Altered amyloid-ß structure markedly reduces gliosis in the brain of mice harboring the Uppsala APP deletion.

Deposition of amyloid beta (Aß) into plaques is a major hallmark of Alzheimer's disease (AD). Different amyloid precursor protein (APP) mutations cause early-onset AD by altering the production or aggregation properties of Aß. We recently identified the Uppsala APP mutation (APPUpp), which causes Aß pathology by a triple mechanism: increased ß-secretase and altered α-secretase APP cleavage, leading to increased formation of a unique Aß conformer that rapidly aggregates and deposits in the brain. The aim of this study was to further explore the effects of APPUpp in a transgenic mouse model (tg-UppSwe), expressing human APP with the APPUpp mutation together with the APPSwe mutation. Aß pathology was studied in tg-UppSwe brains at different ages, using ELISA and immunohistochemistry. In vivo PET imaging with three different PET radioligands was conducted in aged tg-UppSwe mice and two other mouse models; tg-ArcSwe and tg-Swe. Finally, glial responses to Aß pathology were studied in cell culture models and mouse brain tissue, using ELISA and immunohistochemistry. Tg-UppSwe mice displayed increased ß-secretase cleavage and suppressed α-secretase cleavage, resulting in AßUpp42 dominated diffuse plaque pathology appearing from the age of 5-6 months. The γ-secretase cleavage was not affected. Contrary to tg-ArcSwe and tg-Swe mice, tg-UppSwe mice were [11C]PiB-PET negative. Antibody-based PET with the 3D6 ligand visualized Aß pathology in all models, whereas the Aß protofibril selective mAb158 ligand did not give any signals in tg-UppSwe mice. Moreover, unlike the other two models, tg-UppSwe mice displayed a very faint glial response to the Aß pathology. The tg-UppSwe mouse model thus recapitulates several pathological features of the Uppsala APP mutation carriers. The presumed unique structural features of AßUpp42 aggregates were found to affect their interaction with anti-Aß antibodies and profoundly modify the Aß-mediated glial response, which may be important aspects to consider for further development of AD therapies.