Overexpression of Metallothionein in Pancreatic β-Cells Reduces Streptozotocin-Induced DNA Damage and Diabetes

Abstract

The release of reactive oxygen species (ROS) has been proposed as a cause of streptozotocin (STZ)-induced ␤-cell damage. This initiates a destructive cascade, consisting of DNA damage, excess activation of the DNA repair enzyme poly(ADP-ribose) polymerase, and depletion of cellular NAD ؉ . Metallothionein (MT) is an inducible antioxidant protein that has been shown to protect DNA from chemical damage in several cell types. Therefore, we examined whether overexpression of MT could protect ␤-cell DNA and thereby prevent STZinduced diabetes. Two lines of transgenic mice were produced with up to a 30-fold elevation in ␤-cell MT. Cultured islets from control mice and MT transgenic mice were exposed to STZ. MT was found to decrease STZ-induced islet disruption, DNA breakage, and depletion of NAD ؉ . To assess in vivo protection, transgenic and control mice were injected with STZ. Transgenic mice had significantly reduced hyperglycemia. Ultrastructural examination of islets from STZ-treated mice showed that MT prevented degranulation and cell death. These results demonstrate that MT can reduce diabetes and confirm the DNA damage mechanism of STZ-induced ␤-cell death. Diabetes 50:2040 -2046, 2001 P ancreatic ␤-cells (1) are extremely vulnerable to damage caused by reactive oxygen species (ROS). A striking example of ␤-cell vulnerability is the severe damage done by streptozotocin (STZ). This natural toxin has several destructive actions, including DNA methylation (2), protein modification (3), and ROS generation (4). STZ enters the cytoplasm via GLUT2, which is the ␤-cell's glucose transporter (5). The presence of this transporter may account for part of the specific vulnerability of the ␤-cell. However, GLUT2 is also present in the liver and kidney, tissues that are relatively resistant to STZ damage. The much greater sensitivity of the ␤-cell is probably due to its very low level of antioxidant enzyme expression and activity (6 -8), which leaves it unable to inactivate ROS. It has been demonstrated in vivo that overexpression of the antiapoptotic, antioxidant protein thioredoxin (9), as well as the antioxidant protein catalase (10), protects the ␤-cell from STZ. However, it is not possible to markedly induce these proteins in vivo. Therefore, we are exploring the potential of another antioxidant protein that is highly inducible, metallothionein (MT).MTs are a family of low-molecular weight cysteine-rich proteins that bind heavy metals with high affinity. MT appears to play important roles in zinc homeostasis and ROS protection. Both functions are due to the presence of abundant cysteine residues. MT protects against many agents known to act through ROS, including hydrogen peroxide, radiation, glutathione depletors, adriamycin, and xanthine oxidase (11,12). MT is distinct among ROS scavengers in the breadth of its protection, in that it scavenges nitric oxide radicals (13), superoxide radicals (14), and hydroxyl radicals (15), which are the most destructive ROS species (11). MT scavenging of hydroxyl radicals is especi...

Cytoprotective Effects of KIOM-79 on Streptozotocin Induced Cell Damage by Inhibiting ERK and AP-1

“…[32][33][34][35][36][37][38] In the present study, KIOM-79 was found to decrease intracellular ROS levels, cellular DNA damage, and the lipid peroxidation that is induced by STZ. The cells exposed to STZ exhibited the distinct morphological features of apoptosis, including morphological changes and DNA fragmentation.…”

Molecular mechanisms for hyperinsulinaemia induced by overproduction of selenium-dependent glutathione peroxidase-1 in mice

“…Scale bar, 10 µm. Magnification, 40× insulin concentration nor insulin gene expression in islets was altered by overexpressing catalase by up to 50-fold [9], two forms of metallothionein by up to 30-fold [9,42] or three forms of superoxide dismutase enzymes by up to 10-fold [5,7]. Furthermore, overproduction of metallothionein and catalase in beta cells actually accelerated cytokineinduced beta cell death [9].…”

Gene expression profiles during beta cell maturation and after IL-1? exposure reveal important roles of Pdx-1 and Nkx6.1 for IL-1? sensitivity

“…Exposure to IL-1β resulted in a small further up-regulation of two subclasses of GST in both phenotypes, whereas GP (FC −1.3) was exclusively down-regulated in the beta cell phenotype following IL-1β exposure (Panel B). Downregulation of metallothionein-1 and 2 (FC −2.2, Panel A) may also render the beta cells susceptible to the toxic effects of IL-1β, since it has been shown that over-expression of metallothionein in beta cells reduces streptozotocin-induced DNA damage and diabetes [15]. Exposure to IL-1β resulted in further downregulation of metallothionein-1 and 2 in both phenotypes although significantly (p<0.001) lowest in the beta-cell phenotype (FC −4.7 vs FC −2.2; Panel B).…”

“…Destruction of the beta cells has been associated with induction of highly reactive agents like oxygen-derived free radicals and nitric oxide (NO) [10], increased apoptosis [11], decreased insulin production and release [12] and decreased mitochondrial function [12]. Stimulation or over-expression of different defence mechanisms has been demonstrated to protect beta cells against the toxic effect of cytokines, streptozotocin, NO or reactive oxygen species [13,14,15].…”