Macrophage-derived insulin antagonist ImpL2 induces lipoprotein mobilization upon bacterial infection.

The immune response is an energy-demanding process that must be coordinated with systemic metabolic changes redirecting nutrients from stores to the immune system. Although this interplay is fundamental for the function of the immune system, the underlying mechanisms remain elusive. Our data show that the pro-inflammatory polarization of Drosophila macrophages is coupled to the production of the insulin antagonist ImpL2 through the activity of the transcription factor HIF1α. ImpL2 production, reflecting nutritional demands of activated macrophages, subsequently impairs insulin signaling in the fat body, thereby triggering FOXO-driven mobilization of lipoproteins. This metabolic adaptation is fundamental for the function of the immune system and an individual's resistance to infection. We demonstrated that analogically to Drosophila, mammalian immune-activated macrophages produce ImpL2 homolog IGFBP7 in a HIF1α-dependent manner and that enhanced IGFBP7 production by these cells induces mobilization of lipoproteins from hepatocytes. Hence, the production of ImpL2/IGFBP7 by macrophages represents an evolutionarily conserved mechanism by which macrophages alleviate insulin signaling in the central metabolic organ to secure nutrients necessary for their function upon bacterial infection.

Inceptor counteracts insulin signalling in ß-cells to control glycaemia.

Resistance to insulin and insulin-like growth factor 1 (IGF1) in pancreatic ß-cells causes overt diabetes in mice; thus, therapies that sensitize ß-cells to insulin may protect patients with diabetes against ß-cell failure1-3. Here we identify an inhibitor of insulin receptor (INSR) and IGF1 receptor (IGF1R) signalling in mouse ß-cells, which we name the insulin inhibitory receptor (inceptor; encoded by the gene Iir). Inceptor contains an extracellular cysteine-rich domain with similarities to INSR and IGF1R4, and a mannose 6-phosphate receptor domain that is also found in the IGF2 receptor (IGF2R)5. Knockout mice that lack inceptor (Iir-/-) exhibit signs of hyperinsulinaemia and hypoglycaemia, and die within a few hours of birth. Molecular and cellular analyses of embryonic and postnatal pancreases from Iir-/- mice showed an increase in the activation of INSR-IGF1R in Iir-/- pancreatic tissue, resulting in an increase in the proliferation and mass of ß-cells. Similarly, inducible ß-cell-specific Iir-/- knockout in adult mice and in ex vivo islets led to an increase in the activation of INSR-IGF1R and increased proliferation of ß-cells, resulting in improved glucose tolerance in vivo. Mechanistically, inceptor interacts with INSR-IGF1R to facilitate clathrin-mediated endocytosis for receptor desensitization. Blocking this physical interaction using monoclonal antibodies against the extracellular domain of inceptor resulted in the retention of inceptor and INSR at the plasma membrane to sustain the activation of INSR-IGF1R in ß-cells. Together, our findings show that inceptor shields insulin-producing ß-cells from constitutive pathway activation, and identify inceptor as a potential molecular target for INSR-IGF1R sensitization and diabetes therapy.

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.

Phosphorylation status of fetuin-A is critical for inhibition of insulin action and is correlated with obesity and insulin resistance.

Fetuin-A (Fet-A), a hepatokine associated with insulin resistance, obesity, and incident type 2 diabetes, is shown to exist in both phosphorylated and dephosphorylated forms in circulation. However, studies on fetuin-A phosphorylation status in insulin-resistant conditions and its functional significance are limited. We demonstrate that serum phosphofetuin-A (Ser312) levels were significantly elevated in high-fat diet-induced obese mice, insulin-resistant Zucker diabetic fatty rats, and in individuals with obesity who are insulin resistant. Unlike serum total fetuin-A, serum phosphofetuin-A was associated with body weight, insulin, and markers of insulin resistance. To characterize potential mechanisms, fetuin-A was purified from Hep3B human hepatoma cells. Hep3B Fet-A was phosphorylated (Ser312) and inhibited insulin-stimulated glucose uptake and glycogen synthesis in L6GLUT4 myoblasts. Furthermore, single (Ser312Ala) and double (Ser312Ala + Ser120Ala) phosphorylation-defective Fet-A mutants were without effect on glucose uptake and glycogen synthesis in L6GLUT4 myoblasts. Together, our studies demonstrate that phosphorylation status of Fet-A (Ser312) is associated with obesity and insulin resistance and raise the possibility that Fet-A phosphorylation may play a role in regulation of insulin action.

Catecholamines are the key for explaining the biological relevance of insulin-melatonin antagonisms in type 1 and type 2 diabetes.

In this paper, we analyze the biological relevance of melatonin in diabetogenesis. As has recently been demonstrated, melatonin decreases insulin secretion via specific melatonin receptor isoforms (MT1 and MT2) in the pancreatic ß-cells. In addition, type 2 diabetic rats, as well as patients, exhibit decreased melatonin levels, whereas the levels in type 1 diabetic rats are increased. The latter effects were normalized by insulin substitution, which signifies that a specific receptor-mediated insulin-melatonin antagonism exists. These results are in agreement with several recent genome-wide association studies, which have identified a number of single nucleotide polymorphisms in the MTNR1B gene, encoding the MT2 receptor, that were closely associated with a higher prognostic risk of developing type 2 diabetes. We hypothesize that catecholamines, which decrease insulin levels and stimulate melatonin synthesis, control insulin-melatonin interactions. The present results support this assertion as we show that catecholamines are increased in type 1 but are diminished in type 2 diabetes. Another important line of inquiry involves the fact that melatonin protects the ß-cells against functional overcharge and, consequently, hinders the development of type 2 diabetes. In this context, it is striking that at advanced ages, melatonin levels are reduced and the incidence of type 2 diabetes is increased. Thus, melatonin appears to have a protective biological role. Here, we strongly repudiate misconceptions, resulting from observations that melatonin reduces the plasma insulin level, that the blockage of melatonin receptors would be of benefit in the treatment of type 2 diabetes.

Differential insulin response to myo-inositol administration in obese polycystic ovary syndrome patients.

Polycystic ovary syndrome (PCOS) is characterized by hyperandrogenism, chronic anovulation, polycystic ovaries at ultrasound evaluation, and quite frequently by insulin resistance or compensatory hyperinsulinemia. Attention has been given to the role of inositol-phosphoglycan (IPG) mediators of insulin action and growing evidences suggest that a deficiency of D-chiro-inositol (DCI) containing IPG might be at the basis of insulin resistance, frequent in PCOS patients. On such basis, we investigated the efficacy on insulin sensitivity and hormonal parameters of 8 weeks treatment with myo-inositol (MYO) (Inofert, ItalPharmaco, Milano, Italy) at the dosage of 2 g day in a group (n = 42) of obese PCOS patients,. After the treatment interval body mass index (BMI) and insulin resistance decreased together with luteinizing hormone (LH), LH/FSH and insulin. When subdividing the patients according to their fasting insulin levels, Group A (n = 15) insulin below 12 µU/ml and Group B (n = 27) insulin above 12 µU/ml, MYO treatment induced similar changes in both groups but only patients of Group B showed the significant decrease of both fasting insulin plasma levels (from 20.3 ± 1.8 to 12.9 ± 1.8 µU/ml, p < 0.00001) and of area under the curve (AUC) of insulin under oral glucose tolerance test (OGTT). In conclusion, our study supports the hypothesis that MYO administration is more effective in obese patients with high fasting insulin plasma levels.

Flies on steroids: the interplay between ecdysone and insulin signaling.

In the fruit fly Drosophila melanogaster, the insulin and ecdysone signaling pathways have long been known to regulate growth and developmental timing, respectively. Recent findings reveal that crosstalk between these pathways allows coordination of growth and developmental timing and thus determines final body size.

Activation of muscarinic M-3 receptor may decrease glucose uptake and lipolysis in adipose tissue of rats.

Role of muscarinic receptor in the regulation of glucose uptake or lipolysis in adipose tissue remained unclear. In epididymal white adipose tissue (WAT) isolated from Wistar rats, we observed that acetylcholine (ACh) attenuated the insulin-stimulated glucose uptake and the release of glycerol from WAT in a concentration-dependent manner. Using the blockade of specific antagonists, both actions of ACh were characterized mainly due to an activation of M3 receptors. In the presence of various inhibitors for PLC-PKC pathway, ACh-decreased glucose uptake was also reversed. Taken together, these results suggest that muscarinic M3 receptor is involved in the regulation of glucose uptake and/or lipolysis in adipose tissue.

A novel high-affinity peptide antagonist to the insulin receptor.

In this publication we describe a peptide insulin receptor antagonist, S661, which is a single chain peptide of 43 amino acids. The affinity of S661 for the insulin receptor is comparable to that of insulin and the selectivity for the insulin receptor versus the IGF-1 receptor is higher than that of insulin itself. S661 is also an antagonist of the insulin receptor of other species such as pig and rat, and it also has considerable affinity for hybrid insulin/IGF-1 receptors. S661 completely inhibits insulin action, both in cellular assays and in vivo in rats. A biosynthetic version called S961 which is identical to S661 except for being a C-terminal acid seems to have properties indistinguishable from those of S661. These antagonists provide a useful research tool for unraveling biochemical mechanisms involving the insulin receptor and could form the basis for treatment of hypoglycemic conditions.

Glycogen synthase kinase 3 is an insulin-regulated C/EBPalpha kinase.

CCAAT/enhancer binding protein alpha (C/EBPalpha) is a transcription factor involved in creating and maintaining the adipocyte phenotype. We have shown previously that insulin stimulates dephosphorylation of C/EBPalpha in 3T3-L1 adipocytes. Studies to identify the insulin-sensitive sites of phosphorylation reveal that a C/EBPalpha peptide (amino acids H215 to K250) is phosphorylated on T222, T226, and S230 in vivo. The context of these phosphoamino acids implicates glycogen synthase kinase 3 (GSK3), whose activity is known to be repressed in response to insulin, as a potential kinase for phosphorylation of T222 and T226. Accordingly, GSK3 phosphorylates the predicted region of C/EBPalpha on threonine in vitro, and GSK3 uses C/EBPalpha as a substrate in vivo. In addition, the effect of pharmacological agents on GSK3 activity correlates with regulation of C/EBPalpha phosphorylation. Treatment of 3T3-L1 adipocytes with the phosphatidylinositol 3-kinase inhibitor wortmannin results in phosphorylation of C/EBPalpha, whereas treatment with the GSK3 inhibitor lithium results in dephosphorylation of C/EBPalpha. Collectively, these data indicate that insulin stimulates dephosphorylation of C/EBPalpha on T222 and T226 through inactivation of GSK3. Since dephosphorylation of C/EBPalpha in response to lithium is blocked by okadaic acid, strong candidates for the T222 and T226 phosphatase are protein phosphatases 1 and 2a. Treatment of adipocytes with insulin alters the protease accessibility of widespread sites within the N terminus of C/EBPalpha, consistent with phosphorylation causing profound conformational changes. Finally, phosphorylation of C/EBPalpha and other substrates by GSK3 may be required for adipogenesis, since treatment of differentiating preadipocytes with lithium inhibits their conversion to adipocytes.

L-diabetes--causes, pathogenesis and therapy.

L-diabetes represents a subtype of non-autoimmunopathic and non-adipose diabetes mellitus. It is hypothesized that ATP-sensory brain centres measure the cerebral ATP concentration and announce a hypoglycaemia if the setpoint is undercut. The disease involves a decreased ATP formation in the CNS that is independent of blood glucose levels, and that leads to a "hypoglycaemia" false alarm. UGT1-polymorphisms, a sensitive sympathetic system, an IgM deficit and an increased porousity of the mucous membrane of the small intestine have been postulated in its etiology. These causative factors bring about increasing amounts of toxins and radicals which impair the ATP generation in the CNS so that through the announcement of a non-existing hypoglycaemia the release of the insulin antagonists hGH, cortisol and adrenaline is induced.

Toward a better understanding of Klotho.

klotho mutant mice were originally described as a short-lived mouse model with premature aging-like disorders. The klotho gene responsible for these phenotypes encodes a type I membrane protein with a considerable similarity to beta-glycosidase. klotho is predominantly expressed in tissues functioning in the regulation of calcium homeostasis. Suggested functions of Klotho are (i) a fundamental regulator of calcium homeostasis, namely, a cofactor for the fibroblast growth factor (FGF) receptor 1c in FGF23 signaling and a regulator of parathyroid hormone secretion; (ii) a hormone that interferes with the intracellular signaling of insulin and insulin-like growth factor-1; and (iii) a beta-glucuronidase that activates the transient receptor potential ion channel TRPV5 by trimming its sugar moiety. How can we reconcile these pleiotropic functions of Klotho? Is there any common mechanism? Further in vivo studies, and biochemical as well as physiological analyses, are required for a better understanding of the molecular aspects of Klotho.

Severity, duration, and mechanisms of insulin resistance during acute infections.

Acute infections provoke insulin resistance. These experiments were designed to study the severity, duration, and mechanisms of insulin resistance caused by acute infections. First, we studied eight patients [mean age, 29 +/- 11 (+/- SD) yr; body mass index, 23 +/- 2 kg/m2] with acute viral or bacterial infections during the acute stage of their infection and 1-3 months after recovery. The rate of glucose infusion required to maintain normoglycemia during hyperinsulinemia (approximately 500 pmol/L) was used as a measure of insulin action. During infection, the glucose requirements in the patients [21 +/- 2 (+/- SE) mumol/kg.min] were 52% less than those in weight- and age-matched normal subjects (44 +/- 2 mumol/kg.min; P less than 0.001). Compared to data from a large group of normal subjects, the resistance to insulin during infection corresponded to that predicted for a weight-matched 84-yr-old normal person or an age-matched obese person with a body mass index of 37 kg/m2. One to 3 months after recovery, the patients' glucose requirements were still significantly lower (37 +/- 3 mumol/kg.min; P less than 0.02) than those in matched normal subjects. To assess the mechanism of insulin resistance, seven additional patients were studied during the acute stage of infection using a low dose insulin infusion (plasma insulin, 215 pmol/L) combined with a [3-3H]glucose infusion and indirect calorimetry. Again, the glucose requirements were 59% lower in the patients (14 +/- 2 mumol/kg.min) than in matched normal subjects (34 +/- 2 mumol/kg.min; P less than 0.001). This decrease was due to a defect in glucose utilization (18 +/- 2 vs. 37 +/- 1 mumol/kg.min; P less than 0.001, patients vs. normal subjects) rather than impaired suppression of glucose production (4 +/- 1 vs. 3 +/- 1 mumol/kg.min, respectively). Total carbohydrate oxidation rates were similar in both groups (16 +/- 2 vs. 14 +/- 1 mumol/kg.min, respectively), whereas the apparent glucose storage was neglible in the patients (2 +/- 1 mumol/kg.min) compared to that in normal subjects (22 +/- 2 mumol/kg.min; P less than 0.001). We conclude that acute infections induce severe and long-lasting insulin resistance, which is localized to glucose-utilizing pathways. The rate of carbohydrate oxidation is normal during infections, whereas the rate of nonoxidative glucose disposal, as determined by indirect calorimetry, is nearly zero. The apparent blockade in glucose storage could result from diminished glycogen synthesis, accelerated glycogenolysis, or both.

Evidence that amiloride antagonises insulin-stimulated protein phosphorylation by inhibiting protein kinase activity.

The diuretic drug amiloride antagonises the insulin-dependent increase in phosphorylation of ATP-citrate lyase in hepatocytes isolated from rats that had been starved and refed a fat-free diet. Studies with a range of protein kinases and protein phosphatases that have been shown to phosphorylate or dephosphorylate purified ATP-citrate lyase in vitro revealed that amiloride was a non-specific inhibitor of all protein kinases tested, but did not significantly affect any of the protein phosphatases. These results cast doubt on previous claims that growth factors stimulate phosphorylation of ribosomal protein S6 by activating an amiloride-sensitive Na+/H+ exchange system, and that insulin inhibits a protein phosphatase that is activated by amiloride.

Expression of human islet amyloid polypeptide/amylin impairs insulin secretion in mouse pancreatic beta cells.

Non-insulin-dependent diabetes mellitus (NIDDM) is associated histopathologically with islet amyloid deposits of which a major component is islet amyloid polypeptide (IAPP)/amylin. We examined whether endogenous IAPP controls insulin secretion via a local effect within pancreatic islets and whether overexpression of this peptide contributes to pancreatic beta-cell dysfunction in this disease. Transgenic mice expressing human IAPP in pancreatic beta cell were used in this study. Human IAPP expression did not influence the mouse proinsulin mRNA level and insulin content. Glucose-induced insulin secretion was decreased in the isolated pancreatic islets of transgenic mice. MIN6, a glucose-responsive pancreatic beta-cell line, was transfected with human IAPP cDNA by a lipofectin method. Human IAPP expression was confirmed by RNA blot and immunohistochemical analysis. In two transfectants expressing the largest amount of human IAPP, insulin secretion was increased in response to glucose stimulation; however, the magnitude of the insulin response in cells transfected with human IAPP was smaller than in control clones. Insulin content was not influenced by the expression. We conclude that endogenous IAPP inhibits insulin secretion via an autocrine effect within pancreatic islets, and that the impaired insulin secretion in this disease may be partly caused by overexpression of IAPP.

Regulation of insulin-like growth factor binding protein-1 (IGFBP-1) in insulin-dependent diabetes mellitus. Effects of hyperglycaemia and insulin.

The aim of the present study was to characterize the effect of 44 h of hyperglycaemia on diurnal levels of insulin-like growth factor binding protein-1 (IGFBP-1), insulin-like growth factor-1 (IGF-1), growth hormone (GH) and glucagon in 7 well-controlled subjects with insulin-dependent diabetes mellitus (IDDM). Hyperglycaemia (approximately 15 mmol/l) was induced by a glucose infusion, while the degree of insulinisation was similar to that of a corresponding period with near normoglycaemia (approximately 6.9 mmol/l). Hyperglycaemia for 44 h did not alter the normal diurnal IGFBP-1 levels when the degree of insulinisation was unchanged. The diurnal secretion pattern of IGFBP-1 was preserved in both genders and without any difference between the control and hyperglycaemic periods. However, the IGFBP-1 levels were increased in these IDDM subjects despite a peripheral hyperinsulinemia. An inverse correlation was found between IGFBP-1 and peripheral insulin levels both during periods of rapid changes in IGFBP-1 and insulin concentrations (i.e. morning hours) as well as during the total 24-h sampling period. Total IGF-1 levels were low, but no further decrease was seen after 24 h of hyperglycaemia in the presence of unchanged insulin levels. In conclusion, the present study clearly shows that the increased IGFBP-1 level seen during poor metabolic control in IDDM is not caused by hyperglycaemia. Glucose levels per se do not influence either total IGF-1 or IGFBP-1 concentrations in well-insulinised diabetic patients.

[Hypoglycemic effect of thymosine in an animal experiment]. / Gipoglikemicheskii éffekt timozina v éksperimente na zhivotnykh.

Short-term hypoglycemic effect of thymosin was found in intact mice and in animals with alloxan diabetes: single intramuscular administration of 5 mg/kg of thymosin was accompanied by a decrease in glucose content in blood within 15-30 min. Increase in content of immunoreactive insulin in blood was responsible for the hypoglycemia, while the direct insulinotropic effect of thymosin was not observed in isolated pancreas.

Interference of selenium and selenoproteins with the insulin-regulated carbohydrate and lipid metabolism.

An assumed link between supranutritional intake of the micronutrient selenium (Se) and type 2 diabetes mellitus is discussed controversially. Se concentrations in the habitual diet and in dietary supplements are probably not sufficient to induce overt diabetes in healthy individuals. On the other hand, high plasma Se and selenoprotein P (Sepp1) levels have been found to be associated with biomarkers of an impaired carbohydrate and lipid homeostasis in humans. Moreover, abundant expression of antioxidant selenoproteins due to dietary Se oversupply resulted in hyperinsulinemia and decreased insulin sensitivity in animal models. This review discusses findings from animal and cell culture studies in search of molecular mechanisms underlying an interference of Se and selenproteins such as the Se transport and supply protein Sepp1 and the hydrogen peroxide-reducing selenoenzyme glutathione peroxidase 1 (GPx1) with insulin-controlled metabolic pathways. A probable rationale derives from the positive and negative regulation of both glucose-induced insulin secretion and insulin-induced signaling by hydrogen peroxide. Se status and GPx1 expression have been reported to affect the activity of insulin-antagonistic phosphatases that are regulated by hydrogen peroxide-mediated reversible oxidation of catalytic cysteine residues. GPx1 and/or Sepp1 inhibited phosphorylation (activation) of key mediators in energy metabolism such as protein kinase B (Akt) and AMP-activated protein kinase (AMPK) in liver and/or skeletal muscle. Conversely, a dys-regulated carbohydrate metabolism in diabetes might affect plasma Se and Sepp1 levels, as the hepatic biosynthesis of Sepp1 is suppressed by insulin and stimulated under hyperglycemic conditions.

Islet ß-cell ghrelin signaling for inhibition of insulin secretion.

Ghrelin, an acylated 28-amino acid peptide, was isolated from the stomach, where circulating ghrelin is produced predominantly. In addition to its unique role in regulating growth-hormone release, mealtime hunger, lipid metabolism, and the cardiovascular system, ghrelin is involved in the regulation of glucose metabolism. Ghrelin is expressed in pancreatic islets and released into pancreatic microcirculations. Ghrelin inhibits insulin release in mice, rats, and humans. Pharmacological and genetic blockades of islet-derived ghrelin markedly augment glucose-induced insulin release. The signal transduction mechanisms of ghrelin in islet ß-cells are very unique, being distinct from those utilized for growth-hormone release. Ghrelin attenuates the glucose-induced cAMP production and PKA activation, which drives activation of Kv channels and suppression of the glucose-induced [Ca(2+)](i) increase and insulin release in ß-cells. Insulinostatic function of the ghrelin-GHS-R system in islets is a potential therapeutic target for type 2 diabetes.