Molecular determinants of the prothrombogenic and inflammatory phenotype assumed by the postischemic cerebral microcirculation

Background and Purpose - Circulating blood cells have been implicated in the pathogenesis of cerebral ischemia/reperfusion (I/R) injury and stroke. The objective of this study was to define the magnitude and molecular determinants of the platelet- and leukocyte-endothelial cell adhesive interactions induced by I/R in the mouse brain. Methods - Bilateral common carotid artery occlusion was induced for 1 hour in C57BL/6 mice, followed by either 40 minutes or 4 hours of reperfusion. Fluorescent platelets were administered intravenously, and the frontal brain surface was observed with intravital fluorescence microscopy. Leukocyte-endothelial cell adhesion was monitored with the use of rhodamine-6G. Results - Ischemia followed by 40 minutes of reperfusion resulted in the rolling (125.1±23.6/mm²) and firm adhesion (109.5±25.8/mm²) of leukocytes but not platelets in venules. However, with 4 hours of reperfusion, rolling (138.8±24.6/mm²) and firm adhesion (153.7 ±22.3/mm²) of platelets were detected, and this was accompanied by a more intense recruitment of rolling (374.5±54.6/mm²) and adherent (445.2±57.1/mm²) leukocytes. In mice deficient in either P-selectin (P-selectin^-/-) or intercellular adhesion molecule-1 (ICAM-1) (ICAM-1^-/-), the I/R-induced platelet-endothelial cell (by 80% and 60%, respectively) and leukocyte-endothelial cell (by 84% and 78%, respectively) interactions were significantly blunted compared with those of wild-type mice. Conclusions - These findings indicate that I/R promotes the adhesion of both platelets and leukocytes in cerebral venules, with the accumulation of adherent leukocytes preceding the recruitment of platelets. Both P-selectin and ICAM-1 contribute to the inflammatory and prothrombogenic state induced by cerebral I/R.