PROJECT SUMMARY Bioactive lipid mediator signaling systems evolved coincidently with complex vascular, immune and nervous systems of vertebrates. My laboratory discovered the sphingosine 1-phosphate (S1P) receptor and have contributed to our knowledge of how this lipid mediator regulates the vascular and immune systems. S1P receptor is now a target for a drug (Fingolimod/ Gilenya) that is approved for the treatment of relapsing, remitting multiple sclerosis. Much effort is directed towards developing second generation S1P receptor- targeted therapeutics for several immune, oncologic and vascular diseases. However, our understanding of how S1P signaling contributes to various diseases is limited and S1P receptor-based therapeutic agents suffer from significant mechanism-based adverse events. This proposal aims to fill the gap in our knowledge about how S1P signaling regulates vascular disease and develop novel therapeutic strategies to reduce vascular disease progression and restore endothelial function, an important factor in cardiovascular health. Specifically, we will focus on the S1P chaperones, protein molecules that bind to S1P and target receptor signaling complexes to activate specific biological responses. In particular, we will explore the mechanisms by which HDL-bound S1P suppresses endothelial injury and promote vascular homeostasis by the activation of S1PR1 signaling complexes. Second, we will explore how the S1PR1 signaling system regulates shear stress- induced vascular endothelial cell homeostasis. Mechanistic details of receptor signaling complexes that translate biomechanical forces that result from homeostatic laminar shear stress and pathologic disturbed shear into intracellular biochemical signals and transcriptional output will be elucidated in endothelial cells in vitro and in vivo. Third, mechanisms by which autoimmunity-associated cytokines (type-I interferons) to exacerbate endothelial injury and accelerate vascular disease will be explored in mouse models and correlated with endothelial cells isolated from normal and patients with systemic lupus erythematosus (SLE). Finally, we will develop stabilized recombinant ApoM fusion protein to deliver S1P to endothelial S1PRs to promote vascular homeostasis and reduce endothelial injury. The use of this biological therapeutic in animal models of hypertension, myocardial ischemia/ reperfusion injury, abnormal angiogenesis and tissue fibrosis will be examined. These studies are anticipated to lead to comprehensive understanding of how S1P signaling promotes vascular homeostasis and lead to the development of novel approaches to control vascular injury and disease using cardiovascular targeted S1P therapeutics.