Endogenous neuromedin U has anorectic effects in the Japanese quail

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.

Neuromedin U-deficient rats do not lose body weight or food intake

Studies in genetically modified mice establish that essential roles of endogenous neuromedin U (NMU) are anorexigenic function and metabolic regulation, indicating that NMU is expected to be a potential target for anti-obesity agents. However, in central administration experiments in rats, inconsistent results have been obtained, and the essential role of NMU energy metabolism in rats remain unclear. This study aims to elucidate the role of endogenous NMU in rats. We generated NMU knockout (KO) rats that unexpectedly showed no difference in body weight, adiposity, circulating metabolic markers, body temperature, locomotor activity, and food consumption in both normal and high fat chow feeding. Furthermore, unlike reported in mice, expressions of Nmu and NMU receptor type 2 (Nmur2) mRNA were hardly detectable in the rat hypothalamic nuclei regulating feeding and energy metabolism, including the arcuate nucleus and paraventricular nucleus, while Nmu was expressed in pars tuberalis and Nmur2 was expressed in the ependymal cell layer of the third ventricle. These results indicate that the species-specific expression pattern of Nmu and Nmur2 may allow NMU to have distinct functions across species, and that endogenous NMU does not function as an anorexigenic hormone in rats.

Distribution of neuromedin U (NMU)-like immunoreactivity in the goldfish brain, and effect of intracerebroventricular administration of NMU on emotional behavior in goldfish

Neuromedin U (NMU) is a multifunctional neuropeptide implicated in regulation of smooth muscle contraction in the circulatory and digestive systems, energy homeostasis and the stress response, but especially food intake in vertebrates. Recent studies have indicated the possible involvement of NMU in the regulation of psychomotor activity in rodents. We have identified four cDNAs encoding three putative NMU variants (NMU-21, -25 and -38) from the goldfish brain and intestine. Recently, we have also purified these NMUs and the truncated C-terminal form NMU-9 from these tissues, and demonstrated their anorexigenic action in goldfish. However, there is no information on the brain localization of NMU-like immunoreactivity and the psychophysiological roles of NMU in fish. Here, we investigated the brain distribution of NMU-like immunoreactivity and found that it was localized throughout the fore- and mid-brains. We subsequently examined the effect of intracerebroventricular (ICV) administration of NMU-21, which is abundant only in the brain on psychomotor activity in goldfish. As goldfish prefer the lower to the upper area of a tank, we developed an upper/lower area preference test in a tank for evaluating the psychomotor activity of goldfish using a personal tablet device without an automatic behavior-tracking device. ICV administration of NMU-21 at 10 pmol g^-1 body weight (BW) prolonged the time spent in the upper area of the tank, and this action mimicked that of ICV administration of the central-type benzodiazepine receptor (CBR) agonist tofisopam at 100 pmol g^-1 BW. These results suggest that NMU-21 potently induces anxiolytic-like action in the goldfish brain.

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.

Characterization of neuromedin U (NMU), neuromedin S (NMS) and their receptors (NMUR1, NMUR2) in chickens

Neuromedin U (NMU) and its structurally-related peptide, neuromedin S (NMS), are reported to regulate many physiological processes and their actions are mediated by two NMU receptors (NMUR1, NMUR2) in mammals. However, the information regarding NMU, NMS, and their receptors is limited in birds. In this study, we examined the structure, functionality, and expression of NMS, NMU, NMUR1 and NMUR2 in chickens. The results showed that: 1) chicken (c-) NMU cDNA encodes a 181-amino acid precursor, which may generate two forms of NMU peptide with 9 (cNMU-9) and 25 amino acids (cNMU-25), respectively. 2) Interestingly, two cNMS transcripts encoding two cNMS precursors of different lengths were identified from chicken pituitary, and both cNMS precursors may produce a mature cNMS peptide of 9 amino acids (cNMS-9). 3) cNMU-9, cNMU-25 and cNMS-9 could activate cNMUR1 expressed in HEK293 cells potently, as monitored by three cell-based luciferase reporter systems, indicating that cNMUR1 can act as a receptor common for cNMU and cNMS peptides, whereas cNMUR2 could be potently activated by cNMS-9, but not by cNMU-9/cNMU-25. 4) cNMU and cNMUR1 are widely expressed in chicken tissues with abundant expression noted in the gastrointestinal tract, as detected by quantitative real-time PCR, whereas cNMUR2 expression is mainly restricted to the brain and anterior pituitary, and cNMS is widely expressed in chicken tissues. Collectively, our data helps to elucidate the physiological roles of NMU/NMS peptides in birds and reveal the functional conservation and changes of NMU/NMS-NMUR axis across vertebrates.

Gut Hormones and Regulation of Food Intake in Birds

Gut hormones act as appetite regulatory hormones in mammals. For example, the hunger hormone ghrelin, which is released from the stomach before food intake, stimulates appetite. In contrast, satiety hormones such as cholecystokinin, glucagon-like peptide-1, and peptide YY, which are released from the intestines after food intake, suppress appetite. The effects of these peptides on food intake have been shown to be similar in both mammals and fishes. However, evidence suggests that the physiological roles of these gut hormones may be different between birds and other vertebrates. This review summarizes the current information on the roles of gut hormones in the regulation of food intake in birds, especially in chickens.

Regulation of motivation for food by neuromedin U in the paraventricular nucleus and the dorsal raphe nucleus

BACKGROUND

Motivation for high-fat food is thought to contribute to excess caloric intake in obese individuals. A novel regulator of motivation for food may be neuromedin U (NMU), a highly-conserved neuropeptide that influences food intake. Although these effects of NMU have primarily been attributed to signaling in the paraventricular nucleus of the hypothalamus (PVN), NMU has also been found in other brain regions involved in both feeding behavior and motivation. We investigate the effects of NMU on motivation for food and food intake, and identify the brain regions mediating these effects.

METHODS

The motivational state for a particular reinforcer (e.g., high-fat food) can be assessed using a progressive-ratio schedule of reinforcement under which an increasing number of lever presses are required to obtain subsequent reinforcers. Here, we have used a progressive-ratio operant responding paradigm in combination with an assessment of cumulative food intake to evaluate the effects of NMU administration in rats, and identify the brain regions mediating these effects.

RESULTS

We found that peripheral administration of NMU decreases operant responding for high-fat food in rats. Evaluation of Fos-like immunoreactivity in response to peripheral NMU indicated the PVN and dorsal raphe nucleus (DRN) as sites of action for NMU. NMU infusion into either region mimics the effects of peripheral NMU on food intake and operant responding for food. NMU-containing projections from the lateral hypothalamus (LH) to the PVN and DRN were identified as an endogenous source of NMU.

CONCLUSIONS

These results identify the DRN as a site of action for NMU, demonstrate that the LH provides endogenous NMU to the PVN and DRN and implicate NMU signaling in the PVN and DRN as a novel regulator of motivation for high-fat foods.

Neuropeptide Control of Feeding Behavior in Birds and Its Difference with Mammals

Feeding is an essential behavior for animals to sustain their lives. Over the past several decades, many neuropeptides that regulate feeding behavior have been identified in vertebrates. These neuropeptides are called “feeding regulatory neuropeptides.” There have been numerous studies on the role of feeding regulatory neuropeptides in vertebrates including birds. Some feeding regulatory neuropeptides show different effects on feeding behavior between birds and other vertebrates, particularly mammals. The difference is marked with orexigenic neuropeptides. For example, melanin-concentrating hormone, orexin, and motilin, which are regarded as orexigenic neuropeptides in mammals, have no effect on feeding behavior in birds. Furthermore, ghrelin and growth hormone-releasing hormone, which are also known as orexigenic neuropeptides in mammals, suppress feeding behavior in birds. Thus, it is likely that the feeding regulatory mechanism has changed during the evolution of vertebrates. This review summarizes the recent knowledge of peptidergic feeding regulatory factors in birds and discusses the difference in their action between birds and other vertebrates.

Small lipidated anti-obesity compounds derived from neuromedin U

A small library of truncated/lipid-conjugated neuromedin U (NmU) analogs was synthesized and tested in vitro using an intracellular calcium signaling assay. The selected, most active analogs were then tested in vivo, and showed potent anorexigenic effects in a diet-induced obese (DIO) mouse model. The most promising compound, NM4-C16 was effective in a once-weekly-dose regimen. Collectively, our findings suggest that short, lipidated analogs of NmU are suitable leads for the development of novel anti-obesity therapeutics.

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.

Two chicken neuromedin U receptors: characterization of primary structure, biological activity and tissue distribution

Neuromedin U (NMU) is a bioactive peptide that is involved in a variety of physiological functions. Two of its receptors, NMUR1 and NMUR2, have been identified and characterized in mammals. In this study, we performed cDNA cloning of chicken NMUR1 and NMUR2, and characterized their primary structure, biological activity, and expression patterns in chicken tissues. The chicken NMUR1 and NMUR2 cDNAs encoded 438 and 395 amino acid sequences, respectively. Chicken NMUR1 showed 54.8%-56.5% sequence identity with human, rat, and mouse NMUR1, and NMUR2 shared 67.3%-70.1% sequence identity with mammalian orthologs. Both chicken receptors have typical characteristics of G-protein-coupled receptors with seven transmembrane domains and the D/ERY motif. An increase in intracellular Ca(2+) mobilization was observed in HEK293 cells transfected with chicken NMUR1 or NMUR2 cDNA and treated with chicken or rat NMU. Real-time PCR analysis revealed that NMUR1 mRNA was preferentially expressed in the intestinal tissues such as the duodenum, jejunum, ileum, cecum, and colon/rectum, and brain regions such as the midbrain and optic lobe, and the ovary in adult hens. NMUR2 mRNA was exclusively expressed in the brain regions such as the cerebrum and midbrain. These results indicate that NMUR1 and NMUR2 mRNAs, which encode functional receptor proteins, are expressed in chicken tissues with different distribution patterns.

Isolation and characterisation of two cDNAs encoding the neuromedin U receptor from goldfish brain

Intracerebroventricular administration of neuromedin U (NMU) exerts an anorexigenic effect in a goldfish model. However, little is known about the NMU receptor and its signalling system in fish. In the present study, we isolated and cloned two cDNAs encoding different proteins comprising 429 and 388 amino acid residues from the goldfish brain based on the nucleotide sequences of human NMU receptor 1 (NMU-R1) and receptor 2 (NMU-R2). Hydropathy and phylogenetic analyses suggested that these two proteins were orthologues of NMU-R1 and -R2 of goldfish. We established two human embryonic kidney 293 cell lines stably expressing putative NMU-R1 and -R2, respectively, and showed that NMU induced an increase in intracellular calcium concentration ([Ca(2+)](i)) in these cells. We examined the presence of NMU-R1 and -R2 in the goldfish brain by western blotting analysis using affinity-purified antisera raised against peptide fragments derived from these receptors. NMU-R1-specific and NMU-R2-specific antisera detected a 49-kDa and 45-kDa immunopositive bands, respectively, in the brain extract. The mass of each band corresponded to that of the deduced respective primary structures. Reverse transcriptase-polymerase chain reaction analysis showed that NMU-R1 and -R2 transcripts were detected in several tissues. In particular, both mRNAs were strongly expressed in the goldfish brain. By contrast, NMU-R2 mRNA was also expressed in the gut. These results indicate for the first time that NMU-R orthologues exist in goldfish, and suggest physiological roles of NMU and its receptor system in fish.

Feeding and drinking response following central administration of neuromedin S in chicks

Neuromedin S (NMS) is recognized as an anorexigenic peptide in the brain of mammals. In chicks (Gallus gallus), however, the effect of NMS has not been investigated. Therefore, the purpose of the present study was to investigate whether intracerebroventricular (ICV) injection of NMS affected feeding and drinking behavior in chicks. The injection of NMS (0.01-1 nmol) significantly decreased food intake under both ad libitum and food deprivation-induced feeding conditions. However, NMS did not affect water deprivation-induced drinking behavior. ICV injection of NMS stimulated voluntary locomotion and wing-flapping behavior. In addition, we found that those effects of NMS might be related to the hypothalamus-pituitary-adrenal axis because ICV injection of NMS stimulated corticosterone release. The present study suggests that central NMS functions an anorexigenic factor in chicks.

Neuromedin U-induced anorexigenic action is mediated by the corticotropin-releasing hormone receptor-signaling pathway in goldfish

Our recent research has indicated that neuromedin U (NMU) orthologs exist in goldfish, and that NMU consisting of 21 amino acid residues (NMU-21) can potently inhibit food intake in goldfish, as is the case in rodents. However, the anorexigenic pathway of NMU-21 has not yet been clarified in this species. Corticotropin-releasing hormone (CRH), CRH-related peptides and alpha-melanocyte-stimulating hormone (alpha-MSH), which exert potent anorexigenic effects, are important mediators involved in feeding regulation in fish. We examined whether CRH or alpha-MSH mediates NMU-21-induced anorexigenic action in goldfish. We first investigated the effect of intracerebroventricular (ICV) administration of NMU-21 at 100 pmol/g body weight (BW), which is enough to suppress food intake, on expression levels of mRNA for CRH and proopiomelanocortin (POMC) in the hypothalamus. ICV-injected NMU-21 induced a significant increase in the expression level of CRH mRNA, but not that of POMC mRNA. We also examined the effects of ICV administration of the CRH 1/2 receptor antagonist, alpha-helical CRH((9-41)), and the melanocortin 4 receptor antagonist, HS024, on the anorexigenic action of ICV-injected NMU-21. The anorexigenic effect of NMU-21 was blocked by treatment with alpha-helical CRH((9-41)) at 400 pmol/g BW, but not HS024 at 200 pmol/g BW. These results suggest that the anorexigenic action of NMU-21 is mediated by the CRH 1 or 2 receptor-signaling pathway in goldfish.

The antiobesity effects of centrally administered neuromedin U and neuromedin S are mediated predominantly by the neuromedin U receptor 2 (NMUR2)

Neuromedin U (NMU) and neuromedin S (NMS) are structurally related neuropeptides that have been reported to modulate energy homeostasis. Pharmacological data have shown that NMU and NMS inhibit food intake when administered centrally and that NMU increases energy expenditure. Additionally, NMU-deficient mice develop obesity, whereas transgenic mice overexpressing NMU are lean and hypophagic. Two high-affinity NMU/NMS receptors, NMUR1 and NMUR2, have been identified. NMUR1 is predominantly expressed in the periphery, whereas NMUR2 is predominantly expressed in the brain, suggesting that the effects of centrally administered NMU and NMS are mediated by NMUR2. To evaluate the role of NMUR2 in the regulation of energy homeostasis, we characterized NMUR2-deficient (Nmur2(-/-)) mice. Nmur2(-/-) mice exhibited a modest resistance to diet-induced obesity that was at least in part due to reduced food intake. Acute central administration of NMU and NMS reduced food intake in wild-type but not in Nmur2(-/-) mice. The effects on activity and core temperature induced by centrally administered NMU were also absent in Nmur2(-/-) mice. Moreover, chronic central administration of NMU and NMS evoked significant reductions in body weight and sustained reductions in food intake in mice. In contrast, Nmur2(-/-) mice were largely resistant to these effects. Collectively, these data demonstrate that the anorectic and weight-reducing actions of centrally administered NMU and NMS are mediated predominantly by NMUR2, suggesting that NMUR2-selective agonists may be useful for the treatment of obesity.

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.

Neuroregulation of nonexercise activity thermogenesis and obesity resistance

High levels of spontaneous physical activity in lean people and the nonexercise activity thermogenesis (NEAT) derived from that activity appear to protect lean people from obesity during caloric challenge, while obesity in humans is characterized by dramatically reduced spontaneous physical activity. We have similarly demonstrated that obesity-resistant rats have significantly greater spontaneous physical activity than obesity-prone rats, and that spontaneous physical activity predicts body weight gain. Although the energetic cost of activity varies between types of activity and may be regulated, individual level of spontaneous physical activity is important in determining propensity for obesity. We review the current status of knowledge about the brain mechanisms involved in controlling the level of spontaneous physical activity and the NEAT so generated. Focus is on potential neural mediators of spontaneous physical activity and NEAT, including orexin A (also known as hypocretin 1), agouti-related protein, ghrelin, and neuromedin U, in addition to brief mention of neuropeptide Y, corticotrophin releasing hormone, cholecystokinin, estrogen, leptin, and dopamine effects on spontaneous physical activity. We further review evidence that strain differences in orexin stimulation pathways for spontaneous physical activity and NEAT appear to track with the body weight phenotype, thus providing a potential mechanistic explanation for reduced activity and weight gain.

Central administration of neuromedin U suppresses food intake in chicks

The appetite-suppressive action of brain-gut peptides is similar in both chickens and mammals. In mammals, the brain-gut peptide neuromedin U (NMU) suppresses food intake via hypothalamic neuropeptides, corticotropin-releasing factor (CRF), oxytocin, and arginine-vasopressin. In chickens, central administration of CRF, oxytocin, or arginine-vasotocin (AVT, a nonmammalian equivalent of arginine-vasopressin) suppresses food intake. However, the anorexigenic action of NMU in chickens has not yet been identified. In the present study, we analyzed the effects of the central administration of NMU on food intake and hypothalamic mRNA levels of CRF, AVT and mesotocin (a nonmammalian equivalent of oxytocin) in chicks. Intracerebroventricular administration of NMU in chicks significantly suppressed food intake and induced wing-flapping behavior. NMU also significantly upregulated mRNA expression of CRF and AVT, but did not influence mRNA expression of mesotocin in the hypothalamus. These results suggest that NMU functions as an appetite-suppressive peptide via CRF and AVT in the central nervous system in chicks.

Effect of glucagon-like peptide-1 and -2 on regulation of food intake, body temperature and locomotor activity in the Japanese quail

To investigate the physiological roles of glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) in avian species, we elucidated the effect of intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of GLP-1 and GLP-2 on food intake, body temperature and gross locomotor activity in adult Japanese quail. Both i.p. and i.c.v. administration of GLP-1 suppressed food intake at 2, 4 and 12h after administration. Moreover, both i.p. and i.c.v. administration of GLP-1 significantly decreased both body temperature and gross locomotor activity 2h after administration. On the other hand, both i.p. and i.c.v. administration of GLP-2 had no effect on food intake, body temperature or gross locomotor activity. These results suggest that GLP-1 may have an important role in the regulation of food intake, body temperature and locomotor activity while GLP-2 may have no apparent effect on feeding regulation in adult Japanese quail.

Effect of neuromedin S on feeding regulation in the Japanese quail

Neuromedin S (NMS) was recently isolated from the brains of humans, mice and rats as an endogenous ligand for the orphan G protein-coupled receptors FM-3 and FM-4, which have been identified as neuromedin U (NMU) receptors 1 and 2, respectively. To investigate the role of NMS in avian species, we elucidated the effect of intracerebroventricular (i.c.v.) administration of rat NMS on food intake, body weight, body temperature and gross locomotor activity in adult Japanese quails. NMS significantly decreased food intake (and consequently body weight) in a time-dependent manner during 12-h light period, but increased both body temperature and gross locomotor activity. On the other hand, i.c.v. injection of rat NMU showed the reverse effects of NMS in Japanese quail. These results suggest that NMS may play an important role in regulating food intake and sympathetic nerve activity in the Japanese quail.