expression in the hypothalamus. Melanocortin 2 receptor is a critical component of the HPA axis Melanocortin receptors (MCRs) are a subfamily of seven-transmembrane (TM)-domain G-protein-coupled receptors (GPCRs) that mediate signalling of hormones derived
T V Novoselova, D Jackson, D C Campbell, A J L Clark and L F Chan
Zhen-Chuan Fan, James L Sartin and Ya-Xiong Tao
-translational processing ( Smith & Funder 1988 ). The melanocortin receptors (MCRs) are members of rhodopsin-like (family A) G-protein-coupled receptors (GPCRs). They are expressed on the cell surface, predicted to have seven transmembrane domains (TMDs) connected by
Jacob C Garza, Chung Sub Kim, Jing Liu, Wei Zhang and Xin-Yun Lu
Introduction Melanocortin-4 receptor (MC4R) in the central nervous system (CNS) plays a critical role in the control of energy balance. Activation of MC4R by α-MSH, a derivative of pro-opiomelanocortin (POMC), decreases food intake and increases
AV Vergoni, A Bertolini, G Guidetti, V Karefilakis, M Filaferro, JE Wikberg and HB Schioth
We investigated the effects of continuous intracerebroventricular infusion of a melanocortin 4 receptor antagonist HS014 (cyclic [AcCys11, D-Nal14, Cys18, Asp-NH2(22)]beta-MSH-(11-22)) over 12 days and a subsequent 12-day recovery period on food intake, body weight and copulatory behavior in male rats. The results show that the food intake increased immediately after the start of the infusion of HS014 (0.16 nmol/h) and progressively increased thereafter. No tachyphylaxis was observed. When the infusion of HS014 was terminated, the food-intake levels dropped. The body weights of the rats had increased by 17% by the end of the study, compared with controls. During the recovery period, the body weight decreased towards the levels of the control rats. These results indicate that overeating and the subsequent increases in body weight caused by blockage of the melanocortin 4 (MC4) receptor are reversible when the blockage is ended. We also tested the copulatory behavior of vigorous male rats in the presence of female rats in estrous. We registered mount latency, the number of mounts, the intromission latency, the number of intromissions, the ejaculation latency and the post-ejaculatory interval three times during the study and also after acute administration of HS014 and alpha-MSH. The sexual behavior of the male rats was not affected. These results indicate that the MC receptors, in particular the MC4 receptor, may not be a major mediator of effects on copulatory behavior in male rats.
CR Barb, AS Robertson, JB Barrett, RR Kraeling and KL Houseknecht
A recently discovered class of receptors, melanocortin-3 and -4 receptor (MC3/4-R), are located within the brain and modulate feed intake in rodents. Stimulation of the receptor (agonist) inhibits feed intake whereas blockade (antagonist) of the receptor increases intake. Our knowledge of factors regulating voluntary feed intake in humans and domestic animals is very limited. i.c.v. administration of an MC3/4-R agonist, NDP-MSH, suppressed (P<0.05) feed intake compared with controls at 12, 24, 48 and 72 h after treatment in growing pigs. Fed pigs were more responsive to the MC3/4-R agonist then fasted animals. However, i.c.v. treatment with MC3/4-R antagonist, SHU9119, failed to stimulate intake. The failure of MC3/4-R antagonist to stimulate feed intake suggests involvement of other brain hormone(s) which antagonize the action of SHU9119 at the MC3/4-R, blocking its stimulatory effect on intake. Treatment with NDP-MSH or SHU9119, across a wide dose range, failed to affect LH and GH secretion, except for the 10 micro g dose of NDP-MSH, which exhibited both a stimulatory and an inhibitory effect on GH secretion in fasted animals. Treatment with agouti-related peptide, a natural brain hormone that blocks the MC3/4R, failed to stimulate feed intake. These results do not support the idea that endogenous melanocortin pays a critical role in regulating feed intake and pituitary hormone secretion in the pig. SHU9119 blocked the NDP-MSH-induced increase in cAMP in HEK293 cells expressing the porcine MC4-R sequence without the missense mutation. The EC(50) and IC(50) values were similar to the human MC4-R, confirming that SHU9119 is a pig MC4-R antagonist. However, pigs were heterozygous for an MC4-R gene missense mutation. It is possible that the MC4-R mutation alters function and this may explain the failure to demonstrate MC3/4-R involvement in modulating feeding behavior and LH and GH secretion in the pig.
HB Schioth, R Muceniece, M Larsson and JE Wikberg
ACTH(1-39), and several shorter N- and/or C-terminally truncated fragments of ACTH, with and without N-terminal acetylation and/or C-terminal amidation, were tested for binding on a single eukaryotic cell line transiently and independently expressing the melanocortin MC1, MC3, MC4 and MC5 receptors. The results show that none of these MC receptors has specific binding epitopes for the ACTH peptides beyond the amino acid sequence of alpha-MSH, when tested for their ability to compete with 125I-labelled [Nle4,D-Phe7]alpha-MSH and ACTH. The MC3 receptor favours the natural desacetylated N-terminal end of the ACTH peptides, and it has generally more than 10-fold higher affinity for the ACTH peptides than the MC4 receptor. Considering earlier anatomical localisation data, together with the present data, we suggest that the MC3 receptor is the most likely candidate of the MC receptors to mediate the short-loop negative feedback release of corticotrophin-releasing factor (CRF) caused by ACTH/MSH peptides.
G Li, Y Zhang, JT Wilsey and PJ Scarpace
The effects of the chronic activation of the central melanocortin (MC) system by melanotan II (MTII) were assessed in chow-fed (CH) and high-fat (HF) diet-induced obese (DIO) Sprague-Dawley rats. Six-day central infusion of MTII (1 nmol/day) reduced body weight and visceral adiposity compared with ad libitum-fed control and pair-fed groups and markedly suppressed caloric intake in both CH and DIO rats. The anorexic response to MTII was similar in DIO relative to CH rats. MTII induced a sustained increase in oxygen consumption in DIO but a delayed response in CH rats. In both diet groups, MTII reduced serum insulin and cholesterol levels compared with controls. HF feeding increased brown adipose tissue (BAT) uncoupling protein 1 (UCP1) by over twofold, and UCP1 levels were further elevated in MTII-treated CH and DIO rats. MTII lowered acetyl-CoA carboxylase expression and prevented the reduction in muscle-type carnitine palmitoyltransferase I mRNA by pair-feeding in the muscle of DIO rats. Compared with CH controls, hypothalamic MC3 and MC4 receptor expression levels were reduced in DIO controls. This study has demonstrated that, despite reduced hypothalamic MC3/MC4 receptor expression, anorexic and thermogenic responses to MTII are unabated with an initial augmentation of energy expenditure in DIO versus CH rats. The HF-induced up-regulation of UCP1 in BAT may contribute to the immediate increase in MTII-stimulated thermogenesis in DIO rats. MTII also increased fat catabolism in the muscle of DIO rats and improved glucose and cholesterol metabolism in both groups.
LE Pritchard, D Armstrong, N Davies, RL Oliver, CA Schmitz, JC Brennand, GF Wilkinson and A White
Interactions between pro-opiomelanocortin (POMC)-derived peptides, agouti-related protein (AGRP) and the melanocortin-4 receptor (MC4-R) are central to energy homeostasis. In this study we have undertaken comprehensive pharmacological analysis of these interactions using a CHOK1 cell line stably transfected with human MC4-R. Our main objectives were (1) to compare the relative affinities and potencies of POMC-derived peptides endogenously secreted within the hypothalamus, (2) to investigate the potency of AGRP(83-132) antagonism with respect to each POMC-derived peptide and (3) to determine whether AGRP(83-132) and POMC-derived peptides act allosterically or orthosterically. We have found that beta melanocyte-stimulating hormone (betaMSH), desacetyl alpha MSH (da-alphaMSH) and adrenocorticotrophic hormone all have very similar affinities and potencies at the MC4-R compared with the presumed natural ligand, alphaMSH. Moreover, even MSH precursors, such as beta lipotrophic hormone, showed significant binding and functional activity. Therefore, many POMC-derived peptides could have important roles in appetite regulation and it seems unlikely that alphaMSH is the sole physiological ligand. We have shown that AGRP(83-132) acts as a competitive antagonist. There was no significant difference in the potency of inhibition by AGRP(83-132) or agouti(87-132) at the MC4-R, regardless of which POMC peptide was used as an agonist. Furthermore, we have found that AGRP(83-132) has no effect on the dissociation kinetics of radiolabelled Nle4,D-Phe7 MSH from the MC4-R, indicating an absence of allosteric effects. This provides strong pharmacological evidence that AGRP(83-132) acts orthosterically at the MC4-R to inhibit Gs-coupled accumulation of intracellular cAMP.
Hiroyuki Shimizu, Kinji Inoue and Masatomo Mori
-coupled seven-transmembrane receptors. Five different receptors have been well characterized. Among these, melanocortin-3 receptor (MC3R) and melanocortin-4 receptor (MC4R) are present in the brain and exert their function in the regulation of energy homeostasis
Giulia Baldini and Kevin D Phelan
regions such as the stria terminalis (BNST), the paraventricular nucleus of the thalamus (PVT) and the lateral hypothalamus (LH) ( Betley et al. 2013 ). In the PVN, α-MSH released by POMC neurons interacts with melanocortin-4 receptor (MC4R) expressed by