Melanocortin-4 Receptor Pathway Research Articles

SUN-602 Weight Loss After Glucagon-Like Peptide-1 Receptor Agonist Treatment in Childhood Obesity with Diabetes and Cirrhosis Associated with a Homozygous MC4R Mutation

BackgroundMutations in the melanocortin-4 receptor (MC4R) represent the most common cause of monogenic obesity. Treatment options are limited but glucagon-like peptide-1 receptor agonists (GLP-1 RA) may be of use to induce weight loss.MethodsExome of the patient was captured using the Agilent SureSelect QXT Human All Exon V5 kit and sequenced on Illumina.Clinical findings and resultsWe report obesity-associated diabetes and cirrhosis in a 13-year girl born from consanguineous parents of Afghan origin. Past medical history revealed mild mental retardation and excessive weight gain since infancy. Linear growth was normal. Her father was obese and no diabetes was found in the family. The girl was initially investigated for hoarseness and found to have pulmonary hypertension, later accepted to be secondary to cirrhosis and portal hypertension. Physical examination revealed obesity (BMI 34.9kg/m2) and acanthosis nigricans. Blood exams showed leucopenia and thrombocytopenia without anemia, compatible with portal hypertension. Chest CT revealed important dilatation of the pulmonary arteries, a nodular liver and splenomegaly. Liver biopsy confirmed cirrhosis. An extensive workup including whole exome sequencing identified a homozygous MC4R variant [NM_005912.2 (MC4R): c.63_64del, p.(Tyr21*)], classified as pathogenic according to the ACMG guidelines. Both parents were heterozygous for this variant. An endocrinological workup showed insulin resistance with a HOMA-IR index of 7.27 and diabetes with peak blood glucose of 11.5mmol/l. HbA1c was 5.1% (32mmol/mol). Thyroid tests, leptin, proinsulin levels (3.5pmol/l, n <11.0pmol/l) were normal.The mutation being homozygous with a predicted complete loss of function (https://www.mc4r.org.uk/), no treatment with a MC4R agonist was tried. At the age of 15 years (BMI 36.0kg/m2), the patient underwent liver transplantation because of progressive portal hypertension and to halt the progression of pulmonary hypertension. At the age of 16 years (BMI 33.2kg/m2, HbA1c 4.9% (30.0 mmol/mol), HOMA-IR 5.3) a treatment with GLP-1 RA (liraglutide) was started at a dosage of 0.6mg and progressively increased to 3mg, in an attempt to induce weight loss, avoid the accumulation of liver fat and to protect the graft. GLP-1 RA is supposed to exerts its effects on appetite independently of the MC4R pathway. 2 months after liraglutide introduction, no side effects, a weight loss of 4kg and a decrease of appetite were observed (BMI 31.6kg/m2, HbA1c 4.5% (26mmol/mol), HOMA-IR 3.14).ConclusionObesity-associated MCR4 mutations, in homozygous state, may lead to diabetes, liver cirrhosis and porto-pulmonary hypertension. Treatment options are scarce, but GLP-1 RA seem to have a rapid, positive effect on weight and metabolic control. Would earlier treatment have prevented progression to end-stage-liver disease and need for liver transplantation?

Patients with obesity caused by melanocortin-4 receptor mutations can be treated with a glucagon-like peptide-1 receptor agonist

Summary Pathogenic mutations in the appetite-regulating melanocortin-4 receptor (MC4R) represent the most common cause of monogenic obesity with limited treatment options. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) cause weight loss by reducing appetite. We assessed the effect of the GLP-1 RA liraglutide 3.0 mg for 16 weeks in 14 obese individuals with pathogenic MC4R mutations (BMI 37.5 ± 6.8) and 28 matched control participants without MC4R mutation (BMI 36.8 ± 4.8). Liraglutide decreased body weight by 6.8 kg ± 1.8 kg in individuals with pathogenic MC4R mutations and by 6.1 kg ± 1.2 kg in control participants. Total body fat, waist circumference, and fasting and postprandial glucose concentrations similarly decreased in both groups. Thus, liraglutide induced an equal, clinically significant weight loss of 6% in both groups, indicating that the appetite-reducing effect of liraglutide is preserved in MC4R causal obesity and that liraglutide acts independently of the MC4R pathway. Thus, liraglutide could be an effective treatment of the most common form of monogenic obesity.

Tracing the effect of the melanocortin-4 receptor pathway in obesity: study design and methodology of the TEMPO registry.

Purpose: The hypothalamic melanocortin-4 receptor (MC4R) pathway, a component of the central melanocortin pathway, regulates energy balance and satiety. Rare genetic disorders of obesity may be characterized by impaired MC4R pathway signaling, which results in early-onset severe obesity and insatiable hunger (hyperphagia). The TEMPO registry (NCT03479437) is a voluntary, prospective, open-ended registry of individuals with rare genetic disorders of obesity due to mutations in genes within the MC4R pathway who have early-onset severe obesity. The objective of the TEMPO registry is to evaluate the burden of rare genetic disorders of obesity on individuals, their parents/caregivers, health care providers, and the health care system.Patients and methods: Individuals with rare genetic disorders of obesity (adults aged ≥18 years and children and adolescents aged from 2 to 17 years) will be referred by their health care providers or by a genetic screening study. Individuals must meet age- and sex-specific body mass index values that define the clinical criteria for severe obesity and carry selected variants in MC4R or in one of several genes upstream or downstream of the MC4R. Online surveys will be completed by the individual, parent/caregiver, and health care provider at baseline and annually thereafter and will collect data on demographics, results of genetic testing, medical/family history, disease characteristics, resource utilization, eating habits/hunger episodes, social and emotional impacts, and interest in future clinical trial participation.Conclusions: The TEMPO registry will provide insights into the overall course and disease burden for individuals with rare genetic disorders of obesity. Health care providers may use this resource to improve the identification, diagnosis, and treatment of individuals with rare forms of genetic obesity.

Melanocortin 4 receptor-mediated effects of amylin on thermogenesis and regulation of food intake.

Amylin, a pancreatic hormone cosecreted with insulin, exerts important anorexic and weight-loss effects. Melanocortin 4 receptor (MC4R) signalling plays a critical role in energy homeostasis; however, its role on amylin-dependent regulation of food intake and adaptive thermogenesis of interscapular brown adipose tissue (IBAT) are unclear. In this study, we examined the effects of amylin on food intake and thermogenesis on IBAT via the MC4R pathway in mice. Acute food consumption and thermogenesis in IBAT were measured in male wild-type (WT) and MC4R-deficient mice following intraperitoneal injection of amylin and SHU9119, an MC3R/4R antagonist, to determine the role of the central melanocortin system on the hypothalamus and IBAT. Amylin (50μg/kg) suppressed feeding and stimulated thermogenesis on IBAT via activation of the MC4R system in mice. Pharmacological blockade of MC4R using SHU9119 (50μg/kg) attenuated amylin-induced inhibition of feeding and stimulation of thermogenesis in IBAT. No changes were observed when SHU9119 was injected alone. Moreover, amylin significantly increased MC4R expression and c-Fos neuronal signals in the arcuate nucleus and significantly increased acetyl-CoA carboxylase (ACC) phosphorylation in the hypothalamus and IBAT and uncoupling protein-1 (UCP1) expression in the IBAT of WT mice via the MC4R pathway. The melanocortin system was involved in amylin-induced suppression of food intake and activation of thermogenesis in both the hypothalamus and IBAT via modulation of ACC phosphorylation and UCP1 expression.

Abstract 086: Neuroanatomical Basis of PVN MC4R-Expressing Neurons for Sympathetic Cardiovascular Control

It is well established that the central melanocortin system is critical for autonomic functions and energy homeostasis mainly via signaling at melanocortin-4 receptor (MC4R). Importantly, while obesity is commonly associated with elevated sympathetic tone and blood pressure, severely obese humans and rodents due to genetic MC4R deficiency exhibit normal to low sympathetic tone and blood pressure, suggesting a significant role of MC4R pathway in mediating obesity-associated sympathoexcitation and hypertension. MC4R is widely expressed in the brain including hypothalamic paraventricular nucleus (PVN) which regulates feeding and sympathetic traffic. However, the neuroanatomical basis of PVN MC4R neurons for sympathetic regulation is unclear. The goal of current study is to map the PVN MC4R neural circuits affecting sympathetic tone in mice. To this end, we injected Cre-dependent AAV driving eYFP-fused channel rhodopsin-2 expression into the PVN of MC4R-t2a-Cre knock-in mice, which allow targeted anterograde tract-tracing of PVN MC4R neurons throughout the brain. In addition to known brain region for feeding behavior (i.e. parabrachial nucleus), we found broad innervations of PVN MC4R neurons to various brain regions important for autonomic-cardiovascular control, including, but not limited to, nucleus of solitary tractus, dorsomotor nucleus of vagus, and ventrolateral medulla. Considerable innervation was also evident in spinal cord, which is further confirmed by Fluoro-gold (FG)-mediated retrograde tracing in the spinal cord (thoracic T6-10) of MC4R-GFP transgenic mouse. Double immunofluorescence labeling of GFP and FG revealed that ~50% (58 out of 116) MC4R neurons in the posterior parvocellular subdivision of PVN project to thoracic spinal cord. Furthermore, microinjection of synthetic MC4R agonist (MTII) into the PVN evokes ~42% increase (from baseline) in renal sympathetic nerve activity in anesthetized mice. These results provide important insights into understanding the divergent neural circuits by which PVN MC4R signaling differentially regulates metabolic and cardiovascular functions. Functional dissection of these diverging neural pathways using optogenetic/chemogenetic approaches is ongoing.

Patients with Obesity Caused by Melanocortin-4 Receptor Mutations Can Be Treated with a Glucagon-like Peptide-1 Receptor Agonist

Pathogenic mutations in the appetite-regulating melanocortin-4 receptor (MC4R) represent the most common cause of monogenic obesity with limited treatment options. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) cause weight loss by reducing appetite. We assessed the effect of the GLP-1 RA liraglutide 3.0mg for 16weeks in 14 obese individuals with pathogenic MC4R mutations (BMI 37.5± 6.8) and 28 matched control participants without MC4R mutation (BMI 36.8± 4.8). Liraglutide decreased body weight by 6.8kg ± 1.8kg in individuals with pathogenic MC4R mutations and by 6.1kg ± 1.2kg in control participants. Total body fat, waist circumference, and fasting and postprandial glucose concentrations similarly decreased in both groups. Thus, liraglutide induced an equal, clinically significant weight loss of 6% in both groups, indicating that the appetite-reducing effect of liraglutide is preserved in MC4R causal obesity and that liraglutide acts independently of the MC4R pathway. Thus, liraglutide could be an effective treatment of the most common form of monogenic obesity.

Melanocortin 4 Receptor Pathway Dysfunction in Obesity: Patient Stratification Aimed at MC4R Agonist Treatment.

ContextThe hypothalamic melanocortin 4 receptor (MC4R) pathway serves a critical role in regulating body weight. Loss of function (LoF) mutations in the MC4R pathway, including mutations in the pro-opiomelanocortin (POMC), prohormone convertase 1 (PCSK1), leptin receptor (LEPR), orMC4R genes, have been shown to cause early-onset severe obesity.MethodsThrough a comprehensive epidemiological analysis of known and predicted LoF variants in thePOMC, PCSK1, andLEPR genes, we sought to estimate the number of US individuals with biallelic MC4R pathway LoF variants.ResultsWe predict ~650α-melanocyte-stimulating hormone (MSH)/POMC, 8500PCSK1, and 3600LEPR homozygous and compound heterozygous individuals in the United States, cumulatively enumerating >12,800 MC4R pathway–deficient obese patients. Few of these variants have been genetically diagnosed to date. These estimates increase when we include a small subset of less rare variants:β-MSH/POMC,PCSK1 N221D, and aPCSK1 LoF variant (T640A). To further define the MC4R pathway and its potential impact on obesity, we tested associations between body mass index (BMI) and LoF mutation burden in thePOMC, PCSK1, andLEPR genes in various populations. We show that the cumulative allele burden in individuals with two or more LoF alleles in one or more genes in the MC4R pathway are predisposed to a higher BMI than noncarriers or heterozygous LoF carriers with a defect in only one gene.ConclusionsOur analysis represents a genetically rationalized study of the hypothalamic MC4R pathway aimed at genetic patient stratification to determine which obese subpopulations should be studied to elucidate MC4R agonist (e.g., setmelanotide) treatment responsiveness.

Role of the brain melanocortins in blood pressure regulation

Melanocortins play an important role in regulating blood pressure (BP) and sympathetic nervous system (SNS) activity as well as energy balance, glucose and other metabolic functions in humans and experimental animals. In experimental models of hypertension with high SNS activity, blockade of the melanocortin-4 receptor (MC4R) reduces BP despite causing marked hyperphagia and obesity. Activation of the central nervous system (CNS) pro-opiomelanocortin (POMC)–MC4R pathway appears to be an important link between obesity, SNS activation and hypertension. Despite having severe obesity, subjects with MC4R deficiency exhibit reductions in BP, heart rate, and urinary catecholamine excretion, as well as attenuated SNS responses to cold stimuli compared to obese subjects with normal MC4R function. In this review we discuss the importance of the brain POMC-MC4R system in regulating SNS activity and BP in obesity and other forms of hypertension. We also highlight potential mechanisms and brain circuitry by which the melanocortin system regulates cardiovascular function.

Melanocortin‐4 Receptor Activation Stimulates Hypothalamic Brain‐Derived Neurotrophic Factor Release to Regulate Food Intake, Body Temperature and Cardiovascular Function

In the present study, we aimed to investigate the neuromodulatory role played by hypothalamic brain-derived neurotrophic factor (BDNF) in the regulation of acute cardiovascular and feeding responses to melanocortin-4 receptor (MC4R) activation. In vitro, a selective MC4R agonist, MK1, stimulated BDNF release from isolated rat hypothalami and this effect was blocked by preincubation with the MC3/4R antagonist SHU-9119. In vivo, peripheral administration of MK1 decreased food intake in rats and this effect was blocked by pretreatment with an anti-BDNF antibody administered into the third ventricle. When anorexia was induced with the cannabinoid-1 receptor (CB1R) antagonist AM251, the anti-BDNF antibody did not prevent the reduction in food intake. Peripheral administration of MK1 also increased mean arterial pressure, heart rate and body temperature. These effects were prevented by pretreatment with the anti-BDNF antibody whereas the intracerebroventricular administration of BDNF caused changes similar to those of MK1. These findings demonstrate for the first time that activation of MC4R leads to an acute release of BDNF in the hypothalamus. This release is a prerequisite for MC4R-induced effects on appetite, body temperature and cardiovascular function. By contrast, CB1R antagonist-mediated anorexia is independent of the MC4R/BDNF pathway. Overall, these results show that BDNF is an important downstream mediator of the MC4R pathway.

Regulation of Endogenous Melanocortin-4 Receptor Expression and Signaling by Glucocorticoids

The melanocortin-4 (MC4) receptor plays a pivotal role in regulating food intake and energy expenditure, and obesity results from mutations that interfere with the MC4 receptor pathway. We investigated the effect of glucocorticoids on endogenous MC4 receptors expressed in GT1-1 cells, an immortalized hypothalamic neuronal cell line. Dexamethasone (Dex) caused a 5- to 10-fold increase in the cAMP response to the MC4 receptor agonist, NDP-alphaMSH. The stimulatory effect of Dex reached a maximum within 24 h and was blocked by the glucocorticoid antagonist RU486. This glucocorticoid effect was specific for the MC4 receptor and not a result of up-regulation of another component of the cAMP cascade, because the response to endogenous beta-adrenergic receptor stimulation was not altered by Dex. Dex also potentiated NDP-alphaMSH-mediated ERK1/2 activation. After 12 h, Dex caused a 3- to 5-fold increase in [125I]NDP-alphaMSH binding, which was maintained for at least 48 h and prevented by RU486. Dex withdrawal caused a rapid return of MC4 receptor concentration to the basal level. Dex-mediated increases in MC4 receptor concentration resulted from a rapid but transient increase in MC4 receptor mRNA. This regulation apparently requires genomic regulatory sequences because Dex did not increase MC4 receptor expression or signaling in CHO cells expressing the MC4 receptor under the control of a cytomegalovirus promoter. We conclude that in GT1-1 hypothalamic neurons, glucocorticoids increase the amplitude of MC4 receptor signaling. This regulation may serve as a control to limit the effects of glucocorticoids on food intake.

Pro-opiomelanocortin processing in the hypothalamus: impact on melanocortin signalling and obesity.

Bioactive peptides derived from the prohormone, pro-opiomelanocortin (POMC), are generated in neurons of the hypothalamus and act as endogenous ligands for the melanocortin-4 receptor (MC4R), a key molecule underlying appetite control and energy homeostasis. It is therefore important to understand many aspects of POMC gene regulation in the brain, as pharmacological manipulation of POMC expression/processing could be a potential strategy to combat obesity. Most studies that have analysed POMC gene expression in the hypothalamus have focused on gene transcription experiments. Ultimately, however, factors that regulate post-translational processing and secretion of peptides will have most bearing on melanocortin signalling. This article focuses on (a) current evidence that POMC is involved in obesity, (b) how POMC transcription is regulated in the hypothalamus, (c) the mechanism by which proteolytic processing of POMC is controlled in the hypothalamus and what peptides are produced and (d) which POMC-derived peptides are the most potent ligands at the melanocortin receptor in vitro and in vivo. It seems that post-translational cleavage of POMC in the hypothalamus may be regulated with respect to energy requirement. We predict that further research into hypothalamic POMC processing, and the proteolytic enzymes involved, may yield important new clues on how flux through the MC4R pathway is regulated.

Melanocortin and leptin signaling systems: Central regulation of catabolic energy balance

The recent cloning of the ob gene (leptin) has revolutionized our understanding of obesity and the underlying factors that govern weight homeostasis. There is growing evidence that long term food intake regulation is controlled by the central nervous system by a number of peptide hormones in response to changes in leptin levels. Studies of these hormones, using both genetic and pharmacological approaches, have provided a foundation for decoding the molecular logic of the neuronal circuits which regulate food intake control and energy balance. A review of the current progress in the melanocortin-4 receptor pathway, with particular emphasis on its relation to leptin, neuropeptide Y and other obesity hormones known to modulate weight homeostasis, is presented.