Oligomeric and fibrillar Aβ42 increase levels of endogenous BACE1 in mouse primary astrocyte cultures. Lysates of C57BL/6J mouse primary astrocyte cultures treated with 10 μM oligomeric or fibrillar Aβ42 from Fig. 6 were prepared for BACE1 immunoblot (A, B) or mRNA quantification by TaqMan RT-PCR (C). Treatment times are indicated. Olig., Aβ42 oligomer treatment; Fibr., Aβ42 fibril treatment; OC, oligomer vehicle control; FC, fibril vehicle control. Cell lysate from un-treated BACE1-/- primary astrocytes was used as a negative control, while cell lysate from a stable BACE1-overexpressing HEK-293 cell line was used as a positive control. GFAP immunosignals were loading controls as in Fig. 6A. Aβ42 oligomers and fibrils elevated BACE1 protein levels at 48 h and 96 h of treatment (A, B). BACE1 levels peaked at nearly 300% of control at 96 h that correlated with a rise in BACE1 mRNA level (C). Unlike APP, levels of both BACE1 protein and mRNA did not return to normal but remained elevated at 96 h. Asterisks indicate significant differences as compared to vehicle controls (*: p < 0.05; **: p < 0.01; n = 3). Error bars, SEM.