The MC4 receptor and control of appetite

Development of Human Target Validation Classification that Predicts Future Clinical Efficacy

Fewer new medicines have become available to patients during the last decades. Clinical efficacy failures in late-phase development have been identified as a common cause of this decline. Improved ways to ensure early selection of the right drug targets when it comes to efficacy is therefore a highly desirable goal. The aim of this work was to develop a strategy to facilitate selection of novel targets already in the discovery phase that later on in clinical development would demonstrate efficacy. A cross-functional team at AstraZeneca with extensive experience in drug discovery and development participated in several workshops to identify the critical elements that contribute to building human target validation [(HTV); the relevance of the target from a human perspective]. The elements were consolidated into a 10-point HTV classification system that was ranked from lowest to highest in terms of perceived impact on future clinical efficacy. Using 50 years of legacy research and development data, the ability of the 10-point HTV classification to predict future clinical efficacy was evaluated. Drug targets were classified as having low, medium, or high HTV at the time of candidate drug selection. Comparing this HTV classification with later clinical development efficacy data showed that HTV classification was highly predictive of future clinical efficacy success. This new strategy for HTV assessment provides a novel approach to early prediction of clinical efficacy and a better understanding of portfolio risk.

Associations between Single Nucleotide Polymorphisms and Total Energy, Carbohydrate, and Fat Intakes: A Systematic Review

A better understanding of the genetic underpinning of total energy, carbohydrate, and fat intake is a prerequisite to develop personalized dietary recommendations. For this purpose, we systematically reviewed associations between single nucleotide polymorphisms (SNPs) and total energy, carbohydrate, and fat intakes. Four databases were searched for studies that assessed an association between SNPs and total energy, carbohydrate, and fat intakes. Screening of articles and data extraction was performed independently by 2 reviewers. Articles in English or German language, published between 1994 and September 2017, on human studies in adults and without specific populations were considered for the review. In total, 39 articles, including 86 independent loci, met the inclusion criteria. The fat mass and obesity-associated (FTO) gene as well as the melanocortin 4 receptor (MC4R) locus were most frequently studied. Limited significant evidence of an association between the FTO SNP rs9939609 and lower total energy intake and between the MC4R SNP rs17782313 and higher total energy intake was reported. Most of the other identified loci showed inconsistent results. In conclusion, there is no consistent evidence that the investigated SNPs are associated with and predictive for total energy, carbohydrate, and fat intakes.

Current Status of Sarcopenia in Korea: A Focus on Korean Geripausal Women

Sarcopenia is defined as an age-associated decline in muscle mass and function caused by several etiologies and mechanisms. Muscle mass and function do not decrease concurrently, and a loss of muscle function may be more highly associated with adverse health outcomes. Despite the clinical significance of sarcopenia, no universally operational definition of sarcopenia or standardized intervention programs are currently available. Sarcopenia, osteoporosis, and obesity share several pathophysiological mechanisms, and a combination of these entities may lead to an increased risk of musculoskeletal, cardio-metabolic, and psychological morbidities especially in geripause populations. Treatment for sarcopenia is mainly nonpharmacological, however, various drugs are currently being developed. It is conceivable that sarcopenia is the next immediate clinical target in musculoskeletal science.

Why Do Mice Overeat High-Fat Diets? How High-Fat Diet Alters the Regulation of Daily Caloric Intake in Mice

OBJECTIVE

Ad libitum high-fat diets (HFDs) spontaneously increase caloric intake in rodents, which correlates positively with weight gain. However, it remains unclear why rodents overeat HFDs. This paper investigated how changing the proportion of diet that came from HFDs might alter daily caloric intake in mice.

METHODS

Mice were given 25%, 50%, or 90% of their daily caloric need from an HFD, along with ad libitum access to a low-fat rodent chow diet. Food intake was measured daily to determine how these HFD supplements impacted total daily caloric intake. Follow-up experiments addressed the timing of HFD feeding.

RESULTS

HFD supplements did not alter total caloric intake or body weight. In a follow-up experiment, mice consumed approximately 50% of their daily caloric need from an HFD in 30 minutes during the light cycle, a time when mice do not normally consume food.

CONCLUSIONS

An HFD did not disrupt regulation of total daily caloric intake, even when up to 90% of total calories came from the HFD. However, HFDs increased daily caloric intake when provided ad libitum and were readily consumed by mice outside of their normal feeding cycle. Ad libitum HFDs appear to induce overconsumption beyond the mechanisms that regulate daily caloric intake.

Agouti Signaling Protein and Its Receptors as Potential Molecular Markers for Intramuscular and Body Fat Deposition in Cattle

Transcriptome analyses of bovine muscle tissue differing in intramuscular fat (IMF) content identified agouti signaling protein (ASIP) as a promising candidate gene for fat deposition. The protein is secreted from adipocytes and may serve as a signaling molecule in cross-talk between adipocytes and muscle fibers or other cells. Known receptors for ASIP are the melanocortin receptors (e.g., MC4R) and attractin (ATRN). The present study was conducted to determine relationships between the expression of ASIP and its receptors in different bovine tissues with fat deposition. Adipose tissues, liver, and longissimus muscle tissue were collected from 246 F₂-generation bulls (Charolais × Holstein cross) and gene expression was measured with RT-qPCR. During analysis of subcutaneous fat (SCF) of all bulls, 17 animals were identified with a transposon-derived transcript (Exon2C) inserted in the ASIP gene and dramatically increased ASIP mRNA levels. Significant correlations between normalized mRNA values of SCF and phenotypic traits related to fat deposition were found in bulls without Exon2C. Three retrospectively assigned groups [Exon2C, n = 17; high carcass fat (HCF), n = 20; low carcass fat (LCF), n = 20] were further analyzed to verify expression differences and elucidate molecular reasons. Expression of ASIP could be detected in isolated muscle fibers and adipocytes of Exon2C bulls in contrast to HCF and LCF bulls, indicating ectopic ASIP expression if the transposon is present. Among adipose tissues, highest ASIP mRNA levels were measured in SCF with significantly higher values in HCF compared to LCF bulls (1.6-fold, P < 0.05). However, the protein abundance was below the detection limit in all bulls. Potential ASIP receptors were detected in most investigated tissues. The expression of MC4R was higher and of ATRN was lower in several tissues of LCF compared to HCF bulls, whereas MC1R was not differentially expressed. Bulls of the Exon2C group had lower ATRN mRNA values than HCF and LCF bulls in perirenal fat (PF), but higher (P < 0.05) values in muscle. Receptors were also expressed in tissues where ASIP mRNA was not detected. Consequently, those tissues could be targets for ASIP if it circulates.

Preclinical models for obesity research

A multi-dimensional strategy to tackle the global obesity epidemic requires an in-depth understanding of the mechanisms that underlie this complex condition. Much of the current mechanistic knowledge has arisen from preclinical research performed mostly, but not exclusively, in laboratory mouse and rat strains. These experimental models mimic certain aspects of the human condition and its root causes, particularly the over-consumption of calories and unbalanced diets. As with human obesity, obesity in rodents is the result of complex gene–environment interactions. Here, we review the traditional monogenic models of obesity, their contemporary optogenetic and chemogenetic successors, and the use of dietary manipulations and meal-feeding regimes to recapitulate the complexity of human obesity. We critically appraise the strengths and weaknesses of these different models to explore the underlying mechanisms, including the neural circuits that drive behaviours such as appetite control. We also discuss the use of these models for testing and screening anti-obesity drugs, beneficial bio-actives, and nutritional strategies, with the goal of ultimately translating these findings for the treatment of human obesity.

Summary: We review genetic models of obesity, their optogenetic and chemogenetic successors, and the use of dietary manipulations and meal-feeding regimes.

Stress-induced suppression of neuropeptide Y-induced hunger in anorexic chicks involves corticotrophin-releasing factor signalling and the paraventricular nucleus of the hypothalamus

The Virginia lines of chickens have been selected for low (LWS) or high (HWS) juvenile body weight and have different severities of anorexia and obesity, respectively. The LWS that are exposed to stressors at hatch are refractory to neuropeptide Y (NPY)-induced food intake and the objective of the present study was to determine the underlying mechanisms. Chicks were exposed to a stressor (-20°C for 6 minutes and 22°C and delayed access to food for 24 hours) after hatching and the hypothalamic nuclei, including the lateral hypothalamus (LH), paraventricular nucleus (PVN), ventromedial hypothalamus (VMH) and arcuate nucleus (ARC), were collected 5 days later. In LWS but not HWS, stress exposure up-regulated corticotrophin-releasing factor (CRF), CRF receptor subtypes 1 and 2 (CRFR1 and CRFR2, respectively), melanocortin receptor 4 and urocortin 3 in the PVN, as well as CRFR2 mRNA in the VMH and ARC. In LWS, stress exposure was also associated with greater NPY and NPY receptor subtype 5 mRNA in the ARC and PVN, respectively, as well as decreased agouti-related peptide mRNA in the ARC. In HWS, stress exposure was associated with increased CRFR1 and decreased cocaine- and amphetamine-regulated transcript in the ARC and PVN, respectively. Refractoriness of the food intake response to NPY in LWS may thus result from the over-riding anorexigenic tone in the PVN associated with CRF signalling. Indeed, the orexigenic effect of NPY was restored when LWS were injected with a CRF receptor antagonist, astressin, before stress exposure. The results of the present study provide insights into the molecular basis of eating disorders and suggest that CRF signalling in the PVN may exacerbate the anorexic phenotype in the presence of environmental stressors.

Genetic polymorphisms in genes related to risk-taking behaviours predicting body mass index trajectory among Mexican American adolescents

OBJECTIVES

Obesity is associated with multiple health problems and often originates in childhood. The purpose is to investigate the associations of genetic polymorphisms in genes related to risk-taking behaviours with body mass index (BMI) trajectory over adolescence among Mexican Americans.

METHODS

This study included 1229 Mexican American adolescents who participated in a large population-based cohort study in Houston, Texas. BMI data were obtained at baseline and two follow-ups. The median follow-up time was 59 months. Participants were genotyped for 672 functional and tagging variants in genes involved in the dopamine, serotonin and cannabinoid pathways.

RESULTS

After adjusting for multiple comparisons, three genetic variants, namely, rs933271 and rs4646310 in COMT gene, and rs9567733 in HTR2A gene were significantly associated with BMI growth over adolescence. Using those three variants, we created an allelic score, and the allelic score was associated with BMI growth over adolescence (P < 0.001). With the increase number of variant allele, the rate of BMI growth over adolescence was slower. Finally, we identified another two genetic variants, namely, rs17069005 in HTR2A gene and rs3776511 in SLC6A3A gene were associated with obesity at last follow-up.

CONCLUSIONS

The results suggest that genetic variants in selected genes involved in dopamine and serotonin pathways have noticeable effects on BMI over adolescence.

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

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

Emerging Signaling Pathway in Arcuate Feeding-Related Neurons: Role of the Acbd7

The understanding of the mechanisms whereby energy balance is regulated is essential to the unraveling of the pathophysiology of obesity. In the last three decades, focus was put on the metabolic role played by the hypothalamic neurons expressing proopiomelanocortin (POMC) and cocaine and amphetamine regulated transcript (CART) and the neurons co-localizing agouti-related peptide (AgRP), neuropeptide Y (NPY), and gamma-aminobutyric acid (GABA). These neurons are part of the leptin-melanocortin pathway, whose role is key in energy balance regulation. More recently, the metabolic involvement of further hypothalamic uncharacterized neuron populations has been suggested. In this review, we discuss the potential homeostatic implication of hypothalamic GABAergic neurons that produce Acyl-Coa-binding domain containing protein 7 (ACBD7), precursor of the nonadecaneuropeptide (NDN), which has recently been characterized as a potent anorexigenic neuropeptide capable of relaying the leptin anorectic/thermogenic effect via the melanocortin system.

Melanocortin 4 Receptor Activation Attenuates Mitochondrial Dysfunction in Skeletal Muscle of Diabetic Rats

A previous study has confirmed that the central melanocortin system was able to mediate skeletal muscle AMP-activated protein kinase (AMPK) activation in mice fed a high-fat diet, while activation of the AMPK signaling pathway significantly induced mitochondrial biogenesis. Our hypothesis was that melanocortin 4 receptor (MC4R) was involved in the development of skeletal muscle injury in diabetic rats. In this study, we treated diabetic rats intracerebroventricularly with MC4R agonist R027-3225 or antagonist SHU9119, respectively. Then, we measured the production of reactive oxygen species (ROS), the levels of malondialdehyde (MDA) and glutathione (GSH), the mitochondrial DNA (mtDNA) content and mitochondrial biogenesis, and the protein levels of p-AMPK, AMPK, peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α), sirtuin 1 (SIRT1), and manganese superoxide dismutase (MnSOD) in the skeletal muscle of diabetic rats. The results showed that there was significant skeletal muscle injury in the diabetic rats along with serious oxidative stress and decreased mitochondrial biogenesis. Treatment with R027-3225 reduced oxidative stress and induced mitochondrial biogenesis in skeletal muscle, and also activated the AMPK-SIRT1-PGC-1α signaling pathway. However, diabetic rats injected with MC4R antagonist SHU9119 showed an aggravated oxidative stress and mitochondrial dysfunction in skeletal muscle. In conclusion, our results revealed that MC4R activation was able to attenuate oxidative stress and mitochondrial dysfunction in skeletal muscle induced by diabetes partially through activating the AMPK-SIRT1-PGC-1α signaling pathway. J. Cell. Biochem. 118: 4072-4079, 2017. © 2017 Wiley Periodicals, Inc.

The polymorphism rs17782313 near MC4R gene is related with anthropometric changes in women submitted to bariatric surgery over 60 months

OBJECTIVE

Evaluate whether the polymorphism rs17782313 near MC4R gene influences long-term outcomes after bariatric surgery.

METHODS

The rs16782313 polymorphism was genotyped in 217 individuals undergoing bariatric surgery and analyzed in detail in 141 women. Data for comorbidities, BMI, excess weight loss (EWL), and body composition were obtained before and during 60 months after surgery.

RESULTS

The risk allele was found in 65 (47%) of the 141 women. Pre-surgical body weight and BMI were higher in carriers of the rs17782313 polymorphism (CC + CT group) than in non-carriers (TT group) (p = 0.039 and 0.047, respectively). The number of women who acquired surgical success (EWL > 50%), was lower in CC + CT group compared to TT group (p = 0.015). The minimum BMI seen during the 60 months of follow-up was higher in CC + CT group compared to TT group (p = 0.028). The number of women who presented BMI < 30 kg/m² (no longer classified as obesity) after 24 months of surgery was inferior in CC + CT group (6 out 35 patients - 17%) than in TT group (19 out 49 patients - 37%, p = 0.043). Moreover, the number of patients maintaining BMI > 35 kg/m² were higher carriers (18 out 35 patients - 51%) compare to non-carriers (16 out 49 patients - 32%, p = 0.045).

CONCLUSION

Women with extreme obesity carrying rs17782313 MC4R polymorphism present a higher pre-surgical BMI, are more unlikely to reach non-obesity BMI (<30 kg/m²) and tend to maintain a BMI > 35 kg/m² that characterize treatment failure.

Rs12970134 near MC4R is associated with appetite and beverage intake in overweight and obese children: A family-based association study in Chinese population

Background

Recent studies indicated that eating behaviors are under genetic influence, and the melanocortin 4 receptor (MC4R) gene polymorphisms can affect the total energy intake and the consumption of fat, protein and carbohydrates. Our study aims at investigating the association of the MC4R polymorphism with appetite and food intake among Chinese children.

Methods

A family-based association study was conducted among 151 Chinese trios whose offsprings were overweight/obese children aged 9–15 years. The rs12970134 near MC4R was genotyped, and the Children Eating Behavior Questionnaire (CEBQ) and a self-designed questionnaire measuring food intake were performed. The FBAT and PBAT software packages were used.

Results

The family-based association analysis showed that there was a significant association between rs12970134 and obesity (Z = 2.449, P = 0.014). After adjusting for age, gender and standardized BMI, rs12970134 was significantly associated with food responsiveness (FR) among children (β'_b = 0.077, P_b = 0.028), and with satiety responsiveness (SR) in trios (P = -0.026). The polymorphism was associated with beverage intake (β'_b = 0.331, P_b = 0.00016 in children; P = 0.043 in trios), but not significantly associated with vegetable, fruit or meat intake (P>0.050). We further found a significant mediation effect among the rs12970134, FR and beverage intake (b = 0.177, P = 0.047).

Conclusions

Our study is the first to report that rs12970134 near MC4R was associated with appetite and beverage intake, and food responsiveness could mediate the effect of rs12970134 on beverage intake in overweight and obese Chinese children population. Further studies are needed to uncover the genetic basis for eating behaviors, which could lead to develop and implement effective interventional strategies early in life.

Transcriptome assembly and candidate genes involved in nutritional programming in the swordtail fish Xiphophorus multilineatus

BACKGROUND

Nutritional programming takes place in early development. Variation in the quality and/or quantity of nutrients in early development can influence long-term health and viability. However, little is known about the mechanisms of nutritional programming. The live-bearing fish Xiphophorus multilineatus has the potential to be a new model for understanding these mechanisms, given prior evidence of nutritional programming influencing behavior and juvenile growth rate. We tested the hypotheses that nutritional programming would influence behaviors involved in energy homeostasis as well gene expression in X. multilineatus.

METHODS

We first examined the influence of both juvenile environment (varied in nutrition and density) and adult environment (varied in nutrition) on behaviors involved in energy acquisition and energy expenditure in adult male X. multilineatus. We also compared the behavioral responses across the genetically influenced size classes of males. Males stop growing at sexual maturity, and the size classes of can be identified based on phenotypes (adult size and pigment patterns). To study the molecular signatures of nutritional programming, we assembled a de novo transcriptome for X. multilineatus using RNA from brain, liver, skin, testis and gonad tissues, and used RNA-Seq to profile gene expression in the brains of males reared in low quality (reduced food, increased density) and high quality (increased food, decreased density) juvenile environments.

RESULTS

We found that both the juvenile and adult environments influenced the energy intake behavior, while only the adult environment influenced energy expenditure. In addition, there were significant interactions between the genetically influenced size classes and the environments that influenced energy intake and energy expenditure, with males from one of the four size classes (Y-II) responding in the opposite direction as compared to the other males examined. When we compared the brains of males of the Y-II size class reared in a low quality juvenile environment to males from the same size class reared in high quality juvenile environment, 131 genes were differentially expressed, including metabolism and appetite master regulator agrp gene.

DISCUSSION

Our study provides evidence for nutritional programming in X. multilineatus, with variation across size classes of males in how juvenile environment and adult diet influences behaviors involved in energy homeostasis. In addition, we provide the first transcriptome of X. multilineatus, and identify a group of candidate genes involved in nutritional programming.

Melanocortin neurons: Multiple routes to regulation of metabolism

The burden of disability, premature death, escalating health care costs and lost economic productivity due to obesity and its associated complications including hypertension, stroke, cardiovascular disease and type 2 diabetes is staggering [1,2]. A better understanding of metabolic homeostatic pathways will provide us with insights into the biological mechanisms of obesity and how to fundamentally address this epidemic [3-6]. In mammals, energy balance is maintained via a homeostatic system involving both peripheral and central melanocortin systems; changes in body weight reflect an unbalance of the energetic state [7-9]. Although the primary cause of obesity is unknown, there is significant effort to understand the role of the central melanocortin pathway in the brain as it has been shown that deficiency of proopiomelanocortin (POMC) [10,11] and melanocortin 4 receptors (MC4R) [12-15] in both rodents and humans results in severe hyperphagia and obesity [16-23]. In this review, we will summarize how the central melanocortin pathway helps regulate body mass and adiposity within a 'healthy' range through the 'nutrient sensing' network [24-28]. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

Neuropeptide systems and new treatments for nicotine addiction

RATIONALE

The mildly euphoric and cognitive enhancing effects of nicotine play a role in the initiation of smoking, while dysphoria and anxiety associated with smoking cessation contribute to relapse. After the acute withdrawal phase, smoking cues, a few cigarettes (i.e., lapse), and stressors can cause relapse. Human and animal studies have shown that neuropeptides play a critical role in nicotine addiction.

OBJECTIVES

The goal of this paper is to describe the role of neuropeptide systems in the initiation of nicotine intake, nicotine withdrawal, and the reinstatement of extinguished nicotine seeking.

RESULTS

The reviewed studies indicate that several drugs that target neuropeptide systems diminish the rewarding effects of nicotine by preventing the activation of dopaminergic systems. Other peptide-based drugs diminish the hyperactivity of brain stress systems and diminish withdrawal-associated symptom severity. Blockade of hypocretin-1 and nociceptin receptors and stimulation of galanin and neurotensin receptors diminishes the rewarding effects of nicotine. Both corticotropin-releasing factor type 1 and kappa-opioid receptor antagonists diminish dysphoria and anxiety-like behavior associated with nicotine withdrawal and inhibit stress-induced reinstatement of nicotine seeking. Furthermore, blockade of vasopressin 1b receptors diminishes dysphoria during nicotine withdrawal, and melanocortin 4 receptor blockade prevents stress-induced reinstatement of nicotine seeking. The role of neuropeptide systems in nicotine-primed and cue-induced reinstatement is largely unexplored, but there is evidence for a role of hypocretin-1 receptors in cue-induced reinstatement of nicotine seeking.

CONCLUSION

Drugs that target neuropeptide systems might decrease the euphoric effects of smoking and improve relapse rates by diminishing withdrawal symptoms and improving stress resilience.

The Obesity-Impulsivity Axis: Potential Metabolic Interventions in Chronic Psychiatric Patients

Pathological impulsivity is encountered in a broad range of psychiatric conditions and is thought to be a risk factor for aggression directed against oneself or others. Recently, a strong association was found between impulsivity and obesity which may explain the high prevalence of metabolic disorders in individuals with mental illness even in the absence of exposure to psychotropic drugs. As the overlapping neurobiology of impulsivity and obesity is being unraveled, the question asked louder and louder is whether they should be treated concomitantly. The treatment of obesity and metabolic dysregulations in chronic psychiatric patients is currently underutilized and often initiated late, making correction more difficult to achieve. Addressing obesity and metabolic dysfunction in a preventive manner may not only lower morbidity and mortality but also the excessive impulsivity, decreasing the risk for aggression. In this review, we take a look beyond psychopharmacological interventions and discuss dietary and physical therapy approaches.

Fermented Barley Supplementation Modulates the Expression of Hypothalamic Genes and Reduces Energy Intake and Weight Gain in Rats

Dietary fiber and proteins are individually known to decrease feeding, but could result greater weight management benefit when both are combined. We hypothesized that supplementing the diet with fermented barley, being rich in both dietary fiber and proteins, could lower energy intake by modulating the mRNA expression level of hypothalamic genes associated with the regulation of feeding behavior and satiety; thereby decreasing body weight gain. To test our hypothesis, four groups of Sprague Dawley rats were arranged in a 2 × 2 factorial design (n = 6), low-fat diet with either guar gum (LFD-G) or fermented barley (LFD-FB) and high-fat diet with either guar gum (HFD-G) or fermented barley (HFD-FB). Using oral gavage, fermented barley was given at a dosage of 1500 mg/kg body weight and guar gum was supplemented in an equivalent quantity to that of the fiber in the fermented barley. After 19 weeks, the fermented barley-supplemented groups showed a significant reduction in energy intake, triglyceride, body weight gain, and serum leptin, compared to the guar gum-supplemented groups in both the low- and high-fat diet groups. Likewise, the anorexigenic gene proopiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART) mRNA level were significantly higher in the fermented barley-supplemented groups compared to the guar gum-supplemented groups in rats fed on both high- and low-fat diets. In conclusion, fermented barley supplementation upregulated hypothalamic POMC/CART, decreased energy intake in both low- and high-fat diet groups, and prevented excessive weight gain in rats.

The metabolic sensor Sirt1 and the hypothalamus: Interplay between peptide hormones and pro-hormone convertases

The last decade had witnessed a tremendous progress in our understanding of the causes of metabolic diseases including obesity. Among the contributing factors regulating energy balance are nutrient sensors such as sirtuins. Sirtuin1 (Sirt1), a NAD + - dependent deacetylase is affected by diet, environmental stress, and also plays a critical role in metabolic health by deacetylating proteins in many tissues, including liver, muscle, adipose tissue, heart, endothelium, and in the complexity of the hypothalamus. Because of its dependence on NAD+, Sirt1 also functions as a nutrient/redox sensor, and new novel data show a function of this enzyme in the maturation of hypothalamic peptide hormones controlling energy balance either through regulation of specific nuclear transcription factors or by regulating specific pro-hormone convertases (PCs) involved in the post-translational processing of pro-hormones. The post-translational processing mechanism of pro-hormones is critical in the pathogenesis of obesity as recently shown that metabolic and physiological triggers affect the biosynthesis and processing of many peptides hormones. Specific regulation of pro-hormone processing is likely another key step where final amounts of bioactive peptides can be tightly regulated. Different factors stimulate or inhibit pro-hormones biosynthesis in concert with an increase in the PCs involved in the maturation of bioactive hormones. Adding more complexity to the system, the new studies describe here suggest that Sirt1 could also regulate the fate of peptide hormone biosynthesis. The present review summarizes the recent progress in hypothalamic SIRT1 research with a particular emphasis on the tissue-specific control of neuropeptide hormone maturation. The series of studies done in mouse and rat models strongly advocate for the first time that a deacetylating enzyme could be a regulator in the maturation of peptide hormones and their processing enzymes. These discoveries are the culmination of the first in-depth understanding of the metabolic role of Sirt1 in the brain. It suggests that Sirt1 behaves differently in the brain than in organs such as the liver and pancreas, where the enzyme has been more commonly studied.

The Neuroendocrine Regulation of Food Intake in Fish: A Review of Current Knowledge

Fish are the most diversified group of vertebrates and, although progress has been made in the past years, only relatively few fish species have been examined to date, with regards to the endocrine regulation of feeding in fish. In fish, as in mammals, feeding behavior is ultimately regulated by central effectors within feeding centers of the brain, which receive and process information from endocrine signals from both brain and peripheral tissues. Although basic endocrine mechanisms regulating feeding appear to be conserved among vertebrates, major physiological differences between fish and mammals and the diversity of fish, in particular in regard to feeding habits, digestive tract anatomy and physiology, suggest the existence of fish- and species-specific regulating mechanisms. This review provides an overview of hormones known to regulate food intake in fish, emphasizing on major hormones and the main fish groups studied to date.

Weighted Genetic Risk Scores and Prediction of Weight Gain in Solid Organ Transplant Populations

Background

Polygenic obesity in Solid Organ Transplant (SOT) populations is considered a risk factor for the development of metabolic abnormalities and graft survival. Few studies to date have studied the genetics of weight gain in SOT recipients. We aimed to determine whether weighted genetic risk scores (w-GRS) integrating genetic polymorphisms from GWAS studies (SNP group#1 and SNP group#2) and from Candidate Gene studies (SNP group#3) influence BMI in SOT populations and if they predict ≥10% weight gain (WG) one year after transplantation. To do so, two samples (n_A = 995, n_B = 156) were obtained from naturalistic studies and three w-GRS were constructed and tested for association with BMI over time. Prediction of 10% WG at one year after transplantation was assessed with models containing genetic and clinical factors.

Results

w-GRS were associated with BMI in sample A and B combined (BMI increased by 0.14 and 0.11 units per additional risk allele in SNP group#1 and #2, respectively, p-values<0.008). w-GRS of SNP group#3 showed an effect of 0.01 kg/m² per additional risk allele when combining sample A and B (p-value 0.04). Models with genetic factors performed better than models without in predicting 10% WG at one year after transplantation.

Conclusions

This is the first study in SOT evaluating extensively the association of w-GRS with BMI and the influence of clinical and genetic factors on 10% of WG one year after transplantation, showing the importance of integrating genetic factors in the final model. Genetics of obesity among SOT recipients remains an important issue and can contribute to treatment personalization and prediction of WG after transplantation.

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

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

Relationships between Single Nucleotide Polymorphism Markers and Meat Quality Traits of Duroc Breeding Stocks in Korea

This study was conducted to determine the relationships of five intragenic single nucleotide polymorphism (SNP) markers (protein kinase adenosine monophosphate-activated γ3 subunit [PRKAG3], fatty acid synthase [FASN], calpastatin [CAST], high mobility group AT-hook 1 [HMGA1], and melanocortin-4 receptor [MC4R]) and meat quality traits of Duroc breeding stocks in Korea. A total of 200 purebred Duroc gilts from 8 sires and 40 dams at 4 pig breeding farms from 2010 to 2011 reaching market weight (110 kg) were slaughtered and their carcasses were chilled overnight. Longissimus dorsi muscles were removed from the carcass after 24 h of slaughter and used to determine pork properties including carcass weight, backfat thickness, moisture, intramuscular fat, pH24h, shear force, redness, texture, and fatty acid composition. The PRKAG3, FASN, CAST, and MC4R gene SNPs were significantly associated with the meat quality traits (p<0.003). The meats of PRKAG3 (A 0.024/G 0.976) AA genotype had higher pH, redness and texture than those from PRKAG3 GG genotype. Meats of FASN (C 0.301/A 0.699) AA genotype had higher backfat thickness, texture, stearic acid, oleic acid and polyunsaturated fatty acid than FASN CC genotype. While the carcasses of CAST (A 0.373/G 0.627) AA genotype had thicker backfat, and lower shear force, palmitoleic acid and oleic acid content, they had higher stearic acid content than those from the CAST GG genotype. The MC4R (G 0.208/A 0.792) AA genotype were involved in increasing backfat thickness, carcass weight, moisture and saturated fatty acid content, and decreasing unsaturated fatty acid content in Duroc meat. These results indicated that the five SNP markers tested can be a help to select Duroc breed to improve carcass and meat quality properties in crossbred pigs.

Involvement of the Acyl-CoA binding domain containing 7 in the control of food intake and energy expenditure in mice

Acyl-CoA binding domain-containing 7 (Acbd7) is a paralog gene of the diazepam-binding inhibitor/Acyl-CoA binding protein in which single nucleotide polymorphism has recently been associated with obesity in humans. In this report, we provide converging evidence indicating that a splice variant isoform of the Acbd7 mRNA is expressed and translated by some POMC and GABAergic-neurons in the hypothalamic arcuate nucleus (ARC). We have demonstrated that the ARC ACBD7 isoform was produced and processed into a bioactive peptide referred to as nonadecaneuropeptide (NDN) in response to catabolic signals. We have characterized NDN as a potent anorexigenic signal acting through an uncharacterized endozepine G protein-coupled receptor and subsequently via the melanocortin system. Our results suggest that ACBD7-producing neurons participate in the hypothalamic leptin signalling pathway. Taken together, these data suggest that ACBD7-producing neurons are involved in the hypothalamic control exerted on food intake and energy expenditure by the leptin-melanocortin pathway.

DOI:http://dx.doi.org/10.7554/eLife.11742.001

Obesity is an increasingly common problem worldwide. To treat it effectively, we must understand how the body controls how much food a person consumes and how much energy they expend. The hypothalamus is one region of the brain that plays a critical role in regulating this energy balance. Some of the neurons in the hypothalamus can change their activity when they detect satiety hormones including the leptin, which is produced by fat cells and suppresses appetite. However, it is not clear exactly how the neurons respond to leptin and other energy-related signals.

Recent studies have linked the gene that encodes a protein called ACBD7 with obesity, and showed that it is one of the genes that is overexpressed in neurons that are sensitive to leptin. Now, Lanfray et al. have discovered a population of neurons that produce a new variant of the protein in the hypothalamus of mice. When this protein variant matures, it can be cut down to form a small protein-like molecule called NDN. Further experiments showed that leptin stimulates the production of both the new ABCD7 variant and NDN.

Lanfray et al. then injected mice that had been denied food for a several hours with NDN. The injected mice ate less than untreated mice, and burn more energy.

NDN appears to form part of the signaling pathway through which leptin signals to the hypothalamus to control appetite. In the future, creating mice in which the activity of the gene that encodes ACBD7 can be easily disrupted could help to reveal more about how the hypothalamus helps to control energy balance.

DOI:http://dx.doi.org/10.7554/eLife.11742.002

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

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

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

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

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

The ventrolateral hypothalamic area and the parvafox nucleus: Role in the expression of (positive) emotions?

The lateral hypothalamus has been long suspected of triggering the expression of positive emotions, because stimulations of its tuberal portion provoke bursts of laughter. Electrophysiological studies in various species have indeed confirmed that the lateral hypothalamus contributes to reward mechanisms. However, only the rudiments of the neural circuit underlying the expression of positive emotions are known. The prefrontal cortex, the lateral hypothalamus, and the periaqueductal gray matter (PAG) are involved in these circuits; so, too, are the brainstem nuclei that control the laryngeal muscles and subserve mimicry, as well as the cardiovascular and respiratory systems. The implicated populations of hypothalamic neurons have not been defined either anatomically or molecularly. One promising candidate is the novel parvafox nucleus, which we recently described, in the murine medial forebrain bundle (mfb), which specifically expresses parvalbumin and Foxb1. With the molecularly defined parvafox nucleus as a centerpiece, the inputs from the prefrontal cortex and the projections to the PAG and brainstem can be studied with precision. By drawing on genetic approaches, it will be possible to manipulate the circuitry selectively with spatial and temporal exactitude and to evaluate the concomitant autonomic changes. These data will serve as a basis for imaging studies in humans using various paradigms to provoke the expression of positive emotions. In conclusion, studies of the hypothalamic parvafox nucleus will reveal whether this entity represents the fulcrum for positive emotions, as is the amygdala for fear and the insula for disgust.

Associations between a common variant near the MC4R gene and serum triglyceride levels in an obese pediatric cohort

Polymorphisms near the MC4R gene may be related to an increased risk for obesity, but studies of variations in this gene and its relation to cardiometabolic profiles and food intake are scarce and controversial. The aim of this study is to evaluate the influence of the variants rs12970134 and rs17782313 near the MC4R gene in food intake, binge eating (BE) behavior, anthropometric parameters, body composition, metabolic profile, and cardiometabolic risk factors in obese children and adolescents. This is a cross-sectional study that included obese children and adolescents. We evaluated anthropometric, metabolic parameters and cardiometabolic risk factors, including hypertension, impaired fasting glucose, hypertriglyceridemia, and low HDL-cholesterol. BE was assessed through the BE scale, and a 24-h recall was used to evaluate total caloric intake and percentage of macronutrients and types of dietary fat. The MC4R variants rs12970134 and rs17782313 were genotyped using TaqMan assay. To assess the magnitude of risk, a logistic regression adjusted for Z-BMI, age, and gender was performed, adopting the significance level of 0.05. The study included 518 subjects (52.1 % girls, 12.7 ± 2.7 years old, Z-BMI = 3.24 ± 0.57). Carriers of the variant rs17782313 exhibit increased triglyceride levels (108 ± 48 vs. 119 ± 54, p = 0.034) and an increased risk of hypertriglyceridemia (OR 1.985, 95 % CI 1.288-3.057, p = 0.002). There was no association of the SNP rs12970134 with clinical, metabolic, or nutritional parameters. The variant rs12970134 and rs17782313 did not influence food intake or the presence of BE. The variant rs17782313 is associated with an increased risk of hypertriglyceridemia in obese children and adolescents.

Are obesity risk genes associated with binge eating in adolescence?

OBJECTIVE

Cognitions and behaviors characteristic of binge eating are associated with a polymorphism in the FTO gene, robustly related to body mass index (BMI) and obesity risk. We investigated the association between binge eating and the individual and combined effect of 32 SNPs robustly associated with BMI in a population-based sample. We hypothesized that higher BMI and binge eating might share a common genetic etiology.

METHODS

Binge eating was assessed in adolescents from the Avon Longitudinal Study of Parents and Children at age 14 (n = 5,958) and 16 years (n = 4,948). We tested associations between 32 BMI-related SNPs and binge eating in crude and BMI-, age-, and gender-adjusted regression models.

RESULTS

Crude analyses showed an association between binge eating and rs1558902 (FTO) that persisted after adjustment for BMI (OR = 1.20, P = 8 × 10(-3) ). A weighted allelic score consisting of all 32 BMI-related SNPs was associated with binge eating (P = 8 × 10(-4) ); this association attenuated (P = 0.08) when rs1558902 was removed from the weighted allelic score.

CONCLUSIONS

BMI-related genes are associated with adolescent binge eating, in particular an FTO polymorphism. Although replication is needed, our findings have biological plausibility and are consistent with a postulated effect of FTO on appetite and food intake. Future studies should aim to understand the mechanisms underlying the relationship between FTO, binge eating, and obesity.

Analysis of MC4R rs17782313, POMC rs1042571, APOE-Hha1 and AGRP rs3412352 genetic variants with susceptibility to obesity risk in North Indians

BACKGROUND

Obesity is a multi-factorial disorder influenced by genetic and environmental factors. The physiological pathways associated with obesity are complex and involve several genes.

AIM

The aim of this survey is to evaluate the association of genetic variants of melanocortin-4-receptor (MC4R), pro-opiomelanocortin (POMC), apolipoprotein E (APOE) and agouti-related protein (AGRP) with obesity in the North Indian population.

METHODS

MC4R rs17782313, POMC rs1042571, APOE-Hha1 and AGRP rs3412352 polymorphisms were investigated for their association in 396 obese individuals with BMI ≥ 30 kg/m(2) and 300 healthy non-obese individuals with BMI < 30 kg/m(2). Genotyping was performed using Taqman probes and PCR-RFLP methods. Single locus logistic regression analysis was conducted using (SPSS), ver.19 and PLINK software Version 1.01 and high order genetic interactions associated with obesity risk were analysed using MDR software (version 2.3.0.2).

RESULTS

The genotypes of MC4R rs17782313, POMC rs1042571 and APOE-Hha1 were significantly associated with obese individuals (BMI ≥ 30 kg/m(2)) when compared with non-obese individuals (BMI < 30 kg/m(2)). No association of AGRP rs34123523 was seen with obesity.

CONCLUSIONS

The best interaction model for predicting obesity risk by MDR analysis was the three factor model including POMC (C > T), MC4R (T > C) and APOE (Hha1) polymorphisms. Genetic variants in MC4R, POMC and APOE genes might play significant roles in predisposing obesity (BMI ≥ 30 kg/m(2)) in the North Indian population.

Effects of genetic variants for the swine FABP3, HMGA1, MC4R, IGF2, and FABP4 genes on fatty acid composition

This study aimed to verify genetic relationships between fatty acid composition (FAC) and genotypes of several genes (FABP3, HMGA1, MC4R, IGF2, and FABP4) using pig breeds. The effects of genetic variations on FAC of the longissimus muscle were statistically significant with additive and dominance effects. The polymorphisms of FABP3 and IGF2 had the largest effects on stearic (C18:0, P=0.009) and γ-linoleic (C18:3n6, P=0.039) acids, respectively, whereas HMGA1 and FABP4 did not show significances. The analysis revealed that MC4R was significantly associated with palmitoleic acid (C16:ln7) and MUFA. Allele frequencies of the genes examined in this analysis were significantly skewed or fixed in the Korean native pig (KNP), whereas the allele frequencies of the crossbreds tended to fall between those of the purebreds except that HMGA1 and FABP4 had approximately the same allele frequencies with Duroc and KNP, respectively. The polymorphisms found in this study could be used as genetic markers in breeding programs to simultaneously change proportions of fatty acids in muscle tissues.

The association of MC4R rs17782313 polymorphism with dietary intake in Iranian adults

BACKGROUND

Malfunction in the energy homeostasis system is a major cause of developing obesity. Melanocortin-4 receptor (MC4R) plays a crucial role in this system as a key receptor. Although MC4R gene as an obesity candidate gene is associated with higher BMI, only few attempts have been carried out to understand the mechanism underlying body-weight regulation.

OBJECTIVE

The aim of this study is to investigate the association between variant rs17782313 near MC4R gene and both dietary energy and macronutrient intakes.

METHODS

An Iranian population, 400 adults aged over 22years were selected from the Iranian Multicenter Osteoporosis Study (IMOS). Genotyping for the near MC4R rs17782313 was performed by PCR-RFLP. Weight and height were measured. Dietary intake and physical activity were assessed by using validated questionnaires. Analysis was carried out in two groups with regard to BMI. Multiple linear regression models adjusted for covariates were used to examine the association between rs17782313 and dietary intake.

RESULTS

MC4R rs17782313 was associated with high energy intake (P<0.001), and low carbohydrate and protein intakes (P<0.001 and P<0.01 respectively). In addition, the significant association between variant rs17782313 and fat intake disappeared after adjusting for energy.

CONCLUSIONS

The rs17782313 variant contributes to the variety of dietary energy and energy-dense macronutrient intakes. Moreover, a novel association was suggested between this polymorphism and dietary fat intake.

A critical role for the melanocortin 4 receptor in stress-induced relapse to nicotine seeking in rats

Tobacco addiction is characterized by a lack of control over smoking and relapse after periods of abstinence. Smoking cessation leads to a dysphoric state that contributes to relapse to smoking. After the acute withdrawal phase, exposure to stressors increases the risk for relapse. Blockade of melanocortin 4 (MC4 ) receptors has anxiolytic and antidepressant-like effects in animal models. The aim of these studies was to investigate the role of MC4 receptors in the dysphoria associated with nicotine withdrawal and stress-induced reinstatement of nicotine seeking. To study stress-induced reinstatement, rats self-administered nicotine for 16 days and then nicotine seeking was extinguished by substituting saline for nicotine. Nicotine seeking was reinstated by intermittent footshock stress. The intracranial self-stimulation (ICSS) procedure was used to assess the negative mood state associated with nicotine withdrawal. Elevations in the ICSS thresholds are indicative of a dysphoric state. The selective MC4 receptor antagonists HS014 and HS024 prevented stress-induced reinstatement of extinguished nicotine seeking. Drug doses that prevented stress-induced relapse did not affect responding for food pellets, which indicates that the drugs did not induce sedation or motor impairments. In the ICSS experiments, the nicotinic acetylcholine receptor antagonist mecamylamine elevated the ICSS thresholds of the nicotine-dependent rats. Pre-treatment with HS014 or HS024 did not prevent the elevations in ICSS thresholds. These studies indicate that MC4 receptors play a critical role in stress-induced reinstatement of nicotine seeking, but these receptors may not play a role in the dysphoria associated with acute nicotine withdrawal.

Melanocortin-4 receptor modulators for the treatment of obesity: a patent analysis (2008–2014)

The central melanocortin system and particularly the melanocortin-4 receptor (MC4R) subtype, plays an important role in the regulation of body weight. The discovery of orally active MC4R agonists suitable for evaluation in human clinical trials as weight loss agents has attracted considerable interest over the past decade, but has proved challenging, in part because of cardiovascular and behavioral side effects. Currently, the only MC4R agonist in clinical trials is a peptide identified as RM-493. To avoid some of the undesirable side effects associated with MC4R activation, new pharmacological approaches for modulating the MC system have been investigated. In this article, we provide a review of the MC4R patent landscape from 2008 to 2014 and analyze the physicochemical properties of compounds described herein.

An essential role for the K+-dependent Na+/Ca2+-exchanger, NCKX4, in melanocortin-4-receptor-dependent satiety

K(+)-dependent Na(+)/Ca(2+)-exchangers are broadly expressed in various tissues, and particularly enriched in neurons of the brain. The distinct physiological roles for the different members of this Ca(2+) transporter family are, however, not well described. Here we show that gene-targeted mice lacking the K(+)-dependent Na(+)/Ca(2+)-exchanger, NCKX4 (gene slc24a4 or Nckx4), display a remarkable anorexia with severe hypophagia and weight loss. Feeding and satiety are coordinated centrally by melanocortin-4 receptors (MC4R) in neurons of the hypothalamic paraventricular nucleus (PVN). The hypophagic response of Nckx4 knock-out mice is accompanied by hyperactivation of neurons in the PVN, evidenced by high levels of c-Fos expression. The activation of PVN neurons in both fasted Nckx4 knock-out and glucose-injected wild-type animals is blocked by Ca(2+) removal and MC4R antagonists. In cultured hypothalamic neurons, melanocyte stimulating hormone induces an MC4R-dependent and sustained Ca(2+) signal, which requires phospholipase C activity and plasma membrane Ca(2+) entry. The Ca(2+) signal is enhanced in hypothalamic neurons from Nckx4 knock-out animals, and is depressed in cells in which NCKX4 is overexpressed. Finally, MC4R-dependent oxytocin expression in the PVN, a key essential step in satiety, is prevented by blocking phospholipase C activation or Ca(2+) entry. These findings highlight an essential, and to our knowledge previously unknown, role for Ca(2+) signaling in the MC4R pathway that leads to satiety, and a novel non-redundant role for NCKX4-mediated Ca(2+) extrusion in controlling MC4R signaling and feeding behavior. Together, these findings highlight a novel pathway that potentially could be exploited to develop much needed new therapeutics to tackle eating disorders and obesity.

The increase in body weight induced by lack of methyl CpG binding protein-2 is associated with altered leptin signalling in the hypothalamus

Methyl CpG binding protein-2 (MECP2) is a chromatin-remodelling factor with a dual role in gene expression. Evidence from patients carrying MECP2 mutations and from transgenic mouse models demonstrates that this protein is involved in the control of body weight. However, the mechanism for this has not been fully elucidated. To address this, we used a previously characterized Mecp2-null mouse model and found that the increase in body weight is associated with an increased amount of adipose tissue and high leptin levels. Appropriate body weight control requires the proper expression of pro-opiomelanocortin (Pomc) and agouti-related peptide (Agrp), two neuropeptides essential for satiety and appetite signals, respectively. Our results show that in the absence of Mecp2, Pomc and Agrp mRNA expression are altered, and the mice are leptin resistant. To determine the mechanism underlying the defective leptin sensing, we evaluated the expression of genes and the post-translational modifications associated with leptin signalling, which are fundamental to Pomc and Agrp transcriptional control and proper leptin response. We found a decrease in the phosphorylation level of Akt and its target protein Foxo1, which indicate an alteration in leptin-induced signal transduction. Our results demonstrate that the absence of Mecp2 disrupted body weight balance by altering post-translational modifications in leptin-signalling components that regulate Pomc and Agrp expression.

Evaluation of MC4R [rs17782313, rs17700633], AGRP [rs3412352] and POMC [rs1042571] Polymorphisms with Obesity in Northern India

OBJECTIVE

Genetic variants of the melanocortin-4 receptor gene (MC4R), agouti related protein (AGRP) and proopiomelanocortin (POMC) are reported to be associated with obesity. Therefore, the aim of this study is to examine MC4R rs17782313, MC4R rs17700633, AGRP rs3412352 and POMCrs1042571 for any association with obesity in North Indian subjects.

METHODS

The variants were investigated for association in 300 individuals with BMI ≥30 kg/m(2) and 300 healthy non-obese individuals BMI <30 kg/m(2.) The genotyping were analyzed by Taqman probes. The statistical analysis was performed by the SPSS software, ver.19 and p≤0.05 was considered statistically significant.

RESULTS

The genotypes of MC4R rs17782313 and POMC rs1042571 were significantly associated with obesity (C), (p=0.02; OR=1.7 and p=0.01; OR=1.6, respectively); however, MC4Rrs17700633 (p=0.001; OR=0.55) was associated with low risk. In addition, AGRPrs3412352 (p=0.93; OR=0.96) showed no association with obesity (BMI ≥30 kg/m(2)) in North Indian subjects.

CONCLUSION

This study provides the report about the significant association of MC4R (rs17782313) and POMC (rs1042571) with morbid obesity (BMI ≥30 kg/m(2)), but MC4R (rs17700633) and AGRP (rs34123523) did not show any association with obesity in the studied North Indian population.

Association of melanocortin 4 receptor gene variation with satiation and gastric emptying in overweight and obese adults

Melanocortin 4 receptor (MC4R) has a major role in energy homeostasis. The rs17782313 polymorphism, mapped 188 kb downstream from MC4R, has been associated with satiety, higher body mass index (BMI) and total calorie intake in adults. To assess the association of rs17782313 with gastric functions, satiation, or satiety, we studied 178 predominantly Caucasian overweight and obese people: 120 females, 58 males; mean BMI 33.4 ± 5.3 kg/m(2) (SD); age 37.7 ± 11.2 years. Quantitative traits assessed were gastric emptying (GE) of solids and liquids; fasting and postprandial gastric volume; satiation by maximum tolerated volume and 4 symptoms by 100-mm visual analog scales (VAS); and satiety by ad libitum buffet meal. Associations of genotype and quantitative traits were assessed by analysis of covariance (using gender and BMI as covariates), based on a dominant [TC (n = 72) - CC (n = 12) vs. TT (n = 94)] genetic model. rs17782313(C) was associated with postprandial satiation symptoms (median Δ total VAS 26.5 mm, p = 0.036), reduced proportion of solid GE at 2 h (median Δ 6.7 %, p = 0.008) and 4 h (median Δ 3.2 %, p = 0.006), and longer t ½ (median Δ 6 min, p = 0.034). Associations of rs17782313 with obesity may be explained by reduced satiation and GE. The role of MC4R mechanisms in satiation and gastric function deserves further study.

Paraventricular nucleus Sim1 neuron ablation mediated obesity is resistant to high fat diet

Single minded 1 (SIM1) is a transcription factor involved in brain patterning and control of energy balance. In humans, haploinsufficiency of SIM1 causes early-onset obesity. Mice deficient in the homologous gene, SIM1, also exhibit early onset obesity and increased sensitivity to a high fat diet. SIM1 is expressed in several areas of the brain implicated in control of energy balance including the paraventricular nucleus (PVN), the supraoptic nucleus (SON), the medial amygdala and nucleus of the lateral olfactory tract. We have previously shown that mice with global Sim1 neuron ablation exhibit obesity with hyperphagia as the primary defect. The PVN has a critical role in feeding and in high-fat appetite, thus, we sought to determine the effect of Sim1 neuron ablation limited to the PVN. We achieved PVN-SIM1 limited ablation through stereotactic injection of diphtheria toxin into the PVN of Sim1Cre-iDTR mice. The specificity of this ablation was confirmed by immunohistochemistry and quantitative real time PCR of the PVN, supraoptic nucleus and the amygdala. Mice with PVN Sim1 neuron ablation, similar to mice with global Sim1 neuron ablation, exhibit early onset obesity with hyperphagia as the primary defect. However, PVN-Sim1 neuron ablated mice have a decreased response to fasting-induced hyperphagia. Consistent with this decrement, PVN-Sim1 neuron ablated mice have a decreased hyperphagic response to PVN injection of agouti-related peptide (AgRP). When PVN-Sim1 neuron ablated mice are placed on a high fat diet, surprisingly, their intake decreases and they actually lose weight. When allowed ad lib access to high fat diet and normal chow simultaneously, PVN-Sim1 neuron ablated mice exhibit overall decreased intake. That is, in PVN-Sim1 neuron ablated mice, access to fat suppresses overall appetite.

Family of melanocortin receptor (MCR) genes in mammals-mutations, polymorphisms and phenotypic effects

The melanocortin receptor gene family consists of five single-exon members, which are located on autosomes. Three genes (MC2R, MC4R and MC5R) are syntenic in the human, mouse, cattle and dog genomes, while in the pig, the syntenic group comprises MC1R, MC2R and MC5R. Two genes (MC1R and MC4R) have been extensively studied due to their function in melanogenesis (MC1R) and energy control (MC4R). Conservative organisation of these genes in five mammalian species (human, mouse, cattle, pig and dog), in terms of the encoded amino acid sequence, is higher in the case of MC4R compared to MC1R. Polymorphisms of these two genes are responsible or associated with variation of pigmentation (MC1R) and adipose tissue deposition (MC4R). Polymorphic variants in MC1R, causing coat colour variation, were described in humans and domestic mammals (cattle, horse, pig, sheep, dog), as well as farm red and arctic foxes. The MC4R gene is very polymorphic in humans and it is well known that some variants cause monogenic obesity or significantly contribute to the development of polygenic obesity. Such relationships are not so evident in domestic mammals; however, at least one missense substitution (298Asp > Asn) in the porcine MC4R significantly contributes, at least in some breeds, to fat tissue accumulation, feed conversion ratio and daily weight gain. Knowledge on the phenotypic effects of polymorphisms of MC2R, MC3R and MC5R in domestic mammals is scarce, probably due to the small number of reports addressing these genes. Thus, further studies focused on these genes should be undertaken.

Melanocortin-4 receptor polymorphism rs17782313: association with obesity and eating in the absence of hunger in Chilean children

OBJECTIVE

The aim of this study was to assess the association between melanocortin-4 receptor (MC4R) rs17782313 alleles with obesity and eating behavior scores in Chilean children.

METHODS

A case-control study was conducted with 139 normal-weight and 238 obese children (ages 6-12 y). MC4R rs17782313 genotypes were determined by quantitative-polymerase chain reaction allelic-discrimination assays. Eating behavior scores were evaluated in a subset of participants using the Chilean version of the Child Eating Behavior Questionnaire (CEBQ). Additionally, five normal-weight C-allele carriers of rs17782313 were matched by sex, age, and body mass index (BMI) to five TT homozygous children to carry out the Eating in the Absence of Hunger (EAH) test.

RESULTS

The frequency of the C-allele of MC4R rs17782313 was higher in the obese group than in the control group, without achieving statistical significance (odds ratio, 1.4; 95% confidence interval, 0.8-2.4; P = 0.16). CEBQ scores of "enjoyment of food" were higher (P = 0.04) and "satiety responsiveness" were lower (P = 0.02) in children with CC genotype than in those with TT genotype matched by sex, age, and BMI. In the EAH test, all five non-obese carriers of the C-allele (three CC and two CT) showed increased sweet snack consumption compared with five matched (by sex-age-BMI) non-carriers after a preload meal, without achieving statistical significance (P = 0.06).

CONCLUSION

MC4R polymorphism rs17782313 may contribute to childhood obesity, affecting enjoyment of food, satiety responsiveness, and possibly eating in the absence of hunger.

Gene amplification and functional diversification of melanocortin 4 receptor at an extremely polymorphic locus controlling sexual maturation in the platyfish

In two swordtail species of the genus Xiphophorus, the onset of puberty has been shown to be modulated at the P locus by sequence polymorphism and gene copy-number variation affecting the type 4 melanocortin hormone receptor Mc4r. The system works through the interaction of two allelic types, one encoding wild type and the other dominant-negative receptors. We have analyzed the structure and evolution of the P locus in the platyfish Xiphophorus maculatus, where as many as nine alleles of P determining the onset of sexual maturity in males and females, fecundity in females, and adult size in males are located on both the X and Y chromosomes in a region linked to the master sex-determining locus. In this species, mc4r has been amplified to up to 10 copies on both the X and Y chromosomes through recent large serial duplications. Subsequently, mc4r paralogues have diverged considerably into many different subtypes. Certain copies have acquired new untranslated regions through genomic rearrangements, and transposable element insertions and other mutations have accumulated in promoter regions, possibly explaining observed deviations from the classical mc4r transcriptional pattern. In the mc4r-coding sequence, in-frame insertions and deletions as well as nonsense and missense mutations have generated a high diversity of Mc4r-predicted proteins. Most of these variants are expressed in embryos, adults, and/or tumors. Functional receptor characterization demonstrated major divergence in pharmacological behavior for Mc4r receptors encoded by different copies of platyfish mc4r, with differences in constitutive activity as well as binding and stimulation by hormones. The high degree of allelic and copy-number variation observed between individuals can explain the high level of polymorphism for sexual maturation, fecundity, and body size in the platyfish: multiple combinations of Mc4r variants with different biochemical properties might interact to modulate the melanocortin signaling that regulates the hypothalamus-pituitary-gonadal axis.

Variation at the melanocortin 4 receptor gene and response to weight-loss interventions in the diabetes prevention program

OBJECTIVE

To assess associations and genotype × treatment interactions for melanocortin 4 receptor (MC4R) locus variants and obesity-related traits.

DESIGN AND METHODS

Diabetes prevention program (DPP) participants (N = 3,819, of whom 3,356 were genotyped for baseline and 3,234 for longitudinal analyses) were randomized into intensive lifestyle modification (diet, exercise, weight loss), metformin or placebo control. Adiposity was assessed in a subgroup (n = 909) using computed tomography. All analyses were adjusted for age, sex, ethnicity and treatment.

RESULTS

The rs1943218 minor allele was nominally associated with short-term (6 month; P = 0.032) and long-term (2 year; P = 0.038) weight change. Eight SNPs modified response to treatment on short-term (rs17066856, rs9966412, rs17066859, rs8091237, rs17066866, rs7240064) or long-term (rs12970134, rs17066866) reduction in body weight, or diabetes incidence (rs17066829) (all Pinteraction < 0.05).

CONCLUSION

This is the first study to comprehensively assess the role of MC4R variants and weight regulation in a weight loss intervention trial. One MC4R variant was directly associated with obesity-related traits or diabetes; numerous other variants appear to influence body weight and diabetes risk by modifying the protective effects of the DPP interventions.

Taking two to tango: a role for ghrelin receptor heterodimerization in stress and reward

The gut hormone, ghrelin, is the only known peripherally derived orexigenic signal. It activates its centrally expressed receptor, the growth hormone secretagogue receptor (GHS-R1a), to stimulate food intake. The ghrelin signaling system has recently been suggested to play a key role at the interface of homeostatic control of appetite and the hedonic aspects of food intake, as a critical role for ghrelin in dopaminergic mesolimbic circuits involved in reward signaling has emerged. Moreover, enhanced plasma ghrelin levels are associated with conditions of physiological stress, which may underline the drive to eat calorie-dense "comfort-foods" and signifies a role for ghrelin in stress-induced food reward behaviors. These complex and diverse functionalities of the ghrelinergic system are not yet fully elucidated and likely involve crosstalk with additional signaling systems. Interestingly, accumulating data over the last few years has shown the GHS-R1a receptor to dimerize with several additional G-protein coupled receptors (GPCRs) involved in appetite signaling and reward, including the GHS-R1b receptor, the melanocortin 3 receptor (MC3), dopamine receptors (D1 and D2), and more recently, the serotonin 2C receptor (5-HT2C). GHS-R1a dimerization was shown to affect downstream signaling and receptor trafficking suggesting a potential novel mechanism for fine-tuning GHS-R1a receptor mediated activity. This review summarizes ghrelin's role in food reward and stress and outlines the GHS-R1a dimer pairs identified to date. In addition, the downstream signaling and potential functional consequences of dimerization of the GHS-R1a receptor in appetite and stress-induced food reward behavior are discussed. The existence of multiple GHS-R1a heterodimers has important consequences for future pharmacotherapies as it significantly increases the pharmacological diversity of the GHS-R1a receptor and has the potential to enhance specificity of novel ghrelin-targeted drugs.

Melanocortin MC(4) receptor-mediated feeding and grooming in rodents

Decades ago it was recognized that the pharmacological profile of melanocortin ligands that stimulated grooming behavior in rats was strikingly similar to that of Xenopus laevis melanophore pigment dispersion. After cloning of the melanocortin MC1 receptor, expressed in melanocytes, and the melanocortin MC4 receptor, expressed mainly in brain, the pharmacological profiles of these receptors appeared to be very similar and it was demonstrated that these receptors mediate melanocortin-induced pigmentation and grooming respectively. Grooming is a low priority behavior that is concerned with care of body surface. Activation of central melanocortin MC4 receptors is also associated with meal termination, and continued postprandial stimulation of melanocortin MC4 receptors may stimulate natural postprandial grooming behavior as part of the behavioral satiety sequence. Indeed, melanocortins fail to suppress food intake or induce grooming behavior in melanocortin MC4 receptor-deficient rats. This review will focus on how melanocortins affect grooming behavior through the melanocortin MC4 receptor, and how melanocortin MC4 receptors mediate feeding behavior. This review also illustrates how melanocortins were the most likely candidates to mediate grooming and feeding based on the natural behaviors they induced.

Association between LEPR and MC4R genes polymorphisms and composition of milk from sows of dam line

The polymorphisms of LEPR and MC4R genes are involved in appetite control mechanisms and indirectly associated with level of fat content in pig carcasses. Therefore, the aim of our study was to determine if both polymorphisms have an effect on components of colostrum and milk of sows. In our study we used gilts of two Polish breeds: Polish Landrace and Polish Large White, which belong to dam-line in Polish breeding. Colostrum and milk of sows were collected in 7, 14 and 21 day of lactation to assay solids, total protein, fat and lactose. The obtained results showed, that the observed mutation (G/A 1426 MC4R) had a significant effect mainly on the fat and solids content of colostrum. Animals with the MC4R (AA) genotype had 2.13 and 1.91 % (P ≤ 0.01) lower fat content of colostrum compared to sows with the MC4R (GG) genotype and heterozygous MC4R (AG). The presence of the MC4R (A) allele in the animals' genotype contributed to a decrease in fat and solids content of colostrum. The LEPR/HpaII mutation was found to have a considerable effect on the level of most colostrum components (fat, protein and solids) in both pig breeds. Significant decrease in the value of the colostrum components (except lactose) was observed only for animals with the allele LEPR (B). The results obtained suggest that these genes might be used in selection of dam-line pigs as genetic markers of milk quality.