We previously showed that leucine deprivation decreases abdominal fat mass largely by increasing energy expenditure, as demonstrated by increased lipolysis in white adipose tissue (WAT) and uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT). The goal of the present study was to investigate the possible involvement of central nervous system (CNS) in this regulation and elucidate underlying molecular mechanisms. For this purpose, levels of genes and proteins related to lipolysis in WAT and UCP1 expression in BAT were analyzed in wild-type mice after intracerebroventricular administration of leucine or corticotrophin-releasing hormone antibodies, or in mice deleted for three β-adrenergic receptors, after being maintained on a leucine-deficient diet for 7 d. Here, we show that intracerebroventricular administration of leucine significantly attenuates abdominal fat loss and blocks activation of hormone sensitive lipase in WAT and induction of UCP1 in BAT in leucine-deprived mice. Furthermore, we provide evidence that leucine deprivation stimulates fat loss by increasing expression of corticotrophin-releasing hormone in the hypothalamus via activation of stimulatory G protein/cAMP/protein kinase A/cAMP response element-binding protein pathway. Finally, we show that the effect of leucine deprivation on fat loss is mediated by activation of the sympathetic nervous system. These results suggest that CNS plays an important role in regulating fat loss under leucine deprivation and thereby provide novel and important insights concerning the importance of CNS leucine in the regulation of energy homeostasis.

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It is well established that the central nervous system (CNS), especially the hypothalamus, plays an important role in regulating energy homeostasis and lipid metabolism. We have previously shown that hypothalamic corticotropin-releasing hormone (CRH) is critical for stimulating fat loss in response to dietary leucine deprivation. The molecular mechanisms underlying the CNS regulation of leucine deprivation–stimulated fat loss are, however, still largely unknown. Here, we used intracerebroventricular injection of adenoviral vectors to identify a novel role for hypothalamic p70 S6 kinase 1 (S6K1), a major downstream effector of the kinase mammalian target of rapamycin, in leucine deprivation stimulation of energy expenditure. Furthermore, we show that the effect of hypothalamic S6K1 is mediated by modulation of Crh expression in a melanocortin-4 receptor–dependent manner. Taken together, our studies provide a new perspective for understanding the regulation of energy expenditure by the CNS and the importance of cross-talk between nutritional control and regulation of endocrine signals.