Mammalian Melanin-concentrating Hormone Research Articles

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.

Involvement of melanin-concentrating hormone 2 in background color adaptation of barfin flounder Verasper moseri

In teleosts, melanin-concentrating hormone (MCH) plays a key role in skin color changes. MCH is released into general circulation from the neurohypophysis, which causes pigment aggregation in the skin chromatophores. Recently, a novel MCH (MCH2) precursor gene, which is orthologous to the mammalian MCH precursor gene, has been identified in some teleosts using genomic data mining. The physiological function of MCH2 remains unclear. In the present study, we cloned the cDNA for MCH2 from barfin flounder, Verasper moseri. The putative prepro-MCH2 contains 25 amino acids of MCH2 peptide region. Liquid chromatography-electrospray ionization mass spectrometry with a high resolution mass analyzer were used for confirming the amino acid sequences of MCH1 and MCH2 peptides from the pituitary extract. In vitro synthesized MCH1 and MCH2 induced pigment aggregation in a dose-dependent manner. A mammalian cell-based assay indicated that both MCH1 and MCH2 functionally interacted with both the MCH receptor types 1 and 2. Mch1 and mch2 are exclusively expressed in the brain and pituitary. The levels of brain mch2 transcript were three times higher in the fish that were chronically acclimated to a white background than those acclimated to a black background. These results suggest that in V. moseri, MCH1 and MCH2 are involved in the response to changes in background colors, during the process of chromatophore control.

The melanin-concentrating hormone receptors: neuronal and non-neuronal functions.

Melanin-concentrating hormone (MCH) is a cyclic peptide highly conserved in vertebrates and was originally identified as a skin-paling factor in Teleosts. In fishes, MCH also participates in the regulation of the stress-response and feeding behaviour. Mammalian MCH is a hypothalamic neuropeptide that displays multiple functions, mostly controlling feeding behaviour and energy homeostasis. Transgenic mouse models and pharmacological studies have shown the importance of the MCH system as a potential target in the treatment of appetite disorders and obesity as well as anxiety and psychiatric diseases. Two G-protein-coupled receptors (GPCRs) binding MCH have been characterized so far. The first, named MCH-R1 and also called SLC1, was identified through reverse pharmacology strategies by several groups as a cognate receptor of MCH. This receptor is expressed at high levels in many brain areas of rodents and primates and is also expressed in peripheral organs, albeit at a lower rate. A second receptor, designated MCH-R2, exhibited 38% identity to MCH-R1 and was identified by sequence analysis of the human genome. Interestingly, although MCH-R2 orthologues were also found in fishes, dogs, ferrets and non-human primates, this MCH receptor gene appeared either lacking or non-functional in rodents and lagomorphs. Both receptors are class I GPCRs, whose main roles are to mediate the actions of peptides and neurotransmitters in the central nervous system. However, examples of action of MCH on neuronal and non-neuronal cells are emerging that illustrate novel MCH functions. In particular, the functionality of endogenously expressed MCH-R1 has been explored in human neuroblastoma cells, SK-N-SH and SH-SY5Y cells, and in non-neuronal cell types such as the ependymocytes. Indeed, we have identified mitogen-activated protein kinase (MAPK)-dependent or calcium-dependent signalling cascades that ultimately contributed to neurite outgrowth in neuroblastoma cells or to modulation of ciliary beating in ependymal cells. The putative role of MCH on cellular shaping and plasticity on one side and volume transmission on the other must be now considered.

Identification of mRNAs coding for mammalian-type melanin-concentrating hormone and its receptors in the scalloped hammerhead shark Sphyrna lewini

Melanin-concentrating hormone (MCH) is a neuromodulator, synthesized in the hypothalamus, that regulates both appetite and energy homeostasis in mammals. MCH was initially identified in teleost fishes as a pituitary gland hormone that induced melanin aggregation in chromatophores in the skin; however, this function of MCH has not been observed in other vertebrates. Recent studies suggest that MCH is involved in teleost feeding behavior, spurring the hypothesis that the original function of MCH in early vertebrates was appetite regulation. The present study reports the results of cDNAs cloning encoding preproMCH and two MCH receptors from an elasmobranch fish, Sphyrna lewini, a member of Chondrichthyes, the earliest diverged class in gnathostomes. The putative MCH peptide is composed of 19 amino acids, similar in length to the mammalian MCH. Reverse-transcription polymerase chain reaction revealed that MCH is expressed in the hypothalamus in S. lewini MCH cell bodies and fibers were identified by immunochemistry in the hypothalamus, but not in the pituitary gland, suggesting that MCH is not released via the pituitary gland into general circulation. MCH receptor genes mch-r1 and mch-r2 were expressed in the S. lewini hypothalamus, but were not found in the skin. These results indicate that MCH does not have a peripheral function, such as a melanin-concentrating effect, in the skin of S. lewini hypothalamic MCH mRNA levels were not affected by fasting, suggesting that feeding conditions might not affect the expression of MCH in the hypothalamus.

Signalling pathway of goldfish melanin-concentrating hormone receptors 1 and 2

Melanin-concentrating hormone (MCH) is the natural ligand for the MCH-1 receptor (MCHR1) and MCH-2 receptor (MCHR2). The MCH–MCHR1 system plays a central role in energy metabolism in rodents. Recently, we identified MCHR1 and MCHR2 orthologues in goldfish, designated gfMCHR1 and gfMCHR2. In a mammalian cell-based assay, calcium mobilization was evoked by gfMCHR2 via both Gαi/o and Gαq, while the gfMCHR1-mediated response was exclusively dependent on Gαq. This coupling capacity to G proteins is in contrast to human MCHR1 and MCHR2. Here, we extended our previous characterization of the two gfMCHRs by examining their different signalling pathway. We found that MCH caused activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) via both gfMCHR1 and gfMCHR2 in dose-dependent manners. Unlike the case for gfMCHR2, gfMCHR1 signalling was not sensitive to pertussis toxin, suggesting Gαq coupling of gfMCHR1 in the ERK1/2 pathway as well as a calcium mobilization system. Cyclic AMP assays revealed that gfMCHR2 was efficiently coupled to Gαi/o, while gfMCHR1 was weakly coupled to Gαs. Finally, we investigated the transduction features stimulated by two mammalian MCH analogues. As expected, Compound 15, which is a full agonist of human MCHR1, was a potent gfMCHR1 agonist in multiple signalling pathways. On the other hand, Compound 30, which is a human MCHR1-selective antagonist with negligible agonist potency, unexpectedly acted as a selective agonist of gfMCHR1. These results are the first to demonstrate that gfMCHR1 and gfMCHR2 have quite different signalling properties from human MCHRs.

Characterization of two melanin‐concentrating hormone genes in zebrafish reveals evolutionary and physiological links with the mammalian MCH system

Melanin-concentrating hormone (MCH) regulates feeding and complex behaviors in mammals and pigmentation in fish. The relationship between fish and mammalian MCH systems is not well understood. Here, we identify and characterize two MCH genes in zebrafish, Pmch1 and Pmch2. Whereas Pmch1 and its corresponding MCH1 peptide resemble MCH found in other fish, the zebrafish Pmch2 gene and MCH2 peptide share genomic structure, synteny, and high peptide sequence homology with mammalian MCH. Zebrafish Pmch genes are expressed in closely associated but non-overlapping neurons within the hypothalamus, and MCH2 neurons send numerous projections to multiple MCH receptor-rich targets with presumed roles in sensory perception, learning and memory, arousal, and homeostatic regulation. Preliminary functional analysis showed that whereas changes in zebrafish Pmch1 expression correlate with pigmentation changes, the number of MCH2-expressing neurons increases in response to chronic food deprivation. These findings demonstrate that zebrafish MCH2 is the putative structural and functional ortholog of mammalian MCH and help elucidate the nature of MCH evolution among vertebrates.

Melanin-concentrating hormone reduces somatolactin release from cultured goldfish pituitary cells

Melanin-concentrating hormone (MCH)-containing neurons directly innervate the adenohypophysis in the teleost pituitary. We examined immunohistochemically the relationship between MCH-containing nerve fibres or endings and somatolactin (SL)-producing cells in the goldfish pituitary. Nerve fibres or endings with MCH-like immunoreactivity were identified in the neurohypophysis in close proximity to the adenohypophysial cells showing SL-like immunoreactivity. We also examined the effect of MCH on SL release from cultured goldfish pituitary cells and SL synthesis using a cell immunoblot and a real-time PCR method. Treatment of individually dispersed pituitary cells with MCH 10(-7) M for 3 h decreased the area of SL-like immunoreactivity on immunoblots, and MCH-induced reductions in SL release were blocked by treatment with the mammalian MCH receptor (MCHR) antagonist, compound-30, at a concentration of 10(-5) M. Treatment with 10(-7) M MCH for 3 h did not affect sl-alpha and -beta (smtla and -b as given in the Zfin Database) mRNA expression levels. These led us to explore the signal transduction mechanism leading to the inhibition of SL release, for which we examined whether MCH-induced reductions in SL release are mediated by the G(i) or G(q) protein-coupled signalling pathway. The MCH-induced reductions in SL release were abolished by treatment with the G(i/o) protein inhibitors, NF023 (10(-5) M) or pertussis toxin (260 ng/ml), but not by the phospholipase C inhibitor, U-73122 (3x10(-6) M). These results indicate that MCH can potentially function as a hypothalamic factor suppressing SL release via the MCHR, and subsequently through the G(i) protein to inhibit the adenylate cyclase/cAMP/protein kinase A-signalling pathway in goldfish pituitary cells.

Functions of melanin‐concentrating hormone in fish

Melanin-concentrating hormone (MCH) was originally discovered in fish, in which it causes aggregation or concentration of melanin granules in melanophores, thus regulating body color. MCH is a cyclic neuropeptide synthesized as a preprohormone in the hypothalamus of all vertebrates. Mammalian MCH plays an important role as a neurotransmitter or neuromodulator in regulating food intake and energy homeostasis. MCH signaling system may involve in regulating food intake also in fish. This neuropeptide binds to G-protein-coupled seven transmembrane receptor[s] to mediate its functions. This article reviews MCH and MCH receptor signaling systems in body color change and food intake in fish.

Identification and Pharmacological Characterization of a Novel Human Melanin-concentrating Hormone Receptor, MCH-R2

Melanin-concentrating hormone (MCH) is a neuropeptide highly expressed in the brain that regulates several physiological functions mediated by receptors in the G protein-coupled receptor family. Recently an orphan receptor, SLC-1, has been identified as an MCH receptor (MCH-R1). Herein we identify and characterize a novel receptor for human MCH (MCH-R2). The receptor is composed of 340 amino acids encoded by a 1023-base pair cDNA and is 35% homologous to SLC-1. (125)I-MCH specifically bound to Chinese hamster ovary cells stably expressing MCH-R2. MCH stimulated dose-dependent increases in intracellular free Ca(2+) and inositol phosphate production in these cells but did not affect cAMP production. The pharmacological profile for mammalian MCH, [Phe(13),Tyr(19)]MCH, and salmon MCH at MCH-R2 differed compared with MCH-R1 as assessed by intracellular signaling and radioligand binding assays. The EC(50) in signaling assays and the IC(50) in radioligand binding assays of salmon MCH was an order of magnitude higher than mammalian MCH at MCH-R2. By comparison, the EC(50) and IC(50) values of salmon MCH and mammalian MCH at MCH-R1 were relatively similar. Blot hybridization revealed exclusive expression of MCH-R2 mRNA in several distinct brain regions, particularly in the cortical area, suggesting the involvement of MCH-R2 in the central regulation of MCH-mediated functions.

Synthesis and Characterization of New Radioligands for the Mammalian Melanin-Concentrating Hormone (MCH) Receptor

Melanin-concentrating hormone (MCH) is a neuropeptide present in the brain of all vertebrates. For the characterization of MCH receptors, a monoiodinated [Phe13, Tyr19]-MCH radioligand analogue was developed. The high susceptibility of [125I]-[Phe13, Tyr19]-MCH to oxidative damage and its very lipophilic nature made it necessary to develop new MCH radioligands. To increase the stability, native methionines were replaced by non-sulphur containing amino acid residues. In one analogue, the L-enantiomer of the phenylalanine residue at position 13 was substituted by the D-enantiomer, which increased the relative affinity of the ensuing [125I]-[D-Phe13, Tyr19]-MCH about 7-fold. The different analogues were iodinated by an enzymatic reaction and used for binding studies with mouse melanoma cells. [125I]-[Met(O)4,8, Phe13, Tyr19]-MCH and [125I]-[Hse4,8, Phe13, Tyr19]-MCH showed only about 19% of total binding and [125I]-[Ser4,8, Phe13, Tyr19]-MCH displayed about 44% of total binding when compared with [125I]-[Phe13, Tyr19]-MCH. Non-specific binding for all tracers was below 11% of total binding of [125I]-[Phe13, Tyr19]-MCH binding. [125I]-[D-Phe13, Tyr19]-MCH was used for saturation binding studies and revealed a KD of 122.7 ± 15.3 pmol/l. This radioligand was further characterized by association and dissociation binding studies.

Cloning and sequence analysis of hypothalamus cDNA encoding tilapia melanin-concentrating hormone

Melanin-concentrating hormone (MCH) is a neuroendocrine peptide involved in the regulation of skin pigmentation in teleosts. We isolated and sequenced a 543 bp hypothalamic cDNA encoding the MCH-preprohormone of tilapia (Oreochromis mossambicus). Initially, polymerase chain reaction (PCR) experiments were performed on hypothalamic RNA with a synthetic oligonucleotide primer corresponding to a conserved region of salmon and mammalian MCH peptide and an oligo dT primer. A 0.2 kb PCR fragment was obtained and found to have low but significant nucleotide sequence similarity with the 3' ends of known MCH-mRNAs. Subsequently, the PCR fragment was used to screen λZAP cDNA libraries constructed from tilapia hypothalamic poly(A(+)) RNA. The cloned tilapia MCH preprohormone cDNA encodes a 133-amino acid protein of which 17 amino acids belong to the signal peptide. The MCH peptide sequence is located at the carboxy terminus of the preprohormone structure and is preceded by a pair of arginine residues which can serve as a proteolytic cleavage site. 23 to 25 amino acids further upstream in the prohormone structure three consecutive basic residues are present. Cleavage at this site would yield a 22-amino acid MCH gene-related peptide (Mgrp), which is much larger than (12- to 13-amino acid) salmon and mammalian Mgrp. A comparative structural analysis between tilapia preproMCH and its salmon and mammalian counterparts revealed that the MCH peptide sequence is very well conserved (100% identity with salmon and 75% identity with both rat and human MCH). In contrast, the remaining parts of the preproMCH structures have diverged considerably. Northern blot analysis revealed the presence of tilapia preproMCH mRNA in the hypothalamus and not in other brain regions nor in several peripheral tissues.