Neuromedin U can exert colon-specific, enteric nerve-mediated prokinetic activity, via a pathway involving NMU1 receptor activation

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

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

Neuromedin U is a gut peptide that alters oral glucose tolerance by delaying gastric emptying via direct contraction of the pylorus and vagal-dependent mechanisms

The gut-brain peptide neuromedin U (NMU) decreases food intake and body weight and improves glucose tolerance. Here, we characterized NMU as an enteropeptide and determined how it impacts glucose excursion. NMU was expressed predominantly in the proximal small intestine, and its secretion was triggered by ingestion of a mixed meal. Although a single peripheral injection of NMU in C57BL/6NRj mice prevented the rise of glycemia upon an oral but not an intraperitoneal load of glucose, it unexpectedly prevented insulin secretion, only slightly improved peripheral insulin sensitivity, and barely reduced intestinal glucose absorption. Interestingly, peripheral administration of NMU abrogated gastric emptying. NMU receptors 1 and 2 were detected in pyloric muscles and NMU was able to directly induce pyloric contraction in a dose-dependent manner ex vivo in isometric chambers. Using a modified glucose tolerance test, we demonstrate that improvement of oral glucose tolerance by NMU was essentially, if not exclusively, because of its impact on gastric emptying. Part of this effect was abolished in vagotomized (VagoX) mice, suggesting implication of the vagus tone. Accordingly, peripheral injection of NMU was associated with increased number of c-FOS-positive neurons in the nucleus of the solitary tract, which was partly prevented in VagoX mice. Finally, NMU kept its ability to improve oral glucose tolerance in obese and diabetic murine models. Together, these data demonstrate that NMU is an enteropeptide that prevents gastric emptying directly by triggering pylorus contraction and indirectly through vagal afferent neurons. This blockade consequently reduces intestinal nutrient absorption and thereby results in an apparent improved tolerance to oral glucose challenge.-Jarry, A.-C., Merah, N., Cisse, F., Cayetanot, F., Fiamma, M.-N., Willemetz, A., Gueddouri, D., Barka, B., Valet, P., Guilmeau, S., Bado, A., Le Beyec, J., Bodineau, L., Le Gall, M. Neuromedin U is a gut peptide that alters oral glucose tolerance by delaying gastric emptying via direct contraction of the pylorus and vagal-dependent mechanisms.

Differential effects of selective agonists of neuromedin U1 and U2 receptors in obese and diabetic mice

BACKGROUND AND PURPOSE

Neuromedin U (NmU) may be a novel target for obesity treatment owing to its anorectic and energy expenditure enhancing effects. Although two receptors, NMU1 and NMU2, are both responsible for the NmU-mediated anti-obesity effects, the receptor agonist with the most appropriate profiles for treating obesity and diabetes in terms of efficacy and safety is as yet unknown. Thus, we developed and evaluated novel NMU1/2 receptor-selective agonists.

EXPERIMENTAL APPROACH

Efficacy and safety were assessed in mice with diet-induced obesity (DIO) and those with leptin-deficient diabetes (ob/ob) through repeated peripheral administration of selective agonists to NMU1 (NMU-6102) and NMU2 (NMU-2084), along with non-selective NMU1/2 agonists (NMU-0002 and NMU-6014). We also performed immunohistochemistry for c-Fos protein expression in the brain to probe their mechanisms of action.

KEY RESULTS

Although both non-selective NMU1/2 agonists and the NMU2-selective agonist had high efficacy compared with the NMU1-selective agonist, only the NMU2-selective agonist led to relatively low adverse effects, such as diarrhoea, in DIO mice. However, the non-selective NMU1/2 agonist and the NMU1-selective agonist, but not the NMU2-selective agonist, were effective in diabetic ob/ob mice. Mechanistically, NMU2-selective agonists preferentially activate pro-opiomelanocortin neurons in the hypothalamic arcuate nucleus but not in the paraventricular nucleus.

CONCLUSIONS AND IMPLICATIONS

These results suggest that an NMU2 receptor-selective agonist may be a well-balanced drug for the treatment of obesity and that an NMU1 receptor-selective agonist may also be beneficial for treating obesity and diabetes once its side effects are minimized.

PEGylated neuromedin U-8 shows long-lasting anorectic activity and anti-obesity effect in mice by peripheral administration

Neuromedin U (NMU) is a neuropeptide found in the brain and gastrointestinal tract. The NMU system has been shown to regulate energy homeostasis by both a central and a peripheral mechanism. Peripheral administration of human NMU-25 was recently shown to inhibit food intake in mice. We examined the possibility that other NMU-related peptides exert an anorectic activity by intraperitoneal (i.p.) administration. We found that rat NMU-23 and its structurally-related peptide rat neuromedin S (NMS) significantly reduced food intake in lean mice, whereas NMU-8, an active fragment of the octapeptide sequence conserved in porcine, human and mouse NMU, had no effect. When rat NMU-23, NMU-8, and rat NMS were covalently conjugated to polyethylene glycol (PEG) (PEGylation) at the N-terminus of these peptides, PEGylated NMU-8 showed the most long-lasting and robust anorectic activity. The exploration of the linker between NMU-8 and PEG using hetero-bifunctional chemical cross-linkers led to an identification of PEGylated NMU-8 analogs with higher affinity for NMU receptors and with more potent anorectic activity in lean mice. The PEGylated NMU-8 showed potent and robust anorectic activity and anti-obesity effect in diet-induced obesity (DIO) mice by once-daily subcutaneous (s.c.) administration. These results suggest that PEGylated NMU-8 has the therapeutic potential for treatment of obesity.

Defining the transcriptomic landscape of the developing enteric nervous system and its cellular environment

BACKGROUND

Motility and the coordination of moving food through the gastrointestinal tract rely on a complex network of neurons known as the enteric nervous system (ENS). Despite its critical function, many of the molecular mechanisms that direct the development of the ENS and the elaboration of neural network connections remain unknown. The goal of this study was to transcriptionally identify molecular pathways and candidate genes that drive specification, differentiation and the neural circuitry of specific neural progenitors, the phox2b expressing ENS cell lineage, during normal enteric nervous system development. Because ENS development is tightly linked to its environment, the transcriptional landscape of the cellular environment of the intestine was also analyzed.

RESULTS

Thousands of zebrafish intestines were manually dissected from a transgenic line expressing green fluorescent protein under the phox2b regulatory elements [Tg(phox2b:EGFP) ^w37 ]. Fluorescence-activated cell sorting was used to separate GFP-positive phox2b expressing ENS progenitor and derivatives from GFP-negative intestinal cells. RNA-seq was performed to obtain accurate, reproducible transcriptional profiles and the unbiased detection of low level transcripts. Analysis revealed genes and pathways that may function in ENS cell determination, genes that may be identifiers of different ENS subtypes, and genes that define the non-neural cellular microenvironment of the ENS. Differential expression analysis between the two cell populations revealed the expected neuronal nature of the phox2b expressing lineage including the enrichment for genes required for neurogenesis and synaptogenesis, and identified many novel genes not previously associated with ENS development. Pathway analysis pointed to a high level of G-protein coupled pathway activation, and identified novel roles for candidate pathways such as the Nogo/Reticulon axon guidance pathway in ENS development.

CONCLUSION

We report the comprehensive gene expression profiles of a lineage-specific population of enteric progenitors, their derivatives, and their microenvironment during normal enteric nervous system development. Our results confirm previously implicated genes and pathways required for ENS development, and also identify scores of novel candidate genes and pathways. Thus, our dataset suggests various potential mechanisms that drive ENS development facilitating characterization and discovery of novel therapeutic strategies to improve gastrointestinal disorders.

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.

Neuromedin U inhibits food intake partly by inhibiting gastric emptying

Neuromedin U (NMU) is a gut-brain peptide, implicated in energy and glucose homeostasis via the peripherally expressed NMU receptor 1 (NMUR1) and the central NMUR2. We investigated the effects of a lipidated NMU analog on gastric emptying (GE), glucose homeostasis and food intake to evaluate the use of a NMU analog as drug candidate for treatment of obesity and diabetes. Finally mRNA expression of NMU and NMUR1 in the gut and NMUR2 in the hypothalamus was investigated using a novel chromogen-based in situ hybridization (ISH) assay. Effects on food intake (6 and 18 h post dosing) were addressed in both mice and rats. The effects on GE and glycaemic control were assessed in mice, immediately after the first dose and after seven days of bidaily (BID) dosing. The lipidated NMU analog exerted robust reductions in GE and food intake in mice and improved glycaemic control when measured immediately after the first dose. No effects were observed after seven days BID. In rats, the analog induced only a minor effect on food intake. NMU mRNA was detected in the enteric nervous system throughout the gut, whereas NMUR1 was confined to the lamina propria. NMUR2 was detected in the paraventricular (PVN) and arcuate nuclei (ARC) in mice, with a reduced expression in ARC in rats. In summary, the anorectic effect of the lipidated NMU is partly mediated by a decrease in gastric emptying which is subject to tachyphylaxis after continuous dosing. Susceptibility to NMU appears to be species specific.

Neuromedin U: a multifunctional neuropeptide with pleiotropic roles

BACKGROUND

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

CONTENT

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

SUMMARY

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

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

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

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.

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.

Nmur1-/- mice are not protected from cutaneous inflammation

Neuromedin U (Nmu) is a neuropeptide expressed primarily in the gastrointestinal tract and central nervous system. Previous reports have identified two G protein-coupled receptors (designated Nmur1 and Nmur2) that bind Nmu. Recent reports suggest that Nmu mediates immune responses involving mast cells, and Nmur1 has been proposed to mediate these responses. In this study, we generated mice with an Nmur1 deletion and then profiled the responses of these mice in a cutaneous inflammation model utilizing complete Freund's adjuvant (CFA). We report here that mice lacking Nmur1 had normal inflammation responses with moderate changes in serum cytokines compared to Nmur1(+/+) littermates. Although differences in IL-6 were observed in mice lacking Nmu peptide, these mice exhibited a normal response to CFA. Our data argues against a major role for Nmur1 in mediating the reported inflammatory functions of NmU.