Ciliary neurotrophic factor corrects obesity and diabetes associated with leptin deficiency and resistance

Exerkines: Benign adaptation for exercise and benefits for non-alcoholic fatty liver disease

Exercise has multiple beneficial effects on human metabolic health and is regarded as a "polypill" for various diseases. At present, the lack of physical activity usually causes an epidemic of chronic metabolic syndromes, including obesity, cardiovascular diseases, and non-alcoholic fatty liver disease (NAFLD). Remarkably, NAFLD is emerging as a serious public health issue and is associated with the development of cirrhosis and hepatocellular carcinoma. Unfortunately, specific drug therapies for NAFLD and its more severe form, non-alcoholic steatohepatitis (NASH), are currently unavailable. Lifestyle modification is the foundation of treatment recommendations for NAFLD and NASH, especially for exercise. There are under-appreciated organs that crosstalk to the liver during exercise such as muscle-liver crosstalk. Previous studies have reported that certain exerkines, such as FGF21, GDF15, irisin, and adiponectin, are beneficial for liver metabolism and have the potential to be targeted for NAFLD treatment. In addition, some of exerkines can be modified for the new proteins and get enhanced functions, like IL-6/IC7Fc. Another importance of exercise is the physiological adaptation that combats metabolic diseases. Thus, this review aims to summarize the known exerkines and utilize a multi-omics mining tool to identify more exerkines for the future research. Overall, understanding the mechanisms by which exercise-induced exerkines exert their beneficial effects on metabolic health holds promise for the development of novel therapeutic strategies for NAFLD and related diseases.

The Anti-Obesogenic Effects of Muscadine Grapes through Ciliary Neurotrophic Factor Receptor (Cntfr) and Histamine Receptor H1 (Hrh1) Genes in 3T3-L1 Differentiated Mouse Cells

Obesity and type 2 diabetes are prevalent metabolic diseases that have significant links to several chronic diseases, including cancer, diabetes, hypertension, and cardiovascular disease. Muscadine grape extracts have shown the potential to reduce adiposity and improve insulin sensitivity and glucose control. Thus, this study was designed to determine the potential of muscadine grape berries extract (Pineapple and Southern Home) for its antiobesity properties in 3T3-L1 cells as a model for obesity research. The current study's data indicated the total phenolic content (TPC) and 2,2-diphenyl-1-picrylhydraziyl (DPPH) activity were higher in cultivar (CV) Southern Home, meanwhile, elevated the total flavonoid content (TFC) in Pineapple. Both extracts were safe across the tested range (0-5 mg/mL). A noticeable reduction in lipid accumulation was also found in extract-treated cells. In preadipocytes and adipocytes, the tested extracts showed significant alterations in various genes involved in glucose homeostasis and obesity. The most remarkable findings of the current study are the upregulation of two genes, Cntfr (+712.715-fold) and Hrh1 (+270.11-fold) in CV Pineapple extract-treated adipocytes 3T3-L1 and the high fold increase in Ramp3 induced by both Pineapple and Southern Home in pre-adipose cells. Furthermore, the tested extracts showed a potential to alter the mRNA of various genes, including Zfp91, B2m, Nr3c1, Insr, Atrn, Il6ra, Hsp90ab1, Sort1, and Npy1r. In conclusion, the data generated from the current study suggested that the two extracts under investigation are considered potential candidates for controlling insulin levels and managing obesity.

Exerkines and cardiometabolic benefits of exercise: from bench to clinic

Regular exercise has both immediate and long-lasting benefits on cardiometabolic health, and has been recommended as a cornerstone of treatment in the management of diabetes and cardiovascular conditions. Exerkines, which are defined as humoral factors responsive to acute or chronic exercise, have emerged as important players conferring some of the multiple cardiometabolic benefits of exercise. Over the past decades, hundreds of exerkines released from skeletal muscle, heart, liver, adipose tissue, brain, and gut have been identified, and several exerkines (such as FGF21, IL-6, and adiponectin) have been exploited therapeutically as exercise mimetics for the treatment of various metabolic and cardiovascular diseases. Recent advances in metagenomics have led to the identification of gut microbiota, a so-called "hidden" metabolic organ, as an additional class of exerkines determining the efficacy of exercise in diabetes prevention, cardiac protection, and exercise performance. Furthermore, multiomics-based studies have shown the feasibility of using baseline exerkine signatures to predict individual responses to exercise with respect to metabolic and cardiorespiratory health. This review aims to explore the molecular pathways whereby exerkine networks mediate the cardiometabolic adaptations to exercise by fine-tuning inter-organ crosstalk, and discuss the roadmaps for translating exerkine-based discovery into the therapeutic application and personalized medicine in the management of the cardiometabolic disease.

Efficacy of PEGylated ciliary neurotrophic factor superagonist variant in diet-induced obesity mice

Ciliary neurotrophic factor (CNTF) is a neurotrophic cytokine able to induce appetite reduction, weight loss and antidiabetic effects. However, its susceptibility to neutralizing anti-CNTF antibodies in patients hampered its use for treatment of human obesity and diabetes. In addition, CNTF has a very short plasma half-life, which limits its use as a therapeutic agent. Solutions, directed to prolong its in vivo effects, vary from the implantation of encapsulated secreting cells to identification of more active variants or chemical modification of the protein itself. PEGylation is a widely used modification for shielding proteins from circulating antibodies and for increasing their plasma half-life. Here, we have selected DH-CNTF, a CNTF variant which has a 40-fold higher affinity for the CNTF receptor α accompanied by an increased activity in cellular assays. The PEGylated DH-CNTF retained the biological activity of native protein in vitro and showed a significant improvement of pharmacokinetic parameters. In an acute model of glucose tolerance, the PEG-DH-CNTF was able to reduce the glycemia in diet-induced obese animals, with a performance equaled by a 10-fold higher dose of DH-CNTF. In addition, the PEGylated DH-CNTF analog demonstrated a more potent weight loss effect than the unmodified protein, opening to the use of CNTF as weight reducing agent with treatment regimens that can better meet patient compliance thanks to reduced dosing schedules.

IL-6 family cytokines as potential therapeutic strategies to treat metabolic diseases

Metabolic disease is highly prevalent. Here we discuss the therapeutic utility of using gp130 receptor ligands as a therapeutic strategy to treat metabolic disease.

Disease Modification Through Trophic Factor Delivery

Huntington's disease (HD) is characterized by a significant loss of striatal neurons that project to the globus pallidus and substantia nigra, together with loss of cortical projection neurons in varying regions. Mutant huntingtin is suggested to drive the pathogenesis partially by downregulating corticostriatal brain-derived neurotrophic factor (BDNF) levels and signaling. Neurotrophic factors are endogenous peptides that promote the survival and maintenance of neurons. BDNF and other neurotrophic factors have shown neuroprotective benefits in various animal models of neurodegeneration, and are interesting candidates to protect the cell populations that are destined to die in HD. In an attempt to enhance the delivery of neurotrophic factors, several methods have been established to deliver long-term neurotrophic factor gene therapy to human target tissues. This chapter discusses two alternative approaches that have been shown to have potential to deliver neurotrophic factors as a neuroprotective gene therapy for HD. The methods are (1) ex vivo approach where encapsulated cells engineered to express neurotrophic factor are inserted into brain parenchyma or ventricle, and (2) in vivo viral vector therapy, in which viral vector is injected into desired brain area to express gene of interest in the host cells.

Biological Effects of Ciliary Neurotrophic Factor on hMADS Adipocytes

Administration of ciliary neurotrophic factor (CNTF) to experimental animals exerts anti-obesity effects by acting on multiple targets. In white adipose tissue CNTF reduces lipid content, promotes fatty acid (FA) oxidation and improves insulin sensitivity. This study was performed to establish whether CNTF exerts similar effects on human white adipocytes. To this end, adipose differentiation was induced in vitro in human multipotent adipose-derived stem (hMADS) cells. CNTF receptor α (CNTFRα) expression was assessed in hMADS cells and adipocytes by qRT-PCR, Western blotting, and immunocytochemistry. After administration of human recombinant CNTF, signaling pathways and gene expression were evaluated by Western blotting and qRT-PCR. Glucose uptake was assessed by measuring 2-nitrobenzodeoxyglucose uptake with a fluorescence plate reader. Lastly, CNTF-induced anti-inflammatory responses were evaluated in hMADS adipocytes stressed with tumor necrosis factor α (TNFα) for 24 h. Results showed that CNTFRα protein expression was higher in undifferentiated hMADS cells than in hMADS adipocytes, where it was however clearly detectable. In hMADS adipocytes, 1 nM CNTF strongly activated the JAK-STAT3 (Janus kinase-signaling transducer and activator of transcription 3) pathway and acutely and transiently activated the AMPK (AMP-activated protein kinase) and AKT (protein kinase B) pathways. Acute CNTF treatment for 20 min significantly increased basal glucose uptake and was associated with increased AKT phosphorylation. Longer-term (24 and 48 h) treatment reduced the expression of lipogenic markers (FA synthase and sterol regulatory element-binding protein-1) and increased the expression of lipolytic [hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL)] and mitochondrial (peroxisome proliferator-activated receptor γ coactivator-1α and carnitine palmitoyltransferase 1) markers. In TNFα-treated hMADS adipocytes, CNTF significantly reduced the expression of monocyte chemoattractant protein 1 and TNFα-induced AKT inhibition. Collectively, these findings demonstrate for the first time that CNTF plays a role also in human adipocytes, driving their metabolism toward a less lipid-storing and more energy-consuming phenotype.

MANF: A New Player in the Control of Energy Homeostasis, and Beyond

All human behaviors, including the control of energy homeostasis, are ultimately mediated by neuronal activities in the brain. Neurotrophic factors represent a protein family that plays important roles in regulating neuronal development, function, and survival. It has been well established that canonical neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF), play important roles in the central regulation of energy homeostasis. Recently, a class of non-canonical neurotrophic factors, represented by mesencephalic astrocyte-derived neurotrophic factor (MANF), has been discovered. MANF is structurally and functionally distinct from those canonical neurotrophic factors, hence raising the issue of MANF being non-canonical. Nonetheless, emerging evidence suggests that MANF is critically involved in many neuronal activities. Here, we review our current understanding about the functions of MANF in the brain, with a primary focus on the control of energy homeostasis.

Cachexia-associated adipose loss induced by tumor-secreted leukemia inhibitory factor is counterbalanced by decreased leptin

Cachexia syndrome consists of adipose and muscle loss, often despite normal food intake. We hypothesized that cachexia-associated adipose wasting is driven in part by tumor humoral factors that induce adipocyte lipolysis. We developed an assay to purify secreted factors from a cachexia-inducing colon cancer line that increases lipolysis in adipocytes and identified leukemia inhibitory factor (LIF) by mass spectrometry. Recombinant LIF induced lipolysis in vitro. Peripheral LIF administered to mice caused >50% loss of adipose tissue and >10% reduction in body weight despite only transient hypophagia due to decreasing leptin. LIF-injected mice lacking leptin (ob/ob) resulted in persistent hypophagia and loss of adipose tissue and body weight. LIF's peripheral role of initiating lipolysis in adipose loss was confirmed in pair-fed ob/ob mouse studies. Our studies demonstrate that (a) LIF is a tumor-secreted factor that promotes cachexia-like adipose loss when administered peripherally, (b) LIF directly induces adipocyte lipolysis, (c) LIF has the ability to sustain adipose and body weight loss through an equal combination of peripheral and central contributions, and (d) LIF's central effect is counterbalanced by decreased leptin signaling, providing insight into cachexia's wasting, despite normophagia.

mTORC1 pathway disruption abrogates the effects of the ciliary neurotrophic factor on energy balance and hypothalamic neuroinflammation

Ciliary neurotrophic factor (CNTF) potently decreases food intake and body weight in diet-induced obese mice by acting through neuronal circuits and pathways located in the arcuate nucleus (ARC) of the hypothalamus. CNTF also exerts pro-inflammatory actions within the brain. Here we tested whether CNTF modifies energy balance by inducing inflammatory responses in the ARC and whether these effects depend upon the mechanistic target of rapamycin complex 1 (mTORC1) pathway, which regulates both energy metabolism and inflammation. To this purpose, chow- and high fat diet (HFD)- fed mice lacking the S6 kinase 1 (S6K1^-/-), a downstream target of mTORC1, and their wild-type (WT) littermates received 12 days continuous intracerebroventricular (icv) infusion of the CNTF analogue axokine (CNTF_Ax15). Behavioral, metabolic and molecular effects were evaluated. Central chronic administration of CNTF_Ax15 decreased body weight and feed efficiency in WT mice only, when fed HFD, but not chow. These metabolic effects correlated with increased number of iba-1 positive microglia specifically in the ARC and were accompanied by significant increases of IL-1β and TNF-α mRNA expression in the hypothalamus. Hypothalamic iNOS and SOCS3 mRNA, molecular markers of pro-inflammatory response, were also increased by CNTF_Ax15. All these changes were absent in S6K1^-/- mice. This study reveals that CNTF_Ax15 requires a functional S6K1 to modulate energy balance and hypothalamic inflammation in a diet-dependent fashion. Further investigations should determine whether S6K1 is a suitable target for the treatment of pathologies characterized by a high neuroinflammatory state.

Effect of human very low-density lipoproteins on cardiotrophin-like cytokine factor 1 (CLCF1) activity

The cytokines CLCF1 and CNTF are ligands for the CNTF receptor and the apolipoprotein E (ApoE) receptor sortilin. Both share structural similarities with the N-terminal domain of ApoE, known to bind CNTF. We therefore evaluated whether ApoE or ApoE-containing lipoproteins interact with CLCF1 and regulate its activity. We observed that CLCF1 forms complexes with the three major isoforms of ApoE in co-immunoprecipitation and proximity assays. FPLC analysis of mouse and human sera mixed with CLCF1 revealed that CLCF1 co-purifies with plasma lipoproteins. Studies with sera from ApoE^-/- mice indicate that ApoE is not required for CLCF1-lipoprotein interactions. VLDL- and LDL-CLCF1 binding was confirmed using proximity and ligand blots assays. CLCF1-induced STAT3 phosphorylation was significantly reduced when the cytokine was complexed with VLDL. Physiological relevance of our findings was asserted in a mouse model of oxygen-induced retinopathy, where the beneficial anti-angiogenic properties of CLCF1 were abrogated when co-administrated with VLDL, indicating, that CLCF1 binds purified lipoproteins or lipoproteins in physiological fluids such as serum and behave as a "lipocytokine". Albeit it is clear that lipoproteins modulate CLCF1 activity, it remains to be determined whether lipoprotein binding directly contributes to its neurotrophic function and its roles in metabolic regulation.

High fat induces acute and chronic inflammation in the hypothalamus: effect of high-fat diet, palmitate and TNF-α on appetite-regulating NPY neurons

BACKGROUND

Consumption of dietary fat is one of the key factors leading to obesity. High-fat diet (HFD)-induced obesity is characterized by induction of inflammation in the hypothalamus; however, the temporal regulation of proinflammatory markers and their impact on hypothalamic appetite-regulating neuropeptide Y/agouti-related peptide (NPY/AgRP) neurons remains undefined.

METHODS

Mice were injected with an acute lipid infusion for 24 h or fed a HFD over 8-20 weeks. Characterized mouse NPY/AgRP hypothalamic cell lines were used for in vitro experimentation. Immunohistochemistry in brain slices or quantitative real-time PCR in cell lines, was performed to determine changes in the expression of key inflammatory markers and neuropeptides.

RESULTS

Hypothalamic inflammation, indicated by tumor necrosis factor (TNF)-α expression and astrocytosis in the arcuate nucleus, was evident following acute lipid infusion. HFD for 8 weeks suppressed TNF-α, while significantly increasing heat-shock protein 70 and ciliary neurotrophic factor, both neuroprotective components. HFD for 20 weeks induced TNF-α expression in NPY/AgRP neurons, suggesting a detrimental temporal regulatory mechanism. Using NPY/AgRP hypothalamic cell lines, we found that palmitate provoked a mixed inflammatory response on a panel of inflammatory and endoplasmic reticulum (ER) stress genes, whereas TNF-α significantly upregulated IκBα, nuclear factor (NF)-κB and interleukin-6 mRNA levels. Palmitate and TNF-α exposure predominantly induced NPY mRNA levels. Utilizing an I kappa B kinase β (IKKβ) inhibitor, we demonstrated that these effects potentially occur via the inflammatory IKKβ/NF-κB pathway.

CONCLUSIONS

These findings indicate that acute lipid and chronic HFD feeding in vivo, as well as acute palmitate and TNF-α exposure in vitro, induce markers of inflammation or ER stress in the hypothalamic appetite-stimulating NPY/AgRP neurons over time, which may contribute to a dramatic alteration in NPY/AgRP content or expression. Acute and chronic HFD feeding in vivo temporally regulates arcuate TNF-α expression with reactive astrocytosis, which suggests a time-dependent neurotrophic or neurotoxic role of lipids.

The role of gp130 receptor cytokines in the regulation of metabolic homeostasis

It is well known that obesity is responsible, at least in part, for the increased incidence of chronic diseases such as type 2 diabetes, cardiovascular disease and certain types of cancer. Despite public education programs emphasizing lifestyle modifications to arrest this global pandemic, it is now estimated that 10-15% of the world's population are overweight or obese. As a result, new therapeutic options for the treatment of obesity-related disorders are clearly warranted. Much of the benefit of physical activity has been attributed to several mechanisms including reduced adiposity, increased cardiorespiratory fitness, reduced circulating lipids and the maintenance of muscle mass. However, the observation that the gp130 receptor cytokine interleukin-6 (IL-6) was released from skeletal muscle during exercise to improve metabolic homeostasis altered our understanding of the health benefits of exercise and opened avenues for research into potential novel therapeutics to treat metabolic disease. One gp130 receptor cytokine in particular, ciliary neurotrophic factor (CNTF), a pluripotent neurocytokine, showed efficacy as a potential anti-obesogenic therapy. This review examines the potential of gp130 receptor ligands, with a focus on IL-6 and CNTF as therapeutic strategies to treat obesity-related disorders.

A combination of cytokines EGF and CNTF protects the functional beta cell mass in mice with short-term hyperglycaemia

AIMS/HYPOTHESIS

When the beta cell mass or function declines beyond a critical point, hyperglycaemia arises. Little is known about the potential pathways involved in beta cell rescue. As two cytokines, epidermal growth factor (EGF) and ciliary neurotrophic factor (CNTF), restored a functional beta cell mass in mice with long-term hyperglycaemia by reprogramming acinar cells that transiently expressed neurogenin 3 (NGN3), the current study assesses the effect of these cytokines on the functional beta cell mass after an acute chemical toxic insult.

METHODS

Glycaemia and insulin levels, pro-endocrine gene expression and beta cell origin, as well as the role of signal transducer and activator of transcription 3 (STAT3) signalling, were assessed in EGF+CNTF-treated mice following acute hyperglycaemia.

RESULTS

The mice were hyperglycaemic 1 day following i.v. injection of the beta cell toxin alloxan, when the two cytokines were applied. One week later, 68.6 ± 4.6% of the mice had responded to the cytokine treatment and increased their insulin(+) cell number to 30% that of normoglycaemic control mice, resulting in restoration of euglycaemia. Although insulin(-) NGN3(+) cells appeared following acute EGF+CNTF treatment, genetic lineage tracing showed that the majority of the insulin(+) cells originated from pre-existing beta cells. Beta cell rescue by EGF+CNTF depends on glycaemia rather than on STAT3-induced NGN3 expression in acinar cells.

CONCLUSIONS/INTERPRETATION

In adult mice, EGF+CNTF allows the rescue of beta cells in distress when treatment is given shortly after the diabetogenic insult. The rescued beta cells restore a functional beta cell mass able to control normal blood glucose levels. These findings may provide new insights into compensatory pathways activated early after beta cell loss.

Action of Administered Ciliary Neurotrophic Factor on the Mouse Dorsal Vagal Complex

Ciliary neurotrophic factor (CNTF) induces weight loss in obese rodents and humans through activation of the hypothalamic Jak-STAT (Janus kinase-signal transducer and activator of transcription) signaling pathway. Here, we tested the hypothesis that CNTF also affects the brainstem centers involved in feeding and energy balance regulation. To this end, wild-type and leptin-deficient (ob/ob and db/db) obese mice were acutely treated with intraperitoneal recombinant CNTF. Coronal brainstem sections were processed for immunohistochemical detection of STAT3, STAT1, STAT5 phosphorylation and c-Fos. In wild-type mice, CNTF treatment for 45 min induced STAT3, STAT1, and STAT5 phosphorylation in neurons as well as glial cells of the area postrema; here, the majority of CNTF-responsive cells activated multiple STAT isoforms, and a significant proportion of CNTF-responsive glial cells bore the immaturity and plasticity markers nestin and vimentin. After 120 min CNTF treatment, c-Fos expression was intense in glial cells and weak in neurons of the area postrema, it was intense in several neurons of the rostral and caudal solitary tract nucleus (NTS), and weak in some cholinergic neurons of the dorsal motor nucleus of the vagus. In the ob/ob and db/db mice, Jak-STAT activation and c-Fos expression were similar to those induced in wild-type mouse brainstem. Treatment with CNTF (120 min, to induce c-Fos expression) and leptin (25 min, to induce STAT3 phosphorylation) demonstrated the co-localization of the two transcription factors in a small neuron population in the caudal NTS portion. Finally, weak immunohistochemical CNTF staining, detected in funiculus separans, and meningeal glial cells, matched the modest amount of CNTF found by RT-qPCR in micropunched area postrema tissue, which in contrast exhibited a very high amount of CNTF receptor. Collectively, the present findings show that the area postrema and the NTS exhibit high, distinctive responsiveness to circulating exogenous and, probably, endogenous CNTF.

Loss of Oncostatin M Signaling in Adipocytes Induces Insulin Resistance and Adipose Tissue Inflammation in Vivo

Oncostatin M (OSM) is a multifunctional gp130 cytokine. Although OSM is produced in adipose tissue, it is not produced by adipocytes. OSM expression is significantly induced in adipose tissue from obese mice and humans. The OSM-specific receptor, OSM receptor β (OSMR), is expressed in adipocytes, but its function remains largely unknown. To better understand the effects of OSM in adipose tissue, we knocked down Osmr expression in adipocytes in vitro using siRNA. In vivo, we generated a mouse line lacking Osmr in adiponectin-expressing cells (OSMR(FKO) mice). The effects of OSM on gene expression were also assessed in vitro and in vivo OSM exerts proinflammatory effects on cultured adipocytes that are partially rescued by Osmr knockdown. Osm expression is significantly increased in adipose tissue T cells of high fat-fed mice. In addition, adipocyte Osmr expression is increased following high fat feeding. OSMR(FKO) mice exhibit increased insulin resistance and adipose tissue inflammation and have increased lean mass, femoral length, and bone volume. Also, OSMR(FKO) mice exhibit increased expression of Osm, the T cell markers Cd4 and Cd8, and the macrophage markers F4/80 and Cd11c Interestingly, the same proinflammatory genes induced by OSM in adipocytes are induced in the adipose tissue of the OSMR(FKO) mouse, suggesting that increased expression of proinflammatory genes in adipose tissue arises both from adipocytes and other cell types. These findings suggest that adipocyte OSMR signaling is involved in the regulation of adipose tissue homeostasis and that, in obesity, OSMR ablation may exacerbate insulin resistance by promoting adipose tissue inflammation.

Ciliary neurotrophic factor upregulates follistatin and Pak1, causes overexpression of muscle differentiation related genes and downregulation of established atrophy mediators in skeletal muscle

INTRODUCTION

The Ciliary Neurotrophic Factor (CNTF) is a pluripotent cytokine with anorexigenic actions in the hypothalamus that improves insulin sensitivity, increases energy expenditure and induces weight loss. Since CNTF also has an established myotrophic role, we sought to examine whether skeletal muscle contributes to the CNTF-induced metabolic improvement and identify the molecular mechanisms mediating these effects.

METHODS

We used a mouse model of diet-induced obesity, to which high or low CNTF doses were administered for 7days. Whole transcriptome expression levels were analyzed in dissected soleus muscles using microarrays and data were then confirmed using qRT-PCR.

RESULTS

We demonstrate that CNTF administration significantly downregulates leptin, while it upregulates follistatin and Pak1; a molecule associated with insulin sensitization in skeletal muscle. A significant overexpression of muscle differentiation related genes and downregulation of established atrophy mediators was observed.

CONCLUSIONS

The overall gene expression changes suggest an indirect, beneficial effect of CNTF on metabolism, energy expenditure and insulin sensitivity, exerted by the pronounced stimulation of muscle growth, with similarities to the described effect of follistatin and the activation of the Akt pathway in skeletal muscle.

Neurotrophic factor control of satiety and body weight

Energy balance--that is, the relationship between energy intake and energy expenditure--is regulated by a complex interplay of hormones, brain circuits and peripheral tissues. Leptin is an adipocyte-derived cytokine that suppresses appetite and increases energy expenditure. Ironically, obese individuals have high levels of plasma leptin and are resistant to leptin treatment. Neurotrophic factors, particularly ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF), are also important for the control of body weight. CNTF can overcome leptin resistance in order to reduce body weight, although CNTF and leptin activate similar signalling cascades. Mutations in the gene encoding BDNF lead to insatiable appetite and severe obesity.

Central Administration of the Ciliary Neurotrophic Factor Analogue, Axokine, Does Not Play a Role in Long-Term Energy Homeostasis in Adult Mice

BACKGROUND/AIMS

Ciliary neurotrophic factor (CNTF) exerts powerful anorectic effects and has been suggested to regulate long-term energy balance by inducing adult neurogenesis in the arcuate nucleus of the hypothalamus.

METHODS

The CNTF analogue, Axokine, was infused into the lateral ventricle of high-fat-fed mice for 1 week. Food intake, energy expenditure, body mass, glucose metabolism, and neurogenesis in the arcuate nucleus (ARC) of the hypothalamus were assessed 3 weeks after cessation of Axokine treatment.

RESULTS

Short-term administration of Axokine induced an anorexic response but did not promote sustained weight loss. Instead, a rapid rebound in food intake and body mass occurred immediately after cessation of Axokine treatment, and this tended to reduce insulin sensitivity. Immunolabeling of 5-bromo-2'-deoxyuridine revealed limited neurogenesis in the ARC 3 weeks after Axokine treatment.

CONCLUSION

These findings suggest that Axokine/CNTF does not induce substantial or sustained ARC neurogenesis or contribute to the long-term regulation of energy balance in mice.

Ciliary neurotrophic factor (CNTF): New facets of an old molecule for treating neurodegenerative and metabolic syndrome pathologies

Ciliary neurotrophic factor (CNTF) is the most extensively studied member of the cytokine family that signal through intracellular chains of the gp130/LIFRβ receptor. The severe phenotype in patients suffering from mutations inactivating LIFRβ indicates that members of this cytokine family play key, non-redundant roles during development. Accordingly, three decades of research has revealed potent and promising trophic and regulatory activities of CNTF in neurons, oligodendrocytes, muscle cells, bone cells, adipocytes and retinal cells. These findings led to clinical trials to test the therapeutic potential of CNTF and CNTF derivatives for treating neurodegenerative and metabolic diseases. Promising results have encouraged continuation of studies for treating retinal degenerative diseases. Results of some clinical trials showed that side-effects may limit the systemically administrated doses of CNTF. Therefore, therapies being currently tested rely on local delivery of CNTF using encapsulated cytokine-secreting implants. Since the side effects of CNTF might be linked to its ability to activate the alternative IL6Rα-LIFRβ-gp130 receptor, CNTFR-specific mutants of CNTF have been developed that bind to the CNTFRα-LIFRβ-gp130 receptor. These developments may prove to be a breakthrough for therapeutic applications of systemically administered CNTF in pathologies such as multiple sclerosis or Alzheimer's disease. The "designer cytokine approach" offers future opportunities to further enhance specificity by conjugating mutant CNTF with modified soluble CNTFRα to target therapeutically relevant cells that express gp130-LIFRβ and a specific cell surface marker.

Deletion of the Neurotrophic Factor neudesin Prevents Diet-induced Obesity by Increased Sympathetic Activity

Some neurotrophic factors, which are potent regulators of neuronal development and function, have recently been implicated in the control of energy balance by increasing energy expenditure. We previously identified neudesin as a novel neurotrophic factor with potential roles in the central nervous system. Although neudesin is also expressed in various peripheral tissues including adipose tissue, its physiological roles have not yet been elucidated. We found that neudesin knockout (KO) mice were resistant to high-fat diet-induced obesity and obesity-related metabolic dysfunctions. neudesin KO mice exhibited increased energy expenditure due to increased sympathetic activity, which resulted in increased heat production and fatty acid oxidation in brown adipose tissue and enhanced lipolysis in white adipose tissue. Thus, neudesin, which may be a negative regulator of sympathetic activity, could represent a novel regulator of the development of obesity and obesity-related metabolic dysfunctions.

Oncostatin m modulation of lipid storage

Oncostatin M (OSM) is a cytokine belonging to the gp130 family, whose members serve pleiotropic functions. However, several actions of OSM are unique from those of other gp130 cytokines, and these actions may have critical roles in inflammatory mechanisms influencing several metabolic and biological functions of insulin-sensitive tissues. In this review, the actions of OSM in adipose tissue and liver are discussed, with an emphasis on lipid metabolism.

Can neuropeptides treat obesity? A review of neuropeptides and their potential role in the treatment of obesity

Obesity is a major worldwide public health issue. The physiological systems that regulate body weight are thus of great interest as targets for anti-obesity agents. Peptidergic systems are critical to the regulation of energy homeostasis by key regions in the hypothalamus and brainstem. A number of neuropeptide systems have therefore been investigated as potential treatments for obesity. Blocking orexigenic peptide signals such as neuropeptide Y, melanin-concentrating hormone, orexins, relaxin-3 and galanin-like peptide or stimulating anorectic signalling pathways used by peptides such as the melanocortins, ciliary neurotrophic factor and brain-derived neurotrophic factor, are approaches that have shown some promise, but which have also highlighted possible concerns. Manipulation of central peptidergic systems poses a number of therapeutic problems, including brain access and side effects. Given that the homeostatic defence of body weight may limit the effectiveness of any single-target therapy developed, a combination therapy approach may offer the best hope for the effective prevention and treatment of obesity.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Effects of detraining on motor unit potential area, muscle function and physical performance based on CNTF gene polymorphism

[Purpose]

The purpose of this study was to identify the effect of detraining on motor unit potential area (SMUP), muscular function and physical performance, according to CNTF gene polymorphism.

[Methods]

For this study, GG (normal homozygote, n = 8) group and GA + AA (mutation heterozygote and homozygote, n = 10) group were divided by CNTF gene polymorphism and both groups were performed detraining for 4 weeks. The data was analyzed by two-way repeated measures ANOVA for verifying the differences between two groups and interaction using SPSS (ver. 20.0) statistical program.

[Results]

The results were as follows. First, changes in body composition were measured but there was no significant interaction effect between time and group. Seconds, changes in SMUP were measured by SEMG. Interaction effect between time and group was found lateral vastus during isokinetic exercise of 180°/sec (p < .05). Third, changes in isokinetic muscle strength of 60°/sec and 180°/sec were measured but there was no significant interaction effect. Fourth, significant statistical differences were not showed changes of sports performance after detraining.

[Conclusion]

In conclusion, there were no significantly differences between GG and GA + AA group after detraining, therefore, further study will be considered a matter in various its interventions such as serum levels of CNTF and changes in receptors and muscle fiber types.

The amino acid exchange R28E in ciliary neurotrophic factor (CNTF) abrogates interleukin-6 receptor-dependent but retains CNTF receptor-dependent signaling via glycoprotein 130 (gp130)/leukemia inhibitory factor receptor (LIFR)

Ciliary neurotrophic factor (CNTF) is a neurotrophic factor with therapeutic potential for neurodegenerative diseases. Moreover, therapeutic application of CNTF reduced body weight in mice and humans. CNTF binds to high or low affinity receptor complexes consisting of CNTFR·gp130·LIFR or IL-6R·gp130·LIFR, respectively. Clinical studies of the CNTF derivative Axokine revealed intolerance at higher concentrations, which may rely on the low-affinity binding of CNTF to the IL-6R. Here, we aimed to generate a CNTFR-selective CNTF variant (CV). CV-1 contained the single amino acid exchange R28E. Arg(28) is in close proximity to the CNTFR binding site. Using molecular modeling, we hypothesized that Arg(28) might contribute to IL-6R/CNTFR plasticity of CNTF. CV-2 to CV-5 were generated by transferring parts of the CNTFR-binding site from cardiotrophin-like cytokine to CNTF. Cardiotrophin-like cytokine selectively signals via the CNTFR·gp130·LIFR complex, albeit with a much lower affinity compared with CNTF. As shown by immunoprecipitation, all CNTF variants retained the ability to bind to CNTFR. CV-1, CV-2, and CV-5, however, lost the ability to bind to IL-6R. Although all variants induced cytokine-dependent cellular proliferation and STAT3 phosphorylation via CNTFR·gp130·LIFR, only CV-3 induced STAT3 phosphorylation via IL-6R·gp130·LIFR. Quantification of CNTF-dependent proliferation of CNTFR·gp130·LIFR expressing cells indicated that only CV-1 was as biologically active as CNTF. Thus, the CNTFR-selective CV-1 will allow discriminating between CNTFR- and IL-6R-mediated effects in vivo.

Oncostatin m is produced in adipose tissue and is regulated in conditions of obesity and type 2 diabetes

CONTEXT

Adipose tissue is a highly active endocrine organ that secretes many factors that affect other tissues and whole-body metabolism. Adipocytes are responsive to several glycoprotein 130 (gp130) cytokines, some of which have been targeted as potential antiobesity therapeutics.

OBJECTIVE

Oncostatin M (OSM) is a gp130 family member known to inhibit adipocyte differentiation in vitro, but its effects on other adipocyte properties are not characterized. The expression of OSM in white adipose tissue (WAT) has not been evaluated in the context of obesity. Thus, our objective was to examine the expression of adipose tissue OSM in obese animals and humans.

DESIGN

OSM expression was examined in adipose tissues from mice with diet-induced and genetic obesity and in obese humans as well as in fractionated adipose tissue from mice. Murine adipocytes were used to examine OSM receptor expression and the effects of OSM on adipocytes, including the secretion of factors such as plasminogen activator inhibitor 1 and IL-6, which are implicated in metabolic diseases.

RESULTS

OSM expression is increased in rodent and human obesity/type 2 diabetes mellitus. In humans, OSM levels correlate with body weight and insulin and are inversely correlated with glucose disposal rate as measured by hyperinsulinemic-euglycemic clamp. OSM is not produced from the adipocytes in WAT but derives from cells in the stromovascular fraction, including F4/80(+) macrophages. The specific receptor of OSM, OSM receptor-β, is expressed in adipocytes and adipose tissue and increased in both rodent models of obesity examined. OSM acts on adipocytes to induce the expression and secretion of plasminogen activator inhibitor 1 and IL-6.

CONCLUSIONS

These data indicate that WAT macrophages are a source of OSM and that OSM levels are significantly induced in murine and human obesity/type 2 diabetes mellitus. These studies suggest that OSM produced from immune cells in WAT acts in a paracrine manner on adipocytes to promote a proinflammatory phenotype in adipose tissue.

Exercise training does not enhance hypothalamic responsiveness to leptin or ghrelin in male mice

The detection of hormone and nutrient signals by the hypothalamus is blunted in obesity and contributes to dysregulated energy homeostasis. We investigated whether aerobic exercise training would improve long-term hypothalamic sensitivity to both leptin and ghrelin, independent of acute exercise-induced signalling. Male C57Bl/6J mice were fed either a chow or high-fat diet for 6 weeks, then remained sedentary on their respective diet, or completed 6 weeks of treadmill exercise training with a progressive increase in exercise volume and intensity. Food intake and hypothalamic signalling were assessed in mice injected with leptin or ghrelin at least 24 h after the last exercise bout. Exercise training reduced body mass, increased daily food intake and improved glucose tolerance. Intraperitoneal leptin administration reduced food intake in lean and obese mice, and this was not enhanced after exercise training. Leptin-mediated activation of phosphorylated signal transducer and activator of transcription 3 in the arcuate nucleus and ventromedial nucleus of the hypothalamus was not enhanced with exercise training. Ghrelin increased food intake and c-Fos positive neurones in the hypothalamus in lean and obese mice, and these physiological and molecular responses were not enhanced with exercise training. This suggests that the previously reported exercise effects on sensitising hypothalamic signalling and food intake responses may be limited to the period immediately after an exercise bout, and are not a result of stable structural or molecular changes that occur with exercise training.

Neurotrophins and the regulation of energy balance and body weight

Complex interactions between the brain and peripheral tissues mediate the effective control of energy balance and body weight. Hypothalamic and hindbrain neural circuits integrate peripheral signals informing the nutritional status of the animal and in response regulate nutrient intake and energy utilization. Obesity and its many medical complications emerge from the dysregulation of energy homeostasis. Excessive weight gain might also arise from alterations in reward systems of the brain that drive consumption of calorie dense, palatable foods in the absence of an energy requirement. Several neurotrophins, most notably brain-derived neurotrophic factor, have been implicated in the molecular and cellular processes underlying body weight regulation. Here, we review investigations interrogating their roles in energy balance and reward centers of the brain impacting feeding behavior and energy expenditure.

Transient cytokine treatment induces acinar cell reprogramming and regenerates functional beta cell mass in diabetic mice

Reprogramming of pancreatic exocrine cells into cells resembling beta cells may provide a strategy for treating diabetes. Here we show that transient administration of epidermal growth factor and ciliary neurotrophic factor to adult mice with chronic hyperglycemia efficiently stimulates the conversion of terminally differentiated acinar cells to beta-like cells. Newly generated beta-like cells are epigenetically reprogrammed, functional and glucose responsive, and they reinstate normal glycemic control for up to 248 d. The regenerative process depends on Stat3 signaling and requires a threshold number of Neurogenin 3 (Ngn3)-expressing acinar cells. In contrast to previous work demonstrating in vivo conversion of acinar cells to beta-like cells by viral delivery of exogenous transcription factors, our approach achieves acinar-to-beta-cell reprogramming through transient cytokine exposure rather than genetic modification.

Opposite effects of a high-fat diet and calorie restriction on ciliary neurotrophic factor signaling in the mouse hypothalamus

In the mouse hypothalamus, ciliary neurotrophic factor (CNTF) is mainly expressed by ependymal cells and tanycytes of the ependymal layer covering the third ventricle. Since exogenously administered CNTF causes reduced food intake and weight loss, we tested whether endogenous CNTF might be involved in energy balance regulation. We thus evaluated CNTF production and responsiveness in the hypothalamus of mice fed a high-fat diet (HFD), of ob/ob obese mice, and of mice fed a calorie restriction (CR) regimen. RT-PCR showed that CNTF mRNA increased significantly in HFD mice and decreased significantly in CR animals. Western blotting confirmed that CNTF expression was higher in HFD mice and reduced in CR mice, but high interindividual variability blunted the significance of these differences. By immunohistochemistry, hypothalamic tuberal and mammillary region tanycytes stained strongly for CNTF in HFD mice, whereas CR mice exhibited markedly reduced staining. RT-PCR and Western blotting disclosed that changes in CNTF expression were paralleled by changes in the expression of its specific receptor, CNTF receptor α (CNTFRα). Injection of recombinant CNTF and detection of phospho-signal transducer and activator of transcription 3 (P-STAT3) showed that CNTF responsiveness by the ependymal layer, mainly by tanycytes, was higher in HFD than CR mice. In addition, in HFD mice CNTF administration induced distinctive STAT3 signaling in a large neuron population located in the dorsomedial and ventromedial nuclei, perifornical area and mammillary body. The hypothalamic expression of CNTF and CNTFRα did not change in the hyperphagic, leptin-deficient ob/ob obese mice; accordingly, P-STAT3 immunoreactivity in CNTF-treated ob/ob mice was confined to ependymal layer and arcuate neurons. Collectively, these data suggest that hypothalamic CNTF is involved in controlling the energy balance and that CNTF signaling plays a role in HFD obese mice at specific sites.

Hypothalamic neurogenesis in the adult brain

Adult-born new neurons are continuously added to the hippocampus and the olfactory bulb to serve aspects of learning and perceptual functions. Recent evidence establishes a third neurogenic niche in the ventral hypothalamic parenchyma surrounding the third ventricle that ensures the plasticity of specific brain circuits to stabilize physiological functions such as the energy-balance regulatory system. Hypothalamic lesion studies have demonstrated that regions associated with reproduction-related functions are also capable of recruiting newborn neurons to restore physiological functions and courtship behavior. Induced by lesion or other stimulation, elevated neurotrophic factors trigger neurogenic cascades that contribute to remodeling of certain neural circuits to meet specific transient functions. This insight raises the possibility that event-specific changes, such as increased GnRH, may be mediated by courtship-sensitive neurotrophic factors. We will discuss the potentially integral and ubiquitous roles of neurogenesis in physiological and biological phenomena, roles that await future experimental exploration.

The role of leptin on the organization and expression of cytoskeleton elements in nucleus pulposus cells

Obesity is an important risk factor for intervertebral disc degeneration and leptin is a biomarker of obesity. However, the expression of leptin receptors has not been determined in disc tissue. It is not known whether leptin has a direct effect on the nucleus pulposus (NP) cells. To determine whether the NP tissues and cells express leptin receptors (OBRa and OBRb) and whether leptin affects the organization and the expression of major cytoskeletal elements in NP cells. Messenger RNA (mRNA) and protein levels of OBRa and OBRb were measured by real-time PCR and Western blot, respectively, in NP tissues and cells. Immunofluorescence and real-time PCR and Western blot were performed to investigate the effect of leptin on cytoskeleton reorganization and expression. Results show that mRNA and proteins of OBRa and OBRb were expressed in all NP tissues and cells, and that OBRb expression was correlated with patients' body weight. Increased expression of β-actin and reorganization of F-actin were evident in leptin-stimulated NP cells. Leptin also induced vimentin expression but had no effect on β-tubulin in NP cells. These findings provide novel evidence supporting the possible involvement of leptin in the pathogenesis of intervertebral disc degeneration.

Central regulation of metabolism by protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) are important regulators of intracellular signaling pathways via the dephosphorylation of phosphotyrosyl residues on various receptor and non-receptor substrates. The phosphorylation state of central nervous system (CNS) signaling components underlies the molecular mechanisms of a variety of physiological functions including the control of energy balance and glucose homeostasis. In this review, we summarize the current evidence implicating PTPs as central regulators of metabolism, specifically highlighting their interactions with the neuronal leptin and insulin signaling pathways. We discuss the role of a number of PTPs (PTP1B, SHP2, TCPTP, RPTPe, and PTEN), reviewing the findings from genetic mouse models and in vitro studies which highlight these phosphatases as key central regulators of energy homeostasis.

Molecular pathways linking metabolic inflammation and thermogenesis

Obesity is caused by chronic positive energy balance because of higher energy intake relative to energy expenditure. Thermogenesis, the capacity of an organism to produce heat, is an important component of energy expenditure. Thus targeting the molecular mechanisms controlling thermogenesis could be an effective strategy for the prevention or treatment of obesity. Thermogenesis is modulated by three major factors: environmental temperature, nutrient quantity and quality, and by systemic inflammation. Obesity is now recognized to be a state of chronic low-grade systemic inflammation, which has been proposed to play a major role in the pathogenesis of obesity and obesity-associated diseases. This review discussed the molecular pathways that are recruited during metabolic inflammation and that are also implicated in the control of thermogenesis and energy balance. It emerges that the complex signalling network recruited during metabolic inflammation exerts a balanced action on the modulation of thermogenesis and energy balance, with some pathways promoting weight gain whereas other pathways have opposite actions. It is thus concluded that immunomodulation of metabolic inflammation, rather than an anti-inflammatory intervention aiming at its suppression, may be a more promising strategy to increase thermogenesis for the treatment or prevention of obesity and its associated diseases.

Assess the effect of ciliary neurotrophic factor on extracellular level of neuropeptide Y in paraventricular nucleus using microdialysis

In this study we investigated the effect of ciliary neurotrophic factor (CNTF) on dynamic changes in the release of hypothalamic neuropeptide Y (NPY) of freely moving rats using radioimmunoassay-microdialysis procedure. NPY concentrations in paraventricular nucleus (PVN) dialysate rapidly decreased to the lowest point, 47% of basal level (P&lt;0.01), in 30 minutes after intracerebroventricular injection 5&#956;g CNTF, and then increased slowly to 58%, 78% and 85% of basal level respectively at 60, 90 and 120 min (P<0.05). It became no significant difference with basal level at 150 and 180 min. These results suggested CNTF administration could directly down-regulate NPY release from hypothalamic PVN to reduce food intake and PVN was a target of CNTF's anorectic effect.

Obesity genetics: a monopoly game of genes

Obesity is a complex disease that affects all ethnic populations worldwide. The etiology of this disease is based on the interaction of genetic factors, environment and lifestyles indicators. Genetic contribution to the epidemic has gained attention from 2 sources: monogenic syndromes that display severe obesity, and the polygenic model of common obesity. Single mutations can render a syndrome with severe obesity resulting from alteration in central o peripheral appetite control mechanisms. The interaction of several polymorphisms and epigenetic modifications constitute the basic plot for common obesity, molecular ingredients that should not confuse the investigator-they make this riddle even harder to decipher.

Hypothalamic dysfunction in obesity

A growing number of studies have shown that a diet high in long chain SFA and/or obesity cause profound changes to the energy balance centres of the hypothalamus which results in the loss of central leptin and insulin sensitivity. Insensitivity to these important anorexigenic messengers of nutritional status perpetuates the development of both obesity and peripheral insulin insensitivity. A high-fat diet induces changes in the hypothalamus that include an increase in markers of oxidative stress, inflammation, endoplasmic reticulum (ER) stress, autophagy defect and changes in the rate of apoptosis and neuronal regeneration. In addition, a number of mechanisms have recently come to light that are important in the hypothalamic control of energy balance, which could play a role in perpetuating the effect of a high-fat diet on hypothalamic dysfunction. These include: reactive oxygen species as an important second messenger, lipid metabolism, autophagy and neuronal and synaptic plasticity. The importance of nutritional activation of the Toll-like receptor 4 and the inhibitor of NF-κB kinase subunit β/NK-κB and c-Jun amino-terminal kinase 1 inflammatory pathways in linking a high-fat diet to obesity and insulin insensitivity via the hypothalamus is now widely recognised. All of the hypothalamic changes induced by a high-fat diet appear to be causally linked and inhibitors of inflammation, ER stress and autophagy defect can prevent or reverse the development of obesity pointing to potential drug targets in the prevention of obesity and metabolic dysfunction.

The anorectic effect of CNTF does not require action in leptin-responsive neurons

Leptin resistance is a feature of obesity that poses a significant therapeutic challenge. Any treatment that is effective to reduce body weight in obese patients must overcome or circumvent leptin resistance, which promotes the maintenance of excess body fat in obese individuals. Ciliary neurotrophic factor (CNTF) is unique in its ability to reduce food intake and body weight in obese, leptin-resistant humans and rodents. Although attempts to use CNTF as an obesity therapy failed due to the development of neutralizing antibodies to the drug, efforts to understand mechanisms for CNTF's anorectic effects provide an opportunity to develop new drugs for leptin-resistant individuals. CNTF and leptin share several structural, anatomic, and signaling properties, but it is not understood whether or how the two cytokines might interact to affect energy balance. Here, we conditionally deleted the CNTF receptor (CNTFR) subunit, CNTFRα, in cells expressing leptin receptors. We found that CNTFR signaling in leptin-responsive neurons is not required for endogenous maintenance of energy balance and is not required for the anorectic response to exogenous administration of a CNTF agonist. These results indicate that despite anatomical overlap for CNTF and leptin action, CNTF appears to act within a distinct neuronal population to elicit its potent anorectic effect.

Ciliary neurotrophic factor (CNTF) protects non-obese Swiss mice against type 2 diabetes by increasing beta cell mass and reducing insulin clearance

AIMS/HYPOTHESIS

Ciliary neurotrophic factor (CNTF) improves metabolic variables of obese animals with characteristics of type 2 diabetes, mainly by reducing insulin resistance. We evaluated whether CNTF was able to improve other metabolic variables in mouse models of type 2 diabetes, such as beta cell mass and insulin clearance, and whether CNTF has any effect on non-obese mice with characteristics of type 2 diabetes.

METHODS

Neonatal mice were treated with 0.1 mg/kg CNTF or citrate buffer via intraperitoneal injections, before injection of 250 mg/kg alloxan. HEPG2 cells were cultured for 3 days in the presence of citrate buffer, 1 nmol/l CNTF or 50 mmol/l alloxan or a combination of CNTF and alloxan. Twenty-one days after treatment, we determined body weight, epididymal fat weight, blood glucose, plasma insulin, NEFA, glucose tolerance, insulin resistance, insulin clearance and beta cell mass. Finally, we assessed insulin receptor and protein kinase B phosphorylation in peripheral organs, as well as insulin-degrading enzyme (IDE) protein production and alternative splicing in the liver and HEPG2 cells.

RESULTS

CNTF improved insulin sensitivity and beta cell mass, while reducing glucose-stimulated insulin secretion and insulin clearance in Swiss mice, improving glucose handling in a non-obese type 2 diabetes model. This effect was associated with lower IDE production and activity in liver cells. All these effects were observed even at 21 days after CNTF treatment.

CONCLUSIONS/INTERPRETATION

CNTF protection against type 2 diabetes is partially independent of the anti-obesity actions of CNTF, requiring a reduction in insulin clearance and increased beta cell mass, besides increased insulin sensitivity. Furthermore, knowledge of the long-term effects of CNTF expands its pharmacological relevance.

The anorexigenic cytokine ciliary neurotrophic factor stimulates POMC gene expression via receptors localized in the nucleus of arcuate neurons

Ciliary neurotrophic factor (CNTF) is a neural cytokine that reduces appetite and body weight when administrated to rodents or humans. We have demonstrated recently that the level of CNTF in the arcuate nucleus (ARC), a key hypothalamic region involved in food intake regulation, is positively correlated with protection against diet-induced obesity. However, the comprehension of the physiological significance of neural CNTF action was still incomplete because CNTF lacks a signal peptide and thus may not be secreted by the classical exocytosis pathways. Knowing that CNTF distribution shares similarities with that of its receptor subunits in the rat ARC, we hypothesized that CNTF could exert a direct intracrine effect in ARC cells. Here, we demonstrate that CNTF, together with its receptor subunits, translocates to the cell nucleus of anorexigenic POMC neurons in the rat ARC. Furthermore, the stimulation of hypothalamic nuclear fractions with CNTF induces the phosphorylation of several signaling proteins, including Akt, as well as the transcription of the POMC gene. These data strongly suggest that intracellular CNTF may directly modulate POMC gene expression via the activation of receptors localized in the cell nucleus, providing a novel plausible mechanism of CNTF action in regulating energy homeostasis.

Integrative role of neuropeptides and cytokines in cancer anorexia-cachexia syndrome

BACKGROUND

The cachexia anorexia syndrome is a complex metabolic syndrome associated with cancer and some other palliative conditions characterized by involuntary weight loss involving fat and muscle, weight loss, anorexia, early satiety, fatigue, weakness due to shifts in metabolism caused by tumour by-products and cytokines. Various neuropeptides like Leptin, neuropeptide Y, melanocortin, agouti-related peptides have been known to regulate appetite and body weight.

METHOD

A comprehensive literature search was carried out on the websites of Pubmed Central (http://www.pubmedcentral.nih.gov/), National Library of Medicine (http://www.ncbl.nlm.nih.gov) and various other net resources.

RESULT

Data from observational studies shows that various cytokines (TNF-α, IL-6 and IL-1) are associated with metabolic changes resulting in cachexia in cancer patients. These cytokines may mimic the action of various neuropeptides resulting in anorexia, various metabolic effects resulting from enhanced catabolic state and weight loss.

CONCLUSION

There is a need to understand and explore the role of various neuropeptides and cytokines in the pathophysiology of cancer-anorexia syndrome so that therapeutic measures may be designed for effective palliative care.

Peptides and their potential role in the treatment of diabetes and obesity

It is estimated that 347 million people worldwide have diabetes and that over 1.5 billion adults worldwide are overweight. Predictions suggest these rates are increasing. Diabetes is a common complication in overweight and obese subjects, and in 2004, an estimated 3.4 million people died from consequences of high blood sugar. Thus, there is great interest in revealing the physiological systems that regulate body weight and blood sugar. Several peptidergic systems within the central nervous system and the periphery regulate energy homeostasis. A number of these systems have been investigated as potential treatments for obesity and the metabolic syndrome. However, manipulation of peptidergic systems poses many problems. This review discusses the peptidergic systems currently attracting research interest for their clinical potential to treat obesity. We consider first neuropeptides in the brain, including the orexigenic neuropeptide Y and melanin-concentrating hormone, and anorectic factors such as the melanocortins, ciliary neurotrophic factor, and neuromedin U. We subsequently discuss the utility of targeting peripheral gut peptides, including pancreatic polypeptide, peptide YY, amylin, and the gastric hormone ghrelin. Also, we analyze the evidence that these factors or drugs based on them may be therapeutically useful, while considering the disadvantages of using such peptides in a clinical context.

A peptide derived from the CD loop-D helix region of ciliary neurotrophic factor (CNTF) induces neuronal differentiation and survival by binding to the leukemia inhibitory factor (LIF) receptor and common cytokine receptor chain gp130

Ciliary neurotrophic factor (CNTF) induces neuronal differentiation and promotes the survival of various neuronal cell types by binding to a receptor complex formed by CNTF receptor α (CNTFRα), gp130, and the leukemia inhibitory factor (LIF) receptor (LIFR). The CD loop-D helix region of CNTF has been suggested to be important for the cytokine interaction with LIFR. We designed a peptide, termed cintrofin, that encompasses this region. Surface plasmon resonance analysis demonstrated that cintrofin bound to LIFR and gp130, but not to CNTFRα, with apparent KD values of 35 nM and 1.1 nM, respectively. Cintrofin promoted the survival of cerebellar granule neurons (CGNs), in which cell death was induced either by potassium withdrawal or H2O2 treatment. Cintrofin induced neurite outgrowth from CGNs, and this effect was inhibited by specific antibodies against both gp130 and LIFR, indicating that these receptors are involved in the effects of cintrofin. The C-terminal part of the peptide, corresponding to the D helix region of CNTF, was shown to be essential for the neuritogenic action of the peptide. CNTF and LIF induced neurite outgrowth in CGNs plated on laminin-coated slides. On uncoated slides, CNTF and LIF had no neuritogenic effect but were able to inhibit cintrofin-induced neuronal differentiation, indicating that cintrofin and cytokines compete for the same receptors. In addition, cintrofin induced the phosphorylation of STAT3, Akt, and ERK, indicating that it exerts cell signaling properties similar to those induced by CNTF and may be a valuable survival agent with possible therapeutic potential.

The gp130 receptor cytokine family: regulators of adipocyte development and function

Gp130 cytokines are involved in the regulation of numerous biological processes, including hematopoiesis, immune response, inflammation, cardiovascular action, and neuronal survival. These cytokines share glycoprotein 130 as a common signal transducer in their receptor complex and typically activate STAT3. Most gp130 cytokines have paracrine or endocrine actions, and their levels can be measured in circulation in rodents and humans. In recent years, various laboratories have conducted studies to demonstrate that gp130 cytokines can modulate adipocyte development and function. Therefore, these studies suggest that some gp130 cytokines may be viable anti-obesity therapeutics. In this review, we will summarize the reported effects of gp130 cytokines on adipocyte differentiation and adipocyte function. In addition, the modulation of gp130 cytokines in conditions of obesity, insulin resistance, and Type 2 diabetes will be presented.

Induction of leptin resistance by activation of cAMP-Epac signaling

Leptin regulates energy balance and glucose homeostasis. Shortly after leptin was identified, it was established that obesity is commonly associated with leptin resistance, though the molecular mechanisms remain to be identified. To explore potential mechanisms of leptin resistance, we employed organotypic brain slices to identify candidate signaling pathways that negatively regulate leptin sensitivity. We found that elevation of adenosine 3', 5'-monophosphate (cAMP) levels impairs multiple signaling cascades activated by leptin within the hypothalamus. Notably, this effect is independent of protein kinase A activation. In contrast, activation of Epac, a cAMP-regulated guanine nucleotide exchange factor for the small G protein Rap1, was sufficient to impair leptin signaling with concomitant induction of SOCS-3 expression. Epac activation also blunted leptin-induced depolarization of hypothalamic POMC neurons. Finally, central infusion of an Epac activator blunted the anorexigenic actions of leptin. Thus, activation of hypothalamic cAMP-Epac pathway is sufficient to induce multiple indices of leptin resistance.