Glutathione dependent and thioredoxin dependent peroxidase systems in neural cells

Abstract

Amongst the different reactive oxygen species (ROS) that are produced during normal physiologic and pathologic conditions in the brain, peroxides are of special interest. Two important thiol systems are responsible for peroxide scavenging the glutathione (GSH) and thioredoxin (Trx) dependent systems. It seems possible that upregulation of these endogenous antioxidants is a potential way to inhibit/decrease ROS-mediated effects during oxidative stress. I found that the ability of astrocytes to withstand oxidative stress better than neurons is related to: (1) A higher GSH content as well as higher glutathione reductase activity and glutathione peroxidase (GSH-Px) activity in astrocytes. (2) Higher Trx, Trx reductase (Trx-R) and Trx-dependent peroxidase (peroxiredoxin [Prx]) activities in astrocytes. Examination of the distribution of three isoforms of Prx showed that astrocytes have a higher content of Prx1 and Prx3 while neurons have a higher content of Prx2. GSH-Px but not Prx activity can be increased in astrocytes by nerve growth factor and epidermal growth factor. The phase 2 enzyme inducer tertiary-butylhydroquinone (tBHQ) increased both the GSH- and Trx-dependent peroxide scavenging systems in astrocytes, but not in neurons. Glutathione reductase activity and GSH content of astrocytes, but not neurons, can be increased upon exposure to the phase 2 enzyme inducer tertiary butylhydroquinone (tBHQ). To delineate the role of Trx system to cope with thiol oxidation in astrocytes, Trx-R activity was inhibited with CDDP and then exposed to thimerosal, a thiol oxidant. Inhibition of Trx-R resulted in a more rapid drop of mitochondria) membrane potential than in vehicle-treated control astrocytes. The conclusion is that upregulation of phase 2 enzymes better enabled astrocytes to cope with a variety of oxidative insults. The final question addressed in this thesis was whether astrocytes release factors that enable neurons to better cope with oxidative stress. Transient co-cultures of astrocytes with neurons were established and neuronal capacity to scavenge hydrogen peroxide was examined. Co-culture of neurons with astrocytes increased neuronal GH content, partially accounting for the enhanced ability of neurons to scavenge hydrogen peroxide. This increase in neuronal GSH was correlated with release by astrocyte of the compounds cysteine and glutamyl-cysteine that promote neuronal GSH synthesis. (Abstract shortened by UMI.)