sphingosine-kinase and Hypoxia-Ischemia--Brain

The induction of ischemic tolerance by preconditioning provides a platform to elucidate endogenous mechanisms of stroke protection. In these studies, we characterize the relationship between hypoxia-inducible factor (HIF), sphingosine kinase 2 (SphK2), and chemokine (C-C motif) ligand 2 (CCL2) in models of hypoxic or pharmacological preconditioning-induced ischemic tolerance. A genetics-based approach using SphK2- and CCL2-null mice showed both SphK2 and CCL2 to be necessary for the induction of ischemic tolerance following preconditioning with hypoxia, the hypoxia-mimetic cobalt chloride, or the sphingosine-1-phosphate (S1P) agonist FTY720. A pharmacological approach confirmed the necessity of HIF signaling for all three preconditioning stimuli, and showed that the SphK/S1P pathway transduces tolerance via the S1P(1) receptor. In addition, our data suggest significant cross-talk between HIF and SphK2-produced S1P signaling, which together act to up-regulate CCL2 expression. Overall, HIF, SphK, S1P, and CCL2 participate in a signaling cascade to induce the gene expression responsible for the stroke-tolerant phenotype established by hypoxic and FTY720 preconditioning. The identification of these common molecular mediators involved in signaling the genomic response to multiple preconditioning stimuli provides several targets for therapeutic manipulation.

Topics: Animals; Chemokine CCL2; CX3C Chemokine Receptor 1; Enzyme Inhibitors; Female; Hypoxia-Inducible Factor 1, alpha Subunit; Hypoxia-Ischemia, Brain; Ischemic Preconditioning; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Phenotype; Phosphotransferases (Alcohol Group Acceptor); Receptors, Chemokine; Signal Transduction; Stroke

The importance of bioactive lipid signaling under physiological and pathophysiological conditions is progressively becoming recognized. The disparate distribution of sphingosine kinase (SphK) isoform activity in normal and ischemic brain, particularly the large excess of SphK2 in cerebral microvascular endothelial cells, suggests potentially unique cell- and region-specific signaling by its product sphingosine-1-phosphate. The present study sought to test the isoform-specific role of SphK as a trigger of hypoxic preconditioning (HPC)-induced ischemic tolerance.. Temporal changes in microvascular SphK activity and expression were measured after HPC. The SphK inhibitor dimethylsphingosine or sphingosine analog FTY720 was administered to adult male Swiss-Webster ND4 mice before HPC. Two days later, mice underwent a 60-minute transient middle cerebral artery occlusion and at 24 hours of reperfusion, infarct volume, neurological deficit, and hemispheric edema were measured.. HPC rapidly increased microvascular SphK2 protein expression (1.7+/-0.2-fold) and activity (2.5+/-0.6-fold), peaking at 2 hours, whereas SphK1 was unchanged. SphK inhibition during HPC abrogated reductions in infarct volume, neurological deficit, and ipsilateral edema in HPC-treated mice. FTY720 given 48 hours before stroke also promoted ischemic tolerance; when combined with HPC, even greater (and dimethylsphingosine-reversible) protection was noted.. These findings indicate hypoxia-sensitive increases in SphK2 activity may serve as a proximal trigger that ultimately leads to sphingosine-1-phosphate-mediated alterations in gene expression that promote the ischemia-tolerant phenotype. Thus, components of this bioactive lipid signaling pathway may be suitable therapeutic targets for protecting the neurovascular unit in stroke.

Topics: Animals; Arterioles; Brain Edema; Cerebral Arteries; Cerebrovascular Circulation; Disease Models, Animal; Fingolimod Hydrochloride; Hypoxia-Ischemia, Brain; Immunosuppressive Agents; Infarction, Middle Cerebral Artery; Ischemic Preconditioning; Lysophospholipids; Male; Mice; Microcirculation; Phosphotransferases (Alcohol Group Acceptor); Propylene Glycols; Reperfusion Injury; RNA, Messenger; Sphingosine