Finally, we tested whether the pathway that controls APP production via cFos activation in cultured neurons operates in vivo. Owing to the multitude of secreted glial factors that stimulate the pathway, we could not address this question by manipulating mouse ApoE as one of multiple signaling factors. Instead, we tested in mice whether the downstream, final regulatory event, the activation of App transcription via AP-1 binding to its promoter, operates in vivo. For this purpose, we stereotactically injected into the cortex of newborn mice AAVs that express a control protein or DN-cFos, the dominant-negative form of cFos, or AAVs that express dCAS9 with a control guide RNA or the guide RNA directed to the AP-1 binding sequence of the App promoter, thereby attempting to perform in vivo CRISPRi (Fig. 7A, S7H). We found that both manipulations significantly suppressed APP expression at the protein and mRNA levels (Fig. 7B, 7C, S7I, S7J). L1-CAM, Hsc70, and GDI as control proteins were not changed. Both manipulations only partially decreased APP levels, as would be expected for an impairment of only one element in
