Intracellular Accumulation of Detergent-Soluble Amyloidogenic Aβ Fragment of Alzheimer's Disease Precursor Protein in the Hippocampus of Aged Transgenic Mice.

To study amyloid β-protein (Aβ) production and aggregation in vivo, we created two transgenic (Tg) mouse lines expressing the C-terminal 100 amino acids of human amyloid precursor protein (APP): Tg C100.V717F and Tg C100.WT. Western blot analysis showed that human APP-C100 and Aβ were produced in brain and some peripheral tissues and Aβ was produced in serum. Using antibodies specific for the Aβ C terminus we found that Tg C100.V717F produced a 1.6-fold increase in Aβ42/Aβ40 compared with Tg C100.WT. Approximately 30% of total brain Aβ (∼122 ng/g of wet tissue) was water-soluble. The remaining 70% of Aβ partitioned into the particulate fraction and was completely sodium dodecyl sulfate-soluble. In contrast, human Alzheimer's disease brain has predominantly sodium dodecyl sulfate-insoluble Aβ. Immunohistochemistry with an Aβ(5-8) antibody showed that Aβ or Aβ-containing fragments accumulated intracellularly in the hippocampus of aged Tg C100.V717F mice. The soluble Aβ levels in Tg brain are similar to those in normal human brain, and this may explain the lack of microscopic amyloid deposits in the Tg mice. However, this mouse model provides a system to study the intracellular processing and accumulation of Aβ or Aβ-containing fragments and to screen for compounds directed at the γ-secretase activity. [ABSTRACT FROM AUTHOR]