101
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Leptin and insulin pathways in POMC and AgRP neurons that modulate energy balance and glucose homeostasis. EMBO Rep 2012; 13:1079-86. [PMID: 23146889 DOI: 10.1038/embor.2012.174] [Citation(s) in RCA: 274] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Accepted: 10/22/2012] [Indexed: 11/08/2022] Open
Abstract
With the steady rise in the prevalence of obesity and its associated diseases, research aimed at understanding the mechanisms that regulate and control whole body energy homeostasis has gained new interest. Leptin and insulin, two anorectic hormones, have key roles in the regulation of body weight and energy homeostasis, as highlighted by the fact that several obese patients develop resistance to these hormones. Within the brain, the hypothalamic proopiomelanocortin and agouti-related protein neurons have been identified as major targets of leptin and insulin action. Many studies have attempted to discern the individual contributions of various components of the principal pathways that mediate the central effects of leptin and insulin. The aim of this review is to discuss the latest findings that might shed light on, and lead to a better understanding of, energy balance and glucose homeostasis. In addition, recently discovered targets and mechanisms that mediate hormonal action in the brain are highlighted.
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102
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Rho-kinase regulates energy balance by targeting hypothalamic leptin receptor signaling. Nat Neurosci 2012; 15:1391-8. [PMID: 22941110 PMCID: PMC3458121 DOI: 10.1038/nn.3207] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Accepted: 08/06/2012] [Indexed: 12/23/2022]
Abstract
Leptin regulates energy balance. However, knowledge of the critical intracellular transducers of leptin signaling remains incomplete. Here we report that Rho-kinase 1 (ROCK1) regulates leptin action on body weight homeostasis by activating JAK2, an initial trigger of leptin receptor signaling. Leptin promotes the physical interaction of JAK2 and ROCK1, thereby increasing phosphorylation of JAK2 and downstream activation of Stat3 and FOXO1. Mice lacking ROCK1 in either POMC or AgRP neurons, mediators of leptin action, display obesity and impaired leptin sensitivity. In addition, deletion of ROCK1 in the arcuate nucleus markedly enhances food intake, resulting in severe obesity. Of note, ROCK1 is a specific mediator of leptin, but not insulin, regulation of POMC neuronal activity. Our data identify ROCK1 as a key regulator of leptin action on energy homeostasis.
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103
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Coppari R, Bjørbæk C. Leptin revisited: its mechanism of action and potential for treating diabetes. Nat Rev Drug Discov 2012; 11:692-708. [PMID: 22935803 PMCID: PMC4019022 DOI: 10.1038/nrd3757] [Citation(s) in RCA: 204] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Since the discovery of leptin in 1994, we now have a better understanding of the cellular and molecular mechanisms underlying its biological effects. In addition to its established anti-obesity effects, leptin exerts antidiabetic actions that are independent of its regulation of body weight and food intake. In particular, leptin can correct diabetes in animal models of type 1 and type 2 diabetes. In addition, long-term leptin replacement therapy improves glycaemic control, insulin sensitivity and plasma triglycerides in patients with severe insulin resistance due to lipodystrophy. These results have spurred enthusiasm for the use of leptin therapy to treat diabetes. Here, we review the current understanding of the glucoregulatory functions of leptin, emphasizing its central mechanisms of action and lessons learned from clinical studies, and discuss possible therapeutic applications of leptin in the treatment of type 1 and type 2 diabetes.
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Affiliation(s)
- Roberto Coppari
- Department of Internal Medicine, Division of Hypothalamic Research, The University of Texas Southwestern Medical Center, Dallas TX, 75390, USA
- Department of Cellular Physiology and Metabolism, Faculty of Medicine, University of Geneva, 1211 Geneva, Switzerland
- The Center for Epigenetics and Metabolism, University of California Irvine, Irvine, CA, 92697, USA
| | - Christian Bjørbæk
- Department of Medicine, Division of Endocrinology and Metabolism, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston MA, 02215, USA
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104
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Elias CF, Purohit D. Leptin signaling and circuits in puberty and fertility. Cell Mol Life Sci 2012; 70:841-62. [PMID: 22851226 PMCID: PMC3568469 DOI: 10.1007/s00018-012-1095-1] [Citation(s) in RCA: 110] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 07/05/2012] [Accepted: 07/09/2012] [Indexed: 12/22/2022]
Abstract
Leptin is an adipocyte-derived hormone involved in a myriad of physiological process, including the control of energy balance and several neuroendocrine axes. Leptin-deficient mice and humans are obese, diabetic, and display a series of neuroendocrine and autonomic abnormalities. These individuals are infertile due to a lack of appropriate pubertal development and inadequate synthesis and secretion of gonadotropins and gonadal steroids. Leptin receptors are expressed in many organs and tissues, including those related to the control of reproductive physiology (e.g., the hypothalamus, pituitary gland, and gonads). In the last decade, it has become clear that leptin receptors located in the brain are major players in most leptin actions, including reproduction. Moreover, the recent development of molecular techniques for brain mapping and the use of genetically modified mouse models have generated crucial new findings for understanding leptin physiology and the metabolic influences on reproductive health. In the present review, we will highlight the new advances in the field, discuss the apparent contradictions, and underline the relevance of this complex physiological system to human health. We will focus our review on the hypothalamic circuitry and potential signaling pathways relevant to leptin’s effects in reproductive control, which have been identified with the use of cutting-edge technologies of molecular mapping and conditional knockouts.
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Affiliation(s)
- Carol F Elias
- Division of Hypothalamic Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Y6-220B, Dallas, TX, 75390-9077, USA.
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105
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The dietary flavonoids naringenin and quercetin acutely impair glucose metabolism in rodents possibly via inhibition of hypothalamic insulin signalling. Br J Nutr 2012; 109:1040-51. [DOI: 10.1017/s0007114512003005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Secondary metabolites of herbs and spices are widely used as an alternative strategy in the therapy of various diseases. The polyphenols naringenin, quercetin and curcumin have been characterised as anti-diabetic agents. Conversely, in vitro, naringenin and quercetin are described to inhibit phosphoinositide-3-kinase (PI3K), an enzyme that is essential for the neuronal control of whole body glucose homoeostasis. Using both in vitro and in vivo experiments, we tested whether the inhibitory effect on PI3K occurs in neurons and if it might affect whole body glucose homoeostasis. Quercetin was found to inhibit basal and insulin-induced phosphorylation of Akt (Ser473), a downstream target of PI3K, in HT-22 cells, whereas naringenin and curcumin had no effect. In Djungarian hamsters (Phodopus sungorus) naringenin and quercetin (10 mg/kg administered orally) diminished insulin-induced phosphorylation of Akt (Ser473) in the arcuate nucleus, indicating a reduction in hypothalamic PI3K activity. In agreement with this finding, glucose tolerance in naringenin-treated hamsters (oral) and mice (oral and intracerebroventricular) was reduced compared with controls. Dietary quercetin also impaired glucose tolerance, whereas curcumin was ineffective. Circulating levels of insulin and insulin-like growth factor-binding protein were not affected by the polyphenols. Oral quercetin reduced the respiratory quotient, suggesting that glucose utilisation was impaired after treatment. These data demonstrate that low doses of naringenin and quercetin acutely and potently impair glucose homoeostasis. This effect may be mediated by inhibition of hypothalamic PI3K signalling. Whether chronic impairments in glucose homoeostasis occur after long-term application remains to be identified.
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106
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Dagon Y, Hur E, Zheng B, Wellenstein K, Cantley LC, Kahn BB. p70S6 kinase phosphorylates AMPK on serine 491 to mediate leptin's effect on food intake. Cell Metab 2012; 16:104-12. [PMID: 22727014 PMCID: PMC3407689 DOI: 10.1016/j.cmet.2012.05.010] [Citation(s) in RCA: 201] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2011] [Revised: 02/28/2012] [Accepted: 05/11/2012] [Indexed: 11/30/2022]
Abstract
The PI3K-AKT, mTOR-p70S6 kinase and AMPK pathways play distinct and critical roles in metabolic regulation. Each pathway is necessary for leptin's anorexigenic effects in the hypothalamus. Here we show that these pathways converge in an integrated phosphorylation cascade to mediate leptin action in the hypothalamus. We identify serine(491) on α2AMPK as the site of convergence and show that p70S6 kinase forms a complex with α2AMPK, resulting in phosphorylation on serine(491). Blocking α2AMPK-serine(491) phosphorylation increases hypothalamic AMPK activity, food intake, and body weight. Serine(491) phosphorylation is necessary for leptin's effects on hypothalamic α2AMPK activity, neuropeptide expression, food intake, and body weight. These results identify an inhibitory AMPK kinase, p70S6 kinase, and demonstrate that AMPK is a substrate for mTOR-p70S6 kinase. This discovery has broad biologic implications since mTOR-p70S6 kinase and AMPK have multiple, fundamental and generally opposing cellular effects that regulate metabolism, cell growth, and development.
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Affiliation(s)
- Yossi Dagon
- Division of Endocrinology, Diabetes, and Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
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107
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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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108
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Abstract
In in vitro studies class-I PI3Ks (phosphoinositide 3-kinases), class-II PI3Ks and mTOR (mammalian target of rapamycin) have all been described as having roles in the regulation of glucose metabolism. The relative role each plays in the normal signalling processes regulating glucose metabolism in vivo is less clear. Knockout and knockin mouse models have provided some evidence that the class-I PI3K isoforms p110α, p110β, and to a lesser extent p110γ, are necessary for processes regulating glucose metabolism and appetite. However, in these models the PI3K activity is chronically reduced. Therefore we analysed the effects of acutely inhibiting PI3K isoforms alone, or PI3K and mTOR, on glucose metabolism and food intake. In the present study impairments in glucose tolerance, insulin tolerance and increased hepatic glucose output were observed in mice treated with the pan-PI3K/mTOR inhibitors PI-103 and NVP-BEZ235. The finding that ZSTK474 has similar effects indicates that these effects are due to inhibition of PI3K rather than mTOR. The p110α-selective inhibitors PIK75 and A66 also induced these phenotypes, but inhibitors of p110β, p110δ or p110γ induced only minor effects. These drugs caused no significant effects on BMR (basal metabolic rate), O2 consumption or water intake, but BEZ235, PI-103 and PIK75 did cause a small reduction in food consumption. Surprisingly, pan-PI3K inhibitors or p110α inhibitors caused reductions in animal movement, although the cause of this is not clear. Taken together these studies provide pharmacological evidence to support a pre-eminent role for the p110α isoform of PI3K in pathways acutely regulating glucose metabolism.
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109
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Shp2 controls female body weight and energy balance by integrating leptin and estrogen signals. Mol Cell Biol 2012; 32:1867-78. [PMID: 22431513 DOI: 10.1128/mcb.06712-11] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
In mammals, leptin regulates food intake and energy balance mainly through the activation of LepRb in the hypothalamus, and estrogen has a leptin-like effect in the hypothalamic control of metabolism. However, it remains to be elucidated how estrogen signaling is intertwined with the leptin pathway. We show here that Shp2, a nonreceptor tyrosine phosphatase, acts to integrate leptin and estrogen signals. The expression of a dominant-active mutant (Shp2(D61A)) in forebrain neurons conferred female, but not male, transgenic mice resistance to high-fat diet (HFD)-induced obesity and liver steatosis, accompanied by improved insulin sensitivity and glucose homeostasis. Fed with either HFD or regular chow food, Shp2(D61A) female mice showed dramatically enhanced leptin sensitivity. Microinjection of Shp2(D61A)-expressing adeno-associated virus into mediobasal hypothalamus elicited a similar antiobese effect in female mice. Biochemical analyses showed a physical association of Shp2 with estrogen receptor alpha, which is necessary for the synergistic and persistent activation of Erk by leptin and estrogen. Together, these results elucidate a mechanism for the direct cross talk of leptin and estrogen signaling and offer one explanation for the propensity of postmenopausal women to develop obesity.
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110
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Electrophysiological analysis of circuits controlling energy homeostasis. Mol Neurobiol 2012; 45:258-78. [PMID: 22331510 DOI: 10.1007/s12035-012-8241-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Accepted: 01/26/2012] [Indexed: 10/28/2022]
Abstract
Since the discovery of leptin and the central melanocortin circuit, electrophysiological studies have played a major role in elucidating mechanisms underlying energy homeostasis. This review highlights the contribution of findings made by electrophysiological measurements to the current understanding of hypothalamic neuronal networks involved in energy homeostasis with a specific focus on the arcuate-paraventricular nucleus circuit.
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111
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Sohn JW, Williams KW. Functional heterogeneity of arcuate nucleus pro-opiomelanocortin neurons: implications for diverging melanocortin pathways. Mol Neurobiol 2012; 45:225-33. [PMID: 22328135 DOI: 10.1007/s12035-012-8240-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Accepted: 01/26/2012] [Indexed: 01/04/2023]
Abstract
Arcuate nucleus (ARC) pro-opiomelanocortin (POMC) neurons are essential regulators of food intake, energy expenditure, and glucose homeostasis. POMC neurons integrate several key metabolic signals that include neurotransmitters and hormones. The change in activity of POMC neurons is relayed to melanocortin receptors in distinct regions of the central nervous system. This review will summarize the role of leptin and serotonin receptors in regulating the activity of POMC neurons and provide a model in which different melanocortin pathways regulate energy and glucose homeostasis.
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Affiliation(s)
- Jong-Woo Sohn
- Division of Hypothalamic Research, Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390-9077, USA
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112
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The acute effects of leptin require PI3K signaling in the hypothalamic ventral premammillary nucleus. J Neurosci 2011; 31:13147-56. [PMID: 21917798 DOI: 10.1523/jneurosci.2602-11.2011] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Evidence suggests that the role played by the adipocyte-derived hormone leptin in female reproductive physiology is mediated in part by neurons located within the ventral premammillary nucleus (PMV). Leptin activates PMV neurons; however, the intracellular signaling pathway and channel(s) involved remain undefined. Notably, leptin's excitatory and inhibitory effects within hypothalamic and brainstem nuclei share the intracellular signaling cascade phosphoinositide 3 kinase (PI3K). Therefore, we assessed whether PI3K signaling is required for the acute effect of leptin to alter cellular activity of PMV neurons that express leptin receptors (LepR PMV neurons). Leptin caused a rapid depolarization in the majority of LepR PMV neurons in patch-clamp recordings of hypothalamic slices, while a subset of LepR PMV neurons were hyperpolarized in response to leptin. Data were obtained from both male and female mice and results demonstrate that the acute effect of leptin on LepR PMV neurons was identical for both sexes. Pharmacological inhibition of PI3K prevented the acute leptin-induced change in neuronal activity of LepR PMV neurons, indicating a PI3K-dependent mechanism of leptin action. Similarly, mice with genetically disrupted PI3K signaling in LepR PMV neurons failed to alter cellular activity in response to leptin. Moreover, the leptin-induced depolarization was dependent on a putative TRPC channel. In contrast, the leptin-induced-hyperpolarization required the activation of a putative Katp channel. Collectively, these results suggest that PI3K signaling in LepR PMV neurons is essential for leptin-induced alteration in cellular activity, and these data may suggest a cellular correlate in which leptin contributes to the initiation of reproductive development.
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113
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Sohn JW, Xu Y, Jones JE, Wickman K, Williams KW, Elmquist JK. Serotonin 2C receptor activates a distinct population of arcuate pro-opiomelanocortin neurons via TRPC channels. Neuron 2011; 71:488-97. [PMID: 21835345 DOI: 10.1016/j.neuron.2011.06.012] [Citation(s) in RCA: 149] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/04/2011] [Indexed: 01/17/2023]
Abstract
VIDEO ABSTRACT Serotonin 2C receptors (5-HT(2C)Rs) expressed by pro-opiomelanocortin (POMC) neurons of hypothalamic arcuate nucleus regulate food intake, energy homeostasis and glucose metabolism. However, the cellular mechanisms underlying the effects of 5-HT to regulate POMC neuronal activity via 5-HT(2C)Rs have not yet been identified. In the present study, we found the putative transient receptor potential C (TRPC) channels mediate the activation of a subpopulation of POMC neurons by mCPP (a 5-HT(2C)R agonist). Interestingly, mCPP-activated POMC neurons were found to be a distinct population from those activated by leptin. Together, our data suggest that 5-HT(2C)R and leptin receptors are expressed by distinct subpopulations of arcuate POMC neurons and that both 5-HT and leptin exert their actions in POMC neurons via TRPC channels.
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Affiliation(s)
- Jong-Woo Sohn
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, USA
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114
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Scherer T, Buettner C. Yin and Yang of hypothalamic insulin and leptin signaling in regulating white adipose tissue metabolism. Rev Endocr Metab Disord 2011; 12:235-43. [PMID: 21713385 PMCID: PMC3253350 DOI: 10.1007/s11154-011-9190-4] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Fatty acids released from white adipose tissue (WAT) provide important energy substrates during fasting. However, uncontrolled fatty acid release from WAT during non-fasting states causes lipotoxicity and promotes inflammation and insulin resistance, which can lead to and worsen type 2 diabetes (DM2). WAT is also a source for insulin sensitizing fatty acids such as palmitoleate produced during de novo lipogenesis. Insulin and leptin are two major hormonal adiposity signals that control energy homeostasis through signaling in the central nervous system. Both hormones have been implicated to regulate both WAT lipolysis and de novo lipogenesis through the mediobasal hypothalamus (MBH) in an opposing fashion independent of their respective peripheral receptors. Here, we review the current literature on brain leptin and insulin action in regulating WAT metabolism and discuss potential mechanisms and neuro-anatomical substrates that could explain the opposing effects of central leptin and insulin. Finally, we discuss the role of impaired hypothalamic control of WAT metabolism in the pathogenesis of insulin resistance, metabolic inflexibility and type 2 diabetes.
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115
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De Jonghe BC, Hayes MR, Bence KK. Melanocortin control of energy balance: evidence from rodent models. Cell Mol Life Sci 2011; 68:2569-88. [PMID: 21553232 PMCID: PMC3135719 DOI: 10.1007/s00018-011-0707-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2011] [Revised: 04/19/2011] [Accepted: 04/20/2011] [Indexed: 01/18/2023]
Abstract
Regulation of energy balance is extremely complex, and involves multiple systems of hormones, neurotransmitters, receptors, and intracellular signals. As data have accumulated over the last two decades, the CNS melanocortin system is now identified as a prominent integrative network of energy balance controls in the mammalian brain. Here, we will review findings from rat and mouse models, which have provided an important framework in which to study melanocortin function. Perhaps most importantly, this review attempts for the first time to summarize recent advances in our understanding of the intracellular signaling pathways thought to mediate the action of melanocortin neurons and peptides in control of longterm energy balance. Special attention will be paid to the roles of MC4R/MC3R, as well as downstream neurotransmitters within forebrain and hindbrain structures that illustrate the distributed control of melanocortin signaling in energy balance. In addition, distinctions and controversy between rodent species will be discussed.
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Affiliation(s)
- Bart C. De Jonghe
- Dept. of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, 19104
| | - Matthew R. Hayes
- Dept. of Psychiatry, School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104
| | - Kendra K. Bence
- Dept. of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, 19104
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116
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Donato J, Frazão R, Elias CF. The PI3K signaling pathway mediates the biological effects of leptin. ACTA ACUST UNITED AC 2011; 54:591-602. [PMID: 21085763 DOI: 10.1590/s0004-27302010000700002] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 09/28/2010] [Indexed: 01/12/2023]
Abstract
The activation of the leptin receptor recruits several intracellular signaling pathways, including the phosphatidylinositol 3-kinase (PI3K) pathway. While some of the leptin-induced signaling pathways, such as the JAK2/STAT3 pathway, induce cellular responses primarily through changes in gene expression, the PI3K pathway affects cellular properties more rapidly, through post-translational changes such as protein phosphorylation. Accordingly, several studies have shown that the PI3K pathway is required for the acute effects of leptin, such as a leptin-induced decrease in food intake. Leptin signaling through PI3K also affects the electrophysiological properties of neurons, including changes in their membrane potential and firing rates. In this review, we summarize the recent advances in our understanding of the role played by the PI3K signaling pathway in controlling food intake and energy balance. In particular, we focus on the importance of the PI3K signaling pathway as a mediator of the effects of leptin on hypothalamic neurons.
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Affiliation(s)
- Jose Donato
- Division of Hypothalamic Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9077, United States.
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117
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Marino JS, Xu Y, Hill JW. Central insulin and leptin-mediated autonomic control of glucose homeostasis. Trends Endocrinol Metab 2011; 22:275-85. [PMID: 21489811 PMCID: PMC5154334 DOI: 10.1016/j.tem.2011.03.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2010] [Revised: 02/25/2011] [Accepted: 03/05/2011] [Indexed: 12/17/2022]
Abstract
Largely as a result of rising obesity rates, the incidence of type 2 diabetes is escalating rapidly. Type 2 diabetes results from multi-organ dysfunctional glucose metabolism. Recent publications have highlighted hypothalamic insulin- and adipokine-sensing as a major determinant of peripheral glucose and insulin responsiveness. The preponderance of evidence indicates that the brain is the master regulator of glucose homeostasis, and that hypothalamic insulin and leptin signaling in particular play a crucial role in the development of insulin resistance. This review discusses the neuronal crosstalk between the hypothalamus, autonomic nervous system, and tissues associated with the pathogenesis of type 2 diabetes, and how hypothalamic insulin and leptin signaling are integral to maintaining normal glucose homeostasis.
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Affiliation(s)
- Joseph S Marino
- Center for Diabetes and Endocrine Research, College of Medicine, The University of Toledo, Toledo, OH 43614, USA
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118
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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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119
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Kim KW, Sohn JW, Kohno D, Xu Y, Williams K, Elmquist JK. SF-1 in the ventral medial hypothalamic nucleus: a key regulator of homeostasis. Mol Cell Endocrinol 2011; 336:219-23. [PMID: 21111025 PMCID: PMC3057357 DOI: 10.1016/j.mce.2010.11.019] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 11/14/2010] [Accepted: 11/14/2010] [Indexed: 11/15/2022]
Abstract
The ventral medial hypothalamic nucleus (VMH) regulates food intake and body weight homeostasis. The nuclear receptor NR5A1 (steroidogenic factor 1; SF-1) is a transcription factor whose expression is highly restricted in the VMH and is required for the development of the nucleus. Neurons expressing SF-1 in the VMH have emerged as playing important roles in the regulation of body weight and energy homeostasis. Many of these studies have used site-specific gene KO approaches, providing insights into the molecular mechanisms underlying the regulation of energy homeostasis by the SF-1 neurons of the VMH. In this brief review, we will focus on recent studies defining the molecular mechanisms regulating energy homeostasis and body weight in the VMH, particularly stressing the SF-1 expressing neurons.
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Affiliation(s)
- Ki Woo Kim
- Division of Hypothalamic Research, Department of Internal Medicine, UT Southwestern Medical Center, Dallas, TX 75390-9077, United States
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PDK1-Foxo1 in agouti-related peptide neurons regulates energy homeostasis by modulating food intake and energy expenditure. PLoS One 2011; 6:e18324. [PMID: 21694754 PMCID: PMC3072380 DOI: 10.1371/journal.pone.0018324] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Accepted: 03/03/2011] [Indexed: 01/05/2023] Open
Abstract
Insulin and leptin intracellular signaling pathways converge and act synergistically on the hypothalamic phosphatidylinositol-3-OH kinase/3-phosphoinositide-dependent protein kinase 1 (PDK1). However, little is known about whether PDK1 in agouti-related peptide (AGRP) neurons contributes to energy homeostasis. We generated AGRP neuron-specific PDK1 knockout (AGRPPdk1−/−) mice and mice with selective expression of transactivation-defective Foxo1 (Δ256Foxo1AGRPPdk1−/−). The AGRPPdk1−/− mice showed reductions in food intake, body length, and body weight. The Δ256Foxo1AGRPPdk1−/− mice showed increased body weight, food intake, and reduced locomotor activity. After four weeks of calorie-restricted feeding, oxygen consumption and locomotor activity were elevated in AGRPPdk1−/− mice and reduced in Δ256Foxo1AGRPPdk1−/− mice. In vitro, ghrelin-induced changes in [Ca2+]i and inhibition of ghrelin by leptin were significantly attenuated in AGRPPdk1−/− neurons compared to control neurons. However, ghrelin-induced [Ca2+]i changes and leptin inhibition were restored in Δ256Foxo1AGRPPdk1−/− mice. These results suggested that PDK1 and Foxo1 signaling pathways play important roles in the control of energy homeostasis through AGRP-independent mechanisms.
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Sahu A. Intracellular leptin-signaling pathways in hypothalamic neurons: the emerging role of phosphatidylinositol-3 kinase-phosphodiesterase-3B-cAMP pathway. Neuroendocrinology 2011; 93:201-10. [PMID: 21464566 PMCID: PMC3130491 DOI: 10.1159/000326785] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/15/2010] [Accepted: 02/24/2011] [Indexed: 01/02/2023]
Abstract
Leptin is secreted primarily by fat cells and acts centrally, particularly in the hypothalamus, to reduce food intake and body weight. Besides the classical JAK2 (Janus kinase-2)-STAT3 (signal transducer and activator of transcription-3) pathway, several non-STAT3 pathways play an important role in mediating leptin signaling in the hypothalamus. We have demonstrated that leptin action in the hypothalamus is mediated by an insulin-like signaling pathway involving stimulation of PI3K (phosphatidylinositol-3 kinase) and PDE3B (phosphodiesterase-3B), and reduction in cAMP levels, and that a PI3K-PDE3B-cAMP pathway interacting with the JAK2-STAT3 pathway constitutes a critical component of leptin signaling in the hypothalamus. It appears that defective regulation of multiple signaling pathways in the hypothalamus causes central leptin resistance, a major cause of obesity. In this regard, we have shown that leptin resistance in hypothalamic neurons following chronic central infusion of this hormone is associated with a defect in the PI3K-PDE3B-cAMP, and not due to compromised signaling in the JAK2-STAT3 pathway. Similarly, the PI3K, but not the STAT3, pathway is impaired in the hypothalamus during the development of diet-induced obesity. Additionally, our recent work suggests that suppressor of cytokine signaling-3 negatively regulates the PI3K pathway of leptin signaling in the hypothalamus, a mechanism expected to play a significant role in diet-induced obesity. Together, the PI3K-PDE3B-cAMP pathway appears to emerge as a major mechanism of leptin signaling in the hypothalamus in regulating energy balance.
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Affiliation(s)
- Abhiram Sahu
- Department of Obstetrics, Gynecology and Reproductive Sciences, University of Pittsburgh School of Medicine, Magee-Womens Research Institute, Pittsburgh, PA 15213, USA.
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Claret M, Smith MA, Knauf C, Al-Qassab H, Woods A, Heslegrave A, Piipari K, Emmanuel JJ, Colom A, Valet P, Cani PD, Begum G, White A, Mucket P, Peters M, Mizuno K, Batterham RL, Giese KP, Ashworth A, Burcelin R, Ashford ML, Carling D, Withers DJ. Deletion of Lkb1 in pro-opiomelanocortin neurons impairs peripheral glucose homeostasis in mice. Diabetes 2011; 60:735-45. [PMID: 21266325 PMCID: PMC3046834 DOI: 10.2337/db10-1055] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE AMP-activated protein kinase (AMPK) signaling acts as a sensor of nutrients and hormones in the hypothalamus, thereby regulating whole-body energy homeostasis. Deletion of Ampkα2 in pro-opiomelanocortin (POMC) neurons causes obesity and defective neuronal glucose sensing. LKB1, the Peutz-Jeghers syndrome gene product, and Ca(2+)-calmodulin-dependent protein kinase kinase β (CaMKKβ) are key upstream activators of AMPK. This study aimed to determine their role in POMC neurons upon energy and glucose homeostasis regulation. RESEARCH DESIGN AND METHODS Mice lacking either Camkkβ or Lkb1 in POMC neurons were generated, and physiological, electrophysiological, and molecular biology studies were performed. RESULTS Deletion of Camkkβ in POMC neurons does not alter energy homeostasis or glucose metabolism. In contrast, female mice lacking Lkb1 in POMC neurons (PomcLkb1KO) display glucose intolerance, insulin resistance, impaired suppression of hepatic glucose production, and altered expression of hepatic metabolic genes. The underlying cellular defect in PomcLkb1KO mice involves a reduction in melanocortin tone caused by decreased α-melanocyte-stimulating hormone secretion. However, Lkb1-deficient POMC neurons showed normal glucose sensing, and body weight was unchanged in PomcLkb1KO mice. CONCLUSIONS Our findings demonstrate that LKB1 in hypothalamic POMC neurons plays a key role in the central regulation of peripheral glucose metabolism but not body-weight control. This phenotype contrasts with that seen in mice lacking AMPK in POMC neurons with defects in body-weight regulation but not glucose homeostasis, which suggests that LKB1 plays additional functions distinct from activating AMPK in POMC neurons.
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Affiliation(s)
- Marc Claret
- Laboratory of Diabetes and Obesity, Endocrinology and Nutrition Unit, Institut d'Investigacions Biomèdiques August Pi i Sunyer, Hospital Clinic de Barcelona, Barcelona, Spain
- Corresponding author: Dominic J. Withers, , or Marc Claret,
| | - Mark A. Smith
- Metabolic Signalling Group, Medical Research Council (MRC) Clinical Sciences Centre, Imperial College London, London, U.K
- Biomedical Research Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee, U.K
| | - Claude Knauf
- Institut National de la Santé et de la Recherche Médicale U858, Institut de Médecine Moléculaire de Rangueil, Toulouse, France
| | - Hind Al-Qassab
- Metabolic Signalling Group, Medical Research Council (MRC) Clinical Sciences Centre, Imperial College London, London, U.K
| | - Angela Woods
- Cellular Stress Group, MRC Clinical Sciences Centre, Imperial College London, London, U.K
| | - Amanda Heslegrave
- Cellular Stress Group, MRC Clinical Sciences Centre, Imperial College London, London, U.K
| | - Kaisa Piipari
- Metabolic Signalling Group, Medical Research Council (MRC) Clinical Sciences Centre, Imperial College London, London, U.K
| | - Julian J. Emmanuel
- Centre for Diabetes and Endocrinology, Rayne Institute, University College London, London, U.K
| | - André Colom
- Institut National de la Santé et de la Recherche Médicale U858, Institut de Médecine Moléculaire de Rangueil, Toulouse, France
| | - Philippe Valet
- Institut National de la Santé et de la Recherche Médicale U858, Institut de Médecine Moléculaire de Rangueil, Toulouse, France
| | - Patrice D. Cani
- Louvain Drug Research Institute, Unit of Pharmacokinetics, Metabolism, Nutrition, and Toxicology, Université Catholique de Louvain, Brussels, Belgium
| | - Ghazala Begum
- Faculties of Life Sciences and Medical and Human Sciences, Manchester Academic Health Sciences Centre, University of Manchester, Manchester, U.K
| | - Anne White
- Faculties of Life Sciences and Medical and Human Sciences, Manchester Academic Health Sciences Centre, University of Manchester, Manchester, U.K
| | - Phillip Mucket
- Cellular Stress Group, MRC Clinical Sciences Centre, Imperial College London, London, U.K
| | - Marco Peters
- Centre for the Cellular Basis of Behaviour, Institute of Psychiatry, King’s College London, London, U.K
| | - Keiko Mizuno
- Centre for the Cellular Basis of Behaviour, Institute of Psychiatry, King’s College London, London, U.K
| | - Rachel L. Batterham
- Centre for Diabetes and Endocrinology, Rayne Institute, University College London, London, U.K
| | - K. Peter Giese
- Centre for the Cellular Basis of Behaviour, Institute of Psychiatry, King’s College London, London, U.K
| | - Alan Ashworth
- The Breakthrough Breast Cancer Research Centre, Institute of Cancer Research, London, U.K
| | - Remy Burcelin
- Institut National de la Santé et de la Recherche Médicale U858, Institut de Médecine Moléculaire de Rangueil, Toulouse, France
| | - Michael L. Ashford
- Biomedical Research Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee, U.K
| | - David Carling
- Cellular Stress Group, MRC Clinical Sciences Centre, Imperial College London, London, U.K
| | - Dominic J. Withers
- Metabolic Signalling Group, Medical Research Council (MRC) Clinical Sciences Centre, Imperial College London, London, U.K
- Corresponding author: Dominic J. Withers, , or Marc Claret,
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Metlakunta AS, Sahu M, Yasukawa H, Dhillon SS, Belsham DD, Yoshimura A, Sahu A. Neuronal suppressor of cytokine signaling-3 deficiency enhances hypothalamic leptin-dependent phosphatidylinositol 3-kinase signaling. Am J Physiol Regul Integr Comp Physiol 2011; 300:R1185-93. [PMID: 21325649 DOI: 10.1152/ajpregu.00794.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Suppressor of cytokine signaling-3 (SOCS3) is thought to be involved in the development of central leptin resistance and obesity by inhibiting STAT3 pathway. Because phosphatidylinositol 3-kinase (PI3K) pathway plays an important role in transducing leptin action in the hypothalamus, we examined whether SOCS3 exerted an inhibition on this pathway. We first determined whether leptin sensitivity in the hypothalamic PI3K pathway was increased in brain-specific Socs3-deficient (NesKO) mice. In NesKO mice, hypothalamic insulin receptor substrate-1 (IRS1)-associated PI3K activity was significantly increased at 30 min and remained elevated up to 2 h after leptin intraperitoneal injection, but in wild-type (WT) littermates, the significant increase was only at 30 min. Hypothalamic p-STAT3 levels were increased up to 5 h in NesKO as opposed to 2 h in WT mice. In food-restricted WT mice with reduced body weight, leptin increased hypothalamic PI3K activity only at 30 min, and p-STAT3 levels at 30-120 min postinjection. These results suggest increased leptin sensitivity in both PI3K and STAT3 pathways in the hypothalamus of NesKO mice, which was not due to a lean phenotype. In the next experiment with a clonal hypothalamic neuronal cell line expressing proopiomelanocortin, we observed that whereas leptin significantly increased IRS1-associated PI3K activity and p-JAK2 levels in cells transfected with control vector, it failed to do so in SOCS3-overexpressed cells. Altogether, these results imply a SOCS3 inhibition of the PI3K pathway of leptin signaling in the hypothalamus, which may be one of the mechanisms behind the development of central leptin resistance and obesity.
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Affiliation(s)
- Anantha S Metlakunta
- Dept. of Obstetrics, Gynecology and Reproductive Sciences, University of Pittsburgh School of Medicine, Magee-Womens Research Institute, 204 Craft Avenue, Pittsburgh, PA 15213, USA
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Williams KW, Scott MM, Elmquist JK. Modulation of the central melanocortin system by leptin, insulin, and serotonin: co-ordinated actions in a dispersed neuronal network. Eur J Pharmacol 2011; 660:2-12. [PMID: 21211525 DOI: 10.1016/j.ejphar.2010.11.042] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2010] [Revised: 10/08/2010] [Accepted: 11/02/2010] [Indexed: 10/18/2022]
Abstract
Over the past century, prevalent models of energy and glucose homeostasis have been developed from a better understanding of the neural circuits underlying obesity and diabetes. From the early hypothalamic lesion reports to the more recent pharmacological and molecular/genetic studies, the hypothalamic melanocortin system has been shown to play a critical role in the regulation of metabolism. This review attempts to highlight contributions to our current understanding of how numerous neuromodulators (leptin, insulin, and serotonin) integrate with the central melanocortin system to coordinate alterations in energy and glucose balance.
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Affiliation(s)
- Kevin W Williams
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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125
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Acosta-Martínez M. PI3K: An Attractive Candidate for the Central Integration of Metabolism and Reproduction. Front Endocrinol (Lausanne) 2011; 2:110. [PMID: 22654843 PMCID: PMC3356143 DOI: 10.3389/fendo.2011.00110] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Accepted: 12/13/2011] [Indexed: 12/19/2022] Open
Abstract
In neurons, as in a variety of other cell types, the enzyme phosphatidylinositol-3-kinase (PI3K) is a key intermediate that is common to the signaling pathways of a number of peripheral metabolic cues, including insulin and leptin, which are well known to regulate both metabolic and reproductive functions. This review article will explore the possibility that PI3K is a key integrator of metabolic and neural signals regulating gonadotropin releasing hormone (GnRH)/luteinizing hormone (LH) release and explore the hypothesis that this enzyme is pivotal in many disorders where gonadotropin release is at risk. Although the mechanisms mediating the influence of metabolism and nutrition on fertility are currently unclear, the strong association between metabolic disorders and infertility is undeniable. For example, women suffering from anorectic disorders experience amenorrhea as a consequence of malnutrition-induced impairment of LH release, and at the other extreme, obesity is also commonly co-morbid with menstrual dysfunction and infertility. Impaired hypothalamic insulin and leptin receptor signaling is thought to be at the core of reproductive disorders associated with metabolic dysfunction. While low levels of leptin and insulin characterize states of negative energy balance, prolonged nutrient excess is associated with insulin and leptin resistance. Metabolic models known to alter GnRH/LH release such as diabetes, diet-induced obesity, and caloric restriction are also accompanied by impairment of PI3K signaling in insulin and leptin sensitive tissues including the hypothalamus. However, a clear link between this signaling pathway and the control of GnRH release by peripheral metabolic cues has not been established. Investigating the role of the signaling pathways shared by metabolic cues that are critical for a normal reproductive state can help identify possible targets in the treatment of metabolic and reproductive disorders such as polycystic ovarian syndrome.
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Affiliation(s)
- Maricedes Acosta-Martínez
- Department of Physiology and Biophysics, Medical Center, Stony Brook UniversityStony Brook, NY, USA
- *Correspondence: Maricedes Acosta-Martínez, Department of Physiology and Biophysics, Medical Center, Stony Brook University, Stony Brook, NY 11794-8661, USA. e-mail:
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Belgardt BF, Brüning JC. CNS leptin and insulin action in the control of energy homeostasis. Ann N Y Acad Sci 2010; 1212:97-113. [PMID: 21070248 DOI: 10.1111/j.1749-6632.2010.05799.x] [Citation(s) in RCA: 194] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The obesity and diabetes pandemics have made it an urgent necessity to define the central nervous system (CNS) pathways controlling body weight, energy expenditure, and fuel metabolism. The pancreatic hormone insulin and the adipose tissue-derived leptin are known to act on diverse neuronal circuits in the CNS to maintain body weight and metabolism in a variety of species, including humans. Because these homeostatic circuits are disrupted during the development of obesity, the pathomechanisms leading to CNS leptin and insulin resistance are a focal point of research. In this review, we summarize the recent findings concerning the mechanisms and novel neuronal mediators of both insulin and leptin action in the CNS.
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Affiliation(s)
- Bengt F Belgardt
- Department of Mouse Genetics and Metabolism, Institute for Genetics, Center for Molecular Medicine, University of Cologne, Zülpicher Strasse 47a, Cologne, Germany
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127
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Stephens L, Hawkins P. Signalling via class IA PI3Ks. ACTA ACUST UNITED AC 2010; 51:27-36. [PMID: 21035483 DOI: 10.1016/j.advenzreg.2010.09.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Accepted: 09/23/2010] [Indexed: 11/28/2022]
Affiliation(s)
- Len Stephens
- The Babraham Institute, Babraham, Cambridge, UK.
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Gratacap MP, Guillermet-Guibert J, Martin V, Chicanne G, Tronchère H, Gaits-Iacovoni F, Payrastre B. Regulation and roles of PI3Kβ, a major actor in platelet signaling and functions. ACTA ACUST UNITED AC 2010; 51:106-16. [PMID: 21035500 DOI: 10.1016/j.advenzreg.2010.09.011] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Accepted: 09/06/2010] [Indexed: 01/12/2023]
Abstract
Phosphoinositide 3-kinases (PI3Ks) are important signaling enzymes involved in the regulation of a number of critical cell functions. Significant progress has been made during the last few years in defining the implication of individual PI3K isoforms. The role of the class IA PI3Kβ in different cell types has only been recently uncovered by the use of isoform-selective inhibitors and the development of mouse models harboring p110β catalytic subunit knock-out or germline knock-in of a kinase-dead allele of p110β. Although it is classically admitted that class IA PI3Ks are activated by receptor tyrosine kinases through recruitment of the regulatory subunits to specific tyrosine phosphorylated motifs via their SH2 domains, PI3Kβ is activated downstream of G protein-coupled receptors, and by co-operation between heterotrimeric G proteins and tyrosine kinases. PI3Kβ has been extensively studied in platelets where it appears to play an important role downstream of ITAM signaling, G protein-coupled receptors and aIIbβ3 integrin. Accordingly, mouse exhibiting p110β inactivation selectively in megakaryocyte/platelets are resistant to thromboembolism induced by carotid injury. The present review summarizes recent data concerning the mechanisms of PI3Kβ regulation and the roles of this PI3K isoform in blood platelet functions and other cell types.
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Affiliation(s)
- Marie-Pierre Gratacap
- Inserm, U563, Université Toulouse III, Centre de Physiopathologie de Toulouse Purpan, CHU-Purpan, Toulouse, France
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Tups A, Anderson GM, Rizwan M, Augustine RA, Chaussade C, Shepherd PR, Grattan DR. Both p110alpha and p110beta isoforms of phosphatidylinositol 3-OH-kinase are required for insulin signalling in the hypothalamus. J Neuroendocrinol 2010; 22:534-42. [PMID: 20236230 DOI: 10.1111/j.1365-2826.2010.01975.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Both insulin and leptin action in the brain are considered to involve activation of phosphoinositide 3-kinase (PI3K), although the roles of different PI3K isoforms in insulin signalling in the hypothalamus are unknown. In the present study, we characterised the roles of these isoforms in hypothalamic insulin and leptin signalling and investigated the cross-talk of both hormones. To evaluate PI3K levels in the hypothalamus, PI3K was immunoprecipitated using an antibody directed against the p85 subunit, and then total PI3K activity was measured in the presence of novel isoform-selective pharmacological inhibitors of each isoform of PI3K. Subsequently, these inhibitors were administered into the lateral ventricle of male Sprague-Dawley rats, followed by vehicle, insulin, leptin or both hormones 45 min later. PI3K activity was determined by immunohistochemical detection of phosphorylated AKT (S473). In a separate study, the effects of the inhibitors on the anorexigenic action of insulin and leptin were determined. Hypothalamic insulin signalling was specifically mediated by the combined actions of the class Ia isoforms p110alpha and p110beta. Total hypothalamic PI3K activity was inhibited 65% by a p110alpha inhibitor, and 35% by a p110beta inhibitor, with a combination of inhibitors being equally effective as the broad-spectrum PI3K inhibitor wortmannin. Individual i.c.v. administration of p110alpha and p110beta inhibitors partly prevented insulin-induced phosphorylated AKT (S473) in the arcuate nucleus, whereas simultaneous application completely blocked insulin action. Unlike insulin, leptin did not induce phosphorylated AKT in the hypothalamus, as detected by immunohistochemistry, and the anorectic effects of leptin were not affected by pre-treatment with a combination of p110alpha and p110beta inhibitors. The enhanced anorectic effect of a combined i.c.v. application of both insulin and leptin could be prevented by pre-treatment with the combination of p110alpha and p110beta inhibitors. The data suggest that p110alpha and p110beta isoforms of PI3K are necessary to mediate insulin action in the hypothalamus. The role of PI3K in leptin action is less clear, but it may be involved by means of an insulin-dependent sensitisation of leptin action.
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Affiliation(s)
- A Tups
- Department of Anatomy and Structural Biology, Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.
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130
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Abstract
Melanocortin peptides, derived from POMC (pro-opiomelanocortin) are produced in the ARH (arcuate nucleus of the hypothalamus) neurons and the neurons in the commissural NTS (nucleus of the solitary tract) of the brainstem, in anterior and intermediate lobes of the pituitary, skin and a wide range of peripheral tissues, including reproductive organs. A hypothetical model for functional roles of melanocortin receptors in maintaining energy balance was proposed in 1997. Since this time, there has been an extraordinary amount of knowledge gained about POMC-derived peptides in relation to energy homoeostasis. Development of a Pomc-null mouse provided definitive proof that POMC-derived peptides are critical for the regulation of energy homoeostasis. The melanocortin system consists of endogenous agonists and antagonists, five melanocortin receptor subtypes and receptor accessory proteins. The melanocortin system, as is now known, is far more complex than most of us could have imagined in 1997, and, similarly, the importance of this system for regulating energy homoeostasis in the general human population is much greater than we would have predicted. Of the known factors that can cause human obesity, or protect against it, the melanocortin system is by far the most significant. The present review is a discussion of the current understanding of the roles and mechanism of action of POMC, melanocortin receptors and AgRP (agouti-related peptide) in obesity and Type 2 diabetes and how the central and/or peripheral melanocortin systems mediate nutrient, leptin, insulin, gut hormone and cytokine regulation of energy homoeostasis.
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131
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Sahu A. A role of phosphodiesterase-3B pathway in mediating leptin action on proopiomelanocortin and neurotensin neurons in the hypothalamus. Neurosci Lett 2010; 479:18-21. [PMID: 20471454 DOI: 10.1016/j.neulet.2010.05.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2010] [Revised: 04/12/2010] [Accepted: 05/07/2010] [Indexed: 11/30/2022]
Abstract
Leptin signaling in the hypothalamus is required for normal food intake and body weight homeostasis. Recent evidence suggests that besides the signal transducer and activator of transcription-3 (STAT3) pathway, several non-STAT3 pathways mediate leptin signaling in the hypothalamus. We have previously demonstrated that leptin stimulates phosphodiesterase-3B (PDE3B) activity in the hypothalamus, and PDE3 inhibitor cilostamide reverses anorectic and body weight reducing effects of leptin. To establish the physiological role of PDE3B signaling in the hypothalamus, we examined if leptin signaling through the PDE3B pathway is responsible for the activation of proopiomelanocortin (POMC) and neurotensin (NT) neurons, which are known to play a critical role in energy homeostasis. To this end, we assessed the effect of cilostamide on leptin-induced POMC and NT gene expression in the rat hypothalamus. Results showed that while central injection of leptin significantly increased both POMC and NT mRNA levels in the medial basal hypothalamus, cilostamide completely reversed this effect of leptin suggesting a PDE3B-activation dependent induction of POMC and NT gene expression by leptin. This result further suggests that the PDE3B pathway plays an important role in mediating leptin action in the hypothalamus.
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Affiliation(s)
- Abhiram Sahu
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
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132
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Hill JW, Elias CF, Fukuda M, Williams KW, Berglund ED, Holland WL, Cho YR, Chuang JC, Xu Y, Choi M, Lauzon D, Lee CE, Coppari R, Richardson JA, Zigman JM, Chua S, Scherer PE, Lowell BB, Brüning JC, Elmquist JK. Direct insulin and leptin action on pro-opiomelanocortin neurons is required for normal glucose homeostasis and fertility. Cell Metab 2010; 11:286-97. [PMID: 20374961 PMCID: PMC2854520 DOI: 10.1016/j.cmet.2010.03.002] [Citation(s) in RCA: 286] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/05/2009] [Revised: 10/30/2009] [Accepted: 03/05/2010] [Indexed: 02/03/2023]
Abstract
Circulating leptin and insulin convey information regarding energy stores to the central nervous system, particularly the hypothalamus. Hypothalamic pro-opiomelanocortin (POMC) neurons regulate energy balance and glucose homeostasis and express leptin and insulin receptors. However, the physiological significance of concomitant leptin and insulin action on POMC neurons remains to be established. Here, we show that mice lacking both leptin and insulin receptors in POMC neurons (Pomc-Cre, Lepr(flox/flox) IR(flox/flox) mice) display systemic insulin resistance, which is distinct from the single deletion of either receptor. In addition, Pomc-Cre, Lepr(flox/flox) IR(flox/flox) female mice display elevated serum testosterone levels and ovarian abnormalities, resulting in reduced fertility. We conclude that direct action of insulin and leptin on POMC neurons is required to maintain normal glucose homeostasis and reproductive function.
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Affiliation(s)
- Jennifer W Hill
- Center for Diabetes and Endocrine Research, Department of Physiology and Pharmacology, College of Medicine, The University of Toledo, Toledo, OH 43614, USA
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Segregation of acute leptin and insulin effects in distinct populations of arcuate proopiomelanocortin neurons. J Neurosci 2010; 30:2472-9. [PMID: 20164331 DOI: 10.1523/jneurosci.3118-09.2010] [Citation(s) in RCA: 263] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Acute leptin administration results in a depolarization and concomitant increase in the firing rate of a subpopulation of arcuate proopiomelanocortin (POMC) cells. This rapid activation of POMC cells has been implicated as a cellular correlate of leptin effects on energy balance. In contrast to leptin, insulin inhibits the activity of some POMC neurons. Several studies have described a "cross talk" between leptin and insulin within the mediobasal hypothalamus via the intracellular enzyme, phosphoinositol-3-kinase (PI3K). Interestingly, both insulin and leptin regulate POMC cellular activity by activation of PI3K; however, it is unclear whether leptin and insulin effects are observed in similar or distinct populations of POMC cells. We therefore used dual label immunohistochemistry/in situ hybridization and whole-cell patch-clamp electrophysiology to map insulin and leptin responsive arcuate POMC neurons. Leptin-induced Fos activity within arcuate POMC neurons was localized separate from POMC neurons that express insulin receptor. Moreover, acute responses to leptin and insulin were largely segregated in distinct subpopulations of POMC cells. Collectively, these data suggest that cross talk between leptin and insulin occurs within a network of cells rather than within individual POMC neurons.
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Kim KS, Yoon YR, Lee HJ, Yoon S, Kim SY, Shin SW, An JJ, Kim MS, Choi SY, Sun W, Baik JH. Enhanced hypothalamic leptin signaling in mice lacking dopamine D2 receptors. J Biol Chem 2010; 285:8905-17. [PMID: 20080963 DOI: 10.1074/jbc.m109.079590] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dopamine D(2) receptor (D2R) plays a critical role in diverse neurophysiological functions. D2R knock-out mice (D2R(-/-)) show reduced food intake and body weight while displaying an increased basal energy expenditure level, compared with their wild type littermates. Thus, these mice show a lean phenotype. D2R(-/-) mice displayed increased leptin sensitivity, and leptin injection induced increased phosphorylation of the hypothalamic signal transducer and activator of transcription 3 (STAT3) in D2R(-/-) mice relative to wild type littermates. Using double immunofluorescence histochemistry, we have demonstrated that D2Rs are present in leptin-sensitive STAT3-positive cells in the arcuate nucleus of the hypothalamus and that leptin injection induces STAT3 phosphorylation in hypothalamic neurons expressing D2Rs. Stimulation of D2R by the D2R agonist quinpirole suppressed the leptin-induced STAT3 phosphorylation and nuclear trans-localization of phospho-STAT3 in the hypothalamus of wild type mice. However, this regulation was not detected in the D2R(-/-) mice. Treatment of D2R agonist and antagonist could modulate the leptin-induced food intake and body weight changes in wild type mice but not in D2R(-/-) mice. Together, our findings suggest that the interaction between the dopaminergic system and leptin signaling in hypothalamus is important in control of energy homeostasis.
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Affiliation(s)
- Kyu Seok Kim
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Korea
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Abstract
The Insulin Receptor/PI 3-kinase (INSR/PI3K) signalling pathway is a key regulator of cell and organismal metabolism. Phosphoinositides generated by PI 3-kinases following insulin and other metabolic hormone receptor activation give rise to signalling cascades involving a multitude of effector molecules. The physiological roles of these molecules have been dissected with the use of both pharmacological and genetic tools. Furthermore, tissue-specific mutagenesis has revealed the extent to which individual insulin-target organs and signalling molecules contribute to whole-body carbohydrate and lipid homeostasis. These studies have generated important information with respect to the function of these molecules in normal physiology and their implication in the development of metabolic diseases such as type-2 diabetes and obesity.
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