Transforming growth factor alpha disrupts the normal program of cellular differentiation in the gastric mucosa of transgenic mice

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.

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

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

Abomasal dysfunction and cellular and mucin changes during infection of sheep with larval or adult Teladorsagia circumcincta

This is the first integrated study of the effects on gastric secretion, inflammation and fundic mucins after infection with L3 T. circumcincta and in the very early period following transplantation of adult worms. At 3 months-of-age, 20 Coopworth lambs were infected intraruminally with 35,000 L3; infected animals were killed on Days 5, 10, 15, 20 and 30 post-infection and 6 controls on either Day 0 or 30 post-infection. Another 15 Romney cross lambs received 10,000 adult worms at 4-5 months-of-age though surgically-implanted abomasal cannulae and were killed after 6, 12, 24 and 72 hours; uninfected controls were also killed at 72 hours. Blood was collected at regular intervals from all animals for measurement of serum gastrin and pepsinogen and abomasal fluid for pH measurement from cannulated sheep. Tissues collected at necropsy were fixed in Bouin's fluid for light microscopy, immunocytochemistry and mucin staining and in Karnovsky's fluid for electron microscopy. Nodules around glands containing developing larvae were seen on Day 5 p.i., but generalised effects on secretion occurred only after parasite emergence and within hours after transplantation of adult worms. After L3 infection, there were maximum worm burdens on Days 10-15 post-infection, together with peak tissue eosinophilia, inhibition of gastric acid secretion, hypergastrinaemia, hyperpepsinogenaemia, loss of parietal cells, enlarged gastric pits containing less mucin and increased numbers of mucous neck cells. After adult transplantation, serum pepsinogen was significantly increased after 9 hours and serum gastrin after 18 hours. Parallel changes in host tissues and the numbers of parasites in the abomasal lumen suggest that luminal parasites, but not those in the tissues, are key drivers of the pathophysiology and inflammatory response in animals exposed to parasites for the first time. These results are consistent with initiation of the host response by parasite chemicals diffusing across the surface epithelium, possibly aided by components of ES products which increased permeability. Parietal cells appear to be a key target, resulting in secondary increases in serum gastrin, pit elongation, loss of surface mucins and inhibition of chief cell maturation. Inflammation occurs in parallel, and could either cause the pathology or exacerbate the direct effects of ES products.

Cytokeratin 19 promoter directs the expression of Cre recombinase in various epithelia of transgenic mice

Cytokeratin 19 (K19) is expressed in various differentiated cells, including gastric, intestinal and bronchial epithelial cells, and liver duct cells. Here, we generated a transgenic mouse line, K19-Cre, in which the expression of Cre recombinase was controlled by the promoter of K19. To test the tissue distribution and excision activity of Cre recombinase, K19-Cre transgenic mice were bred with Rosa26 reporter strain and a mouse strain that carries PTEN conditional alleles (PTENLoxp/Loxp). At mRNA level, Cre was strongly expressed in the stomach, lung and intestine, while in stomach, lung, and liver at protein level. The immunoreactivity to Cre was strongly observed the cytoplasm of gastric, bronchial and intestinal epithelial cells. Cre activity was detectable in gastric, bronchial and intestinal epithelial cells, according to LacZ staining. In K19-Cre/PTEN Loxp/Loxp mice, PTEN was abrogated in stomach, intestine, lung, liver and breast, the former two of which were verified by in situ PCR. There appeared breast cancer with PTEN loss. These data suggest that K19 promoter may be a useful tool to study the pathophysiological functions of cytokeratin 19-positive cells, especially gastrointestinal epithelial cells. Cell specificity of neoplasia is not completely attributable to the cell-specific expression of oncogenes and cell-specific loss of tumor suppressor genes.

MIB2 variants altering NOTCH signalling result in left ventricle hypertrabeculation/non-compaction and are associated with Ménétrier-like gastropathy

We performed whole exome sequencing in individuals from a family with autosomal dominant gastropathy resembling Ménétrier disease, a premalignant gastric disorder with epithelial hyperplasia and enhanced EGFR signalling. Ménétrier disease is believed to be an acquired disorder, but its aetiology is unknown. In affected members, we found a missense p.V742G variant in MIB2, a gene regulating NOTCH signalling that has not been previously linked to human diseases. The variant segregated with the disease in the pedigree, affected a highly conserved amino acid residue, and was predicted to be deleterious although it was found with a low frequency in control individuals. The purified protein carrying the p.V742G variant showed reduced ubiquitination activity in vitro and white blood cells from affected individuals exhibited significant reductions of HES1 and NOTCH3 expression reflecting alteration of NOTCH signalling. Because mutations of MIB1, the homolog of MIB2, have been found in patients with left ventricle non-compaction (LVNC), we investigated members of our family with Ménétrier-like disease for this cardiac abnormality. Asymptomatic left ventricular hypertrabeculation, the mildest end of the LVNC spectrum, was detected in two members carrying the MIB2 variant. Finally, we identified an additional MIB2 variant (p.V984L) affecting protein stability in an unrelated isolated case with LVNC. Expression of both MIB2 variants affected NOTCH signalling, proliferation and apoptosis in primary rat cardiomyocytes.In conclusion, we report the first example of left ventricular hypertrabeculation/LVNC with germline MIB2 variants resulting in altered NOTCH signalling that might be associated with a gastropathy clinically overlapping with Ménétrier disease.

Pepsinogen C expression, regulation and its relationship with cancer

Pepsinogen C (PGC) belongs to the aspartic protease family and is secreted by gastric chief cells. PGC could be activated to pepsin C and digests polypeptides and amino acids, but as a zymogen PGC’s functions is unclear. In normal physiological conditions, PGC is initially detected in the late embryonic stage and is mainly expressed in gastric mucosa. The in situ expression of PGC in gastric mucosa is decreased considerably in the process of superficial gastritis → atrophic gastritis → gastric cancer (GC), proving that PGC is a comparatively ideal negative marker of GC. Serum PGC, and PGA levels and the PGA/PGC ratio have satisfactory sensitivity, specificity and price–quality ratio for predicting high GC risk. Ectopic PGC expression is significantly increased in prostate cancer, breast cancer, ovary cancer and endometrial cancer. In those sex-related cancers high level PGC expression indicates better prognosis and longer survival. The regulation of PGC expression involves genetic and epigenetic alteration of the encoding PGC gene, hormones modulation and interactions between PGC with other transcription factors and protein kinases. More and more research evidence hinted that PGC has strong correlation with cancer. In the systematic review, we respectively elaborate the structure, potential physiological functions, expression characteristics and regulation of PGC, and especially focus on the relationship between PGC expression and cancer to highlight the role of PGC in the tumorigenesis and its application value in clinical practice.

Transgenic and gene knockout mice in gastric cancer research

Mouse models are useful tool for carcinogenic study. They will greatly enrich the understanding of pathogenesis and molecular mechanisms for gastric cancer. However, only few of mice could develop gastric cancer spontaneously. With the development and improvement of gene transfer technology, investigators created a variety of transgenic and knockout/knockin mouse models of gastric cancer, such as INS-GAS mice and gastrin knockout mice. Combined with helicobacter infection and carcinogens treatment, these transgenic/knockout/knockin mice developed precancerous or cancerous lesions, which are proper for gene function study or experimental therapy. Here we review the progression of genetically engineered mouse models on gastric cancer research, and emphasize the effects of chemical carcinogens or infectious factors on carcinogenesis of genetically modified mouse. We also emphasize the histological examination on mouse stomach. We expect to provide researchers with some inspirations on this field.

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.

Recapitulating Human Gastric Cancer Pathogenesis: Experimental Models of Gastric Cancer

This review focuses on the various experimental models to study gastric cancer pathogenesis, with the role of genetically engineered mouse models (GEMMs) used as the major examples. We review differences in human stomach anatomy compared to the stomachs of the experimental models, including the mouse and invertebrate models such as Drosophila and C. elegans. The contribution of major signaling pathways, e.g., Notch, Hedgehog, AKT/PI3K is discussed in the context of their potential contribution to foregut tumorigenesis. We critically examine the rationale behind specific GEMMs, chemical carcinogens, dietary promoters, Helicobacter infection, and direct mutagenesis of relevant oncogenes and tumor suppressor that have been developed to study gastric cancer pathogenesis. Despite species differences, more efficient and effective models to test specific genes and pathways disrupted in human gastric carcinogenesis have yet to emerge. As we better understand these species differences, "humanized" versions of mouse models will more closely approximate human gastric cancer pathogenesis. Towards that end, epigenetic marks on chromatin, the gut microbiota, and ways of manipulating the immune system will likely move center stage, permitting greater overlap between rodent and human cancer phenotypes thus providing a unified progression model.

Using stem cells to produce insulin

INTRODUCTION

Tremendous progress has been made in generating insulin-producing cells from pluripotent stem cells. The best outcome of the refined protocols became apparent in the first clinical trial announced by ViaCyte, based on the implantation of pancreatic progenitors that would further mature into functional insulin-producing cells inside the patient's body.

AREAS COVERED

Several groups, including ours, have contributed to improve strategies to generate insulin-producing cells. Of note, the latest results have gained a substantial amount of interest as a method to create a potentially functional and limitless supply of β-cell to revert diabetes mellitus. This review analyzes the accomplishments that have taken place over the last few decades, summarizes the state-of-art methods for β-cell replacement therapies based on the differentiation of embryonic stem cells into glucose-responsive and insulin-producing cells in a dish and discusses alternative approaches to obtain new sources of insulin-producing cells.

EXPERT OPINION

Undoubtedly, recent events preface the beginning of a new era in diabetes therapy. However, in our opinion, a number of significant hurdles still stand in the way of clinical application. We believe that the combination of the private and public sectors will accelerate the process of obtaining the desired safe and functional β-cell surrogates.

The gastric mucosa 25 years after proximal gastric vagotomy

OBJECTIVE

Vagotomy causes inhibition of basal and post-prandial acid secretion in humans, but the knowledge about the trophic effect of the vagal nerves is limited. Vagotomy is known to induce hypergastrinemia and we aimed to study the long-term effects of proximal gastric vagotomy (PGV) on the oxyntic mucosa and the enterochromaffin-like (ECL) cell density in particular.

MATERIAL AND METHODS

Eleven patients operated with PGV because of duodenal ulcer and age- and sex-matched controls were examined 26 to 29 years postoperatively by gastroscopy with biopsies from the antrum and oxyntic mucosa. Neuroendocrine cell volume densities were calculated after immunohistochemical labeling of gastrin, the general neuroendocrine cell marker chromogranin A (CgA) and the ECL cell marker vesicular monoamine transporter 2 (VMAT2). Gastritis was graded and Helicobacter pylori (H. pylori) status was determined by polymerase chain reaction of gastric biopsies. Fasting serum gastrin and CgA were measured.

RESULTS

Serum gastrin was higher in the PGV group compared to controls (median 21.0 [interquartile range (IQR) = 22.0] pmol/L vs 13.0 [IQR = 4.0] pmol/L, p = 0.04). However, there was neither a significant difference in serum CgA or in CgA (neuroendocrine) nor VMAT2 (ECL cell) immunoreactive cell volume density in the oxyntic mucosa. There was significantly more inflammation and atrophy in H. pylori-positive patients, but PGV did not influence the grade of gastritis.

CONCLUSION

Despite higher serum gastrin concentrations, patients operated with PGV did not have higher ECL cell mass or serum CgA. Vagotomy may prevent the development of ECL cell hyperplasia caused by a moderate hypergastrinemia.

The role of pancreatic and duodenal homeobox 1 as a therapeutic target in pancreatic cancer

INTRODUCTION

Pancreatic cancer is one of the most lethal cancer types known with no successful clinical therapy available and a 5-year survival rate of < 5%. Demographic calculations predict pancreatic cancer to be the second-leading cause of cancer-related deaths by 2030. Hence, the identification of novel drug targets and the subsequent development of novel therapeutic strategies are of utmost importance.

AREAS COVERED

In this review, the authors describe the role of the transcription factor pancreatic and duodenal homeobox 1 (Pdx1) in pancreatic organ development and pancreatic cancer. Published data suggest that Pdx1 possesses oncogenic traits fostering cell proliferation, inhibition of apoptosis and increased cell invasion. Resulting from these findings, the authors discuss the potential use of Pdx1 as an anticancer drug target.

EXPERT OPINION

In summary, Pdx1 should be considered as an interesting potential molecular target in future therapeutic approaches. Although no specific therapies exploiting Pdx1 are available at the moment and more preclinical data has to be accumulated, several putative applications in the areas of cancer diagnostics and therapy are conceivable.

Transcriptional control of mammalian pancreas organogenesis

The field of pancreas development has markedly expanded over the last decade, significantly advancing our understanding of the molecular mechanisms that control pancreas organogenesis. This growth has been fueled, in part, by the need to generate new therapeutic approaches for the treatment of diabetes. The creation of sophisticated genetic tools in mice has been instrumental in this progress. Genetic manipulation involving activation or inactivation of genes within specific cell types has allowed the identification of many transcription factors (TFs) that play critical roles in the organogenesis of the pancreas. Interestingly, many of these TFs act at multiple stages of pancreatic development, and adult organ function or repair. Interaction with other TFs, extrinsic signals, and epigenetic regulation are among the mechanisms by which TFs may play context-dependent roles during pancreas organogenesis. Many of the pancreatic TFs directly regulate each other and their own expression. These combinatorial interactions generate very specific gene regulatory networks that can define the different cell lineages and types in the developing pancreas. Here, we review recent progress made in understanding the role of pancreatic TFs in mouse pancreas formation. We also summarize our current knowledge of human pancreas development and discuss developmental pancreatic TFs that have been associated with human pancreatic diseases.

Mouse models of gastric carcinogenesis

Gastric cancer is one of the most common cancers in the world. Animal models have been used to elucidate the details of the molecular mechanisms of various cancers. However, most inbred strains of mice have resistance to gastric carcinogenesis. Helicobacter infection and carcinogen treatment have been used to establish mouse models that exhibit phenotypes similar to those of human gastric cancer. A large number of transgenic and knockout mouse models of gastric cancer have been developed using genetic engineering. A combination of carcinogens and gene manipulation has been applied to facilitate development of advanced gastric cancer; however, it is rare for mouse models of gastric cancer to show aggressive, metastatic phenotypes required for preclinical studies. Here, we review current mouse models of gastric carcinogenesis and provide our perspectives on future developments in this field.

Activin A regulates growth of gastro-intestinal epithelial cells by mediating epithelial-mesenchymal interaction

The importance of epithelial-mesenchymal interaction on the development of gastro-intestinal (GI) organs has been repeatedly reported, but its molecular mechanism has not been fully understood though several factors including hepatocyte growth factor and endothelin-3 have been shown to mediate it. Activins have been demonstrated to play important roles in the regulation of organogenesis in vertebrates, but their roles in the regulation of growth and differentiation of GI organs remain to be solved. In the present study, we examined expression of activins in developing rat GI tract, and found that inhibin bA encoding activin A was specifically expressed by GI mesenchymes, while inhibin bB encoding activin B was expressed by both epithelial and mesenchymal components. We then examined the effect of activin A on the growth of fetal rat GI epithelial cells in primary culture. We found that activin A inhibited the growth of forestomach and glandular stomach epithelial cells while it stimulated the growth of colonic epithelial cells. These results suggest that activin A secreted from GI mesenchymes region-specifically regulates the growth of attaching epithelial cells. We thus conclude that activin A mediates epithelial-mesenchymal interaction in the developing GI tract.

Autosomal dominant Ménétrier-like disease

BACKGROUND

Familial occurrence of Ménétrier disease is rare and has been reported only in few instances.

METHODS

Affected patients from a large pedigree were evaluated at the clinical, endoscopic, and pathological levels.

RESULTS

Affected members presented with gastropathy of variable severity but without protein loss. Endoscopy and pathology findings were consistent with Ménétrier disease; however, gastric transforming growth factor α (TGF-α) immunohistochemistry and real-time polymerase chain reaction showed no increase in TGF-α expression.

CONCLUSIONS

We describe a unique, 4-generation pedigree with autosomal dominant gastropathy exhibiting the typical clinical, endoscopic, and pathological findings of Ménétrier-like disease, though in the absence of protein loss and with no increase in the levels of gastric TGF-α. Members of this family may be affected by a novel and previously unrecognised hereditary form of gastric hyperplasia.

Cytodifferentiation of the postnatal mouse stomach in normal and Huntingtin-interacting protein 1-related-deficient mice

Huntingtin-interacting protein 1-related (Hip1r) is highly expressed in gastric parietal cells, where it participates in vesicular trafficking associated with acid secretion. Hip1r-deficient mice have a progressive remodeling of the mucosa, including apoptotic loss of parietal cells, glandular hypertrophy, mucous cell metaplasia, and reduced numbers of zymogenic cells. In this study, we characterized gastric gland development in wild-type and Hip1r-deficient mice to define normal development, as well as the timing and sequence of the cellular transformation events in the mutant stomach. Postnatal (newborn to 8-wk-old) stomachs were examined by histological and gene expression analysis. At birth, gastric glands in wild-type and mutant mice were rudimentary and mature gastric epithelial cells were not apparent, although marker expression was detected for most cell lineages. Interestingly, newborns exhibited unusual cell types, including a novel surface cell filled with lipid and cells that coexpressed markers of mature mucous neck and zymogenic cells. Glandular morphogenesis proceeded rapidly in both genotypes, with gastric glands formed by weaning at 3 wk of age. In the Hip1r-deficient stomach, epithelial cell remodeling developed in a progressive manner. Initially, in the perinatal stomach, cellular changes were limited to parietal cell apoptosis. Other epithelial cell changes, including apoptotic loss of zymogenic cells and expansion of metaplastic mucous cells, emerged several weeks later when the glands were morphologically mature. Thus, parietal cell loss appeared to be the initiating event in Hip1r-deficient mice, with secondary remodeling of the other gastric epithelial cells.

Loss of parietal cell expression of Sonic hedgehog induces hypergastrinemia and hyperproliferation of surface mucous cells

BACKGROUND & AIMS

Sonic Hedgehog (Shh) is expressed in the adult stomach, but its role as a gastric morphogen is unclear. We sought to identify mechanisms by which Shh might regulate gastric epithelial cell function and differentiation.

METHODS

Mice with a parietal cell-specific deletion of Shh (HKCre/Shh(KO)) were created. Gastric morphology and function were studied in control and HKCre/Shh(KO) mice between 1 and 8 months of age.

RESULTS

In contrast to control mice, HKCre/Shh(KO) mice developed gastric hypochlorhydria, hypergastrinemia, and a phenotype that resembled foveolar hyperplasia. The fundic mucosa of HKCre/Shh(KO) mice had an expanded surface pit cell lineage that was documented by increased incorporation of bromodeoxyuridine and was attributed to the hypergastrinemia. Compared with controls, numbers of total mucous neck and zymogen cells were significantly decreased in stomachs of HKCre/Shh(KO) mice. In addition, zymogen and neck cell markers were coexpressed in the same cell populations, indicating disrupted differentiation of the zymogen cell lineage from the mucous neck cells in the stomachs of HKCre/Shh(KO) mice. Laser capture microdissection of the surface epithelium, followed by quantitative reverse-transcription polymerase chain reaction, revealed a significant increase in expression of Indian Hedgehog, glioma-associated oncogene homolog 1, Wnt, and cyclin D1. Laser capture microdissection analysis also showed a significant increase in Snail with a concomitant decrease in E-cadherin.

CONCLUSIONS

In the stomachs of adult mice, loss of Shh from parietal cells results in hypochlorhydria and hypergastrinemia. Hypergastrinemia might subsequently induce increased Hedgehog and Wnt signaling in the surface pit epithelium, resulting in hyperproliferation.

Islet cell development

Over the last years, there has been great success in driving stem cells toward insulin-expressing cells. However, the protocols developed to date have some limitations, such as low reliability and low insulin production. The most successful protocols used for generation of insulin-producing cells from stem cells mimic in vitro pancreatic organogenesis by directing the stem cells through stages that resemble several pancreatic developmental stages. Islet cell fate is coordinated by a complex network of inductive signals and regulatory transcription factors that, in a combinatorial way, determine pancreatic organ specification, differentiation, growth, and lineage. Together, these signals and factors direct the progression from multipotent progenitor cells to mature pancreatic cells. Later in development and adult life, several of these factors also contribute to maintain the differentiated phenotype of islet cells. A detailed understanding of the processes that operate in the pancreas during embryogenesis will help us to develop a suitable source of cells for diabetes therapy. In this chapter, we will discuss the main transcription factors involved in pancreas specification and beta-cell formation.

Mice lacking neurofibromin develop gastric hyperplasia

Gastrointestinal (GI) neoplasms are among many manifestations of the genetic disease neurofibromatosis type 1 (NF1). However, the physiological and pathological functions of the Nf1 gene in the GI system have not been fully studied, possibly because of a lack of mouse models. In this study, we generated conditional knockout mice with Nf1 deficiency in the GI tract. These mice develop gastric epithelial hyperplasia and inflammation together with increased cell proliferation and apoptosis. The gastric phenotypes observed in these mutant mice seem to be the consequence of loss of Nf1 in gastric fibroblasts, resulting in paracrine hyperactivation of the ERK pathway in the gastric epithelium. These mice provide a useful model to study the pathogenesis of GI lesions in a subset of patients with NF1 and to investigate the role of the Nf1 gene in the development of GI neoplasms.

Mechanisms of Gastric Mucosal Cell Loss In Autoimmune Gastritis

The causes of target cell death in organ-specific autoimmune diseases are not precisely known. In the case of EAG, parietal cell death depends on Th1 CD4 T cells and Fas/Fas-ligand, either through interaction between infiltrating CD4 T cells with gastric parietal cells that have upregulated Fas expression or through homotypic interactions between the parietal cells. TNF-alpha does not appear to have a role in this process. The accompanying loss of zymogenic cells is likely a consequence of the interruption of the normal developmental pathway in the gastric mucosa that follows the destruction of parietal cells in the gastric mucosa.

Alterations in gastric mucosal lineages before or after acute oxyntic atrophy in gastrin receptor and H2 histamine receptor-deficient mice

Spasmolytic polypeptide (SP/TFF2)-expressing metaplasia (SPEM) is induced by oxyntic atrophy and is known as a precancerous or paracancerous lesion. We seek to determine whether the gastrin receptor or H(2) histamine receptor influence the development of SPEM. DMP-777 was administered to gastrin receptor and/or H(2) receptor-deficient mice and wild-type mice. Gastric mucosal lineage changes were analyzed. The mucosa from double knockout mice and H(2) receptor knockout mice contained elevated numbers of dual TFF2 and intrinsic factor immunoreactive cells even before DMP-777 treatment. All genotypes of mice showed SPEM after 7-day treatment. In all types of knockout mice, the number of TFF2 immunoreactive cells remained elevated after cessation of treatment. The H(2) receptor and gastrin receptor do not affect emergence of SPEM. However, it is suggested that the absence of H(2) receptor signaling causes a delay in the maturation of chief cells from mucous neck cells.

Altered gastric chief cell lineage differentiation in histamine-deficient mice

The orderly differentiation of cell lineages within gastric glands is regulated by a complicated interplay of local mucosal growth factors and hormones. Histamine secreted from enterochromaffin-like cells plays an important role in not only stimulated gastric acid secretion but also coordination of intramucosal growth and lineage differentiation. We have examined histidine-decarboxylase (HDC)-deficient mice, which lack endogenous histamine synthesis, to evaluate the influence of histamine on differentiation of fundic mucosal lineages and the development of metaplasia following induction of acute oxyntic atrophy. Stomachs from HDC-deficient mice and wild-type mice were evaluated at 8 wk and 12 mo of age. DMP-777 was administrated orally to 6-wk-old mice for 1 to 14 days. Sections of gastric mucosa were stained with antibodies against Mist1, intrinsic factor, H/K-ATPase, trefoil factor 2 (TFF2), chromogranin A, and Ext1 and for the cell cycle marker phospho-histone H3. HDC-deficient mice at 8 wk of age demonstrated a prominent increase in chief cells expressing Mist1 and intrinsic factor. Importantly Mist1-positive mature chief cells were present in the midgland region as well as at the bases of fundic glands, indicating a premature differentiation of chief cells. Mice dually deficient for both HDC and gastrin showed a normal distribution of chief cells in fundic glands. Treatment of HDC-deficient mice with DMP-777 led to loss of parietal cells and an accelerated and exaggerated emergence of mucous cell metaplasia with the presence of dual intrinsic factor and TFF2-expressing cells throughout the gland length, indicative of the emergence of spasmolytic polypeptide-expressing metaplasia (SPEM) from chief cells. These findings indicate that histamine, in concert with gastrin, regulates the appropriate differentiation of chief cells from mucous neck cells as they migrate toward the bases of fundic glands. Nevertheless, histamine is not required for emergence of SPEM following acute oxyntic atrophy.

The gastric epithelial progenitor cell niche and differentiation of the zymogenic (chief) cell lineage

In the mammalian gastrointestinal tract, the cell fate decisions that specify the development of multiple, diverse lineages are governed in large part by interactions of stem and early lineage progenitor cells with their microenvironment, or niche. Here, we show that the gastric parietal cell (PC) is a key cellular component of the previously undescribed niche for the gastric epithelial neck cell, the progenitor of the digestive enzyme secreting zymogenic (chief) cell (ZC). Genetic ablation of PCs led to failed patterning of the entire zymogenic lineage: progenitors showed premature expression of differentiated cell markers, and fully differentiated ZCs failed to develop. We developed a separate mouse model in which PCs localized not only to the progenitor niche, but also ectopically to the gastric unit base, which is normally occupied by terminally differentiated ZCs. Surprisingly, these mislocalized PCs did not maintain adjacent zymogenic lineage cells in the progenitor state, demonstrating that PCs, though necessary, are not sufficient to define the progenitor niche. We induced this PC mislocalization by knocking out the cytoskeleton-regulating gene Cd2ap in Mist1(-/-) mice, which led to aberrant E-cadherin localization in ZCs, irregular ZC-ZC junctions, and disruption of the ZC monolayer by PCs. Thus, the characteristic histology of the gastric unit, with PCs in the middle and ZCs in the base, may depend on establishment of an ordered adherens junction network in ZCs as they migrate into the base.

Ménétrier disease and gastrointestinal stromal tumors: hyperproliferative disorders of the stomach

Ménétrier disease and gastrointestinal stromal tumors (GISTs) are hyperproliferative disorders of the stomach caused by dysregulated receptor tyrosine kinases (RTKs). In Ménétrier disease, overexpression of TGF-alpha, a ligand for the RTK EGFR, results in selective expansion of surface mucous cells in the body and fundus of the stomach. In GISTs, somatic mutations of the genes encoding the RTK KIT (or PDGFRA in a minority of cases) result in constitutive kinase activity and neoplastic transformation of gut pacemaker cells (interstitial cells of Cajal). On the basis of the involvement of these RTKs in the pathogenesis of these disorders, Ménétrier disease patients have been effectively treated with a blocking monoclonal antibody specific for EGFR and GIST patients with KIT and PDGFRA tyrosine kinase inhibitors.

Tales from the crypts: regulatory peptides and cytokines in gastrointestinal homeostasis and disease

The gastrointestinal (GI) tract is composed of a diverse set of organs that together receive extracorporeal nutrition and convert it to energy substrates and cellular building blocks. In the process, it must sort through all that we ingest and discriminate what is useable from what is not, and having done that, it discards what is "junk." To accomplish these many and varied tasks, the GI tract relies on endogenous enteric hormones produced by enteroendocrine cells and the enteric nervous system. In many instances, the mediators of these tasks are small peptides that home to the CNS and accessory gut organs to coordinate oral intake with digestive secretions. As the contents of ingested material can contain harmful agents, the gut is armed with an extensive immune system. A breach of the epithelial barrier of the GI tract can result in local and eventually systemic disease if the gut does not mount an aggressive immune response.

Reg I-knockout mice reveal its role in regulation of cell growth that is required in generation and maintenance of the villous structure of small intestine

Reg I (regenerating gene product I) is a growth factor that plays a central role in the generation and regeneration of the gastric mucosal architecture. On the other hand, mouse Reg I mRNA is expressed at the highest levels in the small intestine among the gastrointestinal tissues. In the current study, with the aim to clarify the role of Reg I protein in the small intestine, the temporal and spatial pattern of Reg I expression and the phenotype of Reg I-knockout mice in the tissue were examined. In the wild-type mice, immunohistochemistry localized Reg I protein expression in absorptive cells located in the lower half of the intestinal villi. Reg I expression was undetectable until embryonic day 13 (E13), when the fetal intestine still lacks villous structure; however, it dramatically increased at E17 along with the formation and maturation of the fetal intestinal villi. In the small intestine of the adult Reg I-knockout mice, less densely packed, round-shaped aberrant morphology of the absorptive cells was observed light microscopically, and electron microscopical examination revealed a strikingly loose connection of these cells to the basement membrane. Antiproliferating cell nuclear antigen staining and anti-Ki67 staining demonstrated the marked decrease in the number of proliferating cells in the small intestinal mucosa of the knockout mice. The cell migration speed visualized by one shot labeling of 5-bromodeoxyuridine was significantly slower in the knockout mice. These phenotypes of Reg I-knockout mice emerged, in accordance with the temporal pattern of Reg I expression described above, from E17. Reg I was considered to be a regulator of cell growth that is required to generate and maintain the villous structure of the small intestine.

Control of ErbB signaling through metalloprotease mediated ectodomain shedding of EGF-like factors

Epidermal growth factor (EGF)-like proteins comprise a group of structurally similar growth factors, which contain a conserved six-cysteine residue motif called the EGF-domain. EGF-like factors are synthesized as transmembrane precursors, which can undergo proteolytic cleavage at the cell surface to release a mature soluble ectodomain; a process often referred to as "ectodomain shedding". Ectodomain shedding of EGF-like factors has been linked to multiple zinc-binding metalloproteases of the matrix metalloprotease (MMP) and a disintegrin and metalloprotease (ADAM) families. Shedding can be activated by a variety of pharmacological and physiological stimuli and these activation events have been linked to the enhancement of metalloprotease activity, possibly via the action of intracellular signaling modules. Once shed from the cell surface, EGF-like factors bind to a family of four cell surface receptors named ErbB-1, -2, -3 and -4. Heterodimerization or homodimerization of these receptors following ligand binding drives intracellular signal transduction cascades, which eventuate in diverse cell fates including proliferation, differentiation, migration and inhibition of apoptosis. In addition to its role in driving normal developmental processes, a wealth of evidence now exists showing that de-regulated ErbB signaling is associated with the formation of tumors in a variety of tissues and that ectodomain shedding of EGF-like factors plays a critical event in this process. Thus, knowledge of the molecular mechanisms by which EGF-like factors are shed from the cell surface and the nature of the proteases and cellular signals that govern this process is crucial to understanding ErbB receptor signaling and potentially also in the development of novel cancer therapeutics targeting the ErbB pathway. This review focuses on the structure and function of EGF-like factors, and the mechanisms that govern the shedding of these transmembrane molecules from the cell surface.

FGF10 is required for cell proliferation and gland formation in the stomach epithelium of the chicken embryo

The development of digestive organs in vertebrates involves active epithelial-mesenchymal interactions. In the chicken proventriculus (glandular stomach), the morphogenesis and cytodifferentiation of the epithelium are controlled by the inductive signaling factors that are secreted from the underlying mesenchyme. Previous studies have shown that Fgf10 is expressed in the developing chicken proventricular mesenchyme, whereas its receptors are present in the epithelium. In our present study, we show that FGF10 is an early mesenchymal signal that is critically associated with the developmental processes in the proventricular epithelium. Furthermore, virus-mediated Fgf10 overexpression in ovo results in a hypermorphic epithelial structure and an increase in epithelial cell number. In contrast, the overexpression of a secreted FGFR2b (sFGFR2b), an FGF10 antagonist, blocks cell proliferation and gland formation in the proventricular epithelium in ovo. This downregulation of proliferative activity was subsequently found to retard gland formation and also to delay differentiation of the epithelium. These results demonstrate that FGF10 signaling, mediated by FGFR1b and/or FGFR2b, is required for proliferation and gland formation in the epithelium in the developing chick embryo.

Altered metaplastic response of waved-2 EGF receptor mutant mice to acute oxyntic atrophy

Metaplastic cell lineages are putative precursors for the development of gastric adenocarcinoma. The loss of parietal cells (oxyntic atrophy) is the initiating step in the evolution of gastric fundic mucosal lineage changes including metaplasia and hyperplasia. However, the intrinsic mucosal factors that promote and modulate the emergence of metaplastic phenotypes remain obscure. Over the past several years, we have studied pharmacologically induced, reversible oxyntic atrophy in rodents treated with DMP-777, a drug that acts as a parietal cell secretory membrane protonophore. DMP-777 elicits a rapid loss of parietal cells followed by the emergence of foveolar hyperplasia and spasmolytic polypeptide (SP)-expressing metaplasia (SPEM). The objective of the present study was to provide further insights into the intrinsic mucosal factors regulating the emergence of SPEM in the setting of oxyntic atrophy. We therefore studied the effects of DMP-777 administration on both SP/trefoil factor (TFF)2-deficient mice, which lack SP/TFF2, a marker of SPEM, and waved-2 mice, which harbor a point mutation in the EGF receptor that attenuates its tyrosine kinase activity. As in wild-type mice, treatment with DMP-777 for 7 days did elicit SPEM in SP/TFF2-deficient mice. These results suggest that SP/TFF2 does not impact on the development of metaplasia after the induction of parietal cell loss. In contrast, waved-2 homozygous mice displayed accelerated SPEM development by 3 days of treatment with DMP-777. These findings indicate that attenuation of EGF receptor signaling in waved-2 mice does elicit a more rapid emergence of SPEM. The results support a role for EGF receptor ligands in the regulation of gastric metaplasia.

Involvement of cyclooxygenase-2 in gastric mucosal hypertrophy in gastrin transgenic mice

Gastrin promotes gastric mucosal growth, and hypergastrinemia induces gastric mucosal hypertrophy. Recently, it has been reported that gastrin induces cyclooxygenase-2 (COX-2) in human gastric and colorectal cancer cell lines. However, whether COX-2 is involved in gastrin-induced gastric mucosal growth in vivo is unknown. We investigated the role of COX-2 in gastrin-induced gastric mucosal hypertrophy using gastrin transgenic mice. Hypergastrinemic mice [mice with mutated gastrin under the control of the beta-actin promoter (ACT-GAS mice)] received the COX-2 inhibitor celecoxib (0, 200, or 500 mg/kg of diet) from 5 wk of age and were killed at 16 or 24 wk. Some ACT-GAS mice received celecoxib from 16 wk and were killed at 24 wk. Eighty-week-old ACT-GAS mice without celecoxib treatment were also examined. The thickness of the gastric mucosa, cell populations, COX-2 expression, and PGE(2) levels were evaluated. All ACT-GAS mice showed gastric mucosal hypertrophy, and four of six 80-wk-old ACT-GAS mice developed gastric cancer. COX-2 was expressed in interstitial cells of the hypertrophic gastric mucosa and gastric cancers. Moreover, PGE(2) levels in the gastric mucosa of ACT-GAS mice were significantly higher than those of normal mice. With treatment with celecoxib, PGE(2) levels, the gastric mucosal thickness, and the number of total gastric cells per gastric gland of ACT-GAS mice were significantly decreased. The decrease in gastric mucosal thickness was caused by a reduction of foveolar hyperplasia. The thickness of glandules and the number of Ki67-positive cells were not significantly changed. In conclusion, COX-2 contributes to gastrin-induced mucosal hypertrophy of the stomach.

Differential alteration of stem and other cell populations in ducts and lobules of TGFα and c-Myc transgenic mouse mammary epithelium

Genes associated with proliferation are active in stem and progenitor cells, and their over-expression can promote cancer. Two such genes, c-Myc and TGFalpha, promote morphologically dissimilar mammary tumors in transgenic mice. We investigated whether their over-expression affects population size and cell cycle activity in stem and other cell populations in non-neoplastic mammary epithelia. Results indicated that both cell population and cell cycle regulation are cell type- and microenvironment-specific. To create a tool for identifying and categorizing the five cellular phenotypes by light microscopy, we adapted previously established ultrastructural criteria. Using nulliparous MMTV-c-myc or MT-tgfalpha mice, we determined and compared the relative sizes the putative stem, progenitor and differentiated cell populations. PCNA staining was used to compare the portion of each cell population in the cell cycle. Cell population sizes were analyzed relative to: (1) their location in ducts versus lobules (microenvironment), (2) genotype, and (3) cell type. Population sizes differed significantly by genotype, depending on microenvironment (p=0.0008), by genotype, depending on cell type (p<0.0001), and by microenvironment, depending on cell type (p=0.03). The number of cycling cells was also affected by all three factors, confirming that the interplay of cell type, gene expression and three-dimensional organization are very important in tissue morphogenesis and function. We describe a structure in mammary epithelium consistent with that of a stem cell niche, and show that it is altered in MMTV-c-myc and likely altered in MT TGFalpha transgenic epithelia.

Gastric achlorhydria in H/K-ATPase-deficient (Atp4a(-/-)) mice causes severe hyperplasia, mucocystic metaplasia and upregulation of growth factors

BACKGROUND

Gastric neoplasia is common in humans, yet controversy remains over contributions of chronic achlorhydria, gastrinemia and hyperplasia, to cancer risk. To study this, mice lacking the gastric H/K-ATPase (Atp4a(-/-) mice) were used to determine whether chronic loss of acid secretion, with attendant hypergastrinemia, predisposes to cancer phenotype.

METHODS

Atp4a(-/-) and Atp4a(+/+) mice, paired for age and gender, were examined at 3, 8, 12 and 20 months for histopathology, and for expression of the trefoil factor family (TFF)1-3, Reg IIIbeta, gamma and delta, osteopontin, CD44, chromogranin A, Crp-ductin, and galectin, all of which are important in cell growth.

RESULTS

By 8 months, the glandular stomach of the Atp4a(-/-) mice doubled in weight and thickness, and several modulators of growth were increased. Female Atp4a(-/-) mice were more hyperplastic than Atp4a(-/-) males at 12 and 20 months. By 1 year, severe mucocystic hyperplasia, incomplete intestinal metaplasia, ciliated metaplasia, a shift in mucins from neutral to acidic, and inflammation were widespread. Cells in the mucus pit zone developed a pyloric-type appearance, containing large hyaline-like, periodic acid-Schiff (PAS)-negative/alcian blue-negative inclusions. But critical characteristics of gastric neoplasia, such as nuclear atypia, invasion into the muscularis mucosa, and metastases were absent. In Atp4a(-/-) mice, chromogranin A and histidine decarboxylase, RegIIIgamma and delta, TFF3, osteopontin and CD44 were upregulated while Reg IIIbeta, and TFF1 were reduced.

CONCLUSIONS

Chronic achlorhydria and hypergastrinemia in aged Atp4a(-/-) mice produced progressive hyperplasia, mucocystic and incomplete intestinal metaplasia, and the upregulation of growth factors without histological evidence of neoplasia.

The molecular mechanisms of stomach development in vertebrates

The tissue interactions between endodermal epithelium and mesenchyme originated from splanchnic mesoderm are essential during the formation of digestive tract. In this review, we introduce a series of works to elucidate the molecular mechanisms of the epithelial-mesenchymal interaction of stomach development in mainly the chicken embryo. We also describe some molecular studies in mouse stomach development.

Evidence for repatterning of the gastric fundic epithelium associated with Ménétrier's disease and TGFalpha overexpression

BACKGROUND & AIMS

Increase of intramucosal transforming growth factor alpha (TGFalpha) levels in the gastric fundus leads to oxyntic atrophy and massive foveolar hyperplasia in both metallothionein (MT)-TGFalpha mice and patients with Ménétrier's disease. We have evaluated the hypothesis that increased levels of TGFalpha in the fundus induces an antral pattern of cell differentiation in fundic glands by studying Pdx1, a transcription factor whose expression normally is confined to the gastric antrum.

METHODS

Induction of Pdx1 expression was evaluated in Pdx1(lacZ/+)/MT-TGFalpha bigenic mice treated with zinc. The distribution of Pdx1 in MT-TGFalpha mice and Ménétrier's disease patients was evaluated with anti-Pdx1 antibodies. Transcript levels were evaluated by quantitative polymerase chain reaction in mouse and human tissues and AGS cells.

RESULTS

In Pdx1(lacZ/+) mice, Pdx1 was expressed in antral mucosal cells including gastrin cells and TFF2-expressing deep glandular mucous cells. Zinc treatment for 2 to 8 weeks in Pdx1(lacZ/+)/MT-TGFalpha transgenic mice resulted in expression of Pdx1 throughout the fundus. No ectopic fundic Pdx1 expression was observed in either H. felis-infected or DMP777-treated mice. In MT-TGFalpha mice, 8 weeks of zinc treatment elicited nuclear Pdx1 staining throughout the fundic mucosa. TGFalpha treatment in AGS cells led to increases in Pdx1 and gastrin messenger RNA expression. Fundic sections from Ménétrier's disease patients showed nuclear Pdx1 staining throughout the fundic glands. Treatment of a Ménétrier's disease patient with an anti-epidermal growth factor receptor monoclonal antibody reduced fundic expression of both Pdx1 and gastrin.

CONCLUSIONS

Overexpression of TGFalpha in MT-TGFalpha mice and Ménétrier's disease patients elicits ectopic expression in the fundus of Pdx1, consistent with the phenotype of antralization.

Alterations in gastric mucosal lineages induced by acute oxyntic atrophy in wild-type and gastrin-deficient mice

In addition to their role in gastric acid secretion, parietal cells secrete a number of growth factors that may influence the differentiation of other gastric lineages. Indeed, oxyntic atrophy is considered the most significant correlate with increased risk for gastric adenocarcinoma. We studied the alterations in gastric mucosal lineages elicited by acute oxyntic atrophy induced by treatment of C57BL/6 and gastrin-deficient mice with the parietal cell protonophore [S-(R*,S*)]-N-[1-(1,3-benzodioxol-5-yl)butyl]-3,3-diethyl-2-[4-[(4-methyl-1-piperazinyl)carbonyl]phenoxy]-4-oxo-1-azetidinecarboxamide (DMP-777). In both wild-type and gastrin knockout mice, DMP-777 elicited the rapid loss of parietal cells within 2 days of treatment. In wild-type mice, oxyntic atrophy was accompanied by a rapid increase in 5-bromo-2'-deoxyuridine-labeled proliferative cells and attendant increase in surface cell numbers. However, gastrin knockout mice did not demonstrate significant foveolar hyperplasia and showed a blunted proliferative response. After 7 days of treatment in wild-type mice, a second proliferative population emerged at the base of fundic glands along with the development of a mucous cell metaplasia expressing TFF2/spasmolytic polypeptide (SPEM). However, in gastrin knockout mice, SPEM expressing both TFF2 mRNA and protein developed after only 1 day of DMP-777 treatment. In wild-type mice, all changes induced by DMP-777 were reversed 14 days after cessation of treatment. In gastrin-deficient mice, significant SPEM was still present 14 days after the cessation of treatment. The results indicate that foveolar hyperplasia requires the influence of gastrin, whereas SPEM develops in response to oxyntic atrophy independent of gastrin, likely through transdifferentiation of chief cells.

Immunological and morphogenic basis of gastric mucosa atrophy and metaplasia

Chronic gastritis with gastric mucosa atrophy, intestinal metaplasia and endocrine cell hyperplasia are alterations with an increased risk for the development of gastric neoplasias. Immunological studies in autoimmune gastritis, in atrophic Helicobacter pylori gastritis and in studies with transgenic mice point to a central role of the parietal cell in the development of gastric mucosa atrophy. Destruction of gastric epithelial cells alone might not be sufficient for the loss of complete gastric glands. Gastric atrophy, endocrine cell hyperplasia and intestinal and pancreatic metaplasia can be regarded as the result of altered morphogenesis within the gastric mucosa. Impaired expression of the gastric morphogenic factor Sonic Hedgehog by parietal cells and increased expression of the transcriptional activators of intestinal and pancreatic differentiation, namely CDX2 and PDX1, seem to be crucial for the development of gastric atrophy and for intestinal, endocrine and pancreatic transdifferentiation processes. Altered expression of these morphogenic factors is partly caused by changes in the gastric milieu. Further studies concerning the normal and pathological morphogenesis of the gastric mucosa and related tissues might give new insight into the pathogenesis of gastric atrophy and metaplasia.

The Akt and MAPK signal-transduction pathways regulate growth factor actions in isolated gastric parietal cells

BACKGROUND & AIMS

Incubation of purified (>95%) canine parietal cells in primary culture with epidermal growth factor for 7-16 hours stimulates H(+)K(+)-adenosine triphosphatase gene expression. In this study, we examined the effect of prolonged stimulation (72 hours) of the parietal cells with epidermal growth factor.

METHODS

H(+)K(+)-adenosine triphosphatase protein and gene expression were assessed by immunohistochemistry and Northern blots. Mitogen-activated protein kinase and Akt activation were quantitated by kinase assays and Western blots with specific antiphospho antibodies. Akt overexpression was achieved by adenovirus-mediated gene transfer of a constitutively active Akt gene.

RESULTS

Epidermal growth factor changed the morphology of the cultured cells, which acquired the appearance of fusiform cells, and it inhibited H(+)K(+)-adenosine triphosphatase gene expression. Staining of the cells both with anti-H(+)K(+)-adenosine triphosphatase antibodies and with Texas Red-labeled Dolichos biflorus lectin confirmed that the fusiform cells expressed markers of parietal cell differentiation. Epidermal growth factor stimulated mitogen-activated protein kinase with 2 peaks of activation, observed after 5 minutes and 72 hours, whereas it activated Akt after 5 minutes but not 72 hours of incubation. Overexpression of Akt blocked both epidermal growth factor-induced morphological transformation and inhibition of H + K + -adenosine triphosphatase gene expression. Identical results were observed in the presence of the mitogen-activated protein kinase inhibitor PD98059.

CONCLUSIONS

Activation of the Akt signal-transduction pathway seems to be a crucial event for the induction of parietal cell maturation and differentiation.

Heightened susceptibility to chronic gastritis, hyperplasia and metaplasia in Kcnq1 mutant mice

Increased susceptibility to gastric cancer has been associated with a wide range of host genetic and environmental factors, including Helicobacter pylori infection. Helicobacter pylori infection is postulated to initiate a progression through atrophic gastritis, metaplasia and dysplasia to cancer, and has been associated with reduction of acid output and dysregulation of stomach mucins. Here, we present the characterization of two mouse lines carrying mutant alleles of the gene encoding the Kcnq1 potassium channel, which very rapidly establish chronic gastritis in a pathogen-exposed environment. These mice develop gastric hyperplasia, hypochlorhydria and mucin dysregulation independent of infection. Metaplasia, dysplasia and pre-malignant adenomatous hyperplasia of the stomach have been observed in these Kcnq1 mutant mice, also independent of infection. The data presented here suggest that Kcnq1 mutant mice can be used both as an efficient model for the development of atrophic gastritis after infection and to determine the processes during the later stages of progression to gastric cancer independent of infection. Thus, Kcnq1 mutant mice are a powerful new tool for investigating the connection between acid balance, Helicobacter infection and mucin disruption in the progression to gastric cancer.

Transgenic overexpression of Reg protein caused gastric cell proliferation and differentiation along parietal cell and chief cell lineages

Reg (regenerating gene product) was originally identified as a growth factor involved in pancreatic regeneration. During the healing course of gastric erosion, Reg expression is highly increased in the enterochromaffin-like (ECL) cells surrounding the ulcer crater, suggesting its role as a regulator of gastric mucosal regeneration. However, there has been no direct in vivo evidence of a growth-promoting role of Reg for the gastric mucosal cells. In the current study, Reg-transgenic mice were created and gastric mucosa were analysed for histological changes. Transgenic mice showed a marked increase in the thickness of the fundic mucosa. Anti-proliferating cell nuclear antigen (PCNA) staining of the fundic mucosa demonstrated the enlargement of the proliferating neck zone and the lower PCNA-negative zone. Histological analysis employing antibodies against cell-type markers revealed expansion of the chief cell and parietal cell populations and no change in the number of surface mucus-producing cells, ECL cells, or G cells. In conclusion, Reg has a growth-promoting effect on gastric progenitor cells and an activity to direct the differentiation of the cells into chief cell and parietal cell lineages. This was in contrast to other factors, all of which had been shown to drive differentiation towards mucus producing cells in vivo. In the injured gastric mucosa, Reg may play a unique and important part in the reconstruction of the properly organized mucosal architecture.

Review article: How useful are the rodent animal models of gastric adenocarcinoma?

Gastric cancer is the second most common cause of cancer-related mortality world-wide. In most cases, it develops via the pre-malignant stages of atrophic gastritis, intestinal metaplasia and dysplasia, following Helicobacter pylori infection of susceptible individuals. A number of rodent models have recently provided valuable insights into the host, bacterial and environmental factors involved in gastric carcinogenesis. Wild-type rodents do not develop gastric adenocarcinoma, but early studies showed that the disease could be induced in several rodent species by chemical carcinogens. More recently, it has been demonstrated that gastric adenocarcinoma can be induced in Mongolian gerbils by H. pylori infection and in C57BL/6 mice by long-term H. felis infection. These models have allowed the importance of Helicobacter virulence genes, host factors, such as gender, strain and immune response, and environmental factors, such as dietary salt, to be explored. A number of transgenic mice with alterations in various pathways, including the immune response, gastrin biosynthesis, parietal cell development, growth factors and tumour suppressors, have also provided models of various stages of gastric carcinogenesis. One model that has proved to be particularly valuable is the hypergastrinaemic INS-GAS mouse, in which gastric carcinoma develops spontaneously in old animals, but the process is greatly accelerated by Helicobacter infection.

Utilization of knockout mice to examine the potential role of gastric histamine H2-receptors in Menetrier's disease

Menetrier's disease is characterized by giant gastric folds with foveolar hyperplasia and cystic dilatation, hypoproteinemia, and enhanced mucus secretion. The etiology remains unresolved and an effective treatment has yet to be established. Here we show that histamine H(2)-receptor deficient mice developed gastric pathophysiological changes resembling Menetrier's disease for up to 17 months of observation. Mutant mice were found to have an increased stomach weight, enlarged gastric folds with cystic dilatation, hypergastrinemia, hypoalbuminemia, increased mucus secretion and overexpression of mucosal transforming growth factor (TGF) alpha. Both a cholecystokinin (CCK)(2)-receptor antagonist and an epidermal growth factor (EGF)-receptor tyrosine kinase inhibitor significantly reduced the increase in stomach weight. It appears that lack or downregulation of histamine H(2)-receptors might be involved in the pathogenesis of Menetrier's disease.

Defining epithelial cell progenitors in the human oxyntic mucosa

In the human stomach, the oxyntic epithelium includes numerous tubular invaginations consisting of short pits opening into long glands. The pit is lined by pit cells, whereas the gland is composed of three regions: the base, containing zymogenic cells; the neck, containing neck cells; and the isthmus, composed of little known immature cells and of parietal cells, which are also scattered through the neck and base. The aim of this study was to examine the ultrastructure of the immature cells and to determine their relation to mature cells. To do so, normal oxyntic mucosal biopsies from subjects ranging from 20-43 years old were fixed in aldehydes and postfixed in reduced osmium for electron microscopy and morphometric analysis. The immature cells were sorted out into four classes, whose roles were clarified by comparison with the thoroughly investigated mouse oxyntic epithelium. The first class was composed of the least differentiated immature cells, which were rare and characterized by minute, dense, or cored secretory granules and were accordingly named mini-granule cells. Their function was not clarified. The second class consisted of pre-pit cells, which were characterized by few dense mucous granules and give rise to pit cells that ascend the pit wall and, after reaching the luminal surface, die or are extruded. Both pre-pit and pit cells underwent continuous renewal and, therefore, together constituted a renewal system referred to as pit cell lineage. The third class, or pre-neck cells, characterized by cored secretory granules, give rise to neck cells that descend toward the base region and differentiate further into pre-zymogenic cells, which finally become zymogenic cells. The latter eventually degenerate and die. Thus pre-neck cells and their progeny constitute a renewing system, designated zymogenic cell lineage. The fourth class, or pre-parietal cells, characterized by long microvilli and few tubulovesicles, differentiate into parietal cells that descend along the neck and base regions and eventually degenerate and die. Pre-parietal and parietal cells represent a renewing system referred to as parietal cell lineage. While the origin of the last three classes of progenitor cells has not been elucidated, it is likely that they arise either from an unidentified multipotential stem cell, possibly the mini-granule cell itself, or from the mitotic activity of pre-pit and pre-neck cells. In conclusion, the human oxyntic epithelium is composed of continually renewing cells organized in distinct cell lineages.

Involvement of the signal transduction pathway mediated by epidermal growth factor receptor in the differentiation of chicken glandular stomach

During the development of the chicken proventriculus (glandular stomach), the initially undifferentiated epithelium differentiates into two distinct cell populations: the glandular epithelium, cells of which secrete embryonic chicken pepsinogen (ECPg), and luminal epithelial cells, which express the chicken spasmolytic polypeptide gene (cSP). Based on knowledge of the adult mouse stomach, the ligands of epidermal growth factor (EGF) receptor (EGFR) were expected to affect differentiation of the proventricular epithelium. When EGF was added to the medium in which proventriculi were cultured in vitro, gland formation was suppressed in a dose-dependent manner and the amount of ECPg mRNA decreased, whereas morphological differentiation of luminal epithelium was stimulated. Simultaneous treatment of the proventriculus with EGF and tyrphostin 47 resulted in the attenuation of the effect of EGF, suggesting that EGF, or other ligands of EGFR, may actually be involved in the normal course of development of the proventricular epithelium.

Gastric hyperplasia in mice with targeted disruption of the carbonic anhydrase gene Car9

BACKGROUND & AIMS

Carbonic anhydrase (CA) IX is a highly active enzyme with adhesion capacity that is functionally implicated in acid-base balance and intercellular communication. It is normally present in basolateral membranes of gastrointestinal epithelial cells and ectopically expressed in various carcinomas. To show its physiologic relevance, we have cloned the Car9 gene and generated CA IX-deficient mice.

METHODS

The mice with null mutation of the Car9 gene were obtained by targeted gene disruption. Tissue architecture and expression of markers were determined by histochemical and immunohistochemical techniques.

RESULTS

Mice homozygous for the mutation developed gastric hyperplasia of the glandular epithelium with numerous cysts. The first changes were observed in the newborn animals, and the hyperplasia became prominent at the end of gastric morphogenesis in 4-week-old mice. Loss of CA IX led to overproduction of mucus-secreting pit cells and depletion of pepsinogen-positive chief cells. The proportion of H(+)/K(+)-adenosine triphosphatase-positive parietal cells significantly decreased, but their absolute number was not reduced. Correspondingly, CA IX-deficient mice had normal gastric pH, acid secretion, and serum gastrin levels.

CONCLUSIONS

Phenotypic consequences of the Car9 null mutation show the important role of CA IX in morphogenesis and homeostasis of the glandular gastric epithelium via the control of cell proliferation and differentiation.

Expression of TGF-beta type II receptors in the olfactory epithelium and their regulation in TGF-alpha transgenic mice

Numerous in vitro studies of neurogenesis of olfactory receptor neurons (ORNs) suggest that transforming growth factor (TGF)-beta promotes the maturation/differentiation of olfactory progenitors. We demonstrate that in vivo both mature and immature ORNs, and possibly a basal neuronal progenitor cell, express the TGF-beta type II receptor (TGF-betaRII), suggesting that these cells are targets for TGF-beta signaling. In a previous study of neurogenesis in the OE of TGF-alpha overexpressing transgenic (T) mice, we observed an apparent reduction in the expression of olfactory marker protein (OMP), a marker of terminal differentiation in ORNs in T mice compared to nontransgenic (NT) littermate controls; this was confirmed by Western blotting and immunohistochemistry. In contrast, there was no apparent difference between T and NT mice in the intensity of immunoreactivity for a neuronal marker, protein gene product 9.5. Because TGF-alpha overexpression has been reported to affect TGF-beta signaling in other epithelia, we compared the expression of the TGF-beta type II receptor (TGF-betaRII) in T and NT mice. The intensity of TGF-betaRII immunoreactivity on ORNs was substantially reduced in T compared to NT mice. Similar reductions in TGF-betaRII expression in vomeronasal receptor neurons and in other epithelia in the nasal cavity of T mice were also observed. Taken together, these results indicate that TGF-beta signaling regulates terminal differentiation of ORNs in vivo and suggest ways in which interactions between TGF-alpha and TGF-beta signaling pathways may interact in the OE.

Obligate roles for p16(Ink4a) and p19(Arf)-p53 in the suppression of murine pancreatic neoplasia

Epithelial tumors of the pancreas exhibit a wide spectrum of histologies with varying propensities for metastasis and tissue invasion. The histogenic relationship among these tumor types is not well established; moreover, the specific role of genetic lesions in the progression of these malignancies is largely undefined. Transgenic mice with ectopic expression of transforming growth factor alpha (TGF-alpha) in the pancreatic acinar cells develop tubular metaplasia, a potential premalignant lesion of the pancreatic ductal epithelium. To evaluate the cooperative interactions between TGF-alpha and signature mutations in pancreatic tumor genesis and progression, TGFalpha transgenic mice were crossed onto Ink4a/Arf and/or p53 mutant backgrounds. These compound mutant mice developed a novel pancreatic neoplasm, serous cystadenoma (SCA), presenting as large epithelial tumors bearing conspicuous gross and histological resemblances to their human counterpart. TGFalpha animals heterozygous for both the Ink4a/Arf and the p53 mutation showed a dramatically increased incidence of SCA, indicating synergistic interaction of these alleles. Inactivation of p16(Ink4a) by loss of heterozygosity, intragenic mutation, or promoter hypermethylation was a common feature in these SCAs, and correspondingly, none of the tumors expressed wild-type p16(Ink4a). All tumors sustained loss of p53 or Arf, generally in a mutually exclusive fashion. The tumor incidence data and molecular profiles establish a pathogenic role for the dual inactivation of p16(Ink4a) and p19(Arf)-p53 in the development of SCA in mice, demonstrating that p16(Ink4a) is a murine tumor suppressor. This genetically defined model provides insights into the molecular pathogenesis of SCA and serves as a platform for dissection of cell-specific programs of epithelial tumor suppression.

The gastrins: their production and biological activities

Gastric epithelial organization and function are controlled and maintained by a variety of endocrine and paracrine mediators. Peptides encoded by the gastrin gene are an important part of this system because targeted deletion of the gene, or of the gastrin-CCKB receptor gene, leads to decreased numbers of parietal cells and decreased gastric acid secretion. Recent studies indicate that the gastrin precursor, preprogastrin, gives rise to a variety of products, each with a distinctive spectrum of biological activity. The conversion of progastrin to smaller peptides is regulated by multiple mechanisms including prohormone phosphorylation and secretory vesicle pH. Progastrin itself stimulates colonic epithelial proliferation; biosynthetic intermediates (Gly-gastrins) stimulate colonic epithelial proliferation and gastric epithelial differentiation; and C-terminally amidated gastrins stimulate colonic proliferation, gastric epithelial proliferation and differentiation, and acid secretion. The effects of progastrin-derived peptides on gastric epithelial function are mediated in part by release of paracrine factors that include histamine, epidermal growth factor (EGF)-receptor ligands, and Reg. The importance of the appropriate regulation of this system is shown by the observation that prolonged moderate hypergastrinemia in transgenic mice leads to remodelling of the gastric epithelium, and in the presence of Helicobacter, to gastric cancer.

Effects of in vivo heregulin beta1 treatment in wild-type and ErbB gene-targeted mice depend on receptor levels and pregnancy

Mice heterozygous (+/-) for either heregulin (HRG), ErbB2, or ErbB3 were created by gene targeting, resulting in the loss of one functional gene copy and an associated decrease in targeted protein. We examined the in vivo activity of recombinant HRG peptide, rHRG beta1 (amino acids 177 to 241), in the three heterozygous mouse lines and in wild-type (WT) mice, both pregnant and nonpregnant. Nonpregnant WT and HRG(+/-) mice of both sexes were sensitive to rHRG beta1 treatment as evidenced by a high mortality rate associated with abdominal enlargement and parietal cell loss. However, pregnant WT mice and ErbB2 and ErbB3 heterozygous mice treated with rHRG beta1 were less affected, with significantly lower mortality rates and a less severe abdominal phenotype. Histological analysis revealed extensive breast ductal hyperplasia in females of all genotypes after rHRG beta1 treatment. Hyperplasia of other epithelial tissues such as the pancreas and intestine and the growth of cardiac nerve bundles were also observed, independent of sex.