Exocytotic proteins in enterochromaffin-like (ECL) cells of the rat stomach

Tissue distribution of cysteine string protein/DNAJC5 in C. elegans analysed by CRISPR/Cas9-mediated tagging of endogenous DNJ-14

Cysteine string protein (CSP) is a member of the DnaJ/Hsp40 family of molecular chaperones. CSP is enriched in neurons, where it mainly localises to synaptic vesicles. Mutations in CSP-encoding genes in flies, worms, mice and humans result in neuronal dysfunction, neurodegeneration and reduced lifespan. Most attention has therefore focused on CSP's neuronal functions, although CSP is also expressed in non-neuronal cells. Here, we used genome editing to fluorescently tag the Caenorhabditis elegans CSP orthologue, dnj-14, to identify which tissues preferentially express CSP and hence may contribute to the observed mutant phenotypes. Replacement of dnj-14 with wrmScarlet caused a strong chemotaxis defect, as seen with other dnj-14 null mutants. In contrast, inserting the reporter in-frame to create a DNJ-14-wrmScarlet fusion protein had no effect on chemotaxis, indicating that C-terminal tagging does not impair DNJ-14 function. WrmScarlet fluorescence appeared most obvious in the intestine, head/pharynx, spermathecae and vulva/uterus in the reporter strains, suggesting that DNJ-14 is preferentially expressed in these tissues. Crossing the DNJ-14-wrmScarlet strain with GFP marker strains confirmed the intestinal and pharyngeal expression, but only a partial overlap with neuronal GFP was observed. DNJ-14-wrmScarlet fluorescence in the intestine was increased in response to starvation, which may be relevant to mammalian CSPα's role in microautophagy. DNJ-14's enrichment in worm reproductive tissues (spermathecae and vulva/uterus) parallels the testis-specific expression of CSPβ and CSPγ isoforms in mammals. Furthermore, CSPα messenger RNA is highly expressed in the human proximal digestive tract, suggesting that CSP may have a conserved, but overlooked, function within the gastrointestinal system.

History of key regulatory peptide systems and perspectives for future research

Throughout the 20th Century, regulatory peptide discovery advanced from the identification of gut hormones to the extraction and characterization of hypothalamic hypophysiotropic factors, and to the isolation and cloning of multiple brain neuropeptides. These discoveries were followed by the discovery of G-protein-coupled and other membrane receptors for these peptides. Subsequently, the systems physiology associated with some of these multiple regulatory peptides and receptors has been comprehensively elucidated and has led to improved therapeutics and diagnostics and their approval by the US Food and Drug Administration. In light of this wealth of information and further potential, it is truly a time of renaissance for regulatory peptides. In this perspective, we review what we have learned from the pioneers in exemplified fields of gut peptides, such as cholecystokinin, enterochromaffin-like-cell peptides, and glucagon, from the trailblazing studies on the key stress hormone, corticotropin-releasing factor, as well as from more recently characterized relaxin-family peptides and receptors. The historical viewpoints are based on our understanding of these topics in light of the earliest phases of research and on subsequent studies and the evolution of knowledge, aiming to sharpen our vision of the current state-of-the-art and those studies that should be prioritized in the future.

Neuroendocrine mechanism of gastric acid secretion: Historical perspectives and recent developments in physiology and pharmacology

The physiology of gastric acid secretion is one of the earliest subjects in medical literature and has been continuously studied since 1833. Starting with the notion that neural stimulation alone drives acid secretion, progress in understanding the physiology and pathophysiology of this process has led to the development of therapeutic strategies for patients with acid-related diseases. For instance, understanding the physiology of parietal cells led to the developments of histamine 2 receptor blockers, proton pump inhibitors (PPIs), and recently, potassium-competitive acid blockers. Furthermore, understanding the physiology and pathophysiology of gastrin has led to the development of gastrin/CCK2 receptor (CCK2 R) antagonists. The need for refinement of existing drugs in patients have led to second and third generation drugs with better efficacy at blocking acid secretion. Further understanding of the mechanism of acid secretion by gene targeting in mice has enabled us to dissect the unique role for each regulator to leverage and justify the development of new targeted therapeutics for acid-related disorders. Further research on the mechanism of stimulation of gastric acid secretion and the physiological significances of gastric acidity in gut microbiome is needed in the future.

Histidine decarboxylase and urinary methylimidazoleacetic acid in gastric neuroendocrine cells and tumours

AIM: To study histidine decarboxylase (HDC) expression in normal and neoplastic gastric neuroendocrine cells in relationship to the main histamine metabolite.

METHODS: Control tissues from fundus (n = 3) and corpus (n = 3) mucosa of six patients undergoing operations for gastric adenocarcinoma, biopsy and/or gastric surgical specimens from 64 patients with primary gastric neuroendocrine tumours (GNETs), as well as metastases from 22 of these patients, were investigated using conventional immunohistochemistry and double immunofluorescence with commercial antibodies vs vesicular monoamine transporter 2 (VMAT-2), HDC and ghrelin. The urinary excretion of the main histamine metabolite methylimidazoleacetic acid (U-MeImAA) was determined using high-performance liquid chromatography in 27 of the 64 patients.

RESULTS: In the gastric mucosa of the control tissues, co-localization studies identified neuroendocrine cells that showed immunoreactivity only to VMAT-2 and others with reactivity only to HDC. A third cell population co-expressed both antigens. There was no co-expression of HDC and ghrelin. Similar results were obtained in the foci of neuroendocrine cell hyperplasia associated with chronic atrophic gastritis type A and also in the tumours. The relative incidence of the three aforementioned markers varied in the tumours that were examined using conventional immunohistochemistry. All of these GNETs revealed both VMAT-2 and HDC immunoreactivity, and their metastases showed an immunohistochemical pattern and frequency similar to that of their primary tumours. In four patients, increased U-MeImAA excretion was detected, but only two of the patients exhibited related endocrine symptoms.

CONCLUSION: Human enterochromaffin-like cells appear to partially co-express VMAT-2 and HDC. Co-expression of VMAT-2 and HDC might be required for increased histamine production in patients with GNETs.

Nociceptin/orphanin FQ and stress regulate synaptophysin expression in the rat fundic and colonic mucosa

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the N/OFQ peptide (NOP) receptor, is a neuropeptide regulating gastrointestinal functions. The present study investigated the influence of acute cold-restraint stress and of short- and long-lasting peripheral infusion of N/OFQ on the level of synaptophysin, an exocytotic protein involved in neural plasticity. Exposure to cold-restraint stress for 3h or subcutaneous infusion of N/OFQ, 1 μg/kg/h for 4h, induced a significant increase of the area of synaptophysin-immunoreactive nerve fibers in the fundic mucosa, while prolonged subcutaneous infusion of N/OFQ, 1 μg/kg/h for 52 h and for 14 days, did not modify the synaptophysin-immunostained fibers. In the colonic mucosa stress exposure and subcutaneous infusion of N/OFQ, at any time point considered, had no significant effect on the area of synaptophysin-immunoreactive nerve fibers. Synaptophysin immunoreactive nerve fibers were decreased in knockout rats for the NOP receptor gene both in the fundic and colonic mucosa. Synaptophysin-immunoreactivity was demonstrated in cells located in the basal portion of the fundic mucosa. Our study is the first to show that the N/OFQ/NOP receptor system influences the expression of synaptophysin and hence the process of exocytosis both in nerve terminals and in cells.

CSPα-chaperoning presynaptic proteins

Synaptic transmission relies on precisely regulated and exceedingly fast protein-protein interactions that involve voltage-gated channels, the exocytosis/endocytosis machinery as well as signaling pathways. Although we have gained an ever more detailed picture of synaptic architecture much remains to be learned about how synapses are maintained. Synaptic chaperones are “folding catalysts” that preserve proteostasis by regulating protein conformation (and therefore protein function) and prevent unwanted protein-protein interactions. Failure to maintain synapses is an early hallmark of several degenerative diseases. Cysteine string protein (CSPα) is a presynaptic vesicle protein and molecular chaperone that has a central role in preventing synaptic loss and neurodegeneration. Over the past few years, a number of different “client proteins” have been implicated as CSPα substrates including voltage-dependent ion channels, signaling proteins and proteins critical to the synaptic vesicle cycle. Here we review the ion channels and synaptic protein complexes under the influence of CSPα and discuss gaps in our current knowledge.

New model for gastroenteropancreatic large-cell neuroendocrine carcinoma: establishment of two clinically relevant cell lines

Recently, a novel WHO-classification has been introduced that divided gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN) according to their proliferation index into G1- or G2-neuroendocrine tumors (NET) and poorly differentiated small-cell or large-cell G3-neuroendocrine carcinomas (NEC). Our knowledge on primary NECs of the GEP-system is limited due to the rarity of these tumors and chemotherapeutic concepts of highly aggressive NEC do not provide convincing results. The aim of this study was to establish a reliable cell line model for NEC that could be helpful in identifying novel druggable molecular targets. Cell lines were established from liver (NEC-DUE1) or lymph node metastases (NEC-DUE2) from large cell NECs of the gastroesophageal junction and the large intestine, respectively. Morphological characteristics and expression of neuroendocrine markers were extensively analyzed. Chromosomal aberrations were mapped by array comparative genomic hybridization and DNA profiling was analyzed by DNA fingerprinting. In vitro and in vivo tumorigenicity was evaluated and the sensitivity against chemotherapeutic agents assessed. Both cell lines exhibited typical morphological and molecular features of large cell NEC. In vitro and in vivo experiments demonstrated that both cell lines retained their malignant properties. Whereas NEC-DUE1 and -DUE2 were resistant to chemotherapeutic drugs such as cisplatin, etoposide and oxaliplatin, a high sensitivity to 5-fluorouracil was observed for the NEC-DUE1 cell line. Taken together, we established and characterized the first GEP large-cell NEC cell lines that might serve as a helpful tool not only to understand the biology of these tumors, but also to establish novel targeted therapies in a preclinical setup.

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.

Cysteine-string protein's neuroprotective role

Cysteine-string protein (CSP), a member of the DnaJ/Hsp40 family of cochaperones, is critical for maintaining neurotransmitter release and preventing neurodegeneration. CSP likely forms a chaperone complex on synaptic vesicles together with the 70-kDa heat shock cognate (Hsc70) and the small glutamine-rich tetratricopeptide repeat (TPR)-containing protein (SGT) that may control or protect the assembly and activity of SNARE proteins and various other protein substrates. Here, the author summarizes studies that elucidated CSP's neuroprotective role.

CSPalpha: the neuroprotective J protein

Cysteine string protein (CSPalpha, also called DnaJC5) is unique among J proteins. Similar to other J proteins, CSPalpha interacts with and activates the ATPase of Hsc70s (heat shock proteins of 70 kDa), thereby harnessing the ATPase activity for conformational work on client proteins. In contrast to other J proteins, CSPalpha is anchored to synaptic vesicles, as well as to exocrine, endocrine and neuroendocrine secretory granules, and has been shown to have an essential anti-neurodegenerative role. CSPalpha-null organisms exhibit progressive neurodegeneration, behavioural deficits, and premature death, most likely due to the progressive misfolding of one or more client proteins. Here we highlight recent advances in our understanding of the critical role that CSPalpha plays in governing exocytotic secretory functions.

RDJ2 (DNAJA2) chaperones neural G protein signaling pathways

A number of structurally divergent proteins with J domains, called J proteins, interact with and activate the ATPase of Hsp70s, thereby harnessing the ATPase activity for conformational work on target proteins. The precise role of most mammalian J proteins remains undefined. In this paper, we demonstrate that transient expression of the J protein, Rdj2, in HEK 293 cells increased cellular cyclic adenosine monophosphate (cAMP) levels in the presence of the beta-adrenergic agonist isoproterenol. In CNS-derived catecholaminergic neuronal cell line (CAD) neuroblastoma cells, expression of Rdj2 increased isoproterenol-stimulated phosphorylation of cAMP response element binding protein (CREB). Moreover, we have characterized the binding properties of Rdj2 and observed a direct interaction between Rdj2 and receptor-coupled trimeric GTP-binding proteins (G proteins). We further show that the composition of the Rdj2-chaperone complex and the cysteine string protein (CSPalpha)-chaperone complex, another J protein, is distinct. Our data demonstrate that Rdj2 modulates G protein signaling and further suggest that chaperoning G proteins is an emerging theme of the J protein network.

Immunohistochemical study of enterochromaffin-like cell in human gastric mucosa

Enterochromaffin-like (ECL) cell has been identified as the histamine-containing argyrophil cell in rat gastric mucosa and vigorously studied. However, there are few reports of the distribution of ECL cell in human stomach. The aim of the present study was to determine the precise distribution of ECL cell by immunohistochemical staining of histidine decarboxylase (HDC) and gastrin-cholecystokinin B receptor (CCK-BR) in human stomach, and the correlation between their distribution and that of parietal cells. Thirty specimens of surgically resected stomach were used. Parietal cell, Grimelius-silver-positive cell, gastrin, HDC- and CCK-BR-immunoreactive cell were studied on continuous cell counting in the restricted field along the lamina muscularis from the oral to the anal ends. The percentage of HDC-immunoreactive cells of endocrine cells was smaller (15%) than that of a previous report (35%) in the fundic region. HDC- and CCK-BR-immunoreactive cells were found not only in the fundic region, but also in the intermediate and pyloric regions. In the pyloric region, HDC- and CCK-BR-immunoreactive cells were found mainly in the mucosa with intestinal metaplasia. Double-positive cells were also found, but only in small numbers. This suggests that ECL cell, or a cell sharing its function, is present in the pyloric region.

Characteristics of gastrin controlled ECL cell specific gene expression

BACKGROUND

The ECL cells are histamine-producing endocrine cells in the oxyntic mucosa that synthesize and secrete proteins and peptides. They are the primary target for gastrin and mediate the control of gastrin on acid secretion and oxyntic mucosal growth. Knowledge of the molecular biology of the ECL cell is therefore important for understanding gastric physiology. Accordingly, we wanted to identify genes that are characteristically expressed in the ECL cells and controlled by gastrin.

METHODS

Using Affymetrix GeneChips, RNA expression profiles were generated from ECL cells isolated by counterflow elutriation from hyper- or hypogastrinemic rats. Contamination from non-endocrine cells was eliminated by subtraction of the expression profiles of the fundic and antral mucosa.

RESULTS

The expression of 365 genes was ECL cell characteristic. Gastrin was found to control the expression of 120 which could be divided into two major groups depending on the known or anticipated biological function of the encoded protein: genes encoding proteins involved in the secretory process and genes encoding proteins needed to generate energy for secretion. Interestingly, gastrin stimulation also increased ECL cells expression of anti-apoptotic genes.

CONCLUSION

The ECL cell specific expression profile is reminiscent of that of neurons and other endocrine cells exhibiting high expression of genes encoding proteins involved in the synthesis, storage and secretion of neuropeptides or peptide hormones. Gastrin regulated the expression of one third of these genes and is thus involved in the control of secretion from the ECL cells.

The CSPα/G protein complex in PC12 cells

Cysteine string proteinalpha (CSPalpha) is a regulated vesicle protein and molecular chaperone that has been found to be critical for continuous synaptic transmission and is implicated in the defense against neurodegeneration. Previous work has revealed links between CSPalpha and heterotrimeric GTP binding protein (G protein) signal transduction pathways. We have shown that CSPalpha is a guanine nucleotide exchange factor (GEF) for Galphas. In vitro Hsc70 (70 kDa heat shock cognate protein) and SGT (small glutamine-rich tetratricopeptide repeat domain protein) switch CSPalpha from an inactive GEF to an active GEF. Here we have examined the cellular distribution of the CSPalpha system in the PC12 neuroendocrine cell line. CSPalpha, an established secretory vesicle protein, was found to concentrate in the processes of NGF-differentiated PC12 cells as expected. Gbeta subunits co-localized and Galphas subunits partially co-localized with CSPalpha. However, under the conditions examined, the GEF activity of CSPalpha is expected to be inactive, in that Hsc70 was not found in PC12 processes. These results indicate that CSPalpha activity is subject to regulation by factors that alter Hsc70 distribution and translocation within the cell.

The cysteine string protein multimeric complex

Cysteine string protein (CSPalpha) is a member of the cellular folding machinery that is located on regulated secretory vesicles. We have previously shown that CSPalpha in association with Hsc70 (70kDa heat shock cognate protein) and SGT (small glutamine-rich tetratricopeptide repeat domain protein) is a guanine nucleotide exchange factor (GEF) for G(alphas). Association of this CSPalpha complex with N-type calcium channels, a channel key in coupling calcium influx with synaptic vesicle exocytosis, triggers tonic G protein inhibition of the channels. Syntaxin 1A, a plasma membrane SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) critical for neurotransmission, coimmunoprecipitates with the CSPalpha/G protein/N-type calcium channel complex, however the significance of syntaxin 1A as a component of this complex remains unknown. In this report, we establish that syntaxin 1A interacts with CSPalpha, Hsc70 as well as the synaptic protein interaction (synprint) region of N-type channels. We demonstrate that huntingtin(exon1), a putative biologically active fragment of huntingtin, displaces both syntaxin 1A and CSPalpha from N-type channels. Identification of the protein components of the CSPalpha/GEF system is essential in establishing its precise role in synaptic transmission.

Secretory organelles in ECL cells: effects of pharmacological blockade of the gastrin/CCK2 receptor versus its elimination by gene targeting

Histamine-producing ECL cells are numerous in the stomach. They express gastrin/CCK2 receptors and respond to gastrin by releasing histamine. Ultrastructurally, they display numerous and very characteristic secretory organelles: granules, secretory vesicles and microvesicles. This paper focuses on the impact of the gastrin/CCK2 receptor on the ultrastructure of the ECL cells. The effects of pharmacological blockade of the receptor are compared with the effects of receptor elimination following selective gene targeting. Long-term administration of powerful gastrin/CCK2 receptor antagonists was found to induce hypotrophy of rat stomach ECL cells with reduced number of granules, secretory vesicles and microvesicles. In gastrin/CCK2 receptor knockout mice ECL cells, i.e., histamine-storing cells with the characteristic ultrastructure of ECL cells, had disappeared from the oxyntic mucosa and been replaced by a novel population of endocrine-like cells. These cells harbored granules and microvesicles, but were devoid of histamine and secretory vesicles. We suggest that the gastrin/CCK2 receptor is important for the proper differentiation of the ECL cells and for maintaining their characteristic ultrastructure.

Ca2+ and N-Ethylmaleimide-sensitive Factor Differentially Regulate Disassembly of SNARE Complexes on Early Endosomes

The endosome-associated protein Hrs inhibits the homotypic fusion of early endosomes. A helical region of Hrs containing a Q-SNARE motif mediates this effect as well as its endosomal membrane association via SNAP-25, an endosomal receptor for Hrs. Hrs inhibits formation of an early endosomal SNARE complex by displacing VAMP-2 from the complex, suggesting a mechanism by which Hrs inhibits early endosome fusion. We examined the regulation of endosomal SNARE complexes to probe how Hrs may function as a negative regulator. We show that although NSF dissociates the VAMP-2.SNAP-25.syntaxin 13 complex, it has no effect on the Hrs-containing complex. Whereas Ca(2+) dissociates the Hrs-containing complex but not the VAMP-2-containing SNARE complex. This is the first demonstration of differential regulation of R/Q-SNARE and all Q-SNARE-containing SNARE complexes. Ca(2+) also reverses the Hrs-induced inhibition of early endosome fusion in a tetanus toxin-sensitive manner and removes Hrs from early endosomal membranes. Moreover, Hrs inhibition of endosome fusion and its endosomal localization are sensitive to bafilomycin, implying a role for luminal Ca(2+). Thus, Hrs may bind a SNARE protein on early endosomal membranes negatively regulating trans-SNARE pairing and endosomal fusion. The release of Ca(2+) from the endosome lumen dissociates Hrs, allowing a VAMP-2-containing complex to form enabling fusion.

Physiology of gastric enterochromaffin-like cells

Enterochromaffin-like (ECL) cells are neuroendocrine cells in the gastric mucosa that control acid secretion by releasing histamine as a paracrine stimulant. The antral hormone gastrin and the neural messenger pituitary adenylyl cyclase-activating peptide (PACAP) potently stimulate histamine synthesis, storage, and secretion by ECL cells. Histamine is stored in secretory vesicles via V-type ATPases and vesicular monoamine transporters of subtype 2 (VMAT-2). Plasmalemmal calcium entry occurs via L-type calcium channels upon stimulation with secretagogues. K(+) and Cl(-) channels maintain the membrane potential. Calcium-triggered exocytosis of histamine is mediated by interacting SNARE proteins, especially by synaptobrevin and SNAP-25. Dynamins and amphiphysins appear to play a key role in endocytosis. ECL cells are under transcriptional control of various hormones. Gastrin stimulates transcriptional activity of the histidine decarboxylase (HDC), VMAT-2, and chromogranin A promoter by activation of Sp1 elements and CREB. During chronic Helicobacter pylori infection, pro-inflammatory cytokines are released that can also affect ECL cells, thus impairing their secretory function and viability, which can predispose to hypochlorhydria and gastric carcinogenesis.

Differentiation of gastric ECL cells is altered in CCK(2) receptor-deficient mice

BACKGROUND & AIMS

Gastrin stimulation of the type 2 cholecystokinin (CCK(2)) receptor results in ECL cell proliferation and histamine secretion. This report describes the effects of targeted disruption of the CCK(2) receptor gene on ECL cell morphology and function.

METHODS

The ECL cells in the oxyntic mucosa of CCK(2) receptor-deficient (knockout [KO]) vs. wild-type (WT) mice were investigated by immunocytochemical and biochemical approaches, as well as by electron microscopy.

RESULTS

Immunocytochemistry demonstrates similar numbers (cells per millimeter of horizontal length of mucosa) of pancreastatin- or vesicle monoamine transporter-2 (VMAT-2)-immunoreactive cells in WT mice and KO mice. However, only WT mice harbor histamine-immunoreactive ECL cells. The mucosal histamine content in KO mice (likely originating from mast cells) is only a minute fraction of that present in WT animals. The activity of the histamine forming enzyme, histidine decarboxylase (a marker of ECL cells), was undetectable in the oxyntic mucosa of KO mice yet was readily apparent in the mucosa from WT animals. Electron microscopy revealed numerous ECL cells in WT mice. In KO animals, these cells were replaced by an "ECL-like" cell type, characterized by a lack of secretory vesicles (a hallmark feature of normal ECL cells) and the presence of dense-core granules and microvesicles in numbers comparable to those found in WT ECL cells. Based on ultrastructural features, the ECL-like cells in KO mice can be readily distinguished from other gastric endocrine cells, including A-like cells and D cells.

CONCLUSIONS

Absence of a single gene product, the CCK(2) receptor, alters the differentiation and function of gastric ECL cells.

Time-course changes of ECL cell markers in acetic acid-induced gastric ulcers in rats

BACKGROUND AND AIM

Enterochromaffin-like (ECL) cells are the major source of histamine for the regulation of gastric acid secretion, and also contain histidine decarboxylase (HDC), vesicular monoamine transporter 2 (VMAT2), and chromogranin A (CgA). Although gastric acid secretion is suppressed during ulcer healing, the role of ECL cells in that process is not yet fully understood. In the present study, we investigated the changes in ECL cell number during healing of experimental ulcers in rats.

MATERIALS AND METHODS

Seven-week-old male Wistar rats were used. Acetic acid-induced ulcers were caused by an application of 100% acetic acid to the serosal surface of the rat stomachs. At different time points following the induction (12 h-15 days), time-course changes of HDC, VMAT2, and CgA mRNA expression were investigated by Northern blot analysis. The expressions of HDC, VMAT2, and CgA were immunostained on gastric mucosal sections with ulcers.

RESULTS

HDC, VMAT2, and CgA mRNA in gastric mucosa each showed an initial marked transient decrease, followed by an increase on day 10 back to the initial value. HDC, VMAT2, and CgA-immunoreactive cells at the ulcer margin were reduced in number on day 3, compared with those in distant areas. On day 10, however, they returned to levels similar to those in distant areas.

CONCLUSION

The present study revealed a local down-regulation of HDC, VMAT2, and CgA in ECL cells at the ulcer margin. As a result, we concluded that a suppression of ECL cell activity during ulcer healing may be involved in suppressed gastric acid secretion.

Classification of gastric endocrine cells at the light and electron microscopical levels

This review discusses the current concepts for the classification of gastric endocrine cells subdivided according to the type of mucosa in which they are located. In the oxyntic mucosa, the most important cell type is the ECL cell, involved in the synthesis and secretion of histamine. Proteins involved in many aspects of the biology of ECL cells including the response to the gastrin stimulus, membrane transport and docking, prevention of apoptosis, calcium homeostasis, autocrine activity, and maintenance of the differentiated cell phenotype have been localized to this cell type. Other cells of the oxyntic mucosa include: the D and EC cells producing somatostatin and serotonin, respectively, delivered through long cell processes; the X (or A-like) cells, possibly producing endothelin; and the D(1) and P cells of unknown function and possibly representing morphological variants of other cell types. In the antral mucosa, the three important cell types are represented by: the gastrin-producing G cells; the somatostatin-producing D cells, which are anatomically and functionally associated with G cells; and the serotonin-producing EC cells, which are located at the bottom of antral glands.

New molecular aspects in the diagnosis and therapy of neuroendocrine tumors of the gastroenteropancreatic system

The nature and biology of neuroendocrine cells and of tumors derived therefrom have been the subject of intense research using cell biological and molecular approaches. Diagnostic procedures for establishing the diagnosis of a neuroendocrine tumor have been improved through the development of new serological markers and imaging procedures. Histopathological diagnosis has been refined by the introduction of a broad spectrum of marker proteins for different subtypes of neuroendocrine neoplasms. The high receptor specificity of somatostatin analogues such as octreotide or lanreotide has made these drugs valuable tools in diagnosis and therapy, and some of the achievements made as well as future directions are reviewed in this article. Another substance in use for therapy of neuroendocrine tumors is interferon-a, whose signal transduction mechanism has been investigated considerably during the past several years. In addition to biotherapy with somatostatin analogues and/or interferon-a, chemotherapy is an accepted strategy in the treatment of advanced neuroendocrine tumor disease derived from the foregut. In this context, streptozotocin has caught some attention due to its somewhat selective toxicity against neuroendocrine tumor cells. Some recent studies on the role of the glucose transporter isoform GLUT2 may provide insight into streptozotocin's action. The multiple endocrine neoplasia type-1 gene has recently been cloned, sequenced and identified as a gene potentially involved in the development of the familial cancer syndrome of multiple endocrine neoplasia type 1 (MEN-1). Mutations of this putative tumor suppressor gene have been described, and the abundance of mutations in MEN-1-related tumors as well as sporadic neuroendocrine tumors at MEN-1 locations have been demonstrated. Whether determination of MEN-1 mutations will be valuable for clinical routine is under investigation.

Histamine depletion does not affect pancreastatin secretion from isolated rat stomach ECL cells

ECL cells co-secrete histamine and pancreastatin, a chromogranin A-derived peptide, in response to gastrin. The aim of the study was to explore possible ways to deplete ECL cells of histamine without affecting pancreastatin and to examine how histamine depletion affects pancreastatin secretion. Isolated rat stomach ECL cells (80-85% purity), prepared by counter-flow elutriation, were cultured for 48 h in the presence of alpha-fluoromethylhistidine (histidine decarboxylase inhibitor), bafilomycin A(1) (inhibitor of vacuolar-type proton-translocating ATPase) or reserpine (inhibitor of vesicular monoamine transporter). At this stage, the cells were challenged with 10 nM (EC(100)) gastrin-17 for 30 min. Histamine and pancreastatin were determined by radioimmunoassay. Maximally effective concentrations of alpha-fluoromethylhistidine, bafilomycin A(1) and reserpine were found to lower ECL-cell histamine (by 60%, 78% and 80%, respectively) without affecting pancreastatin. Basal histamine secretion was reduced in a dose-dependent manner by all three drugs. Gastrin-evoked histamine secretion was reduced greatly by the three agents, while pancreastatin secretion was unaffected. The results show that histamine can be depleted not only by inhibiting its formation (alpha-fluoromethylhistidine), but also (and more effectively) by inhibiting histamine vesicular uptake, directly (reserpine) or indirectly (bafilomycin A(1)). The results also indicate that although histamine is co-stored with pancreastatin, it is not required for either storage or secretion of pancreastatin.

The mechanism of histamine secretion from gastric enterochromaffin-like cells

Enterochromaffin-like (ECL) cells play a pivotal role in the peripheral regulation of gastric acid secretion as they respond to the functionally important gastrointestinal hormones gastrin and somatostatin and neural mediators such as pituitary adenylate cyclase-activating peptide and galanin. Gastrin is the key stimulus of histamine release from ECL cells in vivo and in vitro. Voltage-gated K(+) and Ca(2+) channels have been detected on isolated ECL cells. Exocytosis of histamine following gastrin stimulation and Ca(2+) entry across the plasma membrane is catalyzed by synaptobrevin and synaptosomal-associated protein of 25 kDa, both characterized as a soluble N-ethylmaleimide-sensitive factor attachment protein receptor protein. Histamine release occurs from different cellular pools: preexisting vacuolar histamine immediately released by Ca(2+) entry or newly synthesized histamine following induction of histidine decarboxylase (HDC) by gastrin stimulation. Histamine is synthesized by cytoplasmic HDC and accumulated in secretory vesicles by proton-histamine countertransport via the vesicular monoamine transporter subtype 2 (VMAT-2). The promoter region of HDC contains Ca(2+)-, cAMP-, and protein kinase C-responsive elements. The gene promoter for VMAT-2, however, lacks TATA boxes but contains regulatory elements for the hormones glucagon and somatostatin. Histamine secretion from ECL cells is thereby under a complex regulation of hormonal signals and can be targeted at several steps during the process of exocytosis.

Gastrin-induced gene expression in oxyntic mucosa and ECL cells of rat stomach

The histamine-producing ECL cells are numerous in the acid-producing (oxyntic) mucosa. They respond to gastrin by secretion of histamine that acts on parietal cells to produce acid. In addition, gastrin has a trophic effect on the oxyntic mucosa which is exerted on stem cells and ECL cells. To elucidate the molecular actions of gastrin on the stomach we attempted to identify genes that are regulated by gastrin in oxyntic mucosa and in isolated ECL cells. Differential display polymerase chain reaction was used to identify mRNAs that are differentially expressed in rats that are hypergastrinemic after treatment with the proton pump inhibitor omeprazole for 48 h compared with rats that are hypogastrinemic after 24 h fasting. Differences in mRNA levels were confirmed by Northern blot analysis (comparing mRNA from fasted rats, omeprazole-treated rats and rats treated with omeprazole + the CCK2 (cholecystokinin) receptor antagonist YF476). The cDNAs were identified by sequencing followed by data base search. Hypergastrinemia induced by omeprazole treatment resulted in overexpression of mRNA for histidine decarboxylase, fetuin, pepsinogen and cytochrome P450 in the oxyntic mucosa. This was prevented by CCK2 receptor blockade. In isolated ECL cells gastrin upregulated mRNAs for histidine decarboxylase and synaptotagmin V as well as one mRNA transcript without known homology.

Differential expression of SNAP-25a and SNAP-25b RNA transcripts in cranial nerve nuclei

Synaptosomal-associated protein of 25 kDa (SNAP-25) is involved in the molecular regulation of neurotransmitter release. SNAP-25 exists in two isoforms, SNAP-25a and SNAP-25b, which arise from alternate splicing and which are differentially expressed throughout the nervous system. In situ hybridization was used to examine the presence and subcellular localization of SNAP-25a and SNAP-25b RNA transcript expression in motor and parasympathetic nuclei associated with cranial nerves. SNAP-25a RNA transcripts were strongly expressed in the parasympathetic Edinger-Westphal nucleus and dorsal motor nucleus of the vagus nerve but weakly expressed in motor nuclei such as the oculomotor, trochlear, trigeminal, facial, ambiguus, hypoglossal and accessory nuclei and in motoneurons of mouse lumbar spinal cord. In contrast, SNAP-25b RNA transcripts were not detectable in the Edinger-Westphal nucleus and dorsal motor nucleus of the vagus nerve but were strongly expressed in the oculomotor, trochlear, trigeminal, facial, ambiguus, hypoglossal, and accessory nuclei and in the motoneurons of mouse lumbar spinal cord. In the parasympathetic cranial nerve nuclei, displaying high levels of SNAP-25a RNA transcripts, the labeling was cytoplasmic, whereas the labeling was nuclear in the cranial nerve motor nuclei, displaying lower levels of transcripts. In contrast, labeling of SNAP-25b RNA transcripts was cytoplasmic in cranial nerve motor nuclei and not detectable in parasympathetic cranial nerve nuclei. Possible explanations for the region-specific and differential subcellular localization of SNAP-25a and SNAP-25b RNA transcripts are discussed.

Antisera against rat recombinant histidine decarboxylase: immunocytochemical studies in different species

Histamine is involved in many important biological processes such as allergic reactions, gastric acid secretion and neurotransmission. The formation of histamine is catalysed by the enzyme histidine decarboxylase. In order to understand the role of histamine in different tissues, information about the cellular localisation of the decarboxylase is important. However, the availability of antisera against the enzyme, which can be used in immunocytochemical techniques, has so far been limited, mainly due to the difficulties in purifying sufficient amounts of histidine decarboxylase from various tissues. In the present study we describe the use of antisera raised against rat recombinant histidine decarboxylase to localise the enzyme immunocytochemically in the gastric mucosa of different mammals and submammalian vertebrates. The antisera specifically stained histidine decarboxylase-immunoreactive cells in the gastric mucosa of not only rat, but also of species like frog, chicken, mouse and dog. This is the first report describing the immunocytochemical distribution of the decarboxylase in the gastric mucosa of species other than rat. These antisera are likely to become valuable tools for further studies of the immunocytochemical localisation of histidine decarboxylase.

Rat stomach ECL cells up-date of biology and physiology

The ECL cell is the predominant endocrine cell type in the oxyntic mucosa, displaying typical ultrastructure with numerous cytoplasmic vesicles and electron-dense granules. ECL cells have many features in common with neurons and other peptide hormone-producing endocrine cells, including the ability to produce, store, and secrete chromogranin-A and chromogranin A-derived peptides. In addition, they produce and store histamine and respond with activation and growth to a gastrin challenge. ECL cells are stimulated to secrete histamine as well as other products by gastrin and PACAP and are inhibited by somatostatin, galanin, and prostaglandins. The cytoplasmic vesicles are thought to contain histamine and other secretory products. Mature secretory vesicles occur in the docking zone of the ECL cells, where they constitute the releasable pool of secretory products. Gastrin stimulation will induce exocytosis and degranulation. Histamine released from ECL cells plays a key role in the regulation of parietal cell activity (the gastrin-ECL cell-parietal cell axis). In response to long-term gastrin stimulation, vacuoles and lipofuscin bodies develop in the ECL cells, forming part of a crinophagic pathway by which the ECL cell strives to eliminate superfluous secretory products.