Central Exercise Action Increases the AMPK and mTOR Response to Leptin Eduardo R. Ropelle., Maria Fernanda A. Fernandes., Marcelo B. S. Flores, Mirian Ueno, Silvana Rocco, Rodrigo Marin, Dennys E. Cintra, Lı´cio A. Velloso, Kleber G. Franchini, Mario J. A. Saad, Jose´ B. C. Carvalheira* Department of Internal Medicine, FCM, State University of Campinas (UNICAMP), Campinas, Sa˜o Paulo, Brazil Abstract AMP-activated protein kinase (AMPK) and mammalian Target of Rapamycin (mTOR) are key regulators of cellular energy balance and of the effects of leptin on food intake. Acute exercise is associated with increased sensitivity to the effects of leptin on food intake in an IL-6-dependent manner. To determine whether exercise ameliorates the AMPK and mTOR response to leptin in the hypothalamus in an IL-6-dependent manner, rats performed two 3-h exercise bouts, separated by one 45-min rest period. Intracerebroventricular IL-6 infusion reduced food intake and pretreatment with AMPK activators and mTOR inhibitor prevented IL-6-induced anorexia. Activators of AMPK and fasting increased food intake in control rats to a greater extent than that observed in exercised ones, whereas inhibitor of AMPK had the opposite effect. Furthermore, the reduction of AMPK and ACC phosphorylation and increase in phosphorylation of proteins involved in mTOR signal transduction, observed in the hypothalamus after leptin infusion, were more pronounced in both lean and diet-induced obesity rats after acute exercise. Treatment with leptin reduced food intake in exercised rats that were pretreated with vehicle, although no increase in responsiveness to leptin-induced anorexia after pretreatment with anti-IL6 antibody, AICAR or Rapamycin was detected. Thus, the effects of leptin on the AMPK/mTOR pathway, potentiated by acute exercise, may contribute to appetite suppressive actions in the hypothalamus. Citation: Ropelle ER, Fernandes MFA, Flores MBS, Ueno M, Rocco S, et al. (2008) Central Exercise Action Increases the AMPK and mTOR Response to Leptin. PLoS ONE 3(12): e3856. doi:10.1371/journal.pone.0003856 Editor: Jose A. L. Calbet, University of Las Palmas de Gran Canaria, Spain Received August 7, 2008; Accepted November 6, 2008; Published December 4, 2008 Copyright: 2008 Ropelle et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: These studies were supported by grants from Fundaca˜o de Amparo a` Pesquisa do Estado de Sa˜o Paulo (FAPESP), Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de N´ıvel Superior (CAPES) and Conselho Nacional de desenvolvimento cient´ıfico e tecnolo´ gico (CNPq). Competing Interests: The authors have declared that no competing interests exist. * E-mail: carvalheirajbc@uol.com.br . These authors contributed equally to this work. Introduction Prolonged exercise of medium to high intensity is known to profoundly affect energy balance [1–3]. Studies of individuals who have maintained significant weight loss for .1 year have demonstrated that dieters who achieve long-term success are often those who engage in regular and extensive exercise programs [4]. Although the energy expenditure aspects of such exercise may contribute to the effects of weight maintenance, it has been suggested that exercise may also contribute to the energy balance by altering food intake [5,6]. Rodents submitted to exercise have increased sensitivity to leptin, conversely animals with diet-induced obesity and most obese humans are resistant to leptin [5,7,8]. Thus, the mechanism for leptin increased responsiveness in exercise is of great interest and understanding this mechanism could lead to new approaches to prevent or treat obesity. The hypothalamus plays a central role in integrating hormonal (leptin and insulin) and nutritional signals from the periphery and modulating food intake, energy expenditure, and peripheral metabolism [9]. Multiple factors control food intake, including hormones, fuels and behaviour. AMPK is the downstream component of a kinase cascade that acts as a sensor of cellular energy charge, being activated by rising AMP coupled with falling ATP. Once activated, AMPK phosphorylates acetyl-CoA carbox- ylase (ACC) and switches on energy-producing pathways at the expense of energy-depleting processes [10–12]. Another target molecule for the control of food intake and energy homeostasis is represented by the phosphoprotein mammalian target of rapamy- cin, mTOR, in which the PI(3)K/Akt pathway has been suggested to affect the mTOR phosphorylation state and catalytic activity [13]. Activated signaling through mTOR phosphorylates the serine/threonine kinase p70S6K and the translational repressor eukaryotic initiation factor (eIF) 4E binding protein (4EBP1) [14,15]. mTOR signaling is inhibited under conditions of low nutrients, such as glucose and amino acids and low intracellular ATP levels [16]. While mTOR was presumed to serve as the direct cellular sensor for ATP levels [17], mounting evidence has implicated AMPK in the regulation of mTOR activity [15,18–20]. The level of circulating interleukin-6 (IL-6) increases dramat- ically in response to exercise [21], with IL-6 being produced by working muscle [22,23] and adipose tissue [24,25] and its concentration correlates temporally with increases in AMPK in multiple tissues [26]. In addition, AMPK activity is diminished in IL-6 deficient mice at rest and the absolute increases in AMPK activity in these tissues caused by exercise is diminished compared with control mice [27]. It also appears that centrally-acting IL-6 plays a role in the regulation of appetite, energy expenditure, and body composition [5,28]. The signaling mechanism of IL-6 in the PLoS ONE | www.plosone.org 1 December 2008 | Volume 3 | Issue 12 | e3856