In this merit extension proposal, we are requesting funds to extend the critical findings of S1P release and signaling in the vasculature. The first major aim of the research is to understand how S1P metabolic enzymes are regulated in the vascular endothelial cells to impact local (autocrine) as well as systemic S1P signaling. Secondly, we will fully explore the basic mechanisms and physiological impact of the S1P signaling system as a sensor of biomechanical shear stress on the endothelial cells. First, we hypothesize that Sphk1 in the endothelial cell is primarily involved in local/autocrine signaling mode important for endothelial cell homeostatic and angiogenic reactions. We will derive an endothelial cell-specific inducible knockout of Sphk1 and examine angiogenesis, endothelial cell patterning, pathologic angiogenesis, vascular permeability and inflammation. To examine the effect of systemic S1P, which is derived primarily by red blood cells, we will examine endothelial cell functions in the red blood cell-specific Sphk1 knockout. Localized S1P signaling will be defined at the morphologic and ultrastructural level by immunolocalization studies in vivo as well as in primary cells. Second, we will explore the novel hypothesis that S1P metabolism and signaling constitutes a novel shear sensor/ signaling module in the endothelial cells. Mechanisms of how SIP is formed and released will be explored in detail in cultured vascular endothelial cells. In particular, we will focus on mechanisms that down regulate SIP lyase enzyme.Interestingly, laminar shear-induced downstream signaling mechanisms are critically dependent on S1P1 receptor signaling, suggesting that this receptor is a sensor of physiological shear stress. We will explore this mechanism in detail using cultured endothelial cells. We anticipate that these experiments will allow us to better understand the role of sphingolipid metabolism and signaling in vascular endothelial cells. Since SIP receptor modulators have entered the therapeutic era, this knowledge is likely to have important clinical utility.
SI P receptor modulators have entered the clinic;the first generation compound, called FTY720 has completed phase III studies for the control of autoimmune inflammation. This research will deepen our understanding of how SI P functions in essential cardiovascular functions important for normal health and how SIP system is dysregulated in cardiovascular disease in mouse models.
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