prevention of tumorigenesis is the exclusion of cancer cells during cell reprogramming. The risk of cancer formation is dependent on mutations of oncogenes and tumor suppressor genes during the conversion of stem cells to cancer cells and on the environmental effects of pluripotent stem cells. Dissecting the processes of epigenetic regulation and chromatin regulation may be helpful for achieving correct cell reprogramming without inducing tumor formation and for developing new drugs for cancer treatment. This review focuses on the risk of tumor formation by human pluripotent stem cells, and on the possible treatment options if it occurs. Potential new techniques that target epigenetic processes and chromatin regulation provide opportunities for human cancer modeling and clinical applications of regenerative medicine.

Tracing the Dynamics of Stem Cell Fate

The mechanisms that regulate the balance between stem cell duplication and differentiation in adult tissues remain in debate. Using a combination of genetic lineage tracing and marker-based assays, the quantitative statistical analysis of clone size and cell composition has provided insights into the patterns of stem cell fate across a variety of tissue types and organisms. These studies have emphasized the role of niche factors and environmental cues in promoting stem cell competence, fate priming, and stochastic renewal programs. At the same time, evidence for injury-induced "cellular reprogramming" has revealed the remarkable flexibility of cell states, allowing progenitors to reacquire self-renewal potential during regeneration. Together, these findings have questioned the nature of stem cell identity and function. Here, focusing on a range of canonical tissue types, we review how quantitative modeling-based approaches have uncovered conserved patterns of stem cell fate and provided new insights into the mechanisms that regulate self-renewal.

Tools and Concepts for Interrogating and Defining Cellular Identity

Defining the mechanisms that generate specialized cell types and coordinate their functions is critical for understanding organ development and renewal. New tools and discoveries are challenging and refining our definitions of a cell type. A rapidly growing toolkit for single-cell analyses has expanded the number of markers that can be assigned to a cell simultaneously, revealing heterogeneity within cell types that were previously regarded as homogeneous populations. Additionally, cell types defined by specific molecular markers can exhibit distinct, context-dependent functions; for example, between tissues in homeostasis and those responding to damage. Here we review the current technologies used to identify and characterize cells, and we discuss how experimental and pathological perturbations are adding increasing complexity to our definitions of cell identity.

GPR30-Expressing Gastric Chief Cells Do Not Dedifferentiate But Are Eliminated via PDK-Dependent Cell Competition During Development of Metaplasia

BACKGROUND & AIMS

Gastric chief cells, a mature cell type that secretes digestive enzymes, have been proposed to be the origin of metaplasia and cancer through dedifferentiation or transdifferentiation. However, studies supporting this claim have had technical limitations, including issues with the specificity of chief cell markers and the toxicity of drugs used. We therefore sought to identify genes expressed specifically in chief cells and establish a model to trace these cells.

METHODS

We performed transcriptome analysis of Mist1-CreERT-traced cells, with or without chief cell depletion. Gpr30-rtTA mice were generated and crossed to TetO-Cre mice, and lineage tracing was performed after crosses to R26-TdTomato mice. Additional lineage tracing experiments were performed using Mist1-CreERT, Kitl-CreERT, Tff1-Cre, and Tff2-Cre mice crossed to reporter mice. Mice were given high-dose tamoxifen or DMP-777 or were infected with Helicobacter pylori to induce gastric metaplasia. We studied mice that expressed mutant forms of Ras in gastric cells, using TetO-Kras^G12D, LSL-Kras^G12D, and LSL-Hras^G12V mice. We analyzed stomach tissues from GPR30-knockout mice. Mice were given dichloroacetate to inhibit pyruvate dehydrogenase kinase (PDK)-dependent cell competition.

RESULTS

We identified GPR30, the G-protein-coupled form of the estrogen receptor, as a cell-specific marker of chief cells in gastric epithelium of mice. Gpr30-rtTA mice crossed to TetO-Cre;R26-TdTomato mice had specific expression of GPR30 in chief cells, with no expression noted in isthmus stem cells or lineage tracing of glands. Expression of mutant Kras in GPR30⁺ chief cells did not lead to the development of metaplasia or dysplasia but, instead, led to a reduction in labeled numbers of chief cells and a compensatory expansion of neck lineage, which was derived from upper Kitl⁺ clones. Administration of high-dose tamoxifen, DMP-777, or H pylori decreased the number of labeled chief cells. Chief cells were eliminated from epithelia via GPR30- and PDK-dependent cell competition after metaplastic stimuli, whereas loss of GRP30 or inhibition of PDK activity preserved chief cell numbers and attenuated neck lineage cell expansion.

CONCLUSIONS

In tracing studies of mice, we found that most chief cells are lost during metaplasia and therefore are unlikely to contribute to gastric carcinogenesis. Expansion of cells that coexpress neck and chief lineage markers, known as spasmolytic polypeptide-expressing metaplasia, does not occur via dedifferentiation from chief cells but, rather, through a compensatory response from neck progenitors to replace the eliminated chief cells.

Responses of gastric epithelial stem cells and their niche to Helicobacter pylori infection

Helicobacter pylori (H. pylori) are gram-negative bacteria that are able to colonize and persist in the stomach. Gastric cancer is tightly linked to chronic infection with this bacterium. Research over the last decades has illuminated the molecular interactions between H. pylori and host cells. It is now well established that H. pylori have multiple sophisticated means to adhere to epithelial cells and to manipulate their behavior. This interaction with the epithelium can lead to altered cell signaling, DNA damage and aberrant epithelial immunity. H. pylori are known to colonize the mucus layer of the stomach and surface epithelial cells. In addition, it has recently become clear that they can also penetrate the glands and directly interact with specialized epithelial cells deep in the glands. Understanding the biogeography of infection is important because gastric epithelial glands are composed of various types of short-lived differentiated cells that are constantly regenerated by a limited pool of long-lived stem cells located in base of gastric glands. Recent advances in gastric stem cell research not only led to identification of stem cell populations using specific markers but has also uncovered specific regulatory pathways and principles that govern gastric stem cell behavior and regeneration. Particularly, the stem cell state is largely dependent on signals from the niche cells that surround the stem cell compartment. The subpopulation of H. pylori that colonizes in the stem cell compartment triggers specific inflammatory responses and drives epithelial pathology. Colonization of gastric glands induces responses of the stem cell niche, simultaneously enhancing the cell turnover kinetics and driving the formation of antimicrobial cells in the gland base. These data reveal the high plasticity of the epithelium and its ability to adapt to the environment, which is necessary to regenerate and counterbalance infection, but simultaneously lays the grounds for development of gastric pathology and carcinogenesis.

Metaplastic Paneth Cells in Extra-Intestinal Mucosal Niche Indicate a Link to Microbiome and Inflammation

Paneth cells are residents of the intestinal epithelium. Abnormal appearance of Paneth cells has been widely documented in non-intestinal tissues within the digestive tract and even observed in non-gastrointestinal organs. Although metaplastic Paneth cells are part of the overarching pathology of intestinal metaplasia (IM), only a fraction of intestinal metaplastic lesions contain Paneth cells. We survey literature documenting metaplastic Paneth cells to gain insights into mechanism underlying their etiologic development as well as their potential relevance to human health. A synthesized view from this study suggests that the emergence of metaplastic Paneth cells at extra-intestinal mucosal sites likely represents a protective, anti-bacterial, and inflammatory response evoked by an altered microbial activity.

Correlation of Clinicopathological Features and LGR5 Expression in Triple-Negative Breast Cancer

LGR5 is the most robust known stem cell marker for gastrointestinal tumors, but there are few reports in breast cancer. Triple negative breast cancer (TNBC) is the most malignant subtype of breast cancer, and thus identification of new cancer stem cell populations in TNBC may help to identify targeted therapies. LGR5 expression was evaluated by RNAscope, a newly developed RNA in situ hybridization technique, using a tissue microarray consisting of 43 patient samples of TNBC selected from the medical archives at our hospital. Patients were stratified into negative and positive LGR5 expression groups. Tumor necrosis was greater in the LGR5-positive group compared with the LGR5-negative group (P = .026). Mitosis tended to show a high value in the LGR5-positive group compared with the LGR5-negative group (P = .0831), while stage tended to show a high stage in the LGR5-positive group compared with the LGR5-negative group (P = .0617). Cox proportional hazards models revealed that the LGR5-positive group (overall survival (OS) = 2.12; 95% CI: 2.12-2.12; P = 0.1575) had no relationship with OS. LGR5 expression is associated with tumor necrosis of TNBC and suggested higher malignant potential.

ALDH1A3-mTOR axis as a therapeutic target for anticancer drug-tolerant persister cells in gastric cancer

Tumors consist of heterogeneous cell populations that contain cancer cell subpopulations with anticancer drug-resistant properties called "persister" cells. While this early-phase drug tolerance is known to be related to the stem cell-like characteristic of persister cells, how the stem cell-related pathways contribute to drug resistance has remained elusive. Here, we conducted a single-cell analysis based on the stem cell lineage-related and gastric cell lineage-related gene expression in patient-derived gastric cancer cell models. The analyses revealed that 5-fluorouracil (5-FU) induces a dynamic change in the cell heterogeneity. In particular, cells highly expressing stem cell-related genes were enriched in the residual cancer cells after 5-FU treatment. Subsequent functional screening identified aldehyde dehydrogenase 1A3 (ALDH1A3) as a specific marker and potential therapeutic target of persister cells. ALDH1A3 was selectively overexpressed among the ALDH isozymes after treatment with 5-FU or SN38, a DNA topoisomerase I inhibitor. Attenuation of ALDH1A3 expression by RNA interference significantly suppressed cell proliferation, reduced the number of persister cells after anticancer drug treatment and interfered with tumor growth in a mouse xenograft model. Mechanistically, ALDH1A3 depletion affected gene expression of the mammalian target of rapamycin (mTOR) cell survival pathway, which coincided with a decrease in the activating phosphorylation of S6 kinase. Temsirolimus, an mTOR inhibitor, reduced the number of 5FU-tolerant persister cells. High ALDH1A3 expression correlated with worse prognosis of gastric cancer patients. These observations indicate that the ALDH1A3-mTOR axis could be a novel therapeutic target to eradicate drug-tolerant gastric cancer cells.

The RUNX1 Enhancer Element eR1: A Versatile Marker for Adult Stem Cells

The identification of adult stem cells is challenging because of the heterogeneity and plasticity of stem cells in different organs. Within the same tissue, stem cells may be highly proliferative, or maintained in a quiescent state and only to be activated after tissue damage. Although various stem cell markers have been successfully identified, there is no universal stem cell marker, which is exclusively expressed in all stem cells. Here, we discuss the roles of master developmental regulator RUNX1 in stem cells and the development of a 270 base pair fragment of the Runx1 enhancer (eR1) for use as stem cell marker. Using eR1 to identify stem cells offers a distinct advantage over gene promoters, which might not be expressed exclusively in stem cells. Moreover, RUNX1 has been strongly implicated in various cancer types, such as leukemia, breast, esophageal, prostate, oral, skin, and ovarian cancers?it has been suggested that RUNX1 dysfunction promotes stem cell dysfunction and proliferation. As tissue stem cells are potential candidates for cancer cells-of-origin and cancer stem cells, we will also discuss the use of eR1 to target oncogenic gene manipulations in stem cells and to track subsequent neoplastic changes.

AQP5 enriches for stem cells and cancer origins in the distal stomach

LGR5 marks resident adult epithelial stem cells at the gland base in the mouse pyloric stomach¹, but the identity of the equivalent human stem cell population remains unknown owing to a lack of surface markers that facilitate its prospective isolation and validation. In mouse models of intestinal cancer, LGR5⁺ intestinal stem cells are major sources of cancer following hyperactivation of the WNT pathway². However, the contribution of pyloric LGR5⁺ stem cells to gastric cancer following dysregulation of the WNT pathway-a frequent event in gastric cancer in humans³-is unknown. Here we use comparative profiling of LGR5⁺ stem cell populations along the mouse gastrointestinal tract to identify, and then functionally validate, the membrane protein AQP5 as a marker that enriches for mouse and human adult pyloric stem cells. We show that stem cells within the AQP5⁺ compartment are a source of WNT-driven, invasive gastric cancer in vivo, using newly generated Aqp5-creERT2 mouse models. Additionally, tumour-resident AQP5⁺ cells can selectively initiate organoid growth in vitro, which indicates that this population contains potential cancer stem cells. In humans, AQP5 is frequently expressed in primary intestinal and diffuse subtypes of gastric cancer (and in metastases of these subtypes), and often displays altered cellular localization compared with healthy tissue. These newly identified markers and mouse models will be an invaluable resource for deciphering the early formation of gastric cancer, and for isolating and characterizing human-stomach stem cells as a prerequisite for harnessing the regenerative-medicine potential of these cells in the clinic.

Proliferation and Differentiation of Gastric Mucous Neck and Chief Cells During Homeostasis and Injury-induced Metaplasia

BACKGROUND & AIMS

Adult zymogen-producing (zymogenic) chief cells (ZCs) in the mammalian gastric gland base are believed to arise from descending mucous neck cells, which arise from stem cells. Gastric injury, such as from Helicobacter pylori infection in patients with chronic atrophic gastritis, can cause metaplasia, characterized by gastric cell expression of markers of wound-healing; these cells are called spasmolytic polypeptide-expressing metaplasia (SPEM) cells. We investigated differentiation and proliferation patterns of neck cells, ZCs, and SPEM cells in mice.

METHODS

C57BL/6 mice were given intraperitoneal injections of high-dose tamoxifen to induce SPEM or gavaged with H pylori (PMSS1) to induce chronic gastric injury. Mice were then given pulses of 5-bromo-2'-deoxyuridine (BrdU) in their drinking water, followed by chase periods without BrdU, or combined with intraperitoneal injections of 5-ethynyl-2'-deoxyuridine. We collected gastric tissues and performed immunofluorescence and immunohistochemical analyses to study gastric cell proliferation, differentiation, and turnover.

RESULTS

After 8 weeks of continuous BrdU administration, fewer than 10% of homeostatic ZCs incorporated BrdU, whereas 88% of neck cells were labeled. In pulse-chase experiments, various chase periods decreased neck cell label but did not increase labeling of ZCs. When mice were given BrdU at the same time as tamoxifen, more than 90% of cells were labeled in all gastric lineages. After 3 months' recovery (no tamoxifen), ZCs became the predominant BrdU-labeled population, whereas other cells, including neck cells, were mostly negative. When we tracked the labeled cells in such mice over time, we observed that the proportion of BrdU-positive ZCs remained greater than 60% up to 11 months. In mice whose ZCs were the principal BrdU-positive population, acute injury by tamoxifen or chronic injury by H pylori infection resulted in SPEM cells becoming the principal BrdU-positive population. After withdrawal of tamoxifen, BrdU-positive ZCs reappeared.

CONCLUSIONS

We studied mice in homeostasis or with tamoxifen- or H pylori-induced SPEM. Our findings indicated that mucous neck cells do not contribute substantially to generation of ZCs during homeostasis and that ZCs maintain their own census, likely through infrequent self-replication. After metaplasia-inducing injury, ZCs can become SPEM cells, and then redifferentiate into ZCs on injury resolution.

Early TP53 alterations engage environmental exposures to promote gastric premalignancy in an integrative mouse model

Somatic alterations in cancer genes are being detected in normal and premalignant tissue, thus placing greater emphasis on gene-environment interactions that enable disease phenotypes. By combining early genetic alterations with disease-relevant exposures, we developed an integrative mouse model to study gastric premalignancy. Deletion of Trp53 in gastric cells confers a selective advantage and promotes the development of dysplasia in the setting of dietary carcinogens. Organoid derivation from dysplastic lesions facilitated genomic, transcriptional and functional evaluation of gastric premalignancy. Cell cycle regulators, most notably Cdkn2a, were upregulated by p53 inactivation in gastric premalignancy, serving as a barrier to disease progression. Co-deletion of Cdkn2a and Trp53 in dysplastic gastric organoids promoted cancer phenotypes but also induced replication stress, exposing a susceptibility to DNA damage response inhibitors. These findings demonstrate the utility of mouse models that integrate genomic alterations with relevant exposures and highlight the importance of gene-environment interactions in shaping the premalignant state.

Single cell and genetic analyses reveal conserved populations and signaling mechanisms of gastrointestinal stromal niches

Stomach and intestinal stem cells are located in discrete niches called the isthmus and crypt, respectively. Recent studies have demonstrated a surprisingly conserved role for Wnt signaling in gastrointestinal development. Although intestinal stromal cells secrete Wnt ligands to promote stem cell renewal, the source of stomach Wnt ligands is still unclear. Here, by performing single cell analysis, we identify gastrointestinal stromal cell populations with transcriptome signatures that are conserved between the stomach and intestine. In close proximity to epithelial cells, these perictye-like cells highly express telocyte and pericyte markers as well as Wnt ligands, and they are enriched for Hh signaling. By analyzing mice activated for Hh signaling, we show a conserved mechanism of GLI2 activation of Wnt ligands. Moreover, genetic inhibition of Wnt secretion in perictye-like stromal cells or stromal cells more broadly demonstrates their essential roles in gastrointestinal regeneration and development, respectively, highlighting a redundancy in gastrointestinal stem cell niches.

Gastric squamous-columnar junction contains a large pool of cancer-prone immature osteopontin responsive Lgr5-CD44+ cells

Areas of a junction between two types of epithelia are known to be cancer-prone in many organ systems. However, mechanisms for preferential malignant transformation at the junction areas remain insufficiently elucidated. Here we report that inactivation of tumor suppressor genes Trp53 and Rb1 in the gastric squamous-columnar junction (SCJ) epithelium results in preferential formation of metastatic poorly differentiated neoplasms, which are similar to human gastroesophageal carcinoma. Unlike transformation-resistant antral cells, SCJ cells contain a highly proliferative pool of immature Lgr5⁻CD44⁺ cells, which are prone to transformation in organoid assays, comprise early dysplastic lesions, and constitute up to 30% of all neoplastic cells. CD44 ligand osteopontin (OPN) is preferentially expressed in and promotes organoid formation ability and transformation of the SCJ glandular epithelium. OPN and CD44 overexpression correlate with the worst prognosis of human gastroesophageal carcinoma. Thus, detection and selective targeting of the active OPN-CD44 pathway may have direct clinical relevance.

Cancers arising from the gastric squamous-columnar junction have high incidence and are characterized by a poor prognosis. Here, the authors use genetic mouse models to show that loss of p53 and Rb1 expression results in preferential tumour development at the gastric squamous-columnar junction that contains a large pool of osteopontin responsive Lgr5-CD44+ cells.

Gastric lesions in free-living sea turtles: An underestimated disease that reflects the health of the ecosystem

Free-living marine turtles are constantly exposed to aggression factors and the gastrointestinal tract is one of the main gateways of entry. The objective of this study was to identify, and describe the anatomopathological alterations in the stomach of free-living marine turtles found dead on the beaches of the Microrregião dos Lagos, Rio de Janeiro, Brazil. Twenty-two sea turtles were necropsied, and stomach fragments were collected, fixed, and processed routinely. The presence of gastritis, parasitism, and adaptative morphological alteration of the cells were evaluated in a microscopic analysis. Descriptive statistics and Fisher's exact test were performed. Of the samples, 59.1% had stomach hyperemia. Microscopically, gastritis was found in 86.4% of cases, parasitism in 72.7%, and adaptive morphological alteration in 59.1%. There was an association between the presence of cellular adaptive morphological alteration and chronic inflammation. This the first report to describe the adaptive morphological changes observed in the stomach cells. The chronicity of the lesions was due to continuous aggressions to the tissue, with parasitism, garbage ingestion, and environmental pollutants as possible causes. The results obtained in this study demonstrate that the chronicity of the stomach lesions is due to continuous aggressions to this tissue, and the irritating factors have environmental origin, such as parasites, garbage, and toxic pollutants, including heavy metals, which are ingested by free-living sea turtles. This article demonstrates that stomach injuries in free-living marine turtles are frequent, severe, and possibly underdiagnosed; these lesions reflect the diseased ecosystem in which those animals live.

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.

Defining the Identity and Dynamics of Adult Gastric Isthmus Stem Cells

The gastric corpus epithelium is the thickest part of the gastrointestinal tract and is rapidly turned over. Several markers have been proposed for gastric corpus stem cells in both isthmus and base regions. However, the identity of isthmus stem cells (IsthSCs) and the interaction between distinct stem cell populations is still under debate. Here, based on unbiased genetic labeling and biophysical modeling, we show that corpus glands are compartmentalized into two independent zones, with slow-cycling stem cells maintaining the base and actively cycling stem cells maintaining the pit-isthmus-neck region through a process of "punctuated" neutral drift dynamics. Independent lineage tracing based on Stmn1 and Ki67 expression confirmed that rapidly cycling IsthSCs maintain the pit-isthmus-neck region. Finally, single-cell RNA sequencing (RNA-seq) analysis is used to define the molecular identity and lineage relationship of a single, cycling, IsthSC population. These observations define the identity and functional behavior of IsthSCs.

Lgr5+ pericentral hepatocytes are self-maintained in normal liver regeneration and susceptible to hepatocarcinogenesis

Emerging evidence suggests that hepatocytes are primarily maintained by self-renewal during normal liver homeostasis, as well as in response to a wide variety of hepatic injuries. However, how hepatocytes in distinct anatomic locations within the liver lobule are replenished under homeostasis and injury-induced regeneration remains elusive. Using a newly developed bacterial artificial chromosome (BAC)-transgenic mouse model, we demonstrate that Lgr5 expression in the liver is restricted to a unique subset of hepatocytes most adjacent to the central veins. Genetic lineage tracing revealed that pericentral Lgr5⁺ hepatocytes have a long lifespan and mainly contribute to their own lineage maintenance during postnatal liver development and homeostasis. Remarkably, these hepatocytes also fuel the regeneration of their own lineage during the massive and rapid regeneration process following two-thirds partial hepatectomy. Moreover, Lgr5⁺ hepatocytes are found to be the main cellular origin of diethylnitrosamine (DEN)-induced hepatocellular carcinoma (HCC) and are highly susceptible to neoplastic transformation triggered by activation of Erbb pathway. Our findings establish an unexpected self-maintaining mode for a defined subset of hepatocytes during liver homeostasis and regeneration, and identify Lgr5⁺ pericentral hepatocytes as major cells of origin in HCC development.

Correlation of clinicopathological features and leucine-rich repeat-containing G-protein-coupled receptor 5 expression in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common form of pancreatic cancer. Previous studies have established leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) as a cancer stem cell marker in gastrointestinal cancers. However, few reports have examined LGR5 in PDAC. Here we examined LGR5 expression and its clinicopathological significance in PDAC. We evaluated LGR5 expression in 78 PDAC patients who underwent surgical resection in our institution using RNAscope, a newly described RNA in situ hybridization technique. All 78 PDAC cases expressed LGR5 in cancer tissues, and LGR5 expression was prominent in the gland-forming part. LGR5 expression was significantly higher in patients with low histological grade (G1-G2) (p <  0.001) and early clinical stage (p =  0.004). Univariate analysis showed that low LGR5 expression (p =  0.034) was significantly associated with worse overall survival. However, LGR5 expression did not remain a predictor of prognosis in multivariate analysis (p =  0.639). All PDAC cases showed LGR5 expression to varying degrees, indicating LGR5 might be a cancer stem cell marker of PDAC, as in gastrointestinal cancer. Reduced LGR5 expression in tumor cells was associated with worse prognosis in PDAC. Further studies are required to elucidate the relationship between tumor progression and LGR5 expression in PDAC.

Decrease in MiR-148a Expression During Initiation of Chief Cell Transdifferentiation

Gastric chief cells differentiate from mucous neck cells and develop their mature state at the base of oxyntic glands with expression of secretory zymogen granules. After parietal cell loss, chief cells transdifferentiate into mucous cell metaplasia, designated spasmolytic polypeptide-expressing metaplasia (SPEM), which is considered a candidate precursor of gastric cancer. We examined the range of microRNA (miRNA) expression in chief cells and identified miRNAs involved in chief cell transdifferentiation into SPEM. Among them, miR-148a was strongly and specifically expressed in chief cells and significantly decreased during the process of chief cell transdifferentiation. Interestingly, suppression of miR-148a in a conditionally immortalized chief cell line induced up-regulation of CD44 variant 9 (CD44v9), one of the transcripts expressed at an early stage of SPEM development, and DNA methyltransferase 1 (Dnmt1), an established target of miR-148a. Immunostaining analyses showed that Dnmt1 was up-regulated in SPEM cells as well as in chief cells before the emergence of SPEM in mouse models of acute oxyntic atrophy using either DMP-777 or L635. In the cascade of events that leads to transdifferentiation, miR-148a was down-regulated after acute oxyntic atrophy either in xCT knockout mice or after sulfasalazine inhibition of xCT. These findings suggest that the alteration of miR-148a expression is an early event in the process of chief cell transdifferentiation into SPEM.

The Function of Lgr5+ Cells in the Gastric Antrum Does Not Require Fzd7 or Myc In Vivo

The extreme chemical and mechanical forces endured by the gastrointestinal tract drive a constant renewal of the epithelial lining. Stem cells of the intestine and stomach, marked by the cell surface receptor Lgr5, preserve the cellular status-quo of their respective tissues through receipt and integration of multiple cues from the surrounding niche. Wnt signalling is a critical niche component for gastrointestinal stem cells and we have previously shown that the Wnt receptor, Frizzled-7 (Fzd7), is required for gastric homeostasis and the function of Lgr5⁺ intestinal stem cells. Additionally, we have previously shown a requirement for the Wnt target gene Myc in intestinal homeostasis, regeneration and tumourigenesis. However, it is unknown whether Fzd7 or Myc have conserved functions in gastric Lgr5⁺ stem cells. Here we show that gastric Lgr5⁺ stem cells do not require Fzd7 or Myc and are able to maintain epithelial homeostasis, highlighting key differences in the way Wnt regulates homeostasis and Lgr5⁺ stem cells in the stomach compared to the intestinal epithelium. Furthermore, deletion of Myc throughout the epithelium of the gastric antrum has no deleterious effects suggesting therapeutic targeting of Myc in gastric cancer patients will be well tolerated by the surrounding normal tissue.

Helicobacter pylori infection and gastric cancer biology: tempering a double-edged sword

Helicobacter pylori (H. pylori) infection affects an estimated 4.4 billion people globally. Moreover, H. pylori presents the most significant risk factor for gastric cancer and low-grade mucosa-associated lymphoid tissue (MALT) lymphoma, and it is the first example of bacterial infection linked to carcinogenesis. Here, we contend that H. pylori research, which focuses on a cancer-causing pathogen resident in a relatively accessible organ, the stomach, could constitute an exemplar for microbial-related carcinogenesis in less tractable organs, such as the pancreas and lung. In this context, molecular biological approaches that could reap rewards are reviewed, including: (1) gastric cancer dynamics, particularly the role of stem cells and the heterogeneity of neoplastic cells, which are currently being investigated at the single-cell sequencing level; (2) mechanobiology, and the role of three-dimensional organoids and matrix metalloproteases; and (3) the connection between H. pylori and host pathophysiology and the gut microbiome. In the context of H. pylori's contribution to gastric cancer, several important conundrums remain to be fully elucidated. From among them, this article discusses (1) why H. pylori infection, which causes both gastric and duodenal inflammation, is only linked to gastric cancer; (2) whether a "precision oncomicrobiology" approach could enable a fine-tuning of the expression of only cancer-implicated H. pylori genes while maintaining beneficial H. pylori-mediated factors in extra-gastric tissues; and (3) the feasibility of using antibiotics targeting the microbial DNA damage system, which shares commonalities with mechanisms for human cell replication, as chemopreventives. Additional therapeutic perspectives are also discussed.

The cyclical hit model: how paligenosis might establish the mutational landscape in Barrett's esophagus and esophageal adenocarcinoma

PURPOSE OF REVIEW

In this review, we explore a paligenosis-based model to explain Barrett's esophagus development and progression: 'the cyclical hit model.'

RECENT FINDINGS

Genomic analyses have highlighted the high mutational burden of esophageal adenocarcinoma, Barrett's esophagus, and even normal esophageal epithelium. Somatic mutations in key genes including TP53 occur early in the neoplastic progression sequence of Barrett's esophagus, whereas chromosomal amplification resulting in oncogene activation occurs as a critical late event. Paligenosis is a shared injury response mechanism characterized by activation of autophagy, expression of progenitor markers, and increased mTORC signaling-induced cell-cycle reentry. In the setting of chronic injury/inflammation, cycles of paligenosis may allow accumulation of mutations until eventually the mutational burden, in concert perhaps with mutations in key driver oncogenes, finally alters the cell's ability to redifferentiate, leading to the emergence of a potential neoplastic clone.

SUMMARY

Under conditions of chronic gastroesophageal refluxate exposure, the normal esophageal squamous epithelium might undergo multiple cycles of paligenosis, allowing initially silent mutations to accumulate until key events impart mutant clones with an oncogenic survival advantage.

R-spondin-3 induces secretory, antimicrobial Lgr5+ cells in the stomach

Wnt signalling stimulated by binding of R-spondin (Rspo) to Lgr-family members is crucial for gastrointestinal stem cell renewal. Infection of the stomach with Helicobacter pylori stimulates increased secretion of Rspo by myofibroblasts, leading to an increase in proliferation of Wnt-responsive Axin2⁺Lgr5^- stem cells in the isthmus of the gastric gland and finally gastric gland hyperplasia. Basal Lgr5⁺ cells are also exposed to Rspo3, but their response remains unclear. Here, we demonstrate that-in contrast to its known mitogenic activity-Rspo3 induces differentiation of basal Lgr5⁺ cells into secretory cells that express and secrete antimicrobial factors, such as intelectin-1, into the lumen. The depletion of Lgr5⁺ cells or the knockout of Rspo3 in myofibroblasts leads to hypercolonization of the gastric glands with H. pylori, including the stem cell compartment. By contrast, systemic administration or overexpression of Rspo3 in the stroma clears H. pylori from the gastric glands. Thus, the Rspo3-Lgr5 axis simultaneously regulates both antimicrobial defence and mucosal regeneration.

The Role of Wnt and R-spondin in the Stomach During Health and Disease

The Wnt signaling pathway is one of the most prominent developmental signals. In addition to its functions in development, there is emerging evidence that it is also crucial for various organ functions in adult organisms, where Wnt signaling controls tissue stem cell behavior, proliferation and differentiation. Deregulation of Wnt signaling is involved in various pathological conditions and has been linked to malignant tissue transformation in different organ systems. The study of the Wnt signaling pathway has revealed a complex regulatory network that tightly balances the quality and strength of Wnt signaling in tissues. In this context, R-spondins are secreted proteins that stabilize Wnt receptors and enhance Wnt signaling. In this review we focus on new insights into the regulatory function of Wnt and R-spondin signaling in the stomach. In addition to its function in the healthy state, we highlight the connection between Wnt signaling and infection with Helicobacter pylori (H. pylori), a pathogen that colonizes the stomach and is the main risk factor for gastric cancer. In addition to experimental data that link Wnt signaling to carcinogenesis, we discuss that Wnt signaling is affected in a substantial proportion of patients with gastric cancer, and provide examples for potential clinical implications for altered Wnt signaling in gastric cancer.

Distinct Localization of Mature HGF from its Precursor Form in Developing and Repairing the Stomach

Hepatocyte growth factor (HGF) is secreted as an inactive single-chain HGF (scHGF); however, only proteolytically processed two-chain HGF (tcHGF) can activate the MET receptor. We investigated the localization of tcHGF and activated/phosphorylated MET (pMET) using a tcHGF-specific antibody. In day 16.5 mouse embryos, total HGF (scHGF + tcHGF) was mainly localized in smooth muscle cells close to, but separate from, MET-positive epithelial cells in endodermal organs, including the stomach. In the adult stomach, total HGF was localized in smooth muscle cells, and tcHGF was mainly localized in the glandular base region. Immunostaining for pMET and Lgr5-driven green fluorescent protein (GFP) indicated that pMET localization overlapped with Lgr5⁺ gastric stem cells. HGF promoted organoid formation similar to EGF, indicating the potential for HGF to promote the survival and growth of gastric stem cells. pMET and tcHGF localizations changed during regeneration following gastric injury. These results indicate that MET is constantly activated in gastric stem cells and that the localization of pMET differs from the primary localization of precursor HGF but has a close relationship to tcHGF. Our results suggest the importance of the microenvironmental generation of tcHGF in the regulation of development, regeneration, and stem cell behavior.

Voltage-dependent calcium channel α2δ1 subunit is a specific candidate marker for identifying gastric cancer stem cells

Purpose: Cancer stem cells (CSCs) are a subpopulation of cancer cells with self-renewal property and responsible for tumor malignancy, progression and drug resistance. Researches on CSC-specific markers in gastric cancer remain limited. Our current study explored the expression of voltage-dependent calcium channel α2δ1 subunit and the potential of using α2δ1 as a CSC marker in gastric cancer. We also compared the specificity of α2δ1 and CD44 in identifying gastric cancer stem cells (GCSCs).

Materials and methods: Expression of α2δ1 was analyzed in gastric cancer cell lines, patient-derived xenograft (PDX) models and clinical samples of malignant ascites of gastric cancer patients. α2δ1⁺ gastric cancer cells were isolated from gastric cancer cell lines. CSC properties of α2δ1⁺ gastric cancer cells were then verified by subsequent tests both in vitro and in vivo.

Results: The expression level of α2δ1 was found to differ drastically among gastric cancer cell lines, PDX models and clinical samples of malignant ascites. α2δ1⁺ gastric cancer cells sorted from HGC-27 and SGC-7901 cell lines demonstrated significant self-renewal properties, including tumorigenic capacity, sphere-formation capacity and asymmetric differentiation potential. Knockdown of α2δ1 in α2δ1⁺ HGC-27 significantly inhibited CSC properties and rendered HGC-27 more sensitive to chemotherapy. Flow cytometry showed that α2δ1⁺ gastric cancer cells accounted for a small fraction of CD44⁺ gastric cancer cells. Isolated CD44⁺α2δ1⁺ HGC-27 cells displayed more significant tumorigenic capacity and sphere-forming capacity compared with their CD44⁺α2δ1⁻ counterparts.

Conclusion: α2δ1⁺ gastric cancer cells possessed CSC properties. α2δ1 could be a proper marker in identifying GCSCs with superior specificity than CD44. The combination of α2δ1 and CD44 could be used to identify GCSCs with improved accuracy. Knockdown of α2δ1 combined with chemotherapy displayed higher therapeutic efficacy on gastric cancer cells, suggesting that α2δ1 could be a potential target for anticancer treatment.

Cystine/Glutamate Antiporter (xCT) Is Required for Chief Cell Plasticity After Gastric Injury

BACKGROUND & AIMS

Many differentiated epithelial cell types are able to reprogram in response to tissue damage. Although reprogramming represents an important physiological response to injury, the regulation of cellular plasticity is not well understood. Damage to the gastric epithelium initiates reprogramming of zymogenic chief cells into a metaplastic cell lineage known as spasmolytic polypeptide-expressing metaplasia (SPEM). The present study seeks to identify the role of xCT, a cystine/glutamate antiporter, in chief cell reprogramming after gastric injury. We hypothesize that xCT-dependent reactive oxygen species (ROS) detoxification is required for the reprogramming of chief cells into SPEM.

METHODS

Sulfasalazine (an xCT inhibitor) and small interfering RNA knockdown were used to target xCT on metaplastic cells in vitro. Sulfasalazine-treated wild-type mice and xCT knockout mice were analyzed. L635 or DMP-777 treatment was used to chemically induce acute gastric damage. The anti-inflammatory metabolites of sulfasalazine (sulfapyridine and mesalazine) were used as controls. Normal gastric lineages, metaplastic markers, autophagy, proliferation, xCT activity, ROS, and apoptosis were assessed.

RESULTS

xCT was up-regulated early as chief cells transitioned into SPEM. Inhibition of xCT or small interfering RNA knockdown blocked cystine uptake and decreased glutathione production by metaplastic cells and prevented ROS detoxification and proliferation. Moreover, xCT activity was required for chief cell reprogramming into SPEM after gastric injury in vivo. Chief cells from xCT-deficient mice showed decreased autophagy, mucus granule formation and proliferation, as well as increased levels of ROS and apoptosis compared with wild-type mice. On the other hand, the anti-inflammatory metabolites of sulfasalazine did not affect SPEM development.

CONCLUSIONS

The results presented here suggest that maintaining redox balance is crucial for progression through the reprogramming process and that xCT-mediated cystine uptake is required for chief cell plasticity and ROS detoxification.

Tumor organoids: From inception to future in cancer research

Tumor models have created new avenues for personalized medicine and drug development. A new culture model derived from a three-dimensional system, the tumor organoid, is gradually being used in many fields. An organoid can simulate the physiological structure and function of tissue in situ and maintain the characteristics of tumor cells in vivo, overcoming the disadvantages of traditional experimental tumor models. Organoids can mimic pathological features of tumors and maintain genetic stability, making them suitable for both molecular mechanism studies and pharmacological experiments of clinical transformation. In addition, the application of tumor organoids combined with other technologies, such as liquid biopsy technology, microraft array (MRA), and high-content screening (HCS), for the development of personalized diagnosis and cancer treatment has a promising future. In this review, we introduce the evolution of organoids and discuss their specific application and advantages. We also summarize the characteristics of several tumor organoids culture systems.

RAL GTPases Drive Intestinal Stem Cell Function and Regeneration through Internalization of WNT Signalosomes

Ral GTPases are RAS effector molecules and by implication a potential therapeutic target for RAS mutant cancer. However, very little is known about their roles in stem cells and tissue homeostasis. Using Drosophila, we identified expression of RalA in intestinal stem cells (ISCs) and progenitor cells of the fly midgut. RalA was required within ISCs for efficient regeneration downstream of Wnt signaling. Within the murine intestine, genetic deletion of either mammalian ortholog, Rala or Ralb, reduced ISC function and Lgr5 positivity, drove hypersensitivity to Wnt inhibition, and impaired tissue regeneration following damage. Ablation of both genes resulted in rapid crypt death. Mechanistically, RALA and RALB were required for efficient internalization of the Wnt receptor Frizzled-7. Together, we identify a conserved role for RAL GTPases in the promotion of optimal Wnt signaling, which defines ISC number and regenerative potential.

Deficiency of Stomach-Type Claudin-18 in Mice Induces Gastric Tumor Formation Independent of H pylori Infection

BACKGROUND & AIMS

Epithelial cells are joined by tight junctions (TJs) to form a cell sheet. In the stomach, epithelial cell sheet forms an essential barrier against gastric material, including gastric acid. Although the decreased expression of stomach-type claudin-18 (stCldn18), a TJ protein, is generally observed in human gastritis and gastric cancer, its pathological roles are not fully understood. We previously reported that mice lacking stCldn18 (stCldn18-/-) exhibit gastric acid leakage through TJs, which induces active gastritis at a young age. Here, we examined the gastric pathologies in mice after long-term stCldn18 deficiency.

METHODS

The gastric pathologies in stCldn18-/- mice were sequentially analyzed from youth to old age, and compared to those in humans. To examine the relationship between stCldn18 deficiency-induced gastric pathologies and Wnt-dependent tumorigenesis, we generated Wnt1-overexpressing stCldn18-/- mice.

RESULTS

StCldn18-/- mice developed chronic active gastritis at middle age, with expression of the chemoattractant CCL28. At old age, 20-30% of these mice developed gastric tumors with CXCL5 expression, indicative of EMT. In this process, spasmolytic polypeptide-expressing metaplasia (SPEM) cells appeared. Increased expressions of CD44-variants, TLR2, and CXCL5 indicated age-dependent changes in cell characteristics. Some features of the stCldn18-/- mouse gastric tumorigenesis resembled H pylori-infection-related human carcinogenesis. The gastric tumorigenesis was accelerated in Wnt1-overexpressing stCldn18-/- mice, indicating that Wnt is involved in the stCldn18-/- mouse gastric tumorigenesis.

CONCLUSIONS

StCldn18 deficiency induced gastric tumorigenesis in mice without H pylori infection. Our findings revealed that several signaling networks, including the cytokine-, stemness-, and Wnt-signaling pathways, may be activated under the stCldn18-deficiency-induced chronic active gastritis to accelerate the gastric tumorigenesis.

Single-cell transcriptome analysis identifies distinct cell types and niche signaling in a primary gastric organoid model

The diverse cellular milieu of the gastric tissue microenvironment plays a critical role in normal tissue homeostasis and tumor development. However, few cell culture model can recapitulate the tissue microenvironment and intercellular signaling in vitro. We used a primary tissue culture system to generate a murine p53 null gastric tissue model containing both epithelium and mesenchymal stroma. To characterize the microenvironment and niche signaling, we used single cell RNA sequencing (scRNA-Seq) to determine the transcriptomes of 4,391 individual cells. Based on specific markers, we identified epithelial cells, fibroblasts and macrophages in initial tissue explants during organoid formation. The majority of macrophages were polarized towards wound healing and tumor promotion M2-type. During the course of time, the organoids maintained both epithelial and fibroblast lineages with the features of immature mouse gastric stomach. We detected a subset of cells in both lineages expressing Lgr5, one of the stem cell markers. We examined the lineage-specific Wnt signaling activation, and identified that Rspo3 was specifically expressed in the fibroblast lineage, providing an endogenous source of the R-spondin to activate Wnt signaling. Our studies demonstrate that this primary tissue culture system enables one to study gastric tissue niche signaling and immune response in vitro.

Tropism for Spasmolytic Polypeptide-Expressing Metaplasia Allows Helicobacter pylori to Expand Its Intragastric Niche

BACKGROUND & AIMS

In patients with chronic Helicobacter pylori (H pylori) infection, parietal and chief cell atrophy in the gastric corpus, a process known as spasmolytic polypeptide-expressing metaplasia (SPEM), increases the risk for progression to cancer. The relation between H pylori and these metaplastic changes is unclear. We investigated whether H pylori localizes to regions of SPEM.

METHODS

We developed an in situ adherence assay in which we incubated H pylori with free-floating tissue sections from the gastric corpora of mice; we assessed H pylori distribution along the gastric unit by immunofluorescence. We analyzed the interactions of H pylori with tissue collected from mice with acute SPEM, induced by high-dose tamoxifen. We also evaluated how adhesin-deficient H pylori strains, chemical competition assays, and epithelial glycosylation affected H pylori adhesion to SPEM glands. Mice colonized with the mouse-adapted PMSS1 strain were analyzed for H pylori colonization in vivo during tamoxifen-induced SPEM or after decrease of stomach acid with omeprazole.

RESULTS

Compared with uninjured glands, H pylori penetrated deep within SPEM glands, in situ, through interaction of its adhesin, SabA, with sialyl-Lewis X, which expanded in SPEM. H pylori markedly increased gastric corpus colonization when SPEM was induced, but this proximal spread reversed in mice allowed to recover from SPEM. Decreasing corpus acidity also promoted proximal spread. However, H pylori penetrated deep within corpus glands in vivo only when sialyl-Lewis X expanded during SPEM.

CONCLUSIONS

Helicobacter pylori differentially binds SPEM glands in situ and in mice, in large part by interacting with sialyl-Lewis X. Our findings indicate that H pylori expands its niche into the gastric corpus by promoting and exploiting epithelial metaplastic changes that can lead to tumorigenesis.

E-cadherin is Required for the Homeostasis of Lgr5+ Gastric Antral Stem Cells

Lgr5-expressing stem cells contribute to the epithelial turnover of the gastric antrum. However, the mechanism controlling the homeostasis of Lgr5⁺ antral stem cells is not fully understood. Here, we demonstrate the key role of E-cadherin in the homeostasis of Lgr5⁺ gastric antral stem cells. The deletion of E-cadherin in these cells results in their apoptosis, thereby leading to a marked decrease in their number. A reduced Lgr5⁺ stem cell pool caused by the loss of E-cadherin impairs gastric antral epithelial homeostasis in vivo and organoid growth in vitro. Furthermore, p53 contributes to the apoptosis of Lgr5⁺ stem cells following E-cadherin loss, while the simultaneous deletion of p53 rescues the phenotype in E-cadherin mutants. Our study reveals the critical pro-survival function of E-cadherin in Lgr5⁺ gastric antral stem cells and the key role of the Lgr5⁺ stem cell pool in the maintenance of gastric epithelial homeostasis.

Gastric Cancer Stem Cells Effect on Th17/Treg Balance; A Bench to Beside Perspective

Gastric cancer stem cells (GCSCs), a small population among tumor cells, are responsible for tumor initiation, development, metastasis, and recurrence. They play a crucial role in immune evasion, immunomodulation, and impairment of effector immunity and believed to be emerged to change the balance of the immune system, importantly CD4⁺ T cells in the chronic inflamed tumor site. However, different subtypes of innate and adaptive immune cells are involved in the formation of the immune system in the tumor microenvironment, we would look at T cells in this study. Tumor microenvironment induces differentiation of CD4⁺ T cells into different subsets of T cells, mainly suppressive regulatory T cells (Treg), and T helper 17 (Th17) cells, although their exact role in tumor immunity is still under debate depending on tumor types and stages. Counterbalance between Th17 and Treg cells in the gastrointestinal system result in the homeostasis and normal function of the immune system, particularly mucosal immunity. Recent data demonstrated a high infiltration of Th17 and Treg cells into the gastric tumor site and proved that tumor microenvironment might disturb the balance between Th17 and Treg. It is possible to assume an association between activation of CSCs which contribute to metastasis in late stages, and the imbalanced Th17/Treg cells observed in advanced gastric cancer patients. This review intends to clarify the importance of gastric tumor microenvironment specifically CSCs in relation to Th17/Tregs balance firstly and to highlight the relevance of imbalanced Th17/Treg subsets in determining the stages and behavior of the tumor secondly. Finally, the present study suggests a clinical approach looking at the plasticity of T cells with a focus on Th17 as a promising dedicated arm in cancer immunotherapy.

Cellular Plasticity in Intestinal Homeostasis and Disease

The intestinal epithelium is one the fastest renewing tissues in mammals and is endowed with extensive adaptability. The more traditional view of a hierarchical organization of the gut has recently given way to a more dynamic model in which various cell types within the intestinal epithelium can de-differentiate and function as an alternative source of stem cells upon tissue damage and stress conditions such as inflammation and tumorigenesis. Here, we will review the mechanistic principles and key players involved in intestinal plasticity and discuss potential therapeutic implications of cellular plasticity in regenerative medicine and cancer.

Hedgehog signaling induces PD-L1 expression and tumor cell proliferation in gastric cancer

Tumor cells expressing programmed cell death ligand 1 (PD-L1) interact with PD-1 on CD8+ cytotoxic T lymphocytes (CTLs) to inhibit CTL effector function. In gastric cancer, the mechanism regulating PD-L1 is unclear. The Hedgehog (Hh) signaling pathway is reactivated in various cancers including gastric. Here we tested the hypothesis that Hh-induced PD-L1 inactivates effector T cell function and allows gastric cancer cell proliferation. Mouse organoids were generated from tumors of a triple-transgenic mouse model engineered to express an activated GLI2 allele, GLI2A, in Lgr5-expressing stem cells, (mTGOs) or normal mouse stomachs (mGOs). Bone marrow-derived dendritic cells (DCs) were pulsed with conditioned media collected from normal (mGOCM) or cancer (mTGOCM) organoids. Pulsed DCs and CTLs were then co-cultured with either mGOs or mTGOs in the presence of PD-L1 neutralizing antibody (PD-L1Ab). Human-derived gastric cancer organoids (huTGOs) were used in drug and xenograft assays. Hh/Gli inhibitor, GANT-61 significantly reduced the expression of PD-L1 and tumor cell proliferation both in vivo and in vitro. PD-L1Ab treatment induced tumor cell apoptosis in mTGO/immune cell co-cultures. GANT-61 treatment sensitized huTGOs to standard-of-care chemotherapeutic drugs both in vivo and in vitro. Thus, Hh signaling mediates PD-L1 expression in gastric cancer cells and subsequently promotes tumor proliferation.

Three types of metaplasia model through Kras activation, Pten deletion, or Cdh1 deletion in the gastric epithelium

Chronic inflammation and intestinal metaplasia are strongly associated with gastric carcinogenesis. Kras activation and Pten deletion are observed in intestinal-type gastric cancer, and Cdh1 mutation is associated with diffuse-type gastric cancer. Although various mouse models of gastric carcinogenesis have been reported, few mouse lines enable gene manipulation selectively in the stomach. Here we established a Tff1-Cre bacterial artificial chromosome transgenic mouse line in an attempt to induce gene modification specifically in the gastric pit lineage. In the stomach, Tff1-Cre-mediated recombination was most evident in the pit lineage in the corpus and in entire antral glands; recombination was also observed in a few gastric chief and parietal cells. Outside the stomach, recombination was patchy throughout the intestines, and particularly frequently in the duodenum (Brunner glands), cecum, and proximal colon. In the stomachs of Tff1-Cre;LSL-Kras^G12D mice, proliferating cell clusters expanded throughout the corpus glands, with foveolar cell expansion with ectopic Alcian blue-positive mucins, oxyntic atrophy, and pseudopyloric changes with spasmolytic polypeptide-expressing metaplasia; however, gastric cancer was not observed even at 12 months of age. Corpus-derived organoids from Tff1-Cre;LSL-Kras^G12D mice exhibited accelerated growth and abnormal differentiation with a loss of chief and parietal cell markers. Tff1-Cre;Pten^flox/flox mice displayed similar changes to those seen in Tff1-Cre;LSL-Kras^G12D mice, both with aberrant ERK activation within 3 months. In contrast, Tff1-Cre;Cdh1^flox/flox mice initially showed signet ring-like cells that were rapidly lost with disruption of the mucosal surface, and later developed gastric epithelial shedding with hyperproliferation and loss of normal gastric lineages. Eventually, the glandular epithelium in Tff1-Cre;Cdh1^flox/flox mice was completely replaced by squamous epithelium which expanded from the forestomach. Tff1-Cre mice offer an additional useful tool for studying gastric carcinogenesis both in vivo and in vitro. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Guilt by association: intestinal metaplasia does not progress to gastric cancer

PURPOSE OF REVIEW

This review integrates the new thinking about relationships between gastric cancer and intestinal metaplasia/pseudopyloric metaplasia (SPEM). We address whether recent studies have closed or widened the knowledge gap regarding gastric cancer pathogenesis in mice or humans.

RECENT FINDINGS

Recent studies in mouse models have provided a variety of new insights into the cellular origin and progression of events resulting in gastric cancer. Many suggest a direct transformation from intestinal metaplasia/pseudopyloric metaplasia/SPEM to gastric cancer. However, results from different investigator and models are conflicting and often describe events not present in studies in humans.

SUMMARY

Both Helicobacter pylori-associated and autoimmune gastritis may produce gastric atrophy with extensive intestinal metaplasia and an abnormal gastric microbiome. However, only H. pylori gastritis carries a risk for adenocarcinoma. The differences reported with mouse models can best be explained as the results of different models of regeneration and repair rather than as models of gastric cancer. Overall, the data remains consistent with the original hypothesis that gastric cancer results from increased genetic instability of gastric stem cells rather than a direct transition from metaplasia to cancer. Intestinal metaplasia, pseudopyloric metaplasia, and SPEM have all been falsely accused based on guilt by association.

Gastric Stem Cell and Cellular Origin of Cancer

Several stem cell markers within the gastrointestinal epithelium have been identified in mice. One of the best characterized is Lgr5 (leucine-rich repeat-containing G-protein coupled receptor 5) and evidence suggests that Lgr5+ cells in the gut are the origin of gastrointestinal cancers. Reserve or facultative stem or progenitor cells with the ability to convert to Lgr5+ cells following injury have also been identified. Unlike the intestine, where Lgr5+ cells at the crypt base act as active stem cells, the stomach may contain unique stem cell populations, since gastric Lgr5+ cells seem to behave as a reserve rather than active stem cells, both in the corpus and in the antral glands. Gastrointestinal stem cells are supported by a specific microenvironment, the stem cell niche, which also promotes tumorigenesis. This review focuses on stem cell markers in the gut and their supporting niche factors. It also discusses the molecular mechanisms that regulate stem cell function and tumorigenesis.

The application of transgenic and gene knockout mice in the study of gastric precancerous lesions

Gastric intestinal metaplasia is a precursor for gastric dysplasia, which is in turn, a risk factor for gastric adenocarcinoma. Gastric metaplasia and dysplasia are known as gastric precancerous lesions (GPLs), which are essential stages in the progression from normal gastric mucosa to gastric cancer (GC) or gastric adenocarcinoma. Genetically-engineered mice have become essential tools in various aspects of GC research, including mechanistic studies and drug discovery. Studies in mouse models have contributed significantly to our understanding of the pathogenesis and molecular mechanisms underlying GPLs and GC. With the development and improvement of gene transfer technology, investigators have created a variety of transgenic and gene knockout mouse models for GPLs, such as H/K-ATPase transgenic and knockout mutant mice and gastrin gene knockout mice. Combined with Helicobacter infection, and treatment with chemical carcinogens, these mice develop GPLs or GC and thus provide models for studying the molecular biology of GC, which may lead to the discovery and development of novel drugs. In this review, we discuss recent progress in the use of genetically-engineered mouse models for GPL research, with particular emphasis on the importance of examining the gastric mucosa at the histological level to investigate morphological changes of GPL and GC and associated protein and gene expression.