Diet-induced obesity induces endoplasmic reticulum stress and insulin resistance in the amygdala of rats

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOInsulin acts in the hypothalamus, decreasing food intake (FI) by the IR/PI3K/Akt pathway. This pathway is impaired in obese animals and endoplasmic reticulum (ER) stress and low-grade inflammation are possible mechanisms involved in this impairment. Here, we highlighted the amygdala as an important brain region for FI regulation in response to insulin. This regulation was dependent on PI3K/AKT pathway similar to the hypothalamus. Insulin was able to decrease neuropeptide Y (NPY) and increase oxytocin mRNA levels in the amygdala via PI3K, which may contribute to hypophagia. Additionally, obese rats did not reduce FI in response to insulin and AKT phosphorylation was decreased in the amygdala, suggesting insulin resistance. Insulin resistance was associated with ER stress and low-grade inflammation in this brain region. The inhibition of ER stress with PBA reverses insulin action/signaling, decreases NPY and increases oxytocin mRNA levels in the amygdala from obese rats, suggesting that ER stress is probably one of the mechanisms that induce insulin resistance in the amygdala. © 2013 The Authors.Insulin acts in the hypothalamus, decreasing food intake (FI) by the IR/PI3K/Akt pathway. This pathway is impaired in obese animals and endoplasmic reticulum (ER) stress and low-grade inflammation are possible mechanisms involved in this impairment. Here, we highlighted the amygdala as an important brain region for FI regulation in response to insulin. This regulation was dependent on PI3K/AKT pathway similar to the hypothalamus. Insulin was able to decrease neuropeptide Y (NPY) and increase oxytocin mRNA levels in the amygdala via PI3K, which may contribute to hypophagia. Additionally, obese rats did not reduce FI in response to insulin and AKT phosphorylation was decreased in the amygdala, suggesting insulin resistance. Insulin resistance was associated with ER stress and low-grade inflammation in this brain region. The inhibition of ER stress with PBA reverses insulin action/signaling, decreases NPY and increases oxytocin mRNA levels in the amygdala from obese rats, suggesting that ER stress is probably one of the mechanisms that induce insulin resistance in the amygdala31443449FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçã

Hypothalamic S1p/s1pr1 axis controls energy homeostasis

Sphingosine 1-phosphate receptor 1 (S1PR1) is a G-protein-coupled receptor for sphingosine-1-phosphate (S1P) that has a role in many physiological and pathophysiological processes. Here we show that the S1P/S1PR1 signalling pathway in hypothalamic neurons regulates energy homeostasis in rodents. We demonstrate that S1PR1 protein is highly enriched in hypothalamic POMC neurons of rats. Intracerebroventricular injections of the bioactive lipid, S1P, reduce food consumption and increase rat energy expenditure through persistent activation of STAT3 and the melanocortin system. Similarly, the selective disruption of hypothalamic S1PR1 increases food intake and reduces the respiratory exchange ratio. We further show that STAT3 controls S1PR1 expression in neurons via a positive feedback mechanism. Interestingly, several models of obesity and cancer anorexia display an imbalance of hypothalamic S1P/S1PR1/STAT3 axis, whereas pharmacological intervention ameliorates these phenotypes. Taken together, our data demonstrate that the neuronal S1P/S1PR1/STAT3 signalling axis plays a critical role in the control of energy homeostasis in rats.Sphingosine 1-phosphate receptor 1 (S1PR1) is a G-protein-coupled receptor for sphingosine-1-phosphate (S1P) that has a role in many physiological and pathophysiological processes. Here we show that the S1P/S1PR1 signalling pathway in hypothalamic neurons regulates energy homeostasis in rodents. We demonstrate that S1PR1 protein is highly enriched in hypothalamic POMC neurons of rats. Intracerebroventricular injections of the bioactive lipid, S1P, reduce food consumption and increase rat energy expenditure through persistent activation of STAT3 and the melanocortin system. Similarly, the selective disruption of hypothalamic S1PR1 increases food intake and reduces the respiratory exchange ratio. We further show that STAT3 controls S1PR1 expression in neurons via a positive feedback mechanism. Interestingly, several models of obesity and cancer anorexia display an imbalance of hypothalamic S1P/S1PR1/STAT3 axis, whereas pharmacological intervention ameliorates these phenotypes. Taken together, our data demonstrate that the neuronal S1P/S1PR1/STAT3 signalling axis plays a critical role in the control of energy homeostasis in rats5485

Hypothalamic S1p/s1pr1 Axis Controls Energy Homeostasis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Sphingosine 1-phosphate receptor 1 (S1PR1) is a G-protein-coupled receptor for sphingosine-1-phosphate (S1P) that has a role in many physiological and pathophysiological processes. Here we show that the S1P/S1PR1 signalling pathway in hypothalamic neurons regulates energy homeostasis in rodents. We demonstrate that S1PR1 protein is highly enriched in hypothalamic POMC neurons of rats. Intracerebroventricular injections of the bioactive lipid, S1P, reduce food consumption and increase rat energy expenditure through persistent activation of STAT3 and the melanocortin system. Similarly, the selective disruption of hypothalamic S1PR1 increases food intake and reduces the respiratory exchange ratio. We further show that STAT3 controls S1PR1 expression in neurons via a positive feedback mechanism. Interestingly, several models of obesity and cancer anorexia display an imbalance of hypothalamic S1P/S1PR1/STAT3 axis, whereas pharmacological intervention ameliorates these phenotypes. Taken together, our data demonstrate that the neuronal S1P/S1PR1/STAT3 signalling axis plays a critical role in the control of energy homeostasis in rats.5Capes-12900-13-3; CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Schwartz, M.W., Woods, S.C., Porte, D., Jr., Seeley, R.J., Baskin, D.G., Central nervous system control of food intake (2000) Nature, 404, pp. 661-671Munzberg, H., Huo, L., Nillni, E.A., Hollenberg, A.N., Bjorbaek, C., Role of signal transducer and activator of transcription 3 in regulation of hypothalamic proopiomelanocortin gene expression by leptin (2003) Endocrinology, 144, pp. 2121-2131Myers, M.G., Cowley, M.A., Munzberg, H., Mechanisms of leptin action and leptin resistance (2008) Annu. Rev. Physiol., 70, pp. 537-556Janoschek, R., Gp130 signaling in proopiomelanocortin neurons mediates the acute anorectic response to centrally applied ciliary neurotrophic factor (2006) Proc. Natl Acad. Sci. USA, 103, pp. 10707-10712Johnen, H., Tumor-induced anorexia and weight loss are mediated by the TGF-beta superfamily cytokine MIC-1 (2007) Nat. Med., 13, pp. 1333-1340Ropelle, E.R., IL-6 and IL-10 anti-inflammatory activity links exercise to hypothalamic insulin and leptin sensitivity through IKKbeta and ER stress inhibition (2010) PLoS Biol., 8El-Haschimi, K., Pierroz, D.D., Hileman, S.M., Bjorbaek, C., Flier, J.S., Two defects contribute to hypothalamic leptin resistance in mice with diet-induced obesity (2000) J. Clin. Invest., 105, pp. 1827-1832Ernst, M.B., Enhanced Stat3 activation in POMC neurons provokes negative feedback inhibition of leptin and insulin signaling in obesity (2009) J. Neurosci., 29, pp. 11582-11593Gao, Q., Anorectic estrogen mimics leptin's effect on the rewiring of melanocortin cells and Stat3 signaling in obese animals (2007) Nat. Med., 13, pp. 89-94Ghilardi, N., Defective STAT signaling by the leptin receptor in diabetic mice (1996) Proc. Natl Acad. Sci. USA, 93, pp. 6231-6235Frias, M.A., James, R.W., Gerber-Wicht, C., Lang, U., Native and reconstituted HDL activate Stat3 in ventricular cardiomyocytes via ERK1/2: Role of sphingosine-1-phosphate (2009) Cardiovasc. Res., 82, pp. 313-323Gurgui, M., Broere, R., Kalff, J.C., Van Echten-Deckert, G., Dual action of sphingosine 1-phosphate in eliciting proinflammatory responses in primary cultured rat intestinal smooth muscle cells (2010) Cell Signal., 22, pp. 1727-1733Lee, H., STAT3-induced S1PR1 expression is crucial for persistent STAT3 activation in tumors (2010) Nat. Med., 16, pp. 1421-1428Liang, J., Sphingosine-1-phosphate links persistent STAT3 activation, chronic intestinal inflammation, and development of colitis-associated cancer (2013) Cancer Cell, 23, pp. 107-120Spiegel, S., Milstien, S., The outs and the ins of sphingosine-1-phosphate in immunity (2011) Nat. Rev. Immunol., 11, pp. 403-415Spiegel, S., Milstien, S., Functions of the multifaceted family of sphingosine kinases and some close relatives (2007) J. Biol. Chem., 282, pp. 2125-2129Loh, K.C., Sphingosine-1-phosphate enhances satellite cell activation in dystrophic muscles through a S1PR2/STAT3 signaling pathway (2012) PLoS One, 7Lopez, M., Hypothalamic fatty acid metabolism mediates the orexigenic action of ghrelin (2008) Cell. Metab., 7, pp. 389-399Oo, M.L., Engagement of S1P(1)-degradative mechanisms leads to vascular leak in mice (2011) J. Clin. Invest., 121, pp. 2290-2300Means, C.K., Brown, J.H., Sphingosine-1-phosphate receptor signalling in the heart (2009) Cardiovasc. Res., 82, pp. 193-200Schwartz, M.W., Leptin increases hypothalamic pro-opiomelanocortin mRNA expression in the rostral arcuate nucleus (1997) Diabetes, 46, pp. 2119-2123Cowley, M.A., Leptin activates anorexigenic POMC neurons through a neural network in the arcuate nucleus (2001) Nature, 411, pp. 480-484Bates, S.H., STAT3 signalling is required for leptin regulation of energy balance but not reproduction (2003) Nature, 421, pp. 856-859Mynard, V., Guignat, L., Devin-Leclerc, J., Bertagna, X., Catelli, M.G., Different mechanisms for leukemia inhibitory factor-dependent activation of two proopiomelanocortin promoter regions (2002) Endocrinology, 143, pp. 3916-3924Bousquet, C., Zatelli, M.C., Melmed, S., Direct regulation of pituitary proopiomelanocortin by STAT3 provides a novel mechanism for immunoneuroendocrine interfacing (2000) J. Clin. Invest., 106, pp. 1417-1425Bousquet, C., Melmed, S., Critical role for STAT3 in murine pituitary adrenocorticotropin hormone leukemia inhibitory factor signaling (1999) J. Biol. Chem., 274, pp. 10723-10730Andreux, P.A., Systems genetics of metabolism: The use of the BXD murine reference panel for multiscalar integration of traits (2012) Cell, 150, pp. 1287-1299Guissouma, H., Froidevaux, M.S., Hassani, Z., Demeneix, B.A., In vivo siRNA delivery to the mouse hypothalamus confirms distinct roles of TR beta isoforms in regulating TRH transcription (2006) Neurosci. Lett., 406, pp. 240-243Froidevaux, M.S., The co-chaperone XAP2 is required for activation of hypothalamic thyrotropin-releasing hormone transcription in vivo (2006) EMBO Rep., 7, pp. 1035-1039Nagahashi, M., Sphingosine-1-phosphate produced by sphingosine kinase 1 promotes breast cancer progression by stimulating angiogenesis and lymphangiogenesis (2012) Cancer Res., 72, pp. 726-735Brinkmann, V., Fingolimod (FTY720): Discovery and development of an oral drug to treat multiple sclerosis (2010) Nat. Rev. Drug Discov., 9, pp. 883-897Graler, M.H., Goetzl, E.J., The immunosuppressant FTY720 down-regulates sphingosine 1-phosphate G-protein-coupled receptors (2004) FASEB J., 18, pp. 551-553Guo, H., An activated protein C analog stimulates neuronal production by human neural progenitor cells via a PAR1-PAR3-S1PR1-Akt pathway (2013) J. Neurosci., 33, pp. 6181-6190Ishii, I., Fukushima, N., Ye, X., Chun, J., Lysophospholipid receptors: Signaling and biology (2004) Annu. Rev. Biochem., 73, pp. 321-354Walter, D.H., Sphingosine-1-phosphate stimulates the functional capacity of progenitor cells by activation of the CXCR4-dependent signaling pathway via the S1P3 receptor (2007) Arterioscler. Thromb. Vasc. Biol., 27, pp. 275-282Grossberg, A.J., Arcuate nucleus proopiomelanocortin neurons mediate the acute anorectic actions of leukemia inhibitory factor via gp130 (2010) Endocrinology, 151, pp. 606-616Febbraio, M.A., Gp130 receptor ligands as potential therapeutic targets for obesity (2007) J. Clin. Invest., 117, pp. 841-849Samad, F., Hester, K.D., Yang, G., Hannun, Y.A., Bielawski, J., Altered adipose and plasma sphingolipid metabolism in obesity: A potential mechanism for cardiovascular and metabolic risk (2006) Diabetes, 55, pp. 2579-2587Bence, K.K., Neuronal PTP1B regulates body weight, adiposity and leptin action (2006) Nat. Med., 12, pp. 917-924Chiarreotto-Ropelle, E.C., Acute exercise suppresses hypothalamic PTP1B protein level and improves insulin and leptin signaling in obese rats (2013) Am. J. Physiol. Endocrinol. Metab., 305, pp. E649-E659Picardi, P.K., Reduction of hypothalamic protein tyrosine phosphatase improves insulin and leptin resistance in diet-induced obese rats (2008) Endocrinology, 149, pp. 3870-3880Milanski, M., Saturated fatty acids produce an inflammatory response predominantly through the activation of TLR4 signaling in hypothalamus: Implications for the pathogenesis of obesity (2009) J. Neurosci., 29, pp. 359-370Purkayastha, S., Zhang, G., Cai, D., Uncoupling the mechanisms of obesity and hypertension by targeting hypothalamic IKK-beta and NF-kappaB (2011) Nat. Med., 17, pp. 883-887Zhang, X., Hypothalamic IKKbeta/NF-kappaB and ER stress link overnutrition to energy imbalance and obesity (2008) Cell, 135, pp. 61-73Laviano, A., Meguid, M.M., Rossi-Fanelli, F., Cancer anorexia: Clinical implications, pathogenesis, and therapeutic strategies (2003) Lancet Oncol., 4, pp. 686-694Tisdale, M.J., Biology of cachexia (1997) J. Natl Cancer Inst., 89, pp. 1763-1773Pchejetski, D., Circulating sphingosine-1-phosphate inversely correlates with chemotherapy-induced weight gain during early breast cancer (2010) Breast Cancer Res. Treat., 124, pp. 543-549Ponnusamy, S., Communication between host organism and cancer cells is transduced by systemic sphingosine kinase 1/sphingosine 1-phosphate signalling to regulate tumour metastasis (2012) EMBO Mol. Med., 4, pp. 761-775Mellon, P.L., Immortalization of hypothalamic GnRH neurons by genetically targeted tumorigenesis (1990) Neuron, 5, pp. 1-1

Effect of obesity on insulin signaling through JAK2 in rat aorta

Pathway specific resistance to insulin signaling through PI 3-kinase/Akt/eNOS associated with a normal or hyperactivated MAP kinase signaling in vascular tissues has recently been proposed as a candidate link between cardiovascular disease and insulin resistance. Growth stimulatory pathways other than ERK/MAP kinase, such as JAK/STAT have not yet been investigated in vessels of animal models of insulin resistance. Here we have examined whether insulin is able to activate JAK2/STAT pathway in rat aorta and also the regulation of this pathway in an animal model of obesity/insulin resistance. Our results demonstrate that insulin activates JAK2 tyrosine kinase activity in rat aorta in parallel with the activation of STAT3 and STAT5a/b. Moreover, it is shown that, in obese animals, JAK2/STAT and MAP kinase pathways are hyperactivated in response to insulin, which occurs in association with a reduced activation of PI 3-kinase/Akt pathway in aorta. The results of the present study suggest that, besides ERK/MAP kinase pathway, another potentially pro-atherogenic pathway, JAK2/STAT is hyperactivated in vessels in a state of insulin resistance and this phenomenon, in association with the inhibition of the PI 3-kinase/Akt pathway, may play an important role in the pathogenesis of cardiovascular diseases43534635

Statin modulates insulin signaling and insulin resistance in liver and muscle of rats fed a high-fat diet

Recent studies have shown that statins might have relevant effects on insulin resistance in animal models and in humans. However, the molecular mechanisms that account for this improvement in insulin sensitivity are not well established. The aim of the present study was to investigate the effect of a statin on insulin sensitivity and insulin signaling in liver and muscle of rats fed on a high-fat diet (HFD) for 4 weeks, treated or not with lovastatin during the last week. Our data show that treatment with lovastatin results in a marked improvement in insulin sensitivity characterized by an increase in glucose disappearance rate during the insulin tolerance test. This increase in insulin sensitivity was associated with an increase in insulin-induced insulin receptor (IR) tyrosine phosphorylation and, in parallel, a decrease in IR serine phosphorylation and association with PTP1B. Our data also show that lovastatin treatment was associated with an increase in insulin-stimulated insulin receptor substrate (IRS) 1/phosphatidylinositol 3-kinase/Akt pathway in the liver and muscle of HFD-fed rats in parallel with a decrease in the inflammatory pathway (c-jun N-terminal kinase and I kappa β kinase (IKKβ)/inhibitor of κB/nuclear factor κB) related to insulin resistance. In summary, statin treatment improves insulin sensitivity in HFD-fed rats by reversing the decrease in the insulin-stimulated IRS-1/phosphatidylinositol 3-kinase/Akt pathway in liver and muscle. The effect of statins on insulin action is further supported by our findings that HFD rats treated with statin show a reduction in IRS-1 serine phosphorylation, I kappa kinase (IKK)/inhibitor of κB/nuclear factor κB pathway, and c-jun N-terminal kinase activity, associated with an improvement in insulin action. Overall, these results provide important new insight into the mechanism of statin action in insulin sensitivity. © 2008 Elsevier Inc. All rights reserved.Recent studies have shown that statins might have relevant effects on insulin resistance in animal models and in humans. However, the molecular mechanisms that account for this improvement in insulin sensitivity are not well established. The aim of the present study was to investigate the effect of a statin on insulin sensitivity and insulin signaling in liver and muscle of rats fed on a high-fat diet (HFD) for 4 weeks, treated or not with lovastatin during the last week. Our data show that treatment with lovastatin results in a marked improvement in insulin sensitivity characterized by an increase in glucose disappearance rate during the insulin tolerance test. This increase in insulin sensitivity was associated with an increase in insulin-induced insulin receptor (IR) tyrosine phosphorylation and, in parallel, a decrease in IR serine phosphorylation and association with PTP1B. Our data also show that lovastatin treatment was associated with an increase in insulin-stimulated insulin receptor substrate (IRS) 1/phosphatidylinositol 3-kinase/Akt pathway in the liver and muscle of HFD-fed rats in parallel with a decrease in the inflammatory pathway (c-jun N-terminal kinase and 1 kappa beta kinase (IKK beta/inhibitor of kappa B/nuclear factor kappa B) related to insulin resistance. In summary,, statin treatment improves insulin sensitivity in HFD-fed rats by reversing the decrease in the insulin-stimulated IRS-1/phosphatidylinositol 3-kinase/Akt pathway in liver and muscle. The effect of statins on insulin action is further supported by our findings that HFD rats treated with statin show a reduction in IRS-1 serine phosphorylation, I kappa kinase (IKK)/inhibitor of kappa B/ nuclear factor kappa B pathway, and c-jun N-terminal kinase activity, associated with an improvement in insulin action. Overall, these results provide important new insight into the mechanism of statin action in insulin sensitivity571576

Oral supplementation with L-glutamine alters gut microbiota of obese and overweight adults: a pilot study

The aim of this study was to determine whether oral supplementation with L-glutamine (GLN) modifies the gut microbiota composition in overweight and obese adults. Thirty-three overweight and obese adults, ages between 23 and 59 y and body mass index between 25.03 and 47.12 kg/m(2), were randomly assigned to receive either oral supplementation with 30 g of L-alanine (ALA group control) or 30 g of GLN (GLN group) daily for 14 d. We analyzed the gut microbiota composition with new-generation sequencing techniques and bioinformatics analysis. After 14 d of supplementation, adults in the GLN group exhibited statistically significant differences in the Firmicutes and Actinobacteria phyla compared with those in the ALA group. The ratio of Firmicutes to Bacteroidetes, a good biomarker for obesity, decreased in the GLN group from 0.85 to 0.57, whereas it increased from 0.91 to 1.12 in the ALA group. At the genus level, Dialister, Dorea, Pseudobutyrivibrio, and Veillonella, belonging to the Firmicutes phylum, had statistically significant reduction. Oral supplementation with GLN, for a short time, altered the composition of the gut microbiota in overweight and obese humans reducing the Firmicutes to Bacteroidetes ratio, which resembled weight loss programs already seen in the literature.The aim of this study was to determine whether oral supplementation with L-glutamine (GLN) modifies the gut microbiota composition in overweight and obese adults. Thirty-three overweight and obese adults, ages between 23 and 59 y and body mass index between 25.03 and 47.12 kg/m(2), were randomly assigned to receive either oral supplementation with 30 g of L-alanine (ALA group control) or 30 g of GLN (GLN group) daily for 14 d. We analyzed the gut microbiota composition with new-generation sequencing techniques and bioinformatics analysis. After 14 d of supplementation, adults in the GLN group exhibited statistically significant differences in the Firmicutes and Actinobacteria phyla compared with those in the ALA group. The ratio of Firmicutes to Bacteroidetes, a good biomarker for obesity, decreased in the GLN group from 0.85 to 0.57, whereas it increased from 0.91 to 1.12 in the ALA group. At the genus level, Dialister, Dorea, Pseudobutyrivibrio, and Veillonella, belonging to the Firmicutes phylum, had statistically significant reduction. Oral supplementation with GLN, for a short time, altered the composition of the gut microbiota in overweight and obese humans reducing the Firmicutes to Bacteroidetes ratio, which resembled weight loss programs already seen in the literature31688488

Low salt intake modulates insulin signaling, JNK activity and IRS-1(ser307) phosphorylation in rat tissues

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOA severe restriction of sodium chloride intake has been associated with insulin resistance and obesity. The molecular mechanisms by which the low salt diet (LS) can induce insulin resistance have not yet been established. The c-jun N-terminal kinase (JNK) activity has been involved in the pathophysiology of obesity and induces insulin resistance by increasing inhibitory IRS-1(ser307) phosphorylation. In this study we have evaluated the regulation of insulin signaling, JNK activation and IRS-1(ser307) 7 phophorylation in liver, muscle and adipose tissue by immunoprecipitation and immunoblotting in rats fed with LS or normal salt diet (NS) during 9 weeks. LS increased body weight, visceral adiposity, blood glucose and plasma insulin levels, induced insulin resistance and did not change blood pressure. In LS rats a decrease in PI3-K/Akt was observed in liver and muscle and an increase in this pathway was seen in adipose tissue. JNK activity and IRS-1(ser307) phosphorylation were higher in insulin-resistant tissues. In summary, the insulin resistance, induced by LS, is tissue-specific and is accompanied by activation of JNK and IRS-1(ser307) phosphorylation. The impairment of the insulin signaling in these tissues, but not in adipose tissue, may lead to increased adiposity and insulin resistance in LS rats1853429437FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçã

Intracerebroventricular injection of citrate inhibits hypothalamic AMPK and modulates feeding behavior and peripheral insulin signaling

We hypothesized that citrate might modulate the AMP-activated protein kinase/acetyl-CoA carboxylase (AMPK)/(ACC) pathway and participate in neuronal feeding control and glucose homeostasis. To address this issue, we injected citrate into the lateral ventricle of rats. Intracerebroventricular (ICV) injection of citrate diminished the phosphorylation of hypothalamic AMPK/ACC, increased the expression of anorexigenic neuropeptide (pro-opiomelanocortin and corticotropin-releasing hormone), elevated the level of malonyl-CoA in the hypothalamus, and reduced food intake. No change was observed in the concentration of blood insulin after the injection of citrate. With a euglycmic-hyperinsulinemic clamp, the glucose infusion rate was higher in the citrate group than in the control group (28.6 +/- 0.8 vs 19.3 +/- 0.2 mU/kg body weight/min respectively), and so was glucose uptake in skeletal muscle and the epididymal fat pad. Concordantly, insulin receptor (IR), IR substrate type 1 (IRS1), IRS2, and protein kinase B (AKT) phosphorylation in adipose tissue and skeletal muscle was improved by citrate ICV treatment. Moreover, the treatment with citrate for 7 days promoted body weight loss and decreased the adipose tissue. Our results suggest that citrate and glucose may serve as signals of energy and nutrient availability to hypothalamic cells198115716