Figure 1. Proteolytic Processing of Amyloid Precursor Protein (APP) by β- and γ-Secretases to Generate Amyloid β (Aβ) Protein.

When APP undergoes nonamyloidogenic proteolytic cleavage by α- and γ-secretases, p3 instead of Aβ is generated. A small number of APP molecules is proteolytically processed by β-secretase and generates an N-terminal soluble APP and a 12-kDa C-terminal stub of APP, which is cleaved by γ-secretase to yield Aβ and amyloid intracellular domain. The PS1 and PS2 genes carry the active site of γ-secretase complex. Proteins encoded by multiple risk genes associated with late-onset Alzheimer disease are involved in Aβ clearance. The SORL1, PICALM, and CD2AP genes regulate APP endocytosis (vs retromer-mediated APP recycling) and Aβ generation in endosome-lysosomes.