Project Description and Summary The objective of this proposal is to evaluate and characterize the interplay between the lipid-derived, vasoactive factor Sphingosine-1-phosphate (S1P) and Notch1 Receptor in the vasculature. S1P and Notch1 are both critical, potent regulators of cell-cell adhesion, barrier, and angiogenesis. Currently, it is thought that these proteins act through distinct, separate pathways. However, the investigator has recently found that these two pathways are highly interconnected, such that S1P activates Notch1 to promote Rac1 activation and barrier enhancement. The goals of this proposal are to characterize why, how, and in what contexts Notch1 is essential in S1P signaling. These goals will be addressed through three Aims. Specific Aim 1 will evaluate and characterize the role of cortical Notch in S1P-mediated barrier. Specific Aim 2 will investigate how S1P activates Notch1. Specific Aim 3 will explore the interplay between S1P Receptor1 and cortical Notch1 in angiogenic sprouting and morphogenesis. Together, these studies will unveil and characterize a novel connection between two key proteins in barrier and angiogenic regulation. Furthermore, connecting Notch to S1P will open up a new suite of drugs and therapies to target and control Notch signaling, as G-coupled protein receptors are common druggable targets.