Studying the Neuroprotective mechanism of tPA-S481A

Dr. Abd Al-Roof Higazi

Traumatic brain injury (TBI) remains a major medical problem, resulting in 50,000 deaths/year in the US and continues to be an important cause of long-term morbidity.  In the present application, we propose to explore the mechanism by which a tPA mutant (tPA-S481A) that lacks fibrinolytic activity and promotes blood-brain-barrier (BBB) permeability exerts a powerful neuroprotective effect after TBI.  Our data help explain this seemingly paradoxical outcome by showing the beneficial effects of prolonging BBB permeability by accelerating the clearance of the neurotoxic amino acid glutamate from the brain and CSF and by competing with endogenous tPA for activation of the N-methyl-D-aspartate receptor (NMDA-R).

We will examine in detail the mechanism that mediates the neuroprotective effect of tPA-S481A in animal models of TBI through two inter-related specific aims.  In Specific Aim 1, we will ask whether transient opening of the BBB by tPA-S481A is itself part of the neuroprotective mechanism.  We will measure the effect of the mutant tPA on the post-TBI clearance of glutamate from the CSF by measuring its effect on the clearance of radiolabled glutamate injected into the brain and by examining the consequences of blocking tPA-S481A-induced BBB permeability.  In Specific Aim 2, we will pursue the alternative hypothesis that tPA-S481A-induced BBB permeability increases delivery of the mutant to the brain parenchyma where it competes with WT-tPA for binding and activation of the NMDA-1, blocking the ensuing neurotoxic effects.