Glutathione Peroxidase-Catalase Cooperativity Is Required for Resistance to Hydrogen Peroxide by Mature Rat Oligodendrocytes

Abstract

Oxidative mechanisms of injury are important in many neurological disorders, including hypoxic-ischemic brain damage. Cerebral palsy after preterm birth is hypothesized to be caused by hypoxic-ischemic injury of developing oligodendrocytes (OLs). Here we examined the developmental sensitivity of OLs to exogenous hydrogen peroxide (H 2 O 2 ) with stage-specific rat oligodendrocyte cultures. We found that H 2 O 2 itself or that generated by glucose oxidase was more toxic to developing than to mature OLs. Mature OLs were able to degrade H 2 O 2 faster than developing OLs, suggesting that higher antioxidant enzyme activity might be the basis for their resistance. Catalase expression and activity were relatively constant during oligodendrocyte maturation, whereas glutathione peroxidase (GPx) was upregulated with a twofold to threefold increase in its expression and activity. Thus, it appeared that the developmental change in resistance to H 2 O 2 was caused by modulation of GPx but not by catalase expression. To test the relative roles of catalase and GPx in the setting of oxidative stress, we measured enzyme activity in cells exposed to H 2 O 2 and found that H 2 O 2 induced a decrease in catalase activity in developing but not in mature OLs. Inhibition of GPx by mercaptosuccinate led to an increase in the vulnerability of mature OLs to H 2 O 2 as well as a reduction in catalase activity. Finally, H 2 O 2 -dependent inactivation of catalase in developing OLs was prevented by the GPx mimic ebselen. These data provide evidence for a key role for GPx-catalase cooperativity in the resistance of mature OLs to H 2 O 2 -induced cell death.

Hyperoxia Causes Maturation-Dependent Cell Death in the Developing White Matter

“…This study used the oligodendroglial cell line OLN-93 (Richter-Landsberg and Heinrich, 1996). Previously studied examples of maturation-dependent toxicity in OLs have not been found to be caspase dependent (Back et al, 1998;Rosenberg et al, 2003;Baud et al, 2004b). The goal of the present study was to examine whether this maturation and caspasedependent vulnerability could also be observed in primary OLs and also to characterize the oxidative stress that is involved upstream of the apoptotic pathway.…”

“…There is a developmental mismatch in GPx and catalase expression and activity during oligodendrocyte maturation. GPx is upregulated with a twofold to threefold increase in its expression and activity in mature OLs versus pre-OLs (Baud et al, 2004b). Exposure to hydrogen peroxide causes downregulation of catalase activity and death in pre-OLs.…”

Maturation-dependent sensitivity of oligodendrocyte lineage cells to apoptosis: implications for normal development and disease

“…In rat OL cultures, catalase, GSH reductase and steadystate GSH levels 55 were found to be similar between OPCs and mature OLs. However, GSH peroxidase levels were higher in OLs than OPCs.…”

“…In hydrogen peroxide clearance assays, mature rat OLs in culture had an eight fold greater antioxidant capacity compared to pro-OLs. 55 GSH is a cellular antioxidant formed from cysteine, glutamate and glycine. GSH peroxidase 1 (GSHPx1) is both a cytosolic and a mitochondrial enzyme that utilizes GSH to detoxify peroxides.…”

“…This elevation of GSHPx was 'doubly protective' in that catalase activity was maintained in the face of oxidative stress in OLs, while OPCs (with less GSHPx) were found to have inactivated catalase in the same condition. 54,55 The authors found that chemically inhibiting GSHPx in mature OLs led to an increased vulnerability to hydrogen peroxide and a reduction of catalase activity, indicating that GSHPx help maintain antioxidant defenses as a primary peroxidase in addition to protecting catalase activity. Independent studies have also confirmed that OPCs have less GSHPx activity than OLs.…”