RESUMO
Diabetes, obesity, and cancer affect upward of 15% of the world's population. Interestingly, all three diseases juxtapose dysregulated intracellular signaling with altered metabolic state. Exactly which genetic factors define stable metabolic set points in vivo remains poorly understood. Here, we show that hedgehog signaling rewires cellular metabolism. We identify a cilium-dependent Smo-Ca(2+)-Ampk axis that triggers rapid Warburg-like metabolic reprogramming within minutes of activation and is required for proper metabolic selectivity and flexibility. We show that Smo modulators can uncouple the Smo-Ampk axis from canonical signaling and identify cyclopamine as one of a new class of "selective partial agonists," capable of concomitant inhibition of canonical and activation of noncanonical hedgehog signaling. Intriguingly, activation of the Smo-Ampk axis in vivo drives robust insulin-independent glucose uptake in muscle and brown adipose tissue. These data identify multiple noncanonical endpoints that are pivotal for rational design of hedgehog modulators and provide a new therapeutic avenue for obesity and diabetes.
Assuntos
Tecido Adiposo Marrom/metabolismo , Glicólise , Proteínas Hedgehog/metabolismo , Células Musculares/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Transdução de Sinais , Quinases Proteína-Quinases Ativadas por AMP , Adipócitos/metabolismo , Animais , Linhagem Celular , Células Cultivadas , Cílios/metabolismo , Diabetes Mellitus/metabolismo , Humanos , Camundongos , Neoplasias/metabolismo , Obesidade/metabolismo , Proteínas Quinases/metabolismo , Receptor SmoothenedRESUMO
Hepatic insulin resistance is a major risk factor for the development of type 2 diabetes and is associated with the accumulation of lipids, including diacylglycerol (DAG), triacylglycerols (TAG) and ceramide. There is evidence that enzymes involved in ceramide or sphingolipid metabolism may have a role in regulating concentrations of glycerolipids such as DAG and TAG. Here we have investigated the role of sphingosine kinase (SphK) in regulating hepatic lipid levels. We show that mice on a high-fat high-sucrose diet (HFHS) displayed glucose intolerance, elevated liver TAG and DAG, and a reduction in total hepatic SphK activity. Reduced SphK activity correlated with downregulation of SphK1, but not SphK2 expression, and was not associated with altered ceramide levels. The role of SphK1 was further investigated by overexpressing this isoform in the liver of mice in vivo. On a low-fat diet (LFD) mice overexpressing liver SphK1, displayed reduced hepatic TAG synthesis and total TAG levels, but with no change to DAG or ceramide. These mice also exhibited no change in gluconeogenesis, glycogenolysis or glucose tolerance. Similarly, overexpression of SphK1 had no effect on the pattern of endogenous glucose production determined during a glucose tolerance test. Under HFHS conditions, normalization of liver SphK activity to levels observed in LFD controls did not alter hepatic TAG concentrations. Furthermore, DAG, ceramide and glucose tolerance were also unaffected. In conclusion, our data suggest that SphK1 plays an important role in regulating TAG metabolism under LFD conditions.
Assuntos
Dieta com Restrição de Gorduras , Dieta Hiperlipídica , Gorduras na Dieta/metabolismo , Fígado/enzimologia , Fosfotransferases (Aceptor do Grupo Álcool)/biossíntese , Triglicerídeos/metabolismo , Animais , Ceramidas/metabolismo , Sacarose Alimentar/metabolismo , Glucose/metabolismo , Homeostase , Masculino , Camundongos Endogâmicos C57BL , Fosfotransferases (Aceptor do Grupo Álcool)/genética , RNA Mensageiro/biossíntese , Fatores de Tempo , Regulação para CimaRESUMO
Nitric oxide influences intramuscular signaling that affects skeletal muscle glucose uptake during exercise. The role of the main NO-producing enzyme isoform activated during skeletal muscle contraction, neuronal nitric oxide synthase-µ (nNOSµ), in modulating glucose uptake has not been investigated in a physiological exercise model. In this study, conscious and unrestrained chronically catheterized nNOSµ(+/+) and nNOSµ(-/-) mice either remained at rest or ran on a treadmill at 17 m/min for 30 min. Both groups of mice demonstrated similar exercise capacity during a maximal exercise test to exhaustion (17.7 ± 0.6 vs. 15.9 ± 0.9 min for nNOSµ(+/+) and nNOSµ(-/-), respectively, P > 0.05). Resting and exercise blood glucose levels were comparable between the genotypes. Very low levels of NOS activity were detected in skeletal muscle from nNOSµ(-/-) mice, and exercise increased NOS activity only in nNOSµ(+/+) mice (4.4 ± 0.3 to 5.2 ± 0.4 pmol·mg(-1)·min(-1), P < 0.05). Exercise significantly increased glucose uptake in gastrocnemius muscle (5- to 7-fold) and, surprisingly, more so in nNOSµ(-/-) than in nNOSµ(+/+) mice (P < 0.05). This is in parallel with a greater increase in AMPK phosphorylation during exercise in nNOSµ(-/-) mice. In conclusion, nNOSµ is not essential for skeletal muscle glucose uptake during exercise, and the higher skeletal muscle glucose uptake during exercise in nNOSµ(-/-) mice may be due to compensatory increases in AMPK activation.
Assuntos
Proteínas Quinases Ativadas por AMP/metabolismo , Glicemia/metabolismo , Músculo Esquelético/metabolismo , Óxido Nítrico Sintase Tipo I/genética , Condicionamento Físico Animal , Animais , Feminino , Glucose/metabolismo , Masculino , Camundongos , Camundongos Knockout , FosforilaçãoRESUMO
RATIONALE: Cardiac metabolism is thought to be altered in insulin resistance and type 2 diabetes (T2D). Our understanding of the regulation of cardiac substrate metabolism and insulin sensitivity has largely been derived from ex vivo preparations which are not subject to the same metabolic regulation as in the intact heart in vivo. Studies are therefore required to examine in vivo cardiac glucose metabolism under physiologically relevant conditions. OBJECTIVE: To determine the temporal pattern of the development of cardiac insulin resistance and to compare with dynamic approaches to interrogate cardiac glucose and intermediary metabolism in vivo. METHODS AND RESULTS: Studies were conducted to determine the evolution of cardiac insulin resistance in C57Bl/6 mice fed a high-fat diet (HFD) for between 1 and 16 weeks. Dynamic in vivo cardiac glucose metabolism was determined following oral administration of [U-(13)C] glucose. Hearts were collected after 15 and 60 min and flux profiling was determined by measuring (13)C mass isotopomers in glycolytic and tricarboxylic acid (TCA) cycle intermediates. Cardiac insulin resistance, determined by euglycemic-hyperinsulinemic clamp, was evident after 3 weeks of HFD. Despite the presence of insulin resistance, in vivo cardiac glucose metabolism following oral glucose administration was not compromised in HFD mice. This contrasts our recent findings in skeletal muscle, where TCA cycle activity was reduced in mice fed a HFD. Similar to our report in muscle, glucose derived pyruvate entry into the TCA cycle in the heart was almost exclusively via pyruvate dehydrogenase, with pyruvate carboxylase mediated anaplerosis being negligible after oral glucose administration. CONCLUSIONS: Under experimental conditions which closely mimic the postprandial state, the insulin resistant mouse heart retains the ability to stimulate glucose metabolism.
Assuntos
Dieta Hiperlipídica , Técnica Clamp de Glucose , Glucose/metabolismo , Hiperinsulinismo/metabolismo , Metabolômica , Miocárdio/metabolismo , Animais , Cromatografia Gasosa-Espectrometria de Massas , Resistência à Insulina , Masculino , Camundongos , Camundongos Endogâmicos C57BLRESUMO
Obesity and type 2 diabetes lessen the quality of life of those afflicted and place considerable burden on the healthcare system. Furthermore, the detrimental impact of these pathologies is expected to persist or even worsen. Diabetes is characterized by impaired insulin action and glucose homeostasis. This has led to a rapid increase in the number of mouse models of metabolic disease being used in the basic sciences to assist in facilitating a greater understanding of the metabolic dysregulation associated with obesity and diabetes, the identification of therapeutic targets, and the discovery of effective treatments. This review briefly describes the most frequently utilized models of metabolic disease. A presentation of standard methods and technologies on the horizon for assessing metabolic phenotypes in mice, with particular emphasis on glucose handling and energy balance, is provided. The article also addresses issues related to study design, selection and execution of metabolic tests of glucose metabolism, the presentation of data, and interpretation of results.
Assuntos
Glucose/metabolismo , Homeostase , Animais , Estado de Consciência , Metabolismo Energético , Glucose/química , Resistência à Insulina/genética , Doenças Metabólicas/diagnóstico , Doenças Metabólicas/genética , Doenças Metabólicas/metabolismo , Metaboloma , Metabolômica/métodos , Camundongos , Camundongos Transgênicos , Modelos Animais , Mutação , FenótipoRESUMO
Nitric oxide (NO) is an important vasodilator and regulator in the cardiovascular system, and this link was the subject of a Nobel prize in 1998. However, NO also plays many other regulatory roles, including thrombosis, immune function, neural activity, and gastrointestinal function. Low concentrations of NO are thought to have important signaling effects. In contrast, high concentrations of NO can interact with reactive oxygen species, causing damage to cells and cellular components. A less-recognized site of NO production is within skeletal muscle, where small increases are thought to have beneficial effects such as regulating glucose uptake and possibly blood flow, but higher levels of production are thought to lead to deleterious effects such as an association with insulin resistance. This review will discuss the role of NO in skeletal muscle during and following exercise, including in mitochondrial biogenesis, muscle efficiency, and blood flow with a particular focus on its potential role in regulating skeletal muscle glucose uptake during exercise.
Assuntos
Exercício Físico/fisiologia , Glucose/metabolismo , Músculo Esquelético/metabolismo , Óxido Nítrico/metabolismo , Animais , Humanos , Modelos Biológicos , Contração Muscular/fisiologia , Músculo Esquelético/química , Óxido Nítrico Sintase/metabolismo , Transdução de Sinais/fisiologiaRESUMO
Skeletal muscle glucose uptake increases dramatically in response to physical exercise. Moreover, skeletal muscle comprises the vast majority of insulin-sensitive tissue and is a site of dysregulation in the insulin-resistant state. The biochemical and histological composition of the muscle is well defined in a variety of species. However, the functional consequences of muscle biochemical and histological adaptations to physiological and pathophysiological conditions are not well understood. The physiological regulation of muscle glucose uptake is complex. Sites involved in the regulation of muscle glucose uptake are defined by a three-step process consisting of: (1) delivery of glucose to muscle, (2) transport of glucose into the muscle by GLUT4 and (3) phosphorylation of glucose within the muscle by a hexokinase (HK). Muscle blood flow, capillary recruitment and extracellular matrix characteristics determine glucose movement from the blood to the interstitium. Plasma membrane GLUT4 content determines glucose transport into the cell. Muscle HK activity, cellular HK compartmentalization and the concentration of the HK inhibitor glucose 6-phosphate determine the capacity to phosphorylate glucose. Phosphorylation of glucose is irreversible in muscle; therefore, with this reaction, glucose is trapped and the uptake process is complete. Emphasis has been placed on the role of the glucose transport step for glucose influx into muscle with the past assertion that membrane transport is rate limiting. More recent research definitively shows that the distributed control paradigm more accurately defines the regulation of muscle glucose uptake as each of the three steps that define this process are important sites of flux control.
Assuntos
Glucose/metabolismo , Músculo Esquelético/metabolismo , Proteínas Quinases Ativadas por AMP/metabolismo , Animais , Transporte Biológico , Exercício Físico , Transportador de Glucose Tipo 4/metabolismo , Humanos , Insulina/metabolismo , Resistência à Insulina , Óxido Nítrico Sintase/metabolismo , FosforilaçãoRESUMO
Hepatic glucagon action increases in response to accelerated metabolic demands and is associated with increased whole body substrate availability, including circulating lipids. The hypothesis that increases in hepatic glucagon action stimulate AMP-activated protein kinase (AMPK) signaling and peroxisome proliferator-activated receptor-α (PPARα) and fibroblast growth factor 21 (FGF21) expression in a manner modulated by fatty acids was tested in vivo. Wild-type (gcgr(+/+)) and glucagon receptor-null (gcgr(-/-)) littermate mice were studied using an 18-h fast, exercise, and hyperglucagonemic-euglycemic clamps plus or minus increased circulating lipids. Fasting and exercise in gcgr(+/+), but not gcgr(-/-) mice, increased hepatic phosphorylated AMPKα at threonine 172 (p-AMPK(Thr(172))) and PPARα and FGF21 mRNA. Clamp results in gcgr(+/+) mice demonstrate that hyperlipidemia does not independently impact or modify glucagon-stimulated increases in hepatic AMP/ATP, p-AMPK(Thr(172)), or PPARα and FGF21 mRNA. It blunted glucagon-stimulated acetyl-CoA carboxylase phosphorylation, a downstream target of AMPK, and accentuated PPARα and FGF21 expression. All effects were absent in gcgr(-/-) mice. These findings demonstrate that glucagon exerts a critical regulatory role in liver to stimulate pathways linked to lipid metabolism in vivo and shows for the first time that effects of glucagon on PPARα and FGF21 expression are amplified by a physiological increase in circulating lipids.
Assuntos
Adenilato Quinase/metabolismo , Emulsões Gordurosas Intravenosas/metabolismo , Fatores de Crescimento de Fibroblastos/biossíntese , Glucagon/metabolismo , Fígado/metabolismo , PPAR alfa/biossíntese , Adenilato Quinase/genética , Animais , Área Sob a Curva , Glicemia/metabolismo , Catecolaminas/sangue , Ácidos Graxos não Esterificados/sangue , Feminino , Fatores de Crescimento de Fibroblastos/genética , Fatores de Crescimento de Fibroblastos/metabolismo , Técnica Clamp de Glucose , Insulina/sangue , Fígado/enzimologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , PPAR alfa/genética , PPAR alfa/metabolismo , Condicionamento Físico Animal/fisiologia , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Receptores de Glucagon/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de SinaisRESUMO
Endothelial nitric oxide synthase (eNOS) is associated with a number of physiological functions involved in the regulation of metabolism; however, the functional role of eNOS is poorly understood. We tested the hypothesis that eNOS is critical to muscle cell signaling and fuel usage during exercise in vivo, using 16-wk-old catheterized (carotid artery and jugular vein) C57BL/6J mice with wild-type (WT), partial (+/-), or no expression (-/-) of eNOS. Quantitative reductions in eNOS expression ( approximately 40%) elicited many of the phenotypic effects observed in enos(-/-) mice under fasted, sedentary conditions, with expression of oxidative phosphorylation complexes I to V and ATP levels being decreased, and total NOS activity and Ca(2+)/CaM kinase II Thr(286) phosphorylation being increased in skeletal muscle. Despite these alterations, exercise tolerance was markedly impaired in enos(-/-) mice during an acute 30-min bout of exercise. An eNOS-dependent effect was observed with regard to AMP-activated protein kinase signaling and muscle perfusion. Muscle glucose and long-chain fatty acid uptake, and hepatic and skeletal muscle glycogenolysis during the exercise bout was markedly accelerated in enos(-/-) mice compared with enos(+/-) and WT mice. Correspondingly, enos(-/-) mice exhibited hypoglycemia during exercise. Thus, the ablation of eNOS alters a number of physiological processes that result in impaired exercise capacity in vivo. The finding that a partial reduction in eNOS expression is sufficient to induce many of the changes associated with ablation of eNOS has implications for chronic metabolic diseases, such as obesity and insulin resistance, which are associated with reduced eNOS expression.
Assuntos
Metabolismo Energético/fisiologia , Músculo Esquelético/enzimologia , Óxido Nítrico Sintase Tipo III/metabolismo , Esforço Físico/fisiologia , Transdução de Sinais/fisiologia , Proteínas Quinases Ativadas por AMP/metabolismo , Animais , Composição Corporal/fisiologia , Peso Corporal/fisiologia , Calorimetria Indireta , Feminino , Gluconeogênese/fisiologia , Glicogênio/metabolismo , Hipoglicemia/metabolismo , Hipoglicemia/fisiopatologia , Insulina/sangue , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Mutantes , Mitocôndrias/fisiologia , Músculo Esquelético/irrigação sanguínea , Óxido Nítrico Sintase Tipo III/genética , Fosforilação Oxidativa , Fotoperíodo , Condicionamento Físico Animal/fisiologia , Gravidez , Fluxo Sanguíneo Regional/fisiologiaRESUMO
AMP-activated protein kinase (AMPK) has been extensively studied in whole muscle biopsy samples of humans, yet the fiber type-specific expression and/or activation of AMPK is unknown. We examined basal and exercise AMPK-alpha Thr(172) phosphorylation and AMPK subunit expression (alpha(1), alpha(2), and gamma(3)) in type I, IIa, and IIx fibers of human skeletal muscle before and after 10 days of exercise training. Before training basal AMPK phosphorylation was greatest in type IIa fibers (P < 0.05 vs. type I and IIx), while an acute bout of exercise increased AMPK phosphorylation in all fibers (P < 0.05), with the greatest increase occurring in type IIx fibers. Exercise training significantly increased basal AMPK phosphorylation in all fibers, and the exercise-induced increases were uniformly suppressed compared with pretraining exercise. Expression of AMPK-alpha(1) and -alpha(2) was similar between fibers and was not altered by exercise training. However, AMPK-gamma(3) was differentially expressed in skeletal muscle fibers (type IIx > type IIa > type I), irrespective of training status. Thus skeletal muscle AMPK phosphorylation and AMPK expression are fiber type specific in humans in the basal state, as well as during exercise. Our findings reveal fiber type-specific differences that have been masked in previous studies examining mixed muscle samples.
Assuntos
Proteínas Quinases Ativadas por AMP/metabolismo , Exercício Físico/fisiologia , Fibras Musculares Esqueléticas/enzimologia , Aptidão Física/fisiologia , Proteínas Quinases Ativadas por AMP/biossíntese , Biomarcadores/metabolismo , Humanos , Imuno-Histoquímica , Masculino , Fibras Musculares Esqueléticas/química , Fibras Musculares Esqueléticas/classificação , Consumo de Oxigênio , Fosforilação , Adulto JovemRESUMO
Insulin regulates glucose metabolism by eliciting effects on peripheral tissues as well as the brain. Insulin receptor (IR) signaling inhibits AgRP-expressing neurons in the hypothalamus to contribute to the suppression of hepatic glucose production (HGP) by insulin, whereas AgRP neuronal activation attenuates brown adipose tissue (BAT) glucose uptake. The tyrosine phosphatase TCPTP suppresses IR signaling in AgRP neurons. Hypothalamic TCPTP is induced by fasting and degraded after feeding. Here we assessed the influence of TCPTP in AgRP neurons in the control of glucose metabolism. TCPTP deletion in AgRP neurons (Agrp-Cre;Ptpn2fl/fl ) enhanced insulin sensitivity, as assessed by the increased glucose infusion rates, and reduced HGP during hyperinsulinemic-euglycemic clamps, accompanied by increased [14C]-2-deoxy-d-glucose uptake in BAT and browned white adipose tissue. TCPTP deficiency in AgRP neurons promoted the intracerebroventricular insulin-induced repression of hepatic gluconeogenesis in otherwise unresponsive food-restricted mice, yet had no effect in fed/satiated mice where hypothalamic TCPTP levels are reduced. The improvement in glucose homeostasis in Agrp-Cre;Ptpn2fl/fl mice was corrected by IR heterozygosity (Agrp-Cre;Ptpn2fl/fl ;Insrfl/+ ), causally linking the effects on glucose metabolism with the IR signaling in AgRP neurons. Our findings demonstrate that TCPTP controls IR signaling in AgRP neurons to coordinate HGP and brown/beige adipocyte glucose uptake in response to feeding/fasting.
Assuntos
Proteína Relacionada com Agouti/metabolismo , Ingestão de Alimentos/fisiologia , Gluconeogênese/genética , Glucose/metabolismo , Insulina/metabolismo , Neurônios/metabolismo , Proteína Tirosina Fosfatase não Receptora Tipo 2/fisiologia , Tecido Adiposo Marrom/metabolismo , Animais , Metabolismo dos Carboidratos/fisiologia , Metabolismo Energético/genética , Jejum , Técnica Clamp de Glucose , Fígado/metabolismo , Camundongos , Camundongos Transgênicos , Proteína Tirosina Fosfatase não Receptora Tipo 2/genética , Receptor de Insulina/metabolismo , Transdução de Sinais/genéticaRESUMO
Hypothalamic neurons respond to nutritional cues by altering gene expression and neuronal excitability. The mechanisms that control such adaptive processes remain unclear. Here we define populations of POMC neurons in mice that are activated or inhibited by insulin and thereby repress or inhibit hepatic glucose production (HGP). The proportion of POMC neurons activated by insulin was dependent on the regulation of insulin receptor signaling by the phosphatase TCPTP, which is increased by fasting, degraded after feeding and elevated in diet-induced obesity. TCPTP-deficiency enhanced insulin signaling and the proportion of POMC neurons activated by insulin to repress HGP. Elevated TCPTP in POMC neurons in obesity and/or after fasting repressed insulin signaling, the activation of POMC neurons by insulin and the insulin-induced and POMC-mediated repression of HGP. Our findings define a molecular mechanism for integrating POMC neural responses with feeding to control glucose metabolism.
Assuntos
Glucose/metabolismo , Insulina/farmacologia , Plasticidade Neuronal/efeitos dos fármacos , Neurônios/metabolismo , Pró-Opiomelanocortina/metabolismo , Animais , Humanos , Hipoglicemiantes/administração & dosagem , Hipoglicemiantes/farmacologia , Hipotálamo/citologia , Insulina/administração & dosagem , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Plasticidade Neuronal/genética , Pró-Opiomelanocortina/genética , Proteína Tirosina Fosfatase não Receptora Tipo 2/genética , Proteína Tirosina Fosfatase não Receptora Tipo 2/metabolismo , Receptor de Insulina/genética , Receptor de Insulina/metabolismoRESUMO
OBJECTIVE: The development of skeletal muscle insulin resistance is an early physiological defect, yet the intracellular mechanisms accounting for this metabolic defect remained unresolved. Here, we have examined the role of glucose-6-phosphate dehydrogenase (G6PDH) activity in the pathogenesis of insulin resistance in skeletal muscle. METHODS: Multiple mouse disease states exhibiting insulin resistance and glucose intolerance, as well as obese humans defined as insulin-sensitive, insulin-resistant, or pre-diabetic, were examined. RESULTS: We identified increased glucose-6-phosphate dehydrogenase (G6PDH) activity as a common intracellular adaptation that occurs in parallel with the induction of insulin resistance in skeletal muscle and is present across animal and human disease states with an underlying pathology of insulin resistance and glucose intolerance. We observed an inverse association between G6PDH activity and nitric oxide synthase (NOS) activity and show that increasing NOS activity via the skeletal muscle specific neuronal (n)NOSµ partially suppresses G6PDH activity in skeletal muscle cells. Furthermore, attenuation of G6PDH activity in skeletal muscle cells via (a) increased nNOSµ/NOS activity, (b) pharmacological G6PDH inhibition, or (c) genetic G6PDH inhibition increases insulin-independent glucose uptake. CONCLUSIONS: We have identified a novel, previously unrecognized role for G6PDH in the regulation of skeletal muscle glucose metabolism.
Assuntos
Glucose/metabolismo , Glucosefosfato Desidrogenase/metabolismo , Músculo Esquelético/metabolismo , Animais , Glucose-6-Fosfato , Humanos , Insulina , Resistência à Insulina , Camundongos , Fibras Musculares Esqueléticas , Óxido NítricoRESUMO
One serious side effect of statin drugs is skeletal muscle myopathy. Although the mechanism(s) responsible for statin myopathy remains to be fully determined, an increase in muscle atrophy gene expression and changes in mitochondrial content and/or function have been proposed to play a role. In this study, we examined the relationship between statin-induced expression of muscle atrophy genes, regulators of mitochondrial biogenesis, and markers of mitochondrial content in slow- (ST) and fast-twitch (FT) rat skeletal muscles. Male Sprague Dawley rats were treated with simvastatin (60 or 80 mg·kg(-1)·day(-1)) or vehicle control via oral gavage for 14 days. In the absence of overt muscle damage, simvastatin treatment induced an increase in atrogin-1, MuRF1 and myostatin mRNA expression; however, these were not associated with changes in peroxisome proliferator gamma co-activator 1 alpha (PGC-1α) protein or markers of mitochondrial content. Simvastatin did, however, increase neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS) and AMPK α-subunit protein expression, and tended to increase total NOS activity, in FT but not ST muscles. Furthermore, simvastatin induced a decrease in ß-hydroxyacyl CoA dehydrogenase (ß-HAD) activity only in FT muscles. These findings suggest that the statin-induced activation of muscle atrophy genes occurs independent of changes in PGC-1α protein and mitochondrial content. Moreover, muscle-specific increases in NOS expression and possibly NO production, and decreases in fatty acid oxidation, could contribute to the previously reported development of overt statin-induced muscle damage in FT muscles.
Assuntos
Regulação da Expressão Gênica/efeitos dos fármacos , Inibidores de Hidroximetilglutaril-CoA Redutases/farmacologia , Mitocôndrias Musculares/metabolismo , Proteínas Musculares/biossíntese , Atrofia Muscular/metabolismo , Sinvastatina/farmacologia , Fatores de Transcrição/metabolismo , Animais , Masculino , Mitocôndrias Musculares/patologia , Atrofia Muscular/patologia , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Ratos , Ratos Sprague-DawleyRESUMO
Accumulation of diacylglycerol (DG) in muscle is thought to cause insulin resistance. DG is a precursor for phospholipids, thus phospholipid synthesis could be involved in regulating muscle DG. Little is known about the interaction between phospholipid and DG in muscle; therefore, we examined whether disrupting muscle phospholipid synthesis, specifically phosphatidylethanolamine (PtdEtn), would influence muscle DG content and insulin sensitivity. Muscle PtdEtn synthesis was disrupted by deleting CTP:phosphoethanolamine cytidylyltransferase (ECT), the rate-limiting enzyme in the CDP-ethanolamine pathway, a major route for PtdEtn production. While PtdEtn was reduced in muscle-specific ECT knockout mice, intramyocellular and membrane-associated DG was markedly increased. Importantly, however, this was not associated with insulin resistance. Unexpectedly, mitochondrial biogenesis and muscle oxidative capacity were increased in muscle-specific ECT knockout mice and were accompanied by enhanced exercise performance. These findings highlight the importance of the CDP-ethanolamine pathway in regulating muscle DG content and challenge the DG-induced insulin resistance hypothesis.
Assuntos
Cistina Difosfato/análogos & derivados , Diglicerídeos/metabolismo , Etanolaminas/metabolismo , Resistência à Insulina , Músculo Esquelético/metabolismo , Biogênese de Organelas , Animais , Cistina Difosfato/metabolismo , Glucose/metabolismo , Metabolismo dos Lipídeos , Camundongos , Camundongos Knockout , Obesidade/genética , Obesidade/metabolismo , RNA Nucleotidiltransferases/genética , RNA Nucleotidiltransferases/metabolismoRESUMO
Interleukin-6 (IL-6) plays a paradoxical role in inflammation and metabolism. The pro-inflammatory effects of IL-6 are mediated via IL-6 "trans-signaling," a process where the soluble form of the IL-6 receptor (sIL-6R) binds IL-6 and activates signaling in inflammatory cells that express the gp130 but not the IL-6 receptor. Here we show that trans-signaling recruits macrophages into adipose tissue (ATM). Moreover, blocking trans-signaling with soluble gp130Fc protein prevents high-fat diet (HFD)-induced ATM accumulation, but does not improve insulin action. Importantly, however, blockade of IL-6 trans-signaling, unlike complete ablation of IL-6 signaling, does not exacerbate obesity-induced weight gain, liver steatosis, or insulin resistance. Our data identify the sIL-6R as a critical chemotactic signal for ATM recruitment and suggest that selectively blocking IL-6 trans-signaling may be a more favorable treatment option for inflammatory diseases, compared with current treatments that completely block the action of IL-6 and negatively impact upon metabolic homeostasis.
Assuntos
Tecido Adiposo/metabolismo , Dieta Hiperlipídica/efeitos adversos , Resistência à Insulina/fisiologia , Interleucina-6/metabolismo , Macrófagos/metabolismo , Macrófagos/fisiologia , Transdução de Sinais/fisiologia , Tecido Adiposo/fisiologia , Animais , Receptor gp130 de Citocina/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Receptores de Interleucina-6/metabolismoRESUMO
T follicular helper cells (Tfh) are critical for the longevity and quality of antibody-mediated protection against infection. Yet few signaling pathways have been identified to be unique solely to Tfh development. ROQUIN is a post-transcriptional repressor of T cells, acting through its ROQ domain to destabilize mRNA targets important for Th1, Th17, and Tfh biology. Here, we report that ROQUIN has a paradoxical function on Tfh differentiation mediated by its RING domain: mice with a T cell-specific deletion of the ROQUIN RING domain have unchanged Th1, Th2, Th17, and Tregs during a T-dependent response but show a profoundly defective antigen-specific Tfh compartment. ROQUIN RING signaling directly antagonized the catalytic α1 subunit of adenosine monophosphate-activated protein kinase (AMPK), a central stress-responsive regulator of cellular metabolism and mTOR signaling, which is known to facilitate T-dependent humoral immunity. We therefore unexpectedly uncover a ROQUIN-AMPK metabolic signaling nexus essential for selectively promoting Tfh responses.
Assuntos
Proteínas Quinases Ativadas por AMP/metabolismo , Diferenciação Celular , Transdução de Sinais , Linfócitos T Auxiliares-Indutores/fisiologia , Ubiquitina-Proteína Ligases/metabolismo , Animais , Camundongos , Deleção de Sequência , Ubiquitina-Proteína Ligases/genéticaRESUMO
Induction of heat shock protein (HSP)72 protects against obesity-induced insulin resistance, but the underlying mechanisms are unknown. Here, we show that HSP72 plays a pivotal role in increasing skeletal muscle mitochondrial number and oxidative metabolism. Mice overexpressing HSP72 in skeletal muscle (HSP72Tg) and control wild-type (WT) mice were fed either a chow or high-fat diet (HFD). Despite a similar energy intake when HSP72Tg mice were compared with WT mice, the HFD increased body weight, intramuscular lipid accumulation (triacylglycerol and diacylglycerol but not ceramide), and severe glucose intolerance in WT mice alone. Whole-body VO2, fatty acid oxidation, and endurance running capacity were markedly increased in HSP72Tg mice. Moreover, HSP72Tg mice exhibited an increase in mitochondrial number. In addition, the HSP72 coinducer BGP-15, currently in human clinical trials for type 2 diabetes, also increased mitochondrial number and insulin sensitivity in a rat model of type 2 diabetes. Together, these data identify a novel role for activation of HSP72 in skeletal muscle. Thus, the increased oxidative metabolism associated with activation of HSP72 has potential clinical implications not only for type 2 diabetes but also for other disorders where mitochondrial function is compromised.
Assuntos
Respiração Celular , Diabetes Mellitus Tipo 2/metabolismo , Proteínas de Choque Térmico HSP72/metabolismo , Resistência à Insulina , Mitocôndrias Musculares/metabolismo , Obesidade/metabolismo , Proteínas Quinases Ativadas por AMP/metabolismo , Animais , Glicemia , Western Blotting , Peso Corporal , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/fisiopatologia , Dieta Hiperlipídica , Metabolismo Energético , Ácidos Graxos/metabolismo , Leptina/metabolismo , Masculino , Camundongos , Músculo Esquelético/metabolismo , Obesidade/genética , Obesidade/fisiopatologia , Oxirredução , Fosforilação Oxidativa , Receptores Ativados por Proliferador de Peroxissomo/metabolismo , Ratos , Reação em Cadeia da Polimerase em Tempo Real , Sirtuína 1/metabolismoRESUMO
FTY720 is a sphingosine-1-phosphate analog that has been shown to inhibit ceramide synthesis in vitro. Because ceramide accumulation in muscle is associated with insulin resistance, we aimed to examine whether FTY720 would prevent muscle ceramide accumulation in high fat-fed mice and subsequently improve glucose homeostasis. Male C57Bl/6 mice were fed either a chow or high fat-diet (HFD) for 6 wk, after which they were treated with vehicle or FTY720 (5 mg/kg) daily for a further 6 wk. The ceramide content of muscle was examined and insulin action was assessed. Whereas the HFD increased muscle ceramide, this was prevented by FTY720 treatment. This was not associated with alterations in the expression of genes involved in sphingolipid metabolism. Interestingly, the effects of FTY720 on lipid metabolism were not limited to ceramide because FTY720 also prevented the HFD-induced increase in diacylglycerol and triacylglycerol in muscle. Furthermore, the increase in CD36 mRNA expression induced by fat feeding was prevented in muscle of FTY720-treated mice. This was associated with an attenuation of the HFD-induced increase in palmitate uptake and esterification. In addition, FTY720 improved glucose homeostasis as demonstrated by a reduction in plasma insulin, an improvement in whole-body glucose tolerance, an increase in insulin-stimulated glucose uptake, and Akt phosphorylation in muscle. In conclusion, FTY720 exerts beneficial effects on muscle lipid metabolism that prevent lipid accumulation and improve glucose tolerance in high fat-fed mice. Thus, FTY720 and other compounds that target sphingosine-1-phosphate signaling may have therapeutic potential in treating insulin resistance.
Assuntos
Ceramidas/metabolismo , Gorduras na Dieta/efeitos adversos , Glucose/metabolismo , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/metabolismo , Propilenoglicóis/uso terapêutico , Esfingosina/análogos & derivados , Animais , Cloridrato de Fingolimode , Resistência à Insulina/fisiologia , Metabolismo dos Lipídeos/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Obesidade/tratamento farmacológico , Obesidade/metabolismo , Esfingosina/uso terapêuticoRESUMO
The objective of this study was to test the hypothesis that exercise-stimulated muscle glucose uptake (MGU) is augmented by increasing mitochondrial reactive oxygen species (mtROS) scavenging capacity. This hypothesis was tested in genetically altered mice fed chow or a high-fat (HF) diet that accelerates mtROS formation. Mice overexpressing SOD2 (sod2(Tg)), mitochondria-targeted catalase (mcat(Tg)), and combined SOD2 and mCAT (mtAO) were used to increase mtROS scavenging. mtROS was assessed by the H(2)O(2) emitting potential (JH(2)O(2)) in muscle fibers. sod2(Tg) did not decrease JH(2)O(2) in chow-fed mice, but decreased JH(2)O(2) in HF-fed mice. mcat(Tg) and mtAO decreased JH(2)O(2) in both chow- and HF-fed mice. In parallel, the ratio of reduced to oxidized glutathione (GSH/GSSG) was unaltered in sod2(Tg) in chow-fed mice, but was increased in HF-fed sod2(Tg) and both chow- and HF-fed mcat(Tg) and mtAO. Nitrotyrosine, a marker of NO-dependent, reactive nitrogen species (RNS)-induced nitrative stress, was decreased in both chow- and HF-fed sod2(Tg), mcat(Tg), and mtAO mice. This effect was not changed with exercise. Kg, an index of MGU was assessed using 2-[(14)C]-deoxyglucose during exercise. In chow-fed mice, sod2(Tg), mcat(Tg), and mtAO increased exercise Kg compared with wild types. Exercise Kg was also augmented in HF-fed sod2(Tg) and mcat(Tg) mice but unchanged in HF-fed mtAO mice. In conclusion, mtROS scavenging is a key regulator of exercise-mediated MGU and this regulation depends on nutritional state.