Hypothalamic sensing of fatty acids

Seasonal and comparative evidence of adaptive gene expression in mammalian brain size plasticity

Contrasting almost all other mammalian wintering strategies, Eurasian common shrews, Sorex araneus, endure winter by shrinking their brain, skull, and most organs, only to then regrow to breeding size the following spring. How such tiny mammals achieve this unique brain size plasticity while maintaining activity through the winter remains unknown. To discover potential adaptations underlying this trait, we analyzed seasonal differential gene expression in the shrew hypothalamus, a brain region that both regulates metabolic homeostasis and drastically changes size, and compared hypothalamus gene expression across species. We discovered seasonal variation in suites of genes involved in energy homeostasis and apoptosis, shrew-specific upregulation of genes involved in the development of the hypothalamic blood-brain barrier and calcium signaling, as well as overlapping seasonal and comparative gene expression divergence in genes implicated in the development and progression of human neurological and metabolic disorders, including CCDC22. With high metabolic rates and facing harsh winter conditions, S. araneus have evolved both adaptive and plastic mechanisms to sense and regulate their energy budget. Many of these changes mirrored those identified in human neurological and metabolic disease, highlighting the interactions between metabolic homeostasis, brain size plasticity, and longevity.

Role of saturated fatty acid metabolism in posttranslational modifications of the Tau protein

The relationship between metabolic alterations induced by the consumption of a high-fat diet (HFD) and the risk of developing neurodegenerative diseases such as Alzheimer's disease (AD) has been extensively studied. In particular, the induction of neuronal insulin resistance, endoplasmic reticulum stress, and the production of reactive oxygen species by chronic exposure to high concentrations of saturated fatty acids (sFAs), such as palmitic acid (PA), have been proposed as the cellular and molecular mechanisms underlying cognitive decline. Lipid metabolism affects many processes critical for cellular homeostasis. However, questions remain as to whether neuronal exposure to high sFA levels contributes to the onset and progression of AD features, and how their metabolism plays a role in this process. Therefore, the aim of this work is to review the accumulated evidence for the potential mechanisms by which the neuronal metabolism of sFAs affects signaling pathways that may induce biochemical changes in the AD hallmark protein Tau, ultimately promoting its aggregation and the subsequent generation of neurofibrillary tangles. In particular, the data presented here provide evidence that PA-dependent metabolic stress results in an imbalance in the activities of protein kinases and deacetylases that potentially contribute to the post-translational modifications (PTMs) of Tau.

Association between sleep behaviors and adiposity indices among U.S. adults: a cross-sectional study

Objectives

This study aimed to clarify the relationship between sleep behaviors and adiposity indices.

Methods

We analyzed NHANES data from 2011 to 2018 for adults aged 20-80, assessing BMI, waist circumference (WC), lean mass, and body fat percentage with DEXA scans and physical measurements. Sleep duration was categorized into short (<7 h), normal (7-9 h), and long (>9 h), as well as their sleep status based on questionnaires. Furthermore, we examined the interaction effects between sleep duration and sleep patterns.

Results

Among 19,951 participants providing BMI and WC data, and 10,716 for lean mass and body fat percentage, short sleep duration correlated with higher BMI (β = 0.56, 95% CI: 0.36-0.76), WC (β = 0.90, 95% CI: 0.43-1.37), and lean mass (β = 0.70, 95% CI: 0.32-1.07). Individuals with sleep disorders showed increased values across all indices: BMI (β = 0.93, 95% CI: 0.72-1.13), WC (β = 2.40, 95% CI: 1.92-2.88), lean mass (β = 0.71, 95% CI: 0.30-1.12), and body fat percentage (β = 0.64, 95% CI: 0.37-0.90). No significant interaction effects were found between sleep duration and sleep disorders.

Conclusion

Our findings indicate that individuals with short sleep duration and sleep disorders are likely to carry a higher weight burden, indicating potential targets for addressing obesity-related health issues.

Central Downregulation of S-Resistin Alleviates Inflammation in EWAT and Liver and Prevents Adipocyte Hypertrophy

The hypothalamus integrates peripheral signals and modulates food intake and energy expenditure by regulating the metabolic function of peripheral tissues, including the liver and adipose tissue. In a previous study, we demonstrated that s-resistin, an intracellular resistin isoform highly expressed in the hypothalamus and upregulated during aging, is important in the central control of energy homeostasis, affecting mainly the peripheral response to insulin by still unknown mechanisms. Herein, using an intracerebroventricular injection of a specific lentiviral RNAi against s-resistin, we assessed, in the Wistar rat, the effects of central s-resistin downregulation on the expression and phosphorylation levels of intermediates involved in insulin signaling and the inflammatory response in epididymal white adipose tissue (eWAT) and liver. Additionally, we studied the imbalance of eWAT hypertrophy/hyperplasia remodeling. Our results indicate that central downregulation of s-resistin regulates insulin signaling cascade in a tissue-specific manner, reduces the inflammatory status both in the liver and eWAT, and prevents eWAT hypertrophy. Taken together, our results highlight the pivotal role of central s-resistin in maintaining metabolic homeostasis in AT and the liver. This suggests a direct association between its function and the modulation of the inflammatory response in these tissues.

Central NUCB2/nesfatin-1 signaling ameliorates liver steatosis through suppression of endoplasmic reticulum stress in the hypothalamus

BACKGROUND & AIMS

Nucleobindin-2 (NUCB2)/nesfatin-1, a signal with recognized anorexigenic and insulin-sensitizing properties in peripheral tissues, is expressed within the hypothalamus. However, the potential involvement of central nesfatin-1 signaling in the pathophysiology of hepatic steatosis remains unknown. This study aimed to determine whether and how central NUCB2/nesfatin-1 plays a role in liver steatosis.

METHODS

We generated Nucb2 knockout (Nucb2-/-) rats and administered continuous intracerebroventricular (ICV) nesfatin-1 infusion, while observing its effect on liver steatosis. The molecular mechanism of action of nesfatin-1 was elucidated via proteomics, phosphoproteomics and molecular biology methods.

RESULTS

Herein, we present compelling evidence indicating diminished NUCB2 expression in the hypothalamus of obese rodents. We demonstrated that chronic ICV infusion of nesfatin-1 mitigated both diet-induced obesity and liver steatosis in high-fat diet (HFD)-fed Nucb2-/- rats by regulating hypothalamic endoplasmic reticulum (ER) stress and Akt phosphorylation. Furthermore, we revealed that the increase in hypothalamic insulin resistance (IR) and ER stress induced by tunicamycin infusion or Ero1α overexpression exacerbated hepatic steatosis and offset the favorable influence of central nesfatin-1 on hepatic steatosis. The metabolic action of central nesfatin-1 is contingent upon vagal nerve transmission to the liver. Mechanistically, nesfatin-1 impedes ER stress and interacts with Ero1α to repress its Ser106 phosphorylation. This leads to the enhancement of Akt activity in the hypothalamus, culminating in the inhibition of hepatic lipogenesis.

CONCLUSIONS

These findings underscore the importance of hypothalamic NUCB2/nesfatin-1 as a key mediator in the top-down neural mechanism that combats diet-induced liver steatosis.

Neuron stress-related genes serve as new biomarkers in hypothalamic tissue following high fat diet

Objective

Energy homeostasis is modulated by the hypothalamic is essential for obesity progression, however, the gene expression profiling remains to be fully understood.

Methods

GEO datasets were downloaded from the GEO website and analyzed by the R packages to obtain the DEGs. And, the WGCNA analysis and PPI networks of co-expressed DEGs were designed using STRING to get key genes. In addition, the single-cell sequencing datasets and GTEx database were utilized to receive the neuron-stress genes from the key genes. Further, high-fat diet (HFD)-induced hypothalamic tissue of mice was used as an animal model to validate the mRNA up-regulation of neuron-stress genes. In addition, the Bmi1 gene was identified as a hub gene through the LASSO model and nomogram analysis. Western blot confirmed the high expression of Bmi1 in hypothalamic tissue of HFD mice and PA-stimulated microglia. Immunofluorescence staining showed that HFD induced the activation of microglia and the expression of Bmi1 in hypothalamic tissue.

Results

We found that six genes (Sacm1l, Junb, Bmi1, Erbb4, Dkc1, and Suv39h1) are neuron stress-related genes and increased in the HFD-induced mice obesity model, Bmi1gene was identified as a key genes that can reflect the pathophysiology of obesity.

Conclusions

Our research depicted a comprehensive activation map of cell abnormality in the obese hypothalamus and Bim1 may be a diagnostic marker in the clinic, which provides a new perspective and basis for investigating the pathogenesis of obesity.

Unraveling brain palmitic acid: Origin, levels and metabolic fate

In the human brain, palmitic acid (16:0; PAM) comprises nearly half of total brain saturates and has been identified as the third most abundant fatty acid overall. Brain PAM supports the structure of membrane phospholipids, provides energy, and regulates protein stability. Sources underlying the origin of brain PAM are both diet and endogenous synthesis via de novo lipogenesis (DNL), primarily from glucose. However, studies investigating the origin of brain PAM are limited to tracer studies utilizing labelled (14C/11C/3H/2H) PAM, and results vary based on the model and tracer used. Nevertheless, there is evidence PAM is synthesized locally in the brain, in addition to obtained directly from the diet. Herein, we provide an overview of brain PAM origin, entry to the brain, metabolic fate, and factors influencing brain PAM kinetics and levels, the latter in the context of age, as well as neurological diseases and psychiatric disorders. Additionally, we briefly summarize the role of PAM in signaling at the level of the brain. We add to the literature a rudimentary summary on brain PAM metabolism.

Brain lipid sensing and the neural control of energy balance

The central nervous system continuously detects circulating concentrations of lipids such as fatty acids and troglycerides. Once information has been detected, the central nervous system can in turn participate in the control of energy balance and blood sugar levels and in particular regulate the secretion and action of insulin. Neurons capable of detecting circulating lipid variations are located in the hypothalamus and in other regions such as the nucleus accumbens, the striatum or the hippocampus. An excess of lipids will have deleterious effects and may induce central lipotoxicity, in particular following local production of ceramides and the appearance of neuroinflammation which may lead to metabolic diseases such as obesity and type 2 diabetes.

Maternal obesity increases hypothalamic miR-505-5p expression in mouse offspring leading to altered fatty acid sensing and increased intake of high-fat food

In utero exposure to maternal obesity programs increased obesity risk. Animal models show that programmed offspring obesity is preceded by hyperphagia, but the mechanisms that mediate these changes are unknown. Using a mouse model of maternal obesity, we observed increased intake of a high-fat diet (HFD) in offspring of obese mothers that precedes the development of obesity. Through small RNA sequencing, we identified programmed overexpression of hypothalamic miR-505-5p that is established in the fetus, lasts to adulthood and is maintained in hypothalamic neural progenitor cells cultured in vitro. Metabolic hormones and long-chain fatty acids associated with obesity increase miR-505-5p expression in hypothalamic neurons in vitro. We demonstrate that targets of miR-505-5p are enriched in fatty acid metabolism pathways and overexpression of miR-505-5p decreased neuronal fatty acid metabolism in vitro. miR-505-5p targets are associated with increased BMI in human genetic studies. Intra-cerebroventricular injection of miR-505-5p in wild-type mice increased HFD intake, mimicking the phenotype observed in offspring exposed to maternal obesity. Conversely, maternal exercise intervention in an obese mouse pregnancy rescued the programmed increase of hypothalamic miR-505-5p in offspring of obese dams and reduced HFD intake to control offspring levels. This study identifies a novel mechanism by which maternal obesity programs obesity in offspring via increased intake of high-fat foods.

trans-Palmitoleic acid promotes adipose thermogenesis to reduce obesity via hypothalamic FFAR1 signaling

Diet-induced thermogenesis (DIT) is crucial for maintaining body weight homeostasis, and the role of dietary fatty acids in modulating DIT is essential. However, the underlying mechanism of fatty acid regulated diet-induced thermogenesis remains elusive. Utilizing the diet- and genetic ablation-induced obese mice models, we found that the C16 unsaturated fatty acids, trans-palmitoleic acid (TPA) and cis-palmitoleic acid (CPA), significantly increased the energy expenditure by promoting the thermogenesis of brown adipose tissues and the production of beige cells in white adipose. As a result, there is a significant reduction in the occurrence of obesity, associated hepatic steatosis and hyperglycemia. Notably, TPA exhibited more potent effects on promoting DIT and alleviating obesity than CPA did. Using inhibitor and gene deletion mice models, we unveiled that TPA acted as a signaling molecule to play a biological function, which could be sensed by the hypothalamic FFAR1 to activate the sympathetic nervous system in promoting adipose tissue thermogenesis. Together, these results demonstrate the underlying mechanism of free fatty acids associated-DIT and will provide fresh insights into the roles of trans-fatty acids in the development of obesity.

Metabolomic profiles of 38 acylcarnitines in major depressive episodes before and after treatment

BACKGROUND

Major depression is associated with changes in plasma L-carnitine and acetyl-L-carnitine. But its association with acylcarnitines remains unclear. The aim of this study was to assess metabolomic profiles of 38 acylcarnitines in patients with major depression before and after treatment compared to healthy controls (HCs).

METHODS

Metabolomic profiles of 38 plasma short-, medium-, and long-chain acylcarnitines were performed by liquid chromatography-mass spectrometry in 893 HCs from the VARIETE cohort and 460 depressed patients from the METADAP cohort before and after 6 months of antidepressant treatment.

RESULTS

As compared to HCs, depressed patients had lower levels of medium- and long-chain acylcarnitines. After 6 months of treatment, increased levels of medium- and long-chain acyl-carnitines were observed that no longer differed from those of controls. Accordingly, several medium- and long-chain acylcarnitines were negatively correlated with depression severity.

CONCLUSIONS

These medium- and long-chain acylcarnitine dysregulations argue for mitochondrial dysfunction through fatty acid β-oxidation impairment during major depression.

Reappraisal of Adipose Tissue Inflammation in Obesity

Chronic low-grade inflammation is a central component in the pathogenesis of obesity-related expansion of adipose tissue and complications in other metabolic tissues. Five different signaling pathways are defined as dominant determinants of adipose tissue inflammation: These are increased circulating endotoxin due to dysregulation in the microbiota-gut-brain axis, systemic oxidative stress, macrophage accumulation, and adipocyte death. Finally, the nucleotide-binding and oligomerization domain (NOD) leucine-rich repeat family pyrin domain-containing 3 (NLRP3) inflammasome pathway is noted to be a key regulator of metabolic inflammation. The NLRP3 inflammasome and associated metabolic inflammation play an important role in the relationships among fatty acids and obesity. Several highly active molecules, including primarily leptin, resistin, adiponectin, visfatin, and classical cytokines, are abundantly released from adipocytes. The most important cytokines that are released by inflammatory cells infiltrating obese adipose tissue are tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), monocyte chemoattractant protein 1 (MCP-1) (CCL-2), and IL-1. All these molecules mentioned above act on immune cells, causing local and then general inflammation. Three metabolic pathways are noteworthy in the development of adipose tissue inflammation: toll-like receptor 4 (TLR4)/phosphatidylinositol-3'-kinase (PI3K)/Protein kinase B (Akt) signaling pathway, endoplasmic reticulum (ER) stress-derived unfolded protein response (UPR), and inhibitor of nuclear factor kappa-B kinase beta (IKKβ)-nuclear factor kappa B (NF-κB) pathway. In fact, adipose tissue inflammation is an adaptive response that contributes to a visceral depot barrier that effectively filters gut-derived endotoxin. Excessive fatty acid release worsens adipose tissue inflammation and contributes to insulin resistance. However, suppression of adipose inflammation in obesity with anti-inflammatory drugs is not a rational solution and paradoxically promotes insulin resistance, despite beneficial effects on weight gain. Inflammatory pathways in adipocytes are indeed indispensable for maintaining systemic insulin sensitivity. Cannabinoid type 1 receptor (CB1R) is important in obesity-induced pro-inflammatory response; however, blockade of CB1R, contrary to anti-inflammatory drugs, breaks the links between insulin resistance and adipose tissue inflammation. Obesity, however, could be decreased by improving leptin signaling, white adipose tissue browning, gut microbiota interactions, and alleviating inflammation. Furthermore, capsaicin synthesized by chilies is thought to be a new and promising therapeutic option in obesity, as it prevents metabolic endotoxemia and systemic chronic low-grade inflammation caused by high-fat diet.

The Unrestrained Overeating Behavior and Clinical Perspective

Obesity-related co-morbidities decrease life quality, reduce working ability, and lead to early death. In the adult population, eating addiction manifests with excessive food consumption and the unrestrained overeating behavior, which is associated with increased risk of morbidity and mortality and defined as the binge eating disorder (BED). This hedonic intake is correlated with fat preference and the total amount of dietary fat consumption is the most potent risk factor for weight gain. Long-term BED leads to greater sensitivity to the rewarding effects of palatable foods and results in obesity fatefully. Increased plasma concentrations of non-esterified free fatty acids and lipid-overloaded hypertrophic adipocytes may cause insulin resistance. In addition to dietary intake of high-fat diet, sedentary lifestyle leads to increased storage of triglycerides not only in adipose tissue but also ectopically in other tissues. Lipid-induced apoptosis, ceramide accumulation, reactive oxygen species overproduction, endoplasmic reticulum stress, and mitochondrial dysfunction play role in the pathogenesis of lipotoxicity. Food addiction and BED originate from complex action of dopaminergic, opioid, and cannabinoid systems. BED may also be associated with both obesity and major depressive disorder. For preventing morbidity and mortality, as well as decreasing the impact of obesity-related comorbidities in appropriately selected patients, opiate receptor antagonists and antidepressant combination are recommended. Pharmacotherapy alongside behavioral management improves quality of life and reduces the obesity risk; however, the number of licensed drugs is very few. Thus, stereotactic treatment is recommended to break down the refractory obesity and binge eating in obese patient. As recent applications in the field of non-invasive neuromodulation, transcranial magnetic stimulation and transcranial direct current stimulation are thought to be important in image-guided deep brain stimulation in humans. Chronic overnutrition most likely provides repetitive and persistent signals that up-regulate inhibitor of nuclear factor kappa B (NF-κB) kinase beta subunit/NF-κB (IKKβ/NF-κB) in the hypothalamus before the onset of obesity. However, how the mechanisms of high-fat diet-induced peripheral signals affect the hypothalamic arcuate nucleus remain largely unknown.

Maternal High Fat Diet in Lactation Impacts Hypothalamic Neurogenesis and Neurotrophic Development, Leading to Later Life Susceptibility to Obesity in Male but Not Female Mice

Early life nutrition can reprogram development and exert long-term consequences on body weight regulation. In mice, maternal high-fat diet (HFD) during lactation predisposed male but not female offspring to diet-induced obesity when adult. Molecular and cellular changes in the hypothalamus at important time points are examined in the early postnatal life in relation to maternal diet and demonstrated sex-differential hypothalamic reprogramming. Maternal HFD in lactation decreased the neurotropic development of neurons formed at the embryo stage (e12.5) and impaired early postnatal neurogenesis in the hypothalamic regions of both males and females. Males show a larger increased ratio of Neuropeptide Y (NPY) to Pro-opiomelanocortin (POMC) neurons in early postnatal neurogenesis, in response to maternal HFD, setting an obese tone for male offspring. These data provide insights into the mechanisms by which hypothalamic reprograming by early life overnutrition contributes to the sex-dependent susceptibility to obesity in adult life in mice.

CerS6-dependent ceramide synthesis in hypothalamic neurons promotes ER/mitochondrial stress and impairs glucose homeostasis in obese mice

Dysregulation of hypothalamic ceramides has been associated with disrupted neuronal pathways in control of energy and glucose homeostasis. However, the specific ceramide species promoting neuronal lipotoxicity in obesity have remained obscure. Here, we find increased expression of the C16:0 ceramide-producing ceramide synthase (CerS)6 in cultured hypothalamic neurons exposed to palmitate in vitro and in the hypothalamus of obese mice. Conditional deletion of CerS6 in hypothalamic neurons attenuates high-fat diet (HFD)-dependent weight gain and improves glucose metabolism. Specifically, CerS6 deficiency in neurons expressing pro-opiomelanocortin (POMC) or steroidogenic factor 1 (SF-1) alters feeding behavior and alleviates the adverse metabolic effects of HFD feeding on insulin sensitivity and glucose tolerance. POMC-expressing cell-selective deletion of CerS6 prevents the diet-induced alterations of mitochondrial morphology and improves cellular leptin sensitivity. Our experiments reveal functions of CerS6-derived ceramides in hypothalamic lipotoxicity, altered mitochondrial dynamics, and ER/mitochondrial stress in the deregulation of food intake and glucose metabolism in obesity.

Taste receptor type 1 member 3 enables western diet-induced anxiety in mice

BACKGROUND

Accumulating evidence supports that the Western diet (WD), a diet high in saturated fat and sugary drinks, contributes to the pathogenesis of anxiety disorders, which are the most prevalent mental disorders worldwide. However, the underlying mechanisms by which WD causes anxiety remain unclear. Abundant expression of taste receptor type 1 member 3 (TAS1R3) has been identified in the hypothalamus, a key brain area involved in sensing peripheral nutritional signals and regulating anxiety. Thus, we investigated the influence of excessive WD intake on anxiety and mechanisms by which WD intake affects anxiety development using wild-type (WT) and Tas1r3 deficient (Tas1r3-/-) mice fed a normal diet (ND) or WD for 12 weeks.

RESULTS

WD increased anxiety in male WT mice, whereas male Tas1r3-/- mice were protected from WD-induced anxiety, as assessed by open field (OF), elevated plus maze (EPM), light-dark box (LDB), and novelty-suppressed feeding (NSF) tests. Analyzing the hypothalamic transcriptome of WD-fed WT and Tas1r3-/- mice, we found 1,432 genes significantly up- or down-regulated as a result of Tas1r3 deficiency. Furthermore, bioinformatic analysis revealed that the CREB/BDNF signaling-mediated maintenance of neuronal regeneration, which can prevent anxiety development, was enhanced in WD-fed Tas1r3-/- mice compared with WD-fed WT mice. Additionally, in vitro studies further confirmed that Tas1r3 knockdown prevents the suppression of Creb1 and of CREB-mediated BDNF expression caused by high levels of glucose, fructose, and palmitic acid in hypothalamic neuronal cells.

CONCLUSIONS

Our results imply that TAS1R3 may play a key role in WD-induced alterations in hypothalamic functions, and that inhibition of TAS1R3 overactivation in the hypothalamus could offer therapeutic targets to alleviate the effects of WD on anxiety.

Perinatal metabolic inflammation in the hypothalamus impairs the development of homeostatic feeding circuitry

Over the past few decades, there has been a global increase in childhood obesity. This rise in childhood obesity contributes to the susceptibility of impaired metabolism during both childhood and adulthood. The hypothalamus, specifically the arcuate nucleus (ARC), houses crucial neurons involved in regulating homeostatic feeding. These neurons include proopiomelanocortin (POMC) and agouti-related peptide (AGRP) secreting neurons. They play a vital role in sensing nutrients and metabolic hormones like insulin, leptin, and ghrelin. The neurogenesis of AGRP and POMC neurons completes at birth; however, axon development and synapse formation occur during the postnatal stages in rodents. Insulin, leptin, and ghrelin are the essential regulators of POMC and AGRP neurons. Maternal obesity and postnatal overfeeding or a high-fat diet (HFD) feeding cause metabolic inflammation, disrupted signaling of metabolic hormones, netrin-1, and neurogenic factors, neonatal obesity, and defective neuronal development in animal models; however, the mechanism is unclear. Within the hypothalamus and other brain areas, there exists a wide range of interconnected neuronal populations that regulate various aspects of feeding. However, this review aims to discuss how perinatal metabolic inflammation influences the development of POMC and AGRP neurons within the hypothalamus.

The Role of Acyl-CoA β-Oxidation in Brain Metabolism and Neurodegenerative Diseases

This review highlights the complex role of fatty acid β-oxidation in brain metabolism. It demonstrates the fundamental importance of fatty acid degradation as a fuel in energy balance and as an essential component in lipid homeostasis, brain aging, and neurodegenerative disorders.

Links between Childhood Obesity, High-Fat Diet, and Central Precocious Puberty

In recent years, the existing relationship between excess overweight and central precocious puberty (CPP) has been reported, especially in girls. Different nutritional choices have been associated with different patterns of puberty. In particular, the involvement of altered biochemical and neuroendocrine pathways and a proinflammatory status has been described in connection with a high-fat diet (HFD). In this narrative review, we present an overview on the relationship between obesity and precocious pubertal development, focusing on the role of HFDs as a contributor to activating the hypothalamus-pituitary-gonadal axis. Although evidence is scarce and studies limited, especially in the paediatric field, the harm of HFDs on PP is a relevant problem that cannot be ignored. Increased knowledge about HFD effects will be useful in developing strategies preventing precocious puberty in children with obesity. Promoting HFD-avoiding behavior may be useful in preserving children's physiological development and protecting reproductive health. Controlling HFDs may represent a target for policy action to improve global health.

Pathogenesis of Dementia

According to Alzheimer's Disease International, 55 million people worldwide are living with dementia. Dementia is a disorder that manifests as a set of related symptoms, which usually result from the brain being damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, usually accompanied by emotional problems, difficulties with language, and decreased motivation. The most common variant of dementia is Alzheimer's disease with symptoms dominated by cognitive disorders, particularly memory loss, impaired personality, and judgmental disorders. So far, all attempts to treat dementias by removing their symptoms rather than their causes have failed. Therefore, in the presented narrative review, I will attempt to explain the etiology of dementia and Alzheimer's disease from the perspective of energy and cognitive metabolism dysfunction in an aging brain. I hope that this perspective, though perhaps too simplified, will bring us closer to the essence of aging-related neurodegenerative disorders and will soon allow us to develop new preventive/therapeutic strategies in our struggle with dementia, Alzheimer's disease, and Parkinson's disease.

Molecular Mechanisms and Health Benefits of Ghrelin: A Narrative Review

Ghrelin, an endogenous brain-gut peptide, is secreted in large quantities, mainly from the stomach, in humans and rodents. It can perform the biological function of activating the growth hormone secretagogue receptor (GHSR). Since its discovery in 1999, ample research has focused on promoting its effects on the human appetite and pleasure-reward eating. Extensive, in-depth studies have shown that ghrelin is widely secreted and distributed in tissues. Its role in neurohumoral regulation, such as metabolic homeostasis, inflammation, cardiovascular regulation, anxiety and depression, and advanced cancer cachexia, has attracted increasing attention. However, the effects and regulatory mechanisms of ghrelin on obesity, gastrointestinal (GI) inflammation, cardiovascular disease, stress regulation, cachexia treatment, and the prognosis of advanced cancer have not been fully summarized. This review summarizes ghrelin's numerous effects in participating in a variety of biochemical pathways and the clinical significance of ghrelin in the regulation of the homeostasis of organisms. In addition, potential mechanisms are also introduced.

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.

Portal Glucose Infusion, Afferent Nerve Fibers, and Glucose and Insulin Tolerance of Insulin-Resistant Rats

BACKGROUND

The role of hepatoportal glucose sensors is poorly understood in the context of insulin resistance.

OBJECTIVES

We assessed the effects of glucose infusion in the portal vein on insulin tolerance in 2 rat models of insulin resistance, and the role of capsaicin sensitive nerves in this signal.

METHODS

Male Wistar rats, 8 weeks old, weighing 250-275 g, were used. Insulin and glucose tolerance were assessed following a 4-hour infusion of either glucose or saline through catheterization in the portal vein in 3 paradigms. In experiment 1, for diet-induced insulin resistance, rats were fed either a control diet (energy content: proteins = 22.5%, carbohydrates = 64.1%, and lipids = 13.4%) or a high-fat diet (energy content: proteins = 15.3%, carbohydrates = 40.3%, and lipids =44.4%) for 4 months. In experiment 2, for centrally induced peripheral insulin resistance, catheters were inserted in the carotid artery to deliver either an emulsion of triglycerides [intralipid (IL)] or saline towards the brain for 24 hours. In experiment 3, for testing the role of capsaicin-sensitive nerves, experiment 2 was repeated following a periportal treatment with capsaicin or vehicle.

RESULTS

In experiment 1, when compared to rats fed the control diet, rats fed the high-fat diet exhibited decreased insulin and glucose tolerance (P ≤ 0.05) that was restored with a glucose infusion in the portal vein (P ≤ 0.05). In experiment 2, infusion of a triglyceride emulsion towards the brain (IL rats) decreased insulin and glucose tolerance and increased hepatic endogenous production when compared to saline-infused rats (P ≤ 0.05). Glucose infusion in the portal vein in IL rats restored insulin and glucose tolerance, as well as hepatic glucose production, to controls levels (P ≤ 0.05). In experiment 3, portal infusion of glucose did not increase insulin tolerance in IL rats that received a periportal pretreatment with capsaicin.

CONCLUSIONS

Stimulation of hepatoportal glucose sensors increases insulin tolerance in rat models of insulin resistance and requires the presence of capsaicin-sensitive nerves.

The central nervous system control of energy homeostasis: high fat diet induced hypothalamic microinflammation and obesity

Obesity is believed to arise through the imbalance of energy homeostasis controlled by the central nervous system, where the hypothalamus plays the fundamental role in energy metabolism. In this review, we will provide an overview regarding the functions of POMC neurons and AgRP neurons in acute nucleus of the hypothalamus which mediated the energy metabolism, highlighting their interactions with peripheral organs derived hormones in control of energy homeostasis. Furthermore, the role of high fat diet induced hypothalamic microinflammation in the pathogenesis of obesity will be discussed. We hope this review could help researchers to understand the mechanism of hypothalamus in control of energy metabolism, and design related drugs to block the pathways involving in the impaired metabolism in obese patients.

Diet-Induced Metabolic Dysfunction of Hypothalamic Nutrient Sensing in Rodents

A sedentary lifestyle and excessive nutrient intake resulting from the consumption of high-fat and calorie-rich diets are environmental factors contributing to the rapid growth of the current pandemic of type 2 diabetes mellitus (DM2). Fasting hyperglycemia, an established hallmark of DM2, is caused by excessive production of glucose by the liver, resulting in the inability of insulin to suppress endogenous glucose production. To prevent inappropriate elevations of circulating glucose resulting from changes in nutrient availability, mammals rely on complex mechanisms for continuously detecting these changes and to respond to them with metabolic adaptations designed to modulate glucose output. The mediobasal hypothalamus (MBH) is the key center where nutritional cues are detected and appropriate modulatory responses are integrated. However, certain environmental factors may have a negative impact on these adaptive responses. For example, consumption of a diet enriched in saturated fat in rodents resulted in the development of a metabolic defect that attenuated these nutrient sensing mechanisms, rendering the animals prone to developing hyperglycemia. Thus, high-fat feeding leads to a state of “metabolic disability” in which animals’ glucoregulatory responses fail. We postulate that the chronic faltering of the hypothalamic glucoregulatory mechanisms contributes to the development of metabolic disease.

An H2R-dependent medial septum histaminergic circuit mediates feeding behavior

Novel targets for treating feeding-related diseases are of great importance, and histamine has long been considered an anorexigenic agent. However, understanding its functions in feeding in a circuit-specific way is still limited. Here, we report a medial septum (MS)-projecting histaminergic circuit mediating feeding behavior. This MS-projecting histaminergic circuit is functionally inhibited during food consumption, and bidirectionally modulates feeding behavior via downstream H2, but not H1, receptors on MS glutamatergic neurons. Further, we observed a pathological decrease of histamine 2 receptors (H2Rs) expression in MS glutamatergic neurons in diet-induced obesity (DIO) mice. Genetically, down-regulation of H2Rs expression in MS glutamatergic neurons accelerates body-weight gain. Importantly, chronic activation of H2Rs in MS glutamatergic neurons (with its clinical agonist amthamine) significantly slowed down the body-weight gain in DIO mice, providing a possible clinical utility to treat obesity. Together, our results demonstrate that this MS-projecting histaminergic circuit is critically involved in feeding, and H2Rs in MS glutamatergic neurons is a promising target for treating body-weight problems.

Limited cheese intake reduces HPA axis and behavioral stress responses in male rats

Eating palatable foods reduces behavioral and hypothalamic-pituitary-adrenocortical (HPA) axis responses to stress - an idea referred to by the colloquial term "comfort" food. To study the underlying stress-relieving mechanisms of palatable foods, we previously developed a paradigm of limited sucrose feeding in which male rats are given twice-daily access to a small amount of sucrose drink and subsequently have reduced stress responses. Prior research in humans and rodents implicates high dietary sugars/carbohydrates with reduced stress responsivity. However, it is not clear whether the stress-relieving effects of the limited sucrose paradigm depend upon its macronutrient content. To test this idea, the current work measures stress responses in male rats following the limited intermittent intake of cheese - a highly palatable food that is low in sugar and other carbohydrates. The data show that a history of limited cheese intake (LCI) reduced HPA axis responses to acute psychological (restraint) and physiological (hypoxia) stressors. LCI also reduced behavioral struggling during restraint, increased sociability during a social interaction test, and increased open arm activity in the elevated plus-maze test. Z-score analyses evaluated the extent to which these behavioral effects extended within and across assays, and indicated that there was an overall reduction in stress-related behaviors following LCI. Finally, LCI increased immunolabeling for FosB/deltaFosB (a protein associated with repeated or chronic neuronal activation) in the nucleus accumbens. These results indicate that palatable foods can provide stress blunting regardless of their sugar/carbohydrate composition, and support the idea that food reward per se contributes to stress relief.

Sexually Dimorphic Effects of a Western Diet on Brain Mitochondrial Bioenergetics and Neurocognitive Function

A Western diet (WD), high in sugars and saturated fats, impairs learning and memory function and contributes to weight gain. Mitochondria in the brain provide energy for neurocognitive function and may play a role in body weight regulation. We sought to determine whether a WD alters behavior and metabolic outcomes in male and female rodents through impacting hippocampal and hypothalamic mitochondrial bioenergetics. Results revealed a sexually dimorphic macronutrient preference, where males on the WD consumed a greater percentage of calories from fat/protein and females consumed a greater percentage of calories from a sugar-sweetened beverage. Both males and females on a WD gained body fat and showed impaired glucose tolerance when compared to same-sex controls. Males on a WD demonstrated impaired hippocampal functioning and an elevated tendency toward a high membrane potential in hippocampal mitochondria. Comprehensive bioenergetics analysis of WD effects in the hypothalamus revealed a tissue-specific adaption, where males on the WD oxidized more fat, and females oxidized more fat and carbohydrates at peak energy demand compared to same-sex controls. These results suggest that adult male rats show a susceptibility toward hippocampal dysfunction on a WD, and that hypothalamic mitochondrial bioenergetics are altered by WD in a sex-specific manner.

Maternal diet before and during pregnancy modulates microglial activation and neurogenesis in the postpartum rat brain

The implications of poor maternal diet on offspring metabolic and neuroimmune development are well established. Increasing evidence now suggests that maternal obesity and poor diet can also increase the risk of postpartum mood disorders, but the mechanisms are unknown. Here we investigated the effects of a poor, high-fat-high-sugar diet (HFSD) on peripheral and central inflammation, neurogenesis and postpartum anxiety-like behaviours. We hypothesised that long-term consumption of a HFSD pre- and post-conception would increase the levels of circulating cytokines and induce microglial activation, particularly in the arcuate nucleus of the hypothalamus (ARC), as the primary brain region involved in the integration of satiety signalling; and this would lead to increased anxiety, stress responsivity and disrupted neurogenesis. We further hypothesised that these effects would be ameliorated by consumption of a healthier diet during pregnancy - specifically a diet high in omega-3 polyunsaturated fatty acids (PUFAs). As expected, the HFSD significantly increased pre-conception body weight, elevated circulating cytokines and activated microglia in the ARC, as well as in the basolateral amygdala. The HFSD also significantly increased the numbers of immature (doublecortin (DCX)-positive) neurons in the subgranular/granular region of the hippocampus, a neurogenic response that was, surprisingly, mimicked by consumption of a diet high in omega-3 PUFAs. Despite these effects of peri-pregnancy dietary imbalance, we detected no differences in anxiety-like behaviours or hypothalamic-pituitary-adrenal (HPA) axis reactivity between the groups. A shift to a healthier diet post-conception reversed the peripheral inflammation and alleviated the microglial activation. These novel data indicate the importance of a balanced peri-pregnancy diet and highlight the need for future research into key triggers that alter the neuroimmune balance in the maternal brain.

The response to prolonged fasting in hypothalamic serotonin transporter availability is blunted in obesity

BACKGROUND AND AIMS

Serotonergic and dopaminergic systems in the brain are essential for homeostatic and reward-associated regulation of food intake and systemic energy metabolism. It is largely unknown how fasting influences these systems or if such effects are altered in humans with obesity. We therefore aimed to evaluate the effects of fasting on hypothalamic/thalamic serotonin transporter (SERT) and striatal dopamine transporter (DAT) availability in lean subjects and subjects with obesity.

METHODS

In this randomized controlled cross-over trial, we assessed the effects of 12 vs 24 h of fasting on SERT and DAT availability in the hypothalamus/thalamus and striatum, respectively, using SPECT imaging in 10 lean men and 10 men with obesity.

RESULTS

As compared with the 12-h fast, a 24-h fast increased hypothalamic SERT availability in lean men, but not in men with obesity. We observed high inter-individual variation in the effects of fasting on thalamic SERT and striatal DAT, with no differences between lean men and those with obesity. In all subjects, fasting-induced increases in circulating free fatty acid (FFA) concentrations were associated with an increase in hypothalamic SERT availability and a decrease in striatal DAT availability. Multiple regression analysis showed that changes in plasma insulin and FFAs together accounted for 44% of the observed variation in striatal DAT availability.

CONCLUSION

Lean men respond to prolonged fasting by increasing hypothalamic SERT availability, whereas this response is absent in men with obesity. Inter-individual differences in the adaptations of the cerebral serotonergic and dopaminergic systems to fasting may, in part, be explained by changes in peripheral metabolic signals of fasting, including FFAs and insulin.

Blood Level of 2-arachidonoyl glycerol (2-AG), Neuropeptide Y and Omentin and Their Correlation with Food Habits in Obese Women

Background:

Despite growing concern about the increasing global burden of obesity, there are still many uncertainties in understanding the pathogenesis of this disease. This study aimed to investigate the serum levels of 2-arachidonoylglycerol (2-AG), neuropeptide Y (NPY), and omentin, concerning dietary patterns in obese women.

Materials and Methods:

This case-control study was carried on an equal number of obese (case group) and normal-weight women (n=45 each). Dietary intake was determined based on the food frequency questionnaire. Serum levels of 2-AG, NPY, and omentin were determined using ELISA.

Results:

The obese group showed significantly higher 2-AG and NPY levels than the controls(P<0.001). There were significant positive correlations between the serum level of 2-AG and calorie intake (r=0.219, P=0.038), carbohydrates (r=0.238, P=0.024), fat (r=0.227, P=0.032), saturated fatty acids (r=0.272, P=0.009), and monounsaturated fatty acids (r=0.265, P=0.012).

Conclusion:

Our study revealed that dietary patterns, in particular, the type of fatty acids used may influence levels of 2-AG, NPY, and omentin, which all are involved in pathways resulting in obesity.

Dietary lipids as regulators of reward processes: multimodal integration matters

The abundance of energy-dense and palatable diets in the modern food environment tightly contributes to the obesity pandemic. The reward circuit participates to the regulation of body homeostasis by integrating energy-related signals with neural substrates encoding cognitive and motivational components of feeding behaviors. Obesity and lipid-rich diets alter dopamine (DA) transmission leading to reward dysfunctions and food overconsumption. Recent reports indicate that dietary lipids can act, directly and indirectly, as functional modulators of the DA circuit. This raises the possibility that nutritional or genetic conditions affecting 'lipid sensing' mechanisms might lead to maladaptations of the DA system. Here, we discuss the most recent findings connecting dietary lipid sensing with DA signaling and its multimodal influence on circuits regulating food-reward processes.

Interleukin-6 actions in the hypothalamus protects against obesity and is involved in the regulation of neurogenesis

Background

Interleukin-6 (IL6) produced in the context of exercise acts in the hypothalamus reducing obesity-associated inflammation and restoring the control of food intake and energy expenditure. In the hippocampus, some of the beneficial actions of IL6 are attributed to its neurogenesis-inducing properties. However, in the hypothalamus, the putative neurogenic actions of IL6 have never been explored, and its potential to balance energy intake can be an approach to prevent or attenuate obesity.

Methods

Wild-type (WT) and IL6 knockout (KO) mice were employed to study the capacity of IL6 to induce neurogenesis. We used cell labeling with Bromodeoxyuridine (BrdU), immunofluorescence, and real-time PCR to determine the expression of markers of neurogenesis and neurotransmitters. We prepared hypothalamic neuroprogenitor cells from KO that were treated with IL6 in order to provide an ex vivo model to further characterizing the neurogenic actions of IL6 through differentiation assays. In addition, we analyzed single-cell RNA sequencing data and determined the expression of IL6 and IL6 receptor in specific cell types of the murine hypothalamus.

Results

IL6 expression in the hypothalamus is low and restricted to microglia and tanycytes, whereas IL6 receptor is expressed in microglia, ependymocytes, endothelial cells, and astrocytes. Exogenous IL6 reduces diet-induced obesity. In outbred mice, obesity-resistance is accompanied by increased expression of IL6 in the hypothalamus. IL6 induces neurogenesis-related gene expression in the hypothalamus and in neuroprogenitor cells, both from WT as well as from KO mice.

Conclusion

IL6 induces neurogenesis-related gene expression in the hypothalamus of WT mice. In KO mice, the neurogenic actions of IL6 are preserved; however, the appearance of new fully differentiated proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons is either delayed or disturbed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02242-8.

Glutaredoxin1 knockout promotes high-fat diet-induced obesity in male mice but not in female ones

This study aims to explore how a high-fat diet and glutaredoxin1 (Glrx1) deficiency affect the development of obesity in male and female mice. A high-fat diet induced great differences in calorie intake and body weight gain between male and female mice; furthermore, the Glrx1 deficiency made male mice more sensitive to a high-fat diet than females. Male mice had higher glucose intolerance, and Glrx1 deficiency aggravated gender differences in glucose intolerance. Glrx1 deficiency aggravated high-fat diet-induced hyperlipidemia. The mRNA levels of HMGCR, Srebf-1c, Srebf-2, CD36, FASN and SCD1 were consistently lower in females than in males. Glrx1 deficiency exacerbated high-fat diet induced liver injury and oxidative stress. Diet but not gender or genotype altered the composition of gut microbiota. These findings provide a new insight into the different susceptibilities to obesity caused by a high-fat diet between males and females.

Mechanistic insight into high-fat diet-induced metabolic inflammation in the arcuate nucleus of the hypothalamus

A high-fat diet (HFD) is linked with cytokines production by non-neuronal cells within the hypothalamus, which mediates metabolic inflammation. These cytokines then activate different inflammatory mediators in the arcuate nucleus of the hypothalamus (ARC), a primary hypothalamic area accommodating proopiomelanocortin (POMC) and agouti-related peptide (AGRP) neurons, first-order neurons that sense and integrate peripheral metabolic signals and then respond accordingly. These mediators, such as inhibitor of κB kinase-β (IKKβ), suppression of cytokine signaling 3 (SOCS3), c-Jun N-terminal kinases (JNKs), protein kinase C (PKC), etc., cause insulin and leptin resistance in POMC and AGRP neurons and support obesity and related metabolic complications. On the other hand, inhibition of these mediators has been shown to counteract the impaired metabolism. Therefore, it is important to discuss the contribution of neuronal and non-neuronal cells in HFD-induced hypothalamic inflammation. Furthermore, understanding few other questions, such as the diets causing hypothalamic inflammation, the gender disparity in response to HFD feeding, and how hypothalamic inflammation affects ARC neurons to cause impaired metabolism, will be helpful for the development of therapeutic approaches to prevent or treat HFD-induced obesity.

Modulation of the Hypothalamic Nutrient Sensing Pathways by Sex and Early-Life Stress

There are sex differences in metabolic disease risk, and early-life stress (ES) increases the risk to develop such diseases, potentially in a sex-specific manner. It remains to be understood, however, how sex and ES affect such metabolic vulnerability. The hypothalamus regulates food intake and energy expenditure by sensing the organism's energy state via metabolic hormones (leptin, insulin, ghrelin) and nutrients (glucose, fatty acids). Here, we investigated if and how sex and ES alter hypothalamic nutrient sensing short and long-term. ES was induced in mice by limiting the bedding and nesting material from postnatal day (P)2-P9, and the expression of genes critical for hypothalamic nutrient sensing were studied in male and female offspring, both at P9 and in adulthood (P180). At P9, we observed a sex difference in both Ppargc1a and Lepr expression, while the latter was also increased in ES-exposed animals relative to controls. In adulthood, we found sex differences in Acacb, Agrp, and Npy expression, whereas ES did not affect the expression of genes involved in hypothalamic nutrient sensing. Thus, we observe a pervasive sex difference in nutrient sensing pathways and a targeted modulation of this pathway by ES early in life. Future research is needed to address if the modulation of these pathways by sex and ES is involved in the differential vulnerability to metabolic diseases.

Palmitic acid induces insulin resistance by a mechanism associated with energy metabolism and calcium entry in neuronal cells

Palmitic acid (PA) is a saturated fatty acid whose high consumption has been largely associated with the development of different metabolic alterations, such as insulin resistance, metabolic syndrome, and type 2 diabetes. Particularly in the brain, insulin signaling disruption has been linked to cognitive decline and is considered a risk factor for Alzheimer's disease. Cumulative evidence has demonstrated the participation of PA in the molecular cascade underlying cellular insulin resistance in peripheral tissues, but its role in the development of neuronal insulin resistance and the mechanisms involved are not fully understood. It has generally been accepted that the brain does not utilize fatty acids as a primary energy source, but recent evidence shows that neurons possess the machinery for fatty acid β-oxidation. However, it is still unclear under what conditions neurons use fatty acids as energy substrates and the implications of their oxidative metabolism in modifying insulin-stimulated effects. In the present work, we have found that neurons differentiated from human neuroblastoma MSN exposed to high but nontoxic concentrations of PA generate ATP through mitochondrial metabolism, which is associated with an increase in the cytosolic Ca²⁺ and diminished insulin signaling in neurons. These findings reveal a novel mechanism by which saturated fatty acids produce Ca²⁺ entry and insulin resistance that may play a causal role in increasing neuronal vulnerability associated with metabolic diseases.

Adult food choices depend on sex and exposure to early-life stress: Underlying brain circuitry, adipose tissue adaptations and metabolic responses

Exposure to early-life stress (ES) increases the risk to develop obesity later in life, and these effects may be sex-specific, but it is currently unknown what underlies the ES-induced metabolic vulnerability. We have previously shown that ES leads to a leaner phenotype under standard chow diet conditions, but to increased fat accumulation when exposed to an unhealthy obesogenic diet. However these diets were fed without a choice. An important, yet under investigated, element contributing to the development of obesity in humans is the choice of the food. There is initial evidence that ES leads to altered food choices but a thorough testing on how ES affects the choice of both the fat and sugar component, and if this is similar in males and females, is currently missing. We hypothesized that ES increases the choice for unhealthy foods, while it at the same time also affects the response to such a diet. In a mouse model for ES, in which mice are exposed to limited nesting and bedding material from postnatal day (P)2–P9, we investigated if ES exposure affected i) food choice with a free choice high-fat high-sugar diet (fcHFHS), ii) the response to such a diet, iii) the brain circuits that regulate food intake and food reward and iv) if such ES effects are sex-specific. We show that there are sex differences in food choice under basal circumstances, and that ES increases fat intake in females when exposed to a mild acute stressor. Moreover, ES impacts the physiologic response to the fcHFHS and the brain circuits regulating food intake in sex-specific manner. Our data highlight sex-specific effects of ES on metabolic functioning and food choice.

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Strong sex differences exist in food choice and metabolism in mice.

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Early-life stress (ES) increases fat intake in females after mild acute stress exposure.

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The physiological response to the diet is affected by ES in a sex-dependent manner.

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ES modulates the hedonic feeding circuitry.

Drp1 is required for AgRP neuronal activity and feeding

The hypothalamic orexigenic Agouti-related peptide (AgRP)-expressing neurons are crucial for the regulation of whole-body energy homeostasis. Here, we show that fasting-induced AgRP neuronal activation is associated with dynamin-related peptide 1 (DRP1)-mediated mitochondrial fission and mitochondrial fatty acid utilization in AgRP neurons. In line with this, mice lacking Dnm1l in adult AgRP neurons (Drp1 cKO) show decreased fasting- or ghrelin-induced AgRP neuronal activity and feeding and exhibited a significant decrease in body weight, fat mass, and feeding accompanied by a significant increase in energy expenditure. In support of the role for mitochondrial fission and fatty acids oxidation, Drp1 cKO mice showed attenuated palmitic acid-induced mitochondrial respiration. Altogether, our data revealed that mitochondrial dynamics and fatty acids oxidation in hypothalamic AgRP neurons is a critical mechanism for AgRP neuronal function and body-weight regulation.

Hypothalamic hormone-sensitive lipase regulates appetite and energy homeostasis

Objective

The goal of this study was to investigate the importance of central hormone-sensitive lipase (HSL) expression in the regulation of food intake and body weight in mice to clarify whether intracellular lipolysis in the mammalian hypothalamus plays a role in regulating appetite.

Methods

Using pharmacological and genetic approaches, we investigated the role of HSL in the rodent brain in the regulation of feeding and energy homeostasis under basal conditions during acute stress and high-fat diet feeding.

Results

We found that HSL, a key enzyme in the catabolism of cellular lipid stores, is expressed in the appetite-regulating centers in the hypothalamus and is activated by acute stress through a mechanism similar to that observed in adipose tissue and skeletal muscle. Inhibition of HSL in rodent models by a synthetic ligand, global knockout, or brain-specific deletion of HSL prevents a decrease in food intake normally seen in response to acute stress and is associated with the increased expression of orexigenic peptides neuropeptide Y (NPY) and agouti-related peptide (AgRP). Increased food intake can be reversed by adeno-associated virus-mediated reintroduction of HSL in neurons of the mediobasal hypothalamus. Importantly, metabolic stress induced by a high-fat diet also enhances the hyperphagic phenotype of HSL-deficient mice. Specific deletion of HSL in the ventromedial hypothalamic nucleus (VMH) or AgRP neurons reveals that HSL in the VMH plays a role in both acute stress-induced food intake and high-fat diet-induced obesity.

Conclusions

Our results indicate that HSL activity in the mediobasal hypothalamus is involved in the acute reduction in food intake during the acute stress response and sensing of a high-fat diet.

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HSL is expressed in appetite-regulating nuclei of the mouse hypothalamus.

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HSL in the hypothalamus is activated via β-adrenergic receptor signaling.

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The anorexic response to acute stress is blunted in mice without hypothalamic HSL.

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Central HSL deficiency results in obesity in mice on a high-fat diet.

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HSL in SF1-positive neurons contributes to the anorexigenic stress response.

Understanding the possible role of endocannabinoid system in obesity

BACKGROUND

Maintenance of weight is essential for sustenance, well-being and to endorse prolonged life. The prevalence of obesity is increasing at an alarming rate globally, due to modern lifestyle and dietary habits. Endocannabinoids are fatty acid derivatives and numerous studies are carried out which focuses and targets their relationship with obesity, via multiple signals which have been recently known for exerting crucial role in regulating energy balance.

PURPOSE

This article aims at examining the prospects of endocannabinoids in obesity via directing the role of ECs in stimulating hunger.

RESULT

In last few years, irregular stimulation of endocannabinoid system has been suggested as a chief element in the progression of obesity-associated metabolic complications. Certainly, this cascade system comprises of cannabinoid type1 and 2 receptors (CB1R and CB2R) along with their endogenous lipid ligands which are responsible for enhanced feeding behavior as well as lipid metabolism. Significantly, inhibiting CB1R activity might reduce metabolic abnormality linked with obesity.

CONCLUSION

Conclusion withdrawn on the basis of supporting scientific data and evidences report that the blockade of cannabinoids can serve as a therapeutic potential for treatment of obesity. Future prospective aims at assessing molecular pathways which contributes towards ECS, elicited weight control and to evaluate how these mechanisms are presently relocated into the production of novel cannabinoid drugs exhibiting enriched care.

Glucose and fat sensing in the human hypothalamus

Energy balance is centrally regulated by the brain through several interacting neuronal systems involving external, peripheral, and central factors within the brain. The hypothalamus integrates these factors and is the key brain area in the regulation of energy balance. In this review, we will explain the structure of the hypothalamus and its role in the regulation of energy balance. An important part of energy balance regulation is the sensing of nutrient status and availability. This review will focus on the sensing of the two main sources of energy by the hypothalamus: glucose and fat. As many common health problems and chronic diseases can be traced back to a disrupted hypothalamic function, we will also discuss hypothalamic sensing of glucose and fats in these pathologies. Finally, we will summarize the current knowledge and discuss how this may be applied clinically and for future research perspectives.

The return of malonyl-CoA to the brain: Cognition and other stories

Nutrients, hormones and the energy sensor AMP-activated protein kinase (AMPK) tightly regulate the intracellular levels of the metabolic intermediary malonyl-CoA, which is a precursor of fatty acid synthesis and a negative regulator of fatty acid oxidation. In the brain, the involvement of malonyl-CoA in the control of food intake and energy homeostasis has been known for decades. However, recent data uncover a new role in cognition and brain development. The sensing of malonyl-CoA by carnitine palmitoyltransferase 1 (CPT1) proteins regulates a variety of functions, such as the fate of neuronal stem cell precursors, the motility of lysosomes in developing axons, the trafficking of glutamate receptors to the neuron surface (necessary for proper synaptic function) and the metabolic coupling between astrocytes and neurons. We discuss the relevance of those recent findings evidencing how nutrients and metabolic disorders impact cognition. We also enumerate all nutritional and hormonal conditions that are known to regulate malonyl-CoA levels in the brain, reflect on protein malonylation as a new post-translational modification, and give a reasoned vision of the opportunities and challenges that future research in the field could address.

Long Chain Fatty Acids Differentially Regulate Sub-populations of Arcuate POMC and NPY Neurons

Long chain fatty acids (LCFAs) have been suggested to influence the activity of hypothalamic neurons, however, limited studies have attempted to identify the neurochemical phenotype of these neurons. We aimed to determine if physiological levels of LCFAs alter the electrical excitability of pro-opiomelanocortin (POMC) and neuropeptide Y (NPY) neurons in the arcuate nucleus of the hypothalamus. We utilised whole-cell patch-clamp electrophysiology on brain slice preparations from genetic mouse models where green fluorescent protein was expressed in either POMC or NPY expressing cells. All animals had undergone an overnight fast to replicate conditions in which fatty acids would usually increase. Bath application of LCFAs were found to predominantly inhibit POMC neurons and predominantly excite NPY neurons. Differences between oleic and palmitic acid were not observed. These results suggest that LCFAs in the cerebrospinal fluid exert an underlying orexigenic tone to key hypothalamic neurons known to regulate energy homeostasis.

Long-chain fatty acyl-CoA esters regulate metabolism via allosteric control of AMPK β1 isoforms

Long-chain fatty acids (LCFAs) play important roles in cellular energy metabolism, acting as both an important energy source and signalling molecules¹. LCFA-CoA esters promote their own oxidation by acting as allosteric inhibitors of acetyl-CoA carboxylase, which reduces the production of malonyl-CoA and relieves inhibition of carnitine palmitoyl-transferase 1, thereby promoting LCFA-CoA transport into the mitochondria for β-oxidation^2-6. Here we report a new level of regulation wherein LCFA-CoA esters per se allosterically activate AMP-activated protein kinase (AMPK) β1-containing isoforms to increase fatty acid oxidation through phosphorylation of acetyl-CoA carboxylase. Activation of AMPK by LCFA-CoA esters requires the allosteric drug and metabolite site formed between the α-subunit kinase domain and the β-subunit. β1 subunit mutations that inhibit AMPK activation by the small-molecule activator A769662, which binds to the allosteric drug and metabolite site, also inhibit activation by LCFA-CoAs. Thus, LCFA-CoA metabolites act as direct endogenous AMPK β1-selective activators and promote LCFA oxidation.

Stress, glucocorticoid signaling pathway, and metabolic disorders

BACKGROUND AND AIMS

Glucocorticoids and the GR serve as an essential molecular mediator of stress and different physiologic processes. This review summarizes main findings from studies on the role of the GC/GR signaling in the modulation of genes for nutrient processing by the different organs involved in metabolic diseases.

METHODS

Descriptive review of relevant papers known to the author was conducted.

RESULTS

Several high-throughput screenings in the past 15 years have identified potential GR DNA-binding regions in different cell types with genes that are annotated to be important for the control of metabolism. Transcriptional regulation of these GC-responsive genes provides links between the hypothalamic-pituitary-adrenal axis (HPA) and systemic energy homeostasis in both physiological and pathophysiological states. Future studies must reconsider the use of agonist, the utilization of animal models of stress and metabolic disorders, and validation in humans.

CONCLUSION

This review recapitulates the significant role of the GC/GR signaling in molecular metabolic control and metabolic disorders. Potential future research focus and optimizations have also been identified.

Giant Island Mice Exhibit Widespread Gene Expression Changes in Key Metabolic Organs

Island populations repeatedly evolve extreme body sizes, but the genomic basis of this pattern remains largely unknown. To understand how organisms on islands evolve gigantism, we compared genome-wide patterns of gene expression in Gough Island mice, the largest wild house mice in the world, and mainland mice from the WSB/EiJ wild-derived inbred strain. We used RNA-seq to quantify differential gene expression in three key metabolic organs: gonadal adipose depot, hypothalamus, and liver. Between 4,000 and 8,800 genes were significantly differentially expressed across the evaluated organs, representing between 20% and 50% of detected transcripts, with 20% or more of differentially expressed transcripts in each organ exhibiting expression fold changes of at least 2×. A minimum of 73 candidate genes for extreme size evolution, including Irs1 and Lrp1, were identified by considering differential expression jointly with other data sets: 1) genomic positions of published quantitative trait loci for body weight and growth rate, 2) whole-genome sequencing of 16 wild-caught Gough Island mice that revealed fixed single-nucleotide differences between the strains, and 3) publicly available tissue-specific regulatory elements. Additionally, patterns of differential expression across three time points in the liver revealed that Arid5b potentially regulates hundreds of genes. Functional enrichment analyses pointed to cell cycling, mitochondrial function, signaling pathways, inflammatory response, and nutrient metabolism as potential causes of weight accumulation in Gough Island mice. Collectively, our results indicate that extensive gene regulatory evolution in metabolic organs accompanied the rapid evolution of gigantism during the short time house mice have inhabited Gough Island.