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Query: UNIPROT:P06889 (Mol)
 630,302 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.
Mol Cell 1998 Mar
PMID:Identification of SOCS-3 as a potential mediator of central leptin resistance. 966 Sep 46

At present, leptin is quantitated using immuno-assays that measure leptin mass. Leptin biological activity is determined using protocols that measure feed consumption and weight reduction. These in vivo protocols are semi-quantitative and require large quantities of leptin. We describe a rapid, sensitive and quantitative in vitro assay for leptin using HEK-293 cells stably co-transfected with the leptin receptor Ob-Rb isoform and a STAT-inducible promoter regulating the firefly luciferase cDNA. The assay, performed in a 96-well format, has an EC50 of 150 pM and is linear from 3 to 700 pM of leptin. We demonstrate that the assay is capable of measuring leptin in plasma samples. We demonstrate that bacterially-expressed, recombinant leptin and in vivo expressed leptin are equipotent. Furthermore, we demonstrate that a leptin-derived peptide, leptin fragment 22-56, previously shown to be capable of reducing feed intake following ICV injection does not act directly through the leptin receptor.
Mol Cell Endocrinol 1998 Aug 25
PMID:A rapid, quantitative functional assay for measuring leptin. 980 56

Leptin plays an important role in reproductive function. In patients with acute anorexia nervosa, serum leptin levels have repeatedly been shown to be lower than in age-matched controls. We have previously hypothesized that the amenorrhea characteristic of anorexia nervosa is related to this low leptin secretion. In an attempt to address this hypothesis, serum levels of leptin and follicle stimulating hormone (FSH) and luteinizing hormone (LH) of 16 female inpatients with anorexia nervosa or an eating disorder not otherwise specified (atypical anorexia nervosa) were measured on a biweekly basis during weight gain. We hypothesized that a serum leptin level of 1.85 microg L(-1) would be associated with gonadotropin levels at or above the minimal level observed during the menstrual cycle in healthy adult fertile females. Our results revealed that increments of LH levels generally tracked increments of leptin levels during the first weeks of treatment. Similarly, in those patients with low referral leptin levels, FSH initially also tracked leptin levels. In contrast, a relationship between gonadotropin levels and leptin secretion was no longer discernible after LH and FSH levels had peaked. Those patients with exceedingly low leptin levels upon admission revealed a slow increase of gonadotropin levels. Our hypothesis of a threshold leptin level of 1.85 microg L(-1) was supported for LH only.
Mol Psychiatry 1999 Jan
PMID:Serum leptin and gonadotropin levels in patients with anorexia nervosa during weight gain. 1008 13

Leptin is a cytokine secreted from adipose tissue at a rate commensurate with the size of the body's fat stores. In addition to its anorectic and thermogenic central actions, leptin is known to act on peripheral tissues, including the pancreatic beta-cell where it inhibits insulin secretion and reduces insulin transcript levels. However, the role of leptin signalling through its full-length receptor, OB-Rb, in the beta-cell remains unclear. In the present study, we show that leptin activates a signal transducer and activator of transcription (STAT)3 signalling mechanism in pancreatic islets and in a rat model of the pancreatic beta-cell, RINm5F. Leptin induced DNA binding to a STAT consensus oligonucleotide and resulted in transcriptional activation from STAT reporter constructs in a manner consistent with STAT3 activation. Western blot analysis confirmed activation of STAT3 in RINm5F and isolated rat islets. Conditions that mimic increased metabolic activity resulted in attenuation of leptin-mediated STAT DNA binding but had no significant effect on STAT3 tyrosine phosphorylation in RINm5F cells. In addition, leptin activated the mitogen activated protein (MAP) kinase pathway in RINm5F cells. The present study provides a framework for OB-Rb signalling mechanisms in the programming of the beta-cell by leptin and suggests that increased metabolic activity may modulate this function.
J Mol Endocrinol 1999 Apr
PMID:Leptin signalling in pancreatic islets and clonal insulin-secreting cells. 1019 20

The short-term effects of leptin and a beta 3-adrenoceptor agonist on thermogenesis and expression of uncoupling proteins (UCPs) in brown adipose tissue (BAT) and muscle and their possible interactions were assessed. One hour after administration of the beta 3-adrenoceptor agonist Trecadrine, a statistically significant increase in UCP1 messenger RNA (mRNA) expression in BAT was observed, whereas UCP2 and UCP3 in both BAT and gastrocnemius muscle were unaffected. Leptin induced an upregulation of UCP3 mRNA in muscle, with no changes in BAT UCP1 mRNA. A statistical interaction was found between leptin and Trecadrine in rectal temperature. The present study provides evidence, for the first time, of the induction of UCP3 mRNA expression in skeletal muscle by leptin in nongenetically obese animals.
Cell Mol Life Sci 1999 Jun
PMID:Leptin, but not a beta 3-adrenergic agonist, upregulates muscle uncoupling protein-3 messenger RNA expression: short-term thermogenic interactions. 1041 76

Leptin, the obese (ob) gene product, is secreted by adipocytes and regulates appetite through interaction with hypothalamic leptin receptors. Leptin may also have a stimulatory effect on reproductive function. Furthermore, leptin receptor mRNA is expressed in the ovary, suggesting a direct effect on its function. The present study examines the direct role of leptin on the oestrogen-producing activity in human luteinized granulosa cells. The cells were obtained from in-vitro fertilization pre-ovulatory follicles, precultured for 24 h in the presence of 5% charcoal-treated serum, and incubated for 48-96 h in a serum-free medium containing recombinant human leptin, follicle stimulating hormone (FSH), and/or insulin-like growth factor-I (IGF-I). A single addition of leptin (0. 5-10 ng/ml) stimulated aromatase activity with the incubation time of up to 96 h. The addition of leptin (1 ng/ml) further augmented the stimulation by a single addition of FSH (100 ng/ml) or IGF-I (100 ng/ml), or a combination of both. A single addition of leptin (1 ng/ml) or a combination of leptin (1 ng/ml), FSH (100 ng/ml), and IGF-I (100 ng/ml) gave rise to an increase in each parameter of oestrogen-producing activity measured, i.e. P450arom mRNA level, P450arom protein level, aromatase specific activity, and the oestradiol concentration in the culture supernatant. However, the production of progesterone did not change. These results indicate that leptin stimulates oestrogen production by increasing P450arom mRNA and P450arom protein expression and, consequently, aromatase activity by its direct action on the human luteinized granulosa cells.
Mol Hum Reprod 1999 Aug
PMID:Leptin directly stimulates aromatase activity in human luteinized granulosa cells. 1042 96

The recent discovery of leptin as a major controller of appetite has led to a detailed analysis of its specific actions in this process as well as any potential role in the etiology of obesity. It has also emerged that leptin has a wider spectrum of biological activities and has been strongly implicated in fertility and reproduction. The structural similarity between leptin and its receptor and cytokine-receptor systems that control hemopoiesis has also prompted investigation of the potential for this hormone to influence blood cell formation. Recent studies have shown that the leptin receptor is expressed on a diverse range of hemopoietic cells. Leptin itself appears to enhance proliferation of hemopoietic cells in vitro, particularly in combination with other cytokines and may augment some mature hemopoietic cell functions. Although only relatively minor hemopoietic deficiencies have been reported in mice lacking leptin or its receptor, these emerging studies suggest that further analysis of leptin actions in hemopoiesis may be warranted.
Mol Biotechnol 1999 Apr
PMID:A role for leptin in hemopoieses? 1046 69

Leptin has recently been implicated as having a role in sexual maturation and reproduction. This review describes recent findings regarding the putative reproductive functions of leptin within the context of the attainment of sufficient long-term fuel reserves to sustain and support pregnancy and lactation. The review considers the evidence, within the context of the development of hyperleptinaemia during pregnancy, that leptin has an important function to modulate maternal nutrient partitioning in order to optimise the provision of nutrients for fetal growth and development. It is suggested that, through modulation of maternal insulin secretion and hepatic metabolism, leptin integrates maternal nutrient storage to the nutrient requirements of the fetus. The importance of the placenta as a site of leptin synthesis and the potential role(s) of placentally derived leptin are evaluated in relation to maternal-fetal interactions during intrauterine development. The review also examines whether intrauterine growth retardation due to nutritional restriction reflects dysregulation of such cross-talk. Finally, the review describes emerging evidence for participation of leptin in lactation and neonatal growth.
Mol Cell Endocrinol 1999 Nov 25
PMID:Current concepts concerning the role of leptin in reproductive function. 1061 93

Leptin regulates energy homeostasis via binding to receptors in the hypothalamus and peripheral tissues. We have investigated the signaling pathways and effects of leptin on glucose transport in C2C12 muscle cells. Long and short forms of leptin receptor are expressed in differentiated C2C12 myotubes. Leptin enhanced the DNA-binding activity of the transcription factor STAT3 and extracellular signal-regulated kinase 2 (ERK2) activity was stimulated by leptin after 15 min. Leptin increased glucose uptake and GLUT4 recruitment to the cell surface after 30 min, whereas no changes in GLUT1 was observed. PD98059, an ERK2 kinase-1 inhibitor, and wortmannin, an inhibitor of phosphatidylinositol 3-kinase blocked the leptin-induced increase in glucose uptake and GLUT4 recruitment to the cell surface. In contrast, insulin-stimulated glucose transport and GLUT4 translocation was inhibited by wortmannin, but not by PD98059. Our results suggest that leptin may regulate glucose metabolism by acting directly on skeletal muscle and that the signaling pathways involved may be different from that activated by insulin.
Mol Cell Endocrinol 1999 Nov 25
PMID:Leptin stimulates glucose uptake in C2C12 muscle cells by activation of ERK2. 1061 3

Sulpiride (SUL, 20 mg kg-1 day-1) induces weight gain, hyperphagia, hyperprolactinemia, hypogonadism, and perhaps increased insulin sensitivity in rats. Leptin seems to signal the brain about the size of body fat stores and nutrient metabolism. We evaluated the basal serum leptin levels in rats after acute (1 h) or prolonged SUL or vehicle administration (10, 20 and 30 days). At days 10 and 30 leptin was also assessed during a glucose overload test. As the maximal weight gain during SUL administration is observed at days 10-15 of treatment, leptin was measured in a comparison group of insulin-treated rats (5 IU day-1 for 10 days). SUL-treated rats significantly gained weight. However, leptin levels were not significantly increased at any time-point of treatment. SUL did not affect insulin levels either. By contrast, leptin levels were significantly elevated after insulin administration, along with weight gain and hyperinsulinemia. An opposite correlation was also observed at day 10: leptin and insulin correlated negatively in the SUL group and positively in the insulin group. In addition, leptin and the magnitude of weight gain tended to correlate positively after SUL treatment, but negatively after insulin administration. SUL-treated rats, thus, appear to exhibit an unusual type of weight gain, characterized by normal circulating leptin and insulin levels. Such a particular leptin profile may be related to hyperprolactinemia, hypogonadism or lack of hyperinsulinemia. Molecular Psychiatry (2000) 5, 70-76.
Mol Psychiatry 2000 Jan
PMID:Antipsychotic drug-induced obesity in rats: correlation between leptin, insulin and body weight during sulpiride treatment. 1067 71


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