The Nrf2-Inducible Antioxidant Defense in Astrocytes can be Both Up- and Down-Regulated by Activated Microglia: Involvement of p38 MAPK

The effects of microglia-conditioned medium (MCM) on the inducible Nrf2 system in astrocyte-rich cultures were investigated by determination of glutathione (GSH) levels, gamma glutamylcysteine ligase (gamma GCL) activity, the protein levels of Nrf2, Keap1, the modulatory subunit of gamma GCL (gamma GCL-M) and activated MAP kinases (ERK1/2, JNK and p38). Microglia were either cultured for 24 h in serum-free culture medium to achieve microglia-conditioned medium from non-activated cells (MCM0), used as control condition, or activated with different concentrations (0.1-1,000 ng mL(-1)) of lipopolysaccharide (LPS) to produce MCM0.1-1,000. Acute exposure (24 h) to MCM100 increased GSH, gamma GCL activity, the protein levels of gamma GCL-M, Nrf2, and activated JNK and ERK1/2 in astrocyte-rich cultures. In contrast, treatment with MCM10 for 24 h decreased components of the Nrf2 system in parallel with activation of p38 MAPK. Stimulation of the Nrf2 system by tBHQ was partly intact after 24 h but blocked after 72 h treatment with MCM10 and MCM100. This down-regulation after 72 h correlated with activation of p38 MAPK and lack of ERK1/2 and JNK activation. The negative effects were partly reversed by an inhibitor of p38 which restored tBHQ mediated protection against oxidative stress. In conclusion, the study showed a negative effect of MCM10 on the inducible anti-oxidant defense in astrocyte-rich cultures at both 24 and 72 h that correlated with activation of p38 and was partly reversed by a p38 inhibitor. A transient protective effect of MCM100 on astrocyte-rich cultures against H2O2 toxicity was observed at 24 h which coincided with activation of JNK and ERK1/2. (c) 2011 Wiley-Liss, Inc.