We hypothesized that repurposing the FDA-approved proteasome inhibitor, bortezomib (Velcade®; BTZ), protects blood–brain barrier P-gp from degradation in hAPP mice in vivo. We treated hAPP mice with the proteasome inhibitor BTZ or a combination of BTZ with the P-gp inhibitor cyclosporin A (CSA) for 2 weeks. Vehicle-treated wild-type (WT) mice were used as a reference for normal P-gp protein expression and transport activity. In addition, we used the opioid receptor agonist loperamide as a P-gp substrate in tail flick assays. We also determined P-gp protein expression by Western blotting, measured P-gp transport activity levels in isolated brain capillaries with live cell confocal imaging and assessed Aβ plasma and brain levels with ELISA. We found that 2-week BTZ treatment of hAPP mice restored P-gp protein expression and transport activity in brain capillaries to levels found in WT mice. We also observed that hAPP mice displayed significant loperamideinduced central antinociception compared to WT mice indicating impaired P-gp transport activity at the blood–brain barrier of hAPP mice in vivo. Furthermore, BTZ treatment prevented loperamide-induced antinociception suggesting BTZ protected P-gp loss in hAPP mice. Further, BTZ-treated hAPP mice had lower Aβ40 and Aβ42 brain levels compared to vehicle-treated hAPP mice. Conclusions Our data indicate that BTZ protects P-gp from proteasomal degradation in hAPP mice, which helps to reduce Aβ brain levels. Our data suggest that the proteasome system could be exploited for a novel therapeutic strategy in AD, particularly since increasing Aβ transport across the blood–brain barrier may prove an effective treatment for patients.
