20 years of leptin: from the discovery of the leptin gene to leptin in our therapeutic armamentarium

Association between hypothalamic Alzheimer's disease pathology and body mass index: The Hisayama study

The hypothalamus is the region of the brain that integrates the neuroendocrine system and whole-body metabolism. Patients with Alzheimer's disease (AD) have been reported to exhibit pathological changes in the hypothalamus, such as neurofibrillary tangles (NFTs) and amyloid plaques (APs). However, few studies have investigated whether hypothalamic AD pathology is associated with clinical factors. We investigated the association between AD-related pathological changes in the hypothalamus and clinical pictures using autopsied brain samples obtained from deceased residents of a Japanese community. A total of 85 autopsied brain samples were semi-quantitatively analyzed for AD pathology, including NFTs and APs. Our histopathological studies showed that several hypothalamic nuclei, such as the tuberomammillary nucleus (TBM) and lateral hypothalamic area (LHA), are vulnerable to AD pathologies. NFTs are observed in various neuropathological states, including normal cognitive cases, whereas APs are predominantly observed in AD. Regarding the association between hypothalamic AD pathologies and clinical factors, the degree of APs in the TBM and LHA was associated with a lower body mass index while alive, after adjusting for sex and age at death. However, we found no significant association between hypothalamic AD pathology and the prevalence of hypertension, diabetes, or dyslipidemia. Our study showed that a lower BMI, which is a poor prognostic factor of AD, might be associated with hypothalamic AP pathology and highlighted new insights regarding the disruption of the brain-whole body axis in AD.

Central inhibition of HDAC6 re-sensitizes leptin signaling during obesity to induce profound weight loss

Leptin resistance during excess weight gain significantly contributes to the recidivism of obesity to leptin-based pharmacological therapies. The mechanisms underlying the inhibition of leptin receptor (LepR) signaling during obesity are still elusive. Here, we report that histone deacetylase 6 (HDAC6) interacts with LepR, reducing the latter's activity, and that pharmacological inhibition of HDAC6 activity disrupts this interaction and augments leptin signaling. Treatment of diet-induced obese mice with blood-brain barrier (BBB)-permeable HDAC6 inhibitors profoundly reduces food intake and leads to potent weight loss without affecting the muscle mass. Genetic depletion of Hdac6 in Agouti-related protein (AgRP)-expressing neurons or administration with BBB-impermeable HDAC6 inhibitors results in a lack of such anti-obesity effect. Together, these findings represent the first report describing a mechanistically validated and pharmaceutically tractable therapeutic approach to directly increase LepR activity as well as identifying centrally but not peripherally acting HDAC6 inhibitors as potent leptin sensitizers and anti-obesity agents.

Milestones in the journey towards addressing obesity; Past trials and triumphs, recent breakthroughs, and an exciting future in the era of emerging effective medical therapies and integration of effective medical therapies with metabolic surgery

The 21st century is characterized by an increasing incidence and prevalence of obesity and the burden of its associated comorbidities, especially cardiometabolic diseases, which are reaching pandemic proportions. In the late '90s, the "black box" of adipose tissue and energy homeostasis was opened with the discovery of leptin, transforming the adipose tissue from an "inert fat-storage organ" to the largest human endocrine organ and creating the basis on which more intensified research efforts to elucidate the pathogenesis of obesity and develop novel treatments were based upon. Even though leptin was eventually not proven to be the "standalone magic bullet" for the treatment of common/polygenic obesity, it has been successful in the treatment of monogenic obesity syndromes. Additionally, it shifted the paradigm of treating obesity from a condition due to "lack of willpower" to a disease due to distinct underlying biological mechanisms for which specific pharmacotherapies would be needed in addition to lifestyle modification. Subsequently, the melanocortin pathway proved to be an equally valuable pathway for the pharmacotherapy of obesity. Melanocortin receptor agonists have recently been approved for treating certain types of syndromic obesity. Other molecules- such as incretins, implicated in energy and glucose homeostasis- are secreted by the gastrointestinal tract. Glucagon-like peptide 1 (GLP-1) is the most prominent one, with GLP-1 analogs approved for common/polygenic obesity. Unimolecular combinations with other incretins, e.g., GLP-1 with gastric inhibitory polypeptide and/or glucagon, are expected to be approved soon as more effective pharmacotherapies for obesity and its comorbidities. Unimolecular combinations with other compounds and small molecules activating the receptors of these molecules are currently under investigation as promising future pharmacotherapies. Moreover, metabolic and bariatric surgery has also demonstrated impressive results, especially in the case of morbid obesity. Consequently, this broadening therapeutic armamentarium calls for a well-thought-after and well-coordinated multidisciplinary approach, for instance, through cardiometabolic expertise centers, that would ideally address effectively and cost-effectively obesity and its comorbidities, providing tangible benefits to large segments of the population.

Serum Leptin Receptor and the rs1137101 Variant of the LEPR Gene Are Associated with Bladder Cancer

Globally, bladder cancer (BC) is one of the ten most common tumors. Obesity is a worldwide problem associated with an increased BC risk. Considering that levels of leptin and/or its receptor are often deregulated in obese individuals, we hypothesized that they could contribute to BC. To test this hypothesis, we utilized a case-control study in which 116 patients with a confirmed diagnosis of BC and 116 controls were recruited. The serum levels of leptin and leptin receptor were measured. Patients and controls were also genotyped for SNPs in the LEP (rs7799039, rs791620, and rs2167270) and LEPR genes (rs1137100, rs1137101, and rs1805094). The univariate analysis indicated that BC patients had significantly higher levels of leptin and lower levels of leptin receptor (p < 0.05). Moreover, rs7799039 of LEP and rs1137101 of LEPR were associated with BC (p < 0.05). In the multivariate analysis, leptin receptor levels were protective (OR: 0.98, 95% CI = 0.97-0.99, p = 0.002) while the GG genotype of rs1137101 of LEPR increased BC risk (OR: 3.42, 95% CI = 1.27-9.20, p = 0.02). These findings highlight that lifestyle changes could be useful in preventing BC and that disturbances in energy metabolism could play a role in the pathobiology of BC.

The Mechanism of the Gut-Brain Axis in Regulating Food Intake

With the increasing prevalence of energy metabolism disorders such as diabetes, cardiovascular disease, obesity, and anorexia, the regulation of feeding has become the focus of global attention. The gastrointestinal tract is not only the site of food digestion and absorption but also contains a variety of appetite-regulating signals such as gut-brain peptides, short-chain fatty acids (SCFAs), bile acids (BAs), bacterial proteins, and cellular components produced by gut microbes. While the central nervous system (CNS), as the core of appetite regulation, can receive and integrate these appetite signals and send instructions to downstream effector organs to promote or inhibit the body's feeding behaviour. This review will focus on the gut-brain axis mechanism of feeding behaviour, discussing how the peripheral appetite signal is sensed by the CNS via the gut-brain axis and the role of the central "first order neural nuclei" in the process of appetite regulation. Here, elucidation of the gut-brain axis mechanism of feeding regulation may provide new strategies for future production practises and the treatment of diseases such as anorexia and obesity.

Intermittent energy restriction changes the regional homogeneity of the obese human brain

Background

Intermittent energy restriction (IER) is an effective weight loss strategy. However, the accompanying changes in spontaneous neural activity are unclear, and the relationship among anthropometric measurements, biochemical indicators, and adipokines remains ambiguous.

Methods

Thirty-five obese adults were recruited and received a 2-month IER intervention. Data were collected from anthropometric measurements, blood samples, and resting-state functional magnetic resonance imaging at four time points. The regional homogeneity (ReHo) method was used to explore the effects of the IER intervention. The relationships between the ReHo values of altered brain regions and changes in anthropometric measurements, biochemical indicators, and adipokines (leptin and adiponectin) were analyzed.

Results

Results showed that IER significantly improved anthropometric measurements, biochemical indicators, and adipokine levels in the successful weight loss group. The IER intervention for weight loss was associated with a significant increase in ReHo in the bilateral lingual gyrus, left calcarine, and left postcentral gyrus and a significant decrease in the right middle temporal gyrus and right cerebellum (VIII). Follow-up analyses showed that the increase in ReHo values in the right LG had a significant positive correlation with a reduction in Three-factor Eating Questionnaire (TFEQ)-disinhibition and a significant negative correlation with an increase in TFEQ-cognitive control. Furthermore, the increase in ReHo values in the left calcarine had a significant positive correlation with the reduction in TFEQ-disinhibition. However, no significant difference in ReHo was observed in the failed weight loss group.

Conclusion

Our study provides objective evidence that the IER intervention reshaped the ReHo of some brain regions in obese individuals, accompanied with improved anthropometric measurements, biochemical indicators, and adipokines. These results illustrated that the IER intervention for weight loss may act by decreasing the motivational drive to eat, reducing reward responses to food cues, and repairing damaged food-related self-control processes. These findings enhance our understanding of the neurobiological basis of IER for weight loss in obesity.

The Molecular and Genetic Interactions between Obesity and Breast Cancer Risk

Breast cancer (BC) is considered the leading cause of death among females worldwide. Various risk factors contribute to BC development, such as age, genetics, reproductive factors, obesity, alcohol intake, and lifestyle. Obesity is considered to be a pandemic health problem globally, affecting millions of people worldwide. Obesity has been associated with a high risk of BC development. Determining the impact of obesity on BC development risk in women by demonstrating the molecular and genetic association in pre- and post-menopause females and risk to BC initiation is crucial in order to improve the diagnosis and prognosis of BC disease. In epidemiological studies, BC in premenopausal women was shown to be protective in a certain pattern. These altered effects between the two phases could be due to various physiological changes, such as estrogen/progesterone fluctuating levels. In addition, the relationship between BC risk and obesity is indicated by different molecular alterations as metabolic pathways and genetic mutation or epigenetic DNA changes supporting a strong connection between obesity and BC risk. However, these molecular and genetic alteration remain incompletely understood. The aim of this review is to highlight and elucidate the different molecular mechanisms and genetic changes occurring in obese women and their association with BC risk and development.

Diabetogenic and Obesogenic Effects of Cadmium in Db/Db Mice and Rats at a Clinically Relevant Level of Exposure

Studies show an association between cadmium (Cd) exposure and prediabetes or type II diabetes mellitus. We have previously reported that Cd causes decreased levels of serum leptin in rats following 12 weeks of daily Cd dosing (0.6 mg/kg/b.w./day). Since leptin plays an important role in metabolism, we examined the effects of Cd on rats and db/db mice, which are deficient in leptin receptor activity. We gave rats and mice daily subcutaneous injections of saline (control) or CdCl₂ at a dose of 0.6 mg/kg of Cd for 2 weeks, followed by 2 weeks of no dosing. At the end of the 4-week study, exposure to Cd resulted in a more rapid increase in blood glucose levels following an oral glucose tolerance test in db/db vs. lean mice. During the two weeks of no Cd dosing, individual rat bodyweight gain was greater (p ≤ 0.05) in Cd-treated animals. At this time point, the combined epididymal and retroperitoneal fat pad weight was significantly greater (p ≤ 0.05) in the Cd-treated lean mice compared to saline-treated controls. Although this pilot study had relatively low N values (4 per treatment group for mice and 6 for rats) the results show that clinically relevant levels of Cd exposure resulted in diabetogenic as well as obesogenic effects.

Eosinophils regulate intra-adipose axonal plasticity

Neuronal innervation in the adipose tissues plays a crucial role in regulating adipose thermogenic capacity and metabolic homeostasis. The tissue-wide nerves display a large extent of structural plasticity under physiological and pathological conditions that alter the neuronal control of metabolic states. We find here that neuronal plasticity is regulated by immune cells, which constitutes an appealing way to reshape neural-controlled energy balance by targeting immune components.

Sympathetic innervation regulates energy balance, and the nerve density in the adipose tissues changes under various metabolic states, resulting in altered neuronal control and conferring resilience to metabolic challenges. However, the impact of the immune milieu on neuronal innervation is not known. Here, we examined the regulatory role on nerve plasticity by eosinophils and found they increased cell abundance in response to cold and produced nerve growth factor (NGF) in the white adipose tissues (WAT). Deletion of Ngf from eosinophils or depletion of eosinophils impairs cold-induced axonal outgrowth and beiging process. The spatial proximity between sympathetic nerves, IL-33–expressing stromal cells, and eosinophils was visualized in both human and mouse adipose tissues. At the cellular level, the sympathetic adrenergic signal induced calcium flux in the stromal cells and subsequent release of IL-33, which drove the up-regulation of IL-5 from group 2 innate lymphoid cells (ILC2s), leading to eosinophil accretion. We propose a feed-forward loop between sympathetic activity and type 2 immunity that coordinately enhances sympathetic innervation and promotes energy expenditure.

Insulin resistance and decreased spexin in Indian Patients with Type 2 Diabetes Mellitus

Spexin is novel biomarker, which plays a potential role in glucose and lipid metabolisms. However, there was paucity of serum spexin levels in obesity and diabetes mellitus subjects. Hence the current study was aimed to find the relationship between the serum spexin levels in type 2 Diabetes mellitus (type 2 DM) with extrapolation of cardiovascular disease (CVD) risk. A cross-sectional study included 330 participants, subdivided as control (n=110), type 2 DM (n=110) and type 2 DM with CVD groups (n=110). HbA1c, insulin, lipid profile, spexin & leptin including blood pressure and body mass index were analyzed from all the participants. The serum spexin levels (ng/ml) were significantly decreased in type 2 DM (mean ± sd: 0.65 ± 0.03) and type 2 DM with CVD (0.48 ± 0.02) groups compared to the control (0.79 ± 0.03) group (p<0.001). The decreased spexin levels were observed in type 2 DM, and further more decreased in type 2 DM with CVD patients compared to controls indicating that spexin levels could be served as an early prediction of obesity-induced T2DM with CVD risk.

Hypothalamic primary cilium: A hub for metabolic homeostasis

Obesity is a global health problem that is associated with adverse consequences such as the development of metabolic disorders, including cardiovascular disease, neurodegenerative disorders, and type 2 diabetes. A major cause of obesity is metabolic imbalance, which results from insufficient physical activity and excess energy intake. Understanding the pathogenesis of obesity, as well as other metabolic disorders, is important in the development of methods for prevention and therapy. The coordination of energy balance takes place in the hypothalamus, a major brain region that maintains body homeostasis. The primary cilium is an organelle that has recently received attention because of its role in controlling energy balance in the hypothalamus. Defects in proteins required for ciliary function and formation, both in humans and in mice, have been shown to cause various metabolic disorders. In this review, we provide an overview of the critical functions of primary cilia, particularly in hypothalamic areas, and briefly summarize the studies on the primary roles of cilia in specific neurons relating to metabolic homeostasis.

The nutrient sensing pathways FoxO1/3 and mTOR in the heart are coordinately regulated by central leptin through PPARβ/δ. Implications in cardiac remodeling

BACKGROUND

Cardiovascular disease in obese individuals with type 2 diabetes is often associated with hyperleptinemia and leptin resistance, while other studies support that leptin has cardioprotective effects. Besides, the role of leptin in regulating cardiac atrophy or hypertrophy remains to be clearly defined. In fact, in rats with normal leptin sensitivity, the molecular underpinnings of the effects of central leptin regulating cardiac structural pathways remain poorly understood.

OBJECTIVE

Hence, we assessed the effects of intracerebroventricular (icv) leptin infusion on cardiac remodeling analyzing FOXO1/3 and mTORC1 pathways, focusing special attention to PPARβ/δ as mediator of central leptin's effects on cardiac metabolism.

METHODS

Male 3-months-old Wistar rats, infused with icv leptin (0.2 μg/day) for 7 days, were daily co-treated intraperitoneally with the specific PPARβ/δ antagonist GSK0660, at 1 mg/kg per day along leptin treatment.

RESULTS

Central leptin regulated dynamically, in an opposite manner, the network between FOXOs and mTORC1 and induced an atrophy-related gene program in cardiac tissue. Leptin activated the anti-hypertrophic kinase GSK3β and increased the protein levels of muscle-specific ubiquitin ligases, muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx)/Atrogin-1 involved in limiting cardiac hypertrophy. FOXO1 activity and the expression of their target genes, Sod2 and Lpl, were also increased in the heart upon central leptin infusion. Besides, Beclin-1 and LC3B-II, gene products of the autophagic pathway response, were upregulated, while the content and expression levels of phenotypic markers of cardiac hypertrophy as ANP and β-myosin heavy chain, gene product of Myh7 were significantly decreased. On the other hand, mTORC1 activity and OXPHOS protein levels were decreased suggesting a key role of central leptin preventing cardiac oxidative stress. In fact, the content of carbonylated proteins, TBARS and ROS/RSN were not increased in cardiac tissue in response to central leptin infusion. Finally, the pharmacological inhibition of PPARβ/δ, via in vivo administration of the selective antagonist GSK0660, blunted the induction of FOXO1/3, Atrogin-1, MuRF1 and GSK3β in the heart mediated by icv leptin infusion.

CONCLUSIONS

Our results demonstrate that, in lean rats with normal leptin sensitivity, central leptin regulates nutrient sensing pathways in heart contributing to balance cardiac remodeling through the anti- and pro-hypertrophic programs, and in this process is involved PPARβ/δ.

Lipodystrophies-Disorders of the Fatty Tissue

Lipodystrophies are a heterogeneous group of physiological changes characterized by a selective loss of fatty tissue. Here, no fat cells are present, either through lack of differentiation, loss of function or premature apoptosis. As a consequence, lipids can only be stored ectopically in non-adipocytes with the major health consequences as fatty liver and insulin resistance. This is a crucial difference to being slim where the fat cells are present and store lipids if needed. A simple clinical classification of lipodystrophies is based on congenital vs. acquired and generalized vs. partial disturbance of fat distribution. Complications in patients with lipodystrophy depend on the clinical manifestations. For example, in diabetes mellitus microangiopathic complications such as nephropathy, retinopathy and neuropathy may develop. In addition, due to ectopic lipid accumulation in the liver, fatty liver hepatitis may also develop, possibly with cirrhosis. The consequences of extreme hypertriglyceridemia are typically acute pancreatitis or eruptive xanthomas. The combination of severe hyperglycemia with dyslipidemia and signs of insulin resistance can lead to premature atherosclerosis with its associated complications of coronary heart disease, peripheral vascular disease and cerebrovascular changes. Overall, lipodystrophy is rare with an estimated incidence for congenital (<1/1.000.000) and acquired (1-9/100.000) forms. Due to the rarity of the syndrome and the phenotypic range of metabolic complications, only studies with limited patient numbers can be considered. Experimental animal models are therefore useful to understand the molecular mechanisms in lipodystrophy and to identify possible therapeutic approaches.

Short-term metreleptin treatment of patients with anorexia nervosa: rapid on-set of beneficial cognitive, emotional, and behavioral effects

To examine the hypothesis that normalization of low circulating leptin levels in patients with anorexia nervosa ameliorates hyperactivity, three seriously ill females with hyperactivity were treated off-label with metreleptin (recombinant human leptin) for up to 14 days. Drive for activity, repetitive thoughts of food, inner restlessness, and weight phobia decreased in two patients. Surprisingly, depression improved rapidly in all patients. No serious adverse events occurred. Due to obvious limitations of uncontrolled case series, placebo-controlled clinical trials are mandatory to confirm the observed rapid onset of beneficial effects. Our findings suggest an important role of hypoleptinemia in the mental and behavioral phenotype of anorexia nervosa.

Impact of adipokines and myokines on fat browning

Since the discovery of leptin in 1994, the adipose tissue (AT) is not just considered a passive fat storage organ but also an extremely active secretory and endocrine organ that secretes a large variety of hormones, called adipokines, involved in energy metabolism. Adipokines may not only contribute to AT dysfunction and obesity, but also in fat browning, a process that induces a phenotypic switch from energy-storing white adipocytes to thermogenic brown fat-like cells. The fat browning process and, consequently, thermogenesis can also be stimulated by physical exercise. Contracting skeletal muscle is a metabolically active tissue that participates in several endocrine functions through the production of bioactive factors, collectively termed myokines, proposed as the mediators of physical activity-induced health benefits. Myokines affect muscle mass, have profound effects on glucose and lipid metabolism, and promote browning and thermogenesis of white AT in an endocrine and/or paracrine manner. The present review focuses on the role of different myokines and adipokines in the regulation of fat browning, as well as in the potential cross-talk between AT and skeletal muscle, in order to control body weight, energy expenditure and thermogenesis.

Amino acid-based compound activates atypical PKC and leptin receptor pathways to improve glycemia and anxiety like behavior in diabetic mice

Differences in glucose uptake in peripheral and neural tissues account for the reduced efficacy of insulin in nervous tissues. Herein, we report the design of short peptides, referred as amino acid compounds (AAC) with and without a modified side chain moiety. At nanomolar concentrations, a candidate therapeutic molecule, AAC2, containing a 7-(diethylamino) coumarin-3-carboxamide side-chain improved glucose control in human peripheral adipocytes and the endothelial brain barrier cells by activation of insulin-insensitive glucose transporter 1 (GLUT1). AAC2 interacted specifically with the leptin receptor (LepR) and activated atypical protein kinase C zeta (PKCς) to increase glucose uptake. The effects induced by AAC2 were absent in leptin receptor-deficient predipocytes and in Lepr^db mice. In contrast, AAC2 established glycemic control altering food intake in leptin-deficient Lep^ob mice. Therefore, AAC2 activated the LepR and acted in a cytokine-like manner distinct from leptin. In a monogenic Ins2^Akita mouse model for the phenotypes associated with type 1 diabetes, AAC2 rescued systemic glucose uptake in these mice without an increase in insulin levels and adiposity, as seen in insulin-treated Ins2^Akita mice. In contrast to insulin, AAC2 treatment increased brain mass and reduced anxiety-related behavior in Ins2^Akita mice. Our data suggests that the unique mechanism of action for AAC2, activating LepR/PKCς/GLUT1 axis, offers an effective strategy to broaden glycemic control for the prevention of diabetic complications of the nervous system and, possibly, other insulin insensitive or resistant tissues.

Familial Partial Lipodystrophy (FPLD): Recent Insights

Lipodystrophies are a heterogeneous group of congenital or acquired disorders, characterized by partial or generalized loss of adipose tissue. Familial partial lipodystrophy (FPLD) presents with genetic and phenotypic variability with insulin resistance, hypertriglyceridemia and hepatic steatosis being the cardinal metabolic features. The severity of the metabolic derangements is in proportion with the degree of lipoatrophy. The underpinning pathogenetic mechanism is the limited capacity of adipose tissue to store lipids leading to lipotoxicity, low-grade inflammation, altered adipokine secretion and ectopic fat tissue accumulation. Advances in molecular genetics have led to the discovery of new genes and improved our knowledge of the regulation of adipose tissue biology. Diagnosis relies predominantly on clinical findings, such as abnormal fat tissue topography and signs of insulin resistance and is confirmed by genetic analysis. In addition to anthropometry and conventional imaging, new techniques such as color-coded imaging of fat depots allow more accurate assessment of the regional fat distribution and differentiation of lipodystrophic syndromes from common metabolic syndrome phenotype. The treatment of patients with lipodystrophy has proven to be challenging. The use of a human leptin analogue, metreleptin, has recently been approved in the management of FPLD with evidence suggesting improved metabolic profile, satiety, reproductive function and self-perception. Preliminary data on the use of glucagon-like peptide 1 receptor agonists (GLP1 Ras) and sodium-glucose co-transporter 2 (SGLT2) inhibitors in cases of FPLD have shown promising results with reduction in total insulin requirements and improvement in glycemic control. Finally, investigational trials for new therapeutic agents in the management of FPLD are underway.

The Role of Adipokines in Breast Cancer: Current Evidence and Perspectives

PURPOSE

The current review shows evidence for the role of adipokines in breast cancer (BC) pathogenesis summarizing the mechanisms underlying the association between adipokines and breast malignancy. Special emphasis is given also on intriguing insights into the relationship between obesity and BC as well as on the role of novel adipokines in BC development.

RECENT FINDINGS

Recent evidence has underscored the role of the triad of obesity, insulin resistance, and adipokines in postmenopausal BC. Adipokines exert independent and joint effects on activation of major intracellular signal networks implicated in BC cell proliferation, growth, survival, invasion, and metastasis, particularly in the context of obesity, considered a systemic endocrine dysfunction characterized by chronic inflammation. To date, more than 10 adipokines have been linked to BC, and this catalog is continuously increasing. The majority of circulating adipokines, such as leptin, resistin, visfatin, apelin, lipocalin 2, osteopontin, and oncostatin M, is elevated in BC, while some adipokines such as adiponectin and irisin (adipo-myokine) are generally decreased in BC and considered protective against breast carcinogenesis. Further evidence from basic and translational research is necessary to delineate the ontological role of adipokines and their interplay in BC pathogenesis. More large-scale clinical and longitudinal studies are awaited to assess their clinical utility in BC prognosis and follow-up. Finally, novel more effective and safer adipokine-centered therapeutic strategies could pave the way for targeted oncotherapy.

Expression of leptin and leptin receptors in colorectal cancer-an immunohistochemical study

Obesity is demonstrated to be a risk factor in the development of cancers of various organs, such as colon, prostate, pancreas and so on. Leptine (LEP) is the most renowned of the adipokines. As a hormone, it mediates its effect through leptin receptor (LEPR), which is widely expressed in various tissues including colon mucosa. In this study, we have investigated the degree of expression of LEP and LEPR in colorectal cancer (CRC). We collected 44 surgically resected colon cancer tissues along with normal adjacent colon tissue (NACT) from a sample of CRC patients from the Malaysian population and looked for leptin and leptin receptors using immunohistochemistry (IHC). All the samples showed low presence of both LEP and LEPR in NACT, while both LEP and LEPR were present at high intensity in the cancerous tissues with 100% and 97.7% prevalence, respectively. Both were sparsed in the cytoplasm and were concentrated beneath the cell membrane. However, we did not find any significant correlation between their expression and pathological parameters like grade, tumor size, and lymph node involvement. Our study further emphasizes the possible causal role of LEP and LEPR with CRC, and also the prospect of using LEPR as a possible therapeutic target.

Effect of resveratrol on adipokines and myokines involved in fat browning: Perspectives in healthy weight against obesity

Obesity is a globally widespread metabolic disorder, characterized by immoderate fat accumulation in the body. There are different types of body fats such as white adipose tissue (WAT), which stores surplus energy in the body, and brown adipose tissue (BAT) which utilize energy to produce heat during metabolism. BAT acts many beneficial functions in metabolic disorders including type 2 diabetes and obesity. Recent studies have investigated methods for promoting the fat browning process of WAT in obesity because of various reasons such as the improvement of insulin resistance, and weight loss. Among natural polyphenolic compounds, resveratrol has been highlighted due to its anti-oxidant and anti-obesity as well as anti-inflammation and anti-cancer properties. Recent studies have paid a lot of attention to that resveratrol may act as a fat browning activator, involved in the secretion of many myokines and adipokines. Here, we reviewed the role of resveratrol in fat browning and also the association between resveratrol and adipokines/myokines in the fat browning process. Our review may provide novel insight into the role of resveratrol in fat browning, leading to the maintenance of a healthy weight against obesity.

Preclinical Assessment of Leptin Transport into the Cerebrospinal Fluid in Diet-Induced Obese Minipigs

OBJECTIVE

A minipig model was employed to explore the changes in endogenous leptin transport into the central nervous system and in hypothalamic sensitivity to exogenous leptin when individuals are placed on high-fat diet (HFD) compared with standard diet.

METHODS

Serum and cerebrospinal fluid (CSF) leptin concentrations during 10 weeks of HFD versus standard diet and exogenous leptin-induced STAT3 phosphorylation in the hypothalamus of minipigs were assessed, and the hypothalamic leptin-sensitive cells were characterized by immunofluorescence.

RESULTS

The efficiency of the passage of endogenous blood-borne leptin into the CSF (measured as the log [CSF:serum leptin ratio]) decreased over time in minipigs fed a HFD (β = -0.04 ± 0.005 per kilogram of weight gain in HFD; P < 0.0001), while it remained stable in minipigs fed a standard diet. However, the ability of peripherally administered leptin to activate its receptor in hypothalamic neurons was preserved in obese minipigs at 10 weeks of HFD.

CONCLUSIONS

Together, these data are consistent with the existence of an early-onset tranport deficiency for endogenous circulating leptin into the brain in individuals developing obesity, preceding the acquisition of hypothalamic leptin resistance. Although additional studies are required to identify the underlying mechanisms, our study paves the way for the development of new preclinical pharmacological models targeting the restoration of the shuttling of peripheral leptin into the central nervous system to manage obesity.

Pegylated Human Leptin D23L Mutant-Preparation and Biological Activity In Vitro and In Vivo in Male ob/ob Mice

Recombinant monomeric human leptin (hLEP) and its D23L mutant were prepared in Escherichia coli and pegylated at their N-terminus using 20-kDa methoxy pegylated (PEG)-propionylaldehyde. As determined by both SDS-PAGE and size-exclusion chromatography, the pegylated proteins consisted of >90% monopegylated and <10% double-pegylated species. Circular dichroism spectra showed that their secondary structure, characteristic of all four α-helix bundle cytokines, was not affected by either the D23L mutation or pegylation. Because of the D23L mutation, affinity for hLEP receptor increased 25- and 40-fold for the pegylated and nonpegylated mutant, respectively. However, whereas the proliferation-promoting activity in vitro of nonmutated and mutated nonpegylated hLEP was identical, that of the respective pegylated mutant was approximately sixfold higher compared with the pegylated nonmutated hLEP. This difference was also seen in vivo. Both pegylated hLEPs at all doses significantly decreased body weight and food consumption, as compared with the vehicle-treated control. Once-daily administration of pegylated hLEP D23L at doses of 0.1, 0.3, and 1 mg/kg for 14 consecutive days in ob/ob mice resulted in significantly decreased body weight and food consumption as compared with respective pegylated hLEP-treated animals, with the biggest difference observed at 0.1 mg/kg. Repeated administration of either pegylated hLEP D23L or pegylated hLEP significantly decreased blood glucose levels compared with the control before glucose challenge and after oral glucose tolerance test, but with no difference between the two treatments. The pegylated hLEP D23L mutant seems to be a more potent reagent suitable for in vivo studies than the pegylated nonmutated hLEP.

Neurocognitive and Hormonal Correlates of Voluntary Weight Loss in Humans

Insufficient responses to hypocaloric diets have been attributed to hormonal adaptations that override self-control of food intake. We tested this hypothesis by measuring circulating energy-balance hormones and brain functional magnetic resonance imaging reactivity to food cues in 24 overweight/obese participants before, and 1 and 3 months after starting a calorie restriction diet. Increased activity and functional connectivity in prefrontal regions at month 1 correlated with weight loss at months 1 and 3. Weight loss was also correlated with increased plasma ghrelin and decreased leptin, and these changes were associated with food cue reactivity in reward-related brain regions. However, the reduction in leptin did not counteract weight loss; indeed, it was correlated with further weight loss at month 3. Activation in prefrontal regions associated with self-control could contribute to successful weight loss and maintenance. This work supports the role of higher-level cognitive brain function in body-weight regulation in humans.

Regulation of Hepatic Lipid Accumulation and Distribution by Agouti-Related Protein in Male Mice

Proper regulation of energy metabolism requires neurons in the central nervous system to respond dynamically to signals that reflect the body's energy reserve, and one such signal is leptin. Agouti-related protein (AgRP) is a hypothalamic neuropeptide that is markedly upregulated in leptin deficiency, a condition that is associated with severe obesity, diabetes, and hepatic steatosis. Because deleting AgRP in mice does not alter energy balance, we sought to determine whether AgRP plays an indispensable role in regulating energy and hepatic lipid metabolism in the sensitized background of leptin deficiency. We generated male mice that are deficient for both leptin and AgRP [double-knockout (DKO)]. DKO mice and ob/ob littermates had similar body weights, food intake, energy expenditure, and plasma insulin levels, although DKO mice surprisingly developed heightened hyperglycemia with advancing age. Overall hepatic lipid content was reduced in young prediabetic DKO mice, but not in the older diabetic counterparts. Intriguingly, however, both young and older DKO mice had an altered zonal distribution of hepatic lipids with reduced periportal lipid deposition. Moreover, leptin stimulated, whereas AgRP inhibited, hepatic sympathetic activity. Ablating sympathetic nerves to the liver, which primarily innervate the portal regions, produced periportal lipid accumulation in wild-type mice. Collectively, our results highlight AgRP as a regulator of hepatic sympathetic activity and metabolic zonation.

Buprenorphine Depresses Respiratory Variability in Obese Mice with Altered Leptin Signaling

BACKGROUND

Opiate-induced respiratory depression is sexually dimorphic and associated with increased risk among the obese. The mechanisms underlying these associations are unknown. The present study evaluated the two-tailed hypothesis that sex, leptin status, and obesity modulate buprenorphine-induced changes in breathing.

METHODS

Mice (n = 40 male and 40 female) comprising four congenic lines that differ in leptin signaling and body weight were injected with saline and buprenorphine (0.3 mg/kg). Whole-body plethysmography was used to quantify the effects on minute ventilation. The data were evaluated using three-way analysis of variance, regression, and Poincaré analyses.

RESULTS

Relative to B6 mice with normal leptin, buprenorphine decreased minute ventilation in mice with diet-induced obesity (37.2%; P < 0.0001), ob/ob mice that lack leptin (62.6%; P < 0.0001), and db/db mice with dysfunctional leptin receptors (65.9%; P < 0.0001). Poincaré analyses showed that buprenorphine caused a significant (P < 0.0001) collapse in minute ventilation variability that was greatest in mice with leptin dysfunction. There was no significant effect of sex or body weight on minute ventilation.

CONCLUSIONS

The results support the interpretation that leptin status but not body weight or sex contributed to the buprenorphine-induced decrease in minute ventilation. Poincaré plots illustrate that the buprenorphine-induced decrease in minute ventilation variability was greatest in mice with impaired leptin signaling. This is relevant because normal respiratory variability is essential for martialing a compensatory response to ventilatory challenges imposed by disease, obesity, and surgical stress.

Translating Mechanism-Based Strategies to Break the Obesity-Cancer Link: A Narrative Review

Prevalence of obesity, an established risk factor for many cancers, has increased dramatically over the past 50 years in the United States and across the globe. Relative to normoweight cancer patients, obese cancer patients often have poorer prognoses, resistance to chemotherapies, and are more likely to develop distant metastases. Recent progress on elucidating the mechanisms underlying the obesity-cancer connection suggests that obesity exerts pleomorphic effects on pathways related to tumor development and progression and, thus, there are multiple opportunities for primary prevention and treatment of obesity-related cancers. Obesity-associated alterations, including systemic metabolism, adipose inflammation, growth factor signaling, and angiogenesis, are emerging as primary drivers of obesity-associated cancer development and progression. These obesity-associated host factors interact with the intrinsic molecular characteristics of cancer cells, facilitating several of the hallmarks of cancer. Each is considered in the context of potential preventive and therapeutic strategies to reduce the burden of obesity-related cancers. In addition, this review focuses on emerging mechanisms behind the obesity-cancer link, as well as relevant dietary interventions, including calorie restriction, intermittent fasting, low-fat diet, and ketogenic diet, that are being implemented in preclinical and clinical trials, with the ultimate goal of reducing incidence and progression of obesity-related cancers.

Differential contribution of POMC and AgRP neurons to the regulation of regional autonomic nerve activity by leptin

Objectives

The autonomic nervous system is critically involved in mediating the control by leptin of many physiological processes. Here, we examined the role of the leptin receptor (LepR) in proopiomelanocortin (POMC) and agouti-related peptide (AgRP) neurons in mediating the effects of leptin on regional sympathetic and parasympathetic nerve activity.

Methods

We analyzed how deletion of the LepR in POMC neurons (POMC^Cre/LepR^fl/fl mice) or AgRP neurons (AgRP^Cre/LepR^fl/fl mice) affects the ability of leptin to increase sympathetic and parasympathetic nerve activity. We also studied mice lacking the catalytic p110α or p110β subunits of phosphatidylinositol-3 kinase (PI3K) in POMC neurons.

Results

Leptin-evoked increase in sympathetic nerve activity subserving thermogenic brown adipose tissue was partially blunted in mice lacking the LepR in either POMC or AgRP neurons. On the other hand, loss of the LepR in AgRP, but not POMC, neurons interfered with leptin-induced sympathetic nerve activation to the inguinal fat depot. The increase in hepatic sympathetic traffic induced by leptin was also reduced in mice lacking the LepR in AgRP, but not POMC, neurons whereas LepR deletion in either AgRP or POMC neurons attenuated the hepatic parasympathetic nerve activation evoked by leptin. Interestingly, the renal, lumbar and splanchnic sympathetic nerve activation caused by leptin were significantly blunted in POMC^Cre/LepR^fl/fl mice, but not in AgRP^Cre/LepR^fl/fl mice. However, loss of the LepR in POMC or AgRP neurons did not interfere with the ability of leptin to increase sympathetic traffic to the adrenal gland. Furthermore, ablation of the p110α, but not the p110β, isoform of PI3K from POMC neurons eliminated the leptin-elicited renal sympathetic nerve activation.

Finally, we show trans-synaptic retrograde tracing of both POMC and AgRP neurons from the kidneys.

Conclusions

POMC and AgRP neurons are differentially involved in mediating the effects of leptin on autonomic nerve activity subserving various tissues and organs.

•

Both POMC and AgRP neurons contribute to leptin-elicited increase in BAT SNA and hepatic PSNA.

•

AgRP neurons mediate leptin-evoked increase in SNA subserving WAT and liver.

•

Leptin-induced increase in lumbar, splanchnic and renal SNA is mediated by POMC neurons.

•

The p110α, but not p110β, subunit of PI3K in POMC neurons is required for the effect of leptin on renal SNA.

Sex Steroid Hormones Regulate Leptin Transcript Accumulation and Protein Secretion in 3T3-L1 Cells

Leptin is an adipokine produced by fat cells that regulates food consumption and metabolic activity. Sexual dimorphism in leptin and fat stores have been observed in humans and rodents with females having more leptin and greater levels of subcutaneous fat than males. One potential mechanism leading to this dimorphism is steroid hormone regulated synthesis of transcripts encoding leptin. Identification of direct regulatory mechanisms is difficult in animals or primary adipocytes due to these intertwined dimorphisms. We used well-characterized 3T3-L1 murine adipocytes to demonstrate that dihydrotestosterone (DHT) reduced Leptin (Lep) transcript abundance and cytosolic and secreted leptin protein. The magnitude of this effect was greatest on secreted leptin, which was decreased by DHT to 30% of the control. In contrast, 17β-estradiol significantly increased the abundance of transcripts encoding leptin and increased secreted leptin to 230% of the control. Treatment with estrogen and androgen receptor antagonists had opposite effects on Lep transcript abundance to steroid treatments, indicating that these transcriptional effects are mediated through the canonical steroid hormone signaling pathways. These results indicate that short-term treatments with steroid hormones are sufficient to alter both Lep transcript accumulation and leptin protein secretion, and may play a role in the sexual dimorphism of this adipokine.

Mapping of leptin and its syntenic genes to chicken chromosome 1p

Background

Misidentification of the chicken leptin gene has hampered research of leptin signaling in this species for almost two decades. Recently, the genuine leptin gene with a GC-rich (~70%) repetitive-sequence content was identified in the chicken genome but without indicating its genomic position. This suggests that such GC-rich sequences are difficult to sequence and therefore substantial regions are missing from the current chicken genome assembly.

Results

A radiation hybrid panel of chicken-hamster Wg3hCl2 cells was used to map the genome location of the chicken leptin gene. Contrary to our expectations, based on comparative genome mapping and sequence characteristics, the chicken leptin was not located on a microchromosome, which are known to contain GC-rich and repetitive regions, but at the distal tip of the largest chromosome (1p). Following conserved synteny with other vertebrates, we also mapped five additional genes to this genomic region (ARF5, SND1, LRRC4, RBM28, and FLNC), bridging the genomic gap in the current Galgal5 build for this chromosome region. All of the short scaffolds containing these genes were found to consist of GC-rich (54 to 65%) sequences comparing to the average GC-content of 40% on chromosome 1. In this syntenic group, the RNA-binding protein 28 (RBM28) was in closest proximity to leptin. We deduced the full-length of the RBM28 cDNA sequence and profiled its expression patterns detecting a negative correlation (R = − 0.7) between the expression of leptin and of RBM28 across tissues that expressed at least one of the genes above the average level. This observation suggested a local regulatory interaction between these genes. In adipose tissues, we observed a significant increase in RBM28 mRNA expression in breeds with lean phenotypes.

Conclusion

Mapping chicken leptin together with a cluster of five syntenic genes provided the final proof for its identification as the true chicken ortholog. The high GC-content observed for the chicken leptin syntenic group suggests that other similar clusters of genes in GC-rich genomic regions are missing from the current genome assembly (Galgal5), which should be resolved in future assemblies of the chicken genome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-017-0543-1) contains supplementary material, which is available to authorized users.

Catalase overexpression modulates metabolic parameters in a new 'stress-less' leptin-deficient mouse model

Oxidative stress plays a key role in obesity by modifying the function of important biological molecules, thus altering obesogenic pathways such as glucose and lipid signaling. Catalase, is an important endogenous antioxidant enzyme that catabolizes hydrogen peroxide produced by the dismutation of superoxide. Recent studies have shown knockdown of catalase exacerbates insulin resistance and leads to obesity. We hypothesized that overexpressing catalase in an obese mouse will modulate obesogenic pathways and protect against obesity. Therefore, we bred catalase transgenic ([Tg(CAT)^+/-] mice with Ob/Ob mice to generate the hybrid "Bob-Cat" mice. This newly generated "stress-less" mouse model had decreased oxidative stress (oxidized carbonylated proteins). ECHO-MRI showed lower fat mass but higher lean mass in "Bob-Cat" mice. Comprehensive Lab Animal Monitoring System (CLAMS) showed light and dark cycle increase in energy expenditure in Bob-Cat mice compared to wild type controls. Circulating levels of leptin and resistin showed no change. Catalase mRNA expression was increased in key metabolic tissues (adipose, liver, intestinal mucosa, and brain) of the Bob-Cat mice. Catalase activity, mRNA and protein expression was increased in adipose tissue. Expression of the major adipokines leptin and adiponectin was increased while pro-inflammatory genes, MCP-1/JE and IL-1β were lowered. Interestingly, sexual dimorphism was seen in body composition, energy expenditure, and metabolic parameters in the Bob-Cat mice. Overall, the characteristics of the newly generated "Bob-Cat" mice make it an ideal model for studying the effect of redox modulators (diet/exercise) in obesity.

Relation of antioxidant capacity of diet and markers of oxidative status with C-reactive protein and adipocytokines: a prospective study

BACKGROUND

The role of dietary antioxidants and plasma oxidant-antioxidant status in low-grade chronic inflammation and adipocytokine levels is not established yet.

OBJECTIVES

We aimed to evaluate whether total dietary antioxidant capacity (assessed by dietary ferric reducing antioxidant potential (FRAP)), serum uric acid (UA) and gamma glutamyltransferase (GGT) were associated with low-grade chronic inflammation and circulating adipocytokines.

METHODS

Data of 4506 participants aged ≥55years from the Rotterdam Study were analyzed. Baseline (1990-1993) FRAP score was assessed by a food frequency questionnaire. Baseline UA and GGT levels were assessed in non-fasting serum samples. Serum high sensitivity C-reactive protein (hs-CRP) was measured at baseline and 10years later. Plasma leptin, adiponectin, plasminogen activator inhibitor-1 (PAI-1) and resistin levels were assessed 10years later.

RESULTS

A high FRAP score was associated with lower levels of UA and GGT. Overall, no association was found between FRAP and hs-CRP levels. FRAP score was associated with lower levels of leptin and PAI-1, higher levels of adiponectin, and no difference in resistin levels. Increased levels of UA were associated with higher levels of hs-CRP, PAI-1 and leptin; lower levels of adiponectin and no difference in resistin levels. Similarly, GGT was associated with higher levels of hs-CRP whereas no association was observed between GGT and adipocytokines.

CONCLUSION

These findings suggest that overall antioxidant capacity of diet and low levels of UA are associated with circulating adipocytokines whereas no consistent association was found with hs-CRP.

Novel Hypothalamic Mechanisms in the Pathophysiological Control of Body Weight and Metabolism

The incidence of obesity, with its impact on the development of comorbidities, including diabetes and cardiovascular disease, represents one of the greatest global health threats of the 21st century. This is particularly damning considering the vast progress that has been made in understanding the factors and molecular mechanisms playing a role in the control of energy balance by the central nervous system, especially during the past 3 decades. Despite the wealth of newfound knowledge, effective therapies for prevention of and/or intervention in obesity have not been forthcoming. That said, recent technological advances and the revisiting of previously discarded concepts have identified novel neural mechanisms involved in the control of energy homeostasis, thereby providing potential new targets and experimental approaches that may bring us closer to effective therapies to improve metabolic control. This review summarizes some of the most recent findings, with special emphasis on the role of neural circuits of the hypothalamus.

The sympathetic neuro-adipose connection and the control of body weight

In recent decades, obesity has become a global public health crisis irrespective of age or gender [20]. But according to historic records, concerns over appropriate maintenance of body size have been long established. For more than to 2 millennia, the main therapeutic approach to curb excess weight has been to recommend dietary restrictions and regular exercise (Haslam, 2016). Nevertheless, more contemporary studies indicate that the employment of such approaches in the treatment of severely obese patients causes metabolic adaptions which impair their long-term success in weight management [8]. These evidences highlight thus, the urgency in the search for a more comprehensive knowledge of the mechanisms that underlie the control of body weight, which would be essential for the development of effective strategies for the treatment of obesity and its comorbidities. Importantly, the discovery of the hormone leptin [33]and the use of novel techniques in targeted transgenesis [32] have enabled progress in defining some of the key players and the molecular mechanisms that are involved in the processes that control body size homeostasis and energy balance, and how obesity may disrupt leptin's feedback loop and lead to the pathology of metabolic syndrome. On the light of such findings, here we review how the sympathetic nervous system modulates adipose tissue metabolism downstream of leptin's action on the CNS, with particular focus on how this system may be disrupted in the context of excess adiposity, plus highlight the potential clinical implications arising from a better understanding of the physiologic control of the sympathetic neuro-adipose connection.

Crosstalk between adipokines and myokines in fat browning

Skeletal muscle is the largest organ determining whole-body insulin sensitivity and metabolic homoeostasis. Adaptive changes of skeletal muscle in response to physical activity include adjustments in the production and secretion of muscle-derived bioactive factors, known as myokines, such as myostatin, IL-4, IL-6, IL-7 and IL-15, myonectin, follistatin-like 1 or leukaemia inhibitory factor. These myokines not only act locally in the muscle in an autocrine/paracrine manner, but also are released to the bloodstream as endocrine factors to regulate physiological processes in other tissues. Irisin, derived from the cleavage of FNDC5 protein, constitutes a myokine that induces myogenesis and fat browning (switch of white adipocytes to brown fat-like cells) together with a concomitant increase in energy expenditure. Besides being a target for irisin actions, the adipose tissue also constitutes a production site of FNDC5. Interestingly, irisin secretion from subcutaneous and visceral fat depots is decreased by long-term exercise training and fasting, suggesting a discordant regulation of FNDC5/irisin in skeletal muscle and adipose tissue. Accordingly, our group has recently reported that the adipokine leptin differentially regulates FNDC5/irisin expression in skeletal muscle and fat, confirming the crosstalk between both tissues. Moreover, irisin secretion and function are regulated by other myokines, such as follistatin or myostatin, as well as by other adipokines, including fibroblast growth factor 21 and leptin. Taken together, myokines have emerged as novel molecular mediators of fat browning and their activity can be modulated by adipokines, confirming the crosstalk between skeletal muscle and adipose tissue to regulate thermogenesis and energy expenditure.

Role of the gut microbiota in host appetite control: bacterial growth to animal feeding behaviour

The life of all animals is dominated by alternating feelings of hunger and satiety - the main involuntary motivations for feeding-related behaviour. Gut bacteria depend fully on their host for providing the nutrients necessary for their growth. The intrinsic ability of bacteria to regulate their growth and to maintain their population within the gut suggests that gut bacteria can interfere with molecular pathways controlling energy balance in the host. The current model of appetite control is based mainly on gut-brain signalling and the animal's own needs to maintain energy homeostasis; an alternative model might also involve bacteria-host communications. Several bacterial components and metabolites have been shown to stimulate intestinal satiety pathways; at the same time, their production depends on bacterial growth cycles. This short-term bacterial growth-linked modulation of intestinal satiety can be coupled with long-term regulation of appetite, controlled by the neuropeptidergic circuitry in the hypothalamus. Indeed, several bacterial products are detected in the systemic circulation, which might act directly on hypothalamic neurons. This Review analyses the data relevant to possible involvement of the gut bacteria in the regulation of host appetite and proposes an integrative homeostatic model of appetite control that includes energy needs of both the host and its gut bacteria.

Beyond thermoregulation: metabolic function of cetacean blubber in migrating bowhead and beluga whales

The processes of lipid deposition and utilization, via the gene leptin (Lep), are poorly understood in taxa with varying degrees of adipose storage. This study examines how these systems may have adapted in marine aquatic environments inhabited by cetaceans. Bowhead (Balaena mysticetus) and beluga whales (Delphinapterus leucas) are ideal study animals-they possess large subcutaneous adipose stores (blubber) and undergo bi-annual migrations concurrent with variations in food availability. To answer long-standing questions regarding how (or if) energy and lipid utilization adapted to aquatic stressors, we quantified variations in gene transcripts critical to lipid metabolism related to season, age, and blubber depth. We predicted leptin tertiary structure conservation and assessed inter-specific variations in Lep transcript numbers between bowheads and other mammals. Our study is the first to identify seasonal and age-related variations in Lep and lipolysis in these cetaceans. While Lep transcripts and protein oscillate with season in adult bowheads reminiscent of hibernating mammals, transcript levels reach up to 10 times higher in bowheads than any other mammal. Data from immature bowheads are consistent with the hypothesis that short baleen inhibits efficient feeding. Lipolysis transcripts also indicate young Fall bowheads and those sampled during Spring months limit energy utilization. These novel data from rarely examined species expand the existing knowledge and offer unique insight into how the regulation of Lep and lipolysis has adapted to permit seasonal deposition and maintain vital blubber stores.

Subcellular localization of leptin and leptin receptor in breast cancer detected in an electron microscopic study

Leptin (LEP) and leptin receptor (LEPR) have long been found associated with breast cancer. So far no high-resolution method such as electron microscopy has been used to investigate the subcellular localization of leptin and leptin receptor in breast cancer. We collected cancer and non-cancer breast tissues from 51 women with invasive ductal breast cancer. Leptin and leptin receptor in the tissues were estimated using immunohistochemistry (IHC). LEP and LEPR were localized at subcellular level by immunocytochemistry (ICC) using ultra-fine gold particle conjugated antibody, and visualized with transmission electron microscopy (TEM). IHC showed high presence of LEP and LEPR in 65% and 67% respectively of the breast cancer samples, 100% and 0% respectively of the adipose tissue samples, and no high presence in the non-cancer breast tissue samples. On TEM views both LEP and LEPR were found highly concentrated within the nucleus of the cancer cells, indicating that nucleus is the principal seat of action. However, presence of high concentration of LEP does not necessarily prove its over-expression, as often concluded, because LEP could be internalized from outside by LEPR in the cells. In contrast, LEPR is definitely over-expressed in the ductal breast cancer cells. Therefore, we hypothesize that over-expression of LEPR, rather than that of LEP has a fundamental role in breast carcinogenesis in particular, and probably for LEP-LEPR associated tumors in general.

Metabolic Vascular Syndrome: New Insights into a Multidimensional Network of Risk Factors and Diseases

BACKGROUND

Since 1981, we have used the term metabolic syndrome to describe an association of a dysregulation in lipid metabolism (high triglycerides, low high-density lipoprotein cholesterol, disturbed glucose homeostasis (enhanced fasting and/or prandial glucose), gout, and hypertension), with android obesity being based on a common soil (overnutrition, reduced physical activity, sociocultural factors, and genetic predisposition). We hypothesized that main traits of the syndrome occur early and are tightly connected with hyperinsulinemia/insulin resistance, procoagulation, and cardiovascular diseases.

METHODS

To establish a close link between the traits of the metabolic vascular syndrome, we focused our literature search on recent original work and comprehensive reviews dealing with the topics metabolic syndrome, visceral obesity, fatty liver, fat tissue inflammation, insulin resistance, atherogenic dyslipidemia, arterial hypertension, and type 2 diabetes mellitus.

RESULTS

Recent research supports the concept that the metabolic vascular syndrome is a multidimensional and interactive network of risk factors and diseases based on individual genetic susceptibility and epigenetic changes where metabolic dysregulation/metabolic inflexibility in different organs and vascular dysfunction are early interconnected.

CONCLUSION

The metabolic vascular syndrome is not only a risk factor constellation but rather a life-long abnormality of a closely connected interactive cluster of developing diseases which escalate each other and should continuously attract the attention of every clinician.

Implications of thermogenic adipose tissues for metabolic health

Excess and ectopic fat accumulation in obesity is a major risk factor for developing hyperlipidemia, type 2 diabetes and cardiovascular disease. The activation of brown and/or beige adipocytes is a promising target for the treatment of metabolic disorders as the combustion of excess energy by these thermogenic adipocytes may help losing weight and improving plasma parameters including triglyceride, cholesterol and glucose levels. The regulation of heat production by thermogenic adipose tissues is based on a complex crosstalk between the autonomous nervous system, intracellular and secreted factors. This multifaceted alignment regulates thermogenic demands to environmental circumstances in dependence on available energy resources. This review summarizes the current knowledge how thermogenic tissues can be targeted to combat the burden of diseases with a special focus on lipid metabolism and diseases related to lipoprotein metabolism.

A weighty problem: metabolic perturbations and the obesity-cancer link

Obesity is an established risk factor for several cancers, including breast, colon, endometrial, ovarian, gastric, pancreatic and liver, and is increasingly a public health concern. Obese cancer patients often have poorer prognoses, reduced response to standard treatments, and are more likely to develop metastatic disease than normo-weight individuals. Many of the pathologic features of obesity promote tumor growth, such as metabolic perturbations, hormonal and growth factor imbalances, and chronic inflammation. Although obesity exacerbates tumor development, the interconnected relationship between the two conditions presents opportunities for new treatment approaches, some of which may be more successful in obese cohorts. Here, we discuss the many ways in which excess adiposity can impact cancer development and progression and address potential preventive and therapeutic strategies to reduce the burden of obesity-related cancers.

The JAK/STAT pathway in obesity and diabetes

Diabetes mellitus are complex, multi-organ metabolic pathologies characterized by hyperglycemia. Emerging evidence shows that the highly conserved and potent JAK/STAT signaling pathway is required for normal homeostasis, and, when dysregulated, contributes to the development of obesity and diabetes. In this review, we analyze the role of JAK/STAT activation in the brain, liver, muscle, fat and pancreas, and how this affects the course of the disease. We also consider the therapeutic implications of targeting the JAK/STAT pathway in treatment of obesity and diabetes.

Leptin-mediated ion channel regulation: PI3K pathways, physiological role, and therapeutic potential

Leptin is produced by adipose tissue and identified as a "satiety signal," informing the brain when the body has consumed enough food. Specific areas of the hypothalamus express leptin receptors (LEPRs) and are the primary site of leptin action for body weight regulation. In response to leptin, appetite is suppressed and energy expenditure allowed. Beside this hypothalamic action, leptin targets other brain areas in addition to neuroendocrine cells. LEPRs are expressed also in the hippocampus, neocortex, cerebellum, substantia nigra, pancreatic β-cells, and chromaffin cells of the adrenal gland. It is intriguing how leptin is able to activate different ionic conductances, thus affecting excitability, synaptic plasticity and neurotransmitter release, depending on the target cell. Most of the intracellular pathways activated by leptin and directed to ion channels involve PI3K, which in turn phosphorylates different downstream substrates, although parallel pathways involve AMPK and MAPK. In this review we will describe the effects of leptin on BK, KATP, KV, CaV, TRPC, NMDAR and AMPAR channels and clarify the landscape of pathways involved. Given the ability of leptin to influence neuronal excitability and synaptic plasticity by modulating ion channels activity, we also provide a short overview of the growing potentiality of leptin as therapeutic agent for treating neurological disorders.

The BBSome Controls Energy Homeostasis by Mediating the Transport of the Leptin Receptor to the Plasma Membrane

Bardet-Biedl syndrome (BBS) is a highly pleiotropic autosomal recessive disorder associated with a wide range of phenotypes including obesity. However, the underlying mechanism remains unclear. Here, we show that neuronal BBSome is a critical determinant of energy balance through its role in the regulation of the trafficking of the long signaling form of the leptin receptor (LRb). Targeted disruption of the BBSome by deleting the Bbs1 gene from the nervous system causes obesity in mice, and this phenotype is reproduced by ablation of the Bbs1 gene selectively in the LRb-expressing cells, but not from adipocytes. Obesity developed as a consequence of both increased food intake and decreased energy expenditure in mice lacking the Bbs1 gene in LRb-expressing cells. Strikingly, the well-known role of BBS proteins in the regulation of ciliary formation and function is unlikely to account for the obesogenic effect of BBS1 loss as disruption of the intraflagellar transport (IFT) machinery required for ciliogenesis by deleting the Ift88 gene in LRb-expressing cells caused a marginal increase in body weight and adiposity. Instead, we demonstrate that silencing BBS proteins, but not IFT88, impair the trafficking of the LRb to the plasma membrane leading to central leptin resistance in a manner independent of obesity. Our data also demonstrate that postnatal deletion of the Bbs1 gene in the mediobasal hypothalamus can cause obesity in mice, arguing against an early neurodevelopmental origin of obesity in BBS. Our results depict a novel mechanism underlying energy imbalance and obesity in BBS with potential implications in common forms of human obesity.

The brain plays an important role in maintaining energy homeostasis. The hormone leptin is a critical afferent signal in metabolic homeostasis through its action in the brain. Here we show that neuronal Bardet-Biedl syndrome (BBS) proteins, encoded by genes that cause obesity when mutated, govern energy homeostasis through the control of cell surface expression of the leptin receptor. Selective disruption of BBS proteins causes obesity in mice and impairs the transport of the leptin receptor to the plasma membrane leading to leptin resistance in a manner independent of obesity. These results establish BBS proteins as a fundamental mechanism underlying transport of the leptin receptor and explain why BBS patients develop obesity.

Sex, the brain and hypertension: brain oestrogen receptors and high blood pressure risk factors

Hypertension is a major contributor to worldwide morbidity and mortality rates related to cardiovascular disease. There are important sex differences in the onset and rate of hypertension in humans. Compared with age-matched men, premenopausal women are less likely to develop hypertension. However, after age 60, the incidence of hypertension increases in women and even surpasses that seen in older men. It is thought that changes in levels of circulating ovarian hormones as women age may be involved in the increase in hypertension in older women. One of the key mechanisms involved in the development of hypertension in both men and women is an increase in sympathetic nerve activity (SNA). Brain regions important for the regulation of SNA, such as the subfornical organ, the paraventricular nucleus and the rostral ventral lateral medulla, also express specific subtypes of oestrogen receptors. Each of these brain regions has also been implicated in mechanisms underlying risk factors for hypertension such as obesity, stress and inflammation. The present review brings together evidence that links actions of oestrogen at these receptors to modulate some of the common brain mechanisms involved in the ability of hypertensive risk factors to increase SNA and blood pressure. Understanding the mechanisms by which oestrogen acts at key sites in the brain for the regulation of SNA is important for the development of novel, sex-specific therapies for treating hypertension.

Mechanisms of Microbe-Host Interaction in Crohn's Disease: Dysbiosis vs. Pathobiont Selection

Crohn’s disease (CD) is a systemic chronic inflammatory condition mainly characterized by discontinuous transmural pathology of the gastrointestinal tract and frequent extraintestinal manifestations with intermittent episodes of remission and relapse. Genome-wide association studies identified a number of risk loci that, catalyzed by environmental triggers, result in the loss of tolerance toward commensal bacteria based on dysregulated innate effector functions and antimicrobial defense, leading to exacerbated adaptive immune responses responsible for chronic immune-mediated tissue damage. In this review, we discuss the inter-related role of changes in the intestinal microbiota, epithelial barrier integrity, and immune cell functions on the pathogenesis of CD, describing the current approaches available to investigate the molecular mechanisms underlying the disease. Substantial effort has been dedicated to define disease-associated changes in the intestinal microbiota (dysbiosis) and to link pathobionts to the etiology of inflammatory bowel diseases. A cogent definition of dysbiosis is lacking, as well as an agreement of whether pathobionts or complex shifts in the microbiota trigger inflammation in the host. Among the rarely available animal models, SAMP/Yit and TNF^deltaARE mice are the best known displaying a transmural CD-like phenotype. New hypothesis-driven mouse models, e.g., epithelial-specific Caspase8^−/−, ATG16L1^−/−, and XBP1^−/− mice, validate pathway-focused function of specific CD-associated risk genes highlighting the role of Paneth cells in antimicrobial defense. To study the causal role of bacteria in initiating inflammation in the host, the use of germ-free mouse models is indispensable. Unraveling the interactions of genes, immune cells and microbes constitute a criterion for the development of safe, reliable, and effective treatment options for CD.

Adipocyte-derived factors in age-related dementia and their contribution to vascular and Alzheimer pathology

Age-related dementia is increasingly recognized as having a mixed pathology, with contributions from both cerebrovascular factors and pathogenic factors associated with Alzheimer's disease (AD). Furthermore, there is accumulating evidence that vascular risk factors in midlife, e.g., obesity, diabetes, and hypertension, increase the risk of developing late-life dementia. Since obesity and changes in body weight/adiposity often drive diabetes and hypertension, understanding the relationship between adiposity and age-related dementia may reveal common underlying mechanisms. Here we offer a brief appraisal of how changes in body weight and adiposity are related to both AD and dementia on vascular basis, and examine the involvement of two key adipocyte-derived hormones: leptin and adiponectin. The evidence suggests that in midlife increased body weight/adiposity and subsequent changes in adipocyte-derived hormones may increase the long-term susceptibility to dementia. On the other hand, later in life, decreases in body weight/adiposity and related hormonal changes are early manifestations of disease that precede the onset of dementia and may promote AD and vascular pathology. Understanding the contribution of adiposity to age-related dementia may help identify the underlying pathological mechanisms common to both vascular dementia and AD, and provide new putative targets for early diagnosis and therapy. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia, edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Metabolic and Non-Cognitive Manifestations of Alzheimer's Disease: The Hypothalamus as Both Culprit and Target of Pathology

Alzheimer's disease (AD) is increasingly recognized as a complex neurodegenerative disease beginning decades prior to the cognitive decline. While cognitive deficits remain the cardinal manifestation of AD, metabolic and non-cognitive abnormalities, such as alterations in body weight and neuroendocrine functions, are also present, often preceding the cognitive decline. Furthermore, hypothalamic dysfunction can also be a driver of AD pathology. Here we offer a brief appraisal of hypothalamic dysfunction in AD and provide insight into an underappreciated dual role of the hypothalamus as both a culprit and target of AD pathology, as well as into new opportunities for therapeutic interventions and biomarker development.

Adipose tissue and metabolic syndrome: too much, too little or neither

Obesity is strongly associated with metabolic syndrome. Recent research suggests that excess adipose tissue plays an important role in development of the syndrome. On the other hand, persons with a deficiency of adipose tissue (e.g. lipodystrophy) also manifest the metabolic syndrome. In some animal models, expansion of adipose tissue pools mitigates adverse metabolic components (e.g. insulin resistance, hyperglycaemia and dyslipidemia). Hence, there are conflicting data as to whether adipose tissue worsens the metabolic syndrome or protects against it. This conflict may relate partly to locations of adipose tissue pools. For instance, lower body adipose tissue may be protective whereas upper body adipose tissue may promote the syndrome. One view holds that in either case, the accumulation of ectopic fat in muscle and liver is the driving factor underlying the syndrome. If so, there may be some link between adipose tissue fat and ectopic fat. But the mechanisms underlying this connection are not clear. A stronger association appears to exist between excessive caloric intake and ectopic fat accumulation. Adipose tissue may act as a buffer to reduce the impact of excess energy consumption by fat storage; but once a constant weight has been achieved, it is unclear whether adipose tissue influences levels of ectopic fat. Another mechanism whereby adipose tissue could worsen the metabolic syndrome is through release of adipokines. This is an intriguing mechanism, but the impact of adipokines on metabolic syndrome risk factors is uncertain. Thus, many potential connections between adipose tissue and metabolic syndrome remain to unravelled.

60 YEARS OF NEUROENDOCRINOLOGY: MEMOIR: Harris' neuroendocrine revolution: of portal vessels and self-priming

Geoffrey Harris, while still a medical student at Cambridge, was the first researcher (1937) to provide experimental proof for the then tentative view that the anterior pituitary gland was controlled by the CNS. The elegant studies carried out by Harris in the 1940s and early 1950s, alone and in collaboration with John Green and Dora Jacobsohn, established that this control was mediated by a neurohumoral mechanism that involved the transport by hypophysial portal vessel blood of chemical substances from the hypothalamus to the anterior pituitary gland. The neurohumoral control of anterior pituitary secretion was proved by the isolation and characterisation of the 'chemical substances' (mainly neuropeptides) and the finding that these substances were released into hypophysial portal blood in a manner consistent with their physiological functions. The new discipline of neuroendocrinology - the way that the brain controls endocrine glands and vice versa - revolutionised the treatment of endocrine disorders such as growth and pubertal abnormalities, infertility and hormone-dependent tumours, and it underpins our understanding of the sexual differentiation of the brain and key aspects of behaviour and mental disorder. Neuroendocrine principles are illustrated in this Thematic Review by way of Harris' major interest: hypothalamic-pituitary-gonadal control. Attention is focussed on the measurement of GnRH in hypophysial portal blood and the role played by the self-priming effect of GnRH in promoting the onset of puberty and enabling the oestrogen-induced surge or pulses of GnRH to trigger the ovulatory gonadotrophin surge in humans and other spontaneously ovulating mammals.