1 Scientific RepoRts | 6:23673 | DOI: 10.1038/srep23673 www.nature.com/scientificreports Ghrelin Regulates Glucose and Glutamate transporters in Hypothalamic Astrocytes esther Fuente-Martín 1,† , Cristina García-Cáceres 1,‡ , pilar Argente-Arizón 1 , Francisca Díaz 1 , Miriam Granado 1 , Alejandra Freire-Regatillo 1 , David Castro-González 1 , María L. Ceballos 2 , Laura M. Frago 1 , suzanne L. Dickson 3 , Jesús Argente 1 & Julie A. Chowen 1 Hypothalamic astrocytes can respond to metabolic signals, such as leptin and insulin, to modulate adjacent neuronal circuits and systemic metabolism. Ghrelin regulates appetite, adiposity and glucose metabolism, but little is known regarding the response of astrocytes to this orexigenic hormone. We have used both in vivo and in vitro approaches to demonstrate that acylated ghrelin (acyl-ghrelin) rapidly stimulates glutamate transporter expression and glutamate uptake by astrocytes. Moreover, acyl-ghrelin rapidly reduces glucose transporter (GLUT) 2 levels and glucose uptake by these glial cells. Glutamine synthetase and lactate dehydrogenase decrease, while glycogen phosphorylase and lactate transporters increase in response to acyl-ghrelin, suggesting a change in glutamate and glucose metabolism, as well as glycogen storage by astrocytes. These efects are partially mediated through ghrelin receptor 1A (GHSR-1A) as astrocytes do not respond equally to desacyl-ghrelin, an isoform that does not activate GHSR-1A. Moreover, primary astrocyte cultures from GHSR-1A knock-out mice do not change glutamate transporter or GLUT2 levels in response to acyl-ghrelin. Our results indicate that acyl- ghrelin may mediate part of its metabolic actions through modulation of hypothalamic astrocytes and that this efect could involve astrocyte mediated changes in local glucose and glutamate metabolism that alter the signals/nutrients reaching neighboring neurons. Te coordination of energy intake and expenditure is a complex process that is infuenced by both peripheral and central signals that ultimately regulate body weight and glucose homeostasis. Our understanding of the neuronal circuits controlling energy balance and metabolism has advanced considerably; however, it is only recently that glial cells have been recognized as important protagonists in this neuroendocrine process. Activation of hypo- thalamic microglia and astrocytes in response to high fat diet (HFD)-induced weight gain is accompanied by increased glial production of cytokines and activation of infammatory signaling pathways in the hypothalamus 1–6 which is suggested to promote central insulin/leptin resistance and metabolic disequilibrium 7 . Tis infammatory process can be directly triggered by nutrients such as free fatty acids 8 , while circulating metabolic factors such as the anti-obesity hormone, leptin, can also activate glial cells 2–5,9 . Evidence has accumulated to substantiate an important role for glial cells in pathological responses to excess weight gain 1–4,9 , but their participation in the physiological control of metabolism is less well understood. Hypothalamic astrocytes express receptors for numerous hormones involved in metabolic control, including adipostatic hormones such as leptin, but also obesity-promoting hormones such as ghrelin 6,10 . Leptin afects hypothalamic astrocyte morphology and their capacity to capture glucose and glutamate 4,5,9 and the loss of leptin receptors specifcally in astrocytes reduces the physiological anorexigenic response to this hormone and modifes the response to fasting and the appetite stimulating efect of ghrelin 9 , indicating the physiological importance of 1 Hospital infantil Universitario niño Jesús, Department of endocrinology, instituto de investigación La Princesa, University Autónoma of Madrid and centro de investigación Biomédica en Red (ciBeR) de la fisiopatología de la Obesidad y nutrición (ciBeROBn), instituto de Salud carlos iii, Madrid, Spain. 2 instituto cajal, Dept. of cellular, Molecular and Developmental neurobiology, and ciBeRneD, cSic, Madrid, Spain. 3 Dept. Physiology/endocrine, the Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden. † Present address: Pancreatic islet Development and Regeneration Unit, Department of Stem cells, cABiMeR-Andalusian center for Molecular Biology and Regenerative Medicine, Seville, Spain. ‡ Present address: Helmholtz Diabetes center, Helmholtz Zentrum München, 85764 Neuherberg, Germany. Correspondence and requests for materials should be addressed to J.A.C. (email: julieann.chowen@salud.madrid.org) Received: 26 November 2015 Accepted: 07 March 2016 Published: 30 March 2016 OPEN