Analysis of enteroendocrine cell populations in the human colon

Limited evidence for anatomical contacts between intestinal GLP-1 cells and vagal neurons in male mice

The communication between intestinal Glucagon like peptide 1 (GLP-1)-producing cells and the peripheral nervous system has garnered renewed interest considering the availability of anti-obesity and anti-diabetic approaches targeting GLP-1 signaling. While it is well-established that intestinal GLP-1 cells can exert influence through paracrine mechanisms, recent evidence suggests the possible existence of synaptic-like connections between GLP-1 cells and peripheral neurons, including those of the vagus nerve. In this study, using a reporter Phox2b-Cre-Tomato mouse model and super-resolution confocal microscopy, we demonstrated that vagal axons made apparent contacts with less than 0.5% of GLP-1 cells. Moreover, immunohistochemistry combined with super-resolution confocal microscopy revealed abundant post-synaptic density 95 (PSD-95) immunoreactivity within the enteric plexus of the lower intestines of C57/BL6 mice, with virtually none in its mucosa. Lastly, utilizing RNAScope in situ hybridization in the lower intestines of mice, we observed that GLP-1 cells expressed generic markers of secretory cells such as Snap25 and Nefm, but neither synaptic markers such as Syn1 and Nrxn2, nor glutamatergic markers such as Slc17a7. Through theoretical considerations and a critical review of the literature, we concluded that intestinal GLP-1 cells primarily communicate with vagal neurons through paracrine mechanisms, rather than synaptic-like contacts.

Linking serotonin homeostasis to gut function: Nutrition, gut microbiota and beyond

Serotonin (5-HT) produced by enterochromaffin (EC) cells in the digestive tract is crucial for maintaining gut function and homeostasis. Nutritional and non-nutritional stimuli in the gut lumen can modulate the ability of EC cells to produce 5-HT in a temporal- and spatial-specific manner that toning gut physiology and immune response. Of particular interest, the interactions between dietary factors and the gut microbiota exert distinct impacts on gut 5-HT homeostasis and signaling in metabolism and the gut immune response. However, the underlying mechanisms need to be unraveled. This review aims to summarize and discuss the importance of gut 5-HT homeostasis and its regulation in maintaining gut metabolism and immune function in health and disease with special emphasis on different types of nutrients, dietary supplements, processing, and gut microbiota. Cutting-edge discoveries in this area will provide the basis for the development of new nutritional and pharmaceutical strategies for the prevention and treatment of serotonin homeostasis-related gut and systematic disorders and diseases.

The cckOMA syndrome and its relation to the Zollinger-Ellison syndrome: a diagnostic challenge

OBJECTIVE

Among patients with enteropancreatic neuroendocrine tumor syndromes only one case with a cholecystokinin (CCK) secreting tumor has been reported. She had significant hyperCCKemia leading to a specific syndrome of severe diarrheas, weight loss, repeated duodenal ulcers and a permanently contracted gallbladder with gallstones. There are, however, reasons to believe that further CCKomas exist, for instance among Zollinger-Ellison patients with normal plasma gastrin concentrations. The present review is a call to gastroenterologists for awareness of such CCKoma patients.

METHOD

After a short case report, the normal endocrine and oncological biology of CCK is described. Subsequently, the CCKoma symptoms are discussed with particular reference to the partly overlapping symptoms of the Zollinger-Ellison syndrome. In this context, the diagnostic use of truly specific CCK and gastrin assays are emphasized. The discussion also entails the problem of access to accurate CCK measurements.

CONCLUSION

Obviously, the clinical awareness about the CCKoma syndrome is limited. Moreover, it is also likely that the knowledge about the necessary specificity demands of diagnostic gastrin and CCK assays have obscured proper diagnosis of the CCKoma syndromes in man.

Enterochromaffin Cells-Gut Microbiota Crosstalk: Underpinning the Symptoms, Pathogenesis, and Pharmacotherapy in Disorders of Gut-Brain Interaction

Disorders of gut-brain interaction (DGBIs) are common conditions in community and clinical practice. As specialized enteroendocrine cells, enterochromaffin (EC) cells produce up to 95% of total body serotonin and coordinate luminal and basolateral communication in the gastrointestinal (GI) tract. EC cells affect a broad range of gut physiological processes, such as motility, absorption, secretion, chemo/mechanosensation, and pathologies, including visceral hypersensitivity, immune dysfunction, and impaired gastrointestinal barrier function. We aim to review EC cell and serotonin-mediated physiology and pathophysiology with particular emphasis on DGBIs. We explored the knowledge gap and attempted to suggest new perspectives of physiological and pathophysiological insights of DGBIs, such as (1) functional heterogeneity of regionally distributed EC cells throughout the entire GI tract; (2) potential pathophysiological mechanisms mediated by EC cell defect in DGBIs; (3) cellular and molecular mechanisms characterizing EC cells and gut microbiota bidirectional communication; (4) differential modulation of EC cells through GI segment-specific gut microbiota; (5) uncover whether crosstalk between EC cells and (i) luminal contents; (ii) enteric nervous system; and (iii) central nervous system are core mechanisms modulating gut-brain homeostasis; and (6) explore the therapeutic modalities for physiological and pathophysiological mechanisms mediated through EC cells. Insights discussed in this review will fuel the conception and realization of pathophysiological mechanisms and therapeutic clues to improve the management and clinical care of DGBIs.

Role of the Ghrelin System in Colorectal Cancer

The ghrelin system contains several components (e.g., ghrelin with growing number of alternative peptides, growth hormone secretagogue receptors (GHS-Rs), and ghrelin-O-acyl-transferase (GOAT) and participates in regulation of a number of key processes of gastrointestinal (GI) tract cancer progression, including cell proliferation, migration, invasion, apoptosis, inflammation, and angiogenesis. However, its exact role in promoting or inhibiting cancer progression is still unclear. Colorectal cancer (CRC) is one of the most common human malignancies worldwide. Molecular studies suggest an autocrine/paracrine mechanism for the secretion of ghrelin in colorectal carcinogenesis and its contribution to its initial stages. However, the signalling pathways of CRC development involving the ghrelin system are poorly understood. Potential mechanisms of colon carcinogenesis involving components of the ghrelin system were previously described in an animal model and in in vitro studies. However, the diagnostic–prognostic role of serum ghrelin concentrations, tissue expression, or genetic changes of this system in various stages of CRC progression remains an open case. Thus, the aim of this study is to discuss the role of the ghrelin system in colon carcinogenesis, diagnostics and CRC prognostics, as well as the results of studies on the use of ghrelin and its analogues in the therapy of CRC-related syndromes (e.g., cachexia and sarcopenia).

Digital Spatial Profiling Reveals Functional Shift of Enterochromaffin Cell in Patients With Ulcerative Colitis

As a major component of the enteroendocrine system, enterochromaffin (EC) cells play a key role in ulcerative colitis (UC). However, the scarcity of EC cells has limited the investigation of their function. In this study, we applied digital spatial profiling to acquire transcriptomic data for EC cells and other epithelial cells from colonoscopic biopsy samples from eight patients with UC and seven healthy controls. Differential expression analysis, gene set enrichment analysis, and weighted gene coexpression network analysis were performed to identify differentially expressed genes and pathways and coexpression networks. Results were validated using an online dataset obtained by single-cell RNA sequencing, along with immunofluorescence staining and quantitative real-time PCR. In healthy participants, 10 genes were significantly enriched in EC cells, functionally concentrated in protein and bioamine synthesis. A coexpression network containing 17 hub genes, including TPH1, CHGA, and GCLC, was identified in EC cells. In patients with UC, EC cells gained increased capacity for protein synthesis, along with novel immunological functions such as antigen processing and presentation, whereas chemical sensation was downregulated. The specific expression of CHGB and RGS2 in EC cells was confirmed by immunofluorescence staining. Our results illuminate the transcriptional signatures of EC cells in the human colon. EC cells’ newly observed functional shift from sensation to secretion and immunity indicates their pivotal role in UC.

Neurotensin secretion after Roux-en-Y gastric bypass, sleeve gastrectomy, and truncal vagotomy with pyloroplasty

OBJECTIVE

Neurotensin (NT) is released from enteroendocrine cells and lowers food intake in rodents. We evaluated postprandial NT secretion in humans after surgeries associated with accelerated small intestinal nutrient delivery, and after Roux-en-Y gastric bypass (RYGB) when glucagon-like peptide-1 (GLP-1) signalling and dipeptidyl peptidase 4 (DPP-4) were inhibited, and during pharmacological treatments influencing entero-pancreatic functions.

METHODS

We measured NT concentrations in plasma from meal studies: (I) after truncal vagotomy with pyloroplasty (TVP), cardia resection +TVP (CTVP), and matched controls (n = 10); (II) after RYGB, sleeve gastrectomy (SG), and in matched controls (n = 12); (III) after RYGB (n = 11) with antagonism of GLP-1 signalling using exendin(9-39) and DPP-4 inhibition using sitagliptin; (IV) after RYGB (n = 11) during a run-in period and subsequent treatment with, sitagliptin, liraglutide (GLP-1 receptor agonist), verapamil (calcium antagonist), acarbose (alpha glucosidase inhibitor), and pasireotide (somatostatin analogue), respectively.

RESULTS

(I) NT secretion was similar after TVP/CTVP (p = 0.9), but increased vs. controls (p < 0.0001). (II) NT secretion was increased after RYGB vs. SG and controls (p < 0.0001). NT responses were similar in SG and controls (p = 0.3), but early postprandial NT concentrations were higher after SG (p < 0.05). (III) Exendin (9-39) and sitagliptin did not change NT responses vs placebo (p > 0.2), but responses were lower during sitagliptin vs. exendin(9-39) (p = 0.03). (IV) Pasireotide suppressed NT secretion (p = 0.004). Sitagliptin tended to lower NT secretion (p = 0.08). Liraglutide, verapamil, and acarbose had no effect (p > 0.9).

CONCLUSION

Neurotensin secretion is increased after surgeries associated with accelerated gastric emptying and lowered by pasireotide.

Somatostatin and Its Receptor System in Colorectal Cancer

Somatostatin (SST)/somatotropin release-inhibiting factor (SRIF) is a well-known neuropeptide, widely distributed in the central and peripheral nervous systems, that regulates the endocrine system and affects neurotransmission via interaction with five SST receptors (SST1-5). In the gastrointestinal tract, the main SST-producing cells include intestinal enteroendocrine cells (EECs) restricted to the mucosa, and neurons of the submucosal and myenteric plexuses. The action of the SRIF system is based on the inhibition of endocrine and exocrine secretion, as well as the proliferative responses of target cells. The SST1–5 share common signaling pathways, and are not only widely expressed on normal tissues, but also frequently overexpressed by several tumors, particularly neuroendocrine neoplasms (NENs). Furthermore, the SRIF system represents the only peptide/G protein-coupled receptor (GPCR) system with multiple approved clinical applications for the diagnosis and treatment of several NENs. The role of the SRIF system in the histogenesis of colorectal cancer (CRC) subtypes (e.g., adenocarcinoma and signet ring-cell carcinoma), as well as diagnosis and prognosis of mixed adenoneuroendocrine carcinoma (MANEC) and pure adenocarcinoma, is poorly understood. Moreover, the impact of the SRIF system signaling on CRC cell proliferation and its potential role in the progression of this cancer remains unknown. Therefore, this review summarizes the recent collective knowledge and understanding of the clinical significance of the SRIF system signaling in CRC, aiming to evaluate the potential role of its components in CRC histogenesis, diagnosis, and potential therapy.

Expression of Cholecystokinin and its Receptors in the Intestinal Tract of Type 2 Diabetes Patients and Healthy Controls

BACKGROUND

Cholecystokinin (CCK) is a gut hormone originally known for its effects on gallbladder contraction and release of digestive enzymes. CCK, however, also mediates satiety and stimulate insulin secretion. Knowledge of the distribution of CCK-producing enteroendocrine cells (I cells) in humans is sparse. The general notion, based on animal data, is that I cells are present mainly in the proximal small intestine. We examined the occurrence of I cells (immunohistochemically) and the expression of CCK messenger RNA (mRNA) as well as CCK1 and CCK2 receptor mRNA along the intestines in healthy individuals and patients with type 2 diabetes.

METHODS

Mucosal biopsies collected with 30-cm intervals in the small intestine and from seven anatomical locations in the large intestine (using double-balloon enteroscopy) from 12 patients with type 2 diabetes and 12 gender-, age-, and body mass index-matched healthy individuals were analyzed using mRNA sequencing and immunohistochemical staining.

RESULTS

We observed a gradual decrease in CCK mRNA expression and density of CCK-immunoreactive cells from duodenum to ileum. Very few CCK-immunoreactive cells and nearly undetectable CCK mRNA expression were found in the large intestine. No significant differences were seen between the groups. Expression of CCK receptors was observed in the duodenum of both groups.

CONCLUSIONS

Both density of CCK cells and expression of CCK mRNA decreased through the small intestine in both groups with low levels in the large intestine. Patients with type 2 diabetes did not have altered density of CCK cells or expression of CCK mRNA in intestinal mucosa.

Serotonin Deficiency Is Associated With Delayed Gastric Emptying

BACKGROUND & AIMS

Gastrointestinal (GI) motility is regulated by serotonin (5-hydroxytryptamine [5-HT]), which is primarily produced by enterochromaffin (EC) cells in the GI tract. However, the precise roles of EC cell-derived 5-HT in regulating gastric motility remain a major point of conjecture. Using a novel transgenic mouse line, we investigated the distribution of EC cells and the pathophysiologic roles of 5-HT deficiency in gastric motility in mice and humans.

METHODS

We developed an inducible, EC cell-specific Tph1CreERT2/+ mouse, which was used to generate a reporter mouse line, Tph1-tdTom, and an EC cell-depleted line, Tph1-DTA. We examined EC cell distribution, morphology, and subpopulations in reporter mice. GI motility was measured in vivo and ex vivo in EC cell-depleted mice. Additionally, we evaluated 5-HT content in biopsy and plasma specimens from patients with idiopathic gastroparesis (IG).

RESULTS

Tph1-tdTom mice showed EC cells that were heterogeneously distributed throughout the GI tract with the greatest abundance in the antrum and proximal colon. Two subpopulations of EC cells were identified in the gut: self-renewal cells located at the base of the crypt and mature cells observed in the villi. Tph1-DTA mice displayed delayed gastric emptying, total GI transit, and colonic transit. These gut motility alterations were reversed by exogenous provision of 5-HT. Patients with IG had a significant reduction of antral EC cell numbers and 5-HT content, which negatively correlated with gastric emptying rate.

CONCLUSIONS

The Tph1CreERT2/+ mouse provides a powerful tool to study the functional roles of EC cells in the GI tract. Our findings suggest a new pathophysiologic mechanism of 5-HT deficiency in IG.

Neuroendocrine Peptides of the Gut and Their Role in the Regulation of Food Intake

The regulation of food intake encompasses complex interplays between the gut and the brain. Among them, the gastrointestinal tract releases different peptides that communicate the metabolic state to specific nuclei in the hindbrain and the hypothalamus. The present overview gives emphasis on seven peptides that are produced by and secreted from specialized enteroendocrine cells along the gastrointestinal tract in relation with the nutritional status. These established modulators of feeding are ghrelin and nesfatin-1 secreted from gastric X/A-like cells, cholecystokinin (CCK) secreted from duodenal I-cells, glucagon-like peptide 1 (GLP-1), oxyntomodulin, and peptide YY (PYY) secreted from intestinal L-cells and uroguanylin (UGN) released from enterochromaffin (EC) cells. © 2021 American Physiological Society. Compr Physiol 11:1679-1730, 2021.

Expression of TAS2R14 in the intestinal endocrine cells of non-human primates

BACKGROUND

Recent studies have demonstrated that genes related to bitter taste receptors (TAS2Rs) on various chromosomes are expressed in extra-oral organs of various animals. The bitter taste receptor TAS2R14 is conserved among primate species and shows broad ligand sensitivity. Mice have a number of orthologues to primate TAS2R14 located in tandem on chromosome 16; however, their expression patterns are not unique.

OBJECTIVE

We characterized the expression of TAS2R14 in various cell types in the intestines of the rhesus macaque and evaluated its role in hormone production in the gut.

METHODS

TAS2R14 expression was examined in the intestines of rhesus macaques, a common non-human primate model, by RT-qPCR and immunohistochemical staining.

RESULTS

Mean expression levels of TAS2R14 in the duodenum, ileum, and colon were similar to each other and were lower than those in circumvallate papillae. An immunohistochemical analysis revealed TAS2R14 immunoreactivity in enteroendocrine cells positive for cholecystokinin, serotonin, and the G protein GNAT3.

CONCLUSION

These results suggest that primate TAS2R14 is broadly expressed in the intestine, mainly in enteroendocrine cells, and promotes gut hormone secretion in response to bitter stimuli.

The distribution and chemical coding of enteroendocrine cells in Trypanosoma cruzi-infected individuals with chagasic megacolon

Chagas disease is caused by the parasite, Trypanosoma cruzi that causes chronic cardiac and digestive dysfunction. Megacolon, an irreversible dilation of the left colon, is the main feature of the gastrointestinal form of Chagas disease. Patients have severe constipation, a consequence of enteric neuron degeneration associated with chronic inflammation. Dysmotility, infection, neuronal loss and a chronic exacerbated inflammation, all observed in Chagas disease, can affect enteroendocrine cells (EEC) expression, which in turn, could influence the inflammatory process. In this study, we investigated the distribution and chemical coding of EEC in the dilated and non-dilated portion of T. cruzi-induced megacolon and in non-infected individuals (control colon). Using immunohistochemistry, EECs were identified by applying antibodies to chromogranin A (CgA), glucagon-like peptide 1 (GLP-1), 5-hydroxytryptamine (5-HT), peptide YY (PYY) and somatostatin (SST). Greater numbers of EEC expressing GLP-1 and SST occurred in the dilated portion compared to the non-dilated portion of the same patients with Chagas disease and in control colon, but numbers of 5-HT and PYY EEC were not significantly different. However, it was noticeable that EEC in which 5-HT and PYY were co-expressed were common in control colon, but were rare in the non-dilated and absent in the dilated portion of chagasic megacolon. An increase in the number of CgA immunoreactive EEC in chagasic patients reflected the increases in EEC numbers summarised above. Our data suggests that the denervation and associated chronic inflammation are accompanied by changes in the number and coding of EEC that could contribute to disorders of motility and defence in the chagasic megacolon.

Effects of Flavanols on Enteroendocrine Secretion

Some beneficial effects of grape seed proanthocyanidin extract (GSPE) can be explained by the modulation of enterohormone secretion. As GSPE comprises a combination of different molecules, the pure compounds that cause these effects need to be elucidated. The enterohormones and chemoreceptors present in the gastrointestinal tract differ between species, so if humans are to gain beneficial effects, species closer to humans-and humans themselves-must be used. We demonstrate that 100 mg/L of GSPE stimulates peptide YY (PYY) release, but not glucagon-like peptide 1 (GLP-1) release in the human colon. We used a pig ex vivo system that differentiates between apical and basolateral intestinal sides to analyse how apical stimulation with GSPE and its pure compounds affects the gastrointestinal tract. In pigs, apical GSPE treatment stimulates the basolateral release of PYY in the duodenum and colon and that of GLP-1 in the ascending, but not the descending colon. In the duodenum, luminal stimulation with procyanidin dimer B2 increased PYY secretion, but not CCK secretion, while catechin monomers (catechin/epicatechin) significantly increased CCK release, but not PYY release. The differential effects of GSPE and its pure compounds on enterohormone release at the same intestinal segment suggest that they act through chemosensors located apically and unevenly distributed along the gastrointestinal tract.

Quantitation and chemical coding of enteroendocrine cell populations in the human jejunum

Recent studies reveal substantial species and regional differences in enteroendocrine cell (EEC) populations, including differences in patterns of hormone coexpression, which limit extrapolation between animal models and human. In this study, jejunal samples, with no histologically identifiable pathology, from patients undergoing Whipple's procedure were investigated for the presence of gastrointestinal hormones using double- and triple-labelling immunohistochemistry and high-resolution confocal microscopy. Ten hormones (5-HT, CCK, secretin, proglucagon-derived peptides, PYY, GIP, somatostatin, neurotensin, ghrelin and motilin) were localised in EEC of the human jejunum. If only single staining is considered, the most numerous EEC were those containing 5-HT, CCK, ghrelin, GIP, motilin, secretin and proglucagon-derived peptides. All hormones had some degree of colocalisation with other hormones. This included a population of EEC in which GIP, CCK and proglucagon-derived peptides are costored, and four 5-HT cell populations, 5-HT/GIP, 5-HT/ghrelin, 5-HT/PYY, and 5-HT/secretin cell groups, and a high degree of overlap between motilin and ghrelin. The presence of 5-HT in many secretin cells is consistent across species, whereas lack of 5-HT and CCK colocalisation distinguishes human from mouse. It seems likely that the different subclasses of 5-HT cells subserve different roles. At a subcellular level, we examined the vesicular localisation of secretin and 5-HT, and found these to be separately stored. We conclude that hormone-containing cells in the human jejunum do not comply with a one-cell, one-hormone classification and that colocalisations of hormones are likely to define subtypes of EEC that have different roles.

Expression patterns of L-amino acid receptors in the murine STC-1 enteroendocrine cell line

Regulation of gut function depends on the detection and response to luminal contents. Luminal L-amino acids (L-AA) are detected by several receptors including metabotropic glutamate receptors 1 and 4 (mGluR1 and mGluR4), calcium-sensing receptor (CaSR), GPRC family C group 6 subtype A receptor (GPRC6A) and umami taste receptor heterodimer T1R1/T1R3. Here, we show that murine mucosal homogenates and STC-1 cells, a murine enteroendocrine cell line, express mRNA for all L-AA receptors. Immunohistochemical analysis demonstrated the presence of all L-AA receptors on STC-1 with CaSR being most commonly expressed and T1R1 least expressed (35% versus 15% of cells); mGluRs and GPRC6a were intermediate (~ 20% of cells). Regarding coexpression of L-AA receptors, the mGluRs and T1R1 were similarly coexpressed with CaSR (10-12% of cells) whereas GPRC6a was coexpressed least (7% of cells). mGluR1 was coexpressed with GPRC6a in 11% of cells whereas coexpression between other receptors was less (2-8% of cells). CaSR and mGluR1 were coexpressed with glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) in 20-25% of cells whereas T1R1 and GPRC6a were coexpressed with GLP-1 and PYY less (8-12% of cells). Only mGluR4 showed differential coexpression with GLP-1 (13%) and PYY (21%). L-Phenylalanine (10 mM) caused a 3-fold increase in GLP-1 release, which was strongly inhibited by siRNA to CaSR indicating functional coupling of CaSR to GLP-1 release. The results suggest that not all STC-1 cells express (and coexpress) L-AA receptors to the same extent and that the pattern of response likely depends on the pattern of expression of L-AA receptors.

Enterochromaffin cells and gastrointestinal diseases

Enterochromaffin cells (ECs), known for their special histochemical characteristics, originate from enteroblasts. For their important role in physiological and pathophysiological conditions, ECs in the gut could synthesize and secrete about 95% of 5-hydroxytryptamine (5-HT) in the body, which is an important humoral factor. As a chemosensor, ECs can regulate nutrition absorption and satiety through the sensory neural pathways. In addition, ECs participate in immune regulation. What's more, ECs and 5-HT are closely related to many kinds of gastrointestinal diseases.

Relationships of endocrine cells to each other and to other cell types in the human gastric fundus and corpus

Gastric endocrine cell hormones contribute to the control of the stomach and to signalling to the brain. In other gut regions, enteroendocrine cells (EECs) exhibit extensive patterns of colocalisation of hormones. In the current study, we characterise EECs in the human gastric fundus and corpus. We utilise immunohistochemistry to investigate EECs with antibodies to ghrelin, serotonin (5-HT), somatostatin, peptide YY (PYY), glucagon-like peptide 1, calbindin, gastrin and pancreastatin, the latter as a marker of enterochromaffin-like (ECL) cells. EECs were mainly located in regions of the gastric glands populated by parietal cells. Gastrin cells were absent and PYY cells were very rare. Except for about 25% of 5-HT cells being a subpopulation of ECL cells marked by pancreastatin, colocalisation of hormones in gastric EECs was infrequent. Ghrelin cells were distributed throughout the fundus and corpus; most were basally located in the glands, often very close to parietal cells and were closed cells i.e., not in contact with the lumen. A small proportion had long processes located close to the base of the mucosal epithelium. The 5-HT cells were of at least three types: small, round, closed cells; cells with multiple, often very long, processes; and a subgroup of ECL cells. Processes were in contact with their surrounding cells, including parietal cells. Mast cells had very weak or no 5-HT immunoreactivity. Somatostatin cells were a closed type with long processes. In conclusion, four major chemically defined EEC types occurred in the human oxyntic mucosa. Within each group were cells with distinct morphologies and relationships to other mucosal cells.

Diversity of enteroendocrine cells investigated at cellular and subcellular levels: the need for a new classification scheme

Enteroendocrine cells were historically classified by a letter code, each linked to a single hormone, deduced to be the only hormone produced by the cell. One type, the L cell, was recognised to store and secrete two products, peptide YY (PYY) and glucagon-related peptides. Many other exceptions to the one-cell one-hormone classifications have been reported over the last 40 years or so, and yet the one-hormone dogma has persisted. In the last 6 years, a plethora of data has appeared that makes the concept unviable. Here, we describe the evidence that multiple hormone transcripts and their products reside in single cells and evidence that the hormones are often, but not always, processed into separate storage vesicles. It has become clear that most enteroendocrine cells contain multiple hormones. For example, most secretin cells contain 5-hydroxytryptamine (5-HT), and in mouse many of these also contain cholecystokinin (CCK). Furthermore, CCK cells also commonly store ghrelin, glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1), neurotensin, and PYY. Several hormones, for example, secretin and 5-HT, are in separate storage vesicles at a subcellular level. Hormone patterns can differ considerably between species. Another complication is that relative levels of expression vary substantially. This means that data are significantly influenced by the sensitivities of detection techniques. For example, a hormone that can be detected in storage vesicles by super-resolution microscopy may not be above threshold for detection by conventional fluorescence microscopy. New nomenclature for cell clusters with common attributes will need to be devised and old classifications abandoned.

In Pursuit of the Epithelial Mechanosensitivity Mechanisms

Mechanosensation is critical for normal gastrointestinal (GI) function. Disruption in GI mechanosensation leads to human diseases. Mechanical forces in the GI tract are sensed by specialized mechanosensory cells, as well as non-specialized mechanosensors, like smooth muscle cells. Together, these cellular mechanosensors orchestrate physiologic responses. GI epithelium is at the interface of the body and the environment. It encounters a variety of mechanical forces that range from shear stress due to flow of luminal contents to extrinsic compression due to smooth muscle contraction. Mechanical forces applied to the GI mucosa lead to a large outflow of serotonin, and since serotonin is concentrated in a single type of an epithelial cell, called enterochromaffin cell (ECC), it was assumed that ECC is mechanosensitive. Recent studies show that a subset of ECCs is indeed mechanosensitive and that Piezo2 mechanosensitive ion channels are necessary for coupling force to serotonin release. This review aims to place this mechanism into the larger context of ECC mechanotransduction.

Costorage of Enteroendocrine Hormones Evaluated at the Cell and Subcellular Levels in Male Mice

Recent studies reveal complex patterns of hormone coexpression within enteroendocrine cells (EECs), contrary to the traditional view that gut hormones are expressed individually in EECs. Moreover, different hormones have been found in separate subcellular vesicles. However, detailed analysis of relative expression of multiple hormones has not been made. Subcellular studies have been confined to peptide hormones, and have not included the indolamine 5-hydroxytryptamine (5-HT) or the neuroendocrine protein chromogranin A (CgA). In the present work, coexpression of 5-HT, CgA, secretin, cholecystokinin (CCK), ghrelin, and glucagonlike peptide (GLP)-1 in mouse duodenum was quantified at a cellular and subcellular level by semiautomated cell counting and quantitative vesicle measurements. We investigated whether relative numbers of cells with colocalized hormones analyzed at a cell level matched the numbers revealed by examination of individual storage vesicles within cells. CgA and 5-HT were frequently expressed in EECs that contained combinations of GLP-1, ghrelin, secretin, and CCK. Separate subcellular stores of 5-HT, CgA, secretin, CCK, ghrelin, and GLP-1 were identified. In some cases, high-resolution analysis revealed small numbers of immunoreactive vesicles in cells dominated by a different hormone. Thus the observed incidence of cells with colocalized hormones is greater when analyzed at a subcellular, compared with a cellular, level. Subcellular analysis also showed that relative numbers of vesicles differ considerably between cells. Thus separate packaging of hormones that are colocalized is a general feature of EECs, and EECs exhibit substantial heterogeneity, including the colocalization of hormones that were formerly thought to be in cells of different lineages.

Heterogeneity of enterochromaffin cells within the gastrointestinal tract

Enterochromaffin cells were the first endocrine cells of the gastrointestinal tract to be chemically distinguished, almost 150 years ago. It is now known that the chromaffin reaction of these cells was due to their content of the reactive aromatic amine, 5-hydroxytryptamine (5-HT, also known as serotonin). They have commonly been thought to be a special class of gut endocrine cells (enteroendocrine cells) that are distinct from the enteroendocrine cells that contain peptide hormones. The study by Martin et al. in the current issue of this journal reveals that the patterns of expression of nutrient receptors and transporters differ considerably between chromaffin cells of the mouse duodenum and colon. However, even within regions, chromaffin cells differ; in the duodenum there are chromaffin cells that contain both secretin and 5-HT, cholecystokinin and 5-HT, and all three of secretin, cholecystokinin, and 5-HT. Moreover, the ratios of these different cell types differ substantially between species. And, in terms of function, 5-HT has many roles, including in appetite, motility, fluid secretion, release of digestive enzymes and bone metabolism. The paper thus emphasizes the need to define the many different classes of enterochromaffin cells and relate this to their roles.

Distribution and characterisation of CCK containing enteroendocrine cells of the mouse small and large intestine

There is general consensus that enteroendocrine cells, EEC, containing the enteric hormone cholecystokinin (CCK) are confined to the small intestine and predominate in the duodenum and jejunum. Contrary to this, EEC that express the gene for CCK have been isolated from the large intestine of the mouse and there is evidence for EEC that contain CCK-like immunoreactivity in the mouse colon. However, the human and rat colons do not contain CCK cells. In the current study, we use immunohistochemistry to investigate CCK peptide presence in endocrine cells, PCR to identify cck transcripts and chromatography to identify CCK peptide forms in the mouse small and large intestine. The colocalisation of CCK and 5-HT, hormones that have been hypothesised to derive from cells of different lineages, was also investigated. CCK immunoreactivity was found in EEC throughout the mouse small and large intestine but positive cells were rare in the rectum. Immunoreactive EEC were as common in the caecum and proximal colon as they were in the duodenum and jejunum. CCK gene transcripts were found in the mucosa throughout the intestine but mRNA for gastrin, a hormone that can bind some anti-CCK antibodies, was only found in the stomach and duodenum. Characterisation of CCK peptides of the colon by extraction, chromatographic separation and radioimmunoassay revealed bioactive amidated and sulphated forms, including CCK-8 and CCK-33. Moreover, CCK-containing EEC in the large intestine bound antibodies that target the biologically active sulfated form. Colocalisation of CCK and 5-HT occurred in a proportion of EEC throughout the small intestine and in the caecum but these hormones were not colocalised in the colon, where there was CCK and PYY colocalisation. It is concluded that authentic, biologically active, CCK occurs in EEC of the mouse large intestine.

Mechanosensitive ion channel Piezo2 is inhibited by D-GsMTx4

Enterochromaffin (_EC) cells are the primary mechanosensors of the gastrointestinal (GI) epithelium. In response to mechanical stimuli_EC cells release serotonin (5-hydroxytryptamine; 5-HT). The molecular details of_EC cell mechanosensitivity are poorly understood. Recently, our group found that human and mouse_EC cells express the mechanosensitive ion channel Piezo2. The mechanosensitive currents in a human_EC cell model QGP-1 were blocked by the mechanosensitive channel blocker D-GsMTx4. In the present study we aimed to characterize the effects of the mechanosensitive ion channel inhibitor spider peptide D-GsMTx4 on the mechanically stimulated currents from both QGP-1 and human Piezo2 transfected HEK-293 cells. We found co-localization of 5-HT and Piezo2 in QGP-1 cells by immunohistochemistry. QGP-1 mechanosensitive currents had biophysical properties similar to dose-dependently Piezo2 and were inhibited by D-GsMTx4. In response to direct displacement of cell membranes, human Piezo2 transiently expressed in HEK-293 cells produced robust rapidly activating and inactivating inward currents. D-GsMTx4 reversibly and dose-dependently inhibited both the potency and efficacy of Piezo2 currents in response to mechanical force. Our data demonstrate an effective inhibition of Piezo2 mechanosensitive currents by the spider peptide D-GsMTx4.