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

NPYR modulation: Potential for the next major advance in obesity and type 2 diabetes management?

The approval of the glucagon-like peptide 1 (GLP-1) mimetics semaglutide and liraglutide for management of obesity, independent of type 2 diabetes (T2DM), has initiated a resurgence of interest in gut-hormone derived peptide therapies for the management of metabolic diseases, but side-effect profile is a concern for these medicines. However, the recent approval of tirzepatide for obesity and T2DM, a glucose-dependent insulinotropic polypeptide (GIP), GLP-1 receptor co-agonist peptide therapy, may provide a somewhat more tolerable option. Despite this, an increasing number of non-incretin alternative peptides are in development for obesity, and it stands to reason that other hormones will take to the limelight in the coming years, such as peptides from the neuropeptide Y family. This narrative review outlines the therapeutic promise of the neuropeptide Y family of peptides, comprising of the 36 amino acid polypeptides neuropeptide Y (NPY), peptide tyrosine-tyrosine (PYY) and pancreatic polypeptide (PP), as well as their derivatives. This family of peptides exerts a number of metabolically relevant effects such as appetite regulation and can influence pancreatic beta-cell survival. Although some of these actions still require full translation to the human setting, potential therapeutic application in obesity and type 2 diabetes is conceivable. However, like GLP-1 and GIP, the endogenous NPY, PYY and PP peptide forms are subject to rapid in vivo degradation and inactivation by the serine peptidase, dipeptidyl-peptidase 4 (DPP-4), and hence require structural modification to prolong circulating half-life. Numerous protective modification strategies are discussed in this regard herein, alongside related impact on biological activity profile and therapeutic promise.

Small molecule- and peptide-drug conjugates addressing integrins: A story of targeted cancer treatment

Targeted cancer treatment should avoid side effects and damage to healthy cells commonly encountered during traditional chemotherapy. By combining small molecule or peptidic ligands as homing devices with cytotoxic drugs connected by a cleavable or non-cleavable linker in peptide-drug conjugates (PDCs) or small molecule-drug conjugates (SMDCs), cancer cells and tumours can be selectively targeted. The development of highly affine, selective peptides and small molecules in recent years has allowed PDCs and SMDCs to increasingly compete with antibody-drug conjugates (ADCs). Integrins represent an excellent target for conjugates because they are overexpressed by most cancer cells and because of the broad knowledge about native binding partners as well as the multitude of small-molecule and peptidic ligands that have been developed over the last 30 years. In particular, integrin αVβ3 has been addressed using a variety of different PDCs and SMDCs over the last two decades, following various strategies. This review summarises and describes integrin-addressing PDCs and SMDCs while highlighting points of great interest.

Reductions of food intake and body weight in diet-induced obese rats following chronic treatment with a monomeric peptide multiagonist

INTRODUCTION

While therapies based on endogenous gut peptides such as glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1RAs) have been compelling therapeutic agents for obesity and type 2 diabetes (T2D), only a few have achieved long-term weight loss and all have shown significant side-effects, including nausea/malaise and gastrointestinal ailments.

OBJECTIVE

As the pathophysiology of obesity is driven by dysregulation of multiple, inter-related, pathways, we tested a novel peptide targeting multiple receptors of complementary neurocircuits regulating the controls of energy balance.

METHODS

Response to daily injections of GEP44, a GLP-1R and neuropeptide Y1R and Y2R receptor (Y1R/Y2R) triple agonist was tested vs. the GLP-1R agonist liraglutide (LIRA) in diet-induced obese (DIO) male and female rats. Glucose tolerance tests after intraperitoneal injection of glucose (IPGTT) were performed at baseline and after 14-d of treatment in GEP44 treated rats. Other metabolic parameters were assessed in blood at the end of a 28-d intervention.

RESULTS

Upon conclusion at 28-d, body weight reduction compared to vehicle was -15.6%/-11.9% in response to GEP44, vs. -9.7%/-5.1% after LIRA, males, and females, respectively. Significant reductions of cumulative food intake occurred over 28-d in female rats treated with GEP44 (-30%; p < 0.0001), vs. LIRA (-10%), and in male rats GEP44 (-39%; p < 0.0001), vs. LIRA (-20%; p = 0.003). In IPGTTs, a similar stimulation glucose induced insulin secretion was noted in rats treated with GEP44 and LIRA.

CONCLUSION

The strong reductions of body weight in response to long-term applications of the triple agonist GEP44 confirms the therapeutic potential of targeting multiple receptors for achieving more robust and potentially more sustained improvement of energy balance.

Effect of gut hormones on bone metabolism and their possible mechanisms in the treatment of osteoporosis

Bone is a highly dynamic organ that changes with the daily circadian rhythm. During the day, bone resorption is suppressed due to eating, while it increases at night. This circadian rhythm of the skeleton is regulated by gut hormones. Until now, gut hormones that have been found to affect skeletal homeostasis include glucagon-like peptide-1 (GLP-1), glucagon-like peptide-2 (GLP-2), glucose-dependent insulinotropic polypeptide (GIP), and peptide YY (PYY), which exerts its effects by binding to its cognate receptors (GLP-1R, GLP-2R, GIPR, and Y1R). Several studies have shown that GLP-1, GLP-2, and GIP all inhibit bone resorption, while GIP also promotes bone formation. Notably, PYY has a strong bone resorption-promoting effect. In addition, gut microbiota (GM) plays an important role in maintaining bone homeostasis. This review outlines the roles of GLP-1, GLP-2, GIP, and PYY in bone metabolism and discusses the roles of gut hormones and the GM in regulating bone homeostasis and their potential mechanisms.

Neuropeptide Y and its receptors in prostate cancer: associations with cancer invasiveness and perineural spread

PURPOSE

Neuropeptide Y (NPY) is a pleiotropic peptide, which is involved in many biological mechanisms important in regulation of cell growth and survival. The aim of this study was a comprehensive analysis of the NPY system in prostate pathology.

METHODS

The study was based on immunohistochemical analysis of NPY and its receptors, Y1R, Y2R and Y5R, in tissue samples from benign prostate (BP), primary prostate cancer (PCa) and PCa bone metastases. Tissue microarray (TMA) technique was employed, with analysis of multiple cores from each specimen. Intensity of the immunoreactivity and expression index (EI), as well as distribution of the immunostaining in neoplastic cells and stromal elements were evaluated. Perineural invasion (PNI) and extraprostatic extension (EPE) were areas of special interests. Moreover, a transwell migration assay on the LNCaP PCa cell line was used to assess the chemotactic properties of NPY.

RESULTS

Morphological analysis revealed homogeneous membrane and cytoplasmic pattern of NPY staining in cancer cells and its membrane localization with apical accentuation in BP glands. All elements of the NPY system were upregulated in pre-invasive prostate intraepithelial neoplasia, PCa and metastases. EI and staining intensity of NPY receptors were significantly higher in PCa then in BP with correlation between Y2R and Y5R. The strength of expression of the NPY system was further increased in the PNI and EPE areas. In bone metastases, Y1R and Y5R presented high expression scores.

CONCLUSION

The results of our study suggest that the NPY system is involved in PCa, starting from early stages of its development to disseminated states of the disease, and participates in the invasion of PCa into the auto and paracrine matter.

Stereochemistry-Driven Interactions of α,γ-Peptide Ligands with the Neuropeptide Y Y4-Receptor

The G-protein-coupled Y₄-receptor (Y₄R) and its endogenous ligand, pancreatic polypeptide (PP), suppress appetite in response to food intake and, thus, are attractive drug targets for body-weight control. The C-terminus of human PP (hPP), T³²-R³³-P³⁴-R³⁵-Y³⁶-NH₂, penetrates deep into the binding pocket with its tyrosine-amide and di-arginine motif. Here, we present two C-terminally amidated α,γ-hexapeptides (1a/b) with sequence Ac-R³¹-γ-CBAA³²-R³³-L³⁴-R³⁵-Y³⁶-NH₂, where γ-CBAA is the (1R,2S,3R)-configured 2-(aminomethyl)-3-phenylcyclobutanecarboxyl moiety (1a) or its mirror image (1b). Both peptides bind the Y₄R (K_i of 1a/b: 0.66/12 nM) and act as partial agonists (intrinsic activity of 1a/b: 50/39%). Their induced-fit binding poses in the Y₄R pocket are unique and build ligand-receptor contacts distinct from those of the C-terminus of the endogenous ligand hPP. We conclude that energetically favorable interactions, although they do not match those of the native ligand hPP, still guarantee high binding affinity (with 1a rivaling hPP) but not the maximum receptor activation.

A peptide triple agonist of GLP-1, neuropeptide Y1, and neuropeptide Y2 receptors promotes glycemic control and weight loss

Mechanisms underlying long-term sustained weight loss and glycemic normalization after obesity surgery include changes in gut hormone levels, including glucagon-like peptide 1 (GLP-1) and peptide YY (PYY). We demonstrate that two peptide biased agonists (GEP44 and GEP12) of the GLP-1, neuropeptide Y1, and neuropeptide Y2 receptors (GLP-1R, Y1-R, and Y2-R, respectively) elicit Y1-R antagonist-controlled, GLP-1R-dependent stimulation of insulin secretion in both rat and human pancreatic islets, thus revealing the counteracting effects of Y1-R and GLP-1R agonism. These agonists also promote insulin-independent Y1-R-mediated glucose uptake in muscle tissue ex vivo and more profound reductions in food intake and body weight than liraglutide when administered to diet-induced obese rats. Our findings support a role for Y1-R signaling in glucoregulation and highlight the therapeutic potential of simultaneous receptor targeting to achieve long-term benefits for millions of patients.

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.

Peptide YY 3-36 attenuates trinitrobenzene sulfonic acid-induced colitis in mice by modulating Th1/Th2 differentiation

Peptide YY (PYY) 3–36, the main circulatory form of PYY, plays important roles in gastrointestinal motility, secretion, and absorption. However, it is unknown whether PYY 3–36 has underlying functions in colitis. The Crohn’s disease (CD)-like mouse model in which CD is induced by trinitrobenzene sulfonic acid (TNBS) was established and utilized to investigate this potential role for PYY 3–36. The results showed that the expression of colonic mucosal PYY and PYY receptors Y1, Y2, Y4 were significantly increased in mice with TNBS-induced colitis. In vitro, PYY 3–36 remarkably inhibited the production of proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) from lipopolysaccharide (LPS)-induced macrophages. In vivo, a high concentration of PYY 3–36 robustly decreased the weight loss and death rate and attenuated the pathological colon tissue damage observed in mice with TNBS-induced colitis. Further studies uncovered that PYY 3–36 treatment reduced the levels of colon myeloperoxidase (MPO) and both colonic and systemic TNF-α and IL-6 observed in murine colitis. Furthermore, flow cytometric analysis showed PYY 3–36 altered the proportion of Th1/Th2 splenocytes in the disease model of colitis. Collectively, these results suggest that PYY 3–36 may be a promising candidate for the improvement of colitis, reflected by the attenuation of colon inflammatory responses observed in experimental murine colitis.

CYCLOBUTANES IN SMALL MOLECULE DRUG CANDIDATES

Cyclobutanes are increasingly used in medicinal chemistry in the search for relevant biological properties. Important characteristics of the cyclobutane ring include its unique puckered structure, longer C−C bond lengths, increased C−C π‐character and relative chemical inertness for a highly strained carbocycle. This review will focus on contributions of cyclobutane rings in drug candidates to arrive at favorable properties. Cyclobutanes have been employed for improving multiple factors such as preventing cis/trans‐isomerization by replacing alkenes, replacing larger cyclic systems, increasing metabolic stability, directing key pharmacophore groups, inducing conformational restriction, reducing planarity, as aryl isostere and filling hydrophobic pockets.

Binding of Natural Peptide Ligands to the Neuropeptide Y5 Receptor

The binding mode of natural peptide ligands to the Y5 G protein-coupled receptor (Y5 R), an attractive therapeutic target for the treatment of obesity, is largely unknown. Here, we apply complementary biochemical and computational approaches, including scanning of the receptor surface with a genetically encoded crosslinker, Ala-scanning of the ligand and double-cycle mutagenesis, to map interactions in the ligand-receptor interface and build a structural model of the NPY-Y5 R complex guided by the experimental data. In the model, the carboxyl (C)-terminus of bound NPY is placed close to the extracellular loop (ECL) 3, whereas the characteristic α-helical segment of the ligand drapes over ECL1 and is tethered towards ECL2 by a hydrophobic cluster. We further show that the other two natural ligands of Y5 R, peptide YY (PYY) and pancreatic polypeptide (PP) dock to the receptor in a similar pose.

Neuropeptide Y Y2 and Y5 receptors as potential targets for neuroprotective and antidepressant therapies: Evidence from preclinical studies

There is currently no effective treatment either for neurological illnesses (ischemia and neurodegenerative diseases) or psychiatric disorders (depression), in which the Glu/GABA balance is disturbed and accompanied by significant excitotoxicity. Therefore, the search for new and effective therapeutic strategies is imperative for these disorders. Studies conducted over the last several years indicate that the neuropeptide Y (NPY)-ergic system may be a potential therapeutic target for neuroprotective or antidepressant compounds. This review focuses on the neuroprotective roles of Y2 and Y5 receptors (YRs) in neurological disorders such as ischemia, Alzheimer's disease, Parkinson's disease, Huntington's disease, and in psychiatric disorders such as depression. It summarizes current knowledge on the possible mechanisms underlying the neuroprotective or antidepressant-like actions of Y2R and Y5R ligands. The review also discusses ligands acting at Y2R and Y5R and their limitations as in vivo pharmacological tools. The results from the preclinical studies discussed here may be useful in developing effective therapeutic strategies to treat neurological diseases on the one hand and psychiatric disorders on the other, and may pave the way for the development of novel Y2R and Y5R ligands as candidate drugs for the treatment of these diseases.

Established and emerging roles peptide YY (PYY) and exploitation in obesity-diabetes

PURPOSE OF REVIEW

The antiobesity effects of activation of hypothalamic neuropeptide Y2 receptors (NPYR2) by the gut-derived hormone, peptide YY (PYY), are established. However, more recent insight into the biology of PYY has demonstrated remarkable benefits of sustained activation of pancreatic beta-cell NPYR1, that promises to open a new therapeutic avenue in diabetes.

RECENT FINDINGS

The therapeutic applicability of NPYR2 agonists for obesity has been considered for many years. An alternative pathway for the clinical realisation of PYY-based drugs could be related to the development of NPYR1 agonists for treatment of diabetes. Thus, although stimulation of NPYR1 on pancreatic beta-cells has immediate insulinostatic effects, prolonged activation of these receptors leads to well defined beta-cell protective effects, with obvious positive implications for the treatment of diabetes. In this regard, NPYR1-specific, long-acting enzyme resistant PYY analogues, have been recently developed with encouraging preclinical effects observed on pancreatic islet architecture in diabetes. In agreement, the benefits of certain types of bariatric surgeries on beta-cell function and responsiveness have also been linked to elevated PYY secretion and NPY1 receptor activation.

SUMMARY

Enzymatically stable forms of PYY, that selectively activate NPYR1, may have significant potential for preservation of beta-cell mass and the treatment of diabetes.

Photoinduced receptor confinement drives ligand-independent GPCR signaling

Cell-cell communication relies on the assembly of receptor-ligand complexes at the plasma membrane. The spatiotemporal receptor organization has a pivotal role in evoking cellular responses. We studied the clustering of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) and established a photoinstructive matrix with ultrasmall lock-and-key interaction pairs to control lateral membrane organization of hormone neuropeptide Y₂ receptors in living cells by light. Within seconds, receptor clustering was modulated in size, location, and density. After in situ confinement, changes in cellular morphology, motility, and calcium signaling revealed ligand-independent receptor activation. This approach may enhance the exploration of mechanisms in cell signaling and mechanotransduction.

Structural basis for ligand recognition of the neuropeptide Y Y2 receptor

The human neuropeptide Y (NPY) Y₂ receptor (Y₂R) plays essential roles in food intake, bone formation and mood regulation, and has been considered an important drug target for obesity and anxiety. However, development of drugs targeting Y₂R remains challenging with no success in clinical application yet. Here, we report the crystal structure of Y₂R bound to a selective antagonist JNJ-31020028 at 2.8 Å resolution. The structure reveals molecular details of the ligand-binding mode of Y₂R. Combined with mutagenesis studies, the Y₂R structure provides insights into key factors that define antagonistic activity of diverse antagonists. Comparison with the previously determined antagonist-bound Y₁R structures identified receptor-ligand interactions that play different roles in modulating receptor activation and mediating ligand selectivity. These findings deepen our understanding about molecular mechanisms of ligand recognition and subtype specificity of NPY receptors, and would enable structure-based drug design.

The human neuropeptide Y receptor Y₂ (Y₂R) is a drug target for the treatment of obesity and anxiety. Crystal structure of Y₂R bound to a selective antagonist and accompanying mutagenesis provide insights into ligand recognition and subtype specificity of NPY receptors.

NPY and Gene Therapy for Epilepsy: How, When,... and Y

Neuropeptide Y (NPY) is a neuropeptide abundantly expressed in the mammalian central and peripheral nervous system. NPY is a pleiotropic molecule, which influences cell proliferation, cardiovascular and metabolic function, pain and neuronal excitability. In the central nervous system, NPY acts as a neuromodulator, affecting pathways that range from cellular (excitability, neurogenesis) to circuit level (food intake, stress response, pain perception). NPY has a broad repertoire of receptor subtypes, each activating specific signaling pathways in different tissues and cellular sub-regions. In the context of epilepsy, NPY is thought to act as an endogenous anticonvulsant that performs its action through Y2 and Y5 receptors. In fact, its overexpression in the brain with the aid of viral vectors can suppress seizures in animal models of epilepsy. Therefore, NPY-based gene therapy may represent a novel approach for the treatment of epilepsy patients, particularly for pharmaco-resistant and genetic forms of the disease. Nonetheless, considering all the aforementioned aspects of NPY signaling, the study of possible NPY applications as a therapeutic molecule is not devoid of critical aspects. The present review will summarize data related to NPY biology, focusing on its anti-epileptic effects, with a critical appraisal of key elements that could be exploited to improve the already existing NPY-based gene therapy approaches for epilepsy.

Peptide YY (PYY) Is Associated with Cardiovascular Risk in Patients with Acute Myocardial Infarction

AIMS

Recent studies have found circulating concentrations of the gastrointestinal hormone GLP-1 to be an excellent predictor of cardiovascular risk in patients with myocardial infarction. This illustrates a yet not appreciated crosstalk between the gastrointestinal and cardiovascular systems, which requires further investigation. The gut-derived hormone Peptide YY (PYY) is secreted from the same intestinal L-cells as GLP-1. Relevance of PYY in the context of cardiovascular disease has not been explored. In this study, we aimed to investigate PYY serum concentrations in patients with acute myocardial infarction and to evaluate their association with cardiovascular events.

MATERIAL AND METHODS

PYY levels were assessed in 834 patients presenting with acute myocardial infarction (553 Non-ST-Elevation Myocardial Infarction (NSTEMI) and 281 ST-Elevation Myocardial Infarction (STEMI)) at the time of hospital admission. The composite outcomes of first occurrence of cardiovascular death, nonfatal myocardial infarction, nonfatal stroke (3-P-MACE), and all-cause mortality were assessed with a median follow-up of 338 days.

RESULTS

PYY levels were significantly associated with age and cardiovascular risk factors, including hypertension, diabetes, and kidney function in addition to biomarkers of heart failure (NT-pro BNP) and inflammation (hs-CRP). Further, PYY was significantly associated with 3-P-MACE (HR: 1.7; 95% CI: 1-2.97; p = 0.0495) and all-cause mortality (HR: 2.69; 95% CI: 1.61-4.47; p = 0.0001) by univariable Cox regression analyses, which was however lost after adjusting for multiple confounders.

CONCLUSIONS

PYY levels are associated with parameters of cardiovascular risk as well as cardiovascular events and mortality in patients presenting with acute myocardial infarction. However, this significant association is lost after adjustment for further confounders.

Neuropeptide Y plasma levels and suicidal behavior in combat veterans

War veterans are at increased risk of suicide that may be related to deployment and/or post-deployment stressors and to adjustment-related factors. The aim of this study was to examine whether levels of plasma neuropeptide Y (NPY) might distinguish combat veterans who have made a post-deployment suicide attempt from those who have never made a suicide attempt. We focused on NPY because of prior findings linking NPY with the neurobiology of resilience, stress-related and other disorders, and suicidal behavior. Demographic and clinical parameters of suicide attempters and non-attempters were assessed and plasma NPY was determined by radioimmunoassay. NPY levels were higher among attempters in comparison to non-attempters, controlling for sex and body-mass index. Suicide attempters had higher Scale for Suicidal Ideation (SSI) scores than non-attempters. There was a positive correlation between NPY levels and SSI scores among non-attempters but not among attempters. Likewise, NPY levels positively correlated with Brown-Goodwin Aggression Scale scores among suicide attempters but not among non-attempters. This is the first demonstration of altered plasma NPY levels in association with suicide attempt history and suicidal ideation in veterans. Our findings suggest that clinical differences between combat veterans with or without a history of suicide attempt may have a neurobiological origin.

Generation and characterisation of C-terminally stabilised PYY molecules with potential in vivo NPYR2 activity

BACKGROUND

Activation of neuropeptide Y2 receptors (NPYR2) by the N-terminally truncated, dipeptidyl peptidase-4 (DPP-4) generated, Peptide YY (PYY) metabolite, namely PYY(3-36), results in satiating actions. However, PYY(3-36) is also subject to C-terminal enzymatic cleavage, which annuls anorectic effects.

METHODS

Substitution of l-Arg³⁵ with d-Arg³⁵ in the DPP-4 stable sea lamprey PYY(1-36) peptide imparts full C-terminal stability. In the current study, we have taken this molecule and introduced DPP-4 susceptibility by Iso³ substitution.

RESULTS

As expected, [Iso³]sea lamprey PYY(1-36) and [Iso³](d-Arg³⁵)sea lamprey PYY(1-36) were N-terminally degraded to respective PYY(3-36) metabolites in plasma. Only [Iso³](d-Arg³⁵)sea lamprey PYY(1-36) was C-terminally stable. Both peptides possessed similar insulinostatic and anti-apoptotic biological actions to native PYY(1-36) in beta-cells. Unlike native PYY(1-36) and [Iso³](d-Arg³⁵)sea lamprey PYY(1-36), [Iso³]sea lamprey PYY(1-36) displayed some proliferative actions in Npyr1 knockout beta-cells. In addition, [Iso³]sea lamprey PYY(1-36) induced more rapid NPYR2-dependent appetite suppressive effects in mice than its C-terminally stable counterpart. Twice daily administration of either peptide to high fat fed (HFF) mice resulted in significant body weight reduction and improvements in circulating triglyceride levels. [Iso³]sea lamprey PYY(1-36) treatment also prevented elevations in glucagon. Both peptides, and especially [Iso³]sea lamprey PYY(1-36), improved glucose tolerance. The treatment interventions also partially reversed the deleterious effects of sustained high fat feeding on pancreatic islet morphology.

CONCLUSION

The present study confirms that sustained NPYR2 receptor activation by [Iso³](d-Arg³⁵)sea lamprey induced significant weight lowering actions. However, identifiable benefits of this peptide over [Iso³]sea lamprey PYY(1-36), which was not protected against C-terminal degradation, were not pronounced.

Effects of Y1 receptor agonist on the pancreatic islet of diet-induced obese and diabetic mice

AIMS

Agonists of the NPY receptor might be potential in protecting pancreatic islets from injury. We aimed to characterize the role of [Leu31, Pro34]-PYY, an NPYR1 agonist, in pancreatic islets of a diet-induced obesity and insulin resistance model.

METHODS

We studied long-term high-fat diet intake as a model and selective agonist of the Y1 receptor to explore the pancreatic islet architecture and stereology, and insulin secretion in isolated islets and a whole animal model. Gene and protein expressions were assessed in isolated islets investigating the signaling cascades involved in inflammation, insulin signaling, and secretion. Also, the insulin release potential was studied in vitro.

RESULTS

Our data reveal that an infusion of NPYR1 for 14 days did not change the body mass of mice and eating behavior. NPYR1 did not modify the islet and beta-cell mass but positively impacted the inflammatory process by lowering the expressions of Tnf alpha and If gamma. Besides, NPYR1 restored the insulin signaling and the exocytose pattern by activating the PDX1/STAT3 pathway and improving the leptin signaling cascade.

CONCLUSIONS

The findings are compellingly indicating the potential effect of the NPYR1 as a target for improving the insulin resistance condition. As such, the infusion of the NPYR1 agonist would help to enhance insulin secretion by the beta-cell from the PDX1/STAT3 pathway and the improvement of the inflammatory process.

Peptide YY (1-36) peptides from phylogenetically ancient fish targeting mammalian neuropeptide Y1 receptors demonstrate potent effects on pancreatic β-cell function, growth and survival

AIM

To investigate the antidiabetic efficacy of enzymatically stable Peptide YY (PYY) peptides from phylogenetically ancient fish.

MATERIALS AND METHODS

N-terminally stabilized, PYY (1-36) sequences from Amia calva (bowfin), Oncorhynchus mykiss (trout), Petromyzon marinus (sea lamprey) and Scaphirhynchus albus (sturgeon), were synthesized, and both biological actions and antidiabetic therapeutic efficacy were assessed.

RESULTS

All fish PYY (1-36) peptides were resistant to dipeptidyl peptidase-4 (DPP-4) degradation and inhibited glucose- and alanine-induced (P < 0.05 to P < 0.001) insulin secretion. In addition, PYY (1-36) peptides imparted significant (P < 0.05 to P < 0.001) β-cell proliferative and anti-apoptotic benefits. Proliferative effects were almost entirely absent in β cells with CRISPR-Cas9-induced knockout of Npyr1. In contrast to human PYY (1-36), the piscine-derived peptides lacked appetite-suppressive actions. Twice-daily administration of sea lamprey PYY (1-36), the superior bioactive peptide, for 21 days significantly (P < 0.05 to P < 0.001) decreased fluid intake, non-fasting glucose and glucagon in streptozotocin (STZ)-induced diabetic mice. In addition, glucose tolerance, insulin sensitivity, pancreatic insulin and glucagon content were significantly improved. Metabolic benefits were linked to positive changes in pancreatic islet morphology as a result of augmented (P < 0.001) proliferation and decreased apoptosis of β cells. Sturgeon PYY (1-36) exerted similar but less impressive effects in STZ mice.

CONCLUSION

These observations reveal, for the first time, that PYY (1-36) peptide sequences from phylogenetically ancient fish replicate the pancreatic β-cell benefits of human PYY (1-36) and have clear potential for the treatment of type 2 diabetes.

Increases in PYY and uncoupling of bone turnover are associated with loss of bone mass after gastric bypass surgery

CONTEXT

The gut hormones peptide YY (PYY) and ghrelin mediate in part the metabolic benefits of Roux-en-Y gastric bypass (RYGB) surgery. However, preclinical data suggest these hormones also affect the skeleton and could contribute to postoperative bone loss.

OBJECTIVE

We investigated whether changes in fasting serum total PYY and ghrelin were associated with bone turnover marker levels and loss of bone mineral density (BMD) after RYGB.

DESIGN, SETTING, PARTICIPANTS

Prospective cohort of adults undergoing RYGB (n=44) at San Francisco academic hospitals.

MAIN OUTCOME MEASURES

We analyzed 6-month changes in PYY, ghrelin, bone turnover markers, and BMD by dual-energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT). We calculated the uncoupling index (UI), reflecting the relative balance of bone resorption and formation.

RESULTS

Postoperatively, there was a trend for an increase in PYY (+25pg/mL, p=0.07) and a significant increase in ghrelin (+192pg/mL, p<0.01). PYY changes negatively correlated with changes in spine BMD by QCT (r=-0.36, p=0.02) and bone formation marker P1NP (r=-0.30, p=0.05). Relationships were significant after adjustments for age, sex, and weight loss. No consistent relationships were found between ghrelin and skeletal outcomes. Mean 6-month UI was -3.3; UI correlated with spine BMD loss by QCT (r=0.40, p=0.01).

CONCLUSIONS

Postoperative PYY increases were associated with attenuated increases in P1NP and greater declines in spine BMD by QCT. Uncoupling of bone turnover correlated with BMD loss. These findings suggest a role for PYY in loss of bone mass after RYGB and highlight the relationship between intestinal and skeletal metabolism.

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.

Effects of 2 Novel PYY(1-36) Analogues, (P3L31P34)PYY(1-36) and PYY(1-36)(Lys12PAL), on Pancreatic Beta-Cell Function, Growth, and Survival

Recent studies have identified a beneficial role for peptide tyrosine tyrosine (PYY) on pancreatic beta-cell function and survival. These effects are linked to the activation of neuropeptide Y1 receptors (NPYR1s) by PYY(1-36). However, PYY(1-36) is subject to rapid degradation by dipeptidyl peptidase-4 (DPP-4), resulting is the loss of NPYR1 activity. Therefore, the aim of this study was to develop 2 enzymatically stable PYY(1-36) analogues, namely, (P³L³¹P³⁴)PYY(1-36) and PYY(1-36)(Lys¹²PAL), with further structural modifications to enhance NPYR1 specificity. As expected, (P³L³¹P³⁴)PYY(1-36) was fully resistant to DPP-4-mediated degradation in vitro, whereas PYY(1-36) and PYY(1-36)(Lys¹²PAL) were both liable to DPP-4 breakdown. PYY(1-36) and (P³L³¹P³⁴)PYY(1-36) induced significant reductions in glucose-stimulated insulin secretion (GSIS) from BRIN BD11 cells, but only PYY(1-36) diminished alanine-stimulated insulin secretion. In contrast, PYY(1-36)(Lys¹²PAL) had no impact on GSIS or alanine-induced insulin release. All 3 PYY peptides significantly enhanced proliferation in BRIN BD11 and 1.1B4 beta-cell lines, albeit only at the highest concentration examined, 10^-6 M, for (P³L³¹P³⁴)PYY(1-36) and PYY(1-36)(Lys¹²PAL) in BRIN BD11 cells. Regarding the protection of beta-cells against cytokine-induced apoptosis, PYY(1-36) induced clear protective effects. Both (P³L³¹P³⁴)PYY(1-36) and PYY(1-36)(Lys¹²PAL) offered some protection against apoptosis in BRIN BD11 cells, but were significantly less efficacious than PYY(1-36). Similarly, in 1.1B4 cells, both PYY analogues (10^-6 M) protected against cytokine-induced apoptosis, but (P³L³¹P³⁴)PYY(1-36) was significantly less effective than PYY(1-36). All 3 PYY peptides had no impact on refeeding in overnight fasted mice. These data underline the beta-cell benefits of PYY(1-36) and highlight the challenges of synthesising stable, bioactive, NPYR1-specific, PYY(1-36) analogues.

C-terminal degradation of PYY peptides in plasma abolishes effects on satiety and beta-cell function

The importance of dipeptidyl peptidase-4 mediated N-terminal metabolism of the enteroendocrine-derived hormone, peptide YY (PYY), for receptor binding and subsequent biological action profile is well established. However, an intact C-terminus may be fundamental also for bioactivity of PYY peptides. The current study has demonstrated C-terminal degradation of the major recognised circulating forms of PYY, PYY(1-36) and PYY(3-36), in plasma, resulting in production of PYY(1-34) and PYY(3-34). Interestingly, the angiotensin-converting-enzyme (ACE) inhibitor, captopril, blocked formation of PYY(3-34) from PYY(3-36) in plasma, but did result in the appearance of PYY(3-35). In addition, we were able to evidence C-terminal truncation of PYY(1-35) and PYY(3-35) to PYY(1-34) and PYY(3-34), respectively. As expected, PYY(1-36) and PYY(3-36) inhibited (P < 0.05-P < 0.001) glucose- and alanine-stimulated insulin secretion from BRIN-BD11 beta-cells. In contrast, PYY(1-34), PYY(3-34), PYY(1-35) and PYY(3-35) were devoid of insulinostatic actions. Both PYY(1-36) and PYY(3-36), but not related PYY metabolites, significantly (P < 0.05-P < 0.001) enhanced proliferation of BRIN BD11 and 1.1B4 beta-cell lines, and protected (P < 0.01-P < 0.001) these cell lines against cytokine-induced apoptosis. As expected, PYY(3-36) induced clear (P < 0.05-P < 0.01) appetite suppressive effects in mice, but this action was eliminated by mono- or di-peptide C-terminal truncation. Interestingly, captopril significantly (P < 0.05) augmented the anorexigenic effects of PYY(3-36) in mice. PYY(1-36), PYY(3-36), PYY(1-34) and PYY(3-34) lacked effects on in vivo glucose tolerance or glucose-induced insulin release. Taken together, these data highlight the unrecognised importance of C-terminal integrity of PYY peptides for biological activity and therapeutic usefulness in obesity-diabetes.

Mutational Analysis of Neuropeptide Y Reveals Unusual Thermal Stability Linked to Higher-Order Self-Association

Neuropeptide Y (NPY) is a 36-residue peptide, abundant in the central and peripheral nervous system. The peptide interacts with membrane-bound receptors to control processes such as food intake, vasoconstriction, and memory retention. The N-terminal polyproline sequence of NPY folds back onto a C-terminal α-helix to form a hairpin structure. The hairpin undergoes transient unfolding to allow the monomer to interact with its target membranes and receptors and to form reversible dimers in solution. Using computational, functional, and biophysical approaches, we characterized the role of two conserved tyrosines (Y20 and Y27) located within the hydrophobic core of the hairpin fold. Successive mutation of the tyrosines to more hydrophobic phenylalanines increased the thermal stability of NPY and reduced functional activity, consistent with computational studies predicting a more stable hairpin structure. However, mutant stability was high relative to wild-type: melting temperatures increased by approximately 20 °C for the single mutants (Y20F and Y27F) and by 30 °C for the double mutant (Y20F + Y27F). These findings suggested that the mutations were not just simply enhancing hairpin structure stability, but might also be driving self-association to dimer. Using analytical ultracentrifugation, we determined that the mutations indeed increased self-association, but shifted the equilibrium toward hexamer-like species. Notably, these latter species were not unique to the NPY mutants, but were found to preexist at low levels in the wild-type population. Collectively, the findings indicate that NPY self-association is more complex than previously recognized and that the ensemble of NPY quaternary states is tunable by modulating hairpin hydrophobicity.

Emerging therapeutic potential for peptide YY for obesity-diabetes

The vast majority of research to date on the gut hormone Peptide YY (PYY) has focused on appetite suppression and body weight regulation effects. These biological actions are believed to occur through interaction of PYY with hypothalamic Y₂ receptors. However, more recent studies have added additional knowledge to understanding of the physiological, and potential therapeutic, roles of PYY beyond obesity alone. Thus, PYY has now been shown to impart improvements in pancreatic beta-cell survival and function, with obvious benefits for diabetes. This effect has been linked mainly to binding and activation of Y₁ receptors by PYY, but more evidence is still required in this regard. Given the potential therapeutic promise of PYY-derived compounds, and complexity of receptor interactions, it is important to fully understand the complete biological action profile of PYY. Therefore, the current review aims to compile, evaluate and summarise current knowledge on PYY, with particular emphasis on obesity and diabetes treatment, and the importance of specific Y receptor interactions for this.

Elucidation of the Binding Mode of the Carboxyterminal Region of Peptide YY to the Human Y2 Receptor

Understanding the agonist-receptor interactions in the neuropeptide Y (NPY)/peptide YY (PYY) signaling system is fundamental for the design of novel modulators of appetite regulation. We report here the results of a multidisciplinary approach to elucidate the binding mode of the native peptide agonist PYY to the human Y₂ receptor, based on computational modeling, peptide chemistry and in vitro pharmacological analyses. The preserved binding orientation proposed for full-length PYY and five analogs, truncated at the amino terminus, explains our pharmacological results where truncations of the N-terminal proline helix showed little effect on peptide affinity. This was followed by receptor mutagenesis to investigate the roles of several receptor positions suggested by the modeling. As a complement, PYY-(3-36) analogs were synthesized with modifications at different positions in the common PYY/NPY C-terminal fragment (³²TRQRY³⁶-amide). The results were assessed and interpreted by molecular dynamics and Free Energy Perturbation (FEP) simulations of selected mutants, providing a detailed map of the interactions of the PYY/NPY C-terminal fragment with the transmembrane cavity of the Y₂ receptor. The amidated C-terminus would be stabilized by polar interactions with Gln288^6.55 and Tyr219^5.39, while Gln130^3.32 contributes to interactions with Q³⁴ in the peptide and T³² is close to the tip of TM7 in the receptor. This leaves the core, α-helix of the peptide exposed to make potential interactions with the extracellular loops. This model agrees with most experimental data available for the Y₂ system and can be used as a basis for optimization of Y₂ receptor agonists.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Neuropeptide Y as a Biomarker and Therapeutic Target for Neuroblastoma

Neuroblastoma (NB) is a pediatric malignant neoplasm of sympathoadrenal origin. Challenges in its management include stratification of this heterogeneous disease and a lack of both adequate treatments for high-risk patients and noninvasive biomarkers of disease progression. Our previous studies have identified neuropeptide Y (NPY), a sympathetic neurotransmitter expressed in NB, as a potential therapeutic target for these tumors by virtue of its Y5 receptor (Y5R)-mediated chemoresistance and Y2 receptor (Y2R)-mediated proliferative and angiogenic activities. The goal of this study was to determine the clinical relevance and utility of these findings. Expression of NPY and its receptors was evaluated in corresponding samples of tumor RNA, tissues, and sera from 87 patients with neuroblastic tumors and in tumor tissues from the TH-MYCN NB mouse model. Elevated serum NPY levels correlated with an adverse clinical presentation, poor survival, metastasis, and relapse, whereas strong Y5R immunoreactivity was a marker of angioinvasive tumor cells. In NB tissues from TH-MYCN mice, high immunoreactivity of both NPY and Y5R marked angioinvasive NB cells. Y2R was uniformly expressed in undifferentiated tumor cells, which supports its previously reported role in NB cell proliferation. Our findings validate NPY as a therapeutic target for advanced NB and implicate the NPY/Y5R axis in disease dissemination. The correlation between elevated systemic NPY and NB progression identifies serum NPY as a novel NB biomarker.

Single Cell Peptide Heterogeneity of Rat Islets of Langerhans

Measuring the chemical composition of individual cells in mammalian organs can provide critical insights toward understanding the mechanisms leading to their normal and pathological function. In this work, single cell heterogeneity of islets of Langerhans is characterized with high throughput by microscopy-guided single cell matrix-assisted laser desorption/ionization mass spectrometry. Two levels of chemical heterogeneity were observed from the analysis of more than 3000 individual cells. Within a single islet, cellular heterogeneity was evident from the exclusive expression of the canonical biomarkers glucagon, insulin, pancreatic polypeptide (PP), and somatostatin within α-, β-, γ-, and δ-cells, respectively. We localized the neuropeptide WE-14, a known cell-to-cell signaling molecule, to individual δ-cells. Moreover, several unreported endogenous peptides generated by dibasic site cleavages of PP were detected within individual γ-cells. Of these, PP(27-36) was previously shown to activate the human Y4 receptor, suggesting it has a signaling role in vivo. Heterogeneity in cell composition was also observed between islets as evidenced by a 50-fold larger α-cell population in islets of the dorsal pancreas compared to the ventral-derived pancreatic islets. Finally, PP(27-36) was more abundant in γ-cells from the ventral region of the pancreas, indicating differences in the extent of PP-prohormone processing in the two regions of the pancreas.

Development of neuropeptide Y-mediated heart innervation in rats

Neuropeptide Y (NPY) plays a trophic role in the nervous and vascular systems and in cardiac hypertrophy. However, there is no report concerning the expression of NPY and its receptors in the heart during postnatal development. In the current study, immunohistochemistry and Western blot analysis was used to label NPY, and Y1R, Y2R, and Y5R receptors in the heart tissue and intramural cardiac ganglia from rats of different ages (newborn, 10 days old, 20 days old, 30 days old, 60 days old, 1 year old, and 2 years old).The obtained data suggest age-dependent changes of NPY-mediated heart innervation. The density of NPY-immunoreactive (IR) fibers was the least in newborn animals and increased in the first 20 days of life. In the atria of newborn and 10-day-old rats, NPY-IR fibers were more abundant compared with the ventricles. The vast majority of NPY-IR fibers also contained tyrosine hydroxylase, a key enzyme in catecholamine synthesis.The expression of Y1R increased between 10 and 20 days of life. Faint Y2R immunoreactivity was observed in the atria and ventricles of 20-day-old and older rats. In contrast, the highest level of the expression of Y5R was found in newborn pups comparing with more adult rats. All intramural ganglionic neurons were also Y1R-IR and Y5R-IR and Y2R-negative in all studied animals.Thus, the increasing of density of NPY-containing nerve fibers accompanies changes in relation of different subtypes of NPY receptors in the heart during development.

Proteolytic degradation of neuropeptide Y (NPY) from head to toe: Identification of novel NPY-cleaving peptidases and potential drug interactions in CNS and Periphery

The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application. The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application.

PYY3-36: Beyond food intake

The gastrointestinal hormone peptide tyrosine tyrosine 3-36 (PYY(3-36)) has attained broad recognition with respect to its involvement in energy homeostasis and the control of food intake. It is mainly secreted by distal intestinal enteroendocrine L-cells in response to eating and exerts neurally mediated, paracrine and endocrine effects on various target organs. In addition to its gastrointestinal effects, PYY(3-36) has long been known to inhibit food intake. Recent closer examination of the effects of PYY(3-36) revealed that this gut-derived peptide also influences a wide spectrum of behavioral and cognitive functions that are pivotal for basic processes of perception and judgment, including central information processing, salience learning, working memory, and behavioral responding to novelty. Here, we review the effects of PYY(3-36) that go beyond food intake and provide a conceptual framework suggesting that several apparently unrelated behavioral actions of PYY(3-36) may actually reflect different manifestations of modulating the central dopamine system.

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.

Hypoxia shifts activity of neuropeptide Y in Ewing sarcoma from growth-inhibitory to growth-promoting effects

Ewing sarcoma (ES) is an aggressive malignancy driven by an oncogenic fusion protein, EWS-FLI1. Neuropeptide Y (NPY), and two of its receptors, Y1R and Y5R are up-regulated by EWS-FLI1 and abundantly expressed in ES cells. Paradoxically, NPY acting via Y1R and Y5R stimulates ES cell death. Here, we demonstrate that these growth-inhibitory actions of NPY are counteracted by hypoxia, which converts the peptide to a growth-promoting factor. In ES cells, hypoxia induces another NPY receptor, Y2R, and increases expression of dipeptidyl peptidase IV (DPPIV), an enzyme that cleaves NPY to a shorter form, NPY3-36. This truncated peptide no longer binds to Y1R and, therefore, does not stimulate ES cell death. Instead, NPY3-36 acts as a selective Y2R/Y5R agonist. The hypoxia-induced increase in DPPIV activity is most evident in a population of ES cells with high aldehyde dehydrogenase (ALDH) activity, rich in cancer stem cells (CSCs). Consequently, NPY, acting via Y2R/Y5Rs, preferentially stimulates proliferation and migration of hypoxic ALDHhigh cells. Hypoxia also enhances the angiogenic potential of ES by inducing Y2Rs in endothelial cells and increasing the release of its ligand, NPY3-36, from ES cells. In summary, hypoxia acts as a molecular switch shifting NPY activity away from Y1R/Y5R-mediated cell death and activating the Y2R/Y5R/DPPIV/NPY3-36 axis, which stimulates ES CSCs and promotes angiogenesis. Hypoxia-driven actions of the peptide such as these may contribute to ES progression. Due to the receptor-specific and multifaceted nature of NPY actions, these findings may inform novel therapeutic approaches to ES.

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.

Synthetic routes to the Neuropeptide Y Y1 receptor antagonist 1229U91 and related analogues for SAR studies and cell-based imaging

The potent Y1 receptor antagonist, 1229U91 has an unusual cyclic dimer structure that makes syntheses of analogue series quite challenging. We have examined three new routes to the synthesis of such peptides that has given access to novel structural variants including heterodimeric compounds, ring size variants and labelled conjugates. These compounds, including a fluorescently labelled analogue VIII show potent antagonism that can be utilised in studying Y1 receptor pharmacology.

Altered expression of neuropeptide Y, Y1 and Y2 receptors, but not Y5 receptor, within hippocampus and temporal lobe cortex of tremor rats

As an endogenous inhibitor of glutamate-mediated synaptic transmission in mammalian central nervous system, neuropeptide Y (NPY) plays a crucial role in regulating homeostasis of neuron excitability. Loss of balance between excitatory and inhibitory neurotransmission is thought to be a chief mechanism of epileptogenesis. The abnormal expression of NPY and its receptors observed following seizures have been demonstrated to be related to the production of epilepsy. The tremor rat (TRM) is a hereditary epileptic animal model. So far, there is no report concerning whether NPY and its receptors may be involved in TRM pathogenesis. In this study, we focused on the expression of NPY and its three receptor subtypes: Y1R, Y2R and Y5R in the TRM brain. We first found the expression of NPY in TRM hippocampus and temporal lobe cortex was increased compared with control (Wistar) rats. The mRNA and protein expression of Y1R was down-regulated in hippocampus but up-regulated in temporal lobe cortex, whereas Y2R expression was significantly increased in both areas. There was no significant change of Y5R expression in either area. The immunohistochemistry data showed that Y1R, Y2R, Y5R were present throughout CA1, CA3, dentate gyrus (DG) and the entorhinal cortex which is included in the temporal lobe cortex of TRM. In conclusion, our results showed the altered expression of NPY, Y1R and Y2R but not Y5R in hippocampus and temporal lobe cortex of TRM brain. This abnormal expression may be associated with the generation of epileptiform activity and provide a candidate target for treatment of genetic epilepsy.