S100B-stimulated NO production by BV-2 microglia is independent of RAGE transducing activity but dependent on RAGE extracellular domain.

The Ca(2+)-modulated protein, S100B, is expressed in high abundance in and released by astrocytes. At the low levels normally found in the brain, extracellular S100B acts as a trophic factor, protecting neurons against oxidative stress and stimulating neurite outgrowth through its binding to the receptor for advanced glycation end products (RAGE). However, upon accumulation in the brain extracellular space, S100B might be detrimental to neurons. At relatively high concentrations, S100B stimulates NO release by microglia in the presence of lipid A or interferon-gamma (IFN-gamma). We analyzed further the S100B-microglia interaction to elucidate the molecular mechanism by which the protein brings about this effect. We found that S100B increased NO release by BV-2 microglia by stimulating reactive oxygen species (ROS) production and activating the stress-activated kinases, p38 and JNK. However, S100B stimulated NO production to the same extent in microglia overexpressing a transduction-incompetent mutant of RAGE and in microglia overexpressing full-length RAGE, with a significantly smaller effect in mock-transfected microglia. This suggests that the RAGE transducing activity has little or no role in S100B-stimulated NO production by microglia, whereas RAGE extracellular domain is important, probably serving to concentrate S100B on the BV-2 cell surface. On the other hand, S100B stimulated NF-kappaB transcriptional activity in BV-2 microglia in a manner that was strictly dependent on RAGE transducing activity, pointing to additional, RAGE-mediated effects of the protein on microglia that remain to be investigated.