Deregulation of transcription factors controlling intestinal epithelial cell differentiation; a predisposing factor for reduced enteroendocrine cell number in morbidly obese individuals.

Morbidly obese patients exhibit impaired secretion of gut hormones that may contribute to the development of obesity. After bariatric surgery there is a dramatic increase in gut hormone release. In this study, gastric and duodenal tissues were endoscopically collected from lean, and morbidly obese subjects before and 3 months after laparoscopic sleeve gastrectomy (LSG). Tissue morphology, abundance of chromogranin A, gut hormones, α-defensin, mucin 2, Na+/glucose co-transporter 1 (SGLT1) and transcription factors, Hes1, HATH1, NeuroD1, and Ngn3, were determined. In obese patients, the total number of enteroendocrine cells (EEC) and EECs containing gut hormones were significantly reduced in the stomach and duodenum, compared to lean, and returned to normality post-LSG. No changes in villus height/crypt depth were observed. A significant increase in mucin 2 and SGLT1 expression was detected in the obese duodenum. Expression levels of transcription factors required for differentiation of absorptive and secretory cell lineages were altered. We propose that in obesity, there is deregulation in differentiation of intestinal epithelial cell lineages that may influence the levels of released gut hormones. Post-LSG cellular differentiation profile is restored. An understanding of molecular mechanisms controlling epithelial cell differentiation in the obese intestine assists in the development of non-invasive therapeutic strategies.

Expression of cannabinoid CB1 receptors by vagal afferent neurons: kinetics and role in influencing neurochemical phenotype.

The intestinal hormone cholecystokinin (CCK) inhibits food intake via stimulation of vagal afferent neurons (VAN). Recent studies suggest that CCK also regulates the expression of some G protein-coupled receptors and neuropeptide transmitters in these neurons. The aim of the present study was to characterize the expression of cannabinoid (CB)1 receptors in VAN and to determine whether stimulation of these receptors plays a role in regulating neurochemical phenotype. Expression of CB1 in rat VAN was detectable by in situ hybridization or immunohistochemistry after 6 h of fasting and increased to a maximum after 24 h when approximately 50% of neurons in the mid and caudal regions expressed the receptor. Melanin-concentrating hormone (MCH)1 receptors also increased with fasting, but the changes were delayed compared with CB1; in contrast Y2 receptors (Y2R) exhibited reciprocal changes in expression to CB1. Administration of CCK8s (10 nmol ip) to fasted rats decreased expression of CB1 with a t(1/2) of approximately 1 h compared with 3 h for MCH1. The action of CCK8s was inhibited by ghrelin and orexin-A. The CB1 agonist anandamide (intraperitoneally) reversed the effect of CCK8s on CB1, MCH1, and Y2 receptor expression. In contrast, in rats fasted for 18 h, administration of a CB1 antagonist/inverse agonist (AM281 ip) downregulated CB1 expression and increased Y2 receptor expression. Activation of vagal CB1 receptors therefore influences the neurochemical phenotype of these neurons, indicating a new and hitherto unrecognized role for endocannabinoids in gut-brain signaling.

Cholecystokinin regulates expression of Y2 receptors in vagal afferent neurons serving the stomach.

The intestinal hormones CCK and PYY3-36 inhibit gastric emptying and food intake via vagal afferent neurons. Here we report that CCK regulates the expression of Y2R, at which PYY3-36 acts. In nodose ganglia from rats fasted up to 48 h, there was a fivefold decrease of Y2R mRNA compared with rats fed ad libitum; Y2R mRNA in fasted rats was increased by administration of CCK, and by refeeding through a mechanism sensitive to the CCK1R antagonist lorglumide. Antibodies to Y2R revealed expression in both neurons and satellite cells; most of the former (89 +/- 4%) also expressed CCK1R. With fasting there was loss of Y2R immunoreactivity in CCK1R-expressing neurons many of which projected to the stomach, but not in satellite cells or neurons projecting to the ileum or proximal colon. Expression of a Y2R promoter-luciferase reporter (Y2R-luc) in cultured vagal afferent neurons was increased in response to CCK by 12.3 +/- 0.1-fold and by phorbol ester (16.2 +/- 0.4-fold); the response to both was abolished by the protein kinase C inhibitor Ro-32,0432. PYY3-36 stimulated CREB phosphorylation in rat nodose neurons after priming with CCK; in wild-type mice PYY3-36 increased Fos labeling in brainstem neurons but in mice null for CCK1R this response was abolished. Thus Y2R is expressed by functionally distinct subsets of nodose ganglion neurons projecting to the stomach and ileum/colon; in the former expression is dependent on stimulation by CCK, and there is evidence that PYY3-36 effects on vagal afferent neurons are CCK dependent.

Identification of ezrin as a target of gastrin in immature mouse gastric parietal cells.

The gastric acid-secreting parietal cell exhibits profound morphological changes on stimulation. Studies in gastrin null (Gas-KO) mice indicate that maturation of parietal cell function depends on the hormone gastrin acting at the G-protein-coupled cholecystokinin 2 receptor. The relevant cellular mechanisms are unknown. The application of differential mRNA display to samples of the gastric corpus of wild-type (C57BL/6) and Gas-KO mice identified the cytoskeletal linker protein, ezrin, as a previously unsuspected target of gastrin. Gastrin administered in vivo or added to gastric glands in vitro increased ezrin abundance in Gas-KO parietal cells. In parietal cells of cultured gastric glands from wild-type mice treated with gastrin, histamine or carbachol, ezrin was localized to vesicular structures resembling secretory canaliculi. In contrast, in cultured parietal cells from Gas-KO mice, ezrin was typically distributed in the cytosol, and this did not change after incubation with gastrin, histamine or carbachol. However, priming with gastrin for approximately 24 h, either in vivo prior to cell culture or by addition to cultured gastric glands, induced the capacity for secretagogue-stimulated localization of ezrin to large vesicular structures in Gas-KO mice. Similarly, in a functional assay based on measurement of intracellular pH, cultured parietal cells from Gas-KO mice were refractory to gastrin unless primed. The priming effect of gastrin was not attributable to the paracrine mediator histamine, but was prevented by inhibitors of protein kinase C and transactivation of the epidermal growth factor receptor. We conclude that in gastrin null mice there is reduced ezrin expression and a defect in ezrin subcellular distribution in gastric parietal cells, and that both can be reversed by priming with gastrin.

Ghrelin receptors in rat and human nodose ganglia: putative role in regulating CB-1 and MCH receptor abundance.

Intact vagal afferent neurons are required for the satiety effects of the intestinal hormone cholecystokinin (CCK) and the orexigenic effects of the gastric regulatory peptide ghrelin. In this study, we examined the localization of ghrelin receptors in nodose ganglia and their function in regulating the expression of other orexigenic receptors, notably cannabinoid (CB)-1 and melanin-concentrating hormone (MCH)-1 receptors. With the use of RT-PCR, transcripts corresponding to both functional [growth hormone secretagogue receptor (GHS-R)1a] and truncated forms (GHS-R1b) of the ghrelin receptor were detected in rat nodose ganglia. There was no difference in expression between rats fed ad libitum or fasted for up to 48 h. Immunohistochemical studies using antibodies directed at GHS-R1a revealed expression in over 75% of neurons also expressing CCK-1 receptors in the mid- and caudal regions of the ganglion. There was also expression in human nodose ganglia. In fasted rats in which CB-1 and MCH-1 receptor expression was increased, administration of ghrelin prevented the downregulation by refeeding. We conclude that the actions of CCK and ghrelin are mediated by a common population of vagal afferent neurons. Ghrelin may act to limit the action of CCK in depressing expression of CB-1 and MCH-1 receptors and other receptors.

Expression of cannabinoid CB1 receptors by vagal afferent neurons is inhibited by cholecystokinin.

Both inhibitory (satiety) and stimulatory (orexigenic) factors from the gastrointestinal tract regulate food intake. In the case of the satiety hormone cholecystokinin (CCK), these effects are mediated via vagal afferent neurons. We now report that vagal afferent neurons expressing the CCK-1 receptor also express cannabinoid CB1 receptors. Retrograde tracing established that these neurons project to the stomach and duodenum. The expression of CB1 receptors determined by RT-PCR, immunohistochemistry and in situ hybridization in rat nodose ganglia was increased by withdrawal of food for > or =12 hr. After refeeding of fasted rats there was a rapid loss of CB1 receptor expression identified by immunohistochemistry and in situ hybridization. These effects were blocked by administration of the CCK-1 receptor antagonist lorglumide and mimicked by administration of CCK to fasted rats. Because CCK is a satiety factor that acts via the vagus nerve and CB1 agonists stimulate food intake, the data suggest a new mechanism modulating the effect on food intake of satiety signals from the gastrointestinal tract.

Identification of a novel protein complex containing annexin A4, rabphilin and synaptotagmin.

Rabphilin is a synaptic vesicle-associated protein proposed to play a role in regulating neurotransmitter release. Here we report the isolation and identification of a novel protein complex containing rabphilin, annexin A4 and synaptotagmin 1. We show that the rabphilin C2B domain interacts directly with the N-terminus of annexin A4 and mediates the co-complexing of these two proteins in PC12 cells. Analyzing the cellular localisation of these co-complexing proteins we find that annexin A4 is located on synaptic membranes and co-localises with rabphilin at the plasma membrane in PC12 cells. Given that rabphilin and synaptotagmin are synaptic vesicle proteins involved in neurotransmitter release, the identification of this complex suggests that annexin A4 may play a role in synaptic exocytosis.

Localization of orexin-1 receptors to vagal afferent neurons in the rat and humans.

BACKGROUND & AIMS: Orexin-A and -B are brain-gut peptides that stimulate food intake via orexin-R1 and -R2 receptors. Cholecystokinin (CCK) inhibits food intake via CCK(A) receptors expressed on vagal afferent neurons. The purpose of the study was to determine whether vagal afferent neurons express OX-R1 and OX-R2 and whether orexin-A inhibits responses to CCK. METHODS: OX-R1 and -R2 expression by rat and human nodose ganglia was examined by reverse-transcriptase polymerase chain reaction (RT-PCR). Receptor localization was determined by immunohistochemistry. Responses of rat jejunal afferent fibers were examined by electrophysiology. RESULTS: Both rat and human nodose ganglia expressed OX-R1 as detected by RT-PCR, and humans also expressed OX-R2. The identity of the products was confirmed by sequencing. Immunohistochemistry indicated expression of OX-R1 in both species in neurons that also expressed CCK(A) and leptin receptors. In human ganglia there was also expression in glial cells that was absent in rats. Orexin-A had no effect on the resting discharge of afferent nerve fibers but inhibited responses to CCK. CONCLUSIONS: OX-R1 and CCK(A) receptors are expressed by human and rat vagal afferent neurons. Orexin inhibits responses to CCK suggesting a role in modulation of gut to brain signaling.