Figure 2.

BBB breakdown, neuron loss, and behavioral deficits after endothelial-specific Lrp1 deletion. (A) Immunostaining for IgG (left, purple), fibrinogen (right, purple), and lectin⁺ endothelium (green) shows perivascular capillary leakages of blood-derived proteins in the cortex of 2-mo-old Lrp1^lox/lox; Tie2-Cre mice compared with Lrp1^lox/lox littermate controls. Scale bar = 20 µm. (B and C) Quantification of IgG (B) and fibrin (C) deposits in the cortex (Ctx) and hippocampus (Hp) in 2- and 4-mo-old Lrp1^lox/lox; Tie2-Cre mice and Lrp1^lox/lox controls. Mean ± SEM, n = 5 mice/group. (D and E) Capillary leakages of intravenously administered 40 kD FITC-dextran in the cortex of 2-mo-old Lrp1^lox/lox; Tie2-Cre mice compared with Lrp1^lox/lox control mice (D), and quantification of the BBB permeability–surface area product (PS) to 40 kD FITC-dextran in 2- and 4-mo-old mice (E). Scale bar = 50 µm. Mean ± SEM, n = 6 mice/group. (F and G) Cortical uptake of intravenously administered Alexa Fluor 555–cadaverine (red) in 2-mo-old Lrp1^lox/lox; Tie2-Cre and Lrp1^lox/lox mice (F), and quantification of cadaverine cortical uptake in 2- and 4-mo-old mice (G). Scale bar = 25 µm. White, lectin⁺ endothelium. Mean ± SEM, n = 5 mice/group. (H–J) NeuN⁺ neurons and SMI312⁺ neurites (H), and quantification of NeuN⁺ neurons and SMI312⁺ neurites in the cortex and hippocampus in 2- and 4-mo-old Lrp1^lox/lox; Tie2-Cre and Lrp1^lox/lox mice (I and J). Scale bar = 50 µm. Mean ± SEM, n = 5 mice/group. (K–N) Burrowing (K), nest construction (L), novel object location (M), and recognition (N) in 2- and 4-mo-old Lrp1^lox/lox; Tie2-Cre and Lrp1^lox/lox mice. Mean ± SEM, n = 12 (K and L) and n = 15–17 (M and N) mice/group. In B, C, E, G, and I–N, significance was determined by one-way ANOVA followed by Bonferroni post hoc test; ns, not significant; *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. In B, C, E, and G, asterisks above red dots indicate comparisons with control group.