title: Dual TNFα-induced effects on NRF2 mediated antioxidant defence in astrocyte-rich cultures: role of protein kinase activation.
abstract: Tumor necrosis factor-α (TNFα) is a pleiotropic molecule that can have both protective and detrimental effects in neurodegeneration. Here we have investigated the temporal effects of TNFα on the inducible Nrf2 system in astrocyte-rich cultures by determination of glutathione (GSH) levels, γglutamylcysteine ligase (γGCL) activity, the protein levels of Nrf2, Keap1, the catalytic and modulatory subunit of γGCL (γGCL-C and γGCL-M respectively). Astrocyte-rich cultures were exposed for 24 or 72 h to different concentrations of TNFα. Acute exposure (24 h) of astrocyte-rich cultures to 10 ng/mL of TNFα increased GSH, γGCL activity, the protein levels of γGCL-M, γGCL-C and Nrf2 in parallel with decreased levels of Keap1. Antioxidant responsive element (ARE)-mediated transcription was blocked by inhibitors of ERK1/2, JNK and Akt whereas inactivation of p38 and GSK3β further enhanced transcription. In contrast treatment with TNFα for 72 h decreased components of the Nrf2 system in parallel with an increase of Keap1. Stimulation of the Nrf2 system by tBHQ was intact after 24 h but blocked after 72 h treatment with TNFα. This down-regulation after 72 h correlated with activation of p38 MAPK and GSK3β, since inhibition of these signalling pathways reversed this effect. The upregulation of the Nrf2 system by TNFα (24 h treatment) protected the cells from oxidative stress through elevated γGCL activity whereas the down-regulation (72 h treatment) caused pronounced oxidative toxicity. One of the important implications of the results is that in a situation where Nrf2 is decreased, such as in Alzheimer's disease, the effect of TNFα is detrimental.
authors.affiliation: Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, PO BOX 420, 405 30 Göteborg, Sweden. fernando.correa@medkem.gu.se
authors.forename: Fernando
authors.initials: F
authors.lastname: Correa
authors.forename: Carina
authors.initials: C
authors.lastname: Mallard
authors.forename: Michael
authors.initials: M
authors.lastname: Nilsson
authors.forename: Mats
authors.initials: M
authors.lastname: Sandberg
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D001253:Astrocytes / Q000166:cytology*; D015153:Blotting, Western; D002478:Cells, Cultured; D004789:Enzyme Activation; D051267:NF-E2-Related Factor 2 / Q000502:physiology*; D018384:Oxidative Stress; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D051267:NF-E2-Related Factor 2; C495637:Nfe2l2 protein, rat; D014409:Tumor Necrosis Factor-alpha; D011494:Protein Kinases