Role of the S1P pathway and inhibition by fingolimod in preventing hemorrhagic transformation after stroke

Hemorrhagic transformation (HT) is a complication of severe ischemic stroke after revascularization. Patients with low platelet counts do not receive reperfusion therapies due to high risk of HT. The immunomodulatory drug fingolimod attenuated HT after tissue plasminogen activator in a thromboembolic stroke model, but the underlying mechanism is unknown. Fingolimod acts on several sphingosine-1-phosphate (S1P) receptors, prevents lymphocyte trafficking to inflamed tissues, and affects brain and vascular cells. This study aimed to investigate changes in S1P-signaling in response to brain ischemia/reperfusion and the effects of the S1P receptor modulator fingolimod on HT. We studied brain expression of S1P signaling components, S1P concentration, and immune cell infiltration after ischemia/reperfusion in mice. We administered fingolimod after ischemia to wild-type mice, lymphocyte-deficient Rag2 mice, and mice with low platelet counts. Ischemia increased S1P-generating enzyme SphK1 mRNA, S1P concentration, and S1P receptor-1 (S1P1) T-cells in the brain. Fingolimod prevented lymphocyte infiltration, and attenuated the severity of HT in Rag2 mice but it was ineffective under thrombocytopenia. Fingolimod prevented β-catenin degradation but not Evans blue extravasation. Ischemia/reperfusion upregulates brain S1P signaling pathway, and fingolimod exerts local effects that attenuate HT. Although fingolimod seems to act on the brain tissue, it did not prevent blood-brain barrier leakage.Supported by a grant from the Spanish Ministerio de Economía y Competitividad (SAF2017-87459-R to AMP), and a grant FIS (PI15/00430 to AC) co-financed by the Instituto de Salud Carlos III (ISCIII)-Subdirección General de Evaluación y el Fondo Europeo de Desarrollo Regional (FEDER).We are grateful to David Bellido from the Centres Científics i Tecnològics of the University of Barcelona for the mass spectrometry analyses. We thank the Pla Estratègic de Recerca i Innovació en Salut (PERIS) program of the Health Department of the Generalitat de Catalunya for supporting FMM, the Centre de Recerca Biomèdica Cellex, Barcelona, where part of this work was performed, and the Centres de Recerca de Catalunya (CERCA) Programme of the Generalitat de Catalunya for supporting the Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS)