Hypothalamic Insulin Signaling Research Articles

Profound Sensitivity of the Liver to the Direct Effect of Insulin Allows Peripheral Insulin Delivery to Normalize Hepatic but Not Muscle Glucose Uptake in the Healthy Dog.

Endogenous insulin secretion is a key regulator of postprandial hepatic glucose metabolism, but this process is dysregulated in diabetes. Subcutaneous insulin delivery alters normal insulin distribution, causing relative hepatic insulin deficiency and peripheral hyperinsulinemia, a major risk factor for metabolic disease. Our aim was to determine whether insulin's direct effect on the liver is preeminent even when insulin is given into a peripheral vein. Postprandial-like conditions were created (hyperinsulinemia, hyperglycemia, and a positive portal vein to arterial glucose gradient) in healthy dogs. Peripheral (leg vein) insulin infusion elevated arterial and hepatic levels 8.0-fold and 2.8-fold, respectively. In one group, insulin's full effects were allowed. In another, insulin's indirect hepatic effects were blocked with the infusion of triglyceride, glucagon, and inhibitors of brain insulin action (intracerebroventricular) to prevent decreases in plasma free fatty acids and glucagon, while blocking increased hypothalamic insulin signaling. Despite peripheral insulin delivery the liver retained its full ability to store glucose, even when insulin's peripheral effects were blocked, whereas muscle glucose uptake markedly increased, creating an aberrant distribution of glucose disposal between liver and muscle. Thus, the healthy liver's striking sensitivity to direct insulin action can overcome the effect of relative hepatic insulin deficiency, whereas excess insulin in the periphery produces metabolic abnormalities in nonhepatic tissues.

Hypothalamic Hnscr regulates glucose balance by mediating central inflammation and insulin signal.

Hypothalamic dysfunction leads to glucose metabolic imbalance; however, the mechanisms still need clarification. Our current study was to explore the role of hypothalamic Hnscr in glucose metabolism. Using Hnscr knockout or htNSC-specific Hnscr overexpression mice, we evaluated the effects of Hnscr on glucose metabolism through GTTs, ITTs, serum indicator measurements, etc. Immunofluorescence staining and Western blotting were performed to test inflammation levels and insulin signalling in hypothalamus. Conditioned medium intervene were used to investigate the effects of htNSCs on neuronal cell line. We also detected the glucose metabolism of mice with htNSCs implantation. Hnscr expression decreased in the hypothalamus after high-fat diet feed. Hnscr-null mice displayed aggravated systematic insulin resistance, while mice with htNSC-specific Hnscr overexpression had the opposite phenotype. Notably, Hnscr-null mice had increased NF-κB signal in htNSCs, along with enhanced inflammation and damaged insulin signal in neurons located in arcuate nucleus of hypothalamus. The secretions, including sEVs, of Hnscr-deficient htNSCs mediated the detrimental effects on the CNS cell line. Locally implantation with Hnscr-depleted htNSCs disrupted glucose homeostasis. This study demonstrated that decreased Hnscr in htNSCs led to systematic glucose imbalance through activating NF-κB signal and dampening insulin signal in hypothalamic neurons.

Benfotiamine protects against hypothalamic dysfunction in a STZ-induced model of neurodegeneration in rats

The neurodegeneration of Alzheimer's disease (AD) affects not only brain structures associate with cognition early in the progression of the disease, but other areas such as the hypothalamus, a region involved in the control of metabolism and appetite. In this context, we evaluated the effects of benfotiamine (BFT), a vitamin B1 analog that is being proposed as a therapeutical approach for AD-related cognitive alterations, which were induced by intracerebroventricular injection of streptozotocin (STZ). In addition to the already described effect of STZ on cognition, we show that this drug also causes metabolic changes which are linked to changes in hypothalamic insulin signaling and orexigenic and anorexigenic circuitries, as well as a decreased cellular integrated stress response. As expected, the supplementation with 150 mg/kg of BFT for 30 days increased blood concentrations of thiamine and its phosphate esters. This led to the prevention of body weight and fat loss in STZ-ICV-treated animals. In addition, we also found an improvement in food consumption, despite hypothalamic gene expression linked to anorexia after STZ exposure. Additionally, decreased apoptosis signaling was observed in the hypothalamus. In in vitro experiments, we noticed a high ability of BFT to increase insulin sensitivity in hypothalamic neurons. Furthermore, we also observed that BFT decreases the mitochondrial unfolded stress response damage by preventing the loss of HSP60 and reversed the mitochondria dysfunction caused by STZ. Taken together, these results suggest that benfotiamine treatment is a potential therapeutic approach in the treatment of hypothalamic dysfunction and metabolic disturbances associated with sporadic AD.

Combination of chronic stress with fructose diet increases AMP-activated protein kinase phosphorylation and affects agouti-related protein and proopiomelanocortin expression in the hypothalamus of male Wistar rats.

Appetite regulation in the hypothalamus is dependent on hormonal signals from the periphery, such as insulin and leptin, and can be modulated by both sugar-rich diet and stress. Our aim was to explore the effects of 9-week feeding with 20% fructose solution combined with 4-week chronic unpredictable stress, on appetite-regulating neuropeptides and modulatory role of leptin and insulin signalling in the hypothalamus of male Wistar rats. Energy intake, body mass and adiposity, as well as circulatory leptin and insulin concentrations were assessed. Hypothalamic insulin signalling was analysed at the level of glucose transporters, as well as at the protein level and phosphorylation of insulin receptor, insulin receptor supstrate-1, Akt and ERK. Phosphorylation of AMP-activated protein kinase (AMPK), level of protein tyrosine phosphatase 1B (PTP1B) and expression of leptin receptor (ObRb) and suppressor of cytokine signalling 3 (SOCS3) were also analysed, together with the expression of orexigenic agouti-related protein (AgRP) and anorexigenic proopiomelanocortin (POMC) neuropeptides. The results revealed that stress decreased body mass and adiposity, blood leptin level and expression of ObRb, SOCS3 and POMC, while combination with fructose diet led to marked increase of AgRP, associated with AMPK phosphorylation despite increased plasma insulin. Reduced Akt, enhanced ERK activity and elevated PTP1B were also observed in the hypothalamus of these animals. In conclusion, our results showed that joint effects of fructose diet and stress are more deleterious than the separate ones, since inappropriate appetite control in the hypothalamus may provide a setting for the disturbed energy homeostasis in the long run.

1309-P: Central Mechanisms of Pollution-Induced Metabolic Disease

There is growing evidence linking exposure to volatile organic compounds (VOC) in ambient air with metabolic disease in humans. Benzene is a prominent VOC present in water, food, detergents, vehicle exhaust, tobacco smoke, and e-cigarettes. However, a direct link between exposure to VOC and metabolic homeostasis is not yet established. We performed a meta-analysis and found a positive association between exposure to VOC and metabolic impairments. Using a highly controlled mouse exposure system, we have recently demonstrated that chronic exposure of mice to VOC induces neuroinflammation and insulin resistance predisposing to T2D. To establish a timeline for the onset of VOC-triggered metabolic effects, we monitored glucose changes of exposed mice using continuous glucose monitoring (CGM) system. Surprisingly, we detected significant changes in glycemic control of male mice starting at day 4 of exposure. Further, mice exhibited impaired parameters of energy homeostasis within 6h of exposure. This was associated with activation of hypothalamic gliosis via stimulation of the NF-κB signaling and dysregulation of hypothalamic insulin signaling, contributing to blunted responses to glucose stimulation in glucose-sensing neurons. To determine the role of the central inflammatory mechanism in VOC-induced metabolic imbalance, we genetically ablated NF-κB signaling in microglia using Cx3cr1creERΔIKK mice. Selective inhibition of microglial NF-κB signaling completely restored hypothalamic insulin signaling, astrocytes activation, and hypothalamic glucose-sensing, consequently protecting from whole-body metabolic imbalance induced by VOC exposure. Importantly, this effect was mediated via hypothalamic ER stress response. Collectively, our data provide evidence that neuroinflammatory responses precede and mechanistically contribute to whole-body metabolic imbalance and identify air pollution-induced cellular and molecular targets in the hypothalamus that lead to metabolic disease. Disclosure L.K.Debarba: n/a. L.Koshko: None. H.M.Jayarathne: None. Z.Yi: None. U.Klueh: Research Support; Dexcom, Inc. M.Sadagurski: None. Funding American Diabetes Association (1-18-JDF-063)

Activation of PI3K/Akt Signaling Pathway in Rat Hypothalamus Induced by an Acute Oral Administration of D-Pinitol.

D-Pinitol (DPIN) is a natural occurring inositol capable of activating the insulin pathway in peripheral tissues, whereas this has not been thoroughly studied in the central nervous system. The present study assessed the potential regulatory effects of DPIN on the hypothalamic insulin signaling pathway. To this end we investigated the Phosphatidylinositol-3-kinase (PI3K)/Protein Kinase B (Akt) signaling cascade in a rat model following oral administration of DPIN. The PI3K/Akt-associated proteins were quantified by Western blot in terms of phosphorylation and total expression. Results indicate that the acute administration of DPIN induced time-dependent phosphorylation of PI3K/Akt and its related substrates within the hypothalamus, indicating an activation of the insulin signaling pathway. This profile is consistent with DPIN as an insulin sensitizer since we also found a decrease in the circulating concentration of this hormone. Overall, the present study shows the pharmacological action of DPIN in the hypothalamus through the PI3K/Akt pathway when giving in fasted animals. These findings suggest that DPIN might be a candidate to treat brain insulin-resistance associated disorders by activating insulin response beyond the insulin receptor.

BACE2 suppression in mice aggravates the adverse metabolic consequences of an obesogenic diet

ObjectivePancreatic β-cell dysfunction is a central feature in the pathogenesis of type 2 diabetes (T2D). Accumulating evidence indicates that β-site APP-cleaving enzyme 2 (BACE2) inhibition exerts a beneficial effect on β-cells in different models of T2D. Thus, targeting BACE2 may represent a potential therapeutic strategy for the treatment of this disease. Here, we aimed to investigate the effects of BACE2 suppression on glucose homeostasis in a model of diet-induced obesity. MethodsBACE2 knock-out (BKO) and wild-type (WT) mice were fed with a high-fat diet (HFD) for 2 or 16 weeks. Body weight, food intake, respiratory exchange ratio, locomotor activity, and energy expenditure were determined. Glucose homeostasis was evaluated by glucose and insulin tolerance tests. β-cell proliferation was assessed by Ki67-positive nuclei, and β-cell function was determined by measuring glucose-stimulated insulin secretion. Leptin sensitivity was evaluated by quantifying food intake and body weight after an intraperitoneal leptin injection. Neuropeptide gene expression and insulin signaling in the mediobasal hypothalamus were determined by qPCR and Akt phosphorylation, respectively. ResultsAfter 16 weeks of HFD feeding, BKO mice exhibited an exacerbated body weight gain and hyperphagia, in comparison to WT littermates. Glucose tolerance was similar in both groups, whereas HFD-induced hyperinsulinemia, insulin resistance, and β-cell expansion were more pronounced in BKO mice. In turn, leptin-induced food intake inhibition and hypothalamic insulin signaling were impaired in BKO mice, regardless of the diet, in accordance with deregulation of the expression of hypothalamic neuropeptide genes. Importantly, BKO mice already showed increased β-cell proliferation and glucose-stimulated insulin secretion with respect to WT littermates after two weeks of HFD feeding, before the onset of obesity. ConclusionsCollectively, these results reveal that BACE2 suppression in an obesogenic setting leads to exacerbated body weight gain, hyperinsulinemia, and insulin resistance. Thus, we conclude that inhibition of BACE2 may aggravate the adverse metabolic effects associated with obesity.

The Importance of the Mechanisms by Which Insulin Regulates Meal-Associated Liver Glucose Uptake in the Dog.

Hepatic glucose uptake (HGU) is critical for maintaining normal postprandial glucose metabolism. Insulin is clearly a key regulator of HGU, but the physiologic mechanisms by which it acts have yet to be established. This study sought to determine the mechanisms by which insulin regulates liver glucose uptake under postprandial-like conditions (hyperinsulinemia, hyperglycemia, and a positive portal vein-to-arterial glucose gradient). Portal vein insulin infusion increased hepatic insulin levels fivefold in healthy dogs. In one group (n = 7), the physiologic response was allowed to fully occur, while in another (n = 7), insulin's indirect hepatic effects, occurring secondary to its actions on adipose tissue, pancreas, and brain, were blocked. This was accomplished by infusing triglyceride (intravenous), glucagon (portal vein), and inhibitors of brain insulin action (intracerebroventricular) to prevent decreases in plasma free fatty acids or glucagon, while blocking increased hypothalamic insulin signaling for 4 h. In contrast to the indirect hepatic effects of insulin, which were previously shown capable of independently generating a half-maximal stimulation of HGU, direct hepatic insulin action was by itself able to fully stimulate HGU. This suggests that under hyperinsulinemic/hyperglycemic conditions insulin's indirect effects are redundant to direct engagement of hepatocyte insulin receptors.

Insulin signaling in AgRP neurons regulates meal size to limit glucose excursions and insulin resistance.

The importance of hypothalamic insulin signaling on feeding and glucose metabolism remains unclear. We report that insulin acts on AgRP neurons to acutely decrease meal size and thereby limit postprandial glucose and insulin excursions. The promotion of insulin signaling in AgRP neurons decreased meal size without altering total caloric intake, whereas the genetic ablation of the insulin receptor had the opposite effect. The promotion of insulin signaling also decreased the intake of sucrose-sweetened water or high-fat food over standard chow, without influencing food-seeking and hedonic behaviors. The ability of heightened insulin signaling to override the hedonistic consumption of highly palatable high-fat food attenuated the development of systemic insulin resistance, without affecting body weight. Our findings define an unprecedented mechanism by which insulin acutely influences glucose metabolism. Approaches that enhance insulin signaling in AgRP neurons may provide a means for altering feeding behavior in a nutrient-dense environment to combat the metabolic syndrome.

Hypothalamic insulin signalling as a nexus regulating mood and metabolism.

Insulin has long been known as a metabolic hormone critical in the treatment of diabetes for its peripheral effects on blood glucose. However, in the last 50years, insulin has entered the realm of neuroendocrinology and many studies have described its function on insulin receptors in the brain in relation to both metabolic and mood disorders. Indeed, rodent models of impaired insulin signalling show signs of dysregulated energy and glucose homeostasis, as well as anxiety-like and depressive behaviours. Importantly, many metabolic diseases such as obesity and diabetes increase the risk of developing mood disorders; however, the brain mechanisms underlying the connection between metabolism and mood remain unresolved. We present the current literature on the importance of the insulin receptor with respect to regulating glucose and energy homeostasis and mood-related behaviours. Specifically, we hypothesise that the insulin receptor in the hypothalamus, classically known as the homeostatic centre of the brain, plays a causal role in linking metabolic and behavioural effects of insulin signalling. In this review, we discuss insulin signalling in the hypothalamus as a critical point of neural integration controlling metabolism and mood.

Olanzapine-induced insulin resistance may occur via attenuation of central KATP channel-activation

Antipsychotic use is associated with an increased risk of type 2 diabetes. Recent work suggests antipsychotics can induce insulin resistance immediately and independently of weight gain, and that this may occur via the central nervous system (CNS). We have previously shown that the highly effective and widely prescribed antipsychotic, olanzapine inhibits CNS insulin-mediated suppression of hepatic glucose production, but the mechanisms remain unknown. The ATP-sensitive potassium (KATP) channel is a key metabolic sensor downstream of hypothalamic insulin signalling, involved in the maintenance of glucose homeostasis. Thus, the possibility arises that olanzapine inhibits central KATP channel activation to disrupt glucose metabolism. We replicate that intracerebroventricular (ICV) administration of the KATP channel activator, diazoxide, suppresses hepatic glucose production and additionally demonstrate stimulation of peripheral glucose utilization. We report that olanzapine inhibits the effects of central KATP channel activation resulting in perturbation of whole body insulin sensitivity, specifically via inhibition of glucose utilization, while leaving central KATP channel-mediated suppression of glucose production intact. Perturbation of KATP channel action in the CNS could represent a novel mechanism of antipsychotic-induced diabetes.

Overexpression of Smad7 in hypothalamic POMC neurons disrupts glucose balance by attenuating central insulin signaling

ObjectiveAlthough the hypothalamus is crucial for peripheral metabolism control, the signals in specific neurons involved remain poorly understood. The aim of our current study was to explore the role of the hypothalamic gene mothers against decapentaplegic homolog 7 (Smad7) in peripheral glucose disorders. MethodsWe studied glucose metabolism in high-fat diet (HFD)-fed mice and middle-aged mice with Cre-mediated recombination causing 1) overexpression of Smad7 in hypothalamic proopiomelanocortin (POMC) neurons, 2) deletion of Smad7 in POMC neurons, and 3) overexpression of protein kinase B (AKT) in arcuate nucleus (ARC) in Smad7 overexpressed mice. Intracerebroventricular (ICV) cannulation of insulin was used to test the hypothalamic insulin sensitivity in the mice. Hypothalamic primary neurons were used to investigate the mechanism of Smad7 regulating hypothalamic insulin signaling. ResultsWe found that Smad7 expression was increased in POMC neurons in the hypothalamic ARC of HFD-fed or middle-aged mice. Furthermore, overexpression of Smad7 in POMC neurons disrupted the glucose balance, and deletion of Smad7 in POMC neurons prevented diet- or age-induced glucose disorders, which was likely to be independent of changes in body weight or food intake. Moreover, the effect of Smad7 was reversed by overexpression of AKT in the ARC. Finally, Smad7 decreased AKT phosphorylation by activating protein phosphatase 1c in hypothalamic primary neurons. ConclusionsOur results demonstrated that an excess of central Smad7 in POMC neurons disrupts glucose balance by attenuating hypothalamic insulin signaling. In addition, we found that this regulation was mediated by the activity of protein phosphatase 1c.

Icariin Attenuates Amyloid-β (Aβ)-Induced Neuronal Insulin Resistance Through PTEN Downregulation.

Neuronal insulin resistance is implicated in neurodegenerative diseases. Icariin has been reported to improve insulin resistance in skeletal muscle cells and to restore impaired hypothalamic insulin signaling in the rats with chronic unpredictable mild stress. In addition, icariin can exert the neuroprotective effects in the mouse models of neurodegenerative diseases. However, the molecular mechanisms by which icariin affects neuronal insulin resistance are poorly understood. In the present study, amyloid-β (Aβ) was used to induce insulin resistance in human neuroblastoma SK-N-MC cells. Insulin sensitivity was evaluated by measuring insulin-stimulated Akt T308 phosphorylation and glucose uptake. We found that the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) mediated Aβ-induced insulin resistance. Icariin treatment markedly reduced Aβ-enhanced PTEN protein levels, leading to an improvement in Aβ-induced insulin resistance. Accordingly, PTEN overexpression obviously abolished the protective effects of icariin on Aβ-induced insulin resistance. Furthermore, icariin activated proteasome activity. The proteasome inhibitor MG132 attenuated the effects of icariin on PTEN protein levels. Taken together, these results suggest that icariin protects SK-N-MC cells against Aβ-induced insulin resistance by activating the proteasome-dependent degradation of PTEN. These findings provide an experimental background for the identification of novel molecular targets of icariin, which may help in the development of alternative therapeutic approaches for neurodegenerative diseases.

Maternal Obesity Alters Neurotrophin-Associated MAPK Signaling in the Hypothalamus of Male Mouse Offspring.

PurposeMaternal obesity has emerged as an important risk factor for the development of metabolic disorders in the offspring. The hypothalamus as the center of energy homeostasis regulation is known to function based on complex neuronal networks that evolve during fetal and early postnatal development and maintain their plasticity into adulthood. Development of hypothalamic feeding networks and their functional plasticity can be modulated by various metabolic cues, especially in early stages of development. Here, we aimed at determining the underlying molecular mechanisms that contribute to disturbed hypothalamic network formation in offspring of obese mouse dams.MethodsFemale mice were fed either a control diet (CO) or a high-fat diet (HFD) after weaning until mating and during pregnancy and gestation. Male offspring was sacrificed at postnatal day (P) 21. The hypothalamus was subjected to gene array analysis, quantitative PCR and western blot analysis.ResultsP21 HFD offspring displayed increased body weight, circulating insulin levels, and strongly increased activation of the hypothalamic insulin signaling cascade with a concomitant increase in ionized calcium binding adapter molecule 1 (IBA1) expression. At the same time, the global gene expression profile in CO and HFD offspring differed significantly. More specifically, manifest influences on several key pathways of hypothalamic neurogenesis, axogenesis, and regulation of synaptic transmission and plasticity were detectable. Target gene expression analysis revealed significantly decreased mRNA expression of several neurotrophic factors and co-factors and their receptors, accompanied by decreased activation of their respective intracellular signal transduction.ConclusionTaken together, these results suggest a potential role for disturbed neurotrophin signaling and thus impaired neurogenesis, axogenesis, and synaptic plasticity in the pathogenesis of the offspring’s hypothalamic feeding network dysfunction due to maternal obesity.

Crosstalk between hypothalamic leptin and insulin signalling in obesity

Crosstalk between hypothalamic leptin and insulin signalling in obesity

52. Antipsychotics Perturb Glucose Homeostasis by Inhibiting Hypothalamic KATP Channel Activation

Antipsychotics are associated with high rates of obesity and type 2 diabetes. Moreover, these agents can immediately and independently of weight gain induce insulin resistance via the central nervous system (CNS). We recently demonstrated that olanzapine abolishes the ability of a CNS insulin infusion to restrain hepatic glucose production and to suppress feeding in rodents. Across rodents and humans, the ATP-sensitive potassium (KATP) channel is a critical metabolic sensor downstream of hypothalamic insulin signaling in maintenance of energy and glucose homeostasis. Here, we examined whether olanzapine inhibits central KATP channels to disrupt glucose metabolism.

Chronic Stress Combined with a Fructose Diet Reduces Hypothalamic Insulin Signaling and Antioxidative Defense in Female Rats

Background: Increased fructose consumption and chronic exposure to stress have been associated with the development of obesity and insulin resistance. In the hypothalamus, a crossroad of stress responses and energy balance, insulin and glucocorticoids regulate the expression of orexigenic neuropeptides, neuropeptide Y (NPY) and agouti-related protein (AgRP), and anorexigenic neuropeptides, proopio­melanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART). Objectives: We investigated whether chronic stress and fructose diet disrupt these hormonal signaling pathways and appetite control in the hypothalamus, contributing to the development of insulin resistance and obesity. Potential roles of hypothalamic inflammation and oxidative stress in the development of insulin resistance were also analyzed. Methods: Insulin, glucocorticoid, and leptin signaling, expression of orexigenic and anorexigenic neuropeptides, and antioxidative and inflammatory statuses in the whole hypothalamus of fructose-fed female rats exposed to unpredictable stress for 9 weeks were analyzed using quantitative PCR and Western blotting. Results: Chronic stress combined with a fructose-enriched diet reduced protein content and stimulatory phosphorylation of Akt kinase, and elevated 11β-hydroxysteroid dehydrogenase 1 and glucocorticoid receptor expression, while alterations in appetite regulation (NPY, AgRP, POMC, CART, leptin receptor, and SOCS3 expression) were not observed. The expression of antioxidative defense enzymes (mitochondrial manganese superoxide dismutase 2, glutathione reductase, and catalase) and proinflammatory cytokines (IL-1β, IL-6, and TNFα) was reduced. Conclusions: Our results underline the combination of long-term stress exposure and fructose overconsumption as more detrimental for hypothalamic function than for either of the factors separately, as it enhanced glucocorticoid and impaired insulin signaling, antioxidative ­defense, and inflammatory responses of this homeostasis- regulating center.

Studying the Hypothalamic Insulin Signal to Peripheral Glucose Intolerance with a Continuous Drug Infusion System into the Mouse Brain.

Insulin regulates systematic metabolism in the hypothalamus and the peripheral insulin response. An inflammatory reaction in peripheral adipose tissues contributes to type 2 diabetes mellitus (T2DM) development and appetite regulation in the hypothalamus. Chemokine CCL5 and C-C chemokine receptor type 5 (CCR5) levels have been suggested to mediate arteriosclerosis and glucose intolerance in type 2 diabetes mellitus (T2DM). In addition, CCL5 plays a neuroendocrine role in the hypothalamus by regulating food intake and body temperature, thus, prompting us to investigate its function in hypothalamic insulin signaling and the regulation of peripheral glucose metabolism.The micro-osmotic pump brain infusion system is a quick and precise way to manipulate CCL5 function and study its effect in the brain. It also provides a convenient alternative approach to generating a transgenic knockout animal. In this system, CCL5 signaling was blocked by intracerebroventricular (ICV) infusion of its antagonist, MetCCL5, using a micro-osmotic pump. The peripheral glucose metabolism and insulin responsiveness was detected by the Oral Glucose Tolerance Test (OGTT) and Insulin Tolerance Test (ITT). Insulin signaling activity was then analyzed by protein blot from tissue samples derived from the animals.After 7-14 days of MetCCL5 infusion, the glucose metabolism and insulin responsiveness was impaired in mice, as seen in the results of the OGTT and ITT. The IRS-1 serine302 phosphorylation was increased and the Akt activity was reduced in mice hypothalamic neurons following CCL5 inhibition. Altogether, our data suggest that blocking CCL5 in the mouse brain increases the phosphorylation of IRS-1 S302 and interrupts hypothalamic insulin signaling, leading to a decrease in insulin function in peripheral tissues as well as the impairment of glucose metabolism.

Studying the Hypothalamic Insulin Signal to Peripheral Glucose Intolerance with a Continuous Drug Infusion System into the Mouse Brain

Insulin regulates systematic metabolism in the hypothalamus and the peripheral insulin response. An inflammatory reaction in peripheral adipose tissues contributes to type 2 diabetes mellitus (T2DM) development and appetite regulation in the hypothalamus. Chemokine CCL5 and C-C chemokine receptor type 5 (CCR5) levels have been suggested to mediate arteriosclerosis and glucose intolerance in type 2 diabetes mellitus (T2DM). In addition, CCL5 plays a neuroendocrine role in the hypothalamus by regulating food intake and body temperature, thus, prompting us to investigate its function in hypothalamic insulin signaling and the regulation of peripheral glucose metabolism. The micro-osmotic pump brain infusion system is a quick and precise way to manipulate CCL5 function and study its effect in the brain. It also provides a convenient alternative approach to generating a transgenic knockout animal. In this system, CCL5 signaling was blocked by intracerebroventricular (ICV) infusion of its antagonist, MetCCL5, using a micro-osmotic pump. The peripheral glucose metabolism and insulin responsiveness was detected by the Oral Glucose Tolerance Test (OGTT) and Insulin Tolerance Test (ITT). Insulin signaling activity was then analyzed by protein blot from tissue samples derived from the animals. After 7-14 days of MetCCL5 infusion, the glucose metabolism and insulin responsiveness was impaired in mice, as seen in the results of the OGTT and ITT. The IRS-1 serine302 phosphorylation was increased and the Akt activity was reduced in mice hypothalamic neurons following CCL5 inhibition. Altogether, our data suggest that blocking CCL5 in the mouse brain increases the phosphorylation of IRS-1 S302 and interrupts hypothalamic insulin signaling, leading to a decrease in insulin function in peripheral tissues as well as the impairment of glucose metabolism.

Safflower (n-6) and flaxseed (n-3) high-fat diets differentially regulate hypothalamic fatty acid profiles, gene expression, and insulin signalling

Polyunsaturated fatty acids (PUFA) have important signalling roles in the hypothalamus, a region of the brain that regulates whole-body energy homeostasis. While evidence suggests that high PUFA intake can impact hypothalamic activity, the underlying molecular mechanisms regulated by essential dietary n-6 and n-3 PUFA (i.e., linoleic acid and α-linolenic acid, respectively) remain poorly described in this brain region. To differentiate the roles of essential dietary PUFA on hypothalamic function, we fed male rats high-fat diets (35% kcal/d) containing either safflower (linoleic acid) or flaxseed (α-linolenic acid) oil for 2 months. Control rats were fed a low-fat (16% kcal/d) diet containing soybean oil. Hypothalamic fatty acids and gene expression were investigated by gas chromatography and microarray, respectively. Safflower-fed rats had higher total n-6 PUFA content due to increases in linoleic acid, arachidonic acid, and osbond acid compared to the other diet groups, while flaxseed-fed rats had higher total n-3 content due to increases in α-linolenic acid, eicosapentaenoic acid, docosapentaenoic acid, and docosahexaenoic acid. Safflower-fed rats showed augmented expression of genes related to hypothalamic insulin signalling compared to controls. This was mirrored by significant increases in phosphorylated AKTthr308 and AKTser473 levels; indicative of increased PI(3)K/AKT pathway activity. These changes were not observed in the hypothalamus of flaxseed-fed rats. Our findings provide new molecular insights into how essential fatty acids influence the hypothalamus and, potentially, whole-body energy homeostasis. This work also provides new knowledge to better understand the impact of essential fatty acids on metabolic and behavioral phenotypes.