Figure 4A Temporal MRM analysis of unlabeled Aβ17-28 and 13C-Lys Aβ17-28 in the soluble brain fraction after 13C-Lys APPtg brain extract i.p. injection (n = 3 mice per time point at 1-10 d, n = 4 mice per time point at 25-100 d). Data information: measurements in technical triplicates, normalization to 13C15N-Lys Aβ17-28 intensity as a spiked internal standard and brain weight (mg). All error bars show mean ± SD.Comparative MRM analysis of 13C-Lys Aβ17-28 (B) in the insoluble brain fraction after 13C-Lys-APPtg brain extract (donors labeled for 50-125 d) and 13C-Lys-non-tg brain extract (donors labeled for 10 d) i.p. injection (n = 3 mice per group and time point at 1-10 d, n = 4 mice per group and time point at 25, 50, 100 d, n = 3 mice in the APPtg extract group and n = 4 in the non-tg extract group at 75 d), right side zoom for time points 1-10 d. Unpaired two-tailed t-test * p<0.05 (P=0.0129 at 3 d, P=0.0156 at 10 d, P=0.0109 at 25 d), ** p<0.01 (P=0.0091 at 1 d, P=0.0011 at 5 d), *** p<0.001 (P=0.0006 at 7 d), 13C-Lys APPtg extract-injected vs 13C-Lys non-tg extract-injected for each time point. Data information: measurements in technical triplicates, normalization to 13C15N-Lys Aβ17-28 intensity as a spiked internal standard and brain weight (mg). All error bars show mean ± SD.C Comparative MRM analysis of unlabeled Aβ17-28 (C) in the insoluble brain fraction after 13C-Lys-APPtg brain extract (donors labeled for 50-125 d) and 13C-Lys-non-tg brain extract (donors labeled for 10 d) i.p. injection (n = 3 mice per group and time point at 1-10 d, n = 4 mice per group and time point at 25, 50, 100 d, n = 3 mice in the APPtg extract group and n = 4 in the non-tg extract group at 75 d), right side zoom for time points 1-10 d. Unpaired two-tailed t-test * p<0.05 (P=0.0129 at 3 d, P=0.0156 at 10 d, P=0.0109 at 25 d), ** p<0.01 (P=0.0091 at 1 d, P=0.0011 at 5 d), *** p<0.001 (P=0.0006 at 7 d), 13C-Lys APPtg extract-injected vs 13C-Lys non-tg extract-injected for each time point. Data information: measurements in technical triplicates, normalization to 13C15N-Lys Aβ17-28 intensity as a spiked internal standard and brain weight (mg). All error bars show mean ± SD.D Comparative 4G8 immunoassay quantification of Aβ42 in the insoluble brain fraction after 13C-Lys APPtg or 13C-Lys non-tg brain extract i.p. injection (n = 3 mice per group and time point at 1-10 d, n = 4 mice per group and time point at 25-100 d), right side zoom for time points 1-10 d. Normalization to protein concentration.E Representative chromatograms of unlabeled Aβ17-28 (left) and 13C-Lys Aβ17-28 (right) in the brain of an unlabeled 50-day-old APPtg mouse not injected with labeled brain extract. Note the absence of 13C-Lys Aβ17-28.F MRM analysis of unlabeled and 13C-Lys-labeled Aβ17-28 in APPtg mouse brains after 13C-Lys-labeled diet for 1 or 3 d (n = 3 mice per time point). Data information: measurements in technical triplicates, normalization to 13C15N-Lys Aβ17-28 intensity as a spiked internal standard and brain weight (mg). All error bars show mean ± SD.G Comparative MRM analysis of 13C-Lys Aβ17-28 in the insoluble brain fraction after 13C-Lys APPtg and 13C-Lys non-tg brain extract (all donors labeled for 100 d) i.p. injection (n = 6 mice per group). Data information: measurements in technical triplicates, normalization to 13C15N-Lys Aβ17-28 intensity as a spiked internal standard and brain weight (mg). All error bars show mean ± SD.H MRM analysis of unlabeled and 13C-Lys-labeled Aβ17-28 in non-APPtg mouse brains after 13C-Lys-labeled diet for 1 d (n = 3 mice) or at 1 d after 13C-Lys-APPtg brain extract i.p. injection (n = 3 mice). Data information: measurements in technical triplicates, normalization to 13C15N-Lys Aβ17-28 intensity as a spiked internal standard and brain weight (mg). All error bars show mean ± SD.