Ciliary neurotrophic factor improves diabetic parameters and hepatic steatosis and increases basal metabolic rate in db/db mice

Hypertrophic cardiomyopathy in high-fat diet-induced obesity: role of suppression of forkhead transcription factor and atrophy gene transcription

Cellular hypertrophy is regulated by coordinated pro- and antigrowth machineries. Foxo transcription factors initiate an atrophy-related gene program to counter hypertrophic growth. This study was designed to evaluate the role of Akt, the forkhead transcription factor Foxo3a, and atrophy genes muscle-specific RING finger (MuRF)-1 and atrogin-1 in cardiac hypertrophy and contractile dysfunction associated with high-fat diet-induced obesity. Mice were fed a low- or high-fat diet for 6 mo along with a food-restricted high-fat weight control group. Echocardiography revealed decreased fractional shortening and increased end-systolic diameter and cardiac hypertrophy in high-fat obese but not in weight control mice. Cardiomyocytes from high-fat obese but not from weight control mice displayed contractile and intracellular Ca2+ defects including depressed maximal velocity of shortening/relengthening, prolonged duration of shortening/relengthening, and reduced intracellular Ca2+ rise and clearance. Caspase activities were greater in high-fat obese but not in weight control mouse hearts. Western blot analysis revealed enhanced basal Akt and Foxo3a phosphorylation and reduced insulin-stimulated phosphorylation of Akt and Foxo3a without changes in total protein expression of Akt and Foxo3a in high-fat obese hearts. RT-PCR and immunoblotting results displayed reduced levels of the atrogens atrogin-1 and MuRF-1, the upregulated hypertrophic markers GATA4 and ciliary neurotrophic factor receptor-alpha, as well as the unchanged calcineurin and proteasome ubiquitin in high-fat obese mouse hearts. Transfection of H9C2 myoblast cells with dominant-negative Foxo3a adenovirus mimicked palmitic acid (0.8 mM for 24 h)-induced GATA4 upregulation without an additive effect. Dominant-negative Foxo3a-induced upregulation of pAkt and repression of phosphatase and tensin homologue were abrogated by palmitic acid. These results suggest a cardiac hypertrophic response in high-fat diet-associated obesity at least in part through inactivation of Foxo3a by the Akt pathway.

Metabolic remodeling in adipocytes promotes ciliary neurotrophic factor-mediated fat loss in obesity

Obesity is characterized by an expanded adipose tissue mass, and reversing obesity reduces the risk of insulin resistance and cardiovascular disease. Ciliary neurotrophic factor (CNTF) reverses obesity by promoting the preferential loss of white adipose tissue. We evaluated the cellular and molecular mechanisms by which CNTF regulates adiposity. Obese mice fed a high-fat diet were treated with saline or recombinant CNTF for 10 d, and adipose tissue was removed for analysis. Another group fed a high-fat diet was pair fed to CNTF mice. In separate experiments, 3T3-L1 adipocytes were treated with CNTF to examine metabolic responses and signaling. CNTF reduced adipose mass that resulted from reductions in adipocyte area and triglyceride content. CNTF treatment did not affect lipolysis but resulted in decreases in fat esterification and lipogenesis and enhanced fatty acid oxidation. The enhanced fat oxidation was associated with the expression of peroxisome proliferator-activated receptor coactivator-1alpha (PGC1alpha) and nuclear respiratory factor 1 and increases in oxidative phosphorylation subunits and mitochondrial biogenesis as determined by electron microscopy. Studies in cultured adipocytes revealed that CNTF activates p38 MAPK and AMP-activated protein kinase. Inhibiting p38 activation prevented the CNTF-induced increase in PGC1alpha but not AMP-activated protein kinase activation. Diminished food intake with pair feeding induced similar decreases in fat mass, but this was related to increased expression of uncoupling protein 1. We conclude that CNTF reprograms adipose tissue to promote mitochondrial biogenesis, enhancing oxidative capacity and reducing lipogenic capacity, thereby resulting in triglyceride loss.

Ciliary neurotrophic factor receptor alpha subunit-modulated multiple downstream signaling pathways in hepatic cancer cell lines and their biological implications

Ciliary neurotrophic factor (CNTF) plays important roles in a variety of tissues including neural and non-neural systems, but the function of CNTF and its receptor (CNTFR) in liver remains unclear. In this study, we demonstrate that CNTFRalpha is expressed heterogeneously in normal human liver and hepatocellular carcinoma (HCC) specimens but not in hepatoblastoma specimens. We choose the CNTFRalpha(+)/CNTFRalpha(-) (CNTFRalpha positive/ CNTFRalpha negative) cell models of hepatic origin to study multiple downstream pathways of CNTFRalpha. We show that the presence of CNTFRalpha determines the temporal activation patterns of downstream signaling molecules and serves as a key modulator in regulating PI3K and AMP-activated protein kinase (AMPK) dynamically under CNTF stimulation, thus resulting in the increase of glucose uptake and translocation of glucose transporter 4 (GLUT4). Furthermore, CNTF-induced mitogen-activated protein kinase (MAPK) activation suppresses AMPK activity in the early phase of CNTF stimulation. Moreover, the protective role of CNTF against cell-cycle arrest is dependent on the presence of CNTFRalpha and is modulated by the glucose concentration of the culture medium.

CONCLUSION

Our results demonstrate the importance of CNTFRalpha-mediated downstream signaling pathways and their functional implications in hepatic cancer cells, thus highlighting a better understanding of the biological roles of CNTFRalpha in human liver abnormalities, including metabolic diseases and hepatocarcinogenesis.

Loss of cytokine-STAT5 signaling in the CNS and pituitary gland alters energy balance and leads to obesity

Signal transducers and activators of transcription (STATs) are critical components of cytokine signaling pathways. STAT5A and STAT5B (STAT5), the most promiscuous members of this family, are highly expressed in specific populations of hypothalamic neurons in regions known to mediate the actions of cytokines in the regulation of energy balance. To test the hypothesis that STAT5 signaling is essential to energy homeostasis, we used Cre-mediated recombination to delete the Stat5 locus in the CNS. Mutant males and females developed severe obesity with hyperphagia, impaired thermal regulation in response to cold, hyperleptinemia and insulin resistance. Furthermore, central administration of GM-CSF mediated the nuclear accumulation of STAT5 in hypothalamic neurons and reduced food intake in control but not in mutant mice. These results demonstrate that STAT5 mediates energy homeostasis in response to endogenous cytokines such as GM-CSF.

Association of NTRK3 and its interaction with NGF suggest an altered cross-regulation of the neurotrophin signaling pathway in eating disorders

Eating disorders (EDs) are complex psychiatric diseases that include anorexia nervosa and bulimia nervosa, and have higher than 50% heritability. Previous studies have found association of BDNF and NTRK2 to ED, while animal models suggest that other neurotrophin genes might also be involved in eating behavior. We have performed a family-based association study with 151 TagSNPs covering 10 neurotrophin signaling genes: NGFB, BDNF, NTRK1, NGFR/p75, NTF4/5, NTRK2, NTF3, NTRK3, CNTF and CNTFR in 371 ED trios of Spanish, French and German origin. Besides several nominal associations, we found a strong significant association after correcting for multiple testing (P = 1.04 x 10(-4)) between ED and rs7180942, located in the NTRK3 gene, which followed an overdominant model of inheritance. Interestingly, HapMap unrelated individuals carrying the rs7180942 risk genotypes for ED showed higher levels of expression of NTRK3 in lymphoblastoid cell lines. Furthermore, higher expression of the orthologous murine Ntrk3 gene was also detected in the hypothalamus of the anx/anx mouse model of anorexia. Finally, variants in NGFB gene appear to modify the risk conferred by the NTRK3 rs7180942 risk genotypes (P = 4.0 x 10(-5)) showing a synergistic epistatic interaction. The reported data, in addition to the previous reported findings for BDNF and NTRK2, point neurotrophin signaling genes as key regulators of eating behavior and their altered cross-regulation as susceptibility factors for EDs.

The role of interleukin-6 in insulin resistance, body fat distribution and energy balance

Interleukin-6 (IL-6) is a central player in the regulation of inflammation, haematopoiesis, immune response and host defense mechanisms. During the last decade, an accumulating amount of data suggested a pivotal role for IL-6 in metabolic processes, thus fortifying the picture of IL-6 as a multifaceted, pleiotropic cytokine. Because of its secretion by adipose tissue and contracting skeletal muscle and its broad action on central and peripheral organs, IL-6 has been termed an adipokine and a myokine. Its quantitative release from adipose tissue results in a subclinical, systemic elevation of IL-6 plasma levels with increasing body fat content, which may be implicated in the proinflammatory state leading to insulin resistance. On the other hand, IL-6 produced in the working muscle during physical activity could act as an energy sensor by activating AMP-activated kinase and enhancing glucose disposal, lipolysis and fat oxidation. In addition, both impaired IL-6 secretion and action are risk factors for weight gain. Thus, IL-6 clearly has lipolytic effects and anti-obesity potential. However, the application of IL-6 itself is at least limited by a narrow therapeutic range and its important function for a balanced inflammatory response. Further studies on the molecular basis of the metabolic effects of IL-6 could elucidate novel therapeutic strategies for custom-designed, IL-6-related substances.

Peptide YY regulates bone turnover in rodents

BACKGROUND & AIMS

Peptide YY (PYY) and pancreatic polypeptide (PPY) are members of the neuropeptide Y peptide family. The neuropeptide Y receptor signaling pathway has been implicated in a number of physiologic processes, including the regulation of energy balance and bone mass. To investigate the contribution of endogenous PYY and PPY to these processes, we generated both Pyy- and Ppy-deficient mice.

METHODS

Pyy(-/-) and Ppy(-/-) mice and their respective wild-type littermates were studied from 8 weeks to 9 months of age. Food intake, metabolic parameters, and locomotor activity were monitored using indirect calorimetry. Body composition and bone parameters were analyzed using dual energy x-ray absorptiometry, histomorphometry, and vertebral compression testing.

RESULTS

Studies in these mice showed an osteopenic phenotype specific to the Pyy-deficient line, which included a reduction in trabecular bone mass and a functional deficit in bone strength. Furthermore, female Pyy(-/-) mice showed a greater sensitivity to ovariectomy-induced bone loss compared with wild-type littermates. No food intake or metabolic phenotype was apparent in male or female Pyy(-/-) mice on standard chow. However, female Pyy(-/-) mice on a high-fat diet showed a greater propensity to gain body weight and adiposity. No metabolic or osteopenic phenotype was observed in Ppy-deficient mice.

CONCLUSIONS

These results indicate that endogenous PYY plays a critical role in regulating bone mass. In comparison, its role in regulating body weight is minor and is confined to situations of high-fat feeding.

PTEN expression contributes to the regulation of muscle protein degradation in diabetes

OBJECTIVE

Conditions accelerating muscle proteolysis are frequently associated with defective phosphatidylinositol 3-kinase (PI3K)/Akt signaling and reduced PI3K-generated phosphatidylinositol 3,4,5-triphosphate (PIP(3)). We evaluated the control of muscle protein synthesis and degradation in mouse models of type 1 and 2 diabetes to determine whether defects besides PI3K/Akt activities affect muscle metabolism.

RESEARCH DESIGN AND METHODS

We evaluated the expression and activity of PTEN, the phosphatase converting PIP(3) to inactive phosphatidylinositol 4,5-bisphosphate, and studied how PTEN influences muscle protein in diabetic wild-type mice and in mice with partial deficiency of PTEN(+/-).

RESULTS

In acutely diabetic mice, muscle PTEN expression was decreased. It was increased by chronic diabetes or insulin resistance. In cultured C2C12 myotubes, acute suppression of PI3K activity led to decreased PTEN expression, while palmitic acid increased PTEN in myotubes in a p38-dependent fashion. To examine whether PTEN affects muscle protein turnover, we studied primary myotubes cultures from wild-type and PTEN(+/-) mice. The proteolysis induced by serum deprivation was suppressed in PTEN(+/-) cells. Moreover, the sizes of muscle fibers in PTEN(+/-) and wild-type mice were similar, but the increase in muscle proteolysis caused by acute diabetes was significantly suppressed by PTEN(+/-). This antiproteolytic response involved higher PIP(3) and p-Akt levels and a decrease in caspase-3-mediated actin cleavage and activation of the ubiquitin-proteasome system as signified by reduced induction of atrogin-1/MAFbx or MurF1 (muscle-specific RING finger protein 1).

CONCLUSIONS

Changes in PTEN expression participate in the regulation of muscle proteolytic pathways. A decrease in PTEN could be a compensatory mechanism to prevent muscle protein losses.

Influence of maternal undernutrition and overfeeding on cardiac ciliary neurotrophic factor receptor and ventricular size in fetal sheep

Intrauterine nutrition status is reported to correlate with risk of cardiovascular diseases in adulthood. Either under- or overnutrition during early to mid gestation contributes to altered fetal growth and ventricular geometry. This study was designed to examine myocardial expression of ciliary neurotrophic factor receptor alpha (CNTFRalpha) and its downstream mediator signal transducer and activator of transcription 3 (STAT3) on maternal undernutrition- or overnutrition-induced changes in fetal heart weight. Multiparous ewes were fed with 50% [nutrient-restricted (NR)], 100% (control) or 150% [overfed (OF)] of National Research Council requirements from 28 to 78 days of gestation (dG; term, 148 dG). Ewes were euthanized on Day 78, and the gravid uteri and fetuses recovered. Ventricular protein expression of CNTFRalpha, STAT3, phosphorylated STAT3, insulin-like growth factor I receptor (IGF-1R), and IGF binding protein 3 (IGFBP3) were quantitated using Western blot. Plasma cortisol levels were higher in both NR and OF fetuses, whereas plasma IGF-1 levels were lower and higher in NR and OF fetuses. Fetal weights were reduced by 29.9% in NR ewes and were increased by 22.2% in fetuses from OF ewes compared to control group. Nutrient restriction did not affect fetal heart or ventricular weights, whereas overfeeding increased heart and ventricular weights. Protein expression of CNTFRalpha in fetal ventricular tissue was reduced in OF group, whereas STAT3 and phosphorylated STAT3 levels were reduced in both NR and OF groups. Expression of IGF-1R and IGFBP3 was unaffected in either NR or OF group. These data suggested that, compared with maternal undernutrition, intrauterine overfeeding during early to mid gestation is associated with increases in fetal blood concentrations of cortisol and IGF-1, in association with ventricular hypertrophy where reduced expression of CNTFRalpha and STAT3 may play a role.

Activation of astrocytes by CNTF induces metabolic plasticity and increases resistance to metabolic insults

High energy demands of neurons make them vulnerable to adverse effects of energy impairment. Recently, astrocytes were shown to regulate the flux of energy substrates to neurons. In pathological situations, astrocytes are activated but the consequences on brain energy metabolism are still poorly characterized. We found that local lentiviral-mediated gene transfer of ciliary neurotrophic factor (CNTF), a cytokine known to activate astrocytes, induced a stable decrease in the glycolytic flux in the rat striatum in vivo as measured by 2-[18F]-2-deoxy-D-glucose autoradiography and micro-positron emission tomography imaging. The activity of the mitochondrial complex IV enzyme cytochrome oxidase was not modified, suggesting maintenance of downstream oxidative steps of energy production. CNTF significantly increased the phosphorylation level of the intracellular energy sensor AMP-activated protein kinase (AMPK), supporting a specific reorganization of brain energy pathways. Indeed, we found that different key enzymes/transporters of fatty acids beta-oxidation and ketolysis were overexpressed by CNTF-activated astrocytes within the striatum. In primary striatal neuron/astrocyte mixed cultures exposed to CNTF, the AMPK pathway was also activated, and the rate of oxidation of fatty acids and ketone bodies was significantly enhanced. This metabolic plasticity conferred partial glial and neuronal protection against prolonged palmitate exposure and glycolysis inhibition. We conclude that CNTF-activated astrocytes may have a strong protective potential to face severe metabolic insults.

Recombinant human ciliary neurotrophic factor reduces weight partly by regulating nuclear respiratory factor 1 and mitochondrial transcription factor A

Ciliary neurotrophic factor (CNTF) can lead to weight loss by up-regulating energy metabolism and the expression of UCP-1 in mitochondria. To investigate the up-stream regulators of the expression of UCP-1, recombinant human CNTF (rhCNTF) (0.1, 0.3, 0.9 mg/kg/day s.c.) administered to KK-Ay mice for 30 days resulting in reductions in body weight and perirenal fat mass. In brown adipose tissues, the gene expressions of nuclear respiratory factor (NRF)-1, mitochondrial transcription factor A (TFam) and uncoupling protein (UCP)-1 were found up-regulated by rhCNTF. To the best of our knowledge, these effects represent new insights on the mechanisms of action of weight loss by rhCNTF. In addition, we also found that rhCNTF increased the activity of mitochondrial complex IV. The stimulation of NRF-1, TFam, UCP-1 and the enhanced activity of mitochondrial complex IV may be associated with remedying obesity. The result indicates that rhCNTF can enhance the expressions of NRF-1 and TFam, both of which can up-regulate the expression of UCP-1.

Genetic deletion of Trb3, the mammalian Drosophila tribbles homolog, displays normal hepatic insulin signaling and glucose homeostasis

Trb3, a mammalian homolog of Drosophila tribbles, was proposed as a suppressor of Akt activity, predominantly in conditions of fasting and diabetes. Given these prior studies, we sought to determine whether Trb3 plays a major role in modulating hepatic insulin sensitivity. To answer this question, we produced mice in which a lacZ reporter was knocked into the locus containing the gene Trib3, resulting in a Trib3 null animal. Trib3 expression analyses demonstrated that the Trib3 is expressed in liver, adipose tissues, heart, kidney, lung, skin, small intestine, stomach, and denervated, but not normal, skeletal muscle. Trib3(-/-) mice are essentially identical to their wild-type littermates in overall appearance and body composition. Phenotypic analysis of Trib3(-/-) mice did not detect any alteration in serum glucose, insulin, or lipid levels; glucose or insulin tolerance; or energy metabolism. Studies in Trib3(-/-) hepatocytes revealed normal Akt and glycogen synthase kinase- 3beta phosphorylation patterns, glycogen levels, and expressions of key regulatory gluconeogenic and glycolytic genes. These data demonstrate that deletion of Trib3 has minimal effect on insulin-induced Akt activation in hepatic tissue, and, as such, they question any nonredundant role for Trb3 in the maintenance of glucose and energy homeostasis in mice.

Bezafibrate regulates the expression and enzyme activity of 11beta-hydroxysteroid dehydrogenase type 1 in murine adipose tissue and 3T3-L1 adipocytes

A clinically employed antihyperlipidemic drug, bezafibrate, has been characterized as a PPAR(alpha, -gamma, and -delta) pan-agonist in vitro. Recent extended trials have highlighted its antidiabetic properties in humans. However, the underlying molecular mechanism is not fully elucidated. The present study was designed to explore potential regulatory mechanisms of intracellular glucocorticoid reactivating enzyme, 11beta-HSD1 and anti-diabetic hormone, adiponectin by bezafibrate in murine adipose tissue, and cultured adipocytes. Treatment of db/db mice with bezafibrate significantly ameliorated hyperglycemia and insulin resistance, accompanied by a marked reduction of triglyceride and nonesterified fatty acids. Despite equipotent in lipid-lowering effects, another fibrate, fenofibrate, did not show such beneficial effects on glycemic control. Treatment of bezafibrate caused a marked decrease in the mRNA level of 11beta-HSD1 preferentially in adipose tissue of db/db mice (-47%, P<0.05), concomitant with a significant increase in plasma adiponectin level (+37%, P<0.01). Notably, treatment of bezafibrate caused a marked decrease in the mRNA level (-34%, P<0.01) and enzyme activity (-32%, P<0.01) of 11beta-HSD1, whereas the treatment substantially augmented the expression (+71%, P<0.01) and secretion (+27%, P<0.01) of adiponectin in 3T3-L1 adipocytes. Knockdown of 11beta-HSD1 by siRNA confirmed that 11beta-HSD1 acts as a distinct oxoreductase in adipocytes and validated the enzyme activity assays in the present study. Effects of bezafibrate on regulation of 11beta-HSD1 and adiponectin in murine adipocytes were comparable with those in thiazolidinediones. This is the first demonstration that bezafibrate directly regulates 11beta-HSD1 and adiponectin in murine adipocytes, both of which may contribute to metabolically-beneficial effects by bezafibrate.

gp130 receptor ligands as potential therapeutic targets for obesity

Obesity and its related cluster of pathophysiologic conditions including insulin resistance, glucose intolerance, dyslipidemia, and hypertension are recognized as growing threats to world health. It is now estimated that 10% of the world's population is overweight or obese. As a result, new therapeutic options for the treatment of obesity are clearly warranted. Recent research has focused on the role that gp130 receptor ligands may play as potential therapeutic targets in obesity. One cytokine in particular, ciliary neurotrophic factor (CNTF), acts both centrally and peripherally and mimics the biologic actions of the appetite control hormone leptin, but unlike leptin, CNTF appears to be effective in obesity and as such may have therapeutic potential. In addition, CNTF suppresses inflammatory signaling cascades associated with lipid accumulation in liver and skeletal muscle. This review examines the potential role of gp130 receptor ligands as part of a therapeutic strategy to treat obesity.

Decreased hepatic futile cycling compensates for increased glucose disposal in the Pten heterodeficient mouse

Despite altered regulation of insulin signaling, Pten(+/-) heterodeficient standard diet-fed mice, approximately 4 months old, exhibit normal fasting glucose and insulin levels. We report here a stable isotope flux phenotyping study of this "silent" phenotype, in which tissue-specific insulin effects in whole-body Pten(+/-)-deficient mice were dissected in vivo. Flux phenotyping showed gain of function in Pten(+/-) mice, seen as increased peripheral glucose disposal, and compensation by a metabolic feedback mechanism that 1) decreases hepatic glucose recycling via suppression of glucokinase expression in the basal state to preserve hepatic glucose production and 2) increases hepatic responsiveness in the fasted-to-fed transition. In Pten(+/-) mice, hepatic gene expression of glucokinase was 10-fold less than wild-type (Pten(+/+)) mice in the fasted state and reached Pten(+/+) values in the fed state. Glucose-6-phosphatase expression was the same for Pten(+/-) and Pten(+/+) mice in the fasted state, and its expression for Pten(+/-) was 25% of Pten(+/+) in the fed state. This study demonstrates how intra- and interorgan flux compensations can preserve glucose homeostasis (despite a specific gene defect that accelerates glucose disposal) and how flux phenotyping can dissect these tissue-specific flux compensations in mice presenting with a "silent" phenotype.

Continued administration of ciliary neurotrophic factor protects mice from inflammatory pathology in experimental autoimmune encephalomyelitis

Multiple sclerosis is an inflammatory disease of the central nervous system that leads to loss of myelin and oligodendrocytes and damage to axons. We show that daily administration (days 8 to 24) of murine ciliary neurotrophic factor (CNTF), a neurotrophic factor that has been described as a survival and differentiation factor for neurons and oligodendrocytes, significantly ameliorates the clinical course of a mouse model of multiple sclerosis. In the acute phase of experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein peptide 35-55, treatment with CNTF did not change the peripheral immune response but did reduce the number of perivascular infiltrates and T cells and the level of diffuse microglial activation in spinal cord. Blood brain barrier permeability was significantly reduced in CNTF-treated animals. Beneficial effects of CNTF did not persist after it was withdrawn. After cessation of CNTF treatment, inflammation and symptoms returned to control levels. However, slight but significantly higher numbers of oligodendrocytes, NG2-positive cells, axons, and neurons were observed in mice that had been treated with high concentrations of CNTF. Our results show that CNTF inhibits inflammation in the spinal cord, resulting in amelioration of the clinical course of experimental autoimmune encephalomyelitis during time of treatment.

Interleukin-6 trans-signalling in chronic inflammation and cancer

Interleukin-6 (IL-6) is a cytokine, which plays an important role in many chronic inflammatory diseases. IL-6 belongs to a family of 10 cytokines, which all act via receptor complexes containing the cytokine receptor subunit gp130. On cells, IL-6 first binds to a specific membrane-bound IL-6R and the complex of IL-6 and IL-6R interacts with gp130 leading to signal initiation. Whereas gp130 is widely expressed throughout the body, the IL-6R is only found on some cells including hepatocytes and some leucocytes. A soluble form of the IL-6R is an agonist capable of transmitting signals through interaction with the gp130 protein. In vivo, the IL-6/soluble IL-6R complex stimulates several types of target cells, which are unresponsive to IL-6 alone, as they do not express the membrane-bound IL-6R. We have named this process trans-signalling. We provided evidence that a soluble form of the IL-6 family signalling receptor subunit gp130 is the natural inhibitor of IL-6 trans-signalling responses. We showed that in chronic inflammatory diseases such as inflammatory bowel disease, peritonitis, rheumatoid arthritis, asthma as well as in colon cancer, IL-6 trans-signalling is critically involved in the maintenance of the disease state. Moreover, in all these animal models, the progression of the disease can be interrupted by specifically interfering with IL-6 trans-signalling using recombinant-soluble gp130Fc protein. The pathophysiologic mechanisms by which the IL-6/soluble IL-6R complex perpetuates the inflammatory state are discussed.

Ciliary neurotrophic factor prevents acute lipid-induced insulin resistance by attenuating ceramide accumulation and phosphorylation of c-Jun N-terminal kinase in peripheral tissues

Ciliary neurotrophic factor (CNTF) is a member of the gp130 receptor cytokine family recently identified as an antiobesity agent in rodents and humans by mechanisms that remain unclear. We investigated the impact of acute CNTF treatment on insulin action in the presence of lipid oversupply. To avoid confounding effects of long-term high-fat feeding or genetic manipulation on whole-body insulin sensitivity, we performed a 2-h Intralipid infusion (20% heparinized Intralipid) with or without recombinant CNTF pretreatment (Axokine 0.3 mg/kg), followed by a 2-h hyperinsulinemic-euglycemic clamp (12 mU/kg.min) in fasted, male Wistar rats. Acute Intralipid infusion increased plasma free fatty acid levels from 1.0 +/- 0.1 to 2.5 +/- 0.3 mM, which subsequently caused reductions in skeletal muscle (insulin-stimulated glucose disposal rate) and liver (hepatic glucose production) insulin sensitivity by 30 and 45%, respectively. CNTF pretreatment completely prevented the lipid-mediated reduction in insulin-stimulated glucose disposal rate and the blunted suppression of hepatic glucose production by insulin. Although lipid infusion increased triacylglycerol and ceramide accumulation and phosphorylation of mixed linage kinase 3 and c-Jun N-terminal kinase 1 in skeletal muscle, CNTF pretreatment prevented these lipid-induced effects. Alterations in hepatic and muscle insulin signal transduction as well as phosphorylation of c-Jun N-terminal kinase 1/2 paralleled alterations in insulin sensitivity. These data support the use of CNTF as a potential therapeutic means to combat lipid-induced insulin resistance.

CNTF reverses obesity-induced insulin resistance by activating skeletal muscle AMPK

Ciliary neurotrophic factor (CNTF) induces weight loss and improves glucose tolerance in humans and rodents. CNTF is thought to act centrally by inducing hypothalamic neurogenesis to modulate food intake and peripherally by altering hepatic gene expression, in a manner similar to that of leptin. Here, we show that CNTF signals through the CNTFRalpha-IL-6R-gp130beta receptor complex to increase fatty-acid oxidation and reduce insulin resistance in skeletal muscle by activating AMP-activated protein kinase (AMPK), independent of signaling through the brain. Thus, our findings further show that the antiobesogenic effects of CNTF in the periphery result from direct effects on skeletal muscle, and that these peripheral effects are not suppressed by diet-induced or genetic models of obesity, an essential requirement for the therapeutic treatment of obesity-related diseases.

Activation of the cardiac ciliary neurotrophic factor receptor reverses left ventricular hypertrophy in leptin-deficient and leptin-resistant obesity

Disruption of the leptin signaling pathway within the heart causes left ventricular hypertrophy (LVH). Because human obesity is a syndrome of leptin resistance, which is not amenable to leptin treatment, the identification of parallel signal transduction pathways is of potential therapeutic value. Ciliary neurotrophic factor (CNTF), which acts parallel to leptin in the hypothalamus, is not previously recognized to have cardiac activity. We hypothesized that CNTF receptors are present on cardiomyocytes and their activation reverses LVH in both leptin-deficient ob/ob and leptin-resistant db/db mice. The localization of CNTF receptors (CNTFRalpha) to the sarcolemma in C57BL/6, ob/ob and db/db was confirmed in situ with immunohistochemistry, and immunoblotting (60 and 40 kDa) on isolated myocytes. ob/ob mice were randomly assigned to receive s.c. recombinant CNTF (CNTF(Ax15); 0.1 mg x kg(-1) per day; n = 11) calorie-restriction (n = 9), or feeding ad libitum (n = 11). db/db mice were allocated to three similar groups (n = 8, 7, and 8, respectively) plus a leptin group (1 mg x kg(-1) per day; n = 7). Echocardiography showed that CNTF(Ax15) reduced cardiac hypertrophy [posterior wall thickness decreased by 29 +/- 8% (P < 0.01) in ob/ob and by 21 +/- 3% in db/db mice (P < 0.01)], which was consistent with the reduction of myocyte width. Western blotting showed that leptin and CNTF(Ax15) activated Stat3 and ERK1/2 pathway in cultured adult mice cardiomyocytes and cardiac tissue from in ob/ob and db/db mice. Together, these findings support the role of a previously undescribed signaling pathway in obesity-associated cardiac hypertrophy and have therapeutic implications for patients with obesity-related cardiovascular disease and other causes of LVH.

Ciliary neurotrophic factor restores gallbladder contractility in leptin-resistant obese diabetic mice

BACKGROUND

Obesity and diabetes are major risk factors for cholesterol gallstones, and the majority of obese people are leptin-resistant. Our previous work has shown that both leptin-deficient (Lepob) and leptin-resistant (Lepdb) obese diabetic mice have decreased in vitro gallbladder motility. Leptin administration to leptin-deficient (Lepob) animals restores gallbladder motility and reverses obesity and hyperinsulinemia. However, additional leptin in leptin-resistant obesity would not be expected to improve obesity-related parameters. Recent studies demonstrate that ciliary neurotrophic factor (CNTF) reduces weight and hyperinsulinemia in leptin-resistant obesity. Our hypothesis is that CNFT would cause weight loss, lower blood sugars, and restore gallbladder contractility in leptin-resistant (Lepdb) mice.

MATERIALS AND METHODS

20 C57b/6J and 20 Lepdb 8-week-old female mice were injected daily with either intraperitoneal saline or 0.3 microg/g CNTFAx15 for 17 days. Gallbladders were mounted in muscle baths and stimulated with acetylcholine, neuropeptide Y, and cholecystokinin. Gallbladder volume, serum glucose, insulin, liver weight, liver fat, and gallbladder responses were measured. Data were analyzed by ANOVA.

RESULTS

Saline treated obese mice had greater body weight and obesity parameters, but decreased gallbladder contractility to neurotransmitters compared to saline treated lean mice. CNTF administration to obese mice decreased body weight and obesity parameters, and restored gallbladder contractility. CNTF treated lean animals had weight loss and decreased gallbladder contraction to acetylcholine and cholecystokinin compared to saline treated lean animals.

CONCLUSIONS

Ciliary neurotrophic factor (CNTF) causes 1) weight loss, 2) improvement of diabetes, and 3) alterations in gallbladder motility that is improved in obese mice but decreased in lean mice. We conclude that CNTF may improve gallbladder contractility in leptin-resistant obesity with diabetes.

Absence of ghrelin protects against early-onset obesity

The gut peptide ghrelin, the endogenous ligand for the growth hormone secretagogue receptor, has been implicated not only in the regulation of pituitary growth hormone (GH) secretion but in a number of endocrine and nonendocrine functions, including appetitive behavior and carbohydrate substrate utilization. Nevertheless, recent genetic studies have failed to show any significant defects in GH levels, food intake, or body weight in adult ghrelin-deficient (Ghrl-/-) mice. Here we demonstrate that male Ghrl-/- mice are protected from the rapid weight gain induced by early exposure to a high-fat diet 3 weeks after weaning (6 weeks of age). This reduced weight gain was associated with decreased adiposity and increased energy expenditure and locomotor activity as the animals aged. Despite the absence of ghrelin, these Ghrl-/- mice showed a paradoxical preservation of the GH/IGF-1 axis, similar to that reported in lean compared with obese humans. These findings suggest an important role for endogenous ghrelin in the metabolic adaptation to nutrient availability.

Circulating resistin in lean, obese, and insulin-resistant mouse models: lack of association with insulinemia and glycemia

Resistin is an adipocyte-secreted hormone proposed to link obesity with insulin resistance and diabetes, but no previous study has performed a joint quantitative evaluation of white adipose tissue (WAT) resistin mRNA expression and serum levels in relation to insulinemia and glycemia in mice. We have thus comparatively assessed WAT resistin mRNA expression and serum resistin levels in lean C57BL/6J mice and various mouse models of obesity, including diet-induced obese (DIO) C57BL/6J mice, high fat-fed TNF-alpha-/- mice, and brown adipose tissue (BAT)-deficient uncoupling protein-diphtheria toxin A chain (UCP1-DTA) mice. We also studied whether treatment with the weight-reducing and insulin-sensitizing compounds, MTII, an alpha-melanocyte-stimulating hormone analog, or CNTF(Ax15), a ciliary neurotrophic factor analog, alters resistin mRNA expression and/or circulating levels in lean and DIO C57BL/6J mice. We find that resistin mRNA expression is similar in DIO and lean C57BL/6J mice, as well as in TNF-alpha-/- and wild-type (WT) mice. Circulating resistin levels, however, are higher in DIO C57BL/6J, high fat-fed TNF-alpha-/-, and UCP1-DTA mice compared with lean controls. Moreover, although resistin mRNA expression is upregulated by MTII treatment for 24 h and downregulated by CNTF(Ax15) treatment for 3 or 7 days, circulating resistin levels are not altered by MTII or CNTF(Ax15) treatment. In addition, serum resistin levels, but not resistin mRNA expression levels, are correlated with body weight, and neither resistin mRNA expression nor serum resistin levels are correlated with serum insulin or glucose levels. We conclude that transcriptional regulation of resistin in WAT does not correlate with circulating resistin levels and that circulating resistin is unlikely to play a major endocrine role in insulin resistance or glycemia in mice.

Absence of the lipid phosphatase SHIP2 confers resistance to dietary obesity

Genetic ablation of Inppl1, which encodes SHIP2 (SH2-domain containing inositol 5-phosphatase 2), was previously reported to induce severe insulin sensitivity, leading to early postnatal death. In the previous study, the targeting construct left the first eighteen exons encoding Inppl1 intact, generating a Inppl1(EX19-28-/-) mouse, and apparently also deleted a second gene, Phox2a. We report a new SHIP2 knockout (Inppl1(-/-)) targeted to the translation-initiating ATG, which is null for Inppl1 mRNA and protein. Inppl1(-/-) mice are viable, have normal glucose and insulin levels, and normal insulin and glucose tolerances. The Inppl1(-/-) mice are, however, highly resistant to weight gain when placed on a high-fat diet. These results suggest that inhibition of SHIP2 would be useful in the effort to ameliorate diet-induced obesity, but call into question a dominant role of SHIP2 in modulating glucose homeostasis.

Intrahepatic gene expression during chronic hepatitis C virus infection in chimpanzees

Hepatitis C virus (HCV) infections represent a global health problem and are a major contributor to end-stage liver disease including cirrhosis and hepatocellular carcinoma. An improved understanding of the parameters involved in disease progression is needed to develop better therapies and diagnostic markers of disease manifestation. To better understand the dynamics of host gene expression resulting from persistent virus infection, DNA microarray analyses were conducted on livers from 10 chimpanzees persistently infected with HCV. A total of 162 genes were differentially regulated in chronically infected animals compared to uninfected controls. Many genes exhibited a remarkable consistency in changes in expression in the 10 chronically infected animals. A second method of analysis identified 971 genes altered in expression during chronic infection at a 99% confidence level. As with acute-resolving HCV infections, many interferon (IFN)-stimulated genes (ISGs) were transcriptionally elevated, suggesting an ongoing response to IFN and/or double-stranded RNA which is amplified in downstream ISG expression. Thus, persistent infection with HCV results in a complex and partially predictable pattern of gene expression, although the underlying mechanisms regulating the different pathways are not well defined. A single genotype 3-infected animal was available for analysis, and this animal exhibited reduced levels of ISG expression compared to levels of expression with genotype 1 infections and increased expression of a number of genes potentially involved in steatosis. Gene expression data in concert with other observations from HCV infections permit speculation on the regulation of specific aspects of HCV infection.

Ciliary neurotrophic factorAx15 alters energy homeostasis, decreases body weight, and improves metabolic control in diet-induced obese and UCP1-DTA mice

Ciliary neurotrophic factor (CNTF) potently reduces appetite and body weight in rodents and humans. We studied the short- and long-term effects of CNTF(Ax15), a second-generation CNTF analog, in diet-induced obese C57BL/6J mice and brown adipose tissue (BAT)-deficient obese UCP1-DTA (uncoupling protein 1-diphtheria toxin A) mice. CNTF(Ax15) administration (0.1, 0.3, or 1.0 microg . g(-1) . day(-1) s.c.) for 3 or 7 days reduced food intake and body weight (mainly body fat mass). The effect of CNTF(Ax15) on food intake and body weight was more pronounced in CNTF(Ax15)-treated diet-induced obese C57BL/6J mice compared with pair-fed controls and was associated with suppressed expression of hypothalamic neuropeptide Y and agouti gene-related protein. Moreover, CNTF(Ax15) increased uncoupling protein 1 mRNA expression in BAT and energy expenditure in diet-induced obese C57BL/6J mice. Longitudinal observations revealed a sustained reduction in body weight for several days post-CNTF(Ax15) treatment of CNTF(Ax15)-treated but not pair-fed mice, followed by a gradual regain in body weight over 28 days. Finally, CNTF(Ax15) administration improved the metabolic profile in both diet-induced obese C57BL/6J and UCP1-DTA mice and resulted in a significantly improved glycemic response to oral glucose tolerance tests in CNTF(Ax15)-treated UCP1-DTA compared with pair-fed mice of similar body weight. These data suggest that CNTF(Ax15) may act through a pathway downstream of the putative point responsible for leptin resistance in diet-induced obese C57BL/6J and UCP1-DTA mice to alter food intake, body weight, body composition, and metabolism. CNTF(Ax15) has delayed and persistent effects in diet-induced obese C57BL/6J mice, which account for a reduction in body weight over and above what would be expected based on decreased foot intake alone.

Genetic deletion of ghrelin does not decrease food intake but influences metabolic fuel preference

Ghrelin is a recently identified growth hormone (GH) secretogogue whose administration not only induces GH release but also stimulates food intake, increases adiposity, and reduces fat utilization in mice. The effect on food intake appears to be independent of GH release and instead due to direct activation of orexigenic neurons in the arcuate nucleus of the hypothalamus. The effects of ghrelin administration on food intake have led to the suggestion that inhibitors of endogenous ghrelin could be useful in curbing appetite and combating obesity. To further study the role of endogenous ghrelin in appetite and body weight regulation, we generated ghrelin-deficient (ghrl(-/-)) mice, in which the ghrelin gene was precisely replaced with a lacZ reporter gene. ghrl(-/-) mice were viable and exhibited normal growth rates as well as normal spontaneous food intake patterns, normal basal levels of hypothalamic orexigenic and anorexigenic neuropeptides, and no impairment of reflexive hyperphagia after fasting. These results indicate that endogenous ghrelin is not an essential regulator of food intake and has, at most, a redundant role in the regulation of appetite. However, analyses of ghrl(-/-) mice demonstrate that endogenous ghrelin plays a prominent role in determining the type of metabolic substrate (i.e., fat vs. carbohydrate) that is used for maintenance of energy balance, particularly under conditions of high fat intake.

Ciliary neurotrophic factor and leptin induce distinct patterns of immediate early gene expression in the brain

Ciliary neurotrophic factor (CNTF) and leptin decrease food intake and body weight. Lipopolysaccharide (LPS) is a potent exogenous pyrogen and produces anorexia via cytokine production. CNTF-, leptin-, and LPS-induced cytokines all act on type I cytokine receptors. However, it is not known if these cytokines engage similar central nervous system (CNS) pathways to exert their effects. To assess mechanisms by which these cytokines act, we examined the patterns of immediate early gene expression (SOCS-3, c-fos, and tis-11) in the brain following intravenous administration. CNTF and LPS induced gene expression in circumventricular organs; ependymal cells of the ventricles, meninges, and choroid plexus; and the arcuate nucleus of the hypothalamus. CNTF administration also induced fever and cyclooxygenase-2 mRNA expression. In contrast, we found no evidence of leptin-induced inflammation. CNTF and leptin are being assessed as potential therapeutic anti-obesity agents, and both potently reduce food intake. Our findings support the hypothesis that CNTF and leptin engage distinct CNS sites and CNTF possesses inflammatory properties distinct from leptin.