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

The Importance of Th2 Immune Responses in Mediating the Progression of Gastritis-Associated Metaplasia to Gastric Cancer

Gastric cancer is one of the leading causes of cancer deaths worldwide, with chronic gastritis representing the main predisposing factor initiating the cascade of events leading to metaplasia and eventually progressing to cancer. A widely accepted classification distinguishes between autoimmune and environmental atrophic gastritis, mediated, respectively, by T cells promoting the destruction of the oxyntic mucosa, and chronic H. pylori infection, which has also been identified as the major risk factor for gastric cancer. The original dogma posits Th1 immunity as a main causal factor for developing gastritis and metaplasia. Recently, however, it has become evident that Th2 immune responses play a major role in the events causing chronic inflammation leading to tumorigenesis, and in this context, many different cell types and cytokines are involved. In particular, the activity of cytokines, such as IL-33 and IL-13, and cell types, such as mast cells, M2 macrophages and eosinophils, are intertwined in the process, promoting chronic gastritis-dependent and more diffuse metaplasia. Herein, we provide an overview of the critical events driving the pathology of this disease, focusing on the most recent findings regarding the importance of Th2 immunity in gastritis and gastric metaplasia.

The bHLH transcription factor ASCL1 promotes differentiation of endocrine cells in the stomach and is regulated by Notch signaling

Notch signaling regulates gastrointestinal stem cell proliferation and differentiation yet Notch-regulated transcriptional effectors of gastric epithelial cell differentiation are poorly understood. Here we tested the role of the bHLH transcription factor Achaete-Scute homolog 1 (ASCL1) in gastric epithelial cell differentiation, and its regulation by Notch. Newborn Ascl1 null mice showed a loss of expression of markers of neurogenin-3-dependent enteroendocrine cells, with normal expression of enterochromaffin-like cells, mucous cells, chief cells, and parietal cells. In adult mice, Ascl1 gene expression was observed in the stomach, but not the intestine, with higher expression in antral than corpus epithelium. Lineage tracing in Ascl1-CreERT2; Rosa26-LSL-tdTomato mice revealed single, scattered ASCL1+ cells in the gastric epithelium, demonstrating expression in antral gastrin- and serotonin-producing endocrine cells. ASCL1-expressing endocrine cells persisted for several weeks posttamoxifen labeling with a half-life of approximately 2 months. Lineage tracing in Gastrin-CreERT2 mice demonstrated a similar lifespan for gastrin-producing cells, confirming that gastric endocrine cells are long-lived. Finally, treatment of Ascl1-CreERT2; Rosa26-LSL-tdTomato mice with the pan-Notch inhibitor dibenzazepine increased the number of lineage-labeled cells in the gastric antrum, suggesting that Notch signaling normally inhibits Ascl1 expression. Notch regulation of Ascl1 was also demonstrated in a genetic mouse model of Notch activation, as well as Notch-manipulated antral organoid cultures, thus suggesting that ASCL1 is a key downstream Notch pathway effector promoting endocrine cell differentiation in the gastric epithelium.NEW & NOTEWORTHY Although Notch signaling is known to regulate cellular differentiation in the stomach, downstream effectors are poorly described. Here we demonstrate that the bHLH transcription factor ASCL1 is expressed in endocrine cells in the stomach and is required for formation of neurogenin-3-dependent enteroendocrine cells but not enterochromaffin-like cells. We also demonstrate that Ascl1 expression is inhibited by Notch signaling, suggesting that ASCL1 is a Notch-regulated transcriptional effector directing enteroendocrine cell fate in the mouse stomach.

Gastric epithelial stem cells in development, homeostasis and regeneration

The stem/progenitor cell pool is indispensable for the development, homeostasis and regeneration of the gastric epithelium, owing to its defining ability to self-renew whilst supplying the various functional epithelial lineages needed to digest food efficiently. A detailed understanding of the intricacies and complexities surrounding the behaviours and roles of these stem cells offers insights, not only into the physiology of gastric epithelial development and maintenance, but also into the pathological consequences following aberrations in stem cell regulation. Here, we provide an insightful synthesis of the existing knowledge on gastric epithelial stem cell biology, including the in vitro and in vivo experimental techniques that have advanced such studies. We highlight the contributions of stem/progenitor cells towards patterning the developing stomach, specification of the differentiated cell lineages and maintenance of the mature epithelium during homeostasis and following injury. Finally, we discuss gaps in our understanding and identify key research areas for future work.

Time-resolved transcriptomics of mouse gastric pit cells during postnatal development reveals features distinct from whole stomach development

Whole-organ transcriptomic analyses have emerged as a common method for characterizing developmental transitions in mammalian organs. However, it is unclear if all cell types in an organ follow the whole-organ defined developmental trajectory. Recently, a postnatal two-stage developmental process was described for the mouse stomach. Here, using laser capture microdissection to obtain in situ transcriptomic data, we show that mouse gastric pit cells exhibit four postnatal developmental stages. Interestingly, early stages are characterized by the up-regulation of genes associated with metabolism, a functionality not typically associated with pit cells. Hence, beyond revealing that not all constituent cells develop according to the whole-organ determined pathway, these results broaden our understanding of the pit cell phenotypic landscape during stomach development.

Regulation of Parietal Cell Homeostasis by Bone Morphogenetic Protein Signaling

Background and Aims

Loss of bone morphogenetic protein (BMP) signaling in the stomach, achieved by transgenic expression of the BMP inhibitor noggin (H + /K + -Nog mice), causes parietal cell (PC) loss, spasmolytic polypeptide-expressing metaplasia, a marker of preneoplasia, and activation of cell proliferation. We examined if specific inhibition of BMP signaling in PCs leads to aberrations in epithelial homeostasis.

Methods

Mice with floxed alleles of BMP receptor 1a (Bmpr1a flox/flox mice) were crossed to H + /K + -Cre mice to generate H + /K + -Cre;Bmpr1a flox/flox mice. Morphology of the mucosa was analyzed by hematoxylin and eosin staining. Distribution of H+/K+-ATPase-, IF-, and Ki-67-positive cells was analyzed by immunostaining. Expression of pit and neck cell mucins was determined by staining with the lectins Ulex Europaeus Agglutinin 1 and Griffonia (Bandeiraea) simplicifolia lectin II, respectively. Isolation of PCs from control and Nog-expressing mice was achieved by crossing H + /K + -Nog mice to Rosa26-tdTomato (Tom) mice to generate H + /K + -Nog;Rosa26-tdTom mice. H + /K + -Cre mice were then crossed to H + /K + -Nog;Rosa26-tdTom mice to generate H + /K + -Cre;H + /K + -Nog;Rosa26-tdTom mice. Tom-labeled PCs were purified by flow cytometry. Changes in PC transcripts were measured by RNA-Seq.

Results

Six-month-old H + /K + -Cre;Bmpr1a flox/flox mice exhibited increased epithelial cell proliferation, presence of transitional cells showing colocalization of IF with both Griffonia (Bandeiraea) simplicifolia lectin II-binding mucins and the H+/K+-ATPase, and expansion of Ulex Europaeus Agglutinin 1-positive cells. PC transcripts from Nog-expressing mice demonstrated induction of markers of Spasmolytic Polypeptide-Expressing Metaplasia.

Conclusion

PC-specific loss of BMP signaling alters the homeostasis of the gastric epithelium leading to the development of metaplasia.

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

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

Histomorphological, ultrastructural and morphometrical age-related changes of fundic region of New Zealand rabbits (Oryctolagus cuniculus)

This study investigated the histomorphological, ultrastructural and morphometrical postnatal developmental changes in the rabbit fundic region, especially during changing of the feeding intake. Seventy-two New Zealand rabbits (V-Line breed) at the ages of 1, 7, 15, 23, 30 and 60 days were obtained for light and electron microscopy and morphometric studies of the fundic region. The newborn rabbit's fundic wall was thin and organized into mucosa, submucosa, musclosa and serosa, with a significant increase in thickness with ageing. The fundic glands were few at the first week of life, then increased in length and diameter compared to the preceding age with prominent zonation at 23 days. The gastric pits appeared wide and deep at the first week of life then became typically narrow and shallow at the third week. The mucous cells were the main cell types lining the fundic glands in the first week of life. These cells showed remoulding with a marked increase in Periodic Acid-Schiff reactivity with age. Parietal cells were differentiated earlier (on the first day of life) than the chief cells and distributed at the neck and basal zones. Chief cells differentiated at 15 days old at the base of the glands, followed by an increase in the number and activity. Few active enteroendocrine cells were first seen at 15 days old and then widely distributed throughout the glands. Conclusion: Pronounced histomorphological changes in the fundic mucosal layer, especially the surface and glandular epithelium, correlate with the postnatal rabbit-feeding intake changes.

Delta-like 1-Expressing Cells at the Gland Base Promote Proliferation of Gastric Antral Stem Cells in Mouse

BACKGROUND & AIMS

Notch pathway signaling maintains gastric epithelial cell homeostasis by regulating stem cell proliferation and differentiation. We previously identified NOTCH1 and NOTCH2 as the key Notch receptors controlling gastric stem cell function. Here, we identify the niche cells and critical Notch ligand responsible for regulating stem cell proliferation in the distal mouse stomach.

METHODS

Expression of Notch ligands in the gastric antrum was determined by quantitative reverse-transcriptase polymerase chain reaction and cellular localization was determined by in situ hybridization and immunostaining. The contribution of specific Notch ligands to regulate epithelial cell proliferation in adult mice was determined by inducible gene deletion, or by pharmacologic inhibition using antibodies directed against specific Notch ligands. Mouse gastric organoid cultures were used to confirm that Notch ligand signaling was epithelial specific.

RESULTS

Delta-like 1 (DLL1) and Jagged 1 (JAG1) were the most abundantly expressed Notch ligands in the adult mouse stomach, with DLL1 restricted to the antral gland base and JAG1 localized to the upper gland region. Inhibition of DLL1 alone or in combination with other Notch ligands significantly reduced epithelial cell proliferation and the growth of gastric antral organoids, while inhibition of the other Notch ligands, DLL4, JAG1, and JAG2, did not affect proliferation or organoid growth. Similarly, DLL1, and not DLL4, regulated proliferation of LGR5+ antral stem cells, which express the NOTCH1 receptor.

CONCLUSIONS

DLL1 is the key Notch ligand regulating epithelial cell proliferation in the gastric antrum. We propose that DLL1-expressing cells at the gland base are Notch niche cells that signal to adjacent LGR5+ antral stem cells to regulate stem cell proliferation and epithelial homeostasis.

Shaped by the epithelium - postnatal immune mechanisms of oral homeostasis

The first encounter of mucosal barriers with the microbiota initiates host-microbiota feedback loops instructing the tailored development of both the immune system and microbiota at each mucosal site. Once established, balanced immunological interactions enable symbiotic relationships with the microbiota in adult life. This process has been extensively investigated in the mammalian monolayer epithelium-covered intestine and lung mucosae; however, the postnatal mechanisms engaged by the oral mucosa to establish homeostasis are currently being discovered. Here, we discuss the early life dialogue between the oral mucosa and the microbiota, with particular emphasis on the central role the multilayer epithelium plays to protect the oral mucosa. These intricate and unique postnatal immunological processes shape oral homeostasis, which can potentially affect buccal and systemic health in adult life.

DDIT4 Licenses Only Healthy Cells to Proliferate During Injury-induced Metaplasia

BACKGROUND AND AIMS

In stomach, metaplasia can arise from differentiated chief cells that become mitotic via paligenosis, a stepwise program. In paligenosis, mitosis initiation requires reactivation of the cellular energy hub mTORC1 after initial mTORC1 suppression by DNA damage induced transcript 4 (DDIT4 aka REDD1). Here, we use DDIT4-deficient mice and human cells to study how metaplasia increases tumorigenesis risk.

METHODS

A tissue microarray of human gastric tissue specimens was analyzed by immunohistochemistry for DDIT4. C57BL/6 mice were administered combinations of intraperitoneal injections of high-dose tamoxifen (TAM) to induce spasmolytic polypeptide-expressing metaplasia (SPEM) and rapamycin to block mTORC1 activity, and N-methyl-N-nitrosourea (MNU) in drinking water to induce spontaneous gastric tumors. Stomachs were analyzed for proliferation, DNA damage, and tumor formation. CRISPR/Cas9-generated DDIT4-/- and control human gastric cells were analyzed for growth in vitro and in xenografts with and without 5-fluorouracil (5-FU) treatment.

RESULTS

DDIT4 was expressed in normal gastric chief cells in mice and humans and decreased as chief cells became metaplastic. Paligenotic Ddit4-/- chief cells maintained constitutively high mTORC1, causing increased mitosis of metaplastic cells despite DNA damage. Lower DDIT4 expression correlated with longer survival of patients with gastric cancer. 5-FU-treated DDIT4-/- human gastric epithelial cells had significantly increased cells entering mitosis despite DNA damage and increased proliferation in vitro and in xenografts. MNU-treated Ddit4-/- mice had increased spontaneous tumorigenesis after multiple rounds of paligenosis induced by TAM.

CONCLUSIONS

During injury-induced metaplastic proliferation, failure of licensing mTORC1 reactivation correlates with increased proliferation of cells harboring DNA damage, as well as increased tumor formation and growth in mice and humans.

HIP1R acts as a tumor suppressor in gastric cancer by promoting cancer cell apoptosis and inhibiting migration and invasion through modulating Akt

Background

Huntingtin‐interacting protein 1‐related (HIP1R) is a multi‐domain gene that exerts many cellular functions including altering T cell–mediated cytotoxicity and controlling intracellular trafficking. However, its clinical significance and function in gastric cancer (GC) have not been described.

Methods

The expression levels of HIP1R were tested by the transcriptional and translational expression analysis and immunohistochemistry (IHC) in matched adjacent non‐tumorous vs tumor tissue specimens. The biological function of HIP1R on apoptosis, migration, and proliferation was evaluated by flow cytometry, Transwell, Cell Counting Kit‐8 (CCK‐8) assays, colony formation assays, and EdU labeling assays, respectively.

Results

We found downregulated HIP1R in GC compared with adjacent non‐tumorous tissue, and HIP1R expression associated with N classification. We further found that the expression of HIP1R could induce apoptosis and inhibit proliferation, migration, invasion of GC cells, possibly through modulating Akt.

Conclusions

Our data indicate that HIP1R may act as a potential diagnostic biomarker and a tumor suppressor gene in GC, potentially representing a novel therapeutic target for future GC treatment.

Gastric Corpus Mucosal Hyperplasia and Neuroendocrine Cell Hyperplasia, but not Spasmolytic Polypeptide-Expressing Metaplasia, Is Prevented by a Gastrin Receptor Antagonist in H+/K+ATPase Beta Subunit Knockout Mice

Proton pump inhibitor use is associated with an increased risk of gastric cancer, which may be mediated by hypergastrinemia. Spasmolytic polypeptide-expression metaplasia (SPEM) has been proposed as a precursor of gastric cancer. We have examined the effects of the gastrin receptor antagonist netazepide (NTZ) or vehicle on the gastric corpus mucosa of H⁺/K⁺ATPase beta subunit knockout (KO) and wild-type (WT) mice. The gastric corpus was evaluated by histopathology, immunohistochemistry (IHC), in situ hybridization (ISH) and whole-genome gene expression analysis, focusing on markers of SPEM and neuroendocrine (NE) cells. KO mice had pronounced hypertrophy, intra- and submucosal cysts and extensive expression of SPEM and NE cell markers in the gastric corpus, but not in the antrum. Numerous SPEM-related genes were upregulated in KO mice compared to WT mice. NTZ reduced hypertrophia, cysts, inflammation and NE hyperplasia. However, NTZ neither affected expression of SPEM markers nor of SPEM-related genes. In conclusion, NTZ prevented mucosal hypertrophy, cyst formation and NE cell hyperplasia but did not affect SPEM. The presence of SPEM seems unrelated to the changes caused by hypergastrinemia in this animal model.

Immediate and Late Effects of Early Weaning on Rat Gastric Cell Differentiation

Background: Gastric glands grow and cells reach differentiation at weaning in rats. By considering that early weaning (EW) can affect the timing of development, we aimed to compare molecular and cellular markers of differentiation in pups and adults. Methods: Wistar rats were separated into suckling-control (S) and EW groups at 15 days. Stomachs were collected at 15, 18, and 60 days for RNA and protein extraction, and morphology. Results: After EW, the expression of genes involved in differentiation (Atp4b, Bhlha15 and Pgc) augmented (18 days), and Atp4b and Gif were high at 60 days. EW increased the number of zymogenic cells (ZC) in pups and adults and augmented mucous neck cells only at 18 days, whereas parietal and transition cells (TC) were unchanged. Conclusions: EW affected the gastric mucosa mostly in a transient manner as the changes in gene expression and distribution of differentiated cells that were detected in pups were not fully maintained in adults, except for the size of ZC population. We concluded that though most of EW effects were immediate, such nutritional change in the infancy might affect part of gastric digestive functions in a permanent manner, as some markers were kept unbalanced in the adulthood.

Notch and mTOR Signaling Pathways Promote Human Gastric Cancer Cell Proliferation

Notch pathway signaling is known to promote gastric stem cell proliferation, and constitutive pathway activation induces gastric tumors via mTORC1 activation in mouse genetic models. The purpose of this study was to determine whether human gastric adenocarcinomas are similarly dependent on Notch and mTORC1 signaling for growth. Gene expression profiling of 415 human gastric adenocarcinomas in The Cancer Genome Atlas, and a small set of locally obtained gastric cancers showed enhanced expression of Notch pathway components, including Notch ligands, receptors and downstream target genes. Human gastric adenocarcinoma tissues and chemically induced mouse gastric tumors both exhibited heightened Notch and mTORC1 pathway signaling activity, as evidenced by increased expression of the NOTCH1 receptor signaling fragment NICD, the Notch target HES1, and the mTORC1 target phosphorylated S6 ribosomal protein. Pharmacologic inhibition of either Notch or mTORC1 signaling reduced growth of human gastric cancer cell lines, with combined pathway inhibition causing a further reduction in growth, suggesting that both pathways are activated to promote gastric cancer cell proliferation. Further, mTORC1 signaling was reduced after Notch inhibition suggesting that mTOR is downstream of Notch in gastric cancer cells. Analysis of human gastric organoids derived from paired control and gastric cancer tissues also exhibited reduced growth in culture after Notch or mTOR inhibition. Thus, our studies demonstrate that Notch and mTOR signaling pathways are commonly activated in human gastric cancer to promote cellular proliferation. Targeting these pathways in combination might be an effective therapeutic strategy for gastric cancer treatment.

Plasticity of differentiated cells in wound repair and tumorigenesis, part I: stomach and pancreas

For the last century or so, the mature, differentiated cells throughout the body have been regarded as largely inert with respect to their regenerative potential, yet recent research shows that they can become progenitor-like and re-enter the cell cycle. Indeed, we recently proposed that mature cells can become regenerative via a conserved set of molecular mechanisms ('paligenosis'), suggesting that a program for regeneration exists alongside programs for death (apoptosis) and division (mitosis). In two Reviews describing how emerging concepts of cellular plasticity are changing how the field views regeneration and tumorigenesis, we present the commonalities in the molecular and cellular features of plasticity at homeostasis and in response to injury in multiple organs. Here, in part 1, we discuss these advances in the stomach and pancreas. Understanding the extent of cell plasticity and uncovering its underlying mechanisms may help us refine important theories about the origin and progression of cancer, such as the cancer stem cell model, as well as the multi-hit model of tumorigenesis. Ultimately, we hope that the new concepts and perspectives on inherent cellular programs for regeneration and plasticity may open novel avenues for treating or preventing cancers.

Neonatal- maternal separation primes zymogenic cells in the rat gastric mucosa through glucocorticoid receptor activity

Neonatal- Maternal Separation (NMS) deprives mammals from breastfeeding and maternal care, influencing growth during suckling- weaning transition. In the gastric mucosa, Mist1 (encoded by Bhlha15 gene) and moesin organize the secretory apparatus for pepsinogen C in zymogenic cells. Our current hypothesis was that NMS would change corticosterone activity through receptors (GR), which would modify molecules involved in zymogenic cell differentiation in rats. We found that NMS increased corticosterone levels from 18 days onwards, as GR decreased in the gastric mucosa. However, as nuclear GR was detected, we investigated receptor binding to responsive elements (GRE) and observed an augment in NMS groups. Next, we demonstrated that NMS increased zymogenic population (18 and and 30 days), and targeted Mist1 and moesin. Finally, we searched for evolutionarily conserved sequences that contained GRE in genes involved in pepsinogen C secretion, and found that the genomic regions of Bhlha15 and PgC contained sites highly likely to be responsive to glucocorticoids. We suggest that NMS triggers GR- GRE to enhance the expression and to prime genes that organize cellular architecture in zymogenic population for PgC function. As pepsinogen C- pepsin is essential for digestion, disturbance of parenting through NMS might alter functions of gastric mucosa in a permanent manner.

Expression of the Fatty Acid Receptors GPR84 and GPR120 and Cytodifferentiation of Epithelial Cells in the Gastric Mucosa of Mouse Pups in the Course of Dietary Transition

During weaning, the ingested food of mouse pups changes from exclusively milk to solid food. In contrast to the protein- and carbohydrate-rich solid food, high fat milk is characterized primarily by fatty acids of medium chain length particularly important for the suckling pups. Therefore, it seems conceivable that the stomach mucosa may be specialized for detecting these important nutrients during the suckling phase. Here, we analyzed the expression of the G protein coupled receptors GPR84 and GPR120 (FFAR4), which are considered to be receptors for medium and long chain fatty acids (LCFAs), respectively. We found that the mRNA levels for GPR84 and GPR120 were high during the suckling period and progressively decreased in the course of weaning. Visualization of the receptor-expressing cells in 2-week-old mice revealed a high number of labeled cells, which reside in the apical as well as in the basal region of the gastric glands. At the base of the gastric glands, all GPR84-immunoreactive cells and some of the GPR120-positive cells also expressed chromogranin A (CgA), suggesting that they are enteroendocrine cells. We demonstrate that the majority of the CgA/GPR84 cells are X/A-like ghrelin cells. The high degree of overlap between ghrelin and GPR84 decreased post-weaning, whereas the overlap between ghrelin and GPR120 increased. At the apical region of the glands the fatty acid receptors were mainly expressed in unique cell types. These contain lipid-filled vacuole- and vesicle-like structures and may have absorptive functions. We detected decreased immunoreactivity for GPR84 and no lipid droplets in surface cells post-weaning. In conclusion, expression of GPR84 in ghrelin cells as well as in surface cells suggests an important role of medium chain fatty acids (MCFAs) in the developing gastric mucosa of suckling mice.

Notch1 and Notch2 receptors regulate mouse and human gastric antral epithelial cell homoeostasis

OBJECTIVE

We tested the ability of Notch pathway receptors Notch1 and Notch2 to regulate stem and epithelial cell homoeostasis in mouse and human gastric antral tissue.

DESIGN

Mice were treated with the pan-Notch inhibitor dibenzazepine (DBZ) or inhibitory antibodies targeting Notch1 and/or Notch2. Epithelial proliferation, apoptosis and cellular differentiation were measured by histological and molecular approaches. Organoids were established from mouse and human antral glands; growth and differentiation were measured after treatment with Notch inhibitors.

RESULTS

Notch1 and Notch2 are the predominant Notch receptors expressed in mouse and human antral tissue and organoid cultures. Combined inhibition of Notch1 and Notch2 in adult mice led to decreased epithelial cell proliferation, including reduced proliferation of LGR5 stem cells, and increased apoptosis, similar to the response to global Notch inhibition with DBZ. Less pronounced effects were observed after inhibition of individual receptors. Notch pathway inhibition with DBZ or combined inhibition of Notch1 and Notch2 led to increased differentiation of all gastric antral lineages, with remodelling of cells to express secretory products normally associated with other regions of the GI tract, including intestine. Analysis of mouse and human organoids showed that Notch signalling through Notch1 and Notch2 is intrinsic to the epithelium and required for organoid growth.

CONCLUSIONS

Notch signalling is required to maintain gastric antral stem cells. Notch1 and Notch2 are the primary Notch receptors regulating epithelial cell homoeostasis in mouse and human stomach.

Corticosterone activity during early weaning reprograms molecular markers in rat gastric secretory cells

Gastric epithelial cells differentiate throughout the third postnatal week in rats, and become completely functional by weaning time. When suckling is interrupted by early weaning (EW), cell proliferation and differentiation change in the gastric mucosa, and regulatory mechanisms might involve corticosterone activity. Here we used EW and RU486 (glucocorticoid receptor antagonist) to investigate the roles of corticosterone on differentiation of mucous neck (MNC) and zymogenic cells (ZC) in rats, and to evaluate whether effects persisted in young adults. MNC give rise to ZC, and mucin 6, Mist1, pepsinogen a5 and pepsinogen C are produced to characterize these cells. We found that in pups, EW augmented the expression of mucins, Mist1 and pepsinogen C at mRNA and protein levels, and it changed the number of MNC and ZC. Corticosterone regulated pepsinogen C expression, and MNC and ZC distributions. Further, the changes on MNC population and pepsinogen C were maintained until early- adult life. Therefore, by using EW as a model for altered corticosterone activity in rats, we demonstrated that the differentiation of secretory epithelial cells is sensitive to the type of nutrient in the lumen. Moreover, this environmental perception activates corticosterone to change maturation and reprogram cellular functions in adulthood.

Targeted Apoptosis of Parietal Cells Is Insufficient to Induce Metaplasia in Stomach

Parietal cell atrophy is considered to cause metaplasia in the stomach. We developed mice that express the diphtheria toxin receptor specifically in parietal cells to induce their death, and found this to increase proliferation in the normal stem cell zone and neck but not to cause metaplastic reprogramming of chief cells. Furthermore, the metaplasia-inducing agents tamoxifen or DMP-777 still induced metaplasia even after previous destruction of parietal cells by diphtheria toxin. Atrophy of parietal cells alone therefore is not sufficient to induce metaplasia: completion of metaplastic reprogramming of chief cells requires mechanisms beyond parietal cell injury or death.

NOTCH1 and NOTCH2 regulate epithelial cell proliferation in mouse and human gastric corpus

The Notch signaling pathway is known to regulate stem cells and epithelial cell homeostasis in gastrointestinal tissues; however, Notch function in the corpus region of the stomach is poorly understood. In this study we examined the consequences of Notch inhibition and activation on cellular proliferation and differentiation and defined the specific Notch receptors functioning in the mouse and human corpus. Notch pathway activity was observed in the mouse corpus epithelium, and gene expression analysis revealed NOTCH1 and NOTCH2 to be the predominant Notch receptors in both mouse and human. Global Notch inhibition for 5 days reduced progenitor cell proliferation in the mouse corpus, as well as in organoids derived from mouse and human corpus tissue. Proliferation effects were mediated through both NOTCH1 and NOTCH2 receptors, as demonstrated by targeting each receptor alone or in combination with Notch receptor inhibitory antibodies. Analysis of differentiation by marker expression showed no change to the major cell lineages; however, there was a modest increase in the number of transitional cells coexpressing markers of mucous neck and chief cells. In contrast to reduced proliferation after pathway inhibition, Notch activation in the adult stomach resulted in increased proliferation coupled with reduced differentiation. These findings suggest that NOTCH1 and NOTCH2 signaling promotes progenitor cell proliferation in the mouse and human gastric corpus, which is consistent with previously defined roles for Notch in promoting stem and progenitor cell proliferation in the intestine and antral stomach.

NEW & NOTEWORTHY

Here we demonstrate that the Notch signaling pathway is essential for proliferation of stem cells in the mouse and human gastric corpus. We identify NOTCH1 and NOTCH2 as the predominant Notch receptors expressed in both mouse and human corpus and show that both receptors are required for corpus stem cell proliferation. We show that chronic Notch activation in corpus stem cells induces hyperproliferation and tissue hypertrophy, suggesting that Notch may drive gastric tumorigenesis.

Wnt/β-catenin promotes gastric fundus specification in mice and humans

Despite the global prevalence of gastric disease, there are few adequate models in which to study the fundus epithelium of the human stomach. We differentiated human pluripotent stem cells (hPSCs) into gastric organoids containing fundic epithelium by first identifying and then recapitulating key events in embryonic fundus development. We found that disruption of Wnt/β-catenin signalling in mouse embryos led to conversion of fundic to antral epithelium, and that β-catenin activation in hPSC-derived foregut progenitors promoted the development of human fundic-type gastric organoids (hFGOs). We then used hFGOs to identify temporally distinct roles for multiple signalling pathways in epithelial morphogenesis and differentiation of fundic cell types, including chief cells and functional parietal cells. hFGOs are a powerful model for studying the development of the human fundus and the molecular bases of human gastric physiology and pathophysiology, and also represent a new platform for drug discovery.

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.

Stomach development, stem cells and disease

The stomach, an organ derived from foregut endoderm, secretes acid and enzymes and plays a key role in digestion. During development, mesenchymal-epithelial interactions drive stomach specification, patterning, differentiation and growth through selected signaling pathways and transcription factors. After birth, the gastric epithelium is maintained by the activity of stem cells. Developmental signals are aberrantly activated and stem cell functions are disrupted in gastric cancer and other disorders. Therefore, a better understanding of stomach development and stem cells can inform approaches to treating these conditions. This Review highlights the molecular mechanisms of stomach development and discusses recent findings regarding stomach stem cells and organoid cultures, and their roles in investigating disease mechanisms.

Notch regulation of gastrointestinal stem cells

The gastrointestinal (GI) tract epithelium is continuously replenished by actively cycling stem and progenitor cells. These cell compartments are regulated to balance proliferation and stem cell renewal with differentiation into the various mature cell types to maintain tissue homeostasis. In this topical review we focus on the role of the Notch signalling pathway to regulate GI stem cell function in adult small intestine and stomach. We first present the current view of stem and progenitor cell populations in these tissues and then summarize the studies that have established the Notch pathway as a key regulator of gastric and intestinal stem cell function. Notch signalling has been shown to be a niche factor required for maintenance of GI stem cells in both tissues. In addition, Notch has been described to regulate epithelial cell differentiation. Recent studies have revealed key similarities and differences in how Notch regulates stem cell function in the stomach compared to intestine. We summarize the literature regarding Notch regulation of GI stem cell proliferation and differentiation, highlighting tissue-specific functions to compare and contrast Notch in the stomach and intestine.

Stomach Organ and Cell Lineage Differentiation: from Embryogenesis to Adult Homeostasis

Gastric diseases cause considerable worldwide burden. However, the stomach is still poorly understood in terms of the molecular-cellular processes that govern its development and homeostasis. In particular, the complex relationship between the differentiated cell types located within the stomach and the stem and progenitor cells that give rise to them is significantly understudied relative to other organs. In this review, we will highlight the current state of the literature relating to specification of gastric cell lineages from embryogenesis to adulthood. Special emphasis is placed on substantial gaps in knowledge about stomach specification that we think should be tackled to advance the field. For example, it has long been assumed that adult gastric units have a granule-free stem cell that gives rise to all differentiated lineages. Here we will point out that there are also other models that fit all extant data, such as long-lived lineage-committed progenitors that might serve as a source of new cells during homeostasis.

Ghrelin and GHS-R in the rat gastric mucosa: Are they involved in regulation of growth during early weaning?

OBJECTIVES

Based on previous evidence showing that early weaning disturbs the ontogenesis of rat gastric glands, which are the major site of ghrelin synthesis, we investigated the distribution of ghrelin and its receptor (GHS-R) in the rat gastric epithelium during postnatal development and evaluated the effects of early weaning on their levels. Additionally, we studied the contribution of ghrelin to gastric growth during the abrupt nutrient transition.

METHODS

Wistar rats were submitted to early weaning at 15 d and suckling counterparts were taken as controls.

RESULTS

By running quantitative reverse transcription polymerase chain reaction, immunoblots, and immunohistochemistry, we detected a variation of ghrelin levels and an increase of expression and number of immunolabeled cells, 3 d after treatment (P < 0.05). Through confocal microscopy, we identified GHS-R in the neck region of the gland and did not observe changes in protein levels. Growth was evaluated after ghrelin antagonist ([D-Lys-3]-GHRP-6) administration, which reduced DNA synthesis index in early-weaned rats (P < 0.05) as determined by bromodeoxyuridine incorporation.

CONCLUSION

The present study demonstrated that ghrelin and GHS-R are distributed in gastric mucosa during the postnatal development, indicating that they can signal and function in epithelial cells. We concluded that early weaning increased ghrelin levels in the stomach, and it takes part of cell proliferation control that is essential for stomach growth. Therefore, among the many effects previously described for early weaning, this abrupt nutrient transition also changed ghrelin levels, which might represent an additional element in the complex mechanism that coordinates stomach development.

Notch signaling regulates gastric antral LGR5 stem cell function

The major signaling pathways regulating gastric stem cells are unknown. Here we report that Notch signaling is essential for homeostasis of LGR5(+) antral stem cells. Pathway inhibition reduced proliferation of gastric stem and progenitor cells, while activation increased proliferation. Notch dysregulation also altered differentiation, with inhibition inducing mucous and endocrine cell differentiation while activation reduced differentiation. Analysis of gastric organoids demonstrated that Notch signaling was intrinsic to the epithelium and regulated growth. Furthermore, in vivo Notch manipulation affected the efficiency of organoid initiation from glands and single Lgr5-GFP stem cells, suggesting regulation of stem cell function. Strikingly, constitutive Notch activation in LGR5(+) stem cells induced tissue expansion via antral gland fission. Lineage tracing using a multi-colored reporter demonstrated that Notch-activated stem cells rapidly generate monoclonal glands, suggesting a competitive advantage over unmanipulated stem cells. Notch activation was associated with increased mTOR signaling, and mTORC1 inhibition normalized NICD-induced increases in proliferation and gland fission. Chronic Notch activation induced undifferentiated, hyper-proliferative polyps, suggesting that aberrant activation of Notch in gastric stem cells may contribute to gastric tumorigenesis.

Reserve stem cells: Differentiated cells reprogram to fuel repair, metaplasia, and neoplasia in the adult gastrointestinal tract

It has long been known that differentiated cells can switch fates, especially in vitro, but only recently has there been a critical mass of publications describing the mechanisms adult, postmitotic cells use in vivo to reverse their differentiation state. We propose that this sort of cellular reprogramming is a fundamental cellular process akin to apoptosis or mitosis. Because reprogramming can invoke regenerative cells from mature cells, it is critical to the long-term maintenance of tissues like the pancreas, which encounter large insults during adulthood but lack constitutively active adult stem cells to repair the damage. However, even in tissues with adult stem cells, like the stomach and intestine, reprogramming may allow mature cells to serve as reserve ("quiescent") stem cells when normal stem cells are compromised. We propose that the potential downside to reprogramming is that it increases risk for cancers that occur late in adulthood. Mature, long-lived cells may have years of exposure to mutagens. Mutations that affect the physiological function of differentiated, postmitotic cells may lead to apoptosis, but mutations in genes that govern proliferation might not be selected against. Hence, reprogramming with reentry into the cell cycle might unmask those mutations, causing an irreversible progenitor-like, proliferative state. We review recent evidence showing that reprogramming fuels irreversible metaplastic and precancerous proliferation in the stomach and pancreas. Finally, we illustrate how we think reprogrammed differentiated cells are likely candidates as cells of origin for cancers of the intestine.

Heterogeneity in mouse spasmolytic polypeptide-expressing metaplasia lineages identifies markers of metaplastic progression

OBJECTIVES

Spasmolytic polypeptide-expressing metaplasia (SPEM) develops as a preneoplastic lesion in the stomachs of mice and humans after parietal cell loss. To identify the commonalities and differences between phenotypic SPEM lineages, SPEM were studied from three different mouse models of parietal cell loss: with chronic inflammation with Helicobacter felis infection; with acute inflammation with L635 treatment; and without inflammation following DMP-777 treatment.

DESIGN

RNA transcripts from laser capture microdissected normal chief cells and SPEM lineages were compared using gene microarray. Alterations in transcripts were validated by quantitative real-time PCR. Clusterin and cystic fibrosis transmembrane conductance regulator (CFTR) were selected for immunohistochemical analysis in all mouse models as well as in human SPEM, intestinal metaplasia and gastric cancer.

RESULTS

Transcript expression patterns demonstrated differences among the phenotypic SPEM models. Clusterin expression was significantly upregulated in all three mouse SPEM models as well as in human SPEM. The highest clusterin expression in human gastric cancers correlated with poor survival. Conversely, CFTR expression was upregulated only in SPEM with inflammation in mice. In humans, intestinal metaplasia, but not SPEM, expressed CFTR.

CONCLUSIONS

While markers such as clusterin are expressed in all phenotypic SPEM lineages, distinct patterns of upregulated genes including CFTR are present in murine metaplasia associated with inflammation, indicative of progression of metaplasia towards a more intestinalised metaplastic phenotype.

Reciprocal expression of the endocytic protein HIP1R and its repressor FOXP1 predicts outcome in R-CHOP-treated diffuse large B-cell lymphoma patients

We previously identified autoantibodies to the endocytic-associated protein Huntingtin-interacting protein 1-related (HIP1R) in diffuse large B-cell lymphoma (DLBCL) patients. HIP1R regulates internalization of cell surface receptors via endocytosis, a process relevant to many therapeutic strategies including CD20 targeting with rituximab. In this study, we characterized HIP1R expression patterns, investigated a mechanism of transcriptional regulation and its clinical relevance in DLBCL patients treated with immunochemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone, R-CHOP). HIP1R was preferentially expressed in germinal center B-cell-like DLBCL (P<0.0001) and inversely correlated with the activated B-cell-like DLBCL (ABC-DLBCL) associated transcription factor, Forkhead box P1 (FOXP1). HIP1R was confirmed as a direct FOXP1 target gene in ABC-DLBCL by FOXP1-targeted silencing and chromatin immunoprecipitation. Lower HIP1R protein expression (≤ 10% tumoral positivity) significantly correlated with inferior overall survival (OS, P=0.0003) and progression-free survival (PFS, P=0.0148) in R-CHOP-treated DLBCL patients (n=157). Reciprocal expression with ≥ 70% FOXP1 positivity defined FOXP1(hi)/HIP1R(lo) patients with particularly poor outcome (OS, P=0.0001; PFS, P=0.0016). In an independent R-CHOP-treated DLBCL (n=233) microarray data set, patients with transcript expression in lower quartile HIP1R and FOXP1(hi)/HIP1R(lo) subgroups exhibited worse OS, P=0.0044 and P=0.0004, respectively. HIP1R repression by FOXP1 is strongly associated with poor outcome, thus further understanding of FOXP1-HIP1R and/or endocytic signaling pathways might give rise to novel therapeutic options for DLBCL.

MAPKs and signal transduction in the control of gastrointestinal epithelial cell proliferation and differentiation

Mitogen-activated protein kinase (MAPK) pathways are activated by several stimuli and transduce the signal inside cells, generating diverse responses including cell proliferation, differentiation, migration and apoptosis. Each MAPK cascade comprises a series of molecules, and regulation takes place at different levels. They communicate with each other and with additional pathways, creating a signaling network that is important for cell fate determination. In this review, we focus on ERK, JNK, p38 and ERK5, the major MAPKs, and their interactions with PI3K-Akt, TGFβ/Smad and Wnt/β-catenin pathways. More importantly, we describe how MAPKs regulate cell proliferation and differentiation in the rapidly renewing epithelia that lines the gastrointestinal tract and, finally, we highlight the recent findings on nutritional aspects that affect MAPK transduction cascades.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Lack of cholinergic innervation in gastric mucosa does not affect gastrin secretion or basal acid output in neurturin receptor GFRα2 deficient mice

Efferent signals from the vagus nerve are thought to mediate both basal and meal-induced gastric acid secretion, and provide trophic support of the mucosa. However, the underlying mechanisms are incompletely understood. Neurturin, signalling via glial cell line-derived neurotrophic factor (GDNF)-family receptor α2 (GFRα2), is essential for parasympathetic innervation of many target tissues but its role in gastric innervation is unknown. Here we show that most nerve fibres in wild-type mouse gastric mucosa, including all positive for gastrin-releasing peptide, are cholinergic. GFRα2-deficient (KO) mice lacked virtually all cholinergic nerve fibres and associated glial cells in the gastric (oxyntic and pyloric) mucosa but not in the smooth muscle, consistent with the selective expression of neurturin mRNA in the gastric mucosa. 2-Deoxyglucose and hexamethonium failed to affect acid secretion in the GFRα2-KO mice indicating the lack of functional innervation in gastric mucosa. Interestingly, basal and maximal histamine-induced acid secretion did not differ between wild-type and GFRα2-KO mice. Moreover, circulating gastrin levels in both fasted and fed animals, thickness of gastric mucosa, and density of parietal and different endocrine cells were similar. Carbachol-stimulated acid secretion was higher in GFRα2-KO mice, while atropine reduced basal secretion similarly in both genotypes. We conclude that cholinergic innervation of gastric mucosa depends on neurturin-GFRα2 signalling but is dispensable for gastrin secretion and for basal and maximal acid output. Basal acid secretion in the KO mice appears to be, at least partly, facilitated by constitutive activity of muscarinic receptors.

Loss of anterior gradient 2 (Agr2) expression results in hyperplasia and defective lineage maturation in the murine stomach

Recent studies of epithelial tissues have revealed the presence of tissue-specific stem cells that are able to establish multiple cell lineages within an organ. The stem cells give rise to progenitors that replicate before differentiating into specific cell lineages. The mechanism by which homeostasis is established between proliferating stem or progenitor cells and terminally differentiated cells is unclear. This study demonstrates that Agr2 expression by mucous neck cells in the stomach promotes the differentiation of multiple cell lineages while also inhibiting the proliferation of stem or progenitor cells. When Agr2 expression is absent, gastric mucous neck cells increased in number as does the number of proliferating cells. Agr2 expression loss also resulted in the decline of terminally differentiated cells, which was supplanted by cells that exhibited nuclear SOX9 labeling. Sox9 expression has been associated with progenitor and stem cells. Similar effects of the Agr2 null on cell proliferation in the intestine were also observed. Agr2 consequently serves to maintain the balance between proliferating and differentiated epithelial cells.

IFNγ contributes to the development of gastric epithelial cell metaplasia in Huntingtin interacting protein 1 related (Hip1r)-deficient mice

Huntingtin interacting protein 1 related (Hip1r) is an F-actin- and clathrin-binding protein involved in vesicular trafficking that is crucial for parietal cell function and epithelial cell homeostasis in the stomach. Gastric parietal cells in Hip1r-deficient mice are lost by apoptotic cell death, which leads to a progressive epithelial cell derangement, including glandular hypertrophy, zymogenic cell loss and expansion of a metaplastic mucous cell lineage known as spasmolytic polypeptide-expressing metaplasia (SPEM). The epithelial cell changes are associated with infiltration of inflammatory cells. As inflammatory mediators, such as IFNγ, have been shown to contribute to the development of the gastric epithelial cell metaplasia after Helicobacter infection, we tested whether IFNγ played a role in the spontaneous progressive epithelial metaplasia observed in Hip1r-deficient mice. Hip1r-deficient mice were crossed with IFNγ-deficient mice and single- and double-mutant mice were analyzed at 3 and 12 months of age. Histopathology scoring showed that loss of IFNγ tempered the spontaneous development of metaplastic lesions in Hip1r-deficient mice. Loss of IFNγ was observed to abrogate the glandular hypertrophy evident in Hip1r mutant stomach, although increased epithelial cell proliferation and elevated gastrin levels were not affected by the presence or absence of this pro-inflammatory cytokine. An analysis of cell lineage markers in the double-mutant mice demonstrated that IFNγ specifically affected the development of metaplastic mucous cells in the neck region, whereas the parietal cell, surface mucous cell and zymogenic cell alterations remained similar to the histopathology in the Hip1r mutant. Morphometric analysis showed that IFNγ was required for the mucous cell hypertrophy and hyperplasia observed in Hip1r-deficient mice. Together, these findings demonstrate that IFNγ is critical for the development of the gastric epithelial cell metaplasia that results from parietal cell atrophy in the Hip1r-deficient mice.

Deficiency of claudin-18 causes paracellular H+ leakage, up-regulation of interleukin-1β, and atrophic gastritis in mice

BACKGROUND & AIMS

Although defects in tight junction (TJ) epithelial paracellular barrier function are believed to be a primary cause of inflammation, the mechanisms responsible remain largely unknown.

METHODS

We generated knockout mice of stomach-type claudin-18, a major component of TJs in the stomach.

RESULTS

Cldn18(-/-) mice were afflicted with atrophic gastritis that started on postnatal day 3. This coincided with a decrease in intragastric pH due to H(+) secretion from parietal cells and concomitant up-regulation of the cytokines, interleukin-1β, cyclooxygenase-2, and KC, resulting in spasmolytic polypeptide-expressing metaplasia (SPEM). Oral administration of hydrochloric acid on postnatal day 1 induced the expression of these cytokines in Cldn18(-/-) infant stomach, but not in Cldn18(+/+) mice. A paracellular H(+) leak in Cldn18(-/-) stomach was detected by electrophysiology and H(+) titration, and freeze-fracture electron microscopy showed structural defects in the TJs, in which the tightly packed claudin-18 (stomach-type)-based TJ strands were lost, leaving a loose meshwork of strands consisting of other claudin species.

CONCLUSIONS

These findings provide evidence that claudin-18 normally forms a paracellular barrier against H(+) in the stomach and that its deficiency causes paracellular H(+) leak, a persistent up-regulation of proinflammatory cytokines, chronic recruitment of neutrophils, and the subsequent development of SPEM in atrophic gastritis.

Notch signaling modulates proliferation and differentiation of intestinal crypt base columnar stem cells

Notch signaling is known to regulate the proliferation and differentiation of intestinal stem and progenitor cells; however, direct cellular targets and specific functions of Notch signals had not been identified. We show here in mice that Notch directly targets the crypt base columnar (CBC) cell to maintain stem cell activity. Notch inhibition induced rapid CBC cell loss, with reduced proliferation, apoptotic cell death and reduced efficiency of organoid initiation. Furthermore, expression of the CBC stem cell-specific marker Olfm4 was directly dependent on Notch signaling, with transcription activated through RBP-Jκ binding sites in the promoter. Notch inhibition also led to precocious differentiation of epithelial progenitors into secretory cell types, including large numbers of cells that expressed both Paneth and goblet cell markers. Analysis of Notch function in Atoh1-deficient intestine demonstrated that the cellular changes were dependent on Atoh1, whereas Notch regulation of Olfm4 gene expression was Atoh1 independent. Our findings suggest that Notch targets distinct progenitor cell populations to maintain adult intestinal stem cells and to regulate cell fate choice to control epithelial cell homeostasis.

The origin of pre-neoplastic metaplasia in the stomach: chief cells emerge from the Mist

The digestive-enzyme secreting, gastric epithelial chief (zymogenic) cell is remarkable and underappreciated. Here, we discuss how all available evidence suggests that mature chief cells in the adult, mammalian stomach are postmitotic, slowly turning over cells that arise via a relatively long-lived progenitor, the mucous neck cell, The differentiation of chief cells from neck cells does not involve cell division, and the neck cell has its own distinct pattern of gene expression and putative physiological function. Thus, the ontogeny of the normal chief cell lineage exemplifies transdifferentiation. Furthermore, under pathophysiogical loss of acid-secreting parietal cell, the chief cell lineage can itself trasndifferentiate into a mucous cell metaplasia designated Spasmolytic Polypeptide Expressing Metaplasia (SPEM). Especially in the presence of inflammation, this metaplastic lineage can regain proliferative capacity and, in humans may also further differentiate into intestinal metaplasia. The results indicate that gastric fundic lineages display remarkable plasticity in both physiological ontogeny and pathophysiological pre-neoplastic metaplasia.

Gastric tuft cells express DCLK1 and are expanded in hyperplasia

Epithelial tuft cells are named after their characteristic microtubule bundles located at the cell apex where these are exposed to the luminal environment. As such, tuft cells are found in multiple organs, including the gastrointestinal (GI) tract where the apical "tuft" is hypothesized to detect and transmit environmental signals. Thus, the goal of our study was to characterize gastric tuft cells during GI tract development, then subsequently in the normal and metaplastic adult stomach. GI tracts from mouse embryos, and newborn and postnatal mice were analyzed. Tuft cells were identified by immunohistochemistry using acetylated-α-tubulin (acTub) antibody to detect the microtubule bundle. Additional tuft cell markers, e.g., doublecortin-like kinase 1 (DCLK1), were used to co-localize with acTub. Tuft cells were quantified in human gastric tissue arrays and in mouse stomachs with or without inflammation. In the developing intestine, tuft cells in both the crypts and villi expressed all markers by E18.5. In the stomach, acTub co-localized with DCLK1 and other established tuft cell markers by E18.5 in the antrum, but not until postnatal day 7 in the corpus, with the highest density of tuft cells clustered at the forestomach ridge. Tuft cell numbers increased in hyperplastic human and mouse stomachs. In the adult GI tract, the tuft cell marker acTub co-expressed with DCKL1 and chemosensory markers, e.g.,TRPM5. In summary, tuft cells appear in the gastric antrum and intestine at E18.5, but their maximal numbers in the corpus are not achieved until after weaning. Tuft cell numbers increase with inflammation, hyperplasia, and metaplasia.