Abstract
Accumulating evidence has indicated that gain‐of‐function in β‐amyloid production may be not the necessary mechanism for mutant presenilin‐1 (PS1) or PS2 to cause familial Alzheimer's disease (AD). In the present article, we show that conditional knockout of PS1 from the adult stage in the forebrain of mice with the PS2 null mutation triggers robust AD‐like neurodegeneration including brain shrinkage, cortical and hippocampal atrophy,ventricular enlargement, severe neuronal loss, gliosis, tau hyperphosphorylation, neurofillament tangle‐like structures, and intracellular filaments. Learning and memory functions in these mice are almost completely lost. Notably, there is no β‐amyloid deposition, indicating that presenilin dysfunction can directly cause neurodegeneration without the involvement of β‐amyloid. Furthermore, neurodegeneration occurs in a progressive manner following aging, suggesting that an accumulating effect of presenilin dysfunction over time might be a pathogenic mechanism for the involvement of mutant PS1/PS2 in causing AD. These results validate a mouse model characterized by the presence of many features of AD pathology. Furthermore, the demonstration of AD‐like neurodegeneration in the absence of β‐amyloid deposition challenges the long‐standing β‐amyloid cascade hypothesis and encourages an open debate on the role of β‐amyloid in causing AD. Most important, our results strongly suggest that to develop γ‐secretase inhibitors for the pharmacological treatment of AD may be not a reasonable strategy because antagonism of presenilin function may worsen neurodegeneration. © 2008 Wiley‐Liss, Inc.