Tissue-Type Plasminogen Activator-A296-299 Prevents Impairment of Cerebral Autoregulation After Stroke Through Lipoprotein-Related Receptor-Dependent Increase in cAMP and p38.

BACKGROUND AND PURPOSE The sole Food and Drug Administration-approved treatment for stroke is tissue-type plasminogen activator (tPA), but its brief therapeutic window and complications of treatment constrain its use. One limitation may be its potential to exacerbate impairment of cerebral autoregulation after stroke. Vasodilation is maintained by elevations in cAMP. However, cAMP levels fall after stroke because of overactivation of N-methyl-d-aspartate receptors by toxic levels of glutamate, an effect that is exacerbated by tPA. Binding of wild-type (wt) tPA to the low-density lipoprotein-related receptor (LRP) mediates dilation. We propose that binding of wt-tPA to N-methyl-d-aspartate receptor reduces cAMP and impairs vasodilation. We hypothesize that tPA-A(296-299), a variant that is fibrinolytic but cannot bind to N-methyl-d-aspartate receptor, preferentially binds to LRP and increases cAMP and p38, limiting autoregulation impairment after stroke. METHODS Stroke was induced by photothrombosis in pigs equipped with a closed cranial window, cerebral blood flow determined by microspheres, and cerebrospinal fluid cAMP and p38 determined by ELISA. RESULTS Stroke decreased cerebral blood flow. Cerebral blood flow was reduced further during hypotension, indicating impairment of autoregulation. Autoregulation was further impaired by wt-tPA, which was prevented by MK801 and tPA-A(296-299). Protection by tPA-A(296-299) was blocked by anti-LRP Ab, the LRP antagonist receptor-associated protein, and the p38 inhibitor SB 203580, but not by control IgG. Stroke reduced cerebrospinal fluid cAMP, which was reduced further by wt-tPA, but augmented by tPA-A(296-299). Cerebrospinal fluid p38 was unchanged by wt-tPA, increased by tPA-A(296-299), and decreased by anti-LRP Ab and receptor-associated protein. CONCLUSIONS tPA-A(296-299) prevents impairment of cerebral autoregulation after stroke through an LRP-dependent increase in cAMP and p38.