Mechanism Of Leptin Research Articles

PREDICTING THE PROBABILITY OF DEVELOPING OBESITY DEPENDING ON LEPTIN AND LEPTIN RECEPTOR POLYMORPHISMS

Introduction. Metabolic syndrome is a heterogeneous pathological condition that combines different stages of obesity, impaired glucose tolerance, atherogenic dyslipidemia and arterial hypertension. Obesity itself is a key element of this syndrome. Hormonal disorders, the central one of which is insulin resistance, trigger a cascade of neuroendocrine changes that lead to the progression of MetS. Monogenic mutations are often detected in patients with severe obesity, as well as with early (up to 10 years) its debut. In recent years, it has been increasingly investigated for a genetically determined breakdown in the mechanism of leptin's influence on the development of obesity. The aim of this study – to evaluate the probability of obesity development in patients with LEP and LEPR polymorphisms in Ukrainian population. Research Methods. 53 obesity and 43 non-obesity patients underwent genotyping of the LEP and LEPR genes (K109R (rs1137100), Q223R (rs1137101), K656N (rs1805094), G2548A (rs7799039)) polymorphism was performed using TaqMan™ SNP Genotyping Human Assays (Thermo Fisher Scientific, USA). Results and Discussion. Comparing rs1137101 Allele A, rs1137101 Allele G statistically significant differences were revealed, while comparing rs1805094 Allele C, rs1805094 Allele G, rs7799039 Allele A, rs7799039 Allele G, rs1137100 Allele A, rs1137100 Allele G depending on group indicated no statistically significant differences. SNP (rs1137101) Allele A statistically significant differences depending on obesity degree (p < 0.001). Comparing the rest of SNP`s Allele`s (rs1805094 Allele C, rs1805094 Allele G, rs7799039 Allele A, rs7799039 Allele G, rs1137101 Allele G, rs1137100 Allele A, rs1137100 Allele G, rs696217 Allele G) no statistically significant differences was noted. Prediction of the probability of developing obesity depending on the polymorphism of leptin and leptin receptors revealed the dependence of only mutations in LEPR (Q223R (rs1137101)) in the Ukrainian population. According to the results of the ROC analysis sensitivity and specificity of the method were 65.5 % and 67.8 %, respectively. Conclusions. Our analysis showed that LEPR Q223R (rs1137101) polymorphism could be a potential genetic risk factor for obesity in Ukrainian population regardless of the homozygous or heterozygous genotype (genotypes AA, AG, GG). At the same time, allele A was found in 70.83 % of cases of patients with 2nd and 3rd degree obesity. And homozygous AA and GG genotypes in 24.5 % and 28.3 %, respectively. The results obtained can be used in the practice for early diagnosis of different types of obesity and for prognosing of results of bariatric surgery.

Aberrant miR-874-3p/leptin/EGFR/c-Myc signaling contributes to nasopharyngeal carcinoma pathogenesis

BackgroundLeptin is important in physiological and pathological functions in various cancers, however, the significance and mechanisms of leptin in nasopharyngeal carcinoma remain ambiguous.MethodsLeptin expression was analyzed by QPCR, immunohistochemistry, Western blotting, and TCGA database. The impact of gain- or loss-of-function of leptin were determined by MTT, colony formation, wound healing, and Transwell assays in NPC cells, and by a xenograft tumor model. Leptin-modulated glucose consumption and lactate production were assessed by ELISA. Furthermore, leptin-regulated signaling pathways were examined by QPCR and Western blotting assays. The immunoprecipitation assay was conducted to determine interaction between leptin and EGFR. In addition, miR-874-3p-regulated leptin expression was evaluated using bioinformatics, QPCR, luciferase assay, AGO2-RIP assay, and Western blotting.ResultsIn this study, we found that leptin was highly expressed in the sera and tumor tissues of patients with NPC, and elevated leptin expression was associated with advanced clinical features and poor prognosis. Functional assays demonstrated that leptin remarkably promoted NPC cell growth, motility, and glycolysis in vitro and in vivo. Mechanistically, leptin associated with EGFR, resulting in enhanced cell growth through the regulation of cell-cycle related markers, glycolysis-related genes, and EGFR/AKT/c-Myc signaling. Moreover, leptin potentiated the invasive capacity of NPC cells by promoting EMT. We further explored that miR-874-3p influenced leptin-mediated NPC progression. Overexpression of miR-874-3p prevented cell growth, motility, glucose consumption, and lactate production in NPC cells, whereas miR-874-3p inhibition had the opposite effects. AGO-RIP assays confirmed that Argonaute 2 (AGO2), a protein associated with miR-874-3p, regulated leptin expression in NPC cells. The rescue assays indicated that inhibition of leptin suppressed the effects of miR-874-3p inhibitor. In clinical specimens, miR-874-3p was negatively correlated with leptin.ConclusionsLeptin may serve as a novel prognostic factor and potential therapeutic target for patients with NPC. In addition, a newly discovered regulatory axis of leptin/EGFR/AKT/c-Myc can provide a novel therapeutic strategy for NPC.

Leptin relieves ischemia/reperfusion induced acute kidney injury through inhibiting apoptosis and autophagy.

Acute kidney injury (AKI) can be caused by ischemia/reperfusion (I/R), nephrotoxin, and sepsis, with poor prognosis and high mortality. Leptin is a protein molecule that regulates the body's energy metabolism and reproductive activities via binding to its specific receptor. Leptin can inhibit cardiomyocyte apoptosis caused by I/R, but its effect on I/R kidney injury and the underlying mechanisms are still unclear. This study aims to investigate the effect and mechanisms of leptin on renal function, renal histopathology, apoptosis, and autophagy during acute I/R kidney injury. Healthy adult male mice were randomly divided into 4 groups: a sham+wild-type mice (ob/+) group, a sham+leptin gene-deficient mice (ob/ob) group, an I/R+ob/+ group, and an I/R+ob/ob group (n=8 per group). For sham operation, a longitudinal incision was made on the back of the mice to expose and separate the bilateral kidneys and renal arteries, and no subsequent treatment was performed. I/R treatment was ischemia for 30 min and reperfusion for 48 h. The levels of BUN and SCr were detected to evaluate renal function; HE staining was used to observe the pathological changes of renal tissue; TUNEL staining was used to observe cell apoptosis, and apoptosis-positive cells were counted; Western blotting was used to detect levels of apoptosis-related proteins (caspase 3, caspase 9), autophagy-related proteins [mammalian target of rapamycin (mTOR), phosphorylated mTOR (p-mTOR), LC3 I, LC3 II], mTOR-dependent signaling pathway proteins [phosphate and tension homology (PTEN), adenosine monophosphate-activated protein kinase (AMPK), protein kinase B (AKT), extracellular regulated protein kinase (ERK), phosphorylated PTEN (p-PTEN), phosphorylated AMPK (p-AMPK), phosphorylated AKT (p-AKT), phosphorylated ERK (p-ERK)]. There was no significant difference in the levels of BUN and SCr between the sham+ob/+ group and the sham+ob/ob group (both P>0.05). The levels of BUN and SCr in the I/R+ob/+ group were significantly higher than those in the sham+ob/+ group (both P<0.05). Compared with the mice in the sham+ob/ob group or the I/R+ob/+ group, the levels of BUN and SCr in the I/R+ob/ob group were significantly increased (all P<0.05). There was no obvious damage to the renal tubules in the sham+ob/+ group and the sham+ob/ob group. Compared with sham+ob/+ group and sham+ob/ob group, both the I/R+ob/+ group and the I/R+ob/ob group had cell damage such as brush border shedding, vacuolar degeneration, and cast formation. Compared with the I/R+ob/+ group, the renal tubules of the mice in the I/R+ob/ob group were more severely damaged. The pathological score of renal tubular injury showed that the renal tubular injury was the most serious in the I/R+ob/ob group (P<0.05). Compared with the sham+ob/+ group, the protein levels of caspase 3, caspase 9, PTEN, and LC3 II were significantly up-regulated, the ratio of LC3 II to LC3 I was significantly increased, and the protein levels of p-mTOR, p-PTEN, p-AMPK, p-AKT, and p-ERK were significantly down-regulated in the I/R+ob/+ group (all P<0.05). Compared with the sham+ob/ob group, the protein levels of caspase 3, caspase 9, PTEN, and LC3 II were significantly up-regulated, and the ratio of LC3 II to LC3 I was significantly increased, while the protein levels of p-mTOR, p-PTEN, p-AMPK, p-AKT, and p-ERK were significantly down-regulated in the I/R+ob/ob group (all P<0.05). Compared with the I/R+ob/+ group, the levels of p-mTOR, p-PTEN, p-AMPK, p-AKT were more significantly down-regulated, while the levels of caspase 3, caspase 9, PTEN, and LC3 II were more significantly up-regulated, and the ratio of LC3 II to LC3 I was more significantly increase in the I/R+ob/ob group (all P<0.05). Renal function and tubular damage, and elevated levels of apoptosis and autophagy are observed in mice kidneys after acute I/R. Leptin might relieve I/R induced AKI by inhibiting apoptosis and autophagy that through a complex network of interactions between mTOR-dependent signaling pathways.

Leptin participation in the processes of nervous impulse transmission and its influence on the formation of neuro-mental development of children

Review of publications on the functional features of leptin in the central nervous system in children. The participation of leptin mechanisms in the transmission of nerve impulses, the effect of leptin on cognitive functions in children. The article reveals the general mechanisms of maturation of the central nervous system in children, the participation of leptin and leptin receptors in the formation of cognitive abilities in children. Possible interrelationships of impairments in cognitive development and lipid metabolism including obesity are revealed.

Positive Association of Leptin and Artery Calcification of Lower Extremity in Patients With Type 2 Diabetes Mellitus: A Pilot Study.

ObjectiveWe aimed to explore the role and possible mechanism of leptin in lower-extremity artery calcification in patients with type 2 diabetes mellitus (T2DM).MethodsWe recruited 59 male patients with T2DM and 39 non-diabetic male participants. All participants underwent computed tomography scan of lower-extremity arteries. The calcification scores (CSs) were analyzed by standardized software. Plasma leptin level was determined by radioimmunoassay kits. Human vascular smooth muscle cells (VSMCs) calcification model was established by beta-glycerophosphate and calcium chlorideinduction. Calcium deposition and mineralization were measured by the o-cresolphthalein complexone method and Alizarin Red staining. The mRNA expression of bone morphogenic protein 2 (BMP2), runt-related transcription factor 2 (Runx2), osteocalcin (OCN) and osteopontin (OPN) was determined by quantitative RT-PCR. The protein levels of BMP2, Runx2, α-smooth muscle actin (α-SMA) and (p)-Akt was determined by Western-blot analysis, and α-SMA was also measured by immunofluorescence analysis.ResultsCompared with controls, patients with T2DM showed higher median calcification score in lower-extremity artery [286.50 (IQR 83.41, 1082.00) vs 68.66 (3.41, 141.30), p<0.01]. Plasma leptin level was higher in patients with calcification score ≥300 than ≥100 (252.67 ± 98.57 vs 189.38 ± 44.19 pg/ml, p<0.05). Compared with calcification medium, intracellular calcium content was significantly increased in VSMCs treated by leptin (200, 400 and 800 ng/ml) combined with calcification medium [11.99 ± 3.63, 15.18 ± 4.55, and 24.14 ± 5.85 mg/ml, respectively, vs 7.27 ± 1.54 mg/ml, all p<0.01]. Compared with calcification medium, Alizarin Red staining showed calcium disposition was more obvious, and the mRNA level of BMP2, Runx2 and OCN was significantly increased, and immunofluorescence and Western blot analysis showed that the expression of α-SMA was downregulated in VSMCs treated by leptin (400 ng/ml) combined with calcification medium, respectively. Compared with calcification medium, the protein level of BMP2 and Runx2 was upregulated in VSMCs treated by leptin (400 ng/ml) combined with calcification medium. Moreover, blocking PI3K/Akt signaling pathway can decrease the protein expression of BMP2 and Runx2 in VSMCs treated by leptin (400 ng/ml) combined with calcification medium.ConclusionsLeptin promoted lower-extremity artery calcification of T2DM by upregulating the expression of BMP2 and Runx2, and regulating phenotypic switch of VSMCs via PI3K/Akt signaling pathway.

The mechanism of leptin and IGF-1 in the diabetic rheumatoid arthritis Iraqi patients

We aimed here to study the impact of leptin on insulin like growth factor-1 (IGF-1) level to imply its antidiabetic effect on Iraqi rheumatoid arthritis’s, who was with and without diabetes mellitus.Rheumatoid arthritis is a chronic inflammatory disease, primarily targets the synovium and articular cartilage, which causes joint damage. Although the role of adipocytokines in mediating damages of joint has recently suggested, it is still a matter of considerable debate.METHODS: Patients diagnosed as diabetic rheumatoid arthritis aged from 33-60 years and others diagnosed as non-diabetic rheumatoid arthritis were compared with healthy control (aged 33-46 years). Some biochemical parameters have determined, such as fasting serum glucose, glycated hemoglobin, lipid profile, serum fasting insulin, IGF-1, and leptin, using ELISA and immune radiometric assay. Results indicated an elevation in some biochemical parameters in diabetic rheumatoid arthritis’s when compared with patients without diabetes. There was a significant increase in fasting serum glucose and some of the lipid components in diabetic rheumatoid arthritis patients compared to that non-diabetic. A significant elevation of leptin in diabetic rheumatoid arthritis patients compared to control (p<0.003). However, a non-significant difference of leptin was detected between diabetic rheumatoid arthritis and non-diabetic patients. In addition, some other parameters were significantly reduced in diabetic rheumatoid arthritis patients when compared to non-diabetic patients, such as high-density lipoprotein and IGF-1. This study highlights that leptin could act as pro-inflammatory mediator in rheumatoid arthritis. The negative correlation between leptin level and IGF-1 plays an important role in understanding the metabolic pathogenesis of rheumatoid arthritis.

The Nutritional Cytokine Leptin Promotes NSCLC by Activating the PI3K/AKT and MAPK/ERK Pathways in NSCLC Cells in a Paracrine Manner

Purpose Leptin is a nutritional cytokine encoded by the obesity gene whose concentration in the tumor microenvironment is closely related to the occurrence and progression of cancer. However, previous evidence has suggested that there is no clear relationship between serum leptin concentrations and lung cancer progression. Cancer-associated fibroblasts (CAFs), the most abundant component of the tumor microenvironment in a variety of solid tumors, were recently reported to produce leptin. Therefore, it was inferred that leptin is most likely to affect non-small-cell lung cancer (NSCLC) through an autocrine and paracrine mechanism. In the current study, we investigated the paracrine effect and mechanism of leptin produced by CAFs on NSCLC by establishing a novel in vitro cell coculture system. Methods A noncontact coculture device was designed and made by 3D printing. CAFs and paired normal lung fibroblasts (NLFs) from 5 patients were successfully isolated and cocultured with two NSCLC cell lines in a coculture system. The background expression of leptin was detected by western blot. The in situ expression of leptin and its receptor (Ob-R) in NSCLC tissues and paired normal lung tissues was analyzed by immunohistochemistry. Furthermore, we downregulated the expression of leptin in CAFs and assessed changes in its promotion on NSCLC cells in the coculture system. Finally, changes in the phosphorylation of ERK1/2 and AKT were examined to investigate the molecular mechanisms responsible for the paracrine promotion of NSCLC cells by leptin. Results Leptin was overexpressed in nearly all five primary CAF lines compared with its expression in paired NLFs. IHC staining showed that the expression of leptin was high in NSCLC cells, slightly lower in CAF, and negative in normal lung tissue. Ob-R was strongly expressed in NSCLC cells. The ability of A549 and H1299 cells to proliferate and migrate was enhanced by high leptin levels in both the cocultured fibroblasts and the culture medium. Furthermore, western blot assays suggested that the MAPK/ERK1/2 and PI3K/AKT signaling pathways were activated by leptin produced by CAFs, which demonstrated that the functions of paracrine leptin in NSCLC are as those of the serum leptin to other cancers. Conclusion Leptin produced by CAF promotes proliferation and migration of NSCLC cells probably via PI3K/AKT and MAPK/ERK1/2 signaling pathways in a paracrine manner.

Mechanisms of Leptin and Ghrelin Action on Maturation and Functions of Dendritic Cells.

Molecular mechanisms of the immunomodulatory effects of leptin and ghrelin in concentrations typical for pregnancy on the maturation and functional activity of dendritic cells (DCs) generated from the peripheral blood monocytes of women are investigated. The presence of leptin during DC maturation did not affect the levels of CD83+CD1c+, CD86+CD1c+, and HLA-DR+CD1c+ DCs, but increased the amount and the activity of the enzyme indoleamine 2,3-dioxygenase (IDO). Cell culturing in the presence of ghrelin or combination of leptin and ghrelin reduced the percentage of CD86+CD1c+ DCs but did not affect the levels of CD83+CD1c+ and HLA-DR+CD1c+ DCs. In addition, ghrelin reduced the number of IDO molecules without affecting its activity. Simultaneous presence of leptin and ghrelin increased induced IDO activity without affecting the amount of the enzyme in DCs. The effects of leptin and ghrelin on the investigated functions of DCs in some cases correlated with high levels of cAMP. New mechanisms for leptin and ghrelin regulation of tolerogenic functions of DCs in pregnancy are proposed.

Roles and mechanisms of leptin in osteogenic stimulation in cervical ossification of the posterior longitudinal ligament

BackgroundHyperleptinemia is a common feature of obese people, and leptin, an adipocyte-derived cytokine, is believed to be an important factor in the pathogenesis of cervical ossification of the posterior longitudinal ligament(C-OPLL). So this research was to identify the relation between the serum leptin and bone metabolic markers and how the leptin induced osteogenic effect in C-OPLL.MethodsSixty-four samples were selected to determine the concentration of leptin, insulin, and alkaline phosphatase. And the association of leptin with these factors was also examined. We also evaluate the effect of leptin on the development of C-OPLL and further explored the possible underlying mechanism in vitro.ResultsWe found that serum leptin concentrations were higher in females than in males. Serum leptin and ALP concentrations were increased significantly in C-OPLL females compared to non-OPLL females. In OPLL subjects, the serum leptin concentration corrected for body mass index correlated negatively with the ALP concentrations. In C-OPLL cells, leptin treatment led to a significant increase in mRNA expressions of ALP and OCN and formation of mineralized nodule. Our experiments reported here that osteogenic effect of leptin in C-OPLL cells could be mediated via ERK1/2, p38 MAPK, and/or JNK signaling pathways.ConclusionsFrom this research, we got that leptin treatment led to a significant increase in mRNA expressions of ALP and OCN and formation of mineralized nodule. And the osteogenic effect of leptin in C-OPLL cells could be mediated via ERK1/2, p38 MAPK, and/or JNK signaling pathways.

Leptin Attenuates the Contractile Function of Adult Rat Cardiomyocytes Involved in Oxidative Stress and Autophagy.

Leptin has been identified as an important protein involved in obesity. As a chronic metabolic disorder, obesity is associated with a high risk of developing cardiovascular and metabolic diseases, including heart failure. The aim of this paper was to investigate the effects and the mechanism of leptin on the contractile function of cardiomyocytes in the adult rat. Isolated adult rat cardiomyocytes were exposed to leptin (1, 10, and 100 nmol/L) for 1 hour. The calcium transients and the contraction of adult rat cardiomyocytes were recorded with SoftEdge MyoCam system. Apocynin, tempol and rapamycin were added respectively, and Western blotting was employed to evaluate the expression of LC3B and Beclin-1. The peak shortening and maximal velocity of shortening/relengthening (± dL/dtmax) of cell shortening were significantly decreased, and the time to 50% relengthening was prolonged with leptin perfusion. Leptin also significantly reduced the baseline, peak and time to 50% baseline of calcium transient. Leptin attenuated autophagy as indicated by decreased LC3-II and Beclin-1. All of the abnormalities were significantly attenuated by apocynin, tempol or rapamycin. Our results indicated that leptin depressed the intracellular free calcium and myocardial systolic function via increasing oxidative stress and inhibiting autophagy.

PLASMA LEPTIN LEVELS IN METABOLIC SYNDROME PATIENTS WITH ISCHEMIC HEART DISEASE

Aim. To assess leptin level in blood serum of patients with metabolic syndrome (MS), including comorbidity with ischemic heart disease (IHD), to reveal possible predictive value of this marker for IHD development in MS. Material and methods. Totally, 43 MS patients studied, of those 36 with IHD, and 33 non-MS, among those had been diagnosed with IHD 18. Mean age of the MS patients at baseline was 62,7±10,3 y.o. Controls (non-MS) were 60±14,7 y.o. Leptin level in serum was measured via immune-enzyme assay “Platinum ELISA”. Results. Mean level of leptin in MS groups was significantly higher — 41,89±33,28 ng/mL comparing to non-MS — 17,64±16,87 ng/mL (р<0,001). Women had higher leptin level — 38,65±29,23 ng/mL, comparing to men — 19,54±27,23 ng/mL (р=0,006). A direct correlation of leptin and IHD was found (r=0,258, p=0,024). Conclusion. Leptin level in MS patients is higher than non-MS. Leptin plasma level in MS and IHD is higher than MS non-IHD. Further study and understanding of possible leptin mechanisms of action might be applied in improvement of effectiveness of earlier IHD diagnostics in MS.

Leptin promotes apoptosis and inhibits autophagy of chondrocytes through upregulating lysyl oxidase-like 3 during osteoarthritis pathogenesis

Leptin has been found highly expressed in human osteoarthritis. We aimed to explore the possible effects and mechanisms of leptin on the apoptosis and autophagy of chondrocytes during osteoarthritis pathogenesis. Gene expression profile from osteoarthritis affected and preserved cartilage were downloaded from NCBI's Gene Expression Omnibus database (GSE57218). Lysyl oxidase-like 3 (LOXL3) mRNA expression in cartilage tissues and leptin concentration in joint synovial fluid (SF) was measured in samples from 45 osteoarthritis patients and 25 healthy donors by real-time PCR and radioimmunoassay, respectively. Rat osteoarthritis model was induced by anterior cruciate ligament transection (ACLT). The expression of apoptosis regulators and autophagy markers were detected by Western blot. Cell survival and cell apoptosis were identified by CCK-8 and flow cytometry, respectively. Re-analysis on GSE57218 indicated that LOXL3 mRNA was upregulated in osteoarthritis affected cartilage. LOXL3 mRNA was upregulated in osteoarthritis patients, which was positively correlated with SF leptin concentration. Similar results were obtained in rat osteoarthritis model. Moreover, ACLT surgery led to a significant increase in the protein levels of cleaved caspase 3, and a notable decrease in the protein levels of Bcl-2, LC3 II/LC3 I and Beclin1. Silencing of LOXL3 in ACLT and leptin treated primary chondrocytes significantly inhibited cell apoptosis, and promoted cell proliferation and autophagy. Moreover, overexpression of LOXL3 remarkably inhibited autophagy of chondrocytes via activating mTORC1. LOXL3, a downstream of leptin, stimulated the apoptosis, but inhibited the autophagy of chondrocytes. LOXL3 is a potential therapy target for osteoarthritis.

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

Regulation and mechanism of leptin on lipid metabolism in ovarian follicle cells from yellow catfish Pelteobagrus fulvidraco

The present study was conducted to determine the effect of leptin on lipid metabolism in ovarian follicle cells of yellow catfish Pelteobagrus fulvidraco. For that purpose, primary ovarian follicle cells were isolated from yellow catfish, cultured and subjected to different treatments (control, 0.1% DMSO, 500ng/ml leptin, 500ng/ml leptin plus 100μM wortmannin, 500ng/ml leptin plus 50nM AG490, respectively) for 48h. Intracellular triglyceride (TG) content, the activities (CPT I, FAS, G6PD, and 6PGD) and/or expression level of several enzymes (CPT I, FAS, G6PD, 6PGD, ACCa and ACCb), as well as the mRNA expression of transcription factors (PPARα, PPARγ and SREBP-1) involved in lipid metabolism were determined. Recombinant human leptin (rt-hLEP) incubation significantly reduced intracellular TG content, activities and mRNA levels of FAS, G6PD and 6PGD, SREBP-1 and PPARγ, but enhanced activity and mRNA level of CPT I, PPARα and ACCa. Specific inhibitors AG490 and wortmannin of JAK–STAT and IRS–PI3K signaling pathways prevented leptin-induced changes, indicating that JAK–STAT and IRS–PI3K signaling pathways were involved in the process of leptin-induced changes of lipid metabolism. Based on these observations above, for the first time, our study indicated that leptin reduced lipid deposition by activating lipolysis and suppressing lipogenesis in ovarian follicles of yellow catfish, and both JAK–STAT and IRS–PI3K signaling pathways were involved in the changes of leptin-induced lipid metabolism.

Leptin: a potential anxiolytic by facilitation of fear extinction.

Anxiety disorders are characterized by a deficient extinction of fear memory. Evidence is growing that leptin influences numerous neuronal functions. The aims of this study were to investigate the effects and the mechanism of leptin on fear extinction. Leptin (1 mg/kg, i.p) was applied to evaluate the anxiolytic effect in rat behavioral tests. Field potentials recording were used to investigate the changes in synaptic transmission in the thalamic-lateral amygadala (LA) pathway of rat. We found that leptin produced strong anxiolytic effects under basal condition and after acute stress. Systemic administration and intra-LA infusions of leptin facilitated extinction of conditioned fear responses. The antagonist of NMDA receptor, MK-801, blocked the effect of leptin on fear extinction completely. Furthermore, these effects of leptin on fear extinction were accompanied by a reversal of conditioning-induced synaptic potentiation in the LA. Leptin facilitated NMDA receptor-mediated synaptic transmission, and reversed amygdala long-term potentiation (LTP) in a dose-dependent manner in vitro, and this LTP depotentiation effect was mediated by NMDA receptor and MAPK signaling pathway. These results identify a key role of leptin in dampening fear conditioning-induced synaptic potentiation in the LA through NMDA receptor and indicate a new strategy for treating anxiety disorders.

Leptin confers protection against TNF-α-induced apoptosis in rat cardiomyocytes

Leptin, an important adipose-derived hormone, is recognized as a crucial protein in energy homeostasis. Recent studies indicated that leptin is associated with cardiac pathophysiology, however, the role and mechanisms of leptin in cardiomyocytes apoptosis are poorly understood. Here we investigated whether leptin exerted protective effect on cardiomyocytes exposed to tumor necrosis factor-alpha (TNF-α) and the possible mechanisms. Neonatal rat cardiomyocytes were subjected to TNF-α in the presence or absence of leptin. By FITC/Annexin V flow cytometry and Western blot, we noticed that TNF-α increased Annexin V binding and cleaved caspase-3/PARP, which were attenuated by leptin pretreatment. Moreover, leptin protected cardiomyocytes against mitochondrial apoptosis by inhibiting cytochrome C elevation and Bcl-2 decreasing. TNF-α-induced P38 MAPK and NF-κB activation were abolished by leptin addition, and the P38 and NF-κB inhibitor, SB203580 and Bay117082, also mitigated the apoptotic effect of TNF-α, indicating that their activation might be responsible for the apoptosis in TNF-α-treated cardiomyocytes. Therefore, leptin conferred anti-apoptotic effect in cardiomyocytes exposed to TNF-α possibly by inhibiting TNF-α-activated P38 MAPK and NF-κB pathways.

What Fans the Fire: Insights into Mechanisms of Leptin in Metabolic Syndrome- Associated Heart Diseases

Obesity and metabolic syndrome are one of the most devastating risk factors for cardiovascular diseases. The obesity gene product leptin plays a central role in the regulation of food intake and energy expenditure. The physiological and pathophysiological roles of leptin in cardiovascular system have been investigated extensively since its discovery in 1994. In addition to its well-established metabolic effects, more recent evidence have depicted a rather pivotal role of leptin in inflammation, oxidative stress, endoplasmic reticulum stress, apoptosis and tissue remodeling en route to the pathogenesis of type 2 diabetes mellitus, hypertension, atherosclerosis, and insulin resistance. Under physiological condition, leptin is known to reduce appetite, promote energy expenditure, increase sympathetic activity, facilitate glucose utilization and improve insulin sensitivity. In addition, leptin may regulate cardiac and vascular function through a nitric oxide-dependent mechanism. However, hyperleptinemia usually occurs with progressively increased body weight and metabolic syndrome development, leading to a state of global or selective leptin resistance. Both central and peripheral leptin resistance may be present under pathophysiological conditions such as inflammation, insulin resistance, hyperlipidemia and a cadre of other cardiovascular diseases including hypertension, atherosclerosis, obesity, ischemic heart disease and heart failure. In this review, we will discuss cardiovascular actions of leptin related to various components of metabolic syndrome. Particular emphasis will be given to insights derived from therapeutic interventions with lifestyle modification, cardiovascular drugs, anti-diabetic and anti-obesity drugs.

Leptin promotes ossification through multiple ways of bone metabolism in osteoblast: a pilot study

Leptin may be a potential option in preventing osteoporosis for menopausal women. The objective of this study is to explore the molecular mechanism of leptin on bone metabolism in osteoblast. Primary osteoblasts were isolated from parietal bone of adult female rats. mRNA level of OB-Rb in osteoblasts was inhibited by siRNA to block leptin signal transmission. The whole genome expression was tested by using gene chip to preliminarily explore the molecular mechanism of leptin in regulating osteoblast activity. The optimal concentration of siRNA was 25 nM, resulting in a maximal inhibition of OB-Rb mRNA. Ossification (p < 0.05) and bone mineralization (p = 0.0001) were downregulated by inhibiting leptin signal transmission, while bone resorption (p = 0.007), osteoblast differentiation (p = 0.026) and negative regulation of bone remodeling (p = 0.004) were upregulated. The expressions of some genes were regulated by OB-Rb siRNA. The expressions of alkaline phosphatase (p = 0.014) and osteocalcin (p = 0.002) were reduced, while that of vascular endothelial growth factor A (p = 0.0076) and IL-6 (p = 0.021) were increased. In a model of osteoblast, leptin positively promotes ossification through multiple ways including bone mineralization, remodeling, resorption and osteoblast differentiation, but which way plays the most critical role is not discussed in this study and needs to be clarified in future.

Leptin promotes the expression of hTERT via STAT3 in breast cancer cells

To discussion the in vitro molecular mechanism of leptin promoting the expression of hTERT in breast cancer cells. The hTERT mRNA expression of STAT3 knockdown on leptin-induced hTERT was measured by reverse transcription-polymerase chain reaction (RT-PCR). Determine the expression of hTERT protein after different treatments in MCF7 by Western blot. Chromatin immunoprecipitation assay (ChIP) was performed to detect the binding of STAT3 to hTERT promoter in MCF7. Luciferase assay was used to confirm the effects of leptin and STAT3 phosphorylation inhibitor on the transcriptional activity of hTERT promoter. The RT-PCR analysis showed that knockdown of STAT3 significantly reduced the leptin-induced transcription of hTERT. Western blot showed that the expression of hTERT were 3.109 ± 0.051 and 1.025 ± 0.031 after leptin or both of leptin and AG490 treatments. The results of CHIP showed that the mRNA of control and leptin (160 ng/ml) treatment were 1 and 3.311 ± 0.017. Leptin increased the combination of STAT3 and hTERT promoter. Luciferase assay showed that when the concentration of leptin was 160 ng/ml, the hTERT promoter activity was 80.98 ± 0.18 while the control was 20.76 ± 0.31. After AG490 treatment, the hTERT promoter activity was 18.65 ± 0.32,significantly reduced the leptin-induced activity of hTERT promoter. Leptin/STAT3 signaling is a novel pathway for the up-regulation of hTERT expression in breast cancer cells.

Leptin-induced Cardiomyocyte Hypertrophy Reveals both Calcium-dependent and Calcium-independent/RhoA-dependent Calcineurin Activation and NFAT Nuclear Translocation

Leptin, a product of the obesity gene, has been shown to produce cardiac hypertrophy. Although leptin's mechanism of action is poorly understood activation of the RhoA/ROCK pathway has been proposed as a contributing mechanism. The Ca2+-dependent phosphatase calcineurin plays a critical role in the hypertrophic program although it is not known whether leptin can activate this signaling pathway or whether there is a relationship between RhoA activation and calcineurin. Accordingly, we determined the effect of leptin on calcineurin activation and assessed the possible role of RhoA. Experiments were performed using cultured neonatal rat ventricular myocytes exposed to 50ng/ml leptin for 24h which resulted in a robust hypertrophic response. Moreover, leptin significantly increased intracellular Ca2+ and Na+ concentrations which was associated with significantly reduced activity of the 3Na+-2K+ATPase. The hypertrophic response to leptin were completely abrogated by both C3 exoenzyme (C3), a RhoA inhibitor as well as the reverse mode 3Na+-1Ca2+ exchange inhibitor KB-R7943 ((2-[2-[4-(4-nitrobenzyloxy)phenyl] ethyl]isothiourea methanesulfonate), however only the effect of the latter was associated with attenuation of intracellular Ca2+ concentrations whereas Ca2+ concentrations were unaffected by C3. Similarly, C3 and KB-R7943 significantly attenuated early leptin-induced increase in calcineurin activity as well as the increase in nuclear translocation of the transcriptional factor nuclear factor of activated T cells. The hypertrophic response to leptin was also associated with increased p38 and ERK1/2 MAPK phosphorylation and increased p38, but not ERK1/2, translocation into nuclei. Both p38 responses as well as hypertrophy were abrogated by KB-R7943 as well as the calcineurin inhibitor FK-506 although ERK1/2 phosphorylation was unaffected. Our study therefore demonstrates a critical role for the calcineurin pathway in mediating leptin-induced hypertrophy. Moreover, we report a novel RhoA-dependent leptin-induced calcineurin activation which acts independently of changes in intracellular Ca2+ concentrations.