Binge eating as a phenotype of melanocortin 4 receptor gene mutations

The Melanocortin System behind the Dysfunctional Eating Behaviors

The dysfunction of melanocortin signaling has been associated with obesity, given the important role in the regulation of energy homeostasis, food intake, satiety and body weight. In the hypothalamus, the melanocortin-3 receptor (MC3R) and melanocortin-4 receptor (MC4R) contribute to the stability of these processes, but MC3R and MC4R are also localized in the mesolimbic dopamine system, the region that responds to the reinforcing properties of highly palatable food (HPF) and where these two receptors seem to affect food reward and motivation. Loss of function of the MC4R, resulting from genetic mutations, leads to overeating in humans, but to date, a clear understanding of the underlying mechanisms and behaviors that promote overconsumption of caloric foods remains unknown. Moreover, the MC4R demonstrated to be a crucial modulator of the stress response, factor that is known to be strictly related to binge eating behavior. In this review, we will explore the preclinical and clinical studies, and the controversies regarding the involvement of melanocortin system in altered eating patterns, especially binge eating behavior, food reward and motivation.

Structural Complexity and Plasticity of Signaling Regulation at the Melanocortin-4 Receptor

The melanocortin-4 receptor (MC4R) is a class A G protein-coupled receptor (GPCR), essential for regulation of appetite and metabolism. Pathogenic inactivating MC4R mutations are the most frequent cause of monogenic obesity, a growing medical and socioeconomic problem worldwide. The MC4R mediates either ligand-independent or ligand-dependent signaling. Agonists such as α-melanocyte-stimulating hormone (α-MSH) induce anorexigenic effects, in contrast to the endogenous inverse agonist agouti-related peptide (AgRP), which causes orexigenic effects by suppressing high basal signaling activity. Agonist action triggers the binding of different subtypes of G proteins and arrestins, leading to concomitant induction of diverse intracellular signaling cascades. An increasing number of experimental studies have unraveled molecular properties and mechanisms of MC4R signal transduction related to physiological and pathophysiological aspects. In addition, the MC4R crystal structure was recently determined at 2.75 Å resolution in an inactive state bound with a peptide antagonist. Underpinned by structural homology models of MC4R complexes simulating a presumably active-state conformation compared to the structure of the inactive state, we here briefly summarize the current understanding and key players involved in the MC4R switching process between different activity states. Finally, these perspectives highlight the complexity and plasticity in MC4R signaling regulation and identify gaps in our current knowledge.

Gain-of-function variants in the melanocortin 4 receptor gene confer susceptibility to binge eating disorder in subjects with obesity: a systematic review and meta-analysis

The association between coding variants in the melanocortin 4 receptor gene (MC4R) and binge eating disorder (BED) in patients with obesity is controversial. Two independent reviewers systematically searched MEDLINE, Embase, PsycINFO, BIOSIS Previews, Web of Science Core Collection and Google Scholar up to February 2018, using terms describing the MC4R gene and BED. Six of 103 identified references were included. Studies examined associations between at least one coding variant/mutation in MC4R and BED and screened for BED as per the Diagnostic and Statistical Manual of Mental Disorders. Risk of bias was assessed using a modified version of the Q-Genie tool, and overall quality of evidence was assessed using Grading of Recommendations Assessment, Development and Evaluation guidance. Meta-analysis was conducted via logistic regression models. A positive association between gain-of-function (GOF) variants in the MC4R and BED was observed (odds ratio [OR] = 3.05; 95% confidence interval [CI]: 1.82, 5.04; p = 1.7 × 10^-5 ), while no association was detected between loss-of-function (LOF) mutations and BED (OR = 1.50; 95% CI: 0.73, 2.96; p = 0.25). Similar results were found after accounting for study quality (GOF variants: OR = 3.15; 95% CI: 1.76, 5.66; p = 1.1 × 10^-4 ; LOF mutations: OR = 1.50; 95% CI: 0.73, 2.97; p = 0.25). Our systematic review and meta-analysis provides evidence that GOF variants as opposed to LOF mutations in MC4R are associated with BED in subjects with obesity.

Signal Transduction and Pathogenic Modifications at the Melanocortin-4 Receptor: A Structural Perspective

The melanocortin-4 receptor (MC4R) can be endogenously activated by binding of melanocyte-stimulating hormones (MSH), which mediates anorexigenic effects. In contrast, the agouti-related peptide (AgRP) acts as an endogenous inverse agonist and suppresses ligand-independent basal signaling activity (orexigenic effects). Binding of ligands to MC4R leads to the activation of different G-protein subtypes or arrestin and concomitant signaling pathways. This receptor is a key protein in the hypothalamic regulation of food intake and energy expenditure and naturally-occurring inactivating MC4R variants are the most frequent cause of monogenic obesity. In general, obesity is a growing problem on a global scale and is of social, medical, and economic relevance. A significant goal is to develop optimized pharmacological tools targeting MC4R without adverse effects. To date, this has not been achieved because of inter alia non-selective ligands across the five functionally different MCR subtypes (MC1-5R). This motivates further investigation of (i) the three-dimensional MC4R structure, (ii) binding mechanisms of various ligands, and (iii) the molecular transfer process of signal transduction, with the aim of understanding how structural features are linked with functional-physiological aspects. Unfortunately, experimentally elucidated structural information is not yet available for the MC receptors, a group of class A G-protein coupled receptors (GPCRs). We, therefore, generated MC4R homology models and complexes with interacting partners to describe approximate structural properties associated with signaling mechanisms. In addition, molecular insights from pathogenic mutations were incorporated to discriminate more precisely their individual malfunction of the signal transfer mechanism.

Microduplication of 15q13.3 and Microdeletion of 18q21.32 in a Patient with Moyamoya Syndrome

Moyamoya angiopathy (MA) is a cerebrovascular disease determining a progressive stenosis of the terminal part of the internal carotid arteries (ICAs) and their proximal branches and the compensatory development of abnormal “moyamoya” vessels. MA occurs as an isolated cerebral angiopathy (so-called moyamoya disease) or in association with various conditions (moyamoya syndromes) including several heritable conditions such as Down syndrome, neurofibromatosis type 1 and other genomic defects. Although the mechanism that links MA to these genetic syndromes is still unclear, it is believed that the involved genes may contribute to the disease susceptibility. Herein, we describe the case of a 43 years old woman with bilateral MA and peculiar facial characteristics, having a 484-kb microduplication of the chromosomal region 15q13.3 and a previously unreported 786 kb microdeletion in 18q21.32. This patient may have a newly-recognized genetic syndrome associated with MA. Although the relationship between these genetic variants and MA is unclear, our report would contribute to widening the genetic scenario of MA, in which not only genic mutation, but also genome unbalances are possible candidate susceptibility factors.

Binding, Thermodynamics, and Selectivity of a Non-peptide Antagonist to the Melanocortin-4 Receptor

The melanocortin-4 receptor (MC4R) is a potential drug target for treatment of obesity, anxiety, depression, and sexual dysfunction. Crystal structures for MC4R are not yet available, which has hindered successful structure-based drug design. Using microsecond-scale molecular-dynamics simulations, we have investigated selective binding of the non-peptide antagonist MCL0129 to a homology model of human MC4R (hMC4R). This approach revealed that, at the end of a multi-step binding process, MCL0129 spontaneously adopts a binding mode in which it blocks the agonistic-binding site. This binding mode was confirmed in subsequent metadynamics simulations, which gave an affinity for human hMC4R that matches the experimentally determined value. Extending our simulations of MCL0129 binding to hMC1R and hMC3R, we find that receptor subtype selectivity for hMC4R depends on few amino acids located in various structural elements of the receptor. These insights may support rational drug design targeting the melanocortin systems.

Eating Behavior, Low-Frequency Functional Mutations in the Melanocortin-4 Receptor (MC4R) Gene, and Outcomes of Bariatric Operations: A 6-Year Prospective Study

OBJECTIVE

Data on the effects of eating behavior and genetics on outcomes of gastrointestinal surgery for diabesity have been sparse, often flawed, and controversial. We aimed to assess long-term outcomes of bariatric operations in patients characterized for eating behavior and rare mutations in the melanocortin-4 receptor (MC4R) gene, which is strongly implicated in energy balance.

RESEARCH DESIGN AND METHODS

Between 1996 and 2005, 1,264 severely obese Swiss patients underwent current laparoscopic adjustable gastric banding, gastroduodenal bypass, or a hybrid operation. Of these, 872 patients were followed for a minimum of 6 years and were screened for MC4R mutations. Using regression models, we studied relationships between eating behavior and MC4R mutations and postoperative weight loss, complications, and reoperations after 6 years.

RESULTS

At baseline, rare functional MC4R mutation carriers exhibited a significantly higher prevalence of binge eating disorder (BED) or loss-of-control eating independent of age, sex, and BMI. Six years after bariatric surgery, the mutation carriers had more major complications than wild-type subjects independent of age, baseline BMI, sex, operation type, and weight loss. Furthermore, high baseline BMI, male sex, BED, and functional MC4R mutations were independent predictors of higher reoperation rates.

CONCLUSIONS

Sequencing of MC4R and eating typology, combined with stratification for sex and baseline BMI, might significantly improve patient allocation to banding or bypass operations for diabesity as well as reduce both complication and reoperation rates.

Ring Finger Protein 11 Inhibits Melanocortin 3 and 4 Receptor Signaling

Intact melanocortin signaling via the G protein-coupled receptors (GPCRs), melanocortin receptor 4 (MC4R), and melanocortin receptor 3 (MC3R) is crucial for body weight maintenance. So far, no connection between melanocortin signaling and hypothalamic inflammation has been reported. Using a bimolecular fluorescence complementation library screen, we identified a new interaction partner for these receptors, ring finger protein 11 (RNF11). RNF11 participates in the constitution of the A20 complex that is involved in reduction of tumor necrosis factor α (TNFα)-induced NFκB signaling, an important pathway in hypothalamic inflammation. Mice treated with high-fat diet (HFD) for 3 days demonstrated a trend toward an increase in hypothalamic Rnf11 expression, as shown for other inflammatory markers under HFD. Furthermore, Gs-mediated signaling of MC3/4R was demonstrated to be strongly reduced to 20-40% by co-expression of RNF11 despite unchanged total receptor expression. Cell surface expression was not affected for MC3R but resulted in a significant reduction of MC4R to 61% by co-expression with RNF11. Mechanisms linking HFD, inflammation, and metabolism remain partially understood. In this study, a new axis between signaling of specific body weight regulating GPCRs and factors involved in hypothalamic inflammation is suggested.

Genes and the hypothalamic control of metabolism in humans

Heritability of obesity and body weight variation is high. Molecular genetic studies have led to the identification of mutations in a few genes, with a major effect on obesity (major genes and monogenic forms). Analyses of these genes have helped to unravel important pathways and have created a more profound understanding of body weight regulation. For most individuals, a polygenic basis is relevant for the genetic predisposition to obesity. Small effect sizes are conveyed by the polygenic variants. Hence, only if a number of these variants is harboured, a sizeable phenotypic effect is detectable. Most, if not all, of the genes relevant to weight regulation are expressed in the hypothalamus. This underscores the major role of this region of the brain in body weight regulation.

Loss of melanocortin-4 receptor function attenuates HPA responses to psychological stress

The melanocortin 4 receptor (MC4R), well-known for its role in the regulation of energy balance, is widely expressed in stress-regulatory brain regions, including the paraventricular nucleus of the hypothalamus (PVH) and the medial amygdala (MeA). In agreement with this, MC4R has been implicated in hypothalamic-pituitary-adrenocortical axis (HPA) regulation. The present work investigated the role of chronic Mc4r function to modulate basal HPA axis tone and to facilitate acute HPA responses to psychological stress, using a novel rat model with Mc4r loss-of-function. In this study, adult male rats were placed into 3 groups (n=15/group) according to genotype [wild-type (WT); heterozygous mutant (HET); and homozygous mutant (HOM)]. Basal (pre-stress) plasma adrenocorticotropic hormone (ACTH) and corticosterone were measured in the AM and PM, and the HPA axis response to restraint was assessed in the AM. Rats were perfused at 2h after restraint to assess the effect of loss of MC4R on stress-induced c-Fos immunolabeling in stress-regulatory brain regions. We find that basal (non-stress) AM and PM plasma ACTH and corticosterone showed a normal diurnal rhythm that was not altered according to genotype. Consistent with this, adrenal and thymus weights were unaffected by genotype. However, the plasma ACTH and corticosterone responses to restraint were significantly reduced by loss of MC4R function. Likewise, stress-induced c-Fos immunolabeling in both PVH and MeA was significantly reduced by loss of Mc4r function. These results support the hypothesis that endogenous MC4R signaling contributes to the HPA axis response to stress. Because MC4R plays a critical role in the regulation of energy balance, the present work suggests that it may also serve as an important communication link between brain metabolic and stress systems.

Genetics of eating disorders

Disordered eating behavior is the core symptom of the complex disorders anorexia nervosa and bulimia nervosa. Twin and family studies derive high heritability estimates. Hence, substantial genetic influences on the etiology can be assumed for both. Initially, candidate gene studies pertaining to the monoaminergic neurotransmitter systems and to body weight regulation comprised the core of the genetic analyses. Unfortunately, confirmed, solid findings substantiated in meta-analyses are rare, so that eventually none of these associations is unequivocal. Thus, systematic, genome-wide approaches emerged to identify genes with no a priori evidence for their involvement in eating disorders. Genome-wide association studies have hinted to formerly unknown genetic regions. However, significant genome-wide findings have not yet been reported.

Melanocortin-4 receptor expression in different classes of spinal and vagal primary afferent neurons in the mouse

Melanocortin-4 receptor (MC4R) ligands are known to modulate nociception, but the site of action of MC4R signaling on nociception remains to be elucidated. The current study investigated MC4R expression in dorsal root ganglia (DRG) of the MC4R-GFP reporter mouse. Because MC4R is known to be expressed in vagal afferent neurons in the nodose ganglion (NG), we also systematically compared MC4R-expressing vagal and spinal afferent neurons. Abundant green fluorescent protein (GFP) immunoreactivity was found in about 45% of DRG neuronal profiles (at the mid-thoracic level), the majority being small-sized profiles. Immunohistochemistry combined with in situ hybridization confirmed that GFP was genuinely produced in MC4R-expressing neurons in the DRG. While a large number of GFP profiles in the DRG coexpressed Nav1.8 mRNA (84%) and bound isolectin B4 (72%), relatively few GFP profiles were positive for NF200 (16%) or CGRP (13%), suggesting preferential MC4R expression in C-fiber nonpeptidergic neurons. By contrast, GFP in the NG frequently colocalized with Nav1.8 mRNA (64%) and NF200 (29%), but only to a moderate extent with isolectin B4 (16%). Lastly, very few GFP profiles in the NG expressed CGRP (5%) or CART (4%). Together, our findings demonstrate variegated MC4R expression in different classes of vagal and spinal primary afferent neurons, and underscore the role of the melanocortin system in modulating nociceptive and nonnociceptive peripheral sensory modalities.

Discrete melanocortin-sensitive neuroanatomical pathway linking the ventral premmamillary nucleus to the paraventricular hypothalamus

The physiological effects of melanocortin-4 receptor (MC4-R) on metabolism have been hypothesized to be mediated individually or collectively by neuronal groups innervating the paraventricular nucleus of the hypothalamus (PVH). The present study was designed to identify MC4-R-expressing neurons that innervate the PVH using retrograde tract tracing techniques in the MC4-R-GFP reporter mice. Our initial mapping identified very limited projections from MC4-R-expressing neurons to the PVH. This included a defined population of MC4-R-positive neurons located in the ventral premmamillary nucleus (PMv). Anterograde tracing experiments confirmed projections from PMv neurons to the medial parvicellular subdivision of the PVH, in close proximity to oxytocin neurons and β-endorphin-containing fibers. Given the known stimulatory effects of leptin and sexual odorants exposure on many PMv neurons, it was expected that MC4-R-expressing neurons in the PMv might be responsive to leptin and activated by odors exposure. Contrary to expectation, MC4-R-GFP neurons in the PMv do not respond to leptin as demonstrated by double labeling for GFP and leptin-induced phosphorylated STAT3. However, we found that Fos expression is induced in a large subset of MC4-R-GFP neurons in the PMv in response to opposite sex odors. Collectively, these results provide evidence for a previous unrecognized role of MC4-R expressed by neurons innervating the PVH that are also sensitive to reproductive cues.

Inhibition of melanocortin-4 receptor dimerization by substitutions in intracellular loop 2

Obesity is one of the most challenging global health problems. One key player in energy homeostasis is the melanocortin-4 receptor (MC4R), which is a family A G-protein-coupled receptor (GPCR). It has recently been shown that MC4R has the capacity to form homo- or heterodimers. Dimerization of GPCRs is of great importance for signaling regulation, with major pharmacological implications. Unfortunately, not enough is yet known about the detailed structural properties of MC4R dimers or the functional consequences of receptor dimerization. Our goal, therefore, was to explore specific properties related to MC4R dimerization. First, we aimed to induce the dissociation of dimers to monomers and to compare the functional parameters of wild-type and MC4R variants. To inhibit homodimerization, we designed MC4R chimeras with the cannabinoid-1 receptor, a receptor that does not interact with MC4R. Indeed, we identified several substitutions in the intracellular loop 2 (ICL2) and adjacent regions of transmembrane helix 3 (TMH3) and TMH4 that lead to partial dimer dissociation. Interestingly, the capacity for signaling activity was generally increased in these MC4R variants, although receptor expression remained unchanged. This increase in activity for dissociated receptors might indicate a link between receptor dimerization and signaling capacity. Moreover, dimer dissociation was also observed in a naturally occurring activating MC4R mutation in ICL2. Taken together, this study provides new information on the structural prerequisites for MC4R dimerization and identifies an approach to induce the dissociation of MC4R dimers. This might be useful for further investigation of pharmacological properties.

Eating behaviour in obese patients with melanocortin-4 receptor mutations: a literature review

Melanocortin-4 receptor (MC4R) mutations are the most common known cause of monogenic obesity and an important contributor to polygenic obesity. MC4R mutations with partial or total loss of function, as well as the variant rs17782313 mapped near MC4R, are positively associated with obesity. MC4R is involved in the leptin-melanocortin signalling system, located in hypothalamic nuclei, that controls food intake via both anorexigenic or orexigenic signals. Impairment in this receptor might affect eating behaviours. Thus, in the case of MC4R mutation carriers, obesity could be related, at least partly, to inadequate control over eating behaviours. Many published studies address eating behaviours in MC4R mutation carriers. Most studies focus on binge eating disorder, whereas others examine various aspects of intake and motivation. Up to now, no evaluation of this literature has been performed. In this review, we examine the available literature on eating behaviours in carriers of MC4R mutations and variant rs17782313 near MC4R gene. We address binge eating disorder, bulimia nervosa, mealtime hyperphagia, snacking, psychological factors, satiety responsiveness and intake of energy and macro/micronutrient. In a small number of studies, MC4R mutations seem to impair eating behaviours or motivation, but no clear causal effects can be found in the balance of the evidence presented. Improvements in methodologies will be necessary to clarify the behavioural effects of MC4R mutations.

Genetic testing in patients with obesity

The obesity epidemic is associated with the recent availability of highly palatable and inexpensive caloric food as well as important changes in lifestyle. Genetic factors, however, play a key role in regulating energy balance and numerous twin studies have estimated the BMI heritability between 40 and 70%. While common variants, identified through genome-wide association studies (GWAS) point toward new pathways, their effect size are too low to be of any use in the clinic. This review therefore concentrates on genes and genomic regions associated with very high risks of human obesity. Although there are no consensus guidelines, we review how the knowledge on these "causal factors" can be translated into the clinic for diagnostic purposes. We propose genetic workups guided by clinical manifestations in patients with severe early-onset obesity. While etiological diagnoses are unequivocal in a minority of patients, new genomic tools such as Comparative Genomic Hybridization (CGH) array, have allowed the identification of novel "causal" loci and next-generation sequencing brings the promise of accelerated pace for discoveries relevant to clinical practice.

The neuroendocrine circuitry controlled by POMC, MSH, and AGRP

Obesity is one of the most challenging health problems worldwide. Over the past few decades, our knowledge concerning mechanisms of weight regulation has increased tremendously leading to the identification of the leptin-melanocortin pathway. The filling level of energy stores is signaled to the brain, and the information is integrated by hypothalamic nuclei, resulting in a well-orchestrated response to food intake and energy expenditure to ensure constant body weight. One of the key players in this system is proopiomelanocortin (POMC), a precursor of a variety of neuropeptides. POMC-derived alpha- and beta-MSH play an important role in energy homeostasis by activating melanocortin receptors expressed in the arcuate nucleus (MC3R) and in the nucleus paraventricularis (MC4R). Activation of these two G protein-coupled receptors is antagonized by agouti-related peptide (AgRP). Naturally occurring mutations in this system were identified in patients suffering from common obesity as well as in patients demonstrating a phenotype of severe early-onset obesity, adrenal insufficiency, red hair, and pale skin. Detailed understanding of the complex system of POMC-AgRP-MC3R-MC4R and their interaction with other hypothalamic as well as peripheral signals is a prerequisite to combat the obesity epidemic.

Functional studies on twenty novel naturally occurring melanocortin-4 receptor mutations

The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor critically involved in regulating energy balance. MC4R activation results in decreased food intake and increased energy expenditure. Genetic and pharmacological studies demonstrated that the MC4R regulation of energy balance is conserved from fish to mammals. In humans, more than 150 naturally occurring mutations in the MC4R gene have been identified. Functional study of mutant MC4Rs is an important component in proving the causal link between MC4R mutation and obesity as well as the basis of personalized medicine. In this article, we studied 20 MC4R mutations that were either not characterized or not fully characterized. We showed that 11 mutants had decreased or absent cell surface expression. D126Y was defective in ligand binding. Three mutants were constitutively active but had decreased cell surface expression. Eleven mutants had decreased basal signaling, with two mutants defective only in this parameter, suggesting that impaired basal signaling might also be a cause of obesity. Five mutants had normal functions. In summary, we provided detailed functional data for further studies on identifying therapeutic approaches for personalized medicine to treat patients harboring these mutations.

The melanocortin-4 receptor: physiology, pharmacology, and pathophysiology

The melanocortin-4 receptor (MC4R) was cloned in 1993 by degenerate PCR; however, its function was unknown. Subsequent studies suggest that the MC4R might be involved in regulating energy homeostasis. This hypothesis was confirmed in 1997 by a series of seminal studies in mice. In 1998, human genetic studies demonstrated that mutations in the MC4R gene can cause monogenic obesity. We now know that mutations in the MC4R are the most common monogenic form of obesity, with more than 150 distinct mutations reported thus far. This review will summarize the studies on the MC4R, from its cloning and tissue distribution to its physiological roles in regulating energy homeostasis, cachexia, cardiovascular function, glucose and lipid homeostasis, reproduction and sexual function, drug abuse, pain perception, brain inflammation, and anxiety. I will then review the studies on the pharmacology of the receptor, including ligand binding and receptor activation, signaling pathways, as well as its regulation. Finally, the pathophysiology of the MC4R in obesity pathogenesis will be reviewed. Functional studies of the mutant MC4Rs and the therapeutic implications, including small molecules in correcting binding and signaling defect, and their potential as pharmacological chaperones in rescuing intracellularly retained mutants, will be highlighted.

Influence of lys656asn polymorphism of leptin receptor gene on surgical results of biliopancreatic diversion

BACKGROUND

Bariatric surgery is the most effective long-term treatment for morbid obesity, reducing obesity-associated comorbidities. The purpose of the present study was to evaluate Lys656Asn polymorphism of leptin receptor gene on outcomes 1 year after biliopancreatic diversion.

METHODS

A sample of 41 morbidly obese patients (body mass index (BMI) > 40 kg/m(2)) were operated on. Biochemical and anthropometric evaluation were realized at basal visit and at each visit. The frequency of patients with diabetes mellitus, hypertension, and hyperlipidemia was recorded at each visit.

RESULTS

Thirty-two patients (78%) had genotype Lys656/Lys656, eight patients (19.5%) Lys656/Asn656 genotype, and one patient (2.4%) Asn656/Asn656 genotype. In the wild-type group, body mass index, weight, glucose, total cholesterol, LDL cholesterol, triacylglycerol, and systolic blood pressure decreased. In the mutant group, the same parameters improved. Initial weight percent loss at 1 year of follow-up was higher in mutant group than in wild-type group (38.9% vs 29.9%; p < 0.05). Total weight loss was higher in mutant group than wild-type group (50.7 vs 37.2 kg; p < 0.05). Basal weight and BMI were higher in mutant group than wild type.

CONCLUSION

Weight loss was higher in mutant group (Lys656Asn and Asn656Asn) than wild-type group (Lys656Lys) after bariatric surgery. Carriers of the allelic variant (Asn) had higher basal weight.

Regulation of the hypothalamic thyrotropin releasing hormone (TRH) neuron by neuronal and peripheral inputs

The hypothalamic-pituitary-thyroid (HPT) axis plays a critical role in mediating changes in metabolism and thermogenesis. Thus, the central regulation of the thyroid axis by Thyrotropin Releasing Hormone (TRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) is of key importance for the normal function of the axis under different physiological conditions including cold stress and changes in nutritional status. Before the TRH peptide becomes biologically active, a series of tightly regulated processes occur including the proper folding of the prohormone for targeting to the secretory pathway, its post-translational processing, and targeting of the processed peptides to the secretory granules near the plasma membrane of the cell ready for secretion. Multiple inputs coming from the periphery or from neurons present in different areas of the brain including the hypothalamus are responsible for the activation or inhibition of the TRH neuron and in turn affect the output of TRH and the set point of the axis.

Regulation of lipid metabolism by energy availability: a role for the central nervous system

The central nervous system (CNS) is crucial in the regulation of energy homeostasis. Many neuroanatomical studies have shown that the white adipose tissue (WAT) is innervated by the sympathetic nervous system, which plays a critical role in adipocyte lipid metabolism. Therefore, there are currently numerous reports indicating that signals from the CNS control the amount of fat by modulating the storage or oxidation of fatty acids. Importantly, some CNS pathways regulate adipocyte metabolism independently of food intake, suggesting that some signals possess alternative mechanisms to regulate energy homeostasis. In this review, we mainly focus on how neuronal circuits within the hypothalamus, such as leptin- ghrelin-and resistin-responsive neurons, as well as melanocortins, neuropeptide Y, and the cannabinoid system exert their actions on lipid metabolism in peripheral tissues such as WAT, liver or muscle. Dissecting the complicated interactions between peripheral signals and neuronal circuits regulating lipid metabolism might open new avenues for the development of new therapies preventing and treating obesity and its associated cardiometabolic sequelae.

Eating disorders: the current status of molecular genetic research

Anorexia nervosa (AN) and bulimia nervosa (BN) are complex disorders characterized by disordered eating behavior where the patient's attitude towards weight and shape, as well as their perception of body shape, are disturbed. Formal genetic studies on twins and families suggested a substantial genetic influence for AN and BN. Candidate gene studies have initially focused on the serotonergic and other central neurotransmitter systems and on genes involved in body weight regulation. Hardly any of the positive findings achieved in these studies were unequivocally confirmed or substantiated in meta-analyses. This might be due to too small sample sizes and thus low power and/or the genes underlying eating disorders have not yet been analyzed. However, some studies that also used subphenotypes (e.g., restricting type of AN) led to more specific results; however, confirmation is as yet mostly lacking. Systematic genome-wide linkage scans based on families with at least two individuals with an eating disorder (AN or BN) revealed initial linkage regions on chromosomes 1, 3 and 4 (AN) and 10p (BN). Analyses on candidate genes in the chromosome 1 linkage region led to the (as yet unconfirmed) identification of certain variants associated with AN. Genome-wide association studies are under way and will presumably help to identify genes and pathways involved in these eating disorders. The elucidation of the molecular mechanisms underlying eating disorders might improve therapeutic approaches.

Critical determinants of hypothalamic appetitive neuropeptide development and expression: species considerations

Over the last decade there has been a striking increase in the early onset of metabolic disease, including obesity and diabetes. The regulation of energy homeostasis is complex and involves the intricate integration of peripheral and central systems, including the hypothalamus. This review provides an overview of the development of brain circuitry involved in the regulation of energy homeostasis as well as recent findings related to the impact of both prenatal and postnatal maternal environment on the development of these circuits. There is surprising evidence that both overnutrition and undernutrition impact the development of these circuits in a similar manner as well as having similar consequences of increased obesity and diabetes later in life. There is also a special focus on relevant species differences in the development of hypothalamic circuits. A deeper understanding of the mechanisms involved in the development of brain circuitry is needed to fully understand how the nutritional and/or maternal environments impact the functional circuitry as well as the behavior and physiological outcomes.

Genetic findings in anorexia and bulimia nervosa

Anorexia nervosa (AN) and bulimia nervosa (BN) are complex disorders associated with disordered eating behavior. Heritability estimates derived from twin and family studies are high, so that substantial genetic influences on the etiology can be assumed for both. As the monoaminergic neurotransmitter systems are involved in eating disorders (EDs), candidate gene studies have centered on related genes; additionally, genes relevant for body weight regulation have been considered as candidates. Unfortunately, this approach has yielded very few positive results; confirmed associations or findings substantiated in meta-analyses are scant. None of these associations can be considered unequivocally validated. Systematic genome-wide approaches have been performed to identify genes with no a priori evidence for their relevance in EDs. Family-based scans revealed linkage peaks in single chromosomal regions for AN and BN. Analyses of candidate genes in one of these regions led to the identification of genetic variants associated with AN. Currently, an international consortium is conducting a genome-wide association study for AN, which will hopefully lead to the identification of the first genome-wide significant markers.

From monogenic to polygenic obesity: recent advances

The heritability of obesity and body weight in general is high. A small number of confirmed monogenic forms of obesity-the respective mutations are sufficient by themselves to cause the condition in food abundant societies-have been identified by molecular genetic studies. The elucidation of these genes, mostly based on animal and family studies, has led to the identification of important pathways to the disorder and thus to a deeper understanding of the regulation of body weight. The identification of inborn deficiency of the mostly adipocyte-derived satiety hormone leptin in extremely obese children from consanguineous families paved the way to the first pharmacological therapy for obesity based on a molecular genetic finding. The genetic predisposition to obesity for most individuals, however, has a polygenic basis. A polygenic variant by itself has a small effect on the phenotype; only in combination with other predisposing variants does a sizeable phenotypic effect arise. Common variants in the first intron of the 'fat mass and obesity associated' gene (FTO) result in an elevated body mass index (BMI) equivalent to approximately +0.4 kg/m(2) per risk allele. The FTO variants were originally detected in a genome wide association study (GWAS) pertaining to type 2 diabetes mellitus. Large meta-analyses of GWAS have subsequently identified additional polygenic variants. Up to December 2009, polygenic variants have been confirmed in a total of 17 independent genomic regions. Further study of genetic effects on human body weight regulation should detect variants that will explain a larger proportion of the heritability. The development of new strategies for diagnosis, treatment and prevention of obesity can be anticipated.

Environmental and genetic risk factors in obesity

Because of its high prevalence and the associated medical and psychosocial risks, research into the causes of childhood obesity has experienced a tremendous upswing. Formal genetic data based on twin, adoption, and family studies lead to the conclusion that at least 50% of the interindividual variance of the body mass index (BMI; defined as weight in kilograms divided by height in meters squared) is due to genetic factors. As a result of the recent advent of genome-wide association studies, the first polygenes involved in body weight regulation have been detected. Each of the predisposing alleles explain a few hundred grams of body weight. More polygenes will be detected in the near future, thus for the first time allowing in-depth analyses of gene-gene and gene-environment interactions. They also will enable developmental studies to assess the effect of such alleles throughout childhood and adulthood. The recent increase in obesity prevalence rates illustrates the extreme relevance of environmental factors for body weight. Similar to polygenes, the effect sizes of most such environmental factors are likely to be small, thus rendering their detection difficult. In addition, the validation of the true causality of such factors is not a straightforward task. Important factors are socioeconomic status and television consumption. The authors conclude by briefly assessing implications for treatment and prevention of childhood obesity.

Genetic susceptibility to eating disorders: associated polymorphisms and pharmacogenetic suggestions

Anorexia nervosa (AN), bulimia nervosa (BN) and binge-eating disorder (BED) are characterized by abnormal eating behaviors often resulting in dramatic physical consequences for the patients. The etiology of eating disorders (EDs) is currently unknown; however, a strong genetic contribution is likely to be involved. To date, the majority of genetic studies have focused on candidate genes, and polymorphic variants of genes coding for substances likely to be involved in the etiopathogenesis of EDs have been assessed for association with AN, BN, BED and/or ED-related phenotypic traits. Results have been generally inconsistent and cannot be considered conclusive because of several methodological flaws and differences, such as small sample sizes, ethnic heterogeneity of studied populations, lack of statistical correction for multiple testing, adoption of different diagnostic criteria and population stratification. Although, at present, no convincing evidence for associations of candidate genes with EDs has been provided, the 5-HT2A receptor gene and the BDNF gene seem to be promising candidates for genetic influences on AN, since polymorphic variants of these genes have been found quite consistently, although not specifically, linked to AN restricting subtype in large sample studies. Moreover, pharmacogenetic investigations have suggested a possible role of some gene polymorphisms in predicting the response to treatment with selective serotonin reuptake inhibitors in BN, but results are still preliminary. The heterogeneity of ED phenotypes is believed to represent the most relevant variable responsible for contradictory and not conclusive results. Future studies should focus on more homogeneous subgroups, either relying on specific ED traits or identifying endophenotypes. This will be useful also for prevention and treatment of EDs.

Influence of G308A polymorphism of tumor necrosis factor alpha gene on surgical results of biliopancreatic diversion

BACKGROUND

Bariatric surgery is the most effective long-term treatment for morbid obesity, reducing obesity-associated comorbidities. The purpose of the present study was to evaluate G308A polymorphism of the tumor necrosis factor (TNF) alpha gene on outcomes 1 year after biliopancreatic diversion.

METHODS

A sample of 41 morbidly obese patients (body mass index > 40 kg/m(2)) were operated on. Weight, fat mass, blood pressure, creatinine, uric acid, basal glucose, triacylglycerols, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were measured at basal visit and at each visit. Adipocytokines were measured at basal time and 12 months after surgery. The frequency of patients with diabetes mellitus, hypertension, and hyperlipidemia was recorded at each visit.

RESULTS

Thirty-two patients (78%) had genotype G308G [wild-type group and nine patients (22%) with G308A genotype (mutant-type group)]. Genotype A308A was not detected. In the wild group, body mass index, weight, uric acid, glucose, total cholesterol, low-density lipoprotein cholesterol, triacylglycerol, leptin, and systolic blood pressure decreased. In the mutant group, the same parameters improved. Adiponectin levels increased after surgery in both genotypes. Initial weight percent loss at 1 year of follow up was similar in both groups (32.2% vs 28.6%; ns).

CONCLUSION

The present study demonstrates that the G308A polymorphism in the TNF-alpha gene is not related to clinical outcomes after bariatric surgery.

Influence of -55CT polymorphism of UCP3 gene on surgical results of biliopancreatic diversion

BACKGROUND

Bariatric surgery is the most effective long-term treatment for morbid obesity, reducing obesity-associated comorbidities. The purpose of the present study was to evaluate the UCP3 promotor (-55C-->T) polymorphism outcomes 1 year after biliopancreatic diversion in morbidly obese patients.

METHODS

A sample of 40 morbidly obese patients (BMI >40 kg/m(2)) were operated. Weight, fat mass, blood pressure, basal glucose, triacylglycerols, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were measured at basal visit and at each visit. The frequency of patients with diabetes mellitus, hypertension, and hyperlipidemia was recorded at each visit.

RESULTS

Twenty-eight patients (70%) had the genotype C/C (wild group) and 12 (30%) patients C/T (mutant group). In wild type group, body mass index, weight, fat mass, systolic blood pressure, glucose, total cholesterol, low-density lipoprotein cholesterol, and triacylglycerols concentrations decreased. In mutant type group, the same parameters improved, without statistical differences with wild group. Initial weight percent loss at 1 year of follow-up was similar in both genotypes (34.1% vs 28.6%; ns).

CONCLUSION

Polymorphism -55C/T of the UCP3 promotor did not have an effect on weight loss or clinical outcomes after bariatric surgery.

Pharmacological analyses of two naturally occurring porcine melanocortin-4 receptor mutations in domestic pigs

The melanocortin-4 receptor (MC4R) is critical in regulating mammalian food intake and energy expenditure. Numerous mutations in the MC4R gene have been identified from obese humans. So far two naturally occurring porcine MC4R (pMC4R) mutations, D298N and R236H, have been identified from various strains of pigs and D298N is being utilized as a genetic marker to screen performance traits of pigs. In this study, we performed functional analyses of pMC4R D298N and R236H, including their ligand binding and signaling properties in transiently transfected HEK293T cells. Ligand binding assays showed that both D298N and R236H pMC4Rs had similar binding capacities and affinities for the natural agonist alpha-MSH and the natural antagonist Agouti-related protein as wild-type pMC4R. In signaling assays, both mutants had normal EC50 and maximal signaling to alpha-MSH. In summary, pMC4R mutants D298N and R236H do not have any overt functional defects; therefore we suggest caution using these mutations as selection markers in breeding programs.

Influence of Ala54Thr polymorphism of fatty acid-binding protein-2 on clinical results of biliopancreatic diversion

OBJECTIVE

Bariatric surgery is the most effective long-term treatment for morbid obesity, reducing obesity-associated comorbidities. The purpose of the present study was to evaluate the fatty acid-binding protein-2 Ala54Thr polymorphism outcomes 1 y after biliopancreatic diversion in morbidly obese patients.

METHODS

A sample of 41 morbidly obese patients (body mass index >40 kg/m(2)) were operated upon from December 2004 to December 2006. Weight, fat mass, blood pressure, basal glucose, triacylglycerides, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were measured at the basal visit and at each visit. The frequency of patients with diabetes mellitus, hypertension, and hyperlipidemia was recorded at each visit.

RESULTS

Twenty-three patients (56.1%) had genotype Ala54/Ala54 (wild group) and 18 patients had genotype Ala54/Thr54 (15 patients, 36.5%) or Thr54/Thr54 (3 patients, 7.4%; mutant group). In the wild group, body mass index, weight, fat mass, systolic blood pressure, glucose, total cholesterol, low-density lipoprotein cholesterol, and triacylglycerol concentrations decreased. Diastolic blood pressure remained unchanged. In the mutant group, the same parameters improved, without statistical differences from the wild group. Initial excess weight percent loss at 1 y of follow-up was similar in both genotype groups (61.8% versus 61.9%, NS).

CONCLUSION

Polymorphism Ala54Thr of fatty acid-binding protein did not have an effect on weight loss or clinical outcomes after bariatric surgery.

Aspects génétiques de l'obésité

Genetic, specifically monogenic, obesity must be suspected: in cases of early severe obesity, developing in the first months of life; in cases of severely abnormal dietary behavior; in cases of associated endocrine abnormalities or pigmentation disorders; in cases of parental consanguinity. Mutations of the MC4R gene are the leading cause of oligogenic obesity. Discovery of a mutation of the MC4R gene furnishes a biologic source for some patients' susceptibility to obesity. Most human obesity nonetheless results from the interaction of multiple genetic factors and the environment. Molecules acting on the melanocortin pathway are currently under development by the pharmaceutical industry.

Melanocortin 4 receptor mutations in obese Czech children: studies of prevalence, phenotype development, weight reduction response, and functional analysis

BACKGROUND

Mutations in the melanocortin 4 receptor gene (MC4R) represent the most common known cause of monogenic human obesity.

AIMS

The aims of this study were the following: 1) to estimate the prevalence of MC4R mutations in obese Czech children; 2) to evaluate phenotypic features of the mutation carriers; 3) to compare weight, height, and body mass index of MC4R mutation carriers with noncarriers in longitudinal studies; 4) to determine the effect of a weight management program among MC4R mutation carriers; and 5) to perform a functional analysis of a novel variant.

SUBJECTS AND METHODS

We analyzed the coding region of MC4R in a cohort of 289 Czech children and adolescents with early-onset obesity by direct sequencing. Information on weight, height, body mass index, baseline biochemical data, and a weight loss follow-up study was obtained. In vitro functional analysis of one novel variant was performed.

RESULTS

We identified six different mutations in seven probands: one novel missense mutation Cys84Arg and five previously reported variants, Arg7Cys, Ser19fsdelA, Phe51Leu, Ser127Leu, and Gly181Asp. The Gly181Asp variant was detected in one homozygous carrier from unrelated parents. None of the mutation carriers fulfilled the MC4R syndrome criteria. A comparison of anthropometrics in mutation carriers and noncarriers during 13 yr of follow-up did not reveal any significant differences. MC4R mutation carriers exhibited a similar ability to lose weight as obese noncarriers. The novel variant Cys84Arg showed a significant reduction in cAMP signal properties of the MC4R.

CONCLUSIONS

Among obese Czech children, we found a prevalence of 2.4% of MC4R homozygous and heterozygous mutations and showed a similar response to diet management of MC4R mutation carriers and noncarriers.

Peripheral tissue-brain interactions in the regulation of food intake

More than 70 years ago the glucostatic, lipostatic and aminostatic hypotheses proposed that the central nervous system sensed circulating levels of different metabolites, changing feeding behaviour in response to the levels of those molecules. In the last 20 years the rapid increase in obesity and associated pathologies in developed countries has involved a substantial increase in the knowledge of the physiological and molecular mechanism regulating body mass. This effort has resulted in the recent discovery of new peripheral signals, such as leptin and ghrelin, as well as new neuropeptides, such as orexins, involved in body-weight homeostasis. The present review summarises research into energy balance, starting from the original classical hypotheses proposing metabolite sensing, through peripheral tissue-brain interactions and coming full circle to the recently-discovered role of hypothalamic fatty acid synthase in feeding regulation. Understanding these molecular mechanisms will provide new pharmacological targets for the treatment of obesity and appetite disorders.

A novel mutation Thr162Arg of the melanocortin 4 receptor gene in a Spanish children and adolescent population

OBJECTIVE

The melanocortin 4 receptor gene (MC4R) is involved in body weight regulation. While many studies associated MC4R mutations with childhood obesity, information on MC4R mutations in Spanish children and adolescents is lacking. Our objective was to screen a population of children and adolescents from the north of Spain (Navarra) for MC4R mutations and to study the phenotypes of carriers and their families. In addition, functional assays were performed for a novel MC4R mutation.

METHODS

The study was composed of 451 Spanish children and adolescents (49% boys), aged 5-18 year. According to the International Obesity Task Force (IOTF) criteria, the groups included 160 obese, 132 overweight and 159 normal-weight control subjects.

RESULTS

One novel (Thr162Arg) and three known nonsynonymous mutations in the MC4R gene (Ser30Phe, Thr150Ile, Ala244Glu) were detected heterozygously. The MC4R mutations were found in three male (one obese and two overweight) and two female subjects (one obese and one overweight). The novel mutation did not appear to lead to an impaired receptor function. An unequivocal relationship of MC4R mutations with obesity in pedigrees together with an impaired function of the encoded receptor could not be established for any of the mutations.

CONCLUSIONS

The presence of heterozygous MC4R mutations in obese and overweight subjects indicates that these mutations may be a susceptibility factor for obesity development, but lifestyle factors, such as exercise or sedentary activities, may modify their effect.

The V103I polymorphism of the MC4R gene and obesity: population based studies and meta-analysis of 29 563 individuals

BACKGROUND

Previous studies have suggested that a variant in the melanocortin-4 receptor (MC4R) gene is important in protecting against common obesity. Larger studies are needed, however, to confirm this relation.

METHODS

We assessed the association between the V103I polymorphism in the MC4R gene and obesity in three UK population based cohort studies, totalling 8304 individuals. We also did a meta-analysis of relevant studies, involving 10 975 cases and 18 588 controls, to place our findings in context.

FINDING

In an analysis of all studies, individuals carrying the isoleucine allele had an 18% (95% confidence interval 4-30%, P=0.015) lower risk of obesity compared with non-carriers. There was no heterogeneity among studies and no apparent publication bias.

INTERPRETATION

This study confirms that the V103I polymorphism protects against human obesity at a population level. As such it provides proof of principle that specific gene variants may, at least in part, explain susceptibility and resistance to common forms of human obesity. A better understanding of the mechanisms underlying this association will help determine whether changes in MC4R activity have therapeutic potential.

Therapy insight: Use of melanocortin antagonists in the treatment of cachexia in chronic disease

Cachexia is a process that accompanies many chronic diseases, and consists of a combination of wasting of lean body mass, increased energy expenditure, and a paradoxical loss of appetite. Cachexia both worsens quality of life and negatively affects treatment of the underlying disease. Conditions as diverse as cancer, renal failure, and heart failure show a remarkable similarity in their associated cachexia, exhibiting changes in metabolism and endocrinology, including marked increases in levels of cytokines that accompany these diseases. So far, it has been difficult to treat disease-associated cachexia successfully. One treatment that has shown promise in animal trials, however, involves antagonism of the central melanocortin system, an anorexigenic pathway in the hypothalamus and brainstem. Humans who have genetic mutations involving pro-opiomelanocortin or the melanocortin 4 receptor in this pathway exhibit increased appetite and increased lean body mass. Recent research has shown that in rodent models of cancer and renal failure, administration of melanocortin 4 receptor antagonists results in an attenuation of symptoms of cachexia, including maintenance of appetite, lean body mass, and basal energy expenditure. Although this research needs to be substantiated in humans, it provides a promising direction for treating the wasting that is associated with a variety of disease states.

Cachexia: lessons from melanocortin antagonism

It is well established that disruptions in melanocortin signaling in the CNS result in morbid obesity, but only recently has evidence linked the activation of this system with the production of cachexia, also known as disease-associated wasting. Pro-opiomelanocortin-producing neurons, which express cytokine receptors, show increased activation in the presence of several cytokines that are increased in diseases that are associated with cachexia. Recent experiments show that blockade of melanocortin signaling using antagonists to the melanocortin MC(4) receptor attenuates disease-associated anorexia and wasting in rodent models of cancer and renal failure. This successful inhibition of cachexia is important because loss of appetite and lean body mass worsen the prognosis of many the diseases with which cachexia is associated.

Génétique de l'obésité humaine

BACKGROUND

Both genetic and environmental aspects are recognized in the obesity field but we are not able to elucidate multiple genes and gene-environment interactions with the present resources and tools used in the study of this complex disease. The purpose of this paper is to present some examples of the knowledge acquired in the field of obesity genetics and the new ongoing tools and developments that aim at studying the contribution of genes to obesity and their response to environmental changes.

MAIN POINTS

In rare cases of monogenic obesities, genetic tools have proved extremely powerful for identifying the genes responsible and for defining new syndromes. However, in common obesity, most studies include the search for genotype-phenotype associations without taking into account the influence of environment (diet, sedentary lifestyle) in the relationship. Among the limitations to this integrated approach, one can cite the difficulty of having large enough samples as well as biocomputing tools that are still in their infancy for accessing the question of multiple interactions with no "a priori hypotheses". This picture will probably change rapidly in the future.

PERSPECTIVE

Large databases and DNA and biological sample banks will be available with updated environmental information and precise phenotypes thanks especially to European working groups. The capacity for studying multiple genes at once at the DNA or RNA levels is rapidly growing. Finally, tremendous progress in biocomputing will allow the integration of information from different sources (i.e. environment, phenotype, genotype, gene expression) and thus improve our ability to deal with complexity.

Genetics of human obesity

The rapid development of new concepts and tools has led to a change in the way in which researchers carry out nutrition-related research. Obesity is determined by the interaction between predisposing genetic and environmental aspects, but at present the gene-gene and gene-environment interactions contributing to the development of this complex disease cannot be analysed in detail. The purpose of the present paper is to provide some examples of the knowledge that is available in the field of obesity genetics, and also the new strategies being developed that are aimed at studying the relative contribution of numerous genes to obesity and their responses to environmental changes. In the rare cases of monogenic obesities in which a major gene is the cause the molecular approach has proved extremely powerful in the identification of the genes responsible and in defining new syndromes. However, in the common forms of obesity (polygenic obesity) most studies have analysed genotype-phenotype associations without sometimes taking into account the influence of environmental factors (diet, sedentary lifestyle). Among the aspects limiting this integrated approach to obesity are the difficulty of having large enough samples and the expansion of biocomputing tools developed for accessing the question of multiple interactions with no a priori hypotheses. This picture is rapidly changing. Large databases of clinical data and DNA and biological sample banks with more precise environmental information and patient phenotypes are being compiled. The capacity for studying multiple genes simultaneously at the DNA or RNA levels is also possible. Finally, the tremendous progress in biocomputing will allow the integration of these different types of data (relating to environment, phenotype, genotype, gene expression) and will improve the ability to deal with this complex disease.

Beyond Energy Balance: There Is More to Obesity than Kilocalories

Using an epidemiologic model of the interactions between environmental agents and human hosts to explain obesity, we explored food, medications, physical inactivity, toxins, and viruses as environmental agents that interact with a genetically programmed host to disturb energy balance and cause obesity. Large portion sizes, high fat intakes, easy access to calorically sweetened beverages, and lack of any need to be physically active all play a role in the toxic environment that leads to obesity. The genetic and physiologic responses of a host determine whether or not this toxic environment will produce obesity. Reversing the current trends of obesity requires a new look at the limits of the energy balance concept, and a better understanding of how environmental factors acutely and chronically change the responses of susceptible hosts.

Comparison of Gene Expression in Intra-Abdominal and Subcutaneous Fat: A Study of Men with Morbid Obesity and Nonobese Men Using Microarray and Proteomics

Extent of intra-abdominal fat had significant linear relations with six metabolic coronary risk factors: systolic and diastolic blood pressure, fasting blood concentrations of glucose, high density lipoprotein (HDL) cholesterol, triglyceride, and plasminogen activator inhibitor-1. Tumor necrosis factor-alpha and adiponectin can be biological mediators from the intra-abdominal fat to the metabolic coronary risk factors. Complementarily, we describe a new study that will analyze the gene expression in intra-abdominal and subcutaneous fat on mRNA and protein level using high throughput methods. The study will elucidate further whether intra-abdominal obesity is the common denominator for the different components of the metabolic syndrome.

The critical role of the melanocortin system in the control of energy balance

Animals have developed highly adaptive and redundant mechanisms to maintain energy balance by matching caloric intake to caloric expenditure. Recent evidence has pointed to a variety of peripheral signals that inform specific central nervous system (CNS) circuits about the status of peripheral energy stores as critical to the maintenance of energy balance. A critical component of these CNS circuits is the melanocortin system. Regulation of signaling by melanocortin 3 and melanocortin 4 receptors in the CNS is controlled via neuronal cell bodies in the arcuate nucleus of the hypothalamus that synthesize melanocortin receptor agonists such as alpha-melanocyte-stimulating hormone (alpha-MSH) or antagonists such as agouti-related protein (AgRP). The activity of these two populations of neurons is reciprocally regulated by a number of peripheral and central systems that influence energy balance. Further, increased melanocortin signaling via pharmacological or genetic means in the CNS causes potent reductions in food intake and weight loss. Decreased melanocortin signaling via pharmacological or genetic means results in increased food intake and weight gain. Reviewed here is the wide range of evidence that points to the melanocortin system as a critical node in the diverse neurocircuitry that regulates food intake and body weight.

The yellow agouti mutation alters some but not all responses to diet and exercise

OBJECTIVE

Effects of ectopic expression of the agouti signaling protein were studied on responses to diet restriction and exercise in C57BL/6J (B6) mice and obese B6 mice congenic for the yellow agouti mutation [B6.Cg-Ay (Ay)].

RESEARCH METHODS AND PROCEDURES

Adult male Ay mice were either kept sedentary or exercised on a running wheel and fed ad libitum or diet restricted until weight matched to ad libitum-fed B6 control mice. Body composition, plasma lipids, leptin, and adiponectin were measured. mRNA levels for leptin, adiponectin, lipoprotein lipase, and pyruvate dehydrogenase kinase 4 were measured in a visceral (epididymal) and a subcutaneous (femoral) fat depot by real-time polymerase chain reaction.

RESULTS

Correlations among traits exhibited one of three patterns: similar lines for B6 and Ay mice, different slopes for B6 and Ay mice, and/or different intercepts for B6 and Ay mice. Correlations involving plasma leptin, mesenteric and epididymal adipose weights, or low-density lipoprotein-cholesterol were most likely to have different slopes and/or intercepts in B6 and Ay mice. mRNA levels for leptin, Acrp30, pyruvate dehydrogenase kinase 4, and lipoprotein lipase in epididymal adipose tissue were not correlated with corresponding levels in femoral adipose tissue.

DISCUSSION

The agouti protein interferes with leptin signaling at melanocortin receptors in the hypothalamus of Ay mice. Our results are consistent with the hypothesis that the melanocortin portion of the leptin-signaling pathway mediates effects primarily on certain fat depots and on some, but not all, components of cholesterol homeostasis.