Figure 1. Brain Aβ deposits potentiate Tat-induced disruption of the BBB integrity.

(A) Young (3 month old) C57BL/6 mice were injected with the indicated doses of Tat (5, 25, 50 μg), vehicle (Veh) or bovine serum albumin (BSA) into the internal carotid artery (ICA). The BBB integrity was evaluated 3 and 24 h post Tat administration by injecting 100 μl 2% sodium fluorescein (NaF) into the ICA. Fifteen minutes post NaF injection, permeability across the BBB was calculated as the ratio of fluorescence in the brain tissue to plasma. Mannitol (20% in PBS, 200 μl; 15 min exposure) was used as positive control. (B) Tat-induced disruption of the BBB integrity was compared in aged (12 month old) B6C3-Tg mice overexpressing Aβ, age-matched littermate wild type (wt) controls, and young (3 month old) wt C57BL/6 mice. Tat (25 μg) was administered as in (A) and heat-inactivated Tat (Tat_hi) was used as negative control. Selected groups of mice were also injected with hydroxyfasudil (HF; Rho inhibitor; 100 μM, i.p.) 12 h prior to Tat administration. Permeability across the BBB was assessed as in (A). (C) Integrity of the cerebral microvasculature as determined by leakage of FITC-albumin. Young and aged mice were injected with 25 μg Tat as in (A). Twenty four hours later, the animals were perfused with saline, followed by 4 ml 5% FITC-albumin. Control brains show normal staining pattern in which fluorescence is retained within the cerebral vessels. In contrast, the staining is diffused in the ipsilateral hemisphere of Tat-injected brains, indicating albumin leakage. Images shown are the representative data from 4 experiments; the arrows indicate albumin leakage. (D) A typical amyloid plaque in the brain of 12 month old B6C3-Tg mice. Vessel integrity was evaluated as in (C). An advanced amyloid plaque is surrounded by a diffused microvessel network with substantial capillary leakage (arrows), indicating compromised BBB integrity. Data in A and B are mean ±SEM, n= 4–10 in each group; *, p< 0.05; ^†, p< 0.01. The scale bar, 20 μm.