Quantifying Alzheimer's Protein Secretion

To analyze protein secretion under the serum-deprived condition, the culture medium was changed to Opti-MEM and samples were incubated at 37 °C under 5% CO₂ for 12 h. The culture medium was collected and centrifuged at 3000g for 10 min at 4 °C, and the supernatant was collected and stored at −80 °C. The proteins levels of Aβ1-40 (27713, IBL), Aβ1-42 (27711, IBL), phospho-tau (pT181) (KHO0631, Invitrogen), and total-tau (KHB0041, Invitrogen) were measured by enzyme-linked immunosorbent assay (ELISA) according to manufacturer’s instructions. BCA analysis was performed with the same samples, and the data were normalized by the total protein content. Levels of Aβs secreted from E3^par and E4^iso iCOs were further measured using xMAP technology (Bioplex 200 systems). The utilized protocol is also described in our previous paper^{66 (link)}.