Insulin Receptor Substrate-1 Levels Research Articles

Effects of GPR81 agonist on insulin resistance in rats with nonalcoholic fatty liver disease

Objective: To investigate the effects of NOD-like receptor protein 3 (NLRP3) signaling pathway on insulin resistance and the intervention of lactic acid receptor G protein-coupled receptor 81 (GPR81) agonist in nonalcoholic fatty liver disease (NAFLD) rats. Methods: Thirty SD male rats were randomly divided into three groups: control group, NAFLD group and GPR81 agonist group, with 10 rats in each group. Nonalcoholic fatty liver rat model was established by high fat diet. The rats in GPR81 agonist group were injected intraperitoneally with GPR81 specific agonist lactate (50 nmol/L) on the basis of nonalcoholic fatty liver model once a week, and the other two groups were injected with the same amount of normal saline for 12 weeks. The levels of liver biochemical indexes, fasting blood glucose, insulin and inflammatory factors in liver homogenate were measured, and the histopathological morphology of liver in each group was observed. The protein expressions of NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), cysteinyl aspartate specific proteinase-1 (caspase-1), insulin receptor substrate 1 (IRS-1), Tyr465-IRS-1, Ser636-IRS-1, glucose transporter 4 (GLUT4) in liver tissue were detected by Western blot. The mRNA expression levels of NLRP3, ASC, caspase-1, IRS-1 and GLUT4 in liver tissue were detected by qRT-PCR. Results: Compared with the control group, the serum levels of triglyceride (TG), alanine aminotransfease (ALT), aspartate aminotransfease (AST), fasting plasma glucose (FPG), fasting insulin (FINS) and homeostasis model assessment of insulin resistance (HOMA-IR) of NAFLD group were increased significantly (P＜ 0.05). The results of liver histopathology showed that in NAFLD group, there were obvious fatty changes in liver tissue, fat droplets in hepatocytes and inflammatory cell infiltration. And the mRNA and protein expressions of NLRP3, ASC, caspase-1 and the protein expression of Ser636-IRS-1 in NAFLD group were increased significantly, and the contents of interleukin 1β (IL-1β) and interleukin 18 (IL-18) in liver and serum were increased, while the mRNA and protein expressions of IRS-1 and GLUT4 and Tyr465-IRS-1 were decreased significantly (P＜0.05). Compared with NAFLD group, the above indexes of GPR81 agonist group were all significantly improved. Conclusion: The activation of NLRP3 signaling pathway mediates the production of inflammatory factors and promotes the development of NAFLD. GPR81 agonist may be a potential treatment for NAFLD.

Arsenic disrupts neuronal insulin signaling through increasing free PI3K-p85 and decreasing PI3K activity

Previously, we reported that prolonged arsenic exposure impaired neuronal insulin signaling. Here we have further identified novel molecular mechanisms underlying neuronal insulin signaling impairment by arsenic. Arsenic treatment altered insulin dose-response curve and reduced maximum insulin response in differentiated human neuroblastoma SH-SY5Y cells, suggesting that arsenic hindered neuronal insulin signaling in a non-competitive like manner. Mechanistically, arsenic suppressed insulin receptor (IR) kinase activity, as witnessed by a decreased insulin-activated autophosphorylation of IR at Y1150/1151. Arsenic decreased the level of insulin receptor substrate 1 (IRS1) but increased the protein ratio between PI3K regulatory subunit, p85, and PI3K catalytic subunit, p110. Interestingly, co-immunoprecipitation demonstrated that arsenic did not alter a level of PI3K-p110/PI3K-p85 complex while increased PI3K-p85 levels in a PI3K-p110 depletion supernatant resulted from PI3K-p110 immunoprecipitation. These results indicated that arsenic increased PI3K-p85 which was free from PI3K-p110 binding. In addition, arsenic significantly increased interaction between IRS1 and PI3K-p85 but not PI3K-p110, suggesting that there may be a fraction of free PI3K-p85 interacting with IRS1. In vitro PI3K activity demonstrated that arsenic lowered PI3K activity in both basal and insulin-stimulated conditions. These results suggested that the increase in free PI3K-p85 by arsenic might compete with PI3K heterodimer for the same IRS1 binding site, in turn blocking the activation of its catalytic subunit, PI3K-p110. Taken together, our results provide additional insights into mechanisms underlying the impairment of neuronal insulin signaling by arsenic through the reduction of IR autophosphorylation, the increase in free PI3K-p85, and the impeding of PI3K activity.

DOX and MET treatment induces cognitive impairment through downregulation of IL-1-alpha and IRS-1 in the rat brain.

Chemotherapeutic drugs are effective in the treatment of various types of cancers. However, the secondary side effects of chemotherapy, such as cardiotoxicity, hepatotoxicity, and cognitive impairment, limit its clinical effectiveness in cancer treatment. The present study was aimed at investigating the effects of doxorubicin (DOX) on cognitive impairment through its effects on interleukin (IL)-1, insulin receptor substrate 1 (IRS-1), IL-6, Akt, and tumor necrosis factor (TNF)-alpha expression. Rats were treated with DOX, metformin (MET), and DOX+MET, and IL-1, IRS-1, IL-6, Akt, and TNF-alpha expression levels were assessed using Enzyme-Linked Immunosorbent Assay kits. The DOX-treated rats showed significantly decreased IL-1 and IRS-1 expression in the brain, and the expression of these proteins was rescued on MET administration. On the other hand, IL-6, protein kinase B (PKB/Akt), and TNF-alpha expression was unaltered in the brain of DOX- and MET-treated rats. Our findings showed that DOX induces cognitive impairment by modulating IL-1-alpha and IRS-1 expression and that MET administration failed to rescue the DOX-mediated memory impairment.

Palmitic Acid Regulates miRNA-3148 via Insulin Receptor Substrate-1 and is Involved in Insulin Resistance

Previous studies reported that saturated fatty acid palmitic acid (PA) is closely related to insulin resistance. miR-3148 regulates insulin receptor substrate-1 (IRS1) predicted by MiRDB analysis. However, whether PA regulates IRS1 via miR-3148 remains to be elucidated. Therefore, in this work, we assessed whether PA regulates miRNA-3148 via IRS1 in insulin resistance. We cultured HepG2 cells in vitro and classified them into control group (NC group), miR-3148 Mimics group, and miR-3148 Mimics+ pFBD-IRS1 group. We used qRT-PCR to detect miR-3148 and IRS1 mRNA; used Dual-Luciferase Reporter Assays to detect miR-3148 with 3′-UTR region of IRS1 mRNA; and utilized Western blot (WB) to detect IRS1, p-AKT, AKT and Tubulin. Our results showed that PA could increase miR-3148 and decrease IRS1 which is a target protein of miR-3148, as shown by Dual-Luciferase Reporter assays. miR-3148 significantly inhibited the impact of insulin on p-AKT level (P < 0.01) and over-expression of IRS1 by pFBD-IRS1 can partially alleviate the inhibitory effect of miR-3148 mimics on p-AKT. In HepG2 cells, PA regulates miR-3148. Via targeting IRS1 mRNA, miR-3148 impairs insulin signaling pathway, leading to insulin resistance. Over-expression of IRS1 by pFBD-IRS1 alleviates miR-3148-induced insulin resistance.

Mechanism of Electroacupuncture Regulating IRS-1 Phosphorylation in Skeletal Muscle to Improve Insulin Sensitivity.

Objective To explore the possible mechanism of electroacupuncture to improve insulin sensitivity in type 2 diabetes rats. Methods Fourteen Zucker Diabetic Fatty (ZDF) rats were randomly divided into two groups: a model group and an electroacupuncture group, with 7 rats in each group. Seven Zucker Lean (ZL) rats served as a control group. All rats were fed with Purina #5008 for 4 weeks, and the electroacupuncture group received 4-week electroacupuncture intervention, while the control group and model group received no intervention. We measured fasting blood glucose (FBG) on the fourth weekend. After 4 weeks of intervention, the expression levels of insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, IRS-1 serine/threonine phosphorylation, and GLUT4 in quadriceps femoris muscles were detected by western Blot. Results Compared with the model group, the electroacupuncture group had a lower level of fasting blood glucose, serum insulin level, and insulin resistance index (P < 0.05). The electroacupuncture group had lower IRS-1 serine/threonine phosphorylation than the model group, with the difference showing statistical significance (P < 0.05). Furthermore, the mean score (MS) of the control group showed the lowest phosphorylation expression, followed by the electroacupuncture group, while the model group had the highest level of phosphorylated protein expression. The level of IRS-1 tyrosine phosphorylation at Tyr895 sites was compared, and the result showed that there was no significant difference between the electroacupuncture group and the control group (P > 0.05), and the electroacupuncture group had higher phosphorylation expression than the model group (P < 0.05). Compared with the control group and the model group, the expression level of GLUT4 protein in the electroacupuncture group was significantly increased (P < 0.05). Conclusion Electroacupuncture has the effect to improve the insulin sensitivity of type 2 diabetic ZDF rats by reducing fasting blood glucose, insulin level, and insulin resistance index, effectively up regulating the expression of GLUT4 protein in quadriceps femoris muscle. The mechanism is related to the regulation of skeletal muscle IRS-1 serine/threonine and tyrosine phosphorylation levels.

MicroRNA-191 blocking the translocation of GLUT4 is involved in arsenite-induced hepatic insulin resistance through inhibiting the IRS1/AKT pathway

Environmental exposure to arsenic can cause a variety of health problems. Epidemiological and experimental studies have established a diabetogenic role for arsenic, but the mechanisms responsible for arsenic-induced impairment of insulin action are unclear. MicroRNAs (miRNAs) are involved in various metabolic disorders, particularly in the development of insulin resistance. The present study investigated whether arsenite, an active form of arsenic, induces hepatic insulin resistance and the mechanisms underlying it. After male C57BL/6J mice were exposed to arsenite (0 or 20 ppm) in drinking water for 12 months, intraperitoneal glucose tolerance tests (IPGTTs) and insulin tolerance tests (ITTs) revealed an arsenite-induced glucose metabolism disorder. Hepatic glycogen levels were lower in arsenite-exposed mice. Further, for livers of mice exposed to arsenite, miR-191 levels were higher, and protein levels of insulin receptor substrate 1 (IRS1), p-IRS1, and phospho-protein kinase B (p-AKT) were lower. Further, glucose transporter 4 (GLUT4) had lower levels on the plasma membrane. For insulin-treated L-02 cells, arsenite decreased glucose consumption and glycogen levels, increased miR-191 levels, and inhibited the IRS1/AKT pathway and the translocation of GLUT4 from the cytoplasm to the plasma membrane. For insulin-treated L-02 cells, the decreases of glucose consumption, glycogen levels, GLUT4 on the plasma membrane, and p-AKT levels induced by arsenite were reversed by SC79 (agonist of AKT) and an miR-191 inhibitor; these effects caused by miR-191 inhibitor were restored by IRS1 siRNA. In insulin-treated L-02 cells, miR-191, via IRS1, was involved in the arsenite-induced decreases of glucose consumption and glycogen levels and in inhibition of the translocation of GLUT4. Thus, miR-191 blocking the translocation of GLUT4 was involved in arsenite-induced hepatic insulin resistance through inhibiting the IRS1/AKT pathway. Our study reveals a mechanism for arsenite-induced hepatic insulin resistance, which provides clues for discovering biomarkers for the development of type 2 diabetes and for prevention and treatment of arsenic poisoning.

Potential mechanistic pathways underlying intestinal and hepatic effects of kefir in high-fructose-fed rats

Excess intake of fructose may contribute to the high prevalence of metabolic disorder. In this study, we investigated the effects of kefir supplementation on the intestine-liver-adipose tissue axis in metabolic disorder induced by high-fructose diet in rats to describe mechanistic action and potential therapeutic value of kefir. Fructose was given to the rats as a 20% solution in drinking water for 15 weeks. Kefir was administrated by gastric gavage once a day during the final six weeks. Kefir supplementation improved metabolic parameters, including plasma triglyceride and insulin levels; hepatic weight, triglyceride content and fatty degeneration; omental fat mass in fructose-fed rats. Kefir supplementation decreased the ratio of Firmicutes/Bacteroidetes in feces, as well as necrotic degeneration, expression levels of nuclear factor-kappa B (NF-κB), and inducible nitric oxide synthase (iNOS), but increased expression of tight-junction proteins occludin and claudin-1, in the ileum of the fructose-fed rats. Kefir treatment also reduced the mRNA levels of key lipogenic genes sterol regulatory element-binding protein (SREBP-1c) and fatty acid synthase (FASN) together with a decline in expression of tumor necrosis factor-alpha (TNF-α), NF-κB, and glycosylated glycoprotein (CD68) in the liver. Moreover, kefir treatment improved insulin signaling at the level of insulin receptor substrate 1 (IRS-1) and phospho-endothelial nitric oxide synthase (peNOS) as well as fructose transporters (GLUT2 and GLUT5) in the liver, but not in the adipose tissue, of high-fructose-fed rats. Consequently, kefir supplementation suppresses hepatic lipogenesis and inflammatory status, but promotes insulin signaling, in association with a change of the fecal microbiota and attenuation of the intestinal permeability factors in high-fructose-fed rats. Thus, we propose that kefir has favorable effects on the hepatic and intestinal irregularities induced by fructose overconsumption.

Upregulation of long non-coding RNA SNHG16 promotes diabetes-related RMEC dysfunction via activating NF-κB and PI3K/AKT pathways

Diabetic retinopathy (DR) is a severe diabetes-induced eye disease, in which its pathological phenomena basically include abnormal proliferation, migration, and angiogenesis of microvascular endothelial cells in the retina. Long non-coding RNAs (lncRNAs) have been proven to be important regulators in various biological processes, but their participation in DR remains largely undiscovered. In the present study, we aimed to unveil the role of lncRNA small nucleolar RNA host gene 16 (SNHG16) in regulating the functions of human retinal microvascular endothelial cells (hRMECs) under a high-glucose (HG) condition. We found that SNHG16 expression was significantly upregulated in hRMECs treated with HG. Functionally, SNHG16 could facilitate hRMEC proliferation, migration, and angiogenesis. Moreover, SNHG16 was associated with nuclear factor κB (NF-κB) and phosphatidylinositol 3-kinase (PI3K)/AKT pathways. Mechanistically, SNHG16 could promote hRMEC dysfunction by sequestering microRNA (miR)-146a-5p and miR-7-5p to act as a competing endogenous RNA (ceRNA) with interleukin-1 receptor-associated kinase 1 (IRAK1) and insulin receptor substrate 1 (IRS1). In conclusion, our results illustrated the potential role of SNHG16 in facilitating hRMEC dysfunction under HG treatment, providing a novel approach for DR therapy.

Neutrophil Elastase Deficiency Ameliorates Myocardial Injury Post Myocardial Infarction in Mice.

Neutrophils are recruited into the heart at an early stage following a myocardial infarction (MI). These secrete several proteases, one of them being neutrophil elastase (NE), which promotes inflammatory responses in several disease models. It has been shown that there is an increase in NE activity in patients with MI; however, the role of NE in MI remains unclear. Therefore, the present study aimed to investigate the role of NE in the pathogenesis of MI in mice. NE expression peaked on day 1 in the infarcted hearts. In addition, NE deficiency improved survival and cardiac function post-MI, limiting fibrosis in the noninfarcted myocardium. Sivelestat, an NE inhibitor, also improved survival and cardiac function post-MI. Flow cytometric analysis showed that the numbers of heart-infiltrating neutrophils and inflammatory macrophages (CD11b+F4/80+CD206low cells) were significantly lower in NE-deficient mice than in wild-type (WT) mice. At the border zone between intact and necrotic areas, the number of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive apoptotic cells was lower in NE-deficient mice than in WT mice. Western blot analyses revealed that the expression levels of insulin receptor substrate 1 and phosphorylation of Akt were significantly upregulated in NE-knockout mouse hearts, indicating that NE deficiency might improve cardiac survival by upregulating insulin/Akt signaling post-MI. Thus, NE may enhance myocardial injury by inducing an excessive inflammatory response and suppressing Akt signaling in cardiomyocytes. Inhibition of NE might serve as a novel therapeutic target in the treatment of MI.

Relationship Between Insulin-Receptor Substrate 1 and Langerhans' Islet in a Rat Model of Type 2 Diabetes Mellitus.

In vivo studies on pathogenesis of type 2 diabetes mellitus (T2DM) have been reported, however, the relationship between insulin-receptor substrate 1 (IRS1) and the area of Langerhans' islets was unknown. Therefore, a correlation between both parameters was assessed. Diabetic groups were fed with a high-fat diet (HFD) and injected with three different doses of streptozotocin, namely 25, 35 and 45 mg/kg, and compared to a control group after 9 weeks. Administration of HFD/streptozotocin increased the level of fasting blood glucose but reduced the level of IRS1 and the area of Langerhans' islets in diabetic groups. The coefficient of correlation between IRS1 and area of Langerhans' islets was 0.259 (p=0.232). In addition, the coefficient of correlation for fasting blood glucose with the area of Langerhans' islets and IRS1 was -0.520 (p=0.011) and -0.603 (p=0.002), respectively. The reduction of IRS1 was weakly correlated with the destruction of Langerhans' islets, suggesting there is an intermediate step between both parameters.

Geniposide improves insulin resistance through AMPK-mediated Txnip protein degradation in 3T3-L1 adipocytes.

Thioredoxin-interacting protein (Txnip) has emerged as a key regulator of insulin resistance. In this study, we investigated the roles of geniposide and Txnip in insulin resistance in differentiated 3T3-L1 adipocytes. Our results revealed that geniposide markedly enhanced glucose uptake, increased the protein levels of insulin receptor substrate (IRS)-1 and GLUT-1, and prevented the phosphorylation of IRS-1 and Akt Thr308 induced by insulin resistance in 3T3-L1 adipocytes. We also observed that geniposide accelerated protein degradation of Txnip through proteasome pathway, and knockdown of Txnip with small interfering RNA attenuated the effect of geniposide on insulin signaling molecules, implying that Txnip played a pivotal role in the regulation of insulin signaling molecules by geniposide in 3T3-L1 adipocytes. Furthermore, geniposide induced the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) in the presence of high glucose in differentiated 3T3-L1 adipocytes, while compound C, an inhibitor of AMPK, prevented the effect of geniposide on Txnip degradation and the regulation of glucose uptake and insulin signaling molecules including p-IRS-1, IRS-1, and GLUT-1 in differentiated 3T3-L1 adipocytes. Taken together, all these findings suggest that geniposide improves the insulin signaling defect possibly by AMPK-mediated Txnip degradation in 3T3-L1 adipocytes.

Ethno-pharmacological insulin signaling induction of aqueous extract of Syzygium paniculatum fruits in a high-fat diet induced hepatic insulin resistance

Ethnopharmacological relevanceThe ethnopharmacological significance of the fruits of Syzygium paniculatum Gaertn (Magenta Cherry) is widely recognized in the Indian traditional medicine system to treat various disorders, such as diabetes, hyperlipidaemia, hypertension, and cardiovascular problems. Aim of the studyThis research work investigated the supplementation of the aqueous extract of S. paniculatum fruit (AESPF) on liver function; the molecular effects on the expression of the protein of insulin receptor (IR) and insulin receptor substrate 1 (IRS-1) in high-fat diet-induced hepatic insulin resistance in the rat model. Materials and methodsHigh-fat diet was used to induce obesity in albino Wistar for 120 days. Biochemical, enzymatic, and histopathological analysis, as well as analysis of hepatic insulin resistance proteins and expression of IRS-1, were performed. ResultsThe supplementation of AESPF with a dose of 100 mg/kg bw significantly reduced bodyweight, blood sugar, insulin, lipid profiles, and liver enzymes. Hepatic insulin resistance was improved with a reduced level of IR and IRS-1 to protein levels. HFD alters the sensitivity of hepatocytes to insulin due to the down-regulation of insulin receptor proteins. ConclusionsThe fruits of S. paniculatum possess biological activities to alleviate all risky effects by regulating hepatic lipogenesis activity that can be used in the progress of medication for HFD-induced hepatic insulin resistance and metabolic disorders.

Carbohydrate-Induced Insulin Signaling Activates Focal Adhesion Kinase: A Nutrient and Mechanotransduction Crossroads.

Research has suggested that nutrient, exercise, and metabolism-related proteins interact to regulate mammalian target of rapamycin complex one (mTOR) post-exercise and their interactions needs clarification. In a double-blind, cross-over, repeated measures design, ten participants completed four sets to failure at 70% of 1-repitition maximum (1-RM) with 45 s rest on angled leg press with or without pre-exercise maltodextrin (2 g/kg) after a 3 h fast. Vastus lateralis biopsies were collected at baseline before supplementation and 1 h post-exercise to analyze Focal Adhesion Kinase (FAK), ribosomal protein S6 kinase beta-1 (p70S6K), insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and 5′ AMP-activated protein kinase (AMPK) activation. FAK and IRS-1 activity were only elevated 1 h post-exercise with carbohydrate ingestion (p < 0.05). PI3K and p70S6K activation were both elevated after exercise in both conditions (p < 0.05). However, AMPK activity did not change from baseline in both conditions (p > 0.05). We conclude that FAK does not induce mTOR activation through PI3K crosstalk in response to exercise alone. In addition, FAK may not be regulated by AMPK catalytic activity, but this needs further research. Interestingly, carbohydrate-induced insulin signaling appears to activate FAK at the level of IRS-1 but did not enhance mTOR activity 1 h post-exercise greater than the placebo condition. Future research should investigate these interactions under different conditions and within different time frames to clearly understand the interactions between these signaling molecules.

Insulin receptor substrate 1 gene expression is strongly up-regulated by HSPB8 silencing in U87 glioma cells.

Objective. The aim of the present investigation was to study the expression of genes encoding IRS1 (insulin receptor substrate 1) and some other functionally active proteins in U87 glioma cells under silencing of polyfunctional chaperone HSPB8 for evaluation of the possible significance of this protein in intergenic interactions.Methods. Silencing of HSPB8 mRNA was introduced by HSPB8 specific siRNA. The expression level of HSPB8, IRS1, HK2, GLO1, HOMER3, MYL9, NAMPT, PER2, PERP, GADD45A, and DEK genes was studied in U87 glioma cells by quantitative polymerase chain reaction.Results. It was shown that silencing of HSPB8 mRNA by specific to HSPB8 siRNA led to a strong down-regulation of this mRNA and significant modification of the expression of IRS1 and many other genes in glioma cells: strong up-regulated of HOMER3, GLO1, and PERP and down-regulated of MYL9, NAMPT, PER2, GADD45A, and DEK gene expressions. At the same time, no significant changes were detected in the expression of HK2 gene in glioma cells treated by siRNA, specific to HSPB8. Moreover, the silencing of HSPB8 mRNA enhanced the glioma cells proliferation rate.Conclusions. Results of this investigation demonstrated that silencing of HSPB8 mRNA affected the expression of IRS1 gene as well as many other genes encoding tumor growth related proteins. It is possible that the dysregulation of most of the studied genes in glioma cells after silencing of HSPB8 is reflected by a complex of intergenic interactions and that this polyfunctional chaperone is an important factor for the stability of genome function and regulatory mechanisms contributing to the tumorigenesis control.

The Insulin Receptor Adaptor IRS2 is an APC/C Substrate That Promotes Cell Cycle Protein Expression and a Robust Spindle Assembly Checkpoint

Insulin receptor substrate 2 (IRS2) is an essential adaptor that mediates signaling downstream of the insulin receptor and other receptor tyrosine kinases. Transduction through IRS2-dependent pathways is important for coordinating metabolic homeostasis, and dysregulation of IRS2 causes systemic insulin signaling defects. Despite the importance of maintaining proper IRS2 abundance, little is known about what factors mediate its protein stability. We conducted an unbiased proteomic screen to uncover novel substrates of the Anaphase Promoting Complex/Cyclosome (APC/C), a ubiquitin ligase that controls the abundance of key cell cycle regulators. We found that IRS2 levels are regulated by APC/C activity and that IRS2 is a direct APC/C target in G1 Consistent with the APC/C's role in degrading cell cycle regulators, quantitative proteomic analysis of IRS2-null cells revealed a deficiency in proteins involved in cell cycle progression. We further show that cells lacking IRS2 display a weakened spindle assembly checkpoint in cells treated with microtubule inhibitors. Together, these findings reveal a new pathway for IRS2 turnover and indicate that IRS2 is a component of the cell cycle control system in addition to acting as an essential metabolic regulator.

Relationships among pancreatic beta cell function, the Nrf2 pathway, and IRS2: a cross-sectional study

ABSTRACT Objectives This study aimed to investigate the relationships among islet function, the Nrf2 pathway, and insulin receptor substrate 2 (IRS2) in type 2 diabetes mellitus (T2DM), prediabetes mellitus (IGR), and normal glucose tolerance (NGT) populations. Methods Three hundred cases each were selected for the NGT, IGR, and T2DM groups; FBG, 2hPG, HbA1 c, FINS, TG, TC, HDL-C, and LDL-C levels and serum levels of nuclear factor in E2-related factor 2 (Nrf2), insulin receptor substrate 2 (IRS2), tumor necrosis factor alpha (TNF-α), and heme oxygenase 1 (HO-1) were evaluated. Results The T2DM group had lower islet β-cell function index and insulin sensitivity index than the NGT and IGR groups (P < 0.05). The Nrf2, IRS2, and HO-1 levels in the NGT, IGR, and T2DM groups followed a decreasing trend in the order mentioned, whereas the TNF-α levels followed an increasing trend. Conclusions Upon impairment of glucose regulation, the expression of TNF-α in the human body increased, which indicated the aggravation of oxidative stress (OS) and the inflammatory response. Islet function was maintained in the pre-diabetic population, and concurrently, the TNF-α, Nrf2, and HO-1 levels were moderately elevated, the expression of IRS2 was marginally inhibited, and the Nrf2 pathway was activated under mild OS stimulus to resist OS, inflammation, and injury, which may have been mediated through PI3 K/AKT. In patients with T2DM, islet function was significantly poorer, TNF-α amplification was enhanced significantly, and Nrf2, HO-1, and IRS2 expression reduced significantly; this suggested that, along with the aggravation of OS and the inflammatory response, Nrf2 pathway activation and HO-1 expression were both inhibited, the antioxidant capacity of the body was reduced, IRS2 degradation increased, and islet function was impaired.

Insulin receptor substrate in brain-enriched exosomes in subjects with major depression: on the path of creation of biosignatures of central insulin resistance.

Insulin signaling is critical for neuroplasticity, cerebral metabolism as well as for systemic energy metabolism. In rodent studies impaired brain insulin signaling with resultant insulin resistance (IR) modulates synaptic plasticity and the corresponding behavioral functions. Despite discoveries of central actions of insulin, in-vivo molecular mechanisms of brain IR until recently has proven difficult to study in the human brain. In the current study, we leveraged recent technological advances in molecular biology and herein report an increased number of exosomes enriched for L1CAM, a marker predominantly expressed in the brain, in subjects with major depressive disorder (MDD) as compared to age- and sex-matched healthy controls (HC). We also report increased concentration of the insulin receptor substrate-1 (IRS-1) in L1CAM+ exosomes in subjects with MDD as compared to age- and sex-matched HC. We found a relationship between expression of IRS-1 in L1CAM+ exosomes and systemic IR as assessed by homeostatic model assessment of IR in HC, but not in subjects with MDD. The increased IRS-1 levels in L1CAM+ exosomes were greater in subjects with MDD and were associated with suicidality and anhedonia. Finally, our data suggested sex differences in serine-312 phosphorylation of IRS-1 in L1CAM+ exosomes in subjects with MDD. These findings provide a starting point for creating mechanistic framework of brain IR in further development of personalized medicine strategies to effectively treat MDD.

Biotin, coenzyme Q10, and their combination ameliorate aluminium chloride-induced Alzheimer's disease via attenuating neuroinflammation and improving brain insulin signaling.

Insulin is important for brain function and neuronal survival. Insulin signaling is initiated by the phosphorylation of insulin receptor substrate-1 (IRS-1) at tyrosine (pTyr) residue. However, IRS-1 is inhibited by phosphorylation at serine (pSer). In Alzheimer's disease (AD), oxidative stress and accumulation of amyloid beta (Aβ) induce neuroinflammation, which augments pSer-IRS-1 and reduces pTyr-IRS-1 disturbing insulin signaling pathway. Coenzyme Q10 (CoQ10) and biotin possess antioxidant and anti-inflammatory properties, and, in this study, their impact on insulin signaling is investigated in an aluminium chloride (AlCl3 ) model of AD. AD was induced by oral administration of AlCl3 (75 mg/kg) for 60 days. Biotin (2 mg/kg), CoQ10 (10 mg/kg), and their combination were supplemented concomitantly with AlCl3 for 60 days. Memory test and histological examination were performed. Brain levels of lipid peroxides, antioxidants (reduced glutathione and superoxide dismutase), inflammatory markers (tumor necrosis factor-α, interleukin-6 [IL-6], IL-1, and nuclear factor κB), and phosphorylated Akt (survival kinase) as well as protein levels of Aβ, IRS-1 (pTyr and pSer), and caspase-3 (apoptotic marker) were determined. AlCl3 resulted in impaired memory, significant increase in Aβ, lipid peroxides, inflammatory markers, caspase-3, and pSer-IRS-1, with significant reduction of the antioxidants, pTyr-IRS-1, and p-Akt reflecting Aβ-induced inflammation and defective insulin signaling. Histological examination revealed focal aggregations of inflammatory cells and neuronal degeneration. The biochemical deviations and histological changes were attenuated by the concomitant treatment with biotin and, to greater extent, with CoQ10 and the combination. In conclusion, biotin and CoQ10 could protect against AD via attenuating inflammatory response and enhancing insulin signaling.

Linagliptin affects IRS1/Akt signaling and prevents high glucose-induced apoptosis in podocytes

Diabetes-induced podocyte apoptosis is considered to play a critical role in the pathogenesis of diabetic kidney disease (DKD). We proposed that hyperglycaemia can induce podocyte apoptosis by inhibiting the action of podocyte survival factors, thus inactivating the cellular effects of insulin signalling. In this study, we aimed to determine the effects of linagliptin on high glucose-induced podocyte apoptosis. Linagliptin reduced the increase in DNA fragmentation as well as the increase in TUNEL-positive cells in podocytes induced by high-glucose condition. Furthermore, linagliptin improved insulin-induced phosphorylation of insulin receptor substrate 1 (IRS1) and Akt, which was inhibited in high-glucose conditions. Adenoviral vector-mediated IRS1 overexpression in podocytes partially normalised DNA fragmentation in high-glucose conditions, while downregulation of IRS1 expression using small interfering RNA increased DNA fragmentation even in low-glucose conditions. Because reactive oxygen species inhibit glomerular insulin signalling in diabetes and Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway is one of the most important intrinsic antioxidative systems, we evaluated whether linagliptin increased Nrf2 in podocytes. High-glucose condition and linagliptin addition increased Nrf2 levels compared to low-glucose conditions. In summary, linagliptin offers protection against DKD by enhancing IRS1/Akt insulin signalling in podocytes and partially via the Keap1/Nrf2 pathway. Our findings suggest that linagliptin may induce protective effects in patients with DKD, and increasing IRS1 levels could be a potential therapeutic target in DKD.

Stat3 activation induces insulin resistance via a muscle-specific E3 ubiquitin ligase Fbxo40.

Cellular mechanisms causing insulin resistance (IR) in chronic kidney disease (CKD) are poorly understood. One potential mechanism is that CKD-induced inflammation activates the signal transducer and activator of transcription 3 (Stat3) in muscle. We uncovered increased p-Stat3 in muscles of mice with CKD or mice fed high-fat diet (HFD). Activated Stat3 stimulates the expression of Fbxo40, a muscle-specific E3 ubiquitin ligase that stimulates ubiquitin conjugation leading to degradation of insulin receptor substrate 1 (IRS1). Evidence that Stat3 activates Fbxo40 includes 1) potential Stat3 binding sites in Fbxo40 promoters; 2) Stat3 binding to the Fbxo40 promoter; and 3) constitutively active Stat3 stimulating both Fbxo40 expression and its promoter activity. We found that IL-6 activates Stat3 in myotubes, increasing Fbxo40 expression with reduced IRS1 and p-Akt. Knockdown Fbxo40 using siRNA from myotubes results in higher levels of IRS1 and p-Akt despite the presence of IL-6. We treated mice with a small-molecule inhibitor of Stat3 (TTI-101) and found improved glucose tolerance and insulin signaling in skeletal muscles of mice with CKD or fed an HFD. Finally, we uncovered improved glucose tolerance in mice with muscle-specific Stat3 KO versus results in Stat3f/f mice in response to the HFD. Thus Stat3 activation in muscle increases IR in mice. Inhibition of Stat3 by TTI-101 could be developed into clinical strategies to improve muscle insulin signaling in inflammation and other catabolic diseases.