Glucose transporters and cellular antioxidant potential

 描述（由申请人提供）：活性氧（ROS）能够引起胰岛素抵抗和氧化损伤。一些专门的细胞类型具有细胞外抗坏血酸循环的能力。在这个过程中，抗坏血酸作为抗氧化剂输出，并且在其被氧化成脱氢抗坏血酸（DHA）之后，DHA被吸收并在细胞内还原成抗坏血酸用于另一轮抗氧化剂流出。我们已经获得的初步数据表明，小鼠骨骼肌有能力减少细胞外电子受体的过程中，是依赖于抗坏血酸的释放。因此，该项目的目的是阐明骨骼肌细胞外抗坏血酸再循环的机制、调节和生理后果。目的1是确定骨骼肌细胞外抗坏血酸再循环是否提供细胞外抗氧化剂。目标1的假设是，肌肉细胞可以减少细胞外电子受体，电子由抗坏血酸携带，H2 O2在这个过程中起着抵消作用。另外的假设是GLUT 1介导的DHA转运支持抗坏血酸再循环，阴离子通道负责细胞外还原活性和抗坏血酸流出。目的2是确定骨骼肌细胞外还原和抗坏血酸再循环是否受胰岛素和AMP活化蛋白激酶（AMPK）活化的调节。具体而言，目的是确定胰岛素是否产生DHA转运、葡萄糖6-磷酸脱氢酶（G6 PD）活性和抗坏血酸流出的协同增加，并确定AMPK是否刺激DHA转运而不刺激G6 PD活性或抗坏血酸流出。目的3是确定抗坏血酸再循环的功能作用，如防止氧化损伤和维持胰岛素作用。以前，抗坏血酸循环被描述为相对于骨骼肌较小的专门组织，骨骼肌含有40%的全身抗坏血酸。这个项目将建立骨骼肌作为细胞外抗氧化剂的主要产生者，因此是全身抗氧化状态的重要组织。此外，它可以建立抗坏血酸循环的重要性，特别是肌肉DHA摄取在控制ROS，从而维持正常的胰岛素作用。如果成功，该项目将引入骨骼肌抗坏血酸循环的操纵作为解决胰岛素抵抗的新手段。

 DESCRIPTION (provided by applicant): Reactive oxygen species (ROS) have the capacity to cause insulin resistance and oxidative damage. A few specialized cell types have the capacity for extracellular ascorbate cycling. In this process, ascorbate is exported as an antioxidant, and after it is oxidized to dehydroascorbic acid (DHA), the DHA is taken up and reduced intracellularly to ascorbate for another round of antioxidant efflux. We have obtained preliminary data showing that mouse skeletal muscle has the ability to reduce extracellular electron acceptors in a process that is dependent on ascorbate release. Accordingly, the aims of the project are to elucidate the mechanism for, the regulation of, and the physiological consequences of extracellular ascorbate recycling by skeletal muscle. Aim 1 is to determine whether extracellular ascorbate recycling by skeletal muscle provides extracellular antioxidants. The hypotheses for Aim 1 are that muscle cells can reduce extracellular electron acceptors, that the electrons are carried by ascorbate, and that H2O2 plays a countervailing role in this process. Additional hypotheses are that GLUT1-mediated DHA transport supports ascorbate recycling and that anion channels are responsible for extracellular reduction activity and ascorbate efflux. Aim 2 is to determine whether extracellular reduction and ascorbate recycling by skeletal muscle are regulated by insulin and activation of the AMP-activated protein kinase (AMPK). In particular, the aim is to determine whether insulin produces a synergistic increase in DHA transport, glucose 6-phosphate dehydrogenase (G6PD) activity, and ascorbate efflux and to determine whether AMPK stimulates DHA transport but not G6PD activity or ascorbate efflux. Aim 3 is to determine functional roles of ascorbate recycling such as prevention of oxidative damage and maintenance of insulin action. Previously, ascorbate cycling was described for specialized tissues that are small relative to skeletal muscle, which contains 40% of whole-body ascorbate. This project will establish skeletal muscle as a primary generator of extracellular antioxidant and thus an important tissue in whole-body antioxidant status. Further, it could establish the importance of ascorbate cycling and in particular muscle DHA uptake in controlling ROS, thus maintaining normal insulin action. If successful, the project will introduce manipulation of skeletal muscle ascorbate cycling as a novel means for addressing insulin resistance.