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      A 2 Adenosine Receptors Mediate Whole-Body Insulin Sensitivity in a Prediabetes Animal Model: Primary Effects on Skeletal Muscle

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          Abstract

          Epidemiological studies showed that chronic caffeine intake decreased the risk of type 2 diabetes. Previously, we described that chronic caffeine intake prevents and reverses insulin resistance induced by hypercaloric diets and aging, in rats. Caffeine has several cellular mechanisms of action, being the antagonism of adenosine receptors the only attained with human coffee consumption. Here, we investigated the subtypes of adenosine receptors involved on the effects of chronic caffeine intake on insulin sensitivity and the mechanisms and sex differences behind this effect. Experiments were performed in male and female Wistar rats fed either a chow or high-sucrose (HSu) diet (35% of sucrose in drinking water) during 28 days, to induce insulin resistance. In the last 15 days of diet the animals were submitted to DPCPX (A 1 antagonist, 0.4 mg/kg), SCH58261 (A 2A antagonist, 0.5 mg/kg), or MRS1754 (A 2B antagonist, 9.5 μg/kg) administration. Insulin sensitivity, fasting glycaemia, blood pressure, catecholamines, and fat depots were assessed. Expression of A 1, A 2A, A 2B adenosine receptors and protein involved in insulin signaling pathways were evaluated in the liver, skeletal muscle, and visceral adipose tissue. UCP1 expression was measured in adipose tissue. Paradoxically, SCH58261 and MRS1754 decreased insulin sensitivity in control animals, whereas they both improved insulin response in HSu diet animals. DPCPX did not alter significantly insulin sensitivity in control or HSu animals, but reversed the increase in total and visceral fat induced by the HSu diet. In skeletal muscle, A 1, A 2A, and A 2B adenosine receptor expression were increased in HSu group, an effect that was restored by SCH58261 and MRS1754. In the liver, A 1, A 2A expression was increased in HSu group, while A 2B expression was decreased, being this last effect reversed by administration of MRS1754. In adipose tissue, A 1 and A 2A block upregulated the expression of these receptors. A 2 adenosine antagonists restored impaired insulin signaling in the skeletal muscle of HSu rats, but did not affect liver or adipose insulin signaling. Our results show that adenosine receptors exert opposite effects on insulin sensitivity, in control and insulin resistant states and strongly suggest that A 2 adenosine receptors in the skeletal muscle are the majors responsible for whole-body insulin sensitivity.

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          Most cited references 49

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          Global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013: a systematic analysis for the Global Burden of Disease Study 2013.

          In 2010, overweight and obesity were estimated to cause 3·4 million deaths, 3·9% of years of life lost, and 3·8% of disability-adjusted life-years (DALYs) worldwide. The rise in obesity has led to widespread calls for regular monitoring of changes in overweight and obesity prevalence in all populations. Comparable, up-to-date information about levels and trends is essential to quantify population health effects and to prompt decision makers to prioritise action. We estimate the global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013. We systematically identified surveys, reports, and published studies (n=1769) that included data for height and weight, both through physical measurements and self-reports. We used mixed effects linear regression to correct for bias in self-reports. We obtained data for prevalence of obesity and overweight by age, sex, country, and year (n=19,244) with a spatiotemporal Gaussian process regression model to estimate prevalence with 95% uncertainty intervals (UIs). Worldwide, the proportion of adults with a body-mass index (BMI) of 25 kg/m(2) or greater increased between 1980 and 2013 from 28·8% (95% UI 28·4-29·3) to 36·9% (36·3-37·4) in men, and from 29·8% (29·3-30·2) to 38·0% (37·5-38·5) in women. Prevalence has increased substantially in children and adolescents in developed countries; 23·8% (22·9-24·7) of boys and 22·6% (21·7-23·6) of girls were overweight or obese in 2013. The prevalence of overweight and obesity has also increased in children and adolescents in developing countries, from 8·1% (7·7-8·6) to 12·9% (12·3-13·5) in 2013 for boys and from 8·4% (8·1-8·8) to 13·4% (13·0-13·9) in girls. In adults, estimated prevalence of obesity exceeded 50% in men in Tonga and in women in Kuwait, Kiribati, Federated States of Micronesia, Libya, Qatar, Tonga, and Samoa. Since 2006, the increase in adult obesity in developed countries has slowed down. Because of the established health risks and substantial increases in prevalence, obesity has become a major global health challenge. Not only is obesity increasing, but no national success stories have been reported in the past 33 years. Urgent global action and leadership is needed to help countries to more effectively intervene. Bill & Melinda Gates Foundation. Copyright © 2014 Elsevier Ltd. All rights reserved.
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            Adenosine activates brown adipose tissue and recruits beige adipocytes via A2A receptors.

            Brown adipose tissue (BAT) is specialized in energy expenditure, making it a potential target for anti-obesity therapies. Following exposure to cold, BAT is activated by the sympathetic nervous system with concomitant release of catecholamines and activation of β-adrenergic receptors. Because BAT therapies based on cold exposure or β-adrenergic agonists are clinically not feasible, alternative strategies must be explored. Purinergic co-transmission might be involved in sympathetic control of BAT and previous studies reported inhibitory effects of the purinergic transmitter adenosine in BAT from hamster or rat. However, the role of adenosine in human BAT is unknown. Here we show that adenosine activates human and murine brown adipocytes at low nanomolar concentrations. Adenosine is released in BAT during stimulation of sympathetic nerves as well as from brown adipocytes. The adenosine A2A receptor is the most abundant adenosine receptor in human and murine BAT. Pharmacological blockade or genetic loss of A2A receptors in mice causes a decrease in BAT-dependent thermogenesis, whereas treatment with A2A agonists significantly increases energy expenditure. Moreover, pharmacological stimulation of A2A receptors or injection of lentiviral vectors expressing the A2A receptor into white fat induces brown-like cells-so-called beige adipocytes. Importantly, mice fed a high-fat diet and treated with an A2A agonist are leaner with improved glucose tolerance. Taken together, our results demonstrate that adenosine-A2A signalling plays an unexpected physiological role in sympathetic BAT activation and protects mice from diet-induced obesity. Those findings reveal new possibilities for developing novel obesity therapies.
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              Relevance of Sympathetic Nervous System Activation in Obesity and Metabolic Syndrome

              Sympathetic tone is well recognised as being implicit in cardiovascular control. It is less readily acknowledged that activation of the sympathetic nervous system is integral in energy homeostasis and can exert profound metabolic effects. Accumulating data from animal and human studies suggest that central sympathetic overactivity plays a pivotal role in the aetiology and complications of several metabolic conditions that can cluster to form the Metabolic Syndrome (MetS). Given the known augmented risk for type 2 diabetes, cardiovascular disease, and premature mortality associated with the MetS understanding the complex pathways underlying the metabolic derangements involved has become a priority. Many factors have been proposed to contribute to increased sympathetic nerve activity in metabolic abnormalities including obesity, impaired baroreflex sensitivity, hyperinsulinemia, and elevated adipokine levels. Furthermore there is mounting evidence to suggest that chronic sympathetic overactivity can potentiate two of the key metabolic alterations of the MetS, central obesity and insulin resistance. This review will discuss the regulatory role of the sympathetic nervous system in metabolic control and the proposed pathophysiology linking sympathetic overactivity to metabolic abnormalities. Pharmacological and device-based approaches that target central sympathetic drive will also be discussed as possible therapeutic options to improve metabolic control in at-risk patient cohorts.
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                Author and article information

                Contributors
                Journal
                Front Endocrinol (Lausanne)
                Front Endocrinol (Lausanne)
                Front. Endocrinol.
                Frontiers in Endocrinology
                Frontiers Media S.A.
                1664-2392
                28 April 2020
                2020
                : 11
                Affiliations
                1CEDOC, NOVA Medical School, Faculdade de Ciências Médicas, Universidade Nova de Lisboa , Lisbon, Portugal
                2Faculty of Medicine, Institute of Physiology and Institute of Clinical and Biomedical Investigation of Coimbra (iCBR), University of Coimbra , Coimbra, Portugal
                3Escola Superior de Tecnologia da Saúde, Departmento de Ciências Complementares, Instituto Politécnico de Coimbra , Coimbra, Portugal
                4Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, CSIC, Ciber de Enfermedades Respiratorias, CIBERES, Instituto de Biología y Genética Molecular, Instituto de Salud Carlos III, Universidad de Valladolid , Valladolid, Spain
                Author notes

                Edited by: Carolyn Mary Ecelbarger, Georgetown University, United States

                Reviewed by: Xavier Prieur, INSERM U1087 l'Unité de Recherche de l'Institut du Thorax, France; Anne-Francoise Burnol, INSERM U1016 Institut Cochin, France

                *Correspondence: Silvia V. Conde silvia.conde@ 123456nms.unl.pt

                This article was submitted to Diabetes: Molecular Mechanisms, a section of the journal Frontiers in Endocrinology

                Article
                10.3389/fendo.2020.00262
                7198774
                Copyright © 2020 Sacramento, Martins, Rodrigues, Matafome, Ribeiro, Olea and Conde.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                Page count
                Figures: 7, Tables: 3, Equations: 0, References: 57, Pages: 16, Words: 10574
                Categories
                Endocrinology
                Original Research

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