TNFα increases activity of γ‐glutamyl transpeptidase in cultured rat astroglial cells

Abstract

AbstractTo investigate the presence of γ‐glutamyl transpeptidase (γGT) in brain cells, cultures enriched for astroglial cells, neurons, oligodendroglial cells, and microglial cells were studied. Astroglial cultures contained a specific γGT activity of 2.3 ± 0.9 nmol/min/mg protein. A similar specific γGT activity was measured for oligodendroglial cultures, whereas microglial cells and neurons contained less than 30% of the specific γGT activity of astroglial cultures. The activity of γGT in astroglial cultures was elevated strongly by the presence of tumor necrosis factor‐α (TNFα) in a time‐ and concentration‐dependent manner. Maximal activity of γGT was observed after incubation of astroglial cultures for 3 days with 30 ng/mL TNFα. Under these conditions the specific γGT activity was increased by threefold compared to controls. Presence of the γGT‐inhibitor acivicin completely inhibited γGT activity both in TNFα‐treated and in control cells. In addition, the increase in astroglial γGT activity after application of TNFα was prevented completely by the presence of the protein synthesis inhibitor cycloheximide. γGT is involved in extracellular processing of glutathione (GSH) that is exported by astroglial cells. After TNFα‐treatment the concentration of GSH in the medium of astroglial cells was reduced significantly compared to control cells. In conclusion, the data presented demonstrate that TNFα stimulates γGT synthesis in astroglial cells and thereby improves the capacity to process GSH exported by these cells. © 2003 Wiley‐Liss, Inc.