Leptin and leptin receptor-related monogenic obesity

Epigenetic regulation is involved in reversal of obesity

Epigenetic processes play a crucial role in mediating the impact of environmental energetic challenges, from overconsumption to starvation. Over-nutrition of energy-dense foods and sedentary lifestyles contribute to the development of obesity, characterized by excessive fat storage and impaired metabolic signaling, stemming from disrupted brain signaling. Conversely, dieting and physical activity facilitate body weight rebalancing and trigger adaptive neural responses. These adaptations involve the upregulation of neurogenesis, synaptic plasticity and optimized brain function and energy homeostasis, balanced hormone signaling, normal metabolism, and reduced inflammation. The transition of the brain from a maladaptive to an adaptive state is partially guided by epigenetic mechanisms. While epigenetic mechanisms underlying obesity-related brain changes have been described, their role in mediating the reversal of maladaptation/obesity through lifestyle interventions remains less explored. This review focuses on elucidating epigenetic mechanisms involved in hypothalamic adaptations induced by lifestyle interventions. Given that lifestyle interventions are widely prescribed and accessible approaches for weight loss and maintenance, it is our challenge to uncover epigenetic mechanisms moderating these hypothalamic-functional beneficial changes.

Low-calorie diet-induced weight loss is associated with altered brain connectivity and food desire in obesity

OBJECTIVE

The main objective of this study is to better understand the effects of diet-induced weight loss on brain connectivity in response to changes in glucose levels in individuals with obesity.

METHODS

A total of 25 individuals with obesity, among whom 9 had a diagnosis of type 2 diabetes, underwent functional magnetic resonance imaging (fMRI) scans before and after an 8-week low-calorie diet. We used a two-step hypereuglycemia clamp approach to mimic the changes in glucose levels observed in the postprandial period in combination with task-mediated fMRI intrinsic connectivity distribution (ICD) analysis.

RESULTS

After the diet, participants lost an average of 3.3% body weight. Diet-induced weight loss led to a decrease in leptin levels, an increase in hunger and food intake, and greater brain connectivity in the parahippocampus, right hippocampus, and temporal cortex (limbic-temporal network). Group differences (with vs. without type 2 diabetes) were noted in several brain networks. Connectivity in the limbic-temporal and frontal-parietal brain clusters inversely correlated with hunger.

CONCLUSIONS

A short-term low-calorie diet led to a multifaceted body response in patients with obesity, with an increase in connectivity in the limbic-temporal network (emotion and memory) and hormone and eating behavior changes that may be important for recovering the weight lost.

Genetic variants in DBC1, SIRT1, UCP2 and ADRB2 as potential biomarkers for severe obesity and metabolic complications

Introduction

Obesity is a multifactorial disease associated with the development of many comorbidities. This disease is associated with several metabolic alterations; however, it has been shown that some individuals with obesity do not exhibit metabolic syndrome. Adipose tissue neutralizes the detrimental effects of circulating fatty acids, ectopic deposition, and inflammation, among others, through its esterification into neutral lipids that are stored in the adipocyte. However, when the adipocyte is overloaded, i.e., its expansion capacity is exceeded, this protection is lost, resulting in fatty acid toxicity with ectopic fat accumulation in peripheral tissues and inflammation. In this line, this study aimed to investigate whether polymorphisms in genes that control adipose tissue fat storage capacity are potential biomarkers for severe obesity susceptibility and also metabolic complications.

Methods

This study enrolled 305 individuals with severe obesity (cases, BMI≥35 kg/m2) and 196 individuals with normal weight (controls, 18.5≤BMI≤24.9 kg/m2). Demographic, anthropometric, biochemical, and blood pressure variables were collected from the participants. Plasma levels of leptin, resistin, MCP1, and PAI1 were measured by Bio-Plex 200 Multiplexing Analyzer System. Genomic DNA was extracted and variants in DBC1 (rs17060940), SIRT1 (rs7895833 and rs1467568), UCP2 (rs660339), PPARG (rs1801282) and ADRB2 (rs1042713 and rs1042714) genes were genotyped by PCR allelic discrimination using TaqMan® assays.

Results

Our findings indicated that SIRT1 rs7895833 polymorphism was a risk factor for severe obesity development in the overdominant model. SIRT1 rs1467568 and UCP2 rs660339 were associated with anthropometric traits. SIRT1 rs1467568 G allele was related to lower medians of body adipose index and hip circumference, while the UCP2 rs660339 AA genotype was associate with increased body mass index. Additionally, DBC1 rs17060940 influenced glycated hemoglobin. Regarding metabolic alterations, 27% of individuals with obesity presented balanced metabolic status in our cohort. Furthermore, SIRT1 rs1467568 AG genotype increased 2.5 times the risk of developing metabolic alterations. No statistically significant results were observed with Peroxisome Proliferator-Activated Receptor Gama and ADRB2 polymorphisms.

Discussion/Conclusion

This study revealed that SIRT1 rs7895833 and rs1467568 are potential biomarkers for severe obesity susceptibility and the development of unbalanced metabolic status in obesity, respectively. UCP2 rs660339 and DBC1 rs17060940 also showed a significant role in obesity related-traits.

Syndromic and Monogenic Obesity: New Opportunities Due to Genetic-Based Pharmacological Treatment

Obesity is a significant health problem with a continuously increasing prevalence among children and adolescents that has become a modern pandemic during the last decades. Nowadays, the genetic contribution to obesity is well-established. For this narrative review article, we searched PubMed and Scopus databases for peer-reviewed research, review articles, and meta-analyses regarding the genetics of obesity and current pharmacological treatment, published in the English language with no time restrictions. We also screened the references of the selected articles for possible additional articles in order to include most of the key recent evidence. Our research was conducted between December 2022 and December 2023. We used the terms "obesity", "genetics", "monogenic", "syndromic", "drugs", "autosomal dominant", "autosomal recessive", "leptin-melanocortin pathway", and "children" in different combinations. Recognizing the genetic background in obesity can enhance the effectiveness of treatment. During the last years, intense research in the field of obesity treatment has increased the number of available drugs. This review analyzes the main categories of syndromic and monogenic obesity discussing current data on genetic-based pharmacological treatment of genetic obesity and highlighting the necessity that cases of genetic obesity should follow specific, pharmacological treatment based on their genetic background.

Neuroendocrinological and Clinical Aspects of Leptin

Obesity is characterized by an abnormal increase in adipose tissue mass and is regarded as a neurobehavioral as well as a metabolic disorder. Increases in body fat are caused by even slight, long-term discrepancies between energy intake and energy expenditure. It is a chronic condition linked to the metabolic syndrome, a spectrum of risky conditions, such as diabetes, high blood pressure, and heart disease. With a swiftly rising prevalence, obesity has emerged as a significant global health concern. Leptin influences the brain's neuroendocrine and metabolic processes, which is important for maintaining energy homeostasis. White adipose tissue secretes the majority of leptin, and there is a positive correlation between leptin levels in the blood and body fat percentages. The central nervous system is also modulated by leptin levels to modify energy intake and usage. The idea of an obesity cure sparked excitement after it was discovered more than 25 years ago. However, the leptin medication only effectively reduces weight in patients with congenital leptin insufficiency and not in patients with typical obesity who may also have leptin resistance. Recent research has focused on the role of leptin in managing weight reduction and preventing "yo-yo dieting". This review concentrates on the neurological effects of leptin with a focus on therapeutic and diagnostic applications, particularly for childhood obesity.

The Next Generation Fecal Microbiota Transplantation: To Transplant Bacteria or Virome

Fecal microbiota transplantation (FMT) has emerged as a promising therapeutic approach for dysbiosis-related diseases. However, the clinical practice of crude fecal transplants presents limitations in terms of acceptability and reproductivity. Consequently, two alternative solutions to FMT are developed: transplanting bacteria communities or virome. Advanced methods for transplanting bacteria mainly include washed microbiota transplantation and bacteria spores treatment. Transplanting the virome is also explored, with the development of fecal virome transplantation, which involves filtering the virome from feces. These approaches provide more palatable options for patients and healthcare providers while minimizing research heterogeneity. In general, the evolution of the next generation of FMT in global trends is fecal microbiota components transplantation which mainly focuses on transplanting bacteria or virome.

GATA3 as an immunomodulator in obesity-related metabolic dysfunction associated with fatty liver disease, insulin resistance, and type 2 diabetes

Obesity is the leading risk factor associated with Metabolic dysfunction Associated with Fatty Liver Disease (MAFLD), Insulin Resistance (IR), and type 2 diabetes (T2DM). Notably, MAFLD affects 25% of the world's adult population, ranging from 13.5% in Africa to 31.8% in the Middle East. The prevalence of MAFLD is 80-90% in obese adults and 30-50% in patients with diabetes. According to the recent WHO update, more than 400 million people will experience T2DM by 2025. Furthermore, the worldwide obesity incidence rate has risen in the preceding years. Adipogenesis deterioration is a critical step in the induction of obesity correlated with MAFLD, IR and T2DM. The well-known transcription factor GATA3 is highly expressed in the preadipocytes-adipocytes transition of embryonic stem cells and obese people with IR. In this regard, the reduction of GATA3 improves the differentiation of adipocytes. Omental adipose tissue inflammation by upregulation of macrophages infiltration is strongly linked with body mass index in insulin tolerance of obese people. In particular, the dynamic interaction between macrophages and adipocytes significantly regulates obese adipose tissue's inflammatory status and influences IR by reducing the differentiation of adipocytes, macrophage function, and glucose transport. Emerging evidence demonstrated that GATA3 is a master regulator for macrophage polarization and infiltration. Hence, we will shed light on GATA3 as an emerging target for immunomodulation in human obesity associated with MAFLD, IR, and T2DM by reducing macrophages' recruitment and inflammation of muscles and liver.

Immunoinflammatory processes: Overlapping mechanisms between obesity and eating disorders?

Obesity and eating disorders are conditions that involve eating behaviors and are sometimes comorbid. Current evidence supports alterations in immunoinflammatory processes in both obesity and eating disorders. A plausible hypothesis is that immunoinflammatory processes may be involved in the pathophysiology of obesity and eating disorders. The aim of this review is to highlight the link between obesity and eating disorders, with a particular focus on immunoinflammatory processes. First, the relation between obesity and eating disorders will be presented, followed by a brief review of the literature on their association with immunoinflammatory processes. Second, developmental factors will be discussed to clarify the link between obesity, eating disorders, and immunoinflammatory processes. Genetic and epigenetic risk factors as well as the potential roles of stress pathways and early life development will be presented. Finally, implications of these findings for future research are discussed. This review highlighted biological and developmental aspects that overlap between obesity and EDs, emphasizing the need for biopsychosocial research approaches to advance current knowledge and practice in these fields.

Historical and cultural aspects of obesity: From a symbol of wealth and prosperity to the epidemic of the 21st century

World Health Organization defines obesity as abnormal or excess adipose tissue accumulation. Nowadays, this condition is a serious threat to the public health in most countries around the world. Obesity adversely affects physical, mental, and in most cultures, social well-being. However, throughout the ages-from ancient times to the 21st century-this condition has been subject to various interpretations. As a matter of fact, obesity has not always been regarded as a disease. For many decades, excessive body weight has been considered rather a symbol of health. It was a marker of wealth and prosperity, as well as a sign of high social status. The centuries that passed on the development of science and medicine have gradually changed its face, but significant progress in understanding the causes and consequences of obesity has been made in the last 30 years. This paper presents the historical outline of obesity and its treatment from ancient times to the present-from its affirmation to the epidemic in the late 20th and 21st century.

The Interaction of Obesity and Reproductive Function in Adolescents

Obesity is increasing worldwide, including in pediatrics. Adequate nutrition is required for initiation of menses, and there is a clear secular trend toward earlier pubertal onset and menarche in females in countries around the globe. Similar findings of earlier pubertal start are suggested in males. However, as individuals and populations have crossed into over-nutritional states including overweight and obesity, the effect of excess weight on disrupting reproductive function has become apparent. Hypothalamic hypogonadism and polycystic ovary syndrome are two conditions where reproductive function appears to directly relate to excess weight. Clinical findings in individuals with certain polygenic and monogenic obesity syndromes, which also have reproductive disruptions, have helped elucidate neurologic pathways that are common to both. Clinical endocrinopathies such as hypothyroidism or panhypopituitarism also aide in the understanding of the role of the endocrine system in weight gain. Understanding the intersection of obesity and reproductive function may lead to future therapies which can treat both conditions.

Body mass index and adipose distribution have opposing genetic impacts on human blood traits

Body mass index (BMI), hyperlipidemia, and truncal adipose distribution concordantly elevate cardiovascular disease risks, but have unknown genetic effects on blood trait variation. Using Mendelian randomization, we define unexpectedly opposing roles for increased BMI and truncal adipose distribution on blood traits. Elevated genetically determined BMI and lipid levels decreased hemoglobin and hematocrit levels, consistent with clinical observations associating obesity and anemia. We found that lipid-related effects were confined to erythroid traits. In contrast, BMI affected multiple blood lineages, indicating broad effects on hematopoiesis. Increased truncal adipose distribution opposed BMI effects, increasing hemoglobin and blood cell counts across lineages. Conditional analyses indicated genes, pathways, and cell types responsible for these effects, including Leptin Receptor and other blood cell-extrinsic factors in adipocytes and endothelium that regulate hematopoietic stem and progenitor cell biology. Our findings identify novel roles for obesity on hematopoiesis, including a previously underappreciated role for genetically determined adipose distribution in determining blood cell formation and function.

Genetics, epigenetics and transgenerational transmission of obesity in children

Sedentary lifestyle and consumption of high-calorie foods have caused a relentless increase of overweight and obesity prevalence at all ages. Its presently epidemic proportion is disquieting due to the tight relationship of obesity with metabolic syndrome and several other comorbidities which do call for urgent workarounds. The usual ineffectiveness of present therapies and failure of prevention campaigns triggered overtime a number of research studies which have unveiled some relevant aspects of obesity genetic and epigenetic inheritable profiles. These findings are revealing extremely precious mainly to serve as a likely extra arrow to allow the clinician's bow to achieve still hitherto unmet preventive goals. Evidence now exists that maternal obesity/overnutrition during pregnancy and lactation convincingly appears associated with several disorders in the offspring independently of the transmission of a purely genetic predisposition. Even the pre-conception direct exposure of either father or mother gametes to environmental factors can reprogram the epigenetic architecture of cells. Such phenomena lie behind the transfer of the obesity susceptibility to future generations through a mechanism of epigenetic inheritance. Moreover, a growing number of studies suggests that several environmental factors such as maternal malnutrition, hypoxia, and exposure to excess hormones and endocrine disruptors during pregnancy and the early postnatal period may play critical roles in programming childhood adipose tissue and obesity. A deeper understanding of how inherited genetics and epigenetics may generate an obesogenic environment at pediatric age might strengthen our knowledge about pathogenetic mechanisms and improve the clinical management of patients. Therefore, in this narrative review, we attempt to provide a general overview of the contribution of heritable genetic and epigenetic patterns to the obesity susceptibility in children, placing a particular emphasis on the mother-child dyad.

Leptin and Obesity: Role and Clinical Implication

The peptide hormone leptin regulates food intake, body mass, and reproductive function and plays a role in fetal growth, proinflammatory immune responses, angiogenesis and lipolysis. Leptin is a product of the obese (ob) gene and, following synthesis and secretion from fat cells in white adipose tissue, binds to and activates its cognate receptor, the leptin receptor (LEP-R). LEP-R distribution facilitates leptin's pleiotropic effects, playing a crucial role in regulating body mass via a negative feedback mechanism between adipose tissue and the hypothalamus. Leptin resistance is characterized by reduced satiety, over-consumption of nutrients, and increased total body mass. Often this leads to obesity, which reduces the effectiveness of using exogenous leptin as a therapeutic agent. Thus, combining leptin therapies with leptin sensitizers may help overcome such resistance and, consequently, obesity. This review examines recent data obtained from human and animal studies related to leptin, its role in obesity, and its usefulness in obesity treatment.

Protective effect of a novel phosphodiesterase 4 selective inhibitor, compound A, in diabetic nephropathy model mice

Phosphodiesterase subtype 4 (PDE4) hydrolyzes cyclic AMP (cAMP), a secondary messenger that mediates intracellular signaling, and plays key roles in inflammatory and profibrotic responses. Clinical benefits of pentoxifylline, a non-selective PDE inhibitor, have been reported in patients with kidney disease. Here, we identified compound A as a potent and selective PDE4 inhibitor and evaluated its potential as a novel therapeutic agent for diabetic nephropathy (DN). To determine its in vivo efficacy on DN, uninephrectomized (UNx-) db/db mice and KKAy mice were used as DN mice models. Eight-week repeated dosing with compound A (1-10 mg/kg, QD, p.o.) showed dose-dependent and significant suppressive effects on glycosylated hemoglobin (GHb) and urinary albumin/creatinine ratio (UACR) in UNx-db/db mice. These effects are more potent than irbesartan, a clinically approved angiotensin II receptor blocker of DN. Moreover, compound A suppressed pro-fibrotic and pro-inflammatory marker mRNAs and increased anti-reactive oxygen species marker mRNAs in the kidneys of UNx-db/db mice. The similar effect of compound A on UACR was also demonstrated by 8-week repeated dose in KKAy mice, another model for DN with intact leptin axis. Taken together, these data suggest that the PDE4-selective inhibitor compound A has potential as a new therapeutic agent for DN with multiple mechanisms of action including anti-diabetic, anti-fibrotic, and anti-reactive oxygen species effects.

Metabolic Diseases and Down Syndrome: How Are They Linked Together?

Down syndrome is a genetic disorder caused by the presence of a third copy of chromosome 21, associated with intellectual disabilities. Down syndrome is associated with anomalies of both the nervous and endocrine systems. Over the past decades, dramatic advances in Down syndrome research and treatment have helped to extend the life expectancy of these patients. Improved life expectancy is obviously a positive outcome, but it is accompanied with the need to address previously overlooked complications and comorbidities of Down syndrome, including obesity and diabetes, in order to improve the quality of life of Down syndrome patients. In this focused review, we describe the associations between Down syndrome and comorbidities, obesity and diabetes, and we discuss the understanding of proposed mechanisms for the association of Down syndrome with metabolic disorders. Drawing molecular mechanisms through which Type 1 diabetes and Type 2 diabetes could be linked to Down syndrome could allow identification of novel drug targets and provide therapeutic solutions to limit the development of metabolic and cognitive disorders.

Faecal virome transplantation decreases symptoms of type 2 diabetes and obesity in a murine model

OBJECTIVE

Development of obesity and type 2 diabetes (T2D) are associated with gut microbiota (GM) changes. The gut viral community is predominated by bacteriophages (phages), which are viruses that attack bacteria in a host-specific manner. The antagonistic behaviour of phages has the potential to alter the GM. As a proof-of-concept, we demonstrate the efficacy of faecal virome transplantation (FVT) from lean donors for shifting the phenotype of obese mice into closer resemblance of lean mice.

DESIGN

The FVT consisted of viromes with distinct profiles extracted from the caecal content of mice from different vendors that were fed a low-fat (LF) diet for 14 weeks. Male C57BL/6NTac mice were divided into five groups: LF (as diet control), high-fat (HF) diet, HF+ampicillin (Amp), HF+Amp+FVT and HF+FVT. At weeks 6 and 7 of the study, the HF+FVT and HF+Amp+FVT mice were treated with FVT by oral gavage. The Amp groups were treated with Amp 24 hours prior to first FVT treatment.

RESULTS

Six weeks after first FVT, the HF+FVT mice showed a significant decrease in weight gain compared with the HF group. Further, glucose tolerance was comparable between the LF and HF+FVT mice, while the other HF groups all had impaired glucose tolerance. These observations were supported by significant shifts in GM composition, blood plasma metabolome and expression levels of genes associated with obesity and T2D development.

CONCLUSIONS

Transfer of caecal viral communities from mice with a lean phenotype into mice with an obese phenotype led to reduced weight gain and normalised blood glucose parameters relative to lean mice. We hypothesise that this effect is mediated via FVT-induced GM changes.

The Genetic Basis of Obesity and Related Metabolic Diseases in Humans and Companion Animals

Obesity is one of the most prevalent health conditions in humans and companion animals globally. It is associated with premature mortality, metabolic dysfunction, and multiple health conditions across species. Obesity is, therefore, of importance in the fields of medicine and veterinary medicine. The regulation of adiposity is a homeostatic process vulnerable to disruption by a multitude of genetic and environmental factors. It is well established that the heritability of obesity is high in humans and laboratory animals, with ample evidence that the same is true in companion animals. In this review, we provide an overview of how genes link to obesity in humans, drawing on a wealth of information from laboratory animal models, and summarise the mechanisms by which obesity causes related disease. Throughout, we focus on how large-scale human studies and niche investigations of rare mutations in severely affected patients have improved our understanding of obesity biology and can inform our ability to interpret results of animal studies. For dogs, cats, and horses, we compare the similarities in obesity pathophysiology to humans and review the genetic studies that have been previously reported in those species. Finally, we discuss how veterinary genetics may learn from humans about studying precise, nuanced phenotypes and implementing large-scale studies, but also how veterinary studies may be able to look past clinical findings to mechanistic ones and demonstrate translational benefits to human research.

Leptin: Master Regulator of Biological Functions that Affects Breathing

Obesity is a global epidemic in developed countries accounting for many of the metabolic and cardiorespiratory morbidities that occur in adults. These morbidities include type 2 diabetes, sleep-disordered breathing (SDB), obstructive sleep apnea, chronic intermittent hypoxia, and hypertension. Leptin, produced by adipocytes, is a master regulator of metabolism and of many other biological functions including central and peripheral circuits that control breathing. By binding to receptors on cells and neurons in the brainstem, hypothalamus, and carotid body, leptin links energy and metabolism to breathing. In this comprehensive article, we review the central and peripheral locations of leptin's actions that affect cardiorespiratory responses during health and disease, with a particular focus on obesity, SDB, and its effects during early development. Obesity-induced hyperleptinemia is associated with centrally mediated hypoventilation with decrease CO₂ sensitivity. On the other hand, hyperleptinemia augments peripheral chemoreflexes to hypoxia and induces sympathoexcitation. Thus, "leptin resistance" in obesity is relative. We delineate the circuits responsible for these divergent effects, including signaling pathways. We review the unique effects of leptin during development on organogenesis, feeding behavior, and cardiorespiratory responses, and how undernutrition and overnutrition during critical periods of development can lead to cardiorespiratory comorbidities in adulthood. We conclude with suggestions for future directions to improve our understanding of leptin dysregulation and associated clinical diseases and possible therapeutic targets. Lastly, we briefly discuss the yin and the yang, specifically the contribution of relative adiponectin deficiency in adults with hyperleptinemia to the development of metabolic and cardiovascular disease. © 2020 American Physiological Society. Compr Physiol 10:1047-1083, 2020.

Whole Egg Consumption Decreases Cumulative Weight Gain in Diet-Induced Obese Rats

BACKGROUND

Whole egg (WE) consumption has been demonstrated to attenuate body weight (BW) gain and adiposity in genetic animal models of type 2 diabetes (T2D). This finding was accompanied by increased food consumption.

OBJECTIVES

This study aimed to examine the effects of long-term WE intake on BW gain, fat distribution, and food intake in a rat model of diet-induced obesity (DIO).

METHODS

Male Sprague Dawley rats (n = 24) were obtained at 5 wk of age and were randomly weight-matched across 1 of 4 dietary intervention groups (6 rats per group): a casein-based diet (CAS), a high-fat high-sucrose CAS diet (HFHS CAS), a whole egg-based diet (EGG), or a high-fat high-sucrose EGG diet (HFHS EGG). All diets provided 20% (w/w) protein and were provided for 33 wk. HFHS diets provided ∼61% of kilocalories from fat and 10% from sucrose. Daily weight gain and food intake were recorded, biochemical parameters were measured via ELISA, and epididymal fat pad weights were recorded at the end of the study.

RESULTS

At 33 wk, cumulative BW gain in DIO rats fed HFHS EGG resulted in 23% lower weight gain compared with DIO rats fed HFHS CAS (P < 0.0001), but no significant differences in BW gain were observed between the HFHS EGG group and the control EGG and CAS groups (P = 0.71 and P = 0.61, respectively). Relative food intake (grams per kilogram BW) was 23% lower (P < 0.0001) in rats fed HFHS CAS compared with CAS, whereas there was no difference in food intake within the EGG dietary groups. DIO rats fed HFHS EGG exhibited a 22% decrease in epididymal fat weight compared with their counterparts fed the HFHS CAS.

CONCLUSIONS

Our data demonstrate that consumption of a WE-based diet reduced BW gain and visceral fat in the DIO rat, similar to our previous findings in a genetic rat model with T2D.

The Potential Role of Activating the ATP-Sensitive Potassium Channel in the Treatment of Hyperphagic Obesity

To evaluate the potential role of ATP-sensitive potassium (K_ATP) channel activation in the treatment of hyperphagic obesity, a PubMed search was conducted focused on the expression of genes encoding the K_ATP channel, the response to activating the K_ATP channel in tissues regulating appetite and the establishment and maintenance of obesity, the evaluation of K_ATP activators in obese hyperphagic animal models, and clinical studies on syndromic obesity. K_ATP channel activation is mechanistically involved in the regulation of appetite in the arcuate nucleus; the regulation of hyperinsulinemia, glycemic control, appetite and satiety in the dorsal motor nucleus of vagus; insulin secretion by β-cells; and the synthesis and β-oxidation of fatty acids in adipocytes. K_ATP channel activators have been evaluated in hyperphagic obese animal models and were shown to reduce hyperphagia, induce fat loss and weight loss in older animals, reduce the accumulation of excess body fat in growing animals, reduce circulating and hepatic lipids, and improve glycemic control. Recent experience with a K_ATP channel activator in Prader-Willi syndrome is consistent with the therapeutic responses observed in animal models. K_ATP channel activation, given the breadth of impact and animal model and clinical results, is a viable target in hyperphagic obesity.

Molecular pathway analysis associates alterations in obesity-related genes and antipsychotic-induced weight gain

OBJECTIVE

Antipsychotics often induce excessive weight gain. We hypothesised that individuals with genetic variations related to known obesity-risk genes have an increased risk of excessive antipsychotic-induced weight gain (AIWG). This hypothesis was tested in a subset of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) trial data set.

METHODS

The CATIE trial compared effects and side effects of five different antipsychotics through an 18-month period. Based on the maximum weight gain recorded, excessive weight gain was defined as >7% weight gain. Cytoscape and GeneMANIA were instrumental in composing a molecular pathway from eight selected genes linked to obesity. Genetic information on a total of 495.172 single-nucleotide polymorphisms (SNPs) were available from 765 (556 males) individuals. Enrichment test was conducted through ReactomePA and Bioconductor. A permutation test was performed, testing the generated pathway against 105 permutated pathways (p ≤ 0.05). In addition, a standard genome-wide association study (GWAS) analysis was performed.

RESULT

GWAS analysis did not detect significant differences related to excessive weight gain. The pathway generated contained 28 genes. A total of 2067 SNPs were significantly expressed (p < 0.01) within this pathway when comparing excessive weight gainers to the rest of the sample. Affected genes including PPARG and PCSK1 were not previously related to treatment-induced weight gain.

CONCLUSIONS

The molecular pathway composed from high-risk obesity genes was shown to overlap with genetics of patients who gained >7% weight gain during the CATIE trial. This suggests that genes related to obesity compose a pathway of increased risk of excessive AIWG. Further independent analyses are warranted that may confirm or clarify the possible reasoning behind.

Dysregulation of Kisspeptin and Leptin, as Anorexigenic Agents, Plays Role in the Development of Obesity in Postmenopausal Women

During the menopausal period, women have a higher tendency to develop obesity and any other metabolic syndromes. Dysregulation of leptin and kisspeptin signaling as anorexigenic agents is believed to be the connection between metabolic disorders and altered reproductive function. Therefore, this study aimed at investigating the association between leptin, soluble leptin receptor (sOBR), free leptin index, kisspeptin concentrations, and body mass index (BMI) in postmenopausal women. A cross-sectional study was carried out among 171 postmenopausal women aged 40-75 years from 2017 to 2018. Subjects were assigned into 2 groups according to their BMIs: obese group (84 subjects) and nonobese group (87 subjects). In addition to anthropometric measurement, blood sample was collected from each subject for leptin, sOBR, free leptin index (FLI), and kisspeptin evaluation. Bivariate and correlation analysis discovered that leptin and FLI were positively correlated with BMI, while sOBR and kisspeptin were negatively correlated with BMI. Among those variables, multivariate analysis found that leptin, sOBR, and kisspeptin were independently associated with obesity. Therefore, it can be concluded that higher serum leptin concentration and FLI, as well as lower serum sOBR and kisspeptin concentrations, are significantly associated with obesity in postmenopausal women.

Associations of leptin and leptin receptor genetic variants with coronary artery disease: a meta-analysis

Background: Some pilot studies already tried to investigate potential associations of leptin (LEP) and LEP receptor (LEPR) variants with coronary artery disease (CAD). However, the results of these studies were not consistent. Thus, we performed the present meta-analysis to explore associations between LEP/LEPR variants and CAD in a larger pooled population.

Methods: Systematic literature research of PubMed, Web of Science, Embase and CNKI was performed to identify eligible case–control studies on associations between LEP/LEPR variants and CAD. The initial search was conducted in September 2018 and the latest update was performed in December 2018. Q test and I² statistic were employed to assess between-study heterogeneities. If probability value(P-value) of Q test was less than 0.1 or I² was greater than 50%, random-effect models (REMs) would be used to pool the data. Otherwise, fixed-effect models (FEMs) would be applied for synthetic analyses.

Results: A total of ten studies published between 2006 and 2018 were eligible for analyses (1989 cases and 2601 controls). Pooled analyses suggested that LEP rs7799039 variant was significantly associated with CAD under over-dominant model (P=0.0007, odds ratio (OR) = 1.36, 95% confidence interval (CI): 1.14–1.63, I² = 41%, FEM) in overall population, and this significant finding was further confirmed in East Asians in subsequent subgroup analyses. However, no positive findings were observed for LEPR rs1137100 and rs1137101 variants in overall and subgroup analyses.

Conclusions: Our meta-analysis suggested that LEP rs7799039 variant might affect individual susceptibility to CAD.

Identification of novel LEPR mutations in Pakistani families with morbid childhood obesity

Background

Mutations in the genes encoding leptin (LEP), the leptin receptor (LEPR), and the melanocortin 4 receptor (MC4R) are known to cause severe early-onset childhood obesity. The aim of the current study was to examine the prevalence of damaging LEP, LEPR, and MC4R mutations in Pakistani families having a recessive heritance of early-onset obesity.

Methods

Using targeted resequencing, the presence of rare mutations in LEP, LEPR, and MC4R, was investigated in individuals from 25 families suspected of having autosomal recessive early-onset obesity. Segregation patterns of variants were assessed based on chip-based genotyping.

Results

Homozygous LEPR variants were identified in two probands. One carried a deletion (c.3260AG) resulting in the frameshift mutation p.Ser1090Trpfs*6, and the second carried a substitution (c.2675C > G) resulting in the missense mutation p.Pro892Arg. Both mutations were located within regions of homozygosity shared only among affected individuals. Both probands displayed early-onset obesity, hyperphagia and diabetes. No mutations were found in LEP and MC4R.

Conclusions

The current study highlights the implication of LEPR mutations in cases of severe early-onset obesity in consanguineous Pakistani families. Through targeted resequencing, we identified novel damaging mutations, and our approach may therefore be utilized in clinical testing or diagnosis of known forms of monogenic obesity with the aim of optimizing obesity treatment.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0710-x) contains supplementary material, which is available to authorized users.

Contribution of obesity as an effect regulator to an association between serum leptin and incident metabolic syndrome

BACKGROUND

We investigated whether serum leptin can be a predictor for incident cases of MetS in a population-based study.

METHODS

This is a prospective cohort study of 1590 adults aged between 40 and 70 years, who did not have MetS in 2005-2008 (at baseline) and 2008-2011 (follow-up). The baseline serum leptin concentrations were measured by radioimmunoassay.

RESULTS

During an average of 2.8 years of follow-up, 113 men (17.1%) and 148 women (15.9%) developed MetS. In multivariable adjusted models, the odds ratio of incident MetS when comparing the lowest to the highest quartiles of leptin levels was 3.17 in men and 2.79 in women; nevertheless, the significance disappeared after adjusting for the body mass index (BMI). In subsidiary analyses by BMI, logistic regression analysis showed that subjects with the highest tertile of serum leptin level were 3.04 and 2.12 times more likely to have MetS than those with the lowest tertile in lean subjects (OR 3.04; 95% CI 1.44-6.41; p = .004 in men vs. OR 2.12; 95% CI 1.06-4.25; p = .036 in women, respectively).

CONCLUSIONS

Obesity is an effect regulator, which can predict an association between increased serum leptin level and the incidence of MetS in lean subjects.

Functional and Phenotypic Characteristics of Human Leptin Receptor Mutations

Several case series of extreme early-onset obesity due to mutations in the human leptin receptor (LEPR) gene have been reported. In this review we summarize published functional and phenotypic data on mutations in the human LEPR gene causing severe early-onset obesity. Additionally, we included data on six new cases from our obesity center. Literature research was performed using PubMed and OMIM. Functional relevance of mutations was estimated based on reported functional analysis, mutation size, and location, as well as phenotypic characteristics of affected patients. We identified 57 cases with 38 distinct LEPR mutations. We found severe early-onset obesity, hyperphagia, and hypogonadotropic hypogonadism as cardinal features of a complete loss of LEPR function. Other features, for example, metabolic disorders and recurring infections, were variable in manifestation. Obesity degree or other manifestations did not aggregate by genotype. Few patients underwent bariatric surgery with variable success. Most mutations occurred in the fibronectin III and cytokine receptor homology II domains, whereas none was found in cytoplasmic domain. In silico data were available for 25 mutations and in vitro data were available for four mutations, revealing residual activity in one case. By assessing provided information on the clinical phenotype, functional analysis, and character of the 38 mutations, we assume residual LEPR activity for five additional mutations. Functional in vitro analysis is necessary to confirm this assumption.

Genetics of Severe Obesity

PURPOSE OF REVIEW

This review aims to present current information on genes underlying severe obesity, with the main emphasis on the three genes LEP, LEPR and MC4R.

RECENT FINDINGS

There is a substantial amount of evidence that variants in at least ten different genes are the cause of severe monogenic obesity. The majority of these are involved in the leptin-melanocortin signalling pathway. Due to the frequency of some of the identified variants, it is clear that monogenic variants also make a significant contribution to common obesity. The artificial distinction between rare monogenic obesity and common polygenic obesity is now obsolete with the identification of MC4R variants of strong effect in the general population.

The ovarian estrogen synthesis function was impaired in Y123F mouse and partly restored by exogenous FSH supplement

BACKGROUND

LepR tyrosine site mutation mice (Y123F) exhibit decreased serum E2 levels, immature reproductive organs, infertility as well as metabolic abnormalities. Although the actions of leptin and lepR in the control of reproductive function are thought to be exerted mainly via the hypothalamic-pituitary-gonadal axis, relatively less is known regarding their local effects on the peripheral ovary, especially on steroid hormone synthesis. Meanwhile, whether the decreased fertility of Y123F mouse could be restored by gonadotropin has not been clear yet.

METHODS

The serum levels of E2, P4, FSH, LH, T and leptin of Y123F and WT mice at the age of 12 weeks were measured by enzyme-linked immunosorbent assay. Immunohistochemistry was used to compare the distribution of hormone synthases (STAR, CYP11A1, CYP19A1, HSD17B7) and FSHR in adult mouse ovaries of two genotypes. Western blot and real-time PCR were used to detect the expression levels of four ovarian hormone synthases and JAK2-STAT3 / STAT5 signaling pathway in 4 and 12 weeks old mice, as well as the effects of exogenous hFSH stimulation on hormone synthases and FSHR.

RESULTS

Compared with WT mice, the serum levels of FSH, LH and E2 in 12-week-old Y123F mice were significantly decreased; T and leptin levels were significantly increased; but there was no significant difference of serum P4 levels. STAR, CYP11A1, HSD17B7 expression levels and the phosphorylation levels of JAK2 and STAT3 were significantly decreased in adult Y123F mice, while the expression of CYP19A1 and phospho-STAT5 were significantly increased. No significant differences were found between 4-week-old Y123F and WT mice. After exogenous hFSH stimulation, E2 levels and expression of CYP19A1 and HSD17B7 were significantly higher than that in the non-stimulated state, but significant differences still existed between Y123F and WT genotype mice under the same condition.

CONCLUSIONS

Abnormal sex hormone levels of Y123F mice were due to not only decreased gonadotropin levels in the central nervous system, but also ovarian hormone synthase abnormalities in the peripheral gonads. Both FSH signaling pathway and JAK2-STAT3/STAT5 signaling pathway were involved in regulation of ovarian hormone synthases expression. Exogenous FSH just partly improved the blood E2 levels and ovarian hormone synthase expression.

Potential role of gender specific effect of leptin receptor deficiency in an extended consanguineous family with severe early-onset obesity

Congenital Leptin receptor (LEPR) deficiency is a rare genetic cause of early-onset morbid obesity characterised by severe early onset obesity, major hyperphagia, hypogonadotropic hypogonadism and immune and neuroendocrine/metabolic dysfunction. We identified a homozygous loss-of-function mutation, NM_002303.5:c.464 T > G; p.(Tyr155*), in the LEPR in an extended consanguineous family with multiple individuals affected by early-onset severe obesity and hyperphagia. Interestingly, the LEPR-deficient adult females have extremely high body mass index (BMI) with hypogonadal infertility, the BMI of the affected males began to decline around the onset of puberty (13-15 years) with fertility being preserved. These findings lead to the speculation that LEPR deficiency may have a gender-specific effect on the regulation of body weight. In order to elucidate gender-specific effects of LEPR deficiency on reproduction further investigations are needed. The limitations of this study are that our conclusion is based on observations of two males and two females. Further LEPR deficient males and females are required for comparison in order to support this finding more confidently.

Development and Characterization of a Novel Congenic Rat Strain for Obesity and Cancer Research

The association between a Western Diet and colon cancer suggests that dietary factors and/or obesity may contribute to cancer progression. Our objective was to develop a new animal model of obesity and the associated pathophysiology to investigate human cancer independent of dietary components that induce obesity. A novel congenic rat strain was established by introducing the fa allele from the Zucker rat into the Rowett Nude rat to generate a "fatty nude rat". The obese phenotype was first characterized in the new model. To then examine the utility of this model, lean and obese rats were implanted with HT-29 human colon cancer xenografts and tumor growth monitored. Fatty nude rats were visibly obese and did not develop fasting hyperglycemia. Compared to lean rats, fatty nude rats developed fasting hyperinsulinemia, glucose intolerance, and insulin resistance. Colon cancer tumor growth rate and final weight were increased (P < 0.05) in fatty nude compared to lean rats. Final tumor weight was associated with p38 kinase phosphorylation (P < 0.01) in fatty nude rats. We have established a novel model of obesity and pre-type 2 diabetes that can be used to investigate human cancer and therapeutics in the context of obesity and its associated pathophysiology.

Early-onset severe obesity due to complete deletion of the leptin gene in a boy

BACKGROUND

Monogenic obesity results from single gene mutations. Extreme obesity starting at an early age, especially in infancy, which is associated with endocrinopathy and metabolic disturbances is key to the diagnosis of monogenic obesity.

CASE PRESENTATION

A 6-month-old boy was admitted to our clinic with severe obesity and food craving. He was born with a birth weight of 3400 g to first-cousin parents. He started to gain weight at an abnormal rate at the age of 2 months. He had hyperinsulinemia, dyslipidemia and grade 2 hepatosteatosis. He had a 7-year-old, healthy brother with a normal body weight. Because of severe early-onset obesity and abnormal food addiction, his leptin level was measured and found to be 0.55 ng/mL (normal range for his age and sex is 0.7-21 ng/mL). A LEP gene mutation was screened for and a gross leptin gene deletion was detected. To date, no report on a gross deletion of the LEP gene has been published in the literature.

CONCLUSIONS

To the best of our knowledge, a gross deletion of the LEP gene has not been reported so far in the literature. Here we report a unique case with congenital leptin deficiency. Thus, clinicians should search for monogenic obesity in patients with early-onset severe obesity and endocrinopathy. Measuring the leptin level could aid clinicians to identify children with monogenic obesity.

Leptin Receptor Gene Variant rs11804091 Is Associated with BMI and Insulin Resistance in Spanish Female Obese Children: A Case-Control Study

Leptin is an endocrine hormone that has a critical role in body weight homoeostasis and mediates its effects via the leptin receptor (LEPR). Common polymorphisms in the genes coding leptin receptors have been associated with metabolic abnormalities. We assessed the association of 28 LEPR polymorphisms with body mass index (BMI) and their relationship with obesity-related phenotypes, inflammation and cardiovascular disease risk biomarkers. A multicentre case-control study was conducted in 522 children (286 with obesity and 236 with normal-BMI). All anthropometric, metabolic factors and biomarkers were higher in children with obesity except apolipoprotein (Apo)-AI, cholesterol, high-density lipoprotein cholesterol (HDL-c), and adiponectin, which were lower in the obesity group; and glucose, low-density lipoprotein cholesterol (LDL-c), and matrix metalloproteinase-9 that did not differ between groups. We identified the associations between rs11208659, rs11804091, rs10157275, rs9436303 and rs1627238, and BMI in the whole population, as well as the association of rs11804091, rs10157275, and rs1327118 with BMI in the female group, although only the rs11804091 remained associated after Bonferroni correction (p = 0.038). This single nucleotide polymorphisms (SNP) was also associated with insulin (p = 0.004), homeostasis model assessment for insulin resistance (HOMA-IR) (p = 0.006), quantitative insulin sensitivity check index (QUICKI) (p = 0.005) and adiponectin (p = 0.046) after adjusting for age, Tanner stage and BMI. Our results show a sex-specific association between the rs11804091 and obesity suggesting an influence of this SNP on insulin resistance.

Novel Leptin Receptor Mutations Identified in Two Girls with Severe Obesity Are Associated with Increased Bone Mineral Density

BACKGROUND

Recessive mutations in the leptin receptor (LEPR) are a rare cause of hyperphagia and severe early-onset obesity. To date, the phenotype has only been described in 25 obese children, some of whom also had altered immune function, hypogonadotropic hypogonadism, reduced growth hormone secretion, hypothalamic hypothyroidism or reduced adult height. We provide a detailed description of the phenotype of 2 affected girls to add to this knowledge.

METHODS

Whole-exome sequencing and targeted sequencing were used to detect the LEPR mutations. RNA analysis was performed to assess the effect of splice-site mutations.

RESULTS

In 2 unrelated girls with severe obesity, three novel LEPR mutations were detected. Longitudinal growth data show normal childhood growth, and in the older girl, a normal adult height despite hypogonadotropic hypogonadism and the lack of an obvious pubertal growth spurt. Bone age is remarkably advanced in the younger (prepubertal) girl, and bone mineral density (BMD) is high in both girls, which might be directly or indirectly related to leptin resistance.

CONCLUSION

The spectrum of clinical features of LEPR deficiency may be expanded with increased BMD. Future observations in LEPR-deficient subjects should help further unravel the role of leptin in human bone biology.

Ginsenoside Rb1 exerts antidiabetic action on C2C12 muscle cells by leptin receptor signaling pathway

CONTEXT

Ginsenoside Rb1 improves insulin sensitivity and glucose uptake in muscle cells via different signaling pathways; however, it is not clear that it has any effect on leptin signaling in skeletal muscle.

OBJECTIVES

The aim of this study was to investigate the effect of ginsenoside Rb1 on leptin receptors expression and main signaling pathways of leptin (STAT3, PI3 kinase and ERK kinase) in C2C12 skeletal muscle cells.

MATERIALS AND METHODS

C2C12 myotubes were incubated with various concentrations of Rb1 (0.1, 1 and 10 μM) for different incubation times (1-12 h). Leptin receptors expression and GLUT-4 translocation were analyzed using realtime PCR and western blot analyses, respectively. PI3 and ERK kinases were blocked using their specific inhibitors (wortmannin and PD98059) in the presence and absence of RB1 to determine the main signaling pathway related to leptin receptor activation in C2C12 cells.

RESULTS

Rb1 could maximally stimulate both leptin receptors (OBRa and OBRb) mRNA and protein expression and phosphorylation of STAT3, PI3K and ERK2 in C2C12 myotubes at 10 μM for 3 h. Rb1 induced GLUT4 translocation was inhibited by the silencing of OBRb mRNA, demonstrated that glucose uptake was mediated via leptin receptor activation. GLUT4 recruitment to the cell surface induced by Rb1 was inhibited by wortmannin, an inhibitor of PI3K in combination with OBRb siRNA, but not by PD98059 an ERK2 kinase-1 inhibitor, indicating that GLUT4 translocation induced by Rb1 was associated with the leptin receptor upregulation and subsequent activation of PI3K.

CONCLUSIONS

Our results suggest that Rb1 promote translocation of GLUT4 by upregulation of leptin receptors and activation of PI3K.

A Novel Homozygous Frameshift Mutation in Exon 2 of LEP Gene Associated with Severe Obesity: A Case Report

BACKGROUND

Monogenic obesity is a rare type of obesity caused by a mutation in a single gene. Patients with monogenic obesity may develop early onset of obesity and severe metabolic abnormalities.

CASE PRESENTATION

A two-and-half-year-old girl was presented to our clinic because of excessive weight gain and hyperphagia. She was born at full term, by normal vaginal delivery with birth weight of 2.82 kg and no complications during pregnancy. The patient was the second child of two healthy, non-obese Saudis with known consanguinity. She gained weight rapidly leading to obesity at the age of three months.

METHODS

The demographic data and clinical features were recorded. Blood samples were collected and tested for endocrine and metabolic characteristics and genetic studies. Mutations of the LEP gene were screened. The coding exons 2 and 3 and the corresponding exon–intron boundaries were amplified by polymerase chain reaction using specific primers, analyzed by direct sequencing using an ABI sequencer 3500 xL GA (Applied Biosystems), and evaluated using the JSI SeqPilot software. The resulting sequence data were compared with the reference MM_0002302.

CONCLUSION

We report a novel homozygous frameshift mutation c.144delin TAC (G1n49Thrfs*23) in exon 2 of the LEP gene associated with extreme obesity.

Catabolic and proinflammatory effects of leptin in chondrocytes are regulated by suppressor of cytokine signaling-3

BACKGROUND

Previous studies provide evidence that adipokine leptin increases production of catabolic and proinflammatory factors in chondrocytes and serves as a link between obesity and osteoarthritis (OA). However, the magnitude of the response to leptin treatment varies greatly between chondrocytes from different donor patients. In the present study, we investigated the regulatory role of suppressor of cytokine signaling-3 (SOCS-3) in the leptin-induced responses in OA cartilage.

METHODS

Cartilage and synovial fluid samples from 97 patients with OA undergoing knee replacement surgery were collected. Cartilage samples were cultured with leptin (10 μg/ml), and the levels of proinflammatory and catabolic factors in synovial fluid and in the cartilage culture media, and SOCS-3 expression in the cartilage were measured. The role of SOCS-3 in leptin signaling was further studied in H4 murine chondrocytes by downregulating SOCS-3 with siRNA.

RESULTS

Leptin-induced expression of matrix metalloproteinases MMP-1, MMP-3, MMP-13, interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) were higher in the cartilage samples with low SOCS-3 expression. Accordingly, downregulation of SOCS-3 by siRNA in H4 chondrocytes led to enhanced leptin-induced expression of MMP-3, MMP-13, IL-6 and iNOS. Synovial fluid leptin was associated positively, and cartilage SOCS-3 negatively with synovial fluid levels of MMPs in a multivariate model in obese (body mass index (BMI) >30 kg/m²) but not in non-obese (BMI <30 kg/m²) patients.

CONCLUSIONS

Our results show, for the first time, that SOCS-3 regulates leptin-induced responses in cartilage, and could thus be a future drug target in the treatment or prevention of OA, especially in obese patients.

Disruption of Gpr45 causes reduced hypothalamic POMC expression and obesity

A rise in the occurrence of obesity has driven exploration of its underlying genetic basis and potential targets for intervention. GWAS studies have identified obesity susceptibility pathways involving several neuropeptides that control energy homeostasis, suggesting that variations in the genes that regulate food intake and energy expenditure may contribute to obesity. In this study, we identified 5 additional obesity loci, including a neuronal orphan GPCR called Gpr45, in a forward genetic screen of mutant mice generated by piggyBac insertional mutagenesis. Disruption of Gpr45 led to increased adiposity at the time of weaning and increases in body mass, fat content, glucose intolerance, and hepatic steatosis with advancing age. Mice with disruptions in Gpr45 also displayed a reduction in expression of the metabolic regulator POMC and less energy expenditure prior to the onset of obesity. Mechanistically, we determined that GPR45 regulates POMC expression via the JAK/STAT pathway in a cell-autonomous manner. Consistent with this finding, intraventricular administration of melanotan-2, an analog of the POMC derivative α-MSH, suppressed adult obesity in Gpr45 mutants. These results reveal that GPR45 is a regulator of POMC signaling and energy expenditure, which suggests that it may be a potential intervention target to combat obesity.

Role of Leptin Deficiency, Inefficiency, and Leptin Receptors in Obesity

Leptin protein consists of 167 amino acids, which is mainly secreted from the white adipose tissue. This protein acts on the hypothalamic regions of the brain which control eating behavior, thus playing a significant role in maintaining body's metabolism. Leptin receptors belong to glycoprotein 130 (gp130) family of cytokine receptors and exist in six isoforms (LEPR a-f), and all the isoforms are encoded by LEPR gene; out of these isoforms, the LEPR-b receptor is the 'longest form,' and in most of the cases, mutations in this isoform cause severe obesity. Also, mutations in the leptin gene (LEP) or its receptors gene can lead to obesity. Some biochemical pathways affect the bioactivity of leptin and/or its receptors. To date, eleven pathogenic mutations have been reported in the LEP which are p.L72S, p.N103K, p.R105W, p.H118L, p.S141C, p.W121X c.104_106delTCA, c.135del3bp, c.398delG, c.481_482delCT, and c.163C>T. Different mutations in the LEPR have also been reported as c.2396-1 G>T, c.1675 G>A, p.P316T, etc. In some studies, where leptin was deficient, leptin replacement therapy has shown positive impact by preventing weight gain and obesity.

Genome-Wide Association Study Singles Out SCD and LEPR as the Two Main Loci Influencing Intramuscular Fat Content and Fatty Acid Composition in Duroc Pigs

Intramuscular fat (IMF) content and fatty acid composition affect the organoleptic quality and nutritional value of pork. A genome-wide association study was performed on 138 Duroc pigs genotyped with a 60k SNP chip to detect biologically relevant genomic variants influencing fat content and composition. Despite the limited sample size, the genome-wide association study was powerful enough to detect the association between fatty acid composition and a known haplotypic variant in SCD (SSC14) and to reveal an association of IMF and fatty acid composition in the LEPR region (SSC6). The association of LEPR was later validated with an independent set of 853 pigs using a candidate quantitative trait nucleotide. The SCD gene is responsible for the biosynthesis of oleic acid (C18:1) from stearic acid. This locus affected the stearic to oleic desaturation index (C18:1/C18:0), C18:1, and saturated (SFA) and monounsaturated (MUFA) fatty acids content. These effects were consistently detected in gluteus medius, longissimus dorsi, and subcutaneous fat. The association of LEPR with fatty acid composition was detected only in muscle and was, at least in part, a consequence of its effect on IMF content, with increased IMF resulting in more SFA, less polyunsaturated fatty acids (PUFA), and greater SFA/PUFA ratio. Marker substitution effects estimated with a subset of 65 animals were used to predict the genomic estimated breeding values of 70 animals born 7 years later. Although predictions with the whole SNP chip information were in relatively high correlation with observed SFA, MUFA, and C18:1/C18:0 (0.48–0.60), IMF content and composition were in general better predicted by using only SNPs at the SCD and LEPR loci, in which case the correlation between predicted and observed values was in the range of 0.36 to 0.54 for all traits. Results indicate that markers in the SCD and LEPR genes can be useful to select for optimum fatty acid profiles of pork.

Genetics of Adiposity in Large Animal Models for Human Obesity-Studies on Pigs and Dogs

The role of domestic mammals in the development of human biomedical sciences has been widely documented. Among these model species the pig and dog are of special importance. Both are useful for studies on the etiology of human obesity. Genome sequences of both species are known and advanced genetic tools [eg, microarray SNP for genome wide association studies (GWAS), next generation sequencing (NGS), etc.] are commonly used in such studies. In the domestic pig the accumulation of adipose tissue is an important trait, which influences meat quality and fattening efficiency. Numerous quantitative trait loci (QTLs) for pig fatness traits were identified, while gene polymorphisms associated with these traits were also described. The situation is different in dog population. Generally, excessive accumulation of adipose tissue is considered, similar to humans, as a complex disease. However, research on the genetic background of canine obesity is still in its infancy. Between-breed differences in terms of adipose tissue accumulation are well known in both animal species. In this review we show recent advances of studies on adipose tissue accumulation in pigs and dogs, and their potential importance for studies on human obesity.

Satiety and the Self-Regulation of Food Take in Children: a Potential Role for Gene-Environment Interplay

Child eating self-regulation refers to behaviors that enable children to start and stop eating in a manner consistent with maintaining energy balance. Perturbations in these behaviors, manifesting as poorer child eating self-regulation, are associated with higher child weight status. Initial research into child eating self-regulation focused on the role of parent feeding styles and behaviors. However, we argue that child eating self-regulation is better understood as arising from a complex interplay between the child and their feeding environment, and highlight newer research into the heritable child characteristics, such as cognitive ability, that play an important role in this dynamic. Therefore, child eating self-regulation arises from gene-environment interactions. Identifying the genes and environmental influences contributing to these will help us tailor our parental feeding advice to the unique nature of the child. In this way, we will devise more effective advice for preventing childhood obesity.

Common variants in LEPR, IL6, AMD1, and NAMPT do not associate with risk of juvenile and childhood obesity in Danes: a case-control study

Background

Childhood obesity is a highly heritable disorder, for which the underlying genetic architecture is largely unknown. Four common variants involved in inflammatory-adipokine triggering (IL6 rs2069845, LEPR rs1137100, NAMPT rs3801266, and AMD1 rs2796749) have recently been associated with obesity and related traits in Indian children. The current study aimed to examine the effect of these variants on risk of childhood/juvenile onset obesity and on obesity-related quantitative traits in two Danish cohorts.

Methods

Genotype information was obtained for 1461 young Caucasian men from the Genetics of Overweight Young Adults (GOYA) study (overweight/obese: 739 and normal weight: 722) and the Danish Childhood Obesity Biobank (TDCOB; overweight/obese: 1022 and normal weight: 650).

Overweight/obesity was defined as having a body mass index (BMI) ≥25 kg/m²; among children and youths, this cut-off was defined using age and sex-specific cut-offs corresponding to an adult body mass index ≥25 kg/m². Risk of obesity was assessed using a logistic regression model whereas obesity-related quantitative measures were analyzed using a general linear model (based on z-scores) stratifying on the case status and adjusting for age and gender. Meta-analyses were performed using the fixed effects model.

Results

No statistically significant association with childhood/juvenile obesity was found for any of the four gene variants among the individual or combined analyses (rs2069845 OR: 0.94 CI: 0.85–1.04; rs1137100 OR: 1.01 CI: 0.90–1.14; rs3801266: 0.96 CI: 0.84–1.10; rs2796749 OR: 1.02 CI: 0.90–1.15; p > 0.05). However, among normal weight children and juvenile men, the LEPR rs1137100 A-allele significantly associated with lower BMI (β = −0.12, p = 0.0026).

Conclusions

The IL6, LEPR, NAMPT, and AMD1 gene variants previously found to associate among Indian children did not associate with risk of obesity or obesity-related quantitative measures among Caucasian children and juvenile men from Denmark.

Allelic variants of the Melanocortin 4 receptor (MC4R) gene in a South African study group

Obesity is a global epidemic that results in significant morbidity and mortality. Mutations in the melanocortin 4 receptor (MC4R) gene, which codes for a G-protein-coupled receptor responsible for postprandial satiety signaling, have been associated with monogenic obesity. The prevalence of obesity is on the increase in South Africa, and it is hypothesized that mutations in MC4R are a contributing factor. The aim of this study was to perform a retrospective assessment of the relationship between allelic variants of MC4R and BMI in a South African study cohort. DNA was isolated from a demographically representative cohort of 297 individuals and the entire MC4R gene sequenced by Sanger sequencing. Eight previously reported MC4R variants were identified in 42 of the 297 (14.1%) study participants. The most frequently observed MC4R alleles were V103I (4.0%), I170V (1.5%), and I198I (1.2%), while the remaining five variants together constituted 1.18%. Five compound heterozygotes were also detected. Although MC4R variants were rare, the majority of variation was observed in individuals of Black African ancestry. No statistically significant associations with BMI were reported. Given that lifestyle interventions have limited success in decreasing obesity, there is an urgent need to perform large-scale population studies to further elucidate the molecular underpinnings of this disease.

Leptin applications in 2015: what have we learned about leptin and obesity?

PURPOSE OF REVIEW

To summarize previous and current advancements for leptin therapeutics, we described how leptin may be useful in leptin deficient states such as lipodystrophy, for which leptin was recently approved, and how it may be useful in the future for typical obesity.

RECENT FINDINGS

The discovery of leptin in 1994 built the foundation for understanding the pathophysiology and treatment of obesity. Leptin therapy reverses morbid obesity related to congenital leptin deficiency and appears to possibly treat lipodystrophy, a finding which has led to the approval of leptin for the treatment of lipodystrophy in the USA and Japan. Typical obesity, on the other hand, is characterized by hyperleptinemia and leptin tolerance. Thus, leptin administration has proven ineffective for inducing weight loss on its own but could possibly be useful in combination with other therapies or for weight loss maintenance.

SUMMARY

Leptin is not able to treat typical obesity; however, it is effective for reversing leptin deficiency-induced obesity and is possibly useful in lipodystrophy. New mechanisms and pathways involved in leptin resistance are continuously discovered, whereas the development of new techniques and drug combinations which may improve leptin's efficacy and safety regenerate the hope for its use as an effective treatment for typical obesity.

Adipose Tissue as an Endocrine Organ: An Update on Pro-inflammatory and Anti-inflammatory Microenvironment

Adipose tissue is recognized as an active endocrine organ that produces a number of endocrine substances referred to as "adipokines" including leptin, adiponectin, adipolin, visfatin, omentin, tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), resistin, pigment epithelium-derived factor (PEDF), and progranulin (PGRN) which play an important role in the food intake regulation and significantly influence insulin sensitivity and in some cases directly affect insulin resistance in skeletal muscle, liver, and adipose tissue. The review summarizes current knowledge about adipose tissue-derived hormones and their influence on energy homeostasis regulation. The possible therapeutic potential of these adipokines in the treatment of insulin resistance, endothelial dysfunction, a pro-inflammatory response, obesity, eating disorders, progression of atherosclerosis, type 1 diabetes, and type 2 diabetes is discussed.

Direct effects of leptin and adiponectin on peripheral reproductive tissues: a critical review

Obesity is a risk factor for infertility and adverse reproductive outcomes. Adipose tissue is an important endocrine gland that secretes a host of endocrine factors, called adipokines, which modulate diverse physiologic processes including appetite, metabolism, cardiovascular function, immunity and reproduction. Altered adipokine expression in obese individuals has been implicated in the pathogenesis of a host of health disorders including diabetes and cardiovascular disease. It remains unclear whether adipokines play a significant role in the pathogenesis of adverse reproductive outcomes in obese individuals and, if so, whether the adipokines are acting directly or indirectly on the peripheral reproductive tissues. Many groups have demonstrated that receptors for the adipokines leptin and adiponectin are expressed in peripheral reproductive tissues and that these adipokines are likely, therefore, to exert direct effects on these tissues. Many groups have tested for direct effects of leptin and adiponectin on reproductive tissues including the testis, ovary, uterus, placenta and egg/embryo. The hypothesis that decreased fertility potential or adverse reproductive outcomes may result, at least in part, from defects in adipokine signaling within reproductive tissues has also been tested. Here, we present a critical analysis of published studies with respect to two adipokines, leptin and adiponectin, for which significant data have been generated. Our evaluation reveals significant inconsistencies and methodological limitations regarding the direct effects of these adipokines on peripheral reproductive tissues. We also observe a pervasive failure to account for in vivo data that challenge observations made in vitro. Overall, while leptin and adiponectin may directly modulate peripheral reproductive tissues, existing data suggest that these effects are minor and non-essential to human or mouse reproductive function. Current evidence suggests that direct effects of leptin or adiponectin on peripheral reproductive tissues are unlikely to factor significantly in the adverse reproductive outcomes observed in obese individuals.

Cognitive and autonomic determinants of energy homeostasis in obesity

Obesity ensues from an imbalance between energy intake and expenditure that results from gene-environment interactions, which favour a positive energy balance. A society that promotes unhealthy food and encourages sedentary lifestyle (that is, an obesogenic environment) has become a major contributory factor in excess fat deposition in individuals predisposed to obesity. Energy homeostasis relies upon control of energy intake as well as expenditure, which is in part determined by the themogenesis of brown adipose tissue and mediated by the sympathetic nervous system. Several areas of the brain that constitute cognitive and autonomic brain systems, which in turn form networks involved in the control of appetite and thermogenesis, also contribute to energy homeostasis. These networks include the dopamine mesolimbic circuit, as well as the opioid, endocannabinoid and melanocortin systems. The activity of these networks is modulated by peripheral factors such as hormones derived from adipose tissue and the gut, which access the brain via the circulation and neuronal signalling pathways to inform the central nervous system about energy balance and nutritional status. In this Review, I focus on the determinants of energy homeostasis that have emerged as prominent factors relevant to obesity.

Omega-3 fatty acids and adipose tissue function in obesity and metabolic syndrome

The n-3 long-chain polyunsaturated fatty acids (n-3 PUFAs) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) have been reported to improve obesity-associated metabolic disorders including chronic inflammation, insulin resistance and dyslipidaemia. Growing evidence exits about adipose tissue as a target in mediating the beneficial effects of these marine n-3 PUFAs in adverse metabolic syndrome manifestations. Therefore, in this manuscript we focus in reviewing the current knowledge about effects of marine n-3 PUFAs on adipose tissue metabolism and secretory functions. This scope includes n-3 PUFAs actions on adipogenesis, lipogenesis and lipolysis as well as on fatty acid oxidation and mitochondrial biogenesis. The effects of n-3 PUFAs on adipose tissue glucose uptake and insulin signaling are also summarized. Moreover, the roles of peroxisome proliferator-activated receptor γ (PPARγ) and AMPK activation in mediating n-3 PUFAs actions on adipose tissue functions are discussed. Finally, the mechanisms underlying the ability of n-3 PUFAs to prevent and/or ameliorate adipose tissue inflammation are also revised, focusing on the role of n-3 PUFAs-derived specialized proresolving lipid mediators such as resolvins, protectins and maresins.