There is no clearly effective and low risk treatment for ischemic stroke. Thrombolysis may establish early reperfusion, but may also increase the risk of intracerebral hemorrhage and death. These studies focus on local leukocyte adhesion receptor expression, thrombosis, and impaired fibrinolysis as a cause for cerebral microvascular failure. Pilot data with mice subjected to focal cerebral ischemia/reperfusion demonstrate that P-selectin and intercellular adhesion molecule-1 (ICAM-1) expression induce leukocyte capture, postischemic no-reflow, and tissue injury. In addition, fibrin accumulates in the cerebral microvasculature, due largely to integrin GPIIb/IIIa receptor-mediated platelet aggregation and impaired fibrinolysis due to increased local plasminogen activator-inhibitor-1 (PAI-1) expression. Mice deficient for the PAI-1 gene are relatively resistant to ischemic cerebral injury, in contrast to mice lacking the tissue plasminogen activator (tPA)gene. Blockade of GPIIb/IIIa reduces local platelet and fibrin accumulation, conferring cerebral protection Because leukocytes promote thrombosis by interacting with platelets and modulating the local thrombotic/fibrinolytic balance, they hypothesize that leukocyte recruitment and thrombosis synergize to exacerbate cerebral injury following stroke. Preliminary evidence for this synergy is that P-selectin null mice exhibit reduced cerebral thrombosis in stroke.Using this murine model of stroke, the Specific Aims will establish; (1) the role of microvascular thrombosis, examining endogenous modulators of fibrinolysis (using control, tPA, uPA, and PAI-1-deficient mice) and rt-PA or a selective GPIIb/IIIa antagonist; (2) the role of leukocytes and adhesion receptors, using mice deficient for adhesion receptors or counterligands (P-selectin, ICAM-1, ICAM-2, CD18) and novel antiinflammatory strategies (IL-1 receptor blockade and a hybrid molecule to inhibit complement activation and P-selectin). Studies will assess whether leukocytes activate local proinflammatory signal transduction mechanisms such as nuclear factor kB (NF-kB); (3) whether thrombosis, fibrinolysis, and leukocyte recruitment act synergistically, establishing if endogenous fibrinolytic mechanisms alter leukocyte recruitment (or conversely, if leukocyte capture modulates thrombosis), determining if adhesion receptor blockade can minimize the dose of rt-PA needed for cerebral protection. Overall, studies should provide a new stroke paradigm regarding the pathogenic roles of adhesion receptors and microvascular thrombosis, to guide the development of new strategies to interfere with leukocyte adhesion, inflammation, and microvascular thrombosis in evolving stroke.
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