Melanin-concentrating Hormone Receptor Research Articles

Analysis of ciliary status via G-protein-coupled receptors localized on primary cilia.

G-protein-coupled receptors (GPCRs) comprise the largest and most diverse cell surface receptor family, with more than 800 known GPCRs identified in the human genome. Binding of an extracellular cue to a GPCR results in intracellular G protein activation, after which a sequence of events, can be amplified and optimized by selective binding partners and downstream effectors in spatially discrete cellular environments. Because GPCRs are widely expressed in the body, they help to regulate an incredible range of physiological processes from sensation to growth to hormone responses. Indeed, it is estimated that ∼ 30% of all clinically approved drugs act by binding to GPCRs. The primary cilium is a sensory organelle composed of a microtubule axoneme that extends from the basal body. The ciliary membrane is highly enriched in specific signaling components, allowing the primary cilium to efficiently convey signaling cascades in a highly ordered microenvironment. Recent data demonstrated that a limited number of non-olfactory GPCRs, including somatostatin receptor 3 and melanin-concentrating hormone receptor 1 (MCHR1), are selectively localized to cilia on several mammalian cell types including neuronal cells. Utilizing cilia-specific cell biological and molecular biological approaches, evidence has accumulated to support the biological importance of ciliary GPCR signaling followed by cilia structural changes. Thus, cilia are now considered a unique sensory platform for integration of GPCR signaling toward juxtaposed cytoplasmic structures. Herein, we review ciliary GPCRs and focus on a novel role of MCHR1 in ciliary length control that will impact ciliary signaling capacity and neuronal function.

Ciliary melanin-concentrating hormone receptor 1 (MCHR1) is widely distributed in the murine CNS in a sex-independent manner.

Melanin-concentrating hormone (MCH) is a ubiquitous vertebrate neuropeptide predominantly synthesized by neurons of the diencephalon that can act through two G protein-coupled receptors, called MCHR1 and MCHR2. The expression of Mchr1 has been investigated in both rats and mice, but its synthesis remains poorly described. After identifying an antibody that detects MCHR1 with high specificity, we employed immunohistochemistry to map the distribution of MCHR1 in the CNS of rats and mice. Multiple neurochemical markers were also employed to characterize some of the neuronal populations that synthesize MCHR1. Our results show that MCHR1 is abundantly found in a subcellular structure called the primary cilium, which has been associated, among other functions, with the detection of free neurochemical messengers present in the extracellular space. Ciliary MCHR1 was found in a wide range of areas, including the olfactory bulb, cortical mantle, striatum, hippocampal formation, amygdala, midline thalamic nuclei, periventricular hypothalamic nuclei, midbrain areas, and in the spinal cord. No differences were observed between male and female mice, and interspecies differences were found in the caudate-putamen nucleus and the subgranular zone. Ciliary MCHR1 was found in close association with several neurochemical markers, including tyrosine hydroxylase, calretinin, kisspeptin, estrogen receptor, oxytocin, vasopressin, and corticotropin-releasing factor. Given the role of neuronal primary cilia in sensing free neurochemical messengers in the extracellular fluid, the widespread distribution of ciliary MCHR1, and the diverse neurochemical populations who synthesize MCHR1, our data indicate that nonsynaptic communication plays a prominent role in the normal function of the MCH system.

PyRod Enables Rational Homology Model-based Virtual Screening Against MCHR1.

Several encouraging pre‐clinical results highlight the melanin‐concentrating hormone receptor 1 (MCHR1) as promising target for anti‐obesity drug development. Currently however, experimentally resolved structures of MCHR1 are not available, which complicates rational drug design campaigns. In this study, we aimed at developing accurate, homologymodel‐based 3D pharmacophores against MCHR1. We show that traditional approaches involving docking of known active small molecules are hindered by the flexibility of binding pocket residues. Instead, we derived three‐dimensional pharmacophores from molecular dynamics simulations by employing our novel open‐source software PyRod. In a retrospective evaluation, the generated 3D pharmacophores were highly predictive returning up to 35 % of active molecules and showing an early enrichment (EF1) of up to 27.6. Furthermore, PyRod pharmacophores demonstrate higher sensitivity than ligand‐based pharmacophores and deliver structural insights, which are key to rational lead optimization.

The ciliary localized GPCR, MCHR1, modulates odor responses in the olfactory bulb

The sense of smell is essential for maintaining full human health and quality of life. It plays an important role in the detection of environmental dangers as well guiding decisions such as what foods to eat. However, olfactory processing is influenced by the physiological state of an organism. Physiological changes such can be integrated in the hypothalamus, through populations of neurons expressing various neuropeptides. One of these peptides is melanin‐concentrating hormone (MCH) which functions in both promoting feeding and sleep. Neurons expressing MCH project to several areas of the brain including the olfactory bulb (OB), where the MCH receptor, MCHR1, a g‐protein coupled receptor, is expressed. MCH signaling has been implicated in olfactory driven behaviors, however the mechanism by which it does so is unknown. In rodents, there is a single MCH receptor, MCHR1, which is enriched in neuronal primary cilia. To better understand the mechanism by which MCHR1 signaling affects olfactory behaviors we have first analyzed its distribution in the OB. Using antibody labeling, we find that MCHR1 localizes to cilia of interneurons in the granule cell and glomerular layers. To further confirm this, and generate a potential tool for future studies, we used CRISPR/CAS9 to fuse mCherry to the n‐terminus of MCHR1 (mCherry:MCHR1). Expression of mCherry:MCHR1 matches that of endogenous MCHR1, localizing to the primary cilium of granule cells and a subset of periglomerular cells. MCHR1, and mCherry:MCHR1, is not detected in the primary cilia of mitral cells, the primary output neurons of the olfactory bulb. To test the neuromodulatory role of MCHR1 in olfactory signaling, we have performed functional imaging experiments of the OB in response to odorant stimulation. Using epifluorescence calcium imaging, we find that glomerular responses of mitral/tufted cells are enhanced following administration of an MCHR1 antagonist, SNAP‐94847, (t(157) = 5.425, p <0.0001) while application of MCH decreases glomerular responses (t(99) = 10.98, p <0.0001). Together these data suggest that the ciliary GPCR, MCHR1 contributes to modulation of olfactory function. Furthermore, our newly generated mouse line will aid in studying the role of MCHR1 in other brain regions and will aid in determining the importance of ciliary localization of specific GPCRs in modulating neuronal function.Support or Funding InformationSupport was provided by R00DC013555 and pilot grans from the University of Florida Center for Smell and Taste, and a UF MBI pilot project (JCM), T32DC015994 (KRJ) F31DC 016485 (JMR) and R01DC004553 (RRR)

Comparison of tyrosinase antibody, tyrosinase-related protein-1 and -2 antibodies, melanin-concentrating hormone receptor antibody levels with autologous serum skin test and autologous plasma skin test results in patients with vitiligo.

IntroductionAlthough the exact etiopathogenesis of vitiligo is unknown, the autoimmunity hypothesis is much in evidence. The autologous serum skin test (ASST) and autologous plasma skin test (APST) are in vivo methods used in the diagnosis of some autoimmune diseases, which are easy and inexpensive to perform.AimIn this study, we investigated whether or not ASST and APST could determine autoimmunity in patients with vitiligo.Material and methodsIn this study, 30 vitiligo patients presenting to the dermatology outpatient clinic and 30 healthy volunteers without any known autoimmune diseases were included. Antibodies such as tyrosinase, tyrosinase-related protein-1 (TYRP1), tyrosinase-related protein-2 (TYRP2) and melanin-concentrating hormone receptor 1 (MCHR1) antibodies determined to be associated with vitiligo were examined. In addition, the association of these antibodies with the positivity of ASST and APST, which were suggested to be associated with autoimmunity, were examined.ResultsIn our study, tyrosinase antibody was found to be significantly higher in vitiligo patients. ASST was positive in 12 (40%) patients with vitiligo and 8 (26.6%) control subjects. APST was positive in 8 (26.6%) of the patients with vitiligo and in 2 (6.6%) of the controls, and there was a significant difference between the groups in terms of APST positivity (p = 0.032). In addition, in our study, a significant correlation was found between TYRP1 antibody positivity and APST positivity in the patient group (p = 0.005).ConclusionsThese findings suggest that we may use APST to investigate the autoimmune etiopathogenesis of vitiligo.

Identification of a new small molecule chemotype of Melanin Concentrating Hormone Receptor-1 antagonists using pharmacophore-based virtual screening

MCH receptor is a G protein-coupled receptor with two subtypes R1 and R2. Many studies have demonstrated the role of MCH-R1 in feeding and energy homeostasis. It has been proven that oral administration of small molecule MCH-R1 antagonists significantly reduces food intake and causes a dose-dependent weight loss. In this study, two ligand-based pharmacophores were developed and validated based on recently published MCH-R1 antagonists with diverse structures. Successful pharmacophores had one hydrogen bond acceptor, one positive ionizable, one ring aromatic and two or three hydrophobic groups. These 3D-QSAR models were used for virtual screening of the ZINC chemical database resulting in the identification of nine compounds with more than 50% displacement of radiolabeled MCH at a 20 μM concentration. Moreover, four of these compounds showed antagonistic activities in Aequorin functional assay, including MH-3 which is the first MCH-R1 antagonist based on a diazaspiro[4.5]decane scaffold. The most active compounds were also docked into our previously published MCH-R1 homology model to gain insights into their binding determinants. These compounds could represent a viable starting scaffold for the design of potent MCH-R1 antagonists with improved pharmacokinetic properties as an effective treatment for obesity.

Melanin-concentrating hormone is not involved in luminescence emission in the velvet belly lanternshark, Etmopterus spinax

Luminous deep-sea etmopterid sharks use hormonal control to regulate bioluminescence. Melatonin and prolactin trigger light emission and, conversely, α-melanocyte stimulating hormone actively reduces ongoing luminescence. Interestingly, these hormones are also known as regulators of skin pigment motion in teleost fish and epipelagic elasmobranchs. On the other hand, the melanin-concentrating hormone (MCH) is another regulator of the skin pigment motion in fish melanophores. Here, we studied the putative effect of MCH on the light emission control of the velvet belly lanternshark, Etmopterus spinax (Etmopteridae). In parallel, the presence of the MCH receptor in our model is investigated through database searches. Our results show that MCH is not involved in the bioluminescence triggering in the velvet belly lanternshark. Moreover, no MCH receptor transcript was found in a specific transcriptome of the luminous ventral skin of E. spinax.

Melanin Concentrating Hormone Signaling Deficits in Schizophrenia: Association with Memory and Social Impairments and Abnormal Sensorimotor Gating

BackgroundEvidence from anatomical, pharmacological, and genetic studies supports a role for the neuropeptide melanin concentrating hormone system in modulating emotional and cognitive functions. Genome-wide association studies revealed a potential association between the melanin concentrating hormone receptor (MCHR1) gene locus and schizophrenia, and the largest genome-wide association study conducted to date shows a credible genome-wide association.MethodsWe analyzed MCHR1 and pro-melanin concentrating hormone RNA-Seq expression in the prefrontal cortex in schizophrenia patients and healthy controls. Disruptions in the melanin concentrating hormone system were modeled in the mouse brain by germline deletion of MCHR1 and by conditional ablation of melanin concentrating hormone expressing neurons using a Cre-inducible diphtheria toxin system.ResultsMCHR1 expression is decreased in the prefrontal cortex of schizophrenia samples (false discovery rate (FDR) P < .05, CommonMind and PsychEncode combined datasets, n = 901) while pro-melanin concentrating hormone is below the detection threshold. MCHR1 expression decreased with aging (P = 6.6E-57) in human dorsolateral prefrontal cortex. The deletion of MCHR1 was found to lead to behavioral abnormalities mimicking schizophrenia-like phenotypes: hyperactivity, increased stereotypic and repetitive behavior, social impairment, impaired sensorimotor gating, and disrupted cognitive functions. Conditional ablation of pro-melanin concentrating hormone neurons increased repetitive behavior and produced a deficit in sensorimotor gating.ConclusionsOur study indicates that early disruption of the melanin concentrating hormone system interferes with neurodevelopmental processes, which may contribute to the pathogenesis of schizophrenia. Further neurobiological research on the developmental timing and circuits that are affected by melanin concentrating hormone may lead to a therapeutic target for early prevention of schizophrenia.

Melanin-concentrating hormone receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Melanin-concentrating hormone (MCH) receptors (provisional nomenclature as recommended by NC-IUPHAR [31]) are activated by an endogenous nonadecameric cyclic peptide identical in humans and rats (DFDMLRCMLGRVYRPCWQV; mammalian MCH) generated from a precursor (PMCH, P20382), which also produces neuropeptide EI and neuropeptide GE.

Metabolism of Strained Rings: Glutathione S-transferase-Catalyzed Formation of a Glutathione-Conjugated Spiro-azetidine without Prior Bioactivation.

AZD1979 [(3-(4-(2-oxa-6-azaspiro[3.3]heptan-6-ylmethyl)phenoxy)azetidin-1-yl)(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl)methanone] is a melanin-concentrating hormone receptor 1 antagonist designed for the treatment of obesity. In this study, metabolite profiles of AZD1979 in human hepatocytes revealed a series of glutathione-related metabolites, including the glutathionyl, cysteinyl, cysteinylglycinyl, and mercapturic acid conjugates. The formation of these metabolites was not inhibited by coincubation with the cytochrome P450 (P450) inhibitor 1-aminobenzotriazole. In efforts to identify the mechanistic features of this pathway, investigations were performed to characterize the structure of the glutathionyl conjugate M12 of AZD1979 and to identify the enzyme system catalyzing its formation. Studies with various human liver subcellular fractions established that the formation of M12 was NAD(P)H-independent and proceeded in cytosol and S9 fractions but not in microsomal or mitochondrial fractions. The formation of M12 was inhibited by ethacrynic acid, an inhibitor of glutathione S-transferases (GSTs). Several human recombinant GSTs, including GSTA1, A2-2, M1a, M2-2, T1-1, and GST from human placenta, were incubated with AZD1979. All GSTs tested catalyzed the formation of M12, with GSTA2-2 being the most efficient. Metabolite M12 was purified from rat liver S9 incubations and its structure elucidated by NMR. These results establish that M12 is the product of the GST-catalyzed glutathione attack on the carbon atom α to the nitrogen atom of the strained spiro-azetidinyl moiety to give, after ring opening, the corresponding amino-thioether conjugate product, a direct conjugation pathway that occurs without the prior substrate bioactivation by P450. SIGNIFICANCE STATEMENT: The investigated compound, AZD1979, contains a 6-substituted-2-oxa-6-azaspiro[3.3]heptanyl derivative that is an example of strained heterocycles, including spiro-fused ring systems, that are widely used in synthetic organic chemistry. An unusual azetidinyl ring-opening reaction involving a nucleophilic attack by glutathione, which does not involve prior cytochrome P450-catalyzed bioactivation of the substrate and which is catalyzed by glutathione transferases, is reported. We propose a mechanism involving the protonated cyclic aminyl intermediate that undergoes nucleophilic attack by glutathione thiolate anion in this reaction, catalyzed by glutathione transferases.

Conditional deletion of melanin-concentrating hormone receptor 1 from GABAergic neurons increases locomotor activity

ObjectiveMelanin-concentrating hormone (MCH) plays a key role in regulating energy balance. MCH acts via its receptor MCHR1, and MCHR1 deletion increases energy expenditure and locomotor activity, which is associated with a hyperdopaminergic state. Since MCHR1 expression is widespread, the neurons supporting the effects of MCH on energy expenditure are not clearly defined. There is a high density of MCHR1 neurons in the striatum, and these neurons are known to be GABAergic. We thus determined if MCH acts via this GABAergic neurocircuit to mediate energy balance. MethodsWe generated a Mchr1-flox mouse and crossed it with the Vgat-cre mouse to assess if MCHR1 deletion from GABAergic neurons expressing the vesicular GABA transporter (vGAT) in female Vgat-Mchr1-KO mice resulted in lower body weights or increased energy expenditure. Additionally, we determined if MCHR1-expressing neurons within the accumbens form part of the neural circuit underlying MCH-mediated energy balance by delivering an adeno-associated virus expressing Cre recombinase to the accumbens nucleus of Mchr1-flox mice. To evaluate if a dysregulated dopaminergic tone leads to their hyperactivity, we determined if the dopamine reuptake blocker GBR12909 prolonged the drug-induced locomotor activity in Vgat-Mchr1-KO mice. Furthermore, we also performed amperometry recordings to test whether MCHR1 deletion increases dopamine output within the accumbens and whether MCH can suppress dopamine release. ResultsVgat-Mchr1-KO mice have lower body weight, increased energy expenditure, and increased locomotor activity. Similarly, restricting MCHR1 deletion to the accumbens nucleus also increased locomotor activity. Vgat-Mchr1-KO mice show increased and prolonged sensitivity to GBR12909-induced locomotor activity, and amperometry recordings revealed that GBR12909 elevated accumbens dopamine levels to twice that of controls, thus MCHR1 deletion may lead to a hyperdopaminergic state that mediates their observed hyperactivity. Consistent with the inhibitory effect of MCH, we found that MCH acutely suppresses dopamine release within the accumbens. ConclusionsAs with established models of systemic MCH or MCHR1 deletion, we found that MCHR1 deletion from GABAergic neurons, specifically those within the accumbens nucleus, also led to increased locomotor activity. A hyperdopaminergic state underlies this increased locomotor activity, and is consistent with our finding that MCH signaling within the accumbens nucleus suppresses dopamine release. In effect, MCHR1 deletion may disinhibit dopamine release leading to the observed hyperactivity.

In vitro Radiopharmaceutical Evidence for MCHR1 Binding Sites in Murine Brown Adipocytes

[11C]SNAP-7941 and its radiofluorinated, fluoro-ethyl derivative [18F]FE@SNAP have been developed as the first positron emission tomography tracers for melanin-concentrating hormone receptor 1 (MCHR1) imaging. Accumulation of these MCHR1 PET-tracers in rat brown adipose tissue (BAT) in vivo provided first indication of MCHR1 expression in rodent BAT. To rule out off-target binding, affinity of both MCHR1 ligands toward adrenergic beta-3 receptors (ADRB3) was examined. Further, specific binding of [11C]SNAP-7941 to brown adipocytes and effects of MCHR1 ligands on brown adipocyte activation were investigated. SNAP-7941 and FE@SNAP evinced to be highly selective toward MCHR1. [11C]SNAP-7941 binding to brown adipocytes was shown to be mainly MCHR1-specific. This data strongly indicates MCHR1 expression in rodent BAT and moreover, a peripheral, anti-obesity effect of MCHR1 antagonists directly exerted in BAT is proposed. Moreover, MCHR1 expression in murine brown adipocytes was confirmed by protein and mRNA analysis. We conclude that MCHR1 PET imaging contributes to basic research in endocrinology by elucidating the involvement of the MCH system in peripheral tissues, such as BAT.

Dynamic REM Sleep Modulation by Ambient Temperature and the Critical Role of the Melanin-Concentrating Hormone System

Ambient temperature (Ta) warming toward the high end of the thermoneutral zone (TNZ) preferentially increasesrapid eye movement (REM) sleep over non-REM (NREM) sleep across species. The control and function of this temperature-induced REM sleepexpression have remained unknown. Melanin-concentrating hormone (MCH) neurons play an important role in REM sleep control. We hypothesize that the MCH system may modulate REM sleep as a function of Ta. Here, we show that wild-type (WT) mice dynamically increased REM sleep durations specifically during warm Ta pulsing within the TNZ, compared to both the TNZ cool and baseline constant Ta conditions, without significantly affecting either wake or NREM sleep durations. However, genetically engineered MCH receptor-1 knockout (MCHR1-KO) mice showed no significant changes in REM sleep as a function of Ta, even with increased sleep pressure following a 4-h sleep deprivation. Using MCH-cre mice transduced with channelrhodopsin, we then optogenetically activated MCH neurons time locked with Ta warming, showing an increase in REM sleep expression beyond what Ta warming in yellow fluorescent protein (YFP) control mice achieved. Finally, in mice transduced with archaerhodopsin-T, semi-chronic optogenetic MCH neuronal silencing during Ta warming completely blocked the increase in REM sleep seen in YFP controls. These data demonstrate a previously unknown role for the MCH system in the dynamic output expression of REM sleep during Ta manipulation. These findings are consistent with the energy allocation hypothesis of sleep function, suggesting that endotherms have evolved neural circuits to opportunistically express REM sleep when the need for thermoregulatory defense is minimized.

The role of Olfaction in MCH-regulated spontaneous maternal responses

Melanin concentrating hormone (MCH) is involved in the initiation of maternal behavior during the postpartum period. Virgin females also display some aspects of maternal care independent of the hormonal and neurochemical changes associated with pregnancy and parturition. Maternal behavior in virgin females is triggered by pups-generated chemosensory signals. We therefore examined the role of MCH in maternal-related behaviors in virgin mice and whether it involves chemosensory mechanisms. We used mice with germline knock-out of MCH receptor (MCHR1 KO) and mice with conditional ablation of MCH neurons (MCH cKO) using Cre-inducible diphtheria toxin (iDTR) system. We report that germline deletion of MCHR1 and ablation of MCH neurons impair spontaneous maternal behavior that is induced upon pups’ exposure. The latency and duration to retrieve pups by MCHR1 KO and MCH cKO mice are longer than their control littermate mice. In support of this finding, we found that in the three-chamber social test, both MCHR1 KO and MCH cKO mice display a lack of interest in interacting with pups. Strikingly, however, we found that while MCHR1 KO mice were unable to detect pups’ chemosensory signals and displayed impairment in general olfactory discrimination, MCH cKO mice exhibited normal olfactory function. Our findings indicate that the lack of MCHR1 or of normal MCH levels causes defects in maternal behavior in non-sensitized virgin mice, and that disruption of the olfactory signaling might not count for these defects.

Neurotensin Enhances Locomotor Activity and Arousal and Inhibits Melanin-Concentrating Hormone Signaling

Background: Hypothalamic neurotensin (Nts)-secreting neurons regulate fundamental physiological processes including metabolism and feeding. However, the role of Nts in modulation of locomotor activity, sleep, and arousal is unclear. We previously identified and characterized Nts neurons in the zebrafish hypothalamus. Materials and Methods: In order to study the role of Nts, nts mutant (nts–/–), and overexpressing zebrafish were generated. Results: The expression of both nts mRNA and Nts protein was reduced during the night in wild-type zebrafish. Behavioral assays revealed that locomotor activity was decreased during both day and night, while sleep was increased exclusively during the nighttime in nts–/– larvae. Likewise, inducible overexpression of Nts increased arousal in hsp70:Gal4/uas:Nts larvae. Furthermore, the behavioral response to light-to-dark transitions was reduced in nts–/– larvae. In order to elucidate potential contenders that may mediate Nts action on these behaviors, we profiled the transcriptome of 6 dpf nts–/– larvae. Among other genes, the expression levels of melanin-concentrating hormone receptor 1b were increased in nts–/– larvae. Furthermore, a portion of promelanin-concentrating hormone 1 (pmch1) and pmch2 neurons expressed the nts receptor. In addition, expression of the the two zebrafish melanin-concentrating hormone (Mch) orthologs, Mch1 and Mch2, was increased in nts–/– larvae. Conclusion: These results show that the Nts and Mch systems interact and modulate locomotor activity and arousal.

Technical Aspect of the Automated Synthesis and Real-Time Kinetic Evaluation of [11C]SNAP-7941.

Positron emission tomography (PET) is an essential molecular imaging technique providing insights into pathways and using specific targeted radioligands for in vivo investigations. Within this protocol, a robust and reliable remote-controlled radiosynthesis of [11C]SNAP-7941, an antagonist to the melanin-concentrating hormone receptor 1, is described. The radiosynthesis starts with cyclotron produced [11C]CO2 that is subsequently further reacted via a gas-phase transition to [11C]CH3OTf. Then, this reactive intermediate is introduced to the precursor solution and forms the respective radiotracer. Chemical as well as the radiochemical purity are determined by means of RP-HPLC, routinely implemented in the radiopharmaceutical quality control process. Additionally, the molar activity is calculated as it is a necessity for the following real-time kinetic investigations. Furthermore, [11C]SNAP-7941 is applied to MDCKII-WT and MDCKII-hMDR1 cells for evaluating the impact of P-glycoprotein (P-gp) expression on cell accumulation. For this reason, the P-gp expressing cell line (MDCKII-hMDR1) is either used without or with blocking prior to experiments by means of the P-gp substrate (±)-verapamil and the results are compared to the ones observed for the wildtype cells. The overall experimental approach demonstrates the importance of a precise time-management that is essential for every preclinical and clinical study using PET tracers radiolabelled with short-lived nuclides, such as carbon-11 (half-life: 20 min).

Melanin‐concentrating hormone‐R1 in the locus coeruleus may be involved in the regulation of depressive‐like behavior

BackgroundPrevious anatomical and behavioral studies have shown that melanin‐concentrating hormone (MCH) is involved in the modulation of emotional states. However, little is known about brain regions other than the dorsal raphe nucleus that relate the MCH‐ergic system to depressive states. Numerous studies have shown that the locus coeruleus (LC) is involved in the regulation of depression and sleep. Although direct physiological evidence is lacking, previous studies suggest that MCH release in the LC decreases neuronal discharge. However, remaining unclear is whether the MCH‐ergic system in the LC is related to depressive‐like behavior.MethodWe treated rats with an intra‐LC injection of MCH, intracerebroventricular injection of MCH, or chronic subcutaneous injections of corticosterone to induce different depressive‐like phenotypes. We then assessed the effects of the MCH receptor 1 antagonist SNAP‐94847 on depressive‐like behavior in the forced swim test (FST) and the sucrose preference test (SPT).ResultsThe intra‐LC and intracerebroventricular injections of MCH and chronic injections of corticosterone increased immobility time in the FST and decreased sucrose preference in the SPT. All of these depressive‐like behaviors were reversed by an intra‐LC microinjection of SNAP‐94847.ConclusionsThese results suggest that the MCH‐ergic system in the LC might play an important role in the regulation of depressive‐like behavior.Support or Funding InformationThis study was funded by grants from the National Natural Science Foundation of China (No. 81573407, 81872851, 81871038 and 81302746).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Melanin-concentrating hormone receptor-1 is located in primary cilia of the dorsal raphe neurons

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons of the posterior hypothalamus and incerto-hypothalamic area. These neurons project throughout the central nervous system, including the dorsal raphe nucleus (DRN). In rodents, MCH exerts its biological functions through the MCHR-1 receptor. We previously demonstrated that intra-DRN MCH administration increases REM sleep time and induces a pro-depressive behavior. We also determined that MCH modulates the neuronal firing rate and serotonin release within this nucleus. Previous studies in mice identified the presence of MCHR-1 in neurons located in the olfactory tubercle, hypothalamus, and nucleus accumbens, in a specialized neuronal appendage: the neuronal primary cilia. However, the subcellular location of MCHR-1 protein in the DRN is still unknown. Hence, the aim of the present study was to explore, by means of single and double immunohistochemical procedures, whether MCHR-1 is present in neuronal primary cilia in serotonergic and GABAergic neurons located in the DRN of the rat. We demonstrated colocalization of MCHR-1 with type III adenylyl cyclase (AC-III), a neuronal ciliary marker, in the DRN and confirmed their colocalization in the hippocampus and cerebral cortex of the rat. We quantified the proportion of serotoninergic and GABAergic neurons that coexpress MCHR-1 at the mid-caudal and mid-rostral levels of the DRN: 4% and 12%, respectively. Furthermore, approximately 10% of the total number of MCHR-1 immunoreactive primary cilia belonged to serotonergic neurons, whilst 12% were appendages of GABAergic neurons. These morphological data allow us to conclude that the mechanism by which MCH modulates the activity of DRN neurons is through MCHR-1 receptors present in the primary cilia of different neurochemical phenotypes. New experiments are needed to understand the functional rationale of the unexpected localization of these receptors and to explore their presence in other neuronal phenotypes.

Mechanisms for Temperature Modulation of Feeding in Goldfish and Implications on Seasonal Changes in Feeding Behavior and Food Intake.

In fish models, seasonal change in feeding is under the influence of water temperature. However, the effects of temperature on appetite control can vary among fish species and the mechanisms involved have not been fully characterized. Using goldfish (Carassius auratus) as a model, seasonal changes in feeding behavior and food intake were examined in cyprinid species. In our study, foraging activity and food consumption in goldfish were found to be reduced with positive correlation to the gradual drop in water temperature occurring during the transition from summer (28.4 ± 2.2°C) to winter (15.1 ± 2.6°C). In goldfish with a 4-week acclimation at 28°C, their foraging activity and food consumption were notably higher than their counterparts with similar acclimation at 15°C. When compared to the group at 28°C during summer, the attenuation in feeding responses at 15°C during the winter also occurred with parallel rises of leptin I and II mRNA levels in the liver. Meanwhile, a drop in orexin mRNA along with concurrent elevations of CCK, MCH, POMC, CART, and leptin receptor (LepR) transcript expression could be noted in brain areas involved in feeding control. In short-term study, goldfish acclimated at 28°C were exposed to 15°C for 24 h and the treatment was effective in reducing foraging activity and food intake. The opposite was true in reciprocal experiment with a rise in water temperature to 28°C for goldfish acclimated at 15°C. In parallel time-course study with lowering of water temperature from 28 to 15°C, short-term exposure (6–12 h) of goldfish to 15°C could also increase leptin I and II mRNA levels in the liver. Similar to our seasonality study, transcript level of orexin was reduced along with up-regulation of CCK, MCH, POMC, CART, and LepR gene expression in different brain areas. Our results, as a whole, suggest that temperature-driven regulation of leptin output from the liver in conjunction with parallel modulations of orexigenic/anorexigenic signals and leptin responsiveness in the brain may contribute to the seasonal changes of feeding behavior and food intake observed in goldfish.

P114 MCH LINKS IMMUNOMETABOLSIM TO INTESTINAL INFLAMMATION

Melanin concentrating hormone (MCH) was first identified as a hypothalamic neuropeptide regulating feeding behavior and energy balance. The MCH receptor, MCHR1, is present in brain as well as in several peripheral tissues including the gastrointestinal tract where its role is yet to be established. Increased MCH and MCHR1 expression in the mucosa of patients with inflammatory bowel disease (IBD) implies a role of MCH in disease pathogenesis. Our previous studies have shown that MCH-deficient mice develop attenuated colitis, a phenotype that was recapitulated when mice were treated with an anti-MCH antibody. The exact mechanisms by which MCH exerts proinflammatory effects remain under investigation, as well as the cell types involved and have been the focus of the present study. We found MCHR1 upregulation in CD4+ T cells isolated from the lamina propria of patients with Crohn’s disease, in contrast to those derived from peripheral blood. In vitro, MCHR1 was induced upon activation of CD4+ T-cells. Furthermore, treatment with MCH of mucosal explants from patients with IBD resulted in increased cytokine secretion in the culture supernatant (IFNg, IL-17, IL-2, IL-6, IL8, MCP1, TNFa). Most importantly, metabolomics analysis of Jurkat cells, a T-cell line expressing high basal levels of MCHR1 receptor, revealed that treatment with MCH increased glutamine, glutamate and a-ketoglutarate levels 4-, 2.5-, and 3.5-fold, respectively, as well as those of acetyl-CoA (3-fold) while glycolytic intermediates remained unaltered. These findings imply engagement of a “reductive carboxylation” cycle in the presence of MCH, the fuel of which is a-ketoglutarate instead of glucose. The role of a-ketoglutarate in driving T-effector activation and differentiation is well established. In further support of these observations, stimulation with MCH resulted in upregulation of the glutamine transporter SLC1A5 that determines intracellular glutamine levels, as well those of its metabolites glutamate and a-ketoglutarate. In relation to the immune phenotype, MCH-induced metabolic shifts correlated with increased proliferation and reduced apoptosis of Jurkat cells, as well as increased IL-2 secretion. In a more relevant context, treatment of isolated CD4+ T cells with MCH under polarized conditions resulted in 70% increase of IL-17+ cells, in contrast to 32% decrease of IL-4+ and 25% decrease of Foxp3+ cells. Collectively, these findings further support a deleterious effect of aberrant MCH signaling in IBD and potentially illustrate a new target in IBD therapeutics.