Targeting the central melanocortin system for the treatment of metabolic disorders

Modulated regulation of the stress-feeding-growth neuroendocrine cascade in Chinese sea bass (Lateolabrax maculatus) under temperature and salinity changes

Temperature and salinity are among the most important factors affecting food-intake, metabolism, and growth of aquatic animals through their neuroendocrine systems. However, how the regulation of feeding, metabolism and growth are integrated under thermo-saline interaction is still unclear. In this study, modulated transcriptomic responses to temperature and salinity changes were investigated in Chinese sea bass (Lateolabrax maculatus), the economically important fish in East Asia that can adapt to diverse thermo-saline environments. L. maculatus were acclimated at different temperatures (14 °C, 21 °C, 28 °C) and salinities (freshwater and seawater) for 30 days, and their growth rate was better at 21 °C than 14 °C/28 °C (2.76-3.22 times), with mild difference between seawater and freshwater. An interaction between temperature and salinity on L. maculatus growth was detected, and low salinity (0 ppt) may mitigate the temperature (28 °C) effect. Weighted gene co-expression network analysis for L. maculatus brain transcriptomes identified growth-related temperature-salinity responsive modules, revealing the neuroendocrine gene cascade for stress-feeding-growth functions in L. maculatus. Specifically, stress-induced heat shock proteins (hspe1 and hsp30l) may stimulate the hypothalamic-pituitary-interrenal (HPI) axis (crhb and pomc), further activate anorexic genes (cart and prlh) and growth inhibiting somatostatin (sst), which was further verified through both in vitro brain culture and individual feeding test. These results revealed modulated regulation of the stress-feeding-growth cascade in L. maculatus under thermo-saline changes, which may regulate feeding behavior and ultimately control growth. These findings may provide vital guidance for the development of fast-growing L. maculatus in diverse thermo-saline environments like seawater cages, freshwater ponds, or even alkaline waters.

High-resolution deep mutational scanning of the melanocortin-4 receptor enables target characterization for drug discovery

Deep Mutational Scanning (DMS) is an emerging method to systematically test the functional consequences of thousands of sequence changes to a protein target in a single experiment. Because of its utility in interpreting both human variant effects and protein structure-function relationships, it holds substantial promise to improve drug discovery and clinical development. However, applications in this domain require improved experimental and analytical methods. To address this need, we report novel DMS methods to precisely and quantitatively interrogate disease-relevant mechanisms, protein-ligand interactions, and assess predicted response to drug treatment. Using these methods, we performed a DMS of the melanocortin-4 receptor (MC4R), a G-protein-coupled receptor (GPCR) implicated in obesity and an active target of drug development efforts. We assessed the effects of >6600 single amino acid substitutions on MC4R's function across 18 distinct experimental conditions, resulting in >20 million unique measurements. From this, we identified variants that have unique effects on MC4R-mediated Gαs- and Gαq-signaling pathways, which could be used to design drugs that selectively bias MC4R's activity. We also identified pathogenic variants that are likely amenable to a corrector therapy. Finally, we functionally characterized structural relationships that distinguish the binding of peptide versus small molecule ligands, which could guide compound optimization. Collectively, these results demonstrate that DMS is a powerful method to empower drug discovery and development.

Brain sensing of metabolic state regulates circulating monocytes

Changes in energy availability alter the dynamics of circulating immune cells. The existing view is that these effects are due to altered nutrient levels affecting peripheral tissue metabolism. Here, using mice and genetic approaches to manipulate the activity of distinct molecularly defined neurons, we show that the brain's perception of hunger and satiety alone is sufficient to drive these immune changes. Hunger-promoting Agouti-related peptide (AgRP) neurons in the hypothalamus were both sufficient and necessary to reduce circulating Ly6CHi classical monocytes during fasting. Mechanistically, these neurons suppressed hepatic mammalian target of rapamycin signaling via sympathetic regulation, decreasing circulating chemokine ligand 2 and monocyte numbers. AgRP neuron-induced corticosterone release and glucocorticoid receptor activation played a permissive role in this process. These changes in monocyte dynamics can occur independently of actual nutrient levels, revealing an unexpected brain-mediated control of peripheral immunity in response to perceived variation in energy state.

Dopaminergic neurons in the paraventricular hypothalamus extend the food consumption phase

Feeding behavior is controlled by various neural networks in the brain that are involved in different feeding phases: Food procurement, consumption, and termination. However, the specific neural circuits controlling the food consumption phase remain poorly understood. Here, we investigated the roles of dopaminergic neurons in the paraventricular nucleus of the hypothalamus (PVH) in the feeding behavior in mice. Our results indicated that the PVH dopaminergic neurons were critical for extending the food consumption phase and involved in the development of obesity through epigenetic mechanisms. These neurons synchronized with proopiomelanocortin neurons during consumption, were stimulated by proopiomelanocortin activation, and projected to the lateral habenula (LHb), where dopamine receptor D2 was involved in the increase in food consumption. In addition, upregulated tyrosine hydroxylase (TH) expression in PVH was associated with obesity and indispensable for obesity induction in mice lacking Dnmt3a. Taken together, our results highlight the roles of PVH dopaminergic neurons in promoting food consumption and obesity induction.

Transcriptome atlases of rat brain regions and their adaptation to diabetes resolution following gastrectomy in the Goto-Kakizaki rat

Brain regions drive multiple physiological functions through specific gene expression patterns that adapt to environmental influences, drug treatments and disease conditions. To generate a detailed atlas of the brain transcriptome in the context of diabetes, we carried out RNA sequencing in hypothalamus, hippocampus, brainstem and striatum of the Goto-Kakizaki (GK) rat model of spontaneous type 2 diabetes, which was applied to identify gene transcription adaptation to improved glycemic control following vertical sleeve gastrectomy (VSG) in the GK. Over 19,000 distinct transcripts were detected in the rat brain, including 2794 which were consistently expressed in the four brain regions. Region-specific gene expression was identified in hypothalamus (n = 477), hippocampus (n = 468), brainstem (n = 1173) and striatum (n = 791), resulting in differential regulation of biological processes between regions. Differentially expressed genes between VSG and sham operated rats were only found in the hypothalamus and were predominantly involved in the regulation of endothelium and extracellular matrix. These results provide a detailed atlas of regional gene expression in the diabetic rat brain and suggest that the long term effects of gastrectomy-promoted diabetes remission involve functional changes in the hypothalamus endothelium.

GPCRs in hypothalamic neurons and their roles in controlling food intake and metabolism

G-protein coupled receptor (GPCR) subtypes within the hypothalamus play a pivotal role in maintaining body homeostasis, particularly in the regulation of food intake and energy metabolism. This review provides an overview of classical loss and gain-of-function studies on GPCRs related to feeding and metabolism, with a focus on emerging cell-type-specific investigations. These studies reveal that diverse GPCR-expressing neuronal populations are intricately linked to feeding and energy balance. We also discuss recent findings that highlight the interaction of distinct peptide-GPCR systems in modulating complex feeding behaviors.

Orthopedia regulates melanocortin 4 receptor transcription and energy homeostasis

Disruption of hypothalamic melanocortin 4 receptors (MC4Rs) causes obesity in mice and humans. Here, we investigated the transcriptional regulation of MC4R in the hypothalamus. In mice, we show that the homeodomain transcription factor Orthopedia (OTP) is enriched in MC4R neurons in the paraventricular nucleus (PVN) of the hypothalamus and directly regulates Mc4r transcription. Deletion of Otp in PVN neurons during development or adulthood reduced Mc4r expression, causing increased food intake and obesity. In humans, four of the five carriers of rare predicted functional OTP variants in UK Biobank had obesity. To explore a causal role for human OTP variants, we generated mice with a loss-of-function OTP mutation identified in a child with severe obesity. Heterozygous knock-in mice exhibited hyperphagia and obesity, reversed by treatment with an MC4R agonist. Our findings demonstrate that OTP regulates mammalian energy homeostasis and enable the diagnosis and treatment of individuals with obesity due to OTP deficiency.

Medial hypothalamic MC3R signalling regulates energy rheostasis in adult mice

Although mammals resist both acute weight loss and weight gain, the neural circuitry mediating bi-directional defense against weight change is incompletely understood. Global constitutive deletion of the melanocortin-3-receptor (MC3R) impairs the behavioural response to both anorexic and orexigenic stimuli, with MC3R knockout mice demonstrating increased weight gain following anabolic challenges and increased weight loss following anorexic challenges (i.e. impaired energy rheostasis). However, the brain regions mediating this phenotype are not well understood. Here, we utilized MC3R floxed mice and viral injections of Cre-recombinase to selectively delete MC3R from the medial hypothalamus (MH) in adult mice. Behavioural assays were performed on these animals to test the role of MC3R in MH in the acute response to orexigenic and anorexic challenges. Complementary chemogenetic approaches were used in MC3R-Cre mice to localize and characterize the specific medial hypothalamic brain regions mediating the role of MC3R in energy homeostasis. Finally, we performed RNAscope in situ hybridization to map changes in the mRNA expression of MC3R, pro-opiomelanocortin and agouti-related peptide following energy rheostatic challenges, as well as to characterize the MC3R expressing cells in dorsal MH. Our results demonstrate that MC3R deletion in MH increases feeding and weight gain following high-fat diet feeding, and enhances the anorexic effects of semaglutide, in a sexually dimorphic manner. Furthermore, although the arcuate nucleus exerts an important role in MC3R-mediated effects on energy homeostasis, viral deletion in the dorsal MH also resulted in altered energy rheostasis, indicating that brain regions outside of the arcuate nucleus also contribute to the role of MC3R in energy rheostasis. Together, these results demonstrate that MC3R-mediated effects on energy rheostasis result from the loss of MC3R signalling in medial hypothalamic neurons and suggest an important role for dorsal-MH MC3R signalling in energy rheostasis. KEY POINTS: Melanocortin-3-receptor (MC3R) signalling regulates energy rheostasis in adult mice. Medial hypothalamus regulates energy rheostasis in adult mice. Energy rheostatic stimuli alter mRNA levels of agouti-related peptide, pro-opiomelanocortin and MC3R. Dorsal-medial hypothalamus (DMH) MC3R neurons increase locomotion and energy expenditure. MC3R cell types in DMH are sexually dimorphic.

Systematic proteome-wide Mendelian randomization to prioritize causal plasma proteins for skin cancers

Skin cancer is one of the most common cancers worldwide. Some risk factors including sun exposure and MC1R variants are recognized; however, the identification of additional genetic factors is essential for the development of novel therapeutic strategies. Here, we conducted a proteome-wide Mendelian randomization (MR) using plasma protein quantitative trait loci (pQTLs) from a published study and the UK Biobank genome-wide association study (GWAS) of skin cancers. We replicated the published result of ASIP, which was significantly associated with increased risks of basal cell carcinoma (BCC) and malignant melanoma. Moreover, we newly identified CTSS, which was significantly associated with a decreased risk of BCC. A series of replication analyses using the DeCODE pQTLs and the FinnGen GWAS, and sensitivity analyses including Steiger filtering, reverse MR, and Bayesian colocalization, supported our primary results. Our findings highlighted the possibility of prioritizing proteins for novel therapeutic or preventive targets and biomarkers for skin cancers.

Bioactive compounds regulate appetite through the melanocortin system: a review

Obesity, a significant health crisis, arises from an imbalance between energy intake and expenditure. Enhancing appetite regulation has garnered substantial attention from researchers as a novel and effective strategy for weight management. The melanocortin system, situated in the hypothalamus, is recognized as a critical node in the regulation of appetite. It integrates long-term and short-term hormone signals from the periphery as well as nutrients, forming a complex network of interacting feedback mechanisms with the gut-brain axis, significantly contributing to the regulation of energy homeostasis. Appetite regulation by bioactive compounds has been a focus of intensive research due to their favorable safety profiles and easy accessibility. These bioactive compounds, derived from a variety of plant and animal sources, modulate the melanocortin system and influence appetite and energy homeostasis through multiple pathways: central nervous system, peripheral hormones, and intestinal microbiota. Here, we review the anatomy, function, and receptors of the melanocortin system, outline the long-term and short-term regulatory hormones that act on the melanocortin system, and discuss the bioactive compounds and their mechanisms of action that exert a regulatory effect on appetite by targeting the melanocortin system. This review contributes to a better understanding of how bioactive compounds regulate appetite via the melanocortin system, thereby providing nutritional references for citizens' dietary preferences.

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.

Melanocortin-4 receptor antagonist TCMCB07 alleviates chemotherapy-induced anorexia and weight loss in rats

Cancer patients undergoing chemotherapy often experience anorexia and weight loss that substantially deteriorates overall health, reduces treatment tolerance and quality of life, and worsens oncologic outcomes. There are currently few effective therapeutic options to mitigate these side effects. The central melanocortin system, which plays a pivotal role in regulating appetite and energy homeostasis, presents a logical target for treating anorexia and weight loss. In this preclinical study, we evaluated the efficacy of TCMCB07, a synthetic antagonist of the melanocortin-4 receptor, in mitigating anorexia and weight loss in several rat models of chemotherapy: cisplatin, 5-fluorouracil, cyclophosphamide, vincristine, doxorubicin, and a combination of irinotecan and 5-fluorouracil. Our results indicate that peripheral administration of TCMCB07 improved appetite, stabilized body weight, preserved fat and heart mass, and slightly protected lean mass after multiple cycles of chemotherapy. Furthermore, combining TCMCB07 with a growth differentiation factor 15 antibody enhanced treatment effectiveness. Similar effects from TCMCB07 treatment were observed in a rat tumor model following combination chemotherapy. No notable adverse effects nor increased chemotherapy-related toxicities were observed with TCMCB07 treatment. These findings suggest that peripheral administration of TCMCB07 holds promise as a therapeutic approach for alleviating chemotherapy-induced anorexia and weight loss, potentially benefiting numerous patients undergoing chemotherapy.

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.

Neuroactive steroids in the neuroendocrine control of food intake, metabolism, and reproduction

Neuroactive steroids are a type of steroid hormones produced within the nervous system or in peripheral glands and then transported to the brain to exert their neuromodulatory effects. Neuroactive steroids have pleiotropic effects, that include promoting myelination, neuroplasticity, and brain development. They also regulate important physiological functions, such as metabolism, feeding, reproduction, and stress response. The homoeostatic processes of metabolism and reproduction are closely linked and mutually dependent. Reproductive events, such as pregnancy, bring about significant changes in metabolism, and metabolic status may affect reproductive function in mammals. In females, the regulation of reproduction and energy balance is controlled by the fluctuations of oestradiol and progesterone throughout the menstrual cycle. Neurosteroids play a key role in the neuroendocrine control of reproduction. The synthesis of neuroestradiol and neuroprogesterone within the brain is a crucial process that facilitates the release of GnRH and LH, which in turn, regulate the transition from oestrogen-negative to oestrogen-positive feedback. In addition to their function in the reproductive system, oestrogen has a key role in the regulation of energy homoeostasis by acting at central and peripheral levels. The oestrogenic effects on body weight homoeostasis are primarily mediated by oestrogen receptors-α (ERα), which are abundantly expressed in multiple brain regions that are implicated in the regulation of food intake, basal metabolism, thermogenesis, and brown tissue distribution. The tight interplay between energy balance and reproductive physiology is facilitated by shared regulatory pathways, namely POMC, NPY and kisspeptin neurons, which are targets of oestrogen regulation and likely participate in different aspects of the joint control of energy balance and reproductive function. The aim of this review is to present a summary of the progress made in uncovering shared regulatory pathways that facilitate the tight coupling between energy balance and reproductive physiology, as well as their reciprocal interactions and the modulation induced by neurosteroids.

Effect of early administration of tetracosactide on mortality and host response in critically ill patients requiring rescue surgery: a sensitivity analysis of the STOPSHOCK phase 3 randomized controlled trial

BACKGROUND

Undifferentiated shock is recognized as a criticality state that is transitional in immune-mediated topology for casual risk of lethal microcirculatory dysfunction. This was a sensitivity analysis of a drug (tetracosactide; TCS10) targeting melanocortin receptors (MCRs) in a phase 3 randomized controlled trial to improve cardiovascular surgical rescue outcome by reversing mortality and hemostatic disorders.

METHODS

Sensitivity analysis was based on a randomized, two-arm, multicenter, double-blind, controlled trial. The Naïve Bayes classifier was performed by density-based sensitivity index for principal strata as proportional hazard model of 30-day surgical risk mortality according to European System for Cardiac Operative Risk Evaluation inputs-outputs in 100 consecutive cases (from August to September 2013 from Emilia Romagna region, Italy). Patients included an agent-based TCS10 group (10 mg, single intravenous bolus before surgery; n = 56) and control group (n = 44) and the association with cytokines, lactate, and bleeding-blood transfusion episodes with the prior-risk log-odds for mortality rate in time-to-event was analyzed.

RESULTS

Thirty-day mortality was significantly improved in the TCS10 group vs. control group (0 vs. 8 deaths, P < 0.0001). Baseline levels of interleukin (IL)-6, IL-10, and lactate were associated with bleeding episodes, independent of TCS10 treatment [odds ratio (OR) = 1.90, 95% confidence interval (CI) 1.39-2.79; OR = 1.53, 95%CI 1.17-2.12; and OR = 2.92, 95%CI 1.40-6.66, respectively], while baseline level of Fms-like tyrosine kinase 3 ligand (Flt3L) was associated with lower bleeding rates in TCS10-treated patients (OR = 0.31, 95%CI 0.11-0.90, P = 0.03). For every 8 TCS10-treated patients, 1 bleeding case was avoided. Blood transfusion episodes were significantly reduced in the TCS10 group compared to the control group (OR = 0.32, 95%CI 0.14-0.73, P = 0.01). For every 4 TCS10-treated patients, 1 transfusion case was avoided.

CONCLUSIONS

Sensitivity index underlines the quality target product profile of TCS10 in the runway of emergency casualty care. To introduce the technology readiness level in real-life critically ill patients, further large-scale studies are required.

TRIAL REGISTRATION

European Union Drug Regulating Authorities Clinical Trials Database (EudraCT Number: 2007-006445-41 ).

Feasibility, safety, and efficacy of dietary or lifestyle interventions for hypothalamic obesity: A systematic review

BACKGROUND & AIMS

A dysfunctional hypothalamus may result in decreased feelings of satiety (hyperphagia), decreased energy expenditure, and increased fat storage as a consequence of hyperinsulinemia. Hypothalamic dysfunction may thus lead to morbid obesity and can be encountered in childhood as a consequence of congenital, genetic, or acquired disorders. There is currently no effective treatment for hypothalamic obesity (HO). However, comparable to alimentary obesity, dietary and lifestyle interventions may be considered the cornerstones of obesity treatment. We questioned the effect of dietary or lifestyle interventions for HO and systematically searched the literature for evidence on feasibility, safety, or efficacy of dietary or lifestyle interventions for childhood hypothalamic overweight or obesity.

METHODS

A systematic search was conducted in MEDLINE (including Cochrane Library), EMBASE, and CINAHL (May 2023). Studies assessing feasibility, safety, or efficacy of any dietary or lifestyle intervention in children with hypothalamic overweight or obesity, were included. Animal studies, studies on non-diet interventions, and studies with no full text available were excluded. Because the number of studies to be included was low, the search was repeated for adults with hypothalamic overweight or obesity. Risk of bias was assessed with an adapted Cochrane Risk of Bias Tool. Level of evidence was assessed using the GRADE system. Descriptive data were described, as pooled-data analysis was not possible due to heterogeneity of included studies.

RESULTS

In total, twelve studies were included, with a total number of 118 patients (age 1-19 years) of whom one with craniopharyngioma, one with ROHHAD-NET syndrome, 50 with monogenic obesity, and 66 with Prader-Willi syndrome (PWS). Four studies reported a dietary intervention as feasible. However, parents did experience difficulties with children still stealing food, and especially lowering carbohydrates was considered to be challenging. Seven studies reported on efficacy of a dietary intervention: a well-balanced restrictive caloric diet (30% fat, 45% carbohydrates, and 25% protein) and various hypocaloric diets (8-10 kcal/cm/day) were considered effective in terms of weight stabilization or decrease. No negative effect on linear growth was reported. Four studies reported on specific lifestyle interventions, of which three also included a dietary intervention. Combined dietary and lifestyle intervention resulted in decreased BMI, although BMI returned to baseline values on long-term. One additional study was identified in adults after brain trauma and showed a significant reduction in BMI in one out of eight patients after a combined dietary and lifestyle intervention.

CONCLUSIONS

Hypocaloric diet or restrictive macronutrient diet with lower percentage of carbohydrates seems feasible and effective for childhood HO, although most of the studies had a high risk of bias, small cohorts without control groups, and were conducted in children with PWS only, compromising the generalizability. Lifestyle interventions only resulted in BMI decrease in short-term, indicating that additional guidance is needed to sustain its effect in the long-term. Literature on feasibility and efficacy of a dietary or lifestyle intervention for hypothalamic overweight or obesity is scarce, especially in children with acquired HO (following treatment for a suprasellar tumor). There is need for prospective (controlled) studies to determine which dietary and lifestyle intervention are most helpful for this specific patient group.

Control of goal-directed and inflexible actions by dorsal striatal melanocortin systems, in coordination with the central nucleus of the amygdala

The dorsomedial striatum (DMS) is associated with flexible goal seeking, as opposed to routinized habits. Whether local mechanisms brake this function, for instance when habits may be adaptive, is incompletely understood. We find that a sub-population of dopamine D1 receptor-containing striatal neurons express the melanocortin-4 receptor (MC4R) for α-melanocyte stimulating hormone. These neurons within the DMS are necessary and sufficient for controlling the capacity of mice to flexibly adjust actions based on the likelihood that they will be rewarded. In investigating MC4R function, we found that it suppresses immediate-early gene levels in the DMS and concurrently, flexible goal seeking. MC4R+ neurons receive input from the central nucleus of the amygdala, and behavioral experiments indicate that they are functionally integrated into an amygdalo-striatal circuit that suppresses action flexibility in favor of routine. Publicly available spatial transcriptomics datasets were analyzed for gene transcript correlates of Mc4r expression across the striatal subregions, revealing considerable co-variation in dorsal structures. This insight led to the discovery that the function of MC4R in the dorsolateral striatum complements that in the DMS, in this case suppressing habit-like behavior. Altogether, our findings suggest that striatal MC4R controls the capacity for goal-directed and inflexible actions alike.

Functional coupling between MC4R and Kir7.1 contributes to clozapine-induced hyperphagia

Most antipsychotic drugs (APDs) induce hyperphagia and weight gain. However, the neural mechanisms are poorly understood, partly due to challenges replicating their metabolic effects in rodents. Here, we report a new mouse model that recapitulates overeating induced by clozapine, a widely prescribed APD. Our study shows that clozapine boosts food intake by inhibiting melanocortin 4 receptor (MC4R) expressing neurons in the paraventricular nucleus of the hypothalamus. Interestingly, neither clozapine nor risperidone, another commonly used APD, affects receptor-ligand binding or the canonical Gαs signaling of MC4R. Instead, they inhibit neuronal activity by enhancing the coupling between MC4R and Kir7.1, leading to the open state of the inwardly rectifying potassium channel. Deletion of Kir7.1 in Mc4r-Cre neurons prevents clozapine-induced weight gain, while treatment with a selective Kir7.1 blocker mitigates overeating in clozapine-fed mice. Our findings unveil a molecular pathway underlying the effect of APDs on feeding behavior and suggest its potential as a therapeutic target.

The role of central neurotransmitters in appetite regulation of broilers and layers: similarities and differences

The importance of feeding as a vital physiological function, on the one hand, and the spread of complications induced by its disorder in humans and animals, on the other hand, have led to extensive research on its regulatory factors. Unfortunately, despite many studies focused on appetite, only limited experiments have been conducted on avian, and our knowledge of this species is scant. Considering this, the purpose of this review article is to examine the role of central neurotransmitters in regulating food consumption in broilers and layers and highlight the similarities and differences between these two strains. The methodology of this review study includes a comprehensive search of relevant literature on the topic using appropriate keywords in reliable electronic databases. Based on the findings, the central effect of most neurotransmitters on the feeding of broilers and laying chickens was similar, but in some cases, such as dopamine, ghrelin, nitric oxide, and agouti-related peptide, differences were observed. Also, the lack of conducting a study on the role of some neurotransmitters in one of the bird strains made it impossible to make an exact comparison. Finally, it seems that although there are general similarities in appetite regulatory mechanisms in meat and egg-type chickens, the long-term genetic selection appropriate to breeding goals (meat or egg production) has caused differences in the effect of some neurotransmitters. Undoubtedly, conducting future studies while completing the missing links can lead to a comprehensive understanding of this process and its manipulation according to the breeding purposes of chickens.

Therapeutic Strategies Against Metabolic Imbalance in a Male Mouse Model With 5-HT2CR Loss-of-Function

The serotonin 2C receptor (5-HT2CR)-melanocortin pathway plays well-established roles in the regulation of feeding behavior and body weight homeostasis. Dysfunctions in this system, such as loss-of-function mutations in the Htr2c gene, can lead to hyperphagia and obesity. In this study, we aimed to investigate the potential therapeutic strategies for ameliorating hyperphagia, hyperglycemia, and obesity associated with a loss-of-function mutation in the Htr2c gene (Htr2cF327L/Y). We demonstrated that reexpressing functional 5-HT2CR solely in hypothalamic pro-opiomelanocortin (POMC) neurons is sufficient to reduce food intake and body weight in Htr2cF327L/Y mice subjected to a high-fat diet (HFD). In addition, 5-HT2CR expression restores the responsiveness of POMC neurons to lorcaserin, a selective agonist for 5-HT2CR. Similarly, administration of melanotan II, an agonist of the melanocortin receptor 4 (MC4R), effectively suppresses feeding and weight gain in Htr2cF327L/Y mice. Strikingly, promoting wheel-running activity in Htr2cF327L/Y mice results in a decrease in HFD consumption and improved glucose homeostasis. Together, our findings underscore the crucial role of the melanocortin system in alleviating hyperphagia and obesity related to dysfunctions of the 5-HT2CR, and further suggest that MC4R agonists and lifestyle interventions might hold promise in counteracting hyperphagia, hyperglycemia, and obesity in individuals carrying rare variants of the Htr2c gene.

Neuroanatomical dissection of the MC3R circuitry regulating energy rheostasis

Although mammals resist both acute weight loss and weight gain, the neural circuitry mediating bi-directional defense against weight change is incompletely understood. Global constitutive deletion of the melanocortin-3-receptor (MC3R) impairs the behavioral response to both anorexic and orexigenic stimuli, with MC3R knockout mice demonstrating increased weight gain following anabolic challenges and increased weight loss following anorexic challenges (i.e. impaired energy rheostasis). However, the brain regions mediating this phenotype remain incompletely understood. Here, we utilized MC3R floxed mice and viral injections of Cre-recombinase to selectively delete MC3R from medial hypothalamus (MH) in adult mice. Behavioral assays were performed on these animals to test the role of MC3R in MH in the acute response to orexigenic and anorexic challenges. Complementary chemogenetic approaches were used in MC3R-Cre mice to localize and characterize the specific medial hypothalamic brain regions mediating the role of MC3R in energy homeostasis. Finally, we performed RNAscope in situ hybridization to map changes in the mRNA expression of MC3R, POMC, and AgRP following energy rheostatic challenges. Our results demonstrate that MC3R deletion in MH increased feeding and weight gain following acute high fat diet feeding in males, and enhanced the anorexic effects of semaglutide, in a sexually dimorphic manner. Additionally, activation of DMH MC3R neurons increased energy expenditure and locomotion. Together, these results demonstrate that MC3R mediated effects on energy rheostasis result from the loss of MC3R signaling in the medial hypothalamus of adult animals and suggest an important role for DMH MC3R signaling in energy rheostasis.

Novel Cocrystal Structures of Peptide Antagonists Bound to the Human Melanocortin Receptor 4 Unveil Unexplored Grounds for Structure-Based Drug Design

Melanocortin 4 receptor (MC4-R) antagonists are actively sought for treating cancer cachexia. We determined the structures of complexes with PG-934 and SBL-MC-31. These peptides differ from SHU9119 by substituting His6 with Pro6 and inserting Gly10 or Arg10. The structures revealed two subpockets at the TM7-TM1-TM2 domains, separated by N2857.36. Two peptide series based on the complexed peptides led to an antagonist activity and selectivity SAR study. Most ligands retained the SHU9119 potency, but several SBL-MC-31-derived peptides significantly enhanced MC4-R selectivity over MC1-R by 60- to 132-fold. We also investigated MC4-R coupling to the K+ channel, Kir7.1. Some peptides activated the channel, whereas others induced channel closure independently of G protein coupling. In cell culture studies, channel activation correlated with increased feeding, while a peptide with Kir7.1 inhibitory activity reduced eating. These results highlight the potential for targeting the MC4-R:Kir7.1 complex for treating positive and restrictive eating disorders.

Modulation of GABA release by 5-HT1B receptors: An interplay with AMPA-receptors and voltage-gated Ca2+ channels

Obesity has become a worldwide health challenge and commonly results from the intake of more calories than the body requires. The brain represents the master controller of food intake and as such has been the target of obesity medications. However, key mechanisms of druggable targets remain to be defined. Neurons within the arcuate nucleus of the hypothalamus co-expressing neuropeptide Y (NPY), agouti-related protein (AgRP) and GABA (NAG) are fundamental stimulators of hunger and food intake. NAG neurons also inhibit local satiety-promoting pro-opiomelanocortin (POMC) neurons. Agonists of the 1B subtype of metabotropic serotonin receptor (5-HT1BR) reduce food intake in part through the inhibition of hunger-promoting NAG neurons. We first confirmed that 5-HT1BR activation suppressed intake of a palatable Western diet in a mouse model of common dietary-induced obesity and genetically prone obesity. Next, we combined several electrophysiological approaches to analyse the effect of 5-HT1BRs in NAG neuron cell activity and GABA release. 5-HT1BR activation reduced NAG neuron action potential frequency and neurotransmitter release. We found that 5-HT1BR impact on GABA release from NAG neurons is mediated through voltage-gated Ca2+ channels with a critical input from glutamate receptors of AMPA subtype (AMPARs). As a fundamental outcome, this type of interplay provides an uncommon example of metabotropic action of AMPARs which regulates inhibitory signalling due to modulation of GABA release. As a translational outcome, our results provide a key mechanism through which 5-HT1BR drugs inhibit appetite-stimulating neurons within the brain to suppress food intake. This article is part of the Special Issue on "Ukrainian Neuroscience".