Agonists for neuropeptide Y receptors Y1 and Y5 stimulate different phases of feeding in guinea pigs

Receptor-specific recognition of NPY peptides revealed by structures of NPY receptors

In response to three highly conserved neuropeptides, neuropeptide Y (NPY), peptide YY, and pancreatic polypeptide (PP), four G protein-coupled receptors mediate multiple essential physiological processes, such as food intake, vasoconstriction, sedation, and memory retention. Here, we report the structures of the human Y₁, Y₂, and Y₄ receptors in complex with NPY or PP, and the G_i1 protein. These structures reveal distinct binding poses of the peptide upon coupling to different receptors, reflecting the importance of the conformational plasticity of the peptide in recognizing the NPY receptors. The N terminus of the peptide forms extensive interactions with the Y₁ receptor, but not with the Y₂ and Y₄ receptors. Supported by mutagenesis and functional studies, subtype-specific interactions between the receptors and peptides were further observed. These findings provide insight into key factors that govern NPY signal recognition and transduction, and would enable development of selective drugs.

Neuropeptide Y and its receptors are expressed in chicken skeletal muscle and regulate mitochondrial function

Neuropeptide Y (NPY) is a highly conserved 36-amino acid neurotransmitter, which is primarily expressed in the mammalian arcuate nucleus of the hypothalamus. It is a potent orexigenic neuropeptide, stimulating appetite and inducing feed intake in a variety of species. Recent research has shown that NPY and its receptors can be expressed by peripheral tissues, but their role is not yet well defined. Specifically, this information is particularly sparse in avian species. Therefore, the aim of this study was to determine the expression of NPY and its receptors, and determine their regulation by environmental and nutritional stressors, in the skeletal muscle of avian species using in vivo and in vitro approaches. Here, we show that NPY and its receptors are expressed in chicken breast and leg muscle as well as in quail myoblast (QM7) cell line. Intraperitoneal injection of recombinant NPY increased feed intake in 9-d old chicks and upregulated the expression of NPY and NPY receptors in breast and leg muscle, suggesting autocrine and/or paracrine roles for NPY. Additionally, NPY is able to modulate the mitochondrial network. In breast muscle, a low dose of NPY upregulated (P < 0.05) the expression of genes involved in ATP production (uncoupling protein, UCP; nuclear factor erythroid 2 like 2, NFE2L2) and dynamics (mitofusin 1, MFN1), while a high dose decreased (P < 0.05) markers of mitochondrial dynamics (mitofusin 2, MFN2; OPA1 mitochondrial dynamin like GTPase, OPA1) and increased (P < 0.05) genes involved in mitochondrial biogenesis (D-loop, peroxisome proliferator activated receptor gamma, PPARG). In leg muscle, NPY decreased (P < 0.05) markers of mitochondrial biogenesis and ATP synthesis (D-loop; peroxisome proliferator activated receptor alpha, PCG1A; peroxisome proliferator-activated receptor gamma, coactivator 1 beta, PPARGC1B; PPARG; NFE2L2). In QM7 cells, genes associated with mitochondrial biogenesis, dynamics, and ATP synthesis were all upregulated (P < 0.05), even though basal respiration and ATP production were decreased (P < 0.05) with NPY treatment as measured by XF Flux analysis. Together, these data show that the NPY system is expressed in avian skeletal muscle and plays a role in mitochondrial function.

Rational Development of Stable PYY3-36 Peptide Y2 Receptor Agonists

PURPOSE

The anorectic effect of PYY_3-36 makes it a potential pharmacological weight loss treatment. Modifications of the endogenous peptide to obtain commercially attractive pharmacological and biophysical stability properties are examined.

METHODS

Half-life extended PYY_3-36 analogues were prepared and examined regarding Y₂-receptor potency as well as biophysical and stability properties.

RESULTS

Deamidation of asparagine in position 18 and 29 was observed upon incubation at 37°C. Asparagine in position 18 - but not position 29 - could be substituted to glutamine without detrimental effects on Y₂-receptor potency. Covalent dimers were formed via the phenol impurity benzoquinone reacting with two N-terminal residues (Isoleucine-Lysine). Both residues had to be modified to suppress dimerization, which could be done without negatively affecting Y₂-receptor potency or other stability/biophysical properties. Introduction of half-life extending modifications in position 30 and 35 eliminated aggregation at 37°C without negatively affecting other stability properties. Placement of a protracting moiety (fatty acid) in the receptor-binding C-terminal region reduced Y₂-receptor potency substantially, whereas only minor effects of protractor position were observed on structural, biophysical or stability properties. Lipidated PYY_3-36 analogues formed oligomers of various sizes depending on primary structure and solution conditions.

CONCLUSIONS

By rational design, a chemically and physically stable Y₂-receptor selective, half-life extended PYY_3-36 peptide has been developed.

Chemical modification of neuropeptide Y for human Y1 receptor targeting in health and disease

As a very abundant neuropeptide in the brain and widely distributed peptide hormone in the periphery, neuropeptide Y (NPY) appears to be a multisignaling key peptide. Together with peptide YY, pancreatic polypeptide and the four human G protein-coupled receptor subtypes hY1R, hY2R, hY4R and hY5R it forms the NPY/hYR multiligand/multireceptor system, which is involved in essential physiological processes as well as in human diseases. In particular, NPY-induced hY1R signaling plays a central role in the regulation of food intake and stress response as well as in obesity, mood disorders and cancer. Thus, several hY1R-preferring NPY analogs have been developed as versatile tools to unravel the complex NPY/hY1R signaling in health and disease. Further, these peptides provide basic lead structures for the development of innovative drugs. Here, the current research is summarized focusing on the development of differently sized hY1R-preferring NPY analogs as well as their advances with respect to hY1R profiling, potential therapeutic applications and targeted cancer imaging and therapy. Finally, major limitations and innovative strategies for next generation hY1R-preferring NPY analogs are addressed.

Islet neuropeptide Y receptors are functionally conserved and novel targets for the preservation of beta-cell mass

AIMS

Two unmet therapeutic strategies for diabetes treatment are prevention of beta-cell death and stimulation of beta-cell replication. Our aim was to characterize the role of neuropeptide Y receptors in the control of beta-cell mass.

MATERIALS AND METHODS

We used endogenous and selective agonists of the NPY receptor system to explore its role in the prevention of beta-cell apoptosis and proliferation in islets isolated from both mouse and human donors. We further explored the intra-cellular signalling cascades involved, using chemical inhibitors of key signalling pathways. As proof of principle we designed a long-acting analogue of [Leu³¹ Pro³⁴ ]-NPY, an agonist of the islet-expressed Y receptors, to determine if targeting this system could preserve beta-cell mass in vivo.

RESULTS

Our data reveal that NPY Y1, 4 and 5 receptor activation engages a generalized and powerful anti-apoptotic pathway that protects mouse and human islets from damage. These anti-apoptotic effects were dependent on stimulating a Gαi-PLC-PKC signalling cascade, which prevented cytokine-induced NFkB signalling. NPY receptor activation functionally protected islets by restoring glucose responsiveness following chemically induced injury in both species. NPY receptor activation attenuated beta-cell apoptosis, preserved functional beta-cell mass and attenuated the hyperglycaemic phenotype in a low-dose streptozotocin model of diabetes.

CONCLUSION

Taken together, our observations identify the islet Y receptors as promising targets for the preservation of beta-cell mass. As such, targeting these receptors could help to maintain beta-cell mass in both type 1 and type 2 diabetes, and may also be useful for improving islet transplantation outcomes.

Neuropeptide Y in Alcohol Addiction and Affective Disorders

Neuropeptide Y (NPY), a neuropeptide highly conserved throughout evolution, is present at high levels in the central nervous system (CNS), as well as in peripheral tissues such as the gut and cardiovascular system. The peptide exerts its effects via multiple receptor subtypes, all belonging to the G-protein-coupled receptor superfamily. Of these subtypes, the Y1 and the Y2 are the most thoroughly characterized, followed by the Y5 subtype. NPY and its receptors have been shown to be of importance in central regulation of events underlying, for example, affective disorders, drug/alcohol use disorders, and energy homeostasis. Furthermore, within the CNS, NPY also affects sleep regulation and circadian rhythm, memory function, tissue growth, and plasticity. The potential roles of NPY in the etiology and pathophysiology of mood and anxiety disorders, as well as alcohol use disorders, have been extensively studied. This focus was prompted by early indications for an involvement of NPY in acute responses to stress, and, later, also data pointing to a role in alterations within the CNS during chronic, or repeated, exposure to adverse events. These functions of NPY, in addition to the peptide's regulation of disease states, suggest that modulation of the activity of the NPY system via receptor agonists/antagonists may be a putative treatment mechanism in affective disorders as well as alcohol use disorders. In this review, we present an overview of findings with regard to the NPY system in relation to anxiety and stress, acute as well as chronic; furthermore we discuss post-traumatic stress disorder and, in part depression. In addition, we summarize findings on alcohol use disorders and related behaviors. Finally, we briefly touch upon genetic as well as epigenetic mechanisms that may be of importance for NPY function and regulation. In conclusion, we suggest that modulation of NPY-ergic activity within the CNS, via ligands aimed at different receptor subtypes, may be attractive targets for treatment development for affective disorders, as well as for alcohol use disorders.

Homeostasis in anorexia nervosa

Brainstem and hypothalamic “orexigenic/anorexigenic” networks are thought to maintain body weight homeostasis in response to hormonal and metabolic feedback from peripheral sites. This approach has not been successful in managing over- and underweight patients. It is suggested that concept of homeostasis has been misinterpreted; rather than exerting control, the brain permits eating in proportion to the amount of physical activity necessary to obtain food. In support, animal experiments have shown that while a hypothalamic “orexigen” excites eating when food is abundant, it inhibits eating and stimulates foraging when food is in short supply. As the physical price of food approaches zero, eating and body weight increase without constraints. Conversely, in anorexia nervosa body weight is homeostatically regulated, the high level of physical activity in anorexia is displaced hoarding for food that keeps body weight constantly low. A treatment based on this point of view, providing patients with computerized mealtime support to re-establish normal eating behavior, has brought 75% of patients with eating disorders into remission, reduced the rate of relapse to 10%, and eliminated mortality.

Mechanisms by which the orexigen NPY regulates anorexigenic α-MSH and TRH

Protein posttranslational processing is a cellular mechanism fundamental to the generation of bioactive peptides, including the anorectic α-melanocyte-stimulating hormone (α-MSH) and thyrotropin-releasing hormone (TRH) peptides produced in the hypothalamic arcuate (ARC) and paraventricular (PVN) nuclei, respectively. Neuropeptide Y (NPY) promotes positive energy balance in part by suppressing α-MSH and TRH. The mechanism by which NPY regulates α-MSH output, however, is not well understood. Our results reveal that NPY inhibited the posttranslational processing of α-MSH's inactive precursor proopiomelanocortin (POMC) by decreasing the prohormone convertase-2 (PC2). We also found that early growth response protein-1 (Egr-1) and NPY-Y1 receptors mediated the NPY-induced decrease in PC2. NPY given intra-PVN also decreased PC2 in PVN samples, suggesting a reduction in PC2-mediated pro-TRH processing. In addition, NPY attenuated the α-MSH-induced increase in TRH production by two mechanisms. First, NPY decreased α-MSH-induced CREB phosphorylation, which normally enhances TRH transcription. Second, NPY decreased the amount of α-MSH in the PVN. Collectively, these results underscore the significance of the interaction between NPY and α-MSH in the central regulation of energy balance and indicate that posttranslational processing is a mechanism that plays a specific role in this interaction.

Ancient Grandeur of the Vertebrate Neuropeptide Y System Shown by the Coelacanth Latimeria chalumnae

The neuropeptide Y (NPY) family receptors and peptides have previously been characterized in several tetrapods, teleost fishes, and in a holocephalan cartilaginous fish. This has shown that the ancestral NPY system in the jawed vertebrates consisted of the peptides NPY and peptide YY (PYY) and seven G-protein-coupled receptors named Y1–Y8 (Y3 does not exist). The different vertebrate lineages have subsequently lost or gained a few receptor genes. For instance, the human genome has lost three of the seven receptors while the zebrafish has lost two and gained two receptor genes. Here we describe the NPY system of a representative of an early diverging lineage among the sarcopterygians, the West Indian Ocean coelacanth Latimeria chalumnae. The coelacanth was found to have retained all seven receptors from the ancestral jawed vertebrate. The receptors display the typical characteristics found in other vertebrates. Interestingly, the coelacanth was found to have the local duplicate of the PYY gene, called pancreatic polypeptide, previously only identified in tetrapods. Thus, this duplication took place very early in the sarcopterygian lineage, before the origin of tetrapods. These findings confirm the ancient complexity of the NPY system and show that mammals have lost more NPY receptors than any other vertebrate lineage. The coelacanth has all three peptides found in tetrapods and has retained the ancestral jawed vertebrate receptor repertoire with neither gains or losses.

The identification of neuropeptide Y receptor subtype involved in phenylpropanolamine-induced increase in oxidative stress and appetite suppression

Hypothalamic neuropeptide Y (NPY) and superoxide dismutase (SOD) have been reported to participate in the regulation of appetite-suppressing effect of phenylpropanolamine (PPA), a sympathomimetic agent. This study explored whether Y1 receptor (Y1R) and/or Y5 receptor (Y5R) was involved in this regulation. Wistar rats were treated with PPA for 24 h. Changes in food intake and hypothalamic NPY, Y1R, Y5R, and SOD contents were assessed and compared. Results showed that food intake and NPY contents were decreased following PPA treatment, while Y1R and SOD contents were increased and Y5R contents remained unchanged. Moreover, although Y1R or Y5R knockdown by themselves could modify the food intake, Y1R but not Y5R knockdown could modify PPA-induced anorexia as well as NPY and SOD contents. In addition, selective inhibition of Y1R but not Y5R could modulate PPA-induced anorexia. It is suggested that Y1R but not Y5R participates in the anorectic response of PPA via the modulation of NPY and SOD. Results provide molecular mechanism of NPY-mediated PPA anorexia and may aid the understanding of the toxicology of PPA.

Characterization of the neuropeptide Y system in the frog Silurana tropicalis (Pipidae): three peptides and six receptor subtypes

Neuropeptide Y and its related peptides PYY and PP (pancreatic polypeptide) are involved in feeding behavior, regulation of the pituitary and the gastrointestinal tract, and numerous other functions. The peptides act on a family of G-protein coupled receptors with 4-7 members in jawed vertebrates. We describe here the NPY system of the Western clawed frog Silurana (Xenopus) tropicalis. Three peptides, NPY, PYY and PP, were identified together with six receptors, namely subtypes Y1, Y2, Y4, Y5, Y7 and Y8. Thus, this frog has all but one of the ancestral seven gnathostome NPY-family receptors, in contrast to mammals which have lost 2-3 of the receptors. Expression levels of mRNA for the peptide and receptor genes were analyzed in a panel of 19 frog tissues using reverse transcriptase quantitative PCR. The peptide mRNAs had broad distribution with highest expression in skin, blood and small intestine. NPY mRNA was present in the three brain regions investigated, but PYY and PP mRNAs were not detectable in any of these. All receptor mRNAs had similar expression profiles with high expression in skin, blood, muscle and heart. Three of the receptors, Y5, Y7 and Y8, could be functionally expressed in HEK-293 cells and characterized with binding studies using the three frog peptides. PYY had the highest affinity for all three receptors (K(i) 0.042-0.34 nM). Also NPY and PP bound to the Y8 receptor with high affinity (0.14 and 0.50 nM). The low affinity of NPY for the Y5 receptor (100-fold lower than PYY) differs from mammals and chicken. This may suggest a less important role of NPY on Y5 in appetite stimulation in the frog compared with amniotes. In conclusion, our characterization of the NPY system in S. tropicalis with its six receptors demonstrates not only greater complexity than in mammals but also some interesting differences in ligand-receptor preferences.

The selective neuropeptide Y Y5 agonist [cPP(1-7),NPY(19-23),Ala31,Aib32,Gln34]hPP differently modulates emotional processes and body weight in the rat

The neuropeptide Y (NPY) has been suggested to act as a major regulator of emotional processes and body weight. The full spectrum of biological effects of this peptide is mediated by at least four classes of receptors known as the Y(1), Y(2), Y(4), and Y(5) subtypes. However, the respective contribution of each of these receptor subtypes, especially the Y(5) subtype, in emotional processes is still mostly unknown. In the present study, we investigated the effect of long term administration of a selective Y(5) agonist [cPP(1-7),NPY(19-23),Ala(31),Aib(32),Gln(34)]hPP on emotional processes and body weight using two rat models of emotional dysfunctions, the corticosterone (CORT)-induced anxiety model as well as the olfactory bulbectomized (OBX) model of depression and anxiety in Wistar and Sprague-Dawley rats, respectively. The sub-chronic administration of the Y(5) agonist reversed the high levels of locomotion, rearing and grooming in the open field test and the impaired social activity induced by OBX, while increased the percentage of entries and time in the open arm of the elevated plus maze in CORT-treated rats. Furthermore, this Y(5) agonist increased body weight in both strains of control rats. These data further demonstrate that Y(5) receptors are not only involved in the control of body weight but also mediate emotional processing under challenged conditions. Thus, the pharmacotherapeutic administration of a Y(5) agonist could be considered as a potentially novel strategy to alleviate some forms of anxiety and depression in humans.

Neuropeptide Y impairs insulin-stimulated translocation of glucose transporter 4 in 3T3-L1 adipocytes through the Y1 receptor

Neuropeptide Y (NPY) is expressed in adipose tissue and is involved in adipocyte metabolism. Although NPY impacts on glucose utilization in vivo, the underlying cellular mechanism is yet to be fully elucidated. In this study we investigated the effect of NPY on the insulin-stimulated translocation of glucose transporter 4 (GLUT4) from intracellular stores to the cell surface in vitro. Using cellular fractionation and immunofluorescence we analyzed the cellular localization and content of GLUT4 in 3T3-L1 adipocytes. Additionally we investigated the effect of NPY on insulin action in adipocyte cultures by assessing the phosphorylation of Akt and [(3)H]-deoxyglucose uptake. Our data suggest that in 3T3-L1 adipocytes NPY inhibits insulin-stimulated glucose uptake in a GLUT4-dependent manner. The insulin induced translocation of GLUT4 was attenuated by the Y1 receptor agonist [Phe(7),Pro(34)] pNPY, demonstrating an essential role of the Y1 receptor in GLUT4 translocation. Additionally, we observed an NPY dose-dependent impairment of Akt phosphorylation. This study provides evidence that NPY impairs the insulin sensitivity of adipocytes and suggests that the Y1 receptor could be a potential therapeutic target for type 2 diabetes.

The role of neuropeptide Y in energy homeostasis

When administered into the brain, NPY acts at Y1 and Y5 receptors to increase food intake. The response occurs with a short latency and is quite robust, such that exogenous NPY is generally considered to be the most potent of a growing list of orexigenic compounds that act in the brain. The role of endogenous NPY is not so straightforward, however. Evidence from diverse types of experiments suggests that rather than initiating behavioral eating per se, endogenous NPY elicits autonomic responses that prepare the individual to better cope with consuming a calorically large meal.

NPY receptors as potential targets for anti-obesity drug development

The neuropeptide Y system has proven to be one of the most important regulators of feeding behaviour and energy homeostasis, thus presenting great potential as a therapeutic target for the treatment of disorders such as obesity and at the other extreme, anorexia. Due to the initial lack of pharmacological tools that are active in vivo, functions of the different Y receptors have been mainly studied in knockout and transgenic mouse models. However, over recent years various Y receptor selective peptidic and non-peptidic agonists and antagonists have been developed and tested. Their therapeutic potential in relation to treating obesity and other disorders of energy homeostasis is discussed in this review.

NPY receptor subtype specification for behavioral adaptive strategies during limited food access

The neuropeptide Y (NPY) system in the brain regulates a wide variety of behavioral, metabolic and hormonal homeostatic processes required for energy balance control. During times of limited food availability, NPY promotes behavioral hyperactivity necessary to explore and prepare for novel food resources. As NPY can act via 5 different receptor subtypes, we investigated the path through which NPY affects different behavioral components relevant for adaptation to such conditions. We tested NPY Y1 and Y2 receptor knockout mice and their wild-type littermate controls in a daily scheduled limited food access paradigm with unlimited access to running wheel. Here we show that NPY Y1 receptor deficient mice lack the expression of appetitive behavior and that NPY Y2 receptors control the level of hyperactive behavior under these conditions. Thus, receptor specificity determines the differential expression of NPY-mediated behavioral adaptations to overcome a negative energy status.

The role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.

Analysis of multiple polymorphisms in the bovine neuropeptide Y5 receptor gene and structural modelling of the encoded protein

The neuropeptide Y 5 receptor (NPY5R) plays an important role in the regulation of appetite and feeding behaviour in mammals by modulating the effect of the neurotransmitter neuropeptide Y. As single nucleotide polymorphism (SNP) variation in the bovine NPY5R gene is likely to influence the expression and/or function of this gene, the objectives of this study were to identify SNPs in the bovine NPY5R gene and to predict their functional role in the expression and physico-chemical characteristics of the protein product. Nineteen novel SNPs were identified in a 2.1 kb genomic region of the NPY5R gene in a total of 419 beef cattle from 13 Bos taurus breeds and eight Bos indicus animals. Four of these SNPs were non-synonymous (Met → Ile, Leu → Phe, Pro → Leu, Arg → Stop codon), while 10 were synonymous. Of particular interest was one non-synonymous SNP (c.1090C>T) that introduced a stop codon in the third intracellular loop of the NPY5R molecule. This stop codon is predicted to create a truncated NPY5R molecule with different physico-chemical properties compared to the native NPY5R protein. A further four SNPs were located in the 5' untranslated region (UTR) and one in the 3'UTR. Two of the 5'UTR SNPs affected putative transcription factor binding sites (GATA binding factor and snRNA-activating protein complex). In conclusion, regulatory and functional SNPs were identified in the bovine NPY5R gene. These include SNPs which potentially modify transcription factor binding sites as well as SNPs that cause amino acid changes and premature termination of the NPY5R protein. Such polymorphisms are likely to play vital physiological roles in the neuropeptide Y mediated appetite, feed intake and energy homeostasis in cattle.

Regulation of the hypothalamic thyrotropin releasing hormone (TRH) neuron by neuronal and peripheral inputs

The hypothalamic-pituitary-thyroid (HPT) axis plays a critical role in mediating changes in metabolism and thermogenesis. Thus, the central regulation of the thyroid axis by Thyrotropin Releasing Hormone (TRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) is of key importance for the normal function of the axis under different physiological conditions including cold stress and changes in nutritional status. Before the TRH peptide becomes biologically active, a series of tightly regulated processes occur including the proper folding of the prohormone for targeting to the secretory pathway, its post-translational processing, and targeting of the processed peptides to the secretory granules near the plasma membrane of the cell ready for secretion. Multiple inputs coming from the periphery or from neurons present in different areas of the brain including the hypothalamus are responsible for the activation or inhibition of the TRH neuron and in turn affect the output of TRH and the set point of the axis.

Receptors for NPY and PACAP differ in expression and activity during adipogenesis in the murine 3T3-L1 fibroblast cell line

BACKGROUND AND PURPOSE

Neuropeptides are involved in the regulation of food intake in the central nervous system, but they might also act on peripheral fat tissue via neuropeptide receptors.

EXPERIMENTAL APPROACH

We investigated the receptor expression and activity of pituitary adenylate cyclase-activating polypeptide (PACAP) and of neuropeptide Y at the mRNA and protein levels in the 3T3-L1 fibroblast line during differentiation into adipocytes. Intracellular calcium concentration was measured by calcium imaging.

KEY RESULTS

The PACAP receptors PAC(1) and VPAC(2) as well as the neuropeptide Y(1) receptor were expressed at the mRNA level in fibroblasts, pre-adipocytes and adipocytes. The mRNA profile of the PAC(1) receptor isoforms showed the HOP sequence, whereas the HIP-isoform was present in subconfluent 3T3-L1 fibroblasts only. At the protein level, the mature 3T3-L1 adipocytes produced the PAC(1) and Y(1) receptors; only the PAC(1) receptor showed carbohydrate residues. Both neuropeptides induced an increase of intracellular calcium in mature adipocytes, which was absent in the precursor cells. These changes in calcium were mediated by Y(1) and PAC(1) receptors as demonstrated by the effects of specific receptor agonists and antagonists.

CONCLUSIONS AND IMPLICATIONS

As the PAC(1)-HOP receptor variant seems to be responsible for PACAP-mediated calcium influx in many cell types, the HOP sequence might also mediate the increase in intracellular calcium in adipocytes. Because a high intracellular calcium level is associated with lipogenesis, peptidergic innervation of adipose tissue might be involved in stress-induced obesity.

Behavioral neuroendocrinology and treatment of anorexia nervosa

Outcome in anorexia nervosa remains poor and a new way of looking at this condition is therefore needed. To this aim, we review the effects of food restriction and starvation in humans. It is suggested that body weight remains stable and relatively low when the access to food requires a considerable amount of physical activity. In this condition, the human homeostatic phenotype, body fat content is also low and as a consequence, the synthesis and release of brain neurotransmitters are modified. As an example, the role of neuropeptide Y is analyzed in rat models of this state. It is suggested that the normal behavioral role of neuropeptide Y is to facilitate the search for food and switch attention from sexual stimuli to food. Descriptive neuroendocrine studies on patients with anorexia nervosa have not contributed to the management of the patients and the few studies in which hormones have been administered have, at best, reversed an endocrine consequence secondary to starvation. In a modified framework for understanding the etiology and treatment of anorexia nervosa it is suggested that the condition emerges because neural mechanisms of reward and attention are engaged. The neural neuropeptide Y receptor system may be involved in the maintenance of the behavior of eating disorder patients because the localization of these receptors overlaps with the neural systems engaged in cue-conditioned eating in limbic and cortical areas. The eating behavior of patients with anorexia nervosa, and other eating disorders as well, is viewed as a cause of the psychological changes of the patients. Patients are trained to re-learn normal eating habits using external support and as they do, their symptoms, including the psychological symptoms, dissolve.

Responsiveness of obese Zucker rats to [D-Trp34]-NPY supports the targeting of Y5 receptor for obesity treatment

The increased synthesis and release of neuropeptide Y (NPY) in the hypothalamus participate in the development of overeating and obesity in the Zucker fa/fa rat. The orexigenic effects of NPY are mediated through the Y1 and Y5 receptors. The substitution of [D-Trp34] in the NPY amino-acid sequence increases selectivity without lowering potency at the Y5 receptor. In the present study, to address the role of the NPY Y5 receptor in obesity, we investigated the acute effect of [D-Trp 34]-NPY in lean and obese Zucker rats. Obese rats were markedly hyperphagic (27.1 +/- 0.6 vs. 18.7 +/- 0.4 (lean) g/day; p < 0.01). Injection of [D-Trp34]-NPY in the lateral brain ventricle at a dose of 16 microg stimulated food intake to the same extent in both lean (p < 0.01) and obese (p < 0.01) rats 1 h after injection. This effect was still observed after 6 h (p < 0.01). These results indicate, therefore, that the obese rats are responsive to [D-Trp34]-NPY. They support the role of the neuropeptide Y5 receptor in the regulation of food intake and suggest that NPY Y5 antagonism might be useful for treating obesity.

Molecular characterization of neuropeptide Y gene in Chinese perch, an acanthomorph fish

The full-length neuropeptide Y (NPY) cDNA of Chinese perch Siniperca chuatsi was 704 bp in length, and contained a 300 bp open reading frame encoding a prepro-NPY with 99 amino acids. The predicted prepro-NPY peptide contained a putative signal peptide of 28 amino acids and a mature NPY of 36 amino acids, followed by the proteolytic processing site Gly-Lys-Arg and 35 amino acids that comprise the C-terminal peptide of NPY. Amino acid alignment and phylogenetic analysis indicate that the predicted Chinese perch prepro-NPY (composed of 99 amino acids) had high identities to the prepro-NPY of acanthomorph fishes (93-95%), whereas it had much lower identities to the prepro-NPY (composed of 96 or 97 amino acids) of cyprinid fishes (59-60%) or mammals (57-63%). Chinese perch NPY gene consists of four exons and three introns. The ratio of intron 2 to intron 3 was over 14 in Chinese perch NPY gene, whereas this ratio was below 4 in zebrafish and mammalian NPY gene. The total size of the Chinese perch NPY gene was 2223 bp, which was only about 28% of the size of NPY gene in higher vertebrate. Analysis of a 1622 bp promoter region of Chinese perch NPY gene, revealed a typical TATA box, a GC box and an untypical CAAT box, located at 84 bp, 101 bp and 303 bp upstream of the start codon respectively. Three STAT binding site-like elements (TCCAGTA) which were necessary for the leptin-induced transcriptional control of rat NPY gene were identified. In consistence to the effect of cortisol on fish brain NPY mRNA expression, four glucocorticoid-responsive elements were detected. Besides the highest expression in brain, substantial level of Chinese perch NPY mRNA expression was detected in the spleen and liver, and trace level of NPY mRNA expression was also detected in the adipose tissue, intestine and muscle. These results indicated that Chinese perch NPY might be involved in the food intake control by leptin and cortisol system, and diversification of NPY signaling should exist between acanthomorph fishes and cyprinid fishes as well as mammals.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

Cloning and sequence analysis of the neuropeptide Y receptors Y5 and Y6 in the coelacanth Latimeria chalumnae

Two coelacanth species, Latimeria chalumnae and Latimeria menadoensis, the recently discovered second species, have a key evolutionary position at the divergence of bony fishes and tetrapods. Together with lungfishes, they are the only living species separating the species-rich tetrapods from the other major group of vertebrates, the ray-finned fishes. The coelacanth is therefore of great importance for comparisons of gene families that differ between these two groups, such as the neuropeptide Y (NPY) receptor family. In this work we have sequenced the full-length genes for two NPY receptors in Latimeria chalumnae. Phylogenetic analysis indicated that the two sequences are orthologs of the mammalian Y5 and Y6 receptors. The Y5 gene has been implicated in appetite stimulation in mammals but is absent from teleost fishes. The presence of the Y5 receptor in Latimeria together with phylogenetic analysis shows that Y5 existed before the separation of bony fishes and tetrapods. The Latimeria receptor has about 62% identity to tetrapod Y5 sequences and contains the extended third intracellular loop with several highly conserved motifs that may be involved in signal transduction. The Latimeria Y6 receptor has about 60% identity to tetrapod Y6 sequences. The functional role of Y6 is unclear as the gene is seemingly functional in some mammals but is non-functional in others. The Y6 receptor is also missing in teleost fishes. Our results confirm an early vertebrate origin for all NPY receptor subtypes presently found in mammals followed by differential gene loss in the different classes of vertebrates.

Neuropeptide Y-family receptors Y6 and Y7 in chicken. Cloning, pharmacological characterization, tissue distribution and conserved synteny with human chromosome region

The peptides of the neuropeptide Y (NPY) family exert their functions, including regulation of appetite and circadian rhythm, by binding to G-protein coupled receptors. Mammals have five subtypes, named Y1, Y2, Y4, Y5 and Y6, and recently Y7 has been discovered in fish and amphibians. In chicken we have previously characterized the first four subtypes and here we describe Y6 and Y7. The genes for Y6 and Y7 are located 1 megabase apart on chromosome 13, which displays conserved synteny with human chromosome 5 that harbours the Y6 gene. The porcine PYY radioligand bound the chicken Y6 receptor with a K(d) of 0.80 +/- 0.36 nm. No functional coupling was demonstrated. The Y6 mRNA is expressed in hypothalamus, gastrointestinal tract and adipose tissue. Porcine PYY bound chicken Y7 with a K(d) of 0.14 +/- 0.01 nm (mean +/- SEM), whereas chicken PYY surprisingly had a much lower affinity, with a Ki of 41 nm, perhaps as a result of its additional amino acid at the N terminus. Truncated peptide fragments had greatly reduced affinity for Y7, in agreement with its closest relative, Y2, in chicken and fish, but in contrast to Y2 in mammals. This suggests that in mammals Y2 has only recently acquired the ability to bind truncated PYY. Chicken Y7 has a much more restricted tissue distribution than other subtypes and was only detected in adrenal gland. Y7 seems to have been lost in mammals. The physiological roles of Y6 and Y7 remain to be identified, but our phylogenetic and chromosomal analyses support the ancient origin of these Y receptor genes by chromosome duplications in an early (pregnathostome) vertebrate ancestor.

Neuropeptide Y Y5 receptors inhibit kindling acquisition in rats

Neuropeptide Y inhibits neuronal excitability and seizures in various experimental models. This peptide delays kindling epileptogenesis but the receptors involved in this action are unknown. We have studied the role of Y5 receptors in kindling using the selective antagonist GW438014A (IC50=210 nM), a small heterocycle molecule that crosses the blood-brain barrier, and the selective peptide agonist Ala31Aib34 NPY (IC50=6.0 nM). Intraperitoneal injection of GW438014A (10 mg/kg), 30 min before the beginning of a rapid-kindling protocol, significantly accelerated the rate of kindling acquisition as compared to vehicle-injected rats. Thus, the number of electrical stimuli required to reach stages 3 and 4-5 of kindling were reduced by 50% and 25%, respectively. The average afterdischarge duration in the stimulated hippocampus was prolonged by 2-fold. Conversely, kindling rate was delayed by intracerebroventricular administration of 24 nmol Ala31Aib32 NPY. Thus, the number of stimuli necessary to reach stages 2 and 3 of kindling was increased by 3- and 4-fold, respectively. During the stimulation protocol (40 stimuli) none of the rats treated with the Y5 agonist showed stages 4-5 seizures. Twenty-four hours after the last kindling stimulation, thus during the re-test session, Y5 agonist- or antagonist-treated rats had stages 4-5 seizures as their controls. In rats treated with both the antagonist and the agonist, kindling rate was similar to vehicle-injected rats. These data indicate that Y5 receptors mediate inhibitory effects of NPY in kindling and display anticonvulsant rather then antiepileptogenic effects upon agonist stimulation.

Localization of neuropeptide Y receptor Y5 mRNA in the guinea pig brain by in situ hybridization

Neuropeptide Y (NPY) has prominent stimulatory effects on food intake in virtually all animals that have been studied. In mammals, the effect is primarily mediated by receptors Y1 and Y5, which seem to contribute to different aspects of feeding behavior in guinea pigs and rats/mice. Interestingly, differences in receptor distribution among mammalian species have been reported. To get a broader perspective on the role of Y5, we describe here studies of guinea pig (Cavia porcellus), a species which due to its phylogenetic position in the mammalian radiation is an interesting complement to previous studies in rat and mouse. Guinea pig brain sections were hybridized with two 35S-labeled oligonucleotides complementary to Y5 mRNA. The highest expression levels of Y5 mRNA were observed in the hippocampus and several hypothalamic and brain stem nuclei implicated in the regulation of feeding, such as the paraventricular, arcuate and ventromedial hypothalamic nuclei. This contrasts with autoradiography studies that detected low Y5-like binding in these areas, a discrepancy observed also in rat and human. Y5 mRNA expression was also seen in the striatum, in great contrast to mouse and rat. Taken together, these data show that Y5 mRNA distribution displays some interesting species differences, but that its expression in feeding centers seems to be essentially conserved among mammals, adding further support for an important role in food intake.

Molecular evolution of NPY receptor subtypes

The neuropeptide Y (NPY) system consists in mammals of three peptides and 4-5 G-protein-coupled receptors called Y receptors that are involved in a variety of physiological functions such as appetite regulation, circadian rhythm and anxiety. Both the receptor family and the peptide family display unexpected evolutionary complexity and flexibility as shown by information from different classes of vertebrates. The vertebrate ancestor most likely had a single peptide gene and three Y receptor genes, the progenitors of the Y1, Y2 and Y5 subfamilies. The receptor genes were probably located in the same chromosomal segment. Additional gene copies arose through the chromosome quadruplication that took place before the emergence of jawed vertebrates (gnathostomes) whereupon differential losses of the gene copies ensued. The inferred ancestral gnathostome gene repertoire most likely consisted of two peptide genes, NPY and PYY, and no less than seven Y receptor genes: four Y1-like (Y1, Y4/a, Y6, and Yb), two Y2-like (Y2 and Y7), and a single Y5 gene. Whereas additional peptide genes have arisen in various lineages, the most common trend among the Y receptor genes has been further losses. Mammals have lost Yb and Y7 (the latter still exists in frogs) and Y6 is a pseudogene in several mammalian species but appears to be still functional in some. One challenge is to find out if mammals have been deprived of any functions through these gene losses. Teleost fishes like zebrafish and pufferfish, on the other hand, have lost the two major appetite-stimulating receptors Y1 and Y5. Nevertheless, teleost fishes seem to respond to NPY with increased feeding why some other subtype probably mediates this effect. Another challenge is to deduce how Y2 and Y4 came to evolve an inhibitory effect on appetite. Changes in anatomical distribution of receptor expression may have played an important part in such functional switching along with changes in receptor structures and ligand preferences.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.