Fig. 1.

Effect of apoE isoform on tau brain residence.

(a) The time course of tau elimination from the brain of apoE3 mice (12 months of age) was established by examining monomeric biotin-labeled tau (btau) levels (n = 6) and 10 kDa LyD (n = 5) levels in the brain at various time points following intracortical injection. Btau content was analyzed using ELISA while LyD was analyzed via fluorescence and normalized to total protein using the BCA protein assay. The half-life for both btau and LyD were determined using nonlinear regression and a one phase decay fit. (b-d) Following intracortical injection in apoE2, apoE3, or apoE4 mice (12 months of age), the amount of exogenous btau and co-injected LyD residing in the brain was determined at 2 h post injection. Monomeric (b) or aggregated (c) btau content was analyzed using an ELISA, while LyD was analyzed via fluorescence. Values represent mean + SEM (n = 5) and are expressed as pg of btau per μg of LyD. *P < 0.05 as determined by one-way ANOVA and Bonferroni’s multiple comparisons test. (d) Dextran residence values represent mean + SEM (n = 10) and are expressed as μg of LyD per mg protein. *P < 0.05 as determined by one-way ANOVA and Bonferroni’s multiple comparisons test. (e) Isolated cerebrovascular lysates from apoE2, apoE3 or apoE4 mice (12 months of age) were analyzed for caveolin-1 by ELISA and normalized to total protein using the BCA protein assay. Values represent mean + SEM (n = 5). *P < 0.05 as determined by one-way ANOVA and Bonferroni’s multiple comparisons test. (f) Schematic diagram of in vitro BBB model used in (g, h). (g) Monomeric btau was added alongside the known paracellular marker 10 kDa LyD to the basolateral compartment of the monoculture or coculture in vitro BBB model. (h) Monomeric or aggregate enriched btau was added alongside LyD to the basolateral compartment of the coculture in vitro BBB model in the presence or absence of the LRP1 antagonist RAP (100 nM). (g, h) Samples were collected from the apical compartment at 0, 30, and 60 min to determine the permeability of btau and LyD across the BBB model. Values represent mean ± SEM (n = 3) and are expressed as the apparent permeability coefficient (P_app). *P < 0.05 as determined by one-way ANOVA and Bonferroni’s multiple comparisons test. (i) HBMECs were exposed to 1 μg/mL of monomeric btau in the presence or absence of RAP (100 nM) for 1 h at 37 °C. The cell lysates were analyzed for btau content by ELISA and normalized to total protein using the BCA protein assay. Values represent mean + SEM (n = 3). * P < 0.05 as determined by unpaired two-tailed Student’s t-test.