MECHANISMS IN ENDOCRINOLOGY: The physiology of neuronostatin

In 2008, the first evidence of a new hormone called neuronostatin was published. The hormone was discovered using a bioinformatic method and found to originate from the same preprohormone as somatostatin. This small peptide hormone of 13 amino acids and a C-terminal amidation was soon found to exert pleiotropic physiological effects. In animal studies, neuronostatin has been shown to reduce food intake and delay gastric emptying and gastrointestinal transit. Furthermore, neuronostatin has been shown to affect glucose metabolism by increasing glucagon secretion during situations when glucose concentrations are low. Additionally, neuronostatin has been shown to affect neural tissue and cardiomyocytes by suppressing cardiac contractility. The effects of neuronostatin have not yet been delineated in humans, but if the effects found in animal studies translate to humans it could position neuronostatin as a promising target in the treatment of obesity, hypertension and diabetes. In this review, we describe the discovery of neuronostatin and the current understanding of its physiological role and potential therapeutic applicability.

The hypoxia response and nutritional peptides

Hypoxia controls metabolism at several levels, e.g., via mitochondrial ATP production, glucose uptake and glycolysis. Hence it is likely that hypoxia also affects the action and/or production of many peptide hormones linked to food intake and appetite control. Many of those are produced in the gastrointestinal tract, endocrine pancreas, adipose tissue, and selective areas in the brain which modulate and concert their actions. However, the complexity of the hypoxia response and the links to peptides/hormones involved in food intake and appetite control in the different organs are not well known. This review summarizes the role of the hypoxia response and its effects on major peptides linked to appetite regulation, nutrition and metabolism.

Discrete TrkB-expressing neurons of the dorsomedial hypothalamus regulate feeding and thermogenesis

Mutations in the TrkB neurotrophin receptor lead to profound obesity in humans, and expression of TrkB in the dorsomedial hypothalamus (DMH) is critical for maintaining energy homeostasis. However, the functional implications of TrkB-fexpressing neurons in the DMH (DMHTrkB) on energy expenditure are unclear. Additionally, the neurocircuitry underlying the effect of DMHTrkB neurons on energy homeostasis has not been explored. In this study, we show that activation of DMHTrkB neurons leads to a robust increase in adaptive thermogenesis and energy expenditure without altering heart rate or blood pressure, while silencing DMHTrkB neurons impairs thermogenesis. Furthermore, we reveal neuroanatomically and functionally distinct populations of DMHTrkB neurons that regulate food intake or thermogenesis. Activation of DMHTrkB neurons projecting to the raphe pallidus (RPa) stimulates thermogenesis and increased energy expenditure, whereas DMHTrkB neurons that send collaterals to the paraventricular hypothalamus (PVH) and preoptic area (POA) inhibit feeding. Together, our findings provide evidence that DMHTrkB neuronal activity plays an important role in regulating energy expenditure and delineate distinct neurocircuits that underly the separate effects of DMHTrkB neuronal activity on food intake and thermogenesis.

Appetite Regulation of TLR4-Induced Inflammatory Signaling

Appetite is the basis for obtaining food and maintaining normal metabolism. Toll-like receptor 4 (TLR4) is an important receptor expressed in the brain that induces inflammatory signaling after activation. Inflammation is considered to affect the homeostatic and non-homeostatic systems of appetite, which are dominated by hypothalamic and mesolimbic dopamine signaling. Although the pathological features of many types of inflammation are known, their physiological functions in appetite are largely unknown. This review mainly addresses several key issues, including the structures of the homeostatic and non-homeostatic systems. In addition, the mechanism by which TLR4-induced inflammatory signaling contributes to these two systems to regulate appetite is also discussed. This review will provide potential opportunities to develop new therapeutic interventions that control appetite under inflammatory conditions.

Upregulation of Mir342 in Diet-Induced Obesity Mouse and the Hypothalamic Appetite Control

In obesity and type 2 diabetes, numerous genes are differentially expressed, and microRNAs are involved in transcriptional regulation of target mRNAs, but miRNAs critically involved in the appetite control are not known. Here, we identified upregulation of miR-342-3p and its host gene Evl in brain and adipose tissues in C57BL/6 mice fed with high fat-high sucrose (HFHS) chow by RNA sequencing. Mir342 (-/-) mice fed with HFHS chow were protected from obesity and diabetes. The hypothalamic arcuate nucleus neurons co-express Mir342 and EVL. The percentage of activated NPY⁺pSTAT3⁺ neurons were reduced, while POMC⁺pSTAT3⁺ neurons increased in Mir342 (-/-) mice, and they demonstrated the reduction of food intake and amelioration of metabolic phenotypes. Snap25 was identified as a major target gene of miR-342-3p and the reduced expression of Snap25 may link to functional impairment hypothalamic neurons and excess of food intake. The inhibition of miR-342-3p may be a potential candidate for miRNA-based therapy.

Glutamatergic projections from homeostatic to hedonic brain nuclei regulate intake of highly palatable food

Food intake is a complex behavior regulated by discrete brain nuclei that integrate homeostatic nutritional requirements with the hedonic properties of food. Homeostatic feeding (i.e. titration of caloric intake), is typically associated with hypothalamic brain nuclei, including the paraventricular nucleus of the hypothalamus (PVN). Hedonic feeding is driven, in part, by the reinforcing properties of highly palatable food (HPF), which is mediated by the nucleus accumbens (NAc). Dysregulation of homeostatic and hedonic brain nuclei can lead to pathological feeding behaviors, namely overconsumption of highly palatable food (HPF), that may drive obesity. Both homeostatic and hedonic mechanisms of food intake have been attributed to several brain regions, but the integration of homeostatic and hedonic signaling to drive food intake is less clear, therefore we aimed to identify the neuroanatomical, functional, and behavioral features of a novel PVN → NAc circuit. Using viral tracing techniques, we determined that PVN → NAc has origins in the parvocellular PVN, and that PVN → NAc neurons express VGLUT1, a marker of glutamatergic signaling. Next, we pharmacogenetically stimulated PVN → NAc neurons and quantified both gamma-aminobutyric acid (GABA) and glutamate release and phospho-cFos expression in the NAc and observed a robust and significant increase in extracellular glutamate and phospho-cFos expression. Finally, we pharmacogenetically stimulated PVN → NAc which decreased intake of highly palatable food, demonstrating that this glutamatergic circuitry regulates aspects of feeding.

Phoenixin: More than Reproductive Peptide

Phoenixin (PNX) neuropeptide is a cleaved product of the Smim20 protein. Its most common isoforms are the 14- and 20-amino acid peptides. The biological functions of PNX are mediated via the activation of the GPR173 receptor. PNX plays an important role in the central nervous system (CNS) and in the female reproductive system where it potentiates LH secretion and controls the estrus cycle. Moreover, it stimulates oocyte maturation and increases the number of ovulated oocytes. Nevertheless, PNX not only regulates the reproduction system but also exerts anxiolytic, anti-inflammatory, and cell-protective effects. Furthermore, it is involved in behavior, food intake, sensory perception, memory, and energy metabolism. Outside the CNS, PNX exerts its effects on the heart, ovaries, adipose tissue, and pancreatic islets. This review presents all the currently available studies demonstrating the pleiotropic effects of PNX.

Variants in genes of innate immunity, appetite control and energy metabolism are associated with host cardiometabolic health and gut microbiota composition

Identifying the genetic and non-genetic determinants of obesity and related cardiometabolic dysfunctions is cornerstone for their prevention, treatment, and control. While genetic variants contribute to the cardiometabolic syndrome (CMS), non-genetic factors, such as the gut microbiota, also play key roles. Gut microbiota is intimately associated with CMS and its composition is heritable. However, associations between this microbial community and host genetics are understudied. We contribute filling this gap by genotyping 60 variants in 39 genes of three modules involved in CMS risk, measuring cardiometabolic risk factors, and characterizing gut microbiota in a cohort of 441 Colombians. We hypothesized that CMS risk variants were correlated with detrimental levels of clinical parameters and with the abundance of disease-associated microbes. We found several polymorphisms in genes of innate immunity, appetite control, and energy metabolism that were associated with metabolic dysregulation and microbiota composition; the associations between host genetics and cardiometabolic health were independent of the participants' gut microbiota, and those between polymorphisms and gut microbes were independent of the CMS risk. Associations were also independent of the host genetic ancestry, diet and lifestyle. Most microbes explaining genetic-microbiota associations belonged to the families Lachnospiraceae and Ruminococcaceae. Multiple CMS risk alleles were correlated with increased abundance of beneficial microbiota, suggesting that the phenotypic outcome of the evaluated variants might depend upon the genetic background of the studied population and its environmental context. Our results provide additional evidence that the gut microbiota is under the host genetic control and present pathways of host-microbe interactions.

Polymorphism of CLOCK Gene rs3749474 as a Modulator of the Circadian Evening Carbohydrate Intake Impact on Nutritional Status in an Adult Sample

The aim of this study was to evaluate the distribution of energy intake and macronutrients consumption throughout the day, and how its effect on nutritional status can be modulated by the presence of the rs3749474 polymorphism of the CLOCK gene in the Cantoblanco Platform for Nutritional Genomics (“GENYAL Platform”). This cross-sectional study was carried out on 898 volunteers between 18 and 69 years old (65.5% women). Anthropometric measurements, social issues and health, dietary, biochemical, genetic, and physical activity data were collected. Subsequently, 21 statistical interaction models were designed to predict the body mass index (BMI) considering seven dietary variables analyzed by three genetic models (adjusted by age, sex, and physical activity). The average BMI was 26.9 ± 4.65 kg/m², 62.14% presented an excess weight (BMI > 25 kg/m²). A significant interaction was observed between the presence of the rs3749474 polymorphism and the evening carbohydrate intake (% of the total daily energy intake [%TEI]) (adjusted p = 0.046), when predicting the BMI. Participants carrying TT/CT genotype showed a positive association between the evening carbohydrate intake (%TEI) and BMI (β = 0.3379, 95% CI = (0.1689,0.5080)) and (β = 0.1529, 95% CI = (−0.0164,0.3227)), respectively, whereas the wild type allele (CC) showed a negative association (β = −0.0321, 95% CI = (−0.1505,0.0862)). No significant interaction with the remaining model variables was identified. New dietary strategies may be implemented to schedule the circadian distribution of macronutrients according to the genotype. Clinical Trial number: NCT04067921.

Genes associated with body weight gain and feed intake identified by meta-analysis of the mesenteric fat from crossbred beef steers

Mesenteric fat is a visceral fat depot that increases with cattle maturity and can be influenced by diet. There may be a relationship between the accumulation of mesenteric fat and feed efficiency in beef cattle. The purpose of this study was to identify genes that may be differentially expressed in steers with high and low BW gain and feed intake. RNA-Seq was used to evaluate the transcript abundance of genes in the mesenteric fat from a total of 78 steers collected over 5 different cohorts. A meta-analysis was used to identify genes involved with gain, feed intake or the interaction of both phenotypes. The interaction analysis identified 11 genes as differentially expressed. For the main effect of gain, a total of 87 differentially expressed genes (DEG) were identified (P_ADJ<0.05), and 24 were identified in the analysis for feed intake. Genes identified for gain were involved in functions and pathways including lipid metabolism, stress response/protein folding, cell proliferation/growth, axon guidance and inflammation. The genes for feed intake did not cluster into pathways, but some of the DEG for intake had functions related to inflammation, immunity, and/or signal transduction (JCHAIN, RIPK1, LY86, SPP1, LYZ, CD5, CD53, SRPX, and NF2). At P_ADJ<0.1, only 4 genes (OLFML3, LOC100300716, MRPL15, and PUS10) were identified as differentially expressed in two or more cohorts, highlighting the importance of evaluating the transcriptome of more than one group of animals and incorporating a meta-analysis. This meta-analysis has produced many mesenteric fat DEG that may be contributing to gain and feed intake in cattle.

Rare Variants in Genes Linked to Appetite Control and Hypothalamic Development in Early-Onset Severe Obesity

Context: The hypothalamic circuit has an essential role in the regulation of appetite and energy expenditure. Pathogenic variants in genes involved in the hypothalamic leptin-melanocortin pathway, including melanocortin-4-receptor (MC4R), have been associated with monogenic obesity. Objective: To determine the rate and spectrum of rare variants in genes involved in melanocortin pathway or hypothalamic development in patients with severe early-onset obesity (height-adjusted weight >60% before age 10 years). Methods: We used a custom-made targeted exome sequencing panel to assess peripheral blood DNA samples for rare (minor allele frequency <0.5%), pathogenic/likely pathogenic variants in 24 genes related to the hypothalamic circuit in 92 subjects (51% males, median age 13.7 years) with early-onset severe obesity (median body mass index (BMI) Z-score + 4.0). Results: We identified a novel frameshift deletion in MC4R (p.V103Afs5^*) in two unrelated patients and a previously reported MC4R variant (p.T112M) in one patient. In addition, we identified rare heterozygous missense variants in ADCY3 (p.G1110R), MYT1L (p.R807Q), ISL1 (p.I347F), LRP2 (p.R2479I, and p.N3315S) and a hemizygous missense variant in GRPR (p.L87M) (each in one patient), possibly contributing to the obesity phenotype in these patients. Altogether 8 % (7/92) of the subjects had rare pathogenic/likely pathogenic variants in the studied genes. Conclusions: Rare genetic variants within the hypothalamic circuit are prevalent and contribute to the development of severe early-onset obesity. Targeted exome sequencing is useful in identifying affected subjects. Further studies are needed to evaluate the variants' clinical significance and to define optimal treatment.

Progress in understanding the roles of Urocortin3 (UCN3) in the control of appetite from studies using animal models

Urocortin3 (UCN3), the newest member of corticotrophin releasing hormone (CRH) family polypeptides, is an anorexic factor discovered in 2001, which has a strong inhibitory effect on animal appetite regulation. UCN3 is widely distributed in various tissues of animals and has many biological functions. Based on the research progress of UCN3 on mammals and non-mammals, this paper summarized the discovery, tissue distribution, appetite regulation and mechanism of UCN3 in animals, in order to provide a reference for feeding regulation and growth in mammals and fish in further research and production.

Characterisation of endogenous players in fibroblast growth factor-regulated functions of hypothalamic tanycytes and energy-balance nuclei

The mammalian hypothalamus regulates key homeostatic and neuroendocrine functions ranging from circadian rhythm and energy balance to growth and reproductive cycles via the hypothalamic-pituitary and hypothalamic-thyroid axes. In addition to its neurones, tanycytes are taking centre stage in the short- and long-term augmentation and integration of diverse hypothalamic functions, although the genetic regulators and mediators of their involvement are poorly understood. Exogenous interventions have implicated fibroblast growth factor (FGF) signalling, although the focal point of the action of FGF and any role for putative endogenous players also remains elusive. We carried out a comprehensive high-resolution screen of FGF signalling pathway mediators and modifiers using a combination of in situ hybridisation, immunolabelling and transgenic reporter mice, aiming to map their spatial distribution in the adult hypothalamus. Our findings suggest that β-tanycytes are the likely focal point of exogenous and endogenous action of FGF in the third ventricular wall, utilising FGF receptor (FGFR)1 and FGFR2 IIIc isoforms, but not FGFR3. Key IIIc-activating endogenous ligands include FGF1, 2, 9 and 18, which are expressed by a subset of ependymal and parenchymal cells. In the parenchymal compartment, FGFR1-3 show divergent patterns, with FGFR1 being predominant in neuronal nuclei and expression of FGFR3 being associated with glial cell function. Intracrine FGFs are also present, suggestive of multiple modes of FGF function. Our findings provide a testable framework for understanding the complex role of FGFs with respect to regulating the metabolic endocrine and neurogenic functions of hypothalamus in vivo.

Melanocortin 4 receptor-mediated effects of amylin on thermogenesis and regulation of food intake

AIMS

Amylin, a pancreatic hormone cosecreted with insulin, exerts important anorexic and weight-loss effects. Melanocortin 4 receptor (MC4R) signalling plays a critical role in energy homeostasis; however, its role on amylin-dependent regulation of food intake and adaptive thermogenesis of interscapular brown adipose tissue (IBAT) are unclear. In this study, we examined the effects of amylin on food intake and thermogenesis on IBAT via the MC4R pathway in mice.

MATERIALS AND METHODS

Acute food consumption and thermogenesis in IBAT were measured in male wild-type (WT) and MC4R-deficient mice following intraperitoneal injection of amylin and SHU9119, an MC3R/4R antagonist, to determine the role of the central melanocortin system on the hypothalamus and IBAT.

RESULTS

Amylin (50 μg/kg) suppressed feeding and stimulated thermogenesis on IBAT via activation of the MC4R system in mice. Pharmacological blockade of MC4R using SHU9119 (50 μg/kg) attenuated amylin-induced inhibition of feeding and stimulation of thermogenesis in IBAT. No changes were observed when SHU9119 was injected alone. Moreover, amylin significantly increased MC4R expression and c-Fos neuronal signals in the arcuate nucleus and significantly increased acetyl-CoA carboxylase (ACC) phosphorylation in the hypothalamus and IBAT and uncoupling protein-1 (UCP1) expression in the IBAT of WT mice via the MC4R pathway.

CONCLUSION

The melanocortin system was involved in amylin-induced suppression of food intake and activation of thermogenesis in both the hypothalamus and IBAT via modulation of ACC phosphorylation and UCP1 expression.

Vertical Sleeve Gastrectomy Attenuates Hedonic Feeding Without Impacting Alcohol Drinking in Rats

OBJECTIVE

Roux-en-Y gastric bypass surgery and vertical sleeve gastrectomy (VSG) are the most commonly performed bariatric procedures. Whereas studies report new-onset alcohol misuse following Roux-en-Y gastric bypass, the impact of VSG on alcohol intake is less clear. Hedonic feeding, alcohol drinking, and hypothalamic obesity-related gene expression following VSG were evaluated.

METHODS

Male Long-Evans rats underwent VSG or sham surgery. To evaluate hedonic feeding, rats received a high-fat diet following behavioral satiation on chow. Alcohol (5%-10% v/v) drinking was assessed in a two-bottle choice paradigm. Finally, polymerase chain reaction array evaluated gene expression.

RESULTS

VSG induced moderate but significant weight loss. Sham rats significantly escalated high-fat diet intake following behavioral satiation, an effect significantly reduced in VSG rats. A moderate decrease in alcohol intake was observed in VSG rats at low (5%) alcohol concentration. However, overall, no significant between-group differences were evident. Key hypothalamic orexigenic transcripts linked to stimulation of food and alcohol intake were significantly decreased in VSG rats.

CONCLUSIONS

VSG attenuated hedonic feeding without impacting alcohol drinking, an effect potentially mediated by alterations in genetic information flow within the hypothalamus. Importantly, these data highlight VSG as an effective bariatric procedure with a potentially reduced risk of developing alcohol use disorder.

Gene-Environment Interplay in Child Eating Behaviors: What the Role of "Nature" Means for the Effects of "Nurture"

PURPOSE OF REVIEW

This narrative review describes the evidence for both genetic and environmental influences on child appetitive traits and suggests ways of thinking about how these interact and correlate to influence how a child eats.

RECENT FINDINGS

Emerging evidence from social network analysis, and from longitudinal studies questioning the direction of association between parent feeding behaviors and child obesity risk, suggest that children's genes may shape the environmental risk for obesity that they are exposed to. There is strong evidence that child appetitive traits are both heritable and shaped by the environment. Instead of thinking about how genetic and environmental factors operate independently on each appetitive trait, research needs to expand the current paradigm to examine how genes and environments interact and shape each other.

Chemerin: a multifaceted adipokine involved in metabolic disorders

Metabolic syndrome is a global public health problem and predisposes individuals to obesity, diabetes and cardiovascular disease. Although the underlying mechanisms remain to be elucidated, accumulating evidence has uncovered a critical role of adipokines. Chemerin, encoded by the gene Rarres2, is a newly discovered adipokine involved in inflammation, adipogenesis, angiogenesis and energy metabolism. In humans, local and circulating levels of chemerin are positively correlated with BMI and obesity-related biomarkers. In this review, we discuss both peripheral and central roles of chemerin in regulating body metabolism. In general, chemerin is upregulated in obese and diabetic animals. Previous studies by gain or loss of function show an association of chemerin with adipogenesis, glucose homeostasis, food intake and body weight. In the brain, the hypothalamus integrates peripheral afferent signals including adipokines to regulate appetite and energy homeostasis. Chemerin increases food intake in seasonal animals by acting on hypothalamic stem cells, the tanycytes. In peripheral tissues, chemerin increases cell expansion, inflammation and angiogenesis in adipose tissue, collectively resulting in adiposity. While chemerin signalling enhances insulin secretion from pancreatic islets, contradictory results have been reported on how chemerin links to obesity and insulin resistance. Given the association of chemerin with obesity comorbidities in humans, advances in translational research targeting chemerin are expected to mitigate metabolic disorders. Together, the exciting findings gathered in the last decade clearly indicate a crucial multifaceted role for chemerin in the regulation of energy balance, making it a promising candidate for urgently needed pharmacological treatment strategies for obesity.

The inhibitory effect of NUCB2/nesfatin-1 on appetite regulation of Siberian sturgeon (Acipenser baerii Brandt)

Since NUCB2 was discovered, the information about NUCB2/nesfatin-1 in appetite regulation in both mammals and teleost has been still limited. The present study aims to determine the effects of nesfatin-1 on food intake and to explore the appetite mechanism in Siberian sturgeon. In this study, nucb2 cDNA sequence of 1571 bp was obtained, and the mRNA expression of nucb2 was abundant in brain and liver. Levels of nucb2 were appreciably increased in brain after feeding 1 and 3 h, while significantly decreased within fasting 15 days. Except for fasting 1 day, the expression pattern of nucb2 in the liver was similar to the brain. Acute intraperitoneal (i.p.) injection of nesfatin-1 inhibited the food intake during 0-1 h in a dose-dependent manner and 50 or 100 ng/g BW nesfatin-1 significantly decreased the cumulative food intake during 3 h. The daily food intake and cumulative food intake were remarkably reduced post chronic (7 days) i.p. injection. Moreover, chronic i.p. injection of nesfatin-1 affected the expression of appetite factors including cart, apelin and pyy in the brain, stomach and liver with the consistent pattern of change, while the levels of cck, ucn3 and nucb2 in these have different patterns. This study demonstrates that nesfatin-1 acts as a satiety factor in reducing the short-term and long-term food intake of Siberian sturgeon. Therefore, the data suggesting nesfatin-1 inhibits the appetite through different signal pathways in the central and peripheral endocrine systems of Siberian sturgeon.

Reestablishment of Energy Balance in a Male Mouse Model With POMC Neuron Deletion of BMPR1A

The regulation of energy balance involves complex processes in the brain, including coordination by hypothalamic neurons that contain pro-opiomelanocortin (POMC). We previously demonstrated that central bone morphogenetic protein (BMP) 7 reduced appetite. Now we show that a type 1 BMP receptor, BMPR1A, is colocalized with POMC neurons and that POMC-BMPR1A-knockout (KO) mice are hyperphagic, revealing physiological involvement of BMP signaling in anorectic POMC neurons in the regulation of appetite. Surprisingly, the hyperphagic POMC-BMPR1A-KO mice exhibited a lack of obesity, even on a 45% high-fat diet. This is because the brown adipose tissue (BAT) of KO animals exhibited increased sympathetic activation and greater thermogenic capacity owing to a reestablishment of energy balance, most likely stemming from a compensatory increase of BMPR1A in the whole hypothalamus of KO mice. Indeed, control animals given central BMP7 displayed increased energy expenditure and a specific increase in sympathetic nerve activity (SNA) in BAT. In these animals, pharmacological blockade of BMPR1A-SMAD signaling blunted the ability of BMP7 to increase energy expenditure or BAT SNA. Together, we demonstrated an important role for hypothalamic BMP signaling in the regulation of energy balance, including BMPR1A-mediated appetite regulation in POMC neurons as well as hypothalamic BMP-SMAD regulation of the sympathetic drive to BAT for thermogenesis.

What Twin Studies Tell Us About Brain Responses to Food Cues

PURPOSE OF REVIEW

Functional magnetic resonance imaging (fMRI) using visual food cues provides insight into brain regulation of appetite in humans. This review sought evidence for genetic determinants of these responses.

RECENT FINDINGS

Echoing behavioral studies of food cue responsiveness, twin study approaches detect significant inherited influences on brain response to food cues. Both polygenic (whole genome) factors and polymorphisms in single genes appear to impact appetite regulation, particularly in brain regions related to satiety perception. Furthermore, genetic confounding might underlie findings linking obesity to stereotypical response patterns on fMRI, i.e., associations with obesity may actually reflect underlying inherited susceptibilities rather than acquired levels of adiposity. Insights from twin studies show that genes powerfully influence brain regulation of appetite, emphasizing the role of inherited susceptibility factors in obesity risk. Future research to delineate mechanisms of inherited obesity risk could lead to novel or more targeted interventional approaches.

Impaired hypothalamic cocaine- and amphetamine-regulated transcript expression in lateral hypothalamic area and paraventricular nuclei of dehydration-induced anorexic rats

Negative energy balance promotes physiological adaptations that ensure the survival of animals. The hypothalamic-pituitary-thyroid axis regulates basal energy expenditure and its down-regulating adaptation to negative energy balance is well described: in fasting, the serum content of thyrotrophin (TSH) and thyroid hormones (TH) decreases, enhancing the survival odds of individuals. By contrast, dehydration-induced anorexic (DIA) rats present an impaired hypothalamic-pituitary-thyroid (HPT) axis adaptation despite their negative energy balance: increased circulating TSH levels. The implication of cocaine- and amphetamine-regulated transcript (CART), an anorexic peptide, in HPT axis function impairment and food-avoidance behaviour displayed by DIA animals is unknown. Because CART is co-expressed with the peptide that regulates the HPT axis in hypophysiotrophic paraventricular nucleus (PVN) neurones (TSH-releasing hormone), we analysed CART expression and possible implications with respect to high TSH levels of DIA animals. We examined whether changes in CART expression from the lateral hypothalamic area (LHA) and arcuate nucleus (ARC) could participate in food-avoidance of DIA rats. DIA and forced-food restricted (FFR) animals reduced their body weight and food intake. FFR rats had a down-regulation of their HPT axis (reduced serum TH and TSH content), whereas DIA animals had reduced TH but increased TSH levels. CART mRNA expression in the ARC decreased similarly between experimental groups and diminished in anterior, medial PVN and in LHA of FFR animals, whereas DIA animals showed unchanged levels. This impaired CART mRNA expression in the anterior PVN and LHA could be related to the aberrant feeding behaviour of DIA rats but not to their deregulated HPT axis function.

Effects of Endogenous Oxytocin Receptor Signaling in Nucleus Tractus Solitarius on Satiation-Mediated Feeding and Thermogenic Control in Male Rats

Central oxytocin receptor (OT-R) signaling reduces food intake and increases energy expenditure, but the central sites and mechanisms mediating these effects are unresolved. We showed previously that pharmacological activation of OT-R in hindbrain/nucleus tractus solitarius (NTS) amplifies the intake-inhibitory effects of gastrointestinal (GI) satiation signals. Unexplored were the energetic effects of hindbrain OT-R agonism and the physiological relevance of NTS OT-R signaling on food intake and energy expenditure control. Using a virally mediated OT-R knockdown (KD) strategy and a range of behavioral paradigms, this study examined the role of endogenous NTS OT-R signaling on satiation-mediated food intake inhibition and thermogenic control. Results showed that, compared with controls, NTS OT-R KD rats consumed larger meals, were less responsive to the intake-inhibitory effects of a self-ingested preload, and consumed more chow following a 24-hour fast. These data indicate that NTS OT-R signaling is necessary for normal satiation control. Whereas both control and NTS OT-R KD rats increased core temperature following high-fat diet maintenance (relative to chow maintenance), the percent increase in core temperature was greater in control compared with NTS OT-R KD rats during the light cycle. Hindbrain oxytocin agonist delivery increased core temperature in both control and NTS OT-R KD rats and the percent increase relative to vehicle treatment was not significantly different between groups. Together, data reveal a critical role for endogenous NTS OT-R signaling in mediating the intake-inhibitory effects of endogenous GI satiation signals and in diet-induced thermogenesis.

Novel and ultra-rare damaging variants in neuropeptide signaling are associated with disordered eating behaviors

Objective

Eating disorders develop through a combination of genetic vulnerability and environmental stress, however the genetic basis of this risk is unknown.

Methods

To understand the genetic basis of this risk, we performed whole exome sequencing on 93 unrelated individuals with eating disorders (38 restricted-eating and 55 binge-eating) to identify novel damaging variants. Candidate genes with an excessive burden of predicted damaging variants were then prioritized based upon an unbiased, data-driven bioinformatic analysis. One top candidate pathway was empirically tested for therapeutic potential in a mouse model of binge-like eating.

Results

An excessive burden of novel damaging variants was identified in 186 genes in the restricted-eating group and 245 genes in the binge-eating group. This list is significantly enriched (OR = 4.6, p<0.0001) for genes involved in neuropeptide/neurotrophic pathways implicated in appetite regulation, including neurotensin-, glucagon-like peptide 1- and BDNF-signaling. Administration of the glucagon-like peptide 1 receptor agonist exendin-4 significantly reduced food intake in a mouse model of ‘binge-like’ eating.

Conclusions

These findings implicate ultra-rare and novel damaging variants in neuropeptide/neurotropic factor signaling pathways in the development of eating disorder behaviors and identify glucagon-like peptide 1-receptor agonists as a potential treatment for binge eating.

Htr2c Splice Variants and 5HT2CR-Mediated Appetite

Serotonin 2C receptor (5HT_2CR) exists as different isoforms as a result of alternate splicing. A truncated variant (5HT_2CR-trunc) has no canonical receptor function and yet shows robust expression levels throughout the brain. Recent work has demonstrated the biochemical role of this isoform and how altering levels of 5HT_2CR-trunc leads to changes in behaviour.

GPR40 reduces food intake and body weight through GLP-1

G protein-coupled receptor 40 (GPR40) partial agonists lower glucose through the potentiation of glucose-stimulated insulin secretion, which is believed to provide significant glucose lowering without the weight gain or hypoglycemic risk associated with exogenous insulin or glucose-independent insulin secretagogues. The class of small-molecule GPR40 modulators, known as AgoPAMs (agonist also capable of acting as positive allosteric modulators), differentiate from partial agonists, binding to a distinct site and functioning as full agonists to stimulate the secretion of both insulin and glucagon-like peptide-1 (GLP-1). Here we show that GPR40 AgoPAMs significantly increase active GLP-1 levels and reduce acute and chronic food intake and body weight in diet-induced obese (DIO) mice. These effects of AgoPAM treatment on food intake are novel and required both GPR40 and GLP-1 receptor signaling pathways, as demonstrated in GPR40 and GLP-1 receptor-null mice. Furthermore, weight loss associated with GPR40 AgoPAMs was accompanied by a significant reduction in gastric motility in these DIO mice. Chronic treatment with a GPR40 AgoPAM, in combination with a dipeptidyl peptidase IV inhibitor, synergistically decreased food intake and body weight in the mouse. The effect of GPR40 AgoPAMs on GLP-1 secretion was recapitulated in lean, healthy rhesus macaque demonstrating that the putative mechanism mediating weight loss translates to higher species. Together, our data indicate effects of AgoPAMs that go beyond glucose lowering previously observed with GPR40 partial agonist treatment with additional potential for weight loss.

[Ghrelin: a gastric hormone at the crossroad between growth and appetite regulation]

Ghrelin is a 28 amino acid peptide hormone synthesized within the gastrointestinal tract. Initially identified as the endogenous ligand of the GHS-R1a (Growth Hormone Secretagogue Receptor 1a), ghrelin is a powerful stimulator of growth hormone (GH) secretion. At the crossroad between nutrition, growth and long-term energy metabolism, ghrelin also plays a unique role as the first identified gastric hormone increasing appetite and adiposity. However, the role of the ghrelin/GHS-R system in the physiology of growth, feeding behaviour and energy homeostasis needs to be better understood. Utilization of pharmacological tools and complementary animal models with deficiency in preproghrelin, ghrelin-O-acyl-transferase (GOAT - the enzyme that acylates ghrelin -) or GHS-R in situations of chronic undernutrition or high fat diet gives a more precise overview of the role of ghrelin in the pathophysiology of eating and metabolic disorders.

[Hunger and satiety factors in the regulation of pleasure associated with feeding behavior]

Feeding is an instinctive behavior accompanied by rewarding feeling of pleasure during obtaining and ingesting food, corresponding to the preparatory and consummatory phases of motivated behavior, respectively. Perception of this emotional state together with alternating feelings of hunger and satiety drives the feeding behavior. Because alterations of feeding behavior including either overeating or anorexia may lead to obesity and cachexia, respectively, understanding the neurochemical mechanisms of regulation of feeding pleasure may help to develop new therapies of these diseases. The dopamine (DA) system of the mesolimbic projections plays a key role in behavioral reward in general and is also involved in regulating feeding-associated pleasure in the forebrain including the nucleus accumbens (NAc) and the lateral hypothalamic area (LHA). It suggests that this DA system can be selectively activated by factors specific to different types of motivated behavior including hunger- and satiety- related hormones. Indeed, central administrations of either orexigenic ghrelin or anorexigenic α-melanocyte-stimulating hormone (α-MSH) increase DA release in the NAc. However, DA has also been shown to inhibit food intake when injected into the LHA, historically known as a « hunger center », indicating DA functional involvement in regulation of both appetite and feeding pleasure. Although both NAc and LHA contain neurons expressing melanocortin receptors, only the LHA receives the α-MSH containing nerve terminals from the α-MSH producing neurons of the hypothalamic arcuate nucleus, the main relay of the peripheral hunger and satiety signals to the brain. A recent study showed that α-MSH in the LHA enhances satiety and inhibits feeding pleasure while potently stimulating DA release in this area during both preparatory and consummatory phases of feeding. It suggests that altered signaling by α-MSH to the DA system in the LHA may be involved in the pathophysiology of obesity and anorexia and the possible underlying mechanisms are discussed.

Duplication of neuropeptide Y and peptide YY in Nile tilapia Oreochromis niloticus and their roles in food intake regulation

In vertebrates, the neuropeptide Y (NPY) family peptides have been recognized as key players in food intake regulation. NPY centrally promotes feeding, while peptide YY (PYY) and pancreatic polypeptide (PP) mediate satiety. The teleost tetraploidization is well-known to generate duplicates of both NPY and PYY; however, the functional diversification between the duplicate genes, especially in the regulation of food intake, remains unknown. In this study, we identified the two duplicates of NPY and PYY in Nile tilapia (Oreochromis niloticus). Both NPYa and NPYb were primarily expressed in the central nervous system (CNS), but the mRNA levels of NPYb were markedly lower than those of NPYa. Hypothalamic mRNA expression of NPYa, but not NPYb, decreased after feeding and increased after 7-days of fasting. However, both NPYa and NPYb caused a significant increase in food intake after an intracranial injection of 50ng/g body weight dose. PYYb, one of the duplicates of PYY, had an extremely high expression in the foregut and midgut, whereas another form of duplicate PYYa showed only moderate expression in the CNS. Both hypothalamic PYYa and foregut PYYb mRNA expression increased after feeding and decreased after 7-days of fasting. Furthermore, the intracranial injection of PYYb decreased food intake, but PYYa had no significant effect. Our results suggested that although the mature peptides of NPYa and NPYb can both stimulate food intake, NPYa is the main endogenous functional NPY for feeding regulation. A functional division has been identified in the duplicates of PYY, which deems PYYb as a gut-derived anorexigenic peptide and PYYa as a CNS-specific PYY in Nile tilapia.

Maternal Triclosan consumption alters the appetite regulatory network on Wistar rat offspring and predispose to metabolic syndrome in the adulthood

The objectives of this study were to evaluate the effects of maternal oral exposure to the antibacterial Triclosan (TCS) during gestation and lactation on the metabolic status of the adult offspring and on the expression of main genes controlling the appetite regulatory network. Pregnant rats were fed ad-libitum with ground food + TCS (1 mg/kg) from day 14 of gestation to day 20 of lactation (n=3) or ground food (n=3). After litter reduction, 12 males and 12 females born from the TCS exposed rats (TCS, n=24) or not (Control, n=24) were used to evaluate monthly body weight, food intake, plasma levels of cholesterol, glucose and triglycerides, and the hypothalamic mRNA expression of agouti-related protein (Agrp), neuropeptide Y (Npy) and propiomelanocortin (Pomc). Body weight for rats in the TCS group was 12.5% heavier for males at 4 months (p<0.001) and 19% heavier for females at 8 months (p=0.01). Food intake was significantly higher for rats in the TCS group at 5 months of age (p<0.01). Cholesterol and glucose levels were significantly higher for rats in the TCS group at 8 months (p<0.05). mRNA expression of Npy and Agrp were significantly increased in hypothalami of rats in the TCS group at 2 months for males or 8 months for females (p<0.05). In conclusion, low doses of oral TCS consumption by the pregnant and lactating dam increase the hypothalamic expression of the orexigenic neuropeptides Npy and Agrp in the offspring and alter their metabolic status during adulthood, resembling development of the metabolic syndrome.

Hypothalamic Wnt Signalling and its Role in Energy Balance Regulation

Wnt signalling and its downstream effectors are well known for their roles in embryogenesis and tumourigenesis, including the regulation of cell proliferation, survival and differentiation. In the nervous system, Wnt signalling has been described mainly during embryonic development, although accumulating evidence suggests that it also plays a major role in adult brain morphogenesis and function. Studies have predominantly concentrated on memory formation in the hippocampus, although recent data indicate that Wnt signalling is also critical for neuroendocrine control of the developed hypothalamus, a brain centre that is key in energy balance regulation and whose dysfunction is implicated in metabolic disorders such as type 2 diabetes and obesity. Based on scattered findings that report the presence of Wnt molecules in the tanycytes and ependymal cells lining the third ventricle and arcuate nucleus neurones of the hypothalamus, their potential importance in key regions of food intake and body weight regulation has been investigated in recent studies. The present review brings together current knowledge on Wnt signalling in the hypothalamus of adult animals and discusses the evidence suggesting a key role for members of the Wnt signalling family in glucose and energy balance regulation in the hypothalamus in diet-induced and genetically obese (leptin deficient) mice. Aspects of Wnt signalling in seasonal (photoperiod sensitive) rodents are also highlighted, given the recent evidence indicating that the Wnt pathway in the hypothalamus is not only regulated by diet and leptin, but also by photoperiod in seasonal animals, which is connected to natural adaptive changes in food intake and body weight. Thus, Wnt signalling appears to be critical as a modulator for normal functioning of the physiological state in the healthy adult brain, and is also crucial for normal glucose and energy homeostasis where its dysregulation can lead to a range of metabolic disorders.

Appetite regulation in Schizothorax prenanti by three CART genes

In recent years, cocaine- and amphetamine-regulated transcript (CART) has received much attention as mediators of appetite regulation in mammals. However, the involvement of CART in the feeding behavior of teleosts has not been well understood. In this study, three distinct CARTs were cloned from the Schizothorax prenanti (S. prenanti). Real-time quantitative PCR were applied to characterize the tissue distribution and appetite regulatory effects of CARTs in S. prenanti. The S. prenanti CART-1, CART-2 and CART-3 full-length cDNA sequences were 597 bp, 694 bp and 749 bp in length, encoding the peptides of 125, 120 and 104 amino acid residues, respectively. All the S. prenanti CARTs consisted of three exons and two introns. Tissue distribution analysis showed that the high mRNA levels of S. prenanti CART-1 were observed in the telencephalon and eye, followed by the hypothalamus, myelencephalon, and mesencephalon. The S. prenanti CART-2 mRNA was mainly found in the mesencephalon, hypothalamus, telencephalon and myelencephalon. The S. prenanti CART-3 mRNA was widely distributed among the tissues, with the high levels in the hypothalamus and foregut. In the periprandial experiment, all three CARTs mRNA expressions in the hypothalamus were highly elevated after a meal, suggesting that CARTs are postprandial satiety signals. In the fasting experiment, all three CARTs mRNA expressions decreased after fasting and increased after refeeding, suggesting that CARTs might be involved in regulation of appetite in the S. prenanti.

RNA-Seq Analysis of Abdominal Fat Reveals Differences between Modern Commercial Broiler Chickens with High and Low Feed Efficiencies

For economic and environmental reasons, chickens with superior feed efficiency (FE) are preferred in the broiler chicken industry. High FE (HFE) chickens typically have reduced abdominal fat, the major adipose tissue in chickens. In addition to its function of energy storage, adipose tissue is a metabolically active organ that also possesses endocrine and immune regulatory functions. It plays a central role in maintaining energy homeostasis. Comprehensive understanding of the gene expression in the adipose tissue and the biological basis of FE are of significance to optimize selection and breeding strategies. Through gene expression profiling of abdominal fat from high and low FE (LFE) commercial broiler chickens, the present study aimed to characterize the differences of gene expression between HFE and LFE chickens. mRNA-seq analysis was carried out on the total RNA of abdominal fat from 10 HFE and 12 LFE commercial broiler chickens, and 1.48 billion of 75-base sequence reads were generated in total. On average, 11,565 genes were expressed (>5 reads/gene/sample) in the abdominal fat tissue, of which 286 genes were differentially expressed (DE) at q (False Discover Rate) < 0.05 and fold change > 1.3 between HFE and LFE chickens. Expression levels from RNA-seq were confirmed with the NanoString nCounter analysis system. Functional analysis showed that the DE genes were significantly (p < 0.01) enriched in lipid metabolism, coagulation, and immune regulation pathways. Specifically, the LFE chickens had higher expression of lipid synthesis genes and lower expression of triglyceride hydrolysis and cholesterol transport genes. In conclusion, our study reveals the overall differences of gene expression in the abdominal fat from HFE and LFE chickens, and the results suggest that the divergent expression of lipid metabolism genes represents the major differences.

The role of brain somatostatin receptor 2 in the regulation of feeding and drinking behavior

Somatostatin was discovered four decades ago as hypothalamic factor inhibiting growth hormone release. Subsequently, somatostatin was found to be widely distributed throughout the brain and to exert pleiotropic actions via interaction with five somatostatin receptors (sst1-5) that are also widely expressed throughout the brain. Interestingly, in contrast to the predominantly inhibitory actions of peripheral somatostatin, the activation of brain sst2 signaling by intracerebroventricular injection of stable somatostatin agonists potently stimulates food intake and independently, drinking behavior in rodents. The orexigenic response involves downstream orexin-1, neuropeptide Y1 and μ receptor signaling while the dipsogenic effect is mediated through the activation of the brain angiotensin 1 receptor. Brain sst2 activation is part of mechanisms underlying the stimulation of feeding and more prominently water intake in the dark phase and is able to counteract the anorexic response to visceral stressors.

Ancient origins and evolutionary conservation of intracellular and neural signaling pathways engaged by the leptin receptor

In mammals, leptin acts on leptin receptor (LepR) -expressing neurons in the brain to suppress food intake and stimulate whole-body metabolism. A similar action of leptin on food intake has been reported in the frog Xenopus laevis and in several bony fishes. However, the intracellular signaling and neural pathways by which leptin regulates energy balance have not been investigated outside of mammals. Using reporter assays and site-directed mutagenesis we show that the frog LepR signals via signal transducer and activator of transcription (STAT) 3 and STAT5 through evolutionarily conserved tyrosine residues in the LepR cytoplasmic domain. In situ hybridization histochemistry for LepR mRNA in brain and pituitary showed strong expression in the magno- and parvocellular divisions of the anterior preoptic area (homologous to the mammalian paraventricular nucleus), the suprachiasmatic nucleus, ventral hypothalamus, and pars intermedia and pars distalis of the anterior pituitary. Leptin injection increased phosphorylated STAT3 immunoreactivity in LepR mRNA-positive cells, and induced socs3 and pomc mRNAs. Microarray analysis of preoptic area/hypothalamus/pituitary 2 hours after leptin injection identified leptin-regulated genes that included c-fos, a known leptin-activated gene; pituitary follicle-stimulating hormone subunit β, suggesting an important role for leptin in the reproductive axis of frogs; and B-cell translocation factor 2, which has important functions in neurogenesis. Our findings support that the intracellular signaling pathways and neural substrates that mediate leptin actions on energy balance were present in the common ancestor of modern amphibians and amniotes and have been conserved over 350 million years of evolutionary time.

Molecular and physiological evidences for the role in appetite regulation of apelin and its receptor APJ in Ya-fish (Schizothorax prenanti)

Apelin is a recently discovered peptide produced by several tissues with diverse physiological actions mediated by its receptor APJ. In order to better understand the role of apelin in the regulation of appetite in fish, we cloned the cDNAs encoding apelin and APJ, and investigated their mRNA distributions in Ya-fish (Schizothorax prenanti) tissues. We also assessed the effects of different nutritional status on apelin and APJ mRNAs abundance. Apelin and APJ mRNAs were ubiquitously expressed in all tissues tested, relatively high expression levels were detected in the heart, spleen, hypothalamus and kidney. Short-term fasting significant increased APJ mRNA expression, but no significant difference between fasted fish and fed control on 5- and 7-day. Meanwhile, apelin mRNA expression consistently increased during the 7-day food deprivation. In order to further characterize apelin in fish, we performed intraperitoneal (i.p.) injection of apelin-13 and examined food intake of the injected fish. Apelin injected at a dose of 100 ng/g body weight induced a significant increase in food intake compared to saline injected fish. Our results suggest that apelin acts as an orexigenic factor in Ya-fish. Their widespread distributions also suggest that apelin and APJ might play multiple physiological regulating roles in fish.

Ghrelin induces leptin resistance by activation of suppressor of cytokine signaling 3 expression in male rats: implications in satiety regulation

The anorexigenic adipocyte-derived hormone leptin and the orexigenic hormone ghrelin act in opposition to regulate feeding behavior via the vagal afferent pathways. The mechanisms by which ghrelin exerts its inhibitory effects on leptin are unknown. We hypothesized that ghrelin activates the exchange protein activated by cAMP (Epac), inducing increased SOCS3 expression, which negatively affects leptin signal transduction and neuronal firing in nodose ganglia (NG) neurons. We showed that 91 ± 3% of leptin receptor (LRb) -bearing neurons contained ghrelin receptors (GHS-R1a) and that ghrelin significantly inhibited leptin-stimulated STAT3 phosphorylation in rat NG neurons. Studies of the signaling cascades used by ghrelin showed that ghrelin caused a significant increase in Epac and suppressor of cytokine signaling 3 (SOCS3) expression in cultured rat NG neurons. Transient transfection of cultured NG neurons to silence SOCS3 and Epac genes reversed the inhibitory effects of ghrelin on leptin-stimulated STAT3 phosphorylation. Patch-clamp studies and recordings of single neuronal discharges of vagal primary afferent neurons showed that ghrelin markedly inhibited leptin-stimulated neuronal firing, an action abolished by silencing SOCS3 expression in NG. Plasma ghrelin levels increased significantly during fasting. This was accompanied by enhanced SOCS3 expression in the NG and prevented by treatment with a ghrelin antagonist. Feeding studies showed that silencing SOCS3 expression in the NG reduced food intake evoked by endogenous leptin. We conclude that ghrelin exerts its inhibitory effects on leptin-stimulated neuronal firing by increasing SOCS3 expression. The SOCS3 signaling pathway plays a pivotal role in ghrelin's inhibitory effect on STAT3 phosphorylation, neuronal firing, and feeding behavior.

Double deletion of orexigenic neuropeptide Y and dynorphin results in paradoxical obesity in mice

OBJECTIVE

Orexigenic neuropeptide Y (NPY) and dynorphin (DYN) regulate energy homeostasis. Single NPY or dynorphin deletion reduces food intake or increases fat loss. Future developments of obesity therapeutics involve targeting multiple pathways. We hypothesised that NPY and dynorphin regulate energy homeostasis independently, thus double NPY and dynorphin ablation would result in greater weight and/or fat loss than the absence of NPY or dynorphin alone.

DESIGN AND METHODS

We generated single and double NPY and dynorphin knockout mice (NPYΔ, DYNΔ, NPYDYNΔ) and compared body weight, adiposity, feeding behaviour, glucose homeostasis and brown adipose tissue uncoupling protein-1 (UCP-1) expression to wildtype counterparts.

RESULTS

Body weight and adiposity were significantly increased in NPYDYNΔ, but not in NPYΔ or DYNΔ. This was not due to increased food intake or altered UCP-1 expression, which were not significantly altered in double knockouts. NPYDYNΔ mice demonstrated increased body weight loss after a 24-h fast, with no effect on serum glucose levels after glucose injection.

CONCLUSIONS

Contrary to the predicted phenotype delineated from single knockouts, double NPY and dynorphin deletion resulted in heavier mice, with increased adiposity, despite no significant changes in food intake or UCP-1 activity. This indicates that combining long-term opioid antagonism with blockade of NPY-ergic systems may not produce anti-obesity effects.

Chitin synthase B: a midgut-specific gene induced by insect hormones and involved in food intake in Bombyx mori larvae

Chitin synthase (CHS) is the key regulatory enzyme in chitin synthesis and excretion in insects, and a specific target of insecticides. We cloned a CHS B gene of Bombyx mori (BmChsB) and showed it to be midgut specific, highly expressed during the feeding process in the larva. Knockdown of BmChsB expression in the third-instar larvae increased the number of nonmolting and abnormally molting larvae. Exposure to nikkomycin Z, a CHS inhibitor, reduced the amount of chitin in the peritrophic membrane of molted larvae, whereas abnormally elevated BmChsB mRNA levels were readily detected from the end of molting and in the newly molted larvae. Exogenous 20-hydroxyecdysone (20E) and methoprene, a juvenile hormone analogue, significantly upregulated the expression of BmChsB when the levels of endogenous molting hormone (MH) were low and the levels of endogenous juvenile hormone (JH) were high immediately after molting. When levels of endogenous MH were high and those of endogenous JH were low during the molting stage, exogenous 20E did not upregulate BmChsB expression and exogenous methoprene upregulated it negligibly. When the endogenous hormone levels were low during the mulberry-leaf intake process, BmChsB expression was upregulated by exogenous methoprene. We conclude that the expression of BmChsB is regulated by insect hormones, and directly affects the chitin-synthesis-dependent form of the peritrophic membrane and protects the food intake and molting process of silkworm larvae.

Trk B signaling in dopamine 1 receptor neurons regulates food intake and body weight

OBJECTIVE

Loss of BDNF-TrkB signaling results in obesity in both humans and mice; however, the neural circuit that mediates this effect is unknown. The role of TrkB signaling in dopamine-1 receptor expressing neurons in body weight regulation was tested.

METHODS

Mice with a floxed allele of the TrkB gene were paired with mice expressing Cre-recombinase under control of the D1 promoter to conditionally knock out expression of TrkB receptors from D1-neurons.

RESULTS

Deletion of TrkB receptors from D1 neurons results in obesity in chow fed mice due to increased feed efficiency. In contrast, loss of Trk B signaling in D1 neurons induced hyperphagia and hyperglycemia in mice maintained on high fat diet.

CONCLUSIONS

These findings indicate TrkB signaling in D1 neurons regulates body weight by distinct mechanisms for chow and high fat diet and may be important for defending the body against the development of obesity and obesity-related disorders.

Ontogenic expression of putative feeding peptides in the rat fetal brain and placenta

The well-demonstrated "fetal programming" paradigm is based on the observation that environmental changes can reset the developmental path and thus, gene expression during intrauterine development. As appetite-regulatory neural pathways develop in utero, we sought to determine the ontogenic expression of putative orexigenic and anorexigenic feeding-regulatory peptides in the fetal rat brain and placenta during the last third of gestation. Pregnant Sprague-Dawley rats (n = 12) at D14, D16 and D18 were sacrificed and fetal whole brain and placenta removed and examined for mRNA levels of orexigenic (neuropeptide Y (NPY), agouti-related peptide (AgRP)) and anorexigenic (cocaine and amphetamine regulated transcript (CART), pro-opiomelanocortin (POMC)) peptides and leptin receptor (OB-Rb) using real-time reverse transcription polymerase chain reactions (RT-PCR). For adult comparisons, the hypothalamus, cortex and cerebellum from male rats were also examined for feeding peptides. In the fetal brain and placenta, mRNA levels of AgRP decreased 10-fold from D14 to D16 and was undetectable at D18. Appetite inhibitory factors OB-Rb and CART mRNA levels increased from D14 to D18 in the brain and placenta. NPY and POMC expression remained unchanged from D14 to D18. The pattern of expression of feeding regulatory peptides in the fetal brain most closely resembled the expression profile of the adult cerebral cortex. The continued maturation of feeding regulatory mechanisms in late gestation indicates the potential for in utero programming of ingestive behavior.

Association of dopamine D2 receptor and leptin receptor genes with clinically severe obesity

OBJECTIVE

The brain reward circuits that promote drug abuse may also be involved in pleasure seeking behavior and food cravings observed in severely obese subjects. Drug addiction polymorphisms such as the TaqI A1 allele of the dopamine D2 receptor (DRD2) are associated with cocaine, alcohol, and opioid use, but few studies have linked DRD2 to food craving. Other genes such as the leptin receptor gene (LEPR) and mu-opioid receptor gene (OPRM1) that affect appetite and pleasure centers in the brain may also influence food addiction and obesity. The three genes together may function synergistically.

DESIGN AND METHODS

To evaluate associations between candidate genes, food craving, overeating, and BMI, we administered questionnaires including Power of Food Scale and Food Craving Inventory, conducted anthropometric measures, and collected blood from patients undergoing weight-loss treatment. Questionnaires and DNA specimens were collected for 80 participants.

RESULTS

Participants were mostly female (74%) and Caucasian (79%), with an average age of 53 years old. Mean BMI for all participants was 43 kg/m2 and was significantly associated in a linear fashion with Food Craving Inventory scores (P=0.0001) and Power of Food (P=0.02). The DRD2 TaqI A1 allele was significantly associated with BMI (P=0.04), while LEPR Lys109Arg and OPRM1 A118G variants were not. We stratified DRD2 by LEPR and OPRM1, and observed a significant interaction (P = 0.04) between DRD2 and LEPR, and a marginally significant interaction (P=0.06) between DRD2 and OPRM1.

CONCLUSION

Genes associated with addictive behavior and appetite control may therefore, in combination, markedly influence development of clinically severe obesity.

Ghrelin discovery: a decade after

Since its discovery 12 years ago, intensive research has been performed on ghrelin. The significance of ghrelin as a growth hormone-releasing hormone, appetite regulator, energy conservator and sympathetic nerve suppressor has now been well established. In this short essay, we summarize the history of the discovery of ghrelin.

A high-throughput fluorescence-based assay system for appetite-regulating gene and drug screening

The increasing number of people suffering from metabolic syndrome and obesity is becoming a serious problem not only in developed countries, but also in developing countries. However, there are few agents currently approved for the treatment of obesity. Those that are available are mainly appetite suppressants and gastrointestinal fat blockers. We have developed a simple and rapid method for the measurement of the feeding volume of Danio rerio (zebrafish). This assay can be used to screen appetite suppressants and enhancers. In this study, zebrafish were fed viable paramecia that were fluorescently-labeled, and feeding volume was measured using a 96-well microplate reader. Gene expression analysis of brain-derived neurotrophic factor (bdnf), knockdown of appetite-regulating genes (neuropeptide Y, preproinsulin, melanocortin 4 receptor, agouti related protein, and cannabinoid receptor 1), and the administration of clinical appetite suppressants (fluoxetine, sibutramine, mazindol, phentermine, and rimonabant) revealed the similarity among mechanisms regulating appetite in zebrafish and mammals. In combination with behavioral analysis, we were able to evaluate adverse effects on locomotor activities from gene knockdown and chemical treatments. In conclusion, we have developed an assay that uses zebrafish, which can be applied to high-throughput screening and target gene discovery for appetite suppressants and enhancers.

Metabolic jet lag when the fat clock is out of sync

There is a growing appreciation of the importance of circadian regulation in energy homeostasis, and the dysregulation of the circadian clock has been associated with obesity and metabolic abnormalities. A new study shows that adipocyte-specific deletion of a core circadian clock gene, Bmal1 , in mice shifts the timing of their feeding behavior, resulting in obesity (aaa-bbb).

Obesity in mice with adipocyte-specific deletion of clock component Arntl

Adipocytes store excess energy in the form of triglycerides and signal the levels of stored energy to the brain. Here we show that adipocyte-specific deletion of Arntl (also known as Bmal1), a gene encoding a core molecular clock component, results in obesity in mice with a shift in the diurnal rhythm of food intake, a result that is not seen when the gene is disrupted in hepatocytes or pancreatic islets. Changes in the expression of hypothalamic neuropeptides that regulate appetite are consistent with feedback from the adipocyte to the central nervous system to time feeding behavior. Ablation of the adipocyte clock is associated with a reduced number of polyunsaturated fatty acids in adipocyte triglycerides. This difference between mutant and wild-type mice is reflected in the circulating concentrations of polyunsaturated fatty acids and nonesterified polyunsaturated fatty acids in hypothalamic neurons that regulate food intake. Thus, this study reveals a role for the adipocyte clock in the temporal organization of energy regulation, highlights timing as a modulator of the adipocyte-hypothalamic axis and shows the impact of timing of food intake on body weight.

GOAT induced ghrelin acylation regulates hedonic feeding

Ghrelin is an orexigenic hormone that regulates homeostatic and reward-related feeding behavior. Recent evidence indicates that acylation of ghrelin by the gut enzyme ghrelin O-acyl transferase (GOAT) is necessary to render ghrelin maximally active within its target tissues. Here we tested the hypothesis that GOAT activity modulates food motivation and food hedonics using behavioral pharmacology and mutant mice deficient for GOAT and the ghrelin receptor (GHSR). We evaluated operant responding following pharmacological administration of acyl-ghrelin and assessed the necessity of endogenous GOAT activity for operant responding in GOAT and GHSR-null mice. Hedonic-based feeding behavior also was examined in GOAT-KO and GHSR-null mice using a "Dessert Effect" protocol in which the intake of a palatable high fat diet "dessert" was assessed in calorically-sated mice. Pharmacological administration of acyl-ghrelin augmented operant responding; notably, this effect was dependent on intact GHSR signaling. GOAT-KO mice displayed attenuated operant responding and decreased hedonic feeding relative to controls. These behavioral results correlated with decreased expression of the orexin-1 receptor in reward-related brain regions in GOAT-KO mice. In summary, the ability of ghrelin to stimulate food motivation is dependent on intact GHSR signaling and modified by endogenous GOAT activity. Furthermore, GOAT activity is required for hedonic feeding behavior, an effect potentially mediated by forebrain orexin signaling. These data highlight the significance of the GOAT-ghrelin system for the mediation of food motivation and hedonic feeding.

Variations in the gene expression of zona pellucida proteins, zpb and zpc, in female European eel (Anguilla anguilla) during induced sexual maturation

Vertebrate eggs are surrounded by an extracellular glycoprotein coat termed zona pellucida (ZP). Integrity of ZP is critical for a correct embryo development. Two zona pellucida protein genes (zpb and zpc) from European eel were characterized, specific qPCR assays developed and their expression in immature males and females carried out. An experimental group of silver-stage eel females was maintained at 18 °C and hormonally induced to sexual maturation by weekly injections of carp pituitary extract during 12 weeks. Changes in zpb and zpc expression during sexual maturation were studied in liver and ovary by qPCR. In liver, no changes were recorded during hormonal treatment, while in ovary expression of both genes decreased during sexual development. These results are a first step in the characterization of ZP in European eel and in the understanding of the mechanism underlying egg envelope formation.

Recapitulation of the association of the Val66Met polymorphism of BDNF gene with BMI in Koreans

Recent evidence suggests that brain-derived neurotrophic factor (BDNF) regulates food intake and the control of body weight. A common polymorphism in human BDNF, Val66Met (single-nucleotide polymorphism database (dbSNP) no. rs6265), impairs intracellular trafficking, resulting in the reduced secretion of BDNF. Several European studies have indicated that Val66Met is associated with BMI. In this study, we examined the association of the Val66Met polymorphism with BMI in Koreans (n = 20,270) from three independent epidemiological cohorts. All three studies observed a consistent association of this polymorphism with BMI, and their combined analysis demonstrated a robust correlation (β = -0.17 ± 0.03 and P = 5.6 × 10(-8)). We also examined the effect of smoking on the link between Val66Met and BMI. The association of Val66Met with BMI was statistically significant only in the smoking group, reflecting a possible interaction between smoking and the BDNF polymorphism for BMI. Thus, we have confirmed BDNF as a genetic risk factor for BMI in an Asian population and hypothesize that the Val66Met mutation influences individual differences in BMI. In addition, smoking might interact with BDNF Val66Met to modulate BMI.