AHA1 Regulates Aβ Production via Modulation of APP Abundance and γ-Secretase Assembly

Deposition of amyloid β-protein (Aβ) is a hallmark of Alzheimer's disease (AD), produced by γ-secretase-mediated cleavage of amyloid precursor protein (APP). The 90-kDa heat shock protein (Hsp90) co-chaperone, activator of Hsp90 ATPase homolog 1 (AHA1), is known to promote the accumulation of toxic tau species; however, its effects on Aβ production remain unclear. Using cellular models-including human embryonic kidney 293 T (HEK293T) cells, stable HEK-APP cells, presenilin 1/2 double-knockout mouse embryonic fibroblasts (PS-DKO MEFs), and Chinese hamster ovary (CHO) cells-in which AHA1 was experimentally manipulated, together with observational analyses of human iPSC-derived neurons carrying an FAD-linked APP mutation, we demonstrate that AHA1 regulates Aβ generation through two mechanisms: regulation of APP protein abundance through pathways that are at least partially independent of Hsp90 interaction and Hsp90-dependent promotion of γ-secretase assembly. Knockdown of endogenous AHA1 reduces Aβ production and decreases APP and γ-secretase component levels, whereas AHA1 overexpression elevates Aβ generation and increases the expression of these proteins. The AHA1-E67K mutant, which has impaired Hsp90 binding, lowers Aβ production and the levels of APP and γ-secretase components compared with wild-type AHA1. AHA1 associates with APP and APH1, an immature γ-secretase component, indicating its role in APP proteolysis and Aβ production. Disruption of the AHA1/Hsp90 complex-through AHA1 knockdown, the E67K mutant, or a small-molecule inhibitor-reduces γ-secretase assembly. Notably, Familial AD mutations (APP-C99-I45F, PS1-L286V) upregulate AHA1/Hsp90, elevating APP/APH1 and Aβ42 production. AHA1 knockdown rescues FAD-linked Aβ42 overproduction in a mutant cell model, while AHA1 overexpression exacerbates PS1 mutant Aβ production. Collectively, these findings reveal that AHA1 regulates Aβ production by modulating APP abundance and γ-secretase assembly, establishing AHA1 as a potential target for therapeutic intervention in AD.