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Liu Z, Hruby VJ. MC4R biased signalling and the conformational basis of biological function selections. J Cell Mol Med 2022; 26:4125-4136. [PMID: 35818295 PMCID: PMC9344818 DOI: 10.1111/jcmm.17441] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 05/26/2022] [Accepted: 06/01/2022] [Indexed: 11/30/2022] Open
Abstract
The MC4R, a GPCR, has long been a major target for obesity treatment. As the most well‐studied melanocortin receptor subtype, the evolutionary knowledge pushes the drug development and structure–activity relationship (SAR) moving forward. The past decades have witnessed the evolution of scientists' view on GPCRs gradually from the control of a single canonical signalling pathway via a bilateral ‘active‐inactive’ model to a multi‐state alternative model where the ligands' binding affects the selection of the downstream signalling. This evolution brings the concept of biased signalling and the beginning of the next generation of peptide drug development, with the aim of turning from receptor subtype specificity to signalling pathway selectivity. The determination of the value structures of the MC4R revealed insights into the working mechanism of MC4R activation upon binding of agonists. However, new challenge has risen as we seek to unravel the mystery of MC4R signalling selection. Thus, more biased agonists and ligands with representative biological functions are needed to solve the rest of the puzzle.
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Affiliation(s)
- Zekun Liu
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona, USA
| | - Victor J Hruby
- Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona, USA
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Akyuz E, Koklu B, Uner A, Angelopoulou E, Paudel YN. Envisioning the role of inwardly rectifying potassium (Kir) channel in epilepsy. J Neurosci Res 2021; 100:413-443. [PMID: 34713909 DOI: 10.1002/jnr.24985] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2021] [Revised: 09/23/2021] [Accepted: 10/01/2021] [Indexed: 01/29/2023]
Abstract
Epilepsy is a devastating neurological disorder characterized by recurrent seizures attributed to the disruption of the dynamic excitatory and inhibitory balance in the brain. Epilepsy has emerged as a global health concern affecting about 70 million people worldwide. Despite recent advances in pre-clinical and clinical research, its etiopathogenesis remains obscure, and there are still no treatment strategies modifying disease progression. Although the precise molecular mechanisms underlying epileptogenesis have not been clarified yet, the role of ion channels as regulators of cellular excitability has increasingly gained attention. In this regard, emerging evidence highlights the potential implication of inwardly rectifying potassium (Kir) channels in epileptogenesis. Kir channels consist of seven different subfamilies (Kir1-Kir7), and they are highly expressed in both neuronal and glial cells in the central nervous system. These channels control the cell volume and excitability. In this review, we discuss preclinical and clinical evidence on the role of the several subfamilies of Kir channels in epileptogenesis, aiming to shed more light on the pathogenesis of this disorder and pave the way for future novel therapeutic approaches.
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Affiliation(s)
- Enes Akyuz
- Faculty of International Medicine, Department of Biophysics, University of Health Sciences, Istanbul, Turkey
| | - Betul Koklu
- Faculty of Medicine, Namık Kemal University, Tekirdağ, Turkey
| | - Arda Uner
- Faculty of Medicine, Yozgat Bozok University, Yozgat, Turkey
| | - Efthalia Angelopoulou
- Department of Biological Chemistry, Medical School, National and Kapodistrian University of Athens, Athens, Greece
| | - Yam Nath Paudel
- Neuropharmacology Research Strength, Jeffrey Cheah School of Medicine and Health Sciences, Monash University Malaysia, Bandar Sunway, Malaysia
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Ge WR, Wan L, Yang G. Melatonin for an obese child with MC4R gene variant showing epilepsy and disordered sleep: A case report. World J Clin Cases 2021; 9:2688-2695. [PMID: 33889637 PMCID: PMC8040176 DOI: 10.12998/wjcc.v9.i11.2688] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/18/2021] [Accepted: 02/01/2021] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Abnormalities in the melanocortin receptor 4 (MC4R) gene often lead to obesity, but are rarely associated with other conditions such as epilepsy and sleep disorder.
CASE SUMMARY Here, we present a case of a male obese child with a heterozygous variant in MC4R (c.494G>A, p.Arg165Gln) inherited from his father, who presented with disordered sleep and abnormal facial movements. Examination through melatonin rhythm testing and electroencephalography led to a diagnosis of sleep disorder and epilepsy, as his melatonin rhythm was markedly distorted and the electroencephalography revealed epileptic discharges. He received treatment with an antiepileptic drug; however, the therapy was ineffective and the sleep disorder appeared to be deteriorating. Subsequently, we initiated adjuvant treatment with melatonin. Upon re-examination, his body mass index had decreased, the sleep disturbance had resolved, and his seizures were well controlled. Electro-encephalography review was normal, and a typical melatonin rhythm was restored.
CONCLUSION We concluded that, in addition to causing obesity, abnormalities in the MC4R gene may contribute to the development of sleep disorders and epilepsy, and that melatonin can be used as an adjuvant therapy to alleviate these symptoms.
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Affiliation(s)
- Wen-Rong Ge
- Department of Pediatrics, Beijing Friendship Hospital, Capital Medical University, Beijing 100000, China
| | - Lin Wan
- Department of Pediatrics, The First Medical Center of Chinese PLA General Hospital, Beijing 100853, China
| | - Guang Yang
- Department of Pediatrics, The First Medical Center of Chinese PLA General Hospital, Beijing 100853, China
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da Silva AA, do Carmo JM, Wang Z, Hall JE. Melanocortin-4 Receptors and Sympathetic Nervous System Activation in Hypertension. Curr Hypertens Rep 2019; 21:46. [PMID: 31028563 DOI: 10.1007/s11906-019-0951-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
PURPOSE OF REVIEW To highlight the role of the brain melanocortin 4 receptor (MC4R) for sympathetic nervous system (SNS) activation in hypertension. RECENT FINDINGS Hypertension is the most significant risk factor for developing cardiovascular disease. Although excess weight gain is associated with at least two thirds of primary hypertension cases, the pathophysiological mechanisms involved remain the subject of intense investigation. Multiple studies demonstrate an important role for increased sympathetic nervous system (SNS) activity in development and maintenance of hypertension, and that the brain MC4R modulates SNS activity to thermogenic, cardiovascular, and kidney tissues. These studies also support the concept that MC4R activation is critical for obesity-induced hypertension as well as other forms of hypertension associated with increased SNS activity. MC4R is a potential target for antiobesity therapy, although there are challenges in using MC4R agonists to induce weight loss without evoking increases in SNS activity.
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Affiliation(s)
- Alexandre A da Silva
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, and Cardiovascular-Renal Research Center, The University of Mississippi Medical Center, 2500 North State St., Jackson, MS, 39216-4505, USA.
| | - Jussara M do Carmo
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, and Cardiovascular-Renal Research Center, The University of Mississippi Medical Center, 2500 North State St., Jackson, MS, 39216-4505, USA
| | - Zhen Wang
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, and Cardiovascular-Renal Research Center, The University of Mississippi Medical Center, 2500 North State St., Jackson, MS, 39216-4505, USA
| | - John E Hall
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, and Cardiovascular-Renal Research Center, The University of Mississippi Medical Center, 2500 North State St., Jackson, MS, 39216-4505, USA
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Baldini G, Phelan KD. The melanocortin pathway and control of appetite-progress and therapeutic implications. J Endocrinol 2019; 241:R1-R33. [PMID: 30812013 PMCID: PMC6500576 DOI: 10.1530/joe-18-0596] [Citation(s) in RCA: 114] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 01/22/2019] [Indexed: 12/19/2022]
Abstract
The initial discovery that ob/ob mice become obese because of a recessive mutation of the leptin gene has been crucial to discover the melanocortin pathway to control appetite. In the melanocortin pathway, the fed state is signaled by abundance of circulating hormones such as leptin and insulin, which bind to receptors expressed at the surface of pro-opiomelanocortin (POMC) neurons to promote processing of POMC to the mature hormone α-melanocyte-stimulating hormone (α-MSH). The α-MSH released by POMC neurons then signals to decrease energy intake by binding to melanocortin-4 receptor (MC4R) expressed by MC4R neurons to the paraventricular nucleus (PVN). Conversely, in the 'starved state' activity of agouti-related neuropeptide (AgRP) and of neuropeptide Y (NPY)-expressing neurons is increased by decreased levels of circulating leptin and insulin and by the orexigenic hormone ghrelin to promote food intake. This initial understanding of the melanocortin pathway has recently been implemented by the description of the complex neuronal circuit that controls the activity of POMC, AgRP/NPY and MC4R neurons and downstream signaling by these neurons. This review summarizes the progress done on the melanocortin pathway and describes how obesity alters this pathway to disrupt energy homeostasis. We also describe progress on how leptin and insulin receptors signal in POMC neurons, how MC4R signals and how altered expression and traffic of MC4R change the acute signaling and desensitization properties of the receptor. We also describe how the discovery of the melanocortin pathway has led to the use of melanocortin agonists to treat obesity derived from genetic disorders.
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Affiliation(s)
- Giulia Baldini
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
| | - Kevin D. Phelan
- Department of Neurobiology & Developmental Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
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Anderson EJP, Ghamari-Langroudi M, Cakir I, Litt MJ, Chen V, Reggiardo RE, Millhauser GL, Cone RD. Late onset obesity in mice with targeted deletion of potassium inward rectifier Kir7.1 from cells expressing the melanocortin-4 receptor. J Neuroendocrinol 2019; 31:e12670. [PMID: 30561082 PMCID: PMC6533113 DOI: 10.1111/jne.12670] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 11/21/2018] [Accepted: 12/11/2018] [Indexed: 01/01/2023]
Abstract
Energy stores in fat tissue are determined in part by the activity of hypothalamic neurones expressing the melanocortin-4 receptor (MC4R). Even a partial reduction in MC4R expression levels in mice, rats or humans produces hyperphagia and morbid obesity. Thus, it is of great interest to understand the molecular basis of neuromodulation by the MC4R. The MC4R is a G protein-coupled receptor that signals efficiently through GαS , and this signalling pathway is essential for normal MC4R function in vivo. However, previous data from hypothalamic slice preparations indicated that activation of the MC4R depolarised neurones via G protein-independent regulation of the ion channel Kir7.1. In the present study, we show that deletion of Kcnj13 (ie, the gene encoding Kir7.1) specifically from MC4R neurones produced resistance to melanocortin peptide-induced depolarisation of MC4R paraventricular nucleus neurones in brain slices, resistance to the sustained anorexic effect of exogenously administered melanocortin peptides, late onset obesity, increased linear growth and glucose intolerance. Some MC4R-mediated phenotypes appeared intact, including Agouti-related peptide-induced stimulation of food intake and MC4R-mediated induction of peptide YY release from intestinal L cells. Thus, a subset of the consequences of MC4R signalling in vivo appears to be dependent on expression of the Kir7.1 channel in MC4R cells.
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Affiliation(s)
- E. J. P. Anderson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - M. Ghamari-Langroudi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - I. Cakir
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan
| | - M. J. Litt
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Valerie Chen
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California
| | - Roman E. Reggiardo
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California
| | - Glenn L. Millhauser
- Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California
| | - R. D. Cone
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan
- Department of Molecular and Integrative Pharmacology, School of Medicine, University of Michigan, Ann Arbor, Michigan
- Correspondence: Roger D. Cone, Life Sciences Institute, 210 Washtenaw Ave., Ann Arbor, MI 48109,
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