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

Emerging role of spasmolytic polypeptide-expressing metaplasia in gastric cancer

Gastric cancer (GC) ranks among the top five most diagnosed cancers globally, with particularly high incidence and mortality rates observed in Asian regions. Despite certain advancements achieved through early screening and treatment strategies in many countries, GC continues to pose a significant public health challenge. Approximately 20% of patients infected with Helicobacter pylori develop precancerous lesions, among which metaplasia is the most critical. Except for intestinal metaplasia (IM), which is characterized by goblet cells appearing in the stomach glands, one type of mucous cell metaplasia, spasmolytic polypeptide-expressing metaplasia (SPEM), has attracted much attention. SPEM represents a specific epithelial cell alteration within the gastric mucosa, characterized by the expressing trefoil factor 2 (TFF2) in basal glands, resembling the basal metaplasia of deep antral gland cells. It primarily arises from the transdifferentiation of mature chief cells, mucous neck cells (MNCs), or isthmus stem cells. SPEM is commonly regarded as a precursor lesion in the development of gastric inflammation and subsequent carcinogenesis. The formation of SPEM is intricately associated with chronic gastric inflammation, Helicobacter pylori infection, and various other environmental and genetic factors. Recently, with the profound exploration of the biological and molecular mechanisms underlying SPEM, a deeper understanding of its role in GC initiation and progression has emerged. This review summarizes the role, molecular mechanisms, and clinical significance of SPEM in the onset and progression of GC.

Microbiota-derived short-chain fatty acids determine stem cell characteristics of gastric chief cells

The gastric mucosa is a highly dynamic tissue that undergoes constant self-renewal through stem cell differentiation. Chief cells maintain a quiescent state in homeostasis but are responsible for regeneration after injury. Although the role of microbiome-host interactions in the intestine is well studied, less is known about these interactions in the stomach. Using the mouse organoid and germ-free mouse models, we show that microbiota-derived short-chain fatty acids (SCFAs) suppress the proliferation of chief cells in mice. This effect is mediated by activation of G-protein-coupled receptor 43. Most importantly, through metabolomics and transplantation studies, we show butyrate-producing Lactobacillus intestinalis modulates the proliferation of chief cells in mice. Our findings identify a mechanism by which the microbiota regulates the cell characteristics of chief cells, providing insight into the complex interplay between the host and its microbial environment and the mechanisms underlying gastric homeostasis, with potential therapeutic implications for gastric diseases.

H. Pylori-Facilitated TERT/Wnt/β-Catenin Triggers Spasmolytic Polypeptide-Expressing Metaplasia and Oxyntic Atrophy

Persistent H. pylori infection triggers the repair program of the mucosa, such as spasmolytic polypeptide-expressing metaplasia (SPEM). However, the mechanism underlying the initiation of SPEM in gastric tissues by H. pylori remains unclear. Here, an increase in telomerase reverse transcriptase (TERT) protein expression is observed in chief cells upon infection with cagA-positive H. pylori. Tert knockout significantly ameliorated H. pylori-induced SPEM and single-cell RNA sequencing demonstrated that the Wnt/β-Catenin pathway is suppressed in gastric cells with Tert knockout. Mechanism study revealed that CagA elevated TERT abundance by disrupting the interaction between TERT and its novel E3 ligase, SYVN1. Interestingly, Nitazoxanide effectively relieved SPEM via inhibition of the Wnt/β-Catenin signaling in vivo. This results clarified the mechanism underlying which CagA activated the TERT/Wnt/β-Catenin pathway, thus promoting the dedifferentiation of chief cells and the occurrence of SPEM in gastric mucosa. This highlights a molecular basis for targeting CagA-activated Wnt signaling in chief cells for the treatment of gastric precancerous lesions.

KLHL21 suppresses gastric tumourigenesis via maintaining STAT3 signalling equilibrium in stomach homoeostasis

OBJECTIVE

Precancerous metaplasia transition to dysplasia poses a risk for subsequent intestinal-type gastric adenocarcinoma. However, the molecular basis underlying the transformation from metaplastic to cancerous cells remains poorly understood.

DESIGN

An integrated analysis of genes associated with metaplasia, dysplasia was conducted, verified and characterised in the gastric tissues of patients by single-cell RNA sequencing and immunostaining. Multiple mouse models, including homozygous conditional knockout Klhl21-floxed mice, were generated to investigate the role of Klhl21 deletion in stemness, DNA damage and tumour formation. Mass-spectrometry-based proteomics and ribosome sequencing were used to elucidate the underlying molecular mechanisms.

RESULTS

Kelch-like protein 21 (KLHL21) expression progressively decreased in metaplasia, dysplasia and cancer. Genetic deletion of Klhl21 enhances the rapid proliferation of Mist1+ cells and their descendant cells. Klhl21 loss during metaplasia facilitates the recruitment of damaged cells into the cell cycle via STAT3 signalling. Increased STAT3 activity was confirmed in cancer cells lacking KLHL21, boosting self-renewal and tumourigenicity. Mechanistically, the loss of KLHL21 promotes PIK3CB mRNA translation by stabilising the PABPC1-eIF4G complex, subsequently causing STAT3 activation. Pharmacological STAT3 inhibition by TTI-101 elicited anticancer effects, effectively impeding the transition from metaplasia to dysplasia. In patients with gastric cancer, low levels of KLHL21 had a shorter survival rate and a worse response to adjuvant chemotherapy.

CONCLUSIONS

Our findings highlighted that KLHL21 loss triggers STAT3 reactivation through PABPC1-mediated PIK3CB translational activation, and targeting STAT3 can reverse preneoplastic metaplasia in KLHL21-deficient stomachs.

The role of gastric mucins and mucin-related glycans in gastric cancers

Gastric mucins serve as a protective barrier on the stomach's surface, protecting from external stimuli including gastric acid and gut microbiota. Their composition typically changes in response to the metaplastic sequence triggered by Helicobacter pylori infection. This alteration in gastric mucins is also observed in cases of gastric cancer, although the precise connection between mucin expressions and gastric carcinogenesis remains uncertain. This review first introduces the relationship between mucin expressions and gastric metaplasia or cancer observed in humans and mice. Additionally, we discuss potential pathogenic mechanisms of how aberrant mucins and their glycans affect gastric carcinogenesis. Finally, we summarize challenges to target tumor-specific glycans by utilizing lectin-drug conjugates that can bind to specific glycans. Understanding the correlation and mechanism between these mucin expressions and gastric carcinogenesis could pave the way for new strategies in gastric cancer treatment.

Impaired Glycosylation of Gastric Mucins Drives Gastric Tumorigenesis and Serves as a Novel Therapeutic Target

BACKGROUND & AIMS

Gastric cancer is often accompanied by a loss of mucin 6 (MUC6), but its pathogenic role in gastric carcinogenesis remains unclear.

METHODS

Muc6 knockout (Muc6-/-) mice and Muc6-dsRED mice were newly generated. Tff1Cre, Golph3-/-, R26-Golgi-mCherry, Hes1flox/flox, Cosmcflox/flox, and A4gnt-/- mice were also used. Histology, DNA and RNA, proteins, and sugar chains were analyzed by whole-exon DNA sequence, RNA sequence, immunohistochemistry, lectin-binding assays, and liquid chromatography-mass spectrometry analysis. Gastric organoids and cell lines were used for in vitro assays and xenograft experiments.

RESULTS

Deletion of Muc6 in mice spontaneously causes pan-gastritis and invasive gastric cancers. Muc6-deficient tumor growth was dependent on mitogen-activated protein kinase activation, mediated by Golgi stress-induced up-regulation of Golgi phosphoprotein 3. Glycomic profiling revealed aberrant expression of mannose-rich N-linked glycans in gastric tumors, detected with banana lectin in association with lack of MUC6 expression. We identified a precursor of clusterin as a binding partner of mannose glycans. Mitogen-activated protein kinase activation, Golgi stress responses, and aberrant mannose expression are found in separate Cosmc- and A4gnt-deficient mouse models that lack normal O-glycosylation. Banana lectin-drug conjugates proved an effective treatment for mannose-rich murine and human gastric cancer.

CONCLUSIONS

We propose that Golgi stress responses and aberrant glycans are important drivers of and promising new therapeutic targets for gastric cancer.

Revolutionizing Gastric Cancer Prevention: Novel Insights on Gastric Mucosal Inflammation-Cancer Transformation and Chinese Medicine

The progression from gastric mucosal inflammation to cancer signifies a pivotal event in the trajectory of gastric cancer (GC) development. Chinese medicine (CM) exhibits unique advantages and holds significant promise in inhibiting carcinogenesis of the gastric mucosa. This review intricately examines the critical pathological events during the transition from gastric mucosal inflammation-cancer transformation (GMICT), with a particular focus on pathological evolution mechanisms of spasmolytic polypeptide-expressing metaplasia (SPEM). Moreover, it investigates the pioneering applications and advancements of CM in intervening within the medical research domain of precancerous transformations leading to GC. Furthermore, the analysis extends to major shortcomings and challenges confronted by current research in gastric precancerous lesions, and innovative studies related to CM are presented. We offer a highly succinct yet optimistic outlook on future developmental trends. This paper endeavors to foster a profound understanding of forefront dynamics in GMICT research and scientific implications of modernizing CM. It also introduces a novel perspective for establishing a collaborative secondary prevention system for GC that integrates both Western and Chinese medicines.

Gastric intestinal metaplasia: progress and remaining challenges

Most gastric cancers arise in the setting of chronic inflammation which alters gland organization, such that acid-pumping parietal cells are lost, and remaining cells undergo metaplastic change in differentiation patterns. From a basic science perspective, recent progress has been made in understanding how atrophy and initial pyloric metaplasia occur. However, pathologists and cancer biologists have long been focused on the development of intestinal metaplasia patterns in this setting. Arguably, much less progress has been made in understanding the mechanisms that lead to the intestinalization seen in chronic atrophic gastritis and pyloric metaplasia. One plausible explanation for this disparity lies in the notable absence of reliable and reproducible small animal models within the field, which would facilitate the investigation of the mechanisms underlying the development of gastric intestinal metaplasia (GIM). This review offers an in-depth exploration of the current state of research in GIM, shedding light on its pivotal role in tumorigenesis. We delve into the histological subtypes of GIM and explore their respective associations with tumor formation. We present the current repertoire of biomarkers utilized to delineate the origins and progression of GIM and provide a comprehensive survey of the available, albeit limited, mouse lines employed for modeling GIM and engage in a discussion regarding potential cell lineages that serve as the origins of GIM. Finally, we expound upon the myriad signaling pathways recognized for their activity in GIM and posit on their potential overlap and interactions that contribute to the ultimate manifestation of the disease phenotype. Through our exhaustive review of the progression from gastric disease to GIM, we aim to establish the groundwork for future research endeavors dedicated to elucidating the etiology of GIM and developing strategies for its prevention and treatment, considering its potential precancerous nature.

Role and research progress of spasmolytic polypeptide‑expressing metaplasia in gastric cancer (Review)

Gastric cancer ranks as one of the most prevalent cancers worldwide. While the incidence of gastric cancer in Western countries has notably diminished over the past century, it continues to be a leading cause of cancer‑related mortality on a global scale. The majority of gastric cancers in humans are attributed to chronic Helicobacter pylori infection and the progression of gastric cancer is often preceded by gastritis, atrophy, metaplasia and dysplasia. However, the precise mechanisms underlying the development of gastric cancer remain ambiguous, including the formation of gastric polyps and precancerous lesions. In humans, two types of precancerous metaplasia have been identified in relation to gastric malignancies: Intestinal metaplasia and spasmolytic polypeptide‑expressing metaplasia (SPEM). The role of SPEM in the induction of gastric cancer has gained recent attention and its link with early‑stage human gastric cancer is increasingly evident. To gain insight into SPEM, the present study reviewed the role and research progress of SPEM in gastric cancer.

Immunotherapy of gastric cancer: Present status and future perspectives

In this editorial, we comment on the article entitled "Advances and key focus areas in gastric cancer immunotherapy: A comprehensive scientometric and clinical trial review (1999-2023)," which was published in the recent issue of the World Journal of Gastroenterology. We focused on the results of the authors' bibliometric analysis concerning gastric cancer immunotherapy, which they analyzed in depth by compiling the relevant publications of the last 20 years. Before that, we briefly describe the most recent data concerning the epidemiological parameters of gastric cancer (GC) in different countries, attempting to give an interpretation based on the etiological factors involved in the etiopathogenesis of the neoplasm. We then briefly discuss the conservative treatment (chemotherapy) of the various forms of this malignant neoplasm. We describe the treatment of resectable tumors, locally advanced neoplasms, and unresectable (advanced) cases. Special attention is given to modern therapeutic approaches with emphasis on immunotherapy, which seems to be the future of GC treatment, especially in combination with chemotherapy. There is also a thorough analysis of the results of the study under review in terms of the number of scientific publications, the countries in which the studies were conducted, the authors, and the scientific centers of origin, as well as the clinical studies in progress. Finally, an attempt is made to draw some con-clusions and to point out possible future directions.

Elevated stress response marks deeply quiescent reserve cells of gastric chief cells

Gastrointestinal tract organs harbor reserve cells, which are endowed with cellular plasticity and regenerate functional units in response to tissue damage. However, whether the reserve cells in gastrointestinal tract exist as long-term quiescent cells remain incompletely understood. In the present study, we systematically examine H2b-GFP label-retaining cells and identify a long-term slow-cycling population in the gastric corpus but not in other gastrointestinal organs. The label-retaining cells, which reside near the basal layers of the corpus, comprise a subpopulation of chief cells. The identified quiescent cells exhibit induction of Atf4 and its target genes including Atf3, a marker of paligenosis, and activation of the unfolded protein response, but do not show elevated expression of Troy, Lgr5, or Mist. External damage to the gastric mucosa induced by indomethacin treatment triggers proliferation of the quiescent Atf4+ population, indicating that the gastric corpus harbors a specific cell population that is primed to facilitate stomach regeneration.

Wnt activation disturbs cell competition and causes diffuse invasion of transformed cells through NF-κB-MMP21 pathway

Normal epithelial cells exert their competitive advantage over RasV12-transformed cells and eliminate them into the apical lumen via cell competition. However, the internal or external factors that compromise cell competition and provoke carcinogenesis remain elusive. In this study, we examine the effect of sequential accumulation of gene mutations, mimicking multi-sequential carcinogenesis on RasV12-induced cell competition in intestinal epithelial tissues. Consequently, we find that the directionality of RasV12-cell extrusion in Wnt-activated epithelia is reversed, and transformed cells are delaminated into the basal lamina via non-cell autonomous MMP21 upregulation. Subsequently, diffusively infiltrating, transformed cells develop into highly invasive carcinomas. The elevated production of MMP21 is elicited partly through NF-κB signaling, blockage of which restores apical elimination of RasV12 cells. We further demonstrate that the NF-κB-MMP21 axis is significantly bolstered in early colorectal carcinoma in humans. Collectively, this study shows that cells with high mutational burdens exploit cell competition for their benefit by behaving as unfit cells, endowing them with an invasion advantage.

Pathophysiology updates: gastroduodenal injury and repair mechanisms

PURPOSE OF REVIEW

Although the mucosal barrier serves as a primary interface between the environment and host, little is known about the repair of acute, superficial lesions or deeper, persistent lesions that if not healed, can be the site of increased permeability to luminal antigens, inflammation, and/or neoplasia development.

RECENT FINDINGS

Recent studies on acute superficial lesions have focused on calcium signaling and focal adhesion kinase, which regulate cell migration and controlled matrix adhesion during restitution. Microfluidic organ-on-a-chip and gut-on-a-chip models continued in development to support reductionist studies of epithelial-bacterial and/or epithelial-immune cell interactions during mucosal barrier disruption. In fact, these models may allow personalized medicine studies in the future using patient-derived cells to evaluate injury and repair mechanisms. Work done in the past year evaluated the safety and efficacy of acid blocking drugs on ulcer healing, with new animal studies providing evidence that each drug affects the microbiome in a different way that can be correlated with its efficacy in ulcer healing. Lastly, work to understand the way in which mature epithelial cells or committed stem cells dedifferentiate, reprogram, proliferate, and then regenerate the gastroduodenal mucosa after injury was a major focus of studies in the past year.

SUMMARY

Recent studies highlight novel mechanisms that promote restitution and mucosal regeneration after injury of the gastroduodenal mucosa.

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.

GPER governs the immune infiltration of gastric cancer and activates the NF-κB/ROS/Apoptosis pathway in gastric mucosal epithelium

BACKGROUND

Gastric cancer (GC) is with high mortality and morbidity. The GC morbidity of males is twice as high as that of females. G-protein estrogen receptor (GPER) bears on this phenomenon.

METHODS

Networks and experiments assessed the GPER expression in different validity and content. The evidence-based practice involved accessing the clinical relevance of GPER by UALCAN and Kaplan-Meier plotter. Enrichment analyses contributed to guide further experimental validations. Activation of the NF-κB/ROS/Apoptosis pathway was analyzed by WB, immunofluorescence (IF), microplate reader and flow cytometry. TISIDB and TIMER identified the immune infiltration investigations, with credibility boosted by the Kaplan-Meier plotter.

RESULTS

The appraisers revealed that GPER significantly decreased in GC at both gene and protein levels with highly approved prognosis value (P < 0.05). GPER was a significant fate determinant governing the inner part of gastric glands. NF-κB pathway and the following ROS in gastric cells were activated after MNU stimulation (20 μM, 24 h), and the GPER antagonist G15 strengthened the effect of MNU. Furthermore, GPER expression positively correlated with immune cells and various immune markers in GC patients, with highly approved clinical relevance. For example, type-2 helper cells enriched GC patients had a lower survival rate in the GPER-high expression group (P < 0.05).

CONCLUSION

We demonstrated that GPER governs the GC progression by activating the NF-κB/ROS/Apoptosis pathway in gastric cells and regulating the immune environment around them.

Helicobacter pylori plays a key role in gastric adenocarcinoma induced by spasmolytic polypeptide-expressing metaplasia

Heliobacter pylori (H. pylori), a group 1 human gastric carcinogen, is significantly associated with chronic gastritis, gastric mucosal atrophy, and gastric cancer. Approximately 20% of patients infected with H. pylori develop precancerous lesions, among which metaplasia is the most critical. Except for intestinal metaplasia (IM), which is characterized by goblet cells appearing in the stomach glands, one type of mucous cell metaplasia, spasmolytic polypeptide-expressing metaplasia (SPEM), has attracted much attention. Epidemiological and clinicopathological studies suggest that SPEM may be more strongly linked to gastric adenocarcinoma than IM. SPEM, characterized by abnormal expression of trefoil factor 2, mucin 6, and Griffonia simplicifolia lectin II in the deep glands of the stomach, is caused by acute injury or inflammation. Although it is generally believed that the loss of parietal cells alone is a sufficient and direct cause of SPEM, further in-depth studies have revealed the critical role of immunosignals. There is controversy regarding whether SPEM cells originate from the transdifferentiation of mature chief cells or professional progenitors. SPEM plays a functional role in the repair of gastric epithelial injury. However, chronic inflammation and immune responses caused by H. pylori infection can induce further progression of SPEM to IM, dysplasia, and adenocarcinoma. SPEM cells upregulate the expression of whey acidic protein 4-disulfide core domain protein 2 and CD44 variant 9, which recruit M2 macrophages to the wound. Studies have revealed that interleukin-33, the most significantly upregulated cytokine in macrophages, promotes SPEM toward more advanced metaplasia. Overall, more effort is needed to reveal the specific mechanism of SPEM malignant progression driven by H. pylori infection.

SOX9 Modulates the Transformation of Gastric Stem Cells Through Biased Symmetric Cell Division

BACKGROUND & AIMS

Transformation of stem/progenitor cells has been associated with tumorigenesis in multiple tissues, but stem cells in the stomach have been hard to localize. We therefore aimed to use a combination of several markers to better target oncogenes to gastric stem cells and understand their behavior in the initial stages of gastric tumorigenesis.

METHODS

Mouse models of gastric metaplasia and cancer by targeting stem/progenitor cells were generated and analyzed with techniques including reanalysis of single-cell RNA sequencing and immunostaining. Gastric cancer cell organoids were genetically manipulated with clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) for functional studies. Cell division was determined by bromodeoxyuridine-chasing assay and the assessment of the orientation of the mitotic spindles. Gastric tissues from patients were examined by histopathology and immunostaining.

RESULTS

Oncogenic insults lead to expansion of SOX9+ progenitor cells in the mouse stomach. Genetic lineage tracing and organoid culture studies show that SOX9+ gastric epithelial cells overlap with SOX2+ progenitors and include stem cells that can self-renew and differentiate to generate all gastric epithelial cells. Moreover, oncogenic targeting of SOX9+SOX2+ cells leads to invasive gastric cancer in our novel mouse model (Sox2-CreERT;Sox9-loxp(66)-rtTA-T2A-Flpo-IRES-loxp(71);Kras(Frt-STOP-Frt-G12D);P53R172H), which combines Cre-loxp and Flippase-Frt genetic recombination systems. Sox9 deletion impedes the expansion of gastric progenitor cells and blocks neoplasia after Kras activation. Although Sox9 is not required for maintaining tissue homeostasis where asymmetric division predominates, loss of Sox9 in the setting of Kras activation leads to reduced symmetric cell division and effectively attenuates the Kras-dependent expansion of stem/progenitor cells. Similarly, Sox9 deletion in gastric cancer organoids reduces symmetric cell division, organoid number, and organoid size. In patients with gastric cancer, high levels of SOX9 are associated with recurrence and poor prognosis.

CONCLUSION

SOX9 marks gastric stem cells and modulates biased symmetric cell division, which appears to be required for the malignant transformation of gastric stem cells.

The G protein-coupled oestrogen receptor GPER in health and disease: an update

Oestrogens and their receptors contribute broadly to physiology and diseases. In premenopausal women, endogenous oestrogens protect against cardiovascular, metabolic and neurological diseases and are involved in hormone-sensitive cancers such as breast cancer. Oestrogens and oestrogen mimetics mediate their effects via the cytosolic and nuclear receptors oestrogen receptor-α (ERα) and oestrogen receptor-β (ERβ) and membrane subpopulations as well as the 7-transmembrane G protein-coupled oestrogen receptor (GPER). GPER, which dates back more than 450 million years in evolution, mediates both rapid signalling and transcriptional regulation. Oestrogen mimetics (such as phytooestrogens and xenooestrogens including endocrine disruptors) and licensed drugs such as selective oestrogen receptor modulators (SERMs) and downregulators (SERDs) also modulate oestrogen receptor activity in both health and disease. Following up on our previous Review of 2011, we herein summarize the progress made in the field of GPER research over the past decade. We will review molecular, cellular and pharmacological aspects of GPER signalling and function, its contribution to physiology, health and disease, and the potential of GPER to serve as a therapeutic target and prognostic indicator of numerous diseases. We also discuss the first clinical trial evaluating a GPER-selective drug and the opportunity of repurposing licensed drugs for the targeting of GPER in clinical medicine.

Global knowledge mapping and emerging trends in research between spasmolytic polypeptide-expressing metaplasia and gastric carcinogenesis: A bibliometric analysis from 2002 to 2022

Background

Spasmolytic polypeptide expression metaplasia (SPEM) occurs in the corpus of the stomach and is closely related to inflammations caused by H. pylori infection. Recently, SPEM was suggested as one of the dubious precancerous lesions of gastric cancer (GC). Thus, further research on SPEM cell transdifferentiation and its underlying mechanisms could facilitate the development of new molecular targets improving the therapeutics of GC. Using bibliometrics, we analyzed publications, summarized the research hotspots and provided references for scientific researchers engaged in related research fields.

Methods

We searched the Web of Science Core Collection (WoSCC) for publications related to SPEM-GC from 2002 to 2022. The VOSviewer, SCImago, CiteSpace and R software were used to visualize and analyze the data. Gene targets identified in the keyword list were analyzed for functional enrichment using the KEGG and GO databases.

Results

Of the 292 articles identified in the initial search, we observed a stable trend in SPEM-GC research but rapid growth in the number of citations. The United States was the leader in terms of quality publications and international cooperation among them. The total number of articles published by Chinese scholars was second to the United States. Additionally, despite its low centrality and average citation frequency, China has become one of the world's most dynamic countries in academics. In terms of productivity, Vanderbilt University was identified as the most productive institution. Further, we also observed that Gastroenterology was the highest co-cited journal, and Goldenring Jr. was the most prolific author with the largest centrality.

Conclusion

SPEM could serve as an initial step in diagnosing gastric precancerous lesions. Current hotspots and frontiers of research include SPEM cell lineage differentiation, interaction with H. pylori, disturbances of the mucosal microenvironment, biomarkers, clinical diagnosis and outcomes of SPEM, as well as the development of proliferative SPEM animal models. However, further research and collaboration are still required. The findings presented in this study can be used as reference for the research status of SPEM-GC and determine new directions for future studies.

The mechanisms of gastric mucosal injury: focus on initial chief cell loss as a key target

Diffuse gastric mucosal injury is a chronic injury with altered cell differentiation, including spasmolytic polypeptide expression metaplasia (SPEM) and intestinal metaplasia (IM), which are considered precancerous lesions of gastric cancer (GC). Previously, most studies have focused on how parietal cell loss causes SPEM through transdifferentiation of chief cells. In theory, alteration or loss of chief cells seems to be a secondary phenomenon due to initial partial cell loss. However, whether initial chief cell loss causes SPEM needs to be further investigated. Currently, increasing evidence shows that initial chief cell loss is sufficient to induce gastric mucosal injury, including SPEM and IM, and ultimately lead to GC. Therefore, we summarized the two main types of models that explain the development of gastric mucosal injury due to initial chief cell loss. We hope to provide a novel perspective for the prevention and treatment of diffuse gastric mucosal injury.

Identifying Adult Stomach Tissue Stem/Progenitor Cells Using the Iqgap3-2A-CreERT2 Mouse

Identification of unique gene markers of normal and cancer stem cells is an effective strategy to study cells of origin and understand tumor behavior. Lineage tracing experiments using the Cre recombinase driven by a stem cell-specific promoter in the CreERT2 reporter mouse model enables identification of adult stem cells and delineation of stem cell activities in vivo. In our recent research on the mouse stomach, Iqgap3 was identified as a homeostatic stem cell marker located in the isthmus of the stomach epithelium. Lineage tracing with the Iqgap3-2A-CreERT2;Rosa26-LSL-tdTomato mouse model demonstrated stem cell activity in Iqgap3-expressing cells. Using the Iqgap3-2A-CreERT2 mouse model to target oncogenic KrasG12D expression to Iqgap3-expressing cells, we observed the rapid development of precancerous metaplasia in the stomach and proposed that aberrant Iqgap3-expressing cells may be critical determinants of early carcinogenesis. In this chapter, we detail a lineage tracing protocol to assess stem cell activity in the murine stomach. We also describe the procedure of inducing KrasG12D expression in Iqgap3-expressing homeostatic stem cells to explore their role as cells of origin and to trace the early cellular changes that precede neoplastic transformation.

Gastric Stem Cell Biology and Helicobacter pylori Infection

Helicobacter pylori colonizes the human gastric mucosa and persists lifelong. An interactive network between the bacteria and host cells shapes a unique microbial niche within gastric glands that alters epithelial behavior, leading to pathologies such as chronic gastritis and eventually gastric cancer. Gland colonization by the bacterium initiates aberrant trajectories by inducing long-term inflammatory and regenerative gland responses, which involve various specialized epithelial and stromal cells. Recent studies using cell lineage tracing, organoids and scRNA-seq techniques have significantly advanced our knowledge of the molecular "identity" of epithelial and stromal cell subtypes during normal homeostasis and upon infection, and revealed the principles that underly stem cell (niche) behavior under homeostatic conditions as well as upon H. pylori infection. The activation of long-lived stem cells deep in the gastric glands has emerged as a key prerequisite of H. pylori-associated gastric site-specific pathologies such as hyperplasia in the antrum, and atrophy or metaplasia in the corpus, that are considered premalignant lesions. In addition to altering the behaviour of bona fide stem cells, injury-driven de-differentiation and trans-differentation programs, such as "paligenosis", subsequently allow highly specialized secretory cells to re-acquire stem cell functions, driving gland regeneration. This plastic regenerative capacity of gastric glands is required to maintain homeostasis and repair mucosal injuries. However, these processes are co-opted in the context of stepwise malignant transformation in chronic H. pylori infection, causing the emergence, selection and expansion of cancer-promoting stem cells.

Gastroduodenal injury and repair: novel targets for therapeutic intervention

PURPOSE OF REVIEW

Although the mucosal barrier serves as a primary interface between the environment and host, little is understood about the repair of acute, superficial lesions or deeper, persistent lesions that if not healed, can be the site of increased permeability to luminal antigens, inflammation and/or neoplasia development.

RECENT FINDINGS

Recent studies have focused on focal adhesion kinase, which regulates controlled matrix adhesion during restitution after superficial injury. Actin polymerization regulates cell migration and the importance of actin-related proteins was also highlighted. Work on SARS-CoV-2 infection lent important new insights on gastroduodenal mucosal injury in patients with Covid-19 infection and work done with organoids and intestine-on-a-chip contributed new understanding about how coronaviruses infect gastrointestinal tissues and its resulting barrier dysfunction. A novel risk stratification paradigm was proposed to assist with decision making about repeat endoscopy for patients with gastric or duodenal ulcers and new therapeutic options were studied for ulcer disease. Lastly, work to support the mechanism of metaplasia development after deep injury and parietal cell loss was provided using novel transgenic mouse models.

SUMMARY

Recent studies highlight novel molecular targets to promote mucosal healing after injury of the gastroduodenal mucosa.

R-spondin 3 governs secretory differentiation in the gastric oxyntic glands

The gastric oxyntic glands are maintained by gastric stem cells that continuously supply all differentiated cell types within the corpus epithelium. Stem cells are supported by stromal cells that make up the stem cell niche. In this issue of the JCI, Fischer et al. report on their use of genetically engineered mouse models and organoids to study the role of R-spondin 3 (RSPO3) in the stomach. RSPO3, one of the major stem cell niche factors, primarily promoted secretory differentiation in the normal stomach, but also contributed to regeneration following injury. Mechanistically, RSPO3 was upregulated in the stroma by loss of chief cells and then activated the YAP pathway in gastric stem and progenitor cells, which appeared to be critical for regeneration of the secretory lineage. These data substantially advance our understanding of the regulation of gastric stem cells and highlight a function for RSPO3 in the gastrointestinal tract, which is as the gatekeeper of secretory differentiation.

Stem Cell Biomarkers and Tumorigenesis in Gastric Cancer

Stomach cancer has a high mortality, which is partially caused by an absence of suitable biomarkers to allow detection of the initiation stages of cancer progression. Thus, identification of critical biomarkers associated with gastric cancer (GC) is required to advance its clinical diagnoses and treatment. Recent studies using tracing models for lineage analysis of GC stem cells indicate that the cell fate decision of the gastric stem cells might be an important issue for stem cell plasticity. They include leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5⁺), Cholecystokinin receptor 2 (Cckr2⁺), and axis inhibition protein 2 (Axin2⁺) as the stem cell markers in the antrum, Trefoil Factor 2 (TFF2⁺), Mist1⁺ stem cells, and Troy+ chief cells in the corpus. By contrast, Estrogen receptor 1 (eR1), Leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1), SRY (sex determining region Y)-box 2 (Sox2), and B lymphoma Mo-MLV insertion region 1 homolog (Bmi1) are rich in both the antrum and corpus regions. These markers might help to identify the cell-lineage identity and analyze the plasticity of each stem cell population. Thus, identification of marker genes for the development of GC and its environment is critical for the clinical application of cancer stem cells in the prevention of stomach cancers.

LGR5-Expressing Cells in the Healing Process of Post-ESD Ulcers in Gastric Corpus

BACKGROUND

LGR5 is a promising stem cell marker in gastric pylorus, but there are few reports on its expression in human gastric corpus.

AIMS

To investigate the involvement of LGR5 expression in gastric corpus ulcer regeneration in humans.

METHODS

LGR5 expression was analyzed in five post-ESD ulcers during the healing process of regenerating epithelial cells of the gastric corpus. LGR5 expression was detected by mRNA in situ hybridization using an RNA scope kit. Immunohistochemistry of MUC6, HIK1083, and pepsinogen 1 (PG1) was performed to identify cell differentiation.

RESULTS

We defined MUC6+/HIK1083-/PG1-, MUC6+/HIK1083+/PG1-, MUC6+/HIK1083+/PG1+, MUC6+/HIK1083-/PG1+, and MUC6-/HIK1083-/PG1+cells as pseudopyloric mucosa (PPM) phase 1 (PPM1), PPM phase 2 (PPM2), PPM phase 3 (PPM3), immature chief cells (ICC), and mature chief cells (MCC) in order from the ulcer center, respectively. In the regenerated mucosa around post-ESD ulcers, LGR5 expression was observed throughout the gland in PPM1-PPM3, but it was limited to the bottom of the gland in ICC and MCC. Furthermore, LGR5 expression was not identified in the normal gastric corpus. The H-score of PPM2 was significantly higher than that of PPM3 (P = 0.0313). The H-score of PPM3 was significantly higher than that of ICC (P = 0.0313). The LGR5 H-score was higher at the immature stage, which decreased gradually with progression of the differentiation stage.

CONCLUSIONS

LGR5 expression appears to contribute to mucosal regeneration in the human gastric corpus. The application of LGR5 expression analysis to mucosal regeneration and fundic gland-type gastric tumors is expected.

Chief cell plasticity is the origin of metaplasia following acute injury in the stomach mucosa

OBJECTIVE

Metaplasia arises from differentiated cell types in response to injury and is considered a precursor in many cancers. Heterogeneous cell lineages are present in the reparative metaplastic mucosa with response to injury, including foveolar cells, proliferating cells and spasmolytic polypeptide-expressing metaplasia (SPEM) cells, a key metaplastic cell population. Zymogen-secreting chief cells are long-lived cells in the stomach mucosa and have been considered the origin of SPEM cells; however, a conflicting paradigm has proposed isthmal progenitor cells as an origin for SPEM.

DESIGN

Gastric intrinsic factor (GIF) is a stomach tissue-specific gene and exhibits protein expression unique to mature mouse chief cells. We generated a novel chief cell-specific driver mouse allele, GIF-rtTA. GIF-GFP reporter mice were used to validate specificity of GIF-rtTA driver in chief cells. GIF-Cre-RnTnG mice were used to perform lineage tracing during homoeostasis and acute metaplasia development. L635 treatment was used to induce acute mucosal injury and coimmunofluorescence staining was performed for various gastric lineage markers.

RESULTS

We demonstrated that mature chief cells, rather than isthmal progenitor cells, serve as the predominant origin of SPEM cells during the metaplastic process after acute mucosal injury. Furthermore, we observed long-term label-retaining chief cells at 1 year after the GFP labelling in chief cells. However, only a very small subset of the long-term label-retaining chief cells displayed the reprogramming ability in homoeostasis. In contrast, we identified chief cell-originating SPEM cells as contributing to lineages within foveolar cell hyperplasia in response to the acute mucosal injury.

CONCLUSION

Our study provides pivotal evidence for cell plasticity and lineage contributions from differentiated gastric chief cells during acute metaplasia development.

p57Kip2 imposes the reserve stem cell state of gastric chief cells

Adult stem cells constantly react to local changes to ensure tissue homeostasis. In the main body of the stomach, chief cells produce digestive enzymes; however, upon injury, they undergo rapid proliferation for prompt tissue regeneration. Here, we identified p57Kip2 (p57) as a molecular switch for the reserve stem cell state of chief cells in mice. During homeostasis, p57 is constantly expressed in chief cells but rapidly diminishes after injury, followed by robust proliferation. Both single-cell RNA sequencing and dox-induced lineage tracing confirmed the sequential loss of p57 and activation of proliferation within the chief cell lineage. In corpus organoids, p57 overexpression induced a long-term reserve stem cell state, accompanied by altered niche requirements and a mature chief cell/secretory phenotype. Following the constitutive expression of p57 in vivo, chief cells showed an impaired injury response. Thus, p57 is a gatekeeper that imposes the reserve stem cell state of chief cells in homeostasis.

Stem Cells, Helicobacter pylori, and Mutational Landscape: Utility of Preclinical Models to Understand Carcinogenesis and to Direct Management of Gastric Cancer

Several genetic and environmental factors increase gastric cancer (GC) risk, with Helicobacter pylori being the main environmental agent. GC is thought to emerge through a sequence of morphological changes that have been elucidated on the molecular level. New technologies have shed light onto pathways that are altered in GC, involving mutational and epigenetic changes and altered signaling pathways. Using various new model systems and innovative approaches, the relevance of such alterations for the emergence and progression of GC has been validated. Here, we highlight the key strategies and the resulting achievements. A major step is the characterization of epithelial stem cell behavior in the healthy stomach. These data, obtained through new reporter mouse lines and lineage tracing, enabled insights into the processes that control cellular proliferation, self-renewal, and differentiation of gastric stem cells. It has become evident that these cells and pathways are often deregulated in carcinogenesis. Second, insights into how H pylori colonizes gastric glands, directly interacts with stem cells, and alters cellular and genomic integrity, as well as the characterization of tissue responses to infection, provide a comprehensive picture of how this bacterium contributes to gastric carcinogenesis. Third, the development of stem cell- and tissue-specific reporter mice have driven our understanding of the signals and mutations that promote different types of GC and now also enable the study of more advanced, metastasized stages. Finally, organoids from human tissue have allowed insights into gastric carcinogenesis by validating mutational and signaling alterations in human primary cells and opening a route to predicting responses to personalized treatment.

A Bibliometric Analysis of Atrophic Gastritis From 2011 to 2021

Background

Atrophic gastritis (AG), which is characterized by a decreased number or disappearance of the glandular structures and secretory dysfunction, is linked to chronically inflamed stomach. It has been estimated that the annual incidence of gastric cancer (GC) is 0.1% for patients with AG. Early eradication of Helicobacter pylori (H. pylori) can reduce the risk of GC development. Additionally, the follow-up and management of AG are necessary to prevent GC. Exploring novel methods of the automatized analysis of data for apprehending knowledge in any medical field is encouraged, especially when a body of literature suggests the necessity of doing so. Accordingly, herein, we aim to systematically review the current foci and status of AG research using bibliometric analysis.

Methods

Articles and reviews related to AG published from 2011 to 2021 in the Web of Science Core Collection were retrieved. Microsoft Office Excel 2019 and GraphPad Prism were used to show the annual number of publications and scientific productivity of authors through time. CiteSpace and VOSviewer were used to generate network maps about the collaborations among countries, institutions, and authors as well as reveal hotspots of AG research. The relationships among the author's keywords, cited references, and the top authors were summarized by a Sankey plot (three-fields plot).

Results

A total of 1,432 publications were included in the present study. China remained the most productive country, with the highest number of publications (377, 26.32%). Vanderbilt University contributed the most publications of any single institution (56, 3.91%). James R Goldenring was the most active and influential scholar, with the highest number of publications and greatest centrality. The most prolific journal in this field was World Journal of Gastroenterology (62, 4.32%). Gastroenterology (997, 69.62%) was the most co-cited journal. Exploring the origin of gastric metaplasia, especially spasmolytic polypeptide-expressing metaplasia (SPEM) was a major topic in AG research.

Conclusions

This bibliometric study provides a comprehensive analysis of the scientific progress of AG over the past decade. Metaplasia is a hot topic and could be a promising area of research in the coming years.

Cellular Plasticity, Reprogramming, and Regeneration: Metaplasia in the Stomach and Beyond

The mucosa of the body of the stomach (ie, the gastric corpus) uses 2 overlapping, depth-dependent mechanisms to respond to injury. Superficial injury heals via surface cells with histopathologic changes like foveolar hyperplasia. Deeper, usually chronic, injury/inflammation, most frequently induced by the carcinogenic bacteria Helicobacter pylori, elicits glandular histopathologic alterations, initially manifesting as pyloric (also known as pseudopyloric) metaplasia. In this pyloric metaplasia, corpus glands become antrum (pylorus)-like with loss of acid-secreting parietal cells (atrophic gastritis), expansion of foveolar cells, and reprogramming of digestive enzyme-secreting chief cells into deep antral gland-like mucous cells. After acute parietal cell loss, chief cells can reprogram through an orderly stepwise progression (paligenosis) initiated by interleukin-13-secreting innate lymphoid cells (ILC2s). First, massive lysosomal activation helps mitigate reactive oxygen species and remove damaged organelles. Second, mucus and wound-healing proteins (eg, TFF2) and other transcriptional alterations are induced, at which point the reprogrammed chief cells are recognized as mucus-secreting spasmolytic polypeptide-expressing metaplasia cells. In chronic severe injury, glands with pyloric metaplasia can harbor both actively proliferating spasmolytic polypeptide-expressing metaplasia cells and eventually intestine-like cells. Gastric glands with such lineage confusion (mixed incomplete intestinal metaplasia and proliferative spasmolytic polypeptide-expressing metaplasia) may be at particular risk for progression to dysplasia and cancer. A pyloric-like pattern of metaplasia after injury also occurs in other gastrointestinal organs including esophagus, pancreas, and intestines, and the paligenosis program itself seems broadly conserved across tissues and species. Here we discuss aspects of metaplasia in stomach, incorporating data derived from animal models and work on human cells and tissues in correlation with diagnostic and clinical implications.

Induction of Gastric Cancer by Successive Oncogenic Activation in the Corpus

BACKGROUND & AIMS

Metaplasia and dysplasia in the corpus are reportedly derived from de-differentiation of chief cells. However, the cellular origin of metaplasia and cancer remained uncertain. Therefore, we investigated whether pepsinogen C (PGC) transcript-expressing cells represent the cellular origin of metaplasia and cancer using a novel Pgc-specific CreERT2 recombinase mouse model.

METHODS

We generated a Pgc-mCherry-IRES-CreERT2 (Pgc-CreERT2) knock-in mouse model. Pgc-CreERT2/+ and Rosa-EYFP mice were crossed to generate Pgc-CreERT2/Rosa-EYFP (Pgc-CreERT2/YFP) mice. Gastric tissues were collected, followed by lineage-tracing experiments and histologic and immunofluorescence staining. We further established Pgc-CreERT2;KrasG12D/+ mice and investigated whether PGC transcript-expressing cells are responsible for the precancerous state in gastric glands. To investigate cancer development from PGC transcript-expressing cells with activated Kras, inactivated Apc, and Trp53 signaling pathways, we crossed Pgc-CreERT2/+ mice with conditional KrasG12D, Apcflox, Trp53flox mice.

RESULTS

Expectedly, mCherry mainly labeled chief cells in the Pgc-CreERT2 mice. However, mCherry was also detected throughout the neck cell and isthmal stem/progenitor regions, albeit at lower levels. In the Pgc-CreERT2;KrasG12D/+ mice, PGC transcript-expressing cells with KrasG12D/+ mutation presented pseudopyloric metaplasia. The early induction of proliferation at the isthmus may reflect the ability of isthmal progenitors to react rapidly to Pgc-driven KrasG12D/+ oncogenic mutation. Furthermore, Pgc-CreERT2;KrasG12D/+;Apcflox/flox mice presented intramucosal dysplasia/carcinoma and Pgc-CreERT2;KrasG12D/+;Apcflox/flox;Trp53flox/flox mice presented invasive and metastatic gastric carcinoma.

CONCLUSIONS

The Pgc-CreERT2 knock-in mouse is an invaluable tool to study the effects of successive oncogenic activation in the mouse corpus. Time-course observations can be made regarding the responses of isthmal and chief cells to oncogenic insults. We can observe stomach-specific tumorigenesis from the beginning to metastatic development.

Roles of G Protein-Coupled Receptors (GPCRs) in Gastrointestinal Cancers: Focus on Sphingosine 1-Shosphate Receptors, Angiotensin II Receptors, and Estrogen-Related GPCRs

It is well established that gastrointestinal (GI) cancers are common and devastating diseases around the world. Despite the significant progress that has been made in the treatment of GI cancers, the mortality rates remain high, indicating a real need to explore the complex pathogenesis and develop more effective therapeutics for GI cancers. G protein-coupled receptors (GPCRs) are critical signaling molecules involved in various biological processes including cell growth, proliferation, and death, as well as immune responses and inflammation regulation. Substantial evidence has demonstrated crucial roles of GPCRs in the development of GI cancers, which provided an impetus for further research regarding the pathophysiological mechanisms and drug discovery of GI cancers. In this review, we mainly discuss the roles of sphingosine 1-phosphate receptors (S1PRs), angiotensin II receptors, estrogen-related GPCRs, and some other important GPCRs in the development of colorectal, gastric, and esophageal cancer, and explore the potential of GPCRs as therapeutic targets.

Mucosal defense: gastroduodenal injury and repair mechanisms

PURPOSE OF REVIEW

The mucosal barrier serves as a primary interface between the environment and host. In daily life, superficial injury to the gastric or duodenal mucosa occurs regularly but heals rapidly by a process called 'restitution'. Persistent injury to the gastroduodenal mucosa also occurs but initiates a regenerative lesion with specific wound healing mechanisms that attempt to repair barrier function. If not healed, these lesions can be the site of neoplasia development in a chronic inflammatory setting. This review summarizes the past year of advances in understanding mucosal repair in the gastroduodenal mucosa, which occurs as a defense mechanism against injury.

RECENT FINDINGS

Organoids are an emerging new tool that allows for the correlation of in vivo and in vitro models; organoids represent an important reductionist model to probe specific aspects of injury and repair mechanisms that are limited to epithelial cells. Additionally, proof-of-concept studies show that machine learning algorithms may ultimately assist with identifying novel, targetable pathways to pursue in therapeutic interventions. Gut-on-chip technology and single cell RNA-sequencing contributed to new understanding of gastroduodenal regenerative lesions after injury by identifying networks and interactions that are involved in the repair process.

SUMMARY

Recent updates provide new possibilities for identifying novel molecular targets for the treatment of acute and superficial mucosal injury, mucosal regeneration, and regenerative lesions in the gastrointestinal tract.

Iqgap3-Ras axis drives stem cell proliferation in the stomach corpus during homoeostasis and repair

OBJECTIVE

Tissue stem cells are central regulators of organ homoeostasis. We looked for a protein that is exclusively expressed and functionally involved in stem cell activity in rapidly proliferating isthmus stem cells in the stomach corpus.

DESIGN

We uncovered the specific expression of Iqgap3 in proliferating isthmus stem cells through immunofluorescence and in situ hybridisation. We performed lineage tracing and transcriptomic analysis of Iqgap3 +isthmus stem cells with the Iqgap3-2A-tdTomato mouse model. Depletion of Iqgap3 revealed its functional importance in maintenance and proliferation of stem cells. We further studied Iqgap3 expression and the associated gene expression changes during tissue repair after tamoxifen-induced damage. Immunohistochemistry revealed elevated expression of Iqgap3 in proliferating regions of gastric tumours from patient samples.

RESULTS

Iqgap3 is a highly specific marker of proliferating isthmus stem cells during homoeostasis. Iqgap3+isthmus stem cells give rise to major cell types of the corpus unit. Iqgap3 expression is essential for the maintenance of stem potential. The Ras pathway is a critical partner of Iqgap3 in promoting strong proliferation in isthmus stem cells. The robust induction of Iqgap3 expression following tissue damage indicates an active role for Iqgap3 in tissue regeneration.

CONCLUSION

IQGAP3 is a major regulator of stomach epithelial tissue homoeostasis and repair. The upregulation of IQGAP3 in gastric cancer suggests that IQGAP3 plays an important role in cancer cell proliferation.

Stem cells and origins of cancer in the upper gastrointestinal tract

The esophagus and stomach, joined by a unique transitional zone, contain actively dividing epithelial stem cells required for organ homeostasis. Upon prolonged inflammation, epithelial cells in both organs can undergo a cell fate switch leading to intestinal metaplasia, predisposing to malignancy. Here we discuss the biology of gastroesophageal stem cells and their role as cells of origin in cancer. We summarize the interactions between the stromal niche and gastroesophageal stem cells in metaplasia and early expansion of mutated stem-cell-derived clones during carcinogenesis. Finally, we review new approaches under development to better study gastroesophageal stem cells and advance the field.

mTOR signaling regulates gastric epithelial progenitor homeostasis and gastric tumorigenesis via MEK1-ERKs and BMP-Smad1 pathways

mTOR, the sensor of nutrients and growth factors, has important roles in tissue homeostasis and tumorigenesis. However, how mTOR controls gastric epithelial cell turnover and gastric cancer development, a leading malignancy, remains poorly understood. Here, we provide genetic evidence that mTOR activation promotes proliferation and inhibits differentiation of Lgr5⁺ gastric epithelial progenitors (GEPs) in gastric homeostasis and tumorigenesis. mTOR signaling increases MEK1 and Smad1 expression and enhances activation of MEK1-ERKs and BMP-Smad1 pathways, respectively, in GEPs and gastric tumors. Mek1 deletion or inhibition rescues hyperproliferation, whereas Bmpr1a ablation or inhibition rescues differentiation defects of Tsc1^-/- GEPs. Tsc1 deficiency in Lgr5⁺ GEPs accelerates gastric tumor initiation and development, which require MEK1-ERKs for hyperplasia and BMP-Smad1 for differentiation suppression. These findings reveal how mTOR signaling controls Lgr5⁺ GEP homeostasis and cancerization and suggest that ERKs and Smad1 signaling can be safely targeted to substitute mTOR inhibitors in gastric cancer therapy.

Mist1+ gastric isthmus stem cells are regulated by Wnt5a and expand in response to injury and inflammation in mice

BACKGROUND AND AIMS

The gastric epithelium undergoes continuous turnover. Corpus epithelial stem cells located in the gastric isthmus serve as a source of tissue self-renewal. We recently identified the transcription factor Mist1 as a marker for this corpus stem cell population that can give rise to cancer. The aim here was to investigate the regulation of the Mist1+ stem cells in the response to gastric injury and inflammation.

METHODS

We used Mist1CreERT;R26-Tdtomato mice in two models of injury and inflammation: the acetic acid-induced ulcer and infection with Helicobacter felis. We analysed lineage tracing at both early (7 to 30 days) and late (30 to 90 days) time points. Mist1CreERT;R26-Tdtomato;Lgr5DTR-eGFP mice were used to ablate the corpus basal Lgr5+ cell population. Constitutional and conditional Wnt5a knockout mice were used to investigate the role of Wnt5a in wound repair and lineage tracing from the Mist1+ stem cells.

RESULTS

In both models of gastric injury, Mist1+ isthmus stem cells more rapidly proliferate and trace entire gastric glands compared with the normal state. In regenerating tissue, the number of traced gastric chief cells was significantly reduced, and ablation of Lgr5+ chief cells did not affect Mist1-derived lineage tracing and tissue regeneration. Genetic deletion of Wnt5a impaired proliferation in the gastric isthmus and lineage tracing from Mist1+ stem cells. Similarly, depletion of innate lymphoid cells, the main source of Wnt5a, also resulted in reduced proliferation and Mist1+ isthmus cell tracing.

CONCLUSION

Gastric Mist1+ isthmus cells are the main supplier of regenerated glands and are activated in part through Wnt5a pathway.

Cell competition-induced apical elimination of transformed cells, EDAC, orchestrates the cellular homeostasis

Newly emerging transformed cells are often eliminated from the epithelium via cell competition with the surrounding normal cells. A number of recent studies using mammalian cell competition systems have demonstrated that cells with various types of oncogenic insults are extruded from the tissue in a cell death-dependent or -independent manner. Cell competition-mediated elimination of transformed cells, called EDAC (epithelial defense against cancer), represents an intrinsic anti-tumor activity within the epithelial cell society to reduce the risk of oncogenesis. Here we delineate roles and molecular mechanisms of this homeostatic process, especially focusing on mammalian models.

Dysregulated Immune Responses by ASK1 Deficiency Alter Epithelial Progenitor Cell Fate and Accelerate Metaplasia Development during H. pylori Infection

The mechanism of H. pylori-induced atrophy and metaplasia has not been fully understood. Here, we demonstrate the novel role of Apoptosis signal-regulating kinase 1 (ASK1) and downstream MAPKs as a regulator of host immune responses and epithelial maintenance against H. pylori infection. ASK1 gene deficiency resulted in enhanced inflammation with numerous inflammatory cells including Gr-1+CD11b+ myeloid-derived suppressor cells (MDSCs) recruited into the infected stomach. Increase of IL-1β release from apoptotic macrophages and enhancement of TH1-polarized immune responses caused STAT1 and NF-κB activation in epithelial cells in ASK1 knockout mice. Dysregulated immune and epithelial activation in ASK1 knockout mice led to dramatic expansion of gastric progenitor cells and massive metaplasia development. Bone marrow transplantation experiments revealed that ASK1 in inflammatory cells is critical for inducing immune disorder and metaplastic changes in epithelium, while ASK1 in epithelial cells regulates cell proliferation in stem/progenitor zone without changes in inflammation and differentiation. These results suggest that H. pylori-induced immune cells may regulate epithelial homeostasis and cell fate as an inflammatory niche via ASK1 signaling.

The cellular origins of cancer with particular reference to the gastrointestinal tract

Stem cells or their closely related committed progenitor cells are the likely founder cells of most neoplasms. In the continually renewing and hierarchically organized epithelia of the oesophagus, stomach and intestine, homeostatic stem cells are located at the beginning of the cell flux, in the basal layer of the oesophagus, the isthmic region of gastric oxyntic glands and at the bottom of gastric pyloric-antral glands and colonic crypts. The introduction of mutant oncogenes such as KrasG12D or loss of Tp53 or Apc to specific cell types expressing the likes of Lgr5 and Mist1 can be readily accomplished in genetically engineered mouse models to initiate tumorigenesis. Other origins of cancer are discussed including 'reserve' stem cells that may be activated by damage or through disruption of morphogen gradients along the crypt axis. In the liver and pancreas, with little cell turnover and no obvious stem cell markers, the importance of regenerative hyperplasia associated with chronic inflammation to tumour initiation is vividly apparent, though inflammatory conditions in the renewing populations are also permissive for tumour induction. In the liver, hepatocytes, biliary epithelial cells and hepatic progenitor cells are embryologically related, and all can give rise to hepatocellular carcinoma and cholangiocarcinoma. In the exocrine pancreas, both acinar and ductal cells can give rise to pancreatic ductal adenocarcinoma (PDAC), although the preceding preneoplastic states are quite different: acinar-ductal metaplasia gives rise to pancreatic intraepithelial neoplasia culminating in PDAC, while ducts give rise to PDAC via. mucinous cell metaplasia that may have a polyclonal origin.

Tumor microenvironment in gastric cancers

The tumor microenvironment favors the growth and expansion of cancer cells. Many cell types are involved in the tumor microenvironment such as inflammatory cells, fibroblasts, nerves, and vascular endothelial cells. These stromal cells contribute to tumor growth by releasing various molecules to either directly activate the growth signaling in cancer cells or remodel surrounding areas. This review introduces recent advances in findings on the interactions within the tumor microenvironment such as in cancer-associated fibroblasts (CAFs), immune cells, and endothelial cells, in particular those established in mouse gastric cancer models. In mice, myofibroblasts in the gastric stroma secrete R-spondin and support normal gastric stem cells. Most CAFs promote tumor growth in a paracrine manner, but CAF population appears to be heterogeneous in terms of their function and origin, and include both tumor-promoting and tumor-restraining populations. Among immune cell populations, tumor-associated macrophages, including M1 and M2 macrophages, and myeloid-derived suppressor cells (MDSCs), are reported to directly or indirectly promote gastric tumorigenesis by secreting soluble factors or modulating immune responses. Endothelial cells or blood vessels not only fuel tumors with nutrients, but also interact with cancer stem cells and immune cells by secreting chemokines or cytokines, and act as a cancer niche. Understanding these interactions within the tumor microenvironment would contribute to unraveling new therapeutic targets.

Autoimmune gastritis

Autoimmune gastritis (AIG) is an increasingly prevalent, organ-specific, immune-mediated disorder characterized by the destruction of gastric parietal cells, leading to the loss of intrinsic factor and reduced acid output. These alterations result in malabsorption of iron, vitamin B₁₂ (pernicious anaemia) and potentially other micronutrients. For several years, most studies have focused on pernicious anaemia only, generating confusion between the two entities. In AIG, the gastric proton pump, H⁺/K⁺ ATPase, is the major autoantigen recognized by autoreactive T cells. The T cell-dependent activation of B cells stimulates the production of anti-parietal cell antibodies, the serological hallmark of AIG. The role of Helicobacter pylori infection in activating or favouring the autoimmune process is still uncertain. Early histopathological alterations allowing a more precise and prompt recognition have recently been described. AIG is burdened by a substantial diagnostic delay as it can present with varied clinical signs including, among others, gastrointestinal symptoms and neuropsychiatric manifestations. In advanced stages, AIG might progress to neuroendocrine tumours and gastric adenocarcinoma. Management includes early detection through a proactive case-finding strategy, micronutrient supplementation and endoscopic surveillance. This Primer comprehensively describes the most important insights regarding the epidemiology, pathophysiology, diagnosis and management of AIG, focusing on the most controversial, outstanding issues and future directions.