Direct Effect Of Leptin Research Articles

The relationship between BMI, leptin, leptin receptors (LepR) and Foxp3+ Tregs cells in women with asthma

The aim of this study was evaluation whether there is an association between BMI, leptin and its soluble receptor, the expression of FoxP3 in CD4+ pTreg in women with severe asthma. Materials and methods. The study included thirty women with asthma: 17 patients with severe and 13 with mild-moderate disease. The control group comprised of 25 healthy women. Asthma was diagnosed in accordance with the Global Initiative For Asthma guidelines (GINA 2014). The phenotype of CD4+CD25highCD127lowFoxp3+CD152+ cells was evaluated by multicolor flow cytometry. The concentration of leptin and its soluble receptor were determined using an immunoenzymatic method (ELISA). Results. It has been shown significantly increased leptin concentration in the group of women with severe asthma compared with mild-moderate asthma and control group (p <0.05). The concentration of the leptin receptor significantly increased (p <0.05) in women with severe asthma compared with control group. There were no differences in percentage of CD4+FoxP3+ and CD4+CD25highCD127low- FoxP3+CD152+ subsets after leptin stimulation in all tested groups. Conclusions. Our results don’t confirm the direct effect of leptin on the CD4+ pTreg cells and the expression of FoxP3 in these cells, in tested groups.

Effect and mechanism of leptin on bone metabolism in postmenopausal women

Objective To investigate the effects of Leptin on the base of anthropometry, densitometry, and biochemistry and reveal the role of Leptin in bone metabolism in postmenopausal women with osteoporosis (OP). Methods From January 2008 to January 2014, data of 82 postmenopausal females with or without OP were analyzed. They were randomized into two groups: OP (n=40) and conditional control group (CON) (n=42). The expression of Leptin receptors in osteoblasts was observed by immunohistochemistry. 1×10 ng/ml, 1×102 ng/ml, 1×103 ng/ml, 1×104 ng/ml of Leptin were added respectively. Then the proliferation, differentiation and mineralization of osteoblasts were measure at 24 h, 48 h and 96 h. The gene expressions of bone marrow mesenchymal stem cells (BMSCs) derived osteoblasts and adipocytes treated with Leptin were examined by quantitative analysis of Real time-PCR. Results The expression of Leptin receptors in osteoblasts was observed on plasma membranes and cytoplasm in the normal group and osteoporosis group. In osteoporosis group, different concentrations of Leptin enhanced cell proliferation, cell differentiation and cell mineralization. The growth rate of MTT and the concentration of ALP in the serum of were significantly increased with the effects of 1×10 ng/ml, 1×102 ng/ml and 1×103 ng/ml of Leptin, and the action of 1×102 ng/ml Leptin was the most powerful with time dependence. Within 96 hours, the growth rate of osteoblasts increased gradually, and the concentration of ALP increased gradually in 3 weeks. The expression of RANKL/OPG in bone marrow BMSCs derived osteoblasts treated with Leptin were significantly increased. Conclusion Leptin receptor is present in osteoblasts, and Leptin affects biological behaviors of osteoblasts through receptors. The direct effect of Leptin may relate the expression of RANKL/OPG. Then, the balance between bone resorption and bone formation was broken and finally osteoporosis occurred. Lepin may promote osteogenesis and inhibit bone resorption in the differentiation of BMSCs. Key words: Osteoporosis, postmenopausal; Leptin; Bone diseases, metabolic

Abstract P084: Oxidative Stress Preconditioning Is Required for Leptin to Stimulate Renin Release From Mouse Juxtaglomerular Cells

Leptin is enhanced in animal models of obesity. The role of leptin in hypertension is unclear with some studies showing antihypertensive actions and others showing a pro-hypertensive role. In normotensive, non-obese, animals, infusion of leptin induces natriuresis. However, in animal models of enhanced oxidative stress, obesity, or activated renin-angiotensin system, infusion of leptin tends to increase blood pressure. Renin is a critical mediator of angiotensin-II formation, and thus blood pressure control. However, the direct effect of leptin on the release of renin from juxtaglomerular (JG) cells has not been studied. We hypothesize that under normal conditions leptin does not affect renin release whereas during high oxidative stress leptin stimulates renin release. We isolated primary cultures of mouse juxtaglomerular (JG) cells. After treatment with different agonists, renin released to the supernatant was measured by radioimmunoassay. We first tested the direct effect of murine leptin on renin release. We found that 1 hr treatment with leptin (0.1-1 uM) decreased basal renin by 20 ± 5% (p<0.05; n=8). Treatment of JG cells for longer periods (4 and 24 hrs) did not affect renin release (n=6) or total renin expression (n=4). We then tested whether oxidative stress modified the effect of leptin on renin release. For this we pre-incubated JG cells with 10 uM hydrogen peroxide (H2O2) for 1 hr. After this, the medium was removed and H2O2 was completely washed out from JG cells followed by treatment with vehicle (cont) or 10 uM leptin. We found that, in cells pre-treated with H2O2, leptin increased renin release by 49.2 ±16 %(P<0.05 vs vehicle). By Western blot, we detected the expression of the leptin receptor in lysates from JG cells. We concluded that under normal conditions leptin inhibits renin release from JG cells. However, after exposure to H2O2, leptin stimulates renin release. Our data suggest the hypothesis that oxidative stress reverses the inhibitory effect of leptin on renin release and supports a pro-hypertensive role for leptin during chronic inflammatory conditions that induces oxidative stress.

The Effects of Adipokines on Cartilage and Meniscus Catabolism

Obesity is one of the primary risk factors for osteoarthritis. Increased adiposity is associated not only with alterations in joint loading, but also with increased systemic and joint concentrations of adipose tissue-derived cytokines, or “adipokines,” that promote a state of chronic, low-grade inflammation that may act in concert with other cytokines in the joint to increase joint degeneration. However, the direct effect of adipokines, such as leptin, visfatin, and interleukin-6 (IL-6), on joint tissues, such as articular cartilage and meniscus, are not fully understood. In this study, we examined the hypothesis that these adipokines act synergistically with interleukin-1 (IL-1) to increase catabolism and the production of proinflammatory mediators in cartilage and meniscus. Explants of porcine cartilage and meniscus were treated with physiologically relevant concentrations of leptin, IL-6, or visfatin, alone or in combination with IL-1. Visfatin and IL-1 promoted the catabolic degradation of both cartilage and meniscus, as evidenced by increased metalloproteinase activity, nitric oxide production, and proteoglycan release. However, leptin or IL-6 at physiologic concentrations had no effect on the breakdown of these tissues. These findings suggest that the effects of obesity-induced osteoarthritis may not be through a direct effect of leptin or IL-6 on cartilaginous tissues, but support a potential role for increased visfatin levels in this regard. These data provide an important first step in understanding the role of adipokines in regulating cartilage and meniscus metabolism; however, these adipokines may have different effects in the context of the whole joint and must be evaluated further.

Compensation for obesity-induced insulin resistance in dogs: assessment of the effects of leptin, adiponectin, and glucagon-like peptide-1 using path analysis

The hormonal mediators of obesity-induced insulin resistance and compensatory hyperinsulinemia in dogs have not been identified. Plasma samples were obtained after a 24-h fast from 104 client-owned lean, overweight, and obese dogs. Plasma glucose and insulin concentrations were used to calculate insulin sensitivity and β-cell function with the use of the homeostasis model assessment (HOMA insulin sensitivity and HOMA β-cell function, respectively). Path analysis with multivariable linear regression was used to identify whether fasting plasma leptin, adiponectin, or glucagon-like peptide-1 concentrations were associated with adiposity, insulin sensitivity, and basal insulin secretion. None of the dogs were hyperglycemic. In the final path model, adiposity was positively associated with leptin ( P < 0.01) and glucagon-like peptide-1 ( P = 0.04) concentrations. No significant total effect of adiposity on adiponectin in dogs ( P = 0.24) was observed. If there is a direct effect of leptin on adiponectin, then our results indicate that this is a positive relationship, which at least partly counters a negative direct relationship between adiposity and adiponectin. Fasting plasma leptin concentration was directly negatively associated with fasting insulin sensitivity ( P = 0.01) and positively associated with β-cell function ( P < 0.01), but no direct association was observed between adiponectin concentration and either insulin sensitivity or β-cell function ( P = 0.42 and 0.11, respectively). We conclude that dogs compensate effectively for obesity-induced insulin resistance. Fasting plasma leptin concentrations appear to be associated with obesity-associated changes in insulin sensitivity and compensatory hyperinsulinemia in naturally occurring obese dogs. Adiponectin does not appear to be involved in the pathophysiology of obesity-associated changes in insulin sensitivity.

Differential acute and chronic effects of leptin on hypothalamic astrocyte morphology and synaptic protein levels.

Astrocytes participate in neuroendocrine functions partially through modulation of synaptic input density in the hypothalamus. Indeed, glial ensheathing of neurons is modified by specific hormones, thus determining the availability of neuronal membrane space for synaptic inputs, with the loss of this plasticity possibly being involved in pathological processes. Leptin modulates synaptic inputs in the hypothalamus, but whether astrocytes participate in this action is unknown. Here we report that astrocyte structural proteins, such as glial fibrillary acidic protein (GFAP) and vimentin, are induced and astrocyte morphology modified by chronic leptin administration (intracerebroventricular, 2 wk), with these changes being inversely related to modifications in synaptic protein densities. Similar changes in glial structural proteins were observed in adult male rats that had increased body weight and circulating leptin levels due to neonatal overnutrition (overnutrition: four pups/litter vs. control: 12 pups/litter). However, acute leptin treatment reduced hypothalamic GFAP levels and induced synaptic protein levels 1 h after administration, with no effect on vimentin. In primary hypothalamic astrocyte cultures leptin also reduced GFAP levels at 1 h, with an induction at 24 h, indicating a possible direct effect of leptin. Hence, one mechanism by which leptin may affect metabolism is by modifying hypothalamic astrocyte morphology, which in turn could alter synaptic inputs to hypothalamic neurons. Furthermore, the responses to acute and chronic leptin exposure are inverse, raising the possibility that increased glial activation in response to chronic leptin exposure could be involved in central leptin resistance.

Tissue distribution and effects of fasting and obesity on the ghrelin axis in mice

Ghrelin is a 28 amino acid peptide hormone derived from the 117 amino acid proghrelin, following cleavage by proprotein convertase 1 (PC1). In this study, we comprehensively assessed the tissue distribution and the effect of fasting and obesity on preproghrelin, Exon-4D, PC1 and GOAT expression and proghrelin-derived peptide (PGDP) secretion. The stomach was the major source of preproghrelin expression and PDGPs, followed by the small intestine. The remaining peripheral tissues (including the brain and pancreas) contained negligible expression levels. We detected obestatin in all stomach proghrelin cells, however, 22% of proghrelin cells in the small intestine did not express obestatin. There were strain differences in ghrelin secretion in response to fasting between CD1 and C57BL/6 mice. After a 24 hour-fast, CD1 mice had increased plasma levels of total ghrelin and obestatin with no change in preproghrelin mRNA or PGDP tissues levels. C57BL/6 mice showed a different response to a 24 hour-fast having increased proghrelin mRNA expression, stomach acylated ghrelin peptide and no change in plasma obestatin in C57BL/6 mice. In obese mice ( ob/ob and diet-induced obesity (DIO)) there was a significant increase in preproghrelin mRNA levels while tissue and plasma PGDP levels were significantly reduced. Fasting did not affect PGDP in obese mice. Obese models displayed differences in GOAT expression, which was elevated in DIO mice, but reduced in ob/ob mice. We did not find co-localization of the leptin receptor in ghrelin expressing stomach cells, ruling out a direct effect of leptin on stomach ghrelin synthesis and secretion.

Leptin Induces an Inflammatory Phenotype in Lean Wistar Rats

The present study addressed the hypothesis that leptin promotes leukocyte trafficking into adipose tissue. Accordingly, male Wistar rats were treated with saline or recombinant rat leptin (1 mg/kg) via the tail vein. Leukocyte trafficking in mesenteric venules was quantified by intravital microscopy. Treatment with leptin resulted in a 3- and 5-fold increases in rolling and firm adhesion, respectively. Compared to vehicle controls, leptin enhanced mRNA levels of IL-6 (8-fold) and MCP-1 (5-fold) in mesenteric adipose tissue (MAT). Similar increases in these markers were observed in mesenteric venules and in liver. Finally, the direct effect of leptin was assessed in C3A hepatocytes treated with leptin for 24 hours (7.8 ng/mL–125 ng/mL). Consistent with observations in vivo, production of ICAM-1, MCP-1, and IL-6 by hepatocytes was increased significantly. These findings support the hypothesis that leptin directly initiates inflammation in the local environment of mesenteric adipose tissue as well as systemically.

Leptin increases L-type Ca2+ channel expression and GnRH-stimulated LH release in LβT2 gonadotropes

Leptin, a mediator of long-term regulation of energy balance, has been implicated in the release of adenohypophyseal gonadotropins by regulating gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. However, a direct effect of leptin on hormone release from gonadotropes remains virtually unexplored. In the current report, we assessed the long-term (48 h) actions of leptin on voltage-gated channel activity and luteinizing hormone (LH) production in mouse pituitary gonadotrope LbetaT2 cells. Electrophysiological recordings showed that leptin treatment significantly increased whole-cell patch-clamp Ba(2+) current through L-type Ca(2+) channels. Quantitative RT-PCR analysis revealed increased levels of L-type (alpha(1D)) Ca(2+) channel mRNA. Likewise, radioimmunoassays using specific antibodies provided evidence that leptin alone had no effect on LH release but did enhance GnRH-induced secretion of the hormone. Leptin had no apparent effects on LH gene transcription in absence of GnRH, as measured by transient transfection assays using a LH promoter-reporter gene and real-time RT-PCR. These observations suggest that leptin might affect LH release by acting directly on the gonadotropes, favoring hormone production by enhancing responsiveness to GnRH as a result of increased Ca(2+) channel expression.

Abstract 509: Myocardial Fatty Acid Oxidation Rates Remain Elevated in ob/ob Mice Despite Reversal of Obesity and Diabetes by Caloric Restriction

Leptin deficient ob/ob mice are commonly used to study the effects of obesity and insulin resistance on myocardial substrate metabolism. However, it is difficult to discern the specific contribution of obesity, insulin resistance and diabetes versus leptin deficiency to the observed phenotypes. We therefore adopted a strategy using caloric restriction to normalize body weight and reverse insulin resistance to study the effect of leptin deficiency on myocardial metabolism in lean ob/ob mice. Male 4-week old ob/ob mice were “pair fed” to a leptin-treated group (3mg/kg/day by i.p. injection) for three weeks. Glucose tolerance, serum insulin, serum triglycerides and FA oxidation rates in hearts perfused with 0.4mM palmitate ± 1 nM insulin were determined. Leptin-treated ob/ob mice ate significantly less than non-treated ob/ob mice, and their weight returned to wild type levels. Hyperglycemia, hyperinsulinemia, hypertriglyceridemia and cardiac hypertrophy were also completely reversed in leptin-treated ob/ob mice. In contrast, cardiac hypertrophy persisted in pair fed ob/ob mice and despite normalization of glucose tolerance and insulin levels, serum triglyceride concentrations increased by 2 and 6 -fold in pair fed ob/ob mice relative to untreated ob/ob and wildtype mice respectively (p&lt;0.05). As previously reported, palmitate oxidation rates were 2.1-fold increased in ob/ob hearts relative to controls (p&lt;0.005) and were normalized with leptin treatment. In contrast, palmitate oxidation rates remained elevated in pair fed ob/ob mice relative to wildtype controls (1.9-fold, p&lt;0.01). Insulin has a positive inotropic effect in perfused wildtype hearts, and this effect was absent in ob/ob hearts. The insulin-induced inotropic response was restored by leptin treatment in ob/ob mice but was not restored in pair fed ob/ob mice. These data support a direct antihypertrophic effect of leptin in the heart and suggest that leptin deficiency may directly contribute to myocardial insulin resistance and abnormal FA metabolism. Potential mechanisms include increased hepatic triglyceride production in leptin deficiency or direct effects of leptin signaling in the hypothalamus and/or the periphery on myocardial substrate utilization.

Leptin in the bovine corpus luteum: Receptor expression and effects on progesterone production

In cattle, leptin has been implicated in the control of ovarian function and has been shown to modulate steroid production by theca and granulosa cells in a number of species. However, a direct effect of leptin on bovine luteal function has not been demonstrated. This study was conducted to determine if the leptin receptor (OB-R) is expressed in the bovine corpus luteum (CL), and to examine the effects of leptin on progesterone production by dispersed luteal cells in vitro. RT-PCR was used to detect the presence of OB-R and, more specifically, the long, biologically active isoform (OB-Rb), in CL, collected on days 2-18 of the oestrous cycle (n=18). The effects of leptin on progesterone production were investigated in dispersed luteal cells prepared from CL collected on days 5 and 8 (n=14) of the cycle. The dispersed luteal cells were cultured for 24 hr with recombinant human leptin and/or LR3-IGF-1 and/or LH. OB-Rs, in particular, OB-Rb, were expressed in the CL at all stages of development. Progesterone production by luteal cells was increased (P<0.001) by treatment with LH (10 ng/ml) but treatment with leptin alone had no effect. However, in the presence of IGF-1 (100 ng/ml), leptin (10 ng/ml) caused a significant (P<0.005) increase in progesterone production. In conclusion, we have shown that the leptin receptor is expressed in the bovine CL and have demonstrated a modulatory effect of leptin on luteal progesterone production in vitro.

299 LEPTIN ACCELERATES PRONUCLEAR FORMATION FOLLOWING INTRACYTOPLASMIC SPERM INJECTION OF PORCINE OOCYTES: POSSIBLE ROLE OF MITOGEN-ACTIVATED PROTEIN KINASE INACTIVATION

Although evidence suggests that leptin modulates oocyte maturation in vitro, few studies have examined the direct effect of leptin on cytoplasmic maturation and pronuclear formation following fertilization of porcine oocytes.The aim of this studywas to determine microtubule and microfilament assembly following oocyte maturation, and to assess blastocyst formation, mitogen-activated protein kinase (MAPK) activity, and pronuclear formation following parthenogenetic stimuli or intracytoplasmic sperm injection (ICSI) of leptin-treated oocytes.A symmetrical shape of the meiotic spindle was considered to be the normal microtubule assembly, and a clear, thick microfilament area containing a second metaphase chromatin was considered to be morphologically normal. Significant differences were determined using Tukey's multiple range test with P &amp;lt; 0.05 being considered significant. Addition of 10 ng mL-1 of leptin to the in vitro maturation (IVM) medium significantly increased the percentage of zygotes that developed to the blastocyst stage (26.1 � 2.1%; P &amp;lt; 0.05) compared with that of the control (0 ng mL-1: 16.3 � 2.8%) or 1 ng mL-1 (18.6 � 2.6%) leptin treatment groups following parthenogenetic activation. After IVM for 44 h, the percentage of oocytes with normal microtubules was higher in the leptin (10 ng mL-1) group than in the control group (89.1 � 4.3% vs. 78.5 � 4.0%, respectively; P &amp;lt; 0.05). However, the percentage of normal microfilament assembly was similar in the leptin-treated and control groups (85.6 � 4.3% and 82.9 � 5.0%, respectively). In oocytes matured in vitro in the presence of 10 ng mL-1 of leptin and subsequently induced by parthenogenetic activation via chemical stimulation, there was a significant increase in the formation of 2 pronuclei (2PN: 52.1 � 5.2%; P &amp;lt; 0.05) at 6 h, compared with the control non-leptin-treated oocytes (40.7 � 4.0%). Similarly, addition of 10 ng mL-1 of leptin to the IVM medium also increased 2PN formation at the same time point following ICSI (leptin treatment: 47.9 � 4.0; control: 36.2 � 3.8%; P &amp;lt; 0.05). The addition of 10 ng mL-1 of leptin to the IVM medium decreased the level of phospho-ERK1/2 at 6 and 9 h and was lower in the leptin-treated group compared with the control non-leptin-treated group (P &amp;lt; 0.01). These results suggest that exogenous leptin enhances cytoplasmic maturation and pronuclear formation following fertilization, possibly via the MAPK pathway.

Evidence against a direct effect of leptin on insulin-like growth factor-I (IGF-I), IGFBP-2 and IGF-I receptor expression in human SK-N-MC neuroepithelioma cells

The ob gene product, leptin, is synthesized by adipocytes. In rodents, its main role is to regulate energy expenditure and food intake. The growth hormone (GH)–insulin-like growth factor (IGF) system is also ubiquitously expressed, is also involved in energy homeostasis and shares some of the signaling molecules of leptin and its receptors. Therefore, we have asked whether or not leptin interacts with the GH–IGF system in an in vitro model. SK-N-MC cells were chosen for further investigation since they express IGF-I, IGF-I receptor and IGFBP-2 mRNA and secrete IGF-I and IGFBP-2 protein. Specific leptin receptor mRNA, both short and long isoform transcripts, were identified in SK-N-MC cells by RT-PCR. Secondly and most importantly, when SK-N-MC cells were cultured in the presence of leptin, neither IGF-I, nor IGF-I receptor or IGFBP-2 mRNA expression was different than in the absence of leptin. In addition, an increase in leptin did not alter secretion of immunoreactive IGF-I or IGFBP-2 protein into cell culture medium. In conclusion, (1) human SK-N-MC neuroepithelioma cells express ob and leptin receptor mRNA and secrete leptin. (2) Added exogenous leptin does not affect IGF-I, IGFBP-2 or IGF-I receptor mRNA expression and IGF-I and IGFBP-2 secretion by SK-N-MC cells in vitro under the conditions studied. We hypothesize that leptin and the IGF system do not interact directly in a cell culture model of neuroepithelioma cells.

Direct Effect of Leptin on Gastric Ghrelin Secretion

Ghrelin is an orexigenic hormone of gastric origin, and contributes to food intake and body weight regulation [1] [2]. Its postprandial secretion is attenuated by carbohydrate-rich meals [3] [4], while carbohydrate-poor food stimulates ghrelin release [5]. Gastrointestinal factors such as gastrin, somatostatin, or GLP-1 are good candidates for ghrelin inhibitors [6]. Also, there is solid evidence that insulin is a powerful inhibitor of ghrelin release in vivo [7] [8] and in vitro [6].

The direct effect of leptin on skeletal muscle thermogenesis is mediated by substrate cycling between de novo lipogenesis and lipid oxidation

We report here studies that integrate data of respiration rate from mouse skeletal muscle in response to leptin and pharmacological interference with intermediary metabolism, together with assays for phosphatidylinositol 3-kinase (PI3K) and AMP-activated protein kinase (AMPK). Our results suggest that the direct effect of leptin in stimulating thermogenesis in skeletal muscle is mediated by substrate cycling between de novo lipogenesis and lipid oxidation, and that this cycle requires both PI3K and AMPK signaling. This substrate cycling linking glucose and lipid metabolism to thermogenesis provides a novel thermogenic mechanism by which leptin protects skeletal muscle from excessive fat storage and lipotoxicity.

Blockade of the Leptin‐Sensitive Pathway Markedly Reduces Alcohol Consumption in Mice

The neuropeptide leptin links adipose stores with hypothalamic centers and serves as an endocrine signal involved in the regulation of appetite (and possibly in the endorphinergic modulation of the drug reward system). Increased plasma leptin has been observed at the onset of alcohol withdrawal in humans, and ethanol consumption after withdrawal was increased by injection of leptin in mice. We addressed the role of leptin in alcohol-related behaviors by studying ethanol consumption in two strains of spontaneously mutant mice that lack leptin (ob/ob) or the leptin receptor (db/db). Two strains of mutant leptin-deficient (ob/ob) or leptin-resistant (db/db) mice were tested in a two-bottle-choice paradigm and were compared with wild-type (C57BL/6 inbred strain) mice. The effects of leptin injection on voluntary ethanol intake have been investigated in ob/ob and C57BL/6 mice. Males and females of both mutant strains showed a significantly lower preference for alcohol in a two-bottle-choice paradigm compared with wild-type mice. Male ob/ob mice demonstrated slightly higher avoidance of bitter taste, and females of the both mutant strains showed a reduced preference for saccharin solutions. Administration of leptin (1 mg/kg intraperitoneally, daily for 8 days) altered body weight but failed to increase the preference for ethanol in ob/ob mice; i.e., we could not correct the effects of leptin deficiency on alcohol consumption by the injection of leptin. Also, there were no differences between the effects of leptin (1 mg/kg intraperitoneally, daily for 8 days) and saline injections on alcohol consumption in C57BL/6 mice. These data show that blockade of the leptin pathway markedly decreases the preference for alcohol intake, but this decrease may be the result of compensatory or developmental changes in other systems rather than a more direct effect of leptin on alcohol consumption.

The leptin receptor in human osteoblasts and the direct effect of leptin on bone metabolism

It is important to elucidate whether the leptin receptor, especially the long signal-transducing form of the leptin receptor (OB-Rb) is expressed in human osteoblasts. We detected the expression of human OB-Rb in cultured commercially available human osteoblasts (NHOst cells) using real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR). After confirming the expression of OB-Rb, we investigated the effect of leptin on NHOst cells. Leptin enhanced cell proliferation of the cells shown by the MTT assay. Furthermore, leptin changed the copy numbers of Bax and Bcl-2 mRNAs in the cultured cells as shown by real-time quantitative RT-PCR, although the effect was not consistent. Leptin did not change the production of osteocalcin and osteopontin by the cells. Leptin did not change the expression of OB-Rb mRNA in the cells. In conclusion, OB-Rb mRNA is expressed in cultured commercially available human osteoblasts. Leptin may have some effects on bone metabolism by directly modulating cell proliferation and apoptosis of osteoblasts in humans.

Leptin treatment markedly increased plasma adiponectin but barely decreased plasma resistin of ob/ob mice.

Adiponectin (ApN) and leptin are two adipocytokines that control fuel homeostasis, body weight, and insulin sensitivity. Their interplay is still poorly studied. These hormones are either undetectable or decreased in obese, diabetic ob/ob mice. We examined the effects of leptin treatment on ApN gene expression, protein production, secretion, and circulating levels of ob/ob mice. We also briefly tackled the influence of this treatment on resistin, another adipocytokine involved in obesity-related insulin resistance. Leptin-treated (T) obese mice (continuous sc infusion for 6 days) were compared with untreated lean (L), untreated obese (O), and untreated pair-fed obese (PF) mice. Blood was collected throughout the study. At day 3 or day 6, fat pads were either directly analyzed (mRNA, ApN content) or cultured for up to 24 h (ApN secretion). The direct effect of leptin was also studied in 3T3-F442A adipocytes. Compared with L mice, ApN content of visceral or subcutaneous fat and ApN secretion by adipose explants were blunted in obese mice. Accordingly, plasma ApN levels of O mice were decreased by 50%. Leptin treatment of ob/ob mice increased ApN mRNAs, ApN content, and secretion from the visceral depot by 50-80%. Leptin also directly stimulated ApN mRNAs and secretion from 3T3-F442A adipocytes. After 6 days of treatment, plasma ApN of ob/ob mice increased 2.5-fold, a rise that did not occur in PF mice. Plasma resistin of T mice was barely decreased. Leptin treatment, but not mere calorie restriction, corrects plasma ApN in obese mice by restoring adipose tissue ApN concentrations and secretion, at least in part, via a direct stimulation of ApN gene expression. Such a treatment only minimally affects circulating resistin. ApN restoration could, in concert with leptin, contribute to the metabolic effects classically observed during leptin administration.

Leptin Enhances, via AP-1, Expression of Aromatase in the MCF-7 Cell Line

Leptin, a product of adipocytes, is involved in the regulation of body weight and results strongly correlated to body fat content. An excess of fat mass represents a breast cancer risk factor particularly in postmenopausal women, where estrogen production by adipose tissue through its own aromatase activity stimulates tumor progression. Leptin stimulates estrogen production through the increase of aromatase expression and activity in human luteinized granulosa cells and adipose stromal cells. In the present study, we have examined the possible link that exists between leptin and breast cancer, focusing our attention on the direct effect of leptin on aromatase activity, which may enhance estrogen production and induce tumor cell growth stimulation. We have shown that leptin enhances aromatase mRNA expression, aromatase content, and its enzymatic activity in MCF-7. Aromatase expression appears to be regulated by tissue-specific promoter. It has been demonstrated that promoters II and 1.3 are the major promoters that drive aromatase expression in MCF-7. Transient transfection experiments using vector containing human aromatase promoters II and 1.3 sequence fused with luciferase reporter gene demonstrated that leptin is able to activate this promoter. In the presence of either mitogen-activated protein kinase inhibitor PD 98059 or ERK2 dominant negative as well as in the presence of STAT3 dominant negative, the stimulatory effects of leptin on aromatase promoter, enzymatic activity, and aromatase protein content were inhibited. Functional studies of mutagenesis and electrophoretic mobility shift assay revealed that the AP-1 motif is important in determining the up-regulatory effects induced by leptin on aromatase expression in MCF-7.

Direct effect of leptin on endothelial function and their changes in patients with essential hypertension

Direct effect of leptin on endothelial function and their changes in patients with essential hypertension