Department of Biochemistry, Microbiology, and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5.
J Biol Chem. 2012 Nov 16;287(47):39673-85. doi: 10.1074/jbc.M112.393538. Epub 2012 Oct 3.
The role of reactive oxygen species (ROS) in glucose-stimulated insulin release remains controversial because ROS have been shown to both amplify and impede insulin release. In regard to preventing insulin release, ROS activates uncoupling protein-2 (UCP2), a mitochondrial inner membrane protein that negatively regulates glucose-stimulated insulin secretion (GSIS) by uncoupling oxidative phosphorylation. With our recent discovery that the UCP2-mediated proton leak is modulated by reversible glutathionylation, a process responsive to small changes in ROS levels, we resolved to determine whether glutathionylation is required for UCP2 regulation of GSIS. Using Min6 cells and pancreatic islets, we demonstrate that induction of glutathionylation not only deactivates UCP2-mediated proton leak but also enhances GSIS. Conversely, an increase in mitochondrial matrix ROS was found to deglutathionylate and activate UCP2 leak and impede GSIS. Glucose metabolism also decreased the total amount of cellular glutathionylated proteins and increased the cellular glutathione redox ratio (GSH/GSSG). Intriguingly, the provision of extracellular ROS (H(2)O(2), 10 μM) amplified GSIS and also activated UCP2. Collectively, our findings indicate that the glutathionylation status of UCP2 contributes to the regulation of GSIS, and different cellular sites and inducers of ROS can have opposing effects on GSIS, perhaps explaining some of the controversy surrounding the role of ROS in GSIS.
活性氧 (ROS) 在葡萄糖刺激的胰岛素释放中的作用仍存在争议，因为 ROS 既能放大又能阻碍胰岛素的释放。关于防止胰岛素释放，ROS 激活解偶联蛋白 2 (UCP2)，一种线粒体内膜蛋白，通过解偶联氧化磷酸化负调节葡萄糖刺激的胰岛素分泌 (GSIS)。最近我们发现 UCP2 介导的质子泄漏可被可逆的谷胱甘肽化调节，这是一种对 ROS 水平微小变化敏感的过程，我们决定确定谷胱甘肽化是否是 UCP2 调节 GSIS 的必需条件。使用 Min6 细胞和胰岛，我们证明诱导谷胱甘肽化不仅使 UCP2 介导的质子泄漏失活，而且增强 GSIS。相反，发现线粒体基质 ROS 的增加会使 UCP2 去谷胱甘肽化并激活泄漏并阻碍 GSIS。葡萄糖代谢还降低了细胞内总谷胱甘肽化蛋白的量，并增加了细胞内谷胱甘肽氧化还原比 (GSH/GSSG)。有趣的是，提供细胞外 ROS（H2O2，10 μM）可放大 GSIS 并激活 UCP2。总之，我们的研究结果表明 UCP2 的谷胱甘肽化状态有助于 GSIS 的调节，ROS 的不同细胞部位和诱导剂可能对 GSIS 产生相反的影响，这也许可以解释 ROS 在 GSIS 中的作用存在争议的部分原因。
