A pro-nociceptive role of neuromedin U in adult mice

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.

Alleviation of neuropathic pain with neuropeptide Y requires spinal Npy1r interneurons that coexpress Grp

Neuropeptide Y targets the Y1 receptor (Y1) in the spinal dorsal horn (DH) to produce endogenous and exogenous analgesia. DH interneurons that express Y1 (Y1-INs; encoded by Npy1r) are necessary and sufficient for neuropathic hypersensitivity after peripheral nerve injury. However, as Y1-INs are heterogenous in composition in terms of morphology, neurophysiological characteristics, and gene expression, we hypothesized that a more precisely defined subpopulation mediates neuropathic hypersensitivity. Using fluorescence in situ hybridization, we found that Y1-INs segregate into 3 largely nonoverlapping subpopulations defined by the coexpression of Npy1r with gastrin-releasing peptide (Grp/Npy1r), neuropeptide FF (Npff/Npy1r), and cholecystokinin (Cck/Npy1r) in the superficial DH of mice, nonhuman primates, and humans. Next, we analyzed the functional significance of Grp/Npy1r, Npff/Npy1r, and Cck/Npy1r INs to neuropathic pain using a mouse model of peripheral nerve injury. We found that chemogenetic inhibition of Npff/Npy1r-INs did not change the behavioral signs of neuropathic pain. Further, inhibition of Y1-INs with an intrathecal Y1 agonist, [Leu31, Pro34]-NPY, reduced neuropathic hypersensitivity in mice with conditional deletion of Npy1r from CCK-INs and NPFF-INs but not from GRP-INs. We conclude that Grp/Npy1r-INs are conserved in higher order mammalian species and represent a promising and precise pharmacotherapeutic target for the treatment of neuropathic pain.

Neuroimmune communication in infection and pain: Friends or foes?

Clinically, a variety of micro-organisms cause painful infections. Before seen as bystanders in the context of infections, recent studies have demonstrated that, as immune cells, nociceptors can sense pathogen-derived products. Nociceptors and immune cells, therefore, have evolved to communicate with each other to control inflammatory and host responses against pathogens in a complementary way. This interaction is named as neuroimmune communication (or axon-axon immune reflex) and initiates after the release of neuropeptides, such as CGRP and VIP by neurons. By this neurogenic response, nociceptors orchestrate the activity of innate and adaptive immune cells in a context-dependent manner. In this review, we focus on how nociceptors sense pathogen-derived products to shape the host response. We also highlight the new concept involving the resolution of inflammation, which is related to an active and time-dependent biosynthetic shift from pro-inflammatory to pro-resolution mediators, the so-called specialized pro-resolving lipid mediators (SPMs). At very low doses, SPMs act on specific receptors to silence nociceptors, limit pain and neurogenic responses, and resolve infections. Furthermore, stimulation of the vagus nerve induces SPMs production to regulate immune responses in infections. Therefore, harnessing the current understanding of neuro-immune communication and neurogenic responses might provide the bases for reprogramming host responses against infections through well balanced and effective immune response and inflammation resolution.

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.

Targeting spinal neuropeptide Y1 receptor-expressing interneurons to alleviate chronic pain and itch

An accelerating basic science literature is providing key insights into the mechanisms by which spinal neuropeptide Y (NPY) inhibits chronic pain. A key target of pain inhibition is the G_i-coupled neuropeptide Y1 receptor (Y1). Y1 is located in key sites of pain transmission, including the peptidergic subpopulation of primary afferent neurons and a dense subpopulation of small, excitatory, glutamatergic/somatostatinergic interneurons (Y1-INs) that are densely expressed in the dorsal horn, particularly in superficial lamina I-II. Selective ablation of spinal Y1-INs with an NPY-conjugated saporin neurotoxin attenuates the development of peripheral nerve injury-induced mechanical and cold hypersensitivity. Conversely, conditional knockdown of NPY expression or intrathecal administration of Y1 antagonists reinstates hypersensitivity in models of chronic latent pain sensitization. These and other results indicate that spinal NPY release and the consequent inhibition of pain facilitatory Y1-INs represent an important mechanism of endogenous analgesia. This mechanism can be mimicked with exogenous pharmacological approaches (e.g. intrathecal administration of Y1 agonists) to inhibit mechanical and thermal hypersensitivity and spinal neuron activity in rodent models of neuropathic, inflammatory, and postoperative pain. Pharmacological activation of Y1 also inhibits mechanical- and histamine-induced itch. These immunohistochemical, pharmacological, and cell type-directed lesioning data, in combination with recent transcriptomic findings, point to Y1-INs as a promising therapeutic target for the development of spinally directed NPY-Y1 agonists to treat both chronic pain and itch.

Effect of neuromedin U on allergic airway inflammation in an asthma model

Asthma is a major inflammatory airway disease with high incidence and mortality rates. The Global Initiative for Asthma released a report called ‘The Global Burden of Asthma’ in 2004. However, the specific pathogenesis of asthma remains unclear. An increasing number of studies have demonstrated that neuromedin U (NMU) plays a pleiotropic role in the pathogenesis of asthma. NMU is a highly structurally conserved neuropeptide that was first purified from porcine spinal cord and named for its contractile effect on the rat uterus. NMU amplifies type 2 innate lymphoid cell (ILC2)-driven allergic lung inflammation. The NMU receptors (NMURs), designated as NMUR1 and NMUR2, belong to the G protein-coupled receptor family. NMUR1 has also been found in immune cells, including ILC2s, mast cells and eosinophils. In view of the important roles of NMU in the pathogenesis of asthma, the present review evaluates the potential mechanisms underlying the impact of NMU on asthma and its association with asthma therapy.

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.

Circulating neuromedin U levels are similar in subjects with NGT and newly diagnosed T2DM and do not correlate with insulin secretion

AIMS

Neuromedin U (NMU), a highly conserved peptide, is implicated in energy homeostasis and is involved in regulating insulin secretion as a decretin hormone in animals. However, there have been no reports on the relationship between NMU and type 2 diabetes mellitus (T2DM). The aim of this study was to investigate circulating NMU concentrations in healthy subjects and T2DM patients and to evaluate the association between serum NMU levels and glucose-stimulated insulin secretion.

METHODS

We used ELISA to analyze NMU concentrations in blood samples from newly diagnosed T2DM patients (n = 57) and age-, sex- and BMI-matched healthy control subjects (n = 50). Anthropometric parameters, oral glucose tolerance, glycosylated hemoglobin, blood lipids, insulin sensitivity, and insulin secretion were measured.

RESULTS

No difference was observed in serum NMU levels between control subjects and newly diagnosed T2DM patients (p = 0.788). The oral glucose tolerance test (OGTT) results indicated that serum NMU concentrations did not change and did not correlate with insulin levels at fasting and 1 h, 2 h and 3 h after glucose load in both healthy controls and newly diagnosed T2DM patients.

CONCLUSION

Circulating NMU concentrations were similar in control subjects and newly diagnosed T2DM patients and were not associated with glucose-stimulated insulin secretion. Serum NMU is not a human decretin hormone and may not play a role in the pathogenesis of T2DM.

The short interference RNA (siRNA) targeting NMUR2 relieves nociception in a bone cancer pain model of rat through PKC-ERK and PI3K-AKT pathways

BACKGROUND/AIM

Bone cancer pain (BCP) causes troubles and burdens to patients globally. Increasing evidence proved that neuromedin U receptor 2 (NMUR2) was involved in pains. Our study was performed to investigate the role of NMUR2 on BCP and the underlying mechanism.

METHODS

The rats were raised and BCP rat model was established by injection with Walker 256 cells. The RNA and protein expression levels of NMUR2 in rat neurons-dorsal spinal cord cells, RNdsc cells were detected by qRT-PCR and western blot. The administration with NMUR2 was via intrathecal injection with siRNA to silence NMUR2. The tolerance of rat to pain was measured by mechanical allodynia test and presented by paw withdrawal threshold (PWT) value. The effects on protein kinase C (PKC)/extracellular regulated protein kinases (ERK) and phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT) signal pathways were examined by western blot.

RESULTS

The expression of NMUR2 in both mRNA and protein levels was upregulated in BCP rat model. In addition, siRNA injection significantly decreased the expression of NMUR2 on the 3rd, 7th and 14th day. BCP group revealed lower PWT value compared with control while NMUR2 silence increased the PWT value compared with negative control. The phosphorylation of PKC, ERK, PI3K and AKT was increased in BCP model while was decreased by si-NMUR2. PKC/ERK and PI3K/AKT inhibitor administration increased the PWT value compared with BCP group.

CONCLUSION

si-NMUR2 alleviates BCP via inactivation of PKC/ERK and PI3K/AKT signal pathways.

Sex-specific linkage scans in opioid dependence

Sex influences risk for opioid dependence (OD). We hypothesized that sex might interact with genetic loci that influence the risk for OD. Therefore we performed an analysis to identify sex-specific genomic susceptibility regions for OD using linkage. Over 6,000 single nucleotide polymorphism (SNP) markers were genotyped for 1,758 African- and European-American (AA and EA) individuals from 739 families, ascertained via affected sib-pairs with OD and/or cocaine dependence. Autosomewide non-parametric linkage scans, stratified by sex and population, were performed. We identified one significant linkage region, segregating with OD in EA men, at 71.1 cM on chromosome 4 (LOD = 3.29; point-wise P = 0.00005; empirical autosome-wide P = 0.042), which significantly differed from the linkage signal at the same location in EA women (empirical P = 0.002). Three suggestive linkage signals were identified at 181.3 cM on chromosome 7 (LOD = 2.18), 104 cM on chromosome 11 (LOD = 1.85), and 60.9 cM on chromosome 16 (LOD = 1.93) in EA women. In AA men, four suggestive linkage signals were detected at 201.1 cM on chromosome 3 (LOD = 2.32), 152.9 cM on chromosome 6 (LOD = 1.86), 16.8 cM on chromosome 7 (LOD = 1.95), and 36.1 cM on chromosome 17 (LOD = 1.99). The significant region, mapping to 4q12-4q13.1, harbors several OD candidate genes with interconnected functionality, including VEGFR, CLOCK, PDCL2, NMU, NRSF, and IGFBP7. In conclusion, these results provide an evidence for the existence of sex-specific and population-specific differences in OD. Furthermore, these results provide positional information that will facilitate the use of targeted next-generation sequencing to search for genes that contribute to sex-specific differences in OD. © 2016 Wiley Periodicals, Inc.

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.

NMU signaling promotes endometrial cancer cell progression by modulating adhesion signaling

Neuromedin U (NMU) was originally named based on its strong uterine contractile activity, but little is known regarding its signaling/functions in utero. We identified that NMU and one of its receptors, NMUR2, are not only present in normal uterine endometrium but also co-expressed in endometrial cancer tissues, where the NMU level is correlated with the malignant grades and survival of patients. Cell-based assays further confirmed that NMU signaling can promote cell motility and proliferation of endometrial cancer cells derived from grade II tumors. Activation of NMU pathway in these endometrial cancer cells is required in order to sustain expression of various adhesion molecules, such as CD44 and integrin alpha1, as well as production of their corresponding extracellular matrix ligands, hyaluronan and collagen IV; it also increased the activity of SRC and its downstream proteins RHOA and RAC1. Thus, it is concluded that NMU pathway positively controls the adhesion signaling-SRC-Rho GTPase axis in the tested endometrial cancer cells and that changes in cell motility and proliferation can occur when there is manipulation of NMU signaling in these cells either in vitro or in vivo. Intriguingly, this novel mechanism also explains how NMU signaling promotes the EGFR-driven and TGFβ receptor-driven mesenchymal transitions. Through the above axis, NMU signaling not only can promote malignancy of the tested endometrial cancer cells directly, but also helps these cells to become more sensitive to niche growth factors in their microenvironment.

Blood-brain barrier transport kinetics of the neuromedin peptides NMU, NMN, NMB and NT

The neuromedin peptides are peripherally and centrally produced, but until now, it is generally believed that they only function as locally acting compounds without any quantitative knowledge about their blood-brain barrier (BBB) passage. Here, we characterize the transport kinetics of four neuromedins (NMU, NMN, NMB and NT) across the BBB, as well as their metabolization profile, and evaluate if they can act as endocrine hormones. Using the in vivo mouse model, multiple time regression (MTR), capillary depletion (CD) and brain efflux studies were performed. Data was fitted using linear (NMU, NT and NMB) or biphasic modeling (NMU and NMN). Three of the four investigated peptides, i.e. NMU, NT and NMN, showed a significant influx into the brain with unidirectional influx rate constants of 1.31 and 0.75 μL/(g × min) for NMU and NT respectively and initial influx constants (K1) of 72.14 and 7.55 μL/(g × min) and net influx constants (K) of 1.28 and 1.36 × 10(-16) μL/(g×min) for NMU and NMN respectively. The influx of NMB was negligible. Only NMN and NT showed a significant efflux out of the brain with an efflux constant (kout) of 0.042 min(-1) and 0.053 min(-1) respectively. Our results indicate that locally produced neuromedin peptides and/or fragments can be transported through the whole body, including passing the BBB, and taken up by different organs/tissues, supporting the idea that the neuromedins could have a much bigger role in the regulation of biological processes than currently assumed.

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: 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.

In search of analgesia: emerging roles of GPCRs in pain

Of all clinically marketed drugs, greater than thirty percent are modulators of G protein-coupled receptors (GPCRs). Nearly 400 GPCRs (i.e., excluding odorant and light receptors) are encoded within the human genome, but only a small fraction of these seven-transmembrane proteins have been identified as drug targets. Chronic pain affects more than one-third of the population, representing a substantial societal burden in use of health care resources and lost productivity. Furthermore, currently available treatments are often inadequate, underscoring the significant need for better therapeutic strategies. The expansion of the identified human GPCR repertoire, coupled with recent insights into the function and structure of GPCRs, offers new opportunities for the development of novel analgesic therapeutics.

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.

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.

Neuromedin-U inhibits unilateral adrenalectomy-induced compensatory adrenal growth in the rat

Neuromedin-U (NMU) is a brain-gut peptide, which has been previously found to stimulate hypothalamic-pituitary-adrenal axis in the rat and to control the growth of the rat adrenal cortex. The present study aimed to investigate the possible involvement of NMU in the regulation of unilateral adrenalectomy-induced compensatory adrenal growth, a phenomenon known to be neurally mediated. The right adrenal gland of mature female rats was removed, the contralateral gland was then analyzed at 24 and 72h following surgery. Groups of rats were given 3 subcutaneous injections (24, 16 and 8h before decapitation) of NMU8 (1.5 or 3.0 nmol/100g/per injection). Three hours before sacrifice all rats received an intraperitoneal injection of 0.1mg/100g body weight of vincristin. By means of RT-PCR the presence of NMUR1 mRNA was detected in adrenal cortex of both intact and hemiadrenalectomized rats. As expected, unilateral adrenalectomy-induced an increase in adrenal weight, associated with increased plasma ACTH, aldosterone and corticosterone levels. The administration of NMU to hemiadrenalectomized rats did not significantly affect these parameters. NMU administration, however, notably inhibited the unilateral adrenalectomy-induced adrenocortical cell proliferation in both zona glomerulosa and zona fasciculata, as assessed by the metaphase index and the number of parenchymal cell nuclei per unit area of the tissue. When compared to hemiadrenalectomized animals receiving saline, a significant decrease of blood corticosterone levels was observed after 24h in rats treated with the highest dose of NMU. Since these effects were independent on changes in blood ACTH, they could reflect an interaction of NMU with the neural system innervating the adrenal gland.

Distribution of neuromedin U binding sites in the rat CNS revealed by in vitro receptor autoradiography

Neuromedin U (NMU), a neuropeptide implicated in feeding, inflammation, pain control and anxiety-related behaviours, is widely distributed in peripheral organs and the CNS. These effects are thought to be mediated by its receptors NMU(1) and NMU(2). Since its precise sites of interaction in the CNS were to date unknown, we studied the distribution of in vitro binding sites for (125)I-NMU-23 in the rat CNS by receptor autoradiography. High-density specific binding was found in discrete areas of the brain and spinal cord, namely in the limbic system (hippocampal formation, septohippocampal nucleus, indusium griseum, hypothalamus, amygdaloid nuclei), superior colliculus, dorsal raphé, and substantia gelatinosa of the spinal cord. Our findings provide further supportive evidence for a multifunctional role for the peptide in the brain and spinal cord.

Paradoxical behavior of neuromedin U in isolated smooth muscle cells and intact tissue

Neuromedin U (NmU) is a neuropeptide showing high levels of structural conservation across different species. Since its discovery in 1985, NmU has been implicated in numerous physiological roles, including smooth muscle contraction, energy homeostasis, stress, intestinal ion transport, pronociception, and circadian rhythm. Two G-protein-coupled receptors have been identified for NmU and cloned from humans, rats, and mice. Recombinantly expressed NmU receptors couple to both Galpha(q/11) and Galpha(i) G-proteins, and NmU binds essentially irreversibly, preventing signaling to repetitive applications of NmU. However, it is unclear whether these properties reflect those of endogenously expressed NmU receptors or how these properties influence the functional consequences of NmU receptor signaling. Here, we have explored the signaling by rat NmU receptors expressed endogenously in cultured rat colonic smooth muscle cells and explore the functional consequence of this signaling by investigating the NmU-mediated contraction of ex vivo rat colonic smooth muscle preparations. We demonstrate that endogenous rat NmU receptors couple to both Galpha(q/11) and Galpha(i) G-proteins. Furthermore, we show complex patterns of Ca(2+) signaling, including oscillations, and provide evidence of essentially irreversible binding of NmU to smooth muscle cells. Challenge of either circular or longitudinal rat isolated colonic smooth muscle preparations with NmU resulted in robust contractions. Stimulation was direct, and paradoxically, repetitive applications of NmU mediated repetitive contractions with no evidence of desensitization, highlighting a major discrepancy in the behavior of NmU in single cells and in intact tissues. The reason for this discrepancy is presently unknown.

Novel role of the anorexigenic peptide neuromedin U in the control of LH secretion and its regulation by gonadal hormones and photoperiod

Neuromedin U (NMU) is a widely spread neuropeptide, with predominant expression at the gastrointestinal tract and brain, putatively involved in the regulation of a diversity of biological functions, including food intake, energy balance and circadian rhythms; all closely related to reproduction. Yet, the implication of NMU in the control of the gonadotropic axis remains scarcely studied. We report herein analyses on the hypothalamic expression and function of NMU in different physiological and experimental states of the rat reproductive system. Expression of NMU mRNA at the hypothalamus was persistently detected along female postnatal development, with maximum levels in adulthood that fluctuated across the cycle and were modulated by ovarian steroids. Acute central administration of NMU evoked increases of serum LH levels in pubertal female rats, while repeated injection of NMU tended to advance vaginal opening. Likewise, central injection of NMU increased serum LH concentrations in cycling female rats, with peak responses in estrus. In contrast, NMU significantly inhibited preelevated LH secretion in gonadectomized and kisspeptin-treated rats. Finally, in noncycling females due to photoperiodic manipulation (constant light), hypothalamic NMU mRNA levels were markedly depressed, but relative LH responses to exogenous NMU were significantly augmented. All together, our present data support a predominant stimulatory role of NMU in the control of the female gonadotropic axis, which appears under the influence of developmental, hormonal, and photoperiodic cues, and might contribute to the joint regulation of energy balance, biological rhythms, and reproduction.

The role of pacemaker currents in neuropathic pain

Hyperpolarization-activated cation nonselective cyclic nucleotide-gated (HCN) channels mediate pacemaker currents that control basic rhythmic processes including heartbeat. Alterations in HCN channel expression or function have been described in both epilepsy and cardiac arrhythmias. Recent evidence suggests that pacemaker currents may also play an important role in ectopic neuronal activity that manifests as neuropathic pain. Pacemaker currents are subject to endogenous regulation by cyclic nucleotides, pH and perhaps phosphorylation. In addition, a number of neuromodulators with known roles in pain affect current density and kinetics. The pharmacology of a number of drugs that are commonly used to treat neuropathic pain includes effects on pacemaker currents. Altered pacemaker currents in injured tissues may be an important mechanism underlying neuropathic pain, and drugs that modulate these currents may offer new therapeutic options.

Mice genetically deficient in neuromedin U receptor 2, but not neuromedin U receptor 1, have impaired nociceptive responses

Neuromedin U (NMU) has recently been reported to have a role in nociception and inflammation. To clarify the function of the two known NMU receptors, NMU receptor 1 (NMUR1) and NMU receptor 2 (NMUR2), during nociception and inflammation in vivo, we generated mice in which the genes for each receptor were independently deleted. Compared to wild type littermates, mice deficient in NMUR2 showed a reduced thermal nociceptive response in the hot plate, but not in the tail flick, test. In addition, the NMUR2 mutant mice showed a reduced behavioral response and a marked reduction in thermal hyperalgesia following capsaicin injection. NMUR2-deficient mice also showed an impaired pain response during the chronic, but not acute, phase of the formalin test. In contrast, NMUR1-deficient mice did not show any nociceptive differences compared to their wild type littermates in any of the behavioral tests used. We observed the same magnitude of inflammation in both lines of NMU receptor mutant mice compared to their wild type littermates after injection with complete Freund's adjuvant (CFA), suggesting no requirement for either receptor in this response. Thus, the pro-nociceptive effects of NMU in mice appear to be mediated through NMUR2, not NMUR1.

Role of peripheral hyperpolarization-activated cyclic nucleotide-modulated channel pacemaker channels in acute and chronic pain models in the rat

Hyperpolarization-activated, cyclic nucleotide-modulated (HCN) channels contribute to rhythmic spontaneous activity in the heart and CNS. Ectopic spontaneous neuronal activity has been implicated in the development and maintenance of acute and chronic hyperalgesia, allodynia and spontaneous pain. Previously, we documented that systemic administration of ZD7288, a specific blocker of pacemaker current (I(h)), decreased ectopic activity in dorsal root ganglion (DRG) and reversed tactile allodynia in spinal nerve ligated (SNL) rats [Chaplan SR, Guo HQ, Lee DH, Luo L, Liu C, Kuei C, Velumian AA, Butler MP, Brown SM, Dubin AE (2003) Neuronal hyperpolarization-activated pacemaker channels drive neuropathic pain. J Neurosci 23:1169-1178]. Spontaneous pain is the chief clinical manifestation of peripheral nerve injury; however, a role for I(h) in spontaneous pain has not been described. Here, in further rat studies, we report that systemic administration of ZD7288 reversed spontaneous pain induced by mild thermal injury (MTI) and tactile allodynia induced by SNL and MTI. In contrast, ZD7288 did not reduce thermal hyperalgesia. An important locus of action appears to be in the skin since intraplantar (local) administration of ZD7288 completely suppressed tactile allodynia arising from MTI and SNL and reduced spontaneous pain due to MTI. Immunohistochemical staining of plantar skin sections detected HCN1-HCN4 expression in mechanosensory structures (e.g., Meissner's corpuscles and Merkel cells). Collectively, these data suggest that expression and modulation of I(h) in the peripheral nervous system, including specialized sensory structures, may play a significant role in sensory processing and contribute to spontaneous pain and tactile allodynia.

Species-dependent smooth muscle contraction to Neuromedin U and determination of the receptor subtypes mediating contraction using NMU1 receptor knockout mice

The peptide ligand neuromedin U (NMU) has been implicated in an array of biological activities, including contraction of uterine, intestinal and urinary bladder smooth muscle. However, many of these responses appear to be species-specific. This study was undertaken to fully elucidate the range of smooth muscle-stimulating effects of NMU in rats, mice and guinea-pigs, and to examine the extent of the species differences. In addition, the NMU1 receptor knockout mouse was used to determine which receptor subtype mediates the contractile responses generated by NMU in the mouse. A range of isolated organ in vitro bioassays were carried out, which were chosen to re-confirm previous literature reports (uterine and stomach fundus contraction) and also to explore potentially novel smooth muscle responses to NMU. This investigation uncovered a number of previously unidentified NMU-mediated responses: contraction of rat lower esophageal sphinster (LES), rat ileum, mouse gallbladder, enhancement of electrically evoked contractions in rat and mouse vas deferens, and a considerable degree of cross-species differences. Studies using the NMU1 receptor knockout mice revealed that in the mouse fundus and gallbladder assays the NMU contractile response was mediated entirely through the NMU1 receptor subtype, whereas, in assays of mouse uterus and vas deferens, the response to NMU was unchanged in the NMU1 receptor knockout mouse, suggesting that the NMU response may be mediated through the NMU2 receptor subtype. NMU receptor subtype-selective antagonists are required to further elucidate the role of the individual receptor subtypes.

Neuromedin U receptor 2-deficient mice display differential responses in sensory perception, stress, and feeding

Neuromedin U (NMU) is a highly conserved neuropeptide with a variety of physiological functions mediated by two receptors, peripheral NMUR1 and central nervous system NMUR2. Here we report the generation and phenotypic characterization of mice deficient in the central nervous system receptor NMUR2. We show that behavioral effects, such as suppression of food intake, enhanced pain response, and excessive grooming induced by intracerebroventricular NMU administration were abolished in the NMUR2 knockout (KO) mice, establishing a causal role for NMUR2 in mediating NMU's central effects on these behaviors. In contrast to the NMU peptide-deficient mice, NMUR2 KO mice appeared normal with regard to stress, anxiety, body weight regulation, and food consumption. However, the NMUR2 KO mice showed reduced pain sensitivity in both the hot plate and formalin tests. Furthermore, facilitated excitatory synaptic transmission in spinal dorsal horn neurons, a mechanism by which NMU stimulates pain, did not occur in NMUR2 KO mice. These results provide significant insights into a functional dissection of the differential contribution of peripherally or centrally acting NMU system. They suggest that NMUR2 plays a more significant role in central pain processing than other brain functions including stress/anxiety and regulation of feeding.

Neuromedin U is regulated by the metastasis suppressor RhoGDI2 and is a novel promoter of tumor formation, lung metastasis and cancer cachexia

Most deaths from urinary bladder cancer are owing to metastatic disease. A reduction in Rho GDP Dissociation Inhibitor 2 (RhoGDI2) protein has been associated with increased risk of metastasis in patients with locally advanced bladder cancer, whereas in animal models, RhoGDI2 reconstitution in cells without expression results in lung metastasis suppression. Recently, we noted an inverse correlation between tumor RhoGDI2 and Neuromedin U (NMU) expression, suggesting that NMU might be a target of the lung metastasis suppressor effect of RhoGDI2. Here we evaluated whether NMU is regulated by RhoGDI2 and is functionally important in tumor progression. We used small interfering RNA knockdown of endogenous RhoGDI2 in poorly tumorigenic and non-metastatic human bladder cancer T24 cells and observed increased NMU RNA expression. Although NMU overexpression did not increase the monolayer growth of T24 or related T24T poorly metastatic human bladder cancer cells, it did augment anchorage-independent growth for the latter. Overexpression of NMU in T24 and T24T cells significantly promoted tumor formation of both cell lines in nude mice, but did not alter the growth rate of established tumors. Furthermore, NMU-overexpressing xenografts were associated with lower animal body weight than control tumors, indicating a possible role of NMU in cancer cachexia. NMU overexpression in T24T cells significantly enhanced their lung metastatic ability. Bioluminescent in vivo imaging revealed that lung metastases in T24T grew faster than the same tumors in the subcutaneous microenvironment. In conclusion, NMU is a RhoGDI2-regulated gene that appears important for tumorigenicity, lung metastasis and cancer cachexia, and thus a promising therapeutic target in cancer.

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 elicits cytokine release in murine Th2-type T cell clone D10.G4.1

Neuromedin U (NmU), originally isolated from porcine spinal cord and later from other species, is a novel peptide that potently contracts smooth muscle. NmU interacts with two G protein-coupled receptors designated as NmU-1R and NmU-2R. This study demonstrates a potential proinflammatory role for NmU. In a mouse Th2 cell line (D10.G4.1), a single class of high affinity saturable binding sites for (125)I-labeled NmU (K(D) 364 pM and B(max) 1114 fmol/mg protein) was identified, and mRNA encoding NmU-1R, but not NmU-2R, was present. Competition binding analysis revealed equipotent, high affinity binding of NmU isopeptides to membranes prepared from D10.G4.1 cells. Exposure of these cells to NmU isopeptides resulted in an increase in intracellular Ca(2+) concentration (EC(50) 4.8 nM for human NmU). In addition, NmU also significantly increased the synthesis and release of cytokines including IL-4, IL-5, IL-6, IL-10, and IL-13. Studies using pharmacological inhibitors indicated that maximal NmU-evoked cytokine release required functional phospholipase C, calcineurin, MEK, and PI3K pathways. These data suggest a role for NmU in inflammation by stimulating cytokine production by T cells.

Localisation of NMU1R and NMU2R in human and rat central nervous system and effects of neuromedin-U following central administration in rats

RATIONALE

Neuromedin-U (NmU) is an agonist at NMU1R and NMU2R. The brain distribution of NmU and its receptors, in particular NMU2R, suggests widespread central roles for NmU. In agreement, centrally administered NmU affects feeding behaviour, energy expenditure and pituitary output. Further central nervous system (CNS) roles for NmU warrant investigation.

OBJECTIVES

To investigate the CNS role of NmU by mapping NMU1R and NMU2R mRNA and measuring the behavioural, endocrine, neurochemical and c-fos response to intracerebroventricular (i.c.v.) NmU.

METHODS

Binding affinity and functional potency of rat NmU was determined at human NMU1R and NMU2R. Expression of NMU1R and NMU2R mRNA in rat and human tissue was determined using semi-quantitative reverse-transcription polymerase chain reaction. In in-vivo studies, NmU was administered i.c.v. to male Sprague-Dawley rats, and changes in grooming, motor activity and pre-pulse inhibition (PPI) were assessed. In further studies, plasma endocrine hormones, [DOPAC + HVA]/[dopamine] and [5-HIAA]/[5-HT] ratios and levels of Fos-like immunoreactivity (FLI) were measured 20 min post-NmU (i.c.v.).

RESULTS

NmU bound to NMU1R ( K(I), 0.11+/-0.02 nM) and NMU2R ( K(I), 0.21+/-0.05 nM) with equal affinity and was equally active at NMU1R (EC(50), 1.25+/-0.05 nM) and NMU2R (EC(50), 1.10+/-0.20 nM) in a functional assay. NMU2R mRNA expression was found at the highest levels in the CNS regions of both rat and human tissues. NMU1R mRNA expression was restricted to the periphery of both species with the exception of the rat amygdala. NmU caused a marked increase in grooming and motor activity but did not affect PPI. Further, NmU decreased plasma prolactin but did not affect levels of corticosterone, luteinising hormone or thyroid stimulating hormone. NmU elevated levels of 5-HT in the frontal cortex and hypothalamus, with decreased levels of its metabolites in the hippocampus and hypothalamus, but did not affect dopamine function. NmU markedly increased FLI in the nucleus accumbens, frontal cortex and central amygdala.

CONCLUSIONS

These data provide further evidence for widespread roles for NmU and its receptors in the brain.

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.

Neuromedin U is involved in nociceptive reflexes and adaptation to environmental stimuli in mice

Following our recent observations of inactivity and slowed movement in neuromedin U knockout (NMU KO) mice, we compared nociceptive reflexes and environmental adaptation in NMU KO and wild-type mice. Hot plate and formalin tests revealed that reflexes to heat and pain were significantly decreased in NMU KO mice. Conversely, intracerebroventricular injection of NMU into wild-type mice stimulated nociceptive reflexes in a dose-dependent manner. After NMU injection, increased c-Fos expression was observed in a wide range of locations in hypothalamus, brainstem, and spinal cord. NMU mRNA expression increased in the spinal cord, but not in the hypothalamus, 2 and 4 h after formalin injection. When their light-dark cycle was advanced or retarded by 5 h, NMU KO mice required a longer time to re-entrain into the new light-dark cycle than did wild-type mice. Wild-type mice displayed increased blood pressure after their environmental temperature was changed from 23 to 37 degrees C, whereas no such increase was observed in NMU KO mice. Blood corticosterone levels were significantly increased after 10 min of immobilization stress in wild-type mice, but not in NMU KO mice. These results suggest that endogenous NMU may be involved in reflexes and adaptation to environmental stimuli.

Presynaptic modulation by neuromedin U of sensory synaptic transmission in rat spinal dorsal horn neurones

Neuromedin U (NMU) is a brain-gut peptide first isolated from the spinal cord. Recent studies on NMU and its receptors have suggested a role of NMU in sensory transmission. Here we report on the localization of NMU in sensory neurones, and the actions of NMU in the substantia gelatinosa (SG) and the deep layer of the dorsal horn (laminae III-V) in adult rat spinal cord slices using the patch-clamp technique. An immunohistochemical study revealed that NMU peptide was present in most of the dorsal root ganglion neurones. In the spinal cord, NMU-immunoreactive neurones were located in the deep layer (laminae III-V), but not in the SG. However, NMU-positive axon terminals were observed in the SG as well as the deep layer. Bath-applied NMU (10 microm) increased the frequency, but not amplitude, of miniature excitatory postsynaptic currents (mEPSCs) in the SG and deep layer neurones by 146 +/- 14% (P < 0.01, n = 17) and 174 +/- 21% (P < 0.01, n = 6), respectively, without inducing any postsynaptic membrane currents recorded in tetrodotoxin. On the other hand, NMU did not affect miniature inhibitory postsynaptic currents recorded in tetrodotoxin. These findings, taken together, suggest that NMU acts on the presynaptic terminals of the primary afferent fibres working as an autocrine/paracrine neuromodulator to increase mEPSC frequency of the SG and deep layer neurones. This may account for the spinal mechanisms of the NMU-induced hyperalgesia reported previously.