Cardiovascular response, feeding behavior and locomotor activity in mice lacking the NPY Y1 receptor

Sympathetic neuropeptide Y protects from obesity by sustaining thermogenic fat

Human mutations in neuropeptide Y (NPY) have been linked to high body mass index but not altered dietary patterns1. Here we uncover the mechanism by which NPY in sympathetic neurons2,3 protects from obesity. Imaging of cleared mouse brown and white adipose tissue (BAT and WAT, respectively) established that NPY+ sympathetic axons are a smaller subset that mostly maps to the perivasculature; analysis of single-cell RNA sequencing datasets identified mural cells as the main NPY-responsive cells in adipose tissues. We show that NPY sustains the proliferation of mural cells, which are a source of thermogenic adipocytes in both BAT and WAT4-6. We found that diet-induced obesity leads to neuropathy of NPY+ axons and concomitant depletion of mural cells. This defect was replicated in mice with NPY abrogated from sympathetic neurons. The loss of NPY in sympathetic neurons whitened interscapular BAT, reducing its thermogenic ability and decreasing energy expenditure before the onset of obesity. It also caused adult-onset obesity of mice fed on a regular chow diet and rendered them more susceptible to diet-induced obesity without increasing food consumption. Our results indicate that, relative to central NPY, peripheral NPY produced by sympathetic nerves has the opposite effect on body weight by sustaining energy expenditure independently of food intake.

A Maternal High-Fat Diet Causes Anxiety-Related Behaviors by Altering Neuropeptide Y1 Receptor and Hippocampal Volumes in Rat Offspring: the Potential Effect of N-Acetylcysteine

The children of obese mothers are known to have a high risk of obesity and metabolic disease and are prone to developing cognitive deficits, although the underlying mechanism is not yet fully understood. This study investigated the relationship between neuropeptide Y1 receptor (NPY1R) and anxiety-like behaviors in the hippocampi of male rat offspring exposed to maternal obesity and the potential neuroprotective effects of N-acetylcysteine (NAC). A maternal obesity model was created using a high-fat (60% k/cal) diet. NAC (150 mg/kg) was administered by intragastric gavage for 25 days in both the NAC and obesity + NAC (ObNAC) groups. All male rat offspring were subjected to behavioral testing on postnatal day 28, the end of the experiment. Stereological analysis was performed on hippocampal sections, while NPY1R expression was determined using immunohistochemical methods. Stereological data indicated significant decreases in the total volume of the hippocampus and CA1 and dentate gyrus (DG) regions in the obese (Ob) group (p < 0.01). Decreased NPY1R expression was observed in the Ob group hippocampus (p < 0.01). At behavioral assessments, the Ob group rats exhibited increased anxiety and less social interaction, although the ObNAC group rats exhibited stronger responses than the Ob group (p < 0.01). The study results show that NAC attenuated anxiety-like behaviors and NPY1R expression and also protected hippocampal volume against maternal obesity. The findings indicate that a decrease in NPY1R-positive neurons in the hippocampus of male rats due to maternal conditions may be associated with increased levels of anxiety and a lower hippocampal volume. Additionally, although there is no direct evidence, maintenance of NPY1R expression by NAC may be critical for regulating maternal obesity-induced anxiety-related behaviors and hippocampal structure.

Tiered Sympathetic Control of Cardiac Function Revealed by Viral Tracing and Single Cell Transcriptome Profiling

The cell bodies of postganglionic sympathetic neurons innervating the heart primarily reside in the stellate ganglion (SG), alongside neurons innervating other organs and tissues. Whether cardiac-innervating stellate ganglionic neurons (SGNs) exhibit diversity and distinction from those innervating other tissues is not known. To identify and resolve the transcriptomic profiles of SGNs innervating the heart we leveraged retrograde tracing techniques using adeno-associated virus (AAV) expressing fluorescent proteins (GFP or Td-tomato) with single cell RNA sequencing. We investigated electrophysiologic, morphologic, and physiologic roles for subsets of cardiac-specific neurons and found that three of five adrenergic SGN subtypes innervate the heart. These three subtypes stratify into two subpopulations; high (NA1a) and low (NA1b and NA1c) Npy-expressing cells, exhibit distinct morphological, neurochemical, and electrophysiologic characteristics. In physiologic studies in transgenic mouse models modulating NPY signaling, we identified differential control of cardiac responses by these two subpopulations to high and low stress states. These findings provide novel insights into the unique properties of neurons responsible for cardiac sympathetic regulation, with implications for novel strategies to target specific neuronal subtypes for sympathetic blockade in cardiac disease.

Targeting appetite and satiety in diabetes and obesity, via G protein-coupled receptors

Type 2 diabetes and obesity have reached pandemic proportions throughout the world, so much so that the World Health Organisation coined the term "Globesity" to help encapsulate the magnitude of the problem. G protein-coupled receptors (GPCRs) are highly tractable drug targets due to their wide involvement in all aspects of physiology and pathophysiology, indeed, GPCRs are the targets of approximately 30% of the currently approved drugs. GPCRs are also broadly involved in key physiologies that underlie type 2 diabetes and obesity including feeding reward, appetite and satiety, regulation of blood glucose levels, energy homeostasis and adipose function. Despite this, only two GPCRs are the target of approved pharmaceuticals for treatment of type 2 diabetes and obesity. In this review we discuss the role of these, and select other candidate GPCRs, involved in various facets of type 2 diabetic or obese pathophysiology, how they might be targeted and the potential reasons why pharmaceuticals against these targets have not progressed to clinical use. Finally, we provide a perspective on the current development pipeline of anti-obesity drugs that target GPCRs.

The impact of adolescent nicotine exposure on alcohol use during adulthood: The role of neuropeptides

Nicotine and alcohol abuse and co-dependence represent major public health crises. Indeed, previous research has shown that the prevalence of alcoholism is higher in smokers than in non-smokers. Adolescence is a susceptible period of life for the initiation of nicotine and alcohol use and the development of nicotine-alcohol codependence. However, there is a limited number of pharmacotherapeutic agents to treat addiction to nicotine or alcohol alone. Notably, there is no effective medication to treat this comorbid disorder. This chapter aims to review the early nicotine use and its impact on subsequent alcohol abuse during adolescence and adulthood as well as the role of neuropeptides in this comorbid disorder. The preclinical and clinical findings discussed in this chapter will advance our understanding of this comorbid disorder's neurobiology and lay a foundation for developing novel pharmacotherapies to treat nicotine and alcohol codependence.

Regulation of Pancreatic β-Cell Function by the NPY System

The neuropeptide Y (NPY) system has been recognized as one of the most critical molecules in the regulation of energy homeostasis and glucose metabolism. Abnormal levels of NPY have been shown to contribute to the development of metabolic disorders including obesity, cardiovascular diseases, and diabetes. NPY centrally promotes feeding and reduces energy expenditure, while the other family members, peptide YY (PYY) and pancreatic polypeptide (PP), mediate satiety. New evidence has uncovered additional functions for these peptides that go beyond energy expenditure and appetite regulation, indicating a more extensive function in controlling other physiological functions. In this review, we will discuss the role of the NPY system in the regulation of pancreatic β-cell function and its therapeutic implications for diabetes.

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.

Neuropeptide Y Acts Directly on Cartilage Homeostasis and Exacerbates Progression of Osteoarthritis Through NPY2R

Neuropeptide Y (NPY) is known to regulate bone homeostasis; however, its functional role as a risk factor during osteoarthritis (OA) remains elusive. In this study, we aim to investigate the direct effect of NPY on degradation of cartilage and progression of OA and explore the molecular events involved. NPY was overexpressed in human OA cartilage accompanied with increased expression of NPY1 receptor (NPY1R) and NPY2 receptor (NPY2R). Stressors such as cold exposure resulted in the peripheral release of NPY from sympathetic nerves, which in turn promoted upregulation of NPY and NPY2R in articular cartilage in vivo. Intra-articular administration of NPY significantly promoted chondrocyte hypertrophy and cartilage matrix degradation, with a higher OARSI score than that of control mice, whereas inhibition of NPY2R but not NPY1R with its specific antagonist remarkably ameliorated NPY-mediated effects. Moreover, NPY activated mTORC1 pathway in articular chondrocytes, whereas the administration of rapamycin (an mTORC1 inhibitor) in vitro abrogated NPY-mediated effects. Mechanistically, mTORC1 downstream kinase S6K1 interacted with and phosphorylated SMAD1/5/8 and promoted SMAD4 nuclear translocation, resulting in upregulation of Runx2 expression to promote chondrocyte hypertrophy and cartilage degradation. In conclusion, our findings provided the direct evidence and the crucial role of NPY in cartilage homeostasis. © 2020 American Society for Bone and Mineral Research.

A role for NPY-NPY2R signaling in albuminuric kidney disease

Neuropeptide Y (NPY) is implicated in many pathological conditions including obesity, diabetes, and insulin resistance. However, a pathogenic role of NPY in kidney disease has not been described. We found that NPY is produced by the podocyte in the glomerulus, and this production decreases in renal disease, in contrast to an increase in circulating NPY levels. In the glomerulus, NPY signals via the NPY receptor 2 (NPY2R) and modulates PI3K, MAPK, and NFAT signaling, along with RNA processing and cell migration and, if prolonged, predicted nephrotoxicity. The pharmacological inhibition of NPY-NPY2R signaling also protected against albuminuria and kidney disease in a mouse model of glomerulosclerosis, suggesting that inhibiting this pathway may be therapeutically beneficial in the prevention of kidney disease.

Albuminuria is an independent risk factor for the progression to end-stage kidney failure, cardiovascular morbidity, and premature death. As such, discovering signaling pathways that modulate albuminuria is desirable. Here, we studied the transcriptomes of podocytes, key cells in the prevention of albuminuria, under diabetic conditions. We found that Neuropeptide Y (NPY) was significantly down-regulated in insulin-resistant vs. insulin-sensitive mouse podocytes and in human glomeruli of patients with early and late-stage diabetic nephropathy, as well as other nondiabetic glomerular diseases. This contrasts with the increased plasma and urinary levels of NPY that are observed in such conditions. Studying NPY-knockout mice, we found that NPY deficiency in vivo surprisingly reduced the level of albuminuria and podocyte injury in models of both diabetic and nondiabetic kidney disease. In vitro, podocyte NPY signaling occurred via the NPY2 receptor (NPY2R), stimulating PI3K, MAPK, and NFAT activation. Additional unbiased proteomic analysis revealed that glomerular NPY-NPY2R signaling predicted nephrotoxicity, modulated RNA processing, and inhibited cell migration. Furthermore, pharmacologically inhibiting the NPY2R in vivo significantly reduced albuminuria in adriamycin-treated glomerulosclerotic mice. Our findings suggest a pathogenic role of excessive NPY-NPY2R signaling in the glomerulus and that inhibiting NPY-NPY2R signaling in albuminuric kidney disease has therapeutic potential.

The Fight Against Obesity Escalates: New Drugs on the Horizon and Metabolic Implications

PURPOSE OF REVIEW

There is currently a steep rise in the global prevalence of obesity. Pharmaceutical therapy is a valuable component of conservative obesity therapy. Herein, medications currently in the phase of preclinical or clinical testing are reviewed, along with an overview of the mechanisms that regulate energy intake and expenditure. In addition, the current and potential future directions of obesity drug therapy are discussed.

RECENT FINDINGS

Although the current arsenal of obesity pharmacotherapy is limited, a considerable number of agents that exert their actions through a variety of pharmacodynamic targets and mechanisms are in the pipeline. This expansion shapes a potential near future of obesity conservative management, characterized by tailored combined therapeutic regimens, targeting not only weight loss but also improved overall health outcomes. The progress regarding the elucidation of the mechanisms which regulate the bodily energy equilibrium has led to medications which mimic hormonal adaptations that follow bariatric surgery, in the quest for a "Medical bypass." These, combined with agents which could increase energy expenditure, point to a brilliant future in the conservative treatment of obesity.

Nesfatin-1 in cardiovascular orchestration: From bench to bedside

Since the discovery of Nesfatin-1 in 2006, intensive research was finalized to further and deeper investigate the precise physiological functions of the peptide at both central and peripheral levels, rapidly enriching the knowledge regarding this intriguing molecule. Nesfatin-1 is a hypothalamic peptide generated via the post-translational processing of its precursor Nucleobindin 2, a protein supposed to play a role in many biological processes thanks to its ability to bind calcium and to interact with different intracellular proteins. Nesfatin-1 is mainly known for its anorexic properties, but it also controls water intake and glucose homeostasis. Recent experimental evidences describe the peptide as a possible direct/indirect orchestrator of central and peripheral cardiovascular control. A specific Nesfatin-1 receptor still remains to be identified although numerous studies suggest that the peptide activates extra- and intracellular regulatory pathways by involving several putative binding sites. The present paper was designed to systematically review the latest findings about Nesfatin-1, focusing on its cardiovascular regulatory properties under normal and physiopathological conditions. The hope is to provide the conceptual basis to consider Nesfatin-1 not only as a pleiotropic neuroendocrine molecule, but also as a homeostatic modulator of the cardiovascular function and with a crucial role in cardiovascular diseases.

Sustained NPY signaling enables AgRP neurons to drive feeding

Artificial stimulation of Agouti-Related Peptide (AgRP) neurons promotes intense food consumption, yet paradoxically during natural behavior these cells are inhibited before feeding begins. Previously, to reconcile these observations, we showed that brief stimulation of AgRP neurons can generate hunger that persists for tens of minutes, but the mechanisms underlying this sustained hunger drive remain unknown (Chen et al., 2016). Here we show that Neuropeptide Y (NPY) is uniquely required for the long-lasting effects of AgRP neurons on feeding behavior. We blocked the ability of AgRP neurons to signal through AgRP, NPY, or GABA, and then stimulated these cells using a paradigm that mimics their natural regulation. Deletion of NPY, but not AgRP or GABA, abolished optically-stimulated feeding, and this was rescued by NPY re-expression selectively in AgRP neurons. These findings reveal a unique role for NPY in sustaining hunger in the interval between food discovery and consumption.

Activation of Agrp neurons modulates memory-related cognitive processes in mice

Hypothalamic Agrp neurons are critical regulators of food intake in adult mice. In addition to food intake, these neurons have been involved in other cognitive processes, such as the manifestation of stereotyped behaviors. Here, we evaluated the extent to which Agrp neurons modulate mouse behavior in spatial memory-related tasks. We found that activation of Agrp neurons did not affect spatial learning but altered behavioral flexibility using a modified version of the Barnes Maze task. Furthermore, using the Y-maze test to probe working memory, we found that chemogenetic activation of Agrp neurons reduced spontaneous alternation behavior mediated by the neuropeptide Y receptor-5 signaling. These findings suggest novel functional properties of Agrp neurons in memory-related cognitive processes.

Glucocorticoids, genes and brain function

The identification of key genes in transcriptomic data constitutes a huge challenge. Our review of microarray reports revealed 88 genes whose transcription is consistently regulated by glucocorticoids (GCs), such as cortisol, corticosterone and dexamethasone, in the brain. Replicable transcriptomic data were combined with biochemical and physiological data to create an integrated view of the effects induced by GCs. The most frequently reported genes were Errfi1 and Ddit4. Their up-regulation was associated with the altered transcription of genes regulating growth factor and mTORC1 signaling (Gab1, Tsc22d3, Dusp1, Ndrg2, Ppp5c and Sesn1) and progression of the cell cycle (Ccnd1, Cdkn1a and Cables1). The GC-induced reprogramming of cell function involves changes in the mRNA level of genes responsible for the regulation of transcription (Klf9, Bcl6, Klf15, Tle3, Cxxc5, Litaf, Tle4, Jun, Sox4, Sox2, Sox9, Irf1, Sall2, Nfkbia and Id1) and the selective degradation of mRNA (Tob2). Other genes are involved in the regulation of metabolism (Gpd1, Aldoc and Pdk4), actin cytoskeleton (Myh2, Nedd9, Mical2, Rhou, Arl4d, Osbpl3, Arhgef3, Sdc4, Rdx, Wipf3, Chst1 and Hepacam), autophagy (Eva1a and Plekhf1), vesicular transport (Rhob, Ehd3, Vps37b and Scamp2), gap junctions (Gjb6), immune response (Tiparp, Mertk, Lyve1 and Il6r), signaling mediated by thyroid hormones (Thra and Sult1a1), calcium (Calm2), adrenaline/noradrenaline (Adcy9 and Adra1d), neuropeptide Y (Npy1r) and histamine (Hdc). GCs also affected genes involved in the synthesis of polyamines (Azin1) and taurine (Cdo1). The actions of GCs are restrained by feedback mechanisms depending on the transcription of Sgk1, Fkbp5 and Nr3c1. A side effect induced by GCs is increased production of reactive oxygen species. Available data show that the brain's response to GCs is part of an emergency mode characterized by inactivation of non-core activities, restrained inflammation, restriction of investments (growth), improved efficiency of energy production and the removal of unnecessary or malfunctioning cellular components to conserve energy and maintain nutrient supply during the stress response.

Islet neuropeptide Y receptors are functionally conserved and novel targets for the preservation of beta-cell mass

AIMS

Two unmet therapeutic strategies for diabetes treatment are prevention of beta-cell death and stimulation of beta-cell replication. Our aim was to characterize the role of neuropeptide Y receptors in the control of beta-cell mass.

MATERIALS AND METHODS

We used endogenous and selective agonists of the NPY receptor system to explore its role in the prevention of beta-cell apoptosis and proliferation in islets isolated from both mouse and human donors. We further explored the intra-cellular signalling cascades involved, using chemical inhibitors of key signalling pathways. As proof of principle we designed a long-acting analogue of [Leu³¹ Pro³⁴ ]-NPY, an agonist of the islet-expressed Y receptors, to determine if targeting this system could preserve beta-cell mass in vivo.

RESULTS

Our data reveal that NPY Y1, 4 and 5 receptor activation engages a generalized and powerful anti-apoptotic pathway that protects mouse and human islets from damage. These anti-apoptotic effects were dependent on stimulating a Gαi-PLC-PKC signalling cascade, which prevented cytokine-induced NFkB signalling. NPY receptor activation functionally protected islets by restoring glucose responsiveness following chemically induced injury in both species. NPY receptor activation attenuated beta-cell apoptosis, preserved functional beta-cell mass and attenuated the hyperglycaemic phenotype in a low-dose streptozotocin model of diabetes.

CONCLUSION

Taken together, our observations identify the islet Y receptors as promising targets for the preservation of beta-cell mass. As such, targeting these receptors could help to maintain beta-cell mass in both type 1 and type 2 diabetes, and may also be useful for improving islet transplantation outcomes.

Effects of Intracerebroventricular Administration of Neuropeptide Y on Metabolic Gene Expression and Energy Metabolism in Male Rats

Neuropeptide Y (NPY) is an important neurotransmitter in the control of energy metabolism. Several studies have shown that obesity is associated with increased levels of NPY in the hypothalamus. We hypothesized that the central release of NPY has coordinated and integrated effects on energy metabolism in different tissues, resulting in increased energy storage and decreased energy expenditure (EE). We first investigated the acute effects of an intracerebroventricular (ICV) infusion of NPY on gene expression in liver, brown adipose tissue, soleus muscle, and sc and epididymal white adipose tissue (WAT). We found increased expression of genes involved in gluconeogenesis and triglyceride secretion in the liver already 2-hour after the start of the NPY administration. In brown adipose tissue, the expression of thermogenic genes was decreased. In sc WAT, the expression of genes involved in lipogenesis was increased, whereas in soleus muscle, the expression of lipolytic genes was decreased after ICV NPY. These findings indicate that the ICV infusion of NPY acutely and simultaneously increases lipogenesis and decreases lipolysis in different tissues. Subsequently, we investigated the acute effects of ICV NPY on locomotor activity, respiratory exchange ratio, EE, and body temperature. The ICV infusion of NPY increased locomotor activity, body temperature, and EE as well as respiratory exchange ratio. Together, these results show that an acutely increased central availability of NPY results in a shift of metabolism towards lipid storage and an increased use of carbohydrates, while at the same time increasing activity, EE, and body temperature.

Neuropeptide Y (NPY) as a therapeutic target for neurodegenerative diseases

Neuropeptide Y (NPY) and NPY receptors are widely expressed in the mammalian central nervous system. Studies in both humans and rodent models revealed that brain NPY levels are altered in some neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and Machado-Joseph disease. In this review, we will focus on the roles of NPY in the pathological mechanisms of these disorders, highlighting NPY as a neuroprotective agent, as a neural stem cell proliferative agent, as an agent that increases trophic support, as a stimulator of autophagy and as an inhibitor of excitotoxicity and neuroinflammation. Moreover, the effect of NPY in some clinical manifestations commonly observed in Alzheimer's disease, Parkinson's disease, Huntington's disease and Machado-Joseph disease, such as depressive symptoms and body weight loss, are also discussed. In conclusion, this review highlights NPY system as a potential therapeutic target in neurodegenerative diseases.

GPCRs Direct Germline Development and Somatic Gonad Function in Planarians

Planarians display remarkable plasticity in maintenance of their germline, with the ability to develop or dismantle reproductive tissues in response to systemic and environmental cues. Here, we investigated the role of G protein-coupled receptors (GPCRs) in this dynamic germline regulation. By genome-enabled receptor mining, we identified 566 putative planarian GPCRs and classified them into conserved and phylum-specific subfamilies. We performed a functional screen to identify NPYR-1 as the cognate receptor for NPY-8, a neuropeptide required for sexual maturation and germ cell differentiation. Similar to NPY-8, knockdown of this receptor results in loss of differentiated germ cells and sexual maturity. NPYR-1 is expressed in neuroendocrine cells of the central nervous system and can be activated specifically by NPY-8 in cell-based assays. Additionally, we screened the complement of GPCRs with expression enriched in sexually reproducing planarians, and identified an orphan chemoreceptor family member, ophis, that controls differentiation of germline stem cells (GSCs). ophis is expressed in somatic cells of male and female gonads, as well as in accessory reproductive tissues. We have previously shown that somatic gonadal cells are required for male GSC specification and maintenance in planarians. However, ophis is not essential for GSC specification or maintenance and, therefore, defines a secondary role for planarian gonadal niche cells in promoting GSC differentiation. Our studies uncover the complement of planarian GPCRs and reveal previously unappreciated roles for these receptors in systemic and local (i.e., niche) regulation of germ cell development.

Genome-wide analysis of the planarian Schmidtea mediterranea reveals a complement of over 550 G protein-coupled receptors, including two with critical roles in germline development.

G protein-coupled receptors (GPCRs) are the largest and most versatile family of cell-surface receptors. They play critical roles in various cellular and physiological systems and have emerged as a leading group of therapeutic targets. Due to their structural and functional conservation across animals, much has been learned about GPCRs from studies in laboratory models. Here, we performed genome-wide receptor mining to identify and categorize the complement of GPCR-encoding genes in the planarian Schmidtea mediterranea, an emerging model organism for regeneration and germ cell biology. We then conducted two studies implicating planarian GPCRs in the regulation of reproductive function. First, we found the receptor component of a central neuropeptide Y signaling pathway and demonstrated its involvement in the systemic control of reproductive development. Next, we showed that a novel chemoreceptor family member is expressed in somatic cells of the planarian gonads and directs germ cell maturation via the niche. We predict that future studies on the hundreds of other planarian GPCRs identified in this work will not only help us understand the conserved role of these receptors in various physiological pathways but also pave the way for identification of novel therapeutic targets in parasitic relatives of the planarian.

Osteoblastic Actions of the Neuropeptide Y System to Regulate Bone and Energy Homeostasis

Neural pathways are now a well-appreciated factor in the regulatory milieu controlling the maintenance of bone mass. A number of neural pathways from the brain to bone have been identified. These pathways often involve elements of the energy homeostatic apparatus, indicating links between the regulation of bone metabolism and energy balance. Neuropeptide Y is one such factor that co-regulates these two processes. Initial studies outlined the skeletal actions of NPY from within the brain and the interactions with energy homeostatic processes. However, in recent years, an appreciation for the actions of NPY within bone cells has expanded. Cells of the osteoblastic lineage express both NPY ligand and a cognate receptor NPY, Y1R. Murine studies have demonstrated that both ligand and receptor actively control bone mass and osteoblast activity and interact with mechanical signals to integrate with the local loading environment. Local NPY signalling regulates osteoprogenitor production and differentiation, to cover the entire osteoblastic lineage. In addition, several recent studies have demonstrated extra-skeletal actions of osteoblastic NPY signalling, to regulate energy expenditure and with it adiposity, and in a separate study, to control release of a factor-controlling beta cell mass and insulin production/release and with it glucose tolerance. Thus, osteoblastic neuropeptide production and signalling illustrates the rapidly widening sphere of influence of skeletal tissue, and suggests a far more complex and interconnected physiology then is currently appreciated.

Broiler chicken adipose tissue dynamics during the first two weeks post-hatch

Selection of broiler chickens for growth has led to increased adipose tissue accretion. To investigate the post-hatch development of adipose tissue, the abdominal, clavicular, and subcutaneous adipose tissue depots were collected from broiler chicks at 4 and 14 days post-hatch. As a percent of body weight, abdominal fat increased (P<0.001) with age. At day 4, clavicular and subcutaneous fat depots were heavier (P<0.003) than abdominal fat whereas at day 14, abdominal and clavicular weighed more (P<0.003) than subcutaneous fat. Adipocyte area and diameter were greater in clavicular and subcutaneous than abdominal fat at 4 and 14 days post-hatch (P<0.001). Glycerol-3-phosphate dehydrogenase (G3PDH) activity increased (P<0.001) in all depots from day 4 to 14, and at both ages was greatest in subcutaneous, intermediate in clavicular, and lowest in abdominal fat (P<0.05). In clavicular fat, peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer binding protein (CEBP)α, CEBPβ, fatty acid synthase (FASN), fatty acid binding protein 4 (FABP4), lipoprotein lipase (LPL), neuropeptide Y (NPY), and NPY receptor 5 (NPYR5) mRNA increased and NPYR2 mRNA decreased from day 4 to 14 (P<0.001). Thus, there are site-specific differences in broiler chick adipose development, with larger adipocytes and greater G3PDH activity in subcutaneous fat at day 4, more rapid growth of abdominal fat, and clavicular fat intermediate for most traits. Adipose tissue expansion was accompanied by changes in gene expression of adipose-associated factors.

The use of animal models to decipher physiological and neurobiological alterations of anorexia nervosa patients

Extensive studies were performed to decipher the mechanisms regulating feeding due to the worldwide obesity pandemy and its complications. The data obtained might be adapted to another disorder related to alteration of food intake, the restrictive anorexia nervosa. This multifactorial disease with a complex and unknown etiology is considered as an awful eating disorder since the chronic refusal to eat leads to severe, and sometimes, irreversible complications for the whole organism, until death. There is an urgent need to better understand the different aspects of the disease to develop novel approaches complementary to the usual psychological therapies. For this purpose, the use of pertinent animal models becomes a necessity. We present here the various rodent models described in the literature that might be used to dissect central and peripheral mechanisms involved in the adaptation to deficient energy supplies and/or the maintenance of physiological alterations on the long term. Data obtained from the spontaneous or engineered genetic models permit to better apprehend the implication of one signaling system (hormone, neuropeptide, neurotransmitter) in the development of several symptoms observed in anorexia nervosa. As example, mutations in the ghrelin, serotonin, dopamine pathways lead to alterations that mimic the phenotype, but compensatory mechanisms often occur rendering necessary the use of more selective gene strategies. Until now, environmental animal models based on one or several inducing factors like diet restriction, stress, or physical activity mimicked more extensively central and peripheral alterations decribed in anorexia nervosa. They bring significant data on feeding behavior, energy expenditure, and central circuit alterations. Animal models are described and criticized on the basis of the criteria of validity for anorexia nervosa.

DPP4 in cardiometabolic disease: recent insights from the laboratory and clinical trials of DPP4 inhibition

The discovery of incretin-based medications represents a major therapeutic advance in the pharmacological management of type 2 diabetes mellitus (T2DM), as these agents avoid hypoglycemia, weight gain, and simplify the management of T2DM. Dipeptidyl peptidase-4 (CD26, DPP4) inhibitors are the most widely used incretin-based therapy for the treatment of T2DM globally. DPP4 inhibitors are modestly effective in reducing HbA1c (glycated hemoglobin) (≈0.5%) and while these agents were synthesized with the understanding of the role that DPP4 plays in prolonging the half-life of incretins such as glucagon-like peptide-1 and gastric inhibitory peptide, it is now recognized that incretins are only one of many targets of DPP4. The widespread expression of DPP4 on blood vessels, myocardium, and myeloid cells and the nonenzymatic function of CD26 as a signaling and binding protein, across a wide range of species, suggest a teleological role in cardiovascular regulation and inflammation. Indeed, DPP4 is upregulated in proinflammatory states including obesity, T2DM, and atherosclerosis. Consistent with this maladaptive role, the effects of DPP4 inhibition seem to exert a protective role in cardiovascular disease at least in preclinical animal models. Although 2 large clinical trials suggest a neutral effect on cardiovascular end points, current limitations of performing trials in T2DM over a limited time horizon on top of maximal medical therapy must be acknowledged before rendering judgment on the cardiovascular efficacy of these agents. This review will critically review the science of DPP4 and the effects of DPP4 inhibitors on the cardiovascular system.

Hypothalamic Agrp neurons drive stereotypic behaviors beyond feeding

The nervous system evolved to coordinate flexible goal-directed behaviors by integrating interoceptive and sensory information. Hypothalamic Agrp neurons are known to be crucial for feeding behavior. Here, however, we show that these neurons also orchestrate other complex behaviors in adult mice. Activation of Agrp neurons in the absence of food triggers foraging and repetitive behaviors, which are reverted by food consumption. These stereotypic behaviors that are triggered by Agrp neurons are coupled with decreased anxiety. NPY5 receptor signaling is necessary to mediate the repetitive behaviors after Agrp neuron activation while having minor effects on feeding. Thus, we have unmasked a functional role for Agrp neurons in controlling repetitive behaviors mediated, at least in part, by neuropeptidergic signaling. The findings reveal a new set of behaviors coupled to the energy homeostasis circuit and suggest potential therapeutic avenues for diseases with stereotypic behaviors.

Regulation of energy homeostasis by the NPY system

Obesity develops when energy intake exceeds energy expenditure over time. Numerous neurotransmitters, hormones, and factors have been implicated to coordinately control energy homeostasis, centrally and peripherally. However, the neuropeptide Y (NPY) system has emerged as the one with the most critical functions in this process. While NPY centrally promotes feeding and reduces energy expenditure, peptide YY (PYY) and pancreatic polypeptide (PP), the other family members, mediate satiety. Importantly, recent research has uncovered additional functions for these peptides that go beyond the simple feeding/satiety circuits and indicate a more extensive function in controlling energy homeostasis. In this review, we will discuss the actions of the NPY system in the regulation of energy balance, with a particular focus on energy expenditure.

Neuropeptide Y reduces the expression of PLCB2, PLCD1 and selected PLC genes in cultured human endothelial cells

Endothelial cells (EC) are the first elements exposed to mediators circulating in the bloodstream, and react to stimulation with finely tuned responses mediated by different signal transduction pathways, leading the endothelium to adapt. Neuropeptide Y (NPY), the most abundant peptide in heart and brain, is mainly involved in the neuroendocrine regulation of the stress response. The regulatory roles of NPY depend on many factors, including its enzymatic processing, receptor subtypes and related signal transduction systems, including the phosphoinositide (PI) pathway and related phospholipase C (PI-PLC) family of enzymes. The panel of expression of PI-PLC enzymes differs comparing quiescent versus differently stimulated human EC. Growing evidences indicate that the regulation of the expression of PLC genes, which codify for PI-PLC enzymes, might act as an additional mechanism of control of the PI signal transduction pathway. NPY was described to potentiate the activation of PI-PLC enzymes in different cell types, including EC. In the present experiments, we stimulated human umbilical vein EC using different doses of NPY in order to investigate a possible role upon the expression PLC genes. NPY reduced the overall transcription of PLC genes, excepting for PLCE. The most significant effects were observed for PLCB2 and PLCD1, both isoforms recruited by means of G-proteins and G-protein-coupled receptors. NPY behavior was comparable with other PI-PLC interacting molecules that, beside the stimulation of phospholipase activity, also affect the upcoming enzymes' production acting upon gene expression. That might represent a mode to regulate the activity of PI-PLC enzymes after activation.

Can neuropeptides treat obesity? A review of neuropeptides and their potential role in the treatment of obesity

Obesity is a major worldwide public health issue. The physiological systems that regulate body weight are thus of great interest as targets for anti-obesity agents. Peptidergic systems are critical to the regulation of energy homeostasis by key regions in the hypothalamus and brainstem. A number of neuropeptide systems have therefore been investigated as potential treatments for obesity. Blocking orexigenic peptide signals such as neuropeptide Y, melanin-concentrating hormone, orexins, relaxin-3 and galanin-like peptide or stimulating anorectic signalling pathways used by peptides such as the melanocortins, ciliary neurotrophic factor and brain-derived neurotrophic factor, are approaches that have shown some promise, but which have also highlighted possible concerns. Manipulation of central peptidergic systems poses a number of therapeutic problems, including brain access and side effects. Given that the homeostatic defence of body weight may limit the effectiveness of any single-target therapy developed, a combination therapy approach may offer the best hope for the effective prevention and treatment of obesity.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Cardiac autonomic imbalance by social stress in rodents: understanding putative biomarkers

Exposure to stress or traumatic events can lead to the development of depression and anxiety disorders. In addition to the debilitating consequences on mental health, patients with psychiatric disorders also suffer from autonomic imbalance, making them susceptible to a variety of medical disorders. Emerging evidence utilizing spectral analysis of heart rate variability (HRV), a reliable non-invasive measure of cardiovascular autonomic regulation, indicates that patients with depression and various anxiety disorders (i.e., panic, social, generalized anxiety disorders, and post traumatic stress disorder) are characterized by decreased HRV. Social stressors in rodents are ethologically relevant experimental stressors that recapitulate many of the dysfunctional behavioral and physiological changes that occur in psychological disorders. In this review, evidence from clinical studies and preclinical stress models identify putative biomarkers capable of precipitating the comorbidity between disorders of the mind and autonomic dysfunction. Specifically, the role of corticotropin releasing factor, neuropeptide Y and inflammation are investigated. The impetus for this review is to highlight stress-related biomarkers that may prove critical in the development of autonomic imbalance in stress -related psychiatric disorders.

Cloning, phylogeny, and regional expression of a Y5 receptor mRNA in the brain of the sea lamprey (Petromyzon marinus)

The NPY receptors known as Y receptors are classified into three subfamilies, Y1, Y2, and Y5, and are involved in different physiological functions. The Y5 receptor is the only member of the Y5 subfamily, and it is present in all vertebrate groups, except for teleosts. Both molecular and pharmacological studies show that Y5 receptor is highly conserved during vertebrate evolution. Furthermore, this receptor is widely expressed in the mammalian brain, including the hypothalamus, where it is thought to take part in feeding and homeostasis regulation. Lampreys belong to the agnathan lineage, and they are thought to have branched out between the two whole-genome duplications that occurred in vertebrates. Therefore, they are in a key position for studies on the evolution of gene families in vertebrates. Here we report the cloning, phylogeny, and brain expression pattern of the sea lamprey Y5 receptor. In phylogenetic studies, the lamprey Y5 receptor clusters in a basal position, together with Y5 receptors of other vertebrates. The mRNA of this receptor is broadly expressed in the lamprey brain, being especially abundant in hypothalamic areas. Its expression pattern is roughly similar to that reported for other vertebrates and parallels the expression pattern of the Y1 receptor subtype previously described by our group, as it occurs in mammals. Altogether, these results confirm that a Y5 receptor is present in lampreys, thus being highly conserved during the evolution of vertebrates, and suggest that it is involved in many brain functions, the only known exception being teleosts.

Peptides and food intake

The mechanisms for controlling food intake involve mainly an interplay between gut, brain, and adipose tissue (AT), among the major organs. Parasympathetic, sympathetic, and other systems are required for communication between the brain satiety center, gut, and AT. These neuronal circuits include a variety of peptides and hormones, being ghrelin the only orexigenic molecule known, whereas the plethora of other factors are inhibitors of appetite, suggesting its physiological relevance in the regulation of food intake and energy homeostasis. Nutrients generated by food digestion have been proposed to activate G-protein-coupled receptors on the luminal side of enteroendocrine cells, e.g., the L-cells. This stimulates the release of gut hormones into the circulation such as glucagon-like peptide-1 (GLP-1), oxyntomodulin, pancreatic polypeptides, peptide tyrosine tyrosine, and cholecystokinin, which inhibit appetite. Ghrelin is a peptide secreted from the stomach and, in contrast to other gut hormones, plasma levels decrease after a meal and potently stimulate food intake. Other circulating factors such as insulin and leptin relay information regarding long-term energy stores. Both hormones circulate at proportional levels to body fat content, enter the CNS proportionally to their plasma levels, and reduce food intake. Circulating hormones can influence the activity of the arcuate nucleus (ARC) neurons of the hypothalamus, after passing across the median eminence. Circulating factors such as gut hormones may also influence the nucleus of the tractus solitarius (NTS) through the adjacent circumventricular organ. On the other hand, gastrointestinal vagal afferents converge in the NTS of the brainstem. Neural projections from the NTS, in turn, carry signals to the hypothalamus. The ARC acts as an integrative center, with two major subpopulations of neurons influencing appetite, one of them coexpressing neuropeptide Y and agouti-related protein (AgRP) that increases food intake, whereas the other subpopulation coexpresses pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript that inhibits food intake. AgRP antagonizes the effects of the POMC product, α-melanocyte-stimulating hormone (α-MSH). Both populations project to areas important in the regulation of food intake, including the hypothalamic paraventricular nucleus, which also receives important inputs from other hypothalamic nuclei.

Peripheral cardiac sympathetic hyperactivity in cardiovascular disease: role of neuropeptides

High levels of sympathetic drive in several cardiovascular diseases including postmyocardial infarction, chronic congestive heart failure and hypertension are reinforced through dysregulation of afferent input and central integration of autonomic balance. However, recent evidence suggests that a significant component of sympathetic hyperactivity may also reside peripherally at the level of the postganglionic neuron. This has been studied in depth using the spontaneously hypertensive rat, an animal model of genetic essential hypertension, where larger neuronal calcium transients, increased release and impaired reuptake of norepinephrine in neurons of the stellate ganglia lead to a significant tachycardia even before hypertension has developed. The release of additional sympathetic cotransmitters during high levels of sympathetic drive can also have deleterious consequences for peripheral cardiac parasympathetic neurotransmission even in the presence of β-adrenergic blockade. Stimulation of the cardiac vagus reduces heart rate, lowers myocardial oxygen demand, improves coronary blood flow, and independently raises ventricular fibrillation threshold. Recent data demonstrates a direct action of the sympathetic cotransmitters neuropeptide Y (NPY) and galanin on the ability of the vagus to release acetylcholine and control heart rate. Moreover, there is as a strong correlation between plasma NPY levels and coronary microvascular function in patients with ST-elevation myocardial infarction being treated with primary percutaneous coronary intervention. Antagonists of the NPY receptors Y1 and Y2 may be therapeutically beneficial both acutely during myocardial infarction and also during chronic heart failure and hypertension. Such medications would be expected to act synergistically with β-blockers and implantable vagus nerve stimulators to improve patient outcome.

Replacement of Thr32 and Gln34 in the C-terminal neuropeptide Y fragment 25-36 by cis-cyclobutane and cis-cyclopentane β-amino acids shifts selectivity toward the Y(4) receptor

Neuropeptide Y (NPY) and pancreatic polypeptide (PP) control central and peripheral processes by activating the G protein coupled receptors YxR (x = 1, 2, 4, 5). We present analogs of the C-terminal fragments 25-36 and 32-36 of NPY and PP containing (1R,2S)-cyclobutane (βCbu) or (1R,2S)-cyclopentane (βCpe) β-amino acids, which display exclusively Y4R affinity. In particular, [βCpe(34)]-NPY-(25-36) is a Y4R selective partial agonist (EC50 41 ± 6 nM, Emax 71%) that binds Y4R with a Ki of 10 ± 2 nM and a selectivity >100-fold relative to Y1R and Y2R and >50-fold relative to Y5R. Comparably, [Y(32), βCpe(34)]-NPY(PP)-(32-36) selectively binds and activates Y4R (EC50 94 ± 21 nM, Emax 73%). The NMR structure of [βCpe(34)]-NPY-(25-36) in dodecylphosphatidylcholine micelles shows a short helix at residues 27-32, while the C-terminal segment R(33)βCpe(34)R(35)Y(36) is extended. The biological properties of the βCbu- or βCpe-containing NPY and PP C-terminal fragments encourage the future application of these β-amino acids in the synthesis of selective Y4R ligands.

Neuropeptide y gates a stress-induced, long-lasting plasticity in the sympathetic nervous system

Acute stress evokes the fight-or-flight reflex, which via release of the catecholamine hormones affects the function of every major organ. Although the reflex is transient, it has lasting consequences that produce an exaggerated response when stress is reexperienced. How this change is encoded is not known. We investigated whether the reflex affects the adrenal component of the sympathetic nervous system, a major branch of the stress response. Mice were briefly exposed to the cold-water forced swim test (FST) which evoked an increase in circulating catecholamines. Although this hormonal response was transient, the FST led to a long-lasting increase in the catecholamine secretory capacity measured amperometrically from chromaffin cells and in the expression of tyrosine hydroxylase. A variety of approaches indicate that these changes are regulated postsynaptically by neuropeptide Y (NPY), an adrenal cotransmitter. Using immunohistochemistry, RT-PCR, and NPY(GFP) BAC mice, we find that NPY is synthesized by all chromaffin cells. Stress failed to increase secretory capacity in NPY knock-out mice. Genetic or pharmacological interference with NPY and Y1 (but not Y2 or Y5) receptor signaling attenuated the stress-induced change in tyrosine hydroxylase expression. These results indicate that, under basal conditions, adrenal signaling is tonically inhibited by NPY, but stress overrides this autocrine negative feedback loop. Because acute stress leads to a lasting increase in secretory capacity in vivo but does not alter sympathetic tone, these postsynaptic changes appear to be an adaptive response. We conclude that the sympathetic limb of the stress response exhibits an activity-dependent form of long-lasting plasticity.

The brain–adipose axis: A review of involvement of molecules

Many molecules are involved in the regulation of feeding behavior, and they and their receptors are located in the brain hypothalamus and adipocytes. On the basis of evidence suggesting an association between the brain and adipose tissue, we propose the concept of the brain-adipose axis. This model consists of (l) the expression of endogenous molecules and/or their receptors in the hypothalamus and peripheral adipose tissue, (2) the function of these molecules as appetite regulators in the brain, (3) their existence in the general circulation as secreted proteins and (4) the physiological affects of these molecules on fat cell size and number. These molecules can be divided into two anorexigenic and orexigenic classes. In adipose tissue, all orexigenic molecules possess adipogenic activity, and almost all anorexigenic molecules suppress fat cell proliferation. Although the manner, in which they present in the circulating blood connect the brain and peripheral adipocytes, remains to be well-organized, these observations suggest the positive feedback axis affecting molecules in the hypothalamus and adipose tissue. Analysis of the disturbance and dysregulation of this axis might promote the development of new anti-obesity drugs useful in treating the metabolic syndrome.

Bone-specific overexpression of NPY modulates osteogenesis

OBJECTIVES

Neuropeptide Y (NPY) is a peptide involved in the regulation of appetite and energy homeostasis. Genetic data indicates that NPY decreases bone formation via central and peripheral activities. NPY is produced by various cell types including osteocytes and osteoblasts and there is evidence suggesting that peripheral NPY is important for regulation of bone formation. We sought to investigate the role of bone-derived NPY in bone metabolism.

METHODS

We generated a mouse where NPY was over-expressed specifically in mature osteoblasts and osteocytes (Col2.3NPY) and characterized the bone phenotype of these mice in vivo and in vitro.

RESULTS

Trabecular and cortical bone volume was reduced in 3-month-old animals, however bone formation rate and osteoclast activity were not significantly changed. Calvarial osteoblast cultures from Col2.3NPY mice also showed reduced mineralization and expression of osteogenic marker genes.

CONCLUSIONS

Our data suggest that osteoblast/osteocyte-derived NPY is capable of altering osteogenesis in vivo and in vitro and may represent an important source of NPY for regulation of bone formation. However, it is possible that other peripheral sources of NPY such as the sympathetic nervous system and vasculature also contribute to peripheral regulation of bone turnover.

Nodose ganglia-modulatory effects on respiration

The key role of the vagus nerves in the reflex control of breathing is generally accepted. Cardiopulmonary vagal receptors and their afferent connection with the medullary respiratory centers secures the proper regulatory feedback. Section of the vagi at the midcervical level interrupts primary vagal reflexes and those due to activation of lung afferents by neuroactive substances. In this context the present review focuses on the reflex contribution of the inferior (nodose) vagal ganglia to the respiratory pattern, considering that this structure contains perikarya of vagal afferent neurons which house neurotransmitters, neuropeptides and neurochemical substances. In experimental animals with removed sensory input from the lungs (midcervical vagotomy) the following evidence was reported. Transient respiratory suppression in the form of apnoea, occurring after systemic injection of serotonin, adenosine triphosphate and anandamide (N-arachidonoyl-ethanolamine-endogenous cannabinoid neurotransmitter), which was abrogated by nodose ganglionectomy. Preserved nodose-NTS connection conditioned respiratory depression affecting the timing component of the breathing pattern evoked by N-6-cyclopentyl-adenosine (CPA) and inhibition of both respiratory constituents induced by NPY. Stimulatory effect of NPY13-36 on tidal volume required nodosal connection. The cardiovascular effects of majority of the tested substances occurred beyond the nodose ganglia (with exclusion of serotonin and anandamide).

Nesfatin-1 as a novel cardiac peptide: identification, functional characterization, and protection against ischemia/reperfusion injury

Nesfatin-1 is an anorexic nucleobindin-2 (NUCB2)-derived hypothalamic peptide. It controls feeding behavior, water intake, and glucose homeostasis. If intracerebrally administered, it induces hypertension, thus suggesting a role in central cardiovascular control. However, it is not known whether it is able to directly control heart performance. We aimed to verify the hypothesis that, as in the case of other hypothalamic satiety peptides, Nesfatin-1 acts as a peripheral cardiac modulator. By western blotting and QT-PCR, we identified the presence of both Nesfatin-1 protein and NUCB2 mRNA in rat cardiac extracts. On isolated and Langendorff-perfused rat heart preparations, we found that exogenous Nesfatin-1 depresses contractility and relaxation without affecting coronary motility. These effects did not involve Nitric oxide, but recruited the particulate guanylate cyclase (pGC) known as natriuretic peptide receptor A (NPR-A), protein kinase G (PKG) and extracellular signal-regulated kinases1/2 (ERK1/2). Co-immunoprecipitation and bioinformatic analyses supported an interaction between Nesfatin-1 and NPR-A. Lastly, we preliminarily observed, through post-conditioning experiments, that Nesfatin-1 protects against ischemia/reperfusion (I/R) injury by reducing infarct size, lactate dehydrogenase release, and postischemic contracture. This protection involves multiple prosurvival kinases such as PKCε, ERK1/2, signal transducer and activator of transcription 3, and mitochondrial K(ATP) channels. It also ameliorates contractility recovery. Our data indicate that: (1) the heart expresses Nesfatin-1, (2) Nesfatin-1 directly affects myocardial performance, possibly involving pGC-linked NPR-A, the pGC/PKG pathway, and ERK1/2, (3) the peptide protects the heart against I/R injury. Results pave the way to include Nesfatin-1 in the neuroendocrine modulators of the cardiac function, also encouraging the clarification of its clinical potential in the presence of nutrition-dependent physio-pathologic cardiovascular diseases.

Action of Neurotransmitter: A Key to Unlock the AgRP Neuron Feeding Circuit

The current obesity epidemic and lack of efficient therapeutics demand a clear understanding of the mechanism underlying body weight regulation. Despite intensive research focus on obesity pathogenesis, an effective therapeutic strategy to treat and cure obesity is still lacking. Exciting studies in last decades have established the importance of hypothalamic agouti-related protein-expressing neurons (AgRP neurons) in the regulation of body weight homeostasis. AgRP neurons are both required and sufficient for feeding regulation. The activity of AgRP neurons is intricately regulated by nutritional hormones as well as synaptic inputs from upstream neurons. Changes in AgRP neuron activity lead to alterations in the release of mediators, including neuropeptides Neuropeptide Y (NPY) and AgRP, and fast-acting neurotransmitter GABA. Recent studies based on mouse genetics, novel optogenetics, and designer receptor exclusively activated by designer drugs have identified a critical role for GABA release from AgRP neurons in the parabrachial nucleus and paraventricular hypothalamus in feeding control. This review will summarize recent findings about AgRP neuron-mediated control of feeding circuits with a focus on the role of neurotransmitters. Given the limited knowledge on feeding regulation, understanding the action of neurotransmitters may be a key to unlock neurocircuitry that governs feeding.

The role of NMDA receptors in human eating behavior: evidence from a case of anti-NMDA receptor encephalitis

Research in animal models has implicated N-methyl-D-aspartate (NMDA) receptors (NMDARs) in the control of food intake. Until now, these findings have been not replicated in humans. Here we describe a 22-year-old woman with anti-NMDAR encephalitis and no prior neurological or psychiatric history. Her clinical course was marked by successive eating disorders: anorexia followed by hyperphagia. We propose that, much as they do in other animals, NMDARs in humans interact with the neuroendocrine, homeostatic, and reward systems controlling food intake in the central and peripheral nervous system structures related to feeding and satiety.

Molecules affecting hypothalamic control of core body temperature in response to calorie intake

Core body temperature (CBT) and calorie intake are main components of energy homeostasis and two important regulators of health, longevity, and aging. In homeotherms, CBT can be influenced by calorie intake as food deprivation or calorie restriction (CR) lowers CBT whereas feeding has hyperthermic effects. The finding that in mice CBT prolonged lifespan independently of CR, suggested that the mechanisms modulating CBT may represent important regulators of aging. Here we summarize the current knowledge on the signaling molecules and their receptors that participate in the regulation of CBT responses to calorie intake. These include hypothalamic neuropeptides regulating feeding but also energy expenditure via modulation of thermogenesis. We also report studies indicating that nutrient signals can contribute to regulation of CBT by direct action on hypothalamic preoptic warm-sensitive neurons that in turn regulate adaptive thermogenesis and hence CBT. Finally, we show the role played by two orphans G protein-coupled receptor: GPR50 and GPR83, that were recently demonstrated to regulate temperature-dependent energy expenditure.

Distribution of Y-receptors in murine lingual epithelia

Peptide hormones and their cognate receptors belonging to neuropeptide Y (NPY) family mediate diverse biological functions in a number of tissues. Recently, we discovered the presence of the gut satiation peptide YY (PYY) in saliva of mice and humans and defined its role in the regulation of food intake and body weight maintenance. Here we report the systematic analysis of expression patterns of all NPY receptors (Rs), Y1R, Y2R, Y4R, and Y5R in lingual epithelia in mice. Using four independent assays, immunohistochemistry, in situ hybridization, immunocytochemistry and RT PCR, we show that the morphologically different layers of the keratinized stratified epithelium of the dorsal layer of the tongue express Y receptors in a very distinctive yet overlapping pattern. In particular, the monolayer of basal progenitor cells expresses both Y1 and Y2 receptors. Y1Rs are present in the parabasal prickle cell layer and the granular layer, while differentiated keratinocytes display abundant Y5Rs. Y4Rs are expressed substantially in the neuronal fibers innervating the lamina propria and mechanoreceptors. Basal epithelial cells positive for Y2Rs respond robustly to PYY(3-36) by increasing intracellular Ca(2+) suggesting their possible functional interaction with salivary PYY. In taste buds of the circumvallate papillae, some taste receptor cells (TRCs) express YRs localized primarily at the apical domain, indicative of their potential role in taste perception. Some of the YR-positive TRCs are co-localized with neuronal cell adhesion molecule (NCAM), suggesting that these TRCs may have synaptic contacts with nerve terminals. In summary, we show that all YRs are abundantly expressed in multiple lingual cell types, including epithelial progenitors, keratinocytes, neuronal dendrites and TRCs. These results suggest that these receptors may be involved in the mediation of a wide variety of functions, including proliferation, differentiation, motility, taste perception and satiation.

Y1 and Y5 receptors are both required for the regulation of food intake and energy homeostasis in mice

Neuropeptide Y (NPY) acting in the hypothalamus is one of the most powerful orexigenic agents known. Of the five known Y receptors, hypothalamic Y1 and Y5 have been most strongly implicated in mediating hyperphagic effects. However, knockout of individual Y1 or Y5 receptors induces late-onset obesity – and Y5 receptor knockout also induces hyperphagia, possibly due to redundancy in functions of these genes. Here we show that food intake in mice requires the combined actions of both Y1 and Y5 receptors. Germline Y1Y5 ablation in Y1Y5^−/− mice results in hypophagia, an effect that is at least partially mediated by the hypothalamus, since mice with adult-onset Y1Y5 receptor dual ablation targeted to the paraventricular nucleus (PVN) of the hypothalamus (Y1Y5^Hyp/Hyp) also exhibit reduced spontaneous or fasting-induced food intake when fed a high fat diet. Interestingly, despite hypophagia, mice with germline or hypothalamus-specific Y1Y5 deficiency exhibited increased body weight and/or increased adiposity, possibly due to compensatory responses to gene deletion, such as the decreased energy expenditure observed in male Y1Y5^−/− animals relative to wildtype values. While Y1 and Y5 receptors expressed in other hypothalamic areas besides the PVN – such as the dorsomedial nucleus and the ventromedial hypothalamus – cannot be excluded from having a role in the regulation of food intake, these studies demonstrate the pivotal, combined role of both Y1 and Y5 receptors in the mediation of food intake.

Food deprivation explains effects of mouthbrooding on ovaries and steroid hormones, but not brain neuropeptide and receptor mRNAs, in an African cichlid fish

Feeding behavior and reproduction are coordinately regulated by the brain via neurotransmitters, circulating hormones, and neuropeptides. Reduced feeding allows animals to engage in other behaviors important for fitness, including mating and parental care. Some fishes cease feeding for weeks at a time in order to provide care to their young by brooding them inside the male or female parent's mouth. Maternal mouthbrooding is known to impact circulating hormones and subsequent reproductive cycles, but neither the full effects of food deprivation nor the neural mechanisms are known. Here we ask what effects mouthbrooding has on several physiological processes including gonad and body mass, brain neuropeptide and receptor gene expression, and circulating steroid hormones in a mouthbrooding cichlid species, Astatotilapia burtoni. We ask whether any observed changes can be explained by food deprivation, and show that during mouthbrooding, ovary size and circulating levels of androgens and estrogens match those seen during food deprivation. Levels of gonadotropin-releasing hormone 1 (GnRH1) mRNA in the brain were low in food-deprived females compared to controls and in mouthbrooding females compared to gravid females. Levels of mRNA encoding two peptides involved in regulating feeding, hypocretin and cholecystokinin, were increased in the brains of food-deprived females. Brain mRNA levels of two receptors, GnRH receptor 2 and NPY receptor Y8c, were elevated in mouthbrooding females compared to the fed condition, but NPY receptor Y8b mRNA was differently regulated by mouthbrooding. These results suggest that many, but not all, of the characteristic physiological changes that occur during mouthbrooding are consequences of food deprivation.

Molecular analysis of central feeding regulation by neuropeptide Y (NPY) neurons with NPY receptor small interfering RNAs (siRNAs)

Hypothalamic neuropeptides play important roles in central feeding behavior. Among them, neuropeptide Y (NPY) has the strongest orexigenic action. It is synthesized in NPY-expressing neurons in the arcuate nucleus (ARC), which projects to other nuclei, mainly to the paraventricular nucleus (PVN). PVN, which possesses NPY-Y1, -Y2 and -Y4, -Y5 receptors, is considered as feeding center for central feeding behavior. Herein I review recent results on feeding behavior obtained by gene knockdown technologies. The small interfering RNA (siRNA) plasmid-based vectors, which drive transcription of siRNA by U6 RNA polymerase III promoter to produce knockdown of the NPY and its receptor (Y1, Y2, Y4 and Y5) genes, were stereotaxically injected into mouse ARC and PVN. Feeding behaviors were measured for 6days after siRNA vector injection. NPY and its receptor mRNA levels were decreased, which were measured by RT-PCR and in situ hybridization, and simultaneous decrease in their proteins was also detected in separate nuclei by immunohistochemistry. In the NPY system, decrease in NPY, Y1 and Y5 expressions in specialized nuclei diminished central feeding behavior, whereas decrease in Y2 or Y4 expression in both ARC or PVN did not affect feeding behavior. Thus, specialized change in expressions of NPY and its receptors (especially Y1 and Y5) are important for regulation of endogenous feeding behavior in central regulation. Further analysis of NPY receptors may provide better understanding of feeding behavior and of potential therapeutic targets.

Hypothalamic neuropeptides and the regulation of appetite

Neuropeptides released by hypothalamic neurons play a major role in the regulation of feeding, acting both within the hypothalamus, and at other appetite regulating centres throughout the brain. Where classical neurotransmitters signal only within synapses, neuropeptides diffuse over greater distances affecting both nearby and distant neurons expressing the relevant receptors, which are often extrasynaptic. As well as triggering a behavioural output, neuropeptides also act as neuromodulators: altering the response of neurons to both neurotransmitters and circulating signals of nutrient status. The mechanisms of action of hypothalamic neuropeptides with established roles in feeding, including melanin-concentrating hormone (MCH), the orexins, α-melanocyte stimulating hormone (α-MSH), agouti-gene related protein (AgRP), neuropeptide Y, and oxytocin, are reviewed in this article, with emphasis laid on both their effects on appetite regulating centres throughout the brain, and on examining the evidence for their physiological roles. In addition, evidence for the involvement of several putative appetite regulating hypothalamic neuropeptides is assessed including, ghrelin, cocaine and amphetamine-regulated transcript (CART), neuropeptide W and the galanin-like peptides. This article is part of a Special Issue entitled 'Central control of Food Intake'.

Central functions of neuropeptide Y in mood and anxiety disorders

INTRODUCTION

Neuropeptide Y (NPY) is a highly conserved neuropeptide belonging to the pancreatic polypeptide family. Its potential role in the etiology and pathophysiology of mood and anxiety disorders has been extensively studied. NPY also has effects on feeding behavior, ethanol intake, sleep regulation, tissue growth and remodeling. Findings from animal studies have delineated the physiological and behavioral effects mediated by specific NPY receptor subtypes, of which Y1 and Y2 are the best understood.

AREAS COVERED

Physiological roles and alterations of the NPYergic system in anxiety disorders, depression, posttraumatic stress disorder (PTSD), alcohol dependence and epilepsy. For each disorder, studies in animal models and human investigations are outlined and discussed, focusing on behavior, neurophysiology, genetics and potential for novel treatment targets.

EXPERT OPINION

The wide implications of NPY in psychiatric disorders such as depression and PTSD make the NPYergic system a promising target for the development of novel therapeutic interventions. These include intranasal NPY administration, currently under study, and the development of agonists and antagonists targeting NPY receptors. Therefore, we are proposing that via this mode of administration, NPY might exert CNS therapeutic actions without untoward systemic effects. Future work will show if this is a feasible approach.

Central and peripheral mechanisms of the NPY system in the regulation of bone and adipose tissue

Skeletal research is currently undergoing a period of marked expansion. The boundaries of "bone" research are being re-evaluated and with this, a growing recognition of a more complex and interconnected biology than previously considered. One aspect that has become the focus of particular attention is the relationship between bone and fat homeostasis. Evidence from a number of avenues indicates that bone and adipose regulation are both related and interdependent. This review examines the neuropeptide Y (NPY) system, known to exert powerful control over both bone and fat tissue. The actions of this system are characterized by signaling both within specific nuclei of the hypothalamus and also the target tissues, mediated predominantly through two G-protein coupled receptors (Y1 and Y2). In bone tissue, elevated NPY levels act consistently to repress osteoblast activity. Moreover, both central Y2 receptor and osteoblastic Y1 receptor signaling act similarly to repress bone formation. Conversely, loss of NPY expression or receptor signaling induces increased osteoblast activity and bone mass in both cortical and cancellous envelopes. In fat tissue, NPY action is more complex. Energy homeostasis is powerfully altered by elevations in hypothalamic NPY, resulting in increases in fat accretion and body-wide energy conservation, through the action of locally expressed Y1 receptors, while local Y2 receptors act to inhibit NPY-ergic tone. Loss of central NPY expression has a markedly reduced effect, consistent with a physiological drive to promote fat accretion. In fat tissue, NPY and Y1 receptors act to promote lipogenesis, consistent with their roles in the brain. Y2 receptors expressed in adipocytes also act in this manner, showing an opposing action to their role in the hypothalamus. While direct investigation of these processes has yet to be completed, these responses appear to be interrelated to some degree. The starvation-based signal of elevated central NPY inducing marked inhibition of osteoblast activity, whilst promoting fat accretion, indicating skeletal tissue is a component of the energy conservation system. Moreover, when NPY expression is reduced, consistent with high calorie intake and weight gain, bone formation is stimulated, strengthening the skeleton. In conclusion, NPY acts to regulate both bone and fat tissue in a coordinated manner, and remains a strong candidate for mediating interactions between these two tissues.

Peptides and their potential role in the treatment of diabetes and obesity

It is estimated that 347 million people worldwide have diabetes and that over 1.5 billion adults worldwide are overweight. Predictions suggest these rates are increasing. Diabetes is a common complication in overweight and obese subjects, and in 2004, an estimated 3.4 million people died from consequences of high blood sugar. Thus, there is great interest in revealing the physiological systems that regulate body weight and blood sugar. Several peptidergic systems within the central nervous system and the periphery regulate energy homeostasis. A number of these systems have been investigated as potential treatments for obesity and the metabolic syndrome. However, manipulation of peptidergic systems poses many problems. This review discusses the peptidergic systems currently attracting research interest for their clinical potential to treat obesity. We consider first neuropeptides in the brain, including the orexigenic neuropeptide Y and melanin-concentrating hormone, and anorectic factors such as the melanocortins, ciliary neurotrophic factor, and neuromedin U. We subsequently discuss the utility of targeting peripheral gut peptides, including pancreatic polypeptide, peptide YY, amylin, and the gastric hormone ghrelin. Also, we analyze the evidence that these factors or drugs based on them may be therapeutically useful, while considering the disadvantages of using such peptides in a clinical context.