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Ramzy A, Kieffer TJ. Altered islet prohormone processing: A cause or consequence of diabetes? Physiol Rev 2021; 102:155-208. [PMID: 34280055 DOI: 10.1152/physrev.00008.2021] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Peptide hormones are first produced as larger precursor prohormones that require endoproteolytic cleavage to liberate the mature hormones. A structurally conserved but functionally distinct family of nine prohormone convertase enzymes (PCs) are responsible for cleavage of protein precursors of which PC1/3 and PC2 are known to be exclusive to neuroendocrine cells and responsible for prohormone cleavage. Differential expression of PCs within tissues define prohormone processing; whereas glucagon is the major product liberated from proglucagon via PC2 in pancreatic α-cells, proglucagon is preferentially processed by PC1/3 in intestinal L cells to produce glucagon-like peptides 1 and 2 (GLP-1, GLP-2). Beyond our understanding of processing of islet prohormones in healthy islets, there is convincing evidence that proinsulin, proIAPP, and proglucagon processing is altered during prediabetes and diabetes. There is predictive value of elevated circulating proinsulin or proinsulin : C-peptide ratio for progression to type 2 diabetes and elevated proinsulin or proinsulin : C-peptide is predictive for development of type 1 diabetes in at risk groups. After onset of diabetes, patients have elevated circulating proinsulin and proIAPP and proinsulin may be an autoantigen in type 1 diabetes. Further, preclinical studies reveal that α-cells have altered proglucagon processing during diabetes leading to increased GLP-1 production. We conclude that despite strong associative data, current evidence is inconclusive on the potential causal role of impaired prohormone processing in diabetes, and suggest that future work should focus on resolving the question of whether altered prohormone processing is a causal driver or merely a consequence of diabetes pathology.
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Affiliation(s)
- Adam Ramzy
- Laboratory of Molecular and Cellular Medicine, Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Timothy J Kieffer
- Laboratory of Molecular and Cellular Medicine, Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada.,Department of Surgery, University of British Columbia, Vancouver, BC, Canada.,School of Biomedical Engineering, University of British Columbia, Vancouver, BC, Canada
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Abstract
The kexin-like proprotein convertases perform the initial proteolytic cleavages that ultimately generate a variety of different mature peptide and proteins, ranging from brain neuropeptides to endocrine peptide hormones, to structural proteins, among others. In this review, we present a general introduction to proprotein convertase structure and biochemistry, followed by a comprehensive discussion of each member of the kexin-like subfamily of proprotein convertases. We summarize current knowledge of human proprotein convertase insufficiency syndromes, including genome-wide analyses of convertase polymorphisms, and compare these to convertase null and mutant mouse models. These mouse models have illuminated our understanding of the roles specific convertases play in human disease and have led to the identification of convertase-specific substrates; for example, the identification of procorin as a specific PACE4 substrate in the heart. We also discuss the limitations of mouse null models in interpreting human disease, such as differential precursor cleavage due to species-specific sequence differences, and the challenges presented by functional redundancy among convertases in attempting to assign specific cleavages and/or physiological roles. However, in most cases, knockout mouse models have added substantively both to our knowledge of diseases caused by human proprotein convertase insufficiency and to our appreciation of their normal physiological roles, as clearly seen in the case of the furin, proprotein convertase 1/3, and proprotein convertase 5/6 mouse models. The creation of more sophisticated mouse models with tissue- or temporally-restricted expression of specific convertases will improve our understanding of human proprotein convertase insufficiency and potentially provide support for the emerging concept of therapeutic inhibition of convertases.
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Affiliation(s)
- Manita Shakya
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Iris Lindberg
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
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3
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do Carmo JM, da Silva AA, Moak SP, da Silva FS, Spradley FT, Hall JE. Role of melanocortin 4 receptor in hypertension induced by chronic intermittent hypoxia. Acta Physiol (Oxf) 2019; 225:e13222. [PMID: 30466186 DOI: 10.1111/apha.13222] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 11/13/2018] [Accepted: 11/15/2018] [Indexed: 12/23/2022]
Abstract
AIM We previously demonstrated that central nervous system (CNS) melanocortin 4 receptors (MC4R) play a key role in regulating blood pressure (BP) in some conditions associated with increased SNS activity, including obesity. In this study, we examined whether activation of CNS MC4R contributes to chronic intermittent hypoxia (CIH)-induced hypertension and ventilatory responses to hypercapnia. METHODS Rats were instrumented with an intracerebroventricular (ICV) cannula in the lateral cerebral ventricle for continuous infusion of MC4R antagonist (SHU-9119) and telemetry probes for measuring mean arterial pressure (MAP) and heart rate (HR). Untreated and SHU-9119-treated rats as well as obese and lean MC4R-deficient rats were exposed to CIH for 7-18 consecutive days. RESULTS Chronic intermittent hypoxia reduced cumulative food intake by 18 ± 5 g while MAP and HR increased by 10 ± 3 mm Hg and 9 ± 5 bpm in untreated rats. SHU-9119 increased food intake (from 15 ± 1 to 46 ± 3 g) and prevented CIH-induced reduction in food intake. CIH-induced hypertension was not attenuated by MC4R antagonism (average increase of 10 ± 1 vs 9 ± 1 mm Hg for untreated and SHU-9119 treated rats). In obese MC4R-deficient rats, CIH for 7 days raised BP by 11 ± 4 mm Hg. However, when MC4R-deficient rats were food restricted to prevent obesity, CIH-induced hypertension was attenuated by 32%. We also found that MC4R deficiency was associated with impaired ventilatory responses to hypercapnia independently of obesity. CONCLUSION These results show that obesity and the CNS melanocortin system interact in complex ways to elevate BP during CIH and that MC4R may be important in the ventilatory responses to hypercapnia.
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Affiliation(s)
- Jussara M. do Carmo
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular‐Renal Research Center University of Mississippi Medical Center Jackson Mississippi
| | - Alexandre A. da Silva
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular‐Renal Research Center University of Mississippi Medical Center Jackson Mississippi
- Barão de Mauá University Center Ribeirão Preto Brazil
- Universidade Estadual de Minas Gerais Passos Brazil
| | - Sydney P. Moak
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular‐Renal Research Center University of Mississippi Medical Center Jackson Mississippi
| | - Fernanda S. da Silva
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular‐Renal Research Center University of Mississippi Medical Center Jackson Mississippi
- Barão de Mauá University Center Ribeirão Preto Brazil
| | - Frank T. Spradley
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular‐Renal Research Center University of Mississippi Medical Center Jackson Mississippi
- Department of Surgery University of Mississippi Medical Center Jackson Mississippi
| | - John E. Hall
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular‐Renal Research Center University of Mississippi Medical Center Jackson Mississippi
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Harno E, Gali Ramamoorthy T, Coll AP, White A. POMC: The Physiological Power of Hormone Processing. Physiol Rev 2019; 98:2381-2430. [PMID: 30156493 DOI: 10.1152/physrev.00024.2017] [Citation(s) in RCA: 112] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Pro-opiomelanocortin (POMC) is the archetypal polypeptide precursor of hormones and neuropeptides. In this review, we examine the variability in the individual peptides produced in different tissues and the impact of the simultaneous presence of their precursors or fragments. We also discuss the problems inherent in accurately measuring which of the precursors and their derived peptides are present in biological samples. We address how not being able to measure all the combinations of precursors and fragments quantitatively has affected our understanding of the pathophysiology associated with POMC processing. To understand how different ratios of peptides arise, we describe the role of the pro-hormone convertases (PCs) and their tissue specificities and consider the cellular processing pathways which enable regulated secretion of different peptides that play crucial roles in integrating a range of vital physiological functions. In the pituitary, correct processing of POMC peptides is essential to maintain the hypothalamic-pituitary-adrenal axis, and this processing can be disrupted in POMC-expressing tumors. In hypothalamic neurons expressing POMC, abnormalities in processing critically impact on the regulation of appetite, energy homeostasis, and body composition. More work is needed to understand whether expression of the POMC gene in a tissue equates to release of bioactive peptides. We suggest that this comprehensive view of POMC processing, with a focus on gaining a better understanding of the combination of peptides produced and their relative bioactivity, is a necessity for all involved in studying this fascinating physiological regulatory phenomenon.
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Affiliation(s)
- Erika Harno
- Division of Diabetes, Endocrinology and Gastrointestinal Sciences, Faculty of Biology, Medicine and Health, University of Manchester , Manchester , United Kingdom ; and MRC Metabolic Diseases Unit, Wellcome Trust-MRC Institute of Metabolic Science , Cambridge , United Kingdom
| | - Thanuja Gali Ramamoorthy
- Division of Diabetes, Endocrinology and Gastrointestinal Sciences, Faculty of Biology, Medicine and Health, University of Manchester , Manchester , United Kingdom ; and MRC Metabolic Diseases Unit, Wellcome Trust-MRC Institute of Metabolic Science , Cambridge , United Kingdom
| | - Anthony P Coll
- Division of Diabetes, Endocrinology and Gastrointestinal Sciences, Faculty of Biology, Medicine and Health, University of Manchester , Manchester , United Kingdom ; and MRC Metabolic Diseases Unit, Wellcome Trust-MRC Institute of Metabolic Science , Cambridge , United Kingdom
| | - Anne White
- Division of Diabetes, Endocrinology and Gastrointestinal Sciences, Faculty of Biology, Medicine and Health, University of Manchester , Manchester , United Kingdom ; and MRC Metabolic Diseases Unit, Wellcome Trust-MRC Institute of Metabolic Science , Cambridge , United Kingdom
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5
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Novoselova TV, Chan LF, Clark AJL. Pathophysiology of melanocortin receptors and their accessory proteins. Best Pract Res Clin Endocrinol Metab 2018; 32:93-106. [PMID: 29678289 DOI: 10.1016/j.beem.2018.02.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The melanocortin receptors (MCRs) and their accessory proteins (MRAPs) are involved in regulation of a diverse range of endocrine pathways. Genetic variants of these components result in phenotypic variation and disease. The MC1R is expressed in skin and variants in the MC1R gene are associated with ginger hair color. The MC2R mediates the action of ACTH in the adrenal gland to stimulate glucocorticoid production and MC2R mutations result in familial glucocorticoid deficiency (FGD). MC3R and MC4R are involved in metabolic regulation and their gene variants are associated with severe pediatric obesity, whereas the function of MC5R remains to be fully elucidated. MRAPs have been shown to modulate the function of MCRs and genetic variants in MRAPs are associated with diseases including FGD type 2 and potentially early onset obesity. This review provides an insight into recent advances in MCRs and MRAPs physiology, focusing on the disorders associated with their dysfunction.
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Affiliation(s)
- T V Novoselova
- Centre for Endocrinology, William Harvey Research Institute, Queen Mary University of London, Chartehouse Square, London, EC1M 6BQ, United Kingdom.
| | - L F Chan
- Centre for Endocrinology, William Harvey Research Institute, Queen Mary University of London, Chartehouse Square, London, EC1M 6BQ, United Kingdom
| | - A J L Clark
- Centre for Endocrinology, William Harvey Research Institute, Queen Mary University of London, Chartehouse Square, London, EC1M 6BQ, United Kingdom
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do Carmo JM, da Silva AA, Wang Z, Fang T, Aberdein N, Perez de Lara CE, Hall JE. Role of the brain melanocortins in blood pressure regulation. Biochim Biophys Acta Mol Basis Dis 2017; 1863:2508-2514. [PMID: 28274841 DOI: 10.1016/j.bbadis.2017.03.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 02/27/2017] [Accepted: 03/02/2017] [Indexed: 10/20/2022]
Abstract
Melanocortins play an important role in regulating blood pressure (BP) and sympathetic nervous system (SNS) activity as well as energy balance, glucose and other metabolic functions in humans and experimental animals. In experimental models of hypertension with high SNS activity, blockade of the melanocortin-4 receptor (MC4R) reduces BP despite causing marked hyperphagia and obesity. Activation of the central nervous system (CNS) pro-opiomelanocortin (POMC)-MC4R pathway appears to be an important link between obesity, SNS activation and hypertension. Despite having severe obesity, subjects with MC4R deficiency exhibit reductions in BP, heart rate, and urinary catecholamine excretion, as well as attenuated SNS responses to cold stimuli compared to obese subjects with normal MC4R function. In this review we discuss the importance of the brain POMC-MC4R system in regulating SNS activity and BP in obesity and other forms of hypertension. We also highlight potential mechanisms and brain circuitry by which the melanocortin system regulates cardiovascular function.
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Affiliation(s)
- Jussara M do Carmo
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, MS, USA.
| | - Alexandre A da Silva
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, MS, USA; Barão de Mauá University Center, Ribeirão Preto, São Paulo, Brazil; Universidade Estadual de Minas Gerais, Passos, Minas Gerais, Brazil
| | - Zhen Wang
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, MS, USA
| | - Taolin Fang
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, MS, USA
| | - Nicola Aberdein
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, MS, USA
| | - Cecilia E Perez de Lara
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, MS, USA
| | - John E Hall
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, MS, USA
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do Carmo JM, da Silva AA, Moak SP, Houghton HJ, Smith A, Hall JE. Regulation of Blood Pressure, Appetite, and Glucose by CNS Melanocortin System in Hyperandrogenemic Female SHR. Am J Hypertens 2016; 29:832-40. [PMID: 26584577 DOI: 10.1093/ajh/hpv182] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 10/20/2015] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Hyperandrogenemia in females may be associated with sympathetic nervous system (SNS) activation and increased blood pressure (BP). However the importance of hyperandrogenemia in causing hypertension in females and the mechanisms involved are still unclear. We tested whether chronic hyperandrogenemia exacerbates hypertension in young female spontaneously hypertensive rats (SHR) and whether endogenous melanocortin-3/4 receptor (MC3/4R) activation contributes to the elevated BP. METHODS Cardiovascular and metabolic effects of chronic MC3/4R antagonism were assessed in female SHR treated with dihydrotestosterone (DHT, beginning at 5 weeks of age) and placebo-treated female SHR. BP and heart rate (HR) were measured by telemetry and an intracerebroventricular (ICV) cannula was placed in the lateral ventricle for infusions. After control measurements, the MC3/4R antagonist (SHU-9119) was infused for 10 days (1 nmol/hour, ICV, at 15 weeks of age) followed by a 5-day recovery period. RESULTS MC3/4R antagonism increased food intake and body weight in DHT-treated SHR (14±1 to 35±1g/day and 244±3 to 298±8g) and controls (14±1 to 34±2g/day and 207±4 to 269±8g). Compared to untreated SHR, DHT-treated SHR had similar BP but lower HR (146±3 vs. 142±4mm Hg and 316±2 vs. 363±4 bpm). Chronic SHU-9119 infusion reduced BP and HR in DHT-treated SHR (-12±2mm Hg and -14±4 bpm) and control female SHR (-19±2mm Hg and -21±6 bpm). CONCLUSION These results indicate that hyperandrogenemia does not exacerbate hypertension in female SHR. MC3/4R antagonism reduces BP and HR despite marked increases in food intake and body weight in hyperandrogenemic and control female SHR.
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Affiliation(s)
- Jussara M do Carmo
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, Mississippi, USA;
| | - Alexandre A da Silva
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, Mississippi, USA; Barão de Mauá University Center, Ribeirão Preto, São Paulo, Brazil
| | - Sydney P Moak
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, Mississippi, USA
| | - Haley J Houghton
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, Mississippi, USA
| | - Andrew Smith
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, Mississippi, USA; Department of Radiology, University of Mississippi Medical Center, Jackson, Mississippi, USA
| | - John E Hall
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, Cardiovascular-Renal Research Center, University of Mississippi Medical Center, Jackson, Mississippi, USA
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8
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Schweda F. Salt feedback on the renin-angiotensin-aldosterone system. Pflugers Arch 2014; 467:565-76. [DOI: 10.1007/s00424-014-1668-y] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 12/02/2014] [Accepted: 12/02/2014] [Indexed: 12/21/2022]
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Abstract
The melanocortin 3 receptor (MC3R) regulates several physiological functions, including feed efficiency, nutrient partitioning, fasting response, natriuresis, and immune reactions. Naturally occurring mutations in the MC3R gene have been shown to be associated with increased adiposity and lung diseases such as tuberculosis and cystic fibrosis. The DRY motif at the cytoplasmic end of transmembrane domain 3 (TM3) and the second intracellular loop 2 (ICL2) are known to be important for receptor function in several G protein-coupled receptors (GPCRs). To gain a better understanding of the functions of this domain in MC3R, we performed alanine-scanning mutagenesis on 18 residues. We showed that alanine mutation of 11 residues reduced the maximal binding and maximal cAMP production stimulated by agonists. Mutation of two residues did not change maximal binding but resulted in impaired signaling in the Gs-cAMP pathway. Mutation of five residues impaired signaling in the ERK1/2 pathway. We have also shown that alanine mutants of seven residues that were defective in the cAMP pathway were not defective in the ERK1/2 pathway, demonstrating biased signaling. In summary, we demonstrated that the cytoplasmic end of TM3 and the ICL2 were critical for MC3R function. We also reported for the first time biased signaling in MC3R.
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Affiliation(s)
- Hui Huang
- Department of AnatomyPhysiology and Pharmacology, College of Veterinary Medicine, Auburn University, 212 Greene Hall, Auburn, Alabama 36849, USA
| | - Ya-Xiong Tao
- Department of AnatomyPhysiology and Pharmacology, College of Veterinary Medicine, Auburn University, 212 Greene Hall, Auburn, Alabama 36849, USA
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Lute B, Jou W, Lateef DM, Goldgof M, Xiao C, Piñol RA, Kravitz AV, Miller NR, Huang YG, Girardet C, Butler AA, Gavrilova O, Reitman ML. Biphasic effect of melanocortin agonists on metabolic rate and body temperature. Cell Metab 2014; 20:333-45. [PMID: 24981835 PMCID: PMC4126889 DOI: 10.1016/j.cmet.2014.05.021] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 04/03/2014] [Accepted: 05/22/2014] [Indexed: 11/30/2022]
Abstract
The melanocortin system regulates metabolic homeostasis and inflammation. Melanocortin agonists have contradictorily been reported to both increase and decrease metabolic rate and body temperature. We find two distinct physiologic responses occurring at similar doses. Intraperitoneal administration of the nonselective melanocortin agonist MTII causes a melanocortin-4 receptor (Mc4r)-mediated hypermetabolism/hyperthermia. This is preceded by a profound, transient hypometabolism/hypothermia that is preserved in mice lacking any one of Mc1r, Mc3r, Mc4r, or Mc5r. Three other melanocortin agonists also caused hypothermia, which is actively achieved via seeking a cool environment, vasodilation, and inhibition of brown adipose tissue thermogenesis. These results suggest that the hypometabolic/hypothermic effect of MTII is not due to a failure of thermoregulation. The hypometabolism/hypothermia was prevented by dopamine antagonists, and MTII selectively activated arcuate nucleus dopaminergic neurons, suggesting that these neurons may contribute to the hypometabolism/hypothermia. We propose that the hypometabolism/hypothermia is a regulated response, potentially beneficial during extreme physiologic stress.
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Affiliation(s)
- Beth Lute
- Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - William Jou
- Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Dalya M Lateef
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Margalit Goldgof
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Cuiying Xiao
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Ramón A Piñol
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Alexxai V Kravitz
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Nicole R Miller
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, MD 20892, USA
| | - Yuning George Huang
- Kidney Disease Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Clemence Girardet
- Department of Metabolism and Aging, The Scripps Research Institute, Jupiter, FL 33458, USA
| | - Andrew A Butler
- Department of Metabolism and Aging, The Scripps Research Institute, Jupiter, FL 33458, USA
| | - Oksana Gavrilova
- Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Marc L Reitman
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA.
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Alsmadi O, Melhem M, Hebbar P, Thareja G, John SE, Alkayal F, Behbehani K, Thanaraj TA. Leptin in association with common variants of MC3R mediates hypertension. Am J Hypertens 2014; 27:973-81. [PMID: 24487982 DOI: 10.1093/ajh/hpt285] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
BACKGROUND Recent research illustrates the role of central melanocortin signaling and leptin in the regulation of arterial blood pressure in animal models. Unraveling the genetic basis of interactions between melanocortin and leptin in humans will provide new insight into the regulation of arterial pressure. METHOD Our study population consisted of 332 Kuwaiti natives. Polymorphisms from exons of leptin, MC3R, and MC4R genes were identified by Sanger sequencing. MC3R expression and leptin levels were determined. Linear regression models, adjusted for age, gender, antihypertensive medication, and body mass index, were used to perform statistical association tests. RESULTS We observed a significant association between the MC3R missense variant (rs3827103 [Val81 Ile]) and systolic blood pressure (SBP; P = 0.01, β = 4.9). The N-terminus variant (rs3746619 [Thr6→Lys]) is in linkage disequilibrium (r2 = 0.65) with the rs3827103 variant. The AA haplotype of rs3746619-rs3827103 is significantly associated with SBP (P = 0.005, β=5.03). Minor allele frequencies of these two variants in the Kuwaiti population are twice those seen in European population. In individuals who harbor these variants, we found that the plasma leptin levels were positively correlated with SBP and that the expression of MC3R was downregulated. Leptin levels correlated with obesity traits irrespective of the genotypes at the variant positions. CONCLUSION An increase in leptin levels is known to increase sympathetic nerve activity that, in turn, increases blood pressure. Thus, it is possible that the observed MC3R variants in association with leptin levels are involved in regulation of blood pressure in humans.
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Affiliation(s)
- Osama Alsmadi
- Dasman Genome Centre, Dasman Diabetes Institute, Kuwait
| | | | - Prashantha Hebbar
- Integrative Informatics Department, Dasman Diabetes Institute, Kuwait
| | - Gaurav Thareja
- Integrative Informatics Department, Dasman Diabetes Institute, Kuwait
| | - Sumi E John
- Integrative Informatics Department, Dasman Diabetes Institute, Kuwait
| | - Fadi Alkayal
- Dasman Genome Centre, Dasman Diabetes Institute, Kuwait
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Cope G, Flanagan ET, Houghton BL, Walsh SA, Johns EJ, Healy V. [Nle3,d-Phe6 ]-γ2 -melanocyte-stimulating hormone possesses the renal excretory but not the cardiovascular actions of the native γ2 -melanocyte-stimulating hormone in anaesthetized rats. Clin Exp Pharmacol Physiol 2013; 40:5-12. [PMID: 23106106 DOI: 10.1111/1440-1681.12025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Revised: 10/17/2012] [Accepted: 10/21/2012] [Indexed: 11/29/2022]
Abstract
The present study compared the cardiovascular and renal actions of γ(2) -melanocyte-stimulating hormone (γ(2) MSH) with those of the synthetic analogue [Nle(3) ,d-Phe(6) ]-γ(2) MSH (NDP-γ(2) MSH) and explored the effects of high dietary salt intake on the renal actions of NDP-γ(2) MSH. Both peptides were infused systemically (3-1000 nmol/kg) and intrarenally (500 fmol/min) into innervated and renally denervated rats fed either a normal (0.4% NaCl) or high-salt (4% NaCl; HS) diet. Mean arterial pressure (MAP), glomerular filtration rate (GFR), urinary sodium excretion (U(N) (a) V), urinary output (UV) and fractional sodium excretion were determined, as was expression of the melanocortin MC(3) receptor in inner medullary collecting duct (IMCD) epithelial cells. Both renal and systemic infusion of γ(2) MSH increased MAP by 23 ± 2% and 54 ± 4%, respectively, but equivalent doses of NDP-γ(2) MSH had no significant pressor effects. Both peptides had similar natriuretic and diuretic effects in rats fed a normal salt diet. However, NDP-γ(2) MSH increased U(N) (a) V and UV by two- to threefold in rats fed the normal salt diet and by six- to sevenfold in rats fed the HS diet. Furthermore, NDP-γ(2) MSH induced a 3.5-fold increase in GFR only in rats fed the HS diet. These renal effects of NDP-γ(2) MSH were not abolished by prior renal denervation. Rats fed the HS diet also exhibited a 4.5-fold increase in MC(3) receptor expression in IMCD epithelial cells. Intrarenal infusion of NDP-γ(2) MSH induced the natriuretic but not the cardiovascular effects exhibited by γ(2) MSH. The renal activities may be attributed to a direct binding of NDP-γ(2) MSH to MC(3) receptors expressed in IMCD cells, leading to a potent natriuretic effect that is independent of renal innervation.
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Affiliation(s)
- Georgina Cope
- Department of Physiology, University College Cork, Cork, Ireland
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Cope G, Kaushik G, O'Sullivan SM, Healy V. Gamma-melanocyte stimulating hormone regulates the expression and cellular localization of epithelial sodium channel in inner medullary collecting duct cells. Peptides 2013; 47:54-9. [PMID: 23871693 DOI: 10.1016/j.peptides.2013.07.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Revised: 07/08/2013] [Accepted: 07/08/2013] [Indexed: 10/26/2022]
Abstract
Gamma(2)-melanocyte-stimulating hormone (γ2MSH) is a peptide hormone released by the pituitary gland which is thought to act directly on the renal inner medulla to promote increased sodium excretion into urine (natriuresis). The aim of this study was to determine if a stable analog, [Nle(3), D-Phe(6)]-γ2MSH (NDP-γ2MSH), of the native peptide regulated the activity, expression and cellular localization of epithelial sodium channel (ENaC) in a murine inner medullary collecting duct (mIMCD-3) cell line. Our results indicate that expression of the γ2MSH receptor, melanocortin receptor 3 receptor (MC3R), is up-regulated by culturing the cells in media with an increased osmolality (∼400mOsm/kg). Furthermore, stimulation of cAMP signaling and sodium transport by 1nM NDP-γ2MSH occurs only in cells cultured in the high osmolality media. Finally, treatment of mIMCD-3 cells cultured in high osmolality medium for 1h with 1nM NDP-γ2MSH causes a reduction in expression of serum- and glucocorticoid-induced kinase (sgk1) and a reduction in expression and cell surface abundance of the alpha subunit of ENaC. Collectively, this data suggest that γ2MSH directly regulates both ENaC expression and cellular localization in the inner medulla to exert its natriuretic effect.
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Affiliation(s)
- Georgina Cope
- Department of Physiology, University College Cork, Ireland
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14
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Girardet C, Butler AA. Neural melanocortin receptors in obesity and related metabolic disorders. Biochim Biophys Acta Mol Basis Dis 2013; 1842:482-94. [PMID: 23680515 DOI: 10.1016/j.bbadis.2013.05.004] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Revised: 04/16/2013] [Accepted: 05/03/2013] [Indexed: 12/11/2022]
Abstract
Obesity is a global health issue, as it is associated with increased risk of developing chronic conditions associated with disorders of metabolism such as type 2 diabetes and cardiovascular disease. A better understanding of how excessive fat accumulation develops and causes diseases of the metabolic syndrome is urgently needed. The hypothalamic melanocortin system is an important point of convergence connecting signals of metabolic status with the neural circuitry that governs appetite and the autonomic and neuroendocrine system controling metabolism. This system has a critical role in the defense of body weight and maintenance of homeostasis. Two neural melanocortin receptors, melanocortin 3 and 4 receptors (MC3R and MC4R), play crucial roles in the regulation of energy balance. Mutations in the MC4R gene are the most common cause of monogenic obesity in humans, and a large literature indicates a role in regulating both energy intake through the control of satiety and energy expenditure. In contrast, MC3Rs have a more subtle role in energy homeostasis. Results from our lab indicate an important role for MC3Rs in synchronizing rhythms in foraging behavior with caloric cues and maintaining metabolic homeostasis during periods of nutrient scarcity. However, while deletion of the Mc3r gene in mice alters nutrient partitioning to favor accumulation of fat mass no obvious role for MC3R haploinsufficiency in human obesity has been reported. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.
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MESH Headings
- Animals
- Body Weight/genetics
- Cardiovascular Diseases/complications
- Cardiovascular Diseases/metabolism
- Cardiovascular Diseases/pathology
- Diabetes Mellitus, Type 2/complications
- Diabetes Mellitus, Type 2/metabolism
- Diabetes Mellitus, Type 2/pathology
- Humans
- Metabolic Diseases/genetics
- Metabolic Diseases/metabolism
- Metabolic Diseases/pathology
- Mice
- Obesity/complications
- Obesity/genetics
- Obesity/metabolism
- Obesity/pathology
- Receptor, Melanocortin, Type 3/genetics
- Receptor, Melanocortin, Type 3/metabolism
- Receptor, Melanocortin, Type 4/genetics
- Receptor, Melanocortin, Type 4/metabolism
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Affiliation(s)
- Clemence Girardet
- Department of Metabolism and Aging, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA
| | - Andrew A Butler
- Department of Metabolism and Aging, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA.
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Abstract
The melanocortin-3 receptor-deficient (MC3-R(-/-)) mouse exhibits mild obesity without hyperphagia or hypometabolism. MC3-R deletion is reported to increase adiposity, reduce lean mass and white adipose tissue inflammation, and increase sensitivity to salt-induced hypertension. We show here that the MC3-R(-/-) mouse exhibits defective fasting-induced white adipose tissue lipolysis, fasting-induced liver triglyceride accumulation, fasting-induced refeeding, and fasting-induced regulation of the adipostatic and hypothalamic-adrenal-pituitary axes. Close examination of the hypothalamic-pituitary-adrenal axis showed that MC3-R(-/-) mice exhibit elevated nadir corticosterone as well as a blunted fasting-induced activation of the axis. The previously described phenotypes of this animal and the reduced bone density reported here parallel those of Cushing syndrome. Thus, MC3-R is required for communicating nutritional status to both central and peripheral tissues involved in nutrient partitioning, and this defect explains much of the metabolic phenotype in the model.
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McCormick JA, Nelson JH, Yang CL, Curry JN, Ellison DH. Overexpression of the sodium chloride cotransporter is not sufficient to cause familial hyperkalemic hypertension. Hypertension 2011; 58:888-94. [PMID: 21896937 DOI: 10.1161/hypertensionaha.110.167809] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The sodium chloride cotransporter (NCC) is the primary target of thiazides diuretics, drugs used commonly for long-term hypertension therapy. Thiazides also completely reverse the signs of familial hyperkalemic hypertension (FHHt), suggesting that the primary defect in FHHt is increased NCC activity. To test whether increased NCC abundance alone is sufficient to generate the FHHt phenotype, we generated NCC transgenic mice; surprisingly, these mice did not display an FHHt-like phenotype. Systolic blood pressures of NCC transgenic mice did not differ from those of wild-type mice, even after dietary salt loading. NCC transgenic mice also did not display hyperkalemia or hypercalciuria, even when challenged with dietary electrolyte manipulation. Administration of fludrocortisone to NCC transgenic mice, to stimulate NCC, resulted in an increase in systolic blood pressure equivalent to that of wild-type mice (approximately 20 mm Hg). Although total NCC abundance was increased in the transgenic animals, phosphorylated (activated) NCC was not, suggesting that the defect in FHHt involves either activation of ion transport pathways other than NCC, or else direct activation of NCC, in addition to an increase in NCC abundance.
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Affiliation(s)
- James A McCormick
- Division of Nephrology and Hypertension, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Mail Code: L463, Portland, OR 97239-3098, USA.
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18
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Kathpalia PP, Charlton C, Rajagopal M, Pao AC. The natriuretic mechanism of Gamma-Melanocyte-Stimulating Hormone. Peptides 2011; 32:1068-72. [PMID: 21335042 PMCID: PMC3112371 DOI: 10.1016/j.peptides.2011.02.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2011] [Revised: 02/08/2011] [Accepted: 02/09/2011] [Indexed: 11/24/2022]
Abstract
Gamma-Melanocyte Stimulating Hormone (Gamma-MSH) regulates sodium (Na(+)) balance and blood pressure through activation of the melanocortin receptor 3 (MC3-R). The mechanism of the natriuretic effect is proposed to involve binding of MC3-R either in the kidney to directly inhibit tubular Na(+) transport or in the brain to inhibit central neural pathways that control renal tubular Na(+) absorption. This study aimed to clarify the mechanism involved in the natriuretic effect of Gamma-MSH on MC3-R in kidney cells. In Ussing chamber studies, we observed no effects of Gamma-MSH on NaCl transport in the mouse inner medullary collecting duct cell line (mIMCD-K2). We also found that neither MC3-R protein nor mRNA was expressed in mouse kidney, suggesting that renal Gamma-MSH action may not be mediated through direct effects on tubular Na(+) transport but rather through effects on central neural pathways that innervate the kidney.
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Affiliation(s)
- Paru P Kathpalia
- Department of Medicine, Division of Nephrology, Stanford University, Stanford, CA 94305, United States
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19
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Peter JC, Zipfel G, Lecourt AC, Bekel A, Hofbauer KG. Antibodies raised against different extracellular loops of the melanocortin-3 receptor affect energy balance and autonomic function in rats. J Recept Signal Transduct Res 2011; 30:444-53. [PMID: 21091037 DOI: 10.3109/10799893.2010.534485] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Melanocortin receptors (MCR) play an important role in the regulation of energy balance and autonomic function. In the present studies, we used active immunization against peptide sequences from the first and the third extracellular loop (EL1 and EL3) of the MC3R to generate selective antibodies (Abs) against this MCR subtype in rats. Immunization with the EL1 peptide resulted in Abs that enhanced the effects of the endogenous ligand α-melanocyte-stimulating hormone (α-MSH), whereas immunization with the EL3 peptide resulted in Abs acting as non-competitive antagonists. The phenotype of immunized rats chronically instrumented with telemetry transducers was studied under four different conditions: a high-fat diet was followed by standard lab chow, by fasting, and finally by an intraperitoneal injection of lipopolysaccharide (LPS). Under high-fat diet, food intake and body weight were higher in the EL3 than in the EL1 or the control group. Blood pressure was increased in EL3 rats and locomotor activity was reduced. Plasma concentrations of triglycerides, insulin, and leptin tended to rise in the EL3 group. After switching to standard lab chow, the EL1 group showed a small significant increase in blood pressure that was more pronounced and associated with an increase in heart rate during food restriction. No differences between the EL1 or the EL3 group were observed after LPS injection. These results show that immunization against the MC3R resulted in the production of Abs with positive or negative allosteric properties. The presence of such Abs induced small changes in metabolic and cardiovascular parameters.
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20
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Physiological roles of the melanocortin MC₃ receptor. Eur J Pharmacol 2011; 660:13-20. [PMID: 21211527 DOI: 10.1016/j.ejphar.2010.12.025] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Revised: 12/11/2010] [Accepted: 12/15/2010] [Indexed: 11/23/2022]
Abstract
The melanocortin MC(3) receptor remains the most enigmatic of the melanocortin receptors with regard to its physiological functions. The receptor is expressed both in the CNS and in multiple tissues in the periphery. It appears to be an inhibitory autoreceptor on proopiomelanocortin neurons, yet global deletion of the receptor causes an obesity syndrome. Knockout of the receptor increases adipose mass without a readily measurable increase in food intake or decrease in energy expenditure. And finally, no melanocortin MC(3) receptor null humans have been identified and associations between variant alleles of the melanocortin MC(3) receptor and diseases remain controversial, so the physiological role of the receptor in humans remains to be determined.
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21
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Humphreys MH, Ni XP, Pearce D. Cardiovascular effects of melanocortins. Eur J Pharmacol 2011; 660:43-52. [PMID: 21199648 DOI: 10.1016/j.ejphar.2010.10.102] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 10/02/2010] [Accepted: 10/12/2010] [Indexed: 01/04/2023]
Abstract
Melanocortins (MSH's) are three structurally related peptides derived from proopiomelanocortin. They regulate several physiologic functions including energy metabolism, appetite, and inflammation. Recent work in rodents has also identified important effects of MSH's, particularly γ-MSH, on sodium metabolism and blood pressure regulation. Normal rats and mice respond to a high sodium diet with an increase in the plasma concentration of γ-MSH, and remain normotensive, while those with genetic or pharmacologic γ-MSH deficiency become hypertensive on a high sodium diet. This hypertension is corrected by exogenous administration of the peptide. Mice lacking the γ-MSH receptor (the melanocortin 3 receptor, Mc3r) also become hypertensive on a high sodium diet but remain so when administered γ-MSH, and infusions of physiologic levels of the peptide stimulate urinary sodium excretion in normal rats and mice, but not in mice with deletion of Mc3r. The salt-sensitive hypertension in rodents with impaired γ-MSH signaling appears due to stimulation of noradrenergic activity, since plasma noradrenaline is increased and the hypertension is rapidly corrected with infusion of the α-adrenoceptor antagonist phentolamine. In contrast to the antihypertensive property of physiologic levels of γ-MSH, intravenous or intracerebroventricular injections of high levels of the peptide raise blood pressure. This occurs in mice lacking Mc3r, indicating an interaction with some other central receptor. Finally, the salt-sensitive hypertension in rodents with disruption of γ-MSH signaling is accompanied by insulin resistance, an observation which offers a new window into the study of the association of salt-sensitive hypertension with insulin resistance and type II diabetes.
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Affiliation(s)
- Michael H Humphreys
- Division of Nephrology, San Francisco General Hospital and Department of Medicine, University of California San Francisco, San Francisco, CA 94143, USA.
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22
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Genetic deficiency for proprotein convertase subtilisin/kexin type 2 in mice is associated with decreased adiposity and protection from dietary fat-induced body weight gain. Int J Obes (Lond) 2010; 34:1599-607. [PMID: 20498660 DOI: 10.1038/ijo.2010.90] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
BACKGROUND Proprotein convertase subtilisin/xexin type 2 (PCSK2) is an endoproteinase responsible for proteolytic activation of a number of precursors to active neuropeptides and peptide hormones, known to influence glucose homeostasis, food intake and ultimately body mass. In this study, we examined the consequences of PCSK2 deficiency on these phenotypic traits. STUDY DESIGN Weight gain with age under diets of different fat contents was monitored. White adipose tissue (WAT) and muscle masses were evaluated. Plasma levels of triglycerides, leptin, ghrelin, insulin and proglucagon-derived peptides were measured as well as leptin and acetyl coenzyme-α carboxylase (ACCα) mRNA levels in adipose tissue. RESULTS Compared with their Pcsk2 (+/+) littermates, Pcsk2 (-/-) mice weighed significantly less as weanlings and as adults. As adults, they carried noticeably less fat mass, with similar lean muscle mass: their plasma leptin level and adipose tissue leptin mRNA level were accordingly lower. PCSK2 deficiency did not affect food intake or the level of the orexigenic hormone ghrelin. However, PCSK2 deficiency resulted in decreased plasma triglycerides and reduced ACCα mRNA levels in WAT. Interestingly, unlike their Pcsk2 (+/+) littermates, Pcsk2 (-/-) were resistant to enhanced body weight gain when fed a high-fat diet. Consistent with a role of PCSK2 in body mass gain, diet-induced or genetically obese mice were found to contain significantly higher levels of PCSK2 mRNA in their brain and stomach than their lean counterparts. CONCLUSION Collectively, these results suggest that PCSK2 contributes to increase in body mass through the various regulatory peptides generated through its action. It represents a potential target in the prevention and treatment of obesity.
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23
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Corander MP, Fenech M, Coll AP. Science of self-preservation: how melanocortin action in the brain modulates body weight, blood pressure, and ischemic damage. Circulation 2009; 120:2260-8. [PMID: 19948994 PMCID: PMC2880450 DOI: 10.1161/circulationaha.109.854612] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Marcus P Corander
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Treatment Centre, Addenbrooke's Hospital, Hills Rd, Cambridge, CB2 0QQ UK
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24
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Beaumont KA, Liu YY, Sturm RA. The melanocortin-1 receptor gene polymorphism and association with human skin cancer. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2009; 88:85-153. [PMID: 20374726 DOI: 10.1016/s1877-1173(09)88004-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The melanocortin-1 receptor (MC1R) is a key gene involved in the regulation of melanin synthesis and encodes a G-protein coupled receptor expressed on the surface of the melanocyte in the skin and hair follicles. MC1R activation after ultraviolet radiation exposure results in the production of the dark eumelanin pigment and the tanning process in humans, providing physical protection against DNA damage. The MC1R gene is highly polymorphic in Caucasian populations with a number of MC1R variant alleles associated with red hair, fair skin, freckling, poor tanning, and increased risk of melanoma and nonmelanoma skin cancer. Variant receptors have shown alterations in biochemical function, largely due to intracellular retention or impaired G-protein coupling, but retain some signaling ability. The association of MC1R variant alleles with skin cancer risk remains after correction for pigmentation phenotype, indicating regulation of nonpigmentary pathways. Notably, MC1R activation has been linked to DNA repair and may also contribute to the regulation of immune responses.
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Affiliation(s)
- Kimberley A Beaumont
- Melanogenix Group, Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld 4072, Australia
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25
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Ni XP, van Dijk C, Pearce D, Humphreys MH. Evidence for a noradrenergic mechanism causing hypertension and abnormal glucose metabolism in rats with relative deficiency of gamma-melanocyte-stimulating hormone. Exp Physiol 2009; 94:867-76. [PMID: 19429645 DOI: 10.1113/expphysiol.2009.046748] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
A close association between salt-sensitive hypertension and insulin resistance has been recognized for more than two decades, although the mechanism(s) underlying this relationship have not been elucidated. Recent data in mice with genetic disruption of the gamma-melanocyte-stimulating hormone (gamma-MSH) system suggest that this system plays a role in the pathophysiological relationship between hypertension and altered glucose metabolism during ingestion of a high-sodium diet (8% NaCl, HSD). We tested the hypothesis that these two consequences of interrupted gamma-MSH signalling were the result of sympathetic activation by studying rats treated with the dopaminergic agonist bromocriptine (5 mg kg(-1) i.p., daily for 1 week; Bromo) to cause relative gamma-MSH deficiency. Bromo-treated rats fed the HSD developed hypertension and also exhibited fasting hyperglycaemia (P < 0.005) and hyperinsulinaemia (P < 0.025). Furthermore, Bromo-treated rats on the HSD had impaired glucose tolerance and blunted insulin-mediated glucose disposal. Intravenous infusion of gamma(2)-MSH, or of the alpha-adrenergic receptor antagonist phentolamine, to Bromo-HSD rats lowered both mean arterial pressure (MAP) and blood glucose to normal after 15 min (P < 0.001 versus control), but had no effect in rats receiving vehicle and fed the HSD; gamma(2)-MSH infusion also reduced the elevated plasma noradrenaline to control levels in parallel with the reductions in MAP and blood glucose concentration. Infusion of hydralazine to Bromo-HSD rats lowered MAP but had only a trivial effect on blood glucose. We conclude that rats with relative gamma-MSH deficiency develop abnormal glucose metabolism, with features of insulin resistance, in association with hypertension when ingesting the HSD. Elevated plasma noradrenaline concentration in Bromo-HSD rats is normalized by gamma(2)-MSH infusion, suggesting that an adrenergic mechanism may link the salt-sensitive hypertension and the impaired glucose metabolism of relative gamma-MSH deficiency.
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Affiliation(s)
- Xi-Ping Ni
- Division of Nephrology, San Francisco General Hospital and Department of Medicine, University of California San Francisco, San Francisco, CA 94143-1341, USA
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26
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Zhan S, Zhao H, J White A, Minami M, Pignataro G, Yang T, Zhu X, Lan J, Xiong Z, Steiner DF, Simon RP, Zhou A. Defective neuropeptide processing and ischemic brain injury: a study on proprotein convertase 2 and its substrate neuropeptide in ischemic brains. J Cereb Blood Flow Metab 2009; 29:698-706. [PMID: 19142196 PMCID: PMC3878611 DOI: 10.1038/jcbfm.2008.161] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Using a focal cerebral ischemia model in rats, brain ischemia-induced changes in expression levels of mRNA and protein, and activities of proprotein convertase 2 (PC2) in the cortex were examined. In situ hybridization analyses revealed a transient upregulation of the mRNA level for PC2 at an early reperfusion hour, at which the level of PC2 protein was also high as determined by immunocytochemistry and western blotting. When enzymatic activities of PC2 were analyzed using a synthetic substrate, a significant decrease was observed at early reperfusion hours at which levels of PC2 protein were still high. Also decreased at these reperfusion hours were tissue levels of dynorphin-A(1-8) (DYN-A(1-8)), a PC2 substrate, as determined by radioimmunoassay. Further examination of PC2 protein biosynthesis by metabolic labeling in cultured neuronal cells showed that in ischemic cells, the proteolytic processing of PC2 was greatly attenuated. Finally, in mice, an intracerebroventricular administration of synthetic DYN-A(1-8) significantly reduced the extent of ischemic brain injury. In mice those lack an active PC2, exacerbated brain injury was observed after an otherwise non-lethal focal ischemia. We conclude that brain ischemia attenuates PC2 and PC2-mediated neuropeptide processing. This attenuation may play a role in the pathology of ischemic brain injury.
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Affiliation(s)
- Shuqin Zhan
- Robert S. Dow Neurobiology Laboratories, Legacy Research, Portland, Oregon 97232, USA
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27
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Ni XP, Humphreys MH. Abnormal glucose metabolism in hypertensive mice with genetically interrupted gamma-melanocyte stimulating hormone signaling fed a high-sodium diet. Am J Hypertens 2008; 21:1284-7. [PMID: 18802429 DOI: 10.1038/ajh.2008.290] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND Rodents with deficiency of or resistance to the proopiomelanocortin-derived peptide gamma-melanocyte stimulating hormone (gamma-MSH) develop marked salt-sensitive hypertension. We asked whether this hypertension was accompanied by abnormal glucose metabolism. METHODS gamma-MSH-deficient Pc2(-/-) mice, and resistant Mc3r(-/-) mice were studied acutely for measurement of blood pressure and glucose and insulin concentrations after > or =1 week of a high-sodium diet (HSD; 8% NaCl) compared to a normal-sodium diet (NSD; 0.4% NaCl). Mc3r(-/-) also underwent glucose tolerance test (GTT) and insulin tolerance test. RESULTS Both knockout strains were hypertensive and also exhibited fasting hyperglycemia and hyperinsulinemia on the HSD. Mc3r(-/-) mice on the HSD had impaired glucose tolerance and insulin-mediated glucose disposal compared to wild-type mice on either the HSD or the NSD, or to Mc3r(-/-) mice on the NSD. CONCLUSIONS These results indicate an interaction of interrupted gamma-MSH signaling with the HSD to cause hypertension on the one hand and abnormal glucose metabolism, with the characteristics of insulin resistance, on the other. Further study of the nature of this interaction should provide new insight into the mechanisms by which salt-sensitive hypertension and insulin resistance are linked.
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Proneth B, Pogozheva ID, Portillo FP, Mosberg HI, Haskell-Luevano C. Melanocortin tetrapeptide Ac-His-DPhe-Arg-Trp-NH2 modified at the para position of the benzyl side chain (DPhe): importance for mouse melanocortin-3 receptor agonist versus antagonist activity. J Med Chem 2008; 51:5585-93. [PMID: 18800761 DOI: 10.1021/jm800291b] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The melanocortin-3 and -4 receptors (MC3R, MC4R) have been implicated in energy homeostasis and obesity. Whereas the physiological role of the MC4R is extensively studied, little is known about the MC3R. One caveat is the limited availability of ligands that are selective for the MC3R. Previous studies identified Ac-His-DPhe(p-I)-Arg-Trp-NH 2, which possessed partial agonist/antagonist pharmacology at the mMC3R while retaining full nanomolar agonist pharmacology at the mMC4R. These data allowed for the hypothesis that the DPhe position in melanocortin tetrapeptides can be used to examine ligand side-chain determinants important for differentiation of mMC3R agonist versus antagonist activity. A series of 15 DPhe (7) modified Ac-His-DPhe (7)-Arg-Trp-NH 2 tetrapeptides has been synthesized and pharmacologically characterized. Most notable results include the identification of modifications that resulted in potent antagonists/partial agonists at the mMC3R and full, potent agonists at the mMC4R. These SAR studies provide experimental evidence that the molecular mechanism of antagonism at the mMC3R differentiates this subtype from the mMC4R.
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Affiliation(s)
- Bettina Proneth
- Department of Pharmacodynamics, University of Florida, Gainesville, Florida 32610, USA
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29
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Wang SX, Fan ZC, Tao YX. Functions of acidic transmembrane residues in human melanocortin-3 receptor binding and activation. Biochem Pharmacol 2008; 76:520-30. [PMID: 18614155 DOI: 10.1016/j.bcp.2008.05.026] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2008] [Revised: 05/22/2008] [Accepted: 05/23/2008] [Indexed: 10/22/2022]
Abstract
The melanocortin-3 receptor (MC3R) is an important regulator of energy homeostasis, inflammation, and cardiovascular function. Inactivating mutations in MC3R gene are associated with childhood obesity. How MC3R binds to its ligands has rarely been studied. In the present study, we systematically mutated all ten acidic residues in transmembrane (TM) domains and measured the cell surface expression levels as well as ligand binding and signaling properties of these mutants. Our results showed that of the 19 mutants stably expressed in HEK293 cells, all were expressed on the cell surface, although some mutants had decreased levels of cell surface expression. We showed that with the superpotent analog [Nle(4), D-Phe(7)]-alpha-melanocyte stimulating hormone (MSH), E92, E131, D154, D158, D178, and D332 are important for ligand binding. D121 and D332 are important for binding and signaling. Further experiments using other ligands such as D-Trp(8)-gamma-MSH, alpha-MSH and gamma-MSH showed that different ligands induce or select different conformations. In summary, we showed that acidic residues in TMs 1 and 3 are important for ligand binding whereas the acidic residues in TMs 2 and 7 are important for both ligand binding and signaling.
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Affiliation(s)
- Shu-Xiu Wang
- Department of Anatomy, Physiology and Pharmacology, 213 Greene Hall, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, USA
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Nyan DC, Anbazhagan R, Hughes-Darden CA, Wachira SJM. Endosomal colocalization of melanocortin-3 receptor and beta-arrestins in CAD cells with altered modification of AKT/PKB. Neuropeptides 2008; 42:355-66. [PMID: 18291523 DOI: 10.1016/j.npep.2007.12.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Revised: 12/20/2007] [Accepted: 12/21/2007] [Indexed: 01/14/2023]
Abstract
The melanocortin 3-receptor is involved in regulating energy metabolism, body fluid composition and inflammatory responses. Melanocortin receptors function by activating membrane bound adenylate cyclase. However, the literature reports indicate that some G protein coupled receptors (GPCRs) can also activate mitogen activated protein kinase (MAPK) or phosphoinositide 3 kinase (PI3K) signaling pathways consequent to their endocytosis. These studies were undertaken to evaluate the role of these pathways in MC3R signaling in brain-stem neuronal cells. Recruitment of arrestins is implicated in the activation of secondary pathways by GPCRs and our data shows the colocalization of either arrestin B1 or B2 with MC3R in endosomes. An alteration in PKB phosphorylation pattern was observed in MC3R expressing cells independent of agonist stimulation. MC3R transfectants exhibited increased proliferation rates and inhibition of PKB pathway with triciribine abrogated cell proliferation in both vector control and MC3R transfectants. PKB is constitutively active in proliferating CAD cells but could be further activated by culturing the cells in differentiation medium. These studies suggest that the AKT/PKB pathway plays an important role in the proliferation of CAD cells and suggest a link between MC3R and cell growth pathways that may involve the alteration of AKT/PKB signaling pathway.
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Affiliation(s)
- D C Nyan
- Department of Biology, Morgan State University, Baltimore, MD 21251, USA
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Wong J, Nock NL, Xu Z, Kyle C, Daniels A, White M, Yue DK, Elston RC, Mountjoy KG. A polymorphism (D20S32e) close to the human melanocortin receptor 3 is associated with insulin resistance but not the metabolic syndrome. Diabetes Res Clin Pract 2008; 80:203-7. [PMID: 18180070 DOI: 10.1016/j.diabres.2007.11.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2007] [Accepted: 11/06/2007] [Indexed: 11/17/2022]
Abstract
Insulin resistance (IR) is postulated to underlie diabetes, the metabolic syndrome (MS) and cardiovascular disease (CVD). The D20S32e marker close to the melanocortin receptor-3 (hMC3-R) has been shown to be associated with IR in a large New Zealand Māori kindred, a population at high risk for MS and CVD. Here we examine the potential association of the D20S32e marker with the MS in this 60 member Māori kindred. There was a significant association between the D20S32e "B" allele and the fasting insulin component under both polygenic (beta=-5.3077; p=0.008) and common sibship effect (beta=-4.2161; p=0.03) models. No significant association between the same allele of D20S32e and the MS was observed after adjusting for age under a polygenic (p=0.103) or sibling (p=0.09) correlation model. We conclude that in this Māori kindred, the D20S32e polymorphism is significantly associated with insulin resistance but not with MS. Our data supports the hypothesis that multiple gene variants are necessary for the development of the MS.
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Affiliation(s)
- Jencia Wong
- Diabetes Centre, Royal Prince Alfred Hospital, Sydney, Australia; Discipline of Medicine, University of Sydney, Sydney, Australia
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Targeting melanocortin receptors: an approach to treat weight disorders and sexual dysfunction. Nat Rev Drug Discov 2008; 7:307-23. [PMID: 18323849 DOI: 10.1038/nrd2331] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The melanocortin system has multifaceted roles in the control of body weight homeostasis, sexual behaviour and autonomic functions, and so targeting this pathway has immense promise for drug discovery across multiple therapeutic areas. In this Review, we first outline the physiological roles of the melanocortin system, then discuss the potential of targeting melanocortin receptors by using MC3 and MC4 agonists for treating weight disorders and sexual dysfunction, and MC4 antagonists to treat anorectic and cachectic conditions. Given the complexity of the melanocortin system, we also highlight the challenges and opportunities for future drug discovery in this area.
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Rodriguez-Iturbe B, Romero F, Johnson RJ. Pathophysiological Mechanisms of Salt-Dependent Hypertension. Am J Kidney Dis 2007; 50:655-72. [PMID: 17900467 DOI: 10.1053/j.ajkd.2007.05.025] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Accepted: 05/18/2007] [Indexed: 12/29/2022]
Abstract
Changes in salt intake are associated in general with corresponding changes in arterial blood pressure. An exaggerated increment in blood pressure driven by a salt load is characteristic of salt-sensitive hypertension, a condition affecting more than two thirds of individuals with essential hypertension who are older than 60 years. In the last decade, significant insight was gained about the role of the kidney in the increment in blood pressure induced by sodium retention. The present review focuses on the pathophysiological characteristics of the blood pressure increase driven by expansion of extracellular fluid and the increment in plasma sodium concentration. In addition, we discuss systemic and renal conditions that result in decreased urinary sodium excretion and were implicated in the development of salt-sensitive hypertension.
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Wachira SJM, Guruswamy B, Uradu L, Hughes-Darden CA, Denaro FJ. Activation and endocytic internalization of melanocortin 3 receptor in neuronal cells. Ann N Y Acad Sci 2007; 1096:271-86. [PMID: 17405938 DOI: 10.1196/annals.1397.093] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Melanocortins play a central role in autonomic modulation of metabolism by acting through a family of highly homologous G protein-coupled receptors. Studies with gene knockout mice have implicated neural melanocortin receptors, MC3R and MC4R, in the etiology of obesity, insulin resistance, and salt-sensitive hypertension. In an attempt to better understand the mechanisms of function of these receptors, we expressed MC3R and MC4R in neuronal cells and demonstrated their co-localization to several membrane regions. We now show that in cultured neuronal cells, MC3R localizes to lipid rafts and undergoes endocytic internalization upon activation by gamma-MSH through a protein kinase-sensitive pathway. The appearance of the internalized receptor in lysosomes suggests that it is subsequently degraded. The expression of protein kinase A regulatory subunits and of c-Jun and c-Fos was analyzed by either immunoblotting or real-time PCR. No discernable changes were observed in the expression levels of these protein kinase A and protein kinase C responsive genes. Immunohistochemical studies showed a robust expression of MC3R protein in brain nuclei with relevance to cardiovascular function and fluid homeostasis further supporting the notion that the physiological effects of melanocortins on the cardiovascular system arise from effects on the central nervous system.
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Affiliation(s)
- S J M Wachira
- Department of Biology, Morgan State University, 1700 E. Cold Spring Lane, Baltimore, MD 21251, USA.
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Ellacott KL, Cone RD. The role of the central melanocortin system in the regulation of food intake and energy homeostasis: lessons from mouse models. Philos Trans R Soc Lond B Biol Sci 2007; 361:1265-74. [PMID: 16815803 PMCID: PMC1642695 DOI: 10.1098/rstb.2006.1861] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A little more than a decade ago, the molecular basis of the lipostat was largely unknown. At that time, many laboratories were at work attempting to clone the genes encoding the obesity, diabetes, fatty, tubby and agouti loci, with the hope that identification of these obesity genes would help shed light on the process of energy homeostasis, appetite and energy expenditure. Characterization of obesity and diabetes elucidated the nature of the adipostatic hormone leptin and its receptor, respectively, while cloning of the agouti gene eventually led to the identification and characterization of one of the key neural systems upon which leptin acts to regulate intake and expenditure. In this review, we describe the neural circuitry known as the central melanocortin system and discuss the current understanding of its role in feeding and other processes involved in energy homeostasis.
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Tai MH, Weng WT, Lo WC, Chan JYH, Lin CJ, Lam HC, Tseng CJ. Role of nitric oxide in alpha-melanocyte-stimulating hormone-induced hypotension in the nucleus tractus solitarii of the spontaneously hypertensive rats. J Pharmacol Exp Ther 2007; 321:455-61. [PMID: 17283224 DOI: 10.1124/jpet.106.118299] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Pro-opiomelanocortin (POMC) is expressed in the nucleus tractus solitarii (NTS) of the brainstem, where nitric oxide (NO) plays an important role in cardiovascular regulation. The POMC-derived neuropeptides and their receptors are important regulators of energy homeostasis and cardiovascular functions in the central nervous system. In this study, we investigated the cardiovascular effect of alpha-melanocyte-stimulating hormone (alpha-MSH), a POMC-derived neuropeptide, and its relationship with NO pathway in the NTS of spontaneously hypertensive rats (SHR). Unilateral microinjection of alpha-MSH (0.3-300 pmol) into the NTS resulted in a dose-dependent hypotension and bradycardia in urethane-anesthetized SHR. The alpha-MSH-induced hypotension was abolished by pretreatment with the antagonist of melanocortin-3/4 receptor (MC-3/4R), Ac-Nle-c[Asp-His-D-Nal(2')-Arg-Trp-Lys]-NH2 (SHU9119). Blockade of cAMP/protein kinase A (PKA), the downstream effector of melanocortin receptors, by previous injection of N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89) also ablated the cardiovascular effect of alpha-MSH. To elucidate the role of NO pathway in alpha-MSH-evoked hypotension, pretreatment with Nomega-nitro-L-arginine methyl ester, a universal inhibitor of nitric-oxide synthase (NOS), partially reversed the depressor and bradycardic effects of alpha-MSH. Furthermore, previous application of the inducible NOS (iNOS) inhibitor, aminoguanidine, but not the neuronal NOS inhibitor, 7-nitroindazole, attenuated the cardiovascular effect of alpha-MSH. Histological analysis revealed the colocalization of MC-4R, but not MC-3R, with iNOS in the NTS of SHR. In summary, intra-NTS injection of alpha-MSH induces hypotension and bradycardia of SHR via MC-4R signaling, which activates cAMP/PKA and iNOS.
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Affiliation(s)
- Ming-Hong Tai
- Department of Medical Education and Research, Kaohsiung Veterans General Hospital, and Graduate Institute of Biochemistry, Kaohsiung Medical University, 386 Ta-Chung 1st Road, Kaohsiung 813, Taiwan
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Abstract
PURPOSE OF REVIEW Melanocyte stimulating hormones (MSHs, melanocortins) have important roles in feeding and energy metabolism and in inflammation. Recent observations have uncovered major functions for these peptides, particularly gamma-MSH, in cardiovascular regulation and sodium metabolism. RECENT FINDINGS Both alpha- and gamma-MSH acutely elevate blood pressure and heart rate through central stimulation of sympathetic nervous outflow. This action of alpha-MSH is mediated by the melanocortin 4 receptor (MC4R), whereas sympathetic nervous stimulation by gamma-MSH does not involve its receptor MC3R but rather is likely due to activation of a sodium channel in the central nervous system. In contrast, gamma-MSH deficiency in rodents, or disruption of MC3R, leads to marked salt-sensitive hypertension, again through a central mechanism: a small dose of exogenous peptide delivered into the cerebroventricular system of mice with gamma-MSH deficiency restores blood pressure to normal. This salt-sensitive hypertension is accompanied by the development of insulin resistance; the mechanism linking these two consequences of a high-salt diet is not yet known but may involve activation of the sympathetic nervous system. SUMMARY The study of MSH peptides in blood pressure regulation offers a new opportunity to gain insight into the mechanisms underlying salt sensitivity and its link to insulin resistance, and to new therapies.
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Affiliation(s)
- Michael H Humphreys
- Division of Nephrology, San Francisco General Hospital, University of California San Francisco, San Francisco, CA 94143, USA.
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Tung YCL, Piper SJ, Yeung D, O'Rahilly S, Coll AP. A comparative study of the central effects of specific proopiomelancortin (POMC)-derived melanocortin peptides on food intake and body weight in pomc null mice. Endocrinology 2006; 147:5940-7. [PMID: 16959830 PMCID: PMC2204083 DOI: 10.1210/en.2006-0866] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Functional disruption of either MC3R or MC4R results in obesity, implicating both in the control of energy homeostasis. The ligands for these receptors are derived from the prohormone proopiomelancortin (POMC), which is posttranslationally processed to produce a set of melanocortin peptides with a range of activities at the MC3R and MC4R. The relative importance of each of these peptides alpha-MSH, gamma3-MSH, gamma2-MSH, gamma-lipotropin (gamma-LPH) and, in man but not in rodents, beta-MSH] in the maintenance of energy homeostasis is, as yet, unclear. To investigate this further, equimolar amounts (2 nmol) of each peptide were centrally administered to freely feeding, corticosterone-supplemented, Pomc null (Pomc-/-) mice. After a single dose at the onset of the dark cycle, alpha-MSH had the most potent anorexigenic effect, reducing food intake to 35% of sham-treated animals. beta-MSH, gamma-LPH, and gamma3- and gamma2-MSH all reduced food intake but to a lesser degree. The effects of peptide administration over 3 d were also assessed. Only alpha-MSH significantly reduced body weight, affecting both fat and lean mass. Other peptides had no significant effect on body weight. Pair-feeding of sham-treated mice to those treated with alpha-MSH resulted in identical changes in total weight, fat and lean mass indicating that the effects of alpha-MSH were primarily due to reduced food intake rather than increased energy expenditure. Although other melanocortins can reduce food intake in the short-term, only alpha-MSH can reduce the excess fat and lean mass found in Pomc-/- mice, mediated largely through an effect on food intake.
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Affiliation(s)
- Y C Loraine Tung
- Department of Clinical Biochemistry, Cambridge Institute for Medical Research, Addenbrooke's Hospital, Cambridge CB2 2QR, United Kingdom
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Abstract
The melanocortin system refers to a set of hormonal, neuropeptidergic, and paracrine signaling pathways that are defined by components that include the five G protein-coupled melanocortin receptors; peptide agonists derived from the proopiomelanocortin preprohormone precursor; and the endogenous antagonists, agouti and agouti-related protein. This signaling system regulates a remarkably diverse array of physiological functions including pigmentation, adrenocortical steroidogenesis, energy homeostasis, natriuresis, erectile responses, energy homeostasis, and exocrine gland secretion. There are many complex and unique aspects of melanocortin signaling, such as the existence of endogenous antagonists, the agouti proteins, that act at three of the five melanocortin receptors. However, there is an aspect of melanocortin signaling that has facilitated highly reductionist approaches aimed at understanding the physiological functions of each receptor and peptide: in contrast to many peptides, the melanocortin agonists and antagonists are expressed in a limited number of very discrete locations. Similarly, the melanocortin receptors are also expressed in a limited number of discrete locations where they tend to be involved in rather circumscribed physiological functions. This review examines my laboratory's participation in the cloning of the melanocortin receptors and characterization of their physiological roles.
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Affiliation(s)
- Roger D Cone
- Center for the Study of Weight Regulation and Associated Disorders, and Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239-3098, USA.
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40
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Ni XP, Butler AA, Cone RD, Humphreys MH. Central receptors mediating the cardiovascular actions of melanocyte stimulating hormones. J Hypertens 2006; 24:2239-46. [PMID: 17053546 DOI: 10.1097/01.hjh.0000249702.49854.fa] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE Alpha and gamma-melanocyte stimulating hormones (MSH) are peptides that possess potent hypertensinogenic actions when injected intravenously or intracerebroventricularly. We sought to define the central receptor(s) mediating these cardiovascular actions. METHODS We gave bolus injections of synthetic alpha or gamma-MSH intravenously or intracerebroventricularly to anesthetized wild-type (Mc3r+/+, Mc4r+/+) mice and mice with targeted disruption of the gamma-MSH receptor (Mc3r-/-) or the melanocortin 4 receptor (Mc4r-/-). RESULTS Gamma-MSH injected intravenously increased mean arterial pressure (MAP) and heart rate (HR) dose-dependently, with the effect being evident at 10 mol/kg; the maximum increase, at 10 mol/kg, was 38 mmHg in both strains from similar control MAP. Parallel increases in HR also occurred. Injection of the sodium channel blocker, benzamil, 4 microg/kg intracerebroventricularly, before intravenous gamma-MSH completely prevented the increases in MAP and HR in both strains. Injection of 2 x 10 mol/g body weight alpha-MSH intravenously had no effect on MAP or HR in Mc4r wild-type or -/- mice. However, the same dose given intracerebroventricularly to wild-type mice increased MAP from 76 +/- 4 to 95 +/- 5 mmHg at 10 min (P < 0.01) and HR from 416 +/- 15 to 480 +/- 15 beats/min (P < 0.01). In Mc4r-/- mice, the intracerebroventricular administration of the peptide did not alter these variables, in contrast to the results in wild-type mice. CONCLUSION Both MSH peptides exert their hypertensinogenic effects through central sites of action, which probably reflect the activation of sympathetic outflow. The actions of intracerebroventricular alpha-MSH appear to be mediated via Mc4r, whereas those of gamma-MSH are independent of its receptor Mc3r, but reflect the activation of a sodium channel in the central nervous system. These results help to reconcile the hypertensive action of gamma-MSH injections with the hypertension observed in states of gamma-MSH deficiency.
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MESH Headings
- Amiloride/analogs & derivatives
- Amiloride/pharmacology
- Animals
- Blood Pressure/drug effects
- Blood Pressure/physiology
- Dose-Response Relationship, Drug
- Heart Rate/drug effects
- Heart Rate/physiology
- Hypertension/metabolism
- Hypertension/physiopathology
- Mice
- Mice, Knockout
- Models, Animal
- Receptor, Melanocortin, Type 3/genetics
- Receptor, Melanocortin, Type 3/physiology
- Receptor, Melanocortin, Type 4/genetics
- Receptor, Melanocortin, Type 4/physiology
- Sodium Channel Blockers/pharmacology
- Sympatholytics/pharmacology
- alpha-MSH/pharmacology
- gamma-MSH/pharmacology
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Affiliation(s)
- Xi-Ping Ni
- Division of Nephrology, San Francisco General Hospital and University of California San Francisco, San Francisco, California 94143-1341, USA
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Caeiro X, Hansen C, García N, Vivas L. β-Endorphin involvement in the regulatory response to body sodium overload. Neuroscience 2006; 142:557-65. [PMID: 16887279 DOI: 10.1016/j.neuroscience.2006.06.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2005] [Revised: 06/13/2006] [Accepted: 06/14/2006] [Indexed: 11/20/2022]
Abstract
The present study was performed to examine the role of the endogenous beta-endorphinergic system on blood pressure regulation, sympathetic and brain activity during body sodium overload. Beta-endorphin knockout (beta end-/-), heterozygous (beta end+/-) and wild-type (beta end+/+) mice were submitted for two weeks to either a normal- or a high-sodium diet (NSD and HSD, respectively), and systolic blood pressure (SBP), urinary catecholamines (as an index of sympathetic nervous system activity), and the brain pattern of Fos-like immunoreactivity (as a marker of neuronal activation) were evaluated in each group. HSD caused a significant increase in SBP in beta end-/- mutant mice compared with beta end+/+ mice kept in the same experimental conditions (P < 0.01), but no statistical differences were observed between beta end+/- and beta end+/+ on a HSD. Moreover, when animals from the three genetic lines were fed with a NSD no changes in SBP were evidenced. With regard to brain activity, beta end-/- mice maintained on a HSD showed a significant increase in Fos-like immunoreactive neurons in the median preoptic nucleus (P < 0.01) compared with beta end+/- and beta end+/+ animals. Additionally, beta end-/- mice had higher levels of urinary epinephrine excretion (P < 0.05) on a HSD in comparison to beta end+/+ and beta end+/- animals in the same experimental conditions. No differences, however, were registered in norepinephrine and dopamine urinary excretion in animals from the three genetic lines after two weeks on either a HSD or a NSD. In summary, our results indicate that the beta-endorphinergic system may play a part in the compensatory response to sodium overload, since the absence of beta-endorphin causes an increase in systolic blood pressure, and increases median preoptic nucleus neural activity and urinary epinephrine excretion.
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Affiliation(s)
- X Caeiro
- Instituto de Investigación Médica Mercedes y Martín Ferreyra, Casilla de correo 389, 5000 Córdoba, Argentina
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42
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Abstract
The melanocortins, a family of peptides produced from the post-translational processing of pro-opiomelanocortin (POMC), regulate ingestive behavior and energy expenditure. Loss of function mutations of genes encoding POMC, or of either of two melanocortin receptors expressed in the central nervous system (MC3R, MC4R), are associated with obesity. The analyses of MC4R knockout mice indicate that activation of this receptor is involved in the regulation of appetite, the adaptive metabolic response to excess caloric consumption, and negative energy balance associated with cachexia induced by cytokines. In contrast, MC3R knockout mice exhibit a normal, or even exaggerated, response to signals that induce a state of negative energy balance. However, loss of the MC3R also results in an increase in adiposity. This article discusses the regulation of energy balance by the melanocortins. Published and newly presented data from studies analyzing of energy balance of MC3R and MC4R knockout mice indicate that increased adiposity observed in both models involves an imbalance in fat intake and oxidation.
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Ni XP, Bhargava A, Pearce D, Humphreys MH. Modulation by dietary sodium intake of melanocortin 3 receptor mRNA and protein abundance in the rat kidney. Am J Physiol Regul Integr Comp Physiol 2005; 290:R560-7. [PMID: 16195498 DOI: 10.1152/ajpregu.00279.2005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gamma-melanocyte stimulating hormone (gamma-MSH) is a circulating natriuretic peptide hormone derived from proopiomelanocortin (POMC); its concentration in plasma and pituitary POMC mRNA abundance, increase in rats ingesting a high-sodium diet (HSD, 8% NaCl) compared with a low-sodium diet (LSD, 0.07% NaCl). RT-PCR of rat kidney RNA demonstrated reaction products of the expected size in both cortex and medulla for MC3-R, MC4-R, and MC5-R mRNA; no signal for MC1-R or MC2-R was detected. Relative to beta-actin or cyclophilin, abundance of the three receptor transcripts after 1 wk of the LSD was approximately equal in both cortex and medulla. After 1 wk of the HSD, mRNA abundance of MC4-R and MC5-R was unchanged, whereas that of MC3-R in medulla more than doubled, the ratio of MC3-R/beta-actin signal increasing from 0.38 +/- 0.04 on LSD to 0.84 +/- 0.04 on HSD (P < 0.001). No significant increase occurred in the cortex. The increase in MC3-R expression induced by dietary sodium was observed in inner medullary collecting duct (IMCD) cells isolated from the kidneys of HSD rats, suggesting that these cells were the major site of receptor expression in the medulla. Immunoblots of whole medullary and IMCD cell homogenates detected MC3-R immunoreactive protein; its expression was twice as great in samples from HSD vs. LSD rat kidneys, paralleling the increase in MC3-R mRNA abundance on the HSD. No changes in MC4-R or MC5-R protein expression were observed. Incubation of IMCD cell suspensions with increasing concentrations of gamma2-MSH led to increased cAMP accumulation, with values from rats on the HSD being roughly double the values from LSD rats. Intrarenal infusion of gamma2-MSH (500 fmol/min) increased sodium and cAMP excretion from the infused but not contralateral kidney of HSD rats, while having no effect in LSD rats. These data show that MC3-R is expressed in rat IMCD cells in a manner modulated by dietary sodium intake. Because MC3-R is the receptor with which gamma-MSH interacts, our findings suggest the existence of a sodium-regulating system, activated in response to a HSD, which increases urinary sodium excretion to balance the high-sodium intake.
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Affiliation(s)
- Xi-Ping Ni
- Division of Nephrology, San Francisco General Hospital, California, USA
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44
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Tallam LS, Stec DE, Willis MA, da Silva AA, Hall JE. Melanocortin-4 receptor-deficient mice are not hypertensive or salt-sensitive despite obesity, hyperinsulinemia, and hyperleptinemia. Hypertension 2005; 46:326-32. [PMID: 16027245 DOI: 10.1161/01.hyp.0000175474.99326.bf] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The purpose of this study was to test whether the melanocortin-4 receptor (MC4R) is critical in the development of hypertension associated with obesity and its metabolic disorders. MC4R-deficient homozygous (-/-) and heterozygous (+/-) and wild-type (WT) C57BL/6J mice 17 to 19 weeks old (n=5 to 7 per group) were implanted with telemetry devices for monitoring 24-hour mean arterial pressure (MAP) and heart rate (HR). After 3-day stable control measurements on normal-salt diet (NSD; 0.4% NaCl), mice received a high-salt diet (HSD; 4% NaCl) for 7 days, followed by 3-day recovery on NSD. MC4R (-/-) mice were severely obese compared with MC4R (+/-) and WT mice (body weight 48+/-1.5 versus 31+/-0.6 and 30+/-0.5 g respectively). On NSD, MAP was similar in all groups of mice (MC4R (-/-) 110+/-3 mm Hg; MC4R (+/-) 109+/-2 mm Hg; WT 114+/-2 mm Hg), and HR in MC4R (-/-) was lower than in WT (604+/-5 versus 645+/-9 bpm; P<0.05) but not different from MC4R (+/-) (625+/-13 bpm) mice. HSD did not significantly alter MAP or HR in any of the groups. Epididymal and retroperitoneal fat weights and plasma leptin levels were several-fold greater in MC4R (-/-) compared with MC4R (+/-) and WT mice. Plasma insulin and glucose levels were also significantly greater in MC4R (-/-) than in MC4R (+/-) and WT mice. These data suggest that despite obesity, visceral adiposity, hyperleptinemia, and hyperinsulinemia, MC4R (-/-) mice are neither hypertensive nor salt sensitive, indicating that a functional MC4R may be necessary for the development of hypertension associated with obesity and its metabolic abnormalities.
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Affiliation(s)
- Lakshmi S Tallam
- Department of Physiology and Biophysics, University of Mississippi Medical Center, 2500 N State St, Jackson, MS 39216-4505, USA.
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45
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Tao YX. Molecular mechanisms of the neural melanocortin receptor dysfunction in severe early onset obesity. Mol Cell Endocrinol 2005; 239:1-14. [PMID: 15975705 DOI: 10.1016/j.mce.2005.04.012] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Revised: 04/10/2005] [Accepted: 04/20/2005] [Indexed: 11/23/2022]
Abstract
The neural melanocortin receptors, melanocortin-3 and -4 receptors (MC3R and MC4R), have been shown to regulate different aspects of energy homeostasis in rodents. Human genetic studies showed that mutations in the MC4R gene are the most common monogenic form of obesity. Functional analyses of the mutant receptors revealed multiple defects. A classification scheme is presented for cataloguing the ever-increasing array of MC4R mutations. Functional analysis of the only inactivating MC3R mutation is also summarized. Insights from the analyses of the naturally occurring mutations in the MC3R and MC4R on the structure and function of these receptors are highlighted.
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Affiliation(s)
- Ya-Xiong Tao
- Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, AL 36849, USA.
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Cone RD. Anatomy and regulation of the central melanocortin system. Nat Neurosci 2005; 8:571-8. [PMID: 15856065 DOI: 10.1038/nn1455] [Citation(s) in RCA: 1087] [Impact Index Per Article: 57.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Accepted: 03/15/2005] [Indexed: 12/12/2022]
Abstract
The central melanocortin system is perhaps the best-characterized neuronal pathway involved in the regulation of energy homeostasis. This collection of circuits is unique in having the capability of sensing signals from a staggering array of hormones, nutrients and afferent neural inputs. It is likely to be involved in integrating long-term adipostatic signals from leptin and insulin, primarily received by the hypothalamus, with acute signals regulating hunger and satiety, primarily received by the brainstem. The system is also unique from a regulatory point of view in that it is composed of fibers expressing both agonists and antagonists of melanocortin receptors. Given that the central melanocortin system is an active target for development of drugs for the treatment of obesity, diabetes and cachexia, it is important to understand the system in its full complexity, including the likelihood that the system also regulates the cardiovascular and reproductive systems.
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Affiliation(s)
- Roger D Cone
- Vollum Institute and the Center for the Study of Weight Regulation, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA.
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Meneton P, Jeunemaitre X, de Wardener HE, MacGregor GA. Links between dietary salt intake, renal salt handling, blood pressure, and cardiovascular diseases. Physiol Rev 2005; 85:679-715. [PMID: 15788708 DOI: 10.1152/physrev.00056.2003] [Citation(s) in RCA: 447] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Epidemiological, migration, intervention, and genetic studies in humans and animals provide very strong evidence of a causal link between high salt intake and high blood pressure. The mechanisms by which dietary salt increases arterial pressure are not fully understood, but they seem related to the inability of the kidneys to excrete large amounts of salt. From an evolutionary viewpoint, the human species is adapted to ingest and excrete <1 g of salt per day, at least 10 times less than the average values currently observed in industrialized and urbanized countries. Independent of the rise in blood pressure, dietary salt also increases cardiac left ventricular mass, arterial thickness and stiffness, the incidence of strokes, and the severity of cardiac failure. Thus chronic exposure to a high-salt diet appears to be a major factor involved in the frequent occurrence of hypertension and cardiovascular diseases in human populations.
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Affiliation(s)
- Pierre Meneton
- Institut National de la Santé et de la Recherche Médicale U367, Département de Santé Publique et d'Informatique Médicale, Faculté de Médecine Broussais Hôtel Dieu, Paris, France.
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Humphreys MH. Gamma-MSH, sodium metabolism, and salt-sensitive hypertension. Am J Physiol Regul Integr Comp Physiol 2004; 286:R417-30. [PMID: 14761863 DOI: 10.1152/ajpregu.00365.2003] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Alpha-, beta-, and gamma-melanocyte stimulating hormones (MSHs) are melanotropin peptides that are derived from the ACTH/beta-endorphin prohormone proopiomelanocortin (POMC). They have been highly conserved through evolutionary development, although their functions in mammals have remained obscure. The identification in the last decade of a family of five membrane-spanning melanocortin receptors (MC-Rs), for which the melanotropins are the natural ligands, has permitted the characterization of a number of important actions of these peptides, although the physiological function(s) of gamma-MSH have remained elusive. Much evidence indicates that gamma-MSH stimulates sympathetic outflow and raises blood pressure through a central mechanism. However, this review focuses on newer cardiovascular and renal actions of the peptide, acting in most cases through the MC3-R. In rodents, a high-sodium diet (HSD) increases the pituitary abundance of POMC mRNA and of gamma-MSH content and results in a doubling of plasma gamma-MSH concentration. The peptide is natriuretic and acts through renal MC3-Rs, which are also upregulated by the HSD. Thus the system appears designed to participate in the integrated response to dietary sodium excess. Genetic or pharmacologic induction of gamma-MSH deficiency results in marked salt-sensitive hypertension that is corrected by the administration of the peptide, probably through a central site of action. Deletion of the MC3-R also produces salt-sensitive hypertension, which, however, is not corrected by infusion of the hormone. These observations in aggregate suggest the operation of a hormonal system important in blood pressure control and in the regulation of sodium excretion. The relationship of these two actions to each other and the significance of this system in humans are important questions for future research.
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Affiliation(s)
- Michael H Humphreys
- Division of Nephrology, San Francisco General Hospital, San Francisco, California 94143, USA.
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Affiliation(s)
- Gunter Wolf
- Department of Medicine, Division of Nephrology, Rheumatology and Osteology, University of Hamburg, University Hospital Eppendorf, Pavilion N26, Martinistrasse 52, D-20246 Hamburg, Germany.
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Mayan H, Ni XP, Almog S, Humphreys MH. Suppression of gamma-melanocyte-stimulating hormone secretion is accompanied by salt-sensitive hypertension in the rat. Hypertension 2003; 42:962-7. [PMID: 14568996 DOI: 10.1161/01.hyp.0000097601.83235.f8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Gamma-melanocyte-stimulating hormone (gamma-MSH) is a natriuretic peptide derived from proopiomelanocortin (POMC) in the pituitary neurointermediate lobe (NIL); its plasma concentration in rats doubles after ingestion of a high (HSD; 8% NaCl) compared with a low sodium diet (LSD; 0.07%). Because NIL function is regulated through dopaminergic pathways, we asked whether dopaminergic stimulation with bromocriptine (5 mg/kg IP daily for 1 week) or inhibition with haloperidol (5 mg/kg IP for 1 week) alters the gamma-MSH response to a HSD. In vehicle-treated rats, plasma gamma-MSH and NIL gamma-MSH content on the HSD were both markedly elevated over values in rats on the LSD (P<0.001); no difference in mean arterial pressure (MAP) occurred. In haloperidol-treated rats on the LSD, both plasma gamma-MSH and NIL gamma-MSH content were greater than in vehicle-treated rats (P<0.05) and did not increase further on the HSD; MAP was also no different. In bromocriptine-treated rats, neither plasma gamma-MSH nor NIL gamma-MSH content increased on the HSD versus LSD, and MAP was markedly elevated on the HSD (132+/-3 versus 106+/-3 mm Hg, P<0.001). Intravenous infusion of gamma-MSH (0.4 pmol/min) to bromocriptine-treated rats on the HSD restored plasma gamma-MSH concentration to a level appropriate for the HSD and lowered MAP from 131+/-6 to 108+/-5 mm Hg (P<0.01). These results demonstrate that the increases in NIL content and plasma concentration of gamma-MSH normally occurring during ingestion of the HSD are prevented by dopaminergic suppression of NIL function. This results in deficiency of gamma-MSH on the HSD and is accompanied by elevated blood pressure, which is corrected by infusion of the peptide. gamma-MSH may be an important component in the normal response to a HSD; interruption of this response leads to salt-sensitive hypertension.
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Affiliation(s)
- Haim Mayan
- Institute of Clinical Pharmacology and Toxicology, Chaim Sheba Medical Center, Tel-Aviv University, Israel
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