Regulation of insulin-stimulated tyrosine phosphorylation of Shc and Shc/Grb2 association in liver, muscle, and adipose tissue of epinephrine-and streptozotocin-treated rats

Shc protein phosphorylation has been extensively characterized as the initial step that activates a complex mitogenic pathway through its association with Grb2. In the present study, we investigated the adrenergic control of insulin-induced Shc phosphorylation and Shc-Grb2 association, and the modulating effect of streptozotocin-induced diabetes mellitus on Shc phosphorylation and Shc/Grb2 association. Acute treatment with epinephrine, which leads to a normoglycemic insulin-resistant state, does not affect insulin-induced Shc tyrosine phosphorylation or Shc-Grb2 association in liver, muscle, or fat. By contrast, a significiant increase in insulin-induced Shc phosphorylation is observed in liver and muscle of rats treated with streptozotocin. The association of Shc/Grb2 is also increased in both tissues following insulin treatment. These data suggest that while epinephrine preserves the insulininduced phosphorylation of Shc and the mitogenic pathway stimulated by Shc-Grb2 association, treatment with strep toxotoc in leads to a tissue-specific increase in the activity of the initial step that ultimately results in the activation of the Shc/Grb2 mitogenic pathway.     

OLETF大鼠肝脏、肌肉、脂肪组织中胰岛素受体底物的蛋白表达

各种靶组织的胰岛素抵抗和胰腺β细胞分泌功能受损是导致2型糖尿病的主要原因[1],但机制不明;为探讨2型糖尿病胰岛素抵抗的分子机制,以一种自发发病的2型糖尿病模型-OLETF大鼠为对象,研究其肝脏、骨胳肌、脂肪组织内胰岛素信号传导分子胰岛素受体底物1(IRS-1)蛋白表达水平.     

妊娠期糖尿病发病患者脂肪组织胰岛素受体底物1的表达及其酪氨酸磷酸化水平

目的 研究胰岛素受体底物1(insulin receptor substrate-1,IRS-1)在妊娠期糖尿病(gestational diabetes mellitus,GDM)患者脂肪组织中的表达及其蛋白质酪氨酸磷酸化程度,探讨其与GDM发病的关系.方法 用RT-PCR和Western印迹法分别检测20例GDM患者(GDM组)、20例糖耐量正常孕妇(对照组)脂肪组织中IRS-1 mRNA和蛋白质的表达,用免疫沉淀及增强化学发光法检测IRS-1蛋白酪氨酸磷酸化程度,采用葡萄糖氧化酶法检测两组血糖水平.结果 (1)GDM组脂肪组织中IRS-1 mRNA的表达明显低于对照组(0.61 ±0.06 us 1.12±0.17,P<0.01).(2)与RT-PCR结果一致,GDM组脂肪组织IRS-1蛋白的表达也明显低于对照组(0.57±0.08 us 0.83±0.07,P<0.01).(3)IRS-1蛋白质酪氨酸磷酸化程度GDM组明显低于对照组(0.23±0.06 us 0.62±0.04,P<0.01).结论 GDM患者脂肪组织中IRS-1蛋白的表达及酪氨酸磷酸化下降,可能是GDM胰岛素受体后信号转导障碍而引起胰岛素抵抗的分子机制之一.     

Activation of liver and muscle insulin receptor tyrosine kinase activity during in vivo insulin administration in rats

Summary We have studied autophosphorylation and tyrosine kinase activity of the insulin receptor purified from liver and muscle of fasted rats before and after infusion of insulin (100 mU/h) during a 2.5 h glucose clamp. Recovery of insulin receptors and insulin binding to the solubilised receptors was unaffected by the glucose clamp. Autophosphorylation of the insulin receptor subunit was increased in liver receptors prepared from rats at the end of the glucose clamp compared to rats in the basal state both in the absence of insulin in vitro (109% increase, p<0.001) and after in vitro stimulation with 10^–7 mol/l insulin (clamped vs fasted; 96% increase, p<0.001). Insulin (10^–7 mol/l) stimulated autophosphorylation was also increased in muscle receptor preparations from clamped rats compared with rats in the basal state (58% increase, p<0.05). In both liver and muscle receptors, the clamp increased the amount of [³²P]-phosphate incorporated into the subunit without changing the sensitivity of the insulin stimulation. HPLC analysis of the tryptic phosphopeptides derived from the subunit after insulin stimulated autophosphorylation of liver receptors revealed an increase of ³²P in all phosphorylation sites without any change in the overall pattern. Tyrosine kinase activity of liver and muscle insulin receptors from clamped rats was also increased approximately twofold (p<0.05) when analysed using a synthetic substrate (poly Glu₄ Tyr₁). Our results support the notion that the insulin receptor exists in an active and inactive form, and that elevated plasma insulin concentrations increases the proportion of active receptors.     

Modulation of fatty acid synthesis in vivo in brown adipose tissue, liver and white adipose tissue of cold-acclimated rats

The present experiment was an appraisal of the relative importance of fatty acid synthesis in brown adipose tissue (BAT) in young 28 or 5 degrees C adapted rats (9 weeks old). With a low-fat diet in vivo incorporation of 3H2O into BAT fatty acids was 8 times lower during the day than during the night and was not modified by a 6-hour fast during the day (28 degrees C). Cold acclimation doubled (night) or increased 8 times (day) BAT lipogenesis. Fasting led to a halving of the diurnal rate. A high-fat diet led to large decrease in synthesis rate during the night but had a weak effect on diurnal synthesis. The specific activity of fatty acids was 3 times lower in phospholipids than in neutral lipids. A comparison between 9- and 15-week-old rats indicated that in older warm-adapted rats BAT lipogenesis decreased by half but that cold stimulation was unaltered. These results were compared with hepatic and epididymal white adipose tissue lipogenesis. In conclusion, we showed that BAT of 5 degrees C rats is an important but not the major site for the conversion of carbohydrate to fat and that the proportional involvement of each tissue is age-dependent.     

Influence of insulin on cyclic 3′,5′-AMP phosphodiesterase activity in liver,skeletal muscle,adipose tissue,and kidney

Summary Influence of insulin on liver glycogen metabolism and on lipolysis appears to be mediated by a decreased intracellular 3,5-AMP concentration. Reduced formation of 3,5-AMP had been shown in adipose tissue incubated with insulin. The influence of insulin on 3,5-AMP degradation has been investigated. — 3,5-AMP phosphodiesterase (PDE) activity was reduced in liver, adipose tissue and, insignificantly, in skeletal muscle of insulin deficient, i.e. alloxan diabetic or starved rats. I.V. injection of a low dose of insulin (0.5 U/kg) or stimulation of endogenous insulin secretion by injection of glucose led to a rapid increase of PDE activity in these tissues. 15 min after insulin injection liver PDE activity was increased. The maximal effect occurred after 30–45 min. Renal PDE activity was not decreased in alloxan diabetes, insulin injection has been found ineffective. —In vitro, there was an activating effect of crystalline insulin on PDE purified from beef heart. Insulin concentration required for duplication of enzyme activity was of the order of 2 · 10^–5 M. Treatment with actinomycin D nearly prevented stimulation of liver PDE by insulin. This may indicate that the action of insulin on PDE activity is essentially based on an increased enzyme synthesis. — Owing to the influence of insulin secretion on liver and adipose tissue 3,5-AMP concentration, glycogen metabolism and lipolysis can be quickly adapted to food intake.

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Der Einfluß von Insulin auf die 3,5-AMP-Phosphodiesterase-Aktivität in Leber, Skeletmuskulatur, Fettgewebe und Niere

Zusammenfassung An der Steigerung der Glykogensynthese der Leber und der Verminderung der Lipolyse durch Insulin ist eine Abnahme der 3,5-AMP-Konzentration wesentlich beteiligt. Die 3,5-AMP-Bildung ist in Fettgewebe, das mit Insulin inkubiert wird, vermindert. Insulin beeinflußt jedoch auch den 3,5-AMP-Abbau. -Die 3,5-AMP-Phosphodiesterase (PDE)-Aktivität des Fettgewebes, der Leber und, in geringerem Grade, der Skeletmuskulatur ist im Insulinmangel vermindert, d.h. bei alloxandiabetischen oder hungernden Ratten. I.v. Injektion von 0,5 E/kg Insulin oder eine erhöhte Abgabe von Insulin aus dem Pankreas nach Glucoseinjektion führen in diesen Geweben zu einem raschen Anstieg der PDE-Aktivität. Dieser ist in der Leber schon 15 min nach Insulingabe nachweisbar und erreicht nach 30–45 min sein Maximum. In der Niere ist kein Einfluß von Insulin auf die PDE-Aktivität nachweisbar. — Aus Rinderherz isolierte PDE wirdin vitro durch Insulin aktiviert, jedoch werden2 · 10^–5 M zur Verdopplung der Aktivität benötigt. Actinomycin D verhindert die Steigerung der Leber-PDE-Aktivität nach Insulininjektion. So kann die Wirkung des Hormons im wesentlichen auf eine gesteigerte PDE-Synthese zurückgeführt werden. — Durch diesen Einfluß der Insulininkretion auf die 3,5-AMP-Konzentration in Leber und Fettgewebe können Glykogenstoffwechsel und Lipolyse rasch an die Nahrungsaufnahme angepaßt werden.

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Influence de l'insuline sur l'activité de la 3,5-AMP-phosphodiestérase dans le foie, le muscle strié, le tissu adipeux et le rein

Résumé L'influence de l'insuline sur le métabolisme du glycogène hépatique et sur la lipolyse semble s'exercer par l'intermédiaire d'une diminution de la concentration de 3,5-AMP intracellulaire. Onamontré une diminution de la formation de 35-AMP dans le tissu adipeux incubé avec de l'insuline. L'influence de l'insuline sur la dégradation du 3,5-AMP est étudiée. — L'activité de la 3,5-AMP-phos-phodiestérase (PDE) est diminuée dans le foie, le tissu adipeux et, de façon non-significative, dans le muscle strié des rats qui manquent d'insuline, c-à-d les rats rendus diabétiques par l'alloxane ou les rats privés de nourriture. L'injection intraveineuse d'une faible dose d'insuline (0.5 U/kg) ou la stimulation de la sécrétion d'insuline endogène par une injection de glucose provoquent une augmentation rapide de l'activité de la phosphodiestérase dans ces tissus. 15 min après l'injection d'insuline, l'activité de la phosphodiesterase du foie est augmentée. L'effet maximum est atteint après 30–45 min. L'activité de la phosphodiestérase rénale n'est pas diminuée dans le diabète alloxanique, l'injection d'insuline s'est avérée inefficace.In vitro, l'insuline cristalline a un effet activant sur la phosphodiestérase purifiée du coeur de boeuf. La concentration d'insuline requise pour doubler l'activité de l'enzyme est de l'ordre de 2 · 10^–5 M. Le traitement avec actinomycin D empêche la stimulation par l'insuline de la PDE dans le foie. Ceci peut indiquer que l'action de l'insuline sur l'activité de la phosphodiestérase est essentiellement basée sur une synthèse accrue de l'enzyme. A cause de l'influence de la sécrétion d'insuline sur la concentration en 3,5-AMP du foie et du tissu adipeux, le métabolisme du glycogène et la lipolyse peuvent s'adapter rapidement à la prise de nourriture.

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Non-Standard Abbreviations G 6 P Glucose-6-phosphate - UDPG UDP-glucose - FFA non-esterifled, free fatty acids - 3,5-AMP cyclic adenosine-3,5-monophosphate - PDE 3,5-AMP phosphodiesterase This study was supported by the Deutsche Forschungsgemeinschaft.Deceased October 31, 1967.     

非酒精性脂肪性肝病中脂肪组织胰岛素抵抗与肝巨噬细胞的相互作用

【据《J Hepatol》2019年11月报道】题:非酒精性脂肪性肝病中脂肪组织胰岛素抵抗与肝巨噬细胞的相互作用(作者Rosso C等)非酒精性脂肪性肝病(NAFLD)和脂肪性肝炎(NASH)的发病机制可能是由于紊乱的代谢环境与肝脏炎症和纤维化的局部介质之间的相互作用。该研究旨在阐明巨噬细胞活化、靶器官/组织胰岛素抵抗(IR)与肝损伤之间的相互作用。     

Impact of visceral adipose tissue on liver metabolism and insulin resistance. Part II: Visceral adipose tissue production and liver metabolism

Excess visceral adipose tissue is associated with anomalies of blood glucose homoeostasis, elevation of plasma triglycerides and low levels of high-density lipoprotein cholesterol that contribute to the development of type-2 diabetes and cardiovascular syndromes. Visceral adipose tissue releases a large amount of free fatty acids and hormones/cytokines in the portal vein that are delivered to the liver. The secreted products interact with hepatocytes and various immune cells in the liver. Altered liver metabolism and determinants of insulin resistance associated with visceral adipose tissue distribution are discussed, as well as, determinants of an insulin-resistant state promoted by the increased free fatty acids and cytokines delivered by visceral adipose tissue to the liver.     

Insulin induces tyrosine phosphorylation of Shc and stimulates Shc/GRB2 association in insulin-sensitive tissues of the intact rat

Shc is a novel type of tyrosine-phosphorylated protein activated in response to a wide variety of polypeptide ligands. In this study, we used immunoprecipitation and immunoblotting to examine the effect of insulin on Shc tyrosine phosphorylation and Shc/GRB2 association in insulin-sensitive tissues of the intact rat. Following an infusion of insulin, Shc was tyrosine-phosphorylated in the liver, skeletal muscle, and adipose tissue in a time- and dose-dependent fashion, which peaked 5 min after exposure to the hormone and, except in the case of adipose tissue, returned to basal values after 15 min. There was coimmunoprecipitation of Shc and the insulin receptor after stimulation with insulin. Receptor tyrosine kinase activity toward Shc was also observed. Following an infusion of insulin, Shc was found to associate with GRB2. These results demonstrate that after stimulation of rat tissues with insulin, Shc binds to the insulin receptor, is tyrosine-phosphorylated, and subsequently associates with GRB2.     

Role of insulin receptor substrate-1 serine 307 phosphorylation and adiponectin in adipose tissue insulin resistance in late pregnancy

Insulin resistance is a hallmark of late pregnancy both in human and rat. Adipose tissue is one of the tissues that most actively contributes to this reduced insulin sensitivity. The aim of the present study was to characterize the molecular mechanisms of insulin resistance in adipose tissue at late pregnancy. To this end, we analyzed the insulin signaling cascade in lumbar adipose tissue of nonpregnant and pregnant (d 20) rats both under basal and insulin-stimulated conditions. We found that the levels of relevant signaling proteins, such as insulin receptor (IR), IR substrate-1 (IRS-1), phosphatidylinositol 3-kinase, 3-phosphoinositide-dependent kinase-1, ERK1/2, and phosphatase and tensin homolog (PTEN) did not change at late pregnancy. However, insulin-stimulated tyrosine phosphorylation of both IR and IRS-1 were significantly decreased, coincident with decreased IRS-1/p85 association and impaired phosphorylation of AKR mouse thymoma viral protooncogene (Akt) and ERK1/2. This impaired activation of IRS-1 occurred together with an increase of IRS-1 phosphorylation at serine 307 and a decrease in adiponectin levels. To corroborate the role of IRS-1 in adipose tissue insulin resistance during pregnancy, we treated pregnant rats with the antidiabetic drug englitazone. Englitazone improved glucose tolerance, and this pharmacological reversal of insulin resistance was paralleled by an increase of adiponectin levels in adipose tissue as well as by a reduction of IRS-1 serine phosphorylation. Furthermore, the impaired insulin-stimulated tyrosine phosphorylation of IRS-1 in adipose tissue of pregnant animals could be restored ex vivo by treating isolated adipocytes with adiponectin. Together, our findings support a role for adiponectin and serine phosphorylation of IRS-1 in the modulation of insulin resistance in adipose tissue at late pregnancy.     

Evidence for insulin degradation by muscle and fat tissue in an insulin resistant diabetic patient

Summary The period before, during and after resistance to subcutaneous insulin in a 20-year-old, non-obese insulin-dependent patient with brittle diabetes is documented and clinical observations are correlated with experimental results of insulin degradation in vitro. Treatment with intravenous but not subcutaneous aprotinin markedly reduced subcutaneous insulin requirements. Insulin resistance recurred following cessation of aprotinin. Serum free insulin levels were low during the subcutaneous resistant phase compared with those during the more sensitive phase. Insulin degradation in vitro by adipose tissue and muscle taken from the patient during a resistant phase was increased compared with degradation by tissue taken during a sensitive phase and by tissue from normal subjects. Chromatography of incubation media revealed that during the resistant phase, tissue from the patient degraded insulin to small fragments. It is concluded that, in this patient, insulin resistance was caused by excessive degradation in both muscle and adipose tissue.     

Effects of glucose, insulin and adrenalin on glycerol metabolism in adipose tissue from hypothyroid rats

The in vitro metabolism of glycerol by epididymal fat pads from thyroidectomized rats daily injected with either 0, 0.1 or 1.8 μg of L-thyroxine/100 g body wt. was compared with that from intact controls. The basal as well as the adrenalin- or glucose-enhanced release of glycerol to the medium were similar in the tissues from all the groups. The effect of insulin in decreasing the lipolytic action of adrenalin was greater in the thyroidectomized animals treated with either 0 or 0.1 μg of thyroxine than in the other two groups. The utilization of (1-¹⁴C]glycerol for the formation of CO₂ and glyceride glycerol was increased in the thyroidectomized rats; this effect was smaller when the animals were treated with 0.1 μg of thyroxine and disappeared when they were treated with 1.8 μg. In the presence of glucose the difference in utilization of glycerol between the groups disappeared. The formation of fatty acids from glycerol was greater in the presence than in the absence of glucose and was similar in the hypothyroid animals and the controls. The effect of adrenalin in decreasing the utilization of (1-¹⁴C]glycerol was less in the tissues from hypothyroid rats than in the controls. The decrease of the action of adrenalin by insulin in the tissues from thyroidectomized rats treated with 0 or 0.1 μg of thyroxine was greater than in the controls. The increased capacity to form glyceride glycerol from glycerol in tissues from hypothyroid animals contributes to the high re-esterificatfon of fatty acids described for these animals. The effect of glucose is explained in terms of its competition with glycerol for the synthesis of -glycerophosphate.