Molecular Changes Associated with the Protective Effects of Angiopoietin-1 During Blood-Brain Barrier Breakdown Post-Injury

Blood-brain barrier (BBB) breakdown to plasma proteins leads to vasogenic edema which when diffuse is a life threatening complication in many types of acute brain injury. In our previous studies, early BBB breakdown was associated with increased expression of endothelial caveolin-1 alpha (Cav-1) protein and decreased expression of occludin. In order to attenuate these changes, the effects of intra-cortical angiopoietin-1 (Ang1), a potent anti-permeability factor, on BBB breakdown was assessed in the cold injury model at day 1 post-injury. Overall vascular permeability at the lesion site was assessed in Ang1 non-treated and treated cold-injured rats, using horseradish peroxidase (HRP) as a tracer and in individual vessels by dual labeling immunofluorescence for Cav-1 or occludin and fibronectin, a marker of BBB breakdown. In addition, Cav-1, occludin, Akt, and ERK1/2 expression at the lesion site was detected by immunoblotting. Non-treated cold-injured rats showed focal HRP leakage at the lesion site which was significantly decreased (P < 0.001) in the Ang1-treated group. Increased endothelial Cav-1 and decreased occludin immunoreactivity was observed in arterioles and corresponding-sized venules with BBB breakdown in the non-treated cold-injured rats, and similar expression of these proteins was detected at the lesion site by immunoblotting associated with increased expression of Akt and ERK2 proteins. These alterations were attenuated by Ang1 treatment which resulted in Cav-1, occludin, Akt, and ERK1/2 protein expression that was similar to that of the control groups as was the endothelial Cav-1 and occludin immunoreactivity in leaky vessels. These data suggest that Ang1 administered early post-injury has potential in attenuating the degree of vascular alterations and subsequent vasogenic edema.