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Keywords:

  • advanced glycation endproducts;
  • Alzheimer's disease;
  • amyloid plaques;
  • astrocytes;
  • immunocytochemistry;
  • transgenic mouse brain

Abstract

Increased expression and altered processing of the amyloid precursor protein (APP) and generation of β-amyloid peptides is important in the pathogenesis of amyloid plaques in Alzheimer's disease (AD). Transgenic Tg2576 mice overexpressing the Swedish mutation of human APP exhibit β-amyloid deposition in the neocortex and limbic areas, accompanied by gliosis and dystrophic neurites. However, murine plaques appear to be less cross-linked and the mice show a lower degree of inflammation and neurodegeneration than AD patients. ‘Advanced glycation endproducts (AGEs)’, formed by reaction of proteins with reactive sugars or dicarbonyl compounds, are able to cross-link proteins and to activate glial cells, and are thus contributing to plaque stability and plaque-induced inflammation in AD. In this study, we analyze the tissue distribution of AGEs and the pro-inflammatory cytokines IL-1β and TNF-α in 24-month-old Tg2576 mice, and compare the AGE distribution in these mice with a younger age group (13 months old) and a typical Alzheimer's disease patient. Around 70% of the amyloid plaque cores in the 24-month-old mice are devoid of AGEs, which might explain their solubility in physiological buffers. Plaque associated glia, which express IL-1β and TNF-α, contain a significant amount of AGEs, suggesting that plaques, i.e. Aβ as its major component, can induce intracellular AGE formation and the expression of the cytokines on its own. In the 13-month-old transgenic mice, AGEs staining can neither be detected in plaques nor in glial cells. In contrast, AGEs are present in high amounts in both plaques and glia in the human AD patient. The data obtained in this show interesting differences between the transgenic mouse model and AD patients, which should be considered using the transgenic approach to test therapeutical strategies to eliminate plaques or to attenuate the inflammatory response in AD.