Melanin-concentrating hormone stimulates human growth hormone secretion: a novel effect of MCH on the hypothalamic-pituitary axis

Crosstalk between Melanin Concentrating Hormone and Endocrine Factors: Implications for Obesity

Melanin-concentrating hormone (MCH) is a 19aa cyclic peptide exclusively expressed in the lateral hypothalamic area, which is an area of the brain involved in a large number of physiological functions and vital processes such as nutrient sensing, food intake, sleep-wake arousal, memory formation, and reproduction. However, the role of the lateral hypothalamic area in metabolic regulation stands out as the most relevant function. MCH regulates energy balance and glucose homeostasis by controlling food intake and peripheral lipid metabolism, energy expenditure, locomotor activity and brown adipose tissue thermogenesis. However, the MCH control of energy balance is a complex mechanism that involves the interaction of several neuroendocrine systems. The aim of the present work is to describe the current knowledge of the crosstalk of MCH with different endocrine factors. We also provide our view about the possible use of melanin-concentrating hormone receptor antagonists for the treatment of metabolic complications. In light of the data provided here and based on its actions and function, we believe that the MCH system emerges as an important target for the treatment of obesity and its comorbidities.

Growth Hormone Upregulates Melanocyte-Inducing Transcription Factor Expression and Activity via JAK2-STAT5 and SRC Signaling in GH Receptor-Positive Human Melanoma

Growth hormone (GH) facilitates therapy resistance in the cancers of breast, colon, endometrium, and melanoma. The GH-stimulated pathways responsible for this resistance were identified as suppression of apoptosis, induction of epithelial-to-mesenchymal transition (EMT), and upregulated drug efflux by increased expression of ATP-binding cassette containing multidrug efflux pumps (ABC-transporters). In extremely drug-resistant melanoma, ABC-transporters have also been reported to mediate drug sequestration in intracellular melanosomes, thereby reducing drug efficacy. Melanocyte-inducing transcription factor (MITF) is the master regulator of melanocyte and melanoma cell fate as well as the melanosomal machinery. MITF targets such as the oncogene MET, as well as MITF-mediated processes such as resistance to radiation therapy, are both known to be upregulated by GH. Therefore, we chose to query the direct effects of GH on MITF expression and activity towards conferring chemoresistance in melanoma. Here, we demonstrate that GH significantly upregulates MITF as well as the MITF target genes following treatment with multiple anticancer drug treatments such as chemotherapy, BRAF-inhibitors, as well as tyrosine-kinase inhibitors. GH action also upregulated MITF-regulated processes such as melanogenesis and tyrosinase activity. Significant elevation in MITF and MITF target gene expression was also observed in mouse B16F10 melanoma cells and xenografts in bovine GH transgenic (bGH) mice compared to wild-type littermates. Through pathway inhibitor analysis we identified that both the JAK2-STAT5 and SRC activities were critical for the observed effects. Additionally, a retrospective analysis of gene expression data from GTEx, NCI60, CCLE, and TCGA databases corroborated our observed correlation of MITF function and GH action. Therefore, we present in vitro, in vivo, and in silico evidence which strongly implicates the GH-GHR axis in inducing chemoresistance in human melanoma by driving MITF-regulated and ABC-transporter-mediated drug clearance pathways.

Effects of chronic growth hormone overexpression on appetite-regulating brain gene expression in coho salmon

Organisms must carefully regulate energy intake and expenditure to balance growth and trade-offs with other physiological processes. This regulation is influenced by key pathways controlling appetite, feeding behaviour and energy homeostasis. Growth hormone (GH) transgenesis provides a model where food intake can be elevated, and is associated with dramatic modifications of growth, metabolism, and feeding behaviour, particularly in fish. RNA-Seq and qPCR analyses were used to compare the expression of multiple genes important in appetite regulation within brain regions and the pituitary gland (PIT) of GH transgenic (fed fully to satiation or restricted to a wild-type ration throughout their lifetime) and wild-type coho salmon (Oncorhynchus kisutch). RNA-Seq results showed that differences in both genotype and ration levels resulted in differentially expressed genes associated with appetite regulation in transgenic fish, including elevated Agrp1 in hypothalamus (HYP) and reduced Mch in PIT. Altered mRNA levels for Agrp1, Npy, Gh, Ghr, Igf1, Mch and Pomc were also assessed using qPCR analysis. Levels of mRNA for Agrp1, Gh, and Ghr were higher in transgenic than wild-type fish in HYP and in the preoptic area (POA), with Agrp1 more than 7-fold higher in POA and 12-fold higher in HYP of transgenic salmon compared to wild-type fish. These data are consistent with the known roles of orexigenic factors on foraging behaviour acting via GH and through MC4R receptor-mediated signalling. Igf1 mRNA was elevated in fully-fed transgenic fish in HYP and POA, but not in ration-restricted fish, yet both of these types of transgenic animals have very pronounced feeding behaviour relative to wild-type fish, suggesting IGF1 is not playing a direct role in appetite stimulation acting via paracrine or autocrine mechanisms. The present findings provide new insights on mechanisms ruling altered appetite regulation in response to chronically elevated GH, and on potential pathways by which elevated feeding response is controlled, independently of food availability and growth.

The roles of melanin-concentrating hormone in energy balance and reproductive function: Are they connected?

Melanin-concentrating hormone (MCH) is an anabolic neuropeptide with multiple and diverse physiological functions including a key role in energy homoeostasis. Rodent studies have shown that the ablation of functional MCH results in a lean phenotype, increased energy expenditure and resistance to diet-induced obesity. These findings have generated interest among pharmaceutical companies vigilant for potential anti-obesity agents. Nutritional status affects reproductive physiology and behaviours, thereby optimising reproductive success and the ability to meet energetic demands. This complex control system entails the integration of direct or indirect peripheral stimuli with central effector systems and involves numerous mediators. A role for MCH in the reproductive axis has emerged, giving rise to the premise that MCH may serve as an integratory mediator between those discrete systems that regulate energy balance and reproductive function. Hence, this review focuses on published evidence concerning i) the role of MCH in energy homoeostasis and ii) the regulatory role of MCH in the reproductive axis. The question as to whether the MCH system mediates the integration of energy homoeostasis with the neuroendocrine reproductive axis and, if so, by what means has received limited coverage in the literature; evidence to date and current theories are summarised herein.

Role of melanin-concentrating hormone in the nucleus accumbens shell in rats behaviourally sensitized to methamphetamine

Melanin-concentrating hormone (MCH) is a neuropeptide and its receptor is extensively expressed throughout the brain. MCH has been suggested to regulate the rewarding and reinforcing effects of psychostimulants by potentiating the dopaminergic system within the midbrain. Moreover, MCH and its receptor can regulate ERK activity. The present study investigated the role of MCH in the nucleus accumbens (NAc) in rats behaviourally sensitized to methamphetamine (Meth). We found that the development of Meth-induced locomotor sensitization was attenuated by MCH infused into the NAc shell but not core. Moreover, the elevation of ERK phosphorylation in the NAc shell induced by Meth was inhibited by locally infused MCH. Infusion of the MCH receptor 1 (MCHR1) antagonist SNAP 94847 into the NAc shell but not core augmented the initiation of locomotor sensitization and amplitude of elevated phosphorylated ERK levels induced by Meth. The expression of Meth-induced locomotor sensitization and ERK alterations after 1 wk withdrawal were not affected by either MCH or SNAP 94847 infused into the NAc shell or core. These results indicate that MCH in the NAc shell plays a critical role in the development but not expression of Meth-induced locomotor sensitization in rats, which might be mediated by the ERK signalling pathway. Our study suggests that MCH might be a potential target for the treatment of Meth addiction.

Molecular cloning and SNP association analysis of chicken PMCH gene

The pre-melanin-concentrating hormone (PMCH) gene is an important gene functionally concerning the regulations of body fat content, feeding behavior and energy balance. In this study, the full-length cDNA of chicken PMCH gene was amplified by SMART RACE method. The single nucleotide polymorphisms (SNPs) in the PMCH gene were screened by comparative sequence analysis. The obtained non-synonymous coding SNPs (ncSNPs) were designed for genotyping firstly. Its effects on growth, carcass characteristics and meat quality traits were investigated employing the F2 resource population of Gushi chicken crossed with Anak broiler by AluI CRS-PCR-RFLP. Our results indicated that the cDNA of chicken PMCH shared 67.25 and 66.47% homology with that of human and bovine PMCH, respectively. The deduced amino acid sequence of chicken PMCH (163 amino acids) were 52.07 and 50.89% identical to those of human and bovine PMCH, respectively. The PMCH protein sequence is predicted to have several functional domains, including pro-MCH, CSP, IL7, XPGI and some low complexity sequence. It has 8 phosphorylation sites and no signal peptide sequence. gga-miR-18a, gga-miR-18b, gga-miR-499 microRNA targeting site was predicted in the 3' untranslated region of chicken PMCH mRNA. In addition, a total of seven SNPs including an ncSNP and a synonymous coding SNP, were identified in the PMCH gene. The ncSNP c.81 A>T was found to be in moderate polymorphic state (polymorphic index=0.365), and the frequencies for genotype AA, AB and BB were 0.3648, 0.4682 and 0.1670, respectively. Significant associations between the locus and shear force of breast and leg were observed. This polymorphic site may serve as a useful target for the marker assisted selection of the growth and meat quality traits in chicken.

Melanin concentrating hormone (MCH) is involved in the regulation of growth hormone in Cichlasoma dimerus (Cichlidae, Teleostei)

Growth hormone (GH) is the main pituitary hormone involved in somatic growth. In fish, the neuroendocrine control of GH is multifactorial due to the interaction of multiple inhibitors and stimulators. Melanin-concentrating hormone (MCH) is a cyclic peptide involved in skin color regulation of fish. In addition, MCH has been related to the regulation of food intake in both mammals and fish. There is only one report presenting evidences on the GH release stimulation by MCH in mammals in experiments in vitro, but there are no data on non-mammals. In the present work, we report for the first time the sequence of MCH and GH cDNA in Cichlasoma dimerus, a freshwater South American cichlid fish. We detected contacts between MCH fibers and GH cells in the proximal pars distalis region of the pituitary gland by double label confocal immunofluorescence indicating a possible functional relationship. Besides, we found that MCH increased GH transcript levels and stimulated GH release in pituitary cultures. Additionally, C. dimerus exposed to a white background had a greater number of MCH neurons with a larger nuclear area and higher levels of MCH transcript than those fish exposed to a black background. Furthermore, fish reared for 3 months in a white background showed a greater body weight and total length compared to those from black background suggesting that MCH might be related to somatic growth in C. dimerus. Our results report for the first time, that MCH is involved in the regulation of the synthesis and release of GH in vitro in C. dimerus, and probably in the fish growth rate.

Anatomical organization of the melanin-concentrating hormone peptide family in the mammalian brain

More than 20 years ago, melanin-concentrating hormone (MCH) and its peptide family members - neuropeptide EI (NEI) and neuropeptide GE (NGE) - were described in various species, including mammals (rodents, humans, and non-human primates). Since then, most studies have focused on the role of MCH as an orexigenic peptide, as well as on its participation in learning, spatial memory, neuroendocrine control, and sleep. It has been shown that MCH mRNA or the neuropeptide MCH are present in neurons of the prosencephalon, hypothalamus and brainstem. However, most of the neurons containing MCH/NEI are within the incerto-hypothalamic and lateral hypothalamic areas. In addition, the terminals of those neurons are distributed widely throughout the central nervous system. In this review, we will discuss the relationship between those territories and the roles played by MCH/NEI, as well as the importance of MCH receptor 1 in the respective terminal fields. Certain neurochemical features of MCH- and NEI-immunoreactive (MCH-ir and NEI-ir) neurons will also be discussed. The overarching theme is the anatomical organization of an inhibitory neuropeptide colocalized with an inhibitory neurotransmitter in integrative territories of the central nervous system, such as the IHy and LHA. Although these territories have connections to few brain regions, the regions to which they are connected are relevant, being responsible for the organization of motivated behaviors. All available information on this peptidergic system (anatomical, neurochemical, hodological, physiological, pharmacological and behavioral data) suggests that MCH is intimately involved in arousal and the initiation of motivated behaviors.

Cross-talk between orexins (hypocretins) and the neuroendocrine axes (hypothalamic-pituitary axes)

Lesioning and electrical stimulation experiments carried out during the first half of the twentieth century showed that the lateral hypothalamic area (LHA) is involved in the neuroendocrine control of hormone secretion. However, the molecular basis of this phenomenon remained unclear until fifty years later when in 1998, two different laboratories discovered a new family of hypothalamic neuropeptides, the orexins or hypocretins (OX-A/Hcrt1 and OX-B/Hcrt2). Since then, remarkable evidence has revealed that orexins/hypocretins play a prominent role in regulating virtually all the neuroendocrine axes, acting as pivotal signals in the coordination of endocrine responses with regards to sleep, arousal and energy homeostasis. The clinical relevance of these actions is supported by human data showing impairment of virtually all the neuroendocrine axes in orexin/hypocretin-deficient narcoleptic patients. Here, we summarize more than ten years of knowledge about the orexins/hypocretins with particular focus on their role as neuroendocrine regulators. Understanding this aspect of orexin/hypocretin physiology could open new therapeutic possibilities in the treatment of sleep, energy homeostasis and endocrine pathologies.

Orexins (hypocretins) actions on the GHRH/somatostatin-GH axis

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system that includes two major hypothalamic regulators, namely GH-releasing hormone (GHRH) and somatostatin (SST) that stimulate and inhibit, respectively, GH release. Classical experiments involving damage and electrical stimulation suggested that the lateral hypothalamic area (LHA) modulated the somatotropic axis, but the responsible molecular mechanisms were unclear. Evidence obtained during the last decade has demonstrated that orexins/hypocretins, a family of peptides expressed in the LHA controlling feeding and sleep, play an important regulatory role on GH, by inhibiting its secretion modulating GHRH and SST neurones. Considering that GH release is closely linked to the sleep-wake cycle and feeding state, understanding orexin/hypocretin physiology could open new therapeutic possibilities in the treatment of sleep, energy homeostasis and GH-related pathologies, such as GH deficiency.

Growth hormone and selective attention: a review

INTRODUCTION

The relation between growth hormone (GH) secretion and general cognitive function has been established. General cognitive functioning depends on core functions including selective attention, which have not been addressed specifically in relation to GH. The present review addresses current insights about specific effects of growth hormone deficiency (GHD) on varieties of selective attention, as well as effects of GH suppletion.

MATERIALS AND METHODS

Studies investigating relationships between GH status and valid measures of selective or divided attention were reviewed.

RESULTS AND DISCUSSION

There are no indications that GHD is characterized by impaired attribute selection, interference control, or attentional switching. In contrast, a few studies point to a deficit in integrated processing of multiple dimensions, as well as speed of information processing. There is also weak evidence for beneficial effects of GH replacement in the opposite direction in these domains.

CONCLUSIONS

The function of integrated processing of multiple stimulus dimensions may be based on neural mechanisms in the anterior cingulate cortex and its extensive connections to the hippocampus, the latter being known to be rich in GH receptors.

Chronic MCH infusion causes a decrease in energy expenditure and body temperature, and an increase in serum IGF-1 levels in mice

Melanin concentrating hormone (MCH) is an orexigenic peptide secreted from the lateral hypothalamus. Various observations suggest a role for MCH in energy expenditure in transgenic mice; however, the influence of MCH on energy expenditure and body temperature in WT mice was inadequately studied. Therefore, our first goal was to characterize the influence of chronic intracerebroventrical MCH infusion on energy homeostasis in mice. Our second goal was to explore the effect of MCH on the GH-insulin like growth factor 1 (IGF-1) axis in vivo. We have recently published that MCH directly increased GH-secretion from pituitary cells in vitro, suggesting that MCH may exert part of its effects on energy balance via direct pituitary hormone regulation. Mice were centrally infused with MCH for 14 days, resulting in a significant increase in food intake, body weight, fat mass and plasma IGF-1 levels, while decreasing body temperature and energy expenditure. Our data emphasize the role of MCH as a key regulator of energy homeostasis by means of appetite regulation, regulation of energy expenditure, and an integrator of energy balance with the neuroendocrine system regulating pituitary hormone secretion. They also support the notion that MCH may have a physiologic role in GH regulation that may, in turn, contribute to its effect on body weight.

Anatomy, function and regulation of neuropeptide EI (NEI)

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

Organization of the human medial preoptic nucleus

The organization of the adult human medial preoptic nucleus was studied by using chemoarchitectonic markers for acetylcholinesterase, nonphosphorylated neurofilament protein (SMI-32), calbindin-D28k, neuropeptide Y (NPY), melanin-concentrating hormone (MCH), cocaine- and amphetamine-regulated transcript (CART), and 3-fucosyl-N-acetyl-lactosamine (CD15) to establish human homologs to the subnuclei making up MPO in the rat, where their connections and functional significance are better understood. The human MPO comprises three subnuclei, the medial MPO, the lateral MPO, and the dorsomedially positioned uncinate subnucleus. As in the rat, the human medial MPO is magnocellular and contains numerous NPY- and CART-immunoreactive fibers and terminals as well as calbindin-positive neurons. The human lateral MPO, like its homolog in the rat, distinctively features numerous MCH-positive fibers and terminals as well as SMI-32-immunoreactive fibers. The uncinate subnucleus is wedged between the lateral surface of the paraventricular nucleus and the medial MPO and is characterized by variable NPY- and CART-immunoreactive fibers and terminals, also seen in the rat central MPO, suggesting that the subnuclei are homologues. The intermediate nucleus was distinguished by CD15-positive neuronal staining, whereas the majority of its neurons also contained acetylcholinesterase. The human intermediate nucleus is positioned on the lateral surface of MPO and by its chemo- and cytoarchitecture constitutes a distinct nucleus of the preoptic area characterized by close structural association with the MPO complex. These findings demonstrate that the human MPO is organized similarly to the rat MPO, in chemo- and cytoarchitectonically distinct subnuclei, which implies differences in their functional specialization, as seen in the rat.

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

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