RESUMO
Maternal metabolic homeostasis exerts long-term effects on the offspring's health outcomes. Here, we demonstrate that maternal high-fat diet (HFD) feeding during lactation predisposes the offspring for obesity and impaired glucose homeostasis in mice, which is associated with an impairment of the hypothalamic melanocortin circuitry. Whereas the number and neuropeptide expression of anorexigenic proopiomelanocortin (POMC) and orexigenic agouti-related peptide (AgRP) neurons, electrophysiological properties of POMC neurons, and posttranslational processing of POMC remain unaffected in response to maternal HFD feeding during lactation, the formation of POMC and AgRP projections to hypothalamic target sites is severely impaired. Abrogating insulin action in POMC neurons of the offspring prevents altered POMC projections to the preautonomic paraventricular nucleus of the hypothalamus (PVH), pancreatic parasympathetic innervation, and impaired glucose-stimulated insulin secretion in response to maternal overnutrition. These experiments reveal a critical timing, when altered maternal metabolism disrupts metabolic homeostasis in the offspring via impairing neuronal projections, and show that abnormal insulin signaling contributes to this effect.
Assuntos
Dieta Hiperlipídica , Hiperglicemia/metabolismo , Hipotálamo/metabolismo , Insulina/metabolismo , Lactação , Obesidade/metabolismo , Animais , Axônios/metabolismo , Feminino , Masculino , Doenças Metabólicas/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Neurônios/metabolismo , Gravidez , Pró-Opiomelanocortina/metabolismo , Receptor de Insulina/metabolismo , Transdução de SinaisRESUMO
c-Jun N-terminal kinase (JNK) 1-dependent signaling plays a crucial role in the development of obesity-associated insulin resistance. Here we demonstrate that JNK activation not only occurs in peripheral tissues, but also in the hypothalamus and pituitary of obese mice. To resolve the importance of JNK1 signaling in the hypothalamic/pituitary circuitry, we have generated mice with a conditional inactivation of JNK1 in nestin-expressing cells (JNK1(DeltaNES) mice). JNK1(DeltaNES) mice exhibit improved insulin sensitivity both in the CNS and in peripheral tissues, improved glucose metabolism, as well as protection from hepatic steatosis and adipose tissue dysfunction upon high-fat feeding. Moreover, JNK1(DeltaNES) mice also show reduced somatic growth in the presence of reduced circulating growth hormone (GH) and insulin-like growth factor 1 (IGF1) concentrations, as well as increased thyroid axis activity. Collectively, these experiments reveal an unexpected, critical role for hypothalamic/pituitary JNK1 signaling in the coordination of metabolic/endocrine homeostasis.
Assuntos
Glucose/metabolismo , Hipotálamo/metabolismo , Proteína Quinase 8 Ativada por Mitógeno/metabolismo , Hipófise/metabolismo , Adiposidade/fisiologia , Animais , Peso Corporal/fisiologia , Gorduras na Dieta/administração & dosagem , Hormônio do Crescimento/metabolismo , Sistema Hipotálamo-Hipofisário/metabolismo , Insulina/metabolismo , Resistência à Insulina/fisiologia , Proteínas de Filamentos Intermediários/metabolismo , Camundongos , Camundongos Obesos , Camundongos Transgênicos , Proteína Quinase 8 Ativada por Mitógeno/deficiência , Proteína Quinase 8 Ativada por Mitógeno/genética , Proteínas do Tecido Nervoso/metabolismo , Nestina , Transdução de Sinais , Glândula Tireoide/metabolismoRESUMO
Leptin-stimulated Stat3 activation in proopiomelanocortin (POMC)-expressing neurons of the hypothalamus plays an important role in maintenance of energy homeostasis. While Stat3 activation in POMC neurons is required for POMC expression, the role of elevated basal Stat3 activation as present in the development of obesity has not been directly addressed. Here, we have generated and characterized mice expressing a constitutively active version of Stat3 (Stat3-C) in POMC neurons (Stat3-C(POMC) mice). On normal chow diet, these animals develop obesity as a result of hyperphagia and decreased POMC expression accompanied by central leptin and insulin resistance. This unexpected finding coincides with POMC-cell-specific, Stat3-mediated upregulation of SOCS3 expression inhibiting both leptin and insulin signaling as insulin-stimulated PIP(3) (phosphatidylinositol-3,4,5 triphosphate) formation and protein kinase B (AKT) activation in POMC neurons as well as with the fact that insulin's ability to hyperpolarize POMC neurons is largely reduced in POMC cells of Stat3-C(POMC) mice. These data indicate that constitutive Stat3 activation is not sufficient to promote POMC expression but requires simultaneous PI3K (phosphoinositide 3-kinase)-dependent release of FOXO1 repression. In contrast, upon exposure to a high-fat diet, food intake and body weight were unaltered in Stat3-C(POMC) mice compared with control mice. Taken together, these experiments directly demonstrate that enhanced basal Stat3 activation in POMC neurons as present in control mice upon high-fat feeding contributes to the development of hypothalamic leptin and insulin resistance.
Assuntos
Insulina/metabolismo , Leptina/metabolismo , Proteínas de Membrana/metabolismo , Inibição Neural/fisiologia , Neurônios/fisiologia , Obesidade/fisiopatologia , Pró-Opiomelanocortina/metabolismo , Proteína Relacionada com Agouti/genética , Proteína Relacionada com Agouti/metabolismo , Animais , Composição Corporal/genética , Peso Corporal/genética , Modelos Animais de Doenças , Ingestão de Alimentos/genética , Ensaio de Desvio de Mobilidade Eletroforética , Ensaio de Imunoadsorção Enzimática/métodos , Retroalimentação/fisiologia , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/genética , Teste de Tolerância a Glucose , Proteínas de Fluorescência Verde/genética , Hipotálamo/patologia , Técnicas In Vitro , Resistência à Insulina/genética , Fator Inibidor de Leucemia/farmacologia , Proteínas de Membrana/genética , Camundongos , Camundongos Transgênicos , Inibição Neural/efeitos dos fármacos , Inibição Neural/genética , Neuropeptídeo Y/genética , Neuropeptídeo Y/metabolismo , Obesidade/genética , Obesidade/metabolismo , Técnicas de Patch-Clamp/métodos , Fosfatidilinositol 3-Quinases/metabolismo , Transdução de Sinais/genética , Proteína 3 Supressora da Sinalização de Citocinas , Proteínas Supressoras da Sinalização de Citocina/genética , Proteínas Supressoras da Sinalização de Citocina/metabolismo , TransfecçãoRESUMO
Insulin- and leptin-stimulated phosphatidylinositol-3 kinase (PI3K) activation has been demonstrated to play a critical role in central control of energy homeostasis. To delineate the importance of pathways downstream of PI3K specifically in pro-opiomelanocortin (POMC) cell regulation, we have generated mice with selective inactivation of 3-phosphoinositide-dependent protein kinase 1 (PDK1) in POMC-expressing cells (PDK1(DeltaPOMC) mice). PDK1(DeltaPOMC) mice initially display hyperphagia, increased body weight, and impaired glucose metabolism caused by reduced hypothalamic POMC expression. On the other hand, PDK1(DeltaPOMC) mice exhibit progressive, severe hypocortisolism caused by loss of POMC-expressing corticotrophs in the pituitary. Expression of a dominant-negative mutant of FOXO1 specifically in POMC cells is sufficient to ameliorate positive energy balance in PDK1(DeltaPOMC) mice but cannot restore regular pituitary function. These results reveal important but differential roles for PDK1 signaling in hypothalamic and pituitary POMC cells in the control of energy homeostasis and stress response.
Assuntos
Metabolismo Energético , Fatores de Transcrição Forkhead/metabolismo , Pró-Opiomelanocortina/metabolismo , Proteínas Serina-Treonina Quinases/deficiência , Estresse Fisiológico , Proteínas Quinases Dependentes de 3-Fosfoinositídeo , Animais , Peso Corporal/efeitos dos fármacos , Corticosterona/metabolismo , Corticosterona/farmacologia , Feminino , Proteína Forkhead Box O1 , Fatores de Transcrição Forkhead/antagonistas & inibidores , Fatores de Transcrição Forkhead/genética , Deleção de Genes , Regulação da Expressão Gênica , Hiperfagia/genética , Hipotálamo/citologia , Hipotálamo/metabolismo , Insulina/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Hipófise/metabolismo , Pró-Opiomelanocortina/deficiência , Pró-Opiomelanocortina/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismoRESUMO
Insulin action in the central nervous system regulates energy homeostasis and glucose metabolism. To define the insulin-responsive neurons that mediate these effects, we generated mice with selective inactivation of the insulin receptor (IR) in either pro-opiomelanocortin (POMC)- or agouti-related peptide (AgRP)-expressing neurons of the arcuate nucleus of the hypothalamus. While neither POMC- nor AgRP-restricted IR knockout mice exhibited altered energy homeostasis, insulin failed to normally suppress hepatic glucose production during euglycemic-hyperinsulinemic clamps in AgRP-IR knockout (IR(DeltaAgRP)) mice. These mice also exhibited reduced insulin-stimulated hepatic interleukin-6 expression and increased hepatic expression of glucose-6-phosphatase. These results directly demonstrate that insulin action in POMC and AgRP cells is not required for steady-state regulation of food intake and body weight. However, insulin action specifically in AgRP-expressing neurons does play a critical role in controlling hepatic glucose production and may provide a target for the treatment of insulin resistance in type 2 diabetes.
Assuntos
Proteína Relacionada com Agouti/metabolismo , Glucose/metabolismo , Insulina/farmacologia , Fígado/metabolismo , Neurônios/efeitos dos fármacos , Animais , Western Blotting , Peso Corporal , Eletrofisiologia , Feminino , Teste de Tolerância a Glucose , Glucose-6-Fosfatase/metabolismo , Homeostase , Hiperinsulinismo/metabolismo , Hipotálamo/metabolismo , Técnicas Imunoenzimáticas , Integrases/metabolismo , Interleucina-6/metabolismo , Fígado/citologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neurônios/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Fosfatos de Fosfatidilinositol/metabolismo , Pró-Opiomelanocortina/metabolismo , Receptor de Insulina/genéticaRESUMO
Leptin and insulin have been identified as fuel sensors acting in part through their hypothalamic receptors to inhibit food intake and stimulate energy expenditure. As their intracellular signaling converges at the PI3K pathway, we directly addressed the role of phosphatidylinositol3,4,5-trisphosphate-mediated (PIP3-mediated) signals in hypothalamic proopiomelanocortin (POMC) neurons by inactivating the gene for the PIP3 phosphatase Pten specifically in this cell type. Here we show that POMC-specific disruption of Pten resulted in hyperphagia and sexually dimorphic diet-sensitive obesity. Although leptin potently stimulated Stat3 phosphorylation in POMC neurons of POMC cell-restricted Pten knockout (PPKO) mice, it failed to significantly inhibit food intake in vivo. POMC neurons of PPKO mice showed a marked hyperpolarization and a reduction in basal firing rate due to increased ATP-sensitive potassium (KATP) channel activity. Leptin was not able to elicit electrical activity in PPKO POMC neurons, but application of the PI3K inhibitor LY294002 and the KATP blocker tolbutamide restored electrical activity and leptin-evoked firing of POMC neurons in these mice. Moreover, icv administration of tolbutamide abolished hyperphagia in PPKO mice. These data indicate that PIP3-mediated signals are critical regulators of the melanocortin system via modulation of KATP channels.