Background-All treatments of acute myocardial infarction are aimed at rapid revascularization of the occluded vessel; however, no clinical strategies are currently available to protect the heart from ischemia/reperfusion injury after restitution of blood flow. We hypothesized that some of the cholesterol transport-independent biological properties of high-density lipoprotein (HDL) implied in atheroprotection may also be beneficial in settings of acute myocardial reperfusion injury. Methods and Results-In an in vivo mouse model of myocardial ischemia/reperfusion, we observed that HDL and its sphingolipid component, sphingosine-1-phosphate (S1P), dramatically attenuated infarction size by Ϸ20% and 40%, respectively. The underlying mechanism was an inhibition of inflammatory neutrophil recruitment and cardiomyocyte apoptosis in the infarcted area. In vitro, HDL and S1P potently suppressed leukocyte adhesion to activated endothelium under flow and protected rat neonatal cardiomyocytes against apoptosis. In vivo, HDL-and S1P-mediated cardioprotection was dependent on nitric oxide (NO) and the S1P 3 lysophospholipid receptor, because it was abolished by pharmacological NO synthase inhibition and was completely absent in S1P 3 -deficient mice. Conclusions-Our data demonstrate that HDL and its constituent, S1P, acutely protect the heart against ischemia/ reperfusion injury in vivo via an S1P 3 -mediated and NO-dependent pathway. A rapid therapeutic elevation of S1P-containing HDL plasma levels may be beneficial in patients at high risk of acute myocardial ischemia. Key Words: lipoproteins Ⅲ inflammation Ⅲ apoptosis Ⅲ endothelium Ⅲ sphingolipids Ⅲ microcirculation Ⅲ reperfusion T he main therapeutic goals in patients with acute myocardial infarction are to minimize myocardial damage, improve cardiac repair, and reduce myocardial remodeling. State-of-the-art therapy is rapid reperfusion of the infarcted myocardium through revascularization of the occluded vessel. However, the benefit of reperfusion is compromised by the endothelial injury and inflammation that follow reinstitution of blood flow, leading to additional myocardial damage, a process termed "ischemia/reperfusion injury." Despite all efforts to prevent the sequelae of reperfusion injury in Clinical Perspective p 1409 patients, 1 there are currently no clinical strategies available to effectively protect cardiac tissue from the inflammatory damage inherent to reperfusion. 2 High-density lipoproteins (HDLs) are the most powerful independent negative predictor of cardiovascular events evident in all large prospective epidemiological studies. The constituents of the HDL particle that mediate its diverse biological effects are still under investigation. 8 Recently, we and others have identified several sphingolipids, such as sphingosine-1-phosphate (S1P), as constituents of human HDL and have found them responsible for part of the nitric oxide (NO)-mediated vasodilatory effect of HDL. 9 -11 Acute administration of reconstituted HDL has been shown to normalize the en...

HDL is a major atheroprotective factor, but the mechanisms underlying this effect are still obscure. HDL binding to scavenger receptor-BI has been shown to activate eNOS, although the responsible HDL entities and signaling pathways have remained enigmatic. Here we show that HDL stimulates NO release in human endothelial cells and induces vasodilation in isolated aortae via intracellular Ca2+ mobilization and Akt-mediated eNOS phosphorylation. The vasoactive effects of HDL could be mimicked by three lysophospholipids present in HDL: sphingosylphosphorylcholine (SPC), sphingosine-1-phosphate (S1P), and lysosulfatide (LSF). All three elevated intracellular Ca2+ concentration and activated Akt and eNOS, which resulted in NO release and vasodilation. Deficiency of the lysophospholipid receptor S1P3 (also known as LPB3 and EDG3) abolished the vasodilatory effects of SPC, S1P, and LSF and reduced the effect of HDL by approximately 60%. In endothelial cells from S1P3-deficient mice, Akt phosphorylation and Ca2+ increase in response to HDL and lysophospholipids were severely reduced. In vivo, intra-arterial administration of HDL or lysophospholipids lowered mean arterial blood pressure in rats. In conclusion, we identify HDL as a carrier of bioactive lysophospholipids that regulate vascular tone via S1P3-mediated NO release. This mechanism may contribute to the vasoactive effect of HDL and represent a novel aspect of its antiatherogenic function

No abstract

Rationale:The role of sphingosine-1-phosphate (S1P) and its receptors in the pathogenesis of atherosclerosis has not been investigated. Objective:We hypothesized that the S1P receptor 3 (S1P 3 ) plays a causal role in the pathogenesis of atherosclerosis. Methods and Results:We examined atherosclerotic lesion development in mice deficient for S1P 3 and apolipoprotein (Apo)E. Although S1P 3 deficiency did not affect lesion size after 25 or 45 weeks of normal chow diet, it resulted in a dramatic reduction of the monocyte/macrophage content in lesions of S1P 3 ؊/؊ /ApoE ؊/؊ double knockout mice. To search for putative defects in monocyte/macrophage recruitment, we examined macrophagedriven inflammation during thioglycollate-induced peritonitis. Elicited peritoneal macrophages were reduced in S1P 3 -deficient mice and expressed lower levels of tumor necrosis factor-␣ and monocyte chemoattractant protein-1. Bone marrow-derived S1P 3 -deficient macrophages produced less MCP-1 in response to lipopolysaccharide stimulation. In vitro, S1P was chemotactic for wild-type but not S1P 3 -deficient peritoneal macrophages. In vivo, S1P concentration increased rapidly in the peritoneal cavity after initiation of peritonitis. Treatment with the S1P analog FTY720 attenuated macrophage recruitment to the peritoneum. Studies in bone marrow chimeras showed that S1P 3 in both hematopoietic and nonhematopoietic cells contributed to monocyte/macrophage accumulation in atherosclerotic lesions. Finally, S1P 3 deficiency increased the smooth muscle cell content of atherosclerotic lesions and enhanced neointima formation after carotid ligation arguing for an antiproliferative/antimigratory role of S1P 3 in the arterial injury response. Conclusions:Our data suggest that S1P 3 mediates the chemotactic effect of S1P in macrophages in vitro and in vivo and plays a causal role in atherosclerosis by promoting inflammatory monocyte/macrophage recruitment and altering smooth muscle cell behavior. (Circ Res. 2011;108:314-323.)Key Words: sphingosine-1-phosphate (S1P) Ⅲ atherosclerosis Ⅲ macrophages Ⅲ inflammation Ⅲ vascular biology Ⅲ lipid metabolites S phingosine-1-phosphate (S1P) is a bioactive lipid with key functions in the immune, inflammatory, and cardiovascular systems. S1P is abundant in plasma (200 to 1000 nmol/L 1,2 ), where it is contained mainly in the high-density lipoprotein fraction 3 in a biologically active form. 4 Accordingly, plasma S1P levels correlate positively with plasma high-density lipoprotein cholesterol and apolipoprotein AI. 2 As a component of both plasma and interstitial fluid, S1P interacts with all vascular and nonvascular cell types that participate in the pathogenesis of atherosclerosis. All these cells have functional S1P receptors and respond to S1P in a number of different ways, 5 which has prompted the question whether S1P and its receptors may play a role in the pathogenesis of atherosclerosis. A positive association between serum S1P levels and the severity of coronary artery stenosis has been described in ...

Sphingosine-1-phosphate (S1P) signaling influences bone metabolism, but its therapeutic potential in bone disorders has remained unexplored. We show that raising S1P levels in adult mice through conditionally deleting or pharmacologically inhibiting S1P lyase, the sole enzyme responsible for irreversibly degrading S1P, markedly increased bone formation, mass and strength and substantially decreased white adipose tissue. S1P signaling through S1P potently stimulated osteoblastogenesis at the expense of adipogenesis by inversely regulating osterix and PPAR-γ, and it simultaneously inhibited osteoclastogenesis by inducing osteoprotegerin through newly discovered p38-GSK3β-β-catenin and WNT5A-LRP5 pathways. Accordingly, S1P-deficient mice were osteopenic and obese. In ovariectomy-induced osteopenia, S1P lyase inhibition was as effective as intermittent parathyroid hormone (iPTH) treatment in increasing bone mass and was superior to iPTH in enhancing bone strength. Furthermore, lyase inhibition in mice successfully corrected severe genetic osteoporosis caused by osteoprotegerin deficiency. Human data from 4,091 participants of the SHIP-Trend population-based study revealed a positive association between serum levels of S1P and bone formation markers, but not resorption markers. Furthermore, serum S1P levels were positively associated with serum calcium , negatively with PTH , and curvilinearly with body mass index. Bone stiffness, as determined through quantitative ultrasound, was inversely related to levels of both S1P and the bone formation marker PINP, suggesting that S1P stimulates osteoanabolic activity to counteract decreasing bone quality. S1P-based drugs should be considered as a promising therapeutic avenue for the treatment of osteoporotic diseases.