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At least 73 records · Page 4Linked to original sources
PubMed2003

Soluble leptin receptor and soluble receptor-bound fraction of leptin in the metabolic syndrome.

OBJECTIVE: In obesity, plasma leptin is high and soluble leptin receptor (sOb-R) levels are low, resulting in a low fraction of bound leptin. The aim of this study was to investigate the influence of insulin resistance (IR) and the metabolic syndrome (MS) on sOb-R concentration and the bound-free ratio of leptin. RESEARCH METHODS AND PROCEDURES: sOb-R, leptin levels, and homeostasis model assessment (HOMA) index for IR were determined in 76 middle-aged obese or overweight men. RESULTS: Concentration of sOb-R and soluble receptor-bound fraction of leptin were lowest in the highest tertile of HOMA-IR. sOb-R and the bound-free ratio of leptin correlated with HOMA-IR, leptin concentration, and waist-to-hip ratio independently of age, BMI, and fat mass. Leptin and waist-to-hip ratio were the sole independent determinants of sOb-R concentration, and BMI, HOMA-IR, and visceral adipose tissue were independent determinants of the bound fractin of leptin. sOb-R concentration and the bound fraction of leptin decreased with increasing numbers of components of the MS, resulting in lower sOb-R concentration and a lower fraction of bound leptin in men with the MS. DISCUSSION: IR and abdominal obesity are associated with low sOb-R concentration and low bound-free ratio of leptin independent of fat mass. Low sOb-R concentration and low bound-free ratio of leptin segregate with components of the MS. We suggest that low sOb-R levels and a low fraction of specifically bound leptin are markers of leptin resistance, which is independently associated with IR and abdominal obesity and may constitute an additional component of the MS.

Adipose Tissue↗
PubMed2006

Leptin induces TGF-beta synthesis through functional leptin receptor expressed by human peritoneal mesothelial cell.

Marked increase in leptin concentration in spent peritoneal dialysate has been reported following continuous ambulatory peritoneal dialysis treatment. The present study was designed to determine whether functional leptin receptor is expressed by human peritoneal mesothelial cells and if so, the possible implication in dialysis. Expression of leptin receptors in cultured mesothelial cells and omental tissue was examined. The effect of leptin on the production of transforming growth factor-beta (TGF-beta) by mesothelial cells in the presence or absence of high glucose was determined using in vitro culture model of human peritoneal mesothelial cells and adipocytes. The signaling mechanism involved in leptin-induced TGF-beta synthesis by mesothelial cells was studied. Both mRNA and protein of the full-length leptin receptor are constitutively expressed in mesothelial cells. The leptin receptor expression in mesothelial cells was upregulated by glucose but not leptin. In adipocytes, glucose increased the mRNA expression and synthesis of leptin. The Janus kinase-signal transducers and activation (JAK-STAT) signal transduction pathway in mesothelial cells was activated by either exogenous or adipocytes-derived leptin. Exogenous leptin induced the release of TGF-beta by mesothelial cells. The TGF-beta synthesis induced by leptin was amplified by glucose through increased leptin receptor expression. Our novel findings reveal that functional leptin receptor is present on human peritoneal mesothelial cells. The leptin-induced TGF-beta synthesis in mesothelial cells is associated with the expression of leptin receptor and the activation of the JAK-STAT signal transduction pathway.

Cells, Cultured↗
PubMed2004

Soluble leptin receptor and leptin levels in pregnant women before and after delivery.

Soluble leptin receptor is an extracellular domain of the leptin receptor that serves as the main leptin-binding protein and may play a role in the regulation of leptin tissue effects. The aim of our study was to assess serum concentrations of leptin, soluble leptin receptor, and other hormones involved in the regulation of leptin secretion in pregnant women before and after delivery. Serum leptin, cortisol, and tumor necrosis factor alpha (TNF-alpha) concentrations in 19 pregnant women before delivery were significantly higher than in healthy nonpregnant women (33.3+/-21.0 vs. 7.9+/-3.5 ng/mL, 1068.9+/-442.2 vs. 546.6+/-165.3 nmol/L, 4.4+/-1.1 vs. 3.4+/-1.2 ng/mL, respectively). In contrast, no differences between these groups were found in soluble leptin receptor levels. Delivery significantly decreased serum leptin and cortisol levels and increased soluble leptin receptor levels (12.3+/-9.1 ng/mL, 749.6+/-205.3 nmol/L, 23.3+/-7.9 U/mL, respectively). Soluble leptin receptor levels after delivery became higher than in the control group. We conclude that serum leptin and serum soluble leptin-receptor levels are significantly affected by pregnancy and delivery. The regulation of leptin levels in this group of patients appears to be distinct and independent of soluble leptin-receptor levels.

Female↗
PubMed2000

Leptin secretion and leptin receptor in the human stomach.

BACKGROUND AND AIM: The circulating peptide leptin produced by fat cells acts on central receptors to control food intake and body weight homeostasis. Contrary to initial reports, leptin expression has also been detected in the human placenta, muscles, and recently, in rat gastric chief cells. Here we investigate the possible presence of leptin and leptin receptor in the human stomach. METHODS: Leptin and leptin receptor expression were assessed by immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR), and western blot analysis on biopsy samples from 24 normal individuals. Fourteen (10 healthy volunteers and four patients with non-ulcer dyspepsia and normal gastric mucosa histology) were analysed for gastric secretions. Plasma and fundic mucosa leptin content was determined by radioimmunoassay. RESULTS: In fundic biopsies from normal individuals, immunoreactive leptin cells were found in the lower half of the fundic glands. mRNA encoding ob protein was detected in the corpus of the human stomach. The amount of fundic leptin was 10.4 (3.7) ng leptin/g mucosa, as determined by radioimmunoassay. Intravenous infusions of pentagastrin or secretin caused an increase in circulating leptin levels and leptin release into the gastric juice. The leptin receptor was present in the basolateral membranes of fundic and antral gastric cells. mRNA encoding Ob-RL was detected in both the corpus and antrum, consistent with a protein of approximately 120 kDa detected by immunoblotting. CONCLUSION: These data provide the first evidence of the presence of leptin and leptin receptor proteins in the human stomach and suggest that gastric epithelial cells may be direct targets for leptin. Therefore, we conclude that leptin may have a physiological role in the human stomach, although much work is required to establish this.

Adult↗
PubMed1998

The acute effect of dexamethasone on plasma leptin concentrations and the relationships between fasting leptin, the IGF-I/IGFBP system, dehydroepiandrosterone, androstenedione and testosterone in an elderly population.

OBJECTIVE: To investigate the acute effect of dexamethasone administration on serum leptin levels and the relationships between dehydroepiandrosterone (DHEAS), androstenedione, testosterone and the IGF-I/IGFBP system and leptin levels in healthy elderly humans. METHODS: In 209 healthy elderly individuals (95 men, 114 women, aged 55-80 years) measurements were made in the fasting state (0800 h) and after an overnight dexamethasone suppression test (1 mg p.o. at 2300 h. RESULTS: Mean leptin levels increased from 6.2 +/- 0.4 (SE) micrograms/l to 7.3 +/- 0.5 (SE) micrograms/l in men and from 18.9 +/- 1.4 (SE) micrograms/l to 23.9 +/- 1.8 (SE) micrograms/l in women after 1 mg dexamethasone overnight ('post treatment')(P < 0.001 for both sexes). There was a significant relationship between post-treatment leptin and dexamethasone levels (men: P = 0.002; women: P < 0.001). The increase in leptin levels after dexamethasone administration was only partially related to the increase in plasma insulin concentrations. Cortisol levels were not related to leptin. In multivariate analyses the relationship between post-treatment leptin and dexamethasone levels remained after adjustment for post-treatment insulin levels, BMI, waist:hip ratio (WHR) and age (men: P < 0.001; women: P = 0.001). Plasma (free and total) IGF-I and IGFBP-3 levels were not related to leptin levels in men or women. IGFBP-1 levels were inversely related to leptin levels (P = 0.02), but this relationship was lost after adjustment for insulin, and/or BMI. In multivariate analyses the relationship between leptin and DHEAS was inverse in women (P = 0.04) (after adjustment for BMI, WHR, insulin and glucose), while there was no relationship between leptin and DHEAS in men. CONCLUSIONS: Administration of dexamethasone acutely increased leptin levels within 9 h in this elderly population. This increase was only partly related to changes in circulating insulin concentrations, but was independent of BMI and waist:hip ratio. No relation existed between leptin and (free or total) IGF-I and IGFBP-3 in men or women. Dehydroepiandrosterone was inversely related to leptin in women. These findings suggest a contributory regulatory role for corticosteroids in modulating circulating leptin concentrations in elderly healthy individuals of both sexes, which is at least in part independent of insulin, BMI and waist:hip ratio. Dehydroepiandrosterone might play a role in the gender-specific differences in serum leptin levels.

Aged↗
PubMed1998

UCP2, UCP3 and leptin gene expression: modulation by food restriction and leptin.

To determine the effects of food restriction and leptin administration on several transcripts involved in energy homeostasis, we examined leptin, uncoupling proteins (UCP) 1, 2 and 3, lipoprotein lipase (LPL), beta3-adrenergic receptors (beta3AR) and hormone-sensitive lipase (HSL) mRNA levels in brown adipose tissue (BAT) and epididymal (EWAT) and perirenal (PWAT) white adipose tissue in three groups of rats. The groups were administered leptin for 1 week, or had food restricted to the amount of food consumed by the leptin-treated animals, or had free access to food. Leptin administration increased serum leptin concentrations 50-fold and decreased food consumption by 43%, whereas serum insulin and corticosterone concentrations were unchanged. Leptin increased LPL mRNA by 80%, UCP1 mRNA twofold, and UCP3 mRNA levels by 62% in BAT, and increased UCP2 mRNA levels twofold in EWAT. In contrast, UCP2 mRNA levels were unchanged in PWAT and BAT. In WAT from food-restricted rats, leptin gene expression was diminished by 40% compared with those fed ad libitum. With leptin administration, there was a further 50% decrease in leptin expression. LPL mRNA levels were decreased by food restriction but not by leptin in WAT, whereas beta3AR and HSL mRNA levels were unchanged with either food restriction or leptin treatment. The present study indicates that leptin increases the gene expression of UCP2 in EWAT and that of UCP1, UCP3 and LPL in BAT, whereas reduced food consumption but not leptin, decreases LPL expression in WAT. In addition, with leptin administration there is a decrease in leptin gene expression in WAT, independent of food intake and serum insulin and corticosterone concentrations.

Adipose Tissue↗
PubMed1998

Expression of placental leptin and leptin receptor transcripts in early pregnancy and at term.

OBJECTIVE: To demonstrate the expression of messenger RNA (mRNA) transcripts for placental leptin and leptin receptor in early gestation and at term, to quantitate transcriptional changes relative to stage of gestation, to localize transcripts within specific placental cell types, and to determine if transcripts also are expressed in cultured cells. METHODS: Expression of leptin and leptin receptor was assessed by reverse transcriptase-polymerase chain reaction, and leptin quantitated against a leptin mRNA competitor (MIMIC), in human placental villous tissue collected at term cesarean deliveries and earlier during gestation (7-14 weeks) upon elective terminations. In situ hybridization was used to identify cell types exhibiting transcripts for genes of interest. Additionally, tissue was dispersed enzymatically, cytotrophoblast cells progressed to syncytiotrophoblastic maturity in culture, and transcripts were assessed. RESULTS: Placental leptin and leptin receptor transcripts were identified in early (n = 6) and late (n = 5) gestation. Although no changes (P > .05) were apparent for receptor, leptin mRNA declined (P < .005) from (mean+/-standard error) 1.815+/-.491 attomoles/microg total RNA early in gestation to .013+/-.003 attomoles/microg total RNA at term. Leptin and leptin receptor transcripts were localized in trophoblast by in situ hybridization and were expressed in culture. CONCLUSION: Results suggest an ontogenetic decline in leptin mRNA with advancing gestation. Localization of leptin and leptin receptor transcripts in syncytiotrophoblasts, cells also responsible for the production of hormones vital to pregnancy maintenance, suggest a potential for autocrine or paracrine interactions within this tissue. Finally, transcript expression in cultured cells suggests the suitability of in vitro paradigms for future studies of leptin in pregnancy.

Adipose Tissue↗
PubMedDate not supplied

Leptin and leptin receptor in anterior pituitary function.

Leptin is a 16 kDa protein that exerts important effects on the regulation of food intake and energy expenditure by interacting with the leptin receptor in the brain and in many other tissues. Although leptin is produced mainly by white adipose tissue, several laboratories have shown low levels of leptin production by a growing number of tissues including the anterior pituitary gland. Many studies have implicated leptin in anterior pituitary function including the observation that homozygous mutations of the leptin receptor gene led to morbid obesity, lack of pubertal development and decreased GH and TSH secretion. In addition, leptin functions as a neuroendocrine hormone and regulates many metabolic activities. Leptin also interacts with and regulates the hypothalamic-pituitary-adrenal, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-gonadal axes. All of the anterior pituitary cell types express the leptin receptor. However, leptin has been localized in specific subtypes of anterior pituitary cells indicating cell type-specific production of leptin in the anterior pituitary. Subcellular localization of leptin indicates co-storage with secretory granules and implicates hypothalamic releasing hormones in leptin secretion from anterior pituitary hormone cells. Leptin signal transduction in the anterior pituitary has been shown to involve the janus protein-tyrosine kinase (JAK)/signal transducer and activation of transcription (STAT) as well as suppressor of cytokine signalling (SOCS). These proteins are activated by tyrosine-phosphorylation in anterior pituitary cells. The various steps in pituitary leptin signal transduction remain to be elucidated.

Aging↗
PubMed2002

Increased leptin expression in endometriosis cells is associated with endometrial stromal cell proliferation and leptin gene up-regulation.

Endometriosis is a polygenic disease with complex, multifactorial aetiologies affecting approximately 10% of women of reproductive age. Leptin is the product of the ob gene, which is related to reproductive function and immunological alteration. The angiogenic and mitogenic action of leptin may influence the formation of endometriosis. This study was aimed at determining whether leptin and leptin receptor expression differs in eutopic and ectopic endometria collected from laparoscopy and at investigating the pathophysiological role of leptin in the development of endometriosis. Leptin mRNA was undetectable in seven out of 14 eutopic endometria and only a minute amount was detected in the remaining samples. In contrast, there was a marked increase in leptin mRNA and protein expression in ectopic endometriotic lesions of patients with endometriosis (P < 0.05). Receptors for leptin were immunologically stained in eutopic endometrium as well as in ectopic endometriotic implants. However, the levels of mRNA for the long and total forms of leptin receptors were suppressed in association with the severity of endometriosis (P < 0.05). Administration of leptin stimulated its own mRNA expression in ectopic endometriotic stromal cells but decreased steady-state concentrations of mRNA encoding for leptin receptor (n = 6). In addition, leptin significantly enhanced both eutopic and ectopic endometrial stromal cell proliferation (P < 0.05). In conclusion, the differential distribution of mRNA for leptin and its receptor suggests an important autocrine and paracrine role for leptin in human endometriosis. The mitogenic and auto-augmentation effects of leptin may further contribute to the pathogenesis of endometriosis.

Adult↗
PubMed2000

Expression of leptin and leptin receptor isoforms in the human stomach.

BACKGROUND: Leptin is an important regulator of food intake and energy expenditure. Initially it was thought to be expressed exclusively in and secreted by adipocytes. Recently, leptin expression was also noted in other tissues, including rat gastric mucosa. Information on leptin and leptin receptor expression in the human stomach is lacking. AIM: To investigate expression of leptin and its corresponding receptors in human gastric epithelial cells. METHODS: Fundic and antral gastric mucosal biopsies, primary cultures of human gastric epithelial cells, and the human gastric cancer cell line AGS were screened for expression of leptin and different leptin receptor isoform mRNA by reverse transcriptase-polymerase chain reaction. Immunohistochemistry was performed for localisation of leptin and leptin receptor proteins in gastric mucosa. RESULTS: mRNA of leptin and its four receptor isoforms (huOB-R, long receptor isoform; huB219.1-3, short receptor isoforms) was detected in gastric mucosal biopsies, cultured human gastric epithelial cells, and gastric cancer cells. Immunohistochemistry demonstrated that chief as well as parietal cells were reactive to leptin and leptin receptors. CONCLUSIONS: Leptin and leptin receptors are expressed in human gastric mucosa. These findings suggest a paracrine and/or autocrine effect of leptin on gastric epithelial cell function.

Biopsy↗
PubMed2004

Modulation of direct leptin signaling by soluble leptin receptor.

Soluble leptin receptor (SLR) represents the major leptin binding activity in plasma. It is generated by alternative splicing of OB-R mRNA (OB-Re) and/or ectodomain shedding of membrane-spanning receptors. To determine the role of SLR in leptin activation of its long-form receptor, OB-Rb, we established in vitro assays using a cell line stably expressing OB-Rb. Human embryonic kidney 293 cell lines stably overexpressing OB-Rb show a dose-dependent leptin-induced signal transducer and activator of transcription 3 (STAT3) tyrosine phosphorylation and STAT3-responsive luciferase (STAT3-luc) activity. We demonstrate that when SLR is incubated with free leptin, binding of leptin to OB-Rb is reduced, with corresponding decrease of leptin-induced STAT3 tyrosine phosphorylation and STAT3-luc activity. However, by preparing leptin/SLR mixtures containing the same amount of free leptin but increasing amounts of leptin-SLR complex, we show that leptin-SLR complex does not inhibit OB-Rb activation by free leptin. These results suggest that in settings in which leptin and SLR coexist, SLR may sequester leptin from productive interactions with OB-Rb. Because plasma SLR levels are independently regulated by many different physiological and pathophysiological conditions, SLR may modulate the actions of leptin in tissues in which direct action of leptin has been demonstrated.

Blotting, Western↗
PubMed2006

Gh and IGF-I increase leptin receptor expression in prepubertal pig ovaries: the role of leptin in steroid secretion and cell apoptosis.

Leptin (L) is recognised as an important regulator of puberty and a factor which controls reproduction. Whole pig ovarian follicles were incubated with different doses of leptin (2, 20 and 200 ng/ml) added alone or in combination with 100 ng/ml of GH or 50 ng/ml of IGF-I. The expression of the functional long form leptin receptor (Ob-Rb) mRNA was examined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) in follicular cells cultured with GH or IGF-I. Both GH and IGF-I increased leptin receptor expression in prepubertal pig ovaries. In separate experiments, the action of leptin on ovarian follicular steroidogenesis and cell apoptosis was examined. After 24 h of incubation with leptin alone or in combination with GH or IGF-I, oestradiol (E2) levels were determined in the culture medium while follicular tissue was used for the estimation of caspase-3 activity. Leptin increased E2 secretion and significantly diminished caspase-3 activity at all doses used. Both GH and IGF-I stimulated oestradiol secretion and decreased caspase-3 activity. No differences were demonstrable in oestradiol secretion and caspase-3 activity between cells treated with GH plus leptin and GH alone or cells treated with IGF-I plus leptin as compared to cultures treated with GH or IGF-I alone. However, GH diminished leptin-stimulated oestradiol secretion while IGF-I was without effect on it. Both GH and IGF-I reversed the anti-apoptotic action of leptin. In conclusion, we infer that (1) leptin directly affects ovarian function in prepubertal animals by its action on oestradiol secretion and cell apoptosis, (2) GH and IGF-I modulate the action of leptin, and (3) at least in part, the direct effect of GH/IGF-I on leptin production is due to an action on leptin receptor expression.

Animals↗
PubMed2003

Developmental changes in plasma leptin and hypothalamic leptin receptor expression in the rat: peripubertal changes and the emergence of sex differences.

Leptin, the peptide hormone product of the ob gene, regulates food intake and energy expenditure at the hypothalamic level via the long-form of the leptin receptor (Ob-Rb). Leptin also plays a key role in determining the onset of puberty, but there is controversy as to whether leptin provides a trigger for puberty or is a permissive signal. Thus, although leptin administration can advance puberty onset in rodents, circulating leptin appears stable across puberty. While these data suggest a permissive role for leptin in rat puberty, it is possible that a change in hypothalamic response to leptin (e.g. via increased Ob-Rb expression) could enhance leptin action and thus trigger puberty without a rise in circulating leptin. In the present study we assessed developmental changes in hypothalamic Ob-Rb mRNA and protein expression in female and male rats from late fetal to postpubertal life. Quantitative RT-PCR showed that Ob-Rb mRNA increased (P<0.05) by around fivefold from fetal to postpubertal life in both females and males. These increases in Ob-Rb mRNA expression were gradual, but did not increase significantly between postnatal day 30 (pre-puberty) and day 51 (post-puberty). By day 51, hypothalamic Ob-Rb mRNA expression was higher (P<0.05) in females relative to males. Hypothalamic Ob-Rb protein showed a comparable developmental pattern (approximate threefold increase from fetal to postpubertal life), although a significant increase (15%; P<0.05) was observed between days 30 and 51 in females. Plasma leptin levels exhibited a dynamic pattern in both male and female rats during the prepubertal period, characterised by a precipitous fall after birth, relative stability to day 5, then a rapid increase to a transient peak on day 12. Plasma leptin then remained unchanged from day 15 in female rats but increased in males after puberty, thus confirming the well-recognised sex difference in adult rat leptin levels. In conclusion, this study shows that developmental increases occur not only in plasma leptin but also in hypothalamic Ob-Rb expression, suggesting that both are likely to influence the timing of puberty onset. Moreover, our data show that sex differences in both hypothalamic Ob-Rb and plasma leptin emerge only after puberty.

Animals↗
PubMed2000

Soluble leptin receptor in serum of subjects with complete resistance to leptin: relation to fat mass.

Leptin resistance and obesity have been related to mutations of the leptin receptor gene in rodents and, recently, in a consanguineous family. The latter mutation results in a receptor lacking transmembrane and intracellular domains. Homozygous and heterozygous individuals with this mutation had serum leptin levels higher than expected, given their BMIs: 600, 670, and 526 ng/ml and 145, 362, 294, 240, and 212 ng/ml, respectively. Their serum leptin was fractionated by gel filtration: >80% was present as a high-molecular size complex vs. 7.5% in the nonmutated sister. Western blot analysis showed a band at 146 kDa reacting specifically with an antibody directed against the leptin receptor ectodomain. In 10 obese control subjects, as in the mutated patients, free leptin levels correlated with BMI (r = 0.70, P = 0.0011) and reflected fat mass, regardless of leptin receptor functioning. In the patients, bound leptin levels correlated with BMI (r = 0.99, P = 0.0002) and were related to the number of mutated alleles. These data demonstrate that the truncated receptor is secreted into blood and binds the majority of serum leptin, markedly increasing bound and total leptin. Free serum leptin was similarly correlated with BMI in the mutated and nonmutated obese individuals, providing evidence that the relationship between BMI and circulating free leptin is preserved in this family. This finding suggests that the leptin receptor itself may not be specifically involved in the control of leptin secretion, and it supports the concept of relative resistance to leptin in common obesity.

Adipose Tissue↗
PubMed2002

Regulation of circulating soluble leptin receptor levels by gender, adiposity, sex steroids, and leptin: observational and interventional studies in humans.

Leptin is an adipocyte-secreted hormone important in energy homeostasis and diverse physiological processes. A circulating soluble form of the leptin receptor [soluble leptin receptor (sOB-R)] is the main leptin-binding protein and determinant of free leptin index (FLI), the presumed biologically active form of leptin. We performed observational and interventional studies to elucidate the regulation of sOB-R and FLI in humans. In a cross-sectional study (n = 118), leptin, gender, and adiposity were significant determinants of sOB-R. By multivariate analysis, estradiol (E2) and testosterone predict sOB-R, whereas insulin predicts leptin and FLI. In a frequent-sampling study (n = 6), sOB-R followed a significant circadian rhythm inverse to that of leptin, suggesting that leptin's biological activity may have an even more pronounced diurnal variation than originally thought. A 72-h fast in eight men decreased leptin levels by 80% and increased lymphocyte expression of leptin receptor mRNA and serum sOB-R levels by 100%. Physiological and pharmacological doses of recombinant-methionyl human leptin (rhLeptin) administered to fasted men prevented the fasting-induced increase of sOB-R levels, and pharmacological doses resulted in a decrease in sOB-R levels. These studies provide evidence that sOB-R is regulated by gender, adiposity, hormones, and rhLeptin administration. This may have important implications for the biological activity of leptin in disease states associated with abnormal leptin levels (e.g., obesity and anorexia nervosa).

Adolescent↗
PubMed2000

Serum leptin and leptin receptor isoforms in omental adipose tissue of nondiabetic women undergoing gynecologic surgery for benign disease.

BACKGROUND AND PURPOSE: Leptin is important in the regulation of fat mass and body weight. Adipose tissue not only secretes leptin but also serves as a site of action for leptin. This study was designed to examine the relationships among tissue expression of leptin receptors, serum leptin, and body mass index. METHODS: Omental adipose tissue and fasting blood samples were obtained from 57 nondiabetic women who underwent surgery for either myoma of the uterus or ovarian cyst. Tissue RNA was extracted using Trizol reagent and serum leptin concentrations were determined with commercial kits. The leptin receptor isoforms in tissues were quantified using real-time Taqman technology. RESULTS: Three leptin receptor isoforms, Ob-Rb, HuB219.1, and HuB219.3, were found in human omental adipose tissue. The amounts of HuB219.1 and HuB219.3 mRNA relative to that of Ob-Rb were 1314.2 and 16.7, respectively. Higher body mass index was significantly correlated with an increase in serum leptin concentration and a decrease in leptin receptor HuB219.1 isoform in omental fat, even after adjustment for age and menopausal status. There was no direct association between serum leptin concentration and tissue HuB219.1 mRNA level. CONCLUSIONS: HuB219.1 is the major isoform of leptin receptor expressed in human omental adipose tissue. Our findings suggest that the shorter leptin receptor isoforms in human omental adipose tissue might play an important role in body weight control. Further studies on the inter-relationship between leptin concentrations and multiple leptin receptor isoforms are needed to elucidate the exact mechanism of obesity.

Adipose Tissue↗
PubMed2002

Chronic ethanol consumption increases plasma leptin levels and alters leptin receptors in the hypothalamus and the perigonadal fat of C57BL/6 mice.

BACKGROUND: Leptin, a protein secreted from adipocytes, and leptin receptors, expressed in the hypothalamus and fat tissue, regulate energy balance and adiposity. Leptin receptors exist as several forms that are delineated by the length of their cytoplasmic domains. Only the longest form is physiologically active through stimulation of the signal transducers and activators of transcription (STAT) second messenger system. Previous studies demonstrated that chronic ethanol consumption increases body adiposity and circulating leptin levels. This study examined the effect of chronic alcohol intake on the expression of leptin receptors and associated STAT second messengers in the hypothalamus and fat tissue. METHODS: Female C57BL/6 mice were given water or 20% w/v ethanol and Purina 5001 laboratory chow ad libitum for 2 or 5 weeks. Plasma leptin levels were determined by radioimmunoassay and body adiposity was evaluated by measuring the amount of perigonadal fat. Expression of leptin receptors as well as STAT molecules in whole-cell lysates of the hypothalamus and the perigonadal fat were assayed by Western blot analysis. RESULTS: Plasma leptin and perigonadal fat were increased after 5 weeks. The overall expression of leptin receptors was increased while the expression of the physiologically active long form of leptin receptor was decreased in the hypothalamus and the perigonadal fat of ethanol-consuming mice. Ethanol consumption also decreased hypothalamic expression of STAT3, a protein associated with leptin receptor activation in this region of the brain. In contrast, STAT1, a protein associated with leptin receptor activation in adipose tissue, was significantly elevated in the perigonadal fat of ethanol-consuming mice. CONCLUSIONS: Chronic ethanol consumption increases the circulating level of leptin, and this is accompanied by altered expression of leptin-sensing molecules in the hypothalamus and peripheral adipose tissue. These results suggest that chronic ethanol intake affects metabolism by altering the leptin system that regulates energy balance.

Adipose Tissue↗
PubMed2000

Preparation of recombinant bovine, porcine, and porcine W4R/R5K leptins and comparison of their activity and immunoreactivity with ovine, chicken, and human leptins.

Recombinant ovine Ala-leptin (GenBank Accession No. U84247, of ovine leptin), previously prepared in our laboratory in prokaryotic expression plasmid pMON3401, was mutated using a mutagenesis kit to prepare plasmids encoding for bovine (GenBank Accession No. U50365) and porcine (GenBank Accession No. U59894) leptins and for porcine leptin analogue W4R/R5K. Escherichia coli cells transformed with these plasmids overexpressed large amounts of these proteins upon induction with nalidixic acid. The expressed proteins, found in inclusion bodies, were refolded and purified to homogeneity using subsequently anion- and cation-exchange chromatography. All three purified proteins showed a single band of the expected molecular mass of 16 kDa in SDS-PAGE in the presence of reducing agent and were composed of 90-100% monomers. Proper refolding was evidenced by comparing their CD spectra to those of previously prepared chicken and ovine leptins and to commercially available human leptin. The amino acid content of the purified proteins closely resembled the predicted composition. The biological activity of bovine leptin, porcine leptin, and porcine leptin analogue W4R/R5K was evidenced by their ability to stimulate proliferation of leptin-sensitive BAF/3 cells transfected with a long form of human leptin receptor. All three proteins, as well as ovine and chicken leptins, but not human leptin, exhibited a very high degree of cross-immunoreactivity against antiserum raised against ovine leptin in rabbits. In contrast, none or very low cross-immunoreactivity was observed against antiserum raised against ovine leptin in goats.

Amino Acid Sequence↗