Insulin Receptor Antagonist Research Articles

Maternal Gestational Diabetes Mellitus and High-Fat Diet Influenced Hepatic Polyunsaturated Fatty Acids Profile in the Offspring of C57BL/6J Mice.

This research examines the effects of maternal high-fat (HF) diet and gestational diabetes mellitus (GDM) on offspring lipid metabolism and polyunsaturated fatty acids (PUFA) profile. GDM is induced using the insulin receptor antagonist S961. Weaning offspring are categorized into HF-GDM, HF-CON, NC-GDM, and NC-CON groups based on maternal diet or GDM. Adult offspring are then grouped into NC-CON-NC, NC-CON-HF, NC-GDM-NC, NC-GDM-HF, HF-CON-NC, HF-CON-HF, HF-GDM-NC, and HF-GDM-HF according to dietary patterns. Gas chromatography determines PUFA composition. Western blot assesses PI3K/Akt signaling pathway-related protein expression. Feeding a normal chow diet until adulthood improves the distribution of hepatic PUFA during weaning across the four groups. PI3K expression is upregulated during weaning in HF-CON and HF-GDM, particularly in HF-CON-NC and HF-GDM-NC, compared to NC-CON-NC during adulthood. Akt expression increases in NC-GDM-NC after weaning with a normal diet. The hepatic PUFA profile in HF-CON-HF significantly distinguishes among the maternal generation health groups. Maternal HF diet exacerbates the combined impact of maternal GDM and offspring HF diet on hepatic PUFA and PI3K/Akt signaling pathway-related proteins during adulthood. Early exposure to HF diets and GDM affects hepatic PUFA profiles and PI3K/Akt signaling pathway protein expression in male offspring during weaning and adulthood.

Insulin enhances acid-sensing ion channel currents in rat primary sensory neurons

Insulin has been shown to modulate neuronal processes through insulin receptors. The ion channels located on neurons may be important targets for insulin/insulin receptor signaling. Both insulin receptors and acid-sensing ion channels (ASICs) are expressed in dorsal root ganglia (DRG) neurons. However, it is still unclear whether there is an interaction between them. Therefore, the purpose of this investigation was to determine the effects of insulin on the functional activity of ASICs. A 5 min application of insulin rapidly enhanced acid-evoked ASIC currents in rat DRG neurons in a concentration-dependent manner. Insulin shifted the concentration–response plot for ASIC currents upward, with an increase of 46.2 ± 7.6% in the maximal current response. The insulin-induced increase in ASIC currents was eliminated by the insulin receptor antagonist GSK1838705, the tyrosine kinase inhibitor lavendustin A, and the phosphatidylinositol-3 kinase antagonist wortmannin. Moreover, insulin increased the number of acid-triggered action potentials by activating insulin receptors. Finally, local administration of insulin exacerbated the spontaneous nociceptive behaviors induced by intraplantar acid injection and the mechanical hyperalgesia induced by intramuscular acid injections through peripheral insulin receptors. These results suggested that insulin/insulin receptor signaling enhanced the functional activity of ASICs via tyrosine kinase and phosphatidylinositol-3 kinase pathways. Our findings revealed that ASICs were targets in primary sensory neurons for insulin receptor signaling, which may underlie insulin modulation of pain.

Identification of Two Insulin Receptors from the Swimming Crab Portunus trituberculatus: Molecular Characterization, Expression Analysis, and Interactions with Insulin-Like Androgenic Gland Hormone.

AbstractThe insulin-like androgenic gland hormone is a crucial sexual regulator that is involved in the masculine sexual differentiation of crustaceans. As an insulin-like peptide, the insulin-like androgenic gland hormone has been proposed to act through the insulin receptor-mediated pathway. The present study cloned and characterized two insulin receptors (PtIR1 and PtIR2) from the swimming crab Portunus trituberculatus hallmarked with a conserved intracellular tyrosine kinase catalytic domain and several other typical insulin receptor domains in their deduced amino acid sequences. Both insulin receptors were predominately expressed in the testis and the insulin-like androgenic gland hormone-producing organ androgenic gland. Their testicular expression during the annual cycle suggested that they may play critical roles in spermatogenesis. By using the protein colocalization analysis in HEK293 cells, interactions of PtIAG with the two PtIRs were further confirmed. In addition, the insulin receptor antagonist was found to attenuate the stimulatory effects of androgenic gland homogenate on the phosphorylated MAPK levels in testis explants, suggesting that the insulin receptor-dependent MAPK pathway may be essential for insulin-like androgenic gland hormone functions.

Insulin and TLR4 Inhibitor Improve Motor Impairments in a Rat Model of Parkinson’s Disease

Background: Insulin resistance is an important pathological hallmark of Parkinson’s disease (PD). Proinflammatory cytokines during neuroinflammation decrease insulin sensitivity by suppressing insulin signaling elements. Toll-like receptor 4 (TLR4), the main receptor involved in neuroinflammation, is also associated with the pathogenesis of PD. Objectives: The present study evaluated the effect of insulin, an insulin receptor antagonist, and a TLR4 inhibitor on behavioral deficits and insulin resistance induced by 6-hydroxydopamine (6-OHDA). Methods: Male Wistar rats were divided into nine groups: (1) sham (normal saline [NS] in the medial forebrain bundle [MFB]); (2) 6-OHDA (20 µg in the MFB); (3) 6-OHDA + NS; (4) 6-OHDA + dimethyl sulfoxide (DMSO); (5) 6-OHDA + insulin (2.5 IU/day, intracerebroventricular ([ICV]); (6) 6-OHDA + insulin (5 IU/day, intranasal [IN]); (7) 6-OHDA + insulin receptor antagonist (S961; 6.5 nM/kg, ICV); (8) 6-OHDA + TLR4 inhibitor (TAK242; 0.01 µg/rat, ICV); (9) 6-OHDA + insulin + TLR4 inhibitor. All treatments were administered for seven consecutive days. Motor performance was evaluated using apomorphine-induced rotation and cylinder tests. Gene expression and protein levels of α-synuclein, TLR4, insulin receptor substrate (IRS) 1, IRS2, and glycogen synthase kinase 3β (GSK3β) were measured by real-time PCR and western blotting, respectively, in the striatum. Results: Insulin, alone and with TAK242, improved motor deficits induced by 6-OHDA. Administration of the insulin receptor antagonist had no effect on motor deficits. The increased expression of α-synuclein and TLR4 following 6-OHDA was attenuated by insulin and TAK242. GSK3β levels, both mRNA and protein, were significantly increased by 6-OHDA and attenuated with insulin and TAK242. Conclusions: The findings suggest that 6-OHDA induces neurodegeneration via activation of TLR4 and GSK3β, indicating insulin resistance, and that insulin can improve these impairments. Moreover, TLR4 inhibition prevents insulin signaling dysfunction and improves behavioral and molecular impairments, highlighting the critical role of TLR4 in the development of insulin resistance in PD pathology.

Effect of high-fat diet on the fatty acid profiles of brain in offspring mice exposed to maternal gestational diabetes mellitus.

Fatty acids play a critical role in the proper functioning of the brain. This study investigated the effects of a high-fat (HF) diet on brain fatty acid profiles of offspring exposed to maternal gestational diabetes mellitus (GDM). Insulin receptor antagonist (S961) and HF diet were used to establish the GDM animal model. Brain fatty acid profiles of the offspring mice were measured by gas chromatography at weaning and adulthood. Protein expressions of the fatty acid transport pathway Wnt3/β-catenin and the target protein major facilitator superfamily domain-containing 2a (MFSD2a) were measured in the offspring brain by Western blot. Maternal GDM increased the body weight of male offspring (P < 0.05). In weaning offspring, factorial analysis showed that maternal GDM increased the monounsaturated fatty acid (MUFA) percentage of the weaning offspring's brain (P < 0.05). Maternal GDM decreased offspring brain arachidonic acid (AA), but HF diet increased brain linoleic acid (LA) (P < 0.05). Maternal GDM and HF diet reduced offspring brain docosahexaenoic acid (DHA), and the male offspring had higher DHA than the female offspring (P < 0.05). In adult offspring, factorial analysis showed that HF diet increased brain MUFA in offspring, and male offspring had higher brain MUFA than female offspring (P < 0.05). The HF diet increased brain LA in the offspring. Male offspring had higher level of AA than female offspring (P < 0.05). HF diet reduced DHA in the brains of female offspring. The brain protein expression of β-catenin and MFSD2a in both weaning and adult female offspring was lower in the HF + GDM group than in the CON group (P < 0.05). Maternal GDM increased the susceptibility of male offspring to HF diet-induced obesity. HF diet-induced adverse brain fatty acid profiles in both male and female offspring exposed to GDM.

Regulation of insulin entry into the brain

AbstractBackgroundCentral nervous system (CNS) insulin has repeatedly been shown to play a role in cognition. Little, if any, insulin is synthesized in the brain and therefore requires navigation of the blood‐brain barrier (BBB) to act. The BBB is a unique structure in the brain that regulates the entry of serum substrates and can act as both a barrier and signaling structure. We hypothesize the BBB is a critical structure involved in the regulation of CNS insulin signaling and CNS insulin availability. We have investigated the regulation of insulin BBB transport and interactions under various conditions including exercise, brain insulin resistance, and have begun to explore the mechanisms for insulin transport across the BBB.MethodFor exercise, male and female mice were habituated to locked voluntary running wheels. After habituation, wheels were unlocked in some cages (exercise) for 24 hours while remaining locked (sedentary) in the others. For brain insulin resistance, mice were treated with an intracerebroventricular delivery of the insulin receptor antagonist, S961. For mechanisms involved in insulin BBB transport and interactions, endocytosis inhibitors were used to differentiate between clathrin and caveolin endocytosis. Following manipulation, insulin BBB pharmacokinetics were assessed with the quantitative multiple‐time regression analysis using radioactively labeled insulin and albumin, a marker for vascular space. Mice were injected intravenously or perfused in situ with the radiolabeled substrates and at timepoints up to 10 min, blood and brains collected and radioactivity measured. 125I‐insulin entry and binding to the BBB was assessed.ResultExercise enhanced 125I‐insulin interactions at the BBB. Specifically, exercise increased insulin BBB transport by two‐fold in males and increased insulin binding at the BBB in females. Brain insulin resistance impaired 125I‐insulin transport across the BBB, particularly in females. Lastly, caveolin‐mediated endocytosis may be involved in hypothalamic 125I‐insulin BBB transport.ConclusionWe have shown insulin BBB transport is highly regulated and can be impacted by exercise, brain insulin resistance, and may involve various endocytic pathways in a regional‐dependent manner. Continued investigation on the pathways involved in insulin BBB transport is warranted to aid in treating or preventing brain insulin resistance as occurs in Alzheimer’s disease.

The liver-derived exosomes stimulate insulin gene expression in pancreatic beta cells under condition of insulin resistance.

An insufficient functional beta cell mass is a core pathological hallmark of type 2 diabetes (T2D). Despite the availability of several effective pharmaceuticals for diabetes management, there is an urgent need for novel medications to protect pancreatic beta cells under diabetic conditions. Integrative organ cross-communication controls the energy balance and glucose homeostasis. The liver and pancreatic islets have dynamic cross-communications where the liver can trigger a compensatory beta cell mass expansion and enhanced hormonal secretion in insulin-resistant conditions. However, the indispensable element(s) that foster beta cell proliferation and insulin secretion have yet to be completely identified. Exosomes are important extracellular vehicles (EVs) released by most cell types that transfer biological signal(s), including metabolic messengers such as miRNA and peptides, between cells and organs. We investigated whether beta cells can take up liver-derived exosomes and examined their impact on beta cell functional genes and insulin expression. Exosomes isolated from human liver HepG2 cells were characterized using various methods, including Transmission Electron Microscopy (TEM), dynamic light scattering (DLS), and Western blot analysis of exosomal markers. Exosome labeling and cell uptake were assessed using CM-Dil dye. The effect of liver cell-derived exosomes on Min6 beta cells was determined through gene expression analyses of beta cell markers and insulin using qPCR, as well as Akt signaling using Western blotting. Treatment of Min6 beta cells with exosomes isolated from human liver HepG2 cells treated with insulin receptor antagonist S961 significantly increased the expression of beta cell markers Pdx1, NeuroD1, and Ins1 compared to the exosomes isolated from untreated cells. In line with this, the activity of AKT kinase, an integral component of the insulin receptor pathway, is elevated in pancreatic beta cells, as represented by an increase in AKT's downstream substrate, FoxO1 phosphorylation. This study suggests that liver-derived exosomes may carry a specific molecular cargo that can affect insulin expression in pancreatic beta cells, ultimately affecting glucose homeostasis.

Insulin potentiates inhibitory synaptic currents between fast-spiking and pyramidal neurons in the rat insular cortex

Insulin plays roles in brain functions such as neural development and plasticity and is reported to be involved in dementia and depression. However, little information is available on the insulin-mediated modulation of electrophysiological activities, especially in the cerebral cortex. This study examined how insulin modulates the neural activities of inhibitory neurons and inhibitory postsynaptic currents (IPSCs) in rat insular cortex (IC; either sex) by multiple whole-cell patch-clamp recordings. We demonstrated that insulin increased the repetitive spike firing rate with a decrease in the threshold potential without changing the resting membrane potentials and input resistance of fast-spiking GABAergic neurons (FSNs). Next, we found a dose-dependent enhancement of unitary IPSCs (uIPSCs) by insulin in the connections from FSNs to pyramidal neurons (PNs). The insulin-induced enhancement of uIPSCs accompanied decreases in the paired-pulse ratio, suggesting that insulin increases GABA release from presynaptic terminals. The finding of miniature IPSC recordings of the increased frequency without changing the amplitude supports this hypothesis. Insulin had little effect on uIPSCs under the coapplication of S961, an insulin receptor antagonist, or lavendustin A, an inhibitor of tyrosine kinase. The PI3–K inhibitor wortmannin or the PKB/Akt inhibitors, deguelin and Akt inhibitor VIII, blocked the insulin-induced enhancement of uIPSCs. Intracellular application of Akt inhibitor VIII to presynaptic FSNs also blocked insulin-induced enhancement of uIPSCs. In contrast, uIPSCs were enhanced by insulin in combination with the MAPK inhibitor PD98059. These results suggest that insulin facilitates the inhibition of PNs by increases in FSN firing frequency and IPSCs from FSNs to PNs. (250 words).

374-OR: Exercise Training Decreases ß-Cell Senescence in Mice and Humans

Increased β-cell senescence contributes to the development of type 2 diabetes (T2D). Exercise is critical in the treatment of T2D and can attenuate aging-associated cellular changes, but exercise effects on β-cell senescence are unknown. We tested the effects of treadmill running (1h/day for 10 days) on two insulin resistance models: high-fat diet and insulin receptor antagonist (S961). Exercise improved glucose responsiveness and decreased senescence markers (SA-βGal activity, p21Cip1 and p16Ink4a mRNA and protein levels). RNAseq from pancreatic islets of exercised mice revealed decreased expression of senescence effector genes and senescence associated secretory phenotype factors. Exercise increased AMPK activity in islets as assessed by alpha catalytic subunit phosphorylation. Islets from sedentary mice cultured for 2 days with serum from exercised mice showed decreased senescence, suggesting a circulatory factor was responsible for these effects. Pathway analysis of RNASeq revealed that exercise upregulated glucagon type ligand receptors. Glucagon treatment of mouse and human islets activated AMPK and decreased senescence in β-cells, an affect attenuated by an AMPK inhibitor (compound C). Exercised mice treated with a glucagon antagonist (adomeglivant) blocked AMPK phosphorylation and increased p21Cip1 and p16Ink4. Exercise increased nuclear translocation of the AMPK substrate NRF2 in mouse islets while downregulation of Nrf2 with siRNA in MIN6 cells increased transcription of p16Ink4a, suggesting a potential mechanism linking exercise, AMPK activation and downregulation of β-cell senescence. Treatment of human donor islets with serum obtained pre- and post-exercise training for 10 weeks in people with T2D showed that training activated AMPK and decreased senescence markers. These findings demonstrate that exercise training decreases β-cell senescence and suggest that this important response to exercise occurs through circulating factors mediating an AMPK-dependent pathway. Disclosure P.Carapeto: None. J.Kahng: None. A.T.Alves wagner: None. R.J.W.Middelbeek: Research Support; Novo Nordisk. M.F.Hirshman: Stock/Shareholder; Abbott, AbbVie Inc., Amgen Inc., Colgate-Palmolive, Eli Lilly and Company, Medtronic. G.A.Rutter: Consultant; Sun Pharmaceutical Industries Ltd. L.Goodyear: None. C.Aguayo-mazzucato: None. Funding Joslin Diabetes Center (to C.A-M.); Richard and Susan Smith Family Foundation; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (001)

Antagonistic Insulin Derivative Suppresses Insulin-Induced Hypoglycemia.

Insulin derivatives provide new functions that are distinctive from native insulin. We investigated insulin modifications on the C-terminal A chain with insulin receptor (IR) peptide binders and presented a full and potent IR antagonist. We prepared insulin precursors featuring a sortase A (SrtA) recognition sequence, LPETGG, at the C-terminal A chain and used a SrtA-mediated ligation method to synthesize insulin derivatives. The insulin precursor exhibits full IR agonism potency, similar to native human insulin. We explored derivatives with linear IR binding peptides attached to the insulin C-terminal A chain. One insulin derivative with an IR binder (Ins-AC-S2) can fully antagonize IR activation by insulin, as confirmed by cell-based assays. This IR antagonist suppresses insulin-induced hypoglycemia in a streptozotocin-induced diabetic rat model. This study provides a new direction toward insulin antagonist development.

The mammalian insulin antagonist S961 does not exhibit insulin receptor antagonism in rainbow trout in vivo.

Due to their reported 'glucose-intolerant' phenotype, rainbow trout have been the focus of comparative studies probing underlying endocrine mechanisms at the organismal, tissue and molecular level. A particular focus has been placed on the investigation of the comparative role of insulin, an important glucoregulatory hormone, and its interaction with macronutrients. A limiting factor in the comparative investigation of insulin is the current lack of reliable assays to quantify circulating mature and thus bioactive insulin. To circumvent this limitation, tissue-specific responsiveness to postprandial or exogenous insulin has been quantified at the level of post-translational modifications of cell signalling proteins. These studies revealed that the insulin responsiveness of these proteins and their post-translational modifications are evolutionarily highly conserved and thus provide useful and quantifiable proxy indices to investigate insulin function in rainbow trout. While the involvement of specific branches of the intracellular insulin signalling pathway (e.g., mTor) in rainbow trout glucoregulation have been successfully probed through pharmacological approaches, it would be useful to have a functionally validated insulin receptor antagonist to characterize the glucoregulatory role of the insulin receptor pathway in its entirety for this species. Here, we report two separate in vivo experiments to test the ability of the mammalian insulin receptor antagonist, S961, to efficiently block insulin signalling in liver and muscle in response to endogenously released insulin and to exogenously infused bovine insulin. We found that, irrespective of the experimental treatment or dose, activation of the insulin pathway in liver and muscle was not inhibited by S961, showing that its antagonistic effect does not extend to rainbow trout.

Clearance of p16Ink4a-positive cells in a mouse transgenic model does not change β-cell mass and has limited effects on their proliferative capacity

Type 2 diabetes is partly characterized by decreased β-cell mass and function which have been linked to cellular senescence. Despite a low basal proliferative rate of adult β-cells, they can respond to growth stimuli, but this proliferative capacity decreases with age and correlates with increased expression of senescence effector, p16Ink4a. We hypothesized that selective deletion of p16Ink4a-positive cells would enhance the proliferative capacity of the remaining β-cells due to the elimination of the local senescence-associated secretory phenotype (SASP). We aimed to investigate the effects of p16Ink4a-positive cell removal on the mass and proliferative capacity of remaining β-cells using INK-ATTAC mice as a transgenic model of senolysis. Clearance of p16Ink4a positive subpopulation was tested in mice of different ages, males and females, and with two different insulin resistance models: high-fat diet (HFD) and insulin receptor antagonist (S961). Clearance of p16Ink4a-positive cells did not affect the overall β-cell mass. β-cell proliferative capacity negatively correlated with cellular senescence load and clearance of p16Ink4a positive cells in 1-year-old HFD mice improved β-cell function and increased proliferative capacity in a subset of animals. Single-cell sequencing revealed that the targeted p16Ink4a subpopulation of β-cells is non-proliferative and non-SASP producing whereas additional senescent subpopulations remained contributing to continued local SASP secretion. In conclusion, deletion of p16Ink4a cells did not negatively impact beta-cell mass and blood glucose under basal and HFD conditions and proliferation was restored in a subset of HFD mice opening further therapeutic targets in the treatment of diabetes.

Placental Fatty Acid Metabolism and Transport in a Rat Model of Gestational Diabetes Mellitus.

Gestational diabetes mellitus (GDM) is a form of heightened insulin resistance triggered during gestation. This study examines how insulin resistance alters placental long-chain polyunsaturated fatty acid (LCPUFA) transport and metabolism in a rat model of lean GDM. Pregnant Sprague Dawley rats were administered with S961, an insulin receptor antagonist (30 nmol/kg s.c. daily), or vehicle from gestational day (GD) 7 to 20. Daily maternal body weight, food, and water intake were measured. Blood pressure assessment and glucose tolerance test were done on GD20. Fetal plasma and placenta were collected on GD20 and processed for fatty acid measurement using LC-mass spectrometry. The expression of fatty acid metabolism-related genes in the placenta was assessed using RT2 Profiler PCR arrays. The results were validated by qRT-PCR. Blockade of insulin receptors with S961 in pregnant rats resulted in glucose intolerance with increased fasting glucose and insulin levels. Maternal body weight gain and food and water intake were not affected; however, S961 significantly increased maternal blood pressure and heart rate. The placenta n3 and n6 LCPUFA concentrations were significantly decreased by 8% and 11%, respectively, but their levels in the fetal plasma were increased by 15% and 4%. RT2 profiler arrays revealed that placental expressions of 10 genes related to fatty acid β-oxidation (Acaa1a, Acadm, Acot2, Acox2, Acsbg1, Acsl4, Acsm5, Cpt1b, Eci2, Ehhadh) and 3 genes related to fatty acid transport pathway (Fabp2, Fabp3, Slc27a3) were significantly upregulated. In summary, lack of insulin action increased the expression of genes related to placental fatty acid β-oxidation and transport with an increased transfer of LCPUFA to the fetus. The increased lipid levels routed toward the fetus may lead to fat adiposity and later-life metabolic dysfunction.

Cerebrovascular insulin receptors are defective in Alzheimer's disease.

Central response to insulin is suspected to be defective in Alzheimer's disease. As most insulin is secreted in the bloodstream by the pancreas, its capacity to regulate brain functions must, at least partly, be mediated through the cerebral vasculature. However, how insulin interacts with the blood-brain barrier and whether alterations of this interaction could contribute to Alzheimer's disease pathophysiology both remain poorly defined. Here, we show that human and murine cerebral insulin receptors (INSRs), particularly the long isoform INSRα-B, are concentrated in microvessels rather than in the parenchyma. Vascular concentrations of INSRα-B were lower in the parietal cortex of subjects diagnosed with Alzheimer's disease, positively correlating with cognitive scores, leading to a shift towards a higher INSRα-A/B ratio, consistent with cerebrovascular insulin resistance in the Alzheimer's disease brain. Vascular INSRα was inversely correlated with amyloid-β plaques and β-site APP cleaving enzyme 1, but positively correlated with insulin-degrading enzyme, neprilysin and P-glycoprotein. Using brain cerebral intracarotid perfusion, we found that the transport rate of insulin across the blood-brain barrier remained very low (<0.03 µl/g·s) and was not inhibited by an insulin receptor antagonist. However, intracarotid perfusion of insulin induced the phosphorylation of INSRβ that was restricted to microvessels. Such an activation of vascular insulin receptor was blunted in 3xTg-AD mice, suggesting that Alzheimer's disease neuropathology induces insulin resistance at the level of the blood-brain barrier. Overall, the present data in post-mortem Alzheimer's disease brains and an animal model of Alzheimer's disease indicate that defects in the insulin receptor localized at the blood-brain barrier strongly contribute to brain insulin resistance in Alzheimer's disease, in association with β-amyloid pathology.

Hindbrain insulin controls feeding behavior

ObjectivePancreatic insulin was discovered a century ago, and this discovery led to the first lifesaving treatment for diabetes. While still controversial, nearly one hundred published reports suggest that insulin is also produced in the brain, with most focusing on hypothalamic or cortical insulin-producing cells. However, specific function for insulin produced within the brain remains poorly understood. Here we identify insulin expression in the hindbrain's dorsal vagal complex (DVC), and determine the role of this source of insulin in feeding and metabolism, as well as its response to diet-induced obesity in mice. MethodsTo determine the contribution of Ins2-producing neurons to feeding behavior in mice, we used the cross of transgenic RipHER-cre mouse and channelrhodopsin-2 expressing animals, which allowed us to optogenetically stimulate neurons expressing Ins2 in vivo. To confirm the presence of insulin expression in Rip-labeled DVC cells, in situ hybridization was used. To ascertain the specific role of insulin in effects discovered via optogenetic stimulation a selective, CNS applied, insulin receptor antagonist was used. To understand the physiological contribution of insulin made in the hindbrain a virogenetic knockdown strategy was used. ResultsInsulin gene expression and presence of insulin-promoter driven fluorescence in rat insulin promoter (Rip)-transgenic mice were detected in the hypothalamus, but also in the DVC. Insulin mRNA was present in nearly all fluorescently labeled cells in DVC. Diet-induced obesity in mice altered brain insulin gene expression, in a neuroanatomically divergent manner; while in the hypothalamus the expected obesity-induced reduction was found, in the DVC diet-induced obesity resulted in increased expression of the insulin gene. This led us to hypothesize a potentially divergent energy balance role of insulin in these two brain areas. To determine the acute impact of activating insulin-producing neurons in the DVC, optic stimulation of light-sensitive channelrhodopsin 2 in Rip-transgenic mice was utilized. Optogenetic photoactivation induced hyperphagia after acute activation of the DVC insulin neurons. This hyperphagia was blocked by central application of the insulin receptor antagonist S961, suggesting the feeding response was driven by insulin. To determine whether DVC insulin has a necessary contribution to feeding and metabolism, virogenetic insulin gene knockdown (KD) strategy, which allows for site-specific reduction of insulin gene expression in adult mice, was used. While chow-fed mice failed to reveal any changes of feeding or thermogenesis in response to the KD, mice challenged with a high-fat diet consumed less food. No changes in body weight were identified, possibly resulting from compensatory reduction in thermogenesis. ConclusionsTogether, our data suggest an important role for hindbrain insulin and insulin-producing cells in energy homeostasis.

E2F1 transcription factor mediates a link between fat and islets to promote β cell proliferation in response to acute insulin resistance.

SUMMARYPrevention or amelioration of declining β cell mass is a potential strategy to cure diabetes. Here, we report the pathways utilized by β cells to robustly replicate in response to acute insulin resistance induced by S961, a pharmacological insulin receptor antagonist. Interestingly, pathways that include CENP-A and the transcription factor E2F1 that are independent of insulin signaling and its substrates appeared to mediate S961-induced β cell multiplication. Consistently, pharmacological inhibition of E2F1 blocks β-cell proliferation in S961-injected mice. Serum from S961-treated mice recapitulates replication of β cells in mouse and human islets in an E2F1-dependent manner. Co-culture of islets with adipocytes isolated from S961-treated mice enables β cells to duplicate, while E2F1 inhibition limits their growth even in the presence of adipocytes. These data suggest insulin resistance-induced proliferative signals from adipocytes activate E2F1, a potential therapeutic target, to promote β cell compensation.

Brain Insulin Receptor Antagonism Augments The Blood Pressure Response To Activation Of The Exercise Pressor Reflex

Type 2 diabetes mellitus (T2DM) results in abnormal control of blood pressure (BP). However, the underlying mechanisms remain to be elucidated. The transport of insulin into the central nervous system is decreased in T2DM. The resultant central hypoinsulinemia reduces neuronal excitability. The nucleus tractus solitarius (NTS) is a key central integration site for incoming signals from peripheral sensory neurons including input from working skeletal muscle and arterial baroreceptors. Working skeletal muscle activates primary sensory fibers and evokes the exercise pressor reflex (EPR) to reflexively increase BP, a response modulated by the baroreflex. Central hypoinsulinemia in T2DM may influence how neurons in the NTS process this sensory information during exercise affecting BP responsiveness. PURPOSE: To determine whether acute antagonism of insulin receptors in the NTS alters EPR function in baro-intact and barodenervated rats. METHODS: L4 and L5 ventral roots were electrically stimulated in healthy decerebrated male Sprague-Dawley rats to evoke hindlimb muscle contraction and EPR activation in intact and sino-aortic barodenervated rats. Mean arterial pressure (MAP) responses to activation of the EPR were assessed before and 30 min following NTS microinjections of the insulin receptor antagonist, GSK1838705 (100uM), or vehicle, dimethyl sulfoxide (DMSO). RESULTS: In baro-intact rats, contraction-induced changes in MAP were significantly greater following GSK1838705 (Pre, 16 ± 10 mmHg vs. Post, 23 + 13 mmHg, n = 11, p < 0.01) but not DMSO (Pre, 15 ± 8 mmHg vs. Post, 15 + 8 mmHg, n = 9). In barodenervated rats, neither GSK1838705 (Pre, 27 ± 16 mmHg vs. Post, 28 ± 21 mmHg, n = 8) nor DMSO (Pre, 34 ± 17 mmHg vs. Post, 30 ± 27 mmHg, n = 9) affected the MAP response to contraction. CONCLUSIONS: The findings demonstrate that central insulin receptor antagonism augments the BP response to EPR activation, which is abolished by barodenervation. The findings also suggest that insulin in the NTS maintains the capacity to buffer EPR-mediated increases in BP via baroreflex-mediated mechanisms. Alterations in this buffering capacity due to the central hypoinsulinemia in T2DM could account, in part, for the exaggerated pressor response to exercise in this disease. Supported by NIH-NHLBI, Lawson & Rogers Lacy Research Fund.

199-OR: Exercise Decreases Mouse and Human Islet Senescence through Glucagon-Mediated AMPK Activation

Aging is a major risk factor for type 2 diabetes (T2D) and cellular senescence plays a critical role in β-cell dysfunction leading to T2D. Exercise is a central component in the treatment of T2D and has been shown to attenuate many of the biochemical changes that occur with aging including senescence, but nothing is known about the effects of exercise on β-cells and their aging process. To test the hypothesis that exercise decreases β-cell senescence we used two mouse models of insulin resistance: high-fat diet (HFD, 60% kcal from fat, 6 wks) and insulin receptor antagonist S961 (40nM/wk for 2 wks) . Exercise (treadmill, 1 h/day, 5 times/wk for 2 wks at 17 cm/s and 5% incline) prevented entrance of β-cells into senescence and reversed established senescence in both males and females across the lifespan (started at 1.5-9m or 14m old mice) as seen by a decrease in one or several of the following markers: βGal, p21Cip1 and p16Ink4a. This decrease in senescence was accompanied by improved glucose stimulated insulin secretion characterized by recovery of glucose responsiveness in islets from HFD and S961 exercised animals. Islets cultured with serum from trained animals showed decreased p21Cip1 mRNA, indicating a circulatory factor (s) was responsible for these effects. Exercise increased serum glucagon expression, identified as such factor. Incubation of human and mouse islets with glucagon (1nM) decreased p21Cip1 mRNA, and using AMPK agonist (1uM C99) and antagonist (5uM Compound C) , we found that AMPK mediates the glucagon-stimulated decrease in p21Cip1. Human cadaveric donor islets treated with serum obtained before and after 10-weeks of exercise-training in people with T2D demonstrated that training decreased senescence markers through AMPK activation. In conclusion, exercise has anti-aging effects on mouse and human pancreatic islets by decreasing senescence and improving function. This is a novel mechanism of the effects of exercise on β-cell aging with implications for the treatment of T2D. Disclosure P.Carapeto: None. J.Kahng: None. A.T.Alves wagner: None. R.Middelbeek: Research Support; Novo Nordisk. M.F.Hirshman: Stock/Shareholder; Abbott, AbbVie Inc., Amgen Inc., Colgate-Palmolive, Eli Lilly and Company, Medtronic. L.J.Goodyear: None. C.Aguayo-mazzucato: Consultant; eGenesis. Funding American Diabetes Association (1-17-PMF-009) ; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001; Short-Term Research Experience for Underrepresented Persons (1R25DK113652) ; NIDDK grant (K23-DK114550) ; NIH grant (R01DK099511) and the Joslin Diabetes Center DRC (P30 DK36836) .

1320-P: Insulin Receptors and Their Signal Transduction Pathways in Choroid Plexus

The insulin receptor (IR) is a tyrosine kinase receptor present in cell membranes. It is highly expressed in hepatocytes (where it promotes glycogenesis and inhibits gluconeogenesis) , and skeletal muscle and fat (where it facilitates glucose uptake by translocation of the glucose transporter GLUT4) . IR expression is also found throughout the brain, both in neurons and all glial cell types, and for decades impaired insulin signaling has been implicated in the onset and development of Alzheimer’s disease. IR expression pattern in the brain parenchyma is heterogeneous, with highest levels of expression found in olfactory bulb, hypothalamus, and hippocampus. However, the choroid plexus (CP) , a structure present in all 4 ventricles of the brain and responsible for the secretion of cerebrospinal fluid, has the highest affinity for insulin binding compared to any other brain region. This work aims to characterize the insulin signaling in the epithelial cells of the choroid plexus (EChP) and its possible implications in diseases of the brain. Relative expression levels of specific splicing variants of the Insr gene in dissected CP of adult mice were evaluated by qPCR and revealed predominant expression of the variant coding for isoform IR-A when compared to isoform IR-B. In vitro stimulation of EChP with insulin elicits a classical tyrosine kinase cascade, with activation of both the mitogenic (ERK) and metabolic (Akt) arms of the insulin signaling pathway, in a time-and concentration-dependent manner. Using pharmacological (S961, an insulin receptor antagonist) and genetic (insulin receptor shRNA, and Insr cre-loxP) approaches, we show that downregulation of IR in these cells not only impairs insulin signaling, but it also decreases IGF2’s ability to activate ERK and Akt, even when IGF1R levels are unaltered. Finally, using a viral vector coding for an IR shRNA, we show that downregulation of Insr expression in CP of adult mice has a profound effect on its structure, as demonstrated by MRI and histological technique. Disclosure C.Mazucanti: None. V.L.Kennedy: None. A.Cho: None. Q.Liu: None. J.F.O’connell: None. S.Camandola: None. J.M.Egan: None.

80-OR: Proinflammatory Macrophage Impairs Retrograde Axonal Transport via Inflammation and Insulin Resistance in Sensory Neurons

Inflammation, insulin resistance (IR) , and deficit of retrograde axonal transport (RAT) are implicated in the pathogenesis of diabetic polyneuropathy (DPN) . Pro-inflammatory macrophage (M1) skewed by diabetic insults causes IR in adipose tissue. The activation of Advanced Glycation End products (AGEs) - Receptor for AGEs (RAGE) signaling is involved in the macrophage polarization into M1, while its contribution to the deficit of RAT in DPN is still unclear. In this study, we investigated the implication of M1-related inflammation to RAT deficit in sensory neurons. We evaluated the activation of macrophage cell line RAW 264.7 (RAW) and neurons isolated from dorsal root ganglia (DRG) of C57BL/6 mice stimulated by 200 μg/ml of AGE. A DRG neurons-RAW co-culture system was established by seeding RAW onto DRG neurons. After 12h co-culturing, we added AGE to the co-culture and stimulated RAW. A DRG neuronal mono-culture was treated with 500 nM of insulin receptor antagonist (BMS-754807) , and 20 ng/ml of TNF-α with/without 50 nM JNK inhibitor (SP600125) . Axonal transport was visualized by Lysotracker and captured by time-lapse microscopy. The movements were quantified on kymographs generated from 100 μm axonal segments. AGE induced the M1 phenotype in RAW with elevated expressions of iNOS and TNF-α mRNA, while no effects on DRG neuron were identified. In the co-culture, the frequency of RAT (RAT%) was significantly reduced when RAW was stimulated by AGE compared to naive RAW (p &amp;lt; 0.001) . In the mono-culture, RAT% was significantly reduced when neurons were treated with BMS-7548 and TNFα (vs. control, both p &amp;lt; 0.001) . TNFα stimulation also increased the phosphorylation of JNK in the axons, a major target of TNFα, which was confirmed by immunofluorescence. The reduction of RAT% by TNFα was rescued by SP600125. In summary, RAT could be impaired by TNF-α and IR, which suggests inflammation induced by M1 in SN can attenuate RAT, which contributes to the DPN pathology. Disclosure S.Osonoi: None. H.Mizukami: None. S.Ogasawara: None. K.Kudoh: None. M.Daimon: None. S.Yagihashi: None. Funding Japan Society for the Promotion of Science (18K16220)