Time- and activation-dependency of the protective effect of microglia on astrocytes exposed to peroxide-induced oxidative stress.

Microglial as well as astroglial activation (gliosis) are common phenomena of neuropathological processes in the brain. Nevertheless, the role of glial cell communication during gliosis is still not completely understood. The data we present with this work are a part of a bigger study on microglial-astroglial cell communication. The purpose of this study was to examine the impact of microglial-astroglial cell interactions on the cytotoxic effect of hydrogen peroxide (H2O2) on astrocytes and to characterize the microglia-induced astroprotective effect in detail. Therefore, purified cell cultures of microglia and astroglia from neonatal rat brains were used. Astrocytes were pre-treated with conditioned medium from lipopolysaccharides (LPS)-activated microglia and then exposed to oxidative stress induced by H2O2 under varying conditions. Activated microglia significantly reduced the cytotoxic effect of H2O2. As well in the indirect co-culture model using conditioned medium of microglia as in a direct co-culture model with different portions of microglial cells on the astroglial monolayer the astroprotective effect clearly correlated with the degree of microglial activation. The protective effect on astrocytes was induced in less than 24 h and lasted more than 4 days. Taken together, our results indicate that microglial activation might play an important role in the modulation of the oxidative stress resistance of glial tissue during gliosis.