Endothelial Sphingolipid Synthesis and Tissue Inflammatory Response

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Endothelial injury promotes the development of atherosclerosis at the site of disturbed flow. Sphingosine-1-phosphate (S1P), produced by sphingolipid metabolism, is a secreted lipid mediator that interacts with G protein-coupled receptors, named S1P1-5. Locally produced and circulating S1P activate S1P receptors, particularly S1P1 the most abundant in the endothelium, to maintain vascular homeostasis. Altered sphingolipid metabolism and S1P signaling has been implicated in vascular disease, including coronary artery diseases (CAD). The current grant led to several advances. First, we discovered a novel mechanism by which endothelial sphingolipid biosynthesis is regulated. Nogo-B, a membrane protein of the ER, highly expressed in blood vessels, binds to and inhibits serine palmitoyltransferase (SPT), the rate-limiting enzyme of the de novo sphingolipid production. Second, we revealed that Nogo-B/SPT interaction downregulates local S1P signaling contributing to inflammation, hypertension and heart failure. Third, we found that inflammatory stimuli and ox-LDL induce Nogo-B phosphorylation, which further inhibits SPT activity contributing to endothelial injury. Fourth, following TNF-α, the N-terminus of Nogo-B is cleaved and translocates to the nucleus to impact endothelial transcriptome. Our long-term goal is to understand how Nogo-B regulates local sphingolipid signaling and its impact on coronary functions in the pathogenesis of CAD. Our hypothesis is that Nogo-B controls endothelial-derived S1P signaling, which is a key regulator of vascular homeostasis and disease- thereby influencing coronary plaque progression. Mechanistically, we hypothesize that Nogo-B promotes vascular inflammation and diseases via two major mechanisms; SPT inhibition, thus disrupting locally-derived S1P signaling, and the activation of gene profile. The rational is that the discovery of new mechanisms regulating endothelial inflammation will provide potential therapeutic targets for CAD. For the renewal, we propose to: 1) Investigate the role of endothelial Nogo-B in the susceptibility of mice to coronary atherosclerosis; 2) Determine the importance of endothelial S1P signaling and its role as downstream effector of Nogo-B in the onset of coronary atherosclerosis; 3) Dissecting the mechanism of Nogo-B signaling in myocardial endothelial injury. This contribution is significant since will identify novel targets for the treatment of CAD, especially since available therapies have been only partially successful, and beyond the statins, there are currently no effective pharmacological strategies that effectively address vascular inflammation. The proposed research is innovative because we investigate the effects of altered sphingolipid homeostasis and S1P signaling on the progression of coronary atherosclerosis, by using a novel mouse model of CAD and myocardial infarction that better recapitulates the human disease, a heretofore-unexamined process.