Ligand internalization by cloned neuropeptide Y Y5 receptors excludes Y2 and Y4 receptor-selective peptides

Neuropeptide Y Signaling in the Lateral Hypothalamus Modulates Diet Component Selection and is Dysregulated in a Model of Diet-Induced Obesity

The preclinical multicomponent free-choice high-fat high-sucrose (fcHFHS) diet has strong validity to model diet-induced obesity (DIO) and associated maladaptive molecular changes in the central nervous system. fcHFHS-induced obese rats demonstrate increased sensitivity to intracerebroventricular infusion of the orexigenic Neuropeptide Y (NPY). The brain region-specific effects of NPY signaling on fcHFHS diet component selection are not completely understood. For example, fcHFHS-fed rats have increased intake of chow and fat following intracerebroventricular NPY infusion, whereas NPY administration in the nucleus accumbens, a key hub of the reward circuitry, specifically increases fat intake. Here, we investigated whether NPY infusion in the lateral hypothalamic area (LHA), which is crucially involved in the regulation of intake, regulates fcHFHS component selection, and if LHA NPY receptor subtypes 1 or 5 (NPYR1/5) are involved. Male Wistar rats were fed a chow or fcHFHS diet for at least seven days, and received intra-LHA vehicle or NPY infusions in a cross-over design. Diet component intake was measured two hours later. Separate experimental designs were used to test the efficacy of NPY1R- or NPY5R antagonism to prevent the orexigenic effects of intra-LHA NPY. Intra-LHA NPY increased caloric intake in chow- and fcHFHS-fed rats. This effect was mediated specifically by chow intake in fcHFHS-fed rats. The orexigenic effects of intra-LHA NPY were prevented by NPY1R and NPY5R antagonism in chow-fed rats, but only by NPY5R antagonism in fcHFHS-fed rats. Thus, NPY signaling has brain region-specific effects on fcHFHS component selection and LHA NPYR sensitivity is dysregulated during consumption of a fcHFHS diet.

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.

Intracellular Trafficking of Neuropeptide Y Receptors

The multireceptor multiligand system of neuropeptide Y receptors and their ligands is involved in the regulation of a multitude of physiological and pathophysiological processes. Specific expression patterns, ligand-binding modes, and signaling properties contribute to the complex network regulating distinct cellular responses. Intracellular trafficking processes are important key steps that are regulated in context with accessory proteins. These proteins exert their influence by interacting directly or indirectly with the receptors, causing modification of the receptors, or operating as scaffolds for the assembly of larger signaling complexes. On the intracellular receptor faces, sequence-specific motifs have been identified that play an important role in this process. Interestingly, it is also possible to influence the receptor internalization by modification of the peptide ligand.

Circadian integration of sleep-wake and feeding requires NPY receptor-expressing neurons in the mediobasal hypothalamus

Sleep and feeding rhythms are highly coordinated across the circadian cycle, but the brain sites responsible for this coordination are unknown. We examined the role of neuropeptide Y (NPY) receptor-expressing neurons in the mediobasal hypothalamus (MBH) in this process by injecting the targeted toxin, NPY-saporin (NPY-SAP), into the arcuate nucleus (Arc). NPY-SAP-lesioned rats were initially hyperphagic, became obese, exhibited sustained disruption of circadian feeding patterns, and had abnormal circadian distribution of sleep-wake patterns. Total amounts of rapid eye movement sleep (REMS) and non-REMS (NREMS) were not altered by NPY-SAP lesions, but a peak amount of REMS was permanently displaced to the dark period, and circadian variation in NREMS was eliminated. The phase reversal of REMS to the dark period by the lesion suggests that REMS timing is independently linked to the function of MBH NPY receptor-expressing neurons and is not dependent on NREMS pattern, which was altered but not phase reversed by the lesion. Sleep-wake patterns were altered in controls by restricting feeding to the light period, but were not altered in NPY-SAP rats by restricting feeding to either the light or dark period, indicating that disturbed sleep-wake patterns in lesioned rats were not secondary to changes in food intake. Sleep abnormalities persisted even after hyperphagia abated during the static phase of the lesion. Results suggest that the MBH is required for the essential task of integrating sleep-wake and feeding rhythms, a function that allows animals to accommodate changeable patterns of food availability. NPY receptor-expressing neurons are key components of this integrative function.

Neuropeptide Y receptors: ligand binding and trafficking suggest novel approaches in drug development

NPY, PYY and PP constitute the so-called NPY hormone family, which exert its biological functions in humans through YRs (Y₁, Y₂, Y₄ and Y₅). Systematic modulation of YR function became important as this multireceptor/multiligand system is known to mediate various essential physiological key functions and is involved in a variety of major human diseases such as epilepsy, obesity and cancer. As several YRs have been found to be overexpressed on different types of malignant tumors they emerge as promising target in modern drug development. Here, we summarize the current understanding of YRs function and the molecular mechanisms of ligand binding and trafficking. We further address recent advances in YR-based drug design, the development of promising future drug candidates and novel approaches in YR-targeted tumor diagnostics and therapy opportunities.

Non-specific binding and general cross-reactivity of Y receptor agonists are correlated and should importantly depend on their acidic sectors

Non-specific binding of Y receptor agonists to intact CHO cells, and to CHO cell or rat brain particulates, is much greater for human neuropeptide Y (hNPY) compared to porcine peptide Y (pPYY), and especially relative to human pancreatic polypeptide (hPP). This binding of hNPY is reduced by alkali cations in preference to non-ionic chaotrope urea, while the much lower non-specific binding of pPYY is more sensitive to urea. The difference could mainly be due to the 10-16 stretch in 36-residue Y agonists (residues 8-14 in N-terminally clipped 34-peptides), located in the sector that contains all acidic residues of physiological Y agonists. Anionic pairs containing aspartate in the 10-16 zone could be principally responsible for non-specific attachments, but may also aid the receptor site binding. Two such pairs are found in hNPY, one in pPYY, and none in hPP. The hydroxyl amino acid residue at position 13 in mammalian PYY and PP molecules could lower conformational plasticity and the non-selective binding via intrachain hydrogen bonding. The acidity of this tract could also be important in agonist selectivity of the Y receptor subtypes. The differences point to an evolutionary reduction of promiscuous protein binding from NPY to PP, and should also be important for Y agonist selectivity within NPY receptor group, and correlate with partial agonism and out-of group cross-reactivity with other receptors.

Regulatory effects of Y4 receptor agonist (BVD-74D) on food intake

The objective of this study was to clarify the role of a novel agonist with high selectivity and affinity for Y4 receptors in the regulation of food intake. The Y4 receptor agonist BVD-74D was administered to C57BL/6J mice that were fed with a normal or high-fat diet, and to fatty liver Shionogi (FLS)-ob/ob mice; the food intake, water intake, and body weight gain were measured in these mice. In the mice fed with a normal diet, the cumulative food intake significantly decreased at 20 min and 1 h after the administration of 1 mg/kg of BVD-74D and at 1, 2, 4, 8, and 24 h after the administration of 10 mg/kg of BVD-74D. Moreover, the cumulative water intake and body weight gain significantly decreased in these mice. Among the mice that were fed with a high-fat diet, the cumulative food intake and water intake significantly decreased 1, 2, and 4 h after BVD-74D (10 mg/kg) administration. Furthermore, the cumulative food intake significantly decreased 2 and 4 h after BVD-74D (10 mg/kg) administration in the FLS-ob/ob mice. Thus, we propose that the novel Y4 receptor agonist BVD-74D has suppressive effects on food intake, water intake, and weight gain in normal mice fed with normal diets and on food intake in normal mice fed with high-fat diets and in FLS-ob/ob mice. These findings indicate that the Y4 receptor and its agonist would be promising targets for obesity.

Neuropeptide Y Y2 receptor in health and disease

We briefly survey the current knowledge and concepts regarding structure and function of the neuropeptide Y Y2 receptor and its agonists, especially as related to pharmacology of the receptor and its roles in pathological processes. Specific structural features are considered that could be responsible for the known compartmentalization and participation of the receptor in cell and tissue organization. This is further discussed in relation to changes of levels of the Y2 receptor in pathological conditions (especially in epilepsy and drug abuse), to endocytosis and recycling, and to participation in wound healing, retinopathy and angiogenesis. Properties of the receptor and of Y2 agonists are considered and reviewed in connection to the negative regulation of transmitter release, feeding, mood and social behavior. The possible involvement of the Y2 receptor in diabetes, carcinogenesis and bone formation is also reviewed.

Co-expression of neuropeptide Y Y1 and Y5 receptors results in heterodimerization and altered functional properties

Centrally administered neuropeptide Y (NPY) produces anxiolytic and orexigenic effects by interacting with Y1 and Y5 receptors that are colocalized in many brain regions. Therefore, we tested the hypothesis that co-expression of Y1 and Y5 receptors results in heterodimerization, altered pharmacological properties and altered desensitization. To accomplish this, the carboxyl-termini of Y1 and Y5 receptors were fused with Renilla luciferase and green fluorescent protein and the proximity of the tagged receptors assessed using bioluminescent resonance energy transfer. Under basal conditions, cotransfection of tagged Y1 receptor and Y5 produced a substantial dimerization signal that was unaffected by the endogenous, nonselective agonists, NPY and peptide YY (PYY). Selective Y5 agonists produced an increase in the dimerization signal while Y5 antagonists also produced a slight but significant increase. In the absence of agonists, selective antagonists decreased dimerization. In functional studies, Y5 agonists produced a greater inhibition of adenylyl cyclase activity in Y1/Y5 cells than cells expressing Y5 alone while NPY and PYY exhibited no difference. With PYY stimulation, the Y1 antagonist became inactive and the Y5 antagonist exhibited uncompetitive kinetics in the Y1/Y5 cell line. In confocal microscopy studies, Y1/Y5 co-expression resulted in increased Y5 signaling following PYY stimulation. Addition of both Y1 and Y5 receptor antagonists was required to significantly decrease PYY-induced internalization. Therefore, Y1/Y5 co-expression results in heterodimerization, altered agonist and antagonist responses and reduced internalization rate. These results may account for the complex pharmacology observed when assessing the responses to NPY and analogs in vivo.

Tracking of human Y receptors in living cells--a fluorescence approach

Non-invasive methods for studying biological processes in living cells have become very important, also in the field of GPCR biochemistry. Great advancements in the application of fluorescence techniques as well as in the development and improvement of novel fluorophores allow the visualization of dynamic processes. Using these technologies, problems concerning receptor biosynthesis, internalization, recycling and degradation can be investigated. Here we compare the application of the different fluorescent tags EYFP, Lumiotrade mark and SNAPtrade mark to track hY(1) and hY(5) receptors in living cells.

Self-regulation of agonist activity at the Y receptors

Neuropeptide Y (NPY) is one of the most abundant neuropeptides, and is likely to be present at nanomolar levels over extended periods in the synaptic space of many forebrain areas. This might be linked to an evolved generalized toning activity through a number of other peptide receptors that use C-terminally amidated agonists (with LHRH and orexin receptors and GIR as examples). However, the Y1 and Y2 receptors (which constitute the bulk of Y receptors active in the neural matrix) possess subnanomolar affinities that, at saturating NPY levels, could produce excessive signaling, as well as receptor losses via repeated endocytosis. The related Y4 receptor shows an even higher agonist affinity, and faces the same problem in visceral and neural locations accessible to pancreatic polypeptide (PP). An examination of agonist peptide interaction with Y receptors shows that Y1 and Y4 receptors in particular (as located on either the intact cells, or on particulates derived from various cell types) develop a blockade dependent on ligand concentration, with the blocking ranks of [NPY]>>[peptide YY] (PYY) for the Y1, and [human PP]>>>[PYY-related Y4 agonist] for the Y4 receptor. This blockade is also echoed in a concentration-related reduction in biological activity of primary agonists (NPY and PP), resembling a partial agonism, and is influenced especially by the allosteric interactivity of agonists. With the Y2 receptor, the blocking by agonists is less pronounced, but the signaling by NPY-related peptides is apparently less than with PYY-related agonists. The extended occupancy and self-attenuation of primary agonist activity at Y receptors could represent an evolutionary solution contributing to a balancing of metabolic signaling, agonist clearance and receptor conservation.

Increased brain neuropeptide Y1 and Y2 receptor binding in NPY knock out mice does not result in increased receptor function

The brain neuropeptide Neuropeptide Y (NPY) is an important modulator of a number of centrally mediated processes including feeding, anxiety-like behaviors, blood pressure and others. NPY produces its effects through at least four functional G-protein coupled receptors termed Y1, Y2, Y4 and Y5. In the brain, the Y1 and Y2 receptor subtypes are the predominant receptor population. To better understand the roles of NPY, genetically modified mice lacking NPY were produced but lacked the expected phenotypes. These mice have previously been reported to have a marked increase in Y2 receptor binding. In the present study, we found an upregulation of both Y1 and Y2 receptor binding and extended these findings to the female. These increases were as large as 10-fold or greater in many brain regions. To assess functional coupling of the receptors, we performed agonist-induced [(35)S]GTPgammaS autoradiography. In the mouse brain, the Y1/Y4/Y5 agonist Leu(31),Pro(34)-NPY increased [(35)S]GTPgammaS binding with a regional distribution consistent with that produced when labeling adjacent sections with [(125)I]-Leu(31),Pro(34)-PYY. In a few brain regions, minor increases were noted in the agonist-induced binding when comparing knock out mice to wild type. The Y2 agonist C2-NPY stimulated [(35)S]GTPgammaS binding in numerous brain areas with a regional distribution similar to the binding observed with [(125)I]-PYY3-36. Again, no major increases were noted in the functional activation of Y2 receptors between knock out and wild type mice. Therefore, the increased Y1 and Y2 binding observed in the NPY knock out mice does not represent an increase in NPY receptor mediated signaling and is likely due to an increase in spare (uncoupled) receptors.

BODIPY-conjugated neuropeptide Y ligands: new fluorescent tools to tag Y1, Y2, Y4 and Y5 receptor subtypes

N-terminal labelled fluorescent BODIPY-NPY peptide analogues were tested in Y1, Y2, Y4 and Y5 receptor-binding assays performed in rat brain membrane preparations and HEK293 cells expressing the rat Y1, Y2, Y4 and Y5 receptors. BODIPY TMR/FL-[Leu31, Pro34]NPY/PYY were able to compete for specific [125][Leu31, Pro34]PYY-binding sites with an affinity similar to that observed for the native peptide at the Y1 (Ki=1-6 nM), Y2 (Ki>1000 nM), Y4 (Ki=10 nM) and Y5 (Ki=1-4 nM) receptor subtypes. BODIPY FL-PYY(3-36) was able to compete for specific Y2 (Ki=10 nM) and Y5 (Ki=30 nM) binding sites, but had almost no affinity in Y1 and Y4 assays. BODIPY FL-hPP was able to compete with high affinity (Ki; 1 and 15 nM) only in Y4 and Y5 receptor-binding assays. BODIPY TMR-[cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP and BODIPY TMR-[hPP(1-17), Ala31, Aib32]NPY were potent competitors only on specific Y5-binding sites (Ki=0.1-0.6 nM). As expected, these fluorescent peptides inhibited forskolin-induced cAMP accumulation, demonstrating that they retained their agonist properties. When tested in confocal microscopy imaging, fluorescent Y1 and Y5 agonists internalized in a time-dependent manner in Y1 and Y5 transfected cells, respectively. These results demonstrate that BODIPY-conjugated NPY analogues retain their selectivity, affinity and agonist properties for the Y1, Y2, Y4 and Y5 receptor subtypes, respectively. Thus, they represent novel tools to study and visualize NPY receptors in living cells.

Angiogenesis and rhodopsin-like receptors: a role for N-terminal acidic residues?

Numerous rhodopsin-like G-protein coupling receptors induce or inhibit angiogenesis. The active human receptors include several chemokine receptors, apelin APJ receptor, neuropeptide Y Y2 receptor, Duffy antigen, and herpes virus-8 receptor. A common and striking feature of these receptors is the large fraction (up to 42%) of residues with anionic sidechains (Asp, Glu, and benzene anions Tyr, Trp, and Phe) in the N-terminal extracellular domain. These residues (which are frequently clustered) can assist the binding of ligand peptides, but should also support interactions that help tubular arraying of cells, e.g., via cationic bridges and/or hydrogen bonding with cell-connecting receptors such as integrins, or with proteins of the extracellular matrix.

Lithium inhibits internalization and endosomal processing of both neuropeptide Y (NPY) Y1 and transferrin receptors

Low concentrations of Li+ reduce the rate of internalization of neuropeptide Y (NPY) Y1 receptors [M.S. Parker, S.L. Parker, J.K. Kane, Internalization of neuropeptide Y Y1 and Y5 and of pancreatic polypeptide Y4 receptors is inhibited by lithium in preference to sodium and potassium ions, Regul. Pept., 118 (2004) 67-74]. This Li+-induced decrease in Y1 receptor internalization could be alleviated by Y1 receptor agonists. As shown by fractionation on Percoll gradients, lithium treatment induces a concentration-related decrease of intermediate and higher endosomal densities that contain the internalized Y1 ligand-receptor complex. This indicates an inhibition of endosome processing and maturation. Internalization of human transferrin shows [Li+] sensitivity similar to that of the Y1 receptor, and a similar Li+-induced decrease in endosomal processing. Lithium treatment thus decreases activity of the endosome system shared in the recycling endocytosis of the Y1 and transferrin receptors.