Monogenic obesity in humans

Hypothalamic AMP-activated protein kinase as a mediator of whole body energy balance

The AMP-activated protein kinase (AMPK) is the downstream constituent of a kinase cascade that acts as a sensor of cellular energy levels. Current data unequivocally indicate that hypothalamic AMPK plays a key role in the control of the whole body energy balance, by integrating peripheral signals, such as hormones and metabolites, with central signals, such as neuropeptides, and eliciting allostatic changes in energy homeostasis. Although the molecular details of these interactions are not fully understood, recent evidence has suggested that the interaction between AMPK with hypothalamic lipid metabolism and other metabolic sensors, such as the uncoupling protein 2 (UCP-2), the mammalian target of rapamycin (mTOR) and the deacetylase sirtuin 1 (SIRT1), may play a main role in the hypothalamic control of feeding and energy expenditure. Here, we summarize the role of hypothalamic AMPK as whole body energy gauge. Understanding this key molecule and especially its functions at central level may provide new therapeutic targets for the treatment of metabolic alterations and obesity.

Melanocortin control of energy balance: evidence from rodent models

Regulation of energy balance is extremely complex, and involves multiple systems of hormones, neurotransmitters, receptors, and intracellular signals. As data have accumulated over the last two decades, the CNS melanocortin system is now identified as a prominent integrative network of energy balance controls in the mammalian brain. Here, we will review findings from rat and mouse models, which have provided an important framework in which to study melanocortin function. Perhaps most importantly, this review attempts for the first time to summarize recent advances in our understanding of the intracellular signaling pathways thought to mediate the action of melanocortin neurons and peptides in control of longterm energy balance. Special attention will be paid to the roles of MC4R/MC3R, as well as downstream neurotransmitters within forebrain and hindbrain structures that illustrate the distributed control of melanocortin signaling in energy balance. In addition, distinctions and controversy between rodent species will be discussed.

Different effects of hyperlipidic diets in human lactation and adulthood: growth versus the development of obesity

After birth, the body shifts from glucose as primary energy substrate to milk-derived fats, with sugars from lactose taking a secondary place. At weaning, glucose recovers its primogeniture and dietary fat role decreases. In spite of human temporary adaptation to a high-fat (and sugars and protein) diet during lactation, the ability to thrive on this type of diet is lost irreversibly after weaning. We could not revert too the lactating period metabolic setting because of different proportions of brain/muscle metabolism in the total energy budget, lower thermogenesis needs and capabilities, and absence of significant growth in adults. A key reason for change was the limited availability of foods with high energy content at weaning and during the whole adult life of our ancestors, which physiological adaptations remain practically unchanged in our present-day bodies. Humans have evolved to survive with relatively poor diets interspersed by bouts of scarcity and abundance. Today diets in many societies are largely made up from choice foods, responding to our deeply ingrained desire for fats, protein, sugars, salt etc. Consequently our diets are not well adjusted to our physiological needs/adaptations but mainly to our tastes (another adaptation to periodic scarcity), and thus are rich in energy roughly comparable to milk. However, most adult humans cannot process the food ingested in excess because our cortical-derived craving overrides the mechanisms controlling appetite. This is produced not because we lack the biochemical mechanisms to use this energy, but because we are unprepared for excess, and wholly adapted to survive scarcity. The thrifty mechanisms compound the effects of excess nutrients and damage the control of energy metabolism, developing a pathologic state. As a consequence, an overflow of energy is generated and the disease of plenty develops.

Hyperphagia and leptin resistance in tissue inhibitor of metalloproteinase-2 deficient mice

Obesity is a complex genetic and behavioural disorder arising from the improper integration of peripheral signals at central autonomic centres. For the hypothalamus to respond to dynamic physiological alterations, it must retain a degree of plasticity throughout life. Evidence is mounting that an intricate balance between matrix metalloproteinase (MMP)-mediated extracellular matrix proteolysis and tissue inhibitor of metalloproteinase (TIMP)-mediated proteolysis inhibition contributes to tissue remodelling. However, few studies have examined the role of MMPs/TIMPs in hypothalamic remodelling and energy homeostasis. To determine the contribution of TIMP-2 to the hypothalamic regulation of feeding, body mass and food consumption were monitored in TIMP-2 knockout (KO) mice fed a standard chow or high-fat diet (HFD). TIMP-2 KO mice of both sexes gained more weight than wild-type (WT) mice, even when fed the chow diet. Before the onset of obesity, TIMP-2 KO mice were hyperphagic, without increased orexigenic or decreased anorexigenic neuropeptide expression, but leptin resistant (i.e. reduced leptin-induced anorexigenic response and signal transducer and activator of transcription 3 activation). HFD exacerbated weight gain and hyperleptinaemia. In addition, proteolysis was increased in the arcuate nucleus of TIMP-2 KO mice. These data suggest a role for TIMP-2 in hypothalamic control of feeding and energy homeostasis.

Melanocortin signalling and the regulation of blood pressure in human obesity

Obesity has reached epidemic proportions worldwide. Sympathetic nervous system activation has been shown to play a major role linking obesity to the development of associated metabolic complications, such as hypertension. Recent evidence has implicated central melanocortin signalling in the regulation of blood pressure in rodents and humans. The importance of sympathetic neural activity in mediating this association has been highlighted. Humans with loss-of-function mutations in the melanocortin 4 receptor (MC4R) are an ideal group of subjects in whom the importance of melanocortin signalling in linking obesity to hypertension can be studied. Consistent with rodent studies, it was recently demonstrated that humans with MC4R deficiency have lower blood pressure, less hypertension, lower 24-h urinary catecholamine excretion, lower resting heart rate and attenuated insulin-mediated sympathetic activation compared to equally-obese humans. In overweight and obese humans without MC4R mutations, the infusion of a highly-selective MC4R agonist led to dose-dependent increases in blood pressure and heart rate. All effects were independent of insulin. This evidence supports the notion that the melanocortin system regulates blood pressure and sympathetic neural function. The results obtained in rodent and human studies, in relation to blood pressure and sympathetic function, may limit the use of MC4R agonists for the treatment of obesity. Future studies will determine whether MC4R deficiency is associated with protection from development of the detrimental cardiovascular consequences that accompany obesity.

Conditional expression of the FTO gene product in rat INS-1 cells reveals its rapid turnover and a role in the profile of glucose-induced insulin secretion

Common polymorphisms within the FTO (fat mass and obesity-associated) gene correlate with increased BMI (body mass index) and a rising risk of Type 2 diabetes. FTO is highly expressed in the brain but has also been detected in peripheral tissues, including the endocrine pancreas, although its function there is unclear. The aim of the present study was to investigate the role of FTO protein in pancreatic β-cells using a conditional expression system developed in INS-1 cells. INS-1 cells were stably transfected with FTO–HA (haemagluttinin) incorporated under the control of a tetracycline-inducible promoter. Induction of FTO protein resulted in localization of the tagged protein to the nucleus. The level of FTO–HA protein achieved in transfected cells was tightly regulated, and experiments with selective inhibitors revealed that FTO–HA is rapidly degraded via the ubiquitin/proteasome pathway. The nuclear localization was not altered by proteasome inhibitors, although following treatment with PYR-41, an inhibitor of ubiquitination, some of the protein adopted a perinuclear localization. Unexpectedly, modestly increased expression of FTO–HA selectively enhanced the first phase of insulin secretion when INS-1 monolayers or pseudoislets were stimulated with 20 mM glucose, whereas the second phase remained unchanged. The mechanism responsible for the potentiation of glucose-induced insulin secretion is unclear; however, further experiments revealed that it did not involve an increase in insulin biosynthesis or any changes in STAT3 (signal transducer and activator of transcription 3) expression. Taken together, these results suggest that the FTO protein may play a hitherto unrecognized role in the control of first-phase insulin secretion in pancreatic β-cells.

Common variants near MC4R: exploring gender effects in overweight and obese children and adolescents participating in a lifestyle intervention

OBJECTIVE

Association with obesity and increased insulin levels have been reported for two variants (rs17782313 and rs12970134) located downstream of the melanocortin-4 receptor gene (MC4R).

METHODS

We investigated whether these variants have sex-specific effects on overweight, obesity and 14 related phenotypes in 889 overweight and obese children and adolescents. We also explored the impact of the variants on weight change in 367 of the 889 cases who participated in an intervention program. Prior to these analyses we showed that both variants were associated with overweight/obesity in the analyzed 889 cases versus 442 normal-weight and lean controls (case-control study).

RESULTS

In explorative analyses we observed higher diastolic blood pressure levels in males (rs17782313: β = 2.52 mm Hg per risk allele; p = 0.003) but reduced blood pressure level in females for the same risk allele (β = -1.72 mm Hg; p = 0.039). We also detected a greater BMI standard deviation score (BMI-SDS) reduction in females with the risk allele at rs17782313 (β = 0.086 per risk allele; p = 0.021). Additionally, we observed evidence for an association of the same risk allele with insulin levels (β = 0.029 log (μU/ml); p = 0.044) with no sex-specific effect. For the remaining 11 phenotypes, we observed no evidence for a (sex-specific) association.

CONCLUSIONS

In sum, our data support the associations of variants rs17782313 and rs12970134 near MC4R with early onset obesity and increased insulin levels. Exploratory evidence for sex-specific effects of the risk alleles were observed for diastolic blood pressure and BMI-SDS reduction.

Introduction to genetics and childhood obesity: relevance to nursing practice

PURPOSE

The aims for this article are to provide an overview of the current state of research on genetic contributions to the development of childhood obesity and to suggest genetic-focused nursing practices to prevent childhood obesity.

ORGANIZING CONSTRUCTS

Genetic epidemiology of childhood obesity, modes to identifying obesity genes, types of human obesity genes, and nursing implications are discussed.

CLINICAL RELEVANCE

The successful integration of genetics into nursing practice will provide opportunities for nurses to participate fully as major agents and collaborators in the health care revolution.

CONCLUSIONS

Practicing nurses across the profession will need to become knowledgeable about genetics and take part in obesity prevention through genetic assessment of susceptibility and appropriate environmental interventions.

The genetic epidemiology of obesity: a case study

Obesity (OMIM #601665) is a disease where excessive stores of body fat impact negatively on health. The first law of thermodynamics dictates that energy cannot be created or destroyed so if energy is taken into the body, but not transformed to ATP for metabolic work or dissipated as heat, it will be stored as fat. Therefore, the ultimate cause of obesity is a long-term positive energy imbalance [energy intake (EI) exceeds energy expenditure (EE)]. Despite this simple explanation, there is no single reason why EI may exceed EE meaning that the proximate causes of obesity are multi-factorial in origin involving a complex interplay of genetic, behavioural, and environmental influences on metabolism, diet, and activity.

Evidences on three relevant obesogenes: MC4R, FTO and PPARγ. Approaches for personalized nutrition

Obesity is a complex disease that results from the interaction between lifestyle (dietary patterns and sedentary habits) and genetic factors. The recognition of a genetic basis for human obesity has driven to identify putative causal genes to understand the pathways that control body mass and fat deposition in humans as well as to provide personalized treatments and prevention strategies to fight against obesity. More than 120 candidate genes have been associated with obesity-related traits. Genome-wide association study has so far identified over 20 novel loci convincingly associated with adiposity. This review is specifically focused on the study of the effects of melanocortin 4 receptor, Peroxisome proliferator-activated receptor γ and fat mass and obesity associated (FTO) gene variants and their interactions with dietary intake, physical activity or drug administration on body weight control. The advances in this field are expected to open new ways in genome-customized diets for obesity prevention and therapy following personalized approaches.

Life-threatening infectious diseases of childhood: single-gene inborn errors of immunity?

The hypothesis that inborn errors of immunity underlie infectious diseases is gaining experimental support. However, the apparent modes of inheritance of predisposition or resistance differ considerably among diseases and among studies. A coherent genetic architecture of infectious diseases is lacking. We suggest here that life-threatening infectious diseases in childhood, occurring in the course of primary infection, result mostly from individually rare but collectively diverse single-gene variations of variable clinical penetrance, whereas the genetic component of predisposition to secondary or reactivation infections in adults is more complex. This model is consistent with (i) the high incidence of most infectious diseases in early childhood, followed by a steady decline; (ii) theoretical modeling of the impact of monogenic or polygenic predisposition on the incidence distribution of infectious diseases before reproductive age; (iii) available molecular evidence from both monogenic and complex genetics of infectious diseases in children and adults; (iv) current knowledge of immunity to primary and secondary or latent infections; (v) the state of the art in the clinical genetics of noninfectious pediatric and adult diseases; and (vi) evolutionary data for the genes underlying single-gene and complex disease risk. With the recent advent of new-generation deep resequencing, this model of single-gene variations underlying severe pediatric infectious diseases is experimentally testable.

Current trends in targeting the hormonal regulation of appetite and energy balance to treat obesity

With the eruption of the obesity pandemic over the past few decades, much research has been devoted to understanding the molecular mechanisms by which the human body regulates energy balance. These studies have revealed several mediators, including gut/pancreatic/adipose hormones and neuropeptides that control both short- and long-term energy balance by regulating appetite and/or metabolism. These endogenous mediators of energy balance have been the focus of many anti-obesity drug-development programs aimed at either amplifying endogenous anorexigenic/lipolytic signaling or blocking endogenous orexigenic/lipogenic signaling. Here, we discuss the efficacy and safety of targeting these pathways for the pharmacologic treatment of obesity.

"Mens sana in corpore sano": exercise and hypothalamic ER stress

A novel mechanism explains how exercise exerts its beneficial effects on energy balance through an effect at the level of the hypothalamus.

Melanocortin-4 receptor gene variants in Chilean families: association with childhood obesity and eating behavior

OBJECTIVE

To screen for mutations in the coding region of the melanocortin-4 receptor (MC4R) gene and to assess the association between the rs17782313 variant near MC4R with childhood obesity and eating behavior.

SUBJECTS AND METHODS

A cross-sectional sample of 221 obese Chilean children and 268 parents were incorporated in the study to assemble 134 case-parent trios. We performed direct sequencing of the MC4R coding region while the rs17782313 variant was genotyped by a Taqman assay. Eating behavior scores were calculated using the Child Eating Behavior and Three Factor Eating Questionnaires adapted for Chilean families.

RESULTS

A low frequency of genetic variation in the coding region of MC4R was found in Chilean obese children (Thr150Ile mutation and polymorphisms Ile251Leu and Val103Ile). The rs17782313 variant is possibly associated with satiety responsiveness (P = 0.01) and enjoyment of food scores (P = 0.03).

CONCLUSION

The rs17782313 variant may influence eating behavior in obese children.

Leptin in human physiology and therapeutics

Leptin regulates energy homeostasis and reproductive, neuroendocrine, immune, and metabolic functions. In this review, we describe the role of leptin in human physiology and review evidence from recent "proof of concept" clinical trials using recombinant human leptin in subjects with congenital leptin deficiency, hypoleptinemia associated with energy-deficient states, and hyperleptinemia associated with garden-variety obesity. Since most obese individuals are largely leptin-tolerant or -resistant, therapeutic uses of leptin are currently limited to patients with complete or partial leptin deficiency, including hypothalamic amenorrhea and lipoatrophy. Leptin administration in these energy-deficient states may help restore associated neuroendocrine, metabolic, and immune function and bone metabolism. Leptin treatment is currently available for individuals with congenital leptin deficiency and congenital lipoatrophy. The long-term efficacy and safety of leptin treatment in hypothalamic amenorrhea and acquired lipoatrophy are currently under investigation. Whether combination therapy with leptin and potential leptin sensitizers will prove effective in the treatment of garden-variety obesity and whether leptin may have a role in weight loss maintenance is being greatly anticipated.

Functional role of suppressor of cytokine signaling 3 upregulation in hypothalamic leptin resistance and long-term energy homeostasis

OBJECTIVE

Hypothalamic leptin resistance is found in most common forms of obesity, such as diet-induced obesity, and is associated with increased expression of suppressor of cytokine signaling 3 (Socs3) in the hypothalamus of diet-induced obese animals. This study aims to determine the functional consequence of Socs3 upregulation on leptin signaling and obesity, and to investigate whether Socs3 upregulation affects energy balance in a cell type-specific way.

RESEARCH DESIGN AND METHODS

We generated transgenic mice overexpressing Socs3 in either proopiomelanocortin (POMC) or leptin receptor-expressing neurons, at levels similar to what is observed in diet-induced obesity.

RESULTS

Upregulation of Socs3 in POMC neurons leads to impairment of STAT3 and mammalian target of rapamycin (mTOR)-S6K-S6 signaling, with subsequent leptin resistance, obesity, and glucose intolerance. Unexpectedly, Socs3 upregulation in leptin receptor neurons results in increased expression of STAT3 protein in mutant hypothalami, but does not lead to obesity.

CONCLUSIONS

Our study establishes that Socs3 upregulation alone in POMC neurons is sufficient to cause leptin resistance and obesity. Socs3 upregulation impairs both STAT3 and mTOR signaling before the onset of obesity. The lack of obesity in mice with upregulated Socs3 in leptin receptor neurons suggests that Socs3's effect on energy balance could be cell type specific. Our study indicates that POMC neurons are important mediators of Socs3's effect on leptin resistance and obesity, but that other cell types or alteration of other signaling regulators could contribute to the development of obesity.

Defining the role of cholecystokinin in the lipid-induced human brain activation matrix

BACKGROUND & AIMS

In human beings, as in most vertebrates, the release of the intestinal peptide cholecystokinin (CCK) by ingested food plays a major role both in digestion and the regulation of further food intake, but the changes in brain function and their underlying activation mechanisms remain unknown. Our aim was to explore, using a novel physiologic magnetic resonance imaging approach, the temporospatial brain activation matrix, in response to ingestion of a lipid meal and, by use of a CCK-1 receptor antagonist, to define the role of CCK in this activation.

METHODS

We studied, in 19 healthy subjects, the brain activation responses to ingested lipid (dodecanoic acid) or saline (control) with magnetic resonance imaging. Gallbladder volume, plasma CCK levels, and subjective hunger and fullness scores were also recorded. The experiment was then repeated, with and without prior administration of the CCK-1 receptor antagonist dexloxiglumide (600 mg orally) with a controlled, randomized order, latin-square design.

RESULTS

Ingested lipid activated bilaterally a matrix of brain areas, particularly the brain stem, pons, hypothalamus, and also cerebellum and motor cortical areas. These activations were abolished by dexloxiglumide, indicating a CCK-mediated pathway, independent of any nutrient-associated awareness cues.

CONCLUSION

The identification of these activations now defines the lipid-activated brain matrix and provides a means by which the gut-derived homeostatic mechanisms of food regulation can be distinguished from secondary sensory and hedonic cues, thereby providing a new approach to exploring aberrant human gastrointestinal responses and eating behavior.

Postnatal Sim1 deficiency causes hyperphagic obesity and reduced Mc4r and oxytocin expression

Single-minded 1 (SIM1) mutations are one of the few known causes of nonsyndromic monogenic obesity in both humans and mice. Although the role of Sim1 in the formation of the hypothalamus has been described, its postdevelopmental, physiological functions have not been well established. Here we demonstrate that postnatal CNS deficiency of Sim1 is sufficient to cause hyperphagic obesity. We conditionally deleted Sim1 after birth using CaMKII-Cre (alpha-calcium/calmodulin-dependent protein kinase II-Cre) lines to recombine a floxed Sim1 allele. Conditional Sim1 heterozygotes phenocopied germ line Sim1 heterozygotes, displaying hyperphagic obesity and increased length. We also generated viable conditional Sim1 homozygotes, demonstrating that adult Sim1 expression is not essential for mouse or neuron survival and revealing a dosage-dependent effect of Sim1 on obesity. Using stereological cell counting, we showed that the phenotype of both germ line heterozygotes and conditional Sim1 homozygotes was not attributable to global hypocellularity of the paraventricular nucleus (PVN) of the hypothalamus. We also used retrograde tract tracing to demonstrate that the PVN of germ line heterozygous mice projects normally to the dorsal vagal complex and the median eminence. Finally, we showed that conditional Sim1 homozygotes and germ line Sim1 heterozygotes exhibit a remarkable decrease in hypothalamic oxytocin (Oxt) and PVN melanocortin 4 receptor (Mc4r) mRNA. These results demonstrate that the role of Sim1 in feeding regulation is not limited to formation of the PVN or its projections and that the hyperphagic obesity in Sim1-deficient mice may be attributable to changes in the leptin-melanocortin-oxytocin pathway.

Maternal Obesity and Associated Reproductive Consequences

The prevalence of obesity is continuing to increase among women. Women who are in their reproductive years are disproportionately affected by obesity. The link between obesity and increased morbidity from various conditions, including cardiovascular disease, Type 2 diabetes, osteoarthritis and malignancies, is well established. This article discusses the current state of obesity among reproductive age women in the USA and reviews the impact of maternal obesity on reproduction. The genetic contribution to human obesity is also discussed, as is reproduction following weight reduction surgery.

From monogenic to polygenic obesity: recent advances

The heritability of obesity and body weight in general is high. A small number of confirmed monogenic forms of obesity-the respective mutations are sufficient by themselves to cause the condition in food abundant societies-have been identified by molecular genetic studies. The elucidation of these genes, mostly based on animal and family studies, has led to the identification of important pathways to the disorder and thus to a deeper understanding of the regulation of body weight. The identification of inborn deficiency of the mostly adipocyte-derived satiety hormone leptin in extremely obese children from consanguineous families paved the way to the first pharmacological therapy for obesity based on a molecular genetic finding. The genetic predisposition to obesity for most individuals, however, has a polygenic basis. A polygenic variant by itself has a small effect on the phenotype; only in combination with other predisposing variants does a sizeable phenotypic effect arise. Common variants in the first intron of the 'fat mass and obesity associated' gene (FTO) result in an elevated body mass index (BMI) equivalent to approximately +0.4 kg/m(2) per risk allele. The FTO variants were originally detected in a genome wide association study (GWAS) pertaining to type 2 diabetes mellitus. Large meta-analyses of GWAS have subsequently identified additional polygenic variants. Up to December 2009, polygenic variants have been confirmed in a total of 17 independent genomic regions. Further study of genetic effects on human body weight regulation should detect variants that will explain a larger proportion of the heritability. The development of new strategies for diagnosis, treatment and prevention of obesity can be anticipated.

Obesity: is it a mental disorder?

OBJECTIVE

Using Wakefield's conceptualization of mental disorder as "harmful mental dysfunction" (Wakefield, Am Psychol, 47, 373-388, 1992), we examined the evidence for including obesity as a mental disorder in DSM-V.

METHOD

We searched computer databases and examined reference lists from review articles published in the last 10 years to identify empirical papers relevant to the present review.

RESULTS

Obesity is a condition of heterogeneous etiology that is harmful for most individuals. However, there is scant evidence that obesity, in general, is caused by mental dysfunction. Although recent work examining the neurocircuitry of energy balance has suggested that mental dysfunction may be involved in the etiology of specific obesity phenotypes, findings are too preliminary to support classification of obesity as a mental disorder. Nevertheless, there is evidence that obesity is related to mental disorder and many of the medications used to treat psychiatric illness.

DISCUSSION

There is little evidence for including obesity as a mental disorder in DSM-V. However, results confirm the importance of monitoring adiposity routinely among patients with psychiatric illness.

Genetic variation in the hypothalamic pathways and its role on obesity

Over recent decades, the prevalence of obesity has increased dramatically worldwide. Although this epidemic is mainly attributable to modern (western) lifestyle, multiple twin and adoption studies indicate the significant role of genes in the individual's predisposition to becoming obese. As the hypothalamus plays a central role in controlling body weight, its regulatory circuits may represent a crucial system in the pathogenesis of the disorder. Genetic variations in genes in the hypothalamic pathways may therefore contribute to the susceptibility for obesity in humans and animals. We summarize current knowledge on the physiological role of the hypothalamus in body-weight regulation and review genetic studies on the hypothalamic candidate genes in relation to obesity. Together, data from functional and genetic studies as well as the new, common, obesity loci identified in genome-wide association scans support an important role for the hypothalamic genes in predisposing to obesity. However, findings are still inconclusive for many candidate genes. To improve our understanding of the genetic architecture of common obesity, we suggest that specific obesity phenotypes should be considered and different analytical approaches used. Such studies should consider multiple genes from the same physiological pathways, together with environmental risk factors.

Leptin receptor signaling and the regulation of mammalian physiology

The adipocyte-derived hormone, leptin, signals the status of body energy stores to the central nervous system to regulate appetite and energy expenditure. A specific long-form leptin receptor (LepRb), a type I cytokine receptor, mediates leptin action on LepRb-expressing neurons in the brain. Leptin binding to LepRb activates the associated Janus kinase-2 (Jak2) tyrosine kinase to promote the phosphorylation of Jak2 and three residues on LepRb; each of these sites mediates a distinct aspect of downstream LepRb signaling, with differing physiologic functions. Tyr(1138) --> STAT3 signaling suppresses feeding, but is not required for a number of other leptin actions. Tyr(985) binds SH2-containing tyrosine phosphatase-2 and suppressor of cytokine signaling-3 and primarily mediates the attenuation of LepRb signaling in vivo. The role for Tyr(1077), the major regulator of signal transducer and activator of transcription-5 (STAT5) during leptin signaling, in the physiologic response to leptin remains unclear, although the obese phenotype of animals deleted for STAT5 in the brain suggests the potential importance of this signaling pathway. Leptin also modulates a number of other signaling pathways in the brain, including PI 3-kinase, mammalian target of rapamycin and AMP-dependent protein kinase; the pathways by which leptin controls these signals remain unclear, however, and may involve some indirect mechanisms. Important issues regarding leptin action and LepRb signaling in the future include not only the more thorough analysis of intracellular signaling pathways, but the neural substrate by which leptin acts, as most major populations of LepRb neurons remain poorly studied.

Hypothalamic lipotoxicity and the metabolic syndrome

Ectopic accumulation of lipids in peripheral tissues, such as pancreatic beta cells, liver, heart and skeletal muscle, leads to lipotoxicity, a process that contributes substantially to the pathophysiology of insulin resistance, type 2 diabetes, steatotic liver disease and heart failure. Current evidence has demonstrated that hypothalamic sensing of circulating lipids and modulation of hypothalamic endogenous fatty acid and lipid metabolism are two bona fide mechanisms modulating energy homeostasis at the whole body level. Key enzymes, such as AMP-activated protein kinase (AMPK) and fatty acid synthase (FAS), as well as intermediate metabolites, such as malonyl-CoA and long-chain fatty acids-CoA (LCFAs-CoA), play a major role in this neuronal network, integrating peripheral signals with classical neuropeptide-based mechanisms. However, one key question to be addressed is whether impairment of lipid metabolism and accumulation of specific lipid species in the hypothalamus, leading to lipotoxicity, have deleterious effects on hypothalamic neurons. In this review, we summarize what is known about hypothalamic lipid metabolism with focus on the events associated to lipotoxicity, such as endoplasmic reticulum (ER) stress in the hypothalamus. A better understanding of these molecular mechanisms will help to identify new drug targets for the treatment of obesity and metabolic syndrome.

A deletion of the HBII-85 class of small nucleolar RNAs (snoRNAs) is associated with hyperphagia, obesity and hypogonadism

Genetic studies in patients with severe early-onset obesity have provided insights into the molecular and physiological pathways that regulate body weight in humans. We report a 19-year-old male with hyperphagia and severe obesity, mild learning difficulties and hypogonadism, in whom diagnostic tests for Prader-Willi syndrome (PWS) had been negative. We carried out detailed clinical and metabolic phenotyping of this patient and investigated the genetic basis of this obesity syndrome using Agilent 185 k array comparative genomic hybridization (aCGH) and Affymetrix 6.0 genotyping arrays. The identified deletion was validated using multiplex ligation-dependent probe amplification and long-range PCR, followed by breakpoint sequencing which enabled precise localization of the deletion. We identified a approximately 187 kb microdeletion at chromosome 15q11-13 that encompasses non-coding small nucleolar RNAs (including HBII-85 snoRNAs) which were not expressed in peripheral lymphocytes from the patient. Characterization of the clinical phenotype revealed increased ad libitum food intake, normal basal metabolic rate when adjusted for fat-free mass, partial hypogonadotropic hypogonadism and growth failure. We have identified a novel deletion on chromosome 15q11-13 in an individual with hyperphagia, obesity, hypogonadism and other features associated with PWS, which is normally caused by deficiency of several paternally expressed imprinted transcripts within chromosome 15q11-13, a region that includes multiple protein-coding genes as well as several non-coding snoRNAs. These findings provide direct evidence for the role of a particular family of non-coding RNAs, the HBII-85 snoRNA cluster, in human energy homeostasis, growth and reproduction.

Effects of trans-10,cis-12 conjugated linoleic acid on body composition in genetically obese mice

Conjugated linoleic acid (CLA) has shown a number of biologically beneficial effects, including prevention of obesity. The purpose of this study was to test effects of dietary supplementation of 0.5% trans-10,cis-12 CLA in a high fat diet in neuronal basic helix-loop-helix 2 knock-out animals (N2KO), which is a unique animal model representing adult-onset inactivity-related obesity. Eight wild-type (WT) and eight N2KO female mice were fed either 0.5% trans-10,cis-12 CLA-containing diet or control diet (with 20% soybean oil diet) for 12 weeks. Body weights, food intake, adipose tissue weights, body compositions, and blood parameters were analyzed. Overall, N2KO animals had greater body weights, food intake, adipose tissue weights, and body fat compared to WT animals. CLA supplementation decreased overall body weights and total fat, and the effect of dietary CLA on adipose tissue reduction was greater in N2KO than in WT mice. Serum leptin and triglyceride levels were reduced by CLA in both N2KO and WT animals compared to control animals, while there was no effect by CLA on serum cholesterol. The effect of CLA to lower fat mass, increase lean body mass, and lower serum leptin and triglycerides in sedentary mice supports the possibility of using CLA to prevent or alleviate ailments associated with obesity.

Childhood obesity: are genetic differences involved?

This brief review focuses on the genetic contribution to childhood obesity. Evidence for a genetic component to excess body weight during growth is presented from the perspective of genetic epidemiology studies. Parental obesity is a predictor of childhood excess weight. The familial risk ratio for childhood obesity when a parent is obese reaches >2.5. Birth weight is characterized by a genetic heritability component on the order of 30%, with significant maternal and paternal effects in addition to the newborn genes. About 5% of childhood obesity cases are caused by a defect that impairs function in a gene, and >/=5 of these genes have been uncovered. However, the common forms of childhood obesity seem to result from a predisposition that primarily favors obesogenic behaviors in an obesogenic environment. Candidate gene and genomewide association studies reveal that these obesogenic genes have small effect sizes but that the risk alleles for obesity are quite common in populations. The latter may translate into a highly significant population-attributable risk of obesity. Gene-environment interaction studies suggest that the effects of predisposing genes can be enhanced or diminished by exposure to relevant behaviors. It is possible that the prevalence of childhood obesity is increasing across generations as a result of positive assortative mating with obese husbands and wives contributing more obese offspring than normal-weight parents.

SLC6A3 and body mass index in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial

Background

To investigate the contribution of the dopamine transporter to dopaminergic reward-related behaviors and anthropometry, we evaluated associations between polymorphisms at the dopamine transporter gene(SLC6A3) and body mass index (BMI), among participants in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial.

Methods

Four polymorphisms (rs6350, rs6413429, rs6347 and the 3' variable number of tandem repeat (3' VNTR) polymorphism) at the SLC6A3 gene were genotyped in 2,364 participants selected from the screening arm of PLCO randomly within strata of sex, age and smoking history. Height and weight at ages 20 and 50 years and baseline were assessed by questionnaire. BMI was calculated and categorized as underweight, normal, overweight and obese (<18.5, 18.5–24.9, 25.0–29.9, or ≥ 30 kg/m², respectively). Odds ratios (ORs) and 95% confidence intervals (CIs) of SLC6A3 genotypes and haplotypes were computed using conditional logistic regression.

Results

Compared with individuals having a normal BMI, obese individuals at the time of the baseline study questionnaire were less likely to possess the 3' VNTR variant allele with 9 copies of the repeated sequence in a dose-dependent model (** is referent; OR_*9 = 0.80, OR₉₉ = 0.47, p_trend = 0.005). Compared with individuals having a normal BMI at age 50, overweight individuals (A-C-G-* is referent; OR_A-C-G-9 = 0.80, 95% CI 0.65–0.99, p = 0.04) and obese individuals (A-C-G-* is referent; OR_A-C-G-9 = 0.70, 95% CI 0.49–0.99, p = 0.04) were less likely to possess the haplotype with the 3'variant allele (A-C-G-9).

Conclusion

Our results support a role of genetic variation at the dopamine transporter gene, SLC6A3, as a modifier of BMI.

Endoplasmic reticulum stress plays a central role in development of leptin resistance

Leptin has not evolved as a therapeutic modality for the treatment of obesity due to the prevalence of leptin resistance in a majority of the obese population. Nevertheless, the molecular mechanisms of leptin resistance remain poorly understood. Here, we show that increased endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) in the hypothalamus of obese mice inhibits leptin receptor signaling. The genetic imposition of reduced ER capacity in mice results in severe leptin resistance and leads to a significant augmentation of obesity on a high-fat diet. Moreover, we show that chemical chaperones, 4-phenyl butyric acid (PBA), and tauroursodeoxycholic acid (TUDCA), which have the ability to decrease ER stress, act as leptin-sensitizing agents. Taken together, our results may provide the basis for a novel treatment of obesity.

Modulation of blood pressure by central melanocortinergic pathways

BACKGROUND

Weight gain and weight loss are associated with changes in blood pressure through unknown mechanisms. Central melanocortinergic signaling is implicated in the control of energy balance and blood pressure in rodents, but there is no information regarding such an association with blood pressure in humans.

METHODS

We assessed blood pressure, heart rate, and urinary catecholamines in overweight or obese subjects with a loss-of-function mutation in MC4R, the gene encoding the melanocortin 4 receptor, and in equally overweight control subjects. We also examined the effects of an MC4R agonist administered for 7 days in 28 overweight or obese volunteers.

RESULTS

The prevalence of hypertension was markedly lower in the MC4R-deficient subjects than in the control subjects (24% vs. 53%, P=0.009). After the exclusion of subjects taking antihypertensive medications, blood-pressure levels were significantly lower in MC4R-deficient subjects than in control subjects, with mean (+/-SE) systolic blood pressures of 123+/-14 mm Hg and 131+/-12 mm Hg, respectively (P=0.02), and mean diastolic blood pressures of 73+/-10 mm Hg and 79+/-7 mm Hg, respectively (P=0.03). As compared with control subjects, MC4R-deficient subjects had a lower increase in heart rate on waking (P=0.007), a lower heart rate during euglycemic hyperinsulinemia (P<0.001), and lower 24-hour urinary norepinephrine excretion (P=0.04). The maximum tolerated daily dose of 1.0 mg of the MC4R agonist led to significant increases of 9.3+/-1.9 mm Hg in systolic blood pressure and of 6.6+/-1.1 mm Hg in diastolic blood pressure (P<0.001 for both comparisons) at 24 hours, as compared with placebo. Differences in blood pressure were not explained by changes in insulin levels; there were no significant adverse events.

CONCLUSIONS

Results of our genetic and pharmacologic studies implicate melanocortinergic signaling in the control of human blood pressure through an insulin-independent mechanism.

Hypothalamic lipids and the regulation of energy homeostasis

The hypothalamus is a specialised area in the brain that integrates the control of energy homeostasis, regulating both food intake and energy expenditure. The classical theory for hypothalamic feeding control is mainly based on the relationship between peripheral signals and neurotransmitters/neuromodulators in the central nervous system. Thus, hypothalamic neurons respond to peripheral signals, such as hormones and nutrients, by modifying the synthesis of neuropeptides. Despite the well-established role of these hypothalamic networks, increasing evidence indicates that the modulation of lipid metabolism in the hypothalamus plays a critical role in feeding control. In fact, the pharmacologic and genetic targeting of key enzymes from these pathways, such as AMP-activated protein kinase, acetyl-CoA carboxylase, carnitine palmitoyltransferase 1, fatty acid synthase, and malonyl-CoA decarboxylase, has a profound effect on food intake and body weight. Here, we review what is currently known about the relationship between hypothalamic lipid metabolism and whole body energy homeostasis. Defining these novel mechanisms may offer new therapeutic targets for the treatment of obesity and its associated pathologies.

Environmental and genetic risk factors in obesity

Because of its high prevalence and the associated medical and psychosocial risks, research into the causes of childhood obesity has experienced a tremendous upswing. Formal genetic data based on twin, adoption, and family studies lead to the conclusion that at least 50% of the interindividual variance of the body mass index (BMI; defined as weight in kilograms divided by height in meters squared) is due to genetic factors. As a result of the recent advent of genome-wide association studies, the first polygenes involved in body weight regulation have been detected. Each of the predisposing alleles explain a few hundred grams of body weight. More polygenes will be detected in the near future, thus for the first time allowing in-depth analyses of gene-gene and gene-environment interactions. They also will enable developmental studies to assess the effect of such alleles throughout childhood and adulthood. The recent increase in obesity prevalence rates illustrates the extreme relevance of environmental factors for body weight. Similar to polygenes, the effect sizes of most such environmental factors are likely to be small, thus rendering their detection difficult. In addition, the validation of the true causality of such factors is not a straightforward task. Important factors are socioeconomic status and television consumption. The authors conclude by briefly assessing implications for treatment and prevention of childhood obesity.

Leptin resistance: a prediposing factor for diet-induced obesity

Obesity is a resilient and complex chronic disease. One potential causative factor in the obesity syndrome is leptin resistance. Leptin behaves as a potent anorexic and energy-enhancing hormone in most young or lean animals, but its effects are diminished or lacking in the obese state associated with a normal genetic background. Emerging evidence suggests that leptin resistance predisposes the animal to exacerbated diet-induced obesity (DIO). Elevation of central leptin in young, lean rats induces a leptin resistance that precludes obesity on a chow diet but accelerates high-fat (HF)-induced obesity. Similarly, chronic dietary fructose consumption evokes a leptin resistance that causes obesity only upon HF exposure. Inherent central leptin insensitivity also contributes to dietary weight gain in certain obesity-prone rats. Conversely, aged, leptin-resistant animals are obese with continuous chow feeding and demonstrate aggravated obesity when challenged with an HF diet. Additionally, a submaximal central blockade with a leptin antagonist leads to obesity on both chow and HF diets, as is the case in rodents with leptin receptor deficiency of genetic origin. Despite the differences in the incidence of obesity on a chow diet, all of these forms of leptin resistance predispose rodents to aggravated HF-mediated obesity. Moreover, once leptin resistance takes hold, it aggravates DIO, and the leptin resistance and obesity compound one another, promoting a vicious cycle of escalating weight gain.

An obesity-associated FTO gene variant and increased energy intake in children

BACKGROUND

Variation in the fat mass and obesity-associated (FTO) gene has provided the most robust associations with common obesity to date. However, the role of FTO variants in modulating specific components of energy balance is unknown.

METHODS

We studied 2726 Scottish children, 4 to 10 years of age, who underwent genotyping for FTO variant rs9939609 and were measured for height and weight. A subsample of 97 children was examined for possible association of the FTO variant with adiposity, energy expenditure, and food intake.

RESULTS

In the total study group and the subsample, the A allele of rs9939609 was associated with increased weight (P=0.003 and P=0.049, respectively) and body-mass index (P=0.003 and P=0.03, respectively). In the intensively phenotyped subsample, the A allele was also associated with increased fat mass (P=0.01) but not with lean mass. Although total and resting energy expenditures were increased in children with the A allele (P=0.009 and P=0.03, respectively), resting energy expenditure was identical to that predicted for the age and weight of the child, indicating that there is no defect in metabolic adaptation to obesity in persons bearing the risk-associated allele. The A allele was associated with increased energy intake (P=0.006) independently of body weight. In contrast, the weight of food ingested by children who had the allele was similar to that in children who did not have the allele (P=0.82).

CONCLUSIONS

The FTO variant that confers a predisposition to obesity does not appear to be involved in the regulation of energy expenditure but may have a role in the control of food intake and food choice, suggesting a link to a hyperphagic phenotype or a preference for energy-dense foods.

Human obesity as a heritable disorder of the central control of energy balance

In the spirit of celebration associated with the 20th anniversary of the Pennington Biomedical Research Center, we have seized the opportunity of taking a highly personal and not at all comprehensive 'whistle-stop tour' of a large body of evidence that, we feel, supports the following conclusions: (1) that body fat stores are regulated by biological control processes in humans as they are in lower animals; (2) that there are major inherited influences on the efficiency whereby such control processes operate in humans; (3) that the precise nature of those genetic and biological influences and how they interact with environmental factors are beginning to be understood; (4) that most of the genes discovered thus far have their principal impact on hunger, satiety and food intake; (5) that while there is understandable resistance to the notion that genes can influence a human behavior such as the habitual ingestion of food, the implications of these discoveries are essentially benign. Indeed, we hope that they may eventually lead to improved treatment for patients and, in addition, help to inculcate a more enlightened attitude to the obese with a reduction in their experience of social and economic discrimination.

The FTO gene and measured food intake in children

OBJECTIVE

Polymorphisms in the obesity-associated gene, FTO, have been linked with sensitivity to satiety in children, indicating FTO may be influencing one of the regulatory drivers underlying food intake. In this study, we tested the hypothesis that food intake in a standard eating behaviour paradigm in which palatable food is offered under conditions of satiety would be associated with FTO genotype status, after controlling for differences in body mass index (BMI).

METHODS

Participants were 131 children aged 4-5 years, taking part in a behavioural study of food intake for whom DNA was available for genotyping. The phenotypic indicator of intake was the child's consumption of palatable food presented after having eaten a meal. We also assessed physical activity using parental reports of the child's enjoyment of active games, their level of activity relative to other children and a standard measure of fidgetiness. Associations between polymorphisms of the intronic FTO single nucleotide polymorphism (rs9939609) and behaviour (food intake and activity) were assessed by analysis of variance controlling for sex, age and BMI s.d. scores.

RESULTS

The distribution of AA (homogenous for A allele), AT (heterogeneous T and A alleles) and TT (homogenous for T allele) genotypes was 18, 50 and 32%, respectively. As predicted, TT homozygotes ate significantly less than heterozygotes (P=0.03) or AA homozygotes (P=0.02). The effect was not diminished by controlling for BMI s.d. scores. There were no significant associations between FTO genotype and any marker of physical activity.

CONCLUSIONS

We showed that children with two copies of the lower-risk FTO alleles ate less than those with one or two higher-risk alleles. We conclude that the T allele is protective against overeating by promoting responsiveness to internal signals of satiety.

The contribution of animal models to the study of obesity

Obesity results from prolonged imbalance of energy intake and energy expenditure. Animal models have provided a fundamental contribution to the historical development of understanding the basic parameters that regulate the components of our energy balance. Five different types of animal model have been employed in the study of the physiological and genetic basis of obesity. The first models reflect single gene mutations that have arisen spontaneously in rodent colonies and have subsequently been characterized. The second approach is to speed up the random mutation rate artificially by treating rodents with mutagens or exposing them to radiation. The third type of models are mice and rats where a specific gene has been disrupted or over-expressed as a deliberate act. Such genetically-engineered disruptions may be generated through the entire body for the entire life (global transgenic manipulations) or restricted in both time and to certain tissue or cell types. In all these genetically-engineered scenarios, there are two types of situation that lead to insights: where a specific gene hypothesized to play a role in the regulation of energy balance is targeted, and where a gene is disrupted for a different purpose, but the consequence is an unexpected obese or lean phenotype. A fourth group of animal models concern experiments where selective breeding has been utilized to derive strains of rodents that differ in their degree of fatness. Finally, studies have been made of other species including non-human primates and dogs. In addition to studies of the physiological and genetic basis of obesity, studies of animal models have also informed us about the environmental aspects of the condition. Studies in this context include exploring the responses of animals to high fat or high fat/high sugar (Cafeteria) diets, investigations of the effects of dietary restriction on body mass and fat loss, and studies of the impact of candidate pharmaceuticals on components of energy balance. Despite all this work, there are many gaps in our understanding of how body composition and energy storage are regulated, and a continuing need for the development of pharmaceuticals to treat obesity. Accordingly, reductions in the use of animal models, while ethically desirable, will not be feasible in the short to medium term, and indeed an expansion in activity using animal models is anticipated as the epidemic continues and spreads geographically.

Further evidence for the role of ENPP1 in obesity: association with morbid obesity in Finns

The aim of this study was to investigate a series of single-nucleotide polymorphisms (SNPs) in the genes MC2R, MC3R, MC4R, MC5R, POMC, and ENPP1 for association with obesity. Twenty-five SNPs (2-7 SNPs/gene) were genotyped in 246 Finns with extreme obesity (BMI > or = 40 kg/m2) and in 481 lean subjects (BMI 20-25 kg/m2). Of the obese subjects, 23% had concomitant type 2 diabetes. SNPs and SNP haplotypes were tested for association with obesity and type 2 diabetes. Allele frequencies differed between obese and lean subjects for two SNPs in the ENPP1 gene, rs1800949 (P = 0.006) and rs943003 (P = 0.0009). These SNPs are part of a haplotype (rs1800949 C-rs943003 A), which was observed more frequently in lean subjects compared to obese subjects (P = 0.0007). Weaker associations were detected between the SNPs rs1541276 in the MC5R, rs1926065 in the MC3R genes and obesity (P = 0.04 and P = 0.03, respectively), and between SNPs rs2236700 in the MC5R, rs2118404 in the POMC, rs943003 in the ENPP1 genes and type 2 diabetes (P = 0.03, P = 0.02 and P = 0.02, respectively); these associations did not, however, remain significant after correction for multiple testing. In conclusion, a previously unexplored ENPP1 haplotype composed of SNPs rs1800949 and rs943003 showed suggestive evidence for association with adult-onset morbid obesity in Finns. In this study, we did not find association between the frequently studied ENPP1 K121Q variant, nor SNPs in the MCR or POMC genes and obesity or type 2 diabetes.

Hypothalamic regulation of appetite

The prevalence of obesity is steadily rising and has huge health and financial implications for society. Weight gain is due to an imbalance between dietary intake and energy expenditure and research has focused on trying to understand the complex pathways involved in controlling these aspects. This review highlights the key areas of research in the hypothalamic control of appetite. The hypothalamus consists of several nuclei that integrate peripheral signals, such as adiposity and caloric intake, to regulate important pathways within the CNS controlling food intake. The best characterized pathways are the orexigenic neuropeptide Y/Agouti-related protein and the anorexigenic pro-opiomelanocortin/cocaine- and amphetamine-related transcript neurons in the arcuate nucleus of the hypothalamus. These project from the arcuate nucleus to other key hypothalamic nuclei, such as the paraventricular, dorsomedial, ventromedial and lateral hypothalamic nuclei. There are also projections to and from the brainstem, cortical areas and reward pathways, all of which influence food intake. The challenge at present is to understand the complexity of these pathways and try to find ways of modulating them in order to find potential therapeutic targets.

Obesity associated genetic variation in FTO is associated with diminished satiety

CONTEXT

Polymorphisms within the FTO gene have consistently been associated with obesity across multiple populations. However, to date, it is not known whether the association between genetic variation in FTO and obesity is mediated through effects on energy intake or energy expenditure.

OBJECTIVE

Our objective was to examine the association between alleles of FTO known to increase obesity risk and measures of habitual appetitive behavior.

METHODS

The intronic FTO single nucleotide polymorphism (rs9939609) was genotyped in 3337 United Kingdom children in whom measures of habitual appetitive behavior had been assessed using two scales (Satiety Responsiveness and Enjoyment of Food) from the Child Eating Behaviour Questionnaire, a psychometric tool that has been validated against objective measures of food intake. Associations of FTO genotype with indices of adiposity and appetite were assessed by ANOVA.

RESULTS

As expected, the A allele was associated with increased adiposity in this cohort and in an independent case-control replication study of United Kingdom children of similar age. AA homozygotes had significantly reduced Satiety Responsiveness scores (P = 0.008, ANOVA). Mediation analysis indicated that the association of the AA genotype with increased adiposity was explained in part through effects on Satiety Responsiveness.

CONCLUSIONS

We have used a unique dataset to examine the relationship between a validated measure of children's habitual appetitive behavior and FTO obesity risk genotype and conclude that the commonest known risk allele for obesity is likely to exert at least some of its effects by influencing appetite.

Endocrine functions of adipose tissue

Obesity is a risk factor for type 2 diabetes, dyslipidemia, and cardiovascular disease. Dissection of the molecular mechanisms underlying obesity and its relationship to insulin resistance and the metabolic syndrome are essential for developing new strategies for prevention and treatment of these disorders. Both excess adipose tissue and lack of adipose tissue cause insulin resistance and dyslipidemia, suggesting that normal fat is required for the maintenance of systemic glucose and lipid homeostasis. Recent advances in obesity research have led to the recognition that adipose tissue is an active endocrine organ that secretes multiple bioactive factors termed adipokines. Secretion of adipokines provides a link between adipose tissue lipid accumulation and the metabolic function of other tissues such as liver and muscle. Dysregulation of adipokines is emerging as an important mechanism by which adipose tissue contributes to systemic insulin resistance and metabolic disease.

Relevance of animal models to human eating disorders and obesity

BACKGROUND AND RATIONALE

This review addresses the role animal models play in contributing to our knowledge about the eating disorders anorexia nervosa (AN) and bulimia nervosa (BN) and obesity.

OBJECTIVES

Explore the usefulness of animal models in complex biobehavioral familial conditions, such as AN, BN, and obesity, that involve interactions among genetic, physiologic, psychological, and cultural factors.

RESULTS AND CONCLUSIONS

The most promising animal model to mimic AN is the activity-based anorexia rodent model leading to pathological weight loss. The paradigm incorporates reward elements of the drive for activity in the presence of an appetite and allows the use of genetically modified animals. For BN, the sham-feeding preparation in rodents equipped with a gastric fistula appears to be best suited to reproduce the postprandial emesis and the defects in satiety. Animal models that incorporate genes linked to behavior and mood may clarify biobehavioral processes underlying AN and BN. By contrast, a relative abundance of animal models has contributed to our understanding of human obesity. Both environmental and genetic determinants of obesity have been modeled in rodents. Here, we consider single gene mutant obesity models, along with models of obesigenic environmental conditions. The contributions of animal models to obesity research are illustrated by their utility for identifying genes linked to human obesity, for elucidating the pathways that regulate body weight and for the identification of potential therapeutic targets. The utility of these models may be further improved by exploring the impact of experimental manipulations on the behavioral determinants of energy balance.