Sphingosine 1 Phosphate and Embolic Stroke

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DESCRIPTION(Adapted from applicant?s abstract): Thrombosis and embolism are responsible for approximately 80 percent of human stroke, a major cause of morbidity and mortality, and significant economic loss. This application will explore the hypothesis that a novel system regulating cerebrovascular tone (sphingosine-1-phosphate, its metabolizing enzymes and receptors) can be pharmacologically manipulated in order to effectively reduce embolic infarct size in a rat model. Sphingosine-1-phosphate (S1P) is released by activated platelets and binds to G-protein coupled receptors termed Edg-l, Edg-3, Edg-5, Edg-6, and Edg-8. We found that this lipid is a potent constrictor of cerebral, but not peripheral arteries, an effect likely to be mediated by Edg-3 receptors. Preliminary evidence shows that this cerebral selectivity might be accounted for by the high SIP phosphatase levels in peripheral arteries that do not constrict to added S1P. Two aims are proposed to determine which components of this novel system can be targeted to decrease infarct size. In the first aim, we will use in vitro preparations to test the hypothesis that Rho kinases are required for S1P-induced constriction (Y-27632 should inhibit). We will expand upon preliminary data by showing that the high expression of S1P phosphatase (S1PP) mRNA in peripheral, but not cerebral arteries, is paralleled by a high [32P]S1P degrading activity with an inhibition profile corresponding to that of S1PP. Finally, studies with adenovirus bearing sense and antisense S1PP constructs will establish that S1PP is responsible for the lack of S1P-mediated constriction in peripheral arteries. The second aim will test the hypothesis that interfering with SIP signaling reduces infarct size primarily by a blood flow-dependent mechanism. This will first be achieved by blocking Edg-3 receptors with suramin and by inhibiting Rho kinases with Y-27632. Similarly, blocking S1P synthesis by treating rats with the sphingosine kinase inhibitor dimethylsphingosine (DMS) should also decrease infarct size (blood flow will be assessed using laser speckle analysis and [14C]iodoantipyrine autoradiography), without altering PKC substrates. An effect of other sphingosine kinase inhibitors (F-12509 and B-5354C), devoid of PKC inhibiting activity, will further establish the role of S1P-mediated constriction in embolic stroke. Finally, we will test the hypothesis that sphingolipid levels are elevated after clot more than after filament occlusion, and therefore, DMS protection should be less apparent in the latter model. Together, these studies will explore the significance of a novel system, which appear to be cerebro-selective, and potentially a useful therapeutic target for stroke therapy.