Medium from neuronal cultures was harvested and stored at -80 ° C . Cell lysates were collected for cellular protein normalization and analysis of p - tau levels by western blot analysis . Human and mouse Aβ peptides were measured with MSD Human V - PLEX Aβ Peptide Panel 1 ( 6E10 ) Kit ( K15200E , Meso Scale Discovery ) and Thermo Fisher Mouse Aβ Peptide ELISA Kits ( KMB3481 and KMB3441 , Thermo Fisher Scientific ) according to the product manuals . For human Aβ measurement , the plates were read with a Sector Imager 2400 , and the data were acquired and analyzed with Discovery Workbench software . For mouse Aβ measurement , the plates were read with a FlexStation - III , and the data were analyzed with Prism-6 software . For experiments with secretase inhibitors , neuronal cultures were treated with a γ - secretase inhibitor ( compound E , Copd - E , at a final concentration of 200 nM ) , a β - secretase inhibitor ( OM99 - 2 , final concentration of 750 nM ) , or dimethyl sulfoxide ( vehicle ) as described 10 . All inhibitors were from EMD Millipore .