Attenuation of the obesity syndrome of ob/ob mice by the loss of neuropeptide Y

Npy transcription is regulated by noncanonical STAT3 signaling in hypothalamic neurons: Implication with lipotoxicity and obesity

Neuropeptide Y (Npy) is an abundant neuropeptide expressed in the central and peripheral nervous systems. NPY-secreting neurons in the hypothalamic arcuate nucleus regulate energy homeostasis, and Npy mRNA expression is regulated by peripheral nutrient and hormonal signals like leptin, interleukin-6 (IL-6), and fatty acids. This study demonstrates that IL-6, which phosphorylates tyrosine 705 (Y705) of STAT3, decreased Npy mRNA in arcuate immortalized hypothalamic neurons. In parallel, inhibitors of STAT3-Y705 phosphorylation, stattic and cucurbitacin I, robustly upregulated Npy mRNA. Chromatin-immunoprecipitation showed high baseline total STAT3 binding to multiple regulatory regions of the Npy gene, which are decreased by IL-6 exposure. The STAT3-Npy interaction was further examined in obesity-related pathologies. Notably, in four different hypothalamic neuronal models where palmitate potently stimulated Npy mRNA, Socs3, a specific STAT3 activity marker, was downregulated and was negatively correlated with Npy mRNA levels (R2 = 0.40, p < 0.001), suggesting that disrupted STAT3 signaling is involved in lipotoxicity-mediated dysregulation of Npy. Finally, human NPY SNPs that map to human obesity or body mass index were investigated for potential STAT3 binding sites. Although none of the SNPs were linked to direct STAT3 binding, analysis show that rs17149106 (-602 G > T) is located on an upstream enhancer element of NPY, where the variant is predicted to disrupt validated binding of KLF4, a known inhibitory cofactor of STAT3 and downstream effector of leptin signaling. Collectively, this study demonstrates that STAT3 signaling negatively regulates Npy transcription, and that disruption of this interaction may contribute to metabolic 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.

Sympathetic NPY controls glucose homeostasis, cold tolerance, and cardiovascular functions in mice

Neuropeptide Y (NPY) is best known for its effects in the brain as an orexigenic and anxiolytic agent and in reducing energy expenditure. NPY is also co-expressed with norepinephrine (NE) in sympathetic neurons. Although NPY is generally considered to modulate noradrenergic responses, its specific roles in autonomic physiology remain under-appreciated. Here, we show that sympathetic-derived NPY is essential for metabolic and cardiovascular regulation in mice. NPY and NE are co-expressed in 90% of prevertebral sympathetic neurons and only 43% of paravertebral neurons. NPY-expressing neurons primarily innervate blood vessels in peripheral organs. Sympathetic-specific NPY deletion elicits pronounced metabolic and cardiovascular defects in mice, including reductions in insulin secretion, glucose tolerance, cold tolerance, and pupil size and elevated heart rate, while notably, however, basal blood pressure was unchanged. These findings provide insight into target tissue-specific functions of NPY derived from sympathetic neurons and imply its potential involvement in metabolic and cardiovascular diseases.

Fasting Modulates GABAergic Synaptic Transmission to Arcuate Kisspeptin Neurons in Female Mice

It is well-established that the hypothalamic-pituitary-gonadal (HPG) axis is suppressed due to negative energy balance. However, less information is available on whether kisspeptin neuronal activity contributes to fasting-induced responses. In the present study, female and male mice were fasted for 24 hours or provided food ad libitum (fed group) to determine whether acute fasting is sufficient to modulate kisspeptin neuronal activity. In female mice, fasting attenuated luteinizing hormone (LH) and prolactin (PRL) serum levels and increased follicle-stimulating hormone levels compared with the fed group. In contrast, fasting did not affect gonadotropin or PRL secretion in male mice. By measuring genes related to LH pulse generation in micropunches obtained from the arcuate nucleus of the hypothalamus (ARH), we observed that fasting reduced Kiss1 mRNA levels in female and male mice. In contrast, Pdyn expression was upregulated only in fasted female mice, whereas no changes in the Tac2 mRNA levels were observed in both sexes. Interestingly, the frequency and amplitude of the GABAergic postsynaptic currents recorded from ARH kisspeptin neurons (ARHKisspeptin) were reduced in 24-hour fasted female mice but not in males. Additionally, neuropeptide Y induced a hyperpolarization in the resting membrane potential of ARHKisspeptin neurons of fed female mice but not in males. Thus, the response of ARHKisspeptin neurons to fasting is sexually dependent with a female bias, associated with changes in gonadotropins and PRL secretion. Our findings suggest that GABAergic transmission to ARHKisspeptin neurons modulates the activity of the HPG axis during situations of negative energy balance.

Recent progress in leptin signaling from a structural perspective and its implications for diseases

As a multi-potency cytokine, leptin not only plays a crucial role in controlling weight and energy homeostasis but also participates in the metabolic balance in the human body. Leptin is a small helical protein with a molecular weight of 16 kDa. It can interact with multiple subtypes of its receptors to initiate intracellular signal transduction and exerts physiological effects. Disturbances in leptin signaling may lead to obesity and a variety of metabolic diseases. Leptin was also found to be a critical factor in many diseases of the elderly. In this review, we focus on recent advances in the structural and molecular mechanisms of leptin signaling through its receptors with the aim of a deeper understanding of leptin-related diseases.

Sympathetic NPY controls glucose homeostasis, cold tolerance, and cardiovascular functions in mice

Neuropeptide Y (NPY) is best known for its effects in the brain as an orexigenic and anxiolytic agent and in reducing energy expenditure. NPY is also co-expressed with Norepinephrine (NE) in sympathetic neurons. Although NPY is generally considered to modulate noradrenergic responses, its specific roles in autonomic physiology remain under-appreciated. Here, we show that sympathetic-derived NPY is essential for metabolic and cardiovascular regulation in mice. NPY and NE are co-expressed in 90% of prevertebral sympathetic neurons and only 43% of paravertebral neurons. NPY-expressing neurons primarily innervate blood vessels in peripheral organs. Sympathetic-specific deletion of NPY elicits pronounced metabolic and cardiovascular defects in mice, including reductions in insulin secretion, glucose tolerance, cold tolerance, pupil size, and an elevation in heart rate, while notably, however, basal blood pressure was unchanged. These findings provide new knowledge about target tissue-specific functions of NPY derived from sympathetic neurons and imply its potential involvement in metabolic and cardiovascular diseases.

Effects of undernutrition and low energy availability on reproductive functions and their underlying neuroendocrine mechanisms

It has been well established that undernutrition and low energy availability disturb female reproductive functions in humans and many animal species. These reproductive dysfunctions are mainly caused by alterations of some hypothalamic factors, and consequent reduction of gonadotrophin-releasing hormone (GnRH) secretion. Evidence from literature suggests that increased activity of orexigenic factors and decreased activity of anorexigenic/satiety-related factors in undernourished conditions attenuate GnRH secretion in an integrated manner. Likewise, the activity of kisspeptin neurons, which is a potent stimulator of GnRH, is also reduced in undernourished conditions. In addition, it has been suggested that gonadotrophin-inhibitory hormone, which has anti-GnRH and gonadotrophic effects, may be involved in reproductive dysfunctions under several kinds of stress conditions. It should be remembered that these alterations, i.e., promotion of feeding behavior and temporary suppression of reproductive functions, are induced to prioritize the survival of individual over that of species, and that improvements in metabolic and nutritional conditions should be considered with the highest priority.

Agouti-related peptide neuronal silencing overcomes delayed puberty in neonatally underfed male mice

Agouti-related peptide (AgRP) neurons are thought to indirectly regulate the activity of hypothalamic gonadotrophin-releasing hormone neurons which control fertility. AgRP neurons also drive caloric intake and are modulated by metabolically-relevant hormones, providing a link to the hypothalamic-pituitary-gonadal axis. In mice expressing Cre-dependant designer receptors (DREADDs) in AgRP neurons, we activated or silenced these neurons in vivo using the synthetic ligand clozapine-N-oxide (CNO) to observe the effect of AgRP neuron activity on timing of puberty. To validate these animals, we chronically treated both stimulatory (hM3Dq) and inhibitory (hM4Di) DREADD × AgRP-Cre mice with CNO, observing a pronounced increase and decrease of food intake, respectively, consistent with the known orexigenic effects of these neurons. RNAscope was performed to visually confirm the activation of AgRP neurons. Puberty onset was assessed in males and females. There was no effect on preputial separation in males or vaginal opening and first oestrus in females after CNO treatment from day 26 to 30 to chronically modulate AgRP neurons. Next, to determine whether the delay in puberty onset occurring in response to neonatal underfeeding could be overcome by inhibiting AgRP neuronal activity, mice were raised in large (neonatally underfed) or normal litter sizes. The delay in puberty from underfeeding was completely reversed in CNO-treated AgRP-hM4Di male mice. These data highlight the inhibitory role of AgRP neurons to delay puberty onset when undernutrition occurs during the neonatal period, at least in male mice. TRAIL REGISTRATION NUMBER: JNE-22-0081-OA.R2.

Role of insulin resistance and the gut microbiome on urine oxalate excretion in ob/ob mice

Ob/ob mice have recently emerged as a model for obesity-related hyperoxaluria as they are obese and excrete more urine oxalate compared to wild type mice. Ob/ob mice are deficient of leptin and develop obesity with hyperphagia and hyperinsulinemia. We hypothesized that insulin resistance and the gut microbiome contribute to hyperoxaluria in ob/ob mice. We developed a new liquid chromatography-mass spectrometry assay for urine oxalate and first compared urine oxalate excretion in ob/ob mice before and after ablation of intestinal bacteria with a standard antibiotic cocktail. We then compared urine oxalate excretion in ob/ob mice before and after leptin replacement or pioglitazone treatment, two maneuvers that reduce insulin resistance in ob/ob mice. Ob/ob mice excreted more oxalate into the urine in a 24-h period compared to wild type mice, but antibiotic, leptin, or pioglitazone treatment did not change urine oxalate excretion in ob/ob mice. Unexpectedly, we found that when food intake was carefully matched between ob/ob and wild type mice, the amount of 24-h urine oxalate excretion did not differ between the two mouse strains, suggesting that ob/ob mice excrete more urine oxalate because of hyperphagia. Since the level of urine oxalate excretion in wild type mice in our study was higher than those reported in prior studies, future work will be needed to standardize the measurement of urine oxalate and to define the range of urine oxalate excretion in wild type mice so that accurate and valid comparisons can be made between wild type mice and ob/ob mice or other mouse models.

Roles of Neuropeptides in Sleep-Wake Regulation

Sleep and wakefulness are basic behavioral states that require coordination between several brain regions, and they involve multiple neurochemical systems, including neuropeptides. Neuropeptides are a group of peptides produced by neurons and neuroendocrine cells of the central nervous system. Like traditional neurotransmitters, neuropeptides can bind to specific surface receptors and subsequently regulate neuronal activities. For example, orexin is a crucial component for the maintenance of wakefulness and the suppression of rapid eye movement (REM) sleep. In addition to orexin, melanin-concentrating hormone, and galanin may promote REM sleep. These results suggest that neuropeptides play an important role in sleep–wake regulation. These neuropeptides can be divided into three categories according to their effects on sleep–wake behaviors in rodents and humans. (i) Galanin, melanin-concentrating hormone, and vasoactive intestinal polypeptide are sleep-promoting peptides. It is also noticeable that vasoactive intestinal polypeptide particularly increases REM sleep. (ii) Orexin and neuropeptide S have been shown to induce wakefulness. (iii) Neuropeptide Y and substance P may have a bidirectional function as they can produce both arousal and sleep-inducing effects. This review will introduce the distribution of various neuropeptides in the brain and summarize the roles of different neuropeptides in sleep–wake regulation. We aim to lay the foundation for future studies to uncover the mechanisms that underlie the initiation, maintenance, and end of sleep–wake states.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

The regulation of PKA signaling in obesity and in the maintenance of metabolic health

The cAMP-dependent protein kinase (PKA) system represents a primary cell-signaling pathway throughout systems and across species. PKA facilitates the actions of hormones, neurotransmitters and other signaling molecules that bind G-protein coupled receptors (GPCR) to modulate cAMP levels. Through its control of synaptic events, exocytosis, transcriptional regulation, and more, PKA signaling regulates cellular metabolism and emotional and stress responses making it integral in the maintenance and dysregulation of energy homeostasis. Neural PKA signaling is regulated by afferent and peripheral efferent signals that link specific neural cell populations to the regulation of metabolic processes in adipose tissue, liver, pancreas, adrenal, skeletal muscle, and gut. Mouse models have provided invaluable information on the roles for PKA subunits in brain and key metabolic organs. While limited, human studies infer differential regulation of the PKA system in obese compared to lean individuals. Variants identified in PKA subunit genes cause Cushing syndrome that is characterized by metabolic dysregulation associated with endogenous glucocorticoid excess. Under healthy physiologic conditions, the PKA system is exquisitely regulated by stimuli that activate GPCRs to alter intracellular cAMP concentrations, and by PKA cellular localization and holoenzyme stability. Adenylate cyclase activity generates cAMP while phosphodiesterase-mediated cAMP degradation to AMP decreases cAMP levels downstream of GPCRs. Chronic perturbations in PKA signaling appear to be capable of resetting PKA regulation at several levels; in addition, sex differences in PKA signaling regulation, while not well understood, impact the physiologic consequences of metabolic dysregulation and obesity. This review explores the roles for PKA signaling in the pathogenesis of metabolic diseases including obesity, type 2 diabetes mellitus and associated co-morbidities through neural-peripheral crosstalk and cAMP/PKA signaling pathway targets that hold therapeutic potential.

Neuroendocrine mechanisms of reproductive dysfunctions in undernourished condition

It is well known that undernourished conditions disturb female reproductive functions in many species, including humans. These alterations are mainly caused by a reduction in gonadotrophin-releasing hormone (GnRH) secretion from the hypothalamus. Evidence from the literature suggests that some hypothalamic factors play pivotal roles in the coordination of reproductive functions and energy homeostasis in response to environmental cues and internal nutritional status. Generally, anorexigenic/satiety-related factors, such as leptin, alpha-melanocyte-stimulating hormone, and proopiomelanocortin, promote GnRH secretion, whereas orexigenic factors, such as neuropeptide Y, agouti-related protein, orexin, and ghrelin, attenuate GnRH secretion. Conversely, gonadotrophin-inhibitory hormone, which exerts anti-GnRH and gonadotrophic effects, promotes feeding behavior in many species. In addition, the activity of kisspeptin, which is a potent stimulator of GnRH, is reduced by undernourished conditions. Under normal nutritional conditions, these factors are coordinated to maintain both feeding behavior and reproductive functions. However, in undernourished conditions their activity levels are markedly altered to promote feeding behavior and temporarily suppress reproductive functions, in order to prioritize the survival of the individual over that of the species.

Effects of low energy availability on female reproductive function

Background

It is known that metabolic and nutritional disturbances induce reproductive dysfunction in females. The main cause of these alterations is reduced gonadotrophin‐releasing hormone (GnRH) secretion from the hypothalamus, and the underlying mechanisms have gradually been elucidated.

Methods

The present review summarizes current knowledge about the effects of nutrition/metabolism on reproductive functions, especially focusing on the GnRH regulation system.

Main findings

Various central and peripheral factors are involved in the regulation of GnRH secretion, and alterations in their activity combine to affect GnRH neurons. Satiety‐related factors, i.e., leptin, insulin, and alpha‐melanocyte‐stimulating hormone, directly and indirectly stimulate GnRH secretion, whereas orexigenic factors, i.e., neuropeptide Y, Agouti‐related protein, orexin, and ghrelin, attenuate GnRH secretion. In addition, kisspeptin, which is a potent positive regulator of GnRH, expression is reduced by metabolic and nutritional disturbances.

Conclusion

These neuroendocrine systems may be defensive mechanisms, which help organisms to survive adverse conditions by temporarily suppressing reproduction.

Neuropeptide Y1 receptor antagonism protects β-cells and improves glycemic control in type 2 diabetes

OBJECTIVES

Loss of functional β-cell mass is a key factor contributing to poor glycemic control in advanced type 2 diabetes (T2D). We have previously reported that the inhibition of the neuropeptide Y1 receptor improves the islet transplantation outcome in type 1 diabetes (T1D). The aim of this study was to identify the pathophysiological role of the neuropeptide Y (NPY) system in human T2D and further evaluate the therapeutic potential of using the Y1 receptor antagonist BIBO3304 to improve β-cell function and survival in T2D.

METHODS

The gene expression of the NPY system in human islets from nondiabetic subjects and subjects with T2D was determined and correlated with the stimulation index. The glucose-lowering and β-cell-protective effects of BIBO3304, a selective orally bioavailable Y1 receptor antagonist, in high-fat diet (HFD)/multiple low-dose streptozotocin (STZ)-induced and genetically obese (db/db) T2D mouse models were assessed.

RESULTS

In this study, we identified a more than 2-fold increase in NPY1R and its ligand, NPY mRNA expression in human islets from subjects with T2D, which was significantly associated with reduced insulin secretion. Consistently, the pharmacological inhibition of Y1 receptors by BIBO3304 significantly protected β cells from dysfunction and death under multiple diabetogenic conditions in islets. In a preclinical study, we demonstrated that the inhibition of Y1 receptors by BIBO3304 led to reduced adiposity and enhanced insulin action in the skeletal muscle. Importantly, the Y1 receptor antagonist BIBO3304 treatment also improved β-cell function and preserved functional β-cell mass, thereby resulting in better glycemic control in both HFD/multiple low-dose STZ-induced and db/db T2D mice.

CONCLUSIONS

Our results revealed a novel causal link between increased islet NPY-Y1 receptor gene expression and β-cell dysfunction and failure in human T2D, contributing to the understanding of the pathophysiology of T2D. Furthermore, our results demonstrate that the inhibition of the Y1 receptor by BIBO3304 represents a potential β-cell-protective therapy for improving functional β-cell mass and glycemic control in T2D.

Central nervous system regulation of organismal energy and glucose homeostasis

Growing evidence implicates the brain in the regulation of both immediate fuel availability (for example, circulating glucose) and long-term energy stores (that is, adipose tissue mass). Rather than viewing the adipose tissue and glucose control systems separately, we suggest that the brain systems that control them are components of a larger, highly integrated, 'fuel homeostasis' control system. This conceptual framework, along with new insights into the organization and function of distinct neuronal systems, provides a context within which to understand how metabolic homeostasis is achieved in both basal and postprandial states. We also review evidence that dysfunction of the central fuel homeostasis system contributes to the close association between obesity and type 2 diabetes, with the goal of identifying more effective treatment options for these common metabolic disorders.

Leptin in Leanness and Obesity: JACC State-of-the-Art Review

Leptin has emerged over the past 2 decades as a key hormone secreted by adipose tissue that conveys information on energy stores. Leptin is considered an important regulator of both neuroendocrine function and energy homeostasis. Numerous studies (mainly preclinical and much less in humans) have investigated the mechanisms of leptin's actions both in the healthy state as well as in a wide range of metabolic diseases. In this review, the authors present leptin physiology and review the main findings from animal studies, observational and interventional studies, and clinical trials in humans that have investigated the role of leptin in metabolism and cardiometabolic diseases (energy deficiency, obesity, diabetes, cardiovascular diseases, nonalcoholic fatty liver disease). The authors discuss the similarities and discrepancies between animal and human biology and present clinical applications of leptin, directions for future research, and current approaches for the development of the next-generation leptin analogs.

Sex differences in behavioral and metabolic effects of gene inactivation: The neuropeptide Y and Y receptors in the brain

Brain and gonadal hormones interplay controls metabolic and behavioral functions in a sex-related manner. However, most translational neuroscience research related to animal models of endocrine and psychiatric disorders are often carried out in male animals only. The Neuropeptide Y (NPY) system shows sex-dependent differences and is sensitive to gonadal steroids. Based on published data from our and other laboratories, in this review we will discuss the sex related differences of NPY action on energy balance, bone homeostasis and behavior in rodents with the genetic manipulation of genes encoding NPY and its Y1, Y2 and Y5 cognate receptors. Comparative analyses of the phenotype of transgenic and knockout NPY and Y receptor rodents unravels sex dependent differences in the functions of this neurotransmission system, potentially helping to develop therapeutics for a variety of sex-related disorders including metabolic syndrome, osteoporosis and ethanol addiction.

Sirtuin (SIRT)-1: At the crossroads of puberty and metabolism

In the arcuate nucleus (ARC) of the hypothalamus reside two neuronal systems in charge of regulating feeding control and reproductive development. The melanocortin system responds to metabolic fluctuations adjusting food intake, whereas kisspeptin neurons are in charge of the excitatory control of Gonadotropin Hormone Releasing Hormone (GnRH) neurons. While it is known that the melanocortin system regulates GnRH neuronal activity, it was recently demonstrated that kisspeptin neurons not only innervate melanocortin neurons, but also play an active role in the control of metabolism. These two neuronal systems are intricately interconnected forming loops of stimulation and inhibition according to metabolic status. Furthermore, intracellular and epigenetic pathways respond to external environmental signals by changing DNA conformation and gene expression. Here we review the role of Silent mating type Information Regulation 2 homologue 1 (Sirt1), a class III NAD+ dependent protein deacetylase, in the ARC control of pubertal development and feeding behavior.

PKA functions in metabolism and resistance to obesity: lessons from mouse and human studies

Both direct and indirect evidence demonstrate a central role for the cAMP-dependent protein kinase (PKA) signaling pathway in the regulation of energy balance and metabolism across multiple systems. However, the ubiquitous pattern of PKA expression across cell types poses a challenge in pinpointing its tissue-specific regulatory functions and further characterizing its many downstream effects in certain organs or cells. Mouse models of PKA deficiency and over-expression and studies in living cells have helped clarify PKA function in adipose tissue (AT), liver, adrenal, pancreas, and specific brain nuclei, as they pertain to energy balance and metabolic dysregulation. Limited studies in humans suggest differential regulation of PKA in AT of obese compared to lean individuals and an overall dysregulation of PKA signaling in obesity. Despite its complexity, under normal physiologic conditions, the PKA system is tightly regulated by changes in cAMP concentrations upstream via adenylate cyclase and downstream by phosphodiesterase-mediated cAMP degradation to AMP and by changes in PKA holoenzyme stability. Adjustments in the PKA system appear to be important to the development and maintenance of the obese state and its associated metabolic perturbations. In this review we discuss the important role of PKA in obesity and its involvement in resistance to obesity, through studies in humans and in mouse models, with a focus on the regulation of PKA in energy expenditure, intake behavior, and lipid and glucose metabolism.

Leptin signalling on arcuate NPY neurones controls adiposity independent of energy balance or diet composition

Central action of the adipocyte hormone leptin via the neuropeptide Y (NPY) system is considered critical for energy homeostatic control. However, the precise mechanisms for this control are still not clear. To specifically investigate how leptin signalling on the NPY neurone contributes to the control of energy homeostasis, we generated an inducible adult-onset NPY neurone-specific leptin receptor (Lepr) knockout model and performed a comprehensive metabolic phenotyping study. Here, we show that the NPY neurone subpopulation that is directly responsive to leptin is not required for the inhibition of fasting-induced hyperphagia by leptin, although it is essential for the regulation of adiposity independent of changes in energy balance or diet composition. Furthermore, under obesogenic conditions such as a high-fat diet, a lack of Lepr signalling on NPY neurones results in significant increases in food intake and concomitant reductions in energy expenditure, leading to accelerated accumulation of fat mass. Collectively, these findings support the notion that Lepr-expressing NPY neurones act as the key relay point where peripheral adipose storage information is sensed, and corresponding responses are initiated to protect adipose reserves.

The Effect of a 2-Week Red Ginseng Supplementation on Food Efficiency and Energy Metabolism in Mice

Red ginseng (RG) ingestion reportedly affects body weight, food intake, and fat accumulation reduction. It also induces changes in energy metabolism regulation and glycemic control. Previously, 2-week RG ingestion with endurance training was found to enhance fat oxidation during exercise. However, such effects on energy metabolism and the expression of mRNAs related to energy substrate utilization in resting mice (untrained mice) are still unclear. Here, we determined the effect of RG on energy metabolism and substrate utilization in untrained male mice. Twenty-four mice were separated into an RG group that received a daily dosage of 1 g/kg RG for 2 weeks, and a control (CON). Energy expenditure, blood and tissue glycogen levels, and expression of mRNAs related to energy substrate utilization in muscles were measured before and 2 weeks after treatment. Total food intake was significantly lower in the RG than in the CON group (p < 0.05), but final body weights did not differ. Carbohydrate and fat oxidation over 24 h did not change in either group. There were no significant differences in gastrocnemius GLUT4, MCT1, MCT4, FAT/CD36, and CPT1b mRNA levels between groups. Thus, the effects of RG ingested during rest differ from the effects of RG ingestion in combination with endurance exercise; administering RG to untrained mice for 2 weeks did not change body weight and energy metabolism. Therefore, future studies should consider examining the RG ingestion period and dosage for body weight control and improving energy metabolism.

Glucocorticoid-Induced Fatty Liver Disease

Glucocorticoids (GCs) are commonly used at high doses and for prolonged periods (weeks to months) in the treatment of a variety of diseases. Among the many side effects are increased insulin resistance with disturbances in glucose/insulin homeostasis and increased deposition of lipids (mostly triglycerides) in the liver. Here, we review the metabolic pathways of lipid deposition and removal from the liver that become altered by excess glucocorticoids. Pathways of lipid deposition stimulated by excess glucocorticoids include 1) increase in appetite and high caloric intake; 2) increased blood glucose levels due to GC-induced stimulation of gluconeogenesis; 3) stimulation of de novo lipogenesis that is augmented by the high glucose and insulin levels and by GC itself; and 4) increased release of free fatty acids from adipose stores and stimulation of their uptake by the liver. Pathways that decrease hepatic lipids affected by glucocorticoids include a modest stimulation of very-low-density lipoprotein synthesis and secretion into the circulation and inhibition of β-oxidation of fatty acids. Role of 11β-hydroxysteroid dehydrogenases-1 and -2 and the reversible conversion of cortisol to cortisone on intracellular levels of cortisol is examined. In addition, GC control of osteocalcin expression and the effect of this bone-derived hormone in increasing insulin sensitivity are discussed. Finally, research focused on gaining a better understanding of the dose and duration of treatment with glucocorticoids, which leads to increased triglyceride deposition in the liver, and the reversibility of the condition is highlighted.

A GPR17-cAMP-Lactate Signaling Axis in Oligodendrocytes Regulates Whole-Body Metabolism

The CNS plays a pivotal role in energy homeostasis, but whether oligodendrocytes are involved has been largely unexplored. Here, we show that signaling through GPR17, a G-protein-coupled receptor predominantly expressed in the oligodendrocyte lineage, regulates food intake by modulating hypothalamic neuronal activities. GPR17-null mice and mice with an oligodendrocyte-specific knockout of GPR17 have lean phenotypes on a high-fat diet, suggesting that GPR17 regulates body weight by way of oligodendrocytes. Downregulation of GPR17 results in activation of cAMP-protein kinase A (PKA) signaling in oligodendrocytes and upregulated expression of pyruvate dehydrogenase kinase 1 (PDK1), which promotes lactate production. Elevation of lactate activates AKT and STAT3 signaling in the hypothalamic neurons, leading to increased expression of Pomc and suppression of Agrp. Our findings uncover a critical role of oligodendrocytes in metabolic homeostasis, where GPR17 modulates the production of lactate, which, in turn, acts as a metabolic signal to regulate neuronal activity.

Growth Hormone Receptor Deletion Reduces the Density of Axonal Projections from Hypothalamic Arcuate Nucleus Neurons

The arcuate nucleus (ARH) is an important hypothalamic area for the homeostatic control of feeding and other metabolic functions. In the ARH, proopiomelanocortin- (POMC) and agouti-related peptide (AgRP)-expressing neurons play a key role in the central regulation of metabolism. These neurons are influenced by circulating factors, such as leptin and growth hormone (GH). The objective of the present study was to determine whether a direct action of GH on ARH neurons regulates the density of POMC and AgRP axonal projections to major postsynaptic targets. We studied POMC and AgRP axonal projections to the hypothalamic paraventricular (PVH), lateral (LHA) and dorsomedial (DMH) nuclei in leptin receptor (LepR)-deficient mice (Lepr^db/db), GH-deficient mice (Ghrhr^lit/lit) and in mice carrying specific ablations of GH receptor (GHR) either in LepR- or AgRP-expressing cells. Lepr^db/db mice presented reduction in the density of POMC innervation to the PVH compared to wild-type and Ghrhr^lit/lit mice. Additionally, both Lepr^db/db and Ghrhr^lit/lit mice showed reduced AgRP fiber density in the PVH, LHA and DMH. LepR GHR knockout mice showed decreased density of POMC innervation in the PVH and DMH, compared to control mice, whereas a reduction in the density of AgRP innervation was observed in all areas analyzed. Conversely, AgRP-specific ablation of GHR led to a significant reduction in AgRP projections to the PVH, LHA and DMH, without affecting POMC innervation. Our findings indicate that GH has direct trophic effects on the formation of POMC and AgRP axonal projections and provide additional evidence that GH regulates hypothalamic neurocircuits controlling energy homeostasis.

Incendiary Leptin

Leptin is a hormone released by adipose tissue that plays a key role in the control of energy homeostasis through its binding to leptin receptors (LepR), mainly expressed in the hypothalamus. Most scientific evidence points to leptin’s satiating effect being due to its dual capacity to promote the expression of anorexigenic neuropeptides and to reduce orexigenic expression in the hypothalamus. However, it has also been demonstrated that leptin can stimulate (i) thermogenesis in brown adipose tissue (BAT) and (ii) the browning of white adipose tissue (WAT). Since the demonstration of the importance of BAT in humans 10 years ago, its study has aroused great interest, mainly in the improvement of obesity-associated metabolic disorders through the induction of thermogenesis. Consequently, several strategies targeting BAT activation (mainly in rodent models) have demonstrated great potential to improve hyperlipidemias, hepatic steatosis, insulin resistance and weight gain, leading to an overall healthier metabolic profile. Here, we review the potential therapeutic ability of leptin to correct obesity and other metabolic disorders, not only through its satiating effect, but by also utilizing its thermogenic properties.

Estradiol and high fat diet associate with changes in gut microbiota in female ob/ob mice

Estrogens protect against diet-induced obesity in women and female rodents. For example, a lack of estrogens in postmenopausal women is associated with an increased risk of weight gain, cardiovascular diseases, low-grade inflammation, and cancer. Estrogens act with leptin to regulate energy homeostasis in females. Leptin-deficient mice (ob/ob) exhibit morbid obesity and insulin resistance. The gut microbiome is also critical in regulating metabolism. The present study investigates whether estrogens and leptin modulate gut microbiota in ovariectomized ob/ob (obese) or heterozygote (lean) mice fed high-fat diet (HFD) that received either 17β-Estradiol (E2) or vehicle implants. E2 attenuated weight gain in both genotypes. Moreover, both obesity (ob/ob mice) and E2 were associated with reduced gut microbial diversity. ob/ob mice exhibited lower species richness than control mice, while E2-treated mice had reduced evenness compared with vehicle mice. Regarding taxa, E2 was associated with an increased abundance of the S24-7 family, while leptin was associated with increases in Coriobacteriaceae, Clostridium and Lactobacillus. Some taxa were affected by both E2 and leptin, suggesting these hormones alter gut microbiota of HFD-fed female mice. Understanding the role of E2 and leptin in regulating gut microbiota will provide important insights into hormone-dependent metabolic disorders in women.

The pathogenesis of obesity

Body fat mass increases when energy intake exceeds energy expenditure. In the long term, a positive energy balance will result in obesity. The worldwide prevalence of obesity has increased dramatically, posing a serious threat to human health. Therefore, insight in the pathogenesis of obesity is important to identify novel prevention and treatment strategies. This review describes the physiology of energy expenditure and energy intake in the context of body weight gain in humans. We focus on the components of energy expenditure and the regulation of energy intake. Finally, we describe rare monogenetic causes leading to an impairment in central regulation of food intake and obesity.

Growth hormone regulates neuroendocrine responses to weight loss via AgRP neurons

Weight loss triggers important metabolic responses to conserve energy, especially via the fall in leptin levels. Consequently, weight loss becomes increasingly difficult with weight regain commonly occurring in most dieters. Here we show that central growth hormone (GH) signaling also promotes neuroendocrine adaptations during food deprivation. GH activates agouti-related protein (AgRP) neurons and GH receptor (GHR) ablation in AgRP cells mitigates highly characteristic hypothalamic and metabolic adaptations induced by weight loss. Thus, the capacity of mice carrying an AgRP-specific GHR ablation to save energy during food deprivation is impaired, leading to increased fat loss. Additionally, administration of a clinically available GHR antagonist (pegvisomant) attenuates the fall of whole-body energy expenditure of food-deprived mice, similarly as seen by leptin treatment. Our findings indicate GH as a starvation signal that alerts the brain about energy deficiency, triggering key adaptive responses to conserve limited fuel stores.

Reduction in food intake elicits neuroendocrine adaptations to counterregulate the negative energy balance, e.g. via reduction in leptin levels. Here, the authors identify an additional starvation signal, growth hormone (GH). Blocking GH receptor attenuates the fall of whole body energy expenditure during food deprivation in mice.

GEOFFREY HARRIS PRIZE LECTURE 2018: Novel pathways regulating neuroendocrine function, energy homeostasis and metabolism in humans

The discovery of leptin, an adipocyte-secreted hormone, set the stage for unraveling the mechanisms dictating energy homeostasis, revealing adipose tissue as an endocrine system that regulates appetite and body weight. Fluctuating leptin levels provide molecular signals to the brain regarding available energy reserves modulating energy homeostasis and neuroendocrine response in states of leptin deficiency and to a lesser extent in hyperleptinemic states. While leptin replacement therapy fails to provide substantial benefit in common obesity, it is an effective treatment for congenital leptin deficiency and states of acquired leptin deficiency such as lipodystrophy. Current evidence suggests that regulation of eating behavior in humans is not limited to homeostatic mechanisms and that the reward, attention, memory and emotion systems are involved, participating in a complex central nervous system network. It is critical to study these systems for the treatment of typical obesity. Although progress has been made, further studies are required to unravel the physiology, pathophysiology and neurobehavioral mechanisms underlying potential treatments for weight-related problems in humans.

Neuroanatomical Framework of the Metabolic Control of Reproduction

A minimum amount of energy is required for basic physiological processes, such as protein biosynthesis, thermoregulation, locomotion, cardiovascular function, and digestion. However, for reproductive function and survival of the species, extra energy stores are necessary. Production of sex hormones and gametes, pubertal development, pregnancy, lactation, and parental care all require energy reserves. Thus the physiological systems that control energy homeostasis and reproductive function coevolved in mammals to support both individual health and species subsistence. In this review, we aim to gather scientific knowledge produced by laboratories around the world on the role of the brain in integrating metabolism and reproduction. We describe essential neuronal networks, highlighting key nodes and potential downstream targets. Novel animal models and genetic tools have produced substantial advances, but critical gaps remain. In times of soaring worldwide obesity and metabolic dysfunction, understanding the mechanisms by which metabolic stress alters reproductive physiology has become crucial for human health.

A genome-wide detection of selection signatures in conserved and commercial pig breeds maintained in Poland

BACKGROUND

Identification of selection signatures can provide a direct insight into the mechanism of artificial selection and allow further disclosure of the candidate genes related to the animals' phenotypic variation. Domestication and subsequent long-time selection have resulted in extensive phenotypic changes in domestic pigs, involving a number of traits, like behavior, body composition, disease resistance, reproduction and coat color. In this study, based on genotypes obtained from PorcineSNP60 Illumina assay we attempt to detect both diversifying and within-breed selection signatures in 530 pigs belonging to four breeds: Polish Landrace, Puławska, Złotnicka White and Złotnicka Spotted, of which the last three are a subject of conservative breeding and substantially represent the native populations.

RESULTS

A two largely complementary statistical methods were used for signatures detection, including: pairwise F_ST and relative extended haplotype homozygosity (REHH) test. Breed-specific diversifying selection signals included several genes involved in processes connected with fertility, growth and metabolism which are potentially responsible for different phenotypes of the studied breeds. The diversifying selection signals also comprised PPARD gene that was previously found to have a large effect on the shape of the external ear in pigs or two genes encoding neuropeptide Y receptors (Y2 and Y5) involved in fat deposition and stress response which are important features differentiating the studied breeds. REHH statistics allowed detecting several within-breed selection signatures overlapping with genes connected with a range of functions including, among others: metabolic pathways, immune system response or implantation and development of the embryo.

CONCLUSIONS

The study provides many potential candidate genes with implication for traits selected in the individual breeds and gives strong basis for further studies aiming at identification of sources of variation among the studied pig breeds.

Neural Regulation of Bone and Bone Marrow

Bones provide both skeletal scaffolding and space for hematopoiesis in its marrow. Previous work has shown that these functions were tightly regulated by the nervous system. The central and peripheral nervous systems tightly regulate compact bone remodeling, its metabolism, and hematopoietic homeostasis in the bone marrow (BM). Accumulating evidence indicates that the nervous system, which fine-tunes inflammatory responses and alterations in neural functions, may regulate autoimmune diseases. Neural signals also influence the progression of hematological malignancies such as acute and chronic myeloid leukemias. Here, we review the interplay of the nervous system with bone, BM, and immunity, and discuss future challenges to target hematological diseases through modulation of activity of the nervous system.

Effects of Low Energy Availability on Reproductive Functions and Their Underlying Neuroendocrine Mechanisms

It is known that metabolic disturbances suppress reproductive functions in females. The mechanisms underlying metabolic and nutritional effects on reproductive functions have been established based on a large body of clinical and experimental data. From the 1980s to 1990s, it was revealed that disrupted gonadotropin-releasing hormone (GnRH) secretion is the main cause of reproductive impairments in metabolic and nutritional disorders. From the late 1990s to early 2000s, it was demonstrated that, in addition to their primary functions, some appetite- or metabolism-regulating factors affect GnRH secretion. Furthermore, in the early 2000s, kisspeptin, which is a potent positive regulator of GnRH secretion, was newly discovered, and it has been revealed that kisspeptin integrates the effects of metabolic status on GnRH neurons. Recent studies have shown that kisspeptin mediates at least some of the effects of appetite- and metabolism-regulating factors on GnRH neurons. Thus, kisspeptin might be a useful clinical target for treatments aimed at restoring reproductive functions in individuals with metabolic or nutritional disturbances, such as those who exercise excessively, experience marked weight loss, or suffer from eating disorders. This paper presents a review of what is currently known about the effects of metabolic status on reproductive functions and their underlying mechanisms by summarizing the available evidence.

Hypocretin as a Hub for Arousal and Motivation

The lateral hypothalamus is comprised of a heterogeneous mix of neurons that serve to integrate and regulate sleep, feeding, stress, energy balance, reward, and motivated behavior. Within these populations, the hypocretin/orexin neurons are among the most well studied. Here, we provide an overview on how these neurons act as a central hub integrating sensory and physiological information to tune arousal and motivated behavior accordingly. We give special attention to their role in sleep-wake states and conditions of hyper-arousal, as is the case with stress-induced anxiety. We further discuss their roles in feeding, drug-seeking, and sexual behavior, which are all dependent on the motivational state of the animal. We further emphasize the application of powerful techniques, such as optogenetics, chemogenetics, and fiber photometry, to delineate the role these neurons play in lateral hypothalamic functions.

Regulation of Hepatic Lipid Accumulation and Distribution by Agouti-Related Protein in Male Mice

Proper regulation of energy metabolism requires neurons in the central nervous system to respond dynamically to signals that reflect the body's energy reserve, and one such signal is leptin. Agouti-related protein (AgRP) is a hypothalamic neuropeptide that is markedly upregulated in leptin deficiency, a condition that is associated with severe obesity, diabetes, and hepatic steatosis. Because deleting AgRP in mice does not alter energy balance, we sought to determine whether AgRP plays an indispensable role in regulating energy and hepatic lipid metabolism in the sensitized background of leptin deficiency. We generated male mice that are deficient for both leptin and AgRP [double-knockout (DKO)]. DKO mice and ob/ob littermates had similar body weights, food intake, energy expenditure, and plasma insulin levels, although DKO mice surprisingly developed heightened hyperglycemia with advancing age. Overall hepatic lipid content was reduced in young prediabetic DKO mice, but not in the older diabetic counterparts. Intriguingly, however, both young and older DKO mice had an altered zonal distribution of hepatic lipids with reduced periportal lipid deposition. Moreover, leptin stimulated, whereas AgRP inhibited, hepatic sympathetic activity. Ablating sympathetic nerves to the liver, which primarily innervate the portal regions, produced periportal lipid accumulation in wild-type mice. Collectively, our results highlight AgRP as a regulator of hepatic sympathetic activity and metabolic zonation.

Analysis of association of gene variants with obesity traits in New Zealand European children at 6 years of age

Childhood obesity is a public health problem, which is associated with a long-term increased risk of cardiovascular disease and premature mortality. Several gene variants have previously been identified that have provided novel insights into biological factors that contribute to the development of obesity. As obesity tracks through childhood into adulthood, identification of the genetic factors for obesity in early life is important. The objective of this study was to identify putative associations between genetic variants and obesity traits in children at 6 years of age. We recruited 1208 children of mothers from the New Zealand centre of the international Screening for Pregnancy Endpoints (SCOPE) study. Eighty common genetic variants associated with obesity traits were evaluated by the Sequenom assay. Body mass index standardised scores (BMI z-scores) and percentage body fat (PBF; measured by bio-impedance assay (BIA)) were used as anthropometric measures of obesity. A positive correlation was found between BMI z-scores and PBF (p < 0.001, r = 0.756). Two subsets of gene variants were associated with BMI z-scores (HOXB5-rs9299, SH2B1-rs7498665, NPC1-rs1805081 and MSRA-rs545854) and PBF (TMEM18-rs6548238, NPY-rs17149106, ETV-rs7647305, NPY-rs16139, TIMELESS-rs4630333, FTO-rs9939609, UCP2-rs659366, MAP2K5-rs2241423 and FAIM2-rs7138803) in the genotype models. However, there was an absence of overlapping association between any of the gene variants with BMI z-scores and PBF. A further five variants were associated with BMI z-scores (TMEM18-rs6548238, FTO-rs9939609 and MC4R-rs17782313) and PBF (SH2B1-rs7498665 and FTO-rs1421085) once separated by genetic models (additive, recessive and dominant) of inheritance. This study has identified significant associations between numerous gene variants selected on the basis of prior association with obesity and obesity traits in New Zealand European children.

Connecting metabolism and gonadal function: Novel central neuropeptide pathways involved in the metabolic control of puberty and fertility

Albeit essential for perpetuation of species, reproduction is an energy-demanding function that can be adjusted to body metabolic status. Reproductive maturation and function can be suppressed in conditions of energy deficit, but can be altered also in situations of persistent energy excess, e.g., morbid obesity. This metabolic-reproductive integration, of considerable pathophysiological relevance to explain different forms of perturbed puberty and sub/infertility, is implemented by the concerted action of numerous central and peripheral regulators, which impinge at different levels of the hypothalamic-pituitary-gonadal (HPG) axis, permitting a tight fit between nutritional/energy status and gonadal function. We summarize here the major physiological mechanisms whereby nutritional and metabolic cues modulate the maturation and function of the HPG axis. We will focus on recent progress on the major central neuropeptide pathways, including kisspeptins, neurokinin B and the products of POMC and NPY neurons, which convey metabolic information to GnRH neurons, as major hierarchical hub of our reproductive brain.

Neuronal Control of Bone Remodeling

Although the brain is well established as a master regulator of homeostasis in peripheral tissues, central regulation of bone mass represents a novel and rapidly expanding field of study. This review examines the current understanding of central regulation of the skeleton, exploring several of the key pathways connecting brain to bone and their implications both in mice and the clinical setting. Our understanding of central bone regulation has largely progressed through examination of skeletal responses downstream of nutrient regulatory pathways in the hypothalamus. Mutations and modulation of these pathways, in cases such as leptin deficiency, induce marked bone phenotypes, which have provided vital insights into central bone regulation. These studies have identified several central neuropeptide pathways that stimulate well-defined changes in bone cell activity in response to changes in energy homeostasis. In addition, this work has highlighted the endocrine nature of the skeleton, revealing a complex cross talk that directly regulates other organ systems. Our laboratory has studied bone-active neuropeptide pathways and defined osteoblast-based actions that recapitulate central pathways linking bone, fat, and glucose homeostasis. Studies of neural control of bone have produced paradigm-shifting changes in our understanding of the skeleton and its relationship with the wider array of organ systems.

Neuropeptides in Obesity and Metabolic Disease

BACKGROUND

The global rise in the prevalence of obesity and associated comorbidities such as type 2 diabetes, cardiovascular disease, and cancer represents a major public health concern.

CONTENT

Studies in rodents with the use of global and targeted gene disruption, and mapping of neurocircuitry by using optogenetics and designer receptors exclusively activated by designer drugs (DREADDs) have greatly advanced our understanding of the neural control of body weight. In conjunction with analytical chemistry techniques involving classical immunoassays and mass spectrometry, many neuropeptides that are key to energy homeostasis have been identified. The actions of neuropeptides are diverse, from paracrine modulation of local neurotransmission to hormonal control of distant target organs.

SUMMARY

Multiple hormones, such as the adipocyte-derived leptin, insulin, and gut hormones, and nutrients signal peripheral energy state to the central nervous system. Neurons in distinct areas of the hypothalamus and brainstem integrate and translate this information by both direct inhibitory/excitatory projections and anorexigenic or orexigenic neuropeptides into actions on food intake and energy expenditure. The importance of these neuropeptides in human energy balance is most powerfully illustrated by genetic forms of obesity that involve neuropeptides such as melanocortin-4-receptor (MC4R) deficiency. Drugs that mimic the actions of neuropeptides are being tested for the treatment of obesity. Successful therapeutic strategies in obesity will require in-depth knowledge of the neuronal circuits they are working in, the downstream targets, and potential compensatory mechanisms.

EFFECTS OF METHAMPHETAMINE ON LOCOMOTOR ACTIVITY AND THALAMIC GENE EXPRESSION IN LEPTIN-DEFICIENT OBESE MICE

Leptin is an adipose-derived hormone that regulates energy balance. Leptin receptors are expressed in extrahypothalamic sites and several reports showed that leptin can influence feeding and locomotor behavior via direct actions on dopaminergic neurons. The leptin deficient mouse (ob/ob) has been used as an animal model of blunted leptin action, and presents with obesity and mild type 2 diabetes. We used ob/ob mice to study the effect of repeated 7-day methamphetamine (METH) administration analyzing locomotion, behavioral sensitization, and somatosensory thalamic mRNA expression of voltage-gated calcium channels and glutamatergic receptors using RT-PCR. We observed reduced METH-mediated responses in ob/ob mice associated with enhanced in mRNA expression of key voltage-gated and glutamate receptors in the somatosensory thalamus. Results described here are important for understanding the control of locomotion and thalamocortical excitability by leptin.

The role of leptin in health and disease

Leptin is a master regulator of energy balance and body adiposity. Additionally, leptin exerts important control on glucose homeostasis, thermogenesis, autonomic nervous system and neuroendocrine axes. In metabolic diseases, such as obesity and diabetes mellitus, leptin signaling may be compromised, indicating the important role of this hormone in the etiology and pathophysiological manifestations of these conditions. In the present manuscript, we reviewed important concepts of leptin signaling, as well as about the effects of leptin on several biologic functions. We also discussed the possible therapeutic use of leptin administration and how our current obesogenic environment contributes to the development of leptin resistance. Our objective was to provide a comprehensive and state-of-the-art review about the importance of leptin to maintain the homeostasis and during pathological conditions.

Novel genes involved in severe early-onset obesity revealed by rare copy number and sequence variants

Obesity is a multifactorial disorder with high heritability (50–75%), which is probably higher in early-onset and severe cases. Although rare monogenic forms and several genes and regions of susceptibility, including copy number variants (CNVs), have been described, the genetic causes underlying the disease still remain largely unknown. We searched for rare CNVs (>100kb in size, altering genes and present in <1/2000 population controls) in 157 Spanish children with non-syndromic early-onset obesity (EOO: body mass index >3 standard deviations above the mean at <3 years of age) using SNP array molecular karyotypes. We then performed case control studies (480 EOO cases/480 non-obese controls) with the validated CNVs and rare sequence variants (RSVs) detected by targeted resequencing of selected CNV genes (n = 14), and also studied the inheritance patterns in available first-degree relatives. A higher burden of gain-type CNVs was detected in EOO cases versus controls (OR = 1.71, p-value = 0.0358). In addition to a gain of the NPY gene in a familial case with EOO and attention deficit hyperactivity disorder, likely pathogenic CNVs included gains of glutamate receptors (GRIK1, GRM7) and the X-linked gastrin-peptide receptor (GRPR), all inherited from obese parents. Putatively functional RSVs absent in controls were also identified in EOO cases at NPY, GRIK1 and GRPR. A patient with a heterozygous deletion disrupting two contiguous and related genes, SLCO4C1 and SLCO6A1, also had a missense RSV at SLCO4C1 on the other allele, suggestive of a recessive model. The genes identified showed a clear enrichment of shared co-expression partners with known genes strongly related to obesity, reinforcing their role in the pathophysiology of the disease. Our data reveal a higher burden of rare CNVs and RSVs in several related genes in patients with EOO compared to controls, and implicate NPY, GRPR, two glutamate receptors and SLCO4C1 in highly penetrant forms of familial obesity.

Although there is strong evidence for a high genetic component of obesity, the underlying genetic causes are largely unknown, mostly due to the highly heterogeneous nature of the disorder. In this work, we have focused on the most severe end of the spectrum, severe obesity with early-onset in childhood, which is more likely due to genetic alterations. We screened for rare copy number variation (CNV) a sample of 157 Spanish children with early-onset obesity using molecular karyotypes and then studied the genes altered by CNVs in 480 cases and 480 non-obese controls. We identified a higher burden of gain-type CNVs in cases as well as several CNVs and sequence variants that were specific of the obese population. Interestingly, the genes identified shared co-expression partners with known obesity genes. Among those, the genes encoding the neuropeptide Y (NPY), two glutamate receptors (GRIK1, GRM7), the X-linked gastrin-peptide receptor (GRPR), and the organic anion transporter (SLCO4C1) are novel obesity candidate genes that may contribute to highly penetrant forms of familial obesity.