Regulation Of Leptin Receptor Expression Research Articles

Regulation of leptin receptor expression in human papillary thyroid cancer cells

Epidemiological studies suggest an important link between obesity and thyroid cancer. The adipose tissue-derived polypeptide leptin acting via leptin receptor may modulate cell migration of thyroid cancer cells. Previously we have demonstrated that leptin receptor is overexpressed in papillary thyroid cancer and is associated with tumor aggressiveness. The present study was undertaken to explore the possible regulatory factors which would influence leptin receptor expression in papillary thyroid cancer cells. We found that DNA methyltransferase inhibitor (5-Aza-2′-deoxycytidine) and histone deacetylase inhibitor (trichostatin A) reduced leptin receptor expression. Conversely, insulin upregulated leptin receptor expression in a time- and dose-dependent manner. Hypoxia-mimicking agent (cobalt chloride) had no effect on leptin receptor expression. Taken together, our study provides evidence that epigenetic events and insulin stimulation take part in regulation of leptin receptor expression in papillary thyroid cancer cells.

Regulation of Leptin Receptor Expression in Human Polarized Caco-2/15 Cells

Leptin receptors (LEPR) are expressed in intestinal epithelial cells from the duodenum to the colon. Since their role is fundamental for the proper control of nutrient absorption, mucus secretion and mucosa renewal, the regulation of LEPR expression is for the first time investigated as a function of various potential effectors. Fully differentiated Caco-2/15 cells were incubated for 24 hours with nutrients [carbohydrates, fatty acids (FA), amino acids and sterols], hormones (leptin, insulin, hydrocortisone and epithelial growth factor), inflammatory agents (Interferon-γ, LPS, TNF-α), and PPAR agonists (rosiglitazone and WY14643). Levels of LEPR mRNA and protein expressions were measured by RT-PCR and Western blots, respectively. Long (219.1) and short (219.3) isoforms of the LEPR were detected in Caco-2/15 cells, while absence of the isoform 219.2 was noted. Their gene expression was modulated by carbohydrates, FA, PPAR agonists, biliary salts, insulin and leptin itself. On the other hand, LEPR protein expression was modulated by FA, cholesterol, biliary salts, PPAR agonists and insulin. Interestingly, the same effectors may have opposite effects on the short and the long LEPR isoforms, as well as on mRNA and protein levels. Finally, Caco-2/15 cells were found to be sensitive to the effector location, i.e. apical or basolateral compartment. Our results suggest that (i) the expression of LEPR in Caco-2/15 cell line is not constitutive; (ii) the agents present in the apical or basolateral medium have different effects on LEPR mRNA and/or protein levels; and (iii) short and long isoforms of LEPR follow different patterns of regulation.

Leucine promotes leptin receptor expression in mouse C2C12 myotubes through the mTOR pathway

Leptin plays a critical role in regulating muscle protein metabolism by binding with leptin receptors in a 1:1 stoichiometry. However, the role for leucine in the regulation of leptin receptor expression in muscle has not been investigated. The present study was conducted to test the hypothesis that leucine regulates leptin receptor levels in C2C12 myotubes. Cells were cultured in the presence of DMEM/F12 medium containing supplemental 0 or 5 mM L: -leucine. Leptin receptor expression by C2C12 myotubes peaked at 2 h post-supplementation. Additionally, leucine stimulated leptin receptor expression at both mRNA and protein levels in a dose-dependent manner. Furthermore, leucine enhanced the phosphorylation of mammalian target of rapamycin (mTOR). Addition of rapamycin (an inhibitor of mTOR) to culture medium completely suppressed leucine-induced activation of mTOR and inhibited leucine-stimulated leptin receptor production. These results indicate that leucine affects leptin receptor expression in muscle cells via the mTOR signaling pathway.

Detection and estrogen regulation of leptin receptor expression in rat dorsal root ganglion

Leptin receptor (OB-R) is a polypeptide consisting of a single transmembrane-spanning component. OB-R widely distributes in various tissues, including the peripheral nervous system (PNS). However, there is no data about the expression of OB-R in the dorsal root ganglion (DRG). In the present study, we first detected the expressions of OB-R protein and mRNA in the rat DRG using the methods of immunohistochemistry, western blot and reverse transcriptase polymerase chain reaction (RT-PCR). Estrogen is known to influence different functions on the DRG. In this study, we observed that 17beta-estradiol (E(2)) can increase the expressions of OB-R protein and mRNA (P<0.05) in ovariectomized rat DRG and these actions can be prevented by tamoxifen which is a specific estrogen receptors (ERs) antagonist. In addition, the results of dual labeling of OB-R with the two ER isoforms, ERalpha and ERbeta indicate that 100% colocalization of ERalpha with OB-R and about 15% colocalization of ERbeta with OB-R in DRG neurons. These results indicate that OB-R is expressed in the rat DRG and E(2) may up-regulate the expression of the OB-R protein and mRNA in an ERalpha-dependent way.

Down regulation of leptin receptor expression and increase the spontaneous unit discharge in arcuate nucleus of hypothalamus in obese rats

Arcuate nucleus neurons (ArcNs) of hypothalamus plays an important role in food ingestion. Abnormal expression of leptin receptor(ObR) in ArcN of hypothalamus was found in obese rodent. This study aims to investigate whether change of ObR was related to electrophysiological activity of ArcNs in obese rats. 30 male Sprague Dawley (SD) rats were divided into control (con.), overweight(ow) and obese rats (ob) induced by high fat diet. The expression of ObR in ArcN of hypothalamus was detected by immunofluorescence combined with confocal laser scanning microscopy (CLSM) and measured by western blotting. Stereomicroscopy micro-glass electrode was inserted into Arc nucleus and the discharge of neurons(Ns) was recorded in the basal status and after glucose and insulin was given intravenously in rat in vivo. The protein expression of ObR in hypothalamus decreased significantly in obese rats (ob: 0.237+/-0.0126 vs ow: 0.640+/-0.0453 vs con: 1.0+/-0.02, p<0.01), while the discharge frequency of Arc Ns was significantly higher in obese rats than that of overweight and control rats in the basal status (ob: 20.10+/-7.55 vs ow:16.69+/-5.93 vs con: 11.02+/-2.58, p<0.01). There was a significant positive correlation between discharge frequency of ArcNs and the body weight of rats(r=0.809, p<0.001) and serum leptin level(r=0.562, p<0.001), but, ObR expression of hypothalamus was negatively correlated with the discharge frequency of ArcNs in control and obese rats(r=-0.693, p<0.001). Administration of glucose induced a significant decrease in spike of discharge of ArcNs in control and overweight rats, especially in the control rats. In contrast, the effect of glucose on discharge of ArcNs was not observed in obese rats. After stimulation with insulin intravenously, the discharge frequency of ArcNs increased among three groups, but obese rats showed less response cthan those other two groups. ObR down-regulation in hypothalamus and the activation of electrophysiological activities of arcuate neurons probably play an important role in the central pathogenesis of obesity.

Hormonal regulation of leptin receptor expression in primary cultures of porcine hepatocytes

A study was conducted to elucidate hormonal control of leptin receptor gene expression in primary cultures of porcine hepatocytes. Hepatocytes were isolated from pigs (52 kg) and seeded into collagen-coated T-25 flasks. Monolayer cultures were established in medium containing fetal bovine serum for 1 day and switched to a serum-free medium for the remainder of the 3-day culture period. To establish basal conditions hepatocytes were maintained in serum-free William's E medium containing 10 nM dexamethasone and 1 ng/ml insulin. For the final 24 h, insulin (1 or 100 ng/ml) or glucagon (100 ng/ml), were added in the presence or absence of 100 nM triiodothyronine (T3). RNA was extracted and quantitative RT-PCR was performed with primers specific for the long form and total porcine leptin receptors. Leptin receptor expression was calculated relative to co-amplified 18S rRNA. Expression of the long form of the leptin receptor was confirmed under basal conditions. Insulin, glucagon and synthetic human proteins (ghrelin and GLP-1) at 100 ng/ml had no influence on leptin receptor expression; the addition of T3 was associated with a marked increase ( P < 0.001) in expression of total and long forms of the leptin receptor by 1.6 and 2.4-fold, respectively. Addition of leptin to cells which were pre-treated with T3 for 24 h (to up-regulate leptin receptor expression), confirmed the lack of a direct effect of leptin on glucagon-induced glycogen turnover and cAMP production. These data suggest that porcine hepatocytes may be insensitive to leptin stimulation even when leptin receptor expression is enhanced by T3.

Minireview: A hypothalamic role in energy balance with special emphasis on leptin.

The hypothalamus is a major site for integration of central and peripheral signals that regulate energy homeostasis. Within the hypothalamus, neurons residing in the ARC (arcuate nucleus)-PVN (paraventricular)-PF/LH (perifornical/lateral hypothalamus) axis communicate among each other and are subjected to the influence of several peripheral factors, including leptin and insulin. Proper signaling in the hypothalamus by leptin, a long-sought peripheral factor that relays the status of fat stores, is critical to normal regulation of food intake and body weight. Leptin action in the hypothalamus is mediated by a large number of orexigenic and anorectic peptide-producing neurons of the ARC-PVN-PF/LH axis. Not only the classical JAK2 (Janus kinase 2)-STAT3 (signal transducer and activator of transcription 3) pathway, but also the phosphatidylinositol-3 kinase-phosphodiesterase 3B-cAMP pathway mediates hypothalamic leptin receptor signaling. It appears that hypothalamic leptin resistance, possibly due to defective nutritional regulation of leptin receptor expression and/or reduced STAT3 signaling in the hypothalamus, contributes to the development of obesity associated with high-fat feeding and aging. Interestingly, hypothalamic neurons may develop leptin resistance despite an intact JAK2-STAT3 signaling path. The role of suppressor of cytokine signaling 3 and other negative regulators of leptin signaling in central leptin resistance needs to be established, an important area of future investigation. Further understanding of the neural circuitry and leptin signaling in the hypothalamus is critical not only for the advancement of our knowledge on the hypothalamic role in energy balance but also for future development of drugs for the attenuation or treatment of obesity and related disorders in humans.

Differential Regulation of Leptin Receptor Expression by Insulin and Leptin in Neuroblastoma Cells

Leptin exerts its effects by interacting with specific membrane receptors (Ob-R). We studied the exact localization of long intracellular domain form (Ob-Rb) in human brain. In addition, we analyzed the regulatory features of Ob-Rb expression in two neuroblastoma cell lines. The Ob-Rb mRNAs were abundant in putamen, frontal lobe, medulla, cerebral cortex, cerebellum, thalamus, hippocampus, corpus callosum, caudate nucleus, and amygdala, indicating that Ob-Rb transcripts are expressed differently from that of other Ob-R isoforms. In SK-N-MC cells, the expression of Ob-Rb mRNA was induced by increasing doses of insulin, and the maximum amount of mRNA expression was 9.4-fold higher in the presence of insulin (100 nM for 24 h), compared to the absence of insulin. In IMR32 cells, the transcripts were increased 4.0-fold when cells were incubated with 1 nM of insulin for 48 h. In contrast, Ob-Rb expression in IMR32 cells decreased to 18% of control following a 24-h incubation period with 50 ng/mL of leptin, compared to incubation in the absence of leptin. These results indicate that expression of Ob-Rb is differentially regulated by inhibitory signals of energy balance in neuroblastoma cells. The identification of the novel regulatory mechanisms involving the Ob-Rb isoform by insulin and leptin now makes it possible to elucidate the underlying mechanisms involving increased food intake and uncontrolled energy balance associated with leptin resistance in obese individuals.