Alzheimer's disease is associated with dense aggregations of proteins in the brain called amyloid plaques that contain beta-amyloid fragments as a primary component. If the development of amyloid plaques is responsible for neurodegeneration in Alzheimer's disease, reduction of beta-amyloid formation may prevent the development and progression of disease symptoms. Beta-amyloid fragments are derived from proteolytic processing of amyloid precursor protein (APP) in neurons, and the subsequent release of fragments into the extracellular space. APP in the ER is cleaved at residue 17 by alpha-secretase protease activity encoded by ADAM-10 and TACE. Beta-secretase activity, recently identified as BACE, cleaves in the N-terminus of the beta-amyloid fragment. Gamma-secretase cuts APP within the transmembrane domain at amino acids 40 and 42, releasing the beta-amyloid fragment containing residues 1-40/42 as well as shorter products such as p3 (residues 17-40/42) that requires alpha-secretase cleavage. The gamma-secretase activity requires the transmembrane protein Presenilin-1 that is itself cleaved into an N-terminal and C-terminal fragment that both are required for gamma-secretase activity. Mutations in presenilin-1 have been genetically associated with familial forms of Alzheimer's disease, further supporting the role of APP processing the development of the disease. Inhibition of the beta- or gamma-secretases may provide a mechanism to treat this disease. Other mechanisms may include altering degradation of beta-amyloid, and the use of vaccines against beta-amyloid to remove aggregates.
