Insulin Receptor Substrate-1 In Skeletal Muscle Research Articles

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.

Quantitative phosphoproteomic analysis of IRS1 in skeletal muscle from men with normal glucose tolerance or type 2 diabetes: A case-control study

Background & aimsThe physiological regulation and contribution of the multiple phosphorylation sites of insulin receptor substrate 1 (IRS1) to the pathogenesis of insulin resistance is unknown. Our aims were to map the phosphorylated motifs of IRS1 in skeletal muscle from people with normal glucose tolerance (NGT; n = 11) or type 2 diabetes mellitus (T2DM; n = 11). MethodsSkeletal muscle biopsies were obtained under fasted conditions or during a euglycemic clamp and IRS1 phosphorylation sites were identified by mass spectrometry. ResultsWe identified 33 phosphorylation sites in biopsies from fasted individuals, including 2 previously unreported sites ([Ser393] and [Thr1017]). In men with NGT and T2DM, insulin increased phosphorylation of 5 peptides covering 10 serine or threonine sites and decreased phosphorylation of 6 peptides covering 9 serine, threonine or tyrosine sites. Insulin-stimulation increased phosphorylation of 2 peptides, and decreased phosphorylation of 2 peptides only in men with NGT. Insulin increased phosphorylation of 2 peptides only in men with T2DM. ConclusionsDespite severe skeletal muscle insulin resistance, the pattern of IRS1 phosphorylation was not uniformly altered in T2DM. Our results contribute to the evolving understanding of the physiological regulation of insulin signaling and complement the comprehensive map of IRS1 phosphorylation in T2DM.

Effects of Modified Sanzi Yangqin Decoction on Tyrosine Phosphorylation of IRS-1 in Skeletal Muscle of Type 2 Diabetic Rats.

This study aimed to investigate the effect of Modified Sanzi Yangqin Decoction on tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) in skeletal muscle of type 2 diabetic rats. The rat model of type 2 diabetes was induced by high-fat diet and multiple low-dose streptozotocin injections. Diabetic model rats were randomly divided into 5 groups: the model control group, the metformin group, and Modified Sanzi Yangqin Decoction groups of low, medium, and high doses. OGTT was conducted every two weeks during treatment period. At the end of the treatment, the fasting blood glucose (FBG) level and the fasting C-peptide level were measured to calculate insulin resistance index. The levels of IRS-1, p-IRS-1(Tyr895), and protein tyrosine phosphates 1B (PTP1B) in skeletal muscle were also measured. Modified Sanzi Yangqin Decoction significantly reduced the FBG level, increased the fasting C-peptide level, and lowered the insulin resistance index in type 2 diabetic rats. It also significantly increased the protein level of p-IRS-1(Tyr895) and reduced the PTP1B protein level in skeletal muscle of type 2 diabetic rats. Modified Sanzi Yangqin Decoction increases tyrosine phosphorylation of IRS-1 in skeletal muscle of type 2 diabetic rats, which results from the increase of p-IRS-1(Tyr895) protein and is related to the suppression of PTP1B protein.

MG53-IRS-1 (Mitsugumin 53-Insulin Receptor Substrate-1) Interaction Disruptor Sensitizes Insulin Signaling in Skeletal Muscle

Mitsugumin 53 (MG53) is an E3 ligase that interacts with and ubiquitinates insulin receptor substrate-1 (IRS-1) in skeletal muscle; thus, an MG53-IRS-1 interaction disruptor (MID), which potentially sensitizes insulin signaling with an elevated level of IRS-1 in skeletal muscle, is an excellent candidate for treating insulin resistance. To screen for an MID, we developed a bimolecular luminescence complementation system using an N-terminal luciferase fragment fused with IRS-1 and a C-terminal luciferase fragment fused with an MG53 C14A mutant that binds to IRS-1 but does not have E3 ligase activity. An MID, which was discovered using the bimolecular luminescence complementation system, disrupted the molecular association of MG53 with IRS-1, thus abolishing MG53-mediated IRS-1 ubiquitination and degradation. Thus, the MID sensitized insulin signaling and increased insulin-elicited glucose uptake with an elevated level of IRS-1 in C2C12 myotubes. These data indicate that this MID holds promise as a drug candidate for treating insulin resistance.

Neurolytic celiac plexus block enhances skeletal muscle insulin signaling and attenuates insulin resistance in GK rats.

Non-insulin-dependent diabetes mellitus (NIDDM) is associated with chronic inflammatory activity and disrupted insulin signaling, leading to insulin resistance (IR). The present study investigated the benefits of neurolytic celiac plexus block (NCPB) on IR in a rat NIDDM model. Goto-Kakizaki rats fed a high-fat, high-glucose diet to induce signs of NIDDM were randomly divided into NCPB and control groups; these received daily bilateral 0.5% lidocaine or 0.9% saline injections into the celiac plexus, respectively. Following 14 and 28 daily injections, rats were subject to oral glucose tolerance tests (OGTTs) or sacrificed for the analysis of serum free fatty acids (FFAs), serum inflammatory cytokines and skeletal muscle insulin signaling. Compared with controls, rats in the NCPB group demonstrated significantly (P<0.05) lower baseline, 60-min and 120-min OGTT values, lower 120-min serum insulin, lower IR [higher insulin sensitivity index (ISI1) and lower ISI2) and lower serum FFAs, tumor necrosis factor-α, interleukin (IL)-1β and IL-6. Conversely, NCPB rats exhibited higher basal and insulin-stimulated skeletal muscle glucose uptake and higher skeletal muscle insulin receptor substrate-1 (IRS-1) and glucose transporter type 4 expression. There were no differences between the groups in insulin receptor β (Rβ) or Akt expression; however Rβ-Y1162/Y1163 and Akt-S473 phosphorylation levels were higher and IRS-1-S307 phosphorylation were lower in NCPB rats than in the controls. These results indicate that NCPB improved insulin signaling and reduced IR, possibly by inhibiting inflammatory cytokine release.

Heat stress increases insulin sensitivity in pigs.

Proper insulin homeostasis appears critical for adapting to and surviving a heat load. Further, heat stress (HS) induces phenotypic changes in livestock that suggest an increase in insulin action. The current study objective was to evaluate the effects of HS on whole-body insulin sensitivity. Female pigs (57 ± 4 kg body weight) were subjected to two experimental periods. During period 1, all pigs remained in thermoneutral conditions (TN; 21°C) and were fed ad libitum. During period 2, pigs were exposed to: (i) constant HS conditions (32°C) and fed ad libitum (n = 6), or (ii) TN conditions and pair-fed (PFTN; n = 6) to eliminate the confounding effects of dissimilar feed intake. A hyperinsulinemic euglycemic clamp (HEC) was conducted on d3 of both periods; and skeletal muscle and adipose tissue biopsies were collected prior to and after an insulin tolerance test (ITT) on d5 of period 2. During the HEC, insulin infusion increased circulating insulin and decreased plasma C-peptide and nonesterified fatty acids, similarly between treatments. From period 1 to 2, the rate of glucose infusion in response to the HEC remained similar in HS pigs while it decreased (36%) in PFTN controls. Prior to the ITT, HS increased (41%) skeletal muscle insulin receptor substrate-1 protein abundance, but did not affect protein kinase B or their phosphorylated forms. In adipose tissue, HS did not alter any of the basal or stimulated measured insulin signaling markers. In summary, HS increases whole-body insulin-stimulated glucose uptake.

Jiaotai pill (交泰丸) enhances insulin signaling through phosphatidylinositol 3-kinase pathway in skeletal muscle of diabetic rats

To investigate the effect of Jiaotai Pill (, JTP) at different constitutional proportions on insulin signaling through phosphatidylinositol 3-kinase (PI3K) pathway in the skeletal muscle of diabetic rats. The rat model of type 2 diabetes mellitus (T2DM) was established by intravenous injection of a small dose of streptozotoein plus high fat diet feeding. JTP at the same dosage of cinnamon and the increasing dosage of Coptis chinensis was administered to diabetic rats for nine weeks respectively. Plasma glucose and insulin levels were assayed. The expressions of proteins were determined by Western blot method. All the three formulations of JTP decreased plasma glucose and fasting insulin levels as well as increased the protein expressions of insulin receptor β (InsRβ) subunit, insulin receptor substrate-1 (IRS-1), PI3K p85 subunit and glucose transporter 4 (GLUT4) in skeletal muscle. Meanwhile, JTP increased the tyrosine phosphorylation of InsRβ subunit and IRS-1, and reduced the serine phosphorylation of IRS-1 in skeletal muscle. Interestingly, the effect of JTP on improving insulin sensitivity was not dose-dependent. In contrast, JTP containing the least amount of Coptis chinensis exhibited the best effect. JTP at different constitutional proportions attenuates the development of diabetes in a rat model of T2DM. The mechanism might be associated with enhancing insulin signaling through PI3K pathway in the skeletal muscle.

Abnormal myocardial insulin signalling in type 2 diabetes and left-ventricular dysfunction

Whole body and myocardial insulin resistance are features of non-insulin-dependent diabetes mellitus (NIDDM) and left-ventricular dysfunction (LVD). We determined whether abnormalities of insulin receptor substrate-1 (IRS1), IRS1-associated PI3K (IRS1-PI3K), and glucose transporter 4 (GLUT4) contribute to tissue-specific insulin resistance. We collected skeletal muscle (n = 27) and myocardial biopsies (n = 24) from control patients (n = 7), patients with NIDDM (n = 9) and patients with LVD (n = 8), who were characterized by euglycaemic-hyperinsulinaemic clamp and positron emission tomography. Comparative studies were carried out in three mouse models. We demonstrate an unrecognized reduction of IRS1 in skeletal muscle of LVD patients and an unexpected increase in cardiac IRS1-PI3K activity in NIDDM and LVD patients. In NIDDM, there was a concomitant reduction in sarcolemmal GLUT4, whereas in patients with LVD sarcolemmal GLUT4 was increased. We confirm activation of IRS1-PI3K and reduction in sarcolemmal GLUT4 in the insulin resistant ob/ob mouse heart where we also demonstrate perturbation of GLUT4 docking and fusion. A direct relationship between PI3K and GLUT4 was demonstrated in mice expressing activated PI3K in the heart and increased GLUT4 at the sarcolemma was confirmed in a mouse model of LVD. Our data show that the mechanisms of myocardial insulin resistance are different between NIDDM and LVD.

Comparative effects of N-acetyl-l-cysteine and ramipril on arterial hypertension, insulin resistance, and oxidative stress in chronically glucose-fed rats

Beneficial effects of an antioxidant (N-acetyl-L-cysteine, NAC) and an angiotensin I-converting enzyme (ACE) inhibitor (ramipril) were assessed in a rat model of insulin resistance induced by 10% glucose feeding for 20 weeks. Treatments with NAC (2 g/kg per day) and ramipril (1 mg/kg per day) were initiated at 16 weeks in the drinking fluid. Systolic blood pressure, plasma levels of insulin and glucose, and insulin resistance were significantly higher in rats treated with glucose for 20 weeks. This was associated with a higher production of superoxide anion and NADPH oxidase activity in aorta and liver and with a marked reduction in protein expression of skeletal muscle insulin receptor substrate-1 (IRS-1) in the gastrocnemius muscle. NAC prevented all these alterations. Although ramipril also reversed high blood pressure, it had a lesser effect on insulin resistance (including IRS-1) and blocked superoxide anion production only in aorta. Ramipril, in contrast to NAC, did not reduce NADPH oxidase activity in aorta and liver or plasma levels of 4-hydroxynonenal and malondialdehyde. Results suggest that the inhibition of the oxidative stress in hypertensive and insulin-resistant states contributes to the therapeutic effects of NAC and ramipril. Whereas NAC exerts effective antioxidant activity in multiple tissues, ramipril appears to preferentially target the vasculature.

Reversal of insulin resistance postpartum is linked to enhanced skeletal muscle insulin signaling.

The restoration of maternal insulin sensitivity postpartum represents an important physiological and metabolic adaptation in a woman's reproductive lifespan. The present study was conducted to examine the potential cellular mechanisms underlying the changes in insulin sensitivity from late pregnancy to postpartum in human skeletal muscle. Nine nonobese women (age, 32 +/- 2 yr; body mass index, 21.2 +/- 0.8 kg/m(2)) with normal glucose tolerance were studied during late pregnancy (30-36 wk) and again approximately 1 yr postpartum using a euglycemic-hyperinsulinemic clamp (5 mm glucose, 40 mU/m(2).min insulin) to determine insulin sensitivity. Biopsies of the vastus lateralis muscle were obtained in the basal state before each clamp. Insulin sensitivity improved by 74% from late pregnancy to 1 yr postpartum (5.5 +/- 0.6 vs. 9.6 +/- 0.9 mg/kg fat-free mass.min; P < 0.005). Skeletal muscle insulin receptor (IR) protein expression increased by 42% postpartum, as measured by ELISA (4.0 +/- 0.6 vs. 5.7 +/- 0.6 ng/g protein; P < 0.05) and by Western blotting of the IR beta-subunit (28.7 +/- 4.7 vs. 42.0 +/- 4.8 arbitrary units; P < 0.003). However, in vitro studies showed that when adjusted for IR concentration, maximal insulin-stimulated (100 nm) IR tyrosine phosphorylation (0.75 +/- 0.06 vs. 0.92 +/- 0.08 U) and IR tyrosine kinase activity (183.8 +/- 27.0 vs. 204.3 +/- 23.7 fmol ATP/ng IR) were unchanged. There was a 69% increase in IR substrate-1 (IRS-1) protein expression (P = 0.05) in muscle postpartum. In addition, the p85alpha regulatory subunit of phosphatidylinositol 3-kinase was markedly reduced by 55% (P < 0.02) postpartum. The change in insulin sensitivity from late pregnancy to postpartum correlated highly with the corresponding change in IRS-1 protein (r = 0.84; P < 0.007). Downstream signaling proteins, including total Akt and p70s6 kinase, and the glucose transporter protein GLUT-4, were similar at both time points. These data suggest that reduced IR tyrosine kinase activity is not a major factor in the IR of pregnancy in lean women with normal glucose tolerance. Rather, the reversal of insulin resistance 1 yr postpartum is accompanied by increased skeletal muscle IRS-1 along with a down-regulation of the p85alpha subunit of phosphatidylinositol 3-kinase. These changes may allow for greater p85/p110 binding to IRS-1 and play a significant physiological role in the underlying metabolic adaptation to normal human pregnancy and restoration of insulin sensitivity postpartum.

Insulin signal transduction in skeletal muscle from glucose-intolerant relatives of type 2 diabetic patients [corrected

To determine whether defects in the insulin signal transduction cascade are present in skeletal muscle from prediabetic individuals, we excised biopsies from eight glucose-intolerant male first-degree relatives of patients with type 2 diabetes (IGT relatives) and nine matched control subjects before and during a euglycemic-hyperinsulinemic clamp. IGT relatives were insulin-resistant in oxidative and nonoxidative pathways for glucose metabolism. In vivo insulin infusion increased skeletal muscle insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation (P = 0.01) and phosphatidylinositide 3-kinase (PI 3-kinase) activity (phosphotyrosine and IRS-1 associated) in control subjects (P < 0.02) but not in IGT relatives (NS). The incremental increase in insulin action on IRS-1 tyrosine phosphorylation was lower in IGT relatives versus control subjects (P < 0.05). The incremental defects in signal transduction noted for IRS-1 and PI 3-kinase may be attributed to elevated basal phosphorylation/activity of these parameters, because absolute phosphorylation/activity under insulin-stimulated conditions was similar between IGT relatives and control subjects. Insulin increased Akt serine phosphorylation in control subjects and IGT relatives, with a tendency for reduced phosphorylation in IGT relatives (P = 0.12). In conclusion, aberrant phosphorylation/activity of IRS-1, PI 3-kinase, and Akt is observed in skeletal muscle from relatives of patients with type 2 diabetes with IGT. However, the elevated basal activity of these signaling intermediates and the lack of a strong correlation between these parameters to glucose metabolism suggests that other defects of insulin signal transduction and/or downstream components of glucose metabolism may play a greater role in the development of insulin resistance in skeletal muscle from relatives of patients with type 2 diabetes.

Ramipril increases the protein level of skeletal muscle IRS-1 and alters protein tyrosine phosphatase activity in spontaneously hypertensive rats.

To investigate mechanisms by which angiotensin converting enzyme (ACE)-inhibition increases insulin sensitivity, spontaneously hypertensive (SH) rats were treated with or without ramipril (1 mg/kg per day) for 12 weeks. Insulin binding and protein levels of insulin receptor substrate-1 (IRS-1), p85-subunit of phosphatidylinositol 3'-kinase (p85) and Src homology 2 domain-containing phosphatase-2 (SHP2) were then determined in hindlimb muscle and liver. Additionally, protein tyrosine phosphatase (PTPase) activities towards immobilized phosphorylated insulin receptor or phosphorylated IRS-1 of membrane (MF) and cytosolic fractions (CF) of these tissues were measured. Ramipril treatment increased IRS-1-protein content in muscle by 31+/-9% (P<0.05). No effects were observed on IRS-1 content in liver or on insulin binding or protein expression of p85 or SHP2 in both tissues. Ramipril treatment also increased dephosphorylation of insulin receptor by muscle CF (22.0+/-1.0%/60 min compared to 16.8+/-1.5%/60 min; P<0.05), and of IRS-1 by liver MF (37.2+/-1.7%/7.5 min compared to 33.8+/-1.7%/7.5 min; P<0.05) and CF (36.8+/-1.0%/7.5 min compared to 33.2+/-1.0%/7.5 min; P<0.05). We conclude that the observed effects of ACE-inhibition by ramipril on the protein expression of IRS-1 and on PTPase activity might contribute to its effect on insulin sensitivity.

Human skeletal muscle insulin receptor substrate-1. Characterization of the cDNA, gene, and chromosomal localization

Human skeletal muscle insulin receptor substrate-1. Characterization of the cDNA, gene, and chromosomal localization