Insulin signalling in the hypothalamus plays a role in maintaining body weight. The forkhead transcription factor Foxo1 is
an important mediator of insulin signalling in the hypothalamus. Foxo1 ...stimulates the transcription of the orexigenic neuropeptide
Y and Agouti-related protein through the phosphatidylinositol-3-kinase/Akt signalling pathway, but the role of hypothalamic
Foxo1 in insulin resistance and obesity remains unclear. Here, we identify that a high-fat diet impaired insulin-induced hypothalamic
Foxo1 phosphorylation and degradation, increasing the nuclear Foxo1 activity and hyperphagic response in rats. Thus, we investigated
the effects of the intracerebroventricular ( i.c.v. ) microinfusion of Foxo1-antisense oligonucleotide (Foxo1-ASO) and evaluated the food consumption and weight gain in normal
and diet-induced obese (DIO) rats. Three days of Foxo1-ASO microinfusion reduced the hypothalamic Foxo1 expression by about
85%. i.c.v. infusion of Foxo1-ASO reduced the cumulative food intake (21%), body weight change (28%), epididymal fat pad weight (22%)
and fasting serum insulin levels (19%) and increased the insulin sensitivity (34%) in DIO but not in control animals. Collectively,
these data showed that the Foxo1-ASO treatment blocked the orexigenic effects of Foxo1 and prevented the hyperphagic response
in obese rats. Thus, pharmacological manipulation of Foxo1 may be used to prevent or treat obesity.
Obesity and type 2 diabetes are characterized by insulin resistance, and the common basis of these events is a chronic and systemic inflammatory process marked by the activation of the c-Jun ...N-terminal kinase (JNK) and inhibitor-κB kinase (IKKβ)/nuclear factor-κB (NFκB) pathways, up-regulated cytokine synthesis, and endoplasmic reticulum dysfunction. The aim of this study was to evaluate the effects of diacerhein administration, an antiinflammatory drug that reduces the levels of inflammatory cytokines, on insulin sensitivity and signaling in diet-induced obese (DIO) mice. Swiss mice were fed with conventional chow (control group) or a high-fat diet (DIO group). Later, DIO mice were randomly subdivided into a new subgroup (DAR) that received 20 mg/kg diacerhein for 10 d. Western blotting was used to quantify the expression and phosphorylation of insulin receptor, insulin receptor substrate 1, and Akt and of inflammatory mediators that modulate insulin signaling in a negative manner (IKKβ, JNK, and inducible nitric oxide synthase). We show here, for the first time, that the administration of diacerhein in DIO mice improved endoplasmic reticulum stress, reduced JNK and IKKβ phosphorylation, and resulted in a marked improvement in fasting glucose, a decrease in macrophage infiltration in adipose tissue, and a reduced expression and activity of proinflammatory mediators accompanied by an improvement in the insulin signaling mainly in the liver and adipose tissue. Taken together, these results indicate that diacerhein treatment improves insulin sensitivity in obesity, mediated by the reversal of subclinical inflammation, and that this drug may be an alternative therapy for insulin resistance.
The pathogenesis of cancer anorexia is multifactorial and associated with disturbances of the central physiological mechanisms controlling food intake. However, the neurochemical mechanisms ...responsible for cancer-induced anorexia are unclear. Here we show that chronic infusion of 5-amino-4imidazolecarboxamide-riboside into the third cerebral ventricle and a chronic peripheral injection of 2 deoxy-d-glucose promotes hypothalamic AMP-activated protein kinase (AMPK) activation, increases food intake, and prolongs the survival of anorexic tumor-bearing (TB) rats. In parallel, the pharmacological activation of hypothalamic AMPK in TB animals markedly reduced the hypothalamic production of inducible nitric oxide synthase, IL-1β, and TNF-α and modulated the expression of proopiomelanocortin, a hypothalamic neuropeptide that is involved in the control of energy homeostasis. Furthermore, the daily oral and intracerebroventricular treatment with biguanide antidiabetic drug metformin also induced AMPK phosphorylation in the central nervous system and increased food intake and life span in anorexic TB rats. Collectively, the findings of this study suggest that hypothalamic AMPK activation reverses cancer anorexia by inhibiting the production of proinflammatory molecules and controlling the neuropeptide expression in the hypothalamus, reflecting in a prolonged life span in TB rats. Thus, our data indicate that hypothalamic AMPK activation presents an attractive opportunity for the treatment of cancer-induced anorexia.
The actions of acetylcholine (ACh) on endothelium mainly are mediated through muscarinic receptors, which are members of the G protein-coupled receptor family. In the present study, we show that ACh ...induces rapid tyrosine phosphorylation and activation of Janus kinase 2 (JAK2) in rat aorta. Upon JAK2 activation, tyrosine phosphorylation of insulin receptor substrate (IRS)-1 is detected. In addition, ACh induces JAK2/IRS-1 and IRS-1/phosphatidylinositol (PI) 3-kinase associations, downstream activation of Akt/protein kinase B, endothelial cell-nitric oxide synthase (eNOS), and extracellular signal-regulated kinase (ERK)-1/2. The pharmacological blockade of JAK2 or PI 3-kinase reduced ACh-stimulated eNOS phosphorylation, NOS activity, and aorta relaxation. These data indicate a new signal transduction pathway for IRS-1/PI 3-kinase/Akt/eNOS activation and ERK1/2 by means of JAK2 tyrosine phosphorylation stimulated by ACh in vessels. Moreover, we demonstrate that in aorta of obese rats (high-fat diet), there is an impairment in the insulin- and ACh-stimulated IRS-1/PI 3-kinase pathway, leading to reduced activation with lower protein levels of eNOS associated with a hyperactivated ERK/mitogen-activated protein kinase pathway. These results suggest that in aorta of obese rats, there not only is insulin resistance but also ACh resistance, probably mediated by a common signaling pathway that controls the activity and the protein levels of eNOS.
To evaluate the effects of intensity of exercise on insulin resistance and the expression of inflammatory proteins in the skeletal muscle of diet-induced obese (DIO) rats after a single bout of ...exercise.
In the first exercise protocol, the rats swam for two 3-h bouts, separated by a 45-min rest period (with 6 h in duration--O + EXE), and in the second protocol, the rats were exercised with 45 min of swimming at 70% of the maximal lactate steady state--SS (DIO + MLSS).
Our data demonstrated that both protocols of exercise increased insulin sensitivity and increased insulin-stimulated tyrosine phosphorylation of insulin receptor and insulin receptor substrate 1 and serine phosphorylation of protein kinase B in the muscle of DIO rats by the same magnitude. In parallel, both exercise protocols also reduced protein tyrosine phosphatase 1B activity and insulin receptor substrate 1 serine phosphorylation, with concomitant reduction in c-jun N-terminal kinase and IJB kinase activities in the muscle of DIO rats in a similar fashion.
Thus, our data demonstrate that either exercise protocols with low intensity and high volume or exercise with moderate intensity and low volume represents different strategies to restore insulin sensitivity with the same efficacy.
Consumption of dietary fats is amongst the most important environmental factors leading to obesity. In rodents, the consumption of fat-rich diets blunts leptin and insulin anorexigenic signaling in ...the hypothalamus by a mechanism dependent on the in situ activation of inflammation. Since inflammatory signal transduction can lead to the activation of apoptotic signaling pathways, we evaluated the effect of high-fat feeding on the induction of apoptosis of hypothalamic cells. Here, we show that consumption of dietary fats induce apoptosis of neurons and a reduction of synaptic inputs in the arcuate nucleus and lateral hypothalamus. This effect is dependent upon diet composition, and not on caloric intake, since pair-feeding is not sufficient to reduce the expression of apoptotic markers. The presence of an intact TLR4 receptor, protects cells from further apoptotic signals. In diet-induced inflammation of the hypothalamus, TLR4 exerts a dual function, on one side activating pro-inflammatory pathways that play a central role in the development of resistance to leptin and insulin, and on the other side restraining further damage by controlling the apoptotic activity.
Objective: To investigate whether insulin and leptin share common intracellular signal transduction pathways and to determine whether these hormonal signaling systems modulate each other's action in ...rat hypothalamus.
Research Methods and Procedures: Male Wistar rats were studied after chronic implantation of an intracerebroventricular catheter into the third ventricle. Immunoprecipitation and immunoblotting were used to examine the activation of insulin and leptin signaling molecules in the rat hypothalamus.
Results: Insulin alone is able to produce molecular activation of insulin receptor substrates (IRSs)/phosphatidylinositol 3‐kinase (PI 3‐kinase)/Akt and mitogen‐activated protein (MAP) kinase signaling pathways in hypothalamus, whereas leptin alone activates MAP kinase and IRSs/PI 3‐kinase signaling with no effect on Akt. Combined infusion of leptin and insulin provokes a dual action. There was no quantitative potentialization of any single hormone's action on the elements of the insulin signaling pathway, IRSs/PI 3‐kinase/Akt, and MAP kinase. Conversely, leptin plus insulin leads to quantitative potentialization of molecular signaling through the Janus kinase/signal transducer and activator of transcription pathway.
Discussion: We provide evidence for a convergence of leptin and insulin signaling at the level of IRSs‐PI 3‐kinase and a divergence at the level of Akt. Moreover, our results indicate a direct and positive cross‐talk between insulin and leptin at the level of Janus kinase 2 and signal transducer and activator of transcription 3 tyrosine phosphorylation. This mechanism may serve to potentiate the activity of both insulin and leptin pathways and to increase stimulation in physiological processes such as the control of food intake and body weight, which are under the combined control of insulin and leptin.
Evidence demonstrates that exogenous nitric oxide (NO) and the NO produced by inducible nitric oxide synthase (iNOS) can induce insulin resistance in muscle. Here, we investigated whether this ...insulin resistance could be mediated by S-nitrosation of proteins involved in early steps of the insulin signal transduction pathway. Exogenous NO donated by S-nitrosoglutathione (GSNO) induced in vitro and in vivo S-nitrosation of the insulin receptor beta subunit (IRbeta) and protein kinase B/Akt (Akt) and reduced their kinase activity in muscle. Insulin receptor substrate (IRS)-1 was also rapidly S-nitrosated, and its expression was reduced after chronic GSNO treatment. In two distinct models of insulin resistance associated with enhanced iNOS expression-diet-induced obesity and the ob/ob diabetic mice-we observed enhanced S-nitrosation of IRbeta/IRS-1 and Akt in muscle. Reversal of S-nitrosation of these proteins by reducing iNOS expression yielded an improvement in insulin action in both animal models. Thus, S-nitrosation of proteins involved in insulin signal transduction is a novel molecular mechanism of iNOS-induced insulin resistance.
In experimental models, hypothalamic inflammation is an early and determining factor in the installation and progression of obesity. Pharmacological and gene-based approaches have proven efficient in ...restraining inflammation and correcting the obese phenotypes. However, the role of nutrients in the modulation of hypothalamic inflammation is unknown.
Here we show that, in a mouse model of diet-induced obesity, partial substitution of the fatty acid component of the diet by flax seed oil (rich in C18:3) or olive oil (rich in C18:1) corrects hypothalamic inflammation, hypothalamic and whole body insulin resistance, and body adiposity. In addition, upon icv injection in obese rats, both ω3 and ω9 pure fatty acids reduce spontaneous food intake and body mass gain. These effects are accompanied by the reversal of functional and molecular hypothalamic resistance to leptin/insulin and increased POMC and CART expressions. In addition, both, ω3 and ω9 fatty acids inhibit the AMPK/ACC pathway and increase CPT1 and SCD1 expression in the hypothalamus. Finally, acute hypothalamic injection of ω3 and ω9 fatty acids activate signal transduction through the recently identified GPR120 unsaturated fatty acid receptor.
Unsaturated fatty acids can act either as nutrients or directly in the hypothalamus, reverting diet-induced inflammation and reducing body adiposity. These data show that, in addition to pharmacological and genetic approaches, nutrients can also be attractive candidates for controlling hypothalamic inflammation in obesity.
The insulin resistance associated with aging is improved by exercise, but the molecular mechanisms of this improvement are not fully understood. We investigated whether the improvement in insulin ...action, associated with acute exercise in old rats is dependent on the modulation of pIRS-1Ser307, JNK, IkBα and PTP-1B. Aging rats were subjected to swimming for two 1.5-h long bouts, separated by a 45
min rest period. Sixteen hours after the exercise, the rats were killed and proteins from the insulin signaling pathway were analyzed by immunoblotting. Our results show that the reduction in glucose disappearance rate (Kitt), observed in aged rats, was restored at 16
h after exercise. Aging led to an increase in Ser307 phosphorylation of IRS-1, and this was reversed by exercise in the skeletal muscle, in parallel with a reduction in pJNK and IkBα degradation. Moreover, aging induced an increase in the expression of PTP-1B and attenuated insulin signaling in the muscle of rats, a phenomenon that was reversed by exercise. Interestingly, the decrease in PTP-1B expression in the muscle of exercised old rats was accompanied by an increase in SIRT1 expression. These results provide new insights into the mechanisms by which exercise restores insulin sensitivity during aging.
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