CTSB and Alzheimer disease: Legumain (LGMN), also known as asparagine endopeptidase (AEP), a cysteine protease that cleaves substrates after asparagine (N), is gradually escalated in the brain with aging and simultaneously cleaves APP N585 to promote Aβ production[15] and Tau N368 to facilitate its aggregation,[16] triggering Alzheimer's disease (AD) pathologies.