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

Spinal Nmur2-positive Neurons Play a Crucial Role in Mechanical Itch

The dorsal spinal cord is crucial for the transmission and modulation of multiple somatosensory modalities, such as itch, pain, and touch. Despite being essential for the well-being and survival of an individual, itch and pain, in their chronic forms, have increasingly been recognized as clinical problems. Although considerable progress has been made in our understanding of the neurochemical processing of nociceptive and chemical itch sensations, the neural substrate that is crucial for mechanical itch processing is still unclear. Here, using genetic and functional manipulation, we identified a population of spinal neurons expressing neuromedin U receptor 2 (Nmur2+) as critical elements for mechanical itch. We found that spinal Nmur2+ neurons are predominantly excitatory neurons, and are enriched in the superficial laminae of the dorsal horn. Pharmacogenetic activation of cervical spinal Nmur2+ neurons evoked scratching behavior. Conversely, the ablation of these neurons using a caspase-3-based method decreased von Frey filament-induced scratching behavior without affecting responses to other somatosensory modalities. Similarly, suppressing the excitability of cervical spinal Nmur2+ neurons via the overexpression of functional Kir2.1 potassium channels reduced scratching in response to innocuous mechanical stimuli, but not to pruritogen application. At the lumbar level, pharmacogenetic activation of these neurons evoked licking and lifting behaviors. However, ablating these neurons did not affect the behavior associated with acute pain. Thus, these results revealed the crucial role of spinal Nmur2+ neurons in mechanical itch. Our study provides important insights into the neural basis of mechanical itch, paving the way for developing novel therapies for chronic itch. PERSPECTIVE: Excitatory Nmur2+ neurons in the superficial dorsal spinal cord are essential for mechanical but not chemical itch information processing. These spinal Nmur2+ neurons represent a potential cellular target for future therapeutic interventions against chronic itch. Spinal and supraspinal Nmur2+ neurons may play different roles in pain signal processing.

Neuromedin U receptor 1 deletion leads to impaired immunotherapy response and high malignancy in colorectal cancer

Colorectal cancer (CRC) exhibits significant heterogeneity, impacting immunotherapy efficacy, particularly in immune desert subtypes. Neuromedin U receptor 1 (NMUR1) has been reported to perform a vital function in immunity and inflammation. Through comprehensive multi-omics analyses, we have systematically characterized NMUR1 across various tumors, assessing expression patterns, genetic alterations, prognostic significance, immune infiltration, and pathway associations at both the bulk sequencing and single-cell scales. Our findings demonstrate a positive correlation between NMUR1 and CD8+ T cell infiltration, with elevated NMUR1 levels in CD8+ T cells linked to improved immunotherapy outcomes in patients with CRC. Further, we have validated the NMUR1 expression signature in CRC cell lines and patient-derived tissues, revealing its interaction with key immune checkpoints, including lymphocyte activation gene 3 and cytotoxic T-lymphocyte-associated protein 4. Additionally, NMUR1 suppression enhances CRC cell proliferation and invasiveness. Our integrated analyses and experiments open new avenues for personalized immunotherapy strategies in CRC treatment.

Pharmacomodulation of brain neuromedin U signaling as a potential therapeutic strategy

Neuromedin U (NMU) belongs to a family of multifunctional neuropeptides that modulate the activity of several neural networks of the brain. Acting via metabotropic receptor NMUR2, NMU plays a role in the regulation of multiple systems, including energy homeostasis, stress responses, circadian rhythms, and endocrine signaling. The involvement of NMU signaling in the central regulation of important neurophysiological processes and its disturbances is a potential target for pharmacological modulation. Number of preclinical studies have proven that both modified NMU analogues such as PASR8-NMU or F4R8-NMU and designed NMUR2 agonists, for example, CPN-116, CPN-124 exhibit a distinct pharmacological activity especially when delivered transnasally. Their application can potentially be useful in the more convenient and safe treatment of obesity, eating disorders, Alzheimer's disease-related memory impairment, alcohol addiction, and sleep disturbances. Accumulating findings suggest that pharmacomodulation of the central NMU signaling may be a promising strategy in the treatment of several neuropsychiatric disorders.

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.

A genome-wide association study implicates the pleiotropic effect of NMUR2 on asthma and COPD

Asthma and chronic obstructive pulmonary disease (COPD) are two distinct diseases that are associated with chronic inflammation. They share common features in terms of their advanced stages and genetic factors. This study aimed to identify novel genes underlying both asthma and COPD using genome-wide association study (GWAS) to differentiate between the two diseases. We performed a GWAS of asthma and COPD in 7828 Koreans from three hospitals. In addition, we investigated genetic correlations. The UK Biobank dataset was used for the replication studies. We found that rs2961757, located near neuromedin U receptor 2 (NMUR2) on chromosome 5, was genome-wide significant ([Formula: see text] = 0.44, P-value_Asthma-COPD = 3.41 × 10^-8), and significant results were replicated with the UK Biobank data ([Formula: see text] = 0.04, P-value_Asthma-COPD = 0.0431). A positive genetic correlation was observed between asthma and COPD (39.8% in the Korean dataset and 49.8% in the UK Biobank dataset). In this study, 40-45% of the genetic effects were common to asthma and COPD. Moreover, NMUR2 increases the risk of asthma development and suppresses COPD development. This indicates that NMUR2 allows for better differentiation of both diseases, which can facilitate tailored medical therapy.

Increased NMUR1 Expression in Mast Cells in the Synovial Membrane of Obese Osteoarthritis Patients

Obesity is a risk factor for knee osteoarthritis (KOA). Neuromedin U (NMU) and NMU receptors (NMUR1 and NMUR2) are associated with obesity-related disorders and found in mast cells (MCs), which are elevated in osteoarthritis. However, NMU/NMUR expression was not examined in the synovial membrane (SM) or synovial MCs of obese osteoarthritis patients. We compared expression of NMU, NMUR1, NMUR2, and the mast cell (MC) marker, CPA3, in the SM of KOA patients categorized as normal weight (NW; BMI < 25 kg/m2, n = 79), overweight (OW; BMI ≥ 25 and <30 kg/m2, n = 87), and obese (OB; ≥30 kg/m2, n = 40). To study NMU/NMUR expression in MCs, we compared the MC-rich fraction (MC-RF), CD88(+) MC-RF, and CD88(−) MC-RF, extracted using magnetic isolation, with the MC-poor fraction (MC-PF). While NMU and NMUR2 expression were comparable, NMUR1 was significantly elevated in OW and OB compared to NW. Moreover, CPA3 levels were significantly greater in OB than NW. NMUR1 and CPA3 expression were significantly higher in both the CD88(+) and CD88(−) MC-RF than MC-PF. Therefore, NMUR1 expression was elevated in the SM of OB KOA patients, and its expression was found in MCs. Further investigation to analyze the NMU/NMUR1 pathway in MC may provide a link between obesity and KOA pathology.

Unanticipated Characteristics of a Selective, Potent Neuromedin-U Receptor 2 Agonist

Neuromedin-U (NMU) mediates several physiological functions via its two cognate receptors, NMUR1 and NMUR2. Disentangling the individual roles of each receptor has largely been undertaken through the use of transgenic mice bearing a deletion in one of the two receptors or by testing native molecules (NMU or its truncated version NMU-8) in a tissue-specific manner, in effect, taking advantage of the distinct receptor expression profiles. These strategies have proved quite useful despite the inherent limitations of overlapping receptor roles and potential compensatory influences of germline gene deletion. With these considerations in mind, the availability of potent, selective NMU compounds with appropriate pharmacokinetic profiles would advance the capabilities of investigators undertaking such efforts. Here, we evaluate a recently reported NMUR2-selective peptide (compound 17) for its in vitro potency (mouse and human), binding affinity, murine pharmacokinetic properties, and in vivo effects. Despite being designed as an NMUR2 agonist, our results show compound 17 unexpectedly binds but does not have functional activity on NMUR1, thereby acting as an R1 antagonist while simultaneously being a potent NMUR2 agonist. Furthermore, evaluation of compound 17 across all known and orphan G-protein-coupled receptors demonstrates multiple receptor partners beyond NMUR2/R1 binding. These properties need to be appreciated for accurate interpretation of results generated using this molecule and may limit the broader ability of this particular entity in disentangling the physiological role of NMU receptor biology.

Escitalopram alters local expression of noncanonical stress-related neuropeptides in the rat brain via NPS receptor signaling

BACKGROUND

Neuropeptide S (NPS) is a multifunctional regulatory factor that exhibits a potent anxiolytic activity in animal models. However, there are no reports dealing with the potential molecular relationships between the anxiolytic activity of selective serotonin reuptake inhibitors (SSRIs) and NPS signaling, especially in the context of novel stress-related neuropeptides action. The present work therefore focused on gene expression of novel stress neuropeptides in the rat brain after acute treatment with escitalopram and in combination with neuropeptide S receptor (NPSR) blockade.

METHODS

Studies were carried out on adult, male Sprague-Dawley rats that were divided into five groups: animals injected with saline (control) and experimental rats treated with escitalopram (at single dose 10 mg/kg daily), escitalopram and SHA-68, a selective NPSR antagonist (at a single dose of 40 mg/kg), SHA-68 alone and corresponding vehicle (solvent SHA-68) control. To measure anxiety-like behavior and locomotor activity the open field test was performed. All individuals were killed under anaesthesia and the whole brain was excised. Total mRNA was isolated from homogenized samples of the amygdala, hippocampus, hypothalamus, thalamus, cerebellum, and brainstem. Real-time PCR was used for estimation of related NPS, NPSR, neuromedin U (NMU), NMU receptor 2 (NMUR2) and nesfatin-1 precursor nucleobindin-2 (NUCB2) gene expression.

RESULTS

Acute escitalopram administration affects the local expression of the examined neuropeptides mRNA in a varied manner depending on brain location. An increase in NPSR and NUCB2 mRNA expression in the hypothalamus and brainstem was abolished by SHA-68 coadministration, while NMU mRNA expression was upregulated after NPSR blockade in the hippocampus and cerebellum.

CONCLUSIONS

The pharmacological effects of escitalopram may be connected with local NPSR-related alterations in NPS/NMU/NMUR2 and nesfatin-1 gene expression at the level of selected rat brain regions. A novel alternative mode of SSRI action can be therefore cautiously proposed.

Effect of Escitalopram on the Number of DCX-Positive Cells and NMUR2 Receptor Expression in the Rat Hippocampus under the Condition of NPSR Receptor Blockade

BACKGROUND

Neuropeptide S (NPS) is a multifunctional regulatory factor that exhibits a potent anxiolytic activity in animal models. However, there are no reports dealing with the potential molecular interactions between the activity of selective serotonin reuptake inhibitors (SSRIs) and NPS signaling, especially in the context of adult neurogenesis and the expression of noncanonical stress-related neuropeptides such as neuromedin U (NMU). The present work therefore focused on immunoexpression of neuromedin U receptor 2 (NMUR2) and doublecortin (DCX) in the rat hippocampus after acute treatment with escitalopram and in combination with selective neuropeptide S receptor (NPSR) blockade.

METHODS

Studies were carried out on adult, male Sprague-Dawley rats that were divided into five groups: animals injected with saline (control) and experimental individuals treated with escitalopram (at single dose 10 mg/kg daily), escitalopram + SHA-68, a selective NPSR antagonist (at single dose 40 mg/kg), SHA-68 alone, and corresponding vehicle control. All animals were sacrificed under halothane anaesthesia. The whole hippocampi were quickly excised, fixed, and finally sliced for general qualitative immunohistochemical assessment of the NPSR and NMUR2 expression. The number of immature neurons was enumerated using immunofluorescent detection of doublecortin (DCX) expression within the subgranular zone (SGZ).

RESULTS

Acute escitalopram administration affects the number of DCX and NMUR2-expressing cells in the adult rat hippocampus. A decreased number of DCX-expressing neuroblasts after treatment with escitalopram was augmented by SHA-68 coadministration.

CONCLUSIONS

Early pharmacological effects of escitalopram may be at least partly connected with local NPSR-related alterations of neuroblast maturation in the rat hippocampus. Escitalopram may affect neuropeptide and DCX-expression starting even from the first dose. Adult neurogenesis may be regulated via paracrine neuropeptide S and NMU-related signaling.

Neuromedin U modulates neuronal excitability in rat hippocampal slices

Neuromedin U (NMU) is a neuropeptide that was initially isolated from the porcine spinal cord and later from several species. Although NMU receptors exist in the CA1 region of the hippocampus, the role of NMU in hippocampal synaptic transmission remains unknown. In the present study, we demonstrated that the colocalization ratio of NMU type 1 (NMUR1) or type 2 (NMUR2) receptors was higher with neuronal nuclei (a neuronal marker) than with glial fibrillary acidic protein (an astrocyte marker) in the CA1 region of rats. Moreover, we revealed that the bath application of NMU (1 μM) enhanced extracellular field excitatory postsynaptic potentials at Schaffer collateral-CA1 synapses in rat hippocampal slices (+28.9 ± 1.3%; P < 0.05). After extracellular recordings, we examined the pattern of neuronal activation induced by NMU using c-Fos immunohistochemistry (Fos-IR). Histological analyses revealed that NMU increased Fos-IR in the CA1 region, but reduced the proportion of Fos-IR colocalized with glutamic acid decarboxylase (a GABA neuron marker). These results suggest that the activation of NMU receptors contributes to GABAergic neuronal activity in the CA1 region of the hippocampus.

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.

Neuromedins NMU and NMS: An Updated Overview of Their Functions

More than 35 years have passed since the identification of neuromedin U (NMU). Dozens of publications have been devoted to its physiological role in the organism, which have provided insight into its occurrence in the body, its synthesis and mechanism of action at the cellular level. Two G protein-coupled receptors (GPCRs) have been identified, with NMUR1 distributed mainly peripherally and NMUR2 predominantly centrally. Recognition of the role of NMU in the control of energy homeostasis of the body has greatly increased interest in this neuromedin. In 2005 a second, structurally related peptide, neuromedin S (NMS) was identified. The expression of NMS is more restricted, it is predominantly found in the central nervous system. In recent years, further peptides related to NMU and NMS have been identified. These are neuromedin U precursor related peptide (NURP) and neuromedin S precursor related peptide (NSRP), which also exert biological effects without acting via NMUR1, or NMUR2. This observation suggests the presence of another, as yet unrecognized receptor. Another unresolved issue within the NMU/NMS system is the differences in the effects of various NMU isoforms on diverse cell lines. It seems that development of highly specific NMUR1 and NMUR2 receptor antagonists would allow for a more detailed understanding of the mechanisms of action of NMU/NMS and related peptides in the body. They could form the basis for attempts to use such compounds in the treatment of disorders, for example, metabolic disorders, circadian rhythm, stress, etc.

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.

Development of DNA methylation markers for sperm, saliva and blood identification using pyrosequencing and qPCR/HRM

Discrimination of body fluids can provide important information in the investigation of crime scenes. The goal of this project was to identify new sets of tissue specific differentially methylated regions (tDMRs) and develop assays that can be utilized for forensic discrimination of body fluids, in particular sperm, saliva and blood. In this study, a sample set containing semen with sperm, semen without sperm, buccal swabs, saliva (oral fluids), venous blood, menstrual blood, vaginal secretions, and sweat/skin samples were used to develop four assays. Two methods for the analysis of DNA methylation biomarkers were developed in this paper: pyrosequencing and quantitative PCR/high resolution melt (HRM) analysis. Using an epigenome wide association study, two markers, NMUR2 and UBE2U, were found to be specific for sperm, based on the fact that mean DNA methylation levels for semen (containing sperm cells) were significantly lower than mean DNA methylation levels of other body fluids. In addition, one marker (SA-6) was hypermethylated in saliva when compared to other body fluids. The assays developed for NMUR2, UBE2U and SA-6 markers can be applied in forensic tissue identification using both pyrosequencing and HRM analysis. Additionally, a set of CpG sites in the AHRR locus were hypomethylated in blood when compared to other tissues using pyrosequencing. However, this locus was not amenable to HRM analysis. Overall, this work demonstrates the discovery and application of tDMRs for forensic applications.

Comparison of physiological functions between neuromedin U-related peptide and neuromedin S-related peptide in the rat central nervous system

Two novel peptides, neuromedin U precursor-related peptide (NURP) and neuromedin S precursor-related peptide (NSRP), are produced from neuromedin U (NMU) and neuromedin S (NMS) precursors, respectively, as these precursors have multiple consensus sequences for proteolytic processing. Our group has shown previously that one of these two novel peptides, NURP, stimulates body temperature and locomotor activity, but not food intake. However, the physiological function of the other peptide, NSRP, has remained unclear. Therefore, the aim of this study was to characterize differences in the regions of the rat brain targeted by the NMU/NMS peptide family, including NURP and NSRP, and their physiological functions. First, we explored the regions of c-Fos expression after intracerebroventricular (i.c.v.) injection of NURP and NSRP and found that these were fewer than after i.c.v. injection of NMU and NMS in the hypothalamus, possibly because NURP and NSRP cannot activate NMU/NMS receptors. In the ventral subiculum, which is one region of the hippocampus, c-Fos expression was evident only after i.c.v. injection of NURP. We also examined the effects of NSRP on food intake, body temperature and locomotor activity. Like NURP, NSRP increased both body temperature and locomotor activity, but not food intake, indicating that NSRP is also a functional peptide. However, these effects of NSRP were distinctly weaker than those of NURP. These findings suggest differences in the affinity of NURP and/or NSRP for specific receptors, or in their respective biological activities.

Neuromedin U: A Small Peptide in the Big World of Cancer

Neuromedin U (NMU), a neuropeptide isolated from porcine spinal cord and named because of its activity as a rat uterus smooth muscle contraction inducer, is emerging as a new player in the tumorigenesis and/or metastasis of many types of cancers. Expressed in a variety of tissues, NMU has been shown to possess many important activities in the central nervous system as well as on the periphery. Along with the main structural and functional features of NMU and its currently known receptors, we summarized a growing number of recently published data from different tissues and cells that associate NMU activity with cancer development and progression. We ask if, based on current reports, NMU can be included as a marker of these processes and/or considered as a therapeutic target.

Comparison of glucose tolerance between wild-type mice and mice with double knockout of neuromedin U and neuromedin S

Recently, it has been proposed that neuromedin U (NMU) is "decretin", which suppresses insulin secretion from the pancreas in vitro. Here we examined the possible involvement of NMU in insulin secretion in vivo by comparing the plasma glucose and insulin levels of wild-type mice with those of double knockout (D-KO) of the NMU and neuromedin S (NMS) genes, as NMS binds to the neuromedin U receptor. If NMU is, in fact, "decretin", which inhibits insulin secretion from the pancreas, then NMU-deficient mice might result in higher plasma insulin levels than is the case in wild-type mice, or injection of NMU lead to suppression of plasma insulin level. In this study, we found that the fasting plasma level of insulin was not increased in D-KO mice. Glucose tolerance tests revealed no significant difference in plasma insulin levels between wild-type mice and D-KO mice under non-fasting conditions. After peripheral injection of NMU, plasma glucose and insulin levels did not show any significant changes in either wild-type or D-KO mice. Glucose tolerance testing after 3 weeks of high fat feeding revealed no significant difference in plasma insulin levels during 60 min after glucose injection between wild-type and D-KO mice. These results suggest that even if NMU is a decretin candidate, its physiological involvement in suppression of insulin secretion may be very minor in vivo.

Neuromedin U Does Not Act as a Decretin in Rats

Studies on isolated pancreatic islets suggest that neuromedin U (NMU), a brain and gastrointestinal peptide, acts as a decretin hormone, inhibiting glucose-stimulated insulin secretion. We investigated whether this effect could be reproduced in vivo and in isolated perfused rat pancreas. Unlike the incretin hormone, glucagon-like peptide 1 (GLP-1), intravenous NMU administration had no effects on blood glucose and plasma insulin and glucagon in vivo. Moreover, NMU neither changed insulin, glucagon, or somatostatin secretion from isolated perfused rat pancreas, nor affected GLP-1-stimulated insulin and somatostatin secretion. For NMU to act as a decretin hormone, its secretion should increase following glucose ingestion; however, glucose did not affect NMU secretion from isolated perfused rat small intestine, which contained extractable NMU. Furthermore, the two NMU receptors were not detected in endocrine rat or human pancreas. We conclude that NMU does not act as a decretin hormone in rats.

Binge-Type Eating in Rats is Facilitated by Neuromedin U Receptor 2 in the Nucleus Accumbens and Ventral Tegmental Area

Binge-eating disorder (BED) is the most common eating disorder, characterized by rapid, recurrent overconsumption of highly palatable food in a short time frame. BED shares an overlapping behavioral phenotype with obesity, which is also linked to the overconsumption of highly palatable foods. The reinforcing properties of highly palatable foods are mediated by the nucleus accumbens (NAc) and the ventral tegmental area (VTA), which have been implicated in the overconsumption behavior observed in BED and obesity. A potential regulator of binge-type eating behavior is the G protein-coupled receptor neuromedin U receptor 2 (NMUR2). Previous research demonstrated that NMUR2 knockdown potentiates binge-type consumption of high-fat food. We correlated binge-type consumption across a spectrum of fat and carbohydrate mixtures with synaptosomal NMUR2 protein expression in the NAc and VTA of rats. Synaptosomal NMUR2 protein in the NAc demonstrated a strong positive correlation with binge intake of a “lower”-fat (higher carbohydrate) mixture, whereas synaptosomal NMUR2 protein in the VTA demonstrated a strong negative correlation with binge intake of an “extreme” high-fat (0% carbohydrate) mixture. Taken together, these data suggest that NMUR2 may differentially regulate binge-type eating within the NAc and the VTA.

Neuroendocrine regulation of innate lymphoid cells

The activities of the immune system in repairing tissue injury and combating pathogens were long thought to be independent of the nervous system. However, a major regulatory role of immunomodulatory molecules released locally or systemically by the neuroendocrine system has recently emerged. A number of observations and discoveries support indeed the notion of the nervous system as an immunoregulatory system involved in immune responses. Innate lymphoid cells (ILCs), including natural killer (NK) cells and tissue-resident ILCs, form a family of effector cells present in organs and mucosal barriers. ILCs are involved in the maintenance of tissue integrity and homeostasis. They can also secrete effector cytokines rapidly, and this ability enables them to play early roles in the immune response. ILCs are activated by multiple pathways including epithelial and myeloid cell-derived cytokines. Their functions are also regulated by mediators produced by the nervous system. In particular, the peripheral nervous system, through neurotransmitters and neuropeptides, works in parallel with the hypothalamic-pituitary-adrenal and gonadal axis to modulate inflammatory events and maintain homeostasis. We summarize here recent findings concerning the regulation of ILC activities by neuroendocrine mediators in homeostatic and inflammatory conditions.

Ligand-Specific Signaling Profiles and Resensitization Mechanisms of the Neuromedin U2 Receptor

The structurally related, but distinct neuropeptides, neuromedin U (NmU) and neuromedin S (NmS) are ligands of two G protein-coupled NmU receptors (NMU1 and NMU2). Hypothalamic NMU2 regulates feeding behavior and energy expenditure and has therapeutic potential as an anti-obesity target, making an understanding of its signaling and regulation of particular interest. NMU2 binds both NmU and NmS with high affinity, resulting in receptor-ligand co-internalization. We have investigated whether receptor trafficking events post-internalization are biased by the ligand bound and can therefore influence signaling function. Using recombinant cell lines expressing human NMU2, we demonstrate that acute Ca²⁺ signaling responses to NmU or NmS are indistinguishable and that restoration of responsiveness (resensitization) requires receptor internalization and endosomal acidification. The rate of NMU2 resensitization is faster following NmU compared with NmS exposure, but is similar if endothelin-converting enzyme-1 activity is inhibited or knocked down. Although acute activation of extracellular signal-regulated kinase (ERK) is also similar, activation by NMU2 is longer lasting if NmS is the ligand. Furthermore, when cells are briefly challenged before removal of free, but not receptor-bound ligand, activation of ERK and p38 mitogen-activated protein kinase by NmS is more sustained. However, only NmU responses are potentiated and extended by endothelin-converting enzyme-1 inhibition. These data indicate that differential intracellular ligand processing produces different signaling and receptor resensitization profiles and add to the findings of other studies demonstrating that intracellular ligand processing can shape receptor behavior and signal transduction.

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.

The neuropeptide NMU amplifies ILC2-driven allergic lung inflammation

Type 2 innate lymphoid cells (ILC2s) both contribute to mucosal homeostasis and initiate pathologic inflammation in allergic asthma. However, the signals that direct ILC2s to promote homeostasis versus inflammation are unclear. To identify such molecular cues, we profiled mouse lung-resident ILCs using single-cell RNA sequencing at steady state and after in vivo stimulation with the alarmin cytokines IL-25 and IL-33. ILC2s were transcriptionally heterogeneous after activation, with subpopulations distinguished by expression of proliferative, homeostatic and effector genes. The neuropeptide receptor Nmur1 was preferentially expressed by ILC2s at steady state and after IL-25 stimulation. Neuromedin U (NMU), the ligand of NMUR1, activated ILC2s in vitro, and in vivo co-administration of NMU with IL-25 strongly amplified allergic inflammation. Loss of NMU-NMUR1 signalling reduced ILC2 frequency and effector function, and altered transcriptional programs following allergen challenge in vivo. Thus, NMUR1 signalling promotes inflammatory ILC2 responses, highlighting the importance of neuro-immune crosstalk in allergic inflammation at mucosal surfaces.

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: An insight into its types, receptors and therapeutic opportunities

Neuropeptides are small protein used by neurons in signal communications. Neuromedin U was the first neuropeptide discovered from the porcine spinal and showed its potent constricting activities on uterus hence was entitled with neuromedin U. Following neuromedin U another of its isoform was discovered neuromedin S which was observed in suprachiasmatic nucleus hence was entitled neuromedin S. Neuromedin K and neuromedin L are of kanassin class which belong to tachykinin family. Bombesin family consists of neuromedin B and neuromedin C. All these different neuromedins have various physiological roles like constrictive effects on the smooth muscles, control of blood pressure, pain sensations, hunger, bone metastasis and release and regulation of hormones. Over the years various newer physiological roles have been observed thus opening ways for various novel therapeutic treatments. This review aims to provide an overview of important different types of neuromedin, their receptors, signal transduction mechanism and implications for various diseases.

Identifying a Neuromedin U Receptor 2 Splice Variant and Determining Its Roles in the Regulation of Signaling and Tumorigenesis In Vitro

Neuromedin U (NMU) activates two G protein-coupled receptors, NMUR1 and NMUR2; this signaling not only controls many physiological responses but also promotes tumorigenesis in diverse tissues. We recently identified a novel truncated NMUR2 derived by alternative splicing, namely NMUR2S, from human ovarian cancer cDNA. Sequence analysis, cell surface ELISA and immunocytochemical staining using 293T cells indicated that NMUR2S can be expressed well on the cell surface as a six-transmembrane protein. Receptor pull-down and fluorescent resonance energy transfer assays demonstrated that NMUR1, NMUR2 and this newly discovered NMUR2S can not only form homomeric complexes but also heteromeric complexes with each other. Although not activated by NMU itself, functional assay in combination with receptor quantification and radio-ligand binding in 293T cells indicated that NMUR2S does not alter the translocation and stability of NMUR1 or NMUR2, but rather effectively dampens their signaling by blocking their NMU binding capability through receptor heterodimerization. We further demonstrated that NMU signaling is significantly up-regulated in human ovarian cancers, whereas expression of NMUR2S can block endogenous NMU signaling and further lead to suppression of proliferation in SKOV-3 ovarian cancer cells. In contrast, in monocytic THP-1 cells that express comparable levels of NMUR1 and NMUR2S, depletion of NMUR2S restored both the signaling and effect of NMU. Thus, these results not only reveal the presence of previously uncharacterized heteromeric relationships among NMU receptors but also provide NMUR2S as a potential therapeutic target for the future treatment of NMU signaling-mediated cancers.

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.

Functional genomics of the rat neuromedin U receptor 1 reveals a naturally occurring deleterious allele

Neuromedin U (NMU) plays an important role in a number of physiological processes, but the relative contribution of its two known receptors, NMUR1 and NMUR2, is still poorly understood. Here we report the existence of a SNP T1022→A (Val341→Glu) in the third exon of the rat Nmur1 gene that leads to an inactive receptor. This SNP is present within the coding region of the highly conserved NPXXY motif found within all class A type G protein-coupled receptors and translates to an NMUR1 receptor that is not expressed on the cell surface. Genetic analysis of the Nmur1 gene in a population of Sprague-Dawley rats revealed that this strain is highly heterogeneous for the inactivating polymorphism. The loss of functional NMUR1 receptors in Sprague-Dawley rats homozygous for the inactive allele was confirmed by radioligand binding studies on native tissue expressing NMUR1. The physiological relevance of this functional genomics finding was examined in two nociceptive response models. The pronociceptive effects of NMU were abolished in rats lacking functional NMUR1 receptors. The existence of naturally occurring NMUR1-deficient rats provides a novel and powerful tool to investigate the physiological role of NMU and its receptors. Furthermore, it highlights the importance of verifying the NMUR1 single nucleotide polymorphism status for rats used in physiological, pharmacological or toxicological studies conducted with NMUR1 modulators.

Neuromedin U type 1 receptor stimulation of A-type K+ current requires the βγ subunits of Go protein, protein kinase A, and extracellular signal-regulated kinase 1/2 (ERK1/2) in sensory neurons

Although neuromedin U (NMU) has been implicated in analgesia, the detailed mechanisms still remain unclear. In this study, we identify a novel functional role of NMU type 1 receptor (NMUR1) in regulating the transient outward K(+) currents (I(A)) in small dorsal root ganglion (DRG) neurons. We found that NMU reversibly increased I(A) in a dose-dependent manner, instead the sustained delayed rectifier K(+) current (I(DR)) was not affected. This NMU-induced I(A) increase was pertussis toxin-sensitive and was totally reversed by NMUR1 knockdown. Intracellular application of GDPβS (guanosine 5'-O-(2-thiodiphosphate)), QEHA peptide, or a selective antibody raised against the Gα(o) or Gβ blocked the stimulatory effects of NMU. Pretreatment of the cells with the protein kinase A (PKA) inhibitor or ERK inhibitor abolished the NMU-induced I(A) response, whereas inhibition of phosphatidylinositol 3-kinase or PKC had no such effects. Exposure of DRG neurons to NMU markedly induced the phosphorylation of ERK (p-ERK), whereas p-JNK or p-p38 was not affected. Moreover, the NMU-induced p-ERK increase was attenuated by PKA inhibition and activation of PKA by foskolin would mimic the NMU-induced I(A) increase. Functionally, we observed a significant decrease of the firing rate of neuronal action potential induced by NMU and pretreatment of DRG neurons with 4-AP could abolish this effect. In summary, these results suggested that NMU increases I(A) via activation of NMUR1 that couples sequentially to the downstream activities of Gβγ of the G(o) protein, PKA, and ERK, which could contribute to its physiological functions including neuronal hypoexcitability in DRG neurons.

Intrathecal neuromedin U induces biphasic effects on sympathetic vasomotor tone, increases respiratory drive and attenuates sympathetic reflexes in rat

BACKGROUND

Neuromedin U (NMU) is a brain-gut peptide that plays regulatory roles in feeding, anxiety, smooth muscle contraction, blood flow, pain and adrenocortical function via two receptors, the NMU receptor 1 and NMU receptor 2. NMU has several known functions in the periphery, but its role in central cardiorespiratory regulation remains poorly understood.

EXPERIMENTAL APPROACH

Experiments were conducted on urethane-anaesthetized, vagotomized and artificially ventilated male Sprague-Dawley rats (n= 42) to determine if NMU modulates sympathetic vasomotor output at the spinal level or modulates baro-, chemo- and somato-sympathetic reflexes.

KEY RESULTS

Intrathecal (i.t.) injections of NMU (2.5-20 nmol) caused a dose-dependent biphasic response, initially a brief period of hypertension and sympatho-excitation followed by prolonged hypotension and sympatho-inhibition. Peak excitatory as well as inhibitory responses were observed at 20 nmol. NMU (20 nmol) initially increased mean arterial pressure and splanchnic sympathetic nerve activity by 24 mmHg and 27% and then reduced these by 37 mmHg and 47%, respectively. NMU also dose-dependently increased respiratory drive, as indicated by a rise in phrenic nerve amplitude, an increase in neural minute ventilation and a shortening of the inspiratory period. Both sympatho-excitatory peaks of the somato-sympathetic reflex were abolished by i.t. NMU. Pressor, sympatho-excitatory and tachycardiac responses to chemoreceptor activation (100% N₂) were blocked or significantly reduced following i.t. NMU. NMU also reduced barosensitivity.

CONCLUSIONS

The data demonstrate that NMU, acting in the spinal cord, differentially contributes to the control of sympathetic tone and adaptive sympathetic reflexes.

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.

Neuropeptides controlling energy balance: orexins and neuromedins

In this chapter, we review the feeding and energy expenditure effects of orexin (also known as hypocretin) and neuromedin. Orexins are multifunctional neuropeptides that affect energy balance by participating in regulation of appetite, arousal, and spontaneous physical activity. Central orexin signaling for all functions originates in the lateral hypothalamus-perifornical area and is likely functionally differentiated based on site of action and on interacting neural influences. The effect of orexin on feeding is likely related to arousal in some ways but is nonetheless a separate neural process that depends on interactions with other feeding-related neuropeptides. In a pattern distinct from other neuropeptides, orexin stimulates both feeding and energy expenditure. Orexin increases in energy expenditure are mainly by increasing spontaneous physical activity, and this energy expenditure effect is more potent than the effect on feeding. Global orexin manipulations, such as in transgenic models, produce energy balance changes consistent with a dominant energy expenditure effect of orexin. Neuromedins are gut-brain peptides that reduce appetite. There are gut sources of neuromedin, but likely the key appetite-related neuromedin-producing neurons are in the hypothalamus and parallel other key anorectic neuropeptide expression in the arcuate to paraventricular hypothalamic projection. As with other hypothalamic feeding-related peptides, hindbrain sites are likely also important sources and targets of neuromedin anorectic action. Neuromedin increases physical activity in addition to reducing appetite, thus producing a consistent negative energy balance effect. Together with the other various neuropeptides, neurotransmitters, neuromodulators, and neurohormones, neuromedin and orexin act in the appetite network to produce changes in food intake and energy expenditure, which ultimately influences the regulation of body weight.

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.

Methamphetamine-induced dopamine-independent alterations in striatal gene expression in the 6-hydroxydopamine hemiparkinsonian rats

Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle are used extensively as a model of Parkinson's disease. The present experiments sought to identify genes that were affected in the dopamine (DA)-denervated striatum after 6-hydroxydopamine-induced destruction of the nigrostriatal dopaminergic pathway in the rat. We also examined whether a single injection of methamphetamine (METH) (2.5 mg/kg) known to cause changes in gene expression in the normally DA-innervated striatum could still influence striatal gene expression in the absence of DA. Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle resulted in METH-induced rotational behaviors ipsilateral to the lesioned side and total striatal DA depletion on the lesioned side. This injection also caused decrease in striatal serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels. DA depletion was associated with increases in 5-HIAA/5-HT ratios that were potentiated by the METH injection. Microarray analyses revealed changes (±1.7-fold, p<0.025) in the expression of 67 genes on the lesioned side in comparison to the intact side of the saline-treated hemiparkinsonian animals. These include follistatin, neuromedin U, and tachykinin 2 which were up-regulated. METH administration caused increases in the expression of c-fos, Egr1, and Nor-1 on the intact side. On the DA-depleted side, METH administration also increased the expression of 61 genes including Pdgf-d and Cox-2. There were METH-induced changes in 16 genes that were common in the DA-innervated and DA-depleted sides. These include c-fos and Nor-1 which show greater changes on the normal DA side. Thus, the present study documents, for the first time, that METH mediated DA-independent changes in the levels of transcripts of several genes in the DA-denervated striatum. Our results also implicate 5-HT as a potential player in these METH-induced alterations in gene expression because the METH injection also caused significant increases in 5-HIAA/5-HT ratios on the DA-depleted side.

Activation of neuromedin U type 1 receptor inhibits L-type Ca2+ channel currents via phosphatidylinositol 3-kinase-dependent protein kinase C epsilon pathway in mouse hippocampal neurons

Neuromedin U (NMU) plays very important roles in the central nervous system. However, to date, any role of NMU in hippocampal neurons and the relevant mechanisms still remain unknown. In the present study, we report that NMU selectively inhibits L-type high-voltage-gated Ca(2+) channels (HVGCC) in mouse hippocampal neurons, in which NMU type 1 receptor (NMUR1), but not NMUR2, is endogenously expressed. In wild type mice, NMU (0.1 microM) reversibly inhibited HVGCC barium currents (I(Ba)) by approximately 28%, while in NMUR1(-/-) mice NMU had no significant effects. Intracellular infusion of GDP-beta-S or a selective antibody raised against the G(o)alpha, as well as pretreatment of the neurons with pertussis toxin, blocked the inhibitory effects of NMU, indicating the involvement of G(o)-protein. This NMUR1-mediated effect did not display the characteristics of a direct interaction between G-protein betagamma subunit (G(betagamma)) and L-type HVGCC, but was abolished by dialyzing cells with QEHA peptide or an antibody to the G(beta). The classical and novel protein kinase C (PKC) antagonist calphostin C, as well as phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, abolished NMU responses, whereas the classical PKC antagonist Gö6976 had no such effects. Cells dialyzed with a PKC epsilon isoform (PKCepsilon) specific inhibitor peptide, GAVSLLPT, abolished NMU responses. In contrast, in cells dialyzed with an inactive PKCepsilon control scramble peptide, LSGTLPAV, no significant effects were observed. In summary, these results suggest that NMU inhibits L-type HVGCC via activation of NMUR1 and downstream G(betagamma), PI3K, and a novel PKCepsilon signaling pathway.

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.

Central NMU signaling in body weight and energy balance regulation: evidence from NMUR2 deletion and chronic central NMU treatment in mice

To investigate the role of the central neuromedin U (NMU) signaling system in body weight and energy balance regulation, we examined the effects of long-term intracerebroventricular (icv) infusion of NMU in C57Bl/6 mice and in mice lacking the gene encoding NMU receptor 2. In diet-induced obese male and female C57BL/6 mice, icv infusion of NMU (8 microg x day(-1) x mouse(-1)) for 7 days decreased body weight and total energy intake compared with vehicle treatment. However, these parameters were unaffected by NMU treatment in lean male and female C57BL/6 mice fed a standard diet. In addition, female (but not male) NMUR2-null mice had increased body weight and body fat mass when fed a high-fat diet but lacked a clear body weight phenotype when fed a standard diet compared with wild-type littermates. Furthermore, female (but not male) NMUR2-null mice fed a high-fat diet were protected from central NMU-induced body weight loss compared with littermate wild-type mice. Thus, we provide the first evidence that long-term central NMU treatment reduces body weight, food intake, and adiposity and that central NMUR2 signaling is required for these effects in female but not male mice.

Appetite-modifying actions of pro-neuromedin U-derived peptides

Neuromedin U (NMU) is known to have potent actions on appetite and energy expenditure. Deletion of the NMU gene in mice leads to an obese phenotype, characterized by hyperphagia and decreased energy expenditure. Conversely, transgenic mice that overexpress proNMU exhibit reduced body weight and fat storage. Here, we show that central administration of NMU or the related peptide neuromedin S (NMS) dose-dependently decreases food intake, increases metabolic rate, and leads to significant weight loss in mice. The effects of NMU and NMS on both feeding and metabolism are almost completely lost in mice lacking the putative CNS receptor for NMU and NMS, NMUr2. However, NMUr2 knockout mice do not exhibit overt differences in body weight or energy expenditure compared with wild-type mice, suggesting that the dramatic phenotype of the NMU gene knockout mouse is not due simply to the loss of NMU/NMUr2 signaling. Putative proteolytic cleavage sites indicate that an additional peptide is produced from the NMU precursor protein, which is extremely well conserved between human, mouse, and rat. Here, we demonstrate that this peptide, proNMU(104-136), has a pronounced effect on energy balance in mice. Specifically, central administration of proNMU(104-136) causes a significant but transient ( approximately 4 h) increase in feeding, yet both food intake and body weight are decreased over the following 24 h. proNMU(104-136) administration also significantly increased metabolic rate. These results suggest that proNMU(104-136) is a novel modulator of energy balance and may contribute to the phenotype exhibited by NMU knockout mice.