metallothionein and Insulin-Resistance

Much attention has been paid to lifestyle-related diseases including type 2 diabetes mellitus, cardiovascular disease, hypertension, and hyperlipidemia because the incidence rates of these diseases are increasing in developed countries. Elucidation of factors contributing to the development of obesity and insulin resistance is needed. Metallothionein (MT), a ubiquitous metal-binding protein, is induced not only by heavy metals but also by various kinds of stresses. Endoplasmic reticulum (ER) stress is caused by accumulation of misfolded proteins in ER. Recently, increased ER stress by obesity and impairment of insulin action by ER stress have been reported. Exposure to ER stress increased induction of MT synthesis, and an enhanced response to ER stress evaluated as expression of Bip/GRP78mRNA was observed in the liver of MT-null mice, suggesting that MT attenuates expression of ER stress. MT may prevent ER stress and thereby modulate the development of obesity and insulin resistance. A possible role of metallothionein in response reaction for ER stress is discussed.

Topics: Animals; Diabetes Mellitus, Type 2; Endoplasmic Reticulum; Humans; Insulin Resistance; Metallothionein; Mice; Obesity; Stress, Physiological; Zinc

Cardiac insulin resistance is a key pathogenic factor for diabetic cardiomyopathy (DCM), but the mechanism remains largely unclear. We found that diabetic hearts exhibited decreased phosphorylation of total Akt and isoform Akt2 but not Akt1 in wild-type (WT) male FVB mice, which was accompanied by attenuation of Akt downstream glucose metabolic signal. All of these signal changes were not observed in metallothionein cardiac-specific transgenic (MT-TG) hearts. Furthermore, insulin-induced glucose metabolic signals were attenuated only in WT diabetic hearts. In addition, diabetic hearts exhibited increased Akt-negative regulator tribbles pseudokinase 3 (TRB3) expression only in WT mice, suggesting that MT may preserve Akt2 function via inhibiting TRB3. Moreover, MT prevented tert-butyl hydroperoxide (tBHP)-reduced insulin-stimulated Akt2 phosphorylation in MT-TG cardiomyocytes, which was abolished by specific silencing of Akt2. Specific silencing of TRB3 blocked tBHP inhibition of insulin-stimulated Akt2 phosphorylation in WT cardiomyocytes, whereas overexpression of TRB3 in MT-TG cardiomyocytes and hearts abolished MT preservation of insulin-stimulated Akt2 signals and MT prevention of DCM. Most importantly, supplementation of Zn to induce MT preserved cardiac Akt2 signals and prevented DCM. These results suggest that diabetes-inhibited cardiac Akt2 function via TRB3 upregulation leads to aberrant cardiac glucose metabolism. MT preservation of cardiac Akt2 function by inhibition of TRB3 prevents DCM.

Topics: Animals; Cell Cycle Proteins; Cells, Cultured; Diabetes Mellitus, Type 1; Heart; Hypoglycemic Agents; Insulin; Insulin Resistance; Lipopolysaccharides; Male; Metallothionein; Mice; Mice, Mutant Strains; Mice, Transgenic; Myocardium; Myocytes, Cardiac; Organ Specificity; Oxidants; Oxidative Stress; Phosphorylation; Protein Processing, Post-Translational; Proto-Oncogene Proteins c-akt; RNA Interference

Obesity continues to rise as an alarming global epidemic. System level mechanisms, diagnostics, and therapeutics are sorely needed so as to identify at risk individuals and design appropriate population scale interventions. The present study evaluated the protective role of metallothioneins (MTs) against obesity and high-fat diet-induced effects such as insulin resistance in both male and female MT-1+2 knockout and MT-3 knockout mice. As the metabolome is closest to the functional phenotype, changes in metabolite levels were also evaluated, and the direct or indirect involvement of MTs in metabolism examined. MT-1+2-, MT-3 knockout, and wild-type mice were given a high-fat diet for 2 months. Variation in body weight gain, tissue weight, and response to oral glucose tolerance test and insulin tolerance test were determined and compared to mice that received the control diet. Effect of the high-fat diet on the knockout mice were investigated on the metabolome level in specific tissues using metabolomics. Both knockout mice strains were more susceptible to high-fat diet-induced effects, such as weight gain and moderate insulin resistance, with the MT-3 knockout mice most susceptible. Brain tissue of the knockout mice showed most metabolic variation and pointed to possible impairment of mitochondrial function. The protective effect of MTs against high-fat diet and obesity-induced effects such as insulin resistance was evident from our observations. The putative role MTs play in mitochondrial function is possibly the main contributor to the lack of these effects in wild-type mice. Considering the expression profiles of the MT isoforms and similarity in brain metabolic variation in the knockout strains, it appears that they promote mitochondrial function in the hypothalamus, thereby limiting weight gain and insulin resistance. Furthermore, metabolomics research in preclinical models of obesity and in the clinic is warranted in the near future.

Topics: Adipose Tissue; Animals; Blood Glucose; Body Weight; Cerebral Cortex; Diet, High-Fat; Disease Models, Animal; Female; Glucose Tolerance Test; Insulin; Insulin Resistance; Male; Metabolome; Metabolomics; Metallothionein; Metallothionein 3; Mice; Mice, Knockout; Obesity

Insulin resistance plays an important role in the pathogenesis of type 2 diabetes and the metabolic syndrome. Many of the genes and pathways involved have been identified but some remain to be defined. Metallothioneins (Mts) are a family of anti-oxidant proteins and metallothionein 2a (Mt2a) polymorphims have been recently associated with type 2 diabetes and related complications. Our objective was to determine the Mt2a gene expression levels in adipose tissues from diabetic patients and the effect of Mt treatment on adipocyte insulin sensitivity.. Samples of subcutaneous and visceral adipose tissues from lean, type 2 diabetic and non-diabetic obese patients were analysed using RT-qPCR for Mt2a mRNA abundance. The regulation of Mt2a expression was further studied in 3T3-L1 adipocytes treated or not with TNFα (10 ng/ml, 72 h) to induce insulin resistance. The effects of Mt on glucose uptake were investigated in cultured adipocytes treated with recombinant Mt protein.. We found that the Mt2a gene expression was significantly higher in adipose tissue of type 2 diabetic patients in comparison to that of lean (p=0.003) subjects. In 3T3-L1 adipocytes, insulin resistance induced by TNFα increased Mt2a mRNA levels (p=3×10(-4)) and insulin-stimulated glucose uptake was significantly inhibited by 53% (p=8×10(-4)) compared to vehicle, when 3T3-L1 adipocytes were treated with Mt protein.. These data suggest that Mt2a might be involved in insulin resistance through the up-regulation of Mt gene expression, which may lead to the modulation of insulin action in fat cells. These results suggest the concept of considering Mt proteins as markers and potential targets in type 2 diabetes.

Topics: Adipose Tissue; Diabetes Mellitus, Type 2; Humans; Insulin Resistance; Metallothionein; Reactive Oxygen Species; Real-Time Polymerase Chain Reaction; Subcutaneous Fat

Metallothioneins (MTs) are intracellular low-molecular-weight, cysteine-rich proteins with potent metal-binding and redox functions, but with limited membrane permeativity. The aim of this study was to investigate whether we could enhance delivery of MT-1 to pancreatic islets or β cells in vitro and in vivo. The second goal was to determine whether increased MT-1 could prevent cellular toxicity induced by high glucose and free fatty acids in vitro (glucolipotoxicity) and ameliorate the development of diabetes induced by streptozotocin in mice or delay the development of diabetes by improving insulin secretion and resistance in the OLETF rat model of type 2 diabetes. Expression of HIV-1 Tat-MT-1 enabled efficient delivery of MT into both INS-1 cells and rat islets. Intracellular MT activity increased in parallel with the amount of protein delivered to cells. The formation of reactive oxygen species, glucolipotoxicity, and DNA fragmentation due to streptozotocin decreased after treating pancreatic β cells with Tat-MT in vitro. Importantly, in vivo, intraperitoneal injection resulted in delivery of the Tat-MT protein to the pancreas as well as liver, muscle, and white adipose tissues. Multiple injections increased radical-scavenging activity, decreased apoptosis, and reduced endoplasmic reticulum stress in the pancreas. Treatment with Tat-MT fusion protein delayed the development of diabetes in streptozotocin-induced mice and improved insulin secretion and resistance in OLETF rats. These results suggest that in vivo transduction of Tat-MT may offer a new strategy to protect pancreatic β cells from glucolipotoxicity, may improve insulin resistance in type 2 diabetes, and may have a protective effect in preventing islet destruction in type 1 diabetes.

Topics: Animals; Cells, Cultured; Diabetes Mellitus, Type 2; Disease Models, Animal; Gene Products, tat; Gene Transfer Techniques; HIV-1; Insulin; Insulin Resistance; Insulin Secretion; Male; Metallothionein; Mice; Mice, Inbred ICR; Rats; Rats, Inbred OLETF; Rats, Sprague-Dawley; Reactive Oxygen Species; Recombinant Fusion Proteins; Streptozocin

Insulin-like growth factor I (IGF-I) is normally produced from hepatocytes and various other cells and tissues, including the pancreas, and is known to stimulate islet cell replication in vitro, prevent Fas-mediated beta-cell destruction and delay the onset of diabetes in nonobese diabetic mice. Recently, however, the notion that IGF-I stimulates islet cell growth has been challenged by the results of IGF-I and receptor gene targeting. To test the effects of a general, more profound increase in circulating IGF-I on islet cell growth and glucose homeostasis, we have characterized MT-IGF mice, which overexpress the IGF-I gene under the metallothionein I promoter. In early reports, a 1.5-fold-elevated serum IGF-I level caused accelerated somatic growth and pancreatic enlargement. We demonstrated that the transgene expression, although widespread, was highly concentrated in the beta-cells of the pancreatic islets. Yet, islet cell percent and pancreatic morphology were unaffected. IGF-I overexpression resulted in significant hypoglycemia, hypoinsulinemia, and improved glucose tolerance but normal insulin secretion and sensitivity. Pyruvate tolerance test indicated significantly suppressed hepatic gluconeogenesis, which might explain the severe hypoglycemia after fasting. Finally, due to a partial prevention of beta-cell death against onset of diabetes and/or the insulin-like effects of IGF-I overexpression, MT-IGF mice (which overexpress the IGF-I gene under the metallothionein I promoter) were significantly resistant to streptozotocin-induced diabetes, with diminished hyperglycemia and prevention of weight loss and death. Although IGF-I might not promote islet cell growth, its overexpression is clearly antidiabetic by improving islet cell survival and/or providing insulin-like effects.

Topics: Animals; Blotting, Northern; Cell Proliferation; Diabetes Mellitus, Experimental; Fluorescent Antibody Technique; Gluconeogenesis; Glucose Tolerance Test; Humans; Hypoglycemia; Immunohistochemistry; Insulin; Insulin Resistance; Insulin-Like Growth Factor I; Islets of Langerhans; Metallothionein; Mice; Mice, Transgenic; Pyruvates; Rats; Reverse Transcriptase Polymerase Chain Reaction; RNA

Insulin resistance is concomitant with metabolic syndrome, oxidative stress and cardiac contractile dysfunction. However, the causal relationship between oxidative stress and cardiac dysfunction is unknown. This study was designed to determine the impact of overexpression of the cardiac antioxidant metallothionein on cardiac dysfunction induced by insulin resistance in mice.. Whole-body insulin resistance was generated in wild-type FVB and metallothionein transgenic mice by feeding them with sucrose for 12 weeks. Contractile and intracellular Ca(2+) properties were evaluated in ventricular myocytes using an IonOptix system. The contractile indices analysed included: peak shortening (PS), time to 90% PS (TPS(90)), time to 90% relengthening (TR(90)), half-width duration, maximal velocity of shortening (+dL/dt) and relengthening (-dL/dt), fura-fluorescence intensity change (DeltaFFI) and decay rate (tau).. The sucrose-fed mice displayed glucose intolerance, enhanced oxidative stress, hyperinsulinaemia, hypertriglyceridaemia and normal body weight. Compared with myocytes in starch-fed mice, those from sucrose-fed mice exhibited depressed PS, +dL/dt, -dL/dt, prolonged TR(90) and decay rate, and reduced DeltaFFI associated with normal TPS(90) and half-width duration. Western blot analysis revealed enhanced basal, but blunted insulin (15 mU/g)-stimulated Akt phosphorylation. It also showed elevated expression of insulin receptor beta, insulin receptor tyrosine phosphorylation, peroxisome proliferator-activated receptor gamma, protein tyrosine phosphatase 1B and phosphorylation of the transcription factor c-Jun, associated with a reduced fold increase of insulin-stimulated insulin receptor tyrosine phosphorylation in sucrose-fed mice. All western blot findings may be attenuated or ablated by metallothionein.. These data indicate that oxidative stress may play an important role in cardiac contractile dysfunction associated with glucose intolerance and possibly related to alteration in insulin signalling at the receptor and post-receptor levels.

Topics: Animals; Insulin; Insulin Resistance; JNK Mitogen-Activated Protein Kinases; Male; Metallothionein; Mice; Mice, Inbred Strains; Mice, Transgenic; Myocardial Contraction; Myocytes, Cardiac; Oncogene Protein v-akt; Oxidative Stress; Phosphorylation; PPAR gamma; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Protein Tyrosine Phosphatases; Receptor, Insulin; Signal Transduction