RESUMO
Irs2-mediated insulin/IGF1 signaling in the CNS modulates energy balance and glucose homeostasis; however, the site for Irs2 function is unknown. The hormone leptin mediates energy balance by acting on leptin receptor (LepR-b)-expressing neurons. To determine whether LepR-b neurons mediate the metabolic actions of Irs2 in the brain, we utilized Lepr(cre) together with Irs2(L/L) to ablate Irs2 expression in LepR-b neurons (Lepr(ΔIrs2)). Lepr(ΔIrs2) mice developed obesity, glucose intolerance, and insulin resistance. Leptin action was not altered in young Lepr(ΔIrs2) mice, although insulin-stimulated FoxO1 nuclear exclusion was reduced in Lepr(ΔIrs2) mice. Indeed, deletion of Foxo1 from LepR-b neurons in Lepr(ΔIrs2) mice normalized energy balance, glucose homeostasis, and arcuate nucleus gene expression. Thus, Irs2 signaling in LepR-b neurons plays a crucial role in metabolic sensing and regulation. While not required for leptin action, Irs2 suppresses FoxO1 signaling in LepR-b neurons to promote energy balance and metabolism.
Assuntos
Fatores de Transcrição Forkhead/metabolismo , Proteínas Substratos do Receptor de Insulina/metabolismo , Leptina/metabolismo , Neurônios/metabolismo , Receptores para Leptina/metabolismo , Animais , Encéfalo/metabolismo , Proteínas do Citoesqueleto/genética , Proteínas do Citoesqueleto/metabolismo , Metabolismo Energético , Feminino , Proteína Forkhead Box O1 , Fatores de Transcrição Forkhead/deficiência , Fatores de Transcrição Forkhead/genética , Expressão Gênica , Glucose/genética , Glucose/metabolismo , Intolerância à Glucose/genética , Intolerância à Glucose/metabolismo , Homeostase , Insulina/genética , Insulina/metabolismo , Proteínas Substratos do Receptor de Insulina/genética , Resistência à Insulina/genética , Leptina/genética , Masculino , Camundongos , Camundongos Transgênicos , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Obesidade/genética , Obesidade/metabolismo , Receptores para Leptina/genética , Transdução de SinaisRESUMO
Brown adipose tissue (BAT) thermogenesis is critical to maintain homoeothermia and is centrally controlled via sympathetic outputs. Body temperature and BAT activity also impact energy expenditure, and obesity is commonly associated with decreased BAT capacity and sympathetic tone. Severely obese mice that lack leptin or its receptor (LepRb) show decreased BAT capacity, sympathetic tone, and body temperature and thus are unable to adapt to acute cold exposure (Trayhurn et al., 1976). LepRb-expressing neurons are found in several hypothalamic sites, including the dorsomedial hypothalamus (DMH) and median preoptic area (mPOA), both critical sites to regulate sympathetic, thermoregulatory BAT circuits. Specifically, a subpopulation in the DMH/dorsal hypothalamic area (DHA) is stimulated by fever-inducing endotoxins or cold exposure (Dimicco and Zaretsky, 2007; Morrison et al., 2008). Using the retrograde, transsynaptic tracer pseudorabies virus (PRV) injected into the BAT of mice, we identified PRV-labeled LepRb neurons in the DMH/DHA and mPOA (and other sites), thus indicating their involvement in the regulation of sympathetic BAT circuits. Indeed, acute cold exposure induced c-Fos (as a surrogate for neuronal activity) in DMH/DHA LepRb neurons, and a large number of mPOA LepRb neurons project to the DMH/DHA. Furthermore, DMH/DHA LepRb neurons (and a subpopulation of LepRb mPOA neurons) project and synaptically couple to rostral raphe pallidus neurons, consistent with the current understanding of BAT thermoregulatory circuits from the DMH/DHA and mPOA (Dimicco and Zaretsky, 2007; Morrison et al., 2008). Thus, these data present strong evidence that LepRb neurons in the DMH/DHA and mPOA mediate thermoregulatory leptin action.