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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Leptin affects food intake and body weight by actions on the hypothalamus. Although leptin resistance is common in obesity, mechanisms have not been identified. We examined the effect of leptin on expression of the suppressors-of-cytokine-signaling (SOCS) family of proteins. Peripheral leptin administration to ob/ob, but not db/db mice, rapidly induced SOCS-3 mRNA in hypothalamus, but had no effect on CIS, SOCS-1, or SOCS-2. A leptin-dependent increase of SOCS-3 mRNA was seen in areas of hypothalamus expressing high levels of the leptin receptor long form. In mammalian cell lines, SOCS-3, but not CIS or SOCS-2, blocked leptin-induced signal transduction. Expression of SOCS-3 mRNA in the arcuate and dorsomedial hypothalamic nuclei is increased in Ay/a mice, a model of leptin-resistant murine obesity. In conclusion, SOCS-3 is a leptin-inducible inhibitor of leptin signaling, and a potential mediator of leptin resistance in obesity.
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PMID:Identification of SOCS-3 as a potential mediator of central leptin resistance. 966 Sep 46

Leptin concentrations are elevated in the majority of obese individuals raising the possibility that leptin resistance contributes to their obesity. Peripheral leptin administration for 48 h caused a several-fold increase in mRNA encoding the suppressors of cytokine signaling SOCS-3 and CIS in hypothalamus and peripheral tissues. Paradoxically, CIS and SOCS-3 mRNAs are also elevated in the leptin-deficient ob/ob mouse. Forced expression of CIS in insulinoma cells prevented transactivation mediated by leptin. Thus tissues continuously exposed to leptin and/or other factors associated with obesity accumulate excessive amounts of SOCS-3 and CIS which could provide a potential mechanism for leptin resistance.
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PMID:Leptin treatment increases suppressors of cytokine signaling in central and peripheral tissues. 1042 95

We earlier demonstrated that leptin induces expression of SOCS-3 mRNA in the hypothalamus. Furthermore, transfection data suggest that SOCS-3 is an inhibitor of leptin signaling. However, little is known about the regulation of SOCS-3 expression by leptin and the mechanism by which SOCS-3 inhibits leptin action. We here show that in CHO cells stably expressing the long form of the leptin receptor (CHO-OBRl), leptin induces transient expression of endogenous SOCS-3 mRNA but not of CIS, SOCS-1, or SOCS-2 mRNA. SOCS-3 protein levels were maximal after 2-3 h of leptin treatment and remained elevated at 20 h. Furthermore, in leptin-pretreated CHO-OBRl cells, proximal leptin signaling was blocked for more than 20 h after pretreatment, thus correlating with increased SOCS-3 expression. Leptin pretreatment did not affect cell surface expression of leptin receptors as measured by (125)I-leptin binding assays. In transfected COS cells, forced expression of SOCS-3 results in inhibition of leptin-induced tyrosine phosphorylation of JAK2. Finally, JAK2 co-immunoprecipitates with SOCS-3 in lysates from leptin-treated COS cells. These results suggest that SOCS-3 is a leptin-regulated inhibitor of proximal leptin signaling in vivo. Excessive SOCS-3 activity in leptin-responsive cells is therefore a potential mechanism for leptin resistance, a characteristic feature in human obesity.
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PMID:The role of SOCS-3 in leptin signaling and leptin resistance. 1051 92

Liver-derived hyperleptinemia induced in normal rats by adenovirus-induced gene transfer causes rapid disappearance of body fat, whereas the endogenous adipocyte-derived hyperleptinemia of obesity does not. Here we induce liver-derived hyperleptinemia in rats with adipocyte-derived hyperleptinemia of acquired obesity caused by ventromedial hypothalamus lesioning (VMH rats) or by feeding 60% fat (DIO rats). Liver-derived hyperleptinemia in obese rats caused only a 5-7% loss of body weight, compared to a 13% loss in normoleptinemic lean animals; but in actual grams of weight lost there was no significant difference between obese and lean groups, suggesting that a subset of cells remain leptin-sensitive in obesity. mRNA and protein of a putative leptin-resistance factor, suppressor of cytokine signaling (SOCS)-1 or -3, were both increased in white adipose tissues (WAT) of VMH and DIO rats. Since transgenic overexpression of SOCS-3 in islets reduced the lipopenic effect of leptin by 75%, we conclude that the increased expression of SOCS-1 and -3 in WAT of rats with acquired obesity could have blocked leptin's lipopenic action in the leptin-resistant WAT population.
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PMID:Leptin resistance of adipocytes in obesity: role of suppressors of cytokine signaling. 1102 33

Leptin mediates neuroendocrine responses to fasting and restores the starvation-induced changes of several hypothalamic neuropeptides. Ciliary neurotrophic factor (CNTF), a cytokine closely related to leptin, reduces food intake and reverses obesity, but its role in restoring the starvation-induced changes of hormones or hypothalamic neuropeptides remains largely unknown. To comparatively assess the roles of CNTF and leptin in reversing the starvation-induced changes of hypothalamic neuropeptides and endocrine function and in inducing expression of hypothalamic inhibitors of leptin and CNTF signaling (suppressor of cytokine signaling 3 [SOCS-3]) and mediators of energy expenditure (cyclo-oxygenase 2 [COX-2]), we studied the effect of CNTF and leptin administered by intraperitoneal injections (1 microg/g twice daily) in C57Bl/6J mice fasted for 48 h. Serum corticosterone levels increased with fasting, and leptin administration partially normalized them, whereas CNTF administration had no effect. Hypothalamic neuropeptide Y (NPY) and agouti-related protein (AgRP) mRNA expression increased and pro-opiomelanocortin (POMC) decreased in response to fasting. Leptin administration decreased NPY and AgRP and increased POMC mRNA levels toward baseline, but CNTF administration in fasted mice had no effect of comparable significance. Both leptin and CNTF administration in fasted mice resulted in an induction of SOCS-3 mRNA expression. CNTF also induced hypothalamic SOCS-2 mRNA expression. Finally, neither leptin nor CNTF administration in mice fasted for 48 h alters hypothalamic COX-2 expression. Our data suggest that only falling leptin levels mediate the starvation-induced alterations in corticosterone levels and expression of hypothalamic neuropeptides, but inhibitors of leptin signaling are induced by both leptin and CNTF. This may be of clinical importance because both agents are now being evaluated for the treatment of obesity in humans.
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PMID:Unlike leptin, ciliary neurotrophic factor does not reverse the starvation-induced changes of serum corticosterone and hypothalamic neuropeptide levels but induces expression of hypothalamic inhibitors of leptin signaling. 1107 56

Several lines of evidence suggest that obese individuals have a higher set point for body weight regulation relative to lean subjects. Since obese rodents and humans have high serum levels of leptin, it has been hypothesized that this may be the result of an insensitivity to this weight reducing hormone. In this experiment we assessed whether feeding of a high-fat diet to rats affects leptin receptor (OB-R) transcript levels or induces up-regulation of the suppressors of leptin/cytokine induced signaling, SOCS-3 and PIAS-3. We found that despite a significant weight gain associated with markedly increased circulating leptin levels neither OB-R gene expression nor SOCS-3 or PIAS-3 mRNA levels were significantly altered in the high-fat fed rats. This was in contrast to control experiments where administration of exogenous leptin induced a several-fold increase in SOCS-3. It is concluded that high-caloric food intake per se is not sufficient to provoke suppression of leptin signaling via these factors in animals without genetic predisposition to obesity.
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PMID:Leptin receptor expression and suppressor of cytokine signaling transcript levels in high-fat-fed rats. 1113 9

Leptin resistance has been implicated in the pathogenesis of obesity-related complications involving abnormalities of lipid metabolism that resemble those of old age. To determine whether development of leptin resistance in advancing age might account for such abnormalities, we compared the effects of hyperleptinemia (>40 ng/ml) induced in 2-month-old and 18-month-old lean wild-type (+/+) Zucker diabetic fatty rats by adenovirus gene transfer. The decline in food intake, body weight, and body fat in old rats was only 25%, 50%, and 16%, respectively, of the young rats. Whereas in young rats plasma free fatty acids fell 44% and triacylglycerol (TG) 94%, neither changed in the rats. In hyperleptinemic young rats, adipocyte expression of preadipocyte factor 1 increased dramatically and leptin mRNA virtually disappeared; there was increased expression of acyl CoA oxidase, carnitine palmitoyl transferase 1, and their transcription factor peroxisome proliferator-activated receptor alpha, accounting for the reduction in body fat. These hyperleptinemia-induced changes were profoundly reduced in the old rats. On a high-fat diet, old rats consumed 28% more calories than the young and gained 1.5x as much fat, despite greater endogenous hyperleptinemia. Expression of a candidate leptin resistance factor, suppressor of cytokine signaling 3 (SOCS-3), was compared in the hypothalamus and white adipocytes of young and old rats before and after induction of hyperleptinemia; hypothalamic SOCS-3 mRNA was approximately 3x higher in old rats before, whereas it was 3x higher in WAT after, hyperleptinemia. We conclude that the anorexic and antilipopenic actions of leptin decline with age, possibly through increased SOCS-3 expression, and that this could account for the associated abnormalities in lipid metabolism of the elderly.
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PMID:The role of leptin resistance in the lipid abnormalities of aging. 1114 98

SOCS (suppressor of cytokine signaling) proteins are inhibitors of cytokine signaling involved in negative feedback loops. We have recently shown that insulin increases SOCS-3 mRNA expression in 3T3-L1 adipocytes. When expressed, SOCS-3 binds to phosphorylated Tyr(960) of the insulin receptor and prevents Stat 5B activation by insulin. Here we show that in COS-7 cells SOCS-3 decreases insulin-induced insulin receptor substrate 1 (IRS-1) tyrosine phosphorylation and its association with p85, a regulatory subunit of phosphatidylinositol-3 kinase. This mechanism points to a function of SOCS-3 in insulin resistance. Interestingly, SOCS-3 expression was found to be increased in the adipose tissue of obese mice, but not in the liver and muscle of these animals. Two polypeptides known to be elevated during obesity, insulin and tumor necrosis factor-alpha (TNF-alpha), induce SOCS-3 mRNA expression in mice. Insulin induces a transient expression of SOCS-3 in the liver, muscle, and the white adipose tissue (WAT). Strikingly, TNF-alpha induced a sustained SOCS-3 expression, essentially in the WAT. Moreover, transgenic ob/ob mice lacking both TNF receptors have a pronounced decrease in SOCS-3 expression in the WAT compared with ob/ob mice, providing genetic evidence for a function of this cytokine in obesity-induced SOCS-3 expression. As SOCS-3 appears as a TNF-alpha target gene that is elevated during obesity, and as SOCS-3 antagonizes insulin-induced IRS-1 tyrosine phosphorylation, we suggest that it is a player in the development of insulin resistance.
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PMID:SOCS-3 inhibits insulin signaling and is up-regulated in response to tumor necrosis factor-alpha in the adipose tissue of obese mice. 1160 92

Aged Wistar rats are characterized by leptin and insulin resistance. The expression of SOCS-3 in hypothalamus increases with ageing. Food restriction during 3 months decreases obesity Lee index in aged rats with respect to their ad libitum aged-mates and brings serum leptin concentrations to values close to those of young rats. Food restriction partially reverts the increases in SOCS-3 mRNA levels associated with ageing. These results suggest that SOCS-3 may be a mediator of hypothalamic leptin resistance in the aged Wistar rat and that the hyperleptinemia associated with ageing is, at least in part, responsible for the increase of SOCS-3 expression in hypothalamus.
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PMID:Ageing increases SOCS-3 expression in rat hypothalamus: effects of food restriction. 1216 36

Interleukin-6 (IL-6) is one of several pro-inflammatory cytokines implicated in insulin resistance during infection, cachexia, and obesity. We recently demonstrated that IL-6 inhibits insulin signaling in hepatocytes (Senn, J. J., Klover, P. J., Nowak, I. A., and Mooney, R. A. (2002) Diabetes 51, 3391-3399). Members of the suppressors of cytokine signaling (SOCS) family associate with the insulin receptor (IR), and their ectopic expression inhibits IR signaling. Since several SOCS proteins are induced by IL-6, a working hypothesis is that IL-6-dependent insulin resistance is mediated, at least in part, by induction of SOCS protein(s) in insulin target cells. To examine the involvement of SOCS protein(s) in IL-6-dependent inhibition of insulin receptor signaling, HepG2 cells were treated with IL-6 (20 ng/ml) for periods from 1 min to 8 h. IL-6 induced SOCS-3 transcript at 30 min with a maximum effect at 1 h. SOCS-3 protein levels were also markedly elevated at 1 h. Transcript and protein levels returned to near basal levels by 2 h. SOCS-3 induction by IL-6 paralleled IL-6-dependent inhibition of IR signal transduction. Ectopically expressed SOCS-3 associated with the IR and suppressed insulin-dependent receptor autophosphorylation, insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, association of IRS-1 with the p85 subunit of phosphatidylinositol 3-kinase, and activation of Akt. SOCS-3 was also a direct inhibitor of insulin receptor autophosphorylation in vitro. In mice exposed to IL-6 for 60-90 min, hepatic SOCS-3 expression was increased. This was associated with inhibition of hepatic insulin-dependent receptor autophosphorylation and IRS-1 tyrosine phosphorylation. These data suggest that induction of SOCS-3 in liver may be an important mechanism of IL-6-mediated insulin resistance.
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PMID:Suppressor of cytokine signaling-3 (SOCS-3), a potential mediator of interleukin-6-dependent insulin resistance in hepatocytes. 1256 Mar 30


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