Hypothalamic Glucose Research Articles

Moderate aerobic training enhances the effectiveness of insulin therapy through hypothalamic IGF1 signaling in rat model of Alzheimer's disease

Alzheimer's disease (AD) is a neurological condition that is connected with a decline in a person's memory as well as their cognitive ability. One of the key topics of AD research has been the exploration of metabolic causes. We investigated the effects of treadmill exercise and intranasal insulin on learning and memory impairment and the expression of IGF1, BDNF, and GLUT4 in hypothalamus. The animals were put into 9 groups at random. In this study, we examined the impact of insulin on spatial memory in male Wistar rats and analyzed the effects of a 4-week pretreatment of moderate treadmill exercise and insulin on the mechanisms of improved hypothalamic glucose metabolism through changes in gene and protein expression of IGF1, BDNF, and GLUT4. We discovered that rat given Aβ25–35 had impaired spatial learning and memory, which was accompanied by higher levels of Aβ plaque burden in the hippocampus and lower levels of IGF1, BDNF, and GLUT4 mRNA and protein expression in the hypothalamus. Additionally, the administration of exercise training and intranasal insulin results in the enhancement of spatial learning and memory impairments, the reduction of plaque burden in the hippocampus, and the enhancement of the expression of IGF1, BDNF, and GLUT4 in the hypothalamus of rats that were treated with Aβ25–35. Our results show that the improvement of learning and spatial memory due to the improvement of metabolism and upregulation of the IGF1, BDNF, and GLUT4 pathways can be affected by pretreatment exercise and intranasal insulin.

OR12-06 Hypothalamic Adgrl1 Is A Potential Glucoreceptor Involved In Regulating Energy Balance, Glucose Homeostasis, And Leptin Sensitivity In Mice

Abstract Disclosure: D.J. Samuel: None. T.S. Faniyan: None. M.U. Raza: None. S. Bathina: None. K.H. Chhabra: None. The hypothalamus regulates energy and glucose homeostasis by influencing glucose-stimulated insulin secretion, insulin sensitivity, and activating the hypoglycemia counterregulatory response. Although hypothalamic glucose transporters coupled with glucose metabolism are involved in mediating some of these effects, it is unknown whether a plasma membrane receptor that directly binds to glucose can contribute to hypothalamic glucose signaling. We used affinity chromatography and biotin-labeled glucose to enrich glucose-binding plasma membrane proteins/receptors in the mouse hypothalamus and then performed proteomic analyses. Adhesion G-protein Coupled Receptor L1 (Adgrl1) was a top candidate as a potential glucoreceptor. Therefore, we generated Adgrl1loxp/loxp mice to knockout Adgrl1 in the ventromedial hypothalamus (VMH; a region known for glucose sensing) using the Cre-Lox system to determine the role of Adgrl1VMH in glucose homeostasis, energy balance, and leptin sensitivity. We measured body weight, food intake, 6h fasting blood glucose and plasma insulin levels. We also determined leptin sensitivity in the Adgrl1VMH deficient mice. We observed that 24 weeks old male Adgrl1VMH deficient mice had higher (p<0.05) body weight (49 ±3.6 vs 35 ±1.3 g), blood glucose (210 ±4 vs 180 ±5 mg/dl), plasma insulin levels (2.92 ±0.24 vs 1.63 ±0.09 ng/ml), and leptin levels (21.11 ±1.72 vs 8.38 ±0.80 ng/ml) compared to their control littermates. Hyperinsulinemia and hyperleptinemia persisted in the Adgrl1VMH knockout mice even when they were weight-matched to their littermate controls, indicating the direct role of Adgrl1VMH in regulating plasma insulin and leptin levels. Ovariectomy in female mice was necessary to unmask the effects of Adgrl1VMH deficiency on energy and glucose homeostasis. To assess acute leptin sensitivity, we injected Adgrl1VMH deficient mice and their littermate control mice with recombinant mouse leptin (5 mg/Kg, i.p., twice a day for two days), and monitored their body weight and food intake. Male Adgrl1VMH deficient mice were more susceptible (p<0.05) to leptin mediated decrease in food intake (-1 ±0.1 vs -0.5 ±0.005, g/day; these values are relative to each group’s corresponding baseline food intake) than their littermate controls. Decrease in body weight was similar in both groups with this acute leptin treatment. These findings suggest that Adgrl1VMH is essential in regulating energy and glucose homeostasis in a sex-specific manner. Moreover, Adgrl1VMH contributes to leptin’s acute effects on food intake. Therefore, hypothalamic Adgrl1 could be a target to enhance leptin sensitivity in future therapies for treating type 2 diabetes and obesity. Presentation: Friday, June 16, 2023

Hyperglycemia increases SCO-spondin and Wnt5a secretion into the cerebrospinal fluid to regulate ependymal cell beating and glucose sensing.

Hyperglycemia increases glucose concentrations in the cerebrospinal fluid (CSF), activating glucose-sensing mechanisms and feeding behavior in the hypothalamus. Here, we discuss how hyperglycemia temporarily modifies ependymal cell ciliary beating to increase hypothalamic glucose sensing. A high level of glucose in the rat CSF stimulates glucose transporter 2 (GLUT2)-positive subcommissural organ (SCO) cells to release SCO-spondin into the dorsal third ventricle. Genetic inactivation of mice GLUT2 decreases hyperglycemia-induced SCO-spondin secretion. In addition, SCO cells secrete Wnt5a-positive vesicles; thus, Wnt5a and SCO-spondin are found at the apex of dorsal ependymal cilia to regulate ciliary beating. Frizzled-2 and ROR2 receptors, as well as specific proteoglycans, such as glypican/testican (essential for the interaction of Wnt5a with its receptors) and Cx43 coupling, were also analyzed in ependymal cells. Finally, we propose that the SCO-spondin/Wnt5a/Frizzled-2/Cx43 axis in ependymal cells regulates ciliary beating, a cyclic and adaptive signaling mechanism to control glucose sensing.

Hypothalamic Glucose Hypersensitivity-Induced Insulin Secretion in the Obese Zücker Rat Is Reversed by Central Ghrelin Treatment.

Aims: Part of hypothalamic (mediobasal hypothalamus [MBH]) neurons detect changes in blood glucose levels that in turn coordinate the vagal control of insulin secretion. This control cascade requires the production of mitochondrial reactive oxygen species (mROS), which is altered in models of obesity and insulin resistance. Obese, insulin-resistant Zücker rats are characterized by hypothalamic hypersensitivity to glucose. This initiates an abnormal vagus-induced insulin secretion, associated with an overproduction of mROS in response to a low glucose dose. Here, we hypothesized that ghrelin, known to buffer reactive oxygen species (ROS) via mitochondrial function, may be a major component of the hypothalamic glucose hypersensitivity in the hypoghrelinemic obese Zücker rat. Results: Hypothalamic glucose hypersensitivity-induced insulin secretion of Zücker obese rats was reversed by ghrelin pretreatment. The overproduction of MBH mROS in response to a low glucose load no longer occurred in obese rats that had previously received the cerebral ghrelin infusion. This decrease in mROS production was accompanied by a normalization of oxidative phosphorylation (OXPHOS). Conversely, blocking the action of ghrelin with a growth hormone secretagogue receptor antagonist in a model of hyperghrelinemia (fasted rats) completely restored hypothalamic glucose sensing-induced insulin secretion that was almost absent in this physiological situation. Accordingly, ROS signaling and mitochondrial activity were increased by the ghrelin receptor antagonist. Innovation: These results demonstrate for the first time that ghrelin addressed only to the brain could have a protective effect on the defective control of insulin secretion in the insulin-resistant, hypoghrelinemic obese subject. Conclusions: Ghrelin, through its action on OXPHOS, modulates mROS signaling in response to cerebral hyperglycemia and the consequent vagal control of insulin secretion. In insulin-resistant obese states, brain hypoghrelinemia could be responsible for the nervous defect in insulin secretion.

Alterations of the expression levels of glucose, inflammation, and iron metabolism related miRNAs and their target genes in the hypothalamus of STZ-induced rat diabetes model

BackgroundThe hypothalamus of the central nervous system is implicated in the development of diabetes due to its glucose-sensing function. Dysregulation of the hypothalamic glucose-sensing neurons leads to abnormal glucose metabolism. It has been described that fractalkine (FKN) is involved in the development of hypothalamic inflammation, which may be one of the underlying causes of a diabetic condition. Moreover, iron may play a role in the pathogenesis of diabetes via the regulation of hepcidin, the iron regulatory hormone synthesis. MicroRNAs (miRNAs) are short non-coding molecules working as key regulators of gene expression, usually by inhibiting translation. Hypothalamic miRNAs are supposed to have a role in the control of energy balance by acting as regulators of hypothalamic glucose metabolism via influencing translation.MethodsUsing a miRNA array, we analysed the expression of diabetes, inflammation, and iron metabolism related miRNAs in the hypothalamus of a streptozotocin-induced rat type 1 diabetes model. Determination of the effect of miRNAs altered by STZ treatment on the target genes was carried out at protein level.ResultsWe found 18 miRNAs with altered expression levels in the hypothalamus of the STZ-treated animals, which act as the regulators of mRNAs involved in glucose metabolism, pro-inflammatory cytokine synthesis, and iron homeostasis suggesting a link between these processes in diabetes. The alterations in the expression level of these miRNAs could modify hypothalamic glucose sensing, tolerance, uptake, and phosphorylation by affecting the stability of hexokinase-2, insulin receptor, leptin receptor, glucokinase, GLUT4, insulin-like growth factor receptor 1, and phosphoenolpyruvate carboxykinase mRNA molecules. Additional miRNAs were found to be altered resulting in the elevation of FKN protein. The miRNA, mRNA, and protein analyses of the diabetic hypothalamus revealed that the iron import, export, and iron storage were all influenced by miRNAs suggesting the disturbance of hypothalamic iron homeostasis.ConclusionIt can be supposed that glucose metabolism, inflammation, and iron homeostasis of the hypothalamus are linked via the altered expression of common miRNAs as well as the increased expression of FKN, which contribute to the imbalance of energy homeostasis, the synthesis of pro-inflammatory cytokines, and the iron accumulation of the hypothalamus. The results raise the possibility that FKN could be a potential target of new therapies targeting both inflammation and iron disturbances in diabetic conditions.Graphical

Glucose Stimulates Glial Cell Line-Derived Neurotrophic Factor Gene Expression in Microglia through a GLUT5-Independent Mechanism.

Feeding-regulating neurotrophic factors are expressed in both neurons and glial cells. However, nutritional regulation of anorexigenic glial cell line-derived neurotrophic factor (GDNF) and orexigenic mesencephalic astrocyte-derived neurotrophic factor (MANF) expression in specific cell types remains poorly understood. Hypothalamic glucose sensing plays a critical role in the regulation of food intake. It has been theorized that local glucose concentration modulates microglial activity partially via glucose transporter 5 (GLUT5). We hypothesized that an increased local glucose concentration stimulates GDNF expression while inhibiting MANF expression in the hypothalamus and microglia via GLUT5. The present study investigated the effect of glucose on Gdnf and Manf mRNA expression in the mouse hypothalamus and murine microglial cell line SIM-A9. Intracerebroventricular glucose treatment significantly increased Gdnf mRNA levels in the hypothalamus without altering Manf mRNA levels. Exposure to high glucose caused a significant increase in Gdnf mRNA expression and a time-dependent change in Manf mRNA expression in SIM-A9 cells. GLUT5 inhibitor treatment did not block glucose-induced Gdnf mRNA expression in these cells. These findings suggest that microglia are responsive to changes in the local glucose concentration and increased local glucose availability stimulates the expression of microglial GNDF through a GLUT5-independent mechanism, contributing to glucose-induced feeding suppression.

153-OR: Ventromedial Hypothalamic Nucleus Controls Glucose Metabolism through Adipose Tissue Lipolysis

The central nervous system (CNS) coordinates metabolic target organ function to optimize blood glucose levels, while dysregulation of this system leads to impaired glycemia. Attempts to improve glucose control through CNS targeting are hindered by a incomplete understanding of the specific neuronal populations involved and how these cells coordinate peripheral metabolic target organ function. We found that cholecystokinin b receptor-expressing neurons of the ventromedial nucleus of the hypothalamus (VMN; VMNCCKBR neurons) mediate glucose mobilization during counter-regulatory responses to hypoglycemia and regulate glucose levels in normal and diabetic mice. Silencing VMNCCKBR neurons with tetanus toxin (CCKBRTT) attenuates hyperglycemia in ob/ob mice and decreases baseline blood glucose by suppressing hepatic gluconeogenesis despite decreased insulin and elevated glucagon. CCKBRTT mice have elevated hepatic gluconeogenic enzyme expression and normal glycemic responses to exogenous gluconeogenic substrates, suggesting that silencing VMNCCKBR neurons decreases blood glucose through impaired gluconeogenic substrate mobilization. To determine which gluconeogenic substrates contribute to VMNCCKBR-neuron mediated glucose production, we expressed channel rhodopsin in VMNCCKBR neurons to optogenetically activate VMNCCKBR neurons in freely moving mice. In addition to elevating plasma glucose, optogenetic activation resulted in a β3-adrenergic receptor-dependent increase in plasma ketones and glycerol, suggesting that VMNCCKBR neurons increase lipolysis though SNS innervation of white adipose tissue (WAT) . Consistent with this observation, CCKBRTT mice exhibited decreased fasting plasma glycerol and in vivo lipolysis, while β3-agonist treatment elevated these appropriately. Hence, VMNCCKBR neuron-mediated SNS outflow to WAT promotes lipolysis to provide gluconeogenic substrates and support baseline blood glucose in mice. Disclosure A.Affinati: Other Relationship; Novo Nordisk A/S. J.Flak: Research Support; Eli Lilly and Company. N.Kodur: None. A.Hashsham: None. A.J.Tomlinson: None. N.Bozadjieva kramer: None. C.Li: Employee; Novo Nordisk. M.G.Myers: Advisory Panel; Regeneron Pharmaceuticals Inc., Research Support; AstraZeneca, Novo Nordisk. Funding National Institutes of Health (F32DK122660)

Tanycytic networks mediate energy balance by feeding lactate to glucose-insensitive POMC neurons.

Hypothalamic glucose sensing enables an organism to match energy expenditure and food intake to circulating levels of glucose, the main energy source of the brain. Here, we established that tanycytes of the arcuate nucleus of the hypothalamus, specialized glia that line the wall of the third ventricle, convert brain glucose supplies into lactate that they transmit through monocarboxylate transporters to arcuate proopiomelanocortin neurons, which integrate this signal to drive their activity and to adapt the metabolic response to meet physiological demands. Furthermore, this transmission required the formation of extensive connexin-43 gap junction-mediated metabolic networks by arcuate tanycytes. Selective suppression of either tanycytic monocarboxylate transporters or gap junctions resulted in altered feeding behavior and energy metabolism. Tanycytic intercellular communication and lactate production are thus integral to the mechanism by which hypothalamic neurons that regulate energy and glucose homeostasis efficiently perceive alterations in systemic glucose levels as a function of the physiological state of the organism.

Environmental Enrichment Potentiates Glucose-Induced Anorexia in Mice

The hypothalamus controls food intake and metabolism by integrating nutrient and hormonal signals from peripheral tissues. Both central and peripheral administration of glucose leads to a reduction in food intake in rodents. Similarly, administration of the adipocyte hormone leptin or the gastrointestinal hormone xenin reduces food intake. In contrast, impairments in hypothalamic signaling of these factors cause hyperphagia and obesity in rodents and humans. Environmental factors affect behavior including feeding behavior and energy metabolism in rodents and humans. Studies have found that environmental enrichment (EE), in which mice interact with complex sensory and motor stimulation, led to a significant reduction in adiposity and resistance to diet-induced obesity in mice. This effect is independent of energy expenditure and is associated with enhanced hypothalamic signaling, but the exact mechanism is unknown. We hypothesized that EE potentiates the feeding suppressing effects of anorectic signals. To address this hypothesis, 4-week-old male C57BL/6 mice were group housed (5/cage) under standard laboratory conditions or EE conditions with free access to regular rodent chow and feeding response to glucose, leptin and xenin was examined. EE cages were supplemented with a house, running wheels, igloos, wood logs, maze and nesting materials. Four weeks after initiating EE protocol, mice were fasted for 8 h and received an intraperitoneal injection of glucose (2 mg/g b.w.) or saline just before the onset of the dark phase. Treatment assignments were reversed for the second injection so that each animal received both treatments with a washout period of 1 week. Mice were given food immediately after the injection and food intake was measured for 4 h after the injection at 0.5–1 h intervals. The same design was repeated using leptin (2.5 μg/g b.w.) and xenin (15 or 50 μg/g b.w.). Glucose injection caused a significant reduction of food intake in both control and EE mice. However, anorexic effect of glucose was more significant in EE group compared to the control group (main effect of treatment: P = 0.0016 for control and P < 0.0001 for EE, two-way ANOVA). Significant reductions in food intake were observed between 0.5 and 2.5 h after glucose injection in EE mice, while no significant reduction was observed thereafter. Moreover, three-way ANOVA showed a significant interaction between housing condition and treatment (P = 0.0086). In contrast, although both leptin and xenin caused a significant reduction in food intake, there was no significant interaction between housing condition and treatment. These data suggest that environmental enrichment enhances the anorectic action of glucose without altering feeding response to leptin and xenin. It is speculated that enhanced hypothalamic glucose sensing may mediate beneficial effects of environmental enrichment on metabolism.

Neuroimaging of hypothalamic mechanisms related to glucose metabolism in anorexia nervosa and obesity.

BACKGROUNDGiven the heightened tolerance to self-starvation in anorexia nervosa (AN), a hypothalamic dysregulation of energy and glucose homeostasis has been hypothesized. Therefore, we investigated whether hypothalamic reactivity to glucose metabolism is impaired in AN.METHODSTwenty-four participants with AN, 28 normal-weight participants, and 24 healthy participants with obesity underwent 2 MRI sessions in a single-blind, randomized, case-controlled crossover study. We used an intragastric infusion of glucose and water to bypass the cephalic phase of food intake. The responsivity of the hypothalamus and the crosstalk of the hypothalamus with reward-related brain regions were investigated using high-resolution MRI.RESULTSNormal-weight control participants displayed the expected glucose-induced deactivation of hypothalamic activation, whereas patients with AN and participants with obesity showed blunted hypothalamic reactivity. Furthermore, patients with AN displayed blunted reactivity in the nucleus accumbens and amygdala. Compared with the normal-weight participants and control participants with obesity, the patients with AN failed to show functional connectivity between the hypothalamus and the reward-related brain regions during water infusion relative to glucose infusion. Finally, the patients with AN displayed typical baseline levels of peripheral appetite hormones during a negative energy balance.CONCLUSIONThese results indicate that blunted hypothalamic glucose reactivity might be related to the pathophysiology of AN. This study provides insights for future research, as it is an extended perspective of the traditional primary nonhomeostatic understanding of the disease.FUNDINGThis study was supported by a grant from the DFG (SI 2087/2-1).

Circadian-timed dopamine agonist treatment reverses high-fat diet-induced diabetogenic shift in ventromedial hypothalamic glucose sensing.

IntroductionWithin the ventromedial hypothalamus (VMH), glucose inhibitory (GI) neurons sense hypoglycaemia while glucose excitatory (GE) neurons sense hyperglycaemia to initiate counter control mechanisms under normal conditions. However, potential electrophysiological alterations of these two neuronal types in vivo in insulin‐resistant states have never been simultaneously fully documented. Further, the anti‐diabetic effect of dopamine agonism on this VMH system under insulin resistance has not been studied.MethodsThis study examined the impact of a high‐fat diet (HFD) on in vivo electrophysiological recordings from VMH GE and GI neurons and the ability of circadian‐timed dopamine agonist therapy to reverse any adverse effect of the HFD on such VMH activities and peripheral glucose metabolism.ResultsHFD significantly inhibited VMH GE neuronal electrophysiological response to local hyperglycaemia (36.3%) and augmented GI neuronal excitation response to local hypoglycaemia (47.0%). Bromocriptine (dopamine agonist) administration at onset of daily activity (but not during the daily sleep phase) completely reversed both VMH GE and GI neuronal aberrations induced by HFD. Such timed treatment also normalized glucose intolerance and insulin resistance. These VMH and peripheral glucose metabolism effects of circadian‐timed bromocriptine may involve its known effect to reduce elevated VMH noradrenergic activity in insulin‐resistant states as local VMH administration of norepinephrine was observed to significantly inhibit VMH GE neuronal sensing of local hyperglycaemia in insulin‐sensitive animals on regular chow diet (52.4%).ConclusionsHFD alters VMH glucose sensing in a manner that potentiates hyperglycaemia and this effect on the VMH can be reversed by appropriately circadian‐timed dopamine agonist administration.

119-OR: Amplified Glucagon Response to Hypoglycemia following AMP-Activated Protein Kinase (AMPK) Activator R481 Treatment in Healthy Rats

Episodes of insulin-induced hypoglycemia are frequent in type 1 and advanced type 2 diabetes, but pharmaceutical approaches to prevent these are lacking. Cellular stresses such as low blood sugar activate AMPK, which has emerged as a whole body and cellular energy sensor. Direct delivery of AMPK activator to the ventromedial hypothalamus of rodents leads to increased hepatic glucose-production, observed during hyperinsulinemic-hypoglycemic clamp studies, and genetic activation of AMPK in the pancreatic alpha cell increases glucagon release. It may therefore be suitable to target AMPK for hypoglycemia prevention. Here, R481, a novel metformin-like brain permeable AMPK activator, was used to assess the impact of AMPK pathway activation on the counterregulatory response to hypoglycemia. Hypothalamic glucose sensing GT1-7 cells were treated with R481 and activation of AMPK pathway by phosphorylation assessed using Western Blotting. R481 was administered orally to male Sprague Dawley rats prior to insulin-induced hypoglycemia, following which blood glucose and feeding were measured. A separate cohort of rats underwent a hyperinsulinemic-hypoglycemic clamp study where glucose infusion rates and counterregulatory hormones levels were determined. Nanomolar concentrations of R481 increased AMPK pathway phosphorylation in GT1-7 neurons. Administration of R481 (5-20 mg/kg) to rats attenuated insulin-mediated drop in blood glucose during acute insulin-induced hypoglycemia, without altering fast-induced refeeding. R481 decreased the glucose infusion rate during hyperinsulinemic-hypoglycemic clamps, by amplifying plasma glucagon secretion, without altering epinephrine. Peripheral administration of AMPK activator R481 amplified glucagon release to improve counterregulatory response to hypoglycemia in healthy rats. Disclosure A.M.L. Cruz: None. Y. Malekizadeh: None. J.M. Vlachaki Walker: None. S.J. Shaw: Employee; Self; Rigel Pharmaceuticals. K.L. Ellacott: None. C. Beall: None. Funding JDRF; Diabetes UK

The median eminence as the hypothalamic area involved in rapid transfer of glucose to the brain: functional and cellular mechanisms.

Our data proposes that glucose is transferred directly to the cerebrospinal fluid (CSF) of the hypothalamic ventricular cavity through a rapid "fast-track-type mechanism" that would efficiently stimulate the glucosensing areas. This mechanism would occur at the level of the median eminence (ME), a periventricular hypothalamic zone with no blood-brain barrier. This "fast-track" mechanism would involve specific glial cells of the ME known as β2 tanycytes that could function as "inverted enterocytes," expressing low-affinity glucose transporters GLUT2 and GLUT6 in order to rapidly transfer glucose to the CSF. Due to the large size of tanycytes, the presence of a high concentration of mitochondria and the expression of low-affinity glucose transporters, it would be expected that these cells accumulate glucose in the endoplasmic reticulum (ER) by sequestering glucose-6-phosphate (G-6-P), in a similar way to that recently demonstrated in astrocytes. Glucose could diffuse through the cells by micrometric distances to be released in the apical region of β2 tanycytes, towards the CSF. Through this mechanism, levels of glucose would increase inside the hypothalamus, stimulating glucosensing mechanisms quickly and efficiently. KEY MESSAGES: • Glucose diffuses through the median eminence cells (β2 tanycytes), towards the hypothalamic CSF. • Glucose is transferred through a rapid "fast-track-type mechanism" via GLUT2 and GLUT6. • Through this mechanism, hypothalamic glucose levels increase, stimulating glucosensing.

Mitochondrial Dynamin-Related Protein 1 (DRP1) translocation in response to cerebral glucose is impaired in a rat model of early alteration in hypothalamic glucose sensing

ObjectiveHypothalamic glucose sensing (HGS) initiates insulin secretion (IS) via a vagal control, participating in energy homeostasis. This requires mitochondrial reactive oxygen species (mROS) signaling, dependent on mitochondrial fission, as shown by invalidation of the hypothalamic DRP1 protein. Here, our objectives were to determine whether a model with a HGS defect induced by a short, high fat-high sucrose (HFHS) diet in rats affected the fission machinery and mROS signaling within the mediobasal hypothalamus (MBH). MethodsRats fed a HFHS diet for 3 weeks were compared with animals fed a normal chow. Both in vitro (calcium imaging) and in vivo (vagal nerve activity recordings) experiments to measure the electrical activity of isolated MBH gluco-sensitive neurons in response to increased glucose level were performed. In parallel, insulin secretion to a direct glucose stimulus in isolated islets vs. insulin secretion resulting from brain glucose stimulation was evaluated. Intra-carotid glucose load-induced hypothalamic DRP1 translocation to mitochondria and mROS (H2O2) production were assessed in both groups. Finally, compound C was intracerebroventricularly injected to block the proposed AMPK-inhibited DRP1 translocation in the MBH to reverse the phenotype of HFHS fed animals. ResultsRats fed a HFHS diet displayed a decreased HGS-induced IS. Responses of MBH neurons to glucose exhibited an alteration of their electrical activity, whereas glucose-induced insulin secretion in isolated islets was not affected. These MBH defects correlated with a decreased ROS signaling and glucose-induced translocation of the fission protein DRP1, as the vagal activity was altered. AMPK-induced inhibition of DRP1 translocation increased in this model, but its reversal through the injection of the compound C, an AMPK inhibitor, failed to restore HGS-induced IS. ConclusionsA hypothalamic alteration of DRP1-induced fission and mROS signaling in response to glucose was observed in HGS-induced IS of rats exposed to a 3 week HFHS diet. Early hypothalamic modifications of the neuronal activity could participate in a primary defect of the control of IS and ultimately, the development of diabetes.

Hypothalamic Glucose Concentrations Are Higher in Subjects with Type 1 Diabetes (T1D) and Impaired Awareness of Glycemia (IAH) than in T1D without IAH

IAH occurs commonly in patients with T1D but its pathogenesis remains uncertain. Previous investigation has suggested that recurrent hypoglycemia leads to an upregulation of brain glucose transport thereby assuring that the brain will have better fuel delivery during subsequent episodes of hypoglycemia. If so, subjects with T1D and IAH should have higher hypothalamic brain glucose concentrations than subjects with T1D without IHA when studied at the same level of glycemia. Here we used 1H-magnetic resonance spectroscopy at 7 T to measure (Glucose+Taurine)/ total Creatine in a 13x12x10 mm3 hypothalamic voxel in such patient groups while they were maintained at euglycemia and then hypoglycemia using a glucose clamp. Since taurine and creatine do not change with glycemia, this is a valid measure of brain glucose concentrations. IAH was defined using the Clarke questionnaire with subjects found indeterminate further classified using the Gold questionnaire. We found that hypothalamic (Glucose+Taurine)/ total Creatine was significantly higher in T1D with IAH at both euglycemia and hypoglycemia when compared to T1D without IAH. These data support the hypothesis that a change in glucose transport may contribute to the pathogenesis of IAH. T1D with IAH (n=9)T1D without IAH (n=9)Age (years)47.6 ± 1729.2 ± 8Hemoglobin A1c (%)7.3 ± 0.97.3 ± 0.7Glycemia at euglycemia (mg/dl)98 ± 495 ± 7Glycemia during hypoglycemia (mg/dl)48 ± 348 ± 5Epinephrine during hypoglycemia (pg/ml)250 ± 155711±442*Symptom score during hypoglycemia8 ± 936 ± 14**Hypothalamic glucose at euglycemia (Glucose+Taurine)/ total Creatine (mM)0.43 ± 0.110.27 ± 0.08**Hypothalamic glucose at hypoglycemia (Glucose+Taurine)/ total Creatine (mM)0.23 ± 0.040.15 ± 0.02***p=0.03, **p &amp;lt; 0.001. Disclosure A. Moheet: None. D. Deelchand: None. A. Kumar: None. G. Oz: Research Support; Self; Takeda Pharmaceuticals U.S.A., Inc. E.R. Seaquist: Advisory Panel; Self; Eli Lilly and Company. Consultant; Self; Eli Lilly and Company, Sanofi, Zucera, InfoMed, 360 consulting. Other Relationship; Self; Novo Nordisk Inc..

Leptin enhances hypothalamic lactate dehydrogenase A (LDHA)–dependent glucose sensing to lower glucose production in high-fat–fed rats

The responsiveness of glucose sensing per se to regulate whole-body glucose homeostasis is dependent on the ability of a rise in glucose to lower hepatic glucose production and increase peripheral glucose uptake in vivo In both rodents and humans, glucose sensing is lost in diabetes and obesity, but the site(s) of impairment remains elusive. Here, we first report that short-term high-fat feeding disrupts hypothalamic glucose sensing to lower glucose production in rats. Second, leptin administration into the hypothalamus of high-fat-fed rats restored hypothalamic glucose sensing to lower glucose production during a pancreatic (basal insulin)-euglycemic clamp and increased whole-body glucose tolerance during an intravenous glucose tolerance test. Finally, both chemical inhibition of hypothalamic lactate dehydrogenase (LDH) (achieved via hypothalamic LDH inhibitor oxamate infusion) and molecular knockdown of LDHA (achieved via hypothalamic lentiviral LDHA shRNA injection) negated the ability of hypothalamic leptin infusion to enhance glucose sensing to lower glucose production in high fat-fed rats. In summary, our findings illustrate that leptin enhances LDHA-dependent glucose sensing in the hypothalamus to lower glucose production in high-fat-fed rodents in vivo.

Hypothalamic Glucose Transport in Humans During Experimentally Induced Hypoglycemia-Associated Autonomic Failure.

Upregulated brain glucose transport in response to recurrent hypoglycemia may contribute to the development of hypoglycemia-associated autonomic failure (HAAF) and impaired awareness of hypoglycemia. Whether recurrent hypoglycemia alters glucose transport in the hypothalamus is unknown. To test the hypothesis that hypothalamic glucose transport will increase in healthy volunteers preconditioned with recurrent hypoglycemia to induce HAAF. University medical center. Thirteen healthy subjects underwent paired euglycemic and hypoglycemic preconditioning studies separated by at least 1 month. Following preconditioning, hypothalamic glucose transport was measured by magnetic resonance spectroscopy (MRS) in the afternoon on day 2 of each preconditioning protocol. The ratio of maximal transport rate to cerebral metabolic rate of glucose (Tmax/CMRglc), obtained from MRS-measured glucose in the hypothalamus as a function of plasma glucose. HAAF was successfully induced based on lower epinephrine, glucagon, and cortisol during the third vs first hypoglycemic preconditioning clamp (P ≤ 0.01). Hypothalamic glucose transport was not different following recurrent euglycemia vs hypoglycemia (Tmax/CMRglc 1.62 ± 0.09 after euglycemia preconditioning and 1.75 ± 0.14 after hypoglycemia preconditioning; P was not significant). Hypothalamic glucose concentrations measured by MRS were not different following the two preconditioning protocols. Glucose transport kinetics in the hypothalamus of healthy humans with experimentally induced HAAF were not different from those measured without HAAF. Future studies of patients with diabetes and impaired awareness of hypoglycemia will be necessary to determine if the existence of the diabetes state is required for this adaptation to hypoglycemia to occur.

Hypoxia-inducible Factor 2 Alpha Mediates Exercise-induced Hypothalamic Glucose Sensing

PURPOSE: The hypothalamus controls the energy homeostasis integrating of hormonal and nutritional signals. In this context, glucose plays a critical role in the control of energy balance acting in specific hypothalamic neurons. It has been demonstrated that the lost selective of glucose sensibility in the hypothalamic neurons are related to the hyperphagia and obesity. Recently, the hypoxia-inducible factor 2 alpha (HIF2α) have emerged as regulated important in maintenance of glucose sensibility in hypothalamic neurons. In this context, the maintenance of neuronal HIF2α function can be considerate a determinate strategy for maintenance of lean phenotype. At the same time, the physical exercise is considered a main contributor to the control of body weight and energy expenditure. Thus, sought evaluate the effects of physical exercise on HIF2α protein levels and on glucose sensibility in the hypothalamus of rodents. METHODS:Physical exercise, Western blot and stereotaxic surgery were combined to explore HIF2a protein levels and hypothalamic glucose sensibility. The intracerebroventricular (ICV) injection of glucose was performed to measure the food intake and the quantification of HIF2α pathway in hypothalamus of both lean and obese (diet-induced obesity) male Wistar rats. For statistical analysis were used the ANOVA one-way. RESULTS:We observed the reduction of hypothalamic glucose sensitivity in obese mice, which was accompanied by a lower protein expression of HIF-2α, as well as reduction of prolyl hydroxylases (PHDs) and ubiquitin E3 ligase PVH, product Hippel-Lindau (VHL) gene, when compared to the control group. Interestingly, we found that the exercise restored hypothalamic of HIF-2α expression and glucose sensitivity in obese rats. CONCLUSIONS:Our preliminary results demonstrate that high-fat diet disrupts hypothalamic HIF-2α protein and affects the glucose sensitivity in neurons, contributing with hyperphagia. On the other hand, exercise increased HIF-2α protein levels in the hypothalamus and potentiated glucose sensitivity in obese rats, reducing the food intake.

Intrauterine Growth Restriction Programs the Hypothalamus of Adult Male Rats: Integrated Analysis of Proteomic and Metabolomic Data

Programming of hypothalamic functions regulating energy homeostasis may play a role in intrauterine growth restriction (IUGR)-induced adulthood obesity. The present study investigated the effects of IUGR on the hypothalamus proteome and metabolome of adult rats submitted to 50% protein-energy restriction throughout pregnancy. Proteomic and metabolomic analyzes were performed by data independent acquisition mass spectrometry and multiple reaction monitoring, respectively. At age 4 months, the restricted rats showed elevated adiposity, increased leptin and signs of insulin resistance. 1356 proteins were identified and 348 quantified while 127 metabolites were quantified. The restricted hypothalamus showed down-regulation of 36 proteins and 5 metabolites and up-regulation of 21 proteins and 9 metabolites. Integrated pathway analysis of the proteomics and metabolomics data indicated impairment of hypothalamic glucose metabolism, increased flux through the hexosamine pathway, deregulation of TCA cycle and the respiratory chain, and alterations in glutathione metabolism. The data suggest IUGR modulation of energy metabolism and redox homeostasis in the hypothalamus of male adult rats. The present results indicated deleterious consequences of IUGR on hypothalamic pathways involved in pivotal physiological functions. These results provide guidance for future mechanistic studies assessing the role of intrauterine malnutrition in the development of metabolic diseases later in life.

Reduced metabolism in the hypothalamus of the anorectic anx/anx mouse.

The anorectic anx/anx mouse exhibits a mitochondrial complex I dysfunction that is related to aberrant expression of hypothalamic neuropeptides and transmitters regulating food intake. Hypothalamic activity, i.e. neuronal firing and transmitter release, is dependent on glucose utilization and energy metabolism. To better understand the role of hypothalamic activity in anorexia, we assessed carbohydrate and high-energy phosphate metabolism, in vivo and in vitro, in the anx/anx hypothalamus. In the fasted state, hypothalamic glucose uptake in the anx/anx mouse was reduced by ~50% of that seen in wild-type (wt) mice (P < 0.05). Under basal conditions, anx/anx hypothalamus ATP and glucose 6-P contents were similar to those in wt hypothalamus, whereas phosphocreatine was elevated (~2-fold; P < 0.001) and lactate was reduced (~35%; P < 0.001). The anx/anx hypothalamus had elevated total AMPK (~25%; P < 0.05) and GLUT4 (~60%; P < 0.01) protein contents, whereas GLUT1 and GLUT3 were similar to that of wt hypothalamus. Interestingly, the activation state of AMPK (ratio of phosphorylated AMPK/total AMPK) was significantly decreased in hypothalamus of the anx/anx mouse (~60% of that in wt; P < 0.05). Finally, during metabolic stress (ischemia), accumulation of lactate (measure of glycolysis) and IMP and AMP (breakdown products of ATP) were ~50% lower in anx/anx vs wt hypothalamus. These data demonstrate that carbohydrate and high-energy phosphate utilization in the anx/anx hypothalamus are diminished under basal and stress conditions. The decrease in hypothalamic metabolism may contribute to the anorectic behavior of the anx/anx mouse, i.e. its inability to regulate food intake in accordance with energy status.