Aβ ELISA
An aliquot of cortical homogenate generated for Western analysis described above was subjected to a three-step sequential extraction using PBS, 2% SDS, and 70% formic acid (FA). At each step, the sample was sonicated in appropriate buffer and centrifuged at 100,000g for 30 min (1- to 1.5-mo samples) or 60 min (6- to 12-mo samples) at 4 °C as previously described [23–25]. The supernatant was removed for analysis, and the pellet was sonicated in the next solution in sequence. The 2% SDS extracts were diluted in EC buffer, and the FA extracts neutralized with 1M Tris-phosphate buffer (pH 11) then diluted with EC buffer prior to testing. Human Aβ was measured in each fraction using BAN50 for capture (epitope Aβ1–16) and BA27 and BC05 for detection (Aβ40 and Aβ42, respectively) (Takeda Chemical Industries, Osaka, Japan). Total Aβ (mouse + human; 1- to 1.5-mo samples only) was measured in each fraction using BNT77 for capture (epitope Aβ11–28) and BA27 and BC05 for detection. All values were calculated as picomoles per gram based on the initial weight of cortical tissue.