Essential role of sphingosine 1–phosphate receptor 2 in pathological angiogenesis of the mouse retina

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, and angiogenesis. In this study, we explored the role of S1P 2 receptor (S1P 2 R) in normal vascularization and hypoxia-triggered pathological angiogenesis of the mouse retina. S1P 2 R is strongly induced in ECs during hypoxic stress. When neonatal mice were subjected to ischemia-driven retinopathy, pathologic neovascularization in the vitreous chamber was suppressed in S1p2 -/-mice concomitant with reduction in endothelial gaps and inflammatory cell infiltration. In addition, EC 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 eNOS were observed in the S1p2 -/-mouse retina. S1P 2 R activation in ECs induced COX-2 expression and suppressed the expression of eNOS. These data identify the S1P 2 R-driven inflammatory process as an important molecular event in pathological retinal angiogenesis. We propose that antagonism of the S1P 2 R may be a novel therapeutic approach for the prevention and/or treatment of pathologic ocular neovascularization. IntroductionSphingosine 1-phosphate (S1P) is a lipid mediator that regulates various biological processes, such as cell proliferation, migration, survival, and differentiation (1). S1P, generated by the phosphorylation of sphingosine by sphingosine kinase 1 and 2 (Sphk1 and Sphk2), is degraded by S1P-specific phosphatases and a lyase (1). It is also a high-affinity ligand for 5 G protein-coupled S1P receptors, S1P 1 R, S1P 2 R, S1P 3 R, S1P 4 R, and S1P 5 R, which regulate distinct intracellular signaling pathways (2, 3). S1P 1 R, S1P 2 R, and S1P 3 R are widely expressed, whereas S1P 4 and S1P 5 expression is prominent in cells of the immune and nervous systems, respectively. S1P 1 receptor couples exclusively to G i signaling pathway, whereas S1P 2 and S1P 3 receptors couple to G i , G q , and G 12/13 pathways. However, S1P 2 activates G 12/13 potently, whereas S1P 3 activates G q preferentially (4, 5). S1P receptors regulate important physiological functions of the vascular system, such as vascular morphogenesis and maturation, cardiac function, vascular permeability, and tumor angiogenesis (6-10). Indeed, S1p1 receptor-null embryos die due to hemorrhage at E12.5-E14.5. We found that the S1P 1 R signaling in ECs promotes the formation of strong N-cadherin-based junctions between endothelial and vascular smooth muscle cells and thus stabilizes the nascent vasculature (11, 12). However, mice that lack either the S1P 2 R or the S1P 3 R are viable and fertile. Interestingly, S1p1/S1p2-double-null embryos showed a more severe phenotype than S1p1-single-null embryos, suggesting that S1P 2 R also regu-

Sphingosine-1–Phosphate, FTY720, and Sphingosine-1–Phosphate Receptors in the Pathobiology of Acute Lung Injury

“…Similar to the protective role of S1P 1 , S1P 2 -null mice and mice with a reduced expression of S1P 3 (generated by treating with a specific siRNA against S1P 3 ) also offered significant protection against LPS-induced barrier disruption and leakage, compared with wild-type mice (106). However, S1P 2 seems to mediate enhanced vascular permeability in newborn mice exposed to a hypoxia-induced model of retinopathy (107) and a hydrogen peroxide-induced model of barrier dysfunction (103). In RILI, the roles of S1P 2 and S1P 3 in barrier regulation appear to be conflicting, as observed in a preclinical model of LPS-induced ALI.…”

Lipid signalling in disease

“…As an example, S1P (probably through S1P receptors 130 ) and PtdIns(3,4,5)P 3 (through PKB/Akt) both lead to the activation of endothelial nitric oxide synthase (eNOS) and the release of nitric oxide (NO•) radicals. NO• acts through the NO-cyclic GMP pathway and, to some degree, through the formation of reactive nitrogen species to dilate blood vessels, decrease the bloodtumour barrier and to promote angiogenesis.…”

Sphingosine Interaction with Acidic Leucine-rich Nuclear Phosphoprotein-32A (ANP32A) Regulates PP2A Activity and Cyclooxygenase (COX)-2 Expression in Human Endothelial Cells

“…In addition, S1P was shown to induce COX-2 in epithelial cells (33). Our recent data suggest that S1P 2 receptor activation in endothelial cells induces COX-2 expression by transcriptional activation (34). However, the novel findings in this report indicate that sphingoid base interaction with ANP32A induces COX-2 expression via a p38-dependent pathway.…”