Leptin Gene Expression In Adipocytes Research Articles

Increased Expression of the Leptin Gene in Adipose Tissue of Patients with Chronic Kidney Disease-The Possible Role of an Abnormal Serum Fatty Acid Profile.

Chronic kidney disease (CKD) is associated with an increased level of leptin and an abnormal fatty acid (FA) profile in the serum. However, there are no data on the associations between them, and the reason for increased serum levels in patients with CKD is not well elucidated. Recently, we found that a CKD-related abnormal FA profile caused significant changes in the expression of genes involved in lipid metabolism in hepatocytes. The aim of this study was to examine whether leptin gene expression in subcutaneous adipose tissue (SAT) of patients with CKD may contribute to increased serum levels of this adipokine and whether the abnormal serum FA profile observed in CKD patients has an impact on leptin gene expression in adipocytes. The FA profile was measured in serum samples from patients with CKD and controls by GC–MS. The relative mRNA levels of leptin were measured in SAT by Real-Time PCR. Moreover, the effect of the CKD-related abnormal FA profile on leptin gene expression was studied in in vitro cultured 3T3-L1 adipocytes. Patients with CKD had higher concentrations of serum leptin than controls and higher expression level of the leptin gene in SAT. They also had increased serum monounsaturated FAs and decreased polyunsaturated FAs. The incubation of adipocytes with FAs isolated from CKD patients resulted in an increase of the levels of leptin mRNA. Increased leptin gene expression in SAT may contribute to elevated concentrations of these adipokine in patients with CKD. CKD-related alterations of the FA profile may contribute to elevated serum leptin concentrations in patients with CKD by increasing the gene expression of this adipokine in SAT.

Platycodon grandiflorus Root Extract Attenuates Body Fat Mass, Hepatic Steatosis and Insulin Resistance through the Interplay between the Liver and Adipose Tissue.

The Platycodon grandiflorus root, a Korean medicinal food, is well known to have beneficial effects on obesity and diabetes. In this study, we demonstrated the metabolic effects of P. grandiflorus root ethanol extract (PGE), which is rich in platycodins, on diet-induced obesity. C57BL/6J mice (four-week-old males) were fed a normal diet (16.58% of kilocalories from fat), high-fat diet (HFD, 60% of kilocalories from fat), and HFD supplemented with 5% (w/w) PGE. In the HFD-fed mice, PGE markedly suppressed the body weight gain and white fat mass to normal control level, with simultaneous increase in the expression of thermogenic genes (such as SIRT1, PPARα, PGC1α, and UCP1), that accompanied changes in fatty acid oxidation (FAO) and energy expenditure. In addition, PGE improved insulin sensitivity through activation of the PPARγ expression, which upregulates adiponectin while decreasing leptin gene expression in adipocytes. Furthermore, PGE improved hepatic steatosis by suppressing hepatic lipogenesis while increasing expression of FAO-associated genes such as PGC1α. PGE normalized body fat and body weight, which is likely associated with the increased energy expenditure and thermogenic gene expression. PGE can protect from HFD-induced insulin resistance, and hepatic steatosis by controlling lipid and glucose metabolism.

TCF7L2 and Wnt Signalling Positively Regulate Leptin Gene Expression in Adipocytes

Recent genome-wide association studies (GWAS) have revealed that the Wnt signalling pathway effector TCF7L2 is among the most important diabetes risk genes. Intensive explorations on metabolic function of TCF7L2 in pancreas and liver, however, have generated controversial suggestions. As TCF7L2 is also abundantly expressed in adipocytes, we investigated its expression and function in rodent fat tissue and primary adipocytes. We found that TCF7L2 expression in mouse epididymal fat tissue was physiologically upregulated by feeding, and downregulated in db/db mice and Zucker (fa/fa) rats, 2 obese rodent models. In rat primary adipocytes, 1 nM insulin stimulated TCF7L2 and leptin mRNA expression levels, and the stimulation can be attenuated by iCRT14, an inhibitor of β-catenin-responsive transcription. Insulin at the dosage of 100 nM, however, repressed both TCF7L2 and leptin mRNA levels. The canonical Wnt ligand Wnt3a, but not the non-canonical Wnt ligand Wnt11, was shown to stimulate leptin mRNA expression level and leptin gene promoter activity. Although Wnt3a repressed the differentiation of 3T3-L1 cells toward adipocytes, in either fully differentiated or partially differentiated 3T3-L1 cells, Wnt3a significantly stimulated leptin mRNA levels. Together, our observations suggest that adipocytes TCF7L2 level is metabolic regulated. More importantly, Wnt pathway plays a dual function in adipocytes, including the repression of adipogenesis in pre-adipocytes and the stimulation of leptin production in mature adipocytes, in response to nutritional challenge.

LEPTIN AND PROSTAGLANDIN F RECEPTOR GENE EXPRESSION OF ADIPOCYTES OBTAINED AT ESTRUS AND THE MID-LUTEAL STAGE OF THE ESTROUS CYCLE OF HEIFERS TREATED WITH PROSTAGLANDIN F2α AND 15-KETOPROSTAGLANDIN F2α REVISITED

Leptin is a potent satiety hormone synthesized and secreted by adipocytes. It was first documented in morbidly obese infertile mice (ob/ob) in the 1950's; however, the gene was not cloned until 1994. The discovery has lead to various studies in both nutrition and reproduction. The absence of leptin in circulation results in infertility suggesting that leptin may be signaling the brain of the body's energy reserves in the form of fat, which is required for reproductive function. Interestingly, leptin gene expression has been reported to differ relative to stage of the estrous cycle in adipose tissue. In heifers, leptin gene expression is higher in adipose tissue obtained during estrus and the early to mid-luteal stage of the estrous cycle when compared with the late-luteal and the follicular phase when expression was lower. Prostaglandin F2α (PGF2α), which is quickly metabolized to 15-keto-prostaglandin F2α (15-keto-PGF2α), is present during the estrous cycle when the change in leptin gene expression was reported. Therefore, our hypothesis is that leptin gene expression will decrease in adipocytes obtained at estrus and mid-luteal stage of the bovine estrous cycle treated with PGF2α or 15-keto-PGF2α. Subcutaneous adipose tissue (∼6 g) was obtained at estrus and the midluteal stage of the estrous cycle of Brahman influenced heifers (n=10). Approximately 4 g of tissue was digested and cultured with PGF2α and 15-keto-PGF2α at concentrations of 10−11, 10−10, 10−9, 10−8 and 0 M respectively for 18 h. The remaining two grams were immediately snap frozen in liquid nitrogen in order to measure leptin and prostaglandin F receptor (PGFr) gene expression at the time of tissue collection. Prostaglandin F2α has been reported to have the ability to regulate its receptor; therefore, PGFr gene expression was quantitated as a control for treatment of adipocytes. Leptin and PGFr mRNA was quantitated using real time PCR. Values obtained from adipose tissue were transformed to log10 and the values obtained from culture were expressed as a percentage of 0 M (0 M=100%). The effect of treatment, stage and stage X treatment were determined using the MIXED procedure of SAS. The ESTIMATE procedure of SAS was used to determine the differences between treatment dose means. As previously reported leptin production did not differ in adipose tissue collected during the estrus or the mid-luteal stage of the estrous cycle. Similarly, PGFr gene expression did not differ relative to stage in tissue. Neither leptin nor PGFr gene expression was affected by 15-keto-PGF2α in adipocytes. However, PGF2α tended (P≤0.1) to decrease leptin gene expression in adipocytes obtained at estrus at physiological doses (10−8 M 80.5%±12.7%). PGFr gene expression tended (P≤0.1) to increase in adipocytes obtained at estrus at concentrations of 10−11 (162.5%±42.4%), and 10−9 M (165.7%±42.4%) implying that adipocytes were responding to treatment. No effect on leptin gene expression was determined in adipocytes obtained during the mid-luteal stage of the estrous cycle. However, PGF2α tended (P≤0.1) to decrease PGFr gene expression at 10−11 (75.0%±11.4%) dose. Collectively, the data suggests that PGF2α and its primary metabolite may not affect leptin gene expression alone; suggesting a combination of reproductive hormones may be responsible for the differences reported during the estrous cycle. (poster)

Genistein restricts leptin secretion from rat adipocytes

The isoflavones – genistein and daidzein – compounds found in high concentrations in soy play an important role in prevention of many diseases and affect some metabolic pathways. In the performed experiment it was demonstrated that genistein (5 mg/kg b.w.) administered intragastrically for three days to male Wistar rats substantially diminished blood leptin level. Studies with isolated rat adipocytes revealed that this phytoestrogen strongly restricted leptin secretion from these cells. These effects were not accompanied by any changes in leptin gene expression in adipocytes. Daidzein – an analogue of genistein – used at similar concentrations did not affect blood leptin concentration, leptin secretion and expression of its gene. To determine the influence of genistein and daidzein on leptin release, adipocytes isolated from the epididymal fat tissue were incubated for 2 h in Krebs–Ringer buffer. Leptin secretion stimulated by glucose with insulin was significantly diminished by genistein (0.25–1 mM). This effect of genistein may arise from several aspects of its action in adipocytes documented in the literature such as the inhibition of glucose transport and metabolism, the attenuation of insulin signalling, the inhibition of cAMP phosphodiesterase and the stimulation of lipolysis. However, the bypassing of the restrictive action of genistein on glucose transport and glycolysis (by the use of alanine instead of glucose) and on insulin action (by the use of nicotinic acid) was not sufficient to restore leptin secretion from isolated adipocytes. It was also demonstrated that the restriction of the stimulatory influence of genistein on cAMP/protein kinase A (PKA) pathway (by the inhibition of PKA activity) did not improve leptin release. Results obtained in our experiments point at the restriction of glucose metabolism following formation of pyruvate as the pivotal reason of the inhibitory action of genistein on leptin release.

Interacting Appetite-Regulating Pathways in the Hypothalamic Regulation of Body Weight*

Various aspects of the complex spatio-temporal patterning of hypothalamic signaling that leads to the development of synchronized nocturnal feeding in the rat are critically examined. Undoubtedly, as depicted in Fig. 7, a distinct ARN in the hypothalamus is involved in the control of nocturnal appetite. At least four basic elements operate within this ARN. These are: 1) A discrete appetite-driving or orexigenic network of NPY, NE, GABA, GAL, EOP, and orexin transduces and releases appetite-stimulating signals. 2) Similarly, anorexigenic signal-producing pathways (e.g., CRH, GLP-1, alpha MSH, and CART) orchestrate neural events for dissipation of appetite and to terminate feeding, possibly by interrupting NPY efflux and action at a postsynaptic level within the hypothalamus. It is possible that some of these may represent the physiologically relevant "off" switches under the influence of GABA alone, or AgrP alone, or in combination with NPY released from the NPY-, GABA-, and AgrP-coproducing neurons. 3) Recent evidence shows that neural elements in the VMN-DMN complex tonically restrain the orexigenic signals during the intermeal interval; the restraint is greatly aided by leptin's action via diminution of orexigenic (NPY) and augmentation of anorexigenic (GLP-1, alpha MSH, and CART) signals. Since interruption of neurotransmission in the VMN resulted in hyperphagia and development of leptin resistance, it seems likely that the VMN is an effector site for the restraint exercised by leptin. The daily rhythms in leptin synthesis and release are temporally dissociable because the onset of daily rise in leptin gene expression in adipocytes precedes that in leptin secretion. Nevertheless, these rhythms are in phase with daily ingestive behavior because the peak in circulating leptin levels occurs during the middle of the feeding period. These observations, coupled with the fact that circulating levels of leptin are directly related to adiposity, pose a new challenge for elucidating the precise role of leptin in daily patterning of feeding in the rat. 4) A neural timing mechanism also operates upstream from the ARN in the daily management of energy homeostasis. Although the precise anatomical boundaries are not clearly defined, this device is likely to be composed of a group of neurons that integrate incoming internal and external information for the timely onset of the drive to eat. Evidently, this network operates independently in primates, but it is entrained to the circadian time keeper in the SCN of rodents. Apart from its role in the onset of drive to eat, the circadian patterns of gene expression of NPY, GAL, and POMC denote independent control of the timing device on the synthesis and availability for release of orexigenic signals. The VMN-DMN-PVN complex is apparently an integrated constituent of the timing mechanism in this context, because lesions in each of these sites result in loss of regulated feeding. The accumulated evidence points to the PVN and surrounding neural sites within this framework as the primary sites of release and action of various orexigenic and anorexigenic signals. A novel finding is the identification of the interconnected wiring of the DMN-mPVN axis that may mediate leptin restraint on NPY-induced feeding. The chemical phenotypes of leptin and NPY target neurons in this axis remain to be identified. These multiple orexigenic and anorexigenic pathways in the hypothalamic ARN appear to represent redundancy, a characteristic of regulated biological systems to provide a "fail-safe" neural mechanism to meet an organism's constant energy needs for growth and maintenance. Within this formulation, the coexisting orexigenic signals (NPY, NE, GAL, GABA, and AgrP) represent either another level of redundancy or it is possible that these signals operate within the ARN as reinforcing agents to varying degrees under different circumstances. (ABSTRACT TRUNCATED)

Reduced expression of the leptin gene (ob) by catecholamine through a G(S) protein-coupled pathway in 3T3-L1 adipocytes.

Leptin, a recently identified hormone, is believed to reduce appetite and maintain body weight. The mRNA of leptin is expressed only in mature adipose cells. To clarify the regulation of leptin gene expression in adipocytes, 3T3-L1 adipocytes were treated for 16 h with various agents known to modulate lipid metabolism, and then the leptin mRNA was measured by the reverse transcription-polymerase chain reaction method. Interestingly, both norepinephrine and isoproterenol reduced the level of leptin mRNA to about 20% of that found in untreated control cells in a dose-dependent fashion. The maximum reduction occurred at 100 nmol/l of either norepinephrine or isoproterenol, and the half-maximal effect was observed at approximately 3 nmol/l norepinephrine and approximately 1 nmol/l isoproterenol. Propranolol reversed about 50% of the reduction by either norepinephrine or isoproterenol. In contrast, phentolamine did not inhibit the reduction by either norepinephrine or isoproterenol. Moreover, both cholera toxin and dibutyryl cAMP decreased the level of leptin mRNA to about 10% of that in control cells in a dose-dependent fashion. The maximum effect was elicited at 100 ng/ml cholera toxin and 100 micromol/l dibutyryl cAMP. The concentration producing the half-maximal effect was approximately 1 ng/ml cholera toxin and approximately 50 micromol/l dibutyryl cAMP. Dibutyryl cGMP, however, did not affect leptin gene expression. These results suggest that a signaling pathway that results in the activation of protein kinase A regulates leptin gene expression in 3T3-L1 adipocytes.