Isolation, structural characterization, and bioactivity of a novel neuromedin U analog from the defensive skin secretion of the Australasian tree frog, Litoria caerulea

The neuromedin U system: Pharmacological implications for the treatment of obesity and binge eating behavior

Neuromedin U (NMU) is a bioactive peptide produced in the gut and in the brain, with a role in multiple physiological processes. NMU acts by binding and activating two G protein coupled receptors (GPCR), the NMU receptor 1 (NMU-R1), which is predominantly expressed in the periphery, and the NMU receptor 2 (NMU-R2), mainly expressed in the central nervous system (CNS). In the brain, NMU and NMU-R2 are consistently present in the hypothalamus, commonly recognized as the main "feeding center". Considering its distribution pattern, NMU revealed to be an important neuropeptide involved in the regulation of food intake, with a powerful anorexigenic ability. This has been observed through direct administration of NMU and by studies using genetically modified animals, which revealed an obesity phenotype when the NMU gene is deleted. Thus, the development of NMU analogs or NMU-R2 agonists might represent a promising pharmacological strategy to treat obese individuals. Furthermore, NMU has been demonstrated to influence the non-homeostatic aspect of food intake, playing a potential role in binge eating behavior. This review aims to discuss and summarize the current literature linking the NMU system with obesity and binge eating behavior, focusing on the influence of NMU on food intake and the neuronal mechanisms underlying its anti-obesity properties. Pharmacological strategies to improve the pharmacokinetic profile of NMU will also be reported.

Moniezia benedeni infection enhances neuromedin U (NMU) expression in sheep (Ovis aries) small intestine

BACKGROUND

Neuromedin U (NMU) plays an important role in activating the group 2 innate lymphoid cells (ILC2s) and initiating the host's anti-parasitic immune responses. It is aimed to explore the distribution characteristics of NMU in the sheep small intestine and the influence of Moniezia benedeni infection on them. In the present study, the pET-28a-NMU recombinant plasmids were constructed, and Escherichia coli. BL21 (DE3) were induced to express the recombinant protein. And then, the rabbit anti-sheep NMU polyclonal antibody was prepared and immunofluorescence staining was performed with it. The expression levels of NMU in the intestine of normal and Moniezia benedeni-infected sheep were detected by ELISA.

RESULTS

The results showed that the molecular weight of the obtained NMU recombinant protein was consistent with the expected molecular (13 kDa) and it was expressed in the form of inclusion body. The titer and specificity of obtained rabbit anti-sheep NMU polyclonal antibody were good. The results of immunofluorescence analysis showed that the nerve fibers which specifically expressed NMU mainly extended from the ganglion in the submucosal to lamina propria (LP) in the sheep small intestine, and the expression level was relatively high; especially on the nerve fibers of LP around the intestinal glands. The expression levels were gradually increased from the duodenum to the ileum, and the levels in the jejunum and ileum were significantly higher than that in the duodenum (P < 0.05). In addition, scattered NMU positive cells were distributed in the epithelium of the jejunal crypts. Moniezia benedeni infection increased the expression of NMU in each intestinal segment, especially in the jejunum and ileum there were significant increase (P < 0.05).

CONCLUSIONS

It was suggested that Moniezia benedeni infection could be detected by the high expression of NMU in sheep enteric nervous, and which laid the foundation for further studies on whether NMU exerts anti-parasitic immunity by activating ILC2s. In addition, NMU was expressed in some intestinal gland epitheliums, which also provided a basis for studying its roles in regulation of the immune homeostasis. The present study laid the foundation for further revealing the molecular mechanism of sheep's neural-immune interaction network perceiving the colacobiosis of parasites.

Insights Into the Research Status of Neuromedin U: A Bibliometric and Visual Analysis From 1987 to 2021

Neuromedin U (NMU) is a regulatory peptide that is widely distributed throughout the body and performs a variety of physiological functions through its corresponding receptors. In recent years, NMU has become the focus of attention in various fields of research as its diverse and essential functions have gradually been elucidated. However, there have been no bibliometrics studies on the development trend and knowledge structure of NMU research. Therefore, in this study, we used VOSviewer software to statistically analyze scientific data from articles related to NMU to track the developmental footprint of this research field, including relevant countries, institutions, authors, and keywords. We retrieved a total of 338 papers related to NMU, written by 1,661 authors from 438 organizations of 41 countries that were published in 332 journals. The first study on NMU was reported by a group in Japan in 1985. Subsequently, nine articles on NMU were published from 1987 to 2006. A small leap in this field could be detected in 2009, with 30 articles published worldwide. Among the various countries in which this research has been performed, Japan and the United States have made the most outstanding contributions. Miyazato M, Kangawa K, and Mori K from the Department of Biochemistry, National Retrain and Cardiovascular Center Research Institute in Japan were the most productive authors who have the highest number of citations. Keyword analysis showed six clusters: central-nervous-system, homeostasis, energy metabolism, cancer, immune inflammation, and food intake. The three most highly cited articles were associated with inflammation. Overall, this study demonstrates the research trends and future directions of NMU, providing an objective description of the contributions in this field along with reference value for future research.

Neuromedin U, a Key Molecule in Metabolic Disorders

Obesity is now a public health concern. The leading cause of obesity is an energy imbalance between ingested and expended calories. The mechanisms of feeding behavior and energy metabolism are regulated by a complex of various kinds of molecules, including anorexigenic and orexigenic neuropeptides. One of these neuropeptides, neuromedin U (NMU), was isolated in the 1980s, and its specific receptors, NMUR1 and NMUR2, were defined in 2000. A series of subsequent studies has revealed many of the physiological roles of the NMU system, including in feeding behavior, energy expenditure, stress responses, circadian rhythmicity, and inflammation. Particularly over the past decades, many reports have indicated that the NMU system plays an essential and direct role in regulating body weight, feeding behavior, energy metabolism, and insulin secretion, which are tightly linked to obesity pathophysiology. Furthermore, another ligand of NMU receptors, NMS (neuromedin S), was identified in 2005. NMS has physiological functions similar to those of NMU. This review summarizes recent observations of the NMU system in relation to the pathophysiology of obesity in both the central nervous systems and the peripheral tissues.

Neuromedin U: potential roles in immunity and inflammation

Since the discovery of neuromedin U (NmU) from porcine spinal cord in 1985, this neuropeptide has been subsequently identified in many other species with multiple physiological and pathophysiological roles detected, ranging from smooth muscle contraction, feeding, energy balance to tumorigenesis. Intriguingly, NmU is also emerging to play pro-inflammatory roles involving immune cell activation and cytokine release in a neuron-dependent or neuron-independent manner. The NmU-mediated inflammatory responses have already been observed in worm infection, sepsis, autoimmune arthritis and allergic animal models. In this review, we focus on the roles of NmU in immunity and inflammation by highlighting the interactions between NmU and immune cells, summarizing the signalling mechanism involved in their reactions and discussing its potential contributions to inflammatory diseases.

Cloning and expression patterns of neuromedin U and its receptors in pigs

Neuromedin U (NMU) is a highly conserved neuropeptide that performs a variety of physiological functions in animals via neuromedin U receptor-1 (NMUR1) and neuromedin U receptor-2 (NMUR2). In this study, we cloned the pig NMU, NMUR1 and NMUR2 genes. Bioinformatics analysis demonstrated that the pig NMU cDNA encoded the amino acids Phe-Leu-Phe-Arg-Pro-Arg-Asn-NH2 at the C-terminus and that the NMU receptors, which are G-protein-coupled receptors (GPCRs), contained the seven transmembrane domains typical of GPCRs. Systemic NMU, NMUR1 and NMUR2 mRNA expression was investigated in various pig tissues using real-time RT-PCR. NMU mRNA was expressed both in the central nervous system (CNS) and in peripheral tissues. NMUR1 mRNA was widely expressed in peripheral tissues, whereas NMUR2 mRNA was mainly expressed in the CNS. Immunohistochemistry (IHC) was used to determine the expression patterns of NMU and NMUR1, which were predominantly located in the gastrointestinal tract, genitourinary organs, and immune organs. This study presents molecular and morphological data to aid in additional NMU research in pigs.

Neuromedin U: a multifunctional neuropeptide with pleiotropic roles

BACKGROUND

Neuromedin U (NmU) belongs to the neuromedin family, comprising a series of neuropeptides involved in the gut-brain axis and including neuromedins B and C (bombesin-like), K (neurokinin B), L (neurokinin A or neurotensin), N, S, and U.

CONTENT

Although initially isolated from porcine spinal cord on the basis of their ability to induce uterine smooth muscle contraction, these peptides have now been found to be expressed in several different tissues and have been ascribed numerous functions, from appetite regulation and energy balance control to muscle contraction and tumor progression. NmU has been detected in several species to date, particularly in mammals (pig, rat, rabbit, dog, guinea pig, human), but also in amphibian, avian, and fish species. The NmU sequence is highly conserved across different species, indicating that this peptide is ancient and plays an important biological role. Here, we summarize the main structural and functional characteristics of NmU and describe its many roles, highlighting the jack-of-all-trades nature of this neuropeptide.

SUMMARY

NmU involvement in key processes has outlined the possibility that this neuropeptide could be a novel target for the treatment of obesity and cancer, among other disorders. Although the potential for NmU as a therapeutic target is obvious, the multiple functions of this molecule should be taken into account when designing an approach to targeting NmU and/or its receptors.

Neuromedins U and S involvement in the regulation of the hypothalamo-pituitary-adrenal axis

We reviewed neuromedin U (NMU) and neuromedin S (NMS) involvement in the regulation of the hypothalamo-pituitary-adrenal (HPA) axis function. NMU and NMS are structurally related and highly conserved neuropeptides. They exert biological effects via two GPCR receptors designated as NMUR1 and NMUR2 which show differential expression. NMUR1 is expressed predominantly at the periphery, while NMUR2 in the central nervous system. Elements of the NMU/NMS and their receptors network are also expressed in the HPA axis and progress in molecular biology techniques provided new information on their actions within this system. Several lines of evidence suggest that within the HPA axis NMU and NMS act at both hypothalamic and adrenal levels. Moreover, new data suggest that NMU and NMS are involved in central and peripheral control of the stress response.

Neuromedin U: physiology, pharmacology and therapeutic potential

Neuromedin U (NmU), a multifunctional neuropeptide, belongs to a family of neuropeptides, the neuromedins. It is ubiquitously distributed with highest levels found in the gastrointestinal tract and pituitary. The conservation of structural elements of NmU across species, the widespread distribution of NmU and its receptors throughout the body point to a fundamental role in key physiological processes. Two G protein coupled receptors for NmU have been cloned NmU R1 and NmU R2. NmU R1 is expressed pre-dominantly in the periphery especially the gastrointestinal tract whereas NmU R2 is expressed pre-dominantly in the central nervous system. Current evidence suggests a role of NmU in pain, in regulation of feeding and energy homeostasis, stress, cancer, immune mediated inflammatory diseases like asthma, inflammatory diseases, maintaining the biological clock, in the regulation of smooth muscle contraction in the gastrointestinal and genitourinary tract, and in the control of blood flow and blood pressure. With the development of drugs selectively acting on receptors and knockout animal models, exact pathophysiological roles of NmU will become clearer.

PdT-2: a novel myotropic type-2 tryptophyllin from the skin secretion of the Mexican giant leaf frog, Pachymedusa dacnicolor

Amphibian skin secretions represent a unique resource for the discovery of new bioactive peptides. Here we report the isolation, structural and functional characterization of a novel heptapeptide amide, DMSPPWHamide, from the defensive skin secretion of the Mexican giant leaf frog, Pachymedusa dacnicolor. This peptide is of unique primary structure and has been classified as a member of the rather heterogenous tryptophyllin-2 (T-2) family of amphibian skin peptides and named P. dacnicolor Tryptophyllin-2 (PdT-2) in accordance. PdT-2 is the first Type 2-tryptophyllin to possess discrete bioactivity. Both natural and synthetic replicates of the peptide were found to contract the smooth muscle of rat urinary bladder, the latter displaying an EC50 of 4 nM.

Emerging pharmacology and physiology of neuromedin U and the structurally related peptide neuromedin S

Neuromedin U (NMU) has been paired with the G-protein-coupled receptors (GPRs) NMU(1) (formerly designated as the orphan GPR66 or FM-3) and NMU(2) (FM-4 or hTGR-1). Recently, a structurally related peptide, neuromedin S (NMS), which shares an amidated C-terminal heptapeptide motif, has been identified in both rat and human, and has been proposed as a second ligand for these receptors. Messenger RNA encoding NMU receptor subtypes shows differential expression: NMU(1) is predominantly expressed in peripheral tissues, particularly the gastrointestinal tract, whereas NMU(2) is abundant within the brain and spinal cord. NMU peptide parallels receptor distribution with highest expression in the gastrointestinal tract and specific structures within the brain, reflecting its major role in the regulation of energy balance. The NMU knockout mouse has an obese phenotype and, in agreement, the Arg165Trp amino acid variant of NMU-25 in humans, which is functionally inactive, co-segregated with childhood-onset obesity. Emerging physiological roles for NMU include vasoconstriction mediated predominantly via NMU(1) with nociception and bone remodelling via NMU(2). The NMU system has also been implicated in the pathogenesis of septic shock and cancers including bladder carcinoma and acute myeloid leukaemia. Intriguingly, NMS is more potent at NMU(2) receptors in vivo where it has similar central actions in suppression of feeding and regulation of circadian rhythms to NMU. Taken together with its vascular actions, NMU may be a functional link between energy balance and the cardiovascular system and may provide a future target for therapies directed against the disorders that comprise metabolic syndrome.

Does somatostatin confer insulinostatic effects of neuromedin u in the rat pancreas?

OBJECTIVES

Neuromedin U (NmU) is a neuropeptide with anorexigenic activity. Two receptor subtypes (NmUR1 and NmUR2) confer the effects of NmU on target cells. We have recently demonstrated that NmU reduces insulin secretion from isolated pancreatic islets. Aim of our current study is to investigate the role of somatostatin at mediating the effects of NmU on insulin secretion.

METHODS

Expression of NmU in the pancreas was detected by immunohistochemistry. Insulin and somatostatin secretion from in situ perfused rat pancreas and isolated pancreatic islets was measured by radioimmunoassay. The paracrine effects of somatostatin within pancreatic islets were blocked by cyclosomatostatin, a somatostatin receptor antagonist.

RESULTS

Receptor subtype NmUR1, but not NmUR2, was expressed in the endocrine pancreas, predominantly in the periphery. Neuromedin U reduced insulin secretion from in situ perfused rat pancreas and stimulated somatostatin secretion from isolated pancreatic islets. Neuromedin U stimulated somatostatin secretion at both physiological and supraphysiological glucose concentrations. Cyclosomatostatin increased insulin secretion and reduced NmU-induced inhibition of insulin secretion.

CONCLUSIONS

Neuromedin U reduces insulin and increases somatostatin secretion. Blockade of somatostatin action abolishes the inhibition of insulin secretion by NmU. The results of the study suggest that somatostatin mediates the inhibitory action of NmU on insulin secretion.

Expression and vasoconstrictor function of anorexigenic peptides neuromedin U-25 and S in the human cardiovascular system

AIMS

Neuromedin U-25 (NMU-25), a brain-gut peptide with anorexigenic actions, was paired with the G-protein-coupled receptors NMU1 and NMU2 in 2000. NMU-25 elicited a potent hypertensive effect in rats but little is known about its cardiovascular effects in humans. We examined the hypothesis that NMU fulfils the criteria for controlling vascular reactivity within the human cardiovascular system.

METHODS AND RESULTS

The radioligand [125I]-NMU-25 demonstrated specific, saturable, and high affinity (K(D) = 0.26 +/- 0.06 nM) binding in the human left ventricle and coronary artery, and quantitative reverse transcription-polymerase chain reaction revealed that mRNA encoding NMU1 predominated in these tissues. NMU-25-like immunoreactivity was detected in human plasma, left ventricle, coronary artery, saphenous vein, and epicardial adipose tissue, and both NMU-25 and a related peptide, neuromedin S (NMS), were identified by high-performance liquid chromatography in the left ventricle. NMU receptor and peptide were localized to endothelial cells, with the receptor also present on vascular smooth muscle cells. NMU-25 was a potent vasoconstrictor of isolated rings of human coronary and mammary artery and saphenous vein. Compared with NMU-25, NMS had a significantly reduced maximum response in saphenous vein, and the Arg165Trp variant of NMU-25, associated with childhood-onset obesity, was without effect. NMU-25 precursor mRNA was upregulated in the left ventricle from patients with dilated cardiomyopathy and ischaemic heart disease.

CONCLUSION

We have detected the expression of both NMU receptor and peptide in human cardiovascular tissues and have shown that NMU-25 and NMS act as potent vasoconstrictors in human vascular beds.

Heterologous expression of human Neuromedin U receptor 1 and its subsequent solubilization and purification

Human Neuromedin U receptor 1 (hNmU-R1) is a member of G protein-coupled receptor family. For structural determination of hNmU-R1, the production of hNmU-R1 in milligram amounts is a prerequisite. Here we reported two different eukaryotic expression systems, namely, Semliki Forest virus (SFV)/BHK-21 and baculovirus/Spodoptera frugiperda (Sf9) cell systems for overproduction of this receptor. In the SFV-based expression system, hNmU-R1 was produced at a level of 5 pmol receptor/mg membrane protein and the yield could be further increased to 22 pmol receptor/mg membrane protein by supplementation with 2% dimethyl sulfoxide (DMSO). Around 8 pmol receptor/mg membrane protein could be achieved in baculovirus-infected Sf9 cells. The recombinant hNmU-R1 from SFV- and baculovirus-based systems was functional, with a Kd value of [125I] NmU-23 (rat) similar to that from transiently transfected COS-7 cells, where hNmU-R1 was first identified. With the aid of 1% n-dodecyl-beta-D-maltoside (LM)/0.25% cholesteryl hemisuccinate (CHS), the yield of functional hNmU-R1 could reach 80%. The recombinant receptor from Sf9 cells was purified to homogeneity. The specific binding of the purified receptor to [125I] NmU-23 (rat) indicated that the receptor is bioactive. This is the first report of successful solubilization and purification of hNmU-R1, and will enable functional and structural studies of the hNmU-R1.

Neuromedin U stimulates contraction of human long saphenous vein and gastrointestinal smooth muscle in vitro

The neuropeptide Neuromedin U (NMU) stimulates smooth muscle contraction, and modulates local blood flow and adrenocortical function via two endogenous receptors, NMU1 and NMU2. Although its amino-acid sequence is highly conserved across species, the physiological effects of NMU are variable between species and little is known of its effects on human tissues. We have examined the contractile effects of NMU-25 on human smooth muscles of the gastrointestinal (GI) tract (ascending colon, gallbladder) and long saphenous vein (LSV) using in vitro organ bath bioassays. From LSV, ileum, gallbladder, caecum and colon, NMU receptor transcripts were amplified by RT-PCR and expression levels were determined by semi-quantitative scanning densitometry. NMU-25 produced a concentration-dependent, sustained contraction of isolated smooth muscle (p[A](50)+/-s.e.m., ascending colon, 8.93+/-0.18; gallbladder, 7.01+/-0.15; LSV, 8.67+/-0.09). NMU1 and NMU2 receptor transcription was detected in all tissues; transcription of both receptors was similar in gallbladder, but NMU1 receptor transcription was predominant in the sigmoid colon and LSV. In summary, these studies indicate that NMU may control tone in the human GI tract and LSV through an action on smooth muscle. Development of NMU receptor subtype-selective ligands will aid the further elucidation of the physiological roles of NMU and its two receptors.

Structural and functional analogs of the novel mammalian neuropeptide, neuromedin S (NmS), in the dermal venoms of Eurasian bombinid toads

We report the isolation and structural characterization of two neuromedin S (NmS) analogs, (NmS-17 and NmS-33), from the dermal venoms of Eurasian bombinid toads. NmS is a novel neuromedin U (NmU)-related peptide with potent anorexigenic and circadian rhythm-modulating properties recently discovered in mammals. Cloning of NmS precursor-encoding cDNAs from skin venom-derived libraries revealed the presence of a high degree of transcript splice variation comparable to that found previously for NmU in both amphibian skin and mammalian brain. Synthetic replicates of both amphibian NmS peptides evoked robust and dose-dependent transient increases in intracellular calcium ion concentrations in CHO cells that had been stably transfected with either FM-3/GPR66 or FM-4/TGR-1 human NmU receptors. The potency and efficacy of these amphibian skin peptides at such receptors were comparable to those observed with human NmS and rat NmS. These data show that NmS and NmU genes had already diverged at the level of the Amphibia and that differential splicing of their transcribed mRNAs has been highly conserved throughout tetrapod vertebrate evolution indicative of fundamental biological function. NmS is additionally a novel neuropeptide homolog that can be added to the biologically active peptide arsenal of amphibian venom/defensive skin secretions.

Identification and molecular cloning of a novel neuromedin U analog from the skin secretions of toad Bombina maxima

Amphibian skin contains rich neuropeptides. In the present study, a novel neuromedin U (NmU) analog was isolated from skin secretions of Chinese red belly toad Bombina maxima. Being 17-amino acids long, its primary structure was established as DSSGIVGRPFFLFRPRN-NH2, in which the C-terminal 8-residue segment (FFLFRPRN) is the same as that of rat NmU, while the N-terminal part DSSGIVGRP shows a great sequence variation compared with those of NmU peptides from different resources. The peptide, named Bm-NmU-17, was found to elicit concentration-dependent contractile effects on smooth muscle of rat uterus horns. The cDNA structure of the peptide, as obtained by a 3'-RACE strategy and subsequently cloning from a skin cDNA library, was found to contain a coding region of 438 nucleotides. The encoded precursor is composed of 145 amino acids with a single copy of Bm-NmU-17 located towards the C-terminus. The sequence of the peptide is preceded by a dibasic site (Lys-Arg) and followed by the sequence of Gly-Arg-Lys, providing the sites of cleavage and releasing of the mature peptide.

The neuropeptide neuromedin U promotes inflammation by direct activation of mast cells

Neuromedin U (NMU) is a neuropeptide that is expressed in the gastrointestinal tract and central nervous system. NMU interacts with two G protein–coupled receptors, NMU-R1 and NMU-R2. Whereas NMU-R2 localizes predominantly to nerve cells, NMU-R1 is expressed in peripheral tissues including lymphocytes and monocytes, suggesting a role of NMU in immunoregulation. However, the functions of NMU in peripheral tissues have not been clarified. In this study, using NMU-deficient mice, we first demonstrated that NMU plays an important role in mast cell-mediated inflammation. Complete Freund's adjuvant-induced mast cell degranulation as well as edema and neutrophil infiltration, which occurred weakly in mast cell–deficient WBB6F₁-W/W^v mice, did not occur in NMU-deficient mice. Moreover, intraplantar injection of NMU into paws induced early inflammatory responses such as mast cell degranulation, vasodilation, and plasma extravasation in WT mice but not in WBB6F₁-W/W^v mice. NMU-R1 was highly expressed in primary mast cells, and NMU induced Ca²⁺ mobilization and degranulation in peritoneal mast cells. These data indicate that NMU promotes mast cell–mediated inflammation; therefore, NMU receptor antagonists could be a novel target for pharmacological inhibition of mast cell–mediated inflammatory diseases.

Neuromedin U and its receptors: structure, function, and physiological roles

Neuromedin U (NmU) is a structurally highly conserved neuropeptide. It is ubiquitously distributed, with highest levels found in the gastrointestinal tract and pituitary. Originally isolated from porcine spinal cord, it has since been isolated and sequenced from several species. Amino acid alignment of NmU from different species reveals a high level of conservation, and particular features within its structure are important for bioactivity. Specifically, the C terminus, including a terminal asparagine-linked amidation, is essential for activity. The conservation of NmU across a wide range of species indicates a strong evolutionary pressure to conserve this peptide and points to its physiological significance. Despite this, the precise physiological and indeed pathophysiological roles of NmU have remained elusive. NmU was first isolated based on its ability to contract rat uterine smooth-muscle (hence the suffix "U") and has since been implicated in the regulation of smooth-muscle contraction, blood pressure and local blood flow, ion transport in the gut, stress responses, cancer, gastric acid secretion, pronociception, and feeding behavior. Two G-protein-coupled receptors for NmU have recently been cloned. These receptors are widespread throughout the body but have differential distributions suggesting diverse but specific roles for the receptor subtypes. Here we detail the isolation and characterization of NmU, describe the discovery, cloning, distribution, and structure of its two receptors, and outline its possible roles in both physiology and pathophysiology. Ultimately the development of receptor-specific ligands and the generation of animals in which the receptors have been selectively knocked out will hopefully reveal the true extent of the biological roles of NmU and suggest novel therapeutic indications for selective activation or blockade of either of its receptors.

Chemical and olfactory characterization of odorous compounds and their precursors in the parotoid gland secretion of the green tree frog, Litoria caerulea

When stressed or challenged by a predator, the Australian green tree frog, Litoria caerulea, emits a characteristic nutty odor from its parotoid glands. This study identifies the source of the odor as the cyclic amide 2-pyrrolidone (2-PyrO). In addition, we demonstrate the presence of 2-PyrO's straight chain form, gamma-aminobutyric acid or GABA, in the frog's glandular secretion and propose an odorant-precursor relationship. What role both compounds play in the frog's defensive strategy remains unknown. Prolonged exposure to the odor is shown to result in adverse effects that may be attributed to a GABAergic mechanism. It is our hypothesis, however, that the odor acts as an aposematic signal, indicating the toxicity of the frog's nonvolatile secretion.

Neuropeptides in anterior pituitary development

Recent studies using biotechnological methods have achieved significant advances in our knowledge of molecular mechanisms underlying pituitary gland development and the differentiation of pituitary cytotypes. A large number of neuropeptides have been reported in the adult pituitary gland as well as in the central and peripheral nervous system. The early presence of neuropeptides during pituitary development is reviewed here. Neuromedin U (NmU), galanin and the polypeptide 7B2 have been localised to different endocrine cells of the gland. Their expression seems to be manifold even though it is temporally and spatially regulated. There is now firm immunocytochemical evidence that neuropeptides are present during morphogenesis of the pituitary and can be present simultaneously with all pituitary hormones.

Granular gland transcriptomes in stimulated amphibian skin secretions

Amphibian defensive skin secretions are complex, species-specific cocktails of biologically active molecules, including many uncharacterized peptides. The study of such secretions for novel peptide discovery is time-limited, as amphibians are in rapid global decline. While secretion proteome analysis is non-lethal, transcriptome analysis has until now required killing of specimens prior to skin dissection for cDNA library construction. Here we present the discovery that polyadenylated mRNAs encoding dermal granular gland peptides are present in defensive skin secretions, stabilized by endogenous nucleic acid-binding amphipathic peptides. Thus parallel secretory proteome and transcriptome analyses can be performed without killing the specimen in this model amphibian system--a finding that has important implications in conservation of biodiversity within this threatened vertebrate taxon and whose mechanistics may have broader implications in biomolecular science.

Cloning and characterization of murine neuromedin U receptors

Neuromedin U (NmU) is a neuropeptide involved in various physiological functions such as feeding behavior, muscle contractile activity, and regulation of intestinal ion transport. Recently, two human G protein-coupled receptors have been identified as NmU-specific receptors, NmU-R1 and NmU-R2, which share 55% amino acid identity. It is unclear however, which of the two receptors mediates responses to NmU observed in rodent models. Attempts to define the pharmacological profile of the two receptors are confounded by overlapping expression of the two receptors and a lack of subtype-selective compounds. In order to establish a basis to further our understanding of the function of these receptors, we cloned and characterized the mouse homologues of the two human NmU receptors. Mouse NmU-R1 and mouse NmU-R2 are 79 and 81% identical to their respective human homologues. Expression of NmU-R1 was mainly observed in testis, gastrointestinal (GI) tract, and immune system, while NmU-R2 was primarily expressed in brain tissues. Each mouse receptor was independently expressed in HEK293 cells and demonstrated a dose-dependent calcium flux in response to NmU-8, NmU-23 and NmU-25. In an attempt to identify a synthetic NmU peptide that would exhibit selectivity at one of the two receptors, we examined the functional activity of eight alanine-substituted NmU-8 peptides. These experiments demonstrated that alanine substitution at positions 5 and 7 affects the functional activity of the peptide at both receptors. The arginine residue at position 7 is required for NmU-8 activity at either receptor while alanine substitution at position 5 selectively affects the potency and the efficacy at mNmU-R1. These experiments validate the use of rodent models to characterize NmU function relative to humans and suggest that substitution at Arginine-5 of NmU-8 may provide a receptor selective peptide.

Characterization of neuromedin U effects in canine smooth muscle

Two endogenous receptors for the potent smooth muscle-stimulating peptide neuromedin U (NmU) have recently been identified and cloned. Pharmacological, binding, and expression studies were conducted in an attempt to determine the receptor(s) involved in the smooth muscle-stimulating effects of NmU. The NmU peptides caused a concentration-dependent contraction of canine isolated urinary bladder. NmU did not have this same effect in the urinary bladder from rat, guinea pig, rabbit, mouse, or ferret. Although NmU had no effect on canine uterus it did cause contraction of canine stomach, ileum, and colon. As well as causing contraction of canine bladder in vitro, NmU administered systemically resulted in a significant increase in urinary bladder pressure in vivo. High-affinity binding sites for NmU were identified in canine bladder. The four NmU peptides porcine NmU-8, rat NmU-23, human NmU-25, and porcine NmU-25 displaced (125)I-NmU-25 binding with similar K(i) values (0.08-0.24 nM). A different binding profile was revealed in human embryonic kidney-293 cells transiently expressed with the canine NmU-2 receptor where porcine NmU-8 (K(i) = 147.06 nM) was much less potent than the other NmU peptides. Using TaqMan, expression of NmU-1 was detected in human urinary bladder, small intestine, colon, and uterus. Expression of NmU-2 was much lower or absent in these human tissues and undetectable in canine bladder and stomach. The results of this study reveal significant species differences in the activity of NmU. The contractile activity in human and canine smooth muscle seems to be mediated by the recently cloned NmU-1 receptor.

Identification of a novel neuromedin U receptor subtype expressed in the central nervous system

Neuromedin U is a neuropeptide prominently expressed in the upper gastrointestinal tract and central nervous system. Recently, GPR66/FM-3 (NmU-R1) was identified as a specific receptor for neuromedin U. A BLAST search of the GenBank(TM) genomic database using the NmU-R1 cDNA sequence revealed a human genomic fragment encoding a G protein-coupled receptor that we designated NmU-R2 based on its homology to NmU-R1. The full-length NmU-R2 cDNA was subsequently cloned, stably expressed in 293 cells, and shown to mobilize intracellular calcium in response to neuromedin U. This response was dose-dependent (EC(50) = 5 nm) and specific in that other neuromedins did not induce a calcium flux in receptor-transfected cells. Expression analysis of human NmU-R2 demonstrated its mRNA to be most highly expressed in central nervous system tissues. Based on these data, we conclude that NmU-R2 is a novel neuromedin U receptor subtype that is likely to mediate central nervous system-specific neuromedin U effects.

Identification of a human gastrointestinal tract and immune system receptor for the peptide neuromedin U

Neuromedin U (NmU) is a 25 amino acid peptide prominently expressed in the upper gastrointestinal (GI) tract and central nervous system. It is highly conserved throughout evolution and induces smooth muscle contraction in a variety of species. Our understanding of NmU biology has been limited because the identity of its receptor was unknown. Here we demonstrate that GPR66/FM-3 is specifically stimulated by NmU, causing the mobilization of intracellular calcium. This response was dose-dependent (EC(50) = 10 nM) and specific in that none of over 1000 ligands tested, including other neuromedins (NmB, C, L, K, N), induced a calcium flux in GPR66/FM-3-transfected cells. The GPR66/FM-3 mRNA is prominently expressed in the upper GI tract of humans, as is the mRNA for NmU, consistent with role for this receptor-ligand pair in regulating the function of this organ system. In addition, we show that whereas neuromedin U is expressed by monocytes and dendritic cells, GPR66/FM-3 is expressed by T cells and NK cells. These data suggest a previously unrecognized role for NmU as an immunoregulatory molecule.

Purification and identification of neuromedin U as an endogenous ligand for an orphan receptor GPR66 (FM3)

GPR66 is an orphan G-protein-coupled receptor (GPCR) whose structure is similar to the ghrelin and motilin receptors. We have tried to purify a natural ligand for GPR66 in rat tissues and identified a 23-amino-acid peptide as the endogenous ligand. Sequence analysis revealed the peptide as neuromedin U (NMU), a smooth-muscle-contracting peptide that was first purified from porcine spinal cord by our group. NMU binds to GPR66-expressing cells with high specificity to induce intracellular calcium mobilization. When NMU was injected intracerebroventricularly (ICV) into rats, it potently suppressed food intake. In contrast, ICV injection of NMU-antibody increased food intake. These results suggest that NMU is a potent endogenous anorexic peptide.

Neuromedin U is a potent agonist at the orphan G protein-coupled receptor FM3

Neuromedins are a family of peptides best known for their contractile activity on smooth muscle preparations. The biological mechanism of action of neuromedin U remains unknown, despite the fact that the peptide was first isolated in 1985. Here we show that neuromedin U potently activates the orphan G protein-coupled receptor FM3, with subnanomolar potency, when FM3 is transiently expressed in human HEK-293 cells. Neuromedins B, C, K, and N are all inactive at this receptor. Quantitative reverse transcriptase-polymerase chain reaction analysis of neuromedin U expression in a range of human tissues showed that the peptide is highly expressed in the intestine, pituitary, and bone marrow, with lower levels of expression seen in stomach, adipose tissue, lymphocytes, spleen, and the cortex. Similar analysis of FM3 expression showed that the receptor is widely expressed in human tissue with highest levels seen in adipose tissue, intestine, spleen, and lymphocytes, suggesting that neuromedin U may have a wide range of presently undetermined physiological effects. The discovery that neuromedin U is an endogenous agonist for FM3 will significantly aid the study of the full physiological role of this peptide.