A critical update on the leptin-melanocortin system.

Leptin regulates energy balance through central circuits that control food intake and energy expenditure, including proopiomelanocortin (POMC) neurons. POMC neuron-specific deletion of protein tyrosine phosphatase 1B (PTP1B) (Ptpn1(loxP/loxP) POMC-Cre), a negative regulator of CNS leptin signaling, results in resistance to diet-induced obesity and improved peripheral leptin sensitivity in mice, thus establishing PTP1B as an important component of POMC neuron regulation of energy balance. POMC neurons are expressed in the pituitary, the arcuate nucleus of the hypothalamus (ARH), and the nucleus of the solitary tract (NTS) in the hindbrain, and it is unknown how each population might contribute to the phenotype of POMC-Ptp1b(-/-) mice. It is also unknown whether improved leptin sensitivity in POMC-Ptp1b(-/-) mice involves altered melanocortin receptor signaling. Therefore, we examined the effects of hindbrain administration (4th ventricle) of leptin (1.5, 3, and 6 μg) or the melanocortin 3/4R agonist melanotan II (0.1 and 0.2 nmol) in POMC-Ptp1b(-/-) (KO) and control PTP1B(fl/fl) (WT) mice on food intake, body weight, spontaneous physical activity (SPA), and core temperature (T(C)). The results show that KO mice were hypersensitive to hindbrain leptin- and MTII-induced food intake and body weight suppression and SPA compared with WT mice. Greater increases in leptin- but not MTII-induced T(C) were also observed in KO vs. WT animals. In addition, KO mice displayed elevated hindbrain and hypothalamic MC4R mRNA expression. These studies are the first to show that hindbrain administration of leptin or a melanocortin receptor agonist alters energy balance in mice likely via participation of hindbrain POMC neurons.

ABSTRACTThe central nervous system monitors modifications in metabolic parameters or hormone levels (leptin) and elicits adaptive responses such as food intake and glucose homeostasis regulation. Particularly, within the hypothalamus, pro-opiomelanocortin (POMC) neurons are crucial regulators of energy balance. Consistent with a pivotal role of the melanocortin system in the control of energy homeostasis, disruption of the Pomc gene causes hyperphagia and obesity. Pomc gene expression is tightly controlled by different mechanisms. Interestingly, recent studies pointed to a key role for micro ribonucleic acid (miRNAs) in the regulation of gene expression. However, the role of miRNAs in the leptin sensitivity in hypothalamic melanocortin system has never been assessed. We developed a transgenic mouse model (PDKO) with a partial deletion of the miRNA processing enzyme DICER specifically in POMC neurons. PDKO mice exhibited a normal body weight but a decrease of food intake. Interestingly, PDKO mice had decreased metabolic rate by reduction of VO2 consumption and CO2 production which could explain that PDKO mice have normal weight while eating less. Interestingly, we observed an increase of leptin sensitivity in the POMC neurons of PDKO mice which could explain the decrease of food intake in this model. We also observed an increase in the expression of genes involved in the function of brown adipose tissue that is in polysynaptic contact with the POMC neurons. In summary, these results support the hypothesis that Dicer-derived miRNAs may be involved in the effect of leptin on POMC neurons activity.

Sirt6 in pro-opiomelanocortin neurons controls energy metabolism by modulating leptin signaling

TAp63 is a transcription factor that has been reported to be important for energy and glucose homeostasis. However, where and how TAp63 functions is unclear. Chow-fed mutant mice with TAp63 deleted from pro-opiomelanocortin (POMC) neurons showed normal body weight and glucose metabolism in both sex. However, HFD fed male and female mice that lack TAp63 from POMC neurons both showed glucose intolerance (GTT) and insulin resistance independent of body weight. Strikingly, deletion of TAp63 in POMC neurons confers “male-like” diet-induced obesity (DIO) to female mice, but does not affect DIO phenotypes in male mice. In contrast, overexpression of TAp63 in POMC neurons partially prevents DIO in male mice but not in female mice. Here we show that POMC neurons in female mice display higher neural activities and express higher POMC mRNAs compared to male counterparts, and both these enhancements in female POMC neurons are correlated to higher expression levels of TAp63. Further, we found that the deletion of TAp63 reduced POMC neuronal activity and diminished the sexual dimorphism of POMC neural activity by decreasing the responsiveness of ERα-positive POMC neurons to the ERα agonist. Finally, we found that TAp63 binds to the promoter of POMC gene and regulate POMC gene expression in POMC neurons. In addition, the expression of energy homeostasis related genes like SRC-1, ERα and TAp63 target genes Sirt1, AMPKα2, LKB1 were also decreased in mice lacking TAp63 in POMC neurons. Collectively, TAp63 in mature POMC neurons regulates glucose homeostasis and TAp63 is one key molecular driver for the sexual dimorphism in energy homeostasis. Disclosure C. Wang: None. Y. He: None. P. Xu: None. Y. Yang: None. Y. Xu: None.

Hypothalamic Fatty Acid Synthase (FASN) plays a critical role in regulating energy balance by influencing food intake and body weight. This study aimed to investigate the neuronal mechanisms by which FASN impacts metabolism, focusing on its role in Pro-Opiomelanocortin (POMC) neurons. We used transgenic mouse models with pre- or postnatal deletion of FASN specifically in POMC neurons in male mice. We evaluated changes in adiposity, glucose metabolism and metabolic parameters including food intake, energy expenditure and substrate utilization using metabolic chambers. Changes in neuronal activity were assessed using electrophysiology and further validated by optogenetic stimulation of POMC neurons. Additionally, the role of adrenergic signaling was examined using pharmacological approaches and gene expression analyses. FASN deletion in POMC neurons reduced food intake, decreased adiposity, and altered glucose metabolism. FASN-deficient POMC neurons exhibited increased baseline activity. The developmental stage of FASN deletion influenced its effects on energy expenditure and body weight regulation. Additionally, FASN in POMC neurons was found to be essential for maintaining glucose homeostasis and insulin release via adrenergic signaling. FASN in POMC neurons plays an age- and neuron-specific role in regulating feeding, energy expenditure, and glucose homeostasis through mechanisms including the sympathetic nervous system. These findings highlight FASN as a potential therapeutic target for metabolic diseases by improving energy expenditure and insulinemia. Given the developmental programming of metabolic outcomes, interventions aimed at modulating FASN activity may have long-lasting benefits in managing metabolic diseases.

Although it is popularly assumed that changes in body weight reflect the choices an individual makes about what food to eat, how much to eat and how much to exercise, the long-term balance between energy intake and energy output is mainly determined by unconscious physiological systems. The UK Department of Health Estimated Average Requirements for energy intake stipulate 2079 calories day−1 for women and 2605 for men (Scientific Advisory Committee on Nutrition, 2011). If, over a year, energy intake exceeds energy expenditure by merely 1% (20 calories day−1 for women, or about one banana per week), it will result in a gain of 2.6 kg in fat mass. This rate of weight gain will take a woman from normal weight to obesity in ∼10 years. The message is not that we should avoid eating bananas, but that despite large variations in both day-by-day food intake and voluntary energy expenditure, we generally have a near-miraculous ability to maintain a near-constant body weight over decades of life. This is ultimately because in humans, as in all mammals, energy intake and energy expenditure are tightly co-regulated by conserved neuronal and endocrine circuits. Obesity does not imply gluttony; gluttons might escape obesity and, conversely, obesity can arise from a perfectly ordinary level of food intake as the long-term result of a near-imperceptible imbalance in homeostatic mechanisms. Blaming the obese for their obesity is rather like blaming the poor for their poverty; they might be able to do something about their condition, but in practice it is often far from easy. Indeed, efforts to ‘cure themselves’ are often counterproductive; one of the strongest predictors of weight gain is weight-loss dieting. One of the largest studies to demonstrate this was The Growing Up Today Study (GUTS), a prospective study of >16,000 adolescents (Field et al. 2003). At the 3 year follow-up, adolescents who were frequent or infrequent dieters had gained significantly more weight than non-dieters. The strong evolutionary conservation of the mechanisms that regulate energy balance has meant that knowledge gained from animal models translates well into understanding of human physiology and behaviour; for example, mutations in genes that affect signalling in these pathways generally have very similar effects in rodents and humans. Two tightly conserved endocrine signals in particular have attracted massive attention. Ghrelin, secreted from the empty stomach, reaches maximal levels after a fast, and activates neurons in the arcuate nucleus of the hypothalamus that make two potent orexigens, neuropeptide Y (NPY) and agouti-related peptide (AgRP). Leptin, secreted by adipocytes, reports on the body's fat reserves; it inhibits NPY/AgRP neurons, while activating others that express anorexigenic factors, notably neurons that express pro-opiomelanocortin (POMC). According to current dogma (supported by extensive evidence from many sources), POMC neurons and NPY/AgRP neurons are reciprocally linked, and which population is dominant determines how much (on average) an animal will eat. As an animal eats, neural and endocrine signals from the gut report on the volume ingested and on its composition, including its complement of fat, carbohydrates and protein. These signals converge on the ghrelin- and leptin-sensing circuits of the hypothalamus (Murphy & Bloom, 2006). These in turn project to other limbic sites, including the paraventricular nucleus, which is the primary regulator of the sympathetic nervous system and which also influences the pituitary–adrenal axis to regulate catabolic glucocorticoid secretion and the pituitary–thyroid axis to regulate metabolic rate. While this account is seductively simple, difficulties are arising from many different directions. First, a recent paper (MacFarlane et al. 2014) questions whether ghrelin (to date, the only known orexigenic hormone) has any physiological role in regulating energy balance. That paper adopted a classic ‘physiological’ approach and suggests that ghrelin affects food intake only at concentrations well in excess of those that are ever seen in physiological circumstances. Bariatric surgery is a very effective treatment for obesity in humans and, while this is far from an optimal intervention, understanding exactly why it is so effective may lead to new therapies that are more deliverable. The papers from Behary & Miras (2014) and le Roux & Bueter (2014) in this issue address this important area. It has been suggested that bariatric surgery might be effective in part through its consequences for ghrelin secretion. This has not been consistently supported by experimental evidence, but there are profound changes in the secretion of gut-derived anorexigenic hormones that seem likely to contribute, and which may provide leads for the development of pharmacological therapies for obesity. A particularly intriguing and important outcome of Roux-en-Y gastric bypass is an immediate improvement in glycaemia, and the mechanisms underlying this remain to be clarified fully. Second, the status of the POMC/NPY neurons as the primary neurons governing food intake has been disturbed by the demonstration that they are dominantly governed by a descending input from the paraventricular nucleus (Krashers et al. 2014). Indeed, some have argued that our conventional understanding of appetite regulation is inappropriately ‘hypothalamocentric’ and that regions of the caudal brainstem have been given relatively scant attention. The paper in this issue from Abraham et al. (2014) is a reminder that insulin also has an important role in energy balance and that its primary target may be in the dorsal vagal complex. Increasing attention is also now being given to both the hedonic pathways regulating food reward as targets for hormones (see Skibicka & Dickson, 2013) and to sensory pathways (see Spetter et al. 2014). Third, leptin is only one of many anorexogenic hormones and, while its levels correlate with fat mass, this correlation is quite weak; leptin concentrations may differ by 10-fold or more in individuals with the same body mass. Significant advances have been made in understanding the growth, function and regulation of adipose tissue, as the review from Boudina & Graham (2014) in this issue illustrates. However, there are still major gaps in our knowledge; 20 years after its discovery, we still know almost nothing about how leptin secretion is regulated. Animal studies and human genetics studies have also framed the contributions of genetic and epigenetic influences on body weight. Body weight in people is estimated (from twin studies) to be up to 80% heritable (Wardle et al. 2008), but an extensive search for the genes responsible has (so far) revealed associations that account for relatively little of the interindividual variation. This has focused attention on other heritable mechanisms and, in particular, on the consequences of events in uterine and early postnatal life. Notably, stress and impaired nutrition during gestation and in early postnatal life are now known to have lifelong ‘programming’ effects on physiology and metabolism. In mice, exposure to a maternal diet rich in sucrose leads to obesity and glucose intolerance in female offspring, and this is addressed in the paper by Samuelsson (2014) in this issue. Whether these effects are transmitted across generations remains to be established. The unfolding global obesity epidemic apparently reflects powerful interactions between genes and our changing environment. Although it seems likely that the key change in our environment is the increased availability of highly palatable, energy-dense food, there are many other environmental influences that may play a role. In those counties most affected to date, reduction in the cost of food has meant that the opportunity to become obese through overeating is now nearly universal. Our food is not only cheaper and tastier, it is also safer than ever; the prevalence of food-related infections has generally declined over recent decades, and the episodes of involuntary fasting that accompany minor infections are less common. The reduction in cigarette smoking is eliminating a potent anorexigen. Central heating is now nearly universal, and raised night-time ambient temperatures imply reduced involuntary energy expenditure. The increased consumption of high-fructose corn syrup, especially in drinks, is of particular concern in some countries, because there is evidence that fructose is more potently obesogenic than sucrose in rodents. Patterns of activity and food intake have also changed and, as touched on by the paper by Johnston (2014), the time of day alters lipid and glucose profiles following individual meals and, over a longer time scale, meal timing regulates adiposity and body weight. These changes may occur via the ability of timed feeding to synchronize local circadian rhythms in metabolically active tissues, including those in adipose tissue itself. Tempting though it is to blame fast food manufacturers, it is likely that many factors contribute to the increased prevalence of obesity. Meanwhile, there remains much to be done to understand the complex inter-relationship between appetite, metabolism, glucose hoemesostasis and adiposity and the various roles of diverse brain areas and multiple endocrine and neural pathways. In particular, we need a clearer understanding of those signals from the gastrointestinal tract that modulate both hedonic and homeostatic pathways. If we want public health policies to be informed by evidence rather than by ‘gut instinct’, perhaps we should begin by seeking to understand gut instinct better. None declared. Appetite-related research in Gareth Leng's laboratory is supported by European Commission Seventh Framework grants (FP7-KBBE-2010-4-266408, Full4Health; FP7-KBBE-2009-3-245009, NeuroFAST; and FP7/2007-2013 under Grant Agreement 607310, Nudge-it).

Proopiomelanocortin (POMC) neurons contribute to the regulation of many physiological processes; the majority of which have been attributed to the release of peptides produced from the POMC prohormone such as α-MSH, which plays key roles in food intake and metabolism. However, it is now clear that POMC neurons also release amino acid transmitters that likely contribute to the overall function of POMC cells. Recent work indicates that constitutive deletion of these transmitters can affect metabolic phenotypes, but also that the expression of GABAergic or glutamatergic markers changes throughout development. The goal of the present study was to determine whether the release of glutamate or GABA from POMC neurons in the adult mouse contributes notably to energy balance regulation. Disturbed release of glutamate or GABA specifically from POMC neurons in adult mice was achieved using a tamoxifen-inducible Cre construct (Pomc-CreERT2) expressed in mice also carrying floxed versions of Slc17a6 (vGlut2) or Gad1 and Gad2, encoding the vesicular glutamate transporter type 2 and GAD67 and GAD65 proteins, respectively. All mice in the experiments received tamoxifen injections, but control mice lacked the tamoxifen-inducible Cre sequence. Body weight was unchanged in Gad1- and Gad2- or vGlut2-deleted female and male mice. Additionally, no significant differences in glucose tolerance or refeeding after an overnight fast were observed. These data collectively suggest that the release of GABA or glutamate from POMC neurons in adult mice does not significantly contribute to the metabolic parameters tested here. In light of prior work, the data also suggest that amino acid transmitter release from POMC cells may contribute to separate functions in the adult versus the developing mouse.

A high-fat diet (HFD) is linked with cytokines production by non-neuronal cells within the hypothalamus, which mediates metabolic inflammation. These cytokines then activate different inflammatory mediators in the arcuate nucleus of the hypothalamus (ARC), a primary hypothalamic area accommodating proopiomelanocortin (POMC) and agouti-related peptide (AGRP) neurons, first-order neurons that sense and integrate peripheral metabolic signals and then respond accordingly. These mediators, such as inhibitor of κB kinase-β (IKKβ), suppression of cytokine signaling 3 (SOCS3), c-Jun N-terminal kinases (JNKs), protein kinase C (PKC), etc., cause insulin and leptin resistance in POMC and AGRP neurons and support obesity and related metabolic complications. On the other hand, inhibition of these mediators has been shown to counteract the impaired metabolism. Therefore, it is important to discuss the contribution of neuronal and non-neuronal cells in HFD-induced hypothalamic inflammation. Furthermore, understanding few other questions, such as the diets causing hypothalamic inflammation, the gender disparity in response to HFD feeding, and how hypothalamic inflammation affects ARC neurons to cause impaired metabolism, will be helpful for the development of therapeutic approaches to prevent or treat HFD-induced obesity.

The arcuate nucleus of the hypothalamus is essential for metabolic homeostasis and responds to leptin by producing several neuropeptides including proopiomelanocortin (POMC). We previously reported that high-dose erythropoietin (Epo) treatment in mice while increasing hematocrit reduced body weight, fat mass, and food intake and increased energy expenditure. Moreover, we showed that mice with Epo receptor (EpoR) restricted to erythroid cells (ΔEpoRE) became obese and exhibited decreased energy expenditure. Epo/EpoR signaling was found to promote hypothalamus POMC expression independently from leptin. Herein we used WT and ΔEpoRE mice and hypothalamus-derived neural culture system to study the signaling pathways activated by Epo in POMC neurons. We show that Epo stimulation activated STAT3 signaling and upregulated POMC expression in WT neural cultures. ΔEpoRE mice hypothalamus showed reduced POMC levels and lower STAT3 phosphorylation, with and without leptin treatment, compared to in vivo and ex vivo WT controls. Collectively, these data show that Epo regulates hypothalamus POMC expression via STAT3 activation, and provide a previously unrecognized link between Epo and leptin response.

Leptin regulates energy balance, in part, by modulating the activity of neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus. Leptin-deficient (ob/ob) mice differ from wild-type mice in the number of excitatory and inhibitory post-synaptic densities and currents onto NPY and POMC neurons. When leptin was delivered to ob/ob mice, the synaptic density rapidly normalized, an effect detectable within 6 hours, several hours before leptin's effect on food intake. Synaptic currents were also shifted toward wild-type values in leptin-replaced ob/ob mice. These data suggest that leptin-mediated plasticity in the ob/ob hypothalamus may underlie some of the hormone's behavioral effects. In an effort to determine whether the observed synaptic plasticity is leptin specific, we analyzed the effects of an orexigenic hormone, ghrelin, and anorexigenic hormone, estradiol. Ghrelin rearranged synapses in wild type animals to support suppressed POMC tone, whereas the estradiol triggered a robust increase in the number of excitatory, glutamate inputs of POMC neurons. The rearrangement of synapses by estradiol was leptin independent, because it was also evident in leptin- (ob/ob) and leptin receptor-deficient (db/db) mice and was paralleled with decreased food intake and increased energy expenditure in these mutant, obese animals. Such plasticity was also observed in other hypothalamic regions and extrahypothalamic sites. These observations raise the notion that synaptic plasticity is a major way through which peripheral metabolic hormones influence brain functions.

Obesity is a global epidemic that reflects a chronic state of energy imbalance. There is critical need to better understand integrative mechanisms of obesity and related cardiovascular complications to develop more targeted therapies with mitigated adverse effects. The control of energy balance involves interactions of circulating hormones with brain regions including the arcuate nucleus of the hypothalamus. Within the arcuate nucleus, activation of proopiomelanocortin (POMC) neurons decreases food intake and increases energy expenditure, whereas stimulation of agouti-related protein neurons has converse effects. Our goal is to identify novel hormonal targets that can engage these neural circuits to restore energy balance in obesity. Angiotensin-(1-7), a cardioprotective renin-angiotensin hormone, induces weight loss in obese mice and may provide this ideal target. Angiotensin-(1-7) binds mas receptors, which based on our preliminary data are highly localized to arcuate POMC neurons. The extent to which angiotensin-(1-7) activates POMC neurons, however, is unknown. Thus, in this study, we tested the hypothesis that systemic angiotensin-(1-7) administration activates arcuate POMC neurons. To test this, male C57BL/6J mice were placed on a control diet or 60% high fat diet for 12 weeks (n=4-6 per group). Mice then received a single subcutaneous injection of either angiotensin-(1-7) [2 mg/kg] or saline, with brains harvested at 60 minutes post-injection. RNAscope in situ hybridization was used to determine the presence of c-fos mRNA, a marker of acute neuronal activity, in POMC neurons within the arcuate nucleus. We found that angiotensin-(1-7) significantly increases c-fos expression in arcuate POMC neurons in control diet mice (percentage c-fos/POMC positive neurons: 53±8 vs. 26±5 saline; p=0.033). This ability of angiotensin-(1-7) to increase c-fos expression, however, was not observed in high fat diet mice (percentage c-fos/POMC positive neurons: 30±13 vs. 25±6 saline; p=0.706). These findings suggest that angiotensin-(1-7) can activate arcuate POMC neurons under normal conditions, with changes to this circuit observed in the context of diet-induced obesity. Additional studies are needed to determine the physiological relevance of these findings, such as whether angiotensin-(1-7) activates these neurons to provide cardiometabolic protection. NIH R01 HL156986, NIH F31 HL170693, Pennsylvania Department of Health Tobacco CURE Funds This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

DRP1 Suppresses Leptin and Glucose Sensing of POMC Neurons

Serotonin 2C Receptor Activates a Distinct Population of Arcuate Pro-opiomelanocortin Neurons via TRPC Channels

Peroxisome proliferator-activated receptor-γ (PPARγ), a master regulator of adipogenesis, was recently shown to affect energy homeostasis through its actions in the brain. Deletion of PPARγ in mouse brain, and specifically in the pro-opiomelanocortin (POMC) neurons, results in resistance to diet-induced obesity. To study the mechanisms by which PPARγ in POMC neurons controls energy balance, we constructed a Cre-recombinase-dependent conditionally activatable transgene expressing either wild-type (WT) or dominant-negative (P467L) PPARγ and the tdTomato reporter. Inducible expression of both forms of PPARγ was validated in cells in culture, in liver of mice infected with an adenovirus expressing Cre-recombinase (AdCre), and in the brain of mice expressing Cre-recombinase either in all neurons (NES(Cre)/PPARγ-P467L) or selectively in POMC neurons (POMC(Cre)/PPARγ-P467L). Whereas POMC(Cre)/PPARγ-P467L mice exhibited a normal pattern of weight gain when fed 60% high-fat diet, they exhibited increased weight gain and fat mass accumulation in response to a 10% fat isocaloric-matched control diet. POMC(Cre)/PPARγ-P467L mice were leptin sensitive on control diet but became leptin resistant when fed 60% high-fat diet. There was no difference in body weight between POMC(Cre)/PPARγ-WT mice and controls in response to 60% high-fat diet. However, POMC(Cre)/PPARγ-WT, but not POMC(Cre)/PPARγ-P467L, mice increased body weight in response to rosiglitazone, a PPARγ agonist. These observations support the concept that alterations in PPARγ-driven mechanisms in POMC neurons can play a role in the regulation of metabolic homeostasis under certain dietary conditions.

In mammals, males consume more food, which is considered a masculinized behavior, but the underlying mechanism of this sex-specific feeding behavior is unknown. In mice, neonatal testosterone (NT) is critical to masculinize the developing brain, leading to sex differences in reproductive physiology. The proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus (ARC) are critical to suppress energy intake and POMC innervation of hypothalamic feeding circuits develops to a large extent neonatally. We hypothesized that NT programs the masculinization of energy intake by programming POMC neurons. We tested this hypothesis by comparing control females and control males (CMs) with female mice neonatally androgenized with testosterone (NTFs). We show that increased food intake in CMs is associated with reduced POMC expression and decreased intensity of neuronal projections from POMC neurons within the ARC compared with control females. We found that NTFs display a masculinized energy intake and ARC POMC expression and innervation as observed in CMs, which can be mimicked by neonatal exposure to the androgen receptor agonist dihydrotestosterone (DHT). NTFs also exhibit hyperleptinemia and a decreased ability of leptin to up-regulate POMC, suppress food intake, and prevent adipose tissue accumulation, independent of signal transducer and activator of transcription 3. However, this leptin resistance is specific to NTFs, is not a consequence of masculinization, and is reproduced by neonatal exposure to estrogen but not DHT. Thus, NT programs a sexual differentiation of POMC neurons in female mice via DHT but also predisposes to leptin resistance and obesity in an estrogen-dependent manner.