PPIB and Alzheimer disease: As an AD triggering molecule, Aβ is a proteolytic product of the amyloid precursor protein (APP) via the amyloidogenic pathway, in which APP is cleaved by β-secretase (BACE1) to produce extracellular release part-soluble APP peptide-β (sAPPβ), and C-terminal fragment-β (CTFβ)—also known as C99.