Hypothalamic Insulin Research Articles

Insulin signalling in tanycytes gates hypothalamic insulin uptake and regulation of AgRP neuron activity

Insulin acts on neurons and glial cells to regulate systemic glucose metabolism and feeding. However, the mechanisms of insulin access in discrete brain regions are incompletely defined. Here we show that insulin receptors in tanycytes, but not in brain endothelial cells, are required to regulate insulin access to the hypothalamic arcuate nucleus. Mice lacking insulin receptors in tanycytes (IR∆Tan mice) exhibit systemic insulin resistance, while displaying normal food intake and energy expenditure. Tanycytic insulin receptors are also necessary for the orexigenic effects of ghrelin, but not for the anorexic effects of leptin. IR∆Tan mice exhibit increased agouti-related peptide (AgRP) neuronal activity, while displaying blunted AgRP neuronal adaptations to feeding-related stimuli. Lastly, a highly palatable food decreases tanycytic and arcuate nucleus insulin signalling to levels comparable to those seen in IR∆Tan mice. These changes are rooted in modifications of cellular stress responses and of mitochondrial protein quality control in tanycytes. Conclusively, we reveal a critical role of tanycyte insulin receptors in gating feeding-state-dependent regulation of AgRP neurons and systemic insulin sensitivity, and show that insulin resistance in tanycytes contributes to the pleiotropic manifestations of obesity-associated insulin resistance.

Hypothalamic miR-1983 Targets Insulin Receptor β and the Insulin-mediated miR-1983 Increase Is Blocked by Metformin.

MicroRNAs (miRNAs) expressed in the hypothalamus are capable of regulating energy balance and peripheral metabolism by inhibiting translation of target messenger RNAs (mRNAs). Hypothalamic insulin resistance is known to precede that in the periphery, thus a critical unanswered question is whether central insulin resistance creates a specific hypothalamic miRNA signature that can be identified and targeted. Here we show that miR-1983, a unique miRNA, is upregulated in vitro in 2 insulin-resistant immortalized hypothalamic neuronal neuropeptide Y-expressing models, and in vivo in hyperinsulinemic mice, with a concomitant decrease of insulin receptor β subunit protein, a target of miR-1983. Importantly, we demonstrate that miR-1983 is detectable in human blood serum and that its levels significantly correlate with blood insulin and the homeostatic model assessment of insulin resistance. Levels of miR-1983 are normalized with metformin exposure in mouse hypothalamic neuronal cell culture. Our findings provide evidence for miR-1983 as a unique biomarker of cellular insulin resistance, and a potential therapeutic target for prevention of human metabolic disease.

Parental high-fat high-sugar diet programming and hypothalamus adipose tissue axis in male Wistar rats.

Maternal nutrition during early development and paternal nutrition pre-conception can programme offspring health status. Hypothalamus adipose axis is a target of developmental programming, and paternal and maternal high-fat, high-sugar diet (HFS) may be an important factor that predisposes offspring to develop obesity later in life. This study aims to investigate Wistar rats' maternal and paternal HFS differential contribution on the development, adiposity, and hypothalamic inflammation in male offspring from weaning until adulthood. Male progenitors were fed a control diet (CD) or HFS for 10weeks before mating. After mating, dams were fed CD or HFS only during pregnancy and lactation. Forming the following male offspring groups: CD-maternal and paternal CD; MH-maternal HFS and paternal CD; PH-maternal CD and paternal HFS; PMH-maternal and paternal HFS. After weaning, male offspring were fed CD until adulthood. Maternal HFS diet increased weight, visceral adiposity, and serum total cholesterol levels, and decreased hypothalamic weight in weanling male rats. In adult male offspring, maternal HFS increased weight, glucose levels, and hypothalamic NFκBp65. Paternal HFS diet lowered hypothalamic insulin receptor levels in weanling offspring and glucose and insulin levels in adult offspring. The combined effects of maternal and paternal HFS diets increased triacylglycerol, leptin levels, and hypothalamic inflammation in weanling rats, and increased visceral adiposity in adulthood. Male offspring intake of CD diet after weaning reversed part of the effects of parental HFS diet during the perinatal period. However, maternal and paternal HFS diet affected adiposity and hypothalamic inflammation, which remained until adulthood.

Insulin receptors in the CA1 field of hippocampus and selected blood parameters in diabetic rats fed with bilberry fruit.

Bilberry fruit is believed to be a promising factor in the treatment of diabetes mellitus. Chronic hyperglycaemia affects the function of the central nervous system, which may be manifested as changes in hypothalamic insulin signalling. Using DPPH and ABTS assays, total phenolic content in bilberry fruit and its antioxidant activities were examined. The selected biochemical parameters of blood (glucose, fructosamine, total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides), as well as the expression of insulin receptors, were studied in the hippocampal CA1 field of healthy and diabetic (streptozotocin-induced; 60 mg kg-1 body weight) Wistar rats fed with bilberry fruit (16 g kg-1 body weight per day; 6 weeks), as well as of the corresponding control groups. Biochemical analyses revealed ambiguous results, but a significantly (P<0.05) decrease in the level of LDL-cholesterol was observed in the group of healthy rats supplemented with bilberry pulp after 6 weeks of the treatment. There was also a difference (P<0.05) in the level of LDL-cholesterol in the mentioned healthy animals fed with bilberry, versus the healthy control group. An increased number of insulin receptors-immunoreactive neurons as well as nerve fibres in the CA1 field of diabetic rats fed with bilberry fruit was also found. An inclusion of bilberry fruit in the daily diet during the course of diabetes can lead to plasticity of hippocampal neurons/nerve fibres, manifested by changes in insulin receptors expression. Whether or not the observed changes had protective effects (by reducing damages caused by diabetes mellitus) on the function of the central nervous system neurons needs further study.

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.

Central Acting Hsp10 Regulates Mitochondrial Function, Fatty Acid Metabolism, and Insulin Sensitivity in the Hypothalamus.

Mitochondria are critical for hypothalamic function and regulators of metabolism. Hypothalamic mitochondrial dysfunction with decreased mitochondrial chaperone expression is present in type 2 diabetes (T2D). Recently, we demonstrated that a dysregulated mitochondrial stress response (MSR) with reduced chaperone expression in the hypothalamus is an early event in obesity development due to insufficient insulin signaling. Although insulin activates this response and improves metabolism, the metabolic impact of one of its members, the mitochondrial chaperone heat shock protein 10 (Hsp10), is unknown. Thus, we hypothesized that a reduction of Hsp10 in hypothalamic neurons will impair mitochondrial function and impact brain insulin action. Therefore, we investigated the role of chaperone Hsp10 by introducing a lentiviral-mediated Hsp10 knockdown (KD) in the hypothalamic cell line CLU-183 and in the arcuate nucleus (ARC) of C57BL/6N male mice. We analyzed mitochondrial function and insulin signaling utilizing qPCR, Western blot, XF96 Analyzer, immunohistochemistry, and microscopy techniques. We show that Hsp10 expression is reduced in T2D mice brains and regulated by leptin in vitro. Hsp10 KD in hypothalamic cells induced mitochondrial dysfunction with altered fatty acid metabolism and increased mitochondria-specific oxidative stress resulting in neuronal insulin resistance. Consequently, the reduction of Hsp10 in the ARC of C57BL/6N mice caused hypothalamic insulin resistance with acute liver insulin resistance.

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.

Coordinated regulation of energy and glucose homeostasis by insulin and the NPY system.

Insulin is a major contributor to many important physiological processes. Although its function in the periphery has been studied in detail, the contributions that it makes to functions in the brain are far less understood. The neuropeptide Y (NPY) neurones comprise a major target of insulin in the brain and are inhibited by its action. In particular, NPY neurones in the arcuate nucleus of the hypothalamus are critical control centres for insulin's central action on control energy homeostasis, as well as glucose homeostasis regulation. However, the colocalisation of insulin receptors with NPY neurones is also found in many other brain areas, although very little is known about their interactions and control functions. In this review, we explore the recent advances that have been made to further the understanding of the hypothalamic insulin receptor-NPY network, as well as provide insights from other lesser explored areas, such as the amygdala and hippocampus. We will also look at the peripheral interaction of the NPY system with insulin release, thereby closing the loop between these two energy and glucose homeostasis controlling systems and highlighting the critical interaction points that may be dysregulated in conditions of obesity and diabetes.

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.

Peripheral and central regulation of insulin by the intestine and microbiome.

Blood glucose and insulin homeostasis is disrupted during the progression of type 2 diabetes. Insulin levels and action are regulated by both peripheral and central responses that involve the intestine and microbiome. The intestine and its microbiota process nutrients and generate molecules that influence blood glucose and insulin. Peripheral insulin regulation is regulated by gut-segment-dependent nutrient sensing and microbial factors such as short-chain fatty acids and bile acids that engage G-protein-coupled receptors. Innate immune sensing of gut-derived bacterial cell wall components and lipopolysaccharides also alter insulin homeostasis. These bacterial metabolites and postbiotics influence insulin secretion and insulin clearance in part by altering endocrine responses such as glucagon-like peptide-1. Gut-derived bacterial factors can promote inflammation and insulin resistance, but other postbiotics can be insulin sensitizers. In parallel, activation of small intestinal sirtuin 1 increases insulin sensitivity by reversing high fat-induced hypothalamic insulin resistance through a gut-brain neuronal axis, whereas high fat-feeding alters small intestinal microbiome and increases taurochenodeoxycholic acid in the plasma and the dorsal vagal complex to induce insulin resistance. In summary, emerging evidence indicates that intestinal molecular signaling involving nutrient sensing and the host-microbe symbiosis alters insulin homeostasis and action. Gut-derived host endocrine and paracrine factors as well as microbial metabolites act on the liver, pancreas, and the brain, and in parallel on the gut-brain neuronal axis. Understanding common nodes of peripheral and central insulin homeostasis and action may reveal new ways to target the intestinal host-microbe relationship in obesity, metabolic disease, and type 2 diabetes.

Type 2 diabetes risk gene Dusp8 regulates hypothalamic Jnk signaling and insulin sensitivity.

Recent genome-wide association studies (GWAS) identified DUSP8, encoding a dual-specificity phosphatase targeting mitogen-activated protein kinases, as a type 2 diabetes (T2D) risk gene. Here, we reveal that Dusp8 is a gatekeeper in the hypothalamic control of glucose homeostasis in mice and humans. Male, but not female, Dusp8 loss-of-function mice, either with global or corticotropin-releasing hormone neuron-specific deletion, had impaired systemic glucose tolerance and insulin sensitivity when exposed to high-fat diet (HFD). Mechanistically, we found impaired hypothalamic-pituitary-adrenal axis feedback, blunted sympathetic responsiveness, and chronically elevated corticosterone levels driven by hypothalamic hyperactivation of Jnk signaling. Accordingly, global Jnk1 ablation, AAV-mediated Dusp8 overexpression in the mediobasal hypothalamus, or metyrapone-induced chemical adrenalectomy rescued the impaired glucose homeostasis of obese male Dusp8-KO mice, respectively. The sex-specific role of murine Dusp8 in governing hypothalamic Jnk signaling, insulin sensitivity, and systemic glucose tolerance was consistent with functional MRI data in human volunteers that revealed an association of the DUSP8 rs2334499 risk variant with hypothalamic insulin resistance in men. Further, expression of DUSP8 was increased in the infundibular nucleus of T2D humans. In summary, our findings suggest the GWAS-identified gene Dusp8 as a novel hypothalamic factor that plays a functional role in the etiology of T2D.

Maternal High-Fat-High-Carbohydrate Diet-Induced Obesity Is Associated with Increased Appetite in Peripubertal Male but Not Female C57Bl/6J Mice.

Diet-induced maternal obesity might play a critical role in altering hypothalamic development, predisposing the offspring to obesity and metabolic disease later in life. The objective of this study was to describe both phenotypic and molecular sex differences in peripubertal offspring energy homeostasis, using a mouse model of maternal obesity induced by a high-fat–high-carbohydrate (HFHC) diet. We report that males, not females, exposed to a maternal HFHC diet had increased energy intake. Males exposed to a maternal HFHC diet had a 15% increased meal size and a 46% increased frequency, compared to the control (CON) males, without a change in energy expenditure. CON and HFHC offspring did not differ in body weight, composition, or plasma metabolic profile. HFHC diet caused decreased hypothalamic glucocorticoid expression, which was further decreased in males compared to females. Maternal weight, maternal caloric intake, and male offspring meal frequency were inversely correlated with offspring hypothalamic insulin receptor (IR) expression. There was a significant interaction between maternal-diet exposure and sex in hypothalamic IR. Based on our preclinical data, we suggest that interventions focusing on normalizing maternal nutrition might be considered to attenuate nutritional influences on obesity programming and curb the continuing rise in obesity rates.

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.

Maternal obesity causes fetal hypothalamic insulin resistance and disrupts development of hypothalamic feeding pathways

ObjectivePerinatal exposure to maternal obesity results in predisposition of offspring to develop obesity later in life. Increased weight gain in offspring exposed to maternal obesity is usually associated with hyperphagia, implicating altered central regulation of food intake as a cause. We aimed to define how maternal obesity impacts early development of the hypothalamus to program lasting dysfunction in feeding regulatory pathways. MethodsMice offspring of diet-induced obese mothers were compared to the offspring of lean control mothers. We analysed gene expression in the fetal hypothalamus, alongside neurosphere assays to investigate the effects of maternal obesity on neural progenitor cell proliferation in vitro. Western blotting was used to investigate the insulin signalling pathway in the fetal hypothalamus. Characterisation of cell type and neuropeptide profile in adulthood was linked with analyses of feeding behaviour. ResultsThere was a reduction in the expression of proliferative genes in the fetal hypothalamus of offspring exposed to maternal obesity. This reduction in proliferation was maintained in vitro when hypothalamic neural progenitor cells were grown as neurospheres. Hypothalamic fetal gene expression and neurosphere growth correlated with maternal body weight and insulin levels. Foetuses of obese mothers showed hypothalamic insulin resistance, which may be causative of reduced proliferation. Furthermore, maternal obesity activated the Notch signalling pathway in neonatal offspring hypothalamus, resulting in decreased neurogenesis. Adult offspring of obese mothers displayed an altered ratio of anorexigenic and orexigenic signals in the arcuate nucleus, associated with an inability to maintain energy homeostasis when metabolically challenged. ConclusionsThese findings show that maternal obesity alters the molecular signature in the developing hypothalamus, which is associated with disrupted growth and development of hypothalamic precursor cells and defective feeding regulation in adulthood. This is the first report of fetal hypothalamic insulin resistance in an obese pregnancy and suggests a mechanism by which maternal obesity causes permanent changes to hypothalamic structure and function.

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.

148-OR: Empagliflozin Improves Insulin Sensitivity of the Hypothalamus in Humans with Prediabetes

Insulin action in the human brain reduces food intake, improves whole-body insulin sensitivity, and modulates adiposity. In most cases of obesity and diabetes, the brain becomes insulin resistant with impaired brain-derived modulation of peripheral metabolism. As treatment with the SGLT2-inhibitor empagliflozin not only improves glucose metabolism but also reduces body weight and cardiovascular risk, we hypothesized that improved brain insulin sensitivity could be involved. Methods: In this double blind study, 40 participants with prediabetes (according to ADA’s OGTT criteria) were 1:1 randomized to receive 25 mg empagliflozin qd or placebo (mean ± SD: age: 60 ± 9 years; BMI: 31.5 ± 3.8 kg/m²). Before and after 8 weeks of treatment, brain insulin sensitivity was assessed by functional MRI combined with the intranasal administration of insulin to the brain. Results: In healthy persons, intranasal insulin administration significantly decreases cerebral blood flow in the hypothalamus. In the current study, volunteers with prediabetes were unresponsive to this, as insulin could not induce hypothalamic inhibition prior treatment. We identified a significant interaction between treatment and the hypothalamic response to insulin (p&amp;lt;0.05, corrected for multiple comparisons). Post-hoc analyses showed that only participants on empagliflozin showed a significant insulin-induced decrease in hypothalamic blood flow after treatment. The group receiving placebo showed no such improvement. Conclusion: Our current results corroborate insulin resistance of the human hypothalamus in humans with prediabetes. Treatment with empagliflozin for 8 weeks was able to restore hypothalamic insulin sensitivity; a favorable response that could contribute to the positive effects of SGLT2 inhibitors. These findings reveal that brain insulin resistance is treatable by pharmacological interventions with potential benefits for cognition, adiposity, and whole-body metabolism. Disclosure M. Heni: Research Support; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi. Speaker’s Bureau; Self; Novo Nordisk A/S. S. Kullmann: None. R. Wagner: Advisory Panel; Self; Novo Nordisk A/S. Speaker’s Bureau; Self; Novo Nordisk A/S. Other Relationship; Self; Eli Lilly and Company. J. Hummel: None. C. Dannecker: None. A. Vosseler: None. L. Fritsche: None. K. Kantartzis: None. J. Machann: None. H. Haering: None. A. Fritsche: None. H. Preissl: None. Funding Boehringer Ingelheim

1766-P: Androgen Action in Hypothalamic Arcuate Nucleus Neurons Increases Hepatic Glucose Production in Female Mice

Androgen excess predisposes females to type 2 diabetes. Using mouse models, we reported that androgen excess causes insulin resistance via activation of the androgen receptor (AR) in the brain. Neurons of the arcuate nucleus of the hypothalamus (ARC) regulate hepatic glucose production (HGP). Thus, we hypothesized that in female mice, androgen excess in neurons of the ARC causes peripheral insulin resistance by increasing HGP. To test this, we injected AaV-Cre-GFP or AaV-GFP into the ARC of ARlox/lox female mice to generate ARC-specific AR knockout (ARC-ARKO) and control mice, respectively. When exposed to a Western diet, control female mice chronically treated with dihydrotestosterone (DHT) developed insulin resistance and fasting hyperglycemia compared to vehicle-treated control mice. In contrast, DHT-treated ARC-ARKO mice remained insulin sensitive and normoglycemic compared to vehicle-treated ARC-ARKO mice. During a hyperinsulinemic-euglycemic clamp, insulin’s ability to suppress HGP was blunted in DHT-treated control mice. In contrast, insulin was still able to suppress HGP in DHT-treated ARC-ARKO females. Additionally, during the clamp, DHT-treated control mice showed no alteration in hepatic activation of AKT, a marker of hepatocyte insulin sensitivity, but exhibited reduced activation of hepatic STAT3, a marker of hypothalamic insulin sensitivity. In contrast, in DHT-treated ARC-ARKO mice activation of hepatic STAT3 was increased. Together these results suggest that in female mice exposed to a Western diet, androgen excess causes insulin resistance in ARC neurons via action at the AR leading to impairments in the brain-IL6-STAT3 pathway which results in unsuppressed HGP. Disclosure J. Morford: None. F. Mauvais-Jarvis: None. Funding National Institutes of Health (R01DK074970, R01107444); U.S. Department of Veterans Affairs (BX003725)