[Show abstract][Hide abstract] ABSTRACT: We investigated the direct effect of a nitric oxide donor (spermine NONOate) on glucose transport in isolated human skeletal muscle and L6 skeletal muscle cells. We hypothesised that pharmacological treatment of human skeletal muscle with N-(2-aminoethyl)-N-(2-hydroxy-2-nitrosohydrazino)-1,2-ethylenediamine (spermine NONOate) would increase intracellular cyclic GMP (cGMP) levels and promote glucose transport.
Skeletal muscle strips were prepared from vastus lateralis muscle biopsies obtained from seven healthy men. Muscle strips were incubated in the absence or presence of 5 mmol/l spermine NONOate or 120 nmol/l insulin. The L6 muscle cells were treated with spermine NONOate (20 micromol/l) and incubated in the absence or presence of insulin (120 nmol/l). The direct effect of spermine NONOate and insulin on glucose transport, cGMP levels and signal transduction was determined.
In human skeletal muscle, spermine NONOate increased glucose transport 2.4-fold (p < 0.05), concomitant with increased cGMP levels (80-fold, p < 0.001). Phosphorylation of components of the canonical insulin signalling cascade was unaltered by spermine NONOate exposure, implicating an insulin-independent signalling mechanism. Consistent with this, spermine NONOate increased AMP-activated protein kinase (AMPK)-alpha1-associated activity (1.7-fold, p < 0.05). In L6 muscle cells, spermine NONOate increased glucose uptake (p < 0.01) and glycogen synthesis (p < 0.001), an effect that was in addition to that of insulin. Spermine NONOate also elicited a concomitant increase in AMPK and acetyl-CoA carboxylase phosphorylation. In the presence of the guanylate cyclase inhibitor LY-83583 (10 micromol/l), spermine NONOate had no effect on glycogen synthesis and AMPK-alpha1 phosphorylation.
Pharmacological treatment of skeletal muscle with spermine NONOate increases glucose transport via insulin-independent signalling pathways involving increased intracellular cGMP levels and AMPK-alpha1-associated activity.
[Show abstract][Hide abstract] ABSTRACT: The transcriptional coactivator PGC-1alpha promotes mitochondrial biogenesis and thermogenic programs in brown adipose tissue. Pan et al. (2009) identify the transcription factor twist-1 as a negative feedback regulator of PGC-1alpha.
[Show abstract][Hide abstract] ABSTRACT: In skeletal muscle, insulin stimulates glucose transport activity three- to fourfold, and a large part of this stimulation is associated with a net translocation of GLUT4 from an intracellular compartment to the cell surface. We examined the extent to which insulin or the AMP-activated protein kinase activator AICAR can lead to a stimulation of the exocytosis limb of the GLUT4 translocation pathway and thereby account for the net increase in glucose transport activity.
Using a biotinylated photoaffinity label, we tagged endogenous GLUT4 and studied the kinetics of exocytosis of the tagged protein in rat and human skeletal muscle in response to insulin or AICAR. Isolated epitrochlearis muscles were obtained from male Wistar rats. Vastus lateralis skeletal muscle strips were prepared from open muscle biopsies obtained from six healthy men (age 39 +/- 11 years and BMI 25.8 +/- 0.8 kg/m2).
In rat epitrochlearis muscle, insulin exposure leads to a sixfold stimulation of the GLUT4 exocytosis rate (with basal and insulin-stimulated rate constants of 0.010 and 0.067 min(-1), respectively). In human vastus lateralis muscle, insulin stimulates GLUT4 translocation by a similar sixfold increase in the exocytosis rate constant (with basal and insulin-stimulated rate constants of 0.011 and 0.075 min(-1), respectively). In contrast, AICAR treatment does not markedly increase exocytosis in either rat or human muscle.
Insulin stimulation of the GLUT4 exocytosis rate constant is sufficient to account for most of the observed increase in glucose transport activity in rat and human muscle.
[Show abstract][Hide abstract] ABSTRACT: Type 2 (non-insulin-dependent) diabetes mellitus is a progressive metabolic disorder arising from genetic and environmental factors that impair beta cell function and insulin action in peripheral tissues. We identified reduced diacylglycerol kinase delta (DGKdelta) expression and DGK activity in skeletal muscle from type 2 diabetic patients. In diabetic animals, reduced DGKdelta protein and DGK kinase activity were restored upon correction of glycemia. DGKdelta haploinsufficiency increased diacylglycerol content, reduced peripheral insulin sensitivity, insulin signaling, and glucose transport, and led to age-dependent obesity. Metabolic flexibility, evident by the transition between lipid and carbohydrate utilization during fasted and fed conditions, was impaired in DGKdelta haploinsufficient mice. We reveal a previously unrecognized role for DGKdelta in contributing to hyperglycemia-induced peripheral insulin resistance and thereby exacerbating the severity of type 2 diabetes. DGKdelta deficiency causes peripheral insulin resistance and metabolic inflexibility. These defects in glucose and energy homeostasis contribute to mild obesity later in life.
[Show abstract][Hide abstract] ABSTRACT: Aberrant insulin signaling and glucose metabolism in skeletal muscle from type 2 diabetic patients may arise from genetic defects and an altered metabolic milieu. We determined insulin action on signal transduction and glucose transport in isolated vastus lateralis skeletal muscle from normal glucose-tolerant first-degree relatives of type 2 diabetic patients (n = 8, 41 +/- 3 years, BMI 25.1 +/- 0.8 kg/m(2)) and healthy control subjects (n = 9, 40 +/- 2 years, BMI 23.4 +/- 0.7 kg/m(2)) with no family history of diabetes. Basal and submaximal insulin-stimulated (0.6 and 1.2 nmol/l) glucose transport was comparable between groups, whereas the maximal response (120 nmol/l) was 38% lower (P < 0.05) in the relatives. Insulin increased phosphorylation of Akt and Akt substrate of 160 kDa (AS160) in a dose-dependent manner, with comparable responses between groups. AS160 phosphorylation and glucose transport were positively correlated in control subjects (R(2) = 0.97, P = 0.01) but not relatives (R(2) = 0.46, P = 0.32). mRNA of key transcriptional factors and coregulators of mitochondrial biogenesis were also determined. Skeletal muscle mRNA expression of peroxisome proliferator-activated receptor (PPAR) gamma coactivator (PGC)-1alpha, PGC-1beta, PPARdelta, nuclear respiratory factor-1, and uncoupling protein-3 was comparable between first-degree relatives and control subjects. In conclusion, the uncoupling of insulin action on Akt/AS160 signaling and glucose transport implicates defective GLUT4 trafficking as an early event in the pathogenesis of type 2 diabetes.
[Show abstract][Hide abstract] ABSTRACT: AMP-activated protein kinase (AMPK) regulates metabolic adaptations in skeletal muscle. The aim of this study was to investigate whether AMPK modulates the expression of skeletal muscle genes that have been implicated in lipid and glucose metabolism under fed or fasting conditions.
Two genetically modified animal models were used: AMPK gamma3 subunit knockout mice (Prkag3(-/-)) and skeletal muscle-specific transgenic mice (Tg-Prkag3(225Q)) that express a mutant (R225Q) gamma3 subunit. Levels of mRNA transcripts of genes involved in lipid and glucose metabolism in white gastrocnemius muscles of these mice (under fed or 16-h fasting conditions) were assessed by quantitative real-time PCR.
Wild-type mice displayed a coordinated increase in the transcription of skeletal muscle genes encoding proteins involved in lipid/oxidative metabolism (lipoprotein lipase, fatty acid transporter, carnitine palmitoyl transferase-1 and citrate synthase) and glucose metabolism (glycogen synthase and lactate dehydrogenase) in response to fasting. In contrast, these fasting-induced responses were impaired in Prkag3(-/-) mice. The transcription of genes involved in lipid and oxidative metabolism was increased in the skeletal muscle of Tg-Prkag3(225Q) mice compared with that in wild-type mice. Moreover, the expression of the genes encoding hexokinase II and 6-phosphofrucktokinase was decreased in Tg-Prkag3(225Q) mice after fasting.
AMPK is involved in the coordinated transcription of genes critical for lipid and glucose metabolism in white glycolytic skeletal muscle.
[Show abstract][Hide abstract] ABSTRACT: The primary gene mutated in Charcot-Marie-Tooth type 2A is mitofusin-2 (Mfn2). Mfn2 encodes a mitochondrial protein that participates in the maintenance of the mitochondrial network and that regulates mitochondrial metabolism and intracellular signaling. The potential for regulation of human Mfn2 gene expression in vivo is largely unknown. Based on the presence of mitochondrial dysfunction in insulin-resistant conditions, we have examined whether Mfn2 expression is dysregulated in skeletal muscle from obese or nonobese type 2 diabetic subjects, whether muscle Mfn2 expression is regulated by body weight loss, and the potential regulatory role of tumor necrosis factor (TNF)alpha or interleukin-6. We show that mRNA concentration of Mfn2 is decreased in skeletal muscle from both male and female obese subjects. Muscle Mfn2 expression was also reduced in lean or in obese type 2 diabetic patients. There was a strong negative correlation between the Mfn2 expression and the BMI in nondiabetic and type 2 diabetic subjects. A positive correlation between the Mfn2 expression and the insulin sensitivity was also detected in nondiabetic and type 2 diabetic subjects. To determine the effect of weight loss on Mfn2 mRNA expression, six morbidly obese subjects were subjected to weight loss by bilio-pancreatic diversion. Mean expression of muscle Mfn2 mRNA increased threefold after reduction in body weight, and a positive correlation between muscle Mfn2 expression and insulin sensitivity was again detected. In vitro experiments revealed an inhibitory effect of TNFalpha or interleukin-6 on Mfn2 expression in cultured cells. We conclude that body weight loss upregulates the expression of Mfn2 mRNA in skeletal muscle of obese humans, type 2 diabetes downregulates the expression of Mfn2 mRNA in skeletal muscle, Mfn2 expression in skeletal muscle is directly proportional to insulin sensitivity and is inversely proportional to the BMI, TNFalpha and interleukin-6 downregulate Mfn2 expression and may participate in the dysregulation of Mfn2 expression in obesity or type 2 diabetes, and the in vivo modulation of Mfn2 mRNA levels is an additional level of regulation for the control of muscle metabolism and could provide a molecular mechanism for alterations in mitochondrial function in obesity or type 2 diabetes.
[Show abstract][Hide abstract] ABSTRACT: AS160 is a newly described substrate for the protein kinase Akt that links insulin signaling and GLUT4 trafficking. In this study, we determined the expression of and in vivo insulin action on AS160 in human skeletal muscle. In addition, we compared the effect of physiological hyperinsulinemia on AS160 phosphorylation in 10 lean-to-moderately obese type 2 diabetic and 9 healthy subjects. Insulin infusion increased the phosphorylation of several proteins reacting with a phospho-Akt substrate antibody. We focused on AS160, as this Akt substrate has been linked to glucose transport. A 160-kDa phosphorylated protein was identified as AS160 by immunoblot analysis with an AS160-specific antibody. Physiological hyperinsulinemia increased AS160 phosphorylation 2.9-fold in skeletal muscle of control subjects (P < 0.001). Insulin-stimulated AS160 phosphorylation was reduced 39% (P < 0.05) in type 2 diabetic patients. AS160 protein expression was similar in type 2 diabetic and control subjects. Impaired AS160 phosphorylation was related to aberrant Akt signaling; insulin action on Akt Ser(473) phosphorylation was not significantly reduced in type 2 diabetic compared with control subjects, whereas Thr(308) phosphorylation was impaired 51% (P < 0.05). In conclusion, physiological hyperinsulinemia increases AS160 phosphorylation in human skeletal muscle. Moreover, defects in insulin action on AS160 may impair GLUT4 trafficking in type 2 diabetes.
[Show abstract][Hide abstract] ABSTRACT: Activators of peroxisome proliferator-activated receptor (PPAR)gamma have been studied intensively for their insulin-sensitizing properties and antidiabetic effects. Recently, a specific PPARdelta activator (GW501516) was reported to attenuate plasma glucose and insulin levels when administered to genetically obese ob/ob mice. This study was performed to determine whether specific activation of PPARdelta has direct effects on insulin action in skeletal muscle. Specific activation of PPARdelta using two pharmacological agonists (GW501516 and GW0742) increased glucose uptake independently of insulin in differentiated C2C12 myotubes. In cultured primary human skeletal myotubes, GW501516 increased glucose uptake independently of insulin and enhanced subsequent insulin stimulation. PPARdelta agonists increased the respective phosphorylation and expression of AMP-activated protein kinase 1.9-fold (P < 0.05) and 1.8-fold (P < 0.05), of extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase (MAPK) 2.2-fold (P < 0.05) and 1.7-fold (P < 0.05), and of p38 MAPK 1.2-fold (P < 0.05) and 1.4-fold (P < 0.05). Basal and insulin-stimulated protein kinase B/Akt was unaltered in cells preexposed to PPARdelta agonists. Preincubation of myotubes with the p38 MAPK inhibitor SB203580 reduced insulin- and PPARdelta-mediated increase in glucose uptake, whereas the mitogen-activated protein kinase kinase inhibitor PD98059 was without effect. PPARdelta agonists reduced mRNA expression of PPARdelta, sterol regulatory element binding protein (SREBP)-1a, and SREBP-1c (P < 0.05). In contrast, mRNA expression of PPARgamma, PPARgamma coactivator 1, GLUT1, and GLUT4 was unaltered. Our results provide evidence to suggest that PPARdelta agonists increase glucose metabolism and promote gene regulatory responses in cultured human skeletal muscle. Moreover, we provide biological validation of PPARdelta as a potential target for antidiabetic therapy.
[Show abstract][Hide abstract] ABSTRACT: The molecular signaling mechanisms by which insulin leads to increased glucose transport and metabolism and gene expression are not completely elucidated. We have characterized the nature of insulin signaling defects in skeletal muscle from Type 2 diabetic patients. Insulin receptor substrate (IRS-1) phosphorylation, phosphatidylinositol (PI) 3-kinase activity, and glucose transport activity are impaired as a consequence of functional defects, whereas insulin receptor tyrosine phosphorylation, mitogen-activated protein kinase (MAPK) phosphorylation, and glycogen synthase activity are normal. Using biotinylated photoaffinity labeling, we have shown that reduced cell surface GLUT4 levels can explain glucose transport defects in skeletal muscle from Type 2 diabetic patients under insulin-stimulated conditions. Current work is focused on mechanisms behind insulin-dependent and insulin-independent regulation of glucose uptake. We have recently determined the independent effects of insulin and hypoxia/AICAR exposure on glucose transport and cell surface GLUT4 content in skeletal muscle from nondiabetic and Type 2 diabetic subjects. Hypoxia and AICAR increase glucose transport via an insulin-independent mechanism involving activation of 5'-AMP-activated kinase (AMPK). AMPK signaling is intact, because 5-aminoimidazole-4-carboxamide 1-beta-D-ribonucleoside (AICAR) increased AMPK and acetyl-CoA carboxylase (ACC) phosphorylation to a similar extent in Type 2 diabetic and nondiabetic subjects. However, AICAR responses on glucose uptake were impaired. Our studies highlight important AMPK-dependent and independent pathways in the regulation of GLUT4 and glucose transport activity in insulin resistant skeletal muscle. Understanding signaling mechanisms to downstream metabolic responses may provide valuable clues to a future therapy for Type 2 diabetes.
Medicine & Science in Sports & Exercise 08/2004; 36(7):1212-7. · 4.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adipose tissue secretes several molecules that may participate in metabolic cross-talk to other insulin-sensitive tissues. Thus, adipose tissue is a key endocrine organ that regulates insulin sensitivity in other peripheral insulin target tissues. We have studied the expression and acute insulin regulation of novel genes expressed in adipose tissue that are implicated in the control of whole body insulin sensitivity.
Expression of adiponectin, c-Cbl-associated protein (CAP), 11-beta hydroxysteroid dehydrogenase type 1 (11beta-HSD-1), and sterol regulatory element binding protein (SREBP)-1c was determined in subcutaneous adipose tissue from type 2 diabetic and age- and BMI-matched healthy men by real-time polymerase chain reaction analysis.
Expression of adiponectin, CAP, 11beta-HSD-1, and SREBP-1c was similar between healthy and type 2 diabetic subjects. Insulin infusion for 3 hours did not affect expression of CAP, 11beta-HSD-1, or adiponectin mRNA in either group. However, insulin infusion increased SREBP-1c expression by 80% in healthy, but not in type 2 diabetic, subjects.
Our results provide evidence that insulin action on SREBP-1c is dysregulated in adipose tissue from type 2 diabetic subjects. Impaired insulin regulation on gene expression of select targets in adipose tissue may contribute to the pathogenesis of type 2 diabetes.
Obesity research 02/2004; 12(1):25-31. · 4.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: AMP-activated protein kinase (AMPK) activation by AICAR (5-amino-imidazole carboxamide riboside) is correlated with increased glucose transport in rodent skeletal muscle via an insulin-independent pathway. We determined in vitro effects of insulin and/or AICAR exposure on glucose transport and cell-surface GLUT4 content in skeletal muscle from nondiabetic men and men with type 2 diabetes. AICAR increased glucose transport in a dose-dependent manner in healthy subjects. Insulin and AICAR increased glucose transport and cell-surface GLUT4 content to a similar extent in control subjects. In contrast, insulin- and AICAR-stimulated responses on glucose transport and cell-surface GLUT4 content were impaired in subjects with type 2 diabetes. Importantly, exposure of type 2 diabetic skeletal muscle to a combination of insulin and AICAR increased glucose transport and cell-surface GLUT4 content to levels achieved in control subjects. AICAR increased AMPK and acetyl-CoA carboxylase phosphorylation to a similar extent in skeletal muscle from subjects with type 2 diabetes and nondiabetic subjects. Our studies highlight the potential importance of AMPK-dependent pathways in the regulation of GLUT4 and glucose transport activity in insulin-resistant skeletal muscle. Activation of AMPK is an attractive strategy to enhance glucose transport through increased cell surface GLUT4 content in insulin-resistant skeletal muscle.
[Show abstract][Hide abstract] ABSTRACT: In many cells and specially in muscle, mitochondria form elongated filaments or a branched reticulum. We show that Mfn2 (mitofusin 2), a mitochondrial membrane protein that participates in mitochondrial fusion in mammalian cells, is induced during myogenesis and contributes to the maintenance and operation of the mitochondrial network. Repression of Mfn2 caused morphological and functional fragmentation of the mitochondrial network into independent clusters. Concomitantly, repression of Mfn2 reduced glucose oxidation, mitochondrial membrane potential, cell respiration, and mitochondrial proton leak. We also show that the Mfn2-dependent mechanism of mitochondrial control is disturbed in obesity by reduced Mfn2 expression. In all, our data indicate that Mfn2 expression is crucial in mitochondrial metabolism through the maintenance of the mitochondrial network architecture, and reduced Mfn2 expression may explain some of the metabolic alterations associated with obesity.
Journal of Biological Chemistry 06/2003; 278(19):17190-7. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Glucose intolerance or overt diabetes occurs in 80% of patients with pancreatic cancer (PC). This associated metabolic disorder includes peripheral insulin resistance, which may be caused by factors produced by the PC. The mechanism underlying PC-associated insulin resistance has not been clearly defined.
To characterize basal and insulin-stimulated glucose transport, phosphatidylinositol (PI) 3-kinase activity, and glucose transporter 4 (GLUT4) in skeletal muscles of PC patients.
Skeletal muscle samples were obtained from the abdominal wall of 17 PC patients during surgery. Control muscles were sampled in the same way from 11 donors undergoing abdominal surgery for benign diseases. PI 3-kinase activity, glucose transport, and GLUT4 were assessed in vitro in these muscles.
In the presence of physiologic concentrations of insulin, glucose transport and PI 3-kinase activity were significantly decreased in the PC group compared with controls. At supraphysiologic insulin concentrations, glucose transport was significantly decreased but PI 3-kinase activity was normalized. In the absence of insulin, these parameters were not significantly different between PC and control groups. Muscle GLUT4 contents were similar between PC and control groups.
Defects in insulin-mediated PI 3-kinase activity and glucose transport contribute to the insulin resistance in patients with PC.
[Show abstract][Hide abstract] ABSTRACT: Introduction: Glucose intolerance or overt diabetes occurs in 80% of patients with pancreatic cancer (PC). This associated metabolic disorder includes peripheral insulin resistance, which may be caused by factors produced by the PC. The mechanism underlying PC-associated insulin resistance has not been clearly defined.
Aim: To characterize basal and insulin-stimulated glucose transport, phosphatidylinositol (PI) 3-kinase activity, and glucose transporter 4 (GLUT4) in skeletal muscles of PC patients.
Methodology: Skeletal muscle samples were obtained from the abdominal wall of 17 PC patients during surgery. Control muscles were sampled in the same way from 11 donors undergoing abdominal surgery for benign diseases. PI 3-kinase activity, glucose transport, and GLUT4 were assessed in vitro in these muscles.
Results: In the presence of physiologic concentrations of insulin, glucose transport and PI 3-kinase activity were significantly decreased in the PC group compared with controls. At supraphysiologic insulin concentrations, glucose transport was significantly decreased but PI 3-kinase activity was normalized. In the absence of insulin, these parameters were not significantly different between PC and control groups. Muscle GLUT4 contents were similar between PC and control groups.
Conclusion: Defects in insulin-mediated PI 3-kinase activity and glucose transport contribute to the insulin resistance in patients with PC.
[Show abstract][Hide abstract] ABSTRACT: Exercise and improved diet is known to be beneficial in the management of type 2 (non-insulin dependent) diabetes mellitus. In practice, however, it is difficult for patients to implement these changes unaided. We hypothesized that a lifestyle modification programme involving residential visits would result in beneficial effects on glycaemic control and lipid profile. Three hundred and four individuals with type 2 diabetes participated in a lifestyle modification programme, involving three residential visits (2 weeks, 1 week and one 3-day visit) spaced over 31 weeks. The subjects were all referred for treatment following repeated failure to achieve metabolic control in primary care settings. Participants received information and practical guidance regarding exercise training, nutrition, as well as stress management and psychological counselling. Clinical parameters were determined at each visit. After completion of the programme, subjects showed significant improvements in glycaemic control (P<0.0001). Oxygen uptake was significantly improved (P<0.0001) and blood pressure (P<0.0001), body mass index (P<0.0001) and serum cholesterol (P<0.001) was significantly reduced, while HDL cholesterol (P<0.05) was significantly increased. There were no changes in LDL cholesterol values. Subjects also reported increased well-being and reduced stress. In conclusion, a 31-week lifestyle modification programme results in marked improvements in glycaemic control, blood pressure and well-being in subjects with type 2 diabetes. Thus, this type of lifestyle modification programme is a powerful treatment option to reduce risk factors associated with diabetes and diabetic complications, even in patients who have not responded to conventional diabetic therapy.
[Show abstract][Hide abstract] ABSTRACT: The gene of the p85alpha regulatory subunit of phosphatidylinositol (PI) 3-kinase gives rise to several splice variants. We hypothesized that the expression of p85alpha splice variants may be altered in skeletal muscle from subjects with type 2 diabetes mellitus. Skeletal muscle biopsies were obtained from nine type 2 diabetic and eight healthy men, matched for age, body mass index (BMI) and physical fitness. PI 3-kinase activity in skeletal muscle following in vitro insulin stimulation was reduced in subjects with type 2 diabetes. p85alpha mRNA was elevated fourfold in type 2 diabetic as compared to healthy control subjects ( P<0.05). p85alpha mRNA abundance was positively correlated with plasma insulin concentration ( P<0.01) and serum glucose concentration ( P<0.01). Despite this, protein levels of p85alpha, p55alpha, and the novel human p50alpha were not altered in type 2 diabetic subjects. Thus, although gene expression of full-length p85alpha is increased in skeletal muscle from type 2 diabetics, this is not reflected by increased protein levels. Therefore, defects in PI 3-kinase activity are likely due to impaired activation of the enzyme rather than changes in protein expression of the isoforms of the regulatory subunit.
Pflügers Archiv - European Journal of Physiology 10/2002; 445(1):25-31. · 4.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Insulin resistance is a characteristic feature of type II diabetes mellitus and obesity. Although defects in glucose homeostasis have been recognized for decades, the molecular mechanisms accounting for impaired whole body glucose uptake are still not fully understood. Skeletal muscle constitutes the largest insulin-sensitive organ in humans; thus, insulin resistance in this tissue will have a major impact on whole body glucose homeostasis. Intense efforts are under way to define the molecular mechanisms that regulate glucose metabolism and gene expression in insulin-sensitive tissues. Knowledge of the human genome sequence, used in concert with gene and/or protein array technology, will provide a powerful means to facilitate efforts in revealing molecular targets that regulate glucose homeostasis in type II diabetes mellitus. This will offer quicker ways forward to identifying gene expression profiles in insulin-sensitive and insulin-resistant human tissue. This review will present our current understanding of potential defects in insulin signal transduction pathways, with an emphasis on mechanisms regulating glucose transport in skeletal muscle from people with type II diabetes mellitus. Elucidation of the pathways involved in the regulation of glucose homeostasis will offer insight into the causation of insulin resistance and type II diabetes mellitus. Furthermore, this will identify biochemical entry points for drug intervention to improve glucose homeostasis.
Annals of the New York Academy of Sciences 07/2002; 967:120-34. · 4.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The 5'AMP-activated protein kinase is an important mediator of muscle contraction-induced glucose transport and a target for pharmacological treatment of Type II (non-insulin-dependent) diabetes mellitus. The 5'AMP-activated protein kinase can be activated by 5-aminoimidazole-4-carboxamide ribonucleoside. We hypothesised that 5-aminoimidazole-4-carboxamide ribonucleoside treatment could restore glucose homeostasis in ob/ob mice.
Lean and ob/ob mice were given 5-aminoimidazole-4-carboxamide ribonucleoside (1 mg.g body wt(-1).day(-1) s.c) or 0.9 % NaCl (vehicle) for 1-7 days.
Short-term 5-aminoimidazole-4-carboxamide ribonucleoside treatment normalised glucose concentrations in ob/ob mice within 1 h, with effects persisting over 4 h. After 1 week of daily injections, 5-aminoimidazole-4-carboxamide ribonucleoside treatment corrected hyperglycaemia, improved glucose tolerance, and increased GLUT4 and hexokinase II protein expression in skeletal muscle, but had deleterious effects on plasma non-esterified fatty acids and triglycerides. Treatment with 5-aminoimidazole-4-carboxamide ribonucleoside increased liver glycogen in fasted and fed ob/ob mice and muscle glycogen in fasted, but not fed ob/ob and lean mice. Defects in insulin-stimulated phosphatidylinositol 3-kinase and glucose transport in skeletal muscle from ob/ob mice were not corrected by 5-aminoimidazole-4-carboxamide ribonucleoside treatment. While ex vivo insulin-stimulated glucose transport was reduced in isolated muscle from ob/ob mice, the 5-aminoimidazole-4-carboxamide ribonucleoside stimulated response was normal.
The 5-aminoimidazole-4-carboxamide ribonucleoside mediated improvements in glucose homeostasis in ob/ob mice can be explained by effects in skeletal muscle and liver. Due to the apparently deleterious effects of 5-aminoimidazole-4-carboxamide ribonucleoside on the blood lipid profile, strategies to develop tissue-specific and pathway-specific activators of 5'AMP-activated protein kinase should be considered in order to improve glucose homeostasis.