Insulin-Like Growth Factor I Couples Metabolism With Circadian Activity Through Hypothalamic Orexin Neurons

Uncoupling of metabolism and circadian activity is associated with an increased risk of various pathologies, including neurodegeneration. Recently, insulin and the closely related insulin-like growth factor I (IGF-I) were shown to entrain feeding patterns with circadian rhythms. Moreover, both hormones act centrally to modulate peripheral glucose metabolism; however, whereas central targets of insulin actions are intensely scrutinized, those mediating the actions of IGF-I remain undefined. We analyzed whether IGF-I targets orexin neurons in the lateral hypothalamus, as these neurons are involved in circadian rhythms and energy allocation, and are modulated by IGF-I. Mice with disrupted IGF-IR activity in orexin neurons show phase shifts in circadian feeding behavior, loss of circadian orexin expression, and gradually develop sex-dependent metabolic alterations. In addition, modulation by IGF-I of hepatic KLF transcription factors involved in peripheral glucose metabolism is mediated by orexin neurons. Thus, IGF-I entrains energy metabolism and circadian rhythms through hypothalamic orexin neurons.