Sensing the fuels: glucose and lipid signaling in the CNS controlling energy homeostasis

T266M variants of ANGPTL4 improve lipid metabolism by modifying their binding affinity to acetyl-CoA carboxylase in obstructive sleep apnea

BACKGROUND

Angiopoietin-like protein 4 (ANGPTL4) is recognized as a crucial regulator in lipid metabolism. Acetyl-CoA carboxylases (ACACAs) play a role in the β-oxidation of fatty acids. Yet, the functions of ANGPTL4 and ACACA in dyslipidemia of obstructive sleep apnea (OSA) remain unclear.

METHODS

This study included 125 male OSA subjects from the Shanghai Sleep Health Study (SSHS) who were matched for age, body mass index (BMI), and lipid profile. Serum ANGPTL4 levels were measured via ELISA. The ANGPTL4 T266M variants of 4455 subjects along with their anthropometric, fasting biochemical, and standard polysomnographic parameters were collected. Linear regression was used to analyze the associations between quantitative traits and ANGPTL4 T266M. Molecular docking and molecular dynamic simulation were employed to compare the effects of the wild-type ANGPTL4 and its T266M mutation on ACACA.

RESULTS

Serum ANGPTL4 levels significantly decreased with increasing OSA severity (non-OSA: 59.6 ± 17.4 ng/mL, mild OSA: 50.0 ± 17.5 ng/mL, moderate OSA: 46.3 ± 15.5 ng/mL, severe OSA: 19.9 ± 14.3 ng/mL, respectively, p = 6.02 × 10-16). No associations were found between T266M and clinical characteristics. Molecular docking indicated that mutant ANGTPL4 T266M had stronger binding affinity for the ACACA protein, compared with wild-type ANGPTL4. In terms of protein secondary structure, mutant ANGTPL4 T266M demonstrated greater stability than wild-type ANGPTL4.

CONCLUSIONS

Serum ANGTPL4 levels were significantly decreased in OSA patients, particularly among individuals with severe OSA. Although functional ANGTPL4 T266M variants were not associated with lipid levels in OSA, ANGTPL4 T266M could enhance binding affinity for the ACACA protein, potentially regulating lipid metabolism.

Systemic Glucose Regulation by a Hindbrain Inhibitory Circuit in a Mouse Model of Type 1 Diabetes

INTRODUCTION

Previous work showed that increasing the electrical activity of inhibitory neurons in the dorsal vagal complex (DVC) is sufficient to increase whole-body glucose concentration in normoglycemic mice. Here we tested the hypothesis that deactivating GABAergic neurons in the dorsal hindbrain of hyperglycemic mice decreases synaptic inhibition of parasympathetic motor neurons in the dorsal motor nucleus of the vagus (DMV) and reduces systemic glucose levels.

METHODS

Chemogenetic activation or inactivation of GABAergic neurons in the nucleus tractus solitarius (NTS) was used to assess effects of modulating parasympathetic output on blood glucose concentration in normoglycemic and hyperglycemic mice. Patch-clamp electrophysiology in vitro was used to assess cellular effects of chemogenetic manipulation of NTS GABA neurons.

RESULTS

Chemogenetic activation of GABAergic NTS neurons in normoglycemic mice increased their action potential firing, resulting in increased inhibitory synaptic input to DMV motor neurons and elevated blood glucose concentration. Deactivation of GABAergic DVC neurons in normoglycemic mice altered their electrical activity but did not alter systemic glucose levels. Conversely, stimulation of GABAergic DVC neurons in mice that were hyperglycemic subsequent to treatment with streptozotocin changed their electrical activity but did not alter whole-body glucose concentration, while deactivation of this inhibitory circuit significantly decreased circulating glucose concentration. Peripheral administration of a brain impermeant muscarinic acetylcholine receptor antagonist abolished these effects.

CONCLUSION

Disinhibiting vagal motor neurons decreases hyperglycemia in a mouse model of type 1 diabetes. This inhibitory brainstem circuit emerges as a key parasympathetic regulator of whole-body glucose homeostasis that undergoes functional plasticity in hyperglycemic conditions.

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.

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.

Regional sex differences in neurochemical profiles of healthy mice measured by magnetic resonance spectroscopy at 9.4 tesla

Objective

To determine sex differences in the neurochemical concentrations measured by in vivo proton magnetic resonance spectroscopy (1H MRS) of healthy mice on a genetic background commonly used for neurodegenerative disease models.

Methods

1H MRS data collected from wild type mice with C57BL/6 or related genetic backgrounds in seven prior studies were used in this retrospective analysis. To be included, data had to be collected at 9.4 tesla magnetic field using advanced 1H MRS protocols, with isoflurane anesthesia and similar animal handling protocols, and a similar number of datasets from male and female mice had to be available for the brain regions analyzed. Overall, 155 spectra from female mice and 166 spectra from male mice (321 in total), collected from six brain regions (brainstem, cerebellum, cortex, hippocampus, hypothalamus, and striatum) at various ages were included.

Results

Concentrations of taurine, total creatine (creatine + phosphocreatine), ascorbate, glucose and glutamate were consistently higher in male vs. female mice in most brain regions. Striatum was an exception with similar total creatine in male and female mice. The sex difference pattern in the hypothalamus was notably different from other regions. Interaction between sex and age was significant for total creatine and taurine in the cerebellum and hippocampus.

Conclusion

Sex differences in regional neurochemical levels are small but significant and age-dependent, with consistent male-female differences across most brain regions. The neuroendocrine region hypothalamus displays a different pattern of sex differences in neurochemical levels. Differences in energy metabolism and cellular density may underlie the differences, with higher metabolic rates in females and higher osmoregulatory and antioxidant capacity in males.

The 26RFa (QRFP)/GPR103 neuropeptidergic system in mice relays insulin signalling into the brain to regulate glucose homeostasis

AIMS/HYPOTHESIS

26RFa (pyroglutamilated RFamide peptide [QRFP]) is a biologically active peptide that regulates glucose homeostasis by acting as an incretin and by increasing insulin sensitivity at the periphery. 26RFa is also produced by a neuronal population localised in the hypothalamus. In this study we investigated whether 26RFa neurons are involved in the hypothalamic regulation of glucose homeostasis.

METHODS

26Rfa^+/+, 26Rfa^-/- and insulin-deficient male C57Bl/6J mice were used in this study. Mice received an acute intracerebroventricular (i.c.v.) injection of 26RFa, insulin or the 26RFa receptor (GPR103) antagonist 25e and were subjected to IPGTTs, insulin tolerance tests, acute glucose-stimulated insulin secretion tests and pyruvate tolerance tests (PTTs). Secretion of 26RFa by hypothalamic explants after incubation with glucose, leptin or insulin was assessed. Expression and quantification of the genes encoding 26RFa, agouti-related protein, the insulin receptor and GPR103 were evaluated by quantitative reverse transcription PCR and RNAscope in situ hybridisation.

RESULTS

Our data indicate that i.c.v.-injected 26RFa induces a robust antihyperglycaemic effect associated with an increase in insulin production by the pancreatic islets. In addition, we found that insulin strongly stimulates 26Rfa expression and secretion by the hypothalamus. RNAscope experiments revealed that neurons expressing 26Rfa are mainly localised in the lateral hypothalamic area, that they co-express the gene encoding the insulin receptor and that insulin induces the expression of 26Rfa in these neurons. Concurrently, the central antihyperglycaemic effect of insulin is abolished in the presence of a GPR103 antagonist and in 26RFa-deficient mice. Finally, our data indicate that the hypothalamic 26RFa neurons are not involved in the central inhibitory effect of insulin on hepatic glucose production, but mediate the central effects of the hormone on its own peripheral production.

CONCLUSION/INTERPRETATION

We have identified a novel mechanism in the hypothalamic regulation of glucose homeostasis, the 26RFa/GPR103 system, and we provide evidence that this neuronal peptidergic system is a key relay for the central regulation of glucose metabolism by insulin.

Hypothalamic Estrogen Signaling and Adipose Tissue Metabolism in Energy Homeostasis

Obesity has become a global epidemic, and it is a major risk factor for other metabolic disorders such as type 2 diabetes and cardiometabolic disease. Accumulating evidence indicates that there is sex-specific metabolic protection and disease susceptibility. For instance, in both clinical and experimental studies, males are more likely to develop obesity, insulin resistance, and diabetes. In line with this, males tend to have more visceral white adipose tissue (WAT) and less brown adipose tissue (BAT) thermogenic activity, both leading to an increased incidence of metabolic disorders. This female-specific fat distribution is partially mediated by sex hormone estrogens. Specifically, hypothalamic estrogen signaling plays a vital role in regulating WAT distribution, WAT beiging, and BAT thermogenesis. These regulatory effects on adipose tissue metabolism are primarily mediated by the activation of estrogen receptor alpha (ERα) in neurons, which interacts with hormones and adipokines such as leptin, ghrelin, and insulin. This review discusses the contribution of adipose tissue dysfunction to obesity and the role of hypothalamic estrogen signaling in preventing metabolic diseases with a particular focus on the VMH, the central regulator of energy expenditure and glucose homeostasis.

Targeting appetite and satiety in diabetes and obesity, via G protein-coupled receptors

Type 2 diabetes and obesity have reached pandemic proportions throughout the world, so much so that the World Health Organisation coined the term "Globesity" to help encapsulate the magnitude of the problem. G protein-coupled receptors (GPCRs) are highly tractable drug targets due to their wide involvement in all aspects of physiology and pathophysiology, indeed, GPCRs are the targets of approximately 30% of the currently approved drugs. GPCRs are also broadly involved in key physiologies that underlie type 2 diabetes and obesity including feeding reward, appetite and satiety, regulation of blood glucose levels, energy homeostasis and adipose function. Despite this, only two GPCRs are the target of approved pharmaceuticals for treatment of type 2 diabetes and obesity. In this review we discuss the role of these, and select other candidate GPCRs, involved in various facets of type 2 diabetic or obese pathophysiology, how they might be targeted and the potential reasons why pharmaceuticals against these targets have not progressed to clinical use. Finally, we provide a perspective on the current development pipeline of anti-obesity drugs that target GPCRs.

Intestine-to-neuronal signaling alters risk-taking behaviors in food-deprived Caenorhabditis elegans

Animals integrate changes in external and internal environments to generate behavior. While neural circuits detecting external cues have been mapped, less is known about how internal states like hunger are integrated into behavioral outputs. Here, we use the nematode C. elegans to examine how changes in internal nutritional status affect chemosensory behaviors. We show that acute food deprivation leads to a reversible decline in repellent, but not attractant, sensitivity. This behavioral change requires two conserved transcription factors MML-1 (MondoA) and HLH-30 (TFEB), both of which translocate from the intestinal nuclei to the cytoplasm during food deprivation. Next, we identify the insulin-like peptide INS-31 as a candidate ligand relaying food-status signals from the intestine to other tissues. Further, we show that neurons likely use the DAF-2 insulin receptor and AGE-1/PI-3 Kinase, but not DAF-16/FOXO to integrate these intestine-released peptides. Altogether, our study shows how internal food status signals are integrated by transcription factors and intestine-neuron signaling to generate flexible behaviors via the gut-brain axis.

Simultaneous exposure to electromagnetic field from mobile phone and unimpeded fructose drinking during pre-, peri-, and post-pubertal stages perturbs the hypothalamic and hepatic regulation of energy homeostasis by early adulthood: experimental evidence

The present-day children-adolescents ubiquitously use the mobile phones and unrestrictedly consume fructose-laden diet. Unfortunately, a rise in the incidence of insulin resistance and fatty liver syndrome in young adults has also been recorded. To delineate a possible correlate, the effect of exposure to electromagnetic field (EMF) from the mobile phone and unrestricted fructose intake during pre-, peri-, and post-pubertal stages of development on orexigenic and anorexigenic signals arising from the hypothalamus and liver of rats is investigated here. The study design included four arms, i.e., "Normal", "Exposure Only (ExpO)", "Fructose Only (FruO)", and "Exposure with Fructose (EF)", wherein weaned rats received either "normal chow and drinking water" or "normal chow and fructose (15%) drinking solution" in presence and absence of EMF exposure (2 h/day) for 8 weeks. The results indicate that the total calories consumed by the EF were higher by early adulthood than normal, possibly under the influence of the raised levels of the orexigenic hormone, i.e., ghrelin, and it reflected as raised rate of weight gain. At early adulthood, the EF recorded mitigated response and sensitivity of insulin. Despite EF being a "fed-state", both centrally and peripherally, the glycolysis was restrained, but the gluconeogenesis was raised. Additionally, the altered lipid profile and the glycogen levels indicate that the EF developed fatty liver. The energy homeostasis of the EF was compromised as evidenced by (a) reduced expression of the glucosensors-GLUT2 and glucokinase in the hypothalamus and liver and (b) reduced expression of the cellular energy regulator-AMPK, orexigenic peptide-NPY, and anorexigenic peptide-POMC in the hypothalamus. Taken together, the present study evidences that the exposure to EMFfrom the mobile phone and unrestricted fructose intake during childhood-adolescence impairs the central and peripheral pathways that mediate the glucosensing, glucoregulation, feeding, and satiety behavior by early adulthood.

Beneficial Effects on Brain Micro-Environment by Caloric Restriction in Alleviating Neurodegenerative Diseases and Brain Aging

Aging and neurodegenerative diseases are frequently associated with the disruption of the extracellular microenvironment, which includes mesenchyme and body fluid components. Caloric restriction (CR) has been recognized as a lifestyle intervention that can improve long-term health. In addition to preventing metabolic disorders, CR has been shown to improve brain health owing to its enhancing effect on cognitive functions or retarding effect on the progression of neurodegenerative diseases. This article summarizes current findings regarding the neuroprotective effects of CR, which include the modulation of metabolism, autophagy, oxidative stress, and neuroinflammation. This review may offer future perspectives for brain aging interventions.

Whole-Brain Mapping of the Expression Pattern of T1R2, a Subunit Specific to the Sweet Taste Receptor

Chemosensory receptors are expressed primarily in sensory organs, but their expression elsewhere can permit ligand detection in other contexts that contribute to survival. The ability of sweet taste receptors to detect natural sugars, sugar alcohols, and artificial sweeteners suggests sweet taste receptors are involved in metabolic regulation in both peripheral organs and in the central nervous system. Our limited knowledge of sweet taste receptor expression in the brain, however, has made it difficult to assess their contribution to metabolic regulation. We, therefore, decided to profile the expression pattern of T1R2, a subunit specific to the sweet taste receptor complex, at the whole-brain level. Using T1r2-Cre knock-in mice, we visualized the overall distribution of Cre-labeled cells in the brain. T1r2-Cre is expressed not only in various populations of neurons, but also in glial populations in the circumventricular organs and in vascular structures in the cortex, thalamus, and striatum. Using immunohistochemistry, we found that T1r2 is expressed in hypothalamic neurons expressing neuropeptide Y and proopiomelanocortin in arcuate nucleus. It is also co-expressed with a canonical taste signaling molecule in perivascular cells of the median eminence. Our findings indicate that sweet taste receptors have unidentified functions in the brain and suggest that they may be a novel therapeutic target in the central nervous system.

Microglial Lipid Biology in the Hypothalamic Regulation of Metabolic Homeostasis

In mammals, myeloid cells help maintain the homeostasis of peripheral metabolic tissues, and their immunologic dysregulation contributes to the progression of obesity and associated metabolic disease. There is accumulating evidence that innate immune cells also serve as functional regulators within the mediobasal hypothalamus (MBH), a critical brain region controlling both energy and glucose homeostasis. Specifically, microglia, the resident parenchymal myeloid cells of the CNS, play important roles in brain physiology and pathology. Recent studies have revealed an expanding array of microglial functions beyond their established roles as immune sentinels, including roles in brain development, circuit refinement, and synaptic organization. We showed that microglia modulate MBH function by transmitting information resulting from excess nutrient consumption. For instance, microglia can sense the excessive consumption of saturated fats and instruct neurons within the MBH accordingly, leading to responsive alterations in energy balance. Interestingly, the recent emergence of high-resolution single-cell techniques has enabled specific microglial populations and phenotypes to be profiled in unprecedented detail. Such techniques have highlighted specific subsets of microglia notable for their capacity to regulate the expression of lipid metabolic genes, including lipoprotein lipase (LPL), apolipoprotein E (APOE) and Triggering Receptor Expressed on Myeloid Cells 2 (TREM2). The discovery of this transcriptional signature highlights microglial lipid metabolism as a determinant of brain health and disease pathogenesis, with intriguing implications for the treatment of brain disorders and potentially metabolic disease. Here we review our current understanding of how changes in microglial lipid metabolism could influence the hypothalamic control of systemic metabolism.

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.

Revealing Alteration in the Hepatic Glucose Metabolism of Genetically Improved Carp, Jayanti Rohu Labeo rohita Fed a High Carbohydrate Diet Using Transcriptome Sequencing

Although feed cost is the greatest concern in aquaculture, the inclusion of carbohydrates in the fish diet, and their assimilation, are still not well understood in aquaculture species. We identified molecular events that occur due to the inclusion of high carbohydrate levels in the diets of genetically improved 'Jayanti rohu' Labeo rohita. To reveal transcriptional changes in the liver of rohu, a feeding experiment was conducted with three doses of gelatinized starch (20% (control), 40%, and 60%). Transcriptome sequencing revealed totals of 15,232 (4464 up- and 4343 down-regulated) and 15,360 (4478 up- and 4171 down-regulated) differentially expressed genes. Up-regulated transcripts associated with glucose metabolisms, such as hexokinase, PHK, glycogen synthase and PGK, were found in fish fed diets with high starch levels. Interestingly, a de novo lipogenesis mechanism was found to be enriched in the livers of treated fish due to up-regulated transcripts such as FAS, ACCα, and PPARγ. The insulin signaling pathways with enriched PPAR and mTOR were identified by Kyoto Encyclopedia of Genes and Genome (KEGG) as a result of high carbohydrates. This work revealed for the first time the atypical regulation transcripts associated with glucose metabolism and lipogenesis in the livers of Jayanti rohu due to the inclusion of high carbohydrate levels in the diet. This study also encourages the exploration of early nutritional programming for enhancing glucose efficiency in carp species, for sustainable and cost-effective aquaculture production.

Cellular and systemic mechanisms for glucose sensing and homeostasis

Glucose is a major source of energy in animals. Maintaining blood glucose levels within a physiological range is important for facilitating glucose uptake by cells, as required for optimal functioning. Glucose homeostasis relies on multiple glucose-sensing cells in the body that constantly monitor blood glucose levels and respond accordingly to adjust its glycemia. These include not only pancreatic β-cells and α-cells that secrete insulin and glucagon, but also central and peripheral neurons regulating pancreatic endocrine function. Different types of cells respond distinctively to changes in blood glucose levels, and the mechanisms involved in glucose sensing are diverse. Notably, recent studies have challenged the currently held views regarding glucose-sensing mechanisms. Furthermore, peripheral and central glucose-sensing cells appear to work in concert to control blood glucose level and maintain glucose and energy homeostasis in organisms. In this review, we summarize the established concepts and recent advances in the understanding of cellular and systemic mechanisms that regulate glucose sensing and its homeostasis.

Animal Models of Metabolic Epilepsy and Epilepsy Associated Metabolic Dysfunction: A Systematic Review

Epilepsy is a serious neurological disorder affecting around 70 million people globally and is characterized by spontaneous recurrent seizures. Recent evidence indicates that dysfunction in metabolic processes can lead to the alteration of neuronal and network excitability, thereby contributing to epileptogenesis. Developing a suitable animal model that can recapitulate all the clinical phenotypes of human metabolic epilepsy (ME) is crucial yet challenging. The specific environment of many symptoms as well as the primary state of the applicable neurobiology, genetics, and lack of valid biomarkers/diagnostic tests are the key factors that hinder the process of developing a suitable animal model. The present systematic review summarizes the current state of available animal models of metabolic dysfunction associated with epileptic disorders. A systematic search was performed by using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) model. A range of electronic databases, including google scholar, Springer, PubMed, ScienceDirect, and Scopus, were scanned between January 2000 and April 2020. Based on the selection criteria, 23 eligible articles were chosen and are discussed in the current review. Critical analysis of the selected literature delineated several available approaches that have been modeled into metabolic epilepsy and pointed out several drawbacks associated with the currently available models. The result describes available models of metabolic dysfunction associated with epileptic disorder, such as mitochondrial respiration deficits, Lafora disease (LD) model-altered glycogen metabolism, causing epilepsy, glucose transporter 1 (GLUT1) deficiency, adiponectin responsive seizures, phospholipid dysfunction, glutaric aciduria, mitochondrial disorders, pyruvate dehydrogenase (PDH) α-subunit gene (PDHA1), pyridoxine dependent epilepsy (PDE), BCL2-associated agonist of cell death (BAD), Kcna1 knock out (KO), and long noncoding RNAs (lncRNA) cancer susceptibility candidate 2 (lncRNA CASC2). Finally, the review highlights certain focus areas that may increase the possibilities of developing more suitable animal models and underscores the importance of the rationalization of animal models and evaluation methods for studying ME. The review also suggests the pressing need of developing precise robust animal models and evaluation methods for investigating ME.

Brain Metabolism Alterations in Type 2 Diabetes: What Did We Learn From Diet-Induced Diabetes Models?

Type 2 diabetes (T2D) is a metabolic disease with impact on brain function through mechanisms that include glucose toxicity, vascular damage and blood–brain barrier (BBB) impairments, mitochondrial dysfunction, oxidative stress, brain insulin resistance, synaptic failure, neuroinflammation, and gliosis. Rodent models have been developed for investigating T2D, and have contributed to our understanding of mechanisms involved in T2D-induced brain dysfunction. Namely, mice or rats exposed to diabetogenic diets that are rich in fat and/or sugar have been widely used since they develop memory impairment, especially in tasks that depend on hippocampal processing. Here we summarize main findings on brain energy metabolism alterations underlying dysfunction of neuronal and glial cells promoted by diet-induced metabolic syndrome that progresses to a T2D phenotype.

Recording and Decoding of Vagal Neural Signals Related to Changes in Physiological Parameters and Biomarkers of Disease

Our bodies have built-in neural reflexes that continuously monitor organ function and maintain physiological homeostasis. Whereas the field of bioelectronic medicine has mainly focused on the stimulation of neural circuits to treat various conditions, recent studies have started to investigate the possibility of leveraging the sensory arm of these reflexes to diagnose disease states. To accomplish this, neural signals emanating from the body's built-in biosensors and propagating through peripheral nerves must be recorded and decoded to identify the presence or levels of relevant biomarkers of disease. The process of acquiring these signals poses several technical challenges related to the neural interfaces, surgical techniques, and data-processing framework needed to record and analyze them. However, these challenges can be addressed with a rigorous experimental approach and new advances in implantable electrodes, signal processing, and machine learning methods. Outlined in this review are studies decoding vagus nerve activity as it related to inflammatory, metabolic, and cardiopulmonary biomarkers. Successfully decoding peripheral nerve activity related to disease states will not only enable the development of real-time diagnostic devices, but also help advancing truly closed-loop neuromodulation technologies.

Identification of hypoglycemia-specific neural signals by decoding murine vagus nerve activity

BACKGROUND

Glucose is a crucial energy source. In humans, it is the primary sugar for high energy demanding cells in brain, muscle and peripheral neurons. Deviations of blood glucose levels from normal levels for an extended period of time is dangerous or even fatal, so regulation of blood glucose levels is a biological imperative. The vagus nerve, comprised of sensory and motor fibres, provides a major anatomical substrate for regulating metabolism. While prior studies have implicated the vagus nerve in the neurometabolic interface, its specific role in either the afferent or efferent arc of this reflex remains elusive.

METHODS

Here we use recently developed methods to isolate and decode specific neural signals acquired from the surface of the vagus nerve in BALB/c wild type mice to identify those that respond robustly to hypoglycemia. We also attempted to decode neural signals related to hyperglycemia. In addition to wild type mice, we analyzed the responses to acute hypo- and hyperglycemia in transient receptor potential cation channel subfamily V member 1 (TRPV1) cell depleted mice. The decoding algorithm uses neural signals as input and reconstructs blood glucose levels.

RESULTS

Our algorithm was able to reconstruct the blood glucose levels with high accuracy (median error 18.6 mg/dl). Hyperglycemia did not induce robust vagus nerve responses, and deletion of TRPV1 nociceptors attenuated the hypoglycemia-dependent vagus nerve signals.

CONCLUSION

These results provide insight to the sensory vagal signaling that encodes hypoglycemic states and suggest a method to measure blood glucose levels by decoding nerve signals.

TRIAL REGISTRATION

Not applicable.

Brain Trauma Disrupts Hepatic Lipid Metabolism: Blame It on Fructose?

SCOPE

The action of brain disorders on peripheral metabolism is poorly understood. The impact of traumatic brain injury (TBI) on peripheral organ function and how TBI effects can be influenced by the metabolic perturbation elicited by fructose ingestion are studied.

METHODS AND RESULTS

It is found that TBI affects glucose metabolism and signaling proteins for insulin and growth hormone in the liver; these effects are exacerbated by fructose ingestion. Fructose, principally metabolized in the liver, potentiates the action of TBI on hepatic lipid droplet accumulation. Studies in isolated cultured hepatocytes identify GH and fructose as factors for the synthesis of lipids. The liver has a major role in the synthesis of lipids used for brain function and repair. TBI results in differentially expressed genes in the hypothalamus, primarily associated with lipid metabolism, providing cues to understand central control of peripheral alterations. Fructose-fed TBI animals have elevated levels of markers of inflammation, lipid peroxidation, and cell energy metabolism, suggesting the pro-inflammatory impact of TBI and fructose in the liver.

CONCLUSION

Results reveal the impact of TBI on systemic metabolism and the aggravating action of fructose. The hypothalamic-pituitary-growth axis seems to play a major role in the regulation of the peripheral TBI pathology.

Dissecting the Brain/Islet Axis in Metabesity

The high prevalence of type 2 diabetes mellitus (T2DM), together with the fact that current treatments are only palliative and do not avoid major secondary complications, reveals the need for novel approaches to treat the cause of this disease. Efforts are currently underway to identify therapeutic targets implicated in either the regeneration or re-differentiation of a functional pancreatic islet β-cell mass to restore insulin levels and normoglycemia. However, T2DM is not only caused by failures in β-cells but also by dysfunctions in the central nervous system (CNS), especially in the hypothalamus and brainstem. Herein, we review the physiological contribution of hypothalamic neuronal and glial populations, particularly astrocytes, in the control of the systemic response that regulates blood glucose levels. The glucosensing capacity of hypothalamic astrocytes, together with their regulation by metabolic hormones, highlights the relevance of these cells in the control of glucose homeostasis. Moreover, the critical role of astrocytes in the response to inflammation, a process associated with obesity and T2DM, further emphasizes the importance of these cells as novel targets to stimulate the CNS in response to metabesity (over-nutrition-derived metabolic dysfunctions). We suggest that novel T2DM therapies should aim at stimulating the CNS astrocytic response, as well as recovering the functional pancreatic β-cell mass. Whether or not a common factor expressed in both cell types can be feasibly targeted is also discussed.

The Central Role of Glucokinase in Glucose Homeostasis: A Perspective 50 Years After Demonstrating the Presence of the Enzyme in Islets of Langerhans

It is hypothesized that glucokinase (GCK) is the glucose sensor not only for regulation of insulin release by pancreatic β-cells, but also for the rest of the cells that contribute to glucose homeostasis in mammals. This includes other cells in endocrine pancreas (α- and δ-cells), adrenal gland, glucose sensitive neurons, entero-endocrine cells, and cells in the anterior pituitary. Glucose transport is by facilitated diffusion and is not rate limiting. Once inside, glucose is phosphorylated to glucose-6-phosphate by GCK in a reaction that is dependent on glucose throughout the physiological range of concentrations, is irreversible, and not product inhibited. High glycerol phosphate shuttle, pyruvate dehydrogenase, and pyruvate carboxylase activities, combined with low pentose-P shunt, lactate dehydrogenase, plasma membrane monocarboxylate transport, and glycogen synthase activities constrain glucose-6-phosphate to being metabolized through glycolysis. Under these conditions, glycolysis produces mostly pyruvate and little lactate. Pyruvate either enters the citric acid cycle through pyruvate dehydrogenase or is carboxylated by pyruvate carboxylase. Reducing equivalents from glycolysis enter oxidative phosphorylation through both the glycerol phosphate shuttle and citric acid cycle. Raising glucose concentration increases intramitochondrial [NADH]/[NAD⁺] and thereby the energy state ([ATP]/[ADP][Pi]), decreasing [Mg²⁺ADP] and [AMP]. [Mg²⁺ADP] acts through control of K_ATP channel conductance, whereas [AMP] acts through regulation of AMP-dependent protein kinase. Specific roles of different cell types are determined by the diverse molecular mechanisms used to couple energy state to cell specific responses. Having a common glucose sensor couples complementary regulatory mechanisms into a tightly regulated and stable glucose homeostatic network.

Apolipoprotein CIII and diabetes. Is there a link?

Apolipoprotein CIII (ApoCIII), a small protein that resides on the surface of lipoprotein particles, is a key regulator of triglyceride metabolism. The inhibition of lipoprotein lipase (LPL), the increased assembly and secretion of very low-density lipoproteins (VLDL) and the decreased reuptake of triglyceride-rich lipoproteins (TRLs) by the liver are mechanisms associating elevated serum ApoCIII levels and hypertriglyceridemia. ApoCIII concentration is high in individuals with diabetes mellitus, indicating a possible positive correlation with impairment of glucose metabolism. The aim of this review (based on a Pubmed search until August 2018) is to present the possible mechanisms linking ApoCIII and deterioration of carbohydrate homeostasis. ApoCIII enhances pancreatic β-cells apoptosis via an increase of the cytoplasmic Ca²⁺ levels in the insulin-producing cells. In addition, overexpression of ApoCIII enhances non-alcoholic fatty liver disease and exacerbates inflammatory pathways in skeletal muscles, affecting insulin signalling and thereby inducing insulin resistance. Moreover, recent studies reveal a possible mechanism of body weight increase and glucose production through a potential ApoCIII-induced LPL inhibition in the hypothalamus. Also, the presence of ApoCIII on the surface of high-density lipoprotein particles is associated with impairment of their antiglycemic and atheroprotective properties. Modulating ApoCIII may be a potent therapeutic approach to manage hypertriglyceridemia and improve carbohydrate metabolism.

Glucose Activates Vagal Control of Hyperglycemia and Inflammation in Fasted Mice

Sepsis is a leading cause of death in hospitalized patients. Many experimental treatments may have failed in clinical trials for sepsis, in part, because they focused on immune responses of healthy animals that did not mimic the metabolic settings of septic patients. Epidemiological studies show an association between metabolic and immune alterations and over 1/3 of septic patients are diabetic, but the mechanism linking these systems is unknown. Here, we report that metabolic fasting increased systemic inflammation and worsened survival in experimental sepsis. Feeding and administration of glucose in fasted mice activated the vagal tone without affecting blood pressure. Vagal stimulation attenuated hyperglycemia and serum TNF levels in sham but only hyperglycemia in splenectomized mice. Vagal stimulation induced the production of dopamine from the adrenal glands. Experimental diabetes increased hyperglycemia and systemic inflammation in experimental sepsis. Fenoldopam, a specific dopaminergic type-1 agonist, attenuated hyperglycemia and systemic inflammation in diabetic endotoxemic mice. These results indicate that glucose activates vagal control of hyperglycemia and inflammation in fasted septic mice via dopamine.

Comparison of Low Glycaemic Index and High Glycaemic Index Potatoes in Relation to Satiety: A Single-Blinded, Randomised Crossover Study in Humans

High glycaemic index (GI) foods have been proposed to reduce satiety and thus promote overweight and obesity. Generally, potatoes have a high GI, but they also provide many beneficial nutrients and they are a highly important food source globally. In this study, we investigated how a low GI potato affected subjective satiety as compared to a high GI potato. Twenty healthy men (aged 18–40 years; body mass index (BMI) 18–27 kg/m²) participated in this single-blinded, controlled, randomised crossover trial. On each of the two trial days, the subjects were given a 500-gram portion of either a low or high GI potato variety (Carisma^® low GI and Arizona high GI). Subjective appetite sensations were measured at baseline and at +15 min, +45 min, +75 min, +105 min, and +135 min after consumption of the test meal until an ad libitum meal was served at +150 min. No significant differences in the primary endpoint, satiety, were found between the two potato varieties (all p > 0.05). Furthermore, no significant differences were found in the secondary endpoints; hunger, fullness, and prospective food consumption, or ad libitum energy intake (all p > 0.05). In conclusion, the results of this study do not indicate that the GI of potatoes is important for satiety in normal-weight men.

Effect of oral supplementation of composite leaf extract of medicinal plants on biomarkers of oxidative stress in induced diabetic Wistar rats

Present study was conducted to evaluate the effect of oral supplementation of composite extract of leaves (CLE) of four medicinal plants; Aegle marmelos, Ocimum sanctum, Murraya koenigii and Azadirachta indica on markers of oxidative stress in brain tissues of alloxan-induced diabetic rats in vivo. Enhanced lipid peroxidation, protein oxidation and reduced antioxidative defence systems were measured in brain tissues of diabetic rats. Supplementation of CLE, once in a day for 35 days significantly (p < .05) protected the peroxidation of lipid, oxidation of protein and ameliorated the antioxidant defence in brain tissue of diabetic rats. It was observed that the insulin-like effect of CLE was dose dependent; higher effect at higher doses. The results of the study suggest that supplementation CLE may provide an overall homeostasis and significant neuro-protection through rescuing brain cells from oxidative abuse and accelerating brain antioxidative defence during advanced stage of hyperglycaemia.

Intense physical exercise potentiates glucose inhibitory effect over food intake of male Wistar rats

NEW FINDINGS

What is the central question of this study? How does an acute session of exercise affect food intake of male Wistar rats? What is the main finding and its importance? Food intake in male Wistar rats is decreased in the first hour after physical exercise independent of the intensity. Moreover, high-intensity exercise potentiates the anorexic effect of peripheral glucose administration. This work raises new feeding-related targets that would explain how exercise drives body weight loss.

ABSTRACT

Obesity has emerged as a critical metabolic disorder in modern society. An adequate lifestyle with a well-oriented programme of diet and physical exercise (PE) can prevent or potentially even cure obesity. Additionally, PE might lead to weight loss by increasing energy expenditure and decreasing hunger perception. In this article, we hypothesize that an acute exercise session would potentiate the glucose inhibitory effects on food intake in male Wistar rats. Our data show that moderate- or high-intensity PE significantly decreased food intake, although no changes in the expression of feeding-related neuropeptide in the arcuate nucleus of the hypothalamus were found. Exercised animals demonstrated a reduced glucose tolerance and increased blood insulin concentration. Intraperitoneal administration of glucose decreased food intake in control animals. In the animals submitted to moderate-intensity PE, the decrease in food intake promoted by glucose was similar to controls; however, an interaction was observed when glucose was injected in the high-intensity PE group, in which food intake was significantly lower than the effect produced by glucose alone. A different pattern of expression was observed for the monocarboxylate transporter isoforms (MCT1, 2 and 4) and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFBP3) in the hypothalamus, which was dependent on the exercise intensity. In conclusion, PE decreases food intake independently of the intensity. However, an interaction between PE and the anorexic effect of glucose is only observed when a high-intensity exercise is performed. These data show an essential role of exercise intensity in the modulation of the glucose inhibitory effect on food intake.

The Versatile Tanycyte: A Hypothalamic Integrator of Reproduction and Energy Metabolism

The fertility and survival of an individual rely on the ability of the periphery to promptly, effectively, and reproducibly communicate with brain neural networks that control reproduction, food intake, and energy homeostasis. Tanycytes, a specialized glial cell type lining the wall of the third ventricle in the median eminence of the hypothalamus, appear to act as the linchpin of these processes by dynamically controlling the secretion of neuropeptides into the portal vasculature by hypothalamic neurons and regulating blood-brain and blood-cerebrospinal fluid exchanges, both processes that depend on the ability of these cells to adapt their morphology to the physiological state of the individual. In addition to their barrier properties, tanycytes possess the ability to sense blood glucose levels, and play a fundamental and active role in shuttling circulating metabolic signals to hypothalamic neurons that control food intake. Moreover, accumulating data suggest that, in keeping with their putative descent from radial glial cells, tanycytes are endowed with neural stem cell properties and may respond to dietary or reproductive cues by modulating hypothalamic neurogenesis. Tanycytes could thus constitute the missing link in the loop connecting behavior, hormonal changes, signal transduction, central neuronal activation and, finally, behavior again. In this article, we will examine these recent advances in the understanding of tanycytic plasticity and function in the hypothalamus and the underlying molecular mechanisms. We will also discuss the putative involvement and therapeutic potential of hypothalamic tanycytes in metabolic and fertility disorders.

Acute anti-obesity effects of intracerebroventricular 11β-HSD1 inhibitor administration in diet-induced obese mice

The hypothalamus is the regulatory centre of both appetite and energy balance and endoplasmic reticulum (ER) stress in the hypothalamus is involved in the pathogenesis of obesity. Recently, inhibition of 11 β hydroxysteroid dehydrogenase type1 (11β-HSD1) was reported to have an anti-obesity effect by reducing fat mass. However, the link between the role of 11β-HSD1 in the hypothalamus and obesity has yet to be determined. In the present study, embryonal primary hypothalamic neurones and high-fat diet (HFD) fed mice were used to investigate the anorexigenic effects of 11β-HSD1 inhibitors both in vitro and in vivo. In hypothalamic neurones, carbenoxolone (a non selecitve 11β-HSD inhibitor) alleviated ER stress and ER stress-induced neuropeptide alterations. In HFD mice, i.c.v. administration of carbenoxolone or KR67500 (nonselective and selective 11β-HSD1 inhibitors, respectively) was associated with less weight gain compared to control mice for 24 hours after treatment, presumably by reducing food intake. Furthermore, glucose regulated protein (Grp78), spliced X-box binding protein (Xbp-1s), c/EBP homologous protein (chop) and ER DnaJ homologue protein (Erdj4) expression was decreased in the hypothalami of mice administrated 11β-HSD1 inhibitors compared to controls. Conversely, the phosphorylation of protein kinase B (PKB/Akt), signal transducer and activator of transcription 3 (Stat3), mitogen-activated protein kinase (MAPK/ERK) and S6 kinase1 (S6K1) in the hypothalamus was induced more in mice treated using the same regimes. In conclusion, acute 11β-HSD1 inhibition in the hypothalamus could reduce food intake by decreasing ER stress and increasing insulin, leptin, and mammalian target of rapamycin complex 1 (mTORC1) signalling.

Role of hypothalamic leptin-LepRb signaling in NPY-CART-mediated appetite suppression in amphetamine-treated rats

Leptin is an adipose tissue hormone which plays an important role in regulating energy homeostasis. Amphetamine (AMPH) is a drug of appetite suppressant, which exerts its effect by decreasing the expression of hypothalamic neuropeptide Y (NPY) and increasing that of cocaine- and amphetamine-regulated transcript (CART). This study investigated whether leptin, the leptin receptor (LepRb) and the signal transducer and activator of transcription-3 (STAT3) were involved in NPY/CART-mediated appetite suppression in AMPH-treated rats. Rats were given AMPH daily for four days, and changes in the levels of blood leptin and hypothalamic NPY, CART, LepRb, Janus kinases 2 (JAK2), and STAT3 were assessed and compared. During the AMPH treatment, blood leptin levels and hypothalamic NPY expression decreased, with the largest reduction observed on Day 2. By contrast, the expression of hypothalamic CART, LepRb, JAK2, and STAT3 increased, with the maximum response on Day 2. Furthermore, the binding activity of pSTAT3/DNA increased and was expressed in similar pattern to that of CART, LepRb, and JAK2. An intracerebroventricular infusion of NPY antisense 60min prior to AMPH treatment increased the levels of leptin, as well as the expression in LepRb, JAK2, and CART, whereas an infusion of STAT3 antisense decreased these levels and the expression of these parameters. The results suggest that blood leptin and hypothalamic LepRb-JAK2-STAT3 signaling involved in NPY-CART-regulated appetite suppression in AMPH-treated rats. The findings may aid understanding the role of leptin-LepRb during the treatment of anorectic drugs.

The effect of fasting on the appetite-associated factors and energy sensors expression in the hypothalamus of different TI broilers

Tonic immobility (TI) is a behaviour related to fear and stress response. Birds can exhibit a short (STI) or long (LTI) tonic immobility phenotype on the basis in TI duration. In this study, the differences in the hypothalamic appetite-associated factors and energy sensor gene expression between STI and LTI broilers were evaluated under free feed access or 16-h fasting. The results showed that the concentrations of cholesterol, high density lipoprotein-cholesterol, non-esterified fatty acid, malonaldehyde, lactate dehydrogenase, creatine kinase, alanine aminotransferase and aspartate aminotransferase in plasma were significantly increased (P < 0.05) in fasting broilers compared with broilers fed ad libitum, whereas plasma glucose, triglyceride, and total antioxidant capacity concentrations were decreased (P < 0.05). With respect to TI, however, only low density lipoprotein-cholesterol and glutathione peroxidase concentrations in plasma showed significant differences between LTI and STI broilers, with higher concentrations in LTI compared with STI. Real-time PCR results showed that only NPY mRNA expression demonstrated a tendency to increase in STI broilers compared with LTI (P = 0.095). Fasting downregulated SREBP-1 and its target gene FAS but upregulated CPT1 in the hypothalamus. Additionally, levels of hypothalamic p-GR and p-AMPK protein expression decreased after fasting. These results indicate that a 16-h fasting results in a negative energy status, and is accompanied with changes in expression of hypothalamic energy sensor and appetite-associated factors.

Mitochondria-Bound Hexokinase (mt-HK) Activity Differ in Cortical and Hypothalamic Synaptosomes: Differential Role of mt-HK in H2O2 Depuration

Glucose and oxygen are vital for the brain, as these molecules provide energy and metabolic intermediates that are necessary for cell function. The glycolysis pathway and mitochondria play a pivotal role in cell energy metabolism, which is closely related to reactive oxygen species (ROS) production. Hexokinase (HK) is a key enzyme involved in glucose metabolism that modulates the level of brain mitochondrial ROS by recycling ADP for oxidative phosphorylation (OxPhos). Here, we hypothesize that the control of mitochondrial metabolism by hexokinase differs in distinct areas of the brain, such as the cortex and hypothalamus, in which ROS might function as signaling molecules. Thus, we investigated mitochondrial metabolism of synaptosomes derived from both brain regions. Cortical synaptosomes (CSy) show a predominance of glutamatergic synapses, while in the hypothalamic synaptosomes (HSy), the GABAergic synapses predominate. Significant differences of oxygen consumption and ROS production were related to higher mitochondrial complex II activity (succinate dehydrogenase-SDH) in CSy rather than to mitochondrial number. Mitochondrial HK (mt-HK) activity was higher in CSy than in HSy regardless the substrate added. Mitochondrial O₂ consumption related to mt-HK activation by 2-deoxyglucose was also higher in CSy. In the presence of substrate for complex II, the activation of synaptosomal mt-HK promoted depuration of ROS in both HSy and CSy, while ROS depuration did not occur in HSy when substrate for complex I was used. The impact of the mt-HK inhibition by glucose-6-phosphate (G6P) was the same in synaptosomes from both areas. Together, the differences found between CSy and HSy indicate specific roles of mt-HK and SDH on the metabolism of each brain region, what probably depends on the main metabolic route that is used by the neurons.

Investigating metabolic regulation using targeted neuromodulation

The central nervous system (CNS) plays a vital role in regulating energy balance and metabolism. Over the last 50 years, studies in animal models have allowed us to identify critical CNS regions involved in these processes and even crucial cell populations. Now, techniques for genetically and anatomically targeted manipulation of specific neural populations using light (optogenetic), ligands (chemogenetic), or magnetic fields (radiogenetic/magnetogenetic) allow detailed investigation of circuits involved in metabolic regulation. In this review, we provide a brief overview of recent studies using light- and magnetic field-regulated neural activity to investigate the neural circuits contributing to metabolic control.

Neural circuits of eating behaviour: Opportunities for therapeutic development

Understanding of the neural and physiological substrates of hunger and satiety has increased rapidly over the last three decades, and pharmacological targets have already been identified for the treatment of obesity that has moved from pre-clinical screening to therapies approved by regulatory authorities. Initially, this review describes the way in which physiological signals of energy availability interact with hedonic and rewarding properties of food to modulate the neural circuitry that supports eating behaviour. This is followed by a brief account of current and promising targets for drug development and a review of the wide range of preclinical paradigms that model important influences on human eating behaviour, and can be used to guide early stages of the drug development process.

Opioid Receptor Activation Impairs Hypoglycemic Counterregulation in Humans

Although intensive glycemic control improves outcomes in type 1 diabetes mellitus (T1DM), iatrogenic hypoglycemia limits its attainment. Recurrent and/or antecedent hypoglycemia causes blunting of protective counterregulatory responses, known as hypoglycemia-associated autonomic failure (HAAF). To determine whether and how opioid receptor activation induces HAAF in humans, 12 healthy subjects without diabetes (7 men, age 32.3 ± 2.2 years, BMI 25.1 ± 1.0 kg/m²) participated in two study protocols in random order over two consecutive days. On day 1, subjects received two 120-min infusions of either saline or morphine (0.1 μg/kg/min), separated by a 120-min break (all euglycemic). On day 2, subjects underwent stepped hypoglycemic clamps (nadir 60 mg/dL) with evaluation of counterregulatory hormonal responses, endogenous glucose production (EGP, using 6,6-D2-glucose), and hypoglycemic symptoms. Morphine induced an ∼30% reduction in plasma epinephrine response together with reduced EGP and hypoglycemia-associated symptoms on day 2. Therefore, we report the first studies in humans demonstrating that pharmacologic opioid receptor activation induces some of the clinical and biochemical features of HAAF, thus elucidating the individual roles of various receptors involved in HAAF's development and suggesting novel pharmacologic approaches for safer intensive glycemic control in T1DM.

FGF1 - a new weapon to control type 2 diabetes mellitus

A hypercaloric diet combined with a sedentary lifestyle is a major risk factor for the development of insulin resistance, type 2 diabetes mellitus (T2DM) and associated comorbidities. Standard treatment for T2DM begins with lifestyle modification, and includes oral medications and insulin therapy to compensate for progressive β-cell failure. However, current pharmaceutical options for T2DM are limited in that they do not maintain stable, durable glucose control without the need for treatment intensification. Furthermore, each medication is associated with adverse effects, which range from hypoglycaemia to weight gain or bone loss. Unexpectedly, fibroblast growth factor 1 (FGF1) and its low mitogenic variants have emerged as potentially safe candidates for restoring euglycaemia, without causing overt adverse effects. In particular, a single peripheral injection of FGF1 can lower glucose to normal levels within hours, without the risk of hypoglycaemia. Similarly, a single intracerebroventricular injection of FGF1 can induce long-lasting remission of the diabetic phenotype. This Review discusses potential mechanisms by which centrally administered FGF1 improves central glucose-sensing and peripheral glucose uptake in a sustained manner. Specifically, we explore the potential crosstalk between FGF1 and glucose-sensing neuronal circuits, hypothalamic neural stem cells and synaptic plasticity. Finally, we highlight therapeutic considerations of FGF1 and compare its metabolic actions with FGF15 (rodents), FGF19 (humans) and FGF21.

The impact of ageing, fasting and high-fat diet on central and peripheral glucose tolerance and glucose-sensing neural networks in the arcuate nucleus

Obesity and ageing are risk factors for diabetes. In the present study, we investigated the effects of ageing, obesity and fasting on central and peripheral glucose tolerance and on glucose-sensing neuronal function in the arcuate nucleus of rats, with a view to providing insight into the central mechanisms regulating glucose homeostasis and how they change or are subject to dysfunction with ageing and obesity. We show that, following a glucose load, central glucose tolerance at the level of the cerebrospinal fluid (CSF) and plasma is significantly reduced in rats maintained on a high-fat diet (HFD). With ageing, up to 2 years, central glucose tolerance was impaired in an age-dependent manner, whereas peripheral glucose tolerance remained unaffected. Ageing-induced peripheral glucose intolerance was improved by a 24-hour fast, whereas central glucose tolerance was not corrected. Pre-wean, immature animals have elevated basal plasma glucose levels and a delayed increase in central glucose levels following peripheral glucose injection compared to mature animals. Electrophysiological recording techniques revealed an energy-status-dependent role for glucose-excited, inhibited and adapting neurones, along with glucose-induced changes in synaptic transmission. We conclude that ageing affects central glucose tolerance, whereas HFD profoundly affects central and peripheral glucose tolerance and, in addition, glucose-sensing neurones adapt function in an energy-status-dependent manner.

A comprehensive analysis of mitochondrial genes variants and their association with antipsychotic-induced weight gain

Antipsychotic Induced Weight Gain (AIWG) is a common and severe side effect of many antipsychotic medications. Mitochondria play a vital role for whole-body energy homeostasis and there is increasing evidence that antipsychotics modulate mitochondrial function. This study aimed to examine the role of variants in nuclear-encoded mitochondrial genes and the mitochondrial DNA (mtDNA) in conferring risk for AIWG. We selected 168 European-Caucasian individuals from the CATIE sample based upon meeting criteria of multiple weight measures while taking selected antipsychotics (risperidone, quetiapine or olanzapine). We tested the association of 670 nuclear-encoded mitochondrial genes with weight change (%) using MAGMA software. Thirty of these genes showed nominally significant P-values (<0.05). We were able to replicate the association of three genes, CLPB, PARL, and ACAD10, with weight change (%) in an independent prospectively assessed AIWG sample. We analyzed mtDNA variants in a subset of 74 of these individuals using next-generation sequencing. No common or rare mtDNA variants were found to be significantly associated with weight change (%) in our sample. Additionally, analysis of mitochondrial haplogroups showed no association with weight change (%). In conclusion, our findings suggest nuclear-encoded mitochondrial genes play a role in AIWG. Replication in larger sample is required to validate our initial report of mtDNA variants in AIWG.

Energy imbalance alters Ca2+ handling and excitability of POMC neurons

Satiety-signaling, pro-opiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus play a pivotal role in the regulation of energy homeostasis. Recent studies reported altered mitochondrial dynamics and decreased mitochondria- endoplasmic reticulum contacts in POMC neurons during diet-induced obesity. Since mitochondria play a crucial role in Ca²⁺ signaling, we investigated whether obesity alters Ca²⁺ handling of these neurons in mice. In diet-induced obesity, cellular Ca²⁺ handling properties including mitochondrial Ca²⁺ uptake capacity are impaired, and an increased resting level of free intracellular Ca²⁺ is accompanied by a marked decrease in neuronal excitability. Experimentally increasing or decreasing intracellular Ca²⁺ concentrations reproduced electrophysiological properties observed in diet-induced obesity. Taken together, we provide the first direct evidence for a diet-dependent deterioration of Ca²⁺ homeostasis in POMC neurons during obesity development resulting in impaired function of these critical energy homeostasis-regulating neurons.

DOI:http://dx.doi.org/10.7554/eLife.25641.001

Whey protein effects on energy balance link the intestinal mechanisms of energy absorption with adiposity and hypothalamic neuropeptide gene expression

We tested the hypothesis that dietary whey protein isolate (WPI) affects the intestinal mechanisms related to energy absorption and that the resulting energy deficit is compensated by changes in energy balance to support growth. C57BL/6 mice were provided a diet enriched with WPI with varied sucrose content, and the impact on energy balance-related parameters was investigated. As part of a high-sucrose diet, WPI reduced the hypothalamic expression of pro-opiomelanocortin gene expression and increased energy intake. The energy expenditure was unaffected, but epididymal weight was reduced, indicating an energy loss. Notably, there was a reduction in the ileum gene expression for amino acid transporter SLC6a19, glucose transporter 2, and fatty acid transporter 4. The composition of the gut microbiota also changed, where Firmicutes were reduced. The above changes indicated reduced energy absorption through the intestine. We propose that this mobilized energy in the adipose tissue and caused hypothalamic changes that increased energy intake, acting to counteract the energy deficit arising in the intestine. Lowering the sucrose content in the WPI diet increased energy expenditure. This further reduced epididymal weight and plasma leptin, whereupon hypothalamic ghrelin gene expression and the intestinal weight were both increased. These data suggest that when the intestine-adipose-hypothalamic pathway is subjected to an additional energy loss (now in the adipose tissue), compensatory changes attempt to assimilate more energy. Notably, WPI and sucrose content interact to enable the component mechanisms of this pathway.

Sweet taste receptor in the hypothalamus: a potential new player in glucose sensing in the hypothalamus

The hypothalamic feeding center plays an important role in energy homeostasis. The feeding center senses the systemic energy status by detecting hormone and nutrient levels for homeostatic regulation, resulting in the control of food intake, heat production, and glucose production and uptake. The concentration of glucose is sensed by two types of glucose-sensing neurons in the feeding center: glucose-excited neurons and glucose-inhibited neurons. Previous studies have mainly focused on glucose metabolism as the mechanism underlying glucose sensing. Recent studies have indicated that receptor-mediated pathways also play a role in glucose sensing. This review describes sweet taste receptors in the hypothalamus and explores the role of sweet taste receptors in energy homeostasis.

Appetite Regulation: Hormones, Peptides, and Neurotransmitters and Their Role in Obesity

Understanding body weight regulation will aid in the development of new strategies to combat obesity. This review examines energy homeostasis and food intake behaviors, specifically with regards to hormones, peptides, and neurotransmitters in the periphery and central nervous system, and their potential role in obesity. Dysfunction in feeding signals by the brain is a factor in obesity. The hypothalamic (arcuate nucleus) and brainstem (nucleus tractus solitaris) areas integrate behavioral, endocrine, and autonomic responses via afferent and efferent pathways from and to the brainstem and peripheral organs. Neurons present in the arcuate nucleus express pro-opiomelanocortin, Neuropeptide Y, and Agouti Related Peptide, with the former involved in lowering food intake, and the latter two acutely increasing feeding behaviors. Action of peripheral hormones from the gut, pancreas, adipose, and liver are also involved in energy homeostasis. Vagal afferent neurons are also important in regulating energy homeostasis. Peripheral signals respond to the level of stored and currently available fuel. By studying their actions, new agents maybe developed that disable orexigenic responses and enhance anorexigenic signals. Although there are relatively few medications currently available for obesity treatment, a number of agents are in development that work through these pathways.

Antagonistic modulation of NPY/AgRP and POMC neurons in the arcuate nucleus by noradrenalin

In the arcuate nucleus of the hypothalamus (ARH) satiety signaling (anorexigenic) pro-opiomelanocortin (POMC)-expressing and hunger signaling (orexigenic) agouti-related peptide (AgRP)-expressing neurons are key components of the neuronal circuits that control food intake and energy homeostasis. Here, we assessed whether the catecholamine noradrenalin directly modulates the activity of these neurons in mice. Perforated patch clamp recordings showed that noradrenalin changes the activity of these functionally antagonistic neurons in opposite ways, increasing the activity of the orexigenic NPY/AgRP neurons and decreasing the activity of the anorexigenic POMC neurons. Cell type-specific transcriptomics and pharmacological experiments revealed that the opposing effect on these neurons is mediated by the activation of excitatory α_1A - and β- adrenergic receptors in NPY/AgRP neurons, while POMC neurons are inhibited via α_2A – adrenergic receptors. Thus, the coordinated differential modulation of the key hypothalamic neurons in control of energy homeostasis assigns noradrenalin an important role to promote feeding.

DOI:http://dx.doi.org/10.7554/eLife.25770.001

Involvement of CD36 in Modulating the Decrease of NPY and AgRP Induced by Acute Palmitic Acid Stimulation in N1E-115 Cells

Central nervous system (CNS) fatty acid sensing plays an important role in the regulation of food intake, and palmitic acid (PA) is the most important long chain fatty acid (LCFA) in the mammalian diet. To explore the effect of PA on central neuropeptide expression and the role of the cluster of the differentiation of 36 (CD36) in the process, N1E-115 cells were cultured with PA in the presence or absence of sulfosuccinimidyl-oleate (SSO), a CD36 inhibitor. Results showed that 10 μmol/L PA significantly reduced NPY and AgRP mRNA expression after 20 min of exposure, while the expression of CD36 was upregulated. The presence of SSO significantly attenuated the decrease of NPY and AgRP expression that was induced by PA alone, although no notable effect on PA- induced CD36 gene expression was observed. In conclusion, our study suggests the involvement of CD36 in the PA-induced decrease of NPY and AgRP in N1E-115 cells.

The New Biology and Pharmacology of Glucagon

In the last two decades we have witnessed sizable progress in defining the role of gastrointestinal signals in the control of glucose and energy homeostasis. Specifically, the molecular basis of the huge metabolic benefits in bariatric surgery is emerging while novel incretin-based medicines based on endogenous hormones such as glucagon-like peptide 1 and pancreas-derived amylin are improving diabetes management. These and related developments have fostered the discovery of novel insights into endocrine control of systemic metabolism, and in particular a deeper understanding of the importance of communication across vital organs, and specifically the gut-brain-pancreas-liver network. Paradoxically, the pancreatic peptide glucagon has reemerged in this period among a plethora of newly identified metabolic macromolecules, and new data complement and challenge its historical position as a gut hormone involved in metabolic control. The synthesis of glucagon analogs that are biophysically stable and soluble in aqueous solutions has promoted biological study that has enriched our understanding of glucagon biology and ironically recruited glucagon agonism as a central element to lower body weight in the treatment of metabolic disease. This review summarizes the extensive historical record and the more recent provocative direction that integrates the prominent role of glucagon in glucose elevation with its under-acknowledged effects on lipids, body weight, and vascular health that have implications for the pathophysiology of metabolic diseases, and the emergence of precision medicines to treat metabolic diseases.