The soluble leptin receptor is crucial for leptin action: evidence from clinical and experimental data

Characterization of circulating leptin-receptor levels following acute sleep restriction: A pilot study on healthy adult females

BACKGROUND

Insufficient sleep adversely affects energy homeostasis by decreasing leptin levels. The underlying physiological mechanisms; however, remain unclear. Circulating leptin is well described to be regulated by its soluble receptor (sOB-R). Intriguingly, the impact of short sleep duration on sOB-R levels has never been characterized.

AIM

In this study, we investigated, for the first time, the variation of sOB-R levels and its temporal relationship with circulating leptin upon acute sleep restriction.

METHODS

Five adult females were maintained on an 8-hour sleep schedule (bedtime at 00:00) for 1 week before restricting their sleep to 4.5 h (bedtime at 03:30) on 2 consecutive nights. Balanced meals were scheduled to specific hours and sleep was objectively measured. Four-hour blood samples were regularly collected during waking hours between 08:00 and 00:00.

RESULTS

Sleep restriction resulted in lower leptin (20.9 ± 1.7 vs 25.7 ± 1.7 ng/ml) and higher sOB-R concentrations (24.4 ± 1.2 vs 19.8 ± 1.6 ng/ml). Neither the discordant temporal relationship nor the pattern of leptin and sOB-R were altered in response to sleep restriction.

CONCLUSION

Our results suggest that sleep restriction may modulate circulating leptin levels and possibly metabolism via upregulating its soluble receptor. This observation may have valuable therapeutic implications when considering sOB-R as a potential target during the management of metabolic disturbances.

Pharmacokinetics and pharmacodynamics of mibavademab (a leptin receptor agonist): Results from a first-in-human phase I study

Mibavademab (previously known as REGN4461), a fully human monoclonal antibody, is being investigated for the treatment of conditions associated with leptin deficiency. Here, we report pharmacokinetics (PKs), pharmacodynamics, and immunogenicity from a phase I study in healthy participants (NCT03530514). In part A, lean or overweight healthy participants were randomized to single-ascending-dose cohorts of 0.3, 1.0, 3.0, 10, and 30 mg/kg intravenous (i.v.), or 300 and 600 mg subcutaneous doses of mibavademab or placebo. In part B, overweight or obese participants were randomized to receive multiple doses of mibavademab (15 mg/kg i.v. loading dose and 10 mg/kg i.v. at weeks 3, 6, and 9) or placebo, stratified by body mass index and baseline leptin levels: low leptin (<5 ng/mL) or relatively low leptin (5-8 ng/mL in men and 5-24 ng/mL in women). Fifty-six and 55 participants completed the single-ascending-dose and multiple-dose parts, respectively. In the single-ascending-dose cohorts, mibavademab PKs were nonlinear with target-mediated elimination, greater than dose-proportional increases in exposure, and there were no dose-dependent differences in total soluble leptin receptor (sLEPR) levels in serum over time. Following multiple-dose administration of mibavademab in participants with leptin <8 ng/mL, lower mean mibavademab concentrations, higher mean total sLEPR concentrations, and larger mean decreases in body weight than in the relatively low leptin cohorts were observed. Baseline leptin was correlated with mibavademab PKs and pharmacodynamics. No treatment-emergent anti-mibavademab antibodies were observed in any mibavademab-treated participant. Results from this study collectively inform further development of mibavademab to treat conditions associated with leptin deficiency.

Identification and validation of cuproptosis-related molecular clusters in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a major chronic liver disease worldwide. Cuproptosis has recently been reported as a form of cell death that appears to drive the progression of a variety of diseases. This study aimed to explore cuproptosis-related molecular clusters and construct a prediction model. The gene expression profiles were obtained from the Gene Expression Omnibus (GEO) database. The associations between molecular clusters of cuproptosis-related genes and immune cell infiltration were investigated using 50 NAFLD samples. Furthermore, cluster-specific differentially expressed genes were identified by the WGCNA algorithm. External datasets were used to verify and screen feature genes, and nomograms, calibration curves and decision curve analysis (DCA) were performed to verify the performance of the prediction model. Finally, a NAFLD-diet mouse model was constructed to further verify the predictive analysis, thus providing new insights into the prediction of NAFLD clusters and risks. The role of cuproptosis in the development of non-alcoholic fatty liver disease and immune cell infiltration was explored. Non-alcoholic fatty liver disease was divided into two cuproptosis-related molecular clusters by unsupervised clustering. Three characteristic genes (ENO3, SLC16A1 and LEPR) were selected by machine learning and external data set validation. In addition, the accuracy of the nomogram, calibration curve and decision curve analysis in predicting NAFLD clusters was also verified. Further animal and cell experiments confirmed the difference in their expression in the NAFLD mouse model and Mouse hepatocyte cell line. The present study explored the relationship between non-alcoholic fatty liver disease and cuproptosis, providing new ideas and targets for individual treatment of the disease.

Mechanism of receptor assembly via the pleiotropic adipokine Leptin

The adipokine Leptin activates its receptor LEP-R in the hypothalamus to regulate body weight and exerts additional pleiotropic functions in immunity, fertility and cancer. However, the structure and mechanism of Leptin-mediated LEP-R assemblies has remained unclear. Intriguingly, the signaling-competent isoform of LEP-R is only lowly abundant amid several inactive short LEP-R isoforms contributing to a mechanistic conundrum. Here we show by X-ray crystallography and cryo-EM that, in contrast to long-standing paradigms, Leptin induces type I cytokine receptor assemblies featuring 3:3 stoichiometry and demonstrate such Leptin-induced trimerization of LEP-R on living cells via single-molecule microscopy. In mediating these assemblies, Leptin undergoes drastic restructuring that activates its site III for binding to the Ig domain of an adjacent LEP-R. These interactions are abolished by mutations linked to obesity. Collectively, our study provides the structural and mechanistic framework for how evolutionarily conserved Leptin:LEP-R assemblies with 3:3 stoichiometry can engage distinct LEP-R isoforms to achieve signaling.

The role of circulating miRNAs in leptin resistance in obese children

OBJECTIVES

Leptin resistance is one of the important causes of obesity in children. Besides known causes of leptin resistance like mutations in leptin and leptin receptor genes, overexpression of SOCS3 in arcuate nucleus is a potential cause of leptin resistance. We aimed to determine the effects of circulating miRNAs on leptin resistance in obese children by targeting SOCS3 pathway.

METHODS

miRNAs potentially targeting SOCS3 were determined by using online target prediction databases. Polymorphisms in miRNA target sequences were determined by using online genome browsers. miRNA expression levels of obese (n=35) and non-obese (n=30) children were determined by qPCR method, genotyping were performed by real-time PCR method and serum leptin, leptin receptor and SOCS3 levels were measured by ELISA method.

RESULTS

miRNA profiling have shown that serum miR-218-5p levels are significantly (p<0.05) increased in accordance with serum leptin levels in obese children.

CONCLUSIONS

In this study we used target prediction methods for evaluating potential miRNAs which may involve in development of leptin resistance. We have shown that miR-218-5p might be taking part in leptin resistance in obese children.

Plasma Cytokine Atlas Reveals the Importance of TH2 Polarization and Interferons in Predicting COVID-19 Severity and Survival

Although it is now widely accepted that host inflammatory response contributes to COVID-19 immunopathogenesis, the pathways and mechanisms driving disease severity and clinical outcome remain poorly understood. In the effort to identify key soluble mediators that characterize life-threatening COVID-19, we quantified 62 cytokines, chemokines and other factors involved in inflammation and immunity in plasma samples, collected at hospital admission, from 80 hospitalized patients with severe COVID-19 disease who were stratified on the basis of clinical outcome (mechanical ventilation or death by day 28). Our data confirm that age, as well as neutrophilia, lymphocytopenia, procalcitonin, D-dimer and lactate dehydrogenase are strongly associated with the risk of fatal COVID-19. In addition, we found that cytokines related to TH2 regulations (IL-4, IL-13, IL-33), cell metabolism (lep, lep-R) and interferons (IFNα, IFNβ, IFNγ) were also predictive of life-threatening COVID-19.

Potential role of aryl hydrocarbon receptor signaling in childhood obesity

BACKGROUND

There is a growing concern that junk food has contributed to the childhood obesity epidemic. Recently, experimental studies suggested that the aryl hydrocarbon receptor (AHR) gene is strongly linked to western diet-induced obesity.

AIM

This study investigated the potential role of AHR signaling in childhood obesity and the possible associations of the AHR-aryl hydrocarbon receptor repressor (AHRR)-cytochrome P450 1B1 (CYP1B1) axis with fatty acid homeostasis and the appetite-related hormones, leptin and ghrelin.

SUBJECTS AND METHODS

The study included 80 children; 54 obese and 26 non-obese of matched age and sex. Demographic data, anthropometric measurements, and lipid profile were assessed. Expression of AHR signaling genes was analyzed in blood cells by qRT-PCR. Serum insulin, leptin and ghrelin levels were measured using ELISA.

RESULTS

The statistical power of this study, calculated using G*Power version 3.1.9.2, was 90% (α = 0.05). AHR and CYP1B1 gene expression levels were upregulated in the obese group compared to controls, whereas AHRR, stearoyl-CoA desaturase 1 (SCD1), and peroxisome proliferator-activated receptor-γ₂ (PPARγ₂) were downregulated. Serum leptin correlated positively, while serum ghrelin correlated negatively with both AHR and CYP1B1. Stratification of obese children by age revealed more activated AHR signaling in younger than in older children. Receiver-operating-characteristic (ROC) analysis revealed that AHR, AHRR and CYP1B1 could discriminate between obese and normal weight children. Multivariate analysis showed that AHRR, CYP1B1 and ghrelin could be significant independent predictors of obesity.

CONCLUSION

This study provides new insights into the molecular mechanisms contributing to childhood obesity by revealing alterations in the AHR-AHRR-CYP1B1 axis, which could serve as a promising therapeutic target for childhood obesity.

Is "Leptin Resistance" Another Key Resistance to Manage Type 2 Diabetes?

Although novel pharmacological options for the treatment of type 2 diabetes mellitus (DM2) have been observed to modulate the functionality of several key organs in glucose homeostasis, successful regulation of insulin resistance (IR), body weight management, and pharmacological treatment of obesity remain notable problems in endocrinology. Leptin may be a pivotal player in this scenario, as an adipokine which centrally regulates appetite and energy balance. In obesity, excessive caloric intake promotes a low-grade inflammatory response, which leads to dysregulations in lipid storage and adipokine secretion. In turn, these entail alterations in leptin sensitivity, leptin transport across the blood-brain barrier and defects in post-receptor signaling. Furthermore, hypothalamic inflammation and endoplasmic reticulum stress may increase the expression of molecules which may disrupt leptin signaling. Abundant evidence has linked obesity and leptin resistance, which may precede or occur simultaneously to IR and DM2. Thus, leptin sensitivity may be a potential early therapeutic target that demands further preclinical and clinical research. Modulators of insulin sensitivity have been tested in animal models and small clinical trials with promising results, especially in combination with agents such as amylin and GLP-1 analogs, in particular, due to their central activity in the hypothalamus.

Cortisol, leptin and free leptin index (FLI) in newborns in the first days of life and their importance for body weight programming

BACKGROUND

Birth weight and leptin seem to be the factors responsible for early programming of body weight in later life. A marker for leptin action is free leptin index (FLI), which depends on soluble leptin receptor (Ob-Re) (FLI = leptin/Ob-Re). In the present article, we suggest that FLI is modulated partly by cortisol variations observed in newborns in the first days of life and is connected with their postnatal weight loss.

METHODS

The study group consisted of 44 full-term newborns. Leptin, cortisol and Ob-Re concentrations were determined in the umbilical cord blood (UCB) and in the newborns' blood (NB) on the fourth day of life, free leptin index (FLI = leptin/Ob-Re) was calculated. Correlations between the assessed parameters and the somatic features of the newborns were examined.

RESULTS

Birth weight, length and chest circumference of newborns were positively correlated with leptin concentration in the UCB but not with FLI in the UCB. Cortisol and leptin concentrations, as well as FLI values declined concomitantly with body weight, and were lower on the fourth day of life than on the first one; however, Ob-Re concentration increased (p < 0.0001). There was a positive correlation between the newborns' birth weight loss percentage evaluated on the fourth day of life and FLI in newborns (R = 0.39; p < 0.01). Positive correlations between cortisol and Ob-Re in UCB (R = 0.35; p < 0.02) and in NB (R = 0.36; p < 0.01), as well as a negative correlation between cortisol and FLI (R = -0.32; p < 0.03) in NB were noted.

CONCLUSIONS

Our data suggest a possible relationship between cortisol and a soluble leptin receptor (Ob-Re), which changes free leptin index (FLI) and is connected with birth weight loss in newborns. Whether these observations are important for programming of future body weight of children requires further research.

Leptin as a breast milk component for the prevention of obesity

Leptin ingested as a component of breast milk is increasingly recognized to play a role in the postnatal programming of a healthy phenotype in adulthood. Besides its primary function in controlling body weight, leptin may be an essential nutrient required during lactation to ensure that the system controlling fat accumulation and body composition is well organized from the early stages of development. This review delves into the following topics: (1) the imprinted protective function of adequate leptin intake during lactation in future metabolic health; (2) the consequences of a lack of leptin intake or of alterations in leptin levels; and (3) the mechanisms described for the effects of leptin on postnatal programming. Furthermore, it highlights the importance of breastfeeding and the need to establish optimal or reference intake values for leptin during lactation to design patterns of personalized nutrition from early childhood.

No detectable effects of acute tryptophan depletion on short-term immune system cytokine levels in healthy adults

Objectives: Recent research suggested an influence of diminished central nervous serotonin (5-HT) synthesis on the leptin axis via immunological mechanisms in healthy adult females. However, studies assessing immunological parameters in combination with dietary challenge techniques that impact brain 5-HT synthesis in humans are lacking.  Methods: In the present trial, a pilot analysis was conducted on data obtained in healthy adult humans receiving either different dietary acute tryptophan depletion (ATD) challenge or tryptophan (TRP)-balanced control conditions (BAL) to study the effects of reduced central nervous 5-HT synthesis on serum tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β) and IL-6 concentrations. The data of N = 35 healthy adults were analysed who were randomly subjected to one of the following two dietary conditions in a double-blind between-subject approach: (1) The Moja-De ATD challenge (ATD), or (2) TRP-balanced control condition for ATD Moja-De (BAL). Serum concentrations for the assessment of relevant parameters (TNF-α, IL-1β and IL-6) and relevant TRP-related characteristics after the respective challenge procedures were assessed at baseline (T0) and in hourly intervals after administration over a period of 6 h (T1-T6).  Results: The ATD condition did not result in significant changes to cytokine concentrations for the entire study sample, or in male and female subgroups. Depletion of CNS 5-HT via dietary TRP depletion appears to have no statistically significant short-term impact on cytokine concentrations in healthy adults.  Conclusions: Future research on immunological stressors in combination with challenge techniques will be of value in order to further disentangle the complex interplay between brain 5-HT synthesis and immunological pathways.

Platelet Serotonin Levels Are Associated with Plasma Soluble Leptin Receptor Concentrations in Normoglycemic Women

Most peripheral serotonin (5-hydroxytryptamine (5HT)) is synthetized in the gut with platelets being its main circulating reservoir. 5HT is acting as a hormone in key organs to regulate glucose and lipid metabolism. However, the relation between platelet 5HT levels and traits related to glucose homeostasis and lipid metabolism in humans remains poorly explored. The objectives of this study were (a) to assess the association between platelet 5HT levels and plasma concentration of nonesterified fatty acids (NEFAs) and some adipokines including leptin and its soluble leptin receptor (sOb-R), (b) to assess the association between platelet 5HT levels and anthropometric traits and indexes of insulin secretion/sensitivity derived from oral glucose tolerance test (OGTT), and (c) to evaluate changes in platelet 5HT levels in response to OGTT. In a cross-sectional study, 59 normoglycemic women underwent a standard 2-hour OGTT. Plasma leptin, sOb-R, total and high molecular weight adiponectin, TNFα, and MCP1 were determined by immunoassays. Platelet 5HT levels and NEFAs were measured before and after OGTT. The free leptin index was calculated from leptin and sOb-R measurements. Insulin sensitivity indexes derived from OGTT (HOMA-S and Matsuda ISICOMP) and plasma NEFAs (Adipose-IR, Revised QUICKI) were also calculated. Our data show that among metabolic traits, platelet 5HT levels were associated with plasma sOb-R (r = 0.39, p = 0.003, corrected p = 0.018). Platelet 5HT levels were reduced in response to OGTT (779 ± 237 vs.731 ± 217 ng/10⁹ platelets, p = 0.005). In conclusion, platelet 5HT levels are positively associated with plasma sOb-R concentrations and reduced in response to glucose intake possibly indicating a role of peripheral 5HT in leptin-mediated appetite regulation.

Prediction of Circulating Adipokine Levels Based on Body Fat Compartments and Adipose Tissue Gene Expression

BACKGROUND

Adipokines are hormones secreted from adipose tissue (AT), and a number of them have been established as risk factors for chronic diseases. However, it is not clear whether and to what extent adiposity, gene expression, and other factors determine their circulating levels.

OBJECTIVES

To assess to what extent adiposity, as measured by the amount of subcutaneous AT (SAT) and visceral AT (VAT) using magnetic resonance imaging, and gene expression levels in SAT determine plasma concentrations of the adipokines adiponectin, leptin, soluble leptin receptor, resistin, interleukin 6, and fatty acid-binding protein 4 (FABP4).

METHODS

We performed a cross-sectional analysis of 156 participants from the EPIC Potsdam cohort study and analyzed multiple regression models and partial correlation coefficients.

RESULTS

For leptin and FABP4 concentrations, 81 and 45% variance were explained by SAT mass, VAT mass, and gene expression in SAT in multivariable regression models. For the remaining adipokines, AT mass and gene expression explained <16% variance of plasma concentrations. Gene expression in SAT was a less important predictor compared to AT mass. SAT mass was a better predictor than VAT mass for leptin (partial correlation r = 0.81, 95% confidence interval 0.75-0.86, vs. r = 0.58, 95% confidence interval 0.46-0.67), while differences between AT compartments were small for the other adipokines.

CONCLUSIONS

While plasma levels of leptin and FABP4 can be explained in a large and medium part by the amount of AT and SAT gene expression, surprisingly, these predictors explained only little variance for all other investigated adipokines.

Late effects in survivors of childhood acute lymphoblastic leukemia in the context of selected gene polymorphisms

BACKGROUND

It has been shown that approximately half of survivors of childhood acute lymphoblastic leukemia (ALL) have symptomatic late effects (LE) that may be severe or life-threatening. The aim of our study was to assess the health status of childhood ALL survivors after over 10 years of follow-up and to assess its relationships with gene polymorphisms, numbers and types of LEs, as well as with intensity of chemotherapy and cranial radiotherapy (CRT).

METHODS

We conducted a telephone survey in 125 ALL survivors (median time from completion of treatment was 12 years) and compared the results with those obtained in our previous study. Most of the patients were followed-up by local providers.

RESULTS

The prevalence of LEs of approximately 50% was similar in both study groups. More than one LE was found in almost 25% of patients. Endocrine LEs were less frequent than in our previous study (44% vs 22%), probably due to underdiagnosis. The prevalence of hepatitis B/C decreased from 30%/50 to 18% (counted together), and prevalence of neurologic LEs decreased from 18 to 6%. The increase in the rate of second malignancies was not significant (2% vs. 3%). Sixty four percent of patients continued their education at the time of the study. Approximately 51% of ALL survivors who have completed their education by the time of the study had no permanent employment, including 4 mothers of infants and 3 persons qualified for a disability living allowance. These employment problems may have been due to cognitive impairment. The offspring of the ALL survivors included 11 children, all of them healthy. Further analysis showed higher prevalence of hepatitis in patients treated with CRT (p = 0.0001). Genetic studies revealed higher prevalence of hepatitis in patients homozygous for the rs9939609A variant of the FTO gene compared with other patients (p = 0.03). Moreover, wild-type rs1137101 polymorphism (Q223R) of the and leptin receptor gene was more frequent in patients with psychological LEs (p = 0.03).

CONCLUSIONS

The prevalence of LEs in ALL survivors is of key importance. The transition of childhood ALL survivors from pediatric to adult care should be urgently improved to maintain continued follow-up provide high-quality care.

TRIAL REGISTRATION

Bioethics Committee of the Jagiellonian University approved the study protocol. Registration number: KBET/113/B/2006.

The intracellular domain of the leptin receptor prevents mitochondrial depolarization and mitophagy

Hypothalamic leptin receptor (LR) signaling regulates body weight by balancing food intake and energy expenditure. It is well established that the human LR undergoes ectodomain shedding, but little is known about the fate of the remaining cytosolic domain. This study demonstrates that regulated intramembrane proteolysis (RIP) releases the LR intracellular domain (LR ICD), which translocates to the mitochondria where it binds to SOCS6. This LR ICD-SOCS6 interaction stabilizes both proteins on the mitochondrial outer membrane and requires a functional BC box in SOCS6 for mitochondrial association and a central motif in the LR ICD for SOCS6 binding. The LR ICD prevents CCCP-induced mitochondrial depolarization and mitophagy as shown by lowered Parkin translocation and p62 accumulation. Strict regulation of mitochondrial dynamics in the hypothalamus is known to be essential for body weight homeostasis. This is the first study showing that the LR can directly modulate mitochondrial biology.

Leptin receptor q223r polymorphism influences neutrophil mobilization after Clostridium difficile infection

Clostridium difficile is the leading cause of nosocomial infections in the United States. Clinical disease outcomes after C. difficile infection (CDI) are dependent on intensity of host inflammatory responses. Specifically, peak peripheral white blood cell (WBC) count >20 × 10⁹ l^-1 is an indicator of adverse outcomes in CDI patients, and is associated with higher 30-day mortality. We show that homozygosity for a common single nucleotide polymorphism (Q to R mutation in leptin receptor that is present in up to 50% of people), significantly increases the risk of having peak peripheral WBC count >20 × 10⁹ l^-1 (odds ratio=5.41; P=0.0023) in CDI patients. In a murine model of CDI, we demonstrate that mice homozygous for the same single nucleotide polymorphism (RR mice) have more blood and tissue leukocytes (specifically neutrophils), exaggerated tissue inflammation, and higher mortality as compared with control mice, despite similar pathogen burden. Further, we show that neutrophilia in RR mice is mediated by gut microbiota-directed expression of CXC chemokine receptor 2 (CXCR2), which promotes the release of neutrophils from bone marrow reservoir. Overall these studies provide novel mechanistic insights into the role of human genetic polymorphisms and gut microbiota in regulating the fundamental biological process of CDI-induced neutrophilia.

FoxO1 Is Required for Most of the Metabolic and Hormonal Perturbations Produced by Hepatic Insulin Receptor Deletion in Male Mice

Insulin coordinates the complex response to feeding, affecting numerous metabolic and hormonal pathways. Forkhead box protein O1 (FoxO1) is one of several signaling molecules downstream of insulin; FoxO1 drives gluconeogenesis and is suppressed by insulin. To determine the role of FoxO1 in mediating other actions of insulin, we studied mice with hepatic deletion of the insulin receptor, FoxO1, or both. We found that mice with deletion of the insulin receptor alone showed not only hyperglycemia but also a 70% decrease in plasma insulin-like growth factor 1 and delayed growth during the first 2 months of life, a 24-fold increase in the soluble leptin receptor and a 19-fold increase in plasma leptin levels. Deletion of the insulin receptor also produced derangements in fatty acid metabolism, with a decrease in the expression of the lipogenic enzymes, hepatic diglycerides, and plasma triglycerides; in parallel, it increased expression of the fatty acid oxidation enzymes. Mice with deletion of both insulin receptor and FoxO1 showed a much more modest phenotype, with normal or near-normal glucose levels, growth, leptin levels, hepatic diglycerides, and fatty acid oxidation gene expression; however, lipogenic gene expression remained low. Taken together, these data reveal the pervasive role of FoxO1 in mediating the effects of insulin on not only glucose metabolism but also other hormonal signaling pathways and even some aspects of lipid metabolism.

Leptin and soluble leptin receptor in association with gestational diabetes: a prospective case-control study

PURPOSE

To assess the association of serum leptin and its receptor (SLeptinR) with the risk of gestational diabetes mellitus (GDM) and to evaluate the longitudinal circulation of these peptides in pregnancy.

METHODS

This study consisted of 53 subjects diagnosed with GDM and 43 normal glucose tolerance (NGT) pregnant women. Serum leptin and SLeptinR were measured at 24-28 weeks, prior and after delivery, and post-puerperium.

RESULTS

Lower levels of leptin and SLeptinR were observed in GDM compared to NGT. Leptin [OR 0.97 (95% CI 0.94-1.0)] and SLeptinR [OR 0.86 (95% CI 0.79-0.93]) were inversely associated with GDM. Participants in the lowest tertile for leptin and SLeptinR had a 2.8-fold (95% CI 1.0-7.6) and a 5.7-fold (95% CI 1.9-17.3) higher risk of developing GDM compared with the highest tertile, respectively. These relationships were attenuated after adjustment for covariates. In both the groups, peak leptin was observed at 24-28 weeks, decreasing continuously during pregnancy (p > 0.05) and after delivery (p < 0.017). SLeptinR level increased (p < 0.001) during pregnancy and decreased (p < 0.005) after delivery in GDM, however, levels remained the same in NGT. In GDM, leptin and SLeptinR was positively and inversely correlated with BMI and HOMA-IR at 24-28 weeks and post-puerperium, respectively. The cord levels of both leptin and SLeptinR were lower than maternal levels. There were no significant differences in serum cord leptin and SLeptinR levels between the groups.

CONCLUSION

Leptin and SLeptinR are independently and inversely associated with GDM. Lower levels of these peptides may play an important role in the pathophysiology of GDM and pre-diabetic state in post-puerperium.

Immunometabolic profiling of T cells from patients with relapsing-remitting multiple sclerosis reveals an impairment in glycolysis and mitochondrial respiration

BACKGROUND

Metabolic reprogramming is shaped to support specific cell functions since cellular metabolism controls the final outcome of immune response. Multiple sclerosis (MS) is an autoimmune disease resulting from loss of immune tolerance against central nervous system (CNS) myelin. Metabolic alterations of T cells occurring during MS are not yet well understood and their studies could have relevance in the comprehension of the pathogenetic events leading to loss of immune tolerance to self and to develop novel therapeutic strategies aimed at limiting MS progression.

METHODS AND RESULTS

In this report, we observed that extracellular acidification rate (ECAR) and oxygen consumption rate (OCR), indicators of glycolysis and oxidative phosphorylation, respectively, were impaired during T cell activation in naïve-to-treatment relapsing remitting (RR)MS patients when compared with healthy controls. These results were also corroborated at biochemical level by a reduced expression of the glycolitic enzymes aldolase, enolase 1, hexokinase I, and by reduction of Krebs cycle enzymes dihydrolipoamide-S-acetyl transferase (DLAT) and dihydrolipoamide-S-succinyl transferase (DLST). Treatment of RRMS patients with interferon beta-1a (IFN beta-1a) was able to restore T cell glycolysis and mitochondrial respiration as well as the amount of the metabolic enzymes to a level comparable to that of healthy controls. These changes associated with an up-regulation of the glucose transporter-1 (GLUT-1), a key element in intracellular transport of glucose.

CONCLUSIONS

Our data suggest that T cells from RRMS patients display a reduced engagement of glycolysis and mitochondrial respiration, reversible upon IFN beta-1a treatment, thus suggesting an involvement of an altered metabolism in the pathogenesis of MS.

Plasma soluble leptin receptor levels are associated with pancreatic β-cell dysfunction in patients with type 2 diabetes

Aims/Introduction

A soluble form of the leptin receptor (soluble Ob‐R) in the circulation regulates leptin's bioactivity, and is inversely associated with body adiposity and circulating leptin levels. However, no study has examined the clinical impact of soluble Ob‐R on glucose metabolism in diabetes. The present study aimed to investigate the association of plasma soluble Ob‐R levels with insulin resistance and pancreatic β‐cell function in patients with type 2 diabetes.

Materials and Methods

A total of 289 Japanese patients with type 2 diabetes were included in the present study. Fasting plasma soluble Ob‐R levels and plasma leptin levels were measured by enzyme‐linked immunosorbent assay. Insulin resistance and pancreatic β‐cell function were estimated by homeostasis model assessment of insulin resistance, homeostasis model assessment of β‐cell function and fasting C‐peptide index.

Results

The median plasma soluble Ob‐R level and plasma leptin level were 3.4 ng/mL and 23.6 ng/mL, respectively. Plasma soluble Ob‐R levels were negatively correlated with homeostasis model assessment of insulin resistance, homeostasis model assessment of β‐cell function and the C‐peptide index, whereas plasma leptin levels were positively correlated with each index in univariate analyses. Multivariate analyses including plasma soluble Ob‐R levels, plasma leptin levels and use of sulfonylureas, along with age, sex, body mass index and other covariates, showed that soluble Ob‐R levels were independently and negatively associated with homeostasis model assessment of β‐cell function and the C‐peptide index, but not significantly associated with homeostasis model assessment of insulin resistance.

Conclusions

Plasma soluble Ob‐R levels are independently associated with pancreatic β‐cell function, but not with insulin resistance, in patients with type 2 diabetes. The present study implicates the role of soluble Ob‐R in pancreatic β‐cell dysfunction in type 2 diabetes.

Metformin increases hepatic leptin receptor and decreases steatosis in mice

In addition to the ascertained efficacy as antidiabetic drug, metformin is increasingly being used as weight-loss agent in obesity, and as insulin sensitizer in nonalcoholic fatty liver disease (NAFLD). However, the mechanisms underlying these effects are still incompletely understood. Emerging evidence suggest metformin as leptin sensitizer to mediate the weight-loss effect in the brain. In this study, we investigated effects of metformin on expression of leptin receptors in liver and kidney in mice. C57BL/6 mice were fed with chow diet (CD) or high-fat diet (HF) for 5months. Afterward, mice were treated with metformin (50mg/kg or 200mg/kg) for 15days. Metabolic parameters and hepatic gene expression were analyzed at the end of the treatment. We also tested the effects of metformin on plasma-soluble leptin receptor (sOB-R) levels in newly diagnosed type 2 diabetes mellitus (T2DM) patients, and assessed its effect on hepatosteatosis in mice. Results showed that metformin upregulates the expression of leptin receptors (OB-Ra, -Rb, -Rc, and -Rd) in liver but not kidney. The stimulation effect is dose-dependent in both chow and HF mice. Upregulation of OB-Rb, long signaling isoform, needs a relatively higher dose of metformin. This effect was paralleled by increased sOBR levels in mice and T2DM patients, and decreased hepatic triglyceride (TG) content and lipogenic gene expression, including sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthase (FAS) and acetyl-CoA carboxylase-1 (ACC-1). Taken together, these data identify hepatic leptin receptor as target gene being upregulated by metformin which may enhance leptin sensitivity in liver to alleviate steatosis.

Complementary Effects of Genetic Variations in LEPR on Body Composition and Soluble Leptin Receptor Concentration after 3-Month Lifestyle Intervention in Prepubertal Obese Children

In obese individuals, weight loss might be affected by variants of the adipokine-encoding genes. We verified whether selected functional single nucleotide polymorphisms in LEP, LEPR and ADIPOQ are associated with changes in serum levels of the respective adipokines and weight loss in 100 prepubertal obese (SDS-BMI > 2) Caucasian children undergoing lifestyle intervention. Frequencies of the -2548G > A LEP, Q223R LEPR, K656N LEPR, -11377C > G and -11426A > G ADIPOQ polymorphisms were analyzed by restriction fragment length polymorphism. Serum adipokine and soluble leptin receptor (sOB-R) concentrations were measured using the ELISA method. Among the analyzed polymorphisms, only LEPR polymorphisms were associated with changes of SDS-BMI or sOB-R concentrations in children after therapy. Carriers of the wild-type K665N and at least one minor Q223R allele had the greatest likelihood of losing weight (OR = 5.09, p = 0.006), an increase in sOB-R (ptrend = 0.022) and decrease in SDS-BMI correlated with the decrease of fat mass (p < 0.001). In contrast, carrying of the wild-type Q223R and at least one minor K665N allele were associated with a decrease in sOB-R concentrations and a decrease in SDS-BMI correlated with a decrease in fat-free mass (p = 0.002). We suggest that the combination of different LEPR variants, not a single variant, might determine predisposition to weight loss in the prepubertal period.

Serum leptin and serum leptin/serum leptin receptor ratio imbalance in obese rheumatoid arthritis patients positive for anti-cyclic citrullinated peptide antibodies

Introduction

Leptin has a prominent role in the development and maintenance of acute and chronic inflammatory states such as rheumatoid arthritis (RA) and obesity. Nevertheless, the association of serum leptin (sLep) and soluble leptin receptor (sLepR) in RA pathogenesis has not been clarified. The purpose of this study was to evaluate the association of sLep, sLepR and leptin production indexes such as sLep/fat mass ratio with clinical activity and biomarkers and anti-cyclic citrullinated peptide (anti-CCP) antibodies in RA compared with body mass index (BMI) matched control subjects.

Methods

We included 64 RA patients and 66 controls matched for age, gender and BMI. Subjects were evaluated for BMI, fat mass distribution, sLep, sLepR, sLep/fat mass ratio and sLepR/fat mass ratio. Patients were evaluated for clinical activity and anti-CCP antibodies.

Results

We found two or three fold increased sLep levels, sLep/sLepR ratio and sLep/fat mass ratio in obese anti-CCP positive RA patients vs. controls. Partial correlations showed that anti-CCP antibodies were correlated with sLep/fat mass ratio (partial r = 0.347, P = 0.033) after adjustment for age, subcutaneous adipose tissue and fat mass.

Conclusions

In preobese and obese RA patients there is and increased production of sLep according to anti-CCP positivity. This phenomenon suggests there is an additive effect of chronic inflammation resulting from RA and obesity in which leptin favors the humoral response against citrullinated proteins. In summary, the data observed in our study suggests sLep could be a surrogate marker of chronicity and humoral immunity in RA in the presence of obesity.

Longitudinal assessment of immuno-metabolic parameters in multiple sclerosis patients during treatment with glatiramer acetate

OBJECTIVE

We investigated the effect of glatiramer acetate (GA) on the modulation of immune cell subpopulations and serum levels of multiple immune/metabolic markers in patients with relapsing-remitting multiple sclerosis (RRMS) to understand whether the treatment with GA could induce a specific change in the immunometabolic asset of patients with RRMS.

MATERIAL AND METHODS

We performed an extensive peripheral blood immunophenotyping and measured serum levels of several parameters involved in the pathogenesis of RRMS and also relevant in the pathogenesis of metabolic syndrome and obesity such as leptin, soluble leptin-receptor (sLep-R), myeloperoxidase (MPO), soluble CD40 ligand (sCD40-L), soluble tumor necrosis factor-receptor (sTNF-R), monocyte chemoattractant protein 1 (MCP-1), soluble Inter-Cellular Adhesion Molecule-1 (sICAM-1) and osteoprotegerin (OPG), in 20 naïve-to-treatment RRMS patients and 20 healthy controls. We repeated these analyses over time at 6 and 12 months after starting GA treatment.

RESULTS

Our analysis showed that naïve-to-treatment RRMS patients had a lower number of CD16(+)CD56(+) NK cells, CD19(+) B cells, CD4(+) T cells co-expressing the MHC class II activation marker HLA-DR (CD4(+)DR(+)) and naïve CD4(+)CD45RA(+) T cells in basal conditions. GA treatment induced a specific and significant decrease of circulating CD19(+) B cells. Naïve-to-treatment RRMS patients also showed a significantly higher number of CD4(+) T cells with a memory phenotype (CD4(+)CD45RO(+)) whose peripheral frequency was not affected by GA treatment. These changes over time associated with a higher serum concentration of leptin and lower levels of MPO. GA treatment also reduced significantly the circulating levels of sCD40-L and sTNF-R overtime.

CONCLUSIONS

Our data suggest that the clinical outcome of GA treatment is associated with changes in immune cell subpopulations and modulation of specific immunometabolic markers. These data add substantial evidence of the immune modulating effect of GA during RRMS and could be of relevance in understanding the pathogenesis of disease and its follow-up.

Leucine supplementation improves leptin sensitivity in high-fat diet fed rats

Background

Several studies have reported the favorable effect of leucine supplementation on insulin resistance or insulin sensitivity. However, whether or not leucine supplementation improves leptin sensitivity remains unclear.

Design

Forty-eight male Sprague-Dawley rats were fed with either a high-fat diet (HFD) or HFD supplemented with 1.5, 3.0, and 4.5% leucine for 16 weeks. At the end of the experiment, serum leptin level was measured by ELISA, and leptin receptor (ObR) in the hypothalamus was examined by immunohistochemistry. The protein expressions of ObR and leptin-signaling pathway in adipose tissues were detected by western blot.

Results

No significant differences in body weight and food/energy intake existed among the four groups. Serum leptin levels were significantly lower, and ObR expression in the hypothalamus and adipose tissues was significantly higher in the three leucine groups than in the control group. These phenomena suggested that leptin sensitivity was improved in the leucine groups. Furthermore, the expressions of JAK2 and STAT3 (activated by ObR) were significantly higher, and that of SOCS3 (inhibits leptin signaling) was significantly lower in the three leucine groups than in the control group.

Conclusions

Leucine supplementation improves leptin sensitivity in rats on HFD likely by promoting leptin signaling.

Leptin regulates CD16 expression on human monocytes in a sex-specific manner

Fat mass is linked mechanistically to the cardiovascular system through leptin, a 16 kDa protein produced primarily by adipocytes. In addition to increasing blood pressure via hypothalamic‐sympathetic pathways, leptin stimulates monocyte migration, cytokine secretion, and other functions that contribute to atherosclerotic plaque development. These functions are also characteristics of CD16‐positive monocytes that have been implicated in the clinical progression of atherosclerosis. This investigation sought to determine if leptin promoted the development of such CD16‐positive monocytes. Cells from 45 healthy men and women with age ranging from 20 to 59 years were analyzed. Circulating numbers of CD14⁺⁺16⁺⁺ monocytes, which are primary producers of TNFα, were positively related to plasma leptin concentrations (P < 0.0001), with a stronger correlation in men (P < 0.05 for leptin × sex interaction). In vitro, recombinant human leptin induced CD16 expression in a dose‐related manner (P = 0.02), with a stronger influence on monocytes from men (P = 0.03 for leptin × sex interaction). There were no sex‐related differences in total leptin receptor expression on any monocyte subtypes, relative expression of long versus short isoforms of the receptor, or soluble leptin receptor concentrations in the plasma. The number of circulating CD14⁺16⁺⁺ monocytes, which preferentially migrate into nascent plaques, was positively related to systolic blood pressure (R = 0.56, P = 0.0008) and intima‐media thickness (R = 0.37, P = 0.03), and negatively related to carotid compliance (R = −0.39, P = 0.02). These observations indicate that leptin promotes the development of CD16‐positive monocyte populations in a sex‐specific manner and that these subpopulations are associated with diminished vascular function.

e12177

Recombinant leptin induced CD16 expression on human monocytes in vitro in a dose‐ and sex‐specific manner. In vivo, CD16 expression on human monocytes correlated with plasma leptin concentrations in a sex‐specific manner. Blood pressure, carotid intima‐media thickness and carotid compliance were related to the number of circulating CD16‐positive monocytes.

20 years of leptin: connecting leptin signaling to biological function

Hypothalamic leptin action promotes negative energy balance and modulates glucose homeostasis, as well as serving as a permissive signal to the neuroendocrine axes that control growth and reproduction. Since the initial discovery of leptin 20 years ago, we have learned a great deal about the molecular mechanisms of leptin action. An important aspect of this has been the dissection of the cellular mechanisms of leptin signaling, and how specific leptin signals influence physiology. Leptin acts via the long form of the leptin receptor LepRb. LepRb activation and subsequent tyrosine phosphorylation recruits and activates multiple signaling pathways, including STAT transcription factors, SHP2 and ERK signaling, the IRS-protein/PI3Kinase pathway, and SH2B1. Each of these pathways controls specific aspects of leptin action and physiology. Important inhibitory pathways mediated by suppressor of cytokine signaling proteins and protein tyrosine phosphatases also limit physiologic leptin action. This review summarizes the signaling pathways engaged by LepRb and their effects on energy balance, glucose homeostasis, and reproduction. Particular emphasis is given to the multiple mouse models that have been used to elucidate these functions in vivo.

Effects of a short-term reduction in brain serotonin synthesis on the availability of the soluble leptin receptor in healthy women

Serotonin (5-HT) and the hormone leptin have been linked to the underlying neurobiology of appetite regulation with evidence coming from animal and cellular research, but direct evidence linking these two pathways in humans is lacking. We examined the effects of reduced brain 5-HT synthesis due to acute tryptophan depletion (ATD) on levels of soluble leptin receptor (sOb-R), the main high-affinity leptin binding protein, in healthy adults using an exploratory approach. Women, but not men, showed reduced sOb-R concentrations after ATD administration. With females showing reduced baseline levels of central 5-HT synthesis compared to males diminished brain 5-HT synthesis affected the leptin axis through the sOb-R in females, thereby potentially influencing their vulnerability to dysfunctional appetite regulation and co-morbid mood symptoms.

Systemic and placental leptin and its receptors in pregnancies associated with obesity

This study aimed to gain new insights into both systemic and placental leptin and its receptors, with reference to the maternal prepregnancy body mass index (BMI). Thus, 84 women (29 lean, 24 overweight, and 31 obese) were recruited and maternal, cord blood, and placental tissues collected prior to term labor. Plasma levels were measured by enzyme-linked immunosorbent assay and for placenta, immunohistochemistry and messenger RNAs (mRNAs) were quantitated. We confirmed that maternal leptin increased linearly as the soluble receptor decreased with BMI (P = .001). Fetal leptin increased with maternal BMI (P = .02) and birth weight (P = .006) and was higher in female infants (P < .001). Placental mRNA levels of leptin and its receptors showed no change in BMI. However, we show a significant (P = .043) linear increase in leptin in the placental vascular endothelial cells with maternal obesity, while leptin in syncytiotrophoblast showed no statistical change. Leptin receptors localized to syncytiotrophoblast and intravillous macrophages and were unchanged with BMI.

The relation of leptin and soluble leptin receptor levels with metabolic and clinical parameters in obese and healthy children

We investigated the relation of serum leptin, soluble leptin receptor (sLR) and free leptin index (FLI) with metabolic and anthropometric parameters in obese and healthy children. Height, weight, waist circumference (WC), fasting serum glucose, insulin, lipid profile, leptin and sLR levels of 35 obese children and 36 healthy children were measured and FLI was calculated as the ratio of leptin to sLR. In obese children, serum leptin and FLI were found significantly higher, while sLR level was significantly lower than the healthy children. Comparison of obese children regarding the insulin resistance showed significantly higher serum leptin and FLI in the insulin resistant group; however sLR level was not different between the insulin resistant and non-resistant obese children. In obese children, sLR was not correlated with any of the metabolic parameters except total cholesterol, while FLI was significantly and positively correlated with BMI, WC, TC, fasting insulin, and HOMA-IR. However, regression analysis confirmed that the HOMA-IR was the only independent variable significantly correlated with FLI in obese children. Findings of this study suggest that in obese children and adolescents (i) serum leptin and FLI were found significantly higher, while sLR level was significantly lower than the healthy children, (ii) increased FLI might be a compensatory mechanism for increasing leptin effect in peripheral tissue, (iii) FLI is a more accurate marker to evaluate leptin resistance than leptin or sLR alone, and (iv) increased FLI may contribute toward the development of hyperinsulinemia and insulin resistance.

Hormonal signaling in the gut

The gut is anatomically positioned to play a critical role in the regulation of metabolic homeostasis, providing negative feedback via nutrient sensing and local hormonal signaling. Gut hormones, such as cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1), are released following a meal and act on local receptors to regulate glycemia via a neuronal gut-brain axis. Additionally, jejunal nutrient sensing and leptin action are demonstrated to suppress glucose production, and both are required for the rapid antidiabetic effect of duodenal jejunal bypass surgery. Strategies aimed at targeting local gut hormonal signaling pathways may prove to be efficacious therapeutic options to improve glucose control in diabetes.

Age-related changes of leptin and leptin receptor variants in healthy elderly and long-lived adults

AIM

Aging is usually associated with hyperleptinemia and leptin resistance, both increasing the risk of age-related diseases. It was relevant to establish if healthily aging, non-obese individuals develop changes in leptin, the soluble leptin receptor (OB-Re), free leptin index (FLI), in methylation of the leptin receptor gene (LEPR) promoter, and in the expression of long (OB-Rb) and short (OB-Ra) leptin receptor isoforms.

METHODS

We analyzed these parameters in 38 young (aged 26.8 ± 3.6 years), 37 elderly (aged 64.7 ± 3.1 years) and 39 long-lived (aged 94.2 ± 3.7 years) healthy, non-obese Polish Caucasians.

RESULTS

In elderly men, the median concentration of leptin and the median FLI were significantly higher than in young men (P = 0.009 and P = 0.007, respectively), which was probably partly due to a higher mean body mass index of the elderly study participants. In peripheral blood mononuclear cells, the expression of functionally active OB-Rb did not depend on age or sex, whereas the expression of OB-Ra was lower in the elderly and long-lived groups than in the young group (P < 0.0001 and P = 0.002, respectively), mostly due to changes observed in women. Most likely, this age-related decrease was not due to hypermethylation of the LEPR promoter, as methylation of the +20 to +281 fragment of the CpG island did not change with age.

CONCLUSIONS

In healthy, non-obese individuals, only some elements of the leptin axis slightly change with age. On that basis, we suggest that proper function of this axis might be required for this particular phenotype of aging. The present results should, however, be replicated in prospective studies and in other ethnic groups.

Are volumetric bone mineral density and bone micro-architecture associated with leptin and soluble leptin receptor levels in adolescent idiopathic scoliosis?--A case-control study

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is associated with low bone mineral density (BMD). The underlying etiology and how it may relate to the development of osteopenia remains unknown. Leptin has been postulated as one of the etiologic factors of AIS because of its profound effects on bone metabolism and pubertal growth. Its modulator, soluble leptin receptor (sOB-R), may affect leptin bioavailability and signaling. This study aimed to investigate whether serum leptin and sOB-R levels may be associated with bone quality, and whether these relationships may differ between young adolescent girls with and without AIS.

METHODS

This was a case-control study involving 94 newly diagnosed AIS girls (Cobb angle 12-48°) aged 12 to 14 years old and 87 age and gender-matched normal controls. Subjects with BMI>23.0 Kg/m(2) were excluded. Anthropometric measurements including body weight, height, arm span and sitting height were taken. Serum total leptin and sOB-R were assayed with ELISA. Non-dominant distal radius was scanned with High Resolution pQCT for assessing bone quality in terms of bone morphometry, volumetric BMD (vBMD) and trabecular bone micro-architecture.

RESULTS

Compared with normal controls, AIS girls had numerically higher sOB-R (p = 0.006), lower average vBMD (p = 0.048), lower cortical vBMD (p = 0.029), higher cortical bone perimeter (p = 0.014) and higher trabecular area (p = 0.027), but none remained statistically significant after the Hochberg-Benjamini procedure. Correlation analysis on serum leptin level indicated that distinctive correlations with trabecular bone parameters occurred only in AIS.

CONCLUSION

This study showed that bone quality in AIS girls was deranged as compared with controls. In addition, the distinct differences in correlation pattern between leptin and trabecular bone parameters indicated possible abnormalities in bone metabolism and dysfunction of the leptin signaling pathway in AIS.

Leptin signaling in skeletal muscle after bed rest in healthy humans

PURPOSE

This study aimed at determining the effects of bed rest on the skeletal muscle leptin signaling system.

METHODS

Deltoid and vastus lateralis muscle biopsies and blood samples were obtained from 12 healthy young men (mean ± SD, BMI 22.8 ± 2.7 kg/m(2)) before and after 7 days of bed rest. Leptin receptor isoforms (OB-Rs), suppressor of cytokine signaling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) protein expression and signal transducer and activator of transcription 3 (STAT3) phosphorylation were analyzed by Western blot.

RESULTS

After bed rest basal insulin concentration was increased by 53% (P < 0.05), the homeostasis model assessment (HOMA) by 40% (P < 0.05), and serum leptin concentration by 35% (P < 0.05) with no changes in body fat mass. Although the soluble isoform of the leptin receptor (s-OBR) remained unchanged, the molar excess of leptin over sOB-R was increased by 1.4-fold after bed rest (P < 0.05). OB-Rs and SOCS3 protein expression, and STAT3 phosphorylation level remained unaffected in deltoid and vastus lateralis by bed rest, as PTP1B in the deltoid. PTP1B was increased by 90% with bed rest in the vastus lateralis (P < 0.05). There was a linear relationship between the increase in vastus lateralis PTP1B and the increase in both basal insulin concentrations (r = 0.66, P < 0.05) and HOMA (r = 0.68, P < 0.05) with bed rest.

CONCLUSIONS

One week of bed rest is associated with increased leptin levels without augmenting STAT3 phosphorylation indicating some degree of leptin resistance in skeletal muscle, which can be explained, at least in part, by an elevation of PTP1B protein content in the vastus lateralis muscle.

Direct and indirect effects of leptin on adipocyte metabolism

Leptin is hypothesized to function as a negative feedback signal in the regulation of energy balance. It is produced primarily by adipose tissue and circulating concentrations correlate with the size of body fat stores. Administration of exogenous leptin to normal weight, leptin responsive animals inhibits food intake and reduces the size of body fat stores whereas mice that are deficient in either leptin or functional leptin receptors are hyperphagic and obese, consistent with a role for leptin in the control of body weight. This review discusses the effect of leptin on adipocyte metabolism. Because adipocytes express leptin receptors there is the potential for leptin to influence adipocyte metabolism directly. Adipocytes also are insulin responsive and receive sympathetic innervation, therefore leptin can also modify adipocyte metabolism indirectly. Studies published to date suggest that direct activation of adipocyte leptin receptors has little effect on cell metabolism in vivo, but that leptin modifies adipocyte sensitivity to insulin to inhibit lipid accumulation. In vivo administration of leptin leads to a suppression of lipogenesis, an increase in triglyceride hydrolysis and an increase in fatty acid and glucose oxidation. Activation of central leptin receptors also contributes to the development of a catabolic state in adipocytes, but this may vary between different fat depots. Leptin reduces the size of white fat depots by inhibiting cell proliferation both through induction of inhibitory circulating factors and by contributing to sympathetic tone which suppresses adipocyte proliferation. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Impact of leptin receptor gene variants on risk of non-alcoholic fatty liver disease and its interaction with adiponutrin gene

BACKGROUND AND AIM

Genetic polymorphism has been implicated as a factor for the occurrence of non-alcoholic fatty liver disease (NAFLD). This study attempted to assess whether polymorphisms in the leptin receptor (LEPR) gene and its combined effect with patatin-like phospholipase domain-containing protein 3 (PNPLA3/adiponutrin) are associated with risk of NAFLD.

METHODS

A total of 144 biopsy-proven NAFLD and 198 controls were genotyped using the Sequenom MassARRAY platform.

RESULTS

We observed a significant association between the LEPR rs1137100 and rs1137101 with susceptibility to NAFLD (odds ratio [OR] 1.64, 95% confidence interval [CI] 1.18-2.28, P = 0.003; and OR 1.61, 95% CI 1.11-2.34, P = 0.013, respectively) and to non-alcoholic steatohepatitis (OR 1.49, 95% CI 1.05-2.12, P = 0.026; and OR 1.57, 95% CI 1.05-2.35, P = 0.029, respectively). The LEPR rs1137100 is also associated with simple steatosis (OR 2.27, 95% CI 1.27-4.08, P = 0.006). Analysis of gene-gene interaction revealed a strong interaction between the LEPR and PNPLA3 genes (empirical P = 0.001). The joint effect of LEPR and PNPLA3 greatly exacerbated the risk of NAFLD (OR 3.73, 95% CI 1.84-7.55, P < 0.0001). The G allele of rs1137100 is associated with lower fibrosis score (OR 0.47, 95% CI 0.28-0.78, P = 0.001).

CONCLUSIONS

We report an association between variants of LEPR rs1137100 and rs1137101 with risk of NAFLD. This study suggests that rs1137100, specifically the G allele, is associated with a less severe form of liver disease in patients with NAFLD. The interaction between LEPR and PNPLA3 genes showed increased risk of NAFLD compared to either gene alone.

Associations of testosterone and sex hormone binding globulin with adipose tissue hormones in midlife women

OBJECTIVE

Regulators of adipose tissue hormones remain incompletely understood, but may include sex hormones. As adipose tissue hormones have been shown to contribute to numerous metabolic and cardiovascular disorders, understanding their regulation in midlife women is of clinical importance. Therefore, we assessed the associations between testosterone (T) and sex hormone binding globulin (SHBG) with leptin, high molecular weight (HMW) adiponectin, and the soluble form of the leptin receptor (sOB-R) in healthy midlife women.

DESIGN AND METHODS

Cross-sectional analyses were performed using data from 1,881 midlife women (average age 52.6 (±2.7) years) attending the sixth Annual follow-up visit of the multiethnic Study of Women's Health Across the Nation.

RESULTS

T was weakly negatively associated with both HMW adiponectin and sOB-R (r = -0.12 and r = -0.10, respectively; P < 0.001 for both), and positively associated with leptin (r = 0.17; P < 0.001). SHBG was more strongly and positively associated with both HMW adiponectin and sOB-R (r = 0.29 and r = 0.24, respectively; P < 0.001 for both), and more strongly and negatively associated with leptin (r = -0.27; P < 0.001). Adjustment for fat mass, insulin resistance, or waist circumference only partially diminished associations with HMW adiponectin and sOB-R, but attenuated associations with leptin. In conclusion, in these midlife women, lower SHBG values, and to a lesser extent, higher T levels, were associated with lower, or less favorable, levels of adiponectin and sOB-R, independent of fat mass.

CONCLUSIONS

These data suggest that variation in these adipose hormones resulting from lower SHBG levels, and possibly, though less likely, greater androgenicity, may contribute to susceptibility for metabolic and cardiovascular outcomes during midlife in women.

Molecular pathways: adiponectin and leptin signaling in cancer

The increasing percentage of obese individuals in the population and its independent association of increased risk for the development of cancer have heightened the necessity to understand the molecular mechanisms that underlie this connection. The deregulation of adipokines in the setting of obesity and their impact on cancer progression and metastasis is one such area of research. Adipokines are bioactive proteins that mediate metabolism, inflammation, angiogenesis, and proliferation. Altered levels of adipokines or their cognate receptors in cancers can ultimately lead to an imbalance in downstream molecular pathways. Discovery of adipokine receptors in various cancers has highlighted the potential for novel therapeutic targets. Leptin and adiponectin represent two adipokines that elicit generally opposing molecular effects. Epidemiologic studies have highlighted associations between increased serum leptin levels and increased tumor growth, whereas adiponectin exhibits an inverse correlation with cancer development. This review addresses the current level of understanding of molecular pathways activated by adiponectin and leptin to identify the areas of intervention and facilitate advancement in the field.

TNF-α up-regulates protein level and cell surface expression of the leptin receptor by stimulating its export via a PKC-dependent mechanism

Increasing evidence suggests that inflammation/cytokines may modulate hypothalamic responses to leptin, which is a key regulator of energy homeostasis and inflammatory/stress responses. We investigated a possible role of TNF-α, a key early mediator of inflammation, in regulating the expression and trafficking of the long-isoform leptin receptor (LEPRb), the primary mediator of leptin signaling, in cultured cells. We found that TNF-α in a wide range of concentrations up-regulated LEPRb protein level and soluble LEPR (sLEPR) release via ectodomain shedding of LEPRb in multiple cell types, including neuronal cells. TNF-α also acutely increased LEPRb cell surface expression and leptin-induced STAT3 phosphorylation. In contrast, TNF-α had no significant effects on the protein level or cell surface expression of several other transmembrane proteins, including the transferrin receptor and cadherin. The stimulatory effects of TNF-α on LEPRb cell surface expression and sLEPR release were not dependent on de novo protein synthesis or functional lysosomes but were blocked by brefeldin A, suggesting that an intact Golgi or continuous endoplasmic reticulum to Golgi transport of newly synthesized proteins is required for these effects. However, TNF-α did not increase the half-life of cell surface LEPRb. Protein kinase C (PKC) inhibitor GF109203X abrogated the effects of TNF-α, whereas the pan-PKC activator phorbol 12-myristate 13-acetate mimicked the TNF-α effects. Taken together, our results suggest that TNF-α, via activation of PKC, regulates anterograde trafficking and/or degradation of LEPRb in the biosynthetic pathway, leading to concomitant increases in LEPRb protein level, cell surface expression, and sLEPR production. The finding that LEPRb cell surface expression and sLEPR production, key modulators of leptin sensitivity and bioavailability, are direct targets of TNF-α signaling could have a potentially important implication in the regulation of leptin signaling activity in different pathophysiological conditions as diverse as obesity and sepsis.

Clinical impact of the leptin to soluble leptin receptor ratio on subclinical carotid atherosclerosis in patients with type 2 diabetes

AIM

The adipocyte-derived hormone leptin plays a key role in the regulation of food intake and energy expenditure. Recent studies have suggested that leptin is also involved in the pathogenesis of obesity-associated atherosclerosis and cardiovascular disease. In this study, we investigated the associations of leptin and the soluble leptin receptor (sOb-R) with atherosclerosis in patients with type 2 diabetes.

METHODS

Three hundred seventeen type 2 diabetic subjects were enrolled in this cross-sectional study. Fasting plasma leptin and sOb-R concentrations were measured by enzyme-linked immunosorbent assays. The intima-media thickness (IMT) of the common carotid artery was measured by ultrasound.

RESULTS

The IMT was significantly associated with sOb-R concentrations, age, diabetes duration, serum creatinine (sCre) levels, and systolic blood pressure (SBP), but not with leptin concentrations or the leptin/sOb-R ratio. The concentrations of leptin (r=0.478, p<0.001) and the sOb-R (r= -0.404, p<0.001) and the leptin/sOb-R ratio (r=0.501, p<0.001) were strongly correlated with IMT in subjects treated with insulin for glycemic control, but not in those treated with diet alone or oral hypoglycemic agents. Multiple regression analysis, including age, sex, diabetes duration, body mass index, SBP, HbA1c, triglycerides, LDL-cholesterol, sCre, smoking, and insulin therapy, revealed that plasma leptin and the leptin/sOb-R ratio were independently associated with IMT in subjects treated with insulin.

CONCLUSIONS

Plasma leptin and the leptin/sOb-R ratio are associated with atherosclerosis in patients with type 2 diabetes on insulin therapy, and these associations were independent of obesity and other cardiovascular risk factors.

Leptin and soluble leptin receptor in risk of colorectal cancer in the European Prospective Investigation into Cancer and Nutrition cohort

Leptin, a peptide hormone produced primarily by the adipocytes, is hypothesized to play a role in the pathogenesis of colorectal cancer (CRC). Soluble leptin receptor (sOB-R) may regulate leptin's physiologic functions; however its relation to CRC risk is unknown. This study explored the association of leptin and sOB-R with risk of CRC in a prospective nested case-control study within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. A total of 1,129 incident CRC cases (713 colon, 416 rectal) were matched within risk sets to 1,129 controls. Conditional logistic regression was used to calculate relative risks (RR) and 95% confidence intervals (CI). After multivariable adjustment including body mass index (BMI), waist circumference, and baseline leptin concentrations, sOB-R was strongly inversely associated with CRC (RR comparing the highest quintile vs. the lowest, 0.55; 95% CI, 0.40-0.76; P(trend) = 0.0004) and colon cancer (RR, 0.42; 95% CI, 0.28-0.63, P(trend) = 0.0001); whereas no association was seen for rectal cancer (RR adjusted for BMI and waist circumference, 0.83; 95% CI, 0.48-1.44, P(trend) = 0.38). In contrast, leptin was not associated with risk of CRC (RR adjusted for BMI and waist circumference, 0.85; 95% CI, 0.56-1.29, P(trend) = 0.23). Additional adjustments for circulating metabolic biomarkers did not attenuate these results. These novel findings suggest a strong inverse association between circulating sOB-R and CRC risk, independent of obesity measures, leptin concentrations, and other metabolic biomarkers. Further research is needed to confirm the potentially important role of sOB-R in CRC pathogenesis.

Serum leptin is not correlated with body fat in severe food restriction

Leptin is an adipose-derived hormone with established roles in energy balance that can impact the response to refeeding after malnutrition. Although the amount of circulating leptin has traditionally been associated with the amount of adipose tissue, controversy exists as to whether this relationship is constant in both humans and animals and over a wide range of body composition. Our objective was to evaluate whether the leptin - body fat ratio is constant in the range of healthy to low body mass in female Wistar rats. Eight ad libitum fed (C) and eight food-restricted (FR) rats were compared over a period of four weeks. FR rats attained the target 75% of baseline body mass after the first two weeks, which was maintained for the remaining two weeks. Serum leptin and IGF-1 (ELISA) and body composition (DXA) were measured at baseline (t(0)) and once weekly for the remainder of the study (t(1)-t(4)). The leptin - body fat ratio was reduced during the two-week period of weight loss (t(0) = 0.036 ± 0.016 (ng·mL(-1))·g(-1) vs. t(1) = 0.010 ± 0.004 (ng·mL(-1))·g(-1) and t(2) = 0.015 ± 0.007 (ng·mL(-1))·g(-1), p < 0.05). Leptin concentration plateaued at its nadir (~0.24 (ng·mL(-1))·g(-1)) at fat mass < 22 g. IGF-1 was correlated with lean mass (r = 0.45, p < 0.05) and fat mass (r = 0.58, p < 0.05), regardless of body mass. We concluded that the leptin - body fat ratio was reduced early in food restriction and the correlation between these two variables was absent at low body fat.

Novel regulatory mechanisms for generation of the soluble leptin receptor: implications for leptin action

BACKGROUND

The adipokine leptin realizes signal transduction via four different membrane-anchored leptin receptor (Ob-R) isoforms in humans. However, the amount of functionally active Ob-R is affected by constitutive shedding of the extracellular domain via a so far unknown mechanism. The product of the cleavage process the so-called soluble leptin receptor (sOb-R) is the main binding protein for leptin in human blood and modulates its bioavailability. sOb-R levels are differentially regulated in metabolic disorders like type 1 diabetes mellitus or obesity and can, therefore, enhance or reduce leptin sensitivity.

METHODOLOGY/PRINCIPAL FINDINGS

To describe mechanisms of Ob-R cleavage and to investigate the functional significance of differential sOb-R levels we established a model of HEK293 cells transiently transfected with different human Ob-R isoforms. Using siRNA knockdown experiments we identified ADAM10 (A Disintegrin And Metalloproteinase 10) as a major protease for constitutive and activated Ob-R cleavage. Additionally, the induction of lipotoxicity and apoptosis led to enhanced shedding shown by increased levels of the soluble leptin receptor (sOb-R) in cell supernatants. Conversely, high leptin concentrations and ER stress reduced sOb-R levels. Decreased amounts of sOb-R due to ER stress were accompanied by impaired leptin signaling and reduced leptin binding.

CONCLUSIONS

Lipotoxicity and apoptosis increased Ob-R cleavage via ADAM10-dependent mechanisms. In contrast high leptin levels and ER stress led to reduced sOb-R levels. While increased sOb-R concentrations seem to directly block leptin action, reduced amounts of sOb-R may reflect decreased membrane expression of Ob-R. These findings could explain changes of leptin sensitivity which are associated with variations of serum sOb-R levels in metabolic diseases.