metallothionein and Diabetic-Cardiomyopathies

Diabetes is a metabolic disorder characterized by hyperglycemia, resulting in low-grade systemic inflammation. Diabetic cardiomyopathy (DCM) is a common complication among diabetic patients, and the mechanism underlying its induction of cardiac remodeling and dysfunction remains unclear. Numerous experimental and clinical studies have suggested that adaptive immunity, especially T lymphocyte-mediated immunity, plays a potentially important role in the pathogenesis of diabetes and DCM. Metallothioneins (MTs), cysteine-rich, metal-binding proteins, have antioxidant properties. Some potential mechanisms underlying the cardioprotective effects of MTs include the role of MTs in calcium regulation, zinc homeostasis, insulin sensitization, and antioxidant activity. Moreover, metal homeostasis, especially MT-regulated zinc homeostasis, is essential for immune function. This review discusses aberrant immune regulation in diabetic heart disease with respect to endothelial insulin resistance and the effects of hyperglycemia and hyperlipidemia on tissues and the different effects of intracellular and extracellular MTs on adaptive immunity. This review shows that intracellular MTs are involved in naïve T-cell activation and reduce regulatory T-cell (Treg) polarization, whereas extracellular MTs promote proliferation and survival in naïve T cells and Treg polarization but inhibit their activation, thus revealing potential therapeutic strategies targeting the regulation of immune cell function by MTs.

Topics: Adaptive Immunity; Animals; Blood Glucose; Cell Proliferation; Cytokines; Diabetic Cardiomyopathies; Humans; Lipids; Lymphocyte Activation; Metallothionein; Signal Transduction; T-Lymphocyte Subsets; T-Lymphocytes, Regulatory

Impaired zinc homeostasis is observed in diabetes mellitus (DM2) and its complications. Zinc has a specific role in pancreatic β-cells via insulin synthesis, storage, and secretion. Intracellular zinc homeostasis is tightly controlled by zinc transporters (ZnT and Zip families) and metallothioneins (MT) which modulate the uptake, storage, and distribution of zinc. Several investigations in animal models demonstrate the protective role of MT in DM2 and its cardiovascular or renal complications, while a copious literature shows that a common polymorphism (R325W) in ZnT8, which affects the protein's zinc transport activity, is associated with increased DM2 risk. Emerging studies highlight a role of other zinc transporters in β-cell function, suggesting that targeting them could make a possible contribution in managing the hyperglycemia in diabetic patients. This article summarizes the current findings concerning the role of zinc homeostasis in DM2 pathogenesis and development of diabetic cardiomyopathy and nephropathy and suggests novel therapeutic targets. © 2017 BioFactors, 43(6):770-784, 2017.

Topics: Animals; Biological Transport; Diabetes Mellitus, Type 2; Diabetic Cardiomyopathies; Diabetic Nephropathies; Dietary Supplements; Disease Models, Animal; Gene Expression Regulation; Homeostasis; Humans; Insulin; Insulin-Secreting Cells; Metallothionein; Zinc; Zinc Transporter 8

To efficiently prevent diabetic cardiomyopathy (DCM), we have explored and confirmed that metallothionein (MT) prevents DCM by attenuating oxidative stress, and increasing expression of proteins associated with glucose metabolism. To determine whether Akt2 expression is critical to MT prevention of DCM, mice with either global Akt2 gene deletion (Akt2-KO), or cardiomyocyte-specific overexpressing MT gene (MT-TG) or both combined (MT-TG/Akt2-KO) were used. Akt2-KO mice exhibited symptoms of DCM (cardiac remodelling and dysfunction), and reduced expression of glycogen and glucose metabolism-related proteins, despite an increase in total Akt (t-Akt) phosphorylation. Cardiac MT overexpression in MT-TG/Akt2-KO mice prevented DCM and restored glucose metabolism-related proteins expression and baseline t-Akt phosphorylation. Furthermore, phosphorylation of ERK1/2 increased in the heart of MT-TG/Akt2-KO mice, compared with Akt2-KO mice. As ERK1/2 has been implicated in the regulation of glucose transport and metabolism this increase could potentially underlie MT protective effect in MT-TG/Akt2-KO mice. Therefore, these results show that although our previous work has shown that MT preserving Akt2 activity is sufficient to prevent DCM, in the absence of Akt2 MT may stimulate alternative or downstream pathways protecting from DCM in a type 2 model of diabetes, and that this protection may be associated with the ERK activation pathway.

Topics: Animals; Diabetic Cardiomyopathies; Female; Glucose; Humans; Male; Metallothionein; Mice; Mice, Inbred C57BL; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Myocardium; Proto-Oncogene Proteins c-akt; Transgenes; Up-Regulation

We have reported that sulforaphane (SFN) prevented diabetic cardiomyopathy in both type 1 and type 2 diabetes (T2DM) animal models via the upregulation of nuclear transcription factor erythroid 2-related factor 2 (Nrf2) and metallothionein (MT). In this study, we tested whether SFN protects the heart from T2DM directly through Nrf2, MT, or both. Using Nrf2-knockout (KO), MT-KO, and wild-type (WT) mice, T2DM was induced by feeding a high-fat diet for 3 months followed by a small dose of streptozotocin. Age-matched controls were given a normal diet. Both T2DM and control mice were then treated with or without SFN for 4 months by continually feeding a high-fat or normal diet. SFN prevented diabetes-induced cardiac dysfunction as well as diabetes-associated cardiac oxidative damage, inflammation, fibrosis, and hypertrophy, with increases in Nrf2 and MT expressions in the WT mice. Both Nrf2-KO and MT-KO diabetic mice exhibited greater cardiac damage than WT diabetic mice. SFN did not provide cardiac protection in Nrf2-KO mice, but partially or completely protected the heart from diabetes in MT-KO mice. SFN did not induce MT expression in Nrf2-KO mice, but stimulated Nrf2 function in MT-KO mice. These results suggest that Nrf2 plays the indispensable role for SFN cardiac protection from T2DM with significant induction of MT and other antioxidants. MT expression induced by SFN is Nrf2 dependent, but is not indispensable for SFN-induced cardiac protection from T2DM.

Topics: Animals; Anticarcinogenic Agents; Blotting, Western; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Diabetic Cardiomyopathies; Diet, High-Fat; Echocardiography; Heart; Isothiocyanates; Lipid Peroxidation; Male; Metallothionein; Mice; Mice, Knockout; Myocardium; NF-E2-Related Factor 2; Real-Time Polymerase Chain Reaction; Sulfoxides; Up-Regulation

Diabetic cardiomyopathy is a prominent cause of heart failure in patients with diabetes mellitus. Currently, there is no specific treatment for diabetic cardiomyopathy. This study aimed to investigate the effect and underlying mechanisms of Zinc (Zn) supplementation in the protection against diabetic cardiomyopathy in a rat model of type 2 diabetes mellitus (T2DM). T2DM-like lesions in male Wistar rats were induced by introducing the high-fat diet and by administration of streptozocin (STZ). After STZ induction, animals with fasting plasma glucose level ≥16.7 mM were considered as diabetic, and randomly assigned to the group receiving physiological saline (control) or ZnSO4 for 56 days. On days 0, 7, 28 and 56 of treatment, animals were weighed, and their blood samples were analyzed. On day 56, hemodynamic assessment was performed right before the sacrifice of animals. Cardiac tissue specimens were collected and subjected to pathologic assessment, metallothionein (MT) concentration measurement and Western blot analysis of microtubule-associated protein light chain 3 (LC3), the marker of autophagy, and glucose-regulated protein-78 (GRP78), an oxidative stress marker. High-fat diet feeding followed by STZ administration resulted in weight loss, hyperglycemia, polydipsia, polyphagia, hemodynamic anomalies and a significant increase in the myocardial content of LC3 and GRP78 proteins, but not in MT protein. Zn supplementation effectively attenuated all these aberrations induced by high-fat diet and STZ. These findings suggest that Zn might be a protective factor in diabetic cardiomyopathy, acting in two ways: at least partially, through inhibiting autophagy and by endoplasmic reticulum stress.

Topics: Animals; Autophagy; Biomarkers; Blood Glucose; Diabetes Mellitus, Type 2; Diabetic Cardiomyopathies; Diet, High-Fat; Dietary Supplements; Disease Models, Animal; Endoplasmic Reticulum Stress; Heat-Shock Proteins; Male; Metallothionein; Microtubule-Associated Proteins; Rats; Rats, Wistar; Streptozocin; Treatment Outcome; Zinc

The development of diabetic cardiomyopathy is attributed to diabetic oxidative stress, which may be related to the mitogen-activated protein kinase (MAPK) c-Jun NH2-terminal kinase (JNK) activation. The present study tested a hypothesis whether the curcumin analog C66 [(2E,6E)-2,6-bis(2-(trifluoromethyl)benzylidene) cyclohexanone] as a potent antioxidant can protect diabetes-induced cardiac functional and pathogenic changes via inhibition of JNK function. Diabetes was induced with a single intraperitoneal injection of streptozotocin in male C57BL/6 mice. Diabetic and age-matched control mice were randomly divided into three groups, each group treated with C66, JNK inhibitor (JNKi, SP600125), or vehicle (1% CMC-Na solution) by gavage at 5 mg/kg every other day for 3 mo. Neither C66 nor JNKi impacted diabetic hyperglycemia and inhibition of body-weight gain, but both significantly prevented diabetes-induced JNK phosphorylation in the heart. Compared with basal line, cardiac function was significantly decreased in diabetic mice at 3 mo of diabetes but not in C66- or JNKi-treated diabetic mice. Cardiac fibrosis, oxidative damage, endoplasmic reticulum stress, and cell apoptosis, examined by Sirius red staining, Western blot, and thiobarbituric acid assay, were also significantly increased in diabetic mice, all which were prevented by C66 or JNKi treatment under diabetic conditions. Cardiac metallothionein expression was significantly decreased in diabetic mice but was almost normal in C66- or JNKi-treated diabetic mice. These results suggest that, like JNKi, C66 is able to prevent diabetic upregulation of JNK function, resulting in a prevention of diabetes-induced cardiac fibrosis, oxidative stress, endoplasmic reticulum stress, and cell death, along with a preservation of cardiac metallothionein expression.

Topics: Animals; Apoptosis; Benzylidene Compounds; Blood Pressure; Blotting, Western; Coloring Agents; Curcumin; Cyclohexanones; Diabetes Mellitus, Experimental; Diabetic Cardiomyopathies; Echocardiography; Endoplasmic Reticulum Stress; Fibrosis; Heart; JNK Mitogen-Activated Protein Kinases; Lipid Peroxidation; Male; Metallothionein; Mice; Mice, Inbred C57BL; Myocardium; Oxidative Stress; Phosphorylation; Protein Kinase Inhibitors; Real-Time Polymerase Chain Reaction

Diabetic cardiomyopathy is a clinically distinct disease characterized by impaired cardiac function as a result of reduced contractility and hypertension-induced athero- or arteriosclerosis. This may be due either to generalized vascular disease, tissue-based injury such as focal cardiomyocyte dysmorphia, or microvascular damage manifested by myocardial capillary basement membrane (CBM) thickening. Hyperglycemia-driven increases in reactive oxygen species (ROS) have been proposed to contribute to such damage. To address this hypothesis, we utilized light (LM) and transmission electron microscopy (TEM) to demonstrate cardiomyocyte morphology and myocardial CBM thickness in the left ventricles of four mouse genotypes: FVB (background Friend virus B controls), OVE (transgenic diabetics), Mt [transgenics with targeted overexpression of the antioxidant protein metallothionein (MT) in cardiomyocytes], and OVEMt (bi-transgenic cross of OVE and Mt) animals. Mice were prepared for morphometric analysis by vascular perfusion. Focal myocardial disorganization was identified in OVE mice but not in the remaining genotypes. Not unexpectedly, myocardial CBM thickness was increased significantly in OVE relative to FVB (P < 0.05) and Mt (P < 0.05) animals (+28% and +39.5%, respectively). Remarkably, however, OVEMt myocardial CBMs showed no increase in width; rather they were ~3% thinner than FVB controls. Although the molecular mechanisms regulating CBM width remain elusive, it seems possible that despite a significant hyperglycemic environment, MT antioxidant activity may mitigate local oxidative stress and reduce downstream excess microvascular extracellular matrix (ECM) formation. In addition, the reduction of intra- and perivascular ROS may protect against incipient endothelial damage and the CBM thickening that results from such injury.

Topics: Animals; Basement Membrane; Blood Glucose; Capillaries; Coronary Vessels; Diabetic Cardiomyopathies; Disease Models, Animal; Genotype; Glycated Hemoglobin; Humans; Male; Metallothionein; Mice; Mice, Transgenic; Microscopy, Electron, Transmission; Myocytes, Cardiac; Oxidative Stress; Phenotype; Reactive Oxygen Species; Up-Regulation