ABSTRACT
High-fat diet (HFD) feeding induces rapid reprogramming of systemic metabolism. Here, we demonstrate that HFD feeding of mice downregulates glucose transporter (GLUT)-1 expression in blood-brain barrier (BBB) vascular endothelial cells (BECs) and reduces brain glucose uptake. Upon prolonged HFD feeding, GLUT1 expression is restored, which is paralleled by increased expression of vascular endothelial growth factor (VEGF) in macrophages at the BBB. In turn, inducible reduction of GLUT1 expression specifically in BECs reduces brain glucose uptake and increases VEGF serum concentrations in lean mice. Conversely, myeloid-cell-specific deletion of VEGF in VEGF(Δmyel) mice impairs BBB-GLUT1 expression, brain glucose uptake, and memory formation in obese, but not in lean mice. Moreover, obese VEGF(Δmyel) mice exhibit exaggerated progression of cognitive decline and neuroinflammation on an Alzheimer's disease background. These experiments reveal that transient, HFD-elicited reduction of brain glucose uptake initiates a compensatory increase of VEGF production and assign obesity-associated macrophage activation a homeostatic role to restore cerebral glucose metabolism, preserve cognitive function, and limit neurodegeneration in obesity.
Subject(s)
Brain/metabolism , Diet, High-Fat , Glucose/metabolism , Obesity/physiopathology , Vascular Endothelial Growth Factor A/metabolism , Animals , Blood-Brain Barrier/metabolism , Cognition , Endothelial Cells/metabolism , Fatty Acids/metabolism , Glucose Transporter Type 1/genetics , Glucose Transporter Type 1/metabolism , Mice , Myeloid Cells/metabolismABSTRACT
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.
Subject(s)
Diet, High-Fat , Hyperglycemia/metabolism , Hypothalamus/metabolism , Insulin/metabolism , Lactation , Obesity/metabolism , Animals , Axons/metabolism , Female , Male , Metabolic Diseases/metabolism , Mice , Mice, Inbred C57BL , Neurons/metabolism , Pregnancy , Pro-Opiomelanocortin/metabolism , Receptor, Insulin/metabolism , Signal TransductionABSTRACT
Rat insulin promoter (RIP)-expressing neurons in the hypothalamus control body weight and energy homeostasis. However, genetic approaches to study the role of these neurons have been limited by the fact that RIP expression is predominantly found in pancreatic ß-cells, which impedes selective targeting of neurons. To define the function of hypothalamic RIP-expressing neurons, we set out to acutely and selectively eliminate them via diphtheria toxin-mediated ablation. Therefore, the diphtheria toxin receptor transgene was specifically expressed upon RIP-specific Cre recombination using a RIP-Cre line first described by Herrera (RIP(HER)-Cre) [Herrera PL (2000) Development 127:2317-2322]. Using proopiomelanocortin-expressing cells located in the arcuate nucleus of the hypothalamus and in the pituitary gland as a model, we established a unique protocol of intracerebroventricular application of diphtheria toxin to efficiently ablate hypothalamic cells with no concomitant effect on pituitary proopiomelanocortin-expressing corticotrophs in the mouse. Using this approach to ablate RIP(HER) neurons in the brain, but not in the pancreas, resulted in decreased food intake and loss of body weight and fat mass. In addition, ablation of RIP(HER) neurons caused increased c-Fos immunoreactivity of neurons in the paraventricular nucleus (PVN) of the hypothalamus. Moreover, transsynaptic tracing of RIP(HER) neurons revealed labeling of neurons located in the PVN and dorsomedial hypothalamic nucleus. Thus, our experiments indicate that RIP(HER) neurons inhibit anorexigenic neurons in the PVN, revealing a basic orexigenic nature of these cells.
Subject(s)
Arcuate Nucleus of Hypothalamus/metabolism , Insulin/genetics , Neurons/metabolism , Paraventricular Hypothalamic Nucleus/metabolism , Promoter Regions, Genetic , Animals , Arcuate Nucleus of Hypothalamus/cytology , Feeding Behavior , Glucose Tolerance Test , Mice , Paraventricular Hypothalamic Nucleus/cytology , Rats , Real-Time Polymerase Chain Reaction , Weight LossABSTRACT
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.
Subject(s)
Energy Metabolism , Forkhead Transcription Factors/metabolism , Pro-Opiomelanocortin/metabolism , Protein Serine-Threonine Kinases/deficiency , Stress, Physiological , 3-Phosphoinositide-Dependent Protein Kinases , Animals , Body Weight/drug effects , Corticosterone/metabolism , Corticosterone/pharmacology , Female , Forkhead Box Protein O1 , Forkhead Transcription Factors/antagonists & inhibitors , Forkhead Transcription Factors/genetics , Gene Deletion , Gene Expression Regulation , Hyperphagia/genetics , Hypothalamus/cytology , Hypothalamus/metabolism , Insulin/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Transgenic , Pituitary Gland/metabolism , Pro-Opiomelanocortin/deficiency , Pro-Opiomelanocortin/genetics , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolismABSTRACT
A major component of obesity-related insulin resistance is the establishment of a chronic inflammatory state with invasion of white adipose tissue by mononuclear cells. This results in the release of pro-inflammatory cytokines, which in turn leads to insulin resistance in target tissues such as skeletal muscle and liver. To determine the role of insulin action in macrophages and monocytes in obesity-associated insulin resistance, we conditionally inactivated the insulin receptor (IR) gene in myeloid lineage cells in mice (IR(Deltamyel)-mice). While these animals exhibit unaltered glucose metabolism on a normal diet, they are protected from the development of obesity-associated insulin resistance upon high fat feeding. Euglycemic, hyperinsulinemic clamp studies demonstrate that this results from decreased basal hepatic glucose production and from increased insulin-stimulated glucose disposal in skeletal muscle. Furthermore, IR(Deltamyel)-mice exhibit decreased concentrations of circulating tumor necrosis factor (TNF) alpha and thus reduced c-Jun N-terminal kinase (JNK) activity in skeletal muscle upon high fat feeding, reflecting a dramatic reduction of the chronic and systemic low-grade inflammatory state associated with obesity. This is paralleled by a reduced accumulation of macrophages in white adipose tissue due to a pronounced impairment of matrix metalloproteinase (MMP) 9 expression and activity in these cells. These data indicate that insulin action in myeloid cells plays an unexpected, critical role in the regulation of macrophage invasion into white adipose tissue and in the development of obesity-associated insulin resistance.
Subject(s)
Insulin Resistance , Macrophages/immunology , Monocytes/immunology , Obesity/immunology , Receptor, Insulin/immunology , Animals , Cells, Cultured , Disease Models, Animal , Female , Humans , Liver/immunology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Muscle, Skeletal/immunology , Obesity/genetics , Obesity/metabolism , Receptor, Insulin/geneticsABSTRACT
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.
Subject(s)
Glucose/metabolism , Hypothalamus/metabolism , Mitogen-Activated Protein Kinase 8/metabolism , Pituitary Gland/metabolism , Adiposity/physiology , Animals , Body Weight/physiology , Dietary Fats/administration & dosage , Growth Hormone/metabolism , Hypothalamo-Hypophyseal System/metabolism , Insulin/metabolism , Insulin Resistance/physiology , Intermediate Filament Proteins/metabolism , Mice , Mice, Obese , Mice, Transgenic , Mitogen-Activated Protein Kinase 8/deficiency , Mitogen-Activated Protein Kinase 8/genetics , Nerve Tissue Proteins/metabolism , Nestin , Signal Transduction , Thyroid Gland/metabolismABSTRACT
The contribution of different leptin-induced signaling pathways in control of energy homeostasis is only partly understood. Here we show that selective Pten ablation in leptin-sensitive neurons (Pten(DeltaObRb)) results in enhanced Pi3k activation in these cells and reduces adiposity by increasing energy expenditure. White adipose tissue (WAT) of Pten(DeltaObRb) mice shows characteristics of brown adipose tissue (BAT), reflected by increased mitochondrial content and Ucp1 expression resulting from enhanced leptin-stimulated sympathetic nerve activity (SNA) in WAT. In contrast, leptin-deficient ob/ob-Pten(DeltaObRb) mice exhibit unaltered body weight and WAT morphology compared to ob/ob mice, pointing to a pivotal role of endogenous leptin in control of WAT transdifferentiation. Leanness of Pten(DeltaObRb) mice is accompanied by enhanced sensitivity to insulin in skeletal muscle. These data provide direct genetic evidence that leptin-stimulated Pi3k signaling in the CNS regulates energy expenditure via activation of SNA to perigonadal WAT leading to BAT-like differentiation of WAT.
Subject(s)
Adipose Tissue, White/growth & development , Adipose Tissue, White/metabolism , Central Nervous System/metabolism , Leptin/metabolism , Phosphatidylinositol 3-Kinases/metabolism , Adipose Tissue, Brown/growth & development , Adipose Tissue, Brown/metabolism , Animals , Cell Transdifferentiation , Enzyme Activation , Glucose/metabolism , Mice , Mice, Knockout , Mice, Mutant Strains , Mice, Obese , Mice, Transgenic , PTEN Phosphohydrolase/deficiency , PTEN Phosphohydrolase/genetics , Signal Transduction , ThinnessABSTRACT
The unfolded protein response (UPR) or endoplasmic reticulum (ER) stress response is a physiological process enabling cells to cope with altered protein synthesis demands. However, under conditions of obesity, prolonged activation of the UPR has been shown to have deteriorating effects on different metabolic pathways. Here we identify Bax inhibitor-1 (BI-1), an evolutionary conserved ER-membrane protein, as a novel modulator of the obesity-associated alteration of the UPR. BI-1 partially inhibits the UPR by interacting with IRE1alpha and inhibiting IRE1alpha endonuclease activity as seen on the splicing of the transcription factor Xbp-1. Because we observed a down-regulation of BI-1 expression in liver and muscle of genetically obese ob/ob and db/db mice as well as in mice with diet-induced obesity in vivo, we investigated the effect of restoring BI-1 expression on metabolic processes in these mice. Importantly, BI-1 overexpression by adenoviral gene transfer dramatically improved glucose metabolism in both standard diet-fed mice as well as in mice with diet-induced obesity and, critically, reversed hyperglycemia in db/db mice. This improvement in whole body glucose metabolism and insulin sensitivity was due to dramatically reduced gluconeogenesis as shown by reduction of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase expression. Taken together, these results identify BI-1 as a critical regulator of ER stress responses in the development of obesity-associated insulin resistance and provide proof of concept evidence that gene transfer-mediated elevations in hepatic BI-1 may represent a promising approach for the treatment of type 2 diabetes.
Subject(s)
Endoribonucleases/antagonists & inhibitors , Glucose Intolerance/therapy , Insulin Resistance , Membrane Proteins/pharmacology , Obesity/complications , Protein Serine-Threonine Kinases/antagonists & inhibitors , Animals , Endoplasmic Reticulum/pathology , Genetic Therapy/methods , Gluconeogenesis/drug effects , Glucose/metabolism , Hyperglycemia/therapy , Liver/metabolism , Membrane Proteins/administration & dosage , Membrane Proteins/therapeutic use , Mice , Mice, Obese , Unfolded Protein ResponseABSTRACT
Insulin resistance is a hallmark of type 2 diabetes, and many insights into the functions of insulin have been gained through the study of mice lacking the IR. To gain a better understanding of the role of insulin action in the brain versus peripheral tissues, we created 2 mouse models with inducible IR inactivation, 1 in all tissues including brain (IRDeltawb), and 1 restricted to peripheral tissues (IRDeltaper). While downregulation of IR expression resulted in severe hyperinsulinemia in both models, hyperglycemia was more pronounced in IRDeltawb mice. Both strains displayed a dramatic upregulation of hepatic leptin receptor expression, while only IRDeltaper mice displayed increased hepatic Stat3 phosphorylation and Il6 expression. Despite a similar reduction in IR expression in white adipose tissue (WAT) mass in both models, IRDeltawb mice had a more pronounced reduction in WAT mass and severe hypoleptinemia. Leptin replacement restored hepatic Stat3 phosphorylation and normalized glucose metabolism in these mice, indicating that alterations in glucose metabolism occur largely as a consequence of lipoathrophy upon body-wide IR deletion. Moreover, chronic intracerebroventricular insulin treatment of control mice increased fat mass, fat cell size, and adipose tissue lipoprotein lipase expression, indicating that CNS insulin action promotes lipogenesis. These studies demonstrate that central insulin action plays an important role in regulating WAT mass and glucose metabolism via hepatic Stat3 activation.
Subject(s)
Adipose Tissue/metabolism , Gene Expression Regulation , Glucose/metabolism , Insulin/metabolism , Lipogenesis , Animals , Central Nervous System/metabolism , Gene Deletion , Homozygote , Lipoprotein Lipase/biosynthesis , Mice , Mice, Knockout , Models, Biological , Models, Genetic , Tissue DistributionABSTRACT
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.
Subject(s)
Insulin/metabolism , Leptin/metabolism , Membrane Proteins/metabolism , Neural Inhibition/physiology , Neurons/physiology , Obesity/physiopathology , Pro-Opiomelanocortin/metabolism , Agouti-Related Protein/genetics , Agouti-Related Protein/metabolism , Animals , Body Composition/genetics , Body Weight/genetics , Disease Models, Animal , Eating/genetics , Electrophoretic Mobility Shift Assay , Enzyme-Linked Immunosorbent Assay/methods , Feedback/physiology , Gene Expression Regulation/drug effects , Gene Expression Regulation/genetics , Glucose Tolerance Test , Green Fluorescent Proteins/genetics , Hypothalamus/pathology , In Vitro Techniques , Insulin Resistance/genetics , Leukemia Inhibitory Factor/pharmacology , Membrane Proteins/genetics , Mice , Mice, Transgenic , Neural Inhibition/drug effects , Neural Inhibition/genetics , Neuropeptide Y/genetics , Neuropeptide Y/metabolism , Obesity/genetics , Obesity/metabolism , Patch-Clamp Techniques/methods , Phosphatidylinositol 3-Kinases/metabolism , Signal Transduction/genetics , Suppressor of Cytokine Signaling 3 Protein , Suppressor of Cytokine Signaling Proteins/genetics , Suppressor of Cytokine Signaling Proteins/metabolism , TransfectionABSTRACT
To study the role of Fas-Fas ligand (FasL) interaction-mediated apoptosis in lymphocyte homeostasis, we generated a mutant fas allele allowing conditional inactivation of the fas gene through Cre-mediated recombination. Experiments in which Fas was ablated in T cells, B cells, T and B cells, or in a more generalized manner demonstrated that the development of lymphoproliferative disease as seen in Fas-deficient mice requires Fas ablation in lymphoid and nonlymphoid tissues. Selective inactivation of Fas in T cells led to a severe lymphopenia over time, accompanied by up-regulation of FasL on activated T cells and apoptosis of peripheral lymphocytes. In addition, the mutant animals developed a fatal wasting syndrome caused by massive leukocyte infiltration in the lungs together with increased inflammatory cytokine production and pulmonary fibrosis. Inhibition of Fas-FasL interaction in vivo completely prevented the loss of lymphocytes and initial lymphocyte infiltration in the lungs. Thus, FasL-mediated interaction of activated, Fas-deficient T cells with Fas-expressing cells in their environment leads to break down of lymphocyte homeostasis and development of a lung disease strikingly resembling idiopathic pulmonary fibrosis in humans, a common and severe disease for which the mutant mice may serve as a first animal model.
Subject(s)
Lymphocyte Depletion , Membrane Glycoproteins/physiology , Pulmonary Fibrosis/immunology , T-Lymphocytes/immunology , fas Receptor/physiology , Animals , B-Lymphocytes/immunology , Chimera , Crosses, Genetic , Fas Ligand Protein , Female , Flow Cytometry , Inflammation , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Pulmonary Fibrosis/genetics , fas Receptor/geneticsABSTRACT
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.
Subject(s)
Neurons/metabolism , Obesity , PTEN Phosphohydrolase/metabolism , Phosphatidylinositol Phosphates/metabolism , Potassium Channels/metabolism , Pro-Opiomelanocortin/metabolism , Second Messenger Systems/physiology , Animals , Chromones/metabolism , Diet , Eating/drug effects , Female , Hypoglycemic Agents/pharmacology , Hypothalamus/cytology , Hypothalamus/metabolism , Insulin/metabolism , Leptin/metabolism , Male , Membrane Potentials/drug effects , Mice , Mice, Knockout , Morpholines/metabolism , Neurons/cytology , Neurons/drug effects , PTEN Phosphohydrolase/genetics , Phosphatidylinositol 3-Kinases/metabolism , Phosphoinositide-3 Kinase Inhibitors , Tolbutamide/pharmacologyABSTRACT
Multiple hormones controlling energy homeostasis regulate the expression of neuropeptide Y (NPY) and agouti-related peptide (AgRP) in the arcuate nucleus of the hypothalamus. Nevertheless, inactivation of the genes encoding NPY and/or AgRP has no impact on food intake in mice. Here we demonstrate that induced selective ablation of AgRP-expressing neurons in adult mice results in acute reduction of feeding, demonstrating direct evidence for a critical role of these neurons in the regulation of energy homeostasis.
Subject(s)
Arcuate Nucleus of Hypothalamus/cytology , Feeding Behavior/physiology , Gene Expression Regulation/physiology , Neurons/metabolism , Proteins/metabolism , Agouti-Related Protein , Animals , Anorexia/metabolism , Body Weight/drug effects , Body Weight/physiology , Cell Count/methods , Diphtheria Toxin/pharmacology , Eating/drug effects , Gene Expression Regulation/drug effects , Intercellular Signaling Peptides and Proteins , Mice , Mice, Knockout , Neurons/drug effects , Neuropeptide Y/genetics , Neuropeptide Y/metabolism , Pro-Opiomelanocortin/deficiency , Pro-Opiomelanocortin/genetics , Pro-Opiomelanocortin/metabolism , Proteins/genetics , Time Factors , beta-Galactosidase/biosynthesisABSTRACT
Olfactory inputs help coordinate food appreciation and selection, but their role in systemic physiology and energy balance is poorly understood. Here we demonstrate that mice upon conditional ablation of mature olfactory sensory neurons (OSNs) are resistant to diet-induced obesity accompanied by increased thermogenesis in brown and inguinal fat depots. Acute loss of smell perception after obesity onset not only abrogated further weight gain but also improved fat mass and insulin resistance. Reduced olfactory input stimulates sympathetic nerve activity, resulting in activation of ß-adrenergic receptors on white and brown adipocytes to promote lipolysis. Conversely, conditional ablation of the IGF1 receptor in OSNs enhances olfactory performance in mice and leads to increased adiposity and insulin resistance. These findings unravel a new bidirectional function for the olfactory system in controlling energy homeostasis in response to sensory and hormonal signals.
Subject(s)
Obesity/metabolism , Obesity/physiopathology , Olfactory Receptor Neurons/metabolism , Smell , Thermogenesis , Adipose Tissue, Brown/metabolism , Adipose Tissue, Brown/physiopathology , Animals , Diet, High-Fat/adverse effects , Energy Metabolism , Insulin Resistance , Insulin-Like Growth Factor I/metabolism , Lipolysis , Mice , Obesity/etiology , Olfactory Receptor Neurons/pathology , Receptors, Adrenergic, beta/metabolism , Weight GainABSTRACT
Activation of c-Jun N-terminal kinase 1 (JNK1)- and inhibitor of nuclear factor kappa-B kinase 2 (IKK2)-dependent signaling plays a crucial role in the development of obesity-associated insulin and leptin resistance not only in peripheral tissues but also in the CNS. Here, we demonstrate that constitutive JNK activation in agouti-related peptide (AgRP)-expressing neurons of the hypothalamus is sufficient to induce weight gain and adiposity in mice as a consequence of hyperphagia. JNK activation increases spontaneous action potential firing of AgRP cells and causes both neuronal and systemic leptin resistance. Similarly, activation of IKK2 signaling in AgRP neurons also increases firing of these cells but fails to cause obesity and leptin resistance. In contrast to JNK activation, IKK2 activation blunts insulin signaling in AgRP neurons and impairs systemic glucose homeostasis. Collectively, these experiments reveal both overlapping and nonredundant effects of JNK- and IKK-dependent signaling in AgRP neurons, which cooperate in the manifestation of the metabolic syndrome.
Subject(s)
Agouti-Related Protein/metabolism , I-kappa B Kinase/metabolism , Insulin Resistance , JNK Mitogen-Activated Protein Kinases/metabolism , Neurons/enzymology , Obesity/enzymology , Action Potentials/drug effects , Adiposity/drug effects , Animals , Body Weight/drug effects , Enzyme Activation/drug effects , Glucose/metabolism , Homeostasis/drug effects , Insulin/metabolism , Leptin/pharmacology , MAP Kinase Signaling System/drug effects , Male , Mice, Inbred C57BL , Mutant Proteins/metabolism , Neurons/drug effectsABSTRACT
Brown adipose tissue (BAT) is a critical regulator of glucose, lipid, and energy homeostasis, and its activity is tightly controlled by the sympathetic nervous system. However, the mechanisms underlying CNS-dependent control of BAT sympathetic nerve activity (SNA) are only partly understood. Here, we demonstrate that catecholaminergic neurons in the locus coeruleus (LC) adapt their firing frequency to extracellular glucose concentrations in a K(ATP)-channel-dependent manner. Inhibiting K(ATP)-channel-dependent control of neuronal activity via the expression of a variant K(ATP) channel in tyrosine-hydroxylase-expressing neurons and in neurons of the LC enhances diet-induced obesity in mice. Obesity results from decreased energy expenditure, lower steady-state BAT SNA, and an attenuated ability of centrally applied glucose to activate BAT SNA. This impairs the thermogenic transcriptional program of BAT. Collectively, our data reveal a role of K(ATP)-channel-dependent neuronal excitability in catecholaminergic neurons in maintaining thermogenic BAT sympathetic tone and energy homeostasis.
Subject(s)
Adipose Tissue, Brown/metabolism , Cholinergic Neurons/metabolism , Potassium Channels, Inwardly Rectifying/metabolism , Sympathetic Nervous System/metabolism , Animals , Cholinergic Neurons/drug effects , Diet, High-Fat , Energy Metabolism/drug effects , Glucose/pharmacology , Locus Coeruleus/drug effects , Locus Coeruleus/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Transgenic , Mutation , Obesity/etiology , Obesity/metabolism , Potassium Channels, Inwardly Rectifying/genetics , Tyrosine 3-Monooxygenase/metabolismABSTRACT
Dopaminergic midbrain neurons integrate signals on food palatability and food-associated reward into the complex control of energy homeostasis. To define the role of insulin receptor (IR) signaling in this circuitry, we inactivated IR signaling in tyrosine hydroxylase (Th)-expressing cells of mice (IR(ΔTh)). IR inactivation in Th-expressing cells of mice resulted in increased body weight, increased fat mass, and hyperphagia. While insulin acutely stimulated firing frequency in 50% of dopaminergic VTA/SN neurons, this response was abolished in IR(ΔTh) mice. Moreover, these mice exhibited an altered response to cocaine under food-restricted conditions. Taken together, these data provide in vivo evidence for a critical role of insulin signaling in catecholaminergic neurons to control food intake and energy homeostasis.
Subject(s)
Energy Metabolism/drug effects , Homeostasis/drug effects , Insulin/pharmacology , Neurons/metabolism , Action Potentials , Adiposity , Animals , Calorimetry, Indirect , Catecholamines/metabolism , Cocaine/pharmacology , Eating/genetics , Gene Expression , Hyperinsulinism/genetics , Mesencephalon/cytology , Mesencephalon/drug effects , Mice , Mice, Inbred ICR , Mice, Knockout , Motor Activity/drug effects , Motor Activity/genetics , Neurons/drug effects , Receptor, Insulin/genetics , Receptor, Insulin/metabolism , Receptors, Dopamine D2/genetics , Receptors, Dopamine D2/metabolism , Signal Transduction , Tyrosine 3-Monooxygenase/genetics , Tyrosine 3-Monooxygenase/metabolismABSTRACT
Steroidogenic factor 1 (SF-1)-expressing neurons of the ventromedial hypothalamus (VMH) control energy homeostasis, but the role of insulin action in these cells remains undefined. We show that insulin activates phosphatidylinositol-3-OH kinase (PI3K) signaling in SF-1 neurons and reduces firing frequency in these cells through activation of K(ATP) channels. These effects were abrogated in mice with insulin receptor deficiency restricted to SF-1 neurons (SF-1(ΔIR) mice). Whereas body weight and glucose homeostasis remained the same in SF-1(ΔIR) mice as in controls under a normal chow diet, they were protected from diet-induced leptin resistance, weight gain, adiposity and impaired glucose tolerance. High-fat feeding activated PI3K signaling in SF-1 neurons of control mice, and this response was attenuated in the VMH of SF-1(ΔIR) mice. Mimicking diet-induced overactivation of PI3K signaling by disruption of the phosphatidylinositol-3,4,5-trisphosphate phosphatase PTEN led to increased body weight and hyperphagia under a normal chow diet. Collectively, our experiments reveal that high-fat diet-induced, insulin-dependent PI3K activation in VMH neurons contributes to obesity development.
Subject(s)
Dietary Fats/adverse effects , Neurons/drug effects , Obesity/chemically induced , Obesity/pathology , Phosphatidylinositol 3-Kinases/metabolism , Receptor, Insulin/metabolism , Ventromedial Hypothalamic Nucleus/pathology , Action Potentials/drug effects , Action Potentials/genetics , Age Factors , Animals , Animals, Newborn , Blood Glucose/drug effects , Body Weight/drug effects , Calorimetry/methods , Dose-Response Relationship, Drug , Eating/drug effects , Eating/physiology , Enzyme Inhibitors/pharmacology , Enzyme-Linked Immunosorbent Assay/methods , Female , Gene Expression Regulation/drug effects , Glucose Tolerance Test , Green Fluorescent Proteins/genetics , Hypoglycemic Agents/pharmacology , In Vitro Techniques , Injections, Intraventricular/methods , Insulin/pharmacology , Leptin/administration & dosage , Male , Mice , Mice, Inbred C57BL , Mice, Transgenic , Neurons/metabolism , Patch-Clamp Techniques , RNA, Messenger/metabolism , Signal Transduction/drug effects , Signal Transduction/genetics , Steroidogenic Factor 1/genetics , Steroidogenic Factor 1/metabolism , Time Factors , Tolbutamide/pharmacology , Ventromedial Hypothalamic Nucleus/cytologyABSTRACT
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.