The RFamide neuropeptide 26RFa and its role in the control of neuroendocrine functions

QRFP43 modulates the activity of the hypothalamic-pituitary-thyroid axis in female sheep

Since the early discovery of QRFP43, intensive research has been primarily focused on its role in the modulation of food intake. As is widely recognised, the regulation of the body's energy status is a highly complex process involving numerous systems, hormones and neurotransmitters. Among the most important regulators of energy status, alongside the satiety and hunger centre located in the hypothalamus, is the HPT axis, which directly and indirectly affects the regulation of metabolism in all cells of the body. Therefore, it seems highly important to conduct studies aimed at elucidating how QRFP43 may impact the secretory activity of the HPT axis. The objective of this work was to investigate the role of QRFP43 in modulating HPT axis activity in sheep. The study examined mRNA and peptide expression of TRH and TSH in the hypothalamus and pituitary, as well as plasma concentrations of TSH, free T4 (FT4) and free T3 (FT3). Moreover, the relationship between QRFP34 and mRNA expression of the Dio1, Dio2, and Dio3 genes was explored in selected tissues of the HPT axis. The animals (n = 48) were randomly divided into three experimental groups: a control group receiving an ICV infusion of Ringer-Locke solution, and two experimental groups receiving ICV infusions of QRFP43 at doses of 10 and 50 µg per day. Four 50-minute ICV infusions were administered to all sheep at 30 min intervals each of three consecutive days. Hypothalamic, pituitary and thyroid glands were collected and preserved for further immunohistochemical and molecular biological analyses. Additionally, blood samples were collected during the experiment for subsequent RIA determinations. In summary, the results of the experiment have indicated that QRFP43 modulates the secretory activity of the HPT axis at all organisational levels. Moreover, QRFP43 can alter the mRNA expression profiles of DIO1, DIO2 and DIO3 in HPT tissues, leading to discrete changes in the metabolism of the cells studied and their response to signals transmitted by T4 and T3.

QRFP and GPR103 in the paraventricular nucleus play a role in chronic stress-induced depressive-like symptomatology by enhancing the hypothalamic-pituitary-adrenal axis

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis during chronic stress is essential for depression neurobiology. As the latest member of the RFamide peptide family in mammals, pyroglutamylated RFamide peptide (QRFP) is closely implicated in neuroendocrine maintenance by activating G-protein-coupled receptor 103 (GPR103). We hypothesized that QRFP and GPR103 might contribute to chronic stress-induced depression by promoting corticotropin-releasing hormone (CRH) release from neurons in the paraventricular nucleus (PVN), and various methods were employed in this study, with male C57BL/6J mice adopted as the experimental subjects. Chronic stress induced not only depression-like behaviors but also significant enhancement in QRFP and GPR103 in the PVN. Genetic overexpression of QRFP/GPR103 and stereotactic infusion of QRFP-26/QRFP-43 peptide in the PVN all mimicked chronic stress that induced various depression-like phenotypes in naïve mice, and this was mediated by promoting CRH biosynthesis and HPA activity. In contrast, genetic knockdown of QRFP/GPR103 in the PVN produced notable antidepressant-like effects in mice exposed to chronic stress. Furthermore, genetic knockout of QRFP also protected against chronic stress in mice. In addition, both the C-terminal biological region of QRFP and the downstream PKA/PKC-CREB signaling coupled to GPR103 stimulation underlie the role of QRFP and GPR103 in depression. Collectively, QRFP and GPR103 in PVN neurons could be viable targets for novel antidepressants.

Neuropeptides and receptors in the cephalochordate: A crucial model for understanding the origin and evolution of vertebrate neuropeptide systems

Genomes and transcriptomes from diverse organisms are providing a wealth of data to explore the evolution and origin of neuropeptides and their receptors in metazoans. While most neuropeptide-receptor systems have been extensively studied in vertebrates, there is still a considerable lack of understanding regarding their functions in invertebrates, an extraordinarily diverse group that account for the majority of animal species on Earth. Cephalochordates, commonly known as amphioxus or lancelets, serve as the evolutionary proxy of the chordate ancestor. Their key evolutionary position, bridging the invertebrate to vertebrate transition, has been explored to uncover the origin, evolution, and function of vertebrate neuropeptide systems. Amphioxus genomes exhibit a high degree of sequence and structural conservation with vertebrates, and sequence and functional homologues of several vertebrate neuropeptide families are present in cephalochordates. This review aims to provide a comprehensively overview of the recent findings on neuropeptides and their receptors in cephalochordates, highlighting their significance as a model for understanding the complex evolution of neuropeptide signaling in vertebrates.

Single-Cell Profiling Uncovers Evolutionary Divergence of Hypocretin/Orexin Neuronal Subpopulations

Brain nuclei are traditionally defined by their anatomy, activity, and expression of specific markers. The hypothalamus contains discrete neuronal populations that coordinate fundamental behavioral functions, including sleep and wakefulness, in all vertebrates. Particularly, the diverse roles of hypocretin/orexin (Hcrt)-releasing neurons suggest functional heterogeneity among Hcrt neurons. Using single-cell RNA sequencing (scRNA-seq) and high-resolution imaging of the adult male and female zebrafish hypothalamic periventricular zone, we identified 21 glutamatergic and 28 GABAergic cell types. Integration of zebrafish and mouse scRNA-seq revealed evolutionary conserved and divergent hypothalamic cell types. The expression of specific genes, including npvf, which encodes a sleep-regulating neuropeptide, was enriched in subsets of glutamatergic Hcrt neurons in both larval and adult zebrafish. The genetic profile, activity, and neurite processing of the neuronal subpopulation that coexpresses both Hcrt and Npvf (Hcrt+Npvf+) differ from other Hcrt neurons. These interspecies findings provide a unified annotation of hypothalamic cell types and suggest that the heterogeneity of Hcrt neurons enables multifunctionality, such as consolidation of both wake and sleep by the Hcrt- and Npvf-releasing neuronal subpopulation.

The 26RFa (QRFP)/GPR103 Neuropeptidergic System: A Key Regulator of Energy and Glucose Metabolism

BACKGROUND

Obesity and type 2 diabetes are strongly associated pathologies, currently considered as a worldwide epidemic problem. Understanding the mechanisms that drive the development of these diseases would enable to develop new therapeutic strategies for their prevention and treatment. Particularly, the role of the brain in energy and glucose homeostasis has been studied for 2 decades. In specific, the hypothalamus contains well-identified neural networks that regulate appetite and potentially also glucose homeostasis. A new concept has thus emerged, suggesting that obesity and diabetes could be due to a dysfunction of the same, still poorly understood, neural networks.

SUMMARY

The neuropeptide 26RFa (also termed QRFP) belongs to the family of RFamide regulatory peptides and has been identified as the endogenous ligand of the human G protein-coupled receptor GPR103 (QRFPR). The primary structure of 26RFa is strongly conserved during vertebrate evolution, suggesting its crucial roles in the control of vital functions. Indeed, the 26RFa/GPR103 peptidergic system is reported to be involved in the control of various neuroendocrine functions, notably the control of energy metabolism in which it plays an important role, both centrally and peripherally, since 26RFa regulates feeding behavior, thermogenesis and lipogenesis. Moreover, 26RFa is reported to control glucose homeostasis both peripherally, where it acts as an incretin, and centrally, where the 26RFa/GPR103 system relays insulin signaling in the brain to control glucose metabolism.

KEY MESSAGES

This review gives a comprehensive overview of the role of the 26RFa/GPR103 system as a key player in the control of energy and glucose metabolism. In a pathophysiological context, this neuropeptidergic system represents a prime therapeutic target whose mechanisms are highly relevant to decipher.

Cysteine-free cone snail venom peptides: Classification of precursor proteins and identification of mature peptides

The cysteine-free acyclic peptides present in marine cone snail venom have been much less investigated than their disulfide bonded counterparts. Precursor protein sequences derived from transcriptomic data, together with mass spectrometric fragmentation patterns for peptides present in venom duct tissue extracts, permit the identification of mature peptides. Twelve distinct gene superfamiles have been identified with precursor lengths between 64 and 158 residues. In the case of Conus monile, three distinct mature peptides have been identified, arising from two distinct protein precursors. Mature acyclic peptides are often post-translationally modified, with C-terminus amidation, a feature characteristic of neuropeptides. In the present study, 20 acyclic peptides from Conus monile and Conus betulinus were identified. The common modifications of C-terminus amidation, gamma carboxylation of glutamic acid (E to ϒ), N-terminus conversion of Gln (Q) to a pyroglutamyl residue (Z), and hydroxylation of Pro (P) to Hyp (O) are observed in one or more peptides identified in this study. Proteolytic trimming of sequences by cleavage at the C-terminus of Asn (N) residues is established. The presence of an asparagine endopeptidase is strengthened by the identification of legumain-like sequences in the transcriptome assemblies from diverse Conus species. Such sequences may be expected to have a cleavage specificity at Asn-Xxx peptide bonds.

Interactions between the regulatory peptide 26RFa (QRFP) and insulin in the regulation of glucose homeostasis in two complementary models: The high fat 26RFa-deficient mice and the streptozotocin insulin-deficient mice

The regulatory peptide 26RFa (QRFP) is involved in the control of glucose homeostasis at the periphery by acting as an incretin, and in the brain by mediating the central antihyperglycemic effect of insulin, indicating the occurrence of a close relationship between 26RFa and insulin in the regulation of glucose metabolism. Here, we investigated the physiological interactions between 26RFa and insulin in two complementary models i.e. a model of obese/hyperglycemic mice deficient for 26RFa and a model of diabetic mice deficient for insulin. For this, transgenic 26RFa-deficient mice were made obese and chronically hyperglycemic by a 3-month high fat diet (HFD) and second group of mice was made diabetic by destruction of the β cells of the pancreatic islets using a single injection of streptozotocin. Our data reveal that 26RFa deficiency does not impact significantly the "glycemic" phenotype of the HFD mice. The pancreatic islets, liver, white adipose tissue masses are not altered by the lack of 26RFa production but the brown adipose tissue (BAT) weight is significantly increased in these animals. In diabetic insulin-deficient mice, the injection of 26RFa does not exhibit any beneficial effect on the impaired glucose homeostasis characterizing this model. Finally, we show that streptozotocin diabetic mice display lowered plasma 26RFa levels as compared to untreated mice, whereas the expression of the peptide in the duodenum is not affected. Taken together, the present results indicate that dysregulation of glucose homeostasis in obese/hyperglycemic mice is not aggravated by the absence of 26RFa that may be compensated by the increase of BAT mass. In diabetic insulin-deficient mice, the antihypergycemic effect of 26RFa is totally blunted probably as a result of the impaired insulin production characterizing this model, avoiding therefore the action of the peptide.

Blood Levels of Neuropeptide 26RFa in Relation to Anxiety and Aggressive Behavior in Humans-An Exploratory Study

26RFa, also referred to as QRFP, is a hypothalamic neuropeptide mainly known for its role in the regulation of appetite and glucose metabolism. Its possible relevance to emotional regulation is largely unexplored. To address this, in the present exploratory study, we analyzed the plasma concentrations of 26RFa in humans characterized by different levels of anxiety and aggressive behavior. For this purpose, the study included 13 prison inmates who have committed violent crimes and 19 age-matched healthy men from the general population as controls. Anxiety, depression and aggressive behavior were evaluated in both groups using standard questionnaires. The inmate group was characterized by increased aggression and anxiety compared to the controls. We found that the mean plasma levels of 26RFa did not significantly differ between the inmates and the controls. However, several high outliers were present only in the inmate group. The plasma levels of 26RFa correlated positively with the anxiety scores in all the studied subjects and controls. After removing the high outliers in the inmate group, positive correlations of 26RFa with anxiety and a subscale of hostility in the aggression scale were also recorded in this group. No significant correlations of 26RFa with depression scores or other parameters of aggressive behavior were found. Thus, the present results did not support an involvement of 26RFa in aggressive behavior in humans but pointed to a link between this neuropeptide and anxiety. Nevertheless, considering the exploratory nature of the present study, this conclusion should be verified in a larger cohort, including the clinical degree of anxiety.

The 26RFa (QRFP)/GPR103 neuropeptidergic system in mice relays insulin signalling into the brain to regulate glucose homeostasis

AIMS/HYPOTHESIS

26RFa (pyroglutamilated RFamide peptide [QRFP]) is a biologically active peptide that regulates glucose homeostasis by acting as an incretin and by increasing insulin sensitivity at the periphery. 26RFa is also produced by a neuronal population localised in the hypothalamus. In this study we investigated whether 26RFa neurons are involved in the hypothalamic regulation of glucose homeostasis.

METHODS

26Rfa^+/+, 26Rfa^-/- and insulin-deficient male C57Bl/6J mice were used in this study. Mice received an acute intracerebroventricular (i.c.v.) injection of 26RFa, insulin or the 26RFa receptor (GPR103) antagonist 25e and were subjected to IPGTTs, insulin tolerance tests, acute glucose-stimulated insulin secretion tests and pyruvate tolerance tests (PTTs). Secretion of 26RFa by hypothalamic explants after incubation with glucose, leptin or insulin was assessed. Expression and quantification of the genes encoding 26RFa, agouti-related protein, the insulin receptor and GPR103 were evaluated by quantitative reverse transcription PCR and RNAscope in situ hybridisation.

RESULTS

Our data indicate that i.c.v.-injected 26RFa induces a robust antihyperglycaemic effect associated with an increase in insulin production by the pancreatic islets. In addition, we found that insulin strongly stimulates 26Rfa expression and secretion by the hypothalamus. RNAscope experiments revealed that neurons expressing 26Rfa are mainly localised in the lateral hypothalamic area, that they co-express the gene encoding the insulin receptor and that insulin induces the expression of 26Rfa in these neurons. Concurrently, the central antihyperglycaemic effect of insulin is abolished in the presence of a GPR103 antagonist and in 26RFa-deficient mice. Finally, our data indicate that the hypothalamic 26RFa neurons are not involved in the central inhibitory effect of insulin on hepatic glucose production, but mediate the central effects of the hormone on its own peripheral production.

CONCLUSION/INTERPRETATION

We have identified a novel mechanism in the hypothalamic regulation of glucose homeostasis, the 26RFa/GPR103 system, and we provide evidence that this neuronal peptidergic system is a key relay for the central regulation of glucose metabolism by insulin.

Point-Substitution of Phenylalanine Residues of 26RFa Neuropeptide: A Structure-Activity Relationship Study

26RFa is a neuropeptide that activates the rhodopsin-like G protein-coupled receptor QRFPR/GPR103. This peptidergic system is involved in the regulation of a wide array of physiological processes including feeding behavior and glucose homeostasis. Herein, the pharmacological profile of a homogenous library of QRFPR-targeting peptide derivatives was investigated in vitro on human QRFPR-transfected cells with the aim to provide possible insights into the structural determinants of the Phe residues to govern receptor activation. Our work advocates to include in next generations of 26RFa_(20–26)-based QRFPR agonists effective substitutions for each Phe unit, i.e., replacement of the Phe²² residue by a constrained 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid moiety, and substitution of both Phe²⁴ and Phe²⁶ by their para-chloro counterpart. Taken as a whole, this study emphasizes that optimized modifications in the C-terminal part of 26RFa are mandatory to design selective and potent peptide agonists for human QRFPR.

Functional characterization of neuropeptide 26RFa receptors GPR103A and GPR103B in zebrafish, Danio rerio

The hypothalamic neuropeptide 26RFa is the most recently identified member of the RFamide peptide family, and this 26RFa signaling system has been shown to be implicated in regulating a variety of physiological processes. In zebrafish，26RFa and two putative receptors, DrGPR103A and DrGPR103B, have been in silico identified, and in vivo data derived from overexpression and loss of function mutation experiments suggest the 26RFa signaling system plays an important role in the hypothalamic regulation of sleep. However, the biochemical and pharmacological information on DrGPR103A/B receptors is still unknown. Here, after cloning of cDNAs of two putative 26RFa receptor genes, DrGPR103A and B, from the total RNA of zebrafish whole body, functional assays demonstrated that both receptors were activated by synthetic zebrafish 26RFa neuropeptide, leading to a significant increase in CRE-driven luciferase activity and intracellular Ca2+ mobilization in a Gαq inhibitor- and Gαi/o inhibitor-sensitive manner. Upon activation by 26RFa, DrGPR103A and B evoked ERK1/2 phosphorylation and underwent internalization. Further functional determination also revealed that zebrafish kisspeptin-1 exhibited a slight potency for activating both DrGPR103A and B, and vice versa, zebrafish 26RFa also showed some activity at zebrafish GPR54A and B. Our findings provided evidence that zebrafish GPR103A and B are two functional Gαq- and Gαi/o-dually coupled receptors for 26RFa, enabling the further elucidation of the endocrinological roles of zebrafish 26RFa signaling system in the regulation of physiological activities.

Glucose homeostasis is impaired in mice deficient in the neuropeptide 26RFa (QRFP)

INTRODUCTION

26RFa (pyroglutamyl RFamide peptide (QRFP)) is a biologically active peptide that has been found to control feeding behavior by stimulating food intake, and to regulate glucose homeostasis by acting as an incretin. The aim of the present study was thus to investigate the impact of 26RFa gene knockout on the regulation of energy and glucose metabolism.

RESEARCH DESIGN AND METHODS

26RFa mutant mice were generated by homologous recombination, in which the entire coding region of prepro26RFa was replaced by the iCre sequence. Energy and glucose metabolism was evaluated through measurement of complementary parameters. Morphological and physiological alterations of the pancreatic islets were also investigated.

RESULTS

Our data do not reveal significant alteration of energy metabolism in the 26RFa-deficient mice except the occurrence of an increased basal metabolic rate. By contrast, 26RFa mutant mice exhibited an altered glycemic phenotype with an increased hyperglycemia after a glucose challenge associated with an impaired insulin production, and an elevated hepatic glucose production. Two-dimensional and three-dimensional immunohistochemical experiments indicate that the insulin content of pancreatic β cells is much lower in the 26RFa^-/- mice as compared with the wild-type littermates.

CONCLUSION

Disruption of the 26RFa gene induces substantial alteration in the regulation of glucose homeostasis, with in particular a deficit in insulin production by the pancreatic islets. These findings further support the notion that 26RFa is an important regulator of glucose homeostasis.

Origin and Evolution of the Neuroendocrine Control of Reproduction in Vertebrates, With Special Focus on Genome and Gene Duplications

In humans, as in the other mammals, the neuroendocrine control of reproduction is ensured by the brain-pituitary gonadotropic axis. Multiple internal and environmental cues are integrated via brain neuronal networks, ultimately leading to the modulation of the activity of gonadotropin-releasing hormone (GnRH) neurons. The decapeptide GnRH is released into the hypothalamic-hypophysial portal blood system and stimulates the production of pituitary glycoprotein hormones, the two gonadotropins luteinizing hormone and follicle-stimulating hormone. A novel actor, the neuropeptide kisspeptin, acting upstream of GnRH, has attracted increasing attention in recent years. Other neuropeptides, such as gonadotropin-inhibiting hormone/RF-amide related peptide, and other members of the RF-amide peptide superfamily, as well as various nonpeptidic neuromediators such as dopamine and serotonin also provide a large panel of stimulatory or inhibitory regulators. This paper addresses the origin and evolution of the vertebrate gonadotropic axis. Brain-pituitary neuroendocrine axes are typical of vertebrates, the pituitary gland, mediator and amplifier of brain control on peripheral organs, being a vertebrate innovation. The paper reviews, from molecular and functional perspectives, the evolution across vertebrate radiation of some key actors of the vertebrate neuroendocrine control of reproduction and traces back their origin along the vertebrate lineage and in other metazoa before the emergence of vertebrates. A focus is given on how gene duplications, resulting from either local events or from whole genome duplication events, and followed by paralogous gene loss or conservation, might have shaped the evolutionary scenarios of current families of key actors of the gonadotropic axis.

Molecular codes and in vitro generation of hypocretin and melanin concentrating hormone neurons

Hypocretin/orexin (HCRT) and melanin concentrating hormone (MCH) neuropeptides are exclusively produced by the lateral hypothalamus and play important roles in sleep, metabolism, reward, and motivation. Loss of HCRT (ligands or receptors) causes the sleep disorder narcolepsy with cataplexy in humans and in animal models. How these neuropeptides are produced and involved in diverse functions remain unknown. Here, we developed methods to sort and purify HCRT and MCH neurons from the mouse late embryonic hypothalamus. RNA sequencing revealed key factors of fate determination for HCRT (Peg3, Ahr1, Six6, Nr2f2, and Prrx1) and MCH (Lmx1, Gbx2, and Peg3) neurons. Loss of Peg3 in mice significantly reduces HCRT and MCH cell numbers, while knock-down of a Peg3 ortholog in zebrafish completely abolishes their expression, resulting in a 2-fold increase in sleep amount. We also found that loss of HCRT neurons in Hcrt-ataxin-3 mice results in a specific 50% decrease in another orexigenic neuropeptide, QRFP, that might explain the metabolic syndrome in narcolepsy. The transcriptome results were used to develop protocols for the production of HCRT and MCH neurons from induced pluripotent stem cells and ascorbic acid was found necessary for HCRT and BMP7 for MCH cell differentiation. Our results provide a platform to understand the development and expression of HCRT and MCH and their multiple functions in health and disease.

The neuropeptide 26RFa in the human gut and pancreas: potential involvement in glucose homeostasis

OBJECTIVE

Recent studies performed in mice revealed that the neuropeptide 26RFa regulates glucose homeostasis by acting as an incretin and by increasing insulin sensitivity. However, in humans, an association between 26RFa and the regulation of glucose homeostasis is poorly documented. In this study, we have thus investigated in detail the distribution of 26RFa and its receptor, GPR103, in the gut and the pancreas, and determined the response of this peptidergic system to an oral glucose challenge in obese patients.

DESIGN AND METHODS

Distribution of 26RFa and GPR103 was examined by immunohistochemistry using gut and pancreas tissue sections. Circulating 26RFa was determined using a specific radioimmunoassay in plasma samples collected during an oral glucose tolerance test.

RESULTS

26RFa and GPR103 are present all along the gut but are more abundant in the stomach and duodenum. In the stomach, the peptide and its receptor are highly expressed in the gastric glands, whereas in the duodenum, ileum and colon they are present in the enterocytes and the goblet cells. In the pancreatic islets, the 26RFa/GPR103 system is mostly present in the β cells. During an oral glucose tolerance test, plasma 26RFa profile is different between obese patients and healthy volunteers, and we found strong positive correlations between 26RFa blood levels and the BMI, and with various parameters of insulin secretion and insulin resistance.

CONCLUSION

The present data suggest an involvement of the 26RFa/GPR103 peptidergic system in the control of human glucose homeostasis.

Neuropeptide 26RFa (QRFP) is a key regulator of glucose homeostasis and its activity is markedly altered in obese/hyperglycemic mice

Recent studies have shown that the hypothalamic neuropeptide 26RFa regulates glucose homeostasis by acting as an incretin and increasing insulin sensitivity. In this study, we further characterized the role of the 26RFa/GPR103 peptidergic system in the global regulation of glucose homeostasis using a 26RFa receptor antagonist and also assessed whether a dysfunction of the 26RFa/GPR103 system occurs in obese hyperglycemic mice. First, we demonstrate that administration of the GPR103 antagonist reduces the global glucose-induced incretin effect and insulin sensitivity whereas, conversely, administration of exogenous 26RFa attenuates glucose-induced hyperglycemia. Using a mouse model of high-fat diet-induced obesity and hyperglycemia, we found a loss of the antihyperglcemic effect and insulinotropic activity of 26RFa, accompanied with a marked reduction of its insulin-sensitive effect. Interestingly, this resistance to 26RFa is associated with a downregulation of the 26RFa receptor in the pancreatic islets, and insulin target tissues. Finally, we observed that the production and release kinetics of 26RFa after an oral glucose challenge is profoundly altered in the high-fat mice. Altogether, the present findings support the view that 26RFa is a key regulator of glucose homeostasis whose activity is markedly altered under obese/hyperglycemic conditions.

Microinjection of 26RFa, an endogenous ligand for the glutamine RF-amide peptide receptor (QRFP receptor), into the rostral ventromedial medulla (RVM), locus coelureus (LC), and periaqueductal grey (PAG) produces an analgesic effect in rats

26RFa is an endogenous ligand for the QRFP receptor. We previously found that intracerebroventricular injection of 26RFa produces an analgesic effect in a rat formalin test. In the present study, we directly tested the hypothesis that the analgesic effects of 26RFa in the formalin test are mediated in well-recognized regions of the descending inhibitory pain pathways, such as the rostral ventromedial medulla (RVM), locus coeruleus (LC), and periaqueductal grey (PAG) in rats. Injection cannulae were stereotaxically placed in the RVM, LC, or PAG through a burr hole. 26RFa (15 μg) or saline was delivered in a total volume of 0.5 μL. In a formalin test, 50 μL of 5% formalin was injected subcutaneously into the hind paw. In an antagonist study, idazoxan, an α-2 antagonist, or naloxone, an opioid receptor antagonist, was administered. Microinjection of 26RFa into the RVM had no effect compared with that in saline-injected rats. Microinjection of 26RFa into the LC contralateral, but not ipsilateral, to the formalin injection site significantly decreased the number of flinching behaviors compared with that of saline-injected rats. This effect was antagonized by intrathecal injection of idazoxan. Microinjection of 26RFa into the contralateral, but not ipsilateral, PAG produced an analgesic effect, and this effect was partly antagonized by intraperitoneal naloxone. These data suggest that 26RFa microinjected into the contralateral LC induced noradrenaline release in the spinal cord and produced an analgesic effect. In the contralateral PAG, 26RFa activated the opioid system, and some analgesic effects were mediated by opioid system activation.

Design, Synthesis, Molecular Dynamics Simulation, and Functional Evaluation of a Novel Series of 26RFa Peptide Analogues Containing a Mono- or Polyalkyl Guanidino Arginine Derivative

26RFa, the endogenous QRFPR ligand, is implicated in several physiological and pathological conditions such as the regulation of glucose homeostasis and bone mineralization; hence, QRFPR ligands display therapeutic potential. At the molecular level, functional interaction occurs between residues Arg²⁵ of 26RFa and Gln¹²⁵ of QRFPR. We have designed 26RFa_(20-26) analogues incorporating arginine derivatives modified by alkylated substituents. We found that the Arg²⁵ side chain length was necessary to retain the activity of 26RFa_(20-26) and that N-monoalkylation of arginine was accommodated by the QRFPR active site. In particular, [(Me)^ωArg²⁵]26RFa_(20-26) (5b, LV-2186) appeared to be 25-fold more potent than 26RFa_(20-26) and displayed a position in a QRFPR homology model slightly different to that of the unmodified heptapeptide. Other peptides were less potent than 26RFa_(20-26), exhibited partial agonistic activity, or were totally inactive in accordance to different ligand-bound structures. In vivo, [(Me)^ωArg²⁵]26RFa_(20-26) exerted a delayed 26RFa-like hypoglycemic effect. Finally, N-methyl substituted arginine-containing peptides represent lead compounds for further development of QRFPR agonists.

Central regulation of food intake in fish: an evolutionary perspective

Evidence indicates that central regulation of food intake is well conserved along the vertebrate lineage, at least between teleost fish and mammals. However, several differences arise in the comparison between both groups. In this review, we describe similarities and differences between teleost fish and mammals on an evolutionary perspective. We focussed on the existing knowledge of specific fish features conditioning food intake, anatomical homologies and analogies between both groups as well as the main signalling pathways of neuroendocrine and metabolic nature involved in the homeostatic and hedonic central regulation of food intake.

Orphan G protein-coupled receptors: The role in CNS disorders

There are various types of receptors in the central nervous system (CNS). G protein-coupled receptors (GPCRs) have the highest expression with a wide range of physiological functions. A newer sub group of these receptors namely orphan GPCRs have been discovered. GPR3, GPR6, GPR17, GPR26, GPR37, GPR39, GPR40, GPR50, GPR52, GPR54, GPR55, GPR85, GPR88, GPR103, and GPR139 are the selected orphan GPCRs for this article. Their roles in the central nervous system have not been understood well so far. However, recent studies show that they may have very important functions in the CNS. Hence, in the present study, we reviewed most recent findings regarding the physiological roles of the selected orphan GPCRs in the CNS. After a brief presentation of each receptor, considering the results from genetic and pharmacological manipulation of the receptors, their roles in the pathophysiology of different diseases and disorders including anxiety, depression, schizophrenia, epilepsy, Alzheimer's disease, Parkinson's disease, and substance abuse will be discussed. At present, our knowledge regarding the role of GPCRs in the brain is very limited. However, previous limited studies show that orphan GPCRs have an important place in psychopharmacology and these receptors are potential new targets for the treatment of major CNS diseases.

The Neuropeptide 26RFa (QRFP) and Its Role in the Regulation of Energy Homeostasis: A Mini-Review

This mini-review deals with the neuropeptide 26RFa (or QRFP) which is a member of the RFamide peptide family discovered simultaneously by three groups in 2003. 26RFa (or its N-extended form 43RFa) was subsequently shown to be the endogenous ligand of the human orphan receptor GPR103. In the brain, 26RFa and GPR103mRNA are primarily expressed in hypothalamic nuclei involved in the control of feeding behavior, and at the periphery, the neuropeptide and its receptor are present in abundance in the gut and the pancreatic islets, suggesting that 26RFa is involved in the regulation of energy metabolism. Indeed, 26RFa stimulates food intake when injected centrally, and its orexigenic effect is even more pronounced in obese animals. The expression of 26RFa is up-regulated in the hypothalamus of obese animals, supporting that the 26RFa/GPR103 system may play a role in the development and/or maintenance of the obese status. Recent data indicate that 26RFa is also involved in the regulation of glucose homeostasis. 26RFa reduces glucose-induced hyperglycemia, increases insulin sensitivity and insulinemia. Furthermore, an oral ingestion of glucose strongly stimulates 26RFa release by the gut, indicating that 26RFa is a novel incretin. Finally, 26RFa is able to prevent pancreatic β cell death and apoptosis. This brief overview reveals that 26RFa is a key neuropeptide in the regulation of energy metabolism. Further fields of research are suggested including the pathophysiological implication of the 26RFa/GPR103 system.

In the picture: disulfide-poor conopeptides, a class of pharmacologically interesting compounds

During evolution, nature has embraced different strategies for species to survive. One strategy, applied by predators as diverse as snakes, scorpions, sea anemones and cone snails, is using venom to immobilize or kill a prey. This venom offers a unique and extensive source of chemical diversity as it is driven by the evolutionary pressure to improve prey capture and/or to protect their species. Cone snail venom is an example of the remarkable diversity in pharmacologically active small peptides that venoms can consist of. These venom peptides, called conopeptides, are classified into two main groups based on the number of cysteine residues, namely disulfide-rich and disulfide-poor conopeptides. Since disulfide-poor conotoxins are minor components of this venom cocktail, the number of identified peptides and the characterization of these peptides is far outclassed by its cysteine-rich equivalents. This review provides an overview of 12 families of disulfide-poor peptides identified to date as well as the state of affairs.

Anxiolytic effect of the GPR103 receptor agonist peptide P550 (homolog of neuropeptide 26RFa) in mice. Involvement of neurotransmitters

The GPR103 receptor is a G protein-coupled receptor, which plays a role in several physiological functions. However, the role of the GPR103 receptor in anxiety has not been clarified. The first aim of our study was to elucidate the involvement of the GPR103 receptor in anxious behavior. Mice were treated with peptide P550, which is the mouse homolog of neuropeptide 26RFa and has similar activity for the GPR103 receptor as neuropeptide 26RFa. The anxious behavior was investigated using an elevated plus-maze paradigm. The second aim of our study was to investigate the underlying neurotransmissions. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a γ-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a nonselective β-adrenergic receptor antagonist, propranolol. Our results demonstrated that peptide P550 reduces anxious behavior in elevated plus maze test in mice. Our study shows also that GABAA-ergic, α- and β-adrenergic transmissions are all involved in this action, whereas 5-HT1 and 5-HT2 serotonergic, muscarinic cholinergic and D2, D3, D4 dopaminergic mechanisms may not be implicated.

QRFP and Its Receptors Regulate Locomotor Activity and Sleep in Zebrafish

The hypothalamus plays an important role in regulating sleep, but few hypothalamic sleep-promoting signaling pathways have been identified. Here we demonstrate a role for the neuropeptide QRFP (also known as P518 and 26RFa) and its receptors in regulating sleep in zebrafish, a diurnal vertebrate. We show that QRFP is expressed in ∼10 hypothalamic neurons in zebrafish larvae, which project to the hypothalamus, hindbrain, and spinal cord, including regions that express the two zebrafish QRFP receptor paralogs. We find that the overexpression of QRFP inhibits locomotor activity during the day, whereas mutation of qrfp or its receptors results in increased locomotor activity and decreased sleep during the day. Despite the restriction of these phenotypes to the day, the circadian clock does not regulate qrfp expression, and entrained circadian rhythms are not required for QRFP-induced rest. Instead, we find that QRFP overexpression decreases locomotor activity largely in a light-specific manner. Our results suggest that QRFP signaling plays an important role in promoting sleep and may underlie some aspects of hypothalamic sleep control.

SIGNIFICANCE STATEMENT

The hypothalamus is thought to play a key role in regulating sleep in vertebrate animals, but few sleep-promoting signaling pathways that function in the hypothalamus have been identified. Here we use the zebrafish, a diurnal vertebrate, to functionally and anatomically characterize the neuropeptide QRFP. We show that QRFP is exclusively expressed in a small number of neurons in the larval zebrafish hypothalamus that project widely in the brain. We also show that QRFP overexpression reduces locomotor activity, whereas animals that lack QRFP signaling are more active and sleep less. These results suggest that QRFP signaling participates in the hypothalamic regulation of sleep.

New Insights in Anorexia Nervosa

Anorexia nervosa (AN) is classically defined as a condition in which an abnormally low body weight is associated with an intense fear of gaining weight and distorted cognitions regarding weight, shape, and drive for thinness. This article reviews recent evidences from physiology, genetics, epigenetics, and brain imaging which allow to consider AN as an abnormality of reward pathways or an attempt to preserve mental homeostasis. Special emphasis is put on ghrelino-resistance and the importance of orexigenic peptides of the lateral hypothalamus, the gut microbiota and a dysimmune disorder of neuropeptide signaling. Physiological processes, secondary to underlying, and premorbid vulnerability factors-the "pondero-nutritional-feeding basements"- are also discussed.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Effects of intracerebroventricular infusions of ghrelin on secretion of follicle-stimulating hormone in peripubertal female sheep

Reproduction depends on mechanisms responsible for the regulation of energy homeostasis and puberty is a developmental period when reproductive and somatic maturity are achieved. Ghrelin affects the activity of the hypothalamo–pituitary–gonadal axis under conditions of energy insufficiency. An in vivo model based on intracerebroventricular (i.c.v.) infusions was used to determine whether centrally administered acyl ghrelin affects transcriptional and translational activity of FSH in peripubertal lambs and whether ghrelin administration mimics the effects of short-term fasting. Standard-fed lambs received either Ringer–Lock (R-L) solution (120 µL h–1) or ghrelin (120 µL h–1, 100 µg day–1). Animals experiencing a short-term (72 h) fast were treated only with R-L solution. In each experimental group, i.c.v. infusions occurred for 3 consecutive days. Immunohistochemistry, in situ hybridisation and real-time reverse transcription quantitative polymerase chain reaction analyses revealed that short-term fasting, as well as exogenous acyl ghrelin administration to standard-fed peripubertal lambs, augmented FSHβ mRNA expression and immunoreactive FSH accumulation. In addition to the effects of ghrelin on FSH synthesis in standard-fed animals, effects on gonadotrophin release were also observed. Acyl ghrelin increased the pulse amplitude for gonadotrophin release, which resulted in an elevation in mean serum FSH concentrations. In conclusion, the present data suggest that ghrelin participates in an endocrine network that modulates gonadotrophic activity in peripubertal female sheep.

[The neuropeptide 26RFa and its role in the regulation of energy metabolism]

The neuropeptide 26RFa, also referred to as QRFP (for pyroglutamilated RFamide peptide), is the latest member of the RFamide peptide family to be discovered. 26RFa and its N-extended form, 43RFa, have been characterized in all vertebrate classes as the endogenous ligands of the human orphan receptor GPR103. In the brain, 26RFa and GPR103mRNA are primarily expressed in hypothalamic nuclei involved in the control of feeding behavior, and in the periphery, the neuropeptide and its receptor are present in abundance in the gut and the pancreatic islets, suggesting that 26RFa is involved in the regulation of energy metabolism. Indeed, 26RFa stimulates food intake when centrally injected, and its orexigenic effect is even more pronounced in obese animals. The expression of 26RFa is up-regulated in the hypothalamus of obese animals, supporting the view that 26RFa may play a role in the development and/or maintenance of the obese status. Recent data indicate that 26RFa is also involved in the regulation of glucose homeostasis. 26RFa reduces glucose-induced hyperglycemia, increases insulin sensitivity and insulinemia. Furthermore, an oral ingestion of glucose strongly stimulates 26RFa release by the gut, indicating that 26RFa is a novel incretin. Finally, 26RFa is able to prevent pancreatic β cell death and apoptosis. In conclusion, this overview of the literature reveals that 26RFa is a key neuropeptide in the regulation of energy metabolism. Further fields of research are suggested including the pathophysiological implication of the 26RFa/GPR103 system.

Effects of direct QRFP-26 administration into the medial hypothalamic area on food intake in rats

The RFamide peptide family comprises a number of biologically active peptides sharing RF motif at their C-terminal end. These peptides are involved in the control of multiple physiological functions including regulation of metabolism and feeding behavior. QRFP-43 as well as its 26-aminoacid residue QRFP-26 are able to cause orexigenic effect when administered to the rodents' cerebral ventricles. QRFPs have been suggested as the endogenous ligands of the previously orphan GPR103 receptors. GPR103 receptors share amino acid identity with other receptors of neuropeptides involved in feeding (NPY, NPFF, galanin). QRFP-26 expressing neurons and binding sites are densely present in the rat medial hypothalamus (MHA), an area directly responsible for the regulation of feeding. QRFP-26 was delivered to the target area by direct intrahypothalamic microinjection, and the consumption of liquid food was measured over a 60 min period. Both doses (100 and 200 ng) significantly increased food intake. Non-specific receptor antagonist BIBP3226 eliminated the orexigenic effect caused by QRFP-26 administration. Effective doses of QRFP-26 did not modify general locomotor activity and behavioral patterns examined in the open-field test. This study is the first reporting feeding modulating effects following direct intrahypothalamic QRFP-26 administration.

Hypothalamic Neuropeptide 26RFa Acts as an Incretin to Regulate Glucose Homeostasis

26RFa is a hypothalamic neuropeptide that promotes food intake. 26RFa is upregulated in obese animal models, and its orexigenic activity is accentuated in rodents fed a high-fat diet, suggesting that this neuropeptide might play a role in the development and maintenance of the obese status. As obesity is frequently associated with type 2 diabetes, we investigated whether 26RFa may be involved in the regulation of glucose homeostasis. In the current study, we show a moderate positive correlation between plasma 26RFa levels and plasma insulin in patients with diabetes. Plasma 26RFa concentration also increases in response to an oral glucose tolerance test. In addition, we found that 26RFa and its receptor GPR103 are present in human pancreatic β-cells as well as in the gut. In mice, 26RFa attenuates the hyperglycemia induced by a glucose load, potentiates insulin sensitivity, and increases plasma insulin concentrations. Consistent with these data, 26RFa stimulates insulin production by MIN6 insulinoma cells. Finally, we show, using in vivo and in vitro approaches, that a glucose load induces a massive secretion of 26RFa by the small intestine. Altogether, the present data indicate that 26RFa acts as an incretin to regulate glucose homeostasis.

Impact of aflatoxin B1 on hypothalamic neuropeptides regulating feeding behavior

The presence of mycotoxins in food is a major problem of public health as they produce immunosuppressive, hepatotoxic and neurotoxic effects. Mycotoxins also induce mutagenic and carcinogenic effects after long exposure. Among mycotoxins that contaminate food are aflatoxins (AF) such as AFB1, which is the most powerful natural carcinogen. The AF poisoning results in symptoms of depression, anorexia, diarrhea, jaundice or anemia that can lead to death, but very few studies have explored the impact of AF on neuroendocrine regulations. To better understand the neurotoxic effects of AF related to anorexia, we explored in rat the impact of AFB1 on the major hypothalamic neuropeptides regulating feeding behavior, either orexigenic (NPY, Orexin, AgRP, MCH) or anorexigenic (α-MSH, CART, TRH). We also studied the effect of AFB1 on a novel neuropeptide, the secretogranin II (SgII)-derived peptide EM66, which has recently been linked to the control of food intake. For this, adult male rats were orally treated twice a week for 5 weeks with a low dose (150 μg/kg) or a high dose (300 μg/kg) of AFB1 dissolved in corn oil. Repeated exposure to AFB1 resulted in reduced body weight gain, which was highly significant for the high dose of AF. Immunocytochemical and quantitative PCR experiments revealed a dose-related decrease in the expression of all the hypothalamic neuropeptides studied in response to AFB1. Such orexigenic and anorexigenic alterations may underlie appetite disorders as they are correlated to a dose-dependent decrease in body weight gain of treated rats as compared to controls. We also found a decrease in the number of EM66-containing neurons in the arcuate nucleus of AFB1-treated animals, which was associated with a lower expression of its precursor SgII. These findings show for the first time that repeated consumption of AFB1 disrupts the hypothalamic regulation of neuropeptides involved in feeding behavior, which may contribute to the lower body weight gain associated to AF exposure.

Molecular basis of agonist docking in a human GPR103 homology model by site-directed mutagenesis and structure-activity relationship studies

BACKGROUND AND PURPOSE

The neuropeptide 26RFa and its cognate receptor GPR103 are involved in the control of food intake and bone mineralization. Here, we have tested, experimentally, the predicted ligand-receptor interactions by site-directed mutagenesis of GPR103 and designed point-substituted 26RFa analogues.

EXPERIMENTAL APPROACH

Using the X-ray structure of the β2 -adrenoceptor, a 3-D molecular model of GPR103 has been built. The bioactive C-terminal octapeptide 26RFa(19-26) , KGGFSFRF-NH2 , was docked in this GPR103 model and the ligand-receptor complex was submitted to energy minimization.

KEY RESULTS

In the most stable complex, the Phe-Arg-Phe-NH2 part was oriented inside the receptor cavity, whereas the N-terminal Lys residue remained outside. A strong intermolecular interaction was predicted between the Arg(25) residue of 26RFa and the Gln(125) residue located in the third transmembrane helix of GPR103. To confirm this interaction experimentally, we tested the ability of 26RFa and Arg-modified 26RFa analogues to activate the wild-type and the Q125A mutant receptors transiently expressed in CHO cells. 26RFa (10(-6)  M) enhanced [Ca(2+) ]i in wild-type GPR103-transfected cells, but failed to increase [Ca(2+) ]i in Q125A mutant receptor-expressing cells. Moreover, asymmetric dimethylation of the side chain of arginine led to a 26RFa analogue, [ADMA(25) ]26RFa(20-26) , that was unable to activate the wild-type GPR103, but antagonized 26RFa-evoked [Ca(2+) ]i increase.

CONCLUSION AND IMPLICATIONS

Altogether, these data provide strong evidence for a functional interaction between the Arg(25) residue of 26RFa and the Gln(125) residue of GPR103 upon ligand-receptor activation, which can be exploited for the rational design of potent GPR103 agonists and antagonists.

RFamide peptides 43RFa and 26RFa both promote survival of pancreatic β-cells and human pancreatic islets but exert opposite effects on insulin secretion

RFamide peptides 43RFa and 26RFa have been shown to promote food intake and to exert different peripheral actions through G-protein-coupled receptor 103 (GPR103) binding. Moreover, 26RFa was found to inhibit pancreatic insulin secretion, whereas the role of 43RFa on β-cell function is unknown, as well as the effects of both peptides on β-cell survival. Herein, we investigated the effects of 43RFa and 26RFa on survival and apoptosis of pancreatic β-cells and human pancreatic islets. In addition, we explored the role of these peptides on insulin secretion and the underlying signaling mechanisms. Our results show that in INS-1E β-cells and human pancreatic islets both 43RFa and 26RFa prevented cell death and apoptosis induced by serum starvation, cytokine synergism, and glucolipotoxicity, through phosphatidylinositol 3-kinase/Akt- and extracellular signal-related kinase 1/2-mediated signaling. Moreover, 43RFa promoted, whereas 26RFa inhibited, glucose- and exendin-4-induced insulin secretion, through Gαs and Gαi/o proteins, respectively. Inhibition of GPR103 expression by small interfering RNA blocked 43RFa insulinotropic effect, but not the insulinostatic action of 26RFa. Finally, 43RFa, but not 26RFa, induced cAMP increase and glucose uptake. In conclusion, because of their survival effects along with the effects on insulin secretion, these findings suggest potential for 43RFa and 26RFa as therapeutic targets in the treatment of diabetes.

Molecular evolution of GPCRs: 26Rfa/GPR103

Neuropeptides possessing the Arg-Phe-NH2 (RFamide) motif at their C-termini (designated as RFamide peptides) have been characterized in a variety of animals. Among these, neuropeptide 26RFa (also termed QRFP) is the latest member of the RFamide peptide family to be discovered in the hypothalamus of vertebrates. The neuropeptide 26RFa/QRFP is a 26-amino acid residue peptide that was originally identified in the frog brain. It has been shown to exert orexigenic activity in mammals and to be a ligand for the previously identified orphan G protein-coupled receptor, GPR103 (QRFPR). The cDNAs encoding 26RFa/QRFP and QRFPR have now been characterized in representative species of mammals, birds, and fish. Functional studies have shown that, in mammals, the 26RFa/QRFP-QRFPR system may regulate various functions, including food intake, energy homeostasis, bone formation, pituitary hormone secretion, steroidogenesis, nociceptive transmission, and blood pressure. Several biological actions have also been reported in birds and fish. This review summarizes the current state of identification, localization, and understanding of the functions of 26RFaQRFP and its cognate receptor, QRFPR, in vertebrates.

New Hits as Antagonists of GPR103 Identified by HTS

Preclinical data indicate that GPR103 receptor and its endogenous neuropeptides QRFP26 and QRFP43 are involved in appetite regulation. A high throughput screening (HTS) for small molecule GPR103 antagonists was performed with the clinical goal to target weight management by modulation of appetite. A high hit rate from the HTS and initial low confirmation with respect to functional versus affinity data challenged us to revise the established screening cascade. To secure high quality data while increasing throughput, the binding assay was optimized on quality to run at single concentration. This strategy enabled evaluation of a larger fraction of chemical clusters and singletons delivering 17 new compound classes for GPR103 antagonism. Representative compounds from three clusters are presented. One of the identified clusters was further investigated, and an initial structure-activity relationship study is reported. The most potent compound identified had a pIC50 of 7.9 with an improved ligand lipophilic efficiency.

A novel 26RFa peptide containing both analgesic and anti-inflammatory functions from Chinese tree shrew

26RFa is one of neuroendocrine peptide groups in the RFamide peptide family containing conserved Arg-Phe/Tyr-NH2 motif at their C-terminus. They exert multiple biological functions in vertebrates. A novel 26RFa peptide (TC26RFa) with unique structure is identified from the tree shrew of Tupaia belangeri chinensis in the present study. In structure, different from other 26RFa peptides containing conserved Phe-Arg-Phe-NH2 motif at their C-terminus, there is a Phe-Arg-Tyr-NH2 C-terminus in TC26RFa. It has been found that TC26RFa of intraperitoneal injection exerts strong analgesic activities in several mice models including acetic acid-induced abdominal writhing, formalin-induced paw licking, and thermal pain-induced tail withdrawal. It shows comparable analgesic ability with morphine. In addition, this peptide has been found to inhibit inflammatory factor secretion (including tumor necrosis factor-α, interleukin-6, and interleukin-1β) induced by lipopolysaccharides (LPS). Furthermore, it stimulates secretion of the anti-inflammatory factor, interleukin-10. In addition to the identification of a novel 26RFa peptide from tree shrew, a new type of function (anti-inflammation) involved in 26RFa peptide is discovered.

Pyroglutamylated RF-amide peptide (QRFP) gene is regulated by metabolic endotoxemia

Pyroglutamylated RF-amide peptide (QRFP) is involved in the regulation of food intake, thermogenesis, adipogenesis, and lipolysis. The expression of QRFP in adipose tissue is reduced in diet-induced obesity, a mouse model in which plasma concentrations of endotoxins are slightly elevated. The present study investigated the role of metabolic endotoxemia (ME) on QRFP gene regulation. Our results uncovered the expression of QRFP in murine macrophages and cell lines. This expression has been found to be decreased in mice with ME. Low doses of lipopolysaccharide (LPS) transiently down-regulated QRFP by 59% in RAW264.7 macrophages but not in 3T3-L1 adipocytes. The effect of LPS on QRFP expression in macrophages was dependent on the inhibitor of kB kinase and TIR-domain-containing adapter-inducing interferon (IFN)-β (TRIF) but not myeloid differentiation primary response gene 88. IFN-β was induced by ME in macrophages. IFN-β sustainably reduced QRFP expression in macrophages (64%) and adipocytes (49%). IFN-γ down-regulated QRFP (74%) in macrophages only. Both IFNs inhibited QRFP secretion from macrophages. LPS-stimulated macrophage-conditioned medium reduced QRFP expression in adipocytes, an effect blocked by IFN-β neutralizing antibody. The effect of IFN-β on QRFP expression was dependent on phosphoinositide 3-kinase, p38 MAPK, and histone deacetylases. The effect of IFN-γ was dependent on MAPK/ERK kinase 1/2 and histone deacetylases. Macrophage-conditioned medium containing increased amounts of QRFP preserved adipogenesis in adipocytes. In conclusion, LPS induces IFN-β release from macrophages, which reduces QRFP expression in both macrophages and adipocytes in an autocrine/paracrine-dependent manner, suggesting QRFP as a potential biomarker in ME.

Involvement of Mammalian RF-Amide Peptides and Their Receptors in the Modulation of Nociception in Rodents

Mammalian RF-amide peptides, which all share a conserved carboxyl-terminal Arg-Phe-NH2 sequence, constitute a family of five groups of neuropeptides that are encoded by five different genes. They act through five G-protein-coupled receptors and each group of peptide binds to and activates mostly one receptor: RF-amide related peptide group binds to NPFFR1, neuropeptide FF group to NPFFR2, pyroglutamylated RF-amide peptide group to QRFPR, prolactin-releasing peptide group to prolactin-releasing peptide receptor, and kisspeptin group to Kiss1R. These peptides and their receptors have been involved in the modulation of several functions including reproduction, feeding, and cardiovascular regulation. Data from the literature now provide emerging evidence that all RF-amide peptides and their receptors are also involved in the modulation of nociception. This review will present the current knowledge on the involvement in rodents of the different mammalian RF-amide peptides and their receptors in the modulation of nociception in basal and chronic pain conditions as well as their modulatory effects on the analgesic effects of opiates.

The Evolution and Variety of RFamide-Type Neuropeptides: Insights from Deuterostomian Invertebrates

Five families of neuropeptides that have a C-terminal RFamide motif have been identified in vertebrates: (1) gonadotropin-inhibitory hormone (GnIH), (2) neuropeptide FF (NPFF), (3) pyroglutamylated RFamide peptide (QRFP), (4) prolactin-releasing peptide (PrRP), and (5) Kisspeptin. Experimental demonstration of neuropeptide-receptor pairings combined with comprehensive analysis of genomic and/or transcriptomic sequence data indicate that, with the exception of the deuterostomian PrRP system, the evolutionary origins of these neuropeptides can be traced back to the common ancestor of bilaterians. Here, we review the occurrence of homologs of vertebrate RFamide-type neuropeptides and their receptors in deuterostomian invertebrates - urochordates, cephalochordates, hemichordates, and echinoderms. Extending analysis of the occurrence of the RFamide motif in other bilaterian neuropeptide families reveals RFamide-type peptides that have acquired modified C-terminal characteristics in the vertebrate lineage (e.g., NPY/NPF), neuropeptide families where the RFamide motif is unique to protostomian members (e.g., CCK/sulfakinins), and RFamide-type peptides that have been lost in the vertebrate lineage (e.g., luqins). Furthermore, the RFamide motif is also a feature of neuropeptide families with a more restricted phylogenetic distribution (e.g., the prototypical FMRFamide-related neuropeptides in protostomes). Thus, the RFamide motif is both an ancient and a convergent feature of neuropeptides, with conservation, acquisition, or loss of this motif occurring in different branches of the animal kingdom.

Hypothalamic QRFP: regulation of food intake and fat selection

QRFP, a member of the RFamide-related peptide family, is a strongly conserved hypothalamic neuropeptide that has been characterized in various species. Prepro-QRFP mRNA expression is localized to select regions of the hypothalamus, which are involved in the regulation of feeding behavior. The localization of the peptide precursor has led to the assessment of QRFP on feeding behaviors and the orexigenic effects of QRFP have been detected in mice, rats, and birds. QRFP acts in a macronutrient specific manner in satiated rats to increase the intake of a high fat diet, but not the intake of a low fat diet, and increases the intake of chow in food-restricted rats. Studies suggest that QRFP's effects on food intake are mediated by the adiposity signal, leptin, and hypothalamic neuropeptides. Additionally, QRFP regulates the expression and release of hypothalamic Neuropeptide Y and proopiomelanocortin/α-Melanocyte-Stimulating Hormone. QRFP binds to receptors throughout the brain, including regions associated with food intake and reward. Taken together, these data suggest that QRFP is a mediator of motivated behaviors, particularly the drive to ingest high fat food. The present review discusses the role of QRFP in the regulation of feeding behavior, with emphasis on the intake of dietary fat.

Identification, localization and function of a novel neuropeptide, 26RFa, and its cognate receptor, GPR103, in the avian hypothalamus

Several neuropeptides possessing the RFamide motif at their C-termini (designated RFamide peptides) have been characterized in the hypothalamus of a variety of vertebrates. Since the discovery of the 26-amino acid RFamide peptide (termed 26RFa) from the frog brain, 26RFa has been shown to exert orexigenic activity in mammals and to be a ligand of the previously identified orphan G protein-coupled receptor GPR103. Recently, we have identified 26RFa in the avian brain by molecular cloning of the cDNA encoding the 26RFa precursor and mass spectrometry analysis of the mature peptide. 26RFa-producing neurons are exclusively located in the hypothalamus whereas GPR103 is widely distributed in the avian brain. Furthermore, avian 26RFa stimulates feeding behavior in broiler chicks. This review summarizes the advances in the identification, localization, and functions of 26RFa and its cognate receptor GPR103 in vertebrates and highlights recent progress made in birds.

Fluorinated pseudopeptide analogues of the neuropeptide 26RFa: synthesis, biological, and structural studies

A series of four fluorinated dipeptide analogues each containing a fluoro-olefin moiety as peptide bond surrogate has been designed and synthesized. These motifs have been successfully introduced into the bioactive C-terminal heptapeptide of the neuropeptide 26RFa by conventional SPPS. We then evaluated the ability of the generated pseudopeptides to increase [Ca²⁺](i) in GPR103-transfected cells. For these fluorinated analogues, greater stability in human serum was observed. Their conformations were also investigated, leading to the valuable identification of differences depending on the position of the fluoro-olefin moiety in the sequence.

Endogenous mammalian RF-amide peptides, including PrRP, kisspeptin and 26RFa, modulate nociception and morphine analgesia via NPFF receptors

Mammalian RF-amide peptides are encoded by five different genes and act through five different G protein-coupled receptors. RF-amide-related peptides-1 and -3, neuropeptides AF and FF, Prolactin releasing peptides, Kisspeptins and RFa peptides are currently considered endogenous peptides for NPFF1, NPFF2, GPR10, GPR54 and GPR103 receptors, respectively. However, several studies suggest that the selectivity of these peptides for their receptors is low and indicate that expression patterns for receptors and their corresponding ligands only partially overlap. In this study, we took advantage of the cloning of the five human RF-amide receptors to systematically examine their affinity for and their activation by all human RF-amide peptides. Binding experiments, performed on membranes from CHO cells expressing GPR10, GPR54 and GPR103 receptors, confirmed their high affinity and remarkable selectivity for their cognate ligands. Conversely, NPFF1 and NPFF2 receptors displayed high affinity for all RF-amide peptides. Moreover, GTPγS and cAMP experiments showed that almost all RF-amide peptides efficiently activate NPFF1 and NPFF2 receptors. As NPFF is known to modulate morphine analgesia, we undertook a systematic analysis in mice of the hyperalgesic and anti morphine-induced analgesic effects of a representative set of endogenous RF-amide peptides. All of them induced hyperalgesia and/or prevented morphine analgesia following intracerebroventricular administration. Importantly, these effects were prevented by administration of RF9, a highly selective NPFF1/NPFF2 antagonist. Altogether, our results show that all endogenous RF-amide peptides display pain-modulating properties and point to NPFF receptors as essential players for these effects.

Rational design of a low molecular weight, stable, potent, and long-lasting GPR103 aza-β3-pseudopeptide agonist

26RFa, a novel RFamide neuropeptide, is the endogenous ligand of the former orphan receptor GPR103. Intracerebroventricular injection of 26RFa and its C-terminal heptapeptide, 26RFa((20-26)), stimulates food intake in rodents. To develop potent, stable ligands of GPR103 with low molecular weight, we have designed a series of aza-β(3)-containing 26RFa((20-26)) analogues for their propensity to establish intramolecular hydrogen bonds, and we have evaluated their ability to increase [Ca(2+)](i) in GPR103-transfected cells. We have identified a compound, [Cmpi(21),aza-β(3)-Hht(23)]26RFa((21-26)), which was 8-fold more potent than 26RFa((20-26)) in mobilizing [Ca(2+)](i). This pseudopeptide was more stable in serum than 26RFa((20-26)) and exerted a longer lasting orexigenic effect in mice. This study constitutes an important step toward the development of 26RFa analogues that could prove useful for the treatment of feeding disorders.

Orexigenic neuropeptide 26RFa: new evidence for an adaptive profile of appetite regulation in anorexia nervosa

CONTEXT

Restrictive anorexia nervosa (AN) presents an adaptive appetite regulating profile including mainly high levels of ghrelin. Because this adaptive mechanism is not effective on food intake, other appetite-regulating peptides need to be explored. 26RFa is a hypothalamic neuropeptide that stimulates appetite, gonadotropin release, and bone metabolism.

OBJECTIVE

The objective of the study was to evaluate the circadian levels of 26RFa in AN patients compared with healthy subjects, other eating disorders, and constitutional thinness (CT).

DESIGN AND SETTINGS

This was a cross-sectional study performed in an endocrine unit and an academic laboratory.

INVESTIGATED SUBJECTS

Five groups of age-matched young women were included in the study: 19 restrictive AN, 10 AN with bingeing/purging episodes, 14 with CT, 10 bulimic, and 10 normal-weight controls.

MAIN OUTCOME MEASURES

Twelve-point circadian profiles of plasma 26RFa levels were measured in each subject.

RESULTS

Significant circadian variations of 26 RFA were noticed in controls with higher values in the morning and abrupt decrease at noon. Twenty-four-hour mean 26RFa levels were significantly increased in restrictive AN and AN with bingeing/purging episodes (P < 0.001), predominantly in the afternoon and evening when compared with controls. Preprandial rises of 26 RFA were noticed in AN patients. Mean 26RFa levels trend to be higher in CT than in controls (P = 0.06) and significantly lower than in AN. The bulimic patients presented a circadian profile of 26RFa similar to that of controls.

CONCLUSION

High levels of circulating 26RFa observed in AN patients might reflect an adaptive mechanism of the organism to promote energy intake and to increase fat stores in response to undernutrition.