The chemical coding of 5-hydroxytryptamine containing enteroendocrine cells in the mouse gastrointestinal tract

Type 1 diabetes human enteroid studies reveal major changes in the intestinal epithelial compartment

Lack of understanding of the pathophysiology of gastrointestinal (GI) complications in type 1 diabetes (T1D), including altered intestinal transcriptomes and protein expression represents a major gap in the management of these patients. Human enteroids have emerged as a physiologically relevant model of the intestinal epithelium but establishing enteroids from individuals with long-standing T1D has proven difficult. We successfully established duodenal enteroids using endoscopic biopsies from pediatric T1D patients and compared them with aged-matched enteroids from healthy subjects (HS) using bulk RNA sequencing (RNA-seq), and functional analyses of ion transport processes. RNA-seq analysis showed significant differences in genes and pathways associated with cell differentiation and proliferation, cell fate commitment, and brush border membrane. Further validation of these results showed higher expression of enteroendocrine cells, and the proliferating cell marker Ki-67, significantly lower expression of NHE3, lower epithelial barrier integrity, and higher fluid secretion in response to cAMP and elevated calcium in T1D enteroids. Enteroids established from pediatric T1D duodenum identify characteristics of an abnormal intestinal epithelium and are distinct from HS. Our data supports the use of pediatric enteroids as an ex-vivo model to advance studies of GI complications and drug discovery in T1D patients.

Xiao Cheng Qi Decoction, an Ancient Chinese Herbal Mixture, Relieves Loperamide-Induced Slow-Transit Constipation in Mice: An Action Mediated by Gut Microbiota

Xiao Cheng Qi (XCQ) decoction, an ancient Chinese herbal mixture, has been used in treating slow-transit constipation (STC) for years. The underlying action mechanism in relieving the clinical symptoms is unclear. Several lines of evidence point to a strong link between constipation and gut microbiota. Short-chain fatty acids (SCFAs) and microbial metabolites have been shown to affect 5-HT synthesis by activating the GPR43 receptor localized on intestinal enterochromaffin cells, since 5-HT receptors are known to influence colonic peristalsis. The objective of this study was to evaluate the efficacy of XCQ in alleviating clinical symptoms in a mouse model of STC induced by loperamide. The application of loperamide leads to a decrease in intestinal transport and fecal water, which is used to establish the animal model of STC. In addition, the relationship between constipation and gut microbiota was determined. The herbal materials, composed of Rhei Radix et Rhizoma (Rhizomes of Rheum palmatum L., Polygonaceae) 55.2 g, Magnoliae Officinalis Cortex (Barks of Magnolia officinalis Rehd. et Wils, Magnoliaceae) 27.6 g, and Aurantii Fructus Immaturus (Fruitlet of Citrus aurantium L., Rutaceae) 36.0 g, were extracted with water to prepare the XCQ decoction. The constipated mice were induced with loperamide (10 mg/kg/day), and then treated with an oral dose of XCQ herbal extract (2.0, 4.0, and 8.0 g/kg/day) two times a day. Mosapride was administered as a positive drug. In loperamide-induced STC mice, the therapeutic parameters of XCQ-treated mice were determined, i.e., (i) symptoms of constipation, composition of gut microbiota, and amount of short-chain fatty acids in feces; (ii) plasma level of 5-HT; and (iii) expressions of the GPR43 and 5-HT4 receptor in colon. XCQ ameliorated the constipation symptoms of loperamide-induced STC mice. In gut microbiota, the treatment of XCQ in STC mice increased the relative abundances of Lactobacillus, Prevotellaceae_UCG_001, Prevotellaceae_NK3B31_group, Muribaculaceae, and Roseburia in feces and decreased the relative abundances of Desulfovibrio, Tuzzerella, and Lachnospiraceae_ NK4A136_group. The levels of SCFAs in stools from the STC group were significantly lower than those the control group, and were greatly elevated via treatment with XCQ. Compared with the STC group, XCQ increased the plasma level of 5-HT and the colonic expressions of the GPR43 and 5-HT4 receptor, significantly. The underlying mechanism of XCQ in anti-constipation could be related to the modulation of gut microbiota, the increase in SCFAs, the increase in plasma 5-HT, and the colonic expressions of the GPR43 and 5-HT4 receptor. Our results indicate that XCQ is a potent natural product that could be a therapeutic strategy for constipation.

Stratification of enterochromaffin cells by single-cell expression analysis

Dynamic interactions between gut mucosal cells and the external environment are essential to maintain gut homeostasis. Enterochromaffin (EC) cells transduce both chemical and mechanical signals and produce 5-hydroxytryptamine (5-HT) to mediate disparate physiological responses. However, the molecular and cellular basis for functional diversity of ECs remains to be adequately defined. Here, we integrated single-cell transcriptomics with spatial image analysis to identify fourteen EC clusters that are topographically organized along the gut. Subtypes predicted to be sensitive to the chemical environment and mechanical forces were identified that express distinct transcription factors and hormones. A Piezo2+ population in the distal colon was endowed with a distinctive neuronal signature. Using a combination of genetic, chemogenetic and pharmacological approaches, we demonstrated Piezo2+ ECs are required for normal colon motility. Our study constructs a molecular map for ECs and offers a framework for deconvoluting EC cells with pleiotropic functions.

Paracrine relationship between incretin hormones and endogenous 5-hydroxytryptamine in the small and large intestine

BACKGROUND

Enterochromaffin (EC) cell-derived 5-hydroxytryptamine (5-HT) is a mediator of toxin-induced reflexes, initiating emesis via vagal and central 5-HT3 receptors. The amine is also involved in gastrointestinal (GI) reflexes that are prosecretory and promotile, and recently 5-HT's roles in chemosensation in the distal bowel have been described. We set out to establish the efficacy of 5-HT signaling, local 5-HT levels and pharmacology in discrete regions of the mouse small and large intestine. We also investigated the inter-relationships between incretin hormones, glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) and endogenous 5-HT in mucosal and motility assays.

METHODS

Adult mouse GI mucosae were mounted in Ussing chambers and area-specific studies were performed to establish the 5-HT3 and 5-HT4 pharmacology, the sidedness of responses, and the inter-relationships between incretins and endogenous 5-HT. Natural fecal pellet transit in vitro and full-length GI transit in vivo were also measured.

KEY RESULTS

We observed the greatest level of tonic and exogenous 5-HT-induced ion transport and highest levels of 5-HT in ascending colon mucosa. Here both 5-HT3 and 5-HT4 receptors were involved but elsewhere in the GI tract epithelial basolateral 5-HT4 receptors mediate 5-HT's prosecretory effect. Exendin-4 and GIP induced 5-HT release in the ascending colon, while L cell-derived PYY also contributed to GIP mucosal effects in the descending colon. Both peptides slowed colonic transit.

CONCLUSIONS & INFERENCES

We provide functional evidence for paracrine interplay between 5-HT, GLP-1 and GIP, particularly in the colonic mucosal region. Basolateral epithelial 5-HT4 receptors mediated both 5-HT and incretin mucosal responses in healthy colon.

Flavonoids in Amomum tsaoko Crevost et Lemarie Ameliorate Loperamide-Induced Constipation in Mice by Regulating Gut Microbiota and Related Metabolites

Amomum tsaoko (AT) is a dietary botanical with laxative properties; however, the active ingredients and mechanisms are still unclear. The active fraction of AT aqueous extract (ATAE) for promoting defecation in slow transit constipation mice is the ethanol-soluble part (ATES). The total flavonoids of ATES (ATTF) were the main active component. ATTF significantly increased the abundance of Lactobacillus and Bacillus and reduced the dominant commensals, such as Lachnospiraceae, thereby changing the gut microbiota structure and composition. Meanwhile, ATTF changed the gut metabolites mainly enriched in pathways such as the serotonergic synapse. In addition, ATTF increased the serum serotonin (5-HT) content and mRNA expression of 5-hydroxytryptamine receptor 2A (5-HT_2A), Phospholipase A2 (PLA2), and Cyclooxygenase-2 (COX2), which are involved in the serotonergic synaptic pathway. ATTF increased Transient receptor potential A1 (TRPA1), which promotes the release of 5-HT, and Myosin light chain 3(MLC3), which promotes smooth muscle motility. Notably, we established a network between gut microbiota, gut metabolites, and host parameters. The dominant gut microbiota Lactobacillus and Bacillus, prostaglandin J2 (PGJ2) and laxative phenotypes showed the most significant associations. The above results suggest that ATTF may relieve constipation by regulating the gut microbiota and serotonergic synaptic pathway and has great potential for laxative drug development in the future.

Cannabis sativa L. alleviates loperamide-induced constipation by modulating the composition of gut microbiota in mice

MaZiRenWan (MZRW) is the most frequently used Traditional Chinese Medicine formula to treat chronic constipation, Cannabis sativa L. is regarded as a monarch drug in MZRW. However, the targets of Cannabis sativa L. that enhance colonic motility and improve constipation symptoms remain unknown. This study was designed to investigate the laxative effect and underlying mechanism of the water extract of Cannabis sativa L. (WECSL) using a loperamide-induced constipation mouse model. We found that WECSL treatment significantly improved intestinal motility and water-electrolyte metabolism, decreased inflammatory responses, prevented gut barrier damage, and relieved anxiety and depression in constipated mice. WECSL also structurally remodeled the composition of the gut microbiota and altered the abundance of bacteria related to inflammation, specifically Butyricicoccus and Parasutterella. Moreover, WECSL failed to relieve constipation symptoms following intestinal flora depletion, indicating that WECSL alleviates constipation symptoms depending on the gut microbiota. Our research provides a basis for WECSL to be further investigated in the treatment of constipation from the perspective of modern medicine.

Metagenomics and metabolomics analysis to investigate the effect of Shugan decoction on intestinal microbiota in irritable bowel syndrome rats

BACKGROUND

The effect of Shugan Decoction (SGD) on intestinal motility and visceral hypersensitivity in Water avoid stress (WAS)-induced diarrhea predominant irritable bowel syndrome (IBS-D) model rats has been confirmed. However, the mechanisms of its action involved in the treatment of IBS-D need to be further studied. Intestinal microbiota plays an important role in maintaining intestinal homeostasis and normal physiological function. Changes in the intestinal microbiota and its metabolites are thought to participate in the pathophysiological process of IBS.

AIM

This study aimed to analyze the influence of SGD on intestinal microbiota and fecal metabolites in IBS-D rats by multiple omics techniques, including metagenomic sequencing and metabolomics.

METHODS

We measured the intestinal motility and visceral sensitivity of three groups of rats by fecal pellets output and colorectal distension (CRD) experiment. In addition, metagenome sequencing analysis was performed to explore the changes in the number and types of intestinal microbiota in IBS-D model rats after SGD treatment. Finally, we also used untargeted metabolomic sequencing to screen the metabolites and metabolic pathways closely related to the therapeutic effect of SGD.

RESULTS

We found that compared with the rats in the control group, the fecal pellets output of the rats in the WAS group increased and the visceral sensitivity threshold was decreased (P < 0.05). Compared with the rats in the WAS group, the fecal pellets output of the SGD group was significantly decreased, and the visceral sensitivity threshold increased (P < 0.05). Besides, compared with the rats in the WAS group, the relative abundance of Bacteroidetes increased in SGD group, while that of Firmicutes decreased at the phylum level, and at the species level, the relative abundance of Bacteroides sp. CAG:714, Lactobacillus reuteri and Bacteroides Barnesiae in SGD group increased, but that of bacterium D42-87 decreased. In addition, compared with the WAS group, several metabolic pathways were significantly changed in SGD group, including Taurine and hypotaurine metabolism, Purine metabolism, Sulfur metabolism, ABC transporters, Arginine and proline metabolism and Bile secretion.

CONCLUSION

SGD can regulate specific intestinal microbiota and some metabolic pathways, which may explain its effect of alleviating visceral hypersensitivity and abnormal intestinal motility in WAS-induced IBS-D rats.

Enteroendocrine cell types that drive food reward and aversion

Animals must learn through experience which foods are nutritious and should be consumed, and which are toxic and should be avoided. Enteroendocrine cells (EECs) are the principal chemosensors in the GI tract, but investigation of their role in behavior has been limited by the difficulty of selectively targeting these cells in vivo. Here, we describe an intersectional genetic approach for manipulating EEC subtypes in behaving mice. We show that multiple EEC subtypes inhibit food intake but have different effects on learning. Conditioned flavor preference is driven by release of cholecystokinin whereas conditioned taste aversion is mediated by serotonin and substance P. These positive and negative valence signals are transmitted by vagal and spinal afferents, respectively. These findings establish a cellular basis for how chemosensing in the gut drives learning about food.

Mechanisms Underlying the Interaction Between Chronic Neurological Disorders and Microbial Metabolites via Tea Polyphenols Therapeutics

The number of hydroxyl groups and existence of characteristic structural groups in tea polyphenols (TP) make them have antioxidant activity, which gives TP anti-inflammatory effects, toward protecting the intestinal flora and brain neurons. Host-associated microbial metabolites are emerging as dominant modifiers of the central nervous system. As yet, the investigations on host-microbiota crosstalking remain challenging, studies focusing on metabolites such as serotonin, short-chain fatty acids, and others have pinpointed multiple actionable signaling pathways relevant to host health. However, there are still complexities and apparent limitations inherent in transforming complex human diseases to corresponding animal models. Here, we choose to discuss several intestinal metabolites with research value, as crucial areas for assessing TP-mediated chronic brain diseases interactions with microbial.

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.

Potential Roles of Enterochromaffin Cells in Early Life Stress-Induced Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, also known as disorders of the gut–brain interaction; however, the pathophysiology of IBS remains unclear. Early life stress (ELS) is one of the most common risk factors for IBS development. However, the molecular mechanisms by which ELS induces IBS remain unclear. Enterochromaffin cells (ECs), as a prime source of peripheral serotonin (5-HT), play a pivotal role in intestinal motility, secretion, proinflammatory and anti-inflammatory effects, and visceral sensation. ECs can sense various stimuli and microbiota metabolites such as short-chain fatty acids (SCFAs) and secondary bile acids. ECs can sense the luminal environment and transmit signals to the brain via exogenous vagal and spinal nerve afferents. Increasing evidence suggests that an ECs-5-HT signaling imbalance plays a crucial role in the pathogenesis of ELS-induced IBS. A recent study using a maternal separation (MS) animal model mimicking ELS showed that MS induced expansion of intestinal stem cells and their differentiation toward secretory lineages, including ECs, leading to ECs hyperplasia, increased 5-HT production, and visceral hyperalgesia. This suggests that ELS-induced IBS may be associated with increased ECs-5-HT signaling. Furthermore, ECs are closely related to corticotropin-releasing hormone, mast cells, neuron growth factor, bile acids, and SCFAs, all of which contribute to the pathogenesis of IBS. Collectively, ECs may play a role in the pathogenesis of ELS-induced IBS. Therefore, this review summarizes the physiological function of ECs and focuses on their potential role in the pathogenesis of IBS based on clinical and pre-clinical evidence.

Distribution of α-synuclein in normal human jejunum and its relations with the chemosensory and neuroendocrine system

Alpha-synuclein (α-syn) is a presynaptic neuronal protein and its structural alterations play an important role in the pathogenesis of neurodegenerative diseases, such as Parkinson’s disease (PD). It has been originally described in the brain and aggregated α-syn has also been found in the peripheral nerves including the enteric nervous system (ENS) of PD patients. ENS is a network of neurons and glia found in the gut wall which controls gastrointestinal function independently from the central nervous system. Moreover, two types of epithelial cells are crucial in the creation of an interface between the lumen and the ENS: they are the tuft cells and the enteroendocrine cells (EECs). In addition, the abundant enteric glial cells (EGCs) in the intestinal mucosa play a key role in controlling the intestinal epithelial barrier. Our aim was to localize and characterize the presence of α-syn in the normal human jejunal wall. Surgical specimens of proximal jejunum were collected from patients submitted to pancreaticoduodenectomy and intestinal sections underwent immunohistochemical procedure. Alpha-syn has been found both at the level of the ENS and the epithelial cells. To characterize α-syn immunoreactive epithelial cells, we used markers such as choline acetyltransferase (ChAT), useful for the identification of tuft cells. Then we evaluated the co-presence of α-syn with serotonin (5-HT), expressed in EECs. Finally, we used the low-affinity nerve growth factor receptor (p75NTR), to detect peripheral EGCs. The presence of α-syn has been demonstrated in EECs, but not in the tuft cells. Additionally, p75NTR has been highlighted in EECs of the mucosal layer and co-localized with α-syn in EECs but not with ChAT-positive cells. These findings suggest that α-syn could play a possible role in synaptic transmission of the ENS and may contribute to maintain the integrity of the epithelial barrier of the small intestine through EECs.

Action Mode of Gut Motility, Fluid and Electrolyte Transport in Chronic Constipation

Chronic constipation is a common gastrointestinal disorder, with a worldwide incidence of 14–30%. It negatively affects quality of life and is associated with a considerable economic burden. As a disease with multiple etiologies and risk factors, it is important to understand the pathophysiology of chronic constipation. The purpose of this review is to discuss latest findings on the roles of gut motility, fluid, and electrolyte transport that contribute to chronic constipation, and the main drugs available for treating patients. We conducted searches on PubMed and Google Scholar up to 9 February 2021. MeSH keywords “constipation”, “gastrointestinal motility”, “peristalsis”, “electrolytes”, “fluid”, “aquaporins”, and “medicine” were included. The reference lists of searched articles were reviewed to identify further eligible articles. Studies focusing on opioid-induced constipation, evaluation, and clinic management of constipation were excluded. The occurrence of constipation is inherently connected to disorders of gut motility as well as fluid and electrolyte transport, which involve the nervous system, endocrine signaling, the gastrointestinal microbiota, ion channels, and aquaporins. The mechanisms of action and application of the main drugs are summarized; a better understanding of ion channels and aquaporins may be helpful for new drug development. This review aims to provide a scientific basis that can guide future research on the etiology and treatment of constipation.

Ghrelin and its role in gastrointestinal tract tumors (Review)

Ghrelin, an orexigenic hormone, is a peptide that binds to the growth hormone secretagogue receptor; it is secreted mainly by enteroendocrine cells in the oxyntic glands of the stomach. Ghrelin serves a role in both local and systemic physiological processes, and is implicated in various pathologies, including neoplasia, with tissue expression in several types of malignancies in both in vitro and in vivo studies. However, the precise implications of the ghrelin axis in metastasis, invasion and cancer progression regulation has yet to be established. In the case of gastrointestinal (GI) tract malignancies, ghrelin has shown potential to become a prognostic factor or even a therapeutic target, although data in the literature are inconsistent and unsystematic, with reports untailored to a specific histological subtype of cancer or a particular localization. The evaluation of immunohistochemical expression shows a limited outlook owing to the low number of cases analyzed, and in vivo analyses have conflicting data regarding differences in ghrelin serum levels in patients with cancer. The aim of this review was to examine the relationship between ghrelin and GI tract malignancies to demonstrate the inconsistencies in current results and to highlight its clinical significance in the outcome of these patients.

Serotonin involvement in okadaic acid-induced diarrhoea in vivo

The consumption of contaminated shellfish with okadaic acid (OA) group of toxins leads to diarrhoeic shellfish poisoning (DSP) characterized by a set of symptoms including nausea, vomiting and diarrhoea. These phycotoxins are Ser/Thr phosphatase inhibitors, which produce hyperphosphorylation in cellular proteins. However, this inhibition does not fully explain the symptomatology reported and other targets could be relevant to the toxicity. Previous studies have indicated a feasible involvement of the nervous system. We performed a set of in vivo approaches to elucidate whether neuropeptide Y (NPY), Peptide YY (PYY) or serotonin (5-HT) was implicated in the early OA-induced diarrhoea. Fasted Swiss female mice were administered NPY, PYY(3-36) or cyproheptadine intraperitoneal prior to oral OA treatment (250 µg/kg). A non-significant delay in diarrhoea onset was observed for NPY (107 µg/kg) and PYY(3-36) (1 mg/kg) pre-treatment. On the contrary, the serotonin antagonist cyproheptadine was able to block (10 mg/kg) or delay (0.1 and 1 mg/kg) diarrhoea onset suggesting a role of 5-HT. This is the first report of the possible involvement of serotonin in OA-induced poisoning.

Human gastrointestinal epithelia of the esophagus, stomach, and duodenum resolved at single-cell resolution

The upper gastrointestinal tract, consisting of the esophagus, stomach, and duodenum, controls food transport, digestion, nutrient uptake, and hormone production. By single-cell analysis of healthy epithelia of these human organs, we molecularly define their distinct cell types. We identify a quiescent COL17A1high KRT15high stem/progenitor cell population in the most basal cell layer of the esophagus and detect substantial gene expression differences between identical cell types of the human and mouse stomach. Selective expression of BEST4, CFTR, guanylin, and uroguanylin identifies a rare duodenal cell type, referred to as BCHE cell, which likely mediates high-volume fluid secretion because of continual activation of the CFTR channel by guanylin/uroguanylin-mediated autocrine signaling. Serotonin-producing enterochromaffin cells in the antral stomach significantly differ in gene expression from duodenal enterochromaffin cells. We, furthermore, discover that the histamine-producing enterochromaffin-like cells in the oxyntic stomach express the luteinizing hormone, yet another member of the enteroendocrine hormone family.

5-HT containing enteroendocrine cells characterised by morphologies, patterns of hormone co-expression, and relationships with nerve fibres in the mouse gastrointestinal tract

5-HT containing enteroendocrine cells (EEC), the most abundant type of EEC in the gut, regulate many functions including motility, secretion and inflammatory responses. We examined the morphologies of 5-HT cells from stomach to rectum, patterns of hormone co-expression in the stomach and colon, and the relationship of 5-HT cells with nerve fibres. We also reviewed some of the relevant literature. The morphologies of 5-HT cells were distinct, depending on their location in the gut. A noticeable feature of some 5-HT cells in the antrum and colon was their long basal processes, which resembled processes of neurons, whereas 5-HT cells in the small intestinal mucosa lacked basal processes. In the stomach, numerous 5-HT cells, including cells with basal processes, were identified as enterochromaffin-like cells by their expression of histidine decarboxylase. In the colon, we observed a small number of 5-HT cells that were in close contact with, but distinct from, oxyntomodulin (OXM) and PYY immunoreactive EEC. We did not find specific relationships between nerve fibres and the processes of colonic 5-HT cells. We conclude that five major features, i.e., gut region, morphology, hormone content, receptor repertoire and cell lineage, can be used to define 5-HT cells.

Morphologies and distributions of 5-HT containing enteroendocrine cells in the mouse large intestine

Serotonin (5-HT)-containing gastrointestinal endocrine cells contribute to regulation of numerous bodily functions, but whether these functions are related to differences in cell shape is not known. The current study identified morphologies and localization of subtypes of 5-HT-containing enteroendocrine cells in the mouse large intestine. 5-HT cells were most frequent in the proximal colon compared with cecum and distal colon. The large intestine harbored both open (O) cells, with apical processes that reached the lumen, and closed (C) cells, not contacting the lumen, classified into O1, O2, and O3 and C1, C2, and C3 cells, by the lengths of their basal processes. O1 and C1 cells, with basal processes sometimes longer that 100 µm, were most common in the distal colon. Their long basal processes ran against the inner surfaces of the mucosal epithelial cells and were strongly immunoreactive for 5-HT; these processes are ideally placed to communicate with the epithelium and to react to mechanical forces. O2 and C2 cells that had similar but shorter basal processes were also most common in the distal colon. O3 and C3 cells had no or very short basal processes. The O3 open type 5-HT cells were abundant in the proximal colon, particularly at the luminal surface, where they could release 5-HT into the lumen to act on luminal 5-HT receptors. Numerous O3 type 5-HT cells occurred in the lower (submucosal) region of the crypts in all segments and might release 5-HT to influence cell renewal in the crypt proliferative zones.

Versatile Functions of Somatostatin and Somatostatin Receptors in the Gastrointestinal System

Somatostatin (SST) and somatostatin receptors (SSTRs) play an important role in the brain and gastrointestinal (GI) system. SST is produced in various organs and cells, and the inhibitory function of somatostatin-containing cells is involved in a range of physiological functions and pathological modifications. The GI system is the largest endocrine organ for digestion and absorption, SST-endocrine cells and neurons in the GI system are a critical effecter to maintain homeostasis via SSTRs 1-5 and co-receptors, while SST-SSTRs are involved in chemo-sensory, mucus, and hormone secretion, motility, inflammation response, itch, and pain via the autocrine, paracrine, endocrine, and exoendocrine pathways. It is also a power inhibitor for tumor cell proliferation, severe inflammation, and post-operation complications, and is a first-line anti-cancer drug in clinical practice. This mini review focuses on the current function of producing SST endocrine cells and local neurons SST-SSTRs in the GI system, discusses new development prognostic markers, phosphate-specific antibodies, and molecular imaging emerging in diagnostics and therapy, and summarizes the mechanism of the SST family in basic research and clinical practice. Understanding of endocrines and neuroendocrines in SST-SSTRs in GI will provide an insight into advanced medicine in basic and clinical research.

Colokinetic effect of an insulin-like peptide 5-related agonist of the RXFP4 receptor

BACKGROUND

Insulin-like peptide 5 (INSL5) is a hormone stored in colonic enteroendocrine cells that also contain the unrelated hormones, GLP-1 and PYY. It acts at the relaxin family peptide 4, RXFP4, receptor. RXFP4 is expressed by enteric neurons in the colon, and it has been speculated that INSL5, through its action on enteric neurons, might be involved in the control of colonic contractions. Similar to insulin and relaxin, INSL5 consists of A and B peptide chains linked by three disulfide bonds, two between the chains and one intrinsic to the A chain. Because of its complex structure, it is difficult to synthesize and to prepare peptide analogues to investigate its roles. We have recently developed a potent simplified peptide analogue, INSL5-A13 (INSL5 analogue 13).

METHODS

In the present work, we have investigated the actions of INSL5-A13 in mice. We investigated the ability of INSL5-A13 to increase the speed of emptying of a bead from the colon, after expulsion had been slowed by the peripherally restricted opioid agonist, loperamide (1 mg/kg).

KEY RESULTS

INSL5-A13 was a full agonist at the mouse RXFP4 expressed in HEK cells, with an EC50 of ~9 nmol/L. INSL5-A13 caused an acceleration of colorectal bead propulsion in mice constipated by loperamide in the dose range 0.2 to 60 µg/kg, with an EC50 of ~6 µg/kg in vivo. It also accelerated bead propulsion in untreated mice. Bead expulsion was not accelerated in RXFP4-/- mice.

CONCLUSION AND INFERENCES

Our data suggest that RXFP4 agonists could be useful in the treatment of constipation.

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.

Distribution and co-expression patterns of specific cell markers of enteroendocrine cells in pig gastric epithelium

Although the pig is an accepted model species for human digestive physiology, no previous study of the pig gastric mucosa and gastric enteroendocrine cells has investigated the parallels between pig and human. In this study, we have investigated markers for each of the classes of gastric endocrine cells, gastrin, ghrelin, somatostatin, 5-hydroxytryptamine, histidine decarboxylase, and PYY cells in pig stomach. The lining of the proximal stomach consisted of a collar of stratified squamous epithelium surrounded by gastric cardiac glands in the fundus. This differs considerably from human that has only a narrow band of cardiac glands at its entrance, surrounded by a fundic mucosa consisting of oxyntic glands. However, the linings of the corpus and antrum are similar in pig and human. Likewise, the endocrine cell types are similar and similarly distributed in the two species. As in human, gastrin cells were almost exclusively in the antrum, ghrelin cells were most abundant in the oxyntic mucosa and PYY cells were rare. In the pig, 70% of enterochromaffin-like (ECL) cells in the antrum and 95% in the fundus contained 5-hydroxytryptamine (5-HT), higher proportions than in human. Unlike the enteroendocrine of the small intestine, most gastric enteroendocrine cells (EEC) did not contain colocalised hormones. This is similar to human and other species. We conclude that the pig stomach has substantial similarity to human, except that the pig has a protective lining at its entrance that may reflect the difference between a pig diet with hard abrasive components and the soft foods consumed by humans.

Distributions and relationships of chemically defined enteroendocrine cells in the rat gastric mucosa

This paper provides quantitative data on the distributions of enteroendocrine cells (EEC), defined by the hormones they contain, patterns of colocalisation between hormones and EEC relations to nerve fibres in the rat gastric mucosa. The rat stomach has three mucosal types: non-glandular stratified squamous epithelium of the fundus and esophageal groove, a region of oxyntic glands in the corpus, and pyloric glands of the antrum and pylorus. Ghrelin and histamine were both contained in closed cells, not contacting the lumen, and were most numerous in the corpus. Gastrin cells were confined to the antrum, and 5-hydroxytryptamine (5-HT) and somatostatin cells were more frequent in the antrum than the corpus. Most somatostatin cells had basal processes that in the antrum commonly contacted gastrin cells. Peptide YY (PYY) cells were rare and mainly in the antrum. The only numerous colocalisations were 5-HT and histamine, PYY and gastrin and gastrin and histamine in the antrum, but each of these populations was small. Peptide-containing nerve fibres were found in the mucosa. One of the most common types was vasoactive intestinal peptide (VIP) fibres. High-resolution analysis showed that ghrelin cells were closely and selectively approached by VIP fibres. In contrast, gastrin cells were not selectively innervated by VIP or CGRP fibres. The study indicates that there are distinct populations of gastric EEC and selective innervation of ghrelin cells. It also shows that, in contrast to EEC of the small intestine, the majority of EEC within the stomach contained only a single hormone.

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.

A population of gut epithelial enterochromaffin cells is mechanosensitive and requires Piezo2 to convert force into serotonin release

Enterochromaffin (EC) cells constitute the largest population of intestinal epithelial enteroendocrine (EE) cells. EC cells are proposed to be specialized mechanosensory cells that release serotonin in response to epithelial forces, and thereby regulate intestinal fluid secretion. However, it is unknown whether EE and EC cells are directly mechanosensitive, and if so, what the molecular mechanism of their mechanosensitivity is. Consequently, the role of EE and EC cells in gastrointestinal mechanobiology is unclear. Piezo2 mechanosensitive ion channels are important for some specialized epithelial mechanosensors, and they are expressed in mouse and human EC cells. Here, we use EC and EE cell lineage tracing in multiple mouse models to show that Piezo2 is expressed in a subset of murine EE and EC cells, and it is distributed near serotonin vesicles by superresolution microscopy. Mechanical stimulation of a subset of isolated EE cells leads to a rapid inward ionic current, which is diminished by Piezo2 knockdown and channel inhibitors. In these mechanosensitive EE cells force leads to Piezo2-dependent intracellular Ca2+ increase in isolated cells as well as in EE cells within intestinal organoids, and Piezo2-dependent mechanosensitive serotonin release in EC cells. Conditional knockout of intestinal epithelial Piezo2 results in a significant decrease in mechanically stimulated epithelial secretion. This study shows that a subset of primary EE and EC cells is mechanosensitive, uncovers Piezo2 as their primary mechanotransducer, defines the molecular mechanism of their mechanotransduction and mechanosensitive serotonin release, and establishes the role of epithelial Piezo2 mechanosensitive ion channels in regulation of intestinal physiology.

Neuroendocrine structures of the small intestine of the capybara Hydrochoerus hydrochaeris (Mammalia, Rodentia)

A complex network of nerve fibers of the enteric nervous system and enteroendocrine cells is known to regulate the gastrointestinal tract. The distribution and frequency of the argyrophil, argentaffin and serotonin immunoreactive endocrine cells and of the submucosal and myenteric nervous ganglia were studied in the small intestine of the capybara Hydrochoerus hydrochaeris, aiming to verify the existence of possible numerical correlations between endocrine cells and nervous ganglia. Fragments of the duodenum, jejunum and ileum of adult animals were collected and processed according to routine histological techniques. To study the nervous ganglia, hematoxylin and eosin staining was used, while specific staining techniques were used to study the argyrophil, argentaffin and serotonin immunoreactive endocrine cells: Grimelius, modified Masson-Fontana and peroxidase anti-peroxidase, respectively. Endocrine cells were more abundant in the area of the crypts and, in relation to their morphology, ‘open type’ endocrine cells prevailed. The population of argyrophil cells was larger than that of argentaffin cells, and these cells were larger than serotonin immunoreactive cells. The frequency of endocrine cells was apparently greater in the duodenum, indicating the importance of this intestinal segment in digestive and absorptive functions. Prominent nervous ganglia were observed in the submucosal and myenteric plexi, and were larger and more frequent in the myenteric plexus. A numerical correlation was found among the endocrine cells (argentaffin and serotonin immunoreactive cells) and the myenteric nervous ganglia, suggesting the presence of physiological interactions among the endocrine and nervous systems for the control of intestinal activities. The findings in this study contribute to the understanding of the digestive processes of this species, which may also help in its conservation and future survival.

Single-cell RNA-sequencing reveals a distinct population of proglucagon-expressing cells specific to the mouse upper small intestine

OBJECTIVES

To identify sub-populations of intestinal preproglucagon-expressing (PPG) cells producing Glucagon-like Peptide-1, and their associated expression profiles of sensory receptors, thereby enabling the discovery of therapeutic strategies that target these cell populations for the treatment of diabetes and obesity.

METHODS

We performed single cell RNA sequencing of PPG-cells purified by flow cytometry from the upper small intestine of 3 GLU-Venus mice. Cells from 2 mice were sequenced at low depth, and from the third mouse at high depth. High quality sequencing data from 234 PPG-cells were used to identify clusters by tSNE analysis. qPCR was performed to compare the longitudinal and crypt/villus locations of cluster-specific genes. Immunofluorescence and mass spectrometry were used to confirm protein expression.

RESULTS

PPG-cells formed 3 major clusters: a group with typical characteristics of classical L-cells, including high expression of Gcg and Pyy (comprising 51% of all PPG-cells); a cell type overlapping with Gip-expressing K-cells (14%); and a unique cluster expressing Tph1 and Pzp that was predominantly located in proximal small intestine villi and co-produced 5-HT (35%). Expression of G-protein coupled receptors differed between clusters, suggesting the cell types are differentially regulated and would be differentially targetable.

CONCLUSIONS

Our findings support the emerging concept that many enteroendocrine cell populations are highly overlapping, with individual cells producing a range of peptides previously assigned to distinct cell types. Different receptor expression profiles across the clusters highlight potential drug targets to increase gut hormone secretion for the treatment of diabetes and obesity.

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.

The nutrient-sensing repertoires of mouse enterochromaffin cells differ between duodenum and colon

BACKGROUND

Enterochromaffin (EC) cells within the gastrointestinal (GI) tract provide almost all body serotonin (5-hydroxytryptamine [5-HT]). Peripheral 5-HT, released from EC cells lining the gut wall, serves diverse physiological roles. These include modulating GI motility, bone formation, hepatic gluconeogenesis, thermogenesis, insulin resistance, and regulation of fat mass. Enterochromaffin cells are nutrient sensors, but which nutrients they are responsive to and how this changes in different parts of the GI tract are poorly understood.

METHODS

To accurately undertake such an examination, we undertook the first isolation and purification of primary mouse EC cells from both the duodenum and colon in the same animal. This allowed us to compare, in an internally controlled manner, regional differences in the expression of nutrient sensors in EC cells using real-time PCR.

KEY RESULTS

Both colonic and duodenal EC cells expressed G protein-coupled receptors and facilitative transporters for sugars, free fatty acids, amino acids, and lipid amides. We find differential expression of nutrient receptor and transporters in EC cells obtained from duodenal and colonic EC cells. Duodenal EC cells have higher expression of tryptophan hydroxylase-1, sugar transporters GLUT2, GLUT5, and free fatty acid receptors 1 and 3 (FFAR1 and FFAR3). Colonic EC cells express higher levels of GLUT1, FFAR2, and FFAR4.

CONCLUSIONS & INFERENCES

We highlight the diversity of EC cell physiology and identify differences in the regional sensing repertoire of EC cells to an assortment of nutrients. These data indicate that not all EC cells are similar and that differences in their physiological responses are likely dependent on their location within the GI tract.

The Diverse Metabolic Roles of Peripheral Serotonin

Serotonin (5-hydroxytryptamine or 5-HT) is a multifunctional bioamine with important signaling roles in a range of physiological pathways. Almost all of the 5-HT in our bodies is synthesized in specialized enteroendocrine cells within the gastrointestinal (GI) mucosa called enterochromaffin (EC) cells. These cells provide all of our circulating 5-HT. We have long appreciated the important contributions of 5-HT within the gut, including its role in modulating GI motility. However, evidence of the physiological and clinical significance of gut-derived 5-HT outside of the gut has recently emerged, implicating 5-HT in regulation of glucose homeostasis, lipid metabolism, bone density, and diseases associated with metabolic syndrome, such as obesity and type 2 diabetes. Although a new picture has developed in the last decade regarding the various metabolic roles of peripheral serotonin, so too has our understanding of the physiology of EC cells. Given that they are scattered throughout the lining of the GI tract within the epithelial cell layer, these cells are typically difficult to study. Advances in isolation procedures now allow the study of pure EC-cell cultures and single cells, enabling studies of EC-cell physiology to occur. EC cells are sensory cells that are capable of integrating cues from ingested nutrients, the enteric nervous system, and the gut microbiome. Thus, levels of peripheral 5-HT can be modulated by a multitude of factors, resulting in both local and systemic effects for the regulation of a raft of physiological pathways related to metabolism and obesity.

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.

Gastrointestinal hormones and the gut connectome

PURPOSE OF REVIEW

Provision of adequate nutrients by the gut is essential for survival and essential behaviors are linked to the proper ingestion and digestion of food. Recently, a new neural connection has been reported between sensory cells of the gut epithelium and the nervous system that mediates signals from the gut to the brain.

RECENT FINDINGS

This review describes how the gut senses its environment, relays those signals to the brain, and how the brain influences the gut.

SUMMARY

This gut-brain connection provides a pathway for how the body handles food.

The injury of serotonin on intestinal epithelium cell renewal of weaned diarrhoea mice

Diarrhoea is a common cause of death in children and weaned animals. Recent research has found that serotonin (5-HT) in the gastrointestinal tract plays an important role in regulating growth and the maintenance of mucosa, which protect against diarrhoea. To determine the influence of 5-HT on intestinal epithelium cell renewal under weaned stress diarrhoea, a weaned-stress diarrhoea mouse model was established with senna infusion (15 mL/Kg) via intragastric administration and stress restraint (SR). Mice with an increase in 5-HT were induced by intraperitoneal injection with citalopram hydrobromide (CH, 10 mg/Kg). The results demonstrated that compared with the control animals, diarrhoea appeared in weaned stress mice and the 5-HT content in the small intestine was significantly increased (P<0.05). Further, the caspase-3 cells and cells undergoing apoptosis in the small intestine were significantly increased, but the VH (villus height), V/C (villus height /crypt depth), and PCNA-positive rate significantly decreased. Compared with the control animals, CH increased the intestinal 5-HT content, caspase-3 cells and cells undergoing apoptosis but decreased the VH and V/C. Compared with both control and weaned stress animals, weaned stress animals that were pre-treated with CH showed higher 5-HT concentrations, positive caspase-3 cells and cells undergoing apoptosis but lower VH, V/C and PCNA-positive rate. In vitro, a low concentration of 5-HT inhibit, IEC-6 cell line apoptosis but a higher concentration of 5-HT promoted it. Therefore, weaned stress diarrhoea mice were accompanied by a 5-HT increase in the small intestine and vice versa, and the increase in 5-HT induced by CH caused diarrhoea. In brief, 5-HT and diarrhoea slowed the intestinal epithelium cell renewal and injured the abortion function and mucosal barrier by decreasing VH, V/C and proliferation and increasing epithelium cell apoptosis.