Tg-SwDI Transgenic Mice Exhibit Novel Alterations in AβPP Processing, Aβ Degradation, and Resilient Amyloid Angiopathy

Alzheimer's disease (AD) is characterized by the accumulation of extracellular insoluble amyloid, primarily derived from polymerized amyloid-beta (A beta) peptides. We characterized the chemical composition of the A beta peptides deposited in the brain parenchyma and cerebrovascular walls of triple transgenic Tg-SwDI mice that produce a rapid and profuse A beta accumulation. The processing of the N- and C-terminal regions of mutant A beta PP differs substantially from humans because the brain parenchyma accumulates numerous, diffuse, nonfibrillar plaques, whereas the thalamic microvessels; harbor overwhelming amounts of compact, fibrillar, thioflavine-S- and apolipoprotein E-positive amyloid deposits. The abundant accretion of vascular amyloid, despite low A beta PP transgene expression levels, suggests that inefficient A beta proteolysis because of conformational changes and dimerization may be key pathogenic factors in this animal model. The disruption of amyloid plaque cores by immunotherapy is accompanied by increased perivascular deposition in both humans and transgenic mice. This analogous susceptibility and response to the disruption of amyloid deposits suggests that Tg-SwDI mice provide an excellent model in which to study the functional aftermath of immunotherapeutic interventions. These mice might also reveal new avenues to promote amyloidogenic A beta PP processing and fundamental insights into the faulty degradation and clearance of A beta in AD, pivotal issues in understanding AD pathophysiology and the assessment of new therapeutic agents.