Melanocortin-4 Receptor Signalling: Importance for Weight Regulation and Obesity Treatment

Antiobesity Pharmacotherapy for Patients With Genetic Obesity Due to Defects in the Leptin-Melanocortin Pathway

Lifestyle interventions are the cornerstone of obesity treatment. However, insufficient long-term effects are observed in patients with genetic obesity disorders, as their hyperphagia remains untreated. Hence, patients with genetic obesity often require additional pharmacotherapy to effectively manage and treat their hyperphagia and obesity. Recent advancements in antiobesity pharmacotherapy have expanded the range of available antiobesity medications (AOM). This includes the targeted AOM setmelanotide, approved for specific genetic obesity disorders, as well as nontargeted AOMs such as naltrexone-bupropion and glucagon-like peptide-1 analogues. Targeted AOMs have demonstrated significant weight loss, reduced obesity-related comorbidities, and improved hyperphagia and quality of life in patients with specific genetic obesity disorders. Small observational studies have shown that similar benefits from nontargeted AOMs or off-label pharmacotherapies can be achieved in patients with specific genetic obesity disorders, compared to common multifactorial obesity. In the future, novel and innovative pharmacotherapeutical options, including combination therapies and possibly gene therapy, will emerge, offering promising effects on body weight, hyperphagia, and, most importantly, quality of life for patients with a variety of genetic obesity disorders.

Deciphering deleterious missense variants in the MC4R gene in the pathogenesis of obesity

The MC4R gene plays a critical role in regulating food intake, making it an important model for studying genetic mutations that impact the protein function. This study aimed to identify the most deleterious functional and structural variants in individuals with obesity by analyzing SNPs from the NCBI dbSNP database and selecting pathogenic variants from ClinVar. Bioinformatics tools were employed to predict deleterious SNPs, and conservation analysis was performed using ConSurf. Stability predictions were made with MUpro, I-Mutant2.0, and iStable. The 3D structure of the MC4R protein was examined using YASARA view. A total of 20 out of 348 missense mutations were associated with obesity. Fifteen of these variants were predicted to be the most deleterious. Eight variants located in conserved regions were found to significantly reduce protein stability and cause structural changes (S58C, E61K, N62S, I69R, D90N, R165Q, P299H, and I316S), indicating their potential as obesity biomarkers and therapeutic targets.

Management of Obesity-Related Genetic Disorders

Obesity-related genetic disorders are marked by severe, early-onset obesity caused by mutations that disrupt key biological mechanisms regulating hunger, energy balance, and fat storage. These disorders commonly impact systems such as the hypothalamic leptin-melanocortin signaling network, which plays a crucial role in controlling appetite and body weight, mainly through the melanocortin-4 receptor (MC4R) pathway. This review explores current management strategies and emerging therapies for genetic obesity disorders, highlighting the importance of treatment approaches and expanded genetic diagnostics to improve outcomes for affected individuals.

Melanocortin-4 Receptor Antagonism Inhibits Colorectal and Anaplastic Thyroid Cancer In Vitro and In Vivo

Background/Objectives MC4R expression and its role in colorectal and anaplastic thyroid cancers, where resistance to therapy and lack of standard treatments remain significant challenges, are poorly understood. This study aimed to investigate MC4R as a potential therapeutic target in these cancers using the selective antagonist ML00253764 (ML), alone and in combination with vinorelbine (VNR) and irinotecan (or its active metabolite SN-38). Methods: Human colorectal adenocarcinoma HT-29, Caco-2, and anaplastic thyroid carcinoma 8305C cell lines were used. MC4R expression was assessed by Real-Time PCR with validated primers (Assay ID Hs00271877_s1), immunofluorescence, and Western blotting. Proliferation and apoptosis assays were conducted with ML, and synergy with VNR and SN-38 was evaluated by Combination Index and Loewe methods. ERK1/2 phosphorylation was measured using an ELISA assay. In vivo studies were conducted by injecting tumor cells into Athymic Nude-Foxn1nu mice, treated with ML, VNR, irinotecan, or their combinations. Results: MC4R expression was confirmed in all cell lines. ML treatment inhibited MC4R, producing antiproliferative and pro-apoptotic effects, with IC50 values of 7667 ± 2144.6 nM (8305C), 806.4 ± 321.8 nM (HT-29), and 2993 ± 1135.2 nM (Caco-2). In combination with VNR and SN-38, ML exhibited significant synergy in vitro and reduced tumor volume in vivo without causing weight loss or adverse effects in mice. Conclusions This study identifies ML as a promising therapeutic agent that, when combined with chemotherapy, may offer a novel strategy for treating colorectal and anaplastic thyroid cancers.

The interaction between the Circadian Locomotor Output Cycles Kaput and Melanocortin-4-receptor gene variants on obesity and parameters related to obesity

INTRODUCTION

Obesity is a multifactorial disease caused by an interaction between genetic, environmental and behavioral factors. Polymorphisms of the two genes Circadian Locomotor Output Cycles Kaput (CLOCK) rs1801260 and Melanocortin-4-receptor (MC4R) rs17782313, are associated with obesity. Knowledge is limited on the interaction between CLOCK, MC4R and obesity. The aim was to explore the interactions between the CLOCK and MC4R gene variants on markers related to obesity.

METHODS

There were 423 subjects with information on two genetic variants of two genes (CLOCK and MC4R). Their interaction was evaluated with: chronotype, sleeping duration, emotional eating, food timing, stress, dietary intake, appetite, physical activity (assessed by questionnaires), anthropometric measures of obesity (assessed by physical measurements), and also hormonal factors (assessed by ELISA). Generalized Linear Models were applied.

RESULTS

Our results revealed that significant differences were observed between the genotypes of CLOCK rs1801260 for weight, Body Mass Index (BMI), Glucagon-like peptide-1 (GLP-1), cortisol, energy, fat, sleep duration, chronotype, appetite, depression, stress, emotional eating, physical activity, breakfast, lunch, and dinner time (p˂0.05). Also, significant differences were observed between the genotypes of MC4R rs17782313 for weight, BMI, Waist Circumference (WC), Waist to Hip Ratio (WHR), ghrelin, energy, carbohydrate, fat, appetite, depression, stress, breakfast time, and emotional eating (p˂0.05). Our findings also showed significant interactions between the CLOCK (CC)∗MC4R (CT) genotypes for higher appetite, stress and CLOCK (CT)∗ MC4R (CC) genotypes for higher fat and energy intake and CLOCK (CC)∗MC4R (CC) genotypes for higher weight, BMI, energy and fat intake, appetite, emotional eating, stress, ghrelin, cortisol and lower sleep duration and GLP-1 (p˂ 0.05).

CONCLUSION

Due to the non-significance of the interaction in CLOCK (CT)∗ MC4R (CT) genotypes, it seems that the presence of a healthy arm in the CLOCK and MC4R polymorphism is necessary for the proper function of the genes. Thus, these results highlight that gene variants and their interaction should be considered in obesity assessment.

Carbocyclic setmelanotide analogs maintain biochemical potency at melanocortin 4 receptors

The melanocortin 4 receptor (MC4R) plays a critical role in satiety and energy homeostasis, and its dysregulation is implicated in numerous hyperphagic and obese disease states. Setmelanotide, a disulfide-based cyclic peptide, can rescue MC4R activity and treat obesities caused by genetic defects in MC4R signaling. But this peptide has moderate blood-brain barrier penetrance and metabolic stability, which can limit its efficacy in practice. Based on the cryo-electron microscopy structure of setmelanotide-bound MC4R, we hypothesized that replacing its lone disulfide bond with more metabolically stable and permeability-enhancing carbon-based linker groups could improve pharmacokinetic properties without abolishing activity. To test this, we used chemistry developed by our lab to prepare 11 carbocyclic (alkyl, aryl, perfluoroalkyl, and ethereal) analogs of setmelanotide and determined their biochemical potencies at MC4R in vitro. Ten analogs displayed full agonism, showing that disulfide replacement is tolerant of linkers ranging in size, rigidity, and functional groups, with heteroatom- or aryl-rich linkers displaying superior potencies.

The role of G protein-coupled receptors and their ligands in animal domestication

The domestication of plants and animals has resulted in one of the most significant cultural and socio-economical transitions in human history. Domestication of animals, including human-supervised reproduction, largely uncoupled particular animal species from their natural, evolutionary history driven by environmental and ecological factors. The primary motivations for domesticating animals were, and still are, producing food and materials (e.g. meat, eggs, honey or milk products, wool, leather products, jewelry and medication products) to support plowing in agriculture or in transportation (e.g. horse, cattle, camel and llama) and to facilitate human activities (for hunting, rescuing, therapeutic aid, guarding behavior and protecting or just as a companion). In recent years, decoded genetic information from more than 40 domesticated animal species have become available; these studies have identified genes and mutations associated with specific physiological and behavioral traits contributing to the complex genetic background of animal domestication. These breeding-altered genomes provide insights into the regulation of different physiological areas, including information on links between e.g. endocrinology and behavior, with important pathophysiological implications (e.g. for obesity and cancer), extending the interest in domestication well beyond the field. Several genes that have undergone selection during domestication and breeding encode specific G protein-coupled receptors, a class of membrane-spanning receptors involved in the regulation of a number of overarching functions such as reproduction, development, body homeostasis, metabolism, stress responses, cognition, learning and memory. Here we summarize the available literature on variations in G protein-coupled receptors and their ligands and how these have contributed to animal domestication.

Mineralocorticoid receptor activates postnatal adiposity in zebrafish lacking proopiomelanocortin

The proopiomelanocortin (Pomc)-derived peptides, including adrenocorticotropic hormone and α-melanocyte stimulating hormone (α-Msh), play both a central and a peripheral role in modulating the stress response. The central role is predominantly associated with nutrient homeostasis, while peripherally they play an important role in the synthesis of glucocorticoids (GCs) in response to stress. Pomc mutations are a major risk factor in the development of early-onset childhood obesity in humans. This is attributed primarily to their central effects on melanocortin receptor dysfunction leading to hyperphagia and reduced energy expenditure, while the peripheral mechanism contributing to obesity has largely been unexplored. Here, we tested the hypothesis that Pomc mutation-mediated adrenal insufficiency and the associated changes in GC signaling contribute to postnatal adiposity using zebrafish as a model. We generated a ubiquitous Pomc knockout zebrafish that mimicked the mammalian mutant phenotype of adrenal insufficiency and enhanced adiposity. The loss of Pomc inhibited stress-induced cortisol production and reprogrammed GC signaling by reducing glucocorticoid receptor responsiveness, whereas the mineralocorticoid receptor (Mr) signaling was enhanced. Larval feeding led to enhanced growth and adipogenesis in the Pomc mutants, and this was inhibited by eplerenone, an Mr antagonist. Altogether, our results underscore a key role for Mr signaling in early developmental adipogenesis and a possible target for therapeutic intervention for early-onset childhood obesity due to Pomc dysfunction.

A biological rhythm in the hypothalamic system links sleep-wake cycles with feeding-fasting cycles

The hypothalamus senses the appetite-regulating hormones and also coordinates the metabolic function in alignment with the circadian rhythm. This alignment is essential to maintain the physiological conditions that prevent clinically important comorbidities, such as obesity or type-2 diabetes. However, a complete model of the hypothalamus that relates food intake with circadian rhythms and appetite hormones has not yet been developed. In this work, we present a computational model that accurately allows interpreting neural activity in terms of hormone regulation and sleep-wake cycles. We used a conductance-based model, which consists of a system of four differential equations that considers the ionotropic and metabotropic receptors, and the input currents from homeostatic hormones. We proposed a logistic function that fits available experimental data of insulin hormone concentration and added it into a short-term ghrelin model that served as an input to our dynamical system. Our results show a double oscillatory system, one synchronized by light-regulated sleep-wake cycles and the other by food-regulated feeding-fasting cycles. We have also found that meal timing frequency is highly relevant for the regulation of the hypothalamus neurons. We therefore present a mathematical model to explore the plausible link between the circadian rhythm and the endogenous food clock.

The hypothalamus as the central regulator of energy balance and its impact on current and future obesity treatments

The hypothalamus is a master regulator of energy balance in the body. First-order hypothalamic neurons localized in the arcuate nucleus sense systemic signals that indicate the energy stores in the body. Through distinct projections, arcuate nucleus neurons communicate with second-order neurons, which are mostly localized in the paraventricular nucleus and in the lateral hypothalamus. The signals then proceed to third- and fourth-order neurons that activate complex responses aimed at maintaining whole-body energy homeostasis. During the last 30 years, since the identification of leptin in 1994, there has been a great advance in the unveiling of the hypothalamic and extra-hypothalamic neuronal networks that control energy balance. This has contributed to the characterization of the mechanisms by which glucagon-like peptide-1 receptor agonists promote body mass reduction and has opened new windows of opportunity for the development of drugs to treat obesity. This review presents an overview of the mechanisms involved in the hypothalamic regulation of energy balance and discusses how advancements in this field are contributing to the development of new pharmacological strategies to treat obesity.

Branched Short-Chain Fatty Acid-Rich Fermented Protein Food Improves the Growth and Intestinal Health by Regulating Gut Microbiota and Metabolites in Young Pigs

The diet in early life is essential for the growth and intestinal health later in life. However, beneficial effects of a diet enriched in branched short-chain fatty acids (BSCFAs) for infants are ambiguous. This study aimed to develop a novel fermented protein food, enriched with BSCFAs and assess the effects of dry and wet ferment products on young pig development, nutrient absorption, intestinal barrier function, and gut microbiota and metabolites. A total of 18 young pigs were randomly assigned to three groups. The dry corn gluten-wheat bran mixture (DFCGW) and wet corn gluten-wheat bran mixture (WFCGW) were utilized as replacements for 10% soybean meal in the basal diet. Our results exhibited that the WFCGW diet significantly increased the growth performance of young pigs, enhanced the expression of tight junction proteins, and regulated associated cytokines expression in the colonic mucosa. Simultaneously, the WFCGW diet led to elevated levels of colonic isobutyric and isovaleric acid, as well as the activation of GPR41 and GPR109A. Furthermore, more potential probiotics including Lactobacillus, Megasphaera, and Lachnospiraceae_ND3007_group were enriched in the WFCGW group and positively associated with the beneficial metabolites such as 5-hydroxyindole-3-acetic acid. Differential metabolite KEGG pathway analysis suggested that WFCGW might exert gut health benefits by modulating tryptophan metabolism. In addition, the WFCGW diet significantly increased ghrelin concentrations in serum and hypothalamus and promoted the appetite of young pigs by activating hypothalamic NPY/AGRP neurons. This study extends the knowledge of BSCFAs and provides a reference for the fermented food application in the infant diet.

Setmelanotide: A Melanocortin-4 Receptor Agonist for the Treatment of Severe Obesity Due to Hypothalamic Dysfunction

Obesity is a silent global pandemic. It is a condition associated with multiple risk factors and adverse outcomes that arise from the intertwined relationship between environmental factors and genetics. The genetic factors that cause phenotypic expression are variable. Monogenic obesity is a severe early-onset and rarer form of obesity, which presents with co-morbidities such as abnormal feeding behaviour. Monogenic obesity causes impaired weight regulation in the hypothalamus due to defects in the leptin-melanocortin signalling pathway. The emergence of a new therapeutic treatment, the melanocortin-4 receptor agonist setmelanotide (originally RM-493), has represented a breakthrough in the management of monogenic obesity and has raised hope in managing complex obesity. This review provides an overview of the setmelanotide trials that have taken place, as well as its mechanism of action, side effects and weight loss outcomes that led to its approval in the treatment of pro-opiomelanocortin (POMC) deficiency and proprotein convertase subtilisin/kexin type 1 (PCSK1) deficiency. It also explores setmelanotide's role in other genetic forms of obesity, such as hypothalamic obesity, Prader-Willi syndrome, Alström syndrome and other rare genetic conditions that are being investigated. This review aims to help to understand the pathophysiology of genetic obesity and aid in future treatment options for people with severe, complex genetic obesity.

Structure elucidation of a human melanocortin-4 receptor specific orthosteric nanobody agonist

The melanocortin receptor 4 (MC4R) belongs to the melanocortin receptor family of G-protein coupled receptors and is a key switch in the leptin-melanocortin molecular axis that controls hunger and satiety. Brain-produced hormones such as α-melanocyte-stimulating hormone (agonist) and agouti-related peptide (inverse agonist) regulate the molecular communication of the MC4R axis but are promiscuous for melanocortin receptor subtypes and induce a wide array of biological effects. Here, we use a chimeric construct of conformation-selective, nanobody-based binding domain (a ConfoBody Cb80) and active state-stabilized MC4R-β2AR hybrid for efficient de novo discovery of a sequence diverse panel of MC4R-specific, potent and full agonistic nanobodies. We solve the active state MC4R structure in complex with the full agonistic nanobody pN162 at 3.4 Å resolution. The structure shows a distinct interaction with pN162 binding deeply in the orthosteric pocket. MC4R peptide agonists, such as the marketed setmelanotide, lack receptor selectivity and show off-target effects. In contrast, the agonistic nanobody is highly specific and hence can be a more suitable agent for anti-obesity therapeutic intervention via MC4R.

SHU9119 and MBP10 are biased ligands at the human melanocortin-4 receptor

The melanocortin-4 receptor (MC4R), a G protein-coupled receptor, is critically involved in regulating energy homeostasis as well as modulation of reproduction and sexual function. Two peptide antagonists (SHU9119 and MBP10) were derived from the endogenous agonist α-melanocyte stimulating hormone. But their pharmacology at human MC4R is not fully understood. Herein, we performed detailed pharmacological studies of SHU9119 and MBP10 on wild-type (WT) and six naturally occurring constitutively active MC4Rs. Both ligands had no or negligible agonist activity in Gαs-cAMP signaling on WT MC4R, but stimulated extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation on WT and mutant MC4Rs. Mechanistic studies revealed that SHU9119 and MBP10 stimulated ERK1/2 signaling of MC4R by different mechanisms, with SHU9119-stimulated ERK1/2 signaling mediated by phosphatidylinositol 3-kinase (PI3K) and MBP10-initiated ERK1/2 activation through PI3K and β-arrestin. In summary, our studies demonstrated that SHU9119 and MBP10 were biased ligands for MC4R, preferentially activating ERK1/2 signaling through different mechanisms. SHU9119 acted as a biased ligand and MBP10 behaved as a biased allosteric modulator.

MC4R Variants Modulate α-MSH and Setmelanotide Induced Cellular Signaling at Multiple Levels

CONTEXT

The melanocortin-4 receptor (MC4R) plays an important role in body weight regulation. Pathogenic MC4R variants are the most common cause of monogenic obesity.

OBJECTIVE

We have identified 17 MC4R variants in adult and pediatric patients with obesity. Here we aimed to functionally characterize these variants by analyzing 4 different aspects of MC4R signaling. In addition, we aimed to analyze the effect of setmelanotide, a potent MC4R agonist, on these MC4R variants.

MATERIALS AND METHODS

Cell surface expression and α-melanocyte stimulating hormone (α-MSH)- or setmelanotide-induced cAMP response, β-arrestin-2 recruitment, and ERK activation were measured in cells expressing either wild type or variant MC4R.

RESULTS

We found a large heterogeneity in the function of these variants. We identified variants with a loss of response for all studied MC4R signaling, variants with no cAMP accumulation or ERK activation but normal β-arrestin-2 recruitment, and variants with normal cAMP accumulation and ERK activation but decreased β-arrestin-2 recruitment, indicating disrupted desensitization and signaling mechanisms. Setmelanotide displayed a greater potency and similar efficacy as α-MSH and induced significantly increased maximal cAMP responses of several variants compared to α-MSH. Despite the heterogeneity in functional response, there was no apparent difference in the obesity phenotype in our patients.

CONCLUSION

We show that these obesity-associated MC4R variants affect MC4R signaling differently yet lead to a comparable clinical phenotype. Our results demonstrate the clinical importance of assessing the effect of MC4R variants on a range of molecular signaling mechanisms to determine their association with obesity, which may aid in improving personalized treatment.

[Improved Care and Treatment Options for Patients with Hyperphagia-Associated Obesity in Bardet-Biedl Syndrome]

Bardet-Biedl syndrome (BBS) is a rare, autosomal recessive multisystem disease. The pathophysiological origin is a dysfunction of the primary cilium. Clinical symptoms are heterogeneous and variable: retinal dystrophy, obesity, polydactyly, kidney abnormalities, hypogenitalism and developmental delays are the most common features. By the approval of the melanocortin 4 receptor agonist setmelanotide, a drug therapy for BBS-associated hyperphagia and obesity can be offered for the first time. Hyperphagia and severe obesity represent a considerable burden and are associated with comorbidity and increased mortality risk. Due to the limited experience with setmelanotide in BBS, a viable comprehensive therapy concept is to be presented. Therapy decision and management should be conducted in expert centers. For best therapeutic effects with setmelanotide adequate information of the patient about the modalities of the therapy (daily subcutaneous injection) and possible adverse drug events are necessary. Furthermore, the involvement of psychologists, nutritionists and nursing services (support for the application) should be considered together with the patient. The assessment of therapy response should be carried out with suitable outcome measurements and centrally reported to an adequate register.

Melanocortin-4 Receptor PLC Activation Is Modulated by an Interaction with the Monocarboxylate Transporter 8

The melanocortin-4 receptor (MC4R) is a key player in the hypothalamic leptin-melanocortin pathway that regulates satiety and hunger. MC4R belongs to the G protein-coupled receptors (GPCRs), which are known to form heterodimers with other membrane proteins, potentially modulating receptor function or characteristics. Like MC4R, thyroid hormones (TH) are also essential for energy homeostasis control. TH transport across membranes is facilitated by the monocarboxylate transporter 8 (MCT8), which is also known to form heterodimers with GPCRs. Based on the finding in single-cell RNA-sequencing data that both proteins are simultaneously expressed in hypothalamic neurons, we investigated a putative interplay between MC4R and MCT8. We developed a novel staining protocol utilizing a fluorophore-labeled MC4R ligand and demonstrated a co-localization of MC4R and MCT8 in human brain tissue. Using in vitro assays such as BRET, IP1, and cAMP determination, we found that MCT8 modulates MC4R-mediated phospholipase C activation but not cAMP formation via a direct interaction, an effect that does not require a functional MCT8 as it was not altered by a specific MCT8 inhibitor. This suggests an extended functional spectrum of MCT8 as a GPCR signaling modulator and argues for the investigation of further GPCR-protein interactions with hitherto underrepresented physiological functions.

The Association between Obesity Susceptibility and Polymorphisms of MC4R, SH2B1, and NEGR1 in Tibetans

Background: A high-altitude environment has inhibitory effects on obesity. Tibetans are not a high-risk population for obesity, but there are still obese individuals within that population. Obesity has become a worldwide health problem, and previous studies have found that obesity is closely associated with hereditary factors. Few studies have investigated obesity in Tibetans, and the association between gene polymorphisms and obesity in Tibetans remains unclear. Methods: Our study investigated the fat mass of 140 native Tibetan individuals (70 men and 70 women) from Lhasa and analyzed the associations between polymorphisms of melanocortin 4 receptor (MC4R), Src homology 2B adapter protein 1 (SH2B1), and neuronal growth regulator 1 (NEGR1) and obesity. Result: Among Tibetan individuals, there were differences in genotype and allele frequencies between those in the obesity group and those in the healthy group at MC4R (rs17782313) and SH2B1 (rs7359397). The polymorphisms of MC4R (rs17782313) were associated with fat mass and obesity in Tibetan men and women, and there was an association between SH2B1 (rs7359397) polymorphisms and fat mass and obesity in Tibetan men. However, polymorphisms of NEGR1 (rs3101336) were not associated with fat mass or obesity in Tibetan individuals. Conclusion: Among Tibetan individuals, polymorphisms of MC4R (rs17782313) and SH2B1 (rs7359397) were associated with obesity, but NEGR1 (rs3101336) polymorphisms were not associated with obesity.

Setmelanotide for the treatment of acquired hypothalamic obesity: a phase 2, open-label, multicentre trial

BACKGROUND

Hypothalamic obesity resulting from hypothalamic damage might affect melanocortin signalling. We investigated the melanocortin-4 receptor agonist setmelanotide for treatment of hypothalamic obesity.

METHODS

This phase 2, open-label, multicentre trial was done in five centres in the USA. Eligible patients were aged between 6 and 40 years with obesity and history of hypothalamic injury or diagnosis of a non-malignant tumour affecting the hypothalamus that was treated with surgery, chemotherapy, or radiation. Setmelanotide was titrated up to a dose of 3·0 mg and administered subcutaneously once a day for a total duration of 16 weeks. The primary endpoint was the proportion of patients with a reduction in BMI of at least 5% from baseline after 16 weeks, compared with a historic control rate of less than 5% in this population. The primary endpoint was analysed using the full analysis set, which includes all patients with baseline data who received at least one dose of setmelanotide. Safety was assessed in all patients who received at least one dose of study drug. This trial is registered with ClinicalTrials.gov (NCT04725240) and is complete.

FINDINGS

Between June 6, 2021, and Jan 13, 2022, 19 patients were screened for inclusion. One patient was excluded, and 18 were enrolled and received at least one dose of setmelanotide. Patients were primarily White (n=14 [78%]) and male (n=11 [61%]). Enrolled patients had a mean age of 15·0 years (SD 5·3) and a mean BMI of 38·0 kg/m2 (SD 6·5). Of 18 patients enrolled, 16 (89%) of 18 patients completed the study and met the primary endpoint of reduction in BMI of at least 5% from baseline after 16 weeks (p<0·0001). The mean reduction in BMI across all patients was 15% (SD 10). A composite proportion of patients had a clinically meaningful change (89%, 90% CI 69-98%; p<0·0001), comprising a reduction in BMI Z score of at least 0·2 points for patients younger than 18 years (92%, 68-100%; p<0·0001) and reduction in bodyweight of at least 5% for patients aged 18 years or older (80%, 34-99%; p<0·0001). Patients aged 12 years or older had a mean reduction in hunger score of 45%. Frequent adverse events included nausea (61%), vomiting (33%), skin hyperpigmentation (33%), and diarrhoea (22%). Of 14 patients who continued treatment in a long-term extension study (NCT03651765), 12 completed at least 12 months of treatment at the time of publication and had a mean change in BMI of -26% (SD 12) from index trial baseline.

INTERPRETATION

These findings support setmelanotide as a novel effective treatment of hypothalamic obesity.

FUNDING

Rhythm Pharmaceuticals.

Anorexigenic neuropeptides as anti-obesity and neuroprotective agents: exploring the neuroprotective effects of anorexigenic neuropeptides

Since 1975, the incidence of obesity has increased to epidemic proportions, and the number of patients with obesity has quadrupled. Obesity is a major risk factor for developing other serious diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Recent epidemiologic studies have defined obesity as a risk factor for the development of neurodegenerative diseases, such as Alzheimer's disease (AD) and other types of dementia. Despite all these serious comorbidities associated with obesity, there is still a lack of effective antiobesity treatment. Promising candidates for the treatment of obesity are anorexigenic neuropeptides, which are peptides produced by neurons in brain areas implicated in food intake regulation, such as the hypothalamus or the brainstem. These peptides efficiently reduce food intake and body weight. Moreover, because of the proven interconnection between obesity and the risk of developing AD, the potential neuroprotective effects of these two agents in animal models of neurodegeneration have been examined. The objective of this review was to explore anorexigenic neuropeptides produced and acting within the brain, emphasizing their potential not only for the treatment of obesity but also for the treatment of neurodegenerative disorders.

Hypothalamic POMC neuron-specific knockout of MC4R affects insulin sensitivity by regulating Kir2.1

BACKGROUND

Imbalance in energy regulation is a major cause of insulin resistance and diabetes. Melanocortin-4 receptor (MC4R) signaling at specific sites in the central nervous system has synergistic but non-overlapping functions. However, the mechanism by which MC4R in the arcuate nucleus (ARC) region regulates energy balance and insulin resistance remains unclear.

METHODS

The MC4Rflox/flox mice with proopiomelanocortin (POMC) -Cre mice were crossed to generate the POMC-MC4Rflox/+ mice. Then POMC-MC4Rflox/+ mice were further mated with MC4Rflox/flox mice to generate the POMC-MC4Rflox/flox mice in which MC4R is selectively deleted in POMC neurons. Bilateral injections of 200 nl of AAV-sh-Kir2.1 (AAV-sh-NC was used as control) were made into the ARC of the hypothalamus. Oxygen consumption, carbon dioxide production, respiratory exchange ratio and energy expenditure were measured by using the CLAMS; Total, visceral and subcutaneous fat was analyzed using micro-CT. Co-immunoprecipitation assays (Co-IP) were used to analyze the interaction between MC4R and Kir2.1 in GT1-7 cells.

RESULTS

POMC neuron-specific ablation of MC4R in the ARC region promoted food intake, impaired energy expenditure, leading to increased weight gain and impaired systemic glucose homeostasis. Additionally, MC4R ablation reduced the activation of POMC neuron, and is not tissue-specific for peripheral regulation, suggesting the importance of its central regulation. Mechanistically, sequencing analysis and Co-IP assay demonstrated a direct interaction of MC4R with Kir2.1. Knockdown of Kir2.1 in POMC neuron-specific ablation of MC4R restored the effect of MC4R ablation on energy expenditure and systemic glucose homeostasis, indicating by reduced body weight and ameliorated insulin resistance.

CONCLUSION

Hypothalamic POMC neuron-specific knockout of MC4R affects energy balance and insulin sensitivity by regulating Kir2.1. Kir2.1 represents a new target and pathway that could be targeted in obesity.

Non-canonical G protein signaling

The original paradigm of classical - also referred to as canonical - cellular signal transduction of heterotrimeric G proteins (G protein) is defined by a hierarchical, orthograde interaction of three players: the agonist-activated G protein-coupled receptor (GPCR), which activates the transducing G protein, that in turn regulates its intracellular effectors. This receptor-transducer-effector concept was extended by the identification of regulators and adapters such as the regulators of G protein signaling (RGS), receptor kinases like βARK, or GPCR-interacting arrestin adapters that are integrated into this canonical signaling process at different levels to enable fine-tuning. Finally, the identification of atypical signaling mechanisms of classical regulators, together with the discovery of novel modulators, added a new and fascinating dimension to the cellular G protein signal transduction. This heterogeneous group of accessory G protein modulators was coined "activators of G protein signaling" (AGS) proteins and plays distinct roles in canonical and non-canonical G protein signaling pathways. AGS proteins contribute to the control of essential cellular functions such as cell development and division, intracellular transport processes, secretion, autophagy or cell movements. As such, they are involved in numerous biological processes that are crucial for diseases, like diabetes mellitus, cancer, and stroke, which represent major health burdens. Although the identification of a large number of non-canonical G protein signaling pathways has broadened the spectrum of this cellular communication system, their underlying mechanisms, functions, and biological effects are poorly understood. In this review, we highlight and discuss atypical G protein-dependent signaling mechanisms with a focus on inhibitory G proteins (Gi) involved in canonical and non-canonical signal transduction, review recent developments and open questions, address the potential of new approaches for targeted pharmacological interventions.

Gut-brain communication mediates the impact of dietary lipids on cognitive capacity

Cognitive impairment, as a prevalent symptom of nervous system disorders, poses one of the most challenging aspects in the management of brain diseases. Lipids present in the cell membranes of all neurons within the brain and dietary lipids can regulate the cognition and memory function. In recent years, the advancements in gut microbiome research have enabled the exploration of dietary lipids targeting the gut-brain axis as a strategy for regulating cognition. This present review provides an in-depth overview of how lipids modulate cognition via the gut-brain axis depending on metabolic, immune, neural and endocrine pathways. It also comprehensively analyzes the effects of diverse lipids on the gut microbiota and intestinal barrier function, thereby affecting the central nervous system and cognitive capacity. Moreover, comparative analysis of the positive and negative effects is presented between beneficial and detrimental lipids. The former encompass monounsaturated fatty acids, short-chain fatty acids, omega-3 polyunsaturated fatty acids, phospholipids, phytosterols, fungal sterols and bioactive lipid-soluble vitamins, as well as lipid-derived gut metabolites, whereas the latter (detrimental lipids) include medium- or long-chain fatty acids, excessive proportions of n-6 polyunsaturated fatty acids, industrial trans fatty acids, and zoosterols. To sum up, the focus of this review is on how gut-brain communication mediates the impact of dietary lipids on cognitive capacity, providing a novel theoretical foundation for promoting brain cognitive health and scientific lipid consumption patterns.

Combined transcriptome and metabolome analysis reveals breed-specific regulatory mechanisms in Dorper and Tan sheep

BACKGROUND

Dorper and Tan sheep are renowned for their rapid growth and exceptional meat quality, respectively. Previous research has provided evidence of the impact of gut microbiota on breed characteristics. The precise correlation between the gastrointestinal tract and peripheral organs in each breed is still unclear. Investigating the metabolic network of the intestinal organ has the potential to improve animal growth performance and enhance economic benefits through the regulation of intestinal metabolites.

RESULTS

In this study, we identified the growth advantage of Dorper sheep and the high fat content of Tan sheep. A transcriptome study of the brain, liver, skeletal muscle, and intestinal tissues of both breeds revealed 3,750 differentially expressed genes (DEGs). The genes PPARGC1A, LPL, and PHGDH were found to be highly expressed in Doper, resulting in the up-regulation of pathways related to lipid oxidation, glycerophospholipid metabolism, and amino acid anabolism. Tan sheep highly express the BSEP, LDLR, and ACHE genes, which up-regulate the pathways involved in bile transport and cholesterol homeostasis. Hindgut content analysis identified 200 differentially accumulated metabolites (DAMs). Purines, pyrimidines, bile acids, and fatty acid substances were more abundant in Dorper sheep. Based on combined gene and metabolite analyses, we have identified glycine, serine, and threonine metabolism, tryptophan metabolism, bile secretion, cholesterol metabolism, and neuroactive ligand-receptor interaction as key factors contributing to the differences among the breeds.

CONCLUSIONS

This study indicates that different breeds of sheep exhibit unique breed characteristics through various physiological regulatory methods. Dorper sheep upregulate metabolic signals related to glycine, serine, and threonine, resulting in an increase in purine and pyrimidine substances. This, in turn, promotes the synthesis of amino acids and facilitates body development, resulting in a faster rate of weight gain. Tan sheep accelerate bile transport, reduce bile accumulation in the intestine, and upregulate cholesterol homeostasis signals in skeletal muscles. This promotes the accumulation of peripheral and intramuscular fat, resulting in improved meat quality. This work adopts a joint analysis method of multi-tissue transcriptome and gut metabolome, providing a successful case for analyzing the mechanisms underlying the formation of various traits.

The role of genetic and epigenetic GNAS alterations in the development of early-onset obesity

BACKGROUND

GNAS (guanine nucleotide-binding protein, alpha stimulating) is an imprinted gene that encodes Gsα, the α subunit of the heterotrimeric stimulatory G protein. This subunit mediates the signalling of a diverse array of G protein-coupled receptors (GPCRs), including the melanocortin 4 receptor (MC4R) that serves a pivotal role in regulating food intake, energy homoeostasis, and body weight. Genetic or epigenetic alterations in GNAS are known to cause pseudohypoparathyroidism in its different subtypes and have been recently associated with isolated, early-onset, severe obesity. Given the diverse biological functions that Gsα serves, multiple molecular mechanisms involving various GPCRs, such as MC4R, β2- and β3-adrenoceptors, and corticotropin-releasing hormone receptor, have been implicated in the pathophysiology of severe, early-onset obesity that results from genetic or epigenetic GNAS changes.

SCOPE OF REVIEW

This review examines the structure and function of GNAS and provides an overview of the disorders that are caused by defects in this gene and may feature early-onset obesity. Moreover, it elucidates the potential molecular mechanisms underlying Gsα deficiency-induced early-onset obesity, highlighting some of their implications for the diagnosis, management, and treatment of this complex condition.

MAJOR CONCLUSIONS

Gsα deficiency is an underappreciated cause of early-onset, severe obesity. Therefore, screening children with unexplained, severe obesity for GNAS defects is recommended, to enhance the molecular diagnosis and management of this condition.

Validity of Xiphophorus fish as models for human disease

Platyfish and swordtails of the genus Xiphophorus provide a well-established model for melanoma research and have become well known for this feature. Recently, modelling approaches for other human diseases in Xiphophorus have been developed or are emerging. This Review provides a comprehensive summary of these models and discusses how findings from basic biological and molecular studies and their translation to medical research demonstrate that Xiphophorus models have face, construct and predictive validity for studying a broad array of human diseases. These models can thus improve our understanding of disease mechanisms to benefit patients.

Fat mass and obesity-associated gene (FTO) rs9939609 (A/T) polymorphism and food preference in obese people with low-calorie intake and non-obese individuals with high-calorie intake

The purpose of this study was to assess the connection between FTO rs9939609 (A/T) polymorphism and food preference. The study included 77 participants, 36 of whom were obese and had a low-calorie intake, and 41 non-obese participants with a high-calorie intake. Using a food frequency questionnaire (FFQ), the researchers calculated sweet and fatty food propensity scores. Genomic DNA was extracted from a peripheral blood sample from all participants, and FTO rs9939609 (A/T) polymorphism was assessed using standard methods. The study found no significant differences between the two groups in terms of sweet food preference (15.64 ± 10.53 in obese groups vs. 14.72 ± 7.95 in the non-obese group, p = 0.711) and fatty food preference (16.81 ± 8.84 vs. 17.27 ± 8.75; p = 0.833). Additionally, the study did not find any significant correlation between FTO rs9939609 (A/T) polymorphism and sweet and fatty food preferences in the fully adjusted models (p > 0.05). Therefore, the results of this study do not support the hypothesis of different food preferences.

Regulatory effect of NK homeobox 1 (NKX2.1) on melanocortin 4 receptor (Mc4r) promoter in Mandarin fish

The melanocortin 4 receptor (MC4R) is a G protein-coupled transporter that mediates the regulation of thyroid hormones and leptin on energy balance and food intake. However, the mechanisms of transcriptional regulation of Mc4r by thyroid hormone and leptin in fish have been rarely reported. The messenger RNA expression of Mc4r gene was significantly higher in brain than those in other tissues of mandarin fish. We analyzed the structure and function of a 2029 bp sequence of Mc4r promoter. Meanwhile, overexpression of NKX2.1 and incubation with leptin significantly increased Mc4r promoter activity, but triiodothyronine showed the opposite effect. In addition, mutations in the NKX2.1 binding site abolished not only the activation of Mc4r promoter activity by leptin but also the inhibitory effect of thyroid hormones on Mc4r promoter activity. In summary, these results suggested that thyroid hormones and leptin might regulate the transcriptional expression of Mc4r through NKX2.1.

Dimerization of melanocortin 4 receptor controls puberty onset and body size polymorphism

Xiphophorus fish exhibit a clear phenotypic polymorphism in puberty onset and reproductive strategies of males. In X. nigrensis and X. multilineatus, puberty onset is genetically determined and linked to a melanocortin 4 receptor (Mc4r) polymorphism of wild-type and mutant alleles on the sex chromosomes. We hypothesized that Mc4r mutant alleles act on wild-type alleles by a dominant negative effect through receptor dimerization, leading to differential intracellular signaling and effector gene activation. Depending on signaling strength, the onset of puberty either occurs early or is delayed. Here, we show by Förster Resonance Energy Transfer (FRET) that wild-type Xiphophorus Mc4r monomers can form homodimers, but also heterodimers with mutant receptors resulting in compromised signaling which explains the reduced Mc4r signaling in large males. Thus, hetero- vs. homo- dimerization seems to be the key molecular mechanism for the polymorphism in puberty onset and body size in male fish.

Rare genetic forms of obesity in childhood and adolescence, a comprehensive review of their molecular mechanisms and diagnostic approach

Obesity represents a major health problem in the pediatric population with an increasing prevalence worldwide, associated with cardiovascular and metabolic disorders, and due to both genetic and environmental factors. Rare forms of obesity are mostly monogenic, and less frequently due to polygenic influence. Polygenic form of obesity is usually the common obesity with single gene variations exerting smaller impact on weight and is commonly non-syndromic.Non-syndromic monogenic obesity is associated with variants in single genes typically related to the hypothalamic leptin-melanocortin signalling pathway, which plays a key role in hunger and satiety regulation, thus body weight control. Patients with these genetic defects usually present with hyperphagia and early-onset severe obesity. Significant progress in genetic diagnostic testing has recently made for early identification of patients with genetic obesity, which guarantees prompt intervention in terms of therapeutic management of the disease. What is Known: • Obesity represents a major health problem among children and adolescents, with an increasing prevalence worldwide, associated with cardiovascular disease and metabolic abnormalities, and it can be due to both genetic and environmental factors. • Non-syndromic monogenic obesity is linked to modifications in single genes usually involved in the hypothalamic leptin-melanocortin signalling pathway, which plays a key role in hunger and satiety regulation. What is New: • The increasing understanding of rare forms of monogenic obesity has provided significant insights into the genetic causes of pediatric obesity, and our current knowledge of the various genes associated with childhood obesity is rapidly expanding. • A useful diagnostic algorithm for early identification of genetic obesity has been proposed, which can ensure a prompt intervention in terms of therapeutic management of the disease and an early prevention of the development of associated metabolic conditions.

Predisposition of the Common MC4R rs17782313 Female Carriers to Elevated Obesity and Interaction with Eating Habits

The global rise in obesity is attributed to genetic predisposition interaction with an obesogenic environment. Melanocortin 4 receptor (MC4R) rs17782313 polymorphism has been linked to common obesity with varying influence across different populations. MC4R is a crucial player in the leptin proopiomelanocortin pathway that regulates weight hemostasis. We aimed to study MC4R rs17782313 and its interaction with eating behaviors on obesity predisposition in the Israeli population. Adults' (n = 5785, >18 y) genotype and anthropometric and demographic data were analyzed using logistic regression models adjusting for age, sex, T1DM, and T2DM. MC4R rs17782313 significantly predisposes to elevated obesity risk under the recessive and additive models (OR = 1.38, 95% CI: 1.1-1.72, p = 0.005 and OR = 1.1, 95% CI: 1.01-1.2, p = 0.03, respectively) adjusted for confounders (age, sex, T1DM, and T2DM). Stratification by sex demonstrated that carrying the common MC4R rs17782313 is significantly associated with an elevated predisposition to obesity under the recessive model among females only (OR = 1.41, 95% CI: 1.09-1.82, p = 0.01), with an average of 0.85 BMI increment compared with wild type and one risk allele carriers. MC4R rs17782313 significantly interacted with several eating behaviors to enhance the risk of obesity. Our findings demonstrate that MC4R rs17782313 homozygous female carriers are significantly predisposed to obesity amplified by eating behaviors.

Development of Melanocortin 4 Receptor Agonists by Exploiting Animal-Derived Macrocyclic, Disulfide-Rich Peptide Scaffolds

G protein-coupled receptors are among the most widely studied classes of drug targets. A major challenge in this field is to develop ligands that will selectively modulate a single receptor subtype to overcome the disadvantages of undesired "off target" effects caused by lack of target and thus signaling specificity. In the current study, we explored ligand design for the melanocortin 4 receptor (MC4R) since it is an attractive target for developing antiobesity drugs. Endogenously, the receptor is activated by peptide ligands, i.e., three melanocyte-stimulating hormones (α-MSH, β-MSH, and γ-MSH) and by adrenocorticotropic hormone. Therefore, we utilized a peptide drug design approach, utilizing "molecular grafting" of pharmacophore peptide sequence motifs onto a stable nature-derived peptide scaffold. Specifically, protegrin-4-like-peptide-1 (Pr4LP1) and arenicin-1-like-peptide-1 (Ar3LP1) fully activated MC4R in a functional cAMP assay with potencies of 3.7 and 1.0 nM, respectively. In a nanoluciferase complementation assay with less signal amplification, the designed peptides fully recruited mini-Gs with subnanomolar and nanomolar potencies. Interestingly, these novel peptide MC4R ligands recruited β-arrestin-2 with ∼2-fold greater efficacies and ∼20-fold increased potencies as compared to the endogenous α-MSH. The peptides were inactive at related MC1R and MC3R in a cAMP accumulation assay. These findings highlight the applicability of animal-derived disulfide-rich scaffolds to design pathway and subtype selective MC4R pharmacological probes. In the future, this approach could be exploited to develop functionally selective ligands that could offer safer and more effective obesity drugs.

Obesity Characteristics Are Poor Predictors of Genetic Mutations Associated with Obesity

BACKGROUND

The genetic contribution to obesity is substantial and may underpin the altered pathophysiology. One such pathway involves melanocortin signaling in the hypothalamus. Genetic variants can cause dysregulation in the central melanocortin pathway that can result in early onset of hyperphagia and obesity. Clinically identifying patients who are at risk of known genetic mutations is challenging. The main purpose of this study was to identify associations between the clinico-demographical characteristics and the presence of a genetic mutation associated with obesity.

METHODS

We tested samples from 238 adult patients with class III obesity between October 2021 to February 2023 using next-generation sequencing (NGS) (Illumina, NovaSeq 6000 Sequencing System). The results were classified as "no variant identified" or "variant identified".

RESULTS

107 patients (45%) had one or more gene mutation in the leptin-melanocortin pathway. All variants were heterozygous. The patients with a gene mutation had a BMI of 48.4 ± 0.8 kg/m2 (mean ± SEM), and those without a gene mutation had a BMI of 49.4 ± 0.7 kg/m2 (p = 0.4). The mean age of onset of obesity in patients with a gene mutation was 13.9 ± 1.3 years and for those without gene mutations was 11.5 ± 0.9 years (p = 0.1). The incidence of hyperphagia as a child was also not predictive (p = 0.4).

CONCLUSIONS

Gene mutations associated with obesity in patients with a BMI > 40 kg/m2 are common. However, a patient's BMI, age of onset of obesity, or age of onset of hyperphagia did not help to differentiate which patients may be more likely to have genetic mutations associated with obesity.

Bridging Energy Need and Feeding Behavior: The Impact of eIF2α Phosphorylation in AgRP Neurons

Eukaryotic translation initiation factor 2α (eIF2α) is a key mediator of the endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR). In mammals, eIF2α is phosphorylated by overnutrition-induced ER stress and is related to the development of obesity. Here, we studied the function of phosphorylated eIF2α (p-eIF2α) in agouti-related peptide (AgRP) neurons using a mouse model (AgRPeIF2αA/A) with an AgRP neuron-specific substitution from Ser 51 to Ala in eIF2α, which impairs eIF2α phosphorylation in AgRP neurons. These AgRPeIF2αA/A mice had decreases in starvation-induced AgRP neuronal activity and food intake and an increased responsiveness to leptin. Intriguingly, impairment of eIF2α phosphorylation produced decreases in the starvation-induced expression of UPR and autophagy genes in AgRP neurons. Collectively, these findings suggest that eIF2α phosphorylation regulates AgRP neuronal activity by affecting intracellular responses such as the UPR and autophagy during starvation, thereby participating in the homeostatic control of whole-body energy metabolism.

ARTICLE HIGHLIGHTS

This study examines the impact of eukaryotic translation initiation factor 2α (eIF2α) phosphorylation, triggered by an energy deficit, on hypothalamic AgRP neurons and its subsequent influence on whole-body energy homeostasis. Impaired eIF2α phosphorylation diminishes the unfolded protein response and autophagy, both of which are crucial for energy deficit-induced activation of AgRP neurons. This study highlights the significance of eIF2α phosphorylation as a cellular marker indicating the availability of energy in AgRP neurons and as a molecular switch that regulates homeostatic feeding behavior.

Metabolic and feeding adjustments during pregnancy

Eating behaviours are determined by the integration of interoceptive and environmental inputs. During pregnancy, numerous physiological adaptations take place in the maternal organism to provide an adequate environment for embryonic growth. Among them, whole-body physiological remodelling directly influences eating patterns, commonly causing notable taste perception alterations, food aversions and cravings. Recurrent food cravings for and compulsive eating of highly palatable food can contribute to the development and maintenance of gestational overweight and obesity with potential adverse health consequences for the offspring. Although much is known about how maternal eating habits influence offspring health, the mechanisms that underlie changes in taste perception and food preference during pregnancy (which guide and promote feeding) are only just starting to be elucidated. Given the limited and diffuse understanding of the neurobiology of gestational eating patterns, the aim of this Review is to compile, integrate and discuss the research conducted on this topic in both experimental models and humans. This article sheds light on the mechanisms that drive changes in female feeding behaviours during distinct physiological states. Understanding these processes is crucial to improve gestational parent health and decrease the burden of metabolic and food-related diseases in future generations.

Structural insights into ligand recognition and subtype selectivity of the human melanocortin-3 and melanocortin-5 receptors

Members of the melanocortin receptor (MCR) family that recognize different melanocortin peptides mediate a broad spectrum of cellular processes including energy homeostasis, inflammation and skin pigmentation through five MCR subtypes (MC1R-MC5R). The structural basis of subtype selectivity of the endogenous agonist γ-MSH and non-selectivity of agonist α-MSH remains elusive, as the two agonists are highly similar with a conserved HFRW motif. Here, we report three cryo-electron microscopy structures of MC3R-G_s in complex with γ-MSH and MC5R-G_s in the presence of α-MSH or a potent synthetic agonist PG-901. The structures reveal that α-MSH and γ-MSH adopt a "U-shape" conformation, penetrate into the wide-open orthosteric pocket and form massive common contacts with MCRs via the HFRW motif. The C-terminus of γ-MSH occupies an MC3R-specific complementary binding groove likely conferring subtype selectivity, whereas that of α-MSH distances itself from the receptor with neglectable contacts. PG-901 achieves the same potency as α-MSH with a shorter length by rebalancing the recognition site and mimicking the intra-peptide salt bridge in α-MSH by cyclization. Solid density confirmed the calcium ion binding in MC3R and MC5R, and the distinct modulation effects of divalent ions were demonstrated. Our results provide insights into ligand recognition and subtype selectivity among MCRs, and expand the knowledge of signal transduction among MCR family members.

Neuroendocrine Effects on the Risk of Metabolic Syndrome in Children

The endocrine and nervous systems reciprocally interact to manage physiological individual functions and homeostasis. The nervous system modulates hormone release through the hypothalamus, the main cerebrally specialized structure of the neuroendocrine system. The hypothalamus is involved in various metabolic processes, administering hormone and neuropeptide release at different levels. This complex activity is affected by the neurons of various cerebral areas, environmental factors, peripheral organs, and mediators through feedback mechanisms. Therefore, neuroendocrine pathways play a key role in metabolic homeostasis control, and their abnormalities are associated with the development of metabolic syndrome (MetS) in children. The impaired functioning of the genes, hormones, and neuropeptides of various neuroendocrine pathways involved in several metabolic processes is related to an increased risk of dyslipidaemia, visceral obesity, insulin resistance, type 2 diabetes mellitus, and hypertension. This review examines the neuroendocrine effects on the risk of MetS in children, identifying and underlying several conditions associated with neuroendocrine pathway disruption. Neuroendocrine systems should be considered in the complex pathophysiology of MetS, and, when genetic or epigenetic mutations in "hot" pathways occur, they could be studied for new potential target therapies in severe and drug-resistant paediatric forms of MetS.

Genetic Contributors to Obesity

Genetic forms of obesity contribute to ∼7% of severe obesity in children and adolescents. The exact global prevalence of monogenic and syndromic forms of obesity is not well established, most likely due to missed or delayed diagnosis. The challenge in determining the prevalence can be attributed to the lack of consensus on identifying and evaluating symptoms of genetic defects in a timely manner and hence a vastly undertested patient population. Further large-scale and long-term studies are needed to advance the understanding of this unique phenotype of obesity and effective treatment options."

The Melanocortin System: A Promising Target for the Development of New Antidepressant Drugs

Major depression is one of the most prevalent mental disorders, causing significant human suffering and socioeconomic loss. Since conventional antidepressants are not sufficiently effective, there is an urgent need to develop new antidepressant medications. Despite marked advances in the neurobiology of depression, the etiology and pathophysiology of this disease remain poorly understood. Classical and newer hypotheses of depression suggest that an imbalance of brain monoamines, dysregulation of the hypothalamic-pituitary-adrenal axis (HPAA) and immune system, or impaired hippocampal neurogenesis and neurotrophic factors pathways are cause of depression. It is assumed that conventional antidepressants improve these closely related disturbances. The purpose of this review was to discuss the possibility of affecting these disturbances by targeting the melanocortin system, which includes adrenocorticotropic hormone-activated receptors and their peptide ligands (melanocortins). The melanocortin system is involved in the regulation of various processes in the brain and periphery. Melanocortins, including peripherally administered non-corticotropic agonists, regulate HPAA activity, exhibit anti-inflammatory effects, stimulate the levels of neurotrophic factors, and enhance hippocampal neurogenesis and neurotransmission. Therefore, endogenous melanocortins and their analogs are able to complexly affect the functioning of those body’s systems that are closely related to depression and the effects of antidepressants, thereby demonstrating a promising antidepressant potential.

Next-generation sequencing of 12 obesity genes in a Portuguese cohort of patients with overweight and obesity

We examined 12 monogenic obesity genes in 72 Portuguese individuals with overweight and obesity (class 1 and class 2), some of which with suspected genetic obesity, to identify known or unknown potential obesity variants. Genomic DNA was analyzed for variants in genes LEP, LEPR, MC4R, POMC, PCSK1, BDNF, NTRK2, SIM1, SH2B1, UCP3, GCG and ADCY3 through next generation sequencing (NGS). The impact of the rare variants was investigated in the ClinVar database and using in silico tools for prediction of pathogenicity. Four potential pathogenic missense variants were detected at the heterozygous state in five individuals: two in the ADCY3 gene, NM_004036.5:c.1153G > A (p.Val385Ile) (rs756783003) and NM_004036.5:c.1222G > A (p.Gly408Arg) (rs201606553), one in gene SH2B1, NM_001145795.1:c.127C > A (p.Arg43Ser) (rs547678855), and the fourth in gene POMC NM_000939.4:c.706C > G (p.Arg236Gly) (rs28932472), which was found in two individuals. Moreover, six rare variants near splicing sites were also identified, as well as eight rare synonymous variants. In summary, some potential pathogenic rare missense variants were identified, two of them in ADCY3 gene, the most recently identified gene as having a role in monogenic obesity. Further analysis should be performed to confirm the clinical relevance of these variants.

The Genetic Basis of Childhood Obesity: A Systematic Review

Overweight and obesity in childhood and adolescence represents one of the most challenging public health problems of our century owing to its epidemic proportions and the associated significant morbidity, mortality, and increase in public health costs. The pathogenesis of polygenic obesity is multifactorial and is due to the interaction among genetic, epigenetic, and environmental factors. More than 1100 independent genetic loci associated with obesity traits have been currently identified, and there is great interest in the decoding of their biological functions and the gene-environment interaction. The present study aimed to systematically review the scientific evidence and to explore the relation of single-nucleotide polymorphisms (SNPs) and copy number variants (CNVs) with changes in body mass index (BMI) and other measures of body composition in children and adolescents with obesity, as well as their response to lifestyle interventions. Twenty-seven studies were included in the qualitative synthesis, which consisted of 7928 overweight/obese children and adolescents at different stages of pubertal development who underwent multidisciplinary management. The effect of polymorphisms in 92 different genes was assessed and revealed SNPs in 24 genetic loci significantly associated with BMI and/or body composition change, which contribute to the complex metabolic imbalance of obesity, including the regulation of appetite and energy balance, the homeostasis of glucose, lipid, and adipose tissue, as well as their interactions. The decoding of the genetic and molecular/cellular pathophysiology of obesity and the gene-environment interactions, alongside with the individual genotype, will enable us to design targeted and personalized preventive and management interventions for obesity early in life.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

Genetic Obesity-Causes and Treatments

Genetic abnormalities are responsible for up to 70% of severe, early onset obesity. With recent advances in genetic testing, more individuals with genetic etiology of excessive weight are being identified. However, treatment will need to be individualized based on the cause and underlying pathophysiology. Several treatment options are being investigated, and there are several treatment options now commercially available for some of these genetic conditions. [Pediatr Ann. 2023;52(2):e57-e61.].

Functional alterations of two novel MC4R mutations found in Argentinian pediatric patients with early onset obesity

Loss-of-function mutations in melanocortin-4 receptor (MC4R) are the most common cause of monogenic obesity, a severe type of early-onset obesity. Our aim was to determine the prevalence of MC4R mutations in a cohort of 97 Argentinian children with early-onset obesity. We found two novel mutations (p.V52E and p.G233S) and estimated a prevalence of 2.1%. We investigated the pathogenicity of mutations in HEK293T cells expressing wild-type or mutant MC4R and found that both mutants exhibited reduced plasma membrane expression and altered agonist-induced cAMP responses, with no changes in basal activity. Besides, MC4R G233S mutant demonstrated an altered agonist-dependent inhibition of voltage-gated calcium channels type 2.2. Results using a Gα_s protein inhibitor suggest that the G233S mutation could be recruiting a different G-protein signaling pathway. The identification of new mutations in MC4R and characterization of their functional impact provide tools for the diagnosis and treatment of monogenic obesity.

The effect of gender and obesity in modulating cross-bridge function in cardiac muscle fibers

The effect of obesity on cross-bridge (CB) function was investigated in mice lacking functional Melanocortin-4 Receptor (MC4R^-/-), the loss of which causes dilated cardiomyopathy (DCM) in humans and mice. Skinned cardiac muscle fibers from male and female mice were used, and activated in the presence of Ca²⁺. To characterize CB kinetics, we changed the length of fibers in sinewaves (15 frequencies: 1‒187 Hz) at a small amplitude (0.2%L₀), studied concomitant tension transients, and deduced the kinetic constants of the CB cycle from the ATP and Pi effects. In males, active tension and stiffness during full activation and rigor were ~ 1.5X in WT compared to MC4R^-/- mice. This effect was not observed in females. We also observed that ATP binding and subsequent CB detachment steps were not altered by the mutation/gender. The equilibrium constant of the force generation step (K₄) and Pi release step (association constant: K₅) were not affected by the mutation, but there was a gender difference in WT mice: K₄ and K₅ were ~ 2.2X in males than in females. Concomitantly, the forward rate constant (r₄) and backward rate constant (r_-4) of the force generation step were 1.5-2.5X in muscles from female MC4R^-/- mice relative to male MC4R^-/- mice. However, these effects did not cause a significant difference in CB distributions among six CB states. In both genders, Ca²⁺ sensitivity decreased slightly (0.12 pCa unit) in mutants. We conclude that the CB functions are differentially affected both by obesity induced in the absence of functional MC4R^-/- and gender.

Evaluation of Pharmacological Rescue of Melanocortin-4 Receptor Nonsense Mutations by Aminoglycoside

The melanocortin-4 receptor (MC4R) is critical for central satiety regulation, therefore presenting a potent target for pharmacological obesity treatment. Melanocortin-4 receptor mutations prevalently cause monogenetic obesity. A possibility of overcoming stop mutations is aminoglycoside-mediated translational readthrough. Promising results were achieved in COS-7 cells, but data for human cell systems are still missing, so uncertainty surrounds this potential treatment. In transfected HEK-293 cells, we tested whether translational readthrough by aminoglycoside Geneticin combined with high-affinity ligand setmelanotide, which is effective in proopiomelanocortin or leptin receptor deficiency patients, is a treatment option for affected patients. Five MC4R nonsense mutants (W16X, Y35X_D37V, E61X, W258X, Q307X) were investigated. Confocal microscopy and cell surface expression assays revealed the importance of the mutations’ position within the MC4R. N-terminal mutants were marginally expressed independent of Geneticin treatment, whereas mutants with nonsense mutations in transmembrane helix 6 or helix 8 showed wild-type-like expression. For functional analysis, G_s and G_q/11 signaling were measured. N-terminal mutants (W16X, Y35X_D37V) showed no cAMP formation after challenge with alpha-MSH or setmelanotide, irrespective of Geneticin treatment. Similarly, G_s activation was almost impossible in W258X and Q307X with wild-type-like cell surface expression. Results for G_q/11 signaling were comparable. Based on our data, this approach improbably represents a therapeutic option.

Guidelines for treating child and adolescent obesity: A systematic review

Obesity is a chronic disease that compromises the physical and mental health of an increasing proportion of children globally. In high-income countries, prevalence of paediatric obesity is increasing faster in those from marginalised populations such as low-income households, suggesting the disease as one that is largely systemic. Appropriate treatment should be prioritised in these settings to prevent the development of complications and co-morbidities and manage those that already exist. An array of clinical practice guidelines are available for managing overweight and obesity in children and adolescents, but no systematic review has yet compared their quality or synthesised their recommendations. We aimed to narratively review clinical practice guidelines published in English for treating child and adolescent obesity, to identify the highest quality guidelines, and assess similarities, conflicts, and gaps in recommendations. We systematically searched academic databases and grey literature for guidelines published. We used the AGREE II tool to assess the quality, and identified nine high quality guidelines for inclusion in a narrative review of recommendations. Guidelines predominantly recommended the delivery of multi-component behaviour-change interventions aimed at improving nutrition and physical activity. Treatment outcomes were generally focussed on weight, with less emphasis on managing complications or improving quality-of-life. There was no evidence-based consensus on the best mode of delivery, setting, or treatment format. The guidelines rarely included recommendations for addressing the practical or social barriers to behaviour change, such as cooking skills or supervised physical activity. There is insufficient evidence to evaluate pharmaceutical and surgical interventions in children, and these were generally not recommended. It should be noted that this review addressed documents published in English only, and therefore the included guidelines were applicable predominantly to high-resource settings.

The promise of new anti-obesity therapies arising from knowledge of genetic obesity traits

Obesity is a multifactorial and complex disease that often manifests in early childhood with a lifelong burden. Polygenic and monogenic obesity are driven by the interaction between genetic predisposition and environmental factors. Polygenic variants are frequent and confer small effect sizes. Rare monogenic obesity syndromes are caused by defined pathogenic variants in single genes with large effect sizes. Most of these genes are involved in the central nervous regulation of body weight; for example, genes of the leptin-melanocortin pathway. Clinically, patients with monogenic obesity present with impaired satiety, hyperphagia and pronounced food-seeking behaviour in early childhood, which leads to severe early-onset obesity. With the advent of novel pharmacological treatment options emerging for monogenic obesity syndromes that target the central melanocortin pathway, genetic testing is recommended for patients with rapid weight gain in infancy and additional clinical suggestive features. Likewise, patients with obesity associated with hypothalamic damage or other forms of syndromic obesity involving energy regulatory circuits could benefit from these novel pharmacological treatment options. Early identification of patients affected by syndromic obesity will lead to appropriate treatment, thereby preventing the development of obesity sequelae, avoiding failure of conservative treatment approaches and alleviating stigmatization of patients and their families.

Hypothalamic effective connectivity at rest is associated with body weight and energy homeostasis

Hunger and satiety drive eating behaviours via changes in brain function. The hypothalamus is a central component of the brain networks that regulate food intake. Animal research parsed the roles of the lateral hypothalamus (LH) and medial hypothalamus (MH) in hunger and satiety, respectively. Here, we examined how hunger and satiety change information flow between human LH and MH brain networks, and how these interactions are influenced by body mass index (BMI). Forty participants (16 overweight/obese) underwent two resting-state functional MRI scans while being fasted and sated. The excitatory/inhibitory influence of information flow between the MH and LH was modelled using spectral dynamic causal modelling. Our results revealed two core networks interacting across homeostatic state and weight: subcortical bidirectional connections between the LH, MH and the substantia nigra pars compacta (prSN), and cortical top-down inhibition from fronto-parietal and temporal areas. During fasting, we found higher inhibition between the LH and prSN, whereas the prSN received greater top-down inhibition from across the cortex. Individuals with higher BMI showed that these network dynamics occur irrespective of homeostatic state. Our findings reveal fasting affects brain dynamics over a distributed hypothalamic-midbrain-cortical network. This network is less sensitive to state-related fluctuations among people with obesity.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.