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.

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.

Molecular process of glucose uptake and glycogen storage due to hamamelitannin via insulin signalling cascade in glucose metabolism.

Understanding the mechanism by which the exogenous biomolecule modulates the GLUT-4 signalling cascade along with the information on glucose metabolism is essential for finding solutions to increasing cases of diabetes and metabolic disease. This study aimed at investigating the effect of hamamelitannin on glycogen synthesis in an insulin resistance model using L6 myotubes. Glucose uptake was determined using 2-deoxy-D-[1-3H] glucose and glycogen synthesis were also estimated in L6 myotubes. The expression levels of key genes and proteins involved in the insulin-signaling pathway were determined using real-time PCR and western blot techniques. The cells treated with various concentrations of hamamelitannin (20 µM to 100 µM) for 24 h showed that, the exposure of hamamelitannin was not cytotoxic to L6 myotubes. Further the 2-deoxy-D-[1-3H] glucose uptake assay was carried out in the presence of wortmannin and Genistein inhibitor for studying the GLUT-4 dependent cell surface recruitment. Hamamelitannin exhibited anti-diabetic activity by displaying a significant increase in glucose uptake (125.1%) and glycogen storage (8.7 mM) in a dose-dependent manner. The optimum concentration evincing maximum activity was found to be 100 µm. In addition, the expression of key genes and proteins involved in the insulin signaling pathway was studied to be upregulated by hamamelitannin treatment. Western blot analysis confirmed the translocation of GLUT-4 protein from an intracellular pool to the plasma membrane. Therefore, it can be conceived that hamamelitannin exhibited an insulinomimetic effect by enhancing the glucose uptake and its further conversion into glycogen by regulating glucose metabolism.

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.

Prolonged stimulation of ß2-adrenergic receptor with ß2-agonists impairs insulin actions in H9c2 cells.

Insulin resistance is a condition in which there is a defect in insulin actions to induce glucose uptake into the cells. Overstimulation of ß2-adrenergic receptors (ß2ARs) is associated with the pathogenesis of insulin resistance in the heart. However, the mechanisms by which ß2-agonists affect insulin resistance in the heart are incompletely understood. The ß2-agonists are used for treatment of asthma due to bronchodilating effects. We also investigated the effects of ß2-agonists in human bronchial smooth muscle (HBSM) cells. In this study, we demonstrate that chronic treatment with salbutamol, salmeterol, and formoterol inhibited insulin-induced glucose uptake and GLUT4 synthesis in H9c2 myoblast cells. Sustained ß2AR stimulation also attenuated GLUT4 translocation to the plasma membrane, whereas short-term stimulation had no effect. In HBSM cells, prolonged treatment with ß2-agonists had no effect on insulin-induced glucose uptake and did not alter insulin-induced expressions of GLUT1, GLUT4, and GLUT10. In addition, genetic polymorphisms at amino acid positions 16 and 27 of ß2AR are linked to insulin resistance by significant suppression of GLUT4 translocation compared to wild-type. Thus, prolonged ß2AR stimulation by ß2-agonists impairs insulin actions through suppression of GLUT synthesis and translocation only in H9c2 cells.

Hot topic: Ceramide inhibits insulin sensitivity in primary bovine adipocytes.

In nonruminants, the sphingolipid ceramide inhibits insulin sensitivity by inactivating protein kinase B (AKT) within the insulin-signaling pathway. We have established that ceramide accrual develops with impaired systemic insulin action in ruminants during the transition from gestation to lactation, dietary palmitic acid supplementation, or controlled nutrient restriction. We hypothesized that ceramide promotes AKT inactivation and antagonizes insulin sensitivity in primary bovine adipocytes. Stromal-vascular cells were grown from bovine adipose tissue explants and cultured in differentiation media. To modify ceramide supply, we treated differentiated adipocytes with (1) myriocin, an inhibitor of de novo ceramide synthesis, or (2) cell-permeable C2:0-ceramide. Insulin-stimulated AKT activation (i.e., phosphorylation) and 2-deoxy-D-[3H]-glucose (2DOG) uptake were measured. Treatment of adipocytes with myriocin consistently decreased concentrations of ceramide, monohexosylceramide, and lactosylceramide. The insulin-stimulated ratio of phosphorylated AKT to total AKT was increased with myriocin but decreased with C2:0-ceramide. Moreover, adipocyte insulin-stimulated 2DOG uptake was decreased with C2:0-ceramide and increased with myriocin. We conclude that ceramide inhibits insulin-stimulated glucose uptake by downregulating AKT activation in primary bovine adipocytes.

Screening and biological evaluation of myricetin as a multiple target inhibitor insulin, epidermal growth factor, and androgen receptor; in silico and in vitro.

Myricetin is a naturally omnipresent benzo-α-pyrone flavonoids derivative; has potent anticancer activity. Receptor tyrosine kinases family provides the decisive role in cancer initiation and progression. These receptors have recently caught the attention of the researchers as an attractive target to combat cancer, owing to the evidences endorsed their over-expression on cancer cells. This study is a concerted effort to explore the potent and specific multi-targeted inhibitor against RTKs and AR\ER employing molecular docking approach. IR, IGF1R, EGFR, VEGFR1, VEGFR2, and AR\ER were chosen as a protein and natural compounds as a ligand. Molecular docking procedure followed by using Maestro 9.6 (Schrödinger Inc). All natural compounds were docked with the X-ray crystal structures of selected proteins by employing grid-based ligand docking with energetics Maestro 9.6. IBS natural compounds docked with each selected protein molecules by using GLIDE high throughput virtual screening. On the basis of Gscore, we selected 20 compounds from IBS (50,000 compounds) along with 68 anticancer compounds from published literature for GLIDE extra precision molecular docking. Calculated docking free energy yielded the excellent dock score for the myricetin when docked with proteins EGFR, IR, and AR\ER. Protein-ligand interactions profile highlighted that the lipophilic, hydrogen bonding and π-π stacking interactions play a central role in protein-ligand interactions at the active site. The results of MTT assay reveal that the myricetin inhibit the viability and proliferation of cancer cells in a dose-dependent manner. Treatment with the myricetin led to down-regulation of mRNA expression of EGFR, IR, mTOR, and Bcl-2. Although, further in vitro and in vivo experimental studies are required for the experimental validation of our findings.

Design and synthesis of new potassium channel activators derived from the ring opening of diazoxide: study of their vasodilatory effect, stimulation of elastin synthesis and inhibitory effect on insulin release.

Benzenesulfonylureas and benzenesulfonylthioureas, as well as benzenecarbonylureas and benzenecarbonylthioureas, were prepared and evaluated as myorelaxants on 30mMKCl-precontracted rat aortic rings. The most active compounds were further examined as stimulators of elastin synthesis by vascular smooth muscle cells and as inhibitors of insulin release from pancreaticß-cells. The drugs were also characterized for their effects on glycaemia in rats. Benzenesulfonylureas and benzenesulfonylthioureas did not display any myorelaxant activity on precontracted rat aortic rings. Such an effect could be attributed to their ionization at physiological pH. By contrast, almost all benzenecarbonylureas and benzenecarbonylthioureas displayed a myorelaxant activity, in particular the benzenecarbonylureas with an oxybenzyl group linked to the ortho position of the phenyl ring. The vasodilatory activity of the most active compounds was reduced when measured in the presence of 80mMKCl or in the presence of 30mM KCl and 10µM glibenclamide. Such results suggested the involvement, at least in part, of KATP channels. Preservation of a vasodilatory activity in rat aortic rings without endothelium indicated that the site of action of such molecules was located on the vascular smooth muscle cells and not on the endothelial cells. Some of the most active compounds also stimulated elastin synthesis by vascular smooth muscle cells. Lastly, most of the active vasorelaxant drugs, except 15k and 15t at high concentrations, did not exhibit marked inhibitory effects on the insulin releasing process and on glycaemia, suggesting a relative tissue selectivity of some of these compounds for the vascular smooth muscle.

Berberine reduces ischemia/reperfusion-induced myocardial apoptosis via activating AMPK and PI3K-Akt signaling in diabetic rats.

Diabetes increases the risk of cardiovascular diseases. Berberine (BBR), an isoquinoline alkaloid used in Chinese medicine, exerts anti-diabetic effect by lowering blood glucose and regulating lipid metabolism. It has been reported that BBR decreases mortality in patients with chronic congestive heart failure. However, the molecular mechanisms of these beneficial effects are incompletely understood. In the present study, we sought to determine whether BBR exerts cardioprotective effect against ischemia/reperfusion (I/R) injury in diabetic rats and the underlying mechanisms. Male Sprague-Dawley rats were injected with low dose streptozotocin and fed with a high-fat diet for 12 weeks to induce diabetes. The diabetic rats were intragastrically administered with saline or BBR (100, 200 and 400 mg/kg/d) starting from week 9 to 12. At the end of week 12, all rats were subjected to 30 min of myocardial ischemia and 3 h of reperfusion. BBR significantly improved the recovery of cardiac systolic/diastolic function and reduced myocardial apoptosis in diabetic rats subjected to myocardial I/R. Furthermore, in cultured neonatal rat cardiomyocytes, BBR (50 µmol/L) reduced hypoxia/reoxygenation-induced myocardial apoptosis, increased Bcl-2/Bax ratio and decreased caspase-3 expression, together with enhanced activation of PI3K-Akt and increased adenosine monophosphate-activated protein kinase (AMPK) and eNOS phosphorylation. Pretreatment with either PI3K/Akt inhibitor wortmannin or AMPK inhibitor Compound C blunted the anti-apoptotic effect of BBR. Our findings demonstrate that BBR exerts anti-apoptotic effect and improves cardiac functional recovery following myocardial I/R via activating AMPK and PI3K-Akt-eNOS signaling in diabetic rats.

Leucine facilitates the insulin-stimulated glucose uptake and insulin signaling in skeletal muscle cells: involving mTORC1 and mTORC2.

Leucine, a branched-chain amino acid, has been shown to promote glucose uptake and increase insulin sensitivity in skeletal muscle, but the exact mechanism remains unestablished. We addressed this issue in cultured skeletal muscle cells in this study. Our results showed that leucine alone did not have an effect on glucose uptake or phosphorylation of protein kinase B (AKT), but facilitated the insulin-induced glucose uptake and AKT phosphorylation. The insulin-stimulated glucose uptake and AKT phosphorylation were inhibited by the phosphatidylinositol 3-kinase inhibitor, wortmannin, but the inhibition was partially reversed by leucine. The inhibitor of mammalian target of rapamycin complex 1 (mTORC1), rapamycin, had no effect on the insulin-stimulated glucose uptake, but eliminated the facilitating effect of leucine in the insulin-stimulated glucose uptake and AKT phosphorylation. In addition, leucine facilitation of the insulin-induced AKT phosphorylation was neutralized by knocking down the core component of the mammalian target of rapamycin complex 2 (mTORC2) with specific siRNA. Together, these findings show that leucine can facilitate the insulin-induced insulin signaling and glucose uptake in skeletal muscle cells through both mTORC1 and mTORC2, implicating the potential importance of this amino acid in glucose homeostasis and providing new mechanistic insights.

Arcuate nucleus injection of an anti-insulin affibody prevents the sympathetic response to insulin.

Accumulating evidence suggests that insulin acts within the hypothalamus to alter sympathetic nerve activity (SNA) and baroreflex function. Although insulin receptors are widely expressed across the hypothalamus, recent evidence suggests that neurons of the arcuate nucleus (ARC) play an important role in the sympathoexcitatory response to insulin. The purpose of the present study was to determine whether circulating insulin acts directly in the ARC to elevate SNA. In anesthetized male Sprague-Dawley rats (275-425 g), the action of insulin was neutralized by microinjection of an anti-insulin affibody (1 ng/40 nl). To verify the efficacy of the affibody, ARC pretreatment with injection of the anti-insulin affibody completely prevented the increase in lumbar SNA produced by ARC injection of insulin. Next, ARC pretreatment with the anti-insulin affibody attenuated the lumbar sympathoexcitatory response to intracerebroventricular injection of insulin. Third, a hyperinsulinemic-euglycemic clamp increased lumbar, but not renal, SNA in animals that received ARC injection of a control affibody. However, this sympathoexcitatory response was absent in animals pretreated with the anti-insulin affibody in the ARC. Injection of the anti-insulin affibody in the adjacent ventromedial hypothalamus did not alter the sympathoexcitatory response to insulin. The ability of the anti-insulin affibody to prevent the sympathetic effects of insulin cannot be attributed to a general inactivation or nonspecific effect on ARC neurons as the affibody did not alter the sympathoexcitatory response to ARC disinhibition by gabazine. Collectively, these findings suggest that circulating insulin acts within the ARC to increase SNA.

[Comparative structural and functional characteristics of different forms of Saccharomyces cerevisiae red pigment and its synthetic analogue].

Structural and functional characteristics of the yeast red pigment (product of polymerization of N1-(beta-D-ribofuranosyl)-5-aminoimadazole), isolated from adel 1 mutant cells of Saccharomyces cerevisiae, its deribosylated derivatives (obtained by acid hydrolysis) and its synthetic pigment analogue (product of polymerization of N1-methyl-5-aminoimadazole in vitro) has been obtained. Products of in vitro polymerization were identified using mass spectrometry. The ability of these pigments to inhibit amyloid formation using insulin fibrils was compared. The entire compounds studied were able to interact with amyloids and inhibit their growth. Electron and atomic force microscopy revealed a common feature inherent in the insulin fibrils formed in presence of these compounds--they were merged into conglomerates that were more stable and resistant to the effects of ultrasound in comparison with insulin aggregates grown without pigments. We speculate that all these compounds can cause coalescence of fibrils, partially block their loose ends and, thereby, inhibit the attachment of new monomers to growing fibrils.

Insulin-feedback via PI3K-C2alpha activated PKBalpha/Akt1 is required for glucose-stimulated insulin secretion.

Phosphatidylinositide 3-kinases (PI3Ks) play central roles in insulin signal transduction. While the contribution of class Ia PI3K members has been extensively studied, the role of class II members remains poorly understood. The diverse actions of class II PI3K-C2alpha have been attributed to its lipid product PI(3)P. By applying pharmacological inhibitors, transient overexpression and small-interfering RNA-based knockdown of PI3K and PKB/Akt isoforms, together with PI-lipid profiling and live-cell confocal and total internal reflection fluorescence microscopy, we now demonstrate that in response to insulin, PI3K-C2alpha generates PI(3,4)P(2), which allows the selective activation of PKBalpha/Akt1. Knockdown of PI3K-C2alpha expression and subsequent reduction of PKBalpha/Akt1 activity in the pancreatic beta-cell impaired glucose-stimulated insulin release, at least in part, due to reduced glucokinase expression and increased AS160 activity. Hence, our results identify signal transduction via PI3K-C2alpha as a novel pathway whereby insulin activates PKB/Akt and thus discloses PI3K-C2alpha as a potential drugable target in type 2 diabetes. The high degree of codistribution of PI3K-C2alpha and PKBalpha/Akt1 with insulin receptor B type, but not A type, in the same plasma membrane microdomains lends further support to the concept that selectivity in insulin signaling is achieved by the spatial segregation of signaling events.

C-reactive protein inhibits insulin activation of endothelial nitric oxide synthase via the immunoreceptor tyrosine-based inhibition motif of FcgammaRIIB and SHIP-1.

Insulin promotes the cardiovascular protective functions of the endothelium including NO production by endothelial NO synthase (eNOS), which it stimulates via Akt kinase which phosphorylates eNOS Ser1179. C-reactive protein (CRP) is an acute-phase reactant that is positively correlated with cardiovascular disease risk in patients with type 2 diabetes. We previously showed that CRP inhibits eNOS activation by insulin by blunting Ser1179 phosphorylation. We now elucidate the underlying molecular mechanisms. We first show in mice that CRP inhibits insulin-induced eNOS phosphorylation, indicating that these processes are operative in vivo. In endothelial cells we find that CRP attenuates insulin-induced Akt phosphorylation, and CRP antagonism of eNOS is negated by expression of constitutively active Akt; the inhibitory effect of CRP on Akt is also observed in vivo. A requirement for the IgG receptor FcgammaRIIB was demonstrated in vitro using blocking antibody, and reconstitution experiments with wild-type and mutant FcgammaRIIB in NIH3T3IR cells revealed that these processes require the ITIM (immunoreceptor tyrosine-based inhibition motif) of the receptor. Furthermore, we find that endothelium express SHIP-1 (Src homology 2 domain-containing inositol 5'-phosphatase 1), that CRP induces SHIP-1 stimulatory phosphorylation in endothelium in culture and in vivo, and that SHIP-1 knockdown by small interfering RNA prevents CRP antagonism of insulin-induced eNOS activation. Thus, CRP inhibits eNOS stimulation by insulin via FcgammaRIIB and its ITIM, SHIP-1 activation, and resulting blunted activation of Akt. These findings provide mechanistic linkage among CRP, impaired insulin signaling in endothelium, and greater cardiovascular disease risk in type 2 diabetes.

High-Throughput Screening for Insulin Secretion Modulators.

The application of forward chemical genetics to insulin secretion in high-throughput has been uncommon because of high costs and technical challenges. However, with the advancement of secreted luciferase tools, it has become feasible for small laboratories to screen large numbers of compounds for effects on insulin secretion. The purpose of this chapter is to outline the methods involved in high-throughput screening for small molecules that chronically impact pancreatic beta cell function. Attention is given to specific points in the protocol that help to improve the dynamic range and reduce variability in the assay. Using this approach in 384-well format, at least 48 and as many as 144 plates can theoretically be processed per week. This protocol serves as a guideline and can be modified as required for alternate stimulation paradigms and improved upon as new technologies become available.

Ascofuranone prevents ER stress-induced insulin resistance via activation of AMP-activated protein kinase in L6 myotube cells.

The current study presents that ascofuranone isolated from a phytopathogenic fungus, Ascochyta viciae, has antitumor activity against various transplantable tumors and a considerable hypolipidemic activity. AMP-activated protein kinase (AMPK) plays a critical role in cellular glucose and lipid homeostasis. We found that ascofuranone improves ER stress-induced insulin resistance by activating AMPK through the LKB1 pathway. In L6 myotube cells, ascofuranone treatment increased the phosphorylation of the Thr-172 residue of the AMPK alpha subunit and the Ser-79 subunit of acetyl-CoA carboxylase (ACC) and cellular glucose uptake. Ascofuranone-induced phosphorylation of AMPK and ACC was not increased in A549 cells lacking LKB1. Interestingly, ascofuranone treatment also improved insulin signaling impaired by ER stress in L6 myotube cells. These effects were all reversed by pretreatment with Compound C, an AMPK inhibitor or with adenoviral-mediated dominant-negative AMPK alpha 2. Taken together, these results indicated that ascofuranone-mediated enhancement of glucose uptake and reduction of impaired insulin sensitivity in L6 cells is predominantly accomplished by activating AMPK, thereby mediating beneficial effects in type 2 diabetes and insulin resistance.

TNF-alpha inhibits insulin action in liver and adipose tissue: A model of metabolic syndrome.

Several studies suggest that TNF-alpha contributes to the development of insulin resistance (IR). We compared transcriptional profiles of rat H-411E liver cells exposed to insulin in the absence or presence of TNF-alpha. We identified 33 genes whose expression was altered by insulin, and then reversed by TNF-alpha. Twenty-six of these 33 genes created a single network centered around: insulin, TNF-alpha, p38-MAPK, TGFb1; SMAD and STAT1; and enzymes and cytokines involved in apoptosis (CASP3, GADD45B, IL2, TNF-alpha, etc.). We analyzed our data together with other data of gene expression in adipocytes and found a number of processes common to both, for example, cell death and inflammation; intercellular signaling and metabolism; G-Protein, IL-10 and PTEN signaling. Moreover, the two datasets combined generated a single molecular network that further identified PTEN (a phosphatase) as a unique new link between insulin signaling, IR, and apoptosis reflecting the pathophysiology of "metabolic syndrome".

Adropin suppresses insulin expression and secretion in INS-1E cells and rat pancreatic islets.

Adropin is a peptide hormone which is produced in brain and peripheral tissues such as liver. It was found that adropin modulates lipid and glucose homeostasis by interacting with hepatocytes and myocytes. Adropin enhances insulin sensitivity and alleviates hyperinsulinemia in animal models with high-fat diet-induced insulin resistance. However, it is unknown whether adropin regulates insulin secretion and proliferation of beta cells. Therefore, we studied the effects of adropin on insulin secretion in INS-1E cells as well as isolated pancreatic islets. Furthermore, we assessed the influence of adropin on insulin mRNA expression, cell viability and proliferation in INS-1E cells. Pancreatic islets were isolated from male Wistar rats. mRNA expression was evaluated using real-time PCR and cell viability by MTT assay. Cell replication was measured by BrdU incorporation and insulin secretion by RIA. We found that adropin suppresses insulin mRNA expression in INS-1E cells. Moreover, adropin attenuates glucose-induced insulin secretion in INS-1E cells as well as in isolated pancreatic islets. In addition, using INS-1E cells we found that adropin suppresses glucose-induced cAMP production. However, adropin fails to modulate INS-1E cell viability and proliferation. In summary, we found adropin suppresses insulin mRNA expression and secretion, without affecting beta cell viability or proliferation.

The Novel Adipokine Gremlin 1 Antagonizes Insulin Action and Is Increased in Type 2 Diabetes and NAFLD/NASH.

The BMP2/4 antagonist and novel adipokine Gremlin 1 is highly expressed in human adipose cells and increased in hypertrophic obesity. As a secreted antagonist, it inhibits the effect of BMP2/4 on adipose precursor cell commitment/differentiation. We examined mRNA levels of Gremlin 1 in key target tissues for insulin and also measured tissue and serum levels in several carefully phenotyped human cohorts. Gremlin 1 expression was high in adipose tissue, higher in visceral than in subcutaneous tissue, increased in obesity, and further increased in type 2 diabetes (T2D). A similar high expression was seen in liver biopsies, but expression was considerably lower in skeletal muscles. Serum levels were increased in obesity but most prominently in T2D. Transcriptional activation in both adipose tissue and liver as well as serum levels were strongly associated with markers of insulin resistance in vivo (euglycemic clamps and HOMA of insulin resistance), and the presence of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). We also found Gremlin 1 to antagonize insulin signaling and action in human primary adipocytes, skeletal muscle, and liver cells. Thus, Gremlin 1 is a novel secreted insulin antagonist and biomarker as well as a potential therapeutic target in obesity and its complications T2D and NAFLD/NASH.

Short-term prednisone use antagonizes insulin's anabolic effect on muscle protein and glucose metabolism in young healthy people.

Glucocorticoids cause muscle atrophy and weakness, but the mechanisms for these effects are unclear. The purpose of this study was to test a hypothesis that prednisone (Pred) counteracts insulin's anabolic effects on muscle. A randomized, double-blind cross-over design was used to test the effects of 6 days either Pred (0.8 mg x kg(-1) x day(-1)) or placebo use in seven healthy young volunteers. Protein dynamics were measured across the leg using stable isotope tracers of leucine (Leu) and phenylalanine (Phe) after overnight fast and during a hyperinsulinemic (1.5 microU x min(-1) x kg FFM(-1)) euglycemic clamp with amino acid replacement. Fasting glucose, amino acids, insulin, and glucagon were higher (P < 0.01) on Pred vs. placebo, whereas leg blood flow was 18% lower. However, basal whole body and leg kinetics of Leu and Phe were unaltered by Pred. Insulin infusion increased leg glucose uptake in both trials but was 65% lower with Pred than with placebo. Insulin in both trials similarly suppressed whole body flux of Leu and Phe. Importantly, insulin increased net Leu and Phe balance across the leg and the balance between muscle protein synthesis and breakdown, but these changes were 45-140% lower (P < 0.03) in Pred than in placebo. The present study demonstrates that short-term Pred use in healthy people does not alter whole body or leg muscle protein metabolism during the postaborptive state but causes muscle insulin resistance for both glucose and amino acid metabolism, with a blunted protein anabolism. This interactive effect may lead to muscle atrophy with continued use of glucocorticoids.