Appetite-boosting property of pro-melanin-concentrating hormone(131-165) (neuropeptide-glutamic acid-isoleucine) is associated with proteolytic resistance

In vivo uptake of a fluorescent conjugate of melanin-concentrating hormone in the rat brain

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide synthesized by posterior hypothalamic and incerto-hypothalamic neurons that project throughout the central nervous system. The MCHergic system modulates several important functions such as feeding behavior, mood and sleep. MCH exerts its biological functions through interaction with the MCHR-1 receptor, the only functional receptor present in rodents. The internalization process of MCHR-1 triggered by MCH binding was described in vitro in non-neuronal heterologous systems with over-expression of MCHR-1. Reports of in vivo MCHR-1 internalization dynamics are scarce, however, this is an important process to explore based on the critical functions of the MCHergic system. We had previously determined that 60 min after intracerebroventricular (i.c.v.) microinjections of MCH conjugated with fluorophore rhodamine (R-MCH), the dorsal and median raphe nucleus presented R-MCH positive labeled neurons. In the present work, we further studied the in vivo uptake process focusing on the distribution and time-dependent pattern of R-MCH positive cells 10, 20 and 60 min (T10, T20 and T60, respectively) after i.c.v. microinjection of R-MCH. We also explored this uptake process to see whether it was receptor- and clathrin-dependent and examined the phenotype of R-MCH positive cells and their proximity to MCHergic fibers. We found a great number of R-MCH positive cells with high fluorescence intensity in the lateral septum, nucleus accumbens and hippocampus at T20 and T60 (but not at T10), while a lower number with low intensity was observed in the dorsal raphe nucleus. At T20, in rats pre-treated with a MCHR-1 antagonist (ATC-0175) or with phenylarsine oxide (PAO), a clathrin endocytosis inhibitor, a robust decrease (> 50 %) of R-MCH uptake occurred in these structures. The R-MCH positive cells were identified as neurons (NeuN positive, GFAP negative) and some MCHergic fibers run in the vicinities of them. We concluded that neurons localized at structures that were close to the ventricular surfaces could uptake R-MCH in vivo through a receptor-dependent and clathrin-mediated process. Our results support volume transmission of MCH through the cerebrospinal fluid to reach distant targets. Finally, we propose that R-MCH would be an effective tool to study MCH-uptake in vivo.

Control of Feeding Behavior by Cerebral Ventricular Volume Transmission of Melanin-Concentrating Hormone

Classical mechanisms through which brain-derived molecules influence behavior include neuronal synaptic communication and neuroendocrine signaling. Here we provide evidence for an alternative neural communication mechanism that is relevant for food intake control involving cerebroventricular volume transmission of the neuropeptide melanin-concentrating hormone (MCH). Results reveal that the cerebral ventricles receive input from approximately one-third of MCH-producing neurons. Moreover, MCH cerebrospinal fluid (CSF) levels increase prior to nocturnal feeding and following chemogenetic activation of MCH-producing neurons. Utilizing a dual viral vector approach, additional results reveal that selective activation of putative CSF-projecting MCH neurons increases food intake. In contrast, food intake was reduced following immunosequestration of MCH endogenously present in CSF, indicating that neuropeptide transmission through the cerebral ventricles is a physiologically relevant signaling pathway for energy balance control. Collectively these results suggest that neural-CSF volume transmission signaling may be a common neurobiological mechanism for the control of fundamental behaviors.

Melanin-concentrating hormone in peripheral circulation in the human

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide with a well-characterised role in energy homeostasis and emergent roles in diverse physiologic functions such as arousal, mood and reproduction. Work to date has predominantly focused on its hypothalamic functions using animal models; however, little attention has been paid to its role in circulation in humans. The aims of this study were to (a) develop a radioimmunoassay for the detection of MCH in human plasma; (b) establish reference ranges for circulating MCH and (c) characterise the pattern of expression of circulating MCH in humans. A sensitive and specific RIA was developed and cross-validated by RP-HPLC and MS. The effective range was 19.5-1248 pg MCH/mL. Blood samples from 231 subjects were taken to establish a reference range of 19.5-55.4 pg/mL for fasting MCH concentrations. There were no significant differences between male and female fasting MCH concentrations; however, there were correlations between MCH concentrations and BMI in males and females with excess fat (P < 0.001 and P = 0.020) and between MCH concentrations and fat mass in females with excess fat (P = 0.038). Plasma MCH concentrations rose significantly after feeding in a group of older individuals (n = 50, males P = 0.006, females P = 0.023). There were no robust significant correlations between fasting or post-prandial MCH and resting metabolic rate, plasma glucose, insulin or leptin concentrations although there were correlations between circulating MCH and leptin concentrations in older individuals (P = 0.029). These results indicate that the role of circulating MCH may not be reflective of its regulatory hypothalamic role.

Zebrafish sexual behavior: role of sex steroid hormones and prostaglandins

Background

Mating behavior differ between sexes and involves gonadal hormones and possibly sexually dimorphic gene expression in the brain. Sex steroids and prostaglandin E₂ (PGE₂) have been shown to regulate mammalian sexual behavior. The present study was aimed at determining whether exposure to sex steroids and prostaglandins could alter zebrafish sexual mating behavior.

Methods

Mating behavior and successful spawning was recorded following exposure to 17β-estradiol (E2), 11-ketotestosterone (11-KT), prostaglandin D₂ (PGD₂) and PGE₂ via the water. qRT-PCR was used to analyze transcript levels in the forebrain, midbrain, and hindbrain of male and female zebrafish and compared to animals exposed to E2 via the water.

Results

Exposure of zebrafish to sex hormones resulted in alterations in behavior and spawning when male fish were exposed to E2 and female fish were exposed to 11-KT. Exposure to PGD_2, and PGE₂ did not alter mating behavior or spawning success. Determination of gene expression patterns of selected genes from three brain regions using qRT-PCR analysis demonstrated that the three brain regions differed in gene expression pattern and that there were differences between the sexes. In addition, E2 exposure also resulted in altered gene transcription profiles of several genes.

Conclusions

Exposure to sex hormones, but not prostaglandins altered mating behavior in zebrafish. The expression patterns of the studied genes indicate that there are large regional and gender-based differences in gene expression and that E2 treatment alter the gene expression pattern in all regions of the brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12993-015-0068-6) contains supplementary material, which is available to authorized users.

Narcolepsy patients have antibodies that stain distinct cell populations in rat brain and influence sleep patterns

Narcolepsy is a chronic sleep disorder, likely with an autoimmune component. During 2009 and 2010, a link between A(H1N1)pdm09 Pandemrix vaccination and onset of narcolepsy was suggested in Scandinavia. In this study, we searched for autoantibodies related to narcolepsy using a neuroanatomical array: rat brain sections were processed for immunohistochemistry/double labeling using patient sera/cerebrospinal fluid as primary antibodies. Sera from 89 narcoleptic patients, 52 patients with other sleep-related disorders (OSRDs), and 137 healthy controls were examined. Three distinct patterns of immunoreactivity were of particular interest: pattern A, hypothalamic melanin-concentrating hormone and proopiomelanocortin but not hypocretin/orexin neurons; pattern B, GABAergic cortical interneurons; and pattern C, mainly globus pallidus neurons. Altogether, 24 of 89 (27%) narcoleptics exhibited pattern A or B or C. None of the patterns were exclusive for narcolepsy but were also detected in the OSRD group at significantly lower numbers. Also, some healthy controls exhibited these patterns. The antigen of pattern A autoantibodies was identified as the common C-terminal epitope of neuropeptide glutamic acid-isoleucine/α-melanocyte-stimulating hormone (NEI/αMSH) peptides. Passive transfer experiments on rat showed significant effects of pattern A human IgGs on rapid eye movement and slow-wave sleep time parameters in the inactive phase and EEG θ-power in the active phase. We suggest that NEI/αMSH autoantibodies may interfere with the fine regulation of sleep, contributing to the complex pathogenesis of narcolepsy and OSRDs. Also, patterns B and C are potentially interesting, because recent data suggest a relevance of those brain regions/neuron populations in the regulation of sleep/arousal.

The role of melanin-concentrating hormone and its receptors in energy homeostasis

Extensive studies in rodents with melanin-concentrating hormone (MCH) have demonstrated that the neuropeptide hormone is a potent orexigen. Acutely, MCH causes an increase in food intake, while chronically it leads to increased weight gain, primarily as an increase in fat mass. Multiple knockout mice models have confirmed the importance of MCH in modulating energy homeostasis. Animals lacking MCH, MCH-containing neurons, or the MCH receptor all are resistant to diet-induced obesity. These genetic and pharmacologic studies have prompted a large effort to identify potent and selective MCH receptor antagonists, initially as tool compounds to probe pharmacology in models of obesity, with an ultimate goal to identify novel anti-obesity drugs. In animal models, MCH antagonists have consistently shown efficacy in reducing food intake acutely and inhibiting body-weight gain when given chronically. Five compounds have proceeded into clinical testing. Although they were reported as well-tolerated, none has advanced to long-term efficacy and safety studies.

Control of ventricular ciliary beating by the melanin concentrating hormone-expressing neurons of the lateral hypothalamus: a functional imaging survey

The cyclic peptide Melanin Concentrating Hormone (MCH) is known to control a large number of brain functions in mammals such as food intake and metabolism, stress response, anxiety, sleep/wake cycle, memory, and reward. Based on neuro-anatomical and electrophysiological studies these functions were attributed to neuronal circuits expressing MCHR1, the single MCH receptor in rodents. In complement to our recently published work (1) we provided here new data regarding the action of MCH on ependymocytes in the mouse brain. First, we establish that MCHR1 mRNA is expressed in the ependymal cells of the third ventricle epithelium. Second, we demonstrated a tonic control of MCH-expressing neurons on ependymal cilia beat frequency using in vitro optogenics. Finally, we performed in vivo measurements of CSF flow using fluorescent micro-beads in wild-type and MCHR1-knockout mice. Collectively, our results demonstrated that MCH-expressing neurons modulate ciliary beating of ependymal cells at the third ventricle and could contribute to maintain cerebro-spinal fluid homeostasis.

Peripheral injections of melanin-concentrating hormone receptor 1 antagonist S38151 decrease food intake and body weight in rodent obesity models

The compound S38151 is a nanomolar antagonist that acts at the melanin-concentrating hormone receptor 1 (MCH(1)). S38151 is more stable than its purely peptide counterpart, essentially because of the blockade of its N-terminus. Therefore, its action on various models of obesity was studied. Acute intra-cerebroventricular (i.c.v.) administration of S38151 in wild-type rats counteracted the effect of the stable precursor of melanin-concentrating hormone (MCH), NEI-MCH, in a dose-dependent manner (from 0.5 to 50 nmol/kg). In genetically obese Zucker fa/fa rats, daily i.c.v. administration of S38151 induced dose-dependent (5, 10, and 20 nmol/kg) inhibition of food intake, water intake, and body weight gain, as well as increased motility (maximal effect observed at 20 nmol/kg). In Zucker fa/fa rats, intraperitoneal injection of S38151 (30 mg/kg) induced complete inhibition of food consumption within 1 h. Daily intraperitoneal injection of S38151 (10 and 30 mg/kg) into genetically obese ob/ob mice or diet-induced obese mice is able to limit body weight gain. Furthermore, S38151 administration (10 and 30 mg/kg) does not affect food intake, water intake, or body weight gain in MCHR1-deleted mice, demonstrating that its effects are linked to its interaction with MCH(1). These results validate MCH(1) as a target of interest in obesity. S38151 cannot progress to the clinical phase because it is still too poorly stable in vivo.

New aspects of melanocortin signaling: a role for PRCP in α-MSH degradation

The role of the central melanocortin system in the regulation of energy metabolism has received much attention during the past decade since gene mutations of key components in melanocortin signaling cause monogenic forms of obesity in animals and humans. In the arcuate nucleus of the hypothalamus the prohormone proopiomelanocortin (POMC) is posttranslationally cleaved to produce α-melanocyte stimulating hormone (α-MSH), a peptide with anorexigenic effects upon activation of the melanocortin receptors (MCRs). α-MSH undergoes extensive post-translational processing and its in vivo activity is short lived due to rapid degradation. The enzymatic process that controls α-MSH inactivation is incompletely understood. Recent evidence suggests that prolyl carboxypeptidase (PRCP) is an enzyme responsible for α-MSH degradation. As for many key melanocortin peptides, gene mutation of PRCP causes a change in the metabolic phenotype of rodents. This review summarizes the current knowledge on the melanocortin system with particular focus on PRCP, a newly discovered component of the melanocortin system.

MCH and feeding behavior-interaction with peptidic network

Numerous works associate the MCH peptide, and the hypothalamic neurons that produce it, to the feeding behavior and energy homeostasis. It is commonly admitted that MCH is an orexigenic peptide, and MCH neurons could be under the control of arcuate NPY and POMC neurons. However, the literature data is not always concordant. In particular questions about the intrahypothalamic circuit involving other neuropeptides and about the mechanisms through which MCH could act are not yet clearly answered. For example, which receptors mediate a MCH response to NPY or alpha-MSH, does MCH act alone, is there any local anatomical organization within the tuberal LHA? A review of the current literature is then needed to help focus attention on these unresolved and often neglected issues.

S38151 [p-guanidinobenzoyl-[Des-Gly(10)]-MCH(7-17)] is a potent and selective antagonist at the MCH(1) receptor and has anti-feeding properties in vivo

Structure-activity relationships studies have established the minimal sequence of melanin-concentrating hormone (MCH) that retains full agonist potency at the MCH(1), to be the dodecapeptide MCH(6-17). The alpha-amino function is not required for activity since arginine(6) can be replaced by p-guanidinobenzoyl, further improving activity. We report that the deletion of glycine in this short potent agonist (EC(50) 3.4nM) turns it into a potent and new MCH(1) antagonist (S38151, K(B) 4.3nM in the [(35)S]-GTPgammaS binding assay), which is selective versus MCH(2). A compared Ala-scan of the agonist and antagonist sequences reveals major differences in the residues that are mandatory for affinity, including arginine(11) and tyrosine(13) for the agonist and leucine(9) for the antagonist, whereas methionine(8) was necessary for both agonist and antagonist activities. A complete molecular study of the antagonist behavior is described in the present report, with a particular focus on the description of several analogues, attempting to find structure-activity relationships. Finally, S38151 antagonizes food intake when injected intra-cerebroventricularly in the rat. This is in agreement with the in vitro data and with our previous demonstration of a good correlation between in vitro and in vivo data on MCH(1) agonists.

Anatomy, function and regulation of neuropeptide EI (NEI)

This review is focused on the anatomy, role and behavior of neuropeptide-glutamic acid-isoleucine (NEI), providing a general report on the neuropeptide. In addition to hormone release, this peptide also takes part in the regulation of grooming behavior and locomotor activity. NEI is produced by cleavage of prepro-MCH that probably takes place at the Lys(129)-Arg(130) and Arg(145)-Arg(146) sites (the glycine residue on the C-terminus of NEI strongly suggests that this peptide is amidated). This same prohormone is also the precursor of MCH, widely studied in relation to food and water intake, and NGE, of which little is known. NEI and MCH are extensively colocalized throughout the central nervous system (CNS), and NEI is also present in peripheral tissues. The latter is also effective in stimulating luteinizing hormone (LH) release and, to a lesser extent, FSH from primary pituitary cell cultures. In addition to releasing LH from the medial eminence, NEI also acts directly on gonadotropes. Lastly, this neuropeptide also acts at the CNS level on gonadotropin-releasing hormone (GnRH) neurons.

The melanin-concentrating hormone system and its physiological functions

Melanin-concentrating hormone (MCH) is a neuropeptide that was originally isolated from salmon pituitary where it causes pigment aggregation. MCH is also abundantly present in mammalian neurons and expressed in the lateral hypothalamus and zona incerta, brain regions that are known to be at the center of feeding behavior. MCH binds to and activates two G protein-coupled receptors, MCH1R and MCH2R. Although MCH2R is non-functional in rodents, genetic and pharmacological studies have demonstrated that rodent MCH1R is involved in the regulation of feeding behavior and energy balance. Unexpectedly, some antagonists have provided evidence that MCH signaling participates in the regulation of other processes, such as emotion and stress. The discovery of MCH receptors has extensively promoted the progress of MCH studies and may represent an ideal example of how deorphanized receptors can open new directions toward more detailed physiological studies.

Human Th2 cells selectively express the orexigenic peptide, pro-melanin-concentrating hormone

Th1 and Th2 cells represent the two main functional subsets of CD4(+) T helper cell, and are defined by their cytokine expression. Human Th1 cells express IFNgamma, whilst Th2 cells express IL-4, IL-5, and IL-13. Th1 and Th2 cells have distinct immunological functions, and can drive different immunopathologies. Here, we show that in vitro-differentiated human Th2 cells highly selectively express the gene for pro-melanin-concentrating hormone (PMCH), using real-time RT-PCR, enzyme immunoassay, and Western blot analysis. PMCH encodes the prohormone, promelanin-concentrating hormone (PMCH), which is proteolytically processed to produce several peptides, including the orexigenic hormone melanin-concentrating hormone (MCH). PMCH expression by Th2 cells was activation responsive and increased throughout the 28-day differentiation in parallel with the expression of the Th2 cytokine genes. MCH immunoreactivity was detected in the differentiated Th2 but not Th1 cell culture supernatants after activation, and contained the entire PMCH protein, in addition to several smaller peptides. Human Th1 and Th2 cells were isolated by their expression of IFNgamma and CRTH2, respectively, and the ex vivo Th2 cells expressed PMCH upon activation, in contrast to the Th1 cells. Because Th2 cells are central to the pathogenesis of allergic diseases including asthma, expression of PMCH by activated Th2 cells in vivo may directly link allergic inflammation to energy homeostasis and may contribute to the association between asthma and obesity.

Effect of β-adrenoceptors on the behaviour induced by the neuropeptide glutamic acid isoleucine amide

Excessive grooming behaviour is induced by intracerebroventricular injections of the neuropeptide glutamic acid isoleucine amide (neuropeptide-EI), via the activation of A-10 dopaminergic neurons and the noradrenergic system. Our object was to study the latter system involved in these behaviours, using male Wistar rats weighing 250-300 g with i.c.v. implants. The results show that all the adrenoceptor antagonists "per se" do not affect excessive grooming behaviour or motor activity. Intracerebroventricular administration of propranolol, a general beta-adrenoceptor antagonist, before neuropeptide-EI, inhibited the induced excessive grooming behaviour in a dose dependent manner. Metoprolol, a beta(1)-adrenoceptor antagonist, also blocked this behaviour. However, intracerebroventricular injections of phentolamine, an alpha-adrenoceptor antagonist, and ((+/-)-1-[2,3-(Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol), a beta(2)-adrenoceptor antagonist, had no effect on the behaviour induced by neuropeptide-EI induced behaviour for any of the doses tested. On the other hand, isoproterenol, a general beta-adrenoceptor agonist and dobutamine, a beta(1)-adrenoceptor agonist, both elicited similar behaviours as those induced by neuropeptide-EI. These results support the hypothesis that a relationship exists between neuropeptide-EI and beta-adrenoceptors, more specifically the beta(1)-adrenoceptor, as found with other similar endogenous peptides such as neurotensin, cholecystin, substance P and alpha-melanocyte stimulating hormone. Hence, neuropeptide-EI could probably be exerting a neuromodulating effect on the central nervous system.

Effect of ppMCH derived peptides on PBMC proliferation and cytokine expression

The mRNA encoding prepro-Melanin concentrating hormone (ppMCH) is mainly expressed in the central nervous system but has also been detected at lower amount in many peripheral tissues including spleen and thymus. At the peptide level however, several forms of the precursor can be detected in these tissues and are sometimes expressed at similar levels compared to brain. In the present work, we have studied the in vitro action of a wide range of concentration (1 nM to 1 microM) of the different peptides encoded by ppMCH i.e. neuropeptide glycine-glutamic acid (NGE), neuropeptide glutamic acid-isoleucine (NEI), Melanin concentrating hormone (MCH) and the dipeptide NEI-MCH on peripheral blood mononuclear cells (PBMC) proliferation and cytokine production following anti-CD3 stimulation. Among them only MCH decreased PBMC proliferation with a maximal effect of 35% at 100 nM. Moreover as demonstrated by using ELISA, MCH significantly decreases IL-2 production by 25% but not IL-4, INF-gamma or TNF-alpha expression. Interestingly, exogenous IL-2 decreases significantly MCH-mediated inhibition, suggesting that it is an important downstream mediator of MCH action. Finally, we showed that after 7 to 9 days of incubation, MCH also inhibits proliferation of non-stimulated PBMC. Altogether, these data demonstrate that fully mature MCH modulates proliferation of anti-CD3 stimulated PBMC partially through regulation of IL-2 production.

Role of neuropeptides in appetite regulation and obesity--a review

Obesity represents the most prevalent nutritional problem worldwide which in the long run predisposes to development of diabetes mellitus, hypertension, endometrial carcinoma, osteoarthritis, gall stones and cardiovascular diseases. Despite significant reductions in dietary fat consumption, the prevalence of obesity is on a rise and is taking on pandemic proportions. Obesity develops when energy intake exceeds energy expenditure over time. Recently, a close evolutionary relationship between the peripheral and hypothalamic neuropeptides has become apparent. The hypothalamus being the central feeding organ mediates regulation of short-term and long-term dietary intake via synthesis of various orexigenic and anorectic neuropeptides. The structure and function of many hypothalamic peptides (neuropeptide Y (NPY), melanocortins, agouti-related peptide (AGRP), cocaine and amphetamine regulated transcript (CART), melanin concentrating hormone (MCH), orexins have been characterized in rodent models The peripheral neuropeptides such as cholecystokinin (CCK), ghrelin, peptide YY (PYY3-36), amylin, bombesin regulate important gastrointestinal functions such as motility, secretion, absorption, provide feedback to the central nervous system on availability of nutrients and may play a part in regulating food intake. The pharmacological potential of several endogenous peripheral peptides released prior to, during and/or after feeding are being explored. Long-term regulation is provided by the main circulating hormones leptin and insulin. These systems implicated in hypothalamic appetite regulation provide potential targets for treatment of obesity which could potentially pass into clinical development in the next 5 years. This review summarizes various effects and interrelationship of these central and peripheral neuropeptides in metabolism, obesity and their potential role as targets for treatment of obesity.

The melanocortins and melanin-concentrating hormone in the central regulation of feeding behavior and energy homeostasis

A number of different neuropeptides exert powerful concerted controls on feeding behavior and energy balance, most of them being produced in hypothalamic neuronal networks under stimulation by anabolic and catabolic peripheral hormones such as ghrelin and leptin, respectively. These peptide-expressing neurons interconnect extensively to integrate the multiple opposing signals that mediate changes in energy expenditure. In the present review I have summarized our current knowledge about two key peptidic systems involved in regulating appetite and energy homeostasis, the melanocortin system (alpha-MSH, agouti and Agouti-related peptides, MC receptors and mahogany protein) and the melanin-concentrating hormone system (proMCH-derived peptides and MCH receptors) that contribute to satiety and feeding-initiation, respectively, with concurrent effects on energy expenditure. I have focused particularly on recent data concerning transgenic mice and the ongoing development of MC/MCH receptor antagonists/agonists that may represent promising drugs to treat human eating disorders on both sides of the energy balance (anorexia, obesity).

SVK14 cells express an MCH binding site different from the MCH1 or MCH2 receptor

Melanin-concentrating hormone (MCH) is a cyclic peptide, mainly involved in the regulation of skin pigmentation in teleosts and feeding behavior in mammals. The human keratinocyte SVK14 cell line has been previously shown to express binding sites for the MCH analog [125I]-[Phe13,3-iodo-Tyr19]MCH. We report here that: (1) this binding site similarly recognized [125I]-[3-iodo-Tyr13]MCH; (2) its pharmacological profile clearly differed from those observed at the two human MCH receptor subtypes, MCH1-R and MCH2-R; (3) MCH did not induce any effect on second messenger systems (including cAMP, calcium, and MAP kinase signaling pathways), and (4) no mRNAs corresponding to the MCH receptors were found. In conclusion, the binding site characterized in the SVK14 cell line is distinct from the MCH1 and MCH2 receptors and deserves therefore further investigation.