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Keywords:

  • Alzheimer's disease;
  • Borna disease virus;
  • cytokines;
  • microglia

Abstract

Amyloid plaques, one of the neuropathological hallmarks of Alzheimer's disease, and their main constituent, the amyloid β-peptide (Aβ), are triggers of the activation of innate inflammatory mechanisms involving the activation of microglia. To dissect the effects of a non-Aβ-specific microglial activation on the Aβ metabolism, we employed a viral infection-based model. Transgenic mice expressing a mutated form of the human amyloid precursor protein (Tg2576) were used. In preceding experiments, 2-week-old transgenic mice and non-transgenic littermates were infected intracerebrally with the neurotropic Borna disease virus and investigated at 2, 4 and 14 weeks post-infection. The Borna disease virus-inoculated mice showed a persisting, subclinical infection of cortical and limbic brain areas characterized by slight T-cell infiltrates, expression of cytokines and a massive microglial activation in the hippocampus and neocortex. Viral-induced effects reached their peak at 4 weeks post-infection. In 14-month-old Tg2576 mice, characterized by the deposition of diffuse and dense-core amyloid plaques in cortical brain regions, Borna disease virus-induced microglial activation in the vicinity of Aβ deposits was used to investigate the influence of a local inflammatory response on these deposits. At 4 weeks post-infection, histometric analyses employing Aβ immunohistochemistry revealed a decrease of the cortical and hippocampal Aβ-immunopositive area. This overall decrease was accompanied by a decrease of parenchymal thioflavin-S-positive amyloid deposits and an increase of such deposits in the walls of cerebral vessels, which indicates that the elicitation of a non-Aβ-specific microglial activation may contribute to a reduction of Aβ in the brain parenchyma.