Title

Sphingosine 1-phosphate receptor 2 in vascular homeostasis

Date of Completion

January 2008

Keywords

Biology, Molecular|Biology, Cell

Degree

Ph.D.

Abstract

Sphingosine 1-phosphate (S1P), a multifunctional lipid mediator that signals via the S1P family of G protein-coupled receptors (S1PR), regulates vascular maturation, permeability, immunity and angiogenesis. In this study, we explored the role of Sphingosine 1-phosphate receptor 2 (S1PR2) in normal vascularization and hypoxia-triggered pathological angiogenesis of the mouse retina. S1P2 receptor is strongly induced in endothelial cells during hypoxic stress. When neonatal mice were subjected to ischemia-driven retinopathy, pathologic neovascularization in the vitreous chamber was suppressed in the S1p2-/- mice concomitant with reduction in endothelial gaps, and inflammatory cell infiltration. In addition, endothelial cell patterning and normal revascularization into the avascular zones of the retina were augmented. Reduced expression of the proinflammatory enzyme cyclooxygenase-2 (COX-2) and increased expression of endothelial nitric oxide synthase (eNOS) were observed in the S1p2-/- mouse retina. These data identify the S1P2 receptor-driven inflammatory process as an important molecular event in the pathological retinal angiogenesis. ^ Interactions of sphingolipids and cholesterol facilitate the formation of membrane domains and therefore provide platforms for organizing signaling, and other cell functions. We show here that S1P signaling via its S1P 2 receptor (S1PR2) in is critically involved in the mouse ApoE deficient model of atherosclerosis. Lack of S1P2 receptor in the apoe-/- mice reduced atherosclerosis > 70%. This effect is attributed to the effect of S1P on myeloid cells, because transplantation of S1pr2-/-Apoe-/- bone marrow suppressed atherosclerosis to a similar extent. Microarray analysis of bone marrow-derived macrophages from WT and S1pr2-/- mice revealed the diminished expression of caspase-11, an inflammasome-specific enzyme. S1P2R is needed for the positive autoregulatory loop in the toll-like receptor-4 (TLR-4) induction of casp-11 expression in macrophages. Indeed, in the aortic tissues of Apoe-/- mice, S1P 2 receptor expression is essential for optimal NFkB activation, caspase-11 and caspase-1 expression. Furthermore, S1P2 receptor is required for caspase-1 inflammasome composition and pro-inflammatory IL-1 and IL–18 cytokines release in vivo. S1P/S1P2 receptor pathway may be an important signaling paradigm to fine-tune the temporal cascade of inflammatory signaling in the macrophage. Inhibition of this pathway may lead to a novel approach to control vascular disease such as atherosclerosis. ^