ORIGINAL PAPER Journal of Pathology J Pathol 2012; 227: 209–222 Published online 17 February 2012 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/path.3984 Hypothalamic mTOR pathway mediates thyroid hormone-induced hyperphagia in hyperthyroidism Luis Varela, 1,2# Noelia Mart´ ınez-S´ anchez, 1,2# Rosal´ ıa Gallego, 3# Mar´ ıa J V´ azquez, 1,2 Juan Roa, 2,4,5 Marina G´ andara, 3 Erik Schoenmakers, 6 Rub´ en Nogueiras, 1,2 Krishna Chatterjee, 6 Manuel Tena-Sempere, 2,4,5 Carlos Di´ eguez 1,2 and Miguel L´ opez 1,2 * 1 Department of Physiology, School of Medicine–CIMUS, University of Santiago de Compostela, Instituto de Investigaci´ on Sanitaria, Santiago de Compostela (A Coru˜ na) 15782, Spain 2 CIBER Fisiopatolog´ ıa de la Obesidad y Nutrici´ on (CIBERobn), 15706, Spain 3 Department of Morphological Sciences, School of Medicine, University of Santiago de Compostela, 15782, Spain 4 Department of Cell Biology, Physiology and Immunology, University of C´ ordoba, 14004, Spain 5 Instituto Maim´ onides de Investigaciones Biom´ edicas (IMIBIC), 14004 C´ ordoba, Spain 6 Institute of Metabolic Science, Metabolic Research Laboratories, Addenbrooke’s Hospital, University of Cambridge, Cambridge CB2 0QQ, UK *Correspondence to: Miguel L´ opez, Department of Physiology, School of Medicine, University of Santiago de Compostela, Instituto de Investigaci´ on Sanitaria, Santiago de Compostela (A Coru˜ na), 15782, Spain. e-mail: m.lopez@usc.es # These authors contributed equally to this study. Abstract Hyperthyroidism is characterized in rats by increased energy expenditure and marked hyperphagia. Alterations of thermogenesis linked to hyperthyroidism are associated with dysregulation of hypothalamic AMPK and fatty acid metabolism; however, the central mechanisms mediating hyperthyroidism-induced hyperphagia remain largely unclear. Here, we demonstrate that hyperthyroid rats exhibit marked up-regulation of the hypothalamic mammalian target of rapamycin (mTOR) signalling pathway associated with increased mRNA levels of agouti- related protein (AgRP ) and neuropeptide Y (NPY ), and decreased mRNA levels of pro-opiomelanocortin (POMC ) in the arcuate nucleus of the hypothalamus (ARC), an area where mTOR co-localizes with thyroid hormone receptor-α (TRα). Central administration of thyroid hormone (T3) or genetic activation of thyroid hormone signalling in the ARC recapitulated hyperthyroidism effects on feeding and the mTOR pathway. In turn, central inhibition of mTOR signalling with rapamycin in hyperthyroid rats reversed hyperphagia and normalized the expression of ARC-derived neuropeptides, resulting in substantial body weight loss. The data indicate that in the hyperthyroid state, increased feeding is associated with thyroid hormone-induced up-regulation of mTOR signalling. Furthermore, our findings that different neuronal modulations influence food intake and energy expenditure in hyperthyroidism pave the way for a more rational design of specific and selective therapeutic compounds aimed at reversing the metabolic consequences of this disease. Copyright  2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. Keywords: AMPK; energy balance; food intake; hyperthyroidism; hypothalamus; mTOR Received 2 July 2011; Revised 15 December 2011; Accepted 22 December 2011 No conflicts of interest were declared. Introduction The thyroid axis plays an important role in the con- trol of energy homeostasis [1,2]. Alterations in thy- roid function are associated with a large variety of symptoms, including changes in body weight and food intake in humans and rodents. Weight loss is present in 85% of patients with thyrotoxicosis and hyperpha- gia is observed in 65% of hyperthyroid patients [3]. Similarly, hyperthyroid rats display a hyperphagic phe- notype and a marked decrease in body weight [2,4–6]. Despite all this evidence, the hypothalamic mecha- nisms mediating hyperthyroidism-induced increase in feeding remain unclear. Mammalian target of rapamycin (mTOR) is an evolutionarily conserved serine–threonine kinase that modulates cell-cycle progression and growth by sens- ing changes in energy balance, growth factors, nutri- ents and oxygen [7,8]. mTOR is a component of at least two multi-protein complexes: mTOR com- plex 1 (mTORC1) and mTOR complex 2 (mTORC2) [9]. Whereas mTORC2 regulates phosphorylation of Akt/PKB [10], mTORC1 phosphorylates and modu- lates the activity of the serine/threonine ribosomal pro- tein S6 kinase 1 (S6K1), 4E binding protein 1 (4EBP1) and the eukaryotic initiation factor-4G (eiF4G). In turn, S6K1 phosphorylates and activates S6, a ribosomal protein involved in translation [9]. mTOR signalling is inhibited under low nutrient conditions, such as decreased levels of glucose and amino acids (especially leucine) [11,12] and low intracellular ATP levels [7]. On the other hand, elevated cellular ATP levels increase mTOR signalling [7]; thus, mTOR serves as a cellular Copyright  2012 Pathological Society of Great Britain and Ireland. J Pathol 2012; 227: 209–222 Published by John Wiley & Sons, Ltd. www.pathsoc.org.uk www.thejournalofpathology.com