δ-secretase has been found to produce Aβ in the development of AD, which further induces phosphorylation of SGK1 and JAK2, and SGK1 can in turn activate STAT1, and δ-secretase simultaneously cleaves tau proteins and produces the tau(1−368) fragment, which binds to the activated STAT1 and promotes the production of Aβ thereby forming positive feedback regulation with phosphorylated SGK1 (Zhang et al., 2021). Here, SGK1 is linked to Alzheimer disease.