ApoE is not necessarily in the a-beta buildup pathway. One idea that was tossed around was that increased cholesterol yielded alkylation factors (like 9Hydroxy nonenal or oxidized cholesterol metabolites) that then modify a-beta but there's not really any strong evidence that that happens in vivo.

Iirc there's something about lipid raft homeostasis being out of whack leading to increased likelihood of amyloid nucleation, but our ability to measure lipid rafts in vivo is even weaker.