RESUMO
Insulin and leptin intracellular signaling pathways converge and act synergistically on the hypothalamic phosphatidylinositol-3-OH kinase/3-phosphoinositide-dependent protein kinase 1 (PDK1). However, little is known about whether PDK1 in agouti-related peptide (AGRP) neurons contributes to energy homeostasis. We generated AGRP neuron-specific PDK1 knockout (AGRPPdk1(-/-)) mice and mice with selective expression of transactivation-defective Foxo1 (Δ256Foxo1(AGRP)Pdk1(-/-)). The AGRPPdk1(-/-) mice showed reductions in food intake, body length, and body weight. The Δ256Foxo1(AGRP)Pdk1(-/-) mice showed increased body weight, food intake, and reduced locomotor activity. After four weeks of calorie-restricted feeding, oxygen consumption and locomotor activity were elevated in AGRPPdk1(-/-) mice and reduced in Δ256Foxo1(AGRP)Pdk1(-/-) mice. In vitro, ghrelin-induced changes in [Ca(2+)](i) and inhibition of ghrelin by leptin were significantly attenuated in AGRPPdk1(-/-) neurons compared to control neurons. However, ghrelin-induced [Ca(2+)](i) changes and leptin inhibition were restored in Δ256Foxo1(AGRP)Pdk1(-/-) mice. These results suggested that PDK1 and Foxo1 signaling pathways play important roles in the control of energy homeostasis through AGRP-independent mechanisms.
Assuntos
Proteína Relacionada com Agouti/metabolismo , Ingestão de Alimentos , Metabolismo Energético , Fatores de Transcrição Forkhead/metabolismo , Melanocortinas/metabolismo , Neurônios/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Quinases Dependentes de 3-Fosfoinositídeo , Animais , Cálcio/metabolismo , Restrição Calórica , Ingestão de Alimentos/efeitos dos fármacos , Metabolismo Energético/efeitos dos fármacos , Feminino , Proteína Forkhead Box O1 , Técnicas de Inativação de Genes , Grelina/farmacologia , Homeostase/efeitos dos fármacos , Espaço Intracelular/efeitos dos fármacos , Espaço Intracelular/metabolismo , Leptina/metabolismo , Masculino , Camundongos , Neurônios/citologia , Neurônios/efeitos dos fármacos , Neuropeptídeos/metabolismo , Fenótipo , Proteínas Serina-Treonina Quinases/deficiência , Proteínas Serina-Treonina Quinases/genética , Transporte Proteico/efeitos dos fármacos , Ratos , Transdução de Sinais/efeitos dos fármacos , Ativação Transcricional/efeitos dos fármacosRESUMO
OBJECTIVE: Adipose tissue serves as an integrator of various physiological pathways, energy balance, and glucose homeostasis. Forkhead box-containing protein O subfamily (FoxO) 1 mediates insulin action at the transcriptional level. However, physiological roles of FoxO1 in adipose tissue remain unclear. RESEARCH DESIGN AND METHODS: In the present study, we generated adipose tissue-specific FoxO1 transgenic mice (adipocyte protein 2 [aP(2)]-FLAG-Delta 256) using an aP(2) promoter/enhancer and a mutant FoxO1 (FLAG Delta 256) in which the carboxyl terminal transactivation domain was deleted. Using these mice, we analyzed the effects of the overexpression of FLAG Delta 256 on glucose metabolism and energy homeostasis. RESULTS: The aP(2)-FLAG-Delta 256 mice showed improved glucose tolerance and insulin sensitivity accompanied with smaller-sized adipocytes and increased adiponectin (adipoq) and Glut 4 (Slc2a4) and decreased tumor necrosis factor alpha (Tnf) and chemokine (C-C motif) receptor 2 (Ccr2) gene expression levels in white adipose tissue (WAT) under a high-fat diet. Furthermore, the aP(2)-FLAG-Delta 256 mice had increased oxygen consumption accompanied with increased expression of peroxisome proliferator-activated receptor gamma coactivator (PGC)-1 alpha protein and uncoupling protein (UCP)-1 (Ucp1), UCP-2 (Ucp2), and beta 3-AR (Adrb3) in brown adipose tissue (BAT). Overexpression of FLAG Delta 256 in T37i cells, which are derived from the hibernoma of SV40 large T antigen transgenic mice, increased expression of PGC-1 alpha protein and Ucp1. Furthermore, knockdown of endogenous FoxO1 in T37i cells increased Pgc1 alpha (Ppargc1a), Pgc1 beta (Ppargc1b), Ucp1, and Adrb3 gene expression. CONCLUSIONS: These data suggest that FoxO1 modulates energy homeostasis in WAT and BAT through regulation of adipocyte size and adipose tissue-specific gene expression in response to excessive calorie intake.