Gene deletion of the PACAP/VIP receptor, VPAC2R, alters glycemic responses during metabolic and psychogenic stress in adult female mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) and the homologous peptide, vasoactive intestinal peptide (VIP), participate in glucose homeostasis using insulinotropic and counterregulatory processes. The role of VIP receptor 2 (VPAC2R) in these opposing actions needs further characterization. In this study, we examined the participation of VPAC2R on basal glycemia, fasted levels of glucoregulatory hormones and on glycemia responses during metabolic and psychogenic stress using gene-deleted (Vipr2-/- ) female mice. The mean basal glycemia was significantly greater in Vipr2-/- in the fed state and after an 8-h overnight fast as compared to wild-type (WT) mice. Insulin tolerance testing following a 5-h fast (morning fast, 0.38 U/kg insulin) indicated no effect of genotype. However, during a more intense metabolic challenge (8 h, ON fast, 0.25 U/kg insulin), Vipr2-/- females displayed significantly impaired insulin hypoglycemia. During immobilization stress, the hyperglycemic response and plasma epinephrine levels were significantly elevated above basal in Vipr2-/- , but not WT mice, in spite of similar stress levels of plasma corticosterone. Together, these results implicate participation of VPAC2R in upregulated counterregulatory processes influenced by enhanced sympathoexcitation. Moreover, the suppression of plasma GLP-1 levels in Vipr2-/- mice may have removed the inhibition on hepatic glucose production and the promotion of glucose disposal by GLP-1. qPCR analysis indicated deregulation of central gene markers of PACAP/VIP signaling in Vipr2-/- , upregulated medulla tyrosine hydroxylase (Th) and downregulated hypothalamic Vip transcripts. These results demonstrate a physiological role for VPAC2R in glucose metabolism, especially during insulin challenge and psychogenic stress, likely involving the participation of sympathoadrenal activity and/or metabolic hormones.

Early Alterations of PACAP and VIP Expression in the Female Rat Brain Following Spinal Cord Injury

Previous evidence shows that rapid changes occur in the brain following spinal cord injury (SCI). Here, we interrogated the expression of the neuropeptides pituitary adenylyl cyclase-activating peptide (PACAP), vasoactive intestinal peptides (VIP), and their binding receptors in the rat brain 24 h following SCI. Female Sprague-Dawley rats underwent thoracic laminectomy; half of the rats received a mild contusion injury at the level of the T10 vertebrate (SCI group); the other half underwent sham surgery (sham group). Twenty-four hours post-surgery, the hypothalamus, thalamus, amygdala, hippocampus (dorsal and ventral), prefrontal cortex, and periaqueductal gray were collected. PACAP, VIP, PAC1, VPAC1, and VPAC2 mRNA and protein levels were measured by real-time quantitative polymerase chain reaction and Western blot. In SCI rats, PACAP expression was increased in the hypothalamus (104-141% vs sham) and amygdala (138-350%), but downregulated in the thalamus (35-95%) and periaqueductal gray (58-68%). VIP expression was increased only in the thalamus (175-385%), with a reduction in the amygdala (51-68%), hippocampus (40-75%), and periaqueductal gray (74-76%). The expression of the PAC1 receptor was the least disturbed by SCI, with decrease expression in the ventral hippocampus (63-68%) only. The expression levels of VPAC1 and VPAC2 receptors were globally reduced, with more prominent reductions of VPAC1 vs VPAC2 in the amygdala (21-70%) and ventral hippocampus (72-75%). In addition, VPAC1 downregulation also extended to the dorsal hippocampus (69-70%). These findings demonstrate that as early as 24 h post-SCI, there are region-specific disruptions of PACAP, VIP, and related receptor transcript and protein levels in supraspinal regions controlling higher cognitive functions.

The Rat Mammary Gland as a Novel Site of Expression of Melanin-Concentrating Hormone Receptor 1 mRNA and Its Protein Immunoreactivity

Lactation is a complex physiological process, depending on orchestrated central and peripheral events, including substantial brain plasticity. Among these events is a novel expression of pro-melanin-concentrating hormone (Pmch) mRNA in the rodent hypothalamus, such as the ventral part of the medial preoptic area (vmMPOA). This expression reaches its highest levels around postpartum day 19 (PPD19), when dams transition from lactation to the weaning period. The appearance of this lactation-related Pmch expression occurs simultaneously with the presence of one of the Pmch products, melanin-concentrating hormone (MCH), in the serum. Given the relevance of the MPOA to maternal physiology and the contemporaneity between Pmch expression in this structure and the weaning period, we hypothesized that MCH has a role in the termination of lactation, acting as a mediator between central and peripheral changes. To test this, we investigated the presence of the MCH receptor 1 (MCHR1) and its gene expression in the mammary gland of female rats in different stages of the reproductive cycle. To that end, in situ hybridization, RT-PCR, RT-qPCR, nucleotide sequencing, immunohistochemistry, and Western blotting were employed. Although Mchr1 expression was detected in the epidermis and dermis of both diestrus and lactating rats, parenchymal expression was exclusively found in the functional mammary gland of lactating rats. The expression of Mchr1 mRNA oscillated through the lactation period and reached its maximum in PPD19 dams. Presence of MCHR1 was confirmed with immunohistochemistry with preferential location of MCHR1 immunoreactive cells in the alveolar secretory cells. As was the case for gene expression, the MCHR1 protein levels were significantly higher in PPD19 than in other groups. Our data demonstrate the presence of an anatomical basis for the participation of MCH peptidergic system on the control of lactation through the mammary gland, suggesting that MCH could modulate a prolactation action in early postpartum days and the opposite role at the end of the lactation.

Expression of genes for melanotropic peptides and their receptors for morphological color change in goldfish Carassius auratus

To evaluate the association of the melanotropic peptides and their receptors for morphological color change, we investigated the effects of changes in background color, between white and black, on xanthophore density in the scales and expression levels of genes for hormonal peptides and corresponding receptors (MCH-R2, MC1R, and MC5R) in goldfish (Carassius auratus). The xanthophore density in both dorsal and ventral scales increased after transfer from a white to black background. However, xanthophore density in dorsal scales increased after transfer from a black to white background, and that of ventral scales decreased after transfer from a black to black background, which served as the control. In the white-reared fish, melanin-concentrating hormone (mch) mRNA content in the brain was higher than that in black-reared fish, whereas proopiomelanocortin a (pomc-a) mRNA content in the pituitary was lower than that in the black-reared fish. Agouti-signaling protein (asp) mRNA was detected in the ventral skin but not in the dorsal skin. No difference was observed in the asp mRNA content between fish reared in white or black background, suggesting that ASP might not be associated with background color adaptation. In situ hybridization revealed that both mc1r and mc5r were expressed in the xanthophores in scales. The mRNA content of mc1r in scales did not always follow the background color change, whereas those of mc5r decreased in the white background and increased in the black background, suggesting that mc5r might be a major factor reinforcing the function of MSH in morphological color changes. White backgrounds increased mch mRNA content in the brain, but decreased mch-r2 mRNA content in the scales. These altered expression levels of melanotropin receptors might affect reactivity to melanotropins through long-term adaptation to background color.

The Molecular Registry of Pituitary Adenomas (REMAH): A bet of Spanish Endocrinology for the future of individualized medicine and translational research

Pituitary adenomas are uncommon, difficult to diagnose tumors whose heterogeneity and low incidence complicate large-scale studies. The Molecular Registry of Pituitary Adenomas (REMAH) was promoted by the Andalusian Society of Endocrinology and Nutrition (SAEN) in 2008 as a cooperative clinical-basic multicenter strategy aimed at improving diagnosis and treatment of pituitary adenomas by combining clinical, pathological, and molecular information. In 2010, the Spanish Society of Endocrinology and Nutrition (SEEN) extended this project to national level and established 6 nodes with common protocols and methods for sample and clinical data collection, molecular analysis, and data recording in a common registry (www.remahnacional.com). The registry combines clinical data with molecular phenotyping of the resected pituitary adenoma using quantitative real-time PCR of expression of 26 genes: Pituitary hormones (GH-PRL-LH-FSH-PRL-ACTH-CGA), receptors (somatostatin, dopamine, GHRH, GnRH, CRH, arginine-vasopressin, ghrelin), other markers (Ki67, PTTG1), and control genes. Until 2015, molecular information has been collected from 704 adenomas, out of 1179 patients registered. This strategy allows for comparative and relational analysis between the molecular profile of the different types of adenoma and the clinical phenotype of patients, which may provide a better understanding of the condition and potentially help in treatment selection. The REMAH is therefore a unique multicenter, interdisciplinary network founded on a shared database that provides a far-reaching translational approach for management of pituitary adenomas, and paves the way for the conduct of combined clinical-basic innovative studies on large patient samples.

Molecular cloning, expression, and signaling pathway of four melanin-concentrating hormone receptors from Xenopus tropicalis

Melanin-concentrating hormone (MCH) mainly regulates feeding in mammals and pigmentation in teleosts. It acts via two G-protein-coupled receptors, MCH receptor 1 (MCHR1) and MCHR2. Although many studies exploring the MCH system in teleosts and mammals have been carried out, studies on other organisms are limited. In this study, we cloned and characterized four MCHR subtypes from the diploid species Xenopus tropicalis (X-MCHRs; X-MCHR1a, R1b, R2a, and R2b). According to a phylogenetic tree of the X-MCHRs, X-MCHR1a and R2a are close to mammalian MCHRs, while X-MCHR1b and R2b are close to teleostean MCHRs. We previously reported that the G-protein coupling capacity of the MCHR subtypes differed between mammals (R1: Gαi/o and Gαq; R2: Gαq) and teleosts (R1: Gαq; R2: Gαi/o and Gαq) in mammalian cell-based assays. By using Ca(2+) mobilization assays with pertussis toxin in CHO dhfr(-) cells, we found that X-MCHR1a promiscuously coupled to both Gαi/o and Gαq, while X-MCHR1b and R2a exclusively coupled to Gαq. However, no Ca(2+) influx was detected in cells transfected with X-MCHR2b. Reverse transcription-PCR showed that the X-MCHR mRNAs were expressed in various tissues. In particular, both X-MCHR1b and R2b were exclusively found in melanophores of the dorsal skin. In skin pigment migration assays, melanophores were weakly aggregated at low concentrations but dispersed at high concentrations of MCH, suggesting possible interactions between X-MCHR1b and R2b for the regulation of body color. These findings demonstrate that X. tropicalis has four characteristic MCHRs and will be useful for elucidating the nature of MCHR evolution among vertebrates.

Expression of melanin-concentrating hormone receptor 2 protects against diet-induced obesity in male mice

Melanin-concentrating hormone (MCH) is an orexigenic neuropeptide that is a ligand for two subtypes of MCH receptors, MCHR1 and MCHR2. MCHR1 is universally expressed in mammals ranging from rodents to humans, but the expression of MCHR2 is substantially restricted. In mammals, MCHR2 has been defined in primates as well as other species such as cats and dogs but is not seen in rodents. Although the role of MCHR1 in mediating the actions of MCH on energy balance is clearly defined using mouse models, the role of MCHR2 is harder to characterize because of its limited expression. To determine any potential role of MCHR2 in energy balance, we generated a transgenic MCHR1R2 mouse model, where human MCHR2 is coexpressed in MCHR1-expressing neurons. As shown previously, control wild-type mice expressing only native MCHR1 developed diet-induced obesity when fed a high-fat diet. In contrast, MCHR1R2 mice had lower food intake, leading to their resistance to diet-induced obesity. Furthermore, we showed that MCH action is altered in MCHR1R2 mice. MCH treatment in wild-type mice inhibited the activation of the immediate-early gene c-fos, and coexpression of MCHR2 reduced the inhibitory actions of MCHR1 on this pathway. In conclusion, we developed an experimental animal model that can provide insight into the action of MCHR2 in the central nervous system and suggest that some actions of MCHR2 oppose the endogenous actions of MCHR1.

Tandem duplications in the C-terminal domain of the mesotocin receptor exclusively identified among East Eurasian thrushes

Mesotocin is a neurohypophyseal hormone found in some non-mammalian vertebrates, including birds, reptiles, and amphibians. In this study, we identified and characterized 18-amino acid duplications in the C-terminal domain of the mesotocin receptor (MTR), specifically found in Turdus thrushes (Aves: Passeriforms: Turdidae). These duplicated elements are located in the distal part of the C-terminal tails of MTR and consist of amino acids that are highly conserved among major vertebrates. Intraspecific polymorphisms in a variable number of tandem duplications are commonly found in East Eurasian Turdus, but not in any other genus of Turdidae. Moreover, the genus Turdus can be further classified into 2 groups according to the presence or absence of a 3-amino acid deletion just adjacent to the putative palmitoylation site in the cytoplasmic C-terminal tail. The phylogeny presented here strongly supports the conspecific group of 4 East Eurasian thrushes (Turdus pallidus, T. chrysolaus, T. obscurus, and T. celaenops). Our findings, therefore, provide a new synapomorphy that can be used for phylogenetic assumptions and shed a light on the history of diversification within Eurasian Turdus clades.

Oestradiol decreases melanin-concentrating hormone (MCH) and MCH receptor expression in the hypothalamus of female rats

Previous studies have shown that oestradiol (E₂) decreases the orexigenic effect of melanin-concentrating hormone (MCH). In the present study, we examined whether this action of E₂ is mediated by its ability to decrease the expression of MCH or its receptor (MCHR1). Using immunocytochemistry and western blotting, we examined whether E₂ decreases MCH-immunoreactive neurones or MCHR1 protein content in the hypothalamus of female rats. We found that both MCH and MCHR1 protein expression was decreased by acute E₂ treatment in ovariectomised rats, and by the peri-ovulatory increase in circulating E₂ in pro-oestrous rats, relative to rats at other cycle stages. To determine whether these changes in MCH/MCHR1 protein expression may be mediated by E₂'s ability to directly regulate the transcription of MCH and MCHR1 genes, the effect of E₂ treatment on MCH and MCHR1 mRNA expression in a neuronal hypothalamic cell line was examined using real-time reverse transcriptase-polymerase chain reaction. We also determined whether MCH and oestrogen receptor (ER)α are co-expressed in the hypothalamus of female rats. E₂ treatment did not decrease MCH or MCHR1 mRNA expression in vitro, and no hypothalamic neurones were identified that co-expressed MCH and ERα. We conclude that E₂-dependent decreases in hypothalamic MCH/MCHR1 protein expression mediate the ability of E₂ to decrease MCH-induced feeding. The current findings suggest, however, that E₂ exerts these actions indirectly, most likely though interactions with other neuronal systems that provide afferent input to MCH and MCHR1 neurones.

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.

Identification and Characterization of Single-Nucleotide Polymorphisms in MCH-R1 and MCH-R2*

OBJECTIVE

To identify and functionally characterize single-nucleotide polymorphisms (SNPs) in melanin-concentrating hormone (MCH)-R1 and -R2.

RESEARCH METHODS AND PROCEDURES

The entire coding regions and intron/exon splice junction regions of MCH-R1 and MCH-R2 were sequenced from anonymous white (n=45) and African-American (n=46) individuals. DNA was analyzed, and SNPs were identified using Phred, Phrap, and Consed software. DNA constructs containing MCH-R1 and MCH-R2 SNPs were generated and expressed in CHO cells. The effect of the SNPs in MCH-R1 and MCH-R2 were assessed in receptor binding assays and functional assays measuring changes in intracellular cAMP and Ca2+ levels.

RESULTS

We identified 12 SNPs in the MCH-R1 gene. Two of these SNPs are in coding regions, and one produces an arginine-for-glycine substitution at residue 34 in the MCH-R1 sequence. This SNP is present at a minor allele frequency of 15% in the African-American population tested in this study. We identified eight SNPs in the MCH-R2 gene. Four of these SNPs are in coding regions, and two produce amino acid substitutions. Lysine substitutes for arginine at residue 63 of the African-American population, and glutamine substitutes for arginine at residue 152 in whites (minor allele frequency of 2% for both SNPs). No changes in receptor binding or functional signaling were observed with the SNP mutations in MCH-R1 or MCH-R2.

DISCUSSION

These data indicate that potential therapeutics designed to act at the MCH receptor are unlikely to have altered effects in subpopulations that express variant forms of MCH-R1 or MCH-R2.

Cloning, phylogenetic analysis and expression of somatolactin and its receptor in Cichlasoma dimerus: their role in long-term background color acclimation

Somatolactin (SL) and SL receptor (SLR) belong to the growth hormone and cytokine type I receptor superfamilies, respectively. However, further research is required to define the duplications and functions of SL and its receptors in basal vertebrates including environmental background color adaptation in fish. In the present study, we cloned and sequenced SL and its putative receptor (SLR), classified and compared the sequences phylogenetically, and determined SL and SLR mRNA expression levels during long-term background color exposure in Cichlasoma dimerus, a freshwater South American cichlid. Our results show that C. dimerus SL and SLR share high sequence similarity with homologous from other perciform fish. Phylogenetic analysis indicates that C. dimerus SL belongs to the SLα clade sub-group. C. dimerus SLR is clearly a member of the GHR1 receptor subgroup, which includes the experimentally validated SLR from salmonids. Higher transcript levels of SLα in the pituitary and SLR in the epidermis and dermis cells of fish scales were observed in fish following long-term black background color exposure compared to those exposed to a white background. A higher number of melanophores was also observed in fish exposed for 10days to a black background compared to those exposed to a white background. These changes were concomitant to differences in SL or SLR transcript levels found in fish exposed to these two different background colors. Our results suggest, for the first time, that SLR is expressed in fish scales, and that there is an increase in SL in the pituitary and the putative SLR in likely target cells, i.e., melanophores, in long-term black background exposure in C. dimerus.

A preliminary investigation of the role of melanin-concentrating hormone (MCH) and its receptors in appetite regulation of winter flounder (Pseudopleuronectes americanus)

In order to better understand the role of melanin-concentrating hormone (MCH) in the regulation of appetite in fish, the mRNAs of two forms of MCH, prepro-MCH and MCH2, and two forms of MCH receptors, MCH-R1 and MCH-R2, were isolated from winter flounder (Pseudopleuronectes americanus). In addition, the mRNA expressions of these peptides and their receptors were determined under fed and fasted conditions. Both MCHs are expressed in forebrain and midbrain, as well as peripheral tissues including gut and gonads. Both MCH-Rs are ubiquitously expressed in the brain and periphery. Fasting induced an increase in the expression levels of MCH and MCH-R1 mRNAs in optic tectum/thalamus and hypothalamus but had no effect on either MCH2 or MCH-R2 mRNA expressions. Our results suggest that MCH and MCH-R1, but not MCH2 and MCH-R2 might have a role in the regulation of appetite in flounder.

Inhibiting roles of melanin-concentrating hormone for skin pigment dispersion in barfin flounder, Verasper moseri

Barfin flounders change their surface color pattern to match their background. We have reported evidence of the association between hormones and body color changes in this fish. First, bolus intraperitoneal injection with melanin-concentrating hormone (MCH) immediately turned the skin color pale, while injection with melanocyte-stimulating hormone (MSH) did not change the skin color. Second, gene expression levels of MCH change in response to background color, while those of MSH do not. We also reported the expression of an MCH receptor gene (Mch-r2) in the skin of this fish. In this study, we aimed to further evaluate the roles of MCH in skin color change. First, long-term adaptation of adult barfin flounder to black or white background colors induced significantly different pigment migration patterns in both melanophores and xanthophores (P<0.05). However, continuous intraperitoneal injection with MCH did not influence chromatophore proliferation. Then, using in vitro experiments, we found that MCH aggregates both melanophores and xanthophores, and inhibits the pigment-dispersing activity of MSH in a similar manner. Finally, we identified transcripts of Mch-r2 in cells isolated from both melanophores and xanthophores. Taken together, the evidence suggests that MCH aggregates pigments via MCH-R2 in concert with the nervous system by overcoming the melanin-dispersing activities of MSH in barfin flounder.

Identification and characterization of mesotocin and V1a-like vasotocin receptors in a urodele amphibian, Taricha granulosa

The cDNA sequences encoding the mesotocin receptor (MTR) and vasotocin 1a receptor (VTR-1a) were identified in a urodele amphibian, the rough-skinned newt, Taricha granulosa. Saturation binding of [(3)H]oxytocin (OT) to the Taricha MTR (tMTR) was best fit by a two-state model; a high affinity-low abundance site and a lower affinity-high abundance site. Competition-binding studies found the following rank-order affinities for the tMTR: mesotocin (MT)>OT≈vasotocin (VT)>vasopressin (VP)>isotocin (IT). Inositol phosphate (IP) accumulation studies demonstrated functional activity of both the tMTR and Taricha VTR-1a (tVTR-1a) in a heterologous cell culture system. The rank-order potencies for the tMTR were MT>OT>VT≈VP>IT. The combined binding and IP results indicate that VT may act as a partial agonist of the tMTR. Rank-order potencies for the tVTR-1a were VT>VP>MT≈OT>IT. For both receptors, stimulation of IP accumulation was blocked by d(CH(2))(5)[Tyr(Me)(2)]AVP (Manning compound) and d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2)]OVT (OTA). OTA was a more potent antagonist for the transiently expressed tMTR while Manning compound was relatively more potent at inhibiting IP accumulation in tVTR-1a expressing cells. In contradiction to earlier assumptions, the absolute IC(50) of Manning compound was lower for the tMTR (27nM±13) than the tVTR-1a (586nM±166) indicating its potential higher affinity for the tMTR, a finding with special relevance to interpretation of comparative studies investigating the behavioral and physiological actions of neurohypophysial peptides in non-mammalian species.

Generation of mammalian cell lines with gene knock-down for human MCHR2

Appetite regulating neuropeptide melanin-concentrating hormone (MCH) has been implicated in obesity. It functions through its two receptors MCHR1 and MCHR2. While MCH and MCHR1 have been studied more extensively, the function of MCHR2 remains largely unknown, due to the lack of suitable in vitro and in vivo models. To create an in vitro system of genetic knock-down of MCHR2 in mammalian cells, we constructed four small hairpin RNAs (shRNAs) against human MCHR2 in eukaryotic expression vector, and transfected the plasmids into CHO cells that stably express human MCHR2. Using the empty vector or a negative shRNA control plasmid, we show that MCHR2-shRNAs suppressed 45.8% - 66.4% of MCHR2 expression at both mRNA and protein levels. As the result, in cells carrying the MCHR2-shRNAs, binding of MCHR2 to MCH was decreased by 39.4% - 78.7% accompanied by a similar decrease in affinity of the receptor to ligand by 40.9% - 81.9%. These cells still respond to MCH treatment, but intracellular Ca2+ release as the downstream signaling event was also decreased by 114.8% - 822.4%. Together, this study generated a set of shRNAs and cell lines as valuable reagents for further study on MCHR2 functions. These results will ultimately help to advance our knowledge about appetite regulating neuropeptide receptors.

Comparative proteomic analysis of proteins influenced by melanin-concentrating hormone and melanin-concentrating hormone receptor 2 interaction

Melanin-concentrating hormone receptor 2 (MCHR2), a second G protein-coupled receptor for melanin-concentrating hormone (MCH), has been known for many years. However, its physiological function is poorly understood. To identify the proteins involved in MCHR2 physiological function, a comparative proteomic analysis of protein expression in SH-SY5Y cells stably expressing human MCHR2 (SH-SY5Y-MCHR2) and control SH-SY5Y cells (SH-SY5Y-mock) - both treated with MCH - was conducted. Significant changes were observed in the expression of 34 proteins, including isocitrate dehydrogenase (NAD) subunit alpha, mitochondrial (IDH3A), phosphoenolpyruvate carboxykinase 1 (PCK1), 6-phosphofructo-2-kinase/fructose-2.6-biphosphatase 4 (PFKFB4), insulin-induced gene 2 protein (INSIG2), and acyl-coenzyme A thioesterase 8 (ACOT8). Among the proteins, IDH3A, PCK1, PFKFB4 increased significantly, and INSIG2, ACOT8 decreased significantly in experimental cells compared with control cells; these findings were further confirmed by semi-quantitative RT-PCR and Western blot analysis. The comparative proteome data may provide a valuable clue to further understand MCHR2 physiological function, and several differentially regulated proteins may be used as target proteins for the development of novel drugs.

MCH receptors/gene structure-in vivo expression

Melanin-concentrating hormone (MCH) is a cyclic peptide which was originally discovered in fish to lighten skin color by affecting melanosomes aggregation. This peptide is highly conserved and also found in rodents whose gene is overexpressed upon fasting. However, the site of MCH action remained obscure until its receptor was discovered in 1999 as a G protein-coupled receptor. After this receptor structure was identified, the functional domains important for MCH-MCHR interaction were revealed. Moreover, the cloning of the MCH receptor led us to identify the in vivo sites of MCH action which suggested potential physiological functions of the MCH system. Furthermore, the MCH receptor identification allow for designing surrogate molecules which can block MCH activity. Studies using these molecules revealed various physiological functions of the MCH system not only in feeding but also in other physiological responses such as stress and emotion. This review will discuss how the MCH receptor was discovered and its impact on many studies investigating the MCH receptor's structure, signaling pathways, and expression pattern.

Animals models of MCH function and what they can tell us about its role in energy balance

Melanin-concentrating hormone (MCH) has attracted considerable attention because of its effects on food intake and body weight and the MCH receptor (MCHR1) remains one of the viable targets for obesity therapy. This review summarizes the literature examining the effects of MCH on body weight, food intake and energy expenditure in rodent models, and the central sites where MCH acts in regulating energy homeostasis. Emphasis is given on the discrepancies between the genetic and pharmacologic models of MCHR1 inactivation. We propose some solutions to resolve these discrepancies and discuss some future directions in MCH research.

Electrophysiological effects of MCH on neurons in the hypothalamus

Melanin concentrating hormone (MCH) has been implicated in many brain functions and behaviors essential to the survival of animals. The hypothalamus is one of the primary targets where MCH-containing nerve fibers and MCH receptors are extensively expressed and its actions in the brain are exerted. Since the identification of MCH receptors as orphan G protein coupled receptors, the cellular effects of MCH have been revealed in many non-neuronal expression systems (including Xenopus oocytes and cell lines), however, the mechanism by which MCH modulates the activity in the neuronal circuitry of the brain is still under investigation. This review summarizes our current knowledge of electrophysiological effects of MCH on neurons in the hypothalamus, particularly in the lateral hypothalamus. Generally, MCH exerts inhibitory effects on neurons in this structure and may serve as a homeostatic regulator in the lateral hypothalamic area. Given the contrast between the limited data on cellular functions of MCH in the hypothalamus versus a fast growing body of evidence on the vital role of MCH in animal behavior, further investigations of the former are warranted.

Establishment of CHO cell line expressing human MCHR2 gene and research of its molecular characteristics

The whole length of MCHR2 gene cDNA fragment was amplified by PCR using human fetal brain cDNA library as template. The pcDNA3.1 (+)/MCHR2 eukaryotic expression vector was constructed successfully. The recombinant pcDNA3.1 (+)/MCHR2 plasmid was transfected into Chinese hamster ovary (CHO) cell by lipofectamine 2000, after G418 selection and then the CHO cell line expressing MCHR2 gene was established. The MCHR2 gene expression was tested by RT-PCR, western blotting and immunofluorescence. The maximum binding (B(max)) of CHO cell line was 309.97 +/-1.14 fM x mg(-1) protein and the dissociation constant (K(d) value) was 0.170 +/- 0.0006 nM. MCH could stimulate Ca2+ release, its 50% effective concentration (EC50) was 2.32 +/- 0.01 nM. The construction of the CHO cell line and the research of MCHR2 molecular characteristics have established a good experimental basis for the further research about the function of MCHR2 gene.

Melanin-concentrating hormone induces neurite outgrowth in human neuroblastoma SH-SY5Y cells through p53 and MAPKinase signaling pathways

Melanin-concentrating hormone (MCH) peptide plays a major role in energy homeostasis regulation. Little is known about cellular functions engaged by endogenous MCH receptor (MCH-R1). Here, MCH-R1 mRNA and cognate protein were found expressed in human neuroblastoma SH-SY5Y cells. Electrophysiological experiments demonstrated that MCH modulated K(+) currents, an effect depending upon the time of cellular growth. MCH treatments induced a transient phosphorylation of MAPKinases, abolished by PD98059, and partially blocked by PTX, suggesting a Galphai/Galphao protein contribution. MCH stimulated expression and likely nuclear localization of phosphorylated p53 proteins, an effect fully dependent upon MAPKinase activities. MCH treatment also increased phosphorylation of Elk-1 and up-regulated Egr-1, two transcriptional factors targeted by the MAPKinase pathway. Finally, MCH provoked neurite outgrowth after 24h-treatment of neuroblastoma cells. This effect and transcriptional factors activation were partly prevented by PD98059. Collectively, our results provide the first evidence for a role of MCH in neuronal differentiation of endogenously MCH-R1-expressing cells via non-exclusive MAPKinase and p53 signaling pathways.

Molecular cloning and expression of two melanin-concentrating hormone receptors in goldfish

Melanin-concentrating hormone (MCH) is a neurohypophysial hormone and induces melanin aggregation in the skin in teleosts. MCH also has multiple roles in the central regulation of food intake in teleosts and mammals. MCH receptors (MCH-R) are among type I G-protein-coupled receptors. Here, we cloned two MCH receptors from goldfish, Carassius auratus. The amino acid sequence of goldfish MCH-R1 had 57-88% homology with fish MCH-R1 and 49-50% homology with mammalian MCH-R1, while the amino acid sequence of goldfish MCH-R2 had 72-92% homology with fish MCH-R2 and 32% homology with human MCH-R2. Phylogenetic analysis showed that these two MCH-Rs are orthologous to the respective mammalian MCH-Rs. The common amino acid residues for ligand binding, signal transduction, and receptor conformation were well conserved in these receptors, although some intracellular basic-amino-acid-rich domains, which have been shown to exist in human MCH-R1 and MCH-R2, were absent in goldfish MCH-R2. When stably expressed in HEK293 cells, both goldfish MCH-R1 and MCH-R2 displayed a strong, dose-dependent, transient elevation of intracellular calcium in response to salmon MCH (EC(50)=0.8nM and 31.8nM, respectively). In contrast to goldfish MCH-R2, goldfish MCH-R1 signaling is not sensitive to pertussis toxin, suggesting an exclusive Galphaq coupling of goldfish MCH-R1 in the mammalian cell-based assay. Reverse transcriptase PCR revealed that both MCH-R1 and MCH-R2 mRNA are distributed in various tissues in goldfish. The various tissues including the brain and skin express both MCH-R1 and MCH-R2. These results suggest that these functional receptors mediate multiple effects of MCH in goldfish.

Melanin-concentrating hormone and melanin-concentrating hormone receptors in mammalian skin physiopathology

To date, there is a dearth of evidence to support functions for melanin-concentrating hormone (MCH) and melanin-concentrating hormone receptors (MCH-R) in mammalian skin physiology including pigmentation, inflammation and immune responses and skin cell proliferation. Much research is therefore still needed to define the roles of the hormone and its receptors in mammalian skin. This will be a crucial step to identifying pathogenic mechanisms that may involve the MCH/MCH-R system in the context of inflammatory and autoimmune skin diseases as well as skin cancers. The following review summarizes the studies which have been carried out to examine the expression and function of MCH and MCH-R in mammalian skin. Recent findings with regard to humoral immune responses to the MCH-R1 in patients with the skin depigmenting disease vitiligo are also discussed.

Melanin-concentrating hormone and immune function

To date, melanin-concentrating hormone (MCH) has been generally considered as peptide acting almost exclusively in the central nervous system. In the present paper, we revise the experimental evidence, demonstrating that MCH and its receptors are expressed by cells of the immune system and directly influence the response of these cells in some circumstances. This therefore supports the idea that, as with other peptides, MCH could be considered as a modulator of the immune system. Moreover, we suggest that this could have important implications in several immune-mediated disorders and affirm that there is a clear need for further investigation.

Down-regulation of genes encoding steroidogenic enzymes and hormone receptors in late preovulatory follicles of the cow coincides with an accumulation of intrafollicular steroids

The transformation of the dominant follicle into a functional corpus luteum is accompanied by a profound molecular and morphological reorganization of somatic cell layers. Several studies have focused on gene expression during early processes of follicular differentiation as it relates to recruitment and selection of dominant follicles. However, little information exists on changes of gene expression profiles in late preovulatory follicles. This lack of information is addressed here to elucidate molecular mechanisms behind the LH-induced transition from the large dominant estrogen-active to the preovulatory follicle, an intermediate stage toward full luteinization. Transcripts encoding key molecules for the biosynthesis of steroid hormones and prostaglandins, as well as receptors for gonadotropic and growth hormones (Star, Cyp11a1, Hsd3b, Cyp17, Cyp19, Ptgs2, Fshr, Lhr, and Ghr), were quantified by real-time polymerase chain reaction (PCR) in the granulosa and theca of large dominant and late preovulatory follicles. The steroid hormones progesterone (P4) and estradiol-17beta (E2) were monitored to distinguish estrogen-active and estrogen-inactive follicles. We found that (1) independent of the follicular stage, the gene expression profile was very different in granulosa and theca; (2) the abundance of several key transcripts was lower in estrogen-inactive, compared with estrogen-active, dominant follicles; (3) in the granulosa of late preovulatory follicles, transcripts encoding steroidogenic enzymes and hormone receptors were largely down-regulated, whereas (4) progesterone and E2 were found at high concentrations in the follicular fluid. Collectively, our data show that late preovulatory follicles have a transient and unique gene expression profile and are clearly different from both the preceding and subsequent (follicular and luteal, respectively) stages.

A sea lamprey glycoprotein hormone receptor similar with gnathostome thyrotropin hormone receptor

The specificity of the vertebrate hypothalamic-pituitary-gonadal and hypothalamic-pituitary-thyroid axes is explained by the evolutionary refinement of the specificity of expression and selectivity of interaction between the glycoprotein hormones GpH (FSH, LH, and TSH) and their cognate receptors GpH-R (FSH-R, LH-R, and TSH-R). These two finely tuned signaling pathways evolved by gene duplication and functional divergence from an ancestral GpH/GpH-R pair. Comparative analysis of the protochordate and gnathostome endocrine systems suggests that this process took place prior or concomitantly with the emergence of the gnathostome lineage. Here, we report identification and characterization of a novel glycoprotein hormone receptor (lGpH-R II) in the Agnathan sea lamprey. This 781 residue protein was found approximately 43% identical with mammalian TSH-R and FSH-R representative sequences, and similarly with these two classes of mammalian receptors it is assembled from ten exons. A synthetic ligand containing the lamprey glycoprotein hormone beta-chain tethered upstream of a mammalian alpha-chain activated the lGpH-R II expressed in COS-7 cells but in a lesser extent than lGpH-R I. Molecular phylogenetic analysis of vertebrate GpH-R protein sequences suggests a closer relationship between lGpH-R II and gnathostome thyrotropin receptors. Overall, the presence and characteristics of the lamprey glycoprotein hormone receptors suggest existence of a primitive functionally overlapping glycoprotein hormone/glycoprotein hormone receptor system in this animal.

Extracellular loop 3 (ECL3) and ECL3-proximal transmembrane domains VI and VII of the mesotocin and vasotocin receptors confer differential ligand selectivity and signaling activity

Mesotocin (MT) and vasotocin (VT) are the nonmammalian orthologs of mammalian oxytocin (OT) and arginine vasopressin (AVP), respectively. The OT/AVP family of peptides has arisen from gene duplication but has evolved to possess high selectivity toward their cognate receptors. The process of molecular evolution of receptors to confer high selectivity to their cognate ligands, however, is poorly understood. We constructed a series of reciprocal chimeras using a pair of bullfrog MT receptor (MTR) and VT1 receptor (VT1R) DNA fragments. Among the MTR/VT1R chimeras, the MTR chimera containing a region from transmembrane domain (TMD) VI to the carboxyl-terminal tail (C-tail) of VT1R showed an increased sensitivity to VT, while a chimeric VT1R containing TMD VI to C-tail of MTR showed an increased sensitivity to MT. Further dissection of domains using additional chimeras demonstrated that the receptor with the fragment containing extracellular loop 3 (ECL3) and ECL3-proximal TMDs VI and VII of MTR increased MT selectivity. This fragment is also important for receptor conformation that permits the signaling ability of the receptor. Particularly, the amino acids Val/Ile(6.54) in TMD VI and Pro/Glu(7.29) in ECL3 appear to be involved in this activity, since double mutation of these amino acids completely blocked signaling activity while maintaining ligand binding activity. Mutations at these residues in human OT and AVP 1a receptors markedly decreased receptor signaling activity. This study provides clues for understanding molecular coevolution of the OT/AVP peptides and their receptors with regard to receptor-ligand binding and receptor signaling activity.

Genetic study of the melanin-concentrating hormone receptor 2 in childhood and adulthood severe obesity

CONTEXT

The melanin-concentrating hormone receptor 2 (MCHR2) is a G protein-coupled receptor for melanin-concentrating hormone, a neuropeptide that plays an important role in feeding behaviors. MCHR2 maps on chromosome 6q16.3, in a susceptibility locus for childhood obesity.

OBJECTIVE

The aim of this study was to investigate the association between MCHR2 variation and human obesity.

DESIGN

Case control and family-based studies were performed.

PARTICIPANTS

A total of 141 obese children and 24 nonobese adult subjects was sequenced, and case-control analyses were conducted using 628 severely obese children and 1,401 controls.

RESULTS

There were 11 single nucleotide polymorphisms (SNPs) identified. We showed nominal association among -38,245 ATG A/G SNP (P = 0.03; 95% confidence interval 1.02-1.34; odds ratio 1.17), A76A T/C SNP (P = 0.03; 95% confidence interval 0.58-0.97; odds ratio 0.75), and childhood obesity. Analysis of 645 trios with childhood obesity supported further the A76A T/C association, showing an overtransmission to obese children of the at risk T allele (59.0%; P = 0.01), especially in children with most severe forms of obesity (Z score of body mass index > 4) (67.0%; P = 0.003). The A76A at risk T allele was also associated with overeating during meals (P = 0.02) in an additional group of 102 nonobese children. None of the MCHR2 variants, including the A76A SNP, showed association with adult severe obesity, although a trend for association of the T allele of this variant with food disinhibition (P = 0.06) and higher hunger (P = 0.09) was found. This variant was not associated with childhood obesity in an independent case-control study, including 1,573 subjects (P = 0.98). Moreover, the A76A SNP did not explain the linkage on the 6q locus.

CONCLUSION

Our results altogether suggest that MCHR2 is not a major contributor to polygenic obesity and support a modest effect of the A76A SNP on food intake abnormalities in childhood.

The melanin-concentrating hormone receptor 2 (MCH-R2) mediates the effect of MCH to control body color for background adaptation in the barfin flounder

Melanin-concentrating hormone (MCH) is a neuropeptide generated in neurons originating in the hypothalamus, from which axons project to the entire brain and neurohypophysis in fish. MCH has both central and peripheral roles such as food intake and body color change. Here we cloned two MCH receptors (MCH-R) from the barfin flounder, Verasper moseri, Pleuronectiformes. The phylogenetic analysis shows that these are orthologues to the mammalian MCH-R1 and MCH-R2 showing 49 and 30% amino acid sequence identity to the corresponding human receptors while they have 31% amino acid sequence identify between them. Essential amino acid residues for ligand binding, signal transduction and receptor conformation, which have been shown in mammalian MCH-R, are well conserved in the flounder MCH-Rs. MCH-R1 has one intron in the extracellular N-terminal region and MCH-R2 has one intron in the DRY motif, which is a homologous position to one of the five introns of human MCH-R2. Orthologues of MCH-R1 and MCH-R2 may have appeared by gene duplication of the ancestry of MCH-Rs having at least two introns, and then MCH-R1 and MCH-R2 inherited different introns in flounder strains. We also determined their tissue distribution and functional role in rearing condition. Reverse transcription PCR revealed that the expression of MCH-R1 is confined to the brain of the barfin flounder, while transcripts of MCH-R2 were detected in the brain, pituitary, eyeball, gill, atrium, ventricle, head kidney, body kidney, spleen, intestine, inclinator, skeletal muscle testis, ovary, eyed-side skin, and non-eyed-side skin. The expression of MCH-R2 in eyed-side skin was higher in fish reared in a black tank (121 days) than in a white tank while the expression levels of MCH in the brain were significantly greater in the group reared with the white background suggesting down-regulation of this receptor gene with increased levels of MCH. The results suggest that the MCH-R2 mediates the effect of MCH to control body color for background adaptation in the eyed-side skin of the barfin flounder.

Evolution and Differentiation of MSHR Gene in Different Species

Coat color offers some prospects for evolutionary studies due to its large amount of presumably adaptive coat color variation and conserved genetic mechanisms of generating different coat colors in different species. Melanocyte-stimulating hormone receptor (MSHR) gene is responsible for intraspecific and interspecific color variation in mammals and birds. A total number of 206 MSHR gene sequences belonging to 84 species, 58 genera, and 20 families were analyzed to investigate its evolution and differentiation in different species. Most of the species have 954 bp and stop codon TGA. Species in Callithrix and Callimico have a stop codon mutation from TGA to TGG and elongate 81 bp with TAG as stop codon. Species in Phasianidae, Fringillidae, and Lemuridae also use TAG as stop codon. The Sus scrofa had an insertion of AACCAGACC encoding Asn-Gln-Thr from 85 to 93 bp. In Bovidae, a brown strain of cow with 966 bp due to the 12-bp duplication of GGCATTGCCCGG from 670 to 681 bp encoding for Gly-Ile-Ala-Arg was found. Teiidae has the smallest number of total mutations (6), silent mutations (3), nonsynonymous mutations (3), average number of nucleotide differences (1.519), synonymous nucleotide diversity (pi(s) = 0.0030), and nonsynonymous nucleotide diversity (pi(a) = 0.0029), and Hominidae, Lemuridae, Canidae, and Teiidae have higher ratio of pi(a)/pi(s) (0.537-0.973). The reconstructed phylogenetic tree of MSHR gene of families is basically consistent with the taxonomy of National Center for Biotechnology Information.

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.

Interaction of neurochondrin with the melanin-concentrating hormone receptor 1 interferes with G protein-coupled signal transduction but not agonist-mediated internalization

Screening of a human brain cDNA library using the C-terminal tail of the melanin-concentrating hormone receptor 1 (MCHR1) as bait in a yeast two-hybrid assay resulted in the identification of the neurite-outgrowth related factor, neurochondrin. This interaction was verified in overlay, pulldown, and co-immunoprecipitation assays. Deletion mapping confined the binding to the C terminus of neurochondrin and to the proximal C terminus of MCHR1, a region known to be involved in G protein binding and signal transduction. This region of the MCHR1 is also able to interact with the actin- and intermediate filament-binding protein, periplakin. Interactions of MCHR1 with neurochondrin and periplakin were competitive, indicating that these two proteins bind to overlapping regions of MCHR1. Although neurochondrin did not interfere with melanin-concentrating hormone-mediated internalization of the receptor, it did inhibit G protein-coupled signal transduction via both Galpha(i/o) and Galpha(q/11) family G proteins as measured by each of melanin-concentrating hormone-induced G protein-activated inwardly rectifying K(+) channel activity of voltage-clamped amphibian oocytes, by calcium mobilization in transfected mammalian cells, and by reduction in the capacity of melanin-concentrating hormone to promote binding of [(35)S]guanosine 5'-3-O-(thio)triphosphate to both Galpha(o1) and Galpha(11). Immunohistochemistry revealed co-expression of neurochondrin and MCHR1 within the rodent brain, suggesting that neurochondrin may be involved in the regulation of MCHR1 signaling and play a role in modulating melanin-concentrating hormone-mediated functions in vivo.

Development of a time-resolved fluorometric assay for the high throughput screening of melanin concentrating hormone receptor antagonists

INTRODUCTION

Melanin concentrating hormone is an orexigenic hypothalamic neuropeptide, which plays an important role in the complex regulation of energy balance and body weight mediated by the melanin concentrating hormone receptor subtype 1 (MCH1). Compelling pharmacological evidence implicating MCH1 signaling in the regulation of food intake and energy expenditure has generated a great deal of interest by pharmaceutical companies as MCH1 antagonists may have potential therapeutic benefit in the treatment of obesity and metabolic syndrome.

METHODS

Although radioligand receptor binding assay has been one of the most powerful tools for receptor research and drug discovery, the limitations of radioisotopes and the problems related to safety and waste disposal limits their application in high throughput screening and has led to a growing interest in alternative, nonradioactive technologies. To develop a sensitive and reproducible assay system for MCH1, the time-resolved fluorescence (TRF) receptor binding assay with AcroWell filter plates was tested and validated.

RESULTS

Comparing to the radioligand receptor binding assay for MCH1, the TRF assay presented higher Z/Z' factors with the lower signal-to-noise ratio. The known high-affinity MCH1 receptor antagonist, SNAP-7941, exhibited an IC50 value of 1.66+/-0.10 nM that is very similar to the IC50 value of MCH in a radioligand binding assay with an excellent correlation coefficient (0.9884).

DISCUSSION

These results suggest that our TRF receptor binding assay for MCH1 can achieve the desired sensitivity and reproducibility to replace the radioligand receptor assay in a fluorometric system that can be developed for high throughput screening.

Previtellogenic oocyte growth in salmon: relationships among body growth, plasma insulin-like growth factor-1, estradiol-17beta, follicle-stimulating hormone and expression of ovarian genes for insulin-like growth factors, steroidogenic-acute regulatory protein and receptors for gonadotropins, growth hormone, and somatolactin

Body growth during critical periods is known to be an important factor in determining the age of maturity and fecundity in fish. However, the endocrine mechanisms controlling oogenesis in fish and the effects of growth on this process are poorly understood. In this study interactions between the growth and reproductive systems were examined by monitoring changes in various components of the FSH-ovary axis, plasma insulin-like growth factor 1 (Igf1), and ovarian gene expression in relation to body and previtellogenic oocyte growth in coho salmon. Samples were collected from females during two hypothesized critical periods when growth influences maturation in this species. Body growth during the fall-spring months was strongly related to the degree of oocyte development, with larger fish possessing more advanced oocytes than smaller, slower growing fish. The accumulation of cortical alveoli in the oocytes was associated with increases in plasma and pituitary FSH, plasma estradiol-17beta, and ovarian steroidogenic acute regulatory protein (star) gene expression, whereas ovarian transcripts for growth hormone receptor and somatolactin receptor decreased. As oocytes accumulated lipid droplets, a general increase occurred in plasma Igf1 and components of the FSH-ovary axis, including plasma FSH, estradiol-17beta, and ovarian mRNAs for gonadotropin receptors, star, igf1, and igf2. A consistent positive relationship between plasma Igf1, estradiol-17beta, and pituitary FSH during growth in the spring suggests that these factors are important links in the mechanism by which body growth influences the rate of oocyte development.

Genetic inactivation of melanin-concentrating hormone receptor subtype 1 (MCHR1) in mice exerts anxiolytic-like behavioral effects

The biological effects of the melanin-concentrating hormone (MCH) are mediated by the melanin concentrating hormone receptor 1 (MCHR1) in mice. This receptor is enriched in brain areas that are involved in the modulation of mood and affect, suggesting that MCH-dependent signaling may influence neurobiological mechanisms underlying fear and anxiety processes. To test this, we have generated mice lacking functional MCHR1 and characterized phenotypic traits using a number of behavioral tests. Mice carrying a null mutation of the MCHR1 gene display anxiolytic-like behavior across a battery different behavioral paradigms commonly used to assess fear and anxiety responses in rodents: open field, elevated plus maze, social interaction, and stress-induced hyperthermia. The brain serotonin (5-HT) system is central to the control of mood- and anxiety-related processes. To examine the impact of MCHR1 receptor deletion on 5-HT neurotransmission, we used in vivo microdialysis in freely moving knockout and wild-type mice. Baseline dialysate 5-HT levels were significantly lower in MCHR1 knockout mice as compared with wild-type controls (9.53+/-0.24 fmol for wild types vs 6.91+/-0.36 fmol for knockouts) in the prefrontal cortex (PFC), one of the main target structures of the serotonergic system and one that is highly associated with the control of emotional processes. Moreover, forced swim increased 5-HT efflux in the PFC of wild-type but not MCHR1 knockout mice. In summary, we show that MCHR1 can modulate stress- and anxiety-like behaviors and suggest that this may be due to changes in serotonergic transmission in forebrain regions.

Medaka receptors for somatolactin and growth hormone: phylogenetic paradox among fish growth hormone receptors

Somatolactin (SL) in fish belongs to the growth hormone/prolactin family. Its ortholog in tetrapods has not been identified and its function(s) remains largely unknown. The SL-deficient mutant of medaka (color interfere, ci) and an SL receptor (SLR) recently identified in salmon provide a fascinating field for investigating SL's function(s) in vivo. Here we isolated a medaka ortholog of the salmon SLR. The mRNA is transcribed in variable organs. Triglycerides and cholesterol contents in the ci are significantly higher than those in the wild type, providing the first evidence of SL's function in suppressing lipid accumulation to organs. Interestingly, phylogenetic comparisons between the medaka SLR and growth hormone receptor (GHR), which is also isolated in this study, in relation to GHRs of other fish, suggested that all GHRs reported from nonsalmonid species are, at least phylogenetically, SLRs. An extra intron inserted in medaka and pufferfish SLRs and flounder and sea bream GHRs also supports their orthologous relationship, but not with tetrapod GHRs. These results may indicate lineage-specific diversification of SLR and GHR functions among fish or just an inappropriate naming of these receptors. Further functional and comparative reassessments are necessary to address this question.

Arginine residue 155 in the second intracellular loop plays a critical role in rat melanin-concentrating hormone receptor 1 activation

Melanin-concentrating hormone (MCH) receptor 1 (MCH1R) is a class A G protein-coupled receptor. The MCH system has been linked to a variety of physiological functions, including the regulation of feeding and energy metabolism. We recently reported the importance of a dibasic motif in the membrane-proximal C-terminal region for MCH1R function. Here we reveal that an Arg residue in intracellular loop 2 of MCH1R plays a critical role in receptor function. We analyzed the roles of two distinct motifs, BBXXB and BXBB (in which B is a basic residue and X is a nonbasic residue), located in the three intracellular loops of MCH1R. Triple-substitution mutants of intracellular loops 1 and 3 could still activate calcium mobilization, albeit with lower efficacy or potency. However, mutations in intracellular loop 2 led to a complete loss of induction of signal transduction without changing the high affinity constant (Kd) value. By analyzing a series of single-substitution mutants, a point mutation of Arg155 in intracellular loop 2 was found to be responsible for the signaling pathway elicited by MCH. In addition, substitution at positions corresponding to Arg155 in human MCH receptor 2 and rat somatostatin receptor 2 also markedly abolished their ligand-induced signaling capacities, indicating that this Arg is a recognition determinant in several G protein-coupled receptors.

Mutation analysis of the MCHR1 gene in human obesity

OBJECTIVE

The importance of the melanin-concentrating hormone (MCH) system for regulation of energy homeostasis and body weight has been demonstrated in rodents. We analysed the human MCH receptor 1 gene (MCHR1) with respect to human obesity.

DESIGN

This consisted of genomic screening of 13.4 kb encompassing the MCHR1 in extremely obese German children and adolescents and association analyses for two coding single nucleotide polymorphisms (SNPs). To confirm initial positive association results, additional association studies and transmission disequilibrium tests in further German, Danish, French and American samples were conducted. Selected SNPs were investigated using functional in vitro studies and reporter gene assays.

METHODS

Single-stranded conformation polymorphism analysis, re-sequencing, PCR-restriction fragment length polymorphism analyses, tetra-primer amplification refractory mutation systems, matrix-assisted laser desorption/ionization time of flight mass spectrometry and reporter gene assays were carried out as well as measuring inositol phosphate formation, inhibition of cAMP formation and activation of p42/44 MAP kinase.

RESULTS

We identified 11 infrequent variations and two SNPs in the MCHR1 coding sequence and 18 SNPs (eight novel) in the flanking sequence. Association and transmission disequilibrium with obesity were detected for several SNPs in independent study groups of German obese children and adolescents and controls. In two German samples, encompassing 4056 and 295 individuals, trends towards association with obesity were detected. Findings in a second epidemiological German sample and in Danish, French and American samples were negative. Functional in vitro studies as well as reporter gene assays revealed no significant results.

CONCLUSION

Our initial association of MCHR1 alleles/haplotype detected might be related to juvenile-onset obesity, conditional on a particular genetic and/or environmental background. Alternatively, we could not exclude the possibility that the initially detected association represented a false positive finding.

Identification of the salmon somatolactin receptor, a new member of the cytokine receptor family

Somatolactin (SL) is a pituitary hormone of the GH/prolactin (PRL) family that so far has been found only in fish. Compared with GH and PRL, the primary structure of SL is highly conserved among divergent fish species, suggesting it has an important function and a discriminating receptor that constrains structural change. However, SL functions are poorly understood, and receptors for SL have not yet been identified. During cloning of GH receptor cDNA from salmon, we found a variant with relatively high (38-58%) sequence identity to vertebrate GH receptors and low (28-33%) identity to PRL receptors; however, the recombinant protein encoding the extracellular domain showed only weak binding of GH. Ligand binding of the recombinant extracellular domain for this receptor confirmed that the cDNA encoded a specific receptor for SL. The SL receptor (SLR) has common features of a GH receptor including FGEFS motif, six cysteine residues in the extracellular domain, a single transmembrane region, and Box 1 and 2 regions in the intracellular domain. These structural characteristics place the SLR in the cytokine receptor type I homodimeric group, which includes receptors for GH, PRL, erythropoietin, thrombopoietin, granulocyte-colony stimulating factor, and leptin. Transcripts for SLR were found in 11 tissues with highest levels in liver and fat, supporting the notion that a major function of SL is regulation of lipid metabolism. Cloning SLR cDNA opens the way for discovery of new SL functions and target tissues in fish, and perhaps novel members of this receptor family in other vertebrates.

Differential expression of mesotocin receptors in the uterus and ovary of the pregnant tammar wallaby

Mesotocin, an oxytocin-like peptide, is released in highest concentrations during parturition in macropodid marsupials. In late pregnant wallabies, uterine sensitivity to mesotocin increases markedly in the myometrium of the gravid uterus. This coincides with a significant increase in myometrial mesotocin receptor concentrations 3–4 days before term. To date, there is no information on mesotocin receptor gene expression in female wallaby reproductive tissues. This study aimed to examine mesotocin receptor gene expression in the uterus and ovaries of pregnant tammar wallabies, and to localise mesotocin receptors within the uterus. An RT-PCR strategy produced a consensus nucleotide sequence of 834 bp, which encoded 278 amino acids of transmembrane domains I to VI. This protein sequence has approximately 80% homology with the bovine and rat oxytocin receptor exon 2 region. Only one mesotocin receptor was detected in the tammar genome. The myometrium and mammary gland both expressed a 4.1 kb mesotocin receptor gene transcript. Myometrial mesotocin receptor gene expression increased on day 22 of the 26-day gestation and was significantly higher in the gravid than the non-gravid uterus in late pregnancy. This pattern of mesotocin receptor gene expression paralleled mesotocin receptor concentrations. Mesotocin binding sites were localised only to the myometrium, the highest densities being observed in the gravid uterus. Finally, this study showed high expression of mesotocin receptors in the corpus luteum. The pattern of luteal mesotocin receptor expression differed from the myometrium, with a decrease in mesotocin receptors occurring on the day of expected births.

Seasonal Changes in Mesotocin and Localization of Its Receptor in the Prostate of the Brushtail Possum (Trichosurus vulpecula)

The prostate gland in the brushtail possum grows and regresses seasonally. It has similarities to the human prostate and may therefore provide a unique model for investigating prostatic hyperplasia. Oxytocin has been implicated in the regulation of prostate growth in eutherian mammals, and the initial aim of this study was to identify and localize the marsupial equivalent, mesotocin, and its receptor in the prostate of the brushtail possum. Seasonal changes in prostatic mesotocin concentrations and receptor localization were then assessed and related to prostate growth. Mesotocin and mesotocin receptor gene transcripts with high sequence homology to eutherian oxytocin/oxytocin receptors were demonstrated, and mesotocin, neurophysin, and the receptor were all localized predominantly in the epithelial cells of the glandular acini. Western blot analysis confirmed the presence of a single immunoreactive receptor protein of approximately 60 Mr-3. Prostatic mesotocin concentrations were highest immediately before the increases in prostate weight associated with the autumn and spring breeding periods. At this time, mesotocin receptors were also present in the prostatic capsule in addition to those present in the glandular tissue. Mesotocin concentrations proceeded to decrease in association with the regression of prostate size toward the end of the breeding periods. No significant differences were present in serum testosterone or dihydrotestosterone throughout the year. The identification of mesotocin and its receptor in the possum prostate and the demonstration of seasonal changes in local mesotocin concentrations preceding changes in prostate size suggests that mesotocin may play a physiological role in regulating prostate growth and regression.

Increases in melanin-concentrating hormone and MCH receptor levels in the hypothalamus of dietary-obese rats

Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that stimulates feeding and increases body weight in rodents. We studied the role of the system in energy homeostasis and its regulation by the satiety signals, leptin and insulin. We used real-time PCR to measure the hypothalamic expression of MCH and its receptor (MCHR1) in two contrasting models of altered nutritional status, namely, obesity induced by 8 weeks' voluntary overeating and food restriction for 10 days. Diet-fed rats were stratified according to final total fat-pad mass into a 'high fat gain' group (HG) and 'low fat gain' group (LG). MCH mRNA levels were increased by 31% (p>0.05) and 49% (p<0.05) in the LG and HG, respectively, compared with controls. MCHR1 mRNA levels rose by 118% in the LG (p<0.01) and 85% in the HG (p<0.01). There were significant positive correlations (p<0.05) between plasma leptin concentration and both MCH and MCHR1 mRNA levels, and between plasma insulin and MCHR1 expression. A positive correlation was also observed between MCH and MCHR1 mRNA levels (p<0.05). Food-restricted rats showed no significant alterations in the levels of either MCH mRNA or MCHR1 mRNA. In a second experiment, we measured MCH peptide levels in five discrete hypothalamic areas of dietary-obese rats. MCH concentrations were significantly increased in the arcuate nuclei of the HG (p<0.05) and the paraventricular nuclei of both the LG (p<0.05) and HG (p<0.05), compared with their lean counterparts. These results suggest that the MCH system becomes more active in dietary obesity and could be involved in enhancing appetite for palatable food. The possibility that MCH and MCHR1 expression are positively regulated by leptin and insulin, which normally inhibit feeding, is a putative explanation for how appetite for palatable food is able to override mechanisms that prevent the development of obesity.

UV-induced Expression of Key Component of the Tanning Process, the POMC and MC1R Genes, Is Dependent on the p-38-activated Upstream Stimulating Factor-1 (USF-1)

Protection against UV-mediated DNA damage and the onset of oncogenesis is afforded by the tanning response in which UV irradiation triggers melanocytes to increase production of melanin that is then transferred to keratinocytes. A key component of the tanning process is the UV-mediated induction of the pro-opiomelanocortin (POMC) and MC1R genes encoding the alpha-melanocyte-stimulating hormone and its receptor, respectively, which play a crucial role in pigmentation by regulating the intracellular levels of cAMP. How these genes are regulated in response to UV irradiation is not known. Here we have shown that UV-induced activation of the POMC and MC1R promoters is mediated by p38 stress-activated kinase signaling to the transcription factor, upstream stimulating factor-1 (USF-1). Importantly, melanocytes derived from USF-1 -/- mice exhibit a defective UV response and fail to activate POMC and MC1R expression in response to UV irradiation. The results define USF-1 as a critical UV-responsive activator of genes implicated in protection from solar radiation.

Study on SNP of melanocyte stimulating hormone receptor gene in several Chinese indigenous sheep breeds using DHPLC

Single nucleotide polymorphism (SNP) of melanocyte stimulating hormone receptor (MSHR) gene was studied by sequencing and denaturing high performance liquid chromatography (DHPLC) in Mongolian sheep, Kazakstan sheep, Tan sheep and Tibetan sheep. The results showed that there is a mutation at position 317 (T317C) within the length of 415bp and the DHPLC is a high-throughput and simple method for screening this mutation. The heterozygote (TC) with shoulder peak could be detected quickly at the first time of DHPLC, and two homozygotes (TT or CC) could be discriminated easily through two times of DHPLC when each homozygous DNA was mixed with a known homozygous reference sample at the second time of DHPLC. All of the populations for this site are in Hardy-Weinberg equilibrium. The results also indicated that Mongolian sheep and Kazakstan sheep had close relationship, Tibetan sheep and Tan sheep had close relationship. The relationship among breeds was consistent with that of microsatellite DNA.

Melanin-concentrating hormone receptor mutations and human obesity: functional analysis

Melanin-concentrating hormone (MCH), a neuropeptide highly expressed in the lateral hypothalamus, has an important role in the regulation of energy balance and body weight in rodents. We examined whether mutations in the two known MCH receptors might be associated with obesity-related phenotypes in humans. Among 106 subjects with severe early onset obesity and a history of hyperphagia, we found two missense variants in MCHR1: Y181H and R248Q. Neither of these was found in 192 normal weight controls. R248Q cosegregated with obesity across two generations; family data were unavailable for Y181H. When expressed in HEK293 cells, R248Q showed no evidence of constitutive activation or ligand hypersensitivity for extracellular signal-regulated kinase phosphorylation. In addition, R248Q showed no enhanced suppression of cAMP generation. Two common single-nucleotide polymorphisms were found to be in linkage disequilibrium: g.-114A>G and c.39C>T. No association between either of these single-nucleotide polymorphisms and obesity-related phenotypes was found among a population cohort of 541 whites. Only two rare noncoding variants were found in MCHR2. In conclusion, mutations in the MCH receptors are not commonly found in humans with severe early onset obesity. Clarification of the relationship of these variants to obesity must await study in other populations and/or in genetically modified mice.

Expression and characterization of melanin-concentrating hormone receptors on mammalian cell lines

The neuropeptide melanin-concentrating hormone (MCH) is expressed in central and peripheral tissues where it participates in the complex network regulating energy homeostasis as well as in other physiologically important functions. Two MCH receptor subtypes, MCH-R1 and MCH-R2, have been cloned which signal through activation of Gi/o/q proteins and hence regulate different intracellular signals, such as inhibition of cAMP formation, stimulation of IP3 production, increase in intracellular free Ca2+ and/or activation of MAP kinases. Most of the data were obtained with cell systems heterologously expressing either of the MCH receptors. Fewer reports exist on studies with cell lines which endogenously express MCH receptors. Here, we describe human and other mammalian cell lines with which MCH receptor activation can be studied under "natural" conditions and we summarize the characteristics and signaling pathways of the MCH receptors in the different cell systems.

Melanin-concentrating hormone signaling systems in fish

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide synthesized as a preprohormone in the hypothalamus of all vertebrates. This neuropeptide binds to G-protein-coupled seven transmembrane receptor(s) to mediate its function. MCH was named after its function in teleosts, in which it causes aggregation or concentration of melanin granules in melanophores, thus regulating body color. The function of central MCH that has attracted most attention is its involvement in regulating food intake and energy homeostasis in mammals, a role confirmed through a series of experiments, including central administration of MCH or MCH receptor blockers, and genetic manipulation of MCH and its receptors. The aim of this article is to review the recent data on MCH and MCH receptor signaling systems in fish.

Ageing and the diurnal expression of mRNAs for vasoactive intestinal peptide and for the VPAC2 and PAC1 receptors in the suprachiasmatic nucleus of male rats

Ageing alters fundamental aspects of circadian rhythmicity in mammals; the effects include reduced rhythm amplitude and alterations in period length and in entrainment to the light/dark cycle. Such changes may reflect disruptions in cellular function within the suprachiasmatic nucleus (SCN), the site of the predominant circadian pacemaker. In the SCN, vasoactive intestinal peptide (VIP)-synthesizing neurones receive various inputs, including retinohypothalamic projections containing pituitary adenylate cyclase activating peptide (PACAP). SCN VIP cells establish connections with local neurones and send efferents beyond the nucleus. Considerable evidence implicates VIP and PACAP in circadian rhythm maintenance and/or entrainment to photic Zeitgebers. These actions involve members of a distinct family of receptors; mRNAs for two such receptors, VPAC2 and PAC1, are present in the SCN. This study used isotopic in situ hybridization to examine the effects of ageing on expression of mRNAs for VIP, VPAC2 and PAC1 in the SCN of male rats under a 12 : 12 h light/dark cycle. Analysis of film autoradiographs from young adult (2-3 months) or aged (19-20 months) rats, at eight time points across the light/dark cycle, showed loss of diurnal rhythmicity and reduced levels for VIP mRNA in the aged group. A diurnal rhythm of VPAC2 receptor mRNA was present in both groups, but its levels were reduced in the aged rats. There were no differences between the two groups for PAC1 receptor mRNA expression. The present results indicate that ageing reduces VIP and VPAC2 receptor mRNA and eliminates diurnal expression of VIP mRNA within the SCN of aged male rats.

Molecular cloning, pharmacological characterization, and histochemical distribution of frog vasotocin and mesotocin receptors

The neurohypophysial nonapeptides vasotocin (VT) and mesotocin (MT) are the amphibian counterparts of arginine vasopressin (AVP) and oxytocin (OT). We have here reported the cloning and functional characterization of the receptors for vasotocin (VTR) and mesotocin (MTR) in two species of frog, Rana catesbeiana and Rana esculenta. The frog VTR and MTR cDNAs encode proteins of 419 and 384 amino acids respectively. Frog VTR exhibits a high degree of sequence identity with the mammalian AVP-1a (V1a) receptor while the frog MTR possesses a high degree of sequence identity with the mammalian OT receptor. Activation of VTR induced both c-fos promoter- and cAMP-responsive element (CRE)-driven transcriptional activities, while activation of MTR induced c-fos promoter-driven transcriptional activity but failed to evoke CRE-driven transcriptional activity, suggesting differential G protein coupling between VTR and MTR. The VTR exhibited the highest sensitivity for VT followed by OT>AVP approximately MT, whereas the MTR showed preferential ligand sensitivity for MT>OT>VT>AVP. A V1a agonist but not V2 and OT agonists substantially activated both VTR and MTR with a similar sensitivity. V1a, V2 and OT antagonists inhibited MT-induced MTR activation but not VT-induced VTR activation. In the frog brain, VTR and MTR mRNAs were found to be widely expressed in the telencephalon, diencephalon and mesencephalon, and exhibited very similar regional distribution. In the pituitary, VTR and MTR were expressed in the distal and intermediate lobes but were virtually absent in the neural lobe. Taken together, these data indicated that, although the distribution of VTR and MTR largely overlaps in the frog brain and pituitary, VT and MT may play distinct activities owing to the ligand selectivity and different signaling pathways activated by their receptors.