Single-cell transcriptional analyses of spasmolytic polypeptide-expressing metaplasia arising from acute drug injury and chronic inflammation in the stomach

Dissecting the Spatial and Single-Cell Transcriptomic Architecture of Cancer Stem Cell Niche Driving Tumor Progression in Gastric Cancer

Despite significant advancements in identifying novel therapeutic targets and compounds, cancer stem cells (CSCs) remain pivotal in driving therapeutic resistance and tumor progression in gastric cancer (GC). High-resolution knowledge of the transcriptional programs underlying the role of CSC niche in driving tumor stemness and progression is still lacking. Herein, spatial and single-cell RNA sequencing of 32 human gastric mucosa tissues at various stages of malignancy, illuminating the phenotypic plasticity of tumor epithelium and transcriptional trajectory from mature gastric chief cells to the CSC state, which is associated with activation of EGFR and WNT signaling pathways, is conducted. Moreover, the CSCs interact with not only the immunosuppressive CXCL13+ T cells and CCL18+ M2 macrophages to evade immune surveillance, but also the inflammatory cancer-associated fibroblasts (iCAFs) to promote tumorigenesis and maintain stemness, which construct the CSC niche leading to inferior prognosis. Notably, it is uncovered that amphiregulin (AREG) derived from iCAFs promotes tumor stemness by upregulating the expression of SOX9 in tumor cells, and contributes to drug resistance via the AREG-ERBB2 axis. This study provides valuable insight into the characteristics of CSC niche in driving tumor stemness and progression, offering novel perspective for designing effective strategies to overcome GC therapy resistance.

Elucidation of the mechanism of carcinogenic transformation of human gastric epithelial cells in atrophic gastritis

BACKGROUND

Helicobacter pylori infection and subsequent atrophic gastritis (AG) and intestinal metaplasia (IM) are regarded as precursor conditions for gastric cancer (GC). Though diverse mechanisms of carcinogenesis from AG and IM have been clarified using mouse models, few studies using human models have been reported. Here, we describe in vitro modeling of IM, as well as in vivo modeling of the oncogenic transformation from AG using human gastric organoids.

METHODS

Organoids derived from patients with AG were established and characterized by immunohistochemistry and in situ hybridization. Niche factor withdrawal and genetic engineering using CRISPR/Cas9 were conducted for modeling IM, and manipulated organoids were xenografted subcutaneously in mice to establish a GC model.

RESULTS

AG organoids (AGOs) were maintained by Wnt niche factors; withdrawal of these factors led to differentiation toward foveolar cells. Knockout of Runt-related transcription factor 3 (RUNX3), or activation of bone morphogenetic protein (BMP) signaling, resulted in accumulation of the key IM markers caudal-type homeobox 2 (CDX2) and mucin 2 (MUC2) in AGOs; disruption of SMAD4 counteracted the induction of these markers. Organoids doubly deficient for TP53 and SMAD4 formed larger and more proliferative p21 -negative subcutaneous tumors than did RUNX3-deficient organoids, suggesting that induction of a senescent state is a key barrier in stepwise carcinogenesis from AG.

CONCLUSIONS

Wnt signaling is essential for homeostasis of AG, and SMAD4-dependent activation of BMP signaling promotes intestinal differentiation. Combined disruption of TP53 and SMAD4 confers tumorigenic potential to AGOs by inhibiting p21 induction.

Tff2 marks gastric corpus progenitors that give rise to pyloric metaplasia/SPEM following injury

In Brief

Tu et al. show that Tff2 + corpus isthmus cells are TA progenitors, and they, not chief cells, are the primary source of SPEM following injury. Upon Kras mutation, these progenitors directly progress to dysplasia, bypassing metaplasia, highlighting them as a potential origin of gastric cancer.

Highlights

Tff2 + corpus cells are TA progenitors that give rise to secretory cells. Tff2 + progenitors, not chief cells, are the primary source of SPEM after injury. Kras-mutant Tff2 + progenitors progress directly to dysplasia, bypassing metaplasia. Multi-omics analysis reveals distinct trajectories for SPEM and gastric cancer.

Abstract Figure

Pyloric metaplasia, also known as spasmolytic polypeptide-expressing metaplasia (SPEM), arises in the corpus in response to oxyntic atrophy, but its origin and role in gastric cancer remain poorly understood. Using Tff2-CreERT knockin mice, we identified highly proliferative Tff2 + progenitors in the corpus isthmus that give rise to multiple secretory lineages, including chief cells. While lacking long-term self-renewal ability, Tff2 + corpus progenitors rapidly expand to form short-term SPEM following acute injury or loss of chief cells. Genetic ablation of Tff2 + progenitors abrogated SPEM formation, while genetic ablation of GIF + chief cells enhanced SPEM formation from Tff2 + progenitors. In response to H. pylori infection, Tff2 + progenitors progressed first to metaplasia and then later to dysplasia. Interestingly, induction of Kras G12D mutations in Tff2 + progenitors facilitated direct progression to dysplasia in part through the acquisition of stem cell-like properties. In contrast, Kras-mutated SPEM and chief cells were not able to progress to dysplasia. Tff2 mRNA was downregulated in isthmus cells during progression to dysplasia. Single-cell RNA sequencing and spatial transcriptomics of human tissues revealed distinct differentiation trajectories for SPEM and gastric cancer. These findings challenge the conventional interpretation of the stepwise progression through metaplasia and instead identify Tff2 + progenitor cells as potential cells of origin for SPEM and possibly for gastric cancer.

Single-cell eQTL mapping reveals cell-type-specific genes associated with the risk of gastric cancer

Most expression quantitative trait locus (eQTL) analyses have been conducted in heterogeneous gastric tissues, limiting understanding of cell-type-specific regulatory mechanisms. Here, we employed a pooled multiplexing strategy to profile 399,683 gastric cells from 203 Chinese individuals using single-cell RNA sequencing (scRNA-seq). We identified 19 distinct gastric cell types and performed eQTL analyses, uncovering 8,498 independent eQTLs, with a considerable fraction (81%, 6,909/8,498) exhibiting cell-type-specific effects. Integration of these eQTLs with genome-wide association studies for gastric cancer (GC) revealed four co-localization signals in specific cell types. Genetically predicted cell-type-specific gene expression identified 15 genes associated with GC risk, including the upregulation of MUC1 exclusively in parietal cells, linked to decreased GC risk. Our findings highlight substantial heterogeneity in the genetic regulation of gene expression across gastric cell types and provide critical cell-type-specific annotations of genetic variants associated with GC risk, offering new molecular insights underlying GC.

Post-COVID-19 Effects on Chronic Gastritis and Gastric Cellular and Molecular Characteristics in Male Mice

BACKGROUNDS & AIMS

Since the Omicron variant emerged as a major severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant, COVID-19-associated mortality has decreased remarkably. Nevertheless, patients with a history of SARS-CoV-2 infection have been suffering from an aftereffect commonly known as 'long COVID,' affecting diverse organs. However, the effect of SARS-CoV-2 on gastric cells and disease progression was not previously known. We aimed to investigate whether SARS-CoV-2 infection affects stomach cells and if post-COVID-19 conditions can lead to severe gastric disease.

METHODS

Stomach specimens obtained from male K18-hACE2 mice 7 days after SARS-CoV-2 infection were subjected to a transcriptomic analysis for molecular profiling. To investigate the putative role of SARS-CoV-2 in gastric carcinogenesis, K18-hACE2 mice affected by nonlethal COVID-19 were also inoculated with Helicobacter pylori SS1.

RESULTS

Despite the lack of viral dissemination and pathologic traits in the stomach, SARS-CoV-2 infection caused dramatic changes to the molecular profile and some immune subsets in this organ. Notably, the gene sets related to metaplasia and gastric cancer were significantly enriched after viral infection. As a result, chronic inflammatory responses and preneoplastic transitions were promoted in these mice.

CONCLUSION

SARS-CoV-2 infection indirectly leads to profound and post-acute COVID-19 alterations in the stomach at the cellular and molecular levels, resulting in adverse outcomes following co-infection with SARS-CoV-2 and H. pylori. Our results show that 2 prevalent pathogens of humans elicit a negative synergistic effect and provide evidence of the risk of severe chronic gastritis in the post-COVID-19 era.

Integrative analysis of single-cell and bulk RNA sequencing reveals the oncogenic role of ANXA5 in gastric cancer and its association with drug resistance

Background

Gastric cancer (GC) remains a leading cause of cancer-related mortality, with over one million new cases and 769,000 deaths reported in 2020. Despite advancements in chemotherapy, surgery, and targeted therapies, delayed diagnosis due to overlooked early symptoms leads to poor prognosis.

Methods

We integrated bulk RNA sequencing and single-cell RNA sequencing datasets from TCGA, GEO, and OMIX001073, employing normalization, batch effect correction, and dimensionality reduction methods to identify key cell populations associated with GC invasion and epithelial-mesenchymal transition (EMT), as well as analyze the tumor immune microenvironment.

Results

Our analysis identified the MUC5AC+ malignant epithelial cell cluster as a significant player in GC invasion and EMT. Cluster 1, representing this cell population, exhibited higher invasion and EMT scores compared to other clusters. Survival analysis showed that high abundance in cluster 0 correlated with improved survival rates (P=0.012), whereas cluster 1 was associated with poorer outcomes (P=0.045). A prognostic model highlighted ANXA5 and GABARAPL2 as two critical genes upregulated in GC tumors. High-risk patients demonstrated increased immune cell infiltration and worse prognosic. Analysis of tumor mutation burden (TMB) indicated that patients with low TMB in the high-risk group had the worst prognosis. Wet-lab validation experiments confirmed the oncogenic role of ANXA5, showing its facilitation of cell proliferation, invasion, and migration while suppressing apoptosis.

Conclusion

This study offers novel insights into the subpopulations of malignant epithelial cells in GC and their roles in tumor progression. It provides a prognostic model and potential therapeutic targets to combat GC, contributing crucial understanding to the fundamental mechanisms of drug resistance in gastrointestinal cancers.

Mutant GNAS drives a pyloric metaplasia with tumor suppressive glycans in intraductal papillary mucinous neoplasia

BACKGROUND & AIMS

Intraductal Papillary Mucinous Neoplasms (IPMNs) are cystic lesions and bona fide precursors for pancreatic ductal adenocarcinoma (PDAC). Recent studies have shown that pancreatic precancer is characterized by a transcriptomic program similar to gastric metaplasia. The aims of this study were to assay IPMN for pyloric markers, to identify molecular drivers, and to determine a functional role for this program in the pancreas.

METHODS

Pyloric marker expression was evaluated by RNA-seq and multiplex immunostaining in patient samples. Cell lines and organoids expressing KrasG12D +/- GNASR201C underwent RNA sequencing. A PyScenic-based regulon analysis was performed to identify molecular drivers, and candidates were evaluated by RNA-seq, immunostaining, and small interfering RNA knockdown. Glycosylation profiling was performed to identify GNASR201C-driven changes. Glycan abundance was evaluated in patient samples.

RESULTS

Pyloric markers were identified in human IPMN. GNASR201C drove expression of this program as well as an indolent phenotype characterized by distinct glycosyltransferase changes. Glycan profiling identified an increase in LacdiNAcs and loss of pro-tumorigenic Lewis antigens. Knockdown of transcription factors Spdef or Creb3l1 or chitinase treatment reduced LacdiNAc deposition and reversed the indolent phenotype. LacdiNAc and 3-sulfoLeA/C abundance discriminated low from high grade patient IPMN.

CONCLUSION

GNASR201C drives an indolent phenotype in IPMN by amplifying a differentiated, pyloric phenotype through SPDEF/CREB3L1 which is characterized by distinct glycans. Acting as a glycan rheostat, mutant GNAS elevates LacdiNAcs at the expense of pro-tumorigenic acidic Lewis epitopes, inhibiting cancer cell invasion and disease progression. LacdiNAc and 3-Sulfo-LeA/C are mutually exclusive and may serve as markers of disease progression.

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.

ROR2 Regulates Cellular Plasticity in Pancreatic Neoplasia and Adenocarcinoma

Cellular plasticity is a hallmark of pancreatic ductal adenocarcinoma (PDAC) starting from the conversion of normal cells into precancerous lesions, to the progression of carcinoma subtypes associated with aggressiveness and therapeutic response. We discovered that normal acinar cell differentiation, maintained by the transcription factor PDX1, suppresses a broad gastric cell identity that is maintained in metaplasia, neoplasia, and the classical subtype of PDAC in a mouse and human. We identified the receptor tyrosine kinase ROR2 as marker of a gastric metaplasia-like identity in pancreas neoplasms. Ablation of Ror2 in a mouse model of pancreatic tumorigenesis promoted a switch to a gastric pit cell identity that largely persisted through progression to the classical subtype of PDAC. In both human and mouse pancreatic cancer, ROR2 activity continued to antagonize the gastric pit cell identity, strongly promoting an epithelial to mesenchymal transition, conferring resistance to KRAS inhibition, and vulnerability to AKT inhibition. Significance: We discovered the receptor tyrosine kinase ROR2 as an important regulator of cellular identity in pancreatic precancerous lesions and pancreatic cancer. ROR2 drives an aggressive PDAC phenotype and confers resistance to KRAS inhibitors, suggesting that targeting ROR2 will enhance sensitivity to this new generation of targeted therapies. See related commentary by Marasco and Misale, p. 2018.

Berberine safeguards sepsis-triggered acute gastric damage and inhibits pyroptosis in gastric epithelial cells via suppressing the ubiquitination and degradation of Nrf2

Berberine (BBR), a widely recognized traditional Chinese medicine, has attracted considerable attention for its promising anti-inflammatory effects. The activation of nuclear factor erythroid 2-related factor 2 (Nrf2) effectively safeguards against organ damage stemming from sepsis-induced oxidative stress and inflammatory responses. This study examined the potential of BBR in alleviating sepsis-induced acute gastric injury, with a particular focus on elucidating whether its mechanism of action involves the activation of the Nrf2 signaling pathway. Following intraperitoneal injection of BBR, mice were subjected to the cecal ligation and puncture (CLP) method to induce sepsis. In vitro experiments involved pre-treating the normal gastric epithelial cells (GES-1) with BBR, followed by treatment with lipopolysaccharide (LPS). Functional assays were then performed to assess cell proliferation and apoptosis. To validate the role of Nrf2 in pyroptosis and inflammation, siRNA targeting Nrf2 (si-Nrf2) was transfected into LPS-treated GES-1 cells. Additionally, mice were administered the Nrf2 inhibitor ML385 to confirm the protective effects of BBR in vivo. BBR displayed a dose-dependent effect in mitigating gastric tissue damage, suppressing the release of inflammatory cytokines, and reducing the expression of NLRP3, ASC, and GSDMD-N. In vitro, BBR fostered GES-1 cell proliferation, hindered apoptosis, and suppressed the levels of TNF-α, IL-18, IL-1β, NLRP3, ASC, and GSDMD-N. Further analysis revealed that knocking down Nrf2 reversed BBR's inhibitory effect on pyroptosis in LPS-treated GES-1 cells. Through binding to Keap1, BBR efficiently prevented the ubiquitination and degradation of Nrf2, ultimately promoting its nuclear translocation. In vivo experiments confirmed that ML385 reversed the protective effect of BBR on pyroptosis and inflammation. Our research reveals that BBR interacts with Keap1 to activate the Keap1/Nrf2 signaling pathway in gastric epithelial cells, thereby suppressing pyroptosis and inflammation in sepsis-induced acute gastric injury.

Single-cell transcriptomic profiling uncovers cellular complexity and microenvironment in gastric tumorigenesis associated with Helicobacter pylori

INTRODUCTION

Helicobacter pylori (H. pylori) infection is the main risk for gastric cancer (GC). However, the cellular heterogeneity and underlying molecular mechanisms in H. pylori-driven gastric tumorigenesis are poorly understood.

OBJECTIVE

Here, we generated a single-cell atlas of gastric tumorigenesis comprising 18 specimens of gastritis, gastric intestinal metaplasia (IM) and GC with or without H. pylori infection.

METHODS

Single-cell RNA sequencing (scRNA-seq) was performed. Immunofluorescence, immunohistochemistry and qRT-PCR analysis were applied in a second human gastric tissues cohort for validation. Bioinformatics analyses of public TCGA and GEO datasets were applied.

RESULTS

Single-cell RNA profile highlights cellular heterogeneity and alterations in tissue ecology throughout the progression of gastric carcinoma. Various cell lineages exhibited unique cancer-associated expression profiles, such as tumor-like epithelial cell subset (EPC), inflammatory cancer-associated fibroblasts (iCAFs) and Tumor-associated macrophage (TAM). Notably, we revealed that the specific epithelial subset enterocytes from the precancerous lesion GIM, exhibited elevated expression of genes related to lipid metabolism, and HNF4G was predicted as its specific transcription factor. Furthermore, we identified differentially expressed genes in H. pylori-positive and negative epithelial cells, fibroblasts and myeloid cells were identified. Futhermore, H. pylori-positive specimens exhibited enriched cell-cell communication, characterized by significantly active TNF, SPP1, and THY1 signaling networks.

CONCLUSIONS

Our study provides a comprehensive landscape of the gastric carcinogenesis ecosystem and novel insights into the molecular mechanisms of different cell types in H. pylori-induced GC.

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.

Streptococcus anginosus in the development and treatment of precancerous lesions of gastric cancer

The microbiota is strongly association with cancer. Studies have shown significant differences in the gastric microbiota between patients with gastric cancer (GC) patients and noncancer patients, suggesting that the microbiota may play a role in the development of GC. Although Helicobacter pylori (H. pylori) infection is widely recognized as a primary risk factor for GC, recent studies based on microbiota sequencing technology have revealed that non-H. pylori microbes also have a significant impact on GC. A recent study discovered that Streptococcus anginosus (S. anginosus) is more prevalent in the gastric mucosa of patients with GC than in that of those without GC. S. anginosus infection can spontaneously induce chronic gastritis, mural cell atrophy, mucoid chemotaxis, and heterotrophic hyperplasia, which promote the development of precancerous lesions of GC (PLGC). S. anginosus also disrupts the gastric barrier function, promotes the proliferation of GC cells, and inhibits apoptosis. However, S. anginosus is underrepresented in the literature. Recent reports suggest that it may cause precancerous lesions, indicating its emerging pathogenicity. Modern novel molecular diagnostic techniques, such as polymerase chain reaction, genetic testing, and Ultrasensitive Chromosomal Aneuploidy Detection, can be used to gastric precancerous lesions via microbial markers. Therefore, we present a concise summary of the relationship between S. anginosus and PLGC. Our aim was to further investigate new methods of preventing and treating PLGC by exploring the pathogenicity of S. anginosus on PLGC.

Single-cell RNA sequencing to map tumor heterogeneity in gastric carcinogenesis paving roads to individualized therapy

Gastric cancer (GC) is a highly heterogeneous disease with a complex tumor microenvironment (TME) that encompasses multiple cell types including cancer cells, immune cells, stromal cells, and so on. Cancer-associated cells could remodel the TME and influence the progression of GC and therapeutic response. Single-cell RNA sequencing (scRNA-seq), as an emerging technology, has provided unprecedented insights into the complicated biological composition and characteristics of TME at the molecular, cellular, and immunological resolutions, offering a new idea for GC studies. In this review, we discuss the novel findings from scRNA-seq datasets revealing the origin and evolution of GC, and scRNA-seq is a powerful tool for investigating transcriptional dynamics and intratumor heterogeneity (ITH) in GC. Meanwhile, we demonstrate that the vital immune cells within TME, including T cells, B cells, macrophages, and stromal cells, play an important role in the disease progression. Additionally, we also overview that how scRNA-seq facilitates our understanding about the effects on individualized therapy of GC patients. Spatial transcriptomes (ST) have been designed to determine spatial distribution and capture local intercellular communication networks, enabling a further understanding of the relationship between the spatial background of a particular cell and its functions. In summary, scRNA-seq and other single-cell technologies provide a valuable perspective for molecular and pathological disease characteristics and hold promise for advancing basic research and clinical practice in GC.

Metaplastic regeneration in the mouse stomach requires a reactive oxygen species pathway

In pyloric metaplasia, mature gastric chief cells reprogram via an evolutionarily conserved process termed paligenosis to re-enter the cell cycle and become spasmolytic polypeptide-expressing metaplasia (SPEM) cells. Here, we use single-cell RNA sequencing (scRNA-seq) following injury to the murine stomach to analyze mechanisms governing paligenosis at high resolution. Injury causes induced reactive oxygen species (ROS) with coordinated changes in mitochondrial activity and cellular metabolism, requiring the transcriptional mitochondrial regulator Ppargc1a (Pgc1α) and ROS regulator Nf2el2 (Nrf2). Loss of the ROS and mitochondrial control in Ppargc1a-/- mice causes the death of paligenotic cells through ferroptosis. Blocking the cystine transporter SLC7A11(xCT), which is critical in lipid radical detoxification through glutathione peroxidase 4 (GPX4), also increases ferroptosis. Finally, we show that PGC1α-mediated ROS and mitochondrial changes also underlie the paligenosis of pancreatic acinar cells. Altogether, the results detail how metabolic and mitochondrial changes are necessary for injury response, regeneration, and metaplasia in the stomach.

Momordicine-I Suppresses Head and Neck Cancer Growth by Reprogrammimg Immunosuppressive Effect of the Tumor-Infiltrating Macrophages and B Lymphocytes

Head and neck cancer (HNC) is prevalent worldwide, and treatment options are limited. Momordicine-I (M-I), a natural component from bitter melon, shows antitumor activity against these cancers, but its mechanism of action, especially in the tumor microenvironment (TME), remains unclear. In this study, we establish that M-I reduces HNC tumor growth in two different immunocompetent mouse models using MOC2 and SCC VII cells. We demonstrate that the anticancer activity results from modulating several molecules in the monocyte/macrophage clusters in CD45+ populations in MOC2 tumors by single-cell RNA sequencing. Tumor-associated macrophages (TAM) often pose a barrier to antitumor effects, but following M-I treatment, we observe a significant reduction in the expression of Sfln4, a myeloid cell differentiation factor, and Cxcl3, a neutrophil chemoattractant, in the monocyte/macrophage populations. We further find that the macrophages must be in close contact with the tumor cells to inhibit Sfln4 and Cxcl3, suggesting that these TAMs are impacted by M-I treatment. Coculturing macrophages with tumor cells shows inhibition of Agr1 expression following M-I treatment, which is indicative of switching from M2 to M1 phenotype. Furthermore, the total B-cell population in M-I-treated tumors is significantly lower, whereas spleen cells also show similar results when cocultured with MOC2 cells. M-I treatment also inhibits PD1, PD-L1, and FoxP3 expression in tumors. Collectively, these results uncover the potential mechanism of M-I by modulating immune cells, and this new insight can help to develop M-I as a promising candidate to treat HNCs, either alone or as adjuvant therapy.

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.

Highlights of how single-cell analyses are illuminating differentiation and disease in the gastric corpus

Single-cell RNA-sequencing (scRNA-seq) has emerged as a powerful technique to identify novel cell markers, developmental trajectories, and transcriptional changes during cell differentiation and disease onset and progression. In this review, we highlight recent scRNA-seq studies of the gastric corpus in both human and murine systems that have provided insight into gastric organogenesis, identified novel markers for the various gastric lineages during development and in adults, and revealed transcriptional changes during regeneration and tumorigenesis. Overall, by elucidating transcriptional states and fluctuations at the cellular level in healthy and disease contexts, scRNA-seq may lead to better, more personalized clinical treatments for disease progression.

Streptococcus anginosus promotes gastric inflammation, atrophy, and tumorigenesis in mice

Streptococcus anginosus (S. anginosus) was enriched in the gastric mucosa of patients with gastric cancer (GC). Here, we show that S. anginosus colonized the mouse stomach and induced acute gastritis. S. anginosus infection spontaneously induced progressive chronic gastritis, parietal cell atrophy, mucinous metaplasia, and dysplasia in conventional mice, and the findings were confirmed in germ-free mice. In addition, S. anginosus accelerated GC progression in carcinogen-induced gastric tumorigenesis and YTN16 GC cell allografts. Consistently, S. anginosus disrupted gastric barrier function, promoted cell proliferation, and inhibited apoptosis. Mechanistically, we identified an S. anginosus surface protein, TMPC, that interacts with Annexin A2 (ANXA2) receptor on gastric epithelial cells. Interaction of TMPC with ANXA2 mediated attachment and colonization of S. anginosus and induced mitogen-activated protein kinase (MAPK) activation. ANXA2 knockout abrogated the induction of MAPK by S. anginosus. Thus, this study reveals S. anginosus as a pathogen that promotes gastric tumorigenesis via direct interactions with gastric epithelial cells in the TMPC-ANXA2-MAPK axis.

ROR2 regulates cellular plasticity in pancreatic neoplasia and adenocarcinoma

Cellular plasticity is a hallmark of pancreatic ductal adenocarcinoma (PDAC) starting from the conversion of normal cells into precancerous lesions to the progression of carcinoma subtypes associated with aggressiveness and therapeutic response. We discovered that normal acinar cell differentiation, maintained by the transcription factor Pdx1, suppresses a broad gastric cell identity that is maintained in metaplasia, neoplasia, and the classical subtype of PDAC in mouse and human. We have identified the receptor tyrosine kinase Ror2 as marker of a gastric metaplasia (SPEM)-like identity in the pancreas. Ablation of Ror2 in a mouse model of pancreatic tumorigenesis promoted a switch to a gastric pit cell identity that largely persisted through progression to the classical subtype of PDAC. In both human and mouse pancreatic cancer, ROR2 activity continued to antagonize the gastric pit cell identity, strongly promoting an epithelial to mesenchymal transition, conferring resistance to KRAS inhibition, and vulnerability to AKT inhibition.

YAP targetome reveals activation of SPEM in gastric pre-neoplastic progression and regeneration

Peptic ulcer disease caused by environmental factors increases the risk of developing gastric cancer (GC), one of the most common and deadly cancers in the world. However, the mechanisms underlying this association remain unclear. A major type of GC uniquely undergoes spasmolytic polypeptide-expressing metaplasia (SPEM) followed by intestinal metaplasia. Notably, intestinal-type GC patients with high levels of YAP signaling exhibit a lower survival rate and poor prognosis. YAP overexpression in gastric cells induces atrophy, metaplasia, and hyperproliferation, while its deletion in a Notch-activated gastric adenoma model suppresses them. By defining the YAP targetome genome-wide, we demonstrate that YAP binds to active chromatin elements of SPEM-related genes, which correlates with the activation of their expression in both metaplasia and ulcers. Single-cell analysis combined with our YAP signature reveals that YAP signaling is activated during SPEM, demonstrating YAP as a central regulator of SPEM in gastric neoplasia and regeneration.

10-Year observation of a rare presentation of pure fibromyxoid nephrogenic adenoma in the renal pelvis

Nephrogenic adenoma (NA) is an unusual benign epithelial tumor in the genitourinary tract. Here we report a fibromyxoid nephrogenic adenoma in a 37-year-old female presenting with over 10-year slow-growing renal pelvic mass that was diagnosed with bland spindle cell lesion in multiple previous biopsies. This is the first reported case of pure fibromyxoid NA in renal pelvis with close comparison and correlation of biopsy and resection findings over a 10-year span. This will enhance awareness of pathologists to consider this unusual entity when examining spindle cell lesions in this setting, and prevent misdiagnosis and overtreatment of a typically benign process.

Single-cell Profiling Uncovers a Muc4-Expressing Metaplastic Gastric Cell Type Sustained by Helicobacter pylori-driven Inflammation

Mechanisms for Helicobacter pylori (Hp)-driven stomach cancer are not fully understood. In a transgenic mouse model of gastric preneoplasia, concomitant Hp infection and induction of constitutively active KRAS (Hp+KRAS+) alters metaplasia phenotypes and elicits greater inflammation than either perturbation alone. Gastric single-cell RNA sequencing showed that Hp+KRAS+ mice had a large population of metaplastic pit cells that expressed the intestinal mucin Muc4 and the growth factor amphiregulin. Flow cytometry and IHC-based immune profiling revealed that metaplastic pit cells were associated with macrophage and T-cell inflammation. Accordingly, expansion of metaplastic pit cells was prevented by gastric immunosuppression and reversed by antibiotic eradication of Hp. Finally, MUC4 expression was significantly associated with proliferation in human gastric cancer samples. These studies identify an Hp-associated metaplastic pit cell lineage, also found in human gastric cancer tissues, whose expansion is driven by Hp-dependent inflammation.

Significance

Using a mouse model, we have delineated metaplastic pit cells as a precancerous cell type whose expansion requires Hp-driven inflammation. In humans, metaplastic pit cells show enhanced proliferation as well as enrichment in precancer and early cancer tissues, highlighting an early step in the gastric metaplasia to cancer cascade.

The composition and roles of gastric stem cells in epithelial homeostasis, regeneration, and tumorigenesis

The epithelial lining of the stomach undergoes rapid turnover to preserve its structural and functional integrity, a process driven by long-lived stem cells residing in the antral and corpus glands. Several subpopulations of gastric stem cells have been identified and their phenotypic and functional diversities linked to spatiotemporal specification of stem cells niches. Here, we review the biological features of gastric stem cells at various locations of the stomach under homeostatic conditions, as demonstrated by reporter mice, lineage tracing, and single cell sequencing. We also review the role of gastric stem cells in epithelial regeneration in response to injury. Moreover, we discuss emerging evidence demonstrating that accumulation of oncogenic drivers or alteration of stemness signaling pathways in gastric stem cells promotes gastric cancer. Given a fundamental role of the microenvironment, this review highlights the role reprogramming of niche components and signaling pathways under pathological conditions in dictating stem cell fate. Several outstanding issues are raised, such as the relevance of stem cell heterogeneity and plasticity, and epigenetic regulatory mechanisms, to Helicobacter pylori infection-initiated metaplasia-carcinogenesis cascades. With the development of spatiotemporal genomics, transcriptomics, and proteomics, as well as multiplexed screening and tracing approaches, we anticipate that more precise definition and characterization of gastric stem cells, and the crosstalk with their niche will be delineated in the near future. Rational exploitation and proper translation of these findings may bring forward novel modalities for epithelial rejuvenation and cancer therapeutics.

Single-cell transcriptomics uncovers EGFR signaling-mediated gastric progenitor cell differentiation in stomach homeostasis

Defects in gastric progenitor cell differentiation are associated with various gastric disorders, including atrophic gastritis, intestinal metaplasia, and gastric cancer. However, the mechanisms underlying the multilineage differentiation of gastric progenitor cells during healthy homeostasis remain poorly understood. Here, using a single-cell RNA sequencing method, Quartz-Seq2, we analyzed the gene expression dynamics of progenitor cell differentiation toward pit cell, neck cell, and parietal cell lineages in healthy adult mouse corpus tissues. Enrichment analysis of pseudotime-dependent genes and a gastric organoid assay revealed that EGFR-ERK signaling promotes pit cell differentiation, whereas NF-κB signaling maintains gastric progenitor cells in an undifferentiated state. In addition, pharmacological inhibition of EGFR in vivo resulted in a decreased number of pit cells. Although activation of EGFR signaling in gastric progenitor cells has been suggested as one of the major inducers of gastric cancers, our findings unexpectedly identified that EGFR signaling exerts a differentiation-promoting function, not a mitogenic function, in normal gastric homeostasis.

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 Governs Gastric Mucous Neck Cell Identity and Is Required for Injury-Induced Metaplasia

BACKGROUND & AIMS

Acute and chronic gastric injury induces alterations in differentiation within the corpus of the stomach called pyloric metaplasia. Pyloric metaplasia is characterized by the death of parietal cells and reprogramming of mitotically quiescent zymogenic chief cells into proliferative, mucin-rich spasmolytic polypeptide-expressing metaplasia (SPEM) cells. Overall, pyloric metaplastic units show increased proliferation and specific expansion of mucous lineages, both by proliferation of normal mucous neck cells and recruitment of SPEM cells. Here, we identify Sox9 as a potential gene of interest in the regulation of mucous neck and SPEM cell identity in the stomach.

METHODS

We used immunostaining and electron microscopy to characterize the expression pattern of SRY-box transcription factor 9 (SOX9) during murine gastric development, homeostasis, and injury in homeostasis, after genetic deletion of Sox9 and after targeted genetic misexpression of Sox9 in the gastric epithelium and chief cells.

RESULTS

SOX9 is expressed in all early gastric progenitors and strongly expressed in mature mucous neck cells with minor expression in the other principal gastric lineages during adult homeostasis. After injury, strong SOX9 expression was induced in the neck and base of corpus units in SPEM cells. Adult corpus units derived from Sox9-deficient gastric progenitors lacked normal mucous neck cells. Misexpression of Sox9 during postnatal development and adult homeostasis expanded mucous gene expression throughout corpus units including within the chief cell zone in the base. Sox9 deletion specifically in chief cells blunts their reprogramming into SPEM.

CONCLUSIONS

Sox9 is a master regulator of mucous neck cell differentiation during gastric development. Sox9 also is required for chief cells to fully reprogram into SPEM after injury.

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.

Single-cell transcriptome sequencing reveals heterogeneity of gastric cancer: progress and prospects

Gastric cancer is one of the most serious malignant tumor and threatens the health of people worldwide. Its heterogeneity leaves many clinical problems unsolved. To treat it effectively, we need to explore its heterogeneity. Single-cell transcriptome sequencing, or single-cell RNA sequencing (scRNA-seq), reveals the complex biological composition and molecular characteristics of gastric cancer at the level of individual cells, which provides a new perspective for understanding the heterogeneity of gastric cancer. In this review, we first introduce the current procedure of scRNA-seq, and discuss the advantages and limitations of scRNA-seq. We then elaborate on the research carried out with scRNA-seq in gastric cancer in recent years, and describe how it reveals cell heterogeneity, the tumor microenvironment, oncogenesis and metastasis, as well as drug response in to gastric cancer, to facilitate early diagnosis, individualized therapy, and prognosis evaluation.

Role of spasmolytic polypeptide-expressing metaplasia in gastric mucosal diseases

Spasmolytic polypeptide-expressing metaplasia (SPEM) is a trefoil factor 2-expressing metaplasia in the fundic glands that resembles the fundic metaplasia of deep antral glandular cells and arises mainly from transdifferentiation of mature chief cells as well as mucous neck cells or isthmic stem cells. SPEM participates in the regulation of gastric mucosal injury, including focal and diffuse injury. This review focuses on the origin, models, and regulatory mechanisms of SPEM and on its role in the development of gastric mucosal injury. We hope to provide new prospects for the prevention and treatment of gastric mucosal diseases from the perspective of cell differentiation and transformation.

Gastric immune homeostasis imbalance: An important factor in the development of gastric mucosal diseases

The gastric mucosal immune system is a unique immune organ independent of systemic immunity that not only maintains nutrient absorption but also plays a role in resisting the external environment. Gastric mucosal immune disorder leads to a series of gastric mucosal diseases, including autoimmune gastritis (AIG)-related diseases, Helicobacter pylori (H. pylori)-induced diseases, and various types of gastric cancer (GC). Therefore, understanding the role of gastric mucosal immune homeostasis in gastric mucosal protection and the relationship between mucosal immunity and gastric mucosal diseases is very important. This review focuses on the protective effect of gastric mucosal immune homeostasis on the gastric mucosa, as well as multiple gastric mucosal diseases caused by gastric immune disorders. We hope to offer new prospects for the prevention and treatment of gastric mucosal diseases.

Dissection of gastric homeostasis in vivo facilitates permanent capture of isthmus-like stem cells in vitro

The glandular stomach is composed of two regenerative compartments termed corpus and antrum, and our understanding of the transcriptional networks that maintain these tissues is incomplete. Here we show that cell types with equivalent functional roles in the corpus and antrum share similar transcriptional states including the poorly characterized stem cells of the isthmus region. To further study the isthmus, we developed a monolayer two-dimensional (2D) culture system that is continually maintained by Wnt-responsive isthmus-like cells capable of differentiating into several gastric cell types. Importantly, 2D cultures can be converted into conventional three-dimensional organoids, modelling the plasticity of gastric epithelial cells in vivo. Finally, we utilized the 2D culture system to show that Sox2 is both necessary and sufficient to generate enterochromaffin cells. Together, our data provide important insights into gastric homeostasis, establish a tractable culture system to capture isthmus cells and uncover a role for Sox2 in enterochromaffin cells.

Application of single-cell transcriptome sequencing in gastric cancer

Gastric cancer (GC) is the fifth most common cancer worldwide and the third leading cause of cancer death. With the development of single-cell RNA-sequencing (scRNA-seq) technology, the research on GC has gradually developed from the histopathological level to the transcriptional level. In this paper, we discuss the principle of scRNA-seq technology and its application in GC research, including the transcriptional characteristics and origin of GC precancerous lesions, intratumor heterogeneity of primary tumors, tumor microenvironment, and metastatic dissemination.

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.

3'-sulfated LewisA/C: An oncofetal epitope associated with metaplastic and oncogenic plasticity of the gastrointestinal foregut

Metaplasia, dysplasia, and cancer arise from normal epithelia via a plastic cellular transformation, typically in the setting of chronic inflammation. Such transformations are the focus of numerous studies that strive to identify the changes in RNA/Protein expression that drive such plasticity along with the contributions from the mesenchyme and immune cells. However, despite being widely utilized clinically as biomarkers for such transitions, the role of glycosylation epitopes is understudied in this context. Here, we explore 3'-Sulfo-Lewis A/C, a clinically validated biomarker for high-risk metaplasia and cancer throughout the gastrointestinal foregut: esophagus, stomach, and pancreas. We discuss the clinical correlation of sulfomucin expression with metaplastic and oncogenic transformation, as well as its synthesis, intracellular and extracellular receptors and suggest potential roles for 3'-Sulfo-Lewis A/C in contributing to and maintaining these malignant cellular transformations.

Cell plasticity in regeneration in the stomach and beyond

Recent studies using cell lineage-tracing techniques, organoids, and single-cell RNA sequencing analyses have revealed: 1) adult organs use cell plasticity programs to recruit progenitor cells to regenerate tissues after injury, and 2) plasticity is far more common than previously thought, even in homeostasis. Here, we focus on the complex interplay of normal stem cell differentiation and plasticity in homeostasis and after injury, using the gastric epithelium as a touchstone. We also examine common features of regenerative programs and discuss the evolutionarily conserved, stepwise process of paligenosis which reprograms mature cells into progenitors that can repair damaged tissue. Finally, we discuss how conserved plasticity programs may help us better understand pathological processes like metaplasia.

Discovering Immune-Mediated Mechanisms of Gastric Carcinogenesis Through Single-Cell RNA Sequencing

Single-cell RNA sequencing (scRNAseq) technology is still relatively new in the field of gastric cancer immunology but gaining significant traction. This technology now provides unprecedented insights into the intratumoral and intertumoral heterogeneities at the immunological, cellular, and molecular levels. Within the last few years, a volume of publications reported the usefulness of scRNAseq technology in identifying thus far elusive immunological mechanisms that may promote and impede gastric cancer development. These studies analyzed datasets generated from primary human gastric cancer tissues, metastatic ascites fluid from gastric cancer patients, and laboratory-generated data from in vitro and in vivo models of gastric diseases. In this review, we overview the exciting findings from scRNAseq datasets that uncovered the role of critical immune cells, including T cells, B cells, myeloid cells, mast cells, ILC2s, and other inflammatory stromal cells, like fibroblasts and endothelial cells. In addition, we also provide a synopsis of the initial scRNAseq findings on the interesting epithelial cell responses to inflammation. In summary, these new studies have implicated roles for T and B cells and subsets like NKT cells in tumor development and progression. The current studies identified diverse subsets of macrophages and mast cells in the tumor microenvironment, however, additional studies to determine their roles in promoting cancer growth are needed. Some groups specifically focus on the less prevalent ILC2 cell type that may contribute to early cancer development. ScRNAseq analysis also reveals that stromal cells, e.g., fibroblasts and endothelial cells, regulate inflammation and promote metastasis, making them key targets for future investigations. While evaluating the outcomes, we also highlight the gaps in the current findings and provide an assessment of what this technology holds for gastric cancer research in the coming years. With scRNAseq technology expanding rapidly, we stress the need for periodic review of the findings and assess the available scRNAseq analytical tools to guide future work on immunological mechanisms of gastric carcinogenesis.  

Applications and Achievements of Single-Cell Sequencing in Gastrointestinal Cancer

Gastrointestinal cancer represents a public health concern that seriously endangers human health. The emerging single-cell sequencing (SCS) technologies are different from the large-scale sequencing technologies which provide inaccurate data. SCS is a powerful tool for deciphering the single-cell resolutions of cellular and molecular landscapes, revealing the features of single-cell genomes, transcriptomes, and epigenomes. Recently, SCS has been applied in the field of gastrointestinal cancer research for clarifying the origin and heterogeneity of gastrointestinal cancer, acquiring micro-environmental information, and improving diagnostic and treatment methods. This review outlines the applications of SCS in gastrointestinal cancer research and summarizes the most recent advances in the field.

Helicobacter pylori infection induces stem cell-like properties in Correa cascade of gastric cancer

Gastric cancer (GC) is the fourth leading cause of cancer-related death. Its poor prognosis is attributed to unclear pathogenesis. Currently, the most widely accepted model for elucidating the mechanism of GC is the Correa cascade, which covers several histological lesions of the gastric mucosa. GC stem cells (CSCs) are crucial for oncogenesis in the Correa cascade and GC progression. As Helicobacter pylori (H. pylori) is the etiological factor in the Correa cascade, growing evidence suggests that enhancement of gastric stem cell-like properties and increase in CSCs correlate with H. pylori infection. In this paper, we review recent studies that present pathogenic mechanisms by which H. pylori induces gastric stem cell-like properties and CSCs, which may supplement the existing Correa model of GC. First, the dysfunction of developmental signaling pathways associated with H. pylori infection leads to the enhancement of gastric stemness. Second, H. pylori infection promotes alteration of the gastric mucosal microenvironment. In addition, epithelial-mesenchymal transition (EMT) may contribute to H. pylori-induced gastric stemness. Taken together, understanding these pathogeneses will provide potential therapeutic targets for the treatment of CSCs and malignant GC in H. pylori induced-Correa cascade of GC.

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.

Paligenosis: Cellular Remodeling During Tissue Repair

Complex multicellular organisms have evolved specific mechanisms to replenish cells in homeostasis and during repair. Here, we discuss how emerging technologies (e.g., single-cell RNA sequencing) challenge the concept that tissue renewal is fueled by unidirectional differentiation from a resident stem cell. We now understand that cell plasticity, i.e., cells adaptively changing differentiation state or identity, is a central tissue renewal mechanism. For example, mature cells can access an evolutionarily conserved program (paligenosis) to reenter the cell cycle and regenerate damaged tissue. Most tissues lack dedicated stem cells and rely on plasticity to regenerate lost cells. Plasticity benefits multicellular organisms, yet it also carries risks. For one, when long-lived cells undergo paligenotic, cyclical proliferation and redif-ferentiation, they can accumulate and propagate acquired mutations that activate oncogenes and increase the potential for developing cancer. Lastly, we propose a new framework for classifying patterns of cell proliferation in homeostasis and regeneration, with stem cells representing just one of the diverse methods that adult tissues employ.

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.

Single-Cell Transcriptomics Reveals a Conserved Metaplasia Program in Pancreatic Injury

BACKGROUND & AIMS

Acinar to ductal metaplasia (ADM) occurs in the pancreas in response to tissue injury and is a potential precursor for adenocarcinoma. The goal of these studies was to define the populations arising from ADM, the associated transcriptional changes, and markers of disease progression.

METHODS

Acinar cells were lineage-traced with enhanced yellow fluorescent protein (EYFP) to follow their fate post-injury. Transcripts of more than 13,000 EYFP+ cells were determined using single-cell RNA sequencing (scRNA-seq). Developmental trajectories were generated. Data were compared with gastric metaplasia, KrasG12D-induced neoplasia, and human pancreatitis. Results were confirmed by immunostaining and electron microscopy. KrasG12D was expressed in injury-induced ADM using several inducible Cre drivers. Surgical specimens of chronic pancreatitis from 15 patients were evaluated by immunostaining.

RESULTS

scRNA-seq of ADM revealed emergence of a mucin/ductal population resembling gastric pyloric metaplasia. Lineage trajectories suggest that some pyloric metaplasia cells can generate tuft and enteroendocrine cells (EECs). Comparison with KrasG12D-induced ADM identifies populations associated with disease progression. Activation of KrasG12D expression in HNF1B+ or POU2F3+ ADM populations leads to neoplastic transformation and formation of MUC5AC+ gastric-pit-like cells. Human pancreatitis samples also harbor pyloric metaplasia with a similar transcriptional phenotype.

CONCLUSIONS

Under conditions of chronic injury, acinar cells undergo a pyloric-type metaplasia to mucinous progenitor-like populations, which seed disparate tuft cell and EEC lineages. ADM-derived EEC subtypes are diverse. KrasG12D expression is sufficient to drive neoplasia when targeted to injury-induced ADM populations and offers an alternative origin for tumorigenesis. This program is conserved in human pancreatitis, providing insight into early events in pancreas diseases.

Single-cell analysis of gastric pre-cancerous and cancer lesions reveals cell lineage diversity and intratumoral heterogeneity

Single-cell transcriptomic profiles analysis has proposed new insights for understanding the behavior of human gastric cancer (GC). GC offers a unique model of intratumoral heterogeneity. However, the specific classes of cells involved in carcinogenetic passage, and the tumor microenvironment of stromal cells was poorly understood. We characterized the heterogeneous cell population of precancerous lesions and gastric cancer at the single-cell resolution by RNA sequencing. We identified 10 gastric cell subtypes and showed the intestinal and diffuse-type cancer were characterized by different cell population. We found that the intestinal and diffuse-type cancer cells have the differential metaplastic cell lineages: intestinal-type cancer cells differentiated along the intestinal metaplasia lineage while diffuse-type cancer cells resemble de novo pathway. We observed an enriched CCND1 mutation in premalignant disease state and discovered cancer-associated fibroblast cells harboring pro-stemness properties. In particular, tumor cells could be categorized into previously proposed molecular subtypes and harbored specific subtype of malignant cell with high expression level of epithelial-myofibroblast transition which was correlated with poor clinical prognosis. In addition to intratumoral heterogeneity, the analysis revealed different cellular lineages were responsible for potential carcinogenetic pathways. Single-cell transcriptomes analysis of gastric pre-cancerous lesions and cancer may provide insights for understanding GC cell behavior, suggesting potential targets for the diagnosis and treatment of GC.

Preventive and inhibitive effects of Yiwei Xiaoyu granules on the development and progression of spasmolytic polypeptide-expressing metaplasia lesions

BACKGROUND

Spasmolytic polypeptide-expressing metaplasia (SPEM) is a potential preneoplastic lesion.

AIM

To elucidate the microRNA (miR)-7-mediated preventive and inhibitive effects of Yiwei Xiaoyu granules (YWXY) in SPEM lesions.

METHODS

Gastric mucosa biopsies were collected from chronic atrophic gastritis patients and healthy people with signed informed consent. YWXY was administered to the mice with induced SPEM by tamoxifen, and the gastric mucosa was harvested on the tenth day of the experiment. Then immunohistochemistry and immunofluorescence were performed to validate the SPEM, lesions and the potential mechanism was investigated. RNA transcripts were detected with reverse transcription-quantitative polymerase chain reaction.

RESULTS

The expression of miR-7 was downregulated in the SPEM lesions, and expression of trefoil factor 2 (TFF2) and clusterin was high in the human gastric mucosa. In vivo experiments showed that YWXY could inhibit the cell proliferation in the tamoxifen-induced SPEM lesions by regulating Ki67. Simultaneously, YWXY could restore the expression of miR-7 by regulating TFF2 by detection with immunofluorescence but not with reverse transcription-quantitative polymerase chain reaction, indicating its potential mechanism of targeting miR-7 by mediating TFF2. The expression of vascular endothelial growth factor-β and gastric intrinsic factor was restored within 3 d of YWXY administration for the SPEM lesions, speculating that the possible mechanism of YWXY is to inhibit the development and progression of SPEM by regulating vascular endothelial growth factor-β and gastric intrinsic factor.

CONCLUSION

miR-7 downregulation is an early event in SPEM through regulation of TFF2 in human gastric mucosa. YWXY is able to inhibit the cell proliferation and restore the expression of miR-7 by mediating TFF2 in the SPEM mouse model.

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.

IL13 Acts Directly on Gastric Epithelial Cells to Promote Metaplasia Development During Chronic Gastritis

BACKGROUND & AIMS

It is well established that chronic inflammation promotes gastric cancer-associated metaplasia, but little is known regarding the mechanisms by which immune cells and cytokines regulate metaplastic cellular changes. The goals of this study were to identify interleukin 13 (IL13)-producing immune cells, determine the gastric epithelial cell response(s) to IL13, and establish the role(s) of IL13 in metaplasia development.

METHODS

Experiments used an established mouse model of autoimmune gastritis (TxA23), TxA23×Il4ra-/- mice, which develop gastritis but do not express the IL4/IL13-receptor subunit IL4Rα, and TxA23×Il13-Yfp mice, which express yellow fluorescent protein in IL13-producing cells. Flow cytometry was used to measure IL13 secretion and identify IL13-producing immune cells. Mouse and human gastric organoids were cultured with IL13 to determine epithelial cell response(s) to IL13. Single-cell RNA sequencing was performed on gastric epithelial cells from healthy and inflamed mouse stomachs. Mice with gastritis were administered IL13-neutralizing antibodies and stomachs were analyzed by histopathology and immunofluorescence.

RESULTS

We identified 6 unique subsets of IL13-producing immune cells in the inflamed stomach. Organoid cultures showed that IL13 acts directly on gastric epithelium to induce a metaplastic phenotype. IL4Rα-deficient mice did not progress to metaplasia. Single-cell RNA sequencing determined that gastric epithelial cells from IL4Rα-deficient mice up-regulated inflammatory genes but failed to up-regulate metaplasia-associated transcripts. Neutralization of IL13 significantly reduced and reversed metaplasia development in mice with gastritis.

CONCLUSIONS

IL13 is made by a variety of immune cell subsets during chronic gastritis and promotes gastric cancer-associated metaplastic epithelial cell changes. Neutralization of IL13 reduces metaplasia severity during chronic gastritis.

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.