Leptin activates hypothalamic CART neurons projecting to the spinal cord

Neuromodulation in the fish brain for reproductive success

In most teleosts, appropriate sexual behaviors and sexual maturation are essential for reproductive success. Most fish display their unique behavioral patterns for mating. These behaviors are thought to be regulated in the brain by sex steroid hormones since sexual behaviors are displayed only by sexually mature fish. In addition, recent studies have reported that neuropeptides, which are peptides released from neurons and modulate neural activities via their specific receptors in the brain, also play a key role in regulating sexual behavior. On the other hand, not only sexual behavior but also feeding behavior is important for reproductive function since sexual maturation requires sufficient nutrition. Especially feeding-related peptides, a type of neuropeptides, are thought to modulate feeding behavior. Thus, it is conceivable that neuropeptides are crucial modulators in the brain for reproductive success. This review summarizes recent advances in the knowledge of the neuromodulatory systems involved in sexual and feeding behaviors by neuropeptides and gonadal hormones.

Molecular connectomics reveals a glucagon-like peptide 1-sensitive neural circuit for satiety

Liraglutide and other glucagon-like peptide 1 receptor agonists (GLP-1RAs) are effective weight loss drugs, but how they suppress appetite remains unclear. One potential mechanism is by activating neurons that inhibit the hunger-promoting Agouti-related peptide (AgRP) neurons of the arcuate hypothalamus (Arc). To identify these afferents, we developed a method combining rabies-based connectomics with single-nucleus transcriptomics. Here, we identify at least 21 afferent subtypes of AgRP neurons in the mouse mediobasal and paraventricular hypothalamus, which are predicted by our method. Among these are thyrotropin-releasing hormone (TRH)+ Arc (TRHArc) neurons, inhibitory neurons that express the Glp1r gene and are activated by the GLP-1RA liraglutide. Activating TRHArc neurons inhibits AgRP neurons and feeding, probably in an AgRP neuron-dependent manner. Silencing TRHArc neurons causes overeating and weight gain and attenuates liraglutide's effect on body weight. Our results demonstrate a widely applicable method for molecular connectomics, comprehensively identify local inputs to AgRP neurons and reveal a circuit through which GLP-1RAs suppress appetite.

Molecular and functional mapping of the neuroendocrine hypothalamus: a new era begins

BACKGROUND

Recent advances in neuroscience tools for single-cell molecular profiling of brain neurons have revealed an enormous spectrum of neuronal subpopulations within the neuroendocrine hypothalamus, highlighting the remarkable molecular and cellular heterogeneity of this brain area.

RATIONALE

Neuronal diversity in the hypothalamus reflects the high functional plasticity of this brain area, where multiple neuronal populations flexibly integrate a variety of physiological outputs, including energy balance, stress and fertility, through crosstalk mechanisms with peripheral hormones. Intrinsic functional heterogeneity is also observed within classically 'defined' subpopulations of neuroendocrine neurons, including subtypes with distinct neurochemical signatures, spatial organisation and responsiveness to hormonal cues.

AIM

The aim of this review is to critically evaluate past and current research on the functional diversity of hypothalamic neuroendocrine neurons and their plasticity. It focuses on how this neuronal plasticity in this brain area relates to metabolic control, feeding regulation and interactions with stress and fertility-related neural circuits.

CONCLUSION

Our analysis provides an original framework for improving our understanding of the hypothalamic regulation of hormone function and the development of neuroendocrine diseases.

Hypothalamic cannabinoid signaling: Consequences for eating behavior

In parallel to the legalization of cannabis for both medicinal and recreational purposes, cannabinoid use has steadily increased over the last decade in the United States. Cannabinoids, such as tetrahydrocannabinol and anandamide, bind to the central cannabinoid-1 (CB1) receptor to impact several physiological processes relevant for body weight regulation, including appetite and energy expenditure. The hypothalamus integrates peripheral signals related to energy balance, houses several nuclei that orchestrate eating, and expresses the CB1 receptor. Herein we review literature to date concerning cannabinergic action in the hypothalamus with a specific focus on eating behaviors. We highlight hypothalamic areas wherein researchers have focused their attention, including the lateral, arcuate, paraventricular, and ventromedial hypothalamic nuclei, and interactions with the hormone leptin. This review serves as a comprehensive analysis of what is known about cannabinoid signaling in the hypothalamus, highlights gaps in the literature, and suggests future directions.

Adipose thermogenic mechanisms by cold, exercise and intermittent fasting: Similarities, disparities and the application in treatment

Given its nonnegligible role in metabolic homeostasis, adipose tissue has been the target for treating metabolic disorders such as obesity, diabetes and cardiovascular diseases. Besides its lipolytic function, adipose thermogenesis has gained increased interest due to the irreplaceable contribution to dissipating energy to restore equilibrium, and its therapeutic effects have been testified in various animal models. In this review, we will brief about the canonical cold-stimulated adipose thermogenic mechanisms, elucidate on the exercise- and intermittent fasting-induced adipose thermogenic mechanisms, with a focus on the similarities and disparities among these signaling pathways, in an effort to uncover the overlapped and specific targets that may yield potent therapeutic efficacy synergistically in improving metabolic health.

Molecular Connectomics Reveals a Glucagon-Like Peptide 1 Sensitive Neural Circuit for Satiety

Liraglutide and other agonists of the glucagon-like peptide 1 receptor (GLP-1RAs) are effective weight loss drugs, but how they suppress appetite remains unclear. One potential mechanism is by activating neurons which inhibit hunger-promoting Agouti-related peptide (AgRP) neurons of the arcuate hypothalamus (Arc). To identify these afferents, we developed a method combining rabies-based connectomics with single-nuclei transcriptomics. Applying this method to AgRP neurons predicted at least 21 afferent subtypes in the mouse mediobasal and paraventricular hypothalamus. Among these are Trh+ Arc neurons, inhibitory neurons which express the Glp1r gene and are activated by the GLP-1RA liraglutide. Activating Trh+ Arc neurons inhibits AgRP neurons and feeding in an AgRP neuron-dependent manner. Silencing Trh+ Arc neurons causes over-eating and weight gain and attenuates liraglutide's effect on body weight. Our results demonstrate a widely applicable method for molecular connectomics, comprehensively identify local inputs to AgRP neurons, and reveal a circuit through which GLP-1RAs suppress appetite.

The interplay between leptin, glucocorticoids, and GLP1 regulates food intake and feeding behaviour

Nutritional, endocrine, and neurological signals converge in multiple brain centres to control feeding behaviour and food intake as part of the allostatic regulation of energy balance. Among the several neuroendocrine systems involved, the leptin, glucocorticoid, and glucagon-like peptide 1 (GLP1) systems have been extensively researched. Leptin is at the top hierarchical level since its complete absence is sufficient to trigger severe hyperphagia. Glucocorticoids are key regulators of the energy balance adaptation to stress and their sustained excess leads to excessive adiposity and metabolic perturbations. GLP1 participates in metabolic adaptation to food intake, regulating insulin secretion and satiety by parallel central and peripheral signalling systems. Herein, we review the brain and peripheral targets of these three hormone systems that integrate to regulate food intake, feeding behaviour, and metabolic homeostasis. We examine the functional relationships between leptin, glucocorticoids, and GLP1 at the central and peripheral levels, including the cross-regulation of their circulating levels and their cooperative or antagonistic actions at different brain centres. The pathophysiological roles of these neuroendocrine systems in dysregulated intake are explored in the two extremes of body adiposity - obesity and lipodystrophy - and eating behaviour disorders.

Appetite- and Weight-Regulating Neuroendocrine Circuitry in Hypothalamic Obesity

Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.

Novel mechanisms involved in leptin sensitization in obesity

Leptin is a hormone that is secreted by adipocytes in proportion to adipose tissue size, and that informs the brain about the energy status of the body. Leptin acts through its receptor LepRb, expressed mainly in the hypothalamus, and induces a negative energy balance by potent inhibition of feeding and activation of energy expenditure. These actions have led to huge expectations for the development of therapeutic targets for metabolic complications based on leptin-derived compounds. However, the majority of patients with obesity presents elevated leptin production, suggesting that in this setting leptin is ineffective in the regulation of energy balance. This resistance to the action of leptin in obesity has led to the development of "leptin sensitizers," which have been tested in preclinical studies. Much research has focused on generating combined treatments that act on multiple levels of the gastrointestinal-brain axis. The gastrointestinal-brain axis secretes a variety of different anorexigenic signals, such as uroguanylin, glucagon-like peptide-1, amylin, or cholecystokinin, which can alleviate the resistance to leptin action. Moreover, alternative mechanism such as pharmacokinetics, proteostasis, the role of specific kinases, chaperones, ER stress and neonatal feeding modifications are also implicated in leptin resistance. This review will cover the current knowledge regarding the interaction of leptin with different endocrine factors from the gastrointestinal-brain axis and other novel mechanisms that improve leptin sensitivity in obesity.

Dysfunction of the adhesion G protein-coupled receptor latrophilin 1 (ADGRL1/LPHN1) increases the risk of obesity

Obesity is one of the diseases with severe health consequences and rapidly increasing worldwide prevalence. Understanding the complex network of food intake and energy balance regulation is an essential prerequisite for pharmacological intervention with obesity. G protein-coupled receptors (GPCRs) are among the main modulators of metabolism and energy balance. They, for instance, regulate appetite and satiety in certain hypothalamic neurons, as well as glucose and lipid metabolism and hormone secretion from adipocytes. Mutations in some GPCRs, such as the melanocortin receptor type 4 (MC4R), have been associated with early-onset obesity. Here, we identified the adhesion GPCR latrophilin 1 (ADGRL1/LPHN1) as a member of the regulating network governing food intake and the maintenance of energy balance. Deficiency of the highly conserved receptor in mice results in increased food consumption and severe obesity, accompanied by dysregulation of glucose homeostasis. Consistently, we identified a partially inactivating mutation in human ADGRL1/LPHN1 in a patient suffering from obesity. Therefore, we propose that LPHN1 dysfunction is a risk factor for obesity development.

Genome-wide scans identify biological and metabolic pathways regulating carcass and meat quality traits in beef cattle

Genome association studies (GWAS) provides knowledge about the genetic architecture of beef-related traits that allow linking the target phenotype to genomic information aiding breeding decision. Thus, the present study aims to uncover the genetic mechanism involved in carcass (REA: rib eye area, BF: backfat thickness, and HCW: hot carcass weight) and meat quality traits (SF: shear-force, MARB: marbling score, and IMF: intramuscular fat content) in Nellore cattle. For this, 6910 young bulls with phenotypic information and 23,859 animals genotyped with 435 k markers were used to perform the weighted single-step GBLUP (WssGBLUP) approach, considering two iterations. The top 10 genomic regions explained 8.13, 11.81, and 9.58% of the additive genetic variance, harboring a total of 119, 143, and 95 positional candidate genes for REA, BF, and HCW, respectively. For meat quality traits, the top 10 windows explained a large proportion of the total genetic variance for SF (14.95%), MARB (17.56%), and IMF (21.41%) surrounding 92, 155, and 111 candidate genes, respectively. Relevant candidate genes (CAST, PLAG1, XKR4, PLAGL2, AQP3/AQP7, MYLK2, WWOX, CARTPT, and PLA2G16) are related to physiological aspects affecting growth, carcass, meat quality, feed intake, and reproductive traits by signaling pathways controlling muscle control, key signal metabolic molecules INS / IGF-1 pathway, lipid metabolism, and adipose tissue development. The GWAS results provided insights into the genetic control of the traits studied and the genes found are potential candidates to be used in the improvement of carcass and meat quality traits.

Unraveling the lost balance: Adrenergic dysfunction in cancer cachexia

Cancer cachexia, characterized by muscle wasting and widespread inflammation, poses a significant challenge for patients with cancer, profoundly impacting both their quality of life and treatment management. However, existing treatment modalities remain very limited, accentuating the necessity for innovative therapeutic interventions. Many recent studies demonstrated that changes in autonomic balance is a key driver of cancer cachexia. This review consolidates research findings from investigations into autonomic dysfunction across cancer cachexia, spanning animal models and patient cohorts. Moreover, we explore therapeutic strategies involving adrenergic receptor modulation through receptor blockers and agonists. Mechanisms underlying adrenergic hyperactivity in cardiac and adipose tissues, influencing tissue remodeling, are also examined. Looking ahead, we present a perspective for future research that delves into autonomic dysregulation in cancer cachexia. This comprehensive review highlights the urgency of advancing research to unveil innovative avenues for combatting cancer cachexia and improving patient well-being.

Minireview: Glucocorticoid-Leptin Crosstalk: Role of Glucocorticoid-Leptin Counterregulation in Metabolic Homeostasis and Normal Development

Glucocorticoids and leptin are two important hormones that regulate metabolic homeostasis by controlling appetite and energy expenditure in adult mammals. Also, glucocorticoids and leptin strongly counterregulate each other, such that chronic stress-induced glucocorticoids upregulate the production of leptin and leptin suppresses glucocorticoid production directly via action on endocrine organs and indirectly via action on food intake. Altered glucocorticoid or leptin levels during development can impair organ development and increase the risk of chronic diseases in adults, but there are limited studies depicting the significance of glucocorticoid-leptin interaction during development and its impact on developmental programming. In mammals, leptin-induced suppression of glucocorticoid production is critical during development, where leptin prevents stress-induced glucocorticoid production by inducing a period of short-hyporesponsiveness when the adrenal glands fail to respond to certain mild to moderate stressors. Conversely, reduced or absent leptin signaling increases glucocorticoid levels beyond what is appropriate for normal organogenesis. The counterregulatory interactions between leptin and glucocorticoids suggest the potential significant involvement of leptin in disorders that occur from stress during development.

Adipokines and Their Role in Heart Failure: A Literature Review

Obesity is a major risk factor for heart failure (HF). The relationship between adipokines and HF has been implicated in many previous studies and reviews. However, this review article summarizes the basic role of major adipokines, such as apelin, adiponectin, chemerin, resistin, retinol-binding protein 4 (RBP4), vaspin, visfatin, plasminogen activator inhibitor-1, monocyte chemotactic protein-1, nesfatin-1, progranulin, leptin, omentin-1, lipocalin-2, and follistatin-like 1 (FSTL1), in the pathogenesis of HF. Apelin is reduced in patients with HF and upregulated following favorable left ventricular (LV) remodeling. Higher levels of adiponectin have been found in patients with HF compared to in control patients. Also, high plasma chemerin levels are linked to a higher risk of HF. Serum resistin is related to the severity of HF and associated with a high risk for adverse cardiac events. Evidence indicates that RBP4 can contribute to inflammation and damage heart muscle cells, potentially leading to HF. Vaspin might stop the progression of cardiac degeneration, fibrosis, and HF according to experiments on rats with experimental isoproterenol-induced chronic HF. The serum concentrations of visfatin are significantly lower in patients with systolic HF. Leptin levels were found to be correlated with low LV mass and myocardial stiffness, both of which are significant risk factors for the development of HF with preserved ejection fraction (HFpEF). Measuring serum omentin-1 levels appears to be a novel prognostic indicator for risk stratification in HF patients. Increased expression of neutrophil gelatinase-associated lipocalin in both systemic circulation and myocardium in clinical and experimental HF suggests that innate immune responses may contribute to the development of HF. FSTL1 was elevated in patients with HF with reduced ejection fraction and associated with an increase in the size of the left ventricle of the heart. However, other adipokines, such as plasminogen activator inhibitor-1, monocyte chemotactic protein-1, nesfatin-1, and progranulin, have not yet been studied for HF.

Electrophysiological Comparison of Definitive Pro-opiomelanocortin Neurons in the Arcuate Nucleus and the Retrochiasmatic Area of Male and Female Mice

Pro-opiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus (ARC) are considered a major site of leptin action. Due to increasing evidence that POMC neurons are highly heterogeneous and indications that the conventional molecular tools to study their functions have important limitations, a reassessment of leptin's effects on definitive POMC neurons is needed. POMC neurons are also expressed in the retrochiasmatic area (RCA), where their function is poorly understood. Furthermore, the response of POMC neurons to leptin in females is largely unknown. Therefore, the present study aimed to determine the differences in leptin responsiveness of POMC neurons in the ARC and the RCA using a mouse model allowing adult-inducible fluorescent labeling. We performed whole-cell patch clamp electrophysiology on 154 POMC neurons from male and female mice. We confirmed and extended the model by which leptin depolarizes POMC neurons, in both the ARC and the RCA. Furthermore, we characterized the electrophysiological properties of an underappreciated subpopulation representing ∼10% of hypothalamic POMC neurons that are inhibited by leptin. We also provide evidence that sex does not appear to be a major determinant of basal properties and leptin responsiveness of POMC neurons, but that females are overall less responsive to leptin compared to males.

Chronic Pain-Associated Cardiovascular Disease: The Role of Sympathetic Nerve Activity

Chronic pain affects many people world-wide, and this number is continuously increasing. There is a clear link between chronic pain and the development of cardiovascular disease through activation of the sympathetic nervous system. The purpose of this review is to provide evidence from the literature that highlights the direct relationship between sympathetic nervous system dysfunction and chronic pain. We hypothesize that maladaptive changes within a common neural network regulating the sympathetic nervous system and pain perception contribute to sympathetic overactivation and cardiovascular disease in the setting of chronic pain. We review clinical evidence and highlight the basic neurocircuitry linking the sympathetic and nociceptive networks and the overlap between the neural networks controlling the two.

The sympathetic nervous system in the 21st century: Neuroimmune interactions in metabolic homeostasis and obesity

The sympathetic nervous system maintains metabolic homeostasis by orchestrating the activity of organs such as the pancreas, liver, and white and brown adipose tissues. From the first renderings by Thomas Willis to contemporary techniques for visualization, tracing, and functional probing of axonal arborizations within organs, our understanding of the sympathetic nervous system has started to grow beyond classical models. In the present review, we outline the evolution of these findings and provide updated neuroanatomical maps of sympathetic innervation. We offer an autonomic framework for the neuroendocrine loop of leptin action, and we discuss the role of immune cells in regulating sympathetic terminals and metabolism. We highlight potential anti-obesity therapeutic approaches that emerge from the modern appreciation of SNS as a neural network vis a vis the historical fear of sympathomimetic pharmacology, while shifting focus from post- to pre-synaptic targeting. Finally, we critically appraise the field and where it needs to go.

Magel2 knockdown in hypothalamic POMC neurons innervating the medial amygdala reduces susceptibility to diet-induced obesity

Hyperphagia and obesity profoundly affect the health of children with Prader-Willi syndrome (PWS). The Magel2 gene among the genes in the Prader-Willi syndrome deletion region is expressed in proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARC). Knockout of the Magel2 gene disrupts POMC neuronal circuits and functions. Here, we report that loss of the Magel2 gene exclusively in ARC^POMC neurons innervating the medial amygdala (MeA) causes a reduction in body weight in both male and female mice fed with a high-fat diet. This anti-obesity effect is associated with an increased locomotor activity. There are no significant differences in glucose and insulin tolerance in mice without the Magel2 gene in ARC^POMC neurons innervating the MeA. Plasma estrogen levels are higher in female mutant mice than in controls. Blockade of the G protein-coupled estrogen receptor (GPER), but not estrogen receptor-α (ER-α), reduces locomotor activity in female mutant mice. Hence, our study provides evidence that knockdown of the Magel2 gene in ARC^POMC neurons innervating the MeA reduces susceptibility to diet-induced obesity with increased locomotor activity through activation of central GPER.

Medical treatment of weight loss in children and adolescents with obesity

Obesity remains one of the biggest health problems both in adults and children. Lifestyle modification, including diet and exercise, continues to be the mainstay of obesity prevention and treatment. Unfortunately, lifestyle modifications are often unsuccessful. Pharmacological treatment of obesity in pediatric patients can be applied in selected cases, and not before evidence of failure of the multidisciplinary lifestyle intervention. In this narrative review, we revised the most up-to-date evidence on medical treatment of weight loss in children and adolescents with obesity, including FDA- or EMA-approved and -experimented, not approved, drugs for pediatric population. Multidisciplinary treatment of childhood obesity, regulation of appetite control, energy balance and body weight were also discussed, in order to clarify the indications and mechanism action of drugs. Despite a substantial number of medications used for the treatment of obesity in adults, a limited number of drugs are approved by the drug regulatory agencies for pediatric population. Further research is needed to evaluate the efficacy and safety of novel pharmacological approaches for treatment of pediatric obesity in order to optimize weight management for children and adolescents and limit the development obesity-related comorbidities.

Long-term priming of hypothalamic microglia is associated with energy balance disturbances under diet-induced obesity

Exposure of microglia to an inflammatory environment may lead to their priming and exacerbated response to future inflammatory stimuli. Here we aimed to explore hypothalamic microglia priming and its consequences on energy balance regulation. A model of intracerebroventricular administration of neuraminidase (NA, which is present in various pathogens such as influenza virus) was used to induce acute neuroinflammation. Evidences of primed microglia were observed 3 months after NA injection, namely (1) a heightened response of microglia located in the hypothalamic arcuate nucleus after an in vivo inflammatory challenge (high fat diet [HFD] feeding for 10 days), and (2) an enhanced response of microglia isolated from NA-treated mice and challenged in vitro to LPS. On the other hand, the consequences of a previous NA-induced neuroinflammation were further evaluated in an alternative inflammatory and hypercaloric scenario, such as the obesity generated by continued HDF feeding. Compared with sham-injected mice, NA-treated mice showed increased food intake and, surprisingly, reduced body weight. Besides, NA-treated mice had enhanced microgliosis (evidenced by increased number and reactive morphology of microglia) and a reduced population of POMC neurons in the basal hypothalamus. Thus, a single acute neuroinflammatory event may elicit a sustained state of priming in microglial cells, and in particular those located in the hypothalamus, with consequences in hypothalamic cytoarchitecture and its regulatory function upon nutritional challenges.

Literature review on antiobesity medication use for metabolic and bariatric surgery patients from the American Society for Metabolic and Bariatric Surgery Clinical Issues Committee

The following literature search is in response to inquiries made to the American Society for Metabolic and Bariatric Surgery (ASMBS) regarding antiobesity medication (AOM) use in patients who are having or have already had metabolic and bariatric surgery (MBS). These recommendations are based on current clinical knowledge, expert opinion, and published peer-reviewed scientific evidence available at this time. This paper is not intended to establish a local, regional, or national standard of care. The paper will be revised in the future as additional evidence becomes available.

Reviewed and updated Algorithm for Genetic Characterization of Syndromic Obesity Phenotypes

Background: Individuals with a phenotype of early-onset severe obesity associated with intellectual disability can have molecular diagnoses ranging from monogenic to complex genetic traits. Severe overweight is the major sign of a syndromic physical appearance and predicting the influence of a single gene and/or polygenic risk profile is extremely complicated among the majority of the cases. At present, considering rare monogenic bases as the principal etiology for the majority of obesity cases associated with intellectual disability is scientifically poor. The diversity of the molecular bases responsible for the two entities makes the appliance of the current routinely powerful genomics diagnostic tools essential. Objective: Clinical investigation of these difficult-to-diagnose patients requires pediatricians and neurologists to use optimized descriptions of signs and symptoms to improve genotype correlations. Methods: The use of modern integrated bioinformatics strategies which are conducted by experienced multidisciplinary clinical teams. Evaluation of the phenotype of the patient's family is also of importance. Results: The next step involves discarding the monogenic canonical obesity syndromes and considering infrequent unique molecular cases, and/or then polygenic bases. Adequate management of the application of the new technique and its diagnostic phases is essential for achieving good cost/efficiency balances. Conclusion: With the current clinical management, it is necessary to consider the potential coincidence of risk mutations for obesity in patients with genetic alterations that induce intellectual disability. In this review, we describe an updated algorithm for the molecular characterization and diagnosis of patients with a syndromic obesity phenotype.

Hypothalamic Irak4 is a genetically controlled regulator of hypoglycemia-induced glucagon secretion

OBJECTIVES

Glucagon secretion to stimulate hepatic glucose production is the first line of defense against hypoglycemia. This response is triggered by so far incompletely characterized central hypoglycemia-sensing mechanisms, which control autonomous nervous activity and hormone secretion. The objective of this study was to identify novel hypothalamic genes controlling insulin-induced glucagon secretion.

METHODS

To obtain new information on the mechanisms of hypothalamic hypoglycemia sensing, we combined genetic and transcriptomic analysis of glucagon response to insulin-induced hypoglycemia in a panel of BXD recombinant inbred mice.

RESULTS

We identified two QTLs on chromosome 8 and chromosome 15. We further investigated the role of Irak4 and Cpne8, both located in the QTL on chromosome 15, in C57BL/6J and DBA/2J mice, the BXD mouse parental strains. We found that the poor glucagon response of DBA/2J mice was associated with higher hypothalamic expression of Irak4, which encodes a kinase acting downstream of the interleukin-1 receptor (Il-1R), and of Il-ß when compared with C57BL/6J mice. We showed that intracerebroventricular administration of an Il-1R antagonist in DBA/2J mice restored insulin-induced glucagon secretion; this was associated with increased c-fos expression in the arcuate and paraventricular nuclei of the hypothalamus and with higher activation of both branches of the autonomous nervous system. Whole body inactivation of Cpne8, which encodes a Ca++-dependent regulator of membrane trafficking and exocytosis, however, had no impact on insulin-induced glucagon secretion.

CONCLUSIONS

Collectively, our data identify Irak4 as a genetically controlled regulator of hypoglycemia-activated hypothalamic neurons and glucagon secretion.

The PACAP Paradox: Dynamic and Surprisingly Pleiotropic Actions in the Central Regulation of Energy Homeostasis

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP), a pleiotropic neuropeptide, is widely distributed throughout the body. The abundance of PACAP expression in the central and peripheral nervous systems, and years of accompanying experimental evidence, indicates that PACAP plays crucial roles in diverse biological processes ranging from autonomic regulation to neuroprotection. In addition, PACAP is also abundantly expressed in the hypothalamic areas like the ventromedial and arcuate nuclei (VMN and ARC, respectively), as well as other brain regions such as the nucleus accumbens (NAc), bed nucleus of stria terminalis (BNST), and ventral tegmental area (VTA) - suggesting that PACAP is capable of regulating energy homeostasis via both the homeostatic and hedonic energy balance circuitries. The evidence gathered over the years has increased our appreciation for its function in controlling energy balance. Therefore, this review aims to further probe how the pleiotropic actions of PACAP in regulating energy homeostasis is influenced by sex and dynamic changes in energy status. We start with a general overview of energy homeostasis, and then introduce the integral components of the homeostatic and hedonic energy balance circuitries. Next, we discuss sex differences inherent to the regulation of energy homeostasis via these two circuitries, as well as the activational effects of sex steroid hormones that bring about these intrinsic disparities between males and females. Finally, we explore the multifaceted role of PACAP in regulating homeostatic and hedonic feeding through its actions in regions like the NAc, BNST, and in particular the ARC, VMN and VTA that occur in sex- and energy status-dependent ways.

The Head-to-Toe Hormone: Leptin as an Extensive Modulator of Physiologic Systems

Leptin is a well-known hunger-sensing peptide hormone. The role of leptin in weight gain and metabolic homeostasis has been explored for the past two decades. In this review, we have tried to shed light upon the impact of leptin signaling on health and diseases. At low or moderate levels, this peptide hormone supports physiological roles, but at chronically higher doses exhibits detrimental effects on various systems. The untoward effects we observe with chronically higher levels of leptin are due to their receptor-mediated effect or due to leptin resistance and are not well studied. This review will help us in understanding the non-anorexic roles of leptin, including their contribution to the metabolism of various systems and inflammation. We will be able to get an alternative perspective regarding the physiological and pathological roles of this mysterious peptide hormone.

The orphan receptor GPR68 is expressed in the hypothalamus and is involved in the regulation of feeding

Currently, up to 35% off all drugs approved for the treatment of human diseases belong to the G-protein-coupled receptor (GPCR) family. Out of the almost 800 existing GPCRs, 25% have no known endogenous ligands and are regarded as orphan receptors; many of these are currently under investigation as potential pharmacological targets. Here, we hypothesised that orphan GPCRs expressed in the hypothalamus could be targets for the treatment of obesity and other metabolic diseases. Using bioinformatic tools, we identified 78 class A orphan GPCRs that are expressed in the hypothalamus of mice. Initially, we selected two candidates and determined their responsivities to nutritional interventions: GPR162, the GPCR with highest expression in the hypothalamus, and GPR68, a GPCR with intermediate expression in the hypothalamus and that has never been explored for its potential involvement in metabolic regulation. GPR162 expression was not modified by fasting/feeding or by the consumption of a high-fat diet, and was therefore not subsequently evaluated. Conversely, GPR68 expression increased in response to the consumption of a high-fat diet and reduced under fasting conditions. Using immunofluorescence, GPR68 was identified in both proopiomelanocortin-expressing and agouti-related peptide-expressing neurons in the hypothalamic arcuate nucleus. Acute inhibition of GPR68 with an allosteric modulator promoted an increase in the expression of the orexigenic agouti-related peptide and neuropeptide Y, whereas 4- and 12-h inhibition of GPR68 resulted in increased caloric intake. Thus, GPR68 has emerged as an orphan GPCR that is expressed in the hypothalamus and is involved in the regulation of feeding.

Autonomic control of energy balance and glucose homeostasis

Neurons in the central nervous system (CNS) communicate with peripheral organs largely via the autonomic nervous system (ANS). Through such communications, the sympathetic and parasympathetic efferent divisions of the ANS may affect thermogenesis and blood glucose levels. In contrast, peripheral organs send feedback to the CNS via hormones and autonomic afferent nerves. These humoral and neural feedbacks, as well as neural commands from higher brain centers directly or indirectly shape the metabolic function of autonomic neurons. Notably, recent developments in mouse genetics have enabled more detailed studies of ANS neurons and circuits, which have helped elucidate autonomic control of metabolism. Here, we will summarize the functional organization of the ANS and discuss recent updates on the roles of neural and humoral factors in the regulation of energy balance and glucose homeostasis by the ANS.

Cutting-edge techniques should be harnessed to unravel how metabolism is modulated by a key part of the body’s nervous system. The autonomic nervous system (ANS) regulates many involuntary physiological processes, such as heart rate, breathing, and blood pressure. Scientists now believe that the ANS is involved in regulating metabolism, but its precise roles are unclear. Jong-Woo Sohn and Uisu Hyun at the Korea Advanced Institute of Science and Technology, Daejeon, Korea, reviewed understanding of how the ANS regulates energy balance, appetite, and glucose homeostasis. Recently-developed mouse models have provided insights into how ANS neurons translate neuronal and hormonal signals into commands during feeding, sending instructions to the liver, and mediating blood glucose levels. Several hormones have been identified that may act on a specific part of the ANS to influence appetite and metabolism.

An enriched environment reestablishes metabolic homeostasis by reducing obesity-induced inflammation

Obesity can lead to chronic inflammation in different tissues, generating insulin and leptin resistance and alterations in glucose and lipid metabolism, favoring the development of degenerative diseases, including type II diabetes. Congruently, the inflammatory signaling inhibition prevents the development of obesity and restores insulin sensitivity. Via the enhancement of central nervous system activity, an enriched environment (EE) has beneficial effects on learning and memory as well as on immune cell functions and inflammation in different disease models. Here, we explored whether an EE can restore energy balance in obese mice that previously presented metabolic alterations. We discovered that an EE improved glucose metabolism, increased insulin signaling in liver, and reduced hepatic steatosis and inflammation, and increased lipolysis and browning in the white adipose tissue of high-fat diet (HFD)-fed mice. Finally, we found reduced inflammatory signaling and increased anorexigenic signaling in the hypothalamus of HFD-fed mice exposed to an EE. These data indicate that an EE is able to restore the metabolic imbalance caused by HFD feeding. Thus, we propose EE as a novel therapeutic approach for treating obesity-related metabolic alterations.

This article has an associated First Person interview with the first author of the paper.

Summary: A series of physiological, histochemical and molecular analyses reveal that enriched environment decreases inflammation in adipose tissue and in hypothalamus, re-establishing glucose metabolism in metabolically compromised mice.

Rolling out physical exercise and energy homeostasis: Focus on hypothalamic circuitries

Energy balance is the fine regulation of energy expenditure and energy intake. Negative energy balance causes body weight loss, while positive energy balance promotes weight gain. Modern societies offer a maladapted way of life, where easy access to palatable foods and the lack of opportunities to perform physical activity are considered the roots of the obesity pandemic. Physical exercise increases energy expenditure and, consequently, is supposed to promote weight loss. Paradoxically, physical exercise acutely drives anorexigenic-like effects, but the mechanisms are still poorly understood. Using an evolutionary background, this review aims to highlight the potential involvement of the melanocortin system and other hypothalamic neural circuitries regulating energy balance during and after physical exercise. The physiological significance of these changes will be explored, and possible signalling agents will be addressed. The knowledge discussed here might be important for clarifying obesity aetiology as well as new therapeutic approaches for body weight loss.

Leptin Chronic Effect on Differentiation, Ion Currents and Protein Expression in N1E-115 Neuroblastoma Cells

<b>Background and Objective:</b> Arcuate nucleus (ARC), a component of appetite-regulatory factors, contains populations of both orexigenic and anorexigenic neurons and one of the fundamental components of its system is leptin. Studies have evidenced the critical neurotrophic role in the development of ARC. To determine such effects on neuron development, N1E-115 neuroblastoma cells were used as an ARC model. <b>Materials and Methods:</b> N1E-115 neuroblastoma cells were treated with leptin [10 nM] for 24, 48 and 72 hrs. Dimethyl sulfoxide (DMSO) 1.5% was used as a known drug that promotes neurite expression. Cells percentage (%) that developed neurites was evaluated by bright field microscopy. Patch-clamp electrophysiology was used to analyze membrane ion currents, RT-PCR for quantifying changes in mRNA expression of anorexic peptides, proopiomelanocortin (POMC) and cocaine and amphetamine-related transcript (CART), in addition to principal Na<sub>v</sub>, Ca<sub>v</sub> ion channel subunits. <b>Results:</b> N1E-115 cells treated with leptin show neurite expression after 24 hrs of treatment, similar effects were obtained with DMSO. Leptin (time-dependent) increases the inward current in comparison with the control value at 72 hrs. Outward currents were not affected by leptin. Leptin and DMSO increased Na<sup>+</sup> and Ca<sup>2+</sup> current without changes in the kinetic properties. Lastly, leptin promotes an increase in mRNA level expression of transcripts to POMC, CART, Na<sub>v</sub>1.2 and Ca<sub>v</sub>1.3. <b>Conclusion:</b> Leptin chronic treatment promotes neurite expression, Up-regulation of Na<sup>+</sup> and Ca<sup>2+</sup> ion channels determining neuronal excitability, besides increasing the mRNA level expression of anorexic peptides POMC and CART in neuroblastoma N1E-115.

Leptin receptor-deficient (knockout) zebrafish: Effects on nutrient acquisition

In mammals, knockout of LEPR results in a hyperphagic, morbid obese, and diabetic phenotype, which supports that leptin plays an important role in the control of appetite and energy metabolism, and that its receptor, LEPR, mediates these effects. To date, little is known about the role(s) of lepr in teleost physiology. We investigated a zebrafish (Danio rerio) homozygous lepr knockout (lepr^-/-) line generated by CRISPR/Cas9 in comparison to its wt counterpart with respect to nutrient acquisition, energy allocation, and metabolism. The metabolic characterization included oxygen consumption rate and morphometric parameters (yolk sac area, standard length, wet weight, and condition factor) as proxies for use and allocation of energy in developing (embryos, larvae, and juveniles) zebrafish and showed no particular differences between the two lines, in agreement with previous studies. One exception was found in oxygen consumption at 72 hpf, when zebrafish switch from embryonic to early larval stages and food-seeking behavior could be observed. In this case, the metabolic rate was significantly lower in lepr^-/- than in wt. Both phenotypes showed similar responses, with respect to metabolic rate, to acute alterations (22 and 34 °C) in water temperature (measured in terms of Q₁₀ and activation energy) compared to the standard (28 °C) rearing conditions. To assess lepr involvement in signaling the processing and handling of incoming nutrients when an exogenous meal is digested and absorbed, we conducted an in vivo analysis in lepr^-/- and wt early (8 days post-fertilization) zebrafish larvae. The larvae were administered a bolus of protein hydrolysate (0%, 1%, 5%, and 15% lactalbumin) directly into the digestive tract lumen, and changes in the mRNA expression profile before and after (1 and 3 h) administration were quantified. The analysis showed transcriptional differences in the expressions of genes involved in the control of appetite and energy metabolism (cart, npy, agrp, and mc4r), sensing (casr, t1r1, t1r3, t1r2-1, t1r2-2, pept1a, and pept1b), and digestion (cck, pyy, try, ct, and amy), with more pronounced effects observed in the orexigenic than in the anorexigenic pathways, suggesting a role of lepr in their regulations. Differences in the mRNA levels of these genes in lepr^-/-vs. wt larvae were also observed. Altogether, our analyses suggest an influence of lepr on physiological processes involved in nutrient acquisition, mainly control of food intake and digestion, during early development, whereas metabolism, energy allocation, and growth seem to be only slightly influenced.

Overcoming Stress, Hunger, and Pain: Cocaine- and Amphetamine-Regulated Transcript Peptide's Promise

Cocaine- and amphetamine-regulated transcript encodes an eponymous peptide, CARTp, which exerts diverse pharmacologic actions in the central and peripheral nervous systems, as well as in several endocrine organs, including pancreas. Here we review those diverse actions, the physiological relevance of which had remained unestablished until recently. With the identification of a CARTp receptor, GPR160, the physiologic importance and therapeutic potential of CARTp or analogs are being revealed. Not only is the CARTp-GPR160 interaction essential for the circadian regulation of appetite and thirst but also for the transmission of nerve injury-induced pain. Molecular approaches now are uncovering additional physiologically relevant actions and the development of acute tissue-specific gene compromise approaches may reveal even more physiologically relevant actions of this pluripotent ligand/receptor pair.

Sympathetic Innervation of White Adipose Tissue: to Beige or Not to Beige?

Obesity research progresses in understanding neuronal circuits and adipocyte biology to regulate metabolism. However, the interface of neuro-adipocyte interaction is less studied. We summarize the current knowledge of adipose tissue innervation and interaction with adipocytes and emphasize adipocyte transitions from white to brown adipocytes and vice versa. We further highlight emerging concepts for the differential neuronal regulation of brown/beige versus white adipocyte and the interdependence of both for metabolic regulation.

Demystifying functional role of cocaine- and amphetamine-related transcript (CART) peptide in control of energy homeostasis: A twenty-five year expedition

Cocaine- and amphetamine-related transcript (CART) is a neuropeptide first discovered in the striatum of the rat brain. Later, the genetic sequence and function of CART peptide (CARTp) was found to be conserved among multiple mammalian species. Over the 25 years, since its discovery, CART mRNA (Cartpt) expression has been reported widely throughout the central and peripheral nervous systems underscoring its role in diverse physiological functions. Here, we review the localization and function of CARTp as it relates to energy homeostasis. We summarize the expression changes of central and peripheral Cartpt in response to metabolic states and make use of available large data sets to gain additional insights into the anatomy of the Cartpt expressing vagal neurons and their expression patterns in the gut. Furthermore, we provide an overview of the role of CARTp as an anorexigenic signal and its effect on energy expenditure and body weight control with insights from both pharmacological and transgenic animal studies. Subsequently, we discuss the role of CARTp in the pathophysiology of obesity and review important new developments towards identifying a candidate receptor for CARTp signalling. Altogether, the field of CARTp research has made rapid and substantial progress recently, and we review the case for considering CARTp as a potential therapeutic target for stemming the obesity epidemic.

Past, present and future of cocaine- and amphetamine-regulated transcript peptide

The existence of the peptide encoded by the cocaine- and amphetamine-regulated transcript (Cartpt) has been recognized since 1981, but it was not until 1995, that the gene encoding CART peptide (CART) was identified. With the availability of the predicted protein sequence of CART investigators were able to identify sites of peptide localization, which then led to numerous approaches attempting to clarify CART's multiple pharmacologic effects and even provide evidence of potential physiologic relevance. Although not without controversy, a picture emerged of the importance of CART in ingestive behaviors, reward behaviors and even pain sensation. Despite the wealth of data hinting at the significance of CART, in the absence of an identified receptor, the full potential for this peptide or its analogs to be developed into therapeutic agents remained unrealized. There was evidence favoring the action of CART via a G protein-coupled receptor (GPCR), but despite multiple attempts the identity of that receptor eluded investigators until recently. Now with the identification of the previously orphaned GPCR, GPR160, as a receptor for CART, focus on this pluripotent neuropeptide will in all likelihood experience a renaissance and the potential for the development of pharmcotherapies targeting GPR160 seems within reach.

POMC neuronal heterogeneity in energy balance and beyond: an integrated view

Hypothalamic AgRP and POMC neurons are conventionally viewed as the yin and yang of the body's energy status, since they act in an opposite manner to modulate appetite and systemic energy metabolism. However, although AgRP neurons' functions are comparatively well understood, a unifying theory of how POMC neuronal cells operate has remained elusive, probably due to their high level of heterogeneity, which suggests that their physiological roles might be more complex than initially thought. In this Perspective, we propose a conceptual framework that integrates POMC neuronal heterogeneity with appetite regulation, whole-body metabolic physiology and the development of obesity. We highlight emerging evidence indicating that POMC neurons respond to distinct combinations of interoceptive signals and food-related cues to fine-tune divergent metabolic pathways and behaviours necessary for survival. The new framework we propose reflects the high degree of developmental plasticity of this neuronal population and may enable progress towards understanding of both the aetiology and treatment of metabolic disorders.

Signaling in rat brainstem via Gpr160 is required for the anorexigenic and antidipsogenic actions of cocaine- and amphetamine-regulated transcript peptide

Recent work identified Gpr160 as a candidate receptor for cocaine- and amphetamine-regulated transcript peptide (CARTp) and described its role in pain modulation. The aims of the present study were to determine if Gpr160 is required for the CARTp's ability to reduce food intake and water intake and to initially identify the distribution of Gpr160-like immunoreactivity (Gpr160ir) in the rat brain. A passive immunoneutralization approach targeting Gpr160 was used to block the behavioral effects of a pharmacological dose of CARTp in the fourth cerebroventricle (4V) of rats and to determine the importance of endogenously produced CARTp in the control of ingestive behaviors. Passive immunoneutralization of Gpr160 in the 4V blocked the actions of CARTp to inhibit food intake and water intake. Blockade of Gpr160 in the 4V, independent of pharmacological CART treatment, caused an increase in both overnight food intake and water intake. The decrease in food intake, but not water intake, caused by central injection of CARTp was demonstrated to be interrupted by prior administration of a glucagon-like peptide 1 (GLP-1) receptor antagonist. Gpr160ir was observed in several, distinct sites throughout the rat brain, where CARTp staining has been described. Importantly, Gpr160ir was observed to be present in both neuronal and nonneuronal cell types. These data support the hypothesis that Gpr160 is required for the anorexigenic actions of central CARTp injection and extend these findings to water drinking. Gpr160ir was observed in both neuronal and nonneuronal cell types in regions known to be important in the multiple pharmacological effects of CARTp, identifying those areas as targets for future compromise of function studies.

α-MSH-induced activation of spinal MC1R but not MC4R enhances colorectal motility in anaesthetised rats

The central nervous system is involved in regulation of defaecation. It is generally considered that supraspinal regions control the spinal defaecation centre. However, signal transmission from supraspinal regions to the spinal defaecation centre is still unclear. In this study, we investigated the regulatory role of an anorexigenic neuropeptide, α-MSH, in the spinal defaecation centre in rats. Intrathecal administration of α-MSH to the L6-S1 spinal cord enhanced colorectal motility. The prokinetic effect of α-MSH was abolished by severing the pelvic nerves. In contrast, severing the colonic nerves or thoracic cord transection at the T4 level had no impact on the effect of α-MSH. RT-PCR analysis revealed MC1R mRNA and MC4R mRNA expression in the L6-S1 spinal cord. Intrathecally administered MC1R agonists, BMS470539 and SHU9119, mimicked the α-MSH effect, but a MC4R agonist, THIQ, had no effect. These results demonstrate that α-MSH binds to MC1R in the spinal defaecation centre and activates pelvic nerves, leading to enhancement of colorectal motility. This is, to our knowledge, the first report showing the functional role of α-MSH in the spinal cord. In conclusion, our findings suggest that α-MSH is a candidate for a neurotransmitter from supraspinal regions to the spinal defaecation centre.

The anorexigenic effect of adrenomedullin in Japanese quail (Coturnix japonica) involves increased proopiomelanocortin and cocaine- and amphetamine-regulated transcript mRNAs in the arcuate nucleus of the hypothalamus

Central administration of adrenomedullin (AM), a 52-amino acid peptide, is associated with anorexigenic effects in some species, including rodents and chickens. However, the associated hypothalamic mechanisms remain unclear and it is unknown if this peptide exerts satiety-inducing effects in other avian species. The objective of this study was thus to investigate AM-induced anorexigenic effects in 7-day-old Japanese quail (Coturnix japonica). After intracerebroventricular injection of 0.3, 1.0, or 3.0 nmol of AM, quail injected with 3.0 nmol of AM ate and drank less than vehicle-injected quail at 180 min after injection. Except for the 1.0 nmol dose of AM exerting an anorexigenic effect at 90 min after injection, no other inhibitory effects on food or water intake were observed. At 60 min after injection, the AM-injected quail had more c-Fos immunoreactive cells in the arcuate nucleus (ARC) than vehicle-injected birds. In the ARC, AM injection was associated with increased proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) mRNAs. In conclusion, the results suggest that the anorexigenic effect of AM is possibly influenced by the synergistic effect of POMC and CART in the ARC.

Monogenic human obesity syndromes

Neural circuits in the hypothalamus play a key role in the regulation of human energy homeostasis. A critical circuit involves leptin-responsive neurons in the hypothalamic arcuate nucleus (the infundibular nucleus in humans) expressing the appetite-suppressing neuropeptide proopiomelanocortin (POMC) and the appetite-stimulating Agouti-related peptide. In the fed state, the POMC-derived melanocortin peptide α-melanocyte-stimulating hormone stimulates melanocortin-4 receptors (MC4Rs) expressed on second-order neurons in the paraventricular nucleus of the hypothalamus (PVN). Agonism of MC4R leads to reduced food intake and increased energy expenditure. Disruption of this hypothalamic circuit by inherited mutations in the genes encoding leptin, the leptin receptor, POMC, and MC4R can lead to severe obesity in humans. The characterization of these and closely related genetic obesity syndromes has informed our understanding of the neural pathways by which leptin regulates energy balance, neuroendocrine function, and the autonomic nervous system. A broader understanding of these neural and molecular mechanisms has paved the way for effective mechanism-based therapies for patients whose severe obesity is driven by disruption of these pathways.

Optogenetic stimulation of the liver-projecting melanocortinergic pathway promotes hepatic glucose production

The central melanocortin system plays a fundamental role in the control of feeding and body weight. Proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARC) also regulate overall glucose homeostasis via insulin-dependent and -independent pathways. Here, we report that a subset of ARC POMC neurons innervate the liver via preganglionic parasympathetic acetylcholine (ACh) neurons in the dorsal motor nucleus of the vagus (DMV). Optogenetic stimulation of this liver-projecting melanocortinergic pathway elevates blood glucose levels that is associated with increased expression of hepatic gluconeogenic enzymes in female and male mice. Pharmacological blockade and knockdown of the melanocortin-4 receptor gene in the DMV abolish this stimulation-induced effect. Activation of melanocortin-4 receptors inhibits DMV cholinergic neurons and optogenetic inhibition of liver-projecting parasympathetic cholinergic fibers increases blood glucose levels. This elevated blood glucose is not due to altered pancreatic hormone release. Interestingly, insulin-induced hypoglycemia increases ARC POMC neuron activity. Hence, this liver-projecting melanocortinergic circuit that we identified may play a critical role in the counterregulatory response to hypoglycemia.

Hypothalamic Pomc Neurons Innervate the Spinal Cord and Modulate the Excitability of Premotor Circuits

Locomotion requires energy, yet animals need to increase locomotion in order to find and consume food in energy-deprived states. While such energy homeostatic coordination suggests brain origin, whether the central melanocortin 4 receptor (Mc4r) system directly modulates locomotion through motor circuits is unknown. Here, we report that hypothalamic Pomc neurons in zebrafish and mice have long-range projections into spinal cord regions harboring Mc4r-expressing V2a interneurons, crucial components of the premotor networks. Furthermore, in zebrafish, Mc4r activation decreases the excitability of spinal V2a neurons as well as swimming and foraging, while systemic or V2a neuron-specific blockage of Mc4r promotes locomotion. In contrast, in mice, electrophysiological recordings revealed that two-thirds of V2a neurons in lamina X are excited by the Mc4r agonist α-MSH, and acute inhibition of Mc4r signaling reduces locomotor activity. In addition, we found other Mc4r neurons in spinal lamina X that are inhibited by α-MSH, which is in line with previous studies in rodents where Mc4r agonists reduced locomotor activity. Collectively, our studies identify spinal V2a interneurons as evolutionary conserved second-order neurons of the central Mc4r system, providing a direct anatomical and functional link between energy homeostasis and locomotor control systems. The net effects of this modulatory system on locomotor activity can vary between different vertebrate species and, possibly, even within one species. We discuss the biological sense of this phenomenon in light of the ambiguity of locomotion on energy balance and the different living conditions of the different species.

The central melanocortin system and human obesity

The prevalence of obesity and the associated comorbidities highlight the importance of understanding the regulation of energy homeostasis. The central melanocortin system plays a critical role in controlling body weight balance. Melanocortin neurons sense and integrate the neuronal and hormonal signals, and then send regulatory projections, releasing anorexigenic or orexigenic melanocortin neuropeptides, to downstream neurons to regulate the food intake and energy expenditure. This review summarizes the latest progress in our understanding of the role of the melanocortin pathway in energy homeostasis. We also review the advances in the identification of human genetic variants that cause obesity via mechanisms that affect the central melanocortin system, which have provided rational targets for treatment of genetically susceptible patients.

Nicotine' actions on energy balance: Friend or foe?

Obesity has reached pandemic proportions and is associated with severe comorbidities, such as type 2 diabetes mellitus, hepatic and cardiovascular diseases, and certain cancer types. However, the therapeutic options to treat obesity are limited. Extensive epidemiological studies have shown a strong relationship between smoking and body weight, with non-smokers weighing more than smokers at any age. Increased body weight after smoking cessation is a major factor that interferes with their attempts to quit smoking. Numerous controlled studies in both humans and rodents have reported that nicotine, the main bioactive component of tobacco, exerts a marked anorectic action. Furthermore, nicotine is also known to modulate energy expenditure, by regulating the thermogenic activity of brown adipose tissue (BAT) and the browning of white adipose tissue (WAT), as well as glucose homeostasis. Many of these actions occur at central level, by controlling the activity of hypothalamic neuropeptide systems such as proopiomelanocortin (POMC), or energy sensors such as AMP-activated protein kinase (AMPK). However, direct impact of nicotine on metabolic tissues, such as BAT, WAT, liver and pancreas has also been described. Here, we review the actions of nicotine on energy balance. The relevance of this interaction is interesting, because considering the restricted efficiency of obesity treatments, a possible complementary approach may focus on compounds with known pharmacokinetic profile and pharmacological actions, such as nicotine or nicotinic acetylcholine receptors signaling.

Cellular and systemic mechanisms for glucose sensing and homeostasis

Glucose is a major source of energy in animals. Maintaining blood glucose levels within a physiological range is important for facilitating glucose uptake by cells, as required for optimal functioning. Glucose homeostasis relies on multiple glucose-sensing cells in the body that constantly monitor blood glucose levels and respond accordingly to adjust its glycemia. These include not only pancreatic β-cells and α-cells that secrete insulin and glucagon, but also central and peripheral neurons regulating pancreatic endocrine function. Different types of cells respond distinctively to changes in blood glucose levels, and the mechanisms involved in glucose sensing are diverse. Notably, recent studies have challenged the currently held views regarding glucose-sensing mechanisms. Furthermore, peripheral and central glucose-sensing cells appear to work in concert to control blood glucose level and maintain glucose and energy homeostasis in organisms. In this review, we summarize the established concepts and recent advances in the understanding of cellular and systemic mechanisms that regulate glucose sensing and its homeostasis.

Malnourishment during early lactation disrupts the ontogenetic distribution of the CART and α-MSH anorexigenic molecules in the arcuate/paraventricular pathway and lateral hypothalamus in male rats

Developmental malnourishment impacts the energetic metabolism control throughout life. In rat offspring, a 0% protein diet during the first 10 days of lactation results in leptin resistance and in alterations in: feeding behavior, serum leptin and neuropeptide Y (NPY) levels in the hypothalamic arcuate nucleus (ARC)/paraventricular (PVN) pathway. Here, the distributions of alpha-melanocyte stimulating hormone (α-MSH) and cocaine and amphetamine regulated transcript (CART), anorexigenic molecules, were immunohistochemically assessed in the ARC, PVN and lateral hypothalamus (LH) nuclei. Rat dams were subjected to one of the following diet protocols from postnatal day (P) 1-10: 1) Protein-free (PFG, 0% protein chow); 2) Pair-fed (UFG, normoprotein chow); 3) Control group (CG, normoprotein chow). PFG, UFG and CG male offspring were analyzed at different time points, from P5 to P180. In the ARC, PFG α-MSH and CART were increased from P10 to P45 when compared to CG and UFG. In the PVN, α-MSH and CART peaks in PFG animals were delayed from P20 to P30 when compared to CG. In the LH, CART was more intense in PFG animals than in UFG and CG ones by P20, and, by P30, UFG immunostaining became less intense than in CG. In conclusion, aproteic diet altered the ontogenetic distribution of both anorexigenic molecules. In the PVN, the peak was delayed to P30, which coincides with the leptin peak and follows the previously described NPY (orexigenic) peak in this model. The permanent LH CART and α-MSH increase may be associated with the previously observed PFG hypophagia.

The Implication of Gut Hormones in the Regulation of Energy Homeostasis and Their Role in the Pathophysiology of Obesity

PURPOSE OF REVIEW

This review provides an update on the role of gut hormones and their interactions in the regulation of energy homeostasis, describes gut hormone adaptations in obesity and in response to weight loss, and summarizes the current evidence on the role of gut hormone-based therapies for obesity treatment.

RECENT FINDINGS

Gut hormones play a key role in regulating eating behaviour, energy and glucose homeostasis. Dysregulated gut hormone responses have been proposed to be pathogenetically involved in the development and perpetuation of obesity. Summarizing the major gut hormone changes in obesity, obese individuals are characterized by blunted postprandial ghrelin suppression, loss of premeal ghrelin peaks, impaired diurnal ghrelin variability and reduced fasting and postprandial levels of anorexigenic peptides. Adaptive alterations of gut hormone levels are implicated in weight regain, thus complicating hypocaloric dietary interventions, and can further explain the profound weight loss and metabolic improvement following bariatric surgery. A plethora of compounds mimicking gut hormone changes after bariatric surgery are currently under investigation, introducing a new era in the pharmacotherapy of obesity. The current trend is to combine different gut hormone receptor agonists and target multiple systems simultaneously, in order to replicate as closely as possible the gut hormone milieu after bariatric surgery and circumvent the counter-regulatory adaptive changes associated with dietary energy restriction. An increasing number of preclinical and early-phase clinical trials reveal the additive benefits obtained with dual or triple gut peptide receptor agonists in reducing body weight and improving glycaemia. Gut hormones act as potent regulators of energy and glucose homeostasis. Therapeutic strategies targeting their levels or receptors emerge as a promising approach to treat patients with obesity and hyperglycaemia.