Moreover, since recent data reported an influence of amyloid-beta (Aβ), the peptide typically accumulating in the brains of AD patients [29], on neuron and astrocyte cholesterol metabolism (i.e., endogenous synthesis, cell cholesterol content, and cholesterol efflux [30,31]), we also evaluated the effect of PCSK9 in the presence of Aβ fibrils, in order to reproduce an AD-like condition in vitro. Here, PCSK9 is linked to Alzheimer disease.