Ink4a/Arf-Dependent Loss of Parietal Cells Induced by Oxidative Stress Promotes CD44-Dependent Gastric Tumorigenesis

Metabolic regulator ERRγ governs gastric stem cell differentiation into acid-secreting parietal cells

Parietal cells (PCs) produce gastric acid to kill pathogens and aid digestion. Dysregulated PC census is common in disease, yet how PCs differentiate is unclear. Here, we identify the PC progenitors arising from isthmal stem cells, using mouse models and human gastric cells, and show that they preferentially express cell-metabolism regulator and orphan nuclear receptor Estrogen-related receptor gamma (Esrrg, encoding ERRγ). Esrrg expression facilitated the tracking of stepwise molecular, cellular, and ultrastructural stages of PC differentiation. EsrrgP2ACreERT2 lineage tracing revealed that Esrrg expression commits progenitors to differentiate into mature PCs. scRNA-seq indicated the earliest Esrrg+ PC progenitors preferentially express SMAD4 and SP1 transcriptional targets and the GTPases regulating acid-secretion signal transduction. As progenitors matured, ERRγ-dependent metabolic transcripts predominated. Organoid and mouse studies validated the requirement of ERRγ for PC differentiation. Our work chronicles stem cell differentiation along a single lineage in vivo and suggests ERRγ as a therapeutic target for PC-related disorders.

Optimization, Probiotic Characteristics, and Rheological Properties of Exopolysaccharides from Lactiplantibacillus plantarum MC5

This study optimized the exopolysaccharides (EPS) production for Lactiplantibacillus plantarum MC5 (Lp. plantarum MC5) and evaluated the resistance to human simulated digestive juices, antioxidant activity in vitro, and rheological properties of EPS-MC5. The results showed that maximum EPS production of 345.98 mg/L (about 1.5-old greater than the initial production) was obtained at optimal conditions of inoculum size (4.0%), incubation time (30 h), incubation temperature (34.0 °C), and initial pH value (6.40). Furthermore, the resisting-digestion capacity of EPS-MC5 after 180 min in α-amylase, simulated gastric juice (pH 2.0, 3.0, 4.0), and simulated intestinal juice (pH 6.8) was 98.59%, 98.62%, 98.78%, 98.86%, and 98.74%, respectively. In addition, the radical scavenging rates of DPPH•, ABTS•, •OH, and ferric-iron reducing power (OD700) of EPS-MC5 were 73.33%, 87.74%, 46.07%, and 1.20, respectively. Furthermore, rheological results showed that the EPS-MC5 had a higher apparent viscosity (3.01 Pa) and shear stress (41.78 Pa), and the viscoelastic modulus (84.02 and 161.02 Pa at the shear frequency of 100 Hz). These results provide a new insight into the application of EPS in human health and functional foods, which could also improve theoretical guidance for the industrial application of EPS.

MEK Inhibition Suppresses Metastatic Progression of KRAS-Mutated Gastric Cancer

Metastatic progression of tumors is driven by genetic alterations and tumor‐stroma interaction. To elucidate the mechanism underlying the oncogene‐induced gastric tumor progression, we have developed an organoid‐based model of gastric cancer from GAstric Neoplasia (GAN) mice, which express Wnt1 and the enzymes COX2 and microsomal prostaglandin E synthase 1 in the stomach. Both p53 knockout (GAN‐p53KO) organoids and KRAS^G12V‐expressing GAN‐p53KO (GAN‐KP) organoids were generated by genetic manipulation of GAN mouse‐derived tumor (GAN wild‐type [WT]) organoids. In contrast with GAN‐WT and GAN‐p53KO organoids, which manifested Wnt addiction, GAN‐KP organoids showed a Wnt‐independent phenotype and the ability to proliferate without formation of a Wnt‐regulated three‐dimensional epithelial architecture. After transplantation in syngeneic mouse stomach, GAN‐p53KO cells formed only small tumors, whereas GAN‐KP cells gave rise to invasive tumors associated with the development of hypoxia as well as to liver metastasis. Spatial transcriptomics analysis suggested that hypoxia signaling contributes to the metastatic progression of GAN‐KP tumors. In particular, such analysis identified a cluster of stromal cells located at the tumor invasive front that expressed genes related to hypoxia signaling, angiogenesis, and cell migration. These cells were also positive for phosphorylated extracellular signal‐regulated kinase (ERK), suggesting that mitogen‐activated protein kinase (MAPK) signaling promotes development of both tumor and microenvironment. The MEK (MAPK kinase) inhibitor trametinib suppressed the development of GAN‐KP gastric tumors, formation of a hypoxic microenvironment, tumor angiogenesis, and liver metastasis. Our findings therefore establish a rationale for application of trametinib to suppress metastatic progression of KRAS‐mutated gastric cancer.

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

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Antioxidant capacity of soymilk yogurt and exopolysaccharides produced by lactic acid bacteria

Reactive oxygen species (ROS), such as hydroxyl and superoxide anion radicals, are highly reactive molecules derived from the metabolism of oxygen. ROS play positive roles in cell physiology, but they may also damage cell membranes and DNA, inducing oxidation that causes membrane lipid peroxidation and decreases membrane fluidity. Soymilk yogurt, which is soymilk fermented using lactic acid bacteria (LAB), is an excellent food item with numerous functional substances with antioxidant effects. In this study, the antioxidative activities of soymilk yogurt were investigated. Sixteen of the 26 tested LAB strains solidified soymilk. In antioxidant capacity tests for bacterial cells, Leuconostoc mesenteroides MYU 60 and Pediococcus pentosaceus MYU 759 showed the highest values in the oxygen radical antioxidant capacity (ORAC) and hydroxyl radical antioxidant capacity (HORAC) tests, respectively. The supernatant of soymilk yogurt made with Lactobacillus gasseri MYU 1 showed the highest ORAC and HORAC values. L. mesenteroides MYU 60, Lactobacillus plantarum MYU 74, Lactobacillus reuteri MYU 220, and P. pentosaceus MYU 759 showed significantly high N-acetylcysteine equivalent values compared with the control in a total ROS reducing assay (p<0.05). These strains were selected, and a comet assay was performed, which exhibited decreased values in all selected strains compared with the control, indicating DNA protection. An acidic exopolysaccharide produced by P. pentosaceus MYU 759 showed high antioxidant capacity. The antioxidant substances produced by LAB fermentation may be exopolysaccharides, antioxidant peptides, and isoflavone aglycones. Soymilk yogurt can be used as a functional food useful for various diseases related to oxidation.

Regulation of Gastric Lgr5+ve Cell Homeostasis by Bone Morphogenetic Protein (BMP) Signaling and Inflammatory Stimuli

BACKGROUND & AIMS

Gastric Leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) cells exert important functions during injury and homeostasis. Bone morphogenetic protein (BMP) signaling regulates gastric inflammation and epithelial homeostasis. We investigated if BMP signaling controls the fate of Lgr5^+ve cells during inflammation.

METHODS

The H⁺/K⁺-adenosine triphosphatase β-subunit promoter was used to express the BMP inhibitor noggin (Nog) in the stomach (H⁺/K⁺-Nog mice). Inhibition of BMP signaling in Lgr5 cells was achieved by crossing Lgr5-EGFP-ires-CreERT2 (Lgr5-Cre) mice to mice with floxed alleles of BMP receptor 1A (Lgr5-Cre;Bmpr1a^flox/flox mice). Lgr5/GFP^+ve cells were isolated using flow cytometry. Lineage tracing studies were conducted by crossing Lgr5-Cre mice to mice that express Nog and tdTomato (Lgr5-Cre;H⁺/K⁺-Nog;Rosa26-tdTom). Infection with Helicobacter felis was used to induce inflammation. Morphology of the mucosa was analyzed by H&E staining. Distribution of H⁺/K⁺-adenosine triphosphatase-, IF-, Ki67-, CD44-, CD44v9-, and bromodeoxyuridine-positive cells was analyzed by immunostaining. Expression of neck and pit cell mucins was determined by staining with the lectins Griffonia (Bandeiraea) simplicifolia lectin II and Ulex europaeus agglutinin 1, respectively. Id1, Bmpr1a, Lgr5, c-Myc, and Cd44 messenger RNAs were measured by quantitative reverse-transcription polymerase chain reaction.

RESULTS

Lgr5-Cre;Bmpr1a^flox/flox mice showed diminished expression of Bmpr1a in Lgr5/GFP^+ve cells. Infection of Lgr5-Cre;Bmpr1a^flox/flox mice with H felis led to enhanced inflammation, increased cell proliferation, parietal cell loss, and to the development of metaplasia and dysplasia. Infected Lgr5-Cre;H⁺/K⁺-Nog;Rosa26-tdTom mice, but not control mice, showed the presence of tomato^+ve glands lining the lesser curvature that stained positively with Griffonia (Bandeiraea) simplicifolia lectin II and Ulex europaeus agglutinin 1, and with anti-IF, -CD44, -CD44v9, and -bromodeoxyuridine antibodies.

CONCLUSIONS

Inflammation and inhibition of BMP signaling activate Lgr5^+ve cells, which give rise to metaplastic, dysplastic, proliferating lineages that express markers of mucus neck and zymogenic cell differentiation.

The cytoprotective protein clusterin is overexpressed in hypergastrinemic rodent models of oxyntic preneoplasia and promotes gastric cancer cell survival

The cytoprotective protein clusterin is often dysregulated during tumorigenesis, and in the stomach, upregulation of clusterin marks emergence of the oxyntic atrophy (loss of acid-producing parietal cells)-associated spasmolytic polypeptide-expressing metaplasia (SPEM). The hormone gastrin is important for normal function and maturation of the gastric oxyntic mucosa and hypergastrinemia might be involved in gastric carcinogenesis. Gastrin induces expression of clusterin in adenocarcinoma cells. In the present study, we examined the expression patterns and gastrin-mediated regulation of clusterin in gastric tissue from: humans; rats treated with proton pump (H+/K+-ATPase) inhibitors and/or a gastrin receptor (CCK2R) antagonist; H+/K+-ATPase β-subunit knockout (H/K-β KO) mice; and Mongolian gerbils infected with Helicobacter pylori and given a CCK2R antagonist. Biological function of secretory clusterin was studied in human gastric cancer cells. Clusterin was highly expressed in neuroendocrine cells in normal oxyntic mucosa of humans and rodents. In response to hypergastrinemia, expression of clusterin increased significantly and its localization shifted to basal groups of proliferative cells in the mucous neck cell-chief cell lineage in all animal models. That shift was partially inhibited by antagonizing the CCK2R in rats and gerbils. The oxyntic mucosa of H/K-β KO mice contained areas with clusterin-positive mucous cells resembling SPEM. In gastric adenocarcinomas, clusterin mRNA expression was higher in diffuse tumors containing signet ring cells compared with diffuse tumors without signet ring cells, and clusterin seemed to be secreted by tumor cells. In gastric cancer cell lines, gastrin increased secretion of clusterin, and both gastrin and secretory clusterin promoted survival after starvation- and chemotherapy-induced stress. Overall, our results indicate that clusterin is overexpressed in hypergastrinemic rodent models of oxyntic preneoplasia and stimulates gastric cancer cell survival.

Rheostatic CD44 isoform expression and its association with oxidative stress in human malignant mesothelioma

CD44 exists as a standard (CD44s) isoform and different variant isoforms (CD44v) due to alternative splicing. While the complex nature of these different isoforms has not been fully elucidated, CD44v expression has been shown to exert oncogenic effects by promoting tumor progression, metastasis and resistance of tumor cells to chemotherapy. One of the CD44v isoforms, CD44v8-10, was recently shown to protect cancer cells from oxidative stress by increasing the synthesis of glutathione (GSH). However, data regarding CD44 isoform expression in malignant mesothelioma (MM) are still lacking. Here, we show that most of the MM cell lines express both the CD44s and CD44v isoforms, in contrast to non-tumorigenic mesothelial cells, which express only CD44s. Moreover, we show here that these MM cell lines are positive for CD44 variable exon 9, with CD44v8-10 among the variant isoforms expressed. The expression of CD44 variable exon 9 was found to be statistically associated with NF2 inactivation, a common occurrence in MM. Knockdown of CD44 reduced the protein level of xCT, a cystine transporter, and increased oxidative stress. However, an increase in GSH was also observed and was associated with enhanced chemoresistance in CD44-knockdown cells. Increased GSH was mediated by the Nrf2/AP-1-induced upregulation of GCLC, a subunit of the enzyme catalyzing GSH synthesis. Our results thus suggest that the response to CD44 depletion is cell type-dependent and, in cases such as MM cells, compensatory pathway(s) might be activated rheostatically to account for the loss of CD44 and counteract enhanced oxidative stress.

Murine Models of Gastric Corpus Preneoplasia

Intestinal-type gastric adenocarcinoma evolves in a field of pre-existing metaplasia. Over the past 20 years, a number of murine models have been developed to address aspects of the physiology and pathophysiology of metaplasia induction. Although none of these models has achieved true recapitulation of the induction of adenocarcinoma, they have led to important insights into the factors that influence the induction and progression of metaplasia. Here, we review the pathologic definitions relevant to alterations in gastric corpus lineages and classification of metaplasia by specific lineage markers. In addition, we review present murine models of the induction and progression of spasmolytic polypeptide (TFF2)-expressing metaplasia, the predominant metaplastic lineage observed in murine models. These models provide a basis for the development of a broader understanding of the physiological and pathophysiological roles of metaplasia in the stomach.

Identification of alanyl aminopeptidase (CD13) as a surface marker for isolation of mature gastric zymogenic chief cells

Injury and inflammation in the gastric epithelium can cause disruption of the pathways that guide the differentiation of cell lineages, which in turn can cause persistent alterations in differentiation patterns, known as metaplasia. Metaplasia that occurs in the stomach is associated with increased risk for cancer. Methods for isolating distinct gastric epithelial cell populations would facilitate dissection of the molecular and cellular pathways that guide normal and metaplastic differentiation. Here, we identify alanyl aminopeptidase (CD13) as a specific surface marker of zymogenic chief cells (ZCs) in the gastric epithelium. We show that 1) among gastric epithelial cells alanyl aminopeptidase expression is confined to mature ZCs, and 2) its expression is lost en route to metaplasia in both mouse and human stomachs. With this new marker coupled with new techniques that we introduce for dissociating gastric epithelial cells and overcoming their constitutive autofluorescence, we are able to reliably isolate enriched populations of ZCs for both molecular analysis and for the establishment of ZC-derived ex vivo gastroid cultures.