Glutathione peroxidase-1 contributes to the protection of glutamine synthetase in astrocytes during oxidative stress

Glutamine synthetase (GS) is an astrocytic enzyme that is essential for the glutamate - glutamine cycle between neurons and astrocytes. To measure the effects of oxidative stress on the activity of GS in astrocytes, astrocyte-rich primary cultures from the brains of wild-type and glutathione peroxidase-1 deficient mice (GPx1(-/-)) were exposed to a chronic hydrogen peroxide-generating system consisting of xanthine oxidase, hypoxanthine and superoxide dismutase. The specific activity of GS was strongly diminished by chronic exposure to hydrogen peroxide in astrocytes cultured from both mouse lines. After 60 min of oxidative stress in the presence of 5mU/mL, 10mU/mL and 20 mU/mL of xanthine oxidase, the specific GS activity of wild-type astrocytes was reduced to 47%, 22% and 13% of the initial activity, respectively. For all activities of xanthine oxidase applied, astrocytes from GPx1(-/-) mice experienced a significantly greater rate of GS inactivation compared to their wild-type counterparts. These results confirm that GS is sensitive to inactivation by chronic peroxide stress in viable astrocytes and show that glutathione peroxidase-1 helps to protect GS from inactivation by oxidative stress.