The Leptin Receptor Complex: Heavier Than Expected?

A Bird's-Eye Overview of Leptin and Female Reproduction -with Mammalian Comparisons

Leptin, a key regulator of reproductive physiology, influences various processes in vertebrates, including oocyte proliferation, embryogenesis, the onset of puberty, ovarian function, and follicle development. In mammals, leptin affects steroidogenesis, folliculogenesis, and hormonal regulation through the hypothalamic-pituitary-gonadal axis. Instead, in avian species, leptin-controlled mechanisms are poorly understood, because birds do not produce leptin in adipocytes. In birds, leptin is expressed in the brain, pituitary glands, and gonads, where it enhances ovarian function and egg-laying performance, particularly during feed deprivation. In this review, we discuss and summarize the recently discovered role of leptin in regulating ovarian function during different life stages in birds and compare it with its function in mammals.

Inter-organ metabolic interaction networks in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multisystem metabolic disorder, marked by abnormal lipid accumulation and intricate inter-organ interactions, which contribute to systemic metabolic imbalances. NAFLD may progress through several stages, including simple steatosis (NAFL), non-alcoholic steatohepatitis (NASH), cirrhosis, and potentially liver cancer. This disease is closely associated with metabolic disorders driven by overnutrition, with key pathological processes including lipid dysregulation, impaired lipid autophagy, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and local inflammation. While hepatic lipid metabolism in NAFLD is well-documented, further research into inter-organ communication mechanisms is crucial for a deeper understanding of NAFLD progression. This review delves into intrahepatic networks and tissue-specific signaling mediators involved in NAFLD pathogenesis, emphasizing their impact on distal organs.

Regulation of energy balance by leptin as an adiposity signal and modulator of the reward system

BACKGROUND

Leptin is an adipose tissue-derived hormone that plays a crucial role in body weight, appetite, and behaviour regulation. Leptin controls energy balance as an indicator of adiposity levels and as a modulator of the reward system, which is associated with liking palatable foods. Obesity is characterized by expanded adipose tissue mass and consequently, elevated concentrations of leptin in blood. Leptin's therapeutic potential for most forms of obesity is hampered by leptin resistance and a narrow dose-response window.

SCOPE OF REVIEW

This review describes the current knowledge of the brain regions and intracellular pathways through which leptin promotes negative energy balance and restrains neural circuits affecting food reward. We also describe mechanisms that hinder these biological responses in obesity and highlight potential therapeutic interventions.

MAJOR CONCLUSIONS

Additional research is necessary to understand how pathways engaged by leptin in different brain regions are interconnected in the control of energy balance.

Cellular and molecular mechanisms of action of ovarian steroid hormones II: Regulation of sexual behavior in female rodents

Female sexual behaviors in rodents (lordosis and appetitive or "proceptive" behaviors) are induced through a genomic mechanism by the sequential actions of estradiol (E2) and progesterone (P), or E2 and testosterone (T) at their respective receptors. However, non-steroidal agents, such as gonadotropin-releasing hormone (GnRH), Prostaglandin E2 (PGE2), noradrenaline, dopamine, oxytocin, α-melanocyte stimulating hormone, nitric oxide, leptin, apelin, and others, facilitate different aspects of female sexual behavior through their cellular and intracellular effects at the membrane and genomic levels in ovariectomized rats primed with E2. These neurotransmitters often act as intermediaries of E2 and P (or T). The classical model of steroid hormone action through intracellular receptor binding has been complemented by an alternative scenario wherein the steroid functions as a transcription factor after binding the receptor protein to DNA. Another possible mechanism occurs through the activation of second messenger systems (cyclic AMP, cyclic GMP, calcium), which subsequently initiate phosphorylation events via diverse kinase systems (protein kinases A, G, or C). These kinases target the progesterone receptor (PR) or associated effector proteins that connect the PR to the trans-activation machinery. This may also happen to the androgen receptor (AR). In addition, other cellular mechanisms could be involved since the chemical structure of these non-steroidal agents causes a change in their lipophobicity that prevents them from penetrating the cell and exerting direct transcriptional effects; however, they can exert effects on different components of the cell membrane activating a cross-talk between the cell membrane and the regulation of the transcriptional mechanisms.

The role of leptin in the male reproductive system

Leptin is a hormone produced from adipose tissue, targeting the hypothalamus and regulating energy expenditure, adipose tissue mass, and reproductive function. Leptin concentration reflects body weight and the amount of energy stored, as well as the level of reproductive hormones and male fertility. In this review, the aim was to focus on leptin signaling mechanisms and the significant influence of leptin on the male reproductive system and to summarize the current knowledge of clinical and experimental studies. The PubMed database was searched for studies on leptin and the male reproductive system to summarize the mechanism of leptin in the male reproductive system. Studies have shown that obesity-related, high leptin levels or leptin resistance negatively affects male reproductive functions. Leptin directly affects the testis by binding to the hypothalamic-pituitary-gonadal axis and the receptors of testicular cells, and thus the location of leptin receptors plays a key role in the regulation of the male reproductive system with the negative feedback mechanism between adipose tissue and hypothalamus. Based on the current evidence, leptin may totally inhibit male reproduction, and investigation of this role of leptin has established a potential interaction between obesity and male infertility. The mechanism of leptin in the male reproductive system should be further investigated and possible treatments for subfertility should be evaluated, supported by better understanding of leptin and associated signaling mechanisms.

Leptin is a potential biomarker of childhood obesity and an indicator of the effectiveness of weight-loss interventions

Childhood obesity represents a significant public health concern, imposing a substantial burden on the healthcare system. Furthermore, weight-loss programs often exhibit reduced effectiveness in adults who have a history of childhood obesity. Therefore, early intervention against childhood obesity is imperative. Presently, the primary method for diagnosing childhood obesity relies on body mass index (BMI), yet this approach has inherent limitations. Leptin, a satiety hormone produced by adipocytes, holds promise as a superior tool for predicting both childhood and subsequent adulthood obesity. In this review, we elucidate the tools employed for assessing obesity in children, delve into the biological functions of leptin, and examine the factors governing its expression. Additionally, we discuss maternal and infantile leptin levels as predictors of childhood obesity. By exploring the relationship between leptin levels and weight loss, we present leptin as a potential indicator of the effectiveness of obesity interventions.

Protein tyrosine phosphatase 1B (PTP1B) function, structure, and inhibition strategies to develop antidiabetic drugs

Tyrosine protein phosphatase non-receptor type 1 (PTP1B; also known as protein tyrosine phosphatase 1B) is a member of the protein tyrosine phosphatase (PTP) family and is a soluble enzyme that plays an essential role in different physiological processes, including the regulation of metabolism, specifically in insulin and leptin sensitivity. PTP1B is crucial in the pathogenesis of type 2 diabetes mellitus and obesity. These biological functions have made PTP1B validated as an antidiabetic and anti-obesity, and potentially anticancer, molecular target. Four main approaches aim to inhibit PTP1B: orthosteric, allosteric, bidentate inhibition, and PTPN1 gene silencing. Developing a potent and selective PTP1B inhibitor is still challenging due to the enzyme's ubiquitous expression, subcellular location, and structural properties. This article reviews the main advances in the study of PTP1B since it was first isolated in 1988, as well as recent contextual information related to the PTP family to which this protein belongs. Furthermore, we offer an overview of the role of PTP1B in diabetes and obesity, and the challenges to developing selective, effective, potent, bioavailable, and cell-permeable compounds that can inhibit the enzyme.

Total Gestational Weight Gain Is Explained by Leptin and Body Fat, Regardless of Pre-Pregnancy Body Mass Index and Other Adipokines, in Mexican Adolescents

Pre-pregnancy body mass index (pBMI) is a predictor of gestational weight gain (GWG). However, other factors, such as adipokines and inflammation markers, may also be associated with GWG. The aim of the study was to determine the association of leptin, adiponectin, irisin, and C-reactive protein, with GWG in adolescents. A longitudinal study was conducted from 2018 to 2023 in adolescents with a clinically healthy pregnancy. The assessments included sociodemographic and clinical data, pBMI, percent of body fat, serum concentrations of leptin, adiponectin, irisin, and high-sensitivity C-reactive protein (hsCRP), and total GWG adequacy. Cox regression models were performed, the outcome variables were inadequate and excessive GWG. In 198 participants, being overweight/obesity was marginally associated with a protective effect against inadequate GWG (HR = 0.44, 95%CI = 0.18-1.06), regardless of maternal characteristics and adipokines. Leptin (HR = 1.014, 95%CI = 1.008-1.021), and body fat percent (HR = 1.11, 95%CI = 1.05-1.17) were associated with a higher risk of excessive GWG, independent of other maternal variables such as pBMI, while adiponectin was associated with a lower risk. These findings suggest that, in Mexican adolescents, adipose tissue and its adipokines during pregnancy may play a more significant role in the final GWG than body weight.

Evidence That Peripheral Leptin Resistance in Omental Adipose Tissue and Liver Correlates with MASLD in Humans

Leptin regulates lipid metabolism, maximizing insulin sensitivity; however, peripheral leptin resistance is not fully understood, and its contribution to metabolic dysfunction-associated steatotic liver disease (MASLD) is unclear. This study evaluated the contribution of the leptin axis to MASLD in humans. Forty-three participants, mostly female (86.04%), who underwent cholecystectomy were biopsied. Of the participants, 24 were healthy controls, 8 had MASLD, and 11 had metabolic dysfunction-associated steatohepatitis (MASH). Clinical and biochemical data and the gene expression of leptin, leptin receptor (LEPR), suppressor of cytokine signaling 3 (SOCS3), sterol regulatory element-binding transcription factor 1 (SREBF1), stearoyl-CoA desaturase-1 (SCD1), and patatin-like phospholipase domain-containing protein 2 (PNPLA2), were determined from liver and adipose tissue. Higher serum leptin and LEPR levels in the omental adipose tissue (OAT) and liver with MASH were found. In the liver, LEPR was positively correlated with leptin expression in adipose tissue, and SOCS3 was correlated with SREBF1-SCD1. In OAT, SOCS3 was correlated with insulin resistance and transaminase enzymes (p < 0.05 for all. In conclusion, we evidenced the correlation between the peripheral leptin resistance axis in OAT-liver crosstalk and the complications of MASLD in humans.

Adipokines in pregnancy

Reproductive success consists of a sequential events chronology, starting with the ovum fertilization, implantation of the embryo, placentation, and cellular processes like proliferation, apoptosis, angiogenesis, endocrinology, or metabolic changes, which taken together finally conduct the birth of healthy offspring. Currently, many factors are known that affect the regulation and proper maintenance of pregnancy in humans, domestic animals, or rodents. Among the determinants of reproductive success should be distinguished: the maternal microenvironment, genes, and proteins as well as numerous pregnancy hormones that regulate the most important processes and ensure organism homeostasis. It is well known that white adipose tissue, as the largest endocrine gland in our body, participates in the synthesis and secretion of numerous hormones belonging to the adipokine family, which also may regulate the course of pregnancy. Unfortunately, overweight and obesity lead to the expansion of adipose tissue in the body, and its excess in both women and animals contributes to changes in the synthesis and release of adipokines, which in turn translates into dramatic changes during pregnancy, including those taking place in the organ that is crucial for the proper progress of pregnancy, i.e. the placenta. In this chapter, we are summarizing the current knowledge about levels of adipokines and their role in the placenta, taking into account the physiological and pathological conditions of pregnancy, e.g. gestational diabetes mellitus, preeclampsia, or intrauterine growth restriction in humans, domestic animals, and rodents.

Leptin signalling regulates transcriptional differences in granulosa cells from genetically obese mice but not the activation of NLRP3 inflammasome

Obesity is associated with increased ovarian inflammation and the establishment of leptin resistance. We presently investigated the role of impaired leptin signalling on transcriptional regulation in granulosa cells (GCs) collected from genetically obese mice. Furthermore, we characterised the association between ovarian leptin signalling, the activation of the NOD-like receptor protein 3 (NLRP3) inflammasome and macrophage infiltration in obese mice. After phenotype characterisation, ovaries were collected from distinct group of animals for protein and mRNA expression analysis: (i) mice subjected to a diet-induced obesity (DIO) protocol, where one group was fed a high-fat diet (HFD) and another a standard chow diet (CD) for durations of 4 or 16 weeks; (ii) mice genetically deficient in the long isoform of the leptin receptor (ObRb; db/db); (iii) mice genetically deficient in leptin (ob/ob); and (iv) mice rendered pharmacologically hyperleptinemic (LEPT). Next, GCs from antral follicles isolated from db/db and ob/ob mice were subjected to transcriptome analysis. Transcriptional analysis revealed opposing profiles in genes associated with steroidogenesis and prostaglandin action between the genetic models, despite the similarities in body weight. Furthermore, we observed no changes in the mRNA and protein levels of NLRP3 inflammasome components in the ovaries of db/db mice or in markers of M1 and M2 macrophage infiltration. This contrasted with the downregulation of NLRP3 inflammasome components and M1 markers in ob/ob and 16-wk HFD-fed mice. We concluded that leptin signalling regulates NLRP3 inflammasome activation and the expression of M1 markers in the ovaries of obese mice in an ObRb-dependent and ObRb-independent manner. Furthermore, we found no changes in the expression of leptin signalling and NLRP3 inflammasome genes in GCs from db/db and ob/ob mice, which was associated with no effects on macrophage infiltration genes, despite the dysregulation of genes associated with steroidogenesis in homozygous obese db/db. Our results suggest that: (i) the crosstalk between leptin signalling, NLRP3 inflammasome and macrophage infiltration takes place in ovarian components other than the GC compartment; and (ii) transcriptional changes in GCs from homozygous obese ob/ob mice suggest structural rearrangement and organisation, whereas in db/db mice the impairment in steroidogenesis and secretory activity.

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.

Leptin effects: focusing on the relationship between obesity and male infertility

The human male infertility has several causes interconnected to improper lifestyles such as smoking, sedentarism, environmental factors, toxins accumulation and energy imbalances. All these factors contribute to the obesity accompanied metabolic syndrome and hormonal alterations in the leptin-ghrelin axis. The leptin (Lep) has many pleiotropic effects in several biological systems, directly on the peripheral tissues or through the central nervous system. Many studies suggest that Lep is a key player in gonadal functions beside its documented role in reproductive regulation; however, further investigations are still necessary to elucidate all the molecular pathways involved in these mechanisms. Keeping into account that increased Lep levels in obese men are positively correlated with altered sperm parameters and testicular oxidative stress, evidence refers to Lep as a potential link between obesity and male infertility. This review represents an updated version on the concept of the Lep roles in mediating the male reproductive functions in obese patients.

Molecular and Cellular Mechanisms Underlying the Cardiac Hypertrophic and Pro-Remodelling Effects of Leptin

Since its initial discovery in 1994, the adipokine leptin has received extensive interest as an important satiety factor and regulator of energy expenditure. Although produced primarily by white adipocytes, leptin can be synthesized by numerous tissues including those comprising the cardiovascular system. Cardiovascular function can thus be affected by locally produced leptin via an autocrine or paracrine manner but also by circulating leptin. Leptin exerts its effects by binding to and activating specific receptors, termed ObRs or LepRs, belonging to the Class I cytokine family of receptors of which six isoforms have been identified. Although all ObRs have identical intracellular domains, they differ substantially in length in terms of their extracellular domains, which determine their ability to activate cell signalling pathways. The most important of these receptors in terms of biological effects of leptin is the so-called long form (ObRb), which possesses the complete intracellular domain linked to full cell signalling processes. The heart has been shown to express ObRb as well as to produce leptin. Leptin exerts numerous cardiac effects including the development of hypertrophy likely through a number of cell signaling processes as well as mitochondrial dynamics, thus demonstrating substantial complex underlying mechanisms. Here, we discuss mechanisms that potentially mediate leptin-induced cardiac pathological hypertrophy, which may contribute to the development of heart failure.

Hibiscus sabdariffa Linn. Extract Increases the mRNA Expression of the Arcuate Nucleus Leptin Receptor and is Predicted in silico as an Anti-obesity Agent

BACKGROUND

Leptin is predominant in regulating body weight by stimulating energy expenditure through its neuronal action in the brain. Moreover, it is projected to adipose tissue and induces adipocyte browning by activating the β3-adrenergic receptor (β3AR). However, the expression of leptin receptor (Lep-R) and β3AR in people with obesity is downregulated.

AIM

We hypothesized that Hibiscus sabdariffa Linn. extract (HSE) would increase hypothalamus arcuate nucleus (ARC) Lep-R and white adipose tissue (WAT) β3AR mRNA expression in DIO rats. This study also analyzed the potency of H. sabdariffa bioactive compounds as activators of Lep-R and β3AR by an in-silico experiment.

METHODS

Twenty-four male Sprague-Dawley rats were divided into four groups: Control (standard food), DIO (high-fat diet), DIO-Hib200 (HFD+HSE 200 mg/kg BW), and DIO-Hib400 (HFD+HSE400 mg/kg BW). HSE was administered orally for five weeks, once a day.

RESULTS

HSE administration significantly (p <0,05) increased the ARC Lep-R expression. The Lee index significantly decreased to the normal range (≤ 310) with p <0,001 for DIO-Hib200 and p <0,01 for DIO-Hib400. Among 39 bioactive compounds, 5-O-caffeoyl shikimic acid exhibited high free binding scores (-8,63) for Lep-R, and myricetin_3_arabinogalactoside had high free binding scores (-9,39) for β3AR. These binding predictions could activate Lep-R and β3AR.

CONCLUSION

This study highlights that HSE could be a potential therapeutic target for obesity by increasing LepR mRNA and leptin sensitivity, enhancing energy expenditure, and reducing obesity.

Diabetic Encephalopathy: Role of Oxidative and Nitrosative Factors in Type 2 Diabetes

Diabetes mellitus is a set of complex metabolic disorders characterized by chronic hyperglycaemic condition due to defective insulin secretion (Type 1) and action (Type 2), which leads to serious micro and macro-vascular damage, inflammation, oxidative and nitrosative stress and a deranged energy homeostasis due to imbalance in the glucose and lipid metabolism. Moreover, patient with diabetes mellitus often showed the nervous system disorders known as diabetic encephalopathy. The precise pathological mechanism of diabetic encephalopathy by which it effects the central nervous system directly or indirectly causing the cognitive and motor impairment, is not completely understood. However, it has been speculated that like other extracerebellar tissues, oxidative and nitrosative stress may play significant role in the pathogenesis of diabetic encephalopathy. Therefore, the present review aimed to explain the possible association of the oxidative and nitrosative stress caused by the chronic hyperglycaemic condition with the central nervous system complications of the type 2 diabetes mellitus induced diabetic encephalopathy.

Adipo-glial signaling mediates metabolic adaptation in peripheral nerve regeneration

The peripheral nervous system harbors a remarkable potential to regenerate after acute nerve trauma. Full functional recovery, however, is rare and critically depends on peripheral nerve Schwann cells that orchestrate breakdown and resynthesis of myelin and, at the same time, support axonal regrowth. How Schwann cells meet the high metabolic demand required for nerve repair remains poorly understood. We here report that nerve injury induces adipocyte to glial signaling and identify the adipokine leptin as an upstream regulator of glial metabolic adaptation in regeneration. Signal integration by leptin receptors in Schwann cells ensures efficient peripheral nerve repair by adjusting injury-specific catabolic processes in regenerating nerves, including myelin autophagy and mitochondrial respiration. Our findings propose a model according to which acute nerve injury triggers a therapeutically targetable intercellular crosstalk that modulates glial metabolism to provide sufficient energy for successful nerve repair.

Leptin receptor gene deficiency minimally affects osseointegration in rats

Metabolic syndrome represents a cluster of conditions such as obesity, hyperglycaemia, dyslipidaemia, and hypertension that can lead to type 2 diabetes mellitus and/or cardiovascular disease. Here, we investigated the influence of obesity and hyperglycaemia on osseointegration using a novel, leptin receptor-deficient animal model, the Lund MetS rat. Machined titanium implants were installed in the tibias of animals with normal leptin receptor (LepR+/+) and those harbouring congenic leptin receptor deficiency (LepR-/-) and were left to heal for 28 days. Extensive evaluation of osseointegration was performed using removal torque measurements, X-ray micro-computed tomography, quantitative backscattered electron imaging, Raman spectroscopy, gene expression analysis, qualitative histology, and histomorphometry. Here, we found comparable osseointegration potential at 28 days following implant placement in LepR-/- and LepR+/+ rats. However, the low bone volume within the implant threads, higher bone-to-implant contact, and comparable biomechanical stability of the implants point towards changed bone formation and/or remodelling in LepR-/- rats. These findings are corroborated by differences in the carbonate-to-phosphate ratio of native bone measured using Raman spectroscopy. Observations of hypermineralised cartilage islands and increased mineralisation heterogeneity in native bone confirm the delayed skeletal development of LepR-/- rats. Gene expression analyses reveal comparable patterns between LepR-/- and LepR+/+ animals, suggesting that peri-implant bone has reached equilibrium in healing and/or remodelling between the animal groups.

Detecting fa leptin receptor mutation in Zucker rats with tetra-primer amplification-refractory mutation system (ARMS)-PCR

Due to the genetic mutation (fa) in the gene encoding for leptin receptor, homozygous Zucker rats (fa-/-) develop excessive adiposity and become an experimental animal model in obesity and metabolic-related diseases research. Based on tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR), we developed a method to quickly genotype Zucker rats with a mutated fa allele from their wildtype littermates. The three genotypes are clearly discriminated on 2.0% agarose gel. Our method can be used as a reliable tool to set up and maintain the breeding colony in animal facilities as well as assign animals to control and treatment groups based on their genotypes for animal studies.

Rare Antagonistic Leptin Variants and Severe, Early-Onset Obesity

Hormone absence or inactivity is common in congenital disease, but hormone antagonism remains controversial. Here, we characterize two novel homozygous leptin variants that yielded antagonistic proteins in two unrelated children with intense hyperphagia, severe obesity, and high circulating levels of leptin. Both variants bind to the leptin receptor but trigger marginal, if any, signaling. In the presence of nonvariant leptin, the variants act as competitive antagonists. Thus, treatment with recombinant leptin was initiated at high doses, which were gradually lowered. Both patients eventually attained near-normal weight. Antidrug antibodies developed in the patients, although they had no apparent effect on efficacy. No severe adverse events were observed. (Funded by the German Research Foundation and others.).

Obesity and cancer: focus on leptin

Over the past decades, obesity has grown to epidemic proportions worldwide. It has been associated with an increased risk for different types of cancer. In addition, obesity has been associated with a poor prognosis, an increased risk of metastasis and mortality, and resistance to anti-cancer therapies. The pathophysiological mechanisms underlying the obesity-cancer connection have not yet been fully elucidated. However, this connection could result, at least in part, from the action of adipokines, whose levels are increased in obesity. Among these adipokines, evidence suggests leptin's critical role in linking obesity to cancer. In this review, we first summarize the current state of the literature regarding the implication of leptin in tumorigenic processes. Next, we focus on the effects of leptin on the anti-tumor immune response. Then, we discuss the influence of leptin on the efficiency of antineoplastic treatments and the development of tumor resistance. Finally, we highlight the use of leptin as a potential target for the prevention and treatment of cancer.

Fecal and Urinary Adipokines as Disease Biomarkers

The use of biomarkers is of great clinical value for the diagnosis and prognosis of disease and the assessment of treatment efficacy. In this context, adipokines secreted from adipose tissue are of interest, as their elevated circulating levels are associated with a range of metabolic dysfunctions, inflammation, renal and hepatic diseases and cancers. In addition to serum, adipokines can also be detected in the urine and feces, and current experimental evidence on the analysis of fecal and urinary adipokine levels points to their potential as disease biomarkers. This includes increased urinary adiponectin, lipocalin-2, leptin and interleukin-6 (IL-6) levels in renal diseases and an association of elevated urinary chemerin as well as urinary and fecal lipocalin-2 levels with active inflammatory bowel diseases. Urinary IL-6 levels are also upregulated in rheumatoid arthritis and may become an early marker for kidney transplant rejection, while fecal IL-6 levels are increased in decompensated liver cirrhosis and acute gastroenteritis. In addition, galectin-3 levels in urine and stool may emerge as a biomarker for several cancers. With the analysis of urine and feces from patients being cost-efficient and non-invasive, the identification and utilization of adipokine levels as urinary and fecal biomarkers could become a great advantage for disease diagnosis and predicting treatment outcomes. This review article highlights data on the abundance of selected adipokines in urine and feces, underscoring their potential to serve as diagnostic and prognostic biomarkers.

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.

Improvement effect of a next-generation probiotic L. plantarum-pMG36e-GLP-1 on type 2 diabetes mellitus via the gut-pancreas-liver axis

Next-generation probiotics (NGPs) are currently being investigated as therapeutic agents that impact the gut microbiota and disease development. Glucagon-like peptide-1 (GLP-1) shows an excellent therapeutic effect on diabetes, but has an extremely short half-life in vivo. Here, we constructed a novel and diabetes-specific NGP, the genetically engineered strain Lactobacillus plantarum (L. plantarum)-pMG36e-GLP-1, and evaluated its ameliorative effect on type 2 diabetes mellitus (T2DM) in artificially induced mice and transgenic mice. In vitro, L. plantarum-pMG36e-GLP-1 showed good genetic stability and probiotic characteristics. In the high-fat diet combined with streptozotocin (HFD/STZ)-induced T2DM mice, L. plantarum-pMG36e-GLP-1 relieved the diabetic symptoms, regulated the intestinal microbiota, and reduced the inflammatory reaction in the pancreatic tissue. Meanwhile, the apoptosis of pancreatic islet cells was inhibited, while islet tissue morphology repairs, islet β-cell proliferation, and insulin secretion were all promoted by L. plantarum-pMG36e-GLP-1. Furthermore, a similar effect of the engineered strain on diabetic symptoms and the pancreas was observed in db/db mice, and the metabolism of lipids in the liver was regulated. Together, the findings of this study confirmed the anti-hyperglycemic effect of the engineered strain L. plantarum-pMG36e-GLP-1, providing a promising approach for T2DM treatment.

Novel genetic regulators of fibrinogen synthesis identified by an in vitro experimental platform

BACKGROUND

Fibrinogen has an established, essential role in both coagulation and inflammatory pathways, and these processes are deeply intertwined in the development of thrombotic and atherosclerotic diseases. Previous studies aimed to better understand the (patho) physiological actions of fibrinogen by characterizing the genomic contribution to circulating fibrinogen levels.

OBJECTIVES

Establish an in vitro approach to define functional roles between genes within these loci and fibrinogen synthesis.

METHODS

Candidate genes were selected on the basis of their proximity to genetic variants associated with fibrinogen levels and expression in hepatocytes and HepG2 cells. HepG2 cells were transfected with small interfering RNAs targeting candidate genes and cultured in the absence or presence of the proinflammatory cytokine interleukin-6. Effects on fibrinogen protein production, gene expression, and cell growth were assessed by immunoblotting, real-time polymerase chain reaction, and cell counts, respectively.

RESULTS

HepG2 cells secreted fibrinogen, and stimulation with interleukin-6 increased fibrinogen production by 3.4 ± 1.2 fold. In the absence of interleukin-6, small interfering RNA knockdown of FGA, IL6R, or EEPD1 decreased fibrinogen production, and knockdown of LEPR, PDIA5, PLEC, SHANK3, or CPS1 increased production. In the presence of interleukin-6, knockdown of FGA, IL6R, or ATXN2L decreased fibrinogen production. Knockdown of FGA, IL6R, EEPD1, LEPR, PDIA5, PLEC, or CPS1 altered transcription of one or more fibrinogen genes. Knocking down ATXN2L suppressed inducible but not basal fibrinogen production via a post-transcriptional mechanism.

CONCLUSIONS

We established an in vitro platform to define the impact of select gene products on fibrinogen production. Genes identified in our screen may reveal cellular mechanisms that drive fibrinogen production as well as fibrin(ogen)-mediated (patho)physiological mechanisms.

Crosstalk of Inflammatory Cytokines within the Breast Tumor Microenvironment

Several immune and immunocompetent cells, including dendritic cells, macrophages, adipocytes, natural killer cells, T cells, and B cells, are significantly correlated with the complex discipline of oncology. Cytotoxic innate and adaptive immune cells can block tumor proliferation, and others can prevent the immune system from rejecting malignant cells and provide a favorable environment for tumor progression. These cells communicate with the microenvironment through cytokines, a chemical messenger, in an endocrine, paracrine, or autocrine manner. These cytokines play an important role in health and disease, particularly in host immune responses to infection and inflammation. They include chemokines, interleukins (ILs), adipokines, interferons, colony-stimulating factors (CSFs), and tumor necrosis factor (TNF), which are produced by a wide range of cells, including immune cells, such as macrophages, B-cells, T-cells, and mast cells, as well as endothelial cells, fibroblasts, a variety of stromal cells, and some cancer cells. Cytokines play a crucial role in cancer and cancer-related inflammation, with direct and indirect effects on tumor antagonistic or tumor promoting functions. They have been extensively researched as immunostimulatory mediators to promote the generation, migration and recruitment of immune cells that contribute to an effective antitumor immune response or pro-tumor microenvironment. Thus, in many cancers such as breast cancer, cytokines including leptin, IL-1B, IL-6, IL-8, IL-23, IL-17, and IL-10 stimulate while others including IL-2, IL-12, and IFN-γ, inhibit cancer proliferation and/or invasion and enhance the body's anti-tumor defense. Indeed, the multifactorial functions of cytokines in tumorigenesis will advance our understanding of cytokine crosstalk pathways in the tumor microenvironment, such as JAK/STAT, PI3K, AKT, Rac, MAPK, NF-κB, JunB, cFos, and mTOR, which are involved in angiogenesis, cancer proliferation and metastasis. Accordingly, targeting and blocking tumor-promoting cytokines or activating and amplifying tumor-inhibiting cytokines are considered cancer-directed therapies. Here, we focus on the role of the inflammatory cytokine system in pro- and anti-tumor immune responses, discuss cytokine pathways involved in immune responses to cancer and some anti-cancer therapeutic applications.

Metformin induces pyroptosis in leptin receptor-defective hepatocytes via overactivation of the AMPK axis

Metformin is the biguanide of hepatic insulin sensitizer for patients with non-alcohol fatty liver disease (NAFLD). Findings regarding its efficacy in restoring blood lipids and liver histology have been contradictory. In this study, we explore metformin's preventive effects on NAFLD in leptin-insensitive individuals. We used liver tissue, serum exosomes and isolated hepatocytes from high-fat diet (HFD)-induced Zucker diabetic fatty (ZDF) rats and leptin receptor (Lepr) knockout rats to investigate the correlation between hepatic Lepr defective and liver damage caused by metformin. Through immunostaining, RT-PCR and glucose uptake monitoring, we showed that metformin treatment activates adenosine monophosphate (AMP)-activated protein kinase (AMPK) and its downstream cytochrome C oxidase (CCO). This leads to overactivation of glucose catabolism-related genes, excessive energy repertoire consumption, and subsequent hepatocyte pyroptosis. Single-cell RNA sequencing further confirmed the hyper-activation of glucose catabolism after metformin treatment. Altogether, we showed that functional Lepr is necessary for metformin treatment to be effective, and that long-term metformin treatment might promote NAFLD progression in leptin-insensitive individuals. This provides important insight into the clinical application of metformin.

Skin-associated adipocytes in skin barrier immunity: A mini-review

The skin contributes critically to health via its role as a barrier tissue against a multitude of external pathogens. The barrier function of the skin largely depends on the uppermost epidermal layer which is reinforced by skin barrier immunity. The integrity and effectiveness of skin barrier immunity strongly depends on the close interplay and communication between immune cells and the skin environment. Skin-associated adipocytes have been recognized to play a significant role in modulating skin immune responses and infection by secreting cytokines, adipokines, and antimicrobial peptides. This review summarizes the recent understanding of the interactions between skin-associated adipocytes and other skin cells in maintaining the integrity and effectiveness of skin barrier immunity.

Recent Advances in the Knowledge of the Mechanisms of Leptin Physiology and Actions in Neurological and Metabolic Pathologies

Excess body weight is frequently associated with low-grade inflammation. Evidence indicates a relationship between obesity and cancer, as well as with other diseases, such as diabetes and non-alcoholic fatty liver disease, in which inflammation and the actions of various adipokines play a role in the pathological mechanisms involved in these disorders. Leptin is mainly produced by adipose tissue in proportion to fat stores, but it is also synthesized in other organs, where leptin receptors are expressed. This hormone performs numerous actions in the brain, mainly related to the control of energy homeostasis. It is also involved in neurogenesis and neuroprotection, and central leptin resistance is related to some neurological disorders, e.g., Parkinson's and Alzheimer's diseases. In peripheral tissues, leptin is implicated in the regulation of metabolism, as well as of bone density and muscle mass. All these actions can be affected by changes in leptin levels and the mechanisms associated with resistance to this hormone. This review will present recent advances in the molecular mechanisms of leptin action and their underlying roles in pathological situations, which may be of interest for revealing new approaches for the treatment of diseases where the actions of this adipokine might be compromised.

Impact of Paraben Exposure on Adiposity-Related Measures: An Updated Literature Review of Population-Based Studies

Parabens are alkyl esters of p-hydroxybenzoic acid that are commonly used in pharmaceutical and cosmetic products. Humans are exposed to parabens when they use these products and through diet. There are growing concerns that paraben exposure can adversely impact human health. The endocrine-disrupting and obesogenic properties of parabens have been observed in animal studies and in vitro, prompting the increase in population-based studies of paraben exposure and adiposity-related endpoints. In this review, we summarize epidemiological studies published between 2017 and 2022 that examined paraben exposure in utero, between birth and adolescence, and in adulthood, in relation to adiposity-related measures. Overall, these studies provide some evidence that suggests that paraben exposure, especially during critical development windows, is associated with adiposity-related measures. However, we have noted several limitations in these studies, including the predominance of cross-sectional studies, inconsistent sample collection procedures, and small sample sizes, which should be addressed in future studies.

The impact of leptin and its receptor polymorphisms on type 1 diabetes in a population of northwest Iran

BACKGROUND

Diabetes comprises a serious disease with significant growth in the number of cases in recent years. Here, we cover the gap in information between leptin (LEP) and type 1 diabetes in the Iranian population.

AIM

To recognise LEP G2548A and LEP receptor Q223R polymorphisms in Iranian people and their association with type 1 diabetes susceptibility.

SUBJECTS AND METHODS

Characteristics such as fasting blood sugar (FBS) were measured in 80 control non-diabetic individuals and 89 diabetic patients. Moreover, LEP G2548A and LEP receptor Q223R polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism technique.

RESULTS

The frequency of the A allele was nearly three times greater in diabetes patients than in the control group. In addition, in the diabetes group, the AA genotype was five times greater than in the control group (p < 0.01). Furthermore, AA and AA + AG genotype models had higher FBS levels than the GG + AG and GG genotype models, respectively (p < 0.01).

CONCLUSION

The LEP G2548A polymorphism could be related to type 1 diabetes susceptibility, but not LEPR Q223R polymorphism in the Iranian population. Importantly, further studies are essential to examine the impact of LEP G2548A and LEPR Q223R polymorphisms in the endocrinology area.

TET3 epigenetically controls feeding and stress response behaviors via AGRP neurons

The TET family of dioxygenases promote DNA demethylation by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Hypothalamic agouti-related peptide-expressing (AGRP-expressing) neurons play an essential role in driving feeding, while also modulating nonfeeding behaviors. Besides AGRP, these neurons produce neuropeptide Y (NPY) and the neurotransmitter GABA, which act in concert to stimulate food intake and decrease energy expenditure. Notably, AGRP, NPY, and GABA can also elicit anxiolytic effects. Here, we report that in adult mouse AGRP neurons, CRISPR-mediated genetic ablation of Tet3, not previously known to be involved in central control of appetite and metabolism, induced hyperphagia, obesity, and diabetes, in addition to a reduction of stress-like behaviors. TET3 deficiency activated AGRP neurons, simultaneously upregulated the expression of Agrp, Npy, and the vesicular GABA transporter Slc32a1, and impeded leptin signaling. In particular, we uncovered a dynamic association of TET3 with the Agrp promoter in response to leptin signaling, which induced 5hmC modification that was associated with a chromatin-modifying complex leading to transcription inhibition, and this regulation occurred in both the mouse models and human cells. Our results unmasked TET3 as a critical central regulator of appetite and energy metabolism and revealed its unexpected dual role in the control of feeding and other complex behaviors through AGRP neurons.

The promise of new anti-obesity therapies arising from knowledge of genetic obesity traits

Obesity is a multifactorial and complex disease that often manifests in early childhood with a lifelong burden. Polygenic and monogenic obesity are driven by the interaction between genetic predisposition and environmental factors. Polygenic variants are frequent and confer small effect sizes. Rare monogenic obesity syndromes are caused by defined pathogenic variants in single genes with large effect sizes. Most of these genes are involved in the central nervous regulation of body weight; for example, genes of the leptin-melanocortin pathway. Clinically, patients with monogenic obesity present with impaired satiety, hyperphagia and pronounced food-seeking behaviour in early childhood, which leads to severe early-onset obesity. With the advent of novel pharmacological treatment options emerging for monogenic obesity syndromes that target the central melanocortin pathway, genetic testing is recommended for patients with rapid weight gain in infancy and additional clinical suggestive features. Likewise, patients with obesity associated with hypothalamic damage or other forms of syndromic obesity involving energy regulatory circuits could benefit from these novel pharmacological treatment options. Early identification of patients affected by syndromic obesity will lead to appropriate treatment, thereby preventing the development of obesity sequelae, avoiding failure of conservative treatment approaches and alleviating stigmatization of patients and their families.

A nexus of lipid and O-Glcnac metabolism in physiology and disease

Although traditionally considered a glucose metabolism-associated modification, the O-linked β-N-Acetylglucosamine (O-GlcNAc) regulatory system interacts extensively with lipids and is required to maintain lipid homeostasis. The enzymes of O-GlcNAc cycling have molecular properties consistent with those expected of broad-spectrum environmental sensors. By direct protein-protein interactions and catalytic modification, O-GlcNAc cycling enzymes may provide both acute and long-term adaptation to stress and other environmental stimuli such as nutrient availability. Depending on the cell type, hyperlipidemia potentiates or depresses O-GlcNAc levels, sometimes biphasically, through a diversity of unique mechanisms that target UDP-GlcNAc synthesis and the availability, activity and substrate selectivity of the glycosylation enzymes, O-GlcNAc Transferase (OGT) and O-GlcNAcase (OGA). At the same time, OGT activity in multiple tissues has been implicated in the homeostatic regulation of systemic lipid uptake, storage and release. Hyperlipidemic patterns of O-GlcNAcylation in these cells are consistent with both transient physiological adaptation and feedback uninhibited obesogenic and metabolic dysregulation. In this review, we summarize the numerous interconnections between lipid and O-GlcNAc metabolism. These links provide insights into how the O-GlcNAc regulatory system may contribute to lipid-associated diseases including obesity and metabolic syndrome.

Augmented leptin-induced trefoil factor 3 expression and epidermal growth factor receptor transactivation differentially influences neoplasia progression in the stomach and colorectum of dietary fat-induced obese mice

Obesity is a risk factor for gastrointestinal malignancies and tumors. However, which factors either protect or predispose the gastrointestinal organs to high-fat diet (HFD)-induced neoplasia remains unclear. Here, we demonstrate that HFD impacts the stomach to a greater extent as compared to the colorectum, resulting in leptin receptor (LepR) signaling-mediated neoplasia in the tissues. HFD activated leptin signaling, which in turn, accelerates the pathogenesis in the gastric mucosa more than that in the colorectum along with ectopic TFF3 expression. Moreover, in the stomach, higher levels of phosphorylated epidermal growth factor receptor (EGFR) in addition to the activation of STAT3 and Akt were observed as compared to the colorectum. The mice with LepR deletion in the gastrointestinal epithelium exhibited a suppressed induction of leptin, TFF3, and phosphorylated EGFR in the stomach, whereas the levels in the colorectum were insignificant. In co-transfected COS-7 cells with LepR and EGFR plasmid DNA, leptin transactivated EGFR to accelerate TFF3 induction along with activation of STAT3, ERK1/2, Akt, and PI3K p85/p55. Furthermore, TFF3 could bind to EGFR but did not transactivate LepR. Leptin-induced TFF3 induction was markedly suppressed by inhibitors of PI3K (LY294002) and EGFR (Erlotinib). Together, these results suggest a novel role of LepR-mediated signaling in transactivating EGFR that leads to TFF3 expression via the PI3K-Akt pathway. Therefore, this study sheds light on the identification of potentially new therapeutic targets for the treatment of pre-cancerous symptoms in stomach and colorectum.

Leptin receptor signaling sustains metabolic fitness of alveolar macrophages to attenuate pulmonary inflammation

Alveolar macrophages (AMs) are critical mediators of pulmonary inflammation. Given the unique lung tissue environment, whether there exist AM-specific mechanisms that control inflammation is not known. Here, we found that among various tissue-resident macrophage populations, AMs specifically expressed Lepr, encoding receptor for a key metabolic hormone leptin. AM-intrinsic Lepr signaling attenuated pulmonary inflammation in vivo, manifested as subdued acute lung injury yet compromised host defense against Streptococcus pneumoniae infection. Lepr signaling protected AMs from necroptosis and thus constrained neutrophil recruitment and tissue damage secondary to release of proinflammatory cytokine interleukin-1α. Mechanistically, Lepr signaling sustained activation of adenosine monophosphate-activated protein kinase in a Ca²⁺ influx-dependent manner and rewired cellular metabolism, thus preventing excessive lipid droplet formation and overloaded metabolic stress in a lipid-rich alveolar microenvironment. In conclusion, our results defined AM-expressed Lepr as a metabolic checkpoint of pulmonary inflammation and exemplified a macrophage tissue adaptation strategy for maintenance of immune homeostasis.

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

BACKGROUND

Leptin is important in physiological and pathological functions in various cancers, however, the significance and mechanisms of leptin in nasopharyngeal carcinoma remain ambiguous.

METHODS

Leptin expression was analyzed by QPCR, immunohistochemistry, Western blotting, and TCGA database. The impact of gain- or loss-of-function of leptin were determined by MTT, colony formation, wound healing, and Transwell assays in NPC cells, and by a xenograft tumor model. Leptin-modulated glucose consumption and lactate production were assessed by ELISA. Furthermore, leptin-regulated signaling pathways were examined by QPCR and Western blotting assays. The immunoprecipitation assay was conducted to determine interaction between leptin and EGFR. In addition, miR-874-3p-regulated leptin expression was evaluated using bioinformatics, QPCR, luciferase assay, AGO2-RIP assay, and Western blotting.

RESULTS

In this study, we found that leptin was highly expressed in the sera and tumor tissues of patients with NPC, and elevated leptin expression was associated with advanced clinical features and poor prognosis. Functional assays demonstrated that leptin remarkably promoted NPC cell growth, motility, and glycolysis in vitro and in vivo. Mechanistically, leptin associated with EGFR, resulting in enhanced cell growth through the regulation of cell-cycle related markers, glycolysis-related genes, and EGFR/AKT/c-Myc signaling. Moreover, leptin potentiated the invasive capacity of NPC cells by promoting EMT. We further explored that miR-874-3p influenced leptin-mediated NPC progression. Overexpression of miR-874-3p prevented cell growth, motility, glucose consumption, and lactate production in NPC cells, whereas miR-874-3p inhibition had the opposite effects. AGO-RIP assays confirmed that Argonaute 2 (AGO2), a protein associated with miR-874-3p, regulated leptin expression in NPC cells. The rescue assays indicated that inhibition of leptin suppressed the effects of miR-874-3p inhibitor. In clinical specimens, miR-874-3p was negatively correlated with leptin.

CONCLUSIONS

Leptin may serve as a novel prognostic factor and potential therapeutic target for patients with NPC. In addition, a newly discovered regulatory axis of leptin/EGFR/AKT/c-Myc can provide a novel therapeutic strategy for NPC.

Leptin: an entry point for the treatment of peripheral tissue fibrosis and related diseases

Leptin is a small peptide mainly secreted by adipocyte, which acts on the central nervous system of the hypothalamus to regulate the body's energy balance by inhibiting food intake, it also can directly act on specific cells through leptin receptors (for example, ObRa, which exists in the blood-brain barrier or kidneys), thereby affect cell metabolism. Excessive deposition of extracellular matrix (ECM) causes damage to normal tissues or destruction of organ structure, which will eventually lead to tissue or organ fibrosis. The sustainable development of fibrosis can lead to structural damage and functional decline of organs, and even exhaustion, which seriously threatens human health and life. In recent years, studies have found that leptin directly alleviates the fibrosis process of various tissues and organs in mammals. Therefore, we speculate that leptin may become a significant treatment for fibrosis of various tissues and organs in the future. So, the main purpose of this review is to explore the specific mechanism of leptin in the process of fibrosis in multiple tissues and organs, and to provide a theoretical basis for the treatment of various tissues and organs fibrosis and related diseases caused by it, which is of great significance in the future.

Leptin as a key regulator of the adipose organ

Leptin is a hormone primarily produced by the adipose tissue in proportion to the size of fat stores, with a primary function in the control of lipid reserves. Besides adipose tissue, leptin is also produced by other tissues, such as the stomach, placenta, and mammary gland. Altogether, leptin exerts a broad spectrum of short, medium, and long-term regulatory actions at the central and peripheral levels, including metabolic programming effects that condition the proper development and function of the adipose organ, which are relevant for its main role in energy homeostasis. Comprehending how leptin regulates adipose tissue may provide important clues to understand the pathophysiology of obesity and related diseases, such as type 2 diabetes, as well as its prevention and treatment. This review focuses on the physiological and long-lasting regulatory effects of leptin on adipose tissue, the mechanisms and pathways involved, its main outcomes on whole-body physiological homeostasis, and its consequences on chronic diseases.

Relationships Among Gut Microbiota, Ischemic Stroke and Its Risk Factors: Based on Research Evidence

Stroke is a highly lethal disease and disabling illness while ischemic stroke accounts for the majority of stroke. It has been found that inflammation plays a key role in the initiation and progression of stroke, and atherosclerotic plaque rupture is considered to be the leading cause of ischemic stroke. Furthermore, chronic inflammatory diseases, such as obesity, type 2 diabetes mellitus (T2DM) and hypertension, are also considered as the high-risk factors for stroke. Recently, the topic on how gut microbiota affects human health has aroused great concern. The initiation and progression of ischemic stroke has been found to have close relation with gut microbiota dysbiosis. Hence, this manuscript briefly summarizes the roles of gut microbiota in ischemic stroke and its related risk factors, and the practicability of preventing and alleviating ischemic stroke by reconstructing gut microbiota.

Epiregulin as an Alternative Ligand for Leptin Receptor Alleviates Glucose Intolerance without Change in Obesity

The leptin receptor (LepR) acts as a signaling nexus for the regulation of glucose uptake and obesity, among other metabolic responses. The functional role of LepR under leptin-deficient conditions remains unclear. This study reports that epiregulin (EREG) governed glucose uptake in vitro and in vivo in Lep^ob mice by activating LepR under leptin-deficient conditions. Single and long-term treatment with EREG effectively rescued glucose intolerance in comparative insulin and EREG tolerance tests in Lep^ob mice. The immunoprecipitation study revealed binding between EREG and LepR in adipose tissue of Lep^ob mice. EREG/LepR regulated glucose uptake without changes in obesity in Lep^ob mice via mechanisms, including ERK activation and translocation of GLUT4 to the cell surface. EREG-dependent glucose uptake was abolished in Lepr^db mice which supports a key role of LepR in this process. In contrast, inhibition of the canonical epidermal growth factor receptor (EGFR) pathway implicated in other EREG responses, increased glucose uptake. Our data provide a basis for understanding glycemic responses of EREG that are dependent on LepR unlike functions mediated by EGFR, including leptin secretion, thermogenesis, pain, growth, and other responses. The computational analysis identified a conserved amino acid sequence, supporting an evolutionary role of EREG as an alternative LepR ligand.

Synthetic leptin c-fragment peptide minimises heat-induced impairment of spermatogenesis in mice via Stat3 signalling

Mammalian spermatogenesis is a temperature-sensitive process, and an increase in testicular temperature impairs spermatogenesis. Leptin modulates testicular activity, but the effect of leptin or its synthetic analogue on heat-induced testicular impairment is unclear. We investigated the effects of synthetic leptin peptide (116-130 amides) on testicular activity in heat-stressed mice model. 15 adult mice (25.54 ± 1.43 g) were selected for the study. Ten mice were subjected to a single heat stress treatment (HS) at 43 °C for 15 min by submerging the lower half of the body in a thermostatic water bath. After heat treatment, mice were divided into two groups, the heat-stressed HS group (n = 5) and the second group as HSL, treated with leptin peptide (116-130 amide) for 14 days. The HS group showed a significant (p < 0.05) decline in the GSI (0.25 ± 0.018), Johnsenscore (4.5 ±.19), seminiferous tubule diameter (160.75 ± 10.18 μm), germinal epithelium height, (GEH) (37.5 ± 1.59 μm) compared to the CN (GSI-0.37 ± 0.015; Johnsen score-7.9 ± 0.20; GEH- 73.25 ± 1.29 μm; tubule diameter-230.25 ± 1.39 μm) and the HSL groups (GSI-0.38 ± 0.014; Johnsen' score-8.0 ± 0.32; GEH- 37.5 ± 1.59 μm; tubule diameter-160.75 ± 10.18 μm) groups. Heat treatment significantly (p < 0.05) increased the intra-testicular levels of leptin (HS-20.11 ± 2.1 pg/mg protein; CN-10.50 ± 0.17 pg/mg protein; HSL-12.99 ± 0.52 pg/mg protein) with a reduced level of pStat3, suggesting leptin resistance during testicular hyperthermia. Furthermore, heat treatment was associated with significantly (p < 0.05) decreased germ cell proliferation and reduced circulating testosterone levels (HS-2.69 ± 2.01 ng/mL; CN-7.69 ± 0.32 ng/mL; HSL-5.36 ± 0.73 ng/mL). However, the circulating androstenedione levels showed a significant (p < 0.05) increase in the HS group (0.75 ± 0.03 ng/mL) compared to the CN (0.51 ± 0.02 ng/mL) and HSL (0.57 ± 0.07 ng/mL) groups. Immunolocalisation of 3β-HSD showed moderate to faint staining in the Leydig cells in the HS group compared to the CN and HSL groups. Treatment with leptin peptide resulted in decrease in the intra-testicular leptin levels with increased phosphorylation of Stat3, suggesting improved leptin resistance, which was positively associated with increased germ cell proliferation, elevated testosterone levels, and improved testicular histoarchitecture. Testicular hyperthermia may cause leptin resistance and impaired leptin signalling, decreased testosterone biosynthesis and suppressed spermatogenesis, which could be a manifestation of leptin resistance. Treatment with leptin peptide improves leptin signalling and testicular activity in heat-stressed mice, but the underlying mechanism is still unclear.

AgRP/NPY and POMC neurons in the arcuate nucleus and their potential role in treatment of obesity

Obesity is a major health crisis affecting over a third of the global population. This multifactorial disease is regulated via interoceptive neural circuits in the brain, whose alteration results in excessive body weight. Certain central neuronal populations in the brain are recognised as crucial nodes in energy homeostasis; in particular, the hypothalamic arcuate nucleus (ARC) region contains two peptide microcircuits that control energy balance with antagonistic functions: agouti-related peptide/neuropeptide-Y (AgRP/NPY) signals hunger and stimulates food intake; and pro-opiomelanocortin (POMC) signals satiety and reduces food intake. These neuronal peptides levels react to energy status and integrate signals from peripheral ghrelin, leptin, and insulin to regulate feeding and energy expenditure. To manage obesity comprehensively, it is crucial to understand cellular and molecular mechanisms of information processing in ARC neurons, since these regulate energy homeostasis. Importantly, a specific strategy focusing on ARC circuits needs to be devised to assist in treating obese patients and maintaining weight loss with minimal or no side effects. The aim of this review is to elucidate the recent developments in the study of AgRP-, NPY- and POMC-producing neurons, specific to their role in controlling metabolism. The impact of ghrelin, leptin, and insulin signalling via action of these neurons is also surveyed, since they also impact energy balance through this route. Lastly, we present key proteins, targeted genes, compounds, drugs, and therapies that actively work via these neurons and could potentially be used as therapeutic targets for treating obesity conditions.

Amino Acid Nanofibers Improve Glycemia and Confer Cognitive Therapeutic Efficacy to Bound Insulin

Diabetes poses a high risk for debilitating complications in neural tissues, regulating glucose uptake through insulin-dependent and predominantly insulin-independent pathways. Supramolecular nanostructures provide a flexible strategy for combinatorial regulation of glycemia. Here, we compare the effects of free insulin to insulin bound to positively charged nanofibers comprised of self-assembling amino acid compounds (AACs) with an antioxidant-modified side chain moiety (AAC2) in both in vitro and in vivo models of type 1 diabetes. Free AAC2, free human insulin (hINS) and AAC2-bound-human insulin (AAC2-hINS) were tested in streptozotocin (STZ)-induced mouse model of type 1 diabetes. AAC2-hINS acted as a complex and exhibited different properties compared to free AAC2 or hINS. Mice treated with the AAC2-hINS complex were devoid of hypoglycemic episodes, had improved levels of insulin in circulation and in the brain, and increased expression of neurotransmitter taurine transporter, Slc6a6. Consequently, treatment with AAC2-hINS markedly advanced both physical and cognitive performance in mice with STZ-induced and genetic type 1 diabetes compared to treatments with free AAC2 or hINS. This study demonstrates that the flexible nanofiber AAC2 can serve as a therapeutic platform for the combinatorial treatment of diabetes and its complications.

The role of leptin in patients recovering from Anorexia Nervosa

Introduction: Anorexia nervosa (AN) is a mental disorder with the highest death rate. The characteristic feature of AN is endocrine dysregulations, including changes in adipose-tissue secreted hormones, especially adipokines. The most widely studied of them is leptin whose role in the pathophysiology and prognosis of AN is confirmed in more and more studies. The aim of the study was to summarize the role of endocrine disruptions with particular emphasis on leptin in the pathophysiology of AN.

Material and methods: For the literature review, the electronic databases PubMed, Cochrane and Google Scholar search were used with the following keywords: eating disorders, adipokines, leptin, metreleptin, satiety, hunger, anorexia, obesity, for studies listed from database inception to October 2021.

Results: Leptin, produced mainly by white adipose tissue, inhibits the hunger center in the hypothalamus by negative feedback with ghrelin secreted by the gastrointestinal tract. Leptin is involved in numerous biological functions, including body weight regulation, innate and adaptive immunity regulation, reproduction, and bone formation. Studies confirm decreased leptin levels in AN individuals. In recent years, extensive experience has been gained with leptin as a drug in clinical trials. The studies suggested that treatment can restore menstrual function and bone health and improve mood with unclear body weight effects.

Conclusions: Focusing on leptin-related changes is a promising approach to improve AN management. Assessment of leptin levels in AN patients could be a useful tool for therapy monitoring. Treatment with leptin could reverse unfavourable changes induced by diet restriction, including mood symptoms, loss of bone mass and menstrual function. However, the results of these studies need confirmation on larger groups of patients.

The Leptin Axis and Its Association With the Adaptive Immune System in Breast Cancer

Adipose tissue secretes various peptides, including leptin. This hormone acts through the leptin receptor (Ob-R), which is expressed ubiquitously on the surface of various cells, including breast cancer cells and immune cells. Increasing evidence points to an interaction between the tumor microenvironment, tumor cells, and the immune system. Leptin plays an important role in breast cancer tumorigenesis and may be implicated in activation of the immune system. While breast cancer cannot be considered an immunogenic cancer, the triple-negative subtype is an exception. Specific immune cells - tumor infiltrating lymphocytes - are involved in the immune response and act as predictive and prognostic factors in certain breast cancer subtypes. The aim of this article is to review the interaction between adipose tissue, through the expression of leptin and its receptor, and the adaptive immune system in breast cancer.

Molecular mechanism of anti-adipogenic effect of vitexin in differentiating hMSCs

In this study, we evaluated a detailed molecular mechanism of anti-adipogenic activity of vitexin, apigenin flavone glucoside, present in germinated fenugreek seeds, in differentiating human mesenchymal stem cells (hMSCs). The lipid content of differentiated adipocytes was estimated by ORO staining. Effect on mitotic clonal expansion was checked by cell cycle analysis. Expression of early and terminal adipocyte differentiation markers, anti- and pro-adipogenic transcription factors and signalling intermediates regulating them was evaluated at RNA and protein level. We found vitexin to be non-cytotoxic up to 20 μM at which intracellular lipid accumulation was significantly decreased. Cell cycle analysis suggested that vitexin does not affect mitotic clonal expansion. Expression of early and late differentiation markers, such as CEBPα, CEBPβ, PPARγ, FABP4, perilipin, adiponectin and Glut4 was significantly reduced in the presence of vitexin. Expression of KLF4 and KLF15, positive regulators of PPARγ, was decreased, whereas that of negative regulators, namely KLF2, GATA2, miR20a, miR27a, miR27b, miR128, miR130a, miR130b, miR182 and miR548 increased with vitexin treatment. This effect was mediated by the activation of the AMP-activated protein kinase (AMPK) pathway via the activation of LepR and additionally by inhibiting ROS. Thus, our results showed that vitexin regulates the expression of PPARγ and inhibits adipogenesis of hMSCs at an early stage of differentiation.

Obesity-associated leptin promotes chemoresistance in colorectal cancer through YAP-dependent AXL upregulation

Obesity results from an imbalance between caloric intake and energy expenditure, and it is highly associated with colorectal carcinogenesis and therapeutic resistance in patients with colorectal cancer (CRC). Dysregulation of adipokine production in obesity has been reported to cause malignant behaviors in CRC. Leptin, which is the principal hormone secreted by adipocytes and an obesity-associated adipokine, is significantly overexpressed in CRC tissues. However, the effect of leptin on chemoresistance in CRC is unclear. Therefore, the aim of this study was to clarify the role of leptin and the underlying mechanisms in mediating 5-fluorouracil (5-FU) resistance in CRC. We used palmitate to artificially generate obese adipocytes. As expected, lipid accumulation was significantly increased in obese adipocytes. We demonstrated that CRC cells incubated with conditioned media (CM) harvested from obese adipocytes were associated with increased resistance to 5-FU. Notably, this increase in resistance to 5-FU was through the elevated production and secretion of leptin. Leptin could further stimulate the expression of AXL and activate its downstream signaling molecule, PLCγ, thereby resulting in an increased expression of p-glycoprotein (P-gp) in CRC cells. Mechanistically, leptin induced AXL expression via the inhibition of AMPK and subsequent increase in YAP activation and nuclear translocation. In addition, nuclear YAP interacted with TEAD and promoted the occupancy of TEAD on the AXL promoter, thereby stimulating AXL promoter activity after leptin treatment. Furthermore, leptin neutralization rescued the sensitivity of CRC tumors to 5-FU in mice fed on a high-fat diet (HFD). These results indicated that leptin mediated 5-FU resistance through YAP-dependent AXL overexpression in CRC.

Leptin promotes glycolytic metabolism to induce dendritic cells activation via STAT3-HK2 pathway

Leptin is over-secreted in many autoimmune diseases, which can promote dendritic cells (DCs) maturation and up-regulate the expression of inflammatory cytokines, but the underlying mechanisms are not fully elucidated. Considering the major role of leptin in maintaining energy balance and the significant role of glycolysis in DCs activation, our study aims to investigate whether leptin promotes the activation of DCs via glycolysis and its underlying mechanisms. We demonstrated that leptin promoted the activation of DCs, including up-regulating the expression of co-stimulatory molecules and inflammatory cytokines, enhancing the proliferation and T helper 17 (Th17) cell ratio in peripheral blood mononuclear cells (PBMC) co-cultured with leptin-stimulated DCs. Leptin also enhanced DCs glycolysis with increased glucose consumption, lactate production, and the expression of hexokinase 2 (HK2). In addition, the activation of DCs stimulated by leptin could be inhibited by the glycolysis inhibitor 2-deoxy-d-glucose (2-DG). To explore the signaling pathways involved in leptin-induced HK2 expression, we observed that the inhibitors of STAT3 (NSC74859) could repress the enhancement of HK2 triggered by leptin stimulation. Therefore, our results indicated that leptin promoted glycolytic metabolism to induce DCs activation via STAT3-HK2 pathway.

Multiple Leptin Signalling Pathways in the Control of Metabolism and Fertility: A Means to Different Ends?

The adipocyte-derived ‘satiety promoting’ hormone, leptin, has been identified as a key central regulator of body weight and fertility, such that its absence leads to obesity and infertility. Plasma leptin levels reflect body adiposity, and therefore act as an ‘adipostat’, whereby low leptin levels reflect a state of low body adiposity (under-nutrition/starvation) and elevated leptin levels reflect a state of high body adiposity (over-nutrition/obesity). While genetic leptin deficiency is rare, obesity-related leptin resistance is becoming increasingly common. In the absence of adequate leptin sensitivity, leptin is unable to exert its ‘anti-obesity’ effects, thereby exacerbating obesity. Furthermore, extreme leptin resistance and consequent low or absent leptin signalling resembles a state of starvation and can thus lead to infertility. However, leptin resistance occurs on a spectrum, and it is possible to be resistant to leptin’s metabolic effects while retaining leptin’s permissive effects on fertility. This may be because leptin exerts its modulatory effects on energy homeostasis and reproductive function through discrete intracellular signalling pathways, and these pathways are differentially affected by the molecules that promote leptin resistance. This review discusses the potential mechanisms that enable leptin to exert differential control over metabolic and reproductive function in the contexts of healthy leptin signalling and of diet-induced leptin resistance.