Sphingosine Kinase 2 Mediates Cerebral Preconditioning and Protects the Mouse Brain Against Ischemic Injury

Background and Purpose-Cerebral preconditioning provides insights into endogenous mechanisms that protect the brain from ischemic injury. Hypoxia and the anesthetic isoflurane are powerful preconditioning agents. Recent data show that sphingosine 1-phosphate receptor stimulation improves outcome in rodent models of stroke. Endogenous sphingosine 1-phosphate levels are controlled by the expression and activity of sphingosine kinases (SPK). We hypothesize that SPK upregulation mediates preconditioning induced by isoflurane and hypoxia and reduces ischemic injury. Methods-Male wild-type C57BL/J, SPK1(-/-) and SPK2(-/-) mice were exposed to isoflurane or hypoxia preconditioning before transient middle cerebral artery occlusion. Infarct volume and neurological outcome were measured 24 hours later. SPK inhibitors (SKI-II and ABC294640) were used to test the involvement of SPK2. Expressions of SPK1, SPK2, and hypoxia-inducible factor 1 alpha were determined. Primary cultures of mouse cortical neurons were exposed to isoflurane before glutamate-or hydrogen peroxide-induced cell death. Results-Isoflurane preconditioning and hypoxia preconditioning significantly reduced infarct volume and improved neurological outcome in wild-type and SPK1 (/) mice but not in SPK2 (/) mice. Pretreatment with SKI-II or ABC294640 abolished the isoflurane preconditioning-induced tolerance. Western blot showed a rapid and sustained increase in SPK2 level, whereas SPK1 level was similar between preconditioned mice and controls. Hypoxia-inducible factor 1 alpha was upregulated in wild-type isoflurane-preconditioned mice but not in SPK2(-/-). Isoflurane preconditioning protected primary neurons against cell death, which was abolished in ABC294640-treated cells. Conclusions-Applying genetic and pharmacological approaches, we demonstrate that neuronal SPK2 isoform plays an important role in cerebral preconditioning. (Stroke. 2012;43:199-204.)