APP and Alzheimer disease: The amyloid precursor protein (APP) of AD is cleaved by β-secretase to a secreted derivative, sAPP-β, and a 99-residue membrane-bound fragment, CTF-β, which is then cleaved by γ-secretase into CTF-γ and even pathogenic β-amyloid (Aβ) proteins, such as Aβ 40 and Aβ 42 (Kimberly and Wolfe, 2003; Marlow et al., 2003).