FIGURE 1.

The diagram of APP processing. The type 1 transmembrane protein APP is processed by two pathways: the nonamyloidogenic pathway and the amyloidogenic pathway. In the nonamyloidogenic pathway, APP is cleaved by α-secretase to produce the soluble sAPPα and the C-terminal fragments, α-CTF (C83), which is then cleaved by γ-secretase to yield the APP intracellular domain (AICD) and P3 peptide; while in the amyloidogenic pathway, β-secretase cleaves APP to produce the soluble fragment sAPPβ and the C-terminal fragments, β-CTF (C99). C99 is then cleaved by γ-secretase to release AICD and Aβ peptides of varying length.