501
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Abstract
Obesity represents a major risk factor for the development of insulin and leptin resistance, ultimately leading to a pleiotropic spectrum of metabolic alterations. However, resistance to both hormones does not uniformly affect all target cells and intracellular signaling pathways. In contrast, numerous clinical phenotypes arise from selective hormone resistance, leading to inhibition of defined intracellular signaling pathways in some tissues, while in other cell types hormone action is maintained or even overactivated. Here, we review the molecular mechanisms and clinical outcomes resulting from selective insulin and leptin resistance, which should ultimately guide future strategies for the treatment of obesity-associated diseases.
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Affiliation(s)
- A Christine Könner
- Department of Mouse Genetics and Metabolism, Institute for Genetics, Cologne Excellence Cluster on Cellular Stress Responses in Aging Associated Diseases, Center of Molecular Medicine Cologne, University of Cologne, D-50674 Cologne, Germany
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502
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Tam J, Cinar R, Liu J, Godlewski G, Wesley D, Jourdan T, Szanda G, Mukhopadhyay B, Chedester L, Liow JS, Innis RB, Cheng K, Rice KC, Deschamps JR, Chorvat RJ, McElroy JF, Kunos G. Peripheral cannabinoid-1 receptor inverse agonism reduces obesity by reversing leptin resistance. Cell Metab 2012; 16:167-79. [PMID: 22841573 PMCID: PMC3832894 DOI: 10.1016/j.cmet.2012.07.002] [Citation(s) in RCA: 270] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 04/16/2012] [Accepted: 07/06/2012] [Indexed: 12/13/2022]
Abstract
Obesity-related leptin resistance manifests in loss of leptin's ability to reduce appetite and increase energy expenditure. Obesity is also associated with increased activity of the endocannabinoid system, and CB(1) receptor (CB(1)R) inverse agonists reduce body weight and the associated metabolic complications, although adverse neuropsychiatric effects halted their therapeutic development. Here we show that in mice with diet-induced obesity (DIO), the peripherally restricted CB(1)R inverse agonist JD5037 is equieffective with its brain-penetrant parent compound in reducing appetite, body weight, hepatic steatosis, and insulin resistance, even though it does not occupy central CB(1)R or induce related behaviors. Appetite and weight reduction by JD5037 are mediated by resensitizing DIO mice to endogenous leptin through reversing the hyperleptinemia by decreasing leptin expression and secretion by adipocytes and increasing leptin clearance via the kidney. Thus, inverse agonism at peripheral CB(1)R not only improves cardiometabolic risk in obesity but has antiobesity effects by reversing leptin resistance.
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Affiliation(s)
- Joseph Tam
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
- Correspondence: (J.T.), (G.K.)
| | - Resat Cinar
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jie Liu
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Grzegorz Godlewski
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Daniel Wesley
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Tony Jourdan
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Gergö Szanda
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Bani Mukhopadhyay
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Lee Chedester
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jeih-San Liow
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Robert B. Innis
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Kejun Cheng
- Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | - Kenner C. Rice
- Chemical Biology Research Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
| | | | | | | | - George Kunos
- Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA
- Correspondence: (J.T.), (G.K.)
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503
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Marroquí L, Gonzalez A, Ñeco P, Caballero-Garrido E, Vieira E, Ripoll C, Nadal A, Quesada I. Role of leptin in the pancreatic β-cell: effects and signaling pathways. J Mol Endocrinol 2012; 49:R9-17. [PMID: 22448029 DOI: 10.1530/jme-12-0025] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Leptin plays an important role in the control of food intake, energy expenditure, metabolism, and body weight. This hormone also has a key function in the regulation of glucose homeostasis. Although leptin acts through central and peripheral mechanisms to modulate glucose metabolism, the pancreatic β-cell of the endocrine pancreas is a critical target of leptin actions. Leptin receptors are present in the β-cell, and their activation directly inhibits insulin secretion from these endocrine cells. The effects of leptin on insulin occur also in the long term, since this hormone inhibits insulin gene expression as well. Additionally, β-cell mass can be affected by leptin through changes in proliferation, apoptosis, or cell size. All these different functions in the β-cell are triggered by leptin as a result of the large diversity of signaling pathways that this hormone is able to activate in the endocrine pancreas. Therefore, leptin can participate in glucose homeostasis owing to different levels of modulation of the pancreatic β-cell population. Furthermore, it has been proposed that alterations in this level of regulation could contribute to the impairment of β-cell function in obesity states. In the present review, we will discuss all these issues with special emphasis on the effects and pathways of leptin signaling in the pancreatic β-cell.
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Affiliation(s)
- Laura Marroquí
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas-CIBERDEM, Elche, Spain
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504
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Chen D, Liu X, Zhang W, Shi Y. Targeted inactivation of GPR26 leads to hyperphagia and adiposity by activating AMPK in the hypothalamus. PLoS One 2012; 7:e40764. [PMID: 22815809 PMCID: PMC3398048 DOI: 10.1371/journal.pone.0040764] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 06/12/2012] [Indexed: 11/22/2022] Open
Abstract
G-protein coupled receptor 26 (GPR26) is a brain-specific orphan GPCR with high expression in the brain region that controls satiety. Depletion of GPR26 has been shown to increase fat storage in C. elegans, whereas GPR26 deficiency in the hypothalamus is associated with high genetic susceptibility to the onset of obesity in mice. However, the metabolic function of GPR26 in mammals remains elusive. Herein, we investigated a role of GPR26 in regulating energy homeostasis by generating mice with targeted deletion of the GPR26 gene. We show that GPR26 deficiency causes hyperphagia and hypometabolism, leading to early onset of diet-induced obesity. Accordingly, GPR26 deficiency also caused metabolic complications commonly associated with obesity, including glucose intolerance, hyperinsulinemia, and dyslipidemia. Moreover, consistent with hyperphagia in GPR26 null mice, GPR26 deficiency significantly increased hypothalamic activity of AMPK, a key signaling event that stimulates appetite. In further support of a regulatory role of GPR26 in satiety, GPR26 knockout mice also demonstrate hypersensitivity to treatment of rimonabant, an endocannabinoid receptor-1 antagonist commonly used to treat obesity by suppressing appetite in humans. Together, these findings identified a key role of GPR26 as a central regulator of energy homeostasis though modulation of hypothalamic AMPK activation.
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Affiliation(s)
- Daohong Chen
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
| | - Xiaolei Liu
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
- Department of Pharmacology, School of Pharmaceutical Sciences Central South University, Changsha, China
| | - Weiping Zhang
- Department of Pathophysiology, Second Military Medical University Shanghai, China
| | - Yuguang Shi
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
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505
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Lugogo NL, Hollingsworth JW, Howell DL, Que LG, Francisco D, Church TD, Potts-Kant EN, Ingram JL, Wang Y, Jung SH, Kraft M. Alveolar macrophages from overweight/obese subjects with asthma demonstrate a proinflammatory phenotype. Am J Respir Crit Care Med 2012; 186:404-11. [PMID: 22773729 PMCID: PMC3443798 DOI: 10.1164/rccm.201109-1671oc] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
RATIONALE Obesity is associated with increased prevalence and severity of asthma. Adipose tissue macrophages can contribute to the systemic proinflammatory state associated with obesity. However, it remains unknown whether alveolar macrophages have a unique phenotype in overweight/obese patients with asthma. OBJECTIVES We hypothesized that leptin levels would be increased in the bronchoalveolar lavage fluid from overweight/obese subjects and, furthermore, that leptin would alter the response of alveolar macrophages to bacterial LPS. METHODS Forty-two subjects with asthma and 46 healthy control subjects underwent research bronchoscopy. Bronchoalveolar lavage fluid from 66 was analyzed for the level of cellular inflammation, cytokines, and soluble leptin. Cultured primary macrophages from 22 subjects were exposed to LPS, leptin, or leptin plus LPS. Cytokines were measured in the supernatants. MEASUREMENTS AND MAIN RESULTS Leptin levels were increased in overweight/obese subjects, regardless of asthma status (P = 0.013), but were significantly higher in overweight/obese subjects with asthma. Observed levels of tumor necrosis factor-α were highest in overweight/obese subjects with asthma. Ex vivo studies of primary alveolar macrophages indicated that the response to LPS was most robust in alveolar macrophages from overweight/obese subjects with asthma and that preexposure to high-dose leptin enhanced the proinflammatory response. Leptin alone was sufficient to induce production of proinflammatory cytokines from macrophages derived from overweight/obese subjects with asthma. CONCLUSIONS Ex vivo studies indicate that alveolar macrophages derived from overweight/obese subjects with asthma are uniquely sensitive to leptin. This macrophage phenotype, in the context of higher levels of soluble leptin, may contribute to the pathogenesis of airway disease associated with obesity.
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Affiliation(s)
- Njira L Lugogo
- Duke University Medical Center, P.O. Box 2629, Durham, NC 27710, USA.
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506
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Vauthier V, Jaillard S, Journel H, Dubourg C, Jockers R, Dam J. Homozygous deletion of an 80 kb region comprising part of DNAJC6 and LEPR genes on chromosome 1P31.3 is associated with early onset obesity, mental retardation and epilepsy. Mol Genet Metab 2012; 106:345-50. [PMID: 22647716 DOI: 10.1016/j.ymgme.2012.04.026] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 04/30/2012] [Accepted: 04/30/2012] [Indexed: 11/29/2022]
Abstract
CONTEXT The genomic organization of the LEPR gene is complex and generates three independent transcripts whose respective functions are still poorly understood. METHODS/RESULTS We describe here a 7-year old patient with a homozygous 80 kb deletion in the chromosomal 1p31.3 region with early onset obesity, mental retardation and epilepsy. The deleted region comprises the proximal promoter and exons 1 and 2 of the LEPR gene and exons 5 to 19 of the DNAJC6 gene. The deletion leads to the deficiency of all canonical OB-R isoforms but maintains the B219 OB-R short isoforms controlled by the preserved second LEPR promoter. The DNAJC6 gene encodes auxilin-1, a protein required for clathrin-dependent recycling of synaptic vesicles in neurons that is possibly at the origin of the mental retardation and epilepsy phenotype. The obese phenotype and the absence of signaling-competent OB-R are consistent with previously reported individuals with OB-R deficiency. The deletion eliminates an additional transcript of the LEPR gene that encodes endospanin-1, a protein that has been genetically and biochemically linked to OB-R function. CONCLUSIONS Our study confirms the phenotype of individuals with OB-R deficiency and postulates the effects of auxilin-1 deficiency (mental retardation/epilepsy) and endospanin-1 deficiency (OB-R specific functions) in humans.
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507
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Reidelberger R, Haver A, Chelikani PK, Apenteng B, Perriotte-Olson C, Anders K, Steenson S, Blevins JE. Effects of leptin replacement alone and with exendin-4 on food intake and weight regain in weight-reduced diet-induced obese rats. Am J Physiol Endocrinol Metab 2012; 302:E1576-85. [PMID: 22510712 PMCID: PMC3378160 DOI: 10.1152/ajpendo.00058.2012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Weight loss in obese humans produces a relative leptin deficiency, which is postulated to activate potent orexigenic and energy conservation mechanisms to restrict weight loss and promote weight regain. Here we determined whether leptin replacement alone or with GLP-1 receptor agonist exendin-4 attenuates weight regain or promotes greater weight loss in weight-reduced diet-induced obese (DIO) rats. Forty percent restriction in daily intake of a high-fat diet in DIO rats for 4 wk reduced body weight by 12%, body fat by 29%, and plasma leptin by 67% and normalized leptin sensitivity. When food restriction ended, body weight, body fat, and plasma leptin increased rapidly. Daily administration of leptin [3-h intraperitoneal (ip) infusions (4 nmol·kg(-1)·h(-1))] at onset and end of dark period for 3 wk did not attenuate hyperphagia and weight regain, nor did it affect mean daily meal sizes or meal numbers. Exendin-4 (50 pmol·kg(-1)·h(-1)) infusions during the same intervals prevented postrestriction hyperphagia and weight regain by normalizing meal size. Coadministration of leptin and exendin-4 did not reduce body weight more than exendin-4 alone. Instead, leptin began to attenuate the inhibitory effects of exendin-4 on food intake, meal size, and weight regain by the end of the second week of administration. Plasma leptin in rats receiving leptin was sevenfold greater than in rats receiving vehicle and 17-fold greater than in rats receiving exendin-4. Together, these results do not support the hypothesis that leptin replacement alone or with exendin-4 attenuates weight regain or promotes greater weight loss in weight-reduced DIO rats.
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Affiliation(s)
- Roger Reidelberger
- Veterans Affairs Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, 68105, USA.
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508
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Insulin resistance in the defense against obesity. Cell Metab 2012; 15:798-804. [PMID: 22682220 DOI: 10.1016/j.cmet.2012.03.001] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Revised: 01/14/2012] [Accepted: 03/01/2012] [Indexed: 12/18/2022]
Abstract
In the face of the current obesity epidemic, the nature of the relationship between overnutrition and type 2 diabetes is of great importance. Obesity can be considered a state of excessive insulin action that elicits a series of cellular homeostatic responses, producing systemic insulin resistance. These responses occur in four steps: homologous desensitization to insulin action, leptin secretion, inflammation, and, finally, a counter-inflammatory phase that serves to conserve energy storage. The molecular mechanisms underlying these steps are discussed in the context of potential new therapeutic approaches.
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509
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Sadagurski M, Leshan RL, Patterson C, Rozzo A, Kuznetsova A, Skorupski J, Jones JC, Depinho RA, Myers MG, White MF. IRS2 signaling in LepR-b neurons suppresses FoxO1 to control energy balance independently of leptin action. Cell Metab 2012; 15:703-12. [PMID: 22560222 PMCID: PMC3361909 DOI: 10.1016/j.cmet.2012.04.011] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Revised: 02/15/2012] [Accepted: 04/13/2012] [Indexed: 01/17/2023]
Abstract
Irs2-mediated insulin/IGF1 signaling in the CNS modulates energy balance and glucose homeostasis; however, the site for Irs2 function is unknown. The hormone leptin mediates energy balance by acting on leptin receptor (LepR-b)-expressing neurons. To determine whether LepR-b neurons mediate the metabolic actions of Irs2 in the brain, we utilized Lepr(cre) together with Irs2(L/L) to ablate Irs2 expression in LepR-b neurons (Lepr(ΔIrs2)). Lepr(ΔIrs2) mice developed obesity, glucose intolerance, and insulin resistance. Leptin action was not altered in young Lepr(ΔIrs2) mice, although insulin-stimulated FoxO1 nuclear exclusion was reduced in Lepr(ΔIrs2) mice. Indeed, deletion of Foxo1 from LepR-b neurons in Lepr(ΔIrs2) mice normalized energy balance, glucose homeostasis, and arcuate nucleus gene expression. Thus, Irs2 signaling in LepR-b neurons plays a crucial role in metabolic sensing and regulation. While not required for leptin action, Irs2 suppresses FoxO1 signaling in LepR-b neurons to promote energy balance and metabolism.
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Affiliation(s)
- Marianna Sadagurski
- Howard Hughes Medical Institute, Division of Endocrinology Children's Hospital Boston Harvard Medical School Boston, Massachusetts, USA
| | - Rebecca L. Leshan
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine and Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Christa Patterson
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine and Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Aldo Rozzo
- Howard Hughes Medical Institute, Division of Endocrinology Children's Hospital Boston Harvard Medical School Boston, Massachusetts, USA
| | - Alexandra Kuznetsova
- Howard Hughes Medical Institute, Division of Endocrinology Children's Hospital Boston Harvard Medical School Boston, Massachusetts, USA
| | - Josh Skorupski
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine and Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Justin C. Jones
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine and Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Ronald A. Depinho
- Department of Cancer Biology University of Texas MD Anderson Cancer Center Houston, TX 77030
| | - Martin G. Myers
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine and Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan
| | - Morris F. White
- Howard Hughes Medical Institute, Division of Endocrinology Children's Hospital Boston Harvard Medical School Boston, Massachusetts, USA
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510
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Abstract
Obese children have a theoretically increased risk of sustaining an extremity fracture because of potential variations in their bone mineral density, serum leptin levels, and altered balance and gait. Trauma databases suggest an increased rate of extremity fractures in obese children and adolescents involved in polytrauma compared with nonobese children and adolescents. Anesthetic and other perioperative concerns for obese pediatric trauma patients undergoing surgery include higher baseline blood pressures, increased rates of asthma, and obstructive sleep apnea. A child's weight must be considered when choosing the type of implant for fixation of pediatric femoral fractures. Fracture prevention strategies in obese pediatric patients consist of ensuring properly sized safety gear for both motor vehicles and sporting activities and implementing structured weight-loss programs.
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Affiliation(s)
- Meredith A Lazar-Antman
- Pediatrics Division, Department of Orthopaedic Surgery, Winthrop-University Hospital 222 Station Plaza North, Suite 305, Mineola, NY 11501, USA.
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511
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Xu Y, O'Brien WG, Lee CC, Myers MG, Tong Q. Role of GABA release from leptin receptor-expressing neurons in body weight regulation. Endocrinology 2012; 153:2223-33. [PMID: 22334723 PMCID: PMC3339652 DOI: 10.1210/en.2011-2071] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
It is well established that leptin regulates energy balance largely through isoform B leptin receptor-expressing neurons (LepR neurons) in the brain and that leptin activates one subset of LepR neurons (leptin-excited neurons) while inhibiting the other (leptin-inhibited neurons). However, the neurotransmitters released from LepR neurons that mediate leptin action in the brain are not well understood. Previous results demonstrate that leptin mainly acts on γ-aminobutyric acid (GABA)ergic neurons to reduce body weight, and that leptin activates proopiomelanocortin neuron activity by reducing GABA release onto these neurons, suggesting a body weight-promoting role for GABA released from leptin-inhibited neurons. To directly examine the role of GABA release from LepR neurons in body weight regulation, mice with disruption of GABA release specifically from LepR neurons were generated by deletion of vesicular GABA transporter in LepR neurons. Interestingly, these mice developed mild obesity on chow diet and were sensitive to diet-induced obesity, which were associated with higher food intake and lower energy expenditure. Moreover, these mice showed blunted responses in both food intake and body weight to acute leptin administration. These results demonstrate that GABA plays an important role in mediating leptin action. In combination with the previous studies that leptin reduces GABA release onto proopiomelanocortin neurons through leptin-inhibited neurons and that disruption of GABA release from agouti gene-related protein neurons, one subset of LepR-inhibited neurons, leads to a lean phenotype, our results suggest that, under our experimental conditions, GABA release from leptin-excited neuron dominates over leptin-inhibited ones.
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Affiliation(s)
- Yuanzhong Xu
- Brown Foundation Institute of Molecular Medicine, University of Texas Medical School, Houston, Texas 77030, USA
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512
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Affiliation(s)
- B Glenn Stanley
- Department of Psychology, University of California, Riverside, Riverside, California 92521, USA.
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513
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St-Pierre J, Tremblay ML. Modulation of leptin resistance by protein tyrosine phosphatases. Cell Metab 2012; 15:292-7. [PMID: 22405067 DOI: 10.1016/j.cmet.2012.02.004] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Revised: 01/31/2012] [Accepted: 02/06/2012] [Indexed: 10/28/2022]
Abstract
Leptin plays a central role in weight control by suppressing food intake and increasing energy expenditure. The concept of leptin resistance emerged to explain the seemingly paradoxical elevated leptin levels in obesity. Recent discoveries reveal that protein tyrosine phosphatases are key players in leptin resistance by globally suppressing leptin signaling.
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Affiliation(s)
- Julie St-Pierre
- Goodman Cancer Research Centre, McGill University, Montreal, Quebec H3A 1A3, Canada.
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514
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Bourque SL, Komolova M, McCabe K, Adams MA, Nakatsu K. Perinatal iron deficiency combined with a high-fat diet causes obesity and cardiovascular dysregulation. Endocrinology 2012; 153:1174-82. [PMID: 22210741 DOI: 10.1210/en.2011-1700] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Consumption of a high-fat Western diet (WD) and the resultant obesity is linked to a number of chronic pathologies, including cardiovascular dysregulation. The purpose of the present study was to determine whether perinatal iron deficiency (PID) added to the consumption of a WD would precipitate an obese phenotype with exacerbated metabolic and cardiovascular outcomes in adult offspring. Female Sprague Dawley rats were fed either a control (225 mg/kg Fe) or an iron-restricted diet (3-10 mg/kg Fe) prior to and throughout gestation. At birth, all dams were fed an iron-replete diet. At weaning, offspring were fed a normal diet or WD for up to 21 wk. Hemodynamics and locomotor activity were assessed by radiotelemetry starting at 15 wk of age. Iron restriction during pregnancy caused severe anemia in dams and offspring, resulting in 15% lower birth weights in the offspring. PID offspring fed the WD had greater caloric intake and exhibited reduced locomotor activity compared with their normal diet-fed littermates; no such effects were observed in normal iron control offspring. Despite having a similar effect on serum lipid profiles, consumption of the WD had a greater impact on body weight in the PID group, and this weight gain was due largely to visceral adipose tissue accumulation. A significant correlation between visceral adipose tissue weight and mean arterial pressure was observed in the PID offspring but not in controls. These observations demonstrate that PID predisposes offspring to an enhanced response to WD characterized by increased fat accumulation and cardiovascular dysregulation.
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Affiliation(s)
- Stephane L Bourque
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
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515
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Regulation and function of ribosomal protein S6 kinase (S6K) within mTOR signalling networks. Biochem J 2012; 441:1-21. [PMID: 22168436 DOI: 10.1042/bj20110892] [Citation(s) in RCA: 723] [Impact Index Per Article: 60.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The ribosomal protein S6K (S6 kinase) represents an extensively studied effector of the TORC1 [TOR (target of rapamycin) complex 1], which possesses important yet incompletely defined roles in cellular and organismal physiology. TORC1 functions as an environmental sensor by integrating signals derived from diverse environmental cues to promote anabolic and inhibit catabolic cellular functions. mTORC1 (mammalian TORC1) phosphorylates and activates S6K1 and S6K2, whose first identified substrate was rpS6 (ribosomal protein S6), a component of the 40S ribosome. Studies over the past decade have uncovered a number of additional S6K1 substrates, revealing multiple levels at which the mTORC1-S6K1 axis regulates cell physiology. The results thus far indicate that the mTORC1-S6K1 axis controls fundamental cellular processes, including transcription, translation, protein and lipid synthesis, cell growth/size and cell metabolism. In the present review we summarize the regulation of S6Ks, their cellular substrates and functions, and their integration within rapidly expanding mTOR (mammalian TOR) signalling networks. Although our understanding of the role of mTORC1-S6K1 signalling in physiology remains in its infancy, evidence indicates that this signalling axis controls, at least in part, glucose homoeostasis, insulin sensitivity, adipocyte metabolism, body mass and energy balance, tissue and organ size, learning, memory and aging. As dysregulation of this signalling axis contributes to diverse disease states, improved understanding of S6K regulation and function within mTOR signalling networks may enable the development of novel therapeutics.
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516
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Myers MG, Heymsfield SB, Haft C, Kahn BB, Laughlin M, Leibel RL, Tschöp MH, Yanovski JA. Challenges and opportunities of defining clinical leptin resistance. Cell Metab 2012; 15:150-6. [PMID: 22326217 PMCID: PMC3281561 DOI: 10.1016/j.cmet.2012.01.002] [Citation(s) in RCA: 156] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The widespread use of the inadequately defined term "leptin resistance" led the National Institutes of Health to convene a workshop aimed at developing a quantitative definition of this term that would facilitate mechanistic research into leptin's actions in human health and disease. Although leptin-responsive conditions are recognized, the field is limited by a lack of robust, easily quantifiable behavioral or metabolic biomarkers of the hormone's action. Further advances require biomarkers that can be used to identify patients who may benefit from leptin therapy and that are useful for understanding the determinants of clinical leptin responsiveness.
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Affiliation(s)
- Martin G. Myers
- Departments of Internal Medicine and Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI
| | | | - Carol Haft
- Division of Diabetes, Endocrinology and Metabolic Diseases, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD
| | - Barbara B. Kahn
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA
| | - Maren Laughlin
- Division of Diabetes, Endocrinology and Metabolic Diseases, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD
| | - Rudolph L. Leibel
- Department of Pediatrics and Medicine, Columbia University, New York, NY
| | | | - Jack A. Yanovski
- Program in Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD
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517
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Ryan KK, Woods SC, Seeley RJ. Central nervous system mechanisms linking the consumption of palatable high-fat diets to the defense of greater adiposity. Cell Metab 2012; 15:137-49. [PMID: 22244528 PMCID: PMC3278569 DOI: 10.1016/j.cmet.2011.12.013] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 09/01/2011] [Accepted: 10/03/2011] [Indexed: 12/23/2022]
Abstract
The central nervous system (CNS) plays key role in the homeostatic regulation of body weight. Satiation and adiposity signals, providing acute and chronic information about available fuel, are produced in the periphery and act in the brain to influence energy intake and expenditure, resulting in the maintenance of stable adiposity. Diet-induced obesity (DIO) does not result from a failure of these central homeostatic circuits. Rather, the threshold for defended adiposity is increased in environments providing ubiquitous access to palatable, high-fat foods, making it difficult to achieve and maintain weight loss. Consequently, mechanisms by which nutritional environments interact with central homeostatic circuits to influence the threshold for defended adiposity represent critical targets for therapeutic intervention.
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Affiliation(s)
- Karen K Ryan
- Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH 45237, USA
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518
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Coupé B, Grit I, Hulin P, Randuineau G, Parnet P. Postnatal growth after intrauterine growth restriction alters central leptin signal and energy homeostasis. PLoS One 2012; 7:e30616. [PMID: 22291999 PMCID: PMC3264579 DOI: 10.1371/journal.pone.0030616] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Accepted: 12/22/2011] [Indexed: 01/06/2023] Open
Abstract
Intrauterine growth restriction (IUGR) is closely linked with metabolic diseases, appetite disorders and obesity at adulthood. Leptin, a major adipokine secreted by adipose tissue, circulates in direct proportion to body fat stores, enters the brain and regulates food intake and energy expenditure. Deficient leptin neuronal signalling favours weight gain by affecting central homeostatic circuitry. The aim of this study was to determine if leptin resistance was programmed by perinatal nutritional environment and to decipher potential cellular mechanisms underneath.We clearly demonstrated that 5 months old IUGR rats develop a decrease of leptin sentivity, characterized by no significant reduction of food intake following an intraperitoneal injection of leptin. Apart from the resistance to leptin injection, results obtained from IUGR rats submitted to rapid catch-up growth differed from those of IUGR rats with no catch-up since we observed, for the first group only, fat accumulation, increased appetite for food rich in fat and increased leptin synthesis. Centrally, the leptin resistant state of both groups was associated with a complex and not always similar changes in leptin receptor signalling steps. Leptin resistance in IUGR rats submitted to rapid catch-up was associated with alteration in AKT and mTOR pathways. Alternatively, in IUGR rats with no catch-up, leptin resistance was associated with low hypothalamic expression of LepRa and LepRb. This study reveals leptin resistance as an early marker of metabolic disorders that appears before any evidence of body weight increase in IUGR rats but whose mechanisms could depend of nutritional environment of the perinatal period.
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Affiliation(s)
- Bérengère Coupé
- UMR 1280 Physiologie des Adaptations Nutritionnelles, Université de Nantes Atlantique, Nantes, France
- Research Center of Human Nutrition Nantes, Nantes, France
| | - Isabelle Grit
- UMR 1280 Physiologie des Adaptations Nutritionnelles, Université de Nantes Atlantique, Nantes, France
- Research Center of Human Nutrition Nantes, Nantes, France
| | - Philippe Hulin
- Plate-forme MicroPICell IFR26 Institut de Recherche Thérapeutique de l'Université de Nantes, Nantes, France
| | - Gwenaëlle Randuineau
- UMR 1280 Physiologie des Adaptations Nutritionnelles, Université de Nantes Atlantique, Nantes, France
- Research Center of Human Nutrition Nantes, Nantes, France
| | - Patricia Parnet
- UMR 1280 Physiologie des Adaptations Nutritionnelles, Université de Nantes Atlantique, Nantes, France
- Research Center of Human Nutrition Nantes, Nantes, France
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519
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Menzies JRW, Skibicka KP, Egecioglu E, Leng G, Dickson SL. Peripheral signals modifying food reward. Handb Exp Pharmacol 2012:131-58. [PMID: 22249813 DOI: 10.1007/978-3-642-24716-3_6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The pleasure derived from eating may feel like a simple emotion, but the decision to eat, and perhaps more importantly what to eat, involves central pathways linking energy homeostasis and reward and their regulation by metabolic and endocrine factors. Evidence is mounting that modulation of the hedonic aspects of energy balance is under the control of peripheral neuropeptides conventionally associated with homeostatic appetite control. Here, we describe the significance of reward in feeding, the neural substrates underlying the reward pathway and their modification by peptides released into the circulation from peripheral tissues.
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Affiliation(s)
- John R W Menzies
- Centre for Integrative Physiology, School of Biomedical Sciences, University of Edinburgh, Scotland, UK.
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520
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Stevanovic D, Starcevic V, Vilimanovich U, Nesic D, Vucicevic L, Misirkic M, Janjetovic K, Savic E, Popadic D, Sudar E, Micic D, Sumarac-Dumanovic M, Trajkovic V. Immunomodulatory actions of central ghrelin in diet-induced energy imbalance. Brain Behav Immun 2012; 26:150-8. [PMID: 21925262 DOI: 10.1016/j.bbi.2011.08.009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Revised: 08/15/2011] [Accepted: 08/31/2011] [Indexed: 11/19/2022] Open
Abstract
We investigated the effects of centrally administered orexigenic hormone ghrelin on energy imbalance-induced inflammation. Rats were subjected for four weeks to three different dietary regimes: normal (standard food), high-fat (standard food with 30% lard) or food-restricted (70%, 50%, 40% and 40% of the expected food intake in 1st, 2nd, 3rd and 4th week, respectively). Compared to normal-weight controls, starved, but not obese rats had significantly higher levels of proinflammatory cytokines (TNF, IL-1β, IFN-γ) in the blood. When compared to normally fed animals, the hearts of starved and obese animals expressed higher levels of mRNAs encoding proinflammatory mediators (TNF, IL-1β, IL-6, IFN-γ, IL-17, IL-12, iNOS), while mRNA levels of the anti-inflammatory TGF-β remained unchanged. Intracerebroventricular (ICV) injection of ghrelin (1 μg/day) for five consecutive days significantly reduced TNF, IL-1β and IFN-γ levels in the blood of starved rats, as well as TNF, IL-17 and IL-12p40 mRNA expression in the hearts of obese rats. Conversely, ICV ghrelin increased the levels of IFN-γ, IL-17, IL-12p35 and IL-12p40 mRNA in the heart tissue of food-restricted animals. This was associated with an increase of immunosuppressive ACTH/corticosterone production in starved animals and a decrease of the immunostimulatory adipokine leptin both in food-restricted and high-fat groups. Ghrelin activated the energy sensor AMP-activated protein kinase (AMPK) in the hypothalamus and inhibited extracellular signal-regulated kinase (ERK) in the hearts of obese, but not starved rats. Therefore, central ghrelin may play a complex role in energy imbalance-induced inflammation by modulating HPA axis, leptin and AMPK/ERK signaling pathways.
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Affiliation(s)
- Darko Stevanovic
- Institute of Medical Physiology, School of Medicine, University of Belgrade, 11000 Belgrade, Serbia.
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521
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Kim JH, Saxton AM. The TALLYHO mouse as a model of human type 2 diabetes. METHODS IN MOLECULAR BIOLOGY (CLIFTON, N.J.) 2012; 933:75-87. [PMID: 22893402 DOI: 10.1007/978-1-62703-068-7_6] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/31/2023]
Abstract
The TALLYHO/Jng (TH) mouse is an inbred polygenic model for type 2 diabetes (T2D) with moderate obesity. Both male and female TH mice are characterized by increased body and fat pad weights, hyperleptinemia, hyperinsulinemia, and hyperlipidemia. Glucose intolerance and hyperglycemia are exhibited only in males. Reduced 2-deoxy-glucose uptake occurs in adipose tissue and skeletal muscle of male TH mice. While both sexes of TH mice exhibit enlarged pancreatic islets, only males have degranulation and abnormal architecture in islets. Endothelial dysfunction and considerably decreased bone density are also observed in male TH mice. The blood pressure of male TH mice is normal. Genetic outcross experiments with non-diabetic strains revealed multiple susceptibility loci (quantitative trait loci) for obesity, hypertriglyceridemia, hypercholesterolemia, and hyperglycemia. In conclusion, TH mice encompass many aspects of polygenic human diabetes and are a very useful model for T2D.
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Affiliation(s)
- Jung Han Kim
- Department of Pharmacology, Physiology and Toxicology, Marshall University School of Medicine, Huntington, WV, USA.
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522
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Tsou RC, Bence KK. The Genetics of PTPN1 and Obesity: Insights from Mouse Models of Tissue-Specific PTP1B Deficiency. J Obes 2012; 2012:926857. [PMID: 22811891 PMCID: PMC3395189 DOI: 10.1155/2012/926857] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Revised: 04/18/2012] [Accepted: 04/18/2012] [Indexed: 02/05/2023] Open
Abstract
The protein tyrosine phosphatase PTP1B is a negative regulator of both insulin and leptin signaling and is involved in the control of glucose homeostasis and energy expenditure. Due to its prominent role in regulating metabolism, PTP1B is a promising therapeutic target for the treatment of human obesity and type 2 diabetes. The PTP1B protein is encoded by the PTPN1 gene on human chromosome 20q13, a region that shows linkage with insulin resistance, type 2 diabetes, and obesity in human populations. In this paper, we summarize the genetics of the PTPN1 locus and associations with metabolic disease. In addition, we discuss the tissue-specific functions of PTP1B as gleaned from genetic mouse models.
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Affiliation(s)
- Ryan C. Tsou
- Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce Street, Vet 223E, Philadelphia, PA 19104, USA
| | - Kendra K. Bence
- Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce Street, Vet 223E, Philadelphia, PA 19104, USA
- *Kendra K. Bence:
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523
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Thaler JP, Yi CX, Schur EA, Guyenet SJ, Hwang BH, Dietrich MO, Zhao X, Sarruf DA, Izgur V, Maravilla KR, Nguyen HT, Fischer JD, Matsen ME, Wisse BE, Morton GJ, Horvath TL, Baskin DG, Tschöp MH, Schwartz MW. Obesity is associated with hypothalamic injury in rodents and humans. J Clin Invest 2011; 122:153-62. [PMID: 22201683 DOI: 10.1172/jci59660] [Citation(s) in RCA: 1288] [Impact Index Per Article: 99.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Accepted: 11/02/2011] [Indexed: 01/21/2023] Open
Abstract
Rodent models of obesity induced by consuming high-fat diet (HFD) are characterized by inflammation both in peripheral tissues and in hypothalamic areas critical for energy homeostasis. Here we report that unlike inflammation in peripheral tissues, which develops as a consequence of obesity, hypothalamic inflammatory signaling was evident in both rats and mice within 1 to 3 days of HFD onset, prior to substantial weight gain. Furthermore, both reactive gliosis and markers suggestive of neuron injury were evident in the hypothalamic arcuate nucleus of rats and mice within the first week of HFD feeding. Although these responses temporarily subsided, suggesting that neuroprotective mechanisms may initially limit the damage, with continued HFD feeding, inflammation and gliosis returned permanently to the mediobasal hypothalamus. Consistent with these data in rodents, we found evidence of increased gliosis in the mediobasal hypothalamus of obese humans, as assessed by MRI. These findings collectively suggest that, in both humans and rodent models, obesity is associated with neuronal injury in a brain area crucial for body weight control.
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Affiliation(s)
- Joshua P Thaler
- Division of Metabolism, Endocrinology and Nutrition, Diabetes and Obesity Center of Excellence, University of Washington, Seattle, Washington 98109, USA
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524
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Warne JP, Alemi F, Reed AS, Varonin JM, Chan H, Piper ML, Mullin ME, Myers MG, Corvera CU, Xu AW. Impairment of central leptin-mediated PI3K signaling manifested as hepatic steatosis independent of hyperphagia and obesity. Cell Metab 2011; 14:791-803. [PMID: 22152304 PMCID: PMC3240844 DOI: 10.1016/j.cmet.2011.11.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2011] [Revised: 09/13/2011] [Accepted: 11/02/2011] [Indexed: 11/22/2022]
Abstract
Hepatic steatosis is generally thought to develop via peripheral mechanisms associated with obesity. We show that chronic central infusion of leptin suppresses hepatic lipogenic gene expression and reduces triglyceride content via stimulation of hepatic sympathetic activity. This leptin function is independent of feeding and body weight but requires phosphatidylinositol 3-kinase (PI3K) signaling. Attenuation of leptin-induced PI3K signaling, brought about by transgenic expression of phosphatase and tensin homolog (PTEN) in leptin receptor neurons, leads to decreased hepatic sympathetic tone and increased triglyceride levels without affecting adiposity or hepatic insulin signaling. Central leptin's effects on hepatic norepinephrine levels and triglyceride content are blunted in these mutant mice. Simultaneous downregulation of PI3K and signal transducer and activator of transcription-3 (Stat3) in leptin receptor neurons does not exacerbate obesity but causes more severe hepatic steatosis. Together, our results indicate that central cellular leptin resistance in PI3K signaling manifests as hepatic steatosis without causing obesity.
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Affiliation(s)
- James P. Warne
- Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Farzad Alemi
- General Surgery, San Francisco VA Medical Center, University of California, San Francisco, San Francisco, CA 94143
| | - Alison S. Reed
- Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Jillian M. Varonin
- Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Helen Chan
- Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Merisa L. Piper
- Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Mark E. Mullin
- Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Martin G. Myers
- Departments of Internal Medicine and Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Carlos U. Corvera
- General Surgery, San Francisco VA Medical Center, University of California, San Francisco, San Francisco, CA 94143
| | - Allison W. Xu
- Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA
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525
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526
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Expanding neurotransmitters in the hypothalamic neurocircuitry for energy balance regulation. Protein Cell 2011; 2:800-13. [PMID: 22058035 DOI: 10.1007/s13238-011-1112-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2011] [Accepted: 10/10/2011] [Indexed: 01/06/2023] Open
Abstract
The current epidemic of obesity and its associated metabolic syndromes impose unprecedented challenges to our society. Despite intensive research on obesity pathogenesis, an effective therapeutic strategy to treat and cure obesity is still lacking. Exciting studies in last decades have established the importance of the leptin neural pathway in the hypothalamus in the regulation of body weight homeostasis. Important hypothalamic neuropeptides have been identified as critical neurotransmitters from leptin-sensitive neurons to mediate leptin action. Recent research advance has significantly expanded the list of neurotransmitters involved in body weight-regulating neural pathways, including fast-acting neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate. Given the limited knowledge on the leptin neural pathway for body weight homeostasis, understanding the function of neurotransmitters released from key neurons for energy balance regulation is essential for delineating leptin neural pathway and eventually for designing effective therapeutic drugs against the obesity epidemic.
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527
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Arble DM, Vitaterna MH, Turek FW. Rhythmic leptin is required for weight gain from circadian desynchronized feeding in the mouse. PLoS One 2011; 6:e25079. [PMID: 21949859 PMCID: PMC3176308 DOI: 10.1371/journal.pone.0025079] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Accepted: 08/24/2011] [Indexed: 11/24/2022] Open
Abstract
The neuroendocrine and metabolic effects of leptin have been extensively researched since the discovery, and the later identification, of the leptin gene mutated within the ob/ob mouse. Leptin is required for optimal health in a number of physiological systems (e.g. fertility, bone density, body weight regulation). Despite the extensive leptin literature and many observations of leptin's cyclical pattern over the 24-hour day, few studies have specifically examined how the circadian rhythm of leptin may be essential to leptin signaling and health. Here we present data indicating that a rhythmic leptin profile (e.g. 1 peak every 24 hours) leads to excessive weight gain during desynchronized feeding whereas non-rhythmic leptin provided in a continuous manner does not lead to excessive body weight gain under similar feeding conditions. This study suggests that feeding time can interact with leptin's endogenous rhythm to influence metabolic signals, specifically leading to excessive body weight gains during 'wrongly' timed feeding.
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Affiliation(s)
- Deanna Marie Arble
- Northwestern University, Center for Sleep and Circadian Biology, Evanston, Illinois, United States of America
| | - Martha Hotz Vitaterna
- Northwestern University, Center for Sleep and Circadian Biology, Evanston, Illinois, United States of America
| | - Fred W. Turek
- Northwestern University, Center for Sleep and Circadian Biology, Evanston, Illinois, United States of America
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528
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Vong L, Ye C, Yang Z, Choi B, Chua S, Lowell BB. Leptin action on GABAergic neurons prevents obesity and reduces inhibitory tone to POMC neurons. Neuron 2011; 71:142-54. [PMID: 21745644 DOI: 10.1016/j.neuron.2011.05.028] [Citation(s) in RCA: 867] [Impact Index Per Article: 66.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/10/2011] [Indexed: 12/29/2022]
Abstract
Leptin acts in the brain to prevent obesity. The underlying neurocircuitry responsible for this is poorly understood, in part because of incomplete knowledge regarding first-order, leptin-responsive neurons. To address this, we and others have been removing leptin receptors from candidate first-order neurons. While functionally relevant neurons have been identified, the observed effects have been small, suggesting that most first-order neurons remain unidentified. Here we take an alternative approach and test whether first-order neurons are inhibitory (GABAergic, VGAT⁺) or excitatory (glutamatergic, VGLUT2⁺). Remarkably, the vast majority of leptin's antiobesity effects are mediated by GABAergic neurons; glutamatergic neurons play only a minor role. Leptin, working directly on presynaptic GABAergic neurons, many of which appear not to express AgRP, reduces inhibitory tone to postsynaptic POMC neurons. As POMC neurons prevent obesity, their disinhibition by leptin action on presynaptic GABAergic neurons probably mediates, at least in part, leptin's antiobesity effects.
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Affiliation(s)
- Linh Vong
- Division of Endocrinology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, EC/CLS717, Boston, MA 02215, USA
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529
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Södersten P, Bergh C, Zandian M, Ioakimidis I. Obesity and the brain. Med Hypotheses 2011; 77:371-3. [DOI: 10.1016/j.mehy.2011.05.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Accepted: 05/15/2011] [Indexed: 12/27/2022]
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530
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Conroy R, Girotra M, Shane E, McMahon DJ, Pavlovich KH, Leibel RL, Rosenbaum M, Korner J. Leptin administration does not prevent the bone mineral metabolism changes induced by weight loss. Metabolism 2011; 60:1222-6. [PMID: 21489573 PMCID: PMC3139754 DOI: 10.1016/j.metabol.2011.02.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 02/10/2011] [Accepted: 02/18/2011] [Indexed: 01/19/2023]
Abstract
The objective was to examine the effects of weight loss and leptin administration following weight loss on calciotropic hormones and bone turnover. This was a prospective, single-blinded study of 12 subjects (8 women, 4 men; 2 nonobese, 10 obese; age range, 19-46 years) who were studied on an inpatient basis while maintaining their usual weight [Wt(initial)] and during maintenance of 10% weight loss while receiving twice-daily injections of either a placebo [Wt(-10%P)] or replacement doses of leptin [Wt(-10%L)]. The main outcome measures were markers of bone formation (bone alkaline phosphatase and procollagen type 1 amino terminal propeptide) and resorption (N-telopeptide) as well as parathyroid hormone, calcium, and 25-hydroxy vitamin D measured from fasting morning serum. As expected, serum leptin declined with weight loss. Bone alkaline phosphatase decreased by 12.3% ± 3.9% between Wt(initial) and Wt(-10%P) and remained suppressed after leptin administration (both P < .01 compared with baseline). N-telopeptides increased by 37.2% ± 11.3% from Wt(initial) to Wt(-10%L) (P < .01). Procollagen type 1 amino terminal propeptide, parathyroid hormone, calcium, and 25-hydroxy vitamin D did not change. These results suggest that both decreased bone formation and increased bone resorption underlie bone loss associated with weight loss. Leptin administration did not prevent the uncoupling of bone remodeling that accompanies weight loss.
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Affiliation(s)
| | - Monica Girotra
- Columbia University College of Physicians and Surgeons, Department of Medicine, New York, New York 10032
| | - Elizabeth Shane
- Columbia University College of Physicians and Surgeons, Department of Medicine, New York, New York 10032
| | - Donald J. McMahon
- Columbia University College of Physicians and Surgeons, Department of Medicine, New York, New York 10032
| | | | | | | | - Judith Korner
- Columbia University College of Physicians and Surgeons, Department of Medicine, New York, New York 10032
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531
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Gordon CM. Leptin and the skeleton-where is the fat? Metabolism 2011; 60:1203-6. [PMID: 21742353 DOI: 10.1016/j.metabol.2011.05.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 05/23/2011] [Accepted: 05/23/2011] [Indexed: 11/20/2022]
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532
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533
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Ferguson SA, Law CD, Abshire JS. Developmental Treatment with Bisphenol A or Ethinyl Estradiol Causes Few Alterations on Early Preweaning Measures. Toxicol Sci 2011; 124:149-60. [DOI: 10.1093/toxsci/kfr201] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
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534
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A review of weight control strategies and their effects on the regulation of hormonal balance. J Nutr Metab 2011; 2011:237932. [PMID: 21822485 PMCID: PMC3147122 DOI: 10.1155/2011/237932] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Accepted: 05/20/2011] [Indexed: 01/11/2023] Open
Abstract
The estimated prevalence of obesity in the USA is 72.5 million adults with costs attributed to obesity more than 147 billion dollars per year. Though caloric restriction has been used extensively in weight control studies, short-term success has been difficult to achieve, with long-term success of weight control being even more elusive. Therefore, novel approaches are needed to control the rates of obesity that are occurring globally. The purpose of this paper is to provide a synopsis of how exercise, sleep, psychological stress, and meal frequency and composition affect levels of ghrelin, cortisol, insulin GLP-1, and leptin and weight control. We will provide information regarding how hormones respond to various lifestyle factors which may affect appetite control, hunger, satiety, and weight control.
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535
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Abstract
The scientific study of obesity has been dominated throughout the twentieth century by the concept of energy balance. This conceptual approach, based on fundamental thermodynamic principles, states that energy cannot be destroyed, and can only be gained, lost or stored by an organism. Its application in obesity research has emphasised excessive appetite (gluttony), or insufficient physical activity (sloth), as the primary determinants of excess weight gain, reflected in current guidelines for obesity prevention and treatment. This model cannot explain why weight accumulates persistently rather than reaching a plateau, and underplays the effect of variability in dietary constituents on energy and intermediary metabolism. An alternative model emphasises the capacity of fructose and fructose-derived sweeteners (sucrose, high-fructose corn syrup) to perturb cellular metabolism via modification of the adenosine monophosphate (AMP)/adenosine triphosphate (ATP) ratio, activation of AMP kinase and compensatory mechanisms, which favour adipose tissue accretion and increased appetite while depressing physical activity. This conceptual model implicates chronic hyperinsulinaemia in the presence of a paradoxical state of 'cellular starvation' as a key driver of the metabolic modifications inducing chronic weight gain. We combine evidence from in vitro and in vivo experiments to formulate a perspective on obesity aetiology that emphasises metabolic flexibility and dietary composition rather than energy balance. Using this model, we question the direction of causation of reported associations between obesity and sleep duration or childhood growth. Our perspective generates new hypotheses, which can be tested to improve our understanding of the current obesity epidemic, and to identify novel strategies for prevention or treatment.
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Affiliation(s)
- J C K Wells
- Childhood Nutrition Research Centre, UCL Institute of Child Health, London, UK.
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536
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de Lartigue G, Barbier de la Serre C, Espero E, Lee J, Raybould HE. Diet-induced obesity leads to the development of leptin resistance in vagal afferent neurons. Am J Physiol Endocrinol Metab 2011; 301:E187-95. [PMID: 21521717 PMCID: PMC3129833 DOI: 10.1152/ajpendo.00056.2011] [Citation(s) in RCA: 129] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Ingestion of high-fat, high-calorie diets is associated with hyperphagia, increased body fat, and obesity. The mechanisms responsible are currently unclear; however, altered leptin signaling may be an important factor. Vagal afferent neurons (VAN) integrate signals from the gut in response to ingestion of nutrients and express leptin receptors. Therefore, we tested the hypothesis that leptin resistance occurs in VAN in response to a high-fat diet. Sprague-Dawley rats, which exhibit a bimodal distribution of body weight gain, were used after ingestion of a high-fat diet for 8 wk. Body weight, food intake, and plasma leptin levels were measured. Leptin signaling was determined by immunohistochemical localization of phosphorylated STAT3 (pSTAT3) in cultured VAN and by quantifaction of pSTAT3 protein levels by Western blot analysis in nodose ganglia and arcuate nucleus in vivo. To determine the mechanism of leptin resistance in nodose ganglia, cultured VAN were stimulated with leptin alone or with lipopolysaccharide (LPS) and SOCS-3 expression measured. SOCS-3 protein levels in VAN were measured by Western blot following leptin administration in vivo. Leptin resulted in appearance of pSTAT3 in VAN of low-fat-fed rats and rats resistant to diet-induced obesity but not diet-induced obese (DIO) rats. However, leptin signaling was normal in arcuate neurons. SOCS-3 expression was increased in VAN of DIO rats. In cultured VAN, LPS increased SOCS-3 expression and inhibited leptin-induced pSTAT3 in vivo. We conclude that VAN of diet-induced obese rats become leptin resistant; LPS and SOCS-3 may play a role in the development of leptin resistance.
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Affiliation(s)
- Guillaume de Lartigue
- Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California Davis, Davis, California, USA
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537
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Morton GJ, Schwartz MW. Leptin and the central nervous system control of glucose metabolism. Physiol Rev 2011; 91:389-411. [PMID: 21527729 DOI: 10.1152/physrev.00007.2010] [Citation(s) in RCA: 210] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The regulation of body fat stores and blood glucose levels is critical for survival. This review highlights growing evidence that leptin action in the central nervous system plays a key role in both processes. Investigation into underlying mechanisms has begun to clarify the physiological role of leptin in the control of glucose metabolism and raises interesting new possibilities for the treatment of diabetes and related disorders.
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Affiliation(s)
- Gregory J Morton
- Diabetes and Obesity Center of Excellence, Department of Medicine, University of Washington, Seattle, Washington 98195, USA.
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538
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Gautron L, Elmquist JK. Sixteen years and counting: an update on leptin in energy balance. J Clin Invest 2011; 121:2087-93. [PMID: 21633176 DOI: 10.1172/jci45888] [Citation(s) in RCA: 245] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Cloned in 1994, the ob gene encodes the protein hormone leptin, which is produced and secreted by white adipose tissue. Since its discovery, leptin has been found to have profound effects on behavior, metabolic rate, endocrine axes, and glucose fluxes. Leptin deficiency in mice and humans causes morbid obesity, diabetes, and various neuroendocrine anomalies, and replacement leads to decreased food intake, normalized glucose homeostasis, and increased energy expenditure. Here, we provide an update on the most current understanding of leptin-sensitive neural pathways in terms of both anatomical organization and physiological roles.
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Affiliation(s)
- Laurent Gautron
- Department of Internal Medicine, Division of Hypothalamic Research, The University of Texas Southwestern Medical Center, Dallas, Texas, USA
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539
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Williams DL, Schwartz MW. Neuroanatomy of body weight control: lessons learned from leptin. J Clin Invest 2011; 121:2152-5. [PMID: 21606602 DOI: 10.1172/jci58027] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Rather than arising from the passive accumulation of excess calories, obesity is a state in which the biologically defended level of body fat stores increases due to defects in the homeostatic process that matches food intake and energy expenditure over time. By deleting leptin receptors from distinct brain regions and neuronal subsets, researchers are beginning to identify the neuroanatomical substrates responsible for this regulation. In this issue of the JCI, Scott et al. demonstrate that loss of leptin receptors in a subset of hindbrain neurons increases food intake in mice, but, unlike what is observed when leptin receptors are deleted from hypothalamic neurons, these mice compensate by increasing energy expenditure and hence do not become obese. Although many brain areas can regulate energy intake and/or energy expenditure, it is likely that only a small subset of neurons actively matches the two over time. It is vital to clarify how this works if we are to improve our understanding of obesity pathogenesis and options available for its treatment.
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Affiliation(s)
- Diana L Williams
- Department of Psychology and Program in Neuroscience, Florida State University, Tallahassee, Florida, USA
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540
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Nishimura T, Sato Y, Tanaka M, Kurita R, Nakamoto K, Niwa O. Bifunctional tri(ethylene glycol) alkanethiol monolayer modified gold electrode for on-chip electrochemical immunoassay of pg level leptin. ANAL SCI 2011; 27:465. [PMID: 21558650 DOI: 10.2116/analsci.27.465] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
An on-chip enzyme-linked immunosorbent assay combined with an electrochemical detection method (EC-ELISA) was employed to detect a leptin, one of the most important adipose derived hormones, using gold electrodes modified with a tri(ethylene glycol) terminated short alkanethiol (TEGCnSH, Cn = (CH(2))n, n = 2, 4, 6, and 8) monolayer. These TEGCnSH monolayers on gold electrodes can suppress non-specific protein adsorption without affecting the electrochemical activity required for detecting p-aminophenol (PAP), which is an alkaline phosphatase (ALP) product. We measured leptin with a highly sensitive detection range (100 pg mL(-1) to 10 ng mL(-1) level) and with the desired detection limit (13.6 pg mL(-1)) by using electrochemical detection. For detecting leptin, the EC-ELISA method using TEGC4SH modified gold electrode with a poly(dimethylsiloxane) based microchannel was superior to the conventional ELISA method. With the EC-ELISA method, we were able to measure leptin with a satisfactory detection range and a pg level detection limit within 30 min, which is a much lower detection level than that obtained with conventional plate based ELISA.
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Affiliation(s)
- Tetsuya Nishimura
- National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan
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541
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542
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Begriche K, Sutton GM, Butler AA. Homeostastic and non-homeostatic functions of melanocortin-3 receptors in the control of energy balance and metabolism. Physiol Behav 2011; 104:546-54. [PMID: 21497617 DOI: 10.1016/j.physbeh.2011.04.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Revised: 04/04/2011] [Accepted: 04/08/2011] [Indexed: 01/05/2023]
Abstract
The central nervous melanocortin system is a neural network linking nutrient-sensing systems with hypothalamic, limbic and hindbrain neurons regulating behavior and metabolic homeostasis. Primary melanocortin neurons releasing melanocortin receptor ligands residing in the hypothalamic arcuate nucleus are regulated by nutrient-sensing and metabolic signals. A smaller group of primary neurons releasing melanocortin agonists in the nucleus tractus solitarius in the brainstem are also regulated by signals of metabolic state. Two melanocortin receptors regulate energy homeostasis. Melanocortin-4 receptors regulate satiety and autonomic outputs controlling peripheral metabolism. The functions of melanocortin-3 receptors (MC3R) expressed in hypothalamic and limbic structures are less clear. Here we discuss published data and preliminary observations from our laboratory suggesting that neural MC3R regulate inputs into systems governing the synchronization of rhythms in behavior and metabolism with nutrient intake. Mice subjected to a restricted feeding protocol, where a limited number of calories are presented at a 24h interval, rapidly exhibit bouts of increased wakefulness and activity which anticipate food presentation. The full expression of these responses is dependent on MC3R. Moreover, MC3R knockout mice are unique in exhibiting a dissociation of weight loss from improved glucose homeostasis when subject to a restricted feeding protocol. While mice lacking MC3R fed ad libitum exhibit normal to moderate hyperinsulinemia, when subjected to a restricted protocol they develop hyperglycemia, glucose intolerance, and dyslipidemia. Collectively, our data suggest that the central nervous melanocortin system is a point convergence in the control of energy balance and the expression of rhythms anticipating nutrient intake.
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Affiliation(s)
- Karima Begriche
- Department of Metabolism and Aging, The Scripps Research Institute-Florida, Jupiter, FL 33458, USA
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543
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Abstract
Energy homeostasis involves a complex network of hypothalamic and extra-hypothalamic neurons that transduce hormonal, nutrient and neuronal signals into responses that ultimately match caloric intake to energy expenditure and thereby promote stability of body fat stores. Growing evidence suggests that rather than reflecting a failure to regulate caloric intake, common forms of obesity involve fundamental changes to this homeostatic system that favor the defense of an elevated level of body adiposity. This article reviews emerging evidence that during high-fat feeding, obesity pathogenesis involves fundamental alteration of hypothalamic systems that regulate food intake and energy expenditure.
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544
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Fukuda M, Williams KW, Gautron L, Elmquist JK. Induction of leptin resistance by activation of cAMP-Epac signaling. Cell Metab 2011; 13:331-9. [PMID: 21356522 PMCID: PMC3747952 DOI: 10.1016/j.cmet.2011.01.016] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2010] [Revised: 12/14/2010] [Accepted: 01/18/2011] [Indexed: 01/28/2023]
Abstract
Leptin regulates energy balance and glucose homeostasis. Shortly after leptin was identified, it was established that obesity is commonly associated with leptin resistance, though the molecular mechanisms remain to be identified. To explore potential mechanisms of leptin resistance, we employed organotypic brain slices to identify candidate signaling pathways that negatively regulate leptin sensitivity. We found that elevation of adenosine 3', 5'-monophosphate (cAMP) levels impairs multiple signaling cascades activated by leptin within the hypothalamus. Notably, this effect is independent of protein kinase A activation. In contrast, activation of Epac, a cAMP-regulated guanine nucleotide exchange factor for the small G protein Rap1, was sufficient to impair leptin signaling with concomitant induction of SOCS-3 expression. Epac activation also blunted leptin-induced depolarization of hypothalamic POMC neurons. Finally, central infusion of an Epac activator blunted the anorexigenic actions of leptin. Thus, activation of hypothalamic cAMP-Epac pathway is sufficient to induce multiple indices of leptin resistance.
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Affiliation(s)
- Makoto Fukuda
- Division of Hypothalamic Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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545
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Li MD. Leptin and beyond: an odyssey to the central control of body weight. THE YALE JOURNAL OF BIOLOGY AND MEDICINE 2011; 84:1-7. [PMID: 21451778 PMCID: PMC3064240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The 2010 Lasker Award for basic medical research was shared by Douglas Coleman and Jeffery Friedman for their discovery of leptin, a breakthrough that revealed insight into the genetic basis of obesity. This mini-review aims to review landmark studies on the physiologic system of body weight control. The basic research on the leptin system has broad implications for the genetic control of body weight, thus contributing to solve the global obesity crisis.
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546
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Tennese AA, Wevrick R. Impaired hypothalamic regulation of endocrine function and delayed counterregulatory response to hypoglycemia in Magel2-null mice. Endocrinology 2011; 152:967-78. [PMID: 21248145 PMCID: PMC3198964 DOI: 10.1210/en.2010-0709] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Hypothalamic dysfunction may underlie endocrine abnormalities in Prader-Willi syndrome (PWS), a genetic disorder that features GH deficiency, obesity, and infertility. One of the genes typically inactivated in PWS, MAGEL2, is highly expressed in the hypothalamus. Mice deficient for Magel2 are obese with increased fat mass and decreased lean mass and have blunted circadian rhythm. Here, we demonstrate that Magel2-null mice have abnormalities of hypothalamic endocrine axes that recapitulate phenotypes in PWS. Magel2-null mice had elevated basal corticosterone levels, and although male Magel2-null mice had an intact corticosterone response to restraint and to insulin-induced hypoglycemia, female Magel2-null mice failed to respond to hypoglycemia with increased corticosterone. After insulin-induced hypoglycemia, Magel2-null mice of both sexes became more profoundly hypoglycemic, and female mice were slower to recover euglycemia, suggesting an impaired hypothalamic counterregulatory response. GH insufficiency can produce abnormal body composition, such as that seen in PWS and in Magel2-null mice. Male Magel2-null mice had Igf-I levels similar to control littermates. Female Magel2-null mice had low Igf-I levels and reduced GH release in response to stimulation with ghrelin. Female Magel2-null mice did respond to GHRH, suggesting that their GH deficiency has a hypothalamic rather than pituitary origin. Female Magel2-null mice also had higher serum adiponectin than expected, considering their increased fat mass, and thyroid (T(4)) levels were low. Together, these findings strongly suggest that loss of MAGEL2 contributes to endocrine dysfunction of hypothalamic origin in individuals with PWS.
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Affiliation(s)
- Alysa A Tennese
- Department of Medical Genetics, 8-16 Medical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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547
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Arruda AP, Milanski M, Velloso LA. Hypothalamic inflammation and thermogenesis: the brown adipose tissue connection. J Bioenerg Biomembr 2011; 43:53-8. [DOI: 10.1007/s10863-011-9325-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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548
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Denver RJ, Bonett RM, Boorse GC. Evolution of leptin structure and function. Neuroendocrinology 2011; 94:21-38. [PMID: 21677426 DOI: 10.1159/000328435] [Citation(s) in RCA: 146] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Accepted: 04/11/2011] [Indexed: 12/15/2022]
Abstract
Leptin, the protein product of the obese(ob or Lep) gene, is a hormone synthesized by adipocytes that signals available energy reserves to the brain, and thereby influences development, growth, metabolism and reproduction. In mammals, leptin functions as an adiposity signal: circulating leptin fluctuates in proportion to fat mass, and it acts on the hypothalamus to suppress food intake. Orthologs of mammalian Lep genes were recently isolated from several fish and two amphibian species, and here we report the identification of two Lep genes in a reptile, the lizard Anolis carolinensis. While vertebrate leptins show large divergence in their primary amino acid sequence, they form similar tertiary structures, and may have similar potencies when tested in vitro on heterologous leptin receptors (LepRs). Leptin binds to LepRs on the plasma membrane, activating several intracellular signaling pathways. Vertebrate LepRs signal via the Janus kinase (Jak) and signal transducer and activator of transcription (STAT) pathway. Three tyrosine residues located within the LepR cytoplasmic domain are phosphorylated by Jak2 and are required for activation of SH2-containing tyrosine phosphatase-2, STAT5 and STAT3 signaling. These tyrosines are conserved from fishes to mammals, demonstrating their critical role in signaling by the LepR. Leptin is anorexigenic in representatives of all vertebrate classes, suggesting that its role in energy balance is ancient and has been evolutionarily conserved. In addition to its integral role as a regulator of appetite and energy balance, leptin exerts pleiotropic actions in development, physiology and behavior.
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Affiliation(s)
- Robert J Denver
- Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, USA. rdenver @ umich.edu
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549
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Vijayakumar A, Yakar S, LeRoith D. The intricate role of growth hormone in metabolism. Front Endocrinol (Lausanne) 2011; 2:32. [PMID: 22654802 PMCID: PMC3356038 DOI: 10.3389/fendo.2011.00032] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Accepted: 08/30/2011] [Indexed: 11/18/2022] Open
Abstract
Growth hormone (GH), a master regulator of somatic growth, also regulates carbohydrate and lipid metabolism via complex interactions with insulin and insulin-like growth factor-1 (IGF-1). Data from human and rodent studies reveal the importance of GH in insulin synthesis and secretion, lipid metabolism and body fat remodeling. In this review, we will summarize the tissue-specific metabolic effects of GH, with emphasis on recent targets identified to mediate these effects. Furthermore, we will discuss what role GH plays in obesity and present possible mechanisms by which this may occur.
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Affiliation(s)
- Archana Vijayakumar
- Division of Endocrinology, Diabetes and Bone Diseases, Department of Medicine, Mount Sinai School of MedicineNew York, NY, USA
| | - Shoshana Yakar
- Division of Endocrinology, Diabetes and Bone Diseases, Department of Medicine, Mount Sinai School of MedicineNew York, NY, USA
| | - Derek LeRoith
- Division of Endocrinology, Diabetes and Bone Diseases, Department of Medicine, Mount Sinai School of MedicineNew York, NY, USA
- *Correspondence: Derek LeRoith, Division of Endocrinology, Diabetes and Bone Disease, Mount Sinai School of Medicine, One Gustav Levy Place, Box 1055, New York, NY 10029-6574, USA. e-mail:
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