Urokinase-type plasminogen activator receptor (uPAR) augments brain damage in a murine model of ischemic stroke

Urokinase-type plasminogen activator receptor (uPAR) is a key component of the plasminogen activation system at the cell surface. Recent studies showed that uPAR is expressed in the ischemic damaged brain, suggesting its involvement in brain damage. In this study, we evaluated the role of uPAR in ischemic brain damage induced by permanent middle cerebral artery (MCA) occlusion in mice with genetic deficiency of uPAR (uPAR−/−) or of uPA (uPA−/−). Brain damage at 3 days was smaller in uPAR−/− mice (4.5 ± 1.0 mm3) than in littermate wild-type mice (uPAR+/+) (9.1 ± 1.8 mm3, p < 0.05), whereas it was comparable in uPA−/− (8.0 ± 4.1 mm3) and uPA+/+ (6.9 ± 2.6 mm3) mice. uPAR expression was upregulated in the ipsilateral cerebral cortex within 12 h, and remained elevated for up to 3 days. At 1 or 2 days after MCA occlusion, uPAR expression was selectively localized in vessels at the border of the damaged area. These findings suggest that uPAR expressed by endothelial cells augments the ischemic brain damage via a uPA-independent mechanism.