Melanotan II causes hypothermia in mice by activation of mast cells and stimulation of histamine 1 receptors

Intraperitoneal administration of the melanocortin agonist melanotan II (MTII) to mice causes a profound, transient hypometabolism/hypothermia. It is preserved in mice lacking any one of melanocortin receptors 1, 3, 4, or 5, suggesting a mechanism independent of the canonical melanocortin receptors. Here we show that MTII-induced hypothermia was abolished in Kit^W-sh/W-sh mice, which lack mast cells, demonstrating that mast cells are required. MRGPRB2 is a receptor that detects many cationic molecules and activates mast cells in an antigen-independent manner. In vitro, MTII stimulated mast cells by both MRGPRB2-dependent and -independent mechanisms, and MTII-induced hypothermia was intact in MRGPRB2-null mice. Confirming that MTII activated mast cells, MTII treatment increased plasma histamine levels in both wild-type and MRGPRB2-null, but not in Kit^W-sh/W-sh, mice. The released histamine produced hypothermia via histamine H₁ receptors because either a selective antagonist, pyrilamine, or ablation of H₁ receptors greatly diminished the hypothermia. Other drugs, including compound 48/80, a commonly used mast cell activator, also produced hypothermia by both mast cell-dependent and -independent mechanisms. These results suggest that mast cell activation should be considered when investigating the mechanism of drug-induced hypothermia in mice.

Ligand Bias and Its Association With Pro-resolving Actions of Melanocortin Drugs

Resolution Pharmacology identifies drugs developed on the biology of the resolution phase of inflammation, the complex molecular and cellular network of events that ensure the tight temporal and spatial control on the inflammatory response. As such, new anti-inflammatory and pro-resolving drugs could derive from pro-resolving mediators and receptors. To implement faithful screening programs, however, it is important to rely on predictive signaling pathway relevant for the ultimate bio-action of interest. Herein we performed an analysis with four prototypical melanocortin receptor (MC_1,3,4,5) agonists. The choice fell on the natural agonist αMSH, the small molecule BMS-470539, and the synthetic derivatives [D-Trp⁸]-γMSH and [Nle⁴,D-Phe⁷]-αMSH. We used human macrophages and quantified the effect of the four agonists on inhibition of cytokine release and promotion of efferocytosis. All agonists (1–10 μM) significantly inhibited cytokine release by LPS-stimulated cells whereas [D-Trp⁸]-γMSH was the most effective in inducing efferocytosis (∼60% increase). To study the signaling profile, we monitored cAMP accumulation and ERK1/2 phosphorylation, and constructed biased plots that revealed a marked biased profile of [D-Trp⁸]-γMSH toward phospho-ERK1/2. Correlation matrix analysis of all data pointed at phospho-ERK1/2 at any receptor as the most prominent pathway to attain pro-phagocytic actions, and MC₁ receptor as the most relevant to drive anti-cytokine effects. In conclusion, the present study highlights the need to associate single-target signaling data with relevant functional outcomes. In this manner, we would increase our chances to optimize drug discovery programs during the early target validation and hit-to-lead phases.

MRAP deficiency impairs adrenal progenitor cell differentiation and gland zonation

Melanocortin 2 receptor accessory protein (MRAP) is a single transmembrane domain accessory protein and a critical component of the hypothamo-pituitary-adrenal axis. MRAP is highly expressed in the adrenal gland and is essential for adrenocorticotropin hormone (ACTH) receptor expression and function. Human loss-of-function mutations in MRAP cause familial glucocorticoid (GC) deficiency (FGD) type 2 (FGD2), whereby the adrenal gland fails to respond to ACTH and to produce cortisol. In this study, we generated Mrap-null mice to study the function of MRAP in vivo. We found that the vast majority of Mrap-/- mice died at birth but could be rescued by administration of corticosterone to pregnant dams. Surviving Mrap-/- mice developed isolated GC deficiency with normal mineralocorticoid and catecholamine production, recapitulating FGD2. The adrenal glands of adult Mrap-/- mice were small, with grossly impaired adrenal capsular morphology and cortex zonation. Progenitor cell differentiation was significantly impaired, with dysregulation of WNT4/β-catenin and sonic hedgehog pathways. These data demonstrate the roles of MRAP in both steroidogenesis and the regulation of adrenal cortex zonation. This is the first mouse model of isolated GC deficiency and reveals the role of MRAP in adrenal progenitor cell regulation and cortex zonation.-Novoselova, T. V., Hussain, M., King, P. J., Guasti, L., Metherell, L. A., Charalambous, M., Clark, A. J. L., Chan, L. F. MRAP deficiency impairs adrenal progenitor cell differentiation and gland zonation.

Phosphoinositide 3-Kinase Is Integral for the Acute Activity of Leptin and Insulin in Male Arcuate NPY/AgRP Neurons

Neuropeptide Y (NPY)/Agouti-related protein (AgRP) neurons in the arcuate nucleus of the hypothalamus are part of a neuroendocrine feedback loop that regulates feeding behavior and glucose homeostasis. NPY/AgRP neurons sense peripheral signals (including the hormones leptin, insulin, and ghrelin) and integrate those signals with inputs from other brain regions. These inputs modify both long-term changes in gene transcription and acute changes in the electrical activity of these neurons, leading to a coordinated response to maintain energy and glucose homeostasis. However, the mechanisms by which the hormones insulin and leptin acutely modify the electrical activity of these neurons remain unclear. In this study, we show that loss of the phosphoinositide 3-kinase catalytic subunits p110α and p110β in AgRP neurons abrogates the leptin- and insulin-induced inhibition of AgRP neurons. Moreover, continual disruption of p110α and p110β in AgRP neurons results in increased weight gain. The increased adiposity was concomitant with a hypometabolic phenotype: decreased energy expenditure independent of changes in food intake. Deficiency of p110α and p110β in AgRP neurons also impaired glucose homeostasis and insulin sensitivity. In summary, these data highlight the requirement of both p110α and p110β in AgRP neurons for the proper regulation of energy balance and glucose homeostasis.

Pathophysiology of melanocortin receptors and their accessory proteins

The melanocortin receptors (MCRs) and their accessory proteins (MRAPs) are involved in regulation of a diverse range of endocrine pathways. Genetic variants of these components result in phenotypic variation and disease. The MC1R is expressed in skin and variants in the MC1R gene are associated with ginger hair color. The MC2R mediates the action of ACTH in the adrenal gland to stimulate glucocorticoid production and MC2R mutations result in familial glucocorticoid deficiency (FGD). MC3R and MC4R are involved in metabolic regulation and their gene variants are associated with severe pediatric obesity, whereas the function of MC5R remains to be fully elucidated. MRAPs have been shown to modulate the function of MCRs and genetic variants in MRAPs are associated with diseases including FGD type 2 and potentially early onset obesity. This review provides an insight into recent advances in MCRs and MRAPs physiology, focusing on the disorders associated with their dysfunction.

Subdiaphragmatic Vagotomy With Pyloroplasty Ameliorates the Obesity Caused by Genetic Deletion of the Melanocortin 4 Receptor in the Mouse

Background/Objectives: We tested the hypothesis that abolishing vagal nerve activity will reverse the obesity phenotype of melanocortin 4 receptor knockout mice (Mc4r^−/−).

Subjects/Methods: In two separate studies, we examined the efficacy of bilateral subdiaphragmatic vagotomy (SDV) with pyloroplasty in the prevention and treatment of obesity in Mc4r^−/− mice.

Results: In the first study, SDV prevented >20% increase in body weight (BW) associated with this genotype. This was correlated with a transient reduction in overall food intake (FI) in the preventative arm of the study. Initially, SDV mice had reduced weekly FI; however, FI normalized to that of controls and baseline FI within the 8-week study period. In the second study, the severe obesity that is characteristic of the adult Mc4r^−/− genotype was significantly improved by SDV with a magnitude of 30% loss in excess BW over a 4-week period. Consistent with the first preventative study, within the treatment arm, SDV mice also demonstrated a transient reduction in FI relative to control and baseline levels that normalized over subsequent weeks. In addition to the accompanying loss in weight, mice subjected to SDV showed a decrease in respiratory exchange ratio (RER), and an increase in locomotor activity (LA). Analysis of the white fat-pad deposits of these mice showed that they were significantly less than the control groups.

Conclusions: Altogether, our data demonstrates that SDV both prevents gain in BW and causes weight loss in severely obese Mc4r^−/− mice. Moreover, it suggests that an important aspect of weight reduction for this type of monogenic obesity involves loss of signaling in vagal motor neurons.

Melanocortin overexpression limits diet-induced inflammation and atherosclerosis in LDLR-/- mice

Atherosclerosis is a chronic inflammatory disease of the arteries. The disease is initiated by endothelial dysfunction that allows the transport of leukocytes and low-density lipoprotein into the vessel wall forming atherosclerotic plaques. The melanocortin system is an endogenous peptide system that regulates, for example, energy homeostasis and cardiovascular function. Melanocortin treatment with endogenous or synthetic melanocortin peptides reduces body weight, protects the endothelium and alleviates vascular inflammation, but the long-term effects of melanocortin system activation on atheroprogression remain largely unknown. In this study, we evaluated the effects of transgenic melanocortin overexpression in a mouse model of atherosclerosis. Low-density lipoprotein receptor-deficient mice overexpressing alpha- and gamma₃-MSH (MSH-OE) and their wild-type littermates were fed either a regular chow or Western-style diet for 16 weeks. During this time, their metabolic parameters were monitored. The aortae were collected for functional analysis, and the plaques in the aortic root and arch were characterised by histological and immunohistochemical stainings. The aortic expression of inflammatory mediators was determined by quantitative PCR. We found that transgenic MSH-OE improved glucose tolerance and limited atherosclerotic plaque formation particularly in Western diet-fed mice. In terms of aortic vasoreactivity, MSH-OE blunted alpha₁-adrenoceptor-mediated vasoconstriction and enhanced relaxation response to acetylcholine, indicating improved endothelial function. In addition, MSH-OE markedly attenuated Western diet-induced upregulation of proinflammatory cytokines (Ccl2, Ccl5 and Il6) that contribute to the pathogenesis of atherosclerosis. These results show that the activation of the melanocortin system improves glucose homeostasis and limits diet-induced vascular inflammation and atherosclerotic plaque formation.

Repository corticotropin injection in patients with rheumatoid arthritis resistant to biologic therapies

INTRODUCTION

Although synthetic and biologic disease-modifying antirheumatic drugs are available, many patients with rheumatoid arthritis have a difficult-to-control disease and need other treatment options. Repository corticotropin injection (RCI) may alleviate symptoms and exacerbations in patients with refractory disease.

METHODS

Nine patients with refractory rheumatoid arthritis were included in this study. Patients were maintained on their baseline therapies with a minimum of 7.5 mg prednisone daily. RCI was given daily at 40 U for 7 days. Patients who had an adequate disease response were given 40 U twice weekly through Week 12. For patients who had inadequate disease response, the dose was increased to 80 U daily for 7 days, followed by 80 U twice weekly through Week 12.

RESULTS

The primary endpoint was >1.2 point reduction in the Disease Activity Score 28 using C-reactive protein (DAS28-CRP) at Week 12. Secondary endpoints were improvements in Health Assessment Questionnaire-Disease Index and Functional Assessment of Chronic Illness Therapy scores. Six of the nine patients met the primary endpoint. The average change in DAS28-CRP from baseline to Week 12 was numerically greater with 40 U than with 80 U RCI. Functional Assessment of Chronic Illness Therapy and Health Assessment Questionnaire-Disease Index improved as early as Week 1, and the improvements remained throughout treatment.

CONCLUSION

There was no association between cortisol levels and low-dose RCI response. No serious adverse events occurred. RCI produced a clinically meaningful reduction in markers of disease activity, improved health-related quality of life, and a favorable safety profile. The response rate to RCI was substantial and shows promise in this difficult-to-treat population.

Widespread dynamic and pleiotropic expression of the melanocortin-1-receptor (MC1R) system is conserved across chick, mouse and human embryonic development

Background

MC1R, a G‐protein coupled receptor with high affinity for alpha‐melanocyte stimulating hormone (αMSH), modulates pigment production in melanocytes from many species and is associated with human melanoma risk. MC1R mutations affecting human skin and hair color also have pleiotropic effects on the immune response and analgesia. Variants affecting human pigmentation in utero alter the congenital phenotype of both oculocutaneous albinism and congenital melanocytic naevi, and have a possible effect on birthweight.

Methods and Results

By in situ hybridization, RT‐PCR and immunohistochemistry, we show that MC1R is widely expressed during human, chick and mouse embryonic and fetal stages in many somatic tissues, particularly in the musculoskeletal and nervous systems, and conserved across evolution in these three amniotes. Its dynamic pattern differs from that of TUBB3, a gene overlapping the same locus in humans and encoding class III β‐tubulin. The αMSH peptide and the transcript for its precursor, pro‐opiomelanocortin (POMC), are similarly present in numerous extra‐cutaneous tissues. MC1R genotyping of variants p.(V60M) and p.(R151C) was undertaken for 867 healthy children from the Avon Longitudinal Study of Parent and Children (ALSPAC) cohort, and birthweight modeled using multiple logistic regression analysis. A significant positive association initially found between R151C and birth weight, independent of known birth weight modifiers, was not reproduced when combined with data from an independent genome‐wide association study of 6,459 additional members of the same cohort.

Conclusions

These data clearly show a new and hitherto unsuspected role for MC1R in noncutaneous solid tissues before birth.

TrpC5 Mediates Acute Leptin and Serotonin Effects via Pomc Neurons

The molecular mechanisms underlying acute leptin and serotonin 2C receptor-induced hypophagia remain unclear. Here, we show that neuronal and pro-opiomelanocortin (Pomc)-specific loss of transient receptor potential cation 5 (TrpC5) subunits is sufficient to decrease energy expenditure and increase food intake resulting in elevated body weight. Deficiency of Trpc5 subunits in Pomc neurons is also sufficient to block the anorexigenic effects of leptin and serotonin 2C receptor (Ht2Cr) agonists. The loss of acute anorexigenic effects of these receptors is concomitant with a blunted electrophysiological response to both leptin and Ht2Cr agonists in arcuate Pomc neurons. We also demonstrate that the Ht2Cr agonist lorcaserin-induced improvements in glucose and insulin tolerance are blocked by TrpC5 deficiency in Pomc neurons. Together, our results link TrpC5 subunits in the brain with leptin- and serotonin 2C receptor-dependent changes in neuronal activity, as well as energy balance, feeding behavior, and glucose metabolism.

Nucleus Accumbens MC4-R Stimulation Reduces Food and Ethanol Intake in Adult Rats Regardless of Binge-Like Ethanol Exposure during Adolescence

The melanocortin (MC) system regulates feeding and ethanol consumption. Recent evidence shows that melanocortin 4 receptor (MC4-R) stimulation within the nucleus accumbens (NAc) elicits anorectic responses and reduces ethanol consumption and ethanol palatability in adult rats. Ethanol exposure during adolescence causes long-lasting changes in neural pathways critically involved in neurobehavioral responses to ethanol. In this regard, binge-like ethanol exposure during adolescence reduces basal alpha-melanocyte-stimulating hormone (α-MSH) and alters the levels of agouti-related peptide (AgRP) in hypothalamic and limbic areas. Given the protective role of MC against excessive ethanol consumption, disturbances in the MC system induced by binge-like ethanol exposure during adolescence might contribute to excessive ethanol consumption during adulthood. In the present study, we evaluated whether binge-like ethanol exposure during adolescence leads to elevated ethanol intake and/or eating disturbance during adulthood. Toward that aim, Sprague-Dawley rats were treated with ethanol (3 g/kg i.p.; BEP group) or saline (SP group) for 14 days (PND 25 to PND 38). On PND73, all the groups were given access to 20% ethanol on an intermittent schedule. Our results showed that adult rats given intermittent access (IAE) to 20% ethanol achieved high spontaneous ethanol intake that was not significantly enhanced by binge-like ethanol pretreatment during adolescence. However, BEP group exhibited an increase in food intake without a parallel increase in body weight (BW) relative to SP group suggesting caloric efficiency disturbance. Additionally, we evaluated whether binge-like ethanol exposure during adolescence alters the expected reduction in feeding and ethanol consumption following NAc shell administration of a selective MC4-R agonist in adult rats showing high rates of ethanol consumption. For that, animals in each pretreatment condition (SP and BEP) were divided into three subgroups and given bilateral NAc infusions of the selective MC4-R agonist cyclo(NH-CH₂-CH₂-CO-His-D-Phe-Arg-Trp-Glu)-NH₂ (0, 0.75 or 1.5 μg). Results revealed that MC4-R stimulation within the NAc reduced feeding and ethanol intake in high ethanol-drinking adult rats, regardless of previous binge-like ethanol exposure during adolescence, which adds new evidence regarding the dual ability of MC compounds to control excessive ethanol and food intake.

The Role of MicroRNA in the Modulation of the Melanocortinergic System

The central control of energy balance involves a highly regulated neuronal network within the hypothalamus and the dorsal vagal complex. In these structures, pro-opiomelanocortin (POMC) neurons are known to reduce meal size and to increase energy expenditure. In addition, leptin, a peripheral signal that relays information regarding body fat content, modulates the activity of melanocortin pathway neurons including POMC-, Agouti-related peptide (AgRP)/Neuropeptide Y (NPY)-, melanocortin receptors (MC3R and MC4R)-expressing neurons. MicroRNAs (miRNAs) are short non-coding RNAs of 22–26 nucleotides that post-transcriptionally interfere with target gene expression by binding to their mRNAs. Evidence has demonstrated that miRNAs play important roles in the central regulation of energy balance. In this context, different studies identified miRNAs including miR-200 family, miR-103, or miR-488 that could target the genes of melanocortin pathway. More precisely, these different miRNAs can modulate energy homeostasis by affecting leptin transduction pathway in the POMC, or AgRP/NPY neurons. This article reviews the role of identified miRNAs in the modulation of melanocortin pathway in the context of energy homeostasis.

Regulation of Agouti-Related Protein and Pro-Opiomelanocortin Gene Expression in the Avian Arcuate Nucleus

The arcuate nucleus is generally conserved across vertebrate taxa in its neuroanatomy and neuropeptide expression. Gene expression of agouti-related protein (AGRP), neuropeptide Y (NPY), pro-opiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) has been established in the arcuate nucleus of several bird species and co-localization demonstrated for AGRP and NPY. The proteins encoded by these genes exert comparable effects on food intake in birds after central administration to those seen in other vertebrates, with AGRP and NPY being orexigenic and CART and α-melanocyte-stimulating hormone anorexigenic. We have focused on the measurement of arcuate nucleus AGRP and POMC expression in several avian models in relation to the regulation of energy balance, incubation, stress, and growth. AGRP mRNA and POMC mRNA are, respectively, up- and downregulated after energy deprivation and restriction. This suggests that coordinated changes in the activity of AGRP and POMC neurons help to drive the homeostatic response to replace depleted energy stores in birds as in other vertebrates. While AGRP and POMC expression are generally positively and negatively correlated with food intake, respectively, we review here situations in some avian models in which AGRP gene expression is dissociated from the level of food intake and may have an influence on growth independent of changes in appetite. This suggests the possibility that the central melanocortin system exerts more pleiotropic functions in birds. While the neuroanatomical arrangement of AGRP and POMC neurons and the sensitivity of their activity to nutritional state appear generally conserved with other vertebrates, detailed knowledge is lacking of the key nutritional feedback signals acting on the avian arcuate nucleus and there appear to be significant differences between birds and mammals. In particular, recently identified avian leptin genes show differences between bird species in their tissue expression patterns and appear less closely linked in their expression to nutritional state. It is presently uncertain how the regulation of the central melanocortin system in birds is brought about in the situation of the apparently reduced importance of leptin and ghrelin compared to mammals.

Repository corticotropin injection in patients with refractory psoriatic arthritis: a case series

PURPOSE

Although numerous treatment options are available for patients with psoriatic arthritis (PsA), a need for effective and tolerable treatments remains for patients with refractory disease who have failed previous therapies and continue to experience tender and/or swollen joints, pain, and disease activity. Repository corticotropin injection (RCI) is believed to produce steroidogenic, steroid-independent, anti-inflammatory, and immunomodulatory effects in patients with rheumatic disorders, such as PsA. Limited literature exists on the use of RCI in patients with refractory PsA. The objective of this case series is to provide information on the clinical features of patients with refractory PsA and their response to RCI.

PATIENTS

Nine patients treated with RCI for refractory PsA were retrospectively identified and included in the case series.

RESULTS

All the nine patients experienced at least transient improvements in their active skin and joint disease. In some patients, it was necessary to titrate the RCI to an appropriate dose. RCI was used in some patients to bridge with another PsA therapy, such as apremilast or certolizumab. RCI was well tolerated, but discontinued in three patients due to preexisting conditions (hypertension and hyperglycemia).

CONCLUSION

RCI may be a safe and effective option for patients with refractory PsA who failed therapy with multiple previous treatments.

Neuronal systems and circuits involved in the control of food intake and adaptive thermogenesis

With the still-growing prevalence of obesity worldwide, major efforts are made to understand the various behavioral, environmental, and genetic factors that promote excess fat gain. Obesity results from an imbalance between energy intake and energy expenditure, which emphasizes the importance of deciphering the mechanisms behind energy balance regulation to understand its physiopathology. The control of energy balance is assured by brain systems/circuits capable of generating adequate ingestive and thermogenic responses to maintain the stability of energy reserves, which implies a proper integration of the homeostatic signals that inform about the status of the energy stores. In this article, we overview the organization and functionality of key neuronal circuits or pathways involved in the control of food intake and energy expenditure. We review the role of the corticolimbic (executive and reward) and autonomic systems that integrate their activities to regulate energy balance. We also describe the mechanisms and pathways whereby homeostatic sensing is achieved in response to variations of homeostatic hormones, such as leptin, insulin, and ghrelin, while putting some emphasis on the prominent importance of the mechanistic target of the rapamycin signaling pathway in coordinating the homeostatic sensing process.

Loss of Mrap2 is associated with Sim1 deficiency and increased circulating cholesterol

Melanocortin receptor accessory protein 2 (MRAP2) is a transmembrane accessory protein predominantly expressed in the brain. Both global and brain-specific deletion of Mrap2 in mice results in severe obesity. Loss-of-function MRAP2 mutations have also been associated with obesity in humans. Although MRAP2 has been shown to interact with MC4R, a G protein-coupled receptor with an established role in energy homeostasis, appetite regulation and lipid metabolism, the mechanisms through which loss of MRAP2 causes obesity remains uncertain. In this study, we used two independently derived lines of Mrap2 deficient mice (Mrap2(tm1a/tm1a)) to further study the role of Mrap2 in the regulation of energy balance and peripheral lipid metabolism. Mrap2(tm1a/tm1a) mice have a significant increase in body weight, with increased fat and lean mass, but without detectable changes in food intake or energy expenditure. Transcriptomic analysis showed significantly decreased expression of Sim1, Trh, Oxt and Crh within the hypothalamic paraventricular nucleus of Mrap2(tm1a/tm1a) mice. Circulating levels of both high-density lipoprotein and low-density lipoprotein were significantly increased in Mrap2 deficient mice. Taken together, these data corroborate the role of MRAP2 in metabolic regulation and indicate that, at least in part, this may be due to defective central melanocortin signalling.

Lateral hypothalamic melanocortin receptor signaling modulates binge-like ethanol drinking in C57BL/6J mice

Binge ethanol drinking is a highly pervasive and destructive behavior yet the underlying neurobiological mechanisms remain poorly understood. Recent work suggests that overlapping neurobiological mechanisms modulate feeding disorders and excessive ethanol intake, and converging evidence indicates that the melanocortin (MC) system may be a promising candidate. The aims of the present work were to examine how repeated binge-like ethanol drinking, using the 'drinking in the dark' (DID) protocol, impacts key peptides within the MC system and if site-specific manipulation of MC receptor (MCR) signaling modulates binge-like ethanol drinking. Male C57BL/6J mice were exposed to one, three or six cycles of binge-like ethanol, sucrose or water drinking, after which brain tissue was processed via immunohistochemistry (IHC) for analysis of key MC peptides, including alpha-melanocyte stimulating hormone (α-MSH) and agouti-related protein (AgRP). Results indicated that α-MSH expression was selectively decreased, while AgRP expression was selectively increased, within specific hypothalamic subregions following repeated binge-like ethanol drinking. To further explore this relationship, we used site-directed drug delivery techniques to agonize or antagonize MCRs within the lateral hypothalamus (LH). We found that the nonselective MCR agonist melanotan-II (MTII) blunted, while the nonselective MCR antagonist AgRP augmented, binge-like ethanol consumption when delivered into the LH. As these effects were region-specific, the present results suggest that a more thorough understanding of the MC neurocircuitry within the hypothalamus will help provide novel insight into the mechanisms that modulate excessive binge-like ethanol intake and may help uncover new therapeutic targets aimed at treating alcohol abuse disorders.

The correlation between coloration and exploration behaviour varies across hierarchical levels in a wild passerine bird

In vertebrates, darker individuals are often found to be more active and willing to take risks (representing characteristics of a 'proactive' coping style), whereas lighter individuals are instead more cautious and less active (representing characteristics of a 'reactive' coping style). It is thus generally expected that melanin-based coloration and proactivity form a suite of positively integrated traits at the among-individual level. Here, we use a multigenerational pedigree of free-living great tits (Parus major) to partition variation in, and the correlation between, melanin-based breast stripe ('tie') size and exploration behaviour (a proxy for coping style) into its among- and within-individual components. We show that both traits harbour heritable variation. Against predictions, tie size and speed of exploration were negatively correlated at the among-individual level due to the combined influences of permanent environmental and additive genetic effects. By contrast, the two traits were weakly positively correlated within individuals (i.e. individuals increasing in tie size after moult tended to become more explorative). The patterns of among-individual covariance were not caused by correlational selection as we found additive and opposite selection pressures acting on the two traits. These findings imply that testing hypotheses regarding the existence of a 'syndrome' at the among-individual level strictly requires variance partitioning to avoid inappropriate interpretations as the negative 'unpartitioned' phenotypic correlation between exploration and tie size resulted from counteracting effects of within- and among-individual correlations. Identifying sources and levels of (co)variation in phenotypic traits is thus critical to our understanding of biological patterns and evolutionary processes.

Melanocortin 1 Receptor: Structure, Function, and Regulation

The melanocortin 1 receptor (MC1R) is a melanocytic Gs protein coupled receptor that regulates skin pigmentation, UV responses, and melanoma risk. It is a highly polymorphic gene, and loss of function correlates with a fair, UV-sensitive, and melanoma-prone phenotype due to defective epidermal melanization and sub-optimal DNA repair. MC1R signaling, achieved through adenylyl cyclase activation and generation of the second messenger cAMP, is hormonally controlled by the positive agonist melanocortin, the negative agonist agouti signaling protein, and the neutral antagonist β-defensin 3. Activation of cAMP signaling up-regulates melanin production and deposition in the epidermis which functions to limit UV penetration into the skin and enhances nucleotide excision repair (NER), the genomic stability pathway responsible for clearing UV photolesions from DNA to avoid mutagenesis. Herein we review MC1R structure and function and summarize our laboratory's findings on the molecular mechanisms by which MC1R signaling impacts NER.

60 YEARS OF POMC: Regulation of feeding and energy homeostasis by α-MSH

The melanocortin peptides derived from pro-opiomelanocortin (POMC) were originally understood in terms of the biological actions of α-melanocyte-stimulating hormone (α-MSH) on pigmentation and adrenocorticotrophic hormone on adrenocortical glucocorticoid production. However, the discovery of POMC mRNA and melanocortin peptides in the CNS generated activities directed at understanding the direct biological actions of melanocortins in the brain. Ultimately, discovery of unique melanocortin receptors expressed in the CNS, the melanocortin-3 (MC3R) and melanocortin-4 (MC4R) receptors, led to the development of pharmacological tools and genetic models leading to the demonstration that the central melanocortin system plays a critical role in the regulation of energy homeostasis. Indeed, mutations in MC4R are now known to be the most common cause of early onset syndromic obesity, accounting for 2-5% of all cases. This review discusses the history of these discoveries, as well as the latest work attempting to understand the molecular and cellular basis of regulation of feeding and energy homeostasis by the predominant melanocortin peptide in the CNS, α-MSH.

The Melanocortin Receptor Accessory Protein 2 promotes food intake through inhibition of the Prokineticin Receptor-1

The Melanocortin Receptor Accessory Protein 2 (MRAP2) is an important regulator of energy homeostasis and its loss causes severe obesity in rodents. MRAP2 mediates its action in part through the potentiation of the MC4R, however, it is clear that MRAP2 is expressed in tissues that do not express MC4R, and that the deletion of MRAP2 does not recapitulate the phenotype of Mc4r KO mice. Consequently, we hypothesized that other GPCRs involved in the control of energy homeostasis are likely to be regulated by MRAP2. In this study we identified PKR1 as the first non-melanocortin GPCR to be regulated by MRAP2. We show that MRAP2 significantly and specifically inhibits PKR1 signaling. We also demonstrate that PKR1 and MRAP2 co-localize in neurons and that Mrap2 KO mice are hypersensitive to PKR1 stimulation. This study not only identifies new partners of MRAP2 but also a new pathway through which MRAP2 regulates energy homeostasis.

DOI:http://dx.doi.org/10.7554/eLife.12397.001

The brain plays a major role in controlling how much food animals eat. The nerve cells (neurons) involved in this process contain “receptors” that respond to cues from various parts of the body. For example, a receptor called PKR1 acts to limit food intake. The activities of PKR1 and other receptors are tightly regulated in cells, but it is not clear how this works.

A protein called MRAP2 is known to regulate the activity of a receptor that regulates food intake and energy use in the brain. However, MRAP2 may also interact with other receptors to control food intake. Here, Chaly, Srisai et al. investigated whether MRAP2 can regulate the activity of PKR1 in animal cells and rodents.

The experiments show that MRAP2 can interact with and inhibit the activity of PKR1. Furthermore, both MRAP2 and PKR1 can be found in the same neurons. Mutant mice that lack the gene that encodes MRAP2 have higher levels of PKR1 activity and eat less than normal mice when PKR1 is stimulated. Together the experiments suggest that MRAP2 can increase food intake by preventing PKR1 from being activated in the brain. The next steps are to find out if this protein regulates other receptors involved in the control of food intake, and to test whether PKR1 and MRAP2 also play a role in regulating energy usage.

DOI:http://dx.doi.org/10.7554/eLife.12397.002

Inhibitory Effect of the Melanocortin Receptor Agonist Melanotan-II (MTII) on Feeding Depends on Dietary Fat Content and not Obesity in Rats on Free-Choice Diets

Introduction: Conflicting data exist on sensitivity changes of the melanocortin system during diet-induced obesity. We hypothesized that melanocortin sensitivity depends on diet composition, in particular on the fat content rather than the level of obesity. The aim of this study was to determine the influence of diet composition on feeding responses to a melanocortin receptor agonist, using free-choice diets that differ in food components.

Methods: Male Wistar rats were subjected to a chow (CHOW) diet or a free-choice (fc) diet of either chow, saturated fat and liquid sugar (fcHFHS), chow and saturated fat (fcHF), or chow and liquid sugar (fcHS) for 4 weeks. Melanocortin sensitivity was tested by measuring food intake following administration of the melanocortin 3/4 receptor agonist melanotan II (MTII) or vehicle in the lateral ventricle. In a separate experiment, proopiomelanocortin (POMC) and agouti-related protein (AgRP) mRNA levels were determined in the arcuate nucleus with in situ hybridization in rats subjected to the free-choice diets for 4 weeks.

Results: Rats on the fcHFHS diet for 4 weeks show increased caloric intake and body weight gain compared to rats on the CHOW, fcHS and fcHF diet. Caloric intake and body weight gain was comparable between rats on the fcHF, fcHS, and CHOW diet. After 4 weeks diet, POMC and AgRP mRNA levels were not different between diet groups. MTII inhibited caloric intake to a larger extent in rats on the fcHF diet compared to rats on the CHOW, fcHFHS or fcHS diet. Moreover, the fat component was the most inhibited by MTII, and the sugar component the least.

Conclusion: Rats on the fcHF diet show stronger food intake inhibition to the melanocortin receptor agonist MTII than rats on the CHOW, fcHS, and fcHFHS diet, which is independent of caloric intake and body weight gain. Our data point toward an important role for diet composition, particularly the dietary fat content, and not obesity in the sensitivity of the melanocortin system.

Hypothalamic control of brown adipose tissue thermogenesis

It has long been known, in large part from animal studies, that the control of brown adipose tissue (BAT) thermogenesis is insured by the central nervous system (CNS), which integrates several stimuli in order to control BAT activation through the sympathetic nervous system (SNS). SNS-mediated BAT activity is governed by diverse neurons found in brain structures involved in homeostatic regulations and whose activity is modulated by various factors including oscillations of energy fluxes. The characterization of these neurons has always represented a challenging issue. The available literature suggests that the neuronal circuits controlling BAT thermogenesis are largely part of an autonomic circuitry involving the hypothalamus, brainstem and the SNS efferent neurons. In the present review, we recapitulate the latest progresses in regards to the hypothalamic regulation of BAT metabolism. We briefly addressed the role of the thermoregulatory pathway and its interactions with the energy balance systems in the control of thermogenesis. We also reviewed the involvement of the brain melanocortin and endocannabinoid systems as well as the emerging role of steroidogenic factor 1 (SF1) neurons in BAT thermogenesis. Finally, we examined the link existing between these systems and the homeostatic factors that modulate their activities.

Brain signaling systems in the Type 2 diabetes and metabolic syndrome: promising target to treat and prevent these diseases

The changes in the brain signaling systems play an important role in etiology and pathogenesis of Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS), being a possible cause of these diseases. Therefore, their restoration at the early stages of T2DM and MS can be regarded as a promising way to treat and prevent these diseases and their complications. The data on the functional state of the brain signaling systems regulated by insulin, IGF-1, leptin, dopamine, serotonin, melanocortins and glucagon-like peptide-1, in T2DM and MS, are analyzed. The pharmacological approaches to restoration of these systems and improvement of insulin sensitivity, energy expenditure, lipid metabolism, and to prevent diabetic complications are discussed.