Microglial activation by amyloid-beta.

摘要

One of the hallmark features of the Alzheimer's disease (AD) brain is the extracellular deposition of amyloid-beta protein (Abeta) in both fibrillar (senile plaques) and diffuse forms. Significant proinflammatory markers including activated microglia and cytokines have been detected surrounding the plaques but are absent in diffuse areas suggesting that microglial activation is sensitive to Abeta structure. Since Abeta displays structural polymorphism in vitro, we sought to determine the relationship between Abeta aggregation state and microglial proinflammatory response. Size exclusion chromatography (SEC) purification of freshly reconstituted Abeta(1-42) in NaOH/F12 cell culture medium isolated classical 100 nm long curvilinear protofibrils which stimulated a robust production of microglial TNF&agr;. The Abeta(1-42) protofibrils produced a concentration-dependent response in the low micromolar range. In contrast to Abeta(1-42), Abeta(1-40) required a pre-incubation of 24h at 25°C in order to produce protofibrils. Although both preparations were similar in morphology, Abeta(1-42) protofibrils were a much better stimulator of microglia than Abeta(1-40) protofibrils. Abeta(1-40) containing the Arctic mutation (E22G) formed protofibrils as soon as 3h after reconstitution , yet they were largely ineffective in stimulating microglia. None of the Abeta protofibril preparations were toxic to microglia suggesting that Abeta(1-42) protofibrils activate microglia in a manner independent of toxicity. As expected, freshly-purified Abeta(1-42) or Abeta(1-40) monomer were not effective in stimulating microglia, but surprisingly, neither were Abeta(1-42) fibrils even though they exhibited extensive Thioflavin-T fluorescence compared to protofibrils. These findings suggest that Abeta(1-42) protofibrils are the most effective inducers of a proinflammatory response in mouse microglia.