Sphingosine kinase 1 plays a key role in defective elastin-induced arterial hypermuscularization - Project Summary/Abstract Elastin is the major component of circumferential elastic lamellae that alternate with rings of smooth muscle cells (SMC) to form lamellar units in arteries. Loss-of-function mutations in the elastin gene ELN in humans cause supravalvular aortic stenosis (SVAS), which is characterized by aortic SMC accumulation and subsequent lumen obstruction. SVAS occurs as an isolated entity or as part of Williams-Beuren Syndrome (WBS). Defective elastic lamellae and excess SMC accumulation are also observed during physiological closure of the ductus arteriosus (DA). Failure of DA closure (i.e., patent DA [PDA]) leads to blood flow imbalance and subsequent mortality. SMC accumulation is essential for postnatal DA closure and thus promoting SMC accumulation may provide a therapeutic potential for PDA. In contrast, SMC accumulation is detrimental for patients with SVAS/WBS and some congenital heart diseases in which PDA maintains pulmonary or systematic circulation. Although regulating SMC accumulation is desired in these elastin- defective arteries, mechanistic links between defective elastic lamellae and SMC hyperproliferation in SVAS/WBS and DA are not well elucidated. To address this key question, my postdoctoral studies focus on elastin aortopathy (K99), and I will bridge these findings to DA biology during the independent phase (R00). My preliminary data demonstrate that sphingosine kinase 1 (Sphk1), an enzyme that phosphorylates sphingosine into a sphingosine-1-phosphate (S1P), is the most upregulated gene in elastin mutant mouse aortic SMCs at embryonic day 15.5. This day is when differential hyperproliferative SMCs are first observed in Eln(-/-) aorta. Reduced ELN increases levels of SPHK1 in human aortic SMCs in culture and mouse aorta. Upregulated SPHK1 is also observed in mouse and human DAs. Pharmacological inhibition of SPHK1 attenuates SMC proliferation and hypermuscularization in elastin-defective aorta and DA. Although sphingolipids play a key role in vascular development and remodeling, no prior studies have evaluated the role of the sphingolipid pathway in elastin aortopathy or DA biology. SPHK-produced S1P, a highly bioactive sphingolipid, binds and activates S1P receptors. I hypothesize that in the context of SVAS or DA, defective elastin upregulates Sphk1 levels via transcription factors (TFs), leading to increased S1P binding to S1PR1 and thus, SMC proliferation. This proposal has three specific aims: 1) elucidate role of SPHK1 in hypermuscularization of elastin aortopathy (K99); 2) determine which TFs mediate elastin deficiency-induced Sphk1 transcription (K99); and 3) delineate role of SPHK1 in DA closure (R00). These studies will use induced pluripotent stem cells and aortic tissues from SVAS/WBS patients, chromatin immunoprecipitation assay in human aortic SMCs, SMC-specific Sphk1 deletion in mice and S1PR1 signaling transgenic mice. Since SPHK inhibitors are being tested clinically for cancer, modulating SPHK1 is an intriguing therapeutic strategy that warrants intense investigation.
