APP and Alzheimer disease: One of the most characteristic features of AD is Aβ plaques composed of Aβ1–40 and Aβ1–42 forms, which are generated after proteolysis of amyloid precursor protein (APP) by membrane-bound enzymes—secretases: α-secretase, β-secretase (β-site APP-cleaving enzyme (BACE1)) [83], and γ-secretase, which is a complex composed of four proteins: presenilin-1 (PSEN1), nicastrin, anterior pharynx-defective 1 (APH-1), and presenilin enhancer 2 (PEN2) [84].