151
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Levin BE, Magnan C, Migrenne S, Chua SC, Dunn-Meynell AA. F-DIO obesity-prone rat is insulin resistant before obesity onset. Am J Physiol Regul Integr Comp Physiol 2005; 289:R704-11. [PMID: 15879056 DOI: 10.1152/ajpregu.00216.2005] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We previously created a novel F-DIO rat strain derived by crossing rats selectively bred for the diet-induced obesity (DIO) phenotype with obesity-resistant Fischer F344 rats. The offspring retained the DIO phenotype through 3 backcrosses with F344 rats but also had exaggerated insulin responses to oral glucose before they became obese on a 31% fat high-energy (HE) diet. Here, we demonstrate that chow-fed rats from the subsequent randomly bred progeny required 57% lower glucose infusions to maintain euglycemia during a hyperinsulinemic clamp in association with 45% less insulin-induced hepatic glucose output inhibition and 80% lower insulin-induced glucose uptake than F344 rats. The DIO phenotype and exaggerated insulin response to oral glucose in the nonobese, chow-fed state persisted in the F6 generation. Also, compared with F344 rats, chow-fed F-DIO rats had 68% higher arcuate nucleus proopiomelanocortin mRNA expression which, unlike the increase in F344 rats, was decreased by 26% on HE diet. Further, F-DIO lateral hypothalamic orexin expression was 18% lower than in F344 rats and was increased rather than decreased by HE diet intake. Finally, both maternal obesity and 30% caloric restriction during the third week of gestation produced F-DIO offspring which were heavier and had higher leptin and insulin levels than lean F-DIO dam offspring. Third-gestational week dexamethasone also produced offspring with higher leptin and insulin levels but with lower body weight. Thus F-DIO rats represent a novel and potentially useful model for the study of DIO, insulin resistance, and perinatal factors that influence the development and persistence of obesity.
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Affiliation(s)
- Barry E Levin
- Neurology Service (127C), VA Medical Center, 385 Tremont Avenue, E. Orange, NJ 07018-1095, USA.
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152
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Heijboer AC, van den Hoek AM, Pijl H, Voshol PJ, Havekes LM, Romijn JA, Corssmit EPM. Intracerebroventricular administration of melanotan II increases insulin sensitivity of glucose disposal in mice. Diabetologia 2005; 48:1621-6. [PMID: 15971058 DOI: 10.1007/s00125-005-1838-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2004] [Accepted: 02/26/2005] [Indexed: 01/08/2023]
Abstract
AIMS/HYPOTHESIS The present study was conducted to evaluate the effects of central administration of melanotan II (MTII), a melanocortin-3/4 receptor agonist, on hepatic and whole-body insulin sensitivity, independent of food intake and body weight. METHODS Over a period of 24 h, 225 ng of MTII was injected in three aliquots into the left lateral ventricle of male C57Bl/6 mice. The animals had no access to food. The control group received three injections of distilled water. Whole-body and hepatic insulin sensitivity were measured by hyperinsulinaemic-euglycaemic clamp in combination with [(3)H]glucose infusion. Glut4 mRNA expression was measured in skeletal muscle. RESULTS Plasma glucose and insulin concentrations under basal and hyperinsulinaemic conditions were similar in MTII- and placebo-treated mice. Endogenous glucose production (EGP) and glucose disposal in the basal state were significantly higher in MTII-treated mice than in the control group (71+/-22 vs 43+/-12 micromol.min(-1).kg(-1), p<0.01). During hyperinsulinaemia, glucose disposal was significantly higher in MTII-treated mice (151+/-20 vs 108+/-20 micromol.min(-1).kg(-1), p<0.01). In contrast, the inhibitory effect of insulin on EGP was not affected by MTII (relative decrease in EGP: 45+/-27 vs 50+/-20%). Glut4 mRNA expression in skeletal muscle was significantly increased in MTII-treated mice (307+/-94 vs 100+/-56%, p<0.01). CONCLUSIONS/INTERPRETATION Intracerebroventricular administration of MTII acutely increases insulin-mediated glucose disposal but does not affect the capacity of insulin to suppress EGP in C57Bl/6 mice. These data indicate that central stimulation of melanocortin-3/4 receptors modulates insulin sensitivity in a tissue-specific manner, independent of its well-known impact on feeding and body weight.
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MESH Headings
- Animals
- Blood Glucose/metabolism
- Corticosterone/blood
- Fatty Acids, Nonesterified/blood
- Glucose/metabolism
- Glucose Clamp Technique
- Glucose Transporter Type 4
- Injections, Intraventricular
- Insulin/blood
- Insulin/physiology
- Insulin Resistance/physiology
- Kinetics
- Liver/drug effects
- Liver/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Monosaccharide Transport Proteins/metabolism
- Muscle Proteins/metabolism
- Peptides, Cyclic/administration & dosage
- Peptides, Cyclic/pharmacology
- RNA, Messenger/biosynthesis
- Receptor, Melanocortin, Type 3/agonists
- Receptor, Melanocortin, Type 4/agonists
- alpha-MSH/administration & dosage
- alpha-MSH/analogs & derivatives
- alpha-MSH/pharmacology
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Affiliation(s)
- A C Heijboer
- Department of Endocrinology and Metabolic Diseases, Leiden University Medical Center, 2300 RC Leiden, The Netherlands.
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153
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Coll AP, Challis BG, López M, Piper S, Yeo GSH, O'Rahilly S. Proopiomelanocortin-deficient mice are hypersensitive to the adverse metabolic effects of glucocorticoids. Diabetes 2005; 54:2269-76. [PMID: 16046291 DOI: 10.2337/diabetes.54.8.2269] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Congenital lack of proopiomelanocortin (POMC) causes obesity and glucocorticoid deficiency. The responses of Pomc-/- and wild-type mice to the administration of corticosterone were compared. In study 1, mice were given corticosterone-supplemented water (CORT) for 10 days, resulting in plasma CORT levels within the physiological range, with partial suppression of hypothalamic corticotropin-releasing hormone expression to a similar degree between genotypes. Body weight, fat mass, and food intake increased in CORT-treated Pomc-/- but not wild-type mice. CORT increased plasma insulin levels 50-fold in Pomc-/- versus 14-fold in wild-type mice (P < 0.01) and increased hypothalamic agouti-related protein (AgRP) expression by more than 200% in Pomc-/- versus 40% in wild type (P < 0.05). In study 2, mice were given CORT from weaning, and Pomc-/- but not wild-type mice developed hyperglycemia, ketonuria, and hepatic steatosis by 8-12 weeks. Thus, Pomc-/- mice are hypersensitive to the adverse metabolic effects of glucocorticoids. Additionally, as the levels of plasma CORT achieved, especially in study 1, were not grossly supraphysiological, we conclude that glucocorticoid deficiency may afford Pomc-/- mice some protection from the full adverse consequences of melanocortin deficiency. This may occur through a mechanism involving the suppression of AgRP by the hypoadrenal state.
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Affiliation(s)
- Anthony P Coll
- University Department of Medicine,Addenbrooke's Hospital, Cambridge CB2 2QR, UK
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154
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Abstract
There is increasing concern about the rapidly rising incidence of obesity worldwide and its impact both on mortality, morbidity and the cost of healthcare. In the last 15 years, a large volume of research has linked low birth weight to many adult diseases in humans, such as Type II diabetes, cardiovascular disease, hypertension and the metabolic syndrome. Obesity is a causal factor in all these conditions. There are epidemiological studies linking low birth weight to increased adiposity, but the timing of the insult during gestation seems crucial, as reducing maternal nutrition in late gestation and during lactation causes a reduction in later obesity. Recent studies in animal models have provided clues towards mechanisms of altered appetite regulation following alterations in fetal and neonatal growth. The outcome of these and future studies could prove clinically crucial, particularly in the debate over the benefits of breast feeding, which provides a lower plane of nutrition compared with formula feeding.
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Affiliation(s)
- Roselle L Cripps
- Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 2QR, UK.
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155
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Cone RD. Anatomy and regulation of the central melanocortin system. Nat Neurosci 2005; 8:571-8. [PMID: 15856065 DOI: 10.1038/nn1455] [Citation(s) in RCA: 1100] [Impact Index Per Article: 57.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Accepted: 03/15/2005] [Indexed: 12/12/2022]
Abstract
The central melanocortin system is perhaps the best-characterized neuronal pathway involved in the regulation of energy homeostasis. This collection of circuits is unique in having the capability of sensing signals from a staggering array of hormones, nutrients and afferent neural inputs. It is likely to be involved in integrating long-term adipostatic signals from leptin and insulin, primarily received by the hypothalamus, with acute signals regulating hunger and satiety, primarily received by the brainstem. The system is also unique from a regulatory point of view in that it is composed of fibers expressing both agonists and antagonists of melanocortin receptors. Given that the central melanocortin system is an active target for development of drugs for the treatment of obesity, diabetes and cachexia, it is important to understand the system in its full complexity, including the likelihood that the system also regulates the cardiovascular and reproductive systems.
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Affiliation(s)
- Roger D Cone
- Vollum Institute and the Center for the Study of Weight Regulation, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA.
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156
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Abstract
The healthcare burden that the obesity epidemic now poses in highly significant, in part due to increased risk of secondary chronic diseases such as hypertension. A lack of physical activity and high fat diets are major factors contributing to this condition. However, increasingly apparent is the genetic predisposition of individuals and ethnic groups to obesity. Present treatment strategies are currently inadequate and unlikely to have a major effect on the future prevalence of obesity. To slow the obesity epidemic, the source needs to be tackled now through fundamental research into the mechanisms by which obesity is manifest, and education on the risks and how to prevent it. This article will describe current and emerging treatments for obesity and review the recent advances in research that may provide the antiobesity treatments of the future. Research into obesity has escalated at considerable pace, catalysed by the discovery of the obese gene product leptin. Leptin is secreted by adipose tissue and acts via specific receptors in the brain to engage central neural pathways involved in regulating energy homeostasis. Since this discovery, numerous significant advances have been made in our understanding of how the brain integrates and responds to central and peripheral signals involved in maintaining energy homeostasis, and how disruption of these signalling mechanisms can manifest as obesity. As a consequence of these findings, numerous potential sites for therapeutic intervention into this condition have and are materializing. The aim of this review is to highlight current treatment strategies for obesity, recent advances in our understanding of the central neural control of energy balance, and what the authors consider to be the most promising targets for the development of novel antiobesity drugs in the future. Thus, the review focuses on leptin, neuropeptide Y, melanocortin and ghrelin signalling at the level of the CNS, and strategies targeting the sympathetic innervation of fat cells at the periphery.
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Affiliation(s)
- David Spanswick
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK/NeuroSolutions Ltd, Warwick BioVentures, Coventry CV4 7AL, UK
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157
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Lee JH, Bullen JW, Stoyneva VL, Mantzoros CS. Circulating resistin in lean, obese, and insulin-resistant mouse models: lack of association with insulinemia and glycemia. Am J Physiol Endocrinol Metab 2005; 288:E625-32. [PMID: 15522996 DOI: 10.1152/ajpendo.00184.2004] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Resistin is an adipocyte-secreted hormone proposed to link obesity with insulin resistance and diabetes, but no previous study has performed a joint quantitative evaluation of white adipose tissue (WAT) resistin mRNA expression and serum levels in relation to insulinemia and glycemia in mice. We have thus comparatively assessed WAT resistin mRNA expression and serum resistin levels in lean C57BL/6J mice and various mouse models of obesity, including diet-induced obese (DIO) C57BL/6J mice, high fat-fed TNF-alpha-/- mice, and brown adipose tissue (BAT)-deficient uncoupling protein-diphtheria toxin A chain (UCP1-DTA) mice. We also studied whether treatment with the weight-reducing and insulin-sensitizing compounds, MTII, an alpha-melanocyte-stimulating hormone analog, or CNTF(Ax15), a ciliary neurotrophic factor analog, alters resistin mRNA expression and/or circulating levels in lean and DIO C57BL/6J mice. We find that resistin mRNA expression is similar in DIO and lean C57BL/6J mice, as well as in TNF-alpha-/- and wild-type (WT) mice. Circulating resistin levels, however, are higher in DIO C57BL/6J, high fat-fed TNF-alpha-/-, and UCP1-DTA mice compared with lean controls. Moreover, although resistin mRNA expression is upregulated by MTII treatment for 24 h and downregulated by CNTF(Ax15) treatment for 3 or 7 days, circulating resistin levels are not altered by MTII or CNTF(Ax15) treatment. In addition, serum resistin levels, but not resistin mRNA expression levels, are correlated with body weight, and neither resistin mRNA expression nor serum resistin levels are correlated with serum insulin or glucose levels. We conclude that transcriptional regulation of resistin in WAT does not correlate with circulating resistin levels and that circulating resistin is unlikely to play a major endocrine role in insulin resistance or glycemia in mice.
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MESH Headings
- Adipose Tissue/chemistry
- Adipose Tissue/drug effects
- Adipose Tissue/metabolism
- Animals
- Blood Glucose/drug effects
- Blood Glucose/physiology
- Body Weight/drug effects
- Carrier Proteins/genetics
- Ciliary Neurotrophic Factor/analogs & derivatives
- Ciliary Neurotrophic Factor/pharmacology
- Diet
- Diphtheria Toxin/genetics
- Disease Models, Animal
- Eating/drug effects
- Energy Intake/drug effects
- Gene Expression/genetics
- Hormones, Ectopic/blood
- Hormones, Ectopic/genetics
- Hormones, Ectopic/physiology
- Insulin/blood
- Insulin Resistance/physiology
- Ion Channels
- Male
- Membrane Proteins/genetics
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Obese
- Mice, Transgenic
- Mitochondrial Proteins
- Multivariate Analysis
- Obesity/chemically induced
- Obesity/metabolism
- Peptide Fragments/genetics
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Resistin
- Reverse Transcriptase Polymerase Chain Reaction
- Tumor Necrosis Factor-alpha/genetics
- Uncoupling Protein 1
- alpha-MSH/agonists
- alpha-MSH/analogs & derivatives
- alpha-MSH/pharmacology
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Affiliation(s)
- Jennifer H Lee
- Division of Endocrinology, Diabetes and Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave., Stoneman 816, Boston, MA 02215, USA
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158
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Abstract
Regulated energy homeostasis is fundamental for maintaining life. Unfortunately, this critical process is affected in a high number of mentally ill patients. Eating disorders such as anorexia nervosa are prevalent in modern societies. Impaired appetite and weight loss are common in patients with depression. In addition, the use of neuroleptics frequently produces obesity and diabetes mellitus. However, the neural mechanisms underlying the pathophysiology of these behavioral and metabolic conditions are largely unknown. In this review, we first concentrate on the established brain machinery of food intake and body weight, especially on the melanocortin and neuropeptide Y (NPY) systems as illustration. These systems play a critical role in receiving and processing critical peripheral metabolic cues such as leptin and ghrelin. It is also notable that both systems modulate emotion and motivated behavior as well. Secondly, we discuss the significance and potential promise of multidisciplinary molecular and neuroanatomic techniques that will likely increase the understanding of brain circuitries coordinating energy homeostasis and emotion. Finally, we introduce several lines of evidence suggesting a link between the melanocortin/NPY systems and several neurotransmitter systems on which many of the psychotropic agents exert their influence.
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Affiliation(s)
- T Kishi
- Department of Anatomy and Morphological Neuroscience, Shimane University School of Medicine, Izumo 693-8501, Japan.
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159
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Coppari R, Ichinose M, Lee CE, Pullen AE, Kenny CD, McGovern RA, Tang V, Liu SM, Ludwig T, Chua SC, Lowell BB, Elmquist JK. The hypothalamic arcuate nucleus: a key site for mediating leptin's effects on glucose homeostasis and locomotor activity. Cell Metab 2005; 1:63-72. [PMID: 16054045 DOI: 10.1016/j.cmet.2004.12.004] [Citation(s) in RCA: 366] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2004] [Revised: 12/22/2004] [Accepted: 12/23/2004] [Indexed: 11/18/2022]
Abstract
Leptin is required for normal energy and glucose homeostasis. The hypothalamic arcuate nucleus (ARH) has been proposed as an important site of leptin action. To assess the physiological significance of leptin signaling in the ARH, we used mice homozygous for a FLPe-reactivatable, leptin receptor null allele (Lepr(neo/neo) mice). Similar to Lepr(db/db) mice, these mice are obese, hyperglycemic, hyperinsulinemic, infertile, and hypoactive. To selectively restore leptin signaling in the ARH, we generated an adeno-associated virus expressing FLPe-recombinase, which was delivered unilaterally into the hypothalamus using stereotaxic injections. We found that unilateral restoration of leptin signaling in the ARH of Lepr(neo/neo) mice leads to a modest decrease in body weight and food intake. In contrast, unilateral reactivation markedly improved hyperinsulinemia and normalized blood glucose levels and locomotor activity. These data demonstrate that leptin signaling in the ARH is sufficient for mediating leptin's effects on glucose homeostasis and locomotor activity.
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Affiliation(s)
- Roberto Coppari
- Department of Medicine, Division of Endocrinology, Beth Israel Deaconess Medical Center, Harvard Medical School, 99 Brookline Avenue, Boston, Massachusetts 02215, USA
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160
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Savontaus E, Breen TL, Kim A, Yang LM, Chua SC, Wardlaw SL. Metabolic effects of transgenic melanocyte-stimulating hormone overexpression in lean and obese mice. Endocrinology 2004; 145:3881-91. [PMID: 15117873 DOI: 10.1210/en.2004-0263] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The proopiomelanocortin-derived peptide, alpha-MSH, inhibits feeding via melanocortin receptors in the hypothalamus and genetic defects inactivating the melanocortin system have been shown to lead to obesity in experimental animals and humans. To determine whether long-term melanocortinergic activation has significant effects on body weight and composition and insulin sensitivity, transgenic mice overexpressing N-terminal proopiomelanocortin, including alpha- and gamma(3)-MSH, under the control of the cytomegalovirus-promoter were generated. The transgene was expressed in multiple tissues including the hypothalamus, in which both alpha-MSH and gamma(3)-MSH levels were increased approximately 2-fold, compared with wild-type controls. Transgene homozygous mice were also crossed with obese leptin receptor-deficient db(3J) and obese yellow A(y) mice. MSH overexpression led to uniform, dose- dependent darkening of coat color. MSH overexpression reduced weight gain and adiposity and improved glucose tolerance in lean male mice. In female transgenic mice, there was no significant effect on body weight, but there was a significant decrease in insulin levels. Obesity was attenuated in obese db(3J)/db(3J) male and female mice, but there was no improvement in glucose metabolism. In contrast, the MSH transgene improved glucose tolerance in male A(y) mice. These results support the hypothesis that long-term melanocortinergic activation could serve as a potential strategy for anti-obesity and/or antidiabetic therapy.
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Affiliation(s)
- Eriika Savontaus
- Department of Medicine and Pediatrics, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA
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161
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Marks DL, Boucher N, Lanouette CM, Pérusse L, Brookhart G, Comuzzie AG, Chagnon YC, Cone RD. Ala67Thr polymorphism in the Agouti-related peptide gene is associated with inherited leanness in humans. Am J Med Genet A 2004; 126A:267-71. [PMID: 15054840 DOI: 10.1002/ajmg.a.20600] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A role for melanocortin signaling in the regulation of body weight in humans has been clearly established. Haploinsufficiency of the type 4 melanocortin receptor is associated with early-onset obesity, implying that this receptor provides an important tonic inhibition of weight gain. Agouti-related peptide (AGRP) is an endogenous antagonist of melanocortin signaling. Therefore, loss of AGRP function could lead to the expression of a lean phenotype. We investigated the potential role of AGRP in human weight regulation by examining the association between the Ala67Thr AGRP polymorphism and indices of body composition. Significant associations were found between homozygosity for this mutation (n = 8) and body composition phenotype in 874 subjects of the Quebec family study (QFS). By PCR-RFLP analysis, we have identified eight individuals who are homozygous for the 67Thr variant allele within the QFS population, where none were observed in SAFHS. The eight QFS homozygote individuals have lower weight (-16%; P = 0.02), body mass index (-17%; P = 0.01), fat free mass (-9%; P = 0.002), fat mass (FM) (-20%; P = 0.04), and leptin (-20%; P = 0.02) when compared to those carrying at least one 67Ala allele. Individuals homozygous for the 67Thr allele had a BMI that was either at or slightly below an ideal range for their age. Thus, the Ala67Thr AGRP polymorphism is associated with lower body weight in humans, with the largest effect being observed on body FM. We did not observe any difference in the stability or cellular distribution of the mutant protein in a heterologous expression system, thus the mechanism of this effect requires further investigation.
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Affiliation(s)
- Daniel L Marks
- Department of Pediatrics, Oregon Health & Science University, Portland, USA
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162
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Cepoi D, Phillips T, Cismowski M, Goodfellow VS, Ling N, Cone RD, Fan W. Assessment of a small molecule melanocortin-4 receptor-specific agonist on energy homeostasis. Brain Res 2004; 1000:64-71. [PMID: 15053953 DOI: 10.1016/j.brainres.2003.10.041] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/23/2003] [Indexed: 10/26/2022]
Abstract
The central melanocortin system has been demonstrated to play an important role in regulating different aspects of energy homeostasis. Understanding the specific contributions of MC3 and MC4 receptors, however, requires specific agonists and antagonists for each of the predominant forms of brain melanocortin receptors, MC3-R and MC4-R. We report here the characterization of a small peptide mimetic MC4-R-specific agonist that possesses both high affinity (K(i)=11.3 nM) and potency (EC(50)=1.62 nM) in vitro and is capable of inhibiting feeding behavior in mice when administered intracerebroventricularly (i.c.v.). Depending on the paradigm, acute (1 h following an overnight fast) or long-term (greater than 6 h under normal nocturnal feeding conditions) feeding inhibition was observed following icv injection. No effect on long-term feeding inhibition was observed with this compound in MC4-R knockout mice, and central administration of this compound had no effect on either metabolic rate or insulin release.
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Affiliation(s)
- David Cepoi
- Vollum Institute, Oregon Health and Sciences University, 3181 SW Sam Jackson Park Road, Mail Code: L474, Portland, OR 97201, USA
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163
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Haqq AM, René P, Kishi T, Khong K, Lee CE, Liu H, Friedman JM, Elmquist JK, Cone RD. Characterization of a novel binding partner of the melanocortin-4 receptor: attractin-like protein. Biochem J 2004; 376:595-605. [PMID: 14531729 PMCID: PMC1223823 DOI: 10.1042/bj20031241] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2003] [Revised: 09/15/2003] [Accepted: 10/07/2003] [Indexed: 11/17/2022]
Abstract
The gene dosage effect of the MC4-R (melanocortin 4 receptor) on obesity suggests that regulation of MC4-R expression and function is critically important to the central control of energy homoeostasis. In order to identify putative MC4-R regulatory proteins, we performed a yeast two-hybrid screen of a mouse brain cDNA library using the mouse MC4-R intracellular tail (residues 303-332) as bait. We report here on one positive clone that shares 63% amino acid identity with the C-terminal part of the mouse attractin gene product, a single-transmembrane-domain protein characterized as being required for agouti signalling through the melanocortin 1 receptor. We confirmed a direct interaction between this ALP (attractin-like protein) and the C-terminus of the mouse MC4-R by glutathione S-transferase pulldown experiments, and mapped the regions involved in this interaction using N- and C-terminal truncation constructs; residues 303-313 in MC4-R and residues 1280-1317 in ALP are required for binding. ALP is highly expressed in brain, but also in heart, lung, kidney and liver. Furthermore, co-localization analyses in mice showed co-expression of ALP in cells expressing MC4-R in a number of regions known to be important in the regulation of energy homoeostasis by melanocortins, such as the paraventricular nucleus of hypothalamus and the dorsal motor nucleus of the vagus.
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Affiliation(s)
- Andrea M Haqq
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA
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164
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Kuo JJ, da Silva AA, Tallam LS, Hall JE. Role of adrenergic activity in pressor responses to chronic melanocortin receptor activation. Hypertension 2004; 43:370-5. [PMID: 14707160 DOI: 10.1161/01.hyp.0000111836.54204.93] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Acute studies have shown that MC3/4-R stimulation increases sympathetic activity, but the role of adrenergic activation in mediating the cardiovascular and renal responses to chronic melanocortin 3- and 4-receptor (MC3/4-R) activation is unknown. The present study tested whether chronic MC3/4-R activation raises blood pressure and whether these changes are attenuated by alpha1+beta-adrenergic blockade. Rats were instrumented with an intracerebroventricular (ICV) cannula and arterial and venous catheters for measurements of mean arterial pressure (MAP) and heart rate (HR) 24 hours per day, and intravenous infusions. After control measurements, rats were intravenously infused with either saline vehicle (n=7) or alpha1+ beta-adrenergic antagonists (n=6, terazosin+propranolol, 10 mg/kg per day each) for 21 days. Five days after starting the vehicle or adrenergic blockade, the MC3/4-R agonist, MTII (10 ng/h), was infused ICV for 11 days followed by a 5-day recovery period. Another group of rats was infused with the adrenergic antagonists for 21 days but received the saline vehicle ICV for 11 days (n=7). MC3/4-R activation decreased food intake from 21+/-1 to 8+/-2 g/d by day 3 of MC3/4-R activation, and increased MAP and HR by an average of 8+/-2 mm Hg and 9+/-5 bpm, respectively. Adrenergic blockade did not alter the MC3/4-R-mediated decrease in food intake but abolished the increases in MAP and HR (1+/-2 mm Hg and -12+/-5 bpm, respectively, compared with control). ICV vehicle infusion during adrenergic blockade did not alter food intake or MAP. Glomerular filtration rate was unchanged in both the vehicle-infused and adrenergic blocked rats during MC3/4-R activation. These results indicate that the chronic actions of MC3/4-R activation on MAP and HR are mediated by adrenergic activation.
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Affiliation(s)
- Jay J Kuo
- Department of Physiology and Biophysics, 2500 N State St, University of Mississippi Medical Center, Jackson, MS 39216, USA.
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165
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Albarado DC, McClaine J, Stephens JM, Mynatt RL, Ye J, Bannon AW, Richards WG, Butler AA. Impaired coordination of nutrient intake and substrate oxidation in melanocortin-4 receptor knockout mice. Endocrinology 2004; 145:243-52. [PMID: 14551222 DOI: 10.1210/en.2003-0452] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Mutations in the melanocortin-4 receptor (MC4R) are associated with obesity. The obesity syndrome observed in humans with MC4R haploinsufficiency is similar to that observed in MC4R knockout mice, including increased longitudinal growth, hyperphagia, and fasting hyperinsulinemia. For comparison with other commonly investigated models of obesity and insulin resistance, we have backcrossed Mc4r-/- mice into the C57BL/6J (B6) background. Female obese Mc4r-/- mice exhibit reduced energy expenditure and an attenuated increase in fatty acid (FA) oxidation after exposure to high-fat diets compared with obese Lepob/Lepob mice. The reduced energy expenditure and FA oxidation correlates with changes in hepatic gene expression. The expression of genes involved in FA oxidation increased in obese Lepob/Lepob mice compared with wild-type and obese Mc4r-/- mice. In contrast, a key lipogenic enzyme, FA synthase (FAS), is increased in obese Mc4r-/- mice compared with obese Lepob/Lepob mice. Hyperinsulinemia, increased FAS mRNA expression and hepatic steatosis appear to be secondary to obesity in B6 Mc4r-/- mice. However, Mc4r-/- mice in a mixed genetic background develop severe hepatic steatosis at an early age. This might suggest an important role of the MC4R in regulating liver FA metabolism that is masked on the B6 background. Interestingly, the 10- to 20-fold increase in liver triglyceride in the outbred strain of Mc4r-/- mice is not always associated with fasting hyperinsulinemia or increased FAS mRNA expression. This observation suggests that changes in liver secondary to triglyceride accumulation lead to hyperinsulinemia and increased hepatic FAS expression in Mc4r-/- mice.
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Affiliation(s)
- Diana C Albarado
- Pennington Biomedical Research Center/Louisiana State University, Baton Rouge, Louisiana 70808, USA
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166
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Blüher S, Ziotopoulou M, Bullen JW, Moschos SJ, Ungsunan L, Kokkotou E, Maratos-Flier E, Mantzoros CS. Responsiveness to peripherally administered melanocortins in lean and obese mice. Diabetes 2004; 53:82-90. [PMID: 14693701 DOI: 10.2337/diabetes.53.1.82] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
To elucidate mechanisms of melanocortin action, we investigated the effects of a melanocortin receptor agonist (melanotetan II [MTII]) in lean C57BL/6J and obese (DIO, ob/ob, UCP1-DTA) mice. MTII administration (100 microg q.i.d. i.p.) for 24 h results in similar weight loss but a more pronounced decrease of food intake in DIO mice. After 4 and 8 days of MTII treatment, however, the reduction in both food intake and body weight is more pronounced in DIO mice than in lean mice. MTII administration for 24 h prevents food deprivation-induced alterations in hypothalamic neuropeptide Y (NPY) and liver adiponectin receptor 1 and adiponectin receptor 2 mRNA expression, but does not alter hypothalamic mRNA expression of melanocortin 4 receptor or adiponectin serum and mRNA expression levels. NPY and agouti gene-related protein (AgRP) mRNA expression after 8 days of MTII is increased to levels comparable to pair-fed mice. In summary, 1) MTII is an effective treatment for obesity and related metabolic defects in leptin-resistant (DIO, UCP1-DTA) and leptin-sensitive (ob/ob) mouse models of obesity; 2) the effects of MTII on food intake and body weight are more pronounced in DIO mice than in lean mice; 3) the tachyphylactic effect after prolonged MTII administration appears to be, at least in part, caused by a compensatory upregulation of NPY and AgRP mRNA levels, whereas decreasing leptin levels may play a very minor role in mediating tachyphylaxis; and 4) alterations in adiponectin receptor mRNA expression after fasting or MTII treatment may contribute to altered insulin sensitivity and needs to be studied further.
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Affiliation(s)
- Susann Blüher
- Department of Medicine, Division of Endocrinology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA
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167
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Khairallah M, Labarthe F, Bouchard B, Danialou G, Petrof BJ, Des Rosiers C. Profiling substrate fluxes in the isolated working mouse heart using 13C-labeled substrates: focusing on the origin and fate of pyruvate and citrate carbons. Am J Physiol Heart Circ Physiol 2003; 286:H1461-70. [PMID: 14670819 DOI: 10.1152/ajpheart.00942.2003] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The availability of genetically modified mice requires the development of methods to assess heart function and metabolism in the intact beating organ. With the use of radioactive substrates and ex vivo perfusion of the mouse heart in the working mode, previous studies have documented glucose and fatty acid oxidation pathways. This study was aimed at characterizing the metabolism of other potentially important exogenous carbohydrate sources, namely, lactate and pyruvate. This was achieved by using (13)C-labeling methods. The mouse heart perfusion setup and buffer composition were optimized to reproduce conditions close to the in vivo milieu in terms of workload, cardiac functions, and substrate-hormone supply to the heart (11 mM glucose, 0.8 nM insulin, 50 microM carnitine, 1.5 mM lactate, 0.2 mM pyruvate, 5 nM epinephrine, 0.7 mM oleate, and 3% albumin). The use of three differentially (13)C-labeled carbohydrates and a (13)C-labeled long-chain fatty acid allowed the quantitative assessment of the metabolic origin and fate of tissue pyruvate as well as the relative contribution of substrates feeding acetyl-CoA (pyruvate and fatty acids) and oxaloacetate (pyruvate) for mitochondrial citrate synthesis. Beyond concurring with the notion that the mouse heart preferentially uses fatty acids for energy production (63.5 +/- 3.9%) and regulates its fuel selection according to the Randle cycle, our study reports for the first time in the mouse heart the following findings. First, exogenous lactate is the major carbohydrate contributing to pyruvate formation (42.0 +/- 2.3%). Second, lactate and pyruvate are constantly being taken up and released by the heart, supporting the concept of compartmentation of lactate and glucose metabolism. Finally, mitochondrial anaplerotic pyruvate carboxylation and citrate efflux represent 4.9 +/- 1.8 and 0.8 +/- 0.1%, respectively, of the citric acid cycle flux and are modulated by substrate supply. The described (13)C-labeling strategy combined with an experimental setup that enables continuous monitoring of physiological parameters offers a unique model to clarify the link between metabolic alterations, cardiac dysfunction, and disease development.
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Affiliation(s)
- Maya Khairallah
- Department of Experimental Medicine, McGill University, Montreal, Quebec, Canada H2L 4M1
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168
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Mizuno TM, Kelley KA, Pasinetti GM, Roberts JL, Mobbs CV. Transgenic neuronal expression of proopiomelanocortin attenuates hyperphagic response to fasting and reverses metabolic impairments in leptin-deficient obese mice. Diabetes 2003; 52:2675-83. [PMID: 14578285 DOI: 10.2337/diabetes.52.11.2675] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Hypothalamic proopiomelanocortin (POMC) gene expression is reduced in many forms of obesity and diabetes, particularly in those attributable to deficiencies in leptin or its receptor. To assess the functional significance of POMC in mediating metabolic phenotypes associated with leptin deficiency, leptin-deficient mice bearing a transgene expressing the POMC gene under control of the neuron-specific enolase promoter were produced. The POMC transgene attenuated fasting-induced hyperphagia in wild-type mice. Furthermore, the POMC transgene partially reversed obesity, hyperphagia, and hypothermia and effectively normalized hyperglycemia, glucosuria, glucose intolerance, and insulin resistance in leptin-deficient mice. Effects of the POMC transgene on glucose homeostasis were independent of the partial correction of hyperphagia and obesity. Furthermore, the POMC transgene normalized the profile of hepatic and adipose gene expression associated with gluconeogenesis, glucose output, and insulin sensitivity. These results indicate that central POMC is a key modulator of glucose homeostasis and that agonists of POMC products may provide effective therapy in treating impairments in glucose homeostasis when hypothalamic POMC expression is reduced, as occurs with leptin deficiency, hypothalamic damage, and aging.
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Affiliation(s)
- Tooru M Mizuno
- Fishberg Center for Neurobiology, Mount Sinai School of Medicine, New York, New York 10029, USA
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169
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Lin J, Choi YH, Hartzell DL, Li C, Della-Fera MA, Baile CA. CNS melanocortin and leptin effects on stearoyl-CoA desaturase-1 and resistin expression. Biochem Biophys Res Commun 2003; 311:324-8. [PMID: 14592417 DOI: 10.1016/j.bbrc.2003.10.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The objective of this study was to determine whether centrally administered leptin decreased liver and adipose SCD1 expression or adipose resistin expression, and whether these effects were mediated by central melanocortin receptors. Male Sprague-Dawley rats were injected into the lateral cerebral ventricle (i.c.v.) once daily for 4 days with artificial cerebrospinal fluid (aCSF, 5 microl), leptin (10 microg) or MTII (0.1 nmol); two other groups were pretreated icv with the melanocortin antagonist, SHU9119 (1.0 nmol), followed by leptin or MTII. Epididymal and inguinal adipose tissue and liver were collected after rats were killed and mRNA expression of SCD1 and resistin was measured. Both leptin and MTII reduced SCD1 expression and pretreatment with SHU9119 reversed their effects. Neither leptin nor MTII affected resistin expression, but it was increased by SHU9119. These results show that CNS melanocortin receptors are likely mediators of leptin's effects on SCD1 expression in liver and adipose tissue, The findings were inconclusive concerning the effects of leptin and melanocortins on adipose resistin expression.
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Affiliation(s)
- Ji Lin
- Department of Animal and Dairy Science, University of Georgia, Athens, GA 30602, USA
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170
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171
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Cornish J, Callon KE, Mountjoy KG, Bava U, Lin JM, Myers DE, Naot D, Reid IR. alpha -melanocyte-stimulating hormone is a novel regulator of bone. Am J Physiol Endocrinol Metab 2003; 284:E1181-90. [PMID: 12618359 DOI: 10.1152/ajpendo.00412.2002] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
alpha-Melanocyte-stimulating hormone (alpha-MSH), a 13-amino acid peptide produced in the brain and pituitary gland, is a regulator of appetite and body weight, and its production is regulated by leptin, a factor that affects bone mass when administered centrally. alpha-MSH acts via melanocortin receptors. Humans deficient in melanocortin receptor 4 (MC4-R) have increased bone mass, and MC4-R has been identified in an osteoblast-like cell line. Thus alpha-MSH may act directly on the skeleton, a question addressed by the present studies. In primary cultures of osteoblasts and chondrocytes, alpha-MSH dose dependently (>or=10(-9) M) stimulated cell proliferation. In bone marrow cultures, alpha-MSH (>10(-9) M) stimulated osteoclastogenesis. Systemic administration of alpha-MSH to mice (20 injections of 4.5 microg/day) decreased the trabecular bone volume in the proximal tibiae from 19.5 +/- 1.8 to 15.2 +/- 1.4% (P = 0.03) and reduced trabecular number (P = 0.001). Radiographic indexes of trabecular bone, assessed by phase-contrast X-ray imaging, confirmed the bone loss. It is concluded that alpha-MSH acts directly on bone, increasing bone turnover, and, when administered systemically, it decreases bone volume. The latter result may also be contributed to by alpha-MSH effects elsewhere, such as the adipocyte, pancreatic beta-cell, or central nervous system.
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Affiliation(s)
- Jillian Cornish
- Department of Medicine, University of Auckland, Auckland 1001, New Zealand.
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172
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Brennan MB, Costa JL, Forbes S, Reed P, Bui S, Hochgeschwender U. Alpha-melanocyte-stimulating hormone is a peripheral, integrative regulator of glucose and fat metabolism. Ann N Y Acad Sci 2003; 994:282-7. [PMID: 12851327 DOI: 10.1111/j.1749-6632.2003.tb03191.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Melanocortins are known to affect feeding and probably insulin activity through the central nervous system. It was also recently shown that peripheral alpha-melanocyte-stimulating hormone (alpha-MSH) administration can reduce weight gain in both genetic and diet-induced obese mice. As obesity is often associated with disregulation of glucose and insulin, we investigated the nature of glucose homeostasis in the obese pro-opiomelanocortin (POMC) knockout mouse. Here we report that though they are obese, mice deficient in POMC (and, thereby, deficient in alpha-MSH) are euglycemic throughout their lives. While these mice are euinsulinemic, they are hypersensitive to exogenous insulin. This defect can be reversed through administration of alpha-MSH. We demonstrate that the actions of alpha-MSH in the periphery, known from our work to include lipid metabolism effects, are also involved in glucose homeostasis. These findings substantiate a pivotal role of the POMC gene products in integrating metabolism.
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Affiliation(s)
- Miles B Brennan
- Eleanor Roosevelt Institute for Cancer Research, Denver, Colorado 80206, USA.
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173
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Heisler LK, Cowley MA, Kishi T, Tecott LH, Fan W, Low MJ, Smart JL, Rubinstein M, Tatro JB, Zigman JM, Cone RD, Elmquist JK. Central serotonin and melanocortin pathways regulating energy homeostasis. Ann N Y Acad Sci 2003; 994:169-74. [PMID: 12851313 DOI: 10.1111/j.1749-6632.2003.tb03177.x] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
It is now established that the hypothalamus is essential in coordinating endocrine, autonomic, and behavioral responses to changes in energy availability. However, the interaction of key peptides, neuropeptides, and neurotransmitters systems within the hypothalamus has yet to be delineated. Recently, we investigated the mechanisms through which central serotonergic (5-hydroxytryptamine, 5-HT) systems recruit leptin-responsive hypothalamic pathways, such as the melanocortin systems, to affect energy balance. Through a combination of functional neuroanatomy, feeding, and electrophysiology studies in rodents, we found that 5-HT drugs require functional melanocortin pathways to exert their effects on food intake. Specifically, we observed that anorectic 5-HT drugs activate pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (Arc). We provide evidence that the serotonin 2C receptor (5-HT(2C)R) is expressed on POMC neurons and contributes to this effect. Finally, we found that 5-HT drug-induced hypophagia is attenuated by pharmacological or genetic blockade of downstream melanocortin 3 and 4 receptors. We review candidate brain regions expressing melanocortin 3 and 4 receptors that play a role in energy balance. A model is presented in which activation of the melanocortin system is downstream of 5-HT and is necessary to produce the complete anorectic effect of 5-HT drugs. The data reviewed in this paper incorporate the central 5-HT system to the growing list of metabolic signals that converge on melanocortin neurons in the hypothalamus.
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Affiliation(s)
- Lora K Heisler
- Departments of Medicine and Neurology, Beth Israel Deaconess Medical Center and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts 02215, USA
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174
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Kishi T, Aschkenasi CJ, Lee CE, Mountjoy KG, Saper CB, Elmquist JK. Expression of melanocortin 4 receptor mRNA in the central nervous system of the rat. J Comp Neurol 2003; 457:213-35. [PMID: 12541307 DOI: 10.1002/cne.10454] [Citation(s) in RCA: 439] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The melanocortin 4 receptor (MC4-R) plays a pivotal role in maintaining energy homeostasis in rodents and humans. For example, MC4-R deletion or mutation results in obesity, hyperphagia, and insulin resistance. Additionally, subsets of leptin-induced autonomic responses can be blocked by melanocortin receptor antagonism, suggesting that MC4-R-expressing neurons are downstream targets of leptin. However, the critical autonomic control sites expressing MC4-Rs are still unclear. In the present study, we systematically examined the distribution of MC4-R mRNA in the adult rat central nervous system, including the spinal cord, by using in situ hybridization histochemistry (ISHH) with a novel cRNA probe. Autonomic control sites expressing MC4-R mRNA in the hypothalamus included the anteroventral periventricular, ventromedial preoptic, median preoptic, paraventricular, dorsomedial, and arcuate nuclei. The subfornical organ, dorsal hypothalamic, perifornical, and posterior hypothalamic areas were also observed to express MC4-R mRNA. Within extrahypothalamic autonomic control sites, MC4-R-specific hybridization was evident in the infralimbic and insular cortices, bed nucleus of the stria terminalis, central nucleus of the amygdala, periaqueductal gray, lateral parabrachial nucleus, nucleus of the solitary tract, dorsal motor nucleus of the vagus (DMV), and intermediolateral nucleus of the spinal cord (IML). By using dual-label ISHH, we confirmed that the cells expressing MC4-R mRNA in the IML and DMV were autonomic preganglionic neurons as cells in both sites coexpressed choline acetyltransferase mRNA. The distribution of MC4-R mRNA is consistent with the proposed roles of central melanocortin systems in feeding and autonomic regulation.
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Affiliation(s)
- Toshiro Kishi
- Department of Neurology, Beth Israel Deaconess Medical Center, and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts 02215,USA
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175
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Kuo JJ, Silva AA, Hall JE. Hypothalamic melanocortin receptors and chronic regulation of arterial pressure and renal function. Hypertension 2003; 41:768-74. [PMID: 12623994 DOI: 10.1161/01.hyp.0000048194.97428.1a] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This study examined control of cardiovascular and renal function during chronic melanocortin-3/4 receptor (MC3/4-R) activation or inhibition. Arterial and venous catheters were implanted in Sprague-Dawley rats for measurements of mean arterial pressure (MAP) and heart rate (HR) 24 h/d and for intravenous infusions, and the lateral ventricle was cannulated for chronic intracerebroventricular (ICV) infusions. In experiment 1, after a 5-day control period, rats were administered the MC3/4-R agonist MTII (n=7, 10 ng/h ICV) or 0.9% saline (n=6, ICV) for 14 days, followed by a 5-day recovery period. In experiment 2, after a 5-day control period, rats were administered the MC3/4-R antagonist SHU-9119 (n=7, 1 nmol/h ICV) or 0.9% saline vehicle (n=7, ICV), or pair-fed during SHU-9119 infusion (n=5, 1 nmol/h ICV) for 12 days, followed by a 5-day recovery period. MC4-R activation transiently decreased food intake from 23+/-1 to 10+/-2 g/d. Despite the hypophagia, MC3/4-R activation increased MAP by 7+/-1 mm Hg. MC3/4-R inhibition for 12 days increased food intake from 21+/-1 to 35+/-4 g/d, decreased HR by 53+/-11 bpm, and caused no change in MAP despite the marked weight gain. In rats that were pair-fed to prevent increased food intake, MC3/4-R inhibition further decreased HR (-87+/-9 bpm), whereas MAP was unchanged. Thus, chronic hypothalamic MC3/4-R activation raises arterial pressure despite decreased food intake, whereas MC3/4-R inhibition causes marked weight gain without raising arterial pressure. These observations are consistent with the hypothesis that an intact hypothalamic MC3/4-R may be necessary for excess weight gain to raise arterial pressure.
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Affiliation(s)
- Jay J Kuo
- Department of Physiology and Biophysics, Center of Excellence in Cardiovascular-Renal Research, University of Mississippi Medical Center, Jackson 39216-4505, USA
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176
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Raposinho PD, White RB, Aubert ML. The melanocortin agonist Melanotan-II reduces the orexigenic and adipogenic effects of neuropeptide Y (NPY) but does not affect the NPY-driven suppressive effects on the gonadotropic and somatotropic axes in the male rat. J Neuroendocrinol 2003; 15:173-81. [PMID: 12535159 DOI: 10.1046/j.1365-2826.2003.00962.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Neuropeptide Y (NPY) is a strong orexigenic neurotransmitter also known to modulate several neuroendocrine axes. alpha-Melanocyte-stimulating hormone (MSH) is an essential anorectic neuropeptide, acting on hypothalamic MC3/4 receptor subtypes. When given as an intracerebroventricular bolus injection, Melanotan-II (MT-II), a non selective MC receptor agonist, inhibits feeding, suppresses the NPY orexigenic action, and reduces basal insulinaemia. We evaluated the effects of a 7-day central infusion of MT-II (15 nmol/day) given either alone or in association with NPY (5 nmol/day) in male Sprague-Dawley rats. MT-II produced almost full anorexia for 1-2 days but then feeding gradually returned to normal despite continued MT-II infusion. When coinfused with NPY, MT-II also produced the same initial anorectic episode but then maintained feeding to upper normal levels, thus cancelling the hyperphagia driven by NPY. Whereas NPY infusion produced a doubling of fat pad weight, MT-II reduced adiposity by a factor of two compared to pair-fed rats, and vastly curtailed the NPY-driven increase in fat pad weight. MT-II infusion also significantly curtailed the NPY-induced rise in insulin and leptin secretions. NPY infusion significantly inhibited hypothalamic pro-opiomelanocortin mRNA expression, most likely cancelling the alpha-MSH anorectic activity. As expected from previous studies, chronic NPY infusion strongly inhibited both the gonadotropic and somatotropic axes, and coinfusion of MT-II did not reverse these NPY-driven effects, in sharp contrast with that seen for the metabolic data. MT-II infusion alone had little effect on these axes. In conclusion, chronic MT-II infusion generated a severe but transient reduction in feeding, suggesting an escape phenomenon, and clearly reduced fat pad size. When coinfused with NPY, MT-II was able to cancel most of the NPY effects on feeding, but not those on the neuroendocrine axes. It appears therefore that, as expected, NPY and alpha-MSH closely interact in the control of feeding, whereas the neural pathways by which NPY affects growth and reproduction are distinct and not sensitive to MC peptide modulation.
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Affiliation(s)
- P D Raposinho
- Division of Development and Growth, Department of Pediatrics, University of Geneva School of Medicine, Geneva, Switzerland
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177
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Wong J, Love DR, Kyle C, Daniels A, White M, Stewart AW, Schnell AH, Elston RC, Holdaway IM, Mountjoy KG. Melanocortin-3 receptor gene variants in a Maori kindred with obesity and early onset type 2 diabetes. Diabetes Res Clin Pract 2002; 58:61-71. [PMID: 12161058 DOI: 10.1016/s0168-8227(02)00126-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Genetic studies suggest a diabetes susceptibility locus on human chromosome 20, near the melanocortin receptor-3 (MC3-R) gene. We examined the MC3-R as a candidate gene for type 2 diabetes in 12 members of a large Maori kindred with multiple affected members. The coding region of the MC3-R gene was sequenced for both diabetic and non-diabetic individuals. Two separate single base pair substitutions were found in the MC3-R coding sequence and these resulted in amino acid changes, Lysine6Threonine and Isoleucine81Valine. Neither of these MC3-R variants tracked with the presence of diabetes. Furthermore, the variant and wild type MC3-R showed similar functional coupling to adenylyl cyclase. A polymorphic marker (D20S32e) close to the human MC3-R (hMC3-R) coding sequence was investigated in a 60-member pedigree for association with diabetes and other metabolic parameters. There was an association between D20S32e genotype and fasting insulin (P=0.0085) and the insulin resistance index, HOMA-R (P=0.0042). An association was also found between genotype and HDL levels during oral glucose tolerance testing (P=0.0037). These associations were independent of BMI, age, gender and diabetes. Our data do not support a role for variations in the coding region of the hMC3-R in the development of type 2 diabetes in this Maori kindred, but suggest that a locus on chromosome 20 q, close to D20S32e, may contribute to both insulin secretion and action in the Maori kindred.
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Affiliation(s)
- Jencia Wong
- Department of Medicine, University of Auckland, Auckland, New Zealand
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178
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MacNeil DJ, Howard AD, Guan X, Fong TM, Nargund RP, Bednarek MA, Goulet MT, Weinberg DH, Strack AM, Marsh DJ, Chen HY, Shen CP, Chen AS, Rosenblum CI, MacNeil T, Tota M, MacIntyre ED, Van der Ploeg LHT. The role of melanocortins in body weight regulation: opportunities for the treatment of obesity. Eur J Pharmacol 2002; 450:93-109. [PMID: 12176114 DOI: 10.1016/s0014-2999(02)01989-1] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Five G-protein-coupled melanocortin receptors (MC(1)-MC(5)) are expressed in mammalian tissues. The melanocortin receptors support diverse physiological functions, including the regulation of hair color, adrenal function, energy homeostasis, feed efficiency, sebaceous gland lipid production and immune and sexual function. The melanocortins (adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), beta-MSH and gamma-MSH) are agonist peptide ligands for the melanocortin receptors and these peptides are processed from the pre-prohormone proopiomelanocortin (POMC). Peptide antagonists for the melanocortin MC(1), MC(3) and MC(4) receptors include agouti-related protein (AgRP) and agouti. Diverse lines of evidence, including genetic and pharmacological data obtained in rodents and humans, support a role for the melanocortin MC(3) and MC(4) receptors in the regulation of energy homeostasis. Recent advances in the development of potent and selective peptide and non-peptide melanocortin receptor ligands are anticipated to help unravel the roles for the melanocortin receptors in humans and to accelerate the clinical use of small molecule melanocortin mimetics.
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179
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Heisler LK, Cowley MA, Tecott LH, Fan W, Low MJ, Smart JL, Rubinstein M, Tatro JB, Marcus JN, Holstege H, Lee CE, Cone RD, Elmquist JK. Activation of central melanocortin pathways by fenfluramine. Science 2002; 297:609-11. [PMID: 12142539 DOI: 10.1126/science.1072327] [Citation(s) in RCA: 342] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
D-fenfluramine (d-FEN) was once widely prescribed and was among the most effective weight loss drugs, but was withdrawn from clinical use because of reports of cardiac complications in a subset of patients. Discerning the neurobiology underlying the anorexic action of d-FEN may facilitate the development of new drugs to prevent and treat obesity. Through a combination of functional neuroanatomy, feeding, and electrophysiology studies in rodents, we show that d-FEN-induced anorexia requires activation of central nervous system melanocortin pathways. These results provide a mechanistic explanation of d-FEN's anorexic actions and indicate that drugs targeting these downstream melanocortin pathways may prove to be effective and more selective anti-obesity treatments.
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MESH Headings
- Animals
- Appetite Depressants/pharmacology
- Arcuate Nucleus of Hypothalamus/drug effects
- Arcuate Nucleus of Hypothalamus/metabolism
- Feeding Behavior/drug effects
- Fenfluramine/pharmacology
- Male
- Melanocyte-Stimulating Hormones/pharmacology
- Mice
- Mice, Obese
- Mice, Transgenic
- Neurons/drug effects
- Neurons/metabolism
- Paraventricular Hypothalamic Nucleus/drug effects
- Paraventricular Hypothalamic Nucleus/metabolism
- Patch-Clamp Techniques
- Pro-Opiomelanocortin/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptor, Melanocortin, Type 3
- Receptor, Melanocortin, Type 4
- Receptor, Serotonin, 5-HT2C
- Receptors, Corticotropin/metabolism
- Receptors, Serotonin/metabolism
- Serotonin/metabolism
- Serotonin Agents/pharmacology
- alpha-MSH/metabolism
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Affiliation(s)
- Lora K Heisler
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
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180
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Eiden S, Daniel C, Steinbrueck A, Schmidt I, Simon E. Salmon calcitonin - a potent inhibitor of food intake in states of impaired leptin signalling in laboratory rodents. J Physiol 2002; 541:1041-8. [PMID: 12068061 PMCID: PMC2290353 DOI: 10.1113/jphysiol.2002.018671] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
To compare the anorectic effectiveness of leptin and the amylin analogue salmon calcitonin (sCT), rodents were treated on 1 day with subcutaneous injections. In chow-fed C57Bl/6J mice, leptin and sCT reduced energy intake and acted additively. After C57Bl/6J mice had become leptin-resistant on being fed chocolate as a palatable high-caloric supplement to chow, their sCT-induced decrease in energy intake was more pronounced than in chow-fed mice with differential changes in the intake of chocolate (strong reduction) and chow (slight increase). Dose-response relationships for sCT-induced reductions in energy intake were analysed in chow-fed C57Bl/6J mice and two obese strains, ob/ob mice and melanocortin-4 receptor knockout (MC4-r-KO) mice, as well as in wild-type and fatty (fa/fa) rats. Compared to C57Bl/6J mice, reduction in food intake induced by sCT was attenuated in MC4-r-KO mice, and nearly absent in ob/ob mice, over the dose range investigated. Compared to C57Bl/6J mice, wild-type rats responded more sensitively to sCT and its efficiency was only slightly reduced in fatty (fa/fa) rats. Thus, while genetically induced failures of leptin signalling reduce the action of sCT, it effectively inhibits the intake of a palatable, high fat-high sugar diet even in states of diet-induced obesity with functional leptin resistance.
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Affiliation(s)
- Sandra Eiden
- Max-Planck-Institut fuer physiologische und klinische Forschung, W.G. Kerckhoff-Institut, Parkstr.1, D-61231 Bad Nauheim, Germany
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181
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Pierroz DD, Ziotopoulou M, Ungsunan L, Moschos S, Flier JS, Mantzoros CS. Effects of acute and chronic administration of the melanocortin agonist MTII in mice with diet-induced obesity. Diabetes 2002; 51:1337-45. [PMID: 11978628 DOI: 10.2337/diabetes.51.5.1337] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
High-fat diet-induced obesity (DIO) in rodents is associated with hyperleptinemia and resistance to leptin, but the response to agents acting downstream of leptin receptors remains unknown. We assessed the response of mice with DIO to treatment with MTII, an alpha-melanocyte-stimulating hormone analog. MTII delivered four times daily by intraperitoneal injection to C57BL/6J mice produced a dose-responsive effect on food intake, body weight, leptin, corticosterone, insulin, and free fatty acids. In DIO mice, administration of MTII 100 microg q.i.d. i.p. markedly suppressed feeding during the first 4 days of treatment, with food intake returning to control levels at day 5. Progressive weight loss also occurred over the first 4 days, after which weight plateaued at a level below control. After 8 days of treatment, MTII-treated DIO mice had major suppression of both leptin and insulin levels. Central administration of MTII for 4 days (10 nmol/day) in DIO mice significantly suppressed food intake, induced weight loss, and increased energy expenditure. These results indicate that 1) MTII administration to DIO mice causes suppression of food intake and body weight loss, and decreased food intake is primarily responsible for weight loss; 2) peripheral MTII improves insulin resistance in DIO mice; 3) "tachyphylaxis" to the effect of chronic MTII treatment on food intake occurs; and 4) at least some of the effects of MTII are exerted centrally. In conclusion, treatment with a melanocortin agonist is a promising therapeutic approach to DIO and associated insulin resistance.
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Affiliation(s)
- Dominique D Pierroz
- Division of Endocrinology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
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182
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Abstract
Identifying the role of the melanocortin system in regulating energy homeostasis has relied on both genetic and pharmacological studies. The key findings included 1) that the coat color phenotype in the lethal yellow (A(Y)/a) mouse is due to antagonism of the melanocortin-1 receptor (MC1R) by the agouti gene product; 2) the MC3R and MC4R are expressed in CNS centers involved in energy homeostasis, and 3) the combined results of pharmacological studies showing that agouti is an antagonist of the MC4R and transgenic studies showing that inhibition or loss of the MC4R recapitulate the lethal yellow phenotype. Pro-opiomelanocortin (POMC), MC3R, and MC4R knockouts are obese and are now being used to further analyze melanocortin receptor function. The obesity phenotype observed in the MC3R and MC4R knockouts (KO) differ markedly. MC4RKO mice are hyperphagic, do not regulate pathways that increase energy expenditure (diet-induced thermogenesis) and physical activity in response to hyperphagia, and can develop type 2 diabetes. In contrast, MC3R deficient mice are not hyperphagic, have a normal metabolic response to increased energy consumption, and do not develop diabetes. The mechanism underlying the increased adiposity in the MC3R knockout remains unclear, but might be related to changes in nutrient partitioning or physical activity.
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Affiliation(s)
- A A Butler
- Neuropeptides Laboratory, Pennington Biomedical Research Center, Lousiana State university, Baton Rouge, LA70808, USA.
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183
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Crowley VEF, Yeo GSH, O'Rahilly S. Obesity therapy: altering the energy intake-and-expenditure balance sheet. Nat Rev Drug Discov 2002; 1:276-86. [PMID: 12120279 DOI: 10.1038/nrd770] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Obesity is associated with numerous health complications, which range from non-fatal debilitating conditions such as osteoarthritis, to life-threatening chronic diseases such as coronary heart disease, diabetes and certain cancers. The psychological consequences of obesity can range from lowered self-esteem to clinical depression. Despite the high prevalence of obesity and the many advances in our understanding of how it develops, current therapies have persistently failed to achieve long-term success. This review focuses on how fat mass can be reduced by altering the balance between energy intake and expenditure.
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Affiliation(s)
- Vivion E F Crowley
- University Departments of Medicine and Clinical Biochemistry, Addenbrooke's Hospital, Cambridge CB2 2QR, UK
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184
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Schwartz MW. Progress in the search for neuronal mechanisms coupling type 2 diabetes to obesity. J Clin Invest 2001; 108:963-4. [PMID: 11581296 PMCID: PMC200961 DOI: 10.1172/jci14127] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Affiliation(s)
- M W Schwartz
- Division of Metabolism, Endocrinology and Nutrition, University of Washington, Harborview Medical Center, Seattle, Washington 98104-2499, USA.
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185
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Obici S, Feng Z, Tan J, Liu L, Karkanias G, Rossetti L. Central melanocortin receptors regulate insulin action. J Clin Invest 2001; 108:1079-85. [PMID: 11581309 PMCID: PMC200952 DOI: 10.1172/jci12954] [Citation(s) in RCA: 125] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Energy balance and insulin action are tightly coregulated. Leptin regulates energy intake and expenditure partly by modulation of the melanocortin pathway in the hypothalamus. Here we demonstrate potent effects of the melanocortin pathway on insulin action and body distribution of adiposity. Conscious rats received week-long infusions of either a melanocortin receptor agonist, alpha-melanocyte-stimulating hormone (alpha-MSH), or antagonist, SHU9119, in the third cerebral ventricle while food intake was maintained constant in each group. alpha-MSH decreased intra-abdominal fat and markedly enhanced the actions of insulin on both glucose uptake and production, while SHU9119 exerted opposite effects. Our findings elucidate a neuroendocrine network that is likely to play a central role in the coupling of energy intake and insulin action.
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MESH Headings
- Animals
- Glucose/metabolism
- Hypothalamus/metabolism
- Insulin/metabolism
- Insulin Receptor Substrate Proteins
- Intracellular Signaling Peptides and Proteins
- Male
- Melanocyte-Stimulating Hormones/adverse effects
- Melanocyte-Stimulating Hormones/pharmacology
- Oligodeoxyribonucleotides, Antisense
- Phosphoproteins/metabolism
- Phosphorylation
- Rats
- Rats, Sprague-Dawley
- Receptor, Melanocortin, Type 3
- Receptor, Melanocortin, Type 4
- Receptors, Corticotropin/agonists
- Receptors, Corticotropin/antagonists & inhibitors
- Receptors, Corticotropin/metabolism
- Receptors, Peptide/agonists
- Receptors, Peptide/antagonists & inhibitors
- Receptors, Peptide/genetics
- Receptors, Peptide/metabolism
- Signal Transduction
- alpha-MSH/adverse effects
- alpha-MSH/pharmacology
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Affiliation(s)
- S Obici
- Diabetes Research and Training Center, Albert Einstein College of Medicine, Bronx, New York, USA 10461
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186
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Abstract
Obesity is a health problem of epidemic proportions in the industrialized world. The cloning and characterization of the genes for the five naturally occurring monogenic obesity syndromes in the mouse have led to major breakthroughs in understanding the physiology of energy balance and the contribution of genetics to obesity in the human population. However, the regulation of energy balance is an extremely complex process, and it is quickly becoming clear that hundreds of genes are involved. In this article, we review the naturally occurring monogenic and polygenic obese mouse strains, as well as the large number of transgenic and knockout mouse models currently available for the study of obesity and energy balance.
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Affiliation(s)
- S W Robinson
- Vollum Institute, Oregon Health Sciences University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97201, USA.
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