Functional mapping of NPY/PYY receptors in rat and human gastro-intestinal tract

Cross talk about the role of Neuropeptide Y in CNS disorders and diseases

A peptide composed of a 36 amino acid called Neuropeptide Y (NPY) is employed in a variety of physiological processes to manage and treat conditions affecting the endocrine, circulatory, respiratory, digestive, and neurological systems. NPY naturally binds to G-protein coupled receptors, activating the Y-receptors (Y1-Y5 and y6). The findings on numerous therapeutic applications of NPY for CNS disease are presented in this review by the authors. New targets for treating diseases will be revealed by medication combinations that target NPY and its receptors. This review is mainly focused on disorders such as anxiety, Alzheimer's disease, Parkinson's disease, Huntington's disease, Machado Joseph disease, multiple sclerosis, schizophrenia, depression, migraine, alcohol use disorder, and substance use disorder. The findings from the preclinical studies and clinical studies covered in this article may help create efficient therapeutic plans to treat neurological conditions on the one hand and psychiatric disorders on the other. They may also open the door to the creation of novel NPY receptor ligands as medications to treat these conditions.

Contributions of bile acids to gastrointestinal physiology as receptor agonists and modifiers of ion channels

Bile acids (BAs) are known to be important regulators of intestinal motility and epithelial fluid and electrolyte transport. Over the past two decades, significant advances in identifying and characterizing the receptors, transporters, and ion channels targeted by BAs have led to exciting new insights into the molecular mechanisms involved in these processes. Our appreciation of BAs, their receptors, and BA-modulated ion channels as potential targets for the development of new approaches to treat intestinal motility and transport disorders is increasing. In the current review, we aim to summarize recent advances in our knowledge of the different BA receptors and BA-modulated ion channels present in the gastrointestinal system. We discuss how they regulate motility and epithelial transport, their roles in pathogenesis, and their therapeutic potential in a range of gastrointestinal diseases.

Regulation of neuropeptide Y in body microenvironments and its potential application in therapies: a review

Neuropeptide Y (NPY), one of the most abundant neuropeptides in the body, is widely expressed in the central and peripheral nervous systems and acts on the cardiovascular, digestive, endocrine, and nervous systems. NPY affects the nutritional and inflammatory microenvironments through its interaction with immune cells, brain-derived trophic factor (BDNF), and angiogenesis promotion to maintain body homeostasis. Additionally, NPY has great potential for therapeutic applications against various diseases, especially as an adjuvant therapy for stem cells. In this review, we discuss the research progress regarding NPY, as well as the current evidence for the regulation of NPY in each microenvironment, and provide prospects for further research on related diseases.

Age related changes of neuropeptide Y-ergic system in the rat duodenum

Neuropeptide Y (NPY) is widely distributed in the autonomic nervous system and acts as a neurotransmitter and a trophic factor. However, there is no report concerning the expression of NPY and its receptors in the intestine during postnatal ontogenesis. In the current study, immunohistochemistry and western blot analysis was used to label NPY, Y1R, Y2R and Y5R receptors in the duodenum from rats of different ages (1-, 10-, 20-, 30-, 60-day-old and 2-year-old). The obtained data suggest age-dependent changes of NPY-mediated gut innervation. NPY-immunoreactive (IR) neurons were observed in the myenteric (MP) and submucous (SP) plexus from the moment of birth. In the MP, the percentage of NPY-IR neurons was low and varied from 4.1 ± 0.32 in 1-day-old to 2.9 ± 0.62 in 2-year-old rats. The proportion of NPY-IR myenteric neurons did not change significantly through the senescence (p > .05). In the SP, the proportion of NPY-IR neurons significantly increased in the first month of life from 56.3 ± 2.4% in 1-day-old to 78.1 ± 5.18% in 20-day-old and significantly decreased from 75.6 ± 4.62% in 30-day-old rats to 59.8 ± 4.24% in 2-year-old rats. The expression of NPY in the duodenum did not change significantly during the development by western blot analysis. The expression of Y1R and Y2R was low in newborns and upregulated in the first ten days of life. The expression of Y5R was maximal in newborn pups and significantly decreased in in the first 20 days. Thus, there are some fluctuation of the percentage of NPY-IR neurons accompanies changes in relation of different subtypes of NPY receptors in the small intestine during postnatal ontogenesis.

Enteroendocrine Regulation of Nutrient Absorption

Enteroendocrine cells (EECs) in the intestine regulate many aspects of whole-body physiology and metabolism. EECs sense luminal and circulating nutrients and respond by secreting hormones that act on multiple organs and organ systems, such as the brain, gallbladder, and pancreas, to control satiety, digestion, and glucose homeostasis. In addition, EECs act locally, on enteric neurons, endothelial cells, and the gastrointestinal epithelium, to facilitate digestion and absorption of nutrients. Many recent reports raise the possibility that EECs and the enteric nervous system may coordinate to regulate gastrointestinal functions. Loss of all EECs results in chronic malabsorptive diarrhea, placing EECs in a central role regulating nutrient absorption in the gut. Because there is increasing evidence that EECs can directly modulate the efficiency of nutrient absorption, it is possible that EECs are master regulators of a feed-forward loop connecting appetite, digestion, metabolism, and abnormally augmented nutrient absorption that perpetuates metabolic disease. This review focuses on the roles that specific EEC hormones play on glucose, peptide, and lipid absorption within the intestine.

Peptide Tyrosine Tyrosine 3-36 Reduces Meal Size and Activates the Enteric Neurons in Male Sprague-Dawley Rats

BACKGROUND

Peptide tyrosine tyrosine 3-36 (peptide YY 3-36 or PYY 3-36) reduces food intake by unknown site(s).

AIM

To test the hypothesis that the gastrointestinal tract contains sites of action regulating meal size (MS) and intermeal interval (IMI) length by PYY 3-36.

METHODS

Peptide YY 3-36 (0, 1, 5, 10 and 20 nmol/kg) was injected in the aorta, the artery that supplies the gastrointestinal tract, prior to the onset of the dark cycle in free feeding male Sprague-Dawley rats and food intake was measured. Then, PYY 3-36 (25 nmol/kg) was injected intraperitoneally in these rats and Fos-like immunoreactivity (Fos-LI, a marker for neuronal activation) was quantified in the small intestinal enteric neurons, both myenteric and submucosal, and the dorsal vagal complex (DVC) of the hindbrain.

RESULTS

PYY 3-36 reduced first MS, decreased IMI length, shortened duration of first meal and increased Fos-LI in enteric and DVC neurons. However, PYY 3-36 failed to change the size of the second meal, satiety ratio, latency to first meal, number of meals and 24 h intake relative to saline control.

CONCLUSION

The gastrointestinal tract may contain sites of action regulating MS reduction by PYY 3-36.

TLR ligands and butyrate increase Pyy expression through two distinct but inter-regulated pathways

The intestinal epithelium is an active barrier separating the host from its microbiota. It senses microbial compounds through expression of a wide range of receptors including the Toll-like receptors (TLRs). TLRs have been shown to regulate epithelium permeability or secretion of defensin by Paneth cells. However, the expression and function of TLRs in enteroendocrine L-cells, a specific subtype of intestinal cells secreting PYY and GLP-1, have not yet been assessed. PYY and GLP-1 are implicated in regulation of gut motility, food intake and insulin secretion, and are of great interest regarding obesity and type 2 diabetes. Using a cellular model of human L-cells and a reporter system for NF-κB activation pathway, we reported functional expression of TLRs in these cells. Stimulation with specific TLR-agonists increased expression of Pyy but not Proglucagon in an NF-κB-dependent manner. Moreover, the effect of TLR stimulation was additive to butyrate, a product of bacterial fermentation, on Pyy expression. Additionally, butyrate also increased Tlr expression, including Tlr4, and the NF-κB response to TLR stimulation. Altogether, our results demonstrated a role of TLRs in the modulation of Pyy expression and the importance of butyrate, a product of bacterial fermentation in regulation of microbial TLR-dependent sensing.

Gut feedback mechanisms and food intake: a physiological approach to slow carbohydrate bioavailability

Glycemic carbohydrates in foods are an important macronutrient providing the biological fuel of glucose for a variety of physiological processes. A classification of glycemic carbohydrates into rapidly digestible carbohydrate (RDC) and slowly digestible carbohydrate (SDC) has been used to specify their nutritional quality related to glucose homeostasis that is essential to normal functioning of the brain and critical to life. Although there have been many studies and reviews on slowly digestible starch (SDS) and SDC, the mechanisms of their slow digestion and absorption were mostly investigated from the material side without considering the physiological processes of their in vivo digestion, absorption, and most importantly interactions with other food components and the gastrointestinal tract. In this article, the physiological processes modulating the bioavailability of carbohydrates, specifically the rate and extent of their digestion and absorption as well as the related locations, in a whole food context, will be discussed by focusing on the activities of the gastrointestinal tract including glycolytic enzymes and glucose release, sugar sensing, gut hormones, and neurohormonal negative feedback mechanisms. It is hoped that a deep understanding of these physiological processes will facilitate the development of innovative dietary approaches to achieve desired carbohydrate or glucose bioavailability for improved health.

Neuropeptide Y receptors: a promising target for cancer imaging and therapy

Neuropeptide Y (NPY) was first identified from porcine brain in 1982, and plays its biological functions in humans through NPY receptors (Y₁, Y₂, Y₄ and Y₅). NPY receptors are known to mediate various physiological functions and involve in a majority of human diseases, such as obesity, hypertension, epilepsy and metabolic disorders. Recently, NPY receptors have been found to be overexpressed in many cancers, so they emerged as promising target in cancer diagnosis and therapy. This review focuses on the latest research about NPY and NPY receptors, and summarizes the current knowledge on NPY receptors expression in cancers, selective ligands for NPY receptors and their application in cancer imaging and therapy.

Mutations in arrestin-3 differentially affect binding to neuropeptide Y receptor subtypes

Based on the identification of residues that determine receptor selectivity in arrestins and the phylogenetic analysis of the arrestin (arr) family, we introduced fifteen mutations of receptor-discriminator residues in arr-3, which were identified previously using mutagenesis, in vitro binding, and BRET-based recruitment assay in intact cells. The effects of these mutations were tested using neuropeptide Y receptors Y1R and Y2R. NPY-elicited arr-3 recruitment to Y1R was not affected by these mutations, or even alanine substitution of all ten residues (arr-3-NCA), which prevented arr-3 binding to other receptors tested so far. However, NCA and two other mutations prevented agonist-independent arr-3 pre-docking to Y1R. In contrast, eight out of 15 mutations significantly reduced agonist-dependent arr-3 recruitment to Y2R. NCA eliminated arr-3 binding to active Y2R, whereas Tyr239Thr reduced it ~7-fold. Thus, manipulation of key residues on the receptor-binding surface generates arr-3 with high preference for Y1R over Y2R. Several mutations differentially affect arr-3 pre-docking and agonist-induced recruitment. Thus, arr-3 recruitment to the receptor involves several mechanistically distinct steps. Targeted mutagenesis can fine-tune arrestins directing them to specific receptors and particular activation states of the same receptor.

Neuropeptide Y receptors: how to get subtype selectivity

The neuropeptide Y (NPY) system is a multireceptor/multiligand system consisting of four receptors in humans (hY(1), hY(2), hY(4), hY(5)) and three agonists (NPY, PYY, PP) that activate these receptors with different potency. The relevance of this system in diseases like obesity or cancer, and the different role that each receptor plays influencing different biological processes makes this system suitable for the design of subtype selectivity studies. In this review we focus on the latest findings within the NPY system, we summarize recent mutagenesis studies, structure activity relationship studies, receptor chimera, and selective ligands focusing also on the binding mode of the native agonists.

Short communication: expression of peptide YY, proglucagon, neuropeptide Y receptor Y2, and glucagon-like peptide-1 receptor in bovine peripheral tissues

The role of distal gut signals in control of feed intake and metabolism in cattle has received scant attention. Peptide YY (PYY) and glucagon-like peptide-1, which are secreted from enteroendocrine cells of the distal gut in monogastrics have several functions, including regulation of energy balance. However, little is known of the tissue expression of these peptides and their receptors in cattle. The aim of the current study was to characterize the tissue distribution of PYY, neuropeptide Y receptor Y2 (Y2), proglucagon (GCG), and glucagon-like peptide-1 receptor (GLP1R) in various peripheral tissues of cattle. Four male 7-wk-old dairy calves were euthanized and 16 peripheral tissues were collected. Conventional PCR and quantitative real-time PCR were performed to confirm tissue expression and quantify the transcript abundance in various tissues. The results of conventional PCR revealed that mRNA for both PYY and Y2 was detectable in the rumen, abomasum, duodenum, jejunum, ileum, and colon but not in other tissues. Quantitative real-time PCR data demonstrated that PYY mRNA was 2- to 3-fold greater in the pancreas, kidney, and heart relative to the liver. By conventional PCR, GCG mRNA was detected in the abomasum, duodenum, jejunum, ileum, and colon and GLP1R mRNA was expressed in all gut segments, pancreas, spleen, and kidney. Quantitative real-time PCR data demonstrated that, relative to transcript abundance in the liver, GCG mRNA was 4- to 40-fold higher from abomasum to colon, and GLP1R mRNA was 50- to 300-fold higher from the rumen to colon, 14-fold greater in the pancreas, 18-fold higher in the spleen, and 166-fold greater in the kidney. The tissue distribution of PYY, GCG, and their receptors observed in the current study is, in general, consistent with expression patterns in monogastrics. The predominant expression of PYY, Y2, and GCG in the gut, and the presence of GLP1R in multiple peripheral tissues suggest a role for PYY in controlling gut functions and for GLP-1 in regulating multiple physiological functions in cattle.

Peripheral peptide YY inhibits propulsive colonic motor function through Y2 receptor in conscious mice

Peptide YY (PYY) antisecretory effect on intestinal epithelia is well established, whereas less is known about its actions to influence colonic motility in conscious animals. We characterized changes in basal function and stimulated colonic motor function induced by PYY-related peptides in conscious mice. PYY(3-36), PYY, and neuropeptide Y (NPY) (8 nmol/kg) injected intraperitoneally inhibited fecal pellet output (FPO) per hour during novel environment stress by 90%, 63%, and 57%, respectively, whereas the Y(1)-preferring agonists, [Pro(34)]PYY and [Leu(31),Pro(34)]NPY, had no effect. Corticotrophin-releasing factor 2 receptor antagonist did not alter PYY(3-36) inhibitory action. PYY and PYY(3-36) significantly reduced restraint-stimulated defecation, and PYY(3-36) inhibited high-amplitude distal colonic contractions in restrained conscious mice for 1 h, by intraluminal pressure with the use of a microtransducer. PYY suppression of intraperitoneal 5-hydroxytryptophan induced FPO and diarrhea was blocked by the Y(2) antagonist, BIIE0246, injected intraperitoneally and mimicked by PYY(3-36), but not [Leu(31),Pro(34)]NPY. PYY(3-36) also inhibited bethanechol-stimulated FPO and diarrhea. PYY(3-36) inhibited basal FPO during nocturnal feeding period and light phase in fasted/refed mice for 2-3 h, whereas the reduction of food intake lasted for only 1 h. PYY(3-36) delayed gastric emptying after fasting-refeeding by 48% and distal colonic transit time by 104%, whereas [Leu(31),Pro(34)]NPY had no effect. In the proximal and distal colon, higher Y(2) mRNA expression was detected in the mucosa than in muscle layers, and Y(2) immunoreactivity was located in nerve terminals around myenteric neurons. These data established that PYY/PYY(3-36) potently inhibits basal and stress/serotonin/cholinergic-stimulated propulsive colonic motor function in conscious mice, likely via Y(2) receptors.

New method of manometric measurement of gastroduodenal motility in conscious mice: effects of ghrelin and Y2 depletion

Since no previous studies have reported dual measurements of stomach and duodenal motility in conscious mice, we developed a manometric method to measure the gastroduodenal motility in the physiological fed and fasted states of conscious mice. By this method we measured, for the first time, the gastroduodenal motility in Y2 knockout mice and analyzed the effects of ghrelin on the gastroduodenal motility in conscious mice. To evaluate this new method, we provide the comparison on the effects of CCK-8 examined by present and previous methods. In the fasted state of mice, phase III-like contractions with frequencies of 7.8 +/- 0.5 contractions/h in the antrum and 6.6 +/- 0.7 contractions/h in the duodenum were observed. This fasted pattern was disrupted and replaced by the fed pattern after feeding, with an increase of the motor index (MI) immediately after feeding. Intravenous injection of ghrelin induced the fasted pattern in the duodenum when injected in the fed state and increased %MI (114.3 +/- 9.8%) compared with saline-injected controls (64.4 +/- 9.6%) in the antrum. Intravenous injection of CCK-8 disrupted phase III-like contractions in both antrum and duodenum, which were replaced by fed-like motor patterns accompanied with the elevation of baseline pressure. In Y2 knockout mice, the frequency of phase III-like contractions was decreased in the antrum compared with wild-type mice and the immediate increase of MI after feeding seen in wild-type mice was disrupted in Y2 knockout mice. Our model provides a new method for studies of gastrointestinal motility in various mouse models, including transgenic and knockout ones.

The pancreatic polypeptide family and the migrating motor complex of the rat: differential effects in the duodenum and jejunum

AIM

To investigate the effects of members of the pancreatic polypeptide family on migrating myoelectric complexes in rats in vivo.

METHODS

Rats were supplied with bipolar electrodes at 5 (duodenum), 15 and 25 cm (jejunum) distal to pylorus for electromyography. The natural ligands neuropeptide Y, pancreatic polypeptide, peptide YY1-36 and peptide YY3-36 were infused IV at doses of 0.5-400 pmol kg(-1) min(-1). The mechanisms of action were studied after pre-treatment with N(omega)-nitro-L-arginine (L-NNA) 1 mg kg(-1), guanethidine 3 mg kg(-1) and in bilaterally vagotomized animals.

RESULTS

PP inhibited myoelectrical activity dose-dependently in both the duodenum (ED50 5.8 pmol kg(-1) min(-1)) and jejunum (2.6 pmol kg(-1) min(-1)). PYY1-36 and PYY3-36 also had inhibitory effect in the jejunum (4.4 and 130 pmol kg(-1) min(-1), respectively). PYY1-36 had no significant effect in the duodenum, whereas PYY3-36 stimulated myoelectrical activity at the highest doses. NPY was without effect. In the jejunum neither L-NNA, guanethidine or vagotomy had any significant influence on the inhibitory effects of PP, PYY1-36 and PYY3-36. In the duodenum, the effect of PP was inhibited by guanethidine, but not L-NNA or vagotomy. The stimulatory effect of PYY3-36 in the duodenum was blocked by L-NNA and vagotomy, whereas guanethidine was without effect.

CONCLUSION

Peptides of the PP family modulate small bowel motility differentially. Whereas their general effect is inhibitory in the jejunum, the mixing duodenal compartment is stimulated by PYY3-36, suggested to reflect receptor distribution distinction in the gut. This implicates distribution of distinct receptors in the gut being activated by either peptide.

Neuropeptide Y receptors; antisecretory control of intestinal epithelial function

This paper reviews the cellular localisation, mechanisms of release and intestinal absorptive actions of neuropeptide Y and its related peptides, peptide YY, pancreatic polypeptide and major fragments NPY(3-36) and PYY(3-36). While NPY is commonly found in inhibitory enteric neurons that can be interneurons, motor neurons or secretomotor-nonvasodilator in nature, its analogue, peptide YY in contrast, is located in neuroendocrine L-cells that predominate in the colorectal mucosa. Peptide YY is released from these cells when nutrients arrive in the small or large bowel, exerting paracrine as well as hormonal actions. Pancreatic polypeptide is found in relatively few, scattered intestinal endocrine cells, the majority of this peptide being produced by, and released from pancreatic islet F-cells in response to food intake. An introduction to the current pharmacology of this family of peptides is provided and the different types of neuropeptide Y (termed Y) receptors, their agonist preferences, antagonism, and preferred signalling pathways, are described. Our current understanding of specific Y receptor localisation within the intestine as determined by immunohistochemistry, is presented as a prelude to an assessment of functional studies that have monitored ion transport across isolated mucosal preparations. It is becoming clear that three Y receptor types are significant functionally in human colon, as well as particular rodent models (e.g. mouse) and these, namely the Y(1), Y(2) and Y(4) receptors, are discussed in detail. Their presence within the basolateral aspect of the epithelial layer (Y(1) and Y(4) receptors) or on enteric neurons (Y(1) and Y(2) receptors) and their activation by endogenous neuropeptide Y, peptide YY (Y(1) and Y(2) receptors) or pancreatic polypeptide (which prefers Y(4) receptors) results consistently in antisecretory/absorptive responses. The recent use of novel mouse knockouts has helped establish loss of specific intestinal functions including Y(1) and Y(2) receptor-mediated absorptive tone in colon mucosa. Progress in this field has been rapid recently, aided by the availability of selective antagonists and mutant mice lacking either one (e.g. Y(4)-/-, for which no antagonists exist at present) or more Y receptor types. It is therefore timely to review this work and present a rational basis for developing stable synthetic Y receptor agonists as novel anti-diarrhoeals.

Enzyme-based visualization of receptor-ligand binding in tissues

New methods of elucidating the ligand-binding activity of receptors could improve our understanding of receptor function, key events they control, and their presence in normal and pathological states. We describe a method for visualizing receptor-ligand binding in cells and tissues that substitutes fluorescein for radioactive labels, and detects receptor bound, fluoresceinated ligand with an antifluorescein/horseradish peroxidase amplification system. Receptor-bound ligand is then visualized by light microscopy against a standard hemotoxylin-stained background of cell structure. Quantitative versions of the assay provide an apparent dissociation constant and number of receptors per cell at saturation in cell or tissue specimens. Receptors examined include the folate receptor, bombesin peptide-binding receptors, the epidermal growth factor receptor, the neuropeptide Y receptor, the asialoglycoprotein receptor, and RGD peptide-binding integrins. Using fluoresceinated versions of molecules, we show the method can visualize and quantitate receptor-bound ligands in cell culture monolayers and animal tissue specimens. Ligand binding to receptors present in tissues was visualized in normal and pathological samples of human tissue microarrays. The enzyme-amplified detection of receptor-bound fluoresceinated ligand is a simple and nonradioactive-based method that provides information on the receptor activity in tissue specimens.

The regulation of veratridine-stimulated electrogenic ion transport in mouse colon by neuropeptide Y (NPY), Y1 and Y2 receptors

1 Neuropeptide Y (NPY) is a prominent enteric neuropeptide with prolonged antisecretory effects in mammalian intestine. Veratridine depolarises neurons consequently causing epithelial anion secretion across mouse colon mucosa. Our aim was to characterise functionally, veratridine-stimulated mucosal responses and to determine the roles for NPY, Y(1), and Y(2) receptors in modulating these neurogenic effects. 2 Colon mucosae (with intact submucous innervation) from wild-type mice (+/+) and knockouts lacking either NPY (NPY-/-), Y(1)-/- or Y(2)-/- were placed in Ussing chambers and voltage clamped at 0 mV. Veratridine-stimulated short-circuit current (I(sc)) responses in +/+, Y(1) or Y(2) antagonist pretreated +/+ colon, Y(1)-/- and NPY-/- colon were insensitive to cholinergic blockade by atropine (At; 1 microM) and hexamethonium (Hex; 10 microM). Tetrodotoxin (TTX, 100 nM) abolished veratridine responses, but had no effect upon carbachol (CCh) or vasoactive intestinal polypeptide (VIP)-induced secretory responses. 3 To establish the functional roles for Y(1) and Y(2) receptors, +/+ tissues were pretreated with either the Y(1) or Y(2) receptor antagonist (BIBO3304 (300 nM) or BIIE0246 (1 microM), respectively) and veratridine responses were compared with those from Y(1)-/- or Y(2)-/- colon. Neither BIBO3304 nor Y(1)-/- altered veratridine-induced secretion, but Y(1) agonist responses were abolished in both preparations. In contrast, the Y(2) antagonist BIIE0246 significantly amplified veratridine responses in +/+ mucosa. Unexpectedly, NPY-/- colon exhibited significantly attenuated veratridine responses (between 1 and 5 min). 4 We demonstrate that electrogenic veratridine responses in mouse colon are noncholinergic and that NPY can act directly upon epithelia, a Y(1) receptor effect. The enhanced veratridine response observed in +/+ tissue following BIIE0246, indicates that Y(2) receptors are located on submucosal neurons and that their activation by NPY will inhibit enteric noncholinergic secretory neurotransmission. 5 We also demonstrate Y(1) and Y(2) receptor-mediated antisecretory tone in +/+ colon and show selective loss of each in Y(1) and Y(2) null colon respectively. In NPY-/- tissue, only Y(1)-mediated tone was present, this presumably being mediated by endogenous endocrine peptide YY. Y(2) tone was absent from NPY-/- (and Y(2)-/-) colon and we conclude that NPY activation of neuronal Y(2) receptors attenuates secretory neurotransmission thereby providing an absorptive electrolyte tone in isolated colon.

Functional expression of neuropeptide Y receptors in human neuroblastoma cells

Expression of neuropeptide Y (NPY) receptors in human SK-N-MC neuroblastoma cells was investigated. Reverse transcriptase-polymerase chain reaction (RT-PCR) revealed that Y1, Y4, and Y5 receptors were expressed in these cells. Expression was confirmed by Western blot and immunocytochemistry demonstrated abundant presence of all three receptors on cell membranes. NPY peptide was also expressed in these cells, but other members of the larger peptide family (peptide YY and pancreatic polypeptide) were not expressed. Incubation with U0126, a specific mitogen-activated protein kinase (MAPK) inhibitor, decreased cell number in serum-free medium culture. Since NPY activates MAPK via different subtypes of NPY receptors, results suggest that endogenously expressed NPY may control proliferation of these cells through a paracrine/autocrine mechanism.

Differential expression of Y receptors and signaling pathways in intestinal circular and longitudinal smooth muscle

The expression and mechanisms of action of Y receptors were examined in dispersed intestinal smooth muscle cells of the rabbit. The mixed Y1/Y2 agonists, NPY and PYY, and the Y2 agonist, NPY13-36, elicited concentration-dependent contraction of circular muscle cells that was inhibited by the selective Y2 antagonist, BIIE 0246. The Y4 agonist, PP, elicited similar, though weaker, contraction that was insensitive to Y1 and Y2 antagonists. The Y1 agonist, [Leu31, Pro34]NPY, did not elicit contraction of circular muscle cells. All Y receptor agonists inhibited cAMP formation in a PTx-sensitive fashion. In contrast, none of the agonists caused contraction of longitudinal muscle cells, and only the mixed Y1/Y2 agonists, NPY and PYY, and the Y1 agonist, [Leu31, Pro34]NPY, inhibited cAMP formation and VIP-induced muscle cell relaxation. 125I-PYY binding in longitudinal muscle cells was inhibited by NPY, PYY, [Leu31, Pro34]NPY and the Y1 antagonist, BIBP 3226. Contraction of circular but not longitudinal muscle cells by Y2 and Y4 agonists was observed also in cells isolated from human jejunum. The results indicate that Y2 and Y4 receptors are present only in intestinal circular muscle cells where they mediate contraction that is insensitive to PTx or Ca2+ channel blockers. Y1 receptors, negatively coupled to adenylyl cyclase, are present in cells from both layers.

Clinical endocrinology and metabolism. Receptors for gut peptides

Most gut peptides exert their effects through G protein-coupled receptors, a family of about 700 membrane proteins, 87 of which are presently known to have peptide ligands. Three additional gut peptide receptors are not G protein-coupled receptors but regulate intracellular cyclic GMP accumulation. The aim of this review is to illustrate how the sequencing of the human genome and other recent advances in genomics has contributed to our understanding of the role of peptides and their receptors in gastrointestinal function. Recent discoveries include the identification of receptors for the peptides motilin and neuromedin U, and new physiological ligands for the PTH2 receptor, the CRF(2) receptor and the growth hormone secretagogue receptor. Knockout mice lacking specific peptide receptors or their ligands provide informative animal models in which to determine the functions of the numerous peptide-receptor systems in the gut and to predict which of them may be the most fruitful for drug development. Some peptide-receptor signalling systems may be more important in disease states than they are in normal physiology. For example, substance P, galanin, bradykinin and opioids play important roles in visceral pain and inflammation. Other peptides may have developmental roles: for example, disruption of endothelin-3 signalling prevents the normal development of the enteric nervous system and contributes to the pathogenesis of Hirschsprung disease.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

Coexpression of Y1, Y2, and Y4 receptors in smooth muscle coupled to distinct signaling pathways

Coexpression of Y1, Y2, and Y4 receptors on smooth muscle cells was determined by reverse transcription-polymerase chain reaction, and the receptors were characterized by radioligand binding, selective receptor protection, and functional analysis of signaling pathways. 125I-peptide YY (PYY) binding was completely inhibited by neuropeptide Y (NPY) and PYY, and partially inhibited by the Y1 agonist [Leu31, Pro34]NPY or the Y2 agonist NPY13-36. In cells where Y1 receptors were preserved by selective receptor protection, 125I-PYY binding was selectively inhibited by the Y1 agonist or antagonist BIBP 3226 [(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine-amide]. Conversely, in cells where Y2 receptors were preserved, 125I-PYY binding was selectively inhibited by the Y2 agonist or antagonist BIIE 0246 [(S)N2-[1-[2-[4-[(R,S)-5,11-dihydro-6(66H)-oxodibenz[b,e]azepin-11-y]-1piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-35(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide]. All Y receptors activated preferentially Gi2, but only Y2 and Y4 receptors activated Gq. Consequently, Y2 agonists (NPY, PYY, and NPY13-36) and the Y4 agonist (pancreatic polypeptide) induced concentration-dependent contraction, inositol 1,4,5-trisphosphate (IP3) formation, and increase in cytosolic free Ca2+. Contraction induced by Y2 and Y4 agonists was not affected by 0 Ca2+, Ca2+ channel blockers, or pertussis toxin (PTx), but it was abolished by thapsigargin, U73122 [1-(6-(17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-25-dione], or the myosin light chain kinase inhibitor ML-9 [1-(5-chloronaphthalene-1-sulfonyl)homopiperazine, HCl]. Y2-mediated contraction was inhibited by the selective Y2 antagonist BIIE 0246. Insensitivity to PTx implied that the coupling to Gi did not initiate (Y1) or contribute (Y2 and Y4) to contraction. All Y receptor agonists inhibited cAMP formation in a PTx-sensitive manner. The patterns of contraction and inhibition of cAMP by various Y receptors were corroborated by selective receptor protection. The study demonstrates coexpression of Y1, Y2, and Y4 receptors on smooth muscle negatively coupled to adenylyl cyclase via Gi2. Coupling of Y2 and Y4 receptors to Gq determines their ability to induce IP3-dependent Ca2+ release and initiate contraction.