APP and Alzheimer disease: In this sense, we illustrated a greater susceptibility of Prnp0/0 primary cultures to tau overexpression and phosphorylation under treatment of Aβ-derived diffusible ligands (ADDLs), the parallel progression of PrPC and tau expression in APP/PS1 mice, and the inverse correlation between levels of PrPC and tau in postmortem AD brains (ranking from Braak stage I to stage VI) [42].