The ?-Secretase Blocker DAPT Reduces the Permeability of the Blood-Brain Barrier by Decreasing the Ubiquitination and Degradation of Occludin During Permanent Brain Ischemia

Background Tight junction protein degradation is a principal characteristic of the bloodbrain barrier (BBB) damage that occurs during brain ischemia. Aims We investigated the mechanisms of occludin degradation that underlie permanent middle cerebral artery occlusion (pMCAO) in rats. Methods and Results Western blot and Co-immunoprecipitation data indicated ubiquitination and degradation of occludin in brain after pMCAO, which was consistent with ZO-1 degradation in penumbra regions as observed at 24 h after pMCAO. We further investigated candidate protease(s) responsible for the degradation of occludin during pMCAO. The intraventricular administration of ?-secretase blocker DAPT significantly inhibited the pMCAO-induced neurovascular damage, whereas ALLM and Batimastat, which are inhibitors of calpain and metalloproteinase proteases, respectively, were less effective. Notably, we found that DAPT significantly inhibited BBB disruption in comparison with vehicle treatment, as assessed by Evans blue excretion. Interestingly, the confocal immunostaining revealed that activation of the E3 ubiquitin ligase Itch is associated with degradation of occludin in brain microvessels following ischemia. Furthermore, our data demonstrate that the inhibition of ?-secretase signaling and the itch-mediated ubiquitination of occludin likely underlie the vasoprotective effect of DAPT after pMCAO. Conclusion The ?-secretase blocker DAPT reduces the permeability of the BBB by decreasing the ubiquitination and degradation of occludin during permanent brain ischemia, suggesting that ?-secretase may represent a novel therapeutic target for preventing neurovascular damage.